EP1910720A1

EP1910720A1 - Purging valve for a hydraulic circuit

Info

Publication number: EP1910720A1
Application number: EP06791560A
Authority: EP
Inventors: Steven Donders
Original assignee: Brueninghaus Hydromatik GmbH
Current assignee: Brueninghaus Hydromatik GmbH
Priority date: 2005-08-04
Filing date: 2006-08-04
Publication date: 2008-04-16
Also published as: WO2007014785A1; DE102005051324A1; US20090101216A1

Abstract

The invention relates to a purging valve for a closed hydraulic circuit. According to the invention, a valve piston (40) is arranged in a longitudinally displaceable fashion in a recess (36) of a valve housing (35); the purging valve (21) has at least three pressure spaces (41, 42, 43) which are formed in succession in the axial direction; in each case two of the pressure spaces (41, 42, 43) can be connected to one another as a function of a relative position of the valve piston (40) relative to the valve housing (35); and a sealing element (44, 45) which seals against a valve seat face (50) formed on the housing is provided in order to block the connection between the pressure spaces (41, 42, 43).

Description

Flush valve for a hydraulic circuit

The invention relates to a flush valve for a closed hydraulic circuit.

In a closed hydraulic circuit, for example, a hydraulic drive, a pressure medium is conveyed by a hydrostatic pump. The delivered pressure fluid flows to a hydraulic motor, which it drives before it flows back to the suction side of the hydraulic pump. During operation of such a hydrostatic drive, the pressure medium undergoes considerable heating. Since such closed hydraulic circuits are usually designed for delivery in both directions, a cooling of the pressure medium in the closed circuit is difficult. In order to prevent a critical increase in the temperature of the pressure medium, therefore, a quantity of pressure medium is removed from the closed circuit in a controlled manner, which is replaced by a cooled and filtered pressure medium. In order not to reduce the efficiency of the hydraulic drive, it is customary to remove the printing medium from the respective low pressure leading working line. The supply of the cooled pressure medium via a feed device through which the removed volume is replaced in the low-pressure side working line.

For removing the pressure medium flushing devices are known, which are connected to the two arranged between the pump and the motor working lines. In this case, each of the low-pressure leading working line is connected by a flush valve with a pressure relief valve. Such a purge valve is known from DE 31 06 610 Al. In the purge valve shown there, a valve piston is arranged longitudinally displaceably in a valve housing. The valve piston is made by two at opposite end faces of the valve piston centered arranged compression springs. On both sides of the valve piston, a pressure chamber is arranged in each case. Each of the two pressure chambers is connected to one of the two working lines. Between these two pressure chambers, a further space is formed, which is sealed in the rest position of the valve with respect to both pressure chambers. For sealing a fit between sealing portions at the ends of the valve piston and a corresponding bore in the valve housing is formed. When pressure is applied in one of the two pressure chambers, the valve piston is displaced in the direction of the opposite pressure chamber. The sealing portion of the displaced in this way in the direction of the pressure chamber with lower pressure valve piston leaves the trained as a fit portion of the valve housing. This opens a through-flow connection between the pressure chamber with the lower pressure and the further pressure chamber. Via a return line, this additional pressure chamber is connected to a tank volume.

At the known from DE 31 06 610 Al purge valve, it is disadvantageous that the seal between the valve piston and the valve housing via an annular gap. Due to the repeated axial movement of the valve piston occurs in the bore formed in the housing to a wear that deteriorates the sealing effect of the annular gap. In the course of operation, the leakage volume increases, which adjusts along the annular gap in the direction of the tank volume. Since usually flush valves are integrated directly into a housing section of hydraulic pumps or motors, the z. B. gray or nodular cast iron, reworking in case of wear is particularly difficult.

The invention is based on the object to provide a flush valve, which is improved in terms of wear during operation and is easy to overtake in the event of a deteriorated sealing effect. The object is achieved by the flush valve with the features of claim 1.

