Method for controlling a hydraulic cylinder and control system for a work machine

1. A method for controlling a hydraulic cylinder, comprising

detecting a load acting upon the hydraulic cylinder,

controlling opening and closing of a communication path between a piston-rod side and a piston side of the hydraulic cylinder based on the detected load, the piston-rod side and the piston side being connected to a hydraulic system via first and second lines, respectively, the first and second lines being connected by a third line, by opening and closing of a valve in the third line, the controlling comprising

comparing a size of the detected load with a predetermined load level,

closing the valve if the detected load exceeds the predetermined load level,

opening the valve if the detected load is less than the predetermined load level, and

continually variably controlling the communication path between the piston-rod side and piston side of the hydraulic cylinder.

2. The method as claimed in claim 1 , comprising detecting an input from an operator-controlled element and controlling the communication path between the piston-rod side and piston side of the hydraulic cylinder based on this input.

3. The method as claimed in claim 2 , comprising opening up the communication path to an increasing extent when the operating parameter indicates increasingly rapid movement.

4. The method as claimed in claim 2 comprising closing off the communication path when the operating parameter indicates movement below a predetermined speed.

5. The method as claimed in claim 1 , comprising determining a position of the piston in the hydraulic cylinder and controlling the communication path between the piston-rod side and piston side of the hydraulic cylinder based on the determined position.

6. The method as claimed in claim 1 , comprising determining, whether it is desirable to convert a part of the kinetic energy during a lowering movement into heat in the hydraulic fluid and, if so, controlling the communication path between the piston-rod side and piston side of the hydraulic cylinder correspondingly.

7. The method as claimed in claim 1 , wherein the communication involves controlling a pressure on a side of the cylinder that is opposite to a side of the cylinder toward which the piston in the hydraulic cylinder is moved.

8. The method as claimed in claim 1 , wherein the valve is a pressure-reducing valve.

9. The method as claimed in claim 8 , wherein the pressure-reducing valve is arranged to allow a flow in both directions.

10. The method as claimed in claim 1 , comprising driving the hydraulic cylinder with a hydraulic machine.

11. The method as claimed in claim 10 , wherein the communication path is controlled so that hydraulic fluid from a first of the piston-rod side and piston side flows to the second of the piston side and piston-rod side without passing through the hydraulic machine.

12. The method as claimed in claim 1 , wherein the hydraulic cylinder is arranged in a work machine and moves an implement that is connected to the hydraulic cylinder.

13. The method as claimed in claim 12 , wherein the load acts on the implement.

14. A method for controlling a hydraulic cylinder, comprising

detecting at least one operating, parameter,

controlling opening and closing of a communication path between a piston-rod side and a piston side of the hydraulic cylinder based on the detected operating parameter,

detecting an energy level in an energy storage means,

comparing the detected energy level with a predetermined level, and

restricting the communication path between the piston-rod side and piston side of the hydraulic cylinder if the detected energy level exceeds the predetermined level.

15. A control system for a work machine comprising

at least one hydraulic cylinder comprising a piston defining a piston-rod side and a piston side of the cylinder,

a hydraulic system, the piston-rod side and the piston side being connected to the hydraulic system via first and second lines, respectively, the first and second lines being connected by a third line,

an openable and closable valve in the third line for controlling a communication path between the piston-rod side and the piston side of the hydraulic cylinder,

a sensor arranged to detect a load acting upon the hydraulic cylinder, and

a controller arranged to control opening and closing of the valve in response to the load detected by the sensor, the controller being arranged to compare a size of the detected load with a predetermined load level, close the valve if the detected load exceeds the predetermined load level, and open the valve if the detected load is less than the predetermined load level, the controller being arranged to continually variably control the communication path between the piston-rod side and piston side of the hydraulic cylinder.

16. The control system s claimed in claim 15 , wherein the valve comprises an electrically controlled valve.

17. The control system as claimed in claim 15 , wherein the control system comprises an operator-controlled element.

18. The control system as claimed in claim 15 wherein the sensor comprises a pressure sensor arranged on the piston side of the hydraulic cylinder.

19. The control system as claimed in claim 15 , wherein the control system comprises means for determining a position of the piston in the hydraulic cylinder.

20. The control system as claimed in claim 15 , wherein the controller comprises a control unit that is operatively connected to the valve in order to control the valve.

21. The control system as claimed in claim 15 , wherein the hydraulic cylinder is adapted to more an implement in order to perform a work function.

22. The control system as claimed in claim 21 , wherein the hydraulic cylinder comprises a lifting cylinder for moving a loading arm which is pivotably connected to a vehicle frame, the implement being arranged on the loading arm.

23. The control system as claimed in claim 21 , wherein the hydraulic cylinder comprises a tilting cylinder for moving the implement, which is pivotably connected to a loading arm, which is in turn pivotably connected to a vehicle frame.