Abstract: A hydrostatic stepless transmission comprises a hydraulic pump and a hydraulic motor, at least one of the hydraulic pump and motor being variable in displacement; a closed circuit for fluidly connecting the hydraulic pump and motor to each other therethrough, the closed circuit including a pair of oil passages between the hydraulic pump and motor, one of the oil passages being hydraulically higher-pressured and the other being hydraulically depressed when the hydraulic pump delivers oil to the hydraulic motor; a speed change operation device for changing output rotational speed of the hydraulic motor; and a leak valve connected to the speed change operation device.

Abstract: The system includes a hydraulic powered actuator. A pump system having first and second hydraulic lines is coupled to the first and second ports, respectively and is capable of providing hydraulic fluid to either the first and second lines. First and second pressure sensors are coupled to the first and second lines, respectively. A third line is coupled between the first and second lines and includes first and second valves mounted in series therein. Preferably, the first and second valves are capable of latching in the open position. A reservoir is coupled to the third line between the first and second valves. A shut off valve is included for cutting off the flow from the reservoir.

Abstract: A hydraulic control device for a working machine includes hydraulic actuators, a hydraulic pump which functions as a hydraulic power source, control valves which control the actuators on the basis of operations by an operating unit, a common bleed-off valve which returns excess oil to a tank via an unload passage on the basis of the operations by the operating unit, and a control unit which controls the common bleed-off valve. The common bleed-off valve is capable of setting a position for closing the unload passage when the common bleed-off valve is in a non-operating state. The control valves have center bypass passages which function as individual bleed-off passages which open when the control valves are in neutral states. Opening characteristics of the control valves are set such that the center bypass passages are closed in initial stroke periods in which the control valves move toward operating positions.

Abstract: A two-stage pressure relief valve for use with hydraulic systems is disclosed. The two-stage pressure relief valve has a first stage that relieves increases in hydraulic system pressure over the normal operating pressure and up to a selected threshold pressure level, and a second stage that brings the hydraulic system pressure down to a selected reduced operating pressure that is below the normal operating pressure in response to increases in the operating pressure over the threshold pressure level.

Abstract: A system and method of achieving ride control for a work vehicle that replaces a traditional accumulator with a ride control valve, a directional control valve and a fluid pressure source. The fluid pressure source may be a variable displacement hydraulic pump. The ride control valve is set to a first relief pressure that allows fluid to flow from the head end of a hydraulic cylinder when the loading on the cylinder, i.e., the pressure in the head end is equal to or greater than the first relief pressure. A work tool of the vehicle falls from a first position to a second position when fluid flows from the head end. The ride control valve is then reset to a second relief pressure, higher than the first relief pressure and sufficient to move the work tool toward the first position. Afterwards, the directional control valve is opened long enough to allow fluid from the fluid pressure source to enter the head end and move the work tool back to approximately the first position.

Abstract: A hydraulic system for a work machine is disclosed. The hydraulic system includes a tank adapted to store a supply of fluid and a source of pressurized fluid in fluid communication with the tank. A first hydraulic actuator and a second hydraulic actuator are in fluid communication with the source of pressurized fluid. A first fluid return line is adapted to direct a return flow of fluid from the first hydraulic actuator to the tank and a second fluid return line is adapted to direct a return flow of fluid from the second hydraulic actuator to the tank. A pressure control device is disposed in the second fluid return line and is operable to selectively adjust a magnitude of fluid pressure in the second fluid return line.

Abstract: A hydraulic controller for working machine according to the present invention, which presupposes an electronic control system where an integrated bleed-off valve common to hydraulic actuators is used for bleed-off control and the bleed-off valve is controlled by the secondary pressure of a proportional solenoid valve controlled by a controller, is constituted to compensate supply of a pressure oil for the hydraulic actuators even if the secondary pressure of the proportional solenoid valve is stopped, by providing, at the bleed-off valve, a fail-safe position with a fail-safe path which opens with an opening having smaller area than an unload opening.

