【正文】 ，機油黏度會下降，熱機油也會形成機油氧化膜，燃燒室會形成積碳，增加HC排放。 因此，溫度對于發(fā)動機產生動力來說是至關重要的。燃料在發(fā)動機中燃燒，約三分之一的熱能轉化為動力，還有三分之一的熱能從排氣管排出，剩下的三分之一熱能由冷卻系統(tǒng)來處理。 it is constructed to hold a large amount of water in tubes or other passages which provide a large area in contact with the atmosphere.The radiator usually mainly consists of the radiator core, radiator bottom tank, and radiator top tank. Radiator cores are of two basic types, the fin and tube type (fins are placed around the tube to increase the area for radiating the heat) and of the ribbon cellular or honey b type. The popular fin and tube type of radiator core has the advantage of fewer soldered joints and is therefore a stronger construction. It consists of a series of parallel tubes extending from the upper to the lower tank. The honeyb type core consists of a large number of narrow water passages made by soldering pairs of thin metal ribbons together along their edges. These tubes are separated by fins of metal ribbon, which help dissipate the heat.The radiator cap serves not only to prevent the coolant from splashing out the filler opening, but also to prevent evaporation of the coolant.The fan is designed to draw cooling air through the radiator core. The fan is usually mounted on an extension of the water pump shaft and is driven by a Vbelt from a pulley mounted on the front end of the crankshaft. Usually the same belt drives the alternator, and belt tension is adjusted by swinging the alternator on its mounting.An aircooling system contains a centrifugal fan, thermostat, fan drive belt, radiator fin, baffle plates, air control ring39。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.There are generally two different types of cooling system: watercooling system and aircooling system. Watercooling system is mon. The cooling medium, or coolant, in them is either water or some lowfreezing liquid, called antifreeze. A watercooling system consists of the engine water jacket, thermostat, water pump, radiator, radiator cap, fan, fan drive belt and necessary hoses.A watercooling system means that water is used as a cooling agent to circulate through the engine to absorb the hot and carry it to the radiator for disposal. The engine is cooled mainly through heat transfer and heat dissipation. The heat generated by the mixture burned in engine must be transferred from the iron or aluminum cylinder to the water in the water jacket. The outside of the water jacket dissipates some of the heat to the air surrounding it, but most of the heat is carried by the cooling water to the radiator for dissipation. When the coolant temperature in the system reaches 90 176。當氣門關閉時，氣門彈簧彈力減小，彈性墊圈變形為原來的圓錐狀，支撐于殼體的支撐板，鋼球在回位彈簧作用下回到原來位置。 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。發(fā)動機工作時通過氣門的旋轉可以使氣門獲得更均勻的受熱和磨損?？刹鹦妒綒忾T導管采用鑄鐵或金屬陶瓷材料制成，壓入汽缸蓋上的(氣門導管。 有些發(fā)動機的每個氣門裝有兩根彈簧，可以減小所使用的彈簧大小，增加可靠性，使工作更平穩(wěn)。氣門桿身在鑄鐵或金屬陶瓷氣門導管內運動。進氣門采用鉻鋼，排氣門采用耐熱硅鉻鋼。 為使發(fā)動機更好地換氣，進氣門(頭部)直徑大于排氣門。的錐角。氣門頭部相對于氣門平面之間存在45。為了獲得足夠的充氣面積，有些發(fā)動機采用兩個進氣門和兩個排氣門。%氣門的作用是使空氣燃油混合氣進入汽缸。 發(fā)動機氣門向某一萬向運動時開啟通道，而它向相反方向移動時則關閉此通道。搖臂的一端是經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整螺釘，用來調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。搖臂是鋼制的雙臂杠桿。中空的搖臂軸通過支架固定于汽缸蓋。搖臂由鋼制成，安裝于空心的樞軸。推桿的兩端一頭支撐在挺柱的空腔內，另一頭與搖臂調整螺釘端的球形表面配合。 推桿將挺柱傳來的推力傳給搖臂。發(fā)動機工作時，為使磨損均勻，挺柱總是繞其軸線旋轉。挺柱為圓柱形小筒，里面插入推桿。缸體內主油道的機油在壓力作用下到達凸輪軸軸頸提供潤滑。每個凸輪控制一個氣門:進氣門或排氣門。 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閉。必須使用正時齒輪將曲軸的旋轉傳遞到凸輪軸，驅動噴油泵軸、機油泵和其他的裝置。 配氣機構由正時齒輪、凸輪軸、挺柱、氣門、帶有鎖緊裝置的彈簧和氣門導管組成。 when the valve is closed, the valve spring load decrease, the flexible washer deflects to acquire its initial conical shape and abutting against a shoulder in housing, releases the balls which are then forced by their coil springs to return to their starting position.配氣機構 內燃機的配氣機構保證新鮮混合氣可以適時進入汽缸，同時燃燒后的廢氣及時排出。 or 30176。Valves and Valve TrainThe valve gear of an internal bustion engine provides timely admission of the fresh charge into the cylinders and exhaust of spent gases from them. For this purpose the valves at definite moments open and close the i