Oct. 16, 2020
The ignition coil is mainly composed of an iron core, primary and secondary coils, bakelite cover, porcelain cup, etc.
The core is made of laminated silicon steel plates and wrapped in a hard paper sleeve.
A secondary coil is wound on the paper sleeve, and its wire is an enameled wire with a diameter of 0.06 to 0.10 mm, with 11,000 to 23,000 turns.
In order to enhance insulation, the secondary winding is also wrapped with several layers of cable paper. The outside of the primary winding is conducive to heat dissipation. The diameter of the enameled wire is generally 0.5 to 0.8 mm, with 220 to 330 turns, and several layers of insulating cable paper are also wrapped on the outside.
There is also a steel sleeve for magnetic conductivity between the primary coil and the shell. There is an insulating porcelain cup at the bottom of the shell and a bakelite cover on the top. The cover is equipped with a low-voltage connection post for connecting the breaker, a high-voltage line jack, a "switch" connection post, and a "power switch" connection post. There are shaped high edges around the inside of the bakelite cover to ensure the insulation performance of the high voltage joint.
The shell is filled with insulating oil or asphalt to enhance the insulation performance and prevent the intrusion of moisture.
The selection of the ignition coil should be consistent with the polarity of the battery's iron connection, which will help reduce the working voltage of the spark plug and improve the ignition performance.
(1) Normal temperature ignition performance.
Connect the high voltage electricity generated by the secondary coil of the ignition coil to the standard three-needle arrester via the distributor. The ignition coil should emit a continuous non-continuous discharge on the standard three-needle arrester at different speeds of the distributor. The intermittent spark gap should not be less than the specified value.
For example, when the DQ148A ignition coil is combined with a dedicated distributor for testing, its normal temperature characteristics are specified as:
① When the distributor speed is 2500r/min, the continuous uninterrupted spark gap should not be less than 9mm.
②When the speed of the distributor is 2500r/min, and a 1MΩ shunt resistance is connected in parallel between the electrodes of the standard three-needle arrester, the continuous uninterrupted spark gap should not be less than 6mm.
③When the distributor speed is 1500r/min, the continuous uninterrupted spark gap should not be less than 12mm.
(2) The hot ignition performance of the ignition coil.
It includes the following two contents:
① When the temperature of the surrounding medium of the ignition coil is at 70℃ and the specified operating speed of the distributor for 3 hours, the specified continuous and uninterrupted spark gap should be maintained on the standard three-needle arrester during the test. For example, the DQ148A ignition coil works in conjunction with a special distributor at 2250r/min for 3h at the ambient medium temperature of 70℃, and a 9mm continuous spark should be maintained on the standard three-needle arrester during the test.
②After the ignition coil is placed in a constant temperature box at 120℃±50℃ for 1h in different working conditions, the 30s test according to the above method should be able to work reliably, and there should be no insulation overflow after the test.
(3) The cold ignition performance of the ignition coil.
When the ignition coil is placed in a low-temperature box at -40°C in an inoperative state for 3 hours, take it out, and perform a normal temperature ignition performance test within 5 minutes. When the distributor rotates at 2500r/min, the continuous uninterrupted spark should not be less than 9mm.
When testing the performance parameters of the ignition coil, certain test conditions must be provided for it, including ignition power supply voltage, ignition signal, and test load. These test conditions are used to simulate the specific conditions in the actual working process of the car and have actual physical meaning.
Ignition power supply voltage is used to simulate the automotive power supply, including batteries, alternators, and regulators. The two work in parallel, the generator is the main power source, and the battery is the auxiliary power source. The generator is equipped with a regulator, whose main function is to automatically adjust the voltage of the generator to keep it stable when the generator speed increases. Gasoline engines generally use a 12 V electric system. When the engine is started, the battery supplies power to the starter and ignition system; when the engine is idling, the generator supplies power to all electrical equipment except the starter and charges the battery. In the test of the performance parameters of the ignition coil, the power supply voltages provided are 6 V, 14 V, and 20 V, and their physical meanings are as follows.
