Method and apparatus for vibration damping in a powertrain system

A method for controlling an electric machine disposed to generate torque in a powertrain system, wherein the powertrain system includes the electric machine rotatably coupled to a crankshaft of an internal combustion engine that is coupled via a torque converter to a transmission, and wherein an output member of the transmission is coupled to an axle of a driveline, the method comprising:

• monitoring a rotational position of the electric machine;
• periodically determining, at a first periodic rate, a speed of the electric machine based upon the rotational position of the electric machine, a time-based change in the motor speed, and an acceleration rate based upon the change in the motor speed;
• periodically determining, at a second periodic rate, a virtual inertia term based upon the acceleration rate and a torque compensation term based upon the virtual inertia term and the acceleration rate;
• and
• controlling the electric machine to generate torque based upon the torque compensation term.

A powertrain system, comprising:

• an electric machine rotatably coupled to a crankshaft of an internal combustion engine, and a controller;
• the controller operatively connected to the internal combustion engine and the electric machine, the controller including an instruction set, the instruction set executable to:
• monitor, via a position sensor, a rotational position of the electric machine;
• periodically execute a speed observer to determine a rotational speed of the electric machine based upon the monitored rotational position of the electric machine;
• periodically execute an acceleration observer to determine an acceleration rate, wherein the acceleration rate is determined based upon a time-based change in the rotational speed of the electric machine;
• determine a virtual inertia term based upon the acceleration rate;
• determine a torque compensation term based upon the virtual inertia term and the acceleration rate;
• and
• control the electric machine to generate torque based upon the torque compensation term.