GB2095351A

GB2095351A - Mechanically controllable power booster

Info

Publication number: GB2095351A
Application number: GB8207986A
Authority: GB
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1981-03-21
Filing date: 1982-03-18
Publication date: 1982-09-29
Also published as: DE3111188A1; JPS6345338B2; FR2502262B1; FR2502262A1; JPS57164851A; GB2095351B; DE3111188C2

Abstract

In a casing 1 of a power booster, a working piston 5 is located axially slidably which subdivides the casing 1 into a low-pressure chamber 6 and a working chamber 8. Extending from the disc-shaped reinforcing plate 9 of the working piston 5 is a cylindrical portion 24 projecting into the low-pressure chamber 6 and having extending into it the end of a cylindrically control value housing 11, the end surface 47 of the control housing abutting reaction disc 44. In this position, the disc-shaped plate 9 is positively engaged with the control housing via wall portions 30 which are sheared inwardly out of the attachment 24 and extend radially into an annular groove 23 of the control housing 11. In this arrangement, the wall portions 30 will be urged into the annular groove 23 so far that openings 40 will be caused at the attachment 24 interconnecting the low-pressure chamber 6 and the annular groove 23. The annular groove 23 is in communication with a valve elements 16 through a connecting channel 18 accommodated in the control housing 11. Arranged at the free end of the cylindrical portion 24 is a bottom disc portion 50 including a bore 51 through which the push rod 45 extends into the low-pressure chamber 6. <IMAGE>

Description

SPECIFICATION Mechanically controllable power booster This invention relates to a mechanically controllable power booster, in particular for the brake systems of an automotive vehicle, of the kind comprising a working piston located movably in a casing and subdividing the casing into a low-pressure chamber and a working chamber, arranged at which working piston is a cylindrical attachment extending into the low-pressure chamber and having inserted in it the end of a control housing close to a reaction device, the control housing being connected after insertion to the working piston by fastening means which provide positive engagement and projecting out of the working chamber in opposition to the actuating direction, a valve device contained in the control housing communicating via channels with the working chamber, the low-pressure chamber and with atmospheric air and including a control piston coupled to an actuating rod, which control piston governs the working pressure in the working chamber, is bounded in the release movement by a retaining element and acts on the reaction device in the actuating direction, the reaction device being supported on the control housing and on the control piston, on the one hand, and on a force-transmitting member, on the other hand.

A power booster of this type has been described in U.S. Patent Specification 3 952 518. It serves to boost the brake force in an automotive vehicle and is driven by the difference in pressure between a low pressure generated by the engine and the atmospheric pressure.

The control housing includes an annular collar abutting at the end surface of the working piston close to the working chamber. Arranged at this end surface of the annular collar is an annular axial groove in which an annular bead is inserted at the radially inward end of the rolling diaphragm and retained in this position by the working piston. The fastening of the working piston to the control housing is provided by a screw-nut connection which is arranged radially outside the attachment of the working piston. The channel interconnecting the valve device and the low-pressure chamber extends radially within the control housing in the direction of the working piston and terminates in the lowpressure chamber radially outside the cylindrical attachment between two neighbouring screw-bolt connections.This arrangement of the channel as well as of the screw-bolt connections has the disadvantage of the outside diameter of the annular collar being far larger than the substantially cylindrical section of the control housing. This results in a complicated, time-consuming and costly manufacture of the control housing, because oblique slide elements are required to be inserted in the control housing for the formation of the channels connecting the valve device to the low-pressure chamber. Likewise, the fitting of the working piston to the control housing necessitates much effort. The working piston is formed by the cylindrical attachment and by a discshaped plate.The cylindrical attachment engages from behind the inner rim ofthe disc-shaped plate in the working chamber and is secured in this position by an annularcollarwhich latter is urged by the disc-shaped plate against the end surface of the control housing. Additional costs for assembly and manufacture are incurred by the bi-partite design of the working piston.

It is an object of the present invention to simplify the design of a power booster of the kind initially referred to and to reduce its price.

