DK2519748T3

DK2519748T3 - Hydraulic accumulator, especially bellows accumulator

Info

Publication number: DK2519748T3
Application number: DK09801178.6T
Authority: DK
Inventors: Herbert Baltes
Original assignee: Hydac Technology Gmbh
Priority date: 2009-12-30
Filing date: 2009-12-30
Publication date: 2017-01-30
Also published as: EP2519748A1; EP2519748B1; WO2011079852A1

Description

The invention relates to a hydraulic accumulator in the form of a bellows accumulator wherein the bellows serving as the mobile separating element between the gas side and the fluid side has a closing element that closes the interior of the bellows in a fluid-tight manner on its bellows end that can be moved in the axial direction during expansion and compression in the accumulator housing, and is immobilised at its other bellows end relative to the accumulator housing, a sealing system sealing the interior of the bellows from the accumulator housing on the immobile bellows end having, in addition to a first functional area having a sealing effect, a second functional area in the form of an attachment projecting into the interior of the bellows, which attachment forms a flexible buffer for the contact of the closing element of the bellows when the latter is completely compressed, and a metal bellows with a metallic closing element welded to the respective bellows end being provided.

Hydraulic accumulators with a bellows serving as a mobile separating element are known and are used in a variety of technical domains, for example in hydraulic braking systems for vehicles and a wide variety of industrial hydraulic systems. EP 1 052 412 A2 shows a bellows accumulator of the type specified at the start wherein a metal bellows is provided as the mobile separating element between the gas side and the fluid side. Since a sealing system sealing the interior of the bellows on the immobile bellows end from the accumulator housing has, in addition to a first functional area having a sealing effect, a second functional area in the form of an attachment projecting into the interior of the bellows, the advantageous possibility is offered of using the sealing system for an additional function by the flexibility of the sealing material being used for form a flexible buffer. DE 10 2007 036 487 A1 discloses a guide device for a metal bellows that has on at least one bellows end an end element that can be moved along the wall of the housing during the expansion and compression of the bellows, a guide element being provided between this end element and the housing. The guide element is formed by a plurality of separate guide elements arranged spaced apart from one another around the circumference of the end element.

At the end of the accumulator housing that has the fluid port there is a base plate which has a radially outer edge with an elastomer sealing ring disposed in a depression and a metallic centring ring on the upper side facing the fluid side. The metallic centring ring holds the elastomer sealing ring in its fitting position which in this respect forms stop damping for parts of the bellows.

In view of the prior art it is the object of the invention to make available a hydraulic accumulator in the form of a bellows accumulator which is characterised by particularly advantageous operating characteristics, and in particular guarantees reliable operation in the long term.

According to the invention this object is achieved by a hydraulic accumulator that has the features of Claim 1 in its entirety.

According to the invention at least one bulge projecting in the axial direction towards the mobile bellows end is moulded onto the attachment projecting into the interior of the bellows, at which bulge the closing element of the bellows starts to take effect when the bellows is in its fully compressed state.

In particular in applications in which vibrating movements of the mobile closing element of the bellows occur, as is the case, for example, with pulsation dampers, the flexible buffer formed by the second functional area of the sealing system acts not only as a flexible, stroke-limiting end stop for the motion of the closing element, but may also prevent any operating noises that occur due to mobile parts of the bellows striking against inflexible components.

Furthermore, according to the invention the immobile bellows end is fixed to a holding ring secured to the housing by means of a fluid-tight welded connection, the inner ring opening of the holding ring being adjacent to the interior of the bellows forming the fluid side, the sealing system forming with its first functional area the seal between the inner ring opening of the holding ring and the accumulator housing. Since the sealing system at the inner ring opening of the holding ring directly forms a seal from the accumulator housing, sealing of the interior of the bellows from its outside results irrespective of whether the holding ring on its part is sealed at the circumference in a fluid tight manner from the accumulator housing. In other words, it is sufficient if the holding ring is fixed unmovably by means of a welded connection to the housing wall, this type of welded connection not having to be continuously fluid-tight.

In particularly advantageous exemplary embodiments the accumulator housing has a main part and a housing end part on the base side with a central fluid inlet connected to the fluid side, the sealing system having a ring element the first functional area of which forms an annular sealing lip lying radially on the outside and which has a sealing effect with respect to a seat surface on the housing end part and an annular surface on the holding ring with sealing surfaces lying in radial planes.

