Torque effect on vibration behavior of high-speed train gearbox under internal and external excitations

The high-speed train transmission system,experiencing both the internal excitation originating from gear meshing and the external excitation originating from the wheel-rail interaction,exhibits complex dynamic behavior in the actual service environment.This paper focuses on the gearbox in the high-speed train to carry out the bench test,in which various operat-ing conditions(torques and rotation speeds)were set up and the excitation condition covering both internal and external was created.Acceleration responses on multiple positions of the gearbox were acquired in the test and the vibration behavior of the gearbox was studied.Meanwhile,a stochastic excitation modal test was also carried out on the test bench under different torques,and the modal parameter of the gearbox was identified.Finally,the sweep frequency response of the gearbox under gear meshing excitation was analyzed through dynamic modeling.The results showed that the torque has an attenuating effect on the amplitude of gear meshing frequency on the gearbox,and the effect of external excitation on the gearbox vibration cannot be ignored,especially under the rated operating condition.It was also found that the torque affects the modal param-eter of the gearbox significantly.The torque has a great effect on both the gear meshing stiffness and the bearing stiffness in the transmission system,which is the inherent reason for the changed modal characteristics observed in the modal test and affects the vibration behavior of the gearbox consequently.

Measured load spectra of the bearing in high-speed train gearbox under different gear meshing conditions

The load spectrum is a crucial factor for assess-ing the fatigue reliability of in-service rolling element bear-ings in transmission systems.For a bearing in a high-speed train gearbox,a measurement technique based on strain detection of bearing outer ring was used to instrument the bearing and determine the time histories of the distributed load in the bearing under different gear meshing conditions.Accordingly,the load spectrum of the total radial load car-ried by the bearing was compiled.The mean value and class interval of the obtained load spectrum were found to vary non-monotonously with the speed and torque of gear mesh-ing,which was considered to be caused by the vibration of the shaft and the bearing cage.As the realistic service load input of bearing life assessment,the measured load spectrum under different gear meshing conditions can be used to pre-dict gearbox bearing life realistically based on the damage-equivalent principle and actual operating conditions.

中国喀斯特生态系统健康诊断的方法、进展与展望

中国是碳酸盐岩型喀斯特面积最大、分布最广的国家,在喀斯特地区居住着约2亿的人口,经济规模约占全国的10%.尤其是以贵州为中心的西南地区,位于长江和珠江的上游,经济欠发达,但却是国家的重要生态安全屏障.喀斯特地貌重要而特殊,科学诊断其生态系统的健康不仅对生态修复和实现可持续发展至关重要,更是制定应对方案的基本前提.尽管以往开展了大量的研究工作,但是依然缺乏系统性和整体性认识.本文结合前人研究,进一步将喀斯特地貌演化发育总结为6个阶段:成岩阶段、成陆阶段、成山阶段、成丛阶段、成林阶段和成原阶段.在此基础上,又从碳酸盐岩风化成土速率的计算、土壤水的诊断、水土流失的评价、石漠化解译与演变、生态系统服务的科学计量5个方面进行系统的总结和梳理.尽管不同时代、不同学者的不同研究方法,其结果有着非常大的差异.但是,综合考虑已有的研究结果及其使用方法的优点和不足,归纳发现:(1)碳酸盐岩化学风化很快(30~130 mm ka^(−1)),但由于其酸不溶物含量低(5%以内),导致其成土速率极其缓慢,一般在5~50 t km^(−2)a^(−1)之间.(2)土壤少且分布不连续,但是土壤含水量却比较高,在0.2~0.4 m^(3)m^(−3)之间,这可能与周边基岩的汇水效应相关,且未来呈干化趋势.(3)土壤侵蚀模数低,一般在2~200 t km^(−2)a^(−1)之间,但由于坡陡、降雨量大且与岩土突变接触,导致其侵蚀风险极大,并存在一定比例的地下漏失现象.(4)石漠化的演变可分为单变式、渐进式和返变式3种经典类型,但是通过决策树和人机交互的石漠化解译方法相对高效和精准.(5)喀斯特生态系统服务功能的评价模型要基于成土速率来进行修正水土保持功能和基于岩溶地质碳汇修正气候调节功能.当前诊断喀斯特生态系统健康的指标、方法和模型亟须改进和创新,要充分体现喀斯特地区的特殊性和模型方法的匹配性,提高监测数据的时空分辨率,特别是亟须建立喀斯特社会-生态系统耦合模型,准确刻画出喀斯特生态系统对气候变化和人类活动的响应过程,提升诊断模型的准确度和可预测性.总之,本文系统总结了诊断中国喀斯特生态系统健康与可持续性的方法和取得的重大进展,并进一步从“岩-土-水-石-生”的角度提出了未来的研究方向和突破重点,以期为维护喀斯特地区的生态安全和可持续发展提供科技支撑.

Variation in contact load at the most loaded position of the outer raceway of a bearing in high-speed train gearbox

For the fatigue failure and tribological property of a rolling element bearing,the contact load variation plays a significant role while the most loaded position of the bearing outer raceway takes the greatest risk of failure.This paper focuses on the variation in contact load on the most loaded position of the outer raceway of a gearbox bearing in high-speed train.Under operation conditions of different input speeds and torques,the dynamic contact load distribution in a gearbox bearing of high-speed train was measured by instrumenting the bearing with strain gauges.The most loaded position was identified accordingly and the features and reasons of the variation in contact load on this position were suggested.Three factors were found to have varying degrees of impact on the contact load variation under different gear meshing conditions:modal vibration of the cage or shaft,radial geometrical differences among the rollers and vibration of the gearbox housing.