GB2146082A

GB2146082A - Master cylinder

Info

Publication number: GB2146082A
Application number: GB08422088A
Authority: GB
Inventors: Hans-Dieter Reinartz; Helmut Steffes; Derek Lowe
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1983-09-03
Filing date: 1984-08-31
Publication date: 1985-04-11
Also published as: GB8422088D0; GB2146082B; DE3331834A1; FR2551506A1; FR2551506B1

Abstract

A master cylinder (1) comprises a metal sleeve (36) retaining a metal mounting flange (41) against a housing (2) made of plastics material and containing a bore (3) and a piston (4) which is slidable in the bore (3) by an actuating rod and which is sealed towards the bore (3) by a sealing arrangement (19). The piston (4) actuates a valve assembly (18) which, in the release position of the piston (4), connects an axial compensating part (16) to the working chamber (7) and will upon actuation of the piston (4) interrupt this connection. To prevent leakage to the atmosphere during pressure build-up, the peripheral surface (52) of the housing (2) is firmly enclosed in the area of the piston seal (31) by a metal sleeve (36) which at the same time clamps the flange (41) against an abutment on the housing (2) of the master cylinder (1). The metal sleeve may have a threaded (Fig. 1) or bayonet (Fig. 3) connection with the plastics housing or metal flange (41). <IMAGE>

Description

SPECIFICATION Master cylinder This invention relates to a master cylinder, in particular for the hydraulic clutch actuation of an automotive vehicle of the kind comprising a housing made of plastics material and provided with a flange, a piston displaceable in a bore by an actuating rod and sealed in relation to the bore, and a valve assembly actuatable by the piston and connecting a compensating chamber to a pressure chamber, when the master cylinder is in its release position, via a channel that is closable on actuation of the valve assembly.

A master cylinder of this kind is described in British patent application 2,076,095. With a view to avoiding wear, housing expansion and leaks during operation of the master cylinder at the plastics housing in the area of the piston seals, a metal tube has been inserted into the bore. Such a design necessitates a comparatively high accuracy with regard to the size of the parts concerned, increases assembling effort and has as a result a comparatively complicated and expensive construction.

A second metal tube encompassing the first metal tube at its end projecting from the housing serves for axial securement of the push rod, the seal and the tube inserted in the housing bore. With its radially outwardly enlarging portion, this second tube abuts on the flange of the housing and thus, in the mounted condition of the master cylinder, is, via the fastening screws, rigidly coupled to the flange and the vehicle wall. The second tube is a punched and bent sheet-metal part and helps to simplify the master cylinder.

It is an object of the present invention of design a master cylinder made of plastics material in such a way that leaks will be precluded also in the presence of higher pressure. In addition thereto, the master cylinder is required to have a straightforward design and ease of attachment to the retaining wall, while the actuating forces acting from the outside on the master cylinder will be transmitted onto the housing without damaging the latter.

According to the invention in its broadest aspect, a master cylinder of the kind referred to is characterised in that the peripheral surface of the housing is firmly encompassed by a metal sleeve in the area of the piston seal, and in that the flange is made of metal and fitted onto the housing and urged by the sleeve against a stop at the housing.

Upon the occurrence of higher pressures in the pressure chamber, the arrangement according to the invention prevents inadmissible radial expansion of the plastics housing in the area of the piston seal, as a result whereof the piston seal fastened in the housing will always abut reliably on the piston, and thus leaks will not occur. Since, during operation of the master cylinder, the forces acting on the flange may be comparatively great, it is provided for obtaining a durable master cylinder that the flange is made of metal and is held by the sleeve in positive engagement with the housing. The flange which is composed of a punched and bent sheet-metal part affords ease of manufacture at low costs. The same applies to the sleeve. The sleeve and flange may, however, likewise be manufactured by sintered pressure-die casting or by chip-cutting machining operations.

A preferred way of fastening the flange to the housing of the master cylinder that provides for particularly easy and simple manufacture is characterised in that the sleeve is substantially of bowl-type design and is operatively connected with the housing via a bayonet-lock arrangement, the radially inner end of the flange is clamped between the stops of the bayonet lock arrangement and the bottom of the sleeve secures the valve assembly and the piston seal against dropping out. In this arrangement, the sleeve not only serves as a reinforcing and fastening element but simultaneously constitutes the cover of the master cylinder. The simple way of fastening the sheet-metal flange establishes a safe and bend-resistant connection.

