Valve block having a valve assembly

A valve block includes a plurality of control valve disks that form a first block part and a second block part. A supply pressure for the control valve disks of the first block part is limited by a common pressure-limiting valve. The common pressure-limiting valve is arranged such that a prevailing load pressure registered by the control valve disks does not exceed a specific value. The supply pressure for the control valve disks of the second block part is not limited.

This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2013 220 750.6, filed on Oct. 15, 2013 in Germany, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

The disclosure proceeds from a valve assembly and a valve block.

Such a hydraulic valve or control assembly is known in the prior art and comprises so-called “load-sensing” control valves having a control piston for directional and speed control. A metering orifice is formed in the control piston. Here a pressure compensator, which keeps the pressure gradient and therefore also the volumetric flow at the respective metering orifice constant, irrespective of the load, is assigned to a particular control valve. For this purpose the pressure is registered upstream and downstream of the metering orifice and signaled to the pressure compensator. Its piston is biased towards a usually open neutral position by a spring, which exerts an ideally constant force. In addition to the spring the load pressure registered downstream of the metering orifice acts in the opening direction of the piston of the pressure compensator. By contrast only the supply pressure registered upstream of the metering orifice and downstream of the pressure compensator acts in the closing direction of the piston of the pressure compensator.

The load pressure is applied by the load occurring at any given time and cannot be influenced by the control valve; the piston of the pressure compensator on the other hand reacts to load pressure changes and is displaced in the opening direction in the event of an increase in the load pressure or in the closing direction in the event of a fall in the load pressure

The supply pressure is regulated by the pressure compensator and is always high enough to ensure that the force acting in the closing direction due to the supply pressure is in equilibrium with the force of the spring acting in the opening direction and that of the load pressure. The force of the supply pressure thereby always exceeds the force of the load pressure by the constant amount of spring force, thereby resulting in an always constant pressure gradient and consequently a constant volumetric flow at the metering orifice.

The facility for limiting the supply pressure level in order to safeguard the mechanical equipment on the consumer side is also known. This is achieved by allowing a pressure-limiting valve, provided in a load-sensing line, to relay a distorted reading of the actual load pressure to the pressure compensator, in that at a set maximum pressure the pressure-limiting valve opens a connection to the tank, so that the load pressure signaled cannot exceed a specific level. In order to keep the outflow quantity and overall size of the pressure-limiting valve as small as possible, an orifice, through which only a small volumetric flow is able to flow to the tank, is usually arranged in the load-sensing line between the load pick-up and the pressure-limiting valve. The operating principle of this pressure limiter means that the volumetric flow control to the consumer connection of the control valve can be completely disabled. The volumetric flow set by the control piston is fully reduced, for example, if the consumer is being run in opposition to a high resistance, which would require a supply pressure in excess of the set maximum pressure. In this case the supply pressure in the consumer connection will exceed the value set on the pressure-limiting valve by no more than the spring force. Limiting the pressure through multiple pressure-limiting valves for multiple consumer connections is also known.

Such a solution is disclosed by the Rexroth data sheet RD 64276, issue August 2010. In this a valve disk, in which the pressure compensator and the pressure-limiting valve are also arranged, is provided for each control valve. Here the pressure-limiting valve is provided form one consumer. The use of a separate pressure-limiting valve for each of the various actuating devices of the consumer is also disclosed. Disadvantages with this solution are the large amount of space required and the mechanically elaborate design of the valve disk, which leads to high costs.

The Sauer Danvoss data sheet “Series PVG 32, Proportional Valves” proposes to arrange a pressure-reducing valve in a main oil flow. The pressure-reducing valve used for this purpose is of comparatively large design and is designed for a volumetric flow of 200 l/min, for example. A flow passes through the pressure-reducing valve even when no pressure reduction is to ensue, which leads to high pressure losses. In addition, the large overall space required is extremely disadvantageous.

The object of the disclosure, on the other hand, is to create a cost-effective, compact and energy-efficient valve assembly, which serves to limit a supply pressure for all or some hydraulic consumers. A further object of the disclosure is to create a valve block having such a valve assembly, which is of cost-effective and compact design.

