Principle of electronic ignition device and how to control the ignition of fireworks

Working principle of electronic ignition system

First, the generation of electric spark.

We know that matter is made up of molecules, molecules are made up of atoms, and atoms are made up of nuclei (including protons and neutrons) and electrons.

Protons revolve around the nucleus. In general, the negative charge of electrons and the positive charge of protons are equal, and the balance between them makes the total charge of atoms.

The quantity is zero. Under the action of external energy, when the speed of electrons in the outer layer of atoms accelerates to a certain extent, they will be out of orbit and others will be killed.

After atoms "capture" electrons, the amount of negative charge increases, showing negative polarity, which is called "negative ion" and loses charge.

The amount of atomic negative charge decreases, showing positive polarity, which is called "positive ion". The regular directional movement of ions forms an electric current.

According to the above theory, before the mixture enters the cylinder, the micro-molecules will be dissociated into positive ions and negative ions. During cylinder compression,

Because the gas is squeezed and rubbed, it will also produce more positive ions and negative ions. When a voltage is applied to the two electrodes of the spark plug, ions are subjected to electric field force.

Under the action of, positive ions move to the negative electrode and negative ions move to the positive electrode, forming a current. But when the electric field force is small (electricity

Down), the electrons in the atom move at a low speed, and they can't get rid of the gravity of the nucleus to escape from the orbit and form new ions. So, in gas,

Only the original ions conduct electricity. Because their number is very small and the discharge current is very weak, they are only theoretically conductive and equivalent in the circuit.

A large resistor r is connected in series. (See Figure 2)

With the increase of voltage, the electric field force increases and the kinetic energy of atoms increases. A large number of atoms get rid of the nuclear attraction and orbit, producing mixed gas.

A large number of ions are generated, and at the same time, the speed of positive ions and negative ions moving to the poles is accelerated, and the kinetic energy generated by positive ions and negative ions is easily neutralized.

The breaking of sex molecules separates neutral molecules into positive ions and negative ions, and these newly generated positive ions and negative ions are also in a high-speed state under the action of electric field force.

Moving to the two poles and breaking other neutral molecules, this reaction happens continuously like an avalanche, making the positive ions in the gas move to the two poles.

And the number of negative ions increases sharply, which makes the gas lose its insulation and become a conductor (R resistance is small), forming a discharge ionization channel, that is, breakdown jump.

It's on fire. Among them, the high-temperature thermoelectric ionization channel (several thousand degrees) formed by the high-speed movement of positive and negative ions and friction collision emits light, so we see fire.

Flowers, at the same time, the gas around the ionization channel suddenly expands when heated and makes a "snapping" sound.

Second, the influence of engine conditions on ignition

(1) The larger the spark plug electrode gap, the weaker the electric field and the smaller the electric field force, so it is difficult to generate sufficient separation.

Son, so you need a higher voltage to jump fire. Factors that affect the breakdown voltage also include the shape of the spark plug electrode and the polarity of the voltage.

(2) Gas red has a high gas density (rich mixture), and the more neutral molecules per unit volume of gas, the smaller the intermolecular distance.

Positive ions or negative ions are more likely to collide with molecules, and the acceleration distance is short, the speed is not high, and the kinetic energy is small, so it is difficult to break neutral molecules and produce new ions.

Therefore, higher voltage is needed to start a fire. Similarly, the higher the temperature of the spark plug electrode, the smaller the gas density near the electrode, so the less power is needed.

Stress can cause fire.

(3) The higher the temperature of the mixed gas, the greater the molecular internal energy and the easier it is to ionize, so the flashover voltage can be reduced; On the contrary, when the cold car starts,

Because the ion mobility in the mixed gas is low and it is not easy to ionize, a higher flashover voltage is needed. According to the measurement, when the cold car starts, the flashover voltage

The maximum voltage is about 15kv-25 kv. After the temperature is normalized, the automobile only needs 8kV- 12kV breakdown voltage.

