Abstract: A ramping subsystem of a control system for a dual path electronically controlled hydrostatic transmission is used to modify the commanded rate of change of pump and motor acceleration, deceleration and direction change command (performed to command machine motion from forward to reverse or vice versa) in order to achieve desired machine performance and operator feel. Pump and motor acceleration, deceleration and direction change command rates are then further modified using scaling tables based on selected maximum machine speed using operator input device.

Abstract: A hydraulic fluid cooling system for a pair of integrated hydrostatic transmissions includes a common reservoir holding hydraulic fluid and having hydraulic lines connecting the common reservoir to each integrated hydrostatic transmission, a hydraulic fluid reservoir inside each integrated hydrostatic transmission, and a pump for pumping fluid from each transmission's hydraulic fluid reservoir to the other transmission. An auxiliary hydraulic circuit is between the pair of integrated hydrostatic transmissions. The system pumps hydraulic fluid from one of the integrated hydrostatic transmission to the auxiliary hydraulic circuit, and the return line from the auxiliary hydraulic circuit may be connected to the other integrated hydrostatic transmission.

Abstract: This disclosure is directed towards a hydraulic system for providing auxiliary drive to a powertrain (11) and a hydraulic circuit (12) by storing and releasing hydraulic fluid using an accumulator (29). A hydraulic drive system (10) comprises an engine (14), a hydraulic machine (22) operably connected to the engine (14), a pump (17), an accumulator (29) and at least one valve (20, 27). The pump (17) is driven by the engine (14) and is configured to control a hydraulic circuit (12). The accumulator (29) is fluidly connected to the hydraulic circuit (21) and the hydraulic machine (22). In one instance, the at least one valve (20, 27) is operable to direct pressurised fluid from at least one of the hydraulic machine (22) and the pump (17) to charge the accumulator (29). Alternatively, the at least one valve (20, 27) is operable to direct pressurised fluid from the accumulator (29) to at least one of the hydraulic machine (22) and the hydraulic circuit (21).

Abstract: A hydrostatic drive, in particular a fan drive, with a variable displacement pump is configured to drive at least one hydraulic motor. The variable displacement pump is activated via a pressure regulating valve and a following directional valve predetermining the feed direction, via which valves the control spaces of an actuating cylinder can be acted upon with a control pressure difference. The variable displacement pump is prestressed into a basic position in which the feed volume flow is maximum.

Abstract: A hydraulic system is disclosed. The hydraulic system may have a pump configured to draw low-pressure fluid from one of a first and a second passage, and discharge fluid at an elevated pressure into the other of the passages. The hydraulic system may also have an actuator coupled to the pump via the first and second passages, a charge circuit, and a makeup valve movable by a pressure differential between the first and second passages to connect the charge circuit with a lower pressure one of the first and second passages. The hydraulic system may further have a first force modulation control valve configured to selectively direct fluid from the pump through the makeup valve to the second passage to bypass the actuator, and a second force modulation control valve configured to selectively direct fluid from the pump through the makeup valve to the first passage to bypass the actuator.

Abstract: A compact, integrated hydrostatic transmission without reduction gearing wherein the pump and motor are contained within a single housing, and an output shaft extends from the housing inline with a shaft of the motor. The output shaft is directly connectable to a wheel of a vehicle. The pump and motor share a common sump within the housing in which pump and/or motor leakage is collected.

Abstract: A hydraulic drive system for an actuator uses a pair of pressure compensated hydraulic machines to control flow to and from the drive chambers of the actuator by varying the controlled pressure of one of the machines. The machines are mechanically coupled to permit energy recovery and charge an accumulator to store supplies energy. The drive system may be combined with other services including a transmission for incorporation in a vehicle. The transmission uses a pressure compensated supply and torque control of the wheels.

