Patent Grant
7204266
The invention relates to a pilot-operated pressure shut-off valve which, when an upper system limit pressure is reached in a hydraulic system having a hydraulic accumulator, connects an inlet feeding the hydraulic system to an outlet to a tank and separates this connection when removal of hydraulic fluid from the hydraulic accumulator has caused the system pressure to drop to a lower system limit pressure and which has a main control piston and, in order to control the main control piston, a pilot valve arrangement having two pilot pistons and two pilot springs, the adjustment of which makes it possible for the upper system limit pressure and the lower system limit pressure to be set independently of each other.
A pilot-operated pressure shut-off valve of this type is disclosed, for example, in DE 41 12 065 A1 or in DE 36 08 100 C2. In the case of the pressure shut-off valve according to DE 41 12 065 A1, the pilot valve arrangement comprises two complete pilot valves having a respective valve housing, having a pilot piston in a bore of the valve housing and having a pilot spring which is situated in a spring space and the prestress of which can be changed with the aid of a setting screw. The two pilot valves are placed one above the other onto the housing of the main stage. This pressure shut-off valve has a fairly large construction and is relatively expensive.
In the case of the pressure shut-off valve according to DE 36 08 100 C2, the pilot valve arrangement only has one valve housing. In the latter, two valve bores, each of which accommodates one of the two pilot pistons, run at a distance from and parallel to each other. The two pilot springs are accommodated next to each other in an extension of the valve bores in a cover fitted onto the valve housing of the pilot valve arrangement. The pilot valve arrangement in this pressure shut-off valve still has a fairly complex construction.
There are also pilot-operated pressure shut-off valves in which the pilot valve arrangement has just one pilot piston and one pilot spring and an adjustment of the one system limit pressure always also involves an adjustment of the other system unit pressure. The difference between the two limit pressures is a percentage of the upper system limit pressure, this percentage depending on the size of a surface difference on the pilot piston and on the prestress of the pilot spring. A pilot-operated pressure shut-off valve of this type, in which the upper system limit pressure and the lower system limit pressure cannot be set independently of each other, is disclosed, for example, in the applicant's specification sheet RD 26 411/03.98.
The invention is based on the object of developing a pilot-operated pressure shut-off valve having the introductory-mentioned features in such a manner that the pilot valve arrangement is constructed compactly and simply, can be produced cost-effectively and can be interchanged for a pilot valve arrangement of a pressure shut-off valve, in which the upper system limit pressure and the lower system limit pressure cannot be set independently of each other.
The objective which is sought is achieved according to the invention wherein, the two pilot pistons, the two pilot springs and the two setting screws are arranged lying concentrically inside one another, with it being possible to adjust the two pilot pistons mechanically completely independently of each other. In this manner, the pilot valve arrangement is constructed very compactly with a low height. Only one valve housing is needed for the pilot valve arrangement. Instead of a conventional pilot valve arrangement which does not permit any independent setting of the two limit pressures from each other, said pilot valve arrangement can easily be constructed on a main stage. In comparison with a pilot valve arrangement having two valve bores for the two pilot pistons, the machining of the valve housing of a pilot valve arrangement according to the invention is substantially simplified, since only one valve bore is needed for the two pilot pistons. The compact, concentric arrangement of the pilot pistons, the pilot springs and the setting screws also makes possible a cartridge-type construction which it has hitherto not been possible to realize.
The complete mechanical independence of the two pilot pistons in respect of their movement possibilities can thus be achieved in a simple manner wherein the outer pilot piston is situated with an outer collar between two stops fixed on the housing, wherein the one stop is formed on a bushing inserted into the valve housing, and wherein the inner pilot piston penetrates the bushing and is situated with an outer collar between the bushing and a further insert placed in the valve housing.
