GB2080454A - Pad for a disc brake - Google Patents

Abstract

In a disc brake provided with a floating caliper 1 having a cylinder 3 with a piston 2 fitted thereinto and a reactionary portion 4 a pad 6 consists of a friction member 11 and a backing plate 12 for supporting the former, the backing plate being provided with a plurality of through-bores 14 formed only in an area beyond an arc C described with a center coincident with the axis of the disc rotor 5 and passing through the center line O of the piston 2. This arrangement is said to render more uniform the pressure on the friction surface of the pad to eliminate braking effect deterioration due to the elastic deformation of the caliper, the through-bore area being susceptible to compressive deformation. The friction member is molded onto the backing plate so as to be flowed into the plurality of through-bores to firmly stick to the latter. Both the pads 6, 7 may have this construction. <IMAGE>

Description

SPECIFICATION A pad for a disc brake This invention relates to a pad used for a disc brake of floating caliper type.

A disc brake of floating caliper type is one wherein a caliper provided with a cylinder having a piston slidably fitted therein and a reactionary portion disposed in opposition to the former is movably retained in a parallel direction to the axis of a disc rotor by a retaining member.

Due to a reactionary force caused by urging an inner pad by the piston, owing to hydraulic pressure applied to the cylinder, on one surface of the disc rotor the caliper is moved for in turn causing the reactionary portion to urge an outer pad on the other surface of the disc rotor.

It is conventionally known that a fading phenomenon is liable to occur in this type disc brake, and particularly it is remarkable when the brake is applied while the disc rotor is in high speed rotation, which will be hereinafter called as high speed braking time.

The inventors of this invention pursued to find out causes of this fading phenomenon with the aid of other researchers to reach a conclusion that ununiform or uneven contact between the pad and the disc rotor caused by an elastic deformation of the caliper was an important factor. In the high speed braking time large hydraulic power applied to the cylinder enlarges as a general trend an elastic deformation amount in the form of expanding the distance between the cylinder and the reactionary portion of the caliper, which consequently brings about deterioration of degree of parallelism between the acting plane of the piston and that of the reactionary portion. It often makes the surface pressure on the externally biased portion of the pad (in relation to the axis of the disc rotor) higher than that in the internal pbrtion of the pad.In some extreme cases even a perfectly floated state of the internal portion of the pad, being disconnected away from the surface of the disc rotor, can be observed. It causes a fading phenomenon in the externally biased local portion of the pad, leading to deterioration of the braking effect.

This invention was made from such a background. It is therefore a primary object of this invention to provide an improved pad which is capable of eliminating or diminishing the braking effect deterioration in the high speed braking time by means of restraining the ununiformity of the surface pressure applied on the pad and the disc rotor to the greatest extent.

According to this invention there is provided a pad used in a disc brake for being urged onto a disc rotor by a floating type caliper provided with a cylinder having a piston fitted thereinto and a reactionary portion disposed in opposition to said cylinder so as to restrain the rotation of said disc rotor, said pad including a friction member for imparting frictional resistance to said disc rotor through contact therewith and a backing plate fixed to the back side of said friction member characterized in that said backing plate is provided with a plurality of through-bores formed only in a portion thereof external side beyond an arc described with a center coincident with the axis of said disc rotor and passing through the center line of said piston, and none in the rest portion inside said arc.

In the prior art, too, a plurality of through-bores were formed in the backing plate. It was aimed at only improving or reinforcing the sticking of the friction member to the backing plate through flowing of the friction member into the throughbores when it was mold onto the backing plate. As the purpose of forming the through-bores was in preventing the peeling-off of the friction member from the backing plate, they were formed all over the backing plate uniformly, not being limited to a specific portion, which could be said to reversely function to the object and effect of this invention.

