Hybrid powertrain smoothness improvement

The origin of several technologies in automobile industry is from the fact that they have to meet contradicting requirements - high Fuel Economy (FE) for customer satisfaction along with significant emission reduction as our goal. One of the solutions for such challenging problem to deliver high fuel economy, low emission and long range requirement is the hybrid vehicle technology. The hybrid powertrain consists of two power sources - an electric motor and an engine. The hybrid vehicle starts with electric mode and changes to engine operation at a predetermined speed. This helps to achieve best fuel economy and low exhaust emissions in city driving conditions. The electric mode operation is very smooth and it does not have exhaust noise and engine induced vibration at tactile points due to absence of reciprocating parts. However during the changeover from electric mode to engine mode, a step increase in vibration and noise associated with a jerk feel were observed. Achieving the smoothness in all operating conditions is essential to get joy of riding and meet customer requirement. The tools and techniques used to solve the noise and vibration problems in a hybrid powertrain are explained in this paper. The vibration levels at the tactile points were measured using accelerometers in a representative customer usage cycle. The near field noise measurements were done at various engine operating conditions - idling, constant speed and acceleration - using microphones. Using design tools, the critical part parameters were fine-tuned to improve smoothness.