Ignition coil.
With the development of automobile gasoline engine to the direction of high speed, high compression ratio, high power, low fuel consumption and low emission, the traditional ignition device has been unable to meet the requirements of use. The core components of the ignition device are the ignition coil and the switching device, improve the energy of the ignition coil, the spark plug can produce enough energy spark, which is the basic condition of the ignition device to adapt to the operation of modern engines.
principle
There are usually two sets of coils inside the ignition coil, the primary coil and the secondary coil. The primary coil uses a thicker enamelled wire, usually about 0.5-1 mm enamelled wire around 200-500 turns; The secondary coil uses a thinner enamelled wire, usually about 0.1 mm enamelled wire around 15000-25000 turns. One end of the primary coil is connected to the low-voltage power supply (+) on the vehicle, and the other end is connected to the switching device (breaker). One end of the secondary coil is connected with the primary coil, and the other end is connected with the output end of the high voltage line to output high voltage.
The reason why the ignition coil can turn the low voltage into high voltage on the car is that it has the same form as the ordinary transformer, and the primary coil has a larger turn ratio than the secondary coil. But the ignition coil working mode is different from the ordinary transformer, the ordinary transformer working frequency is fixed 50Hz, also known as power frequency transformer, and the ignition coil is in the form of pulse work, can be regarded as a pulse transformer, it according to the different speed of the engine at different frequencies of repeated energy storage and discharge.
When the primary coil is powered on, a strong magnetic field is generated around it as the current increases, and the magnetic field energy is stored in the iron core. When the switching device disconnects the primary coil circuit, the magnetic field of the primary coil decays rapidly, and the secondary coil senses a high voltage. The faster the magnetic field of the primary coil disappears, the greater the current at the moment of current disconnection, and the greater the turn ratio of the two coils, the higher the voltage induced by the secondary coil.
Coil type
Ignition coil according to the magnetic circuit is divided into open magnetic type and closed magnetic type two. The traditional ignition coil is an open magnetic type, and its iron core is stacked with 0.3mm silicon steel sheets, and there are secondary and primary coils around the iron core. The closed magnetic type uses an iron core similar to Ⅲ around the primary coil, and then winds the secondary coil outside, and the magnetic field line is formed by the iron core. The advantages of the closed magnetic ignition coil are less magnetic leakage, small energy loss and small size, so the electronic ignition system generally uses the closed magnetic ignition coil.
Numerical control ignition
In the high-speed gasoline engine of modern automobile, ignition system controlled by microprocessor, also known as digital electronic ignition system, has been adopted. The ignition system consists of three parts: microcomputer (computer), various sensors and ignition actuators.
In fact, in modern engines, both the gasoline injection and ignition subsystems are controlled by the same ECU, which shares a set of sensors. The sensor is basically the same as the sensor in the electronically controlled gasoline injection system, such as the crankshaft position sensor, camshaft position sensor, throttle position sensor, intake manifold pressure sensor, dedetonation sensor, etc. Among them, dedetonation sensor is a very important sensor dedicated to electronically controlled ignition (especially the engine with exhaust gas turbocharging device), which can monitor whether the engine dedetonation and the degree of dedetonation, as a feedback signal to make the ECU command to achieve ignition in advance, so that the engine will not dedetonation and can obtain higher combustion efficiency.
Digital electronic ignition system (ESA) is divided into two types according to its structure: distributor type and non-distributor type (DLI). The distributor type electronic ignition system uses only one ignition coil to generate high voltage, and then the distributor ignites the spark plug of each cylinder in turn according to the ignition sequence. Since the on-off work of the primary coil of the ignition coil is undertaken by the electronic ignition circuit, the distributor has canceled the breaker device and only plays the function of high-voltage distribution.
Two-cylinder ignition
Two-cylinder ignition means that two cylinders share a single ignition coil, so this type of ignition can only be used on engines with an even number of cylinders. If on a 4-cylinder machine, when two cylinder pistons are close to TDC at the same time (one is compression and the other is exhaust), two spark plugs share the same ignition coil and ignite at the same time, then one is effective ignition and the other is ineffective ignition, the former is in the mixture of high pressure and low temperature, the latter is in the exhaust gas of low pressure and high temperature. Therefore, the resistance between the spark plug electrodes of the two is completely different, and the energy generated is not the same, resulting in a much larger energy for effective ignition, accounting for about 80% of the total energy.
Separate ignition
The separate ignition method allocates an ignition coil to each cylinder, and the ignition coil is installed directly on top of the spark plug, which also eliminates the high voltage wire. This method of ignition is achieved by the camshaft sensor or by monitoring the cylinder compression to achieve accurate ignition, it is suitable for any number of cylinder engines, especially for engines with 4 valves per cylinder. Because the spark plug ignition coil combination can be mounted in the middle of the dual overhead camshaft (DOHC), the gap space is fully utilized. Due to the cancellation of the distributor and high voltage line, the energy conduction loss and leakage loss is minimal, there is no mechanical wear, and the ignition coil and spark plug of each cylinder are assembled together, and the external metal package greatly reduces the electromagnetic interference, which can ensure the normal operation of the engine electronic control system.
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