Roll back seal for a disc brake

Abstract: A roll back seal (26) is provided for a disc brake assembly (12,14) that reliably returns a piston (24) to a release position from a braking position with an extended sealing life. The present invention also provides a disc brake assembly that includes a calliper housing (20) with at least one piston receiving opening (26), first and second friction members (22) coupled to the calliper housing (20) and one or more pistons (24) movably coupled to the calliper housing (20) to move one or both of the friction members (22). The first and second friction members (22) form a rotor receiving slot therebetween. At least one of the friction members (22) is movably coupled to the calliper housing (20) and at least one piston (24) is movably coupled in at least one piston receiving opening (36) of the calliper housing (20) to move the at least one friction member (22) between a release position and a braking position. The piston receiving opening (36) has an annular side wall (38) with an annular groove (39) formed therein. The annular roll back seal (26) is located in the annular groove (39) between the calliper housing (20) and the piston (24). The roll back seal (26) has first and second annular end surfaces (50,52) and inner and outer annular sealing surfaces (54,56) extending between the first end surface (50) and the second end surface (52). The second end surface (52) has an annular recess (58) formed therein.

Description: This invention generally relates to a disc brake assembly with a roll back seal that reliably returns a piston to a release position from a braking position with improved sealing characteristics over a longer service life. Bicycling is becoming an increasingly popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving their components. One particular component of the bicycle, which has been extensively redesigned over the past years, is the braking systems of bicycles. In particular, the braking power of the braking systems is constantly being increased. There are several types of bicycle brake devices, which are currently available on the market. Examples of some types of common bicycle brake devices include rim brakes, calliper brakes and disc brakes. If a rider wants a very high performance brake system, then the rider typically wants a disc brake system. Disc brake systems provide a substantial braking power in relationship to the amount of braking force applied to the brake lever. Moreover, disc brake systems typically provide a high level of consistency in all types of weather and riding conditions. Of course, riders constantly desire better performance from disc braking systems, i.e., disc brake systems that have more braking power. Conventionally, a disc brake is composed of a pair of brake pads that are movably mounted to a calliper housing. The brake pads are pressed against a disc or rotor that is fixed to the wheel to halt the rotation of the disc and thus the wheel. The brake pads are moved toward the disc hydraulically or mechanically such as by a cam mechanism. The hydraulic disc brake systems typically provide a high level of consistency in all types of weather and riding conditions. In some hydraulic disc brakes, the seal rings are used to return the pistons from the braking position to the release position. These seal rings do not always reliably return the pistons to the release position which can cause rubbing between the friction pads and the rotor. Moreover, after extended use, these seal rings can become worn and/or fail, which can allow hydraulic fluid to leak from the disc brake assembly. A known seal is described in WO 96/23151, over which the present invention is characterised. The present invention provides a disc brake assembly with a roll back seal in accordance with claim 1. Embodiments of the assembly include a calliper housing with a piston receiving opening, a first and a second friction member coupled to the calliper housing, a piston movably coupled in the piston receiving opening and the annular roll back seal. The piston receiving opening has an annular side wall with an annular groove formed therein. The first and second friction members form a rotor receiving slot between the first and second friction members. At least one of the friction members is movably coupled to the calliper housing. The piston movably coupled in the piston receiving opening of the calliper housing moves at least one of the friction members between a release position and a braking position. The annular roll back seal is located in the annular groove