1.11 Cold Start Emission Reduction Strategy Monitoring

All parameters, that are relevant during the cat heating phase, are monitored by standard monitoring functions:

e.g. MSV80-N51/N52

Fig 1: Illustration Standard Monitoring Functions During Cat Heating - Overview

Courtesy of BMW OF NORTH AMERICA, INC.

To fulfill the legal requirements, the monitoring of the idle speed is now extended to the cold start phase. In case of an error, the specific DTC's:

• P1561 Cold Start Idle Air Control System RPM lower than expected
• P1562 Cold Start Idle Air Control System RPM higher than expected

are set. Look at illustration idle speed control 

During cat heating, it is essential to make sure, that enough thermal energy is applied to the catalyst to heat it up as quickly as possible.

Therefore it is target to limit the ignition timing to the earliest possible value during the cat heating phase.

If there would be a demand for more torque and therefore for an advanced ignition timing beyond the limits, the engine would be allowed to stall instead of fulfilling the demand.

The torque limits are calibrated the way that the emissions stay below 1.5 times of the limits.

Fig 2: Illustration Control Of Air Mass Torque During Cat Heating

Courtesy of BMW OF NORTH AMERICA, INC.

Known System: 

During normal driving, the ignition timing desired torque corresponds to the air mass desired torque, which determines the ignition timing. During the cat heating phase, the cat heating torque is added to the air mass desired torque, resulting in a higher reference air mass torque.

The efficiency, desired torque divided by the reference torque, determines the ignition timing.

New System (BMW-development): 

The earliest possible ignition timing is determined by the limitation of the torque reserve to a minimum value during the cat heating phase. For this, the required minimum cat heating torque is subtracted from the reference air mass torque. The thus reduced efficiency leads to a safe ignition retard and limits the ignition timing during the cat heating measures.

Limitation of ignition timing to the earliest possible ignition timing during the cat heating phase by limitation of torque reserve to the minimum required torque reserve.

Fig 3: Illustration Diagram Torque Characteristic Line And Ignition Timing

Courtesy of BMW OF NORTH AMERICA, INC.

The maximum ignition timing after cold start with new BMW method: 

Fig 4: Illustration Measuring Data

Courtesy of BMW OF NORTH AMERICA, INC.