Positioning the crank shaft for quick and effective start of a single cylinder SI engine for hybrid applications

Abstract

Using hybrid electric drives instead of conventional automotive powertrains is an effective way to reduce fossil fuel consumption and CO₂ emissions. In hybrid drives frequent starting and stopping of the engine is encountered. If the torque needed to start the engine is derived from the drive train it could result in wheel force fluctuations particularly in low power applications. In this work, the starting process in a single cylinder SI engine was analyzed and optimized for reduced torque requirement and cranking time. Engine motoring experiments were conducted to determine the cylinder pressure and crank torque variations on the crank angle (CA) basis. These were then used to build, tune and validate simulation models. Engine starting simulations with different start crank positions were carried out to determine the range of start CAs where the average torque requirement is low. Later, engine shut down simulations were conducted to determine the throttle positions which will result in the engine being stopped at the desired start CA range. As the next step, experiments were conducted by shutting down the engine and it was demonstrated that throttle position control is effective in stopping the engine at the optimal CA. Finally starting experiments were done with controlled and uncontrolled shut down operations. It was validated that with controlled shut down, the engine starting time could be reduced by as much as 32%. Thus throttle controlled stopping of a single cylinder engine will help reduce the starting time and also lower the torque requirement from the drive line motor. This will reduce the jerk in low power parallel hybrid vehicles where the powertrain motor is used to start the engine through clutch actuation.