between the calliper housing and the piston. The roll back seal includes a first annular end surface, a second annular end surface, an inner annular sealing surface and an outer annular sealing surface. The second annular end surface is spaced from the first end surface. The inner annular sealing surface extends between the first end surface and the second end surface. The outer annular sealing surface extends between the first end surface and the second end surface. The second end surface has an annular recess formed therein. These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. Embodiments of the present invention shall now be described, by way of example only, and with reference to the attached drawings which form a part of this original disclosure, in which: Figure 1 is a side elevational view of a bicycle with a front disc brake assembly and a rear disc brake assembly; Figure 2 is a schematic elevational view of the front disc brake assembly coupled to a front fork and a front disc brake operating mechanism of the bicycle illustrated in Figure 1; Figure 3 is a schematic elevational view of the rear disc brake assembly coupled to a rear fork and a rear disc brake operating mechanism of the bicycle illustrated in Figure 1; Figure 4 is an enlarged, side elevational view of a portion of the front disc brake assembly illustrated in Figure 2, with the bicycle frame removed for purposes of illustration; Figure 5 is a partial cross-sectional view of a bicycle hub and disc brake rotor of one of the wheels of the bicycle illustrated in Figure 1; Figure 6 is a partial exploded view of a portion of the front disc brake assembly illustrated in Figures 2 and 4; Figure 7 is an enlarged, partial cross-sectional view of the front disc brake assembly illustrated in Figures 2, 4 and 6 as seen along section line 7-7 of Figure 4 showing a roll back seal and a piston in a release position; Figure 8 is an enlarged, partial cross-sectional view of the front disc brake assembly illustrated in Figures 2, 4 and 6 as seen along section line 7-7 of Figure 4 showing the roll back seal and the piston in a braking position; Figure 9 is an enlarged cross-sectional view of a portion of the front disk brake assembly illustrated in Figure 7 showing one of the pistons and one of the roll back seals in the release position; Figure 10 is an enlarged cross-sectional view of a portion of the front disk brake assembly illustrated in Figure 8 showing one of the pistons and one of the roll back seals in the braking position; Figure 11 is an enlarged, exploded, partial cross-sectional view of the calliper housing, piston and roll back seal illustrated in Figures 9 and 10; Figure 12 is a side elevational view of one of the roll back seals of the front disc brake assembly illustrated in Figures 2, 4 and 6-11; Figure 13 is an end elevational view of the roll back seal illustrated in Figure 12; Figure 14 is a cross-sectional view of the roll back seal illustrated in Figures 12 and 13 as seen along section line 14-14 in Figure 12; Figure 15 is a side elevational view of one of the pistons of the front disc brake assembly illustrated in Figures 2, 4 and 6-11; Figure 16 is a cross-sectional view of the piston illustrated in Figure 15 as seen along section line 16-16 in Figure 15; Figure 17 is a partial, side elevational view of a portion of the calliper housing of the front disc brake assembly illustrated in Figures 2, 4 and 6-11; and Figure 18 is cross-sectional view of the portion of the housing illustrated in Figure 17 as seen along section line 18-18 in Figure 17. Referring initially to Figures 1-10, a bicycle 10 is illustrated with a front disc brake assembly 12 and a rear disc brake assembly 14. Front and rear disc brake assemblies 12 and 14 are relatively conventional fluid operated disc brakes fixedly coupled to a frame 13. Therefore, disc brake assemblies 12 and 14 will not be discussed or illustrated in detail herein, except as modified by the preferred embodiments of the present invention, as discussed below. Specifically, front disc brake assembly 12 is fixedly coupled to a front fork 15 of frame 13, and rear disc brake assembly 14 is fixedly coupled to rear fork 17 of frame 13, as best seen in Figures 2 and 3. Frame 13 includes a handle bar 19 mounted to front fork 15 to steer the bicycle 10. Bicycle 10 includes a pair of wheels 16 rotatably coupled to the bicycle frame 13. One wheel 16 is coupled to front fork 15, and one wheel 16 is coupled to rear fork 17. Each wheel 16 has a disc brake rotor 18 fixedly coupled thereto in a conventional