CONTROL SYSTEM FOR A WORK MACHINE AND METHOD FOR CONTROLLING A HYDRAULIC CYLINDER IN A WORK MACHINE

Abstract

A control system for a work machine (101) including an electric machine (202), a hydraulic machine (204) and at least one hydraulic cylinder (108). The electric machine (202) is connected in a driving manner to the hydraulic machine (204). The hydraulic machine (204) is connected to a piston side (208) of the hydraulic cylinder (108) via a first line (210) and a piston-rod side (212) of the hydraulic cylinder (108) via a second line (214). The hydraulic machine (204) is adapted to be driven by the electric machine (202) and supply the hydraulic cylinder (108) with pressurized hydraulic fluid from a tank (216) in a first operating state and to be driven by a hydraulic fluid flow from the hydraulic cylinder (108) and drive the electric machine in a second operating state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail below with reference to the embodiments shown in the accompanying drawings, in which:

FIG. 1 shows a side view of a wheel loader;

FIGS. 2-6 show different embodiments of a control system for controlling a work function of the wheel loader;

FIG. 7 shows an embodiment of a control system for controlling a number of functions of the wheel loader;

FIG. 8 shows a control system for controlling one or more of the functions of the wheel loader, and

FIG. 9 shows a further embodiment of the control system for controlling a work function of the wheel loader.

Claims

1. A control system for a work machine (101) comprising: an electric machine (202);an hydraulic machine (204); andat least one hydraulic cylinder (108);the electric machine (202) being connected in a driving manner to the hydraulic machine (204);the hydraulic machine (204) being connected to a piston side (208) of the hydraulic cylinder (108) via a first line (210) and a piston-rod side (212) of the hydraulic cylinder (108) via a second line (214); andthe hydraulic machine (204) being adapted to be driven by the electric machine (202) and supply the hydraulic cylinder (108) with pressurized hydraulic fluid from a tank (216) in a first operating state and to be driven by a hydraulic fluid flow from the hydraulic cylinder (108) and drive the electric machine in a second operating state.

2. The control system as recited in claim 1, wherein the hydraulic machine (204) is adapted to control the speed of the piston (218) of the hydraulic cylinder (108) in the first operating state.

3. The control system as recited in claim 1, wherein the control system comprises a control unit (802) which is electrically connected to the electric machine (202) in order to control the speed of the piston (218) of the hydraulic cylinder (108) in the first operating state by controlling the electric machine.

4. The control system as recited in claim 1, wherein the hydraulic machine (204) has a first port (220) which is connected to the piston side (208) of the hydraulic cylinder (108) via the first line (210) and a second port (222) which is connected to the piston-rod side (212) of the hydraulic cylinder (108) via the second line (214).

5. The control system as recited in claim 1, wherein a second port (222) of the hydraulic machine (204) is connected to the tank (216) in order to allow the hydraulic machine (204), in the first operating state, to draw oil from the tank via the second port (222) and supply the oil to the hydraulic cylinder via a first port (220).

6. The control system as recited in claim 4, wherein the system comprises a means (224) for controlling pressure, which pressure means (224) is arranged on a line (226) between the second port (222) of the hydraulic machine and the tank in order to allow pressure build-up on the piston-rod side (212).

7. The control system as claimed in claim 6, wherein the pressure control means (224) comprises an electrically controlled pressure-limiting valve.

8. The control system as recited in claim 1, wherein the system comprises a sensor (228) for sensing pressure on the piston side (208) of the hydraulic cylinder.

9. The control system as recited in claim 1, wherein a first port (220) of the hydraulic machine is connected to the tank (216) via a suction line (230).

10. The control system as recited in claim 9, wherein a means (232, 632) is arranged on the suction line (230) in order to allow suction of hydraulic fluid from the tank and obstruction of a hydraulic fluid flow to the tank.

11. The control system as recited in claim 10, wherein the means comprises a non-return valve (232).

12. The control system as recited in claim 10, wherein the means comprises an electrically controlled on/off valve (632).

13. The control system as recited in claim 1, wherein a second port (222) of the hydraulic machine is connected to the tank (216) via a suction line (234).

14. The control system as recited in claim 13, wherein a means (236, 636) is arranged on the suction line (234) in order to allow suction of hydraulic fluid from the tank and obstruction of a hydraulic fluid flow to the tank.

15. The control system as recited in claim 14, wherein the means comprises a non-return valve (236).

16. The control system as recited in claim 14, wherein the means comprises an electrically controlled on/off valve (636).

