MASTER CYLINDER AND PROPORTIONING VALVE ASSEMBLY

Abstract: A master cylinder (12) and proportioning valve assembly (52), comprise a housing (18) with a pair of pistons (22, 24) movable therein to generate fluid pressure during braking. The proportioning valve assembly (52), forms a mechanical connection (82), with one of the pistons (24) to render the proportioning valve inoperative in response to the position of the one piston in the housing.

Description: A MASTER CYLINDER AND PROPORTIONING VALVE ASSEMBLY This invention relates to a master cylinder and proportioning valve assembly wherein fluid pressure is communicated from the master cylinder to a brake circuit via the proportioning valve assembly. In United States Patent 4,213,655 (Brademeyer), issued July 22, 1980, a screw-in proportioning valve assembly is connected to a master cylinder housing via an outlet port so that the proportioning valve assembly is coupled to the master cylinder as a modular unit. Therefore, the master cylinder and proportioning valve can be inventoried and assembled as a unitary package. However, if a proportioning valve assembly as described in the above patent is used in a conventional front-rear brake system, it is possible for the proportioning valve to function and reduce fluid pressure to the rear brakes even though the front brakes have failed. This situation is not desireable in the failure mode as full braking pressure should be communicated to the rear brakes when the front brakes are inoperable. To avoid the above problems during the failure mode, the present invention provides a master cylinder and proportioning valve assembly comprising a housing defining a bore movably receiving a pair of pistons in cooperation with the housing to form a nair of pressure chambers communi-cating with brake circuits via outlet ports, the proportioning valve assembly being operatively connected with the housing via one of the outlet ports whereby fluid pressure from one of the pressure chambers is communicated directly to the proportioning valve assembly during braking, characterized in that said proportioning valve assembly defines a mechanical connection with one of said pair of pistons and is responsive to movement of said one piston to define a bypass condition wherein said proportioning valve assembly is incapable of altering fluid communication from the one pressure chamber. It is an advantage of the present invention that the proportioning valve assembly is provided with a simple connection with the one piston to control operation of the proportioning valve in response to a failure mode. In the drawings, Figure 1 shows a brake system with a master cylinder and proportioning valve'assembly illustrated in cross section. Figure 2 is a cross sectional view taken along line 2-2 of Figure 1, and Figure 3 is a view of the circumscribed portion in Figure 1 when a failure mode occurs. The brake system in Figure 1 shows a brake pedal lD couple*--to a master cylinder 12 to generate fluid pressure therein and communicate the same to a pair of front brakes 14 and a pair of rear brakes 16. The master cylinder 12 defines a housing 18 with a bore 20-movably receiving a tirst piton and a second piston 24. The first piston 22 cgOpexatas with the second piston 24ato substantially define a first chamber 26, while the second piston 24 cooperates with the housing 18 to substantially define a second chamber 28. The first chamber 26 communicates with the rear brakes 16 via outlet port 30 and conduit 32 and the second chamber 28 communicates with .e front brakes 14 via outlet port 34 and conduit 36. ln a conventional manner, the pistons 22 and 24 are movable-within the bore during braking to generate fluid pressure in the chambers 26 and 28 and communicate the same to respective brakes 16 and 14. During braking, the pedal 10 is pivoted to move piston 22 toward piston 24 and close chamber 26 to the reservoir 42. The spring 42 is collapsed to bias piston 24 to also close chamber 28 to the reservoir so that fluid pressure is generated in the contracting chambers 26 and 28. The fluid pressure in chamber 28 is communicated directly to the outlet port 34, the conduit 36 and the front brakes 14. The fluid pressure in chamber 26 is communicated to the outlet port 30 via opening 84 and opening 82 as the end of stem 66 is slotted to permit fluid communication through opening 82. The shoulder 78 of stem 66 is also slotted to provide fluid communication past the slJuld r 78 and the shoulder 68 so that fluid pressure is communicated to the differential area piston 60 and via an opening 90 on the differential area piston 60 to the conduit 32 and rear brakes 16. As the piston 24 moves away from piston 22, the surface 72 slidably engages the end of stem 66 to maintain the latter in its operative position as shown in Figure 1. Fluid pressure communicated to the stepped bore 58 acts against a small diameter section of piston 60 and against a large diameter section of piston 60 to bias the latter toward the poppet 64. When the fluid pressure in the stepped bore 58 reaches a