GB2131901A

GB2131901A - An automatic ajusting device for a brake

Info

Publication number: GB2131901A
Application number: GB08332294A
Authority: GB
Inventors: Ulrich Wilhelm Danne; Helmut Heubel
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1982-12-03
Filing date: 1983-12-02
Publication date: 1984-06-27
Also published as: AU2186183A; GB8332294D0; BR8306587A; DE3244872C2; ES527697A0; FR2537230A2; US4589527A; IT8323980A1; IT8323980A0; DE3244872A1; ES8504359A1; JPS59110928A; FR2537230B2; GB2131901B; IT1167278B

Description

1 GB 2 131901 A 1

SPECIFICATION

An automatic adjusting device fora brake The invention relatesto an automatic adjusting devicefora brake, in particulara motor vehicle brake in which a strut, whose effective length depends on the relative positions of two strut portions adjustable with respectto each other, is connected in parallel with a brake actuating mechanism, one of said strut 75 portions having at least one portion adjustable transversely of the longitudinal direction of the strut, upon actuation of the braketending to increase the length of the strut with this portion and co-operating with an intermediate memberwhich is disposed between two strucutral members transmitting the actuating force independently of the strut andwhich is rotatable againstthe frictional resistance thereof, provided said resistance does not surpass a given value.

In an adjusting device of thistype, it has been possible for adjustment to occurdueto excessive brake actuation resulting in an elastic deformation of various parts of the brake although the actual state of wear of the brakelinings would not, in itself, give rise 90 to such an adjustment. In our earlier Patent Applica tion No. 8216232, this problem has been overcome by making the intermediate member either displaceable in a straight line or rotatable about an axis. If the intermediate member is rotatable, it can be formed as 95 a gearwheel and be supported for rotation on an arm projecting awayfrom the strut in accordance with one embodiment shown in Figures 5 and 6 of our aforesaid Application. In this case, the strut hasthree strut portions, two of which are screwed together and of these, one is fixed against rotation and the other is formed as a pinion and is provided in addition with ratchetteeth. A pivotable pawl engages with the ratchetteeth, said pawl gradually rotating the strut portion concerned and thus screwing it out of the otherstrut portion when adjustment is necessary. The pinion engages with the intermediate memberformed as gearwheel which is essentially free to rotate upon normal brake actuation but upon particularly forceful brake actuation is clamped between a piston of the 110 hydraulic brake actuating mechanism and an adjacent brake shoe end.

It is an object of the present invention furtherto improve the adjusters described in our aforesaid earlier Patent Application.

According to the invention, in an automatic adjusting device of the aforesaid type, the intermediate member is supported for rotation on one of thetwo structural members transmitting the actuating force.

Thus, according to the invention, the intermediate member is supported on one of those structural members between which it is to be clampled when the actuating force of the brake actuating mechanism generally hydraulicsurpasses a given value. This manner of supporting the intermediate member simiplifiesthe adjusting device as the arm projecting awayfrom the strut according to Figure 5 of our aforesaid Application provided to supportthe intermediate member can be dispensed with.

The invention maybe used in connection with various known struts, for instance, with the strut shown in Figures 5 and 6 of our aforesaid Application which has two strut portions screwed to each other. Uses of the invention on struts of other construction are the subject of further embodiments described below.

Particularly simple developments of the invention result if the intermediate member is rotatable about the axis of the brake actuating mechanism.

A development of this kind can be realised in an adjusting device which, for instance, conforms with the example of embodiment shown in Figure 7 and 8 of our aforesaid Application in that one of the two structural members, between which the intermediate member is disposed, is the head of a plungerwhich is guided for axial displacement in the other one of these two strucutral members and is supported by means of a spring which tends to maintain a spacing larger than the thickness of the intermediate member between the head and the otherstructurai member. In this case, it is expedient if in accordance with the invention,the intermediate member is supported for rotation on the plungeritself.

From the embodiment shown in Figures 7 and 8 of our aforesaid Application in which the intermediate member is component of a gear drive, results a variation according to the present invention in which the intermediate member is a toothed sector of which the toothing engages a face toothing on one of the strut portions, this strut portion being rotatable in a mannerknown per se on the other strut portion around an axis of rotation disposed transversely of the longitudinal direction of the strut and having an eccentric outer surface whose position determines the total length of the strut.