According to the invention in its broadest aspect, a mechanically controllable power booster, in particular for the brake system of an automotive vehicle is characterised in that the control housing contains an annular groove in its periphery within the attachment, in that a connecting channel extending from the valve device terminates in the annular groove, in that the cylindrical attachment includes at least one opening in the area of the annular groove and in that the fastening means providing positive engagement grip into the annular groove. A substantial length reduction and simplification ofthe control housing will be accomplished thereby. A simple and material-saving manufacture of the control housing will result by arranging for the outside diameter of the control housing to remain approximately constant throughout its entire length.It will be obtained by virtue of the connection of the annular groove to the channels providing communication between the valve device and the low-pressure chamber that the control housing can be mounted without radial fixation in respect of the working piston, i.e. the control housing can be inserted in the attachment of the control housing in any twisted position whatsoever.

This affords simplification of the power booster's assembly.

In a preferred embodiment of the present invention, wall portions are sheared inwardly out of the cylindrical attachment and urged into the annular groove so far that openings are formed which extend from the low-pressure chamber and terminate in the annular groove. This provides positive engagement of the working piston with the control housing in a simple way while manufacturing the openings and establishes the necessary duct for the air flow from the low-pressure chamber to the valve device.However, the diameter of the groove is required to be so dimensioned as to enable the inwardly sheared wall surfaces to extend sufficiently deep into the control housing to the end that, on the one hand, the inwardly sheared wall surfaces transmit the boosting force onto the control housing and that, on the other hand, the openings formed by the inwardly sheared wall surfaces have a cross-section large enough to allow propagation of the air flow from the low-pressure chamber into the valve device to a sufficient amount.

Expediently, a circular disc is located in the annular groove which disc abuts at the annular grooves end surface which is closer to the reaction disc and which is axially secured in this position by the wall portions. This design is particularly favourable if the control housing does not consist of a material as solid as plastics, for instance. The boosting force is transmitted evenly via a comparatively large abut ment surface from the annular disc onto the control housing. To fit the annular disc into the annular groove, the annular disc is required to be composed of two disc halves. Securing the radial position of the disc wall will be ensured in that the radially outward end surface of the disc abuts at the inner periphery of the attachment.

Further simplification of the power booster will be attained in that radially inwardly extending sheetmetal lugs are located at the divided disc which penetrate the control housing in channels provided for this purpose and which engage inzo an annular groove of the control piston. Simultaneously, said disc forms the stop for the control piston in the release position. The disc being a stamped metal part, it provides ease of and low-cost manufacture.

Advantageously, the channel connecting the lowpressure chamber to the valve device is arranged in parallel to the control housing and extends at its end radially out of the control housing into the lowpressure chamber. This results in a particularly small overall length of the control housing. The tools used for manufacturing the control housing are of particularly straightforward design, since there is no necessity for oblique slide elements to make the connecting channels and there are merely required elements which extend axially as well as radially into the control housing and form the channels.

The end of the control housing close to the reaction disc abuts suitably at an annular collar of the attachment. Thereby, the control housing will be axially positioned during the assembly of the work ing piston and the working process considerably simplified.

In a preferred embodiment of the present invention, a bottom portion is arranged at the free end of the attachment which contains an opening for the push rod to extend through. This secures the push rod axially, and there is no chance that the push rod will get lost or drop into the booster casing in the event of delivery of a power booster without master cylinder, for example. Expediently, the bottom portion has a cylindrical sleeve in the area of the opening. In this arrangement, the push rod is guided slidably both by the cylindrical sleeve and by the inner periphery of the cylindrical attachment.By virtue of this double support, the pressure plate of the push rod can be made of particularly thin material, which contributes to a reduction of the power booster's weight At the same time, the axial guidance of the push rod will be improved as well, and canting and thus malfunction of the power booster will be avoided.

In another favourable embodiment of the present invention, two diametrally opposite retaining elements project through two openings formed at the attachment into the low-pressure chamber and abut atthe end surface of the disc-shaped plate close to the low-pressure chamber. This establishes in a straightforward manner positive engagement between the working piston and the control housing, providing at the same time the stop for the control piston in the release direction. There is ensured radial positioning of the retaining elements if each one of the projections plate extending into the lowpressure chamber, rests against the radially outward end surface of the retaining elements. It will be necessary to have openings provided at the attachment in the area of the annular groove in order to enable a connection between the annular groove and the low-pressure chamber.

