GB2345106A

GB2345106A - Working cylinder for hydraulic clutch or brake actuation

Info

Publication number: GB2345106A
Application number: GB9926665A
Authority: GB
Inventors: Roland Welter
Original assignee: LuK Lamellen und Kupplungsbau GmbH
Current assignee: LuK Lamellen und Kupplungsbau GmbH
Priority date: 1998-11-11
Filing date: 1999-11-11
Publication date: 2000-06-28
Anticipated expiration: 2019-11-11
Also published as: GB2345106B; ITMI992354A1; DE19953581B4; IT1314029B1; ITMI992354A0; FR2785648B1; FR2785648A1; DE19953581A1; GB9926665D0

Abstract

A working cylinder 1a for a clutch or brake operating device comprises a plastics housing 2 having upper and lower parts 3,4 forming a pressure chamber 5 which serves to hold and guide a spring biased piston 6a, the piston operable via a piston rod 8 which extends out of the housing and is attached for swivel movement thereto. An inlet supply connection 15, is mounted centrally in the upper part 3, and a pressure connection 16 is further provided at right angles to the longitudinal axis of the cylinder. A spring biased control element 9a in the form of a control cage 11a is mounted axially in front of the piston, for opening and closing the inlet supply connection, the control element comprising circumferential holding arms 11a to form a snap-fit nose 12 which engages piston ring 13 so as to be displaceable relative to the piston.

Description

2345106 WORKING CYLINDER FOR HYDRAULIC CLUTCH ACTUATION The present

invention relates to a working cylinder for a vehicle hydraulics system, more particularly for operating a shift and separate clutch mounted between an internal combustion engine and a toothed gear gearbox. Working cylinders of this kind comprise a hollow cylindrical shaped housing forming a pressure chamber and having an inlet supply connection and a pressure connection. A piston is inserted in the pressure chamber and is arranged for axial displacement and sealed from the housing. The piston is associated with a compression spring which - applies force to the piston in the direction of the playfree end position. A piston rod is attached for swivel movement to the piston at the end remote from the pressure chamber. The further end of the piston rod can be fixed for example on a clutch pedal, for manually operating the shift and separate clutch.

From DE 37 13 248 C2 a working cylinder is known of the structural type mentioned above. This working cylinder comprises a piston which is enclosed by a steel sleeve. To seal the ring gap between the piston and the steel sleeve a ring groove is provided on the pressure chamber side in the piston to hold a round sealing ring which is supported sealingly on the steel sleeve. To guide the piston a so-called intermediate sleeve is inserted in the housing, with the length of this intermediate sleeve being clearly shorter than the longitudinal extension of the piston. The intermediate sleeve is secured in position by a holding member whose radially pretensioned snap-fit noses engage in recesses in the housing in the installed position. At both end sides of the intermediate sleeve, grooved ring seals are inserted in recesses to seal the ring gap between the piston and the intermediate sleeve.

The compression spring inserted in the pressure chamber of the housing is supported between a housing base and the piston. In a neutral position the piston occupies as a result of the spring force applied by the compression spring, an end position where it is supported on the intermediate sleeve by a radial piston plate at the end. The construction of the known working cylinder comprises a number of individual component parts which incur increased assembly costs and thus simultaneously raise production costs. The known working cylinder furthermore has an inlet supply connection which is mounted at right angles to the longitudinal axis of the working cylinder and is axially off-set from the pressure connection of the working cylinder. The arrangement of these connections does not permit vertical installation, where the inlet supply connection is mounted above the pressure connection, in order to achieve an automatic ventilation of the hydraulic system.

Taking into account the drawbacks of the known device it is the object of the invention to provide a construction for a working cylinder which has optimised construction of the component parts 25 guarantees automatic ventilation even with a perpendicular installation allows cost advantages to be achieved. According to the invention the piston is connected on the pressure side to a control element which opens or closes the inlet supply connection dependent on the position of the piston. The inlet supply connection is fitted in the housing in the base which is mounted at right angles to a longitudinal axis of the working cylinder. An inlet supply connection of this kind in conjunction with a pressure connection which is mounted in a cylindrical section of the housing axially off-set relative to the inlet supply connection, guarantees an automatic ventilation, i.e. evacuation of the air included in the hydraulic system, even with a vertical installation of the working cylinder.