Abstract: In a hydraulic power steering system employing a power cylinder accommodating therein a piston connected to a steering mechanism for steering assistance, and having first and second hydraulic chambers defined on both sides of the piston, hydraulic pressure is supplied through first and second fluid lines to the respective hydraulic chambers. A communicating circuit is provided to intercommunicate the first and second fluid lines therevia. A directional control valve, disposed in the communicating circuit, has a poppet valve mechanism, which is switched to a valve-open position in presence of a hydraulic power steering system failure, to intercommunicate the first and second fluid lines with the poppet valve mechanism opened.

Abstract: The circuit includes a main pump, a hydraulic motor, two main ducts, a selector for connecting the main ducts to the main pump or to a reservoir or for isolating them therefrom, a boost duct, and two pressure limiters disposed between the main ducts. A relief valve device that can take up a retention position and a relief position in which it connects one main duct (14, 16) to a relief enclosure can take up its relief position when, with the selector isolating the main ducts from the main pump and from the reservoir, the difference between the pressure in the main duct to which the control duct is connected and a relief pressure higher than the boost pressure changes sign.

Abstract: An improved valve for use in a hydrostatic drive apparatus for a vehicle such as a zero turn vehicle. For each hydraulic drive system in the vehicle, a valve is located between the high and low pressure sides of the closed hydraulic circuit connecting the hydraulic pump and motor. The valve opens when the pressure rise rate in the high pressure side reaches a set level to minimize pressure spikes in the high pressure side and thus improve performance of the vehicle. A valve block may be used to mount the valve, and a second valve may also be included therein to connect the two pressure sides of the hydraulic circuit in a similar manner when the vehicle is operated in reverse.

Abstract: A joining directional control valve 13 is disposed to supply, to an arm cylinder 4, not only a hydraulic fluid delivered from a first hydraulic pump 1, but also a hydraulic fluid delivered from a second hydraulic pump 2 when an arm directional control valve 14 is driven. Respective delivery pressures of the hydraulic pumps 1, 2 are detected by pressure sensors 101, 102, and the opening area of a recovery control valve 6 is controlled depending on a lower one of the detected pressures from the pressure sensors 101, 102 such that, even in the combined operation of the arm cylinder 4 and another actuator 3, 4, the hydraulic fluid can be recovered for return to the arm cylinder 4 when the load pressure of the arm cylinder 4 is low. Thus, by supplying the hydraulic fluids from the two hydraulic pumps to the particular actuator for which the hydraulic fluid is to be recovered, a recovery flow rate is ensured when the load of the particular actuator is low in the combined operation.

Abstract: A hydraulic control system including a source (11) of fluid having a pressure responsive means (15) and an actuator. A main control valve (21) has ports (27,29) communicating with the actuator ports by means of first (41) and second (43) conduits, and means to generate a load pressure (45). A pressure spike suppression valve (51) has ports connected across the conduits, the valve including a spool (65) moveable between a first position blocking communication between the ports, and a second position permitting communication. The valve (51) defines a spring chamber (67) including a spring (69) biasing the spool toward the first position. The valve defines a load signal passage (83) to communicate the load pressure to a chamber also to bias the spool toward the first position. The valve defines a pressure chamber (81) in communication with the source, fluid pressure therein biasing the spool toward the second position.

Abstract: The invention relates to a method for controlling at least two hydraulic actuators, to a monitoring valve and a rock drilling apparatus. The monitoring valve (10) is connected to the input channel of a first actuator through a sensing channel (9) and controls a load-sense circuit (6?) of a second actuator. The pressure of the load-sense circuit (6?) is set by a force of a spring element (12) and biased by a control element (42) of the monitoring valve with differential pressure sensing.

Abstract: A pair of zero-turn, hydrostatic transaxles (HZTs) that may be joined to form an integrated, zero-turn, hydrostatic transaxle. Each of the hydrostatic transaxles are further comprised of a casing carrying a hydraulic pump driven by an input shaft, a hydraulic motor driven by a the hydraulic pump through porting contained within a center section, and an axle shaft driven by the hydraulic motor. The hydrostatic transaxles are joined along an interface extending generally perpendicularly to the axle shafts.