A still further simplification of the power booster will be achieved in that the end surface of the annular groove close to the reaction disc is formed by the rolling diaphragm. This has the advantage that the outside diameter of the section of the control housing located outside the cylindrical attachment is equal to that of the annular groove. This results in a particularly small-dimensioned design requiring minimum material. The rolling diaphragm is required to be designed in the area of the annular groove in such a way that the difference in pressure prevailing between the low-pressure chamber and the working chamber does not destroy the rolling diaphragm prematurely.Reinforcement of the rolling diaphragm in this area may also be obtained in that the end surface of the annular groove close to the reaction disc is formed by a disc which is inserted between the disc-shaped plate and the rolling diaphragm and which is guided on the control housing. The latter disc is centered on the cylindrical diameter of the control housing and will be urged against the working piston bythe rolling diaphragm.

Several embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which Figure 1 is a cross-section through a brake booster, wherein the planes of intersection shown above and beneath the centre line are disposed relative to each other at an angle of 90 degrees and the working piston is connected to the control housing by wall surfaces sheared inwardly out of the attachment, Figure 2 is a section through the control housing according to Figure 1, Figure 3 is a cross-section normal to the longitudinal axis of the power booster in the plane of the inwardly sheared wall portions according to Figure 2, Figure 4 is a cross-section through another control housing, wherein the planes of intersection shown above and beneath the centre line are disposed relative to each other at an angle of 90 degrees and the working piston is connected to the control housing by two diametrally opposite retaining elements.

The power booster shown in Figures 1,2 and 3 of the drawing comprises a casing 1 which is subdivided into two casing shells 3,4 interconnected at a connecting point 2. The interior of the casing 1 is subdivided by a working piston 5 into a low-pressure chamber 6, which communicates via a connecting bore 7 with a low-pressure source, and a working chamber 8. The working piston 5 is substantially composed of a disc-shaped plate 9, of a rolling diaphragm 10 abutting in the working chamber 8 at the plate 9 and being clamped in at the connecting point 2 between the casing shells 3,4 in a pressure-tight relationship thereto, and of a cylindrically formed control housing 11 coupled to the working piston 5.

With its cylindrical neck 55, the control housing 11 projects out of the casing shell 3 and is protected against contamination of its surface by means of a pleated bellows 12. The control housing 11 seals the working chamber 8 to the outside by means of a guide ring 13.

In side the control housing 11, the drive unit comprising the actuating rod 14 and the control piston 15 is arranged axially slidably and connectible to a brake pedal of an automotive vehicle via a forked head not shown. Moreover, the control housing 11 accommodates a valve device 16 which is actuated by the control piston 15 and which governs the pressure difference between low-pressure chamber 6 and working chamber8 via connecting channels 17, 18. The valve device 16 is composed of a first valve 19 formed by the control housing 11 and a sealing ring 20 and of a second valve 21 formed by the control piston 15 and the sealing ring 20. Low-pressure chamber 6 and working chamber 8 are interconnected via the connecting channels 17,18 by virtue of the valve device 16.The diametrally opposite connecting channels 17 are displaced by 90 degrees relative to the diametrally opposite connecting channels 18 in the control housing 11. The connecting channels 17 are arranged radially in the control housing 11. The connecting channels 18 are located in parallel to the control housing and extend attheir end, situated in the low-pressure chamber 6, radially in the control housing 11 and terminate in an annular groove 23 located in the periphery 22 of the control housing 11. The plate 9 includes in its radially inward area a cylindrical attachment 24 projecting into the low-pressure chamber 6. When viewed in the actuating direction, the cylindrical attachment 24 contains a first attachment 25 of larger diameter and a second attachment 26 of smaller diameter.The control housing 11 has approximately the same diameter throughout its entire length. The end of the control housing close to the low-pressure chamber 6 projects from the working chamber 8 into the first attachment 25 and is by means of its periphery 22 centered at the bore 27 of the first attachment 25.

