System Management Strategies; Operating Principle; Management Of The Signals - Fiat Bravo Service Manual

Bravo-Brava & i
98 range
S Y S T E M M A N A G E M E N T S T R A T E G I E S

Operating principle

Any engine operating point is identified by t w o parameters;
- rotation speed;
- engine load.
If these parameters are k n o w n by means of appropriate processing it is possible to calculate and then i m -
plement the injection (quantity of fuel supplied and timing w i t h explosion stroke TDC), the ignition (cor-
rect 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 e n -
gine load is determined indirectly, calculating "factor t l " (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 i g n i -
tion, w h i c h (for a certain number of speed-load parameter pairs) contain the ignition advance and injec-
tion 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 deter-
mined through mathematical interpolation from these figures.
The injection time values calcluated are also corrected according to the signal coming from the Lambda
sensor w h i c h , on the basis of suitable operating strategies, ensures that the mixture strength is constant-
ly around the stoichiometric value.
The system is known as the "speed-density-Lambda" type because the injection time is basically deter-
mined from these three parameters.
All the particular operating situations w h i c h 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 w h i c h are vital for the
subsequent operation of all the strategies.
This recognition takes place in t w o successive stages:
- by interpreting the succession of signals coming from the flywheel sensor, on the crankshaft, the c o n -
trol unit recognizes T D C for the pair of cylinders 1-4.
- using a particular strategy the control unit, by failing t o operate a particular injector, is capable, by
evaluating the consequent variation in speed (not perceptible to the driver) of recognizing w h i c h
cylinder the injector w h i c h is not operated belongs to and therefore of determining the correct cylinder
sequence (software t i m i n g ) .
Copyright by Fiat Auto
16v
E n g i n e
Fuel system
10.