Unit -IV Automotive Sensors & Actuators

1 316482 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Unit -IV Automotive Sensors & Actuators By, J BhosaleAsst. ProfessorDept. of Automobile EngineeringGovt. College of Engineering and Research, Avsari(Kd)316482 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Syllabus: Workingprincipleofsensors,Typesofsensors ,Airflowratesensor,Positionsensor,Thrott leanglesensor,Temperaturesensor,MAPsenso rs,Knock/DetonationSensor,Loadcell,Lambd aSensor(ExhaustgasO2 Sensor),yawratesensor,sensorfeedbackcont rol,ElectronicControlUnit(ECU),Principle ofactuator,Typesofactuators,enginecontro lactuators,Solenoidactuators,motorizedac tuators(Steppermotors).316482 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Sensors : Sensorsarethecomponentsofthesystemthatpr ovidetheinputsthatenablethecomputer(ECM) tocarryouttheoperationsthatmakethesystem functioncorrectly.

2 Inthecaseofvehiclesensorsitisusuallyavol tagethatisrepresentedbyacodeatthecompute r Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Types of Sensors used1. Mass air flow (MAF) rate2. Exhaust gas oxygen concentration (possibly heated)3. Throttle plate angular position4. Crankshaft angular position/RPM5. Coolant temperature6. Intake air temperature7. Manifold absolute pressure (MAP)8. Differential exhaust gas pressure9. Vehicle speed10. Transmission gear selector position316482 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Mass air flow (MAF) rate sensor (powertraincontrolmoduleorPCM)whichturns thefuelinjectorsonandoff. Thecomputerthenincreasesordecreasesinjec torduration(ontime)toprovidethecorrectai r/fuelratio. Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Vane type air flow (MAF) rate sensor Anenginerequiresthecorrectair fuelratioandinordertodothisitneedsaconst antflowofinformationabouttheamountofairf lowingtotheengine.

3 Withthisinformation,anddatastoredinitsme mory,theECMcanthensendoutasignaltotheinj ectors,sothattheyprovidethecorrectamount offuel. Airflowmeasurementiscommonlyperformedbya flap (potentiometer).Fig. AFig. B316482 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Figure B. shows the theoretical form of a simple potential divider. A voltage, say 5 V, is applied across terminals A and B. C is a slider which is in contact with the resistor and a voltmeter is connected between A and C. The voltage VACis related to the position of the slider C in the form VAC =VAB* x/l. Intheairflowsensor,themovingprobe(wiper) Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) ,andwhenfullyopenthevoltagewillbe5V. ,itisnotquiteassimpleasthis,becauseallow ancemustbemadeforothercontingencies.

4 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Theflaphasawiperarmthatrotatesagainstase aledpotentiometer(variableresistororrheo stat),allowingthesensor'sresistanceandou tputvoltagetochangeaccordingtoairflow. Thegreatertheairflow, 'sresistanceandincreasesthevoltagereturn signaltothecomputer. Acompensationplateactsasashockabsorberto preventrapidmovementorvibrationsofthemea suringplate. , Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) VANEAIRFLOWSENSORPROBLEMS Vaneairflowsensorsaswellasalltheothertyp esofairflowsensorscan' "unmetered"or"false" ,includingleanmisfire,hesitationandstumb lingwhenaccelerating,andaroughidle. , Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Backfiringintheintakemanifoldcanforcethe flapbackwardsviolently, "backfire" Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Hot Wire Type MAF: ThehotwireMAFsensorisavariationofaclassi cairflowsensorthatwasknownasahotwireanem ometerandwasused,forexample,tomeasurewin dvelocityforweatherforecasting.

5 InthisMAF,thehot-wire,orsensing,elementi sreplacedbyahot-filmstructuremountedonas ubstrate. Ontheairinletsideismountedahoneycombflow straightenerthat smooths theairflow(causingnominallylaminarairflo woverthefilmelement). Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Thefilmelementiselectricallyheatedtoacon stanttemperatureabovethatoftheinletair. Thehot-filmelementisincorporatedinaWheat stonebridgecircuit(Figureattop). Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) TheWheatstonebridgeconsistsofthreefixedr esistorsR1,R2, ,R2,andR3arechosensuchthatvoltagevaandvb areequal( ,thebridgeissaidtobebalanced). Asairflowsacrossthehotfilm, Theheatlostbythefilmtotheairtendstocause theresistanceofthefilmtovary,whichunbala ncesthebridgecircuit,therebyproducingani nputvoltagetotheamplifier.

