HYDRAULIC VALVE BLOCK AND HYDRAULIC UNIT FOR CLOSED CIRCUIT APPLICATIONS

Abstract

A hydraulic valve block for a hydraulic unit includes a high-pressure port, a low pressure port, a pilot valve having a pilot valve spool, and a bypass valve having a bypass valve spool. The pilot valve connects in an initial position a control line to a discharge area. The pilot valve is switched by means of a force whose height depends on the pressure level at the low pressure side to a shifted position in which the pilot valve conducts pressure from the high-pressure port to the control line. The bypass valve switches from a closed position in which a fluid connection between the high pressure port and low pressure port is disabled, to an open position in which a fluid connection between the high pressure port and low pressure port is enabled, if the control line connected to an opening surface of the bypass valve, is not connected to the high-pressure port.

Claims

1. A hydraulic valve block for a hydraulic unit provided to be used in a closed hydraulic circuit application, comprising a high pressure port, a low pressure port, a pilot valve having a pilot valve spool, and a bypass valve having a bypass valve spool, wherein the pilot valve is connected with a pilot valve inlet to the high pressure port, with a discharge port to an discharge area and with a control outlet to a control line, the pilot valve spool is held in an initial position in which the control line is connected to the discharge area by means of a pilot valve spring acting on its first front face, wherein the pilot valve spool can slide into a shifted position and pressure from the pilot valve inlet can be conducted to the control line by means of a force, whose strength of force depends on the pressure level at the low pressure port acting on the second front face of the pilot valve spool against the force of the pilot valve spring; the bypass valve spool comprises a first opening front face connected to the high pressure port and a closing front face to which the control line is connected to and on which a bypass valve spring acts in closing direction, wherein the bypass valve can be switched from a closed position in which a fluid connection between the high pressure port and low pressure port is disabled, to an open position in which a fluid connection between the high pressure port and the low pressure port is enabled, if an opening force exerted by the high pressure on the first opening front face of the bypass valve spool is higher than the sum of closing forces on the closing front face exerted by the pressure in the control line and the force of the bypass valve spring.

2. The hydraulic valve block according to claim 1, wherein the bypass spool comprises a second opening front face connected to the low-pressure port.

3. The hydraulic valve block according to claim 2, wherein the first opening front face and the second opening front face on the bypass-spool are of equal size.

4. The hydraulic valve block according to claim 1, wherein the second front face of the pilot valve spool is fluidly connected to the low-pressure port.

5. The hydraulic valve block according to claim 1, wherein the force on the second front face of the pilot valve spool is exerted by a solenoid.

6. The hydraulic valve block according to claim 1, wherein the pilot valve is a proportional valve.

7. The hydraulic valve block according to claim 1, wherein the force of the pilot valve spring and/or the force of the bypass valve spring is/are adjustable.

8. The hydraulic valve block according to claim 1, wherein an orifice is located in the control line.

9. The hydraulic valve block according to claim 2, wherein a two position switching valve is fluidly connected to the high pressure port and the low pressure port to select and channel high pressure from the high pressure port to the inlet of the pilot valve, and low pressure from the low pressure port onto the second front face of the pilot valve spool.

10. A hydraulic unit for closed circuit applications to which a hydraulic valve block according to claim 1, is connected to at respective high pressure and low-pressure ports of the hydraulic unit.

11. A hydraulic system comprising a hydraulic motor and a hydraulic pump connected via working lines to form part of a closed circuit, the system further comprising the hydraulic valve block according to claim 1.

12. The hydraulic system according to claim 11, wherein the hydraulic valve block is attached to the hydraulic motor or the hydraulic pump.

13. The hydraulic valve block according to claim 2, wherein the second front face of the pilot valve spool is fluidly connected to the low-pressure port.

14. The hydraulic valve block according to claim 3, wherein the second front face of the pilot valve spool is fluidly connected to the low-pressure port.

15. The hydraulic valve block according to claim 2, wherein the force on the second front face of the pilot valve spool is exerted by a solenoid.

16. The hydraulic valve block according to claim 3, wherein the force on the second front face of the pilot valve spool is exerted by a solenoid.

