CONCENTRIC COMPENSATOR CHAMBER AND MASTER CYLINDER FOR DISC BRAKE SYSTEM

Abstract: A disc brake assembly (10; 100) is provided which is hydraulically operated with brake fluid. A master cylinder chamber (30) is formed within a concentric cylinder (18) about which is concentrically disposed an internal thermal compensation chamber (42). The master cylinder chamber (30) and the internal thermal compensation chamber (42) are in fluid communication to allow for the passage of the brake fluid therebetween. A master cylinder piston (32) is slidably disposed in the master cylinder chamber (30) to generate pressure build-up in the brake fluid to cause actuation of disc brakes. A compensator piston (50) is disposed within the internal thermal compensation chamber (42) and is urged by a spring (56) to be in engagement with the brake fluid. By continuously maintaining engagement between the compensator piston (50) and the brake fluid, there can be the prevention of air pocket formation in the brake fluid, thus eliminating the need for air pocket removal through bleeding.

Description: CONCENTRIC COMPENSATOR CHAMBER AND MASTER CYLINDER FOR DISC BRAKE SYSTEM This application claims priority on U.S. Provisional Application No. 60/083,276, filed April 28, 1998. BACKGROUND OF THE INVENTION 1. Field of the Invention. The invention disclosed herein relates to design of disc brake systems for use in connection with vehicles. The present invention is particularly suited for use in connection with bicycle disc brake systems . 2. Description of the Prior Art. The use of vehicle disc brakes has become increasingly popular over the years, and recently has experienced a dramatic increase in connection with "mountain bikes," i.e., bicycles designed to be ridden over rough, off-road terrain. To ease the effort of traversing off-road terrain, there has been a continuous effort to design disc brake systems that are as light as possible, particularly with respect to pedal driven vehicles such as bicycles, the weight of which must be propelled by a rider in addition to the rider's own weight . Another important design criterion for off-road vehicle components in particular, and for vehicle components generally, is durability. In the past, for example, reservoirs used in fluid-based disc brake systems have been made of plastic and have been formed and mounted separately from and/or external to the master cylinder assembly of such disc brake systems . The reservoirs therefore have typically been undesirably exposed and susceptible to being damaged. Typical disc brake systems are also undesirably bulky and therefore less aerodynamic and more unsightly 2 than desirable, due not only to the use of external reservoirs but also to the use in such systems of an unnecessary number of parts . The excess number of parts also results in conventional systems being unnecessarily costly. Accordingly, there is a need for a vehicle disc brake system that is more compact than typical conventional systems, and which may potentially be manufactured at a lower cost due to a reduction and consolidation of parts. In addition, typical hydraulic disc brake systems are designed to have an air pocket disposed above the fluid in the reservoir. Thus, if such a disc brake system is turned upside-down - which occurs frequently in applications such as bicycles - air is able to enter the fluid circuit and cause a deterioration of brake performance, or a loss of braking altogether. As a result, the brakes must be bled when turned upright again. Accordingly, there is a need for a disc brake system having the compact, cost-efficient and durable qualities previously described, and which eliminates the need to bleed the brake system if the system is turned upside-down. It is an object of the subject invention to provide a disc brake assembly which includes concentrically disposed master cylinder and compensator chamber. It is also an object of the subject invention to provide a compensator piston in a disc brake assembly which is responsive to volume changes in the brake fluid. 