To safeguard that the mounting position of the master cylinder will not change during operation, it is advantageous that the flange is adapted to be fixed at the housing by means of a torsion-preventing mechanism. The latter may be for instance a recess at the housing into which a projection of the flange engages.

In an advantageous embodiment of the invention, the spring which urges the piston lock into its position of release is arranged outside of the housing and, on its one side, is supported on the housing while on its other side it bears against a stop washer of the piston projecting from the housing. As a result, the overall axial length of the master cylinder housing will be reduced, since in a plunger piston design, wherein the piston seal is secured in the housing and forms the sliding and sealing surface of the pistons, there is the possibility of removing the spring from the bore of the housing so that it encloses the piston outside of the housing.

To permit utilization of the master cylinder according to the invention in various vehicles which often have different clutch actuation travels, it will be helpful for stroke limitation if a plug is mountable to the closed end of the bore. It is, however, likewise possible to use a sleeve protruding into the working chamber instead of the plug. With the spring disposed inside the housing, the sleeve may at the same time provide means for guidance of the spring.

Several embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a cross-section taken in a longitudinal direction of a master cylinder according to one embodiment of this invention.

Fig. 2 is a partial cross-sectional view of another embodiment of a master cylinder, in the area of fastening of the flange.

Fig. 3 is a top view of the master cylinder of Fig. 2 in the direction of the arrow X, and Fig. 4 is a partial longitudinal cross-sectional view of another embodiment, in the area of the closed end of the bore of the master cylinder.

As shown in Fig. 1 of the drawing, the master cylinder 1 comprises a housing 2 made of plastics material and containing a bore 3 that extends in the longitudinal direction of the housing 2 and wherein a piston 4 made of plastics material is axially-displaceably guided and which projects from the open end 5 of the master cylinder 1. Piston 4 has a blind-end bore 6 which serves for accommodation of an actuating rod, not shown in the drawing, which is displaceable by a clutch pedal of a vehicle. In conjunction with piston 4 and housing 2, the bore 3 forms the working chamber 7 which comprises at its closed end 8 a pressure port 9 establishing hydraulic communication with a hydraulic slave cylinder adapted to actuate a clutch.The pressure port 9 is formed by a pipe coupling which is integrally designed with the housing 2, which carries at the cylindrical periphery of its end a thread 10 serving to mount the connecting line, and which is penetrated by a channel 11.

The bore 3 comprises a portion 12 of small diameter and a portion 1 3 of larger diameter.

The smaller-diameter portion 12 forms the working chamber 7 and can serve to guide the end 14 of the piston 4 that is close to the working chamber. The transition between the portions 13 and 14 is formed by a step 15 into which a channel 16 terminates which channel is connected to a supply reservoir, not shown in the drawing, via a connecting socket 1 7 that is injection-moulded onto the housing 2. Towards the open end 5 of master cylinder 1 the valve assembly 18 and the sealing arrangement 1 9 are guided in portion 13 of bore 3.

The valve assembly 18 comprises a ring seal 21 that is prevulcanized to the end face of an annular disc 20, a spacer ring 22 succeeding the annular disc 20 in the direction of the open end 5, and the valve spring 23. The Valve spring 23 encloses the spacer ring 22 concentrically. Abutting on the end of the spacer ring 22 and of the valve spring 23 is a guiding plate 24 which, on the other side, is adjacent to the sealing arrangement 1 9 and prevents displacement of the valve assembly 18 towards the open end 5. The guiding plate 24 comprises projections 25 directed to the working chamber 7. and arranged on same diameter, these projections bearing with their radially outer periphery against the radially inner periphery of the valve spring 23 and thus serving to guide the valve spring 23.The guiding plate 24 is guided at the wall of the larger diameter bore portion 13.