Abstract: A fluid pressure cylinder (3) is connected to a discharge port (24) of a fluid pressure pump (2). A suction port (25) of the fluid pressure pump (2) is connected to a tank (10) via a suction passage (11) in which a flow restrictor (15) is provided. A change-over valve (4) changes over operation modes of the fluid pressure cylinder (3) between a load mode in which the pressure cylinder (3) is driven by the fluid pressure pump (2) and an unload mode in which the fluid pressure cylinder (3) elongates and contracts according to an external force exerted thereon in response to a differential pressure between the discharge port and the suction port. Automatic change-over of the operation modes of the pressure cylinder (3) in response to an operation of the fluid pressure pump (2) is thereby realized.

Abstract: An electrohydraulic control device and a method for actuating such an electrohydraulic control device include a hydraulic consumer having an actuator element and a pressure medium source that is quantity-adjustable. The speed of the actuator element is controlled by the pressure medium source and the position of the actuator is controlled by digital hydraulics.

Abstract: A hydraulic system is disclosed. The hydraulic system may have a pump, a hydraulic actuator, and first and second passages fluidly connecting the pump to the hydraulic actuator in a closed-loop. The hydraulic system may also have a control valve, and a load-holding valve configured to selectively lock movement of the hydraulic actuator. The load-holding valve may include a valve block at least partially defining a pump passage, an actuator passage, a control passage, a restricted passage connecting the actuator passage and the control passage, and a bypass passage connecting the actuator passage and the control passage. The load-holding valve may also include a valve element movable between a first position at which flow between the pump and the hydraulic actuator is blocked, and a second position at which fluid is allowed to flow between the pump and the hydraulic actuator, the valve element being spring-biased toward the first position.

Abstract: A working machine hydraulic circuit, including: a hydraulic motor; a pilot pressure system configured to supply hydraulic fluid at a pilot pressure to one or more components of the working machine; and a make-up pressure system in hydraulic fluid communication with the pilot pressure system and the hydraulic motor, and configured to supply hydraulic fluid to the hydraulic motor from the pilot pressure system if the hydraulic fluid pressure in a part of the hydraulic motor is below a threshold pressure such that, during deceleration of the hydraulic motor, the make-up pressure system is operable to supply fluid from the pilot pressure system to the hydraulic motor to reduce the risk of cavitation in the hydraulic motor.

Abstract: A fail-safe system for a hybrid vehicle employing an over-center variable-displacement hydraulic motor includes an actuator configured to stroke the motor to a zero angle if each of two control ports is supplied with fluid at an equal pressure. A control valve is configured, in the event of loss of power to the valve, to default to a position in which high-pressure fluid is supplied to both control ports. A pilot-controlled check valve is coupled between high- and low-pressure ports of the motor such that, during normal operation, passage of fluid through the check valve from the high-pressure port to the low-pressure port is checked, while passage of fluid through the check valve from the second port to the first port is enabled. When the pilot control is activated, passage of fluid in the opposite direction is also enabled.

Abstract: A bypass/flushing valve for a hydrostatic system includes a valve body including a central bore, a shuttle valve located in the central bore, and a valve spindle disposed within the central bore. The valve body includes four ports each in communication with the central bore. The shuttle valve blocks flow through the central bore between a first port and a second port. When pressure at the second port is higher than at the first port, the shuttle valve moves to allow flow passage between the first port and the third port. When pressure at the first port is higher than at the second port, the shuttle valve moves to allow flow passages between the second port and a third port. The spindle is movable between a first position to block communication between the second port and the fourth port and a second position to allow for communication between the second port and the fourth port.

Abstract: The present disclosure provides a hydraulic system for controlling a load. The system includes a housing defining an inlet, a first port, and a second port. The system further includes a spool valve and a proportional control element. The spool valve is in fluid communication with the inlet and the second port and the proportional control element is in fluid communication with the first port. The proportional control element can be controllable to exhaust fluid from the first port to a reservoir. In this arrangement, the proportional control element and the spool valve are controlled independently of one another.

Abstract: A hydrostatic transmission includes a closed fluid circuit, a hydraulic motor, a hydraulic pump fluidly connected to the hydraulic motor via the closed fluid circuit, and a fluid charging mechanism which supplies fluid delivered from the hydraulic pump to the closed fluid circuit during driving of the hydraulic pump.

