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1、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 re
2、maining 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 ign
3、ited 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 fr
4、om 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
5、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 .
6、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. Com
7、ponents 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
8、 ( 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 t
9、he 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 ant
10、ifreeze) 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 f
11、rom 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 cool
12、ant 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
13、 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 ci
14、rculates 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 consid
15、erably. 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 spec
16、ified 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 le
17、akage 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 i
18、n 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 hig
19、h 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
20、 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 tr
21、ansmission 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, part
22、icularly 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 mo
23、unted 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.
24、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
25、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
26、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。
27、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，恒温阀全部打开，其倾斜的边缘切断较短的路径(小循环)，使冷却液通过较长的路径(大循环)：水泵一冷
28、却水套一恒温器一散热器上部水箱一散热器芯一下部水箱一水泵。 为了防止冷却液沸腾，冷却系统设计成加压的。在压力下，冷却液沸点大大提高。然而，太大的压力会导致软管和其他管路的爆裂，因此如果压力超过某点，则需要一个系统来减轻压力。维持冷却系统压力的工作归属于散热器盖。如果达到系统设计能承载的指定上限，散热器盖就释放压力。 水泵设计有很多种，但多数是离心式的。它们由一个旋转风扇或叶轮组成，很少是齿轮式或活塞容积式的。许多水泵是有一个弹簧加载式密封，以避免在泵轴周围漏水。一些V形发动机在每列气缸有一个水泵。 散热器是为了散发热量的装置，散发冷却液从发动机吸收热。它被制造成在管道或其他通道中装大量水，提供
29、了与大气接触的巨大面积。散热器芯有两个基本类型，管片式(散热片位于水管周围以增加散热面积)和管带式(或称蜂窝式)。 对于新型的发动机，冷却系统必须维持足够有效燃烧的温度，但又不至于高到使发动机受到损害。这些要求对于保证精确空燃比、追求良好燃油经济性和排放控制的电控发动机是非常关键的。 变速器油冷却器 自动变速器油由一个小型、独立的散热器来冷却。它通常位于较低的水箱里或主散热器边上。发动机冷却液的唯一作用是保持缸体和其上的发动机部件冷却，但变速器油具有三种功能：液压操纵变速器，润滑变速器内部，并保持变速器在适当的工作温度范围内。 大多数车辆可受益于变速器油冷却器的安装，特别是如果车辆是用来拉拖车或用于某些重载运输的。 机油冷却器 一些车辆，特别是采用高性能发动机或柴油发动机的车上，均配备机油冷却器。机油冷却器可位于散热器水箱里(类似于变速器油冷却器)，或单独安装在靠近发动机前方的位置。在售后市场也可以单独加装。另外，通常有一个适配器(转接器)，安装在发动机缸体和机油滤清器之间。如果冷却器安装在散热器水箱里，热量是从机油扩散到冷却液里。单独的机油冷却器通常看起来像一个小散热器，热量从散热器里的管道和散热片发散到空气中。冷却器的目的是降低机油的温度，防止氧化，增加机油的润滑和保护性能。6
