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关键词： 冲挤复合   离合器毂   齿形   极小圆角  

摘要： 对某自动变速器的齿形离合器毂进行冲挤复合成形工艺研究。该零件形状复杂,厚度不均匀,具有极小的圆角半径,金属流动难以控制,成形过程比较困难。利用DEFORM-3D软件,对侧壁部分的减薄工艺和极小圆角的成形过程进行模拟,得到成形过程中影响金属流动的关键因素、金属流动变形机制、等效应力和等效应变分布规律,确定合理的冲挤复合成形模具结构和工艺参数,避免了成形过程中的压缩失稳和毛刺等缺陷。根据模拟结果进行试制,验证了工艺的可行性和模拟的准确性。

关键词： Clutch judder   Frictional lining materials   Taguchi method   Judder resistance   TEMPERATURE   SIMULATION  

摘要： This study examines the judder behavior of a centrifugal clutch from the start of hot spots in the conformal contact, then the repeated developments of thermoelastic instability, and finally the formation of cyclic undulations in the vibrations, friction coefficient and torque. This behavior is proved to be consistent with the testing results. Using the Taguchi method, 18 kinds of frictional lining specimens were prepared in order to investigate their performance in judder resistance and establish a relationship between judder behavior and the T-s/T-d (T-s: static torque; T-d: dynamic torque) and d mu/dV(x) (mu: friction coefficient; V-x: relative sliding velocity of frictional lining and clutch drum) parameters. These specimens are also provided to examine the effects and profitability with regard to the centrifugal clutch, and find the relative importance of the various control factors. Theoretical models for the friction coefficient (mu), the critical sliding velocity (V-c) with clutch judder, and the contact pressure ratio p*/(p) over bar (p*: pressure undulation w.r.t. (p) over bar; (p) over bar: mean contact pressure) and temperature corresponding to judder behavior are developed. The parameters of the contact pressure ratio and temperature are shown to be helpful to explain the occurrence of judder. The frictional torque and the rotational speeds of the driveline, clutch, and clutch drum as functions of engagement time for 100 clutch cycles are obtained experimentally to evaluate d mu/dV(x) and T-s/T-d. A sharp rise in the maximum p*/(p) over bar occurred when the relative sliding velocity reached the critical velocity, V-c. An increase in the maximum p*/(p) over bar generally led to an increase of the (initially negative) d mu/dV(x) value, and thus the severity of judder. The fluctuation intensity of d mu/dV(x) becomes a governing factor of the growth of d mu/dV(x) itself in the engagement process. The mean values of d mu/dV(x) and T-s/T-d for the clutching

关键词： alloparental care   clutch size   cooperative breeding   life history   parent-offspring conflict   NATAL DISPERSAL   DELAYED DISPERSAL   TERRITORY QUALITY   EVOLUTION   LIFE   STRATEGIES   CARE   CONSEQUENCES   PHILOPATRY   BENEFITS  

摘要： Previous theoretical work has suggested that smaller brood sizes helped facilitate the emergence of cooperative breeding in birds. However, recent empirical evidence has found no statistically significant difference between the clutch sizes of cooperative breeders and that of noncooperative breeders. One explanation for this finding is that while small clutch sizes may predispose species to cooperative breeding, the emergence of cooperative breeding itself may influence the evolution of clutch size. Here, we develop a set of models using population dynamics to describe how the emergence of cooperative breeding influences clutch size. We find, in contrast to previous theoretical work, that the emergence of cooperative breeding does not necessarily decrease (and under certain conditions may actually increase) clutch size. In particular, clutch size may increase after the emergence of cooperative breeding if helpers - philopatric individuals that assist their breeding relatives - are able to substantially improve breeder fecundity at low costs to their own survival, and if the association between breeder and helper is brief. In many cases, clutch size increases following the emergence of cooperative breeding not because it is optimal for the breeder, but as the result of breeder-helper conflict over resource allocation.

关键词： Blue tit Cyanistes caeruleus   Clutch size   English oak Quercus robur   Habitat   Laying date   Occupancy   LIFE-HISTORY VARIATION   GREAT TITS   REPRODUCTIVE SUCCESS   PARUS-MAJOR   FOOD SUPPLEMENTATION   BREEDING PERFORMANCE   SEASONAL-VARIATION   TERRITORY QUALITY   SPATIAL VARIATION   POPULATION  

