Bicycle brake disk with arms connecting an inner annular portion to an outer annular portion and tangent to an effective circle

Abstract: A one-piece brake disk (10) for a vehicle includes a radially inner annular portion (20) having a plurality of circumferentially located mounting holes (24) defining a mounting circle (MC); a radially outer annular portion (28) concentric with the radially inner annular portion (20) and having opposite braking surfaces (32, 34); and a plurality of connecting arms (38) extending from an inner peripheral surface (42) of the radially outer annular portion (28) to an outer peripheral surface (43) of the radially inner annular portion (20). Each of the plurality of connecting arms is tangent to an effective circle (EC) concentric with the mounting circle (MC), wherein the effective circle (EC) has a radius greater than a radius of the mounting circle (MC).

Description: BACKGROUND OF THE INVENTION The present invention is directed to bicycle brake devices and, more particularly, to a bicycle brake disk that accommodates heat build up during braking. Disk brake systems are becoming more popular on mountain bicycles because of their superior braking characteristics under severe operating conditions. A typical disk brake system comprises a brake disk that rotates with the bicycle wheel and a brake caliper that sandwiches the brake disk and presses brake pads against opposite sides of the brake disk. The friction between the brake pads and the brake disk causes the braking function. Not surprisingly, substantial heat is generated where the brake pads contact the brake disk during the braking operation. Since the brake pads ordinarily press against the outer radial surfaces of the brake disk, the generated heat is localized at the radially outer portions of the brake disk. As a result of such uneven heating, the radially outer portions of the brake disk expand while the radially inner portions of the brake disk expand very little, if at all. If very high temperatures are generated during the braking operation, this uneven expansion can cause the brake disk to warp. If the brake disk warps to one side, this can cause one of the brake pads to press against one side of the brake disk more than the other brake pad, thus resulting in further uneven heating and a loss of braking efficiency. If the brake disk warps in a wave shape, severe vibration occurs during braking. One brake disk that addresses the problem of uneven expansion is disclosed in U.S. Patent No. 5,848,674. That patent discloses a brake disk having an inner ring and an outer ring interconnected by a plurality of spaced arms. Each arm has a curved L-shape so that the stress in the disk caused by the heat generated in the outer ring can be relieved by radial expansion and contraction of the arms. However, the disadvantage of such a design is that the curved arms are less able to resist the rotational forces of the brake disk during braking because of a cantilevering effect at the curves. Also, the curved arms have lower resistance to side impact forces because the curves act as a pivot point for the outer ring relative to the inner ring during the application of such forces. The patent application WO 99/47409 discloses a brake disk with a plurality of connecting arms. Each of the plurality of connecting arms of this brake disc is tangent to an effective circle EC concentric with a mounting circle MC. The effective circle EC of this brake disk has a radius which is a little bit smaller than the radius of the mounting circle. (Effective circle constructed according to the definition of claim 1). That leads to a concentration of stress. This is because the inner annular portion of the brake disk suffers stress effected by the pressure of the mounting screws connecting the brake disk to the hub. Additionally, the inner annular portion is charged in the same area with stress exerted by the connecting arms upon activation of the brake. SUMMARY OF THE INVENTION The present invention is directed to a brake disk of the type having an inner annular portion and an outer annular portion interconnected by a plurality of spaced arms, wherein stress in the disk caused by expansion of the outer annular portion is relieved without compromising rotational and lateral rigidity. In one embodiment of the present invention, a one-piece brake for a vehicle includes a radially inner annular portion having a plurality of circumferentially located mounting holes defining a mounting circle; a radially outer annular portion concentric with the radially inner annular portion and having opposite braking surfaces; and a plurality of connecting arms extending from an inner peripheral surface of the radially outer annular