automatic differential unit locking system - report
DESCRIPTION
kyi ,hgk gurnnbdu bvrbcvsvgf bvewuysu bvbrgncvncncnvnn gfdTRANSCRIPT
AUTOMATIC DIFFERENTIAL UNIT LOCKING
SYSTEM
A PROJECT REPORT
Submitted by
MURALI KRISHNAN. P 12008114053PRASANNA KUMAR. S 12008114059KISHORE KUMAR. M 12008114042PRAVEEN KUMAR. B 12008114063
in partial fulfillment for the award of the degree
of
BACHELORS OF ENGINEERING
in
MECHANICAL ENGINEERING
VELAMMAL ENGINEERING COLLEGE, CHENNAI.
ANNA UNIVERSITY:: CHENNAI 600 0251
ANNA UNIVERSITY : CHENNAI 600 025
BONAFIDE CERTIFICATE
Certified that this project report ”AUTOMATIC DIFFERENTIAL UNIT
LOCKING SYSTEM” is the bonafide work of MURALI KRISHNAN. P,
PRASANNA KUMAR. S, KISHORE KUMAR. M, PRAVEEN KUMAR. B
who carried out the project work under my supervision.
SIGNATURE SIGNATURE
Dr. M. BALASUBRAMANIAM MR. FRANK GLADSON
HEAD OF THE DEPARTMENT SUPERVISOR, Lecturer
Dept. of Mechanical Engg. Dept. of Mechanical Engg.Velammal Engineering College, Velammal Engineering College,Velammal Nagar, Velammal Nagar,Ambattur – Red hills Road, Ambattur–Red hills Road,Surapet, Chennai – 600 066. Surapet, Chennai – 600 066.
2
ACKNOWLEDGEMENT
At this pleasing moment of having successfully completed our project, we wish to
convey our sincere thanks and gratitude to the management of our college and our
beloved chairman M. V. Muthuramalingam who provided all the facilities to us.
We would like to express our sincere thanks to our principal , for forwarding us to
do our project and offering adequate duration in completing our project.
We are also grateful to the Head of Department Prof. Balasubramaniam for His
constructive suggestions & encouragement during our project.
With deep sense of gratitude, we extend our earnest & sincere thanks to our guide,
Mr. Frank Gladson, Department of Mechanical engineering, for his kind guidance
& encouragement during this project.
We also express our indebt thanks to our Teaching and Non Teaching staffs of
Mechanical Engineering Department, of Velammal Engineering College.
3
TABLE OF CONTENTS
CHAPTER NO. TITLE PAGE NO.
LIST OF FIGURES x
LIST OF ABBREVIATIONS xi
1. INTRODUCTION 8
1.1 SYNOPSIS 8
1.2 INTRODUCTION 9
1.2.1 PROBLEM DEFINITION 9
1.2.2 EXISTING MECHANISM 9
1.3 FEASIBILITY STUDY
1.3.1 TECHNICAL FEASIBILITY 10
1.3.2 ECONOMIC FEASIBILITY 11
1.3.3 OPERATIONAL FEASIBILITY 11
2. LITERATURE SURVEY 12
2.1 DIFFERENTIAL WITH IMPROVED TRACTION 12
2.1.1 INTRODUCTION 12
2.1.2 CHARACTERISTIC FUNCTIONS
2.1.3 DIFFERENTIAL TORQUE TRANSFERS
2.2 LOKKA DISCUSSION – JOURNAL PAPER 17
4
2.2.1 DIFFERENCE TO A NORMAL DIFFERENTIAL 17
2.2.2 SIMPLE EXPLANATION OF
LOKKA'S OPERATION 19
2.2.3 100% POSITIVE LOCKING MECHANISM 21
2.3.3 AUTOMATED INTER-AXLE DLS ACTUATION ENHANCEMENT – JOURNAL
2.3.3.1 INVEX GEARING. 23
2.3.3.2 TORQUE BIAS RATIO 24
2.3.3.3 STRUCTURE FOR ACHIEVING 26
TORQUE BIAS
2.3.3.4 OVERALL BIAS CONTROL 29
2.3.3.5 BIAS RATIOS BETWEEN
DIFFERENT MODES
3. COMPONENTS AND DESCRIPTION 30
3.1 WHAT'S A DIFFERENTIAL?
3.1.1 THE FUNCTION OF A DIFFERENTIAL 32
3.1.2 TYPES OF DIFFERENTIALS
3.2 PNEUMATIC COMPONENTS
3.2.1 PRODUCTION OF COMPRESSED AIR 34
3.2.2 PNEUMATIC SINGLE ACTING CYLINDER 34
3.2.1.1 CYLINDER TECHNICAL DATA 34
3.2.1.2 SOLENOID VALVE 35
5
3.2.1.3 WORKING OF 3/2 SINGLE ACTING
SOLENOID VALVE 37
3.2.1.4 FLOW CONTROL VALVE 38
4. WORKING PRINCIPLE & DESIGN CALCULATIONS 40
4.1 WORKING PRINCIPLE 41
4.2 DESIGN AND DRAWINGS 42
4.2.1 DESIGN OF PNEUMATIC CYLINDER
4.2.2 DESIGN OF PISTON ROD 43
4.3 TECHNICAL DATA 45
4.3.1 SINGLE ACTING CYLINDER
4.3.2 3/2 SOLENOID VALVE 46
4.3.3 FLOW CONTROL VALVE 48
5. PERFORMANCE OF DIFFERENTIAL UNIT 52
5.1 TORSION DIFFERENTIAL PERFORMANCE 54
5.2 VEHICLE TRAVEL ON STRAIGHT ROADS
57
5.3 VEHICLE TRAVEL THROUGH TURNS 58
5.4 CENTER BOX APPLICATION 61
5.5 CONCLUSION 65
6. COST ESTIMATION & CONCLUSION 66
6
7. REFERENCES 69
LIST OF FIGURES
3.1.1 WORKING OF A DIFFERENTIAL UNIT 4.1.1 BLOCK DIAGRAM OF THE WORKING UNIT4.3.2 PNEUMATIC OPERATED SINGLE ACTING CYLINDER 4.3.3 SOLENOID CONTROL VALVE 4.3.4 FLOW CONTROL VALVE 4.3.5 ASSEMBLY LAYOUT OF THE AUTOMATIC DIFFERENTIAL UNIT LOCK SYSTEM
LIST OF ABBERVIATIONS
σy – DESIGN STRESS in N/m2.
d - DIAMETER OF THE PISTON in mm. ft – WORKING STRESS in N/m2. t - MINIMUM THICKNESS OF THE CYLINDER in mm.
ri - INEER RADIUS OF THE CYLINDER in mm.
p - WORKING PRESSURE in N/m2. dp - DIAMETER OF THE PISTON ROD in mm.
7
CHAPTER – 1
1.1 SYNOPSIS
The proposed mechanism is to lock the differential. By locking the differential the
differential is disengaged from the axle. Thus the power is directly transmitted to the axle
and hence to the wheels. This will considerably reduce the power loss in some occasions
when unwanted loss is happening due to the transmission if power from the shaft to the
differential and then to the axle and hence to the wheels. So in mechanism the unwanted
power loss in the due course of transmission through the differential is reduced.
There are some drawbacks in the existing mechanism and we overcome it in the proposed
project. The first is while climbing in steep hills the differential is not really needed as the
speed of the vehicle is low. And also there are some transmission loses in the differential.
So at this time the unit is locked and the loss is overcome. Then when a heavy truck is
struck in a pit or mud it is very difficult to recover the truck as the differential unit cuts
the power which is to be transmitted to the wheel struck. So in this project the unit is
disengaged and power is directly given to the axle by pneumatic means and so the
8
recovery is made easier. This is even made use in the vehicle to be driven in the dense
forests and even in dessert.
