thermal analysis of return line of hydraulic steering

Thermal Analysis Of Return Line of Hydraulic Power Steering System 2014-2015

M.E.S. College Of Engineering, Pune-01 P a g e | I

ABSTRACT

In Hydraulic power steering system, if a fluid with initially high viscosity is

used, it will take a relatively long time to attain a required pressure by the power

source on cold start-up. If a fluid with a very low viscosity is used it will require less

power on start-up but gradually the need of power will increase on operating

temperature. This is why the correct choice of fluid for a hydraulic system in a

particular environment is critical for performance and efficient.

When the system is operated for a long duration the temperature of the system

increases. This gradually increases the temperature of hydraulic fluid. The increased

temperature reduces viscosity of the fluid in a system which makes the fluid thin.

Hence power needed to circulate the fluid through the system increases as thin fluid

increases the load.

The main concern is the change of viscosity with respect to temperature.

Viscosity is inversely proportional to temperature. The main objective of our project

is to present the evaluation of effects of temperature on hydraulic fluid of a hydraulic

system.

When a fluid is heated up, its viscosity will decrease. The formulation of the

fluid is such that it keeps the following in perspective: the fluid must be able to be

pumped through the system as fast as possible when cold on start up in order to flow

with a few seconds of the engine starting. The same fluid must then be able to flow to

all components at normal operating temperature. Different environments will place

different demands on the fluid but it must remain ‘thin’ (low viscosity) enough when

cold so that it can flow and ‘thick’ (high viscosity) enough when hot to perform the

required action.

These characteristics allow hydraulic fluids to supply sufficient viscosity at all

normal operating temperatures. The minute these temperatures go outside the

parameters of the fluid's design the fluid efficiency will be compromised.

KEYWORDS: - Viscosity, Hydraulics, Hydraulic Fluids, Thermal Analysis,

Steering System.


M.E.S. College Of Engineering, Pune-01 P a g e | II

INDEX

ABSTRACT ........................................................................................................................................... I

1 INTRODUCTION ......................................................................................................................... 1

1.1 Power Steering System: .............................................................................................................. 2 1.1.1 Standard Type:.................................................................................................................. 2 1.1.2 P.P.S (Progressive Power Steering) ................................................................................... 4 ........................................................................................................................................................ 4

1.2 Advantages Of Power Steering System ...................................................................................... 4

1.3 Hydraulic Fluids: ......................................................................................................................... 5

1.4 Principles Of Power Steering: ..................................................................................................... 5 1.4.1 Neutral (Straight Ahead Position): .................................................................................... 6 1.4.2 When Turning: .................................................................................................................. 6

2 PROBLEMS IN STEERING SYSTEM & CAUSES OF FAILURE .......................................................... 8

2.1 Problems In Steering System ...................................................................................................... 9

2.2 Causes Of Steering Failure ....................................................................................................... 10

2.3 Pressure Drop Means Heat ...................................................................................................... 10

2.4 Real Life Cases .......................................................................................................................... 12

2.5 Methods For Reducing Temperature Of Fluid .......................................................................... 12

2.6 Beat The Heat ........................................................................................................................... 14

2.7 Signs of Power Steering Failure ................................................................................................ 15

3 LITERATURE SURVEY ............................................................................................................... 20

4 WORKING PRINCIPLE .............................................................................................................. 24

4.1 Working of Power Steering ...................................................................................................... 25

4.2 Fluid Power ............................................................................................................................... 26 4.2.1 Overview:........................................................................................................................ 26

4.3 Basic Principles of Fluid Power: ................................................................................................ 27

4.4 Hydraulic Fluids: ....................................................................................................................... 29 4.4.1 Environmental adaptability ............................................................................................ 31

4.5 Fluid Behaviour......................................................................................................................... 32

4.6 Conduit Flow ............................................................................................................................ 34 4.6.1 Hydraulic Fluid Care ........................................................................................................ 35

5 MATHEMATICAL ANALYSIS & SIMULATION............................................................................. 38

5.1 Mathematical Model ............................................................................................................... 39

5.2 Formula Used ........................................................................................................................... 40

5.3 CALCULATIONS ......................................................................................................................... 42


M.E.S. College Of Engineering, Pune-01 P a g e | III

5.4 ANALYSIS .................................................................................................................................. 46

6 COMPONENTS &PROJECT DETAILS .......................................................................................... 50

6.1 Pump ........................................................................................................................................ 51

6.2 Steering Unit ............................................................................................................................ 52 6.2.1 Steering Unit Design And Function: ................................................................................ 53 6.2.2 Steering Unit Specifications ............................................................................................ 53

6.3 Steering Column ....................................................................................................................... 55

6.4 Actuator ................................................................................................................................... 56

6.5 Filter ......................................................................................................................................... 58

6.6 Reservoirs ................................................................................................................................. 58

6.7 Hoses And Fittings .................................................................................................................... 59

6.8 Project Details. ......................................................................................................................... 59

6.9 Construction. ............................................................................................................................ 59 6.9.1 Support Structure ........................................................................................................... 64 6.9.2 Pump .............................................................................................................................. 64 6.9.3 Reservoir ......................................................................................................................... 64 6.9.4 Steering Assembly .......................................................................................................... 64 6.9.5 Thermocouples ............................................................................................................... 65 6.9.6 Electric Motor ................................................................................................................. 65 6.9.7 Ni Labview ...................................................................................................................... 65

6.10 Setup Specification .............................................................................................................. 66

7 RESULTS & DISCUSSION .......................................................................................................... 67

........................................................................................................................................................... 72

8 CONCLUSION........................................................................................................................... 77

9 REFERENCES ............................................................................................................................ 79


M.E.S. College Of Engineering, Pune-01 P a g e | IV

LIST OF FIGURES

SR No Figure No Name Page No

1 1.1 Schematic Layout of Hydraulic Steering System 3

2 1.2 Progressive Power Steering (P.P.S) 4

3 1.3 Neutral (Straight Ahead Position) 6

4 1.4 When Turning 7

5 1.5 Closed Centre Circuit 11

6 4.1 Typical Steering Circuit 25

7 4.2 Graph of Efficiency v Viscosity 32

8 5.1 Electrical Analogy 39

9 6.1 Layout Of Power Steering System 60

10 6.2 Steering Rack (a) 61

11 6.3 Steering Rack (b) 61

12 6.4 Containers & Hoses 62

13 6.5 Actuator 62

14 6.6 Steering Column 63

15 6.7 Pump & Motor Assembly 63

16 6.8 Labview Software 64


M.E.S. College Of Engineering, Pune-01 P a g e | V

LIST OF TABLES

SR No Table No Name Page No

1 7.1 Veedol oil Without Steering 69

2 7.2 Veedol Oil with Steering 69

3 7.3 HP Oil without Steering 70

4 7.4 HP Oil with weight of 10 KG 70

5 7.5 HP Oil with Steering 71

6 7.6 Comparison between with & without Steering 72

7 7.7 Comparison between with & without weight 73

8 7.8 Comparison between different oils without steering 74

9 7.9 Comparison between different oils with steering 75


M.E.S. College Of Engineering, Pune-01 P a g e | 1

1 INTRODUCTION



1.1 Power Steering System:

Hydraulic systems use mass transfer to achieve desired output with minimum

effort. Earlier, manual steering systems are used based on mechanical linkages, which

needed extra effort for desired effect. Hydraulic power assisted steering systems were

developed, which greatly reduced the driving effort & made driving safer and

comfortable.

1.1.1 Standard Type:

The power steering system consists of three components: the power steering pump,

the power fluid reservoir and the power steering rack and pinion gear. The power

steering pump is a vane-type pump providing hydraulic pressure for the system and is

powered by the engine. It draws on the power steering fluid reservoir, which in turn is

connected to the power steering gear. A pressure-relief valve inside the flow control

valve limits the pump pressure.

The power steering rack and pinion gear has a rotary control valve which

directs hydraulic fluid coming from the power steering pump to one side or the other

side of the rack piston. The integral rack piston is attached to the rack. The rack piston

converts hydraulic pressure to a linear force which moves the rack to the left or the

right. The force is then transmitted through the tie rods and the tie rod ends to the

steering knuckles, which turn the wheels. This system is widely used today.

The expression refers to any of various steering system configurations where a

vehicle is steered solely by means of a hydraulic circuit comprising, as a minimum, a

pump, lines, fluid, valve, and cylinder (actuator) that is to say, the vehicle is steered

(usually via the front wheels) purely by a hydraulically powered steering cylinder.

This is an important distinction from "hydraulically assisted" steering, where

hydraulic power serves only to assist a mechanical steering system (as is the case with

the every-day Saginaw hydraulically assisted power steering on virtually every light

car / truck on the road today), and is also the reason for the inclusion of the word

"full" (as in FULL Hydraulic steering) in common use. It indicates that the vehicle is

steered ONLY by hydraulics, with no other system (mechanical linkage) in place.

Hydraulic steering has been used forever on a huge number and variety of pieces of

equipment - from small forklifts and garden tractors to combine harvesters, large



tractors, massive earth moving equipment, construction and mining equipment,

aircraft, boats, ships, and many others. The correct industry term for this kind of "full"

hydraulic steering is HYDROSTATIC STEERING. There are many different

configurations, all of which share common design features.

Figure 1.1 Schematic layout of hydraulic steering system



1.1.2 P.P.S (Progressive Power Steering)

Vehicle speed is detected by a speed sensor and fluid pressure acting on the

piston is varied accordingly .When the vehicle is stopped or when moving at low

speed, fluid pressure is increased to lighten the force required for steering. At high

speed, pressure is reduced to lessen the amount of assist and provide appropriate

steering wheel response.

1.2 Advantages Of Power Steering System

Power - Depending on system design parameters (flow, pressure, cylinder size,

etc.) hydro steering can develop steering force FAR in excess of any other

mechanical, electrical, or hydraulically boosted system. This is a must for massive

construction equipment. It is also extremely advantageous to 4x4s with big tires,

locker differentials, low tire pressures, the must negotiate and be steered in

Figure 1.2 P.P.S



extremely challenging terrain. For a given amount of steering input effort, no

other system can match the power output of a hydro steering system.

Flexibility - The very nature of fluid power (hydraulics) allows for great

flexibility in system design and mounting. The steering need not be constrained

by the requirements for mechanical linkages.

Operator comfort – Hydraulic steering systems helps to achieve lower levels of

operator input.

Control - Depending on system design and tuning, precise, custom steering can

be arranged, (for example, a system with very few turns of the steering wheel

from lock to lock)

Weight - The power to weight ratio of hydrostatic systems generally far outstrips

traditional hydraulically boosted mechanically actuated steering systems.

Smoothness – Hydraulic steering systems are smooth and quiet in operation.

Vibration is kept to a minimum, kickback, bump steer, and operator fatigue are all

but eliminated.

1.3 Hydraulic Fluids: Hydraulic fluids are the life blood of the hydraulic system. The hydraulic fluid

transmits pressure and energy, seals close-clearance parts against leakage,

minimizes wear and friction, removes heat, flushes away dirt and wears particles,

and protects surfaces against rusting.

Conventional petroleum (mineral) oils are normally used in hydraulic systems,

but fire-resistant, synthetic, and biodegradable fluids are used in other situations.

1.4 Principles of Power Steering: Power steering is one type of hydraulic device for utilizing engine power to

reduce steering effort .Consequently, the engine is used to drive a pump to

develop fluid pressure, and this pressure acts on a piston within the gear box so

that the piston assists the sector shaft effort.

The amount of this assistance depends on the extent of pressure acting on the

piston. Therefore, if more steering force is required, the pressure must be raised.

The variation in the fluid pressure is accomplished by a control valve which is

linked to the intermediate shaft and the steering main shaft.



