GB2371351A

GB2371351A - Bleed valve

Info

Publication number: GB2371351A
Application number: GB0127304A
Authority: GB
Inventors: Jan Grabenstatter; Henry Hahn
Original assignee: LuK Lamellen und Kupplungsbau Beteiligungs KG; LuK Lamellen und Kupplungsbau GmbH
Current assignee: Schaeffler Buehl Verwaltungs GmbH; LuK Lamellen und Kupplungsbau GmbH
Priority date: 2000-11-17
Filing date: 2001-11-14
Publication date: 2002-07-24
Anticipated expiration: 2021-11-14
Also published as: FR2816900B1; BR0105272A; DE10164968B4; DE10155793B4; DE10155793A1; FR2816900A1; GB0127304D0; KR20020038515A; BR0105272B1; GB2371351B; KR100839319B1

Abstract

Valve 1 comprises a housing 2 and a plug 3 having a projection 9 extending into a channel 6. A groove 8 holds a sealing element 7 inclined at an angle to a rotational axis 4 of the plug 3 which when rotated opens or closes the valve. In the open state a gap 11 formed by a longitudinal groove 12 in the housing 2 is exposed and connects the channel 6 to a bore 13 which is sealed by a sealing means 15. An opening 16 between seal 15 and 7 connects channel 6 to a bore 5 in the plug 3. Housing 2 and plug 3 are fixed axially together by a snap fitting device 17 which with stops 19a limit the rotational movement of the plug 3. Valve 1 may also have a non return valve and vent at an angle relative to the axis 4 and housing 2 may also function as an adaptor between two connectors.

Description

- 1 - HYDRAULIC SYSTEM

The invention relates to a hydraulic system more particularly for motor vehicles, comprising a slave 5 cylinder with a pressurised medium inlet, a master cylinder with pressurised medium outlet, a pressurised medium pipe actively connecting the pressurised medium inlet hydraulically to the pressurised medium outlet, a pressurised medium for filling the hydraulic system, a 10 pressurised medium reservoir and a bleed valve consisting of a bleed.plug and a housing containing same.

The bleed valves of hydraulic systems of the generic type generally contain a housing attached to the pressurised 15 medium pipe and into which a plug is screwed axially generally by means of a threaded device to form with the housing an axial sealing seat by means of integrated sealing surfaces in order to close and seal the pressurised medium pipe. Furthermore systems are known 20 where an axial sealing ring is additionally provided. In order to vent the system the sealing seat is disconnected whereby for example the plug is loosened through rotary movement so that the air which is to be removed from the..

system and where applicable also any excess pressurized 25 medium is drawn off through an opening in the plug. To this end pressurised medium is passed from the pressurised medium reservoir back into the pressurised medium pipe by means of the hydrostatic pressure of the higher placed pressurised medium reservoir or by means of pressure 30 applied from outside. This can take place through so-

called "pumping" with the master cylinder, for example by

operating the clutch pedal whereby on relaxing the master cylinder the bleed valve has to be closed in order to prevent air from flowing down from this direction. This is often made difficult since air not only flows through 5 the opening but also through the thread so that a clear ventilation or airflow path is provided in the region of the bleed valve.

The sealing action of the bleed valve depends 10 substantially on the satisfactory functioning of the sealing seat which requires matching undamaged and non-

contaminated sealing faces between the housing and plug as well as a close tolerance tightening torque of the plug.

Particularly with more recent bleed valves plastics is 15 often used as material for the housing so that an exact tightening torque on the one hand for ensuring the tightness of the bleed valve and on the other for avoiding breaking the bleed valve, more particularly breaking the thread through tightening up the plug too severely is 20 avoided. Particularly during maintenance and repair work to the hydraulic system handling bleed valves of this kind is often difficult and faulty.

The object of the invention is therefore to provide a 25 hydraulic system which guarantees secure functioning with simple handling and without any great tooling or personnel costs. Setting the sealing function is to be substantially independent of any predetermined tightening torque and the air flow path through the bleed valve is to 30 be clearly defined. Furthermore a hydraulic system with a bleed valve is to be manufactured on a large scale cost

3 - effectively and is to consist of the fewest possible parts. The assembly and exchange of a bleed valve is furthermore to be simple. With a view to good recycling the bleed valve is to consist of as few different 5 components as possible so that they do not have to be separated out during disposal.

This is achieved through a hydraulic system, more particularly for motor vehicles, comprising a slave 10 cylinder with a pressurised medium inlet, a master cylinder with pressurised medium outlet, a pressurised medium pipe actively connecting the pressurised medium inlet hydraulically to the pressurised medium outlet, a pressurised medium for filling the hydraulic system, a 15 pressurised medium reservoir and a bleed valve consisting of a bleed plug and a housing containing same, wherein in the sealing state of the bleed valve the bleed plug and the housing are sealed radially relative to each other.

