DESCRIPTION & OPERATION
Electronically controlled, variable-assist, speed proportional power steering or Electronic Variable Power Steering (EVPS), provides greater steering assist when stationary and at low speeds. As road speed increases, less power assist is provided to give a firmer, more responsive feel.
Maximum assist is provided from zero to 20 MPH. Operational range of EVPS is from about 20 to 60 MPH, with minimum power available at about 60 MPH.
Variable assist is provided by controlling power steering fluid at power steering gear. Pressure is controlled by regulating fluid flow from steering gear back to power steering pump. A solenoid valve, located on the steering gear, controls power steering pressure by varying size of orifice through which power steering fluid flows back to pump.
The solenoid valve is controlled by a Body Control Module (BCM). The BCM receives a Vehicle Speed Signal (VSS) from the Powertrain Control Module (PCM). On receiving a VSS, the BCM converts VSS into an electrical current used by the solenoid control valve to vary orifice size. (Scheme 1)
