System Management Strategies; Operating Principle - Fiat 1998 Marea Service Manual

Marea- Marea Weekend
99 range

SYSTEM MANAGEMENT STRATEGIES

Operating principle

Any engine operating point is identified by two parameters:
- rotation speed;
- engine load.
If these parameters are known through suitable processing it is possible to calculate and then implement
the injection (quantity of fuel supplied and timing with TDC in explosion stroke), the ignition (correct ig-
nition advance) and any other functions for each engine operating point.
In the BOSCH M1.5.5 system the rotation speed is measured directly through the sensor whilst the engine
load is determined indirectly by calculating a "tl factor" (representing the actual engine load) according to
the absolute pressure and temperture of the air, both measured in the inlet manifold.
During experiments on the engine and the vehicle special maps are produced for the injection and the ig-
nition which contain the injection and ignition advance timing for the correct operation of the engine (for
a certain number of pairs of speed/load parameters).
For any engine operating point not included exactly amongst the values stored in the memory, the figures
are determined by mathematical interpolation.
The injection times calculated are also corrected according to the signal coming from the Lambda sensor
which, according to suitable operating strategies, determines a continuous fluctuation of the mixture
strength around the stoichiometric value.
The system is therefore defined as the speed-density-Lambda type because the injection is basically de-
termined by these three parameters.
All the particular operating situations which require special adjustments to the injection timing and igni-
tion advance values calculated are managed by the engine control unit according to the signals coming
from the various system senors.
Management of the signals
NOTE The term "signals" refers to the collection of signals coming from the sensor on the crankshaft
which feature a precise sequence which the control unit is capable of recognizing.
During starting, the control unit recognizes the injection and ignition timing which is fundamental 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 is capable, by failing to operate a certain injector, of evaluat-
ing the consequent variation in speed (not noticeable by the driver), of recognizing to which cylinder
the injector not operated belongs and, consequently, of determining the correct cylinder sequencing
(software timing).
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Engine
Fuel system
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