Oxygen Sensors 2010/03/14Posted by Michael in 2JZduino.
Oxygen sensors in automotive applications are used for closed-loop fuel control to ensure the right amount of fuel is injected into the engine for combustion to match the incoming air metered at the intake tube. For each type of fuel there is an optimal ratio between air (oxygen) and fuel to ensure complete combustion; the stoichiometric ratio. For petrol this ratio is 14.7:1 by mass. Too little fuel results in incomplete combustion and too much fuel results in unburned reactants. Both cause pollution.
There are two types of commonly available oxygen sensors for use in automotive applications: wideband and narrowband sensors. Narrowband sensors have a nonlinear response. The signal saturates very quickly when the mixture is either rich or lean. When the mixture is at the stoichiometric rate the signal is maintained at the midpoint of the output range.
Wideband sensors have a linear response to air/fuel ratio of a gas mixture. This provides an opportunity to measure by how much a mixture is rich or lean.
The Lexus IS300 is equipped stock with two narrowband oxygen sensors for use in closed-loop fuel control. I will be replacing both of these sensors with wideband oxygen sensors and connecting them to the 2JZduino. 2JZduino will then provide a programmable narrowband output signal for the stock ECU based on measurements of the wideband sensors.
Below is an IS300 narrowband oxygen sensor signal captured using a PC Soundcard-based Oscilloscope while the engine was at idle.
For more information on oxygen sensors see Wikipedia’s entry: http://en.wikipedia.org/wiki/Oxygen_sensor