Hydraulic brake booster

#This invention relates to a hydraulic brake booster wherein a hydraulic input signal derived from a manual input force applied by an operator to a brake pedal is communicated to activate a control valve to supply regulated pressurized fluid to a power piston and develop operational pressurized fluid to effect a brake application as a function of the input force.

#The present invention is of a type hydraulic brake boosters referred to as a “full-power” brake booster, of which the following U.S. Patents may be are considered to be typical: U.S. Pat. No. 4,441,319; 4,490,977; 4,514,981; 4,665,701; 4,685,297; 4,704,867; 4,724,674; 5,526,731 and 5,927,074. In such brake boosters, an accumulator is charged with fluid pressure and selective activated through movement of a control valve by an input member to present pressurized fluid to an actuation chamber that acts on an actuation piston. The actuation piston in turn provides a force for moving pistons of a master cylinder to pressurize operational fluid that is presented to wheel brakes to effect a brake application. The operational pressure that is developed is proportional to the force applied to the actuation piston and inversely proportional to the cross-sectional area of the piston in the master cylinder for a given force applied to an input member by an operator to move the control valve. The resulting travel of the input member and brake pedal is proportional to the travel of the actuation piston in the master cylinder. This type of hydraulic brake booster functions in a satisfactory manner, however during a manual application, the input force applied to move the pistons in the master cylinder is communicated through control and as a result some lost travel is experienced in the development operational pressure to effect a brake application. A reduction in the loss travel can be achieved by the structure disclosed in co-pending patent U.S. patent application Ser. No. 10/061,648 filed Jan. 31, 2002, however, such structure while functioning in a desired manner is very compact.

#In the present invention a hydraulic brake booster has a housing with a piston arrangement located in a power bore that is connected to a control valve located in a separate control bore such that an input force applied to the piston arrangement is hydraulically communicated to activated the control valve to communicate regulated pressurized supply fluid to the power bore that acts on the piston arrangement to develop pressurized operational fluid in effecting a brake application.

#FIG. 1 is schematic illustration of a brake system including a hydraulic brake booster according to the teachings of the present invention;

#FIG. 2 is a sectional view of the hydraulic brake booster of FIG. 1 in a position of rest;

#FIG. 3 is a sectional view of the hydraulic brake booster of FIG. 1 in an actuated position;

#The brake system 10 as shown in FIG. 1 includes a hydraulic brake booster 12 connected by a first conduit 16 to a first set of wheel brakes 14,14′ and by a second conduit 20 to a second set of wheel brakes 18,18′. The hydraulic brake booster 12 receives pressurized supply fluid from a source that may include an accumulator 22 and a motor pump 24. Each wheel in the first set of wheel brakes 14,14′ and the second set of wheel brakes 18,18′ includes a build solenoid valve 15, a decay solenoid valve 15′ and a wheel speed sensor 17 to provide the electronic control unit (ECU) 40 with an input signals relating to a current functional operational of the vehicle. In addition to these input signals, the ECU 40 also receives and evaluates other inputs and data relating to the operation of the vehicle including but not limited to: the operation of the motor pump; the pressure of the pressurized supply fluid; dynamic forces experienced by the vehicle; accumulator fluid supply pressure, the level of fluid in a reservoir and etc. all inputs which relate to the operation of the vehicle and may effect a brake application. The hydraulic brake booster 12 is designed to be selectively activated by either a manual force applied by an operator to brake pedal 28 to effect a first brake application or by a hydraulic force derived from an input signal developed by ECU 40 in response to sensed conditions experienced with respect to the operation of the vehicle to effect a second brake application.

#In more particular detail, the hydraulic brake booster 12 has a housing 42 that is defined by a stepped bore 44 that is separated from a control bore 46, a first outlet port 50 that connects the stepped bore 44 with conduit 16, a second outlet port 52 that connects the control bore 46 with conduit 20, an inlet port 54 connected by conduit 25 to accumulator 22, compensation ports 58,58′ that connect the stepped bore 44 with reservoir 13, a control passage 60 that connects the stepped bore 44 with the control bore 46 and a supply passage 62 that connects the control bore 46 with the stepped bore 44. The stepped bore 44 retains a piston arrangement 100 while the control bore 46 retains a control valve 48 for controlling the communication of pressurized supply fluid from accumulator 24.

#The piston arrangement 100 has a cylindrical member 102 with a first peripheral surface 104 concentrically located in the stepped bore 44 to define an output chamber 106, a relief chamber 108 and a power chamber 110 within the housing 42. The cylindrical member 102 has a first end 112 that is located in the output chamber 106 and a second end 114 that is located in the power chamber 110 and a stepped bore 116 that extends from the first end 112 to the second end 114. The cylindrical member 102 has a first radial passage 118 that connects a groove 120 with the stepped bore 116 and a second radial passage 122 that connects the stepped bore 116 with relief chamber 108. The stepped bore 116 is designed to receive a reaction piston 124 having a peripheral surface 126 thereon that is concentrically located in stepped bore 116.