BACKGROUND

[001] The present disclosure relates to hydraulic control systems, and especially to seal members and seal assemblies used in a master cylinder of a hydraulic braking system.

[002] Conventionally, a master cylinder for developing fluid pressure according to pedal force applied by a brake or clutch pedal is used in a hydraulic brake or clutch system for the purpose of actuating a brake or a clutch. A typical master cylinder for a hydraulic braking system 10, as generally depicted in FIG. 1 , comprises a master cylinder 12 fed by a brake fluid reservoir 14. The master cylinder includes a primary cylinder body 16 and a secondary cylinder body 18 in communication through a common cylinder bore 22. A primary piston 20 is slidably disposed within the cylinder bore 22.

[003] The master cylinder includes sealing members between the cylinder bore 22 and the primary piston 20 (as well as the secondary piston disposed in the secondary cylinder body 18). In some master cylinders, the sealing members are mounted within the cylinder body, with the pistons traversing an inner surface of the sealing members. One such exemplary seal configuration is shown in U.S. Patent No. 7,520,132, assigned to Bosch Corporation, which issued on April 21 , 2009, the disclosure of which is incorporated herein by reference.

[004] In another seal configuration, the primary piston 20 includes a number of sealing members 24, 25 received in corresponding grooves 26, 27 formed in the body of the piston, as depicted in FIG. 1. In this configuration, the sealing members 24, 25 move with the piston within the cylinder bore 22. The seal configuration includes a glide ring formed of TEFLON ^® .

[005] In a hydraulic control system, and especially in a braking system, it is essential to maintain the pressures within the master cylinder and to avoid leakage around the piston(s) in the system. At the same time, the pistons must be capable of relatively free sliding within the cylinder bore to ensure suitable responsiveness of the hydraulic system and to maintain an appropriate activation pressure, particularly for an automotive braking system. There is always a need for a sealing arrangement that is capable of proper sealing at low and high pressures without introducing unnecessary drag to the sliding action of the pistons within the hydraulic cylinder.

SUMMARY

[006] In one embodiment, a hydraulic system comprises a fluid cylinder in communication with a source of hydraulic fluid and defining a cylinder bore, a piston slidably disposed within the cylinder bore, said piston including a piston body defining at least one annular groove opening toward said cylinder bore, and a sealing member disposed within at least one annular groove. In one feature, the sealing member including a seal body having an outer sealing surface arranged to contact the cylinder bore and a glide ring at least partially disposed within the outer sealing surface of the seal body.

[007] In one feature, the glide ring includes an outer surface facing the cylinder bore and the outer sealing surface of the seal body includes at least one seal lip projecting beyond the outer surface of the glide ring. In certain embodiments, the outer sealing surface of the seal body includes two seal lips projecting beyond the outer surface of the glide ring with the glide ring disposed within the seal body between the seal lips.

[008] In a further feature, the seal body includes opposite annular faces and defines a notch between the outer sealing surface and one of the annular faces.

[009] In another aspect, the glide ring is formed of a different material than the seal body. The seal body may be formed of a resilient elastomeric material, while the glide ring is formed of a low sliding friction material which will improve the overall efficiency of the master cylinder. [010] According to another feature, the circumferential sealing surface of the seal body at the seal lip(s) is angled outward relative to the seal body. The seal body may further define a relief portion radially inward from the seal lip(s) to operate as a hinge for deflection of the seal lip(s).

[011] The seal member disclosed herein is less sensitive to wear than traditional seals for hydraulic systems. The configuration of the seal body improves leakage performance relative to standard glide ring arrangements in hydraulic pistons.

DESCRIPTION OF THE FIGURES

[012] FIG. 1 is a general diagram of a hydraulic braking system.

[013] FIG. 2 is a cross-sectional view of a sealing member according to the present disclosure.

[014] FIG. 3 is a cross-sectional view of another sealing member according to the present disclosure.

DETAILED DESCRIPTION

[015] The present disclosure relates to a sealing member mounted within a sliding piston, such as the primary piston 20 of the hydraulic braking system 10. In particular, the sealing member disclosed herein can be mounted within the annular grooves 26, 27 in the piston 20 or similar recesses in other pistons within the system 10.

[016] Referring to FIG. 2, a sealing member 30 according to one embodiment includes a seal body 32 having an inner circumferential surface 34 adapted to seat within an annular groove 26, 27. The seal body 32 preferably has a width W sized for a correct fit within the annular groove 26, 27. The seal body 32 defines a circumferential seal lip 36 at the rear face 37b of the body. The seal lip 36 projects outward at an angle A. The angle A is sufficient so that the seal lip 36 essentially exceeds the inner diameter of the bore 22 of the master cylinder 12. When the seal member 30 is mounted within the piston 20 and introduced into the master cylinder bore 22, the seal lip 36 deflects inward so that the outer sealing surface 36a of the seal lip rides in sealing engagement with the inner bore 22.

[017] In order to facilitate the inward deflection of the seal lip 36, the seal body 32 is formed of a resilient material. In addition, the seal body defines a

circumferential relief or cup portion 38 radially inward from the seal lip. This relief portion 38 thus acts to allow the body behind the relief portion to hinge and allow the seal lip 36 to deflect. The seal lip 36 may also exhibit a tapering thickness from the relief portion to the rear face 37b.

[018] In one aspect, the outer sealing surface 36a of the seal lip may

incorporate micro-grooves (not shown) to help reduce the sliding friction between the sealing member 30 and body of the master cylinder 12. The microgrooves may extend circumferentially around the seal in multiple rows spaced along a portion of the width of the seal body. The micro-grooves are preferably no more than 0.1 " deep in the sealing surface. Alternatively, the sealing surface may be provided with micro-ridges projecting outward from the surface and arranged in several circumferential rows along the width of the seal body.

