Hydraulic drive system

Abstract

The invention relates to a hydraulic drive system, to a method for adjusting a delivery volume in a hydraulic drive system, and to the use of the hydraulic drive system for controlling a hydraulic cylinder. The hydraulic drive system according to the invention is a hydraulic drive system with a first hydraulic machine and a second hydraulic machine which are connected mechanically to one another. The first hydraulic machine and the second hydraulic machine are operated jointly by a variable-speed drive. The first hydraulic machine and the second hydraulic machine are connected hydraulically to at least one first hydraulic cylinder, comprising a first hydraulic cylinder surface and a second hydraulic cylinder surface. The first hydraulic machine and/or the second hydraulic machine have/has an adjustable delivery volume.

Claims

1. A hydraulic drive system having a first hydraulic machine and a second hydraulic machine, which are mechanically connected to one another; wherein the first hydraulic machine and the second hydraulic machine are operated conjointly by a variable-speed drive; wherein the first hydraulic machine and the second hydraulic machine are hydraulically connected to at least a first hydraulic cylinder, comprising a first hydraulic cylinder side with a first hydraulic cylinder surface and a second hydraulic cylinder side with a second hydraulic cylinder surface; wherein the first hydraulic machine or the second hydraulic machine has an adjustable delivery volume, and wherein the first hydraulic machine and the second hydraulic machine are configured as fixed displacement pumps; wherein the first hydraulic machine is connected to a reservoir of the hydraulic drive system, and the reservoir is configured as a pre-stressed reservoir; wherein the second hydraulic machine is hydraulically connected to the first hydraulic cylinder surface and to the second hydraulic cylinder surface; and wherein, when the second hydraulic machine conveys a hydraulic fluid with a volume flow from the second hydraulic cylinder side to the first hydraulic cylinder side, then the second hydraulic machine conveys a full volume flow from the second hydraulic cylinder side to the first hydraulic cylinder side.

2. The hydraulic drive system as claimed in claim 1, wherein a ratio of the delivery volumes of the first hydraulic machine and the second hydraulic machine is mechanically adjustable to a surface ratio of the first hydraulic cylinder surface and the second hydraulic cylinder surface.

3. The hydraulic drive system as claimed in claim 1, wherein a delivery volume of the hydraulic drive system is controlled by a determined adjustment parameter.

4. The hydraulic drive system as claimed in claim 1, wherein the first hydraulic cylinder surface and the second hydraulic cylinder surface are different.

5. The hydraulic drive system as claimed in claim 1, wherein the first hydraulic machine and/or the second hydraulic machine are/is selected from a group of pumps comprising at least a positive displacement pump, in particular an axial piston pump, radial piston pump or vane pump, gear pump, or spindle pump.

6. The hydraulic drive system as claimed in claim 1, wherein the first hydraulic machine is connected to the first hydraulic cylinder surface of the hydraulic cylinder.

7. The hydraulic drive system as claimed in claim 1, wherein the pre-stressed reservoir has a pressure in a fluctuation range preferably of 22 bar, more preferably of 14 bar.

8. The hydraulic drive system as claimed in claim 1, wherein the first hydraulic machine and/or the second hydraulic machine have/has at least one high-pressure port.

9. The hydraulic drive system as claimed in claim 1, configured to control the hydraulic cylinder with a constant total pressure in the hydraulic drive system.

10. The hydraulic drive system as claimed in claim 1, wherein, depending on a direction of rotation, hydraulic fluid is transferred between the first and second hydraulic cylinder surfaces through the second hydraulic machine.

11. The hydraulic drive system as claimed in claim 1, wherein the second hydraulic machine is configured as a 4-quadrant stage.

12. The hydraulic system as claimed in claim 1, wherein the second hydraulic machine has a first pressure port and a second pressure port, each rated for full working pressure, the first pressure port being directly hydraulically connected to the first hydraulic cylinder side and the second pressure port being directly hydraulically connected to the second hydraulic cylinder side.

Description

(1) In the figures:

(2) FIG. 1 shows a first embodiment of the hydraulic drive system according to the present invention;

(3) FIG. 2 shows a further embodiment of the hydraulic drive system according to the present invention; and

(4) FIG. 3 shows a flowchart of an embodiment of a method according to the present invention.

