GB2143916A

GB2143916A - Disc brake

Info

Publication number: GB2143916A
Application number: GB08415478A
Authority: GB
Inventors: Masahito Okajima
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1983-06-20
Filing date: 1984-06-18
Publication date: 1985-02-20
Also published as: GB8415478D0; FR2548312A1; JPS602030U; IT8467632A1; IT1178976B; DE3422878A1; IT8467632A0

Abstract

Such brake includes a caliper straddling a part of the outer circumference of rotatable disc 10 and being displaceable in the direction parallel to the axis of the disc, said caliper having a pair of portions 13a, 13b spaced from each other in the direction of the circumference of the disc 10 and adapted to engage with a back plate 15 of a friction pad 14 for pushing the friction pad against one surface of the disc - the face of the back plate of the friction pad to be engaged with the portions 13a, 13b is inclined relative to the surface of the disc in the circumferential direction. This is said to reduce/prevent squeal. Various embodiments are disclosed e.g. in Fig. 2 the back plate 15 has symmetrically inclined face portions 15a, 15b and portions 13a, 13b are correspondingly inclined - such correspondence is not essential (Figs. 4,9,10). The back plate may be constituted of two wedge shaped plate members bonded to each other (Fig. 5) with a heat insulating or vibration absorbing material (20, 21, Fig. 6) therebetween. Fig. 7 shows an arrangement of another (inner) friction pad 14' with a tapered back plate 23 while (outer) pad 14 also has a tapered back plate 22. Fig. 8 shows alternative arrangement of back plates of two pads 14, 14'. <IMAGE>

Description

SPECIFICATION Disc brake This invention relates to a disc brake and, more particularly to an improvement for preventing squeal phenomenon in the disc brake.

In applying the brakes, there oftenly causes socalled squeal phenomenon. Such squeal phenomenon is attributed to frictional vibrations in mutually frictionally engaging members such as a brake disc and friction pads, which vibrate in self-excited manner and the vibrations are transmitted to associated members such as a caliper and a carrier thereby generating high-pitched noisy sounds usually called as brake squeal. Such squeal phenomenon is caused of a complicated vibration system, it is very difficult to find the solution.

Various proposals have been made with respect to indivisual constituting members of the disc brake for suppressing the squeal phenomenon experimentarily. The present invention aims to provide a disc brake having an improved friction pad.

There is known a disc brake of the kind comprising a carrier which is adapted to be fined to a non-rotatable part of a vehicle, a caliper which is mounted on the carrier to displace in the direction of the axis of a rotatable disc and straddles a part of the outer circumference of the disc, a pair of friction pads disposed on the opposite surface of the disc, a pushing mechanism such as a hydraulic cylinder and piston mechanism incorporated in the caliper for pushing directly one of the friction pads (inner friction pad) against one surface of the disc. The caliper has a pair of pawl portions which are spaced in the direction of the circumference of the disc and engage with a back plate of the other friction pad (an outer friction pad) to apply the same against the other surface of the disc when the caliper is displaced by the reaction force of the pushing mechanism.

In the disc brake of the kind aforementioned, the outer friction pad being pushed by the pawl portions of the caliper is assumed to undergo a primary mode of vibrations as shown in chain lines and broken lines as shown in Fig. 11 with nodes being located at abutting points between the back plate of the friction pad and the pawl portions 1 and 1 of the caliper and a loop being located at the circumferentially intermediate position between the pawl portions.

In this respect, face portions B and B of the back plate of the friction pad to be engaged with the pawl portions are in parallel to a surface A of the disc. Accordingly, the pushing force F transmitted from the pawl portions to the back plate is orthogonal to the face A of the disc and, any transverse force is not generated, thus, it is not effective to damp the vibrations.

The present invention has been made as a result of studying the pushing force transmitted from the pawl portions to the friction pad from the standpoints of dynamics in relation to the face of the back plate of the friction pad, and an object of the invention is to provide a disc brake which enables to prevent or damp the vibrations of the friction pad by utilizing the pushing force transmitted from the pawl portions thereby restricting or preventing the squeal phenomenon.

The disc brake according to the invention has a constitution featured in that the face of the back plate of the friction pad to be engaged with pawl portions of the caliper is inclined relative to the surface of the disc in the circumferential direction.

With this constitutional feature, the pushing force F is counteracted by a reaction force R which is perpendicular to the inclined face of the back plate and a component force f which acts along the inclined face of the back plate.

The component force f acts generally in the wave length direction of the vibrations of the back plate and acts to resist the relative displacement between the pawl portions and the back plate as a frictional force therebetween.

In other words, the component force f acting in the wave length direction of vibrations of the back plate and in one circumferential direction acts as frictional force in a repeated positive and negative sense. Thus a dynamic unbalance is caused between the pawl portions and the back plate in the wave length direction of vibrations of the back plate which serves to improve damping characteristics of the vibrations and to prevent or decrease the squeal phenomenon.