SUMMARY

The object with regard to the valve assembly and with regard to the valve block is achieved according to the features of the disclosure.

Other advantageous developments of the disclosure form the subject matter of further dependent claims.

According to the disclosure a valve assembly is provided with a plurality of control valves. These each have a control piston which serves to control a direction and a speed of a consumer. A metering orifice is formed with the control piston. In addition, a pressure compensator or individual pressure compensator is provided, which is assigned to a particular control valve. A pressure registered upstream and downstream of the metering orifice of a particular control valve is signaled to this compensator. The pressure compensator serves to keep a pressure gradient at the metering orifice substantially constant irrespective of the load. For registering the pressure downstream of each metering orifice a load-sensing flow path is provided.

In addition, the valve assembly comprises a shuttle valve. This connects that load-sensing flow path of the control valves having the highest pressure at any given time to its outlet connection. The shuttle valve therefore has a fluid connection to the load-sensing flow paths in such a way that its outlet connection has a fluid connection to the load-sensing flow path having the highest pressure. For sensing the highest pressure of the load-sensing flow paths the outlet connection can be connected to the variable-capacity pump. A pressure-limiting valve (especially an adjustable one) is advantageously provided downstream of the outlet connection of the shuttle valve. This pressure-limiting valve serves to limit the highest pressure of the load-sensing flow paths at any given time.

This solution has the advantage that one common pressure-limiting valve is simply provided for a plurality of control valves, in order to limit the supply pressure. This saves overall space and reduces the outlay for mechanical devices, thereby reducing costs. With the solution according to the disclosure the inlet connection of the shuttle valve, to which the load-sensing flow path having the highest pressure is connected, is connected to the outlet connection, which advantageously means that the pressure at this outlet connection is limited by the pressure-limiting valve having a fluid connection to the outlet connection, so that the pressure at the inlet connection connected to the outlet connection, and therefore the pressure of the load-sensing flow path having the highest pressure, is also limited.

In a further development of the disclosure at least one further control valve is provided with a control piston as metering orifice and with a pressure compensator assigned to the control valve, the load-sensing flow path of which is connected to a first inlet connection of a further, second shuttle valve. A second inlet connection of the shuttle valve is then connected to an outlet connection of the first shuttle valve. In turn the outlet connection of the second shuttle valve can be connected to the variable-capacity pump for sensing the highest pressure. The pressure-limiting valve is therefore connected to the flow path between the first shuttle valve and the second shuttle valve. The pressure-limiting valve is therefore connected between the outlet connection of the first shuttle valve remote from the pump and the inlet connection of the adjacent, second shuttle valve closer to the pump. On the outlet side the pressure-limiting valve may be connected to the outlet port of the valve assembly. It is advantageous here to limit the supply pressure for hydraulic consumers which are connected to the control valves that are assigned to the first shuttle valve (remote from the pump). In the case of a consumer connected to the further control valve (to which the second shuttle valve, close to the pump, is assigned), on the other hand, the supply pressure is not limited via the pressure-limiting valve. The supply pressure of the consumers remote from the pump is therefore limited to a lower pressure than that of the consumer(s) closer to the pump.

The valve assembly according to the disclosure is preferably used for an agricultural tractor. A number of different mounted implements, which may be quite old, are generally used for a tractor. Such mounted implements often have a resistance to pressure of less than 200 bar. According to the disclosure such mounted implements may be used as consumers remote from the pump and having control valves which are assigned to the first shuttle valve (remote from the pump). Conventional, interchangeable mounted implements having a low maximum supply pressure are therefore intended as consumers remote from the pump. Consumers closer to the pump (steering, front bearings, other consumers fixedly arranged on the tractor, newly developed mounted implements) can then be used at a higher working pressure and can therefore be built correspondingly smaller for the same working forces. In particular, functions intrinsic to the tractor, such as steering, lifting gear or front lifting gear, can therefore be designed for considerably higher pressures, in order to overall space in order to save costs. Individual mounted implements, for example a separate front-end loader, might also be provided as consumers remote from the pump. This can then likewise be operated with a higher supply pressure. Owing to the higher supply pressure, such a front-end loader would then have comparatively smaller hydraulic cylinders, thereby increasing the overall visibility from the tractor and the view of the front-end loader. Besides the size, another advantage of systems having a higher pressure and smaller cylinders is the reduced losses in the lines, since smaller quantities of oil have to be transmitted for the same power output.