Abstract: A hydraulic circuit for a vehicle having at least one selectively actuated hydraulic assist motor. The hydraulic circuit includes a first loop that includes, in serial order, a first hydraulic pump, a first hydraulic line, at least one hydraulic motor and a second hydraulic line. A second hydraulic pump and a third valve is used to control the flow of low pressure fluid from the second pump to the hydraulic motor casing. The low pressure fluid through the third valve maintains the motor pistons retracted when the motor is not being used. For actuating the motor, the third valve is actuated for disconnecting the second pump and relieving pressure from the motor casing. Low pressure is then provided to the first and second lines for extending the motor pistons. The first and second valves are then actuated for isolating the first and second lines from one another, and the first pump is used to power the motor. The first, second and third valves are advantageously solenoid cartridge valves.

Abstract: A valve assembly has a flow summation node coupled to a displacement control port of the first pump. Each valve in the assembly has a variable metering orifice controlling flow from an inlet to a hydraulic actuator and has a variable source orifice conveying fluid from a supply conduit to a flow summation node. The source orifice enlarges as the metering orifice shrinks. Each valve includes a variable bypass orifice and the bypass orifices of all the control valves are connected in series forming a bypass passage between a bypass node and a tank. The bypass node is coupled to the flow summation node and receives fluid from a second pump. At each valve, a source check valve conveys fluid from the supply conduit to the inlet and a bypass supply check valve conveys fluid from the bypass passage to the inlet.

Abstract: A system and method for variator control employs positively directed electronic make-up and flushing relief valves for more precise torque control of a hydraulic variator, especially during torque reversal, as well as improved cold weather operation. This can improve machine response during periods of severe torque change. The ability to more tightly control variator torque allows more precise torque management algorithms for power control and engine matching purposes. Moreover, the ability to positively control venting of the hydraulic circuit for purposes of fluid cooling allows for more consistent machine response regardless of ambient temperature.

Abstract: The invention relates to a hydraulic apparatus comprising a hydraulic pump (30) which is connectable to a hydraulic fluid tank, an electric motor (2) as a drive means for the hydraulic pump (30), which electric motor comprises a motor shaft and a motor housing cover (4), and a control valve assembly (12) connected to the pump (30) to control at least one hydraulic consumer which is connectable to the pump (30) and is to be supplied by the pump (30) with hydraulic fluid from the hydraulic fluid tank, wherein the pump (30) is fixed on the motor housing cover (4) and the motor housing cover (4) comprises a holding adapter (10) on which the control valve assembly (12) is fixed.

Abstract: A hydraulic drive system for an actuator uses a pair of pressure compensated hydraulic machines to control flow to and from the drive chambers of the actuator by varying the controlled pressure of one of the machines. The machines are mechanically coupled to permit energy recovery and charge an accumulator to store supplies energy. The drive system may be combined with other services including a transmission for incorporation in a vehicle. The transmission uses a pressure compensated supply and torque control of the wheels.

Abstract: In the working machine, first and second pilot flow paths are directly or indirectly connected to to a tank flow path (52). A first restrictor is disposed between the first pilot flow path and the tank flow path. A second restrictor is disposed between the second pilot flow path and the tank flow path. An actuator control unit is configured to control an actuator based on a hydraulic pressure detected by a first hydraulic pressure detector unit and that detected by a second hydraulic pressure detector unit.

Abstract: A hydraulic pressure control device including a valve for generating a circulating pressure to a hydraulic power transmission chamber in which power is transmitted between an input- and output side of a hydraulic power transmission element via hydraulic oil; and a valve for generating a lock-up pressure supplied to a lock-up chamber that faces the hydraulic power transmission chamber with a lock-up piston included in a lock-up clutch interposed therebetween.

Abstract: A hydrostatic drive, in particular a fan drive, with a variable displacement pump is configured to drive at least one hydraulic motor. The variable displacement pump is activated via a pressure regulating valve and a following directional valve predetermining the feed direction, via which valves the control spaces of an actuating cylinder can be acted upon with a control pressure difference. The variable displacement pump is prestressed into a basic position in which the feed volume flow is maximum.

