Study On Vibration Characteristics Of Tractor Based On Excitation Of Agricultural Terrain Roughness

Tractor usually operates on very rough field terrain and its vibration caused by terrain profiles is particularly obvious.Severe vibration not only affects the work efficiency and service life of the tractor,increases the compaction of agricultural field soil,but also seriously endangers the health of the driver.Therefore,it is of great significance to study the characteristics of the roughness of the agricultural field and its influence on the vibration characteristics of the tractor.On the basis of summarizing the relevant research work at home and abroad,this paper studies the characteristics of the original roughness of the agricultural field terrain,the effective roughness of the soft terrain,the relationship between the profile parameters and the vibration characteristics of the tractor,and the vibration characteristics of the tractor excited by the profiles of the terrain.The combination of theoretical analysis and experimental research is adopted.The main research work is as follows:1.According to the characteristics of the agricultural field terrain surface,a surface profiling apparatus(profiler)was developed,which is installed in the front of the tractor,and is suitable for measuring agricultural terrain roughness,such as no tillage stubble field,grassland,field road,etc.The data acquisition system is developed with LabVIEW programming language,which can synchronously collect the data of the profiles and the tractor vibration.A compensation algorithm is adopted to eliminate the influence of tractor roll and pitch motion in the profile measurement,which can improve the measurement accuracy.The ability of the terrain profiler was validated by two trapezoidal bumps with known dimensions.The results show that when the profiling speed u?3.58 km/h,the root mean square error RMSE ?6.3 mm,which is much smaller than the bump elevation profile of 100 mm.Considering the large size of the agricultural machinery tires,the resulting accuracy is regarded as adequate.The road profiling validations show that the influence of tractor roll and pitch motion could be effectively subtracted from the profiling measurements with the compensation algorithm.2.The relationship between the amplitude parameter RMS of the profile and the frequency coefficient Cn and the frequency index W was established.The relationship between the amplitude parameter and the spectrum parameter was obtained.The original profiles of grassland,corn stubble,harvested potato field and hard soil road in the field were measured by the profiler,and 15 treatments of data were obtained for each type of measured terrain.After the data preprocessing,the RMS of the amplitude parameters of each profile and the coherence function ? of the profiles at the left and right wheel tracks were calculated.The power spectral density of each profile was calculated and smoothed by octave,then the coefficient of unevenness Cn and frequency index W were obtained by least square fitting.The figures of spectrum parameters Cn-W distribution,coherence function ? and RMS-Cn-W clustering of the measured original profiles were produced,and the characteristics of the measured field terrain roughness were analyzed and summarized.3.The effective profiles of soft agricultural terrain were solved by ICA analysis method.The vibration accelerations of the center position of the two front wheels and the middle position of the front axle measured synchronously in the profile test were regarded as mixed signals.The ground equivalent profile excitation(effective profile)that causes the front wheels of the tractor to move up and down was regarded as the source signal.The independence of the original profile signal and the Gauss characteristics of each profile signal measured on the left and right wheel tracks were analyzed,which indicated the signals of the field terrain profiles were adapted to the separability condition of ICA analysis method.The separation signal of ICA was optimized based on the maximum correlation criterion,so that the amplitude of the separation signal was consistent with the source signal,and its effectiveness was verified by simulation.The vibration accelerations on the tractor front wheel center and front axle measured on the field road were regarded as mixed signals.The effective profiles determined by ICA analysis method were compared with the profiles measured by profiler.The results show that in the range of 2.56 km/h?5.41 km/h,the root mean square error RMSE between the measured value of profiles and the analysis value of ICA was 3.8 mm?5.4 mm.The relative error Ef value ranged from 5.6%to 8.9%.The error index is within the acceptable range,and the error includes the influence of tractor tire envelope effect.The effective profiles of grassland,corn stubble and harvested potato field were obtained by ICA analysis.The relationships between the original and effective profiles of three kinds of agricultural soft terrains were analyzed.4.Taking John Deere 904 tractor as the tested object,the structural parameters needed in the vibration mechanics model were measured,including the mass of the whole vehicle,the mass of the front and rear axles,the position of the mass center,the moment of inertia of the pitch,the moment of inertia of the roll,the rigidity and damping coefficient of the tire,etc.The theoretical calculation formulas of the profile spectrum parameters and the vibration response of the tractor were derived.The main factors affecting the vibration characteristics of tractor were determined.A half-tractor vibration model was established.According to the structural parameters of the experimental tractor and the range of the effective profile parameters obtained from the test and analysis,the relationship between the profile parameters of agricultural terrain and the vibration response of tractor was analyzed.The results show that the vibration response intensity of tractor caused by uneven ground excitation increases with the increase of effective roughness coefficient Cn and vehicle speed u,and decreases with the increase of frequency index W.The vibration model of tractor without suspension was established,and the natural frequency of tractor was calculated.The formula of vibration characteristics such as dynamic load of wheel was derived,and Simulink simulation model was established.The vibration responses of the 1/2 tractor model and the whole tractor model were compared and analyzed by using the ground effective roughness as input excitation obtained from the test and analysis.The results show that the whole tractor model should be used as much as possible in analyzing tractor vibration performance excited by agricultural terrain profiles,which can avoid the influence of the profile difference between the left and right wheel tracks on the vibration characteristics of the tractor.5.Taking John Deere 904 tractor as the research object,the measurements of tractor vibration excited by ground surface profiles were carried out on the hard-agricultural field road and the soft agricultural terrain respectively.Ground roughness was measured by a profiler attached to the tractor.At the meanwhile,the vibration response data of the tractor was measured by the vibration data acquisition instrument called AVANT MI-7016.The verifiability of the vibration characteristic analysis of tractor based on the profile excitation of the terrain is realized.The vertical,pitching and roll vibration acceleration of tractor's centroid and the dynamic load characteristics of front and rear wheels were analyzed based on the test data.The vibration response characteristics of the tractor were analyzed and compared with the test results based on the vibration model of the tractor.The results showed that the natural frequencies of the vertical,pitching and roll vibrations of the tractor were 2.623 Hz,3.148 Hz and 3.575 Hz,respectively.Through theoretical calculation,the natural frequencies of tractor's centroid vertical,pitching and roll vibrations were 2.88 Hz,3.38 Hz and 3.45 Hz respectively,and the error rates were 9.8%,7.4%and 3.5%respectively.The error between the measured values and the calculated values of tractor vibration response was within 11%,and had a good consistency.The error is within the acceptable range for the field test,which shows that the vibration model can reflect the real vibration characteristics of the tractor in actual operation.The vibration characteristics of tractor excited by the original and effective roughness of soft ground were compared and analyzed.The results show that the effective roughness should be used as the input excitation,when using the vibration model to analyze the vibration characteristics of the tractor excited by agricultural soft terrain profiles.The amplitude of the vibration response obtained from the analysis will be too large and there will be a large error,when the original profile is used as the input excitation.