Abstract: A hydraulic fan circuit is provided. The hydraulic fan circuit includes a tank, a motor having a fluid inlet and a fluid outlet and a pump to draw fluid at a low pressure from the tank and discharge the fluid at elevated pressures to the motor via the fluid inlet. The hydraulic fan circuit further includes a directional control valve disposed between the fluid outlet of the motor and the tank. The directional control valve is operable to move between a flow blocking position and a flow passing position. Further, the directional control valve is configured to reduce a positive speed of the motor below a lowest positive speed attainable through control of pump output. Furthermore, the hydraulic fan circuit includes a pressure control circuit configured to provide a pilot fluid flow at varying pressure to move the directional control valve.

Abstract: A hydraulic fan circuit is provided. The hydraulic fan circuit includes a tank, a motor having a fluid inlet and a fluid outlet and a pump to draw fluid at a low pressure from the tank and discharge the fluid at elevated pressures to the motor via the fluid inlet. The hydraulic fan circuit further includes a directional control valve disposed between the fluid outlet of the motor and the tank. The directional control valve is operable to move between a flow blocking position and a flow passing position. Further, the directional control valve is configured to reduce a positive speed of the motor below a lowest positive speed attainable through control of pump output. Furthermore, the hydraulic fan circuit includes a pressure control circuit configured to provide a pilot fluid flow at varying pressure to move the directional control valve.

Abstract: When different implements are attached to an agricultural tractor, various hydraulic actuators on the implement are operated by connection to the hydraulic system on the tractor. A single hydraulic fluid connector on the tractor has first and second ports with a separate valve assembly provided to control fluid of fluid to and from each port. This enables one doubling-acting hydraulic actuator to be connected to both connector ports so that the fluid flow to and from the actuator is controlled. For a different implement, one single-acting hydraulic actuator can be connected to one connector port and another single-acting hydraulic actuator can be connected to the other port of the same connector. Individual operation of the valve assembly for each port in this case allows independent control of the two single-acting hydraulic actuators.

Abstract: A spool type control valve is operated by an electrically driven pilot valve. A pilot piston is attached to the control spool. As an electrical actuator moves the pilot spool, a greater pressure is applied to one side of the pilot piston than the other side, which causes movement of the control spool. When the control spool reaches the desired position, its positional relationship to the pilot valve defines a pressure differential across the pilot piston which exerts a net force on the control spool that counterbalances a spring force acting on the control spool. This defines an equilibrium position at which the control spool remains until subsequent motion of the pilot spool occurs which alters the pressure differential across the pilot piston.

Abstract: A check valve system controls the flow of fluid between a spool valve and a hydraulic actuator and includes a pilot operated check valve that is controlled by a lock-out valve. The check valve has a poppet that engages and disengages a first valve seat in response to a pressure in a control chamber. The lock-out valve has an inlet connected to the control chamber, an outlet connected to an opening in the bore of the spool valve, and an second valve seat between the inlet and the outlet. A valve member that selectively engages and disengages the second valve seat and spool of the spool valve applies force to the valve member which responds by moving into engagement with the second valve seat. Thus in one position, the spool valve maintains the lock-out valve closed which traps pressure in the control chamber which tend to keep the check valve closed.

Abstract: A spool valve section for a multiple valve assembly has a body with two opposing side surfaces. A plurality of mating surfaces are raised from each side surface. The mating surfaces surround the openings of fluid passages through the section and apertures for fasteners that secure the assembly together. The mating surfaces are spaced from a region of each side surface that is adjacent a bore in the body that receives a control spool. The fluid passages also are spaced from and do not intersect the spool bore. These characteristics of the spool valve section reduce distortion of the spool bore which could otherwise result from the pressure and fastening forces in the valve assembly.

