Honda ULEV Accord EX and linear air-fuel ratio sensor

[Zublin, Bryan (SD-MS)]

An article appeared in the August 1995 issue of Car and Driver that 
discusses the Honda ULEV Accord EX, or "ultralow emissions vehicle" for 
California.  It sounds like the linear air-fuel ratio sensor is currently 
being used in the Civic VX, and that the same sensor will be used in the 
Accord ULEV.  And if it is really a $300 option, then the sensor might be a 
low cost alternate to the existing wide range O2 sensors.  Has anyone looked 
into exactly what the Honda sensor can do?

Here is an excerpt:

"Finally, the ULEV vehicle manages to keep extremely precise control over 
the air-fuel ratio, with the help of Honda's linear air-fuel ration sensor 
(LAF), an engineering windfall from Honda's now extinct Formula 1 racing 
program that was first used in the lean-burn Civic VX.  When the engine is 
warm, the system changes the air-fuel ratio from lean to within a hair of 
stoichiometric, where catalyst efficiency is greatest for reducing the three 
major tailpipe pollutants.

"For this mixture-control job, Honda employs an engine-control computer 
twice as powerful as the one in the standard Accord.  To tightly monitor the 
air-fuel ratio for each cylinder, Honda could have inserted four LAF sensors 
in each exhaust manifold port, but that would have been too expensive. 
 Instead, engineers discovered that with intensive use of control theory, 
the computer could be made to reliably calculate each cylinder's ratio by 
comparing the nuances of the single LAF (placed at the merge point in the 
exhaust manifold) with known ignition data.

"This ULEV Accord will probably not be available until the fall of 1997, and 
Honda is still exploring how to sell it to the public.  Mass-produced, it 
could go out the door as a $300 option."

Bryan Zublin
bzublin at gi.com