Abstract: A ride control system adapted for use in a fluid system of a machine to cushion the ride of the machine, the machine having a frame with an actuator arrangement disposed between the frame and a load to raise the load relative to the frame, the actuator arrangement having a raise port and being operative in a raise mode to raise the load to a desired height in response to pressurized fluid being directed to the raise port from a source of the pressurized fluid, the ride control system including an accumulator arrangement and a valve arrangement connected between the accumulator arrangement, the actuator arrangement, and the source of pressurized fluid, and operative to selectively connect the accumulator arrangement to the raise port of the actuator arrangement when in the raise mode while maintaining the load at the desired height.

Abstract: A force feedback popper valve has a valve element for controlling fluid flow from an inlet port to an outlet port. A meter-in orifice communicates pressurized fluid from the inlet port to a control chamber above the valve element. A pilot valve provides a meter-out orifice between the control chamber and the outlet port to selectively reduce the pressure level in the control chamber in response to a control force applied to the pilot valve. A feedback spring is disposed in the control chamber between the valve element and the pilot valve so that displacement of the valve element is proportional to the control force exerted against the pilot valve.

Abstract: Fluid regeneration circuits are useful for filling expanding sides of a hydraulic motor with fluid being exhausted from the other side. The components of the currently available regeneration circuits are disposed in or adjacent to the directional control valve such that the fluid used for regeneration must pass through relatively long motor conduits between the control valve and the hydraulic cylinder. The regeneration circuit of the present invention includes a load check valve which forces the fluid exhausted from the head end chamber of a hydraulic motor to pass through a poppet valve controllably opened by a control signal. A low pressure relief valve causes an increase in the fluid pressure of the exhausted fluid passing through the poppet valve such that when the pressure level exceeds the pressure level of the fluid in an expanding side rod end chamber of the hydraulic motor, the exhausted fluid passes through a regeneration check valve and fills the expanding rod end chamber.

Abstract: Hydraulic control systems are useful for controlling actuation of hydraulic motors. Some such systems use spool type valves while other systems use poppet type valves, both of which have their advantages and disadvantages. The present hydraulic control system is a hybrid system utilizing a combination of both a spool type control valve and poppet type control valves in a single work circuit. Specifically, a spool type control valve has an inlet port connected to a variable displacement pump and a pair of flow amplifying poppet type valves are serially disposed between a pair of motor ports of the spool type valve and a pair of actuating chambers of a double acting hydraulic motor. The spool type control valve is operative to control pump-to-motor flow while one of the poppet type valves is operative to control motor-to-tank flow.

Abstract: Flow amplifying poppet valves are useful in hydraulic circuits requiring low leakage when the circuit is in a load holding condition. Pressure compensation of the known flow amplifying poppet valves has not been totally successful and thus, the output flow varies somewhat with changing pressure drops across the poppet valve. The subject pressure compensated flow amplifying poppet valve utilizes a pressure compensating valve and a compensating orifice disposed in a compensating flow path disposed in parallel with a valve device for controllably regulating fluid flow through a flow regulating passage. Fluid flow through the compensating flow path is restricted by the orifice to a flow rate substantially equal to the amount of fluid that can flow through a flow control slot in a valve element at a closed position of the valve element.

Abstract: Hydraulic motors are conventionally employed in rotating the upper structure of excavators and the like. Protection from inertia induced hydraulic shock loads of some hydraulic control circuits involves the use of a separate bypass valve which continuously interconnects the motor conduits. The subject control circuit includes a pair of shunt valves each of which establishes restricted communication between the first and second motor conduits in a particular direction at their normal spring biased position. This allows limited free swing of the upper structure when the directional control valve is shifted from an operating position to the neutral position. However, shifting the directional control valve to an operating position causes the appropriate one of the shunt valves to shift to a blocking position so that no interconnection between the motor conduits exist.

Abstract: A hydrostatic transmission (10) includes a variable displacement pump (12) for driving a fluid motor (14) in first and second directions. First and second high pressure conduits (20,22) connects the pump (12) and motor (14) in a continuous fluid circuit. A control pump (40) supplies make-up fluid to the first and second high pressure conduits (20,22) and simultaneously provides pressurized control fluid to a system control (50) for controlling the operation of the hydrostatic transmission (10). First and second low pressure conduits (24,26) are respectively disposed about the first and second high pressure conduits (20,22) and defines first and second spaces (28,30) therebetween. A pressure control arrangement (32) is connected to the first and second spaces (28,30) to control the maximum pressure level in the spaces (28,30) upon the failure of one of the high pressure conduits (20,22).

Abstract: An underspeed actuator (18) is connected to the displacement control (17) for controlling the displacement of a variable displacement pump (11) of a hydrostatic transmission (10) in response to the pressure differential between low and high pressure control signals (A,B) wherein the pressure differential is directly proportional to the engine speed. An overspeed control valve means (41) is connected to the low and high pressure signals and decreases the pressure level of the high pressure signal received by the underspeed actuator (18) in response to the pressure differential exceeding a predetermined magnitude. This reduces the displacement of the variable displacement pump (11) thereby controlling the amount of engine overspeed caused by the hydrostatic transmission (10) driving the engine when the vehicle is descending a steep hill.

Abstract: A hydraulic control system having a pump and circuits connecting the pump to a pair of hydraulic motors through first and second circuits is provided with a priority valve system operative to provide a priority of fluid pressure to the first motor up to a predetermined minimum pressure and thereafter to maintain the pressure in the first circuit and simultaneously supply fluid to the second motor of the second circuit. The priority valve system is also responsive to a load on a second motor to split the flow of fluid between the two motors above the predetermined minimum pressure up to a second pressure after which the second predetermined pressure is maintained in the first circuit while fluid is being supplied to the second conduit.