6 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) ,asindicatedbythecalibrationcurvedepicte dinFigure. Fortunately, Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) ,massairflowsensorsuseelectricalcurrentt omeasureairflow. Thesensingelement,whichiseitheraplatinum wire(hotwire)ornickelfoilgrid(hotfilm),i sheatedelectricallytokeepitacertainnumbe rofdegreeshotterthantheincomingair. InthecaseofhotfilmMAFs, ,thewireisheatedto100oCaboveambienttempe rature. Asairflowspastthesensingelement, ,densityandhumidityoftheincomingair,thea mountofcurrentneededtokeeptheelementhoti sdirectlyproportionaltotheair"mass"enter ingtheengine316482 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Positions Sensors : Thepositionssensorsaregenerallyspeedsens orsofdifferentworkingprincipleusedfordet ectingthepositionofdifferentparameters.

7 Parameters Measured, Position Position Wheel Speed Sensor Working Principles used, Reluctance (Variable Reluctance) Effect Type316482 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Crankshaft Position Sensor: Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) MagneticReluctance(orVariableReluctance) typesensor Thistypeofsensorisusedinmanyvehicleappli cations,suchasignitionsystems,enginespee dsensorsforfuelling,andwheelspeedsensors foranti-lockbrakingetc. Airhasagreaterreluctance(resistancetomag netism) ( )maybeunderstoodfromthefollowingdescript ion. Theprincipalelementsofthesensorare: an iron rotor with lobes on it; a permanent magnet; a metallic path (the pole piece) for carrying the magnetic flux; a coil, wound around the metallic path, in which a voltage is Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Thereluctordischasanumberoftabsonitandth esetabsaremadetomovethroughtheairgapinth emagneticcircuit.

8 Themovementofthereluctortabs, ,thesensorvoltageiszero. Asthetabmovesintotheairgaptheflowofmagne tism(flux) ,quitequickly, Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) (a) ,whenthemetaltabisexactlyalignedwiththep olepiece,thesensorvoltagefallsbacktozero (Althoughthemagneticfluxisstrongestatthi spoint,itisnotchangingandthismeansthatth evoltageiszero.) (b) Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Asthemetaltabcontinuestorotateoutoftheai rgapandawayfromthepolepiece,therateofcha ngeofthemagneticfluxisrapid,butoppositei ndirectiontowhenthetabwasmovingintotheai rgap. (c). (d).316482 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) 316482 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Hall Effect: TheHalleffectistheproductionofavoltagedi fference(theHallvoltage)acrossanelectric alconductor, Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) 2.

9 Hall Effect type sensor: WhenconnectedasshowninFig.(a),thebattery willcausecurrenttoflowthroughthesemicond uctorHallelementandbatterycircuit,butthe rewillbenocurrentinthecircuitwhichisatri ghtanglestothebatterycircuit, Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) 316482 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) WhenamagneticfieldisimposedontheHallelem ent,asshowninFig.(b),acurrentwillflowinc ircuit2. Whenthemagneticeffectispreventedfromreac hingtheHallelement,asinFig.(c),thecurren twillceasetoflowincircuit2. Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) 316482 Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Whenthemetalplatethatisinsertedbetweenth emagnetandtheHallelementismountedonarota tingshaft,theHallcurrentcanbeswitchedona ndoffatanydesiredfrequency.

10 TheHalltypesensorproducesanoutputpowerth atisvirtuallyconstantatallspeeds. Halleffectsensorsareusedwhereverotherele ctromagneticsensorsareused, ,ABSwheelsensors,camshaft(cylinder)ident ification(forignitionandfuelling) Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) , Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) Optical Sensor: ,aswiththemagneticsystem,adiskisdirectly coupledtothecrankshaft. Thistime,thediskhasholesinitthatcorrespo ndtothenumberoftabsonthedisksofthemagnet icsystems. (LED)sourcetothephototransistorusedasali ghtsensor. Automotive Electrical & ElectronicsA J BhosaleGovernment College of Engineering and Research, Avsari(Kd) AsshowninFigurebelow, + + Oneoftheproblemswithopticalsensorsisthat theymustbeprotectedfromdirtandoil;otherw ise,theywillnotworkproperly.