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南 京 理 工 大 學(xué) 畢業(yè)設(shè)計(論文)外文資料翻譯 學(xué)院（系）： 南京理工大學(xué)紫金學(xué)院機械系 專 業(yè)： 機械工程及自動化 姓 名： 吳朋波 學(xué) 號： 060104232 (用外文寫) 外文出處： of Industrial and Manufacturing Systems Engineering 附 件： 1.外文資料翻譯譯文；2.外文原文。 指導(dǎo)教師評語： 簽名： 年 月 日 注：請將該封面與附件裝訂成冊。 附件1：外文資料翻譯譯文 第一部分 機械設(shè)計 1.1 機械設(shè)計的簡介 1.1.1 什么是機械設(shè)計 機械設(shè)計是以滿足人類需要為目的，應(yīng)用科學(xué)與技術(shù)裝配新的或改進的產(chǎn)品。這個工程技術(shù)的廣闊領(lǐng)域不僅關(guān)系到與該行為的本身就其大小，形狀和建筑細節(jié)，而且關(guān)系到在生產(chǎn)，銷售和使用該產(chǎn)品中所涉及的各種因素。 一個產(chǎn)品可以被定義為任何生產(chǎn)項目，包括機械，結(jié)構(gòu)，工具和儀器。執(zhí)行機械設(shè)計各種功能的人通常稱為設(shè)計師或者設(shè)計工程師?；旧蟻碚f，機械設(shè)計是一種創(chuàng)造性的活動。 然而，除了創(chuàng)新，設(shè)計工程師也必須在工程技術(shù)基礎(chǔ)上有堅實的背景。 1.1.2 機械設(shè)計的基本背景 設(shè)計工程師必須要有在機械制圖，運動學(xué)，材料工程，材料拓展和制造工藝方面的工作知識。下面的將說明這些基本背景的每個議題與機械設(shè)計是如何關(guān)聯(lián)的： （1） 機械制圖。詳細的圖紙不僅必須注意到確切形狀，大小和每個組件材料的成分，裝配時也必須顯示總產(chǎn)品如何由每個部分以正確的順序緊固在一起。 （2） 動力學(xué)。對有關(guān)這一問題的知識，例如，對以玩具“靈鳥”內(nèi)部構(gòu)造的分析，它包括初步的眼球轉(zhuǎn)動行為。一般情況下，在這種機器的設(shè)計初期階段，玩具和其內(nèi)部構(gòu)造的建立稱為動力學(xué)。 （3） 機械學(xué)。用這一學(xué)說可以解析力量的問題，比如，一個人坐在椅子上，力也作用在放椅子的草地上。很顯然，他不小心從座位上跳起時可以破壞那個椅子。這種現(xiàn)象，實際上是適用于動態(tài)載荷，而不是草坪椅子設(shè)計時考慮到的承載。這種濫用的結(jié)果是過大的力量會造成永久性損傷。因此，在力學(xué)法律的使用中應(yīng)考慮到合理的動態(tài)加載。 （4） 工程材料。由于草坪躺椅一般來說是在戶外環(huán)境中使用，它所使用的油管是由鋁制造而成以有抗腐蝕的作用，所用的織帶是塑料材料制成，不會輕易惡化，即便長期暴露在陽光和水中。很顯然，材料的正確選擇是機械設(shè)計的重要方面。 （5） 材料的強度。這是考慮到材料本身的組成部分是否強大到足以維持它通過力學(xué)的考驗。例如，草坪躺椅的鋁管狀部分的規(guī)格和形狀是以這樣一種方式確定的，這不會由于過度用力和變形而發(fā)生故障（在正常使用情況下）。應(yīng)力和變形程度的大小取決于給定零件的規(guī)模和特定的形狀，以及其材料，結(jié)構(gòu)和實際負荷力。 （6） 生產(chǎn)過程。“靈鳥”不是一個簡單的玩具。每個組件是如何生產(chǎn)和整個玩具如何組裝使用的是生產(chǎn)技術(shù)中的方法。設(shè)計師正是由此來判斷成本的花銷。靈活的軸被應(yīng)用在“靈鳥”上，因為他們簡化了昂貴的部件，并削減安裝和調(diào)整軸系僵化的勞動力成本。在處理結(jié)合的基礎(chǔ)過程使用中，有許多重要的考慮，這些必須在一般機械設(shè)計領(lǐng)域里詳細地闡述，其中包括安全，環(huán)境的影響，外觀和經(jīng)濟。 1.1.3 機械設(shè)計哲學(xué) 一位不知姓名的作家寫過下面一首詩，名為《設(shè)計師》。它在說一個設(shè)計工程師以做出非常復(fù)雜的設(shè)計為樂，但產(chǎn)品的生產(chǎn)幾乎是不可能的。 設(shè)計師 他在電路板上設(shè)計彎道 腦海里儲藏著美妙的設(shè)想 他一邊搓著跳動的豆粒一邊說： “怎樣制造這個粗糙的機器呢？ 現(xiàn)在如果把這個部分造成直的 我知道剛開始會有用 但是那樣的話成型太簡單，也太枯燥了 那樣永遠不會讓機器師覺得有挑戰(zhàn) 所以我最好要弄個角在那兒 然后看那些無知的機器師抓頭發(fā) 那些用來包住螺絲帽的洞 我會再往下放置以讓它們更加難敲打 我敢打賭 現(xiàn)在這樣不會有效果 它不能夠用腳踩或者用卡盤固定 也不能用鉆子鉆或是放在地上 事實上，這樣的設(shè)計是最好不過了?！? 他又看了看，叫起來：“最后成功是我的啦！這簡直是鬼斧神工?！? 很顯然，上述的詩是一個諷刺。但是，它明確強調(diào)了一名設(shè)計師在產(chǎn)品制造中的重要性。如前所述，機械設(shè)計的目的是滿足人類的需求。發(fā)明，發(fā)現(xiàn)和科學(xué)知識本身未必有益于人類，只有它們應(yīng)用于產(chǎn)品的設(shè)計中去，利益才會產(chǎn)生。有時候，人類的需求也許被認可，但是如何實現(xiàn)它卻又很難決定。在這樣的原因可以被簡單地說成，在現(xiàn)階段，必須要花費的時間和努力并不能獲得對等的報酬。但是，如果該決定是為了以生產(chǎn)產(chǎn)品滿足人類需要，那么整個項目必須明確界定。機械設(shè)計應(yīng)被視為是一個機會，這個機會就是如何利用創(chuàng)新人才進行產(chǎn)品設(shè)計，對系統(tǒng)進行分析，然后做出如何將產(chǎn)品合理制造的判斷。重要的是要理解工程的基本事實，而不是背誦純粹的事實和公式。任何事實或方程組，只有用于提供所有正確的決定和設(shè)計良好的產(chǎn)品才能存在。另一方面，任何計算必須做的極其謹慎和精準。例如，如果一個小數(shù)點是錯誤的，否則一個合理的設(shè)計可能無法正常使用。良好的設(shè)計需要嘗試新的想法并愿意冒一定的風(fēng)險，因為他們知道，如果新的想法不起作用的話，那么只能用現(xiàn)存的方法。因此，作為一個設(shè)計師必須要有耐心，因為時間和精力的花費沒有成功的保證。創(chuàng)建一個全新的設(shè)計，一般都需要拋棄很多老的方法。這并不容易，因為很多人都依賴熟悉的思想，技術(shù)和態(tài)度。設(shè)計工程師應(yīng)不斷尋找方法，以改善現(xiàn)有的產(chǎn)品，必須決定什么是陳舊的，應(yīng)該用新的成熟的概念，納入未經(jīng)試驗的想法。新的設(shè)計一般有“錯誤”，或不可預(yù)見的問題，這些問題必須在制定新的設(shè)計的優(yōu)良特性前解決。因此，只有在更高的風(fēng)險下存在有優(yōu)越的行為機會。應(yīng)該強調(diào)的是，如果設(shè)計不保證采納新的方法，這種方法只為了改變起見是不能被采納的。在設(shè)計的初期階段，在無任何制約因素的條件下，應(yīng)允許創(chuàng)造性的蓬勃發(fā)展。雖然許多不切實際的想法可能在設(shè)計的早期階段出現(xiàn)，但通常很容易消除在制定具體細節(jié)之前。這樣一來，創(chuàng)意不會被抑制。很多時候，設(shè)計開發(fā)一個以上的產(chǎn)品時，取決于和其他產(chǎn)品在哪里可以相互比較。最終將現(xiàn)有的思想應(yīng)用在被拒絕的設(shè)計上，并沒有顯示為一個整體預(yù)想的樣子，這是完全有可能的。心理學(xué)家經(jīng)常談?wù)撟屓藗兣m應(yīng)他們的機器運作。