Automobile Suspension Systems

Vehicle suspension is the system of springs and dampers that controls vertical oscillations of the vehicle, determining ride comfort and operating safety. With the technology available today, there are three different functions that can be accomplished with adjustable, electronically controlled suspension. The simplest suspension adjustment is load-leveling used to control ride height for towing and carrying a heavy load in the trunk. Early versions, such as Packards in the fifties, utilized torsion bar rear springs. Ride height was adjusted by rotating the anchored end of the bar with a starter-type motor, a gearbox and heavy bell crank linkage. Since the weight on the front axle doesn't change much, the motor solenoid was controlled with a simple mercury switch mounted parallel to the frame rail, acting as the rear height sensor. Simple load-leveling suspensions today use air-adjustable springs or shock absorbers, an onboard air compressor and a real ride height sensor that supplies data to a control unit or an onboard computer. The next function of an electronic suspension is semi-active suspension. Semi- active suspension works by changing spring and/or dampening rate. The control unit receives information about vehicle behavior, interprets that information as road surface condition and driver intent, then adjusts dampening to a programmed level of firmness. Dampening adjustment is usually accomplished with a shock absorber that has several different orifice valves to control the flow of oil, with a solenoid or stepper motor used to control valve selection. Finally comes the full-active suspension. A fully active system can counteract body motions by actually forcing the suspension to extend in response to measured and anticipated vehicle motion. In many ways, active suspension is simpler than other systems because it doesn't need exotic shock absorbers or air spring technology, just four hydraulic rams and the attendant valves and plumbing.