As opposed to the prior art the sealing of the bleed plug

20 and the housing is not carried out axially force-

controlled by tightening up the thread, but radially whereby the plug adopts a sealing and a non-sealing function in respect of the housing through rotation of the two parts relative to one another. This can be achieved 25 through a combination of the following features: a) rotating the bleed plug relative to the housing causes the setting of at least two distinguishable positions of the bleed plug relative to the housing

- 4 - b) in the first position the bleed plug is sealed radially from the housing c) in the second position the hydraulic system is opened 5 towards the atmosphere d) opening and closing the bleed valve causes no axial relative movement of the bleed plug in respect of the housing. Opening and closing of the bleed valve thereby takes place path- controlled through the relative rotation of the plug and housing opposite one another whereby during this relative movement sealing and non-sealing segments 15 arranged radially between the two parts are covered.

Advantageously the rotation of the bleed plug relative to the housing can thereby be restricted. To this end at least an end stop can be provided on one of these parts 20 for the other part which is rotated relative to same.

Advantageously two end stops are provided wherein one end stop can fix the opening position of the bleed valve and the other end stop can fix the sealing position.

25 According to the inventive idea at least one ring-shaped sealing element can be provided radially between the bleed plug and the housing. In order to fulfil the two sealing states of open/closed the sealing element has a ring-

shaped sealing edge which is arranged in a plane inclined 30 to the common rotational axis of the bleed plug and housing. The plug and housing each have a pressurized

- 5 - medium supply pipe which moves up to the region of the sealing element. By rotating the housing and bleed plug relative to each other the sealing edge is axially displaced on account of its inclined position to the 5 rotational axis relative to the turning part and intersects a pressurised medium supply pipe of the plug or housing arranged correspondingly in the displacement area of the sealing edge so that in the one end area of relative rotation the pressurized medium supply pipes are 10 connected together and in the other end area they are separated from each other by means of the sealing edge.

It is obvious that the sealing element can be assigned to either the housing or the bleed plug, that is, is connected rotationally secured to one of the two parts.

15 An advantageous embodiment for a sealing element can be for example a sealing ring, such as an O-ring which is set in a ring groove provided in the housing or in the bleed plug inclined to the rotational axis. Furthermore a hose section inclined at at least one axial end can also serve 20 as a sealing element, whereby the sealing edge in advantageously provided in the region of the inclined end.

One embodiment according to the inventive idea proposes a hydraulic system with a bleed valve wherein the sealing 25 element is mounted on the bleed plug and at least one radial expansion is provided in the housing where it can be brought into connection with an opening of the bleed plug and ends axially between the two extreme points of the sealing path of the sealing element. It can hereby be 30 particularly advantageous if the opening is a duct arranged centrally round the rotational axis and has a

- 6 - connection such as a puncture opening radially outwards to the radial expansion of the housing whereby the seal which is fitted inclined to the axis of rotation seals the opening in the plug from the radial expansion when the 5 bleed valve is in the closed state and wherein on rotation of the plug opposite the housing the sealing edge of the seal is moved axially relatively to the radial expansion in the housing so that the connection between the radial expansion in the housing and opening in the plug becomes 10 released.

According to the inventive idea, the bleed plug and housing are connected together rotatable relative to each other but axially secured in respect of each other. To 15 this end a correspondingly formed opening can be provided in the housing into which a cramp engages to fix the plug axially, a guide groove for the cramp being provided in the plug. Designs of this kind are known in particular for connecting pipeline parts in hydraulic systems. The 20 formation of a self-locking device, for example a snap-

fitting device can also be particularly advantageous, which in one embodiment can also be releasable. An advantageous embodiment here provides two snap-fitting-

hooks set in the bleed plug and each engaging radially in 25 a grooved segment provided in the circumferential direction. It is obvious that one grooved segment can be recessed out of the housing for both snap hooks. It is also obvious that any other number of snap hooks can also be advantageous whereby these can advantageously be 30 aligned radially outwards whereby the plug is inserted axially into an opening of the housing and the snap hooks

- 7 - snap fit radially outwards with the grooved segments. The wall of at least one grooved segment can thereby also serve as stop for at least one snap hook whereby the rotational capacity of the plug opposite the housing is 5 restricted. It is advantageous to design this restriction in both directions of rotation so that the work area of the bleed valve is fixed for example by one stop defining the open position of the bleed valve and the other stop defining the closed position. Furthermore in this 10 connection it can be advantageous to provide the end positions, at least however the end position in the closed position of the bleed valve, with a detent mechanism to prevent undesired, for example unauthorized, opening of the bleed valve or opening caused by operating states of 15 the vehicle. To this end it can be proposed that at least one snap hook engages axially in the grooved segment for example through pretension in the end area. Furthermore measures can be provided in the bleed valve to compensate torsional balance between the housing and pressurized 20 medium pipe, particularly when the bleed valve is integrated in the pressurized medium pipe.

