Abstract: A hydrostatic drive system includes a differential cylinder connected in a closed circuit to a high-pressure pump. A piston-side compression chamber and a piston-rod-side compression chamber of the differential cylinder are in communication with the high-pressure pump. The closed circuit includes a protection device having first and second protection valve devices that each includes a pressure relief valve and an anti-cavitation valve. The pressure relief valve of the first protection valve device is provided with an override device, by means of which the opening pressure of the pressure relief valve can be varied. When the high-pressure pump delivers into the piston-rod-side compression chamber, the pressure relief valve of the first protection valve device is adjusted by means of the override device to a reduced opening pressure and the differential volumetric flow flows out via the pressure relief valve to a low-pressure system.

Abstract: A hydrostatic positive displacement machine (2) is operated in a closed circuit and delivers hydraulic fluid into a working circuit. The displacement volume is varied by a control device (6) having a variable displacement piston device (7). The machine (2) has a swivel-back device (40) which, in the event of a decrease of the feed pressure from the feed pressure source (11), guarantees actuation of the machine (2) toward a reduction of the displacement volume. The swivel-back device (40) includes at least one pressure sequence valve (41), which is in communication on the input side with the working circuit of the machine (2). In the event of a decrease in the feed pressure from the feed pressure source (11) below a limit pressure, the pressure sequence valve (41) makes it possible to supply the control device (6) of the machine (2) with hydraulic fluid from the working circuit.

Abstract: A hydrostatic positive displacement machine (2) is operated in a closed circuit and delivers hydraulic fluid into a working circuit. The displacement volume is varied by a control device (6) having a variable displacement piston device (7). The machine (2) has a swivel-back device (40) which, in the event of a decrease of the feed pressure from the feed pressure source (11), guarantees actuation of the machine (2) toward a reduction of the displacement volume. The swivel-back device (40) includes at least one pressure sequence valve (41), which is in communication on the input side with the working circuit of the machine (2). In the event of a decrease in the feed pressure from the feed pressure source (11) below a limit pressure, the pressure sequence valve (41) makes it possible to supply the control device (6) of the machine (2) with hydraulic fluid from the working circuit.

Abstract: A hydrostatic pump (1) with a variable delivery volume can be operated in a closed circuit. An electrically controllable actuator device (4) is provided for the control of the delivery volume of the pump (1). The electrically controllable actuator (4) has an electrically actuatable control valve device (6) which generates a positioning pressure which actuates a positioning piston device (5) which is in an operative connection with a delivery volume control device (3) of the pump. An electrical position feedback circuit (21) of the delivery volume control device (3) is provided and the actuator device (4) is provided with a switchable hydraulic neutral position control system (25), by means of which a restoring movement can be generated that acts on the positioning piston device (5) and places the delivery volume control device (3) into a neutral position.

Abstract: A hydrostatic pump (1) with a variable delivery volume can be operated in a closed circuit. An electrically controllable actuator device (4) is provided for the control of the delivery volume of the pump (1). The electrically controllable actuator (4) has an electrically actuatable control valve device (6) which generates a positioning pressure which actuates a positioning piston device (5) which is in an operative connection with a delivery volume control device (3) of the pump. An electrical position feedback circuit (21) of the delivery volume control device (3) is provided and the actuator device (4) is provided with a switchable hydraulic neutral position control system (25), by means of which a restoring movement can be generated that acts on the positioning piston device (5) and places the delivery volume control device (3) into a neutral position.

Abstract: An hydrostatic drive unit for driving a motor vehicle is provided including a pump, a hydraulic motor, connecting means between said pump and motor, a branch line connected to the connecting means, a shut-off means located in said connecting means, measuring means in said shut-off means for measuring the horizontal forces arising in the direction of the longitudinal axis of the vehicle, said shut-off means acting on the hydrostatic drive unit, said measuring means including a mass capable of being displaced in the direction of the longitudinal axis of the vehicle against a forcible stop, resilient means acting on said mass to position the same normally in a center position capable of movement in two directions on the longitudinal axis of the vehicle and in working connection with the shut-off element whereby during the exertion of force upon the forcible stop, said mass acts directly or indirectly on said shut-off element to control fluid flow in said connecting means.