Bellows accumulator

A bellows accumulator has at least one accumulator housing (2) and a separating bellows (20) movably arranged in the accumulator housing (2). The separating bellows 20 has a plurality of bellows folds and separates two media spaces (8, 22) from one another. The stationary open end of the separating bellows (20) is fixed to the accumulator housing (2) by a securing device (24). The separating bellows (20) has, at its movable other end, a closure part (36) having a guide device (40) by which the closure part (36) is guided in the accumulator housing (2). The closure part (36) has, in addition to the guide device (40), a sealing device (50). At least in the one extended end position of the separating bellows (20), the sealing device (50) separates a fluid space (8), in which the bellows folds are arranged in the accumulator housing (2), from a fluid port (12) in the accumulator housing (2). At least in some of the other working positions, the sealing device (50) releases this fluid connection.

FIELD OF THE INVENTION

The invention relates to a bellows accumulator having of at least one accumulator housing and having a separating bellows, which is movably arranged in the accumulator housing. The separating bellows has a plurality of bellows folds and separates two media spaces from each other in the accumulator housing. The stationary open end of the separating bellows is fixed to the accumulator housing by a securing device. The separating bellows has, at its movable other end, a closure part having a guide device used to guide the closure part in the accumulator housing.

BACKGROUND OF THE INVENTION

Bellows accumulators of this type are state of the art, see for instance DE 10 2015 012 253 A1 (corresponding to U.S. Patent Application Publication No. 2018/0245656). Bellows accumulators are advantageously used in hydraulic systems, preferably to reduce or smooth pressure peaks occurring in pressure fluids. To ensure that the separating bellows during operation can move freely and without the risk of damage into its respective working positions, the outer diameter of a bellows is selected to be slightly smaller than the inner diameter of the accumulator housing. The guide device of the closure part is used to guide the bellows such that a gap is formed between the tips of the bellows and the housing wall in the working positions. This gap forms a part of the media chamber of the liquid side and, in operation, is pressurized with the fluid pressure applied from one fluid port. The inside of the bellows, from its open end, is pressurized with the pre-fill pressure existing in the other media chamber. During operation, the pressure balance between the liquid pressure acting in the gap and the pre-fill pressure prevents the bellows from being pressed against the inner wall of the housing and being damaged. However, this prevention is different in operating states, in which the liquid side is depressurized or the liquid pressure drops below the pre-fill pressure. Because of the pressure present in the bellows' interior, when the gap is depressurized or only slightly pressurized, the tips of the bellows are pressed against the inner wall of the housing and damaged thereby.

SUMMARY OF THE INVENTION

With regard to this problem, the invention addresses the problem of providing a bellows accumulator of the genus mentioned above, which is characterized by a high degree of operational reliability compared to the prior art.

According to the invention, this problem is basically solved by a bellows accumulator having, as an essential feature of the invention, the closure part having, in addition to the guide device or guide, a sealing device or seal. At least in the one extended end position of the separating bellows, the sealing device separates a fluid space, in which the bellows folds are arranged in the accumulator housing, from a fluid port in the accumulator housing and releases this fluid connection, at least in some of the other working positions. In this way, in operation when the fluid connection is released, the mode of operation of the bellows accumulator according to the invention equals that of the known bellows accumulator mentioned, as long as the bellows is not in the extended end position and the pressure between the fluid chamber in the gap and the bellows interior is balanced.

As soon as the bellows reaches its extended end position because of a predominant pre-fill pressure, the sealing device of the guide unit blocks the fluid chamber on the outside of the bellows. The enclosed fluid volume supports the bellows against the pre-fill pressure acting from the interior. The bellows is thereby protected against damage at pressure ratios, where the pre-fill pressure is greater than the liquid pressure. If temperature changes occur in the operating state, in which the liquid volume in the gap is enclosed by the sealing device, with a resulting expansion or contraction of the fluid volume corresponding to the coefficient of thermal expansion, this may cause a deformation of the bellows. To keep this deformation and accordingly the stresses in the bellows below a threshold value, which could negatively affect the service life of the bellows, the gap width and accordingly the enclosed liquid volume are set to a small size. As stated in the prior art document DE 10 2015 012 253 A1 cited, the gap dimension in bellows accumulators of this type can be smaller than 1 mm. In such small liquid volumes, temperature changes are not critical even across a wide range. The bellows accumulator according to the invention can therefore also be used advantageously in aerospace applications where high temperature differences must be safely controlled.

Advantageously, the sealing device on the closure part can be set back reduced in the diameter from the guide device. At the housing side, a housing wall part reducing the inner diameter of the housing and forming a sealing surface can be provided for interaction with the sealing device having a reduced diameter.

In advantageous exemplary embodiments, the closure part has a dome at its end facing the fluid port. In the area of the fluid port the convex outer contour of the dome follows the inner contour of the accumulator housing and is brought at least partially into contact with that inner contour in one end position. In the end position, practically no fluid dead volume remains in the area of the accumulator housing adjacent to the fluid port.

Advantageously, a shoulder is formed on the inside of the accumulator housing. Against said shoulder, the separating bellows moves in its one end position, closing the port.

Advantageously, the arrangement can be made in such a way that the shoulder is provided with a slope that tapers in the direction of the port and that forms a blocked fluid transition between the guide device and the sealing device in the one end position that closes the port. The conical surface can form a ramp, up which the sealing device moves onto a projecting sealing surface of the accumulator housing when the end position is reached.