The flush valve according to the invention according to claim 1 has a valve piston, which is arranged longitudinally displaceable in a recess of a valve housing. At least three axially successive sections are formed on the valve. Each of the three successive sections has a pressure chamber, wherein in dependence on the relative position of the valve piston in each case two of the pressure chambers can be connected to one another. In order to interrupt the connection between the individual pressure chambers, a valve seat surface is formed on the housing side, which cooperates sealingly with a sealing element. In this way, there is a respective seat valve between the pressure chambers to be connected to each other for the removal of pressure medium, whereby a significantly reduced wear occurs during operation of the purge valve. In the case of wear, a simple replacement of the sealing elements of the purge valve is also possible. An inserted into the housing of a pump or a motor valve can thus be easily repaired.

In the dependent claims advantageous developments of the purge valve according to the invention are shown.

In particular, it is advantageous that the sealing element is designed as a sleeve, which is penetrated by the valve piston. Between the valve piston and the sealing element designed as a sleeve sealing effect is achieved by a corresponding sealing portion of the valve piston. It is particularly advantageous to choose the radial extent of the sealing portion of the valve piston as small as possible, in particular smaller than the radial extent between the sections formed as a guide portions of the valve piston. Furthermore, it is advantageous to provide a recess on the end face oriented towards the valve seat surface on the sealing element designed as a sleeve, so that an annular sealing surface is formed around this recess. The recess can be determined in its diameter so that adjusts the desired surface pressure on the annular sealing surface. In particular, it is advantageous to center the valve piston via two centering springs which act on the valve piston via a respective sealing element. Therefore, the valve piston is acted upon by an axial force through the centering springs until both centering springs hold the sealing elements in sealing contact with the valve seat surfaces. At the same time, the centering springs provide the required closing force on the sleeves and the surface pressure on the valve seat surfaces.

A preferred embodiment of the purge valve according to the invention is shown in the drawing and will be explained in more detail in the following description. Show it:

Fig. 1 is a hydraulic circuit diagram of a closed hydraulic circuit with a

Flush valve unit;

Fig. 2 shows an embodiment of an inventive

Purge valve in its rest position; and

Fig. 3, the flush valve according to the invention in a deflected position.

Before discussing the flush valve according to the invention, a closed hydraulic circuit will first be explained with reference to the circuit diagram of FIG. 1 for better understanding. Fig. 1 shows a closed hydraulic circuit 1, in which an adjustable hydraulic pump 2 promotes a pressure medium. With the Hydraulic pump 2 is a preferably also adjustable hydraulic motor 3 via a first working line 4 and a second working line 5 connected in a closed circuit. Both the hydraulic pump 2 and the hydraulic motor 3 are reversible in the illustrated embodiment. To drive the hydraulic pump 2 is a drive motor, not shown, which is connected to the hydraulic pump 2 via a drive shaft 6.

Together with the hydraulic pump 2, a feed pump 7 is connected to the drive shaft 6. The feed pump 7 is provided for conveying in only one direction and preferably designed as a constant pump. The feed pump 7 serves to fill the hydraulic circuit.

To fill the hydraulic circuit, the feed pump 7 sucks pressure medium from a tank volume 10 via a suction line 8 and a filter 9 provided therein. The feed pump 7 conveys the sucked-in pressure medium via a feed line 11 and via a first connection line 12 'into the first working line 4 or via a second connecting line 12' 'into the second working line 5. In the first connecting line 12' is a first feed valve 13 ' arranged. Likewise, in the second connecting line 12 '', a second feed valve 13 '' is arranged. The function of the two feed valves 13 'and 13' 'is the same, so that below the structure is explained only with reference to the feed valve 13'.

