Slip control boost braking system
View Patent ↗A master cylinder includes a housing and a first secondary piston disposed in the housing. The first secondary piston cooperates with the housing to define a first secondary chamber which changes volume as the first secondary piston moves in the housing. A second secondary piston is disposed in the housing and cooperates with the housing to define a second secondary chamber which changes volume as the second secondary piston moves in the housing. A stepped primary piston is disposed in the housing. The primary piston cooperates with the housing to define a primary chamber which changes volume as the primary piston moves in the housing. The primary piston defines an abutment surface which can be driven into abutment with the first secondary piston and the second secondary piston to move the first secondary piston and the second secondary piston. A primary piston spring maintains a restorative force on the primary piston when actuated.
1. A braking system for applying pressurized hydraulic brake fluid to a plurality of vehicle brakes comprising:
a source of brake fluid;
a primary brake fluid circuit;
a pump for providing hydraulic brake fluid from said source of brake fluid to said primary brake fluid circuit;
an electric motor for driving said pump;
a pressure accumulator for storing pressurized hydraulic brake fluid from said primary circuit;
a pedal simulator in fluid communication with said primary brake fluid circuit;
a first brake fluid circuit;
a boost valve for controlling a flow of pressurized brake fluid from said primary brake fluid circuit to said first brake fluid circuit;
a first brake actuated by brake fluid from said first brake fluid circuit;
a second brake operated by an application of pressurized brake fluid from said first brake fluid circuit;
a second brake fluid circuit that is hydraulically isolated from the first brake fluid circuit;
a third brake actuated by pressurized brake fluid from said second circuit;
a third circuit brake fluid circuit that is hydraulically isolated from the first and second brake fluid circuits;
a fourth brake actuated by pressurized brake fluid from said third circuit;
a brake pedal for receiving input braking demands from a driver;
a master cylinder for receiving said input demands from said brake pedal, said master cylinder comprising:
a housing;
a first secondary piston disposed in said housing said first secondary piston cooperating with said housing to define a first secondary chamber which changes volume as said first secondary piston moves in said housing, said first secondary chamber being in fluid communication with said second brake fluid circuit for acting on said third brake;
a second secondary piston disposed in said housing cooperating with said housing to define a second secondary chamber which changes volume as said second secondary piston moves in said housing, said second secondary chamber being in fluid communication with said third brake fluid circuit acting on said fourth vehicle brake;
said first secondary piston and said second secondary piston each capable during normal brake operation of being independently operably displaced by an application of pressurized fluid from said first brake fluid circuit to pressurize brake fluid in, respectively, said second brake fluid circuit to operate said third brake actuator and said third brake fluid circuit to operate said fourth brake actuator; and
a primary piston disposed in said housing, said primary piston cooperating with said housing to define a primary chamber which changes volume as the primary piston moves in said housing, said primary piston defining an abutment surface which can be driven into abutment in a manual push-through mode with said first secondary piston and said second secondary piston to move said first secondary piston and said second secondary piston;
said primary chamber is in fluid communication with said pedal simulator during normal braking operation and is switched to communicate with said first and second brakes during said manual push-through operation.