EP1828619A1

EP1828619A1 - Pressure cut off valve unit and hydraulic circuit provided therewith

Info

Publication number: EP1828619A1
Application number: EP05825642A
Authority: EP
Inventors: Markus GEPRÄGS; Bernhard Adler; Reinhold Schniederjan
Original assignee: Brueninghaus Hydromatik GmbH
Current assignee: Brueninghaus Hydromatik GmbH
Priority date: 2004-12-22
Filing date: 2005-12-13
Publication date: 2007-09-05
Also published as: US20080017259A1; JP2008524534A; DE102004061861B4; WO2006069625A1; DE102004061861A1

Abstract

The invention relates to a pressure cut off valve unit (24) comprising a shuttle valve (36), which has a first entry connection (39) and a second entry connection (40) that can be connected to the outlet according to the pressures prevailing at the entry connections (39, 40). The shuttle valve (36) has a shuttle valve closing element (45') that, in a first final position, connects the first entry connection (39) to the outlet, and that, in a second final position, connects the second entry connection (40) to the outlet. The shuttle valve closing element (45') can be stopped in a position located between both final positions and, in this stopped position, the first entry connection (39) is connected to the second entry connection (40).

Description

Pressure cut valve unit and hydraulic circuit provided therewith

The invention relates to a Druckabschneidungsventil- unit with a shuttle valve.

In hydraulic circuits, in which a consumer is driven by a hydraulic pump, it may happen that the set delivery volume of the pump exceeds the displacement of the consumer. Such a situation arises, for example, when the corresponding consumer is blocked, and therefore can no longer absorb pressure. The driven hydraulic pump still promotes further according to their set volume in the delivery-side working line, in which accordingly increases the pressure.

The set delivery volume of the hydraulic pump is dependent on a control pressure, so that a reduction of the control pressure leads to a reduction of the volume pumped by the pump. The result is a decrease in the delivery-side working line pressure. A valve unit, which is provided to limit the control pressure, is known for example from DE 195 12 143 Cl. The proposed there pressure cut valve unit has a pressure cut valve, which is arranged in a bore together with a shuttle valve.

If the pressure applied to a measuring surface of the pressure-reducing valve exceeds a certain, adjustable limit value, then the pressure-cut valve opens a connection between the control pressure line and a tank volume. The available control pressure is thus lowered with increasing opening to the level of the tank pressure and adjusted the hydraulic pump in the direction of a decreasing delivery volume. About the shuttle valve of the corresponding measuring surface of the pressure cut valve is in each case the larger in the supplied to both working lines prevailing pressures. For this purpose, the shuttle valve on a valve piston, which is permanently free to move.

The proposed pressure cutoff valve unit has the disadvantage that the pressure cutoff valve on the side of the measurement surface is permanently connected either to one or to the other working line. On the other hand, there is no possibility to create a connection between the two working pipes. Therefore, in the case of, for example, a towing operation of a vehicle in which pressure fluid is circulated in the circuit by a hydraulic motor, a connection must be made between the two working lines to enable the towing operation. Without such a connection, the hydromotor would be supported by the working pipes on the hydro pump and towing would not be possible.

It is the object of the invention to provide a Druckabschneidungs- valve unit and a hydraulic circuit, in which the two working lines are connected to each other via an integrated in the Druckabschneidungsventileinheit shuttle valve.

The object is achieved by a Druckabschneidungs- valve unit with the features of claim 1 or by the hydraulic circuit with the features of claim 10.

In order to be able to reduce the control pressure when excessive pressures occur in the working lines, the pressure-cut valve unit according to the invention has an exchangeable valve through which a measuring surface of the pressure-reducing valve is connected either to one or the other working line. On the pressure cut valve therefore acts in each case the higher of the prevailing in the two working pressures. In addition to this solely due to the pressure conditions set position of the shuttle valve is another, lockable position provided. In one, such locked position, which is located between the two end positions, the two input ports of the shuttle valve are interconnected. Thus, a hydraulic short circuit of the hydraulic circuit is possible via the shuttle valve of the pressure cut valve unit.

In the case already described above, that due to a defect, for. As a prime mover, the vehicle must be towed with the drive motor, now the pumped by the hydraulic motor in the circuit pressure fluid without having to flow through the hydraulic pump to be pumped in a circle.