17. The control system as recited in claim 1, wherein a second port (222) of the hydraulic machine (204) is connected to the tank (216) via a line (242).

18. The control system as recited in claim 17, wherein a filtering unit (238) is arranged on the line (242) between the second port (222) of the hydraulic machine (204) and the tank (216).

19. The control system as recited in claim 1, wherein the hydraulic machine (204) can be connected via a connection means (502) to a hydraulic actuator (504) which is adapted to perform a work function which is separate from a work function performed by said hydraulic cylinder (108).

20. The control system as recited in claim 4, wherein a first port (220) of the hydraulic machine (204) is connected to the piston-rod side (212) of the hydraulic cylinder (108).

21. The control system as recited in claim 1, wherein the system comprises a line (302) which connects the piston-rod side (212) and the piston side (208) of the hydraulic cylinder (108) in parallel to the hydraulic machine (204).

22. The control system as recited in claim 21, wherein the system comprises a means (304) for flow control, which is arranged on said parallel line (302) in order to control the flow communication between the piston-rod side (212) and the piston side (208).

23. The control system as recited in claim 1, wherein a first port (220) of the hydraulic machine (204) is connected to a piston side (208) of the hydraulic cylinder (108) via a first line (210), and wherein a flow control means (402) is connected between the first line (210) and the tank (216) in order to allow a certain leakage flow from the hydraulic machine (204) to the tank at the start of a lifting movement.

24. The control system as recited in claim 1, wherein a first port (220) of the hydraulic machine (204) is connected to a piston side (208) of the hydraulic cylinder (108) via a first line (210), and wherein a flow control means (406) is connected on the first line (210) in order to control the size of the hydraulic fluid flow from the hydraulic cylinder (108) to the hydraulic machine (204) at the start of a lowering movement.

25. The control system as recited in claim 1, wherein the hydraulic cylinder is adapted to move an implement (107) in order to perform a work function.

26. The control system as recited in claim 25, wherein the hydraulic cylinder comprises a lifting cylinder (108, 109) for moving a loading arm (106) which is pivotably connected to a vehicle frame, the implement (107) being arranged on the loading arm (106).

27. The control system as recited in claim 25, wherein the hydraulic cylinder comprises a tilting cylinder (110, 902) for moving the implement (107), which is pivotably connected to a loading arm (106), which is in turn pivotably connected to a vehicle frame.

28. The control system as recited in claim 27, wherein the tilting cylinder (110) is adapted so that a load (904) which acts on the tilting cylinder draws the piston rod of the tilting cylinder out via its weight.

29. The control system as recited in claim 28, wherein the control system comprises an additional, smaller pump (908), which has a driving connection to the hydraulic machine (204), and wherein this additional pump (908) is connected to the piston side (906) of the tilting cylinder and to the tank (216) in order to pump hydraulic fluid to the piston side during a lowering movement.

30. The control system as recited in claim 29, wherein the control system comprises a non-return valve (914) which is connected between an inlet side (916) and an outlet side (918) of the additional pump (908) so that the pump (908) only pumps hydraulic fluid in a circuit (920) comprising the non-return valve (914) during a lifting movement.

31. A method for controlling a hydraulic cylinder (108, 109, 110) of a work machine (101 ), which hydraulic cylinder is adapted to move an implement (107) which is subjected to a load (116), the hydraulic cylinder being controlled by a hydraulic machine (204), said method comprising: detecting that a lowering movement of the implement is initiated, and of before the lowering movement takes place driving the hydraulic machine (204) in a first rotation direction so that a first line (220) which connects the hydraulic machine (204) to said first side (208) of the piston (218) of the hydraulic cylinder is pressurized, which side is opposite a second side (212) on which said load acts.

32. The method as recited in claim 31, further comprising, after the pressurization, allowing the hydraulic machine (204) to rotate in a second rotation direction, opposite the first rotation direction, whereupon the lowering movement can start and a hydraulic flow from the hydraulic cylinder drives the hydraulic machine (204) in the second rotation direction.

33. The method as recited in claim 31, further comprising a controllable means (243) for opening and closing a flow connection between the hydraulic machine (204) and the hydraulic cylinder (108) being arranged on the first line (210), comprising the steps of keeping the controllable means (243) closed for flow in the direction from the hydraulic cylinder to the hydraulic machine (204) and of pressurizing the line (210) between the hydraulic cylinder (204) and the controllable means (243).

