Hydraulic System and Pressure Limiting Valve

Abstract

A hydraulic system has at least one consumer and at least one hydraulic pump. A pressure limiting valve for limiting the maximum system pressure is connected with the at least one hydraulic pump, and the pressure limiting valve is pilot-controlled for switching a bypass. The invention also concerns a pressure limiting valve for limiting the system pressure inside such a hydraulic system.

Description

[0001] This application claims priority to German Patent Application 10 2012 011 062.6, filed Jun. 4, 2012, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a hydraulic system with at least one consumer and at least one hydraulic pump, wherein a pressure limiting valve for limiting the maximum system pressure is connected with the at least one hydraulic pump.

[0003] Hydraulic circuits and the hydraulic components thereof are designed for a definable maximum system pressure. Exceeding the maximum system pressure possibly leads to damages of the circuit and the components used. For this reason, pressure limiting valves are provided, which pass the delivery flow of the hydraulic pump through to the hydraulic tank, if the existing system pressure exceeds a maximum limit pressure value.

[0004] As an additional safety measure it often is requested that a bypass shutdown is realized via a further valve. By actuating the provided valve, the delivery flow of the hydraulic pump is recirculated directly to the hydraulic tank, the system pressure then will drop.

[0005] In addition, depending on the actuation of the individual hydraulic consumers within the hydraulic circuit, a further pressure build-up or pressure control valve is used. The required system pressure chiefly is determined by the delivery volume of the pump and the valve arrangement for actuating the hydraulic consumers. In addition, the system pressure can selectively be influenced via the used pressure build-up or pressure control valve, in order to reach and hold the desired system pressure level.

[0006] When the consumers are actuated via a 4/3-way technology, i.e. via individual 4/3-way valves (main control valves), the pressure control or build-up valve is arranged after the hydraulic pump and before the main control valves.

[0007] In a 6/3-way technology, the system pressure is looped through the downstream consumers and conveyed back to the hydraulic tank. In this case, it is required to arrange the pressure control or build-up valve not after the hydraulic pump, but after the consumer arrangement.

[0008] The pressure build-up or control valves used mostly are designed as proportional gate-type 2/2-way valves.

[0009] A disadvantage of the aforementioned known design, however, is that there must always be used separate valves for the maximum pressure limitation, the pressure build-up and the bypass function. This increases the complexity of the switching construction as well as the necessary installation space and the manufacturing costs incurred.

SUMMARY OF THE INVENTION

[0010] One object of the present invention is to indicate an improved hydraulic system and pressure limiting valve, which is able to overcome the disadvantages described above.

[0011] This object is solved by a hydraulic system according to the features included in the independent claims below. Further advantageous embodiments of the hydraulic system form the subject-matter of the dependent claims.

[0012] According to the invention, there is proposed a hydraulic system with at least one consumer and at least one hydraulic pump, wherein a pressure limiting valve for limiting the maximum system pressure is connected with the at least one hydraulic pump. The system pressure in particular is applied to the pressure limiting valve at the input side. When the applied system pressure exceeds a certain limit pressure level, the pressure limiting valve will switch through, in order to decrease the applied system pressure.

[0013] Furthermore, the pressure limiting valve is pilot-controlled according to the invention. The pilot control serves for realizing a bypass function within the hydraulic system. In particular, by actuation or non-actuation of the pilot control, the pressure limiting valve is switched for passage, in order to provide for a bypass or parallel shut-down path to the system pressure line. In this case, the system pressure is discharged directly from the hydraulic pump to a hydraulic tank. Expediently, it is provided that the pressure limiting valve is open in its neutral position and can be closed via the pilot control.

[0014] According to an alternative aspect of the invention, there is proposed a hydraulic system with at least one consumer and at least one hydraulic pump. The system comprises a pressure limiting valve connected with at least one hydraulic pump for limiting the maximum system pressure. The system pressure in particular is applied to the pressure limiting valve at the input side. When the applied system pressure exceeds a certain limit pressure level, the pressure limiting valve will switch through, in order to decrease the applied system pressure.

