alishan ppt

8/2/2019 ALISHAN PPT

1/35


2/35

Primary function of the steering system is to achieveangular motion of the front wheels to negotiate the turn.

Secondary functions of steering system are:

1. To provide directional stability to the vehicle goingstraight ahead.

2. To provide perfect steering condition,

i.e. perfect rolling motion of road wheels at all times.

3. To facilitate straight ahead recovery after completing aturn.

4. To minimize tier wear.


3/35

The requirements of a good steering system are:

1. The steering mechanism should be very accurateand easy to handle.

2. The effort required to steer should be minimaland must not be tiresome to the driver.


4/35

1. Steering wheel and column,

2. A manual gearbox and pitman arm or a rack andpinion assembly,

3. Linkages; steering knuckles and ball joints; and 4. The wheel spindle assemblies.


5/35

Power steering systems add a hydraulic pump; fluidreservoir; hoses; lines; and either a power assist unitmounted on, or integral with, a power steering-gear-assembly.

There are several different manual steering gearsin current use. The "rack and pinion" type is the choiceof most manufacturers. The "recirculating ball" type isa past favorite because the balls act as a rolling threadbetween the wormshaft and the ball nut.


6/35

The steering linkage is made of interconnected partswhich move every time the steering wheel is turned.The rotating movement of the steering columnactivates mechanisms inside the steering box. Tie rodends, which join the key parts, pass on the steeringwheel's motion no matter what the angle of the linkageor the vibration from the road.


7/35

For a car to turn smoothly, each wheel must follow a different circle.Since the inside wheel is following a circle with a smaller radius, it isactually making a tighter turn than the outside wheel.


8/35

Energy absorbing steering column

Tilt wheel steering column

.Tilt and telescopic steering column

Steering column with anti-theft lock


9/35

The different types of mechanical steerings used inmodern cars are :

RACK AND PINION STEERING

RECIRCULATING BALL BEARING MANUAL WORM AND SECTOR STEERING

WORM AND TAPERED PEG STEERING

MANUAL WORM AND ROLLER STEERING

WORM AND WHEEL STEERING

WORM AND NUT STEERING


10/35

Rack-and-pinion steering is quickly becoming themost common type of steering on cars, small trucksand SUVs. It is actually a pretty simple mechanism. Arack-and-pinion gear set is enclosed in a metal tube,with each end of the rack protruding from the tube. Arod, called a tie rod, connects to each end of the rack.


11/35


12/35

Recirculating-ball steering is used on many trucks andSUVs (sport utility vehicle) today. The linkages thatturns the wheels is slightly different than on a rack andpinion system. The recirculating ball steering gearcontains aworm gear. You can imagine the gear in twoparts. The first part is a block of metal with a threadedhole in it.
http://auto.howstuffworks.com/gear5.htmhttp://auto.howstuffworks.com/gear5.htm


13/35


14/35

The manual worm and sector steering gear assemblyuses a steering shaft with a three-turn worm gearsupported and straddled by ball bearing assemblies.The worm meshes with a 14-tooth sector attached tothe top end of the pitman arm shaft. In operation, aturn of the steering wheel causes the worm gear torotate the sector and the pitman arm shaft. Thismovement is transmitted to the pitman arm and

throughout the steering train to the wheel spindles.


15/35

The manual worm and tapered peg steering gear has athree-turn worm gear at the lower end of the steeringshaft supported by ball bearing assemblies. Thepitman shaft has a lever end with a tapered peg that

rides in the worm grooves. When the movement of thesteering wheel revolves the worm gear, it causes thetapered peg to follow the worm gear grooves.Movement of the peg moves the lever on the pitman

shaft, which in turn moves the pitman arm and thesteering linkage.


16/35

Various manufacturers use the manual worm androller steering gear. This steering gear has a three-turnworm gear at the lower end of the steering shaft.Instead of a sector or tapered peg on the pitman arm

shaft, the gearbox has a roller assembly (usually withtwo roller teeth) that engages the worm gear.


17/35

The movement of the steering wheel turns the worm,which in turn drives the worm wheel. Attached to thewheel spindle rigidly is drop arm, so that a rotation ofsteering wheel corresponds to a linear motion of the

drop arm end, which is connected to the link rod ashas already been discussed.


18/35

Here the steering wheel rotation rotates theworm, which in turn moves the nut along itslength. This cause the drop arm end to movelinearly, further moving the link rod and thus

steering the wheel.


19/35

POWER RACK AND PINION STEERING

POWER RECIRCULATING BALL BEARINGSTEERING

HYDRAULIC POWER STEERING ELECTROHYDRAULIC POWER STEERING

ELECTRIC POWER STEERING

ACTIVE STEERING

STEER BY WIRE


20/35

POWER RACK AND PINION

When the rack-and-pinion is in a power-steering system, the rack has a slightly different design

as shown in figure no. 4.

