Electro-hydraulic actuator for motor vehicle brake

An electro-hydraulic actuator for a motor vehicle brake-by-wire brake system including a fluid pressure operated wheel brake comprising:

• a housing including a piston bore having a top end and a bottom end,
• a T-shaped piston including a disc-shaped piston head having top side and a bottom side and a tubular stem perpendicular to the bottom side of the disc-shaped head,
• a mounting means operative to support the disc-shaped piston head in the piston bore for linear translation with the tubular stem concurrently guided in and out of the bottom end of the piston bore so that the disc-shaped piston head divides the piston bore into a cylindrical primary chamber between the top end of the piston bore and the top side of the disc-shaped piston head and an annular secondary chamber between the bottom end of the piston bore and the bottom side of the disc-shaped piston,
• a first fluid passage means operative to connect the wheel brake to the primary chamber,
• a drive means operative to effect linear translation of the piston toward the top end of the piston bore to increase fluid pressure in the primary chamber and in the wheel brake,
• a second fluid passage means connecting the primary and secondary chambers;
• means for sensing fluid pressure in the primary chamber;
• and
• a valve in the second fluid passage opening the second fluid passage when the sensed fluid pressure in the primary chamber exceeds a transition fluid pressure in the primary chamber to expose the secondary chamber to the fluid pressure in the primary chamber and otherwise closing the second fluid passage, so that in a low pressure interval of operation of the electro-hydraulic actuator below the transition pressure the effective area of the piston is the area of the top side of the disc-shaped piston head and in an ensuing high pressure interval of operation of the electro-hydraulic actuator above the transition pressure the effective area of the piston is the area of the cross-sectional profile of the stem of the piston.