1.4.1 Neutral (Straight Ahead Position):

Fluid from the pump is sent to the control valve. If the control valve is in the

neutral position, all the fluid will flow through the control valve into the relief port

and back to the pump. At this time, hardly any pressure is created and because the

pressure on the power piston is equal on both sides, the piston will not move in

either direction.

1.4.2 When Turning:

When the steering main shaft is turned in either direction, the control valve

also moves, closing one of the fluid passages. The other passage then opens wider,

causing a change in fluid flow volume and, at the same time, pressure is created

.Consequently, a pressure difference occurs between both sides of the piston and

the piston moves in the direction of the lower pressure so that the fluid in the

cylinder is forced back to the pump through the control valve.

Figure 1.3Neutral (straight ahead position)



Figure 1.4 When turning



2 PROBLEMS IN STEERING SYSTEM &

CAUSES OF FAILURE



2.1 Problems In Steering System

The temperature rise of fluid in the system reduces the viscosity of the fluid.

This increases the pumping power and steering is inconvenient. The temperature of

the fluid in the pressure line is about 75oC to 85oC while that in the return line is about

80oC to 95oC. These high temperatures coupled with high pressures lead to changes in

the fluid properties.

The decrease in viscosity results in thin film of oil between rack & pinion

arrangement. This results in increase contact between mating gear teeth & hence

causes increase in friction. Which eventually increases steering effort. Which may

lead to accidents in actual operation.

Overheating ranks No. 2 in the list of most common problems with hydraulic

equipment. Unlike leaks, which rank No. 1, the causes of overheating and its remedies

are often not well understood by maintenance personnel.

Why Do Hydraulic Systems Overheat?

Heating of hydraulic fluid in operation is caused by inefficiencies.

Inefficiencies result in losses of input power, which are converted to heat. A hydraulic

system’s heat load is equal to the total power lost (PL) through inefficiencies and can

be expressed as:

PLtotal = PLpump + PLvalves + PLplumbing + PLactuators

If the total input power lost to heat is greater than the heat dissipated, the

hydraulic system will eventually overheat. Installed cooling capacity typically ranges

between 25 and 40 percent of input power, depending on the type of hydraulic system.

Hydraulic Fluid Temperature

How hot is too hot? Hydraulic fluid temperatures above 180°F (82°C) damage

most seal compounds and accelerate degradation of the oil. While the operation of any

hydraulic system at temperatures above 180°F should be avoided, fluid temperature is

too high when viscosity falls below the optimum value for the hydraulic system’s

components. This can occur well below 180°F, depending on the fluid’s viscosity

grade.



2.2 Causes Of Steering Failure

The major factor is the long and continuous use of the system. The fluid is

circulated continuously and due to repeated cycles of increase and decrease of

pressure, it is induced upon by thermal stresses. These stresses increase the

temperature of fluid. The friction between fluid and the tube material also leads to

temperature rise due to continuous flow.

Generally the return line passes through the vicinity of the engine which is the

major source of heat dissipation. So the heated surroundings lead to inefficient heat

transfer causing problems. If the fluid is not sufficiently cooled during its passage

from the return line, the same fluid will be circulated in the system at a higher

temperature leading to a gradual increase in the system temperature.

2.3 Pressure Drop Means Heat

Where there is a pressure drop, heat is generated. This means that any

component in the system that has abnormal, internal leakage will increase the heat

load on the system and can cause the system to overheat. This could be anything from

a cylinder that is leaking high-pressure fluid past its piston seal, to an incorrectly

adjusted relief valve. Identify and change-out any heat-generating components.

A common cause of heat generation in closed centre circuits is the setting of

relief valves below, or too close to, the pressure setting of the variable-displacement

pump’s pressure compensator. This prevents system pressure from reaching the

setting of the pressure compensator. Instead of pump displacement reducing to zero,

the pump continues to produce flow, which passes over the relief valve, generating

heat. To prevent this problem in closed centre circuits, the pressure setting of the

relief valve(s) should be 250 PSI above the pressure setting of the pump’s pressure

compensator (Figure 1).



Closed centre circuit showing relief valve (RV) setting 250 PSI above the

pressure compensator (PC) setting of the variable pump (PV):

Continuing to operate a hydraulic system when the fluid is over-temperature is

similar to operating an internal combustion engine with high coolant temperature.

Damage is guaranteed. Therefore, whenever a hydraulic system starts to overheat,

shut it down, identify the cause and fix it.

Figure 1.5 Closed Centre Circuit



2.4 Real Life Cases

Earlier this year, a large-scale recall relating to the failure of power steering was

covered extensively in the news. In late May 2014, 1.4 million vehicles were recalled

by the FORD MOTOR COMPANY. This recall included over 915,000 Ford Escapes

and Mercury Mariners, due to a defect in the torque sensor (the part that manages the

amount of pressure applied by the steering system). In addition to the Ford Escape

and Mercury Mariners, this recall also included some Ford Explorers, due to an

electrical blip in the steering system.

According to a May 29, 2014 write up in USA today, at least 5 accidents and 6

injuries have been linked to the Escape and Mariner defect, and 15 accidents and 2

minor injuries have been linked to the Explorer problem.

In Formula One car hydraulic system generally operate at temperatures 135oC,

versus about 60oC in conventional vehicles. In any hydraulic circuit throttling process

produces heat. With no significant oil mass in the system temperature rises quickly.

As a result viscosity of hydraulic fluid decreases .In conventional vehicles viscosity of

oil is 20-cSt while in Formula One hydraulic system it drops down to 3- 4 cSt at

135oC.Hence hydraulic system fails & it leads to serious accidents at high speed.

2.5 Methods For Reducing Temperature Of Fluid

The return line of the steering system is the region where the temperature of fluid

is maximum. The hot fluid from the return line is passed to the container from where

the cycle again starts. Therefore the best way to reduce the temperature of fluid is to

maximize the heat transfer from return line. The fluid which is passed to the container

gradually cools down. The following ways can be implemented to increase the heat

transfer of the return line.

1) A metal hose instead of rubber hose may be used. Metal provides greater heat

transfer coefficient.

Fins can be provided for increased heat transfer.

Heat transfer with fin is generalized as -

Q fin,max = hAfin ( Tb – To)

Where, h- convective heat transfer coefficient



Afin – Surface area of fin

Tb – Temperature at base of the fin

To – Ambient Temperature

2) The length of the return tube can be increased which will increase the heat

transfer capacity. Heat transfer by conduction as well as convection depends

upon the surface area available for heat dissipation. Increase in length of

return tube increases the surface area.

3) Insulation may be provided over the return line. If the radius of insulation is

above the critical radius then it reverses its property and provides heat transfer.

Critical Radius of Insulation –

Practically, it turns out that adding insulation in cylindrical and

spherical exposed walls initially causes the thermal resistance to decrease,

thereby increasing heat transfer rate because outside area for convection heat

transfer is getting larger. At some critical thickness, the thermal resistance

increases again and heat transfer is reduced.

Rc = k/h

Figure 1.6 Graph of Heat transfer per unit length vs thickness of insulation

So, to increase heat transfer through return line, the radius of insulation must

be less than critical radius of insulation.

4) Along with any one of the above mentioned methods, the fluid which is used

can be replaced by another fluid having better heat transfer properties.



2.6 Beat The Heat

There are two ways to solve overheating problems in hydraulic systems: decrease heat

load or increase heat dissipation.

Hydraulic systems dissipate heat through the reservoir. Therefore, check the

reservoir fluid level and if low, fill to the correct level. Check that there are no

obstructions to airflow around the reservoir, such as a buildup of dirt or debris.

Inspect the heat exchanger and ensure that the core is not blocked. The ability

of the heat exchanger to dissipate heat is dependent on the flow-rate and temperature

of both the hydraulic fluid and the cooling air or water circulating through the

exchanger. Check the performance of all cooling circuit components and replace as

necessary.

An infrared thermometer can be used to check the performance of a heat

exchanger, provided the design flow-rate of hydraulic fluid through the exchanger is

known. To do this, measure the temperature of the oil entering and exiting the

exchanger and substitute the values in the following formula:

Where: kW = heat dissipation of exchanger in kilowatts

L/min = oil flow through the exchanger in liters per minute

T ºC = inlet oil temperature minus outlet oil temperature in Celsius

For example, if the measured temperature drop across the exchanger is 4ºC and

the design oil flow-rate is 90 L/min, the exchanger is dissipating 10 kW of heat.

Relating this to a system with a continuous input power of 100 kW, the exchanger is

dissipating 10 percent of input power. If the system is overheating, it means that either

there is a problem in the cooling circuit or the capacity of the exchanger is insufficient

for the ambient operating conditions.

On the other hand, if the measured temperature drop across the exchanger is

10ºC and the design oil flow-rate is 90 L/min, the exchanger is dissipating 26 kW of



heat. Relating this to a system with a continuous input power of 100 kW, the

exchanger is dissipating 26 percent of input power. If the system is overheating, this

means that the efficiency of the system has fallen below 74 percent.

2.7 Signs of Power Steering Failure

Power steering is the feature in modern cars that allows the driver of a car to

direct the vehicle without exerting the effort it would require to physically turn the

wheel. In a power steering system, movements made on the steering wheel cause fluid

pressure inside the hydraulic pump to move to one side or the other of the pump. This

pressure causes a piston to move, and that piston directs the gears to steer the

car.When the power steering fails, the wheels of the car become exponentially more

difficult to turn. The wheels will turn, but the force required to make this happen can

be unexpected and problematic. If power steering failure occurs while a car is in

motion, an accident can result.

Troubles with the power steering system are usually concerned with hard

steering due to the fact that there is no assist. In such cases, before attempting to make

repairs, it is necessary to determine whether the trouble lies with the pump or with the

gear housing. To do this, an on–vehicle inspection can be made by using a pressure

gauge.

On Line Inspection:

Power steering is a hydraulic device and problems are normally due to

insufficient fluid pressure acting on the piston. This could be caused by either the

pump not producing the specified fluid pressure or the control valve in the gear

housing not functioning properly so that the proper fluid pressure cannot be obtained

.If the fault lies with the pump, the same symptoms will generally occur whether the

steering wheel is turned fully to the right or left. On the other hand, if the fault lies

with the control valve, there will generally be a difference between the amount of

assist when the steering wheel is turned to the left and right, causing harder steering.

However, if the piston seal of the power cylinder is worn, there will be a loss of fluid

pressure whether the steering wheel is turned to the right or left and the symptoms



will be the same for both .Before performing an on–vehicle inspection, a check must

first be made to confirm that the power steering system is completely free of any air.

If there is any air in the system, the volume of this air will change when the fluid

pressure is raised, causing a fluctuation in the fluid pressure so that the power steering

will not function properly.

To determine if there is any air in the system, check to see if there is a change

of fluid level in the reservoir tank when the steering wheel is turned fully to the right

or left .For example, if there is air in the system, it will be compressed to a smaller

volume when the steering wheel is turned, causing a considerable drop in the fluid

level. If the system is free of air, there will be very little change in the level even

when the fluid pressure is raised. This is because the fluid, being a liquid, does not

change volume when compressed. The little change in the fluid level is due to

expansion of the hoses between the pump and gear housing when pressure rises. Also,

air in the system will sometimes result in an abnormal noise occurring from the pump

or gear housing when the steering wheel is fully turned in either direction. This on–

vehicle inspection must be performed every time to ensure that the power steering

system is working properly after overhauling or repairing the pump or gear housing.

Vane Pump:

The main component parts of the vane pump, such as the cam ring, rotor,

vanes and flow control valve are high precision parts and must be handled carefully.

