Hydraulic brake master cylinder with back-up ring

Disclosed herein is a hydraulic master cylinder body having a bore defined at least in part by a bore wall, wherein the bore wall includes an opening for hydraulic fluid to be passed into the bore, and a piston assembly situated at least substantially in the bore, the assembly having a piston with a piston body and at least one cup seal situated substantially around the piston body, the cup seal situated adjacent to the bore wall so as to be in sealing engagement therewith, and a back-up ring that is situated about the piston body, wherein the back-up ring is positioned to at least partially cover a portion of the cup seal that is adjacent to the bore wall and to prevent at least a portion of the cup seal from contacting the bore wall and the opening for hydraulic fluid during piston actuation.

FIELD OF THE INVENTION

The hydraulic master cylinder with back-up ring relates generally to hydraulic brake master cylinders, and more particularly to piston sealing configurations in hydraulic brake master cylinders.

BACKGROUND OF THE INVENTION

Hydraulic brake systems are subjected to pressure created when brakes are applied. More particularly, applying pressure to the brake pedal of a braking system creates pressure in the master cylinder piston bore. In a traditional hydraulic braking system, the pressure created in the master cylinder piston bore is typically generated by a metal or plastic piston sealed by rubber cup seals, such as primary and secondary cup seals.

In higher pressure braking systems, such as Anti-lock Braking Systems (ABS), the pressure in the piston bore is significantly higher during braking operation than in a non-ABS application. In addition, when ABS is activated, the piston in the piston bore oscillates rapidly back and forth exerting substantial stress on the cup seals. The higher pressure, along with the violent reciprocation of the piston during ABS activation, can result in premature wear as well as damage to the cup seals, which can result in a catastrophic failure.

One method of accommodating the oscillating high-pressure effects of ABS is to utilize a central valve positioned inside the piston bore to adjust the internal pressure. The use of a central valve is well known in the art. Although the central valve can reduce the wear and damage of a cup seal by allowing bore cavity pressure to vent through the piston, numerous drawbacks exist with a central valve system. More particularly, a master cylinder assembly that utilizes a central valve contains several additional parts, which increase cost of manufacturing. In addition, the required valve actuation of the central valve can decrease the reliability of a master cylinder assembly, as additional moving parts are required to operate. Also, by adding the additional moving parts, various manufacturing tolerances are introduced that can create a large variation of dead-stroke among master cylinder assemblies manufactured under identical manufacturing specifications. Further, the use of a central valve can increase lead-stroke distance that a piston and a cup seal travel before pressure can begin to build, which reduces the responsiveness and firmness sought during actuation of the master cylinder assembly, leaving a less responsive and undesirable “spongy” feel when the braking system is actuated.

BRIEF SUMMARY OF THE INVENTION

In accordance with at least one embodiment, the hydraulic master cylinder with back-up ring relates to a hydraulic master cylinder body having a bore defined at least in part by a bore wall, wherein the bore wall includes an opening for hydraulic fluid to be passed into the bore, and a piston assembly situated at least substantially in the bore, the position assembly having a piston with a piston body and at least one cup seal situated substantially around the piston body, the cup seal situated adjacent to the bore wall so as to be in sealing engagement therewith, and further including a back-up ring that is situated about the piston body, wherein the back-up ring is positioned to at least partially cover a portion of the cup seal that is adjacent to the bore wall and to prevent at least a portion of the cup seal from contacting the bore wall during piston actuation.

In another embodiment, the hydraulic master cylinder with back-up ring relates to a method of operating a brake master cylinder that includes actuating a piston assembly having a piston and a cup seal, wherein the cup seal is in contact with a bore wall of the master cylinder, supporting at least a portion of the cup seal situated adjacent to the bore wall, passing the cup seal over a port timing hole opening in the bore wall during actuation of the piston; and preventing the at least a portion of the cup seal from extruding into the port timing hole opening during actuation of the piston.

