Hydrostatic steering controller with pressure dams

Abstract

A hydrostatic steering controller including a pair of valve members which are relatively movable in opposite directions from a neutral position to a pair of operating positions to control flow between a fluid pressure source and a hydraulic steering motor. In each of the operating positions the valve members include interfacing surfaces which define part of a first passage directing high pressure fluid to the steering motor and a second passage directing low pressure fluid from the steering motor to a reservoir. The interfacing surfaces of the valve members create a pressure dam between the first and second passages when the valve members are relatively moved by a predetermined amount away from the neutral position and to an operating position. The pressure dam minimizes leakage between the first and second passages. The pressure dam is created in a pressure dam groove formed in a surface of one of the valve members. The pressure dam groove is connected with the fluid pressure source, and is disposed in facing relationship with a low pressure return groove formed in a surface in the other valve member when the valve members are in their neutral position. When the valve members move to their operating position a surface on the other valve member moves into facing relation with the pressure dam groove, thus increasing the pressure in the pressure dam groove.