Also, because this pump produces a very high fluid pressure, O–rings are used for

sealing each part. When reassembling the pump, always use new O–rings. In the flow

control valve, there is a relief valve which controls the maximum pressure of the

pump. The amount of this maximum pressure is very important; if it is too low, there

will be insufficient power steering assist and if too high, it will have an adverse effect

on the pressure hoses, oil seals, etc. If the maximum pressure is either too high or too

low due to a faulty relief valve, does not disassemble or adjust the relief valve, but

replace the flow control valve as an assembly.



Abnormal Noise:

Abnormal noise in hydraulic systems is often caused by aeration or cavitation.

Aeration occurs when air contaminates the hydraulic fluid. Air in the hydraulic fluid

makes an alarming banging or knocking noise when it compresses and decompresses,

as it circulates through the system. Other symptoms include foaming of the fluid and

erratic actuator movement. Aeration accelerates degradation of the fluid and causes

damage to system components through loss of lubrication, overheating and burning of

seals. Air usually enters the hydraulic system through the pump’s inlet. For this

reason, it is important to make sure pump intake lines are in good condition and all

clamps and fittings are tight. Flexible intake lines can become porous with age;

therefore, replace old or suspect intake lines. If the fluid level in the reservoir is low, a

vortex can develop, allowing air to enter the pump intake. Check the fluid level in the

reservoir, and if low, fill to the correct level. In some systems, air can enter the pump

through its shaft seal. Check the condition of the pump shaft seal and if it is leaking,

replace it. Cavitation occurs when the volume of fluid demanded by any part of a

hydraulic circuit exceeds the volume of fluid being supplied. This causes the absolute

pressure in that part of the circuit to fall below the vapour pressure of the hydraulic

fluid. This results in the formation of vapour cavities within the fluid, which implode

when compressed, causing a characteristic knocking noise. The consequences of

cavitation in a hydraulic system can be serious. Cavitation causes metal erosion,

which damages hydraulic components and contaminates the fluid. In extreme cases,

cavitation can cause mechanical failure of system components. While cavitation can

occur just about anywhere within a hydraulic circuit, it commonly occurs at the pump.

A clogged inlet strainer or restricted intake line will cause the fluid in the intake line

to vaporize. If the pump has an inlet strainer or filter, it is important for it not to

become clogged. If a gate-type isolation valve is fitted to the intake line, it must be

fully open. This type of isolation device is prone to vibrating closed. The intake line

between the reservoir and pump should not be restricted. Flexible intake lines are

prone to collapsing with age; therefore, replace old or suspect intake lines.



High Fluid Temperature

Fluid temperatures above 180°F (82°C) can damage seals and accelerate

degradation of the fluid. This means that the operation of any hydraulic system at

temperatures above 180°F is detrimental and should be avoided. Fluid temperature is

too high when viscosity falls below the optimum value for the system’s components.

The temperature at which this occurs is dependent on the viscosity grade of the fluid

in the system and can be well below 180°F. High fluid temperature can be caused by

anything that either reduces the system’s capacity to dissipate heat or increases its

heat load. Hydraulic systems dissipate heat through the reservoir. Therefore, the

reservoir fluid level should be monitored and maintained at the correct level. Check

that there are no obstructions to airflow around the reservoir, such as a build-up of dirt

or debris. It is important to inspect the heat exchanger and ensure that the core is not

blocked. The ability of the heat exchanger to dissipate heat is dependent on the flow

rate of both the hydraulic fluid and the cooling air or water circulating through the

exchanger. Therefore, check the performance of all cooling circuit components and

replace as necessary. When fluid moves from an area of high pressure to an area of

low pressure without performing useful work (pressure drop), heat is generated. This

means that any component that has abnormal internal leakage will increase the heat

load on the system. This could be anything from a cylinder that is leaking high-

pressure fluid past its piston seal, to an incorrectly adjusted relief valve. Identify and

change-out any heat-generating components. Air generates heat when compressed.

This means that aeration increases the heat load on the hydraulic system. As already

explained, cavitation is the formation of vapor cavities within the fluid. These cavities

generate heat when compressed. Like aeration, cavitation increases heat load.

Therefore, inspect the system for possible causes of aeration and cavitation. In

addition to damaging seals and reducing the service life of the hydraulic fluid, high

fluid temperature can cause damage to system components through inadequate

lubrication as a result of excessive thinning of the oil film (low viscosity). To prevent

damage caused by high fluid temperature, a fluid temperature alarm should be

installed in the system and all high temperature indications investigated and rectified

immediately.



Slow Operation

A reduction in machine performance is often the first indication that there is

something wrong with a hydraulic system. This usually manifests itself in longer

cycle times or slow operation. It is important to remember that in a hydraulic system,

flow determines actuator speed and response. Therefore, a loss of speed indicates a

loss of flow. Flow can escape from a hydraulic circuit through external or internal

leakage. External leakage such as a burst hose is usually obvious and therefore easy to

find. Internal leakage can occur in the pump, valves or actuators, and unless you are

gifted with X-ray vision, is more difficult to isolate. As previously noted, where there

is internal leakage there is a pressure drop, and where there is a pressure drop heat is

generated. This makes an infrared thermometer a useful tool for identifying

components with abnormal internal leakage.

However, temperature measurement is not always conclusive in isolating

internal leakage and in these cases the use of a hydraulic flow-tester will be required.

The influence of internal leakage on heat load means that slow operation and high

fluid temperature often appear together. This can be a vicious circle. When fluid

temperature increases, viscosity decreases. When viscosity decreases, internal leakage

increases. When internal leakage increases, heat load increases, resulting in a further

increase in fluid temperature and so the cycle continues.



3 LITERATURE SURVEY



Power steering (Hydraulic) systems provide significant design challenges, they are

essential while finding the fuel economy since it requires continuous operation of

a hydraulic pump. Heat is generated due to its operation and also the heating of

system via other modes of heat transfer like engine radiation & friction generated

in the system .For cooling the system heat exchangers and coolers are required.

This paper provides a transient thermal model of the entire system to simulate the

temperatures during cyclic operation of the system. For the analysis power

steering system was considered to have the following components – Pump,

Steering Gear, Heat Exchanger & Return Fluid Reservoir. Piston/Cylinder

Assembly was not considered3 basic component models and one heat exchange

model was done. A basic study of the effects of changing vehicle speed on

temperature in the power steering system was run using 12 elements. The results

suggest that the temperature goes on increasing with increasing speed of vehicle

also shows that the system cannot remove the heat from the system if the vehicle

is stopped [3].

Currently, hydraulic power steering are used in passenger cars, and reduction of

the driving energy of the pump under non-steering condition. It is important for

energy-saving of the system to improve fuel economy. Power steering is used to

lower steering efforts and improve driving safety. Electric motor requires less

energy to work but the other electronic components make it expensive, so

hydraulic is a cheaper alternative. The author have presented a design of a new

pump with the following advantages.1) Reduce the pump driving torque in non-

steering condition. 2) Lower/reduce the oil temperature in PS system [1] .

In the past few decades analytical tools like CAE which have improved the design

greatly but these tools cannot consider the manufacturing processes, assembly

etc.In recent times the electric power steering is gaining importance but still the

hydraulic steering is important for developing countries This paper presents the

problems faced during the development of power steering rack and pinion

mountings and test procedure developed for reproducing the RLD.Initial results of

Von-Misses Stresses were 62 Kgf/mm2 which was reduced to 25 Kgf/mm2 in final

optimized design [2].



Commercial quality engine oil were tested in taxi field test program. Low

temperature pumpability properties of these oils deteriorated as per the

test.Substantial deterioration in pumpability properties at low temperature were

found when a combination of factory filled oil with aged oil were used. Used oil

affects pumpability properties but in what ways affect the properties is not yet

ascertained. Thus when oil is to be topped previous oil should be fully drained

before adding new one. This could reduce risk of contamination and altering

pumpabilty properties [4].

Effect of compressible and turbulent flow in a hydraulic power steering pump was

studied using CFD.Effects of these flow type were studied , turbulent flow results

shows 10% increase in the temperature. Minimum temperature raised from 460C

to 510C. Also velocity increase in range of 30%.Flow of fluid in pump produces

shear stress & viscosity of power steering fluid generates internal heat. Internal

heat generated may affect rubber bushing and also decrease lubrication which may

add to frictional heat. In compressible flow maximum value is 20% higher at

96.30C.High temperature implies pressure increase as well. These pump tests were

done to correlate the effects of flow on the pump & suggest improvements in

design [5].

Warning to 223,000 Mini drivers after cars suffer sudden failure in power steering

- Daily Mail Reporter – 18 February 2009

Angry drivers are urging Mini to recall almost a quarter of a million cars

following a spate of sudden power steering failures. Many motorists have had

frightening experiences and near-miss crashes after the system abruptly cut out,

making controlling their vehicles extremely difficult. The fault is believed to be a

problem in 223,000 Minis bought between 2001 and 2007.Mini's power steering

pumps are failing so early in the car's life and is concerned by the risks the failure

can cause.



Signs That Your Power Steering Is Going Bad - Bart Beier – 17 June 2014

When the power steering fails, the wheels of the car become exponentially

more difficult to turn. The wheels will turn, but the force required to make this

happen can be unexpected and problematic. If power steering failure occurs

while a car is in motion, an accident can result. A large-scale recall relating to

the failure of power steering was covered extensively in the news. In late May

2014, 1.4 million vehicles were recalled by the Ford Motor Company.

According to a May 29, 2014 article in USA Today, at least 5 accidents and 6

injuries have been linked to the Escape and Mariner defect, and 15 accidents

and 2 minor injuries have been linked to the Explorer problem.



4 WORKING PRINCIPLE



4.1 Working of Power Steering

The reservoir supplies fluid to the pump. The pump pumps the fluid to the

steering unit. When the operator turns the steering wheel, connected to the steering

unit via the steering shaft, the steering unit directs pressurized fluid to and from the

cylinder. In response, the cylinder extends or retracts. The cylinder is connected to the

steered wheels, and therefore the wheels steer. Fluid then returns to the reservoir from

the steering unit via the filter.

Most power steering systems work by using a hydraulic system to steer the

vehicle's wheels. The hydraulic pressure typically comes from a rotary vane

pump driven by the vehicle's engine. A double-acting hydraulic cylinder applies

a force to the steering gear, which in turn steers the wheels. The steering wheel

operates valves to control flow to the cylinder. The more torque the driver applies to

the steering wheel and column, the more fluid the valves allow through to the cylinder

and since the hydraulic pumps are positive-displacement type, the flow rate they

deliver is directly proportional to the speed of the engine. This means that at high

engine speeds the steering would naturally operate faster than at low engine speeds.

Because this would be undesirable, a restricting orifice and flow-control valve direct

some of the pump's output back to the hydraulic reservoir at high engine speeds. A

pressure relief valve prevents a dangerous build-up of pressure when the piston of the

hydraulic cylinder reaches the end of its stroke. The pressure in the pressure line

ranges from about 70 bar to 210 bar depending on the application.

Figure 4.1 Typical Steering Circuit



The component in the top right of the picture is the hydraulic steering directional

control valve / metering section; and is the heart of the system.

Reservoir - This is the hydraulic fluid (or power steering fluid) reservoir that stores

the fluid necessary for the system.

Supply pump - This is the power steering pump, note that in many automotive

applications the pump and reservoir are integrated into one unit.

Relief valve - This is simply a pressure relief valve, such as you might be familiar

with on a shop air compressor. If a malfunction in the system causes the pressure to

rise too high, the relief valve opens and the fluid simply passes back to the reservoir.

In virtually all automotive power steering pumps, the relief valve is built into the

pump. The pressure the pump produced is directly affected by the resistance to the

flow of fluid Steering unit (top right) - similar in function to the automotive "steering

box", it is the part that translates operator input at the steering wheel (shown attached

in the pic) to actual movement of the steered wheels. More details on how it works

later on.

Steering wheel and steering column - These are the means of operator input.