In yet another embodiment, the hydraulic master cylinder with back-up ring relates to a brake master cylinder assembly that includes a hydraulic brake master cylinder body having a piston bore, a piston having a circumferential shoulder and a circumferential support wall; and a circular ring that further includes a tapered annular seal cover surface that extends between a first diameter and a second diameter, wherein the seal cover surface is configured to abut at least a portion of an outer wall of a cup seal, a first seating surface configured to mount onto the circumferential shoulder of the piston, wherein the ring is radially supported by the abutment of the first seating surface with the circumferential shoulder of the piston, and a second seating surface configured to abut the circumferential support wall of the piston, wherein the support wall laterally supports the ring during actuation of the piston.

Other embodiments, aspects, features, objectives, and advantages of the hydraulic master cylinder with back-up ring will be understood and appreciated upon a full reading of the detailed description and the claims that follow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIGS. 1A and 1B, a cross-sectional side view of a portion of an exemplary hydraulic master cylinder assembly2is depicted inFIG. 1Athat includes a body portion4. The master cylinder assembly2can be part of a braking system for one or more of a variety of land-based vehicles, such as a motorcycle, automobile, snowmobile, All Terrain Vehicle (ATV), Utility Terrain Vehicle (UTV), motorized and non-motorized bicycles, etc. In the present embodiment, the master cylinder assembly2is provided for use with an Anti-Lock Braking System (ABS) for use with one or more of such land vehicles. The body portion4houses a piston bore6having a bore wall7, a first bore end8, and a second bore end10. Although the body portion4can be an integral structure, it is contemplated that it can include two or more components secured together.

The master assembly2further includes a piston assembly11having a piston12positioned in the bore6, the piston having a first piston end14and a second piston end16. The first piston end14is situated inside the bore6adjacent the first bore end8. The second piston end16is an actuating end and, as shown, is situated at least partially inside the bore6adjacent the second bore end10. In addition, the second piston end16is in operable association with a brake actuator9(FIG. 4A), such as a brake lever or pedal, either directly or indirectly, wherein one or more components can be positioned in between the brake actuator9and the piston12. When the brake actuator9is activated, the piston12is pushed inside the bore6along a direction indicated by arrow17. This movement of the piston12creates a fluid pressure inside the bore6at the first bore end8as a result of the fluid (not shown) situated between the piston12and the first bore end8. As the fluid has minimal compressibility, the fluid pressure in the bore6is conveyed out of the bore6at the first bore end8, away from the piston12, and downstream to one or more brake components (not shown) through a fluid channel19. The brake components receiving the pressurized brake fluid act upon the piston12, which in turn generates a clamp force on brake friction pads (not shown) that cause a drag on a spinning brake rotor secured to a wheel not shown), thereby reducing wheel speed. Upon release of the brake actuator, a biasing element, such as a spring9(FIG. 4A) can be utilized to return the piston to its pre-actuated position. Further, the brake components are situated about the wheel(s) of the vehicle, where such components can include a brake caliper, brake cylinder, etc.

To maintain alignment of the piston12with the bore wall7, the piston includes one or more guides18that are adjacent to the bore wall7and configured to slide along the bore wall7during movement of the piston12between the first bore end8and the second bore end10. In addition, the dimensions of the guides18can serve to provide a desired path for the flow of brake fluid between the bore wall7and the piston12, particularly when the bore6is being evacuated or filled with brake fluid. To further assist in sealing the piston12with respect to the bore wall7, one or more cup seals20are provided. Further, and although not shown, one or more additional cup seal(s) can also be provided about the piston12to provide additional sealing. In accordance with at least some embodiments, the cup seal20is substantially circular in shape to accommodate the generally cylindrically shaped portion of the shape of the piston12about which it is positioned. The cup seal20typically comprises a pliable material, such as rubber, although other sealing materials can be utilized. The cup seal20has an outer wall22and inner wall24, wherein the outer and inner walls are co-joined about a front cup portion26. The front cup portion26and the inner wall24are substantially situated in a groove25that substantially encircles the piston12. The outer wall22extends from the front cup portion26to an end that is in contact with the bore wall7, thereby providing a fluid seal between the piston12and the bore wall7. Further, the cup seal20is positioned about the piston12such that it intermittently covers an opening28of a port timing hole29, which is formed in the body portion4, as the piston12is moved. The port timing hole29includes a port timing hole passage30that extends from the bore6to a master cylinder reservoir32. In addition, a compensation port15can be provided that includes a compensation port passage21that also extends between the bore6and the roaster cylinder reservoir32.