1.2 INTRODUCTION
1.2.1 PROBLEM DEFINITION
EXISTING MECHANISM
A differential is a device which is used in vehicles over a few decades and when a vehicle
is negotiating a turn, the outside wheel travels a greater distance and turns faster than the
inside wheel. The differential is the device transmitting the power to each wheel, allows
one wheel to turn faster than the other. It splits the engine torque two ways, allowing each
output to spin at a different speed. The differential is found on all modern cars and trucks,
and also in many all-wheel-drive (full-time four-wheel-drive) vehicles.
These all-wheel-drive vehicles need a differential between each set of drive wheels, and
they need one between the front and the back wheels as well, because the front wheels
travel a different distance through a turn than the rear wheels. Part-time four-wheel-drive
systems don't have a differential between the front and rear wheels; instead, they are
locked together so that the front and rear wheels have to turn at the same average speed.
This is why these vehicles are hard to turn on concrete when the four-wheel-drive system
is engaged.
9
1.3 FEASIBILITY STUDY
The objective of a feasibility study is to test the technical, economic, behavioral and
operational feasibility of developing a new mechanism. This is done by investigating and
generating ideas about the same. The proposed project must be evaluated from technical
viewpoints first, and if technically feasible its impact on the environment must be
assessed. If compatible operational and technical aspects can be devised, then they must
be tested for economic feasibility.
1.3.1 TECHNICAL FEASIBILITY
The assessment of technical feasibility must be based on an outline design of project
requirements in terms of the mechanism used and the drives and components used to
execute the above said mechanism. The components used should be correctly utilized and
the drives also should be exactly used to execute a technically feasible mechanism.
1.3.2 ECONOMIC FEASIBILITY
Economic feasibility deals with the analysis of costs against benefits (i.e.) whether the
benefits to be enjoyed due to the new mechanism is worthy when compared with the
costs to be spent on the older mechanism. The cost is observed to be cheaper when it is
produced in a mass production than produced in a small amount.
10
1.3.3 OPERATIONAL FEASIBILITY
Operational feasibility analysis is performed to check whether the proposed mechanism is
operationally feasible. The mechanism is effective and performs the process desired in
very effective manner and thus overcoming the drawbacks found in the already existing
mechanism. In future any sort of alterations can be made in the project as per the
requirements as modification and enhancements in the system is found to be easier.
11
CHAPTER - 2
LITERATURE SURVEY
2.1 THE DEVELOPMENT OF A DIFFERENTIAL FOR THE IMPROVED
TRACTION CONTROL – JOURNAL PAPER.
2.1.1 INTRODUCTION
Traction management the ability to match available power to actual road conditions is a
concern shared by drivers and automotive engineers alike. With the Torsion differential,
the challenge of improving traction management in front and rear wheel drive vehicles,
all-wheel drive vehicles, and in a variety of applications of the various drives for use in
cars, trucks, military vehicles, construction and utility vehicles, and racing cars. This
paper explains the basic operating functions; various design alternatives, and the
possibilities for improving traction management provided by the Torsion differential.
(From the journal - Advanced differential traction control, Proakis J.G, Rader M.C, Ling F,
Nikias C.L. Macmillan Publishing Company, New York, 2006. ISBN- 0-02-396841-9.)
12
2.1.2 CHARACTERISTIC FUNCTIONS
The Torsion differential provides for the selection of an optimal compromise between the
two primary functions of any differential, namely, transmitting power from a single
power source to two drive axles (or shafts) and permitting independent rotation of the two
driven axles (i.e., differentiation).
This compromise enables an increase in the total amount of torque which can be
conveyed by the drive axles under all traction conditions, without unduly restricting
differentiation. Differentiation is necessary to accommodate different rotational speeds
between drive axles due to vehicle turning situations and variations in tire rolling radii.
These objectives are accomplished by associating the function of differentiation with a
proportioning torque between drive axles. The significance of this important
characteristic will be apparent from the following discussion, beginning with an
explanation of torque transfers within a differential.
2.1.3 A GENERAL STATEMENT OF DIFFERENTIAL TORQUE TRANSFERS
One of the two above-mentioned primary differential functions, the transmission of
power from a single driveshaft to the two driven axles is most closely associated with the
objective of traction actually; two types of torque transfers may be identified in
differentials. The first being the one primary function related to the transfer of torque
13
from a single power source (engine) to the two drives axles. The second type is the
transfer of torque between the drive axles. The two types of torque transfer are
interrelated, and it is an important characteristic of the Torsen differential to control
torque transfers between drive axles and thereby enhance the capacity of the differential
to transfer an increased amount of torque to the drive axles collectively.
2.2 LOKKA DIFFERENTIAL UNIT DISCUSSION PAPER
LOKKA is a fully automatic Differential Lock that does not require any manual
operation. It does not have switches, external lines, electric or pneumatic controls of any
sort. It relies on a simple but highly innovative mechanical design which makes use of
two distinct sets of forces - the "ground driven" forces acting on a wheel when cornering
(that force an outside wheel to turn faster) and the forces from the engine (power) turning
the diff. The combination of these two sets of opposing forces and the unique design
allow the automatic engagement and disengagement of the driving gears when a vehicle
turns or requires differential action.
(FORM THE JOURNAL- John. Markel and A. H. Gray, LOKKA electronic differential
concept the MITRE Corporation, Bedford, Massachusetts 01730, Vol. ASSP: 22, April 2007.)
14
2.2.1 DIFFERENCE TO A NORMAL DIFFERENTIAL
1. A normal diff is designed to perform two main (traction related) operations.
A - Transmit engine power via the drive train to the wheels
B - Allow "differential action" – i.e. allow the wheels to travel at different speeds to
allow cornering without drive train and tyre damage.
2. The traditional differential design allows for an infinitely variable rate of
differentiation ranging from the standard 50:50 where both wheels turn at the same speed
(straight line driving & the ideal for off-road) to a ratio of 100:0 where one wheel spins
freely and the other is not driven at all - (the big problem)
3. The design also allows for all power to be transmitted to the "path of least resistance"
which is fine on bitumen because both wheels always have some degree of traction but
off-road you often require substantial power and in this case even a small difference in
traction can result in wheel spin and hence total loss of traction.
4. An LSD (limited slip differential) is simply a standard differential with either a fixed
bias or a dynamic biasing mechanism which serves to only partially "lock up" the two
axles by way of clutch plates or special gear design. However most require that both
wheels still have some traction on the ground to operate and even when new will cause a
15
wheel in the air to spin uncontrollably so as to be completely ineffective where off road
traction is required.
5. LOKKA overcomes the traction deficiency of the standard differential so as to ensure
that 50:50 power split is achieved when driving irrespective of ground (or air !)
conditions, yet at the same time still allowing differential action when cornering on hard
ground.
2.2.2 SIMPLE EXPLANATION OF LOKKA'S OPERATION
The LOKKA mechanism allows a wheel to turn faster than the speed the diff is driving it
- (differential action), but never allows a wheel to turn slower than the speed the diff and
engine is turning it - (traction). Thus a wheel cannot ever stop turning if the engine is
driving it, but in a corner it can be forced to actually turn faster. Unlike a normal diff the
engine can never drive one wheel faster than the other.
2.2.3 100% POSITIVE LOCKING MECHANISM
LOKKA is positive locking, meaning there is no slippage when locked - there is a
mechanically solid engagement of all parts. In contrast an LSD is not positive locking
and does allow slippage and one wheel "spin up" - the spinning of one wheel at twice the
diff speed while the other wheel having traction remains motionless. This means that you
get 100% of drive and traction to both wheels.
