GB2374902A

GB2374902A - Accumulator

Info

Publication number: GB2374902A
Application number: GB0209010A
Authority: GB
Inventors: Heinz Siegel; Rene Schepp; Juergen Lander; Harald Hermann; Guenter Krenz; Harald Ott; Horst Beling
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-04-20
Filing date: 2002-04-19
Publication date: 2002-10-30
Anticipated expiration: 2022-04-19
Also published as: GB2374902B; GB0209010D0; DE10119357C2; DE10119357A1

Abstract

A hydraulic accumulator comprises a housing 2 in which metallic bellows 8 with a moveable bellows cover 12 are accommodated to form separate hydraulic 40 and pneumatic 41 spaces. Housing floor 4 has a port for pressure medium feed into the hydraulic space. The bellows cover has a tappet 17 carrying a lip seal 20 such that it faces pressure medium passage opening 15, enters and adopts a sealing position in the passage opening before the bellows cover contacts the housing floor, thus preventing exhausting of the accumulator. In event of a defective seal the cover stroke continues and the tappet engages ram 27 and moves a path sensor (28 Fig. 2) as a differential transformer (32) to determine a position of the cover that can be attributed to a defective seal. In event of seal failure sealing is maintained by the cover contacting secondary seal 6.

Description

- 1 Hydraulic Energy Storage Device Comprising Bellows with a Testable End

Position Seal The invention is based on a hydraulic energy storage device with a housing in which bellows with a moveable bellows cover are accommodated with the formation of an in each case separate hydraulic space and pneumatic space, the housing having a storage device wall that is actively connected for the pressure medium feed to a pressure medium feed unit leading into the hydraulic space, according to the generic part of claim 1.

Printed specification DE 3048651 Al discloses a hydraulic energy storage device

with a housing having a cylindrical interior and an axially displaceable piston that is sealed relative to the housing by means of a sealing ring and that separates a hydraulic space from a gas space. The gas space contains gas under pressure so that the gas forms a cushion that can be elastically compressed when the hydraulic space is being filled with hydraulic pressure medium. The piston thus forms a type of moveable wall.

The hydraulic space is bounded by a wall through which extends a ram that is aligned along the longitudinal axis of the piston, is guided in a sealing manner within the wall, and on one side projects into the hydraulic space and on the other sides projects from the housing. A switch is rigidly arranged on the wall of the hydraulic energy storage device with the aid of a retaining swap and in alignment with the ram. The ram serves to actuate the switch shortly before the piston has evacuated the hydraulic space and is thereby able to bear against the wall through which the ram is guided. The switch is thus a type of sensor device via which the virtual evacuation of the hydraulic space can be established.

Printed specification DE 1525776 Al discloses another hydraulic energy storage

device with a moveable wall, a ram and a switch that can be actuated by the

- 2 moveable wall and, between the said ram and the switch, an arrangement comprising a rocking lever mechanism that actuates the switch via a control cam that can be swivelled by the mechanism, when the moveable wall approaches its structurally determined end position corresponding to the evacuation position.

The switch then emits a signal for an indicator lamp and/or to switch on a pump drive motor. If desired a potentiometer or a photocell with a relay may also be provided. The moveable wall is formed by part of an elastic bellows or a displaceable piston.

In a yet further hydraulic energy storage device known from printed specification

DE 198 47 325 A1 with metal bellows that surround a gas cushion, a front wall of a moveable end of these bellows is modified to form a valve plate that can bear against a sealing ring that is accommodated in a front wall of a housing of the hydraulic energy storage device in such a way as to form a seal around a storage device/connection/passage opening. This hydraulic energy storage device is, also like the aforementioned device, envisaged in particular for incorporation in a hydraulic vehicle brake system.

Printed specification DE 197 06 427 A1 relates to a pressure medium storage

device, in particular for slip-regulated vehicle brake systems, with a housing having a pressure medium connection and metal bellows filled with gas and moveably arranged in the housing. A spring element is secured to the front face of the bellows that carries a valve element facing the pressure medium connection.

The valve element is provided with a seal element that seals the' chamber containing the pressure medium with respect to the pressure medium connection in the housing of the storage device.