17. The hydraulic valve block according to claim 2, wherein the pilot valve is a proportional valve.

18. The hydraulic valve block according to claim 3, wherein the pilot valve is a proportional valve.

19. The hydraulic valve block according to claim 4, wherein the pilot valve is a proportional valve.

20. The hydraulic valve block according to claim 5, wherein the pilot valve is a proportional valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The preferred embodiment shown in the enclosed figures is for explanation purposes only and should not limit the scope of the inventive idea nor the scope of protection. In the following Figures, it is shown:

[0026] FIG. 1: A schematic diagram of a hydraulic valve block according to the invention in a non-pressurized state.

[0027] FIG. 2: The embodiment of the hydraulic valve block according to the invention of FIG. 1 in a normal operational state of a hydraulic unit.

[0028] FIG. 3: A schematic diagram of the embodiment of the hydraulic valve block according to FIG. 1 in an operational state when a low loop event occurs.

[0029] In the Figures, same parts are indicated by the same reference numbers for an easier legibility.

DETAILED DESCRIPTION

[0030] FIG. 1 shows a hydraulic valve block 100 according to the invention in a non-pressurized state with non-connected pressure ports, for instance. Merely exemplarily, the hydraulic ports on the left in FIG. 1 are indicated as high-pressure ports 2 and the pressure ports on the right side of FIG. 1 are chosen to be the low-pressure ports 3. The two high-pressure ports 2 are connected by a high-pressure line 4 and the two low pressure ports 3 are connected by a low-pressure line 6. Between the two pressure lines 4 and 6, three valves are arranged, wherein the upper one is a switching valve 50, having a high-pressure inlet 51 and a low-pressure inlet 52. Each of the front faces of selectivity valve spool 54 is referenced to one of the pressure levels at inlet 51 or inlet 52 in order to move the switching valve spool 54, when the high-pressure port 2 is interchanged with the low pressure port 3. At least a person with skills in the relevant art derives from the switching valve 50 that when the pressure ports are changing pressure levels the switching valve 50 is switched into its second position (not shown), such that it is always ensured that pressure from the high pressure port 2 is guided to the high pressure outlet 56, and low pressure is guided from the inlet port 2 to the low pressure outlet port 57.

[0031] The two outlet ports 56 and 57 of the switching valve 50 are connected to a pilot valve 10 wherein the high pressure outlet 56 of switching valve 50 is connected to a pilot valve inlet 11, and the outlet port 57 of the switching valve 50 is connected with a second front face 17 of the pilot valve spool 14 of pilot valve 10. On the first front face 16 of the pilot valve 10, a pilot valve spring 15 is located. The pilot valve spring 15 holds the pilot valve 10 in its initial position, as depicted in FIG. 1. Pilot valve 10 also has a discharge port 12 connected to an area of low pressure in this instance to a tank 60 or a discharge area. Pilot valve 10 further comprises an outlet 13 which is connected to a control line 25 conducting towards a bypass valve 30.

[0032] This control line 25 is connected to a closing surface 38 on one front side of a bypass valve spool 34 of a bypass valve 30, on which a bypass valve spring 35 is arranged too. On the opposite side of the bypass valve spool 34, two opening front faces 36 and 37 are provided wherein the first opening front face 36 is connected to the high pressure line 4, and the second opening front face 37 is connected to the low pressure line 6. As the hydraulic valve block 100 shown in FIG. 1 is depicted in the non-pressurized state, the bypass valve spring 35 pushes the bypass valve 30 into the closed position, and so the bypass between the high pressure line 4 and the low pressure line 6 is disabled. At the same time, as no pressure is present neither in the low pressure line 6 nor in the high pressure line 4 the pilot valve spring 15 holds the pilot valve 10 in its initial position, a position in which the pilot valve spool 14 connects the control pressure line 25 with the discharge area 60 so that no pressure force can act on the closing front face 38 of the bypass valve spool 34.

[0033] In FIG. 2, the hydraulic valve block 100 according to the invention is depicted in an operational state in which the low-pressure level is higher than a minimum value and below which any low pressure compensation should start. This means that the low pressure, which is guided via the switching valve 50 on the second front face of pilot valve 10 creates a higher hydraulic force than the spring force exerting on the opposite first front face 16 does. Therefore, pilot valve spool 14 is displaced to its shifted position and the pilot valve guides hydraulic pressure from the high-pressure side, i.e. the high pressure port 2 into the control line 25. The pressure in control line 25 subsequently acts on the closing front face 38 of the bypass valve spool 34. On the same closing surface 38 the bypass valve spring 35 also exerts a closing force on the bypass valve spool 34. On the opposite side, high pressure from the high-pressure line 4 is acting upon the first opening front face 36 which is smaller than the closing front face 38, hence the bypass valve spool 34 is held in its closed position and the bypass valve 30 is closed, i.e. the bypass between the high pressure line 4 and the low pressure line 6 is disabled.