很重要的是，設(shè)計工程師的責(zé)任在于努力讓機器去適應(yīng)人。這不是一項容易的任務(wù)，因為一般人實在不能操作某些層面和最優(yōu)的程序。然而，必須考慮到許多操作者的功能，包括以下幾方面： (1) 尺寸和手輪，旋鈕，開關(guān)和腳踏板的位置; (2) 工作區(qū)的空間分配； (3) 通風(fēng)狀況； (4) 顏色和光線； (5) 操作的力度； (6) 安全裝置； (7) 單調(diào)操作議案； (8) 操作驗收。 1.1.4 設(shè)計的交流 另一個重要的需要被承認的一點就是一個設(shè)計工程師必須能夠與其他人交流意見，如果這些意見被采納的話。一開始，設(shè)計人員必須傳達一個初步設(shè)計從而得到管理層的批準。這通常是由與繪畫的布局和口頭書面材料一并討論。為了有效地溝通，以下幾個問題必須要回答： （1） 設(shè)計是否真正滿足人的需要？ （2） 與對手公司現(xiàn)有產(chǎn)品相比，是否更加具有競爭力？ （3） 生產(chǎn)是否節(jié)儉？ （4） 能不能夠簡單易行？ （5） 是否能賣出獲得利潤？ 只有時間才能提供對上述問題的真正答案，但有關(guān)產(chǎn)品的設(shè)計，制造和推向市場，只有初步肯定回答。設(shè)計師也必須通過使用細節(jié)和裝配圖結(jié)合最終的設(shè)計制造。 很多時候，在制造循環(huán)過程中會發(fā)生問題。這可能是在對產(chǎn)品部件進行尺寸標注或放寬時以便它可以更容易地生產(chǎn)時所需要的一個變化。這是屬于技術(shù)變化類別，設(shè)計師必須接受這種變化以使該產(chǎn)品的功能不會受到不利影響。在其他情況下，在組裝或測試過程中可能會出現(xiàn)設(shè)計不足，恰好在出貨之前。這始終是更好的方法，要做到這一點，設(shè)計者應(yīng)不斷努力，爭取找到更好的方法。 1．1.5活塞發(fā)動機和汪克爾引擎 毫無疑問，汽車是20世紀對人們具有最深遠影響的因素之一。在20世紀的頭70年采用傳統(tǒng)的往復(fù)式活塞發(fā)動機，汽車一直是世界最大的工業(yè)基礎(chǔ)。在美國大多數(shù)人都能夠獲得屬于自己的汽車駕駛執(zhí)照。然而，這導(dǎo)致了大氣污染的新問題，簡單說來就是指大氣層逐漸積累越來越多對人生命有害的化學(xué)污染物。不斷增加地空氣污染導(dǎo)致的結(jié)果之一就是不再相信其他類型的發(fā)動機，那些承諾在廢氣排放過程中產(chǎn)生較少的污染。其中一個類似引擎最近得到了很大發(fā)展的是汪克爾發(fā)動機。 它很可能取代活塞發(fā)動機。另外，同時出現(xiàn)的問題是現(xiàn)有原油相比所需的汽油短缺。因此，一種更有效的以及產(chǎn)生的污染物少得多的引擎也是必要的。令人驚訝的是，第一個四沖程活塞式發(fā)動機是1866年8月由尼可拉斯奧托和德國的尤格朗根制造的。現(xiàn)今的活塞式發(fā)動機工程基本上是和奧托和蘭根建立的發(fā)動機一樣的原則。事實上，在現(xiàn)代活塞熱能操作過程稱為奧托循環(huán)。 另一方面，1954年才出現(xiàn)汪克爾轉(zhuǎn)子發(fā)動機，那是也是德國人的費克爾發(fā)現(xiàn)他能完全地用一個旋轉(zhuǎn)式發(fā)動機實現(xiàn)奧托循環(huán)。從效率的角度來看，汪克爾發(fā)動機優(yōu)越，因為它比較簡單，包含較少的零件和操作更安靜。但是直到20世紀60年代才有人提出為汪克爾發(fā)動機的發(fā)展做出大量努力。這種現(xiàn)象產(chǎn)生最主要的原因是活塞式發(fā)動機在當(dāng)時已經(jīng)是一個成熟可靠的工業(yè)分支。 在60年代初，人類需要一種廢氣排放中污染少得多的引擎，這顯然率先引起了新引擎的發(fā)展。1967年，日本東洋工業(yè)制造業(yè)采用汪克爾發(fā)動機生產(chǎn)馬自達汽車和美國開始見證了70年代初以來發(fā)動機發(fā)展所帶來的影響。認識到汪克爾發(fā)動機的巨大潛力，通用汽車公司在1971年與汪克爾的專利持有人（汪克爾專線H和奧迪NSU在和美國許可證，柯蒂斯賴特）簽署了五千萬美元的協(xié)議。從1971年到1975年，通用汽車公司支付5000萬美元，把汪克爾發(fā)動機發(fā)展為本公司的傳導(dǎo)。1975年以后，通用汽車可以使用自己設(shè)計的無需支付任何額外的許可費。 接下來，讓我們驗證一下活塞式發(fā)動機和汪克爾發(fā)動機的設(shè)計和操作。 附件2：外文原文 PART 1 MACHINE DESIGN 1.1 INTRODUCTION TO MACHINE DESIGN 1.1.1 What Is Machine Design Machine design is the application of science and technology to device new or improved products for the purpose of satisfying human needs. It is a vast field of engineering technology which not only concerns itself with the original conception of the conduct in terms of its size, shape and construction details, but also considers the various factors involved in the manufacture, marketing and use of the product. A product can be defined as any manufactured item, including machines, structures, tools, and instruments. People who perform the various functions of machine design are typically called designer, or design engineer. Machine design is a creative activity Basically. However, in addition to being innovative, a design engineer must also have a solid background in the fundamentals of engineering technology. 1.1.2 Fundamental Background for Machine Design A design engineer must have working knowledge in the areas of mechanical drawing, kinematics, material engineering, strength of materials and manufacturing processes. The following statements will indicate how each of these basic background subjects relates to machine design: (1) Mechanical drawing. Detailed drawings must be prepared noting the exact shape, size and material composition for each component, assembly drawings showing how the total product is put together by fastening each part in proper sequence are also needed. (2) Kinematics. Knowledge of