Apparatus for a disk brake

The present invention is directed to braking devices and, more particularly, to an apparatus for a disk brake.

Disk brake devices for braking vehicles, such as bicycles, operate by applying friction to a disk brake rotor that is non-rotatably mounted to a wheel. A well-known example of such a disk brake device is a piston retraction type brake device disclosed in Japanese Unexamined Patent Application 10-325432. In that device, a caliper has inner peripheral surfaces that form a pair of opposed cylindrical openings, a piston slidably mounted in each cylindrical opening, and an elastic piston ring seal that seals off the clearance space between the piston and the inner peripheral surface of the cylindrical opening. More specifically, each piston ring is mounted in an annular seal groove formed in the inner peripheral surface its associated cylinder. A movement restricting part is formed in the seal groove for restricting movement of an outer peripheral portion of the piston ring in the braking direction, and a movement permitting part is formed in the seal groove for permitting movement of an inner peripheral portion of the piston ring in the braking direction. The movement permitting part typically has the form of a surface that extends radially inwardly from the movement restricting part and inclines in the braking direction.

When the disk brake is activated, the piston moves in the braking direction to press a brake pad toward the disk brake rotor. The piston ring tends to move with the piston as a result of the frictional contact between the inner peripheral surface of the piston ring and the outer peripheral surface of the piston. However, such movement is generally blocked by the movement restricting part of the seal groove. On the other hand, an inner peripheral portion of the piston ring continues to move with the piston and bends toward the surface of the movement permitting part. The elastic resilience of the piston ring, and particularly the energy stored in the inner peripheral portion of the piston ring that bends toward the surface of the movement permitting part, is used to pull the piston away from the disk rotor when the brake is released.

Since the movement permitting part typically has the form of a surface that is inclined relative to the movement restricting part, the point of contact between the piston ring and the seal groove that functions as a fulcrum for the bending portion of the piston ring tends to move radially inwardly as the inner peripheral portion of the piston ring bends in the braking direction. This, in turn, causes the elastic modulus (spring constant) of the piston ring to increase, thus resulting in greater piston ring displacement relative to the applied load and a corresponding deterioration in brake feel due to variation in shoe clearance and brake release timing.

The present invention is directed to various features of an apparatus for a disk brake. In one embodiment, an apparatus for a disk brake comprises a caliper body having an inner peripheral surface and a seal groove disposed at the inner peripheral surface. The inner peripheral surface is dimensioned to slidably receive a piston therein, wherein the piston moves in a direction of a braking direction axis, and the seal groove is dimensioned to receive a seal therein so that the seal can seal a space between the inner peripheral surface and the piston. The seal groove comprises a movement restricting part that restricts movement of the seal in the direction of the braking direction axis, and a movement permitting part formed as a step facing radially inwardly. Additional inventive features will become apparent from the description below, and such features alone or in combination with the above features may form the basis of further inventions as recited in the claims and their equivalents.

FIG. 1 is a side view of a particular embodiment of a bicycle;

FIG. 2 is a partial cross sectional view of a particular embodiment of a disk brake device;

FIG. 3 is a detailed cross sectional view of a particular embodiment of a seal groove;

FIGS. 4A-4E illustrate deformation of a piston ring disposed in the seal groove shown in FIG. 3 upon movement of its corresponding piston in a braking direction;

FIGS. 5A-4E illustrate deformation of a piston ring disposed in a conventional seal groove upon movement of its corresponding piston in a braking direction; and

FIG. 6 is a graph of piston ring displacement relative to load corresponding to the examples shown in FIGS. 4A-4E and 5 A- 5 E.

FIG. 1 is a side view of a particular embodiment of a bicycle 1 . Bicycle 1 is a mountain bicycle comprising a frame 2 with a rear suspension 13 r , a front fork 3 including a front suspension 13 f mounted to the front of frame 2 for rotation around an inclined axis, a handlebar assembly 4 mounted to the upper part of fork 3 , a front wheel 6 rotatably attached to the lower part of fork 3 , a rear wheel 7 rotatably attached to the rear of frame 2 , a drive mechanism 5 including a front transmission 8 and a rear transmission 9 , and a saddle 18 mounted to an upper middle portion of frame 2 .

