Disc brake with the caliper reaction passing through a wheel fixed support axle, preferably for motorcycle front wheels with a peripheral annular disc

Abstract: This brake disc (2), preferably for motorcycle front wheels, with a peripheral annular disc, has the characteristic of having its caliper reaction passing through a fixed axle (14) coaxial with the wheel axis, said caliper (8) being mounted at the end of a radial arm (9) rigid with the axle (14), which is torsionally keyed into at least one antirotation seat at the ends of the wheel support.

Description: This invention relates to a peripheral annular disc brake, preferably for motorcycle front wheels, having its caliper reaction passing through a wheel fixed support axle. It is known that modern motorcycles have considerable power, requiring likewise powerful brakes. The brakes currently used are of the "disc" type and consist of one or more discs fixed parallel to the wheel and braked by their individual caliper, which causes suitable "pads" of high friction coefficient to slide against them. This type of brake uses discs which, being fixed on the wheel hub, have a small centrifugal extension, hence providing two pad sliding tracks which are relatively small and do not allow adequate disposal of the heat produced on them. When motorcycle front wheels are braked, the lateral arrangement of the disc and the fixing of the caliper to one of the two rods of the wheel steering fork creates forces eccentric to the steering axis which create steering moments dangerous for the attitude of the motorcycle. In general braking devices the caliper is fixed to the frame in a rigid manner, causing wheel braking which is immediate and consequently difficult to control gradually. For motorcycle front wheel braking, the caliper is mounted on the fork in an approximately intermediate position which obviously depends on the diameter of the brake disc: the greater the diameter, the further the caliper lies from the point through which the wheel axle passes. Consequently if the fixing of the brake caliper to the fork creates an elastic response due to the flexure of the fork, this response is progressively more rigid the further the caliper lies from the wheel axis. Hence in the case of high-power motorcycles, the use of large brake discs makes braking less progressive, other technical factors being equal: the larger the discs the higher the point in which the caliper is fixed to the fork. This response rigidity also favours lifting of the rear wheel, which consequently loses its adhesion to the ground and reduces the overall braking capacity of the motorcycle. If a single caliper is used, as in the case of the conventional system, wheel turning takes place during braking, with consequent unbalancing of the vehicle. From EP-A-0 382 683 a disk brake system for motorcycles is described. According to this solution, the brake disc is located on the median plane of the wheel and supports means are provided, constituting as a whole the spoke system of the wheel, for supporting the brake disc and firmly connecting it to the tire rim of the wheel. In this case, therefore, the brake disc has necessarily a diameter being reduced with respect to the diameter of the rim, and a substantial part of the braking action is discharged onto the spokes system. An object of the present invention is to define a disc brake provided with very extensive braking tracks which reduce the operating temperature and therefore allow prolonged use. A further object is to reduce the lifting of the rear of the motorcycle consequent on sudden braking of the front wheel. A further object is to define a brake of the aforesaid type, which enables the caliper to undergo initial elastic dragging resulting in a softer braking action, in order to prevent wheel locking and impact against the forks. These and further objects are attained, according to the present invention, by a disc brake system for a wheel, preferably for motorcycles, and a wheel, having the features of the annexed claims 1 and 16. The invention is illustrated by way of non-limiting example on the accompanying drawings, in which: Figure 1 shows a motorcycle front wheel with a caliper engaged on an annular disc brake, fixed internally in a central position to the tyre support rim. Figure 2 is a schematic transverse view of the lower end of a fork. Figure 3 is a schematic cross-section through an upper part of a front wheel equipped with one annular brake disc mounted centrally on the tyre support rim. Figure 4 is a section through a generic wheel projectingly mounted on a horizontal arm and with the brake caliper reacting with the torsion bar. From said Figure 1, it can be seen how the fork of a generic motorcycle is stressed by braking forces. The reference numeral 1 indicates a normal tyre; 2 indicates a brake disc fixed by usual means to a wheel rim 3; 4 indicates the usual bushes for fixing the wheel rim to the brake disc; 5 indicates the unsprung lower part of a fork 6; 7 indicates the spokes joining the wheel hub to its rim 3; 8 indicates a brake caliper supported by a radial arm 9. Assuming that