Abstract: A control means for a variable displacement pump (12) driven by an engine (10) and having a servo-cylinder (78) determining the displacement of the variable pump (12). A charge pump (14) is driven by the engine (10) and supplies charge pressure to the variable pump (12) through an orifice (40). Pilot conduits (42,44) on each side of the orifice (40) sense the pressure drop due to flow and relay the resulting signals to each end of a metering spool (52) in a speed control valve (46), which is arranged to control the pressure in the servo-cylinder (78). A spring (90) biases the servo-cylinder (78) toward an extreme position for the variable pump (12) and opposes the pressure directed to the servo-cylinder (78) by the speed valve (46) in order to provide a smooth transition between the extreme positions for pump displacement.

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

Abstract: A hydraulic circuit is provided to prevent overspeeding the prime mover powering a hydrostatic transmission. The hydrostatic transmission includes a hydraulic motor fluidly coupled to a hydraulic pump. The hydraulic pump is driven by the prime mover and the hydraulic motor drives a rotational load. The hydraulic pump includes a swash plate tilted by a servomechanism. The servomechanism receives hydraulic fluid from a pump powered by the prime mover. A valve is operated to shut-off the hydraulic fluid to the servomechanism in the event that the pressure in either of the two conduits joining together the hydraulic pump and the hydraulic motor exceeds a pre-set maximum value or if the pressure in an auxiliary line exceeds the same pre-set maximum value or if the sum of the two pressures exceeds the pre-set maximum value.

Abstract: A hydraulic system for a vehicle having an engine (10) governed to run within a predetermined speed range; the engine (10) arranged to drive a motive power train (11), a charge pump (14), a variable displacement pump (12) and a fixed displacement pump (15). The variable and fixed pumps (12 and 15) are arranged to supply hydraulic fluid pressure to a work circuit (26). A flow signal is created by passing the output from the charge pump (14) through an orifice (40), which signal is routed to a speed valve (46) which directs fluid to a control ram (78) to reduce the displacement of the pump (15) during a predetermined intermediate portion of said speed range.

Abstract: A fluid control circuit includes a source of pressurized fluid (10) adapted for connection to a hydrostatic transmission (23) upon actuation of a vent control valve (16). The vent control valve (16) is connected to a control and preconditioning valve (17) which functions to ensure that a control lever (14) is in its "vent" position upon starting of an engine and provides for the continuous preconditioning of the control circuit subsequent to such start-up. The control circuit is relatively non-complex in structure and function and does not require positioning of the control lever (14) in a special reset position upon shifting thereof between its "run" and "vent" positions.

Abstract: A fluid control cirucit for selectively varying the displacement of a variable displacement pump (P), such as the type employed in a hydrostatic transmission, comprises a primary control circuit connecting a pressurized fluid source (10) with the pump (P) and adapted to be actuated to selectively vary the displacement of the pump (P) between minimum and maximum values. A separate override control circuit is connected to the primary control circuit to override it to selectively vary the displacement of the pump (P).

Abstract: A hydraulic control system for variable displacement pumps, comprising at least two variable displacement pumps, a prime mover for driving the variable displacement pumps, a fixed displacement pilot pump driven by the common prime mover, a pressure compensating valve comprising a two-stage proportional pressure reducing valve and a negative proportional pressure reducing valve, the pressure compensating valve being connected to the variable displacement pumps and the fixed displacement pilot pump, and at least two servo boosters each being mechanically connected to the respective variable displacement pumps for controlling the displacement therefrom, the servo boosters being connected to the fixed displacement pilot pump and the pressure compensating valve and controlled thereby.

Abstract: A hydraulic control system for a variable displacement pump, comprising a prime mover for driving the variable displacement pump, a fixed displacement pilot pump driven by the common prime mover, a pressure compensating valve connected to the pilot pump and the variable displacement pump, a cut-off control valve connected to the pressure compensating valve and the variable displacement pump, and a servo booster connected to the cut-off control valve and the pilot pump for controlling the displacement of the variable displacement pump.

