Thyristor ignition with optical sensor. Capacitor (thyristor) ignition system
P. ALEXEEV
The thyristor ignition system in a car engine has gained so much popularity that today there are practically no car enthusiasts who do not show interest in it.
A schematic diagram of a tested version of the thyristor ignition system unit is shown in Fig. 1.
Rice. 1. Schematic diagram of a thyristor ignition unit
The dash-dotted lines highlight the components of the block: high voltage source, energy storage device, starting pulse former, ignition switch “Electronic - conventional”.
High voltage source, which is a push-pull transistor converter (single-cycle may not provide the required charging rate for the energy storage device), is designed to convert low voltage (12-14 V) of a car battery or generator into a relatively high constant voltage of 380-400 V. The choice of such voltage is not accidental. The fact is that the energy in the spark plug of an engine with a thyristor ignition system is determined by the expression A=C*U 2 /2. from which it follows that the greater the capacity (C) of the energy storage device and the higher the voltage (U), the greater the energy in the spark. The increase in voltage is limited by the electrical strength of the insulation of the primary winding of the ignition coil (400-450 V), and the increase in capacity is limited by the charging time of the storage capacitor, which should be less than the duration of the inter-spark gap. Based on this, in a thyristor ignition system, the output voltage of the converter is usually 300-400 V, and the capacity of the storage capacitor is 1-2 μF.
The voltage converter transformer is the most labor-intensive element of the ignition system. In amateur conditions, it is not always possible to use transformer steel recommended by the author of this or that article. Most often, magnetic cores with unknown characteristics from disassembled old transformers and chokes are used. As experience has shown, the voltage converter transformer can be made without preliminary calculations, depending on the quality of the transformer steel, but with a slightly increased power, which will only improve the performance of the converter.
The transformer data can be as follows: cross-section of the magnetic circuit 3.5-4.5 cm2; windings I and IV - 9 turns each of wire PEV-2 0.47-0.53; windings II and III - 32 turns of wire PEV-2 1.0-1.1; winding V - 830-880 turns of PELSHO or PEV-2 wire 0.31-0.35.
Between the rows of the high-voltage winding, as well as between the windings, it is necessary to lay varnished cloth or capacitor paper. The magnetic circuit plates are assembled tightly and without gaps (the presence of joining gaps sharply reduces the quality of the transformer).
After assembling the entire converter with a rectifier on diodes D3-D6 in the form of one unit, it should be checked according to the following parameters: the strength of the no-load current consumption, the magnitude of the constant voltage at the output of the converter, the shape of the voltage curve on the output winding V, the frequency of the converter current.
The check is carried out according to the scheme shown in Fig. 2.
Rice. 2. Voltage converter test circuit
At correct inclusion windings I, II, III and IV, the voltage converter should start working immediately (a faint sound created by the magnetic circuit of the transformer can be heard). The current consumed by the voltage converter, measured by the IP1 ammeter, should be in the range of 0.6-0.8 A (depending on the cross-section and grade of steel of the transformer magnetic circuit).
After turning off the power, resistor R1 (see Fig. 2) is removed, the “Y” input of the oscilloscope is switched to points 3 and 4 (see Fig. 1) of the rectifier bridge, and a capacitor with a capacity of 0.25-1 is connected to points 1 and 2, 0 µF for a rated voltage of 600 V and parallel to it a DC voltmeter with a scale of 0-600 V. Having applied power to the converter again, measure the DC voltage at the output of the rectifier. At idle it can reach 480 -550 V (depending on the number of turns of winding V). By selecting resistor R5 (starting from the highest value), we achieve a reduction in this voltage to 370-420 V. At the same time, the shape of the converter output voltage curve is observed on the oscilloscope screen. At idle speed it should correspond to Fig. 3, a (edge surges can reach 25-30% of the secondary voltage amplitude), and with resistor R5 connected - the curve shown in Fig. 3, b (front emissions are reduced to 10 - 15%). Next, using an oscilloscope, the operating frequency of the converter is measured - it can be in the range of 300-800 Hz (a higher frequency, which can occur if the transformer magnetic circuit is not carefully assembled, is undesirable, as it leads to increased heating of the transformer).
Rice. 3. Diagrams of the output voltage of the converter
This completes checking the operation of the voltage converter.
Diodes D1 and D2 limit the voltage that closes the transistors at a level of 0.6-0.8 V, and thereby protect the emitter junctions from breakdown, and also help reduce the amplitude of surges of secondary voltage fronts.
Transistors such as P210A, P209, P217 and others similar to them with a current transfer coefficient of at least 12-15 work well in a voltage converter. Required condition is the selection of a pair of transistors with the same current transfer coefficient.
In the rectifier (D3-D6) you can use any silicon diodes with Uar>500-600 V and Ipr>1 A.
Energy storage is a capacitor with a capacity of 1-2 μF, charged from the rectifier of the converter to a voltage of 400-300 V and discharged at the moment of sparking through the opening thyristor D7 and the primary winding of the ignition coil. In the ignition system under consideration, the role of energy storage is performed by capacitor C2. You can use any paper capacitors (MBGP, MBGO, etc.) with a rated voltage of 500-600 V. It is advisable to select a capacitor whose capacitance is slightly larger than the rated one, which will have a positive effect on the energy in the spark (especially when the rectifier voltage is less than 380 V).
In a thyristor ignition system assembled according to the circuit shown in Fig. 1, in addition to the main energy storage device (capacitor C2), there is a “starting” capacitor C3, connected in parallel to capacitor C2 using relay contacts P1 (relay operating voltage 6-8 V), which is triggered by the voltage supplied to the “VK” terminal during startup engine starter. This was done in order to increase the energy in the spark by increasing the storage capacity while reducing the battery voltage to 7-9 V.