this subject, for example, would permit analysis of the motion of the internal mechanism of "Smarty Bird" This analysis would include the attainment of the desired eye-rolling action. Normally, the very creation of the toy and its internal mechanism would occur during this initial phase of machine design called kinematics. (3) Mechanics. Use of this subject provides an analysis of the forces which, for example, act upon a lawn chair when a person is seated in it. Obviously, a person can damage the lawn chair by carelessly jumping on the seat. This motion, in effect, applies dynamic loading instead of the gradually applied loading taken into consideration when the lawn chair was designed. The result of this misuse is excessively large forces that can cause permanent damage. Therefore, using the laws of mechanics, a reasonable amount of dynamic loading should be taken into Part 1 Machine Design 2account during the early design phase. (4) Materials of engineering. Because the lawn chair is commonly used in an outdoor environment, the tubing is made of aluminum to resist corrosion. The webbing is made of a plastic material that will not readily deteriorate with sustained exposure to sunlight and moisture. Obviously, the proper selection of materials is a vital area of machine design. (5) Strength of materials. The subject concerns itself with whether or not a part is strong enough to sustain the forces it will experience evaluated from mechanics. For example, the size and shape of the aluminum tubular sections of the lawn chair are determined in such a way, that failure will not occur (under normal use) due to excessive stresses and deflections. The magnitude of stresses and deflections depends on the size and shape of a given part as well as on its material, composition, and actual loads. (6) Manufacturing processes. "Smarty Bird" is no simple toy. How each component is produced and how the entire toy is assembled are established by using methods learned in manufacturing technology. It is here that a designer comes to grips with the reality of costs. The flexible shafts are used in "Smarty Bird" because they simplify of manufacturing by eliminating expensive parts and by cutting the labor costs of installing and aligning rigid shafting. In conjunction with the use of the processing fundamentals, there are many significant considerations, which must be detail with in the general field of machine design. Among these are safety, environmental effects, appearance, and economy. 1.1.3 Philosophy of Machine Design An unknown author wrote the following poem called “The designer.” It relates that a designengineer may enjoy making a design so complex that manufacturing of the product is virtually impossible. THE DESIGNER The designer bent across his board Wonderful things in his head wore stored. Said he as he rubbed his throbbing bean, “How can I make this tough machine? Now if I make this part just straight I know that it will work first rate, But that’s too easy to shape and bore It never would make the machinist sore. So I better put an angle there── Then watch those babies tear their hair. And there are the holes that hold the cap I’ll put them down where they’re hard to tap. Now this won’t work, I’ll bet a buck, Technical English Through Reading3 It can’t be held in a shoe or chuck, In can’t be drilled and it can’t be ground, In fact, the design is exceedingly sound.” He looked again and cried: “At last! Success is mine──it can't even be