A still further pressure medium storage device is known from printed specification

DE 199 06 800 A1. This consists of a housing whose interior is subdivided by a central separating element into two chambers, in which the first chamber is filled with a gas and the second chamber is filled with a fluid pressure medium and in

- 3 which a floor valve is provided in a hydraulic connection, the closure body of the floor valve being able to be actuated by the central separating element, thereby permitting a filling of the second chamber with a pressure medium and preventing a complete evacuation of the second chamber. These arrangements provide a considerable improvement in operational reliability since the closure body can through the central separating element be brought into a position in which it fulfils the function of a hydraulic piston. When the front face of the bellows approaches the floor the closure body is incorporated into the hydraulic flow and then floats in the latter and comes to rest against a stop means, whereby the hydraulic connection in the form of an arrested hydraulic piston is closed. In this connection the closure body is guided in a bore provided in the hydraulic connection and is provided with at least one sealing element that forms a seal against the wall of the bore. The bore is preferably formed as a stepped bore, in which the sealing element of the bore co-operates with the section of smaller diameter of the bore.

A hydraulic energy storage device has also already been proposed that consists of a housing that has an installation space for metal bellows, in which the metal bellows separate hydraulic pressure medium from a gas contained under pressure.

The metal bellows are designed so that, in the state in which they are not filled with gas before incorporation in the installation space, they have a length that is longer than the internal length of the installation space, this length being elastically shortened when the bellows are installed. The housing is provided with a sensor device that serves to detect the alignment of the moveable end of the bellows with a sealed-off front wall during the movement of the bellows in the direction of an evacuation position of the hydraulic energy storage device. The housing of the hydraulic energy storage device is provided in a front wall bounding the installation space with a hydraulic connection/passage opening that communicates with a hydraulics block of a hydraulic vehicle brake system. A plate of an evaluation and control circuit of the hydraulic vehicle brake system is associated with the hydraulics block. A longitudinally displaceable ram actuating the sensor device is inserted between the sensor device and front wall of the metal

- 4 bellows. The sensor device may be designed for example in the form of a differential transformer with a moveable coil core.

The hydraulic energy storage device according to the invention having the features disclosed in claim 1 offers on the other hand the advantage that it is provided with a seal that seals off the storage device already before the latter is completely evacuated, whereby the permissible end position and function of this seal can simultaneously be monitored. In this way it can be reliably ensured that gas does not enter the brake circuit and thereby threaten the functional capability of the brake system. The storage device may thereby be separated in good time from the brake circuit. Measures can be taken in good time to prevent a "contamination" of the brake circuit by gas.

According to the invention this is achieved by the fact that the bellows cover has a tappet carrying a seal, which tappet faces the passage opening and can be guided in the latter and the seal adopts a sealing position in the passage opening before the bellows cover makes striking contact with the storage device wall, and a control unit is provided in order to establish an operating position of the bellows cover that can be attributed to a defective seal.

Advantageous modifications and improvements of the hydraulic energy storage device disclosed in claim 1 are possible by means of the measures disclosed in the dependent claims.

The characterising features of claims 2 and 3 permit, in the event of a defective seal of the tappets, a stroke movement directed towards the passage opening of the hydraulic medium feed, in which the stroke is conveyed by the ram to a sensor device (path sensor) that shows that the functioning of the seal (end position seal) is defective.

- s The hydraulic energy storage device according to the invention having the characteristic features of claim 4 has the advantage that, as a result of the dome-

shaped shoulder of the tappet, the bellows cover can rest flat against the (secondary) seal arranged in the storage device wall when the storage device is evacuated. Tolerances and inclinations can be compensated by tilting around the dome-shaped shoulder of the tappet.

Claims 5 and 6 show a variant for another design of the tappet and seal. This

design ensures that the seal (primary end position seal) produced by a tappet on the bellows cover completely seals off the cylindrical region of the pressure medium feed.

The characterizing features of claims 7 to 9 demonstrate a particularly advantageous combination with a hydraulic unit of an electrohydraulic vehicle brake system. Particularly advantageous in this connection is that the sensor device, which is intended to detect the position and/or functioning of the primary seal within the pressure medium feed, is directly employed in an evaluation and control circuit. The embodiment of the sensor device as an inductive path sensor described in claim 8 permits already very small movements of the tappet and/or of the primary seal in the direction of the storage device wall to be detected.