Third, the engine requirements for the ignition system

1. It can generate high enough voltage to break through the gap between spark plugs.

The voltage required to generate sparks between spark plug electrodes is called breakdown voltage or flashover voltage. Under normal circumstances, the output high voltage of the compressor is greater than the flashover voltage, otherwise it will catch fire.

2. The ignition energy can be controlled.

A. In order to ignite the mixture reliably, the spark plug must have enough ignition energy. When the engine works normally, the energy of electric spark is only 1 ~ 10MJ. However, at the time of starting, in order to ensure reliable ignition, the ignition energy of the spark plug can reach100J.

B the ignition energy can be adjusted according to various working conditions of the engine, that is, the primary current (energy) of the high-voltage transformer can be controlled by controlling the on-time of the high-voltage output transistor (traditional mechanical angle-closing control).

3. The ignition time should be adapted to various working conditions of the engine.

A the optimal ignition advance angle required by different engine speeds and loads is different, and the ignition system must be able to automatically adjust the ignition advance angle. Expression of engine ignition advance angle;

Actual ignition advance angle = initial ignition advance angle+basic ignition advance angle+corrected ignition advance angle (or delay angle).

B this digital electronic ignition system can also intelligently control the ignition time within the range of near explosion point or micro explosion point, so that the gasoline engine can achieve the best power, economy, acceleration and emission control.

Four, the composition of digital electronic ignition system

Digital electronic ignition system is another great progress of gasoline engine ignition system after the use of contactless electronic ignition device, which is called microcomputer-controlled semiconductor ignition system.

Classification of ignition system:

A.。 Inductive energy storage ignition system (see Figures 3, 4 and 5 for actual circuits)

Before the ignition system generates high voltage, the ignition energy is stored in the way that the ignition coil establishes magnetic field energy. At present, most ignition systems used in automobiles are inductive energy storage. (Focus on analysis and introduction)

B. Capacitive energy storage ignition system (Figure 6)

Before generating high voltage, the ignition system first obtains energy from the power supply, and stores the ignition energy by establishing electric field energy through the energy storage capacitor. Mostly used in high-speed engines, such as racing cars.

The working principle is to convert a lower power supply voltage into a higher DC voltage (500V- 1000V) to charge the capacitor to store energy, and the ignition time is turned on by electricity.

Capacitor discharge causes transformer to generate high voltage. It is characterized by fast charging and discharging period of capacitor, short duration of high voltage flashover spark (about 65438 0 microseconds) and large current.

No left spark tail. The ECU ignites 1-3 times in an ignition cycle according to the engine working conditions.

The induction energy storage ignition system is mainly composed of three parts: microcomputer (ECU), various sensors and high voltage output part (power tube, transformer, high voltage line and spark plug). (see figure 1)

1. European Currency Unit

ECU is the intelligent control center of the whole vehicle, which commands and coordinates the work of all parts of the vehicle, and at the same time, ECU also has the function of automatic diagnosis.

Among them, handling and controlling the ignition system is one of the most important tasks of ECU. There are more than 5 million groups in the ROM of ECU.

Most of the data are obtained by measuring and optimizing the actual working conditions of the engine, including the whole working range of the gasoline engine.

Including all relevant data such as the optimal ignition advance angle and fuel injection pulse width at various speeds and loads. Storage quantity of ECU for different vehicle types

According to the information, all manufacturers keep the information confidential and do not disclose it; These data ensure the power, acceleration, economy and

Achieve the best combination of emission control.

Principle of ECU controlling ignition

After the engine is started, the ECU collects the dynamic parameters of each sensor of the engine every 10ms and processes them according to the pre-programmed program.

Some data, and stored in RAM; At the same time, ECU should select from its rom according to the power supply voltage.

Take out the current conduction time of the primary coil of the high-voltage transformer that is suitable for the current working condition (that is, ECU outputs square wave voltages with different widths to control the high voltage).

Output the current of the primary winding of the transformer to control the high voltage transmission voltage. ) ECU synthesizes these data and only reads them.