[0015] Furthermore, the pressure limiting valve is pilot-controlled according to the invention. Via the pilot control, a pressure build-up or pressure control function additionally can be realized by a single valve beside the maximum pressure limitation. Expediently, it is provided that the pressure limiting valve is open in its neutral position and can at least partly be closed via the pilot control, in order to be able to adjust the input pressure or system pressure to a certain pressure level. The construction according to the invention provides for the combination of at least two valves or valve functions inside a single valve.

[0016] It is particularly advantageous when beside the bypass function the function of a pressure control or pressure build-up valve additionally is realized via the pilot control of the pressure limiting valve. In this case, three valve functions can be performed by a single valve with a 4/3-way valve actuation of the hydraulic consumers in the hydraulic system. This allows an improved pressure build-up functionality as compared to the conventional pressure build-up valves. In addition, the integration of the various valve functions inside a valve permits a substantial reduction of the required number of hydraulic components. The production or manufacturing costs related therewith can be minimized. The same applies for the required installation space of the hydraulic circuit.

[0017] In a particularly advantageous embodiment, the pressure limiting valve is designed as a proportional pressure limiting valve. This allows a proportional control of the system pressure to be limited between zero and the maximum system pressure.

[0018] The realization of the pilot control in principle is arbitrary. What is conceivable is an electric and/or electro-hydraulic design of the pilot control.

[0019] Alternatively, the pilot control also can be effected hydraulically or pneumatically.

[0020] The embodiment of the pressure limiting valve also is to be chosen arbitrarily in principle. A cartridge or gate design represents a suitable construction.

[0021] A possible configuration of the hydraulic system or the pressure limiting valve provides that the pilot control acts against a spring restoring force of the valve. When the pressure exerted by the pilot control exceeds the spring restoring force, the valve will switch.

[0022] It is likewise conceivable that the pilot control acts against the system pressure of the pressure limiting valve. It is particularly preferred when the pilot control acts against a spring restoring force and the system pressure. Hence, the maximum limit pressure can be adjusted via the force of the pilot control.

[0023] A possible embodiment consists in that the pressure limiting valve is open in the neutral position. The open valve position is held by the spring force. Upon actuation of the pilot control, the same acts against the restoring force of the spring. The variation of the pilot control provides for a partial or complete closure of the pressure limiting valve. The bypass function can be achieved for example by switching off the pilot control. In addition, the pilot control determines the target system pressure to be controlled as well as the maximum system pressure.

[0024] The invention furthermore relates to a pressure limiting valve for limiting the system pressure inside a hydraulic system. According to the invention it is provided that the pressure limiting valve is pilot-controlled and the pilot control acts against a spring restoring force and/or the initially applied system pressure. The actuation or non-actuation of the pilot control leads to the switching of the pressure limiting valve. In addition, the desired system pressure level of a hydraulic system or the maximum system pressure can be adjusted via the control signal of the pilot control.

[0025] It is particularly advantageous when the pressure limiting valve is open in the neutral position, wherein the open valve position is held via the spring restoring force. A partial closure or a blocking position of the pressure limiting valve is achieved by varying the pilot control.

[0026] The pilot control can be carried out hydraulically and/or pneumatically. Alternatively, the pilot control can also be carried out electrically and/or electro-hydraulically. As a suitable construction of the pressure limiting valve, a cartridge or gate design should be mentioned.

[0027] It is particularly advantageous if the pilot control provides for a proportional control of the initially applied system pressure to be limited.

[0028] The construction as well as the properties and advantages of the pressure limiting valve according to the invention preferably correspond to those of the pressure limiting valve used inside the hydraulic system according to the invention, so that a repetitive description will be omitted at this point.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Further advantages and properties of the invention will be explained in detail with reference to the attached drawings, in which:

[0030] FIG. 1 shows a schematic representation of a hydraulic system known from the prior art,

[0031] FIG. 2 shows a schematic representation of the hydraulic system according to the invention in a first design variant,

[0032] FIG. 3 shows a hydraulic circuit diagram of a partial region of the hydraulic system according to the invention as shown in FIG. 2, and

[0033] FIG. 4 shows a further design variant of the hydraulic system according to the invention in a schematic representation.