In the dependent claims advantageous developments of the invention Druckabschneidungsventileinheit are executed.

The invention is illustrated in simplified form in the drawing and will be explained in detail with reference to the following description. Show it:

1 shows a hydraulic circuit with a Druckabschneidungsventil- unit according to the invention;

FIG. 2 shows an embodiment of a structural design of a pressure-reducing valve unit according to the invention; FIG.

Fig. 3 is an enlarged view in the detail III of Figure 2 in an unlocked position. and

Fig. 4 is an enlarged view in the detail IV of Fig. 2 in a locked position. Before discussing a structurally executed example of a pressure cutoff valve unit according to the invention, an example of a hydraulic circuit according to the invention will first be explained. In a hydraulic circuit 1 of FIG. 1, a hydraulic pump 2 is connected to a hydraulic motor 3. The hydraulic pump 2 is designed to be adjustable and connected to the hydraulic motor 3 via a first working line 4 and a second working line 5. The hydraulic pump 2 forms with the first working line 4, the second working line 5 and the hydraulic motor 3 connected thereto from a closed hydraulic circuit. In the illustrated embodiment, the hydraulic pump 2 and the hydraulic motor 3 are preferably designed as hydrostatic axial piston machines. The hydraulic pump 2 is adjustable and provided for conveying pressure medium in two directions. In contrast, the hydraulic motor 3 is permanently set in its displacement as so-called. Constant motor.

The hydraulic circuit 1 is provided, for example, for a vehicle drive of a mobile work machine. For this purpose, the hydraulic pump 2 is connected via a drive shaft 6 with a drive motor, not shown. The drive motor, not shown, is usually a diesel engine of the mobile implement. The hydraulic motor 3 is in turn connected via an output shaft 7 to the vehicle drive. In the simple illustrated embodiment, only one hydraulic motor 3 is provided which is connected via the output shaft 7 e.g. can be connected to a downstream mechanical transmission.

In addition to the hydraulic pump 2 operating in the closed hydraulic circuit 1, a feed pump 8 is also provided, connected to the drive shaft 6. The feed pump 8 is provided for conveying pressure medium in only one direction. The feed pump 8 sucks via a suction line 9 from a tank volume 10 pressure medium and conveys it into a feed line eleventh

During start-up of the hydraulic circuit 1, the working lines 4 and 5 are largely depressurized. For feeding pressure medium into the system, the feed line 11 is connected to a connecting line 13. The connecting line 13 in turn connects the first working line 4 with the second working line 5. In the connecting line 13, a first feed valve unit 14 is disposed between the mouth of the feed line 11 in the connecting line 13 and the first working line 4. Accordingly, between the mouth of the feed line 11 in the connecting line 13 and the second working line 5, a second feed valve unit

15 arranged.

Since the first supply valve unit 14 and the second supply valve unit 15 are similar in construction, only the first supply valve unit 14 will be described below in detail. The first supply valve unit 14 includes a pressure relief valve 16, which is held by a spring 17 in a closed position. Contrary to the force of the spring 17 acts on the pressure limiting valve 16 of the pressure prevailing in the first working line 4. If this pressure in the working line 4 exceeds the threshold value defined by the preferably adjustable spring 17, then the pressure-limiting valve 16 releases a through-flow connection in the connecting line 13.

In addition to the pressure relief valve 16, the first feed valve unit 14 has a check valve 18. The check valve 18 is formed in a bypass line 19 and opens in the direction of the first working line 4. Bypassing the pressure relief valve

16 can therefore, as long as the pressure in the feed line 11 is higher than in the first working line 4, over the Check valve 18 and the bypass line 19 pressure medium are conveyed into the first working line 4.

At the same time, via the first feed valve unit 14 or the second feed valve unit 15, the first working line 4 and the second working line 5 are counteracted by a critical pressure rise in the working chamber. lines 4 and 5 protected. In this case, opens the respective pressure relief valve of the first and second feed valve unit 14 and 15 and relaxes the critical pressure of the respective working line 4 and 5 in the connecting line thirteenth

To secure the feed system against excessive pressures, the connecting line 13 is connected to a feed pressure limiting valve 20. If the pressure prevailing in the connecting line 13 exceeds a limit value that can be set via the feed pressure limiting valve 20, the feed pressure limiting valve 20 opens and relaxes the connecting line 13 into the tank volume 10. At the same time, the maximum feed pressure, which is generated by the feed pump 8, is limited via the feed pressure limiting valve 20 , Since the feed pump 8 is designed as a constant pump, the amount of liquid delivered by the feed pump 8 increases with the speed of the drive motor, not shown. By means of the feed pressure limiting valve 20 is kept in the feed system, of which only the feed line 11 is shown in FIG. 1, at a constant level.

