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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Ignition unit for VAZ-2108 and VAZ-2109. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automobile. Ignition The described ignition unit is designed to operate in the contactless ignition system of VAZ-2108 and VAZ-2109 vehicles equipped with a breaker-distributor 40.3706, as well as the upgraded VAZ-2105 and VAZ-2107 with a breaker-distributor 38.10.3706 and ZAZ-1102 ("Tavria" ) from 53.3706. In these machines, the current switch using the Hall effect serves as a sparking torque sensor. The ignition unit is also suitable for Volga and Moskvich vehicles equipped with a Hall effect "breaker" and a serial ignition coil 27.3705 (TU 37.0031184 - 83) or close to it in terms of parameters. It replaces serial ignition blocks 36.3734, 3620.3734 and foreign ones that perform similar functions. According to the principle of operation, the unit belongs to the class of transistors with normalization of the time of energy accumulation in the ignition coil. This is provided by two waiting multivibrators connected in a certain way, which made it possible to exclude the Norton quad amplifier used in well-known foreign and domestic devices. In addition, the block * is distinguished by the use of widely used parts of domestic production, simple design, does not require special manufacturing technology, therefore it is available in repetition. The device performs the following functions: generates ignition current pulses in the primary winding of the ignition coil; limits the current flowing through the primary winding and the voltage across it and its output transistors; closes these transistors when the ignition is on and the engine is not running. Limiting current pulses eliminates overheating of the ignition coil and output power transistor of the block, and limiting the voltage reduces the wear of spark plugs and the likelihood of failure of the cover and slider of the ignition distributor, transistors of the output stages of the block. Turning off the current through the ignition coil when the engine is not running prevents useless heating of the elements of the block, the ignition coil, the discharge of the battery and increases the fire safety of the car. Main Specifications
The circuit diagram of the considered ignition unit with circuits for connecting it to the vehicle's electrical system is shown in fig. 1. The block contains a trigger node on a VT1 transistor, two single vibrators - the first on VT2, VT3 transistors, and the second on VT4, VT5, a current amplifier on a VT6 transistor, a current switch on VT7, VT8 transistors, connected according to the Darlington circuit.
The timing diagrams shown in fig. 2, explain the operation of the switch and the processes occurring in it with an increase in the frequency of sparking fi. Diagram 4 and 5 are taken directly from the capacitors C4 and C5, diagr. 7 - from the resistor R24, 9 - from the output of the measuring voltage divider 10 MOhm / 1 kOhm, and 10 - from the 10 Ohm resistor connected in series with a spark gap.
The supply voltage to the non-contact neoplasm pulse sensor ("breaker") is supplied through the filter-limiter R19VD1C2C8. Diode VD6 protects the unit from emergency polarity reversal of the supply voltage. When the ignition is on, transistors VT2, VT3 and VT4, VT5 are open, and VT6 and VT7, VT8 are closed. No current flows through the ignition coil. The trigger node transistor VT1 can be in any state depending on the level of the signal coming from the sensor. With the start of rotation of the crankshaft of the engine, triggering pulses of duration Td are received from the sensor at the input of the transistor VT1 (Fig. 1). When the transistor VT1 is closed (Diagram 2), the capacitor C3 is charged through the circuit R3R4 and the emitter junction of the transistor VT3. The timing capacitor C4 is charged to a voltage limited by the zener diode VD1 through transistors VT2, VT3, diode VD2 and resistors R9, R10 (diagram 4). Charging takes place in about 0,4 s; this time mainly depends on the capacitance of the capacitor C4 and the resistance of the resistors R9, R10. The timing capacitor C7 is also charged through transistors VT4, VT5 and resistor R17 (diagram 6). As soon as a high level signal appears at the sensor output, the transistor VT1 opens, the capacitor C3 is discharged through the circuit R4VT1R8, which will lead to the closing of the transistor VT3, the transistor VT2 also closes. The recharging of the capacitor C4 begins through the circuit R5, R6, R12, R11, VD3. Thus, the first one-shot generates a delay pulse of duration T3, necessary to start the second one-shot. When the voltage across the capacitor C4 reaches the level at which the transistor VT2 opens, the first single vibrator returns to its original state. At its output, a pulse decay occurs (Fig. 3), passing through the R1ЗС6 circuit and triggering the second single vibrator; transistors VT4 and VT5 are closed. This leads to an increase in the voltage at the collector of the transistor VT5 (Fig. 6) and recharging the timing capacitor C7 through resistors R14, R18, R17. As a result, transistors VT6-VT8 open, current starts to flow through the primary winding of the ignition coil T1 (diagram 7) from the power source and electromagnetic energy accumulates in it during the time t. Simultaneously with the increase in the voltage on the collector of the transistor VT5, the capacitor C5 is charged through the resistor R18, the diode VD5, the transistor VT3 (diagram 5), and the charging circuit of the time-setting capacitor C4 stops operating, despite the fact that the transistors VT2 and VT3 are open (see Diag. 3 and 4). Its charging is delayed for a time tac until the second one-shot returns to its original state. As soon as the pulse decay appears at the output of the "breaker" sensor, the transistor VT1 of the trigger unit closes, the second one-shot will return to its original state, regardless of the charge on the capacitor C7 due to the connection through the diode VD4 (Fig. 6). Therefore, the current switch VT7, VT8 will close. At this moment, a high voltage pulse is induced in the secondary winding of the ignition coil (Fig. 7-9), which, at the voltage Unp, pierces the spark gap of the glow plug. A spark discharge occurs with a duration of TVW, depending on the burst current Ip in the primary winding of the ignition coil and its parameters (diagram 10). After the return of the second one-shot to its original state, its