汽车专业英语-课件

1、汽车专业英语-课件There are many different types of ignition systems. Most of these systems can be placed into one of three distinct groups: the conventional breaker point type ignition systems (in use since the early 1, 900s) ; the electronic ignition systems (popular since the mid 70s) ; and the distributo

2、rless ignition system (introduced in the mid 80s) .There are many different typesThe automotive ignition system has two basic functions: it must control the spark and timing of the spark plug firing to match varying engine requirements, and it must increase battery voltage to a point where it will o

3、vercome the resistance offered by the spark plug gap and fire the plug.The automotive ignition systemAn automotive ignition system is divided into two electrical circuitsthe primary and secondary circuits (Figure 7-1) . The primary circuit carries low voltage. This circuit operates only on battery c

4、urrent and is controlled by the breaker points and the ignition switch. 1 . Point -Type Ignition SystemAn automotive ignition system .Figure 7-1 A schematic of a typical conventional breaker-point ignition system.Figure 7-1 A schematic of a The distributor is the controlling element of the system. T

5、he distributor is a stationary housing surrounding a rotating shaft. The shaft is driven at one-half engine speed by the engines camshaft through the distributor drive gears. The cam operates the contact points, which are mounted on a plate within the distributor housingThe distributor is the contro

6、lThe coil (Figure 7-2) is the heart of the ignition system. Essentially, it is nothing more than a transformer which takes the relatively low voltage (12 volts) available from the battery and increases it to a point where it will fire the spark plug as much as 40, 000 volts. It is connected to the h

7、igh-tension connection on top of the coil (the tower into which the coil wire from the distributor is plugged) .The coil (Figure 7-2) is the hFigure 7-2 Cutaway view of a conventional coilFigure 7-2 Cutaway view of a Energizing the coil primary circuit with battery voltage produces current flow thro

8、ugh the primary windings, which induces a very large, intense magnetic field. This magnetic field remains as long as current flows and the points remain closed.As the distributor cam rotates, the points are pushed apart, breaking the primary circuit and stopping the flow of current. Energizing the c

9、oil primary ciThe voltage from the coil secondary windings flows through the coil high-tension lead to the center of the distributor cap, where it is distributed by the rotor to one of the outer terminals in the cap. The voltage from the coil secoThe need for higher mileage, reduced emissions and gr

10、eater reliability has led to the development of the electronic ignition systems. These systems generate a much stronger spark, which is needed to ignite leaner fuel mixtures. Electronic Ignition systems are not as complicated as they may first appear. In fact, they differ only slightly from conventi

11、onal point ignition systems. 2 . Electronic Ignition SystemsThe need for higher mileage, rFigure 7-3 Typical electronic ignition systemLike conventional ignition systems, electronic systems have two circuits: a primary circuit and a secondary circuit (Figure 7-3) . Figure 7-3 Typical electronicElect

12、ronic ignition systems differ from conventional ignition systems in the distributor component area. Instead of a distributor cam, breaker plate, points, and condenser, an electronic ignition system has an armature (called by various names such as a trigger wheel, reluctor, etc.) , a pickup coil (sta

13、tor, sensor, etc.) , and an electronic control module.Electronic ignition systems diThe third type of ignition system is the distributorless ignition system. The spark plugs are fired directly from the coils. The spark timing is controlled by an Ignition Control Unit (ICU) and the Engine Control Uni

14、t (ECU) . The distributorless ignition system may have one coil per cylinder, or one coil for each pair of cylinders.3 . Distributorless Ignition Systems ( DIS) The third type of ignition sysFigure 7-4 Typical distributorless ignition schematicsIn this system, each cylinder is paired with the cylind

15、er opposite it in the firing order (usually 1-4 , 2-3 on 4-cylinder engines or 1-4 , 2-5 , 3-6 on V6 engines , Figure 7-4) . Figure 7-4 Typical distributoThese two plugs are on companion cylinders, cylinders that are at Top Dead Center (TDC) at the same time. But, they are paired opposites, because

16、they are always at opposing ends of the 4-stroke engine cycle.The distributorless ignition system uses either a magnetic crankshaft sensor, camshaft position sensor, or both, to determine crankshaft position and engine speed. These two plugs are on compani.The advantages of no distributor, in theory, are:No timing adjustments;No distributor cap and rotor;No moving parts to wear out;No distributor to accumulate moisture and cause starting problems;No distributor to drive thus providing less engine drag.The advantages