摘要： Most birds have specific habitat requirements for breeding. The vegetation structure surrounding nest sites is an important component of habitat quality, and can have large effects on avian breeding performance. We studied 13 years of Blue Tit Cyanistes caeruleus population data to determine whether characteristics of vegetation structure predict site occupancy, laying date and number of eggs laid. Measurements of vegetation structure included the density of English Oak Quercus robur, European Beech Fagus sylvatica, and other deciduous, coniferous and non-coniferous evergreen trees, within a 20-m radius of nest-boxes used for breeding. Trees were further sub-divided into specific classes of trunk circumferences to determine the densities for different maturity levels. Based on Principal Component Analysis (PCA), we reduced the total number of 17 measured vegetation variables to 7 main categories, which we used for further analyses. We found that the occupancy rate of sites and the number of eggs laid correlated positively with the proportion of deciduous trees and negatively with the density of coniferous trees. Laying of the first egg was advanced with a greater proportion of deciduous trees. Among deciduous trees, the English Oak appeared to be most important, as a higher density of more mature English Oak trees was associated with more frequent nest-box occupancy, a larger number of eggs laid, and an earlier laying start. Furthermore, laying started earlier and more eggs were laid in nest boxes with higher occupancy rates. Together, these findings highlight the role of deciduous trees, particularly more mature English Oak, as important predictors of high-quality preferred habitat. These results aid in defining habitat quality and will facilitate future studies on the importance of environmental quality for breeding performance. (C) 2015 Elsevier Masson SAS. All rights reserved.

关键词： Wet dual clutch transmission   Synchronizer   Clutch drag torque   Online estimation method   Supervisor control   ENGAGEMENT   SIMULATION   DYNAMICS   SYSTEMS  

摘要： The objective of this paper is to improve the performance of the synchronizer control strategy by considering the effect of clutch drag torque. The research of synchronization process in wet dual clutch transmission is performed in this paper. The significant effect of clutch drag torque is analyzed by adding a complex clutch drag torque module to synchronizer model. This paper focuses on the development of original estimation method of clutch drag torque. The estimation method offers an effective way to obtain accurate clutch drag torque, and it is applied to develop a new supervisor control strategy. Results have demonstrated that the estimation method has satisfied efficiency and accuracy and the control strategy improves the performance of the synchronizer mechanism significantly. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： JAPANESE-QUAIL EGGS   MATERNAL TESTOSTERONE   OFFSPRING PERFORMANCE   MALE ATTRACTIVENESS   FEEDING EXPERIMENT   CHICKEN   SIZE   DEPOSITION   NUTRIENT   GROWTH  

摘要： In birds, mothers can affect their offspring's phenotype and thereby survival via egg composition. It is not well known to what extent and time-scales environmental variation in resource availability, either via resource constrains or adaptive adjustment to predicted rearing conditions, influences maternal effects. We experimentally studied whether egg and yolk mass and yolk hormone levels respond to short-term changes in food availability during laying in wild great tits Parus major. Our treatment groups were: 1) food supplementation (mealworms) from the 1st until the last egg; 2) food supplementation from the 1st until the 5th egg, where the effect of cessation of the supplementary food treatment could also be studied; 3) no food supplementation (controls). We analysed both nutritional resources (egg, yolk and albumen mass), and the important developmental signals, yolk androgens (testosterone and androstenedione), and for the first time in a wild population, yolk thyroid hormones (thyroxine and 3,5,3-triiodothyronine). Egg mass is a costly resource for females, androgens most likely non-costly signals, whereas thyroid hormones may be costly signals, requiring environmental iodine. In the food supplemented group egg, yolk and albumen mass increased rapidly relative to controls and when food supplementation was halted, egg and albumen mass decreased, indicating rapid responses to resource availability. Yolk androgen and thyroid hormone levels were not affected by food supplementation during laying. Thyroxine showed an increase over the laying sequence and its biological meaning needs further study. The rapid changes in egg mass to variation in within-clutch food availability suggest energetic/protein/nutrient constrains on egg formation. The lack of a response in yolk hormones suggest that perhaps in this species the short-term changes in resource availability during egg laying do not predict offspring rearing conditions, or (for thyroid hormones) do not cause syst

关键词： 编织机   锥齿轮传动系统   结构设计   误差分析   振动分析   热分析  

摘要： 大型卧式立体编织机属于高端重型纺织机械设备且应用场合较多,其中锥齿轮传动系统是其核心部件。在现代工程应用中,齿轮传动也是最常用的、最重要的机械传动方式之一,是机械设备的主要部件。一个完整的锥齿轮传动系统就是一个大型复杂的机械系统,包括齿轮副、传动轴系、润滑系统及支撑机头等各类元件,且工作状况较复杂,其设计是否合理,将直接影响整个设备的运动性能。锥齿轮传动系统在进行传动时,由于外载荷(转速及输出端扭矩)变化、齿轮加工装配、齿轮啮合刚度的时变性、芯模进给时冲击、重型机座重压及旋转摩擦副生热等因素的影响,传动系统将产生相应误差、振动及热效应等方方面面的问题。本文以大型卧式立体编织设备锥齿轮传动系统为研究主体,进行设计与分析,涉及的方法理论有现代机械设计理论,机械精度设计,现代振动理论,理论解析,有限元数值仿真分析等。其主要研究内容如下:首先,根据编织机锥齿轮传动系统要求,进行总体布局设计。其次,进行编织机锥齿轮传动系统结构设计,将系统结构划分为传动链、机头结构及润滑辅助装置等模块,并进行具体设计。最后,针对传动系统相关结构进行误差分析、振动分析与热分析,主要包括传动系统制造误差和装配误差分析,基于制造误差的最优齿廓修形设计,对传动系统支撑机头结构进行模型建立与求解,ANSYS有限元力学分析,即模态分析及动载荷作用下的瞬态响应分析,传动系统用轴承外圈与滚动体摩擦生热分析。

