如何為汽油發(fā)動(dòng)機(jī)和其他機(jī)械設(shè)計(jì)和生產(chǎn)簡(jiǎn)單而有效的凸輪中英二合一

1、<p>　　ELEMENTS OF CAM DESIGN</p><p>　　How to plan and produce simple but efficient cams for petrol engines and other mechanisms</p><p>　　Cams are among the most versatile mechanisms availab

2、le．A cam is a simple two-member device．The input member is the cam itself，while the output member is called the follower．Through the use of cams，a simple input motion can be modified into almost any conceivable output mo

3、tion that is desired．Some of the common applications of cams are</p><p>　　——Camshaft and distributor shaft of automotive engine </p><p>　　——Production machine tools</p><p>　　——Autom

4、atic record players</p><p>　　——Printing machines</p><p>　　——Automatic washing machines</p><p>　　——Automatic dishwashers</p><p>　　The contour of high-speed cams (cam spe

5、ed in excess of 1000 rpm) must be determined mathematically．However，the vast majority of cams operate at low speeds(less than 500 rpm) or medium-speed cams can be determined graphically using a large-scale layout．In gene

6、ral，the greater the cam speed and output load，the greater must be the precision with which the cam contour is machined．</p><p>　　Cams in some form or other are essential to the operation of many kinds of mec

7、hanical devices. Their best-known application is in the valve-operating gear of internal combustion engines, but they play an equally important part in industrial machinery, from printing presses to reaping machines. <

8、;/p><p>　　In general, a cam can be defined as a projection on the face of a disc or the surface of a cylinder for the purpose of producing intermittent reciprocating motion of a contacting member or follower. M

9、ost cams operate by rotary motion, but this is not an essential condition and in special cases the motion may be semi-rotary， oscillatory or swinging. Even straight-line motion of the operating member is possible, though

10、 the term cam may not be considered properly applicable in such circumstances.</p><p>　　Most text books on mechanics give some information on the design of cams and show examples of cam forms plotted to prod

11、uce various orders of motion. Where neither the operating speed nor the mechanical duty is very high, there is a good deal of latitude in the nermissible design of the cam and it is only necessary to avoid excessively st

12、eep contours or abrupt changes which would result in noise, impact shock, and side pressure on the follower. But, with increase of either speed or load, much mor</p><p>　　The design of the cam follower is al

13、so of great importance and bears a definite relation to the shape of the cam itself. This is because the cam cannot make contact with the follower at a single fixed point. Surface contact is necessary to distribute load

14、and avoid excess wear, thus the cam transmits its motion through various points of location on the follower, depending on the shape of the two complementary members. The cams for operating i.c. engine valves presen

15、t specially difficult pr</p><p>　　In the many designs for small four-stroke engines which I have published, I have sought to simplify valve operation and to provide designs for cams which can be simply and a

16、ccurately produced with the facilities of the amateur workshop. Numerous engine designs which have been submitted to me by readers have contained errors in the valve gear and particularly in the cams and in view of preva

17、lent misconceptions in the fundamental principles of these items, I am giving some advice on the matter whi</p><p>　　Tangent cams can only work efficiently in conjunction with a convex curved follower, as th

18、is is the only way in which the flank can be brought progressively and smoothly into action. Some time ago an engine was described having tangent cams in conjunction with flat followers. This was not intended for extreme

19、ly high speed and very likely produced all the power required of it, but it is quite clear that the flat face of the tangent cam. On engaging the flat tappet-over the full length of the flan</p><p>　　Tangent

20、 cams have been used with a certain degree of success for high-performance-engines and were at one time popular on racing motorcycle engines, though usually with some slight modification of shape-often “ designed ” by th

21、e tuner with the aid of .a Carborundum slip! Their more common application, however, has been on gas and oil engines running at relatively slow speeds, where they work well in contact with rollers attached to the ends o

22、f the valve rockers. Cams with convex flanks are exte</p><p>　　Comparatively few examples of concave-flanked cams (Fig. 2c) are to be seen nowadays, though they have been used extensively in the past with th