34. The method as recited in claim 33, further comprising, after the pressurization, opening the controllable means (243) in order to allow the hydraulic machine (204) to rotate in a second rotation direction, opposite the first rotation direction, whereupon the lowering movement can start and a hydraulic flow from the hydraulic cylinder drives the hydraulic machine (204) in the second rotation direction.

35. The method as recited in claim 31, further comprising the step of gradually reducing the pressurization so that a smooth lowering movement is achieved.

36. A method for controlling a hydraulic cylinder (108, 109, 110) of a work machine (101) for the purpose of moving an implement (107) which is connected to the hydraulic cylinder, a hydraulic machine (204) providing the hydraulic cylinder with pressurized hydraulic fluid, said method comprising: detecting a load (116) acting on the implement (107);comparing the size of the detected load with a predetermined load level, and, if the detected load lies below the predetermined load level, bringing the piston-rod side (212) of the hydraulic cylinder into flow communication with the piston side (208) so that hydraulic fluid coming from the piston-rod side (212) is brought to the piston side (208) without passing through the hydraulic machine (204).

37. The method as recited in claim 36, the hydraulic machine (204) providing the hydraulic cylinder with pressurized hydraulic fluid from a first port (220), comprising the step of, if the detected load (116) exceeds the predetermined load level, bringing the piston-rod side (212) of the hydraulic cylinder into flow communication with a second port (222) of the hydraulic machine (204) so that hydraulic fluid coming from the piston-rod side (212) is brought to the second port (220) of the hydraulic machine (204).

38. A method for regenerating energy when an implement (107) of a work machine (101) is moved during movement of the work machine, at least one hydraulic cylinder (108, 109, 110) being connected to the implement for controlling its movements, said method comprising: delivering such a pressure to the hydraulic cylinder that the implement is brought into a basic position, of, in the event of a disturbance which results in a downward movement of the implement;allowing driving of a hydraulic machine (204) by a hydraulic fluid flow from the hydraulic cylinder; andregenerating the energy from the hydraulic machine (204) in an electric machine (202) connected to it in a driving manner.

39. The method as recited in claim 38, comprising the step of bringing a first port (220) of the hydraulic machine (204) into flow communication with a piston side (208) of the hydraulic cylinder via a first line (210) and a second port (222) of the hydraulic machine (204) into flow communication with a piston-rod side (212) of the hydraulic cylinder via a second line (214).

40. The method as recited in claim 38, comprising the step of controlling the hydraulic machine (204) so as to deliver such a pressure to the hydraulic cylinder that the implement is brought into said basic position.

41. The method as recited in claim 38, comprising the steps of repeatedly detecting the position of the implement (107) and of, in the event of a disturbance which results in an upward movement of the implement, supplying a corresponding quantity of hydraulic fluid to the hydraulic cylinder and, in the event of a downward movement of the implement, draining a corresponding quantity of hydraulic fluid from the hydraulic cylinder.

42. The method as recited in claim 38, comprising the step of the electric machine (202) driving the hydraulic machine (204) so that the hydraulic fluid is supplied to the hydraulic cylinder for upward movement of the implement.

43. The method as recited in claim 38, comprising the step of continuously controlling the hydraulic cylinder so that the implement is kept within a predetermined range around the basic position.

44. A method for springing a movement of an implement (107) of a work machine (101) during movement of the work machine, at least one hydraulic cylinder (108, 109, 110) being connected to the implement for controlling its movements, said method comprising: delivering such a pressure to the hydraulic cylinder that the implement is brought into a basic position; andbringing a first port (220) of the hydraulic machine (204) into flow communication with a piston side (208) of the hydraulic cylinder via a first line (210) and a second port (222) of the hydraulic machine (204) into flow communication with a piston-rod side (212) of the hydraulic cylinder via a second line (210), and of, in the event of a disturbance which results in an upward movement of the implement, supplying a corresponding quantity of hydraulic fluid to the hydraulic cylinder and, in the event of a downward movement of the implement, draining a corresponding quantity of hydraulic fluid from the hydraulic cylinder.

45. The method as recited in claim 44, further comprising the steps of, in the event of a disturbance which results in a downward movement of the implement (107), allowing driving of the hydraulic machine (204) by a hydraulic fluid flow from the hydraulic cylinder, and of regenerating the energy from the hydraulic machine (204) in the electric machine (202).

46. The method as recited in claim 44, further comprising the step of the electric machine (202) controlling the hydraulic machine (204) to pump hydraulic fluid to the hydraulic cylinder.

