Hydraulic system

Abstract

The invention relates to a hydraulic system having a hydraulically actuable working cylinder (10) which has a cylinder housing (12) with a piston-rod unit (14) that is guided in longitudinal movement therein, is actuable in opposite directions and subdivides the cylinder housing (12) into a piston chamber (16) and a rod chamber (18), and having two proportional pressure control valves (20, 22), of which one (20) is assigned to the piston chamber (16) and the other (22) is assigned to the rod chamber (18), characterised in that a connecting line (40) is connected in a fluid-conducting connection (34) between the rod chamber (18) and the proportional pressure control valve (22) assigned to the rod chamber (18), said connecting line being guided to an input side (2) of the proportional pressure control valve for the piston chamber (16) such that, when the piston-rod unit (14) is extended, the fluid displaced from the rod chamber (18) passes into the piston chamber (16) of the cylinder housing (12).

Description

[0001] Hydraulic system

[0002] The invention relates to a hydraulic system with a hydraulically controllable working cylinder, which has a cylinder housing with a piston-rod unit which is guided therein so as to be longitudinally displaceable and controllable in opposite directions, which divides the cylinder housing into a piston chamber and a rod chamber and with two proportional pressure control valves, one of which is assigned to the piston chamber and the other to the rod chamber.

[0003] EP 1 642 035 B 1 discloses a generic hydraulic system having a hydraulically controllable drive part with two opposing drive directions, wherein at least one pressure regulator, in particular in the form of a valve, is provided for at least one drive direction, as well as a throttle between the pressure regulator and the drive part, wherein a sensor is provided to detect the load state of the drive part, in the form of a pressure sensor which is connected for each drive direction of the drive part in the associated fluid-carrying line between the throttle and the drive part, wherein the pressure sensor detects the instantaneous load situation on the drive part, wherein the pressure regulator in its basic position connects the secondary side of the system to a tank connection, and wherein when the pressure regulator is controlled, the secondary pressure is regulated to the pressure of the proportional pilot control less the spring force acting on the valve piston of the pressure regulator.

[0004] This results in a control and regulation concept being implemented which, based on a basic system known per se (DE 44 07 370 A1), can be used to detect pressure, path, speed and position for the movable components of the selected drive part in hydraulically controllable drive components such as hydraulic working cylinders or hydraulic drive motors. The respective pressure regulator, particularly in the form of a valve, enables highly dynamic and precise control processes to be implemented depending on the hydraulic application. This known system, which uses pressure regulators and corresponding throttles, eliminates the need for the otherwise conventional directional valve technology for controlling the movement of a drive component, thus reducing power loss and susceptibility to failure while simultaneously increasing the response time of the hydraulic system.

[0005] Despite these advantages, the known solution has an inherently increased energy requirement, since in order to increase or decrease the force on the piston-rod unit of the working cylinder, hydraulic medium, such as oil, must be drained alternately from the rod side or the piston side to the tank, and the pressure control valves are constantly energized and regulating.

[0006] Based on this prior art, the invention is therefore based on the object of further improving the known solution while retaining the advantages of the known solution to enable energy-saving operation. This object is achieved by a hydraulic system having the features of patent claim 1 in its entirety.Because, according to the characterizing part of patent claim 1, a connecting line is connected to a fluid-carrying connection between the rod chamber and the proportional pressure control valve assigned to the rod chamber, which connecting line is led to an inlet side of the proportional pressure control valve for the piston chamber, so that when the piston-rod unit is extended, the fluid displaced from the rod chamber reaches the piston chamber of the cylinder housing, it is possible, within the framework of a type of regeneration operation, that when the working cylinder is extended, the hydraulic medium to be discharged on the rod or ring side is not led to the tank, but is used directly for the piston side for a corresponding lifting movement within the framework of a storage process.

[0007] Due to the pressure ratio in a conventional differential cylinder used as a working cylinder, the hydraulic pressure on the rod or ring side of the working cylinder is always higher than on the piston side, so that the piston side can be supplied with fluid from this higher pressure level in an energy-saving manner. In this way, the hydraulic system according to the invention can easily achieve force control for the working cylinder; for example, the force on the piston-rod unit of the differential cylinder can be kept constant despite the occurrence of disruptive influences. Furthermore, an actuating force can be set according to specifications, and, moreover, position control for the piston-rod unit can be achieved if necessary. This has no equivalent in the prior art.