The optimum ignition advance angle suitable for the current engine working conditions is found (calculated) in the memory ROM and stored in the random access memory RAM.

Then, by using the engine speed (or rotation angle) signal and the crankshaft position signal, the optimal ignition advance angle is converted into the ignition time, that is, the cut-off height.

Primary current moment of voltage transformer.

Under the following circumstances, ECU ignition is controlled by open loop, and the ignition works according to the preset program.

A. when the engine is started. B. under heavy load. When the throttle valve is fully opened.

2. Sensor

Sensors are measuring elements with different types and functions, which are installed in different related parts of the engine and feed back various parameter changes of engine working conditions to ECU for calculation data.

The sensors used in the ignition system mainly include: air flowmeter and air temperature sensor, engine speed and crankshaft position sensor, throttle position sensor, coolant temperature sensor and knock sensor, oxygen sensor, etc.

3. High voltage output

A. High-voltage output power triode: it plays a switching role in the circuit.

B. High-voltage output transformer: converts the low voltage in the circuit into high voltage for spark plug ignition.

C. High-voltage line: transmitting high-voltage electricity to the spark plug in the circuit.

D spark plug: introduce high-voltage electricity into the cylinder in the circuit and convert electric energy into heat energy.

Generation and control principle of high voltage

Basic theory:

A current passing through a conductor will generate a magnetic field, and the greater the current, the stronger the magnetic field.

B. The change of conductor magnetic flux (cutting magnetic field lines) will produce induced electromotive force, and the greater the change rate of magnetic flux, the stronger the induced electromotive force.

C. The direction of induced electromotive force in a conductor always hinders the change of magnetic field lines (current), thus generating impedance.

D: When the inductance element is turned on, the current increment changes exponentially with time.

According to different engine working conditions and power supply voltage, ECU selects the best ignition data stored in read-only memory, that is, output.

Square wave voltages with different widths are provided to the high-voltage output control unit to control the on and off of the three legs of the power supply. → The base of the power transistor receives a square wave.

When the voltage is saturated and turned on, the primary coil current of the high-voltage output transformer begins to turn on, and the inductance in the primary coil generates back electromotive force.

Potential, so the current can't change suddenly, and the current increases exponentially. (theoretically, the current reaches its maximum when time is infinite, but in fact it should be

In use, we only need to apply the rapid rise period of current, because only the power supply voltage and time are variables in the primary circuit, so the ECU is in accordance with

According to this exponential law, the length of conduction time can be calculated to achieve the purpose of controlling high voltage energy. ) → and generate the corresponding magnetic field; → primary

The coil current will quickly rise to the preset value. When the ignition time comes →ECU cuts off the square wave voltage (or adds a reverse voltage) to make the power supply three poles.

Immediately cut off the pipe; → The current in the primary coil of the transformer is suddenly cut off, that is, the magnetic field lines of the transformer suddenly disappear (the flux change rate is very large), which makes

The transformer coil generates induced electromotive force, and → due to the large number of turns in the transformer secondary coil, a higher ignition voltage is generated. If every time

The induced voltage of the coil is e, and the secondary coil has n turns, so the secondary voltage is U=E×N (volts).

Electrical principle of ignition

Simplification of the electrical principle of the whole ignition system: Figure1; Equivalent operation of transformer secondary: Figure 2

The distributed capacitance of the transformer secondary coil, the distributed capacitance of the spark plug and the high voltage line constitute the loop capacitance C. When the circuit is unshielded, C is about 50PF, and when it is shielded, it is about 150PF. Spark plug gap is equivalent to variable resistance R.

The change of high-pressure energy consumption is divided into three stages.

First stage

Discharge period (ignition period) of capacitor C: the ignition high voltage generated by the secondary winding of transformer charges capacitor C. When the voltage of capacitor C rises to.

When the breakdown voltage of the spark plug is reached, the flashover capacitor C of the spark plug rapidly discharges, and the gap voltage of the spark plug rapidly drops to several hundred to several thousand volts.

