DRIVE LINE
DRIVE LINE
Hi
Rear Wheel Drive (RWD)
Components of a Rear Wheel Drive
Slip Joint
Universal Joint Universal Joint
Propeller Shaft
Differential
Propeller Shaft
• A prop shaft (or propeller • The prop shaft is simply a metal
shaft to give it its full tube which is strong enough to • The shaft is connected to the back
name) is used with front transmit the full power of the of the gearbox. It runs beneath
engine rear-wheel drive engine and torque multiplied by the floor to join it to the back axle
vehicles. the gearbox.
Universal Joint (UJ)
• A universal joint (UJ) is • This is because, as the suspension • Without universal joints, as the car
usually needed at either moves up and down, a difference in goes over a bump, suspension
end of a prop shaft. height exists between the rear axle movement will try to bend the prop
and the gearbox. shaft.
Universal Joint (UJ)
• The most common type • The yokes, one on the input shaft
• This is sometimes called a spider.
of universal joint is the and the other on the output shaft,
The spider is formed by two pins are connected to the spider so
Hookes UJ. It is made up
crossing over each other at right that they are at right angles to
of two yokes pivoted on
angles. each other.
a central crosspiece.
• This arrangement allows
the input and output
shafts to rotate together
even when they are at
different angles.
Speed variation of a Hooke-type Universal Joint (UJ)
• This cyclic speed variation, and its
• When a Hooke-type UJ is • Instead, the speed varies
associated vibration, is
transmitting a drive through an every 90° of rotation, and
insignificant when the drive angle
angle, the output shaft does the rate of movement for
is less than about 5°, but becomes
not rotate through 360 ° at a one revolution is fast, slow,
much more intense as the angle is
constant speed. fast, slow
increased.
Speed variation of a Hooke-type Universal Joint (UJ)
• One method of achieving a
constant speed output from • This is called as Phasing. The • This means that as one speeds up
the propeller shaft is to mount universal joints at either end the other slows down, and the
two Hooketype couplings, of the prop shaft are difference in speed is cancelled
back-to-back at the same ‘synchronised’. out.
angle.
CROSS
Universal Joint : Illustration 1
Universal Joint : Illustration 1
Universal Joint : Illustration 1
Universal Joint : Illustration 1
Universal Joint : Illustration 1
Universal Joint : Illustration 1
Universal Joint : Illustration 1
Universal Joint : Illustration 1
Universal Joint : Illustration 2
Universal Joint : Illustration 2
Universal Joint : Illustration 2
Universal Joint : Illustration 2
Universal Joint : Illustration 2
Universal Joint : Illustration 2
Universal Joint : Illustration 2
Universal Joint : Illustration 2
Universal Joint : Illustration 3
Universal Joint : Illustration 3
Universal Joint : Illustration 3
Universal Joint : Illustration 3
Universal Joint : Illustration 3
Universal Joint : Illustration 3
Universal Joint : Illustration 3
Universal Joint : Illustration 3
Need of a Slip Joint
Need of a Slip Joint : Bump and Rebound
Need of a Slip Joint : Acceleration-Torque Reaction
Need of a Slip Joint : Brake-Torque Reaction
Differential
What happens when you drive in straight line
What happens when you turn around a left-hand bend
Distance A < Distance B
RPM of inside wheel < RPM of outside wheel
Driven wheels move at different speeds when
cornering
What happens when you turn around a left-hand bend
Problem with the standard differential
• Consider a situation where a vehicle fitted
with a standard differential moves straight,
and one drive wheel is on a surface with good
traction and the other wheel is on a slippery
track.
• In a standard differential the left and right
axle rotations are completely independent.
• Since one wheel is on a slippery track, the
standard differential will make that wheel
spin in excessive speed, while the good
traction wheel will remain almost dead.
Problem with the standard differential
• This means high power supply to the slippery
wheel and low power flow to the good
traction wheel. So the vehicle won’t be able
to move.
• One way to overcome this problem is to limit
the independency or relative motion between
the left and right axles.