Advantageous designs of the inventive idea propose" arranging the opening duct and a connection in the housing 25 to the pressurized medium pipe substantially on one line, but in other designs it can be advantageous to arrange the opening duct and a connection in the housing to the pressurized medium pipe at an angle, preferably at a right angle, to each other. Furthermore it can be advantageous, 30 particularly to minimise the number of parts in a hydraulic system, to form the housing in one piece with a

- 8 - further component part, for example the housing can be integrated in the slave cylinder, furthermore the housing can hold a device for restricting pressure pulsations and/or for damping vibrations in the pressurized medium 5 pipe. It can be particularly advantageous to mount a non-

return valve in the bleed valve since when filling the system during assembly and during maintenance and repair work a work force can be spared where applicable which during the filling process closes the bleed valve in the 10 absence of filling pressure, for example if the master cylinder is relaxed.

The invention will now be explained in further detail with reference to Figures 1 to 12 in which: Figures 1, la, 2, 2a show a bleed valve for a hydraulic system in the opened and closed positions respectively; 20 Figures 3 to 11 show further design possibilities for a bleed valve; and Figure 12 shows a hydraulic system having a bleed valve according to the inventive 25 idea.

Figures 1 and 2 show the same bleed valve in the opened position (Figure 1) and the closed position (Figure 2).

The bleed valve 1 is formed substantially from a housing 30 part 2 and a plug, such as a bleed plug 3 which are rotatable relative to each other about a common rotational

- 9 - axis 4 to a restricted amount and which are positioned axially relative to each other. The housing 2 is shown only in part and can be a constituent part of a housing of a slave cylinder (see 52 in Figure 12) or can form a 5 component part which is closed per se and which can contain a supply pipe (see 58 in Figure 12) of the hydraulic system (see 50 in Figure 12). The housing 2 has a channel, such as a recess, opening or bore 6 arranged around the rotational axis 4 and into which a pin-like 10 projection 9 of the plug 3 extends. A ring groove 8 is let into a plane 10 inclined about the angle a to the rotational axis 4 and holds the sealing element such as sealing ring or O-ring 7 wherein the latter forms a sealing edge 7a in the plane 10 between the housing 2 and 15 the pin-like projection 9 in the closed state (Figure 2).

In the opened state (Figure 1) the positioning of the sealing ring 7 is moved following relative rotation of the plug 3 opposite the housing 2 so that this sealing edge 7a no longer fully bears against the housing 2 but exposes a 20 gap 11 which is formed by a longitudinal groove 12 in the housing which connects the bore 6 to a radial expansion such as bore 13 towards the free end 14 of the housing 2.

Independently of the rotation of the plug 3 opposite the housing 2 the radially expanded bore 13 is sealed 25 outwardly from the projection 9 by means of the sealing ring such as O-ring IS guided in the ring groove 15a. The connection between the bore 6 and the outwardly directed channel such as air flow bore 5 formed in the plug 3 about the rotational axis 4 is provided by means of a puncture 30 opening 16 which runs from the bore 5 radially outwards on the outer circumference of the plug 3. The puncture

- 10 opening 16 ends axially between the two O-rings 15 and 7.

In the opened state (Figure 1) air included in the hydraulic system (see 50 in Figure 12) as well as any excess pressurized medium escape through the bore 6 and 5 gap 11 through the groove 12 into the ring chamber 13a which is formed by the radially expanded bore 13 between the two O-rings 15 and 7 and from there outwards through the puncture opening 16 into the bore 5.

10 The housing 2 and bleed plug 3 are fixed axially on each other by means of the snap-fitting device 17. To this end the bleed plug 3 has in the direction of the axial projection 9 axially extending radially elastic snap hooks 18 which engage with a radial expansion 18a behind 15 correspondingly formed recesses 19 in the housing 2 so that the housing 2 and plug 3 engage with each other. In the illustrated embodiment the plug 3 is turned relative to the housing 2 to set the positions open/closed whereby a shaped profile 21 is provided, for example a square or 20 hexagon for an open-ended spanner, a wing attachment for manual operation or the like. The free end of the plug 3 is provided with a connecting nipple 22 to hold a hose for drawing off air and any excess pressurized medium.