A respective shuttle valve is preferably provided for each control valve and therefore for each load-sensing flow path. In a further development these can be connected to one another and to the load-sensing flow paths in such a way that the shuttle valve (first shuttle valve)—to the outlet connection of which the pressure-limiting valve is connected—is provided downstream of the load-sensing flow paths of those control valves in which the supply pressure is to be limited.

The shuttle valves may therefore form a shuttle valve cascade.

A restrictor (drain relief) may advantageously be provided in a fluid connection parallel to the pressure-limiting valve. This restrictor then has a fluid connection to the flow path between the first and second shuttle valve and an outlet.

The pressure downstream of a particular metering orifice is preferably registered by way of a restrictor. A comparatively small volumetric flow thereby flows via the pressure-limiting valve, so that the latter can in turn be of relatively small design.

The pressure compensator advantageously comprises a piston arranged in a spool bore. This piston may be biased in its open, neutral position by a spring force of a spring. In addition to the spring force the pressure registered downstream of the metering orifice may act on its first end face in the opening direction of the piston. In opposition to this, the pressure registered upstream of the metering orifice and downstream of the pressure compensator can act on its second end face and hence in the closing direction. The piston, preferably with its first end face, defines a pressure chamber, in particular a closed chamber, in the spool bore. This chamber is connected to the load-sensing flow path by way of a first port section, proceeding from the first end face and extending approximately in a longitudinal direction or axially, and a second radially adjoining port section therein. The restrictor is formed in one of the port sections, preferably in the radial, second port section. The restrictor therefore fulfils a dual function. It ensures firstly that only a small fluid volumetric flow flows off to the outlet via the load-sensing flow path, and secondly that a movement of the piston of the pressure compensator is damped. The pressure chamber may be the spring chamber of the spring.

According to the disclosure a valve block has a valve assembly according to the disclosure. The valve block comprises a plurality of control valve disks. A control valve with the associated pressure compensator is then formed in each of these disks. An additional pressure-limiting valve disk may be provided for the pressure-limiting valve or it is simply arranged in one of the control valve disks. The valve assembly is extremely easy to expand through as valve block.

In a further development of the disclosure provision is made for a plurality of control valve disks in the valve block. The pressure-limiting valve disk can then be arranged as an intermediate plate between at least two control valve disks forming a first block part and at least one control valve disk forming a second block part. The highest pressure of the load-sensing flow paths of the first block part can then be limited by the pressure-limiting valve. The first block part is therefore a low-pressure block part and the send block part is a high-pressure block part. The block parts can be reduced or expanded simply by removing and adding control valve disk. In addition, the pressure-limiting valve disk can easily be shifted. One or more control valve disks can thereby be easily assigned to the first or the second block part.

The first block part is intended for a limited supply pressure (reduced working pressure) and is therefore intended, in particular, to serve for mounted implements on a tractor. The second block part on the other hand is to be used for a maximum possible supply pressure (maximum working pressure) and is therefore intended to serve for lifting gear functions on the tractor. The first block part is accordingly intended for operating consumers, the supply pressure of which will lie below the maximum possible system pressure. The second block part can then supply consumers with the full supply pressure.

The second block part or the pressure-limiting valve disk is preferably connected to a pump part. Here the pump part may comprise a variable-capacity pump having a pressure regulator. In addition, a further hydraulic pump may be provided in the pump part as control oil pump for the control oil supply of a hydraulic control of the control valves. Alternatively it is feasible for the system to be operated by a constant-capacity pump via a suitable input plate.

The first block part may, in particular, be connected on its side facing away from the pressure-limiting valve disk to an end piece.