A front wheel disk brake caliper assembly 12 f operates in conjunction with a front disk brake rotor 20 f attached to a hub 6 a of front wheel 6 for braking front wheel 6 , and a rear wheel disk brake caliper assembly 12 r operates in conjunction with a rear disk brake rotor 20 r attached to a hub 7 a of rear wheel 7 for braking rear wheel 7 . Brake lever assemblies 15 are provided on both ends of handlebar assembly 4 (only one brake lever assembly 15 is shown in FIG. 1 ). One brake lever assembly 15 is connected to front wheel disk brake caliper assembly 12 f through tubing 16 for supplying hydraulic brake fluid to front wheel disk brake caliper assembly 12 f , and the other brake lever assembly 15 is connected to rear wheel disk brake caliper assembly 12 r through tubing 17 for supplying hydraulic brake fluid to rear wheel disk brake caliper assembly 12 r . Front and rear wheel disk brake caliper assemblies 12 f and 12 r have generally the same structure, so only front wheel disk brake caliper assembly 12 f will be described in detail.

As shown in FIG. 2 , front disk brake caliper assembly 12 f comprises a caliper 21 , a pair of pistons 22 a and 22 b slidably mounted in cylindrical openings 30 a and 30 b formed by inner peripheral surfaces of caliper 21 , and a pair of piston rings 23 a and 23 b mounted in corresponding seal grooves 31 a and 31 b formed by the inner peripheral surfaces defining openings 30 a and 30 b . In this embodiment, caliper 21 has a two-part structure that defines an opening 21 a dimensioned to receive the outer circumference of front disk brake rotor 20 f therein. Opening 30 a is closed off by the body of caliper 21 , whereas opening 30 b is closed off by a cap 34 that is screwed into caliper 21 . Oil passages (not shown) are formed in caliper 21 to communicate hydraulic brake fluid from brake tubing 16 into openings 30 a and 30 b in response to the operation of the associated brake lever assembly 15 .

Pistons 22 a and 22 b are cylindrically shaped members with corresponding flanges 32 a and 32 b facing front disk brake rotor 20 f . Brake pads 33 a and 33 b are mounted on flanges 32 a and 32 b , respectively, for contacting front disk brake rotor 20 f . Piston rings 23 a and 23 b are mounted in seal grooves 31 a and 31 b so as to contact the outer peripheral surfaces of pistons 22 a and 22 b , respectively. As a result, piston rings 23 a and 23 b function as seals, to thereby seal off the clearance space between pistons 22 a and 22 b and the inner peripheral surfaces defining openings 30 a and 30 b . Such contact with pistons 22 a and 22 b also return pistons 22 a and 22 b to the brake release position by means of elastic resilience. Piston rings 23 a and 23 b comprise annular members with a generally rectangular cross section and may be formed from nitrile rubber (NBR), including hydrogenated nitrile rubber (HNBR), for example.

FIG. 3 is a detailed cross sectional view of seal groove 31 b . Seal groove 31 a is constructed the same way, albeit in a mirror image. Accordingly, the corresponding reference numbers for seal groove 31 a are shown as well, but a separate description is omitted. As shown in FIG. 3 , seal grooves 31 a and 31 b comprise an inner peripheral surface 31 c , a movement restricting part formed by a surface 35 b extending radially inwardly from inner peripheral surface 31 c , and a movement permitting part formed by a stepped surface 36 b and a surface 37 b extending radially inwardly from stepped surface 36 b . Surface 35 b forming the movement restricting part restricts axial movement of a radially outer portion of piston ring 23 b in a direction of a braking direction axis X when piston 22 b moves toward front disk brake rotor 20 f . On the other hand, surfaces 36 b and 37 b forming the movement-permitting part permit axial movement of a radially inner portion of piston ring 23 b toward front disk brake rotor 20 f with piston 22 b . Inner peripheral surface 31 c of seal groove 31 b is a tapered surface that expands radially outwardly in the direction of braking direction axis X toward front disk brake rotor 20 f . Forming inner peripheral surface 31 c in this manner allows the inner peripheral surface of piston ring 23 b at the portion of piston ring 23 b facing away from front disk brake rotor 20 f to contact the outer peripheral surface of piston 22 b more firmly than the inner peripheral surface of piston ring 23 b at the portion of piston ring 23 b facing front disk brake rotor 20 f , especially when piston ring 23 b has a rectangular cross section. Such differential contact forces promote the deformation of the radially inner portion of piston ring 23 b toward surface 37 b when piston 22 b moves toward front disk brake rotor 20 f.

In general, surface 35 b extends radially inwardly from inner peripheral surface 31 c substantially perpendicular to braking direction axis X, surface 36 b extends from surface 35 b substantially parallel to and facing braking direction axis X, and surface 37 b extends radially inwardly from surface 36 b substantially perpendicular to braking direction axis X. Thus, surface 36 b has an overall cylindrical shape, is parallel to piston 22 b and braking direction axis X, and is substantially perpendicular to both surfaces 35 b and 37 b . A junction between surfaces 35 b and 36 b forms a rounded corner having a radius of curvature R 1 in a range from approximately 0.1 mm to approximately 0.5 mm, and a junction between surfaces 36 b and 37 b forms a rounded corner having a radius of curvature R 2 in a range from approximately 0.1 mm to approximately 0.5 mm.

