Abstract:
A bicycle brake system includes a disc mounted floatingly on a hub and a brake unit mounted floatingly on a fork. A mechanically actuated cam mechanism causes actuation of a first lining which presses against the disc compressing it, due to the above floating assembly, against a second line which remains fixed, thus causing the braking action.

Description:
BACKGROUND 
     The present invention relates to a disc brake system, with mechanical operation, for bicycles, particularly suitable for use on mountain, all-terrain and racing bikes, on road or track. 
     At present, most disc brake systems for bicycles available on the market make use of a hydraulic system to press the brake linings on the disc. All hydraulic disc brakes, according to the known art, have a caliper mounted in a fixed manner and equipped with two opposed pistons which, under the action of the hydraulic system, press the linings against the disc to cause braking. This solution, besides being of excessively complicated construction, requires absolutely precise assembly, to avoid undesirable friction between the linings in the resting position and the disc. 
     Furthermore, hydraulic disc braking systems require replacement of the normal brake levers attached to the handlebar with other types of levers integrated with the hydraulic circuit. 
     Heavy use of the brakes causes overheating of the hydraulic system which results in poor operation and the possibility of breakage. 
     Furthermore, these systems oblige the user to carry out frequent bleeding and/or topping up of the hydraulic circuit, difficult operations even for specialized mechanic-cyclists. 
     Based on what is described above, hydraulic braking systems are clearly subject to some drawbacks such as an excessive cost, poor resistance to high temperatures, and excessively complex installation and maintenance. 
     These drawbacks are solved in part by mixed hydraulic and mechanical braking systems. In these known braking systems, the caliper is hydraulically operated, but is actuated by a cable controlled by traditional levers applied on the handlebar. These calipers are mounted, by means of fixing pins, in a floating manner on the fork, so as to allow self-centering during braking. Braking is achieved by means of the pressure of a single small piston connected to the caliper which thrusts a lining against the disc. With this system the friction due to imperfect alignment or a partial return of a lining to the resting position is eliminated. 
     This mixed braking system, however, has limits to its performance at high temperatures. In fact the “extreme miniaturization” (limited surface of contact during braking) and the difficulty in guaranteeing the complete return of the linings to the resting position under all conditions, prevent heat dissipation. Besides a considerable variability in performance, overheating of the braking system causes boiling of the fluid in the hydraulic circuit and sometimes failure of the seals, which in any case have a limited life. 
     Because of the above mentioned problems, some attempts at totally mechanical disc brakes have been made in the prior art. These known braking systems use a caliper with a fixed mounting, operated by means of a cable controlled by the connected braking lever on the handlebar. Rolling of two/three balls each on an inclined track is exploited to press the linings against the disc. 
     This mechanical system, however, also has various drawbacks. The caliper mounted in a fixed manner does not allow self-centering thereof during braking, causing undesirable friction when the linings are in the resting position. 
     The balls, which have a very small surface of contact, rapidly score the sliding ramps. This causes a considerable increase in friction which, after a few operations, is such as to invalidate the braking system. 
     These known mechanical brake systems, moreover, cannot achieve the performance in terms of power of the present hydraulic braking systems. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to eliminate these drawbacks, providing a bicycle braking system that is economical and simple to make. 
     Another object of the invention is to provide such a braking system with a high braking power and that guarantees excellent reliability under the heaviest working conditions. 
     Another object of the invention is to provide such a braking system that is simple to assemble and maintain and can be installed on existing bicycles without requiring particular modifications. 
     In the bicycle brake system according to the invention, a disc brake comprising a caliper mounted floatingly on pins connected to the fork is used on at least one wheel. To achieve braking, a single lining is pressed on the disc by a small piston operated by a cam system, consisting of at least a pair of inclined opposing ramps, on which the same number of rollers operate. 
     It is preferred to use rollers instead of balls in that the surface of contact of the rollers is considerably greater than that of the balls; as a result there is therefore a drastic reduction in rolling friction. 
     The return of the lining to the resting position is ensured by spring structure and the return of the caliper to the resting position is ensured by self-centering due to the floating assembly thereof and aided by the presence of small snap rings or O-rings placed on the fixing pins. 
     The disc is fixed to the hub by means of splined fitting. This system offers a more rational distribution of the loads than the conventional system, in which screws are inserted directly into the body of the hub, and also makes removal of the wheel faster and easier in the event, for example, of replacement of one or more spokes. The disc is also fixed floatingly, by interposition of a snap ring between its fixing star and the rim on the hub. This allows a certain axial adjustment, facilitating the return thereof to the resting position after braking and thus avoiding the friction that penalizes the other known types of disc brakes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics of the invention will be made clearer by the detailed description that follows, referring to a purely exemplary and therefore non-limiting embodiment thereof, illustrated in the appended drawings, in which: 
     FIG. 1 is a front view of the brake system for bicycles according to the invention; 
     FIG. 2 is a side profile view of the brake system in FIG. 1; 
     FIG. 3 is an enlarged view of the part of FIG. 2 enclosed in the circle indicated by A; 
     FIG. 4 is an exploded view of the brake unit according to the invention; 
     FIG. 5 is an axonometric view of a disc with the brake unit according to the invention connected; and 
     FIG. 6 is an axonometric view of a hub suitable for accommodating the disc in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to FIGS. 1 and 5, a disc  1  is preferably made of steel with a high friction coefficient and has countersunk lightening holes  2 . The disc  1  is suitably subjected to grinding and a final check on flatness. The disc  1  is connected by means of bolts  3  to disc holding star  4  or flange (with five spokes in the example in FIGS.  1  and  5 ). 
