Power assisted master cylinder assemblies

Claim 2

A power-assisted master cylinder assembly comprising a master cylinder which includes a cylinder body, a primary and a secondary piston arranged in tandem in said body, a primary and a secondary pressure space being defined ahead of said primary and said secondary piston respectively, an outlet from each of said pressure spaces for connection to a primary and secondary brake circuit respectively, a power chamber in said cylinder body behind said primary piston and an inlet to said power chamber for connection to a source of fluid under pressure; and a control valve assembly which includes valve means for controlling the supply of fluid from said source to said power chamber, and means for operating said valve means in response to three conditions; firstly to pressure in both of said primary and secondary pressure spaces when both brake circuits are operational, secondly to pressure in said secondary pressure space in the event of a failure of said primary circuit, and thirdly to pressure in said primary space in the event of a failure of said secondary circuit.

Claim 3

A power-assisted master cylinder assembly comprising a master cylinder which includes a cylinder body, a primary and a secondary piston arranged in tandem in said body, a primary and a secondary pressure space being defined ahead of said primary and said secondary piston respectively, an outlet from each of said pressure spaces for connection to a primary and secondary brake circuit respectively, a power chamber in said cylinder body behind said primary piston and an inlet to said power chamber for connection to a source of fluid under pressure; and a control valve assembly which includes valve means for controlling the supply of fluid from said source to said power chamber, and means for operating said valve means in response to three conditions; firstly to pressure in both of said primary and secondary pressure spaces when both brake circuits are operational, secondly to pressure in said secondary pressure space in the event of a failure of said primary circuit, and thirdly to pressure in said primary space in the event of a failure of said secondary circuit.

Claim 4

A power-assisted master cylinder assembly comprising a master cylinder which includes a cylinder body, a primary and a secondary piston arranged in tandem in said body, a primary and a secondary pressure space being defined ahead of said primary and said secondary piston respectively, an outlet from each of said pressure spaces for connection to a primary and secondary brake circuit respectively, a power chamber in said cylinder body behind said primary piston and an inlet to said power chamber for connection to a source of fluid under pressure; and a control valve assembly which includes valve means for controlling the supply of fluid from said source to said power chamber, and means for operating said valve means in response to three conditions; firstly to pressure in both of said primary and secondary pressure spaces when both brake circuits are operational, secondly to pressure in said secondary pressure space in the event of a failure of said primary circuit, and thirdly to pressure in said primary space in the event of a failure of said secondary circuit.

Claim 5

A power-assisted master cylinder assembly as in claim 1 wherein said master cylinder and said control valve assembly are separate units but connected by fluid connections.

Claim 6

A power-assisted master cylinder assembly as in claim 1, wherein said valve operating means comprises a housing having a bore closed at one end, a spool and a control Piston working in tandem in said bore with said spool adjacent said closed end of said bore, said control piston being arranged to actuate said valve means upon axial movement away from said closed end of said bore, said spool and said closed end of said bore defining therebetween a first balance chamber, and said spool and said control piston defining therebetween a second balance chamber, means for connecting each of said chambers to a different one of said outlets to place said chambers in communication with said pressure spaces, and stop means in said bore for limiting axial movement of said spool away from said control piston, whereby the control piston is actuated in response to said first condition by the pressure of fluid in said second balance chamber, in response to another of said conditions by the pressure of fluid in said second balance chamber which also holds said spool against said stop means, and in response to the remaining one of said conditions by the pressure of fluid in said first balance chamber acting through said spool which engages with said control piston.

Claim 7

A power-assisted master cylinder as in claim 3, wherein said stop means comprises a surface at the closed end of said bore for engagement by the spool, said control piston having a surface at its end adjacent to said spool for engagement by the spool, said spool having an axial length only slightly less than the axial distance between said engagement surfaces, whereby upon failure of one brake circuit a minimum volume of fluid is required to be supplied to the balance chamber connected to the other circuit to move said spool into contact with one of said engagement surfaces before full pressure can be developed in that balance chamber to displace the control piston to actuate the valve means.