Advanced multi-spark ignition unit. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automobile. Ignition

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This ignition unit is distinguished by reliable operation at low ambient temperatures and a partially discharged battery, which is very important for starting a cold engine in winter, especially in the northern regions of Russia. In addition, the block is more noise-resistant, easy to set up and allows you to adjust the main parameters.

The basis of the device was the G. Karasev ignition unit, widely known to radio amateurs and motorists, described in [1], therefore only the nodes that have undergone changes are considered in detail here.

Firstly, minor adjustments have been made to the voltage converter: a voltage divider R3R4 has been added (see the diagram in Fig. 1), the capacitor C1 is connected with a positive output to the midpoint of the divider and the Zener diode D817B (VD4) has been replaced by D817A with a stabilization voltage of 56 V. This made it possible to set the output voltage of the converter by selecting the resistor R3, and not the zener diode VD4 or the number of turns of the secondary winding of the transformer T1, as recommended in the description of the block by Yu. Sverchkov [2] (which, by the way, was used by G. Karasev as the initial one).

Now, when using the transformer T1 of the design presented in [1], by changing the resistance of the resistor R3 from zero to 30 Ohm, you can set any voltage at the output of the converter in the range of 330 ... remained the same, the resistance of the resistor R400 is increased to 1 ohms.

The node for generating pulses that control the opening of the trinistor VS1 has undergone a complete rework. Although the design of the assembly has become more complicated and the cost of its manufacture has increased, it has been possible to improve the characteristics of the ignition unit.

The node consists of a charge-discharge circuit (resistors R8, R9, a zener diode VD9, a capacitor C6), a current switch on a transistor VT2 and a voltage divider of the converter R12R13 with a storage capacitor C7. Diode VD8 prevents the charging of capacitor C6 through resistor R8. The current limiting resistor R11 can also be used to measure the collector current of transistor VT2.

When the contacts of the breaker SF1 are closed, the capacitor C6 is charged from the on-board network through the resistor R9 to the stabilization voltage of the zener diode VD9. From the moment the breaker contacts open, the capacitor C6 begins to discharge through the emitter junction of the transistor VT2, the diode VD8, the control junction of the trinistor VS1 and the resistor R10. The transistor VT2 opens, and the discharge pulse of the capacitor C7, charged to about 18 V, is fed to the control electrode of the trinistor.

Such a circuit design of the control pulse generation unit was not chosen by chance. The fact is that with a decrease in the ambient temperature, or, more precisely, the temperature of the case of the trinistor, the current of the opening of the trinistor increases. For example, the opening current of the SCRs of the KU202 series increases by 20 times when the temperature changes from +40 to -1,5 ° C. Often this is the reason that the unit, which worked smoothly in the summer, completely refuses to work in the winter.

Experiments show [3] that a pulse with a current of 160 mA and a duration of 10 μs is sufficient to open any trinistor of the KU202 series at a case temperature of -40°C. It is these impulses that are generated by the described formation unit. This makes it possible to abandon the painstaking and expensive selection of a SCR sample at a minimum temperature. Of course, if it is possible to choose trinistors, then it should be used, since a "sensitive" trinistor allows you to use a VD3 zener diode for a lower stabilization voltage - this will be discussed below.

The use of the VD9 zener diode to limit the charging voltage of the capacitor C6 and the power supply of the collector circuit of the transistor VT2 from a stabilized voltage converter made it possible to stabilize the level of the SCR control pulse during engine start when the battery voltage fluctuates from 7,5 to 14,2 V.

Reducing the voltage on the capacitor C6 increased the noise immunity of the pulse formation unit and the ignition unit as a whole. This problem is usually considered a tertiary one, and in vain. If the effect of interference with open contacts of the interrupter can be neglected, since the spark discharge caused by the interference will occur in the cylinder where the working cycle is going on, then with closed contacts there may be malfunctions in the engine.

But the decrease in the voltage on the capacitor C6 led to the fact that the transistor VT2, with closed contacts, turns out to be a closed voltage equal to the difference between the voltage of the on-board network and the voltage across the capacitor. In other words, in order for the transistor VT2 to open and sparking to occur, the interference level must be greater than this difference, without a zener diode, the voltage across capacitor C6 is equal to the voltage of the on-board network. It follows from this: the lower the stabilization voltage of the zener diode VD9, the higher the noise immunity of the ignition unit.

Capacitors C4 and C5 are designed to additionally protect the unit from interference in the on-board network.

Resistor R10 determines the current through the breaker contacts. This current for self-cleaning contacts should not be too low. It is usually chosen in the range of 0,1 ... 0,2 A.

The pulse shaping circuit for the multi-spark operation mode (diodes VD6, VD7, resistors R5, R6, capacitor C3) remained unchanged, with the exception of an increase in the resistance of resistor R6 to 51 ohms. This is done in order to equalize the voltage of the first pulse of the "multi-spark" circuit with the pulses of the formation unit.

Here it is appropriate to dwell on the current opinion about the uselessness and even harmfulness of the multi-spark ignition mode. In my opinion, this opinion is erroneous, since during the many years of operation of the multi-spark ignition unit, nothing but an easy start of the engine, an increase in engine power and efficiency, a decrease in the content of carbon monoxide in the exhaust gases has been noticed. "As for the increased erosion of candles, then, given the advantages of multi-spark ignition, it should be accepted.

Multi-spark ignition can only be harmful if sparking continues for the entire time the breaker contacts are open [4]. Then, indeed, there is a danger of a spark discharge in the engine cylinder where the compression stroke flows. Such a possibility may arise when the distributor rotor, after opening the contacts, rotates through an angle greater than 45 degrees.