3 SUMMARY OF THE INVENTION The above-stated objects are met by a disc brake assembly which is formed with a concentric cylinder that defines concentrically disposed master cylinder chamber and internal thermal compensation chamber . The two chambers are provided with brake fluid for actuating disc brakes, which may be remotely or directly mounted to the subject invention. Additionally, the invention may be actuated through an actuator, such as a brake lever, mounted directly onto the assembly, or remotely through a brake wire. The combination of the concentrically disposed internal thermal compensation chamber and the master cylinder chamber advantageously provide for a compact design which eliminates the need for an external reservoir. Additionally, a spring-biased compensator piston is disposed within the internal thermal compensation chamber to be pressed into fluid engagement with brake fluid to prevent the creation of an air pocket therein. By eliminating air pockets, the disc brake assembly may be oriented in any manner, without an air pocket being formed which requires removal through bleeding. These and other features of the invention will be better understood through a study of the following detailed description and accompanying drawings. 4 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a first embodiment of the disc brake assembly of the present invention. FIG. 1A is an enlarged partial sectional view of the first embodiment showing the additional feature of using a screw to control depth of the compensator piston during bleeding. FIG. 2 is a sectional view of the first embodiment of the disc brake assembly of FIG. 1, illustrating the actuation of the assembly's master cylinder. FIG. 3 is a partial sectional view of a second embodiment of the disc brake assembly of the present invention, in which the disc brake assembly is connected to a handlebar mounting boss for actuation by a pushrod attached to a brake lever. 5 DETAILED DESCRIPTION OF THE INVENTION The disc brake assembly of the present invention will now be described with reference to the figures. As illustrated in FIGS. 1 and 2, the disc brake assembly 10 of the present invention comprises a main unit 12 and an actuator which extends from a remote location, such as a brake lever. In a first embodiment, the main unit 12 comprises a caliper body 16 and a concentric cylinder 18, which are preferably attached or integrally formed. The caliper body 16 of the disc brake assembly 10 includes two caliper piston bores 20 that house two caliper pistons (not shown) for operation as described, for example, in U.S. Patent No. 5,632,362 to Leitner, issued May 27, 1997 (the "Leitner patent"), the disclosure of which is incorporated herein by reference in its entirety. A cylindrical wall 22 is mounted onto, or as shown in FIGS. 1 and 2 is formed integrally with, the caliper body 16 to define a cylindrical chamber 24 adjacent to the caliper body 16. Alternatively, the cylindrical wall 22, the caliper body 16 and the concentric cylinder 18 can be integrally formed together, thus eliminating the concentric cylinder seals described below. The concentric cylinder 18 has an interior surface 26 and an exterior surface 28. The interior surface 26 defines a master cylinder chamber 30 for receiving a master cylinder piston 32 and a master cylinder spring 34. A master cylinder port 36 extends from the interior surface 26 to define a fluid passage between the master cylinder chamber 30 and one or more caliper piston ports 38 which enable the master cylinder piston 32 to actuate the disc brake. An annular interior surface seal 27 is seated into the interior surface 26 adjacent to the master cylinder port 36. The master cylinder piston 32 is generally 6 tubular shaped with an annular pressure seal 33 and an annular secondary seal 35 being seated on outer portions thereof. The master cylinder spring 34 is disposed between, and preferably connected to, a shoulder 37 formed inside of the master cylinder piston 32 and a flange 39 formed to extend inwardly from the interior surface 26. Accordingly, the master cylinder spring 34 is arranged to urge the master cylinder piston 32 leftward with reference to the figures . A lip 43 may be formed on the interior surface 26 to act as a stop against the master cylinder spring's 34 biasing force. The exterior surface 28 of the concentric cylinder 18 has two portions: a first exterior surface portion 28A and a second exterior surface portion 28B. The first exterior surface portion 28A is preferably formed to define a first diameter D l7 whereas, the second exterior surface portion 28B is preferably formed to define a second diameter D 2 , which is greater than the first diameter D 1 . As a result in the change of the diameters D 1 and D 2 , a generally annular step 41, preferably being planar, is defined. The first exterior surface portion 28A defines an inner surface of an annular-shaped internal thermal compensation chamber 42 that is disposed concentrically about the master cylinder chamber 30. A compensator port 44 and a relief port 46 extend through the first exterior surface portion 28A to communicate the master cylinder chamber 30 with the internal thermal compensation chamber 42. In addition, the first exterior