1、 英文翻译 Motor Cars 1. How the Engine Works An engine that converts heat energy into mechanical energy is called a heat engine ,and the car engine is one type of heat engine. It derives heat from the burning or combustion, of a fuel and converts this heat into useful work for driving the car. The fuel
2、used in the vast majority of car engines is petrol, which is one of the many products obtained from crude oil found in the earth. Petrol, when mixed with the right amount of air, will burn when a flame or spark is applied to it. In the car engine, air mixed with petrol is taken into a confined space
3、 and compressed. The mixture is then ignited and it burns. In burning it heats the air, which expands, and the force of expansion is then converted into a rotary movement to drive the wheels of the car. To be able to use this energy effectively we have to control the burning or combustion process an
4、d the force of expansion. Firstly, we need a tube, or cylinder, closed at one end, in which to compress and burn the petrol and air mixture. Then we need a piston which can slide freely in the cylinder, and which can be driven outwards by the force of expansion. To convert the outward movement of th
5、e piston into a rotary movement we must join it by a connecting rods to a crankshaft. We need one passage for the entry of the mixture into the cylinder and another to let out the used gases. To control the entry of the mixture and the exhaust of the gases we need valves, and these are called the in
6、let and exhaust valves. Finally, we need some means of igniting the mixture in the top of the cylinder, the part called the combustion chamber； and for this we use a sparking plug. By timing the opening and closing of the valves and by timing the arrival of the spark we can control the whole sequenc
7、e of events and make the piston move in and out over and over again. THE CYLINDERS Motor-car engines may have four, six, or eight cylinders. Look at figure 1.These cylinders are usually mounted in a cylinder block on top of the engine. Beneath the cylinder block is the crankcase, which contains two
8、shafts, the crankshaft and the camshaft. As you have read, the crankshaft is revolved by the outward movement of the pistons in the cylinders. This rotary movement of the crankshaft transmits the power developed by the engine through the gearbox to the driving wheels and sets the car in motion. When
9、 the crankshaft rotates it also causes the rotation of the camshaft, which lies alongside it in the crankcase. As the camshaft rotates, it pushes up rods alongside each cylinder to open and shut the valves at the top of the cylinder. There are two valves to each cylinder. The inlet valve lets air an
10、d petrol into the combustion chamber of the cylinder when it is opened. When the exhaust valve is opened the gases formed after the combustion in the chamber are allowed to escape . These gases are led away from the car through an exhaust pipe. Let us examine the action of one of the cylinders in mo
11、re detail. Look at figure 2.In (a) the piston is near the top of the cylinder with the inlet valve open and the exhaust valve closed, If the crankshaft is turned, either by hand or by the starter motor ,the piston is drawn down by the connecting rod and a charge of petrol-air mixture rushes in. When
12、 the piston reaches the bottom of its stroke the inlet valve is closed by the action of a spring. This stroke is called the induction stroke. In (b) both valves are closed and the crankshaft forces the piston up to compress the mixture in the top of the cylinder. This, then, is called the compressio
13、n stroke. Towards the end of the compression stroke a spark from the sparking plug causes the mixture to ignite. In (c) we see that the heat of combustion has caused a rapid rise in pressure in the combustion chamber and this has forced the piston down. Through the connecting rod the piston causes t
14、he crankshaft to continue to rotate. This stroke is called the expansion or power stroke, and we can say now that the engine has fired. At the end of this stroke, as the crankshaft rotates, causing the camshaft alongside it to continue to rotate, one of the cams on the camshaft pushes up the rod, wh
15、ich causes the exhaust valve to open, allowing the exhaust gases to escape. In (d) we see the fourth and final stroke, the exhaust stroke. The exhaust valve has been forced open by the rotation of the camshaft, and the crankshaft, continuing to rotate, drives the piston back up the cylinder, forcing
16、 out the exhaust gases. At the end of this stroke the exhaust valve is closed by the action of a spring, and the camshaft, continuing to rotate, pushes up a second rod to force the inlet valve open. Now the cylinder will receive another charge of petrol-air mixture, and the sequence of four strokes,
17、 induction, compression, expansion or power, and exhaust, will start again. Because there is a four-stroke sequence, or cycle, in this type of internal combustion engine it is called a four-stroke engine. There are also two 一 stroke engines used, for example, for motor scooters, and for some motor c
18、ycles. Let us think of a car with four cylinders. Remember that it is only on the expansion stroke that power is transmitted to make the crankshaft rotate. Let us number the cylinders, 1,2,3,4. They may transmit power in this order. 1,2,4,3. This means that when number 1 cylinder is on the expansion
19、 stroke, number 2 is on the compression stroke, number 4 is on the induction stroke, and number 3 cylinder is on the exhaust stroke. The four pistons, moving up and down inside their cylinders in this order, push down rods connected to the crankshaft at different times and at different points along
20、its shaft. This keeps the crankshaft revolving and the crankshaft, when the gears are engaged, keeps the car moving. 2. The Fuel and Ignition Systems The fuel system includes a fuel tank, a fuel pump, and a carburetor. The fuel pump may be operated either mechanically from the engine camshaft or ele
21、ctrically. Its function is to pump petrol from the petrol tank and deliver it to the carburetor. It contains a fine filler to exclude particles of dust or dirt which may have found their way into the tank. The carburetor is mounted on the inlet pipe, or inlet manifold, which leads to the inlet valve
22、s of each cylinder. Its function is to carburet, or mix, the required amounts of petrol and air for combustion in the cylinders. It regulates automatically the proportions of petrol and air and also allows the driver to control the rate of delivery of the mixture, and so vary the speed of the engine
23、. See figure 3. This is a simple type of carburetor. It makes use of a fuel reservoir or float chamber to which petrol is pumped by the petrol pump. The level of the petrol in. the chamber is kept constant by the action of a float which, as it rises with the petrol, closes a needle valve when the co
24、rrect level is reached. The petrol from the float chamber flows to a small jet situated in a narrow tube called the choke tube. When the engine is running, i.e. when the pistons are moving up and down in the cylinders, air is drawn in and passes through the choke tube. Here it mixes with the petrol
25、and passes out into the inlet manifold of the engine. The amount of mixture allowed to pass is controlled by a butterfly valve, or throttle, situated in the carburetor outlet. This valve is operated by the accelerator pedal. An air cleaner may be connected to the air inlet to remove dust from the air and prevent it getting into the
