Frame and Body of Automobile Introduction to chassis, Classification of chassis, Conventional chassis, Semi forward chassis, Full forward chassis, Engine at the front, Engine at the rear, Engine in mid, Frame of the automobile, Function of Frame, types of frame, conventional frame, semi-integral frame, integral frame, defects in chassis, Body of the automobile, types of the body in automobile,

1. Frame and
Body
By: Ratnadeepsinh Jadeja

2. Introduction to Chassis
• Chassis is a French term and was initially used to denote the frame or main structure of a vehicle.
• The term chassis is now extensively used to denote the complete vehicle except the body for the heavy
vehicle having a separate body.
• The chassis contains all major units necessary to propel the vehicle, direct its motion, stop it, and allow it
to run smoothly over uneven surfaces.
• The chassis of an automobile consists of the following components suitably mounted
• The power plant includes the engine assembly and power transmission assembly.
• The running gear includes the frame, steering system, suspension system, brakes, wheels and tyres.
1. Frame
2. Front axle
3. Steering system
4. Rear axle
5. Suspension system
6. Transmission system
7. Brake system
8. Engine
9. Electrical system

3. • All the mentioned components are
mounted in either of the following
two ways:
1. Conventional construction :-
Separate frame is used.
2. Frameless or unitary construction :-
no separate frame is employed.
Introduction to Chassis

4. • The chassis may be classified as follows:
1. According to its control
- Conventional chassis
- Semi Forward chassis
- Full forward chassis
2. According to fitting of engine
- Engine at front
- Engine fitted in front but crosswise
- Engine fitted at the centre of the chassis
- Engine fitted at the back
3. According to the number of wheels fitted in the vehicles and the number of driving wheels
- 4 × 2, 4 × 4, 6 × 2, 6 × 4 drive chassis vehicle
4. According to the wheel base size.
Classification of Chassis

5. • Engine is fitted in front of the driver
cabin or driver seat.
• So he can not see the road just in front
of the front tyres.
• Slope is provided at the mudguard and
bonnet to enable the driver to see close
to the wheels as far as possible.
• In this arrangement portion of the
chassis where engine is fitted can not be
utilized for carrying passengers and
goods.
Conventional chassis

6. • Half portion of the engine is in the driver
cabin and remaining half is outside the
cabin such as shown in Image.
• A part of the chassis is utilized for carrying
extra passengers.
Semi-forward chassis

7. Full-forward chassis
• The complete engine is mounted inside the driver cabin.
• Floor area is increased to the extent of accommodating 3 extra
seats.
• Also, since driver seat is just above the front wheels he can see full
front road right from the front wheels.

8. (a) Conventionally the engine are
fitted at front and drive is given to the
wheels from the “rear”
• Increased efficiency of cooling
system
• Enough space is available for the
luggage behind the rear seat
• The weight of the vehicle is well
balanced on all wheels
• It is easier to inspect, repair and
adjust the engine clutch and gear
box.
Engine at front

9. (b) The engine is fitted in front and drive is also given to the front wheels only as in Matador vehicles.
Advantages:
• Low bed or floor is available
• The vehicle has more adhesion on the road
• The clutch, gear box and differential are usually made as one unit, thereby cost is reduced.
Engine at front
Disadvantages:
• While accelerating or on gradient, the weight of
the vehicle shift to the rear wheels
• On slippery gradients, under steer condition
develops

10. • Engine is fitted in front not in conventional way but crosswise as in Maruti, BMC Mini and drive is to
front wheels only
Engine fitted in front but crosswise

11. • The engine is fitted at the centre of the chassis i.e., under the chassis as in Royal Tiger World master
buses applied by Delhi Transport Corporation.
• This arrangement provides full space of chassis floor for use.
Engine fitted at the centre of the chassis

12. • Popular vehicles, employing this system are Renault, Dolphin and Volkswagon, where engine is fitted
in at the rear of the vehicle.
Advantages:
• Better adhesion on road specially when climbing hills.
• During braking some of the weight transferred to front wheels, it helps quick stopping when more
load is placed at rear wheels.
• Flat floor is available
• With the elimination of propeller shaft the C.G. is lowered giving stable driving specially at high
speed.
Disadvantages:
• Tractive effort is reduced on the gradients.
• While climbing on hills proper adhesion may be affected since the weight of vehicle moves to the
rear, thereby reducing the weight on the front wheels.
• The repair and adjustment of clutch, gear box and differential become difficult due to congestion at
the rear.
• In order to reduce wind resistance and give a better look at the road it becomes necessary to give
more slope to the bonnet which reduces the space for luggage.
Engine fitted at the back

13. • In the long wheel base chassis vehicle (wheel base is the distance between the centre of the front
and rear wheels), the distance is more thereby providing more floor area of the chassis for passenger
and goods.
• In this type of chassis, the front overhang and particularly the rear overhang are also more.
Wheel base size

14. • The frame or underbody is the main part of the
chassis on which the remaining parts of the chassis
are mounted. It is a rigid structure that forms a
skeleton to hold all the major parts together.
• The engine is mounted in the forward end of the
frame and is connected to the clutch and transmission
unit to form a complete power assembly.
• Rear axle housing is attached through the rear spring
• The wheel and tyre assemblies support the frame
• The steering system has some parts bolted to the
frame and some to the body
• The petrol tank is fastened to the rear of the frame.
• Chassis frames are made of steel section so that they
are strong enough to with stand the load and at the
same time are also light in weight to reduce dead
weight on the vehicle.
FRAME