It is particularly advantageous if the intermediate member is formed by an annular central area of a cam plate with a spiral outer area and forms togetherwith this one of the strut portions. This development of the invention simplifies considerablythe automatic adjusting device as a whole as one of the strut portions is combined with the intermediate memberto form one single structural memberwhich is relatively simple to manufacture.

Examples of embodiment of the invention are described in greaterdetail belowwith referenceto diagrammatic drawings inwhich:

Fig. 1 is a plan view of an internal shoe-drum brake for motor vehicles, Fig. 2 is an enlarged section of Fig. 1, Fig. 3 is cross-section 111-111 of Fig. 2 and Fig. 4 is cross-section W-W of Fig. 2; Fig. 5 is a partial plan view of another internal shoe-drum brakefor motor vehicles, Fig. 6 is cross-section VW] of Fig. 5 and Fig. 7 is cross-section V] W] 1 of Fig. 5.

The internal shoe-drum brake shown in Figs. 1 to 4 has a plate-shaped or dish-shaped brake carrier member 10 which is provided forfixing to a rearwheel axle of a motor vehicle and in installed condition is enclosed by a brake drum. The brake drum is not shown; its axis is referred to in the following as axis A of the drum brake. In Fig. 1 atthe bottom a thrust bearing 12 is fixed to the brake carrier member 10 and onsaidthrust bearing 12two brake 2 GB 2 131 901 A 2 shoes 14 and 16 having T-formed cross-sections are supported pivotably each by the lower end of a brake shoe web 15 and 17 respectively.

Between the upper ends of the brake shoe webs 15 and 17, a hydraulic brake actuating mechanism 18 is disposed diametrically opposite the thrust bearing 12. The principal components of this brake actuating mechanism are a double-ended open cylinder 20 with the axis B, said cylinder being fixed to the brake carrier member 10 and having two pistons 22, one of which is shown in Fig. 2. A plate-shaped intermediate member 24 is supported coaxiallywith this piston 22 on the upper end of the brake shoe web 15 in a manner described in detail below. The other piston, which is masked in the drawings, lies directly atthe upperend of the brake shoe web 17.

The two brake shoes 14 and 16 are biased by three retu rn springs 26,27 and 28 againstthe thrust bearing 12 and the brake actuating mechanism 18.

At the upper end of the brake shoe web 17, a rivet 30 supports a lever 32 which forms part of a mechanical brake actuating mechanism and, as long as this is inoperative, abuts the brake shoe web 17 with a stop 34 formed thereon, as shown in Fig. 1. At a distance from the rivet 30, a notch 36 is formed in the lever 32 and this is positioned opposite a recess 38 in the brake shoe web 15. A strut 40 is supported in the notch 36 and the recess 38 and is composed of th ree strut portions, i.e., of a rod-shaped strut portion 42, a disc-shaped strut portion 44 and a conical strut portion 95 46.

The rod-shaped strut portion 42 is connected to the brake shoe web 15 by means of the relatively long and not particularly strong retu rn spring 27 and is also connected to brake shoe web 17 bythe considerably shorterand stronger return spring 28. The end of the strut portion 42 which is on the right- hand side in Fig. 1 is slotted and engages in the notch 36 of the brake shoe web 17. The other end of the rod-shaped strut portion 42 atthe left of Fig. 1 is guided for displacement between the brake carrier member 10 and the brake shoe web 15 in longitudinal direction of the strut 40 and has a slot 110 which extends in longitudinal direction of the strut 40 and receives an axle journal 112 riveted to the disc-shaped strut portion 44.

The axlejournal 112 forms an axis of rotation C which extends at right angles to the longitudinal direction of the strut 40 and thus also at right angles to the axis B of the cylinder 20 and also at right angles to axis A of the drum brake. The disc-shaped strut portion 44 has an eccentric or spiral outer surface 114 with respectto the axle journal 112 and said outer surface 114 extends approximately over a quadrant and is grooved in parallel to the axis of rotation C.

The conical strut portion 46 is riveted to the 120 rod-shaped strut portion 42 and has a corresponding ly grooved cylindrical outer surface 116 on which the disc-shaped strut portion 44 supports itself with its outersurface 114.The axlejournal 112 is connected to the rod-shaped strut portion 42 by a further return spring 11 8which tends to hold the outer surfaces 114 and 116 together.

