Hydraulic brake booster with variable control valve for regenerative braking

A hydraulic braking system for use in a vehicle employing both hydraulic and regenerative braking, comprising:

• a brake boost pressure source having a motor driven pump and a boost pressure accumulator to provide a boost hydraulic pressure, the motor driven pump selectively actuable to maintain fluid at a pressure in the accumulator;
• a master cylinder having a reservoir inlet port and an outlet port, said cylinder responsive to vehicle operator applied brake pedal pressure to close the inlet port and provide pilot pressure at the outlet port;
• a hydraulic pedal simulator hydraulically coupled to the outlet port through a two position spool valve;
• a proportional pressure source providing a hydraulic proportional pressure proportional to regenerative braking torque;
• and
• a control valve coupled to the brake boost pressure source for providing the boost hydraulic pressure from the brake boost pressure source to a vehicle wheel brake actuator in proportion to a pressure differential between the pilot pressure and the hydraulic proportional pressure, wherein the two position spool valve is operable in a first position to hydraulically couple the master cylinder outlet port with the pedal simulator and in a second position to apply the pilot pressure from the master cylinder outlet port directly to the vehicle wheel brake actuator, the spool valve being spring biased toward the second position and assuming the first position only when the boost pressure is applied thereto.

A hydraulic braking system for use in a vehicle employing both hydraulic and regenerative braking, comprising:

• a master cylinder having an outlet port, said cylinder responsive to vehicle operator applied brake pedal pressure to provide pilot pressure at the outlet port;
• a spool valve having a first position and a second position;
• a hydraulic pedal simulator including a resiliently biased piston defining a variable volume chamber having a port in direct fluid communication with the master cylinder outlet port when the spool valve is in the first position and blocked from direct fluid communication with the master cylinder outlet port when the spool valve is in the second position;
• a proportional pressure source providing a hydraulic proportional pressure proportional to regenerative braking torque;
• and
• a control valve for providing boost hydraulic pressure from a boost pressure source to a vehicle wheel brake actuator in proportion to a pressure differential between the pilot pressure and the hydraulic proportional pressure, the control valve including an actuation piston biased toward a closed position and opening in response to an applied pressure from a pressure differential control piston to supply boost hydraulic fluid at a pressure proportional to the applied pressure from the boost pressure source to the vehicle wheel brake actuator, and the pressure differential control piston configured to control the actuation piston applying pressure and to open the actuation piston when the pilot pressure exceeds the hydraulic proportional pressure, wherein the control valve is configured such that the relationship between pilot pressure and boost hydraulic pressure is substantially linear with constant gain, the hydraulic proportional pressure translating that relationship so as to commence the supply of boost pressure at a different pilot pressure without changing the gain.