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1、1,Motors were formerly divided into two classes: prime movers, which will start on their own once a source of low-grade energy has been supplied, and secondary motors which requires to be started by a prime mover. In this sense a steam engine is a prime mover, but a motor-car engine is not; an elect
2、ric motor is not considered as a prime mover because it requires the prior generation of an electric current by other means. The distinction, however, is not a rigorous one, and the term prime mover is now often loosely use to mean any artificial source of power.,8 Motor,prime movers：原动机(转化自然能使其做功的机
3、器和装置),2,Common usage has also tended to limit the term motor to clockwork, electric, and rocket motors , almost all other forms being described as engines.Most of the traditional kinds of motor apply their energy through rotating parts, and even the jet-engine has rotating components; but solid-fuel
4、 rocket motors and linear electric-motor have no rotating parts. The motors themselves moving as free units under the direct action of the applied forces.,8 Motor,3,Motors providing rotary motion are of two principal kinds：the reciprocating and the turbine. The reciprocating motor is driven by a pis
5、ton moving to-and fro in a cylinder, rotary motion being produced by means of a connecting-rod and a crank. In the turbine a wheel is turned directly and continuously by the action of a stream of high-pressure gas or liquid on vanes set round its periphery. In both types a fuel supplying the initial
6、 energy may be burnt separately, as in steam engines, or in contact with the moving parts of the motor , as in internal combustion engines(内燃机).,8 Motor,4,It is not, however ,necessary to provide either steam or gas to drive either type of motor. In the hot air engine, invented by George Cayley in 1
7、807 and revived in Switzerland in 1947 ,the difference in temperature between hot and cold air is exploited, and in the compressed air motor. Invented before 1799, high-pressure air is used. Though the air has previously to be compressed by some other method and may be stored in steel cylinders.,8 M
8、otor,5,Combustion is word for fire or burning; an internal combustion engine is one in which a fire inside (he engine itself make die engine work- Despite its polluting emissions, this is one of the most significant inventions of all time, especially because of its primary uses as a portable power s
9、ource. The steam engine uses a fire in a boiler rather than inside the engine; for this reason steam engines are sometimes called external combustion engines.,9 Internal combustion engine,6,Experiments with internal combustion go back to the seventeenth century. The first fuel tried was gunpowder wi
10、th a predictably explosive result. Other experiments were made with different kinds of gases including hydrogen which is explosively combustible. It was not until the second half of the nineteenth century that the development of petroleum products made possible todays internal combustion engine. Ker
11、osene for lamps and stoves was the product first sought from petroleum while gasoline seemed nothing more than a dangerous by-product. But after other fuels had been fried it was gasoline dial emerged as the most practical for internal combustion.,9 Internal combustion engine,Gasoline diesel oil Ker
12、osene,汽油 柴油 煤油,7,All reciprocating internal combustion engine need to go through the four processes of intake, compression, expansion and exhaust. The basic difference between two-stroke and four stroke cycle engines is that the two stroke engine accomplishes the four processes in a single revolutio
13、n, or two strokes of the piston. The four stroke engine needs two revolution to complete the cycle.,9 Internal combustion engine,stroke,冲程,8,9 Internal combustion engine,9,The first genuinely marketable internal combustion engine was the work of a German inventor, Nikolaus August Otto. The Olio devi
14、ce was a four- stroke engine in which each piston made four movements (two up and two down) for each combustion in the cylinder using gasoline vaporized and mixed with air in a carburetor. It utilized a cycle in which the combustible mixture is drawn into the cylinder of on internal combustion engin
15、e on a suction stroke, is compressed and ignited by a spark plug on a compression stroke, burns and performs work on an expansion stroke, expels combustion products on a exhaust stroke.,9 Internal combustion engine,10,Since only the third stroke produces work, the piston needs help over the other st
16、rokes. This is given by a flywheel attached to the crankshaft. The flywheel in effect stores energy from the power stroke; this energy then curries the piston through the three strokes until the next power stroke caused by the combustion is repeated.,9 Internal combustion engine,11,Another necessary component of the four stroke engine is a camshaft which controls the cams that open or close valves to let gases in and out of the cylinder. The camshaft makes one revolution for every two of the crankshaft since the valves open only on every other stroke.,
