A hydraulic hybrid powertrain system includes a power plant generating a
high pressure fluid at an output, at least one drive motor responsive to
the high pressure fluid for generating rotary motion at an output, and a
mode selection device connected to the power plant output and the drive
motor for selecting a mode of operation from a plurality of drive motor
modes of operation including at least two of a drive mode, a neutral
mode, a reverse mode and a park mode. The system includes a control
device connected to the power plant and the drive motor for controlling
operation of the drive motor in the plurality of modes of operation, a
selectively actuated brake device for interrupting high pressure fluid
flow to the drive motor, and a check valve bridge circuit for connecting
the drive motor to a low pressure fluid source when the brake device is
actuated.