16
LOKKA design is by sight extremely simple - in fact so simple that most people cannot
understand how it can operate so well. It uses less than half the mechanical components
of others, weighs less because no new carrier is needed and for these reasons costs less.
2.2.4 DYNAMIC LOCKING PRINCIPAL
1. Unlike other types of Lockers the LOKKA has a locking and unlocking principal that
is dynamic. The more power that is applied the harder it locks so it doesn't need large bias
forces constantly operating on it to keep it locked, the bias spring forces are minuscule
and can be easily compressed with two fingers. This results in a locker that is able to lock
and unlock extremely easily even when driving on some of the most slippery of surfaces.
The locking mechanism is so sensitive that a wheel can be disengaged with one finger
when a wheel is jacked up off the ground.
2. LOKKA's engineering principal is based on two sets of opposing forces but
simplified . . . there are two forces acting on the internal gear sets
A. - one acting to unlock the cam and axle gears by the gear tooth design and effects of
the ground driven forces acting on a wheel when cornering,
B. - the other to lock the cam and axle gears due to the camming action of the cross shaft
and axle gear due to a 4 dimensional spiral cut cam groove with bearing surfaces under
the effects of engine power.
17
3. Depending on the situation the locker can either uncouple or couple the driving gears.
i.e. if the differential forces acting on a wheel to turn it faster than the wheel is being
driven by the diff and engine, then that side can freely disengage and hence unlock and
provide differential action. (J.Makhoul, Stable and efficient Methods for Linear traction
variation, Tran. On Advanced torque bias, Vol. ASSP: 25, Oct 2002. )
2.2.5 THE MOST AFFORDABLE LOCKER
LOKKA is by far the lowest cost and value for money diff lock available in the world.
The cost reductions are achieved by the economy of low part numbers, reduction in
materials, assembly labor, machining and an overall weight reduction in freight. In
addition the unit can be fitted DIY and results in substantial savings. It is not just cheaper
at the cost of performance - it out performs and has better road handling characteristics
than opposition products and is more durable, reliable and stronger than other lockers.
i. VERY LOW BACKLASH
LOKKA has approximately half the backlash of some other automatic lockers and
achieves this through its different design principal. In particular it does not suffer from a
large amount of backlash in the driving teeth. LOKKA uses specialized low profile gear
sets (small, wide teeth) which have no backlash (almost zero) when engaged means that
operation is smoother - the backlash in the unit is restricted principally to the ramping
18
and camming action that occurs between the cross shaft acting in the groove cut in the
cam gear. Because the camming action is smooth and progressive rather than sharp and
abrupt it results in well mannered driving characteristics.
ii. LOAD TRANSFER AND STRENGTH
LOKKA design uses a large number of very low profile teeth which collectively do all
the ramping and the driving.
Engine power is transferred through the flats of all 20 teeth at the same time rather than
the original standard diff which has only 2 or 4 teeth driving at a time with all the force
being transmitted between two points on the curved surfaces of the pinion and side gear
teeth. LOKKA has a total linear length of approx. 12 cm and surface area of around 3cm2
and hence has 2-5 times greater surface area over which to transfer the engine power.
This means that LOKKA can handle substantially more power than the original
differential gears and can do so without wearing out, because when driving and locked
there is no longer any of the slipping and sliding that occurs when the traditional spider
and side gear turn and mesh.
iii. ELIMINATION OF EXCESSIVE TYRE WEAR
If a wheel can differentiate easily and the locking and unlocking characteristics are
smooth rather than harsh, then the 4WD owner will eliminate excessive tyre wear and
19
drive train damage common when differential action is hampered or the locker does not
allow easy unlocking.
iv. EXCELLENT ON ROAD HANDLING
2WD on road handling is the best available and a front fitment has no affect, even with
the hubs locked (exception : not suitable for C4WD).
Off road steering with a front fitment is virtually unchanged - you may experience a
slight tightening of the steering wheel in some situations but is barely noticeable except
where the effects of tail shaft windup can occur on hard surfaces (as it does without).
This is because you are feeling the effects of both wheels driving with 100% traction on
the round. Depending on the terrain and driving style there may be some element of
under steer but it is minimal.
v. ELIMINATES THE HARSH NOISY ACTIONS
1. A correctly installed LOKKA to a vehicle in sound condition will be a pleasure to
drive and will rarely yield a noise much louder than a metallic clicking. An occasional
metallic clack can occur in some circumstances and if occurs frequently should be
checked.
20
vi. PREVENTS ONE WHEEL SPIN UP
1. The single cause of one wheel spin up and the resultant axle and drive train damage
that occurs when the spinning wheel suddenly bites onto something solid is caused by an
standard differential allowing all power to flow through the path of least resistance and
differentiate in the ratio 100:0 ie 100% drive to one wheel on a poor traction surface and
0% on firm ground.
2. With LOKKA this can never occur - it is not physically possible to drive one wheel
faster than the other - thus with two wheels constantly driving at exactly the same speed
you will negotiate slippery obstacles in a controlled fashion and alleviate the sudden
stress loading of drive train components. However the increased traction of a vehicle will
often result in the vehicle negotiating seemingly impossibly difficult obstacles and as
such common sense and due care are required for the vehicle to ensure the safety of the
occupants and prevent damage to the vehicle.
vii. APPROACH OBSTACLES AT LOWER SPEED
1. If a vehicle has adequate traction on the ground it does not require such large amounts
of momentum, thus a LOKKA equipped vehicle will be able to negotiate difficult
obstacles that were previously only possible with the use of high speed and momentum.
By eliminating speed from your obstacle negotiation you will be able to drive more
safely, with better planning, improve reaction times and in particular keep all 4 wheels on
the ground thereby improving traction even further and saving your car, your belongings,
21
passengers, drive train and suspension from damage. Better yet you don't have to be an
expert driver to do so because with good traction you need only drive normally.
2.3. AUTOMATED INTER-AXLE DIFFERENTIAL LOCKING SYSTEM
ACTUATION ENHANCEMENT
The just-mentioned characteristic of the Torsen differential may be best appreciated in
comparison with the inherent torque transfer characteristics of an 'open' or conventional
differential. The drive axles associated with an open differential are interconnected by a
bevel gear set designed to divide equal torque between drive axles. This arrangement will
not support any substantial torque difference between the drive axles and, as a
consequence, offers very little resistance to differentiation. Virtually any attempt to
deliver an increased amount of torque to one of the drive axles will result in rotation of
the gear set as evidenced by differential rotation between drive axles. For example, if one
of the drive wheels should lose traction, any attempt to deliver additional torque to the
other drive wheel having better traction will result in undesirable 'spin up' of the wheel
having poorer traction. The maximum amount of torque conveyed by the drive axles
collectively is limited to approximately twice the amount of torque supported by the drive
wheel having the least traction. It is this type of problem which is most often identified
with the need for improved traction management. The Torsen differential addresses this
need by providing for a torque proportioning characteristic between drive axles by
22
interconnecting the drive axles with an Invex gearing arrangement. This gearing is
designed to support a predetermined ratio of torques between drive axles.
(FROM THE JOURNAL - Automated inter-axle differential locking system
actuation enhancement Simon Haykin, 3rd edition, Prentice Hall International, New-Jersey,
ISBN 0-13-397985-7, Aug-2004, Vol-23, No. 8, pp 54-56)
VARIOUS CLAIMS OF THE CONCEPT:
2.3.2 INVEX GEARING:
Index gearing in a this differential includes a gear train arrangement comprised of two or
more pairs of satellite gears (called element gears') in mesh with central helical gears
(called 'side gears'). The pairs of element gears are interconnected with each other by
means of spur tooth engagement. This particular arrangement consists of six element
gears and two side gears. The number of element gear pairs used in a specific design is a
function of overall torque capacity and space requirements.
