Modelling of quarter car suspension system

Definition

Defination

Mechanical system of springs and shock absorbers that connect the wheels and axles of wheeled vehicle.

It uses an onboard system to control the vertical movement of the vehicle's wheels relative to the chassis or vehicle body rather than the passive suspension provided by large springs where the movement is determined entirely by the road surface.

Function

Function

To provide good ride quality by isolating vehicle body from road. To ensure good road holding. To support vehicle static weight. To ensure good handling. These technologies allow car manufacturers to achieve a greater degree of ride quality and car handling by keeping the tires perpendicular to the road in corners, allowing better traction and control. An onboard computer detects body movement from sensors throughout the vehicle and, using that data, controls the action of the active and semi-active suspensions. The system virtually eliminates body roll and pitch variation in many driving situations including cornering, accelerating, and braking.

Picture

Quarter Car

Element on Suspension

Spring: to absorb energy from road bump and convert it into potential energy spring

Shock Absorber/Damper: to dissipate shock energy from road bump without causing undue oscillation in the vehicle.

Elements on Suspension:

Mechanical element

Control arm

Steering knuckle

Ball joints

Control arm bushing

Mechanical elements:

Text

Passive Suspension

passive suspension

Conventional suspension system is also known as a passive suspension system consisting of spring and damper mounted at each wheels of the vehicle in parallel.

The function of spring in vehicle suspension is to support the vehicle body and at the same time it is used to absorb and store the energy.

The damper or shock absorber is a component of the vehicle suspension used to dissipate the vibration energy stored in the spring and control the input from the road that is transmitted to the vehicle.

Other purposes of suspension system are to isolate sprung mass from the unsprang mass vibration, to provide directional stability during cornering and to man oeuvre and provide damping for the high frequency vibration induced fire excitations.

Semi-active Suspension

Semi-active suspension system is quite similar with the conventional suspension system.

This kind of suspension has a spring and controllable damper in which the spring element is used to store the energy meanwhile the controllables damper is used to dissipate the energy.

Some of the semi-active suspension systems use the passive damper and the controllable spring, the controllable damper usually acts with limited capability to produce a controlled force when dissipating energy.

Meanwhile in active system, the components of spring or damper are replaced with an actuator. An actuator is controlled by using the feedback from the vehicle body.

Semi-active Suspension

Fully-active Suspension

Fully-active Suspension

Fully-active suspension system has the ability to response to the vertical changes in the road input.

The damper or spring is interceding by the force actuator.

This force actuator has its own task which is to add or dissipate energy from the system.

The force actuator is control by various types of controller determine by the designer.

The correct control strategy will give better compromise between comfort and vehicle stability.

Therefore active suspension system offer better riding comfort and vehicle handling to the passengers.

In this type of suspension the controller can modify the system dynamics by activating the actuators.

Passive suspension

passive Suspension

Advantage

Simple design and configuration

Lower price in comparison with other suspension systems

Dis advantage

Performance is not as good as active and semi-active systems

Semi-active suspension

Semi-active Suspension

Advantage

Less implementation cost

Lower energy use

Simple control

Simple design

Easy to set up

Disadvantage

Damper limitation

Narrow efficiency range

Better performance than passive systems but performance is not as good as active systems

Fully-active Suspension

Advantage

Extensive range of force

Compatible with any force and velocity Gaining better performance

More efficiency

Dis advantage

More power is needed

Higher weight-to-power ratio

Higher price

Considerable modification should be done before setting it into the existing vehicle

Fully-active suspension

Transfer Function for Passive

Transfer Function

Block digram

Space state Representasion

Signal-Flow Graph

Signal-Flow Graph