A Study of Mechanism of Engine Idling Rattle Noise in Hybrid Transaxles

Quietness is one of the most important characteristics for Hybrid Electric Vehicle quality. Reduction of the rattle noise caused by the torque fluctuation of an internal combustion engine can contribute to get a customer satisfaction. Toyota Hybrid System(THS) also has same requirement. Especially, the rattle noise during idling may happen discontinuously despite of periodical engine combustion excitation. It is necessary to study the mechanism and reduce the rattle noise. At lower engine torque range, decreasing the torsional damper’s stiffness can improve this condition as the manual transaxle done. However, the rattle noise can occur easily in conditions of relatively large torque spike inputs to the torsional system, such as the engine start/stop function of THS using the motor/generator in the transaxle. It is necessary to analyze the dynamics of all related components in lower engine torque range and need to find the new technique satisfying in both the idling and engine start/stop condition. This paper presents one method to clarify the mechanism of rattle noise occurring during engine idling through the measurement of shafts torque, gear speed and gear mesh backlash within a transaxle. The results of the study contributed to the reduction of transaxle rattle noise, positively affecting customer satisfaction.