Experimental Research And Improvement On Acceleration Abnormal Sound Of A Passenger Vehicle Caused By Torsional Vibration Of Crankshaft

As the power source of the vehicle,the engine is also the main vibration source,and its NVH problem will have an important impact on the performance of the vehicle NVH.In this paper,taken a self-developed passenger vehicle acceleration abnormal sound(hereinafter referred to as"gulu"noise)problem as a case,by means of experiments the problem is investigated and analyzed,the source of"gulu"noise is identified as related to the torsional vibration of crankshaft.The crankshaft torsional vibration of the self-developed vehicle was optimized by referring to the test results of the benchmarking vehicle.Combined with the project cycle,the rotational inertia and vibration reduction frequency of the crankshaft pulley are verified respectively.Finally,the optimization scheme is settled to eliminate the acceleration"gulu"noise.First,by subjectively evaluating,testing,and filtering analysis of the problem,the condition and frequency range are determined.The results showed that the problem can be identified in D gear,neutral pedal,3wot,and steady-state conditions.The sound frequency is in the 400±50hz range.Through breaking the path,it is confirmed that there are both air sound and structure sound in the propagation of"gulu"noise.Through the vibration test on the powertrain,it is found that the"gulu"noise is closely related to the front end of the powertrain.By disconnecting the engine belt and removing the crankshaft pulley,the correlation between acceleration"gulu"noise and crankshaft torsional vibration is determined.Secondly,the crankshaft torsional vibration test was carried out on the whole vehicle,and the results showed that the center frequency of the first order torsional vibration of the crankshaft was 400Hz,corresponding to the frequency band of"gulu"noise of acceleration in the vehicle.The crankshaft torsional vibration test is carried out by the same method on the benchmarking vehicle,and the order analysis is compared.The results showed that the order vibration of the self-developed vehicle is obviously higher than that of the benchmarking vehicle,and the peak value of the six order is 2.8 times of that of the benchmarking vehicle.The peak value of the eighth order is 5.9 times and the 10th peak is 7.3 times that of the benchmarking vehicle.The optimization direction of reducing torsional vibration of crankshaft is defined.Finally,the crankshaft pulley was optimized,and the rotational inertia and vibration reduction frequency of the crankshaft pulley were adjusted respectively.The results showed that when the moment of inertia of the crankshaft pulley is 0.00848 kg·m~2and the operating frequency is 252Hz,the first order torsional vibration of the crankshaft decreases from 400Hz to 280Hz,and the corresponding amplitude of the 6th,8th and 10th order all reach the level of the benchmarking vehicle.The"gulu"noise is apparently eliminated.Due to the existence of10%production error of the rubber layer of the crankshaft pulley,the minimum production frequency of crankshaft pulley was finally set at 227Hz for mass production.By reviewing the troubleshooting and optimization process of this problem,we summarized a set of methods for troubleshooting the abnormal sound problem of powertrain on the whole vehicle,and extracted the torsional vibration performance parameters of crankshaft of the whole vehicle engine,which can provide reference for the performance development of subsequent engine NVH.