1、无锡职业技术学院 毕业设计说明书 ( 论文 ) 1 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, a
2、nd 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 char
3、ge 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 d
4、iffers 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 w
5、alls 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
6、 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 concentrat
7、e 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
8、 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 t
9、ransfer the coolant from the engine to radiator and also to the cars heater system 无锡职业技术学院 毕业设计说明书 ( 论文 ) 2 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 cool
10、ant (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 strea
11、m 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
12、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 circu
13、late 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
14、 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 po
15、int 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 rele
16、ase 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 ha
17、ve a spring-loaded seal to avoid leakage of water around the pump shaft. Some V-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 pa
18、ssages, 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 无锡职业技术学院 毕业设计说明书 ( 论文 ) 3 increase the area for radiating the heat) and of the ribbon cellular or honey comb type. For a late-model engi
19、ne, 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 contr
20、ol. Transmission oil cooler Automatic 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 functio
21、ns. It hydraulically operates 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
22、other kind of heavy service. Engine oil cooler Some 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
23、, 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.
