Active suspension

Active suspension is a term that is used mainly in motor sport. In the automotive industry, this is precisely referred to as an active suspension. An actor delivers it all or part of the forces that otherwise be generated passively by springs or dampers. The aim is to reduce the otherwise inevitable rolling and pitching movements of the body through bends or when braking or accelerating. In addition, the distance of the vehicle above the road surface is controlled. These functions consume energy that must be made usually hydraulic, partly electrically available. Must be distinguished from semi-active suspension, which can be switched between different characteristics of the spring or damper elements ( cf. Hydroactive suspension, Magnetic Selective Ride Control).

A first application was the active suspension in Formula 1, where a computer-controlled electronics in the field of the suspension to improve the aerodynamics of the vehicle during the period of the seasons from 1987 to 1993 contributed. The end of 1993 it was banned by the FIA ​​.

History

The development of active suspension was started by Lotus boss Colin Chapman already Engineer 1981/1982. For the first time the car for racing the active suspension was used in 1987 in the Lotus 99T model. In parallel, Williams developed in FW11B also an active suspension. However, the active suspension was still immature and the software could not optimally exploit the potential of this invention, since they could not fully process the information. Nevertheless, the Lotus 99T won with the Brazilian racing driver Ayrton Senna races in Monaco and the USA ( Detroit ). The Brazilian Nelson Piquet won the race in Italy in the Williams - Honda. In 1988, the development especially in Williams and Lotus unabated; However, the technique proved to be too complex and was discontinued until further notice, until she was then added to the end of the 1991 season, Williams again. In the Formula 1 1992 season of the breakthrough; Nigel Mansell was the Williams driver superior world champion, the Williams team secured the Constructors' title. The technique, which gave the Williams team a huge advantage, was acquired at the beginning of the 1993 season from other teams and developed. Alain Prost won this year's title for a second Williams with active suspension.

Operation

All important for the function of the system information (eg driving speed, acceleration, suspension travel, ... ) can be detected by sensors. The on-board computer calculates the required force at each wheel, depending on the application, energy consumption and other criteria are used, different actuators. In spring - base displacement for example, the force is applied hydraulically with a cylinder in series with a spring. This is necessary since each control system has only a limited power. Higher-frequency stimuli that can not be actively regulated, be kept away from the building. The mode of action depends not only on the mechanical components heavily on the software, so here expertise and imagination of the engineers are in demand.

Active suspension in motorsport

Since the aerodynamics of racing cars is very sensitive to changes in the pitch angle and ground clearance, the location of the vehicle is independent of the external conditions ( speed, fuel level, ... ) set so that the aerodynamic parts are flowing low and the ground clearance constant as possible is. The distribution of the wheel load on the front axle and rear axle can also the Under / over-steer in curves, as well as traction when accelerating out of corners to be improved.

Active Suspension in road traffic

Citroen 1995 Citroen Xantia led an active chassis stabilization (AFS ) a. The Xantia Activa was the (technical) of the Xantia top model series from Citroën. The idea was the end of 1994, were built between spring 1995 and autumn 2001, just over 18,000.

Besides Hydractive II Activa still called Active Chassis stabilization (AFS ) had, in the French SC.CAR = systems Citroën de Contrôle Actif you Roulis, which was the first series- offered active anti-roll bar in the automotive industry. With this system, the lateral inclination control is reduced by mechanical with hydraulic cylinders, which act upon the anti-roll bars, at a minimum ( 0.2 ° to 1 °). This technique allows ( according to factory specification ) for optimal grip roadway lateral accelerations up to 1.2 g and provides while still being an exceptionally high ride comfort and thus secure road holding. Compared to the standard models, the Activa seats with reinforced side panels, which also are pneumatically adjustable in the first series ( X1). This more lateral support is guaranteed.

How AFS / SC.CAR: Both ( relatively thick ) cross- stabilizers (front 28 mm, rear 25 mm diameter) are diagonally opposite (front - left and rear - right ) via a differential hydraulic cylinders with the check rails.

These cylinders are connected to a regulator valve, which is operated directly from the front wishbones means of push rods via a spring - lever mechanism. Occurring rolling moment ( side slope ) has the opposite effect on the wishbone - a wheel deflects, the other springs from. The tilt corrector - - This causes the regulator valve is controlled by the push rods in a direction towards from its rest position ( straight ahead ) pulled / pushed, making it sets a the rolling torque proportional pressure in the hydraulic cylinders.

The hydraulic cylinder thereby change their length and thus counteract the strain of the anti-roll bar. In the horizontal, which curve driving possible up to 0.6 g lateral acceleration with -0.2 to 0.5 ° lateral inclination " push" the body through the cross stabilizer bars to the roll moment acting again. From 0.6 g of lateral acceleration, the actuating cylinder to arrive at their stop, from here, the Xantia Activa up to 1 ° tends to reach the curve boundary region in the curve, which corresponds to the value of a good sports car with correspondingly tighter coordination.

Since this active roll stabilizer operates independently of the Hydractive II chassis, the suspension travel remains even in extreme cornering obtained almost entirely, thus ensuring a much better road in these situations than the conventional wheel suspension can. On straight sections of a solenoid valve is actuated via the control unit of the Hydractive suspension also that switches an additional spring ball in the hydraulic control circuit of the actuator cylinder. This, on the one hand, the rigidity of the hard- tuned stabilizer bars "virtually" mitigated by the gas filling of spring ball to reduce copying movements and thus to increase the comfort. It also acts through its memory effect dampening effect on the control loop so that no unwanted vibrations usually occur when driving straight ahead through suspension caused momentary actuation of the tilt corrector.

Mercedes -Benz CL in 1999 led an active suspension system, called Active Body Control one in which the structure of degrees of freedom Huben, pitch, roll were actively influenced. Through additional hydraulic forces at each wheel rolling and pitching movements when cornering or longitudinal acceleration are largely avoided, without suffering the ride comfort on uneven road surfaces. Thus, both a very good handling and a high level of driving comfort is made possible.

Other models by Mercedes -Benz, Porsche, Audi, BMW, Opel and Renault have techniques, in which not all body degrees of freedom can be controlled. Example is the active roll stabilization in the Citroën Xantia Activa. This very simple system was controlled mechanically by the rotation of the stabilizer. Further developments of these techniques rely on electronic control units, which detect the running state of sensors and driving the actuator accordingly.