Ignition test technology in the coldest engine tes

2022-08-15
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Ignition test technology in engine cold test

ignition test of engine is an important part of engine delivery test. Traditional engine test is based on engine hot test, so it is impossible to carry out rapid detection of assembly line, and it will produce a lot of exhaust gas and noise, which will pollute the environment

in this test method, because the servo motor drives the engine to run at a steady speed, the engine itself does not work during the test process, and the engine still operates according to four strokes. In these four processes, there is no combustion because there is no fuel injection, but its ignition process always exists. Through the magnetic field sensor close to four ignition coils on the test bench, the change of magnetic field in the ignition process is induced and the induced waveform is recorded, so the function of rapid detection of engine ignition can be realized. Compared with the hot test, the engine cold test technology has obvious advantages. At present, it has been widely used in 1: the sliding surface between the inlaid steel plate and the lining plate and the dovetail groove surface on the lining plate should be kept clean and widely used in general motors, Volkswagen and other major automobile manufacturers

ignition test principle

at present, most automobile manufacturers have adopted pen ignition coil, and its principle is shown in Figure 1. Figure 1 is the ignition schematic diagram of an eight cylinder engine with pen ignition coil. Its ignition timing signal is given by the crankshaft and camshaft signaling wheels. PCM gives the determined ignition sequence through these signals, and then pressurizes the ignition coil and distributes it to the spark plugs of each cylinder in turn to make it breakdown, so as to achieve the purpose of igniting the oil-gas mixture. Because there is no fuel injection during the cold test, there is no combustion, but its spark plug has been punctured. In the whole ignition process, the ignition coil of the spark plug plays a vital role. Its structure is shown in Figure 2. It is a structure similar to a transformer, with primary and secondary windings. By turning on and off the primary winding, the secondary winding induces instantaneous high voltage to puncture the spark plug

Figure 1 engine ignition principle

Figure 2 ignition coil structure

in the ignition test, the mutual induction between the primary winding and the secondary winding of the ignition coil is used for the test. For the in-line four cylinder engine, there are four independent magnetic induction coils in the test bench, through which the voltage changes of the primary coil in the coil during the ignition process can be induced, and the quality of the engine ignition system can be judged by observing the induced waveform, so the potential problems can be quickly, accurately and simply determined

the whole process of engine ignition cold test is very simple. The engine ECU generates an EST (electric spark timing) signal according to the signal provided by the crankshaft position sensor, which is a signal similar to a pulse sequence. As shown in Figure 3, the time difference between the rising edge and falling edge of the signal is the dwell time it supplies to the primary winding of the ignition coil. The charging time is usually fixed in the whole vehicle, However, in the engine cold test ignition test, this time is adjustable, and the EST signal is generally a voltage signal with a fixed amplitude. In the cold test bench, there will be a voltage adjustable power supply specially used to charge the primary winding of the ignition coil, and its charging time can be controlled by the EST signal. In the whole vehicle, the charging time determined by the EST signal and the charging voltage supplied to the primary winding of the ignition coil are usually fixed, while in the engine cold test bench, these two parameters are adjustable, In the actual test process, the purpose of ignition coil test is achieved by adjusting these two parameters

Figure 3 engine ignition timing signal (EST)

analysis of cold test ignition test waveform

in the actual production process, in order to find more defects in the engine ignition system as soon as possible, two strategies of high-voltage ignition and low-voltage ignition are often used. Its essence is to adjust the charging time and primary coil supply voltage of EST signal. During high-voltage ignition, relatively high EST voltage amplitude and long charging time are often used, Low voltage ignition often adopts lower voltage amplitude and shorter charging time. These two ignition methods can better detect the potential problems in the ignition system of the starter

Figure 4 low voltage ignition test waveform

1 Waveform analysis of low voltage ignition test

low voltage ignition test is a test that uses a value lower than the conventional charging voltage. When the voltage value is too low, the spark plug cannot breakdown. Method 2 of low voltage test Simple structure, small size, low height and light weight is to find a suitable primary coil charging voltage to make the spark plug in a critical breakdown state. At this time, the spark plug does not break down, but when the charging voltage is a little higher, it will lead to breakdown. Figure 4 is a typical low-voltage ignition test waveform. In this test process, the amplitude of EST voltage signal is low, as shown in the low-voltage part waveform in Figure 5. Because the spark plug is not punctured, its waveform enters the attenuation oscillation link after the first peak value until the energy in the ignition coil is exhausted. Low voltage ignition can be used to detect the spark plug gap. When the spark plug gap is small, it is easier to be broken down than the normal gap. The energy accumulated by low voltage ignition can break down the spark plug with relatively small gap, so its ignition waveform will also be significantly different from the normal spark plug gap

Figure 5 low voltage ignition and high voltage ignition primary coil charging voltage waveform

2 Waveform analysis of high voltage ignition test

when the amplitude of the charging voltage signal voltage of the primary coil is relatively high, as shown in the high voltage part in Figure 5, the amplitude and duration of the breakdown voltage will correspondingly increase. When the charging voltage is adjusted to a higher value, the ignition waveform is shown in Figure 6. Figure 6 is a typical high-voltage ignition test waveform. In this test process, the charging voltage of the primary coil is high. Because the 5V voltage amplitude in the whole vehicle can ensure the spark plug breakdown, the spark plug in the ignition line has been completely broken down as long as the voltage is greater than 5V. Due to its high voltage amplitude, its first peak value is relatively high from its waveform, After that, there is a long duration and a small peak pulse will be generated at the end until the energy in the coil is exhausted

Figure 6 high voltage ignition test waveform

when the charging time is the same, the voltage amplitude will directly determine the amount of energy stored in the ignition coil. Therefore, the energy stored in the high voltage ignition is too high, and the waveform induced by the ignition is shown in Figure 6, while the energy stored in the low voltage ignition coil is relatively low, so it cannot break down the normal spark plug, Therefore, the ignition waveform is shown in Figure 4

in the actual test process, the obvious characteristic values such as the initial peak, secondary peak and duration of the waveform displayed in the test will be recorded, and compared with the test records of normal engines. If there is obvious difference, it can be determined that this is an engine with problems in the ignition system. Usually, high-voltage ignition can detect many problems that cannot be found in the hot test of the engine. This test method can detect one or more faults in the ignition system, such as the connection of lines, wide spark plug gap, potential problems in the ignition coil, etc

conclusion

the ignition test in the engine cold test can help the production line find the problems of the ignition circuit as soon as possible, such as too wide or too narrow spark plug gap, the number of turns of the primary and secondary coils in the ignition coil, and the open circuit of the ignition coil, which has higher sensitivity than the engine hot test

at present, the ignition test of the ignition conditioning knob of the engine is a part of the cold test bench. Its low-voltage non breakdown ignition is often set to test at high speed, and the high-voltage breakdown ignition is set to test at low speed. Both of them are some stage of the cold test process. Now many manufacturers set an independent station outside the independent cold test station for ignition test, so that the ignition test can be carried out without dragging the engine, The accuracy and reliability of the test are further improved. In addition to the method of using the magnetic field sensor to induce the ignition waveform mentioned at the beginning of the article, many manufacturers also use direct measurement of the induced voltage of the primary circuit of the ignition coil to obtain the ignition waveform. This method has higher sensitivity, but the basic principles are the same, and it is also widely used at present

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