Chapter 15 closed loop control, 1 description, 2 using closed loop control – Haltech E6S User Manual
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Chapter 15
Closed Loop Control
15.1 Description
By fitting an oxygen sensor to the exhaust system of an engine, the E6S is able to perform a
feedback correction to maintain a consistent air-fuel ratio around stoichiometric mix; i.e..
when exactly the correct amount of fuel is provided to consume all the oxygen of the air
drawn into the engine, without any unburnt fuel remaining after combustion. Using closed
loop fuel control adapts for small variations in fuel quality and day-to-day running, provides
better fuel economy and lower emissions.
Figure 15.1 Typical lambda sensor output.
An oxygen sensor (or lambda sensor) is
placed in the exhaust gas stream usually
after the collector but before the catalytic
converter. The O2 sensor possesses an
output voltage characteristic similar to that
in figure 15-1. When the exhaust gas is free
from oxygen (i.e.. mixture is rich), the
sensor reads around 1 volt. When there is
an excess of oxygen, the sensor reads closer
to 0 volts. Most oxygen sensors' transfer
curves change very suddenly around
stoichiometric mixtures.
The object in closed loop control is to measure the voltage of the oxygen sensor, determine
whether the engine is running lean or rich, and compensate accordingly by adjusting the
injection time. The ECU may overcorrect slightly, and then will pull the mixture back towards
the desired air-fuel ratio. This slight oscillation either side of stoichiometric mixture aids the
function of the catalytic converter.
15.2 Using Closed Loop Control
In order to use the closed loop fuel control function, you must have the following:
- an appropriate lambda sensor mounted in the exhaust stream;
- E6S programming software and cable.
Mounting and connection of the sensor is all that is required in installation. Check figure 15-2
for appropriate wiring for different oxygen sensors. Run the E6S programming software
Online and go to the Output Options Page. Ignition will need to be switched on. Select Closed
Loop Control, and adjust the following parameters as necessary.