Coupled Mechanism of the SelfExcited Torsional Vibration in Vehicle Powertrain

The phase difference and the power spectrum of vertical vibration to powertrain torsional vibration in the whole experiments were studied at first. Coupled mechanism analysis of the selfexcited vibration were presented. The results indicated that the main cause of the selfexcited vibration was the coupled negative damping characteristics of vertical vibration in the whole experiments. The simplified model of vehicle powertrain was established and the relationship of adhesion force and wheel angular velocity and vertical vibration was built.The condition causing the selfexcited vibration was found.Theoretical analysis coincided with experimental result. When the average slip was smaller than the critical slip at 25 ％～30　%,the phase difference of vertical vibration and torsional vibration were changeful with time.The system was not the selfexcited vibration because vertical vibration could not input a continuous energy to powertrain. When the average slip was larger than the critical slip,the phase difference of vertical vibration and torsional vibration was a constant at -90°～-180°. A continuous vertical vibration energy was input to powertrain and was named coupled feedback energy. Negative damping characteristics of adhesion friction coefficient caused negative feedback energy. When coupled feedback and negative feedback energy were adequate to vibration energy consumed by system, it was the selfexcited vibration of the powertrain.The frequency of the selfexcited vibration was 9～10 Hz.The tests covered the range of slip from 5.5 %～47 % and used tires 6.5～16 at 0.32MPa (BJ212).The experiment data were mathematically analysed by CF355 Portable Dual Channel FFT Analyzer and by computer program. Many experiments indicated that the selfexcited vibration of the powertrain generally occurs when the driving force reaches the maximum adhesion force and the adhesion coefficient decreases with the increase of the slip.　The selfexcited torsional vibration in wheeled vehicle powertrain at high slip damaged vehicle performance such as mobility,tractive performance and ride performance.In addition, the selfexcited vibration shortened the lifespan of vehicle transmission parts.