Variable assist power steering using vehicle speed and steering pressure

A variable assist power steering system (10) uses both vehicle speed and steering valve inlet pressure to vary the steering assist provided. A system controller (30) receives speed and pressure data from sensors (24, 26) and produces a control signal for an actuator (28) that shunts fluid flow from the pump (22) to the steering valve (20) thereby affecting steering valve pressure which controls the rack piston (16) which changes the angle of the front vehicle wheels used for steering. The controller (30) employs a calibration table (32) with entries representing actuator current, vehicle speed and inlet pressure wherein the speed and pressure fall into ranges defined by equally spaced speed points and equally or unequally spaced pressure points. Having pressure points spaced with a distance between any two sequential points a power of two in sensor counts allows manageable bilinear interpolation of current versus speed and pressure without complicated divide operators.