Furthermore, the arrangement can advantageously be made so that the closing element of the bellows is in the form of a pot with a circular cylindrical side wall that extends away from the mobile bellows end into the interior of the bellows and is limited by a level pot base, the ring element having on the attachment in the form of a bulge forming the second functional area a rounded annular rib, the axial elevation of which is chosen such that the outside of the pot base rests against the annular rib when the bellows is fully compressed. This design of the closing element in the form of a pot projecting into the interior of the bellows leads to a substantial increase in the volume of the gas side. At the same time, the contact of the level pot base against the annular rib forming the flexible buffer results in centring of the bellows in the fully compressed end position.

The ring element forming the sealing system can advantageously be shaped so that the end surface of the ring element facing the seat surface on the housing end part forms a radial plane passing from the radially outer sealing surface of the sealing lip to the ring opening, the ring element having a tiered form on the opposite side.

If the arrangement is made here such that the tiered form of the outer sealing lip passing radially inwards has a first step at the transition to the attachment forming the second functional part, at which attachment the annular rib forming the buffer projects axially, which annular rib drops further inwards to a second step at which an inner ring edge is formed, this ring edge can engage in an annular space formed between the seat in the housing end part and an undercut in the holding ring. In this way the sealing system is secured against axial lifting on the seat of the housing end part.

Polytetrafluoroethylene, a hydrolysis-resistant polyurethane elastomer or some other elastomer can be used as materials for the production of the ring element forming the sealing system. A polyurethane elastomer marketed by the company Economos Austria Gesellschaft m.b.H. under the product name Ecopur® has proven to be particularly suitable.

In the following the invention will be described in detail by means of an exemplary embodiment shown in the drawings. These show as follows:

Fig. 1 a longitudinal section of a hydraulic accumulator provided for use as a pulsation damper, slightly reduced in size with respect to a practical embodiment and schematically simplified;

Fig. 2 a top view of just a sealing system of the hydraulic accumulator of Fig. 1;

Fig. 3 a section according to section line Ill-Ill of Fig. 2;

Fig. 4 a partial section of just the area identified by IV in Fig. 3, greatly enlarged with respect to Fig. 3;

Fig. 5 a top view of a ring element that forms a component part of a guide device of the bellows of the hydraulic accumulator of Fig. 1, drawn almost in the natural size of a practical embodiment, and

Fig. 6 a sectional illustration of the ring element according to line VI-VI of Fig. 5.

In the drawings the invention is described by means of an exemplary embodiment in the form of a pulsation damper. An accumulator housing, identified as a whole by 1, has a housing main part 3 in the form of a circular cylindrical pot with an end 5 that lies at the top in the drawings, and that is closed apart from a filling opening 7 that is aligned with the longitudinal axis 9 of the housing and is shut off in a medium-tight manner by a stopper 11 in the illustration of Fig. 1. At the opposite end that is at the bottom in Fig. 1 the housing 1 is closed by a housing end part 13 that is welded tightly to the housing main part 3 along a weld line 16. Concentric to the axis 9 there is in the end part 13 a fluid inlet 15 with an outer connecting piece 17. In the illustration of Fig. 1 a thread protection cap 20 is screwed onto the external thread of the connecting piece 17.

Within the accumulator housing a metal bellows unit forms a mobile separating element between a gas side 21 that is adjacent to the housing end 5 and can be filled via the filling opening 7 with a working gas, preferably N2, with a gas pre-filling pressure, and a fluid side 23 adjacent to the fluid inlet 15. In the illustration of Fig. 1 the bellows 19 is in its fully compressed state, the volume of the gas side 21 having the maximum value, while the fluid side 23 adjacent to the fluid inlet 15 has its smallest volume. The bellows unit is welded to the bellows end 29 adjacent to the housing end part 13, more precisely, at the radially outer edge of the last bellows fold, to a metallic holding ring 25 such as to be fluid-tight. The holding ring 25 on its part is welded to the accumulator housing at the separation point between the end part 13 and the main part 3 at the weld line 16. During the welding process for assembling the accumulator housing 1 and fitting the bellows unit the weld line 16 is therefore at least partially thermally isolated from the bellows end 29 by the holding ring 25. The welding region of the bellows end 29 itself at the holding ring 25 is identified by 27 in the figure where the holding ring 25 forms an annular axial elevation.

The mobile bellows end 31 lying opposite the bellows end 29 secured to the housing is welded at the radially outside end edge of the last bellows fold to a metallic end element 35 at 33, which end element forms a closing element that closes the interior of the bellows 19 at the mobile end 31 in a fluid-tight manner and so forms the separation between the gas side 21 and the fluid side 23. The sealing of the outside of the bellows 19 takes place by means of a sealing system 37 in the form of an annular sealing element that seals the holding ring 25 from the housing end part 13. The more detailed configuration and the additional function performed by the sealing system 37 are explained in more detail below by means of Figs. 2 to 4.

