联合收获机割台机架结构参数优化

为降低联合收获机正常工作时的共振,该文利用UG软件对沃得锐龙型稻麦联合收获机割台机架进行建模,求解出割台机架的模态频率和振型,并对割台机架进行模态试验验证及理论分析;在通过分析外部激振频率特点的基础上,使割台机架固有频率避开外部激振频率范围,并对机架进行结构优化与试验。试验结果表明:将割台机架横梁、弯梁厚度减少0.2 mm,底板、侧板厚度减少0.4 mm时,割台机架质量降低了14.02%,前4阶模态频率均避开了联合收获机各激励频率范围;将割台传动轴平衡配重块质量增加254.90 g,使得割台传动轴轴承座处沿联合收获机前进方向、上下方向位移振动幅值分别降低了25.70%和12.70%,并有效避免了割台共振的产生。该文的研究结果为降低联合收获机割台振动提供了设计依据。

Structural parameter optimization of combine harvester cutting bench

Abstract: With the rapid development of agricultural mechanization in China, the combine harvester has been applied widely in the past decade. As the critical component of the combine harvester, the Cutting table frame bears some parts, such as blade and reel, and is subjected to the unbalanced inertial force of blade mechanism, the impact load of cutting the crop, the incentives from the engine and other dynamic loads of road excitation. If its natural frequency is close to that of the dynamic load, resonance would be produced, and even it may happen to the whole header and machine. The dynamic stress produced by resonance will seriously affect the performance of the combine harvester, the service life, reliability and human body comfort. Therefore, it is particularly important to study the vibration of the header frame.In the paper, the parametric modeling of the combine harvester Ruilong-4LZ-2.5B Cutting table frame was developed using the three-dimensional modeling software UG. After meshing, the modal parameters as well as the modal vibration shapes were calculated by utilizing the NX Nastran, and the first 4 modal frequencies were 12.1, 28.96, 46.35 and 76.17 Hz, respectively. In order to verify the accuracy of the modal analysis results, the laboratory modal testing about the combine harvester Ruilong-4LZ-2.5B Cutting table frame was implemented by exciting vibration method with the DH5902 dynamic analysis system. Then experimental modal parameters were obtained, and the first 4 modal frequencies were 12.21, 29.54, 46.88 and 72.27 Hz, respectively. By comparing the above results, it could be seen that the theoretical modal frequencies were close to the experimental modal frequencies (the maximum error was 5.39%) and their mode shapes were also basically same, which verified the correctness of the calculated results and the accuracy of the Cutting table frame finite element model. Then, the excitation frequencies of the exciting vibrations from the pavement as well as the engine, cutter bar, vibrating screen and threshing cylinder of the combine harvester were analyzed, and the result demonstrated that the first natural frequencies of the combine harvester Cutting table frame were close to or similar with the above excitation frequencies, which implied that the combine harvester was vulnerable to resonance in operation. Therefore, in order to improve the modal frequencies to avoid the resonance, a reasonable optimization proposal was conducted by the Global sensitivity method. The optimization results indicated that when the thickness of the every beam of the frame was reduced from 3 to 2.8 mm, the thickness of the floor and the side of the frame was reduced from 1.2 to 0.8 mm, the first 4 order modal frequencies were 8.85, 24.31, 40.92, and 72.96 Hz, respectively, and each of them was beyond the range of the excitation of the combine harvester, which effectively avoided the resonance. The weight of the clump weight for the transmission shaft of the header was increased by 254.90 g, the vibration amplitude of the bearing block of the transmission shaft along the advancing direction of the combine harvester was reduced by 0.691 mm, and the up-and-down vibration amplitude was reduced by 0.216 mm. This research provides valuble information for the design and improvement of the header structure of the combine harvester.