Electronic Ignition System
Difference Between Conventional and Magneto Ignition System
There are some drawbacks in the magneto ignition system. Firstly, the contact breaker points will wear out or burn when it is operated with heavy current. Secondly, the contact breaker is only a mechanical device that cannot operate precisely at high speed due to the dwell period which is not sufficient for building up the magnetic. field to its full value at that particular speed. The conventional contact breaker can give satisfactory performance only about 400 sparks per second which limits the engine speed. At low speeds, relatively high current is drawn from the battery due to the contacts remaining closed for a longer time. Thus, the system becomes inefficient at low speeds.
The disadvantages of the convention contact breaker assisted ignition system can be completely eliminated by the use of an electronic controlled ignition system using contactless triggers to give timing system.
The basic difference between contact point’ and electronic ignition systems is in the primary circuit. In the contact breaker system, the primary circuit is opened and closed by the electronic control unit shown in Figure 2.35. The secondary circuits are practically similar to previous systems.
In the secondary circuit, the distributor, ignition coil, and wiring are altered to handle the higher voltage that the electronic ignition system produces. The high voltage (about 47,OOO volts ) has the advantage that the spark plugs with wider gaps can be used. It results a longer spark that can ignite lean air-fuel mixture. As a result, engines can run on lean mixture for better fuel economy.
Difference between Conventional Ignition System and Electronic Ignition System
Sr. No. Conventional ignition system Electronic ignition system 1. Spark timing is not depends upon speed Proper spark timing is achieved throughout the speed range 2. Moderate energy output from the ignition coil is obtained. High energy output from the ignition
coil is obtained.
3. Noise occurs during high speed It gives noiseless operation at high speed; 4. Some carbon deposition occurs on Spark plug electrode . Spark plug electrode remains clean off carbon deposits & ash deposits. 5. More Emissions occurs Reduction in emission. 6. Less output power Increased output power
Construction of Electronic Ignition System:
A schematic diagram of an electronic ignition system is shown in Figure 2.36. It consists of a battery, ignition switch, electronic control unit, magnetic pick-up, reluctor or armature, ignition coil, distributor, and spark plugs. The construction of the battery, ignition switch. ignition coil, distributor, and spark plug is similar to previous methods. In this system, a magnetic pickup is used instead of contact breaks points in a conventional system. Also a cam is replaced by a reluctor or armature.
The magnetic pick-up is shown in Figure 2.37. It consists of a sensor coil through which the magnetic flux is generated by a permanent magnet. A star-shaped rotor called reluctor or armature is mounted on the distributor shaft which modulates the flux density in the coil and induced voltage in the coil due to the consequent changes in the flux. This voltage serves as a trigger signal for the high voltage generator circuit. Since there is one spark plug per cylinder, the number of teeth of the armature is equal to the number of engine cylinders.
Working of Electronic Ignition System :
When the ignition switch is closed (i.e. the switch is ‘ON’ .), the reluctor rotates which makes the teeth of the reluctor cone closer to the permanent magnet. It reduces the air gap between reluctor tooth and sensor coil. Thus, the reluctor provides a path for the magnetic lines from the magnet. The magnetic field is passed on to the pick up every time when the reluctor teeth pass the pickup coil in which an electric pulse is generated. This small current then triggers the electronic control unit which stops the flow of battery current to the ignition coil. The magnetic field in the primary winding collapses and the high voltage is generated: in the secondary winding. It led to spark in a spark plug via a distributor. Meanwhile, the reluctor , teeth pass past the pickup coil. Therefore, the pulse unit is ended. It causes the electronic control unit to close the primary circuit.
How the primary circuit is triggered in the electronic ignitions system.
The triggering may be done by
- Inductive pickup,
- hall effect or
- Optical method.
One method of triggering is described for illustration.
When a moving metallic shutter diverts the magnetic field from reaching the Hall sensor, the Hallsensor produces a voltage signal. When the shutter blade moves and allows the magnetic field to reach the Hall sensor, the Hall-sensor does not generate voltage signal. After leaving the Hall layer, the signal is routed to an amplifier where it is conditioned, the signal is sent to the ECU (Primary circuit switching unit).
The electronic control units can be designed to either turn on or turn off the ignition coil primary current when the shutter blades are blocking.
As the central shaft of the distributor rotates, the chopper plate attached under the rotor arm alternately covers and uncovers the Hall chip. The number of vanes corresponds with the number of cylinders. In constant dwell systems the dwell is determined by the width of the vanes. The vanes cause the Hall chip to be alternately in and out of a magnetic field. The result of this is that the device will produce almost a square wave output, which can then easily be used to switch further electronic circuits.
The three terminals on the distributor are marked „_ 0 _‟; the terminals _ and _ are for a voltage supply and terminal „0‟ is the output signal. Typically the output from a Hall effect sensor will switch between 0 V and about 8V. The supply voltage is taken from the ignition ECU and on some systems is stabilized at about 10 V to prevent changes to the output of the sensor when the engine is being cranked.
How electronic ignition system improves the performance of the engine ? Justify.
Electronic ignition system improves the performance of the engine:
- It provides sufficiently strong spark between the electrodes of the plugs at correct timing.
- It works efficiently over the entire range of engine speed.
- It is light, effective and reliable in service
- It is compact and easy to maintain.
- It is capable to advance or retard ignition timing as per engine load and speed. Effective to trigger the primary circuit at appropriate time.
- Moving parts are absent-so no maintenance.
- Contact breaker points are absent-so no arcing.
- Spark plug life increases by 50% and they can be used for about 60000 km without any problem.
- Better combustion in combustion chamber, about 90-95% of air-fuel mixture is burnt compared with 70-75% with conventional ignition system.
- With above benefits of electronic ignition system improves power output and performance of the engine.
Advantages of Electronic Ignition System:
1. The parts such as reluctor, magnetic pickup, and electronic control module are not subjected to wear as in case of a mechanical contact breaker.
2. Periodic adjustment of engine timing is not necessary.
3. It gives very accurate control of timing.
Application of Electronic Ignition System :
- Electronic ignition system is used in modern and hypercars like Audi A4, Mahindra XUV-500, etc.and bikes like kTM duke 390cc,Ducati super sports etc. to meet the high reliability and performance need .
- It is also used in aircrafts engine due to its better reliability and less maintenance
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