manner. The bicycle 10 and various components thereof are relatively conventional. Therefore, bicycle 10 and its various components will not be discussed or illustrated in detail herein, except as these components relate to front and rear disc brake assemblies 12 and 14 in accordance with preferred embodiments of the present invention. Moreover, front and rear disc brake assemblies 12 and 14 are substantially identical. Therefore, only front disc brake assembly 12 will be discussed or illustrated in detail herein. However, it will be apparent to one skilled in the art from this disclosure that the descriptions of front disc brake assembly 12 also apply to rear disc brake assembly 14. As seen in Figures 6-8, front disc brake assembly 12 basically includes a calliper housing 20, a pair of friction members 22, a plurality of pistons 24 (typically four) and a plurality of roll back seals 26 (typically four). The term "roll back seal" as used herein is to be understood to be any seal that can promote the retraction of a piston when hydraulic or other fluid pressure that tends to move the piston has reduced. Front disc brake assembly 12 is operatively coupled to a brake operating mechanism 28a (shown in Figure 2 and discussed in more detail below). Calliper housing 20 is fixedly coupled to front forks 15 in a conventional manner (e.g. using threaded fasteners). First and second friction members 22 are coupled to calliper housing 20 to form a rotor receiving slot therebetween. At least one of the friction members 22 is movable relative to calliper housing 20, and preferably both friction members 22 are movable relative to calliper housing 20 as seen in Figures 7 and 8. At least one piston 24 is movably coupled to calliper housing 20. Preferably, each piston 24 is movably coupled to calliper housing 20. Roll back seals 26 are arranged between pistons 24 and calliper housing 20. Referring to Figures 4 and 6-8, calliper housing 20 is preferably formed of rigid metallic material such as cast aluminum. Calliper housing 20 is formed from a first piston body portion 30a and a second piston body portion 30b. First and second piston body portions 30a and 30b are fixedly coupled together by a plurality of bolts. First piston body portion 30a has a fluid inlet opening or first threaded hole 32 formed therein for receiving a fluid coupling unit 33 (shown in Figure 4). Second piston body portion 30b includes a second threaded hole 34 for receiving a bleed valve 35 (shown in Figure 4). Calliper housing 20 preferably includes four ports or piston receiving openings 36 (only two shown). More specifically, each of the first and second piston body portions 30a and 30b preferably has a pair of piston receiving openings 36 formed therein for receiving a pair of pistons 24 as seen in Figure 6. Each pair of piston receiving openings 36 formed in one of piston body portions 30a or 30b is arranged to oppose the pair of piston receiving openings 36 formed in the other one of piston body portions 30a or 30b. Each pair of pistons 24 (i.e. mounted in one of the piston body portions 30a or 30b) is arranged to move one of the friction members 22 toward disc brake rotor 18. Piston receiving openings 36 are in fluid communication with fluid coupling unit 33 and bleed valve 35 via a network of fluid conduits 37 as seen in Figures 7 and 8. Thus, when actuating fluid is supplied to calliper housing 20 through fluid coupling unit 33, the actuating fluid flows through the network of conduits 37 into the piston receiving openings 36. A portion of one of the conduits 37 acts as the fluid inlet opening of piston body portion 30a. Each piston receiving opening 36 is preferably an annular opening sized and configured to receive one of the pistons 24 therein. As best seen in Figures 9-10 and 17-18, each piston receiving opening 36 has an annular side wall 38 with an annular groove 39 formed therein for receiving one of the roll back seals 26. Each piston receiving opening 36 has an open end facing one of the friction members 22. Grooves 39 are preferably adjacent the open ends of piston receiving openings 36. Each piston receiving opening 36 preferably has a minimum diameter A as seen in Figure 18 (i.e. the minimum diameter of side wall 38) smaller than a minimum uninstalled diameter B of each roll back seal 26 as seen in Figure 14. More specifically, uninstalled minimum diameter B is preferably about 0.2 mm larger than minimum diameter A. Additionally, minimum diameter A of each piston receiving opening 36 is preferably about 0.1 mm larger than an external diameter P