Control unit for hydraulic variable displacement pumps and variable displacement pump with a control unit

A control device (20) for a hydraulic variable displacement pump (1) which is operated in an open hydraulic circuit and which is adjustable by means of a servo piston (4) configured to shift inside a servo cylinder (5), to which servo piston (4) pressure is applied by means of pressurized pressure fluid via the control device (20), the control device (20) comprising:

• a housing (11) of a control piston (6), an inlet (26) for the connection of a high pressure line of the variable displacement pump (1), an outlet (18) which is configured to connect to a tank (19) and a servo connection (27) configured to link to the servo cylinder (5),
• the control piston (6) having a first control edge (38) and a second control edge (39), whereby
• the control piston (6) is configured to create a connection between the inlet (26) and the servo connection (27) via the first control edge (38) and
• the control piston is configured to create a connection between the servo connection (27) and the outlet (18) via the second control edge (3),
• the control piston (6) is preloaded by a first spring (7) at a proximal end (28) which is adjacent to the outlet (26),
• at a distal end (29) of the control piston (6) adjacent to the outlet (18) a second spring (8) engages which counteracts a hydraulic force and the preload of the first spring (7),
• a power-adjustable actuator (9) at the proximal end (28) of the control piston (6) engages with a tractive or a compressive force is transmitted to the distal end (29) in parallel with the first spring (7) of the control piston (6) such that the force of the actuator (9) is applied to the control piston (6) toward the distal end (29) independently of the force of the first spring (7) towards the respective the distal end (29),
• whereby pressure can only be applied to the control piston (6) with the pressure fluid under pressure from the variable displacement pump (1) to generate the hydraulic force in the direction of the distal end (29) of the control piston (6),
• a spring guide (13, 14) configured to provide fluid communication between a longitudinal bore (36) of the control piston (6) and a spring chamber (21) in one position of the control piston (6).

A control device (20) for a hydraulic variable displacement pump (1) which is operated in an open hydraulic circuit and which is adjustable by a servo piston (4) configured to shift inside a servo cylinder (5), to which servo piston (4) pressure is applied by pressurized pressure fluid via the control device (20), the control device (20) comprising:

• a housing (11) of a control piston (6), an inlet (26) for the connection of a high pressure line of the variable displacement pump (1), an outlet (18) which is configured to connect to a tank (19) and a servo connection (27) configured to link to the servo cylinder (5),
• the control piston (6) having a first control edge (38) and a second control edge (39), whereby
• the control piston (6) is configured to create a connection between the inlet (26) and the servo connection (27) via the first control edge (38) and
• the control piston is configured to create a connection between the servo connection (27) and the outlet (18) via the second control edge (3),
• the control piston (6) is preloaded by a second spring (8) at a distal end (29) which is adjacent to the inlet (28),
• at a proximal end (28) of the control piston (6) adjacent to the outlet (26) a first spring (7) engages which counteracts a hydraulic force and the preload of the second spring (8),
• a power-adjustable actuator (9) at the distal end (29) of the control piston (6) engages with a tractive or a compressive force is transmitted to the proximal end (28) in parallel with the second spring (8) of the control piston (6) such that the force of the actuator (9) is applied to the control piston (6) toward the proximal end (28) independently of the force of the second spring (8) towards the respective proximal end (28),
• whereby pressure can only be applied to the control piston (6) with the pressure fluid under pressure from the variable displacement pump (1) to generate the hydraulic force in the direction of the proximal end (28) of the control piston (6),
• a spring guide (13, 14) configured to provide fluid communication between a longitudinal bore (36) of the control piston (6) and a spring chamber (21) in one position of the control piston (6).