Abstract: A drive system has an engine that operates a control pump and a hydraulic variable-displacement drive pump having a control element and connected to a hydraulic motor. A servocylinder operates the control element of the drive pump and is pressurized through a control line connected to the control-pump output. A control valve is connected between the control line and the sump of the system and is connected to the hydraulic line between the motor and the drive pump to reduce pressure in the control line when the higher pressure of the line between the drive pump and the motor rises within a predetermined range. Thus it is possible with a substantially constant engine speed to produce a substantially constant output torque, with only the displacement of the pump and pressure in the lines between the pump and the motor varying by appropriate control of the control-line pressure.

Abstract: A hydraulic control system for adjusting the displacement of a variable displacement pump or pumps as dictated by pump output pressure and input speed. Driven by the same prime mover as the pump or pumps is a charging pump which communicates with a restrictor adapted to create a differential in the output fluid pressure therefrom, which pressure differential is sensed by a sensing valve for providing a corresponding output fluid pressure. Servo control means provided to the variable displacement pump or pumps communicates with both the restrictor and the sensing valve for adjusting the pump displacement in response to the fluid pressures delivered therefrom. A flow metering valve assembly is connected in a bypass around the restrictor to permit the passage therethrough of the charging pump output fluid at a rate metered in accordance with the variable displacement pump output pressure.

Abstract: The control system has an adjustable flow-rate pump and a fixed flow-rate pump which is supplied with hydraulic fluid via a supply conduit. A first throttle is interposed in this conduit and produces first signals in form of pressure differentials in dependence upon variations in the rotational speed of an ungoverned combustion engine which powers the hydraulic drive, which signals trigger flow-rate adjustments of the main pump. A second throttle is also interposed in the supply conduit and produces second signals in form of pressure differentials in dependence upon variations in the load upon the hydraulic motor of the hydraulic drive, which signals trigger movements of the throttle flap of the internal combustion engine towards the open or closed position thereof.

Abstract: An automatic control system for a hydrostatic transmission having a control circuit receiving a control flow from a control pump which represents a speed of a prime mover and valve components including a single adjustable valve which creates a delta pressure signal to control the transmission ratio which controls the speed of the prime mover.

Abstract: An arrangement for pumping fluids includes at least one variable-output pump and a drive therefor. An auxiliary pump is also driven by the drive and discharges control fluid at a discharge rate which corresponds to the speed of rotation of the drive. A throttle valve is located in a discharge conduit of the auxiliary pump, and the pressure of the control fluid upstream of the throttle valve controls the displacement of a slide valve between two positions thereof in one of which the control slide controls the variable-output pump toward increasing the output thereof, while in the other of such positions the pump is controlled toward a reduced output thereof. In addition to the pressurized fluid, which acts on the control slide with a first force, a spring is provided which acts on the control slide with a second force opposing the first force.

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 hydraulic system having at least two pumps including a variable-displacement pump and a constant-displacement pump, both driven from a common prime mover, includes a control-pressure pump operated by the shaft of the prime mover and operating with its input a valve which controls the pressure of a control piston acting upon a spring which bears upon the control member in a direction opposite to its setting piston. A cylinder of the setting piston is connected to the output of the adjustable-displacement pump.

Abstract: An underspeed actuator has a piston connected to a control means of a first pump driven by a prime mover and is movable between a first position at which the first pump is at minimum displacement and a second position at which the first pump is at maximum displacement. The underspeed actuator has first and second actuating chambers at opposite ends of the piston and a biasing device urging the piston towards the first position. The piston is movable between the first and second positions in response to pressure differential in said first and second chambers. A signal device controllably develops first and second control signals in response to the operating speed of the prime mover and delivers said first and second signals to respective first and second chambers. A first device controllably reduces the magnitude of fluid pressure in the first chamber in response to the rate of pressure rise of the output fluid of said first pump exceeding a preselected rate of pressure rise.