of each piston 24. As seen in Figures 11 and 18, each annular groove 39 basically includes an annular first interior end surface 40, an annular second interior end surface 42 and an annular contact surface 44. Interior end surface 42 is adjacent the open end of piston receiving opening 36 and spaced from interior end surface 40. Contact surface 44 extends between interior end surfaces 40 and 42. Contact surface 44 is a conical surface tapering radially inwardly from the open end of piston receiving opening 36. Each groove 39 preferably has a maximum diameter C (i.e. maximum diameter of contact surface 44) smaller than a maximum uninstalled diameter D of each roll back seal 26 as seen in Figure 14. More specifically, maximum uninstalled diameter D is preferably about 0.362 mm larger than maximum diameter C. Moreover, each groove 39 preferably has an axial length E larger than an axial length X of each roll back seal 26 and a maximum radial width of about 1.819 mm. First interior end surface 40 includes an annular first tapered section 40a, an annular radial section 40b and an annular second tapered section 40c and second interior end surface 42 includes an annular first tapered section 42a, an annular radial section 42b and an annular second tapered section 42c as seen in Figure 11. Radial sections 40b and 42b are preferably parallel to each other and axially spaced about 2.6 mm from each other. Additionally, radial sections 40b and 42b are preferably perpendicular to side wall 38. Radial section 40b has a larger radial width than radial section 42b. More specifically, axial length E of groove 39 is preferably measured between radial sections 40b and 42b. Contact surface 44 extends between tapered sections 40c and 42c. Contact surface 44 is preferably angled about 6 degrees relative to side wall 38 and has an axial length of about 1.992 mm. Accordingly, contact surface 44 is preferably angled less than 90 degrees relative to radial section 42b. More specifically, contact surface 44 is preferably angled about 84 degrees relative to radial section 42b. Each second tapered section 40c and 42c preferably has an axial length of about 0.304 mm and forms a 135 degree angle with the respective radial sections 40b and 42b. Tapered section 40a is preferably angled about 225 degrees relative to side wall 38 and radial section 40b. Tapered section 42a is preferably angled about 243 degrees relative to side wall 38 and angled about 207 degrees relative to radial section 42b. Tapered section 42a preferably has an axial length of about 0.55 mm and a radial width of about 1.05 mm. Referring to Figures 12-14, each roll back seal 26 is an annular member formed of a resilient material such as rubber or flexible plastic. More specifically, each roll back seal 26 is preferably formed of hydrogenated Nitrile rubber with a hardness of about Hs 75. Moreover, each roll back seal 26 is preferably formed by injection moulding as a one-piece unitary member. Of course it will be apparent to those skilled in the art from this disclosure that roll back seals 26 could be formed of alternate materials and/or manufacturing techniques as needed and/or desired. Each roll back seal 26 is located in one of the annular grooves 39 and acts to circumferentially seal the internal area of one of the piston receiving openings 36 from the outside of calliper housing 20 when pistons 24 are arranged in piston receiving openings 36 as best seen in Figures 9-10. Therefore, when actuating fluid is supplied to piston receiving openings 36, pistons 24 are moved toward rotor 18. Accordingly, friction members 22 are also moved toward disc brake rotor 18 to produce a stopping action on rotor 18, and therefore, wheel 16. Roll back seals 26 also act to bias pistons 24 toward the release position from the braking position. In other words, roll back seals 26 are elastically deformed when pistons 24 are moved to the braking position from the release position, and produce an elastic restoration force to move pistons 24 back to the release position when actuating fluid is drained from piston receiving openings 36. As best seen in Figures 11-14, each roll back seal 26 basically includes a first annular end surface 50, a second annular end surface 52, an inner annular sealing surface 54 and an outer annular sealing surface 56. Second annular end surface 52 is spaced from first annular end surface 50. Inner and outer annular sealing surfaces 54 and 56 extend between first annular end surface 50 and second annular end surface 52. Second annular end surface 52 has an annular recess 58 