FIGURE 4. POWER RACK AND PINION STEERING ASSEMBLY

Part of the rack contains a cylinder with a piston in the middle. The piston is connected to the

rack. There are two fluid ports, one on either side of the piston.

Supplying higher-pressure fluid to one side of the piston forces the piston to move, which in turn

moves the rack, providing the power assist.


21/35

POWER RECIRCULATING BALL BEARING SYSTEM

Power steering in a recirculating-ball system workssimilarly to a rack-and-pinion system. Supplying higher-pressure fluid (fluid is always a oil) to one side of the block

provides assist.HYDRAULIC POWER STEERING SYSTEM

The hydraulic power steering system today is the mostused steering system. It is based on the components of the

mechanical steering system, in addition there is a hydraulicsystem, usually consisting of hydro pump with V-belt drive,hydraulic lines, oil reservoir and steering valve.


22/35

ELECTRO-HYDRAULIC POWER STEERING SYSTEM

The electro-hydraulic power steering

system (Fig. 6) is based on the rack-and-

pinion hydraulic power steering and its

essential new feature is an electrically drivenhydraulic pump, which substitutes the

steering pump driven so far by the vehicle

engine.

FIGURE 6.ELECTROHYDRAULIC POWER


23/35

ELECTRIC POWER STEERING SYSTEM

The electric power steering system (Fig. 7) combines a mechanical steering system with an

electronically controlled electric motor to a dry power steering. The hydraulic system, which so

far delivered the steering boost, is substituted by an electrical system. For this, a torque sensor

measures the steering wheel torque and an electronic control unit calculates the necessary servo

torque.


24/35

The components involved in the electrical powersteering are besides the mechanical steeringcomponents:Electric motor,

Electronic control unit,

Power electronics,

Steering wheel torque sensor and

CAN data bus to other systems


25/35

FUNCTIONAL DESCRIPTION OF ELECTRICAL STEERING SYSTEMS

FIGURE 8. SYSTEM STRUCTURES OF SAFE ELECTRICAL STEERING SYSTEMS


26/35

SAFETY FEATURES

Detecting and evaluating all electrical failuresaccomplish the systems fail-safe behaviour concerningelectrical faults. In case of major electrical faults theelectrical power steering system is switched off


27/35

BMW Active Steering

BMW's Active Steering, a true breakthrough insteering technology, supports the driver at all speeds,particularly in the lower and medium speed rangewhere dynamic steering offers a genuine increase indriving pleasure.


28/35


29/35

STEER BY WIRE SYSTEMS The main feature of future steering systems is the missing

direct mechanical link between steering wheel and steeredwheels. With such a steer-by-wire steering system (Fig.11)

the missing steering columns function must be reproducedin both directions of action. In forward direction the angleset by the driver at the steering wheel is measured by asteering angle sensor and transferred with the suitablesteering ratio to the wheels. In reverse direction the

steering torque occurring at the wheels is picked up via atorque sensor and attenuated respectively, modified fedback to the driver as a counter torque on the steering

wheel.


30/35

FIGURE 11.SBW EXPLANATORY SKETCH


31/35


32/35

Further Advantages Improvement of steering comfort. Road disturbance is first

evaluated and assessed by the system; only useful information isfed to the driver.

Improvement of steering comfort. Road disturbance is first

evaluated and assessed by the system; only useful information isfed to the driver. Steering wheel return torques and steering ratio can be

adjusted variably by software; thus rendering the steering systemadaptable to any target group and driving situation without anyneed to redesign.

Reduction of injury risk in an accident by missing steeringcolumn.

Steering behaviour (understeering, oversteering, self-steeringproperties) can be matched by software


33/35

CONCLUSION This contribution presented various types of electrical

steering systems and their safety aspects. The electrohydraulic power steering does no longer operate the

hydraulic pump via a V-belt drive from the internalcombustion engine. Rather, an electric motor is used,yielding energy savings and flexibility of installation.

Electrical power steering pursues this trend and

offers additional advantages since no hydraulic systemis required. A steer-by-wire system with hydraulicbackup and a purely electrical system were discussed.


34/35

The transition to purely electrical steering systems will proceed step bystep, both for safety reasons and acceptance by the customer. The path

will lead from electrical power steering via a steer-by-wire system witha hydraulic or mechanical backup towards purely electrical steer-by-

wire systems.

REFERENCES Internet : Automotive Engineering International Online, Delphi

AutomotiveSystems;

Joseph, Heitner. Automotive Mechanics, CBS Publishers andDistribution.

Narang G.B.S. Automobile Engineering, S. Chand and Company Ltd. Crouse, W.H. Automotive Mechanics, T ATA McGraw Hill Publishing

Company Ltd.


35/35

THANK YOU

alishan ppt

Documents