The control housing 11 abuts with its annular collar 28 at the annular collar 29 which is formed between the first and the second attachment 25, 26. Radially inwardly extending, V-shaped wall portions 30 are sheared at the first attachment 25 and engage in the annular groove 23 of the control housing 11. Inserted in the annular groove 23 is a circular-ring-shaped disc 31 assembled from two halves which abuts at the end surface 32 of the annular groove 23 close to the working chamber 8 and which is axially secured in this position by the inwardly sheared wall portions 30. The annular groove 23 and the first attachment 25 form the radial position-securing arrangement of the circular-ring-shaped disc 31.Arranged at the circular-ring-shaped disc31 are two diametrally opposite sheet-metal lugs 33 which penetrate the control housing 11 in channels 34, 35 provided for this purpose and which engage into a first annular groove 36 of the control piston 15 and form a stop for the control piston 15 in opposition to the actuating direction of the power booster. In the actuating direction of the power booster, there is located at the control piston 15 in front of the first annular groove 36 a second annular groove 37 wherein an O-ring 38 is located. The O-ring 38 seals the control piston 15 relative to the bore 39 in the control housing in order to prevent propagation of air from the valve device 16 via the channels 34 into the low-pressure chamber 6.Openings 40 are provided at the first attachment 25 by the wall portions 30 sheared inwardly out of the first attachment 25 and projecting into the annular groove 23, these openings providing communication between the channels 18 and the low-pressure chamber 6. The rolling diaphragm 10 abuts at the end surface of the disc-shaped plate 9 close to the working chamber 8 and engages with its annular bead 41 designed at the inner edge into an annular groove 42, which is arranged between the channels 17 and 18 in the periphery 22 of the control housing 11, and separates sealingly the lowpressure chamber 6 from the working chamber 8.

The reaction disc 44 and the pressure plate 46 coupled to the push rod 45 are axially slidably arranged in the bore 43 of the second attachment 26.

The end of the control housing 11 abuts with its end surface 47 at the reaction disc 44. There is a small axial clearance between the end surface 48 located at the end of the control piston 15 and the end surface 49 of the reaction disc 44, the latter surface facing the other. At the free end of the cylindrical attachment 24 is a bottom portion 50 accommodating at its inner section a bore 51 through which the push rod 45 extends into the low-pressure chamber 6. The bore 51 rests against the periphery of the push rod 45 and serves to guide the push rod 45. The end surface 52 of the bottom portion 50 provided in the interior of the second attachment 26 is spaced a predetermined distance from the oppositely disposed end surface of the pressure plate 46.This distance is, on the one hand, so dimensioned that the cylindrical periphery 54 of the pressure plate 46 does not enter into the transition surface 53 arranged between the bottom portion 50 and the second attachment 26, which would result in a canting of the pressure plate, and that there is, on the other hand, still available sufficient axial travel in the actuating direction in the cylindrical bore 43 of the second attachment 26 to enable compensation of the length tolerances occurring during the manufacture of the individual components. This distance is also required to allow the displacing material to expand into free space, the displacement being caused by the contact force of the control piston 11 on the reaction disc 44.

The mode of operation of the power booster described is as follows: In Figure 1 and 2 of the drawing, the power booster according to the present invention is shown in its inactive position. By virtue of the valve device 16, the low-pressure chamber 6 and the working chamber 8 are interconnected via the connecting channels 17, 18. Actuation of the brake pedal will cause displacement of the actuating rod 14 and of the control piston 15 to the left and interruption of the connection between the connecting channels 17, 18 by closure of the first valve 19. The low-pressure chamber 6 and the working chamber 8 will be no more in communication. The end surface 48 of the control piston 15 abuts at the end surface 49 of the reaction disc 44.

The power booster is in its alert position.

When the brake pedal is depressed further, part of the force will take its course via the reaction disc 44 directly onto the push rod 45, however, at the same time, the second valve 21 will open and the channels 17 will be connected to atmosphere via the inlet opening 56 formed by the neck 55. Air will enter into the working chamber 8, and the pressure difference developing between working chamber 8 and the low-pressure chamber 6 will tend to displace the working piston 5 to the left in opposition to the force of the compression spring 57. In this arrangement the push rod 45 will displace the piston in a master brake cylinder (not shown). The pressure developing in the master brake cylinder exerts a reaction force on the reaction disc 44 via the piston (not shown) and via the push rod 45.The booster force acting on the working piston 5 will be fully effective in this position.

