Abstract: The present invention is an expander band for use in hydraulic pumps, motors, and hydrostatic transmissions. The band has a plurality of elongated slots located circumferentially which receive slippers attached to pistons. One reduced dimension slot fixes the position of a slipper relative to the expander band while the other slippers move within the elongated slots. The fixed slipper limits the range of movement of the other slippers relative to the band, and thus the slippers avoid abutting the side ends of the elongated slots.

Abstract: To inhibit potentially damaging cold startup of a hydrostatic unit in a vehicle transmission, a portion of the makeup fluid pump to the hydraulic pump and motor loop circuit of the hydrostatic unit is directed through a branch line including a viscosity insensitive, flow regulating fluidic element and a viscosity sensitive fluidic element. The latter element develops a fluidic signal varying as a function of fluid viscosity, which is utilized to control a valve to prevent over-pressurization of the loop circuit and to control a transmission controller to condition the transmission to neutral until the hydraulic fluid warms to a safe operating viscosity.

Abstract: A hydraulic drive system has first and second flow control valves. Each of the control valves has a main valve of the seat valve type with a valve body for controlling communication between an inlet port and an outlet port which are both connected to a main circuit. Each further have a variable restrictor capable of changing an opening degree thereof in response to displacements of the valve body, and a back pressure chamber communcating with the inlet port through the variable restrictor and producing a control pressure to urge the valve body in the valve-closing direction. A pilot valve is connected to a pilot circuit which is connected between the back pressure chamber and the outlet port of the main valve; and an auxiliary valve is connected to the pilot circuit for controlling a differential pressure between the inlet pressure and the outlet pressure of the pilot valve.

Abstract: A door operator having a fluid drive motor and a manual override. The bidirectional hydraulic motor connects to a drive shaft through a power train including a shiftable --quill--type manual clutch mechanism which allows an alternate connection of the drive shaft to a manually-operated wheel. When the cable which shifts the clutch for manual drive is pulled, a switch disables the control for the hydraulic motor. When the motor is not provided with pressured fluid from the pump a hydraulic brake engages the motor.

Abstract: An improved closed-loop hydrostatic transmission system is provided of the type including a pump (11), a motor (13), and a pair of conduits (15 and 17). The system includes a main control valve (43) and a charge pump (23) which is the sole source of make-up fluid to the closed-loop system and the sole source of control fluid for varying the pump. The system includes a power limiting means comprising first and second pressure relief valve means (75 and 77) operable to provide fluid communication from whichever side of the closed-loop is at high pressure to the system reservoir whenever system pressure exceeds the predetermined maximum pressure. The motor is adapted to transmit drive torque to a reversible load (37) of the type having a known inertia and a predeterminable time of deceleration from maximum speed operation in one direction to a standstill condition.

Abstract: A manifold receives gas streams from a plurality of gas purifiers arranged in parallel. The manifold comprises a plurality of pipe portions wiht a successively increasing diameter forming a main channel in the manifold. A first pipe portion projects into a second pipe portion, whereby, in the gap between the pipe portions a connection channel is formed which is substantially parallel to the main channel. The second pipe portion projects into a third pipe portion, thus forming a gap between the pipe portions and so on. Outlet tube portion from cyclones are connected to the connection channels.

Abstract: An axle driving apparatus which laterally divides a transmission casing into two, a hydraulic pump vertically disposing a pump shaft and a hydraulic motor horizontally disposing a motor shaft are fixed in one transmission casing, the hydraulic pump and hydraulic motor are tight enclosed within the transmission casing in the state of joining both the transmission casing, an oil passage connecting the hydraulic pump and hydraulic motor is open at the bottom surface of the transmission casing, and an oil passage plate provided with connecting oil passages, a short-circuit valve, check valves and oil filter, is attached to the portion of the opening.

Abstract: An axle driving apparatus which fixes a hydraulic pump and a hydraulic motor constituting a hydrostatic transmission to one of laterally dividable transmission casings, and provides check valves capable of sacking operating oil used in the hydrostatic transmission and also used as lubricating oil in the transmission casing, so that both the check valves are open to allow the hydraulic motor to freely rotate when the apparatus hauls a tractor, the transmission casing and hydrostatic transmission being compact to be disposed.

