Transmission Systems Guide

UNIT - 3
TRANSMISSION SYSTEMS
Prepared By:K.Rajesh, AP/Mech,RMKCET

TOPICS TO BE DISCUSSED
 Clutch-types and construction
 Gear boxes
 Gear shift mechanisms
 Over drive
 Transfer box
 Fluid flywheel –torque converter
 Propeller shaft
 Slip joints
 universal joints
 Differential
 Rear axle
 Hotchkiss Drive andTorqueTube Drive

TRANSMISSION SYSTEM
INTRODUCTION
 Transmission system is the system by means of which power
developed by the engine is transmitted to the road wheels to
propel the vehicle.
 In automobiles the power is developed by the engine which is in
turn used to turn the wheels.

REQUIREMENT OF TRANSMISSION SYSTEM
 To provide for disconnecting the engine from the driving wheels.
 When the engine is running, to enable the connection to the
driving wheels to be made smoothly and without shock.
 To enable the leverage between the engine and driving wheels to
be varied.
 It must reduce the drive-line speed from that of the engine to that
of thedriving
 Turn the drive, if necessary, through 90° or perhaps otherwise
realignit.
 Enable the driving wheels to rotate at different speeds.
 Provide for relative movement between the engine and driving
wheels.

COMPONENTS AND ITS FUNCTION

The functions of the components are as follows
 Clutch is used for disconnecting the engine from the driving
wheels and it must also enable the driver to connect the engine.
 Gearbox is to enable the driver to change the leverage between
the engine and driving wheels to suit the prevailing conditions
gradient, load, speed required, etc.
 Propeller shaft transmits the drive on to the back axle
 Universal joints at its ends allow both the engine-and-Gearbox
assembly and the back axle to move relative to one another, as
their spring elements deflect.

 Sliding joint accommodates variations in length of the
propeller shaft as its rear end rises and falls vertically with the
back axle.
 Differential gearing, which shares the driving torque equally
between the two road wheels
 Transfer box is to transfer the power and torque from the
main gearbox to both the front and rear axles.

CLUTCH
 A clutch is a releasable coupling connecting the adjacent ends
of two coaxial shafts. It is said to be engaged or, in, when the
shafts are coupled, and disengaged, or out, when they are
released.
 Mechanical clutches fall into two main categories:
1. Positive engagement
2. Progressive engagement.

 Positive engagement, so that no torque can be transmitted
from the driving to the driven shaft, or positively engaged, in
which case the shafts rotate together, connected by some
mechanical devices such as splines, keys or dogs.
 Progressive type is gradually engaged, so that the speed of the
driving shaft falls while, simultaneously, that of the driven shaft
rises from its initial stationary state until both are rotating at
equal speeds.

FUNCTIONS OF CLUTCH
• To permit engagement or disengagement with gear box
• To transmit the engine power to the rear wheals smoothly
without shock.
• It should dissipate the heat produced due to friction contact
• It should be dynamically balanced to the vibration in the
transmission system.
• To permit the engaging of the gears when the vehicle is in motion
without damaging the gear wheels.

TYPES OF CLUTCH
❖ Single plate
❖ Multiplate
❖ Cone clutch
❖ Centrifugal clutch
❖ Semi centrifugal clutch
❖ Hydraulic clutch
❖ Vaccum clutch
❖ Electromagnetic clutch

PARTS OF THE CLUTCH
1. Fly wheel
2. Clutch plate or disc plate
3. Pressure plate
4. Clutch cover assembly
5. Release mechanism
6. Withdrawal force & rearing
7. Primary or clutch shaft

SINGLE PLATE CLUTCH:
• It is most commonly used in motor vehicle such as cars,trucks
& tractors.

CLUTCH OVERVIEW

T
T
W (axial thrust)W
Friction
plate
Friction
liningPressure
plates
springs
Single-plate Friction Clutch (Disengaged position)
Driving
shaft
Driven
shaft
Flat-plate friction clutches

Single-plate Friction Clutch (Engaged position)
T
T
W (axial
thrust)
W
Friction plate
Friction
lining
Pressure
plates
springs
Driving
shaft
Driven
shaft
Flat-plate friction clutches

ADVANTAGES
• It makes easy to change gears than cone type.
• It is reliable than cone clutch.
DISADVANTAGES
• It requires more force to release.
• Space required to accommodate the clutch is more as
compare to multi plate clutch.