The booster force is directed from the wall portions 30 via the control housing 11 onto the reaction disc 44. The reaction pressure is likewise transmitted onto the control piston 15, whereby the latter will be displaced to the right and will close the second valve 21. As a result, the working chamber 8 is isolated from atmosphere. The valve device will be in its ready-to-function position again. When the brake is released, the second valve 21 of the power booster will be closed by displacement of the control piston 15 to the right, and the first valve 19 will be opened.

The working piston will be moved to assume its initial position by the force of the compression spring 57.

In Figure 3 of the drawing, the point where the working piston 5 is fastened to the control housing 11 is elucidated. Parts corresponding to those of Fig ures 1 and 2 have been assigned like reference numerals. The channels 18 have an annular cross-section and are arranged diametrally opposite to each other in the control housing 11. In the vertical plane of intersection, the channels 18 include radially outwardly extending openings 58 terminating in the annular groove 23 of the control housing 11. The V-shaped wall portions 30 projecting into the annular groove 23 of the control housing 11 establish a positive engagement between the working piston 5 and the control housing 11. By inwardly shearing the wall portions 30 out of the first attachment 25, there will result openings 40 which provide a connection between the annular groove 23 and the low-pressure chamber 6.The wall portions 30 are distributed evenly over the periphery of the first attachment 25.

The disc 31 inserted in the annular groove 23 is composed of two disc halves whose facing ends 59 are just able to be in contact with each other Fitting of the control housing 11 to the working piston 5 will be described in more detail in the following: The push rod 45 with its pressure plate 46 and the reaction disc 44 will be inserted into the second attachment 26 according to Figure 1. The control piston 15 with its O-ring 38 and with its actuating rod 15, as well as the valve device 16 have already been preassembled in the control housing 11. Subsequently, the sheet-metal lugs 33 of the two circularring-shaped disc halves will be inserted into the channels 34,35 of the control housing 11 provided for this purpose.When doing so, the disc halves will be slid into the control housing 11 so far until the radially outward end surface of the assembled disc 31 is flush with the periphery 22 of the control housing 11. Now, the completely preassembled control housing 11 will be slide into the first attachment 25 c.f the working piston 5 until the control housing 11 has moved in abutment with the annular collar 29 of the attachment 24. In the next working step, shearing punches (not shown) will move radially in the direction of the first attachment 25 and will shear inwardly out of the second attachment 26 V-shaped wall portions 30 which engage in the annular groove 23. The radial forces produced during the shearing process will be received by the circular-ring-shaped disc 31 and supported in the annular groove 23 of the control housing 11.This causes faultless sheared surfaces at the first attachment 25, and undesirable deformations will be avoided in this area. During the shearing process, the shearing punches have to be aligned axially in such a mannerthatthe projections 23 abut at the circular-ring-shaped disc 31.

The control housing 11 illustrated in Figure 4 is basically similarto the design according to Figures 1 and 2. Parts corresponding to those of Figures 1 and 2 have been assigned like reference numerals. To avoid repetition, only differing features will be dealt with in the following. The attachment 24 at the working piston 5 and projecting into the low-pressure chamber 6 is formed by a tubular section of constant diameter. Two retaining elements 60 disposed diametrally opposite to each other and designed as a flat plate extend through openings 61 formed at the attachment 24 radially into the control housing 11 and penetrate channels 34 in the control housing 11, these channels being adapted to the corresponding cross-sections of the retaining elements 60, and grip into the first annular groove 36 of the control piston 15. The retaining element 60 projects radially out of the attachment 24 and abuts at the end surface of the disc-shaped plate 9 close to the low-pressure chamber 6. A projection 63 of the working piston 5 protruding into the low-pressure chamber 6 abuts at the radially outward end surface 62 of the retaining element 60. A circular-ring-shaped disc 31 is located in the annular groove 23 behind the retaining elements 60, when viewed in the actuating direction.

This disc serves to distribute the force more evenly onto the control housing 11. Arranged at the same axial height at the cylindrical attachment 24 between the retaining elements 30 are openings 40 which interconnect the low-pressure chamber 6 via the annular collar 23 with the channels 18. The disc 31 is formed of two disc halves.