The modified crossed axis helical gear mesh, element gear to side gear, is designed and
processed to provide instantaneous elliptical contact for reduced tooth stress and
increased tooth overlap engagement. In addition, gear tooth helix angle, pressure angle
and tooth depth proportions are selected to further minimize stress and wear without
sacrifice to function.
23
2.3.2 TORQUE BIAS RATIO
The maximum torque ratio which is supported by a particular differential design is
termed 'bias ratio'. This term is expressed as the quotient of the torque in the higher
torque axle divided by the torque in the lower torque axle in proportion to unity.
The provision of bias ratio significantly affects the operative connection between drive
axles and represents a careful choice for controlling torque transfers between drive axles
to achieve optimum traction. A '4:1' bias ratio design means that the differential is
capable of delivering, to the drive wheel having better traction, four times the amount of
torque which can be supported by the lower traction drive wheel. In comparison with an
open differential, this means that, under the same conditions, a '4:1' bias ratio differential
is capable of delivering approximately two and one-half times more torque to the drive
axles collectively than an open differential.
Other means are also known for modifying the operative connection between drive axles
to provide for the transfer of additional torque to the drive axles collectively. For
example, many limited-slip differentials provide for preloading friction clutches to
oppose the transfer of torque between drive axles.
24
This frictional pre-load represents a particular minimum magnitude of resistance which
must be overcome to permit any relative rotation between drive axles which may
interfere with the operation of anti-lock braking systems. Also, since frictional forces are
continually active to resist differentiation, the friction clutches tend to wear, resulting in a
deterioration of intended differential performance.
In contrast to the limited-slip's continuous magnitude of frictional resistance to
differentiation, the torque biasing characteristic of the differential provides for a
maximum ratio of torque distributions between drive axles. For instance, as the amount
of torque being conveyed by the differential decreases, the amount of resistance to
differentiation also decreases. That is, even though the bias ratio remains relatively
constant, a proportional division of a lower magnitude of torque being conveyed by the
differential results in a smaller torque difference between drive axles.
In braking situations where little or no torque is being conveyed by the differential, a four
to one apportionment of torque between drive axles amounts to little or no torque
difference between drive axles. Thus, the differential will not support any appreciable
torque 'wind-up' between drive axles during braking and so does not interfere with the
operation of anti-lock braking systems. Another known approach to modifying the
operative connection between drive axles is to provide for resisting differentiation as a
function of the speed difference between drive axles.
25
It has long been appreciated that undesirable wheel slip is associated with very high rates
of differentiation. Differentials have been designed using fluid shear friction, which
respond to increased rates of differentiation by increasing fluid shear frictional resistance
to differentiation. The obvious problem with such 'speed sensitive' differentials is that
undesirable wheel slip has already occurred well in advance of its detection. Also, the
fluid shear friction designs generally rely on the changes in fluid temperature associated
with high differential shear rates to increase resistance to differentiation. However,
similar temperature changes may be associated with extended periods of desirable
differentiation, or may be influenced by changes in ambient temperature, so that
resistance to differentiation may vary throughout ordinary conditions of vehicle use.
The bias ratio characteristic of the differential instantly reacts to unequal traction
conditions by delivering an increased amount of torque to the drive wheel having better
traction before the other drive wheel exceeds the limit of traction available to that wheel.
The bias ratio characteristic also remains substantially constant over a wide range of
torque conveyed by the differential, and is not sensitive to changes in ambient
temperature or conditions of vehicle use.
(FROM - L.R Rabiner, B. S. Atal and, M.R. Sambur, analysis of torque control its variation
with position of analysis frame, Tran. on vehicle engineering; Vol. ASSP: 25, Oct 2003.)
2.3.3 STRUCTURE FOR ACHIEVING TORQUE BIAS
26
As previously stated, the torque biasing characteristic of this differential is achieved by
interconnecting the drive axles with an Index gearing configuration which selectively
controls the generation of frictional torques within the differential.
It is important to note that there are no intrinsic forces or pre-loads within the
differentials which affect transfers of torque between drive axles. All of the forces which
are controlled to produce frictional resistance between drive axles are derived from
transfers of torque between a single drive source and the drive axles.
The characteristic of torque bias is achieved in a very simple way. It is well known that
frictional forces are determined by the product of the coefficient of friction of a given
surface and the normal force applied to that surface. Frictional torque, of course, is
merely the application of that normal force at an effective frictional radius. All of the
forces which are active within the differential are derivable from the torque which is
being conveyed by the differential and the friction coefficients of surfaces within the
differential.
Therefore, all of the frictional forces which are generated within the differential, and all
of the resulting resistant torques which oppose the transfer of torque between drive axles,
are proportional to the torque being conveyed by the differential. Since the maximum
difference in torque between drive axles which can be supported by friction is
proportional to the combined torque of the drive axles, the maximum bias ratio remains
constant with respect to changes in the combined drive axle torques.
27
In addition to providing a geared interconnection between drive axles which permits the
usual opposite relative rotation between the drive axles, the gearing also distributes forces
which may be generated to resist differentiation over a large number of different surfaces
within the differential. The surfaces over which the Invex gearing distributes forces are
designed with different coefficients of friction and the Invex gearing is designed to
distribute different loads between the surfaces. Collectively, the surfaces and the gearing
are designed to distribute wear evenly over the surfaces and to control the overall amount
of friction within the differential needed to achieve a desired bias ratio.
The twenty-one components which make up the differential are shown in Figure 4. All
components of the Index gear system are contained within the housing. Input power
usually is transmitted to the housing by way of a ring gear (crown wheel) bolted to the
housing itself. Trunnion are adapted to receive bearings by which the housing is
rotatively supported and retained within the axle carrier assembly. These Trunnion also
receive the respective axle ends which are splined to the side gears within the housing.
Each side gear meshes with element gears arranged at intervals about the periphery of the
associated side gears; tangent to, and in engagement with, the pitch surfaces of the side
gears. Each of these element gears is formed with a helical middle portion and spur gear
end portion. Each side gear meshes with the middle portion of these associated element
gears. At the same time, the integral spur gear portion of each element gear meshes with
the spur portion of its adjacent element gear. Element gears are shaft-mounted by means
28
of their associated journal pins. The number of element gears and associated hardware
may vary.
However, the usual arrangement has three sets of element gear pairs arranged at 120
degree intervals as illustrated. It is this arrangement of Invex gearing that provides for (a)
connecting the drive axles for opposite directions of relative rotation with respect to the
differential housing and, (b) controlling the transfer of torque between drive axles.
Completing the hardware complement are thrust washers used between each end of each
side gear, between side gears and the housing. Selection of thrust washers is important in
determining the operating characteristics for each application. Proprietary Gleason
models permit pre selection of components with a high degree of accuracy with respect to
actual vehicle characteristics.
2.3.4 OVERALL BIAS CONTROL
The differential may be designed with different bias ratios ranging from approximately
'2.5:1' to '6:1' or higher. This may be accomplished by varying the side gear helix angles,
or by altering the friction characteristics for the primary components. An increase in helix
angle increases the thrust component of the side gear meshes along the axis of the side
gears so that smaller portions of the loads communicated by the side gear meshes are
related to rotation of the side gears.
29
In addition, the higher thrust component along the axis of the side gears increases
frictional resistance at the end faces of the side gears which opposes side gear rotation
and thereby further contributes to an increase in bias ratio.