In a further development of the disclosure a particular shuttle valve, which is connected by its first inlet connection to the load-sensing flow path of the control valve, is arranged in a particular control valve disk. A particular shuttle valve can then be connected by its second inlet connection to a first connection side of the control valve disk and by its outlet connection to a second connection side of the control valve disk (facing away from the first connection side). The outlet connection and the second inlet connection can therefore be connected together by adjacent shuttle valves of the control disks. The shuttle valves then simply form a shuttle valve cascade.

The pressure-limiting valve disk may comprise a passage extending between its connection sides, which affords a fluid connection between the outlet connection of the shuttle valve of the adjacent control valve disk of the first block part and the adjacent control valve disk of the second block or the pump part. The pressure-limiting valve is then connected to the passage.

The control valve disks can simply be of identical mechanical design.

In a further development of the disclosure the control valve disks and the pressure-limiting valve disk have a common inlet port, a common outlet port, a common control oil inlet port and a common control oil outlet port.

For connecting a consumer a particular control valve disk may in each case have two working connections, which are connected to the control valve via a feed port and a return port respectively.

DETAILED DESCRIPTION

According toFIG. 1the valve assembly1according to the disclosure is represented in the form of a valve block2. This has a plurality of control valve disks4,6,8,10and12and a pressure-limiting valve disk14. The control valve disks4to8here form a first block part16and the control valve disks10and12form a second block part18. A consumer can be connected to a particular control valve disk4to12via working connections A and B. For controlling a speed and direction of a particular consumer a particular control valve disk4to12comprises a control valve. InFIG. 1, only the control valve20of the control valve disk4is provided with a reference numeral for the sake of clarity.

Since the control valve disks4to12are of identical design, the construction of a particular control valve disk4to12is explained in more detail with reference to the control valve disk4. The working connection A of the control valve disk4is connected to the control valve20via a first port22and the working connection B is connected to the control valve20via a second port24. Here a particular port22or24may be used as feed or return port, depending on the direction in which the consumer is being moved. In addition, an inlet port26and an outlet port28are connected to the control valve20. A pressure compensator30is arranged in the inlet port26. The load pressure is registered via a load-sensing flow path in the form of a load-sensing port32connected to the control valve20. The load-sensing port32is then connected to a first inlet connection E1of a shuttle valve34on the one hand and to the pressure compensator30on the other. The load pressure then acts upon a piston of the pressure compensator30in the direction of its open, neutral position, in which the spring force of a valve spring also acts on the piston. In the closing direction the piston of the pressure compensator30is acted upon by the pressure which is registered between the pressure compensator30and the control valve20. The load pressure is registered by the load-sensing port32via a restrictor36.

A valve spool of the control valve20can be actuated by a pilot valve38. In its neutral position 0 shown inFIG. 1the valve spool of the control valve20is spring-centered by a spring assembly. In the neutral position 0 the load-sensing port32is connected to a control fluid outlet port, whilst the other ports22,24,26and28are separated from one another. If the valve spool, starting from its neutral position 0, is displaced towards shift positions a, the control fluid outlet port40is separated from the load-sensing port32. The load-sensing port32then has a fluid connection to the second port24downstream of a metering orifice42of the control valve20. The first port22has a fluid connection to the outlet port28. If the valve spool of the control valve20, starting from the neutral position 0, is displaced in the opposite direction from the shift positions a towards shift positions b, the control fluid outlet port40is likewise separated from load-sensing port32. The inlet port26is then further connected to the first port22and the load-sensing port32has a fluid connection to the first port22downstream of the metering orifice42. The second port24is connected to the outlet port28. If the valve spool of the control valve20, starting from the shift positions b, is displaced further away from its neutral position 0, this passes into safety positions c, in which the ports22and24have a common fluid connection to the outlet port28. The load-sensing port32and the control fluid outlet port40are here again connected to one another, corresponding to the neutral position 0.

The pilot valve38is supplied with control fluid via a control fluid inlet port44and can deliver control fluid via the control fluid outlet port40.

