GB2347720A

GB2347720A - Working cylinder for vehicle hydraulic system

Info

Publication number: GB2347720A
Application number: GB0005189A
Authority: GB
Inventors: Jeannot Paquay
Original assignee: LuK Lamellen und Kupplungsbau GmbH
Current assignee: LuK Lamellen und Kupplungsbau GmbH
Priority date: 1999-03-11
Filing date: 2000-03-06
Publication date: 2000-09-13
Anticipated expiration: 2020-03-06
Also published as: GB2347720B; IT1317587B1; ITMI20000491A1; GB0005189D0; FR2791739A1; DE10011426A1; FR2791739B1

Abstract

A working cylinder for a vehicle hydraulic system comprises a hollow cylindrical housing 2a open at one end and in which a piston 4a is displaceable. The piston 4a has a guide part 23 which forms a piston stop with a guide sleeve 5a inserted in the housing 2a. A return spring 19 for the piston extends from the closed end of the housing to the base 11 of the piston. The piston may be made from plastics or ceramics, or from sheet metal by a deep drawing process. Areas of the piston may be coated to prevent corrosion and/or to improve the sliding properties. The housing 2a, guide sleeve 5a and retaining ring 6 are preferably made of plastics, with the ring being secured by adhesive or ultrasound welding. Guide part 23 may be replaced by a flange (26, Fig.4).

Description

Working cylinder for vehicle hydraulics Working cylinders are used in vehicle hydraulics, more particularly for operating the shift and separate clutch and the vehicle brake. A working cylinder of this kind used for example as a master cylinder for clutch activation is connected to a pedal device or to a clutch actuator. During manual operation of the pedal the piston which is guided in the working cylinder is for example displaced so that the pressurised fluid located therein is forced in the direction of a slave cylinder which is mounted in the region of the shift and separate clutch and is connected to the master cylinder through a pressurised line. The piston which is inserted in the slave cylinder and is connected to disengagement elements of the shift and separate clutch is thereby displaced.

The invention relates to a working cylinder having a hollow cylindrical housing, open on one side and forming a pressure chamber having at least one pressurised medium connection. The piston which is mounted displaceable in the pressure chamber and is sealed from the housing thereby has a radial step. A piston rod is attached for swivel movement on the piston and is guided out from the housing.

A working cylinder of the type previously mentioned is known from DE 37 13 248 C2. This working cylinder comprises a piston which is enclosed at least in part by a steel sleeve. In order to seal the gap between the piston and the steel sleeve the piston is provided on the pressure chamber side with a ring groove for holding a circular sealing ring which in the installation position sealingly adjoins the inside wall of the steel sleeve. In order to guide the piston an intermediate sleeve is inserted in the housing and is secured in position by a retaining member whose radially pretensioned snap-fit noses engage in the recesses in the housing with detent engagement in the installed position. Recesses are provided at both end sides of the intermediate sleeve for the sealing ring seals which are used to seal the piston from the intermediate sleeve. In order to obtain a pretensioned position of the piston a compression spring is inserted in the pressure chamber of the housing where it is supported between the bottom of the housing and the piston. In a neutral position as a result of the spring force exerted by the compression spring the piston occupies an end position in which it is supported on the intermediate sleeve by a section which is radially stepped on the pressure chamber side. The structure of the known working cylinder comprises a number of individual component parts which incurs high assembly expense and thus at the same time raises the production costs. The structure of the known working cylinder has a housing which completely encloses the piston irrespective of its position and thus requires a large installation space. The housing furthermore forms an area set axially in front of the pressure chamber for holding the spring windings when the piston is engaged.

Taking into account the drawbacks of the known working cylinder the object of the present invention is to produce through suitable design features a working cylinder which has the optimum number of component parts and installation space with reduced costs. In order to solve the problem set a one-piece hollow cylindrical piston is provided which is open on one side. This structural shape for the piston allows a cost-effective production without stock removal wherein the piston when retracted encloses the compression spring on the outside. Furthermore a design can be provided wherein the compression spring which is not sufficiently secure against kinks is guided substantially on the piston wall. In order to ensure an effective centring the compression spring is supported at the end side on the piston base. A piston length is thereby set which agrees substantially with the longitudinal extension of the housing. A working cylinder can thus be produced which solves the problem set, takes up optimum structural space and whose length is substantially determined by the length of the piston. In order to produce a piston stop, the piston is provided on the pressure chamber side with a radially outwardly directed circumferential step.

