Disc for a vehicle disc-brake

A disc for a disc-brake used in a vehicle. The disc is, on the whole surface portion thereof where it contacts the pad, provided with a number of circular machined scores, or in some cases spiral scores which, having a small pitch, are almost circular the center of scores being at the rotation center of the disc. The scores are ground or cut having a surface roughness of 2 microns or more taken in ten point height, that is, in average height at randomly selected ten points, by ISO R 468.

BACKGROUND OF THE INVENTION 
This invention relates to a disc in a disc-brake for vehicle use, more 
particularly to the provision of a disc highly effective in preventing 
noise in the disc-brake. 
Disc-brakes are generally liable to produce an unpleasant noise or squeal 
when the brake pedal is depressed, for which noise various preventive 
attempts have been taken. It is well known that the squeal of the 
disc-brake may be caused by the resonance of a brake-pad (hereinafter 
simply called pad), whereby restriction of pad movement or damping of the 
same is effective preventing squealing. 
The conventional techniques therefor, as, for example, in 
Toku-Kai-Sho-51-38868, Toku-Kai-Sho-51-39311 laid open in Japan, etc., 
possess disadvantages, such as increased component parts, complicated 
parts configuration, or difficulty of assembly. Morover, where restriction 
of pad movement is attempted, a further problem, a drag phenomenon, arises 
often, due to a residual sliding contact of the pad on the disc even after 
the release of the brake pedal. 
The inventor of this invention succeeded some time ago in preventing the 
squeal due to the resonance of a pad, by restricting the movement of the 
pad through an improvement in the disc itself, not in the pad or other 
members carrying the same. That improvement, an invention itself, is now 
pending as with patent application with No. Toku-Gan-Sho-51-134877 filed 
with the Japanese Government Patent Office. 
Since the disc rotates together with the wheel and the pad is stationary, 
being mounted on a non-rotating place through a caliper, a mounting 
bracket, etc., it would seem impossible to restrict the movement of the 
stationary pad by means of the rotating disc. This assumption of 
impossibility has been discovered to be incorrect. 
The present invention is aimed at a further improvement of the 
aforementioned invention. While the previous invention is based on the 
concept of restricting pad movement through its engagement between a few 
great grooves and/or ribs, disposed on the surface of the disc around its 
rotation axis, and mating ribs and/or grooves naturally formed on the 
surface of the pad corresponding to those on the surface of the disc, the 
present invention aims at a drastically altered form of the grooves and/or 
ribs for attaining an effect like that of the previous invention. That is 
to say, a number of circular ground scores or cut scores are formed on the 
surface of the disc around its rotation axis. It will be quite naturally 
understood that ground scores or cut scores having a surface coarseness or 
roughness above a certain level are highly effective in restricting 
movements of the pad in the direction parallel to that of the disc 
surface, by imagining the feeling of cleaning the surface of a phonograph 
record with a wiper. 
SUMMARY OF THE INVENTION 
It is therefore a primary object of this invention to provide a disc for a 
disc-brake highly efficient in preventing the squeal due to the resonance 
of the pad by forming circumferential ground scores or cut scores on the 
surface thereof where it contacts the pad. 
It is another object of this invention to provide a novel disc for the 
purpose, completely eliminating the shortcomings of the conventional 
techniques, i.e., increased component parts, complicated parts, difficulty 
of assembly, and frequent occurrence of undesirable drag. 
It is another object of this invention to provide a novel and economical 
disc for the purpose, by simplifying the complicated manufacturing method 
through the introduction of an ingenious grinding or cutting process in 
place of the conventional one (which has required great care in grinding 
the disc surface), to minimize the variation of the thickness of the disc 
in the circumferential direction (for example, below 0.005 mm). 
Other objects, constructions, and effects of this invention will be 
apparent upon studying the description of a few preferred embodiments in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF A FEW PREFERRED EMBODIMENTS 
In FIGS. 1 and 2 a disc is denoted by the numeral 1; numeral 2 denotes a 
pad, 3 denotes a piston, and 4, a caliper. The pad 2 is, as shown in FIG. 
2, provided with a pair of through-bores 2c at each shoulder portion 
thereof and carried by the caliper 4 through a rod (not shown) passing the 
through-bore. The caliper 4 is fixedly mounted on a non-rotating member 
(not shown) in a straddling posture above the disc 1, and provided with a 
cylinder 4a at one or both end portions thereof, in which cylinder 4a is 
slidably fitted a piston 3. Piston 3 is pushed toward the disc 1, when 
braking fluid pressure is applied within the cylinder 4a, thus pressing 
the pad 2 on to the rotating disc 1 for braking the rotation of the disc 1 
through a sliding contact under pressure. 
