Stabilized car electronic ignition unit. Free Technical Library article

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Stabilized car electronic ignition unit

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Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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The benefits of electronic ignition in internal combustion engines are well known. At the same time, electronic ignition systems that are currently widespread do not yet fully meet the set of design and operational requirements. Systems with pulsed energy storage [1,2, XNUMX] are complex, not always reliable, and practically inaccessible to most car enthusiasts. Simple systems with continuous energy storage do not provide stabilization of the stored energy [3], and when stabilization is achieved, they are almost as complex as impulse systems [3,four].

It is not surprising, therefore, that the article by Yu. Sverchkov [5] published in the journal "Radio" aroused great interest among readers. A well-thought-out, extremely simple stabilized ignition unit can, without any exaggeration, serve as a good example of an optimal solution in the design of such devices.

The results of the operation of the unit according to the scheme of Yu. Sverchkov showed that, despite the generally high quality of its operation and high reliability, it also has significant drawbacks. The main one is the short duration of the spark (no more than 280 μs) and, accordingly, its low energy (no more than 5 mJ).

This disadvantage, inherent in all capacitor ignition systems with one period of oscillation in the coil, leads to unstable operation of a cold engine, incomplete combustion of an enriched mixture during warm-up, and difficult starting of a hot engine. In addition, the voltage stability on the primary winding of the ignition coil in the Yu. Sverchkov unit is somewhat lower than in the best pulse systems. When the supply voltage changes from 6 to 15 V, the primary voltage changes from 330 to 390 V (±8%), while in complex pulse systems this change does not exceed ±2%.

With an increase in the frequency of sparking, the voltage on the primary winding of the ignition coil decreases. So, when the frequency changes from 20 to 200 Hz (the crankshaft speed is 600 and 6000 min^-1respectively) the voltage varies from 390 to 325 V, which is also somewhat worse than in pulse blocks. However, this shortcoming can

practically ignored, since at a frequency of 200 Hz the breakdown voltage of the spark gap of the candles (due to residual ionization and other factors) is almost halved.

The author of these lines, who has been experimenting with various electronic ignition systems for more than 10 years, set the task of improving the energy characteristics of the Yu. Sverchkov block, while maintaining the simplicity of the design. It turned out to be possible to solve it thanks to the internal reserves of the block, since the energy of the storage device was used in it only by half.

This goal was achieved by introducing a mode of multi-period oscillatory discharge of the storage capacitor to the ignition coil, which leads to its almost complete discharge. The very idea of such a solution is not new [6], but is rarely used. As a result, an improved electronic ignition unit has been developed with characteristics that not all impulse designs have.

At a sparking frequency of 20...200 Hz, the unit provides a spark duration of at least 900 µs. The spark energy released in the spark plug with a gap of 0,9 ... 1 mm is not less than 12 mJ. The accuracy of maintaining energy in the storage capacitor when the supply voltage changes from 5,5 to 15 V and the sparking frequency is 20 Hz is no worse than ± 5%. Other characteristics of the block have not changed.

It is significant that the increase in the duration of the spark discharge was achieved precisely by a long oscillatory process of discharging the storage capacitor. The spark in this case is a series of 7-9 independent discharges. Such an alternating spark discharge (frequency about 3,5 kHz) contributes to efficient combustion of the working mixture with minimal spark plug erosion, which favorably distinguishes it from a simple lengthening of the aperiodic discharge of the storage device [2].

The block converter circuit (Fig. 1) has not changed much. Only the transistor has been replaced to slightly increase the power of the converter and facilitate the thermal regime. Elements that ensured an uncontrolled multi-spark operation were excluded. The energy switching circuits and the control circuits for the discharge of the storage capacitor SZ have been significantly changed. It is now discharged for three (and at a frequency below 20 Hz - or more) periods of natural oscillations of the circuit, consisting of the primary winding of the ignition coil and capacitor C2. Elements C3, R4, R6, VDXNUMX provide this mode.

(click to enlarge)

Considering that the operation of the converter is described in detail in [5], we will consider only the process of oscillatory discharge of the capacitor C4. When the breaker contacts open, capacitor C1, discharging through the control transition of the trinistor VS8, diode VD7 and resistors R8, R2, opens the trinistor, which connects the charged capacitor CXNUMX to the primary winding of the ignition coil. The gradually increasing current through the winding at the end of the first quarter of the period has a maximum value, and the voltage on the capacitor CXNUMX at this moment becomes equal to zero (Fig. XNUMX).

