spins, causing fluid to be drawn from the center continuously. The inlet to the pump is located near the center so that fluid returning from the radiator hits the pump vanes. The pump vanes fling the fluid to the outside of the pump, where it can enter the engine.
水泵一旦旋转，水泵产生的离心力将冷却液甩向外侧，源不断从中心吸取冷却液。水泵的入水口位于中心周围，这样当冷却液从散热器流回。冷却液冲击水泵叶片。水泵叶片将冷却液甩向水泵外侧，并进入到发动机。
4.4 The water jacket The water jacket is a collection of passages within the block and head. There passages let the coolant circulate around the hot spots (valve seats and guides, cylinder walls, combustion chamber, etc.) in order to cool them off.
水套是发动机壳体和发动机盖内部冷却液通道的集合。这些通道使得冷却液在热点（气门座和导管，气缸壁，燃烧室等）周围流动，从而冷却它们。
Temperature in the combustion chamber of the engine can reach 4500F, so cooling the area around the cylinder is critical. Areas around the exhaust valves are especially crucial, and the almost all of the space inside the cylinder head around the valves that is not needed for structure is filled with coolant. If the engine goes without cooling for very long, it can seize. When this happens, the metal has actually gotten hot enough for the piston to weld itself to the cylinder. This usually means the complete destruction of the engine.
燃烧室的温度可以达到4500F ，气缸周围区域的冷却非常重要，尤其排气门周围的区域是至关重要的。因此， 在满足结构强度的要求下，缸盖内排气门周围几乎所有的空间都充满了冷却液。如果发动机没有长时间冷却，发动机就会损坏，此时，金属的温度已经可以使得活塞与气缸焊接在一起。这通常意味着发动机彻底的损坏。
One interesting way to reduce the demands on the cooling system is to reduce the amount of heat that is transferred from the combustion chamber to the metal parts of the engine. Some engines do this by coating the inside of the top of the cylinder head with a thin layer of ceramic. Ceramic is a poor conductor of heat, so less heat is conduced through to the metal and more passes out of the exhaust.
一个有趣的减少冷却系统需求的方法是减少燃烧室到发动机金属部件热量的传递。一些发动机通过在发动机盖顶端内侧覆盖上一层薄陶瓷层来实现减少热量的传递。陶瓷导热性很差，这样较少的热量传递到金属，而较多的热量由排放系统带出。
4.3 radiator A radiator is a type of heat exchanger. It is designed to transfer heat from the hot coolant that flows through it to the air blown through it by the fan. 散热器是一种热交换器。它的设计是将流经散热器较热的冷却液的热量传递至由风扇吹过的空气。
Most modern cars use aluminum radiators. These radiators are made by brazing thin aluminum fins to flattened aluminum tubes. The coolant flows from the inlet to the outlet through many tubes mounted in a parallel arrangement. The fins conduct the heat from the tubes and transfer it to the air flowing through the radiator. 大多数现代轿车使用铝散热器。这些散热器由将薄的铝叶片焊接到扁平的铝管上制成。冷却液通过并联布置的铝管从入口流向出口。叶片将热量从铝管导出，并传给流过散热器的空气。 The tubes sometimes have a type of fin inserted into them called turbulator, which increases the turbulence of the fluid flowing through the tubes. If the fluid flowed very smoothly through the tubes, only the fluid actually the tubes would be cooled directly. The amount of heat transferred to the tubes from the fluid running through them depends on the difference in temperature between the tube and the fluid touching it. So if the fluid that is in contact with the tube cools
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down quickly, less heat will be transferred. By creating turbulence inside the tube, all of the fluid mixes together, keeping the temperature of the fluid touching the tubes up so that more heat can be extracted, and all of the fluid inside the tube is used effectively. 有时候铝管插有叫做湍流管的叶片，用来增加管道中冷却液的湍流现象。如果冷却液平滑从管道中流过，实际上只有与管道接触的冷却液能够直接冷却。从管道内流过的冷却液交换到管道的热量取决于管道和与管道接触的冷却液的温度差。因此，如果与管道接触的冷却液迅速冷却，较少的热量被传递。通过制造管道内的湍流，所有的冷却液混合在一起，保持与管道接触的冷却液温度较高，从而更多的热量被传递，有效地利用管道内的所有冷却液。 4.4 pressure cap The radiator cap actually increases the boiling point of your coolant by about 45F. How does this simple cap do this? The same way a pressure cooker increases the boiling temperature of water. The cap is actually a pressure release valve, and on cars it is usually set to 15 psi. The boiling point of water increases when the water is placed under pressure. 散热器盖实际上将冷却液的沸点提高了大约45F。它是如何做到的呢？高压锅使用同样的方法增加水的沸点。压力盖实际上是个压力释放阀。轿车上，它一般被设定为15psi。当水在压力下，水的沸点会提高。
When the fluid in the cooling system heats up, it expands, causing the pressure to build up. The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches 15 psi, the pressure pushes the valve open, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank. This arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled.
