Automotive applications Oxygen sensor

1 automotive applications

1.1 function of lambda probe
1.2 probe
1.3 operation of probe

1.3.1 zirconia sensor
1.3.2 wideband zirconia sensor
1.3.3 titania sensor


1.4 location of probe in system
1.5 sensor surveillance
1.6 sensor failures

automotive applications


a three-wire oxygen sensor suitable use in volvo 240 or similar vehicle

automotive oxygen sensors, colloquially known o2 ( ō 2 ) sensors, make modern electronic fuel injection , emission control possible. determine, in real time, if air–fuel ratio of combustion engine rich or lean. since oxygen sensors located in exhaust stream, not directly measure air or fuel entering engine when information oxygen sensors coupled information other sources, can used indirectly determine air-fuel ratio. closed loop feedback-controlled fuel injection varies fuel injector output according real-time sensor data rather operating predetermined (open-loop) fuel map. in addition enabling electronic fuel injection work efficiently, emissions control technique can reduce amounts of both unburnt fuel , oxides of nitrogen entering atmosphere. unburnt fuel pollution in form of air-borne hydrocarbons, while oxides of nitrogen (nox gases) result of combustion chamber temperatures exceeding 1,300 kelvin due excess air in fuel mixture , contribute smog , acid rain. volvo first automobile manufacturer employ technology in late 1970s, along three-way catalyst used in catalytic converter.

the sensor not measure oxygen concentration, rather difference between amount of oxygen in exhaust gas , amount of oxygen in air. rich mixture causes oxygen demand. demand causes voltage build up, due transportation of oxygen ions through sensor layer. lean mixture causes low voltage, since there oxygen excess.

modern spark-ignited combustion engines use oxygen sensors , catalytic converters in order reduce exhaust emissions. information on oxygen concentration sent engine management computer or engine control unit (ecu), adjusts amount of fuel injected engine compensate excess air or excess fuel. ecu attempts maintain, on average, air–fuel ratio interpreting information gains oxygen sensor. primary goal compromise between power, fuel economy, , emissions, , in cases achieved air-fuel ratio close stoichiometric. spark-ignition engines (such burn gasoline or lpg, opposed diesel), 3 types of emissions modern systems concerned are: hydrocarbons (which released when fuel not burnt completely, such when misfiring or running rich), carbon monoxide (which result of running rich) , nox (which dominate when mixture lean). failure of these sensors, either through normal aging, use of leaded fuels, or fuel contaminated silicones or silicates, example, can lead damage of automobile s catalytic converter , expensive repairs.

tampering or modifying signal oxygen sensor sends engine computer can detrimental emissions control , can damage vehicle. when engine under low-load conditions (such when accelerating gently, or maintaining constant speed), operating in closed-loop mode . refers feedback loop between ecu , oxygen sensor(s) in ecu adjusts quantity of fuel , expects see resulting change in response of oxygen sensor. loop forces engine operate both lean , rich on successive loops, attempts maintain stoichiometric ratio on average. if modifications cause engine run moderately lean, there slight increase in fuel economy, @ expense of increased nox emissions, higher exhaust gas temperatures, , slight increase in power can turn misfires , drastic loss of power, potential engine , catalytic converter (due misfires) damage, @ ultra-lean air-fuel ratios. if modifications cause engine run rich, there slight increase in power point (after engine starts flooding unburned fuel), @ cost of decreased fuel economy, , increase in unburned hydrocarbons in exhaust causes overheating of catalytic converter. prolonged operation @ rich mixtures can cause catastrophic failure of catalytic converter (see backfire). ecu controls spark engine timing along fuel injector pulse width, modifications alter engine operate either lean or rich may result in inefficient fuel consumption whenever fuel ignited or late in combustion cycle.

when internal combustion engine under high load (e.g. wide open throttle), output of oxygen sensor ignored, , ecu automatically enriches mixture protect engine, misfires under load more cause damage. referred engine running in open-loop mode . changes in sensor output ignored in state. in many cars (with exception of turbocharged models), inputs air flow meter ignored, might otherwise lower engine performance due mixture being rich or lean, , increase risk of engine damage due detonation if mixture lean.