According to the invention the working cylinder is only provided with one seal, for sealing the piston.

Through this measure the source of noise is eliminated, whilst at the same time the friction which occurs during displacement of the piston is reduced which has a favourable effect on the sliding properties of the piston and thus on the hysteresis of the entire system.

Compared with the prior art the working cylinder according to the invention which takes up the optimum structural space furthermore has a reduced number of component parts which represents a cost advantage.

The demand for producing a working cylinder in optimum structural space is met by adapting the length of the housing to the longitudinal extension of the piston. During operation, i. e. loading the working cylinder with pressure, the piston is moved out of the housing until the step on the piston on the pressure chamber side adjoins the associated end stop. This construction clearly reduces the length of the housing compared with working cylinders of the type known up until now where the length was designed so that the piston is enclosed by the housing in all positions.

Further advantageous developments of the invention form the subject of claims 2 to 18.

The advantageous design of the invention relates to an assembled piston, i. e. a piston comprising at least two component parts. The base part of the piston on which the piston rod is supported is adjoined on the pressure chamber side by a sleeve-type guide part which widens out radially towards the base part. The guide part is thereby designed so that this is guided on the inside wall of the housing and thus creates an improved piston guide, more particularly when force is introduced inclined into the piston through the piston rod, so that any off-set or crooked position of the piston is effectively prevented.

A further advantageous development of the invention provides a piston which comprises an edge on the pressure chamber side to form the radially outwardly directed step. A piston of this kind can likewise be manufactured cost-effectively through a process involving no stock removal. The wall thickness of the edge corresponds substantially to the wall thickness of the remaining piston sections so that the installation length, i. e. the length extension of the piston remains substantially unchanged by the shaping of the edge.

The inventive design of the piston proposes that it has on the piston rod side a dome-type mounting in which the piston rod is supported. Advantageously this mounting can be formed without stock removal during the shaping of the piston and as a result of this shaping enables the strength of the piston to be improved. On the pressure chamber side the dome-type mounting forms an area protruding axially from the bottom of the piston, which can preferably be utilised for internally centring the compression spring.

The working cylinder according to the invention is provided for guiding the piston with a ring-shaped guide sleeve which is positioned in the opening area of the housing. The guide sleeve can thereby be dimensioned differently and made from different materials. For a piston having a guide part mounted on the pressure chamber side a guide sleeve of reduced length is sufficient since the piston is supported on the pressure chamber side on the inside of the housing additionally through the guide part. For pistons whose step on the pressure chamber is not provided for guiding the piston it is better to increase the longitudinal extension or width of the guide sleeve accordingly.

A deep drawing process where the component part is made from sheet steel without stock removal is particularly suitable for manufacturing the piston or piston base part. This cost-effective method which offers reliable processing for large numbers of pieces has a high production accuracy and great cost advantages. As an alternative a flow pressing method can also be used for manufacturing the piston, and even other suitable manufacturing processes, such as e. g. producing the piston from cast aluminium.

The deep drawing method is suitable for shaping a guide part which is widened out radially from the remaining sleeve face of the piston and which allows the piston to be guided on the inside wall of the housing. For a multi-part piston it is possible to fix the guide part on the base part through material bonding, i. e. for example through welding or adhesive. Alternatively a positive-locking fixing is also suitable.

The end stop for the piston is formed by the guide part which is inserted in the housing of the working cylinder or by the step of the piston which is formed as an edge, together with the guide sleeve inserted in the housing.

A further design of the invention relates to a multipart piston whose component parts are made from the same or different materials. In order to achieve a working cylinder with optimum friction properties, according to the invention a suitable choice of materials can be selected for the component parts which are to be in direct sliding connection, namely the piston, guide sleeve and housing. The choice of materials is in the first instance to be selected to produce sliding partners producing the optimum sliding conditions.