C The instantaneous discharge current is greater than 10-50 amps, and the discharge time is about 1 microsecond. The higher the ignition voltage (that is, the greater the ignition energy), C discharges.

The greater the flow.

Under normal circumstances, the mixture in the cylinder is spark ignited at this time. If the off-line ignition power is disturbed by high speed in the engine cylinder

Blowing, C is recharged by the high pressure of the autoclave, and then C is discharged for the second time to generate ionization channels.

Note: The voltage suddenly drops from 1 0000 V-20000V to 20000 V to several hundred V within1microsecond, thus generating a strong square wave.

Voltage, and radiate electromagnetic waves and interference waves to external appliances through high-voltage lines. A square wave consists of n sine waves, so it forms one.

Interference electromagnetic frequency band centered on 1 microsecond time base.

stage Ⅱ

Induction discharge period (combustion period): low resistance formed by ionization channel generated by capacitor C discharge generates induction discharge. Due to the capacitance c

The ionization conductance (resistance) produced by discharge cannot disappear immediately, and there is enough high-voltage energy in the secondary inductance of transformer, so the inductance

Continue to release ionization conductance, so that the spark lasts.

Due to the change of the discharge current of the secondary coil, the magnetic flux changes, and the secondary inductance coil generates inductive reactance electromotive force, that is, output.

The electromotive force generated in the opposite direction to the discharge current of the inductor prevents the current from melting, so the discharge current is very small, and the current is tens of milliamps.

Therefore, high-voltage energy discharge takes a long time, and the spark duration of this induced discharge is commonly known as spark tail.

A "flame center" is generated after the discharge of the primary capacitor C, and this "flame center" moves with the high-speed turbulence in the cylinder.

Remove the spark plug electrode. At this time, the discharge spark of induced electric energy will ignite another "flame center" of the mixture, which is used to ignite the mixture.

In addition, the "flame center" makes the mixture quickly form the "open flame period" of combustion in the whole cylinder, that is, the combustion temperature of the mixture in the cylinder.

The gas pressure reaches the highest value. This process is called mixed steam combustion period, and the combustion time is between 750 μ s and 2500 μ s.

When the engine starts and runs at low speed, the induced discharge spark is very important. When the engine is started or under abnormal working conditions, the discharge period of capacitor C is extreme.

It is possible that the mixture was not ignited. At this time, the mixture can only be ignited by the spark of induction discharge.

When the cold car starts, the temperature of the mixture in the cylinder is low and the atomization effect is poor, so it takes a long spark period to ignite the mixture. At low speed, due to

The turbulent velocity of the mixture in the cylinder is low, and the first "flame center" moves slowly, so it is necessary to ignite the second "flame center" to accelerate the mixture.

Combustion, so the ignition spark period is longer. However, when the engine speed is higher, the turbulent velocity of the mixture in the cylinder is faster, which is the "flame center"

High-speed movement and rapid propagation ignite the mixture in the cylinder, so there is no need for a second "flame center".

According to the combustion time of mixed steam is between 750 μ s and 2500 μ s, the longest spark duration is about 700μS to ensure mixing.

Complete combustion of mixed gas. Experiments show that too long spark duration can not improve the combustion effect. On the contrary, the high heat generated by the ionization channel increases.

The temperature of the spark plug itself accelerates the ablation of the spark plug electrode, which is the main reason for controlling the ignition energy.

Note: the secondary current cannot be simply calculated by formula I=U/R, because the direction of inductive reactance electromotive force generated by inductance always hinders the magnetic field lines.

(current) changes, so I=U/R+E/R is used to calculate, U high voltage, E induced voltage, R loop resistance; Or I=U/r,

R= equivalent resistance of spark plug+high voltage line resistance+coil DC resistance+inductive reactance resistance. In fact, the resistance of the high-voltage line and the DC resistance of the coil are part of the whole resistance.

The proportion of resistance is small and can be ignored.

In addition, from this principle, it is clear that the ignition energy has nothing to do with the high-voltage line (of course, it does not include damaging the high-voltage line). Take a closer look at this.

