Electric vehicle power steering system with a position calibrating device

Abstract

A power steering system intended for a vehicle having at least one steerable wheel (,) and including an electric servo motor (,), a wheel position related steering control unit (,), and a control unit calibrating device (,) for identifying the straight-ahead position of the steerable wheel (,) as the latter is turned within a steering interval defined by a first extreme end position (A) and a second extreme end position (B), wherein the calibrating device comprises a disc shaped element (,) which is rotatable about a central axis (X) in a conjoint relationship with the steerable wheel (,) and provided with a pattern of open and closed portions (,) and a single immobile sensor (,) for producing digital signals in response to its alignment with the open and closed portions (,), wherein a reference point (Y) corresponding to the straight-ahead position of the wheel (,) is defined by the transition from one open portion (,) to one closed portion (,) of the disc shaped element (,). The open and closed portions (,) are arranged on the disc element (,) so as to define in co-operation with the single sensor (,) the extreme end positions (A,B) of the steering interval. The calibrating device (,) is arranged to provide a continuously repeated check of its own operation order as well as the control unit (,) calibration.