Main components - ECCS control unit, ignition distributor (with crankshaft angle sensor), power transistor and ignition coil, knock (impact)sensor (turbo only), battery and ignition socket.
The ECCS unit receives information from the camshaft/crank angle sensor to determine engine speed and crankshaft (piston) position; from an air flow meter to determine the amount of air entering; from the temperature sensor to determine the engine temperature; from the throttle valve switch to determine the throttle position; and (on Turbo models) from the knock sensor (see below). All information is compared by the control unit and used to determine the optimal ignition timing setting for any engine operating mode, with the information programmed into the unit.
The control unit sends a signal to the power transistor about the selected ignition timing setting. The transistor amplifies this signal and connects and disconnects the low voltage circuit of the ignition coil, thus causing high voltage in the secondary winding of the coil. This is fed through the breaker-distributor cap and rotor to the spark plugs in the usual way.
Figure 4.13. Sectional view of distributor/crankshaft angle sensor
The crankshaft angle sensor assembly inside the distributor consists of a plate, an LED, and a photodiode. The plate, which is attached to the distributor shaft, is located at the bottom of the distributor housing. It has 360 cuts along the outer edge. These cuts correspond to the degree of rotation of the crankshaft. Near the outer row of cuts, there is a row of four large cuts corresponding to each cylinder in the engine. They are separated by 180°. The cut for cylinder #1 is slightly larger than the cuts for the other cylinders (photo).
8.0. Cylinder No.1 180° signal cut "A", 180° signal cuts "B", 1° signal cuts "C"
The signal generating circuit is placed under the plate. The LED is located in the upper half and the photodiode in the lower half of the small housing. When the engine is running, the LED emits a continuous beam of light to the photodiode. Slits pass the beam, producing pulses in the photodiode, which are converted into on-off pulses and fed to the ECCS unit, which uses the signal to determine the crankshaft position and engine speed.
A turbocharged engine, with higher intake manifold pressures and temperatures, requires additional protection in the form of a knock sensor.
This sensor detects detonation as pressure applied to a piezoelectric element. This is converted into a voltage signal which is sent to the ECCS unit. Each time the control unit detects this signal, the ignition timing is reduced until the detonation disappears, at which point the ignition timing is returned to the normal setting.