Functions of the system

FUNCTIONS OF THE SYSTEM

The management programme (software) is inside the control unit memory; it comprises a series of strategies, each of which manages a precise function of the system.

The main functions carried out by the injection/ignition system are:

• - adjustment of the injection times;
• - controlling the ignition advance;
• - controlling and managing the idle speed;
• - controlling cold starting;
• - butterfly transition;
• - deceleration control (cut-off);
• - control of acceleration and full power;
• - limiting the maximum number of revs;
• - controlling combustion via the Lambda sensor;
• - self-adjustment of the system;
• - checking fuel vapour recirculation;
• - connection with the climate control system;
• - connection with the engine immobilizer device (CODE);
• - autodiagnostics.

Adjustment of the injection times

In addition to electronically controlling the moment of ignition, in order to allow the smooth operation of the engine as the environment parameters and loads applied vary, the control unit must control and adjust the injection so that the stoichiometric (air/fuel) ratio is always within the optimum value.

Taking the physical characteristics of the fuel (viscosity and density) and the pressure of the fuel in the inlet manifold as constant, the quantity of fuel injected only depends on the "opening time" of the injectors.

This time is calculated by processing the different engine operating parameters which are listed below:

1. First of all a basic injection time is calculated using one and two dimension maps whose input parameters are the engine rotation angular speed and the pressure value in the inlet manifold.
2. The figure obtained in this way is corrected on the basis of the air intake temperature according to a table in the control unit and on the basis of the battery voltage.
3. The figure calculated in this way is finally corrected using the information from the Lambda sensor in order to keep the mixture strength at the correct stoichiometric value.

Controlling the ignition advance

The electronic control unit also processes the static advance electronic ignition operating strategy.

The optimum advance angle is calculated in this way:

1. A basic advance angle is calculated using a map stored in the memory whose input parameters are the angular rotation speed of the engine and the absolute pressure measured in the inlet manifold. In idle and full load conditions, two distinct one dimension tables are used according to the engine speed.