Stabilizing Steering Weave with Active Torque Versus Semi-Active Damping

A steering stabilizing algorithm for automobiles commands transient steering control torques so that the sum of natural steering restoring torque and the control torque is more nearly in phase with steer angle than the natural restoring torque alone. The resulting reduction in the phase lag from steer angle to restoring torque mitigates the steering weave mode. Natural restoring torque determined from a measured lateral acceleration signal can be compared to expected steady-state restoring torque calculated from steer angle and vehicle speed. Commands to a steering torque actuator depend on the difference signal, which is nonzero during rapid transients only. The character of control torques required is different from passive steering damping, so that an active control torque gives the best, response. Simulations show that a rapidly-controlled variable steering damper could apply the desired weave control torque a fraction of the time, resulting in significant weave mode mitigation. A weave stabilizer which operates by semi-active damping would be safer than an actively controlled steering torque motor in the event of control circuitry failure.