the wheel rotates in the direction S, then when the caliper 8 grips the disc 2 it is also urged to rotate. This does not in fact happen because the caliper 8 is fixed to a fixed part of the motorcycle. In the usual art this caliper is fixed to the unsprung part 5 of the fork, for example at a point P, 50 that the exerted braking force generates a reaction R. This reaction has to provide balance between the friction force T on the road and a weight force Z deriving from the moment created by the weight of the entire motorcycle plus the driver about the point of contact of the front wheel with the ground. In this manner the force R causes flexure of the fork 6 which, by allowing the caliper 8 to retract, results in a certain gradualness in braking. The position of the point P is directly related to the diameter of the annular disc 2, on which it operates; if the braking tracks were of a smaller diameter they would locate said point P in a position closer to the centre of the wheel. This would cause the flexure of the fork 6 to increase and would theoretically make braking more gradual, if it were not for the fact that in practice it would mean less extensive tracks and hence subjected to a higher operating temperature, so making them inoperable. The present invention allows a compromise between said two optimum conditions; in this respect it enables disc tracks to be used which are of considerable length while at the same time increasing to a maximum the elastic retraction of the caliper 8. This is achieved by fixing the caliper not directly on the forks (ie on the point P), but on an arm 9 rigid with a central axle 14 coaxial to the wheel and having its ends keyed to the fork ends 5. In this manner the caliper no longer acts on the fork at the point P, but instead with a "force torque" having its centre at 14, in a position which in cooperation with the weight force Z creates maximum flexure of the fork. This fork flexure is however not an essential element for the purposes of the invention. It is merely one possible consequence which is acceptable to the extent in which it is freely required. In this respect, one requirement of the invention is the elastic retraction of the caliper, this requirement also being achievable with a fork theoretically indeformable by the said flexural stresses. The retraction of the caliper could in fact be totally delegated to the intrinsic torsional elastic deformability of the central axle 14. As can be seen from Figure 3, the axle 14 is made rigid with the central arm 9 by usual means 13 and is keyed at its ends into the unsprung lower part 5 of the fork. This keying is indicatively achievable by a splined profile of the type 11, indicated in Figure 2. This figure shows an example of a constructional detail comprising an end 5a dovetail-inserted and fixed by bolts 12. The axle 14 is provided for supporting the bearings 15 for the spoked wheel 7 which are interposed between the support arm 9 for the caliper 8 and the unsprung lower part 5 of the fork 6, via usual spacers D1-D2. This assembly is tightened together by nuts 16. The axle 14 is axially bored to achieve continuity of a usual hydraulic conduit B for operating the caliper 8. With reference to Figure 4 the illustrated generic wheel could be used as the front wheel of a motorcycle with single arm front suspension, or could be used as the rear drive wheel of a motorcycle, or again could be used as a drive or idle wheel of a motor vehicle. In this figure those parts in common with the described versions are indicated by the same reference numerals plus 200. The caliper 208 is supported by an arm 209 rigid with an axle 214 provided with a splined end 214a keyed into the interior of a tubular cross-member 205a of a swinging support 205. The swinging support 205 is obviously horizontal, is spring-loaded and forms the suspension. With the wheel 207 there can be associated a sprocket 10a for a chain drive or a live axle head 10a. From the indicated embodiments it is apparent that as the caliper derives its reaction from an axial central position, it can be positioned practically at any angle within the 360' of a complete revolution, ie clearly a plurality of calipers positioned at the vertices of two, three, four... support arms can be arranged circumferentially on the brake disc. Advantageously this allows much lower pressures to be used for operation, and likewise to provide large braking surfaces, so making braking more effective. A further advantage offered by the invention is that it allows the use of brake discs of annular shape fixed directly to the wheel rim. A further advantage is that it enables the caliper to be positioned at any angular position without being constrained by the angular position of the motorcycle fork. A further advantage is that in an extremely simple and reliable manner it provides progressive braking which reduces the possibility of wheel locking. A further advantage is that it prevents the sudden generation of moments at the fork in the horizontal plane, resulting from unbalanced braking consequent on only one disc or on discs braked non-simultaneously.