Abstract: An underspeed actuator has a piston connected to a control means of a first pump driven by a prime mover and is movable between a first position at which the first pump is at minimum displacement and a second position at which the first pump is at maximum displacement. The underspeed actuator has first and second actuating chambers at opposite ends of the piston and a biasing device urging the piston toward the first position. The piston is movable between the first and second positions in response to pressure differential in said first and second chambers. A signal device controllably develops first and second control signals in response to the operating speed of the prime mover. First and second conduits deliver said first and second control signals to said first and second chambers, respectively. A shunt valve is connected to the first and second conduits for passing fluid expelled from the first chamber to the second chamber in response to said flow of fluid exceeding a preselected flow rate.

Abstract: A system for controlling the operation of a reversible hydrostatic transmission including an engine-driven pump, particularly for a self-propelled utility vehicle such as a forklift truck, comprises a switchover member coupled with a setting lever of the hydrostatic pump which is biased by a pair of counteracting springs into a normal centered position. A shift lever, upon being moved from "neutral" to "forward" or "reverse", causes a displacement of the switchover member into a corresponding off-normal position by a fluidic or electromagnetic directive force generally proportional to engine speed.

Abstract: A hydraulic circuit for steering control in articulate vehicles which comprises an engine, a fixed displacement pump driven by the engine, a variable displacement pump driven by the engine, an exit port of the variable displacement pump being connected to a control valve of a steering actuator, an orifice provided at an outlet side of the fixed displacement pump and, a controlling cylinder connected to the variable displacement pump for controlling displacement of the variable displacement pump, the controlling cylinder being actuated by a spring disposed therein and a differential hydraulic pressure at the orifice.

Abstract: A servomechanism for pump capacity control includes an adjustable throttle of the "nozzle-gate" type formed with two operating slots communicating through two fixed throttles with duct, a source of supply feeding the duct, an input signal converter whose movable element is connected to the gate of the nozzle-gate throttle and a four-slot, five-line distributor whose control spaces are in communication through two fixed throttles with the duct of the source of supply, two operating slots being formed in the adjustable throttle, whereas its operating spaces communicate with the corresponding spaces of an actuating hydraulic cylinder. The latter is connected to the control element and, by a mechanical position feedback, to the gate. The mechanical position feedback is constituted by a bar which is linked to the movable element of the hydraulic cylinder and has a slanted surface. The slanted surface interacts with a spring-loaded pusher, whose springs act on the gate.

Abstract: A hydraulic power system having a plurality of variable displacement pumps for supplying pressurized fluid for manipulation of one or more implements includes control means operative to automatically adjust pump displacement to the output horsepower of a prime mover driving the pumps of the system. The control system includes an underspeed valve responsive to a deviation in the speed of the prime mover from any of a wide range of selected speeds to transmit a fluid pressure signal to servocontrol means for adjusting the displacement of the pumps. The underspeed control means includes an infinitely variable orifice connected by way of lost motion linkage to the engine throttle control for adjusting the underspeed valves to respond to a deviation of an infinite range of engine speeds.

Abstract: A hydraulic power system having a plurality of variable displacement pumps for supplying pressurized fluid for manipulation of an implement includes a control system operative to automatically adjust pump displacement to the output horsepower of a prime mover driving the pumps of the system. The control system includes underspeed valve means responsive to a deviation in the speed of the prime mover from a predetermined normal speed and a selectable second speed to transmit a fluid pressure signal to a servocontrol means for adjusting the displacement of the pumps. The control system includes a valve for selectively conditioning the control system to cause the underspeed valve to respond to a deviation of the selected engine speed and an indicator for indicating the conditioning of the control system.

Abstract: In a hydraulic system having a plurality of variable displacement pumps driven by a prime mover, each pump has a variable ratio input device connected to a load sensing means. Each variable ratio input device automatically reduces the displacement of its respective pump by the same proportion when the prime mover is overloaded irrespective of the displacement setting of the pump and automatically increases the displacement of its pump by the same proportion up to the set displacement when the prime mover is not overloaded.

