Automotive engine camshaft Brief introduction The camshaft is a part of the piston engine. Its role is to control the opening and closing operation of the valve. Although the camshaft rotational speed in a four-stroke engine is a half of the crankshaft (the same as the camshaft rotational speed in a two-stroke engine with the crankshaft), but usually it is still very high speed, but also need to withstand the large torque, so the design right demanding camshaft in terms of strength and support material is generally a special cast iron, occasionally using forgings. Valve motion law related to engine power and operation characteristics, the design in the design process of the engine camshaft occupies a very important position. Structure The main body of the camshaft is the same as the one with the cylinder length of the cylindrical rod. The above sets have several cam for driving the valve. One end of the camshaft camshaft bearing support and the other end is connected to the drive wheels. Cam side was egg-shaped. The design aims to ensure the the cylinder sufficient air intake and exhaust, specifically, within the shortest possible time to complete the valve opening and closing movements. In addition, taking into account the durability of the engine and the smoothness of operation, the valve can not be generated due to the deceleration process of opening and closing movements too much too large the impact of serious wear and tear of the valve, otherwise it will cause an increase in noise or other serious consequences. Therefore, the cam and the power of the engine torque output as well as the operation of the ride there is a direct relationship. Generally inline engine, a cam corresponding to a valve V-type engine or horizontal opposed type engine, every two valves share a cam. The rotary engine the valveless with gas engine because of its special structure, does not need to cam Position In the long period of time, the bottom-mounted camshaft in an internal combustion engine is most common. Typically such engines, the valve is located in the top of the engine camshaft machine, i.e., so-called the OHV (Over Head Valve, OHV) engines. Usually camshaft located on the side of the crankcase, through the gas distribution agencies (such as tappet, push rod, rocker, etc.) valve control. Bottom-mounted camshaft general also called side-mounted camshaft. Far distance valve, and each cylinder is usually only two valves in such an engine camshaft, so the speed is usually slower, ride comfort is poor, the output power is also relatively low. However, the engine output torque and low-speed performance of this structure is relatively good, relatively simple structure and easy maintenance. Now most of the production cars engine is equipped with overhead camshaft. The overhead camshafts structure closer to the camshaft valve, to reduce the kinetic energy of the waste caused by the bottom-mounted camshaft due to the larger distance between the camshaft and the valve shuttle. Overhead camshaft of the engine valve opening and closing action is relatively rapid, and hence higher speed, and the smooth running is also better. The engine of the the overhead camshafts structure appeared earlier the SOHC (Single Over Head Cam, overhead single camshaft) engine. This engine is only installed at the top of a camshaft, and therefore generally only two to three valves of each cylinder (the intake air a to two exhaust), the high-speed performance has been limited. Technology updates DOHC (Double Over Head Cam, double overhead camshaft) engine, this engine with a two camshafts per cylinder can be installed four to five valves (intake two to three, Pai gas two), high-speed performance significantly improved, but at the same time the low-speed performance will be affected to some degree, the