By way of example a one-piece piston made of steel can be guided in a guide sleeve of plastics. For an assembled multi-part piston it is possible to use a base part of steel which is guided in a guide sleeve of plastics or ceramics. The guide part of plastics of this piston is guided on the inside wall of the housing which is likewise made from plastics. As an alternative the invention also includes a piston with a base part made of plastics and adjoined by a guide part made of ceramics. Furthermore the assembled multi-part piston can comprise component parts which are made exclusively of metal materials.

Furthermore according to the invention a piston is provided which is coated at least in areas to avoid corrosion and/or optimise the sliding properties of the piston.

The sleeve face of the guide part or of the piston edge has according to the invention at least one longitudinal groove or recess or a bore. It is thus guaranteed that when pressure is applied to the working cylinder the circular ring-shaped interspace, defined by the guide sleeve and guide part or edge and filled with pressurised medium, can escape, in order to avoid a detrimental effect on the operation of the working cylinder.

The guide sleeve positioned in the housing is secured according to the invention by a retaining ring which is inserted flush with the end side in the housing of the working cylinder. This component part which is preferably made of a material matching the housing, more particularly plastics, is mounted with sealing action preferably through material bonding through ultrasound welding. Facing towards the guide sleeve the retaining ring is furthermore provided with a circumferential end-side recess in which a sealing ring, more particularly a grooved ring seal, is inserted, with the radially inner sealing lip of the ring sealingly adjoining the sleeve face of the piston under pretension. As an alternative the invention also includes a clip connection between the retaining ring and housing in addition to a welded connection.

An active protection of the piston moving out of the housing in the case of a pressure-loaded working cylinder can be achieved according to the invention through folding bellows. These bellows which are fixed on one side on the opening side of the housing and on the other side on the end of the piston rod remote from the piston allow the piston sleeve face as well as the articulated connection between the piston rod and piston to be effectively protected from dirt of any kind. For fixing, the bellows are provided with a reinforced collar which is mounted with positive engagement in a ring groove of the piston rod or on a circumferential bead of the housing. In order to sustain the positive-locking fixing it is advisable to fix the bellows by adhesive on the housing or piston rod. As an alternative the bellows can likewise be fixed on the housing or piston rod by a clamping or tension ring. The bellows are provided with at least one opening through which air included in the bellows can escape unhindered.

The invention will now be explained in further detail with reference to the embodiments shown in the drawings in which: Figure 1 shows a working cylinder whose piston is provided on the pressure chamber side with a radially expanded guide part; Figure 2 shows the piston in the retracted position of a working cylinder according to Figure 1; Figure 3 shows a working cylinder according to the invention whose piston is provided on the end side with a circumferential radially outwardly aligned angle, formed as an edge; Figure 4 shows the working cylinder according to Figure 3 with a piston shown in the retracted position.

Figure 1 shows a working cylinder la having a hollow cylindrical housing 2a open on one side and made from plastics. The rotationally symmetrically shaped housing 2a forms a pressure chamber 3 for holding a piston 4a. For guiding the piston 4a a guide sleeve 5a is inserted in the opening area of the housing 2a.

Corresponding to the wall thickness of the guide sleeve 5a the housing 2a has a section which widens out radially correspondingly from the remaining housing 2a.

A retaining ring 6 is mounted axially in front of the guide sleeve 5a which is preferably made from a material matching the housing 2a, preferably plastics, and these fit together in the mounting 7 of the housing 2a. The retaining ring 6 of plastics is preferably fixed in position sealed in the housing 2a by material bonding, i. e. through ultrasound welding or adhesive.

On the inside the retaining ring 6 has a ring groove 8 which is open to the guide sleeve 5a and serves to hold a grooved ring seal 9 whose radially inner sealing lip sealingly adjoins the sleeve face 10 of the piston 4a.

Remote from the pressure chamber 3 the piston 4a forms on an end side a dome-shaped mounting 11 which is provided to support a piston rod 12 which for this purposed is designed complementary on the end side and is connected for swivel movement to the piston 4a.