Abstract: A hydraulic power system having a plurality of variable displacement pumps for supplying pressurized fluid for manipulation of one or more implements includes control means operative to automatically adjust pump displacement to the output horsepower of a prime mover driving the pumps of a system. The control means includes an underspeed valve responsive to a deviation in the speed of the prime mover from any one of a wide range of selected speeds to transmit a fluid pressure signal to servo control means for adjusting the displacement of the pumps in proportion to engine output. The control means includes an infinitely variable orifice adjustable with throttle movement for adjusting the underspeed valve to respond to a deviation from a wide range of selected engine speeds.

Abstract: A hydrostatic unit of the type contemplated by the present invention includes one or more pump and motor combinations interconnected by means of a conventional closed loop. Controls for the hydrostatic unit include a speed control and vent valve assembly as well as a venturi manifold which functions to normally establish a selected pressure differential in a pair of supply conduits for determining instant operating conditions for the transmission. In order to automatically regulate displacement of each pump unit in response to prime mover speed, an underspeed actuator valve unit includes a piston which is hydraulically responsive to the differential pressure in order to adjust operation of a lever which controls displacement of the pump unit. A part throttle control valve prevents the underspeed actuator from reducing displacement of the pump unit when speed of the prime mover is reduced by a manual throttle control.

Abstract: A hydrostatic vehicle transmission with a primary and/or secondary part adjustable as to its delivery and its absorption capacity respectively. The hydraulic adjusting elements of said primary and/or secondary part are automatically by spring force adjusted in the direction toward their starting position and are connected to a control circuit which is adapted to be connected to the pressure conduit of a constant delivery pump and is also adapted for controlling the control pressure to be connected to a return line by means of a control member. An adjustable orifice of a limit load control is arranged in the pressure line, which orifice is arranged ahead of the connection of the control member when looking in flow direction. The adjusting member of said limit load control may for instance be connected to the gas pedal or manually operable gas lever of an internal combustion engine for instance a Diesel engine while the hydrostatic vehicle transmission also serves as vehicle brake.

Abstract: This disclosure relates to a fluid transmission for automatically varying the drive ratio in accordance with the load placed thereon and includes a pump unit and a motor unit and wherein the pump unit is of a variable displacement with the displacement thereof being automatically adjustable in accordance with the pressure of the fluid output thereof and the input speed of the pump unit. The pump unit is of the radial piston type and includes a race member engaged by the pistons for controlling the displacement thereof. The race member has a cylindrical race surface and is mounted for tilting movement wherein in a neutral position the pistons have zero displacement and wherein when the race member is tilted, the displacement of the pistons increases.

Abstract: The transmission drives a dispensing apparatus at a speed varying in proportion to a command value furnished by a command device. The transmission includes a hydromotor driving the dispensing apparatus, a main pump driving the hydromotor, and a regulating arrangement for making the variations in the speed of the hydromotor proportional to the variations in the command value. The regulating arrangement includes first and second measuring pumps driven by the hydromotor and by the command device for generating control pressures respectively indicative of the hydromotor speed and the command value. The regulating arrangement further includes a hydraulic control device connected to receive the control pressures and operative for automatically varying the fluid output of the main pump in dependence upon the difference in the control pressures.

Abstract: An improvement in a control system, including a brake device, for a vehicle having a hydrostatic transmission which includes a hydrostatic pump and a hydrostatic motor. The hydraulic control circuit includes a control pump, a high pressure conduit, a low pressure conduit, differential pressure regulator valve means and a directional control valve means interposed in the high and low pressure conduits and a fixed orifice means interposed in the low pressure conduit upstream from the differential pressure regulator valve. The improvement takes the form of an adjustable orifice means interposed in a branch conduit, between the high and low pressure control conduits downstream from the fixed orifice means, with the adjustable orifice means permitting the adjustment of the pressure differential between the high and low pressure control conduits.