The turn-on voltage of the thyristor used in the ignition system must be less than 500 V, and the leakage current at an operating voltage of 400 V must not exceed 1 mA. Unfortunately, the turn-on voltage of thyristors of even one batch can differ significantly, so it is highly advisable to check the thyristor for turn-on voltage and leakage current.
Trigger pulse generator in a thyristor ignition system it performs the most important function: it generates pulses of a certain shape, duration and amplitude and supplies them to the control electrode of the thyristor exactly at the moment the breaker contacts open. We can assume that the quality indicators of the thyristor ignition unit are determined by how perfect the starting pulse shaper is. In addition, it must have high noise immunity to all kinds of surges and voltage drops in the vehicle’s on-board network and be unpretentious to the quality of the breaker’s operation and, first of all, to the rattling of its contacts. The best performance from this point of view is provided by a transformer starting pulse shaper. It consists of a pulse transformer Tr2, diodes D8 and D9, capacitor C4 and resistors R7, R8. When the breaker contacts are closed, the current flowing through resistors R7, R8 and the primary winding of the transformer creates an energy reserve in the transformer windings, ensuring the appearance of a pulse of positive polarity in the secondary winding at the moment the breaker contacts open. This pulse goes directly to the control electrode of thyristor D7, opens it and thereby ensures the discharge of capacitor C2 through the ignition coil.
To eliminate false starting pulses that occur when the breaker contacts bounce, the primary winding of the transformer is shunted by diode D9 and capacitor C4 connected in parallel. The capacitance of this capacitor, depending on the data of the pulse transformer, is selected experimentally. Diode D8 limits at a level of 0.6-0.8 V the negative pulse on winding II of the transformer that occurs when the breaker contacts are closed, protecting the control transition of the thyristor from breakdown.
Reliable opening of the thyristor is ensured by a pulse with an amplitude of about 5-7 V and a duration of 100-200 μs.
For a pulse transformer, you can use any W-shaped magnetic core with a cross section of 0.7-1.5 cm2. First, it is advisable to test an experimental version of the transformer: 80-120 turns of PEV-0.35-0.5 wire are wound onto the frame (winding I), and on top of them 35-40 turns of the same wire (winding II). After assembling the magnetic circuit, without tightening it, to the transformer (Fig. 4)
Rice. 4. Scheme for checking and adjusting the pulse shaper
All elements of the starting pulse former (D8, D9, C4, R7 and R8), the control electrode and the thyristor cathode are temporarily connected (the thyristor anode remains free). As a breaker, contacts P1/1 of the electromagnetic relay P1 (type RES-6 or RES-22) are included in the circuit of the primary winding of the transformer, the winding of which is connected to the mains through a quenching resistor (Rgas) or a step-down transformer. A rubber ring is placed on the relay contact group to reduce contact bounce. Such a device ensures that the starting pulse former operates at a frequency of 100 Hz, corresponding to the crankshaft speed of a four-cylinder engine equal to 3000 rpm. The inevitable bouncing of the relay contacts allows you to configure the trigger pulse shaper to operate under more severe conditions compared to a real breaker (it is for this reason that a polarized relay that does not bounce contacts should not be used). After turning on the power, observe the voltage curve at the thyristor input on the oscilloscope screen, which should look like the one shown in Fig. 5, a, find out the initial parameters of the starting pulse. By reducing or increasing the number of turns of the secondary winding of the transformer, you can correspondingly reduce or increase the amplitude of the pulse, and by selecting the number of turns of the primary winding and the capacitance of capacitor C4, you can change the duration of the pulse and its “purity” from the point of view of protection against bounce of the breaker contacts. As a rule, after two or three tests it is possible to select the details of the parts so that the pulse has the required duration and amplitude, and the bounce of the breaker contacts does not affect the stability of operation and the shape of the voltage curve of the starting pulses. Based on the data obtained as a result of tests, a working version of the pulse transformer is manufactured.
Rice. 5. Diagrams of the voltage of the starting pulse (a) and the discharge pulse of the storage capacitor (b)
Ignition switch “electronic - conventional”, assembled on toggle switches or a biscuit switch, provides a quick transition from one type of ignition to another (to avoid damage to the thyristor ignition unit, switching is carried out only when the power source is turned off). Capacitor C5, connected in normal ignition mode parallel to the breaker contacts (“Pr”), replaces the capacitor located on the ignition distributor housing (it must be removed or turned off, as it disrupts the normal operation of the thyristor ignition system). The terminals of the conductors, designated VK, VKB, General and Pr, are connected to the corresponding terminals of the ignition coil and breaker, and the contacts VKB and VK, circled by dash-dotted lines, are used for connecting wires previously connected to the same terminals of the ignition coil.
A fully assembled thyristor ignition unit should be connected to a breaker and an ignition coil with a spark plug (connected between the high-voltage terminal and the minus of the power source), and then, having applied voltage to it, check the following parameters: current consumption, rectifier output voltage, amplitude and duration of the starting pulse, discharge pulse of a storage capacitor.
The current consumption of the loaded converter, measured by an ammeter connected to the power supply circuit of the unit, should be 1.3-1.5 A. The output voltage of the rectifier (on capacitor C2), measured according to the circuit shown in Fig. 6, should be equal to the open circuit voltage or less than it by 5-7% (sometimes up to 10%).
Rice. 6. Circuit for measuring voltage on an energy storage device with the thyristor ignition unit operating
The amplitude and duration of the trigger pulse, measured by an oscilloscope, should be 5-7 V and 150-250 μs, respectively. In the interval between pulses, small interference with a small amplitude (no more than 0.1-0.2 of the amplitude of the starting pulse) occurs (at the moment the contacts close). If small “notches” are visible (usually at the operating frequency of the converter), then you should select the capacitance of capacitor C1.
The discharge pulse of storage capacitor C2, viewed on the oscilloscope screen, has the form shown in Fig. 5 B. The charging of the capacitor must end no later than 2/3 of the interval between pulses (usually it ends at 1/3-1/2 of the interval).
