Hydrostatic power steering system

Abstract

A hydrostatic power steering system wherein the steering wheel can rotate a pilot pump which is connected with compartments at the opposite ends of a spool reciprocably received in a valve body having ports connected with a main pump, a reservoir, the chambers of a power cylinder whose piston is connected with the steering linkage, and with spaces defined by the valve body with two plungers disposed at the opposite ends of the spool. The spool is normally held in a neutral position by two centering springs which react against the respective plungers and bias two retainers into engagement with the spool. The plungers are connected to each other by a rod which is reciprocable in an axial bore of the spool. When the steering wheel is rotated in one direction, the pilot pump causes fluid to flow into one of the compartments whereby the spool is shifted to one of two operative positions and allows the main pump to supply pressurized fluid to one chamber of the power cylinder while the other chamber discharges fluid into the reservoir. If the steering wheel is rotated in the opposite direction, the main pump supplies pressurized fluid to the other chamber of the power cylinder while the one chamber discharges fluid into the reservoir. If the piston of the power cylinder is displaced in response to external influences, the spool moves to the one or the other operative position unless the steering wheel is held by the hands of the operator whereby the spool reassumes its neutral position. The chambers of the power cylinder receive pressurized fluid by way of the pilot pump.