cast.” Obviously, the foregoing poem is a satire. However, it clearly emphasizes the importance of a design engineer in establishing the manufacturability of a product. As stated previously, the purpose of machine design is to produce a product that willserve a need for man. Inventions, discoveries and scientific knowledge by themselves do not necessarily benefit people; only if they are incorporated into a designed product will a benefit be derived. It should be recognized, therefore, that a human need must be identified before a particular product is designed.Sometimes a human need may be recognized, but a decision is reached to do nothing about it. The reason could simply be that, at the moment, the rewards do not justify the time and effort that must be expended. If, however, the decision is reached to satisfy the human need by manufactured product, the entire project must be clearly defined. Machine design should be considered to be an opportunity to use innovative talents to envision a design of a product, to analyze the system and then make sound judgments on how the product is to be manufactured. It is important to understand the fundamentals of engineering rather than memorize mere facts and equations. There are no facts or equations, which alone can be used to provide all the correct decisions, required producing a good design. On the other hand, any calculations made must be done with the utmost care and precision. For example, if a decimal point is misplaced, an otherwise acceptable design may not function. Good designs require trying new ideas and being willing to take a certain amount of risk, knowing that if the new idea does not work the existing method can be reinstated. Thus a designer must have patience, since there is no assurance of success for the time and effort expended. Creating a completely new design generally requires that many old and will-established methods be thrust aside. This is not easy since many people cling to familiar ideas, techniques, and attitudes. A design engineer should constantly search for ways to improve an existing product and must decide what old, proven concepts should be used and what new, untried ideas should be incorporated. New designs generally have “bugs” or unforeseen problems which must be worked out before the superior characteristics of the new designs, can be enjoyed. Thus, there is a chance for a superior conduct, but only at higher risk. It should be emphasized that, if a design does not warrant radical new methods, such methods should not be applied merely for the sake of change. During the beginning stages of design, creativity should be allowed to flourish without a great number of constraints. Although many impractical ideas may arise, it is usually easy to eliminate them in the early stages of design before manufacturing requires firm details. In this Part 1 Machine Design 4 way, innovative ideas are not inhibited. Quite often, more than one design is developed, up to the point where they can be compared against each other. It is entirely possible that the design that is ultimately accepted, will use ideas existing in one of the rejected designs that did not show as overall promise. Psychologists frequently talk about trying to fit people to the machines they operate. It is essentially the responsibility of the design engineer to strive to fit machines to people. This is not an easy task, since there is really no average person for which certain operating dimensions and procedures are optimums. However, many human operator features must be considered including the following: (1) Size and locations of hand wheels, knobs, switches, and foot pedals; (2) Space allocations for working areas; (3) Ventilation; (4) Colors and lighting; (5) Strength of operator; (6) Safety features; (7) Monotonous operator motions; (8) Operator acceptance. 