BRANCH AUTOMOBILE ENGINEERING
SEM 5TH ,Winter-2021
SUBJECT AUTOMOTIVE TRANSMISSION
CHAPTER 05
TOPIC REAR AXLE
FACULTY Er. BALADHARA JENA
Forces on rear axle
⚫Wt. of the body
⚫Driving trust
⚫Torque reaction
⚫Side thrust
⚫TheHotchkiss driveis a system ofpower
transmission .
⚫It was the dominant form of power transmission
forfront-engine, rear-wheel drive layoutcarsin the
20th century
⚫Simplest and most widely used type of rear axle drive .
⚫The spring besides taking weight of the body also take the
torque reaction , driving thrust and side thrust .
⚫propellarshaft is proviedwith two universal joints also a
sliding joint .
⚫The front end of the spring is fixed rigidly on the frame
while the rear end and is supported in the shackle .
⚫In a Hotchkiss layout,
⚫the axle is suspended by a pair of longitudinally
mounted semi-elliptical leaf springs, which serve to
locate the axle, as well as supporting the weight of the
body.
⚫The front portion of each spring functions like a
trailing arm, transmitting drive torque to the body and
resisting squat and axle tramp .
⚫The rear portion of the spring acts as a leading arm,
resisting wheel hop under braking.
⚫The stiffness of the springs also serves to resist lateral
motions. By making the springs perform multiple
duties, Hotchkiss drive is very simple, and thus very
cheap.
⚫Since it has few parts, it's also very sturdy, which is
useful for heavy-duty vehicles like trucks.
TheHOTCHKISSdriverequiresthatthespringsberigid
enoughtowithstandthetwistingaction(torque)ofthe
rearaxleandthedrivingandbrakingforcesthatthe
springstransmittotheframe.Thistypeofdrive is
commontotheequipmentyouwillencounterinthe
Navy.
⚫The differentiating characteristic of the Hotchkiss
drive is the fact that it usesuniversal
joints atbothends of the driveshaft, which is not
enclosed .
⚫The use of two universal joints, properly phased and
with parallel alignment of the drive and driven shafts,
allows the use of simple cross-type universals .
⚫Usedin pick-up trucksandsport utility vehicles .
⚫The design problem that the torque tube solves is how
to get the traction forces generated by the wheels to
the car frame .
⚫The "torque tube" transmits this force by directly
coupling the axledifferentialto thetransmissionand
therefore propels the car forward by pushing on the
engine and then through the engine mounts to the car
frame .
⚫In contrast, the Hotchkiss drive has the traction forces
transmitted to the car frame by using other suspension
components such asleaf springsortrailing arms .
⚫Aball and sockettype of joint called a "torque ball" is
used at one end of the torque tube to allow relative
motion between the axle and transmission due to
suspension travel
⚫Since the torque tube does not constrain the axle in
the lateral (side-to-side) direction apanhardrodis
often used for this purpose.
⚫The combination of the panhardrod and the torque
tube allows the easy implementation of soft coil
springs in the rear to give good ride quality .
TorquetubesdifferfromtheHotchkissdesignin
that a solid
driveshaftisenclosedinahollowtorquetub
eandrotateswithinasupportbearingtoprevent
whipping
⚫In both types of drive shafts the side thrust is taken the
leaf springs .
⚫A separate member is employed to overcome this
situation : PanhardRod
⚫it sifixed parallel to wheel axis with one end pivoted to
the axle and other to chassis frame
EXAMPLES OF THE TORQUE
TUBE
⚫American cars of the Ford brand up through 1948,
which used the less expensive transverse springs that
could not take the thrust.
⚫The C5 and C6Chevrolet Corvette , Mercedes-Benz
SLS AMG
Loads on rear axle shafts
⚫Shearing force due to wt. of vehicle .
⚫Bending moment on account of load applied through
spring seats .
⚫End thrust caused by side forces on account of
cornering , side wind
⚫Bending moment by end thrust and its reationoffered
by tyreson ground
⚫Driving torque
Types of rear axle shaft
⚫Semi floating axle .
⚫Full floating axle .
⚫Three quarter floating type.
SEMI FLOATING AXLE
⚫With a semi-float axle, the axle shaft both carries the
weight and transmits torque.
⚫The wheel is often bolted directly to the flange on the
axle.
⚫Semi-float axles are seen on cars and light duty trucks.
⚫Semi floats are more limited in capacity, but lighter
and cheaper to manufacture.
FULL FLOATING AXLE
⚫theweightofthevehicleissupportedbytheaxle
housing-morespecifically,abearingspindleattached
totheaxlehousing,andasetofbearingsinaseparate
wheelhub.
⚫Torqueistransmittedbyaseparateaxleshaftthat
carriesnoweight.
⚫Ascommonlybuilt,full-floatersareconsiderably
heavier,butalsomuchstronger
SEMI FLOATING AXLE FULL FLOATING AXLE
THREE QUARTER FLOATING
TYPE
THREE QUARTER FLOATING
TYPE
⚫A three-quarter floating axle is the same as semi-floating, with
one difference. The outer bearing is moved to the outside of the
outer end of the axle tube, supporting a hub assembly via the
bearing's outer circumference edge.
⚫The splinedor keyed shaft drives this hub, to which the wheel is
attached.
The shaft now supports minimal vehicle weight (so has much
reduced radial load), but still locates the wheel axially, and
transfers axial cornering loads (side thrust) to the axle inner
bearing.
Thank You