Abstract: An axle driving apparatus which houses within a casing thereof a hydraulic motor and a hydraulic pump constituting a hydro-static-transmission, provides in the wall of the lower half casing oil passages connecting the hydraulic motor and hydraulic pump, integrally forms a pump mounting surface at the horizontal wall at the lower half casing, and integrally forms a motor mounting surface at the vertical wall of the same, so that the oil passages in the vertical wall are turned vertically, thereby substituting for turning of the rotation direction by the conventional bevel gear.

Abstract: A hydraulic operating circuit for working members of earth-moving machines includes linear and rotary hydraulic actuators each of which is associated with a respective hydraulic distributor supplied from a principal supply and with a pressure compensator of the load-sensing type. A re-supply circuit is also associated with one or more of the rotary actuators for integrating the leakage and includes two anticavitation valves and a valve for boost-feeding the anticavitation valves from the principal supply.

Abstract: A hydraulic brake system with anti-skid control and/or traction slip control has a braking pressure generator (1, 21), a pressure compensation reservoir (4, 4',24, 24', 42), braking pressure control valves (7, 8 V.sub.1 -V.sub.4, AV.sub.1 -AV.sub.4) by which pressure medium can be tapped from the wheel brakes of the controlled wheels in the braking pressure reduction phase. Further, there is provided an auxiliary pressure supply system (10, 10') by which, in case of control, it is possible to supply pressure medium into the wheel brakes. To increase the operational reliability of the brake system, a pressure compensation chamber (18, 28, 28', 28", 39, 39') with a non-return valve (19, 29, 29', 29", 44, 46) connected upstream and opening toward the pressure compensation chamber is inserted into the pressure medium paths from the pressure compensation reservoir (4', 24, 24', 42) to the auxiliary pressure supply system. The outputs of the outlet valves (AV, AV.sub.1 -AV.sub.4, AV.sub.1 '-AV.sub.

Abstract: A hydraulic pressure system comprising a hydraulic pump, a hydraulic motor, a pair of main hydraulic pressure lines connecting the pump and the motor so as to form a closed loop or circuit, a booster line for supplying a hydraulic pressure from a booster pump to the low pressure side of the closed circuit, a pilot line for taking out a pilot pressure from the high pressure side of the circuit to operate an actuator for controlling the hydraulic pump and the hydraulic motor, and a boost pressure regulator for causing the pressure in the booster line to rise only when the differential pressure between the two main hydraulic pressure lines of the closed circuit becomes lower than a predetermined level.

Abstract: The invention contemplates hydraulic-lift mechanism which employs a power integrator in the connection between a charged hydraulic accumulator and the actuator for a vertically positionable load; the power integrator, additionally, has a prime-mover connection, and the pressurized charge of the accumulator is advisedly set to fully accommodate a preselected level of average load upon the actuator. The hydraulic circuit importantly includes check valves, with a pilot-operated check valve interposed between the power integrator and the accumulator and another pilot-operated check valve interposed between the power integrator and the load actuator. The pilot-operated check valves cooperate with other check valves to assure automatic transfer of hydraulic fluid under pressure from the accumulator to the load actuator, and vice versa, as may be determined by selected control of or via the power integrator.

Abstract: A battery-operated electric-motor driven hydraulic-lift mechanism for a fork-lift vehicle employs a hydraulic accumulator which serves an intertia-free counterweight function, designedly to the degree that such counterweight action is a direct offset of a predetermined average-load condition, as seen by the hydraulic-lift actuator of the system. Electric-motor drive is utilized for up/down operation of the fork lift, only to the extend needed to displace hydraulic fluid into or out of the "counterweighted" actuator. In some cases, such displacement will call for expending energy to add to or substract from the counterweight action; in other cases, the necessary fluid displacement results in an energy return to the system, i.e., in restoring energy to the battery.

Abstract: A hydraulic power actuator system flow augmentation scheme of the boot-strap type. The scheme consists of a jet pump to augment pump inlet flow with return flow by reducing the pressure in the jet pump below return pressure. A check valve is installed in the augmentation circuit to prevent back-flow during low flow rate conditions. Two load recovery check valves are used to short circuit the actuator during aiding load conditions.

Abstract: A rotary radial piston pump or motor has a cylinder barrel rotating on a fixed pintle with a fluid exit at the fixed end of the pintle and an inlet at the opposite free end. A fluid impeller boosts the pressure entering the inlet and a filter prevents dirt entering. When applied to a hydrostatic transmission with pump and motor on a common pintle a pair of opposed non-return valves admit make-up fluid at one end of the pintle and a pressure relief valve provides overload relief at the other end of the pintle.

