Released on = September 21, 2006, 2:37 pm

Press Release Author = John Cecil

Industry = Automotive

Press Release Summary = In product literature many times a narrowband oxygen sensor
(4 wires or less) is also called an EGO sensor. Wideband sensors (5 wires or more)
are often called UEGO sensors. We call them NBO2 and WBO2 sensors to make it
clearer.

Press Release Body = In product literature many times a narrowband oxygen sensor (4
wires or less) is also called an EGO sensor. Wideband sensors (5 wires or more) are
often called UEGO sensors. We call them NBO2 and WBO2 sensors to make it clearer.

To understand how a WBO2 works one must first understand how Narrowband sensors
(NBO2\'s) work. There are 2 kinds of NBO2 sensors. By far the most common type is the
Nernst cell sensor described here. A (rarely used) other type is resistance based.
It has a jump in resistance at 14.7 AFR instead of outputting a voltage. A NBO2
sensor consists of a porous ceramic with electrodes of special metal compounds on
either side. One electrode is exposed to outside air, the other side is exposed to
exhaust gas. The free-air side is grounded (one wire or 2 wire NBO2, or fed to the
ECU as signal ground), the exhaust side electrode is connected to the signal wire
coming out of the sensor.

When there is no oxygen in the exhaust gas, but unburned hydrocarbons, hydrogen or
CO, these oxidizable molecules combine with oxygen ions migrating through the porous
ceramic on the exhaust side electrode. This process creates a voltage between 0.07
to 1.1V between the electrodes. This process is not linear, but acts like a switch.
Voltage is there when there are oxidizable molecules, and no (or very small) Voltage
is there when there are none. The switchover point is where there is no oxygen in
the exhaust, but also no oxidizable molecules. The half-way voltage is typically set
to 0.45V for a normal oxygen sensor. For gasoline this would be at 14.7 AFR or the
stochiometric ratio. The stochiometric ratio is where there is exactly the right
amount of air for the amount of fuel. Typical engines produce more power when
richer, because the combustion process is far from ideal and excess fuel assures
that all air is consumed.

If there are unburned combustion products but also oxygen molecules in the exhaust,
the combustion products rather combine directly on the electrode surface with the
oxygen in the exhaust instead of the oxygen coming through the ceramic without
creating a voltage. So even though there is fuel there, the sensor will read as if a
lean condition exists. These sensors require a minimum temperature of about 300C to
work. Single wire sensors relied solely on the heating by exhaust gas. At idle that
may not be enough. Multiwire NBO2 sensors have a built-in heater that helps keep the
sensor at operating temperature at idle and also speeds up the heat up process to
minimize open loop startup time.

The output voltage of a NBO2 sensor changes slightly (higher) the richer the gas is.
Many people believe, that by calibrating this curve and linearizing it, one can make
a cheap AFR meter using a NBO2 sensor. This does not work. Look at the following
curve. This curve was not actually measured but calculated from the material
constants and appropriate equations governing NBO2 sensors.

Because of these characteristics ECU\'s with NBO2 sensors use the sensor only during
cruise and idle. They operate by checking if the voltage is below 0.45V, richen up
until it is above 0.45V, then lean out, then richen up again and so on. Therefore
the mixture oscillates around 14.7AFR. This AFR is optimum for minimum emissions.
The oscillations are caused by the operation of the ECU, not by the sensor as many
people believe. At WOT, as mentioned before, the engine wants a richer mixture to
make power. Because the NBO2 output cannot be used there, all ECU\'s (not WBO2 based)
will ignore the NBO2 signal and purely meter fuel by pre-stored maps relating TPS,
MAP/MAF and IAT. There are products that claim to modify/replace the signal of one
or more NBO2 sensors at WOT or boost to richen up the mixture. These products can\'t
work because of the simple fact that ALL NBO2 based ECU\'s just ignore the signal at
boost/WOT.

Web Site = http://www.innovatemotorsports.com/

Contact Details = Innovate! Technology, Inc.
5 Jenner
Suite 100
Irvine, CA 92618
TEL: 949-502-8400
FAX: 949-502-8439
Email : innovatemotor@gmail.com