Abstract: A hydrostatic continuously variable transmission includes a hydraulic pump and a hydraulic motor, supported by a common support shaft, and hydraulically connectable to each other through a hydraulic circuit including an inside passage and an outside passage. A clutch device includes a valve spool, which is slidably disposed in a hollow internal bore formed in the transmission support shaft. The valve spool is operable to make or interrupt fluid communication between the inside passage and the outside passage, according to the movement thereof. A governor mechanism is mounted to a pump casing of the hydraulic pump, and the governor mechanism generates a governor force corresponding to the rotating speed of a clutch cap, by use of centrifugal force generated by the rotation thereof. The valve spool is effectively moved in the hollow internal bore, using the governor force generated from the governor mechanism, to engage or disengage the clutch.

Abstract: An anti-reaction valve device is configured to open such that a plunger and a sheet member move away from each other in association with first and second set difference pressures. Two anti-reaction valve devices are provided between two pipes fluidically connected to a hydraulically powered actuator such that directional relationship of connection of primary and secondary ports is reversed between the two anti-reaction valve devices so that a reaction of the actuator is inhibited quickly and reliably. A one-way valve is positioned between the secondary port and an open and close control chamber within which the plunger and the sheet member are movable into contact with and away from each other and serves to inhibit a back flow of a hydraulic fluid. The one-way valve is capable of inhibiting the plunger and the sheet member from moving away from each other undesirably, and hence malfunction of the anti-reaction valve devices.

Abstract: For a power assisted steering system for vehicles, in particular passenger cars, there is provided a hydraulic circuit with a servopump, a three-way flow regulator valve which is located at the junction between the pump and a servoactuator and has a measuring throttle, located in the inflow to the servoactuator, as a fixed throttle and an outflow throttle which is located in a bypass of the latter and which determines a variable throttle cross section by means of a piston which is charged alternately as a pressure compensator. The piston, which is charged via an active actuator element, changes the outflow throttle cross section as a function of the current applied in order to change the volume flow which passes via the measuring throttle.

Abstract: A hydrostatic drive system (1) has at least one user. A control valve device (3; 4; 5; 6) to control the user is actuated by an actuation signal. A delivery flow regulation device (11) is triggered by a load pressure signal of the user. The drive system has a safety device (20) with a function position (21b) in which the actuation signal is routed to the control valve device (3; 4; 5; 6) and the load pressure signal is routed to the delivery flow regulation device (11), and a safety position (21a) in which the control valve device (3; 4; 5; 6) is discharged by the actuation signal and the delivery flow regulation device (11) by the load pressure signal. The safety device (20) also has a discharge position (21c) in which the connection of the control valve device (3; 4; 5; 6) with the user is discharged.

Abstract: An electronic control for damping oscillation of a swinging backhoe assembly includes a crossover valve that connects the hydraulic lines that supply hydraulic fluid to the boom swing cylinders to each other whenever an electronic controller senses incipient oscillation or swinging of the backhoe assembly. The electronic controller senses such parameters as pressure in the conduits and the position of the operator controls or the position of the boom swing control valve that the operator controls to determine incipient oscillation when the backhoe assembly is stopped. The crossover valve may remain open for a predetermined period of time.

Abstract: A hydrostatic transmission comprises a housing whose interior space serves as a fluid sump, a pair of first and second fluid passages disposed in the housing, the pair of first and second fluid passages interposed between the hydraulic pump and the hydraulic motor so as to constitute a closed fluid circuit of an HST. A charge fluid passage is disposed in the housing so as to be connected with each of the first and second fluid passages for supplying fluid from the fluid sump into the closed fluid circuit. A drain fluid passage including an orifice is disposed in the housing so as to be connected with at least one of the first and second fluid passages so that, when hydraulic pressure in the at least one of the first and second fluid passages is increased beyond its neutral level, excessive fluid in the at least one of the first and second fluid passages is drained through the drain fluid passage to the fluid sump, thereby expanding the neutral zone of the HST.

