Vehicle Body and Chassis Types: A Comprehensive Analysis
Vehicle Body and Chassis Types
Separate Chassis and Body (Frame + Body)
This construction method is applied in industrial vehicles, off-road vehicles, and some fiber-bodied automobiles. The body is mounted onto a separate frame.
The frame is a structural element typically formed by steel rails along the vehicle’s length, united by crossmembers. This design provides high resistance and rigidity. When mechanical components are added, it forms a complete chassis. This type is sometimes called ‘K’ frame, but it tends to be heavy, offers less stability, and is more costly to produce.
Frame Types:
- Ladder Frame: Two parallel longitudinal stringers (straight or not) connected by several crossmembers.
- Box-Section Column: A strong central beam running along the vehicle’s length.
- Perimetric Frame: The body is supported in a larger area, offering additional protection in case of a lateral impact. Front and rear sections are designed to absorb frontal or rear impacts.
- Tubular Frame: Used in competition vehicles.
Platform Chassis
The body can be attached to the platform by welding, bolting, or riveting. This is often used in large automobiles that carry heavy loads, such as vans, trucks, and many off-road vehicles.
Self-Supporting Body (Unibody)
This is the most common type used by automobile manufacturers. It’s an envelope structure formed by joining elements of different shapes and thicknesses. It has a box shape and is designed to be self-supporting and to support the mechanical components attached to it. This gives shape to the vehicle. For occupant safety, the body panels are designed to absorb impacts in a controlled manner to prevent deformation of the passenger compartment. The passenger compartment must remain rigid. Both front and rear sections are designed to deform in a controlled way during an impact, using predetermined crumple zones.
Body Panel Classification:
- Detachable Panels: These are parts that are frequently impacted and are easy to disassemble (doors, hood, trunk lid, fenders).
- Welded Panels: Reduces the number of detachable parts (doors, hood, trunk lid). Repairing these is more expensive because components cannot be easily disassembled.
Fasteners
Taps:
- Metric: Drill diameter = Outside diameter – Pitch
- Whitworth: Drill diameter = Outside diameter – (1.28 x Pitch)
Screws:
Screws consist of a head, shank, and thread. The head is used to apply clamping force. The strength of the screw is checked; a higher number indicates a stronger screw. The thread is measured by the diameter of the core (root diameter).
Screw Marking:
- Mechanical resistance to traction / 100
- (Yield strength / resistance traction) x 10
Thread Systems:
- ISO-Metric: The thread has a triangular shape with rounded or truncated peaks and roots.
- Whitworth: The peaks and roots are rounded.
- American: The roots and crests are flattened.
Nuts:
Nuts have internal threads that fit onto a screw. When the nut is tightened, it applies force to the joined components, maintaining the assembly.
Washers:
Washers are used under screws, nuts, and other fasteners to provide a stronger clamping force.