In order to prevent too high a feed pressure, the feed line 11 is secured by a feed pressure limiting valve 14. If the pressure in the feed line 11 exceeds a predetermined value, the spring-loaded feed pressure limiting valve 14 opens and releases from the feed line 11 a flow-through connection into an inner tank volume 17 of the hydraulic pump unit. The first feed valve 13 'has a check valve 15 which opens in the direction of the first working line 4. Parallel to the check valve 15, a spring-loaded pressure limiting valve 16 is arranged. As long as the pressure prevailing in the first working line 4 is lower than the pressure supplied via the feed line 11 to the first connecting line 12 ', the check valve 15 opens and the first working line 4 is filled with pressure medium by the feed pump 7. If, on the other hand, the pressure in the first working line 4 exceeds the feed line pressure during operation, the check valve 15 closes. If the pressure rises further, which could lead to a critical loading of the system, the pressure limiting valve 16 opens, so that the first working line 4 via the pressure limiting valve 16 is relaxed to the feed line 11 out. Since the feed line 11 is secured via the feed pressure limiting valve 14, in such a case the pressure of the first working line 4 is released into the tank volume 17.

The second feed valve 13 "provided for filling and securing the second working line 5 corresponds in its construction to the first feed valve 13 ', so that a renewed description is dispensed with.

To cool the pressure medium conveyed in the hydraulic circuit, pressure medium is withdrawn from the closed hydraulic circuit and the pressure removed from the tank volume 10 is replaced by the pressure medium already cooled by the already described feed device. The cooling can be done for example by a suitably designed filter 9 or by additional, not shown in the drawing cooler.

For removing the flushing oil, a flushing device 18 is provided. The flushing device 18 is connected via a first extraction line 25 and a second extraction line 26 to the first working line 4 and the second working line 5, respectively. That over the first Suction line 25 and the second extraction line 26 taken flushing oil is discharged through a return line 19 into the tank volume 10. For removing pressure medium from the respective low-pressure side, a flushing valve 21 is provided, which is designed in the illustrated embodiment as a 3/3 -way valve. By way of the flushing valve 21, in each case that working line 4 or 5 is connected to an outlet connection 31, in which, depending on the conveying direction of the hydraulic pump 2, the lower pressure prevails. The output port 31 of the purge valve 21 is connected to an input of a pressure limiting valve 22. The pressure relief valve 22 opens at a set pressure and thus connects the output port 31 of the purge valve 21 with the tank volume 10 via the return line 19th

The flush valve 21 is held by a first centering spring 23 and a second centering spring 24 in its rest position shown in FIG. In the illustrated rest position all connections of the purge valve 21 are separated from each other. If the pressure in the first working line 4 exceeds, for example, the pressure prevailing in the second working line 5, the working line pressure of the first working line 4 acts via the first withdrawal line 25 and via a throttle point 27 on a first measuring area 29 Pressure is an axial force generated on the purge valve 21, which acts against the second centering spring 24. As a result, the flushing valve 21 is deflected in the direction of a first end position. In this first end position, the second extraction line 26 is connected to the output terminal 31.

Conversely, if the pressure prevailing in the second working line 5 exceeds the pressure prevailing in the first working line 4, the working line pressure of the second working line 5 via the second withdrawal line 26 and a second restriction 28 becomes a second Measuring surface 30 is supplied. The hydraulic force acting there displaces, starting from its rest position, a valve piston of the flush valve 21 against the force of the first centering spring 23. The flush valve 21 is thus deflected in the direction of its second end position, in which the first working line 4 with the outlet port 31 via the first extraction line 25th connected is.

Thus, depending on the pressure conditions in the first working line 4 and in the second working line 5, the flushing valve 21 connects in each case that working line 4, 5 to the outlet 31, in which the lower pressure prevails. To set a minimum pressure in each of the low pressure leading first or second working line 4 or 5, the pressure relief valve 22 is used. The output port 31 is for this purpose connected via an additional throttle point 33 with an input of the pressure relief valve 22. Contrary to the force of a setting spring 34 acts on the pressure limiting valve 22, a hydraulic force which is generated by the pressure prevailing upstream of the further throttle point 33. If this pressure, which prevails upstream of the throttle point 33 and is supplied via a bypass line 32, exceeds a value that can be set via the adjusting spring 34, the pressure relief valve 22 opens and releases the flow path to the return line 19 and thus to the tank volume 10. While via the flush valve 21 always that working line 4 or 5 is connected to the lower pressure to the output port 31, is set by the additional pressure relief valve 22, a minimum pressure for the low pressure leading working line 4 and 5 respectively.