The general principles of ABS are known to persons skilled in the art and as such, a detailed description of such principles is not provided herein. However, it is noted that during the application of an ABS, a high pressure oscillation of fluid occurs in the first bore end8between the first piston end14and the fluid channel19. This oscillation causes the piston12and accordingly the piston front end14to move repeatedly towards and away from the first bore end8adjacent the fluid channel19, first in the direction of arrow17, followed by a movement in the opposite direction of arrow17. During these high pressure episodes, the outer wall22of the cup seal is forcibly pushed against the bore wall7about the opening28of the port timing hole29. The high pressure exerted by the fluid in the bore6against the cup seal20can result in the outer wall22of the cup seal being deformed by or extruded at least partially into the opening28. This can result in the shearing off of a portion of the cup seal20as the piston12moves abruptly over the opening.

The use of a back-up ring34(discussed below) in a hydraulic master cylinder assembly2can extend the operational life of the cup seal20. More particularly, without the back-up ring34, the cup seal20has a greater propensity to tear as a result of exposure to the opening28in the port timing hole29, this can result in a catastrophic failure of the hydraulic master cylinder assembly2. By reducing or eliminating exposure of the cup seal20to the opening28, degradation of the cup seal20can be reduced. In addition, such degradation of the cup seal20can result in decreased performance. Typically, the user can detect the decreased performance and will replace the cup seal20before complete failure occurs, although if the cup seal20has been fatigued by repeated extrusion into the opening29, the cup seal20can fail prematurely, resulting in increased maintenance costs.

Further, as the use of the back-up ring34can significantly reduce the overall wear on the cup seal20, particularly in a high-pressure. ABS application, the life cycle threshold of the cup seal20can be significantly increased. In at least some embodiments, a cup seal lifecycle threshold of over 100,000 cycles can be achieved.

In addition to increased safety and durability, the use of the back-up ring34can reduce the manufacturing time for the hydraulic master cylinder assembly2. For example, the supporting of the cup seal20provided by the back-up ring34reduces the force with which the cup seal20is pushed against the bore wall7during operation. This reduction in force allows for the bore wall7to be honed for a shorter period of time without suffering premature failure due to the increased particle wear as the cup seal20is moved along the bore wall7.

Referring now toFIGS. 2A,2B,2C,2D, and2E, an exemplary back-up ring34is depicted. The back-up ring34is configured to limit the exposure of the cup seal20to the opening28by covering at least a portion of the cup seal20that would otherwise be exposed to the opening28. The positioning of the back-up ring34prevents or partially prevents extrusion of the cup seal20into the opening28. In at least some embodiments, the back-up ring34is sized and shaped to substantially or completely encircle the piston12and to substantially conform to the shape of the bore wall7. The back-up ring34can be a molded, split, or solid ring, configured to fit around at least a portion of the outer wall22of the cup seal and sit on a shoulder38of the piston12. The back-up ring34can be comprised or constructed of one or more materials, such as metal and plastic. In at least some embodiments, the back-up ring34can include a non-ferrous metal that is compatible with both brake fluid and the composition of the bore6. In at least some embodiments, the back-up ring34can be comprised of brass and utilized with an aluminum bore6. In at least some other embodiments, the back-up ring34can include a plastic, such as an acetyl resin, for example, the compositions identified as Delrin 500AF and Delrin 500CL, which are manufactured by DuPont, located in Wilmington, Del. USA.