A second inlet connection E2of the shuttle valve34is connected to a connection side46of the control valve disk4. An outlet connection WA of the shuttle valve34, on the other hand, is connected to a connection side48of the control valve disk4facing away from the connection side46. A shuttle valve50of the adjacent control valve disk6is provided in the fluid flow direction away from the outlet connection WA of the shuttle valve34. The outlet connection WA of the shuttle valve34and a second inlet connection E2of the shuttle valve50therefore have a fluid connection. The same applies to a shuttle valve52of the present control valve disk8, which is arranged downstream of the shuttle valves34and50. Its second inlet connection E2is then in turn connected to the outlet connection WA of the shuttle valve50. A load-sensing port54of the control valve disk6is then connected to the first inlet connection E1of the shuttle valve50and a load-sensing port52is connected to the first inlet connection E1of the shuttle valve52of the control valve disk8The shuttle valves34,50and52therefore form a shuttle valve cascade, which is designed in such a way that to the outlet connection WA of the last shuttle valve52of the first block part16in the direction of flow is connected to that load-sensing port3254or56having the highest pressure. The inlet connection E2of the shuttle valve34of the control valve disk4of the first block part16furthest from the pump is connected to an outlet port60by way of a plate-shaped end piece58. The control valve disk8, which comprises the shuttle valve52of the first block part16situated furthest downstream (or the control valve disk8of the first block16closest to the pump) is arranged adjacent to the pressure-limiting valve disk14.

The pressure-limiting valve disk14comprises a pressure-limiting valve62. This is connected to a passage64, which in turn is connected to the outlet connection WA of the shuttle valve52situated furthest downstream or of the shuttle valve of the first block part16closest to the pump. On the outlet side the pressure-limiting valve62has a fluid connection to the outlet port60. The pressure downstream of the outlet connection WA of the shuttle valve52is therefore limited by the pressure-limiting valve62. Since this outlet connection WA is connected to the load-sensing port32,54or56having the highest pressure, the pressure-limiting valve62serves to limit the pressure in the load-sensing port32,54or56having the highest pressure. If the supply pressure for one of the consumers connected to the control valve disks4,6or8exceeds the maximum pressure allowed by the pressure-limiting valve62, this does not lead to a further rise in the pressure sensed by the load-sensing port32,54or56; instead the pressure signaled to the pressure compensator30of the control valve disk4,6or8does not exceed the maximum pressure predefined by the pressure-limiting valve62. A distorted reading of the actual load pressure is then relayed to the respective pressure compensator30. In contrast to the prior art explained at the outset, with the valve assembly1according to the disclosure it is no longer necessary to provide each control valve disk4to8with a separate pressure-limiting valve, a single pressure-limiting valve62instead being sufficient to completely disable the volumetric flow control of the control valves20of the control valve disks4,6or8.

The pressure-limiting valve disk14separates the first block part16from the second block art18, the control valve disk10being provided adjoining the pressure-limiting valve disk14. A second inlet connection E2of a control valve66of the control valve disk10is then connected to the passage64and therefore to the outlet connection WA of the shuttle valve52. An outlet connection WA of the shuttle valve66then in turn has a fluid connection to the second inlet connection E2of a shuttle valve68of the control valve disk12. According toFIG. 2its outlet connection WA is connected to a pressure regulator70of a variable-capacity pump72. Since the shuttle valves66and68of the control valve disks10and12(close to the pump) of the second block part18are situated downstream of the shuttle valve52, its load pressure registered by way of a load-sensing port74or76is not limited by the pressure-limiting valve62. In contrast to the control valve disks4to8, therefore, the level of a supply pressure for consumers connected to the control valve disks10or12is not limited.

Interchangeable mounted implements for a tractor, for example, which are to be operated at a maximum supply pressure less than a maximum system pressure, are intended as consumers which are connected to the first block part16. Consumers fixedly arranged on the tractor, for example, such as steering, front-end loaders or other lifting gear are intended as consumers for the second block part18. If multiple consumers are to be connected to the first block part16, further control valve disks are simply arranged in this. If fewer consumers are provided, control valve disks are simply removed. The same applies to the second block part18. It is also feasible to simply shift the pressure-limiting valve disk14and to provide this between the control valve disk4and6, or6and8, or10and12, for example. It is also feasible to arrange the pressure-limiting valve disk14downstream of all control valve disks4to12, there then being only one block part, in which the supply pressure for all consumers is then limited.

