Researches On Sensor Dynamic Characteristics For Automobile Engine

In order to improve the work efficiency of the engine, we need to set up the model of the engine. The sensors play a very important part in the engine operation. So we must study the dynamic characteristics of engine related sensors which are the hot film/ wire type of mass air flow sensor, the manifold absolutely pressure sensor and the exhaust gas oxygen sensor.The hot film/ wire type of mass air flow sensor has the nonlinear dynamic characteristics. In order to describe the sensor characteristics the Hammerstein model is adopted, which is based on the multi-amplitude step responses, and the two-step identifying method is utilized in this thesis. Through the dynamic calibration experiments, the step input and output signals with different amplitudes are obtained. Using the amplitudes of these data, the nonlinear static coefficients are determined by the least square method. Moreover, based on input data and nonlinear static coefficient, the output of nonlinear static subsystem is calculated. Furthermore, according to output data, the transfer function of linear dynamic subsystem is identified by the linear regression method. The sensor nonlinear dynamic models in the block format are established. The modeling results show that the nonlinear dynamic models are more accurate than the linear dynamic models to describe the sensor characteristics.As the manifold absolutely pressure sensor possessed the linear dynamic characteristics, the model coefficients are determined by the least square method directly.The nonlinear dynamic characteristics also exist in the exhaust gas oxygen sensor. We only have got the negative step response under one test condition because there are limitations in the experimental equipment. Though analyzing the output data, we have got the sensor rise time and other parameters, which lays the foundation for the further work.