After this article, if you still believe that there is XX high-energy spark, it can only show that your level is very poor.

The third stage

Oscillation decay period: with the increase of discharge time, the energy (voltage) consumption of the inductor coil decreases, which makes more and more electric ions separated from the gas.

The less, the smaller the discharge current of the inductor, the lower the temperature of the ionization channel, and the number of ions rooted in the channel decreases sharply, which is equivalent to on.

The resistance value r of the spark plug gradually rises to infinity, and the spark plug stops firing. At this time, the residual energy of the inductor charges the capacitor C, and the capacitor C is charged.

Repeat the induction discharge until the next ignition cycle comes.

Note: At the same time, the gradually depleted sinusoidal oscillation wave is generated at this stage, which causes interference to the outside world, but its intensity is far less than the electromagnetic wave generated by the first stage capacitor discharge.

mistimed remarks

Cars have a history of 100 years. The cylinder and piston of the engine have not changed, but the technology has been improved. Since microcomputer control was introduced into the engine, qualitative changes have taken place. Therefore, the engine system is more and more perfect, from fuel injection to ignition, air intake to exhaust are closely related and interrelated. It will make my DIY space smaller and smaller, so if I don't have a high professional level, please don't replace the ignition electrical equipment different from the original car, especially the ignition transformer. Please think twice.

In terms of ignition system, many people think that replacing the more expensive spark plugs and high-voltage lines will improve the performance of the engine, but it is not.

