Automotive transmission 1

8/10/2019 Automotive transmission 1

1/13

I CHAPTER

CLUTCH

Power transmission: The power developed by the engine in automobiles should be transmitted

to the road wheel efficiently. The power transmission system basically needs a clutch to transmit

the power from the engine to the remaining parts of the transmission. The power transmission

system is different for different types of vehicles.In case of two wheelers with gears the power is transmitted from the clutch to the gearbox and

then transmitted to the wheels by means of chain drive or gear drive. In case of non geared two

wheelers the power is transmitted from the clutch directly to the wheels through the chain drive /

gear drive or sometimes through the variator mechanism.

In case of LMVs and TVs the power transmission consists of clutch and gearbox as the

common features. In the conventional !front engine rear wheel drive" the power is transmitted

from gearbox to road wheels by means of universal #oint$ propeller shaft$ sliding #oint$

differential and half shaft. In case of front engine front wheel drive transaxle is commonly used.

In this case the gear box is arranged transversely and power transmission may not be provided

with propeller shaft and bevel gear arrangement. This type of arrangement is compact and also

contains less number of moving parts. In the case of four wheel drive$ the arrangement is similarto conventional power transmission with transfer gear box or transfer case as the additional

features. The transfer gear box transmits the power to both the axles uniformly.

Functions of a Clutch:

The tor%ue developed b the engine at starting speed is very low. Therefore$ it is not possible to

start the engine under load. This re%uires that the transmission system should provide a means of

connecting and disconnecting the engine from rest of the transmission system. &uch an operation

must be smooth and without shoc' to the occupants of the vehicle.

Thus the two main functions of a clutch are:

(. To engage and disengage the transmission from engine to the remaining parts of transmission.

!To allow the engine to be separated from rest of the transmission system" This is re%uired when:

!a" &tarting and running the engine at a sufficiently high speed lo generate sufficient power

necessary for moving the vehicle from rest.

!b" &hifting the gears so that damage to gear teeth can be avoided.

!c" &topping the vehicle after applying bra'es.

). The second function of the clutch is to allow the engine to ta'e up the driving load of the

vehicle gradually and without shoc'.

Requirements of clutch:

The main re%uirements of a clutch are as follows:

(. It should be able to transmit maximum tor%ue of the engine.

). It should engage gradually to avoid sudden #er's.

*. It should be able to dissipate large amount of heat generated during clutch operation.

+. It should be dynamically balanced$ particularly in the case of high speed engine clutches.

,. It should have suitable mechanism to damp vibrations and to eliminate noise produced

during power transmission.

-. It should be as small as possible so that it will occupy minimum space.

. It should be easy to operate re%uiring as little exertion as possible on the part of the

driver.


2/13

. It should be made as light as possible so that it will continue to rotate for any length of

time after the clutch has been disengaged.

0. It must be trouble free and have longer life.

(1. It must be easy to inspect$ ad#ust and repair.

Classification of clutches:

Principle of operation of clutches:

2lutch wor's on the principle of friction. 3hen two friction surfaces are brought in contact with

each other and pressed with certain force they are united due to friction between them. If one is

rotated$ other will also rotate during this condition. It can be separated or brought into contact

whenever re%uired. 4ne surface is referred as driving member and other as driven member. The

friction between two surfaces depends upon

(. 5rea of contact surface.

). 6orce applied on them.

*. 2oefficient of friction of surface material.

3hen the driven member is brought in contact with driver$ the clutch slips initially. 5s thepressure increases the driven member is brought to the speed of the driving member. 3hen the

speed of both members becomes e%ual then two members are in frictional contact without any

2L7T2

84&ITIV9 9;5;9M9T

2L7T2

;


3/13

slip and clutch is said to be fully engaged. The driving tor%ue can be increased by increasing the

effective radius of contact$ coefficient of friction$ clamping force$ or the number of contact

surfaces.

SI!LE PLATE CLUTCH

Construction: The main components of the single plate clutch are driving member$ driven

member and the actuating lin'ages.

=riving Members: =riving members of single plate clutch are input shaft !cran' shaft" fixed to

the flywheel$ pressure plate$ and the clutch cover which is bolted to the flywheel. These fly

components rotate along with the cran' shaft in both engaged and disengaged condition. 6ly

wheel is attached to the cran' shaft and has threaded bolts or holes or grooves for bolting the

clutch covers. Machined surface of the flywheel contacts the clutch facing. The pressure plate

applies the re%uired force on the clutch plate which contacts with fly wheel. To apply the

re%uired force pressure springs are attached between the pressure plate and clutch cover. 8ressure

plate can be withdrawn by releasing the spring with the help of release lever. Lugs are provided

on the pressure plate for providing the release fingers. 8ressure plate springs are provided inside$

release finger$ and anti>ratting springs are provided inside the clutch cover and the entireassembly is bolted to fly wheel.