• Limited slip differentials are introduced
for this purpose.
• One of the most commonly used LSD
technology is clutch-pack based.
Constructional features of LSD
• Limited slip differential has got a series of
friction and steel plates packed between the
side gear and the casing.
• Friction discs are having internal teeth and
they are locked with the splines of the side
gear. So the friction discs and the side gear
will always move together.
• Steels plates are having external tabs and are
made to fit in the case groove. So they can
rotate with the case.
Constructional features of LSD
• If any of the clutch pack assembly is well pressed,
the frictional force within them will make it move
as a single solid unit.
• Since steel plates are locked with the case and
friction discs with the side gear, in a well pressed
clutch pack casing and the clutch pack will move
together.
• Or motion from the casing is directly passed to
the corresponding axle.
• Space between the side gears is fitted with a pre-
load spring. Pre load spring will always give a
thrust force and will press clutch pack together.
Separating action of bevel gears
• When torque is transmitted through a bevel
gear system axial forces are also induced
apart from the tangential force. The axial
force tries to separate out the gears.
• The side gear has got a small allowance for
axial movement.
• So during high torque transmission through
spider-side gear arrangement, a high
separating thrust force is also transmitted to
the clutch pack.
• This force presses and locks the clutch pack
assembly against wall of the casing.
Working of limited slip differential
• Since one wheel is on a high traction surface,
the torque transmitted to it will be higher.
• So the thrust force developed due to the
bevel gear separation action also will be high
at that side.
• Thus clutch pack at high traction wheel side
will be pressed firmly and clutch pack will be
locked.
• So power from the differential casing will flow
directly to high traction axle via clutch pack
assembly.
Working of limited slip differential
• On the other hand clutch pack on the low traction
wheel side is not engaged yet, so power flow will
be limited to that side.
• So the vehicle will be able to overcome the
traction difference problem.
• However while taking a turn the LSD can act like a
normal differential. In this case thrust force
developed due to bevel gear separation action
won’t be that high.
• So the plates in clutch pack will easily overcome
frictional resistance and will be able to slip against
each other. Thus the right and left wheel can have
different speed just like an open differential.
REAR DRIVE AXLE
CLASSIFICATIONS
There are three rear drive axle
classifications:
• Semi-floating
• Three-quarter-floating
• Full-floating
These classifications indicate whether the
axle shafts or the axle housing supports the
wheel. The category of a rear drive axle is
determined by how the wheel and wheel
bearing mount to the axle or housing.
REAR DRIVE AXLE
CLASSIFICATIONS Semi-floating
Semi-floating
A single bearing is used, which is
mounted inside the axle casing
(housing). The weight is
supported by the axle. Axle is Axle
subjected to both bending and Housing
torque. The shaft is therefore
strengthened and designed to do
this.
Wheel hub
Axle
Housing
Wheel hub
REAR DRIVE AXLE Three-quarter
CLASSIFICATIONS floating
Three-quarter floating
The three-quarter floating bearing
reduces the main shear and bending
stresses on the axle shaft. The bearing Axle
is mounted on the outside of the axle Housing
housing.
Wheel hub
Axle
Housing
Wheel hub
REAR DRIVE AXLE
CLASSIFICATIONS Fully-floating
Fully-floating
Fully floating systems are generally
used on heavy or off-road vehicles.
This is because the stresses on these
applications are greater. Two widely
spaced bearings are used, which take Axle
all the loads, other than torque, off the Housing
axle shaft.
Wheel hub
Axle
Housing
Wheel hub
Front Wheel Drive
Front Wheel Drive (FWD)
Typical FWD drive axle arrangement
Typical FWD drive axle arrangement
CV Joints
Constant Velocity (CV) Joints
The drive axles must transmit power
These joints are used to transfer from the engine to front wheels that
On FWD or four-wheel-drive cars,
uniform torque at a constant speed, must drive, steer, and cope with the
operating angles of as much as 40
while operating through a wide range severe angles caused by the up and
degrees are common.
of angles. down movement of the vehicle’s
suspension.