When brake lever assembly 15 is operated to supply hydraulic fluid to openings 30 a and 30 b , pistons 22 a and 22 b move toward front disk brake rotor 20 f , and brake pads 33 a and 33 b press against and apply frictional force to front disk brake rotor 20 f , thereby braking front wheel 6 . At that time, as shown by a conducted simulation in FIGS. 4A-4E , the movement of the radially outer portions of piston rings 23 a and 23 b toward front disk brake rotor 20 f is restricted by surfaces 35 a and 35 b , but the radially inner portions of piston rings 23 a and 23 b continue moving toward front disk brake rotor 20 f as a result of the frictional contact between piston rings 23 a and 23 b and their corresponding pistons 22 a and 22 b . This, in turn, causes a bend in piston rings 23 a and 23 b at the junction of surfaces 35 a , 35 b and surfaces 36 a , 36 b . This movement continues until piston ring 23 b contacts surface 37 b and forms a space at a junction between surfaces 36 b and 37 b . Because of the construction of stepped surfaces 36 a and 36 b , a fulcrum position 40 for the bending portion of each piston ring 23 a and 23 b is always near the corners formed at the junctions of surfaces 35 a , 35 b and 36 a , 36 b . This maintains a low spring constant for piston rings 23 a and 23 b . When the hydraulic pressure is released, the elastic resilience of piston rings 23 a and 23 b pull pistons 22 a and 22 b away from front disk brake rotor 20 f , and piston rings return to the state shown in FIG. 4A .

FIGS. 5A-5E show the corresponding movement of a piston ring 123 b in a conducted simulation of a conventional caliper structure. As shown in those Figures, a fulcrum position 140 for the bending portion of piston ring 123 b moves radially inwardly along a movement permitting surface 136 b during operation of the caliper assembly.

FIG. 6 is a graph showing load (friction force between piston and piston ring) as a function of displacement (extent of piston movement) for the simulations shown in FIGS. 4A-4E and 5 A- 5 E. In the simulations, 1 to 10 kgf load was placed on the pistons, resulting in the piston deformation illustrated in FIGS. 4A through 4E and FIGS. 5A through 5E . In FIG. 6 , the white triangles indicate the relationship between displacement and load for the piston ring 23 b mounted in the seal grove 31 b for each situation depicted in FIGS. 4A-4E , and the black circles indicate the relationship between displacement and load for the piston ring 123 b mounted in a conventional seal groove for each situation depicted in FIGS. 5A-5E . In FIG. 6 , FMAX indicates the maximum friction between the piston ring and the piston under all conditions, while FMIN indicates the minimum friction between the piston ring and the piston under all conditions. The lower the displacement between FMAX and FMIN, the lower the piston movement away from front disk brake rotor 20 f (roll back), and hence shoe clearance, when the brakes are released. This also results in a better braking feel.

As shown in FIG. 6 , piston ring 23 b contacted surface 37 b of movement-permitting component 37 b around 0.35 mm. As a result, there was an inflection point of displacement, and the variation in displacement relative to load (friction) was lower. More specifically, the displacement RB 1 between FMAX and FMIN was approximately 0.05 mm. On the other hand, since the fulcrum position 140 for the conventional piston ring 123 b moves radially inwardly as shown in FIGS. 5A-5E as the load is increased, the spring constant of piston ring 123 b correspondingly increases. This results in displacement RB 2 of 0.18 mm between FMAX and FMIN. The variation in piston displacement when the brake was released was about 60 to 70% lower in the present embodiment compared to a conventional caliper assembly.

While the above is a description of various embodiments of inventive features, further modifications may be employed without departing from the spirit and scope of the present invention. For example, surfaces 36 a , 36 b and 37 a , 37 b of the movement permitting parts were flat, and surfaces 37 a , 37 b were parallel to surfaces 35 a and 35 b of the movement restricting parts, but the various surfaces need not be flat as long as they form a radially inward step. For example, the various surfaces may be tapered or curved surfaces. Similarly, while surfaces 36 a and 36 b formed the shape of a cylinder parallel to pistons 22 a and 22 b , surfaces 36 a and 36 b also may be tapered, with or without rounded corners in any event.

The size, shape, location or orientation of the various components may be changed as desired. Components that are shown directly connected or contacting each other may have intermediate structures disposed between them. The functions of one element may be performed by two, and vice versa. The structures and functions of one embodiment may be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). Thus, the scope of the invention should not be limited by the specific structures disclosed or the apparent initial focus or emphasis on a particular structure or feature.