Hydraulic brake fluid pressure proportioning valve

Claim 2

In a separated hydraulic brake system having front and rear brake cylinders and a master cylinder having front and rear sections respectively connected through independent fluid circuits with said front and rear brake cylinders, a brake pressure proportioning valve interposed between the rear section of said master cylinder and said rear brake cylinders, said brake pressure proportioning valve comprising: a housing having a first inlet port communicating with said front section of said master cylinder, a second inlet port communicating with said rear section of said master cylinder, and an outlet port communicating with said rear brake cylinders; first and second chambers formed in said housing, said second chamber providing fluid communication between said second inlet port and said outlet port so as to pass an unmodulated fluid pressure from said second inlet port to said outlet port when a fluid pressure prevailing in said second inlet port is lower than a predetermined level, and said first chamber communicating with said first inlet port to receive fluid pressure from a front brake pressure circuit; a pressure responsive differential piston disposed in said first and second chambers and having an upper stem portion exposed to a fluid pressure in said first chamber, a lower stem portion exposed to a fluid pressure in said second chamber and a valve head formed between said upper and lower stem portions, said pressure responsive differential piston serving to modulate the fluid pressure admitted to said second fluid chamber at a predetermined rate when the fluid pressure in said first and second fluid chambers exceeds said predetermined level under a circumstance in which a braking fluid circuit is held in its normal condition for transmitting a modulated fluid pressure to said outlet port and serving to modify said rate of modulating the fluid pressure in response to a failure in the front brake fluid pressure circuit for transmitting a fluid pressure which is higher than said modulated fluid pressure to said outlet port; a valve member operatively disposed in said second chamber of said housing and being cooperative with said valve head of said pressure responsive differential piston for restricting the flow of said fluid pressure from said second inlet port to said outlet port when said fluid pressure in said first and second chambers increase beyond said predetermined level; and a sealing member operatively disposed in said housing between said first and second chambers and slidably accommodating therein said upper stem portion of said pressure responsive differential piston for providing sealing function between said first and second chambers, said sealing member including an O-ring portion having an outer periphery sealingly engageable with the wall of said first chamber and upper and lower flanges integrally formed with said O-ring portion at its inner periphery, said upper and lower flanges having lip portions respectively which are slightly smaller in diameter before insertion of said upper stem portion of said pressure responsive differential piston and said upper flange being inclined angularly upwardly toward the axis of said pressure responsive differential piston for thereby sealing off said first chamber and said lower flange being inclined angularly downwardly toward the axis of said pressure responsive differential piston for thereby sealing off said second chamber.

Claim 3

In a separated hydraulic brake system having front and rear brake cylinders and a master cylinder having front and rear sections respectively connected through independent fluid circuits with said front and rear brake cylinders, a brake pressure proportioning valve interposed between the rear section of said master cylinder and said rear brake cylinders, said brake pressure proportioning valve comprising; a housing having a first inlet port communicating with said front section of said master cylinder, a second inlet port communicating with said rear section of said master cylinder, and an outlet port communicating with said rear brake cylinder; first and second chambers formed in said housing, said second chamber providing fluid communication between said second inlet port and said outlet port to pass an ummodulated fluid pressure from said second inlet port to said outlet port until a fluid pressure prevailing in said second inlet port exceeds a predetermined level; a first end closure member screwed into one end of said housing for closing an open end of said first chamber and including a longitudinal cylindrical extension having formed at its one end an opening, said longitudinal cylindrical extension also having a cylindrical cavity provided with a fluid passageway communicating with said first inlet port; a second end closure member screwed into another end of said housing for closing an open end of said second chamber; a pressure responsive differential piston disposed in said first and second chambers and having an upper stem portion slidably accommodated in said cylindrical cavity of said first end closure member, said upper stem portion being exposed to a front brake fluid pressUre in said first chamber, a lower stem portion exposed to a fluid pressure in said second chamber and a valve head formed between said upper and lower stem portions, said pressure responsive differential piston serving to modulate the fluid pressure admitted to said second fluid chamber at a predetermined rate when the fluid pressure in said first and second chambers exceeds said predetermined level under circumstance in which a braking fluid circuit is held in its normal condition for transmitting a modulated fluid pressure in said outlet port and serving to modify said rate of modulating the fluid pressure in response to a failure in the front brake fluid pressure circuit for transmitting a fluid pressure which is higher than said modulated fluid pressure to said outlet port; a valve member operatively disposed in said second chamber of said housing and being cooperative with said valve head of said pressure responsive differential piston for restricting the flow of said fluid pressure from said second inlet port to said outlet port when said fluid pressure in said first and second chambers increase beyond said predetermined level; and a sealing member operatively disposed in said housing between said first and second chambers and slidably accommodating said upper stem portion of said pressure responsive differential piston for providing sealing function between said first and second chambers, said sealing member including an O-ring portion formed at an outer periphery thereof sealingly engageable with the wall of said first chamber and upper and lower flanges integrally formed with said O-ring portion at an inner periphery of said sealing member, said upper and lower flanges having lip portions respectively which are slightly smaller in diameter before insertion of said upper stem portion of said pressure responsive differential piston, and said upper flange being inclined angularly upwardly toward the axis of said pressure responsive differential piston for thereby sealing off said first chamber and said lower flange being inclined angularly downwardly toward the axis of said pressure responsive differential piston for thereby sealing off said second chamber.