23、e idea of obtaining the most rapid opening and closing of the valves. Theoretically, they can be designed to produce consant-acceleration, but in practice they render valve control very difficult at high speed and their

24、fierce angle of attack produces heavy side pressure on the tappet. The concave flank must always have a substantially greater radius tha</p><p>　　The shape of the nose in most types of cams is dictated mainl

25、y by the need to decelerate the follower as smoothly as possible. It is one thing to design it in such a way that ideal conditions are obtained, and quite another to ensure in practice that the follower retains close con

26、tact with the cam. If the radius of the nose is too small, the follower will bounce and come down heavily on the return flank of the cam and,. if too great, valve opening efficiency will be reduced. </p><p>

27、　　Of the three types of cams, A, B and C, which all have identically equal lift and angular period, the lobe of B encloses the smallest area, and on first sight it might appear that it is the least efficient in producing

28、 adequate valve opening, or mean lift area, but owing to the use of a flat based tappet, its lift characteristics are not very different from those of a tangent cam with round-based tappet, and not necessarily inferior t

29、o those of a concave-flank cam. </p><p>　　Unsymmetrical cams </p><p>　　It is not common to make the two flanks of a cam of different contours to produce some particular result which the designer

30、 may consider desirable. In some cases, the object is to produce rapid opening and gradual closing, but sometimes the opposite effect is preferred. When all things are considered, however, most attempts to monkey about w

31、ith cam forms lead to complications which may actually defeat their own object, at least at really high speeds.</p><p>　　In many engines, particularly those of motorcycles, the cams operate the valves throug

32、h levers or rockers which move in an arc instead of in a straight line, as in the orthodox motor car tappet. This may be mechanically efficient, but it modifies the lift characteristic of the cam, as the point at which t

33、he latter transmits motion to the follower varies in relation to the radius of the lever arm, (Fig. 3). </p><p>　　With the cam rotating in a clockwise direction, the effective length of the lever will be gre

34、ater in the position.</p><p>　　A during valve opening than in position B during closing, as indicated by dimensions X and Y. This amounts to the same as using an unsymmetrical cam, and in the example shown,

35、would result in slow opening and rapid closing of the valve, or vice versa if either the direction of rotation of the cam, or the relative “ hand ” of the lever, is reversed. The shorter the lever, the greater the discre

36、pancy in the rate of movement, Neither the unsymmetrical cam form nor the pivoted lever is condemned as </p><p>　　The employment of cams with flanks of true circular arc has enabled me to devise means of pro

37、ducing them on the lathe without elaborate attachments and, what is more important still, to produce an entire set of cams for a multi-cylinder engine in correct angular relation to each other by equally simple means. Th

38、ere is no doubt whatever that these methods have enabled many engine constructors (some without previous experience) to tackle successfully a problem which would otherwise have been formi</p><p>　　Many desig

39、ners have attempted to improve valve efficiency by designing cams which hold the valve at maximum opening for as long a period as possible. This is done by providing dwell or, in other words, making the top of the lobe c

40、oncentric with the cam axis over a certain angular distance in the centre of its lift. To do this, however, it is necessary to make the flanks excessively steep, thus producing heavy side thrust on the tappet, and making

41、 control at high speed more difficult, (Fig. 4A).</p><p>　　A little consideration, however, will show that the same result can be achieved, with much less mechanical difficulty, by lifting the valve somewhat

42、 higher at an easier rate, as shown at B. This avoids the need for sudden acceleration and deceleration of the tappet and promotes flow efficiency of the valve. The shaded portions of the two cams show the differences in

43、 the area of the lobe, showing that nothing is really gained by the dwell. Factors in efficiency High valve lift is a desirable feat</p><p>　　Large diameter valves will obviously release and admit gas effici

44、ently but they are more difficult to control and keep cool at high speed than smaller valves. Another point is that the exhaust valve is required to open against a high cylinder pressure, and the larger it is the more th