Moving the piston 4a in the direction of the arrow, i. e. starting from the end position shown in Figure 1, can be undertaken by a clutch pedal which is to be operated manually and which is not shown in Figure 1 but to which the working cylinder la is connected by the piston rod 12. Movement of the piston 4a displaces the pressurised medium contained in the pressure chamber 3 through a pipeline connection 13 of the housing 2a in the direction of a further working cylinder which is connected to the shift and separate clutch, with the working cylinder being connected by a pressure line. In order to protect the piston 4a in its position extended from the housing 2a shown in Figure 1, folding bellows 14 are provided whose ends each have a reinforced collar. The collar 15 engages round an end area of the housing 2a and is fixed in position on its circumferential bead 17. A further collar 16 of the folding bellows 14 is fitted in a ring groove 18 of the piston rod 12.

The position of the piston 4a shown in Figure 1 is achieved by a compression spring 19 which is guided in the piston 4a and is supported with one end on a piston base 20, thereby centred internally on the dome-like mounting of the piston 4. The further end of the compression spring 19 is supported on a housing base 21 and is thereby centred on a shoulder 22. The two-part piston 4 forms a base part 29 which is adjoined on the pressure chamber side by a guide part 23 which widens out radially to the sleeve face 10 of the base part 29 and with which the piston 4a is guided on an inside wall 24 of the housing 2a. In addition to the piston guide the guide part 23 forms together with the guide sleeve 5a an end stop of the piston 4a. The guide part 23 which is shown in Figure 1 is connected integral with the base part 29 of the piston 4a, whereby these component parts can be made from sheet steel without stock removal, preferably by a deep drawing process. Alternatively it is also possible to use an assembled piston, consisting for example of a steel piston 4a which is adjoined by a guide part 23 made from a different material, for example plastics. The guide part 23 allows the use of a relatively narrow guide sleeve 5a and thereby ensures high security against the piston 4a canting in the extended position even when force is introduced inclined through the piston rod 12.

Figure 2 shows the working cylinder la in the retracted position of the piston 4a. This shows the length of the housing 2a practically coinciding with the longitudinal extension of the piston 4a, which leads to a working cylinder la taking up optimised structural space. The length extension of the working cylinder la is accordingly determined substantially by the length of the base part 29 and the width of the guide part 23.

As for the piston 4a, also for the remaining component parts of the working cylinder la the materials are not fixed. Preferably the housing 2a, the guide sleeve 5a as well as the retaining ring 6 are made from the same plastics. In order to obtain optimum sliding conditions the invention also includes different friction partners in order to improve the hysteresis of the entire hydraulic system. The guide part 23 of the piston 4a is provided with at least one longitudinal groove 27 through which the pressurised medium can be balanced. The pressurised medium enclosed in a circular ring shaped chamber defined radially by the sleeve face 10 of the base part 29 and the inside wall 24 of the housing 2a can escape unhindered during displacement of the piston 4a from the position shown in Figure 2 through the longitudinal groove 27 into the remaining area of the pressure chamber 3. The working cylinder la is furthermore provided with a vent 25 which is connected to the pressure chamber 3 and through which the entire hydraulic system can be ventilated when necessary.

In a second embodiment (Figures 3 and 4) of a working cylinder according to the invention the component parts agreeing with the first embodiment (Figure 1 and 2) are provided with the same reference numerals. To avoid repetition therefore, reference is made to the description of the first embodiment.

Figures 3 and 4 show the working cylinder lb whose piston 4b has on the pressure chamber side a radially outwardly directed angled edge or flange to form a step 26. The formation of the step 26 can be such that it undertakes no guidance of the piston 4b. Instead of this the guide sleeve 5b has a greater length extension and thus provides sufficient guidance for the piston 4b.

The step 26 is provided at least with one recess 28, formed for example as a cross bore, to allow the pressurised medium to flow back from the part of the pressure chamber area 3 which is formed between the sleeve face 10 of the piston 4b and the inside wall 24 of the housing 2b. According to the invention the step 26 can be furthermore profiled or toothed along the outer circumference, with the corresponding profiling fitting into an associated shaping of the inside wall 24 of the housing 2b. This measure allows the piston 4b to be aligned in its rotary position relative to the housing 2b.