predetermined value, the piston 60 is movable toward the poppet against the spring 62 so-that the poppet reduces fluid communication through opening 90 to proportion fluid communication to the rear brakes 16. A snap ring 38 is fixedly disposed at an open end of the bore 20 to define a rest position for the first piston 22. A top hat assembly 40 between the pistons 22 and 24 defines a rest position for the second piston 24. Springs 42 and 44 cooperate with the pistons and housing to bias the pistons to their rest positions. A reservoir 42 is coupled to the housing 18 to carry fluid for selective communication to the bore 20. In accordance with the invention, the housing 18 forms an outwardly extending projection 50 defining outlet port 30. A proportioning valve assembly 52 is threadably coupled to the projection 50 and the conduit 32. The proportioning valve assembly comprises a plug 54 with a threaded end 56 coupled to a threaded wall of outlet port 30. The plug 54 forms a stepped bore 58 to movably receive a differential area piston 60, a spring 62 and a poppet 64. A spring 63 biases the poppet 64 to an extended position adjacent the differential area piston 60. The spring 62 opposes movement of the differential area piston 6Q. The poppet 64 includes a stem 66 extending from the poppet 64 through the threaded end 56 to a position inside the bore 20 in engagement with the piston 24. The stepped bore 58 forms a shoulder 68 at the threaded end so that a spring 70 abuts the shoulder 68 and biases the stem 66 in the direction of the piston 24. In the rest position shown in Figure 1, the stem 66 engages a first surface 72 forad by a skirt 74. The first skirt extends from the stem to a second tapered surface 76 so that movement of the piston retains the stem stationary until the second surface comes into engagement with the stem 66. At this time, the second surface 76 is movable relative to the stem 66 to permit the latter to move further into the bore 20 until a shoulder 78 on the stem is engageable with a shoulder 80 on the projection 50, as shown in Figure 3. Turning to Figure 2, the outlet port 30 includes a first opening 82 with an axis A intersecting an axis for the bore 20 and a second opening 84 with an axis B substantially tangential to a wall of bore 20. The axis A for the first opening 82 is coaxial with an axis for the stepped bore 58 and the axis B for the second opening 84 extends through an open end of the outlet port 30. Consequently, both openings 82 and 84 are accessible from the open end of port 30 for drilling the same. A first wall 86 of outlet port 30 extends to shoulder 80 to define an edge 88 intersecting the axis B for opening 84 so that the edge 88 sets the location of axis B. With the opening 84 disposed at the top of bore 20, it is possible to bleed air from the bore 20 while stirs retaining a perpendicular mounting for the stem 66 against the piston 24. So long as the pressure chamber 28 and its associated fluid lines to the front brakes 14 remains closed, the build up of fluid pressure in chamber 28 will prevent piston 24 from completely collapsing spring 44. Therefore, during normal braking the piston 24 moves through a limited distance to retain surface 72 in slidable engagement with stem 66. The proportioning valve assembly 52 is pressure responsive to selectively proportion communication of fluid pressure to the rear brakes 16. In the event the front brakes 14 or conduit 34 fail as a result of a leak, the piston 24 will move with the piston 22 during braking and completely collapse spring 28 until an end face 92 of piston 24 abuts an end wall 94 of housing 18. When the end face 92 approaches the end wall 94, the piston 24 positions the second tapered surface 76 in sliding engagement with the stem 66. The spring 70 biases the stem 66 to move further into the bore 20 along surface 76. The poppet 64 moves with the stem 66 away from the differential area piston 60. Thereafter, when fluid pressure in the stepped bore 58 moves the differential area piston toward the poppet, the poppet will be displaced toward the piston 24 to provide for free flow aS fluid pressure from the chamber 26 to the conduit 32 in the failure mode. When braking is terminated, the piston 24 will return to its rest position as shown in Figure 1 so that the tapered second surface will push the stem and poppet in the direction of the differential area piston until the stem engages the first surface 72 of the piston 24. As a result of the above description, the proportioning valve assembly is position responsive to movement of the piston 24 to define a bypass failure mode wherein the proportioning valve assembly is rendered inoperable. The proportioning valve assembly also cooperates with the piston to reestablish a normal operating position for the proportioning valve assembly when braking is terminated. Therefore, when the failure is corrected, the proportioning valve assembly will be in its normal operating position to control fluid communication to the rear brakes as a function of the fluid pressure generated by the master cylinder.