In the exemplary embodiment shown the end element 35 is in the form of a pot with a circular cylindrical side wall 39 that extends from the pot opening located at the bellows end 31 into the interior of the bellows 19 up to a level pot base 41. In comparison to a level configuration of the end element 35 the pot shape results in an increase in the gas volume of the gas side 21.

At the opening edge of the pot the end element 35 extends radially outwards beyond the adjacent bellows end 31 to the weld point 33 of the bellows end and runs from here from the bellows end 31 radially and axially away so as to form a circumferential edge 43 closer to the housing wall. In the circumferential edge 43 there is a circumferential annular groove 45 that forms the seat for a ring element 47, see Figs. 5 and 6, as a component part of a guide device. As shown in Figs. 5 and 6, this is a flat ring made of a plastic with good sliding properties, in particular made of poytetrafluoroethylene. This ring element 47 has a ring part 49 sitting in the annular groove 45 which forms at its outer circumference first annular surface parts 51 which are separated from one another by second annular surface parts 53. The second annular surface parts 53 are offset radially to the outside with respect to the annular surface parts 51 - see Fig. 5 - such that the second annular surface parts 53 form sliding surfaces resting against the housing wall at guide elements 55 protruding radially from the inner ring part 49. During operation, when the fluid side 23, and so the interior of the bellows 19, is subjected to a pressurised fluid, for example hydraulic oil, via the inlet 15 so that the bellows 19 expands and the end element 35 is thus moved axially out of the position shown in Fig. 1, by means of which the volume of the gas side 21 is reduced, the radially outer annular surface parts 53 then form sliding surfaces of the guide elements 55 with which the mobile end element 35 of the bellows 19 is guided on the housing wall. The inner annular surface parts 51 which are offset radially with respect to the outer annular surface parts 53 thus form fluid passages on the outside of the bellows 19, by means of which the gas side 21 continues on the outside of the bellows 19 to the holding ring 25, the sealing with respect to the fluid side 23 taking place by means of the sealing system 37 that is inserted between the holding ring 25 and the housing end part 13.

Figs. 2 to 4 show more details of the design of the ring element 61 of the sealing system 37. This is a profiled or tiered sealing ring made of a material that has a certain degree of flexibility, for example polytetrafluoroethyelene or an elastomeric polyurethane or some other elastomeric material such as synthetic rubber. ECOPUR® has proven to be particularly suitable as a sealing material.

As shown by Figs. 2 and 4 the ring element 61 is profiled such that an annular sealing lip 63 lying radially on the outside is formed at the radially outer edge region as a first functional area, which sealing lip forms an upper sealing surface 65 and a lower sealing surface 67, the upper, annular sealing surface 65 at the radially inner end passing into a step 69, while the other sealing surface 67 lies in the continuous radial plane of the ring element 61. At the step 69 the ring element 61 passes into an attachment 71 which lies further to the inside radially, which attachment forms the second functional area of the sealing system, a curved annular rib 73 projecting axially from the upper side of this attachment 71. The annular rib 73 passes radially inwards into a descending second step 75 adjoining which is a radially inner ring edge 77.

In the fitted state shown in Fig. 1 the ring element 61 of the sealing system 37 forms between the holding ring 25, which is connected tightly to the interior of the bellows 19 at the weld point 27 and the housing end part 13 the fluid-tight seal. For this purpose the sealing system 37 is received in a seat on the housing end part 13, against the base surface of which the ring element 61 rests with its entire surface with the radial plane forming the continuation of the sealing surface 67. At the radial inner edge opposite the lip 63 the attachment 71 forms a radially inwardly projecting ring edge 77 that is received in an undercut 79 of the housing end part 13 and is thus secured against axial lifting. The sealing lip 63 seals with its sealing surfaces 67 and 65 with respect to the housing end part 13 and the holding ring 25, the ring edge 77 engaging in a sealing space between the seat surface on the housing end part 13 and an inner ring surface 81 formed by a step on the holding ring 25.

As shown by Fig. 1, the depth of the pot on the end element 35 and the axial elevation of the curved annular rib 73 formed as a buffer on the sealing system 37 is chosen such that in the fully compressed state of the bellows 19 shown in Fig. 1, the pot base 41 rests against the rib 73 of the sealing system 37 forming a flexible end stop.

