Overview
The chassis supports and accommodates the engine and related assemblies, shapes the vehicle's overall form, transmits engine power to produce motion, and ensures normal driving. The chassis is composed of four main systems: the powertrain, running gear, steering system, and braking system.
Powertrain (Transmission) System
The powertrain typically includes the clutch, transmission, universal joint, final drive, differential, and half shafts.
Running Gear
The running gear consists of the frame, axles, wheels, and suspension. Its functions include:
- Receiving power from the powertrain and generating traction through the drive wheels interacting with the road surface, enabling vehicle motion.
- Supporting the vehicle's total weight and reacting to ground forces.
- Absorbing shocks from uneven road surfaces, damping vibrations during travel to maintain ride smoothness, and, together with the steering system, ensuring handling stability.
Steering System
The steering system comprises the steering control mechanism and steering transmission mechanism. The steering control mechanism includes the steering wheel and collapsible steering column. The steering transmission mechanism includes the steering box, left and right tie rods, steering knuckle arm, and steering knuckle.
Key components and functions:
- Stabilizer bar: Reduces body roll during steering, improving handling.
- Half shaft: Transmits engine power to the wheels to drive the vehicle.
- Steering tie rod: Controls wheel steering and adjusts toe.
- Lower and upper control arms: Suspension links connecting the wheel to the body.
- Universal joint: Connects two shafts and allows the drive angle between them to change within a certain range, necessary because the front wheels both steer and drive.
Spring: An elastic element that cushions impacts. Coil springs are common in passenger cars, leaf springs in trucks, and some high-end vehicles use air springs.
Shock absorber: A hydraulic damping element that absorbs road impact energy and suppresses rebound forces after spring compression. Combined with the spring, it forms the damping system to reduce body vibration from uneven roads. The damping force of the shock absorber is tuned to match the spring rate, resulting in different chassis characteristics such as sport-oriented or comfort-oriented handling.
When steering, the driver turns the steering wheel. The collapsible steering column and steering gear rotate, causing the steering rack to move laterally. The rack moves the left and right tie rods, which are connected to the steering knuckle arms and cause them to rotate. The steering knuckle, which holds the wheel, pivots and deflects the wheel by the steering angle, changing the vehicle's direction. When the steering wheel returns to center, the wheels return to their original position and the vehicle resumes straight-line travel.
Braking System
The braking system mainly consists of an energy supply device, a control device, a transmission device, and the brake actuators. Its primary functions are to decelerate or stop a moving vehicle, maintain a stable speed during downhill driving, and hold a parked vehicle stationary.
Brake lines: Transmit force from the brake pedal.
Brake caliper/wheel cylinder: Converts hydraulic pressure of the brake fluid into mechanical force, acting on the friction pads in the brake caliper to press against the brake disc, converting the vehicle's kinetic energy into heat and bringing the vehicle to a stop.
Parking brake cable: Engages the rear wheel brakes when the parking brake is applied, similar to a bicycle brake.
Chassis Components
Exhaust flex connection: Interrupts the transmission of engine vibration to the exhaust system.
Subframe: A suspension component that connects control arms to the vehicle body.
Three-way catalytic converter: Converts harmful exhaust gases such as NOx and CO into less harmful gases such as N2 and CO2, reducing emissions.
Muffler: Reduces engine exhaust noise. Without it, the vehicle would be much louder.
Charcoal canister: A small black canister typically located at the rear right side of the vehicle, filled with activated carbon and connected to the fuel tank to adsorb gasoline vapors. During operation, the canister is purged and the stored fuel vapors are drawn into the intake manifold to be burned, reducing evaporative emissions and conserving fuel.
Torsion beam: A component of torsion-beam semi-independent suspension that twists to provide some compliance, placing its behavior between independent and non-independent suspensions. This suspension type is low cost, strong, space-efficient, and commonly used on small cars, with moderate ride comfort.
