Design Of Dynamic Characteristics Test Bench For Oxygen Sensors

Nowadays the environmental pollution is a growing problem for the rapid growth of the automotive industry, and that leads to a stricter environmental protection law of the government. As a key product of the exhaust gas emission control system, a closed-loop control implemented by ECU with a feedback signal from the oxygen sensor to keep the delivered air-fuel ratio within a range close to ideal air-fuel ratio. The presented test bench aims to verify the quality of the oxygen sensor, and helps the company to improve the product quality.The bench is developed based on the switch-type potentiometric oxygen sensor. Firstly the working principle and the output characteristics of the oxygen sensor are introduced, and several test schemes are proposed according to the enterprise demand. Then a proper test bench scheme is required, which is developed on the foundation of a motorcycle engine in this paper. The test bench is made up of an engine, an exhaust system, an oxygen loading platform and host computer. Next is choosing a control board for several core controls including injection control, speed control, CAN communication, etc. The bench test starts from sending commands from host computer to the ECU. Then ECU processes a closed-loop control by acquiring signals from universal exhaust gas oxygen sensor, and makes sure that the actual fuel-to-air can well track the desired fuel-to-air. In the meanwhile, the data logging system collects the data from the switch-type oxygen sensor, and analyses the data to estimate the quality of the oxygen sensor.The key point in this paper is the air-fuel ratio control. Considering that there are two air-fuel ratio methods with different periods, a PID control method with lookup-table and an oil film dynamic compensator are presented respectively. With the help of Matlab/Simulink software, the corresponding Simulink models are built and simulated to verify the feasibility. Once verified, the models can be transferred to codes by using auto code generation in Simulink.During the bench test, the calibrations of PID coefficients and compensator coefficients are implemented, and several test examples are demonstrated to demonstrate the quality of the oxygen sensor. Apart from experiment implementation, the test bench has capacity of data logging and storage, data analysis and report printing, assisting the company to improve and develop its products.