Operation of the probe Oxygen sensor

1 operation of probe

1.1 zirconia sensor
1.2 wideband zirconia sensor
1.3 titania sensor

operation of probe
zirconia sensor

a planar zirconia sensor (schematic picture)

the zirconium dioxide, or zirconia, lambda sensor based on solid-state electrochemical fuel cell called nernst cell. 2 electrodes provide output voltage corresponding quantity of oxygen in exhaust relative in atmosphere.

an output voltage of 0.2 v (200 mv) dc represents lean mixture of fuel , oxygen, amount of oxygen entering cylinder sufficient oxidize carbon monoxide (co), produced in burning air , fuel, carbon dioxide (co2). output voltage of 0.8 v (800 mv) dc represents rich mixture , 1 high in unburned fuel , low in remaining oxygen. ideal setpoint approximately 0.45 v (450 mv) dc. quantities of air , fuel in optimum ratio, ~0.5% lean of stoichiometric point, such exhaust output contains minimal carbon monoxide.

the voltage produced sensor nonlinear respect oxygen concentration. sensor sensitive near stoichiometric point (where λ = 1) , less sensitive when either lean or rich.

the ecu control system uses feedback sensor adjust fuel/air mixture. in control systems, time constant of sensor important; ability of ecu control fuel-air-ratio depends upon response time of sensor. aging or fouled sensor tends have slower response time, can degrade system performance. shorter time period, higher so-called cross count , more responsive system.

the sensor has rugged stainless steel construction internally , externally. due sensor has high resistance corrosion allowing used in aggressive environments high temperature/pressure.

the zirconia sensor of narrow band type, referring narrow range of fuel/air ratios responds.

wideband zirconia sensor


a planar wideband zirconia sensor (schematic picture)

a variation on zirconia sensor, called wideband sensor, introduced ntk in 1992 , has been used car engine management systems in order meet ever-increasing demands better fuel economy, lower emissions , better engine performance @ same time. based on planar zirconia element, incorporates electrochemical gas pump. electronic circuit containing feedback loop controls gas pump current keep output of electrochemical cell constant, pump current directly indicates oxygen content of exhaust gas. sensor eliminates lean-rich cycling inherent in narrow-band sensors, allowing control unit adjust fuel delivery , ignition timing of engine more rapidly. in automotive industry sensor called uego (for universal exhaust gas oxygen) sensor. uego sensors commonly used in aftermarket dyno tuning , high-performance driver air-fuel display equipment. wideband zirconia sensor used in stratified fuel injection systems, , can used in diesel engines satisfy upcoming euro , ulev emission limits.

wideband sensors have 3 elements:

the wiring diagram wideband sensor typically has 6 wires:

titania sensor

a less common type of narrow-band lambda sensor has ceramic element made of titania(it invented ntk) (titanium dioxide). type not generate own voltage, changes electrical resistance in response oxygen concentration. resistance of titania function of oxygen partial pressure , temperature. therefore, sensors used gas temperature sensor compensate resistance change due temperature. resistance value @ temperature 1/1000 change in oxygen concentration. luckily, @ lambda = 1, there large change of oxygen, resistance change typically 1000 times between rich , lean, depending on temperature.

as titania n-type semiconductor structure tio2−x, x defects in crystal lattice conduct charge. so, fuel-rich exhaust (lower oxygen concentration) resistance low, , fuel-lean exhaust (higher oxygen concentration) resistance high. control unit feeds sensor small electric current , measures resulting voltage drop across sensor, varies near 0 volts 5 volts. zirconia sensor, type nonlinear, such simplistically described binary indicator, reading either rich or lean . titania sensors more expensive zirconia sensors, respond faster.

in automotive applications titania sensor, unlike zirconia sensor, not require reference sample of atmospheric air operate properly. makes sensor assembly easier design against water contamination. while automotive sensors submersible, zirconia-based sensors require small supply of reference air atmosphere. in theory, sensor wire harness , connector sealed. air leaches through wire harness sensor assumed come open point in harness - ecu housed in enclosed space trunk or vehicle interior.