=riven members: It is the clutch plate which is splined to the driven shaft !clutch shaft or input

shaft of gear box" clutch plate is used with friction material on both the surfaces. It consists of a

centre hub with internal splines which moves along the splined shaft during the transmission.

The power is transmitted from the clutch to the shaft through these splines. It consists of

torsional or cushioning springs which transmit the force applied to the facing to the central hub.

The spring also reduces torsional vibrations and provides smooth engagement or disengagement

of the clutch. The friction material is normally riveted to the pro#ected portions of the clutch disc

in 2MV& and MV&.

5ctuating members: It consists of release fingers$ withdrawal for' and release bearing. The outer

end of the release finger is located on the pressure plate and inner end is pro#ected towards theclutch shaft and are positioned with the help of anti>rattling springs. 3ithdrawal for' carrying

*


4/13

the release bearing is pivoted in the clutch outer casing. The release bearing actuates the inner

end of the release fingers.

3or'ing / operation: In fully engaged condition the driven plate is firmly clamped between the

flywheel and pressure plate due to the force applied by springs. This forms a non>slip connection

between the driving and driven plates. ence when the flywheel rotates the clutch plate also

rotates and this cause the transmission of power to the input shaft of gear box through splines.

3hen clutch pedal is depressed the pressure on the driven plate is released by compressing the

pressure springs through the release fingers. In this condition there is no force acting on the

clutch plate and is free between the flywheel and pressure plate. This disengaged condition

ensures easier shifting of gears.

"IAPHRA!# CLUTCH

In this type of diagram type springs are used instead of coil / helical springs. This type of clutch

does not re%uire any release levers as the spring itself acts as the series of levers. This type ofsprings do not have constant rate characteristics as in the case of coil springs and the pressure on

the diaphragm springs increases until it is in flat position$ thereafter decreases after passing this

position. ence the driver does not have to exert heavy pedal pressure to hold the clutch out of

engagement compared to coil spring type. In coil spring type the spring pressure increases when

the pedal is depressed to disengage the clutch and high pressure is re%uired to 'eep the clutch in

disengaged position.

This clutch consists of conventional friction clutch$ thrust plate$ diaphragm type spring and

release sleeve. The diaphragm is held between the inner end of the main bearing and its outer

circumstance fits into the counter bore of the thrust plate. The central position of the diaphragm

spring is divided into several segments by radial slots terminating into holes. These segments

acts li'e spring providing the re%uired thrust on the pressure plate. This simple arrangementeliminates the necessity for providing separate release levers.

+


5/13

3or'ing: In the engaged position the spring pivots on the inner pivot rings as it is held on the

clutch cover so that its outer rings contacts with the pressure plate. 5gain in this conical position

the spring exerts through pressure to 'eep the pressure plate in firm contact with the clutch plate

and flywheel. 3hen the pedal is depressed the lin'age moves release bearing toward the

flywheel. 3hen the pedal is depressed the lin'age moves release bearing towards the flywheel to

disengage the clutch. 5s the bearing contacts with inner position of the conical springs it moves

that position forward which cause the lin' to move bac'ward. This removes the pressure on the

pressure plate and release the clutch plate from contact with other driving members.

5nother type of conical spring used is the crown spring. This type differs from the tapered finger

type with its surface corrugated instead of flat and the centre section is continuous without any

spring. The clutch spring fits between the pressure plate and clutch cover. The entire assembly is

held together by six spring retainer located on the pressure plate. The actuation of this type of

spring is similar to integral / split type diaphragm spring.

#ULTI PLATE CLUTCHES

The clutch having more than three discs is referred as multi disc clutch or multi plate clutch. It is

similar to single plate clutch but has more number of frictional and metallic plates. =ue to the

increase in the numbers of plates !friction" the frictional surface in contact is also increased

which increases the capacity of the clutch to transmit the some tor%ue the diameter of the plateclutch. ence the clutches are mostly commonly in two wheelers and three wheelers due to

compact in siAe. It is used in heavy duty transmission system for transmitting higher tor%ue. !6or

,


6/13

example tor%ue transmission in heavy earth moving e%uipments" and power ta'e off !8. T. 4."

transmission in tractors.