In a use of the hydraulic accumulator as a pulsation damper the fluid side 23 is fluidically connected via the inlet 15 to a pressurised fluid, in particular hydraulic fluid, a fuel or a lubricant, so as to smooth out any pressure surges that occur. It has proven to be advantageous here if, as indicated in DE 10 2004 004 341 A1, the gas side 21 is filled not only with working gas, but additionally contains a pre-specifiable volume proportion of a fluid. A combination of nitrogen gas as a working gas and ethylene alcohol as a fluid has proven to be particularly advantageous here on the gas side 21 of the accumulator as a filling. During operation the fluid can form a damping supporting medium between folds and deflections of the bellows 19 on which the folded wall parts of the bellows 19 can be supported on the fluid as a counter-bearing, and this leads to an increased life of the bellows 19 and so to increased functional reliability. This applies in particular to rapid pulsations and fast pressure surges. Due to the projections protruding on both sides of the sealing system 37, in this respect the system 37 is reliably prevented from being pulled out inadvertently during operation of the accumulator due to the undercuts which are produced from this.

Claims

1. Hydraulic accumulator, designed as a bellows accumulator, - in which the bellows (19), which serves as a movable separation element between gas side (21) and fluid side (23), has its end of the bellows (31) which can be moved in the axial direction when it is pulled out and is contracted by the accumulator housing (1), has a closure body (35) which closes fluid-tightly the inner space of the bellows (19) and is held motionless at its other end of the bellows (29) with respect to the accumulator housing (1), (37), which seals the interior space of the bellows (19) towards the accumulator housing (1) at the movable end of the bellows (29), in addition to a first operating area (63) causing the seal, has a second operating area in the form of an attachment ( 71) which protrudes into the inner compartment of the bellows (19) and forms a resilient buffer against which the closing body (35) of the bellows (19) can abut when the bellows is in a fully contracted state, and - where as a bellows (19) is provided with a metal bellows with a closure joint (35) welded to the respective end of the bellows (31), characterized in that the attachment (71) projecting into the inner space of the bellows (19) has at least one vault (73) projecting in the axial direction towards the movable end of the bellows (31) as a resilient buffer against which the closure body (35) may abut, - the non-movable end of the bellows (29) being secured to a retaining ring (25) secured to the housing, by means of a fluid-tight welding joint, the inner ring opening of which adjoins the inner space of the bellows (19) forming the fluid side (23), and - the sealing device (37) having its first functional area (63) forms the seal between the retaining ring ( 25) inner ring opening and the accumulator housing (1).

Hydraulic accumulator according to claim 1, characterized in that the accumulator housing (1) has a main part (3) and a housing end part (13) on the bottom side with a central fluid inlet (15) connected to the fluid side and the sealing device (37). ) has an annular body (61), the first functional area of which forms an annular, radially outer sealing lip (63) which, with sealing faces (65, 67) lying in radial planes, causes the sealing against a fitting surface on the housing end part (13) and a ring surface (81) of the retaining ring (25).

Hydraulic accumulator according to claim 2, characterized in that the closure body (35) of the bellows (19) is in the form of a pot with a circular cylindrical wall extending from the movable end of the bellows (31) away into the inner space of the bellows (19). and is bounded by a flat pot bottom (41) and the annular body (61) of the attachment (71) forming the second functional area has a rounded annular rib (73) as a vault whose axial elevation is selected in such a way that the outside of the pot bottom (41) abuts the annular rib (73) when the bellows (19) is fully contracted.

Hydraulic accumulator according to claim 2 or 3, characterized in that the end surface of the annular body (61) facing the seat surface of the housing end part (13) forms a radial plane extending from the radially outer sealing surface (67) of the sealing lip (63). ) towards the ring opening, and that the ring body (61) on the opposite side has a leveled configuration.

Hydraulic accumulator according to one of Claims 2 to 4, characterized in that the level divided design of the outer sealing lip (63) radially inwards radially inwards a first level (69) at the transition to the application (71) forming the second functional part, at which attachment of the annular rib (73) forming the buffer extends axially, which falls radially further inwardly to another level (75), on which is formed an inner annular edge (77) which engages an annular space (81), which is formed between the fit in the housing end portion (13) and an undercut (79) in the retaining ring (25).

Hydraulic accumulator according to one of claims 1 to 5, characterized in that the annular body (61) forming the sealing device (37) is formed of polytetrafluoroethylene, a hydrolysis resistant polyurethane elastomer or of another elastomer.