FIG. 2 shows a partial section through a flushing valve 21 according to the invention. The flush valve 21 is arranged in a valve housing 35, which is penetrated by a recess 36. Along The longitudinal extent of the recess 36, a first portion 37, a second portion 38 and a third portion 39 is arranged. In the successive sections 37 to 39, a first pressure chamber 41, a second pressure chamber 42 and a third pressure chamber 43 are formed. The pressure chambers 41-43 are formed by an enlargement of the radial extent of the recess 36, so that in each case a volume results around a valve piston 40, which is arranged in the recess 36. Alternatively, the pressure chambers 41-43 can also be generated by a corresponding reduction of a diameter of the valve piston 40.

2, the valve piston 40 is shown in its centered position, in which the purge valve 21 is in the middle position shown in FIG. In this middle position there is no flow-through connection between the pressure chambers 41 and 42 and 42 and 43. For sealing the first pressure chamber 41 relative to the second pressure chamber 42, a sealing element is provided which is formed in the illustrated embodiment as a sleeve 44. Similarly, a second sleeve 45 is provided for sealing the third pressure chamber 43 relative to the second pressure chamber 42, the design of the first sleeve 44 corresponds. To avoid unnecessary repetition, therefore, only the geometric expression of the first sleeve 44 will be explained below.

The first sleeve 44 has a central passage opening, with which the first sleeve 44 is pushed over a cylindrical first end 46 of the valve piston 40. The first end 46 acts as a sealing portion sealingly with the recess of the first sleeve 44 together. On its side facing the second pressure chamber 42, a first recess 48 is made in the end face of the first sleeve 44. Through the first recess 48, an annular portion of the first sleeve 44 remains standing, the end face of which forms a sealing surface 49. These annular sealing surface 49 cooperates sealingly with a valve seat surface 50 which is formed in the housing 35. In order to hold the sealing surface 49 with the valve seat surface 50 in sealing contact, the first sleeve 44 is acted upon by the force of the first centering spring 23 in the axial direction. To accommodate the spring, a second recess 51 is provided at the end remote from the second pressure chamber 42 end of the first sleeve 44. At the opposite end of the first centering spring 23, this is supported on an abutment 52.

In the illustrated embodiment, the first pressure chamber 41, for example, via a running as a bore channel 25 ', which forms the first extraction line 25, connected to the first working line 4. Accordingly, the third pressure chamber 43 is connected via a turn executed as a bore channel 26 ', which corresponds to the second extraction line 26, with the second working line 5. In the first pressure chamber 41 and the third pressure chamber 43, the pressure prevailing in the first working line 4 or the second working line 5 thus acts on the end face of the valve piston 40. An axial force is thus respectively applied to the valve piston at the opposite end faces of the valve piston 40 40, which counteracts the force of the second centering spring 24 and the first centering spring 23, which are arranged in the third and first pressure chamber 43 and 41, respectively.

Between the first portion 37 and the second portion 38 and between the second portion 38 and the third portion 39 of the purge valve 21, a guide 54, 55 is formed in the housing 35 in each case. The guides 54, 55 cooperate with in each case a corresponding guide section 56, 57 of the valve piston 40. In order for an axial displacement of the valve piston 40, a flow-through connection between the first pressure chamber 41 and the second pressure chamber 42 or in a reverse Deflection between the third pressure chamber 43 and the second pressure chamber 42 to allow, in the region of the two guide portions 56, 57 respectively flattened locations are provided. Preferably, a plurality of such flattened locations 56 'and 57' are provided distributed over the circumference of the guide sections 56 and 57. The flattened locations are preferably limited to an axial portion of the guide sections 56 and 57.