DETAILED DESCRIPTION OF THE INVENTION

[0034] FIG. 1 shows a schematic representation of a hydraulic circuit according to the prior art. Via the hydraulic pump 1 three hydraulic consumers 2, 3, 4 are fed, which are controlled jointly or each separately via at least one 4/3-way valve as main control valve. The system pressure inside line 5 is controlled via the delivery volume of the pump 1 as well as the switching position of the non-illustrated directional valves. For safety reasons, a pressure limiting valve 6 is provided, which switches and enables the volume flow to the tank, as soon as the system pressure exceeds the maximum limit pressure.

[0035] The system pressure inside line 5 in addition is controlled via a pressure build-up valve 7. To achieve the desired target pressure inside line 5, the valve 7 partly closes the flow to the tank. The hydraulic circuit as shown in FIG. 1 uses separate valves 6, 7 for both functions, i.e. for the maximum pressure limitation and the pressure build-up. A possible valve arrangement for realizing a parallel shut-down path is not provided.

[0036] FIG. 2 now shows a schematic representation of the hydraulic circuit of the invention according to a first advantageous design variant. The system likewise comprises a hydraulic pump 1, which feeds a total of three hydraulic consumers 2, 3, 4. The individual consumers are connected according to the 4/3-way technology. Beside its actual function of the maximum pressure limitation, the pressure limiting valve 10 according to the invention also has a bypass function as well as the function of a pressure build-up and pressure control valve.

[0037] In detail, the valve 10 is designed as proportional pressure limiting valve and allows a proportional control of the system pressure to be limited inside line 5 between zero and the maximum system pressure. The valve 10 hence combines a proportional control of the system pressure to be limited, the function of the pressure build-up and a bypass function for realizing a parallel shut-down path by delivering the pump volume flow directly to the hydraulic tank.

[0038] The hydraulic circuit diagram of FIG. 3 illustrates the concrete construction of the proportional pressure limiting valve 10 according to the invention. As shown in FIG. 3, an individual consumer 2 is connected with the pump 1 via a 4/3-way valve 6.

[0039] The pressure limiting valve 10 remains in its neutral position due to the restoring force of the spring in the open position, so that hydraulic fluid can flow from the system pressure line 5 to the tank. The pressure limiting valve 10 is controlled directly via the input pressure. The system pressure of line 5 applied at the inlet acts in support of the restoring force of the spring.

[0040] According to the invention, there is furthermore provided a pilot control which acts against the spring force or the system pressure.

[0041] The illustrated drawing shows a hydraulic pilot control of the pressure limiting valve 10 via the hydraulic pressure p.sub.ctrl. However, an electric or electro-hydraulic pilot control also is conceivable just as well. The applied control pressure p.sub.ctrl determines the switching condition of the valve 10.

[0042] For the pressure build-up inside line 5 it is necessary that the control pressure p.sub.ctrl exceeds the restoring force of the spring and at least partly closes or completely blocks the valve 10. Subsequently, the desired pressure level inside the system pressure line 5 now can be varied via the control pressure p.sub.ctrl, in that the valve 10 is partly opened. The function of a pressure build-up or pressure control valve thereby is satisfied. Apart from this, the control pressure level p.sub.ctrl determines the maximum limit pressure at which the pressure limiting valve 10 should open for safety reasons. For this purpose it is required that the system pressure as well as the restoring force of the spring together exceed the control pressure p.sub.ctrl and open the valve 10.

[0043] For realizing the bypass function of the valve, the control pressure p.sub.ctrl simply is shut off during the operation. The spring restoring force opens the valve 10, the parallel shut-down path is activated via the valve 10 to the tank.

