1. CHAPTER: 1. CHASSIS FRAME AND BODY
AUT203
CHAPTER: 1. CHASSIS FRAME AND BODY

2. Objectives Define the most important parts of a vehicle
Explain body design and frame variations
Compare unibody and body-over-frame construction
Identify the major structural parts, sections, and assemblies of body-over-frame vehicles
Explain the vehicle body repair technology

3. Introduction Vehicle construction refers to how a vehicle is made.
Chassis is a French term and was initially used to denote the frame parts or Basic structure of the vehicle. It is the backbone of the vehicle. A vehicle without body is called Chassis. The components of the vehicle like power plant, Transmission system, Axles, Wheels and Tyres, Suspension, Controlling System like Braking, Steering etc,.. and also electrical system parts are mounted on the Cassis frame. It is the main mounting for all the components including the body. So it is also called as Carrying Unit.

4. Layout of Chassis and its main Components

5. Crash Testing
Vehicles must be light, aerodynamic, and yet strong and safe
Computer-simulated crash testing is used before building a prototype to find weak structural areas
Critical that passenger compartment is strong enough to prevent injury
Certified crash tests are done with a real vehicle and sensor equipped-dummies
Crush zones are built into the frame or body to absorb some of the energy of a collision

6. Vehicle Classifications
Vehicle classification relates to the construction, size, shape, number of doors, type of roof, and other criteria of a motor vehicle
To communicate properly in collision repair, you must understand these basic terms
Functions of the chassis frame
To carry load of the passengers or goods carried in body
To support the load of the body, engine, gearbox etc.
To withstand the forces caused due to the sudden braking or acceleration
To withstand the stresses caused due to the bad road condition and To withstand centrifugal force while cornering

7. Types of chassis frames
Conventional frame: 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 used generally.
Channel section – Good resistance to bending
Tabular Section – Good resistance to Torsion
Box Section -Good resistance to both bending and torsion
Integral Frame: This frame is used now days in most of the cars. There is no frame and all the assembly units are attached to body. Only disadvantage is repairing is difficult.
Semi-Integral Frame: In same vehicles half frame is fixed in the front end on which engine gear box and front suspension is mounted.

8. Various loads acting on the frame
Short duration Load- while crossing a broken patch
Momentary duration Load – While taking a curve
Impact loads – due to the collision of the vehicle
Inertia load – while applying brakes
Static Loads – Loads due to chassis parts
Over loads – Beyond Design capacity

9. Vehicle Construction
Part or component refers to the smallest units on a vehicle
An assembly is several parts that fit together
Panel refers to a large removable body part
Pan refers to a floor-related component
Chassis includes everything under the body, consisting of the mechanical systems that support and power the car
Vehicles have different construction methods according to how it can attach to the vehicle frame.
The different most construction methods used are: separate construction, partially self-supporting construction and self-supporting construction.

10. (A) Partially self-supporting /Unibody construction welds major body panels together to form the frame for attaching the engine, drivetrain, suspension, and other parts. This type of construction is commonly used on cars.
(B) Separate /With body-over-frame construction, a thick gauge steel frame provides the foundation for holding other parts. This type of construction is commonly used on large trucks and SUVs. Two very different methods used to construct modern vehicles: unibody and body-over-frame construction

11. Full Frames
Body-over-frame vehicles have separate body and chassis parts bolted to the frame
Full frame vehicle is heavier - high amounts of energy are absorbed by the frame in a collision
Torque boxes allow some twisting to absorb road shock and collision impact
Crossmembers extend sideways across frame rails to support the engine, suspension, chassis
Full- or partial-frame construction is used on most full-size and some small pickup trucks

12. Unibody Construction
Unibody construction uses body parts welded and bolted together
Uses lighter, thinner, high-strength steel alloys
Body shell is formed by welding sheet metal into a box- or egg-like configuration
Strength is achieved through shape and design instead of mass and weight
Stressed hull structure disperses force over the entire body shell

13. Space Frame
Space frame vehicle has a metal body structure covered with an outer skin of plastic or composite panels
Roof and quarter panels may be attached with mechanical fasteners or adhesives
After a collision a space frame is more likely to have hidden damage, or hidden corrosion
Support members are bolted to unibody bottom
Needed in high-stress areas to reduce body flex

14. Joining Parts Fastened parts are held together with fasteners
Welded parts are permanently joined by welding
Press-fit or snap-fit parts use clips or an interface to fit parts together
Adhesive-bonded parts use high-strength epoxy or special glue to hold parts together
Composite unibody is made of plastics and other materials
Keeping metal parts to a minimum cuts weight while increasing strength and performance

15. Note the space frame construction
Note the space frame construction. Composite (plastic) panels fasten to a metal inner body structure. Composite panels can be made flexible to resist door dings and small dents.

16. Major Body Sections Vehicle is divided into three sections
Front, center and rear
Front section includes everything between front bumper and fire wall
Also called nose section, front clip, “doghouse”
Center section or midsection includes body parts that form passenger compartment
Also called a “greenhouse”
Rear section also called tail section, rear clip, “cathouse”

17. This top view of unibody construction shows how structural members are added to support the engine suspension and other mechanical systems.

18. Gaskets and Seals
Various gaskets and rubber seals prevent air and water leakage between body parts
Seals or weatherstripping are often used around doors and the rear deck lid
Rubber seal is partially compressed when door or lid is closed to form a leakproof connection
Rubber gasket often seals stationary glass where it fits into body
Anticorrosion Materials
Anticorrosion materials prevent rusting of metal parts
Undercoating is often a thick tar or synthetic rubber-based material sprayed onto underbody
After performing repairs, you must restore all corrosion protection

19. Sound-Deadening Materials
Sound-deadening materials help quiet passenger compartment
Insulation that prevents engine and road noise from entering passenger area
Roof Designs
Sedan is a body design with a center pillar that supports roof
Hardtop does not have a center pillar to support roof
Hatchback has a large third door at back, commonly found on small compact cars
Convertible has a retractable canvas roof with a steel tube framework, or a removable hardtop
Station wagon extends roof straight back to rear of body with a rear hatch or tailgate

20. Vans and Trucks
Van has a large box-shaped body to increase interior volume or space
Full-size van normally is front-engine, RWD
Minivan is smaller and often uses front-engine FWD with unibody construction
Pickup truck normally has a separate cab and bed, typically with front-engine, RWD

21. Summary
Vehicle classification relates to construction, size, shape, number of doors, type of roof, etc.
Three main types of frame construction
Body-over-frame, unibody, and space frame
Vehicle commonly divided into 3 body sections
Front section, or nose section
Center section, or midsection
Rear section, tail section, or rear clip
Vehicle sizes: compact, intermediate, full size