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With more and more cars entering society and families, car enthusiasts and related personnel are eager to know the working principle and maintenance of some systems on cars. Among them, the electronic ignition system widely used in modern automobile electrical components is a very important part. Why do cars use electronic ignition? Based on the principle of going from shallow to deep, this paper first introduces the principle and shortcomings of traditional automobile mechanical contact ignition (commonly known as platinum contact ignition). The traditional schematic diagram of mechanical contact ignition is 1, which is the schematic diagram of the ignition circuit of a 4-cylinder gasoline engine. It is mainly composed of storage battery, ignition switch, power-off contact, capacitor, spark plug, ignition coil and additional resistor. After the ignition switch is turned off, the ignition current of the battery passes through the ignition switch and the auxiliary battery (or through the starter short-circuit switch, which is closed when starting), reaches the primary winding of the spark coil, passes through the contacts of the circuit breaker, and then returns to the negative pole of the battery through the car body to pick up iron (that is, grounding). At this time, due to the current in the primary winding, a magnetic field is formed in the iron core of the ignition coil to store electromagnetic energy. When the engine runs to drive the cam of the distributor to rotate (the angle of the cam is equal to the number of cylinders of the engine), the corner top of the cam starts the insulating bump on the contact arm to open the contact of the circuit breaker, so the current in the primary winding is interrupted. Because the ignition coil is similar to a step-up transformer, due to mutual inductance, a high voltage of about 20kv is generated in the secondary winding, which will break through the electrode of the spark plug through the electrical appliance and generate sparks to ignite the combustible mixture in the cylinder. In this ignition system, the capacitor (about 0.22μF) connected in parallel on the power-off contact has two important functions: 1. When the power-off contact is disconnected, the self-induced electromotive force of about 300V will be generated in the primary winding due to the disappearance of the magnetic field. If there is no capacitor, this self-induced electromotive force will burn the contacts. When the power-off contact is disconnected, the current flows to charge the capacitor, and then the capacitor and the primary winding form an oscillating discharge. The charged capacitor swings and discharges in the opposite direction of the current through the primary winding, which accelerates the disappearance of the magnetic field and increases the mutual inductance electromotive force of the secondary winding. The whole ignition process can be divided into two stages: the increase of primary winding current of ignition coil when the power-off contact is closed; After the power-off contact is disconnected, high voltage electricity is generated in the secondary winding. In this traditional ignition method, the power-off contact is the frequent point of failure and the breakthrough point of troubleshooting. Essentially, this ignition circuit boosts the low voltage of the battery 12V to the high voltage of tens of thousands of volts through the ignition coil (that is, transformer). As we all know, the transformer only works on alternating current, and there is no alternating current power supply in the car, so the current in the primary winding of the ignition coil is interrupted to generate pulsed direct current to imitate alternating current. So that the secondary winding can generate high-voltage electricity. Knowing this principle, it is not difficult to judge the fault. First, there must be a good pulse low voltage (12V), otherwise there will be no high voltage. The reasons of bad pulse low voltage electricity are mostly caused by contact burning, poor contact and inaccurate gap. The traditional mechanical contact ignition has several fundamental disadvantages: 1. Although the capacitor has arc extinguishing function, the contact is easy to burn. The cam of distributor and the protrusion on the moving contact arm are easy to wear, which leads to poor contact of power-off contact and inaccurate contact gap (normal gap is 0.35-0.45mm), which makes it difficult to start the vehicle and changes the ignition time. The current in the primary winding of the ignition coil cannot be increased (≤5A). Because the primary winding current increases, it is easier to burn out the power-off contact. However, in order to be alert to the mutual inductance electromotive force generated by the secondary winding (i.e. the high voltage of the secondary winding) and be more conducive to igniting the combustible mixture in the cylinder, it is necessary to increase the current passing through the primary winding (i.e. the current passing through the power-off contact) to produce greater magnetic flux change. This is obviously an insoluble contradiction. 1. Once the gap of power-off contact is adjusted, it will not be changed artificially. As we all know, the speed of automobile engine is constantly changing. Take a four-cylinder engine as an example. At low speed, the closing time of power-off contact is long, and the current passing through the primary winding of ignition coil leads to higher mutual inductance electromotive force in the secondary winding. At high speed, the closing time of power-off contact is short, and the current flowing through the primary winding is small, which leads to the reduction of mutual inductance electromotive force generated by the secondary winding. Furthermore, with the increase of engine cylinder number (such as 6-cylinder engine), the closing time of power-off contact will be shortened, the current in the primary winding will be further reduced, and finally the mutual inductance electromotive force generated by the secondary will also be