It is necessary that the pad 2 is carried in such a manner as to be able to 
move in a direction normal to the surface of the disc 1. As a result of 
this, the pad 2 inevitably has a slight freedom of movement in the 
direction parallel to the surface of the disc 1. Numerous repetitions of 
this slight movement, of the pad 2 parallel to the surface of the disc 
eventually results in a vibration which in turn causes the squeal of the 
disc-brake. 
In this embodiment a disc 1 in accordance with the invention has, on the 
opposite surfaces thereof where the disc 1 is to be sandwiched by a pair 
of pads 2, a number of concentric ground scores 1a formed with 
substantially equal distances therebetween, that shown in FIG. 3, in such 
a manner as the center of the scores coincides with the rotation center of 
the disc 1. Consequently, when the brake is applied, an engagement along 
the numerous wavelike ribs in the circumferential direction occurs between 
the friction material 2a of the pad 2 and the disc 1, which restrains the 
vibration of the pad 2 in the direction A and B in FIG. 2. 
The ground scores 1a in this embodiment may be attained by grinding the 
surface of the disc 1 with a pair of grinding tools G.sub.1 and G.sub.2 
symmetrically urged on the opposite sides of the disc 1, which is rotated, 
as shown in FIG. 4, integrally with the rotary shaft H, whereby both sides 
of the disc 1 are simultaneously ground, with an elastic deformation of 
the disc 1 being prevented in the meanwhile. 
Aforementioned grinding tools G.sub.1 and G.sub.2 may be replaced by 
abrasive cloths or papers backed up by resilient bodies. Besides being 
pressed against the disc 1, the grinding tools G.sub.1 and G.sub.2 may 
also be moved in a radial direction, which results in, the forming of a 
plural number of spiral scores, rather than circular scores. 
In order to study the relation between the roughness of the ground scores 
and the squeal preventing effect, many discs having scores of various 
degree of roughness (ten point height) were manufactured and tested in an 
actual disc-brake, the result of which test being shown in FIG. 5. 
The squeal index in the Figure is an index representing a degree of squeal 
occurring likelihood, so to speak, introduced by combining the squeal 
occurring rate and the squeal magnitude. 
Curve A in FIG. 5 indicates the test result in with respect to a brake of 
the type in which 4 pistons, two on each side, are disposed in a secured 
caliper; Curve B relates to a brake of the type in which two pistons, one 
on each side, are disposed in a similarly secured caliper. In both tests, 
effect of remarkable effect of squeal prevention can be observed in cases 
where ground scores are 2 microns or more in the ten point height of ISO R 
468. 
The roughness of a ground surface in the range of 2 to 10 microns can be 
said to be considerably rough as a ground surface in general; it belongs, 
however, an extremely fine range, when considered as wave-like ribs or 
scores. It is surprising to discover that the restraint of vibration of 
the pad 2 and in the prevention of squeal in the brake, can be attained 
only by the presence of such fine wave-like ribs. 
In addition to this, an extremely enhanced durability of the invented disc, 
i.e., durability of scores by the new method is worthy of attention as 
follows: 
(1) In the conventional disc 1', in FIG. 7, ground scores of 2-3 microns 
were erased or worn out by brake repetition of 500 to 1000 times. 
(2) In the invented disc the scores also of 2-3 microns were still in good 
condition even after brake repetition of over 10,000 times. 
Such durable scores on the disc surface can be formed, in addition to the 
abovementioned grinding method, by a cutting method. The cut scores are 
alike with the ground scores durable and effective for squeal prevention. 
For making the scores, the surface of the disc 1 where the pad contacts 
the same may be cut by a cutting machine. 
In this case it is desirable to cut both sides of the disc 1 simultaneously 
with a pair of cutting tools, T.sub.1 and T.sub.2, as shown in FIG. 6, 
disposed on opposite sides of the disc 1, whereby both tools T.sub.1 and 
T.sub.2, are moved in a radial direction of the disc while the same 
rotates integrally with the rotary shaft H. This method is effective in 
preventing the disc 1 from being elastically deformed, and thereby in 
keeping the same in a high working accuracy. 
Although the scores formed by the cutting method can not, exactly speaking, 
be said to be circular and/or concentric, but rather are spiral, the pitch 
of the spirals is so small that they can function, in reality, as 
perfectly circular scores. With the cutting method, it is more difficult 
to form sharp or acute-angled scores in comparison with the grinding 
method; with the former method however, it is far easier to form coarse 
scores than with the latter. 
The embodiments described above are disclosed only by way of examples, so 
the invention should not be construed as being limited to them, but 
naturally includes some modifications and variations which those skilled 
in the art can make, so long as they do not deviate from the spirit of the 
invention.