Claim 4

In a separated hydraulic brake system having front and rear brake cylinders and a master cylinder having front and rear sections respectively connected through independent fluid circuits with said front and rear brake cylinders, a brake pressure proportioning valve interposed between the rear section of said master cylinder and said rear brake cylinders, said brake pressure proportioning valve comprising; a housing having a first inlet port communicating with said front section of said master cylinder, a second inlet port communicating with said rear section of said master cylinder, and an outlet port communicating with said rear brake cylinder; first and second chambers formed in said housing, said second chamber providing fluid communication between said second inlet port and said outlet port to pass an ummodulated fluid pressure from said second inlet port to said outlet port until a fluid pressure prevailing in said second inlet port exceeds a predetermined level; a first end closure member screwed into one end of said housing for closing an open end of said first chamber and including a longitudinal cylindrical extension having formed at its one end an opening, said longitudinal cylindrical extension also having a cylindrical cavity provided with a fluid passageway communicating with said first inlet port; a second end closure member screwed into another end of said housing for closing an open end of said second chamber; a pressure responsive differential piston disposed in said first and second chambers and having an upper stem portion slidably accommodated in said cylindrical cavity of said first end closure member, said upper stem portion being exposed to a front brake fluid pressUre in said first chamber, a lower stem portion exposed to a fluid pressure in said second chamber and a valve head formed between said upper and lower stem portions, said pressure responsive differential piston serving to modulate the fluid pressure admitted to said second fluid chamber at a predetermined rate when the fluid pressure in said first and second chambers exceeds said predetermined level under circumstance in which a braking fluid circuit is held in its normal condition for transmitting a modulated fluid pressure in said outlet port and serving to modify said rate of modulating the fluid pressure in response to a failure in the front brake fluid pressure circuit for transmitting a fluid pressure which is higher than said modulated fluid pressure to said outlet port; a valve member operatively disposed in said second chamber of said housing and being cooperative with said valve head of said pressure responsive differential piston for restricting the flow of said fluid pressure from said second inlet port to said outlet port when said fluid pressure in said first and second chambers increase beyond said predetermined level; and a sealing member operatively disposed in said housing between said first and second chambers and slidably accommodating said upper stem portion of said pressure responsive differential piston for providing sealing function between said first and second chambers, said sealing member including an O-ring portion formed at an outer periphery thereof sealingly engageable with the wall of said first chamber and upper and lower flanges integrally formed with said O-ring portion at an inner periphery of said sealing member, said upper and lower flanges having lip portions respectively which are slightly smaller in diameter before insertion of said upper stem portion of said pressure responsive differential piston, and said upper flange being inclined angularly upwardly toward the axis of said pressure responsive differential piston for thereby sealing off said first chamber and said lower flange being inclined angularly downwardly toward the axis of said pressure responsive differential piston for thereby sealing off said second chamber.

Claim 5

A brake pressure proportioning valve according to claim 2, wherein said housing has a radially extending annular shoulder formed at the lower end portion of said first chamber, and wherein said O-ring portion formed at the outer periphery of said sealing member is sealingly interposed in a cavity formed between an end portion of said cylindrical extension of said first end closure member and said annular shoulder.