(5) FIG. 1 shows a hydraulic drive system 1. The hydraulic drive system 1 includes a first hydraulic machine 2 and a second hydraulic machine 3. The first hydraulic machine 2 and the second hydraulic machine 3 are driven conjointly via a shaft by a variable-speed drive 4. Preferably, the first hydraulic machine 2 and the second hydraulic machine are mechanically connected to one another. The mechanical connection can be established via a shaft. The first hydraulic machine 2 and the second hydraulic machine 3 are configured as fixed displacement pumps. The first hydraulic machine 2 is hydraulically connected to a reservoir 6. A feeder valve (not illustrated) can be interposed between the first hydraulic machine 2 and the reservoir 6. A reservoir 6 (compensation vessel) is understood to mean a vessel which receives the hydraulic oil or the hydraulic medium of the hydraulic drive system 1. The hydraulic fluid or the hydraulic medium can be a special mineral oil. The reservoir 6 is intended to store the hydraulic fluid, but otherwise keeps the latter unpressurized. The reservoir is understood to be a tank without positive pressure. This allows the reservoir 6 to be filled and emptied without risk. The reservoir 6 is embodied as a closed vessel that is connected to the surrounding air via vent valves. This connection is necessary so that pressure equalization can take place. Otherwise, returning hydraulic fluid, or the hydraulic medium, would generate positive pressure, and escaping hydraulic fluid would create negative pressure. The closed system makes it possible to ensure that no cavitation occurs and thus the quality of the hydraulic medium (e.g. oil) is maintained, or the latter does not age and/or ages less rapidly. This reduces premature replacement and/or maintenance intervals.

(6) In a further preferred embodiment, the reservoir 6 can be configured to be under positive pressure. In particular, the reservoir 6 can be configured as a pre-stressed reservoir.

(7) Preferably, a positive pressure can be provided in a range of 2-25 bar, particularly preferably in a range of 2-10 bar. A reservoir with positive pressure enables increased induction by the first hydraulic machine and the second hydraulic machine. Furthermore, this construction allows the hydraulic medium to be separated from the atmosphere and thus counteracts aging of the hydraulic medium.

(8) In a further preferred embodiment, the pre-stressed reservoir 6 is pressurized with a pressure in a fluctuation range, preferably of 22 bar, more preferably of 14 bar. The hydraulic pumps can advantageously be operated in this fluctuation range without their sealing ability and/or quality being reduced. Furthermore, the hydraulic pumps are operated in a range in which the load limits of the pump housing are adhered to in order to prevent damage.

(9) The first hydraulic machine 2 and the second hydraulic machine 3 are hydraulically connected to a first hydraulic cylinder side 5a of a hydraulic cylinder 5. The second hydraulic machine 3 is hydraulically connected to the second hydraulic cylinder side 5b of the hydraulic cylinder 5.

(10) If the variable-speed drive 4 drives the first hydraulic machine 2 and the second hydraulic machine 3, then, depending on the direction of rotation of the variable-speed drive 4, the first hydraulic machine 2 conveys hydraulic fluid from the reservoir 6 into the first hydraulic cylinder side Sa of the hydraulic cylinder, and the second hydraulic machine 3 conveys hydraulic fluid from the second hydraulic cylinder side 5b of the hydraulic cylinder 5 into the first hydraulic cylinder side Sa of the hydraulic cylinder 5. The piston of the hydraulic cylinder 5 is deployed. If the drive 4 drives the first hydraulic machine 2 and the second hydraulic machine 3 in the other direction, the first hydraulic machine 2 conveys hydraulic fluid from the first hydraulic cylinder side 5a of the hydraulic cylinder 5 into the reservoir 6, and the second hydraulic machine 3 delivers hydraulic fluid from the first hydraulic cylinder side 5a of the hydraulic cylinder into the second hydraulic cylinder side 5b of the hydraulic cylinder 5. The piston of the hydraulic cylinder 5 is retracted.

(11) The delivery volume in the hydraulic drive system 1 can be controlled via the rotating speed of the variable-speed drive 4. In this arrangement, the first hydraulic machine 2 only has to compensate for the volume ratio of the first hydraulic cylinder side 5a and of the second hydraulic cylinder side 5b. The delivery volume of the first hydraulic machine 2 can therefore be smaller than in other arrangements. The first hydraulic machine 2 can therefore be designed to be smaller in terms of construction mode.

