Surge suppression control for a motor vehicle drivetrain

This invention relates to the control of a motor vehicle drivetrain including an electrical machine, and more particularly to a control of the electrical machine for suppressing drivetrain oscillations referred to as surge. An improved surge suppression control for a motor vehicle drivetrain detects and suppresses drivetrain oscillation in a predetermined range of frequencies centered on an estimate of the natural frequency of the drivetrain. The drivetrain natural frequency is determined based on the current speed ratio of the vehicle transmission and empirically determined vehicle characteristics, and is used to define the center frequency of a band-pass filter responsive to engine speed. The filter output represents the AC component of the engine speed in a range of frequencies centered on the driveline natural frequency, and such component is differentiated to form an acceleration component in phase synchronism with the torque causing the detected resonance. An electric machine mechanically coupled to the engine is energized in accordance with the inverse of the acceleration component to actively cancel the detected resonance whenever the acceleration component exceeds a noise threshold that also is adjusted based on the estimated natural frequency of the drivetrain.