The tested thyristor ignition unit should be left in working condition for 30-40 minutes to monitor the thermal conditions. During this time, the transformer of the converter should heat up to a temperature not exceeding 70-80 ° C (the hand can tolerate it), and the heat sinks of the transistors - up to 35-45 ° C.
The design of the block is arbitrary. Voltage converter transistors are mounted on plate heat sinks or profiled duralumin 4-5 mm thick with total area 60-80 cm2.
A possible design of a thyristor ignition system unit mounted in a metal case with dimensions 130X130X60 mm is shown in Fig. 7.
Rice. 7. Design of the thyristor ignition system block
The unit should be placed on the car (under the hood) so that its output wires VKB, VK, and “General” can be connected to the corresponding terminals of the ignition coil (the wire connecting the “General” terminal of the ignition coil with the breaker is removed). The wires that were previously located on the ignition coil terminals of the same name are connected to the “VKB” and “VK” contacts of the ignition block.
In ignition systems with energy storage in the electrostatic field of a capacitor, the function of an electronic relay is performed by thyristors controlled by a contact breaker, which is why such systems are called contact-thyristor systems. Systems with pulsed and continuous energy accumulation in an electrostatic field are known.
The system with continuous energy storage contains a push-pull voltage converter consisting of two transistors VT1 and VT2, transformer T1, resistors R2 and R3 and capacitor C1. A full-wave rectifier with a zero point (diodes VD1 and VD2) is used to rectify the output voltage of the converter. The rectifier is loaded with storage capacitor C2, in parallel with which resistor R4 is connected. Thyristor VS interrupts the current in the primary winding L1 of the ignition coil (transformer T2). The thyristor is controlled by contact S2 ignition timing synchronizer.
Rice. Thyristor ignition system with continuous energy accumulation in the electrostatic field of the capacitor
When contacts S1 of the ignition switch are closed, the push-pull voltage converter is activated. At the terminals of the secondary winding L2 of transformer T1, a rectangular alternating voltage with an amplitude of 200-500 V appears. The rectified direct voltage is supplied to charge the storage capacitor C2 if the contacts S2 of the ignition timing synchronizer are closed. The thyristor is in the closed state, since its control circuit is bypassed by the closed contacts S2 of the synchronizer.
At the moment the synchronizer contacts S2 open, the voltage from GB is supplied through resistor R1 to the control electrode of the thyristor VS. Through an open thyristor, capacitor C2 is discharged onto the primary winding L1 of the ignition coil T2, as a result of which a high EMF is induced in its secondary winding L2. With appropriate selection of the parameters of the elements of the considered ignition system, it is possible to ensure a full charge of the capacitor in all engine operating modes and obtain a secondary voltage that is practically independent of the crankshaft speed. Chain C1-R2 ensures reliable start-up of the transistor converter.
In a system with pulsed energy storage, when contacts S1 of the ignition switch are closed and contacts S2 of the ignition timing synchronizer are opened, a positive voltage pulse from the battery GB is supplied to the base of the transistor VT. The transistor goes into saturation state, passing a current through the emitter-collector junction and the primary winding L1 of the transformer, creating a magnetic field in the transformer. At the moment of closing the contacts S2 of the synchronizer, the base circuit of the transistor KG is short-circuited, the transistor goes into a cut-off state, the current in the winding L1 of the transformer disappears, and a high EMF is induced in the secondary winding. At this time, the closed contacts S2 of the synchronizer bypass the thyristor control circuit. The thyristor is closed, and capacitor C is charged through diode VD1 to a voltage of 200-400 V.
Rice. Thyristor ignition system with pulsed energy accumulation in the electrostatic field of a capacitor
The next time the contacts S2 of the synchronizer are closed, voltage from the battery is supplied to the control electrode of the thyristor through resistors Ra, Rl, R3. The thyristor opens. The discharge current of the capacitor passes through the primary winding L1 of the transformer coil and a high voltage pulse appears at the terminals of the secondary winding and is supplied to the spark plug.
Ignition systems that store energy in the electrostatic field of a capacitor provide a higher rate of rise of the secondary voltage, which makes it less sensitive to the presence of soot shunt resistors. However, due to the high rate of growth of the secondary voltage, the breakdown voltage increases compared to systems with energy storage in a magnetic field. In addition, due to the reduction in the duration of the inductive component of the spark discharge, the ignition and combustion of the air-fuel mixture deteriorate when starting the engine and operating it at partial loads.
The advantage of this device is the automatic shutdown of the multi-spark mode after starting the engine. This eliminates the possibility of stopping the engine during multi-spark ignition if the gap size in the breaker contacts is larger than the optimal one. At large open angles of the breaker contacts, a spark may jump into the next cylinder along the distributor, which will cause the engine to stop. The circuit can operate with a supply voltage from 5 to 20 V. At an engine speed of 1000 rpm, the electronic ignition device consumes a current of about 0.3 A. With increasing engine speed, the current consumption increases and at 6000 rpm reaches a value of approximately 1 A .
A voltage of about 4000 V, to which the storage capacitor C8 is charged, is generated using a voltage converter made according to a circuit with external excitation. The master oscillator, made according to a multivibrator circuit using elements D2.1 and D2.2, operates at a frequency of 5...6 kHz when a logical “1” is present at inputs 2 and 13. Isolating inverting cascades on elements D2.3 and D2.4 ensure the transmission of antiphase rectangular multivibrator pulses to the inputs of switches V6, V7 and V8, V9 connected to windings I and II of transformer T1. A rectangular voltage with an amplitude of about 400 V is induced in winding III. This voltage is rectified using bridge V12 and charges the storage capacitor C8.