45、e load imposed on the cam, quite apart from the spring load.</p><p><b>　　凸輪設(shè)計(jì)的基本內(nèi)容</b></p><p>　　如何為汽油發(fā)動(dòng)機(jī)和其他機(jī)械設(shè)計(jì)和生產(chǎn)簡(jiǎn)單而有效的凸輪</p><p>　　凸輪是被應(yīng)用的最廣泛的機(jī)械結(jié)構(gòu)之一。凸輪是一種僅僅有兩個(gè)組件構(gòu)成的設(shè)備。主

46、動(dòng)件本身就是凸輪，而輸出件被稱為從動(dòng)件。通過使用凸輪，一個(gè)簡(jiǎn)單的輸入動(dòng)作可以被修改成幾乎可以想像得到的任何輸出運(yùn)動(dòng)。常見的一些關(guān)于凸輪應(yīng)用的例子有：</p><p>　　——凸輪軸和汽車發(fā)動(dòng)機(jī)工程的裝配</p><p><b>　　——專用機(jī)床</b></p><p><b>　　——自動(dòng)電唱機(jī)</b></p>

47、<p><b>　　——印刷機(jī)</b></p><p><b>　　——自動(dòng)的洗衣機(jī)</b></p><p><b>　　——自動(dòng)的洗碗機(jī)</b></p><p>　　高速凸輪(凸輪超過1000 rpm的速度)的輪廓必須從數(shù)學(xué)意義上來定義。無論如何，大多數(shù)凸輪以低速(少于500 rpm)

48、運(yùn)行而中速的凸輪可以通過一個(gè)大比例的圖形表示出來。一般說來，凸輪的速度和輸出負(fù)載越大，凸輪的輪廓在被床上被加工時(shí)就一定要更加精密。</p><p>　　在多種機(jī)械裝置的操作中凸輪在某種形式下是必不可少。他們最有名的應(yīng)用是在內(nèi)燃機(jī)閥門操作裝置中，但在工業(yè)機(jī)器中，從印刷機(jī)到收割機(jī)械，凸輪機(jī)構(gòu)也是一個(gè)相當(dāng)重要的一部分。</p><p>　　一般來說，一個(gè)凸輪可以被定義為一個(gè)圓盤面或一個(gè)為產(chǎn)生接觸

49、間歇往復(fù)運(yùn)動(dòng)的零件或從動(dòng)件。大多數(shù)凸輪的運(yùn)動(dòng)是旋轉(zhuǎn)運(yùn)動(dòng)，但這不是一個(gè)必要條件，在特殊情況下，它的運(yùn)動(dòng)是半旋轉(zhuǎn)，振動(dòng)或擺動(dòng)。即使原動(dòng)件可能是直線運(yùn)動(dòng)，但在某種情況下凸輪也可能會(huì)適當(dāng)?shù)乇豢紤]，。</p><p>　　在機(jī)構(gòu)學(xué)大多數(shù)文本書籍中給了關(guān)于凸輪設(shè)計(jì)和凸輪類型的實(shí)例設(shè)計(jì)的一些信息，產(chǎn)生各種規(guī)定的運(yùn)動(dòng)。在某種情況運(yùn)行速度和機(jī)械的性能不是非常高，有一個(gè)規(guī)律是凸輪機(jī)構(gòu)設(shè)計(jì)很好的協(xié)議，只需要避免過于陡峭的輪廓或從動(dòng)件產(chǎn)

50、生噪聲，影響沖擊，并側(cè)壓力的突然改變。</p><p>　　然而，凸輪速度或負(fù)荷增加或具有更嚴(yán)格的要求，尋求更精細(xì)的設(shè)計(jì)，并以極高的速度，在慣性運(yùn)動(dòng)部件上的作用最明顯，因此，對(duì)舉升的加速度和速度因素都必須考慮，這些很少在任何詳細(xì)的標(biāo)準(zhǔn)教科書中得到處理。</p><p>　　凸輪從動(dòng)件的設(shè)計(jì)也是非常重要的，并且關(guān)系到凸輪自身的形狀。這是因?yàn)橥馆喤c從動(dòng)件不能在一個(gè)固定點(diǎn)上接觸。表面接觸需要分配