surface portion 28A provides an axial guide for an annular compensator piston described below. The second exterior surface portion 28B is disposed to be at least partially disposed in engagement with the cylindrical wall 22 of the caliper body 16 and is 7 preferably provided with a pair of annular concentric cylinder seals 48 seated thereon. The concentric cylinder seals 48 are used to seal the junction of the master cylinder port 36 and the caliper body 16 around the caliper piston port 38. As clearly shown in the figures, two annular subchambers are formed in the master cylinder chamber 30 that extend about the master cylinder piston 32. Namely, a pressure chamber 45 is located between the interior surface seal 27 and the pressure seal 33, and a relief chamber 47 is located between the pressure seal 33 and the secondary seal 35. As depicted in FIG. 1, the compensator port 44 is in communication with the pressure chamber 45, and the relief port 46 is in communication with the relief chamber 47 in an unactuated state of the disc brake assembly 10 with the master cylinder piston 32 being fully seated leftwardly. In the first embodiment, the concentric cylinder 18 is formed with a cable housing boss 40 at one axial end for connecting to a brake cable housing BCH (shown in FIG. 2) using any technique known by those skilled in the art. A cap or cover 49 may be mounted onto the other axial end of the concentric cylinder 18 to prevent the ingress of dirt and debris into the disc brake assembly. As is readily appreciated by those skilled in the art, a volume of brake fluid (shown schematically by dashed lines in the figures) is disposed within the disc brake assembly 10 to cause actuation thereof. To actuate the caliper pistons, sufficient brake fluid must be provided to flood the caliper piston bores 20, the caliper piston port 38, the master cylinder port 36, and the pressure chamber 45. Due to thermal effects, brake fluid expands and contracts. To ensure a working volume of brake fluid is maintained within the required areas, the internal thermal 8 compensation chamber 42 is also flooded with brake fluid which acts as a reservoir. A compensator piston 50 is disposed in the internal thermal compensation chamber 42. The compensator piston 50 is an annular or thru-hole design with annular inner and outer seals 52 and 54, respectively. The inner seal 52 prevents fluid leakage between the inside diameter of the compensator piston 50 and the first exterior surface portion 28A of the concentric cylinder 18. The outer seal 54 prevents fluid leakage between the outside diameter of the compensator piston 50 and the cylindrical wall 22. As illustrated in FIGS. 1-2, the compensator piston 50 is biased by a compensator spring 56 on one side and acts upon the internal thermal compensation chamber 42 on the other. The compensator spring 56 is disposed between the compensator piston 50 and a surface such as a disc and/or retaining ring, such as the disc described below, to bias the compensator piston 50 in a direction pushing fluid into the master cylinder chamber 30 through the compensator port 44. Preferably, the compensator spring 56 is a coil spring disposed to encircle the concentric cylinder 18. The compensator spring 56 is used both to overcome the friction of the inner and outer compensator piston seals 52, 54 and to ensure positive filling of the master cylinder chamber 30 as the brake fluid volume changes. As shown in FIG. 2, the compensator piston 50 moves axially with respect to the major axis of the concentric cylinder 18 as the brake fluid expands and contracts due to increases and decreases in the temperature of the brake fluid. In addition, the compensator piston 50 moves to the right when the brake fluid contracts due to a decrease in ambient air temperatures, and/or when the caliper pistons move out of the caliper body 16 due to brake pad wear. The compensator piston 50 moves to the 9 left due to the thermal expansion of the fluid as a result of an increase in ambient air temperatures, and/or as a result of braking. A stop 58 may be provided to limit the leftward travel of the compensator piston 50. A disc 60 and a retaining ring 62, as shown in FIGS. 1-2, may be used to fix the concentric cylinder 18 axially to the cylindrical wall 22. In addition, the disc 60 and the retaining ring 62 preferably are configured to allow for the removal and installation of the compensator piston 50 and the compensator spring 56. Unlike disc brake assemblies comprising typical external fluid reservoir systems, the disc brake assembly 10 of the present invention does not require bleeding of the brake system when, for