Abstract: A controller for maintaining a motor operation at a desired rotational speed utilizes a phase locked loop that receives input signals from a tachometer coupled to the motor shaft. Reference frequencies for the phase locked loop are generated by a voltage control oscillator in response to voltages selected in accordance with the desired motor speed. These selected voltages are coupled to the motor speed control to establish a motor speed within the lock-in range of the phase locked loop. Tachometric feedback is applied in parallel for the phase locked loop. The open loop drive provided by the selected voltage guarantees degraded open loop control of the motor should the control circuit fall.

Abstract: A hydraulic circuit is disclosed for driving a bidirectional hydraulic motor from a pump via a hand operated directional control valve, as for propelling an earthmover or actuating an implement assembly thereon. For mitigating an abrupt pressure rise as when the motor is set into or out of rotation, the circuit has a pair of oppositely directed dual pressure relief valves connected in parallel with each other between a pair of main lines extending between motor and directional control valve. Each dual pressure relief valve is normally conditioned to pass at a predetermined lower pressure the pressurized fluid from one of the main lines and to pass at a predetermined higher pressure the pressurized fluid from the other main line.

Abstract: A hydrostatic transmission for a vehicle having a closed loop hydraulic system hydraulically interconnecting a variable displacement hydraulic pump and a hydraulic motor. The closed loop hydraulic system includes first and second conduits forming the closed loop.The first conduit is connected with a first relief valve having high and low setting pressure and the second conduit is connected with a second relief valve having high and low setting pressure.

Abstract: A flushing valve system suitable for use in a closed circuit hydrostatic transmission including a variable displacement hydraulic pump, a hydraulic actuator and two main lines. The flushing valve system includes poppet valves mounted in passages for respectively communicating the main lines with a fluid tank, passages mounting throttles for causing the pressure in the main lines to act on pressure chambers to keep poppets of the poppet valves from moving to an open position, and a change-over valve responsive to the pressure differential between the main lines to communicate the pressure chamber of the poppet valve connected to the main line on the lower pressure side with the fluid tank. The poppet valve connected to the main line on the lower pressure side opens when a predetermined pressure level is exceeded by the pressure in the main line, to thereby allow working fluid in the main line to be drained to the fluid tank.

Abstract: A hydraulic brake valve system for use in a hydraulic circuit consisting of driving and braking fluid lines and including therein at least a hydraulic motor for the actuation of an inertia body such as, for example, a construction vehicle or work implements thereof has a counterbalance valve, a cross-over safety valve, a drain change-over valve and a timer valve. The cross-over safety valve consists of two common relief valves, each having two pressure receiving surfaces and adapted to relieve pressurized fluid acted on one of the pressure receiving surfaces at a low pressure and relieve pressurized fluid acted on the other pressure receiving surface at a high pressure, wherein the first port of one of said relief valves is connected with said driving fluid line and the second port thereof is connected with said braking fluid line, whilst the first port of the other relief valve is connected with said braking fluid line and the second port thereof is connected with said driving fluid line.

Abstract: An hydraulic drive apparatus for use in downhole tools is described. The apparatus provides rotational and translational movement to a cutting tool element disposed in a downhole tool or sonde automatically adjusting advancing motion of the cutting tool to the rate of rotational movement or cutting. The apparatus is controllable from the surface through a wireline and is capable of operating in various modes to facilitate unjamming.

Abstract: Pump pressure in a fluid power assisted steering device is regulated through the suction side of the pump to supply pressurized fluid to a servomotor through a fluid pressure actuated steering control valve. A pre-control valve controls pressure in an actuating chamber of the steering control valve in response to displacement of the hand steering wheel to obtain a variation in servomotor pressure that is a linear function of the force applied to the steering wheel up to a cut-out point, above which the servomotor pressure rises sharply to a maximum value.

Abstract: A servomotor composed of a servovalve controlling a hydraulic drum motor is disclosed. A housing is enclosed on the side of the inclined cylinder head by a cover serving as a bearing for the motor shaft, and on the side of the distribution ports by an enclosing plate serving as a second bearing for said shaft. The enclosing plate, having an essentially parallelopiped shape, includes two longitudinal boreholes disposed in parallel in a plane parallel to the plane of the plate, with each of said boreholes joining together a borehole perpendicular to the plate and opening into the use opening of the servovalve fastened to one of the surfaces of the plate, and another borehole perpendicular to the plate and opening into one of said distribution ports. The plate also includes at least one transversal borehole joining together the two longitudinal boreholes and containing two-way safety valves or their equivalent.