当冷却系统的冷却液被加热，冷却液体膨胀，引起压力上升。散热器盖是压力唯一可以逃离的地方，因此散热器盖的弹簧设置决定了冷却系统的最大压力。当压力达到15psi，压力推开阀门，使得冷却液流出冷却系统。冷却液从溢流管流向溢流箱底部。这个设置使得空气排出冷却系统。当散热器冷却下来，冷却系统内形成一个真空，从而将另一个弹簧阀拉开，将之前排到溢流箱底部的冷却液再次吸回到散热器。
4.5 Thermostat Any liquid-cooled car engine has a small device called the thermostat that sits between the engine and the radiator. The thermostat’s main job is to allow the engine to heat up quickly, and then to keep the engine at a constant temperature. It does this by regulating the amount of water that goes through the radiator. At low temperature, the outlet to the radiator is completely blocked – all of the coolant is re-circulated back through the engine. 任何一个液体冷却的轿车发动机都有一个叫做节温器的装置，位于散热器和发动机之间。节温器使得发动机快速升温，然后保持发动机在一个恒定的温度。节温器通过调节流过散热器冷却液的流量实现以上目的。低温下，节温器的出口完全堵塞，所有的冷却液在发动机内部循环。
Once the temperature of the coolant rises to between 180F to 195F, the thermostat starts to open, allowing fluid to flow through the radiator. By the time the coolant reaches 200F to 218F, the thermostat is open all the way.
一旦冷却液温度升到180F与195F之间，节温器开始工作，使得冷却液流向散热器。当冷却液温度位于200F与218F之间，节温器处于全开状态。
The secret of the thermostat lies in the small cylinder located on the engine-side of the device. This cylinder is filled with a wax that begins to melt at around 180F (different thermostats open
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at different temperatures, but 180F is a common one). A rod connected to the valve presses into this wax. When the wax melts, it expands significantly, pushing the rod out of the cylinder and opening the valve. By letting the engine warm up as quickly as possible, the thermostat reduces engine wear, deposits and emissions.
节温器工作的秘密就在节温器发动机侧的一个小圆缸内。这个圆缸充满了蜡，蜡的熔点大约在180F（不同的节温器在不同的温度下开启，但180F是常用值）。一个与阀门联接的连杆推入到蜡里。当蜡开始溶化，蜡会显著膨胀，从而将连杆推出圆缸，并打开阀门。通过让发动机尽可能快升温，节温器减小了发动机损耗，积炭和排放。
4.6 Fan Like the thermostat, the cooling fan has to be controlled so that it allows the engine to maintain a constant temperature.
和节温器一样，冷却风扇也需要进行控制来使得发动机在恒定的温度下运行。
Front-wheel drive cars have electric fans because the engine is usually mounted transversely, meaning the output of the engine points toward the side of the car. The fans are controller either with a thermostatic switch or by the engine computer, and they turn on when the temperature of the coolant goes above a set point. They turn back off when the temperature drops below that point.
前轮驱动式轿车使用电风扇冷却，这是因为前轮驱动式轿车的发动机通常是横向安置。这就意味着发动机的输出正对着轿车的侧面。冷却系统使用温控开关或者发动机计算机来控制风扇。当冷却液温度高于设定点时，打开风扇。一旦温度低于设定点，风扇关闭。
Rear-wheel drive cars with longitudinal engines usually have engine-driven cooling fans. These fans have a thermostatically controlled viscous clutch. This clutch is positioned at the hub of the fan, in the airflow coming through the radiator.
