发动机冷却系统外文翻译.doc

无锡职业技术学院毕业设计说明书(论文)英文翻译：原文：The Cooling System The engine cooling system actually is a temperature regulation system to protect engine from self-destruction. About one-third of the heat produced in the engine is converted into power, another third goes out through the exhaust pipe un-used, and the remaining third must be carried away by the cooling system (Some is utilized for heating the passenger compartment). To keep the engine temperature in balance is quite essential for an engine to produce power. If the engine runs too hot, it may suffer from pre-ignition since the air-fuel charge is ignited prematurely from excessive combustion chamber temperature. The viscosity of the oil is reduced. Hot oil also forms varnish and carbon deposits may be drawn into the combustion chamber where it may increase HC emissions. The behavior of the metals at excessively high tem perature also differs from that at normal temperature. Those cause poor performance and premature wear, and may even result in engine damage. If the engine runs too cold, the fuel will not vaporize properly. If the liquid fuel reaches the cylinders, it will reduce lubrication by washing the oil from the cylinder walls and diluting the engine oil. That causes a loss of performance, an increase in HC emissions, and premature wear. For these reasons, a cooling system of some kind is necessary in any internal combustion engine. There are two types of cooling systems found on motor vehicles: liquid cooled and air cooled .Air cooled engines are found on a few older cars, like the original Volkswagen Beetle, the Chevrolet Corsair and a few others. Many modern motorcycles still use air cooling, but for the most part, automobiles and trucks use liquid cooled systems and that is what this article will concentrate on. Components of a liquid cooling system include the radiator, radiator cooling fans and fan drive belt, pressure cap & reserve tank, water pump, thermostat, bypass system, freeze plugs, head gaskets & intake manifold gaskets, heater core and hoses. In detail, the cooling system is made up of the passages ( water jacket) inside the engine block and heads, a water pump to circulate the coolant, a thermostat to control the temperature of the coolant, a radiator to cool the coolant, a radiator cap to control the pressure in the system, and some plumbing consisting of interconnecting hoses to transfer the coolant from the engine to radiator and also to the cars heater system where hot coolant is used to warm up the vehicles interior on a cold day. A liquid cooling system works by sending a liquid coolant through passages in the engine block and heads. As the coolant (low freezing liquid called antifreeze) flows through these passages, it picks up heat from the engine. The heated fluid then makes its way through a rubber hose to the radiator in the front of the car. As it flows through the thin tubes in the radiator, the hot liquid is cooled by the air stream entering the engine compartment from the grill in front of the car. Once the fluid is cooled, it returns to the engine to absorb more heat. The water pump has the job of keeping the fluid moving through this system of plumbing and hidden passages. A thermostat is placed between the engine and the radiator to make sure that the coolant stays above a certain preset temperature. If the coolant temperature falls below this temperature, the thermostat blocks the coolant flow to the radiator, forcing the fluid instead through a bypass directly back to the engine. The coolant will continue to circulate like this until it reaches the design temperature, at which point, the thermostat will open a valve and allow the coolant back through the radiator. When the coolant temperature in the system reaches 90C, the thermostat valve open fully, its slanted edge shutting off the shorter circuit (little circulation)so that the coolant circulates through