In order for the first pilot piston to be reliably switched over when the upper system limit pressure is reached and to remain in the one switching position until the system pressure drops to the lower system limit pressure, wherein said pilot piston is a stepped piston along with other features of the invention. A pressure space is formed upstream of the stepped surface with pump pressure being produced in it with the main stage closed and which is relieved of pressure by or for switching over the first pilot piston when the upper system limit pressure is reached. The first pilot piston is acted upon on the stepped surface by the pressure prevailing in the pressure space in the same direction as by the first pilot spring. The first pilot piston is acted upon on a large, first active surface by the system pressure counter to the direction of action of the first pilot spring. The minimal, lower system limit pressure is determined, with an established, upper system limit pressure, by the surface difference between the first active surface, on which the system pressure produces a force, and the second active surface, on which the pump pressure produces a force. According to another feature of the invention the stepped surface of the first pilot piston or, more generally, the active surface on the first pilot piston, at which the pump pressure produces a force directed in the same direction as the spring force, is at least one third of the size of the large active surface, at which the system pressure produces a counterforce. The first pilot piston already reliably switches over at such a ratio of sizes. Preferably, according to another feature of the invention the stepped surface is approximately two thirds of the size of the large active surface. In principle, the stepped surface can also be made even larger in comparison with the large active surface. However, this no longer lies within the sense of a compact construction. In addition, a ratio of sizes of two thirds is sufficient in order also to make possible the greatest desired difference between the upper system limit pressure and the lower system limit pressure.
According to yet other features of the invention the second pilot piston is formed as a stepped piston and is acted upon by pump pressure on the stepped surface in the direction of action of the second pilot spring while it is acted upon on a large, first active surface by the system pressure counter to the direction of action of the second pilot spring. This ensures that the second pilot piston, over the entire pressure and quantity range of the pressure shut-off valve, passes reliably into the switching position determined by the second pilot spring. According to another feature of the invention the size of the stepped surface of the second pilot piston preferably lies in the region of 5% of the large active surface on the end of the second pilot piston.
The objective sought by the invention can be achieved irrespective of which of the two pilot pistons is the outer pilot piston which accommodates the other pilot piston in it. However, with regard to a compact construction, it has proven particularly favorable if, according to another feature of the invention the first pilot piston is the hollow piston in which the second pilot piston is guided.
It is particularly advantageous for controlling the main control piston if, according to another feature of the invention the two pilot pistons of the pilot valve arrangement can be used to control two throughflow cross sections which are arranged in series between the control space of the main control piston and a tank connection. For controlling the throughflow cross sections, the pilot pistons are acted upon, according to other features of the invention by the different pressures and by the pilot springs. It should be pointed out here that the construction according to these features affords advantages over previously known pilot connections even with a detached construction of the pilot valve arrangement, i.e. even if the two pilot pistons are not arranged one inside the other or if there are even two separate pilot valves. However, the control arrangement according to these features is particularly favorable if the two pilot pistons are arranged lying one inside the other, since then, according to features of the invention the relieving of the control space on the main control piston, i.e. the opening of the two throughflow cross sections lying in series, is possible with little structural outlay. If the first pilot piston is the outer pilot piston, then in the case of a construction according to further features of the invention the fluid path across the two throughflow cross sections is formed in a particularly simple manner.
The reliability of switching over to the inlet connection with the system is also increased by a construction according to still other features of the invention. This is because the second pilot piston covers a greater distance in the closing direction owing to the further aperture in the first pilot piston. If then, owing to the rise in pressure in the outer annular space, the first pilot piston moves more rapidly than the second pilot piston in the closing direction, its first apertures are already covered on the outside by the control edge fixed on the housing in the event that said apertures are opened once again on the inside. The small clearance between the pilot pistons and between the first pilot piston and the housing is used in a specific manner for a small leakage flow from the further aperture into the relief space, the leakage flow also being able to include the first apertures and constituting part of the entire leakage flow. Due to the additional leakage flow which is caused by the further aperture and is to be reduced in order to raise the system pressure, the second pilot piston covers the greater distance. In particular, it has turned out that, owing to the further aperture, the opening cross section between the first apertures and the control edge fixed on the housing no longer has to have such precise tolerances, and the pressure shut-off valve nevertheless reliably switches.
Finally, according to still other features of the invention the invention is also already implemented solely by the pilot valve arrangement having the corresponding features from the introductory-mentioned paragraph and having other features of the invention.
Two exemplary embodiments of a pilot-operated pressure shut-off valve according to the invention are illustrated in the drawings. The invention will now be explained in greater detail with reference to the figures of these drawings, in which
According to the connection diagram of
A hydraulic pump 30 which is driven by an electric motor 31 is connected to the inlet connection 12.