51、負(fù)荷，避免過度磨損，凸輪傳送運(yùn)動(dòng)通過從動(dòng)件各點(diǎn)位置，這都取決于兩個(gè)互補(bǔ)零部件形狀。目前凸輪在發(fā)動(dòng)機(jī)氣門設(shè)計(jì)的問題上特別困難。在賽車引擎中，無論是負(fù)載還是速度都可能會(huì)被視為極端，因?yàn)樵诤芏喟l(fā)動(dòng)機(jī)中引擎的閥門上這些限制因素得不到有效控制。在某些方面，微型發(fā)動(dòng)機(jī)凸輪的設(shè)計(jì)的簡(jiǎn)化是由于他們的打火工作部件（以及隨之而來的慣量）的原因，但在另一方面，工作通常具有更大的摩擦和旋轉(zhuǎn)速度，一般都大大高于全尺寸的做法更高。</p><p

52、>　　對(duì)于小型四沖程發(fā)動(dòng)機(jī)的許多設(shè)計(jì)已經(jīng)出版，我力求簡(jiǎn)化操作閥門，并為凸輪可以簡(jiǎn)單而準(zhǔn)確地運(yùn)用在業(yè)余設(shè)計(jì)制作車間的設(shè)施。許多發(fā)動(dòng)機(jī)的設(shè)計(jì)已提交，讀者對(duì)設(shè)計(jì)中包含有錯(cuò)誤的閥門裝置，特別是凸輪和這些項(xiàng)目上的基本原則有普遍的誤解，我給一些對(duì)此事的意見，而我的信任將有助于個(gè)別設(shè)計(jì)人員獲得其發(fā)動(dòng)機(jī)的最佳效果。 </p><p>　　目前有許多關(guān)于發(fā)動(dòng)機(jī)的凸輪設(shè)計(jì)，盡管如此，這些設(shè)計(jì)結(jié)果或多或少令它們不滿意?？梢哉f，它

53、的速度在一定限度內(nèi)可以滿足要求，但在某些情況下，凸輪設(shè)計(jì)不良可以與發(fā)動(dòng)機(jī)配合，但在工作細(xì)節(jié)上會(huì)出現(xiàn)錯(cuò)誤??。 </p><p>　　本文關(guān)注的主要是集成電路的閥門發(fā)動(dòng)機(jī)凸輪設(shè)計(jì)，并且為了避免一些混淆的術(shù)語，圖1顯示了這種類型的凸輪的各個(gè)部分，并解釋它們的功能。凸輪輪廓的同心部分，它沒有操作效果，被稱為基圓；凸輪（顯示陰影）被稱為葉輪，無論是從基圓上升到頂圓，這通常是圓形的側(cè)翼。</p><p&

54、gt;　　推程可以被定義為基圓半徑和頂圓之間的差值。點(diǎn)之間的封閉在兩側(cè)加入基圓的角被稱為周期，代表整個(gè)周期運(yùn)作期間，凸輪齒輪比例閥。</p><p>　　在圖2中，對(duì)用于i.c.發(fā)動(dòng)機(jī)凸輪典型例子進(jìn)行了說明。切線凸輪，一個(gè)已經(jīng)固定在直線兩側(cè)，其中顧名思義形式向基圓的切線。這種凸輪式很容易設(shè)計(jì)和生產(chǎn)，是由一個(gè)圓形銑加工過程形成了一個(gè)最簡(jiǎn)單的方法，它是在表面與基圓同心連續(xù)運(yùn)行了切向那里的兩翼開始和結(jié)束。它也可以產(chǎn)生和