Further objects and advantages of the invention will become apparent from the following detailed descriptions taken with reference to accompanying drawings which exemplifies some preferred embodiments of the invention, in which: Fig. 1 is an end view of a disc brake according to the invention; Fig. 2 through Fig.

8 are partial sectional views showing discs, pawl portions of calipers and friction pads having inclined back plates according to preferred embodiments of the invention; Figs. 9 and 10 are partial sectional views showing further modified form of the invention; and Fig. 11 is a sectional view similar to Figs. 2 through 8 but showing vibrations of a friction pad according to prior art disc brake.

Fig. 1 schematically shows a disc brake of the kind aforementioned, which comprises a carrier 11 adapted to be secured to a nonrotatable part of a vehicle (not shown) by utilizing two bolts (not shown) passing respectively threaded holes shown in Fig. 1, and a caliper 1 2 mounted on the carrier 11 to slidably displace in the direction parallel to the axis of a rotatable disc 10 or in the direction perpendicular to the paper of the drawing.

The caliper 1 2 straddles a part of the outer circumference of the disc 10 and has a pair of pawl portions 1 3a and 1 3b which are spaced in the circumferential direction of the disc 1 0.

Usually, the caliper 1 2 is slidably mounted on a pair of pins (not shown) which are secured to the carrier 11. A pair of friction pads are disposed on opposite surfaces of the disc 10 although only one 1 4 of which is shown in Fig. 1. The caliper 1 2 is incorporated therein a pushing mechanism such as hydraulic cylinder and piston device for pushing one of the friction pads toward the disc 10. The reaction force thereof displaces the caliper 1 2 in the opposite direction so that the friction pad 14 is pushed against adjacent surface of the disc 10 through pawl portions 1 3a and 1 3b.

Fig. 2 shows a first embodiment of the invention, wherein the friction pad 1 4 has a rigid back plate 1 5 which is bent at circumferentially central portion 1 sic as viewed in the direction of a radius of the disc 10. Thus, there are formed generally symmetrically inclined face portions 1 spa and 1 sub for engaging with pawl portions 1 3a and 1 3b of the caliper 1 2 respectively. Thus, face portions 1 spa and 1 sub of the back plate 15 which engage with pawl portions 1 3a and 1 3b respectively, are inclined relative to surface A of the disc 10 in the circumferential direction of the disc 10.In the embodiment, the faces of pawl portions 1 3a and 1 3b for engaging with face portions 1 spa and 1 sub are correspondingly inclined as clearly shown in Fig. 2.

The pushing force applied from the caliper 1 2 to the friction pad 1 4 is orthogonal to the face A of the disc 10 as shown as forces F and F in the drawing which induce reaction forces R and R which are orthogonal to mutually engaging surfaces between pawl portions 1 3a and 1 3b and face portions 1 spa and 1 sub, and component forces f and f acting along mutually engaging surfaces. The component forces f and f act generally in circumferentially opposite directions.The frictional force acting between the disc 10 and the friction pad 14 in applying the brakes tends to induce selfexcited vibrations in the back plate 1 5 which have the wave length directions along the circumference of the disc 10 and the amplitude directions in the vertical directions in Fig.

2. Such self-excited vibrations generate relatively displacing forces between the back plate 1 5 and pawl portions 1 3a and 1 3b in the transverse directions as viewed in Fig. 2. The component forces f act effectively on the relatively displacing forces in repeated positive and negative sense, thereby generating dynamic unbalance in the wave length direction of vibrations of the back plate 1 5 between the back plate 15 and pawl portions 1 3a and 1 3b. Whereby, vibrations of the back plate 1 5 can effectively be restricted and the squeal phenomenon is reduced substantially.

Fig. 3 shows a second embodiment, wherein a back plate 1 6 of the friction pad 14 is bent in the direction opposite to the back plate 15 of Fig. 2. The component forces f and fin Fig. 3 act generally in the directions opposing the each other. The function and operation of the second embodiment are simi lar to the first embodiment.

Fig. 4 shows a third embodiment, wherein a back plate 1 7 of the friction pad 1 4 is formed to have the configuration similar to the back plate 1 6 in the second embodiment, however, engaging surfaces B of the pawl portions 1 3a and 1 3b are not inclined correspondingly and are general in parallel to the surface A of the disc 10. Thus, the pawl portions 1 3a and 1 3b engage at their circumferentially inner ends with the back plate 1 7.

The directions of reaction forces R and component forces f are generally similar to Fig. 3.

As compared with Fig. 3, the points of actions of the pressing forces F and reaction forces R are displaced circumferentially in approaching directions to define a distance I as shown in Fig. 4, the amplitude of vibrations can be reduced which is effective in reducing squeal sounds. Further, by approaching the pushing forces F with each other in the circumferential direction it is possible to make relatively uniform distribution of the surface pressure on the friction pad and, hence, to improve the braking performance such as the fading resistance, the partial-wear resistance and the like.