reduced. Although the ignition circuit has the compensation function of PTC additional resistance, it still cannot fundamentally solve the problem. In a word, the maximum mutual inductance electromotive force of the secondary winding (that is, the discharge voltage that breaks through the spark plug electrode) in the traditional power-off contact ignition system largely depends on the maximum current of the primary winding when the power-off contact is disconnected. The voltage in the secondary winding decreases with the increase of engine speed and the number of engine cylinders. The main reason is that the current in the primary winding of the ignition coil is not constant (although there is PTC additional resistance compensation), and the ignition closing angle cannot be controlled. Therefore, the traditional mechanical contact ignition has come to an end and must be fundamentally changed. The principle and maintenance of contactless electronic ignition appeared in the late 1960s. It cancelled the power-off contact in the traditional mechanical ignition device, so the mechanical wear problems were reduced, and many of them were not even worn. Therefore, it has brought many advantages, such as easy starting, high ignition energy, low fuel consumption, less pollution, less maintenance and so on. Contactless electronic ignition can be divided into two categories: inductive energy storage (the energy storage element is the ignition coil) and capacitive energy storage (the energy storage element is the capacitor). The former is mainly used in automobiles, while the latter is mainly used in motorcycles. The contactless automobile electronic ignition system can be divided into photoelectric electronic ignition, electromagnetic induction (magnetoelectricity) electronic ignition and Hall sensor (Hall effect) electronic ignition according to the signal sensor (signal generator) used. The block diagram of the automobile electronic ignition system is shown in Figure 2. Because the early photoelectric electronic ignition was not ideal, it is basically not used now. At present, magnetoelectric sensor and Hall sensor electronic ignition system are widely used. There are two kinds of ignition controllers: discrete components and integrated circuits, which are equipped with high-energy ignition coils. Other components are similar to the traditional contact ignition system. 1. Principle and maintenance of magnetoelectric electronic ignition system Figure 3 is a schematic diagram of an automobile magnetoelectric electronic ignition circuit. It consists of signal generator L (signal sensor), ignition coil, spark plug, power supply (battery) and so on. The working principle of the signal generator is shown in Figure 4. The signal generator is installed in the distributor and consists of iron core, permanent magnet, signal coil, trigger wheel and air gap. When working, the engine drives the trigger wheel on the distributor shaft to rotate, and uses the principle of electromagnetic induction to output AC signal voltage. The specific working principle is as follows: 1 When the trigger wheel turns to position (a) in Figure 4, the signal coil iron core and the convex teeth of the trigger wheel are in the closed position. At this time, the air gap becomes smaller and smaller, and the magnetic flux gradually increases from this position. When the core of the signal generator coil is located between two convex teeth, the change rate of magnetic flux is the largest. Therefore, the induced electromotive force is the highest, that is, the generated signal voltage is also the highest. According to Lenz's law, terminal A is+and terminal B is-. 2 When the trigger wheel continues to rotate to the position (b) in Figure 4, the center position of the signal coil iron core coincides with the center of the convex teeth of the trigger wheel. At this time, the air gap is the smallest and the magnetic flux is the largest, but the magnetic flux change rate is zero. So the electromotive force induced in the coil is also zero, that is, there is no induced voltage output. 3 When the trigger wheel turns to position (c) in Figure 4, the convex teeth of the trigger wheel begin to gradually leave the signal coil core, the air gap begins to increase, and the magnetic flux begins to decrease. When turning to a certain position between the two convex teeth of the trigger wheel, the change rate of magnetic flux is the largest. At this time, the induced electromotive force is the highest, but the polarity of the induced voltage is opposite to that in Figure A, that is, A is-and B is+. If the trigger wheel keeps turning (when the engine is running), the above work process will happen repeatedly. For a 4-cylinder engine, the trigger wheel rotates 360 degrees to generate four alternating signal voltages at a time, that is, 90 degrees generates one alternating signal voltage. It is actually similar to a small alternator, and the output AC signal voltage is sent to the ignition controller. The working principle is shown in Figure 3, which is one of the electronic ignition circuits of ordinary automobiles. The working principle is very simple, which consists of signal pickup, shaping and amplification, switch and other circuits. Since these circuit principles are introduced in general electronic books and periodicals, here is only a brief description of the working process. When the terminal A of the AC transformer output by the signal generator is+and the terminal B is-,the diode D 1 is turned off, the transistor T 1 is turned on, T2 is turned off, and T3 and T4 are turned on. At this time, current flows into the primary winding of the ignition coil to store energy. When the trigger wheel rotates, the terminal A of the output AC transformer is-,the terminal B is+,the diode D 1 is on, the transistor T 1 is off, T2 is on, and T3 and T4 are off. The current in the primary winding of the ignition coil is cut off. The secondary winding generates high-voltage electricity, which causes the spark plug to discharge and ignite. Fig. 5 is an ignition circuit using the special ignition