For adjusting the conveying direction and the delivery volume of the hydraulic pump 2, an adjusting device 21 is provided. The adjusting device 21 comprises an actuating piston 22 whose position is transmitted via a linkage 23 to the adjusting device of the hydraulic pump 2. The Position of the linkage 23 acts via a coupling rod 24 back to a control valve 25th

The adjusting piston 22 of the adjusting device 21 is arranged in a cylinder. Depending on the forces acting on the two sides of the adjusting piston 22, the adjusting piston 22 moves in FIG. 1 either to the right or to the left. For this purpose, the control piston 22 is acted upon via the control valve 25 from a control pressure line 26 with a control pressure. At the same time, the opposite surface of the actuating piston 22 is acted upon by a lower pressure by the pressure medium acting there is discharged via a flash line 29 into the tank volume 10. For this purpose, the adjusting piston 22 divides the cylinder of the adjusting device 21 into a first actuating pressure chamber 30 and a second actuating pressure chamber 31.

In a first end position of the control valve 25, the first control pressure chamber 30 is connected to the control pressure line 26. At the same time, the second control pressure chamber 31 is connected via the expansion line 29 to the tank volume 10. Due to the different pressure conditions of the adjusting piston 22 is moved in Fig. 1 to the right. The adjusting movement is fed back via the coupling rod 24 to the control valve 25, which then counteracts the adjusting movement. In the example described, therefore, the control valve 25 is adjusted in the direction of its second end position, in which the first control pressure chamber 30 is increasingly connected to the tank volume 10, whereas the second control pressure chamber 31 is increasingly connected to the control pressure line 26. Depending on the level of the control pressure thus sets a state of equilibrium, with which the hydraulic pump 2 can be operated in any position.

The maximum pressure in the control pressure line 26, the feed pressure can be used, in the feed line 11th is applied and which is supplied via a feed branch line 33 and a pressure cut valve 35 of the control pressure line 26. To actuate the control valve 25, the control valve 25 is acted upon by two electromagnets in the direction of its first or second end position with a force. If there is no signal at the two electromagnets, the control valve 25 is brought back into its neutral position by two centering springs, in which all four connections of the control valve 25 are connected to one another in a throttled manner.

If there is a blockage or severe deceleration of the hydraulic motor 3, a strong increase in the delivery-side working line 4 or 5 is the result. In such a case, regardless of the control signals applied to the electromagnet, an adjustment of the hydraulic pump 2 in the direction of minimum delivery volume must be possible. For this purpose, a pressure cutoff valve unit 34 is provided in the hydraulic circuit 1.

The pressure cutoff valve unit 34 comprises the pressure cutoff valve 35 and a shuttle valve 36. The shuttle valve 36 is connected to the first work line 4 and the second work line 5 via a first input line 37 and a second input line 38, respectively. The first input line 37 opens at the shuttle valve 36 at a first input terminal 39. Accordingly, the second input line 38 opens at a second input port 40 of the shuttle valve 36.

Depending on the pressure conditions in the first working line 4 and the second working line 5, the respective higher pressure is supplied to an output 41 of the shuttle valve 36. The output 41 is connected via an output line 42 to a measuring surface 43 of the Druckabschneidungsventils 35. The pressure acting on the measurement surface 43 exerts on the pressure cut valve 35 a hydraulic force which counteracts a pressure cut valve spring 44. The pressure cut valve spring 44 acts on the pressure cut valve 35 in the direction of its rest position in which the control pressure line 26 is connected to the feed line 11. Thus, an opening pressure of the pressure cut valve 35 can be adjusted via the pressure cut valve spring 44, which is preferably designed to be adjustable. Thus, if the pressure in one of the two working lines 4 or 5 exceeds the threshold value set in this way, the pressure cutoff valve 35 opens and releases a flow-through connection from the control pressure line 26 to the tank volume 10.

