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Automotive Sensors and Actuators

P.V.ManivannanPEI Lab, Mechanical Department

Automotive Electronic SensorsAutomotive Electronic Sensors

P.V.Manivannan

Precision Engineering and Instrumentation Laboratory

Mechanical Engineering Department

IIT Madras


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PEI Lab, Mechanical Department

The world has long passed the "dangerous level" for greenhouse gases in the

atmosphere. Earth's atmosphere can only stay this loaded with man-made carbon

dioxide for a couple more decades without changes such as mass extinction, ecosystem

collapse and dramatic sea level rises

James Hansen, NASA Scientist( To USA Congress )

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How to solve the man-made Environmental problems ? (Global Warming)

How to solve the man-made Environmental problems ? (Global Warming)

Reducing utilization of fossil fuel

Reduction in tail pipe emissions

Customer satisfaction


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Trinity of Control SystemTrinity of Control System

Measurement

Algorithm (or) Computation

Control or actuation

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What is an Electronic Sensor ?What is an Electronic Sensor ?A sensing device which converts a physical, mechanical or optical energy into an electrical signal

The sensing device always extracts some energy from the measured medium – loading effect

A good sensors are designed such that the load effect minimal

The output electrical signal has to be conditioned using additional electronic amplifiers and filters

A Smart sensor is an integrated unit with the all the above elements along with signal processing capability.


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Classification of Electronic SensorsClassification of Electronic SensorsResistance change : Strain Gauges, Resistance

Temperature Detector (RTD)

Capacitance change : Capacitive type displacement / Angle sensor

Inductance change : Inductive RPM sensor, Linear Voltage Differential Transformer

Piezo-electric effect : Piezoelectric Pressure transducer, Accelerometer, Knock sensor

Thermoelectric effect: Thermocouples

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Sensors in Electronic Engine Management System

Sensors in Electronic Engine Management System

Engine RPM sensorThrottle Position SensorManifold Pressure Sensor (MAP)Mass Air Flow (MAF) sensor O2 or Lambda sensorInlet air & Engine coolant temperature sensorsCrank Angle sensorHall effect sensorKnock sensor


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Most important sensors used in a EMSMost important sensors used in a EMSThe basic sensors required by Electronic Fuel Injection system are:

Engine rpm sensorManifold Absolute-Pressure sensor (MAP)

or Mass Air Sensor (MAS) Throttle-Position Sensor (TPS).

CAM position sensor

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Electronic Fuel Injection (EFI)Electronic Fuel Injection (EFI)

The ECU of the EFI system needs to know is how much air the engine consumes under a given operating condition to inject the right quantity of fuel.

Three different measurement strategies have evolved to supply the computer with this basic information:

N AlphaSpeed DensityMass Flow metering


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Electronic Fuel Injection (EFI)Electronic Fuel Injection (EFI)N – Alpha :

Look Table based (RPM, TPS value)Open loopGood at Wide open throttleIn-accurate at part throttle: No correction for intake air temperature variation, etc

Speed Density:Look table based with correction for air-density (RPM, load : manifold vacuum in kPa)ECU calculates airflow requirements by referring to a much larger (in comparison to an N Alpha system) preprogrammed lookup table, a map of thousands of values that equates to the engine’s volumetric efficiency (VE) under varying conditions of throttle position and engine speedLambda sensor for closed loop Idle control

Mass FlowDirectly measures the amount of air inducted into the engine. Constant temperature Hot wire Anemometer type The amount of current needed to heat the wire is proportional to the mass of air flowing across the wire. The mass-air meter also includes a temperature sensor that provides a correction for intake air temperature

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Inductive Speed sensorInductive Speed sensor


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Opto electronic Engine RPM sensorOpto electronic Engine RPM sensor

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Hall effect sensorHall effect sensorThe Hall effect refers to the potential difference on opposite sides of a thin sheet of conducting or semi-conducting material through which an electric current is flowing, created by a magnetic field applied perpendicular to the Hall element.

Dr. Edwin Hall discovered this effect in 1879.

The ratio of the voltage created to the amount of current is known as the Hall coefficientand is a characteristic of the material in the element


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Hall effect sensorHall effect sensor

Hall voltage VH = IB / endI is the current across the plate length, B is the magnetic flux densityd is the depth of the platee is the electron chargen is the bulk density of the carrier electrons.

