As yet, active ride has been seen only on the racetracks (banned from F1 at the end of ’93). For a production car it has been considered too expensive and bulky. The Active is the only road car which has gone some way towards encompassing the concept with its active roll control.
A true active ride system ditches springs and dampers and uses electronically-controlled hydraulics to give infinitely variable stiffness according to vertical and lateral load. In communication with a microprocessor hundreds of times per second, the wheels will always follow the contour of a bump exactly, giving a superb ride, and the car will always remain flat and level during cornering.
Ever since the DS of 1955, Citroen has specialised in suspension that does away with springs and dampers. The current variation of this on the Xantia VSX is Hydractive, using a mixture of gas and fluid-filled spheres. It gives two possible levels of stiffness and can automatically select the firmer of these under cornering reverting to the softer one in straightline running. It also has a button which allows you to select the firmer setting full-time.
With this set-up Citroen was already a long way down the road of active suspension. With the Active it has taken a further step by addressing the non-roll part of active ride. But there is no active control of the wheels movements so there are no ride comfort benefits and the Active is still able to pitch and dive just like a conventional car.
The active roll control works through hydraulically-operated rams connected to the suspension arms and the roll bar at each end which effectively push the car level during cornering. These act from the same sensors as those already used to firm up or soften off the Hydractive suspension. The rams are fed by the hydraulic pressure actuator feeding through an auxiliary sphere to cushion the effect when running in a straight line (though they can be tricked into firming up if you run over a pot-hole).
As you turn in, this auxiliary sphere is isolated and this has the effect of doubling the roll-bar’s stiffness.
If roll then reaches more than half a degree the rams themselves come into action and physically push the body level.