aUTOMOOBILE

1. BY
Shri T. Chitharanjan., JE (E&M)

2.  Chassis is a French term and was initially used to
denote the frame parts (or) basic structure of the
vehicle. It is the back bone of the vehicle. A vehicle
without body is called chassis.
 MAIN COMPONENTS OF CHASSIS:
 Frame – it is made up of long two members called
side members riveted together with the help of
number of cross members.
 Engine (or) power plant- it provides the source of
power.
 Clutch – it connects and disconnects the power from
the engine flywheel to the transmission system.
 Gear box, U joints, propeller shafts, differential,
brake system, steering system

3.  a) Conventional chassis
 b) Integral (or) Unit constructional frame
 c) Semi integral (or) Half integral frame
 A) conventional chassis- it has two long side members
and 5 to 6 cross members joined together with the help of
rivets and bolts. The frame sections are generally used
channel section, box section and tubular section.
 Integral frame – this frame is used now a days in most of
the cars. There is no frame and all the assy, units are
attached to the body. All the functions of the frame
carried out by the body it self. Due to elimination of long
frame, it is cheaper and due to less weight most
economical also. The only disadvantage is in repairing is
difficult.

4.  C) semi integrated frame - in some vehs frame is
fixed in the front end in which engine, gear box and
front suspension is mounted. It has the advantage
when the vehicle is met with an accident the front
frame can be taken easily to replace the damaged
chassis frame. This type of frame is used in fiat cars
and some of the European and American cars.
 VARIOUS LOADS ACTING ON THE FRAME:
 Short duration load-while passing/crossing a broken
patch.
 Momentary duration load – while taking curve
 Impact loads – due to collision of vehicle
 Inertia load – while applying brakes
 Static loads – load due to chassis parts
 Over loads – beyond design capacity

5.  MAIN FUNCTIONS OF THE FRAME:
 To support the load of body, engine, gear box and
radiator etc.
 To provide connecting link for front and rear axles
 To carry load of passengers (or) goods carried by the
body
 To with stand stresses caused due to the bad road
condition
 To with stand forces caused due to a sudden braking (or)
acceleration
 To with stand load/force caused due to turning of
vehicle
 CHASSIS REPAIR:
 Usually the chassis frame does not require any repair
throughout the life of a vehicle, but in case vehicle is
abused by overloading (or) run on rough roads at high
speeds, the following defects may arise;-

6.  Loose rivets and cracks
 Loose rivets – check for loose rivets specially in the vehs
which are being over loaded (or) run on bad roads. The
loose rivets can easily be detected by presence of the rust
around the rivets by visual inspection and then tapping it
with a hammer, if found loose it should be removed and
new rivet must be placed immediately, failing which the
rivet hole will become loose.
 Cut the rivet head with a drill (or) welding torch, do not
use a chisel as it will damage the rivet hole. In case the
hole is already damaged drill a bigger hole and use over
size rivets.
 The dia of new rivets should be 01 mm less than hole dia.
 Clean the hole thoroughly, there should be no burr
 Heat the rivet, when hot, fix it in the hole and rivets its
head

7.  Never fix cold rivet as it will not make a good joint
 Do not weld rivet with chassis, if it is loose, remove
and re-fix new one.
 CRACKS:
 Cracks may develop in a chassis when a vehicle is
misused. Cracks can be deleted by inspecting the
chassis carefully. If it is not visible, wash the chassis
first, coat the surface with solution of chalk and
water, when it become dry, tap the area with a
hammer, then the crack will be visible. Incase crack is
observed, it should be immediately repaired failing
which crack will go on extending. In case the repair
facilities do not exist then drill 5 or 6 mm hole at the
end of crack. The drilling hole will stop further
extension of crack. This is only the first aid.

8.  ACCIDENT REPAIR :
 In case chassis has met with an accident it gets bent.
In case of bend, it can be safely be repaired with the
help of screw jack after localized heating at that
portion of chassis. After straightening it is essential
to the alignment of the chassis accurately failing
which the veh may pull to one side (or) eat tyres
excessively and would be difficult to control steering.
 SUSPENSION SYSTEM:
 Suspension system plays an important role for
comfortable ride for passengers besides protecting
the chassis and other working parts from getting
damaged due to road shocks.
 FUNCTIONS OF SUSPENSION SYSTEM:
 Provides comfort
 Gives cushioning effect

9.  Relieves strain on the frame and other components
due to the road shocks .
 It maintains body level and prevent it from rolling.
 Provides a good contact for road holding ie the
system must always keep the tyres in contact with
the road.
 Suspension system transfers driving torque to the
wheels as well as breaking force to the chassis.
 TYPES OF SUSPENSIONS:
 A) Leaf spring b) torsion bars c) coil springs d) air
bags
 Leaf spring types;- i) semi elliptical ii) quarter
elliptical iii) three qtr elliptical iv) traverse v) full
elliptical

10.  SHOCK ABSORBER:
 As the name implies a shock absorber has to absorb
shock, but technically speaking, it does not absorb road
shock. In fact it is road springs which absorb the road
shocks. The function of the shock absorber is to damp
down the oscillation of the road springs (or) it is a
friction damper for the springs and keeps the level of
body straight instead allowing it to jump up (or) down.
 TYPES OF SHOCK ABSORBERS:
 i) frictional shockers ii) hydraulic shockers
 Hydraulic shock absorber further divided in to three
types ;- a) vane type b) piston type c) telescopic type
 Testing of shock absorber;- hold the bumper of car and
bounce it up and down , as you push it down resistance
should be noticed and when you raise it up more
resistance should be noticed. Repeat it again and again
increasing the length of the stroke each time, now release
the bumper at the end of stroke. When released if the up
and down motion stop quickly the shock absorber is
okay.

11.  If vehicle continues its up and down motion, the
shock absorber is defective.
 For checking shock absorber which been taken out
from the vehicle and proceed as under;-
 Place two rods in the eye of shock absorber one at
top and other at the bottom eye. Keep the bottom eye
rod pressed under your feet and upper rod in your
both hands. Now pull the shock with hand and again
push it back. If a uniform resistance is felt through
out its length, shock absorber is okay, if it open
quickly (or) closes quickly, it is defective.