Abstract: A fluid controller (15) of the type which controls the flow of fluid to an unequal area steering cylinder (25), wherein the controller is of the load reaction type. The controller (15) includes valving (27) which, when it is in neutral (FIGS. 1 and 5), defines a load reaction fluid path (LR) permitting fluid communication between the control fluid ports (21, and 23) through the fluid meter (29) in response to an external load imposed on the cylinder (25). In accordance with the invention, the valving (27) includes a fluid path (97,95,99,71,75) between the load reaction fluid path (LR) and the return port (19), when the valving is in neutral. When the rod end chamber (A) is contracting, fluid is drawn from the return port into the load reaction fluid path (LR), preventing cavitation, and when the head end chamber (B) is contracting, fluid flows from the load reaction fluid path (LR) to the return port (19), preventing pressure intensification.

Abstract: An improved fluid controller (17) is disclosed of the type for use in a load sensing hydrostatic steering system. The system includes a load sensing priority flow control valve (15) of the type which operates on a dynamic load signal. The controller includes a spool valve (95) and a sleeve valve (97) which cooperate to define a plurality of orifices including a main variable flow control orifice (71) and a variable orifice (75) through which fluid flows from the return side of a steering cylinder (19) to the return port (25) of the controller. A variable drain orifice (76) communicates between the main flow path, downstream of the main orifice (71) and the return port (25). As the controller valving moves from its neutral position toward an operating position, the orifice (75) begins to open at least as soon as the main orifice (71) and reaches a predetermined flow area before the main orifice (71) reaches that predetermined flow area.

Abstract: A closed-center, non load-sensing controller (15) is disclosed for use with an unequal area steering cylinder (17). The controller includes valving comprising a spool (35) and sleeve (37). The sleeve includes an annular groove (65) in communication with the inlet port (29) and cylinder ports (73,75) in communication with the opposite ends of the steering cylinder. The sleeve defines an annular leakage groove (95) which is disposed to interrupt the flow of leakage fluid from the annular groove (65) to the cylinder ports (73,75), to eliminate undesired piston rod extension. When the valving is in neutral, leakage fluid collected in the annular groove (95) is communicated through radial bore (97), axial slots (83), and annular groove (81), axial slots (91), drain bore (99), drain bore (93), and then to the system reservoir.

Abstract: A vehicle hydraulic system is disclosed of the type including a steering control valve (29), a brake system (31), and an auxiliary load circuit (65). Fluid flow to these load circuits is controlled by a flow control valve assembly (11) including a priority spool valve (85) which controls the flow of fluid from the inlet port (13) to the priority fluid chamber (75). Fluid flows from the priority fluid chamber to the steering control valve and the brake load system, in parallel, and at equal levels of priority. A shuttle valve assembly (83) receives a steering load signal by means of a load signal line (44) and a brake load signal from the load signal chamber (111), and transmits the higher of the two load signals into the load signal chamber (93) which biases the priority spool valve toward a position to permit a greater flow of fluid into the priority fluid chamber.

Abstract: A closed-center controller is disclosed, especially of the type utilized in hydrostatic power steering systems. The controller includes valving which, in the neutral position, defines a bypass passage communicating inlet fluid through the interior of the hollow, primary valve member to the tank port of the controller. The bypass passage includes a variable bypass orifice having a maximum flow area in the neutral position of the valving and decreasing to zero as the valving is displaced from the neutral position. The variable bypass orifice permits the passage of just enough fluid, typically in the range of about 0.25 gpm to about 0.5 gpm, to minimize the temperature difference between the controller valving and the remainder of the hydraulic system, thus minimizing the possibility of thermal seizure of the valving within the controller.

Abstract: A system for providing pressurized fluid to a primary load circuit and an auxiliary load circuit, the primary load circuit being of the type which provides a load pressure signal representative of the demand for fluid in the primary load circuit. The system includes first and second fluid pumps feeding first and second priority flow control valves, respectively, each of which has a primary outlet port connected to the primary load circuit and an auxiliary outlet port connected to the auxiliary load circuit. When the flow demand of the primary load circuit can be satisfied by the first pump, any excess flow available is fed by the first flow control valve to the auxiliary load circuit, and all of the flow from the second pump goes to the auxiliary circuit.