DIAPHRAGM CLUTCH
❖ The construction of this type of clutch is similar to that of single
plate clutch except that here diaphragm spring called belleville
springs are used instead of the ordinary coil springs.
❖ This type of clutch is quite advantage because it requires no
release levers and the spring itself act as series of levers.

Diaphragm clutch

ADVANTAGES
❖ This requires lower operating effort due to reduced
friction in the clutch mechanism.
❖ There is a constant and uniform load on the driven plate
thorughout the life of the clutch.
❖ Due to its compact size, clutch housing required is quite
short.

MULTI-PLATE CLUTCH
• Multi-plate clutch are used in heavy vehicles with racing cars
and motorcycle for transmitting high torque.
• As compare to single plate clutch these are smoother and
easier to operate due to their assembly of friction surfaces
contact.

ADVANTAGES
• Increased torque transmission capacity.
• Highly reliable.
• Suitable for heavy vehicles.

CONE CLUTCH
 The contact surface of this type of clutch are in the form of
cones, it is called as cone clutch.
 It consists of two cones having leather facings.
 The cones are known as male and female cones.

ADVANTAGES
 Normal force acting on the contact surface is larger than the axial
force reduces the effort required to operate the clutch.
DISADVANTAGES
 A small amount of wear on cone surface results in considerable
axial movement of the male cone for which it will be difficult to
allow

CENTRIFUGAL CLUTCH
 This clutch is controlled by the engine speed through an
accelerator.
 When the engine speed falls down, the clutch will automatically
disengaged the speed will raise above the predetermined value
and the clutch is engaged.

Centrifugal clutch

SEMI-CENTRIFUGAL CLUTCH
❖ These clutches are similar to the centrifugal clutches with only
difference that here relatively light clutch pressure springs
exerting low pressure at idling speed are used.
❖ In this clutch, the pressure between the plates is increased as the
speed of rotation of the clutch increases in proportion to the
pressure requirements.

Semi-centrifugal clutchPrepared By:K.Rajesh, AP/Mech,RMKCET

HYDRAULIC CLUTCH
❖ When the clutch is located at distance from the driver its
difficult run cables or rods.
❖ In heavy vehicles in order to transfer large power high spring
pressure clutches are required.
❖ High spring pressure requires more human effort and hence
use of hydralics will reduce effort required.

Hydraulic clutchPrepared By:K.Rajesh, AP/Mech,RMKCET

ELECTRO-MAGNETIC CLUTCH
❖ An electro-magnetic clutch consists of a engine flywheel
provided with electric winding.
❖ A driven plate lined with friction materials is provided.
❖ It is free to move on splines of the gearbox shaft.
❖ A pressure plate is applied for engaging or disengaging the
clutch.

Electro-magnetic clutch

VACUUM CLUTCH
❖ The vacuum clutch is operated in the same way as the hydraulic
clutch.
❖ The only difference is that it is operated by vacuum pressure
whereas the hydraulic clutch is operated by oil pressure.
❖ In vacuum clutches the partial vacuum existing in the engine
manifold is used for operating it.

Vacuum clutch

GEAR BOX
 The transmission is part of the power train. It consists of a
metal case filled with gears.
 It is usually located in the rear of the engine between the clutch
housing and the propeller shaft.
 It transfers engine power from the clutch shaft to the propeller
shaft. It allows the driver or operator to control the power and
speed of the vehicle
 A gearbox is necessary, therefore, so that the driver can regulate
torque by selecting the appropriate speed range or, in other
words, the vehicle speed at which maximum torque is obtainable

gearbox

PURPOSE OF THE TRANSMISSION
 Provide a means to vary torque ratio between the engine and
the road wheels as required.
 According to the requirement the speed can be varied.
 Provides a neutral position.
 A means to back the car by reversing the direction of rotation
of the drive is also provided by the transmission.

TYPES OF GEARBOX
1. Manual transmission
a) Sliding mesh gearbox
b) Constant mesh gearbox
c) Synchromesh gearbox
2. Epicyclic gearbox
3. Automatic gearbox
a) Hydromatic gearbox
b) Torque converter gearbox

GEAR BOXE- MANUAL
1. Constant mesh
gears.
2. Primary shaft
(Clutch shaft)
3. Spigot bearing.
4. Main shaft.
5. Lay shaft (counter
shaft)

SLIDING MESH GEARBOX
PRIMARY SHAFT
 This shaft transmits the drive from the clutch to the gearbox .
 At the end, the shaft is supported by a spigot bearing
positioned close to the splines on to which the clutch driven
plate is connected.
 The main load on this shaft is taken by a bearing; normally a
sealed radial ball type, positioned close to an input gear called
a constant mesh pinion
 The gear is so named because it is always in mesh with a larger
gear
 Small driving gear is called a pinion and a large gear a wheel.

