Hybrid load-sense vehicle hydrostatic steering system

Abstract

In a hydrostatic load sense vehicle steering system, fluid flow from a source is used by a hydrostatic steering controller to effect steering of the vehicle. The controller has a metering unit and a control valve which, in response to a steering effort, moves away from a neutral position to an operating condition in which it (i) establishes a main flow control orifice which directs fluid from the source to the metering unit and (ii) directs metered fluid to a steering motor. A fluid actuator controls the flow of fluid from the source to the hydrostatic steering controller. A pilot fluid circuit directs a pilot flow of fluid to the controller which is used to control the operation of the fluid actuator. In the controller, the control valve directs the pilot fluid to a reservoir when there is no steering. The system is designed to come to a standby condition in which the amount of pilot fluid being directed to the controller is high enough that it can be used to satisfy a range of low demand steering maneuvers. In providing the pilot flow, the system develops hydraulic biasing forces on the components of the fluid actuator. The hydraulic biasing forces help the system respond to a high demand steering maneuver to increase rapidly the amount of fluid which is made available for effecting steering.