Electronic ignition - advantages for distributorless ignition system
The disadvantage of the mechanical system is that it requires regular adjustment to compensate for wear, and the opening of the contact breakers, which is responsible for spark timing, is subject to mechanical variations. In addition, the spark voltage is also dependent on contact effectiveness, and poor sparking can lead to lower engine efficiency. Electronic ignition (EI) solves these problems. In an EI system, the contact breaker points are replaced by an angular sensor of some kind - either optical, where a vaned rotor breaks a light beam, or more commonly using a Hall effect sensor, which responds to a rotating magnet mounted on a suitable shaft. The sensor output is shaped and processed by suitable circuitry, then used to trigger a switching device such as a thyristor, which switches a large flow of current through the coil. The rest of the system (distributor and spark plugs) remains as for the mechanical system. The lack of moving parts compared with the mechanical system leads to greater reliability and longer service intervals. For older cars, it is usually possible to retrofit an EI system in place of the mechanical one.
Background
Modern ECU's use a microprocessor which can process the inputs from the engine sensors in real time. An electronic control unit contains the hardware and software (firmware). The hardware consists of electronic components on a printed circuit board (PCB). The main component on this circuit board is a microcontroller chip (CPU). The software is stored in the microcontroller or other chips on the PCB, typically in EPROM's or flash memory so the CPU can be re-programmed by uploading updated code. This is also referred to as an (electronic) Engine Management System (EMS).
Sophisticated engine management systems receive inputs from other sources, and control other parts of the engine; for instance, some variable valve timing systems are electronically controlled, and turbocharger wastegates can also be managed. They also may interface with electronically-controlled automatic transmissions, traction control systems, and the like.
Such systems are used for many internal combustion engines in other applications. In aeronautical applications, the systems are known as "FADEC's" (Full Authority Digital Engine Controls). This kind of electronic control is less common in piston-engined airplanes than in automobiles, because of the large costs of certifying parts for aviation use, relatively small demand, and the consequent stagnation of technological innovation in this market.
On the Board Diagnostics
Modern CPU-based ECU's have On Board Diagnostics with which they can diagnose engine faults, stored as fault codes in their internal memory. When the vehicle is serviced, an engineer connects a fault-code reader (or scanner) to the engine and inspects the stored fault codes. These codes fall into two categories: industry-standard codes, common to all vehicles in a class, and manufacturer-specific codes.
Functionality
Timing for the distributorless ignition system is controlled by an electronic control unit or ECU. The ECU decides the best time to fire the spark plugs.
The ECU makes its decision on the best time to fire the spark plugs based on information received from sensors such as: the MAP sensor, the throttle position sensor, cam angle sensor, crank angle sensor, engine speed sensor and coolant temperature sensor.
Once the ECU has evaluated all the sensor information it makes a decision on when to fire the spark plugs. To do this, the ECU switches the power transistors that control the primary current for each coil pack.
When the primary current is switched the coil produces a high voltage to produce a spark.
The main sensors required to produce correct timing of the spark are the crank sensors.
Identification of each pair of cylinders and a signal for their triggering is provided by a dual crank sensor fixed to the engine timing cover.
This contains two Hall effect switches sharing a central magnet which forms two air gaps between them.
Two concentric interrupter rings with a number of blades and windows and mounted on the rear of the crankshaft balancer, rotate through the gaps.
The voltage signals provided allow the ignition module to identify which pair of companion cylinders must be provided with ignition.
Source: CDX Global & Wikipedia - en.wikipedia.org