Cylinder. – This is the hydraulic actuator (the bit that does the work when supplied

with a flow of pressurized fluid); it is roughly analogous to the gearbox and

mechanical linkage in a traditional steering setup.

Filter - Fluid returning from the cylinder / steering unit to the reservoir is first filtered

by some sort of filter. This ensures proper condition fluid, the number one factor for

satisfactory hydraulic system performance.

4.2 Fluid Power

4.2.1 Overview:

Fluid power is the transmission of forces and motions using a confined,

pressurized fluid. In hydraulic fluid power systems the fluid is oil, or less commonly

water, while in pneumatic fluid power systems the fluid is air. Fluid power is ideal for

high speed, high force, and high power applications. Compared to all other actuation

technologies, including electric motors, fluidpower is unsurpassed for force and



power density and is capable of generating extremely high forces with relatively

lightweight cylinder actuators.

Fluid power systems have a higher bandwidth than electric motors and can be

used in applications that require fast starts, stops and reversals, or that require high

frequency oscillations. Because oil has a high bulk modulus, hydraulic systems can be

finely controlled for precision motion applications. Another major advantage of fluid

power is compactness and flexibility. Fluid power cylinders are relatively small and

light for their weight and flexible hoses allows power to be snaked around corners,

over joints and through tubes leading to compact packaging without sacrificing high

force and high power. A good example of this compact packaging is Jaws of Life

rescue tools for ripping open automobile bodies to extract those trapped within. Fluid

power is not all good news. Hydraulic systems can leak oil at connection and seals.

Hydraulic power is not as easy to generate as electric power and requires a heavy,

noisy pump.

Hydraulic fluids can cavitate and retain air resulting in spongy performance

and loss of precision. Hydraulic and pneumatic systems become contaminated with

particles and require careful filtering. The physics of fluid power is more complex

than that of electric motors which makes modelling and control more challenging.

University and industry researchers are working hard not only to overcome these

challenges but also to open fluid power to new applications, for example tiny robots

and wearable power-assist tools.

4.3 Basic Principles of Fluid Power:

A) Pressure and Flow:

Fluid power is characterized by two main variables, pressure and flow, whose

product is power. Pressure P is force per unit area and flow Q is volume per time.

Because pneumatics uses compressible gas as the fluid, mass flow rate Qm is used for

the flow variable when analysing pneumatic systems.

For hydraulics, the fluid is generally treated as incompressible, which means

ordinary volume flow Q can be used. Pressure is reported several common units that

include pounds per square inch (common engineering unit in the U.S.), Pascal (one



newton per square meter, the SI unit), mega Pascal and bar. For engineering, it is best

to do calculations and simulations in SI units, but to report in SI and the conventional

engineering unit.

Pressure is an across type variable, which means that it is always measured

with respect to a reference just like voltage in an electrical system. One can talk about

the pressure across a fluid power element such as a pump or a valve, which is the

pressure differential from one side to the other, but when describing the pressure at a

point, for example the pressure of fluid at one point in a hose, it is always with respect

to a reference pressure. Reporting absolute pressure means that the pressure is

measured with respect to a perfect vacuum. It is more common to measure and report

gage pressure, the pressure relative to ambient atmospheric pressure (0.10132 mPa,

14.7 psi at sea level). The distinction is critical when analysing the dynamics of

pneumatic systems because the ideal gas law that models the behaviour of air is based

on absolute pressure. Pressure is measured with a mechanical dial type pressure gauge

or with an electronic pressure transducer that outputs a voltage proportional to

pressure.

Almost all pressure transducers report gage pressure because they expose their

reference surface to atmosphere. Volume flow rate is reported in gallons per minute,

liters per minute and cubic meters per second (SI unit). Flow is a through type

variable, which means it is volume of fluid flowing through an imaginary plane at one

location. Like current in an electrical system, there is no reference point. Flow is

measured with a flow meter placed in-line with the fluid circuit. One common type of

flow meter contains a turbine, vane or paddle wheel that spins with the flow. Another

type has a narrowed passage or an orifice and flow is estimated by measuring the

differential pressure across the obstruction. A Pitot tube estimates velocity by

measuring the stagnation pressure. Because flow meters restrict the flow, they are

used sparingly in systems where small pressure drops matter.

B) Power and Efficiency

The power available at any one point in a fluid power system is the pressure

times the flow at that point.

Power = P * Q



Components such as cylinders, motors and pumps have input and output

powers, which can be used to calculate the efficiency of the component. For example,

pressured fluid flows into a cylinder and the cylinder extends. The input power is the

pressure of the fluid times its flow rate while the output power is the compression

force in the cylinder rod times the rod extension velocity. Dividing output power by

input power yields the efficiency of the component. The same can be done for

components such as an orifice. The efficiency of the orifice is the output pressure

divided by the input pressure because the flow rate is the same on either side of the

orifice.

4.4 Hydraulic Fluids:

The main purpose of the fluid in a fluid power system is to transmit power.

There are other, practical considerations that dictate the specific fluids used in real

hydraulic systems. The fluids must cool the system by dissipation of heat in a radiator

or reservoir, must help with sealing to prevent leaks, must lubricate sliding and

rotating surfaces such as those in motors and cylinders, must not corrode components

and must have a long life without chemical breakdown. The earliest hydraulic systems

used water for the fluid. While water is safe for humans and environment, cheap and

readily available, it has significant disadvantages for hydraulic applications. Water

provides almost no lubrication, has low viscosity and leaks by seals, easily cavitates

when subjected to negative pressures, has a narrow temperature range between

freezing and boiling (0 to 100 OC), is corrosive to the steels used extensively in

hydraulic components and is a friendly environment for bacterial and algae growth,

which is why swimming pools are chlorinated. Modern hydraulic system use

petroleum based oils, with additives to inhibit foaming and corrosion. Petroleum oils

are inexpensive, provide good lubricity and, with additives, have long life. The brake

and automatic transmission fluids in your car are examples. According to ISO there

are three different types of fluids according to their source of availability and purpose

of use.



A) Mineral-Oil Based Hydraulic Fluids

As these have a mineral oil base, so they are named as Mineral-oil-Based

Hydraulic fluids. This kind of fluids will have high performance at lower cost. These

mineral oils are further classified as HH, HL and HM fluids. Type HH fluids are

refined mineral oil fluids which do not have any additives. These fluids are able to

transfer power but have less properties of lubrication and unable to withstand high

temperature. These types of fluid have a limited usage in industries. Some of the uses

are manually used jacks and pumps, low pressure hydraulic system etc. Type HL

fluids are refined mineral oils which contain oxidants and rust inhibitors which help

the system to be protected from chemical attack and water contamination. These

fluids are mainly used in piston pump applications. HM is a version of HL-type fluids

which have improved anti-wear additives. These fluids use phosphorus, zinc and

sulphur components to get their anti-wear properties. These are the fluids mainly used

in the high pressure hydraulic system.

B) Fire resistant fluids

These fluids generate less heat when burnt than those of mineral oil based fluids.

As the name suggests these fluids are mainly used in industries where there are

chances of fire hazards, such as foundries, military, die-casting and basic metal

industry. These fluids are made of lower BTU (British Thermal Unit) compared to

those of mineral oil based fluids, such as water-glycol, phosphate ester and polyol

esters. ISO have classified these fluids as HFAE (soluble oils), HFAS(high water-

based fluids), HFB(invert emulsions), HFC(water glycols), HFDR(phosphate ester)

and HRDU(polyol esters).

C) Environmental Accepted Hydraulic Fluids

These fluids are basically used in the application where there is a risk of leakage

or spills into the environment, which may cause some damage to the environment.

These fluids are not harmful to the aquatic creatures and they are biodegradable.

These fluids are used in forestry, lawn equipment, off-shore drilling, dams and

maritime industries. The ISO have classified these fluids as HETG (based on natural

vegetable oils), HEES (based on synthetic esters), HEPG (polyglycol fluids) and

HEPR (polyalphaolefin types).



4.4.1 Environmental adaptability

Now-a-days the usage of environmentally acceptable hydraulic fluids is

increasing, especially in European countries. These countries are using bio lubricants

since 25 years. According to recent survey the total market share of bio lubricant is

3.2 % in Europe and growth was estimated to be 3.7 % from 2000 to 2006. Germany

is using 15 % of bio lubricants and Scandinavia is not far behind which constitute for

11 %. Not all the bio lubricants are vegetable oil but they are synthetic too.Three main

criteria are considered while selecting the effect of hydraulic fluids on environment.

umulation

A) Toxicity

It is very important to be considered for environment and safety of the people

while selecting the hydraulic fluids. Although many precautions are taken it is

important to be considered during spills and leakages. When there is a compulsory use

of toxic fluid, safety measures are must. The different countries have their own

standards for labelling bio lubricant. Some are

4 34, ASTM standards in USA

B) Biodegradability

The importance of biodegradability is increasing day by day globally, mainly

in the areas of offshore drilling, harbour maintenance, forest machinery and snow

removal. The trend for the use of biodegradable fluids started from Europe. There are

two types of biodegradation tests primary and ultimate.

Primary: It is the minimum change in the identity of substance.

Ultimate: It is complete conversion of substance into carbon dioxide,

water, inorganic salts and biomass.



4.5 Fluid Behaviour

A) Viscosity

All fluids, including oil and air have fundamental properties and follow basic

fluid mechanics laws. The viscosity of a fluid is its resistance to flow. Some fluids,

like water, are thin and have low viscosity while others like honey are thick and have

high viscosity. The fluids for hydraulic systems are a compromise. If the viscosity is

too low, fluid will leak by internal seals causing a volumetric loss of efficiency. If the

viscosity is too high, the fluid is difficult to push through hoses, fittings and valves

causing a loss of mechanical efficiency. A medium viscosity fluid is best for hydraulic

applications. The dynamic viscosity (also known as the absolute viscosity) is the

shearing resistance of the fluid and is measured by placing the fluid between two

plates and shearing one plate with respect to the other. The symbol for dynamic

viscosity is the Greek letter mu (µ). The SI unit for dynamic viscosity is the pascal-

second (Pa-s), but the more common unit is the centipoise (cP), with 1 cP = 0.001 Pa-

s. The dynamic viscosity of water at 20 _ C is 1.00 cP. It is easier to measure and

more common to report the kinematic viscosity of a fluid, the ratio of the viscous

forces to inertial forces. The symbol for kinematic viscosity is the Greek letter nu (n).

Kinematic viscosity can be measured by the time it takes a volume of oil to flow

through a capillary. The SI unit for kinematic viscosity is m2/s but the more common

unit is the centistoke (cSt).If ρ is the fluid density, the kinematic and dynamic

viscosity are related by 𝑛 =µ

𝜌

Figure 4.2 Graph of Efficiency vs Viscosity



The kinematic viscosity of water over a wide range of temperature is 1 cSt

while common hydraulic oils at 40 _ C are in the range of 20-70 cSt. Sometimes

hydraulic oil kinematic viscosity is expressed in Saybolt Universal Seconds (SUS),

which comes from the oil properties being measured on a Saybolt viscometer.

Viscosity changes with temperature; as fluid warms up it flows more easily. One

reason your car is hard to start on a very cold morning is that the engine oil thickened

overnight in the cold. The viscosity index VI expresses how much viscosity changes

with temperature. Fluids with a high VI are desirable because they experience less

change in viscosity with temperature.

B) Bulk Modulus

In many engineering applications, liquids are assumed to be completely

incompressible even though all materials can be compressed to some degree. In some

hydraulic applications, the tiny compressibility of oil turns out to be important

because the pressures are high, up to 5,000 psi. The bulk modulus of the fluid is the

property that indicates the springiness of the fluid and is defined as the pressure

needed to cause a given decrease in volume.