Abstract: The present disclosure relates to a vehicle transmission with jet pump. The jet pump includes a hydraulic control system that has a nozzle fitted between a first and second housing. The nozzle is separable from the first and second housing. The hydraulic control system is configured to produce a jet stream of fluid through a center section of the nozzle.

Abstract: A hydrostatic drive with first and second hydraulic pumps and a dual-acting hydraulic cylinder. The dual-acting hydraulic cylinder has a first working chamber defined by a first piston surface and a second working chamber defined by a second piston surface. The first working chamber is connected to first connections of the first and second hydraulic pumps. The second working chamber is connected to a second connection of the second hydraulic pump. A second connection of the first hydraulic pump is connected to a hydraulic fluid reservoir. The ratio of the first piston surface to the second piston surface differs from the ratio of the total delivery volume of the two hydraulic pumps relative to the delivery volume of the second hydraulic pump. A tapping valve for removing hydraulic fluid is provided for the volumetric flow equalisation.

Abstract: A hydraulic transmission comprises a hydraulic pump and a hydraulic motor, which are mounted onto a center section to be fluidly connected to each other through a closed fluid circuit formed in the center section. A neutral valve is connected to the closed fluid circuit. The neutral valve is fitted into an outward opened end of a vertical slanted oil hole of the closed fluid circuit. Alternatively, the neutral valve is fitted into an outward opened end of a straight oil hole having an opposite outward opened end into which a charge check valve is fitted.

Abstract: A fluid pressure cylinder (3) is connected to a discharge port (24) of a fluid pressure pump (2). A suction port (25) of the fluid pressure pump (2) is connected to a tank (10) via a suction passage (11) in which a flow restrictor (15) is provided. A change-over valve (4) changes over operation modes of the fluid pressure cylinder (3) between a load mode in which the pressure cylinder (3) is driven by the fluid pressure pump (2) and an unload mode in which the fluid pressure cylinder (3) elongates and contracts according to an external force exerted thereon in response to a differential pressure between the discharge port and the suction port. Automatic change-over of the operation modes of the pressure cylinder (3) in response to an operation of the fluid pressure pump (2) is thereby realized.

Abstract: The invention relates to a hydrostatic drive. The hydrostatic drive (1) includes a hydraulic pump (3) and a hydraulic motor (7). The hydraulic pump (3) may be connected by way of a first working line (5) to a first working line connection (8) of the hydraulic motor (7) and by way of a second working line (6) to a second working line connection (9) of the hydraulic motor (7). Furthermore, the hydrostatic drive (1) includes a first storage means (40) for storing pressure energy and a second storage means (41). For recovery of the pressure energy stored in the first storage means, the latter may be connected, at least for one direction of conveying, to a first or second working line (5, 6) which is on the suction side in relation to the hydraulic pump (3) in this direction of conveying.

Abstract: There is provided a multiple pump unit including a pump shaft, a first pump, a pump housing, a second pump and a fluid passage block connected to one end surface in an axis line direction of the pump housing. One or both contacting surfaces of the pump housing and the fluid passage block is formed with a concave portion for accommodating the second pump. The pump housing is provided with a suction fluid passage guiding hydraulic fluid to a suction opening of the first pump and a first pump discharge fluid passage having a distal end that forms a first pump discharge port. The fluid passage block is provided with a second pump discharge port having the second pump as a hydraulic source.

Abstract: The invention relates to a hydrostatic drive (1) and to a method of braking a hydrostatic drive (1). In the hydrostatic drive (1), in a closed circuit a hydraulic pump (3) is connected by a first and a second working line (11, 12) to a hydraulic motor (4). The hydrostatic drive (1) comprises a brake actuation device (37) as well as at least one pressure relief valve (26, 30), which is connected to the working line disposed downstream of the hydraulic motor (4). The hydraulic pump (3) upon detection of an actuation of the brake actuation device (37) is adjustable to a braking delivery rate. The hydraulic motor (4) is adjusted in dependence upon the actuating intensity of the brake actuation device (37) in the direction of a larger absorption volume if the actuating intensity of the brake actuation device (37) increases.

