冷却系统

1、The temperature is quite essential for an engine to produce power（温度对于发动机来说产生能量来说非常的重要）. No engine can work well without suitable operating temperatures（没有适合的工作温度，发动机是不能工作的）. If the engine temperature is too low, fuel economy will suffer and emissions will rise（经济燃油性将会受到影响而且排放量将会上升）; if the temperature is allowed to get too hot for too long, the engine will destroy itself（如果温度过高太久，发动机将会受损）. For optimum engine operation, the cooling system must regulate the engine temperature within a precise and narrow range, so that it is not too hot and not too cold.,（为了优化发动机的工作状况，冷却系统必须使发动机的温度严格的小范围内，不能使之过冷和过热）

2、As fuel is burned in the engine, about one third of the heat energy in the fuel is converted into power（当燃料在发动机内燃烧的时候，大约有三分之一的热能用来做功）. Another third goes out through the exhaust pipe unused（还有三分之一未被利用经排气管道排出）, and the remaining third must be handled by the cooling system（剩下的三分之一必须经过冷却系统处理掉）. This means that the engine can work effectively only when the heat energy is equally handled so as to keep the engine temperature in balance（这就意味着只有当热能被均衡处理掉以后发动机才可以高效运转，以至于保持发动机温度平衡）.So, a cooling system of some kind is necessary in any internal combustion engine（因此某种冷却系统在任何的内燃机上是必须安装的）.

3、Actually, there are two types of cooling systems used on motor vehicles: water-cooling systems and air-cooling systems. But for the most part, automobiles and trucks use water-cooling systems.实际上,有两种类型的冷却系统用于机动车:水冷系统和风冷系统。但在大多数情况下,汽车和卡车`` ``` 用水冷却系统。

Water-Cooling System（重点介绍）

4、A water-cooling system means that water is used as a cooling agent (冷却剂)to circulate（使循环）through the engine to absorb the heat and carry it to the radiator（散热器）for disposal. The engine is cooled mainly through heat transfer （热传递）and heat dissipation（热消散）. The heat generated（产生）by the mixture（混合物）burned in the engine must be transferred（转移，传递）from the cylinder（气缸）to the water in the water jacket.（水套）The outside of the water jacket dissipates（消散）some of the heat to the air surrounding it, but most of the heat is carried by the cooling water to the radiator（散热器）for dissipation.

5、Coolant （冷却剂）The cooling water used in cooling systems is called coolant. Pure water is no longer employed as coolant; today’s coolant is a mixture of water (drinking quality), antifreeze（防冻剂）(generally ethylene glycol（乙二醇）), and various corrosion inhibitors （缓蚀剂）selected for the specific application（各种缓蚀剂被应用）. An antifreeze（防冻剂）concentration（浓度）of 30%-50% raises the coolant mixture’s boiling point （沸点）to allow operating temperatures

（工作温度）of up to 120℃at a pressure of 1.4 bar in passenger cars （乘用车）.

6、Coolant Flow（冷却液流）Engine coolant is forced from the water pump into the engine block（发动机组）. The coolant flows around the outside of the cylinder to cool the cylinder walls. Coolant continues to flow from the engine block through passages（通路）in the head gaskets into the cylinder head（汽缸盖）. The coolant flow through the cylinder head provides cooling for the valves（阀门）, combustion chambers（燃烧室）, and spark plugs（火花塞）. After flowing through the cylinder head, the coolant flows through the thermostat housing and top radiator hose to the inlet tank. As the coolant flows through the radiator（散热器）, heat is transferred to the air flowing through the radiator. Coolant returns from the outlet tank and lower hose to the water pump.

7、When the coolant is cold, the thermostat is closed and the coolant flows through the intake manifold and heater core. Under this condition there is no coolant flow through the radiator. Once the engine reaches normal operating temperature, the thermostat opens and the coolant begins to flow through the radiator. When the thermostat is open, the coolant continues to flow through the intake manifold passage and the heater core（See Fig. 5-1）

8、Water Pump A water pump is used to circulate the coolant. Coolant passages in the engine are connected to the pump. A drive belt