[0044] The construction of the pressure limiting valve 10 according to the invention is arbitrary in principle. Suitable design variants include a cartridge or gate design.

[0045] If one or more consumers 2, 3, 4 are to be actuated according to a 6/3-way technology, it is absolutely necessary that a pressure build-up valve is provided downstream of the consumers. A possible construction of such hydraulic circuit can be taken from the schematic representation of FIG. 4. The individual consumers 2, 3, 4 each are connected with the pump 1 via non-illustrated 6/3-way valves. It thereby is achieved that the system pressure line 5 is looped through the individual consumers 2, 3, 4 and for completion of the hydraulic circuit discharged into a tank. For the pressure build-up it is necessary to provide a suitable pressure build-up valve 20 downstream of the consumers 2, 3, 4.

[0046] According to the first design variant, the pressure limiting valve 10 according to the invention likewise is connected directly to the hydraulic pump 1. As compared to the first variant, however, the function of the pressure build-up is not performed by the valve 10, but the scope of functions is limited to the proportional control of the system pressure to be limited inside line 5 as well as the realization of a bypass function, in order to provide for a parallel shut-down path to the tank. The concrete construction of the hydraulic valve 10 corresponds to the one shown in FIG. 3.

[0047] The used pressure build-up valve 20 for example can be realized by a proportional gate-type 2/2-way valve.

[0048] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

Claims

1. A hydraulic system comprising: at least one consumer, at least one hydraulic pump, and a pressure limiting valve for limiting a maximum system pressure connected with the at least one hydraulic pump, wherein the pressure limiting valve is pilot-controlled for switching a bypass.

2. The hydraulic system according to claim 1, wherein pilot control of the pressure limiting valve provides for a proportional control of the system pressure to be limited.

3. The hydraulic system according to claim 1, wherein pilot control of the pressure limiting valve is effected electrically, electro-hydraulically, or electrically and electro-hydraulically.

4. The hydraulic system according to claim 1, wherein pilot control of the pressure limiting valve is effected hydraulically, pneumatically, or hydraulically and pneumatically.

5. The hydraulic system according to claim 1, wherein the pressure limiting valve has a cartridge design, a gate design, or a cartridge and gate design.

6. The hydraulic system according to claim 1, wherein pilot control of the pressure limiting valve acts against at least one of a spring restoring force and a system pressure.

7. The hydraulic system according to claim 1, wherein the pressure limiting valve does not allow an increase of the system pressure without actuation.

8. A hydraulic system comprising: at least one consumer, at least one hydraulic pump, and a pressure limiting valve for limiting a maximum system pressure connected with the at least one hydraulic pump, wherein the pressure limiting valve is pilot-controlled in order to additionally carry out a pressure build-up or pressure control function as well as limiting the maximum system pressure.

9. The hydraulic system according to claim 8, wherein the pressure limiting valve is pilot-controlled for switching a bypass.

10. The hydraulic system according to claim 8, wherein pilot control of the pressure limiting valve provides for a proportional control of the system pressure to be limited.

11. The hydraulic system according to claim 8, wherein pilot control of the pressure limiting valve is effected electrically, electro-hydraulically, or electrically and electro-hydraulically.

12. The hydraulic system according to claim 8, wherein pilot control of the pressure limiting valve is effected hydraulically, pneumatically, or hydraulically and pneumatically.

13. The hydraulic system according to claim 8, wherein the pressure limiting valve has a cartridge design, a gate design, or a cartridge and gate design.

14. The hydraulic system according to claim 8, wherein pilot control of the pressure limiting valve acts against at least one of a spring restoring force and a system pressure.

15. The hydraulic system according to claim 8, wherein the pressure limiting valve does not allow an increase of the system pressure without actuation.

16. A pressure limiting valve for limiting the system pressure inside a hydraulic system, wherein the pressure limiting valve is pilot-controlled and pilot control of the pressure limiting valve acts against at least one of a spring restoring force and an input pressure.