2.3.5 BIAS RATIOS BETWEEN DRIVE AND COAST MODES
It is also an important design freedom to provide for different effective bias ratios
between vehicle driving and coasting modes. Since the Torsen differential is designed to
have little or no effect on vehicle performance unless torque is being transferred by the
differential, it should be understood that what is meant by the coasting mode is actually
vehicle deceleration caused by engine braking. This mode is most evident with standard
shift vehicles engaged in downshifting.
Index gearing also makes possible this important design alternative. The side gears within
the differential are designed with the same hand of helix angle. When engine power is
applied to the differential (i.e., drive mode), both side gears are thrust against the same
end of the differential housing. Alternatively, when the engine is used to brake the drive
wheels (i.e., coast mode), the side gears are thrust against the opposite end of the housing.
This feature provides an opportunity to vary frictional characteristics between opposite
ends of the housing to vary bias ratios between the opposite directions of power transfer
through the differential. The possibilities for independently varying bias ratios between
the two directions of power transfer enables the differential to be designed with one bias
30
ratio to compensate for undesirable steering effects associated with downshifting and a
second bias ratio which is selected for most other purposes.
CHAPTER - 3
COMPONENTS AND DESCRIPTION
3.1. DIFFERENTIAL:
WHAT'S A DIFFERENTIAL?
When a vehicle is negotiating a corner, the outside wheel has to travel a grater distance
than the inside wheel. Therefore, the outside wheel must turn faster than the inside wheel.
The differential is the device within the axle assembly which, in addition to transmitting
the power to each axle
shaft/wheel, allows one wheel to
turn at a different speed than the
other. A conventional open
differential sends equal amounts
of torque to both axle shafts (top).
31
If one wheel spins because of lost traction, it is sustaining zero engine torque, so zero
engine torque is also going to the wheel with traction. Adding a locking differential—in
this case a No Spin locker (bottom)—mechanically links the two shafts so that power will
be delivered to both axles in all circumstances.
WHY YOU NEED A DIFFERENTIAL
Car wheels spin at different speeds, especially when turning. You can see from the
animation below that each wheel travels a different distance through the turn, and that the
inside wheels travel a shorter distance than the outside wheels. Since speed is equal to the
distance traveled divided by the time it takes to go that distance, the wheels that travel a
shorter distance travel at a lower speed. Also note that the front wheels travel a different
distance than the rear wheels. For the non-driven wheels on your car -- the front wheels
on a rear-wheel drive car, the back wheels on a front-wheel drive car -- this is not an
issue.
There is no connection between them, so they spin independently. But the driven wheels
are linked together so that a single engine and transmission can turn both wheels. If your
car did not have a differential, the wheels would have to be locked together, forced to
spin at the same speed. This would make turning difficult and hard on your car: For the
car to be able to turn, one tire would have to slip. With modern tires and concrete roads, a
great deal of force is required to make a tire slip. That force would have to be transmitted
32
through the axle from one wheel to another, putting a heavy strain on the axle
components.
3.1.2 THE FUNCTION OF A DIFFERENTIAL:
To aim the engine power at the wheels
To act as the final gear reduction in the vehicle, slowing the rotational speed of the
transmission one final time before it hits the wheels
To transmit the power to the wheels while allowing them to rotate at different
speeds (This is the one that earned the differential its name.)
3.1.3 TYPES OF DIFFERENTIALS
Conventional or Open
Limited Slip
Automatic Locking
Manual Locking
i. OPEN DIFFERENTIALS:
Use two side gears inside the differential case. Each gear is splined to accept an axle
shaft. These side gears are in turn driven by a set of spider gears. The spider gears, also
inside the differential case, ride on a shaft which is pinned into the differential case and
through which all the power is transmitted. The case is driven by the ring gear which is
33
bolted fast to the case. The conventional differential is fitted as standard equipment on
most vehicles.
On paved roads this system is very successful, giving predictable handling, even tire wear
and requiring very little maintenance. However, in off road situations where traction
surfaces vary greatly, this type of differential has a major limitation. When one wheel has
greater traction than the other, all the power will be directed to the wheel with the least
traction. For example, if one wheel is in the air and the other wheel is still on a hard
surface, then all the power will be transferred to the wheel in the air. No power will go to
the one on the ground and the vehicle will not move.
34
Fig. 3.1.1 WORKING OF A DIFFERENTIAL UNIT
ii. LIMITED SLIPS:
(LSD's) come in a variety of designs. Most use friction plates, cones and/or gears to
reduce slippage between each of the tires. These units have a dual power path from the
differential case to the axle shafts. Some power is transmitted through the spider gears to
the side gears in the conventional manner. The remainder is transmitted by friction
35
between the differential case and the clutch plates and the side gears. A certain amount of
"clutch preload" is built into the unit in a static condition.
Then, as load is applied to the differential, the separation forces between the spider gears
and the side gears increases this clutch loading. This increase in friction provides for a
good positive power flow from the case directly to the side gears. When traction is
available to both wheels, the power going to the differential causes the plates to bind
tightly together, giving even power to both wheels.
However, in a situation where there is little or no traction available to either one wheel or
the other, the amount of power that can be transmitted to the other wheel which has
traction is dependent on the friction or "preload" in the clutch plates. High levels of
"clutch preload" will result in good torque transfer but some chattering of the clutches
during cornering may occur. Lower levels of preload results in minimal chatter but
reduced levels of torque transfer to the wheel with traction. Because LSD's restrict true
differential action, tire wear is accelerated. Changes in vehicle handling may also occur,
particularly in short wheelbase vehicles. Wear rates on limited slip differentials are
generally higher than on other types due to the reliance on friction to reduce wheel
slippage. Also, special lubricants may be required to minimize rough and noisy operation.
Despite their limitations, LSD's are popular as original equipment options as well as an
aftermarket replace because:
1) Some traction improvement off road is provided
2) Vehicle handling idiosyncrasies are not excessive
36
3) Installation is simple
4) Cost is reasonable
iii. AUTOMATIC LOCKERS:
Transmit power to each wheel through a pair of dog clutches. Differential action, such as
when cornering is provided by automatically disengaging the appropriate clutch when
one wheel rotates faster than the other. This results in differential action which occurs in
ratcheting stages rather than being smooth and progressive. Power received by the
differential is automatically directed to the wheel with greater traction. Therefore, if one
wheel is lifted off the ground, the other wheel will receive the total power applied to the
differential to maintain vehicle mobility.
Traction is far superior to conventional and limited slip differentials. While automatic
locking differential provide excellent performance off road, vehicle handling, particularly
on highway, is sacrificed. Unlocking during cornering can be sudden, resulting in a rapid
change of direction, particularly in short wheel based vehicles. During sharp cornering an
audible ratcheting sound usually occurs as differential action takes place and a loud
banging noise may be heard when the unit locks up again.
Tire wear is usually increase. On 4WD vehicles, installation is normally considered for
the rear axles only. Front axle installations can cause extreme difficulties in steering.
37
iv. MANUALLY LOCKABLE DIFFERENTIALS
Use a conventional differential in conjunction with a mechanical locking device which
can be operated at the driver’s discretion. when locked, both axles will then turn at the
same speed irrespective of the road surface. When it is unlocked, the differential
functions as a conventional differential giving predictable handling, long service life and
no increase in tire wear. It can be installed in both the front and rear axles without
compromising on-road performance. Although manually lockable differentials are
available in tractors and some military style vehicles, the installation in mass produced
recreation type vehicles have been restricted by high cost and complexity of installation
v. VISCOUS COUPLING:
The viscous coupling is often found in all-wheel-drive vehicles. It is commonly used to
link the back wheels to the front wheels so that when one set of wheels starts to slip,
torque will be transferred to the other set.
