EP1714047A2

EP1714047A2 - Brake shoe hold down clip

Info

Publication number: EP1714047A2
Application number: EP05702200A
Authority: EP
Inventors: Marco Monopoli
Original assignee: Automotive Products Italia SV SRL
Current assignee: Automotive Products Italia SV SRL
Priority date: 2004-02-12
Filing date: 2005-01-07
Publication date: 2006-10-25
Also published as: CN1918397A; WO2005085668A3; GB0403091D0; JP2007522413A; GB2424459A; WO2005085668A2; GB2424459B; GB0615024D0

Abstract

A brake shoe hold down clip (23,24) is shaped so as to provide a non-linear spring action to resist movements of the brake shoe (11,12) away from the backplate (13), the hold down clip having a lower spring rate to resist small movements of the brake shoe away from the backplate and a higher spring rate which becomes operative in response to higher movements of the brake shoe away from the backplate. The clip includes a spring loop (33,34) with an end portion (35,36) of the loop designed to contact the brake shoe to provide the lower spring rate and portions (37,38) of the loop further from the end portion being designed to contact the brake shoe to make the loop stiffer and thus provide the higher rate in response to larger movements of the brake shoe (11,12) away from the backplate (13).

Description

BRAKE SHOE HOLD DOWN CLIP

This invention relates to brake shoe hold down clips for use in holding down a brake shoe relative to an associated drum brake backplate. Such hold down clips are conventionally used between the head of a hold down pin and the web of the associated brake shoe, the other end of the hold down pin engaging the backplate of the drum brake.

Such hold down clips are well known and are shown for example in British patents nos. 2000561 and 2320302.

Whilst such hold down clips perform generally satisfactorily problems can be experienced in controlling the movement of the brake shoe away from the backplate in a manner which can deal both with normal brake operation and also the extreme braking loads which can occur in certain dynamic conditions.

It is an object of the present invention to provide an improved form of hold down clip which overcomes or at least partially mitigates the above difficulties.

Thus according to the present invention there is provided a brake shoe hold down clip which is shaped so as to provide a non-linear spring action to resist movements of the brake shoe away from the backplate, the hold down clip having a lower spring rate to resist small movements of the brake shoe away from the backplate and a higher spring rate which becomes operative in response to higher movements of the brake shoe away from the backplate.

As will be appreciated such a non-linear spring rate enables the lower spring rate to be designed to resist movements of the brake shoe away from the backplate during normal operation of the brake and a higher spring rate which comes into operation when certain high dynamic loads occur such as when the brake shoe is actuated to provide a handbrake function and service brake function simultaneously or when violent braking occurs. Thus a more appropriate level of control is provide throughout the entire operating range of the brake shoe. Also, because of the lower spring rate which resists movement of the brake shoe away from the backplate during normal operation of the brake, the friction between the brake shoe and the backplate is lower and thus less of the braking effort is wasted in overcoming this friction force when the brake is applied. The higher spring rate, with consequently higher frictional forces, only comes into operation when necessary.

This non-linear spring rate is achieved as a result of the shape of the hold down clip.

In a preferred construction the hold down clip includes a spring loop with an end portion of the loop designed to contact the brake shoe to provide the lower spring rate and portions of the loop further from the end portion being designed to contact the brake shoe to make the loop stiffer and thus provide the higher rate in response to larger movements of the brake shoe away from the backplate.

In a preferred construction the clip comprises a central fastening portion which engages the head of the associated hold down pin and two outer spring loop portions extending one from each end of the central fastening portion, these loop portions extending towards and contacting the associated brake shoe to normally hold the fastening portion in spaced relation thereto, the spring portions being arranged to deform if the brake shoe tends to move away from the associated backplate.

Conveniently the free ends of the spring loops normally contact the brake shoe and provide the lower spring rate for small movements of the brake shoe away from the backplate, an elbow portion of each spring loop being arranged to contact the brake shoe at higher movements of the brake shoe away from the backplate to make each loop stiffer thus providing the higher spring rate.

Preferably the hold down clip is arranged to limit the possible movement of the brake shoe away from the backplate. This may be done by arranging an abutment on the clip to engage the shoe web so that the hold down clip effectively becomes solid and prevents further movement of the brake shoe away from the backplate or two parts of the clip itself may come into contact to render the clip effectively solid thus limiting the movement of the brake shoe away from the backplate.