LAYSHAFT
 This shaft, which is normally fixed to the gearbox casing,
supports the various-sized driving pinions of the lay shaft gear
cluster
MAIN SHAFT
 This splined output shaft carries spur gearwheels that slide
along the shaft to engage with the appropriate lay shaft gears.
 At the ‘front’ end, the main shaft is supported by a spigot
bearing situated in the centre of the constant mesh pinion.

Sliding mesh gearbox

CONSTANT MESH GEARBOX
 There are many different forms of constant-mesh gearbox, in
some of which the various gears slide axially along their shafts,
while in others they have no axial freedom.
 The characteristic feature of this type of gearbox is, however,
that all the pairs of wheels are always in mesh
 To eliminate the noise developed in the old spur-tooth type
of gears used in the sliding gear transmission, the constant-mesh
transmission that contains helical gears.
 The main shaft meshing gears are arranged so that they cannot
move endwise. They are supported by roller bearings that allow
them to rotate independently of the main shaft

CONSTANT MESH GEARBOX

Layout Of Constantmesh GearboxPrepared By:K.Rajesh, AP/Mech,RMKCET

Constant mesh gearbox

Constantmesh Gear Box Gear Position
NEUTRAL FIRST GEAR
SECOND GEAR THIRD GEAR

FORTH GEAR
REVERSE GEAR
Constantmesh Gear Box Gear Position

SYNCHROMESH GEARBOX
 The synchromesh transmission is a type of constant-
mesh transmission.
 It synchronizes the speeds of mating parts before they engage to
allow the selection of gears without their clashing.
 It employs a combination metal to metal friction cone clutch
and a dog or gear positive clutch.
 These clutches allow the main drive gear and second-speed
main shaft gear to engage with the transmission main shaft.
 The friction cone clutch engages first, bringing the driving
and driven members to the same
speed, after which the dog clutch engages easily without
clashing.

 This process is accomplished in one continuous operation when
the driver declutches and moves the control lever in the usual
manner.
Synchromesh gearboxPrepared By:K.Rajesh, AP/Mech,RMKCET

Synchromesh gearboxPrepared By:K.Rajesh, AP/Mech,RMKCET

Synchromesh gearbox synchronizerPrepared By:K.Rajesh, AP/Mech,RMKCET

ADVANTAGES
 Gear changing is very much simplified.
 Reduction in gear wear occurs.
 It allows the usage of helical gears that runs quickly.
 The design is very much complex.
 Initial cost is high
 Quick change of gears occurs due to noise of crashing.
DISADVANTAGES

AUTOMATIC GEARBOX
 Most modern automatic gearboxes have a set of gears called a
planetary or epicyclic gear train.
 In ordinary gearing, the axes of the various gears are fixed.
These gears are simply rotated about their axes.
 A planetary gear set consists of a central gear called the sun
gear, an outer ring with internal gear teeth (also known as the
annulus, or ring gear), and two or three gears known as planet
gears that rotate between the sun and ring gears.
 The drive train is coupled to a mechanism known as a torque
converter, which acts as a fluid drive between the engine and
transmission.
 If the sun gear is locked and the planets driven by the planet
carrier, the output is taken from the ring gear, achieving a
speed increase.
EPICYCLIC GEARBOX

EPICYCLIC GEARBOX…..
 If the ring gear is locked and the sun gear is driven, the planet
gears transmit drive through the planet carrier and speed is
reduced.
 With power input going to the sun gear and with the planet
carrier locked, the ring gear is driven, but transmits drive in
reverse.
 To achieve direct drive without change of speed or direction of
rotation, the sun is locked to the ring gear and the whole unit
turns as one.
 The same effect can also be achieved by locking the planet gears
to the planet carrier.
 Most automatic gearboxes have three forward speeds, and use
two sets of epicyclic gears.

