linsheng    said: The ignition system is designed to convert the battery voltage to the high voltage required to ignite the air/fuel charge in the cylinder. SAE defines two basic types of ignition systems: Electronic Ignition (EI) and Distributor Ignition (DI). Although both types are electronic types, SAE only assigns the term "electronic ignition" to a no-distributor design. In contrast, Dispenser Ignition (DI) is a term applied to systems that use caps and rotors to provide secondary energy to the spark plug.

　　Ignition system basis

　　The ignition system consists of primary and secondary circuits. The primary circuit is the low voltage part of the system, including the battery, ignition switch, primary coil windings, trigger mechanism and switching device. The trigger mechanism detects the crankshaft position and passes this information directly to the ECM or the ignition control module. Depending on the system, magnetic sensors and magnetoresistors, Hall effect sensors and shutter wheels, or slotted discs and photosensors can be used. The switching device controls the ground side of the primary coil winding based on the crankshaft signal and other sensor inputs (eg, ECT, IAT, etc.). The secondary circuit is the high voltage portion of the ignition system, including the secondary coil windings and spark plugs. The additional secondary components required to distribute the high pressure energy vary depending on the type of system. For example, in conventional dispenser ignition systems, the cover, rotor and high voltage lines are used to transfer coil energy to the plug. However, in a splitterless design, such as coil plugs (COP), caps, rotors and wires are eliminated. When current flows through the primary winding of the ignition coil, it creates a magnetic field around the winding. Once the current is interrupted by the switching device (ie, the ignition control module and/or ECM), the magnetic field collapses and induces voltage into the windings. This "primary voltage" reaches several hundred volts. At the same time, the collapsed magnetic field induces a voltage into the secondary winding. Since the secondary winding is composed of a plurality of thin wires, the "secondary voltage" is measured in units of kilovolts (kV) compared to the several heavy wires used in the primary. Producing enough secondary voltage to trigger the plug ultimately depends on the condition of the primary circuit. This means that there must be a low resistance path from the battery through the dosing ignition switch to the coil and switching device. Excessive voltage drops at any point along the path can cause problems from misfire to no-start conditions.

　　Hall effect sensor

　　Many EI and DI systems use Hall effect sensors to detect crankshaft position. The device has three cables, including external power, signal and ground. The sensor is triggered by a thin metal ring called the shutter wheel. On the DI system, the shutter wheel is splined to the dispenser shaft. On vehicles with EI, it is part of the crankshaft damper. The shutter wheel consists of a series of blades that pass through a narrow area of ​​the sensor. The blade can be thought of as a door, and the space between the blades can be thought of as a window. When the window is inside the Hall effect sensor, the sensor pulls the signal circuit low (near zero volts). When the door is inside the sensor, the sensor is turned off and the signal circuit rises close to the supply voltage. The rotation of the shutter wheel produces a digital (ON / OFF) signal, and the ECM is used to adjust the coil stay and spark timing.

　　Permanent magnet (PM) sensor

　　The PM sensor consists of a soft iron core surrounded by a thin coil. Unlike Hall effect devices, PM sensors generate their own voltages based on their proximity to the rotating wheel (reluctance). Depending on the engine, the magnetoresistor can be mounted at the end of the crankshaft or as part of the crankshaft. As the magnetoresistor rotates past the sensor, it changes the density of the magnetic field radiated from the sensor tip. This results in an AC (alternating current) voltage that varies in proportion to the engine speed. Since the ECM is a digital computer, the AC signal must be adjusted before it can be used for rpm calculations. This is done by an analog to digital converter located inside the ECM.

　　Although not as popular as Hall effect or permanent magnet sensors, optical triggering is another technique used in some ignition systems. With this method, the slotted disk rotates between a pair of light emitting diodes (LEOs) and phototransistors. Depending on the application, the outer diameter of the disc may contain 360 slots, each slot corresponding to a crankshaft rotation, or 350 1 degree slots and a 10 degree synchronization slot. These slots provide high resolution signals to the ECM for precise fuel and spark timing control. The interior of the disc contains a slot for each engine cylinder that provides a low resolution (piston position) signal. On the system in which the synchronization groove is used on the outer diameter of the disk, the inner groove has the same size. However, on systems with 360 degree 1 degree slots near the edge of the disc, the inner slots are asymmetrical to provide cylinder identification. Optical sensors are typically powered by battery voltage, while phototransistors control two 5 volt signal circuits from the ECM. When the slot passes between the LEO and the phototransistor, the beams from the LEO are alternately interrupted. When the light beam from the LED illuminates the phototransistor, the transistor is turned on. This causes the 5 volt signal to be pulled low. When the beam is blocked by the rotating disk, the transistor is turned off, which causes the signal voltage to go high (5 volts).