action on the charging circuit of the capacitor C4 stops, and it is charged again, and the capacitor C5 is discharged through the resistor R10, thus slowing down the charging of the capacitor C4, since a positive voltage is applied to the common point of the resistors R9 and R10 with left according to the scheme of the lining of the capacitor C5. At a low frequency of the neoplasm - when the engine is started - the capacitor C5 has time to discharge almost completely, and at a high frequency it discharges in two stages. The first corresponds to the time of the closed state of the transistor VT1, and the second corresponds to the closed state of the transistors VT2, VT3 (Fig. 5). The higher the frequency, the greater the residual voltage Ures on the capacitor C5 by the end of the first stage and the less charge the capacitor C4 will receive. As follows from the principle of operation of the device, the resistor R9 and the circuit R10C5 increase the charging time of the capacitor C4 in the first one-shot, which is responsible for the time delay in the start of the accumulation of electromagnetic energy in the ignition coil. In this case, the diode VD3 ensures the flow of the discharge current of the capacitor C4 through the resistor R11, bypassing the resistor R9 and the circuit R10C5. The charging time constant of the capacitor C4 is large, therefore, with an increase in the sparking frequency, it does not have time to fully charge, which provides an approximately inversely proportional relationship between the duration of the pulses generated by the first single vibrator and the sparking frequency. At a high frequency, these pulses become even shorter, since the capacitor C4 is also undercharged due to the braking action of the R10C5 circuit. If you turn on the ignition and do not start the engine, and the signal at the output of the "breaker" sensor is high, the current through the primary winding of the ignition coil will stop in about a second, since in this case the second single vibrator returns to its original state as a result of recharging capacitor C7. A selection of resistor R6 sets the time of energy accumulation in the ignition coil, and hence the current flowing through it. By choosing the time constant for the discharge of the capacitor C5, the required law of change of this current is set in the interval of the crankshaft speed from idle to the maximum value. The unit is protected from interference from the vehicle's on-board network by the VD6C8, R19C2VD1 circuits and elements C1, R4, R13. Resistor R23 limits self-induction voltage surges at the output transistors VT7 and VT8 (diagram 8). Resistor R24 limits the current of these transistors and the primary winding of the ignition coil, and the diode VD7 blocks the reverse voltage pulses on the transistors in the transient. The ignition unit used capacitors K73-9 for a voltage of 100 V - C1, C3, C6; K53-1A (16 V) - C2; K73-17 (63 V) - C4, C7; K73-17 (250 V) - C5, C8. Resistor R24 - C5-16V with a rated power of 10 watts. Diodes KD503A (VD2-VD5) can be replaced with KD509A, KD521A or other similar ones. Connector X1 - block plug ONP-ZG-52-7-V-AE (the same as in commercially available ignition units). Almost all parts of the device are mounted on a printed circuit board made of one-sided foil fiberglass 1,5 mm thick. A drawing of a printed circuit board and the location of parts on it are shown in fig. 3. The board is placed in a metal case from the factory block 42.3734. The VT8 transistor is attached to the inner wall of the case through a mica gasket. Resistor R24 is also attached to the inner wall.
To establish the unit, you will need a power source with an output voltage that varies from 5 to 18 V at a current of up to 3 A (ripples should not exceed 0,5 V at a frequency of 100 Hz), a rectangular pulse generator with an output voltage amplitude of 3 ... 5 V , a pulse repetition rate of 10 ... 250 Hz and a duty cycle of 3 + 0,25, an oscilloscope that measures the parameters of rectangular pulses and voltages up to 500 V, an arrester with an adjustable spark gap up to 15 mm and a standard ignition coil 27.3705. After checking the correct installation, a power source and an ignition coil with a spark gap are connected to the unit according to the circuit diagram (a resistor with a resistance of 4,7 ... 5,6 kOhm with a power of at least 2 W is connected in series with it). The signal from the output of the generator is fed to the input of the block through a buffer inverting amplifier with an open collector output, assembled according to the circuit in Fig. 4.
Set the supply voltage of the unit to 14 V and the spark gap of 10 mm. Serving triggering pulses with a duration of 10 ms with a repetition rate of 33,3 Hz, which corresponds to the operation of a four-cylinder four-stroke engine at a crankshaft speed of 1000 min-1, i.e., close to idling. In this case, the current consumed by the unit must be within 0,9 ... 1,2 A, otherwise, resistor R6 should be selected (or even change the resistance of the R5R6 circuit, usually equal to 240 ... 270 kOhm). The amplitude of the voltage pulse at the collector of the transistor VT7 (VT8) is controlled by the oscilloscope. It should be in the range of 380 ... 420 V. If the amplitude is very different from the specified one, resistor R23 should be selected. Next, the supply voltage is reduced to 7,5 V and a spark is observed in the gap of the arrester. If it is unstable or absent at all, check the accuracy of the selection of resistors R5, R6. As a last resort, transistors VT6, VT7, VT8 should be replaced by others with a large value of the static current transfer coefficient. Then they check the operability of the unit at a sparking frequency of 50, 100, 250 Hz at a supply voltage of 14 V. There should be no failures in sparking. It is even easier to adjust the unit if it is installed directly on the car. To do this, in the break of the wire connecting the primary winding of the ignition coil with the on-board network (or with pin 1 of connector X1), you need to include an ammeter that measures the average current value, for example, an avometer. At idle, the resistor R6 is selected so that the ammeter shows a current of 0,9 ... 1,2 A. Instead of R6, you can temporarily solder a variable resistor with a resistance of 68 kOhm. In this case, as in laboratory adjustment, it is very advisable to control the amplitude of the voltage pulse at the collector of the transistor VT8. Author: B.Bespalov, Kemerovo
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