Brake systems with motor-driven master cylinders and electric secondary power transmission units

A brake system for actuating a plurality of wheel brakes comprising first and second pairs of wheel brakes, the system comprising:

• a reservoir;
• a motor-driven master cylinder operable during a normal non-failure braking mode by actuation of an electric motor of the master cylinder to generate brake actuating pressure at first and second MC outputs for hydraulically actuating the first and second pairs of wheel brakes, respectively;
• a secondary power transmission unit configured for selectively providing pressurized hydraulic fluid at first and second PTU outputs for actuating the first and second pairs of wheel brakes in at least one of a normal non-failure braking mode and a backup braking mode, the secondary power transmission unit including an electric PTU motor configured to selectively pressurizing the hydraulic fluid by transmitting rotary motion to at least two pump pistons, each pump piston providing pressurized hydraulic fluid to a corresponding one of the first and second PTU outputs, each of the first and second PTU outputs providing fluid to a corresponding one of the first and second pairs of wheel brakes;
• and
• an electronic control unit for controlling at least one of the power transmission unit and the master cylinder;
• wherein the secondary power transmission unit is indirectly fluidly connected to the reservoir to selectively draw hydraulic fluid therefrom.