Abstract: A hydraulic power system having a plurality of variable displacement pumps for supplying pressurized fluid for manipulation of an implement includes control means operative to automatically adjust pump displacement to the output horsepower of a prime mover driving the pumps of a system. The control system includes underspeed valve means responsive to a deviation in the speed of the prime mover from a predetermined normal speed to transmit a fluid pressure signal to a servo control means for adjusting the displacement of the pumps. The underspeed valve means includes adjusting means for adjusting the underspeed valve to respond to a deviation from other engine speeds different from the normal operating speed.

Abstract: A hydrostatic unit of the type contemplated by the present invention includes one or more pump and motor combinations interconnected by means of a conventional closed loop. Controls for the hydrostatic unit include a speed control and vent valve assembly as well as a venturi manifold which functions to normally establish a selected pressure differential in a pair of supply conduits. In order to automatically regulate displacement of each pump unit in response to both engine or prime mover speed and instant load conditions, an underspeed actuator valve unit is hydraulically responsive to the differential pressure in the two conduits and also to changes in output pressure developed by the pump unit.

Abstract: A hydrostatic unit of the type contemplated by the present invention includes one or more pump and motor combinations interconnected by means of a conventional closed loop. Controls for the hydrostatic unit include a speed control and vent valve assembly together with a venturi manifold which function together to normally establish a selected pressure differential in a pair of supply conduits for determining instant operating conditions for the transmission. In order to automatically regulate displacement of each pump unit in response to engine or prime mover speed as determined by load conditions, an underspeed actuator valve unit includes a piston which is hydraulically responsive to the differential pressure in order to adjust the effective moment arm for a lever which controls displacement of the pump unit.

Abstract: An apparatus for damping the pressure increase of hydrostatic drives, especially axial piston pumps, with swash plate control and pre-biased oil circulation, wherein the pressurized oil compartment of an adjustment cylinder is connected with the low pressure side of the oil infeed of the pump via a check or nonreturn valve which opens in the direction of the low pressure conduit of the oil infeed. There is further provided a supply pump and a mechanical adjustment mechanism. The adjustment cylinder is rigidly connected with the mechanical adjustment and the bottom side of the adjustment cylinder is connected via a regulation throttle and a check valve means with the pressure side of the supply pump.

Abstract: A servo mechanism for a prime mover interconnected to a hydrostatic transmission includes a source of pressurized fluid, a fluid reservoir, an actuator having a piston operatively connected to the hydrostatic transmission and being provided with large and small hydraulic receiving areas which are exposed to first and second hydraulic chambers, respectively within the actuator housing, a first passage for connecting the pressurized fluid source to the second chamber, a second passage for connecting the pressurized fluid source to the first chamber, a third passage for connecting the first chamber to the reservoir, and a pair of spool valve means disposed, respectively, within the second and third passages and responsive to a signal indicative of the power required of the prime mover and an actual speed or feedback signal of the prime mover.

Abstract: A hydraulic control system includes a generating circuit for providing power to a work function. A driving apparatus operates the generating circuit. A control circuit is connected to the generating circuit and the driving apparatus for permitting delivery of power to the work function when the driving apparatus is operating up to a predetermined speed. The control circuit also stops delivery of power to the work function when the driving apparatus runs above the predetermined speed.

Abstract: Apparatus for adjusting a hydraulic machine driven by an adjustable driving motor comprises an adjustment motor which adjusts the machine in one sense under one fluid control input dependent upon actual driving motor speed and in an opposite sense under an opposing such input supplied at a control outlet of a pressure control valve device in dependence upon the position of a valve slide thereof urged by the first input against a biasing force selectively adjustable in dependence upon desired driving motor speed. When the actual speed falls sufficiently relative to the desired speed, the slide travels from one position, blocking flow from a fluid inlet of the valve device to its control outlet, to another position allowing such flow and also allowing the second input thus produced to act on the slide, in the same direction as the first does, until the slide returns to its initial position.