GB2106203A

GB2106203A - A retaining device for holding in position a substantially U-shaped return spring in a drum brake

Info

Publication number: GB2106203A
Application number: GB08223158A
Authority: GB
Inventors: Mitsuo Sakata
Original assignee: Hosei Brake Industry Co Ltd
Current assignee: Hosei Brake Industry Co Ltd
Priority date: 1981-09-04
Filing date: 1982-08-11
Publication date: 1983-04-07
Also published as: DE3232335A1; FR2512510A1; FR2512510B3; GB2106203B; JPS5856435Y2; JPS5836640U

Abstract

The device comprises a spring holder 50 made of an elastic sheet material for holding an intermediate portion of spring 48 and further comprises engaging means for preventing the spring holder 50 from slidably moving more than a preset distance along the length of the return spring 50. The spring holder includes a U-shaped fixing portion 54 elastically gripping a portion of a web 22 of one of two brake shoes 14, 16 which are biased by the return spring. The engaging means may comprise a recess 60 formed in (through) the web and a projection 52 protruding from one of walls of the U-shaped fixing portion. The projection engages the recess with clearances such that the fixing portion can slide across and along the length of the return spring within preset distances. The engaging means is alternatively a pair of protrusions (Figure 4) secured to the surface of the intermediate portion of the return spring, which protrusions are spaced along the length of the return spring with predetermined clearance. <IMAGE>

Description

SPECIFICATION Shoe return spring retainer for drum brake The present invention relates to a retaining device for holding a U-shaped return spring for use in a drum brake, and more particularly to an easily mounted spring holder in such retaining device which allows the return spring to be displaced in response to wearing of brake shoes biased by the return spring.

In the art of drum brakes, it is known to bias a pair of brake shoes by using a return spring made of a wire of spring materials which is bent to a substantially U-shape. While this type of return spring is widely used because of its advantages of simple structure and less chance of interference with other parts of the drum brake, it is preferred to hold in place the return spring at its intermediate portion so as to prevent generation of noises from and damage to the intermediate portion due to oscillatory movements thereof about the ends of the return spring during service of the drum brake.

To hold the intermediate portion of the return spring for the above purposes, there has been used a spring holder which is secured to a web of one of the brake shoes in view of the fact that the web has less movement relative to the return spring during operating movements of the return spring upon brake applications. Thus, this type of spring holder enables the return spring to be securely retained in position thanks to a small degree of said relative movement. On the other hand, however, such spring holder suffers drawbacks resultant from the fixed relation with the shoe web.More specifically, a displacement of the return spring due to progressive wearing of the brake shoes will force the spring holder to be deformed, and the deformed spring holder will hinder the return spring from taking natural biasing actions, thereby causing considerable variations in biasing force imparted to the brake shoes and in the biasing direction.

The invention as claimed is intended to remedy these drawbacks. Accordingly it is an object of the invention to provide a retaining device which is capable of holding securely a U-shaped shoe return spring while allowing the shoe return spring to be displaced in response to wearing of the brake shoes.

According to the present invention, there is provided a retaining device for holding in position an intermediate portion of a substantially U-shaped return spring for use in a drum brake wherein the return spring engages a pair of brake shoes each having a web and facing the inside surface of a brake drum and biases the brake shoes away from the inside surface of the drum, said retaining device comprising a spring holder made of an elastic sheet material which includes a fixing portion and a spring holding portion elastically holding the intermediate portion of the return spring, characterized in that the retaining device comprises an engaging device which prevents the spring holder from slidably moving more than a preset distance in a direction along the length of the return spring, and that the fixing portion is bent to have a first substantially U-shaped structure including a first pair of side walls facing each other, the fixing portion elastically gripping a portion of said web of one of the pair of brake shoes and being slidable on the surface of the web in a direction across the length of the U-shaped return spring.

The advantages offered by the invention are mainly that the fixing portion elastically gripping the web is slidable on the surface of the web in the direction across the length of the U-shaped return spring whereby the return spring can be displaced in response to progressive wearing of the brake shoes while the intermediate portion of the return spring is naturally held by the spring holding portion without otherwise possible application of forces which causes to deform and damage the spring holder and create variation in the biasing force and direction of the return spring.

In addition, the spring holder which prevents oscillatory movements of the return spring about its ends engaging the brake shoes, is prevented by the engaging means from slidably moving more than a present distance in a direction along the length of the return spring. This engaging means is provided mainly for limiting such sliding movements of the spring holder which could otherwise take place against frictional forces between the surfaces of the holder and the surfaces of the return spring and the shoe web due to elasticity of the spring holder. It is noted here that the return spring is normally fixed in a plane parallel to the surfaces of the shoe webs and that the spring holding portion of the holder holding the return spring will not be moved on the return spring in a direction across the length of the return spring.

