Automotive Suspension Dynamics and Components

Dynamics of Suspension

Balance, Center of Gravity, and Roll Axis

The roll center is an imaginary point on an axle where lateral forces are transmitted to the wheels. The imaginary line connecting the front and rear roll centers is called the roll axis. The center of gravity is an imaginary point where the vehicle's entire mass is concentrated.

Charge Transfer and Axes of Rotation

A vehicle pivots around three axes of rotation:

• Longitudinal Axis (Roll): Rotation that occurs when cornering.
• Transverse Axis (Pitch): Rotation that occurs during acceleration or braking.
• Vertical Axis (Yaw): Rotation when the vehicle is subjected to various turning loads.

Sprung and Unsprung Mass

• Sprung Mass: The part of the vehicle that is supported by the suspension system and is not in direct contact with the road.
• Unsprung Mass: The part of the vehicle that is in direct contact with the road and is not supported by the suspension system (e.g., wheels, tires, brakes).

Oscillation

Oscillation is the upward and downward movement of a mass, such as the compression and extension of a spring.

• Period: The time it takes to complete one full oscillation.
• Frequency: The number of oscillations per unit of time.
• Amplitude: The maximum distance traveled from the resting position.
• Resonance: Occurs when an external force drives the mass in rhythm with its natural oscillation, increasing the amplitude of subsequent oscillations.

Suspension Components and Factors

Silentblock

An elastic bridge of rubber and metal that absorbs vibrations and shocks between two moving parts.

Mountings

A rubber element that allows the connection of suspension components while permitting minimal displacement.

Ball Joints

A connecting and fixation element for the suspension and steering that allows pivoting and turning. It should be replaced if backlash (free play) is present.

Steering Knuckle and Hubs

Made of steel or alloy, this component connects the wheel hub to the suspension elements.

Control Arm (or Wishbone)

A link between the chassis (or subframe) and the steering knuckle.

Braces

Steel arms located between the vehicle body and the knuckle or control arm to provide stability.

Stabilizer Bar (Anti-roll Bar)

A U-shaped steel bar attached to the body and the suspension arms on the same axle. It reduces body roll during cornering, improving vehicle stability.

Bump Stops

Elastic or semi-rigid stops that prevent damage from excessive suspension compression.

Elastic Elements (Springs)

Deformable components located between the bodywork/chassis and the wheels to absorb oscillations. Types include rubber springs, torsion bars, leaf springs, and coil springs.

Shock Absorbers (Dampers)

A device that transforms the kinetic energy of suspension movement into thermal energy (heat) to dampen oscillations.

Tasks of a Shock Absorber:

1. Ensure good contact between the wheels and the road.
2. Ensure stability, especially during cornering.
3. Decrease oscillations.
4. Avoid or reduce body roll.
5. Reduce wear on tires and chassis components.

Types of Shock Absorbers:

• Friction: Uses friction between disks connected to the sprung and unsprung masses.
• Lever Arm: Features a cylinder with an internal piston operated by a lever and shaft mechanism.
• Rotary: An arc-shaped arm rotates a paddle within the oil-filled shock casing.
• Telescopic (Monotube, Twin-tube, Adjustable): A piston slides inside an oil-filled cylinder. Orifices in the piston allow oil to pass between chambers, damping the spring's oscillation.

Parts of a Telescopic Shock Absorber:

• Body
• Piston
• Rod
• Valves
• Seals
• Oil

Types of Mechanical Suspensions

Rigid Axle

Consists of a solid metal beam connecting the wheels on opposite sides of the vehicle, attached to the body by the suspension and damping system. The movement of one wheel (e.g., over a bump) directly affects the other.

De Dion Axle

A hybrid design between a rigid axle and an independent suspension. A solid tube connects the rear wheels, but it bends to accommodate the differential, which is mounted to the chassis. This makes the differential part of the sprung mass, improving comfort and performance.

Independent Suspension

Each wheel is mounted on its own axle, allowing it to move independently of the others. With less unsprung mass, the transmission of oscillations from the road to the chassis is reduced.

Common Types of Independent Suspension:

• Deformable Parallelogram (Double Wishbone)
• MacPherson Strut
• Trailing Arm
• Multi-link