As seen inFIGS. 2A and 2B, the back-up ring34can include a separating passage36therethrough for bending and/or expanding the back-up ring34to pass over the piston12during installation onto the shoulder38. In at least some embodiments, the separating passage36can be omitted (FIGS. 2C-2E) to form a continuous loop. Further, in at least some embodiments, the back-up ring34includes the first seating surface40that is configured to sit atop the shoulder38(FIG. 1B) of the piston12, and a second seating surface42that abuts a support wall44(FIG. 1B) of the piston12, where the support wall44extends substantially perpendicular to the bore wall7and the shoulder38. Positioning the back-up ring34on the piston12as such serves to substantially limit movement of the back-up ring during movement of the piston12, as discussed in detail below.

The back-up ring34includes an annular seal cover surface46that abuts at least a portion of the outer wall22of the cup seal20, and in some embodiments is configured to be tapered to substantially match the tapering of the outer wall22of the cup seal20. The seal cover surface46limits the cup seal's deformation when the cup seal20is under pressure, by providing a rigid surface to support at least a portion of the outer wall22of the cup seal20. The back-up ring34also includes a guide surface48situated along an outer circumference of the back-up ring. As seen inFIGS. 1A and 1B, when the back-up ring is in position in the bore6, the guide surface48is situated adjacent to the bore wall7and as such, serves to limit or prevent contact between at least a portion of the outer wall22of the cup seal20and the bore wall7, as the cup seal20passes over the opening28. A portion of the outer wall22that is not covered by the back-up ring provides sealing and passes over the opening28during initial actuation of the piston12. As the piston12is further actuated, the pressure in the first bore end8increases and the portion of the outer wall22that is covered by the back-up ring34passes over the opening28. In this regard, the cup seal20can still provide a fluid seal, while still being protected by the back-up ring34.

In addition, the use of the back-up ring34allows the use of a cup seal designed for lower pressure braking systems in a severe duty and/or higher pressure system, thereby allowing a single cup seal part to be supplied for use in multiple braking systems. As discussed below, the back-up ring can be sized and shaped to accommodate various components, such as pistons12, bores6, and cup seals20having dimensions that include dimensions not discussed or depicted herein. Further, although the back-up ring34has been described for use in a high pressure ABS application, the back-up ring can be utilized in other types of braking systems applications, such as non-ABS and low pressure systems.

Referring toFIGS. 2A,2B,2C,2D, and2E, the back-up ring34can include numerous dimensional variations. In at least some embodiments, the first seating surface40has a thickness T1of about 0.035+/−0.005 inches and a diameter D1of about 0.470+/−0.005 inches. The diameter D1of the first seating surface40is sized to equal or exceed an outside diameter D2(FIGS. 4C,5C,6C,7C,8C) of the first piston end14, such that the back-up ring34can be slid over the first piston end4and onto the shoulder38. As seen inFIGS. 2B and 2D, the seal cover surface46can be tapered and extends between a first diameter D3and a second diameter D4. In at least some embodiments, the first diameter D3is equal to about 0.500+/−0.005 inches and the second diameter D4is equal to about 0.577+/−0.005 inches.

Further, the guide surface48is sized to fit inside the piston bore6and can be tapered as well. The guide surface48has a width W1(FIG. 2E) and in at least some embodiments, the width W1is about 01.00+/−0.005 inches. The back-up ring34includes a longitudinal ring central axis60, and when the back-up ring34is installed, the ring central axis60is coincident or substantially coincident with a central longitudinal axis62of the piston. Additionally, the guide surface48can be offset from the ring central axis60, such that only a portion of the guide surface48abuts the piston wall7. In at least one embodiment, a guide surface offset θ that extends between a line along the guide surface48and a line extending across the diameter D1and perpendicular to the ring central axis60, is equal to about 89+/−1.0 degrees.

