BRAKE-BY-WIRE MODULE INCLUDING PRESSURE BALANCED PSU PISTON WITH WETTED BALL SCREW AND BACKUP PUMP ASSEMBLY

An electro-hydraulic brake system includes a master cylinder (MC) configured to supply fluid into a first MC fluid passageway in response to pressing force on a brake pedal; a pressure supply unit (PSU) assembly having 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 dividing the piston bore into a first chamber and a second chamber and movable by the ball screw actuator, with each of the first chamber and the second chamber containing a hydraulic fluid; and a backup pump assembly including a pump for supplying the brake fluid to at least one of the wheel brakes. 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.