     The disc holding star  4 , preferably of tempered aluminium alloy, has a central hole, in the inner surface of which a splined mating part  6  is made. The splined mating part  6  is able to engage with a complementary splined mating part  7 , made on the outer surface of an end of a hub  8  (FIG.  6 ). A gasket  5  preferably of rubber and of the O-ring type able to impart a certain clearance to the disc  1  is applied to the splined mating part  7  of the hub  8 . Again in the splined mating part  7 , a seat  9  is provided such as to receive a metal ring  10  to block the disc  1 . 
     The hub  8  has at its two ends two cylindrical blocks  11  able to engage in suitable concave seats made in the two ends of a bicycle fork  12 . Fixing of the hub  8  to the fork  12  takes place, in a known manner, by means of levers  13 ,  13 ′ that can also be operated manually. 
     The brake unit, indicated generally by reference numeral  15 , is shown exploded in FIG.  4 . The brake unit  15  comprises a caliper formed by an external caliper body  16  which is positioned externally with respect to the disc  1 . The external caliper body  16  has two through holes  18  (FIG. 5) able to receive the ends of two pins  17 . The pins  17  are retained inside the holes  18 , and O-rings  60  are provided to confer a floating type coupling. The other end of the pins  17  is threaded and is blocked by means of nuts in holes made in the fork  12 . 
     In the outer caliper body  16 , a hollow seat  105  is provided wherein a screw  19  engages to lock a control lever  20  by means of a nut  30 . A return spring  100  is inserted around the screw  19 . In this manner, the position of the control lever  20  is adjusted by acting on the nut  30  in order to be able to regulate the type of braking desired. 
     The control lever  20  has a groove  21  able to accommodate the cable  22  (FIG. 1) to be connected to the lever (not shown) of a brake on the handlebar. The end of the cable  22  is blocked in the cavity  21  by means of a bolt  101 . Again in the outer body  16  of the caliper, a through hole is provided wherein a sheath-fastening pin or revolving pin  23  engages. The pin  23  is blocked at the bottom by an open snap ring  24  (FIG. 4) so as to be able to turn freely inside the through hole. The pin  23  has a through hole  25  through which the cable  22  is inserted, and at one end of the pin  23  the sheath  55  that covers the cable  22  is blocked. 
     The spring  100  around the screw  19  is preferably covered by a dust guard  31  of rubber or synthetic material. 
     A hollow body  13  having a substantially upturned T-shaped section, that is having a cylindrical tang with a disc-shaped base, is positioned inside the outer caliper body  16 . In the base of the hollow body two opposing seats  33  are created (only one visible) able to accommodate a pair of rollers  34 , integral in position with respect to the caliper body  16 . The seats  33  communicate with a pair of opposed cams  35  (only one visible) with an opposite incline. 
     When the brake lever on the handlebar is actuated, pulling of the cable  22  causes shifting of the lever  20  that actuates the screw  19  that is integral with the hollow body  32 . The hollow body  32  thus rotates and is pushed downward through the action of the cams  35  which slide on the pair of rollers  34 . 
     A small piston  36  is inserted freely inside the hollow body  32 . The small piston  36 , descending together with the hollow body  32 , without making any rotation, strikes against an external brake lining  37 , bringing it close against the surface of the disc  1 . In this manner, there being no sliding friction between the contact surfaces of the small piston  36  (which is free to rotate inside the hollow body  32 ) and the brake lining  37 , it is possible to prevent any wear of the contact surfaces of the brake lining and the piston. 
     The brake lining  37  is housed inside a special seat made in the outer caliper body  16  and is held in this seat by a return spring  38  which ensures the return thereof to the resting position when the braking action is finished. 
     An inner brake lining  40  destined to remain fixed in its position is fixed by means of a stop spring  39  to an inner caliper body  41 . The inner caliper body  41  is rigidly connected to the outer caliper body  16  by means of bolts  42  locked at the bottom by stop nuts  43 . 
     When the piston  36  causes the advance of the brake lining  37  that strikes against the disc  1 , thanks to the floating coupling between the brake unit  15  and the fork  12 , and between the disc  1  and the hub  8 , the brake unit  15  and the disc  1  make a slight axial movement and therefore the disc  1  is compressed between the linings  37  and  40  thus obtaining effective and perfectly balanced braking. 
     When the braking action ends, through the action of the return spring  38 , the brake lining  37  returns to its resting position, again thanks to the floating coupling between the brake unit  15  and the fork  12 , and between the disc  1  and the hub  8 , the brake unit  15  and the disc  1  make a slight axial movement and therefore the disc  1  is placed in a perfectly equidistant position between the two brake linings  37  and  40 , thus limiting the sliding friction to a minimum. 
     The above description makes clear the advantages of the solution proposed by the invention, which proposes a disc braking system for bicycles, with floating mounting and completely mechanical twin cam operation.