structure will be complicated and difficult to repair. Classification According to the the camshaft number of how many, can be divided into single overhead camshaft (SOHC) and double overhead camshaft (DOHC), two kinds. The single overhead camshaft camshaft is only one camshaft, double overhead camshaft is two, this is too straightforward explanation. The single overhead camshaft with a camshaft in the cylinder head, direct drive into the exhaust valve, it has a simple structure, suitable for high-speed engine. Generally used in the past side camshaft, the camshaft in the cylinder side, is driven directly by a timing gear. The valve lifter to the rotation of the camshaft is converted into reciprocating motion of the valve must be used to transfer power. Thus, more parts of the reciprocating motion, the inertial mass, is not conducive to high-speed movement of the engine. Moreover, the slender tappet has a certain degree of flexibility, prone to vibration, accelerated component wear, even the valve control is lost. DOHC cylinder head equipped with two camshafts, one is used to drive the intake valve, the other for driving the exhaust valve. Double overhead camshaft camshaft and valve spring design less demanding, especially for the hemispherical combustion chamber of the valve V-shaped configuration, but also facilitate and used in conjunction with four-valve gas distribution agencies. Fault Camshaft common faults including abnormal wear and tear, abnormal wear of the symptoms often first appear before the occurrence of abnormal sound as well as fracture, abnormal sound and fracture. (1) Camshaft almost at the end of the engine lubrication system, lubrication situation is not optimistic. If the oil pump is too long and so insufficient oil pressure or the lubricants Road blockage caused by lubricating oil can not reach the camshaft bearing cap fastening bolts tightening torque caused by excessive oil can not enter the the camshaft gap will causing abnormal wear of the camshaft. (2) the abnormal wear of the camshaft causes the gap increases between the camshaft bearing, the camshaft movement occurs when the axial displacement, resulting in abnormal noise. Abnormal wear will lead to increased gap between the drive cam with hydraulic tappets, cam combined with hydraulic tappets will collide, resulting in abnormal noise. (3) camshaft sometimes fracture and other serious fault, common causes of hydraulic tappet cracked or severely worn, serious poor lubrication the camshaft poor quality and camshaft timing gear rupture. (4) In some cases, the failure of the camshaft is man-made causes, in particular the maintenance of the engine camshaft not correct disassembly. Such as demolition of the camshaft bearing caps with a hammer strength knocking or prying with a screwdriver, or install the bearing cap installed the wrong position does not match the result in the bearing cap and bearing, or bearing cover the fastening bolt tightening torque is too large. Install bearing cap should pay attention to the direction of the arrow and the position number marked on the surface of the bearing cap, and in strict accordance with the provisions of torque using the torque wrench tighten the bearing cap fastening bolts. Refit In order to enhance the power of the engine, some converted stores a modified camshaft engine face lift high angle camshaft (Hi-camshaft CAM) is a common form of modified method. This modification operation is not complicated, but because of the lack of understanding of some modification cam on the camshaft angle and works so that the modified effect is not obvious even lead to the deterioration of the performance of the engine. High angle camshaft relative to ordinary camshaft cam angle of about 240 , high angle camshaft cam angle can often reach over 280 . The