采用发动机纵置的后轮驱动轿车通常采用发动机驱动冷却风扇。这种风扇使用一种温控液体粘性离合器进行控制。这个离合器位于风扇的中心，面向来自散热器的气流。 4 Exercises
1 What is the function of the cooling system?
To remove excess heat from the engine, to keep the engine operating at its most efficient temperature, and to get the engine up to the correct temperature as soon as possible after starting.
2 What are the most common causes of engine overheating?
Fuel burning engines produce enormous amounts of heat. The exhaust system takes away much of the heat, but parts of the engines, such as the cylinder walls, pistons, and cylinder head, absorb large amounts of the heat.
3 Will installing a lower temperature thermostat help the engine run cooler and prevent it from overheating?
No. The thermostat’s main job is to allow the engine to heat up quickly, and then to keep the engine at a constant temperature.
4 Why are liquid-cooling system pressurized? It can increase the boiling point of the coolant.
1The fan’s activity is not always necessary, and it take power from the engine to spin. For this reason a thermostatic control, or fan clutch, is often used to reduce drive torque when it isn’t needed (variable-speed fan).
因为风扇需要从发动机吸取能量来旋转叶片，风扇并不需要持续运转。因此，当不需要风扇运转时，温度控制器或者风扇离合器经常被用来减小转矩（变速风扇）
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2A different type of fan uses centrifugal force to move its flexible plastic blades, by flattening them when the engine rpm is high (flexible-blade fan). The less angle the blade have, the less power they use. The idea of these units is to save horsepower and to reduce the noise the fan makes.
当发动机转速较高时，有一种风扇使用离心力来移动可动的塑料叶片（变叶片风扇）。叶片的迎风角越小，风扇所消耗的功率越小。这些部件的设计是用来减小功率和风扇产生的噪音。 3A fan can have from four to six blades to suck the air through the radiator. Often the radiator has a shroud for the fan to keep it from re-circulating the same hot air that has collected behind the radiator. Many fans have irregularly spaced blades to reduce resonant noise.
风扇拥有4到6个叶片来吸取来自散热器的空气。通常散热器被裹盖，防止风扇将散热器后部聚集的热空气重复循环。许多风扇有着不规则的叶片来减小共振噪音。
4Another function of the expansion tank is to remove air bubbles from the cooling system. Coolant without air-bubbles is much more efficient than coolant with air bubbles, because it absorbs heat much faster. The advantage of the expansion tank is that while the level of coolant contained in it rises and falls, the radiator is always full. 溢流箱的另一个作用是去除来自冷却系统的气泡。没有气泡的冷却液要比含有气泡的冷却液更有效，因为它可以更快地吸收热量。无论溢流箱内的液位上升或下降，散热器总是满的。 Unit 5 Fuel Injection System Fuel injection systems have been used on vehicles for many years. The earliest ones were purely mechanical. As technology advanced, electronic fuel injection systems became more popular. Early mechanical and electronic fuel injection systems did not use feedback controls. As emissions became more of a concern, feedback controls were adapted to both types of fuel injection systems.
燃油喷射系统已经在汽车上运用了许多年。最早期的喷射系统都是机械式的。随着技术的进步，电子燃油喷射系统逐渐得到普及。早期机械式和电子式燃油喷射系统都没有采用反馈控制。由于排放问题越来越得到重视，反馈控制在这两种系统中都得到了应用。
Both mechanical and electronic fuel injection system can be found on gasoline engines. Diesel engines are most commonly found with mechanical type systems, although the newest generation of these engines have been using electronic fuel injection (EFI) 汽油发动机使用机械式或电子式燃油喷射系统。柴油机通常使用机械式燃油喷射系统，但是最新一代的柴油发动机也已经在使用电子式燃油喷射系统了。
5.1 Basic theory EFI uses solenoid valves called injectors to meter fuel delivery. Most vehicles today use 1 injector per cylinder. When the solenoid is energized, fuel sprays out into the valve port. Fuel is delivered to the injector by a high-pressure electric pump at around 40 psi. Fuel delivery is controlled by the injectors which are cycled by the computer. The computer produces a signal to open the injectors for a certain length of time depending on engine conditions relayed by sensors. The longer that the injector is open, the more fuel is injected. As engine load and rpm are increased, the injector open times are increased to match increasing airflow. This computer output signal is called the injector pulse width. The longer the pulse width, the more fuel is injected.
