轮胎胎压和车速对无悬架拖拉机横向乘坐振动特性的影响

Influence of tire pressure and forward speed on lateral ride vibration characteristics for unsuspended tractor

为研究轮胎胎压和行驶速度对驾驶员横向乘坐振动特性的影响,该文以两轮驱动式无悬架国产拖拉机为研究对象,建立无悬架拖拉机横向-垂向平面三自由度模型,通过仿真和试验相结合,分别获取不同轮胎胎压和行驶速度下拖拉机座椅处横向加速度功率谱密度、横向加速度均方值以及总加权加速度均方根值,并分析各自的影响规律。结果表明:拖拉机座椅处横向固有频率试验值与理论计算值的最大相对误差为4.67%,座椅处横向加速度均方根试验值随后轮胎胎压和速度的变化规律与仿真是一致的,且试验值比仿真值要小,其相对误差最大值为5.26%,误差均在可接受范围内,表明建立的理论和仿真模型是可行的;前轮胎压的变化对两轮驱动式拖拉机乘坐横向振动特性的影响不大;当轮胎胎压不变时,试验获取的拖拉机座椅处总加权加速度均方根值随行驶速度的增大而增大;当行驶速度不变时,总加权加速度均方根值随后轮胎压的增大而波浪式增大。该研究为拖拉机多维减振悬架系统的设计提供参考。

The operators of agricultural tractors experience whole-body vibration when they drive tractors, and the main influence factors to ride vibrations of the operators are terrain roughness, tractor speed, tire type, pressure, and so on. In this paper, the effects of tire pressure and forward speed on lateral ride vibration characteristics of a two-wheel drive unsuspended tractor was studied by means of a theoretical simulation and experimental analysis. A CF700 tractor without suspensions from Changfa Group was chosen as the research object, and a new theoretical vibration model was constructed for the two-wheel drive unsuspended tractor with 3 degrees of freedom including the lateral and roll and vertical directions of ride vibration in Y-Z plane. Simulation and real tractor experiments were conducted respectively to obtain the natural frequencies of lateral vibration, root mean square （RMS） of lateral acceleration and RMS of total weighted acceleration on the tractor seat under different tire pressures and forward speeds of the tractor, and thus to analyze their respective influence laws. Simulation model was built up on the basis of the constructed state space equation of tractor seat vibration system by using MATLAB/Simulink software, and then simulation was performed when rear tire pressures varied from 60 to 180 kPa with the increment of 30 kPa and 4 forward speeds of 3.5, 6, 9 and 12 km/h were chosen. Meanwhile, driving experiments of the CF700 tractor were carried out on an ISO-5008 standard trial track with 100 m length under the same conditions of rear tire pressures and forward speeds, while front tire pressures were considered from 120 to 240 kPa with the increment of 30 kPa. Firstly, the tests were repeated 3 times at the different forward speeds, when the front tire pressure was fixed to 210 kPa, while the rear tire pressure was changed from 60 to 180 kPa with the increment of 30 kPa. Then, the tests were repeated 3 times at the different forward speeds, when the rear tire pressure was fixed to 120 kPa, while the front tire pressure was changed from 120 to 240 kPa with the increment of 30 kPa. The experimental values were obtained mainly with the LMS test system and the on-board strain-gage-based transducers and triaxial accelerometers. The discrete time series of the measured data were resolved and reconstructed by wavelet and Fourier analysis. Results were obtained in light of the measurement of both the RMS of acceleration and the frequency, for any axis on the tractor operator seat. The results showed that the maximum relative error between the test value and the calculated value of lateral natural frequency was 4.67%, and the error was within the acceptable range, indicating that it is feasible for the established theoretical and simulation model to estimate the lateral ride natural frequency. The change of the tire pressure and velocity in the experiment was consistent with that in the simulation, and the test value was smaller than the simulation value; the maximum value of the relative error was 5.26%, and the minimum relative error was 0.61%. The change of the front tire pressure had little effect on the lateral vibration characteristics of the two-wheel drive tractor, which could verify that it is appropriate to establish the theoretical model and simulation model without considering the front tire. When the tire pressure is constant, the RMS value of the total weighted acceleration on the tractor seat is increased with the increase of the forward speed. When the forward speed is constant, the RMS value of total weighted acceleration is increased with a wave pattern with the increase of the rear tire pressure. This study provides an important reference for the design of multi-dimension vibration reduction suspension system for an unsuspended agricultural tractor.