Claims: A disc brake system for a wheel, preferably for motorcycles, comprising a rim (3;203) for retaining a tire (1;201) on a substantially outer surface thereof, said rim (3;203) having a substantially inner surface facing the rotational axis of the wheel; a wheel hub; spoke means (7;207) joining said wheel hub to said rim (3;203); wherein a fixed axle (14;214) coaxial with the rotational axis of the wheel is torsionally keyed in an antirotational seat being defined in an end portion of a wheel support (6;205), and an annular disc (2;202) is arranged substantially in the median plane of the wheel, a disc caliper (8;208) being mounted at an end of a caliper support (9;209) rigid with said fixed axle (14; 214), characterized in that said disc (2;202) is secured to first points of said inner surface of said rim (3;203), and said spoke means (7;207) are secured to second points of said inner surface of said rim (3;203), whereby said second points lay in a position being different with respect to the position of said first points, in which said disc (2;202) is secured to said tire rim (3;203). A disc brake system, according to claim 1, characterized in that the outer periphery of said disc (2;202) is adjacent to the said inner surface of said rim (3;203), said outer periphery having a diameter being substantially in the order of the diameter defined by said inner surface. A disc brake system, according to claim 1 or 2, characterized in that said disc (2;202) is directly secured, along its outer periphery, to said inner surface of said rim (3,203), in a substantially middle position thereof. A disc brake system, according to at least one of the previous claims, characterized in that bushes (4) are provided for fixing the outer periphery of said disc (2;202) to said the inner surface of said rim (3;203). A disc brake system, according to claim 1, characterized in that said disc (2;202) is substantially planar and said spoke means (7;207) mostly extends in a plane being approximately parallel to the plane on which said disc (2;202) is arranged. A disc brake system, according to claim 1, characterized in that said fixed axle (14;214) is at least in part bored, for allowing the passage of a hydraulic conduit (B) for operating said caliper. A disc brake system, according to claim 1, characterized in that said wheel support (6;205) comprises a fork (6) having two prongs (5), between which said wheel is arranged, said fixed axle (4) extending between said prongs (5). A disc brake system, according to claim 1, characterized in that said wheel support (6;205) comprises a single arm (205) to which an end of said fixed axle (204) is torsionally keyed. A disc brake system, according to claim 1, characterized in that said fixed axle (14;214) comprises at least a splined end (214A) to be keyed into said wheel support (6;205). A disc brake system, according to claim 1, characterized in that said end portion of said wheel support (6;205) comprises at least a removable part (5a). A disc brake system, according to claim 10, characterized in that said removable part (5A) is dovetail coupled to the remaining part of said wheel support (6;205). A disc brake system, according to one or more of the previous claims, characterized in that said fixed axle (14;214) is structured for realizing an elastic torsion bar function. A disc brake system, according to claim 1, characterized in that said caliper support (9;209) is removable from said fixed axle (14;214). A disc brake system, according to one or more of the previous claims, characterized in that a plurality of calipers (8;208) is provided for said disc (2;202). A motorcycle comprising a support (6;205) for a wheel and a disc brake system for said wheel, characterized in that said disc brake system is realized according to one or more of the preceding claims. A wheel for a motorcycle having a disk brake system, comprising a rim (3;203) for retaining a tire (1;201) on a substantially outer surface thereof, said rim (3;203) having a substantially inner surface facing the rotational axis of the wheel; a wheel hub; spoke means (7;207) joining said wheel hub to said rim (3;203); wherein a fixed axle (14;214) coaxial with the rotational axis of the wheel is provided, for being torsionally keyed in an antirotational seat defined in the end portion of a wheel support (6;205), and an annular disk (2;202) is arranged substantially in the median plane of the wheel, a disc caliper (8; 208) being mounted at an end of a caliper support (9;209) rigid with said fixed axle (14; 214), characterized in that said disc (2,202) is secured to the inner surface of said rim (3;203), said spoke means (7;207) do not realizing any support function for said disc (2,202).

Inventors: TOSON EMANUELE, TOSON, EMANUELE
Applicants: BRAKKO SRL, BRAKKO S.R.L.
Application year: 1995
Main classification: B62L1
IPC codes: B62L1