Vibration Characteristics Of Steering Wheel Of Small Tractor And Its Influence On Driver’s Hand-transmitted Vibration

Tractors often drive on the uneven field ground,limited by the ground conditions and small tractor structure factors,steering wheel vibration problem is particularly prominent,large vibration not only affects the efficiency of tractor operation,but also affects the driver’s physical and mental health.On the basis of summarizing relevant researches at home and abroad,this thesis adopts the method of combining theoretical analysis and experimental research to study the natural frequency,vibration characteristics,hand-transmitted vibration and steering wheel vibration reduction of small tractor.The main research contents are as follows:(1)Modal analysis of tractor steering wheel.Taking the steering wheel of Foton Revo FT-280 tractor as the research object,three-dimensional modeling of steering wheel steering mechanism was carried out.Modal analysis was carried out based on ANSYS to obtain simulation modal parameters.B&K test system was used to extract steering wheel modal parameters.The four order natural frequencies of the front steering wheel were determined to be 19.060Hz,40.317Hz,80.219Hz and 103.572Hz respectively.By comparing the results of the test mode and the simulation mode,it was determined that the error of the simulation mode was small and could be used as a model for vibration reduction optimization.The results of the modal analysis laid a foundation for the analysis of vibration characteristics and the design of vibration reduction.(2)Experimental study on vibration characteristics of tractor steering wheel.Taking the steering wheel of Foton Revo FT-280 tractor as the research object,vibration tests of the steering wheel were carried out on asphalt road,sandy soil road and stubble field,respectively.The vibration characteristics of the steering wheel under different working conditions were characterized by power spectral density curve,peak value of power spectral density,peak frequency and root mean square value of power spectral density,etc.The results show that the z-axis power spectral density peak value of tractor steering wheel is the largest,and the root mean square value of power spectral density z-axis is0.67-2.15 times of Y-axis,and Y-axis is 2.13-10.28 times of X-axis,indicating that the vibration intensity of steering wheel z-axis,namely the vertical direction,is the largest.With the increase of speed,the vibration intensity of the steering wheel decreases.The vibration intensity of the steering wheel on the asphalt road was decreased,while the vibration intensity of the steering wheel on the stubble field was increased obviously.The vibration intensity of steering wheel in tool operation is weakened.The root-mean-square difference of the maximum power spectral density of the first,second and third gear steering wheels is 6.545(m/s2)~2/Hz,2.949(m/s2)~2/Hz and 0.459(m/s2)~2/Hz2,respectively.The vibration intensity of the third gear tractor steering wheel tends to be stable,and the root-mean-square value of the power spectral density is 3.50(m/s2)~2/Hz.The steering wheel vibration sources with and without the steering wheel,the steering wheel with and without the steering wheel were sorted by the normal coherence sequence.Based on the normal coherence sequence,the steering wheel vibration contribution was analyzed by the partial coherence analysis,and the partial coherence coefficients of the front axle,engine and transmission were extracted at the frequency corresponding to the steering wheel power spectral density peak.The results show that the engine partial coherence coefficients are the largest under the three working conditions.The results show that the engine is the most important factor in steering wheel vibration.By further comparing the engine’s partial coherence coefficient,it is found that the steering wheel’s natural frequency corresponds to the maximum partial coherence coefficient,which is 0.563 at39.062Hz and 0.598 at 83.008Hz respectively.The results show that the engine excitation is close to the natural frequency of the steering wheel is the main cause of steering wheel vibration.(3)Evaluation of hand-transmitted vibration of tractor steering wheel.Based on GB/T 14790.1-2009"Standard for Measurement and Evaluation of human Exposure to hand-transmitted Vibration in Mechanical Vibration",hand-transmitted vibration of tractor steering wheel was measured and evaluated.The results showed that the daily vibration exposure of the tractor was 8.964m/s2for the left hand and 9.120m/s2for the right hand,exceeding the EU regulations:The 8h exposure limit of the operator’s arm vibration is 5m/s2,which leads to a high probability of arm vibration disease.(4)Optimization of vibration reduction of tractor steering wheel.Considering that the engine excitation frequency is close to the natural frequency of the steering wheel,which causes the steering wheel resonance,the steering wheel is optimized by changing the steering wheel skeleton structure.After optimization,the first four order natural frequencies of the steering wheel are 17.113Hz,37.461Hz,71.495Hz and 122.31Hz respectively,avoiding the engine excitation frequency.Based on ANSYS random vibration analysis,the vibration amplitudes of the steering wheel before and after optimization are compared.The vibration amplitudes of the steering wheel in the third gear on the asphalt road,the second gear on the sand and gravel dirt road and the first gear on the field and stubble field are reduced by 9.2%,19.8%and 28.9%,respectively.The results show that the optimized steering wheel has obvious vibration reduction effect.