The viscous coupling has two sets of plates inside a sealed housing that is filled with a
thick fluid, as shown in below. One set of plates is connected to each output shaft. Under
normal conditions, both sets of plates and the viscous fluid spin at the same speed. When
one set of wheels tries to spin faster, perhaps because it is slipping, the set of plates
corresponding to those wheels spins faster than the other. The viscous fluid, stuck
between the plates, tries to catch up with the faster disks, dragging the slower disks along.
38
This transfers more torque to the slower moving wheels -- the wheels that are not
slipping.
When a car is turning, the difference in speed between the wheels is not as large as when
one wheel is slipping. The faster the plates are spinning relative to each other, the more
torque the viscous coupling transfers. The coupling does not interfere with turns because
the amount of torque transferred during a turn is so small. However, this also highlights a
disadvantage of the viscous coupling: No torque transfer will occur until a wheel actually
starts slipping.
A simple experiment with an egg will help explain the behavior of the viscous coupling.
If you set an egg on the kitchen table, the shell and the yolk are both stationary. If you
suddenly spin the egg, the shell will be moving at a faster speed than the yolk for a
second, but the yolk will quickly catch up. To prove that the yolk is spinning, once you
have the egg spinning quickly stop it and then let go -- the egg will start to spin again
(unless it is hard boiled). In this experiment, we used the friction between the shell and
the yolk to apply force to the yolk, speeding it up. When we stopped the shell, that
friction -- between the still-moving yolk and the shell -- applied force to the shell, causing
it to speed up. In a viscous coupling, the force is applied between the fluid and the sets of
plates in the same way as between the yolk and the shell.
3.2 PNEUMATIC COMPONENTS
39
The word ‘pneuma’ comes from Greek and means breather wind. The word pneumatics is
the study of air movement and its phenomena is derived from the word pneuma. Today
pneumatics is mainly understood to means the application of air as a working medium in
industry especially the driving and controlling of machines and equipment.
Pneumatics has for some considerable time between used for carrying out the simplest
mechanical tasks in more recent times has played a more important role in the
development of pneumatic technology for automation.
Pneumatic systems operate on a supply of compressed air which must be made available
in sufficient quantity and at a pressure to suit the capacity of the system. When the
pneumatic system is being adopted for the first time, however it wills indeed the
necessary to deal with the question of compressed air supply.
The key part of any facility for supply of compressed air is by means using reciprocating
compressor. A compressor is a machine that takes in air, gas at a certain pressure and
delivered the air at a high pressure. Compressor capacity is the actual quantity of air
compressed and delivered and the volume expressed is that of the air at intake conditions
namely at atmosphere pressure and normal ambient temperature.
The compressibility of the air was first investigated by Robert Boyle in 1962 and that
found that the product of pressure and volume of a particular quantity of gas.
40
PV = C (or) PıVı = P2V2
In this equation the pressure is the absolute pressured which for free is about 14.7 Psi and
is of courage capable of maintaining a column of mercury, nearly 30 inches high in an
ordinary barometer. Any gas can be used in pneumatic system but air is the mostly used
system now a days.
3.2.1 PRODUCTION OF COMPRESSED AIR
Pneumatic systems operate on a supply of compressed air, which must be made available,
in sufficient quantity and at a pressure to suit the capacity of the system. When pneumatic
system is being adopted for the first time, however it wills indeed the necessary to deal
with the question of compressed air supply.
The key part of any facility for supply of compressed air is by means using reciprocating
compressor. A compressor is a machine that takes in air, gas at a certain pressure and
delivered the air at a high pressure. Compressor capacity is the actual quantity of air
compressed and delivered and the volume expressed is that of the air at intake conditions
namely at atmosphere pressure and normal ambient temperature.
Clean condition of the suction air is one of the factors, which decides the life of a
compressor. Warm and moist suction air will result in increased precipitation of condense
from the compressed air. Compressor may be classified in two general types.
41
1. Positive displacement compressor.
2. Turbo compressor
Positive displacement compressors are most frequently employed for compressed air
plant and have proved highly successful and supply air for pneumatic control application
3.2.2 PNEUMATIC SINGLE ACTING CYLINDER:
Pneumatic cylinder consist of A) PISTON B) CYLINDER
The cylinder is a Single acting cylinder one, which means that the air pressure operates
forward and spring returns backward. The air from the compressor is passed through the
regulator which controls the pressure to required amount by adjusting its knob. A
pressure gauge is attached to the regulator for showing the line pressure. Then the
compressed air is passed through the single acting 3/2 solenoid valve for supplying the air
to one side of the cylinder. One hose take the output of the directional Control (Solenoid)
valve and they are attached to one end of the cylinder by means of connectors. One of
the outputs from the directional control valve is taken to the flow control valve from
taken to the cylinder. The hose is attached to each component of pneumatic system only
by connectors.
3.2.2.1 CYLINDER TECHNICAL DATA:
42
Piston Rod:
M.S. hard Chrome plated
Seals:
Nitrile (Buna – N) Elastomer
End Covers:
Cast iron graded fine grained from 25mm to 300mm
Piston:
-Aluminium.
Media:
-Air.
Temperature Range:
0°c to 85°c
Parts of Pneumatic Cylinder
1. Piston:
The piston is a cylindrical member of certain length which reciprocates inside the
cylinder. The diameter of the piston is slightly less than that of the cylinder bore
diameter and it is fitted to the top of the piston rod. It is one of the important parts which
convert the pressure energy into mechanical power.
43
The piston is equipped with a ring suitably proportioned and it is relatively soft rubber
which is capable of providing good sealing with low friction at the operating pressure.
The purpose of piston is to provide means of conveying the pressure of air inside the
cylinder to the piston of the oil cylinder.
Generally piston is made up of
Aluminium alloy-light and medium work.
Brass or bronze or CI-Heavy duty.
The piston is single acting spring returned type. The piston moves forward when the
high-pressure air is turned from the right side of cylinder.
The piston moves backward when the solenoid valve is in OFF condition. The piston
should be as strong and rigid as possible. The efficiency and economy of the machine
primarily depends on the working of the piston. It must operate in the cylinder with a
minimum of friction and should be able to withstand the high compressor force
developed in the cylinder and also the shock load during operation.
The piston should posses the following qualities.
a. The movement of the piston not creates much noise.
b. It should be frictionless.
c. It should withstand high pressure.
44
2. Piston Rod
The piston rod is circular in cross section. It connects piston with piston of other
cylinder. The piston rod is made of mild steel ground and polished. A high finish is
essential on the outer rod surface to minimize wear on the rod seals. The piston rod is
connected to the piston by mechanical fastening. The piston and the piston rod can be
separated if necessary. One end of the piston rod is connected to the bottom of the piston.
The other end of the piston rod is connected to the other piston rod by means of coupling.
The piston transmits the working force to the oil cylinder through the piston rod. The
piston rod is designed to withstand the high compressive force. It should avoid bending
and withstand shock loads caused by the cutting force. The piston moves inside the rod
seal fixed in the bottom cover plate of the cylinder. The sealing arrangements prevent the
leakage of air from the bottom of the cylinder while the rod reciprocates through it.
3. Cylinder Cover Plates
The cylinder should be enclosed to get the applied pressure from the compressor and act
on the pinion. The cylinder is thus closed by the cover plates on both the ends such that
there is no leakage of air. An inlet port is provided on the top cover plate and an outlet
ports on the bottom cover plate. There is also a hole drilled for the movement of the
piston. The cylinder cover plate protects the cylinder from dust and other particle and
maintains the same pressure that is taken from the compressor. The flange has to hold
the piston in both of its extreme positions. The piston hits the top plat during the return
45
stroke and hits the bottom plate during end of forward stroke. So the cover plates must
be strong enough to withstand the load.
4. Cylinder Mounting Plates:
It is attached to the cylinder cover plates and also to the carriage with the help of ‘L’
bends and bolts.