A typical oil will decrease about 0.5% in volume for every 1000 psi increase

in pressure. When the compressibility is significant, it is modelled as a fluid capacitor

(spring) and often is lumped in with the fluid capacitance of the accumulator. When

air bubbles are entrained in the hydraulic oil, the bulk modulus drops and the fluid

becomes springy. You may have experienced this when the brake pedal in your car

felt spongy. The solution was to bleed the brake system, which releases the trapped air

so that the brake fluid becomes stiff again. Another way that the fluid can change

properties is if the pressure fall below the vapour pressure of the liquid causing the

formation of vapour bubbles. When the bubbles collapse, a shock wave is produced

that can erode nearby surfaces. Cavitation damage can be a problem for propellers and

for fluid power pumps with the erosion greatly shortening the lifetime of components.

The bulk modulus β is defined as β=∆𝑃

∆𝑃/𝑉

Where V is the original volume of liquid and ∆𝑉 is the change in volume of the liquid

when subjected to a pressure change of ∆𝑃. Because ∆𝑉 =V is diminsionless, the units

of β are pressure.



C) Pascal’s Law

Pascal’s Law states that in a confined fluid at rest, pressure acts equally in all

directions and acts perpendicular to the confining walls . This means that all

chambers, hoses and spaces in a fluid power system that have open passageways

between them are at equal pressure so long as the fluid is not moving.

D) Density

Density is expressed as mass occupied in a unit volume. The density is inversely

proportional to temperature. The SI unit of density is kg/m3.

E) Viscosity index

It indicates the temperature range with in which the fluid can be used. It is a unit

less value. The higher the VI better the stability of viscosity of fluid. If the VI of the

fluid is low, the viscosity of fluid becomes very high at low temperatures and vice

versa. The standard method to calculate viscosity index of petroleum products is

ASTM D2270 or ISO 2909:2002. There are some limitations in this method as it is

used to calculate the viscosity index of the fluids where the kinematic viscosity is

above 2 cSt at 100°C.

4.6 Conduit Flow

In electromechanical actuation systems, power is carried to motors through

appropriately sized, low-resistance wires with negligible power loss. This is not the

case for fluid power systems where the flow of oil through hydraulic hoses and pipes

can result in energy losses due to internal fluid friction and the friction against the

walls of the conduit. Designers size the diameter and length of hydraulic hoses to

minimize these losses. The other cause of major losses in fluid power systems is the

orifice drag of valves and fittings. Conduit flow properties can analyzed using basic

principles of fluid mechanics. At low velocities, the flow is smooth and uniform while

at higher velocities the flow turns turbulent.

Turbulent flow can also be caused by sudden changes in direction or when the

area suddenly changes, conditions that are common in hydraulic systems. Turbulent

flow has higher friction, which results in greater heat losses and lower operating

efficiencies. This is a practical concern for designers of hydraulic systems because



every right angle fitting designed into the system lowers the system efficiency. The

Reynolds number, the non-dimensional ratio of inertial to viscous forces, is

commonly used to characterize the flow in pipes. For fully developed pipe flow, if Re

< 2000 the flow is laminar, if 2000 <Re < 4000 the flow is in transition, neither

laminar or turbulent, and if Re >4000 the flow is turbulent.

4.6.1 Hydraulic Fluid Care

Hydraulic machines power the moving parts of many kinds industrial

machines by applying the force of a fluid under pressure. Some systems are very

small, simple and straight-forward to very large, high pressure systems with a

complex array of servo valves and pumps. No matter the size or complexity, proper

maintenance of BOTH the system and the hydraulic oil is crucial in maximizing

uptime and reducing repair costs. Hydraulic fluids are the life blood of the hydraulic

system. The hydraulic fluid transmits pressure and energy, seals close-clearance parts

against leakage, minimizes wear and friction, removes heat, flushes away dirt and

wear particles, and protects surfaces against rusting.

Conventional petroleum (mineral) oils are normally used in hydraulic systems,

but fire-resistant, synthetic, and biodegradable fluids are used in other situations.

There are four key objectives that are essential to gaining optimum service life of

hydraulic fluids:

A) Control the Temperature

Heat develops in the fluid as it is forced through the pumps, motor tubing, and

relief valves. In conventional systems, excessive temperatures will oxidize the oil and

can lead to varnish and sludge deposits in the system. Conversely, running the

temperature too low will allow condensation in the reservoir and increase the

likelihood of pump cavitation.

Typical industrial hydraulic system temperatures often range between 110 to

150ºF. Mobil hydraulic system temperatures can operate up to 250ºF. Selection of the

proper grade of hydraulic oil is critical to ensure cold start, high temperature

protection and to obtain the optimum system efficiency. Keep systems which operate

on a water based fluid below 140ºF to prevent the water from evaporating. The

deposits caused by oil degradation can plug valves and suction screens and cause

high-tolerance servo valves to seize and/or operate sluggishly. To allow heat to

radiate from the system, keep the outside of the reservoir clean and the surrounding



area clear of obstructions. Make sure the oil cooler is functioning properly and keep

air-cooled radiators free of dirt. Normal temperature drop for most oil coolers is 5 to

10ºF. Reservoirs should be filled to the proper level to allow enough fluid residence

time for the heat to dissipate and to shed water and dirt.

In modern equipment using servo valves, oil degradation can be even more

damaging. High pressure (up to 4000 psi), high temperatures, and small reservoirs

stress the fluid. With minimal residence time and high pressures, entrained air bubbles

can cause extreme localized heating of the hydraulic fluid. This results in nitrogen

fixation that, when combined with oil oxidation, can form deposits which will plug oil

filters and cause servo valves to stick.

B) Keep Systems Clean

Even new systems may be contaminated and should be cleaned before use.

Prevent contaminants such as dirt, water, cutting fluids, and metal particles from

entering the system around the reservoir cover, openings for suction and drain lines,

through breather fill openings, past piston rod packing, and through leaks in pump

suction lines.

C) Keep Fluid Clean

Keeping hydraulic fluids clean begins with good storage and handling practices.

To prevent contamination before use, store new fluid in a protected area and dispense

it in clean, dedicated containers. Clean the fill cap before removing it to add hydraulic

fluid. On critical NC systems, use quick disconnects hoses and filters all oil added to

the reservoir through a 5 micron filter. Full-flow filters designed into the system keep

the fluid clean while in service. These filters are often forgotten and go into bypass

mode, thus allowing dirty oil to circulate. Inspect fluid filters frequently and change

or clean them before they go into bypass mode. Portable filters will supplement

permanently installed filters and should be constantly rotated from system to system

regardless if you think the system requires filtering or not.

Systems should be filtered long enough to pass the total volume of oil through the

filter at least 10 times. Portable filters should be used when transferring new oil from

drums or storage tank to a system — especially for NC machines.



D) Keep an Oil Analysis Program

OEM’s generally specify that system hydraulic oil be drained annually.

However, with an effective oil analysis program, you can safely increase that interval

while at the same time provide yourself with an “early warning” of possible

mechanical problems.

At minimum, check your critical and large volume hydraulic systems at least

annually by oil analysis. Semi-annual or even quarterly sampling intervals may be

required for extremely critical machines.



5 MATHEMATICAL ANALYSIS & SIMULATION



5.1 Mathematical Model

The return line is the major area of concern. The heat transfer from the steering fluid

to the surroundings is divided into three main modes-

1. Heat transfer by convection between the steering fluid and inner walls of return

line.

2. Heat transfer by conduction along pipe thickness from inner wall to outer wall of

pipe.

3. Heat transfer by convection from outer wall of pipe to surroundings.

Figure 5.1 Electrical Analogy



5.2 Formula Used

Heat Transfer from Fluid to Inner Wall of Return Line

First, Reynolds number is found out to determine whether the flow is laminar or

turbulent.

Re = (VD) / ν

Where, V = Velocity of fluid, m/s

D = Characteristic Length (equal to diameter for flow through pipe), m

ν = Kinematic Viscosity, s/m2

– Flow is Laminar

Re>2300 – Flow is Turbulent

Pr = μCp / k

Where, μ = Dynamic Viscosity, N-s/m2

Cp = Specific heat capacity of fluid, J/KgK

k = Coefficient of thermal conductivity for fluid, J/s-m-K

Depending on the type of flow, Nusselt number is calculated as:

For laminar flow through pipe, Petukhov equation is used:

Nu = (f/8)(Re – 1000)Pr [1 + (D/L)2/3]

1+ 12.7 (f/8)0.5(Pr2/3 – 1)

Where, f = (0.790 ln Re – 1.64)-2



For turbulent flow through pipe, Dittus-Boelter equation is used:

Nu = 0.023 Re0.8 Pr0.4

If Twall > Tfluid

Nu = 0.026 Re0.8 Pr0.3

If Twall < Tfluid

From Nusselt number, Convective heat transfer coefficient (h) is found out using:

Nu = hD/k

Where, h = Convective heat transfer coefficient, J/s-m2K

D = Characteristic Length (equal to diameter for flow through pipe), m

k = Coefficient of thermal conductivity for fluid, J/s-mK

Heat transfer from fluid to inner wall of return line is:

Q = h A (T fluid – Twall)

Where, A = Inner Surface area of pipe, m2

Heat transfer from inner wall to outer wall of return line:

Heat transfer from inner wall to outer wall of return line takes place by conduction.

The heat transfer is given by:

Q= 2ПkL (Tint wall-Text wall)

Ln (Ro/Ri)

Where L= length of pipe, m

Ro = outer radius of pipe, m



Ri = inner radius of pipe, m

Heat transfer from outer wall to surroundings:

The convective heat transfer coefficient of air is given by:

h = 10.45 – V + 10 V1/2

Where V= Velocity of object, m/s

The heat transfer from outer wall to surroundings is given by :

Q = hA(Text wall - Tsurr)

Where, A =external surface area of pipe,m2

5.3 CALCULATIONS

1) Heat transfer through return line is given by –

𝑸 = 𝑼. 𝑨. 𝑳𝑴𝑻𝑫

Where, LMTD = Logarithmic Mean Temperature Difference

𝐿𝑀𝑇𝐷 = ∆𝑇𝐴 − ∆𝑇𝐵

𝑙𝑛∆𝑇𝐴∆𝑇𝐵

∆TA = TR1 – T0

∆TB = TR2 – T0

2) The overall heat transfer coefficient for the return line is given by:

𝑼 = 𝟏

𝑨𝒐

𝑨𝒊𝒉𝒊+

𝑨𝒐

𝟐П𝒌𝑳𝐥𝐧

𝒓𝒐

𝒓𝒊+

𝟏𝒉𝒐

+𝟏

𝑨𝒐𝒎

𝑨𝒊𝒎𝒉𝒊+

𝑨𝒐𝒎

𝟐𝝅𝒌𝑳𝐥𝐧

𝒓𝒐

𝒓𝒊+

𝟏𝒉𝒐

The values required in the above equation are calculated as follows:

a) The convective heat transfer coefficient for surrounding air is calculated by :

𝒉𝒐 = 10.45 – V + 10 (V)0.5

Where,



V – Velocity of object

Assuming velocity of object 6 m/s (approximately 25 km/hr)

ho = 10.45 – 6 + 10 (6)0.5

ho= 28.95 m/s

b) The surface areas based on inner and outer radii of return tube are :

A0 = 2πro (lA + lC)

= 2 x П x 0.02 x 1.1

A0 = 0.13823 m2 (Outer Diameter Of Pipe)

Ai = 2πri (lA + lC)

= 2 x π x 0.01 x 1.1

Ai = 0.06911 m2 (Inner Diameter Of Pipe)

Aom = 2πrL = 2π x 0.01 x 1.38 = 0.08670 m2 (Outer Diameter Of Metal Pipe)

Aim = 2πrL = 2π x 0.009 x 1.38 = 0.07803 m2 (Inner Diameter Of Metal Pipe)

c) The convective heat transfer coefficient for steering fluid is calculated as :