[0008] In a particularly preferred embodiment of the hydraulic system, a preferably spring-loaded check valve is arranged in the fluid-carrying connection between the rod chamber and the proportional pressure control valve assigned to the rod chamber, upstream of a branch point in the connecting line. This check valve opens in the direction of the rod chamber toward the branch point. The aforementioned check valve could also be omitted, but the use of the aforementioned check valve ensures that the volume flow discharged from the rod or ring side also flows to the piston side and does not inadvertently flow back into the tank via the return line.

[0009] Further advantageous embodiments of the system according to the invention are the subject of the subclaims.

[0010] The invention also relates to a method for operating such a hydraulic system, which is characterized in that, by means of a computer control and connected sensors, such as pressure and / or position sensors, both the piston side and the rod side of the working cylinder are checked to determine whether the actuating force to be set is actually achieved. This actuating force is limited by the design in that the associated maximum pressure set on the piston side corresponds to the maximum pressure on the rod side, which in turn corresponds to the supply pressure of the pressure supply source. This advantageously results in the same behavior as with a hydraulic plunger circuit, ie to retract the working cylinder only the annular surface is subjected to pressure, whereas to extend it both sides of the piston are subjected to pressure.Assuming the piston surface is twice as large as the piston surface on the rod side, a predetermined force acts on the piston surface, which is counteracted by a force half as large on the rod or ring surface side. Thus, in an energy-saving manner, the piston extends with only "half the force."

[0011] The solution according to the invention is explained in more detail below using an exemplary embodiment. The single figure shows the basic structure of the hydraulic system in the form of a hydraulic circuit diagram. The figure shows a hydraulic system with a hydraulically controllable working cylinder 10, which is designed as a so-called differential cylinder. The working cylinder 10 conventionally has a cylinder housing 12 with a piston-rod unit 14 guided therein for longitudinal movement and controllable in opposite directions. This piston-rod unit divides the cylinder housing 12 into a piston chamber 16 and a rod chamber 18, which is also referred to in technical terms as an annular chamber. The circuit according to the figure further has two proportional pressure control valves 20, 22, of which one proportional pressure control valve 20 is assigned to the piston chamber 16 and the other pressure control valve 22 is assigned to the rod chamber 18.

[0012] Such proportional valves 20, 22 are common and each form a continuous valve that, with the aid of a proportional magnet 24, not only allows discrete valve switching positions but also permits a continuous transition of the valve opening. In hydraulics, such proportional valves 20, 22 are frequently used, especially where variable volume flows need to be controlled. Accordingly, the valves 20, 22 can assume any intermediate position between one and the other valve position.In the valve position according to the figure, the two valves 20, 22 are shown in their unactuated basic position, which is assumed by the action of a valve spring 26 when the proportional solenoid 24 is de-energized and under the action of a fluid pressure which acts on the spool of the respective valve 20, 22 via a control line 28 in the same direction as the force of the valve spring 26, wherein the respective control line 28 taps the pressure at output 1 of the respective valve 20, 22. Each of the two valves 20, 22 has, in addition to an output 1, two inlets 2, 3, wherein inlet 2 of the proportional pressure control valve 22 is connected to a pressure supply connection P, to which the fluid pressure of a pressure supply source is present, for example realized by a conventional hydraulic pump (not shown).The further inlet 3 of the valve 22, like the inlet 3 of the valve 20, is connected to a return line 32, which leads to a tank T which is usual for such systems.

[0013] A connecting line 40 is connected to a branch point 38 in a fluid-carrying connection 34 between the rod chamber 18 and the proportional pressure control valve 22 assigned to the rod chamber 18, which is led to the other inlet side 2 of the proportional pressure control valve 22 for the piston chamber 16, so that when the piston-rod unit 14 is extended upwards as viewed in the direction of the figure, the fluid displaced from the rod chamber 18 reaches the piston chamber 16 of the cylinder housing 12 when the proportional pressure control valve 20 is activated by actuating the associated proportional magnet 24.