Further, the seal cover surface46of the back-up ring34that extends between the first diameter D3and the second diameter D4can include a seal cover surface offset β that extends between a line along the seal cover surface46and a line extending parallel to the ring central axis60and along the first seating surface40. The seal cover surface offset β, is in at least some embodiments, equal to about 15+/−2.0 degrees. Further, the seal cover surface offset θ can be modified to accommodate various cup seal styles, shapes, materials, thicknesses, etc.

Referring now toFIGS. 3A and 3B, another exemplary hydraulic master cylinder assembly2is provided wherein the piston12includes an integral back-up ring50in accordance with other embodiments of the hydraulic master cylinder with back-up ring. The back-up ring50, as shown, extends integrally from one or more of the guides18that encircles the piston12, as such, the back-up ring50in combination with one or more guides18can take the form of a sleeve or sleeve-like structure with the back-up ring50forming at least in part, a protrusion extending from the piston. As shown inFIG. 3A, the back-up ring50is formed adjacent to the front cup portion26, and is configured to extend the guides18of the piston12to at least partially cover the outer wall22of the cup seal20, while allowing space for the cup seal20to be positioned as expected about a typical piston12. The embodiment inFIG. 3Aserves to provide an efficient design that obviates the need for a back-up ring that is removably positioned about the piston12, thereby reducing the quantity of individual components and the time required for installing the piston12.

In addition, although the piston12is shown to comprise two guides18, which are shown encircling the piston inFIG. 3A, fewer or greater number of such surfaces can be utilized and, accordingly, sized to extend along various lengths of the piston12. For example, in some embodiments, a single guide18can extend around the piston12, and in other embodiments, several guiding surfaces each appropriately spaced apart about the length of the piston can be used. Still further, in other embodiments, the back-up ring50can be configured into a different position about the guiding surface or duplicated to accommodate a secondary cup seal (not shown) situated on the piston12. Additionally, in at least some embodiments, the piston12can comprise a thermoplastic piston material, although other materials can be used, such as steel and aluminum.

Referring now toFIGS. 4A-8B, the back-up ring34can be utilized in numerous embodiments of master cylinder assemblies.FIGS. 4A-8Bare provided to illustrate various exemplary embodiments of hydraulic master cylinder assemblies2that can employ the back-up ring34. More particularly,FIG. 4Ais a perspective view of a radial hand-brake hydraulic master cylinder assembly2employing the back-up ring34, wherein the radial hydraulic master cylinder assembly2is configured to be mounted on the handlebar35of various vehicles, such as a motorcycle, bicycle, All Terrain Vehicle (ATV), snowmobile, etc. The radial hand-brake hydraulic master cylinder assembly2includes a bore6that extends longitudinally parallel to the brake actuation direction58(lever pull) and perpendicular to the handlebar35. In addition, the bore6is situated at an angle to the horizontal plane.

FIG. 4Bis across-sectional side view of the radial hand-brake hydraulic master cylinder assembly2ofFIG. 4A.FIG. 4Cis close-up views of portions ofFIG. 4B.FIG. 4Dis another close-up view of a portion ofFIG. 4Bmore particularly identifying the interface of the back-up ring34with the piston12.FIGS. 5A-8Bdo not include an additional close-up view having the detail ofFIG. 4D, although it is to be understood that the interface of the back-up ring34and piston12shown inFIG. 4D, namely at least, the shoulder38, the first seating surface40, the second seating surface42, and the support wall44, are similar to or the same as the back-up ring34and piston12interface of each of the embodiments shown inFIGS. 1A,1B, and5A-8B.

