GB2133846A - Drum brake - Google Patents

Abstract

A drum brake equipped with an automatic clearance-adjusting mechanism for automatically adjusting the clearance between the inner circumference of a brake drum and the outer peripheries of the linings of a pair of brake shoes (10 and 11). The clearance-adjusting mechanism includes a strut (22) extending between the brake shoes (10 and 11). This strut (22) has its one end so operatively connected to the brake shoe (11) that it can swing in the direction of the axle of a wheel and its other end formed with teeth (16a) operatively engaging with the other brake shoe (10). A spring (23) is connected under tension between the strut (22) and the other brake shoe (10) for biasing the strut (22) to swing in such a direction that the two brake shoes (10 and 11) may be brought apart from each other and toward the inner circumference of the brake drum through the operative engagement between the strut teeth (16a) and the other brake shoe (10). <IMAGE>

Description

SPECIFICATION Drum brake Background of the invention Field of the invention The present invention relates to a drum brake and, more particularly, to a drum brake which is equipped with an automatic clearance-adjusting mechanism for automatically adjusting the clearance between a brake drum and brake shoes.

Description of the prior art In the drum brake, generally speaking, when the linings mounted on the brake shoes wear, the stroke of a brake pedal is so enlarged that the drum brake has its braking performance degraded. This makes it necessary to provide an automatic clearance-adjusting mechanism for holding that clearance at a predetermined level.

Before entering into the detailed description of the present invention, examples of the construction of the brake drum which is equipped with the automatic clearance-adjusting mechanism according to the prior art will be cursorily reviewed with reference to Figs. 1 and 2 of the accompanying drawings.

The example of Fig. 1 is disclosed in U.S.P. No.

3,339,678 and is directed to the drum brake which adopts an automatic clearance-adjusting mechanism of latch type. To a leading shoe 2 made coactive with a wheel cylinder 1 , there is fixed a lever 4 which is made swingable on a pin 3. The lever 4 has its free end formed with teeth 4a which are in meshing engagement with a latch 5.

In accordance with the wear of the lining of the leading shoe 2, moreover, the lever 4 is turned to change the meshing position between the teeth 4a and the latch 5 so that a constant clearance may be ensured at all times.

If the construction thus described is adopted, however, the turning operation of the lever 4 requires such a sufficient clearance from the hub of a wheel axle as is indicated by reference letter A. This makes it remarkably difficult to lay out the construction in case the drum has a small diameter whereas the wheel hub has a large diameter.

Turning to Fig. 2, there is shown another example which is directed to the drum brake using the automatic clearance-adjusting mechanism of strut screw type. A strut 6 to be arranged between a not-shown leading shoe and a trailing shoe 8 is constructed into an assembly of a threaded rod and a nut. An adjust gear 7 is fixed on the threaded rod. In case the linings wear, the adjust gear is turned by means of a notshown adjust lever so that the effective length of the strut 6 may be enlarged to automatically adjust the aforementioned clearance by changing meshing position of the adjust gear 7 with the nut.

If the construction thus far described is adopted, it becomes difficult to actually mount the automatic clearance-adjusting mechanism in the drum brake in case a clearance B between the wheel cylinder 1 and the mating wheel hub is not sufficient.

Summary of the invention The present invention has been conceived so as to eliminate the difficulties concomitant with the prior art and has an object to provide a drum brake which is equipped with such an automatic clearance-adjusting mechanism as has a simple construction and a small space for actual mounting so that it can be mounted in a restricted space of the drum brake.

According to a major feature of the present invention, there is provided a drum brake comprising: a brake drum connected to the axle of a wheel; a pair of brake shoes having linings thereon and mounted diametrically oppositely of each other in said brake drum in a manner to swing back and forth, when they are actuated, so that their linings may be brought into and out of contact with the inner circumference of said brake drum thereby to apply a braking force to said wheel through said brake drum; and actuating means for actuating said brake shoes when it is energized, wherein the improvement comprises automatic clearance-adjusting means for automatically adjusting the clearance between the inner circumference of said brake drum and the outer peripheries of the linings of said brake shoes, said automatic clearance-adjusting means including: a strut extending between said brake shoes and having its one end so operatively connected to a first one of said brake shoes that it can swing in the direction of the axle of said wheel and its other end formed with teeth operatively engaging with a second one of said brake shoes; and an adjust spring connected under tension between said strut and said second brake shoe for biasing said strut to swing in such a direction that said brake shoes may be brought apart from each other and toward the inner circumference of said brake drum through the operative engagement between the teeth of said strut and said second brake shoe.

Brief description of the invention Other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which: Figs. 1 and 2 are schematic views showing the different constructions of the brake drum according to the prior art, respectively; Fig. 3 is a front elevation showing a first embodiment of the drum brake according to the present invention; Fig. 4 is a top plan view showing a strut of the brake drum shown in Fig. 3 in an enlarged scale; Fig. 5 is similar'to Fig. 3 but shows a second embodiment of the present invention; and Fig. 6 is similar to Fig. 4 but shows the strut of Fig.,5 in an enlarged scale.

