GB2234564A

GB2234564A - Adjusting apparatus for a drum brake

Info

Publication number: GB2234564A
Application number: GB9012245A
Authority: GB
Inventors: Uwe Hendrich
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1989-08-04
Filing date: 1990-06-01
Publication date: 1991-02-06
Anticipated expiration: 2010-06-01
Also published as: FR2650646B1; GB9012245D0; GB2234564B; FR2650646A1

Abstract

An internal shoe drum brake for automotive vehicles, comprises a pair of brake shoes which are positioned at a thrust member of a brake carrier plate and are furnished with tension springs, a mechanical actuating apparatus which is operatively located between a pair of brake shoe ends positioned opposite each other and pre-stressed by a spring and by which the brake shoes can be urged against a surrounding brake drum during a braking action and an adjusting member which is positioned at at least one brake shoe web and is extendable in length in the event of a wear of the linings. The adjusting member (39) comprises a two-part strut. The parts are provided with meshing teeth (107, 125) which permit relative movement of the parts to extend the strut (39) and preventing such movement in the opposite direction. <IMAGE>

Description

ADJUSTING APPARATUS FOR A DRUM BRAKE The present invention relates to an adjusting apparatus for a drum brake, in particular for a mechanically actuatable, self-energising, internal shoe drum brake of the kind comprising a pair of brake shoes which are located at a thrust member and are furnished with tension springs, a mechanical actuating apparatus which is operatively located between a pair of brake shoe ends positioned opposite each other and pre-stressed by a spring and by which the brake shoes can be urged against a surrounding brake drum to produce a braking action and an adjusting member which is positioned at a web of a brake shoe and is extendable in length in the event of wear of brake linings.

A drum brake of the above kind is already known from the German version of the Brake Handbook by Alfred Teves GmbH, page 135, 9th edition, published by Bartsch Verlag.

A mechanical actuating apparatus is designed in the shape of an expanding lock, engages web ends of the brake shoes and urges the brake shoes prestressed by springs against the brake drum in contrast to the spring force. At the second, opposed brake shoe ends, a supporting apparatus engages the webs of the brake shoes which is manually adjustable. This adjusting apparatus has the disadvantage that additional manual adjusting and checking operations are required both in the event of assembly and in service in order to maintain the optimum functional capability since manufacturing tolerances of the components and, in particular, the wear of the linings during operation increase the clearance of the brake shoes at an inadmissible extent and influence negatively the effective mechanical lever transmission of the expanding lock.

A drum brake is described in German patent specification No. 2,156,899 in which two brake shoes are movable optionally either by a hydraulic or by a mechanical actuating apparatus. A telescopically adjustable push rod is positioned between the brake shoes. The mechanical actuating means comprise a handbrake lever which is pivoted at one end thereof on a web of a first brake shoe and is actuatable at its other end by means of a cable. A stop surface which can act on the push brace and, thus, on the second brake shoe is provided in an upper third of the handbrake lever being related to the pivotal point.

Disadvantageously, a large number of components is required in this construction in order to safeguard both the hydraulic and the mechanical actuation.

The invention has as an object to provide a simple adjusting member for a drum brake, which offers ease of manufacture, ease of assembly and requires but little space.

In particular, drum brake linings are to be adjustable up to the optimum operational clearance, in accordance with their pattern of wear.

According to the invention there is provided an adjusting apparatus for a drum brake, in particular for a mechanically actuatable self-energising, internal shoe drum brake of the kind comprising a pair of brake shoes which are located at a thrust member and are furnished with tension springs, a mechanical actuating apparatus which is operatively located between a pair of brake shoe ends positioned opposite each other and pre-stressed by a spring and by which the brake shoes can be urged against a surrounding brake drum to produce a braking action and an adjusting member which is positioned at a web of a brake shoe and is extendable in length in the event of wear of brake linings.

The adjusting member comprises a two-part push brace with a push strip guiding a push rod and the push rod and the push strip are furnished with meshing transverse sawtooth toothed parts at surfaces facing each other. With the aid of the transverse toothed parts with meshing saw teeth, it is rendered possible in an advantageous manner that a latching slide movement of the strip and rod one on top of the other in one direction by which the push brace is extended in length with movement being prevented in the opposite direction. If and when the actuating distance is larger than the clearance and than the pitch of the toothed parts, then an adjustment takes place in steps corresponding to the pitch of the teeth of the toothed parts.

In a simple embodiment of the invention both the push strip and the push rod are provided with an end which is bent roughly at right angles to the main section of the strip or rod. The push rod and the push strip are combined into a push brace in such a manner that the push brace is bounded by the two ends which are bent over at right angles and which engage openings of the brake shoe webs. In this way, a simple design is rendered possible since the ends can easily be inserted in to openings provided in the brake shoe webs. In addition, the openings may be dimensioned so that during interaction between the opening and the bent-over end the end is movable in the opening with a play corresponding to the clearance of the brake. The expanding adjustment device is inserted with its hooks into bores provided in opposite brake shoes.If and when the bores are larger than the width in height, then the operating clearance will be ensured.

