Adaptive variable effort power steering system

Abstract

An adaptive, variable effort power steering system is responsive signals from one or more low friction road surface vehicle handling controls which indicate when the system has become active in modifying handling, and thus indicates the existence of a near limit or at limit vehicle handling situation. Such controls include anti-lock braking systems (ABS), traction control systems (TCS) and integrated chassis control systems (ICCS). When such a handling limit signal is received, the power steering system responds by decreasing steering assist to provide a more 'manual' steering feel as long as the handling limit situation is indicated. The handling limit signal may be a binary signal, indicating activity or no activity of an anti-lock brake system, traction control system or a chassis control system such a yaw rate control. Alternatively, or in addition, the handling limit signal may be a magnitude signal indicating the degree or amount of yaw rate error, lateral acceleration error, wheel slip or vehicle side-slip and thus potentially anticipating the vehicle handling limit as indicated by a binary signal. If binary and magnitude signals are used together, the magnitude signal is preferably used as an anticipatory signal with a partial and growing correction to smooth the application of the full correction signaled by the binary signal.