A simple ignition switch. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automobile. Ignition

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It is known that most of the Russian fleet is equipped with simple contact ignition systems based on the principle of interrupting the current flowing through the low-voltage winding of a high-voltage transformer, which is the ignition coil, using a mechanical interrupter, which is a contact switch driven by the ignition distributor shaft.

Such a system has a lot of disadvantages, the current flowing through the primary winding of the ignition coil is too high, and as a result, sparking occurs in the interrupter, which inevitably leads to burning and melting of its contacts, plus, electrochemical erosion of these contacts is added in winter or autumn-spring time. But that's not all, the duration of the spark discharge, as a result of the high current flowing through the contacts of the interrupter, it turns out to be small, 0,3-0,8 mS, and as a result, poor-quality ignition of the combustible mixture, a more enriched mixture is required, poor engine response at low speeds , increased fuel consumption. All these shortcomings have been known for a long time, and since the appearance of high-power high-voltage transistors, the automotive industry is gradually moving to the complete set of new cars with contactless electronic ignition systems, which use a contactless ignition sensor, an electronic switch with a powerful high-voltage transistor at the output, as well as a more powerful ignition coil. with low resistance windings.

You can improve the performance of a car with a contact ignition system by installing a contactless system from a newer modification of this brand. But this method is relatively expensive - a complete replacement of all elements of the ignition system is required, including a distribution sensor, an ignition coil, as well as the purchase of an appropriate electronic switch. In addition, not every model of the old model can be matched with suitable elements from newer models. Nevertheless, it is possible to significantly improve the ignition quality of a simple contact system if a simple transistor switch is connected between the contact current breaker and the standard ignition coil, the output stage of which is made on a high-voltage powerful transistor. In this case, the gain, in comparison with a simple system, will be in several positions:

firstly, the current through the interrupter contacts will decrease and they will no longer burn and correlate, secondly, the duration of the spark discharge will approximately double, which will lead to improved ignition of the mixture, thirdly, in the event of a failure of the transistor switch, it will be possible to simply rearrange the wire to return the system to its original version.

The schematic diagram of the switch is shown in the figure. In practice, this is a simplified version of the switch "131.3734" from the contactless ignition system of the Volga car.

When the contacts of the breaker are closed, a negative voltage is supplied to the base of the transistor VT1 relative to the emitter and this transistor opens. Its opening leads to the fact that through this transistor and R4 a positive voltage is supplied to the base of the powerful transistor VT2, and it opens. The current through it is supplied to the primary winding of the ignition coil L1. When the contacts of the breaker open, the voltage supply to the VT1 base stops and it closes, and VT2 closes after it. In the coil, in the circuit consisting of the primary winding L1 and the capacitor C2, oscillations occur that induce a high voltage pulse in the secondary winding L1. This high-voltage pulse through the distributor enters the candle and a spark discharge occurs. The duration of a spark in air, from the beginning of the capacitive to the end of its inductive phase, is about 2 mS, which is more than twice the duration of a spark of a classical ignition system.

Resistor R1 is not needed at first glance, but as practice shows, when too low current is passed through the breaker contacts, a reliable electrical contact does not always occur, and misfires in the ignition system are possible. To avoid this, a resistor R1 is introduced, which creates the necessary minimum current through these contacts.

The KT973A transistor can be replaced with KT816, and the KT8109A transistor with KT848A.

The switch is assembled by volumetric installation in the case of a faulty switch from the contactless ignition system of Volga or UAZ cars.

The setting consists in selecting the value of R4 (at least 22 O) and R2 (at least 300 O) so that when the ignition coil is connected and the breaker contacts are closed, the voltage on the VT2 collector is minimal (no more than 1,5 V). In this case, the current through the coil will be maximum.

Subjectively, with this switch, the car moves better at low revs, starts off better at idle.

You can increase the spark energy if you install an ignition coil with low-resistance windings from a VAZ-08-099 car, but you will need to refrain from turning the ignition on for a long time with the engine off, since the current through the coil will be high and this can damage the output transistor of the switch.

Author: Kazakov A. T.; Publication: N. Bolshakov, rf.atnn.ru

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