25 Setting the open/closed positions of the bleed valve 1 is by stops 19a and is self-locking. For further explanation of this function Figure la (opened position) and 2a (closed position) show the bleed valve 1 along the section A-A and A' - A'. From this it can clearly be seen that 30 the snap hooks 18 in the opened state (Figure la) and closed state (Figure 2a) each come to bear against a stop

- 11 -

19a which forms the wall for the recesses 19 from which the housing 2 is formed during rotation in the direction about the rotational axis 4 whereby a maximum turning angle of the plug 3 relative to the housing 2 is provided.

5 This maximum turning angle can be for example 180 , but it has however also been shown that angles c 120 are advantageous and sufficient whereby in this embodiment an angle of 106 was selected. Furthermore it is apparent from Figures la and 2a that during the course of rotation 10 of the plug 3 relative to the housing 2 the snap hooks come into contact with further housing webs 23 whereby this contact is produced radially outside on the snap hooks 18 and as a result of their radial elasticity the hooks are pressed radially inwards, namely only so far 15 that the radial projections 18a do not disengage from the recesses 19 so that the axial fixing of the plug 3 and housing 2 remains secure. The rotation of the plug 3 relative to the housing 2 thereby takes place between the two end positions of the opened or closed bleed valve 1 20 with increased energy expense so that accidental opening is avoided and clear end positions are defined.

The bleed valve 1 is advantageously formed from plastics whereby both parts 2, 3 can be made using the injection 25 moulding process whereby the materials should be chosen to conform with one another. If the housing is integrated in a further part of the hydraulic system (SO in Figure 12) for example in the slave cylinder (see Figure 12, 52), a secure bleed valve 1 can be formed with few additional 30 component parts, namely here with the plug 3 and O-rings 7

and 15, which can then be operated by simple rotary movement independently of tightening torque between the opened and closed positions. It is evident that the hexagon 21 can also be modified by other means, such as 5 for example fitted wings, so that for example the plug 3 can be rotated directly by hand.

Figures 3 to 11 show further advantageous embodiments of bleed valves which are similar in principle to the 10 embodiment 1 of Figure 1, with the same component parts thereby having the same reference numerals as in Figure 1, with similar component parts having the same indices, but for distinguishing upgraded by one hundred. Thus Figure 3 shows a bleed valve 101 similar to the bleed valve 1 and 15 in a simplified design. Thus only one single sealing element is used which is cut off as a hose section 107 at the end facing the plug 103 perpendicular to the rotational axis 4 and at the end remote from the plug 103 has an incline 107b and executes both functions of the 20 sealing elements 7, 15 of the bleed valve 1 of Figures 1 and 2. The hose section 107 is formed in an attachment 107a provided in the housing 102 corresponding to the incline 107b and axially adjoins the plug 103 and is fixed in its position.

To fix the plug 103 and housing 102 axially on each other ring grooves 103a, 102a are provided in same having openings facing outwards in which the cramp 118 is inserted from outside. The cramp is shaped so that both 30 the grooves 103a and 102a are axially supported on same.

The housing 102 can furthermore have a recess 119 in the

- 13 circumferential direction in which a correspondingly radially expanded projection 118a of the plug 103 engages so that the capacity of the plug 103 to rotate relative to the housing 102 is restricted.

The bore 105 in the plug 103 is expanded radially outwards through the puncture hole 116 and when the bleed valve 101 is in the opened state the bore connects with a longitudinal groove 112 provided in the housing 102. If 10 the plug 103 is turned opposite the housing 102 about the rotational axis 4 then the puncture opening 116 in the hose section 107 is turned and thus sealed from the bore 106 in the housing 102 and thus the bleed valve 101 is closed. The hose section 107 furthermore seals the 15 housing 102 on the outside. The plug 103 furthermore has in the region between the connecting nipple 122 and the housing 102 spaced therefrom a shaped profile 121 which enables the plug 103 to be turned relative to the housing 102 by hand or by means of a tool, for example an opened 20 ended or hook spanner.

