1.11 Cold Start Emission Reduction Strategy Monitoring

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

e.g. MSD80-N54

Fig 1: Engine Coolant Temperature Versus Time Graph

Courtesy of BMW OF NORTH AMERICA, INC.

To fulfill the legal requirements, the idle speed monitoring has been extended to the cold start phase. When an error occurs, the specific DTCs:

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

are set.

During catalyst heating, it is essential to ensure that enough thermal energy is applied to the catalyst in order to heat it up as quickly as possible.

Therefore, the target is to limit the ignition timing to the earliest possible value during the catalyst heating phase.

When there is a demand for more torque and therefore for advanced ignition timing beyond the limits, the engine is allowed to stall instead of fulfilling the demand.

The torque limits are calibrated this way so that the emissions stay below the threshold value of 1.5 times the limits.

Fig 2: Standard Monitoring Function During Catalyst Heating Chart

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 catalyst heating phase, the catalyst 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 limiting the torque reserve to a minimum value during the catalyst heating phase. In order to accomplish this, the required minimum catalyst heating torque is subtracted from the reference air mass torque. The reduced efficiency then leads to a safe ignition retard and limits the ignition timing during the catalyst heating measures.

The ignition timing is limited to the earliest possible ignition time during the catalyst heating phase by limiting the torque reserve to the minimum required torque reserve:

Fig 3: Air Mass Torque Control During Catalyst Heating Illustration

Courtesy of BMW OF NORTH AMERICA, INC.

Maximum Ignition Timing after Cold Start with new BMW Method:

Fig 4: Torque Characteristic Line And Ignition Timing Diagram

Courtesy of BMW OF NORTH AMERICA, INC.