基于摩擦阻尼的高地隙农机底盘悬架减振特性

根据高地隙自走式农业机械的行驶作业要求,设计了一种包含尼龙摩擦阻尼装置的独立式立轴空气悬架系统。在此基础上,考虑空气弹簧和橡胶轮胎自身阻尼对悬架减振的影响,建立了具有粘性屈服恢复力摩擦阻尼模型的悬架系统垂向动力学模型,并基于该模型进行了仿真分析。最后,将所设计的悬架系统装配到高地隙玉米去雄机上进行实车试验。仿真和试验结果表明,随着摩擦阻尼力的增大,簧载质量和簧下质量加速度均方根值呈现先减小后增大的趋势,且在1 800 N附近时达到最小;悬架动挠度均方根值在摩擦阻尼力增大的整个过程中都持续减小。在1 800 N的摩擦阻尼力下,对仿真和试验数据进行时域和频域分析可得,簧载和簧下质量共振频率分别为1.2、10.7 Hz和1.1、11.4 Hz;加速度均方根值分别为1.874、8.953 m/s2和1.604、9.653 m/s2。结论表明,试验结果和仿真结果具有很好的一致性,所设计的悬架系统可以较好地衰减振动,具有较高的实用性。

Damping characteristics of chassis suspension system of high clearance agricultural machinery based on friction damper

Abstract: As an important part of the agricultural equipment, high clearance agricultural machinery is usually equipped with suspension system to reduce the vibration from uneven road. However, most of the suspensions have not been equipped with dampers and the vibration attenuation mainly depends on the damping of springs and tires. When the machine runs at a higher speed or works on some bad roads, the damping effect of the suspensions will become worse. In this paper, an independent strut type air suspension system with friction damping was designed according to the operating characteristics and requirements of high clearance agricultural machinery. The suspension system uses the Firestone 1T15L-4 air spring as the antivibration element and the nylon 66 resin slider as the damping element. When the suspension works, the vibration energy is consumed via the relative slippage between the nylon slider and the guide frame of the air spring. Since the high clearance agricultural machinery commonly uses the vacuum intertillage radial tire, the impact of tire damping on suspension antivibration cannot be ignored. Based on this, the vertical dynamic model of the suspension system was established, including the tire damping model and the viscous yielding resilience friction damping model, and then the state equation of the system was obtained. On the basis of the state equation and the filtered white noise random road excitation model, the simulation model of the system was created in Matlab/Simulink R2012a. And the designed suspension system was equipped in a high clearance emasculation machine and the field test was carried out in Jiuquan City, Gansu Province in August 2015. Before testing, the internal pressure of the air spring was adjusted to assure the height of the spring close to 280 mm. And the friction damping force was regulated by adjusting the bolt preload using the torque wrench. The Lancetec ULT1001 piezoelectric acceleration sensor was used to measure the acceleration signal of the sprung and unsprung mass. The MIRAN KTC-325 displacement sensor was applied for measuring the suspension dynamic deflection signal. During the test, the emasculation machine was set to run on the field at a constant speed of 8 km/h, and the sampling frequency was set to 200 Hz. The data acquisition card NI USB-6216 and the software LabVIEW were applied to collect the signals of acceleration and displacement. The main purpose of the simulation and experiment was to study the influence of the changing friction damping force on the vibration characteristics of the suspension, and verify the correctness of the mathematical model. The simulation and test results showed that when the friction damping force was equal to zero, the acceleration root mean square (RMS) and the suspension dynamic deflection of the sprung and unsprung mass were relatively large. At this time, the suspension system depended merely on the self-damping of the air spring and rubber tire to attenuate vibration. The suspension was in an underdamped state and the damping effect was poor. With the increase of friction damping force, the RMS of sprung and unsprung mass reduced firstly and increased afterward, which reached the minimum value at the force of 1 800 N and got the best damping effect, and tended to be equal when the force exceeded 5 000 N. That was because the force was too large and the suspension was locked, leading to the direct transmitting of pavement impact load to the vehicle body and thus the worse damping effect. In addition, the RMS of the suspension dynamic deflection continued to decrease in the whole process of friction damping force increasing. According to the time domain and frequency domain analysis of the acceleration data, when the friction damping force was set to 1 800 N, the RMS values of the sprung and unsprung mass accelerations were approximately equal to 1.874 and 8.953 m/s2 respectively in simulation, while the vehicle test results were 1.604 and 9.653 m/s2 respectively. Meanwhile, the resonance frequencies of the masses were approximately equal to 1.2 and 10.7 Hz respectively in simulation, while the vehicle test results were 1.1 and 11.4 Hz respectively. The above data showed that the natural frequency of the designed suspension system was far away from the most sensitive frequency range of human body that is from 4 to 8 Hz. And the acceleration RMS of sprung mass was significantly decreased in contrast with the unsprung mass. In summary, the designed suspension has a good vibration property and the developed mathematical model is reasonable to reflect the dynamic performance of the suspension.