VEHICLE SUSPENSIONS

An active vehicle roll control system is disclosed in which a roll bar (22) has two halves (22a, 22b) which can be rotated relative to each other by a control unit (26) in order to actively control vehicle roll. The control unit (26) receives signals from lateral accelerometers (29, 30). In order to determine accurately when the vehicle is experiencing zero lateral acceleration, the control unit (26) averages the signal from each accelerometer (29, 30) continuously and uses the average signal as an indication of the straight ahead position. The averaging algorithm defines a window of low lateral accelerations to be used, and a gain to be applied to the acceleration signals, each of which is speed dependent so that the averaging process is not affected by abnormal vehicle movements.