As an alternative to the circumferential profiling of the piston 4b or the step 26 which interacts with a complementary shaped inside wall 24 of the housing 2b the invention likewise includes a longitudinal groove in the inside wall 24 on which a piston 4b is guided having a closed step 26. The longitudinal groove likewise allows the pressurised medium to flow back from the circular ring shaped part of the pressure chamber area 3 as soon as the piston 4b has moved from the position shown in Figure 4 into the position according to Figure 3.

Claims

Claims 1. Working cylinder for a vehicle hydraulic system, preferably used for a release device for a shift and separate clutch mounted between an internal combustion engine and a toothed gear gearchange, comprising: -a hollowing cylindrical housing open on one side and forming a pressure chamber and having at least one pipe connection; -a stepped piston mounted axially displaceable in the pressure chamber and sealed from the housing to form a piston stop with an associated component part of the working cylinder; -a piston rod extending out from the housing and attached for swivel movement to the piston ; -a compression spring inserted between the housing base and the piston, characterised in that the working cylinder comprises a one-piece hollow-cylindrical piston open on one side; a seal is provided for sealing the piston; the compression spring in the retracted position of the piston is enclosed by same on the outside; a longitudinal extension of the piston is substantially coterminous with the length of the housing; and the piston forms on the pressure chamber side a radially outwardly directed step.
2. Working cylinder according to claim 1 characterised by a piston comprising at least two component parts, with a base part, adjoined on the pressure chamber side to form a step by a sleeve-like guide part which widens out radially to the base part.
3. Working cylinder according to claim 1 characterised in that the piston which is made without stock removal is provided on the pressure chamber side with a circumferential radially outwardly directed edge which forms a step.
4. Working cylinder according to claim 1 or claim 2 characterised in that the piston base of the piston has at the end side a dome-like mounting in which the piston rod is supported by a piston rod end which is shaped complementary with the mounting.
5. Working cylinder according to claim 1 or claim 2 characterised in that a guide sleeve is inserted in the opening area of the housing for guiding the piston.
6. Working cylinder according to claim 1 or claim 2 characterised in that the piston and/or the base part is/are made without stock removal from sheet metal by a deep drawing process.
7. Working cylinder according to claim 2 characterised in that the guide part which widens out radially on the pressure chamber side to the remaining sleeve face of the piston is guided on the inside wall of the housing.
8. Working cylinder according to claim 2 characterised by a guide part which is fixed on the base part by material bonding.
9. Working cylinder according to claim 2 characterised by a positive-locking fixing between the guide part and the base part.
10. Working cylinder according to claim 2 or claim 3 characterised in that the guide part of the piston or the step of the piston each form together with the guide sleeve an end stop.
11. Working cylinder according to claim 2 characterised by a guide part and a base part of the piston which are made from matching materials or from different materials.
12. Working cylinder according to claim 11 characterised in that the individual component parts of the piston are made wholly or in part from plastics or ceramics.
13. Working cylinder according to claim 1 characterised in that the piston is coated at least in areas in order to prevent corrosion and/or to improve the sliding properties.
14. Working cylinder according to claim 2 or claim 3 characterised in that a sleeve face of the guide part as well as the step of the piston is provided with at least a longitudinal groove or a bore.
15. Working cylinder according to claim 5 characterised in that the guide sleeve is secured by a retaining ring positioned in the housing.
16. Working cylinder according to claim 15 characterised in that the retaining ring is arranged sealed in the housing and positioned through material bonding through ultrasound welding.
17. Working cylinder according to claim 15 characterised in that to seal the piston a grooved ring seal is inserted in a recess on the end side of the retaining ring.
18. Working cylinder according to claim 2 or claim 3 characterised in that folding bellows are mounted between the housing and the piston rod.
19. Working cylinder substantially as herein described with reference to any one embodiment shown in the accompanying drawings.