(12) It is provided that the delivery volume of at least one hydraulic machine 2, 3 is adjusted, or mechanically set and fixed, per pump revolution. For this purpose, the fixed delivery volume of the first hydraulic machine 2 and/or the second hydraulic machine 3 is changed. For example, in a radial piston pump (RKP) it can be provided that the delivery volume is adjusted via the eccentricity of the stroke ring. This leads to an adjustment of the stroke of the pistons or vanes and thus to a change in the delivery volume per pump revolution. The eccentricity of the stroke ring can be adjusted and the delivery volume per pump revolution can be adjusted and fixed using a correspondingly provided spindle. The stroke setting can be locked by mechanical fixing. If the stroke setting is performed using an adjusting spindle, the former can be locked using a lock nut. Advantageously, the inventive construction and use of exclusive fixed displacement pumps (for example external gear 25 pumps, internal gear pumps, screw spindle pumps) or adjustable fixed displacement pumps (for example axial piston pump, radial piston pump, vane pumps) for the first hydraulic machine 2 and the second hydraulic machine 3 is substantially easier to implement and more reliable in operation in comparison to variable-displacement pumps, the delivery volume of the latter being able to be permanently adjusted during operation. Considered on their own, variable-displacement pumps have the disadvantage that the adjustment system requires considerable additional complexity. In the case of variable-displacement pumps, the adjustment is implemented via so-called control pistons, which are subjected to a corresponding pressure or a hydraulic fluid, this requiring an additional proportional valve to regulate the pressure in the control piston. A position-measuring system is also provided to record the position. A control system is moreover required to supply the proportional valve. This represents significant additional complexity. In this regard, the present invention is simpler to implement in terms of its construction and also more reliable due to the smaller number of components to be supplied.

(13) It is furthermore advantageous that the actuation of the hydraulic drive system is configured to be more efficient and simpler, since the delivery volume only needs to be set or adjusted once. The delivery volume of the second hydraulic machine 3 can be matched to the hydraulic cylinder-surface ratio by adjusting the eccentricity of the stroke ring. The volumetric flow conveyed in the hydraulic drive system 1 is controlled via the rotating speed of the first and second hydraulic machines 2, 3.

(14) Preferably, at least one of the hydraulic machines 2, 3 is configured as an axial piston pump, radial piston pump or vane pump, and has a manual mechanical stroke setting of the delivery volume. The further hydraulic machine 2, 3 can be configured as a fixed displacement pump or as an adjustable fixed displacement pump.

(15) In the embodiment illustrated in FIG. 1, the volume of the first hydraulic machine 2 can be smaller in comparison to that used in the first hydraulic machine 2 and illustrated in FIG. 2. In this way, the first hydraulic machine 2 in FIG. 1 can be configured correspondingly smaller, this being reflected in a more cost-effective use. The second hydraulic machine illustrated in FIG. 1 has two ports, both of which can be pressurized to full working pressure.

(16) In FIG. 1 the second hydraulic machine 3 has the adjustment 7. The adjustment 7 is configured to adjust an adjustable delivery volume for the first hydraulic machine 2 and/or the second hydraulic machine 3. In particular, the delivery volume can be adjusted mechanically via the adjustment 7. In FIGS. 1 and 2, the second hydraulic machine 3 has the adjustment 7. This is only an exemplary and not a limiting representation. Optionally, the first hydraulic machine 2 can also have the adjustment 7. For example, in piston pumps and vane pumps, the adjustment 7 can be used to manually adjust the stroke of the pistons or vanes by adjusting the adjustment 7. This stroke setting leads to a change in the delivery volume per revolution. The adjustment 7 can be changed in terms of adjustment according to the determined first adjustment parameter, by driving in or driving out the screw. The adjustment 7 can be locked using a mechanical fixing device. This mechanical fixing device can be configured as a lock nut screwed onto the adjustment 7.

(17) FIG. 2 shows a hydraulic drive system 1 according to a further embodiment. The hydraulic drive system 1 according to FIG. 2 comprises a first hydraulic machine 2 and a second hydraulic machine 3. The first hydraulic machine 2 and the second hydraulic machine 3 are driven conjointly, for example as illustrated via a shaft by a variable-speed drive 4. The first hydraulic machine 2 is hydraulically connected to a first hydraulic cylinder side 5a of a hydraulic cylinder 5. The second hydraulic machine 3 is hydraulically connected to a second hydraulic cylinder side 5b of a hydraulic cylinder 5. The first hydraulic machine 2 and the second hydraulic machine 3 are each connected to a reservoir 6. A feeder valve can be provided between the first hydraulic machine 2 and the reservoir 6 and between the second hydraulic machine 3 and the reservoir 6. In a further embodiment, the first hydraulic machine 2 and the second hydraulic machine 3 are connected conjointly to the reservoir 6 via a feeder valve.

(18) If the variable-speed drive 4 drives the first hydraulic machine 2 and the second hydraulic machine 3, then, depending on the direction of rotation of the variable-speed drive 4, the first hydraulic machine 2 conveys hydraulic fluid from the reservoir 6 into the first hydraulic cylinder side 5a of the hydraulic cylinder 5, and the second hydraulic machine 3 conveys hydraulic fluid from the second hydraulic cylinder side 5b of the hydraulic cylinder into the reservoir 6. The piston is moved to a terminal position; for example, the piston of the hydraulic cylinder 5 is deployed. If the drive 4 drives the first hydraulic machine 2 and the second hydraulic machine 3 in the direction other than the previously described direction, the first hydraulic machine 2 conveys hydraulic fluid from the first hydraulic cylinder side 5a of the hydraulic cylinder 5 into the reservoir 6, and the second hydraulic machine 3 conveys hydraulic fluid from the second hydraulic cylinder side 5b of the hydraulic cylinder 5 into the reservoir 6. The piston of the hydraulic cylinder 5 is retracted. According to the invention, the delivery volume (volume) in the hydraulic drive system 1 is controlled by the adjustment parameter.

