Piston accumulator

Abstract

The invention relates to a piston accumulator having an accumulator housing (10) in which a separating piston (12) is longitudinally movably guided which separates two fluid chambers (14, 16), in particular separates a fluid chamber (14) having a working gas from a further fluid chamber (16) having an operating fluid, such as hydraulic oil, and which separating piston has a damping device (18), characterised in that, in addition to the damping device (18), an inflow device (20) is provided which interacts with the damping device (18) for damping a fluid flow out of the accumulator housing (10) by forming a throttle along a fluid path (22) and which releases a further fluid path (24) by bypassing the other fluid path (22) that has the throttle in order for fluid to flow into the accumulator housing (10).

Description

[0001] The invention relates to a piston accumulator with the features in the preamble of claim 1.

[0002] EP 0 286 777 A2 discloses a generic piston-cylinder unit with piston end-position damping, which has a damping piston projecting from the end face of the piston. This damping piston can be retracted into a damping chamber provided at the opposite end of the cylinder, forming a damping gap that tapers conically towards the fluid connection. A flow path, acting as a return flow device, is provided to initiate a return stroke movement of the piston. This flow path leads from the hydraulic fluid connection for pressurized oil, bypassing the damping gap, to the pressure chamber in the accumulator housing adjacent to the main piston surface. The flow path includes a check valve. This flow path, which is controlled by the check valve, extends within the piston between an inlet opening at the front end of the damping piston, which is designed as a hollow sleeve, and a transverse channel leading from the interior of this sleeve to the outside.The check valve used in this application features a solid valve plate actuated by an energy storage device in the form of a compression spring. This spring controls a large opening cross-section in the damping piston, which leads to leaks in the closed position and is accompanied by turbulence in the flow when the valve is open. Furthermore, rapid opening and closing processes are impossible due to the inertia of the valve plate.

[0003] Further piston accumulators are derived from the GB 755 342 A, the US 3 043 341 A and the JP S60-188601 A.

[0004] Based on this state of the art, the invention therefore aims to further improve the known solution by creating a piston accumulator with improved end-position damping for the separating piston and improved response behavior when fluid flows into and out of the hydraulic accumulator.

[0005] A piston accumulator with the features of claim 1 in its entirety solves such a problem.

[0006] According to the characterizing part of claim 1, the afterflow device for damping a fluid flow out of the storage housing interacts with the damping device to form a throttle along a fluid path, and the afterflow device for the inflow of fluid into the storage housing opens a further fluid path by bypassing the one fluid path with the throttle, resulting in reliable damping of the separating piston during discharge of the piston accumulator, up to its possible stop position against parts of the storage housing, such as a housing cover, and in the opposite direction of movement of the separating piston during charging of the accumulator and flow of operating fluid into the further fluid space, the afterflow device opens by bypassing the one fluid path with the throttle.This causes the entire piston cross-section to be directly pressurized with fluid at a predetermined pressure, initiating the movement of the separating piston against the preload pressure of the working gas in the other fluid chamber. In this way, high dynamics are achieved for the return movement of the separating piston during a storage charging process.

[0007] If, during the further retraction movement of the separating piston towards the fluid chamber with the working gas, the damping device completely disengages from the inflow device, then an additional inflow of fluid into the further fluid chamber is achieved via the fluid cross-section released in this respect, which further helps to accelerate the charging process for the storage device.

[0008] The solution according to the invention therefore not only achieves improved damping behavior during the unloading of the piston accumulator, but also improved, unimpeded backflow during the accumulator charging process, in which the separating piston is moved against the preload pressure of the working gas in one fluid chamber.

[0009] In a preferred embodiment of the piston accumulator according to the invention, the damping device comprises a damping piston on the separating piston, and the return flow device comprises a return flow piston that is movably guided in parts of the accumulator housing. Due to the low inertia of the damping piston and the return flow piston, the fluid flows occurring during the charging and discharging of the piston accumulator can be reliably controlled in rapid succession. This allows piston accumulators, which must withstand a high number of load cycles at potentially high fluid pressures, to be improved in terms of charging and discharging processes compared to prior art solutions.

[0010] In a further preferred embodiment of the piston accumulator according to the invention, the damping piston engages in a recess in the downstream piston, forming a throttle gap in one fluid path, thus acting as a throttle. The throttle gap is a cylindrical annular space with variable volume, formed from adjacent wall sections of the damping and downstream pistons. In this way, a constant throttle gap width is achieved over the entire engagement length of the damping piston in the downstream piston, resulting in significantly improved end-position damping.Since no continuously changing gap geometry with conical sections, as shown in the aforementioned prior art, needs to be taken into account, the engagement length for the damping piston can be chosen to be extremely long within predefinable limits, due to the geometry to be maintained for the piston accumulator, so that in conjunction with the constant gap dimension over the entire engagement length a significantly improved piston end position damping is achieved.