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Hall Effect SensorHall Effect Sensor

Integrated smart sensor = sensor + amplifier in single package

Hall effect devices when appropriately packaged are immune to dust, dirt, mud, and water - better for position sensing than alternative means such as optical and electromechanical sensing

Automotive Ignition, fuel injection and wheel-rotation in ABS

If the magnetic field is provided by a rotating magnet resembling a toothed gear, an output pulse will be generated each time a tooth passes the sensor. This is used in modern automotive primary distributor ignition systems, replacing the earlier "breaker" points


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Throttle Position Sensor (TPS)Throttle Position Sensor (TPS)

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Equivalent circuit of TPS sensorEquivalent circuit of TPS sensor


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Throttle Position Sensor (TPS)Throttle Position Sensor (TPS)Throttle position sensors are typically mounted on the throttle body, directly to the end of the throttle shaft

The Throttle sensor supplies the ECU with information about idle status and driver demand.

This information is used by the ECU to make judgments about power enrichment, deceleration fuel cut-off, idle stability, and spark advance angle corrections

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Engine RPM SensorEngine RPM Sensor

Engine RPM information, along with information from the air flow or manifold pressure sensor, allows the ECU to calculate the engine's basic operating load.

Based on measured load, basic injection and spark advance angle are accurately calculated

5.604.633.603.042.604000

5.304.924.202.962.723000

5.204.163.442.922.682000

4.764.403.472.922.761000

10080694020

Throttle (%)RPM


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Manifold Absolute Pressure sensorManifold Absolute Pressure sensor

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Manifold Absolute Pressure sensorManifold Absolute Pressure sensorIt measures intake air volume by monitoring changes in manifold absolute pressure, a function of engine load.

The sensor consists of a piezoresistive silicon chip and an Integrated Circuit (IC).

A perfect vacuum is applied to one side of the silicon chip and manifold pressure applied to the other side.

When pressure in the intake manifold changes, the silicon chip flexes, causing a change in its resistance. The varying resistance of the sensor causes a change in signal voltage


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MAP sensor working principleMAP sensor working principle

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Air flow sensorsAir flow sensorsMeasurement of amount air entering into the cylinder is necessary to control the fuel injected

The quantity of air entering into cylinder is proportional to inlet air temperature, Manifold pressure, speed and load

Most widely used air flow meters are:

Mass Air Flow (MAF) sensor

Vane Air Flow (VAF) sensor

Karmen Vortex Air Flow sensor


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Hotwire Anemometer type MAF sensor Hotwire Anemometer type MAF sensor

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Hot wire Mass Air Flow sensorHot wire Mass Air Flow sensor


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Working of Hotwire Anemometer type MAF sensor

Working of Hotwire Anemometer type MAF sensor

The primary components of the MAF sensor are a thermistor, a platinum hot wire, and an electronic control circuit.

The thermistor measures the temperature of the incoming air.

The hot wire is maintained at a constant temperature in relation to the thermistor by the electronic control circuit.

An increase in air flow will cause the hot wire to lose heat faster and the electronic control circuitry will compensate by sending more current through the wire.

The electronic control circuit simultaneously measures the current flow and puts out a voltage signal in proportion to current flow

Main advantage is that, the meter is insensitive to the density of the fluid

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Vane type Air Flow MeterVane type Air Flow Meter


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Vane type Mass Air Flow sensorVane type Mass Air Flow sensor

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Vane type Mass Air Flow sensorVane type Mass Air Flow sensorPlaced in series with the throttle body and a potentiometer is used as a measuring deviceIdle speed adjustment and inlet air temperature sensor are build-inIntake air volume is a direct measure of the load placed on an engine and the meter measures air volume, not massBy measuring the air temperature and pressure to determine air density, a true mass airflow calculation can be achieved using ideal gas law. ECU uses this parameter for calculating the fuel quantity and ignition timing


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Karman Vortex type MAF sensorKarman Vortex type MAF sensor

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Working principle of Karman Vortex Airflow Meter



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When air passes through the air flow meter, the vortex generator creates a swirling of the air downstream.

This swirling effect is referred to as a "Karman vortex."

The frequency of this Karman vortex varies with the velocity of the air entering the air flow meter.

The photo-coupler and metal foil mirror are used to detect changes in these vortices.

The metal foil mirror is used to reflect light from the LED to the photo transistor. The foil is positioned directly above a pressure directing hole which causes it to oscillate with the changes in vortex frequency.