In order to enable a seal between the first pressure chamber 41 and the second pressure chamber 42, a fit is formed between the first end 46 of the valve piston 40 and the central recess of the first sleeve 44. In contrast to a previously customary fit in the region of the guide sections 56, 57 of the valve piston 40, this has the advantage that the radial extent of the first and second ends 46, 47 of the valve piston 40 relative to the guide sections 56, 57 is reduced. The leakage of pressure fluid along a fit depends on the cross-section of the gap created by the fit. The arrangement of the fit in the region of the first end 46 and the second end 47 of the valve piston 40 not only has the advantage that an annular gap arising in the region of the fit between the first or second sleeve 44 or 45 and the first or second second end 46, 47 of the valve piston 40 has a total of a smaller cross-sectional area due to the smaller outer diameter, but moreover, a fit with a smaller diameter with a higher precision can be produced.

In the region of the first end 46 of the valve piston 40, for example, a hardened outer surface may be formed on the valve piston 40 to reduce the wear. It is also possible to harden the first sleeve 44 in order to reduce the wear and thus the increase in the leakage during the operating period. Furthermore, the valve seat surface on the side of the valve housing 35th be formed by a pressed valve seat ring, which may also be cured.

The first end 46 of the valve piston 40 is provided with a blind bore 58. In the blind bore 58 engages a pin-shaped extension 59 of the first abutment 52 a. The first counter-bearing 52 is approximately T-shaped in cross-section with a dome-shaped head and is supported by the dome-shaped head on a closure element 60, which is preferably fixed in the recess 36 of the valve housing 35 by a screw connection. The first closure element 60 is sealed relative to the valve housing 35 in a known manner, for example by an O-ring or a copper seal. Due to the dome-shaped outer contour tilting of the pin 59 in the blind bore 58 of the valve 40 is prevented. In this way, it is ensured that the higher frictional forces occurring during tilting do not occur and the function of the valve is not impaired.

The function of the purge valve 21 according to the invention will be explained in more detail with reference to FIG. The diameter of the valve piston 40 in the region of the guide portions 56 and 57 corresponds to the diameter of the first recess 48 of the first sleeve 44 and the corresponding recess on the side of the second sleeve 45. When the valve piston 40 is acted upon by a hydraulic force in the second pressure chamber 43, which is greater than the hydraulic force in the first pressure chamber 41, the valve piston 40 is deflected in Fig. 3 to the left against the force of the first centering spring 23.

At the first guide portion 56 of the valve piston 40 results in the transition to the smaller in the radial expansion of the first end 46 of the valve piston 40, a contact surface 62, by the movement of the valve piston 40 in the axial direction in contact with the Base of the first recess 48 of the first sleeve 44 passes. If the resulting axial force on the valve piston 40 due to the pressure difference in the first pressure chamber 41 and the third pressure chamber 43 exceeds the opposing force of the first centering spring 23, the first centering spring 23 is correspondingly compressed to the axial movement of the valve piston 40. In this case, the first sleeve 44 lifts off from the valve seat surface 50 and releases a flow-through connection from the first pressure chamber 41 and thus the first extraction line 25 to the second pressure chamber 42.

The second pressure chamber is connected in a non-illustrated manner with a tank volume 10. The maximum possible deflection movement of the valve piston 40 results from the selected length of the first end 46 or the resulting distance to the head of the first abutment 52. As the end face of the valve piston 40 is in abutment with the abutment 52 at the first end 46, a further deflection is not possible.

The pins 59 can serve as a hydraulic damping piston, which can let the valve piston 40 attenuated go into its deflected end position and thus wear due to striking stress of the attacks, z. B. when abutment of the end 46 against the abutment 52, avoid.

In the illustrated embodiment, the pressure in the second working line 5 exceeds the pressure of the first working line 4. If the pressure in the second working line 5 decreases, so does the resulting hydraulic force on the valve piston 40 drops. If the force difference of the hydraulic forces falls below one of the Force of the first centering spring 23 predetermined value, the valve piston 40 is moved back toward its center position by the force of the first centering spring 23 on the first sleeve 44. A shift by the force of the first centering spring 23 is so long possible until the sealing surface 49 of the first sleeve 44 is in contact with the valve seat surface 50 of the valve housing 35 and the first pressure chamber 40 is sealed relative to the second pressure chamber 42.

