统的清洁作用，气缸内就会累积过量的积炭。发动机油也有助于吸收振动和减少运动部件产生的噪音。
3.2 Parts of the pressure-lubrication system 3.2.1 oil pan How successful the lubrication system is in performing all these functions depends on a number of factors and conditions. There must be an adequate supply of good-quality lubricant delivered to all moving engine parts under sufficient pressure to provide hydrodynamic lubrication for rotating parts and oil adhesion to surface subject to sliding friction. 一个润滑系统成功实现以上功能取决于许多条件和状态。润滑系统必须要有足够量的高品质润滑油，并在充足的压力下将润滑油提供给发动机所有运动的部件，从而给旋转部件提供液力润滑，并给滑动的表面提供油膜。
The oil pan bolts under the engine block, where it seals off the bottom of engine. Shaped like a trough, this sheet-metal pan serves as the reservoir for about 5 quarts of oil. As oil flows from the engine, it drains downward into the oil pan. The oil pump sucks oil from the top of the oil pan, the oil sump. Many oil pans have baffles, which are thin metal partitions. These keep the oil in the sump when the car corners hard or brakes suddenly. A drain plug at the bottom of the sump allows oil to be drained from the engine. The oil-pan gasket fits between the oil pan and the bottom of the engine block.
油底壳使用螺栓与发动机气缸体连接，并对发动机底部形成密封。油底壳是一个钣金件槽形体，可以储存5夸脱的润滑油。油从发动机流出，并流回到油底壳。机油泵从油底壳上层吸油。许多油底壳有薄金属的挡油板。当车辆急拐弯或者急刹车时，挡油板可以把油保持在油底壳内。油底壳下部有一个放油螺栓，可以把发动机的油排干。油底壳和气缸体之间有油底壳垫圈。
In most engines, the oil circulates in the engine, and then returns to the pan. It stays in the pan until drawn back into the engine by the oil pump. During operation, the sump usually holds 2 to 3 quarts oil. The rest of the oil moves through the passageways of the lubrication system. With the engine off, the pan holds about four quarts of oil. The fifth quart is in the oil filter. Because a pool of oil always rests in the sump, the type of lubrication system is called a wet-sump oiling system. 对于大多数发动机，机油在发动机循环，然后流回到油底壳，并储存在油底壳内，直至被机油泵再次吸回到发动机。在这个循环过程中，油底壳通常储存2-3夸脱油，剩余的油在润滑系统的油管内流动。当发动机停止时，油底壳储存大约4夸脱油，剩余的一夸脱油在机油滤清器内。因为油底壳内总是有机油，这种润滑系统被称作湿式油底壳润滑系统。
A dry-sump oil system is used in many racing engines. This system has a separate storage tank for the oil. A second oil pump draws oil from the oil pan as soon as the oil drains from the engine. As a result, a dry-sump system can circulate more oil through the engine than a wet-sump system. 干式油底壳润滑系统在许多赛车中得到应用。这种系统有一个单独的机油箱。一旦发动机的机油开始循环，一个单独的油泵从油底壳吸油。因此，这个系统能够比湿式油底壳循环更多的油。
3.2.2 oil pump In most cars, the oil pump is in the crankcase above the sump. It draws oil through a tube that extends downward into the sump. This tube, called the oil-pump pickup tube, has a filter screen over its bottom end. The screen keeps large pieces of sludge and dirt from being drawn into the pump. The tube may be hinged on the pump end so that it can move up and down as the oil level changes in the sump. Thus, the pump always draws oil from the top of the sump, not from the bottom where the dirt and sludge tend to settle. Modern cars use one of two common types of oil pump-the gear-type and rotor-type.
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对于大多数汽车，机油泵位于油底壳上部的曲轴箱内。机油泵通过延伸到油底壳的油管吸油。这个油管被称作机油吸油管，在它的末端有一个滤网，可以阻止大块的油泥和污垢吸入到油泵内。油管可以绞接在机油泵底部，这样它就可以随着油底壳内油面的变化上下漂动，从而保证油泵总是从油底壳上部吸油，而不是从油泥和污垢易于沉淀的下部。现代汽车一般使用齿轮式油泵或者转子式油泵。
3.2.3 oil filters A modern engine uses a full-flow filtering system. In this system, the output of the oil pump flows through the oil filter before moving through engine. In other words, the oil is filtered and cleaned before each trip through the engine. When an engine runs at 3,000 rpm, its entire five quarts of oil pass through the filter at least once every minute. Thus the oil filter ensures that only clean oil enters the engine.