Abstract: A method and plural embodiments of apparatus for delivering a pressure-compensated supply of fluid to a hydraulic steering circuit, wherein first and second pumps are respectively operated by a vehicle engine and by a ground wheel when the vehicle is in motion, output fluid from the two pumps being simultaneously directed to the steering circuit by a control valve with inlet relief valve means modulating output pressure of the sources in response to operation of the control valve. One embodiment contemplates dual inlet relief valves for separately modulating output from the two pumps while another embodiment contemplates one of the pumps having a variable output.

Abstract: A sealing structure for use in an oil-cooled disc brake apparatus or the like, having a buffer seal for providing extended life and improved functioning of the face seals thereof. The buffer seal provides a pressure-regulating function in controlling the delivery of lubricating coolant fluid to the brake and face seals.

Abstract: A load check and bypass valve includes a check valve providing fluid flow from an inlet-outlet port to a motor port while blocking reverse flow therethrough and a bypass valve resiliently biased to a closed position for blocking fluid flow through a bypass connecting the motor port with the inlet-outlet port. The bypass valve has an opened position permitting fluid flow therethrough and is movable to its opened position by a selectively controllable actuating device. A first force exerting device is provided for exerting a force on the bypass valve urging it towards its opened position and is connected to the motor port by a first passage. A second force exerting device is provided for exerting a force on the bypass valve urging it towards its closed position and is connected to the motor port through a second passage. A check valve is disposed in the second passage providing fluid flow therethrough from the motor port to the second force exerting device while blocking reverse fluid flow therethrough.

Abstract: A fluid system has first and second hydraulic jacks each having a load supporting end connected to a source of fluid through a control valve. First and second pilot operated valve assemblies are positioned between the control valve and the load supporting ends with each valve assembly having a first check valve positioned in a chamber and being movable between a first position at which communication between the associated load supporting end and the control valve is blocked and a second position at which the associated load supporting end is in fluid communication with the control valve. A second check valve is associated with the first check valve and is movable between a first position at which communication between the chamber and the control valve is blocked and a second position at which the chamber is in fluid communication with the control valve.

Abstract: A control system has override for fluid operated work elements served by at least two variable displacement pumps each serving a separate circuit. At least two work elements are served by the first circuit and at least one work element is served by the second circuit. The discharge rate of the first pump is controlled by a signal delivered from a summing valve in response to the pressures of the first and second circuits during operation of a preselected one of the work elements of the first circuit and controlled by a modified pilot pressure signal in response to operation of only the other work element of the first circuit.

Abstract: A pilot operated, control valve providing for two speed operation of a hydraulic jack in a first direction, the control valve including centering spring means for resisting movement of its spool in either direction and additional spring means for resisting movement of the spool in the first direction in order to establish two operating positions of the spool corresponding to the two speeds of operation for the jack, the first operating speed being accomplished by communicating the rod end of the jack with a drain and simultaneously communicating a source of fluid under the pressure with a head end of the jack, the second operating speed being accomplished by communicating both ends of the jack with the pump, a pilot valve being manually operable to regulate the control valve and having first and second springs to indicate the operating position of the control valve spool and the corresponding speed of operation for the jack in the first direction.

Abstract: A throttling slot is formed in a control valve spool and interconnects a reduced diameter portion and a peripheral surface of a land provided on the spool with the throttling slot including a pocket recessed into the land at an angle inclined in the direction opposite to the normal direction of movement of the spool for effecting fluid flow through the throttling slot, and a longitudinally extending groove from the pocket which terminates in an end intersecting the reduced diameter portion.

Abstract: A hydraulic load lifting system having a vented load check valve disposed in the main control line connected between the load supporting end of a hydraulic motor and a spool-type control valve to normally isolate the load generated pressures from the control valve is provided with venting apparatus which is operative to selectively prepressurize the main control line between the control valve and the load check valve prior to the venting of the load check valve and the shifting of the control valve to effect the lowering of a load being supported by the hydraulic motor so as to substantially balance the pressures on the opposite sides of the load check valve to prevent momentary load drop and hydraulic hammering.

Abstract: A hydraulic circuit is disclosed in which a control valve is connected in parallel between a first and second moving circuits. The first and second moving circuits include interrupted series-type valves responsive to pilot input signals. The control valve is responsive to the input signal to the first series valve wherein a portion of the flow from the first circuit is diverted to the second circuit, thereby permitting the operation of both circuit end functions at maximum speed.

Abstract: A fast exhaust circuit for hydraulic jacks includes a bypass conduit communicating a hydraulic jack with a tank, and a bypass valve disposed in the bypass conduit normally positioned for blocking fluid flow therethrough so that all fluid exhausted from the hydraulic jack passes through and is modulatably controlled by a control valve with the bypass valve being selectively positionable for returning a greater portion of the exhausted fluid directly to the tank and bypassing the control valve.

Abstract: A heavy vehicle, such as a tractor scraper, has oil cooled front disc brakes, and oil cooled rear disc brakes that may be used alone or in conjunction with the front brakes. A rear brake cooling circuit and a front brake cooling circuit, each of which has its own pump and heat exchanger, are cross-connected through a common reservoir, and both pumps and heat exchangers function whenever the rear brakes are applied. The rear circuit heat exchanger is an oil cooler with a fan, the motor for which is driven from the pump output and discharges to the cooler; and the motor may drive a bypass pump which draws some oil from the return line and passes it through the cooler.