55、我在過去的描述如何與一個(gè)在軋輥車床休息備案，它借助與索引齒輪側(cè)面結(jié)合的角度來定位。 </p><p>　　切線凸輪的有效工作只能和一個(gè)凸弧形上的從動(dòng)件一起，因?yàn)檫@是唯一的方式，側(cè)面可以發(fā)揮作用，逐步平穩(wěn)。前一段時(shí)間有一種引擎與切線凸輪一起被描述。這是不適合極高的速度的，極有可能產(chǎn)生力的集中現(xiàn)象，但相當(dāng)清楚的是，它是切線凸輪的盤型平面。平面上推桿以上的側(cè)翼突然變長(zhǎng)，運(yùn)動(dòng)中突然出現(xiàn)運(yùn)動(dòng)噪音，效率低，從長(zhǎng)遠(yuǎn)來看具有破壞

56、性。 </p><p>　　滾子經(jīng)常被用來作為與切線凸輪的從動(dòng)件，并在其形狀方面令人滿意，但在這一點(diǎn)上引入滾動(dòng)運(yùn)動(dòng)的想法并不好??，因?yàn)樗坪跏且幌嗲樵?，因?yàn)樗皇寝D(zhuǎn)移的滑動(dòng)摩擦要小得多，即樞軸銷。然而，在某些情況下，有可能要使用一個(gè)球或滾子的比賽，對(duì)于這一點(diǎn)，無論如何，具有分布和均衡的磨損表面的優(yōu)點(diǎn)。 </p><p>　　切線凸輪已經(jīng)使用于高性能型發(fā)動(dòng)機(jī)的成功，在一定程度上，同一時(shí)間流

57、行的賽車摩托車發(fā)動(dòng)機(jī)，與一些形狀往往是“設(shè)計(jì)”所具有的援助略有修改，但通常調(diào)諧器，碳化硅流失了！然而，他們更常見的應(yīng)用一直在天然氣和石油的發(fā)動(dòng)機(jī)速度相對(duì)緩慢，他們?cè)谀睦锕ぷ鹘佑|良好，附著在滾筒的兩端閥門搖動(dòng)運(yùn)行引擎。凸齒面凸輪廣泛應(yīng)用于汽車及其他大眾生產(chǎn)的發(fā)動(dòng)機(jī)。在這方面的一個(gè)重要優(yōu)勢(shì)是，它們適合于制造一個(gè)復(fù)制過程中形成的準(zhǔn)確數(shù)量從主凸輪。在這頂帽子的挺桿可以使用的事實(shí)也有利于批量生產(chǎn)，他們可以設(shè)計(jì)相當(dāng)默默工作。該側(cè)面輪廓可以繪制，使在

58、凸輪加速度變化是避免突變，更重要的是，推桿將不能出現(xiàn)任何反彈或漂浮，在相當(dāng)高的速度出現(xiàn)回復(fù)運(yùn)動(dòng)。在這種情況下，可能有必要引入一個(gè)小規(guī)模的復(fù)合曲線，但凸輪與兩翼圓弧會(huì)作出合理有效的結(jié)合，并且在任何規(guī)模很容易的產(chǎn)生凹陷。兩側(cè)凸輪的例子現(xiàn)在是比較少看到的，雖然他們已經(jīng)在過去廣泛地使用，獲取最快速的開啟和關(guān)閉的閥門的方法。理論上，他們可以被用來產(chǎn)生永久的加速，但在實(shí)踐中非常高的速度和激烈的攻角時(shí)，閥門控制產(chǎn)生的側(cè)壓力使沉重挺桿困難。凹側(cè)面必須始

59、終比從動(dòng)件半徑更大，或者一個(gè)平面從動(dòng)件切線凸輪產(chǎn)生左右運(yùn)</p><p>　　對(duì)凸輪的三種類型，A，B和C都具有相同的舉升和角度區(qū)間，B葉包圍面積最小，乍一看，它是可能出現(xiàn)的，它在產(chǎn)生足夠的閥門打開效率最低或平均升力面積，但是由于有挺桿的使用，其舉升特性并不十分明顯，不同于基圓的切線凸輪的挺桿，并不見得遜色于凹凸輪的側(cè)面。 </p><p><b>　　非對(duì)稱凸輪 </b&