The resulting digital signal is a 5 volt square wave which increases in frequency in proportion to increases in intake air flow.

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Karman Vortex AFM internal circuit and output signal

Karman Vortex AFM internal circuit and output signal


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Air Intake temperature sensorAir Intake temperature sensorAn intake air temperature monitor is necessary in the EFI system because the pressure and density of air changes with temperature.

Depending upon inlet air temperature, the ECU calculates the necessary fuel correction value and adjusts injected fuel quantity (fuel correction program)

AIT : Normally thermistor type which forms an integral part of the MAF sensor

The sensing element is a Thermistor:Oxides of Cobalt, Nickel, BismuthNegative temperature coefficient

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Engine Coolant temperature sensorEngine Coolant temperature sensorEngine coolant temperature sensor or Water Temperature Sensor (THW) is typically located near the cylinder head water outlet.

Monitors engine coolant temperature using thermistor

The thermistor has a negative temperature coefficient (NTC), so its resistance value decreases as coolant temperature rises


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Engine Coolant temperature sensorEngine Coolant temperature sensorThe coolant temperature sensor is required because fuel vaporization is less efficient when the engine is cold.

Internal engine friction is also higher during cold operation, increasing operating load.

The THW signal is used by the ECU to determine how much fuel enrichment correction is necessary to provide good cold engine performance.

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Stoichiometric ratio Stoichiometric ratio By definition it is the ratio where the fuel is exactly completely consumed by the oxidizer present (normally atmospheric oxygen.)

As the mixture passes from rich, through stoichimetry and on to lean, the CO and HC emission declines while the NOX stays low until the lean side of stoichimetry.

All three are sufficiently low at stoichimetry that a three way cat can clean it up. The three way catalytic converter REQUIRES stoichimetry in order to work.

The Stoichiometric ratio of gasoline can vary from 14:1 to 16:1depending upon type of gasoline composition.

It is varies for different fuels. eg: Methanol is 11:1.


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Lambda SensorLambda Sensor

A Lambda sensor is a device that measures the amount of oxygen in the exhaust gas. It is also called as O2 sensor

Lambda is simply the ratio of the current fuel:air and ideal (stochiometric) fuel:air ratio. Thus a lambda of 1 is stochiometric.

A lambda less than 1 is rich and more than one is lean.

A common term used in fuel injection circles is reciprocal lambda or gamma. This is convenient because it is >1 for richness.

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Types of Lambda sensorsTypes of Lambda sensors

Two types of Lambda sensors:

Binary / narrow band Lambda Sensor: The sensor gives 0 volt when the engine runs lean and about 1 volt when the engine runs rich.

Linear or wide band Lambda sensor: Has a built in oxygen pump and heater circuit to achieve a very low change in output voltage even outside the stoichiometric ratio

The sensor directly measures the ratio of oxygen in the exhaust to the oxygen in a reference chamber normally vented to air


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O2 / Lambda SensorO2 / Lambda SensorIt consists of a zirconium dioxide (Zr02) element sandwiched between two platinum electrodes. This sensor behaves very similar to a single cell battery. The electrodes act as the positive (+) and negative (-) plates, and the zirconium dioxide element acts as the electrolyte

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Characteristic curve of an Nernst Cell type O2 Sensor

Characteristic curve of an Nernst Cell type O2 Sensor


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Working of Binary type Lambda sensorWorking of Binary type Lambda sensorDuring rich operating conditions, the inside, or positive plate, is exposed to a much higher concentration of oxygen than the outside, or negative plate.

The difference in O2 creates a difference in electrical potential, or voltage

When the air/fuel ratio becomes lean, the oxygen content of the exhaust gas increases significantly.

Because both plates are now exposed to a relatively high concentration of oxygen, electrons balance equally between the two plates. This eliminates the electrical potential between theplates.

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Internal construction of Lambda sensorInternal construction of Lambda sensor


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Wide Band Lambda sensorWide Band Lambda sensorThey provide a precise indication of the exact air/fuel ratio, and over a much broader range of mixtures - all the way from 0.7 lambda (11:1 air/fuel ratio) to atmospheric air

oxygen sensors that uses a flat ceramic Zirconia element. It's called a "planar" sensor because the sensor element is a flat strip of ceramic that is only 1.5mm thick.

