1.11.2 Limitation of advance of retarded ignition angle during catalyst heating
The ECM uses a control approach which is based on a torque structure. This torque structure converts the torque demand of the driver (accelerator pedal input) into an air charge based torque and an ignition based torque. So, all requests for air charge or ignition angle are coordinated and commanded using this torque structure.
During the catalyst heating phase, the ignition angle is retarded through a parameter described as ignition based torque reserve. In return, as compensation, the air charge based torque is increased to reach the desired overall torque.
Instead of monitoring the ignition angle the ignition based torque reserve is limited to a necessary minimum which assures that a minimum level of retarded ignition angle is maintained. This minimum is calibrated such that the exhaust emission does not exceed 100% of the emission standard.