When the main control piston 20 takes up its closed position, as is shown in
The main control piston 20 is controlled by the pilot valve arrangement 11 which, as seen in connection terms, has two pilot valves 40 and 41 which are constructed as 2/2-way directional control valves and which lie in series between the control space 26 on the main control piston 20 and the outlet connection 13. The series connection provides for fluid connection, via both of the pilot valves 40 and 41 when both of the valves are open, between the control space 26 and the outlet connection 13, as shown in
The pilot valve 41 has a second pilot piston 48 which is acted upon in the closing direction by a second helical compression spring 49, the prestress of which can be changed in order to set the lower system limit pressure. In the closing direction, the pilot piston 48 is acted upon by the system pressure in precisely the same manner as the pilot piston 44, specifically on an active surface 50 (shown also in
The space in which the helical compression springs 45 and 49 are situated is located on the relief line 42.
If, during operation, the main control piston 20 takes up its closed position and the hydraulic fluid conveyed by the hydraulic pump 30 passes via the nonreturn valve 17 to the hydraulic accumulator 16, the pilot valve 40 is in its closed position and the pilot valve 41 is in its open position. The control space 26 is thus blocked off toward the relief line 42. The pressure in it is equal to the pressure in the inlet connection 12. Under the action of this pressure and under the action of the helical compression spring 27 the main control piston 20 maintains its closed position. Virtually the same pressure is produced on the active surfaces 46 and 147 of the pilot valve 40 and on the active surfaces 50 and 151 of the pilot valve 41. The drop in pressure via the nonreturn valve 17 is negligible. The pressure in the hydraulic accumulator 16 rises with the inflow of pressure medium and is finally of such magnitude that the differential surface between the two active surfaces 46 and 147 as the pressure application surface is sufficient for a throughflow cross section to be opened in the pilot valve 40. The pressure arising on the active surface 147 instantly starts to fall, with the result that the pilot valve 40 reliably switches into its open position. Hydraulic fluid can now flow from the control space 26 via the two pilot valves 40 and 41 and the relief line 42 to the tank 32. The main control piston 20 is relieved of pressure on the spring side and opens. The pressure in the inlet connection 12 drops to a low value determined by the prestressing of the helical compression spring 27. The nonreturn valve 17 closes. The hydraulic fluid conveyed by the hydraulic pump 30 consequently flows via the throughflow cross section between the seat edge 24 of the housing 22 and the frustoconical surface of the main control piston 20 back to the tank 32. Only a small quantity of control oil that is determined by the hydraulic resistance of the nozzle 29 and the pressure equivalent to the force of the helical compression spring 27 flows via the pilot valve arrangement to the tank. The pressure by which the pilot valve 40 can be brought into its open position is equal to the upper system limit pressure. Its magnitude is determined by the prestress of the helical compression spring 45 and can be changed by changing this prestress.
While the hydraulic pump 30 is conveying in circulation, the pressure in the hydraulic accumulator 16 gradually decreases by removal of hydraulic fluid for hydraulic consumers. Finally, the pressure is so low that the force which it produces on the active surface 50 of the second pilot valve 41 becomes smaller than the force of the helical compression spring 49. The latter now moves the pilot piston 48 in the closing direction, as a result of which the throughflow cross section is closed by the valve 41 and pressure builds up in the control space 26, into which pressure medium continues to flow via the nozzle 29, and therefore also on the active surfaces 147 and 151 of the pilot valves 40 and 41. The build up of pressure on the active surface 151 of the pilot piston 48 brings about reliable closing of the pilot valve 41. The pressure in the control space 26 is equal to the pressure in the inlet connection 12, with the result that the main control piston 20 closes under the action of the helical compression spring 27 and the pump pressure acting on a surface remainder outside the seat edge 24. The pressure in the inlet connection 12 and in the control space 26 and on the active surfaces 147 and 151 therefore rises to the system pressure which at this instant is identical to the lower system limit pressure. Even before this lower system limit pressure is reached on the active surface 147, the pilot valve 40 also passes into its closed position. The inflow of hydraulic fluid to the hydraulic accumulator 16 causes the system pressure to rise, with, because of the very small active surface 151 in comparison with the active surface 50, a slight rise above the lower system limit pressure being sufficient in order to bring the pilot valve into its open position again. This does not have any effect on the main control piston, since the pilot valve 40 is already in its closed position and prevents relief of the control space 26. Only when the system pressure is again as high as the upper system limit pressure does the pilot valve 40 switch again into its open position.