Claim 6

A brake pressure proportioning valve according to claim 3, wherein said sealing member is sealingly interposed in said cavity formed between the end portion of said cylindrical extension of said first end closure member and said annular shoulder by means of a thrust washer.

Claim 7

A brake pressure proportioning valve according to claim 4, wherein said thrust washer is made from a material having a low frictional resistance.

Claim 8

A brake pressure proportioning valve according to claim 4, wherein the inner diameter of said thrust washer is such that the clearance between the inner diameter of said thrust washer and said upper flange is minimum so as to prevent a joint portion between said O-ring portion formed at the outer periphery of said sealing member and said flanges formed at the inner periphery thereof from being excessively deflected radially upwardly by the fluid pressure in said second chamber.

Claim 9

A brake pressure proportioning valve according to claim 6, wherein said housing has a cylindrical bore adjacent said annular shoulder in said first chamber into which said lower flange of said sealing member extends, the inner diameter of said cylindrical bore being such that the clearance between the inner diameter of said cylindrical bore and said lower flange is minimum to prevent said joint portion between said O-ring portion formed at the outer periphery of said sealing membEr and said flanges formed at the inner periphery thereof from being excessively deflected radially downwardly by the fluid pressure in said first chamber.

Claim 10

A brake pressure proportioning valve according to claim 4, further comprising a back-up ring which is received in a cylindrical bore which is larger in diameter than said cylindrical cavity of said cylindrical extension and which is formed at an end portion of said cylindrical extension of said first end closure member, the inner diameter of said back-up ring being sized to have a value to slidably accommodate therein said upper stem portion of said pressure responsive differential piston with a minimum clearance to prevent the lip portion of said upper flange from being pressed into a gap formed between said cylindrical cavity of said cylindrical extension and said upper stem portion of said pressure responsive differential piston thereby to prevent said lip portion from being damaged when said upper flange of said sealing member is deflected upwardly by a fluid pressure in said second chamber, the axial thickness of said back-up ring and the depth of said cylindrical bore being determined to provide a minimum clearance between said upper flange and one side of said back-up ring, and clearance between the inner diameter of said cylindrical bore and the outer diameter of said back-up ring being selected to have a sufficient value to permit eccentricity to be caused between said upper stem of said pressure responsive differential piston and said cylindrical extension of said first end closure member.

Claim 11

In a hydraulic brake pressure proportioning valve interposed, in a vehicle having a separated hydraulic brake system with front and rear wheel cylinders and a tandem master cylinder having front and rear sections respectively connected through independent fluid circuits with said front and rear wheel cylinders, said hydraulic brake pressure proportioning valve comprising; a housing having a first inlet port communicating with said front section of said tandem master cylinder, a second inlet port communicating with said rear section of said tandem master cylinder, and an outlet port communicating with said rear wheel cylinder; first and second chambers formed in said housing, said second chamber providing fluid communication between said second inlet port and said outlet port and having incorporated means therein to pass a fluid pressure from said second inlet port to said outlet port until the fluid pressure prevailing in said second inlet port exceeds a predetermined level; a first end closure member screwed into one end of said housing for closing an open end of said first chamber and including a longitudinal cylindrical extension having formed at its one end an opening, said longitudinal cylindrical extension also having a cylindrical cavity provided with a fluid passageway communicating with said first inlet port; a second end closure member screwed into another end of said housing for closing an open end of said second chamber; a pressure responsive differential piston disposed in said first and second chambers, said pressure responsive differential piston serving to modulate the fluid pressure admitted to said second fluid chamber at a predetermined rate when the fluid pressure in said first and second chambers exceeds said predetermined level under a circumstance in which a braking fluid circuit is held in its normal condition for transmitting a modulated fluid pressure to said outlet port and serving to modify said rate of modulating the fluid pressure in response to a failure in the front brake fluid pressure circuit for transmitting a fluid pressure which is higher than said modulated fluid pressure to said outlet port, said pressure responsive differential piston having an upper stem effective sectional area exposed to a fluid pressure in said first inlet port, a lower stem effective sectional area exposed to a fluid pressure in said second inlet port and a contact effective sectional area exposed to a fluid prEssure in said outlet port; a valve member operatively disposed in said second chamber of said housing and being cooperative with a valve head of said pressure responsive differential piston for restricting the flow of said fluid pressure from said second inlet port to said outlet port when said fluid pressure in said first and second chambers increases beyond said predetermined level; a compression spring disposed in said second chamber for urging said pressure responsive differential piston to a position in which said valve head is unseated from said valve member for transmitting a fluid pressure from said second inlet port to said outlet port at a predetermined condition; and a sealing member operatively disposed in said housing between said first and second chambers for sealing off said first and second chambers from each other thereby to raise the starting point of fluid modulation to a higher value and to increase the rate of modulating the fluid pressure in response to a failure in the front brake fluid pressure circuit, said sealing member including an annular O-ring portion which is interposed between an annular shoulder formed in said first chamber of said housing and said cylindrical extension of said first end closure member, an upper flange integral with said O-ring portion and having a lip portion angularly inclined angularly upwardly and a lower flange portion integral with said O-ring portion and having a lip portion angularly inclined angularly downwardly, said lip portions of said upper and lower flanges sealingly engaging with said upper stem portion of said pressure responsive differential piston.