The reason why the invented pad is effective in preventing the braking effect deterioration in the high speed braking time can be understood from the fact that the through-bores are formed only in an area or portion of the backing plate external side beyond a specific line. The formation of the through-bores only in the limited area contributes to the decrease of the restricting force of the backing plate against the friction member, that is, a relative decrease of the rigidity of the friction member in this area.The relatively easy deformability under compression of the friction member in this area prevents an extreme rising of the surface pressure in this area, even when an urging force is applied concentrately on the external area of the pad caused by an elastic deformation of the caliper, which promotes the internal area of the pad where the compressive deformation is less liable to occur than in the external area to effectively work in braking. If the through-bores are formed scatteredly all over the surface of the backing plate, the whole friction member becomes deformable under compression without producing any effect in uniformalizing the surface pressure on the friction member.

It is of course preferable to partly flow the friction member into the through-bores when it is molded onto the backing plate for increasing or reinforcing the sticking of the friction member to the backing plate, but It is not an indispensable factor for this invention. The through-bores left empty without being filled with the friction member are useful all the same in obtaining the effect of this invention.

As can be understood from the above description this invention contributes greatly to eliminating the grave disadvantage inherent to the floating caliper type disc brake, that is, a remarkable decreasing of the braking effect in the high speed braking time, by a slight alteration of the shape of the backing plate without any complication of the structure nor rising of manufacturing cost.

A preferred embodiment of this invention is illustrated by way of example, in the accompanying drawings, in which: Fig. 1 is a sectional view in elevation of an embodiment of a disc brake in accordance with this invention: Fig. 2 is a rear side view of an outer pad used for the disc brake shown in Fig. 1; Fig. 3 is a sectional view, taken along the section line 3-3, of a part of the disc brake shown in Fig. 2; Fig. 4 is an explanatory view for illustrating how the contact of the outer pad onto the disc rotor is improved; Fig. 5 is a rear side view of an example of a conventional type pad;; Fig. 6 is a graph for showing, in comparison with a case in the conventional type pad shown in Fig. 5, the relation between the positional variation of a point P on the nearer side to the disc rotor axis of the pad in Fig. 2 and the value of the hydraulic power applied to the cylinder; and Fig. 7 is a graph for showing the comparison between the braking effect in the high speed braking time of a pad in accordance with this invention and that of the conventional pad shown in Fig. 5.

Referring to Fig. 1, a caliper 1 provided with a cylinder 3 having a piston 2 slidably fitted thereinto and a reactionary portion 4 disposed in opposition to the former is generally of a saddle shape. This caliper 1 is slidably supported in a parallel direction to the axis of a disc rotor 5 by a supporting member 8 via a pair of not-shown slide pins in a posture straddling the disc rotor 5, an outer pad 6 and an inner pad 7 disposed on either side of the disc rotor 5.

The outer pad 6 consists of a friction member 11 for giving frictional resistance to the disc rotor 5 through contact with the surface thereof and a backing plate 12 fixed on the back side of the friction member 11. The friction member 11 is made of asbestos bonded with a synthetic resin to be a plate-like piece desirably adjusted in its coefficient of friction with the disc rotor 5 by adding some anti-friction material or friction increasing material. The backing plate 12 is a piece of steel plate, punched into the shape shown in Fig. 2, provided with a pair of engaging projections 13 projected from either lateral end thereof for being engaged with not-shown recesses formed in the supporting member 8 so as to be slidable in a parallel direction to the axis of the disc rotor 5.The friction member 11 is shaped such that the center of gravity of the friction surface thereof with the disc rotor 5 is almost coincide or aligned with, as shown in Fig. 2, the center line 0 of the piston 2, and the outskirt of the backing plate 12 is protruded slightly from that of the friction member 11 in all directions so as to cover the latter. The externally biased portion of the backing plate 12, that is, the portion located outside beyond an arc C described with a center coincident with the axis of the disc rotor 5 and passing through the center line 0 of the piston 2 is provided with fourthrough-bores 14 arranged along the arc C with an almost equal angular distance from each other.The friction member 11 is secured to the backing plate 12 by the molding method when it is formed; the material of the friction member 11 is flowed into the throughbores 14 before being hardened, as can be seen in Fig. 3, when the molding is conducted, for largely contributing to the improvement of sticking of the material to the backing plate 12. And due to the flowing of the material into the through-bores 14 the ratio of compression of the material when molded is smaller in the neighborhood of the through-bores 14, that is, the extemally biased portion of the outer pad 6 beyond the arc C, than in the internal side area where no through-bores 14 are made. The externally biased area with the through-bores 14 is therefore supposed to be easier to be deformed under compression.As to the inner pad 7 the situation is entirely the same to that previously described on the outer pad 6.