EPICYCLIC GEARBOX…..
 The locking sequences of the epicyclic gear train are achieved by
hydraulic pressure operating brake bands or multi-plate
clutches.
 The bands are tightened round the ring gear to prevent it
turning, and the clutches are used to lock the sun gear and
planets.
 The correct sequence of pressure build-up and release is
controlled by a complex arrangement of hydraulic valves in
conjunction with sensors that respond to engine load, road
speed and throttle opening.
 A mechanism linked to the throttle - known as a kick down - is
used to effect a change-down for rapid acceleration. When you
press down the accelerator suddenly to its full extent, a lower
gear is selected almost instantly.
 Most automatic gearboxes have an override system so that the
driver can hold a low gear as required.

ADVANTAGES
 The planetary gears are in constant mesh. Hence dos clutches or
sliding gears are not used.
 It is distributed over several gears wheels instead of having the load
on only one pair of gears.
 A greater area of gear tooth contact can be obtained due to
distribution of loads.

TRANSFER BOX
 A transfer box is interposed between the gearbox and back axle
unit. The function of transfer box is to transfer the drive from
the main gearbox to both the front and rear axles.

FLUID FLYWHEEL
 A fluid coupling or hydraulic coupling is a
hydrodynamic device used to transmit rotating mechanical
power. It has been used in automobile transmission as an
alternative to a mechanical clutch.
 It couples the driving member with driven member through a
media of fluid.
Two turbines (fan like components):
 One connected to the input shaft; known as
the pump or impellor, primary wheel input turbine
 The other connected to the output shaft, known as
the turbine, output turbine, secondary wheel or runner

Fluid flywheel

ADVANTAGES
 It gives a smoother power takes up than the centrifugal type,
when the engine is accelerated.
 There is no wear on moving parts.
 No need of adjustments is required.
 It is simple in design.
 No skill is required for operation.

DISADVANTAGES
 There is a drag on the gear box-shaft even the slip is 100%.
 It has the gear changing difficult with the ordinary crash type
gearbox.

TORQUE CONVERTER
 A torque converter is a device which performs a function
similar to that of a gearbox.
 But whereas a gearbox provides only a small number of fixed
ratios the torque converter provides a continuous variation of
ratio from the lowest to the highest.
 Torque converters all consist of the driving element (impeller)
which is connected to the engine, the driven element (rotor)
which is connected to the propeller shaft, and the fixed
Element (reaction member) which is fixed to the frame.

TORQUE CONVERTER

GEAR SHIFT MECHANISM
With the gearbox of the conventional car installed right behind the clutch and the gear lever placed
close to the driver, the two must be connected by a remote control rod in the gear box casing.

The striker rod of a sliding selector mechanism is
guided across the gearbox by the driver and moves the
guard to expose the slot in a sleeve. The striker rod
enters the slot, and further movement of the gear lever
slides the sleeve along its rod to engage a gear. A
locking ball engages a recess in the rod to hold the
sleeve.

The ball-type selector has a similar striker
rod but a different guard, which is part of
the locking plunger. When the striker
moves sideways it disengages the plunger
and engages the selector sleeve's slot.
Movement of the plunger also unlocks the
selector sleeve, so it is then free to slide
along its rod and engage a gear.

The rod of a column-mounted gearchange
runs down either the side or centre of the
steering column. Two movements, raising
the lever and turning the rod, select and
engage the gears.

The gearchange used on the Renault 4 ran
through the fascia to the gearbox. Twisting
the rod selected the gear (via the auxiliary
lever) and sliding the rod engaged it.

The selection mechanism of the Vauxhall Viva (GM) had a toothed rod inside
a slotted collar. The rod was turned to engage a shoulder on a selector fork,
then moved backward or forward to slide the selector and dog clutch into
position. The collar ensured that only one fork was engaged at a time.

The Ford Escort system centres on a single rod, on which the forward speed
selector forks are mounted. Connected to the gear lever, this rod also carried an
arm and peg. When the gear lever was moved across the "gate" the rod turned,
and the peg engaged a slot in the appropriate selector fork - that for first/second
gear was engaged here. The gear lever was then moved forward, so sliding the
selector fork backwards, while the other forks were held in position by the locking
plate.

PROPELLER SHAFT
 Propeller shaft transmits the drive from the engine to the
drive axles.
 Propeller shaft consists of three main parts
1. Shaft
2. Universal joints
3. Slip joints

Propeller shaft figurePrepared By:K.Rajesh, AP/Mech,RMKCET

1. SHAFT
 Shaft is the member which transmits the power. It needs to
withstand torsional loads mainly. Normally the shafts are of
tubular cross sections. They needs to be well balanced to
avoid whirling at high speeds.
 Materials used for shafts are steel aluminum or composites
materials.
 The mass of the shaft has to be made small to avoid high
rotational moment of inertia which decreases acceleration
capabilities of the system.

