Modelisation of the engine coolant warming-up behavior

Abstract

This master thesis report describes the development of a physically based model which can predict the coolant temperature of an internal combustion engine during its warm-up phase. The model is used to detect if the thermostat in the cooling system is functioning correctly which is a requirement for present day On-Board Diagnostics II (OBD II). The model uses information available within the Engine Control Unit (ECU) and needs little calibration work. Thereby, the model can easily be extended with extra features to remain applicable with future power train applications. The temperature prediction capability has been tested for steady state conditions as well as for ”real-world” driving and regulated driving cycles, thereby the model has been tested on a vehicle with a start-stop system. The model includes a diagnostic function which is performed at the most accurate prediction of the model. The sensitivity of the temperature prediction to sensor input errors and varying parameters (like fuel quality) has been investigated in a sensitivity study. Finally, a threshold value is proposed for the diagnostic function by determining when an invalid faulty thermostat is detected or a faulty thermostat is not detected.