formed therein. Inner and outer sealing surfaces 54 and 56 are preferably substantially parallel to each other and spaced about 1.9 mm apart from each other prior to installation of roll back seal 26 in groove 39. This space is considered a maximum uninstalled radial width W of roll back seal 26. Additionally, first and second end surfaces 50 and 52 are also preferably substantially parallel and spaced about 1.9 mm apart from each other prior to installation of roll back seal 26 in groove 39. This space is considered a maximum uninstalled axial length X of roll back seal 26. First and second end surfaces 50 and 52 also preferably form 90 degree angles relative to inner and outer sealing surfaces 54 and 56 prior to installation of roll back seal 26 in groove 39. Accordingly, roll back seal 26 has a partially square cross-sectional shape prior to installation of roll back seal 26 in groove 39. As mentioned above, each of the roll back seals 26 has a maximum uninstalled diameter D larger than the maximum diameter C of groove 39 and a minimum uninstalled diameter B larger than the minimum diameter of piston receiving opening 36 as seen in Figures 14 and 18. Accordingly, roll back seals 26 are deformed when installed in grooves 39 as seen in Figures 9-10. More specifically, annular contact surface 44 contacts outer sealing surface 56 when roll back seal 26 is installed in groove 39. Therefore, inner and outer sealing surfaces 54 and 56 are substantially parallel to one another prior to installation but outer seal surface 56 is deformed to be non-parallel to inner sealing surface 54 upon installation of roll back seal 26 between piston body portion 30b and piston 24. Referring again to Figure 11, annular recess 58 basically includes a first annular interior surface 60, a second annular interior surface 62 and a curved annular interior surface 64. Second annular interior surface 62 is spaced from first annular interior surface 60. First and second annular interior surfaces 60 and 62 are preferably substantially parallel to each other. Curved interior surface 64 connects first and second interior surfaces 62 and 64. Curved interior surface 64 is preferably a concave surface with a semicircular cross-section and a radius equal to one half of the radial width of recess 58. In other words, recess 58 has a substantially U-shaped cross-section with an open end adjacent second end surface 52. Moreover, the open end of recess 58 faces first end surface 40 of groove 39 when roll back seal 26 is installed in groove 39. More specifically, each recess 58 has an axial length Y and a radial width Z. The radial width Z of recess 58 is preferably larger than the axial length Y of recess 58. The axial length Y of recess 58 consists of the axial length of interior surfaces 60, 62 and the axial length of curved interior surface 64. Preferably, each of the interior surfaces 60 and 62 has an axial length smaller than the axial length of curved interior surface 64. More specifically, each of the interior surfaces 60, 62 preferably has an axial length of about 0.3 mm and curved interior surface 64 preferably has an axial length of about 0.4 mm. Accordingly, recess 58 preferably has an axial length Y of about 0.7 mm and a radial width Z of about 0.8 mm. In any case, recess 58 preferably has a radial width Z of about 42.1% of the maximum uninstalled radial width W of roll back seal 26 and an axial length Y of about 36.8% of the maximum uninstalled axial length X of roll back seal 26. Furthermore, recess 58 is preferably radially centred relative to inner and outer sealing surfaces 54 and 56 to divide end surface 52 into a radially inner section 52a and a radially outer section 52b prior to installation of roll back seal 26 in groove 39. Accordingly, radially inner section 52a preferably has a radial width equal to a radial width of radially outer section 52b prior to installation of roll back seal 26 in groove 39. Each of the radially inner and outer sections 52a and 52b preferably has a radial width of about 28.9% of the maximum uninstalled radial width W of roll back seal 26. In other words, each of the radially inner and outer sections 52a and 52b preferably has an uninstalled radial width of about 0.55 mm. In use, the or each roll back seal 26 is located in a respective groove 39. When the piston 24 moves, friction between the seal 26 and an outer surface of the piston 24 tends to open or widen the recess 58, and the end surface 50 at the radially inner section 52a of the seal 26 is pushed into the annular tapered section 42a (see Fig. 10), while