The multi-spark ignition mode when starting the engine is ensured using a multivibrator on elements D1.3 and D1.4. The multivibrator frequency of about 200 Hz is set by selecting capacitors C1 and C2. The multivibrator goes into self-oscillating mode when 12 V is supplied from the starter enable relay to the cathode of diode V2 and closes it. From output 3 of element D1.3, rectangular pulses of the multivibrator are supplied to input 4 of the Schmitt trigger, made on elements D1.1 and D1.2. When the breaker contacts are closed, at input 5 of element D1.1. there is a logical “0”, and at its inverse output there is a “logical 1”, regardless of the voltage level at input 4. Then the multivibrator D2.1, D2.2 works, and the storage capacitor is charged to a voltage of 400 V. If the breaker contacts are open, then at output 6 of element D1.1, “logical 1” appears with the frequency of the multivibrator D1.3, D1A. With a negative voltage drop, a differentiated pulse from this output opens transistor V3, which triggers thyristor V10. Capacitor C8 is discharged through the thyristor and the primary winding of the ignition coil, creating a spark in the spark plug. The same negative voltage drop is supplied to inputs 2 to 13 of the multivibrator D2 1, D2.2 and slows it down, due to which the switches V6...V9 are closed and energy from the battery is not consumed. After capacitor C8 is discharged, thyristor V10 closes. Thanks to the oscillatory process in the primary winding of the ignition coil, capacitor C8 is charged to a level of 0.4...0.5 of the initial voltage. The process of repeated sparking occurs as long as the contact plates of the breaker are open. After starting the engine and turning off the starter, diode V2 opens, multivibrator D1.3, D1.4 is inhibited and the device goes into single-spark ignition mode. Capacitor C, a shunt breaker, provides protection against contact bounce. Using switch S1, the voltage converter is turned on to power the electric razor. This toggle switch can be used as an anti-theft agent.
Transformer T1 is wound on a ferrite core Ш16x8 type М2000НМ and consists of four halves Ш8 X 8. Windings I and II each contain 22 turns of PEV-2 0.26 wire. The device uses resistors MLT-0.25, electrolytic capacitors K50-6, S8-MBGO, 1.0 X 600 V. Transistors V6, V8 type KT503, KT630, MP37, V7, V9 - KT817, KT819, KT805 A, KT808 And with a current transfer coefficient of at least 10. Transistors V3 - KT502G, MP25B, MP26B, V4 - KT815 A...G, KT404 A...G. Diodes VI, V2 - any low-power ones. Transistors V7, V9 are installed on separate radiators with a total dissipation area of at least 50 cm2.
When installing an ignition device, it is advisable to adjust the ignition timing using a strobe light. A correctly assembled device does not require adjustment.
It is difficult to imagine a modern car without an ignition. The main advantages that the electronic ignition system provides are well known, they are the following:
more complete combustion of fuel and the associated increase in power and efficiency;
reduction of exhaust gas toxicity;
easier cold start;
increasing the life of spark plugs;
reduction of energy consumption;
possibility of microprocessor ignition control.
But all this mainly applies to the CDI system
On this moment, in the automotive industry there are practically no ignition systems based on the accumulation of energy in a capacitor: CDI (Capacitor Discharge Ignition) - also thyristor (capacitor) (except for 2-stroke imported engines). And ignition systems based on the accumulation of energy in inductance: ICI (ignition coil inductor) survived the transition from contacts to switches, where the breaker contacts were simply replaced by a transistor switch and a Hall sensor without undergoing fundamental changes (an example of ignition in a VAZ 2101...07 and in integrated ignition systems VAZ 2108…2115 and onwards). The main reason for the dominant distribution of ICI ignition systems is the possibility of an integral design, which entails cheaper production, simplified assembly and installation, for which the end user pays.
This, so to speak, ICI system has all the disadvantages, the main one of which is the relatively low rate of magnetization reversal of the core and, as a consequence, a sharp increase in the primary winding current with increasing engine speed, and loss of energy. Which leads to the fact that with increasing speed, the ignition of the mixture worsens, as a result, the phase of the initial moment of growth of the flash pressure is disrupted, and efficiency deteriorates.
Partial, but not far The best decision This problem is solved by the use of dual and quadruple ignition coils (so-called), thereby the manufacturer distributed the load according to the frequency of magnetization reversal from one ignition coil to two or four, thereby reducing the frequency of core magnetization reversal for one ignition coil.
I would like to note that on cars with an ignition circuit (VAZ 2101...2107), where the spark is formed by interrupting the current in a fairly high-resistance coil with a mechanical breaker, that replacing it with an electronic switch from or similar in cars with a high-resistance coil does not give anything except a decrease current load on the contact.
The fact is that the RL parameters of the coil must satisfy conflicting requirements. Firstly, the active resistance R must limit the current to a level sufficient to accumulate the required amount of energy at start-up, when the battery voltage may drop by 1.5 times. On the other hand, too much current leads to premature failure of the contact group, therefore it is limited by the variator or the duration of the pump pulse. Secondly, to increase the amount of stored energy, it is necessary to increase the inductance of the coil. At the same time, as the speed increases, the core does not have time to remagnetize (as described above). As a result, the secondary voltage in the coil does not have time to reach the nominal value, and the spark energy, proportional to the square of the current, sharply decreases at high (more than ~3000) engine speeds.
The advantages of an electronic ignition system are most fully manifested in a capacitor ignition system with energy storage in a container rather than in a core. One of the options for a capacitor ignition system is described in this article. Such devices meet most of the requirements for the ignition system. However, their mass distribution is hampered by the presence in the circuit of a high-voltage pulse transformer, the manufacture of which is known to be difficult (more on this below).
In this circuit, a high-voltage capacitor is charged from a DC/DC converter using P210 transistors; when a control signal is received, the thyristor connects the charged capacitor to the primary winding of the ignition coil, while the DC-DC operating in blocking generator mode is stopped. The ignition coil is used only as a transformer (impact LC circuit).