电子式燃油喷射系统使用被称作喷油器的电磁阀来控制喷油量。今天大多数汽车1个气缸使用1个喷油器。电磁阀一上电，燃油就被喷射至电磁阀口。高压电动燃油泵以大约40psi的压力将燃油送到喷油器。喷油量是由喷油器控制的，而喷油器的开启和关闭又是被计算机控制的。计算机根据传感器送来的工况信号，向喷油器发送开启以及开启持续时间的信号。喷
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油器打开时间越长，喷出的燃油越多。随着发动机负载和转速的增加，喷油器打开的时间也 要增加来匹配进气量的增加。计算机输出信号被称作喷油器脉冲宽度。脉冲宽度越大，喷出的燃油越多。
5.2 Engine Requirements Stand spark ignited, 4 stroke engines require that the correct proportion of fuel be mixed with the incoming air for efficient operation. This proportion is in the range of 13 parts air to 1 part fuel for best power, 15 to 1 for best emission and 17 to 1 for best economy. Most modern engines aim for a ratio of around 14.7 to 1 for the majority of cruising and medium power conditions. This is the chemically correct ratio which results in the lowest average emissions and reasonable power. A rich condition is characterized by an excess of fuel, and a lean condition is characterized by an excess of air or lack of fuel.
标准四冲程点火式发动机为了获得高的效率，要求合适的空燃比。为了获得最佳动力性，空燃比是13比1，为了获得最佳排放，空燃比是15比1，为了获得最佳经济性，空燃比是17比1。大多数现代发动机在大多数巡航工况和适中的动力性条件下，空燃比控制目标为14.7比1。这是化学分析上适当的空燃比，可以获得最低的平均排放和适当的动力性。燃烧浓工况意味着燃料过多，稀工况意味着空气过量或燃料不足。
As rpm is increased, up to a point, airflow also increases and fuel flow must increase to match it. As the throttle is opened at a given rpm, airflow increases to a certain point and again, fuel flow must follow airflow.
当发动机转速上升到某一点，空气进气量也随之上升，此时进油量也必须对应随之上升。在某一发动机转速下，当节气门打开，空气进气量上升到某一数值下，同样进油量必须跟随空气进气量。
5.3 fuel system EFI fuel system consists of a tank, pump, fuel rail,, regulator, out an excess of fuel injectors and return line. Fuel is drawn from the tank by the pump which steps up pressure to around to 40 psi. Fuel pressure is controlled by the fuel pressure regulator located on one end of the fuel rail by bleeding fuel back to the tank through the return line. The pump always puts out an excess of fuel so large quantities are returned back to the tank during idle and low speed conditions and less as engine demand increases. The fuel rail is essentially a tubular fuel manifold designed to carry fuel to the injectors as well as hold them in place on the intake manifold. The injectors are usually sealed with O-rings on each end. One end has the fuel entering from the rail and the other end spigots into the manifold. The injector has a 2 pin electrical plug to carry switching current to the solenoid winding. When energized, the solenoid core is pulled back which pulls back a sealing pintle, disc or ball, allowing fuel to spray out in a fine, conical pattern, 电子喷油系统由油箱、油泵、油轨、调节器、喷油嘴和回油管路组成。燃油由油泵从油箱吸出，并被加压到大约40psi。油压通过位于油轨一端的燃油调节器控制。燃油调节器将燃油通过回油管路放回到油箱实现对油压的控制。油泵总是泵出过多的燃油。因此，空转或低速工况下，多余的燃油就返回到邮箱。随着发动机负载的增加，返回邮箱的燃油减小。油轨实际上就是油路歧管，用来将燃油送到喷油嘴，同时把燃油存在进油歧管内。通常使用O型环把喷油嘴的两端密封。喷油嘴一端与油轨相连，另一端与歧管采用连接管接合。喷油嘴有一个两脚电子开关来承载电磁线圈的开关电流。当电磁线圈上电，衔铁吸回，带动密封轴、密封盘或密封球，从而使得燃油细密呈圆锥形喷出。
5.4 Air metering and measurement The amount of air entering the engine is controlled by a conventional butterfly valve on most engines located in a throttle body assembly.
一般大多数发动机使用一个蝶形阀来控制进入到发动机的空气。这个阀位于节气门体总成上。
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