In advantageous exemplary embodiments, the guide device of the closure part has a guide ring having individual guide segments, which are in contact with the inner wall of the accumulator housing in every working position of the separation bellows and delimit passage spaces for fluid therebetween. When the bellows is in the working positions, the fluid chamber on the outside of the bellows is connected to the fluid port via the passage spaces of the guide ring.

The outer diameter of the bellows folds can advantageously be selected to be slightly smaller than the assignable inner diameter of the accumulator housing such that in the fluid space partial spaces are formed. Those partial spaces in their entirety form a hydraulic damping of the fluid.

The sealing device can advantageously be arranged on the closure part between the guide device and the dome.

Advantageously, the arrangement is further such that in the end position of the separating bellows opposite from the one end position, the bellows folds are in full contact with one another.

In the manner known per se for bellows accumulators, the accumulator housing can be wrapped to increase its resistance to pressure. Such a wrap, technically known as a liner, can be formed from a glass fiber composite.

Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the drawings, discloses a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiment of the bellows accumulator according to the invention shown inFIG. 1has an accumulator housing2. Accumulator housing2has two housing parts, with one part forming a main housing part4and the other part forming a housing closing part6. The main part4has the form of a pot having a circular-cylindrical interior8and a dome-shaped pot bottom10, which is closed except for a fluid port12coaxial with the longitudinal axis14. The closing part6is shaped like a semispherical bowl, which is closed except for a filling opening16coaxial with the axis14. The main part4and the closing part6are welded together along their end rims facing each other at a weld line18. A separating bellows in the form of a metallic bellows20is accommodated in the circular cylindrical interior8between the weld line18and the pot bottom10. As is common with bellows for bellows accumulators, the bellows20is made of a stainless steel. In the present example, a chromium-nickel-molybdenum steel alloy (AM350) is provided. At its end at the top inFIG. 1, the bellows20is open to the gas end22, adjacent to the filling opening16of the accumulator housing2. The last bellows side of the bellows20at its top end is welded to a retaining ring24, which forms the securing device used to fix the immovable bellows end of the bellows20to the accumulator housing2. The retaining ring24is formed of stainless steel, for instance steel 1.4435, and is welded to the housing parts4and6at the weld line18by laser welding.

At its other, movable free end, which is opposite from the open bellows end connected to the retaining ring24, the interior of the bellows20, which is open towards the gas end22, is closed by a closure part36made of stainless steel (such as steel 1.4435), which closure part is firmly welded to the facing bellows end. The closure part36has the shape of a circular bowl, on the outer circumference of which, starting from the open rim of the bowl38, a guide device or guide40and a sealing device or seal42adjoining it are formed, seeFIG. 2. As can be seen most clearly fromFIG. 2, the guide device40has a circumferential annular groove46near the rim of the bowl38. In that annular groove46, a guide ring in the form of a flat ring54is received. The sealing device42has an annular groove48that is offset axially from the annular groove46of the guide device40in the direction towards the pot bottom10and that extends radially inwards. A gasket50is received in the annular groove48. At the underside adjoining the lower annular groove48, the closure part36is closed by a dome part44.

The flat ring54, forming the guide ring of the guide device40in the annular groove46, has the function of guiding the bellows folds along the inner wall during movements out of the end position shown inFIGS. 1 and 2, while maintaining a gap in the interior8between the tips of the bellows and the housing wall. For this purpose, the guide ring is made of a plastic having good sliding properties, such as polytetrafluoroethylene, as shown in FIGS. 5 and 6 of EP 2 519 748 B1. To form passage spaces at the circumference of the flat ring54to permit fluid to pass from the fluid port12into the interior8surrounding the bellows20, recessed areas are formed as passage spaces at the circumference of the flat ring54between guide bodies abutting the housing wall as guide shoes. In operation, therefore, the interior8, surrounding the bellows20, forms a part of the fluid side. When the bellows20is not fully compressed, the spaces between the bellows folds form damping spaces as part of the fluid side. The volumes of the damping spaces change correspondingly during the bellows movements in operation. One damping throttle each is formed between every tip of the folds and the inner wall of the housing. The selected gap dimension between the inner wall of the main part4and the tips of the bellows determines the throttle cross-section.

As is most clearly shown inFIG. 2, a shoulder is formed at the transition between the main housing part4and the pot bottom10. Up against the shoulder, the closure part36of the bellows20runs when in the extended end position. The shoulder is provided with a slope, which tapers in the direction of the fluid port12, thereby forming a ramp surface52. The gasket50of the sealing device42traverses ramp surface52during movement into the end position, and where the gasket comes into contact with a sealing surface56formed by a radially inwardly offset, circular cylindrical wall part of the accumulator housing. As a result, in the end position shown in the figures, the fluid connection between the fluid port12and the interior8is blocked, such that the volume of fluid, located in the gap of the interior8, is enclosed as long as the bellows is in its extended end position. In the working positions, in which the gasket50has left the sealing surface56, the fluid connection between the fluid port12and the gap in the interior8is opened for normal operation.

As shown inFIG. 1, the main housing part4has, starting from a thickened wall part58adjoining to the weld line18, an area of reduced wall thickness extending to the area of the pot bottom10. As indicated inFIG. 1, this area has a fiber wrap60of fiberglass material extending beyond the weld line18up to the beginning area of the housing part6. The fiber wrap60, increasing the compressive strength, with regard to their structure corresponds to the wraps known by the technical name “liner” in pressure vessels.