For the spring-biased control element which is mounted displaceable relative to the piston a stroke or displacement path is provided which is smaller than the maximum stroke of the piston. AS a result of this arrangement in the end position of the piston which - corresponds to the engaged position of the shift and separate clutch, a permanently opened inlet supply is connection is guaranteed through which an automatic ventilation can take place. Furthermore an automatic after flow of pressurised medium out from a reservoir which is connected to the inlet supply connection also becomes possible to fill the hydraulic system with pressurised medium when required. A closed inlet supply connection which is required when building up pressure is automatically set after a partial stroke of the piston. The piston stroke for closing the inlet channel can thereby be determined by the length of the control element which defines at the same time a gap measurement between the control element and the opened inlet supply connection.

Further advantageous developments of the invention are the subject of claims 2 to 19.

Advantageously the control element is formed pot-shaped as a control cage which includes a closed base which is aligned towards the inlet supply connection and is adjoined by holding arms which are circumferentially spread out and aligned axially in the direction of the piston and are fixed with keyed engagement on the piston.

Furthermore according to the invention a compression 5 spring is provided between the control element or the control cage and piston. The spring arrangement ensures the control element is constantly biased with force in the direction of the inlet supply connection. The f ormation of the control element in conjunction with the compression spring ensures that in a neutral position which corresponds at the same time to the upper position of the clutch pedal the inlet supply connection is opened through the formation of a def ined ring gap between the control element and the inlet supply connection. In this position is of the control element the hydraulic system can be f illed or snif ted. By using a spring having a relatively low suspension of the control element a vacuum drop is possible with a snap click of the pedal. In order to operate the clutch wherein the piston of the working cylinder is displaced, after a partial stroke of the piston the control element is sealingly supported on the inlet supply connection and thus allows pressure to build up in the pressure chamber of the working cylinder.

In order to prevent air bubbles from forming inside the control element the control element is slit at the sides or the holding arms are arranged spread so far apart that the pressurised medium can flow unhindered through the control element. One design of the control element proposes that the holding arms are guided on an inner wall of the housing and are angled inwards at right angles at the ends to form holding noses. To f ix the position the holding noses engage with keyed engagement behind an endside piston disc or a radial projection of the piston.

- 5 The invention further proposes a control element whose holding arms engage in longitudinal guides of the housing and whose angled holding noses are snap-fitted on the piston. A guide of the control element of this kind allows an extended piston guide since the areas between the longitudinal guides in the housing can be used to guide the piston.

The holding noses of the holding arms engage in longitudinal grooves of the piston which is closed at the end by an attachment. This design likewise allows a relative displacement between the piston and the control element which is adjusted as soon as the control element sealingly adjoins the inlet supply connection.

In order to ensure an automatic ventilation of the system the invention includes an installation position where the inlet supply connection always occupies the highest static height of the working cylinder. A difference in height is thereby produced between the inlet supply connection and the. pressure connection.

In an advantageous development of the invention a two-part housing is provided for holding the piston and the control element. One upper part is thereby associated with both the inlet supply connection and the pressure connection on whose inner wall the control element is guided alone or jointly with the piston. A further lower part of the housing preferably serves to guide the piston.

The housing structure furthermore includes an inlet supply connection provided centrally on the base of the upper part. A seal inserted in the base of the upper part is mounted concentric with the inlet to form a sealing seat.

The central inlet supply connection in conjunction with the seal produces a relatively large surface support area for the control element and thus prevents a crooked position which could impede the functioning.

The pressure connection is inserted according to the invention at right angles to the longitudinal axis of the working cylinder in the upper part, preferably with a slight axial stagger from the base of the upper part. An unimpeded flow of pressurised medium in the neutral position from the inlet supply connection to the pressure connection is made possible by a groove formed on the inner wall of the upper part and extending from the pressure connection to the base of the upper part.