Assuming volume flow rate of fluid through pipe is 7 lpm and

7 lpm = 16.67 x 10-6 m3/s

The flow rate through pipe(Q) is given by:

Q = A x v

v = 𝑄

𝐴=

16.67 x 10^(−6)

4.91 x 10^(−4)

v = 0.03395 m/s

Reynolds’ number:

𝑅𝑒 = 𝜌v𝐷

𝜇=

v𝐷

𝜐=

0.03395 x 0.0125

3.78 𝑥 10^(−5)

Re = 22.754



Prandtl number:

Pr = 𝜇𝐶𝑝

𝑘=5200

Nusselt number:

Nu = 0.026 Re 0.8 Pr 0.3

= 0.026 (22.754)0.8 (5200)0.3

Nu = 4.12497

𝑁𝑢 = ℎ𝑖𝐷

𝑘

ℎ𝑖 = 𝑁𝑢.𝑘

𝐷=

4.12497 𝑥 1.0909

0.025

ℎ𝑖 = 180 W/m2K

The overall heat transfer coefficient for the return line is given by:

𝑈 = 1

0.0138230.06911x180 +

0.0138232Пx0.13x1.1 ln

0.15 x 10

+ 1

28.75

+1

0.08670.078x180 +

0.08672Пx0.13x1.1 ln

0.01250.010 +

128.75

U = 22.4 W/mK

3) The surface area available for heat transfer is:

Aa = П d (lA + lB)

= 2П x 0.01 x (0.7 + 0.4)

Aa = 0.06911 m2 …. (Area of Rubber Hose)

Ab = 2π x r x L

= 2π x 5 x10-3 x 1.38

= 0.04335 m2 ….(Area of Metal Pipe)

A = Aa + Ab = 0.06911 + 0.04335 = 0.1125 m2



4) Heat transfer through return line is –

Q = 22.4 x 0.1125 x LMTD

Q = 2.52 LMTD

5) Logarithmic Mean Temperature Difference (for reading 9 is)

Tin = 37.26

Tout = 37.05

Tatm = 26

∆TA = Tin -Tatm = 11.26

∆TB = Tout -Tatm = 11.05

∆TA - ∆TB = 0.21

ln∆𝑇𝐴

∆𝑇𝐵= 0.008176

𝐿𝑀𝑇𝐷 = 0.21

0.008176= 25.6849

Q = 64.7259 W



5.4 ANALYSIS

A thermal model can be a valuable tool in at least two ways.First, thermal

information can assist in selection of power steering cooler and in evaluation

of hydraulic line locations. For example, lines can be located so as to

minimize exposure to hot exhaust components and maximize exposure to

areas of high airflow, a power steering cooler may be eliminated or reduced in

size.

Secondly, a thermal analysis can be used to show temperature effects of an

electric power pump or a variable displacement pump. If these result in heat

dissipation, then cost of a more sophisticated pump may be offset by

elimination of a heat exchanger. Finally transient analysis can show how

thermal inertia of components influences the temperature.

Following Analysis can be done with steady state thermal & transient thermal

module.

Temp Range (30-35oC), Time Interval : 20 Minutes





Ansys workbench software was used for analysis of return line of hydraulic

steering. The main module used in this work is Transient Thermal analysis. In

transient thermal analysis temperature distribution at different time intervals is

determined. Oil from reservoir is drawn by the pump. Pump supplies oil to steering



system. Oil first goes through rack and pinion arrangement where it picks up heat as it

moves through mating gear arrangement. Heated fluid flows through pipes & conduits

where it looses its heat to surroundings due to heat transfer. The cold fluid returns

back to reservoir. Thus fluid keeps on circulating in system. As the cycle goes on,

subsequent pumping action & friction in rack and pinion raise the temperature of

fluid.

As can be seen from above transient thermal analysis done on return line, as

time interval increases, temperature at inlet to return line increases. According to it

temperature distribution pattern varies. Temperature at inlet to return line goes on

increasing as the time interval increases. The above conditions have been achieved at

no load and at room temperatures which differs from actual working conditions as in

temperature due to engine as well as other auxillaries which radiate heat near steering

return lines, which will cause further increase in temperature of the fluid.



6 COMPONENTS &PROJECT DETAILS

The main components of Hydraulic steering system are:



Pump

Steering Unit

Steering Column

Actuator

Filter

Reservoirs

Hoses and Fittings

6.1 Pump

All pumps create flow. They operate on the displacement principle. Fluid is

taken in and displaced to another point. Pumps that discharge liquid in a continuous

flow are non-positive-displacement type. Automotive power steering pumps are non-

positive-displacement type pumps.

With this type of pump, the volume of liquid delivered for each cycle depends

on the resistance offered to flow. A pump produces a force on the liquid that is

constant for each particular speed of the pump. Resistance in a discharge line

produces a force in the opposite direction. When these forces are equal, a liquid is in a

state of equilibrium and does not flow. If the outlet of a non positive-displacement

pump is completely closed, the discharge pressure will rise to the maximum for a

pump operating at a maximum speed. A pump will churn a liquid and produce heat.

Non positive-displacement pumps provide a smooth, continuous flow; pressure

can reduce a non positive pump’s delivery. High outlet pressure can stop any output;

the liquid simply recirculates inside the pump. Non positive-displacement pumps,

with the inlets and outlets connected hydraulically, cannot create a vacuum sufficient

for self-priming; they must be started with the inlet line full of liquid and free of air.

The most common pump used steering setup is an automotive power steering pump.

They are cheap, readily available, and easy to mount and run, are designed for the

environment, are relatively cheap, and produce reasonable flow while being capable

of developing sufficient pressure for our needs.



The exact make and type of pump used will likely depend mostly on what fits

the engine application easily. The most popular pump is the venerable Saginaw pump,

which generally comes in 2 broad styles, the "P" style pump and the "TC" style pump.

Regardless of the exact style or part number of automotive power steering pump you

use, it will be a fixed displacement type. That means that it always produces flow (as

opposed to a variable displacement pump that only produces flow in response to

demand) and the GPM output (flow) can be changed only by varying the drive speed

of the pump. If the flow is not required (i.e. the hydraulic circuit is in the neutral

position - that equates in a hydro steering system, to the steering wheel being centered

and there is no steering input from the operator), fluid flow is internally bypassed

back to the reservoir.

This type of pump (fixed displacement) can be used in an open-center system -

the "open-center" means that the control-valve spool (in our case, the steering unit)

must be open in the center to allow pump flow to pass through the valve and return to

the reservoir. This will become very important later, when it comes time to

understand / select the steering unit for the system, as the type of pump and type of

steering unit MUST be compatible. (i.e. you cannot use a fixed displacement type

pump with a steering unit designed for use with a variable displacement pump).

6.2 Steering Unit

The Steering unit is really the heart of the hydro steering system.

There are a large number of different types of steering units available, each with a

huge number of possible options, configurations and valving options. Some are of

interest to us useable for our needs, and some are not.

They fall into the following 3 broad categories:

1. Open Center

2. Open Center Power beyond

3. Closed center



Each of which can further be subdivided into Load sensing or non-load sensing

and load reaction or non-load reaction. Different manufacturers may have slightly

different terms for each design, feature, or configuration. Be advised though, that load

sensing and load reaction ARE NOT the same thing, although they are often

mistakenly described as such.

6.2.1 Steering Unit Design And Function:

The following description of the design and function of a hydraulic steering

unit is taken from the Parker HGA Series Steering Unit Service Manual. However, the

basics hold true for all steering units etc. The hydraulic steering unit consists of a fluid

control valve section and a fluid metering section which are hydraulically and

mechanically inter-connected.

A) Control Valve

The control valve section contains a mechanically actuated linear spool which

is torsion bar centered. The function of the control valve section is to direct the fluid

to and from the metering section, to and from the cylinder, and to regulate the

pressure supplied to the cylinder. The valve is provided with unique pressure

chambers which insure effective circuit isolation.

B) Metering Section

The metering section consists of a commutator and bi-directional gerotor

element, which contains an orbiting rotor and a fixed stator. The commutator rotates

at orbit speed with the rotor and channels the fluid to and from the rotor set and the

valve section. The rotor incorporates unique sealing vanes which are spring and

hydraulically forced into sealing contact between the rotor and stator to reduce

leakage across the metering section. The function of the metering section is to meter

the oil to the power cylinder, maintaining the relationship between the hand wheel and

the steered wheels. An additional function of the metering section is to act as a

manually operated pump providing manual steering in the event of an inoperative

engine-driven pump.

6.2.2 Steering Unit Specifications

Even once you have decided on a "type" of steering unit for your application

(most likely an open canter, load reactive, non-load sensing unit) there are usually

several options available in that type, depending on the specifications. There are a



huge number of technical specification that describe a hydraulic steering unit, which

is why they often have very specific 30 digit part numbers, from maximum system

pressure, to flow requirement, to maximum permissible temperature differentials, to

required ISO filtration levels and required input torque. It can get quite complicated,

which is why ultimately it can be to your advantage to consult / source your

components from a knowledgeable dealer like Performance Off-Road Systems.

However, the important specifications for a steering unit are:

Flow

Displacement

Pressure

How each of these effects your steering performance can only really be fully

understood in the context of all the other components of the system, like the pump and

cylinder(s). This we will cover in the section on "System Design". However, a basic

understanding of what the specifications are can be useful.

A) Flow

This will normally be listed in 2 parts - maximum continuous rating, and

recommended. This would only become a concern if you were running some sort of

industrial or agricultural pump capable of many gpm . Of interest to us is the

recommended flow. This specifies the required flow the pump used must be able to

generate to operate the steering unit FOR A GIVEN STEERING INPUT SPEED. In

other words, a certain flow from the pump is required so that the steering wheel can

be turned at a certain speed without loss of power assist. Normally, the industry

standard steering input speed is two turns of the steering wheel per second. That

means, if you see a steering unit rated at 3.43 gpm recommended, that steering unit

requires a pump deliver at least 3.43 gpm so that you can turn the steering wheel at a

rate of 2 turns per second (incidentally, this is a pretty darn fast rate - try it some time

and see. It would be most unusual if you could rotate your steering wheel at a rate

exceeding 2 full turns per second. 1 to 1.5 turns per second is a more normal input

rate). In this example, if you were only able to supply this steering unit with 2 gpm,

you would either have to reduce the rate at which you turn the steering wheel to

something less than 2 turns per second (yes - in the "design" section we will cover

how to calculate allowable steering speeds for given flow delivery), or, if you do turn



the wheel at more than 2 turns per second while delivering less than 3.43 gpm you

would experience a loss of power assist.

Note also that how fast you want to be able to turn the steering wheel will depend a

lot on how many turns lock to lock your steering system has (which is governed by

the next steering unit spec - it's displacement). For example, if you use a low

displacement steering unit so that your steering has 8 turns lock to lock, you would

want to be able to turn the wheel faster (to navigate a fast twisty section, for example)

than if you used a high displacement steering unit so that you only has 2 turns lock to

lock.

B) Displacement

This spec is the volume of fluid that is metered to the cylinder per revolution

of the steering unit. It is normally specified in cubic inches per revolution (cu.in./rev).

It is important because it, along with the dimensions of the cylinder (volume) will

determine at what rate the cylinder extends and retracts; which translates into how

many turns of the steering wheel it takes to go from lock to lock. Again, we will

discuss the exact calculations in the design section. For now - if steering unit

displacement is to small (in relation to the cylinder specs), the steering will seem slow

and unresponsive. If it is too great, the steering will be twitchy and hard to control.

C) Pressure

This spec will be listed as a maximum operating pressure. It must be greater

than the maximum pressure the pump is capable of, or component damage may result.