[0014] According to the illustration in the figure, both valves 20, 22 are shown in their basic position, in which the respective outlet 1 is in fluid communication with the associated inlet 3, which for both valves 20, 22 leads via the return line 32 to the tank T. In order to prevent an unwanted backflow of fluid from the branch point 38 in the direction of the outlet 1 of the proportional pressure control valve 22, a spring-loaded check valve 42 is connected in the corresponding connecting line 36, which opens in a spring-loaded manner in the direction of the branch point 38.

[0015] In order to extend the piston-rod unit 14 from the cylinder housing 12, the proportional pressure control valve 22 associated with the rod chamber 18 moves into an actuated position, in which fluid under a predeterminable pressure, preferably originating from a hydraulic pump, with the check valve 42 correspondingly opened, enters the piston chamber 16 via the branch point 38 and the connecting line 40 and via the proportional pressure control valve 20 associated with the piston chamber 16, which is also in a actuated position, so that the extension movement of the unit 14 is supported due to the area ratio between the rod or ring side and the piston side.

[0016] For the opposite retraction of the piston-rod unit 14 into the cylinder housing 12 of the working cylinder 10, the proportional pressure control valve 22 associated with the rod chamber 18 moves into an actuated position, in which fluid under a predeterminable pressure, preferably again originating from the hydraulic pump P, enters the rod chamber 18, with simultaneous displacement of fluid from the piston chamber 16 via the associated, unactuated proportional pressure control valve 20 in the direction of the return line 32 to the storage tank T. Since the proportional pressure control valve 20 for the piston chamber 16 then assumes its basic position shown in the figure, the pump pressure present in the connecting line 40 from the pressure supply source P is connected to the inlet 2 of the valve 20 which is blocking in this respect, so that the fluid volume displacement from the piston chamber 16 in the direction of the storage tank T from the Connection point 1 to 3 of valve 20 is not obstructed.As can also be seen from the figure, the same inlet 3 of both proportional pressure control valves 20, 22 is connected to the return line 32, and the respective inlet 3 is connected to the piston chamber 16 in the unactuated initial position of the respective proportional pressure control valve 20, 22, at least in one fluid direction. Since the check valve 42 is not mandatory in the implementation of the hydraulic system according to the figure, if it were omitted, the rod chamber 18 would also be connected to the tank T via the inlet 3 and the return line 32 in the basic position of the valve 22 shown.

[0017] In a higher-level logic system involving a computer control system, it can be checked whether the set force can actually be achieved on the piston-rod unit 14. This is limited by the concept, insofar as the maximum pressure that can be set on the piston side, i.e., the piston chamber 16, corresponds to the maximum ring pressure, i.e., the pressure in the rod chamber 18, which in turn corresponds to the pump pressure of the pressure supply source P. This results in behavior comparable to that of a hydraulic plunger circuit. The following applies: max PKO ^KO PRIORI — p P (Ä Ko Ä Ri ) , with Pmax,Ko Pmax,Ri And Pmax,Ri PP > Where p Ri the pressure on the ring or rod side,

[0018] Ä Ri the area of ​​the piston on the ring or rod side, p Ko the pressure on the piston side, and

[0019] A KO the area of ​​the piston on the piston side.

[0020] Conventional pressure sensors 44 are used to monitor the pressure situation in both the piston chamber 16 and the rod chamber 18. In addition to or as an alternative to the two pressure sensors 44 shown, a position measuring system (not shown or described in detail) could also be used to monitor the position of the piston-rod unit 14, which allows a conclusion to be drawn about the pressure situation in the chambers 16, 18.

[0021] With this operating procedure, a force control for the working cylinder 10 is achieved, whereby an actuating force for the piston-rod unit 14 can be set according to specifications or, if necessary, the force can be kept constant in the event of disturbances on the unit 14. Furthermore, it is possible to carry out a position control for the working cylinder 10 with the hydraulic system in question.

[0022] The solution according to the invention makes it possible to use the oil drained from the ring side of the differential cylinder 10 for the piston side. Due to the selected pressure ratio in the implementation of the differential cylinder, the pressure on the ring side is always higher than that on the piston side, so that the piston side can be supplied from this higher pressure level in an energy-efficient manner.

