Cold Start Emission Reduction Strategy Monitoring

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2008 BMW Z4, 2008 BMW X5, 2008 BMW X3, 2008 BMW 528xi, and 2008 BMW 528i. However, it is still accessible from the selected car via links, so may be relevant.

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

e.g. MSV80-N51/N52:

STANDARD MONITORING FUNCTIONS - CAT HEATING

Relevant Components during Cat Heating Phase						Impact of faulty Component on Cat Heating Parameter
Comp./System	Parameter	needed for	Component Diagnosis	Diagnosis during Cat Heating	Emission Impact > 1,5xGW	Idle Speed	Ignition Angle	Engine Lambda	Transmission Shifting Point	Camshaft Position
Secondary Air	Secondary Air Mass	Enleanment exhaust gas	Secondary Air diagnosis	Yes	Yes, dep. to variant and emission class			X
Injection Valve	Injection time	Enleanment lambda_engine < 1 Enleanment lambda_engine > 1	Output stage diagnosis	Yes	none	x	x	x
			Misfire detection	Yes
			Fuel supply diagnosis	no
Mass Air How Sensor	Air Mass - Input for maps	Larger overlap, VANOS End position	Air mass flew sensor diagnosis	Yes	none	x	x	x
			Air mass model diagnosis	Yes
			Fuel supply diagnosis	no
Throttle Position	Angle	Mass Air Flow	Power stage, accelerator pedal diagnosis	Yes	none	x	x	x
Valvetronic	Valve Lift	Load-control	Valvetronic electrical / mechanical diagnosis	Yes	none	x	x	x
Valvetronic	Valve Lift	Load-control	Air mass model diagnosis	Yes	none	x	x	x
Phase Sensor (Camshaft)	Valve overlap	Larger overlap	RPM sensor diagnosis	Yes	none					x
Camshaft Position Actuator	Valve overlap	Larger overlap	Output stage diagnosis	Yes	none					x
Camshaft Position Actuator	Valve overlap	Larger overlap	Camshaft position actuator	Yes	none					x
RPM Sensor	Engine Speed	Idle speed increase	RPM sensor diagnosis	Yes	none	x
Idle Speed	Engine speed	EVAP, Camshaft Position	Idle speed diagnosis	Yes	none	x				x
CAN-Communication with Transmission	CAN-bus	Shirting point	Timeout CAN-message	Yes	none	x			x
Coolant temperature Sensor	Temperature	Input for maps	Electrical plausibility	Yes	Yes	x	x	x	x	x
Coolant temperature Sensor	Temperature	Input for maps	Stuck signal	no	Yes	x	x	x	x	x
ECM	Signals	Calculation	Self Check RAM, ROM, W-dog	Yes	-
Ignition	Ignition angle	Optimum retarded ignition	Misfire detection	Yes	Yes, dep. to		x

Illustration Standard monitoring functions during Cat Heating - Overview

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 quick 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 1: Control Of Air Mass Torque During Cat Heating

Courtesy of BMW OF NORTH AMERICA, INC.

Illustration Control of air mass torque during cat heating

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 2: Diagram Torque Characteristic Line And Ignition Timing

Courtesy of BMW OF NORTH AMERICA, INC.

Illustration Diagram torque characteristic line and ignition timing

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

Fig 3: Measuring Data

Courtesy of BMW OF NORTH AMERICA, INC.

Illustration Measuring Data