For reliable and rapid switching of the pilot valve 40 from its open position into its closed position, the active surface 147 is to be at least one third of the size of the active surface 46. If, on the other hand, an upper system limit pressure is set by adjustment of the helical compression spring 45, then, from the ratio of the size of the surface 147 to the size of the surface 46, a pressure is produced which acts on the active surface 46 and against which the helical compression spring 45 could bring the pilot valve 40, when the active surface 147 is relieved, into the closed position even without a switching operation of the pilot valve 41. This pressure is therefore the minimum lower system limit pressure which can be maintained at a given upper system limit pressure. If the ratio between the surface 147 and the surface 46 is, for example, one third, then at a set, upper system pressure of 210 bar, the minimum lower system limit pressure would be 140 bar. If the ratio of the surface 147 to the surface 46 is two thirds, as is preferred, then at a set, upper system limit pressure of 210 bar, the minimum lower system limit pressure is 70 bar. Within this range, the lower system limit pressure can be set by adjustment of the helical compression spring 49. However, the presence of the active surface 51 also provides a limitation for the minimum interval between the upper system limit pressure and the lower system limit pressure.
In a structural respect, the two pilot valves 40 and 41 are integrated one inside the other in a very compact manner, so that they, as is apparent in particular from the section according to
Toward the closure screw 57, the section of the pilot piston 44 having the outside diameter of the stepped surface 59 is adjoined by an outer collar 63 with which the pilot piston 44 can strike, on the one hand, in the direction toward the closure screw 57 against a bushing 64, which is inserted into the bore 59 and is held in a fixed position, and, in the opposite direction, can strike against a further step 65 of the valve bore 56. The path of displacement of the pilot piston 44 is defined by the two axial stops and the axial extent of the outer collar 63. A further bushing 66 is situated between the bushing 64 and the closure screw 57. Said further bushing is pressed by the closure screw 57 against the bushing 64 and the latter is pressed in turn against a step of the valve bore 56.
Centrally, the first pilot piston 44 has a continuous axial bore 69 in which the second pilot piston 48 can be displaced axially. The axial bore 69 is a stepped bore having a bore section of larger diameter which opens outward on that end side of the pilot piston 44 which faces the bushing 64, and having a bore section of smaller diameter which is open toward the blind bore 55 of the housing 25. The cross sections of the two bore sections of the bore 69, which merge into each other in the stepped surface 51 on the pilot piston 44, differ from each other only by approximately 5%. Within the bore section having the smaller diameter, the axial bore 69 is connected to the outside of the pilot piston 44 via a plurality of apertures 70 situated axially at the same height. If, as shown in
The pilot piston 48 is stepped corresponding to the stepped axial bore 69 and has a guide section in the region of the bore section of smaller diameter and a guide section which is slightly larger in diameter in the bore section of larger diameter. The two guide sections are spaced far apart, with the diameter of the piston section between the two guide sections being reduced once again relative to the diameter of the smaller guide section. As a result and by the step 51, an annular space 72 has been produced radially between the outer pilot piston 44 and the inner pilot piston 48 and axially between the two guide sections thereof. Said annular space is permanently connected via a radial bore 73 in the pilot piston 44 to the annular space 61 and is therefore fluidically connected to the control space 26 on the main control piston 20. The pressure arising in the annular space 72 produces, on an annular surface of the pilot piston 48, which annular surface corresponds to the size of the stepped surface 51 of the pilot piston 44, a force which acts in the direction of the closure screw 57. The outer edge 74 on that end side of the guide section of smaller diameter of the pilot piston 48 which faces the annular space 72 forms a control edge which interacts with the apertures 70 on the pilot piston 44, which is situated, in the switching position of the pilot piston 48 that is shown in
The second pilot piston 48 protrudes beyond the pilot piston 44 in the direction of the closure screw 57, passes through an inner collar of the bushing 64 and is caught with a head 75 between this inner collar and the bushing 66.