Figure 3a shows as a modification of the embodiment 101 of Figure 3 a shortened hose section 107 and an O-ring 107c provided axially between the contact bearing area 107a and 25 the hose section 107 for precision setting the sealing edge. Figure 4 shows an embodiment of a bleed valve 201 which is a combination of the bleed valves 101 of Figure 3 and 1 of 30 Figure 1. The function of the hose section 107 in Figure 3 is hereby separated out and undertaken by the O-rings

207 and 215 whereby the O-ring 207 as described per se is arranged in an inclined plane to the rotational axis 4 and the O-ring 215 is mounted radially between the plug 203 and the housing 202 and seals the bleed valve 201 on the 5 outside. In the opened state - as shown - air present in the hydraulic system can pass from the bore 206 through a longitudinal groove 203b in the plug 203 into the longitudinal groove 212 in the housing and from there through the puncture opening 216 into the opening 205 to 10 the outside or can be forced through when applying pressure. If the plug 203 is turned relative to the housing 202 then the sealing ring 207 inserted in the plug 203 completely seals against the inner circumference of the housing wall 202 and closes the bleed valve 201.

For embodiments where the housing 202 and the plug 203 are fixed axially by means of the cramp 218 it can be advantageous to design the groove 203a guiding the cramp 218 with an eccentric and/or elliptical cros - section so 20 that the cramp 218 in the open/closed end positions, adjoins, if necessary under pretension, the inner circumference of the groove 203a, for example with an elliptical design on the smaller radius, and when the plug 203a is turned relative to the housing is tensioned 25 radially outwards so that on reaching the end positions a smaller or no pretension exists in the cramp 218 and thus distinguishable open/closed end positions are produced.

Thus according to the details on Figure 1 an unintentional opening is avoided or a clear distinction is produced 30 between the two end states of the bleed valve 201. It is

- 15 evident that this feature can also be advantageous for all similar bleed valves.

Figure 5 shows a bleed valve 301 similar to the bleed 5 valve 201 in Figure 4 and having an additional non-return valve 325 which prevents air from flowing down into the hydraulic system from outside through the bore 305 in the event of underpressure arising in the bore or duct 306.

To hold an elastic hose section 305b which can be made for 10 example from rubber, silicon or the like, a ring groove 305a is formed in the opening 305 at the side end and axially fixes the hose section 305b whereby in order to form the non-return valve 325 the hose section axially covers the puncture opening 316 so that the latter is 15 sealed from the opening 305 in the non-pressurised state.

If in the opened state of the bleed valve 301 (as shown here) a vacuum is produced in the pipeline or opening 306 then this continues through the groove 303b in the plug 303 and the longitudinal groove 312 in the housing 302 20 into the puncture opening 316 so that the hose section 305b is pressed even more severely against the opening of the puncture opening 316. If excess pressure arises in the opening 306 then this is transferred through the same route to the puncture opening 316 and after overcoming the 25 pretension of the hose section 305b a passage is produced to the bore 305 and air, and where applicable any excess pressurized medium, present in the system can escape outwards. Through the elasticity of the hose section 305b it is possible to set the required pretension which has to 30 be overcome in order for the hose section 305b to lift off away from the opening of the puncture opening 316. It has

- 16 been shown that it is particularly advantageous to restrict the pretension to a maximum of 0.5 bar, preferably smaller than or equal to 0. 3 bar.

5 Figure 6 shows a bleed valve 401 which is similar to the bleed valve of Figure 3a but which has in addition a non-

return valve 425 corresponding to the non-return valve 325 of Figure 5.

10 Figures 7 and 8 each show bleed valves 501 and 601 where the connecting nipple 522, 622 is formed at an angle, preferably at a right angle on the housing 502, 602. The housing 502, 602 thereby has both openings 505, 506 and 605, 606 and the plug 503, 603 switches the opening and 15 closing positions of the bleed valve 501, 601 in a similar manner to the preceding embodiments by means of a seal 507, 607 provided in a plane inclined to the rotational axis 4. To this end the axial projection 509, 609 of the plug 503, 603 is passed axially into a hollow cylindrical 20 opening 513, 613 and is provided with the seal 507, 607 which is mounted inclined to the rotational axis 4 and is fitted in a suitably recessed groove 508, 608. The connection between the bores 506, 505 and 605, 606 in the opened position of the bleed valve 501, 601 is through a 25 longitudinal groove-like chamfer 503b, 603b in the axial projection 509, 609 of the plug 503, 603.

The difference between the two bleed valves 501, 601 in Figures 7 and 8 lies in the design with and without non 30 return valve. The bleed valve 601 in Figure 8 has a non return valve 625 which is constructed similar to the non

- 17 return valve 325 in Figure 5 and has a hose section 605b which is fitted substantially completely in a ring groove 605a let into the housing 602. In the region of the opening 605 the ring groove 605a has a connection to same 5 and furthermore a puncture opening 616 is provided on the wall on the inner circumference of the hose section 605b where it is closed by the hose section 605b in the pressureless state as well as in the event of underpressure from the opening 606. If excess pressure 10 arises in the opening 606 leading from the hydraulic system then in a similar way to the non-return valve 325 in Figure 5 after overcoming the pretension set by the hose section the hose section 605b expands when the bleed valve 601 is opened and the non-return valve 625 opens.