Abstract: A hydraulic drive system for an actuator uses a pair of pressure compensated hydraulic machines to control flow to and from the drive chambers of the actuator by varying the controlled pressure of one of the machines. The machines are mechanically coupled to permit energy recovery and charge an accumulator to store supplies energy. The drive system may be combined with other services including a transmission for incorporation in a vehicle. The transmission uses a pressure compensated supply and torque control of the wheels.

Abstract: A hydraulic drive system for storing and releasing hydraulic fluid includes a high pressure storage device, a low pressure storage device, and a pump-motor operating at a range of pump-motor speeds for converting between hydraulic energy and mechanical energy. The pump-motor is disposed between the high pressure device and the low pressure device. In normal operation, the hydraulic drive system enters a motoring mode where hydraulic energy is released from the high pressure storage device and converted to mechanical energy using the pump-motor. It also enters a pumping mode where mechanical energy is converted into hydraulic energy. A neutral state exists where hydraulic energy is neither stored nor released from the high pressure storage device. An approach for compensating for temperature changes using varying pressure limits helps to maintain the hydraulic drive system in normal operation, thereby promoting efficiency within the hydraulic drive system.

Abstract: An exemplary hydraulic reservoir includes a reservoir tank having an interior cavity for retaining a fluid and an aperture fluidly connecting the interior cavity to an exterior region of the reservoir. A cover selectively engages the reservoir tank, and is movable between an open position, wherein the fluid path through the aperture in the reservoir tank is at least partially open, and a closed position, wherein the fluid path through the aperture is substantially closed. The hydraulic reservoir further includes a pressure relief mechanism having at least one pressure responsive fastener for releasably connecting the cover to the reservoir tank. The at least one pressure responsive fastener includes a fastener fixed for concurrent movement with one of the cover and the reservoir tank, and a biasing member operably connecting the fastener to whichever of the cover and reservoir tank is not fixed for concurrent movement with the fastener.

Abstract: A hydraulic system for a machine is disclosed. The hydraulic system may have a pump, a tank, a first actuator with a head-end and a rod-end, and a first valve arrangement configured to control fluid flow from the pump to the first actuator and from the first actuator to the tank. The hydraulic system may also have a second actuator with a head-end and a rod-end, and a second valve arrangement configured to control fluid flow from the pump to the second actuator and from the second actuator to the tank. The hydraulic system may further have a third valve arrangement fluidly connected between the first and second valve arrangements to receive pressurized fluid from the pump in parallel with the first and second valve arrangements. The third valve arrangement may be configured to facilitate fluid regeneration of and supplemental flow to at least one of the first and second actuators.

Abstract: A flushing system for a transmission is disclosed. The system has a first pump and a first actuator connected to the first pump to form a first loop. The system also has a second pump and a second actuator connected to the second pump to form a second loop. The system further has a charge pump configured to replenish the first and second loops. The system also has a single charge relief valve situated to receive fluid from the first pump, the second pump, and the charge pump.

Abstract: A hydraulic drive apparatus comprises a main pump for pumping hydraulic fluid through a hydraulic load, a charge pump for continuously pumping pressurized hydraulic fluid to the main pump, and a hydraulic fluid cooler. At least a portion to the hydraulic fluid pumped through the hydraulic load is returned under pressure to the charge pump and the charge pump pumps the pressurized hydraulic fluid through the hydraulic fluid cooler to the main pump.

Abstract: An open hydraulic circuit comprising a main pump (P), a hydraulic motor (M), two main ducts (10, 12) constituting a feed main duct and a discharge main duct and connected to the pump or to a reservoir (R) via a feed selector (14). The circuit further comprises a multifunction valve device comprising a multifunction selector (20) for connecting the main duct that is at the higher pressure to a pressure limiter (24) and for connecting the main duct that is at the lower pressure to booster means (16), and for interconnecting the main ducts by connecting them to the pressure limiter when the pressures in the main ducts are substantially mutually equal.