Description of the preferred embodiments A first embodiment of the present invention will be described with reference to Figs. 3 and 4.

Reference numerals 10 and 11 appearing in the drawing indicate a leading shoe and a trailing shoe, respectively, to which linings 12 are fixed.

The leading and trailing shoes 10 and 11 have their respective one-side ends are in abutting contact with a wheel cylinder 1 3 while being biassed to return by the actions of return springs 14 and 15, respectively.

The respective other ends of the leading and trailing shoes 10 and 11 are in abutting contact with an anchor 21.

To the leading shoe 10 at a portion close to the wheel cylinder 13, there is fixed a patch 1 6 of a plate member by mechanical means such as welding, rivetting or press-fitting means.

On the other hand, a parking lever 1 8 is so mounted at its one end on the trailing shoe 11 by means of a pin 1 7 that it can swing together with the same. To the free end of the parking lever 18, there is connected a parking cable 20 which is biased to return by the action of a spring 1 9.

Indicated at reference numeral 22 is a strut of a plate member, which acts as an adjust lever. As better seen from Fig. 4, the strut 22 has its one end formed with arcuately arranged teeth 22c which are in meshing engagement with linearly arranged teeth 1 6a formed in the end edge of the aforementioned patch 16, thus preventing any slippage inbetween. Incidentally, the teeth 1 6a of the patch 1 6 may be arranged in an arcuate shape like the teeth 22c of the strut 22. In this modification, a working cutter can be commonly used. In case the patch 1 6 is made of a softer material than that of the strut 22, on the other hand, the teeth 22c of the strut 22 are caused to bite into the patch 1 6 by the action of the parking lever 18 thereby to prevent the slippage if only the strut 22 is formed with the teeth 22c.

Therefore, the patch 16 need not be especially formed with any tooth.

The strut 22 has its other end formed with an arcuate portion 22a, through which it is in abutting contact with the end edge of the parking lever 18.

Incidentally, the center of the arc of the strut teeth 22c is offset from the contact of the arcuate portion 22a with the parking lever 1 8. As a result, when the strut 22 swings in the direction of arrow C of Fig. 4, it changes its meshing position with the patch 1 6 so that the distance between the contacting point and the meshing point is gradually increased.

Moreover, the strut 22 is formed with an Lshaped bent portion 22b which extends obliquely upward, as viewed in Fig. 4. That bent portion 22b is so positioned that it can be fitted in an opening 1 8a formed in the parking lever 18.

An adjust spring 23 is mounted under tension between the strut 22 at a position near the parking lever 18 and the leading shoe 10.

As a result, the strut 22 is always tensed toward the leading shoe 10 and is biased to swing in the clockwise direction, as viewed in Fig.

4, on the arcuate portion 22a thereof.

The operations of the present embodiment having the construction thus far described will be explained in the following.

In the set state, the strut 22 is tensed toward the patch 1 6 by the coactions of the return springs 14, 1 5 and 19 and the adjust spring 23 so that the clearance between the bent portion 22b and the side wall of the opening 1 8a is held at a value b.

If, in this state, an oil pressure is applied to the wheel cylinder 13 so that the leading and trailing shoes 10 and 11 are swung apart from each other toward the brake drum, the strut 22 is caused to follow the motion of the leading shoe 10 by the tension of the spring 23 so that the clearance a is reduced.

When the oil pressure is released, on the other hand, the initial state is restored.

If the wear of the linings progresses to increase the clearance between the brake shoes and the brake drum, on the other hand, the motions of the strut 22 caused to follow those of the leading shoe 10 as a result of the swinging motions of the two shoes are stopped by the engagement between the bent portion 22b and the side wall of the opening 1 8a of the parking lever 1 8 so that the strut 22 and the patch 1 6 leave each other.

Then, the strut 22 is swung clockwise, as indicated by the arrow C in Fig. 4, on the contacting portion between the side wall of the opening 1 8a and the bent portion 22b by the tension of the spring 23.

As a result, the meshing position between the strut 22 and the patch 1 6 is changed to increase the distance between the contacting point of the strut 22 with the parking lever 1 8 and that meshing position so that the distance between the right and left shoes 11 and 10 is accordingly increased to an extent corresponding to the wear of the linings 12 thereby to automatically adjust the clearance between the shoes 10 and 11 and the brake drum.

Since, at this time, the swining motions of the strut 22 are oriented in the direction of the wheel axle, the automatic clearance-adjusting mechanism of the present embodiment can be mounted in a restricted space even in case the brake drum has a small diameter whereas the wheel hub has a large diameter.

Since the strut also acts as the adjust lever, moreover, no spare member is required to make any connecting portion such as a pin unnecessary.