In accordance with one aspect of the invention, the engaging means comprises a recess formed in the web, and a projection protruding from one of the first pair of side walls of the fixing portion. The projection engages the recess with predetermined clearances in the directions across and along the length of the return spring, respectively. The clearances allow the fixing portion to slide in the direction across the length of the return spring but prevents the spring holder from moving in the direction along the length of the return spring beyond a certain point. Alternatively, the engaging means may comprise a pair of protrusions secured to the surface of the intermediate portion of the return spring.The protrusions are spaced along the length of the return spring so that there exits a predetermined clearance along said length between each of the protrusions and the side edge of the spring holding portion of the spring holder.

In this instance, the spring holder is restrained from sliding in the direction along the length of the return spring beyond a certain point but the fixing portion is free to slide on the surface of the web in the direction across said length.

These and other objects, advantages and aspects of the invention will become apparent from the following description of the preferred embodiments with reference to the accompanying drawings.

The invention is illustrated in the accompanying drawings in which: Fig. 1 is an elevational view of a drum brake incorporating one embodiment of a retaining device constructed according to the invention; Fig. 2 is a perspective view of a spring holder which forms a substantive part of the retaining device of Fig. 1: Fig. 3 is a sectional view taken along line 3-3 of Fig. 1; Fig. 4 is an enlarged plan view showing the spring holder and engaging means which cooperate to constitute another embodiment of the retaining device; and Fig. 5 is a view showing one form of a hole acting as part of the engaging means.

There is shown in Fig. 1 a drum brake of duoservo type, wherein a brake drum 10 rotating with a vehicle wheel is removed for illustrating the internal construction of the drum brake and the position of the brake drum 10 is indicated in broken lines.

In this drum brake, there are provided a pair of brake shoes 14, 1 6 which are slidably held on a backing plate 12 with hold-down retainers 1 8, 20 which apply a spring pressure to the shoes 14, 1 6.

The backing plate 1 2 is secured to a non-rotating member not shown. The brake shoes 14, 1 6 each comprises an arcuate shoe web 22, 24, a shoe rim 26, 28 secured to the outer periphery of the shoe web 22, 24 at right angle to the surface of the latter, and a lining 30, 32 fixedly attached to the external surface of the shoe rim 26, 28.

The pair of shoe webs 22 and 24 are connected, at one end thereof, to each other with by an adjusting line 36 which includes an adjusting wheel 34. The other ends of the shoe webs 22 and 24 engage pistons 40 and 42, respectively, which pistons extend in opposite directions from a wheel cylinder 38 fixed to the backing plate 12. A tension spring 44 is spanned between portions of the webs 22 and 24 close to the ends connected by the adjusting link 36 while a strut 46 is in engagement with portions of the same close to the other ends associated with the wheel cylinder 38, so that the distance between the brake shoes is maintained constant.

There is also provided between the brake shoes 14 and 1 6 a U-shaped return spring 48 which engages the shoe webs 22 and 24 and biases the brake shoes in respective directions away from the inside surface of the brake drum, i.e., toward each other. This return spring 48 is made of a wire of spring material and bent to form a substantially U-shaped structure. The return spring 48 has bent portions at both ends thereof, which bent portions are bent normal to a plane including the substantive part of the spring 48, and each of the bent portions has a notch which engages an opening formed in each of the shoe webs 22, 24 such that the substantive or intermediate part of the spring 48, that is, the whole portion of the spring except the bent ends, is kept apart from the shoe webs 22 and 24, and the adjusting link 36.

The intermediate portion of the return spring 48 is held in position by a retaining device including a spring holder 50 which is secured to a portion of the shoe web 22 near the adjusting link 36.

The spring holder 50 is made of a metal sheet of spring material by bending the sheet as shown in Fig. 2. As illustrated in Figs. 2 and 3, the holder 50 comprises: a fixing portion 54; a spring holding portion 58; and a connecting portion 56 extending from one end of the fixing portion 54 and terminating in the spring holding portion 58. The fixing portion 54 is bent to have a first substantially U-shaped structure which includes a first pair of side walls facing each other. The first U-shaped structure includes a projection 52 protruding from one of the first pair of side walls toward the other side wall. The spring holding portion 58 is also bent to have a second substantially U-shaped structure including a second pair of side walls. This second U-shaped structure is open in the same direction as the first U-shaped structure of the fixing portion 54.The projection 52 constitutes a part of engaging means for preventing the spring holder 50 from slidably moving beyond a preset point in a direction along the length of the return spring 48.

The projection 52 is formed of a substantially rectangular area of one of the first pair of side walls by pressing the rectangular area after two parallel slits are cut along the longer sides of the rectangle. The spring holder 50 is bent such that the center lines of their fixing, connecting and spring holding portions 54, 56 and 58 lie in the same plane.