Abstract: A first control valve selectively connects a first port of a double acting actuator to either a pump supply line or a tank return line, and a second control valve selectively connects a second port of the actuator to either a pump supply line or a tank return line. A first pilot operated check valve restricts fluid flow to a direction only from the first control valve to the first workport unless a pilot pressure from the second port is sufficient to open the valve for the opposite flow direction. A second pilot operated check valve restricts fluid flow to a direction only from the first control valve to the second workport unless a pilot pressure from the first port is sufficient to open the valve for the opposite flow direction. A load sense circuit is incorporated to produce signal indicating the greater pressure at the actuator ports.

Abstract: A pilot operated valve has a poppet that is held against a valve seat by pressure in a control chamber on an opposite side of the poppet and by force from a feedback spring. The force feedback spring also engages a pilot valve spool which controls the flow fluid from a control chamber. When a electrically driven actuator moves the pilot valve spool and fluid is released from the control chamber, inlet pressure acting on the poppet causes the valve to open. As the poppet moves away from the valve seat, the feedback spring exerts more force on the pilot valve spool so as to meter the fluid being released from the control chamber. When the force of the feedback spring counterbalances the actuator force, an equilibrium condition occurs and the poppet stops moving at the desired flow control position.

Abstract: A first control valve selectively connects a first port of a double acting actuator to either a pump supply line or a tank return line, and a second control valve selectively connects a second port of the actuator to either a pump supply line or a tank return line. A first pilot operated check valve restricts fluid flow to a direction only from the first control valve to the first workport unless a pilot pressure from the second port is sufficient to open the valve for the opposite flow direction. A second pilot operated check valve restricts fluid flow to a direction only from the first control valve to the second workport unless a pilot pressure from the first port is sufficient to open the valve for the opposite flow direction. A load sense circuit is incorporated to produce signal indicating the greater pressure at the actuator ports.

Abstract: A pilot operated valve has a poppet that is held against a valve seat by pressure in a control chamber on an opposite side of the poppet and by force from a feedback spring. The force feedback spring also engages a pilot valve spool which controls the flow fluid from a control chamber. When a electrically driven actuator moves the pilot valve spool and fluid is released from the control chamber, inlet pressure acting on the poppet causes the valve to open. As the poppet moves away from the valve seat, the feedback spring exerts more force on the pilot valve spool so as to meter the fluid being released from the control chamber. When the force of the feedback spring counterbalances the actuator force, an equilibrium condition occurs and the poppet stops moving at the desired flow control position.

Abstract: Different sections of an agricultural implement can be raised and lowered independently and by varying amounts by a unique hydraulic system. That system incorporates a three-position, four-way primary control valve which selectively connects a supply line and a tank return line to first and second hydraulic lines. A plurality of double acting hydraulic cylinders are provided to produce movement of lift assemblies with respect to a frame of the implement. A separate electrohydraulic lift control valve for each hydraulic cylinder couples one cylinder chamber to the first hydraulic line and the other cylinder chamber is connected directly to the second hydraulic line. Operation of the primary control valve determines the movement direction and selective activation of the lift control valves determines whether the associated section of the implement moves and the amount of such movement.

Abstract: Different sections of an agricultural implement can be raised and lowered independently and by varying amounts by a unique hydraulic system. That system incorporates a three-position, four-way primary control valve which selectively connects a supply line and a tank return line to first and second hydraulic lines. A plurality of double acting hydraulic cylinders are provided to produce movement of lift assemblies with respect to a frame of the implement. A separate electrohydraulic lift control valve for each hydraulic cylinder couples one cylinder chamber to the first hydraulic line and the other cylinder chamber is connected directly to the second hydraulic line. Operation of the primary control valve determines the movement direction and selective activation of the lift control valves determines whether the associated section of the implement moves and the amount of such movement.

Abstract: An assembly of valves controls hydraulic fluid flowing to several hydraulic actuators from a variable displacement pump that produces an output pressure equal to a control input pressure plus a predefined margin pressure. The control input pressure is a function of the greatest load pressure at the hydraulic actuators. Each valve has an associated pressure compensating valve which regulates the pressure differential across a metering orifice of each valve to a predefined level, usually the pump's margin pressure. A flow regulator is associated with at least one of the valves and reduces the output pressure from the pump to produce a reduced pressure that controls the associated pressure compensating valve. Operation of the flow regulator causes the pressure differential across a metering orifice of the associated valve to be less than the pump's margin pressure thus allowing adjustment of the fluid flow.