3.2.2.2. SOLENOID VALVE:
The directional valve is one of the important parts of a pneumatic system. Commonly
known as DCV, this valve is used to control the direction of air flow in the pneumatic
system. The directional valve does this by changing the position of its internal movable
parts. This valve was selected for speedy operation and to reduce the manual effort and
also for the modification of the machine into automatic machine by means of using a
solenoid valve. A solenoid is an electrical device that converts electrical energy into
straight line motion and force. These are also used to operate a mechanical operation
which in turn operates the valve mechanism. Solenoids may be push type or pull type.
The push type solenoid is one in which the plunger is pushed when the solenoid is
energized electrically. The pull type solenoid is one is which the plunger is pulled when
the solenoid is energized. The name of the parts of the solenoid should be learned so
that they can be recognized when called upon to make repairs, to do service work or to
install them.
46
Parts of a Solenoid Valve
1. Coil
The solenoid coil is made of copper wire. The layers of wire are separated by insulating
layer. The entire solenoid coil is covered with an varnish that is not affected by solvents,
moisture, cutting oil or often fluids. Coils are rated in various voltages such as 115 volts
AC, 230 volts AC, 460 volts AC, 575 Volts AC, 6 Volts DC, 12 Volts DC, 24 Volts DC,
115 Volts DC & 230 Volts DC. They are designed for such frequencies as 50 Hz to 60
Hz.
2. Frame
The solenoid frame serves several purposes. Since it is made of laminated sheets, it is
magnetized when the current passes through the coil. The magnetized coil attracts the
metal plunger to move. The frame has provisions for attaching the mounting. They are
usually bolted or welded to the frame. The frame has provisions for receivers, the
plunger. The wear strips are mounted to the solenoid frame, and are made of materials
such as metal or impregnated less fiber cloth.
3. Solenoid Plunger
The Solenoid plunger is the mover mechanism of the solenoid. The plunger is made of
steel laminations which are riveted together under high pressure, so that there will be no
47
movement of the lamination with respect to one another. At the top of the plunger a pin
hole is placed for making a connection to some device. The solenoid plunger is moved
by a magnetic force in one direction and is usually returned by spring action. Solenoid
operated valves are usually provided with cover over either the solenoid or the entire
valve. This protects the solenoid from dirt and other foreign matter, and protects the
actuator. In many applications it is necessary to use explosion proof solenoids.
48
3.2.2.3 WORKING OF 3/2 SINGLE ACTING SOLENOID (OR) CUT OFF
VALVE
The control valve is used to control the flow direction is called cut off valve or solenoid
valve. This solenoid cut off valve is controlled by the emergency push button. The 3/2
Single acting solenoid valve is having one inlet port, one outlet port and one exhaust port.
The solenoid valve consists of electromagnetic coil, stem and spring. The air enters to the
pneumatic single acting solenoid valve when the push button is in ON position.
Technical Data:
Size : ¼”
Pressure : 0 to 7 kg / cm2
Media : Air
Type : 3/2
Applied Voltage : 230V A.C
Frequency : 50 Hz
3.2.2.4 FLOW CONTROL VALVE:
Technical Data:
Size : ¼”
Pressure : 0 to 10 N/m2
Media : Air
49
Purpose:
This valve is used to speed up the piston movement and also it acts as an one – way
restriction valve which means that the air can pass through only one way and it can’t
return back. By using this valve the time consumption is reduced because of the faster
movement of the piston.
50
CHAPTER – 4
WORKING PRINCIPLE & DESIGN CALCULATIONS
4.1 WORKING PRINCIPLE
The main purpose of this project is to lock the differential or to disengage the differential
at the time when it is needed to be. So to lock the differential we need to connect the two
shafts on the either side so that the differential has no effect on the axle. Now to connect
the two shafts we use two circular plates on the either sides of the differential. Both are in
such a way that they get mated as soon as possible even in their rotation. So when the
pneumatic valve is actuated then one of the plates is pushed to the other so that the plates
get mated and hence the shafts are connected. So thus the differential is disengaged. To
engage the differential again a spring is used to push the plates apart. Thus this is the
working principle of this project.
51
BLOCK DIAGRAM
Fig. 4.3.1 BLOCK DIAGRAM OF THE WRKING UNIT
52
COMPRESSOR (OR) AIR TANK
FLOW CONTROL VALVE
SOLENOID OPERATED VALVE
PNEUMATIC CYLINDERLEVER
MECHANISMDIFFERENTIAL
UNIT
PUSH BUTTON OR SWITCH
4.2 DESIGN CALCULATIONS
4.2.1. PNEUMATIC CYLINDER
Design of Piston rod:
Load due to air Pressure.
Diameter of the Piston (d) = 35 mm
Pressure acting (p) = 6 N/m²
Material used for rod = C 45
Yield stress (σy) = 36 N/m²
Assuming factor of safety = 2
Force acting on the rod (P) = Pressure x Area
= p x (Πd² / 4)
= 6 x {( Π x 3.5² ) / 4 }
P = 57.73 N
Design Stress(σy) = σy / FOS
= 36 / 2 = 8 N/m²
= P / (Π d² / 4 )
∴ d = √ 4 p / Π [ σy ]
53
= √ 4 x 57.73 / {Π x 18}
= √ 4.02 = 2.02 mm
∴ Minimum diameter of rod required for the load = 2.02 mm
We assume diameter of the rod = 12.5 mm
Design of cylinder thickness:
Material used = Cast iron
Assuming internal diameter of the cylinder = 35 mm
Ultimate tensile stress = 250 N/m²
Working Stress = Ultimate tensile stress / factor of safety
Assuming factor of safety = 4
Working stress ( ft ) = 2500 / 4 = 625 N/m²
According to ‘LAMES EQUATION’
Minimum thickness of cylinder ( t ) = ri {√ (ft + p) / (ft – p ) -1 }
Where,
ri = inner radius of cylinder in mm.
ft = Working stress (N/m²)
p = Working pressure in N/m²54
∴ Substituting values we get,
t = 1.75 { √ (625 + 6) / ( 625 – 6) -1}
t = 0.0168 cm = 0.17 mm
We assume thickness of cylinder = 2.5 mm
Inner diameter of barrel = 35 mm
Outer diameter of barrel = 35 + 2t
= 35 + ( 2 x 2.5 ) = 40 mm
4.2.2 Design of Piston rod:
Diameter of Piston Rod:
Force of piston Rod (P) = Pressure x area = p x Π/4 (d²)
= 6 x (Π / 4) x (3.5)²
= 57.73 N
Also, force on piston rod (P) = (Π/4) (dp)² x ft
P = (Π/4) x (dp)² x 625
57.73 = (Π/4) x (dp)² x 625
∴ dp ² = 57.73 x (4/Π) x (1/625)
55
= 0.12
dp = 0.34 cm = 3.4 mm
By standardizing dp= 12.5 mm
Length of piston rod:
Approach stroke = 50 mm
Length of threads = 2 x 20 = 40mm
Extra length due to front cover = 12 mm
Extra length of accommodate head = 20 mm
Total length of the piston rod = 50 + 40 + 12 + 20
= 122 mm
By standardizing, length of the piston rod = 130 mm
4.3 TECHNICAL DATA
4.3.1. Single acting pneumatic cylinder
Stroke length : Cylinder stoker length 100 mm
56
Quantity : 1
Seals : Nitride (Buna-N) Elastomer
End cones : Cast iron
Piston : EN – 8
Media : Air
Temperature : 0-80 º C
Pressure Range : 8 N/m²
Fig. 4.3.2 PNEUMATIC OPERATED SINGLE ACTING CYLINDER
57
4.3.2 3/2 solenoid valve:-
Technical Data:
Size : ¼”
Pressure : 0 to 8 N/m2
Media : Air
Type : 3/2
Applied Voltage : 230V A.C
Frequency : 50 Hz
Fig. 4.3.3 SOLENOID CONTROL VALVE
58
4.3.3. Flow control Valve
Port size : 0.635 x 10 ֿ² m
Pressure : 0-8 x 10 ⁵ N/m²
Media : Air
Quantity : 1
59
Fig. 4.3.5 ASSEMBLY LAYOUT OF THE AUTOMATIC DIFFERENTIAL
LOCK UNIT SYSTEM
CHAPTER - 5
PERFORMANCE OF DIFFERENTIAL UNIT
60
5.1 TORSION DIFFERENTIAL PERFORMANCE
The Torsion design makes important contributions to vehicle performance, especially
with respect to the concerns of traction management. These contributions may be better
understood with respect to familiar vehicle operating conditions which give rise to
problems of traction management.