The spring holder 50 thus constructed is mounted on the shoe web 22 and holds the return spring 48 in the following manner. As most clearly shown in Fig. 3, the fixing portion 54 is positioned on the shoe web 22 such that the first pair of side walls elastically grip a portion of the web on the upper and lower surfaces thereof. In this connection, the portion of the web 22 has a round recess 60 formed through the thickness of the web. The projection 52 on the lower wall of the fixing portion 54 is put into engagement with the recess 60 when the portion 54 is press-mounted on the web 22, so that there exist predetermined clearances in both directions across and along the length of the return spring 48 as viewed when the spring holder 50 is finally positioned. These clearances allow the fixing portion 54 to slide on the surface of the web 22 in the direction across the length of the return spring by a distance corresponding to the clearance in that direction (Fig. 3), and at the same time prevents the spring holder 50 from moving in the direction along the length of the return spring 48 more than the preset distance corresponding to the clearance in that direction. The spring holding portion 58 elastically holds the intermediate portion of the return spring 48 which is press-fitted between the second pair of side walls.

To assure secure gripping of the web 22 by the fixing portion 54 and firm holding of the return spring 48 by the spring holding portion 58, it is appreciated that a spacing between the first pair of side walls as measured near the open end of the fixing portion 54 before installation of the spring holder 50 be adapted to be smaller than the thickness of the web 22, and that a spacing between the second pair of side walls as measured near the open end of the spring holding portion 58 before said installation be adapted to be smaller than the spacing measured at any other position of the portion 58.It is also appreciated, for facilitating press-mounting of the fixing portion 54 and press-fitting of the intermediate portion of the return spring 48, that the ends of the first and second pairs of side walls are bent outwardly of the first and second U-shaped structure such that the said spacing increases in a direction from the position near the respective open ends toward the open ends.

As described above, the spring holder 50 in accordance with this invention is easily installed in position in the drum brake simply by pressmounting the fixing portion 54 on the web 22 and press-fitting the intermediate portion of the return spring 48 into the spring holding portion 58, without use of any fasteners such as screws, whereby the assembling procedure of the drum brake is considerably simplified.

There will be described the operation of the drum brake including the retaining device in the above embodiment of the invention.

When the pistons 40 and 42 are forced out by a pressure of brake fluid supplied into the wheel cylinder 38, the brake shoes 14 and 16 are moved outwardly away from each other and the linings 30 and 32 are forced against the inside surface of the brake drum 10, whereby a brake is applied to the brake drum 10 rotating with the vehicle wheel.

The U-shaped return spring 48 is expanded outwardly upon the outward movements of the brake shoes 14 and 1 6. As the brake fluid pressure in the wheel cylinder 38 is reduced, the pistons 40 and 42 are pushed into the cylinder 38 primarily by a biasing force of the return spring 48 acting on the pistons and the linings 30 and 32 are moved away from the inside surface of the brake drum 10 until the shoe webs 22 and 24 abut on the ends of the strut 46.

In the operation of the drum brake, the shoe web 22 and the intermediate portion of the return spring 48 move in the same direction, which means that there arises substantially no relative movement between the two members. This in turn means that the spring holder 50 and the return spring 48 will not be subject to forces which would possibly be created if there was a relative movement between the said two members.

Further, the return spring 48 is supported with its intermediate portion being held apart from the shoe webs 22 and 24 and the adjusting link 36, and prevented by the resilient connection portion 56 from hitting other members of the brake upon vibrations of the vehicle, whereby there will be no hitting sounds and no damage of the return spring due to the hitting actions. Although the projection 52 engages the recess 60 with the clearance left between them in the direction across the length of the return spring as previously indicated, there is no possibility that the fixing portion 54 moves back and forth and the projection 52 rattles within the recess 60 upon vibration of the drum brake.

This is attributed to the elastic force imparted by the fixing portion 54 to the upper and lower surfaces of the web 22. It is noted that the engagement of the projection 52 with the recess 60 prevents possible removal of the spring holder 50 from the web 22 and the return spring 48. In other words, the engaging means consisting of the projection 52 and the recess 60 serves to limit the sliding movements of the fixing portion 54 in the direction across the length of the return spring 48.

As the linings 30 and 32 are worn during repeated braking actions, the brake shoes 1 4 and 1 6 are accordingly displaced outwardly, and the shoe web 22 is moved with respect to the intermediate portion of the return spring 48 held by the spring holder 50. In this instance, the fixing portion 54 slides on the surface of the web 22 in the direction acrosss the length of the return spring 48 to the extent that the previously described clearance is left. Thus, the relative movement between the return spring 4 and the shoe web 22 will neither cause the spring holder 50 to be subject to undesired stress, nor prevent the return spring 48 from taking natural biasing actions.Thus, the retaining device of the invention will not suffer unfavourable variation in the biasing force and direction of the U-shaped spring 48 due to relative movement between the web 22 and the return spring 48 caused by progressive wearing of the linings 30 and 32. In other words, the relative movement is absorbed by the sliding movement of the fixing portion 52 within the range corresponding to the predetermined clearance B.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form may be charged in details of construction.

