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DIGITAL ENGINE CONTROL SYSTEM 7
Figure 7.5
Lookup Table Determination of d , R , and n v
E
a
flow rate (R ). The volumetric efficiency is read from ROM with an address
E
determined from RPM and MAP measurements. The intake air density is read
from another section of ROM with an address determined from MAP and T
i
measurements. The EGR volume flow rate is read from still another section of
ROM with an address determined from differential pressure (DP) and EGR
valve position. These variables are combined to yield the mass air flow rate:
D
MAF = d a RPM R E
------------
---- n v –
60 2
where D is the engine displacement.
Closed-Loop Control
Perhaps the most important adjustment to the fuel injector pulse duration
comes when the control is in the closed-loop mode. In the open-loop mode the
accuracy of the fuel delivery is dependent on the accuracy of the measurements
of the important variables. However, any physical system is susceptible to
changes with either operating conditions (e.g., temperature) or with time
(aging or wear of components).
UNDERSTANDING AUTOMOTIVE ELECTRONICS 233