The invention further proposes centring for the compression spring which is inserted between the piston and the control element. At least one spring end is centred internally or externally on the piston or control element to produce a constantly identical position of the compression spring and to avoid a crooked position which can have a detrimental effect on the functioning of the overall working cylinder. Furthermore it is proposed to provide a piston stop inside the control element. A piston stop of this kind prevents contact against the compression spring which is compressed into a block.

In a further development of the invention a guide sleeve is proposed for guiding the piston, with the sleeve preferably inserted in the lower part of the housing. To optimise wear the guide sleeve is made from a material which preferably has a higher strength compared to the piston.

As an alternative to a two-part housing the invention likewise includes a one-piece housing in which the piston is guided directly on an inner bore of the housing or as an alternative is guided out from a guide sleeve inserted in the housing.

The seal for the piston comprises at least one seal. Preferably a grooved ring seal is provided between the lower part and upper part. The grooved ring seal is thereby guided on the outside in the upper part and is supported by a sealing back at the end on the lower part.

The sealing lips of the grooved ring seal are aligned in the direction of the pressure chamber whereby the radially inner sealing lip is radially pretensioned and sealingly adjoins the sleeve face of the piston.

The formation of a seam between the lower part and upper part of the housing allows an end section of the upper part to be radially expanded. The expansion thereby encloses an end section of the lower part. The radially expanded area of the upper part serves at the same time to hold the grooved ring seal which is supported on a shoulder.

The lower part is preferably pot-shaped with its base having a central opening for a piston rod. The base forms at the same time an end stop for the piston in the neutral position.

In addition to the designs of the invention previously mentioned regarding the configuration of the housing and seal the invention further includes all designs of working cylinders known up until now.

With regard to the control element according to the invention it is proposed to make this preferably of a metal material. Particularly suitable for this is for example a steel plate which can be suitably shaped by a deep-drawing process without stock removal. For the housing of the working cylinder, irrespective of whether it is designed in one part or two, it is proposed to use a plastics, for example a glass fibre reinforced plastics, such as f or example PA 66GF. In order to pair up the materials it is also proposed to make the piston from plastics. A metal material is particularly suitable for making the guide sleeve. The invention obviously also includes material pairings which deviate from the materials mentioned above.

The invention will now be explained in further detail with reference to the two drawings in which:

is Figure 1 is a longitudinal section through a working cylinder according to the invention; and Figure 2 shows a working cylinder with an alternative design of control element.

Figure 1 shows a working cylinder la which comprises a housing 2 made of plastics and having an upper part 3 and lower part 4. The substantially rotationally symmetrical shaped housing 2 f orms a pressure chamber 5 and serves to hold and guide a piston 6a. To guide the piston 6a a guide sleeve 7 which is preferably made of a metal material is inserted in the lower part 4. A displacement of the piston 6a in the direction of the arrow starting from the position shown in Figure 1 is preferably triggered through a manually operated clutch pedal (not shown in Figure 1) to which the working cylinder la is connected through a piston rod 8. The pressure chamber side is adjoined by a control element 9a which is mounted axially in front of the piston 6a and is formed as a control cage. The control element ga comprises a base 10 adjoined by holding arms lia which are spread out symmetrically around the circumference and are aligned coinciding axially in the direction of the piston 6a. At the free end each holding arm lia is angled inwards at right angles to form a snap-fit nose 12 which engages behind a radial overhang relative to the sleeve face of the piston 6a at the piston disc 13 arranged at the end side. A compression spring 14 is inserted between the base 10 of the control element 9a and the piston disc 13 with which the control element 9a is displaced in the direction of an inlet supply connection 15.

The upper part 3 has the inlet supply connection is mounted centrally in the base 17 of the upper part 3. Furthermore the upper part 3 is provided with a pressure connection 16 which is mounted at right angles to a longitudinal axis 18 of the working cylinder la in the cylindrical section of the upper part 3.