Claims: CLAIMS 1. A master cylinder and proportioning valve assembly comprising a housing (18) defining a bore (20) movably receiving a pair of pistons (22, 24) in cooperation with the housing to form a pair of pressure chambers (26, 28) communicating with brake circuits (32, 36) via outlet ports (30, 34), the proportioning valve assembly (52) being operatively connected with the housing (18) via one (30) of the outlet ports whereby fluid pressure from one (26) of the pressure chambers is communicated directly to the proportioning valve assembly (52) during braking, the proportioning valve assembly (52) being operable during braking to alter fluid communication from the one pressure chamber (26) to its associated brake circuit (32), characterized in that said proportioning valve assembly (52) defines a mechanical connection (82) with one (24) of said pair of pistons and is responsive to movement of said one piston (24) to define a bypass condition wherein said proportioning valve assembly (52) is incapable of altering fluid communication from the one pressure chamber (26). 2. The master cylinder and proportioning valve assembly of claim 1 in which said one piston (24) defines a skirt (74) extending into the one pressure chamber (26) and said proportioning valve assembly defines a stem (66) extending into the housing bore (20) to slidably engage said skirt (74). 3. The master cylinder and proportioning valve assembly of claim 2 in which said skirt (74) forms a first surface (72) slidable relative to said stem (66) to maintain the latter in a first position, and a second surface (76) slidable relative to said stem (66) to permit said stem (66) to move to the bypass condition. 4. The master cylinder and proportioning valve assembly of claim 1 in which said housing (18) defines a stop (80) cooperating with said proportioning valve assembly to limit the bypass condition for said proprotioning valve assembly (52). 5. The master cylinder and proportioning valve assembly of claim 1 in which said housing (18) defines an outwardly extending projection (50) forming said one outlet port, said proportioning valve defines a plug (54) threadably cooperating with said projection, a stem (66) extending through said projection to engage sad one piston (24), and a resilient member (70) between said stem (66) and said plug within said projection to bias said stem (66) in the direction of said one piston (24). 6. The master cylinder and proportioning valve assembly of claim 1 in which said proportioning valve assembly (52) includes a stem (66) engageable with said one piston (24), said stem (66) defining a shoulder (78) cooperating with said housing (18) to limit the bypass condition and forming a spring rest for a resilient member (70) biasing said stem (66) in the direction of said one piston. 7. The master cylinder and proportioning valve assembly of claim 1 in which said housing (18) defines an outwardly extending projection (50) forming said one outlet port (30), said outlet port (30) communicating with said housing bore via a pair of openings (82, 84), said proportioning valve assembly extending through one (82) of said pair of openings and the other opening (84) providing secondary fluid communication between said housing bore (20) and said one opening (30). 8. The master cylinder and proportioning valve assembly of claim 7 in which said one opening (82) forms an axis (A) concentrically orientated relative to an axis for said outlet port, said other opening forms an axis (B) angularly disposed relative to said outlet port axis and extending outwardly through an open end of said outlet port to permit ready access to said pair of openings via said outlet port. 9. The master cylinder and proportioning valve assembly of claim 7 in which said outlet port (30) forms a shoulder (80) extending transversely outwardly from said one opening to a wall (86) cooperating with said proportioning valve assembly, said shoulder (80) intersecting said wall at an edge (88) and said other opening axis (B) intersects said edge (88). 10. The master cylinder and proportioning valve assembly of claim 7 in which said one opening (82) defines an axis (A) substantially intersecting an axis for said housing bore and said other opening defines an axis (-B) substan-tially tangential to a wall for said housing bore (20).

Inventors: FULMER, KEITH H.
Applicants: ALLIED CORPORATION
Application year: 1984
Main classification: B60T8
IPC codes: B60T11, B60T8