　　Waste flame ignition

　　Waste spark ignition is a dispenserless system that uses a separate coil to ignite a pair of spark plugs. The coils and plugs are grouped according to the "concomitant cylinders", which is the term applied to cylinders where the piston is at the top dead center. For example, in a typical V6, cylinders 1 / 4, 2 / 5 and 3/6 are companions. When a piston is at TDC during the compression stroke, the piston accompanying the cylinder is at TDC during the exhaust stroke. The cylinders on the compression stroke are referred to as "event" cylinders, while the cylinders on the exhaust stroke are referred to as "exhaust gas" cylinders. Each coil and its connected wires and spark plugs form a series circuit. When the coil is discharged, current flows through a spark plug (center electrode to ground electrode) in a normal manner. To complete the circuit, the current flows in the opposite direction through the opposite plug (ground electrode to center electrode). Although the plugs are fired simultaneously, most of the available energy is applied to the "event" cylinder. This is because the resistance in the cylinder is small during the exhaust stroke. When the cylinder is reversed, current flows through the spark plug along the same path. However, most of the secondary voltage is applied to the opposing cylinders as it is now in the compression stroke.

　　Direct ignition

　　Direct ignition is a general term used to describe a system that uses a separate coil for each cylinder. On some engines, the coil is mounted on the rocker cover and connected to the spark plug using a short cable. In the Coil-Over-Plug system, the coil is mounted directly on top of the spark plug. This design minimizes the secondary resistance by eliminating the plug wire.

　　Ignition waveform analysis

　　As mentioned earlier, generating sufficient secondary voltage depends on the correct operation of the primary circuit. Since the primary waveform cannot be obtained from the distributorless ignition system and since any problems in the primary coil will occur in the secondary line, analysis of the secondary waveform is sufficient for diagnostic purposes.

　　Shooting section

　　The ignition waveform can be decomposed into three specific regions, including the ignition zone, the intermediate zone, and the dwell zone. The emitting portion begins with a high vertical spike called the "emission line." The emission line occurs at an instant interruption of the primary current (the magnetic field of the coil collapses). The height of the ignition wire (ignition kV) depends on the level of secondary resistance in the circuit. For example, if 12kV is required to overcome all of the resistance in the first cylinder, the coil must generate 12,000 volts to create a spark. However, if the secondary resistance exceeds the maximum output of the coil, the cylinder will misfire. Simply put, the ignition kV is the amount of voltage required to initiate a combustion event. In general, the difference in ignition kV between the lowest and highest cylinders should not exceed 20%. Any ignition voltage outside this range indicates a problem with this particular cylinder. If the ignition kV of all cylinders is too high or too low, look for problems that affect all cylinders, such as open coils (DI systems), or excessive air/fuel ratio imbalances (DI and EI systems). Please note that when analyzing the ignition wire in the waste spark system, you will notice that the ignition voltage changes between half of the cylinders exceeds 20%. This is because the reverse ignition plug requires a larger secondary energy than the positive ignition plug. Therefore, the ignition kV of the negative cylinder is usually 20% higher than that of the positive cylinder. Once the spark begins, the horizontal line will appear approximately three-quarters of the position on the firing line. This is called the spark line. The height on the voltage scale corresponding to the spark line is called the "combustion voltage." The combustion voltage represents the energy required to maintain the flow of current on the plug electrodes. The duration of the spark is called the "burning time" and depends on the amount of secondary resistance and coil reserve. Under normal conditions, a functioning coil can hold current for at least 2 milliseconds, which is critical for good combustion. Please note that the launch kV is inversely proportional to the burn time. This means that any increased kV demand will result in a shorter burn time and vice versa. For example, if an injector leaks, the affected cylinders will run too much. Since the fuel is more conductive than air, the added fuel will lower the secondary resistance. Therefore, the ignition kV will be lower and the burning time will be longer. The opposite happens if the injector is restricted. Lean mixtures will result in increased resistance, resulting in higher kV demand and shorter burn times. High internal resistance, such as lean mixture or excessive EGR, will cause the spark line to tilt upward. This is because these conditions increase the need for combustion voltage. As you can see, observing the spark line can pinpoint the problems that affect each cylinder. If all spark lines look irregular, look for problems that may affect all cylinders as well. For example, if all of the spark lines are tilted up, the increased resistance may be the result of low fuel pressure or excess EGR.

　　Intermediate part

　　When looking at the middle part of the waveform, you should see a series of decreasing oscillations representing the residual coil energy. Although the main circuit is still open during this time, there is not enough energy in the coil to maintain the spark. This residual energy is gradually dissipated between the switching device and the coil. Under normal conditions, there will be three to four coil oscillations after the combustion event. Note, however, that the more voltage is required to start and sustain the spark, the less energy is left after that. Therefore, if the ignition kV or the combustion voltage is too high, the oscillation of the intermediate portion will decrease. If the middle portion shows less than normal coil oscillations and the ignition and spark lines look normal, the coil is likely to be shorted. The less the oscillation, the less residual energy due to the weakening of the magnetic field. The most likely symptom of a coil short circuit is a misfire under load or a hard start cold because the secondary resistance is highest under these conditions.

　　Stay section

　　Once the coil energy is completely exhausted, the dwell portion begins. A sharp downward spike indicates that the switching transistor is turned on to initiate the primary current. The few oscillations seen at the beginning of the dwell period are the result of a phenomenon known as "inductive reactance." In short, this is the normal condition of the coil against sudden changes in current. Therefore, there is a slight delay before the primary current reaches its maximum level. Once the ignition module or ECM determines that the coil is saturated enough, it begins to limit the primary current. This is indicated by the slight hump seen near the end of the dwell period.

https://www.linsheng.com