[0034] FIG. 3 depicts another operational state of the hydraulic valve block 100 according to the invention. The pressure in the low-pressure line 6 is lower than a pre-determined threshold value, i.e. when a low loop event occurs. The switching valve 50 remains in the same position as depicted with FIGS. 1 and 2, however, pilot valve 10 is in the initial position again as the low pressure, which is guided onto the second front face 17 of the pilot valve spool 14 does not create a hydraulic force sufficiently high enough to overcome the spring force of the pilot valve spring 15. Hence, the control line 25 is discharged to the discharge area 60 such that the hydraulic force on the closing surface 38 of the bypass valve spool 34 is reduced to a minimum, and only bypass valve spring 35 exerts a closing force on bypass valve spool 34. As at the same time the first opening front face 36 of bypass valve spool 34 is still connected to the high pressure line 4 a higher opening force on bypass valve spool 34 is created, pushing the bypass valve spool 34 into its open position, wherein the hydraulic bypass from the high pressure line 4 to the low pressure line 6 is enabled.

[0035] The bypass valve spool 34 remains in this open position as long as the hydraulic force on the second front face 17 of the pilot valve spool 14 is not capable of overcoming the spring force of the pilot valve spring 15 in order to move the pilot valve spool 13 into the shifted or switched position respectively. When the hydraulic force on the second front face 17 of the pilot valve spool 14 is high enough to overcome the force of pilot valve spring 15 the pilot valve spool 14 is brought into the switched position, and hydraulic pressure from the high pressure port 2 is guided via the pilot valve 10 and the control line 25 onto the closing front face 38 of the bypass valve spool 34 (which is the bigger pressure face) and therefore, bypass valve 30 is closed immediately after the low pressure level in low pressure line 6 is higher than the threshold value for the pre-determined/pre-adjusted minimum low pressure.

[0036] So, from the Figures it can be seen that by adjusting the spring force of the pilot valve spring 15 the threshold value for the minimum pressure level can be held to the pressure level of the low-pressure line 6. This pressure level can be set at any time, especially when the hydraulic system is coupled with a hydraulic valve block, according to the invention.

[0037] Also, a person skilled in the art can derive that it may be beneficial to configure and adjust the bypass valve spring 35 in order to adapt the bypass valve switching to other system parameters of any hydraulic system equipped with the hydraulic valve block 100, according to the invention.

[0038] Furthermore, person skilled in the relevant art will derive that the switching valve 50 can be omitted if the hydraulic valve block 100 and system is operated in only one direction, and without operational mode changing, in other words the high pressure line 4 is never interchanged with the low pressure line 6. A skilled person easily sees that the same working principle as described above is fulfilled by the pilot valve 10 and the bypass valve 30 when the operational mode of a hydraulic system is changed, for instance, from motoring mode to pumping mode (when the high pressure line 4 is interchanged with the low pressure line 6). In this case, the switching valve 50 is switched so that the pressure from the high pressure port 2 is guided to the inlet 11, and hydraulic pressure from the low pressure port 3 is guided onto the second front face 17 of pilot valve spool 14.

[0039] In summary, a hydraulic system equipped with the inventive hydraulic valve block offers the user a reliable, robust and cost-effective system which ensures that, when a minimum low pressure level in a hydraulic system is undercut, a bypass is opened in an optimum manner such that a low pressure compensation is enabled in order to avoid damage to the hydraulic system. In practice, this automatic regulation/controlling is done continuously as shock loads frequently occur to hydraulic systems. In order to avoid frequencies/pressure oscillations within the hydraulic system when shock loads occur, an orifice 27 can be implemented to control line 25 in order to dampen these pressure oscillations.

[0040] From above discussion and the accompanying Figures and claims it will be apparent that the hydraulic valve block 100 according to the invention offers many advantages over the prior art. It will be appreciated further by a person skilled in the art that other various modifications could be made to the device without parting from the spirit and scope of this invention. All such modifications and changes fall within the scope of the claims and are intended to be covered thereby. It should be further understood that the examples and embodiments described herein are for illustrative purposes only, and that various modifications or changes in the light thereof, which will be suggested by a person skilled in the art, are included in the spirit and purview of this application.