[0011] In a further preferred embodiment of the piston accumulator according to the invention, the afterflow piston is housed in a casing cover as part of the accumulator housing and inserted into a fluid connection that establishes a fluid connection to the further fluid chamber containing the operating fluid via the respective fluid path. In this way, both the damping device and the afterflow device, with their respective controlled fluid paths, are housed in the casing cover in a space-saving manner. Due to the chosen design, this arrangement can also be retrofitted into existing piston accumulators of conventional design, thereby improving their damping and afterflow characteristics.

[0012] In a further preferred embodiment of the piston accumulator according to the invention, the afterflow piston is axially movable in the housing cover by means of a snap ring such that, in a lowered position, the further fluid path is blocked and, in a raised position, this fluid path is opened. Due to the snap ring fastening, both the damping device and the afterflow device can be attached to the separating piston at its free end face in a particularly assembly-friendly manner and jointly accommodated in a fluid connection in the adjacent housing cover in one end position of the separating piston. The fluid connection establishes a fluid connection between the further fluid space between the separating piston and the housing cover and a conventional hydraulic circuit with its components, which can be connected to the fluid connection by means of piping.

[0013] In a further preferred embodiment of the piston accumulator according to the invention, the return flow piston is inserted into an enlarged cross-section in the housing cover such that a cylindrical flow chamber is created between the cylindrical outer circumference of the return flow piston and the adjacent, opposite inner circumference of the housing cover, forming part of the further fluid path. Preferably, it is further provided that the return flow piston is provided on its end face facing away from the separating piston with a convexly extending contact surface, which can be brought into contact with a conical bearing surface in the housing cover, forming a valve seat.Thanks to the partially convex valve seat, even when using the snap ring guide, a flexible, clearance-based bearing for the downstream piston on the separating piston is achieved. This compensates for tolerances between the separating piston, including its seal and a guide band, and the adjacent wall or casing components of the storage housing, particularly the associated housing cover. For improved valve seat geometry, the free end face of the downstream piston, facing away from the separating piston, can also be hexagonal or have a "mirror" surface.

[0014] For safe guidance of the damping piston in the afterflow piston, it is preferably provided that, at least in the fully discharged state of the piston accumulator, the damping piston completely penetrates the afterflow piston and preferably engages with an at least partially conical end part as an insertion aid in the afterflow piston until a protrusion is reached at the edge.

[0015] The invention further relates to a method for operating a piston accumulator, as described above and characterized by the following process steps: Throttlement of the volume flow during discharge of the piston accumulator by forming a hollow cylindrical throttling gap between the damping and the afterflow device, bypassing the throttling gap during charging of the piston accumulator by opening the afterflow device, and thereby pressurizing the entire free cross-section of the separating piston with fluid pressure for direct movement of the separating piston towards the fluid space with a working gas.

[0016] The piston accumulator according to the invention will now be explained in more detail using an exemplary embodiment as shown in the drawing. Fig. 1 shows, in the manner of a longitudinal section, the lower part of an otherwise conventional piston accumulator, as exemplified in the aforementioned EP 0 286 777 A2; and Fig. 2 shows one of the Fig. 1 corresponding representation, but in an open piston position, and without the representation of a piston mounting.

[0017] The Fig. 1 Figure 1 shows the lower part of a piston accumulator with a hollow cylindrical wall section 8 of an accumulator housing designated as a whole by 10, in which a separating piston 12 is longitudinally guided, separating two fluid chambers 14, 16 from each other, in particular a fluid chamber 14 containing a working gas, such as nitrogen, from another fluid chamber 16 containing a working fluid, such as hydraulic oil. Furthermore, the separating piston 12 has a damping device 18 integrally connected to it at its free end face. A return flow device 20 is also provided, which, for damping a fluid flow out of the accumulator housing 10, interacts with the damping device 18 to form a throttle along a fluid path 22 and, according to the simplified representation shown in Figure 1, allows fluid to flow into the accumulator housing 10. Fig. 2 , releases another fluid path 24 by bypassing the one fluid path 22 with the throttle.

