Tandem power transmission unit and brake systems using same

A tandem power transmission unit, comprising:

• a ball screw;
• a ball nut having an opening into which the ball screw extends, the ball nut being selectively driven by the ball screw for longitudinal motion relative thereto;
• a primary piston operatively coupled to the ball nut;
• a secondary piston operatively coupled to the primary piston;
• a block housing at least partially enclosing the primary piston, the secondary piston, and the ball screw;
• a primary chamber at least partially defined by the block housing and a face of the primary piston, the primary chamber being configured to contain hydraulic fluid and selectively pressurized by reciprocal motion of the primary piston with respect to the block housing driven directly by longitudinal motion of the ball nut relative to the block housing;
• a secondary chamber at least partially defined by the block housing and a face of the secondary piston, a backside of the secondary piston at least partially defining the primary chamber, the secondary chamber being configured to contain hydraulic fluid and selectively pressurized by reciprocal motion of the secondary piston with respect to the block housing driven indirectly by longitudinal motion of the ball nut relative to the block housing;
• a first output channel selectively placing the primary chamber in fluid communication with at least one component of a brake system for provision of pressurized hydraulic fluid thereto;
• a second output channel selectively placing the secondary chamber in fluid communication with at least one component of a brake system for provision of pressurized hydraulic fluid thereto;
• an electric motor for selectively driving the ball screw to move the ball nut longitudinally relative to the block housing and responsively reciprocate at least one of the primary and secondary pistons within a corresponding primary or secondary chamber;
• and
• a motor housing at least partially enclosing the ball nut and the electric motor.