Claims

1. A mechanically controllable power booster, in particular for the brake systems of an automotive vehicle, of the kind comprising a working piston located movably in a casing and subdividing the casing into a low-pressure chamber and a working chamber, arranged at which working piston is a cylindrical attachment extending into the lowpressure chamber and having inserted in it the end of a control housing close to a reaction device, the control housing being connected after insertion to the working piston by fastening means which provide positive engagement and projecting out of the working chamber in opposition to the actuating direction, a valve device contained in the control housing communicating via channels with the working chamber, the low-pressure chamber and with atmospheric air and including a control piston coupled to an actuating rod, which control piston governs the working pressure in the working chamber, is bounded in the release movement by a retaining element and acts on the reaction device in the actuating direction, said reaction device taking support on the control housing and on the control piston, on the one hand, and on a force-transmitting member, on the other hand, characterized in that the control housing (11) contains an annular groove (23) in its periphery (22) within the attachment (24), in that a connecting channel (18) extending from the valve device (16) terminates in the annular groove (23), in that the cylindrical attachment (24) includes at least one opening (40) in the area of the annular groove (23) and in that the fastening means providing positive engagement grip into the annular groove.

2. A power booster as claimed in claim 1, characterized in that wall portions (30) are sheared inwardly out of the cylindrical attachment (24) and urged into the annular groove (23) so far that openings (40) are formed which extend from the lowpressure chamber (6) and terminate in the annular groove (23).

3. A power booster as claimed in any one of the preceding claims, characterized in that a circular disc (31) is located in the annular groove (23) which disc abuts at the annular groove's end surface (32) which is closer to the reaction disc (44) and which is axially secured in this position by the wall portions (30).

4. A power booster as claimed in any one of the preceding claims, characterized in that the circular disc (31) is composed of two disc halves.

5. A power booster as claimed in any one of the preceding claims, characterized in that the radially outward end surface of the disc (31) abuts at the inner periphery of the attachment (24).

6. A power booster as claimed in any one of the preceding claims, characterized in that radially inwardly extending sheet-metal lugs (33) are located at the divided disc (31) which penetrate the control housing (11) in channels (34,35) provided for this purpose and which engage into a first annular groove (36) of the control piston (1 5).

7. A power booster as claimed in any one of the preceding claims, characterized in that the channel (18) connecting the low-pressure chamber (6) to the valve device (16) is arranged in parallel to the control housing (11) and extends at its end radially out of the control housing (11) into the low-pressure chamber (6).

8. A power booster as claimed in any one of the preceding claims, characterized in that the end of the control housing (11) close to the reaction disc (44) abuts at an annular collar (29) of the attachment (24).

9. A power booster as claimed in any one of the preceding claims, characterized in that a bottom portion (50) is arranged at the free end of the attachment (24) which contains an opening (51) for the push rod (45) to extend through.

10. A powder booster as claimed in any one of the preceding claims, characterized in that the bottom portion (50) has a cylindrical sleeve in the area of the opening (51).

11. A power booster as claimed in any one of the preceding claims, characterized in that two diametrally opposite retaining elements (60) project through openings (61) formed at the attachment (24) into the low-pressure charnber (6) and abut at the end surface of the disc-shaped plate (9) close to the lowpressure chamber (6).

12. A power booster as claimed in any one of the preceding claims, characterized in that each one of the projections (63) of the disc-shaped plate (9), extending into the low-pressure chamber (6), rests against the radially outward end surface (62) of the retaining elements (60).

113. A power booster as claimed in any one of the preceding claims, characterized in that openings (40) are provided at the attachment (24) in the area of the annular groove (23).

14. A power booster as claimed in any one of the preceding claims, characterized in that the end surface of the annular groove (23) close to the reaction disc (44) is formed bathe rolling diaphragm (10).

15. A power booster as claimed in any one of the preceding claims, characterized in that the end surface of the annular groove (23) close to the reaction disc (44) is formed by a disc which is inserted between the disc-shaped plate (9) and the rolling diap hragm (10) and which is guided on the control housing (11).

16. A mechanically controllable power booster, in particularforthe brake system of an automotive vehicle, substantially as described with reference to the accompanying drawings.