Profile Correction

The profile correction software learns the crankshaft tooth spacing under defueled engine conditions. The profile correction requires the engine to be shut down either at key off, or during normal vehicle operation, after the keep alive memory (KAM) reset. The learned corrections improve the high RPM capability of the monitor. The misfire monitor is not active until a profile is learned. The profile correction software learns and corrects for mechanical inaccuracies in the crankshaft position wheel tooth spacing. Since the sum of all the angles between the crankshaft teeth must equal 360 degrees, a correction factor can be calculated for each misfire sample interval that makes all the angles between individual teeth equal. To prevent any fueling or combustion differences from affecting the correction factors, learning is done during engine shutdown. In order to minimize learning time for profile correction factors, the correction factors are learned after an engine shutdown is commanded and fuel is disabled while the generator motor spins the engine. In order to protect the traction battery, and provide vehicle starting, the following conditions must be met to extend the shutdown: traction battery temperature and state of charge must be within operational limits. This condition occurs either when the key is turned to the OFF position (typically 1 key off induced engine shutdown), or when the normal operating strategy shuts the engine down (typically multiple shutdown events during normal operation). During this shutdown, the generator motor spins the engine at approximately 1,100 RPM, while delta time intervals are captured for computation of the correction factors. Average profile correction factors are calculated for each of the 4 combustion intervals over approximately 15 engine cycles. This procedure occurs once per KAM reset during the life of the vehicle. Since inaccuracies in the wheel tooth spacing can produce a false indication of misfire, the misfire monitor is not active until the corrections are learned. In the event of the 12 volt battery disconnection or loss of KAM the correction factors are lost and must be relearned. The software may be unable to learn a profile if the instantaneous profile calculations vary by more than a specified tolerance from the mean values. In this case a DTC P0315 is set. Typical profile correction learning entry conditions are: engine in fuel disabled mode for 4 engine cycles, engine speed between 800 and 1,750 RPM, maximum RPM change during profile correction is 600 RPM, vehicle speed between 0 and 48 km/h (0 and 30 mph), the traction battery voltage above 216 volts, the traction battery temperature above -15°C (5°F), and the traction battery power discharge limit above 12 kW.