Control device for hydrostatic drives

Hydrostatic drive (2) with a closed hydraulic fluid circuit (4), in which there is a hydraulic motor (6) and a variable displacement pump (8), with a feed pump to provide drive fluid (60) under control pressure, and with a control device (10) for the regulated application of control pressure to a double-sided servo control unit (30) of the variable displacement pump (8), whereby the control device (10) comprises:

• a control piston (12) guided in a double-sided control cylinder (11) with a first side and a second side which can be moved from a neutral position in both directions along the longitudinal axis of the control cylinder (11) in such a way that the control piston (12) opens a feed line (18) for drive fluid under control pressure to one side (33, 35) of the servo control unit (30) while, at the same time, opening a discharge line (20) for discharging fluid via the other side of the control piston (12) from the second side (33, 35) of the servo control unit (30) to a drive fluid reservoir (43);
• an actuator (14) at the first side of the control cylinder (11) by means of which a force can be exerted towards the second side of the control cylinder (11) onto the control piston (12);
• only one preload element (16) which acts on the opposite second side of control piston (12) deflecting the control piston (12) on the first side of the control cylinder (11), if the actuator (14) exerts no force on the control piston (12);
• and
• characterized in that a first return line (25) directly connected between the variable displacement pump (8) and a first side of the control piston (12) such that operating pressure generated by the variable displacement pump (8) is returned directly to the first side of the control piston (12) via the first return line (25) in such a way that a force can be exerted in the effective direction of the actuator (14) onto the control piston (12), and that, when the actuator (14) is at constant force, the control piston (12) is maintained by the preload element (16) and the supply pressure of the variable displacement pump (8) in a force-balanced position in the control cylinder (11) so that the hydraulic motor (6) is regulated at a constant hydraulic output dependent on the force of the actuator (14) when the rotational speed of the variable displacement pump (8) fluctuates.

Hydrostatic drive (2) with a closed hydraulic fluid circuit (4), in which there is a hydraulic motor (6) and a variable displacement pump (8), with a feed pump to provide drive fluid (60) under control pressure, and with a control device (10) for the regulated application of control pressure to a double-sided servo control unit (30) of the variable displacement pump (8), whereby the control device (10) comprises:

• a control piston (12) guided in a double-sided control cylinder (11) with a first side and a second side which can be moved from a neutral position in both directions along the longitudinal axis of the control cylinder (11) in such a way that the control piston (12) opens a feed line (18) for drive fluid under control pressure to one side (33, 35) of the servo control unit (30) while, at the same time, opening a discharge line (20) for discharging fluid via the other side of the control piston (12) from the second side (33, 35) of the servo control unit (30) to a drive fluid reservoir (43);
• an actuator (14) at the first side of the control cylinder (11) by means of which a force can be exerted towards the second side of the control cylinder (11) onto the control piston (12);
• only one preload element (16) which acts on the opposite second side of control piston (12) deflecting the control piston (12) on the first side of the control cylinder (11), if the actuator (14) exerts no force on the control piston (12);
• and
• characterized in that a first return line (25) directly connected between the variable displacement pump (8) and a first side of the control piston (12) such that operating pressure generated by the variable displacement pump (8) is returned to the first side of the control piston (12) via the first return line (25) in such a way that the operating pressure from the first return line (25) exerts a force on the control piston (12) such that the operating pressure acts against the preload element (16), whereby the control piston (12) is maintained in a balance of forces at a defined deflected position that adjusts automatically according to the level of the operating pressure.