In the illustrated embodiment, the distance between the two formed on the guide portions 56 and 57 abutment surfaces 62 and 63 is selected so that the axial play of the valve piston 40 at each of the valve seat 50 of the valve housing 35 fitting first sleeve 44 and second sleeve 45 goes to zero.

The arrangement in the second pressure chamber 43 consisting of the second end 47 of the valve piston 40, the second sleeve 45, the second centering spring 24 and the second abutment 63 and the second closure member 61 corresponds to the purge valve 21 shown and described in detail on the opposite side. In a comparison with the example described opposite pressure difference thus takes place a deflection of the valve piston 40 in the opposite direction. A further detailed description is omitted to avoid repetition.

The invention is not limited to the illustrated embodiment. In particular, it is possible, for example, instead of a common second pressure chamber 42 to provide two independent pressure chambers, which are each sealed against the first pressure chamber 41 and the third pressure chamber 43.

The particular advantage of the selected arrangement with sleeves 44 and 45 pushed over the ends 46 and 47 of the valve piston 40 is the reduction in leakage oil losses by the formation of a sealing surface 49 on the sleeve, which sealingly cooperates with a valve seat surface 50 in the valve housing 35. This does not allow the formation of the gap seal completely avoided, however, the gap seal between the central recess of the sleeve 44, 45 and a cooperating sealing portion of the valve piston 40 is formed at its ends 46 and 47. The gap seal, which is inevitably subject to wear, can thus be realized without a complex treatment of the valve housing 35 with hardened components. Moreover, as already explained, the diameter of the gap seal is reduced compared to a conventional design of the purge valve 21. In addition, a simple replacement of the components involved is possible, so that without having to bush out, for example, the valve housing 35, a revision of the purge valve 21 is possible in case of wear.

Claims

claims

1. Flushing valve for a hydraulic circuit, which has a recess (36) of a valve housing (35) longitudinally displaceably arranged valve piston (40), wherein the flush valve (21) has at least three axially consecutively formed pressure chambers (41, 42, 43), wherein in dependence on a relative position of the valve piston (40) relative to the valve housing (35) in each case two of the pressure chambers (41, 42, 42, 43) are connectable to each other, characterized in that to interrupt the connection between the pressure chambers (41, 42; 42, 43) is provided in each case a against a housing side formed valve seat surface (50) sealing sealing element (44).

2. Flushing valve according to claim 1, characterized in that the sealing element (44) is designed as a sleeve, which is penetrated by the valve piston (40) and with a sealing portion (46)> of the valve piston (40) sealingly cooperates.

3. Flushing valve according to claim 2, characterized in that on a in the direction of the valve seat surface (50) oriented end face of the sleeve (44) has a recess (48) for generating a sealing surface (49) is formed.

4. Flushing valve according to claim 2 or 3, characterized in that the radial extent of the sealing portions (46, 47) of the valve piston (40) is smaller than the radial extent between the sections (37, 38, 39) formed guide portions (56, 57 ).

5. Flushing valve according to one of claims 1 to 4, characterized in that the flushing valve (21) has three pressure chambers (41, 42, 43) and, in a centered position of the valve piston (40), the second pressure chamber (42) of a middle section (38) opposite the pressure chambers (41, 43) of the two remaining sections (37, 39) is sealed by a respective sealing element (44, 45).

6. Flushing valve according to claim 5, characterized in that for centering the valve piston (40) of the valve piston (40) on itself on the sealing elements (44, 45) supporting centering springs (23, 24) can be acted upon with an axial force.

7. Flushing valve according to claim 6, characterized in that on the valve piston 40 in each case one in the direction of the first sleeve (44) or in the direction of the second sleeve (45) oriented bearing surface (62, 63) is formed, which is a movement of the valve piston (40) for lifting the respective sleeve (44, 45) from its valve seat surface (50) transmits.