The function and principle of the ignition coil
The ignition coil of a car is a key component in the car ignition system.
The ignition coil of a car is mainly responsible for converting the low voltage (usually 12 volts) provided by the vehicle battery into a high voltage (usually tens of thousands of volts) to generate a spark to ignite the fuel mixture in the engine cylinders. The ignition coil operates based on the principle of electromagnetic induction, converting low-voltage electricity into high-voltage electricity to ensure the normal operation and smooth combustion of the engine . The ignition coil of a car is mainly composed of the ignition coil and the switch device.
The reason why the ignition coil can convert the low-voltage electricity on the vehicle into high voltage is that it has the same form as a common transformer, and the turns ratio of the primary coil to the secondary coil is large. However, the working mode of the ignition coil is different from that of a common transformer. A common transformer operates continuously, while the ignition coil operates intermittently. It repeatedly stores and releases energy at different frequencies according to the different speeds of the engine.
When the primary coil is connected to the power supply, a strong magnetic field is generated around it as the current increases, and the iron core stores the magnetic field energy. When the switch device disconnects the primary coil circuit, the magnetic field of the primary coil rapidly decays, and a very high voltage will be induced in the secondary coil. The faster the magnetic field of the primary coil disappears, the greater the current at the moment of current disconnection, and the larger the turns ratio of the two coils, the higher the voltage induced by the secondary coil.
Ignition coils are classified into two types according to their magnetic circuits: open-magnetic type and closed-magnetic type.
Open-magnetic circuit ignition coil
The open-circuit ignition coil is generally of a can-shaped structure. It is composed of several silicon steel sheets stacked together to form a rod-shaped core, with the secondary coil and the primary coil wound respectively on the outside of the core. The secondary coil has a wire diameter of 0 05 to 1mm enameled wire, with 20,000 to 30,000 turns. The wire diameter of the primary coil is 0. 5 to 1 It is 0mm thick, thicker than the secondary coil, and has only 150 to 300 turns. The primary coil is wound outside the secondary coil, so the change in magnetic flux generated by the secondary coil is exactly the same as that of the primary coil. The winding directions of the primary coil and the secondary coil are the same. The starting end of the secondary coil is connected to the high-voltage output connector, and its end is connected to the starting end of the primary coil and to the "+" terminal of the housing. The end of the primary coil is connected to the "I" terminal of the housing and to the collector of the power transistor inside the igniter. The igniter controls the on-off of the current in the primary coil.
Closed-magnetic circuit ignition coil
The core of a closed magnetic circuit ignition coil is enclosed, and all magnetic flux passes through the interior of the core. The magnetic permeability of the core is approximately ten thousand times that of air. Therefore, if an open magnetic circuit ignition coil is to achieve the same magnetic flux as a closed magnetic circuit ignition coil, its primary coil must have a relatively large magnetic emf (ampere-turns). Therefore, primary coils with more turns and larger wire diameters must be adopted. The number of turns in the primary coil is large. If the same turns ratio is to be achieved, the number of turns in the secondary coil also needs to be increased. Therefore, the miniaturization of the open-circuit ignition coil is impossible. Conversely, for a closed magnetic circuit ignition coil, due to its low magnetic resistance, it can effectively reduce the magnetic emf of the coil and miniaturize the ignition coil. At present, the closed magnetic circuit ignition coil has been quite miniaturized and can be combined with the igniter as one, or even integrated with the spark plug. Ignite the flammable compressed gas in the cylinder through the spark plug. The traditional ignition coil is of the open-magnetic type. Its core is made by stacking silicon steel sheets about 0.3 millimeters thick, and secondary and primary coils are wound around the core. The closed-magnetic type uses an iron core shaped like type Ⅲ to wind the primary coil, and then winds the secondary coil on the outside. The magnetic field lines form a closed magnetic circuit by the iron core. The advantages of the closed-magnetic ignition coil are less magnetic leakage, smaller energy loss and smaller size. Therefore, the closed-magnetic ignition coil is widely used in electronic ignition systems.
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