Brake systems with motor-driven master cylinders and low pressure accumulators

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 brake module 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 brake module including an electric PTU motor configured to selectively pressurize 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;
• a low pressure accumulator interposed hydraulically between the first and second pairs of wheel brakes, the low pressure accumulator being in indirect fluid communication with the reservoir via the first and second MC outputs and the master cylinder;
• and
• an electronic control unit for controlling at least one of the secondary brake module and the master cylinder responsive to at least one brake pressure signal;
• wherein the low pressure accumulator at least partially provides slip control to the first and second pairs of wheel brakes in coordination with the secondary brake module when the brake system is in the normal non-failure braking mode.