Abstract: The position of the blade of a motor grader is controlled to maintain a smoothly graded surface even when the grader's front wheels travel over undulating ungraded ground. This is accomplished by sensing the degree to which the grader frame pivots with respect to the rear wheels and employing the pivot angle to derive the resultant change in blade position. That change is used to operate a mechanism that produces movement of the blade relative to the earth thereby compensating for effects of the pivoting action.

Abstract: A proportional hydraulic control valve assembly has a pair of bores in a valve body with separate control spools in each bore. A pair of force feedback, linear actuators are mounted on the same side of the valve body and each actuator controls the movement of a different one of the control spools. Only one of the control spools governs application of hydraulic power to a first work port of the valve assembly, while connecting a second work port to tank. Only the other control spool governs application of hydraulic power to the second work port of the valve assembly, while connecting a first work port to tank. The force feedback, linear actuators enable each spool to be received very tightly within the respective bore.

Abstract: A pilot-actuated, pressure-compensated flow and directional control valve assembly (11) is provided in which a main valve spool (95) is positioned in response to a pressure differential between a pilot chamber (119) and a reaction chamber (117). Flow of fluid from an inlet port (29) is controlled by means of a pilot valve assembly (97), into the pilot chamber (119), while fluid flows out of the pilot chamber (119) through a fixed orifice (67) to a pump load sense port (61). The main valve spool (95) acts as an inlet compensator. If the pressure at a load L is above inlet pressure, the main valve spool (95) acts as an inlet check, preventing reverse flow. If there is a higher load pressure at another load circuit in the system, such as a steering valve S, there will be an increase in pressure in the reaction chamber (117), thus closing off the main spool (95), reducing the flow from the inlet port (29) to the work port (47), and giving more priority to the steering valve S.

Abstract: An engine-driven pump supplies pressurized hydraulic fluid to vehicle brake and steering circuits. A ground driven variable displacement pump controlled by a control circuit is de-stroked when the engine-driven pump is operational. The variable displacement pump includes a movable piston which divides a bore into a pilot chamber and a pump chamber. An outlet line with a check valve communicates fluid one way from the pump chamber to the vehicle circuits. An inlet line with a check valve communicates fluid one way from a reservoir to the pump chamber. A ground-driven rotatable cam member reciprocates the piston. A spring urges the piston towards the cam member and towards a full stroke position. A pilot line which communicates fluid pressure from an outlet of the engine-driven pump to the pilot chamber. When the engine-driven pump is operational the pressure in the pilot line moves the piston away from the cam member, thus de-stroking the variable displacement pump.

Abstract: A hydraulic control system is provided which includes a pair of transversely spaced rockshaft cylinders which are plumbed in parallel and connected to opposite ends of a rockshaft on the central portion or main frame of a wide implement such as a field cultivor or chisel plow. The left-hand rockshaft cylinder is connected in series with a right-hand outer cylinder located near the right end of the implement. The right-hand rockshaft cylinder is connected in series with a left-hand outer cylinder on the opposite side of the implement. When a ground condition exists which causes, for example, the left side of the implement to dig more deeply and the left-hand wing cylinder to retract, the right-hand rockshaft cylinder will also be caused to retract so the right side of the implement tends to dig in more deeply.

Abstract: A hydraulic motor has its lube drain connected to the motor return line. A motor seal protector valve has a pilot which responds to pressure in the motor return line. Normally, the valve connects system pressure to the motor inlet. High pressure in the return line causes the pilot to move the valve to block the motor feed line and then to connect the motor feed line to sump. In a preferred embodiment, system pressure is connected to the plot to "lock up" the valve in response to return line overpressurization.