As a result of the spaced holding arms lia, longitudinal slits are produced to form a cage-like control element 9a. The position of the piston 6a in connection with the control element 9a in the neutral position produces an annular gap which is set between the base 10 of the control element 9a and a seal 19 in the base 17 of the upper part 3 and which is indicated by 1xl. In this neutral position of the piston 6a pressurised medium can flow through the inlet supply connection 15 unhindered into the hydraulic system, i.e. into the pressure chamber 5 and through the pressure connection 16. Furthermore a vertical installation position of the working cylinder ia' allows according to Figure 1 an automatic ventilation or evacuation of the air included in the hydraulic system,' which can now escape through the inlet supply connection 15 at the statically highest point of the working cylinder la.

When operating the working cylinder la where the piston 6 is displaced in the direction of the arrow, after a partial stroke which corresponds to the annular gap 1xl, the base 10 of the control element ga comes in to contact with the seal 19 and thus closes the inlet supply connection 15. The seal 19 forms together with the base 10 a seal seat 32.

After the control element 9a bears against the seal 19 or against the base 17 of the upper part 3 the piston 6a is is displaced into the control element 9a and compresses the compression spring 14. To position the compression spring 14 this is centred internally on the base 10 of the control element 9a through an attachment 21 which projects axially in the direction of the piston 6a and performs at the same time the function of an end stop for the piston 6a.

The pressure in the pressure chamber 5 (which rises as the piston moves) is transferred, when the inlet supply connection 15 is closed, through the pressure connection 16 and an adjoining hydraulic line to a further working cylinder or slave cylinder (not shown in Figure 1). At the end of a gear shift process or clutch actuation and upon reversal of the piston movement (opposite to the arrow direction) the inlet supply connection 15 remains closed until the snap-fit noses 12 come into contact with the piston disc 13 and thus lift the control element 9a f rom, the seal 19. As a supporting measure which allows unrestricted flow of pressurised medium from the inlet supply connection 15 to the pressure connection 16, or ventilation in the reverse direction, a longitudinal groove 20 is formed in the upper part 3 and reaches from the pressure connection 16 to the base 17.

The upper part 3 is non-detachably connected to the lower part 4. The upper part 3 has for this purpose at the end a radial expansion 22 which engages over an end section of the lower part 4. The component parts upper part 3 and lower part 4 which are made of plastics are connected together non-detachably in the overlapping region of the expansion 22 preferably by ultrasound welding. A grooved sealing ring 23 is supported at one end on the lower part - 4 in the region of the expansion 22. A radially outer sealing lip 24 sealingly adjoins the inner wall of the upper part 3 and a radially inner sealing lip 25 is supported against and seals with the sleeve face of the piston 6a. The pot-shaped lower part 4 is likewise provided with a base 26 which forms an end stop for the piston 6a in its neutral position. Furthermore the base 26 is provided with a central opening 27 for the piston rod 8 which is fixed for swivel movement on the piston 6.

Figure 2 shows the working cylinder Ib which differs from the working cylinder la according to Figure I by a modified coupling between the control element 9b and piston 6b and by a housing 28 which is formed in one piece. A longitudinal guide 29 in the housing 28 is associated with each holding arm 11b of the control element 9b. The snap-fit noses 12 of the holding arms 11b engage in longitudinal grooves 30 of the piston 6b which end at a radially extending shoulder 33. This type of coupling of the control element 9b allows an extended guide of the piston 6b in the housing 28. With the same dimensions for the piston and the same volume for the pressure chamber 5 this design reduces the radial structural space required for the working cylinder lb and thus allows the structural space to be optimised in the desired manner.

At the same time the working cylinder lb illustrated in Figure 2 allows a one-piece housing 28, which has a closure part at the end remote f rom the base 17, to be used to provide a piston stop and secure the grooved sealing ring 23 wherein the closure part 31 is connected preferably by a snap-fit connection to the housing 28.