At its end 14 close to the working chamber, piston 4 includes a step 26 on which the ring seal 21 abuts. In the release position of the master cylinder 1 shown in Fig. 1, the sealing surface 26 of ring seal 21 extends a short way in front of step 1 5, into which latter, channel 1 6 terminates, so that there is fluid connection from the supply reservoir subject to atmospheric pressure to the working chamber 7. This fluid connection extends from the channel 1 6 via the annular chamber 27, between step 1 5 and sealing surface 26, up to the gap 28 formed by piston 4 and bore 3.

In this embodiment, the sealing arrangement 1 9 comprises a plastics spacer sleeve 29 which is guided in the bore portion 13 and which carries at its end adjacent the valve assembly 18 an axial groove 30 with a ring seal 31 contained therein, the latter being in pressure-tight abutment on the peripheral surface 32 of piston 4. Viewing in the actuating direction of the master cylinder 1, a radial groove 33 carrying a ring seal 34 is designed at the radially outer periphery of the spacer sleeve 29 in front of the axial groove 30. The ring seal 34 seals the wall of the bore portion 13 relative to the spacer sleeve 29. The sealing arrangement 1 9 provides for a sealing of working chamber 7 in relation to the atmosphere.

At the radially outer periphery in the area of the open end 5, housing 2 contains a thread 35 onto which a substantially bowl-type sleeve 36 is screwed. The bore 38 formed in the bottom 37 of the sleeve 36 is penetrated by the shaft 39 of piston 4. Because of the force of the valve spring 23, the sleeve 36 constantly bears against the end surface 40 of bottom 37 that is exposed to the working chamber 7. Because of sleeve 36, valve assembly and sealing arrangement 18, 1 9 are held stationarily in the bore portion 3.

The housing 2 of the master cylinder 1 is enclosed by a flange 41 made of sheet-metal which is centered on the housing 2 and which is firmly clamped by sleeve 36 against the stop surface 42 provided at housing 2. The centering surface 43 formed at the housing 2 for centering of the flange 41 is furnished with a radially inwardly directed indentation 44, into which a corresponding projection 45 of flange 41 engages. The flange 41 contains bores 46 spread over its periphery, these bores serving to receive fastening screws not shown in the drawing, by which the master cylinder 1 can be fastened to a splashboard of an automotive vehicle, for instance.

At the end of shaft 39 projecting from the open end 5, the shaft being integrally designed with piston 4, the stop washer 48 is secured by means of a retaining ring 47.

Spring 49 is supported on stop washer 48 and sleeve 36, the spring serving to move piston 4 into its initial position shown after each actuation of the master cylinder 1.

As seen in the drawing, a longitudinal groove 50 extending in a longitudinal direction of master cylinder 1 is formed in the upper part of the wall of smaller diameter portion 1 2. The longitudinal groove 50 serves to ensure a proper fluid supply upon the return stroke of piston 4. There will be need for this longitudinal groove 50, if the gap 28 is required to be very small for safe-guarding proper guiding of the piston 4 in the smallerdiameter portion 12. However, it is likewise possible to replace the longitudinal groove 50 by slots spread over the periphery of the end 14 of piston 4 close to the working chamber, these slots extending from the working chamber 7 to the step 51 at piston 4.

The fact that the piston 4 penetrates the valve assembly 1 9 and engages behind the latter with its end 14 close to the working chamber enables the piston 4 to actuate the valve assembly 19 via the step 51.

The components shown in the sectional views of Figs. 2 to 4 differ only slightly from the respective components according to Fig.

1, so that components corresponding to those of fig. 1 have been assigned like reference numerals. To avoid repetition, only these differences will be dealt with.

In the embodiments shown in Figs. 2 and 3 of the drawings, sleeve 36 is a sheet-metal punched and shaped part which encloses with preload the radially outer peripheral surface 52 of the cylindrical end portion of housing 2 and which abuts with its bottom 37 on the end surface 40 of the spacer sleeve 29. The sleeve 36 comprises two diametrally opposite retaining arms 53, 54 which extend substantially in the direction of the closed end 8 of master cylinder 1 and which engage at their ends 57, 58 behind radially outwardly protuding projections 55, 56 at the peripheral surface 52 of housing 2. Clamped between the ends 57, 58 and the projection 55, 56 is the radially inner area of flange 41 which is thus rigidly connected to the housing 2 via the sleeve 36.

