System management strategies

SYSTEM MANAGEMENT STRATEGIES

Operating principle

Any engine operating point is identified by two parameters;

• - rotation speed;
• - engine load.

If these parameters are known by means of appropriate processing it is possible to calculate and then implement the injection (quantity of fuel supplied and timing with explosion stroke TDC), the ignition (correct ignition advance) and any other functions for each engine operating point.

In the BOSCH 1.5.5 system the rotation speed is measured directly via the relevant sensor whilst the engine load is determined indirectly, calculating "factor tl" (representing the actual engine load) accordint to the absolute pressure and the temperature of the air, both measured in the inlet manifold.

Special maps are experimentally determined for the engine and the vehicle for the injection and the ignition, which (for a certain number of speed-load parameter pairs) contain the ignition advance and injection timing values required for the correct operation of the engine.

For any engine operating point not exactly included in those stored in the maps, the values are determined through mathematical interpolation from these figures.

The injection time values calcluated are also corrected according to the signal coming from the Lambda sensor which, on the basis of suitable operating strategies, ensures that the mixture strength is constantly around the stoichiometric value.

The system is known as the "speed-density-Lambda" type because the injection time is basically determined from these three parameters.

All the particular operating situations which require adjustments to the ignition advance and injection timing values calculated are managed by the engine control unit on the basis of the signals coming from the various system sensors.

Management of the signals

NOTE These signals refer to the collection of signals coming from the sensor on the crankshaft which are characterized by a precise sequence which the control unit is capable of recognizing.

During starting, the control unit recognizes the ignition and the injection timing which are vital for the subsequent operation of all the strategies.

This recognition takes place in two successive stages:

• - by interpreting the succession of signals coming from the flywheel sensor, on the crankshaft, the control unit recognizes TDC for the pair of cylinders 1-4.
• - using a particular strategy the control unit, by failing to operate a particular injector, is capable, by evaluating the consequent variation in speed (not perceptible to the driver) of recognizing which cylinder the injector which is not operated belongs to and therefore of determining the correct cylinder sequence (software timing).