the longer one (full circulation): water pump-cooling jacket-thermostat-radiator top tank-radiator core-bottom tank-pump. In order to prevent the coolant from boiling, the cooling system is designed to be pressurized. Under pressure, the boiling point of the coolant is raised considerably. However, too much pressure will cause hoses and other parts to burst, so a system is needed to relieve pressure if it exceeds a certain point. The job of maintaining the pressure in the cooling system belongs to the radiator cap. The cap is designed to release pressure if it reaches the specified upper limit that the system was designed to handle. Water pumps have many designs, but most are the centrifugal type. They consist of a rotating fan, or impeller, and seldom are of the positive displacement type that uses gear or plungers. Many water pumps have a spring-loaded seal to avoid leakage of water around the pump shaft. SomeV-type engines have a pump on each cylinder block. Radiator is a device designed to dissipate the heat, which the coolant has absorbed from the engine; 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. 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 comb type. For a late-model engine, the cooling system must maintain a temperature that is high enough for efficient combustion but not so high that the engine will be damaged. These requirements are very critical for an engine with electronic controls that must maintain precise air-fuel ratios for fuel econo-my and emission control.Transmission oil coolerAutomatic transmission oil is cooled by a small, separate radiator, usually located in the lower tank or alongside the main radiator. While the only purpose of the engine coolant is to keep the block and upper engine components cool, the transmission oil has three functions. It hydraulicallyoperates the transmission, lubricates the transmission internal and also keeps the transmission within proper operating temperature range. Most vehicles can benefit from the installation of transmission oil cooler, especially if the vehicle is used to pull a trailer or for some other kind of heavy service. Engine oil coolerSome vehicles, particularly high performance or diesel engines, are equipped with engine oil cooler. The oil cooler can be located in one of the radiator tanks (similar to the transmission oil cooler), or mounted separately, near the front of the engine, on aftermarket applications. Also there is usually an adapter mounted between the engine block and the oil filter. If the cooler is mounted in a radiator tank, heat is dispersed from the oil to the coolant. A separate oil cooler usually looks like a small radiator and heat is dispersed from the tubes and fins in the cooler to the air passing through the cooler. The purpose of the cooler is to reduce the temperature of the oil, preventing oxidation and increasing the oils lubricating and protecting properties.译文：冷却系统 发动机冷却系统实际上是一个温度调节系统，以保护发动机不会因为过热损坏。发动机产生的热量大约有三分之一转化成动力，另外三分之一没有使用，通过排气管散发出去，其余的三分之一由冷却系统带走(有些用来加热车厢内部)。保持发动机的温度平衡对发动机产生动力是很有必要的。如果发动机运行过热，过高的燃烧室温度会过早点燃混合气而导致提前点火；机油会粘度下降，热机油也会形成机油氧化膜和燃烧室积炭，这可能增加HC排放；温度过高时金属的性能也与常温时有所不同，这会导致性能下降和过早磨损，甚至可能导致发动机损坏。如果发动机运行温度过低，燃料汽化效果不好。如果液态燃料进入气缸，它将冲刷气缸壁上的机油，稀释机油而降低润滑效果。这也将导致发动机性能下降、HC排放的增加、发动机过早磨损。基于此，内燃机必须有某种形式的冷却系统。 在机动车上有两种类型的冷却系统，液冷和风冷。一些较大的汽车上装用风冷，如原来的大众甲壳虫、雪佛兰考威尔和一些其他车。许多现代摩托车仍然使用风冷，但在大多数情况下，汽车和货车使用液冷系统，这是本文将集中讨论的。 液冷系统的组成部分包括散热器、散热器冷却风扇和风扇传动带、压力盖(散热器盖)、水泵、恒温器、旁路系统、防冻塞、缸盖垫片和进气歧管垫片、加热器芯和软管。具体而言，冷却系统组成包括在发动机缸体和缸盖里的管道(水套)、使冷却液循环的水泵、控制冷却液温度的恒温器、使冷却液冷却的散热器、控制冷却系统压力的散热器盖、一些相互连接的软管组成的管道装置，用来将发动机里冷却液的热传送到散热器，也传送给汽车的加热系统，其中的冷却液用于在冷天加热汽车内部。 液冷系统是通过在发动机缸体和缸盖管道里传送液态冷却液而工作的。当冷却液(低凝点的又称为防冻液)流过这些通道时，它从发动机吸收热量。加热了的冷却液通过橡胶管到达车前散热器。当它流过散热器里的薄壁管时，通过从车前格栅流人的冷空气将热液体冷却。一旦液体冷却，它就会返回发动机，以吸收更多的热量。水泵的任务是保持这些液体流过管道和隐藏的通道系统。 恒温器布置在发动机和散热器之间，以确保冷却液的循环变化设定在某一温度上。如果冷却液温度低于此温度，自动恒温器就会阻断冷却液流向散热器，迫使其绕流，经旁通道而直接回到发动机。冷却液将继续这样流动，直至达到设定温度，此时，自动恒温器将打开阀门，让冷却液返回散热器。当系统中冷却液的温度达到90度时，恒温阀