Furthermore, with this sensor device provided in the hydraulic unit no electrical contact with the storage device is necessary.

The spring provided according to the features of claim 10 serves to pretension the bellows cover and ensures that the gas pressure is always slightly less than the liquid pressure of the hydraulic brake fluid.

According to the features of claim 11 the primary seal acts as a nonreturn valve.

The design of the seal as a lip seal has the advantage that the seal can be overridden by the non-return valve action of the lip seal without excess pressure, when charging the storage device. According to the features of claim 12 the side

wall of the bellows consists of metal. This reliably prevents gas from escaping through the wall of the bellows.

Drawings Embodiments of the hydraulic energy storage device according to the invention are shown in the following drawings, in which: Fig. lis a longitudinal section of a first embodiment of a hydraulic energy storage device in an almost completely evacuated state, Fig. 2shows an embodiment of the sensor device, Fig. 3shows a modification of the first embodiment as regards the design of the tappet in the sealed-off state in a storage device that is almost completely evacuated, and Fig. 4shows the embodiment according to Fig. 3 in another operating state.

The first embodiment of the hydraulic energy storage device 1 according to the invention according to Figs. 1 and 2 has a housing 2 that encloses an installation space 5 for, inter alla, bellows 8. A hydraulics block 33 and a sensor device 28 associated therewith are also shown.

The housing 2 is formed in a simple manner as a hollow cylinder and has a circumferential wall 3 and a storage device wall 4 (storage device floor). The bellows 8 have a fixed end 9 and a moveable end 10 and a bellows cover 12 joined in a gas-tight manner to this end 10. The bellows cover 12 serves to separate a hydraulic space 40 and a pneumatic space 41 in the installation space. 5. The side wall 11 with the concertina arrangement typical of concertina-type bellows is located between the fixed end 9 and the moveable end 10. The side wall 11

consists of metal. Guide means 13 for centring these metal bellows 8 are provided in the housing 2.

The hollow space 6 located outside the metal bellows 8 and bordered by the circumferential wall 3 is provided to contain a gas under pressure. A gas filling pipe is not shown since the filling of hydraulic energy storage devices with the gas serving as energy store already belongs to the prior art.

A spring 7, which in the installed state is pretensioned7 is shown inside the hollow space 6. The object of the spring is to ensure that the gas pressure is always slightly less than the liquid pressure and in the event of a leakage in the bellows 8 is intended to assist the movement of the bellows cover 12 in the direction of the storage device floor 4.

The pressure medium feed 14 terminates in a sunken passage opening 15 in the storage device floor 4 of the hydraulic energy storage device 1, the said passage opening 15 being surrounded by a sealing element 16 against which the bellows cover 12 can rest. The sealing element 16 is in this case partially let into the storage device floor 4. Because such an elastic sealing element belongs to the prior art and performs the same function as the elastic sealing ring described for

example in the printed specification DE 19847325 Al mentioned in the

introduction, a further description is omitted here.

According to the invention the bellows cover 12 is provided with a tappet 17 that accommodates a primary seal 20 that faces the passage opening 15 provided in the storage device floor 4 for the pressure medium feed 14, the storage device being provided with a sensor device 28 for sensing the position of this seal 20. The tappet 17 is in this case arranged preferably concentrically.

According to the embodiment shown in Fig. 1, the tappet 17 is formed dome-

shaped on the shoulder 19 and comprises a recess 18 for accommodating a seal 20,

- 8 the latter being formed as a lip seal. The tappet 17 is secured concentrically to the bellows cover 12 by spot welding so that with an evacuation of the storage device l as a result of a leakage or for test purposes the tappet sinks into the passage opening 15 in the storage device floor 4, the seal 20 formed as a lip seal thereby sealing the pressure medium feed 14 and preventing further movement of the bellows cover 12 and tappet 17.

