Abstract
In today´s automotive field of diagnosis of Electronic actuators used in the area of Engine Control is of great importance. It is possible now to conduct limited diagnostics with an on board Electronic Controller by performing checks of different parameter of an Engine. Engine output parameters like torque and speed depends on input to the engine viz Fuel quantity, Spark and Air Quantity. For diagnosis of engine, the variations of input variables have to be monitored. The input variables may differ because of improper operations of actuator.
Diagnosis of actuators is evolved in a period of time from threshold value check diagnosis to model based diagnosis. This paper focused on model-based diagnosis of ignition system. Algorithms are discussed with test results for predicting the reasons for the improper behaviour of the Spark Plugs for small petrol engines.
The main function of spark plug is to generate right amount spark energy at right time with the help of Electronic Control Unit. Variation from the right amount of spark energy leads to partial misfire and finally to more emissions. So monitoring spark energy is very much important to reduce emissions and to achieve desired performance . In the same way generating spark at wrong timing also leads to emissions as well as poor performance of the engine .So it becomes important to keep a check on spark timing also.
In the initial phase of the work improper working of spark plug is diagnosed by monitoring the variation in Crank Shaft speed. This input is fed to the discrete event based engine model. This model gives the trace of gas pressure variation with respect to crank angle. These traces are compared with the gas pressure data to give information about abnormal pressure variation, which may be resulted, by the partial misfire or a complete misfire. The limitation of the approach lies in certain assumptions like Torsionally rigid crankshaft, Constant load torque and Constant coefficient driveline model made in developing the algorithms.
For monitoring spark energy, primary coil current & voltage of primary is monitored periodically. Here a Hall effect current sensor has been connected to the primary side of the HT coil. Instanious primary current is monitored and converted to spark energy with the help of Primary Voltage value. As a part of this work Spark plug gap is also predicted though experimental way. Analysis has been done using a actual recorded engine crank signal and two wheeler Single cylinder Engine and results are discussed in the paper. The results indicate that both misfire and fault monitoring of ignition system components is possible with the above mentioned algorithm and can be incorporated in a potential controller application.
Keywords:Discrete Event Model, Spark Energy, HT Coil, Primary Winding Voltage, Design of Experiment.