The bushing 66 is provided on the outside with a turned groove 76 which is open toward a bore 77 of the housing 25, said bore being fluidically connected to the system line 15 and therefore to the hydraulic accumulator 16. Those end surfaces of the pilot pistons 44 and 48 which face the closure screw 57 are exposed via radial and axial bores in the bushings 54 and 56 to the pressure arising in the turned groove 76, i.e. to the system pressure. At the pilot pistons, this pressure produces a force which acts upon them such that they move away from the bushings 64 and 66 in the direction into the blind bore 55. The active surface on the pilot piston 44 is identical to an annular surface having an inside diameter, which is identical to the diameter of the larger section of the axial bore 69, and having an outside diameter, which is identical to the outside diameter of the stepped surface 47 of the housing 25. The active surface on the pilot piston 48 is identical to the cross-sectional surface of the larger guide section of this piston.
The two pilot springs 45 and 59 which, like the pilot pistons 44 and 48, are arranged concentrically one inside the other, are situated in the blind bore 55. The outer pilot spring 45 is supported via a spring plate 77 on the first pilot piston 44, loading the latter in the direction of the closure spring 57. On the other hand, it is supported on a setting screw 78 which is screwed into the blind bore 56. The inner pilot spring 49 is supported via a spring plate 78 on the pilot piston 48 protruding beyond the pilot piston 44 and likewise loads said pilot piston in the direction of the closure screw 57. In addition, the pilot spring 49 is supported on a setting screw 80 which is screwed centrally into the setting screw 78 and can be adjusted axially with respect to the setting screw 78 by rotation.
The blind bore 55 is part of the relief channel 42 which also includes a transverse bore 81 in the housing 25, via which bore the relief fluid path leads to the tank 32.
In
During charging for the first time the pilot piston 48 therefore switches over from the switching position shown in
The exemplary embodiment according to
A first difference resides in the fact that the first pilot piston 44 does not, as in the exemplary embodiment according to
Furthermore, the first pilot piston 44 has, in the region of bores 84 which correspond to the apertures 70 according to
When the upper system limit pressure has been reached and the valve is in the state in which the inlet is connected to the outlet, the two pilot pistons 44 and 48 are displaced to the right as far as a stop. In the switching-back phase after the lower system limit pressure is reached, the second pilot piston 48 first of all migrates to the left and closes the bores 84 on the inside, so that the pressure rises in the annular space 61. In this annular space, a certain pressure which is dependent on the upper system limit pressure and on the lower system limit pressure has to be reached so that the pilot piston 44 switches back. Owing to the leakage which is enlarged in comparison with the first exemplary embodiment because of the bore 87, the second pilot piston 48 continues to remove and also closes the bore 87. The pressure in the annular space 61 rises, with then, if the certain pressure is reached, the first pilot piston 44 moving to the left and the bores 84 also being closed on the outside. The main control piston then closes and the pressure in the accumulator rises.
After a certain rise in the pressure in the accumulator, the second pilot piston 48 switches again into its right end position, in which the head 75 bears against the bushing 64. It has been shown that the bore 87 reduces the sensitivity of the closing operation of the main control piston to tolerances in the size and in the position of the bores 84 in comparison to a solution without a bore 87.
| Number | Date | Country | Kind |
|---|---|---|---|
| 100 54 704 | Nov 2000 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP01/12094 | 10/19/2001 | WO | 00 | 4/18/2003 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO02/36967 | 5/10/2002 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3024732 | Nyman | Mar 1962 | A |
| 3273581 | McAfee | Sep 1966 | A |
| 3621881 | Vicari | Nov 1971 | A |
| 4114637 | Johnson | Sep 1978 | A |
| 6135142 | Yokota et al. | Oct 2000 | A |
| Number | Date | Country |
|---|---|---|
| 670873 | Jul 1989 | CH |
| 1043819 | Nov 1958 | DE |
| 3401369 | Aug 1984 | DE |
| 3401360 | Aug 1985 | DE |
| 3608100 | Sep 1987 | DE |
| 4112065 | Oct 1992 | DE |
| 1207085 | Sep 1970 | GB |
| Number | Date | Country | |
|---|---|---|---|
| 20040099828 A1 | May 2004 | US |