TYPES OF PROPELLER SHAFTS
Solid or open type Hollow or enclosed type
1. Used in heavy commercial vehicles
different types of cars and light vehicles.
2. It has tubular cross section.
3.Two universal joints are connected at the
ends.
4. Propeller shaft is long comparatively so it is
made up of two portions.
5. It is connected to the chassis with the help
of bearing.
1. The propeller shaft is of solid cross section.
2. It is fitted to gearbox casing by a ball joint or
large spherical bearing to resist torque reaction.
3. It prevents twisting of axle on its springs during
power transmission.
4.The diameter of this propeller shaft is small
compared to open type.

2. UNIVERSAL JOINTS
 Universal joints are used to transmit power between inclined
shafts.
 Different kinds of universal joints are
 Hooks joint
 Hooks joint with needle roller bearings
 Perfect circle U joints
 Flexible Ring universal joints

 They are mainly used for making flexible connection between
two rigid shaft at an angle.
 It is used to connect propeller shaft and gear box during the
transmission of rotary motion.
 Transmission of power under this varying condition is impossible
without using of a flexible device or universal joint.
 It consist of two yokes, connected to each end of the shaft.
 It does not permit the motion uniformly, if the shafts are
operated at an angle.

CLASSIFICATION OF UNIVERSAL JOINTS
Variable velocity
joints
Constant velocity
joints

VARIABLE VELOCITY JOINTS
 In this joints the driven and driving shafts do not turn at same
speed through each part of revolution is at same speed.
 They are further classified into three types:
1. Cross or spider type.
2. Ring type
3. Ball and trunion type.

Cross or spider type
Ring type Ball and trunion type

CONSTANT VELOCITY JOINTS
 In this type, the driven shaft and the driving shaft turns at the
same speed through each part of the revolution and at the any
degree of flex.
 This is further classified into three types:
1. Rzeppa .
2. BendixWeiss.
3. Tracta.

Rzeppa
Bendix Weiss

3. SLIP JOINT
 Slip joint is provided to accommodate for the variations of
the length of the propeller shaft. This is necessary due to the
relative movements of the axle and the vehicle body due to
the suspension action.
 The slip joint is formed by internal splines on the sleeve and
external splines on the propeller shaft.

Slip joint figure

IMPROVEMENTS in transmission system
 Viscous coupling – which responds to the difference in the
speed. The torque transmitted depends on the slip between
the shafts.
 It consist of silicon based oil which thickens on shearing
action. It consist of cylindrical chamber of fluid with a stack
of perforated rotating discs. The discs are connected
alternatively to the inside and outside shaft and chamber. The
viscosity of the fluid causes the movement of the discs.

Viscous coupling figure

DIFFERENTIAL
 When a vehicle is negotiating a corner, the outside wheel has
to travel a greater distance than the inside wheel. Therefore
the outside wheel must turn faster than the inside wheel.
 The differential is the device within an axle assembly that
differentiates the wheel speed between the two wheels.
 The differential also transmits the power from the ring gear to
the axle shafts and determine how much power is delivered to
each axle.

PARTS OF DIFFERENTIAL
 Pinion Drive Gear: transfers power from the driveshaft to
the ring gear.
 Ring Gear: transfers power to the Differential case assembly.
 Side/spider gears: help both wheels to turn independently
when turning.
 Differential case assembly: holds the Ring gear and other
components that drive the rear axle.
 Rear drive axles: steel shafts that transfer torque from the
differential assembly to the drive wheels
 Rear axle bearings: ball or roller bearings that fit between
the axles and the inside of the axle housing
 Axle housing: metal body that encloses and supports parts of
the rear axle assembly. Prepared By:K.Rajesh, AP/Mech,RMKCET

ADVANTAGES:
 Simple design
 Robust and reliable
 Few moving parts
 Inexpensive to produce
DISADVANTAGES:
 Supplies equal torque to both wheels
APPLICATIONS:
 Most production car applications, both cars and trucks
CONVENTIONAL DIFFERENTIAL

FUNCTIONS
 Transfers power from driveshaft to the wheels.
 Provides final gear reduction.
 Splits amount of torque going to each wheel.
 Allow the wheels to rotate at different speeds in turns.