In a disc brake having the above-mentioned structure, applying of hydraulic power to the cylinder 3 from a not-shown port caused the piston 2 to urge the inner pad 7 onto one surface of the disc rotor 5; a reaction coming on the reactionary portion 4 from the action of the piston 2 will cause the outer pad 6 to be urged onto the other surface of the disc rotor 5. If the disc rotor 5 is in high speed rotation the cylinder 3 must be applied a strong hydraulic pressure so as to restrict the rotation, which is liable to cause the reactionary portion 4 to be deformed as to be diverged or departed from, at the extreme end portion thereof (nearby the axis of the disc rotor 5), the backing plate 12 of the outer pad 6 as shown with a two-dot-chain line in Fig. 1.The caliper 1 is, when observed as a whole, so deformed of course as to diverge the acting surface 1 5 of the piston 2 and the acting surface 16 of the reactionary portion 4; but the cylinder 3 is slanted only slightly because of its being parallely retained to the axis of the disc rotor 5 by the not-shown slide pins, most of the elastic deformation of the caliper 1 being concentratedly observed as a slant of the reactionary portion 4.

Such a manner of slanting of the reactionary portion 4 will naturally result in concentrating the urging force thereof against the outer pad 6 in the vicinity of external side extremity 1 7 of the outer pad 6. The outer pad 6 in this embodiment is made such that the force of the backing plate 12 for restricting or making rigid the friction material 11 is relatively weak on the extemal portion because of the formation of the through-bores 14; the friction member 11 is easily compressible at the external portion than at the internal portion, allowing the backing plate 12 to be slanted according to the slanting of the acting plane or surface of the reactionary portion 4. It results in sufficient urging of the internal portion of the friction member 11 onto the disc rotor 5. In other words, the portion of the friction member 11 where the through-bores 14 are formed is substantially thicker than the otherwise portion; it means that required force in compressing the friction member 11 at the through-bore formed area is smaller than that needed in compressing the same by the identical amount at the area otherwise. As the through-bore formed area is susceptible to compressive deformation, the adjacent area thereto becomes expansible toward the same area under pressure.

Furthermore, the through-bore formed area and the neighboring area thereto are relatively low in the ratio of compression while being molded, which means that those areas are easily compressible. It will presumably justify the readily compressibility of the portion of the outer pad 6 externally positioned away from the axis of the disc rotor 5. It can also be reasoned that diminishing of the rigidity against bending at the externally biased portion of the backing plate 1 2 due to the formation of the through-bores 14 contributes to mitigating the local rising of the surface pressure there.

It is a problem to be studied and solved in the future whether the above-mentioned presumption and assumption is truly proper. However, it has been sufficiently confirmed by a series of experiments that the formation of the throughbores 14 in the backing plate 12 largely improves the braking effect at the high speed braking time through better contacting of the outer pad 6 with the disc rotor 5.

One of the examples will be shown hereunder.

A result of comparison, in respect to the contacting state between the pad and the disc rotor, in two cases, i.e., the invented pad in Fig. 2 and the conventional pad shown in Fig. 5 is illustrated in Fig. 4. The pad 21 shown in Fig. 5 is almost similar to the outer pad 6 in Fig. 2, except for through-bores 22 which are formed all over the backing plate 23 with nearly equal dimension and inter-distance. The loosely hatched area A in Fig. 4 shows the contact area in the conventional pad 21 at the high speed braking time, while the area B finely hatched indicates the increased contact area bt the outer pad 6 in Fig. 2.