For example, flanges formed on the central fastening portion of the hold down clip may be arranged to contact a brake shoe web to limit movement of the brake shoe away from the backplate. Alternatively, flanges on the free ends of the spring loops may be arranged to contact either the central fastening portion of the hold down clip or overlying inclined portions of each respective spring loop adjacent the attachment of the loop to the central fastening portion.

The hold down clip preferably includes a slot which receives the head of the associated hold down pin, the slot having a surrounding contact area which may be conical, spherical or rectangular and which contacts a conical, spherical or rectangular co-operating portion of the head of the associated hold down pin.

The invention also provides a brake shoe hold down clip which comprises a central fastening portion which engages the head of the associated hold down pin and two outer spring portions which extend towards and contact the associated brake shoe to normally hold the fastening portion in spaced relation thereto, the spring portions being arranged to deform if the brake shoe tends to move away from the associated backplate.

The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 is a plan view of a drum brake using a hold down clip in accordance with the present invention; Figures 2 and 3 show sections on line A-A of figure 1 showing the hold d its low spring rate and higher spring rate positions respectively;

Figures 4 and 5 show the hold down clip of figures 2 and 3 on a larger scale and in its lower and higher rate positions respectively;

Figures 6 and 7 show plan and perspective views of the clip of figure 4, and

Figures 8 to 11 show views of alternative forms of hold down clip embodying the present invention.

Referring to figures 1 to 3 there is shown a drum brake 10 having a pair of brake shoes 11 and 12 mounted on a backplate 13. The brake shoes react against a fixed abutment 14 which contacts the lower ends 11 a and 12a of the shoes and a conventional wheel cylinder 15 mounted on backplate 13 is positioned between the upper ends 11b and 12b of the shoes.

As is conventional return springs 16 and 17 act between the brake shoes to retract the brake shoes when the brake is not actuated. An auto adjusting strut 18 also acts between the brake shoes to automatically adjust the clearance between the shoes and the co-operating drum (not shown) when the shoes are in their brake released position thus maintaining the effectiveness of the brake as the brake shoes wear. A suitable form of auto adjusting strut are described in the Applicant's patent EP0538909.

In addition to the brake being hydraulically operated by wheel cylinder 15, a hand brake lever 19 is also pivoted on the underside of brake shoe 12 by pivot 20. As is conventional a hand brake operating cable (not shown) is attached to the lower end 19a of lever 19 to pivot the lever 19 in the direction of arrow B causing the upper portion 19b of the hand brake lever to engage the auto adjusting strut 18 thus forcing the strut to the right as indicated by arrow C and hence bringing the shoe 11 into contact with the associated brake drum and by reaction also causing 12 to engage the drum.

Thus far described the drum brake is conventional in construction.

According to the present invention the brake shoes 11 and 12 are held down onto the back plate 13 by hold down pins 21 and 22 respectively with hold down clips 23 and 24 positioned between the head 21a,22a of each hold down pin and the web 25 and 26 of each brake shoe. This configuration can be most easily seen from figure 2 which also shows that the other end 21 b,22b of each old down pin engages under the backplate 13.

As is clearly shown in figures 4 to 7 the clip 24 (which is identical to the clip 23) has a central fastening portion 30 with a slot 31 which receives the head 22a of the associated hold down pin 22 and includes a part spherical seating portion 32 which co-operates with a part spherical underside of head 22a. Extending from each end of the central fastening portion 30 are spring loop portions 33 and 34 respectively which extend round towards and into contact with the web portion 26 of the associated brake shoe 12. In the hold down clip configuration shown in figures 4 to 7 during normal operation of the brake the free ends 35 and 36 of the spring loops contact the associated brake shoe web (see figures 2 and 4) so that the spring loops 33 and 34 operate with a lower spring rate when resisting movements of the brake shoe away from the backplate. Each spring loop 33,34 also includes an elbow portion 37, 38 respectively which comes into contact with the associated brake shoe 12 (as shown in figures 3 and 5) at larger displacements of the brake shoe away from the backplate. This contact of the elbows 37 and 38 with the brake shoe causes the loops 33 and 34 to provide a higher spring rate. This higher spring rate is particularly effective at resisting movement of the brake shoe away from backplate in certain higher load dynamic conditions such as when the brake shoe is actuated to provide a handbrake function and service brake function simultaneously or when violent braking occurs. Each spring loop is also provided at its free end with a flange 39 and 40 which, at high movements of the brake shoe away from the backplate (see figure 4), is arranged to contact the overlying underside portion 41 and 42 respectively of the central fastening portion 30 to provide a still higher spring rate when the clip is in effect rendered solid and prevents any further movement of the brake shoe away from the backplate.