现代发动机使用全流式滤清器系统。在这个系统，机油泵输出的机油在流入发动机之前先通过机油滤清器。也就是说，在发动机的每次循环之前机油都进行了滤清。当发动机转速为3000转/分时，油底壳内的全部5夸脱油每分钟都得到一次滤清。这样，机油滤清器就确保进入发动机的机油是干净的。
Modern engines use replaceable oil filters. When dirty, such a screw-on filter is replaced with a new one. Inside the steel outer casing of the unit, a special paper acts as a filter. Folded and tightly packed, this paper has just the right porosity. These tiny holes in the paper allow oil to pass through, but filter out dirt and sludge. The paper is treated to protect it from acid or water in the oil.
现代发动机采用可替换型机油滤清器，滤清器和机体采用螺纹固定。这样，可以拆下脏的滤清器，换上新的滤清器。在滤清器钢外壳的内部是特殊的纸滤芯。纸滤芯具有适当的微孔，被折叠并压紧在滤清器里。这些微孔可以让机油通过，但把油泥和杂质截流在滤芯上。滤纸经过特殊的处理，可以抵御机油里的酸和水（抗腐蚀性和抗湿性）。
Normally, oil enters the oil filter from the outside. Oil enters the filter around the outer edge of the base. The oil flows through the paper to the center of the container. It then flows out to the engine. Most filters also have a pressure-relief valve, or bypass valve. Such a valve allows oil to flow to the engine without going through the filter. This is necessary when the filter becomes too clogged for oil to pass through it. Thus, a plugged filter allows dirty oil to circulate through the engine. To prevent this, the oil and oil filter should be changed regularity.
一般而言，机油从滤清器底部的外边缘流入滤清器，并通过滤纸流入滤清器的中心，然后流进发动机。多数滤清器设置了卸压阀或者旁通阀。这个阀可以使机油不通过滤清器直接流入发动机。当滤清器被严重堵塞以至机油无法通过滤芯时，卸压阀就非常必要。被堵塞的滤清器使得没有滤清的机油在发动机内循环。因此，需要定期更换机油和机油滤清器。
3.3 Engine lubrication An internal combustion engine would not run for even a few minutes if the moving parts were allowed to make metal-to-metal contact. The heat generated due to the tremendous amounts of friction would melt the metals, leading to the destruction of the engine. To prevent this, all moving parts ride on a thin film of oil that is pumped between all the moving parts of the engine. Once between the moving parts ,the oil serves two purposes. One purpose is to lubricate the bearing surfaces. The other purpose is to cool the bearing by absorbing the friction-generated heat. The flow of oil to the moving parts is accomplished by the engine’s internal lubricating system.
如果发动机的运动部件是金属与金属的直接接触，内燃机运行无法超过几分钟。摩擦产生的巨大热量可以熔化金属，从而损坏发动机。因此，发动机所有的运动部件之间都要有一层薄油膜。作用在运动部件之间的机油有两个功用。一个作用是润滑轴承面，另一个作用是吸收
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摩擦产生的热量，冷却轴承。发动机的内润滑系统使得机油流到各个运动部件。
The oil pump is of the gear type, consisting essentially of two gears in mesh and requires no attention or adjustment. It is housed in the sump, being driven by a shaft and skew gearing from the camshaft.
齿轮泵式燃油泵实际上由两个相互啮合的齿轮组成，无需调整。它位于油底壳底部，由来自凸轮轴的一根轴和斜齿轮驱动。
3.4 Lubrication oils Motor oils for automobile engines fall into two basic categories: petroleum-based oils and synthetic oils. Petroleum-based oils, however, contain a variety of additives, so in fact they, too, are partly synthetic. Some of the major additives include those described here.
