2.1 THE ELECTRONIC SYSTEMS AND COMPONENTS

2.1.1 Electronic Ignition Systems

For complete combustion, the ignition system must supply properly timed, high-voltage surges across each pair of spark plug electrodes at the proper time under all engine operating conditions.

Purpose of Ignition System are:

• It must generate an electrical spark with enough heat to ignite the air-fuel mixture in the combustion chamber.
• It must maintain that spark long enough to allow total combustion of the fuel in the chamber.
• It must deliver the spark to each cylinder to allow combustion to begin at the right time during the compression stroke.

There are basically two types of ignition systems: distributor ignition (DI) and electronic ignition (EI) or distributorless ignition systems (DIS) 

• Distributor ignition (DI) is the term specified by the Society of Automotive Engineers (SAE) for an ignition system that uses a distributor. 
• Electronic ignition (EI) is the term specified by the Society of Automotive Engineers (SAE) for an ignition system that does not use a distributor.
• Distributorless Ignition System:
• Timing is very precise
• No mechanical parts to wear out
• Requires less maintenance
• Ignition timing is usually not adjustable
• Computer relies on ignition sensors
• On-board computer controls ignition timing usually through a ignition module

2.1.2 Inductive System Operation

• The computer collects and processes information to determine the ideal amount of spark advance for the operating conditions.
• The ignition module uses crank/cam sensor data to control the timing of the primary circuit in the coils.
• The ignition module synchronizes the coils’ firing sequence in relation to crankshaft position and firing order of the engine.
• Therefore, the ignition module takes the place of the distributor.

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2.1.3 Induction Wiring

• All ignition systems consist of two interconnected circuits: 
• Primary Circuit (Low voltage):
• Battery 
• Ignition switch 
• Primary windings of coil 
• Triggering device - Crankshaft position sensor (CKP) 
• Switching device – Control module (igniter) 
• Secondary Circuit (High Voltage): 
• Secondary windings of coil 
• Distributor cap and rotor (if the vehicle is so equipped) 
• Spark plug wires 
• Spark plugs

Primary circuit operations: 

• Current from the battery flows to the primary winding of the ignition coil. 
• Magnetic field is created around ignition coil’s primary winding.
• When piston is approaching TDC on the compression stroke, triggering device signals to switching unit to stop current flow.
• Magnetic field around primary winding collapse across secondary winding. The movement of the magnetic field across the winding induces a high voltage in the secondary winding.
• The action of the secondary circuit begins at this point.

Secondary circuit operations:

• The secondary circuit carries high voltage to the spark plugs.
• The exact manner in which the secondary circuit delivers these high-voltage surges depends on the system.
• Until 1984 all ignition systems used some type of distributor to accomplish this job.
• However, in an effort to reduce emissions, improve fuel economy, and boost component reliability, most auto manufacturers are now using distributorless or electronic ignition (EI) systems.
• EI systems have no distributor; spark distribution is controlled by an electronic control unit and/or the vehicle’s computer. 
• Instead of a single ignition coil for all cylinders, each cylinder may have its own ignition coil, or two cylinders may share one coil.
• The coils are wired directly to the spark plug they control. An ignition control module, controls the firing order and the spark timing and advance.

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2.1.4 Hall Effect Sensors

• A Hall effect sensor is a device that is used to measure the magnitude of a magnetic field. Its output voltage is directly proportional to the magnetic field strength through it. 
• Hall effect sensors are used for proximity sensing, positioning, speed detection, and current sensing applications.
• Frequently, a Hall sensor is combined with threshold detection so that it acts as and is called a switch. Commonly seen in industrial applications such as the pictured pneumatic cylinder, they are also used in consumer equipment; for example some computer printers use them to detect missing paper and open covers. They can also be used in computer keyboards, an application that requires ultra-high reliability.
• Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing, tachometers and anti-lock braking systems. They are used in brushless DC electric motors to detect the position of the permanent magnet. In the pictured wheel with two equally spaced magnets, the voltage from the sensor will peak twice for each revolution. This arrangement is commonly used to regulate the speed of disk drives.[1]

2.1.5 Hall Effect Operation

• A Hall probe contains an indium compound semiconductor crystal such as indium antimonide, mounted on an aluminum backing plate, and encapsulated in the probe head.
• When the Hall probe is held so that the magnetic field lines are passing at right angles through the sensor of the probe, the sensor gives a reading of the value of magnetic flux density (B). A current is passed through the crystal which, when placed in a magnetic field has a “Hall effect” voltage developed across it. The Hall effect is seen when a conductor is passed through a uniform magnetic field. The hall effect voltage produced is an indication of magnetic object passed around it. Hence the Hall effect voltage is the signal output and used to sense an object near it.[2]

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2.1.6 Optical Type Sensors

• An optical sensor converts light rays into an electronic signal. The purpose of an optical sensor is to measure a physical quantity of light and, depending on the type of sensor, then translates it into a form that is readable by an integrated measuring device. Optical Sensors are used for contact-less detection, counting or positioning of parts. Optical sensors can be either internal or external. External sensors gather and transmit a required quantity of light, while internal sensors are most often used to measure the bends and other small changes in direction.
• The measured possible by different optical sensors are Temperature, Velocity Liquid level, Pressure, Displacement (position), Vibrations, Chemical species, Force radiation, pH- value, Strain, Acoustic field and Electric field.[3]