[0018] As the Fig. 1 und 2 As further shown, the damping device 18 has a damping piston 26, which is preferably integrally connected to the separating piston 12 and arranged centrally on the free lower end face 28 of the separating piston 12. Furthermore, the return flow device 20 has a return flow piston 30, which is movably guided in parts of the storage housing 10, here in the form of a housing cover 32. The aforementioned housing cover 32 is screwed into the bottom of the hollow cylindrical wall section 8 of the storage housing 10 and sealed against the rest of the storage housing 10 by means of a ring seal (not shown). The separating piston 12 itself has two annular grooves 34, 36 on its outer circumference for receiving sealing rings and guide bands (not shown).

[0019] For a damping process, the damping piston 26 moves from an upper position into a cylindrical recess 38 ( Fig. 2 ) in the downstream piston 30, forming a throttle gap 40, the fluid enters the first fluid path 22 thus formed. This movement of the separating piston 12 from top to bottom towards the liquid side of the accumulator is completed when, according to the illustration, Fig. 1 The separating piston 12, with its end face 28, comes at least partially into contact with the top surface 42 of the housing cover 32. Individual stop elements 44, distributed circumferentially on the end face 28 of the separating piston 12, serve as stop limits for the end face 28. According to the illustration in the Fig. 1 und 2 Thus, an annular gap 46 is formed between the flat end face 28 of the separating piston 12 and the upper surface 42 of the housing cover 32, extending to the stop elements 44. This gap acts as an additional damping gap and, in a damping function, displaces fluid from the further, second fluid chamber 16 towards the throttling gap 40, formed by the adjacent wall sections of the damping piston 26 and the afterflow piston 30. In the discharge position of the accumulator, the operating fluid thus displaced from the fluid chamber 16 flows towards a fluid connection 48, through which the accumulator can be connected to a hydraulic working circuit by means of conventional piping (not shown). In this respect, the accumulator is held depressurized on the side of the fluid connection 48 for the discharge process, and under the pre-charge pressure of the working gas in the fluid chamber 14, the separating piston 12 moves to its end position shown in the figure.

[0020] The afterflow piston 30 is received in a receiving chamber 50 in the lower housing cover 32 as part of the storage housing 10 and, as already described, is inserted into the fluid connection 48, which establishes a fluid connection to the further fluid chamber 16 with the operating fluid via the respective fluid path 22, 24, as well as via a third fluid path 52, which results when, through the return stroke movement of the separating piston 12 in a storage charging position under the fluid pressure at the fluid connection 48, the damping piston 26 together with the upward movement of the separating piston 12 comes completely out of engagement with the hollow cylindrical recess 38 in the afterflow piston 30.

[0021] Before the damping piston 26 comes out of engagement with the afterflow piston 30, it is, according to the illustration, after the Fig. 2 First, the damping piston 26 is lifted axially upwards by the fluid pressure in the fluid port 48, with the outer circumferential side forming a cylindrical partial guide for this purpose. Therefore, according to the illustration, the following occurs: Fig. 2 The fluid pressure in the fluid port 48 of the downstream piston 30 raises the piston and opens the second fluid path 24 in such a way that more fluid reaches the free end face 28 of the separating piston 12 and, under the fluid pressure, against the preload pressure of the working gas, raises the piston in the fluid chamber 14 together with the damping piston 26. In this way, a fluid connection 54 to the further fluid chamber 16 containing the operating fluid is established, as shown in the illustration. Fig. 2 , produced via the second fluid path 24.

[0022] Both the separating piston 12 and the two pistons 26, 30, as well as the fluid connection 48 in the lower housing cover 32, are arranged concentrically to each other and coaxially to a longitudinal axis 56 of the storage housing 10. This allows the return flow piston 30 to move from its closed position to the Fig. 1 into an open passage position after the Fig. 2 and vice versa, this is achieved by means of an elastic snap ring 58 (only in Fig. 1 (shown) is axially movable in the housing cover 32. For this purpose, the snap ring 58 engages on its outer circumference in a corresponding inner groove in the housing cover 32, and on its inner circumference it is protected only by a Fig. 1 the depicted system shoulder 60 penetrated, which in the raised position of the afterflow piston 30 after the Fig. 2 in conjunction with the inner circumferential side of the snap ring 58 and otherwise can protrude downwards from the snap ring 58 by a predetermined distance, as shown in the illustration. Fig. 1 . In this way, the snap ring 58 makes it possible to block the further fluid path 24 in a lowered position of the afterflow piston 30 ( Fig. 1 ) and in a counter-rotating, raised position this fluid path 24 is released ( Fig. 2 For this function, the afterflow piston 30 is inserted into an enlarged cross-section 62 in the housing cover 32, forming the fluid connection 54, such that a cylindrical flow space is created between the cylindrical outer circumference of the afterflow piston 30 and the adjacent inner circumference of the housing cover 32 to establish the fluid connection 54.