example, the internal thermal compensation chamber 42 is turned upside-down. However, the disc brake assembly 10 still will require bleeding when, for example, the system's brake fluid is changed. When such bleeding is necessary, the compensator piston 50 must be maintained at a specific depth during the bleeding operation. For this purpose, as shown representatively in FIG. 1A, small screws S could be passed through thru-holes 59 in the disc 60, preferably located at evenly-spaced locations in the disc 60, and threaded into threaded holes 61 of the compensator piston 50. The user could then push on the heads of the screws S until the shoulders of the screws S touch the disc 60. The disc brake assembly 10 would then be bled and the screws removed. Although not shown, alternatively, an internal or external machined feature on the compensator piston 50, such as an undercut, could be used to permit special tools with a hook or flange to control the depth of the compensator piston 50 during the bleeding process . As will be appreciated by those having skill in the art, bleed screws 64 shown in FIGS. 1 and 2 (and the 10 filler plug 66 shown in FIG. 3) are used to conduct the bleeding operation. For example, the two bleed screws 64 of the first embodiment may be removed, and fluid may be pumped into one bleed port 63 using a plastic bottle, flexible hose, or other such implement. The other bleed port 63 may be simultaneously observed to detect the presence of air bubbles until the bubbles have dissipated. Alternatively, one of the two bleed screws 64 may be removed and the disc brake assembly may be bled in a vacuum fluid tank. Other methods of and arrangements for bleeding known to those skilled in the art may be utilized, such as that described below with respect to the second embodiment. In operation, the disc brake assembly 10 is initially in an unactuated state as shown in FIG. 1. In the first embodiment, the disc brake assembly 10 is located in proximity to the disc brake which is controlled. Various modes of actuation may be located remotely therefrom and controlled through various methods known in the prior art. Thus, for example, the disc brake assembly 10 is mounted onto the frame of a bicycle adjacent to the tire to be braked, and actuated through a brake cable B which passes through the brake cable housing BCH that is fastened to the cable housing boss 40. Although not shown, the brake cable B is threaded through the flange 29 and connected to the master cylinder piston 32 using any method known to those skilled in the art, such as through mounting to a bar or flange that extends across the inner portion of the master cylinder piston 32. Upon actuation, the brake cable B is caused to be withdrawn from the master cylinder chamber 30, thus applying a pulling force to the master cylinder piston 32 against the biasing force of the master cylinder spring 34. The pulling force of the brake cable B is generated to be 11 greater than the biasing force of the master cylinder spring 34, resulting in movement of the master cylinder piston 32 in a rightward direction relative to the figures. Further, the pressure seal 33 slides with the movement of the master cylinder piston 32 to cause a reduction in volume in the pressure chamber 45. Eventually, the pressure seal 33 passes the compensator port 44 with further reduction in volume in the pressure chamber 45. This action causes pressure build-up in the brake fluid which is communicated through the master cylinder port 36, the caliper piston port 38, and into the caliper piston bores 20. The build-up of pressure of the brake fluid enables actuation of the disc brakes. Any excess brake fluid found in the pressure chamber 45 is expelled through the compensator port 44 during the compression stroke described above . Upon release of the brake cable, the master cylinder spring 34 urges the master cylinder piston 32 leftwardly and back into its unactuated position. As the pressure chamber 45 increases in volume, brake fluid is drawn out of the caliper piston bores 20, thus reducing the pressure therein and allowing for release of the disc brakes . The internal compensation chamber 42 acts as a reservoir for the pressure chamber 45. Under ideal conditions, a fixed volume of brake fluid would be required to actuate the disc brake assembly 10 in a manner as described above. However, losses due to leakage, and thermal effects of expansion and contraction, cause changes in volume of the brake fluid which may result in severe degradation in or altogether a lack of performance. To ensure a sufficient working volume of brake fluid is maintained, the internal thermal compensation