Woodward GECO, Technical Manual, Page: 31 / 90

Manual 03554 GECO

Stoichiometric
Woodward 23
Chapter 4.
Control Operation
Although the GECO™
 Stoichiometric control has many features, its core function
is stoichiometric air/fuel ratio control. As described in the System Description and
Application, the purpose for precise fuel delivery is to maximize the efficiency and
performance of the three-way exhaust catalyst.
Closed Loop Strategy
The GECO
 Stoichiometric control uses exhaust oxygen feedback from both
upstream and downstream of the catalytic converter. This feedback comes from
an automotive-style exhaust gas oxygen (EGO) or “lambda” sensor. This EGO
sensor provides a very “steep” voltage versus air/fuel ratio signal in the vicinity of
stoichiometry for precise fuel control feedback.
Figure 4-1. Pre-Catalyst EGO Closed Loop Control Mode Diagram
The GECO PC Tool will display the EGO feedback value in the form of a DC
voltage between 0 and 1 V. This value is labeled “EGO unfiltered”. It is a “noisy”
signal because of the quick response of the sensor and the high ratio of volts-to-
air/fuel ratio. For this reason a filter is included to help stabilize this signal. The
“EGO1/2 filter tau” value increases or decreases the amount of filtering and the
“EGO filtered” value shows the results of the filtered voltage signal.
This filtered signal is compared to the “EGO target” value and the fuel trim valve
command, “Valve Cmd”, is increased or decreased to make the EGO filtered
value match the EGO target.
+
EGO1
Base
+
-
+
Fuel
Trim
Valve
Pre-Cat
Exhaust
Oxygen
(EGO1)
Filter
EGO1 Target