Abstract: A hydrostatic transmission comprising a housing formed with a fluid sump, a center section disposed within the fluid sump, a hydraulic pump mounted on the center section, and a hydraulic motor mounted on the center section. A fluid passage is formed in the center section for hydraulically connecting the hydraulic pump with the hydraulic motor. A bore is open at an outer surface of the center section in communication with the fluid passage. An output operation device is provided for controlling discharged fluid of the hydraulic pump. The output operation device is moved to an operational position from a neutral position. A piston having an outer surface is reciprocally inserted into the bore so as to be allowed to project outward from the center section. A valve is disposed within the bore for opening and closing the bore to and from the fluid passage. The valve is biased to be closed by a spring disposed between the valve and the piston.

Abstract: A bypass mechanism is provided for use in a hydrostatic transmission, to enable the user to open or close a valve between the two pressure sides of the hydraulic circuit of the transmission. An electrical mechanism is positioned to open or close the valve based on a signal which may be generated by a switch associated with the hydrostatic transmission.

Abstract: An integrated three function valve (ITFV) that combines the functions of a bypass valve (e.g. 183a, 185a, 161a) into a single assembly is disclosed. The ITFV allows continued operation after any two failures.

Abstract: One preferred embodiment of the present invention, provides an auxiliary hydraulic drive system having a total hydraulic flow. The system includes a primary hydraulic pump operable to provide hydraulic flow for an implement, and a flow control valve in communication with the hydraulic flow. The flow control valve operates to allow an optimum flow rate and diverts the excess flow amount when the total hydraulic flow exceeds the optimum flow rate. A secondary hydraulic pump is selectively operable to provide additional hydraulic flow. A control system is operable to engage the secondary pump when the total hydraulic flow drops below a minimum flow level; and the control system operates to disengage the secondary pump when the total hydraulic flow exceeds a maximum flow level. In a further embodiment, the invention provides a control unit for a hydraulic system. The control unit includes a sensor to measure total hydraulic fluid flow in a system; and a controller coupled to the sensor.

Abstract: A hydrostatic stepless transmission comprises a hydraulic pump and a hydraulic motor, at least one of the hydraulic pump and motor being variable in displacement; a closed circuit for fluidly connecting the hydraulic pump and motor to each other therethrough, the closed circuit including a pair of oil passages between the hydraulic pump and motor, one of the oil passages being hydraulically higher-pressured and the other being hydraulically depressed when the hydraulic pump delivers oil to the hydraulic motor; a speed change operation device for changing output rotational speed of the hydraulic motor; and a leak valve connected to the speed change operation device.

Abstract: A suspension for the boom of a loading vehicle includes a hydraulic cylinder for raising and lowering, or for extending and retracting (in the case of a telescopic cylinder), a boom. A direction control valve is provided for selectively routing hydraulic oil to and from at least a head-end chamber of the cylinder. A position sensor senses the position of the hydraulic piston rod, at the start of operation, and sends a sends a target signal representing this beginning position to a control unit which determines the difference between the target signal and a signal representing a current position of the piston rod. When this difference equals a preset difference threshold, a pressure-limiting unit, in the form of a valve or choke, is activated so as to control fluid flow to and from the head-end chamber so as to return the piston rod to its initial position which generated the target signal.

Abstract: A hydraulic drive (1) has a position selection device (2) in communication with a control valve (3) which, as a function of the actuation of the position selection device (2), controls the connection of an actuating cylinder (8) with a hydraulic fluid source (5) and a reservoir (6). A correction device provides a synchronization between the position of the position selection device (2) and the position of the actuating cylinder (8). The correction device has a sliding valve means (15) which detects a reference range of the actuating cylinder (8) and an on-off valve means (16) effectively connected mechanically with the position selection device (2). The on-off valve means (16) is open when the position selection device (2) is in the reference range and is closed when the position selection device (2) is not in the reference range.