function of lambda probe

lambda probes used reduce vehicle emissions ensuring engines burn fuel efficiently , cleanly. robert bosch gmbh introduced first automotive lambda probe in 1976, , first used volvo , saab in year. sensors introduced in 1979, , required on models of cars in many countries in europe in 1993.

by measuring proportion of oxygen in remaining exhaust gas, , knowing volume , temperature of air entering cylinders amongst other things, ecu can use look-up tables determine amount of fuel required burn @ stoichiometric ratio (14.7:1 air:fuel mass gasoline) ensure complete combustion.

the probe

the sensor element ceramic cylinder plated inside , out porous platinum electrodes; whole assembly protected metal gauze. operates measuring difference in oxygen between exhaust gas , external air, , generates voltage or changes resistance depending on difference between two.

the sensors work when heated approximately 316 °c (600 °f), newer lambda probes have heating elements encased in ceramic bring ceramic tip temperature quickly. older probes, without heating elements, heated exhaust, there time lag between when engine started , when components in exhaust system come thermal equilibrium. length of time required exhaust gases bring probe temperature depends on temperature of ambient air , geometry of exhaust system. without heater, process may take several minutes. there pollution problems attributed slow start-up process, including similar problem working temperature of catalytic converter.

the probe typically has 4 wires attached it: 2 lambda output, , 2 heater power, although automakers use metal case ground sensor element signal, resulting in 3 wires. earlier non-electrically-heated sensors had 1 or 2 wires.

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.

location of probe in system

the probe typically screwed threaded hole in exhaust system, located after branch manifold of exhaust system combines, , before catalytic converter. new vehicles required have sensor before , after exhaust catalyst meet u.s. regulations requiring emissions components monitored failure. pre , post-catalyst signals monitored determine catalyst efficiency , if converter not performing expected alert gets reported user through on-board diagnostics systems by, example, lighting indicator in vehicle s dashboard. additionally, catalyst systems require brief cycles of lean (oxygen-containing) gas load catalyst , promote additional oxidation reduction of undesirable exhaust components.

sensor surveillance

the air–fuel ratio , naturally, status of sensor, can monitored means of using air–fuel ratio meter displays output voltage of sensor.

sensor failures

normally, lifetime of unheated sensor 30,000 50,000 miles (50,000 80,000 km). heated sensor lifetime typically 100,000 miles (160,000 km). failure of unheated sensor caused buildup of soot on ceramic element, lengthens response time , may cause total loss of ability sense oxygen. heated sensors, normal deposits burned off during operation , failure occurs due catalyst depletion. probe tends report lean mixture, ecu enriches mixture, exhaust gets rich carbon monoxide , hydrocarbons, , fuel economy worsens.

leaded gasoline contaminates oxygen sensors , catalytic converters. oxygen sensors rated service life in presence of leaded gasoline sensor life shortened little 15,000 miles depending on lead concentration. lead-damaged sensors typically have tips discolored light rusty.

another common cause of premature failure of lambda probes contamination of fuel silicones (used in sealings , greases) or silicates (used corrosion inhibitors in antifreezes). in case, deposits on sensor colored between shiny white , grainy light gray.

leaks of oil engine may cover probe tip oily black deposit, associated loss of response.

an overly rich mixture causes buildup of black powdery deposit on probe. may caused failure of probe itself, or problem elsewhere in fuel rationing system.

applying external voltage zirconia sensors, e.g. checking them types of ohmmeter, may damage them.

some sensors have air inlet sensor in lead, contamination lead caused water or oil leaks can sucked sensor , cause failure.

symptoms of failing oxygen sensor includes:

sensor light on dash indicates problem
increased tailpipe emissions
increased fuel consumption
hesitation on acceleration
stalling
rough idling




^ 30 years of bosch lambda sensor .
^ zirconia sensors in spark plug 411, @ sparkplugs.com
^ oxygen sensor solutions & applications http://sstsensing.com/application/oxygen-sensor-solutions
^ citation: yamada, t., hayakawa, n., kami, y., , kawai, t., universal air-fuel ratio heated exhaust gas oxygen sensor , further applications , sae technical paper 920234, 1992, doi:10.4271/920234.
^ recent car utilising lean-burn or direct-injection engine technology uses wideband sensor , info lambdapower.co.uk
^ ngk: sensors breathe through leads, susceptible contamination of leads.