Injection management

INJECTION MANAGEMENT

The ECU receives information on rpm (n) and throttle valve opening (alpha) and is then able to identify base pulse constant (ti) within a specific map.

Under various different engine service conditions, injector opening times are optimised by correcting times (in accordance with changing conditions) of: coolant temperature (1), air temperature (2) and signal received from lambda probe (3). Injection is synchronous at all times, i.e. timed to coincide with the moment of ignition.

The ECU uses specially selected maps to keep fuel mixture concentration close to stoichiometric levels (14.7 parts air to 1 part petrol).

To maintain this ratio constant, the ECU uses two different modes for the control of injector opening.

The first mode is synchronous operation, where the injector is opened whenever a high tension pulse is sent to the spark plugs (graph A).

The second control mode is asynchronous operation, where the ECU controls injector opening regardless of the number of high tension pulses sent to the spark plugs (graph B).

This occurs because under certain conditions (with base pulse constants too short, ≥ 1.4 milliseconds) mechanical inertia characteristics (hysteresis) of the injector do not permit proper opening and closure. For this reason, a specific strategy must be adopted to suit mechanical injector properties.