关键词： 湿式摩擦离合器   带排转矩   流场分析   瞬态热分析   数值仿真  

摘要： 湿式摩擦离合器因具有启动换向平稳、传递转矩大、磨损小、寿命长等优点而广泛应用于船舶运输、重型卡车等重型机械中,但在使用过程中经常会出现因过热导致摩擦副的翘曲、烧损、表面材料剥落以及热裂纹生成等热失效形式,以及带排转矩的存在引起的功率损耗和传动效率低等问题。针对其不足,本文以某船用湿式摩擦离合器为研究对象,对摩擦片油槽结构形式以及尺寸参数对摩擦片传热以及带排特性的影响规律进行研究,主要研究内容如下:首先,本文分别建立了螺旋带径向油槽、双圆弧油槽、华夫槽三种目前常用的摩擦片流体域参数化有限元模型,在确定湍流模型以及边界条件基础上,进行三维流场数值仿真分析,同时研究了摩擦片在不同转速条件下,流场分布情况,并针对油槽的结构尺寸参数对摩擦片内流场的影响进行了研究。其次,推导了摩擦片瞬态传热的热流密度计算公式,并将热流密度在摩擦副间进行一定比例分配,在流场分析结果的基础上,对摩擦片各油槽部位对流换热系数进行求解。建立三种摩擦片热分析参数化有限元模型,准确施加边界条件,进行三维瞬态热分析,获得摩擦片温度场随时间和空间的变化规律。之后,针对摩擦片在不同油槽结构尺寸参数下的传热特性进行了研究。再次,建立了带排转矩数学模型,对其影响因素进行理论分析;建立三种摩擦片带排转矩流体域参数化有限元模型,分别对上述三种油膜带排特性在各影响因素条件下进行仿真与理论对比分析。然后针对油槽结构尺寸参数对各油槽形式的油膜带排转矩的影响进行了研究。最后,根据前文各摩擦片特性仿真分析结果,提出改进方案,对摩擦片进行结构改进,然后对改进的摩擦片和原结构进行仿真对比分析,并对本文涉及的分析进行计算软件开发。本文的研究可为摩擦片的选型、结构设计以及优化提供一定的参考与借鉴,具有一定的学术意义和工程价值。

关键词： Ergonomics   Knee   Pedal   Tractor  

摘要： Introduction The focus of farm tractor operator is on forward and reverse hydraulic arm's movements in addition to leg-pushing on brake and clutch pedals. Performing all these, with respect to the machine model and operator's position, determines the posture and the loading pattern of the operator's body. Aim The objective here has been the assessment of the pedal control to improve the operator's functionality. Material and methods In this study, 1500 operators were subject to close interviews by the researcher for 3 years in Isfahan Province. Operators with different anthropometries were involved by sitting on MF285, U650, JD3140 and JD950 combiner seats. The operator's knees were photographed in: free (no force enforcement), ready (beginning of force enforcement) and active (force enforcing) conditions. The thigh and leg angle at the knee joint was measured and the exerted force on the leg during leg-pushing was calculated too. Results and discussion Analysis of the obtained data indicated that the MF285 tractor clutch exerted less maximum force on the knee due to the clutch mechanism. The JD3140 clutch needed more maximum force in relation to MF285. The least maximum force was exerted on the brake pedal of JD3140. Under operating conditions, the widest knee extension angle in leg-pushing was of the U650 and JD3140 tractors. Conclusions The U650 and JD3140 model tractors under 'ready' and 'active' conditions need less leg-pushing force. This force exertion from the knee occurs at the widest extension angle. These two models have higher ergonomic level with the least possible disturbance in the knee joint. © 2016 Warmińsko-Mazurska Izba Lekarska w Olsztynie.

关键词： 催化转换器   离合器   制动系统   异味   催化转化器   汽油味   刹车卡钳   热水箱  

摘要： 爱车曾经有发出异味、却又找不到原因的情况吗?其实车内结构细密,突然闻到的异味可能发生在你没想过的地方。以下7种情况很有可能就是让车辆产生异味的原因,提供车主早点发现、及时检修,或许能省下意想不到的额外处理费。1.制动系统/离合器当车主闻到"刺鼻味"时,就要多多注意制动系统或离合器的运作状况,很可能是内部零件有烧焦的情形,其中最直接能闻