The lip seal 20, the tappet 17 and the passage opening 15 of the pressure medium feed 14 are positioned so that the bellows cover 12 is not yet resting on the storage device floor 4 or on the secondary sealing element 16, but executes a further stroke movement in the direction of the storage device floor 4 only in the case of a defective lip seal 20, finally coming to rest on the secondary sealing element 16.

This stroke movement is transmitted by the tappet 17 to the ram 27 and is conveyed by the ram 27 to the sensor device 28 formed as a path sensor, which thereby recognises that the lip seal 20 is defective.

Fig.2 shows an embodiment of the sensor device. In conjunction with Figs. 1 and 3 it can be seen that the passage opening 15 for the pressure medium feed 14 provided in the housing 2 in the storage device floor 4 delimiting the installation space 5 communicates with a hydraulics block 33 of a hydraulic vehicle brake system, in particular an electrohydraulic brake. A plate 34 of an evaluation and control circuit of the electrohydraulic brake is associated with the hydraulics block 33, wherein at least one stationary part of the sensor device 28 is secured to the plate 34 of the evaluation and control circuit and substantially aligned to the longitudinal axis of the bellows 8. A longitudinally displaceably mounted ram 27 actuating the sensor device 28 is incorporated between the said sensor device 28 and the front face of the tappet 17, the ram extending through the passage opening 15 of the hydraulic energy storage device 1 and being hydraulically sealed off with respect to the sensor device 28 within the hydraulics block 33.

- 9 - The sensor device 28 is designed in the form of a path sensor known from the prior art. The ram 27 is for this purpose connected to a soft magnetic coil core 29,

two coils 30, 31 for example of a differential transformer 32 being arranged on the movement path of the coil core 29. In the event that the lip seal 20 is defective, it is possible by means of the differential transformer 32 to detect already very small movements of the bellows cover 12 and of the tappet 17 in the direction of the storage device wall 4.

If the primary end position seal 20 fails the secondary sealing element 16 belonging to the prior art is still available, which prevents inflow of gas in the

event of a fracture of the bellows 8.

Fig. 3 shows a modification of the design of the tappet, the same variant being shown in another operating state in Fig. 4. This embodiment ensures that the seal 24 completely seals off the wall in the cylindrical region of the pressure medium feed 14.

The tappet 17* has for this purpose recess regions 21, 22 corresponding to different diameters of the tappet 21. A conical annular surface 23 is provided between the regions. The recess region 21 with the smaller tappet diameter serves to receive a seal 24 designed as a lip seal and a dome-shaped supporting ring 25.

The recess region 22 with the somewhat larger tappet diameter accommodates a compression spring 26.

The tappet 17* with the compression spring 26 is shown in the uncompressed state in Fig. 4.

When the seal 24 seals off the wall in the cylindrical region of the pressure medium feed 14 according to Fig. 3, the seal extends into the pressure medium feed 14 until the supporting ring 25 rests against the conical annular surface 23 of the tappet 17*.

- 10 The tappet 17* and the passage opening 15 of the pressure medium feed 14 are repositioned so that the bellows cover 12 is not yet resting on the storage device floor 4 or the seal 16, but executes a further stroke movement in the direction of the storage device floor 4 only if the lip seal 24 is defective, until the bellows cover 12 comes to rest against the secondary seal 16. This stroke movement is transmitted from the tappet 17* to the ram 27 and is conveyed via the ram 27 to the sensor device 28 designed as a path sensor, which thereby recognises that the lip seal 24 is defective. The sensor device 28 has already been described in the preceding example. Should the primary end position seal 24 fail, the secondary seal 16 belonging to the prior art is still available, which prevents an inflow of gas

in the event of a fracture of the metal bellows.

Since the seal 16 cannot be monitored, a workshop must be notified in the event of failure of the end position seal 20, 24.

The signal displayed via the path sensor can be used routinely to monitor the functioning of the end position seals 20, 24. Such routine monitoring may be carried out for example after every 100 braking operations, the hydraulic energy storage device being evacuated when starting up the vehicle and checked to see whether the seal is in order. The seal is in order if the path sensor in the sealed-off state of the end position seal 20, 24 does not move any further.

