发布时间 : 星期五 文章中英文翻译更新完毕开始阅读
propeller are the examples of the special components, which are designed for some specific purposes.
Mechanical Design Process
Product design requires much research and development. Many concepts of an idea must be studied, tried, refined, and then either used or discarded. Although the content of each engineering problem is unique, the designers follow the similar process to solve the problems. Recognition of Need
Sometimes, design begins when a designer recognizes a need and decides to do something about it. The need is often not evident at, all; recognition is usually triggered by a particular adverse circumstance or a set of random circumstances, which arise almost simultaneously. Identification of need usually consists of an undefined and vague problem statement. Definition of Problem
Definition of problem is necessary to fully define and understand the problem, after which it is possible to restate the goal in a more reasonable and realistic way than the original problem statement. Definition of the problem must include all the specifications for the thing that is to be designed. Obvious items in the specifications are the speeds, feeds, temperature limitations, maximum range, expected variation in the variables, and dimensional and weight limitations. Synthesis
The synthesis is one in which as many alternative possible design approaches are sought, usually without regard for their value or quality. This is also sometimes called the ideation and invention step in which the largest possible number of creative solutions is generated. The synthesis activity includes the specification of material, addition of geometric features, and inclusion of greater dimensional detail to the aggregate design. Analysis
Analysis is a method of determining or describing the nature of something by separating it into its parts. In the process the elements, or nature of the design, are analyzed to determine the fit between the proposed design and the original design goals.
Evaluation
Evaluation is the final proof of a successful design and usually involves the
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testing of a prototype in the laboratory. Here we wish to discover if the design really satisfies the needs.
The above description may give an erroneous impression that this process can be accomplished in a linear fashion as listed. On the contrary, iteration is required within the entire process, moving from any step back to any previous step, in all possible combinations, and doing this repeatedly. Presentation
Communicating the design to others is the finial, vital presentation step in the design process. Basically, there are only three means of communication. These are the written, the oral, and the graphical forms. A successful engineer will be technically competent and versatile in all three forms of communication. The competent engineer should not be afraid of the possibility of not succeeding in a presentation. In fact, the greatest gains are obtained by those willing to risk defeat. Contents of Machinery Design
Machinery design is an important technological basic course in mechanical engineering education. Its objective is to provide the concepts, procedures, data, and decision analysis techniques necessary to design machine elements commonly found in mechanical devices and systems; to develop engineering students’ competence of machine design that is the primary concern of machinery manufacturing and the key to manufacture good products. Machinery design covers the following contents：
Provides an introduction to the design process, problem formulation, safety factors.
Reviews the material properties and static and dynamic loading analysis, including beam, vibration and impact loading.
Reviews the fundamentals of stress and defection analysis.
Introduces static failure theories and fracture-mechanics analysis for static loads. Introduces fatigue-failure theory with the emphasis on stress-life approaches to high-cycle fatigue design, which is commonly used in the design of rotation machinery.
Discusses thoroughly the phenomena of wear mechanisms, surface contact stresses, and surface fatigue.
Investigates shaft design using the fatigue-analysis techniques. Discusses fluid-film and rolling-element bearing theory and application.
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Gives a thorough introduction to the kinematics, design and stress analysis of spur gears, and a simple introduction to helical, bevel, and worm gearing.
Discusses spring design including helical compression, extension and torsion springs.
Deals with screws and fasteners including power screw and preload fasteners. Introduces the design and specification of disk and drum clutches and brakes.
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机械零件(I)
齿轮
齿轮是直接接触，成对工作的实体，在称为齿的凸出物的连续啮合作用下，齿轮能将运动和力从一个旋转轴传递到另一个旋转轴，或从一个轴传递到一个滑块(齿条)。
齿形轮廓。齿轮的接触面必须以一定的方向排齐，这样可以使得传动是正向的，也就是传递的载荷不必依靠表面的摩擦作用进行传递。如处理直接接触的实体一样，要求垂直于表面的公法线不必经过主动轴或从动轴的轴线。 和我们所知道的直接接触的实体一样，摆线和渐开线轮廓也都提供了一个正方向的驱动和一个均匀的速度比，即共轭作用。
基本关系式。一对齿轮中较小的齿轮称为小齿轮，较大的齿轮称为大齿轮，当小齿轮安装在传动轴上，则这对齿轮用作减速器；反之，若大齿轮安装在传动轴上，则这对齿轮用作加速器。齿轮一般经常用于减速而不是加速。 如果齿轮有N个齿，并以每分钟 n 转的速度旋转，乘积 N* n 表示的是每分钟旋转的齿数，如果每个齿都是通过啮合作用传动另一个齿轮，那么这个乘积对于一对啮合齿轮的两个齿轮来说是相等的。
对于各种不同类型的共轭齿轮，齿轮比和速度比都可以通过大齿轮和小齿轮上的齿数比获得。如果一个大齿轮的齿数为100，小齿轮的齿数为20，齿数比为 100/20=5。这样不管大齿轮的旋转速度为多少，小齿轮的旋转速度总是大齿轮旋转速度的 5 倍。大小齿轮的接触点称为节点，由于节点位于中心线上，因此节点是齿形轮廓线上唯一做纯滚动接触的点。非平行的齿轮，非交叉传动的轴也有节圆，但是不存在纯滚动节圆概念。
齿轮的类型在很大程度上由轴的不同排列决定，另外，即使速度发生改变，原有类型的齿轮传动一般来说也肯定好于采用其他类型的齿轮传动。这就意味着当轴的排列布置形式决定后，齿轮的类型或多或少也就定下来了。另一方面，如果齿轮的速度变化及类型一定的话，那么轴的排列布置形式基本上也就定下来了。
直齿轮和螺旋齿轮。齿形轮廓是直的并且平行于传动轴的齿轮称为直齿轮，直齿轮只能用于连接平行轴。
如果一个渐开线直齿小齿轮是用橡皮制成的，能均匀扭曲，从而一端会绕另一端为轴进行旋转，这样小齿轮上的齿开始将是直的并行于传动轴，最后会变成螺旋形。
蜗杆和伞形齿轮。为了得到线接触和改进螺旋齿轮的横向轴向的传动载荷能力，大齿轮可能被做成弯曲形状以围绕小齿轮，有时类似于螺帽套在螺钉上，这
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