Hydraulic accumulator, in particular bellows accumulator

A bellows accumulator has a bellows (13) serving as a movable separating element between a gas side (11) and a fluid side (21). At the movable bellows end during expansion and contraction in the accumulator housing defining a longitudinal axis (9), a closure body (25) closes off the interior space (33) of the bellows (13) in a fluid-tight manner. At its other bellows end (27), the bellows is immovably fixed to the accumulator housing (1). The immovable bellows end (27) is fixed to an end body (31) fixed to the housing, which end body (31) is in the form of a disk with region (37) projecting axially into the interior (33) of the bellows (13) from the main plane (35) of the disk. At least one fluid passage (41, 43) is formed on the projecting region (37), which fluid passage (41, 43) connects the interior space (33) associated with the fluid side (21) to a fluid connection (17) of the accumulator housing (1).

FIELD OF THE INVENTION

The invention relates to a hydraulic accumulator, in particular in the form of a bellows accumulator, in which the bellows serves as a movable separating element between a gas side and a fluid side and has a closure body closing off the interior space of the bellows in a fluid-tight manner on that end of the bellows that is capable of moving in the axial direction during expansion and contraction in the accumulator housing defining a longitudinal axis. The other bellows end of the bellows is secured to be immovable relative to the accumulator housing.

BACKGROUND OF THE INVENTION

Hydraulic accumulators comprising a bellows that serves as an movable separating element are known and used in a plurality of technical fields, for example, in hydraulic brake systems for vehicles and in various kinds of industrial hydraulic systems. EP 1 052 412 A2, for example, discloses a bellows accumulator with a metal bellows that serves as a movable separating element between a gas side and a fluid side.

In hydraulic accumulators of this type, the bellows represents the element with the highest stress and the component that is critical to operational safety. While the risk of damage is rather low when the bellows is extended so that the folds of the bellows that have approached one another are moved away from each other, compressive strain may occur when the bellows are completely contracted so that the adjacent folds of the bellows are compressed. Such a risk exists especially if total contraction of the bellows occurs suddenly in operation.

SUMMARY OF THE INVENTION

An object of the invention is to provide an improved hydraulic accumulator in the form of a bellows accumulator that effectively avoids the risk of the bellows being damaged in operation.

The object of the invention is basically achieved by a hydraulic accumulator where the immovable end of the bellows has an end body that forms not only the fluid connection between the interior space of the bellows associated with the fluid side and a fluid connection of the accumulator housing, but this end body also has a region that projects axially into the interior of the bellows. In this way, the end body with its projecting region can form, as an additional function, an end or safety stop for the closure body of the movable bellows end that comes to rest against the projecting region during contraction of the bellows. The axial height of the elevation is chosen such that the closure body of the movable end of the bellows end comes to rest against the projecting region of the end body during contraction before the adjacent folds of the bellows are compressed with one another. As a result, increased operational safety is achieved in long term operation.

In especially advantageous embodiments, the projecting region in the interior of the bellows defines a central plane that extends perpendicularly to the longitudinal axis. The result of this arrangement is a flat safety stop with a large surface against which the closure body can rest so as to be tilt proof.

In especially advantageous embodiments, the central plane in relation to the longitudinal axis is defined concentrically and at the edge by an inclined plane sloping downward to the main plane. The fluid passages are passages that are formed at least in the inclined plane and that slope downward in the direction of the longitudinal axis. This configuration of the fluid passages offers the additional advantage that these passages may serve as the flushing ports, because they extend into the bellows interior at the slope between the projecting central part and the bellows interior. During contraction of the bellows, the dirt particles that may have collected in the annular space between the inclined plane and the bellows interior are flushed out of the flushing ports.

It may be advantageous to have, in addition to the downward sloping passages, additional axial passages in the axially projecting region of the end body as the fluid passages. As a result of the additional axial passages the flow cross section between the interior space of the bellows and the fluid connection of the accumulator housing is significantly enlarged.

Advantageously the downward sloping passages can be equidistant from each other on the inclined plane. The axial passages can be arranged in circular rings that are concentric with the longitudinal axis in the axially projecting region.