Figures 9 to 11 show three embodiments of bleed valves 701, 801, 901 in which the housing 702 functions as an adapter between two connectors 703a and 703b. The connector 703a can hereby be in a particularly 20 advantageous way a slave cylinder pipe which can undertake the function of the plug, as shown for example in Figure 1 as the plug 3. The connector 703b can be a pipeline part with pressurized medium inlet 706a which directly represents the pressurised medium pipeline to the master 25 cylinder or a connector member for same. Whereas with the examples previously given a separate connector pipe for the slave cylinder exists when used for a clutch release system for the bleed valve, pressure biasing from the master cylinder to the slave cylinder as well as 30 ventilation of the slave cylinder taken place through a single connector 703a. The connector 703b is as previously

- 18 described fixed axially and rotatable with a cramp 718 and is sealed from the housing 702 by means of the seal 715.

The connector 703a is likewise fixed axially and rotatable in the housing 702 by means of the cramp 718a, the seal 5 between the two parts undertaken by the sealing element 707 or 807, 907 in Figures 10 and 11. At the same time this seal 707, 807, 907 controls the opening and closing position of the bleed valves 701, 801, 901 in a manner corresponding to that already described in the previous 10 Figures. The differences between the bleed valves 701, 801, 901 lie in the choice of sealing element and in the use of a non-return valve. In the embodiments 701 and 901 (Figures 9 and 10) a sealing ring 707 and 907, respectively is used whilst in the embodiment 807 of 15 Figure 10 a hose section is used accordingly. The embodiment 901 has a non-return valve 925 which is formed according to Figure 8 from a hose section 905b which axially covers a puncture opening 916. Furthermore the formation of the connection between the pressurized medium 20 pipeline 706, 806, 906 is produced as a pressurized medium outlet in the slave cylinder direction and the outlet opening 705 of the bleed valves 701, 801, 901 in examples 901, 701 of Figures 9 and 11 by means of a recess 713 in the connector 703a, whilst in the embodiment 801of Figure 25 10 the connector 703b has a recess 813 for connecting the two ducts 705 and 806. Opening and closing the bleed valves 701, 801, 901 preferably takes place by turning the housing 702 relative to the connectors 703a, 703b whereby also in these embodiments stops 719 can be provided to 30 restrict the turning capacity of the connector 703a opposite the housing 702 and the groove for the cramp 718a

- 1 9 - can be provided eccentric or elliptic in order to clearly distinguish the open/closed end positions through a distinct application of energy in the turning direction in which the cramp 718a is radially tensioned in the 5 positions which differ from the end positions.

Figure 12 shows diagrammatically a possible design of a hydraulic system 50 with a bleed valve 1 in respect of a clutch release device having a master cylinder 51 and a 10 slave cylinder 52. The bleed valve 1 is arranged directly on the slave cylinder 52 in the illustrated embodiment and the housing (for example 2 in Figure 1) of the bleed valve 1 can thereby be connected integral with the slave cylinder housing. It is evident that bleed valves of this 15 kind can also be integrated in other hydraulic systems, such as for example brake systems, power assisted steering systems and the like.

The clutch release system 50 operates the clutch 54 20 hydraulically through biasing the master cylinder 51 by means of an operating member 61 which can be a foot pedal, actor, for example an electric actor, or the like.

Pressure is hereby built up in the master cylinder 51 by means of a mechanical transfer means 60, and this builds 25 up pressure in the slave cylinder 52 accordingly through the pipeline 59, through the optional pressure restricting valve 62 and through the power train 58. The slave cylinder 52 can - as shown in the illustrated example -

be arranged concentric about the gear input shaft 57 and 30 can be supported axially on a gearbox housing (not shown in further detail) and can apply the required release

- 20 force through a release bearing on the clutch 54, for example on the release elements thereof such as the plate spring. Further embodiments can provide a slave cylinder 52 which operates a release member through a release 5 mechanism and which can be mounted outside of the clutch bell wherein the latter axially biases the release mechanism by means of a piston housed in the slave cylinder housing and in hydraulic connection to the master cylinder. In order to apply the release force the slave 10 cylinder is attached fixed on the gearbox housing or on another component part fixed relative to the housing.

When the clutch 54 which is mounted on the crankshaft 56 is closed the gear input shaft 57 transfers torque from the internal combustion engine 55 to a gearbox (not shown 15 in further detail) and then to the drive wheels of the motor vehicle.