(1) 6 V is a limited condition, which is suitable for the engine cold-start condition.
When the engine starts, the battery supplies power to the ignition system. On cold days, due to the increase of lubricating oil viscosity, the crankshaft rotation resistance increases, and the electrolyte viscosity of the battery increases at low temperatures, causing the internal resistance to increase, causing the battery terminal voltage to drop, reducing the output power of the starter, and the spark plug jumping The weakening of the fire energy, coupled with the temperature drop of the intake pipe and cylinder, so the fuel vaporization is poor, and the engine is difficult to start.
(2) 14 V applies to the normal working conditions of the engine.
When the engine is idling, the alternator supplies power to the ignition system. When the engine speed and load change in a wide range, the output voltage of the generator can change greatly, so it cannot meet the working requirements of electrical equipment. Based on the above reasons, in order to ensure the normal operation of electrical equipment and prevent the battery from overcharging, the alternator must be equipped with a voltage regulator to keep its output voltage stable. The voltage regulator fixes the output voltage of the alternator near a certain value. For the 12 V system, the voltage value is 13.5~14.8 V.
(3) 20 V is the limit voltage.
The storage battery is equivalent to a large-capacity capacitor. When the generator speed and the electrical load change greatly, it can maintain the relative stability of the automobile grid voltage. Electric equipment, especially electronic components, are not damaged. However, when the regulator is out of regulation or the generator field current is out of control due to faults (such as contact bonding or power transistor breakdown in the electronic regulator), even if the battery is connected, the terminal voltage will rise to more than 17 V. When the battery is disconnected for some reason, the terminal voltage will be even higher and even reach above 80~100 V. This will cause a lot of damage to the entire vehicle's electrical equipment, and the battery will be scrapped prematurely due to overcharging. Therefore, protection devices must be installed to avoid this phenomenon.
The ignition signal is generated by the ignition signal generator when the engine is working, and its frequency and duty cycle can determine the on and off time of the Darlington tube. The conduction time of the Darlington tube determines the current of the primary coil, thereby determining the size of the ignition energy. In order to ensure that the spark plug ignites at the right time, the ignition signal is closely related to information such as the position of the piston in the cylinder and the position of the camshaft. 2.3 Test load. Test load mainly includes standard load (1 MΩ/50 pF parallel load, 100 kΩ/50 pF parallel load, 50 pF capacitive load, etc.) and Zener diode discharge load.
The high-voltage load resistance is set by simulating the pollution of different degrees of carbon deposits and lead deposits of spark plugs in use. When the engine is working, if the lubricating oil is too much, it will cause carbon deposition on the spark plug insulator. The carbon layer is a conductor with a certain resistance, so it is equivalent to connecting a shunt resistor in parallel between the spark plug electrodes to make the secondary circuit form a closed loop. When the Darlington tube is cut off and the secondary voltage increases, leakage current will be generated in the secondary circuit, which consumes part of the electromagnetic energy, thereby reducing the maximum value of the secondary voltage. When the carbon deposit is serious, the maximum value of the secondary voltage will be lower than the spark-over voltage of the spark plug due to serious leakage, forcing the engine to stop working.
The total capacitance of the test load is the total capacitance (including distributed capacitance) of cables and spark plugs used when the ignition system is working on a car engine (in actual use).
When the load is a simulated load, if the ignition energy is constant, for the ignition coil, the higher the maximum secondary voltage, the shorter the spark duration. Therefore, the spark duration measured when the simulated load is used as the test parameter The standard has no practical meaning. Since the maximum value of the secondary voltage of each product is different, the secondary voltage must be clamped to a certain value in order to establish the inspection standard of the product on this parameter to make the measured spark duration comparable.
Therefore, when measuring the spark duration of the ignition coil, the same standard analog load cannot be used as in the conventional secondary voltage measurement, but a dedicated clamp load (Zener diode discharge load) should be used.
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