large angle of the camshaft can extend the valve open time, increase the valve lift, the intake valve and the exhaust valve open as early and late off, so that more air into the cylinder, in order to improve the engine, the power of the high speed output. Should choose for civilian vehicles, modified cam camshaft angle 278, will be a significant increase in working an angle greater than 278 camshaft valve overlap angle, so that the power of the engine high speed improve a lot, but engine cylinder seal is not good at low speed and cause the idling serious jitter or even turn off, so that the vehicle can not adapt to everyday use, and can only be used for competition purposes. Production technology The camshaft is one of the key parts of the engine, the hardness of the camshaft peach apical and white layer depth is to determine the key technical indicators camshaft life and engine efficiency. , Should be considered to ensure that the cam has a sufficiently high hardness and a fairly deep white layer premise journal does not appear high carbide, so that it has a better cutting performance. Currently, the main method of domestic and foreign production camshaft: steel forging blank by cutting the cam peach tip martensitic layer formed some of the high-frequency quenching process. The end of the 1970s, Germany and France have developed a new camshaft argon arc remelting process； hardened cast iron camshaft otherwise dominated by the United States； chilled cast iron camshaft mainly to Japan and France； well cam parts of the Cr-Mn-Mo alloy coatings casting surface alloying production. 汽車發動機凸輪軸 簡介 凸輪軸是 活塞 發動機里的一個部件。它的作用是控制氣門的開啟和閉合動作。雖然在 四沖程發動機 里凸輪軸的轉速是 曲軸 的一半（在 二沖程發動機 中凸輪軸的轉速與曲軸相同），不過通常它的轉速依然很高，而且需要承受很大的 扭矩 ，因此設計中對凸輪軸在強度和支撐方面的要求很高，其材質一般是特種鑄鐵，偶爾也有采用鍛件的。由于氣門運動規律關系到一臺發動機的動力和運轉特性，因此凸輪軸設計在發動機的設計過程中占據著 十分重要的地位。 構造 凸輪軸的主體是一根與汽缸組長度相同的圓柱形棒體。上面套有若干個 凸輪 ，用于驅動氣門。凸輪軸的一端是 軸承 支撐點，另一端與驅動輪相連接。 凸輪的側面呈雞蛋形。其設計的目的在于保證汽缸充分的進氣和排氣，具體來說就是在盡可能短的時間內完成氣門的開、閉動作。另外考慮到發動機的耐久性和運轉的 平順性，氣門也不能因開閉動作中的加減速過程產生過多過大的沖擊，否則就會造成氣門的嚴重磨損、噪聲增加或是其它嚴重后果。因此，凸輪和發動機的功率、 扭矩 輸出以及運轉的平順性有很直接的關系。 一般來說直列式發動機中，一個凸輪都對應一個氣門， V 型發動機 或水平對置式發動機則是每兩個氣門共享一個凸輪。而 轉子發動機 和無閥配氣發動機由于其特殊的結構，并不需要凸輪。 位置 在以前很長的一段時間里，底置式凸輪軸在 內燃機 中最為常見。通常這樣的發動機中，氣門位于發動 機的頂 部，即所謂的 OHV（ Over Head Valve，頂置氣門）式發動機。此時通常凸輪軸位于 曲軸箱 的側面，通過 配氣機構 （如挺桿、推桿、搖臂等）對氣門進行控制。因此底置式凸輪軸一般也叫側置式凸輪軸。由于在這樣的發動機中凸輪軸距離氣門較遠，而且每個 氣缸 通常只有兩個氣門，因此轉速通常較慢，平順性不佳，輸出功率也比較低。不過這種結構的引擎輸出扭矩和低速性能比較出色，結構也比較簡單，易于維修。 現在大多數量產車的發動機配備的是頂置式凸輪軸。頂置式凸輪軸結構使凸輪軸更加接近氣門，減少了底置式凸輪軸由于凸輪軸和氣門之間較大的距離而造成的往返動能的浪費。頂置式凸輪軸的發動機由于氣門開閉動作比較迅速，因而轉速更高，運行的平穩度也比較好。較早出現的頂置式凸輪軸結構的發動機是 SOHC（ Single Over Head Cam，頂置 單凸輪軸 ）式發動機。這種發動機在頂部只安裝了一根凸輪軸，因此一般每個汽缸只有兩到三個氣門（進氣一到兩個，排氣一個），高速性能受到了限制。而技術更新一些的則是 DOHC 式（ Double Over Head Cam，頂置雙凸輪軸）發動機，這種發動機由于配備了兩根凸輪軸，每個 汽缸 可以安裝四到五 個氣門（進氣二到三個，排氣二個），高速性能得到了顯著的提升，不過與此同時低速性能會受到一定的影響，結構也會變得復雜，不易維修。 分類 按凸輪軸數目的多少，可分為單頂置凸輪軸 (SOHC)和 雙頂置凸輪軸 (DOHC)兩種。單頂置凸輪軸就是 只有一根凸輪軸，雙頂 置凸輪軸就是有兩根，這是太直白的解釋。 單頂置凸輪軸 在氣缸蓋上用一根凸輪軸，直接驅動進、排氣門，它具有結構簡單，適用于 高速發動機 。以往一般采用的側置凸輪軸，即凸輪軸在氣缸側面，由正時齒輪直接驅動。為了把凸輪軸的轉動變換為氣門的往復運動，必須使用氣門挺桿來傳遞動力。這樣，往復運動的零件較多，慣 性質量大，不利于發動機高速運動。而且，細長的挺桿具有一定的彈性，容易引起振動，加速零件磨損，甚至使氣門失去控制。 頂置雙凸輪軸是在缸蓋上裝有兩根凸輪軸，一根用于驅動進氣門，另一根用于驅動排氣門。采用雙頂置凸輪軸對凸輪軸和氣門彈簧的設計要求不高，特別適用于氣門 V 形配置的半球形 燃燒室 ，也便于和四氣門配氣機構配合使用。 傳動 底置式凸輪軸通常采用星形齒輪組（即所謂的 “控制輪 ”），輥子鏈或 齒條 與曲軸相連。為了控制噪聲，直徑較大的凸輪軸端傳動輪通常由塑料或者輕金屬制造，而相對直徑較小的曲軸端傳動輪則大多采用鋼材。 鏈條連接也比較多見。這種方式在底置式和頂置式凸輪軸上都可以看到。為了減小噪聲（一般是鏈條在運動中產生的 “振擺噪聲 ”），通常還會附帶一個液壓壓緊裝 置和塑料材質的導軌。 頂置式凸輪軸結構中比較多見的是用一個塑料齒條鏈連接。這個齒條鏈位于發動機 機油腔外，附帶有鋼質的嵌入部件，通過一個可調的輥子幫助張緊。 還有一種結構由于動力在傳輸過程中損耗過大且過于復雜，現在已經比較少見。這種結構通過一個偏心連桿、星形齒輪組或帶中間軸的錐形齒輪組來連接頂置式凸輪軸與曲軸。 凸輪軸與曲軸之間的常見傳動方式包括齒輪傳動、鏈條傳動以及齒形膠帶傳動。下置凸輪軸和中置凸輪 軸與曲軸之間的傳動大多采用圓柱形正時齒輪傳動，一般從曲軸到凸輪軸只需要1 對齒輪傳動，如果傳動齒輪直徑過大，可以再增加 1 個中間惰輪。為了嚙合平穩并降低工作噪聲，正時齒輪大多采用斜齒輪。 鏈條傳動常見于頂置凸輪軸與曲軸之間，但其工作可靠性和耐久性不如齒輪傳動。近年來在高轉速發動機上廣泛使用齒形膠帶代替傳動鏈條，但在一些大功率發動機上仍然使用鏈條傳動。齒形膠帶具有工作噪聲小、工作可靠以及成本低等特點。對于雙頂置凸輪軸，一般是排氣凸輪軸通過正時齒形膠帶或鏈條由曲軸驅動，進氣凸輪軸通過金屬鏈條由排氣凸輪軸驅動，或 進氣凸輪軸和排氣凸輪軸均由曲軸通過齒形膠帶