the radially outer section 52b abuts against annular radial section 42b and annular second tapered section 42c. The radially inner section 52a of the seal 26 is deformed into the annular tapered section 42a and thus stores energy because of the resilience of the material of seal 26. As the force applied to the piston 24 is removed, the resilience of the material that forms the seal 26 tends to reform the seal 26 so that the inner and outer sealing surfaces 54, 56 resume their original configuration (see Fig. 9). This causes the piston 24 to be retracted because of the frictional contact between the seal 26 and the outer surface of the piston 24. The force or pressure that is used to move the piston 24 also acts against the second end surface 52 of the seal 26, and thus, it also acts on the recess 58. In particular, the force acts on the first and second interior surfaces 60, 62 and also on curved annular surface 64 of the recess 58. The force acting on the two interior surfaces 60, 62 urges the seal 26 into contact with the groove 39 and the outer surface of the piston 24. This force helps to maintain the radially inner section 52a in contact with the piston 24, and the radially outer section 52b in contact with the contact surface 44. The force thus acts to keep the seal 26 in contact with the piston 24 during movement thereof. Referring again to Figures 4 and 6-8, preferably two friction members 22 are movably coupled to calliper housing 20 such that a rotor receiving slot is formed therebetween, as discussed above. Each friction member 22 basically includes a plate 70 with a friction material 72 fixedly coupled thereto in a conventional manner. Each plate is preferably formed of a rigid metallic material in a conventional manner. Each plate 70 includes a mounting hole 74 for slidably receiving a mounting pin 76 therethrough. Mounting pin 76 is partially threaded at one end and receives a securing member 77 on the opposite end to secure friction members 22 to calliper housing 20 in a conventional manner. A spring plate or pad spring 71 is arranged between friction members 22 to bias friction members 22 away from each other as shown in Figures 7-8. The pad spring 71 contacts each of the plates 70. Therefore, when actuating fluid is drained from piston receiving openings 36, the pad spring 71 acts to return friction members 22 to a release position from a braking position and roll back seals 26 acts to return pistons 24 to a release position from a braking position. Accordingly, reliable movement of pistons 24 and friction members 22 can be achieved. Referring now to Figures 9-11 and 15-16, each piston 24 is preferably an annular member formed of rigid metallic material, such as cast aluminum. Each piston 24 is preferably movably coupled to calliper housing 20 to move one of the friction members 22 under pressure from the actuating fluid between a release position and a braking position. Roll back seals 26 frictionally retain pistons 24 in piston receiving openings 36. More specifically, each of the pistons 24 has an external diameter P about 0.1 mm smaller than minimum diameter A of each piston receiving opening 36. Each roll back seal 26 is deformed to extend beyond groove 39 into one of the piston receiving openings 36 and contact one of the pistons 24 to retain the piston 24 in piston receiving opening 36. Movement of the pistons 24 from the release position to the braking position is caused by supplying actuating fluid to the piston receiving openings 36, as discussed above. Pistons 24 are returned to the release position from the braking position by roll back seals 26 when actuating fluid is drained from receiving openings 36. Preferably, each piston 24 has an external diameter P of about 15.4 mm. Accordingly, the dimensions of other parts (i.e. roll back seals 26, piston receiving openings 36 and grooves 39) of disc brake assembly 12 are sized and configured according to the dimensional relationships described above. Of course, it will be apparent to those skilled in the art from this disclosure that pistons 24 could be larger and/or smaller as needed and/or desired. For example, alternatively, each piston could have an external diameter P of about 13.5 mm if needed and/or desired. In any case, regardless of the dimensions of pistons 24, the dimensional relationships described above are preferably maintained. As best seen in Figures 9-10 and 15-16, each piston 24 preferably includes an internal recess 78 facing towards one of the respective friction members 22. Each internal recess 78 includes an end wall and a