Abstract: An improved valve for use in a hydrostatic drive apparatus for a vehicle such as a zero turn vehicle. For each hydraulic drive system in the vehicle, a valve is located between the high and low pressure sides of the closed hydraulic circuit connecting the hydraulic pump and motor. The valve opens when the pressure rise rate in the high pressure side reaches a set level to minimize pressure spikes in the high pressure side and thus improve performance of the vehicle. A valve block may be used to mount the valve, and a second valve may also be included therein to connect the two pressure sides of the hydraulic circuit in a similar manner when the vehicle is operated in reverse.

Abstract: A hydrostatic transmission, comprising a housing, an interior space of the housing serving as a fluid sump; a center section disposed in the housing so as to be submerged In the fluid sump; a hydraulic pump mounted on the center section in the housing: a hydraulic motor mounted on the center section in the housing, and a pair of first and second fluid passages formed within the center section so as to fluidly connect the hydraulic pump with the hydraulic motor. The second fluid passage has an upwardly slant opening toward the fluid sump. A draining device including a relief valve is provided in the opening of the second fluid passage. When hydraulic pressure in the second fluid passage is not more than a predetermined value but not less than that in the first fluid passage, the relief valve is opened so as to drain fluid from the second fluid passage to the fluid sump, thereby keeping the hydrostatic transmission in neutral.

Abstract: A member that is driven by a hydraulic actuator tends oscillate when fluid flow to the hydraulic actuator is terminated. A pressure relief device reduces that oscillation by connecting first and second first relief valves to the hydraulic actuator. The first relief valve provides a relatively large first relief passage as long as pressure in the hydraulic actuator remains above a threshold. A second relief valve opens a second relief passage at substantially the same threshold pressure and thereafter remains open as long as the pressure remains above another lower threshold. A timer causes the second relief valve to close a given interval of time, if the pressure does not drop below the other lower threshold.

Abstract: A pressure-control device (20) includes a controllable variable-displacement reversible hydraulic motor (21) having a pressure port (22) and a return port (23); a source of pressurized fluid (Ps); a fluid return (R); and a pressure regulating valve (24) operatively interposed between the source, return and pressure port. The pressure regulating valve is operatively arranged to maintain a predetermined pressure at the pressure port regardless of the direction of flow through the pressure port.

Abstract: In a hydraulic system that has first and second pumps, a pressure compensation circuit is provided to unload the output of the second pump when its operation is not required. The unloading reduces the power demanded of the engine that drives the pumps thus conserving energy. The first pump is directly connected to a supply line and a back flow check valve couples the second pump to the supply line. When pressure in the supply line is significantly greater than the load pressure of the actuators powered by the hydraulic fluid a bypass compensator valve opens to provide a path between the outlet of the second pump and the tank line. This action unloads the second pump and reduces its demand for engine power.

Abstract: An electronic control for damping oscillation of a swinging backhoe assembly includes a crossover valve that connects the hydraulic lines that supply hydraulic fluid to the boom swing cylinders to each other whenever an electronic controller senses incipient oscillation or swinging of the backhoe assembly. The electronic controller senses such parameters as pressure in the conduits and the position of the operator controls or the position of the boom swing control valve that the operator controls to determine incipient oscillation when the backhoe assembly is stopped. The crossover valve may remain open for a predetermined period of time.

Abstract: A combination fitting for flow control devices in an automotive power steering system having channels disposed in the fluid receiving end of the fitting.

Abstract: The present invention relates to a hydraulic type brake system which includes a unit for adjusting a back pressure in a turn driving hydraulic circuit mounted in a construction heavy equipment such as an excavator, etc., and in particular to a hydraulic type brake apparatus which is used together with a relief valve installed various actuator driving hydraulic circuits for adjusting a back pressure in a lower flow side of a relief valve for thereby adjusting an opening pressure of a relief valve. There is provided a back pressure adjusting unit adapted to adjust an opening pressure of the relief valve by adjusting a back pressure of the hydraulic circuit in a lower flow portion of the relief valve based on a co-operation with the actuator.

