【正文】 h and carbon deposits may be drawn into the bustion chamber where it increases HC emission. This also causes poor performance and premature wear, and may even result in engine damage. What39。通常有兩種實現(xiàn)氣門旋轉(zhuǎn)的方式：自由旋轉(zhuǎn)和強制旋轉(zhuǎn)。 氣門導(dǎo)管支撐氣門桿身，對其運動起導(dǎo)向作用，以保證氣門X閉時能準確地與氣門座貼合而不產(chǎn)生偏移。 圓柱氣門桿身的上部有一凹槽用來固定氣門彈簧。通過研磨使氣門平面與氣門座緊密貼合。 氣門由頭部和桿身組成。四行程汽油機或柴油機的每缸一般都裝有進氣門和排氣門。搖臂中部有一帶孔的凸臺，孔內(nèi)壓裝有襯套。搖臂空內(nèi)裝有青銅襯套以減少摩擦。推桿由頂部淬火的鋼柱或由兩端壓入配合的帶球形鋼頭的硬鋁管制成。挺柱材料為鑄鐵或鋼，定位于導(dǎo)管內(nèi)，挺柱導(dǎo)管可以是與缸體一體的或者是可拆卸的。有些汽車發(fā)動機的凸輪軸也與驅(qū)動燃油泵的偏心輪和機油泵的驅(qū)動齒輪做成一體。正時齒輪由鋼制成，采用螺旋狀齒以減少噪聲。為實現(xiàn)這一目的，氣門在一定的時刻打開和關(guān)閉汽缸蓋上的進排氣道，汽缸通過進排氣歧管與進排氣管相溝通。s function is to open the engine valves positively and timely, in a definite sequence, and to control their closing against the return action of the valve springs. The shaft is made integral with its cams and bearing journals. Each cam controls a single valve, either intake or exhaust. In some automobile engines, the camshaft is made integral with fuel pump eccentric wheel and oil pump drive gear. The camshaft bearings are lubricated with oil supplied under pressure from the main gallery in the cylinder block.The tappets serve to transmit the force from the camshaft to the push rods. The tappets are small cylindrical bores receiving the push rods. They are made of cast iron or steel and located in the guides, which may be made integral with the cylinder block or removable as in the engine. When the engines operate, the tappets continuously rotate about their axes for uniform wear. The rotation is ensured by a convex surface of their bottoms and a slanted surface of the cams.The push rods transmits the force from the tappets to the rocker and are made as steel stems with hardened tips or duralumin tubes with spherical steel tips pressfitted at. both ends. The push rod tips bear against the tappet hollow at one end against the spherical surface of rocker adjusting screw at other.The rockers transmit the force from the push rod to the valve. The rockers are made from steel and are installed on a hollow fulcrum. A bronze bush is press fitted into the rocker hole to reduce friction. The hollow fulcrum is supported by standards on the cylinder head. Endplay of the rocker is prevented by a coil rocker arm is a bell crank made of steel. At the middle of the rocker arm, there is a boss with a bore into which is pressed the bushing. A hardened curved pad is provided on the end of the rocker where it contacts the valve stem tip, while a threaded hole is machined in its other end to receive the adjusting screw used to set the valve clearance, the clearance between the rocker contact pad and the valve stem tip, so that the valve will be tightly pressed against its seat when hot. The rocker arm freely oscillates about the rockerarm shaft supported by a series of pedestals or brackets, which are bolted to the top deck of the cylinder head.An engine valve is a device designed to open a passage when moving in one direction and to close it when moving in the opposite direction. Each cylinder of a fourstrokecycle diesel or gasoune engine is monly equipped with an intake valve and an exhaust valve. The purpose of the intake valve is to allow the air fuel mixture or air to enter the cylinder. After the bustion process has been pleted, the burned gases are permitted to escape from the cylinder though the exhaust valve. To obtain sufficient valve area, some automobiles have two intake valves and two exhaust valves.A valve consists of a head and stem. The valve head has a narrow chamfer of 45176。 or 30176。 配氣機構(gòu)由正時齒輪、凸輪軸、挺柱、氣門、帶有鎖緊裝置的彈簧和氣門導(dǎo)管組成。 凸輪軸的功用是按特定的順序準確適時地打開氣門并通過氣門彈簧的回位作用控制氣門的關(guān)閉。缸體內(nèi)主油道的機油在壓力作用下到達凸輪軸軸頸提供潤滑。發(fā)動機工作時，為使磨損均勻，挺柱總是繞其軸線旋轉(zhuǎn)。推桿的兩端一頭支撐在挺柱的空腔內(nèi)，另一頭與搖臂調(diào)整螺釘端的球形表面配合。中空的搖臂軸通過支架固定于汽缸蓋。搖臂的一端是經(jīng)過淬火的圓弧狀長臂，與氣門桿尾端接觸，而車有螺紋孔的另一端安裝有調(diào)整螺釘，用來調(diào)整搖臂與氣門桿尾端之間的氣門間隙，從而保證氣門在受熱后緊緊壓在氣門座上。%氣門的作用是使空氣燃油混合氣進入汽缸。氣門頭部相對于氣門平面之間存在45。 為使發(fā)動機更好地換氣，進氣門(頭部)直徑大于排氣門。氣門桿身在鑄鐵或金屬陶瓷氣門導(dǎo)管內(nèi)運動?？刹鹦妒綒忾T導(dǎo)管采用鑄鐵或金屬陶瓷材料制成，壓入汽缸蓋上的(氣門導(dǎo)管。 當氣門開啟時，彈簧被壓縮，彈力增加，將彈性墊圈壓平，迫使鋼球克服回位彈簧的阻力沿斜坡滾動。s more, the behavior of the metals at excessively high temperature also differs from that at normal temperatures. If the engine runs too cold, the fuel will not vaporize properly. If liquid fuel reaches the cylinders, it will reduce lubrication by washing the oil from the cylinder walls and diluting the engine oil. This causes a loss of performance, an increase in HC emissions, and premature engine wear. For these reasons, a cooling system of some kind is necessary in any internal bustion engine.