When critically high pressures occur in the first working line 4 or the second working line 5, this critical pressure is thus supplied to the pressure cut-off valve 35 by moving a shuttle valve closing element 45 in the shuttle valve 36. The control pressure line 26 is expanded via the pressure cutoff valve unit 34. Accordingly, in the first or second control pressure chamber 30 or 31 connected to the control pressure line 26, the control pressure acting on the control piston 22 decreases. By means of two centering springs arranged in the first control pressure chamber 30 and the second control pressure chamber 31, the control piston 22 is moved counter to its original deflection and thus reduces the delivery volume of the hydraulic pump 2.

In Fig. 1, the shuttle valve closing member 45 is shown in a middle position. In this middle position, on the one hand, a through-flow connection is established between the first input connection 39 and the second input connection 40, but, on the other hand, also a connection of the two input connections 39 and 40 to the output 41. If the hydraulic motor 3, which is designed, for example, as a constant-velocity motor, becomes passive rotated, so he promoted pressure medium in the short-circuited hydraulic circuit is promoted. The pressure medium does not have to be pumped through the hydraulic pump 2 and a vehicle can be towed easily. An example of a structural design of the pressure-cut valve unit 34 according to the invention is shown in FIG. The pressure cut valve unit 34 is shown in the axial arrangement of the pressure cut valve 35 with the shuttle valve 36. For this purpose, a stepped bore 51 is formed in a valve carrier 52. In the bore 51 a valve sleeve 50 is inserted. The valve sleeve 50 is in turn provided with an axial recess in which a Druckabschneidungsventilkolben 53 is arranged longitudinally displaceable.

Furthermore, in the valve sleeve 50 Steuerdruckeingangs- openings 55 and first control pressure outlet openings 56 are formed. When inserted valve sleeve 50 connect the control pressure input ports 55, the axial recess of the valve sleeve 50 with the feed branch 33. The first control pressure outlet openings 56 connect the axial recess of the valve sleeve 50 with the control pressure line 26. The control pressure line 26 and the feed branch 33 are in the illustrated embodiment as drilled channels formed in the valve carrier 52.

The Druckabschneidungsventilkolben 53 also has a circumferential recess 54. In the illustrated in FIG. 2, the lower end position of the Druckabschneidungsventil- piston 53 via the trained between the circumferential recess 54 and the valve sleeve 50 distance a flow-through connection between the control pressure input ports 55 and the first control pressure output ports 56 are prepared. In the illustrated rest position of the Druckabschneidungsventils 35 so that the feed branch line 33 is connected to the control pressure line 26.

At the lower end of the pressure-reducing valve piston 53 in FIG. 2, a radially reduced section 57 is formed. Between the radially reduced Section 57 and the valve sleeve 50 thus creates a further space which communicates via TankanschlussÖffnungen 58 with a tank connection channel 60 in connection. When the pressure cut valve piston 53 is moved out of the rest position shown in FIG. 2, the radially reduced portion 57 of the pressure cut valve piston 53 releases second pilot pressure output ports 59, so that the tank port passage 60 is connected to the pilot pressure passage 26. At the same time, the first control pressure outlet openings 56 are closed by the non-radially reduced portion of the pressure cutoff valve piston 53. Thus, the control pressure line 26 is relaxed in the direction of the tank volume via the tank connection channel 60.

At the end remote from the radially reduced portion 57 of the Druckabschneidungsventilkolbens 53 sits a first spring bearing 61 on the Druckabschneidungsventil- piston 53. An identical second spring bearing is arranged in the opposite direction and between the first spring bearing 61 and the second spring bearing 62, the Druckabschneidungsventilfeder 44 is arranged. The axial recess of the valve sleeve 50 is radially expanded in the region exposed to the outside of the valve carrier 52, so that this extended region together with a corresponding recess of a screw-in closure 64 forms a spring chamber 63. The screw-in closure 64 bears against the end face of the valve sleeve 50 and fixes it in the corresponding section of the bore 51.

Through a passage opening 65 which is formed in the screw-in closure 64, an abutment is brought into abutment with the second spring bearing 62. The counter bearing is z. B. designed as a threaded pin and adjustable in its axial position, so that the spring preload of Druckabschneidungsventilfeder 44 can be adjusted freely. Thus, by adjusting the bias of the pressure cut valve spring 44, the opening pressure of the pressure cut valve 35 can be adjusted. In order to bring the pressure-reducing valve piston 53 out of the position shown in FIG. 2 into the position in which the control pressure line 26 is expanded into the tank connection channel 60, a volumetric flask 67 is provided.