The disc-shaped strut portion 44 also has an arm which extends substantially radially awayfrom the axle journal 112 and engages through the recess 130 38 in which it has a defined clearance d in longitudinal direction of the strut 40. This clearance d corresponds to the distance the brake shoes 14 anu 16 can be spread apart bythe brake actuating mechanism 20 without an adjustmenttaking place. If this distance is surpassed, the left brake shoe 14takes with itto the leftthe disc-shaped strut portion 44whilethe rodshaped strut portion 42 moves together with the right brake shoe 16to the right. As a result, the grooved outer surfaces 114 and 116 of the strut portions 44 and 46 separate and theforce exerted on the arm 120 by the brake shoeweb 15 effects a rotation of the disc-shaped strut portion 44 by several degrees about the axlejournal 112. This in turn has the resuitthat on release of the brake a portion of the outersurface 114 further awayfrom the axis of rotation C comesto rest againstthe outer surface 16.

In orderto avoid over-adjustment, a face toothing 122 is formed on the disc-shaped strut portion 44 and extends in accordance with the outer surface 114 approximately over a quadrant but is arranged so asto be concentricwith the axis of rotation C. The face toothing 122 engages with a radial toothing 124 on the intermediate member 24which is constructed as a toothed sector and is supported on a plunger 126for rotation aboutthe axis B of the cylinder 20. The plunger 126 has a hemispherical head 128, a neck 130 of smaller diameterand a shaft 132 of even smaller diameter. The shaft 132 is received in a helical compression spring which is accommodated with axial bias in a cage 136 atthe upper end of the brake shoeweb 15. The cage 136 is hollowed outfrom the brake shoe web 15 in one piece or isfixed to the same, e.g., welded to it. 100 The neck 130 of the plunger 126 is supported in the direction of axis B on the compression spring 134 and its length is rather greaterthan the thickness of the portion of the intermediate member24 situated between the head 128 and the cage 136 orthe upper end of the brake shoeweb 15. Thus, the intermediate member 24 is supported on the plunger 126for rotation around the axis B provided the force exerted bythe left piston 22 of the brake actuating mechanism 18 is lessthan theforce of the axial bias of the compression spring 134.

However, when theforce exerted bythe piston 22 during forceful brake actuation exceedsthat of the compression spring 134, said compression spring yields and the intermediate member 24 is clamped between the head 128 of the plunger 126 and the cage 136 or upper end of the brake shoe web 15. The intermediate member 24 can thus no longer rotate and then the disc-shaped strut portion 44 is also prevented from rotating about its axle journal 112 bythe mutual engagement of thetoothings 122 and 124. In this way, adjustment of the strut 40 is prevented when the brake actuating force exceeds a value predetermined bythe bias of the compression spring 134.

In orderto increase the effect of the yieldable support of the plunger 126 described, this can befixed against rotation in the cage 136, e.g., by the cage 136 having edge portions which are curved radially inwards and each engage with a longitudinal groove inthe neck 130. The underside of the head 128 andlor the surface of the intermediate member 24facing it i i 3 can be radially grooved so that when the compression spring 134 yields, the head 128 interacts notjust with frictional contact but in positive manner with the intermediate member 24 in orderto prevent this from rotating. Forthe same purpose, the upper end of the brake shoe web 15andlorthe surface of the intermedi ate member 24 assigned thereto can also be grooved radially in relation to the plunger 126.

The internal shoe-drum brake according to Figs. 5 to 7 is largely comparable with that according to Figs. 1 75 to 4 and is therefore only partially shown; the same or similar components are provided with the same reference numbers. The adjusting device shown in Figs. 5 to 7 only is described below and this only in so faras it differs from the device shown in Figs. 1 to 4.

The strut40 according to Figs. 5 to 7 consist only of a rod-shaped strut portion 42 and a disc-shaped strut portion 44. The rod-shaped strut portion 42 embraces fork-like the brake shoe web 15 and has an upwardly bentthrust bearing 150. Between this thrust bearing and a bearing surface 152formed on the brake shoe web 15, is a portion of the disc-shaped strut portion 44whose surface resting againstthe bearing surface 152 is a plane surface whilethe surface resting against the thrust bearing 150 ascends in the form of a 90 spiral with radial clearance around the axis B; the disc-shaped strut portion 44 isthus constructed as an axial cam plate.

Between the disc-shaped strut portion 44 and the brake shoe web 15, a return spring 154 is clamped such that its longitudinal axis keeps a marked radial distance in every possible operating position from the plunger 126whose axis at least approximately con forms with the axis B of the cylinder 20. As a result of this arrangement, the return spring 154 exerts a torque which tendsto rotate the integral member consisting of intermediate member 24 and the disc shaped strut portion 44 around the plunger 126 and moreover, in such a mannerthatthe strut portion 44 pushes wedge-like between thrust bearing 150 and 105 bearing surface 152 and thus enlargesthe effective length of the strut40.