Typically, the voltage on the primary winding is normalized at 450...500V. The presence of a high-frequency generator and voltage stabilization makes the amount of stored energy practically independent of the battery voltage and shaft speed. This structure turns out to be much more economical than when storing energy in inductance, since current flows through the ignition coil only at the moment of spark formation. The use of a 2-stroke self-oscillator converter made it possible to increase the efficiency to 0.85. The scheme below has its advantages and disadvantages. TO merits must be attributed:
normalization of secondary voltage, regardless of the crankshaft speed in the operating speed range.
simplicity of design and, as a result, high reliability;
high efficiency.
Disadvantages:
strong heating and, as a result, it is undesirable to place it in the engine compartment. The best location, in my opinion, is the car bumper.
Compared to the ICI ignition system with energy stored in the ignition coil, the capacitor ignition system (CDI) has the following advantages:
high rate of rise of high voltage voltage;
and a sufficient (0.8 ms) burning time of the arc discharge and, as a consequence, an increase in the pressure of the flash of the fuel mixture in the cylinder, because of this the engine’s resistance to detonation increases;
the energy of the secondary circuit is higher, because normalized by the arc burning time from the moment of ignition (IM) to the top dead center (TDC) and is not limited by the coil core. As a result, better flammability of the fuel;
more complete fuel combustion;
better self-cleaning of spark plugs and combustion chambers;
lack of glow ignition.
less erosive wear of spark plug contacts and distributor. As a result - a longer service life;
confident start in any weather, even with a dead battery. The unit begins to operate confidently from 7 V;
soft engine operation due to only one combustion front.
For the transformer, a ring with magnetic permeability h = 2000, cross-section > = 1.5 cm 2 is used (for example, “core M2000NM1-36 45x28x12” showed good results).
Winding data:
Assembly technology:
The winding is applied turn to turn over a gasket freshly impregnated with epoxy resin.
After finishing a layer or winding in one layer, the winding is covered with epoxy resin until the interturn voids are filled.
The winding is sealed with a gasket over fresh epoxy resin, squeezing out the excess. (due to lack of vacuum impregnation)
You should also pay attention to the termination of the terminals:
A fluoroplastic tube is put on and secured with nylon thread. On the step-up winding, the terminals are flexible, made with wire: MGTF-0.2...0.35.
After impregnation and insulation of the first row (windings 1-2-3, 4-5-6), a step-up winding (7-8) is wound around the entire ring layer by layer, turn to turn. , exposure of layers, “lambs” are not allowed.
The reliability and durability of the unit practically depends on the quality of the transformer.
The location of the windings is shown in Figure 3.
For better heat dissipation, it is recommended to assemble the block in a duralumin finned housing, approximate size - 120 x 100 x 60 mm, material thickness - 4...5 mm.
P210 transistors are placed on the housing wall through an insulating heat-conducting gasket.
Installation is carried out by hanging installation, taking into account the rules for installing high-voltage, pulsed devices.
The control board can be made on a printed circuit board or on a breadboard.
The finished device does not require adjustment; it is only necessary to clarify the inclusion of windings 1, 3 in the base circuit of transistors, and if the generator does not start, swap places.
The capacitor installed on the distributor is turned off when using CDI.
Details
Practice has shown that an attempt to replace P210 transistors with modern silicon ones leads to significant complications electrical diagram(see 2 lower diagrams on KT819 and TL494), the need for careful adjustment, which after one to two years of operation in severe conditions (heating, vibration) has to be repeated.
Personal practice since 1968 has shown that the use of P210 transistors allows you to forget about the electronic unit for 5...10 years, and the use of high-quality components (especially a storage capacitor (MBGC) with a long-lasting dielectric) and careful manufacturing of the transformer - even for a longer period .
1969-2006 All rights to this circuit design belong to V.V. Alekseev. When reprinting, a link is required.
You can ask a question at the address indicated in the lower right corner.
Literature
A. Kuzminsky, V. Lomanovnch
The conventional battery ignition system has serious disadvantages. The most significant of them are: low spark power, rapid wear of the breaker contacts, which switch a current of about 4 A in the circuit of the primary winding of the ignition coil, and high power consumption (about 50 W).
The proposed thyristor ignition systems make it possible to reduce the power consumed from the vehicle's electrical system several times and reduce the current flowing through the breaker contacts by 20-30 times. In this case, the spark power increases by at least 5 times and is almost independent of the condition of the spark plugs and the breaker.
Below is a description of two designs of electronic ignition units based on thyristors “BTZ-1” and “BTZ-2”. They have proven themselves very well during long-term operation on cars of the Moskvich, Volga and Zaporozhets brands. Thyristor ignition units are assembled from common widely used parts.
The schematic diagram of “BTZ-1” is shown in Fig. 1. In addition to powering spark plugs with high-voltage voltage, this unit allows you to use various low-power household appliances in your car, designed to be connected to a 220 V power supply (electric razor, toothbrush, etc.).
Since the starter consumes a large current from the battery, in the cold season the battery voltage when starting the engine can drop to 6-7 V. Naturally, at this moment the conditions for sparking worsen and starting the engine becomes more difficult. To maintain the required spark power
An electromagnetic relay P1 is introduced into the circuit of the BTZ-2 ignition unit (Fig. 2), the winding of which is turned on by the same switch as the starter. Contacts P1/1 and P1/2, when the relay is activated, turn on the additional step-up winding (V) of transformer Tp1. In this way, it is possible to maintain the required spark power even when the battery voltage drops to 5-6 V. The low-frequency filter Dr1 and C1 in the power circuit serves to suppress radio interference.