chamber 42 feeds additional brake fluid through the compensator port 12 44 into the pressure chamber 45. Similarly, excess brake fluid is forced out of the pressure chamber 45 during operation and into the internal thermal compensation chamber 42. The relief chamber 47 accepts excess brake fluid which is passed through the relief port 46. The first embodiment of the present invention as illustrated in FIGS. 1 and 2, in which the concentric cylinder 18 of the present invention is integrally mounted to the caliper body 16 of the disc brake assembly 10, is compact and convenient, and therefore ideal for use on pedal driven vehicles such as bicycles. In a second embodiment, the principles of the present invention may be used in connection with a concentric cylinder 18 housing a lever-actuated master cylinder. Such a disc brake system is shown in FIG. 3 and is generally designated with the reference numeral 100. Like components from the first embodiment are designated with the same reference numerals in FIG. 3 and in discussing the second embodiment. The disc brake assembly 100 operates in conjunction with a remote caliper unit (not shown) connected to the assembly 100 by a brake hose H which conducts the brake fluid to the caliper unit. This type of system is particularly useful, for example, in connection with bicycles, motorcycles, snowmobiles and quad-runners . The disc brake assembly 100 is similar to that of FIGS. 1 and 2. Here, however, the concentric cylinder 18 is housed within a cylindrical wall 68, that is defined by a handlebar mounting boss 70. The handlebar mounting boss 70 is formed with a filler port 72, configured to receive the filler plug 66, and be in communication with the internal thermal compensation chamber 42. Also, the handlebar mounting boss 70 is formed with a delivery port 74 provided to communicate the brake hose H with the 13 pressure chamber 45. Further, a mounting groove or recess is defined in the handlebar mounting boss 76 which is shaped for mounting onto a bicycle handlebar or other location. A modified flange 39A is provided to seal off entirely one axial end of the concentric cylinder 18. A cap 78 is mounted at the other axial end of the concentric cylinder 18 through which passes a pushrod 80. The pushrod 80 is mounted to a brake lever 82 through an articulating connection 84. The brake lever 82 is also pivotally mounted to the handlebar mounting boss 70 through a pivot connection 86. Other than where noted, the first and second embodiments are structurally the same. In operation, the second embodiment relies on the pushrod 80, through manipulation of the brake lever 82, to depress the master cylinder piston 32 and cause actuation of the disc brake assembly 100 in the same manner as described with respect to the first embodiment. Release of the brake lever 82 causes withdrawal of the pushrod 80 and a return of the disc brake assembly 100 to an unactuated state. With respect to bleeding the second embodiment, the filler plug 66 may be removed and fluid may be pumped through the filler port 72 with a plastic bottle, flexible hose, or other such implement. The delivery port 74 on the remote caliper unit connected to the lever-actuated assembly may be opened and observed while pumping fluid through the filler port 72 to detect the presence of bubbles, until the bubbles have dissipated. This design is the most appropriate use of the present invention in connection with motorcycles, snowmobiles and quad-runners due to the ease of bleeding the disc brake system. As shown, the present invention represents an improvement over conventional disc brake assemblies due to 14 use of an internal thermal compensation chamber 42 which replaces and eliminates the external fluid reservoir of such conventional systems. The internal thermal compensation chamber 42 is more compact than typical external fluid reservoir designs due to it being concentric to and integrated with the master cylinder chamber 30. The internal thermal compensation chamber 42 is also less susceptible to damage on open cockpit vehicles such as bicycles, motorcycles, snowmobiles and quad-runners due to the elimination of the external fluid reservoir, which typically is made of plastic. Also unlike external fluid reservoir designs, which typically have an air chamber disposed above the fluid in the reservoir, the internal thermal compensation chamber 42 of the present invention is a sealed system. The internal thermal compensation chamber 42 of the present invention therefore does not suffer the drawback of external fluid reservoir systems which, if turned upside- down, risk having air enter the fluid circuit and cause a