[0023] The afterflow piston 30 has a convexly shaped, in particular convex, contact surface 64 on its end face facing away from the separating piston 12, which forms a kind of valve seat 66 ( Fig. 1 ) in conjunction with a corresponding, conically extending bearing surface 68 in the housing cover 32. Due to the convex design, self-adjustment for the afterflow piston 30 towards the aforementioned valve seat 66 on the housing cover 32 is thus achieved. This also ensures centering for the separating piston 12, provided that it enters the corresponding, hollow cylindrical recess 38 in the afterflow piston 30 by means of the cylindrical damping piston 26, as the throttle gap 40 increases.

[0024] In a fully discharged state, as shown in the illustration below. Fig. 1 The damping piston 26 then completely penetrates the afterflow piston 30 and the damping piston 26 protrudes at least partially with a conically extending end part 70 over the afterflow piston 30 at its edge, whereby the end chamfer formed thereby on the damping piston 26 allows an unimpeded engagement with the afterflow piston 30, with the associated downward movement of the separating piston 12 during a discharge process on the liquid side of the hydraulic or piston accumulator.

[0025] When orientations such as "top" and "bottom" are mentioned in the description, this refers to a typical operating mode of the piston accumulator in a vertical orientation.

[0026] The one in the Fig. 1 und 2 The piston accumulator shown is operated in such a way that at least the following process steps are implemented: Throttlement of the volume flow during discharge of the piston accumulator by the formation of the hollow cylindrical throttling gap 40 between damping piston 26 and the return piston 30, whereby the associated downward movement of the separating piston 12 displaces fluid from the fluid chamber 16 via the throttling gap 40 towards the depressurized fluid connection 48. Further throttling occurs through the annular gap 46 as a damping gap between the free end face 28 of the separating piston 12 and the adjacent opposite top surface 42 of the housing cover 32; bypassing these throttling or damping gaps 40, 46 during charging of the piston accumulator by opening the further fluid connection 24 by lifting the return piston 30 from its valve seat 66 from the closed position. Fig. 1 into the open position after the Fig. 2 Due to the resulting pressure difference, pressurized fluid enters the piston fluid chamber 72 between the separating piston 12 and the housing cover 32 via the fluid connection 48. Consequently, the separating piston 12 lifts upwards (as viewed in the figure) and, with further movement against the pre-charge pressure of the working gas in the fluid chamber 14, the fluid volume on the fluid side of the accumulator with the fluid chamber 16 increases progressively. If, during this upward movement of the separating piston 12, the central recess 38 is released by the extension of the damping piston 26 from the downstream piston 30, a further, third fluid path 52 is opened, allowing fluid of a predetermined pressure to flow directly into the piston fluid chamber 72 via the fluid connection 48.This results in the entire free piston cross-section being pressurized with fluid pressure to directly move the separating piston 12 towards the other fluid chamber 14 containing the working gas. In this way, a storage charging process takes place in the usual manner, and after completing the corresponding operating cycle, the piston storage unit is then available again for a described discharge process.

[0027] According to the presentation after the Fig. 1 In the area of ​​an internal thread 74 of the fluid connection 48, a damping valve, designated as a whole by 76, is provided, with a longitudinally movable valve plate 78 into which a throttle bore 80 is provided coaxially to the longitudinal axis 56 of the piston accumulator. The valve plate 78 is received in a valve housing 82, preferably designed as a tripod, which is screwed flush into the associated fluid connection 48 along the internal thread 74. Since there is a fluid supply 84 between each leg of the valve housing 78, in the position shown, for charging the accumulator via a bottom inlet 86 in the valve housing 78, fluid from the hydraulic working circuit can flow in through the fluid connection 48 at a predeterminable pressure towards the fluid chamber 16 with the afterflow device 20 open. In the opposite direction, i.e., when discharging the accumulator, the valve plate 78 moves from its position in the Fig. 1 The upper travel position shown is moved to a lower closed position, in which the valve plate 78 rests on the inside of the valve housing 82, and fluid passage is then only possible via the throttle bore 80 in the valve plate 78, so that, in addition to the already described throttling measures 40 and / or 46, the damping valve 76 also provides a reduction in the fluid flow. Further details on the function and construction of such damping valves can also be found by way of example in DE 103 37 744 B3.