发动机机油可以分为两类：石油基润滑油和合成润滑油。实际上，石油基润滑油也包含大量的添加剂，因此，部分上它也是合成润滑油。主要使用的添加剂如下所述。
Antiscuff additives help to polish moving parts, including cams, pistons, and cylinder walls. This is particularly important during new engine break-in and after an engine overhaul. Since heat is the prime enemy of antiscuff additives, operating conditions that produce excessively high engine temperatures reduce the life expectancy of these additives. This type of the operation requires more frequent oil changes than does normal operation.
抗磨损添加剂可以抛光运动部件，比如：凸轮、活塞和气缸壁。这对于新发动机磨合和大修后的发动机尤其重要。热量是这种添加剂最大的敌人，使得发动机过热的运行工况就会减小抗磨损添加剂的使用寿命。因此，这种运行工况下要比正常使用要求更加频换的更换机油。 Corrosion inhibitors reduces the formation of harmful acids by attacking the acid-forming ingredients. Combustion produces a number of by-products, including acid and water. Corrosion inhibitors neutralize these combustion by-products before they can do any harm to the engine. A cold engine, rich fuel mixture, a poorly turned engine and much short trip, cold-weather driving increases the amount of acid produced
腐蚀抑制剂可以通过攻击酸形成的成分从而减小有害酸的形成。燃烧会生成大量的副产品，比如：酸和水。腐蚀抑制剂中和这些燃烧副产品，避免其对发动机腐蚀。冷机、成分丰富的可燃混合气、工况较差的发动机以及短途和寒冷天气下的行驰会加剧这些酸的产生。
Detergent-dispersants clean engine parts during operation and keep these contaminants in suspension in the oil. As the oil is forced through the filter, the majority of these contaminants are trapped by the filter.
当发动机运行时，清洁分散剂可以清洁发动机部件，并使得污垢悬浮在油中。当机油通过滤清器，大部分污垢被滤清器过滤掉。
Viscosity index improvers tend to stabilize or improve the viscosity of engine oils at various temperatures. They tend to give the oil more body when the oil is cold. In other words, they improve the body and fluidity of the oil. The ability of the oil to carry a load at high temperature is improved by this additive, and the ability of the oil to flow when cold is also improved 黏度改善剂可以稳定或改善机油在不同温度下的黏度。当机油过冷时，它可以提高机油的流度。也就是它可以改善机油的黏度和流度。高温时，黏度改善剂提高了机油承载的能力，低温时，黏度改善剂提高了机油的流度。
Foam inhibitors reduce the tendency of oil to foam. Heat and agitation mix the the oil with air to create foam. Oil foam reduces the lubrication ability of the oil and causes oil starvation and failure of engine parts. Loss of oil pressure due to foaming increases this problem. 泡沫抑制剂可以阻止机油形成泡沫。热量和搅动使得机油和空气混合形成泡沫。泡沫减少了
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机油的润滑能力，造成了发动机部件表面的供油不足。泡沫形成降低了油压，这也加剧了这个问题。 3 Exercises
1 What is the purpose of automobile lubrication system? Reducing friction to minimize wear and loss of power 3 Explain what the function of oil is.
Form a seal between the pistons, rings, and cylinders. Cool engine parts.
Clean carbon and varnish.
Absorb the shock and dampen the noise.
4 Name at least three common additives used in compounding oils. Antiscuff additives. Corrosion inhibitor. Detergent-dispersant. Foam inhibitor.
Viscosity index improver.
6 Explain how oil reduces friction.
All moving parts ride on a thin film of oil instead of metal-to-metal contact. 7 Define the word viscosity.
The body and fluidity of the oil. 8 What is detergent oil?
Clean engine parts during operation and keep contaminants in suspension in the oil. What is the difference between the full flow filter system and the bypass filter system?
1 The bypass filter system allow oil to circulate through the engine when the filter becomes too clogged for oil to pass through it.
The purpose of the lubrication system is to circulate oil through the engine. Many parts inside the engine, such as the camshaft, crankshaft, connecting rods, and pistons are connected to other metal parts. When parts rub together, friction is created. Friction produce heat. Although two metal surfaces may appear smooth to the naked eye, they may look rough when seen through a microscope.