Incidentally, there has been exemplified a construction in which the patch 1 6 is provided as the member to engage with the free end of the strut 22. In case sufficient strength is ensured, however, the leading shoe 10 and the strut 22 may be made to engage directly with each other.

Turning to Figs. 5 and 6, a second embodiment of the present invention will be described in the following. In this embodiment, the patch 16 is fixed not on the leading shoe 10 but on a pin 24 which is mounted in the former. More specifically, the pin 24 is inserted at a clearance a into an opening 1 Oa, which is formed in the leading shoe 10, and is then fixed in the leading shoe 10 by means of a spring washer 25 and a clip 26. As a result, the patch 1 6 is allowed to slide relative to the leading shoe 10. Moreover, the adjust spring 23 has both its ends connected to the strut 22 and the head 24a of that pin 24, respectively, so that the strut 22 is biased to swing in such a direction that the two brake shoes 10 and 11 may be brought apart from each other.Incidentally, reference numeral 27 indicates a spring which is provided to cause the strut 22 to follow the motions of the trailing shoe 11 and which has a stronger force than that of the adjust spring 23.

The operations of the present embodiment are substantially simiiar to those of the foregoing first embodiment except that, when the wheel cylinder 13 is supplied with the oil pressure, the strut 22 is caused to follow the swinging motions of the trailing shoe 11 by the action of the spring 27 so that the patch 1 6 is slid by the tension of the adjust spring 23, and that, when the pin 24 comes into engagement with the side wall of the opening 1 Oa of the leading shoe 10, the patch 1 6 stops its sliding movement so that the strut 22 is allowed to swing.

As is now apparent from the description thus far made, according to the present invention, the strut acts as the adjust lever of the prior art construction but has its one end operatively connected to one brake shoe and its other end operatively connected to the other brake shoe without any slippage and is biased to swing in such a direction that the paired brake shoes may be brought apart from each other. As a result, the constant clearance can be held at all times even if the wear of the linings of the brake shoes progresses.

Since the swinging motions of the strut are in the direction of the axle of the wheel, moreover, the automatic clearance-adjusting mechanism of the present invention can be actually mounted in a restricted space even in case the drum diameter is small whereas the hub diameter is large.

Claims (11)

Claims

1. A drum brake comprising: a brake drum connected to the axle of a wheel; a pair of brake shoes having linings thereon and mounted diametrically oppositely of each other in said brake drum in a manner to swing back and forth, when they are actuated, so that their linings may be brought into and out of contact with the inner circumference of said brake drum thereby to apply a braking force to said wheel through said brake drum; and actuating means for actuating said brake shoes when it is energized.

wherein the improvement comprises automatic clearance-adjusting means for automatically adjusting the clearance between the inner circumference of said brake drum and the outer peripheries of the linings of said brake shoes, said automatic clearance-adjusting means including: a strut extending between said brake shoes and having its one end so operatively connected to a first one of said brake shoes that it can swing in the direction of the axle of said wheel and its other end formed with teeth operatively engaging with a second one of said brake shoes; and an adjust spring connected under tension between said strut and said second brake shoe for biasing said strut to swing in such a direction that said brake shoes may be brought apart from each other and toward the inner circumference of said brake drum through the operative engagement between the teeth of said strut and said second brake shoe.

2. A drum brake as set forth in Claim 1, further comprising a parking lever mounted on said first brake shoe in a manner to swing together with the same, wherein the one end of said strut is formed with an arcuate portion engaging with said parking lever for providing a center of the swinging motions of said strut.

3. A drum brake as set forth in Claim 1, wherein the teeth formed in the other end of said strut are arranged in such an arcuate form as to have its center offset relative to the center of the swinging motions of said strut

4. A drum brake as set forth in Claim 3, further comprising a parking lever mounted on said first brake shoe in a manner to swing together with the same, wherein the one end of said strut is formed with a bent portion which is fitted at a predetermined clearance in an opening formed in said parking lever.

5. A drum brake as set forth in Claim 4, further comprising a patch fixed on said second brake shoe and engaging with the teeth of said strut.

6. A drum brake as set forth in Claim 3, wherein said second brake shoe is formed with an opening, further comprising: a pin fitted at a predetermined clearance in the opening of said second brake shoe; and a patch connected to said pin member and engaging with the teeth of said strut.

7. A drum brake as set forth in Claim 6, further comprising a tensile spring mounted between said first brake shoe and said strut for causing the former to follow the motions of the latter.

8. A drum brake as set forth in Claim 1, wherein said actuating means includes a wheel cylinder abutting against the respective ends of said brake shoes for forcing the same into engagement with the inner cicumference of said brake drum when a hydraulic pressure is applied thereto.

9. A drum brake substantially as described hereinbefore with reference to the accompanying drawings.

10. A drum brake according to Claim 9 and as shown in Figures 3 and 4 or in Figures 5 and 6 of the accompanying drawings.

11. Any other novel feature or combination disclosed hereinbefore or shown in the accompanying drawings.