Claim 12

In a hydraulic brake pressure proportioning valve interposed, in a vehicle having a separated hydraulic brake system with front and rear wheel cylinders and a tandem master cylinder having front and rear sections respectively connected through independent fluid circuits with said front and rear wheel cylinders, said hydraulic brake pressure proportioning valve comprising; a housing having a first inlet port communicating with said front section of said tandem master cylinder, a second inlet port communicating with said rear section of said tandem master cylinder, and an outlet port communicating with said rear wheel cylinder; first and second chambers formed in said housing, said second chamber providing fluid communication between said second inlet port and said outlet port and having incorporated means therein to pass a fluid pressure from said second inlet port to said outlet port until the fluid pressure prevailing in said second inlet port exceeds a predetermined level; a first end closure member screwed into one end of said housing for closing an open end of said first chamber and including a longitudinal cylindrical extension having formed at its one end an opening, said longitudinal cylindrical extension also having a cylindrical cavity provided with a fluid passageway communicating with said first inlet port; a second end closure member screwed into another end of said housing for closing an open end of said second chamber; a pressure responsive differential piston disposed in said first and second chambers, said pressure responsive differential piston serving to modulate the fluid pressure admitted to said second fluid chamber at a predetermined rate when the fluid pressure in said first and second chambers exceeds said predetermined level under a circumstance in which a braking fluid circuit is held in its normal condition for transmitting a modulated fluid pressure to said outlet port and serving to modify said rate of modulating the fluid pressure in response to a failure in the front brake fluid pressure circuit for transmitting a fluid pressure which is higher than said modulated fluid pressure to said outlet port, said pressure responsive differential piston having an upper stem effective sectional area exposed to a fluid pressure in said first inlet port, a lower stem effective sectional area exposed to a fluid pressure in said second inlet port and a contact effective sectional area exposed to a fluid prEssure in said outlet port; a valve member operatively disposed in said second chamber of said housing and being cooperative with a valve head of said pressure responsive differential piston for restricting the flow of said fluid pressure from said second inlet port to said outlet port when said fluid pressure in said first and second chambers increases beyond said predetermined level; a compression spring disposed in said second chamber for urging said pressure responsive differential piston to a position in which said valve head is unseated from said valve member for transmitting a fluid pressure from said second inlet port to said outlet port at a predetermined condition; and a sealing member operatively disposed in said housing between said first and second chambers for sealing off said first and second chambers from each other thereby to raise the starting point of fluid modulation to a higher value and to increase the rate of modulating the fluid pressure in response to a failure in the front brake fluid pressure circuit, said sealing member including an annular O-ring portion which is interposed between an annular shoulder formed in said first chamber of said housing and said cylindrical extension of said first end closure member, an upper flange integral with said O-ring portion and having a lip portion angularly inclined angularly upwardly and a lower flange portion integral with said O-ring portion and having a lip portion angularly inclined angularly downwardly, said lip portions of said upper and lower flanges sealingly engaging with said upper stem portion of said pressure responsive differential piston.