Ignition System Rex-I

DESIGN AND FUNCTION

Ignition system Rex-I




The Rex-I ignition system can be split up into four sub-systems.
- The sensor system supplies information to the control system so as to achieve optimal ignition regulation.
- The control system ensures that the optimum ignition setting and ignition voltage are supplied at all times.
- The high-tension system produces and distributes high voltage.
- The diagnostic system has two checking functions to simplify troubleshooting.


Rex-I sensor system

Engine temperature sensor



The ignition system uses the same temperature sensor for engine temperature as does the fuel system. The temperature sensor has two NTC-resistors (Negative Temperature Coefficient), one for Rex-I and the other for Regina.

Throttle switch



The ignition system uses the same throttle switch as the fuel system. Rex-I uses only the idle speed switch.

Impulse sensor



The impulse sensor provides information about engine speed and crankshaft position and it is the most important sensor signal to the control unit. Without it, the control unit will not supply any signal to the power stage/ignition coil and the engine cannot be started.
When the holes in the flywheel pass the sensor, the magnetic field is altered thus providing a signal whereby voltage varies as a sine wave signal. Since the flywheel does not have holes in two places, the control unit can read off its position in relation to TDC. By measuring the time between two voltage peaks, the control unit can calculate engine speed.

Knock sensor



The knock sensor consists of piezo-electrical crystals which are sensitive to the vibrations which arise in the engine block when the engine knocks.


Rex-I control system

Control unit




Control of ignition setting
The ignition system's control unit calculates the ignition setting twice per engine revolution, once per ignition cycle. The general ignition setting is based on engine speed and the load signal issued by the fuel system's control unit
The control unit then adjusts the basic ignition setting under certain circumstances to provide optimal combustion and function.
- When the engine is started, the ignition setting is only dependent on engine speed and engine temperature.
- At idle speed the ignition setting is only dependent on engine speed.
- At temperatures below 55°C ignition is retarded depending on temperature.
- Below 60°C no attention is paid to the knock sensor's signal.
- On over-run, the ignition coil's recharging time is reduced so that engine speed does not increase.
- Ignition is retarded in the case of engine knocking.

Control of ignition voltage
The control unit regulates ignition energy so that it is independent of battery voltage and engine speed. At low battery voltage the control unit sends a signal to the power stage to begin recharging earlier, thus extending the recharging time.

Emergency operation



The control unit has a "limp-home" function which is reversible. This means that if the signal resumes satisfactory levels after a faulty reading, the control unit will utilize these values instead of continuing to use the limp-home function.
- If there is no signal from the knock sensor, the ignition is retarded 1O°.
- If there is no load signal from Regina the ignition setting is calculated as for full load except when the throttle switch indicates idle speed.
- If there is no engine temperature signal, the ignition setting is calculated as for a hot engine.
- If there is no throttle signal the control unit will react to load even at idle speed.

Load-related information
Rex-I receives information regarding load from Regina's control unit. At high load (a large volume of fuel/air) the ignition is retarded. If the load is subjected to rapid change, the ignition setting is retarded significantly for all cylinders to prevent knocking.

Knock control



If engine knock arises in any cylinder, the cylinder's ignition is retarded at the next ignition cycle until the knock disappears. Once the knock disappears, ignition is advanced in small increments. The speed of this incremental phase depends on engine speed. It is quicker at low than at high engine speed.

Adaptive knock control
If the engine is subject to a heavy load under a long period, the knock-regulated ignition retardation will be activated often. The control unit will retard ignition by 10 on all cylinders as long as the engine is subjected to higher than normal load, to avoid knocking.


High-tension system

Power stage/ignition coil



In Rex-I the power stage and the ignition coil are integrated. The function, however, is the same as for those systems which feature separate units.
The power stage closes and breaks the supply of current through the ignition coil's primary winding. When the supply of current to the primary winding is interrupted, a 30-35 kV high-tension is produced in the secondary winding.

Ignition Coil, distributor and spark plugs
The high tension system consists of the ignition coil which generates high tension which is then transmitted to the distributor.
The distributor allocates this voltage to the spark plugs via the ignition cables.