Woodward GECO, Technical Manual, Page: 17 / 90

Manual 03554 GECO

Stoichiometric
Woodward 9
Intake
Manifold
Pressure
(MAP)
+
-
Fuel
Trim
Valve
Valve Position
Table
Fuel Flow Valve 1
0.0 40.0
2.0 45.0
4.0 50.0
6.0 60.0
8.0 65.0
10.0 70.0
12.0 72.0
14.0 73.5
Open Loop/
Closed Loop
Pre-Cat
Exhaust
Oxygen
(EGO1)
Filter
Fuel Flow
Estimation
Speed
EGO1 Target
Open Loop
Figure 2-8. Control Logic for Valve-Learn Function
Fuel Valve Dithering
It has been shown that “dithering” the Air/fuel ratio into the catalyst increases the
window of air/fuel ratio variation to enhance the performance of the catalyst. The
GECO includes parameters to adjust the amplitude and frequency of the
dithering to optimize the oxygen storage capability of the catalyst. This strategy
widens the window of operation and will allow the EGO sensors to drift more
without reducing the efficiency of the catalyst.
Diagnostics and Monitoring
For system reliability the GECO control monitors sensor inputs and control
outputs for high and low failure conditions as well as extensive self-diagnostics
for system functionality. Alarm or shutdown control outputs are available to allow
integration into an engine or system control panel for component failure or
emissions compliance requirements. These alarms are configured in the
software. There is an alarm and shutdown LED output as well as an alarm and
shutdown relay.
In addition, the GECO control has oxygen sensor health monitoring. This function
can assess the remaining activity of the oxygen sensors, and preventative
maintenance can be planned before a sensor failure occurs.
Communications
Communication with the system is via a computer (PC) interface or by the hand-
held terminal. Control setup and tuning is accomplished through the PC interface
screens (see Figure 2-9).