Abstract: A hydrostatic transmission of a hydrostatic-mechanical power distribution transmission in which the high-pressure limiting valves in the hydrostatic transmission are eliminated or adjusted to enable a working pressure higher than the working pressure on which the maximum pressure is based. For short time intervals, a pressure substantially higher than the pressure on which the maximum pressure is based under constant load of the hydrostatic transmission, can be adjusted. The hydrostatic transmission has high-pressure sensors connected with the control of the hydrostatic-mechanical power distribution transmission.

Abstract: In an actuator control device that controls an expansion/contraction operation of a hydraulic cylinder, when a main spool 52 is switched to a discharge position for discharging working fluid in the hydraulic cylinder, a back pressure chamber 7 communicates with a tank passage 13 via a first port 14, thereby opening an operate check valve 51, and as a result, the working fluid in the hydraulic cylinder flows into a return passage 4 from an actuator port 1 and into a pilot chamber 20 through a second port 15. A pilot spool 53 is maintained in a balanced position by the pressure of the pilot chamber 20, which is caused to act by a front-rear differential pressure of a control throttle 25, and the biasing force of a spring 22 housed in a spring chamber 21, and therefore the opening area of the first port 14 is controlled to and maintained at a fixed level.

Abstract: The invention relates to a hydrostatic drive comprising a hydraulic pump (1) and at least one hydraulic engine (3). Said hydraulic engine (3) is contacted to a closed circuit via a first working line (5) and a second working line (6). In order to limit the swept volume flowing in one of the two working lines (5) towards the hydraulic pump (1), a volume flow divider (60) is provided in the working line (5) and allows to remove a partial volume flow from the working line (5).

Abstract: The invention concerns a hydraulic system for linear drives with a differential cylinder, in particular for mobile machines which through the use of displacement-control of the drives avoids the many and diverse disadvantages of the state of the art and renders possible a precise and energy-efficient control of linear drives with differential cylinders, and which is economical and simple to maintain and which can be well integrated into the total hydraulic system of such machines.

Abstract: There is provided a hydrostatic transmission (HST) in which a hydraulic pump unit operatively driven by a driving power source and a hydraulic motor unit arranged spaced apart from the hydraulic pump unit and operatively driving a driving-wheel are fluidly connected by way of operation fluid lines so as to form a closed circuit. The hydraulic motor unit is provided with motor-side operation fluid passages forming one part of the operation fluid lines. A motor-side charge fluid passage having a first end opened to an outside to form a motor-side charge port and a second end fluidly connected to at least one of the motor-side operation fluid passages is also included. A check valve is interposed in the motor-side charge fluid passage so as to allow the fluid to flow from the motor-side charge port to one motor-side operation fluid passage while preventing reverse flow.

Abstract: A hydraulic drive system for an actuator uses a pair of pressure compensated hydraulic machines to control flow to and from the drive chambers of the actuator by varying the controlled pressure of one of the machines. The machines are mechanically coupled to permit energy recovery and charge an accumulator to store supplies energy. The drive system may be combined with other services including a transmission for incorporation in a vehicle. The transmission uses a pressure compensated supply and torque control of the wheels.

Abstract: The present invention includes a hydraulic pump (11), a variable displacement hydraulic motor (5) for traveling driven by pressure oil from the hydraulic pump (11), a motor displacement control means (17, 18) for adjusting a displacement of the hydraulic motor (5) in correspondence to a drive pressure at the hydraulic motor (5), an operating member (22) through which a forward travel command and a backward travel command for the vehicle are issued, a control means (12) to be driven in response to an operation of the operating member (22), for controlling a flow of pressure oil from the hydraulic pump (11) to the hydraulic motor (5), a reverse operation detection means (41A, 41B) for detecting a reverse operation of the operating member (22) performed to a reverse side opposite from a direction along which the vehicle is advancing, and a cavitation preventing means (25A,25B) engaged in operation so as to prevent occurrence of cavitation at the hydraulic motor (5) when the reverse operation at the operating mem

Abstract: A flushing system for a transmission is disclosed. The system has a first pump and a first actuator connected to the first pump to form a first loop. The system also has a second pump and a second actuator connected to the second pump to form a second loop. The system further has a charge pump configured to replenish the first and second loops. The system also has a single charge relief valve situated to receive fluid from the first pump, the second pump, and the charge pump.