1.1.4 Communication of Design Another important point which should be recognized, is that a design engineer Must be able to communicate ideas to other people if they are to be incorporated. Initially, the designer must communicate a preliminary design to get management approval. This is usually done by verbal discussions in conjunction with drawing layouts and written material. To communicate effectively, the following questions must be answered: (1) Does the design really serve a human need? (2) Will it be competitive with existing products of rival companies? (3) Is it economical to produce? (4) Can it be readily maintained? (5) Will it sell and make a profit? Only time will provide the true answers to the preceding questions, but the Product should be designed, manufactured, and marketed only with initial affirmative answers. The design engineer also must communicate the finalized design to manufacturing through the use if detail and assembly drawings. Quite often, a problem will occur during the manufacturing cycle. It may be that a change is required in the dimensioning or tolerance of a part so that it can be more readily produced. This falls in the category of engineering changes that must be approved by the design engineer so that the product function will not be adversely affected. In other cases, a deficiency in the design may appear during assembly or testing just prior to shipping. These are always a better way that to do it and the designer should constantly strive towards finding that better way. One Technical English Through Reading 5reality that needs to be kept in mind is that many of the products that will be in existence ten years from now have probably not yet even been conceived. 1.1.5 Piston Engine Versus the Wankel Engine The automobile, without a doubt, has had one of the most profound influences on people in the twentieth century. Powered predominantly by the conventional reciprocating piston engine during the first seven decades of the twentieth century, the automobile has been the basis for the largest industry in the world. Most people in the United States who are old enough to obtain a license own automobiles. This, however, has contributed to the new problem of "air pollution," which, stated simply, means that the atmosphere is gradually accumulating more and more chemical contaminants harmful to human life. One of the results of increasing air pollution has been a hard look at other types of engines which promise to provide fewer pollutants in exhaust emissions. One such engine recently receiving a great deal of development is the Wankel engine. It is a very possible replacement for the piston engine. A second, concurrent problem is a shortage of available crude oil from which gasoline is derived. Thus, there is also a need for a much more efficient engine as well as one which produces far fewer pollutants. Surprisingly enough, the first four stroke piston engine was built in 1866 by Nickolaas August Otto and Euger Langen of Germany. The present-day piston engine works on basically the same principles as the one built by Otto and Langen. In fact, the thermodynamic