Operating strategy

Operating strategy

Injector opening time is calculated by the ECU by processing different engine operating parameters as described below:

1. First of all, a baseline injection time is calculated using certain one and two-dimensional maps whose input parameters are engine angular speed of rotation, absolute pressure in the inlet manifold and barometric pressure measured by the absolute pressure sensor.
2. The resulting value is corrected on the basis of inlet air temperature, using an eight point table, and battery voltage, using a sixteen point table.
3. The resulting value is then corrected using information from the lambda probe in order to maintain a stiochiometric ratio.

According to the amount of fuel to be injected, a decision is taken over whether operation should be synchronous or asynchronous

Injection timing in relation to TDC is also determined in order to optimise fuel distribution. Injection time variation field ranges over 180° of engine rotation (from 0° in relation to TDC up to 180° after BDC).

Modification of operating strategy during transitory stages

The ECU controls additional air (when idling, during over-run etc.) through algorithms of the error in relation to memorized rpm values.

The following operations are carried out:

• At idle speed: comparison between actual rotating speed and an ideal speed mapped in the memory according to coolant temperature level and associated operation (check on by-pass duct section, injection time and advance angle) in order to achieve a displacement as close as possible to zero.
• During start-up: check on quantity of air taken in by the engine during start-up through plunger position (and thus by-pass duct effective cross section) according to coolant temperature and whether air conditioner is on or off.
• During over-run: during this stage of engine use, two strategies are superimposed:

1. A negative transitory strategy to reduce the amount of fuel required by the engine (lower fuel consumption). This stage is recognised by the ECU, when the throttle potentiometer signal undergoes negative changes.
2. A dash-pot strategy to damp the negative torque variation (less engine braking, lower pollution). This strategy is implemented when the potentiometer signal indicates the throttle level is at minimum and the speed is high. As a result, the step motor decreases air flow through the by-pass gradually.