Fig. 6 is a graph showing the relation between the magnitude of the hydraulic pressure applied to the cylinder 3 and the position varying amount or displacement of the point P in Fig. 2. The position varying amount in positive value in Fig. 6 indicates approaching of the point P to the disc rotor 5 and in negative value departing away from the disc rotor 5. The solid line in the graph indicates the experimental data in the conventional pad 21 wherein the position varying amount of the point P increases at first slightly together with the rising of the hydraulic pressure, turning to declining soon afterwards.Although it is maintained in positive value within the usual speed braking range U, it drops into the negative value in the latter half range of the high speed braking range H which means a part of the friction surface is separated from the disc rotor 5, being released of contact therewith at the far away area thereof from the rotor axis. The broken line in the graph indicates the position varying amount of the point P in the case of the outer pad 6 of this invention, wherein the value decreases little within the range U of the usual speed braking and decreases only gently in the range H of the high speed braking, kept in positive throughout the entire range H of the high speed braking. It proves that the friction surface does not depart or separate from the disc rotor 5.

It has been made clear in the above description that this invention largely mitigates the ununiform and uneven contact between the outer pad 6 and the disc rotor 5. And how the braking effect in the high speed braking time has been improved is shown in Fig. 7 as the data actually investigated.

The data are dynamo-test results actually measured of the needed hydraulic pressure for decelerating a disc rotor 5 which is rotating in a high speed at a predetermined rate, that is, decreasing the rotating speed of the disc rotor 5 at a predetermined speed-down rate. In the graph of Fig. 7 the solid lines indicate the test results with a conventional pad 21, and the three points in the graph signify the magnitude of the hydraulic pressure applied at the starting stage, the middle stage, and the final stage of the braking operation.

As clearly observed in the graph, the required hydraulic pressure for getting the desired deceleration rises suddenly high up at the second braking motion in the two successive high speed brakings, which evidently proves the fading phenomenon inherent to the conventional pad 21.

In the pads 6, 7 according to this invention such a sudden rising of the hydraulic pressure did not appear in the experiments of high speed braking operation, which tells eloquently the effective prevention of the fading phenomenon by this invention.

In this embodiment an inner pad 7 having a plurality of through-bores 14 formed only in the externally biased area was employed, in addition to the outer pad 6 with the through-bores 14. It proved a by-effect of interchangeability of the outer pad 6 and the inner pad 7 and of better prevention of local fading phenomenon from occurring. As the slanting of the acting plane takes place even on the side of the cylinder 3, although it is far smaller in comparison to the side of the reactionary portion 4 as earlier explained, the use of the same type inner pad 7 as the outer pad 6 is beneficial in mitigating the uneven contact and the ununiform surface pressure on the inner pad side, i.e., the side of the cylinder. If the acting plane 1 5 of the piston 2 is allowed to slant more on the externally biased area, that is, on the farther area away from the axis of the disc rotor 5, than on the internal area, to be nearer to the disc rotor 5, it will help that much to mitigate the slanting of the acting plane 1 6 of the reactionary portion 4, which contributes to restraining the local fading phenomenon.

In a type of disc brake wherein the caliper is supported not via slide pins but directly by a supporting member at a connecting portion thereof for linking the cylinder and the reactionary portion, a relatively large slanting takes place even in the cylinder, so the use of the same invented type pad to the inner pad side can be said very effective in preventing the fading phenomenon.

Claims (3)

1. A pad used in a disc brake for being urged onto a disc rotor by a floating type caliper provided with a cylinder having a piston fitted thereinto and a reactionary portion disposed in opposition to said cylinder so as to restrain the rotation of said disc rotor, said pad including a friction member for imparting frictional resistance to said disc rotor through contact therewith and a backing plate fixed to the back side of said friction member characterized in that said backing plate is provided with a plurality of through-bores formed only in a portion thereof external side beyond an arc described with a center coincident with the axis of said disc rotor and passing through the center lineU of said piston, and none in the rest portion inside said arc.

2. A pad according to claim 1, wherein material of said friction member is mold onto said backing plate so as to be partly flowed into said plurality of throughmbores before being hardened, with a result of reinforcing sticking of said friction member to said backing plate.

3. A pad used in a disc brake, substantially as hereinbefore described with reference to the accompanying drawings.