An Investigation Of Transmission Gear Rattle Under Idle Condition

In recent years, the automobile enterprises are more and more concerned about abnormal noise, especially gear rattle noise, of manual transmission. Unlike automatic transmissions, manual transmissions do not have the high viscous damping inherent in a hydro-dynamic torque converter to suppress the impacting of gear teeth oscillating through their gear backlash. On idle condition, the engine noise is too weak to cover the rattle noise. So the rattle noise is very noticeable.This paper investigates rattle noise on ide condition, including validating the feasibility that utilizing finite element method to investigate gear rattle, investigating the influence that some parameters have on gear rattle, analyzing the gear rattle phenomenon occurred on a practical transmission finite element model and decreasing its gear rattle noise through increasing drag torque. The main contents can be summed up as follows:①The finite element model of a pair of gears is built and computed under constant rotational velocity to testify the dynamics and kinetics validity of the finite element method.②The gear rattle is describedand analyzed on fluctuate rotational speed which testifies the feasibility that utilizing finite element model to investigate gear rattle and lays a base for the following research.③ The input shaft rotational parameters and transmission parameters are investigated under the sine wave exciter to see their influence on gear rattle. The following conclusions are made: with the increase of mean rotational velocity, the amplitude and the backlash, the gear rattle become worse and worse. Whereas the increase of drag torque and moment of inertia can decrease the gear rattle lever.④A transmission finite element model based on a manual transmission parameter is built and computed whose result shows the radical gear rattle occurs on the fifth and the sixth gear.⑤The transmission overall rattle indices is decreased from 18.115 to 13.048 through reducing the clearance between unloaded gear and second shaft which increases the corresponding drag torque.