TYPES OF DIFFERENTIAL
1. Open or Conventional differential
2. Limited slip differential (LSD)
3. Locking differential
4. AutomaticTorque biasing

LIMITED SLIP DIFFERENTIAL
 A limited slip differential (LSD) or anti-spin is another type of
traction aiding device that uses a mechanical system.
 This is activated under centrifugal force to positively lock the
left and right spider gears together when one wheel spins a
certain amount faster than the other.
 This type behaves as an open differential unless one wheel
begins to spin and exceeds that threshold.
 While positraction units can be of varying strength, some of
them with high enough friction to cause an inside tire to spin
or outside tire to drag in turns like a spooled differential.
 The LSD will remain open unless enough torque is applied to
cause one wheel to lose traction and spin, at which point it
will engage.

 A LSD can use clutches like a posi when engaged, or may also be
a solid mechanical connection like a locker or spool. It is called
limited slip because it does just that; it limits the amount that
one wheel can "slip" (spin).

ADVANTAGES:
 Manages vehicle traction mechanically
 Completely passive system, no user or electrical controller
input required
DISADVANTAGES:
 Many moving components, more susceptible to failure
 Expensive to produce
APPLICATIONS:
 Optional OEM equipment, performance oriented or high
end production vehicles
 Road racing

LOCKING DIFFERENTIAL
 A locking differential, such as ones using differential gears in
normal use but using air or electrically controlled mechanical
system.
 It is the one which when locked allow no difference in speed
between the two wheels on the axle.
 They employ a mechanism for allowing the axles to be locked
relative to each other, causing both wheels to turn at the same
speed regardless of which has more traction.
 This is equivalent to effectively bypassing the differential gears
entirely.
 Other locking systems may not even use differential gears but
instead drive one wheel or both depending on torque value
and direction.

 Automatic mechanical lockers do allow for some differentiation
under certain load conditions, while a selectable locker typically
couples both axles with a solid mechanical connection like a spool
when engaged.

ADVANTAGES:
 No moving parts, extremely durable and strong
 Maintains constant speed between both wheels
 Produces a yaw stabilization force acting through the rear
axle, i.e. resists vehicle rotation
DISADVANTAGES:
 Maintains constant speed between both wheels
APPLICATIONS:
 Purely off-road vehicles, Drag racing, Oval Racing

TORSEN DIFFERENTIAL
 A high-friction 'Automatic Torque Biasing' (ATB) differential,
such as the Torsen differential, where the friction is between the
gear teeth rather than at added clutches.
 This applies more torque to the driven road wheel with highest
resistance (grip or traction) than is available at the other driven
road wheel when the limit of friction is reached at that other
wheel.
 When tested with the wheels off the ground, if one wheel is
rotated with the differential case held, the other wheel will still
rotate in the opposite direction as for an open differential.
 But there will be some frictional losses and the torque will be
distributed at other than 50/50. Although marketed as being
"torque-sensing", it functions the same as a limited-slip
differential

 Shortened from “Torque Sensing” Differential.
 Relies on gear pressure angles to cause a mechanical binding in a gear
train that resists different wheel speeds.
 Non adjustable, and difficult to quantify the performance without
expensive equipment.
 Has a large performance window, which enables it to be used in a
wide range of applications
 Still relies on torque input from the wheels to respond and can only
apply a ratio of the torque to the non-slipping wheel

ACTIVE DIFFERENTIAL
 A relatively new technology is the electronically-controlled
'active differential'.
 An electronic control unit (ECU) uses inputs from multiple
sensors, including yaw rate, steering input angle, and lateral
acceleration and adjusts the distribution of torque to
compensate for undesirable handling behaviors like
understeer.
 Active differentials used to play a large role in the World Rally
Championship, but in the 2006 season the FIA has limited the
use of active differentials only to those drivers who have not
competed in the World Rally Championship in the last five
years.

 Fully integrated active differentials are used on the Ferrari F430,
Mitsubishi Lancer Evolution, and on the rear wheels in the Acura
RL. A version manufactured by ZF is also being offered on the B8
chassis Audi S4 and Audi A4.
 The Volkswagen Golf GTI Mk7 in Performance trim also has an
electronically controlled front-axle transverse differential lock,
also known asVAQ.
 The second constraint of the differential is passive it is actuated by
the friction kinematics chain through the ground. The difference in
torque on the road wheels and tires (caused by turns or bumpy
ground) drives the second degree of freedom, (overcoming the
torque of inner friction) to equalize the driving torque on the
tires.

