发动机状态监测及故障诊断专家系统翻译.docx

1、发动机状态监测及故障诊断专家系统翻译diesel EnginesInternal combustion gasoline engines run on a mixture of gasoline and air. The ideal mixture is 14.7 parts air to one part of gasoline（by weight.）Since gas weights much more than air, we are talking about a whole lot of air and tiny bit of oil. One part of oil that is

2、 completely vaporized into 14.7 parts of air can produce tremendous power when ignited inside an engine. Lets see how the modern engine uses that energy to make the wheels turn. Air enters the engine through the air cleaner and proceeds to the throttle plate. You control the amount of air that passe

3、s through the throttle plate and into the engine with the gas pedal. It is then distributed through a series of passages called the intake manifold, to each cylinder. At some point after the air cleaner, depending on the engine, fuel is added to the air-stream by either a fuel injection system or, i

4、n older vehicles, by the carburetor.1.Engine typeThe engines can be classified in the following several ways: operating cycle; piston action; piston connection; cylinder arrangement; method of fuel injection, and speed.(1) operating cycle Diesel and gas-burning engines can be divided into two groups

5、 based on the number of piston strokes per cycle, either four or two. An engine which needs four strokes t complete one cycle is four-stroke cycle engine or, for short, a four-cycle engine. If it needs only two strokes to complete a cycle, it is called a two-stroke cycle engine or, for short, a two-

6、cycle engine. Thus, a two-cycle engine fires twice as often as a four-cycle engine.(2) piston action An engines piston action may be classified as single-action, double-action, or opposed-piston.Single-acting engines use only one and end of the cylinder and one face of the piston to develop power. T

7、his working space is at the end away from the crankshaft, that is, at the upper end of a vertical engine. Double-acting engine use both ends of the cylinder and both faces of the piston to develop power on the upstroke as well as on the down stroke. The construction is complicated; therefore, double

8、-acting engines are built only in large and comparatively low-speed units, generally to power motor ships. An opposed-piston engine has cylinders in each of which two pistons travel in opposite directions. The combustion space is in the middle of the cylinder between the pistons. There are two crank

9、shafts; the upper pistons drive one, the lower pistons the other. Note that each piston is single-acting; that is, it develops power with only one face of the piston.(3) piston connection The piston may be connected to the upper end of the connecting rod either directly (trunk piston type), or indir

10、ectly (crosshead type).In trunk-piston engines, a horizontal pin within the piston is encircled by the upper end of the connecting rod. This by far the most common construction. In crosshead-type engines, the piston fastens to a vertical piston rod whose lower end is attached to a sliding member cal

11、led a crosshead, which slides up and down in guides. The crosshead carries a crosshead pin which is encircled by the upper end of the connecting rod. This more complicated construction is required in double-acting engines. It is also used in some large, slow-speed, single-acting engines.(4) cylinder

12、 arrangement The four basic cylinder arrangements of a diesel or gas-burning engine are: cylinder-in-line; V-arrangement; Flat, and radial. A cylinder-in-line arrangement. This is the simplest and most common arrangement, with all cylinders arranged vertically in line. This construction is used for

13、engines having up to 12 cylinders. Engines are also built with horizontal cylinders, usually one or two, in a few cases with three cylinders. If an engine has more than eight cylinders, it becomes difficult to make a sufficiently rigid frame and crankshaft with an in-line arrangement. Also, the engi

14、ne becomes quite long and takes up considerable space. The V-arrangement, with two connecting rods attached to each crankpin, permits reducing the engine length by almost one-half, thus making it much more rigid, with a stiff crankshaft. It also costs less to manufacture and install. This is a commo

15、n arrangement for engines with eight, twelve, and sixteen cylinders. Cylinders lying in one line are called a “bank”, and the angle between the banks may vary, in manufacturing practice, from 30to 120, the most common angles being between 40and 75.(A complete circle is 360)A flat engine is a V-engin

16、e with the angle between the banks increased to 180. This arrangement is used where there is little headroom, as in trucks, buses, and rail cars. Flat engines are also called “opposed-cylinder” engines. In a radial engine all the cylinders are set in a circle and all point toward the center of the c