All the remaining component parts provided with reference - numerals in Figure 2 agree with those corresponding to Figure 1 so that reference should be made here to the description of the first embodiment.

The patent claims filed with the application are proposed 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.

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.

The subjects of these sub-claims however also form independent inventions which have a design independent of the subjects of the preceding claims.

The invention is also not restricted to the embodiments of the description. 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 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

Working cylinder for a vehicle hydraulic system, more particularly for operating a shift and separate clutch mounted between an internal combustion engine and a gearwheel change-gear, comprising:

- a hollow cylindrical housing forming a pressure chamber and having an inlet supply connection and a pressure connection; - a piston mounted for axial displacement in the pressure chamber and sealed against the housing; - a piston rod guided out of the housing and attached for swivel movement to the piston; - a compression spring acting on the piston; characterised in that for opening and closing the inlet supply connection in the pressure chamber mounted in the base of the housing there is a spring-biased control element which is connected to the piston and is displaceable relative to the piston.
2. Working cylinder according to claim 1 characterised by a pot-shaped control element which is formed as a control cage and has a closed base which is aligned towards the inlet supply connection and is adjoined by holding arms which are circumferentially spaced out and aligned axially in the direction of the piston.
3. Working cylinder according to claim 1 characterised in that the compression spring is supported between the base of the control element and an end side of the piston.
4. working cylinder according to claim 2 characterised in that the holding arms are guided on an inner wall of - is - the housing and are angled inwards at right angles at the ends to form snap-fit noses which in an installed position engage with keyed engagement behind a piston disc or a radial projection of the piston.
5. working cylinder according to claim 2 characterised in that the holding arms are guided in longitudinal guides of the housing and their snap-fit noses which are angled inwards at the ends at right angles engage in longitudinal grooves of the piston which are defined on the pressure chamber side by an attachment.
6. Working cylinder according to claim 1 characterised by an installation position of the working cylinder where a static height for the inlet supply connection is provided which exceeds a corresponding static height of the pressure connection.
7. working cylinder according to claim 1 characterised by a two-part housing comprising an upper part with which the inlet supply connection and the pressure connection are 20 associated and on whose inner wall the control element is guided; a lower part for guiding the piston.
8. Working cylinder according to claim 1 characterised in that the inlet supply connection fitted centrally in the base of the upper part forms a sealing seat with a seal.
9. Working cylinder according to claim 1 characterised in that the pressure connection is fitted at right angles to a longitudinal axis of the working cylinder in the upper part of the housing or in the housing.
10. working cylinder according to claim 9 characterised in that the pressure connection is associated with a longitudinal groove which runs on the inner wall of the upper part and reaches to the base.
11. Working cylinder according to claim 3 characterised in that the compression spring is centred at least by one end on the piston or on the control element.
12. Working cylinder according to claim 1 characterised in that to guide the piston a guide sleeve is provided 10 which is positioned in the lower part.
13. Working cylinder according to claim 1 characterised in that to seal the piston at least one seal is provided which seals a ring gap between the housing and the piston.
14. Working cylinder according to claim 13 characterised is by a grooved sealing ring which is mounted between the upper part and the lower part and which is enclosed on the outside by an expansion of the upper part and which is supported at the end side by a sealing back on the lower part, with a radially inner sealing lip adjoining the.20 piston.
15. Working cylinder according to claim 7 characterised in that the expansion of the upper part encloses an end section of the lower part with keyed engagement and both component parts are connected together nondetachable in 25 the overlapping zone.
16. Working cylinder according to claim 7 characterised by a pot-shaped lower part whose base has a central opening for the piston rod and furthermore forms an end stop for the piston.
17. Working cylinder according to claim 1 characterised by a control element made of a metal material preferably by a deep-drawing process without any stock removal.
18. Working cylinder according to claim 1 characterised in that the component parts housing and piston are made of plastics.
19. Working cylinder according to claim 1 characterised in that the piston is guided in a guide sleeve made of a metal material.
20. working cylinder substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.