Study on Engine Start Vibration Index in a Hybrid Powertrain Using Torque Sensor and Cylinder Pressure Sensor

This paper presents an investigation of drivability issue of engine start-stop. Hybrid vehicles provide excellent benefits regarding fuel efficiency and emission. However, vibration results from constant engine start and stop events generate drivability issues, thus compromising driving comfort. This paper has designed a high speed torque sensor to capture instantaneous torque at the engine shaft. Its consequences help to find out the most suitable index of vibration severity. This paper is organized in four sections. The first section introduces the powertrain to be studied. The second section introduces development of a specially designed torque sensor. The torque sensor is installed between the engine and ISG (Integrated Starter Generator), alongside with an encoder. The torque sensor is utilized to collect the instantaneous shaft torque on occasion of engine start. In the third section, this paper has performed two experiments. Firstly, a typical engine start process (from 0 to 650 rpm) is studied. Instantaneous shaft torque, encoder signal and cylinder pressure signals are gathered and synchronized. Cranking phase and initial combustion phase is observed. It is concluded that torque generated from cylinder pumping air is the main contributor to the engine torque ripple, which is the main cause of vibration. Use that, three vibration index candidates are bought out, and square of angular acceleration is chosen. Then, this paper performed another experiment with an engine working at 1000 rpm and 100 Nm to examine the performance of vibration index. The results show the effectiveness of vibration index.