Stability Analysis of a Force-Aided Lever Actuation System for Dry Clutches with Negative Stiffness Element

A force-aided lever with a preload spring is not only force-saving but also energy-saving. Therefore, it has great potential to be applied to dry clutch actuations. However, the negative stiffness of the clutch diaphragm spring introduces unstable dynamics which becomes more intensive due to the preload spring. In order to explore the intensified unstability, this paper builds dynamic models for the rotating lever coupling a negative stiffness diaphragm spring and a preload spring. The stability analysis using the Routh-Huiwitz criterion shows that the open-loop system can never be stable due to the negative stiffness. Even if the diaphragm spring stiffness is positive, the system is still unstable when the preload of the spring exceeds an upper limit. A proportionalintegral- derivative (PID) closed-loop scheme addressing this problem is designed to stabilize the system. The stability analysis for the closed-loop system shows that stable region emerges in spite of the negative stiffness; the more the negative stiffness is, the less the allowed preload is. Further, the influences of the dimensions and PID parameters on the stability condition are investigated. Finally, the transient dynamic responses of the system subjected to disturbance are compared between the unstable open-loop and stabilized closed-loop systems.     

岐岭隧道

如果说京九线是目前我国铁路建设天字第一号工程的话,那么岐岭隧道就是天字第一号工点。 罕见的“豆腐渣” 岐岭隧道长2536米,位于赣南信丰和南康两县交界处。岐岭属于南岭山地九连山的余脉。这座隧道地质特殊,主要表现在进口280米长的地段。隧道进口座落在山背面树木茂密的山洼里,这里地表水集中,进口30米范围内有大小水塘8个,雨季泉水漫流,洞口施工场地如同沼泽。专家们认为:这一带地层属特软岩,     

一种交流电机故障诊断中的特征提取与强化

为提高电机故障诊断的准确率和有效性,提出了一种故障特征提取与强化的新方法.即在对所采集的交流电机振动加速度信号进行数据预处理之后,用盲源分离方法进行独立振动源的分离,然后采用小波包分析方法进行特征提取,并进行特征频带的简化及特征强化处理,特征强化后的数据作为交流电机故障诊断模型的输入.该方法通过对振动加速度信号进行分离,能够分离出混合信号中的独立振动源,提高了故障特征提取的正确率和准确度;通过对特征频带化简,减少了故障诊断模型的输入,进而简化了模型的结构;特征强化使模型能够更有效地识别故障状态.     

鄱阳湖水利枢纽航道通航水流条件及优化措施试验研究*

针对鄱阳湖水利枢纽通航水流条件是否满足通航安全要求展开研究，建立鄱阳湖入江水道星子—湖山段物理模型，对鄱阳湖水利枢纽一期围堰阶段现状航道、二期围堰及运营期设计航道各典型工况下的通航水流条件进行试验研究。首先通过物理模型试验验证航道内是否产生不良流态；其次针对航道内出现的不良流态提出相应优化措施并进行方案比选；最后对优化后航道内通航水流条件进行试验验证以确保船舶安全通航。模型试验主要结论：二期围堰及运营期设计航道在大流量工况下存在上游口门区横向流速超标及下游锚地段生成大尺度回流等问题。通过实施调整上游隔流堤形式，航道右侧浅滩开挖，下游锚地段下移等措施后，设计航道各工况下水流条件均满足通航安全要求。