Hydraulic power steering systems for motor vehicles.

摘要

A hydraulic steering system for a motor vehicle has an engine driven hydraulic pump 12, a driver operable control valve 20 for controlling supply of pressure fluid to a motor 10 to effect steering of road wheels 5, and an auxiliary, electric motor driven, hydraulic pump 30 operable through a control unit 36 to supply pressure fluid to the input of control valve 20 in respect to a predetermined low level of fluid pressure being sensed by a pressure switch 35 in the supply line from the engine driven pump 12, the unit 36 including a time delay arrangement for inhibiting operation of the auxiliary pump during eneging start-up. In the event of pump 12 failing therefore, steering capability is maintained.