The electrodes, conductive layer of ceramic, insulation and heater are laminated together on a single strip

The new heater element also requires less electrical power and brings the sensor up to operating temperature in only 10 seconds.

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Linear Lambda sensor constructionLinear Lambda sensor construction


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Wide Band Lambda sensorWide Band Lambda sensor

The Nernst cell still senses oxygen in the same way that a conventional thimble-type O2 sensor does.

To get the added precision, the oxygen pump uses a heated cathode and anode to pull some oxygen from the exhaust into a "diffusion" gap between the two components.

The Nernst cell and oxygen pump are wired together in such a way that it takes a certain amount of current to maintain a balanced oxygen level in the diffusion gap.

The amount of current required to maintain this balance is directly proportional to the oxygen level in the exhaust.

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Wide Band Lambda sensorWide Band Lambda sensorWhen the air/fuel mixture is perfectly balanced at 14.7:1 (the stoichiometric ratio and lambda equals 1), the sensor produces no output current.

For a rich air/fuel mixture, the sensor produces a "negative" current that goes from zero to about 2.0 milliamps when lambda is 0.7 ( air/fuel ratio is near 11:1)

When the air/fuel mixture is lean, the sensor produces a "positive" current that goes from zero up to 1.5 milliamps as the mixture becomes almost air.


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Lambda Sensor in EMSLambda Sensor in EMS

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Late response; any problem ?Late response; any problem ?More pollutants emitted during first few minutes of

engine warm-up.

The sensor does not begin to generate it's full output until it reaches about 600°F.

A typical zirconia sensor has a response time constant of under a millisecond

All these leads no control of emissions in a Gasoline engine inspite of having advanced EMS and Catalytic converter


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Physical Location of a Lambda Sensor in an Engine

Physical Location of a Lambda Sensor in an Engine

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Piezoelectric Pressure transducer Piezoelectric Pressure transducer Certain crystals like Quartz produce electrical charges under mechanical loading

Crystals produce an electrical output only when they experience a change in load - Dynamic Measurements.

True static measurements are not possible

Quartz transducers, paired with adequate signal conditioners, offer excellent quasi-static measuring capability


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Piezoelectric Pressure transducerPiezoelectric Pressure transducerQuartz piezoelectric transducers consist essentially of thin slabs or plates cut in a precise orientation to the crystal axes depending on the application.

Piezoelectric transducers incorporate a quartz element which is sensitive to either compressive or shear loads.

The shear cut is used for patented multi-component force and acceleration measuring transducers.

The transverse cut for some pressure transducers

The polystable cut for high temperature pressure transducers

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Different type of cuts in Quartz crystalDifferent type of cuts in Quartz crystal


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Piezoelectric pressure transducer Piezoelectric pressure transducer

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Properties of Quartz crystal transducerProperties of Quartz crystal transducerQuartz is employed preferentially in transducer designs because of the following excellent properties:

high material stress limit, approximately 20,000 psi

temperature resistance up to 500°C

very high rigidity, high linearity and negligible hysteresis

almost constant sensitivity over a wide temperature range

ultra high insulation resistance (1014 ohms) allowing low frequency measurements (<1 Hz)


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Charge amplifierCharge amplifier

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Typical Frequency Response Curve of Quartz transducer

Typical Frequency Response Curve of Quartz transducer


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Why do we measure cylinder pressure ?Why do we measure cylinder pressure ?

Estimation of IMEP and Frictional losses

Study of pumping losses and the intake and exhaust strokes

Calculation of fuel burning rates

Estimation of gas pressures and temperatures

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Unwanted emissions from SI EnginesUnwanted emissions from SI EnginesCarbon monoxide: A poisonous gas that is colorless and odorless.

Hydrocarbons or volatile organic compounds (VOC's): Produced mostly from unburned fuel that evaporates. Sunlight breaks these down to form oxidants, which react with oxides of nitrogen to cause ground level ozone, a major component of pollution.

Oxides of nitrogen: Contributes to smog and acid rain, and also causes irritation to human mucus membranes


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Three Way Catalytic Converter (TWC)Three Way Catalytic Converter (TWC)"Three-way" refers to the three regulated emissions it helps to reduce -- carbon monoxide, unburnt HC and NOx molecules.

The converter uses two different types of catalysts, a reduction catalyst and an oxidation catalyst.

Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium.