According toFIG. 1a disk-shaped intermediate piece78is connected to the control valve disk12, to which piece a pump part80, seeFIG. 2, is in turn connected, which is represented only schematically according toFIG. 2. The outlet port60continues in the pump part80and opens out in a tank82. The tank82here may be situated outside the pump part80. The variable-capacity pump72delivers fluid into a common inlet port84, which extends through all control valve disks4to12, through the pressure-limiting valve disk14and through the intermediate piece78. In addition, a load-sensing port86, which is connected to the pressure regulator70and which has a fluid connection to the outlet connection WA of the shuttle valve68of the control valve disk12situated furthest downstream (closest to the pump), is provided in the pump part80. In addition, the pump part80comprises a constant-capacity pump88, which is connected to the control fluid inlet port44. In addition, the control fluid outlet port40, which opens out in the tank82, passes through the pump part80.

FIG. 3represents an alternative embodiment of the valve assembly1inFIG. 1. In contrast toFIG. 1, a pressure-limiting valve disk90is provided, which has a restrictor92with a fluid connection parallel to the pressure-limiting valve62. The restrictor92is therefore arranged between the passage64and the outlet port60.

FIG. 4represents a consumer94in the form of a hydraulic cylinder, by way of example. This cylinder is embodied as a differential cylinder and has working connections A and B, which serve for connecting it to the working connections A and B of the control valve disks4to12.

A basic construction of the control valve disks is sufficiently known from the prior art and is explained, for example in the publication DE 10 2009 034 616 A1. For this reason, in the case of the control valve disk98set forth inFIG. 5the description is confined to what is essential for the disclosure, reference otherwise being made to the prior art.

According toFIG. 5a control valve disk96comprises a valve spool or control piston98having a metering orifice100. Visible is the inlet port84, which can be connected to the inlet port26by way of the pressure compensator140. In addition, the ports22and24can be seen, with the working connections A and B. The supply pressure is registered by way of load-sensing port102downstream of the metering orifice100. Here the restrictor36of the load-sensing port102is provided in a piston104of the pressure compensator140. The piston104is guided so that it slides in a spool bore106. The piston104, via a control edge,108serves to control the fluid connection between the inlet port84and the inlet port26. For this purpose the spring force of a spring110acts upon the piston104in the direction of its opening positions. This spring is arranged in a spring chamber112, which is connected to the load-sensing port102by way of the restrictor36. A first end face114of the piston104defines the spring chamber112, so that the fluid in the spring chamber112acts upon this face in the opening direction of the piston104. The fluid in the inlet port26in turn acts upon a second end face116facing away from the end face114in the closing direction of the piston104. For connecting the spring chamber112to the load-sensing port102, an axial blind bore, which forms a first port section, is incorporated in the piston104from the end face114. Adjoining this in the base area thereof is a radial bore120, which forms a second port section, in which the restrictor36is formed. The radial bore120opens out in a ring groove122, which is introduced into the spool bore106and is connected to the load-sensing port102. The spring chamber112therefore has a fluid connection to the load-sensing port102via the radial bore120and the blind bore118. The restrictor36furthermore affords a damping of the piston102in the direction of its closing positions. Extending from the spring chamber112is a load-sensing port124for the first inlet connection E1of a shuttle valve126. In addition, a pilot valve128and non-return valves130,132are provided inFIG. 5.

A valve block is disclosed, having a plurality of control valve disks, which form a first and a second block part. Here a supply pressure for the control valve disks of the first block part is limited by a common pressure-limiting valve. Here this valve is arranged in such a way that a prevailing load pressure registered by the control valve disks does not exceed a specific value. No provision is made, on the other hand, for limiting the supply pressure of the control valve disks of the second block part.

LIST OF REFERENCE NUMERALS