integrated circuit 89SO 1 produced by Motorola. The working principle is similar, but some auxiliary functions are added, such as angle control and ignition constant current control. Principle and maintenance of automotive electronic ignition system (II) Generally speaking, automotive electronic ignition system is reliable, but failure is inevitable. The following are the maintenance steps and methods: Step 1: First, check the wires for obvious short circuit, poor open circuit contact, etc. Don't blindly disassemble the electronic ignition device at the beginning. Because many faults are related to the special use environment of the car, such as road bumps, soil erosion, corrosion and so on. Especially when soil invades the connector of conductor, it is easy to cause faults such as short circuit and poor contact. Step 2: After the above inspection is completed, you can further inspect the components in the ignition system. First, check whether the grounding circuit of each component is in good condition, which is also the fault-prone point. For example, the ignition controller uses its shell and body to ground (or special grounding wire), and then connects with the negative electrode of the battery to form a loop. If the grounding is not good, the ignition system will sometimes fail to work or even fail to work at all. Step 3: Unplug the distributor (signal sensor) and electronic ignition controller after confirming the failure of electronic ignition components. Firstly, the signal sensors are tested separately, and the plugs output by the signal sensors are grounded with the AC voltage of the multimeter, and the engine is started to drive the trigger wheel to rotate. At this time, if the multimeter does not indicate, that is, there is no signal voltage output, it means that the signal sensor is faulty. When measuring its resistance value with a multimeter, it should generally be several hundred ohms (depending on different sensor signal coils). The gap between the trigger wheel and the signal coil core is generally 0.2-0.4mm, otherwise it should be adjusted or replaced. Step 4: Check the electronic ignition controller. The electronic ignition controller is actually a transistor switching circuit, which shapes and amplifies the input signal waveform. First, turn on its working power supply, take a grid of 2V voltage from the storage battery or use 1.5V dry battery to contact the+and-poles (signal voltage output by analog signal sensor) of the inputs A and B of the electronic ignition controller respectively, and monitor the voltage between the primary (power input) of the ignition coil and the ground with a multimeter DC voltage block. If the indication of the multimeter changes alternately around 0V (the tube voltage drop when the switching transistor is turned on) and the power supply voltage 12V, it shows that the electronic ignition controller is good. Otherwise, there is a fault. Step 5: Check the ignition coil. The ignition coil on a car is actually a step-up transformer. The resistance of the primary winding should be 0.5-1.7 Ω, and the resistance of the secondary winding should be 3-4 Ω or10-15 Ω (depending on different ignition coils). The resistance of high voltage ignition wire shall not be greater than 25kΩ, otherwise it shall be replaced. ) generally, after the above steps, you can find out the fault. Of course, the automobile ignition system also has various faults such as good spark plug, ignition head and battery, but that is a common problem that traditional contact ignition systems often encounter. Principle and maintenance of Hall-type automobile electronic ignition Magnetoelectric electronic ignition, because the signal sensor is based on the electromagnetic induction principle, its working property is similar to that of a small alternator. Therefore, when the engine is running at a low speed (such as starting), the output signal voltage is small, and even at a low speed, it cannot generate enough signal voltage. Therefore, there are certain requirements for engine speed. The new Hall sensor type automobile electronic ignition applies the Hall effect principle, and the sensor outputs a switching pulse signal with steep leading edge and steep trailing edge. As long as the engine rotates, there will be Hall signal voltage output, which is not affected by the speed. And can work stably in harsh environment. It greatly improves the timing accuracy and reliability of automobile ignition, greatly reduces the failure rate and is more widely used. Fig. 6 is a schematic diagram of the working principle and structure of the automobile Hall sensor. It consists of a Hall element, a permanent magnet and a shovel-shaped metal sheet (which can block and bypass the magnetic field), and the metal sheet can rotate in the air gap between the Hall element and the permanent magnet. When working, the power supply provides a small working current to the Hall element, and the engine drives the shovel-shaped metal sheet to rotate through the transmission mechanism. When the shovel-shaped metal sheet enters the air gap between the Hall element and the permanent magnet, as shown in fig. 6 (a), the magnetic field is blocked and bypassed by the metal sheet, so the Hall signal voltage is not generated in the Hall sensor. When the shovel-shaped metal sheet leaves the air gap between the Hall element and the permanent magnet, the Hall element is acted by a magnetic field, as shown in fig. 6 (b), and a Hall signal voltage is generated at this time. Fig. 7 is a structural block diagram of the Hall automobile electronic ignition system. Fig. 8 is the schematic diagram of Hall electronic ignition circuit of Shanghai Santana and Hongqi cars. The main components adopt the special integrated circuit L497 or L482 for automobile ignition. It has the protection functions of overvoltage, shutdown, power failure and load rejection. And has that function of constant ignition current and variable closing angle. Pin 5 of the ignition controller provides the working power of the Hall element, and pin 2 and pin 3 are grounded. 6-pin input Hall pulse signal