Fig. 5 shows a fourth embodiment, wherein a back metal 1 8 of the friction pad 1 4 is constituted of two wedge shaped plate members bonded to each other. The thickness of the plate members varies in the direction of the circumference of the disc 10. The relationship between the back plate 1 8 and the pawl portions 1 3a and 1 3b is generally similar to the first embodiment.

Fig. 6 shows a fifth embodiment generally similar to Fig. 3 but having a back plate 1 9 constituted of two wedge shaped plate members which are bonded to each other interposing therebetween a heat insulating material 20 or a vibration absorbing material 21.

The back paltes 1 8 and 1 9 shown in Figs.

5 and 6 act similarly to back plates 1 5 and 1 6 of Figs. 2 and 3 with respect to circumferentially inclined surfaces. Moreover, it is possible to change the rigidity or the mass of portions of the back plate engaging with respective pawl portions 1 3a and 1 3b from each other, which is effective to reduce or damp the vibrations. It will be understood that such effects can be enhanced by changing the dimension or the material of these two plate members from each other.

Further, since the two plate members are joined together along a surface which is inclined relative to the direction orthogonal to the vibration transmitting direction, it is fur ther possible to reduce the transmission of the vibrations and to obtain additional damping effects.

Fig. 7 shows a sixth embodiment, wherein a back plate 22 of the friction pad 1 4 is tapered in the direction of the circumference of the disc 10 with the thickness t1 in one circumferential end differs from the thickness t2 in the other circumferential end as shown in Fig. 7. The difference in the thickness of the back plate in the circumferential direction or in the amplitude-wise direction of vibrations of the back plate is effective to generate a damp ing function. In this case, it is preferable to change the thickness of a back plate 23 of another friction pad 14', in the circumferential direction as shown in Fig. 7.In this connection, the friction material of the outer friction pad 1 4 usually wears much at the downstream side or the outlet side in the rotational direction of the disc as compared with the upstream or inlet side and, the friction material of the inner friction pad 14' wears much at the upstream or the inlet side of the rotational direction, accordingly, the friction pads 14 and 14' in Fig. 7 are preferably arranged as shown in the drawing wherein the rotational direction of the disc 10 is assumed as the rightward direction.

Fig. 8 shows a friction pad 14 having a back plate essentially similar to the back plate 1 5 of Fig. 3. But the back plate of this outer friction pad 1 4 has the thickness t3 which is different from the thickness t4 of a back plate 24 of the inner friction pad 14'. As a result, in addition to the effect of circumferentially inclined surface of the back plate of the outer friction pad 14, the difference in the thickness t3 and t4 of back plates of friction pads 1 4 and 14' will cause unbalanced vibrations on the friction pads 1 4 and 14' thereby providing further a damping force.

Figs. 9 and 10 show modified configurations of pawl portions applicable respectively to embodiments of Figs. 2, 5 and 7 and to embodiments of Figs. 3, 6 and 8 so as to obtain the effects similar to the embodiment of Fig. 4.

As described heretofore in detail, the present invention can induce component forces f which are effective to prevent or reduce vibrations of the friction pad and to improve damping characteristics, whereby the squeal phenomenon is restained or prevented.

Claims

1. A disc brake including a caliper straddling a part of the outer circumference of a rotatable disc and being displaceable in the direction parallel to the axis of the disc, said caliper having a pair of pawl portions which are spaced from each other in the direction of the circumference of the disc and adapted to engage with a back plate of a friction pad for pushing the friction pad against one surface of the disc, characterized in that the face of said back plate to be engaged with the pawl portions of the caliper is inclined relative to said surface of the disc in the circumferential direction of the disc.

2. A disc brake according to Claim 1 wherein a portion of the face of said back plate to be engaged with one of the pawl portions is inclined relative to another portion of the face of said back plate to be engaged with the other of the pawl portions.

3. A disc brake according to Claim 2 wherein said portions of the face of the back plate are inclined symmetrically with each other.

4.-A disc brake according to Claim 1 wherein the back plate has a generally Vshaped cross section with the circumferentially central portion thereof approaching toward the disc.

5. A disc brake according to Claim 1 wherein the back plate has a generally inverted V-shaped cross section with the circumferentially opposite end portions thereof approaching toward the disc.

6. A disc brake according to Claim 1 wherein the surface of said pawl portions engaging with the back plate are inclined correspondingly to the back plate.

7. A disc brake according to Claim 5 wherein the surface of said pawl portions engaging with the back plate are in parallel with the surface of the disc.

8. A disc brake according to Claim 1 wherein the back plate consisting of two or more mutually overlapping plate members with the thickness thereof changing in the direction of the circumference of the disc.

9. A disc brake according to Claim 1 wherein the thickness of the back plate changing in the direction of the circumference of the disc.

10. A disc brake substantially as hereinbefore described with reference to, and as illustrated in, Fig. 1; or Fig. 2; or Fig. 3; or Fig. 4; or Fig. 5, or Fig. 6; or Fig. 7; or Fig.

8; or Fig. 9 and 10 of the accompanying drawings.