Method for controlling regenerative and hydraulic braking

A method for controlling hydraulic braking and regenerative braking in a hybrid brake system having a master cylinder circuit filled with fluid and in fluid communication with a first wheel brake through a first anti-lock brake system (ABS) valve and in fluid communication with a second wheel brake through a second ABS valve, and having a brake actuator in direct communication with the master cylinder circuit, the method comprising:

• allowing depression of the brake actuator in response to a braking request, wherein depression of the brake actuator creates fluid pressure, beginning at a first pressure, in the master cylinder circuit;
• commanding variable regenerative braking upon depression of the brake actuator until the regenerative braking reaches a threshold level;
• and
• commanding variable hydraulic braking upon depression of the brake actuator, such that the first wheel brake reaches a first commanded wheel brake pressure and the second wheel brake reaches a second commanded wheel brake pressure, including:
• preventing transfer of fluid pressure from the master cylinder circuit through the first and second ABS valves to the first and second wheel brakes when the fluid pressure in the master cylinder circuit is between the first pressure and a second pressure;
• partially limiting transfer of fluid pressure from the master cylinder circuit through the first and second ABS valves to the first and second wheel brakes when the fluid pressure in the master cylinder circuit is between the second pressure and a third pressure;
• and
• allowing full transfer of fluid pressure from the master cylinder circuit through the first and second ABS valves to the first and second wheel brakes when the fluid pressure in the master cylinder circuit is greater than the third pressure.