 The sensitivity of the differential depends on the inner friction
through the second degree of freedom. All of the differentials (so
called “active” and “passive”) use clutches and brakes for restricting
the second degree of freedom, so all suffer from the same
disadvantage decreased sensitivity to a dynamically changing
environment.
 The sensitivity of the ECU controlled differential is also limited by
the time delay caused by sensors and the response time of the
actuators.

REAR AXLE
 Rear Axles are structural members on which Rear wheels are
mounted on bearings.
 The weight of the body of the automobile and load due to the
occupants is transmitted through springs to the axle casing.
FORCES AND TORQUES ON THE REAR AXLE
 Weight of the Body
 Driving thrust
 Torque Reaction
 Side thrust

1.WEIGHT OFTHE BODY
 Rear axle behaves like a beam supported at the ends and loaded at two
points.
 The load coming on the axle is due to the weight of the body being
transmitted through the suspension springs.
 Weight causes shear force and bending on the wheels.
2. DRIVINGTHRUST
 Torque produced by the engine causes the thrust on the wheels. This
force is responsible for the forward motion of the vehicle.
 The drive force from the wheels is transmitted to the body or chassis by
means of Radius rods or thrust members. These members are in
longitudinal direction connecting axle casing and the body.

3.TORQUE REACTION
 Torque reaction occurs due to the resistance offered by the wheels to
the motion. This causes a torque produced on the axle in the counter
clockwise direction when viewed from the left side of the vehicle rear
wheel axle.
 The torque produced by the braking torque is just the opposite to the
torque reaction.
 The torque reaction is opposed by Panhard rod which connects the
Rear axle to the vehicle body or chassis and prevents excessive bending
load coming onto the propeller shaft.
4. SIDETHRUST
 Side thrust comes mainly when the vehicle is taking a turn or when the
vehicle is moving along an laterally inclined surface.
 The side thrust coming on to the axle can be taken by Panhard rod.

LOADS COMING ONTO LIVE REAR AXLE SHAFT
 Shearing force due to vehicle weight
 Bending moment due to the offset of the wheel and the
suspension.
 End thrust due to the side forces due to cornering, side wind etc.
 Bending moment due to end thrust and reaction from the tires.
 Driving torque.

TYPES OF REAR AXLE
 DriveAxle
 Semi floating axle
 Full floating axle
 Three quarter floating axle
 Dead axle or Lazy axle

SEMI-FLOATING AXLE
 The wheel hub is connected directly to the rear axle.
 All the loads are taken by the rear axle (Shearing, Bending, End
thrust, Driving torque and brake torque).
ADVANTAGES
 The semi floating axle is the simplest and cheapest and they are
widely used in cars.
DISADVANTAGES
 The axle has to be designed for carrying higher loads i.e. they are of
higher diameter for the same torque transmitted by other types of
axle supporting.

Semi floating axlePrepared By:K.Rajesh, AP/Mech,RMKCET

FULL FLOATING AXLE
 The wheels hubs are mounted directly onto the axle casing and are
supported by two taper roller bearings.
 The load on the axle is very less. It need to take only the drive
torque.
ADVANTAGES
 These are very robust type and are used for heavy vehicles.
 Axle shaft carry only the drive torque so their failure does not affect
the vehicle wheels.
 Vehicle can be towed with the broken axle shaft.
 Axle shaft can be replaced by without jacking.
DISADVANTAGE
 Costliest type of axle supporting.

Full floating axle Prepared By:K.Rajesh, AP/Mech,RMKCET

THREE QUARTER FLOATING AXLE
 The bearing is mounted between the axle and the axle casing.
 The axle shaft has to take drive torque and the end loads.
 The axle casing will take Bending an shearing forces.
ADVANTAGES
 At one time this axle type was commonly used for cars and light
commercial vehicles.
DISADVANTAGES
 These axles are no longer preferred. instead semi floating axles are
used.

Three quarter floating axle figure

REAR AXLE DRIVES
1. Hotchkiss Drive
2. Torque tube drive

HOTCHKISS DRIVE
 Simplest and most widely used rear axle drive.
 The suspension springs take torque reaction driving thrust and side
thrust
 Propeller shaft with two universal joints and a sliding joint. The spring
is fixed rigidly in the middle onto the frame. The drive torque is
transmitted through the front half of the springs.
 The front end of the leaf suspension is rigidly fixed onto the frame
while the rear is connected via a shackle.
 Two universal joints are used to avoid the bending of the propeller
shaft due to the torque reaction.
 Sliding joint is provided to accommodate for the variation of the length
in the transmission shaft.