The pressurized medium reservoir 53 serves to supply pressurized medium. This is then preferably connected to 20 the master cylinder 51 when the latter is in the rest position, that is when no pressure is exerted on the slave cylinder 52. In this position pressurized medium can flow into the master cylinder by means of the hydrostatic differential pressure. During activation of the master 25 cylinder 51 the pressurized medium reservoir 53 is separated from the master cylinder 51 through a valve so that the master cylinder can be formed substantially pressureless. 30 In order to fill the hydraulic system 50 pressurized medium is set up in the pressurized medium reservoir 53

- 21 and the bleed valve 1 is opened. If the pressurized medium reservoir is arranged hydrostatically higher than the remaining component parts, for example slave cylinder 52 and bleed valve 1 then the hydraulic system 50 fills up 5 by means of the hydrostatic pressure For assistance the master cylinder 51 can be biased by means of the operating member 61 so that the pressurized medium is pressed faster into the pipelines by means of the rising pressure and the air located up to then in the pipelines is forced out of 10 the bleed valve. When using a non-return valve in the bleed valve 1 the master cylinder 51 can be operated in succession without having to close the bleed valve 1 each time by hand during reverse movements of the master cylinder 51 during which pressurized medium is sucked in 15 from the pressurized medium reservoir 53. A pre-

requirement for the effective operation of a non-return valve 1 is that it be suitably designed. Hereby the opening pressure of the non-return valve must be smaller than the pressure which is produced by operating the 20 master cylinder 51 with a predetermined air volume in the hydraulic system. It has hereby been shown that in the case of hydraulic systems normally used in motor vehicles an opening pressure of maximum 0. 5 bar and preferably equal to or less than O 3 bar can be particularly 25 advantageous for the non-return valve. Advantageously a pressure is set by a non-return valve during the filling process up to the opening pressure which in volumes with no flow through, for example in special design chambers of slave cylinders compresses the air located there whereby 30 correspondingly larger volumes of pressurized medium flow down and during the subsequent reverse movement of the

- 22 master cylinder through the formation of a vacuum the expanding air is removed more effectively from these volumes. A further advantage is the saving in labour since by using a non-return valve it is possible to spare the 5 second person who is normally required to co-ordinate the opening and closing of the bleed valve 1 as the first person operates the master cylinder.

The patent claims filed with the application are proposed 40 wordings without prejudice for obtaining wider patent protection. The applicant retains the right to claim further features disclosed up until now only in the description and/or drawings.

15 References used in the sub-claims refer to further designs of the subject of the main claim through the features of each relevant sub-claim; they are not to be regarded as dispensing with obtaining an independent subject protection for the features of the sub-claims referred to.

Since the subjects of these sub-claims can form independent inventions in respect of the prior art as it

stands on the day of application the applicant reserves the right to make them the subject of independent claims 25 or declarations. They can furthermore also contain independent inventions which have a configuration independent of the subjects of the preceding sub-claims.

The embodiments are not to be regarded as a restriction of 30 the invention. Rather numerous amendments and modifications are possible within the scope of the

invention, particularly those variations, elements and combinations and/or materials which are inventive for example through combination or modification of individual features or elements or process steps contained in the 5 drawings and described in connection with the general description and embodiments and claims and which through

combinable features lead to a new subject or to new process steps or sequence of process steps insofar as these refer to manufacturing, test and work processes.

Claims

- 24 CLAIMS

1. Hydraulic system, more particularly for motor s vehicles, comprising a slave cylinder with a pressurised medium inlet, a master cylinder with a pressurised medium outlet, a pressurised medium pipe hydraulically connecting the pressurised medium inlet to the pressurised medium outlet, a pressurised medium reservoir and a bleed valve 10 comprising a bleed plug and a housing therefor, characterized in that when the bleed valve is in the sealing state the plug and the housing are sealed radially relative to each other.

15 2. Hydraulic system, more particularly for motor vehicles, comprising a slave cylinder with a pressurised medium inlet, a master cylinder with a pressurised medium outlet, a pressurised medium pipe hydraulically connecting the pressurised medium inlet to the pressurised medium 20 outlet, a pressurised medium reservoir and a bleed valve consisting of a bleed plug and a housing therefor, characterized by the combination of the following features:. 25 a) rotation of the bleed plug relative to the housing causes the setting of at least two distinguishable positions for the bleed plug relative to the housing b) in a first position the bleed plug is sealed radially 30 from the housing

- 25 c) in a second position the hydraulic system is opened towards the atmosphere d) opening and closing of the bleed valve causes no 5 relative axial movement of the bleed plug with respect to the housing.