Abstract: A hydraulic circuit for a hydraulically driven vehicle comprising a pair of variable displacement hydraulic pumps, a pair of hydraulic motors each connected with the respective variable displacement pumps in a closed loop, and a straight run compensator valve connected between the respective closed loops for equalizing fluid pressure in both closed loops when the vehicle is set in a straight run thereby assuring a steady straight run of the vehicle irrespective of the difference in displacement of the respective variable displacement pumps.

Abstract: A hydraulic fluid power system incorporating a supplemental pressurization system at the intake side of a hydraulic pump. The supplemental pressurization system includes a supplementary reservoir in communication with a primary fluid accumulator and an intake conduit of the hydraulic pump. The reservoir supplements hydraulic fluid flow to the intake side of the pump whenever intake line pressure drops below one atmosphere. Should the combined hydraulic fluid flow from the accumulator and the reservoir be insufficient to raise the intake pressure to prevent cavitation of the pump, an air ingestion valve opens to supply air to the intake side of the pump until proper pressurization is achieved, whereby the supplemental pressurization system closes off.

Abstract: Fluid in the relatively long lines (22, 24) between a control valve (16) and a fluid actuator (14) can become overly viscous in cold weather. Herein, fluid is circulated through such lines (22, 24), at least during cold weather, even when the fluid actuator (14) is not being used. This flowing is discontinued in response to shifting of the control valve (16) to a position where it motivates the actuator (14) and in response to pressure in the circulating path (20) exceeding a selected level.

Abstract: A valve to provide a controlled loss of hydraulic fluid from a closed loop hydrostatic transmission. A method of converting a bleed-off valve from one sensitive only to loop pressure to one sensitive to both loop pressure and charging line pressure. A pressure sensitive surface in flow communication with charging line pressure is used to position the valve to shut off flow in the event that charging line pressure is lost. In the event that charging line pressure and loop pressure are normal the valve provides a controlled bleed of hydraulic fluid. Finally, in the event that loop pressure becomes unacceptably high, flow is shut off.

Abstract: A hydraulic fluid flow network, utilizing the fluid returned from by an open center hydraulic system, to augment the charging system of a hydrostatic transmission. The augmented charging system provides oil under pressure to flow into the charging system in the event that charging system pressure flow falls below normal. A back pressure is maintained in the return line header of an open center hydraulic system by a relief valve. Flow is diverted to the charging system by a line containing a non return valve.

Abstract: A hydraulic circuit for a hydraulically driven vehicle comprising a pair of variable displacement pumps each driven by a common engine, a pair of variable displacement motors each connected with the respective variable displacement pumps in a closed loop circuit and driven thereby, a fixed displacement charge pump driven by the engine, and a pair of shuttle valves each connected in parallel with the respective closed loop circuits and has formed therein a neutral position and two offset positions wherein in the neutral positions of the shuttle valves both the closed loop circuits are connected with each other through the shuttle valves.

Abstract: Device for hydraulic control of thrust reversal units activated by jacks in jet engine. The jacks are connected to a rotary hydraulic engine fed by a hydraulic circuit which involves a mechanism for slowing down the speed of the reversal units when they approach the stop units. The hydraulic circuit allows for directly subjecting the engine's capacity to the opposing load on the engine. Application of this invention is possible to a dual flow turbojet in which the reversal units rotate in the cold flow.

Abstract: A hydraulic system having a reservoir fed charge pump supplying pressurized fluid through a charge passage and a filter to the inlet of a supply pump for direction controlled fluid devices includes a reservoir connected unloading valve assembly connected to the charge passage and parallel with the filter. The fluid devices return fluid through a return passage connected to the unloading valve assembly which maintains back pressure on the devices at charge passage pressure. The unloading valve assembly includes an unloading valve movable in response to a predetermined fluid pressure at the inlet of the supply pump to unload the charge and return passage by connecting them to the reservoir. As the devices require more fluid from the supply pump causing the pressure at the inlet of the supply pump to drop, the unloading valve proportionately blocks the charge and return passages from the reservoir to circulate return fluid into the charge passage.

