Patent ID: 6269903
Filing Date: 2001-08-07
Classification: B62D

Abstract:
A vehicle steering system switchable between a normal mode with a steer-by-wire level and an emergency mode with a fall-back level, the fall-back level comprising a hydraulic system which includes a manual-side double-acting piston-cylinder unit actuatable with a steering handle and positively coupled hydraulically to a wheel-side double-acting piston-cylinder unit configured to actuate steered vehicle wheels, a hydraulic charging system having a hydraulic pump with an inlet side operatively connected to a hydraulic-fluid reservoir, a switchable hydraulic coupling for selectively coupling decoupling hydraulically the fall-back level hydraulic system and a steer by wire hydraulic system to the hydraulic charging system, and a boost-hydraulic system for changing the fall-back level to a working pressure greater than a pressure in the hydraulic-fuel reservoir.