Fig. 3 shows the bayonet lock arrangement of Fig 2. in a manner swivelled by 90 in the drawing plane. To enable flange 41 to be shifted via the projections 55, 56 circular sections 59, 60 are designed in the vertical plane of the drawing. A like bayonet-lock arrangement affords simple and easy manufacture.

As seen in Fig. 4 of the drawing, a cylindrical pivot 61 penetrated by channel 11 projects from the bottom of the closed end 8 into the working chamber 7. Fitted onto the cylindrical pivot 61 is a plug 62 which is guided and held in the channel 11 via an extension 63. To permit fluid flow from channel 11 into the working chamber 7, plug 62 is formed with a cross-shaped cross-section, for example.

The mode of operation of the master cylinder according to the invention is as follows.

Actuation of piston 4 to the left as seen in Fig.1 causes ring seal 21 likewise to move to the left until it is in abutment on step 1 5 and sealingly closes the channel 1 6. Upon further actuation of the piston 4, the latter with its step 51 leaves the sealing surface 26, and pressure fluid is supplied into the channel 11 to the slave cylinder of a clutch actuating mechanism not shown in the drawing, separation of the clutch linings being thereby accomplished. The pressure prevailing in the working chamber 7 may cause radial expansion of housings 2 made of plastics material. To avoid such expansion in the area of the sealing arrangement 1 9 which might ensue leaks, the metal sleeve 36 encompasses the end portion of housing 2.

During the return stroke, the sequence of motion will be vice-versa. Resetting of the slave cylinder, for instance due to friction lining wear, is effected by replenishing the working chamber 7 with fluid via the channel 16. In the majority of cases, this action will not take place until the piston 4 has already lifted the ring seal 21 from the step 15. If however replenishment becomes necessary at an earlier point of time, the pressure below atmospheric pressure developing in the working chamber 7 will cause automatic opening of the valve assembly 1 8 in opposition to the force of the spring 23. With valve spring 23 predetermined, the action may be assisted by increasing the cross-section of the channel terminating into step 1 5. The longitudinal groove formed in the bore portion 1 2 of smaller diameter increases the flow cross-section between bore 3 and piston 4. During return stroke of the piston 4 the spring 49 safeguards reliable opening of the valve assembly 18.

Claims

1. A master cylinder, in particular for the hydraulic clutch actuation of an automotive vehicle of the kind comprising a housing made of plastics material and provided with a flange, a piston displaceable in a bore by an actuating rod and sealed in relation to the bore, and a valve assembly actuatable by the piston and connecting a compensating chamber to a pressure chamber when the master cylinder is in its release position, via a channel that is closable on actuation of the valve assembly, characterised in that the peripheral surface (52) of the housing (2) is firmly encompassed by a metal sleeve (36) in the area of the piston seal (31), and in that the flange (41) is made of metal and fitted onto the housing (2) and is urged by the sleeve (36) against a stop (55, 56) at the housing (2).

2. A master cylinder as claimed in claim 1, characterised in that the sleeve (36) is substantially of bowl-type design and is operatively connected to the housing (2) through a bayonet-lock arrangement (55, 56 and 57, 58) the radially inner end of-the flange (41) is clamped between the stops of the bayonetlock arrangement (55, 56 and 57, 58) and the bottom (37) of the sleeve (36) secures the valve assembly (18), the sealing arrangement (19) and the piston (4) against dropping out.

3. A master cylinder as claimed in claim 2, characterised in that the flange (41) is adapted to be fixed at the housing (2) by means of a torsion-preventing mechanism (44, 45)

4. A master cylinder as claimed in claim 2, comprising a spring which urges the piston back into its position of release characterised in that the spring (49) is arranged outside of the housing (2) and, on its one side, is supported on the housing (2), while on its other side it bears against a stop washer (48) of the piston (4) protruding from the housing (2).

5. A master cylinder as claimed in any one of the preceding claims, characterised in that a plug (62) is mountable to the closed end (8) of the bore (3).

6. A master cylinder as claimed in any one of the preceding claims, characterised in that a sleeve protuding into the working chamber (7) is formed at the closed end (8) of the bore (3).

7. A master cylinder substantially as described with reference to the accompanying drawings.