Abstract: There is shown a safety control system for a self-propelled road roller having hydrostatic transmission, which includes a prime mover, an hydraulic pump driven by the prime mover and included in a main hydraulic circuit incorporating a motor with a power-off brake device, a check valve bridge with a ventable relief valve and a main control valve, and means for selecting automatically the speed and a predetermined operating speed, the speed selecting means comprise a secondary hydraulic circuit including means operatively connectible with the prime mover speed control means and controllable by the ventable relief valve in accordance with the operation of the main control valve.

Abstract: A telescoping hydraulic cylinder apparatus for elevator application, wherein telescoping cylinders and a piston rod extend or retract simultaneously, having a compensator pump for automatically replenishing fluid lost due to leakage from the upper cylinders of the apparatus.

Abstract: A control circuit (10) for the variable displacement pump (18) of a hydrostatic transmission (16) or the like comprises an underspeed actuator (31) connected to the servo system (19) of the pump (18), a venturi (15) interconnected between a source of pressurized working fluid (11) and the pump (18) and a pressure regulating valve (36) interconnected between a downstream side of the venturi (15) and the pump (18). A throat (29) and upstream side of the venturi (15) are connected to the underspeed actuator (31) for communicating a differential fluid pressure signal thereto to automatically control the displacement of the pump (18) under certain operating conditions of an engine of a vehicle.

Abstract: A filter device wherein inlet and outlet chambers are spaced from each other by a segment of filter media is positively locked in a condition whereat the chambers are sealed with respect to each other and the atmosphere by a hydraulic power device to which hydraulic pressure fluid is delivered at a predetermined pressure value. Filtrate is then delivered to the inlet chamber at a pressure which increases in value as the filter media becomes fouled with particulate.

Abstract: A transmission having hydraulic components including a hydrostatic unit with a variable displacement component having a hydraulic displacement control with a lubrication circuit for the components and a charge circuit for supplying fluid under pressure. First and second pumps are connected in series, with the first pump having a larger volume than the second pump to provide fluid to the second pump and to a lubricating circuit. A fluid line connects between the charge circuit and the lubrication circuit and has a lubrication priority valve therein which operates to provide fluid flow from the charge circuit to the lubrication circuit when required to maintain pressure in the lubrication circuit. Additionally, the charge circuit has a pair of branch lines, with one branch line having a charge priority valve therein which functions to control the flow through the one branch line leading to the hydraulic displacement control for the hydrostatic unit and to thus provide pressure control in the other branch line.

Abstract: A hydraulic system having a reservoir fed charge pump supplying pressurized fluid through a filter to a supply pump for direction controlled fluid devices includes an unloading valve assembly on the return passage from the devices for limiting back pressure therefrom as long as the charge pump supplies sufficient pressurized fluid for the supply pump. The unloading valve assembly includes an unloading valve movable in response to the pressurized fluid at the connection between the supply pump and the filter to unload the return passage by connecting it to the reservoir and further to control the pressurized fluid going to the filter by connecting the charge pump to the reservoir at a predetermined maximum pressure of pressurized fluid. As the decvices require more fluid from the supply pump causing the pressure to the supply pump to drop, the unloading valve first blocks the charge pump from the reservoir and then the return passage.

Abstract: An automatic control for an automotive-vehicle hydrostatic transmission in which the engine drives a variable-displacement hydrostatic (axial-piston) pump which is connected with the motor by hydraulic lines. The hydrostatic (axial-piston) motor can be connected to the wheels of the vehicle. The control circuit comprises a filling pump, a metering throttle, a reversing valve and an adjusting device. The metering throttle is provided in a bypass between the filling pump and the reversing valve and is connected to the line communicating with the control element. A further throttle is provided in this line and has a diameter/length ratio less than 1.

Abstract: A fuel injection pumping apparatus comprises a displacement piston which is located within the cylinder, an outlet from one end of the cylinder and a fluid pressure operable member mounted within a further cylinder for actuating the piston and causing fuel to be delivered through the outlet. Means is operable upon movement of the displacement piston to a predetermined position to terminate delivery of fuel through the outlet and valve means is provided to control the application of fluid under pressure to the fluid pressure operable member.

Abstract: The control system for a hydraulic transmission comprises a throttle element which consists of a constant throttle and a spring charged adjustable throttle arranged in parallel or, alternatively, comprises a combination of a constant throttle with adjustable throttles. The adjustable throttle has a cross section varying in response to the operating pressure of the hydrostatic transmission. The moment of rotation of a hydrometer included in the transmission is determined by the fluid stream caused by an adjustable pump which is adjusted by a servomechanism controlled by the throttle element and thus forms a transmission control member.