润滑系统的作用是让润滑油在发动机循环。发动机内部许多部件，如：凸轮轴，曲轴，挺杆和活塞都与其他金属部件相连。当这些部件相互接触，就产生了摩擦。摩擦就会产生热量。肉眼看上去，两个金属的表面非常光滑，但通过显微镜观察，它们实际上非常粗糙。
2 An engine must have a good lubrication system. Without it, the friction heat from the contact of the moving parts would wear the parts and causes loss. Oil, when placed between two moving parts, separates them with a film. This oil film prevents the parts from rubbing against each other. This oil film also cushions the parts, giving quieter and smoother engine operation. 发动机必须要有好的润滑系统。没有润滑系统，运动部件之间摩擦产生的热量会磨损部件和耗费功率。当润滑油位于两个运动部件之间时，就会产生一层油膜来分离这两个部件。油膜可以防止两个部件相互摩擦，还起到类似缓冲垫的作用，可以让发动机安静平稳的工作。 Unit 4 The Cooling System The purpose of the engine’s cooling system is 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. Ideally, the cooling system keeps the engine
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running at its most efficient temperature no matter what the operating conditions are.
发动机冷却系统的作用就是取出发动机多余的热量，保持发动机在最佳效率温度点运行，并在启动发动机后尽可能快使得发动机达到适合的温度。理想状态下，无论什么样的运行状态，冷却系统都可以使得发动机运行在最佳效率温度点。
Fuel burning engines produces enormous amounts of heat, tem perature can reach up to 4000 F when the air-fuel mixture burns. However, normal operating temperature is about 2000F.
发动机要产生大量的热量。当可燃混和气燃烧时，温度可以达到4000F，而发动机的运行温度大约是2000F。
The exhaust system takes away much of the heat, but parts of the engine, such as the cylinder walls, pistons, and cylinder head, absorb large amounts of the heat. If a part of the engine gets too hot, the oil film fails to protect it. This lack of lubrication can ruin the engine
排放系统可以带走大量的热量，但是发动机的一些部件，如：气缸壁，活塞和气缸盖会吸收许多热量。如果发动机的部件过热，油膜就会失去保护作用。而缺乏油膜的润滑就会损坏发动机。
On the other hand, if an engine runs at too low a temperature, it is inefficient, the oil gets dirty (adding wear and subtracting horsepower), deposits form, and fuel mileage is poor- not to mention exhaust emissions! For these reasons, the cooling system is designed to stay out of the action until the engine is warmed up. 另一方面，如果发动机运行在过低的温度下，发动机的效率就会低下，燃油变脏（增加损耗，减少马力），积炭形成，燃油里程数变差，更不要说排放了。正是因为这些原因，冷却系统被设计为并不工作直到发动机变热。
There are two types of cooling systems, liquid cooling and air cooling. Most auto engines are cooled by the liquid type, air cooling is used more frequently for airplanes, motorcycles and lawnmowers.
目前有两种冷却系统：液体冷却系统和空气冷却系统。大多数汽车发动机使用液体冷却系统，空气冷却系统经常在飞机、摩托车和除草机上得到应用。
The cooling system of a water-cooled engine consists of the engine’s water jacket, a thermostat, a water pump, a radiator and radiator cap, a cooling fan (electric or belt-driven), hoses, and usually an expansion (overflow) tank.
水冷式发动机冷却系统由发动机水套、节温器、水泵、散热器、散热器盖、冷却风扇（电或皮带驱动）、水管和溢流槽。
The pump sends the fluid into the engine block, where it makes its way through passages in the engine around the cylinders. Then it returns through the cylinder head of the engine. The thermostat is located where the fluid leaves the engine. The plumbing aro und the thermostat send the fluid back to the pump directly if the thermostat is closed. If it is open, the fluid goes through the radiator first and then back to the pump. 水泵将冷却液泵入发动机壳，然后冷却液沿着发动机内的通道在气缸周围流动，接着通过发动机气缸盖流回到水泵。节温器位于冷却液离开发动机的位置。如果节温器关闭，节温器周围的水管将冷却液直接送回到水泵。如果节温器打开，冷却液先流经散热器，之后再流回到水泵。The water pump is a simple centrifugal pump driven by a belt connected to the crankshaft of the engine. The pump circulates fluid whenever the engine is running. 冷却系统的水泵是简单的离心式水泵，由与发动机曲轴相连的皮带驱动。只要发动机在运转，水泵就要循环冷却液。
4.1 The water pump The water pump uses centrifugal force to send fluid to the outside while it
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