The measuring piston 67 is formed in the embodiment substantially mushroom-shaped, wherein on the head of the measuring piston 67, the end face of the radially reduced portion 57 of the Druckabschneidungsventilkolbens 53 rests. The pressure cut valve piston 53 is held in contact with the measuring piston 67 by the force of the pressure cut valve spring 44. The mushroom-shaped volumetric flask 67 penetrates in a direction facing away from the Druckabschneidungsventilkolben 53 a measuring piston receiving bore 68. The volumetric piston receiving bore 68 is formed in the valve sleeve 50 in the axial direction in extension to the axial recess. At the front of the measuring piston 67 projecting from the measuring piston receiving bore 68, a measuring surface 69 is formed. This measuring surface 69 is acted upon against the force of the Druckabschneidungsventilfeder 44 with a hydraulic force. If the hydraulic force acting there exceeds the counteracting force of the pressure cut valve spring 44, then the pressure cut valve piston 53 is brought from the rest position shown in FIG. 2 into the already described active position, in which the tank connection channel 60 is connected to the control pressure line 26.

As has already been described in the explanation of FIG. 1, in each case the higher of the pressures prevailing in the working lines 4 and 5 is supplied to the measuring surface 69 via a shuttle valve 36.

For this purpose, the bore 51 is inserted so deeply into the valve carrier 52 that in the direction of the closed end of the Bore 51, the shuttle valve closing element 45 is used. The shuttle valve closing element 45 is formed in the illustrated embodiment as a valve piston 45 '. In the region of the bore 51, which adjoins directly to the valve sleeve 50, the first EingangsIeitung 37 opens. The mouth of the first input line 37 into the bore 51 corresponds to the first input 39 in FIG. 1.

In the direction towards the closed end of the bore 51, the second input line 38 also discharges into the bore 51. The corresponding region of the orifice is the second input port 40.

The valve piston 45 'is shown in Fig. 2 in a position which it occupies when the pressure in the first input line 37 is higher than the pressure in the second input line 38. Due to the axial position of the valve piston 45' shown there is the first Input line 37 via the first input 39 connected to a first pressure chamber 73. The first pressure chamber 73 is introduced into the valve sleeve 50 as a region extended radially relative to the measuring piston receiving bore 68 and simultaneously forms the outlet 41.

At the opposite end of the shuttle valve closing element 45, however, the valve piston 45 'sits on a sealing element 72. The valve piston 45 'has a guide section 75, with which the valve piston 45' is guided in the bore 51 in the region between the first input line 37 and the second input line 38. The diameter of the guide portion 75 corresponds to the diameter of the bore 51 in this area, so that in the region of the guide portion 75 of the valve piston 45 'cooperating sealingly with the bore 51. As a valve piston 45 'formed shuttle valve closing element 45 has as a connecting channel of the formed on both sides of the valve piston 45' volumes an axial bore 76, extending from a Front side of the shuttle valve closing element 45 extends to the other end side. Thus, in the illustrated position, the first input 39 is connected to a second pressure chamber 74, which is formed at the closed end of the bore 51. However, this second pressure chamber 74 is not connected to the second input 40 because of the installation of the shuttle valve closing element 45 on the sealing element 72.

In the illustrated position of the shuttle valve 36, therefore, the measuring surface 69 is acted upon exclusively with the pressure of the first working line 4, which is supplied to the first pressure chamber 73 via the first input line 37.

In the region of the guide section 75, a circumferential groove 71 is introduced into the valve piston 45 '. The circumferential groove 71 reduces the radial dimensions of the valve piston 45 'so that a threaded pin 70 can engage as a locking element in the circumferential groove 71. The threaded pin 70 is screwed into a threaded hole 77 which is located between the first input port 37 and the second input port 38 in the valve carrier 52. The threaded pin 70 is sharpened on its side directed in the direction of the shuttle valve closing element 45, so that when screwing in the threaded pin 70, the axially displaceable valve piston 45 'of the shuttle valve 36 is displaced out of its position shown in FIG. The threaded hole is sealed to prevent contamination and to prevent leakage of leakage oil by a suitable sealing closure, such as a seal-lock nut.