process operating in the modern piston is called the Otto cycle. On the other hand, the Wankel rotary engine was not invented until 1954, when Felix Wankel, also of Germany, discovered that he could reproduce the Otto cycle with a purely rotary-type engine. From an efficient point of view, the Wankel engine is superior because it is simpler, contains fewer parts and operates more quietly. It wasn’t, however, until the 1960s that much effort was put into the development of the Wankel engine. The main reason for this was that the piston engine was already a proven, reliably working power plant. It was the human needs for an engine with far less polluting exhaust emissions, which apparently spearheaded new engine developments in the early 1960s. In 1967, Toyo Kogyo of Japan was manufacturing Wankel-powered Mazda automobiles and the United States began to witness the impact by the early 1970s. Recognizing the great potential of the Wankel engine, General Motors in 1971 signed a $50 million licensing agreement with Wankel patent holders (Wankel Gmb H and Audi NSU and the U. S. licensee, Curtiss Wright). From 1971 to 1975, General Motors is to pay the $50 million and develop the Wankel engine for is own conduction. After 1975, General Motors can use its own designed Wankel engines without paying any additional licensing fees. Next, let us examine the design and operation of the piston and Wankel engines. 1.1.6 The Four-stroke Automotive Piston Engine Part 1 Machine Design6 Figure 1-1 shows the conventional four-stroke piston engine, which contains a piston reciprocating in a fixed cylinder inside an engine block. A connecting rod is attached to the piston by a wrist pin and to the crank by a crankpin. As the piston reciprocates, the crank, and hence the crankshaft, is forced to rotate inside of bearings. The detailed operation is as follows: (a) Intake stroke (Figure 1-1a). The intake valve opens, allowing a mixture of fuel and air to enter the cylinder. The exhaust valve is closed during most of the stroke. The crankshaft rotates 180 degrees while the piston moves from top dead center (TDC) to bottom dead center (BDC). (b) Compression stroke (Figure 1-1b). Both valves are closed during this stroke. The fuel-air mixture is compressed as the piston rises. Near the end of the stroke, the spark plug fires. The piston moves from BDC to TDC as crankshaft rotates 180 degrees. (c) Power stroke (Figure 1-1c). Both valves are initially closed. The fuel-air mixture burns and increases the temperature. This causes the gas to expand and drive the piston down with power. The exhaust valve opens near the end of the stroke. The power stroke occurs while the crankshaft rotates through 180 degrees. (d) Exhaust stroke (Figure 1-1d). The exhaust valve opens fully as the products of combustion are removed from the cylinder. The intake valve opens near the end of the exhaust stroke. During this stroke, the crankshaft rotates 180 degrees. The following observations should be noted for the four-stroke piston engine: (1) There are four different strokes for one complete cycle of operation. (2) One complete cycle of operation (and thus each power stroke) requires two revolution of the crankshaft. (3) Timing is important. A camshaft is driven by the crankshaft through a gear system or timing chain. One rotation of the camshaft has a separate cam for each intake valve and a separate cam for each exhaust valve. For example, a six-cylinder engine will have twelve cams. (4) Th