portion to an outer peripheral surface of the radially inner annular portion. Each of the plurality of connecting arms is tangent to an effective circle concentric with the mounting circle, wherein the effective circle has a radius greater than a radius of the mounting circle. In a more specific embodiment, an inner peripheral surface of the radially outer annular portion defines an outer arm connecting circle, and an outer peripheral surface of the radially inner annular portion defines an inner arm connecting circle. For each of the plurality of connecting arms, a straight phantom line connecting an outer midpoint of the connecting arm on the outer arm connecting circle and an inner midpoint of the connecting arm on the inner arm connecting circle intersects the connecting arm along an entire length of the connecting arm. To improve ventilation of the disk, the radially inner annular portion includes a plurality of openings disposed radially outwardly of the plurality of mounting holes, wherein the effective circle intersects the plurality of openings. Also, the radially outer annular portion includes a plurality of circumferentially disposed vent holes, wherein the plurality of vent holes are arranged to form a plurality of L-shapes. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of a particular embodiment of a brake disk according to the present invention mounted to a wheel hub and with a superimposed brake caliper; Fig. 2 is a partial cross-sectional front view of the brake disk according to the present invention mounted to the wheel hub; and Fig. 3 is a side view of the brake disk alone. DETAILED DESCRIPTION OF THE EMBODIMENTS Fig. 1 is a side view of a particular embodiment of a brake disk 10 according to the present invention mounted to a bicycle wheel hub 14 and with a superimposed brake caliper 16, Fig. 2 is a partial cross-sectional front view of brake disk 10 mounted to wheel hub 14, and Fig 3 is a side view of brake disk 10 alone. As shown in those Figures, and more particularly in Fig. 3, brake disk 10 includes a radially inner annular portion 20 having a plurality of circumferentially located mounting holes 24 defining a mounting circle MC, a radially outer annular portion 28 concentric with the radially inner annular portion 20 and having opposite braking surfaces 32 and 34 (Fig. 2); and a plurality of equally spaced connecting arms 38 extending from an inner peripheral surface 42 of the radially outer annular portion 28 to an outer peripheral surface 43 of the radially inner annular portion 20. As discussed below, each of the plurality of connecting arms 38 is tangent to an effective circle EC concentric with the mounting circle MC, wherein the effective circle EC has a radius ECR greater than a radius MCR of the mounting circle MC. Brake disk 10 is mounted to a mounting flange 44 of wheel hub 14 by bolts 46 that extend through mounting holes 24 and screw into threaded openings (48) in flange 44. Caliper 16 is of the four piston type wherein two pistons (not shown) press against each brake pad (not shown) to apply a stopping force to braking surfaces 32 and 34 in a well known manner. The mounting circle MC is determined by any circle that intersects the plurality of mounting holes 24. In this embodiment, the mounting circle MC is determined by a circle that intersects the center of each mounting hole 24. To determine the effective circle EC, it should be noted first that inner peripheral surface 42 of the radially outer annular portion 28 defines an outer arm connecting circle OAC, and the outer peripheral surface 43 of the radially inner annular portion 20 defines an inner arm connecting circle IAC. For each connecting arm 38, a straight phantom line P is drawn from an outer midpoint OM of the connecting arm 38 on the outer arm connecting circle OAC through an inner midpoint IM of the connecting arm 38 on the inner arm connecting circle IAC. The effective circle EC is the circle that is tangent to the resulting plurality of phantom lines P as shown in Fig. 3. In this embodiment, the radius of the effective circle EC may be up to twice the radius of the mounting circle MC. In this embodiment, each phantom line P intersects its corresponding connecting arm 38 along an entire length of the connecting arm. This is facilitated by forming the middle portion of each connecting arm 38 as a straight portion 48 having opposite sides 52 and 54. To reduce the weight of brake disk 10 and to increase the ventilation effect, a plurality of openings 60 are formed in radially inner annular portion 20 radially outwardly from the plurality of mounting holes 24. In this embodiment, each opening 60 has a generally triangular shape with rounded comers, and the effective