Brake-by-wire module including pressure balanced PSU piston with wetted ball screw and backup pump assembly

An electro-hydraulic brake system for actuating wheel brakes of a vehicle, comprising:

• a master cylinder (MC) fluidly coupled to a first MC fluid passageway and configured to supply fluid into the first MC fluid passageway in response to pressing force on a brake pedal coupled thereto;
• the first MC fluid passageway directly coupled to a pedal feel emulator (PFE) including a PFE piston movable through a PFE bore and separating an upper chamber from a lower chamber for providing pressure opposing a pressing force on the brake pedal;
• a pressure supply unit (PSU) assembly including a PSU motor coupled to a ball screw actuator, a PSU housing defining a piston bore having a terminal end opposite the PSU motor, and a PSU piston disposed within the piston bore and movable by the ball screw actuator through the piston bore and dividing the piston bore into a first chamber and a second chamber, with each of the first chamber and the second chamber containing a hydraulic fluid;
• a backup pump assembly including a backup pump motor operably coupled to a pump to convey brake fluid for supplying the brake fluid to at least one of the wheel brakes;
• and
• wherein the ball screw actuator includes an actuator nut assembly having a plurality of ball bearings each disposed within the piston bore and submerged in the hydraulic fluid,
• wherein the electro-hydraulic brake system further comprises:
• a PSU fluid passageway configured to transmit fluid from the PSU assembly to at least one wheel brake;
• a control valve manifold including at least one of an apply valve and a release valve for controlling fluid flow between the PSU fluid passageway and the at least one wheel brake;
• and
• a bi-directional check valve disposed between the PSU fluid passageway and the control valve manifold and configured to allow fluid flow in either of two opposite directions therebetween only when a differential pressure thereacross is above a predetermined amount.