AUT 203 CHAPTER 1 CHASSIS FRAME AND BODY

AUT 203 CHAPTER: 1. CHASSIS FRAME AND BODY

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

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.

Layout of Chassis and its main Components

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

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

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.

Various loads acting on the frame 1. Short duration Load- while crossing a broken patch 2. Momentary duration Load – While taking a curve 3. Impact loads – due to the collision of the vehicle 4. Inertia load – while applying brakes 5. Static Loads – Loads due to chassis parts 6. Over loads – Beyond Design capacity

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.

(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

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

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

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

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

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.

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”

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

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 rubberbased material sprayed onto underbody • After performing repairs, you must restore all corrosion protection

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

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

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