Both electronic ignition units are made according to a capacitor-contact circuit with a switching thyristor. To obtain the required sparking energy, a storage capacitor C2 (SZ) is used, which is charged from a high-voltage voltage converter and discharged through a thyristor to the primary winding of the ignition coil. In this case, a high voltage is induced on the secondary winding of the ignition coil, which is supplied to the engine spark plugs through the distributor. The voltage converters in both ignition systems are designed according to a symmetrical blocking generator circuit. The circuit allows you to use a common non-insulated heat sink connected to the chassis (“common minus”) to install transistors 77 and T2. At the same time, in addition to the structural simplification of the converter assembly, the thermal conditions of the entire device are significantly improved and the reliability of its operation is increased.
Let's take a closer look at the diagram of the BTZ-1 ignition unit shown in Fig. 1. The operating principle of push-pull transistor generators with transformer feedback is quite well known. Transistors T1 and T2 operate in switching mode, switching the current in the primary winding of transformer Tp1. In this case, a high voltage of a symmetrical shape (close to rectangular) is induced in the secondary winding Tp1. A rectifier bridge D1-D4 is connected to the secondary winding Tpl, from which a constant voltage of about 400 V is removed, used for
charging capacitor C2. Thyristor D5 is initially closed. At the moment of closing the contacts of the breaker, which short-circuits terminals 3 and 7 of the ignition device, the capacitor SZ is charged through diodes D8-D9 and resistor R7 to almost the full voltage of the battery. Resistor R7 provides some delay in the charging time, eliminating the effect of “bouncing” of the breaker contacts at the moment of closure.
When the breaker contacts open (terminals 3-7 BTZ), the capacitor SZ is discharged through the diode D7, the control electrode of the thyristor D5 and resistors R9-R10. In this case, a positive pulse is sent to the control electrode of thyristor D5, opening the thyristor. Storage capacitor C2, charged to a voltage of about 400 V, is discharged through thyristor-D5 and the primary winding of the ignition coil (terminals 1 and 2 of the BTZ). At the same time, the opened thyristor D5 shunts the output circuit of the voltage converter, disrupting generation.
The negative pulse coming from the primary winding of the ignition coil through the R8-D6 chain after switching the thyristor D5 instantly recharges the capacitor S3. As a result, the duration of the control pulse that opens the thyristor does not exceed 2 μs. This ensures the formation of one spark and at the same time protects the thyristor from switching multiple times. After capacitor C2 is discharged, thyristor D5 closes, generation in the converter resumes, and the whole process is repeated.
To facilitate the launch of the voltage converter, a small negative bias is set to the bases of transistors 77 and T2 from the voltage dividers R1, R2 and R3, R4. In order to prevent spontaneous switching of thyristor D5 under the influence of interference arising during the operation of the voltage converter and some elements of the vehicle's electrical equipment (generator, relay controller, direction indicators, etc.), filter C1 D9 was introduced into the thyristor control circuit. In addition, a protective negative bias of 0.5-0.7 V is additionally set to the control electrode of thyristor D5, which is removed from the chain R6 D8.
The difference between the second voltage converter (Fig. 2) and the first is that it has two step-up windings (I and V). Using the contacts of the electromagnetic relay R1, these windings can be connected in series to increase the voltage supplied to the input of the rectifier bridge D1-D4 when starting the engine is difficult. The second rectifier bridge, assembled on diodes D5-D8, is designed to power additional low-power current consumers. It can provide a power of about 20 W, at a voltage of 220-230 V. Terminal VI (“sync.”) is used to connect auxiliary devices of the engine control and regulation system (tachometer voltage stabilizer, etc.). Details and design of ignition units. When manufacturing an ignition device, special attention should be paid to the voltage converter transformer, on which the reliability of the electronic unit mainly depends. It is best to use a toroidal core made of steel grade E330-E340 (KhVP) or alloy 34NKMP or 79NM (permalloy) to make this transformer. In the first case, you can use an OL25/40X12.5 core or something similar, but with a slightly larger cross-section. For permalloy cores, we can recommend OL25/40X6.5 (2 pcs.).
You can also use a core made of ordinary transformer steel grade E42 or E43 (Sh16 plates, 16 mm set) to make this transformer. When selecting a core, it must be taken into account that the cross-section of its magnetic core must be at least 2 cm2. The frame for the transformer coil is made of electrical cardboard, the terminals of the windings are fixed on the perimeter of the frame cheeks. To give the transformer increased moisture resistance, after winding the coil is impregnated with electrical insulating varnish or compound (for example, KP-10).
The winding data of the transformer Tp1, made on W-shaped and toroidal cores, are given in the table.
First, step-up winding I is wound onto the coil. Cable paper can be used for interlayer insulation. Before laying the step-up winding, the toroidal core is insulated with two or three layers of varnished fabric or fluoroplastic. Then windings II, III and IV are wound. To improve the symmetry of the converter and reduce the leakage inductance of the transformer, the base and emitter windings are wound in two wires, placing the turns of windings III and IV between the turns of winding II.
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Number of turns |
Note |
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core Ш16Х16 |
core OL25/40Х12B |
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Winding is carried out in two wires |
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Transformer Tp1 in the circuit in Fig. 2 is made on a toroidal core of type OL32/50 X 16. Its main step-up winding I contains 1200 turns of PELSHO 0.25 wire; the additional step-up winding V has 600 turns of the same wire; emitter winding II contains 33 + 33 turns of PEV-2 1.0 wire; base windings III and IV each have 10 turns of PELSHO 0.41 wire. The windings are arranged in the same order as Tp1 in the circuit in Fig. 1.
If there are no cores of the specified brands and sizes, then it is easy to determine the suitability of the existing core for the specified transformers. The total power of the transformer used in a voltage converter is determined by its total load. It, in turn, is equal to the power spent on sparking at maximum engine speed and the maximum power of one or more current consumers that can be connected to the electronic unit. If these current consumers are not used while the vehicle is moving, only one of the specified loads (maximum) is taken into account.
The amount of useful power spent on sparking depends on the number of engine cylinders and the speed of rotation of the crankshaft.
For a four-stroke engine, the spark frequency is:
n is the number of crankshaft revolutions per minute; Nc — number of cylinders.