Abstract: A swing speed compensation device is provided for use with a flow sharing hydraulic system. The present invention is mounted within the metering spool of a flow sharing valve and includes a poppet that is attached to a spring retainer. The spring retainer encases a compression spring which pushes against a plug and has a drain hole that, depending upon the position of the spring retainer and poppet combination, can vent excess pressure within the present invention to a hydraulic pump tank. When a flow sharing hydraulic system starts or stops, there is a rush in the fluid flow that can cause a spike in the system pressure. The present invention absorbs this pressure spike, allowing for the fluid flow to gradually increase or decrease as the system starts or stops.

Abstract: A valve manifold controls hydraulic flow in a hydraulic system for an air compressor unit. The manifold includes a pressure relief valve, a cold oil bypass valve, a proportional flow valve, and an anti-cavitation valve. The pressure relief valve diverts flow away from a fan motor when the pressure of hydraulic fluid within the hydraulic system is above a predetermined level. The cold oil bypass valve diverts flow away from a hydraulic cooler when the temperature of hydraulic fluid within the hydraulic system is below a predetermined level. The proportional flow valve diverts flow away from the fan motor when the temperature of hydraulic fluid within the hydraulic system is below a predetermined level. The anti-cavitation valve prevents pressure build up within the hydraulic system when the air compressor unit is shut off.

Abstract: An articulated vehicle with a working device has a first frame having a prime mover mounted thereon and supporting a first transaxle apparatus. The first transaxle apparatus includes an input shalt receiving power from the prime mover, a pair of first axles, and a hydrostatic transmission. The hydrostatic transmission comprises a variable hydraulic pump, a first hydraulic motor fluidly connected to the hydraulic pump via a fluid passage, and a housing with a port fluidly connected to the fluid passage. The second transaxle apparatus includes a pair of second axles having different lengths and a second hydraulic motor. The second hydraulic motor is fluidly connected to the port. Proximal ends of the first and second frames with respect to the vehicle are coupled to each other so that the first and second flames are rotatable around a vertical axis relative to each other when steered.

Abstract: A work machine is operably coupled to an interchangeable hydraulically-driven implement via at least one hydraulic line. When changing the hydraulically-driven implement, high pressure trapped within the hydraulic line may cause difficulties in disengaging the attached hydraulically-driven implement from a body of the work machine. The present invention relieves the pressure in the hydraulic line by energizing at least one electronically controlled valve while an engine of the work machine is inactive. The valve is operably coupled to an electrical actuator and is moveable between, at least, a first position and a second position. When the valve is in the first position, the hydraulic line is fluidly connected to a low pressure line. A control system includes a pressure release controller that is operably coupled to energize the electrical actuator and move the valve to the first position when the engine is inactive.

Abstract: A hydraulic motor comprising a housing having inlet and outlet ports and an access port for connecting a pressure fluid to an accessory of the motor, such as a brake. A shuttle valve integrally contained within the housing selectively communicates the pressure at one of the inlet port or the outlet port to the access port. In addition, the housing has at least two axial sections that are sealed at a parting line therebetween, and the shuttle valve is inserted through an opening in one section so that when the sections are joined, the opening is sealed at the parting line. A ring of bolts holds the sections together, and the shuttle valve is contained at least partially within the envelope formed by the ring.

Abstract: A swing speed compensation device is provided for use with a flow sharing hydraulic system. The present invention is mounted within the metering spool of a flow sharing valve and includes a poppet that is attached to a spring retainer. The spring retainer encases a compression spring which pushes against a plug and has a drain hole that, depending upon the position of the spring retainer and poppet combination, can vent excess pressure within the present invention to a hydraulic pump tank. When a flow sharing hydraulic system starts or stops, there is a rush in the fluid flow that can cause a spike in the system pressure. The present invention absorbs this pressure spike, allowing for the fluid flow to gradually increase or decrease as the system starts or stops.

Abstract: A slotted spool valve for a speed control apparatus offering rapid response to prevent speed searching and cogging at low speed settings. Round port spool valve arrangements are replaced with a valve arrangement having rectangular-shaped ports. Response of the rectangular-shaped ports provides for rapid and sufficient fluid flow or bypass with less movement of a control shaft than that required for use with round port spool valve arrangements.