Values in the 1800-2500 psi range are common. When compared to the common 12-

1500 psi of automotive power steering pumps, again, there shouldn't be a problem for

us. However, some steering units are rated at <1000 psi so care must be taken.

6.3 Steering Column

The steering column is one of the more simple parts of the steering system. It

bolts directly to the steering unit on one end, and then either directly to the steering

wheel on the other end; or can be connected to a further steering shaft that connects to

the steering wheel. It simply provides a means for the operator to control the steering

unit and therefore steer the vehicle.



6.4 Actuator

All cylinders of use to us are piston-type cylinders. A piston-type cylinder is an

actuating cylinder in which the cross sectional area of the piston is less than one-half

the cross-sectional area of the movable element. This type of cylinder is normally

used for applications that require both push and pull functions. This makes sense,

since we will need to both push and pull as we steer both the tires from left to right

and back

There are 3 basic designs of piston-type cylinders. They are:

Single acting - The single-acting piston-type cylinder uses fluid pressure to provide

the force in one direction, and spring tension, gravity, compressed air, or nitrogen is

used to provide the force in the opposite direction. This design is of no use to us.

Tandem Cylinder - A tandem actuating cylinder consists of two or more cylinders

arranged one behind the other but designed as a single unit . This design could be

used for hydro steering, though I have personally never seen it.

Double acting - Most piston-type actuating cylinders are double-acting, which means

that fluid under pressure can be applied to either side of the piston to apply force and

provide movement. The two fluid ports, one near each end of the cylinder, alternate as

inlet and outlet ports, depending on the direction of flow from the steering unit. All of

the hydro steering systems I have ever seen or researched use some sort of double-

acting, piston-type cylinder. Double-acting cylinders can be further broken down into

balanced (often called "double ended") and unbalanced (often called single ended)

types, and there are two possible configurations for steering systems using unbalanced

cylinders - namely two cross connected cylinders or one differential cylinder. I prefer

to use the terms balanced and unbalanced as they have meaning in the hydraulic

industry. The terms "single ended" and "double ended' do not, as obviously, any

cylinder will have 2 "ends", making it "double ended", it's just that both "ends" may

not have pistons extending.

Cylinder Specs.

The most important cylinder specifications are

Bore (piston size)

Shaft / rod size (dia)



Stroke

Swept Volume

Bore - The bore of the cylinder is also the size of the piston. The cylinder works by

means of pressurized fluid acting on the cylinder piston. The bore is often specified in

terms of its diameter, but it is its area that is most useful. From simple geometry, we

know that from diameter we can calculate area as A=pi(d/2)^2. With area, and simple

algebra, we can multiply the pressure of the fluid (as dictated by the pump/relief

valve) by the area of the piston, and we have the force the cylinder can exert in

pounds. This is the "power" of the steering system.

Note - with an unbalanced cylinder, this is valid only for the head end of the cylinder,

i.e. the force calculated is that with which the shaft extends (called "push"). What this

means, is that the steering force, or "power" is greater in one direction (whichever

steered direction is when the shaft extends) than the other. This is because when the

shaft retracts (called "pull") the fluid is acting against a reduced area, since the shaft

area deducts from the available piston area upon which the fluid is able to act. To

calculate pull, multiply pressure by (bore area - shaft area). With a balanced cylinder,

pull is always equal to push, since when one side is extending, the other is retracting

and the piston areas are equal.

Shaft size (diameter) - As described above, shaft diameter (and therefore area) plays

a part in how much force a cylinder can generate, and this is true for both balanced

and unbalanced cylinders. Counter-intuitively, for a given bore size cylinder, the

larger the shaft dia, the less force it is able to generate. Shaft size, in relation to bore

size is also a factor in the volume of the cylinder, as described below. Finally, the size

of the shaft has a direct effect on how rugged the cylinder is, and what sort of side

loads and abuse it is capable of handling.

Stroke - The stroke, or "throw" of the cylinder, along with the length of the steering

arm (measured from kingpin/balljoint to where the cylinder shaft attaches) describes

how much steering motion the system is capable of, i.e. how far it can steer the

wheels left and right. If the stroke is longer than the knuckles can accommodate, and

the steering force is high enough, you risk damaging the knuckles or even breaking

them right off the axle. If the stroke is too short, you will not be able to fully steer left

and right all the way.



Swept Volume - The bore x stroke of the cylinder describes the swept volume of the

head end of an unbalanced cylinder, and the bore area - rod area x stroke describes the

swept volume of the rod end of an unbalanced cylinder, or either end of a balanced

cylinder. The swept volume of a cylinder, in relation to the displacement of the

steering unit, describes how many turns lock to lock the system will have.

6.5 Filter

During use, hydraulic oil picks up contaminating particles from wear of sliding

metallic surface that add to residual contaminants from the oil manufacturing process,

rust from metal and polymer particles from seal wear. These dirt particles are tiny grit

that cause additional abrasive wear. Clumps of particles can clog tiny clearances in

precision valves and cylinders and can lead to corrosion. All practical hydraulic

systems require a filter in the circuit. Inline filters have a fine mesh media formed

from wire, paper or glass fiber, formed to create a large surface area for the fluid to

pass through. The oil filter in your car is an example of a hydraulic filter. Sometimes

the filter is included inside the reservior or is part of an integrated power supply unit

along with the motor, pump and reservoir. Selecting a filter is a tradeoff between a

media that traps fine contaminants and one that passes fluid with minimal resistance.

The dynamic model for a filter is a nonlinear resistance P = f(Q) that can be linearized

about the nominal flow. If the pressure drop across the filter is small compared to

other pressure drops in the system, the effects of the filter on the dynamic model can

be ignored. Resistance values for simulation models can be estimated from the

manufacturer’s data sheet or from a filter characterization experiment.

6.6 Reservoirs

The main function of the reservoir is to provide a source of room temperature oil

at atmospheric pressure. The reservoir is equivalent to the ground in an electrical

system. Conceptually, a reservoir is nothing more than an oil storage tank connected

to atmosphere through a breather and having pump and return lines to deliver and

accept oil. In practice, a reservoir has additional functions including de-arating and



acting as a heat exhanger. The dynamic model of a reservoir is to treat it as a ground,

a source of zero pressure.

6.7 Hoses And Fittings

The glue that connects the various components together are the hydraulic hoses

and fittings. They are modelled as fluid power resistors with with linear or non-linear

pressure-flow characteristics.

6.8 Project Details.

Hydraulic power steering system used belongs to a Fiat Palio. To run this system

as a single unit, we used an electric motor. We used fabrication to support the

various components of the system.

6.9 Construction.

The system consists of the following parts:

Steering system

Pump

Reservoir

Support structure

Thermocouple

Electic Motor



Figure 6. 1 Layout Of Power Steering System



Figure 6. 2 Steering Rack (a)

Figure 6. 3 Steering Rack (b)

Figure 6. 4 Steering Rack (a)


Figure 6. 5 Container & Hoses




Figure 6. 4 Container & Hoses

Figure 6. 5 Actuator

Figure 6. 7 Steering Column

Figure 6. 8 Actuator




Figure 6. 9 Pump & Motor Assembly



Figure 6. 11 Labview Software




6.9.1 Support Structure

We have used MS square bars. We have used welding techniques to fabricate

the structure.Structure supports Rack & Pinion ,The Steering assembly, Motor

& Pump.

6.9.2 Pump

Its Function is to keep the fluid circulating throughout the system.It draws the

fluid from reservoir & supplies it through pipes and conduits.

6.9.3 Reservoir

This is the hydraulic fluid (or power steering fluid) reservoir that stores the

fluid necessary for the system.

6.9.4 Steering Assembly

It consist of steering wheel, Rack & Tie rods.





Steering wheel was used to simulate turning of vehicle.

6.9.5 Thermocouples

We used PT100 as a thermocouple to gauge temperature of fluid at inlet and

outlet.

Having Least count of 0.01oc.

NI Labview Software and their respective module was used to interpret

readings.

6.9.6 Electric Motor

An electrical motor is an electro-mechanical device; converts electrical energy

into mechanical energy.

To run the system, we have selected A.C motor.

A.C motor , 0.5 HP , 1440 rpm (Crompton Greaves)

6.9.7 Ni Labview

The company's instrumentation hardware and graphical software convert

standard PCs into industrial automation and test and measurement systems. These

"virtual instruments" can observe, measure, and control electrical signals and physical

attributes such as voltage and pressure. The company also offers programming

environments (LabVIEW and Measurement Studio) for creating customizable

graphical interfaces, controlling instruments, and capturing and analysing data.

The main objective of our project was to obtain oil temperatures in real time.

To obtain the temperatures in the system we used thermocouples and inserted them at

suitable points in the system .

NI Labview software was used to obtain accurate and real time readings.The

thermocouples were coupled to a NI module which was connected to a computer

running the NI labview software. Direct readings were obtained and tabulated directly

in ms excel.

NI labview software was installed and studied.

We programmed the setup which was required to run the software.

Proper module corresponding to the chosen type of sensors was selected.

In the software the required logic was generated via logic diagram.

The program was run, and the readings were tabulated.



6.10 Setup Specification

Pump – Max. Pressure - 140 bar at 2000 rpm

Max. Flow Rate – 8 lpm at 2000 rpm

Actuator – 1. Bore – 90 mm

2. Stroke – 450 mm

3. Volume – 2862776.3 mm3 = 0.002863 m3

Reservoir Capacity – 1.5 liters

Steering Fluid – Fiat Palio Steering Fluid

1. Specific Gravity – 0.874

2. API Gravity – 30.3

3. Flash Point – 185oC

4. Pour Point - -40oC

5. Viscosity Index – 155

6. Viscosity at 40oC – 37.3 cSt

100oC – 7.1 cSt



7 RESULTS & DISCUSSION



To obtain the results of our experiments we had to find the overall rise in

temperature of oil in the hydraulic system.

While taking the readings we have taken 2 positions for measurement of

the temperature that is before the return line and after the return line.

For accurate and unbiased (Variation due to environmental conditions)

readings we have used thermo-couples along with the NI LabView

software.

To find average change in the temperature over the whole return line we

have opted for finding the Logarithmic Mean Temperature Difference

(LMTD) of the same.

Here the temperature Tin is the temperature at the inlet of the return line.

The temperature Tout is the temperature at the outlet of the return line.

Tatm is the Ambient or Surrounding temperature, taken as 26º C.

TIA is the difference between Inlet and Ambient Temperature.

TOA is the difference between Outlet and Ambient Temperature.

Difference 𝞓T = TIA - TOA

Logarithmic Mean Temperature Difference (LMTD) is

𝐿𝑀𝑇𝐷 =𝛥𝑇

𝐿𝑜𝑔(𝛥𝑇)

Total heat transferred in the system is Q

Q=U*A*LMTD

U is Overall Heat Transfer Rate

A is the Area of the Heat Transfer

The readings were taken in interval of 2 minutes and directly exported to

Microsoft Excel.

These readings where converted into intervals of 5 minutes for tabulation

on results.

The readings are from time 0-60 minutes.

All the required calculations was done and formulated into a table.

This final data was used for analysis and graph plotting.