All the energy of the capacitor (minus heat losses) is converted into the magnetic field of the ignition coil, which, trying to maintain the value and direction of the current, begins to recharge the C0,85 capacitor through an open trinistor. As a result, at the end of the second quarter of the period, the current and the magnetic field of the ignition coil are equal to zero, the capacitor C1 is charged to 280 of the initial (in voltage) level in the opposite polarity. With the termination of the current and the change of polarity on the capacitor C0,7, the trinistor VSXNUMX closes, but the diode VDS opens. The next process of discharging the capacitor CXNUMX begins through the primary winding of the ignition coil, the direction of the current through which changes to the opposite. At the end of the oscillation period (i.e., after approximately XNUMX μs), the capacitor CXNUMX is charged in the original polarity to a voltage equal to XNUMX of the initial one. This voltage closes the VDS diode, breaking the discharge circuit.

In the considered time interval, the low resistance of the alternately opening elements VD5 and VS1 shunts the R3R4C2 circuit connected in parallel to them, as a result of which the voltage at its ends is close to zero. At the end of the period, when the trinistor and the diode are closed, the voltage of the capacitor C250 (about 3 V) is applied to this circuit through the ignition coil. The voltage pulse taken from the resistor R6, passing through the diode VD1, reopens the trinistor VSXNUMX, and all the processes described above are repeated.

This is followed by the third, and sometimes (at start-up) and the fourth discharge cycle. The process continues until the capacitor C3, which loses about 50% of energy with each cycle, is almost completely discharged. As a result, the duration of the spark increases to 900...1200 µs, and its energy - up to 12...16 mJ,

On fig. 2 shows an approximate view of the voltage waveform on the primary winding of the ignition coil. For comparison, the dashed line shows the same oscillogram of Yu. Sverchkov's block (the first periods of oscillations on both oscillograms coincide),

To increase the protection against bounce of the contacts of the breaker, the starting node had to be somewhat changed. The time constant of the charging circuit of the capacitor C4 by selecting the appropriate resistor R6 is increased to 4 ms; the discharge current of the capacitor (i.e., the start-up current of the trinistor), determined by the resistance of the circuit of resistors R7, R8, is also increased.

The electronic ignition unit has been tested for three years on a Zhiguli car and has proven itself very well. The stability of the engine after start-up has sharply increased. Even in winter at a temperature of about -30 ° C, starting the engine was easy, it was possible to start moving after warming up for 5 minutes. Interruptions in engine operation during the first minutes of movement, observed when using the Yu. Sverchkov block, stopped, acceleration dynamics improved.

In the transformer T1, the magnetic circuit SHL16X8 is used. A gap of 0,25 mm is provided by three press-span gaskets. Winding I contains 50 turns of wire PEV-2 0,55; II - 70 turns of PEV-2 0,25; III - 450 turns of PEV-2 0,14. In the last winding, one gasket of capacitor paper should be laid between all layers, and the entire winding should be separated from the rest by one or two layers of cable paper,

The finished transformer is coated 2-3 times with epoxy resin or filled with resin completely in a plastic or metal box. An E-shaped magnetic circuit should not be used, since, as experience shows, it is difficult to maintain a given gap across the entire thickness of the set, and also to avoid shorting the outer plates. Both of these factors, especially the second, sharply reduce the power of the charging pulse generator.

When setting up the generator part of the block, you can use the recommendations of Yu. Sverchkov in [5].

Due to the high reliability, the unit can be connected without connector X1 (disconnection of the capacitor Csp of the interrupter is mandatory), which is intended for a possible emergency transition to battery ignition, but the initial setting of the ignition moment will be much more difficult. While maintaining the X1 connector, the transition to battery ignition is very simple - instead of the block block, a contact block is inserted into the female part of the X1 connector, in which contacts 2, 3 and 4 are connected.

Literature

1. A. Sinelnikov. How do the blocks differ - Behind the wheel. 1977, No. 10. p. 17,

2. A. Sinelnikov. High reliability electronic ignition unit. Sat. "To help the radio amateur", vol. 73.-- M.: DOSAAF USSR, p. 38.

3. A. Sinelnikov. Electronics in the car. - M.: Energy, 1976.

4. A. Sinelnikov. Electronics and car. - M .: Radio and communication, 1985.

5. Yu. Sverchkov. Stabilized multi-spark ignition unit. - Radio, 1982, No. 5. p. 27.

6. E. Litke. Capacitor ignition system. Sat. "To help the radio amateur", issue, 78.- M .: DOSAAF USSR, p. 35.

Author: G. Karasev, Leningrad; Publication: cxem.net

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