circle EC intersects the widest portion of each triangle. Additionally, the side surfaces 52 and 54 of each of the plurality of connecting arms, the inner peripheral surface 42 of outer annular portion 28 and the outer peripheral surface 43 of inner annular portion 20 define a plurality of relatively large circumferentially disposed openings 64. As with openings 60, each opening 64 has a generally triangular shape with rounded corners. Thus, side 52 of each connecting arm 38 forms a curved portion 70 having a radius of curvature of, for example, 7 millimeters where it merges with outer annular portion 28, and a curved portion 74 having a radius of curvature of, for example, 4.5 millimeters where it merges with inner annular portion 20. Side 54 of each connecting arm 38 forms a curved portion 78 having a radius of curvature of, for example, 3.5 millimeters where it merges with outer annular portion 28. Because of the orientation of the connecting arm 38, such a curved portion does not form where side 54 merges with inner annular portion 20. Instead, a slight curve 82 having a radius of curvature of, for example, 10 millimeters, is formed on side 54 near the merge with inner annular portion 20 to further increase the rigidity of brake disk 10 in the rotational direction indicated by arrow A. Finally, a plurality of vent holes 84 are formed along the entire circumference of outer annular portion 28, wherein the plurality of vent holes 84 form a plurality of L-shapes. More specifically, three vent holes 84 form the vertical portion of the L-shape, and two vent holes form the horizontal portion of the L-shape.

Claims: A one piece brake disk (10) for a vehicle comprising: A radially inner annular portion (20) having a plurality of circumferentially located mounting holes (24) defining a mounting circle (MC); a radially outer annular portion (28) concentric with the radially inner annular portion (20) and having opposite braking surfaces (32, 34); a plurality of connecting arms (38) extending from an inner peripheral surface (42) of the radially outer annular portion (28) to an outer peripheral surface (43) of the radially inner annular portion (20); characterized in that an inner peripheral surface (42) of the radially outer annular portion (28) defines an outer arm connecting circle (OAC) and that an outer peripheral surface (43) of the radially inner annular portion (20) defines an inner arm connecting circle (IAC), and that for each of the plurality of connecting arms (38), a straight phantom line (P) connecting an outer midpoint (OM) of the connecting arm (38) on the outer arm connecting circle (OAC) and an inner midpoint (IM) of the connecting arm (38) on the inner arm connecting circle (IAC) intersects the connecting arm (38) along an entire length of the connecting arm (38) and that the straight phantom line (P) of each of the plurality of connecting arms is tangent to an effective circle (EC) concentric with the mounting circle (MC), wherein the effective circle (EC) has a radius greater than a radius of the mounting circle (MC). The brake disk (10) according to claim 1 wherein the radially inner annular portion (20) includes a plurality of first openings (60) disposed radially outwardly of the plurality of mounting holes (24). The brake disk (10) according to claim 2 wherein the effective circle (EC) intersects the plurality of first openings (60). The brake disk (10) according to one of the previous claims wherein a side surface (52, 54) of each of the plurality of connecting arms (38), the inner peripheral surface (42) of the radially outer annular portion (28) and the outer peripheral surface (43) of the radially inner annular portion (20) define a plurality of circumferentially disposed second openings (64). The brake disk (10) according to one of the previous claims wherein each of the plurality of connecting arms (38) has a straight middle portion (48). The brake disk (10) according to one of the previous claims, wherein the plurality of connecting arms (38) are equally spaced. The brake disk (10) according to one of the previous claims wherein the radially outer annular portion (28) includes a plurality of circumferentially disposed vent holes (84). The brake disk (10) according to claim 7 wherein the plurality of vent holes (84) are arranged to form a plurality of L-shapes. The brake disk (10) according to claim 8 wherein, for each L-shape, at least three vent holes form the vertical portion of the L-shape and at least two vent holes form the horizontal portion of the L-shape.

Inventors: MATSUI HISASHI, NAGO DAISUKE, MATSUI, HISASHI, NAGO, DAISUKE
Applicants: SHIMANO KK, SHIMANO INC.
Application year: 2000
Main classification: B62L1
IPC codes: F16D65, B62L1, F16D69