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Catalytic Converter EfficiencyCatalytic Converter Efficiency


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Internal Structure of Three Way Catalytic Converter ( TWC )

Internal Structure of Three Way Catalytic Converter ( TWC )

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Reduction CatalystReduction CatalystUses platinum and rhodium to help reduce the NOx emissions.

When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2.

The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2

2NO => N2 + O2 or 2NO2 => N2 + 2O2


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The Oxidization CatalystThe Oxidization CatalystThe oxidation catalyst is the second stage of the catalytic converter.

It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst.

This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas

2CO + O2 => 2CO2

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Does the location matters ?Does the location matters ?One of the catalytic converter's biggest shortcomings is that itonly works at a fairly high temperature.

Place the catalytic converter closer to the engine. This means that hotter exhaust gases reach the converter and it heats up faster, but this may also reduce the life of the converter by exposing it to extremely high temperatures.

The converter is placed under the front passenger seat, far enough from the engine to keep the temperature down to levels that will not harm it.

Preheating the catalytic converter could be a good way to reduce emissions using electric resistance heaters.


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Optical Crank Angle EncoderOptical Crank Angle Encoder

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Typical Crank Angle Encoder output signals

Typical Crank Angle Encoder output signals


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Piezoelectric sensor internal construction and frequency response curve

Piezoelectric sensor internal construction and frequency response curve

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Knock Signal from Piezo sensorKnock Signal from Piezo sensor


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Crank Angle EncoderCrank Angle Encoder

Crank angle information is needed for calculating Indicated Mean Effective Pressure (IMEP) and heat release

To plot Pressure -Volume diagram

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Knocking in EnginesKnocking in EnginesUncontrolled combustion in an Engine

results in very high rate of pressure rise and results in high pressure pulses. This phenomenon is called as Knock or ping

Reasons for knocking are:Higher compression ratio Fuel qualityHot spots inside the combustion chamber


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Properties of knock signalProperties of knock signal

Knock frequency depends on the mass of the engine

Amplitude of the knock signal depends on the intensity of knock

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Hot spots inside the combustion chamberHot spots inside the combustion chamber


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Type of Knock sensorType of Knock sensor

Microphone

Piezoelectric pressure sensor

Washer type knock sensor

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Knock Sensor (micro phone ) outputKnock Sensor (micro phone ) output


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Cylinder pressure sensor outputCylinder pressure sensor output

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Output of a Knock sensorOutput of a Knock sensor

Vibration Signal During Knock

-40

-20

0

20

40

60

330 350 370 390 410

Crank angle (o)

Acce

lera

tion

(m/s

2 )


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Washer type piezoelectric knock sensorWasher type piezoelectric knock sensor

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Piezoelectric cylinder pressure sensor used for heat release computation

Piezoelectric cylinder pressure sensor used for heat release computation


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Conventional Electromagnetic type fuel injector

Conventional Electromagnetic type fuel injector

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Exhaust Gas Recirculation ( EGR )Exhaust Gas Recirculation ( EGR )The modern multi-valve, high compression engine can create NOx (Nitrous Oxide) during the high temperature combustion process.

NOx reacts with sunlight to create atmospheric problems such as smog and acid rain.

EGR is considered a `metered intake leak' and was developed to reduce the combustion temperatures to below 2,500 degrees, the threshold where NOx is created.


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Vacuum-operated EGR valve Vacuum-operated EGR valve

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Exhaust Gas RecirculationExhaust Gas RecirculationThe EGR valve meters a readily available inert gas into the combustion chamber to effectively reduce the volume.

Smaller effective displacement means less fire, and less heat and thus lower temperatures.

The lower temperature inside the cylinder reduces formation of NOx emissions.


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When EGR control valve is operated ?When EGR control valve is operated ?EGR reduces the volume of the combustion chambers and during sudden acceleration the EGR is turned off when you need full power (Wide Open throttle conditions).

At idle, the engine is very sensitive to air/fuel mixture ratios and swirl in the combustion chamber, so introducing EGR at idle is not on either.

During the cruise condition the Fuel/Air mixture is set as lean as possible for maximum economy and this in turn generates the highest temperatures, which leads to formation of very high level of NOx, pre-ignition and knocking.

At cruise, the EGR valve is operated in order to inject exhaust gas into the inlet manifolds to reduce emissions.

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Components of MPFI SystemComponents of MPFI System


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Thank You

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