1、 外文资料翻译 系 别 中德机电学院 专 业 汽车检测与维修技术 班 级 汽修 0902 班 姓 名 XXXXXXXXX 学 号 XXXXXXX 指导教师 XXXXXXXXXX 2012 年 4 月 1 Ignition System The purpose of the ignition system is to create a spark that will ignite the fuel-air mixture in the cylinder of an engine. It must do this at exactly the right instant and do it at
2、the rate of up to several thousand times per minute for each cylinder in the engine. If the timing of that spark is off by a small fraction of a second, the engine will run poorly or not run at all. The ignition system sends an extremely high voltage to the spark plug in each cylinder when the pisto
3、n is at the top of its compression stroke. The tip of each spark plug contains a gap that the voltage must jump across in order to reach ground. That is where the spark occurs. The voltage that is available to the spark plug is somewhere between 20,000 volts and 50,000 volts or better. The job of th
4、e ignition system is to produce that high voltage from a 12 volt source and get it to each cylinder in a specific order, at exactly the right time. The ignition system has two tasks to perform. First, it must create a voltage high enough (20,000+) to across the gap of a spark plug, thus creating a s
5、park strong enough to ignite the air/fuel mixture for combustion. Second, it must control the timing of that the spark so it occurs at the exact right time and send it to the correct cylinder. The ignition system is divided into two sections, the primary circuit and the secondary circuit. The low vo
6、ltage primary circuit operates at battery voltage (12 to 14.5 volts) and is responsible for generating the signal to fire the spark plug at the exact right time and sending that signal to the ignition coil. The ignition coil is the component that converts the 12 volt signal into the high 20,000+ vol
7、t charge. Once the voltage is stepped up, it goes to the secondary circuit which then directs the charge to the correct spark plug at the right time. The Basics Before we begin this discussion, lets talk a bit about electricity in general. I know that this is basic stuff, but there was a time that y
8、ou didnt know about this and there are people who need to know the basics so that they could make sense of what follows. All automobiles work on DC (Direct Current). This means that current move in one direction, form the positive battery terminal to the negative battery terminal. In the case of the
9、 automobile, the negative battery terminal is connected by a heavy cable directly to the body and the engine block of the vehicle. The body and any metal component in contact with it is called the ground. This means that a circuit that needs to send current back to the negative side of the battery c
10、an be connected to any part of the vehicles metal body or the metal engine block. A good example to see how this works is the headlight circuit. The headlight circuit consists of a wire that goes from the positive battery terminal to the headlight switch. Another wire goes from the headlight switch
11、to one of two terminals on the headlight bulb. Finally, a third wire goes from a second terminal on the bulb to the metal body of car. When you switch the headlight on, you are connecting the wire from the battery with the wire to the headlamps allowing battery current to go directly to the headlamp
12、 bulbs. Electricity passes through the filaments inside the bulb, then out the other wire to the metal body. From there, the current goes back to the negative terminal of the battery completing the circuit. Once the current is flowing through this circuit, the filament inside the headlamp gets hot a
13、nd glows brightly. Let there be light. Now, back to the ignition system, the basic principle of the electrical spark ignition system has not changed for over 75 years. What has changed is the method by which the spark is created and how it is distribute. Currently, there are three distinct types of
14、ignition system. The mechanical ignition system 2 was used prior to 1975. It was mechanical and electrical and used no electronics. By understanding these early system, it will be easier to understand the new electronic and computer controlled ignition system, so dont skip over it. The electronic ig
15、nition system started finding its way to production vehicles during the early 70s and became popular when better control and improved reliability became important with the advent of emission controls. Finally, the distributor less ignition system became available in the mid 80s. This system was alwa
16、ys computer controlled and contained no moving parts, so reliability was greatly improved. Most of these systems required no maintenance except replacing the spark plugs at intervals from 60,000 to over 100,000 miles. Lets take a detailed look at each system and see how they work. The Mechanical Ign
17、ition System The distributor is the nerve center of the mechanical ignition system and has two tasks to perform. First, it is responsible for triggering coil to generate a spark at the precise instant that it is required (which varies depending how fast the engine is turning and how much load it is
18、under). Second, the distributor is responsible for directing that spark to the proper cylinder (which is why it is called a distributor). The circuit that powers the ignition system is simple and straight forward. When you insert the key in the ignition switch and turn the key to the Run position, y
19、ou are sending current from the battery through a wire directly to the positive (+) side of the ignition coil. Inside the coil is a series of copper windings that loop around the coil over a hundred times before exiting out the negative (-) side of the coil. From there, a wire takes this current ove
20、r to the distributor and is connected to a special on/off switch, called the points. When the points are closed, this current goes directly to ground. When current flows from the ignition switch, through the windings in the coil, then to ground, it builds a strong magnetic field inside the coil. The
21、 points are made up of a fixed contact point that is fastened to a plate inside the distributor, and a movable contact point mounted on the end of a spring loaded arm. The movable point rides on a 4, 6, or 8 lobe cam (depending on the number of cylinder in the engine) that is mounted on a rotating s
22、haft inside the distributor. This distributor cam rotates in time with the engine, making one complete revolution for every two revolutions of the engine. As it rotates, the cam pushes the points open and closed. Every time the points open, the flow of current is interrupted through the coil, thereb
23、y collapsing the magnetic field and releasing a high voltage surge through the secondary coil windings. This voltage surge goes out the top of the coil and through the high-tension coil wire. Now, we have the voltage necessary to fire the spark plug, but we still have to get it to the correct cylind
24、er. The coil wire goes from the coil directly to the distributor cap. Under the cap is a rotor that is mounted on top of the rotating shaft. The rotor has a metal strip on the top that is in constant contact with the center terminal of the distributor cap. It receives the high voltage surge from the
25、 coil wire and sends it to the other end of the rotor which rotates past each spark plug terminal inside the cap. As the rotor turns on the shaft, it sends the voltage to the correct spark plug wire, which in turn sends it to the spark plug. The voltage enters the spark plug at the terminal at the t
26、op and travels down the core until it reaches the tip. It then jumps across the tip of the spark plug, creating a spark suitable to ignite the fuel-air mixture inside that cylinder. The description I just provided is the simplified version, but should be helpful to visualize the process, but we left out a few things that make up this type of ignition system. For instance, we didnt talk about the condenser that is connected to the point, nor did we talk about the system to advance the timing. Lets take a look at each section and explore it in more detail.