The width of the circumferential groove 71 in the axial direction of the valve piston 45 'corresponds at most approximately to the diameter of the threaded pin 70. Thus, when the threaded pin 70 is screwed in fully, the shuttle valve closing Lock element 45 in a precisely defined middle position.

In the enlarged view it can be seen that the valve piston 45 'has a first end 78 and a second end 79, which reduces in each case in their radial dimension relative to the guide portion 75 are. At the transition from the end faces to the first end 78 and the second end 79, in each case one phase is formed on the valve piston 45 '. Through this phase, a first sealing surface 80 and a second sealing surface 81 at the two ends of the valve piston 45 'is formed. In the position shown in FIG. 2, the second sealing surface 81 of the valve piston 45 'sealingly cooperates with a peripheral edge of the sealing element 72 and thus separates the second pressure chamber 74 from the second input port 40.

If, on the other hand, the valve piston 45 'is in its opposite end position, then the first sealing surface 80 seals against a corresponding edge of the valve sleeve 50 delimiting the first pressure chamber 73. In this case, the second sealing surface 81 lifts off from the sealing element 72, so that the second input port 40 is connected to the first pressure chamber 73 via the axial bore 76 of the valve piston 45 '. Thus, the hydraulic force acts on the measuring surface 69 of the measuring piston 67 due to the prevailing pressure in the second working line 5, which is forwarded via the axial bore 76 into the first pressure chamber 73. During the transition from the first end 78 into the guide section 75 and from the second end 79 into the guide section 75, a first surface 82 and a second surface 83 are formed.

The first surface 82 is acted upon by the pressure of the first input line 37, regardless of the position of the valve piston 45 '. Accordingly, the second surface 83 also acted upon independently of the position of the valve piston 45 'with the pressure of the second input line 38. On the other hand, because of the first and second pressure chambers 73 and 74 which are connected to one another via the axial bore 76, the remaining end face of the shuttle valve closing element 45 is in each case subjected to the pressure which also acts on the measuring surface 69. With a pressure change in the working lines and thus also in the first input line 37 and in the second input line 38, the valve piston 45 'is therefore displaced into the opposite end position solely on account of the changing pressure gradient.

As has already been explained in detail with reference to FIG. 2, the shuttle valve closing element 45 can also be brought into a specific, lockable position via a threaded pin 70. This lockable position is located between the two possible end positions of the alternating valve closing element 45. Thus, on the one hand, the first sealing surface 80 and on the other hand, the second sealing surface 81 is lifted from its respective sealing seat. The first pressure chamber 73 and the second pressure chamber 74 are thus connected to one another via the axial bore 76, the first pressure chamber 73 also communicating with the first input line 37 and the second pressure chamber 74 with the second input line 38. As a result of the locked shuttle valve closing element 45, the two input lines 37 and 38 and therefore also the two working lines 4 and 5 are thus short-circuited.

In order to bring the shuttle valve closing element 45 in this locked position, a circumferential groove 71 is formed in the manner already described in the region of the guide portion 45. During the transition of the circumferential groove 71 into the guide section 75, a first chamfer 84 and a second chamfer 85 are respectively formed on the valve piston 45 '. By means of the first chamfer 84 and the second chamfer 85, the forces required are reduced are to screw by screwing the threaded pin 70, the shuttle valve closing element 45 axially. The first chamfer 84 and the second chamfer 85 each form a sliding surface, which can be moved without great force along the lateral surface of the sharpened threaded pin 70.

Fig. 4 shows the shuttle valve closing member 45 in the achieved by screwing the threaded pin 70 locked position. It can be seen that the width of the circumferential groove 71 is approximately sized so that it is at most equal to the diameter of the threaded pin 70. Thus, with fully screwed threaded pin 70, the axial position of the shuttle valve closing member 45 is determined exactly. In FIG. 4, it can be clearly seen that both the first sealing surface 80 and the second sealing surface 81 are each lifted from their seat on the edge of the valve sleeve 50 or the edge of the sealing element 72. Thus, in the manner already described, a connection is established between the first input line 37 and the second input line 38.