[019] In a further feature, the sealing member 30 defines a circumferential notch or groove 40 at the outer surface of the seal body. The groove 40 may also intersect the front annular face 37a of the seal body, as illustrated in FIG. 2. A glide ring 45 is positioned within the groove 40. The glide ring 45 is formed of a relatively less resilient material compared to the seal body 32, and most preferably of a material with a low sliding friction characteristic. Thus, in one embodiment the glide ring is formed of TEFLON ^® or DELRIN ^® , or other similar plastic or resin-based materials, provided the materials exhibit suitable friction characteristics and are not susceptible to degradation when contacted by the hydraulic fluids within the braking system 10 or other hydraulic system. The glide ring 45 has an outer circumferential surface 47 that is at least co-extensive with the outer surface of the seal body at the groove 40, but preferably projecting slightly above the groove 40 in the seal body. The outer surface 47 is preferably sized for a close running fit within the cylinder bore 22. This fit may be an interference or clearance fit in the installed condition. As shown in FIG. 2, the glide ring 45 is a substantially solid annular ring, with the groove having a complementary shape. Alternatively the glide ring 45 may incorporate features on its inner diameter 48 to enhance engagement of the glide ring with the seal body 32. The glide ring 45 has a width that is approximately half the width W of the seal body 32. In the illustrated embodiment, the glide ring overlaps an innermost extent of the relief portion 38. However, the relief portion is configured to ensure suitable thickness of the seal body between the circumferential groove 40 and the relief portion 38.

[020] In one embodiment, the glide ring 45 may be affixed to the seal body 32 in a conventional manner, such as with the use of an epoxy or similar adhesive. Alternatively, the seal body 32 may be over-molded onto the glide ring 45 according to known procedures. In another embodiment, the glide ring may be essentially press-fit onto the seal body, which can be sufficient when the seal member is disposed within the annular groove of the piston body. The glide ring may be installed onto the seal body after the seal body is installed in the piston groove 26, 27, and then sized to fit into the groove 40 of the seal body.

[021] In certain applications, such as within a braking system 10, multiple seal members 30 are provided along the length of a particular piston, provided it has sufficient length to accommodate multiple seals. Thus, as shown in FIG. 1 , the primary piston 20 incorporates seals at the opposite ends of the piston. The seal members 30 may be mounted within the annular grooves 26, 27 at each end in a predetermined orientation to provide the best fluid seal possible. Most particularly, the seal members 30 are oriented with the relief portion 38 of the seal body facing the higher pressure end of the piston. In the configuration shown in FIG. 1 , the seal members in the three locations 26 would be oriented with the rear annular face 37b of the seal body facing toward the opening between the fluid reservoir 14 and the master cylinder 12 (i.e., to the left in the figure). With this orientation, any pressurized fluid entering the relief portion 38 will tend to deflect the seal lip 36 outward to provide a tighter fluid seal against the cylinder bore 22. The seal member 25 in the location 27 is not exposed to any pressurized fluid, therefore it may be oriented in either direction.

[022] The seal member 50 shown in FIG. 3 can be assembled within the piston in any orientation - i.e., it is assembly direction independent. The seal member 50 includes a seal body 52 with an inner circumferential surface 54 adapted to seat within an annular groove 26, 27. The seal body defines two circumferential seal lips 56a, 56b at the opposite annular faces 57a, 57b of the seal body 52. Each seal lip 56a, 56b includes a corresponding sealing surface 56c, 56d that is oriented at an angle B. The angle B may be similar to the angle A of the seal member 30. The sealing surfaces 56c, 56d of the seal 50 may incorporate the micro-grooves or micro-ridges described above for the surface 36a of the seal 30. [023] The seal body 52 defines a relief portion 58a, 58b radially inward from each corresponding seal lip 56a, 56b. These relief portions are shallower than the relief portion 38 of the seal member 30, in part because the seal lips 56a, 56b do not extend across as much of the seal width as the seal lip 36, and in part to avoid interference with the groove 60 in the center of the seal body 52.

[024] As indicated above, the seal body 52 defines a circumferential groove 60 in the center portion of the body. A glide ring 62 is disposed within that groove, so that the glide ring is flanked by the two seal lips 56a, 56b. The glide ring 62 may be constructed similar to the glide ring 45 and thus may be formed of a low sliding friction material, such as a plastic or resin, as described above. The outer circumferential surface 64 of the glide ring 60 has a diameter that is less than the outer diameter of the seal lips 56a, 56b, but still sized for a close running fit within the bore 22. The outer circumferential surface 64 that is at least coextensive with the outer surface of the seal body at the groove 60, but preferably projecting slightly above the groove 60 in the seal body.

[025] As can be appreciated from FIG. 3, the seal member 50 can be mounted on the piston in either orientation since the faces 57a, 57b of the piston body 52 are identical and the glide ring 62 is centrally within the seal body. Since both faces 57a, 57b include a relief portion 58a, 58b, high pressure from either side of the seal member will tend to push the corresponding seal lip 56a, 56b outward into a greater sealing contact with the cylinder bore 22. [026] The glide ring 62 may be suitably mounted and retained within the circumferential groove 60. Thus, in certain embodiments, the glide ring may be adhered or press-fit within the groove. Also the glide ring may be installed after the seal is in the piston groove, 26, 27. Alternatively, the seal body may be over- molded onto the glide ring in a conventional manner.

[027] It will be appreciated that various of the above-disclosed and other features, and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.

[028] For instance, in certain embodiments, the relative dimensions of the seal body and glide ring may be different than disclosed herein. While a single glide ring is shown in each of the disclosed embodiments, more than one glide ring may be incorporated into appropriately defined circumferential grooves in the seal body.