3. Hydraulic system more particularly for motor vehicles, comprising a slave cylinder with a pressurized medium 10 inlet, a master cylinder with a pressurized medium outlet, a pressurized medium pipe hydraulically connecting the pressurized medium inlet to the pressurized medium outlet, a pressurized medium reservoir and a bleed valve consisting of a bleed plug and a housing containing same 15 characterized in that opening the bleed valve takes place in a path controlled manner.

4. Hydraulic system more particularly according to one of claims 1 to 3 characterized in that rotation of the bleed 20 plug relative to the housing is restricted.

5. Hydraulic system more particularly according to claim 4, characterized in that the restriction is produced by means of at least one stop.

6. Hydraulic system more particularly according to one of claims 1 to 5 characterized in that at least one ring-

shaped sealing element having a sealing edge mounted in a plane inclined to a common axis of rotation of the bleed 30 plug and housing is provided radially between the bleed plug and the housing.

- 26 7. Hydraulic system more particularly according to claim 6 characterized in that the sealing element is a sealing ring such as an Oring.

8. Hydraulic system more particularly according to claim 6 characterized in that the sealing element is a hose section inclined at at least one axial end.

10 9. Hydraulic system more particularly according to one of claims 6 to 8 characterized in that the sealing element is mounted on the bleed plug and at least one radial expansion is provided in the housing which communicates with an opening duct of the bleed plug and ends axially 15 between the two axial extreme points of the sealing stretch of the sealing element.

10. Hydraulic system more particularly according to claim 9 characterized in that the opening duct is mounted 20 centrally around the axis of rotation and has a connection such as a puncture hole in the region of the radial expansion. 11. Hydraulic system more particularly according to one 25 of claims 1 to 10 characterized in that the bleed plug and the housing are fixed axially secured but rotatable relative to each other along the rotational axis by means of a releasable connection.

30 12. Hydraulic system more particularly according to claim 11 characterized in that the releasable connection is

formed by means of a radially pretensioned cramp which is axially supported on the housing and is guided axially in a groove of the bleed plug.

5 13. Hydraulic system more particularly according to claim 11 characterized in that the releasable connection is a snap-fit connection.

14. Hydraulic system more particularly according to claim 10 12 characterized in that the snap-fit connection is formed from at least two snap hooks provided in the bleed plug and each engaging radially in a grooved segment recessed circumferentially out from the housing.

15 15. Hydraulic system more particularly according to claim 12 characterized in that a single grooved segment is provided for both snap hooks.

16. Hydraulic system more particularly according to claim 20 14 characterized in that at least one axial boundary wall of one of the grooved segments or of the grooved segment forms a stop in the circumferential direction for at least one snap hook.

25 17. Hydraulic system more particularly according to one of claims 1 to 16 characterized in that the opening duct and a connection provided in the housing to the pressurized medium pipe are arranged substantially on one line.

- 28 18. Hydraulic system more particularly according to one of claims 1 to 16 characterized in that the opening duct and a connection provided in the housing to the pressurized medium pipe are arranged at an angle, 5 preferably at a right angle, to each other.

19. Hydraulic system more particularly according to one of claims 1 to 19 characterized in that the housing and the slave cylinder are formed in one piece.

20. Hydraulic system more particularly according to one of claims 1 to 19 characterized in that a device for restricting pressure pulsations in the pressurized medium pipe is integrated in the housing.

21. Hydraulic system more particularly according to one of claims 1 to 20 characterized in that a device for damping vibrations in the pressurized medium pipe is integrated in the housing.

22. Hydraulic system more particularly according to one of claims 1 to 21 characterized in that the bleed valve is provided with a non-return valve.

25 23. Hydraulic system more particularly according to one of claims 1 to 22 characterized in that the bleed valve connects two connectors of the hydraulic system together and has for this purpose a pressurized medium inlet and a pressurized medium outlet as well as an airflow opening.

- 29 24. Hydraulic system more particularly according to one of claims 1 to 23 characterized in that the maximum turning angle between the bleed plug and housing for setting the two operating states of open/closed amounts to 5 180 , preferably 120 .

25. Hydraulic system substantially as herein described with reference to the accompanying drawings.

10 26. A bleed valve for a hydraulic system which has a slave cylinder with a pressurized medium inlet, a master cylinder with a pressurized medium outlet, a pressurized medium pipe hydraulically connecting the pressurized medium inlet to the pressurized medium outlet and a 15 pressurized medium reservoir, wherein the bleed valve comprises a bleed plug and a housing therefor, and when the bleed valve is in the sealing state the plug and the housing are sealed radially relative to each other.

20 27. A bleed valve for a hydraulic system substantially as herein described with reference to any one embodiment shown in the accompanying drawings.