side wall. Preferably, each internal recess 78 is an annular recess with an annular retaining groove formed in the side wall. Each internal recess 78 is preferably sized and configured to receive a heat insulator 79 therein. Each heat insulator 79 is retained in one of the recesses 78 by a retaining ring 79a. Each heat insulator 79 is preferably an annular member formed of a material with a low heat transfer coefficient such as plastic. Moreover, each heat insulator 79 is disposed between one of the friction members 22 and one of the pistons 24 to dissipate the heat transferred from friction members 22 to other parts of disc brake assembly 12. Accordingly, heat transferred to the actuating fluid can also be dissipated. Heat insulators 79 are relatively conventional. Accordingly, heat insulators 79 will not be discussed or illustrated in detail herein. Referring again to Figures 1-3, a pair of brake operating mechanisms 28a and 28b are illustrated and are conventional disc brake operating mechanisms. Therefore, brake operating mechanisms 28a and 28b will not be discussed or illustrated in detail herein. Brake operating mechanisms 28a and 28b are provided to control disc brake assemblies 12 and 14. Brake operating mechanisms 28a and 28b are preferably fixedly mounted on handle bar 19 adjacent the hand portions of handle bar 19. Accordingly, brake operating mechanisms 28a and 28b are operated in a conventional manner such that disc brake assemblies 12 and 14 move friction members 22 from a release position in which bicycle wheels 16 and the disc brake rotors 18 are free to rotate, and a braking position. In the braking position, disc brake assemblies 12 and 14 apply a braking force against disc brake rotor 18 to stop rotation of bicycle wheels 16 and disc brake rotors 18. Brake operating mechanisms 28a and 28b will now be described in more detail. Basically, brake operating mechanisms 28a and 28b are designed to actuate the disc brake assemblies 12 and 14 in a conventional manner to apply a forcible gripping action on disc brake rotor 18 to stop rotation of one of the wheels 16. Brake operating mechanism 28b actuates rear disc brake assembly 14 and brake operating mechanism 28a actuates front disc brake assembly 12. Brake operating mechanism 28b is identical to brake operating mechanism 28a except brake operating mechanism 28b is a mirror image of brake operating mechanism 28a. Each of the brake operating mechanisms 28a and 28b basically includes a brake lever 80, a hydraulic or master cylinder 81, a hydraulic or master piston 82, and an actuation fluid reservoir 83. Preferably, each of the brake operating mechanisms 28a and 28b is a single unit, which is mounted on handlebar 19. In particular, referring to either one of the brake operating mechanisms 28a and 28b, brake lever 80 includes a mounting portion 84 and a lever portion 85. Mounting portion 84 is designed to be clamped onto handle bar 19 in a conventional manner. Mounting portion 84 is integrally formed with master cylinder 81 such that master cylinder 81, master piston 82 and actuation fluid reservoir 83 are all supported on mounting portion 84 of brake lever 80. Lever portion 85 is pivotally coupled to mounting portion 84 for movement between a release position and a braking position. Normally, lever portion 84 is maintained in a release position in a conventional manner. Master piston 82 is movably mounted within master cylinder 81 in a conventional manner. More specifically, actuation fluid reservoir 83 is mounted on master cylinder 81 and is in fluid communication with the interior bore of master cylinder 81 for supplying actuation fluid thereto. Master piston 82 is connected at one end to lever portion 85 for axially moving master piston 82 within master cylinder 81. Accordingly, actuation of lever portion 85 causes master piston 82 to move axially within master cylinder 81. This movement of master piston 82 within master cylinder 81 directs fluid pressure through a hydraulic line 86 which is coupled to one of the disc brake assemblies 12 and 14 via fluid coupling units 33. Thus, the pressurised actuating fluid causes the pistons 24 and friction members 22 to move so as to engage disc brake rotors 18 to stop rotation of wheels 16. The terms of degree such as "substantially", "about" and "approximately" as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms should be construed as including a deviation of ± 25% of the modified term if this would not negate the meaning of the word it modifies. While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims.