5.2 VEHICLE TRAVEL ON STRAIGHT ROADS
On smooth, dry, straight road surfaces, with no apparent traction management problem,
Torsion differential performance is virtually undetectable from that of an open
differential. However, on slippery road surfaces where one of the drive wheels does not
have adequate traction to support at least one-half of the applied engine torque to the
differential housing, the Torsion differential delivers an increased amount of the applied
torque to the drive wheel having better traction. The amount of additional torque which
can be delivered to the wheel having better traction is limited only by the bias ratio or the
amount of traction available to that wheel.
Of course, it is never possible to deliver more torque to the drive wheels than the torque
which combined traction of the drive wheels will support. However, a Torsion
differential designed with an appropriate bias ratio assures that, for most vehicle
61
operating conditions, the vehicle can deliver all of the torque which combined traction of
the drive wheels will support.
5.3 VEHICLE TRAVEL THROUGH TURNS
In turning situations, the outside wheels of a vehicle travel over more distance than the
inside wheels. Accordingly, the inside and outside drive wheels must rotate at slightly
different speeds (i.e., differentiate) to maintain rolling traction with the road. A torque
division between drive axles at the bias ratio is a precondition for differentiation under all
circumstances of operation. Essentially, in order for one drive wheel to rotate faster than
the other, the drive wheel having greater resistance to rotation slows with respect to the
differential case and transfers torque to the other wheel contributing to its faster rotation.
The Torsion differential resists transfers of torque between drive wheels in proportion to
the torque applied to the differential housing, and these results in a larger proportion of
the applied torque being delivered to the slower rotating drive wheel. Therefore, bias
ratio should be selected to provide the maximum traction advantage that will still allow
both drive wheels to deliver significant portions of engine torque in turns. However, even
in turning situations, the Torsion differential enhances traction management.
Since torque is already distributed in increased proportion to the inside drive wheel, it is
exceedingly unlikely that the outside drive wheel will ever exceed available traction and
'spin up'. Alternatively, should the torque of the inside wheel exceed available traction in
a turn, it is equally unlikely for this wheel to 'spin up' since such a 'spin up' would still
62
require a difference in traction between drive wheels which exceeds the bias ratio.
Ordinarily, when the inside wheel exceeds available traction, differentiation ceases and
torque is divided in more even proportion between drive axles determined by the
maximum torque that can be sustained by the inside drive wheel. Thus, in all directions
of travel, the Torsion differential will resist 'spin up' of either drive wheel by instantly
dividing torque between drive axles in proportions up to the bias ratio to match prevailing
traction conditions.
5.4 CENTER BOX APPLICATION
Although the differential has been mostly described with respect to its use between drive
axles, it should be understood that analogous performance can be expected from use of
the differential as an operative connection between drive shafts to the front and rear axles.
For example, traction management is enhanced in such 'center box' applications by
assuring that more of the traction of the front and rear drive wheels is available for use.
5.5 CONCLUSION
63
The Torsion differential exhibits a torque biasing characteristic which matches available
engine power to changing traction conditions.
In particular, Index gearing provides special design opportunities to match different
biasing characteristics with different vehicle applications and conditions of use to best
accommodate traction considerations in each instance. Gleason's applied engineering can
provide optimal Torsion differential designs to meet a wide variety of traction
management requirements.
64
CHAPTER - 6
LIST OF MATERIALS & COST ESTIMATION
6.1 MATERIAL COST:
Sl. No.PARTS
Qty. Material Amount (Rs)
i. Auto Differential 1 Cast iron 1970
ii. Single Acting pneumatic Cylinder 1 Mild Steel 685
iii. Flow control valve 1 Brass 225
iv. Direction control valve 1 Mild Steel 330
v Connecting PU Tube - Polyurethene 200
vi Hose collar and reducer - Brass 250
vii Frame - Mild Steel 1250
Total = Rs. 4910
65
2. LABOUR COST
LATHE, DRILLING, WELDING, GRINDING, POWER HACKSAW, GAS CUTTING:
Cost = 1500/-
3. OVERHEAD CHARGES
The overhead charges are arrived by “Manufacturing cost”
Manufacturing Cost = Material Cost + Labour cost
= 4910 +1500
= RS. 6410.
Overhead Charges = 20% of the manufacturing cost
= Rs. 1282.
4. TOTAL COST
Total cost = Material Cost + Labour cost + Overhead Charges
= 4910 + 1500 + 1282
= Rs. 7692. ( app. 7800)
Total cost for this project = Rs. 7800.
66
6.2 APPLICATIONS & ADVANTAGES
APPLICATIONS
All Four wheeler application
ADVANTAGES
Less Manual force is required to locking the differential unit
This pneumatic system is also working with the help of air tank
Time consumption is less
More efficient system and simple in construction
DISADVANTAGES
High Initial cost.
67
6.3 CONCLUSION
SUMMARY OF THE WORKDONE
This project work has provided us an excellent opportunity and experience, to use our
limited knowledge. We gained a lot of practical knowledge regarding, planning,
purchasing, assembling and machining while doing this project work. We feel that the
project work is a good solution to bridge the gates between institution and industries.
We are proud that we have completed the work with the limited time successfully. The
AUTOMATIC LOCKABLE DIFFERENTIAL is working with satisfactory
conditions. We are able to understand the difficulties in maintaining the tolerances and
also quality. We have done to our ability and skill making maximum use of available
facilities. In conclusion remarks of our project work, let us add a few more lines about
our impression project work.
In concluding the words of our project, since the locking of the differential is very much
useful in reducing a considerable amount of loss due the transmission through the
differential and also in recovering the heavy trucks from pits in rainy season this could be
a source for the above said solutions.
68
BIBLIOGRAPHY
1. G.B.S. Narang, “Automobile Engineering”, Khanna Publishers, Delhi, 1991, pp 671.
2. Pneumatic Control System----Stroll & Bernaud, Tata Mc Graw Hill Publications,
1999.
3. Yoshinari Awaji, Toshiaki Kuri, Wataru Chujo, Mitsuru Naganuma, and Ken-ichi
Kitayama, "Differential-phase-to-intensity conversion based on injection locking of a
semiconductor laser," Opt. Lett. 26, 1538-1540 (2001)
4. Shu Yongping (East China Shipbuilding Institute.Zhenjiang. Jiangsu. Theoretical
Calculation and Experimental Verification of the Exciting Force in Gear
Transmission.
5. Effects of locking differentials on the snaking behavior of articulated steer
vehicles, International Journal of Vehicle Systems Modelling and Testing 2007 -
Vol. 2, No.2 pp. 101 – 127.
6. www.4wdsystems.com.au/pdf/ LOKKA %20discussion%20 paper .pdf
lokka differential locker paper.
69
70