Electrohydraulic effects on the modelling of a vehicle active suspension

A car suspension incorporating a Lotus actuator and a TVR suspension/wheel unit is studied both experimentally and analytically. An emphasis is placed on hydraulic modelling using a series of transfer functions linking the hydraulic and suspension components. This is signi cantly aided by the use of a Moog 2000 programmable servo controller (PSC ) to equalize the extending and retracting ow gains of the servovalve in the Lotus actuator control loop, justifying the use of combined extending and retracting transient data for parameter identi cation. This then allows the system equations to be developed using linear state-space theory, and a suitable form is proposed for further design studies. It is shown that the hydraulic components signi cantly contribute to the system dynamics and hence cannot be neglected when control schemes are formulated. In particular, the signi cance of hydraulic bulk modulus on dynamic performance is evaluated, and the importance of accurately determining all components of velocity-type damping is highlighted.