In a simple and space-saving embodiment, the push rod and the push strip both have a blade-shaped rectangular configuration provided by stampings and are positioned one on top of the other in the longitudinal direction thereof.

The push brace comprises two elements only which feature a wide operating range.

In order to ensure a safe guidance of the push rod relative to the push strip, the push strip is, advantageously, formed with an opening in which the push rod is guided.

In one advantageous embodiment, the push rod is provided with an end section bent in to U-shape with an elastic or flexible stem, the end section gripping around the push strip the manner of a clip, as a result whereof a second guide is realised between the push rod and the push strip.

In an advantageous, simple and space-saving embodiment, the U-shaped end section protrudes through a longitudinal slot of the push strip, the flexible stem has a cruciform configuration and slides with projections thereof on that side of the push strip which faces away from the main section of the rod. The projections at the lower plate or sheet steel element which have a knub-shaped configuration are swung into the opposite window (opening) in the upper plate or sheet steel element. By setting to standard, the knubs are brought from the range of the window on to the plate or sheet, so that any swinging out (back) will no longer be possible and readiness for operation is established.

Advantageously, the push rod is guided at a basic stem of the U-shaped section at the side walls defining the longitudinal slot.

In one advantageous embodiment, the opening at the bent-over end of the push strip extends up into the main section as a result whereof the push rod will allow to be inserted with the elastically bent stem through the oversized opening during assembly of the push brace, so that the readily bent push rod and the push strip will, advantageously, allow to be mounted to each other.

The longitudinal slot is bounded by a web which, advantageously, serves for reinforcement and prevents the lateral parts defining the longitudinal slot from being widened.

In an advantageous manner, the U-shaped end section of the rod is formed with a curved neck, so that the spring effect of the flexible stem on the strip is increased.

Advantageously, the elastic stem is bent over in its end range, so that the bent-over section, too, is guided in the longitudinal slot. Due to the distance of a basic stem and of the bent-over end of the U-shaped section, the transverse slot of the cruciform opening can be advantageously overcome during guiding action.

By way of example the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a front view of a complete drum brake with a mechanical actuating apparatus and with two adjusting members; Figure 2 shows one lateral view of a push strip of an adjusting member of Figure 1; Figure 3 shows a top view of the push strip of Figure 2; Figure 4 shows another lateral view of the push strip of Figure 2; Figure 5 shows transverse teeth on one surface of the push trip; Figure 6 shows a fragmentary lateral view of the transverse teeth of Figure 5; Figure 7 shows a lateral view of a push rod of the adjusting member; Figure 8 shows a top view of the push rod of Figure 7; Figure 9 is a lateral cross-sectional view of the push rod; Figure 10 shows a transverse toothing on one surface of the push rod;; Figures 11 to 13 illustrate the assembling of the push rod and the push strip of Figures 1 to 10 to form a push brace working as an adjusting member; Figure 14 shows the assembled push brace in an initial condition when the brake linings are sound and integral; and Figure 15 shows the push brace in a final condition, when the brake linings are worn out.

Figure 1 of the drawings shows a mechanically actuatable self-energising duo-servo internal shoe-type drum brake with a pair of brake shoes 4,5 in engagement with a thrust member 6 adjacent a brake carrier plate 27 and furnished with a tension spring 7. A mechanical actuating apparatus which takes the form of an expanding lock 3 is operatively located between a pair of brake shoe ends 14,80 which are positioned opposite each other and pre-stressed by a brake shoe tension spring 10. The expanding lock 3 comprises an actuating lever 69, a thrust shackle 70, a traction cable and a hinge pin 72 and the lock 3 is capable of urging the brake shoes 4,5 outwardly against the surrounding brake drum 1 which is illustrated in cross section.In the present construction, an adjusting member 39 is arranged parallel to the expending lock 3 and comprises a two-part variable-length push brace 39 which extends between the brake shoes 4,5 and the ends of which bridge with a minute clearance in at least one of the openings 40,41. A second adjusting member 14,15 is located adjacent a brake shoe web 12 supporting the brake shoe 5 and is furnished with a rotating key 15 and an adjusting thrust member 14 which is slidable in the circumferential direction relative to the shoe 5 and can be brought in to abutment against a supporting block 2. The adjusting thrust member 14 and brake shoe webs 12,13 are formed with openings 46 which extend tangentially with respect to the centre of the drum brake and which receive the rotating key 15.In this arrangement, the rotating key 15 is guided in the radial direction by the adjusting thrust member 14 and-swung about is pivotal point against the adjusting thrust member 14 by an adjusting tension spring 16. The brake shoes 4,5 are biased in the direction of the thrust member 6 and of the expanding lock 3 by the tension springs 7,10. The push brace 39 engages openings 40,41 in the web segment 13 and the brake shoe web 12, respectively. The push brace 39 is safeguarded against being lost by the pre-arranged brake shoe tension spring 10. On its brake shoe web 12, the brake shoe 5 carries the second adjusting apparatus comprising the adjusting thrust member 14, the rotating key 15, and the adjusting tension spring 16.Between the brake shoe web 12 and the web segment 13, the thrust member 14 is inserted so as to be slidable in the circumferential direction of the shoes with respect to the support block 2 and the expanding lock 3. The radial guidance of the thrust member 14 is ensured by the curved internal surface of the lining carrier plate 65 and by a moulding 28 at the marginal edge of the brake shoe web 12. Brake shoe retainers 8 provide parallel alignment of the brake shoes 4,5 with respect to brake carrier plate 27. The brake shoe end is formed as a thrust member 14. An adjusting tension spring 11 is received at one end by an opening at the end of the plate-shaped adjusting thrust member 14, as a result of which the adjusting thrust member 14 can be brought into abutment against the supporting block 2 under the effect of the spring tensile force.The ends of springs 10 and 16 are hooked into openings 68 which serve as spring receptacles.

