Dead stroke reduction valve

A master cylinder for use in a vehicle brake system having individual front and rear wheel brake actuators, comprising:

• a master cylinder housing;
• a generally cylindrical bore in said housing;
• a fluid source in fluid communication with the bore;
• a first piston is reciprocally disposed in said bore;
• a second piston is reciprocally disposed in said bore;
• the first piston defining in conjunction with the second piston and the bore, a first variable volume chamber;
• the second piston defining in conjunction with the bore, a second variable volume chamber;
• said first and second chambers being connected by first and second fluid flow paths to receive fluid from the fluid source and maintain the fluid level in the brake system at a desired level, and being connected respectively to rear and front wheel brake actuators to supply pressurized fluid to effect a brake application;
• a poppet valve in the second fluid flow path and actuated by motion of the second piston for selectively closing the second fluid flow path to allow fluid pressure to build in the second chamber;
• and
• a valve member movable between an open position in which the fluid source is in fluid communication with the first fluid flow path and a closed position in which the fluid source is isolated from fluid communication with the first fluid flow path, the closed position allowing fluid pressure to build in the first variable chamber,
• wherein the second piston is moveable between a first position and a second position, and
• wherein movement of the second piston from the first position to the second position causes the second piston to directly contact the valve member so as to move the valve member from the closed position to the open position.

A method of operating a vehicle master brake cylinder of the tandem type having primary and secondary brake circuits including primary and secondary pistons biased toward brakes released positions by primary and secondary return springs, and primary and secondary conduits for conveying hydraulic fluid between a fluid reservoir and the primary and secondary brake circuits respectively, comprising:

• simultaneously translating the primary and secondary pistons for compressing the secondary return spring and closing the primary conduit, the simultaneously translating the primary and secondary pistons occurring without compressing the primary return spring;
• translating the primary piston relative to the secondary piston and against the primary return spring bias to initially increase the fluid pressure in the primary circuit;
• and
• continuing to translate the primary and secondary pistons to increase primary and secondary brake circuit pressure to arrest vehicle motion.