17、ircle. The connecting rods of all the pistons work on a single crankpin, which rotates around the center of the circle. Such a radial engine occupies little floor space. By attaching the connecting rods to a master disk surrounding the crankpin, as many as twelve cylinders have been made to work on

18、a single crankpin.(5) method of fuel injection Diesel engines are divided into air-injection engines and solid or mechanical injection engines. Air-injection engines use a blast of highly compressed air to blow the fuel into the cylinder. Air injection was commonly use on early diesel engines but wi

19、th the development of solid-injection systems the air-injection engine is rapidly disappearing.(6) speed All diesel and gas-burning engines may be divided into three classes according to speed; low-speed, medium-speed, and high-speed engines. Automotive diesel engines often run faster than 1200 rpm,

20、 but the great majority of other engines run between 350 and 1200 rpm and are termed medium-speed engines.2.How an Engine Works Since the same process occurs in each cylinder, we will take a look at one cylinder to see how the four stroke process works. The four strokes are intake, compression, powe

21、r and exhaust. The piston travels down on the intake stroke, up on the compression stroke, down on the power stroke and up on the exhaust stroke.(1) intake As the piston starts down on the intake stroke, the intake valve opens and the fuel-air mixture is drawn into the cylinder (similar to drawing b

22、ack the plunger on a hypodermic needle to allow fluid to be drawn into the chamber).When the piston reaches the bottom of the intake stroke, the intake valve closes, trapping the air-fuel mixture in the cylinder.(2) compression The piston moves up and compresses the trapped air fuel mixture that was

23、 brought in by the intake stroke. The amount that the mixture is compressed is determined by the compression ratio of the engine. The compression ration on the average engine is in the range of 8:1 to 10:1.This means that when the piston reaches the top of the cylinder, the air-fuel mixture is squee

24、zed to about one tenth of its original volume.(3) power The spark plug fires, igniting the compressed air-fuel mixture which produces a powerful expansion of the vapor. The combustion process pushes the piston down the cylinder with great force turning the crankshaft to provide the power to propel t

25、he vehicle. Each piston fires at a different time, determined by the engine firing order. By the time the crankshaft completes two revolutions, each cylinder in the engine will have gone through one power stroke.(4) exhaust With the piston at the bottom of the cylinder, the exhaust valve opens to al

26、low the burned exhaust gas to be expelled to the exhaust system. Since the cylinder contains so much pressure, when the valve opens, the gas is expelled with a violent force (that is why a vehicle without a muffler sounds so loud.) The piston travels up to the top of the cylinder pushing all the exh

27、aust out before closing the exhaust valve in preparation for starting the four stroke process over again.(5) oiling system Oil is the life-blood of the engine. An engine running without oil will last about as long as a human without blood. Oil pump is mounted at the bottom of the engine in the oil p

28、an and is connected by a gear to either the crankshaft or the camshaft. This way, when the engine is turning, the oil pump is pumping. There is an oil pressure sensor near the oil pump that monitors pressure and sends this information to a warning light or a gauge on the dashboard. When you turn the

29、 ignition key on, but before you start the car, the oil light should light, indicating that there is no oil pressure yet, but also letting you know that the warning system is working. As soon as you start cranking the engine to start it, the light should go out indicating that there is oil pressure.

30、(6) engine cooling Internal combustion engines must maintain a stable operating temperature, not too hot and not too cold. With the massive amounts of heat that is generated from the combustion process, if the engine did not have a method for cooling itself, it would quickly self-destruct. Major eng

31、ine parts can warp causing oil and water leaks and the oil will boil and become useless. While some engines are air-cooled, the vast majority of engines are liquid cooled. The water pump circulates coolant throughout the engine, hitting the hot areas around the cylinders and heads and then sends the

32、 hot coolant to the radiator to be cooled off. 3.Engine Components We have seen how the mixture of air and fuel is delivered by the fuel system to the engine cylinder, where it is compressed, ignited, and burned. We have noted that this combustion produces a high pressure that pushes the piston down

33、 so that the crankshaft is rotated. Now let us examine the various parts of the engine in detail. (1) engine cylinder block The cylinder block of liquid-cooled engines forms the basic framework of the engine. Other parts are attached to the cylinder block or are assembled in it. The block is cast in one piece from gra