C - storage capacitor capacity (farad)
U is the voltage across the storage capacitor. In our case, at C = 1.0 µF to U = 400 V
Power spent on sparking at 6000 rpm:
Approximately the same power is consumed when operating an electric razor (15-18 W). Since the electronic unit is usually used to power one of the specified loads, it is obvious that the maximum power of the converter may not exceed 18-20 W.
In the case when the value of the saturation induction (W) of the available core is unknown, resort to experimental method. Base and emitter windings are wound onto the core for inclusion in the converter. They are connected to each other and connected to transistors T1 and T2, as shown in the diagram in Fig. 1. Winding is carried out in two wires; The base windings should have 10-15 turns of PELSHO 0.25-0.31 wire, the emitter windings should have 30-50 turns of PEL-2 1.0 wire. By connecting the power source, determine the generation frequency and current consumed by the device. To measure frequency, it is best to use an electronic oscilloscope or frequency meter. At home, you can approximately determine
Determine the frequency of the generator by comparing the pitch of the sound heard during operation of the converter with the tone of a musical instrument, for example, a piano. Typically, the generation frequency does not exceed 200-600 Hz (depending on the core). The shape of the generated oscillations should be as close to rectangular as possible, the current consumed by the device should not exceed 0.5-0.6 A at a power source voltage of 12 V. The value of W is determined by the formula:
where f is the frequency generated by the converter, Hz;
Sst — core cross-section, cm2;
Kst is the coefficient of filling of the core with steel;
Ue is the value of the alternating voltage on half of the emitter winding, V.
For strip toroidal cores, the value of Kst is in the range of 0.9 - 0.95. For cores made from ordinary W-shaped plates, Kst = 0.75 -0.8.
The maximum power that can be removed from a transformer made on a given core is determined using the following formula:
The values of I, W, Sst, Kst are already known to us, and the current density in the windings of the transformer (a) is usually chosen within the range of 3-5 A/mm2.
ntР - transformer efficiency (for toroidal cores t) = 0.9, for ShL type cores n = 0.85 and for Sh-shaped cores made of ordinary transformer steel n = 0.75-0.8);
Swindows—section of the core window in cm2;
Copper - the fill factor of the window with windings is chosen in the range of 0.2 - 0.25.
It should be noted that the optimal frequency for a converter with a transformer made on a conventional transformer steel core should not exceed 200 - 250 Hz. Otherwise, thermal
losses in the transformer core increase sharply, so that its heating may exceed the permissible value. Note also that when using cores with low electromagnetic parameters, an increase in the frequency of the converter leads to a distortion of the generated voltage shape and a significant decrease in the efficiency of the converter. For ShL type cores, the optimal frequency of the converter lies in the range of 250-300 Hz and for OL type cores - 600-700 Hz. It is also necessary to take into account that with increasing frequency of the converter, losses in semiconductor devices increase and the current consumption of the converter increases.
In order to increase the reliability of the device, it is advisable to provide a double power reserve for the converter transformer when calculating.
After selecting the core, the winding data of the transformer is determined. The number of turns of half of the emitter winding (per transistor) is found using the following expression:
where Ue = Umax - Uke;
Uke - voltage drop across an open transistor (saturation voltage) = 0.5 - 1 V. If the battery voltage is 12 V, Uts = 12 - 0.5 = 11.5 V. The remaining parameters are also known to us and can be used for calculation .
The number of turns of the boost winding is found using the expression:
Then we determine the wire diameter for all windings of the converter transformer. To do this, we first find the amplitude value of the collector current of transistors T1 and T2.
where Ptotal = 20 W;
npr (converter efficiency) = 0.7;
We find the effective value of the current in the emitter winding Tp1:
If we take the average current gain (Vst) for transistors T1 and T2 equal to 10, then the effective value of the current in the base winding can be determined using the following relationship:
(b - current density in the transformer windings 3-5 A/mm2). Then, given the output voltage of the converter (400 V) at a rated power of 20 W, we determine the effective value of the current in the step-up winding Tp1 in the circuit of Fig. 1:
In the same way, we determine the effective value of the current in the additional step-up winding Tpl in the circuit of Fig. 2:
Before installing transistors on the heat sink, you need to make sure they are in good condition. It is advisable to select transistors with equal (or as close as possible) values of reverse currents of collector junctions and current gain factors (Vst). The plane of the heat sink must be carefully polished to ensure a reliable fit to the surface of the transistors, which are secured to the heat sink using four screws with M3 threads. Note that in the diagrams in Fig. 1 and 2, you can use any powerful transistors (for example, P213-217, P210, etc.). You only need to take into account the permissible voltage between the collector and emitter of the transistor and the power dissipation. The total dissipation power released by transistors 77 and T2 is in the range of 15 - 22 W. The surface of the plate cooler (radiator) used to install transistors T1 and T2 must have an area of at least 25 - 30 cm2. In this case, the maximum temperature for the converter transistors will not exceed 60 - 70 ° C.
All rectifier diodes must be checked before installation in the ignition unit circuit. When diodes D1—D4 and D10 are connected to a constant voltage source of 600 V, the leakage current should not exceed 10 μA. To check diodes D5-D8 in the circuit in Fig. 2, the test voltage can be reduced to 400 V.
It is advisable to check thyristors D5 and D11 for voltage and switching current. To do this, assemble the circuits shown in Fig. 3,a and b. Then, gradually increasing the voltage of the power source (for example, using an autotransformer LATR-1 or LATR-2), the specified parameters of the thyristors are checked. The readings of voltmeter B1 (Fig. 3,a) at the moment of switching thyristor D5 will abruptly drop to zero, and milliammeter A1 will note a sharp increase in current. Note that thyristors with a switching voltage below 500 V should not be used in ignition devices. Likewise, it is not recommended to use it in the circuits in Fig. 1 and 2 thyristors with a leakage current of more than 1 mA (Fig. 3.6). Such thyristors will overheat greatly during operation and quickly fail. When checking thyristors, it is necessary to take into account that for some of them (for example, for thyristors of the KU202N type) the switching voltage can reach 700 V, and the leakage current at an operating voltage of 400-450 V does not exceed several tens of μA.