15. • The main functions of frame are:
1. To support the chassis components and the body.
2. To withstand static and dynamic loads with unique deflection or distortion.
• The various loads dealt with by the frame are:
1. Weight of the vehicle and passengers, causing vertical bending of the side members.
2. Vertical loads when vehicle comes across a bump or hollow, which results in longitudinal torsion.
3. Loads due to road camber, side wind, cornering force while taking a turn, which results in lateral
bending of side members.
4. Load due to wheel impact with road obstacles may cause that particular wheel to remain
obstructed while the other wheel tends to move forward, distorting the frame to parallelogram
shape.
5. Engine torque and braking torque tending to bend the side members in the vertical plane.
6. Sudden impact loads during a collision, which may result in sudden collapse.
Functions of Frame

16. • The frames are made of the following steel sections:
1. Channel section
2. Box section
3. Tubular section
Types of Frame
• Channel section is used in long members of the frame.
• Box section is used in short members of the frame.
• Tubular section is used these days in three wheeler, scooters and matadors, pick-ups frames.
• The channel section is good in bending, tubular section in torsion and box in bending and torsion.

17. • The frame should be strong enough to bear loads, sudden brakes and accidents.
• Basically, there are following three types of frames :
1. Conventional frame.
2. Semi-integral frame.
3. Integral or unit frame.
Types of Frame

18. Conventional Frame
Box section type
X member type

19. Conventional Frame
• It is also known as non-load carrying frame. Here the loads on the vehicle are transferred to the
suspension by the frame, which supports the engine, power train and the body.
• The body work is made of material like wood and completely isolated from the frame deflection
with the help of rubber mountings. This type of construction widely used in trucks.
• This type of frame is not much suited to resist torsion. Use of a tubular or box section backbone
type of frame improves the torsional strength.
Frame used in cars
• The complete frame is fabricated by the welding process.
• The frame tappers from the rear to the front to permit adequate movement of the steering wheel.
The longitudinal members, by sweeping upwards at the rear end, allow for the vertical movement
of the rear axle.
• The torsional rigidity of the frame is increased by providing tubular or box-section cross members.

20. • The rubber body is mounts are
replaced by relative stiff mounts so
that a part of the frame load is
transferred to the body structure also.
• Quite popular for small European cars
and American cars
• Semi-integral frame is heavy.
Semi-Integral frame

21. • There is no frame and all assembly units are attached to the body. The chassis, floor and body are
assembled by welding from a large number of mild steel pressings.
• In this arrangement, the chassis becomes a subframe and other sub frames are used for the front and
rear suspension units.
• This design reduces vehicle weight, lowers production costs and allows a lower floor.
• This is the modern form of construction for almost all cars and lighter commercial vehicles.
Integral or Unitised frame

22. • Normally the various components of a vehicle are bolted directly either on the main frame members or
across members. However, sometimes the engine and gear box are carried on a sub frame support by
the main frame usually at three points. The arrangement helps to isolate the components from the
effect of twisting and flexing of the main frame.
• Rubber mountings are used between the engine gear box unit and the frame to reduce the vibrations.
For the same reason the body is also mounted on rubber blocks on the frame.
• The provisions of sub frame simplifies production on the assembly line and facilities subsequent overall
or repair.
Sub-frames

23. • The following defects may be found in chassis body :
1. Cracks, 2. Dislocated parts, 3. Broken welds, 4. Buckling, 5. Corrosion and Rusting
The following methods are used to avoid rust formation:
1. Use of galvanized sheets.
2. Use of zinc enriched primer paint.
3. Use of plastic coating on panels.
4. Use of rubberized solution.
5. Avoiding tight corners so that moisture can not get settles.
6. Providing plenty of drain holes to allow trapped water to run out.
Defects in Chassis Frame

24. • Body is the super structure of the vehicle. The chassis and body make the complete vehicle. The chassis
and body make the complete vehicle.
• In larger and heavier vehicles, the chassis and the body are made as a separate unit and then bolted
together.
• The body is usually made from a large number of steel pressings which are welded together.
• The body is bolted to the chassis at numerous points, rubber or felt strips being interposed to damp
down vibration and noise.
BODY

25. • The body of motor vehicle should fulfill the following requirements :
1. Light in weight.
2. Cheap and easy in manufacturing.
3. Attractive in shape and color.
4. Minimum number of components.
5. Clear all-round vision through glass area.
6. Long fatigue life.
7. Minimum resistance to air.
8. Good access to the engine and suspension system.
9. Minimum vibration during running of the vehicle.
10. Adequate space for passengers and luggage.
BODY

26. • Different types of bodies for various vehicles are listed below.
BODY
1. Two door sedan
2. Four door sedan
3. Convertible
4. Van
5. Truck Punjab body or straight truck
6. Truck half body
7. Truck platform type
8. Truck with articulated trailer
9. Tanker
10. Dumper truck
11. Jeep
12. Pick-ups
13. Station wagon

27. 1. Two door
sedan

28. 2. Four door
sedan

29. 3.
Convertible

30. 4. Van

31. 5. Truck
Punjab body
or straight
truck

32. 6. Truck half
body

33. 7. Truck
platform
type

34. 8. Truck with
articulated
trailer

35. 9. Tanker

36. 10. Dumper
truck

37. 11. Jeep

38. 12. Pick-ups

39. 13. Station
wagon

40. 14.
Hatchback

41. Vehicle Dimensions
• Two important dimensions used to describe the size of an automobile of the framed or frameless type
are :
1. Wheel Base
2. Wheel track – front wheel track and – rear wheel track.