In the described ignition unit, sparking lasts about 0,9 ms, and even at the maximum engine speed, it stops long before a dangerous moment occurs.

Nevertheless, those who do not share my point of view can insert a switch into the circuit of the VD7 diode of the block. Then, after starting the engine and warming it up, by opening the circuit with a switch, it will always be possible to switch to a single-spark operation mode.

Resistors MLT-0,125 (R1, R3-R9, R11, R13), MLT-2 (R10), MLT-1 (R12) are used in the ignition unit; resistor R2 is made up of two 18 ohm 0,5 watts. Capacitors - MBM (C3), KM or KLS (C5-C7), K50-6 (C4). Diodes KD102A can be replaced by KD102B, KD103A, KD103B. Instead of KT603B, transistors KT603A, KT608A or any of the KT630 ​​series are suitable.

Transformer T1 is assembled on a magnetic circuit ShL8x16 with a non-magnetic gap of 0,25 mm in each of the three joints. Winding I contains 50 turns of PEV-2 0,7 wire, II - 450 turns, and III - 70 turns of PELSHO 0,17 wire.

All parts of the ignition unit are placed in a solid metal box measuring 130x100x50 mm. The circuit board and the transformer are attached to the base of the box, and the VT1 transistor and the VD4 zener diode are attached to its wall, which serves as a heat sink for them. Fuse FU1 is placed either on the block or elsewhere.

The remaining parts are mounted on a printed circuit board made of foil fiberglass 1,5 mm thick. The drawing of the board is shown in fig. 2. It is not superfluous to recall here that the design and installation of the unit must comply with the severe conditions of its operation - vibration, shock, high humidity, splashes of water, fuel and oils, dust, wide temperature limits.

The unit is adjusted using an oscilloscope with the ignition coil and glow plug connected. The unit can be powered from any DC source with a voltage of 8...15 V, capable of providing a load current of up to 2 A.

It is convenient to replace the breaker with a home-made prefix, the diagram of which is shown in fig. 3. A signal is fed to the input of the set-top box from the output of any audio frequency generator, and the collector of the transistor VT1 is connected to the capacitor C6 of the unit for generating control pulses of the ignition unit.

With a supply voltage of 14,2 V and a sparking frequency of 20 Hz, a resistor R3 is selected in the range from zero to 30 Ohms (it is convenient to temporarily replace the resistor R3 with a variable) so that the voltage amplitude on the primary winding of the ignition coil is in the range of 360 ... 380 V Then check the amplitude of the sawtooth voltage across the capacitor C7. If it goes beyond 18 ... 20 V, it is necessary to clarify the resistance of the resistor R13.

Set the supply voltage to 8 V, measure the voltage drop Uy at the control transition of the trinistor VS1 and the voltage drop UR11 across the resistor R11. The current of the opening trinistor pulse is calculated by the formula

Iu.imp \u11d UR11 / R7-Uu / RXNUMX.

If the measured pulse parameters do not correspond to the norm - a current of 160 mA, a duration of at least 10 μs at a level of 0,7, a Zener diode VD9 is selected so that its stabilization voltage is within 5,6 ... 8 V, and the capacitor C7 until the necessary duration.

Then, the supply voltage of the unit is again set to 14,2 V and its performance is checked over the entire operating range of the sparking frequency, i.e., from 20 to 200 Hz. The current of the opening pulse decreases with increasing frequency, and the decrease becomes noticeable only after 100 Hz. This is due to the fact that capacitors C6 and C7 do not have time to charge to the set level.

Further, the sparking frequency is increased to the maximum possible Fmax, at which the ignition unit stops working. The time of protection against bounce impulses of closing contacts is estimated by the formula tz.dr>1/2Fmax. According to [4], this time should be at least 0,2 ms. Adjust the protection time by selecting resistor R9.

With the ratings of the parts indicated in the diagram, the parameters of the ignition unit at a sparking frequency of 20 Hz and a change in supply voltage from 8 to 14,2 V should be as follows: voltage amplitude at the output of the converter - 360 ... 380 V; SCR opening pulse current - at least 160 mA with a pulse duration of at least 10 μs at a level of 0,7; time of protection against impulses of "bounce" of contacts - not less than 1 ms. At a supply voltage of 14,2 V and a sparking frequency of 200 Hz, the SCR opening pulse current decreased to 55 mA.

A fully assembled ignition unit is installed under the hood of the car near the ignition coil. The block is connected to the electrical equipment system with four wires of minimum length: two - to the ignition coil, the third - to the housing, the fourth - to the breaker.

The breaker capacitor must be disconnected. To quickly return to the old ignition option in the event of an electronic unit failure, it is desirable to provide a special switch, as suggested, for example, in [1].

According to experts, when using multi-spark ignition in the operating mode, one should not expect an increase in power and efficiency, a decrease in the content of carbon monoxide in the exhaust gases from the engine. Multi-spark ignition can only make it easier to start the engine in the cold season. Therefore, the installation of a toggle switch in the open circuit of the VD7 diode of the block, as suggested by the author, should be recognized as appropriate.

Literature

1. G. Karasev. Stabilized electronic ignition unit. - Radio, 1988, No. 9, p. 17, 18.
2. Y. Sverchkov. Stabilized multi-spark ignition unit. - Radio, 1982, No. 5, p. 27-30.
3. N. Goryunov. Semiconductor devices. - M.: Energoizdat, 1983, p. 634.
4. A. Sinelnikov. Electronics in the car. - M.: Radio and communication, 1985, p. 6, 16, 17, 32.

Author: V. Yakovlev, Troitsk, Moscow region

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