Abstract: A method for operating a hybrid powertrain system includes monitoring operation of the torque machine, and limiting the motor torque output from the torque machine to a maximum allowable motor torque that is associated with an acceptable audible noise level when the motor speed of the torque machine is within a motor speed range associated with objectionable audible noise.

Abstract: A hybrid powertrain system includes an internal combustion engine and a torque machine wherein electrical energy is controllably transferred between an electric energy storage device and the torque machine by a control system. A method for controlling the hybrid powertrain system includes monitoring a voltage, a current, and a power output of the electric energy storage device. A battery power control scheme is executed to control the output power of the electric energy storage device associated with the electrical energy transferred between the electric energy storage device and the torque machine. The battery power control scheme is disabled when the control system loses a power limit authority associated with the electrical energy transferred between the electric storage device and the torque machine during ongoing operation. The battery power control scheme is re-enabled when the control system regains the power limit authority.