As an alternative, the fluid passages can be arranged such that the region projecting into the interior of the bellows is connected to the central plane at the edge regions of the central plane by connecting parts that slope downward in the direction of the main plane. The fluid passages are formed by intermediate spaces between the connecting parts. In contrast to the formation of downward sloping passages, for example, by introducing oblique drill holes, the exemplary embodiments in which the central plane is connected to the other part of the interior body only at individual edge regions, are characterized by their extreme ease of production and, thus, low manufacturing costs.

The pertinent arrangement can be configured such that the central plane has a square shape and that each corner of the square has a connecting part.

In preferred embodiments, the accumulator housing has a cup-like, hollow cylindrical main part and a housing closure part, which closes the opening of the cup and which is welded to the main part along a weld line. The end body of the bellows is secured on the periphery of the accumulator housing in the region of the weld line. This feature permits an efficient production process in that both the end body is secured and the accumulator housing is closed in one combined welding step.

The side of the end body opposite the projecting region can form an annular area that extends into a radial plane and that surrounds a depression concentric with the axis and defined by the wall of the axially projecting region.

If, in this case, the annular area of the end body surrounds the coaxial fluid connection in the housing closure part in alignment with the radially inner edge of the annular area and the entrance of the depression, the result is advantageously an uninterrupted flow path from the exterior of the accumulator housing to the fluid passages in the end body.

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

DETAILED DESCRIPTION OF THE INVENTION

In the drawing, the invention is described by one exemplary embodiment in the form of a pulsation damper. An accumulator housing1has a housing main part3in the form of a circular cylindrical cup with an end5located at the top in the drawing and closed except for a charging port7. Port7is in alignment with the longitudinal axis9of the housing. In the drawing ofFIG. 1, the charging port7is still open. The gas side11, which borders on the charging port7and which is located on the outside of a metal bellows13, has not yet been filled with a working gas. The housing1is closed by a housing closure part15on the end that is located at the bottom inFIG. 1and is opposite the charging port7. This housing closure part is sealingly welded to the housing main part3along a weld line16. In the closure part15, a fluid inlet17, which is concentric with the axis9and has an inside thread19for a fluid connection, is concentric with the axis9.

In the interior of the accumulator housing1, a metal bellows13forms a movable separating element between the gas side11and the fluid side21, bordering on the fluid inlet17. A closure body25closes off the metal bellows13in a fluid-tight manner at its bellows end23that is located at the top. This closure body is formed by a flat, thin metal plate that is welded to the last bellows fold at the bellows end23. The other bellows end27, the immovable bellows end, located at the bottom inFIG. 1, is welded with the bottommost bellows fold in a fluid-tight manner to a weld region29on a metallic end body31. End body31is welded to the accumulator housing1along the weld line16between the housing main part3and the housing closure part15.

As stated, in the state depicted inFIG. 1, the gas side11has not been provided yet with a working gas under a pre-charge pressure, so that the bellows13is in the extended state, where the closure body25is in proximity to the upper end5of the accumulator housing1. When the pressure prevails on the gas side11, a fill with the working gas, such as N2, and alternating fluid pressure on the fluid side21cause the closure body25to move axially. When the hydraulic accumulator is used as a pulsation damper, in the course of which the fluid side21is in fluid connection with a compressed fluid, in particular a hydraulic fluid, a fuel, or lubricant by the fluid inlet17. In order to smooth any pressure surges that might occur, it has been proven to be advantageous for the gas side11to have not only a fill with the working gas, but also to have a predefined fraction of a fluid. In this case, a combination of nitrogen gas as the working gas and ethyl alcohol as the fluid on the gas side11of the accumulator has been proven to be especially advantageous as the fill. In operation, the fluid between the folds and deflections of the bellows13can form a damping support medium, which can support, as the back support, the folded wall sections of the bellows13on the fluid. As a result of the support, the service life of the bellows13is extended. Consequently, the functional reliability is increased. This aspect applies especially to sudden pulsations and rapid pressure surges.

