The bottom-mounted camshaft usually uses a star-shaped gear train (the so-called control wheel), and the roller chain or rack to be attached to the crankshaft. In order to control noise, drive wheels at the camshaft with large diameter are usually made of plastic or light metals, while that of relatively small diameter crankshaft  are mostly made of steel.  
　　Chain connection is also common. This method is available on the bottom and top camshafts. In order to reduce noise (usually the oscillation noise produced by the chain in motion), a hydraulic clamping device and a plastic material guide are usually attached.  
　　One of the most common types of overhead camshaft structures is the connection of a plastic rack chainThe rack chain is located outside the engine oil chamber and is provided with a steel embedded component that helps to tighten through an adjustable roller. 
　　還有一種結(jié)構(gòu)由于動(dòng)力在傳輸過程中損耗過大且過于復(fù)雜，現(xiàn)在已經(jīng)比較少見。這種結(jié)構(gòu)通過一個(gè)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(dòng)方式包括齒輪傳動(dòng)、鏈條傳動(dòng)以及齒形膠帶傳動(dòng)。下置凸輪軸和中置凸輪軸與曲軸之間的傳動(dòng)大多采用圓柱形正時(shí)齒輪傳動(dòng)，一般從曲軸到凸輪軸只需要１對(duì)齒輪傳動(dòng)，如果傳動(dòng)齒輪直徑過大，可以再增加１個(gè)中間惰輪。為了嚙合平穩(wěn)并降低工作噪聲，正時(shí)齒輪大多采用斜齒輪。There is another kind of structure, because the power consumption is too large and complicated in transmission, it is rare now. The structure is connected to an overhead camshaft and a crankshaft by an eccentric link, a star-shaped gear set, or a conical gear set with an intermediate shaft. The common transmission modes between camshaft and crankshaft include gear transmission, chain drive and toothed belt transmission. Most of thetransmission between the lower camshaft and the middle camshaft and the crankshaft are cylindrical timing gears, Generally, only 1 pair of gear is needed to be driven from the crankshaft to the camshaft. If the diameter of transmission gear  is too large, 1 intermediate idler wheels can be added.To achieve smooth engagement and reduce the working noise, the timing gears mostly adopt helical gears. 
　　Chain transmission is common between overhead camshaft and crankshaft, but its reliability and durability are inferior to gear transmission.In recent years,gear rubber belts is widely used in the high speed engine to replace the transmission chain, but chain transmission is still used in some high-power engines.

The gear rubber belts boast the advantages of small noise, reliable operation and low cost. For the DOHC, generally the exhaust camshaft is driven by a crankshaft through a timing gear rubber belts or chain , the air intake camshaft is by driven by exhaust camshaft through a metal chain ,or both the air intake camshaft and exhaust camshaft are driven by the crankshaft through gear rubber belts or chains. When installing the camshaft, be aware that attention should be payed to the timing mark on the camshaft pulley or sprocket. Some engines have no obvious timing marks, maintenance personnel can mark the exact position of the crankshaft and camshaft before removing the camshaft ,and some engines require special tools to adjust the timing.

     The above is the related knowledge about the camshaft  introduced by Anhui Guanshun Camshaft Manufacturing Co, Ltd. And we hope to help.