(19) The connection of the first hydraulic machine 2 and the second hydraulic machine 3, as illustrated in FIGS. 1 and 2, when using a differential cylinder with an exemplary surface ratio of 2:1, leads to the first hydraulic machine 2 and the second hydraulic machine 3 having the same delivery volume, and in this way at least one hydraulic machine can be made smaller compared to the prior art mentioned at the beginning, which leads to a smaller space requirement and lower economic costs. The volumetric flow conveyed can be influenced by changing the rotating speed of the primary drive, and the displacement speed of the hydraulic cylinder 5 can be changed in this way.

(20) Furthermore, it can be provided that the second hydraulic machine 3 is configured as a 4-quadrant stage. The 4-quadrant stage can be operated in a 4-quadrant operation with a positive torque and a positive direction of rotation, with a positive torque and a negative direction of rotation, with a negative torque and a positive direction of rotation, and with a negative torque and a negative direction of rotation.

(21) In the embodiment illustrated in FIG. 2, the volume of the first hydraulic machine 2 is larger compared to that of the first hydraulic machine of FIG. 1. The second hydraulic machine 2 has two ports, only one of which is pressurized to the full working pressure.

(22) In the construction shown in FIG. 2, the second port of the second hydraulic machine 3 is preferably always fluidically connected to the reservoir 6. The second hydraulic machine 3 can therefore only be configured to be provided with one pressure port. As a result thereof, the internal construction of the second hydraulic machine 3 is of a simpler configuration. The first hydraulic machine 2, on the other hand, now provides the entire volumetric flow requirement of the first cylinder chamber and is therefore larger compared to the embodiment of FIG. 1.

(23) The reservoir 6 can be configured as a tank without positive pressure. The reservoir 6 can likewise be configured as a reservoir under positive pressure. Preferably, a positive pressure is provided in a range of 2-25 bar, particularly preferably in a range of 2-25 bar. This enables an improved induction of the first hydraulic machine 2 and second hydraulic machine 3 on the one hand, and on the other hand such a corresponding design embodiment enables the hydraulic medium to be separated from the atmosphere, thus counteracting the aging of the hydraulic medium.

(24) FIG. 3 shows a flowchart of a method 10 for adjusting a delivery volume in a hydraulic drive system 1. The hydraulic drive system 1 has a first hydraulic machine 2 and a second hydraulic machine 3. The method illustrated in FIG. 3 can comprise the following method steps S1-S3. In a first step S1, a surface ratio between a first hydraulic cylinder surface 5a and a second hydraulic cylinder surface 5b of a hydraulic cylinder 5 of the hydraulic drive system 1 is determined. In a further step S2, a target delivery volume of the first hydraulic machine and/or the second hydraulic machine of the hydraulic drive system 1 is determined. In a further step S3, a first adjustment parameter of the first hydraulic machine 2 and/or the second hydraulic machine 3 is determined. Using the determined first adjustment parameter, the delivery volume of the first hydraulic machine 2 and/or the second hydraulic machine 3 of the hydraulic drive system 1 is adjusted. In a further embodiment it can be provided that further adjustment parameters are determined in order to adjust the delivery volume. In particular, it is provided that the delivery volume of the hydraulic drive system 1 is adjusted by adjusting the delivery volume of the first hydraulic machine 2 and of the second hydraulic machine 3.

(25) Furthermore, it can be provided that the method comprises a further step. The further step comprises testing the first hydraulic machine 2 and/or the second hydraulic machine 3 on a test bench. Furthermore, testing of the first hydraulic machine 2 and/or of the second hydraulic machine 3 can be provided by a test run. It can be determined by the testing whether the adjusted delivery volume corresponds to the surface ratio of the hydraulic cylinder.

(26) Furthermore, it can be provided that the delivery volume is adjusted by adjusting an adjusting element, preferably a threaded spindle, threaded bolt or a threaded screw, using the determined first adjustment parameter. Provision is preferably made to fix the adjusting element via a locking element, preferably a lock nut.

LIST OF REFERENCE SIGNS

(27) 1 Hydraulic drive system 2 First hydraulic machine 3 Second hydraulic machine 4 Variable-speed drive 5 Hydraulic cylinder 5a First hydraulic cylinder surface 5b Second hydraulic cylinder surface 6 Reservoir 7 Adjustment S1-S3 Method steps