Active Suspension Systems

Basic Description

A vehicle's suspension system typically consists of the springs and shock absorbers that help to isolate the vehicle chassis and occupants from sudden vertical displacements of the wheel assemblies during driving. A well tuned suspension system is important for the comfort and safety of the vehicle occupants as well as the long-term durability of the vehicle's electronic and mechanical components.

The suspension systems in most vehicles on the road today are passive. The chassis of the vehicle is attached to the axles or wheel assemblies through coil springs or leaf springs that help to protect the chassis from sudden vertical forces applied to the wheels (e.g. due to bumpy roads, pot holes, etc...). The shock absorbers help to dissipate the energy applied to the springs and damp the oscillations that would normally occur when a brief excitation is applied to a mass-spring system.

Active suspension systems sense the forces being applied to the wheels and constantly adjust the mechanical connections between the chassis and wheel assemblies to keep the chassis level and/or optimally absorb the energy associated with the vertical motion of the wheels.

Systems that are only able to adjust the viscous damping coefficient of the shock absorber and not the spring rate are generally referred to as "semi-active" suspension systems. A basic semi-active suspension uses an electrically controlled valve to adjust the flow of hydraulic fluid inside the shock absorber to change its dampening characteristics. A more recent innovation uses an electrically generated magnetic field to effectively change the viscosity of a shock absorber fluid that holds metallic particles.

Sensors

Acceleration sensors, displacement sensors, steering wheel position

Actuators

Shock absorbers with electrically variable resistance and/or struts that can be extended or retracted based on electric signal input.

Data Communications

Typically CAN

Manufacturers

ArvinMeritor, Bose, Continental, Hitachi, Tanabe, Tenneco, TRW

For More Information

[1] Active Suspension, Wikipedia

[2] Bose Active Suspension, YouTube video, 2006.

[3] Lotus 99T F1 active suspension, YouTube video, 2006.

[4] Suspension III: Active Suspension Systems, Scott Memmer, Edmunds.com.