Abstract: The present invention provides a pump unit including at least one hydraulic pump with inlet and outlet ports, a pump case for accommodating the hydraulic pump having an opening through which the hydraulic pump is insertable, and a lid, called a center section, closing the pump case. The center section forms a pair of inlet/outlet passages communicating an end with the inlet and outlet ports of the hydraulic pump and an end opening through a pump case abutting surface of the center section, and a first charging passage by which hydraulic fluid is fed through the pump case abutting surface of the center section. At least one of the pump case and the center section communicates the first charging passage with the pair of inlet/outlet passages via a first hydraulic fluid feeding valve preventing the reverse flow into said first charging passage.

Abstract: A hydraulic drive system for storing and releasing hydraulic fluid includes a high pressure storage device, a low pressure storage device, and a pump-motor operating at a range of pump-motor speeds for converting between hydraulic energy and mechanical energy. The pump-motor is disposed between the high pressure device and the low pressure device. In normal operation, the hydraulic drive system enters a motoring mode where hydraulic energy is released from the high pressure storage device and converted to mechanical energy using the pump-motor. It also enters a pumping mode where mechanical energy is converted into hydraulic energy. A neutral state exists where hydraulic energy is neither stored nor released from the high pressure storage device. An approach for compensating for temperature changes using varying pressure limits helps to maintain the hydraulic drive system in normal operation, thereby promoting efficiency within the hydraulic drive system.

Abstract: A supply passage 32, a discharge passage 33, an actuator passage 34, and a spool bore 36 are defined in a housing 31. The spool bore 36 accommodates a spool 35 and communicates with the supply passage 32, the discharge passage 33, and the actuator passage 34. Load pressure detection circuit sections 21a, 21b of load pressure detection circuit 21 are provided in correspondence with switch positions 13b, 13c. Each of the load pressure detection circuit sections 21a, 21b detects load pressure when the actuator passage 34 is connected to the supply passage 32. Each load pressure detection circuit section 21a, 21b is defined by a through hole provided in the housing 31 and connected to the spool bore 36. Check valves 22 are each arranged in a corresponding one of the load pressure detection circuit sections 21a, 21b. This simplifies the configuration of each load pressure detection circuit 21 and saves the space for arranging the load pressure detection circuit 21.

Abstract: A shift controlled bypass orifice for a hydrostatic transmission includes a pump valve body with high pressure ports through which hydraulic fluid flows between a pump and a motor, a bypass orifice extending between the high pressure ports and the outside of the pump valve body, a bleed poppet movable between a closed position blocking the bypass orifice and an open position opening the bypass orifice, and a poppet push pin moving the bleed poppet toward the open position if the hydrostatic transmission is in neutral, and toward the closed position if the hydrostatic transmission is in forward or reverse.

Abstract: Improvement in a hydrostatic valve assembly for use in a hydrostatic transmission, for controlling fluid transfer between a first, second and third line, wherein two of the lines define first and second pressure lines within a closed loop circuit. The valve assembly comprises a valve body having ports in communication with the three lines; a spool bore and valve spool reciprocating therewithin, having first and second end portions joined by a connecting portion, and first and second bypass orifices within the valve spool; and dampers for centering the valve spool in a neutral position. The bypass orifices utilize increased cross-sectional areas that permit the passage of substantially the full flow of the charge pump, without using a charge pump relief valve, at a low pressure drop. A hydraulic system utilizing this valve assembly and a method for increasing the transmission efficiency, in the neutral mode, are also set forth.