A further advantage of the clip of the present invention is that the corners 23a and 24a of the clips (see figure 1 ) abut the underside of the tables 11 a and 12a of the shoes thus preventing the clips jutting out beyond the associated shoes and coming into contact with any components which are rotating (e.g. the mounting studs for the associated wheel).

Figures 8, 9, 10 and 11 show further details of alternative forms of hold down clip.

In figure 8 the hold down clip has a central fastening portion 50 which again includes a curved part spherical seating 52 and a slot 51. The clip shown in figure 8 does not have the elbows 37 and 38 shown in the clip of figures 4 to 7 but has generally linear sections 57 and 58 towards the ends of the loops 53 and 54 respectively of the clip. The clip may be arranged so that under normal load conditions and only the free end portions 55 and 56 of the loops contact the associated brake shoe and as the- brake shoe moves away from the backplate progressively more of the linear portion 57 , 58 of each respective loop comes into contact with the brake shoe thus increasing the stiffness of the clip. The movements of the brake shoe away from the backplate may be limited by flanges 59 and 60 which extend from central fastening portion 50 and are designed to contact the web of the associated brake shoe if the shoe is deflected sufficiently far away from the backplate thus rendering the clip effectively solid.

In the clip arrangement shown in figure 9 the central fastening portion 70 has extending therefrom loops 73 and 74 respectively with the free ends of the loops being formed as bifurcated arms 75 and 76 respectively each bifurcated arm having a flange 79,80 respectively which ultimately contacts the underside of the fastening portion 70 to render the clip solid thus limiting movement of the brake shoe away from the backplate. As will be appreciated, the clip shown in figure 9 is again arranged under normal brake operating conditions to only contact the associated brake shoe adjacent the free ends of the arms 75 and 76 and, as the brake shoe tends to move away from the backplate the contact point of the arms moves further away from their free ends thus increasing the stiffness on the spring loops 73 and 74. The clip may also be designed to allow the flanges 79,80 to contact each other to further increase the stiffness of the clip before the clip goes effectively solid.

Figure 10 shows a clip configuration in which the length of the spring loops 73 and 74 (whether bifurcated as shown in figure 9 or not) can be of variable length so that the flanges 79 and 80 may occupy the positions 79a, 79b, 79c and 80a, 80b, 80c. As will be appreciated, if the flanges occupy the positions 79a,80a they will make square abutment with the underside of the central fastening portion 70 whereas if the flanges occupy the position 80b they will tend to contact the bend sections 70a of the central fastening portion 70. When in the outermost position 79c,80c the flanges may not contact the remainder of the clip at all and thus other methods of limiting total movement of the brake shoe away from the backplate may be employed as previously described with reference to the flanges 59 and 60 above. By selecting the position of flanges 79 and 80 the variation in the overall spring rate of the clip with deflection can be adjusted to give the desired characteristics.

In a further alternative form of hold down clip shown in figure 11 the clip has a central fastening portion 90 which has a slot 91 and a flange 92 turned down from one edge of the central portion 90. This flange combined with the large upturned flanges 99 and 100 at the free ends of the loops 93 and 94 provides a solid stop to limit the movement of the associated brake shoe away from the backplate with the flange 92 contacting the associated brake shoe web and the flanges 99 and 100 contacting the underside of the central fastening portion 90. The clip arrangements of figures 8 to 11 may also include the definite ell configuration shown, for example, at 37 and 38 in figure 7.

Figure 12 shows a further form of hold down clip in which the central fastening portion 100 has a generally rectangular slot 101 through which a conventional T-shaped head portion 22c of a hold down pin 22 may be inserted. The hold down pin head 22c is then rotated relative to slot 101 through 90 degrees so that the T-shaped head drops into the rectangular depression 102. The remainder of the hold down clip is similar in shape to clip 24 with loops 103 and 104, elbows 107 and 108 and flanges 109 and 110.