60、gt;</p><p>　　這是一種不常見的凸輪，利用不同的輪廓在凸輪兩側(cè)產(chǎn)生某種特定結(jié)果，這種考慮，設(shè)計(jì)者是可取的。在某些情況下，該對(duì)象產(chǎn)生迅速開放和逐步縮小現(xiàn)象，但有時(shí)相反的效果卻為最佳。然而，當(dāng)所有的因素都考慮在內(nèi)，大多數(shù)試圖與運(yùn)動(dòng)有關(guān)凸輪形式會(huì)引起并發(fā)癥，實(shí)際上可能失敗，至少在非常高的速度。</p><p>　　在很多引擎中，特別是摩托車，凸輪通過杠桿或在一個(gè)搖滾的操作，用一條直線

61、代替圓弧運(yùn)動(dòng)，如正統(tǒng)汽車挺桿。這可能是改善機(jī)械效率，但它修改了凸輪的升降特征，當(dāng)在某點(diǎn)上，后者傳遞運(yùn)動(dòng)給從動(dòng)件和杠桿臂的半徑有關(guān)，（圖3）不同的凸輪升程的特性。隨著凸輪順時(shí)針方向旋轉(zhuǎn)，杠桿的有效長(zhǎng)度將會(huì)更大。</p><p>　　A位置開啟和B位置關(guān)閉閥門，用X和Y的尺寸來表示。與使用非對(duì)稱凸輪是相對(duì)等的，如這個(gè)例子所示，會(huì)產(chǎn)生緩慢開啟和迅速關(guān)閉的閥門的情況，或者相反，如果不論是凸輪的旋轉(zhuǎn)方向，或相同于“手”的杠

62、桿的方向?qū)?huì)產(chǎn)生相反的效果。桿越短，運(yùn)動(dòng)速率的差異就越大，無論是凸輪機(jī)構(gòu)的形式還是非對(duì)稱凸輪樞軸桿不好的設(shè)計(jì)，但我一直在努力避免在我所設(shè)計(jì)的引擎產(chǎn)生這種情況，因?yàn)樗麄兪且粋€(gè)非常復(fù)雜的問題，并保持相對(duì)簡(jiǎn)單的凸輪和直線挺桿因素，人們可以放心，不會(huì)有太多的障礙。</p><p>　　對(duì)于具有圓弧面的凸輪的運(yùn)用，使沒有詳細(xì)說明的情況下，車床生產(chǎn)它們的手段和方法，更重要的是，用正確的關(guān)系來生產(chǎn)多汽缸引擎的關(guān)系具有同樣簡(jiǎn)單的

63、方式。這些方法已使許多發(fā)動(dòng)機(jī)構(gòu)造（不含以前的一些經(jīng)驗(yàn)）成功地解決一個(gè)疑問，至少可以這樣說。</p><p>　　很多設(shè)計(jì)師都試圖改善凸輪的設(shè)計(jì)，以最大時(shí)間來提高閥門的工作效率。換句話說，使得耳垂超過一定在其升力中心的角距離凸輪軸同心的頂部。但是要做到這一點(diǎn)，有必要作出過度陡峭的側(cè)面，從而產(chǎn)生大量的挺桿側(cè)向推力，在高轉(zhuǎn)速時(shí)，使控制更加困難。 </p><p>　　然而幾乎沒有考慮，同樣的結(jié)果

64、表明，這種方法是可以實(shí)現(xiàn)的，出現(xiàn)很少的機(jī)械問題，解除閥也更容易效率也更高，如B所示。這避免了推桿突然加速和減速，并促進(jìn)流動(dòng)閥門的工作效率。兩個(gè)凸輪的陰影部分顯示了葉面積的差異，顯示出真正的高效性。只有在不進(jìn)行額外的控制時(shí)，氣門的高效升程是非常理想的，閥門的最大開口區(qū)，等于閥座直徑的四分之一，但是由于對(duì)閥頭莫名其妙的影響，如果它是可行的，較高的升程流動(dòng)效率將會(huì)更好。 </p><p>　　大口徑閥門能夠很明顯釋放和