The end body31, which is provided on the immovable bellows end27, forms fluid passages as a connection between the interior space33of the bellows13associated with the fluid side21and the fluid inlet. The end body31has the form of a round disk that defines a plurality of radial planes, that is, an outer plane35, which is referred to herein as the main plane and which borders on the peripheral edge, and a plane37, which is centrally located in relation to the longitudinal axis9and which forms a region which projects axially into the interior space33of the bellows13, on the end body31. The plane35, which is referred to herein as the main plane, is located at the edge of the weld region29, which projects slightly beyond this plane35and at which the immovable bellows end27is secured.

The central plane37, which forms the projecting region, is defined at the edge by an inclined plane39at an acute angle to the longitudinal axis9. The inclined plane39has oblique drill holes41, which slope downward in the direction of and at an acute angle relative to the longitudinal axis9and are arranged so as to be uniformly distributed around the periphery of the inclined plane39. The oblique drill holes form a first group of fluid passages between the fluid inlet17and the interior space33of the bellows13. A second group of fluid passages is constructed in the form of axial drill holes43in the projecting region defined by the central plane37. As shown inFIG. 2, the axial drill holes43are arranged so as to be uniformly distributed along two concentric circular lines45and47.

The side of the end body31that is opposite the planes37and35forms an annular area49which extends into a radial plane in the end body31. This annular area surrounds a depression51, which is concentric with the axis9and which is formed by the inner wall of the region. This inner wall projects into the interior space33of the bellows13and is defined by the central plane37. In the present exemplary embodiment, the radial inner edge of the annular area49and, with it, the opening edge of the depression51for opening the fluid inlet17are in alignment. An uninterrupted flow path from the fluid inlet17into the depression51of the end body31is then formed. The fluid passages formed in the end body31, that is, the oblique drill holes41in the inclined plane39as well as the axial drill holes43in the projecting region, continue the flow path into the interior space33.

The plane37of the projecting region is offset axially in relation to the main plane designated as35by such a distance in the interior space33that the plane37forms an end stop against which the closure body25rests at the movable bellows end23when the bellows13is totally contracted. The passages, formed by the oblique drill holes41, remain open as the fluid passages, even if, when the bellows13is totally contracted, with the closure body25resting flush on the plane37and closing the axial drill holes43. Even while the end body31exercises its safety or stop function, the interior space33of the bellows13remains with the remaining residual fluid volume connected to the fluid inlet17. Owing to the arrangement of the oblique drill holes41, which extend into the inclined plane39, these oblique drill holes41serve additionally as flushing ports, through which the dirt particles accumulated at the immovable bellows end27in the region between the inclined plane39and the bellows interior are flushed out during the axial movements. The closure body25carries out these axial movements in operation during contraction of the bellows13. As stated above, the distance by which the plane37projects axially in relation to the immovable bellows end27is chosen such that when the closure body25rests against the plane37, the folds of the bellows13are not pressed against each other. The pertinent arrangement can be configured such that a desired residual volume of fluid remains in the interior space33of the bellows13.

FIGS. 3 to 5depict a second exemplary embodiment, in which an end body31is provided in a simplified type of construction. The end body31of this exemplary embodiment differs from the above-described first embodiment only in the design of the region projecting into the interior33of the bellows13. As in the first example, this projecting region is also formed by a plane37extending perpendicular to the longitudinal axis9as the safety end stop for the closure body25of the bellows13. In contrast to the first described example, the plane37is square in contour. Each of the corner regions has a connecting part61, which slopes downward to the main plane35in a curved inclined course. An intermediate space63is then formed between each of the adjacent corners65. This intermediate space extends along a straight side67of the square, so that a fluid passage is formed on each square side67from the edge of the square to the opening of the depression51. As can be seen from the drawing, this embodiment does not provide that the plane37has additional axial drill holes as the fluid passages. The size of the fluid passages that are formed by the intermediate spaces63causes the flow resistance to be low even without additional axial drill holes.

The end body31in the second type of construction is easy to manufacture in that in the end bodies in the form of the end body31fromFIGS. 1 and 2that are shaped by forming or machining processes, instead of introducing the drill holes41and43at the projecting region, straight cut outs are made. These straight cut outs run along the sides67and form the square shape of the plane37while simultaneously producing the intermediate spaces63as the fluid passages.