2onstruction: 2onstruction of multi plate clutches is similar to single plate clutch except the

arrangement of number of friction plates and metal plates. It consists of inner drum which is

referred to clutch shaft and has a number of plates splined to the outer surface. 5nother drum is

coupled to fly wheel and carries a number of plates splined to it inner surface. The plates are

arranged in alternate manners. The plates can revolve with the drum as well as it can slide

axially. 5 spring 'eeps the outer and inner plates pressed together$ so that the driving members

transmit the power to the driven member. The clutches can be disengaged by pulling the inner

drum against the spring force.

Multi plate clutch can be dry type or wet type. The clutch is partially filled with oil. The

coefficient of friction in oil varies from 1.1 to 1.( of asbestos based fabrics.

(. The oil acts as cushioning medium to provide smooth engagement and disengagement

). The oil also carries the heat dissipated by the clutch due to friction. This reduces

operations temperature and increases the left of the clutch plates.

*. The oil acts as lubricant and reduces axial thrust lost due to bending on splines.+. The ma#or disadvantage is the reduction in coefficient of friction when immersed in oil. It

can be compensated by using high operating pressure of different friction material.

;enerally cor' inserted multi plate clutches are used in wet clutches. In wet clutches the

fluid under pressure is fed along the shaft.

Cone clutch:

They are wedge clutch provides a positive drive when the external face of the male cone member

engages with the internet face of recessed conical member. The facing is usually fitted to the

female or recessed member in order to improve heat dissipation and durability. ormally cone

clutch are used with epicyclic gear trains for a higher tor%ue transmission. The energy which a

cone clutch can absorb during on engagement is less compared to the energy absorbed by a

multiple clutch. But it is compact$ cheaper and re%uires low clamping load due to the wedging

action. The cone clutches are loaded by spring or hydraulic cylinders. 3edge angle and accurate

axial alignment are the two important factors for good cone clutch performance. If the wedgeangle is very less$ it results in excessive wedge action and fierce engagement. This in turn results

in difficult operation for disengagement. If the wedge angle is too large it reduces tor%ue

-


7/13

transmission capacity of the clutch and ma'e the clutches to s'id. &emi>cone angle of ()>(- are

commonly used for effective tor%ue transmission.

The tor%ue transmitted by a cone clutch is given by

T C D3 !r(E r)" / ) sin F

3here$ r(and r)are the radius of large and small cone !friction" in meters. F is the semi G cone

angle.

=uring the engagement of clutch the driven member is forced towards the driving cone by the

spring force. ence the power is transmitted from the engine to the driving cone$ driving cone to

driven cone and driven to the gear box. 3hen the clutch is to be disengaged the driven cone is to

be pulled off by means of actuates cen'ages and contact surfaces are separated hence no power is

transmitted to the clutch shaft.

SE#I$CETRIFU!AL CLUTCHES:

This type of clutch ma'es use of centrifugal force to assist the spring force at high speed. To

reduce the effort of the driver operates the clutch the assistance is ta'en by the centrifugal force.

To transmit small tor%ue$ spring with minimum stiffness is used which is sufficient for applying

the re%uired amount of force and also not so stiff to minimiAe the strain of the driver during

disengagement. 3hen high power is transmitted through the clutch then pressure of the springs

is a considerable factor. In semi>centrifugal clutches help is ta'en by centrifugal force by 'eeping

certain weights in eccentric position. The springs are designed to transmit the power at normal

speeds and at high speed the assistance is ta'en by the weights$ the weighted lever is hanged at

three points at regular intervals. The lever is provided with fulcrum connected to the clutch cover

at one end hinged to the pressure plate ate centre and the weight is connected at the outer end.

The tail of the lever is provided with the ad#usting screw by means of which centrifugal force on

the pressure plate can be ad#usted. =uring the increase in speed the weight moves about fulcrum

due to the centrifugal force of the weight and hence the pressure plate moves towards the

flywheel increasing the tor%ue transmitting capacity.

Centrifu%al Clutch:This type of clutches operates automatically depending on engine speed of elements. The use of

clutch pedal$ pressure spring and also clutch ma'ing the operation very simple of ma'es use of

centrifugal force to apply the force on the floating plate as well as on the pressure plate for


8/13

'eeping the clutch in engaged position. In this type$ transmission of the power is controlled by

the operation of the accelerator. It ma'es the driving operation very easy and convenient. ence

it is used in automatic transmission in two wheelers with variator mechanisms or two>wheeler

without gear mechanism.