[0028] Piston accumulators of this type, as described, regularly exhibit a high preload pressure, which generates large forces on the separating piston 12 and its sealing system, especially during rapid discharge below the gas preload pressure. Upon reaching the pressure in the Fig. 1 und 2 At the piston's end position shown, sudden shock loads act on the separating piston 12 and its associated piston seal. This, in turn, causes the seal to be constantly and abruptly pressed against the groove flank facing the hydraulic oil in the annular groove 34 of the separating piston 12 by the prevailing gas pressure. This dynamic in the sealing system, and the resulting settling effects of the seal in the annular groove 34, lead to increased gas loss from the piston accumulator. Furthermore, the harsh metal-to-metal impacts between the separating piston 12 and the housing cover 32 are acoustically disruptive, and in extreme cases, this can also lead to mechanical damage in this area.

[0029] The hydraulic end-position damping according to the invention, as presented, ensures that the separating piston 12 moves into its position at a reduced speed. Fig. 1The end position shown is maintained. This also reduces the shock load on the sealing system, effectively limiting gas losses and overall wear of the storage tank. This has no equivalent in the prior art.

Claims

1. Piston accumulator having an accumulator housing (10), in which a separating piston (12) is guided so as to be longitudinally displaceable, which separating piston separates two fluid chambers (14, 16) from each other, in particular separates a fluid chamber (14) having a working gas from a further fluid chamber (16) having an operating fluid, such as hydraulic oil, and which separating piston has a damping device (18), an inflow device (20) being provided in addition to the damping device (18), characterised in that the inflow device (20) cooperates with the damping device (18) for damping a fluid flow out of the accumulator housing (10) by forming a throttle along a fluid path (22), and in that the inflow device (20) releases a further fluid path (24) by bypassing the one fluid path (22) that has the throttle in order for fluid to flow into the accumulator housing (10).

2. Piston accumulator according to claim 1, characterised in that the damping device (18) has a damping piston (26) on the separating piston (12) and in that the inflow device (20) has an inflow piston (30) which is movably guided in parts (32) of the accumulator housing (10).

3. Piston accumulator according to claim 2, characterised in that, for a damping process, the damping piston (26) engages in a recess (38) in the inflow piston (30), forming a throttle gap (40) as the throttle in the one fluid path (22).

4. Piston accumulator according to claim 3, characterised in that the throttle gap (40) is a cylindrical annular space with variable volume, formed from adjacent wall parts of the damping (26) and inflow pistons (30).

5. Piston accumulator according to one of claims 2 to 4, characterised in that the inflow piston (30) is accommodated in a housing cover (32) as part of the accumulator housing (10) and is inserted into a fluid port (48), which establishes a fluid connection (54) to the further fluid chamber (16) having the operating fluid via the respective fluid path (22, 24).

6. Piston accumulator according to claim 5, characterised in that the inflow piston (30) is supported in the housing cover (32) in an axially displaceable manner by means of a circlip (58) in such a way that in a lowered position the further fluid path (24) is blocked and in a raised position this fluid path (24) is released.

7. Piston accumulator according to either claim 5 or claim 6, characterised in that the inflow piston (30) is inserted into an enlarged cross-section (62) in the housing cover (32) in such a manner that a cylindrical flow chamber is created between the cylindrical outer circumference of the inflow piston (30) and the adjacent opposing inner circumference of the housing cover (32).

8. Piston accumulator according to one of claims 2 to 7, characterised in that, on its end face directed away from the separating piston (12), the inflow piston (30) is provided with a crowned contact surface (64), which can be brought into contact with a conical support surface (68) in the housing cover (32), forming a valve seat (66).

9. Piston accumulator according to one of claims 2 to 8, characterised in that, in its fully discharged state, the damping piston (26) engages completely through the inflow piston (30) and preferably protrudes over the edge of the inflow piston (30) with an at least partially conical end part (70).

10. Method for operating a piston accumulator according to one of the preceding claims, characterised by the following method steps: - throttling of the volumetric flow during discharging of the piston accumulator by forming a hollow cylindrical throttle gap (40) between the damping device (18) and the inflow device (20), - bypassing the throttle gap (40) during charging of the piston accumulator by opening the inflow device (20), and as a result - applying fluid pressure to the entire free cross-section of the separating piston (12) for directly displacing the separating piston (12) towards the fluid chamber (14) having a working gas.

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