The free flow cross sections between the first sealing surface 80 and the second sealing surface 81 and their corresponding sealing seats must be chosen so that the flow occurring when towing the vehicle can pass virtually unhindered.

On the other hand, it is also possible by forming a targeted throttling in this area a completely free

To prevent roles of the vehicle purposefully. Such

Throttling, for example, by dimensioning the axial bore 76 as a throttle point of the

Shuttle valve closing element 45 can be adjusted. If throttling does not take place, then the diameter must be selected to be correspondingly large.

The arrangement with an inserted in the axial extension of the Druckabschnedungsventils shuttle valve is especially advantageous. In other structural conditions, however, a different arrangement may be required if, for example, the given construction depth is not sufficient. The shuttle valve can then also be arranged offset to the Druckabschneidungsventil. The connection of the output of the shuttle valve then takes place via a channel extending in the valve carrier.

Instead of the arrangement in the bore or a separate bore and the valve sleeve of the

Druckabschneidungsventils in the lower area be designed so that they

Can accommodate shuttle valve closing element. In this case, there is a simplified assembly, since the pressure cut valve unit can be pre-assembled and then used as a cartridge in the valve carrier.

The inventive design of a pressure cut valve unit allows in a simple way the hydraulic shorting of the circuit. This can z. B. the high pressure valves of a hydrostatic drive without bypass function are introduced.

The invention is not limited to the illustrated embodiments. All described elements can be combined with each other.

Claims

claims

A pressure cut valve assembly comprising a shuttle valve (36) having a first input port (39) and a second input port (40) connectable to an output (41) in response to pressures prevailing at the input ports (39, 40), wherein the shuttle valve (36) has a shuttle valve closing element (45, 45 ') which connects the first input port (39) to the output (41) in a first end position and which, in a second end position, connects the second input port (40) to the output port (41). 41), characterized in that the shuttle valve closing element (45, 45 ') can be locked in a position located between the two end positions and in this locked position, the first input port (39) is connected to the second input port (40).

A pressure cut valve assembly according to claim 1, characterized in that in the locked position the output (41) is connected to the first and second input ports (39, 40).

3. Pressure cut valve unit according to claim 1 or 2, characterized in that in the locked position, the first input port (39) is connected to a first pressure chamber (73) and the second input port (40) is connected to a second pressure chamber (74).

4. Druckabschneidungsventileinheit according to one of claims 1 to 3, characterized in that in that the shuttle valve closing element (45, 45 ') can be mechanically blocked by a locking element (70).

5. Druckabschneidungsventileinheit according to claim 4, characterized in that the locking element (70) is designed as a threaded pin for engagement in a recess (71) of the shuttle valve closing element (45, 45 ').

6. Druckabschneidungsventileinheit according to claim 4 or 5, characterized in that the shuttle valve closing element (45, 45 ') as

Valve piston (45 ') is formed on the to

Cooperation with the locking element (70) has a circumferential groove (71) is formed.

7. Druckabschneidungsventileinheit according to claim 6, characterized in that by a in the valve piston (45 ') formed connecting channel (76) of the first pressure chamber (73) with the second pressure chamber (74) is connected.

Pressure cut valve unit according to one of claims 1 to 7, characterized in that the shuttle valve closing element (45, 45 ') for forming the shuttle valve (36) in a bore (51) receiving a pressure cut valve (35) in the axial extension of the pressure cut valve (35). is arranged.

9. Druckabschneidungsventileinheit according to one of claims 1 to 7, characterized in that the shuttle valve closing element (45, 45 ') for forming the shuttle valve (36) in a valve sleeve (50) of a Druckabschneidungsventils (35) is arranged.

10. A hydraulic circuit having a first working line (4) and a second working line (5), wherein the first working line (4) with a first input port (39) and the second working line (5) with a second input port (40) of a shuttle valve ( 36) is connected to a pressure cut valve unit (34), wherein the first input terminal (39) or the second input terminal (40) are connectable to an output (41) in response to the pressures prevailing at the input terminals (39, 40); Shuttle valve (36) has a shuttle valve closing element (45, 45 ') which connects in a first end position, the first input terminal (39) to the output (41) and in a second end position the second input terminal (40) to the output (41) connects, characterized in that the shuttle valve closing element (45, 45 ') can be locked in a position located between the two end positions and arretie in this Position the first input terminal (39) is connected to the second input terminal (40).