Time Tin Tout Tatm TIA TOA ΔT TIA/TIO Log(ΔT) LMTD Q

0 31.58 31.31 26 5.58 5.31 0.27 1.050847 0.02154 12.535 28.655

5 33.98 33.89 26 7.98 7.89 0.09 1.011407 0.004926 18.2708 41.7671

10 35.24 35.1 26 9.24 9.1 0.14 1.015385 0.006631 21.1143 48.2673

15 36.03 35.87 26 10.03 9.87 0.16 1.016211 0.006984 22.9102 52.3728

20 36.5 36.35 26 10.5 10.35 0.15 1.014493 0.006249 24.004 54.8732

25 36.86 36.67 26 10.86 10.67 0.19 1.017807 0.007665 24.7867 56.6624

30 37.08 36.89 26 11.08 10.89 0.19 1.017447 0.007512 25.2933 57.8204

35 37.26 37.05 26 11.26 11.05 0.21 1.019005 0.008176 25.6846 58.7149

40 37.52 37.3 26 11.52 11.3 0.22 1.019469 0.008374 26.2717 60.0571

45 37.72 37.51 26 11.72 11.51 0.21 1.018245 0.007852 26.7438 61.1363

50 38.03 37.86 26 12.03 11.86 0.17 1.014334 0.006181 27.5039 69.3099

55 38.31 38.04 26 12.31 12.04 0.27 1.022425 0.009632 28.0328 70.6427

60 38.77 38.23 26 12.77 12.23 0.54 1.044154 0.018764 28.7778 72.5202

Table 7. 1 Veedol oil Without Steering


0 30.28 30.16 26 4.28 4.16 0.12 1.028846 0.01235 9.7163 22.21136

5 33.86 33.67 26 7.86 7.67 0.19 1.024772 0.010627 17.879 40.87067

10 36.45 36.18 26 10.45 10.18 0.27 1.026523 0.011369 23.75 54.29206

15 38.33 37.99 26 12.33 11.99 0.34 1.028357 0.012144 27.998 64.00254

20 37.9 37.68 26 11.9 11.68 0.22 1.018836 0.008104 27.147 62.05733

25 38.7 38.435 26 12.7 12.435 0.265 1.021311 0.009158 28.937 66.14922

30 38.37 38.15 26 12.37 12.15 0.22 1.018107 0.007793 28.229 64.53135

35 38.7 38.48 26 12.7 12.48 0.22 1.017628 0.007589 28.989 66.26842

40 38.31 38.08 26 12.31 12.08 0.23 1.01904 0.008191 28.079 64.18903

45 35.63 35.4 26 9.63 9.4 0.23 1.024468 0.010498 21.908 50.08176

50 37.33 37.1 26 11.33 11.1 0.23 1.020721 0.008907 25.823 59.03043

55 38.87 37.34 26 12.87 11.34 1.53 1.134921 0.054965 27.836 63.63229

60 39.19 37.69 26 13.19 11.69 1.5 1.128315 0.05243 28.609 65.40113

Table 7. 2 Veedol Oil with Steering




0 32.38 31.73 26 6.38 5.73 0.65 1.1134 0.04667 13.9288 35.1

5 36.02 35.38 26 10.02 9.38 0.64 1.0682 0.02866 22.327 56.264

10 37.05 36.87 26 11.05 10.87 0.18 1.0166 0.00713 25.2358 63.594

15 37.8 37.6 26 11.8 11.6 0.2 1.0172 0.00742 26.9396 67.888

20 38.4 38.2 26 12.4 12.2 0.2 1.0164 0.00706 28.3212 71.369

25 38.7 38.51 26 12.7 12.51 0.19 1.0152 0.00655 29.0235 73.139

30 38.96 38.76 26 12.96 12.76 0.2 1.0157 0.00675 29.6106 74.619

35 39.079 38.88 26 13.079 12.88 0.199 1.0155 0.00666 29.8858 75.312

40 39.18 38.98 26 13.18 12.98 0.2 1.0154 0.00664 30.1172 75.895

45 39.24 39.02 26 13.24 13.02 0.22 1.0169 0.00728 30.2322 76.185

50 39.52 39.28 26 13.52 13.28 0.24 1.0181 0.00778 30.8538 77.752

55 39.72 39.47 26 13.72 13.47 0.25 1.0186 0.00799 31.3028 78.883

60 39.98 39.69 26 13.98 13.69 0.29 1.0212 0.0091 31.8551 80.275

Table 7. 3 HP Oil without Steering


0 32.88 32.79 26 6.88 6.79 0.09 1.013255 0.005719 15.73794 39.65961

5 35.46 35.38 26 9.46 9.38 0.08 1.008529 0.003688 21.69022 54.65936

10 36.98 36.88 26 10.98 10.88 0.1 1.009191 0.003973 25.16708 63.42104

15 37.89 37.72 26 11.89 11.72 0.17 1.014505 0.006254 27.18155 68.4975

20 38.57 38.52 26 12.57 12.52 0.05 1.003994 0.001731 28.88589 72.79245

25 39.15 39.03 26 13.15 13.03 0.12 1.00921 0.003981 30.14063 75.95438

30 39.68 39.54 26 13.68 13.54 0.14 1.01034 0.004467 31.33791 78.97153

35 39.98 39.85 26 13.98 13.85 0.13 1.009386 0.004057 32.04024 80.7414

40 40.31 40.17 26 14.31 14.17 0.14 1.00988 0.00427 32.78855 82.62714

45 40.43 40.28 26 14.43 14.28 0.15 1.010504 0.004538 33.05331 83.29434

50 40.51 40.34 26 14.51 14.34 0.17 1.011855 0.005118 33.21441 83.7003

55 40.54 40.4 26 14.54 14.4 0.14 1.009722 0.004202 33.31815 83.96173

60 40.59 40.53 26 14.59 14.53 0.06 1.004129 0.00179 33.52559 84.48449

Table 7. 4 HP oil with weight of 10 KG




0 30.22 30.18 26 4.22 4.18 0.04 1.009569 0.004136 9.670784 24.37038

5 32.78 32.67 26 6.78 6.67 0.11 1.016492 0.007104 15.48454 39.02104

10 34.18 34.04 26 8.18 8.04 0.14 1.017413 0.007497 18.6735 47.05722

15 35.16 34.99 26 9.16 8.99 0.17 1.01891 0.008136 20.89535 52.65628

20 35.86 35.7 26 9.86 9.7 0.16 1.016495 0.007105 22.51878 56.74733

25 36.4 36.25 26 10.4 10.25 0.15 1.014634 0.006309 23.77377 59.90991

30 36.86 36.65 26 10.86 10.65 0.21 1.019718 0.00848 24.76352 62.40406

35 37.18 36.96 26 11.18 10.96 0.22 1.020073 0.008631 25.48878 64.23172

40 37.42 37.22 26 11.42 11.22 0.2 1.017825 0.007673 26.06459 65.68275

45 37.71 37.49 26 11.71 11.49 0.22 1.019147 0.008237 26.70919 67.30715

50 37.93 37.69 26 11.93 11.69 0.24 1.02053 0.008826 27.19259 68.52534

55 38.01 37.78 26 12.01 11.78 0.23 1.019525 0.008398 27.3884 69.01876

60 38.04 37.8 26 12.04 11.8 0.24 1.020339 0.008744 27.44589 69.16364

Table 7. 5 HP Oil with Steering



Time(min) With Steering (Q) Without Steering (Q)

0 35.10045875 24.37037642

5 56.26396561 39.02103954

10 63.59412872 47.05722343

15 67.88776571 52.65627858

20 71.36935502 56.74732543

25 73.13930958 59.90990779

30 74.61883158 62.40405996

35 75.31226077 64.2317206

40 75.89541005 65.68275473

45 76.18523205 67.30714985

50 77.75161486 68.52533706

55 83.96172889 69.01875871

60 86.015 69.16363541

Table 7. 6 Comparison between with & without steering

The temperature rise in the system with steering was more than that without steering

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Hea

t Tr

ansf

er(Q

)

Time(min)

without streering With Steering



Time(min) Without Weight (Q) With Weight (Q)

0 24.37037642 39.65961312

5 39.02103954 54.65935745

10 47.05722343 63.42104037

15 52.65627858 68.49749911

20 56.74732543 72.79244722

25 59.90990779 75.95438201

30 62.40405996 78.97152509

35 64.2317206 80.74140108

40 65.68275473 82.62713999

45 67.30714985 83.2943368

50 68.52533706 83.70030194

55 69.01875871 83.96172889

60 69.16363541 84.0517

Table 7. 7Comparison between with weight & without weight

This graph shows that the heat transferred in case of steering with weight is greater

than that without weight. Which also tells us that the temperature rise in the former is

greater that the latter.

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70

Hea

t Tr

ansf

er(Q

)

Time(min)

Without Weight With Weight



Time(min) First Oil (Q) Second Oil (Q)

0 22.21135732 35.10045875

5 40.87066508 56.26396561

10 54.29206353 63.59412872

15 64.00253759 67.88776571

20 62.05733453 71.36935502

25 66.14921829 73.13930958

30 64.53134704 74.61883158

35 66.26841657 75.31226077

40 64.18903482 75.89541005

45 50.08175732 76.18523205

50 59.03043321 77.75161486

Table 7. 8 Comparison between Different Oils without steering

Heat transferred in case of first oil is more than second one. Which also tells us that

the temperature rise in the former is greater that the latter.

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60

Hea

t Tr

ansf

er(Q

)

Time(min)

First Oil Second Oil



Heat transferred in case of first oil with steering is more than that of second one.

Which also tells us that the temperature rise in the former is greater that the latter.

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70

Hea

t Tr

ansf

er(Q

)

Time(min)

First oil (2.286) Different oil (2.52)

Table 7. 9 Comparison between Different Oils with steering

Time(min) First oil (2.286) Different oil (2.52)

0 28.65502465 24.37037642

5 41.76708729 39.02103954

10 48.26727875 47.05722343

15 52.37278116 52.65627858

20 54.87322505 56.74732543

25 56.66236201 59.90990779

30 57.82040757 62.40405996

35 58.71494556 64.2317206

40 60.05706493 65.68275473

45 61.13632062 67.30714985

50 62.6395484 68.52533706

55 63.45984231 69.01875871

60 63.98157893 69.16363541



These results tell us that the temperature rise in the hydraulic system increases due

to following reasons:

Abrupt steering practices

Improper properties of hydraulic fluid

Increase in the amount of the steering load due to various reasons

Friction introduced due to pump etc

Bad maintenance.



8 CONCLUSION



In this experiment we studied the hydraulic power steering system.

We looked upon the various advantages and faults of this system.

Among the various reasons for failure of the system the rise in temperature,

was selected for further studies.

In this we performed various test on the system with taking in mind the

various parameters involved.

Tests were conducted to find the relationship between the parameter and the

system failure(Heating of oil)

We found the following:

Wrong oil selection with inappropriate properties leads to heating of

system.

Reduction in the oil volume also heats up the system.

Steering of the wheel introduces a frictional heat into the oil raising

the temperature.

Increases in steering weight also leads to heating up of the oil.

Thus, we can conclude that use of metal hose, increasing length of the

return line, applying the principle of critical radius of insulation, and use of

steering fluid with better properties are the possible solutions to the problem

of Return Line Failure in hydraulic steering systems. The suitable measure

can be employed considering constraints on the system.



9 REFERENCES



References

1. “Energy-Saving and Reduction of Oil Temperature Rising in Hydraulic Power

Steering System”,Yoshiharu Inaguma,Kazuhiro Watanabe and Hideya

Kato,Akira Hibi; International Congress and Exposition Detroit, Michigan;

March 1-4, 1999.

2. “Design Optimization of a Mini-Truck Hydraulic Power Steering System

Based on Road Load Data (RLD)”,Hari Srinivas Babu A, Prashant A

Thakare,Shirguppe A A;SAE Paper 2010-01-0198

3. “Thermal Modelling of Power Steering System Performance”, Timothy C.

Scott, Jason Uphold; SAE Paper 2008-01-1432.

4. “Deterioration in Used Oil Low Temperature Pumpability Properties”,

B.L.Papke , M.A.Dahistrom , C.T.Mansfield , J.C.Dinklage and D.J.Rao;SAE

Paper 2000-01-2942.

5. “Turbulent and Compressible Flow Effects in a Hydraulic Power Steering

Pump”, Rajnish Chandrasekhar; SAE Paper 2006-01-1184.

thermal analysis of return line of hydraulic steering

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