Claims

-11 Claims 1. Hydraulic energy storage device with a housing in which

bellows with a moveable bellows cover are accommodated with the formation of an in each case separate hydraulic space and pneumatic space, the housing having a storage device wall that is actively connected for the pressure medium feed to a pressure medium feed unit guided in the hydraulic space, characterised in that the bellows cover (12) has a tappet (17; 17*) carrying a seal (20; 24), which tappet faces the passage opening (15) and can be guided in the latter and the seal (20; 24) adopts a sealing position in the passage opening (15) before the bellows cover (12) makes striking contact with the storage device wall (4), and a control unit (28) is provided in order to establish an operating position of the bellows cover (12) that can be attributed to a defective seal (20; 24).
2. Hydraulic energy storage device according to claim 1, characterized in that the control unit (28) is a sensor device (28) actively connected to a longitudinally displaceably mounted ram (27), wherein the tappet (17; 17*) on adopting the sealing position of the seal (20; 24) comes into bearing contact with the ram (27).
3. Hydraulic energy storage device according to claim 1, characterized in that the passage opening (15) is enclosed by a sealing element (16) mounted in the hydraulic space (40) on the storage device wall (4), which sealing element comes into bearing and sealing contact with the bellows cover (12) if the seal (20; 24) is defective.
4. Hydraulic energy storage device according to one of the preceding claims, characterized in that the tappet (17) is designed dome-shaped on the shoulder (19) and has a recess (18) for accommodating a seal (20), the seal (20) being designed as a lip seal.

- 12
5. Hydraulic energy storage device according to one of the preceding claims, characterized in that the tappet (17*) has recess regions (21; 22) corresponding to different diameters of the tappet (17*) and a conical annular surface (23) is provided between the recess region (21) with the smaller tappet diameter and the recess region (22) with the somewhat larger tappet diameter, wherein the recess region (21) is provided to receive a seal (24) designed as a lip seal and a dome-shaped supporting ring (25), and the recess region (22) accommodates a compression spring (26).
6. Hydraulic energy storage device according to one of the preceding claims, characterized in that the tappet (17*) can be brought by means of the bellows (8) into a position in which the seal (24) and the supporting ring (25) come to rest on the conical annular surface (23), whereby the seal (24) completely seals off the cylindrical region of the wall of the pressure medium feed (14).
7. Hydraulic energy storage device according to one of the preceding claims, characterized in that the passage opening (15) for the pressure medium feed (14) communicates with a hydraulics block (33) of an electrohydraulic vehicle brake system and that a plate (34) of an evaluation and control circuit of the hydraulic vehicle brake system is associated with the hydraulics block (33), that at least one stationary part of the sensor device (28) is secured to the plate (34) of the evaluation and control circuit substantially in alignment to the longitudinal axis of the bellows (8), and that a longitudinally displaceably mounted ram (27) actuating the sensor device (28) is incorporated between the said sensor device (28) and the front face of the tappet (17; 17*), the said ram extending through the passage opening (15) of the hydraulic energy storage device (1) and being hydraulically sealed off relative to the sensor device (28) within the hydraulics block (33).

-13
8. Hydraulic energy storage device according to one of the preceding claims, characterized in that the sensor device (28) is designed as an inductive path sensor in the form of a differential transformer (32) with a moveable coil core (29), the testing of the operational integrity of the seal (20; 24) being performed by path measurement.
9. Hydraulic energy storage device according to one of the preceding claims, characterized in that if the seal (20; 24) is defective the bellows cover (12) moves and comes into contact with the sealing element (16) enclosing the storage device floor/passage opening (15), the executed change in the position of the tappet (17; 17*) being transmitted via the ram (27) to the sensor device (28).
10. Hydraulic energy storage device according to one of the preceding claims, characterized in that at least one compression spring (7) is provided in the pneumatic space (41) in order to pretension the bellows cover (12) in the direction of the pressure medium feed (14).
Hydraulic energy storage device according to one of the preceding claims, characterized in that the seal (20; 24) has a non-return valve action.
12. Hydraulic energy storage device according to one of the preceding claims, characterized in that the concertina-shaped side wall (11) of the bellows (8) consists of metal.
13. A hydraulic energy storage device substantially as herein described with reference to the accompanying drawings.