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单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,*,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,*,Lesson 8 Ignition System,Lesson 8 Ignition System,1,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 the rate of up to several thousand times per minute for each cylinder in the engine.The ignition system sends an extremely high voltage to the spark plug in each cylinder when the piston is at the top of its compression stroke.,The purpose of the ignition sy,2,The tip of each spark plug contains a gap that the voltage must jump across in order to reach ground.The voltage that is available to the spark plug is somewhere between 20,000 volts and 50,000 volts or better.The job of the 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 tip of each spark plug con,3,The ignition system has two tasks to perform.First,it must create a voltage high enough(20,000+)to arc across the gap of a spark plug,thus creating a spark 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 has two ta,4,The ignition system is divided into two sections,the primary circuit and the secondary circuit.The low voltage 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 system is divided,5,The ignition coil is the component that converts the 12 volt signal into the high 20,000+volt 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 ignition coil is the compo,6,Currently,there are three distinct types of ignition systems.The,Mechanical Ignition System,was used prior to 1975.It was mechanical and electrical and used no electronics.By understanding these early systems,it will be easier to understand the new electronic and computer controlled ignition systems,so dont skip over it.,Currently,there are three dis,7,The,Electronic Ignition 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,Distributorless Ignition System,became available in the mid 80s.This system was always computer controlled and contained no moving parts,so reliability was greatly improved.,The Electronic Ignition System,8,1 The Mechanical Ignition System,1 The Mechanical Ignition Syst,9,The distributor is the nerve center of the mechanical ignition system and has two tasks to perform.First,it is responsible for triggering the ignition 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 under).Second,the distributor is responsible for directing that spark to the proper cylinder(which is why it is called a distributor).,The distributor is the nerve c,10,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,you are sending current from the battery through a wire directly to the positive(+)side of the ignition coil.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 circuit that powers the ig,11,The 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 cylinders in the engine)that is mounted on a rotating shaft inside the distributor.This distributor cam rotates in time with the engine,making one complete revolution for every two revolutions of the engine.,The points are made up of a fi,12,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,thereby 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.,As it rotates,the cam pushes,13,The coil wire goes from the coil directly to the center of 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 coil wire and sends it to the other end of the rotor which rotates past each spark plug terminal inside the cap.,The
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