47. The method as recited in claim 44, further comprising the step of controlling the hydraulic machine so as to deliver such a pressure to the hydraulic cylinder that the implement is brought into said basic position.

48. The method as recited in claim 44, further comprising the steps of at least one operating parameter being detected and of the springing movement being controlled according to a spring characteristic depending on the detected operating parameter.

49. The method as recited in claim 44, further comprising the steps of at least one operating parameter being detected and of a damping movement being controlled depending on the detected operating parameter.

50. The method as recited in claim 48, further comprising the steps of detecting a level of the disturbance force and of controlling the springing and/or the damping depending on the disturbance force level.

51. The method as recited in claim 48, further comprising the steps of detecting the weight of the load and of controlling the springing and/or the damping depending on the weight.

52. The method as recited in claim 48, further comprising the steps of detecting the type of implement and of controlling the springing and/or the damping depending on the detected implement type.

53. The method as recited in claim 48, further comprising the steps of detecting the type of handling mode and of controlling the springing and/or the damping depending on the detected handling mode.

54. A control system for a work machine (101) comprising: a first subsystem (707, 709) for performing a first work operation and a second subsystem (731) for performing at least one second work operation;said first subsystem comprises an electric machine (202), a hydraulic machine (204) and at least one hydraulic cylinder (108, 109, 110), the electric machine (202) being connected in a driving manner to the hydraulic machine (204), the hydraulic machine (204) being connected to a piston side of the hydraulic cylinder via a first line and a piston-rod side of the hydraulic cylinder via a second line, the hydraulic machine being adapted to be driven by the electric machine and supply the hydraulic cylinder with pressurized hydraulic fluid from a tank in a first operating state and to be driven by a hydraulic fluid flow from the hydraulic cylinder and drive the electric machine in a second operating state;said second subsystem (731) comprises a drive unit (734) and a hydraulic actuator (732), the drive unit (734) comprising an electric machine (738) and a hydraulic machine (736), the electric machine being connected in a driving manner to the hydraulic machine, the hydraulic machine (736) being adapted for flow communication with the hydraulic actuator (732), and a means (748, 750, 756, 758) being adapted for controlling the movement of the hydraulic actuator (732).

55. The control system as recited in claim 54, wherein said control means (748, 750) is arranged on an inlet side of the hydraulic actuator (732).

56. The control system as recited in claim 54, wherein said control means (756, 758) is arranged on an outlet side of the hydraulic actuator (732).

57. The control system as recited in claim 54, wherein said control means (748, 750, 756, 758) comprises at least one valve.

58. The control system as recited in claim 54, wherein the control system comprises a third subsystem (711) for frame-steering the vehicle (101) and said third subsystem (711) comprising a first steering cylinder (104) and a second steering cylinder (105), which steering cylinders are adapted for frame-steering the vehicle, a first drive unit (704) and a second drive unit (706), which each comprise an electric machine (708, 710) and a hydraulic machine (712, 714), each electric machine being connected in a driving manner to its associated hydraulic machine, a first (712) of the two hydraulic machines being adapted for flow communication with a piston side (716) of the first steering cylinder (104) and a piston-rod side (718) of the second steering cylinder (105), a second (714) of the two hydraulic machines being adapted for flow communication with a piston side (720) of the second steering cylinder and a piston-rod side (722) of the first steering cylinder.

59. A method for limiting a pressure which is delivered by a hydraulic machine (204, 705, 712, 714, 736) forming part of a control system, when the hydraulic machine is used as a pump, an electric machine (202, 703, 708, 710, 738) being connected in a driving manner to the hydraulic machine (204), said method comprising: detecting an operating parameter and of generating a corresponding parameter signal;determining a level of said pressure based on the level of the detected operating parameter; andcomparing the determined pressure level with a predetermined maximum level and of controlling the hydraulic machine so that a delivered pressure lies below the predetermined maximum level.

60. The method as recited in claim 59, further comprising detecting a torque delivered by the electric machine and of determining the level of said pressure based on the detected torque.

61. The method as recited in claim 60, further comprising calculating a level of said pressure based on at least the detected torque and the displacement of the hydraulic machine.

62. The method as recited in claim 59, further comprising detecting the pressure of the hydraulic fluid in a line downstream of the hydraulic machine and of comparing the detected pressure level with the predetermined maximum level.

63. The method as recited in claim 59, further comprising: providing the hydraulic machine with an hydraulic actuator (104, 105, 108, 109, 110, 732, 902) with pressurized hydraulic fluid.