- Honda Car Owner's Manual

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87
LEAN-BURNOXYGENSENSOR
Anormalzirconiaoxygensensorisonlycapableofmeasuringtheoxygencontentoftheexhaustina
narrow air-fuel mixture range, right around stoichiometric (14.7:1). This is fine for normal operating
conditions.But,whenthecarisrunningintheleanburnmode,theoxygencontentoftheexhaustishigher
thananormaloxygensensoriscapableofmeasuring.
The Insight uses a LAF (Linear Air-Fuel) sensor for the primary oxygen sensor that is capable of
measuringair-fuelratiosasleanas23:1.ThisallowstheECMtomaintainprecisecontroloverthemixture
duringbothnormalandleanburnconditions.
The engine's LAF Sensor is designed to detect air-fuel ratios as lean as 25:1. The fuel-injection
ElectronicControlModuleusesthisdata,alongwithenginerpm,crankshaftangle,throttleangle,carmass,
coolanttemperatureandvalveposition,tomaintainaleanair-fuelratiobelow2500-3200rpm(depending
onthrottlepositionandengineload).
TheVTEC-Eenginecanburnsuchaleanmixturepartlybecauseofastrongair-fuelswirlcreatedin
thecombustionchamber,createdbythemixture'sentrythroughonlyoneoftwointakevalvesduringlow-
rpm operation. Although the overall air-fuel mixture is lean, optimized injection timing, along with the
vortex,createsa"stratified"charge-theair-fuelratioisrichernearthesparkplugandleanertowardthe
combustionchamberperiphery.Therichermixtureignitesmorereadilyandcreatesafast-burning,stable
flamethatpromotesmorecompletecombustion.
A standard zirconia oxygen sensor
usesa thimbleshapedzirconia element
that is exposed to the atmosphere on
one side, and to the exhaust streamon
theotherside.Iftheamountofoxygen
onthetwosidesisdifferent,itgenerates
a voltage. Since the amount of oxygen
on the atmospheric side is fixed, the
generatedvoltagerepresentstheamount
of oxygen in the exhaust. With the
enginenotrunningthereisatmospheric
pressureintheexhaust,andthevoltage
is zero since the same amount of
oxygenexistsonbothsideoftheelement.Whentheengineisrunningthereislessoxygenintheexhaust,
sovoltageisgenerateduptoamaximumofonevolt.
TheLAFsensorhastwozirconiaelementsthatshareadiffusionchamber.Thereareatotalofthree
chambers:
• Exhaustflowchamber
• Diffusionchamber
• Atmospherereferencechamber
Thezirconiaelementthatisincontactwiththeexhaustisthesensorelement.Thediffusionchamberis
thespacebetweenthetwozirconiaelements.Byapplyingvaryingvoltagetothecontrolelement,theECM
cancontroltheamountofoxygeninthediffusionchamber.Sincethediffusionchamberisthereference
chamberforthesensorelement,thisactionchangestheoutputofthesensorelement.
TheECMmonitorstheoutputofthesensorelementastheoxygencontentoftheexhaustchanges,and
it applies voltage to the element to tryto maintain the sensor output at.450 volts.It thenmonitors the
controlvoltagetodeterminetheactualair-fuelratio.
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