FIG. 5Ais a perspective view of a hand-brake hydraulic master cylinder assembly2having an axial bore6and employing the back-up ring34, wherein the hand-brake hydraulic master cylinder assembly2is configured to be mounted on the handlebar35of various vehicles, such as a motorcycle, bicycle, ATV, snowmobile, etc. The hand-brake hydraulic master cylinder assembly2includes a bore6that extends longitudinally perpendicular to the brake actuation direction58and parallel with the handlebar35.FIG. 5Bis a cross-sectional side view of the hand-brake hydraulic master cylinder assembly ofFIG. 5A, andFIG. 5Cis a close-up view of a portion ofFIG. 5B.

FIG. 6Ais a perspective view of a tandem hydraulic master cylinder assembly2employing the back-up ring34, wherein the tandem hydraulic master cylinder assembly2is intended for a dual circuit brake application, such as utilized on a Utility Terrain Vehicle (UTV). The tandem hydraulic master cylinder assembly2includes two pistons12configured to be actuated across two port timing holes29in a single bore6of the body portion4.FIG. 6Bis a cross-sectional side view of the tandem hydraulic master cylinder assembly ofFIG. 6A, andFIG. 6Cis a close-up view of a portion ofFIG. 6B.

FIG. 7Ais a perspective view of a foot-brake hydraulic master cylinder assembly2employing the back-up ring34, wherein the foot-brake hydraulic master cylinder assembly2includes a linear applied single circuit actuator that is actuated by the foot-brake. The foot-brake hydraulic master cylinder assembly2can be installed on various types of vehicles, such as a motorcycle.FIG. 7Bis a cross-sectional side view of the foot-brake hydraulic master cylinder assembly ofFIG. 7A, andFIG. 7Cis a close-up view of a portion ofFIG. 7B.

FIG. 8Ais a perspective view of a dual-input rear hydraulic master cylinder assembly2employing the back-up ring34, wherein the dual-input rear hydraulic master cylinder assembly2can be installed on various types of vehicles where a failsafe type design is desired, such as a motorcycle. The body portion of the dual-input rear hydraulic master cylinder assembly2is configured to allow pressure to be applied to the fluid channel19by either a brake actuator9pushing on the piston12or via hydraulic pressure from the brake fluid of another brake circuit on the vehicle, thereby hydraulically linking the master cylinder assembly2with the another master cylinder assembly.FIG. 8Bis a cross-sectional side view of the dual-input rear hydraulic master cylinder assembly ofFIG. 8A, andFIG. 8Cis a close-up view of a portion ofFIG. 8B.

It shall be generally understood that the term “back-up ring” should be broadly interpreted to include the embodiments described herein as well as variants thereof. For example, the term back-up ring is intended to encompass a structure and/or device and can comprise one or more pieces, components and/or portions. Further, the term back-up ring can be understood to include a structure and/or device that is or can be integrated with respect to another component, such as the piston12, and again, the structure and/or device can include one or more pieces, components and/or portions.

As discussed above, the master cylinder assembly2can be part of a braking system for one or more of a variety of vehicles, such as a motorcycle, automobile, snowmobile, All Terrain Vehicle (ATV), Utility Terrain Vehicle (UTV), bicycle, etc. Regarding a snowmobile application in particular, to reduce premature wear of the cup seal20the opening28of the port timing hole29can be reduced in size to limit extrusion. This provides less surface area for extrusion, but also provides a slower brake response time. More particularly, during cold temperature operation the viscosity of the brake fluid is lowered, thereby slowing the passage of brake fluid through the reduced-size port timing hole during brake actuation. Another issue with reducing the size is that it is particularly difficult to manufacture a master cylinder with a reduced size opening due to inherent limitations of the manufacturing equipment. The use of the back-up ring34can be advantageous when used in a snowmobile application, as it can eliminate the need to reduce the opening of the port timing hole while also limiting extrusion of the cup seal20.

Although the included figures depict numerous embodiments of master cylinders with back-up rings, it is specifically intended that the hydraulic brake master cylinder with back-up ring not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of portions of different embodiments.