All fixed resistors used in the circuits in Fig. 1 and 2, type MLT-0.5 and MLT-2. In the diagram in Fig. 1 capacitor C1 - electrolytic, type K.50-6, C2 - type MBGO for a rated voltage of 400 V, SZ - metal-paper, MBM. In the diagram in Fig. 2 capacitor C1 - electrolytic type K50-6, C2 - three parallel connected capacitors type K50-6 100.0X25 V, SZ - MBGO for a rated voltage of 600 V, C4 - metal paper, MBM.
Throttle Dr1 (Fig. 2) is made on a KD-TD-4 core (ShL 16X20). Its winding contains 120 turns of PEV-2 1.0 wire. Electromagnetic relay P1 (Fig. 2) type RES-9 (passport No. RS4.524.203).
The base of the ignition unit, made according to the diagram in Fig. 1, a duralumin plate measuring 160X70X6 mm is used. Transistors 77 and T2 are strengthened
on a duralumin plate measuring 70 X 45 X 6 mm. It is installed at a distance of 50 mm from the edge of the base plate and secured in a vertical position using two M4 threaded screws. On the upper end part of this plate, three screws with M3 threads secure the part-free edge of the upper board of the columnar module, which combines almost all the small circuit parts of the ignition unit (excluding transformer Tp1, storage capacitor C2, transistors T1 and T2 and thyristor D5). All parts to be installed in the module are placed in the location shown in Fig. 4 order between the top and bottom boards of the module, installed at a distance of 35 mm from each other. The diagram of connecting jumpers on the module boards is shown in Fig. 5,a and b. Note that the quality of installation and reliability of all soldering in the module must be impeccable, otherwise it will quickly fail when working on a car. The module boards can be made using printed circuit boards from foil fiberglass or getinax. However, practice has shown that volumetric modules with attachments mounted on mounting tabs or pistons have proven to be much more reliable in operation. For installation, it is best to use silver-plated copper wire with a diameter of 0.5-0.75 mm.
Having secured the volumetric module to the radiator of transistors T1 and T2, a transformer Tp1 is installed next to it on the base plate. On the other side of the module there is a storage capacitor C2 and a thyristor D5, which is fixed to the base using a small copper or brass elbow, which also serves as an additional heat sink for the thyristor. The thyristor body is insulated using two mica washers 0.05–0.1 mm thick and a fluoroplastic bushing inserted onto a mounting screw.
The ignition unit, made according to the diagram in Fig. 1, placed in a protective metal casing measuring 155X80X75 mm. It can be made from sheet duralumin 1.5-2.0 mm thick or steel sheet 1.0 mm thick. For better sealing, it is recommended to lay a rubber edging between the base and the casing of the unit.
A correctly assembled ignition unit, especially if all parts installed in the circuit are carefully checked, usually does not require additional adjustment. If the ignition device switches to continuous generation mode and is not controlled by the breaker contacts, then either it uses a thyristor with a low switching voltage, or the D9 diode is broken. Sometimes this phenomenon can be observed due to insufficient capacitance of capacitor C1 and a malfunction of diode D6. If transistors T1 and T2 are obviously in good working order, but there is still no generation, then to identify the cause of the malfunction of the voltage converter, first disconnect capacitor C2 from the step-up winding of the transformer Tpl, then thyristor D5 and rectifier bridge D1-D4 and replace the faulty parts. In cases where the operation of the converter is accompanied by a hoarse or hissing sound, check the serviceability of diodes D1-D4 and transistors T1-T2. The cause of a malfunction of the storage capacitor C2 may be a short circuit of one of the terminals to the housing or a breakdown between the plates of the capacitor. In the event of a malfunction of the D5 thyristor, first of all, you need to make sure that the mica washers and the bushing that isolate the thyristor body from the mounting bracket are intact. If the insulation is not damaged and the thyristor itself is working, but there is still no generation even when the step-up winding Tpl is disconnected from all of the listed parts, then the cause of the malfunction should be sought in the voltage converter transformer itself (incorrect connection, break or interturn short circuits in the windings).
The absence of a new formation when the breaker contacts open indicates that the thyristor control circuit is open (for example, if diode D9 is damaged).
When checking the ignition device outside the car, be sure to connect the ignition coil housing to the electronic unit housing, since otherwise breakdown of the coil may occur and damage to parts of the electronic unit.
When installing the ignition unit on a car, it is installed under the hood as far as possible from the engine exhaust manifold and secured with four screws with M5 or M6 threads. The temperature at the installation site of the unit should not exceed + 70° C, otherwise the reliability of the ignition device is reduced due to severe overheating of the semiconductor devices.
To connect the ignition device to the car's on-board network, it is best to use some suitable plug connector (for example, type RSHABPB-14), as shown in Fig. 6. At the same time
provides a quick transition from one type of ignition to another. To do this, simply change the position of the plug in the connector socket by 180°, as shown in Fig. 6 (“OZ” - conventional ignition, “TZ” - thyristor ignition). In addition, the plug can serve as a “key” for the anti-theft device - if you remove it from the socket, both ignition systems will be turned off. Without knowing the “key” diagram, it will be difficult to start the engine, since in addition to those indicated in Fig. 6, many other options for the location of jumpers in the plug are possible.
In the case of using the ignition unit on cars with a 6-volt battery, it is necessary, in addition to recalculating the winding data of the voltage converter transformer, to also adjust the resistance value of resistors R1-R2 and R3-R4 (voltage dividers in the base circuits of transistors T1-T2).
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