Abstract: A combination fitting for flow control devices in an automotive power steering system having channels disposed in the fluid receiving in of the fitting.

Abstract: A differential pressure between a delivery pressure of a fixed displacement hydraulic pump 2 and a maximum load pressure among a plurality of actuators 3a to 3c is maintained at a target differential pressure by an unloading valve 5. A setting pressure of the unloading valve 5 is changed depending on an engine revolution speed by introducing a differential pressure &Dgr;Pp across a throttle 50, which is disposed in a delivery line of a fixed pump 30, to a pressure bearing sector 5d of the unloading valve. With such an arrangement, in a hydraulic drive system including an LS system, it is possible to ensure fine operability based on setting of the engine revolution speed, to perform flow rate control at a good response, and to realize superior operability.

Abstract: A fluid control system includes a pressure supply and a valve arrangement having an inlet and an outlet and being in fluid communication with the pressure supply. The valve arrangement includes a relief operator configured to provide fluid communication between the inlet and the outlet of the valve arrangement in response to a predetermined pressure condition at said inlet. The valve arrangement is configured to provide fluid communication between the inlet and the outlet of the valve arrangement in response to an outlet pressure being greater than an inlet pressure.

Abstract: A hydrostatic transmission including a fluid motor in communication with a variable displacement fluid pump having a first displacement rate and a second greater displacement rate, a pump block having at least one fluid conduit through which fluid flows from the pump to the motor, an external fluid sump, a cylindrical pintle fixed to the block having a first bleed hole and a second bleed hole in communication with the first bleed hole, and a ring in sliding engagement with the pintle and having a slot in selective communication with the second bleed hole. The conduit and the sump are in communication through the bleed holes and the slot at the first displacement rate, and the fluid conduit and the sump are out of fluid communication at the second displacement rate.

Abstract: One preferred embodiment of the present invention, provides an auxiliary hydraulic drive system having a total hydraulic flow. The system includes a primary hydraulic pump operable to provide hydraulic flow for an implement, and a flow control valve in communication with the hydraulic flow. The flow control valve operates to allow an optimum flow rate and diverts the excess flow amount when the total hydraulic flow exceeds the optimum flow rate. A secondary hydraulic pump is selectively operable to provide additional hydraulic flow. A control system is operable to engage the secondary pump when the total hydraulic flow drops below a minimum flow level; and the control system operates to disengage the secondary pump when the total hydraulic flow exceeds a maximum flow level. In a further embodiment, the invention provides a control unit for a hydraulic system. The control unit includes a sensor to measure total hydraulic fluid flow in a system; and a controller coupled to the sensor.

Abstract: A hydrostatic transmission including a fluid motor and a variable displacement fluid pump in fluid communication with the motor and having a first and a second, greater, fluid displacement rate. The pump is mounted on a block having an outer surface, a passage through which fluid flows from the pump to the motor, and a first and a second fluid bleed hole extending from the passage to the outer surface. The passage and a sump external to the pump are in fluid communication through the bleed holes and the void of a sliding element disposed within a bore in the block when the pump is operating at its first rate and the sliding element is in a first position. The first bleed hole and the sump are substantially out of fluid communication when the pump is operating at its second rate and the sliding element is in a second position.

Abstract: An electromotor M of a electrohydraulic motor pump aggregate G drives at least one pump stage P, P1, P3. An attached element C is inserted between at least one pressure side port of the pump stage, a return line 13, and at least one consumer port A, B, 5, 6. A multiways control valve 3 is installed between the consumer port and the pressure side port. A pressure limiting valve R1, R2 constructed as a seated valve is installed between the consumer port A, B, 5, 6 and the return line 13. The motor pump aggregate G has an automatic hydraulic pressure relieving device D for relieving the system pressure whenever the electromotor M is switched off.

Abstract: A bypass mechanism is provided for use in a hydrostatic transmission, to enable the user to open or close a valve between the two pressure sides of the hydraulic circuit of the transmission. An electrical mechanism is positioned to open or close the valve based on a signal which may be generated by a switch associated with the hydrostatic transmission.