Constant Velocity (CV) Joints
To accomplish this, these cars must have a compact
joint that ensures the driven shaft is rotated at a
constant velocity, regardless of angle.
CV joints also allow the length of the axle assembly to
change as the wheel travels up and down.
A Rzeppa ball-type fixed CV joint.
TYPES OF CV JOINTS
Inboard This joint is on the transaxle side
Position
Outboard This joint is on the wheel side
It does not plunge in and out to compensate for
Fixed changes in length. In FWD the outboard joint is a
CV JOINTS Function fixed joint.
Plunge It is capable of in and-out movement. In FWD
applications, the inboard joint is a plunge joint.
Ball-type
Both types are used as either inboard or outboard
Design joints, and both are available in fixed or plunge
Tripod designs.
TYPES OF CV JOINTS
Inboard
Position
Outboard
Fixed
CV JOINTS Function
Plunge
Ball-type
Design
Tripod
Position
Inboard TYPES OF CV JOINTS
Outboard
The Rzeppa joint, or fixed ball-type joint, consists of an
Fixed inner ball race, six balls, a cage to position the balls, and an
CV JOINTS Function
Plunge outer housing. Tracks machined in the inner race and outer
Rzeppa
housing allow the joint to flex. The inner race and outer
Ball-type Fixed
Design
joint housing form a ball-and-socket arrangement. The six balls
Tripod serve both as bearings between the races and the means
of transferring torque from one to the other.
Position
Inboard TYPES OF CV JOINTS
Outboard The double-offset joint uses a cylindrical outer
Fixed
housing with straight grooves and is typically used
Function Double Offset in applications that require higher operating angles
CV JOINTS Plunging Ball-
Plunge
Type Joints (up to 25 degrees) and greater plunge depth (up to
Cross groved
2.4 inches [60 mm]). This type of joint can be found
Ball-type Fixed Rzeppa joint
at the inboard position on some FWD half shafts as
Design well as on the propeller shaft of some FWD shafts.
Tripod
Position
Inboard TYPES OF CV JOINTS
Outboard The cross groove joint has a much flatter design
Fixed
than any other plunge joint. It is used as the
Function Double Offset inboard joint on FWD half shafts or at either end of
CV JOINTS Plunging Ball-
Plunge
Type Joints a RWD independent rear suspension axle shaft. The
Cross groved
feature that makes this joint unique is its ability to
Ball-type Fixed Rzeppa joint
handle a fair amount of plunge (up to 1.8 inches
Design [46 mm]) in a relatively short distance.
Tripod
Position
Inboard
Outboard
TYPES OF CV JOINTS
Tripod plunging joints consist of a central drive part
Fixed or tripod (also known as a “spider”). This has three
Function Double Offset
CV JOINTS Plunge
Plunging Ball- trunnions fitted with spherical rollers on needle
Type Joints
Cross groved bearings and an outer housing (sometimes called a
“tulip” because of its three-lobed, flowerlike
Ball-type Fixed Rzeppa joint
appearance).
Design
Plunging joint
Tripod
Fixed joint
Position
Inboard
Outboard
TYPES OF CV JOINTS
In fixed tripod joint, the trunnion is mounted in
Fixed
Function Double Offset
the outer housing and the three roller bearings turn
CV JOINTS Plunge
Plunging Ball-
Type Joints
against an open tulip on the input shaft. A steel
Cross groved locking spider holds the joint together. The fixed
tripod joint has a much greater angular capability.
Ball-type Fixed Rzeppa joint
Design
Plunging joint
Tripod
Fixed joint
FWD drive axles of different lengths
Unequal & Equal
Length Driveshaft
Unequal-length driveshafts result
in unequal drive axle shaft angles
to the front drive wheels. This
unequal angle side to-side often
results in a pull on the steering in
one direction during hard
acceleration. This imbalance
tendency is called torque steer. By
using an intermediate shaft, both
drive axles are the same angle
and the torque steer effect is
reduced.