This system consists of flywheel as driving member and pressure plate as the driven member.

The pressure plate is provided with friction lining on its outer surface. The pressure plate is

actuated by means of floating spring which exerts pressure on the floating. The spring on the fly

wheel 'eeps the clutch is disengaged position at low speeds. 3hen the speed increases the

weight flees off thereby operating bell cran' lever and pressing the floating plate. The force

acting on the floating plate is transmitted to the pressure plate through the helical spring placed

between floating plate and pressure plated. =ue to this force the pressure plate is pressed on to

flywheel providing the transmission through the friction lining and thereby resulting in

engagement of clutch. The stop provided above the weight limits the amount of centrifugal force

of the speed is increased over this limit the pressure on plate will be constant.

4ther type of centrifugal clutches are used in automobiles !generally in mopeds" consists of

spider as the driving member. The spider has four shoes having the frictional surfaces. These are

'ept in contact with the cylindrical clutch case by means of springs. 5s the speed increases$ the

shoes extend outwards due to centrifugal force and ma'e contact with the cylindrical clutch to

transmit the power. The transmission starts as soon as the spring force exceeds the spring force

and shoes extends outwards. ence the power transmission starts as soon as the engine starts

rotating at a speed enough to develop the re%uired centrifugal force. The transmission stops as


9/13

soon as the engine speed drops below the desired value. ence no power is transmitted to the

road wheels when the engine is idle or running at lesser speed than the desired value.

Electroma%netic Clutch:

In this system the clutch is controlled by means electric current supplied to the field windings in

the flywheel. The fly wheel is attached with the field winding$ which is given electric current by

means of battery$ dynamo or alternator. The construction feature of main components is almost

similar to the single plate clutch. 3hen electric current is supplied to the windings the flywheel

will attract the pressure plate and clutch plate is forced between pressure plate and flywheel

resulting in engagement. 3hen the supply to the winding is cut off the clutch is disengaged by

releasing the pressure plate due to the force exerted by the helical springs or tension springs.

9lectromagnetic clutch consists of a clutch release switch. 3hen then driver holds the gear lever

to change the gear$ the switch is operated cutting off the current to the winding which causes the

clutch disengaged.

3hen the vehicle is stalling$ the engine speed is lower H the dynamo output is low$ the clutch is

not firmly engaged. Therefore$ three springs are also provided on the pressure plate which helps

the clutch engaged firmly at low speed also.

The forces of the electromagnet can be regulated by means of an electrical resistance provided

with acceleration system and controlled by the accelerator pedal. 3hen the speed is increased$the accelerator pedal is pressed and the resistance is gradually cut off and thus in this way$ force

of electromagnet is increased and clutch transmission becomes more rigid.

FRICTI& #ATERIALS

The various types of friction materials are as given under

!i" Mill board type: This material is in the form of sheets made of asbestos and treated with

certain impregnates. 6rom the standard sheet we can cut facing discs according to different siAe

re%uirements. This is the cheapest material and gives satisfactory results.

!ii" Moulded type: 3hen asbestos fibers are mixed with a suitable binder and heated to a definite

temperature and then moulded in dies under pressure$ this type of friction material is called

Jmoulded typeK. To improve the wearing %ualities of the material !sometimes metallic wires arealso inserted". This type of lining is stronger$ dense and capable to transmit heavy loads through

it. The disadvantage is only this that moulding for each siAe lining is very costly.

0


10/13

!iii" 3oven type: This type of material is made by spinning threads from asbestos fibres$ weaving

this thread into a cloth and then impregnating it with a bonding material. This type of material is

further divided into classes !a" the solid woven variety is woven to the re%uired thic'ness in one

operation and has a greater mechanical strength !h" the laminated variety consists of layers of

cloth placed on top of each other and held together by the bonding material. Both types may

incorporate brass wire.

CLUTCH LII! #ATERIALS

2ommon materials used for clutch lining are:

!i" 5sbestos: It can be used at high temperature also and linings of this material have coefficient

of friction of about 1 ).

!ii"


11/13

3hen the throttle is wide opened$ the pressure in the inlet manifold decreases due to which the

non>return valve closes$ isolating the reservoir from the manifold. Thus a vacuum exists in the

reservoir all the time.