deterioration or less of brakes. Thus, unlike such systems which must be bled when turned upright again, the sealed system of the present invention eliminates the need to bleed the brake system. This feature is particularly useful when the present invention is applied to bicycles, which are frequently turned upside-down. The integrated internal thermal compensation chamber 42 and the master cylinder chamber 30 of the present invention allow for the elimination of the conventional external reservoir tank on a disc brake system. The disc brake assembly 10, 100 of the present invention performs all of the same functions as described, for example, in connection with the disc brake assembly of the Leitner patent, such as providing disc brake fluid to the master cylinder chamber through the compensator port, 15 providing a chamber to accommodate increases in brake fluid volume due to thermal expansion or decreases in brake fluid volume due to thermal contraction, and providing additional disc brake fluid to the master cylinder chamber when necessary due to brake pad wear. In addition, however, the assembly of the present invention can be manufactured at a lower cost due to a reduction and consolidation of parts used in such disc brake assemblies. The use of the concentric cylinder of the present invention also enhances the manufacturing cost savings due to the increase in lathe-turned parts, and the reduction in the complexity and number of machining operations required in connection with a caliper body in comparison to those that would be required in connection with designs such as that described in the Leitner patent. While there are shown and described herein certain specific structures comprising aspects of the invention, it will be clear to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept, and that the same is not limited to the particular forms herein shown and described.

Claims: 16 WHAT IS CLAIMED IS; 1. A disc brake assembly which operates hydraulically with brake fluid, said disc brake assembly comprising: a single main unit having a master cylinder chamber, a master cylinder piston slidably disposed in said master cylinder chamber for selectively generating pressure build-up in the brake fluid, and an internal thermal compensation chamber in fluid communication with said master cylinder chamber. 2. A disc brake assembly as in claim 1, wherein said internal thermal compensation chamber is concentrically disposed about said master cylinder chamber. 3. A disc brake assembly as in claim 1, wherein said main unit further having a cylinder with an inner surface and an outer surface, said inner surface defining at least portions of said master cylinder chamber, and said outer surface defining portions of said internal thermal compensation chamber. 4. A disc brake assembly as in claim 3, wherein said main unit further having a cylindrical wall spaced from and facing at least a portion of said outer surface of said cylinder. 5. A disc brake assembly as in claim 4, wherein said cylindrical wall extends from a caliper body. 6. A disc brake assembly as in claim 4, wherein said cylindrical wall extends from a handlebar mounting boss . 17 7. A disc brake assembly which operates hydraulically with brake fluid, said disc brake assembly comprising: a main unit having a master cylinder chamber and a master cylinder piston slidably disposed therein for selectively generating pressure build-up in the brake fluid; a thermal compensation chamber in fluid communication with said master cylinder chamber, at least a portion of the brake fluid being contained in said thermal compensation chamber; a compensator piston disposed in said thermal compensation chamber; and biasing means for urging said compensator piston into engagement with the brake fluid, whereby said biasing means prevents generation of an air pocket between said compensator piston and the brake fluid. 8. A disc brake assembly as in claim 7, wherein said thermal compensation chamber is disposed concentrically about said master cylinder chamber. 9. A disc brake assembly as in claim 8, wherein said compensator piston is annular shaped and disposed about said master cylinder chamber. 10. A disc brake assembly as in claim 9, wherein said biasing means is a coil spring disposed to encircle said master cylinder chamber. 11. A disc brake assembly as in claim 7, wherein said thermal compensation 'chamber is formed in said main unit .

Inventors: BECKER WILLIAM MARTIN, BECKER, WILLIAM, MARTIN
Applicants: BECKER WILLIAM MARTIN, ROCKSHOX INC, BECKER, WILLIAM, MARTIN, ROCKSHOX, INC.
Application year: 1999
Main classification: B60T11
IPC codes: B60T11, B62L1, B62L3