水田作业工况的拖拉机振动特性

为研究拖拉机在水田工况下的振动特性。该文采用轮胎滚动法测取南京江浦农场水田硬底层纵断面空间函数,对数据进行自相关性检验,分析硬底层垂直位移功率谱密度;以CF700型拖拉机(常发集团)为研究对象,基于轮胎-湿软水田土壤系统,建立水田工况下拖拉机三自由度振动微分方程和仿真模型,以水田硬底层纵断面时间函数为输入矢量,对拖拉机振动特性进行仿真研究,并将仿真结果与试验结果进行对比分析。结果表明,水田硬底层高程具有统计相关性,其不平度系数Gx(0.1)=316.7×10-6 m3,拟合指数w=-1.651;试验所得拖拉机前桥、后桥及座椅椅面垂向振动频率分别是2.91、3.6及2.5 Hz,与仿真结果相对误差分别为19.9%、7.2%、16.0%。以上结果为面向水田作业的拖拉机振动研究提供路面参考模型,验证了水田工况下拖拉机三自由度平面振动模型的有效性,为拖拉机减振系统的参数设计提供理论依据。

Vibration characteristics of tractor in condition of paddy operation

When a tractor works in a paddy field, road roughness is the main factor affecting its running, however, there has been no research on road roughness of paddy field. For the study of vibration characteristics of tractor in the condition of paddy field operation, the experiment was conducted in June 2014. Nanking Jiangpu Farm Agronomy Experiment Center which has clayey paddy soil was chosen as the experiment site, and tire rolling was adopted as the experiment method. By a self-designed measuring device, the vertical section function of hard bottom of paddy field was measured and obtained. Then the obtained data was conducted with auto-correlation test, and the power spectral density (PSD) of paddy field was analyzed with hard bottom of vertical displacement. The CF700 tractor was the research object. In addition to the stiffness and damping of the tire, soft and wet paddy soil was another factor affecting the vibration characteristics of the tractor. Based on the tire-soil system, in accordance with the main parameters of the tractor, the three degree of freedom vibration differential equation and simulation model were established under the condition of paddy field operation. The time function of hard bottom profile was set as an inputted incentive. The vibration characteristics of tractor were studied by simulation. In order to verify the reliability of the simulation model, the experiment which CF700 tractor working under the condition of paddy field operation was carried out, and vertical vibration acceleration of front axle, seat surface and rear axle of tractor were measured respectively at the speed of 6km/h. Then time-domain signal of acceleration was translated to frequency-domain signal, and a comparative analysis was conducted between the results of simulation and experiment. The results showed that there existed statistical correlation among paddy hard bottom elevations, and the change of elevation was steady and random; the roughness coefficient Gx(0.1)= 316.7×10-6 m3, and the fit index w=?1.651. When the spatial frequency was below 0.7m-1 (wavelengthλ≥1.43m), the road level of paddy hard bottom was C; when the spatial frequency was above 0.7 m-1 (wavelengthλ≤1.43 m), the road level of paddy hard bottom was between D and E. PSD amplitudes varied a lot within the whole spatial frequency range. The power of low frequency (long wave) was significantly higher than that of the high frequency (short wave). When the tractor moved on this type of road at a certain speed, the excitation frequency range was wide and the tractor could effectively isolate the excitation caused by short waves (high frequency input). And the excitation caused by long waves (low frequency input) was transmitted to the tractor. When the excitation frequency approached the natural frequency, the tractor would vibrate violently due to the potentiation of transfer function. The experiment results showed that the vertical vibration frequencies of front axle, rear axle and seat of the tractor were 2.91Hz, 3.6Hz and 2.5Hz, respectively. The error rates of the results between the experiment and simulation were 19.9%, 7.2% and 16.0%, respectively. The causes of error might be: 1) The simulation used tractor plane vibration model. It did not take the roll-direction vibration into account. In the experiment, there existed a coupling between the roll-direction vibration and vertical vibration; 2) When the tractor worked in the paddy field, its greater driving resistance leaded to increasing vibration of the engine and gearbox. In conclusion, the results above provide a road reference model for tractor vibration in paddy field. They prove that it is effective to establish three degrees of freedom plane vibration model of the tractor based on the tire-soil system. Meanwhile, the results provide theoretical justification for the tractor design of shock mitigation system.