Claims: A disc brake assembly comprising: a calliper housing (20) with a piston receiving opening (36), the piston receiving opening (36) having an annular side wall (38) with an annular groove (39) formed therein; a first and a second friction member (22) coupled to the calliper housing (20) to form a rotor receiving slot between the first and second friction members (22) with at least one of the first and second friction members (22) being movably coupled to the calliper housing (20); a piston (24) movably coupled in the piston receiving opening (36) of the calliper housing (20) to move the at least one of the first and second friction members (22) between a release position and a braking position; and an annular roll back seal (26) located in the annular groove (39) between the calliper housing (20) and the piston (24), the roll back seal (26) having first and second annular end surfaces (50, 52) and inner and outer annular sealing surfaces (54, 56) extending between the first end surface (50) and the second end surface (52), the second end surface (52) having an annular recess (58) formed therein, wherein the annular recess (58) includes a first annular interior surface (60), a second annular interior surface (62) spaced from the first interior surface (60) and a curved annular interior surface (64) connecting the first and second interior surfaces (60, 62); characterised in that the first and second interior surfaces (60, 62) are substantially parallel to one another, and each has an axial length smaller than an axial length of the curved interior surface (64). A disc brake assembly according to claim 1, wherein the curved interior surface (64) is a concave surface with a semicircular cross-section. A disc brake assembly according to any preceding claim, wherein the annular recess (58) has an axial length (Y) and a radial width (Z) larger than the axial length (Y). A disc brake assembly according to claim 3, wherein the radial width (Z) is between 0.7mm and 0.9mm and the axial length (Y) is between 0.6mm and 0.8mm. A disc brake assembly according to any preceding claim, wherein the annular recess (58) is radially centred relative to the inner and outer annular sealing surfaces (54, 56) to divide the second annular end surface (52) into a radially inner section (52a) and a radially outer section (52b) prior to installation of the roll back seal (26) in the groove (39). A disc brake assembly according to claim 5, wherein each of the radially inner and outer sections (52a, 52b) has an uninstalled radial width of between 28% and 30% of a maximum uninstalled radial width (W) of the roll back seal (26). A disc brake assembly according to any preceding claim, wherein the roll back seal (26) is formed as a one-piece unitary member. A disc brake assembly according to any preceding claim, wherein the roll back seal (26) is formed of hydrogenated Nitrile rubber. A disc brake assembly according to any preceding claim, wherein the roll back seal (26) has a maximum uninstalled diameter (D) and the groove (39) has a maximum diameter (c) smaller than the maximum uninstalled diameter (D) of the roll back seal (26). A disc brake assembly according to any preceding claim, wherein the roll back seal (26) has a minimum uninstalled diameter (B) and the piston receiving opening (36) has a minimum diameter (A) smaller than the minimum uninstalled diameter (B) of the roll back seal (26). A disc brake assembly according to any preceding claim, wherein the annular groove (39) has an annular contact surface (44) that contacts the outer sealing surface (56), the inner and outer sealing surfaces (54, 56) are substantially parallel to one another prior to installation but the outer seal surface (56) is deformed to be non-parallel to the inner sealing surface (54) upon installation of the roll back seal (26) between the calliper housing (20) and the piston (24). A disc brake assembly according to any preceding claim, wherein the annular groove (39) has an axial length larger than an axial length (X) of the roll back seal (26). A disc brake assembly according to any preceding claim, wherein the recess (58) has an axial length (Y) of between 36% and 38% of a maximum axial length (X) of the roll back seal (26). A disc brake assembly according to any preceding claim, wherein the recess (58) has a radial width (Z) of between 42% and 43% of a maximum uninstalled radial width (W) of the roll back seal (26).

Inventors: OHISHI RIKIMASA, OHISHI, RIKIMASA
Applicants: SHIMANO KK, SHIMANO INC.
Application year: 2001
Main classification: F16D65
IPC codes: F16D65, B60T1, F16D55