Hotchkiss drive figure

TORQUE TUBE DRIVE
 Torque reaction, Braking torque and drive thrust are taken by Torque
tube.
 The suspension springs are taking only the side thrust and body
weight.
 One end of the torque tube is attached to the axle casing while the
other end is spherical and fits into the cup on the frame. The torque
tube encloses the propeller shaft.
 Torque tube takes the torque reaction and centre line of the bevel
pinion shaft always passes through the centre of the spherical cup.
 Single universal joint is used in the transmission drive because the
universal joint is situated exactly at the centre of the spherical cup.
 No sliding joint is provided since the pinion shaft and the propeller
shaft moves same center ( spherical cup).

TORQUETUBE DRIVE

Torque tube drive figure

REAR AXLE CASINGS
1. Split type.
2. Banjo or Separate carrier type.
3. Salisbury or Integral Carrier type.

1. SPLIT TYPE
 The axle casing is made in two halves and then bolted together
for assembly. But the main disadvantage is whole rear axle has
to be removed as a unit and reassembled in case of a fault. This
kind is no longer used now.

2. BANJO OR SEPARATE CARRIER
 Axle is made as a single piece The complete differential
unit is separate unit and is bolted to the axle casing and the
two shafts are put from two sides.
 In case of repair the shafts can be taken from two sides and
differential can be removed easily.

3. SALISBURY OR INTERGRAL CARRIER TYPE
 This is similar to the banjo type except that the permanent
housing tubes are pressed and welded onto the sides.
 This is the most commonly used kind of rear wheel driven
cars.

Final drive
• Final drive is used to provide a permamanent speed
reduction and to turn the drive through 90 degree.
• The reduction ratio provided by the final drive is 4:1 for cars
and 10:1 for heavy vehicles.
• The reduction ration upto 7:1 can be done in single stage and
above that is done in two stages.This is done to reduce the
size of the gear and to improve the ground clearance.
• Final drive can be bevel pinion and crown wheel or worm
and worm wheel arrangement.

TYPES OF GEARS FOR FINAL DRIVE
1. Straight Bevel Gears.
2. Spiral Bevel Gears.
3. Hypoid Bevel Gears
4. Worm andWormWheel Arrangement.

1. Straight bevel gears
• The gears have straight teeth.
• Advantages
• Simplest and Cheapest
• Disadvantages
• Uneven transmission due to contact of single pair of teeth.
• Less load carrying capacity.
• Noisy and high levels of wear.

Straight bevel gears

2. Spiral bevel gears
• Spiral bevel gears have curved teeth so have greater number
of teeth in contact.The gear tooth have sliding motion also in
between.
• Advantages
• Silent Running.
• They are able to take more loads.

Spiral bevel gears figure

3. Hypoid gears
• The structure of the teeth have hyperboloid in shape. Hyperboloid
is obtained by rotating a hyperbolaAbut an offset axis.
• The gears transmit motion at right at right angles but the axis of
the gears don’t intersect but they lie at an offset distance.
• Advantages
• The hypoid gears permit a lower position of the propeller shaft
and allow more lower chassis height or less chassis height as the
case may be.
• Hypoid gears increases the loads capacity of the gears.
• Disadvantage
• Expensive difficult to assemble and need special lubricant due to
the greater sliding action between the gears.

Hypoid gears figure

4. Worm and worm wheel
• Worm is a single or multi started thread which drives the worm wheel which
has teeth over the periphery of the wheel.
• Higher gear ratios are possible in worm and worm wheel arrangement.
• Advantages
• Worm andWorm wheel arrangement is particularly used in heavy vehicle
where higher gear ratios of greater than 6 needed
• Strong and efficient drive
• Single stage reduction is only necessary for higher gear ratios also.
• Worm gears give low chassis height or more ground clearance as the case may
be.
• Disadvantages
• Higher cost and more weight than bevel gear
• Mechanical efficiency is lower than bevel gear for single stage reduction
• Lubrication is difficult with overhead worm.

Worm and worm wheel Figure

Thank you

Transmission Systems Guide

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

Similaire à Transmission Systems Guide

Similaire à Transmission Systems Guide (20)

Dernier

Dernier (20)

Transmission Systems Guide