As will be appreciated the hold down clip arrangements described above with their non-linear spring characteristics provide a simple but effective solution to the problem of matching the spring characteristic of the hold down clip to the varying operating conditions of the brake. The lower spring rate of the hold down clip is set at a level to provide the necessary control of the movement of the brake shoe during normal operation of the brake and the higher spring rate controls the much higher levels of dynamic force which may be applied to the brake shoe from time to time. The design of the clip to effectively render the clip solid after a pre-determined amount of movement of the brake shoe and the backplate provides even closer control of the movement of the brake shoe.

The hold down clip arrangements described above are suitable for use in all types of drum brake whether hydraulically and/or mechanically or electrically operated.

The general double loop clip configuration described above where the clip loops extend from opposite ends of the central fastening portion can be used in a clip without the non-linear spring characteristic feature. For example, in the arrangement shown in figure 8 the linear sections 57 and 58 may be arranged to make full face contact with the associated brake shoe at all times so that a single spring rate is provided by loop 53 and 54 for all movements of the brake shoe away from the backplate. Similarly in the arrangements shown in figures 9, 10 and 11 the portions of the clips corresponding to the linear sections 57 and 58 of figure 8 ma] designed to make full face contact at all times with the associated brake shoe to provide a single spring rate.

Claims

1. A brake shoe hold down clip which is shaped so as to provide a non-linear spring action to resist movements of the brake shoe away from the backplate, the hold down clip having a lower spring rate to resist small movements of the brake shoe away from the backplate and a higher spring rate which becomes operative in response to higher movements of the brake shoe away from the backplate.

2. A clip according to claim 1 in which the clip includes a spring loop with an end portion of the loop designed to contact the brake shoe to provide the lower spring rate and portions of the loop further from the end portion being designed to contact the brake shoe to make the loop stiffer and thus provide the higher rate in response to larger movements of the brake shoe away from the backplate.

3. A clip according to claim 2 in which the clip comprises a central fastening portion which engages the head of the associated hold down pin and two outer spring loop portions extending one from each end of the central fastening portion, these loop portions extending towards and contacting the associated brake shoe to normally hold the fastening portion in spaced relation thereto, the spring portions being arranged to deform if the brake shoe tends to move away from the associated backplate.

4. A brake shoe hold down clip comprising a central fastening portion which engages the head of the associated hold down pin and two outer spring portions which extend towards and contact the associated brake shoe to normally hold the fastening portion in spaced relation thereto, the spring portions being arranged to deform if the brake shoe tends to move away from the associated backplate.

5. A clip according to claim 3 or 4 in which the free ends of the sprin normally contact the brake shoe and provide the lower spring rate for small movements of the brake shoe away from the backplate, an elbow portion of each spring loop being arranged to contact the brake shoe at higher movements of the brake shoe away from the backplate to make each loop stiffer thus providing the higher spring rate.

6. A clip according to any one of claims 1 to 5 in which the hold down clip is arranged to limit the possible movement of the brake shoe away from the backplate.

7. A clip according to claim 6 in which an abutment on the clip is arranged to engage the shoe web so that the clip effectively becomes solid and prevents further movement of the brake shoe away from the backplate.

8. A clip according to claim 7 in which flanges formed on the central fastening of the clip contact the brake shoe web to limit movement of the brake shoe away from the backplate.

9. A clip according to claim 6 in which two parts of the clip come into contact to render the clip effectively solid thus limiting the movement of the brake shoe away from the backplate.

10. A clip according to claim 9 in which flanges on the free ends of the spring loops are arranged to contact either the central fastening portion of the hold down clip or overlying inclined portions of each respective spring loop adjacent the attachment of the loop to the central fastening portion.

11. A clip according to any one of claims 1 to 10 which includes a slot which receives the head of the associated hold down pin, the slot having a surrounding contact area which may be conical, spherical or rectangular and which contacts a conical, spherical or rectangular co-operating pc head of the associated hold down pin.

12. A clip according to any one of claims 1 to 10 in which the spring loop is arranged to contact the underside of the table of the associated brake shoe to prevent rotation of the clip to a position where the clip juts out beyond the associated shoe.

13. A drum brake having a brake shoe held down against a backplate by a hold down clip according to any one of claims 1 to 12.

14. A brake shoe hold down clip constructed and arranged substantially as hereinbefore described with reference to and as shown in figures 1 to 7, or 8, or 9, or 10, or 11 , or 12 of the accompanying drawings.