[0023] The proportional pressure control valves 20, 22 used here are not to be considered conventional directional control valves; rather, these (20, 22) allow the flow of a specific volume through the valve depending on the pressure difference across the valve and thus regulate the pressure in the system. Accordingly, the pressure in the respective

[0024] Chamber 16, 18 of the hydraulic cylinder 10 can be regulated proportionally to the control signal of the corresponding valve 20, 22, which is not possible with directional valves of the other type.

Claims

Patent claims Hydraulic system with a hydraulically actuated working cylinder (10) comprising a cylinder housing (12) with a longitudinally movable, counter-rotating piston-rod unit (14) therein, which divides the cylinder housing (12) into a piston chamber (16) and a rod chamber (18) and is equipped with two proportional pressure control valves (20, 22), one (20) of which is assigned to the piston chamber (16) and the other (22) to the rod chamber (18), characterized in that a connecting line (40) is connected in a fluid-carrying connection (34) between the rod chamber (18) and the proportional pressure control valve (22) assigned to the rod chamber (18), which is led to an inlet side (2) of the proportional pressure control valve for the piston chamber (16), so that when the piston-rod unit is extended (14) the fluid displaced from the rod chamber (18) enters the piston chamber (16) of the cylinder housing (12).Hydraulic system according to claim 1, characterized in that the proportional pressure control valves (20, 22) are electromagnetically actuated (24) and, in their unactuated initial position, connect via an inlet (3) to a return line (32), which preferably leads to a storage tank (T). Hydraulic system according to claim 1 or 2, characterized in that, for extending the piston-rod unit (14) from the cylinder housing (12), the proportional pressure control valve (22) belonging to the rod chamber (18) moves into an actuated position, in which fluid at a predetermined pressure, preferably originating from a hydraulic pump (P), flows via the connecting line (40) and via the proportional pressure control valve (22), which is also in an actuated position. The proportional pressure control valve (20) associated with the piston chamber (16) enters the piston chamber (16).

4. Hydraulic system according to one of the preceding claims, characterized in that, for the insertion of the piston-rod unit (14) into the cylinder housing (12) of the working cylinder (10), the proportional pressure control valve (22) belonging to the rod chamber (18) enters an actuated position, in which fluid under a predeterminable pressure, preferably originating from a hydraulic pump (P), enters the rod chamber (18), while simultaneously displacing fluid from the piston chamber (16) via the associated and unactuated proportional pressure control valve (20) in the direction of the return line (32) to the storage tank (T).

5. Hydraulic system according to one of the preceding claims, characterized in that the respective proportional pressure control valve (20, 22) is constructed in the same way as the other proportional pressure control valve (22, 20) and preferably consists of a 3 / 2-way proportional valve.

6. Hydraulic system according to one of the preceding claims, characterized in that the same inlet (3) of both proportional pressure control valves (20, 22) is connected to the return line (32), which in the unactuated initial position of the respective proportional pressure control valve (20, 22) is connected to the piston chamber (16) at least in one fluid direction.

7. Hydraulic system according to one of the preceding claims, characterized in that the outlet (1) of the proportional pressure control valve (22) belonging to the rod chamber (18) is at least- dest is temporarily connected via the connecting line (40) to the further inlet (2) of the proportional pressure control valve (20) belonging to the piston chamber (16).

8. Hydraulic system according to one of the preceding claims, characterized in that the further inlet (2) of the proportional pressure control valve (22) belonging to the rod space (18) is connected to a pressure supply line (30) which preferably leads to a pressure supply source P, such as a hydraulic pump.

9. Hydraulic system according to one of the preceding claims, characterized in that a, preferably spring-loaded, check valve (42) is arranged in the fluid-carrying connection (34) between the rod chamber (18) and the proportional pressure control valve (22) associated with the rod chamber (18) in a further connecting line (36) before a branch point (38), which opens in the direction of the rod chamber (18) towards the branch point (38).

10. Method for operating a hydraulic system according to one of the preceding claims, characterized in that, by means of a computer control and connected sensors, such as pressure sensors (44), both the piston side (16) and the rod side (18) of the working cylinder (10) are checked to see whether the actuating force to be set is reached, which is limited by design insofar as the associated maximum pressure on the piston side (16) corresponds to the maximum pressure on the rod side (18), which in turn corresponds to the supply pressure of the pressure supply source (P).

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