This enlargement of the effective length of the strut occurs each time the clearance d is exceeded due to wear of the brake linings when the drum brake is actuated by means of the hydraulic brake actuating mechanism 18. The clearance d is determined accord ing to Fig. 7 by means of the factthat a projection 156 formed on the right end of the rod-shaped strut portion 42 engages with a correspondingly larger 115 recess 158 in the brake shoe web 17.

However, when the force exerted bythe brake actuating mechanism 18 via the plunger 126 and the compression spring 134 on the brake shoe 14 exceeds the bias of the compression spring 134 during particularly forceful brake actuation, the intermediate member 24 is clamped between the head 128 of the plunger 126 and the cage 136 or brake shoe web 15 as in the embodiment shown in Figs. 1 to 4. Due to the intermediate member 24 and the disc-shaped strut portion 44 being integral in the embodiment according to Figs. 5 to 7, this has the direct result that the disc-shaped strut portion 44 can no longer rotate and thus adjustment of the strut 40 does not take place.

In some cases, protection against over-adjustment GB 2 131901 A 3 can be dispensed with, e.g., because all structural members loadable bythe brake actuating mechanism are so amply dimensioned thatthey cannot markedly deform even during particularly forceful brake actua- tion. In such cases, asvariation on Figs. 5to 7, the compression spring 134and the cage 136 can be replaced by a rigid supportforthe plunger 126 on the brake shoe 14.The plunger 126then has onlythe function of ajournal on which the strut portion 44 is supported for rotation without ever being clamped between the piston 22 and the brake shoe 14.

Both embodiments shown in the drawings and the variation on Figures 5to 7 described above can be modified in that plunger 126 and spring 134 are

Claims

guided in the piston 22, similarto the embodiment shown in Figures 7 and 8 of our aforesaid Application No.8216232. CLAIMS

1. An automatic adjusting device fora brake, in particular a motor vehicle brake in which a strut, whose effective length depends on the relative positions of two strut portions adjustable with respect to each other, is connected in parallel with a brake actuating mechanism, one of said strut portions having at least one portion adjustable transversely of the longitudinal direction of the strut, upon actuation of the braketending to increasethe length of the strut with this portion and cooperating with an intermediate memberwhich is disposed between two structural members transmitting the actuating force independently of the strut and which is rotatable againstthe frictional resistance thereof, provided said resistance does notsurpass a given value, wherein said intermediate member is supported for rotation on one of the two said structural members transmitting the actuatingforce.

2. The adjusting device according to claim 1, wherein the intermediate member is rotatable around the axis of the brake actuating mechanism.

3. The adjusting device according to claim 2, wherein one of said two structural members, between which said intermediate member is disposed, is a head of a plunger guided for axial displacement in the other one of these two structural members and supported by means of a spring tending to maintain a spacing largerthan the thickness of the intermediate member between the head and the other structural member, said intermediate member being supported for rotation on said plunger itself.

4. The adjusting device according to claim 2, wherein said intermediate member is a toothed sector whose toothing engages a face toothing on one of said strut portions, this strut portion being rotatable on the other strut portion around an axis of rotation disposed transversely of the longitudinal direction of the strut and having an eccentric outer surface whose position determines thetotal length of the strut.

5. The adjusting device according to anyone of claims 1 to 3, wherein said intermediate member is formed by an annular central area of a cam plate with a spiral outer area and togetherwith thisforms one of said strut portions.

6. An automatic adjusting devicefor a brake, in particular a motor vehicle brake in which a strut, whose effective length depends on the relative 4 GB 2 131901 A 4 positions of two strui porlions adjustable with respect to each other, is connected in parallel with a brake actuating mechanism, one of said strut portions having at least one portion adjustable transversely of the longitudinal direction of the strut, and upon actuation of the brake tending to increase the length of the strutwith this portion, said strut portion being constructed as an axial cam plate rotatable around the axis of said brake actuating mechanism.

7. An automatic adjusting device fora brake substantially as hereinbefore described with referenceto Figures 1 to 4 or Figures Sto 7 of the accompanying drawings.

Printed for Her MajeWs Stationery Office byTheTweeddale Press Ltd., BerWick-upon-Tweed, 1984. Published atthe Patent Office, 25 Southampton Buildings, London WC2A JAYfrom which copies may heobtained.

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