Abstract: A combination shuttle and high pressure relief valve is provided within a hydrostatic drive or transmission system. The valve is constructed with a spool member in two sections. The sections include hooks that interact with one another to lock the spool sections together in one mode of operation, yet permitting the spool sections to act independently in another mode of operation. Complete fluid charging of the fluid system is ensured by dual flow circuitry between the system pump and motor, while a restrictor valve means is connected to the shuttle and pressure relief valve to provide continuous flow of fluid through a system filter.

Abstract: The present hydraulic system for driving a submersible pumping unit has an above-ground pump for pumping oil through a hydraulic motor in the submersible pumping unit, and a check valve between the above-ground pump and that hydraulic motor to prevent the reverse flow of oil after the submersible pumping unit is turned off. A pressure regulating valve limits the oil pressure to the hydraulic motor. The inlet flow to the above-ground pump is filtered.

Abstract: A filter device wherein inlet and outlet chambers are spaced from each other by a segment of filter media is positively locked in a condition whereat the chambers are sealed with respect to each other and the atmosphere by a hydraulic power device to which hydraulic pressure fluid is delivered at a predetermined pressure value. Filtrate is then delivered to the inlet chamber at a pressure which increases in value as the filter media becomes fouled with particulate.

Abstract: An adjustable hydraulic makeup and control system is provided for supplementing the primary hydraulic flow to overcome leakage and thus be able to maintain a constant pulling load on a drill pipe or other tool in a well hole for an indefinite length of time.

Abstract: A control arrangement for a hydrostatic drive comprises a gear pump driven by an internal combustion engine and supplying fluid to a fluid motor. The control arrangement is constructed in such a manner that even at a high number of revolutions per time unit of the internal combustion engine, the fluid motor may be operated at a low number of revolutions.

Abstract: A hydraulic speed change gear designed to automatically control its hydraulic circuit pressure to be held at all times at a substantially constant level irrespective of the loading condition so as to enable the pressure oil in the hydraulic circuit to be used as a pressure source for other various hydraulic equipment. To this end, the gear includes a fixed displacement hydraulic pump adapted to be driven by an input shaft, a variable displacement hydraulic motor having an output shaft, a closed hydraulic circuit connecting between said pump and said motor, a hydraulic supply pump drivably coupled to said input shaft, a supply passage connected with a discharge port of said supply pump and with said closed hydraulic circuit through check valves, and an oil pressure control device connected with said closed hydraulic circuit and said supply passage for reducing the oil pressure in said supply passage in proportion to a pressure rise in said closed hydraulic circuit.

Abstract: A hydrostatic drive system for connecting a prime mover and a hydraulically operable load such as a hydraulic motor connected to the vehicular wheel has a constant-displacement pump and a variable-displacement pump both connected to the prime mover. The variable-displacement pump is completely reversible and is of maximum displacement substantially greater than the constant displacement pump. This variable-displacement pump is permanently connected across the hydraulic motor of the load. A clutch connects the constant-displacement pump to the same shaft as the variable-displacement pump. The outputs of the constant-displacement pump may be connected by a valve either in parallel to the outputs of the variable-displacement pump, or may simply connect them together for operation of the load only by the variable-displacement pump.

Abstract: A jack pump, such as the type capable of use in pumping crude oil from an oil well, the jack pump including a double acting piston and cylinder motor with the piston rod of the motor being adapted to be connected to the polished rod projecting upwardly from a well head. A variable displacement hydraulic pump, which is driven by a motor or engine, is included in a closed hydraulic loop wherein conduits are connected to a pair of output ports of the pump. A pump control means controls the direction and volume of flow in the loop so as to establish a total velocity profile during the complete pumping cycle and to determine the length and position of the stroke of the piston rod.

Abstract: A hydrostatic transmission is disclosed which includes a pump assembly in which a main pump, a charge pump, and an auxiliary pump are commonly housed and are drivingly connected to a single shaft assembly. An external fluid connection is provided through which fluid is directed from the auxiliary pump to a power take off, and valving is provided to short circuit the auxiliary pump when power is not demanded. Means of controlling the rate of operation of the valve are also provided to prevent excessive pressure rise rates at the outlet of the auxiliary pump upon actuation of the valving.