In the normal operation$ the switch in the gear lever remains off$ the solenoid operated valve

remains in its bottom position. In this positions the atmospheric pressure acts on both the side ofthe vacuum cylinder$ because the vacuum cylinder is open$ so also atmosphere though a vent.

3hen the driver holds the lever to change the gear$ the switch is closed energiAing the solenoid

which pulls the valve up. This connects one side of vacuum cylinder to the reservoir. =ue to the

difference of pressure on the vacuum cylinder piston$ it moves. This movement of the piston is

transmitted by a lin'age to the clutch$ causing it to disengage. 3hen the driver is not operating

the gear lever$ the switch is open and the clutch remains engaged due to the force of springs.

H()raulic Clutch

The hydraulic clutch is operated in the same way as the vacuum clutch. 4nly the difference is

that it is operated by oil pressure whereas the vacuum clutch is operated by vacuum.

6ig. shows the mechanism of a hydraulic clutch. It consists of a cylinder with piston$ control

valve$ pump$ accumulator and oil reservoir. The piston is connected to the clutch by a lin'age.

The pump is operated by the engine itself. The oil from the reservoir is pumped into the

accumulator tan'. The accumulator tan' is connected to the cylinder through the control valve.

The control valve is electrically controlled by a switch in the gear lever.

3hen the driver holds the gear lever to change the gears$ the switch is operated to open the

control valve admitting the oil under pressure to the cylinder. =ue to the oil pressure$ the piston

moves causing the clutch to be disengaged. 5s soon as the driver leaves the gear lever$ the switch

is open which closes the control valve and the clutch is engaged.

"o% an) Splines clutch:

((


12/13

This type of clutch is used to loc' two shafts together or to loc' a gear to a shaft. It consists of a

sleeve having two sets of internal splines. It slides on a splined shaft with smaller diameter

splines. The bigger diameter splines match with the external dog clutch teeth on driving shaft.

3hen the sleeve is made to slide on the splined shaft$ its teeth match with the dog clutch teeth of

the driving shaft. Thus the sleeve turns the splined shaft with the driving shaft. The clutch is said

to be engaged. To disengage the clutch$ the sleeve is moved bac' on the splined shaft to have no

contact with the driving shaft.

This type of clutch has no tendency to sup. The driven shaft revolves exactly at the same speedas that of the driving shaft$ as soon as the clutch is engaged. Therefore it is also 'nown as

positive engagement clutch.

&E *A+ CLUTCHES , FREE *HEEL CLUTCHES:

These types of clutches are used to transmit the power in only one direction. The power is

transmitted from the driver to driven and not vice>versa. 3hen the drive rotates in the reverse

direction the clutches slips or disengages. This type of clutch mainly consists of an inner race

and outer race. The inner race is connected to the driver and the outer race is connected to the

driven.

SPRA! CLUTCH:

In this type several sprags are e%ually spaced between the inner and outer races. The sprags can

be installed in the direction as shown in the figure or can be tuned through (1 1to provide anti>

cloc'wise rotation. ;enerally sprags are provided with energiAing springs to hold the individual

sprags against the two races.

3hen the inner race rotates in anticloc'wise direction the sprag tilts in the same direction of

rotation. =ue to this action the sprag wedges between the inner and outer race. 5s a result the

outer race rotates in the same direction as that of inner race and at the same speed. If the outer

race rotates at more speed then the wedging action is removed and no power is transmitted.

&imilar action occurs if the inner race tries to rotate in the opposite direction. 4ne way clutchesare used to transmit the power in cloc'wise or anticloc'wise direction by the proper positioning

of springs.

()


13/13

-ALL A" R&LLER CLUTCH:

In this the inner race and outer races has several ramp li'e grooves in which the clutch elements

!roller or balls" are placed. 5 spring is positioned in front of these elements. Its purpose is to hold

the element against the ramp and race surfaces. 3hen the inner racer is rotated in cloc'wise

direction$ the friction between the inner race and rollers or balls moves them slightly in the same

direction. This wedges the balls or rollers between the ramps and surface of the inner race or

outer race$ causing the outer race to be driven in the same speed as that of the inner race. If the

outer race is rotated faster than the inner race$ distance between the ramp and race increases$

removing the wedging action of the clutch element and no power is transmitted between the

inner and outer race. If the inner race is rotated in the opposite direction it will result in the

similar way where no power is transmitted between the driving and driven member.

(*

Documents

Automotive transmission 1