Lining carrier plates 26 carry friction linings 81,82 and are fixed to the webs 12,12'.

Figures 2,3 and 4 show a push strip 83. The push strip 83 is formed as a stamping and comprises a rectangular plate-like main section 84. The main section 84 is bounded by two ends 85,86 which are bent in the same direction at right angles to the section 84. More precisely, the end 85 joins the main portion 84 with a curved neck section 87.

The section 87 extends over the length 88 which has a smaller width 90 than a width 89 of the main section 84. At the end 86, an opening 91 is provided having a height 92.

With an adjacent opening 93, the opening 91 extends up into the main section 84. At its lower end 94, the opening 91 is formed with curved recesses 95,96, so that no burrs will occur at the angle points between the lateral walls 97,98,99 defining the opening 91. Juxtaposed to the opening 93 extending into the main section 84, a further opening 100 of cruciform shape also referred to as a "window" in the following description, is provided. A longer end 101 of a longitudinal slot 102 of the opening 100 extends in the direction of the opening 93 and is separated from the latter by a web 103'. Lateral portions 102' and 102" of the main section 84 define the longer edges of the longitudinal slot 102. The longitudinal slot 102 extends up to the curved neck section 87. A transverse slot 103 of the opening 100 is positioned near the length 88 having a smaller width 90.

On its upper side the push strip or rod 83 is provided with a smooth surface 104 whereas on its underside 105 it is furnished with transverse teeth 107 over a length of strip 106 extending in the longitudinal direction of the main section 84 over a distance 108.

Figures 5 and 6 show the transverse teeth or toothed section 107 which comprises saw teeth having edges 109 disposed at right angles with respect to the strip surfaces 104 and 105 and with edges 111 inclined at an angle 110.

Figures 7,8,9 show a push rod 112 which comprises a sheet steel or plate steel stamping. The push rod 112 comprises a main section 113, a section 114 which is bent over to provide a U-shaped end and an end 115 which is bent at right angles. The end 115 at right angles to the main section 113 is joined to the main section 113 by means of a generally S-shaped section 116. A curved neck section 117 connects the U-shaped section 114 to the main section 113.

The U-shaped end section 114 is of cruciform configuration being formed with two projections 118 and 119. The end 120 of flexible stem 121 comprising part of the U-shaped section 114 extends towards the main section 113. The rod across the projections 118,119 is as wide as the main section 113, having a width 122. Over a length of rod 124 near the flexible stem 121 and the projections 118,119, an upper surface 123 is provided with a transverse teeth or transverse toothed section 125. The projections 118,119 are arched by a curve 126. By a saw tooth-shape configuration the transverse teeth present edges 128 disposed at right angles with the surface 127 and sloping edges 129. The Ushaped section 114 comprises a basic stem 130.

Figures 11,12, and 13 illustrate the method of assembling the push brace 39, which as a two-part adjusting member comprises the push strip 83 and the push rod 112.

With the section 114 bent over to define U-shaped end foremost the push rod 112 is inserted through the oversized opening 91 of the push strip 83 in the direction 131. The rod is pushed nearly all the way through and is then moved so that the U-shaped section 114 moves in the direction 132.