For example, the engaging means which is constituted by the projection 52 and the recess 60 in the previous embodiment, may be replaced by a pair of protrusions such as a pair of metal pieces 62 shown in Fig. 4 which are fused to the surface of the intermediate portion of the return spring 48 at which the spring is supported. Such protrusions are spaced along the length of the return spring 48 such that there exits a predetermined clearance along said length between each of the projections and the side edge of the spring holding portion 58, so that the spring holder 50 will not slide along the intermediate portion beyond a preset point which is determined by the clearance provided.

It is possible to apply the present invention to drum brakes of other types than previously referred to. For another example of modification, the spring holder 50 may be mounted on the shoe web 24.

As a further example, the recess 60 may be an elongated hole 64 extending in the direction across the length of the return spring 48 as shown in Fig. 5. These recess 60 and hole 64 need not be formed through the thickness of the web.

Other modifications and variations may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A retaining device for holding in position an intermediate portion of a substantially U-shaped return spring for use in a drum brake wherein the return spring engages a pair of brake shoes each having a web and facing the inside surface of a brake drum and biases the brake shoes away from said inside surface, said retaining device comprising a spring holder made of an elastic sheet material which includes a fixing portion and a spring holding portion elastically holding said intermediate portion of the return spring, characterized in that said retaining device comprises an engaging device which prevents said spring holder from slidably moving more than a preset distance in a direction along the length of said return spring, and that said fixing portion is bent to have a first substantially U-shaped structure including a first pair of side walls facing each other, said fixing portion elastically gripping a portion of said web of one of said pair of brake shoes and being slidable on the surface of said web in a direction across the length of said U-shaped return spring.

2. A retaining device as recited irí claim 1, wherein said engaging device comprises a recess formed in said portion of the web, and a projection protruding from one of said first pair of side walls of the fixing portion and engaging said recess with predetermined clearances in said directions across and along the length of said return spring, respectively, said predetermined clearance along the length of the return spring corresponding to said preset distance.

3. A retaining device as recited in claim 2, wherein said projection is formed of a substantially rectangular area of said one of said first pair of side walls, said area being defined by two parallel slits and pressed out to form said projection.

4. A retaining device as recited in claim 2, wherein said recess is a hole formed through the thickness of said portion of the web.

5. A retaining device as recited in claim 4, wherein said hole is an elongated hole extending in the direction across the length of said return spring.

6. A retaining device as recited in claim 1, wherein said engaging device comprises a pair of protrusions secured to the surface of said intermediate portion of the return spring and spaced along the length thereof such that there exits a predetermined clearance along said length between each of said projections and the side edge of said spring holding portion of the spring holder, said predetermined clearance corresponding to said preset distance.

7. A retaining device as recited in claim 6, wherein said pair of protrusions are a pair of metal pieces fused to the surface of said intermediate portion.

8. A retaining device as recited in claim 1, wherein said spring holding portion of the spring holder is bent to have a second substantially U-shaped structure including a second pair of side walls.

9. A retaining device as recited in claim 8, wherein said first and second substantially Ushaped structures are both open in substantially the same directions such that the elastic holding of said intermediate portion by said spring holding portion is effected simultaneously with the elastic gripping of said web by said fixing portion upon mounting of said spring holder.

10. A retaining device as recited in claim 8, wherein a spacing between said second pair of side walls as measured at a position near the open end of said second substantially U-shaped structure before installation of the spring holder, is smaller than the spacing measured at any other position of the same structure, and the ends of said second pair of walls are bent outwardly such that said spacing increases in a direction from said position near said open end toward said open end.

11. A retaining device as recited in claim 1, wherein a spacing between said first pair of side walls as measured at a position near the open end of said first substantially U-shaped structure before mounting of the same on said portion of the web, is smaller than the thickness of said portion of the web, and the ends of said first pair of walls are bent outwardly such that said spacing increases in a direction from said position near said open end toward said open end.

1 2. A retaining device as recited in claim 1, wherein the center lines of said fixing portion and spring holding portion of said spring holder lie in the same plane.

13. A drum brake comprising a substantially U-shaped return spring engaging a pair of brake shoes each having a web and facing the wide surface of a brake drum and biasing the brake shoes away from said wide surface and a retaining device for said return spring in accordance with any one of the preceding claims.

1 4. A retaining device for holding in position an intermediate portion of a substantially U-shaped return spring for use in a drum brake, substantially as hereinbefore described with reference to Figures 1, 2 and 3 or Figures 1 and 4 or Figures 1, 2 and 5.