The openings 91,93 are designed so as to allow the U-shaped section 114 to be inserted smoothly. The flexible stem 121 with its projections 118,119 is moved through the cruciform opening 100 in the direction 132, the transverse slot 103 being designed so that the projections 118,119 pass through it. Thereupon, the push rod 112 is moved with respect to the push strip 83 in the direction 133, so that the projections 118,119 providing the cross-shaped configuration come to be abutted against the surface 104 of the push strip. Due to the fact that the projections 118 and 119 are formed with the curvature 126, the push rod 112 with the projections will be capable of sliding on the push strip even if dirt is present.The S-shaped section 116 will come in to abutment against the end 86 which is bent at right angles, so that a simple guide and a predetermined limit exist for easy insertion of the cross-shaped stem 121 through the cruciform window 100. Upon having been slid on in the direction 133, the push brace will assume a first starting position in which the transverse toothed sections 107 and 125 will lock with each other. The abutment against each other of the tooth surfaces or edges disposed at right angles is controlled and ensured by the height 92 of the opening 91 and by a distance 134 between the flexible stem 121 and the main section 113. On account of the spring action of the stem 121 and on account of the transverse teeth, the push rod 112 is movable in the direction 133.

Only on lifting the flexible stem in the direction 132 and on separating the surfaces of the push rod and of the push strip will the push rod be able to be moved with respect to the strip 83 in contrast to the direction 133.

Figures 14 and 15 show a starting condition of the push brace in which the brace 39 assumes a length 134 when the brake linings are sound and integral and a length 134 increased by the length 135 when the brake linings are completely worn out. In this condition, the bent end 130 of the push rod 112 will have moved against a stop 136 of the push strip 83. The basic stem 113 is guided by the lateral walls defining the longitudinal slot 102.

Claims

CLAIMS:

1. An adjusting apparatus for a drum brake, in particular for a mechanically actuatable self-energising, internal shoe drum brake of the kind comprising a pair of brake shoes which are located at a thrust member and are furnished with tension springs, a mechanical actuating apparatus which is operatively located between a pair of brake shoe ends positioned opposite each other and prestressed by a spring and by which the brake shoes can be urged against a surrounding brake drum to produce a braking action and an adjusting member which is positioned at a web of a brake shoe and is extendable in length in the event of wear of brake linings, characterised in that the adjusting member (39) comprises a two-part push brace (39) having a push strip (83) guiding a push rod (112) and in that at surfaces (105,123) facing each other the push rod (112) and the push strip (83) are provided with meshing transversely extending toothed parts (107,125) having saw-shaped teeth which render possible a latching slide movement of the strip and rod one on top of the other in a direction (133) extending the push brace (39) and which prevent such movement in the opposite direction.

2. An adjusting apparatus as claimed in claim 1, characterised in that the push brace (39) is provided with ends (85,115) which are bent generally at right angles and which engage openings (40,41) in brake shoe webs (12,12').

3. An adjusting apparatus as claimed in claim 1 or claim 2, characterised in that the push rod (112) and the push strip (83) have a generally flat rectangular configuration and are positioned one on top of the other in the longitudinal direction thereof.

4. An adjusting apparatus as claimed in any one of the preceding claims, characterised in that the push strip (83) has an end (86) thereof bent at right angles and provided with an opening (91) having lateral walls (97,98,99) defining the opening (91) and in that the push rod (112) protrudes through the opening (91) and is guided by the lateral walls (97,98,99).

5. An adjusting apparatus as claimed in any one of the preceding claims, characterised in that the push rod (112) is provided with an end section (114) which is bent over to provide a generally U-shaped end and has a flexible stem (121), the end section (114) gripping the push strip (83) in clip-like manner.

6. An adjusting apparatus as claimed in claim 5, characterised in that the U-shaped end section (114) protrudes through a longitudinal slot (102) of the push strip (83) and in that the flexible stem (121) is of cruciform configuration and takes support with projections (118,119) on that side (104) of the push strip (83) which faces away from the main section (113) of the push rod (112).

7. An adjusting apparatus as claimed in claim 6, characterised in that the push rod (112) is guided in the longitudinal slot (102).

8. An adjusting apparatus as claimed in claim 4 or any of claims 5 to 7 as appendant to claim 4, characterised in that the opening (91,93) at the bent end (86) of- the push strip (83) extends up into the main section (84).

9. An adjusting apparatus as claimed in claim 6 or 7 as dependant on claim 4, characterised in that a web (103') divides the longitudinal slot (102) from the said opening (91,93).

10. An adjusting apparatus as claimed in claim 5 or any of claims 6 to 9 appendant to claim 5, characterised in that at the transition from the main section (113) to the Ushaped end section (114) is formed with a curved neck (117) in order to increase the spring radius.

11. An adjusting apparatus as claimed in claim 6, characterised in that the elastic stem (121) is furnished with a bent end (120) which is guided in the longitudinal slot (102).

12. An adjusting apparatus substantially as hereinbefore described with reference to the accompanying drawings.