Automotive Sensors and Actuators

7/25/2019 Automotive Sensors and Actuators

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Automotive Sensors & ActuatorsAutomotive Sensors & ActuatorsAutomotive Sensors & ActuatorsAutomotive Sensors & Actuators

Lecture delivered by:Lecture delivered by:

M.S Ramaiah School of Advanced Studies - Bangalore 1

Prof.Prof. Ashok C.MetiAshok C.Meti

MSRSASMSRSAS--BangaloreBangalore

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Session Objectives

On completion of this session the delegates

would have understood :

e var ous sensors an actuators t at are use

in automotive electronics,

Their working principles,

Their various uses in automotive electronic

systems



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Topics

Introduction to automotive electronics Automotive sensors and actuators

Selection criterion

Different types of sensors

Actuators

A case study Honda City car


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Over the past 30 years, vehicle electronic systems have

changed significantly.

Automotive Electronics - Introduction

electronic systems.

The evolution of microcontroller and sensor technology is

allowing automobile industry to create complex systems

that can provide higher levels of vehicle control and safety.

The overall oal of electronic embedded s stem desi n is


to balance production costs with development time and

cost.


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Automotive Sensors & Actuators

Automotive manufacturers are continuously increasingcontinuously increasing

the use of electronics systems to-

Safety

passenger comfort.

SensorsSensors and actuatorsactuators integrated with automotive control

computers help optimize vehicle performance while

im rovin reliabilit and durabilit .


SensorSensor-- InputInput ActuatorActuator-- OutputOutputMicrocontrollerMicrocontroller


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Measurement System

CPUA/DSIGNALCONDITIONING

SENSOR

VOLTAGE SERIAL

OR

PARALLEL

ELECTRICAL

OUTPUTMEASURED

QUANTITY


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Selection Criteria What is to be measured

Magnitude, range, dynamicsof measured quantity

Required resolution, accuracy

Cost

Environment

Interface Requirements: Output quantity (voltage,

current, resistance,)


Signal conditioning

A/D requirements (#bits, datarate)


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Thermistors

Commonly used for temperature measurementon vehicles.

They are made out of semiconductor materials

such as cobalt or nickel oxides.

Change in temperature causes change inchange in

resistanceresistance of the thermistor.

Most of the thermistors are of the negativenegative

temperature coefficienttemperature coefficient (NTC) type

o


to a few hundred Ohmshundred Ohms at 100o C. Thus it can

be more sensitive.

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Important factors for accuratemeasurements: Supply must be constant

Current through the thermistorshould be negligible ( I.e. No heatingeffect)

These devices are commonly used assensors for-

Air intake

Battery

Engine and transmission temperature


Air conditioning and internal/externalenvironmental temperature

Oil and gas temperatures.


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Temperature sensor

Application Engine management

Function Registration of temperature ofcoo ants, ue an a r

Installation Engine block, coolantcircuit, air-intake tract

Sensing principle NTC technology (hotconductor, negative temperaturecoefficient)


Temperature range: -40C...+150C

Time constant: 5 s...44 s (depending on type) Accuracy: 0.8 K at 100C 1.5 K at 20C

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Thermocouples When two dissimilar metalstwo dissimilar metals are joined together, thethermocouple junction is formed.

Among the two junctions used, one of the junctions is kept

a a cons an nown empera ure w ere as e o er a e

temperature to be measured.

Ex: 70% platinum & 30% rhodium alloy known as B Type

, Has a range of 0 15000C.

Used for measuring Exhaust GasExhaust Gas and turbochargerturbocharger

temperaturestemperatures in a vehicle.



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Magnetic Sensors

Variable Reluctance (VR) SensorsVariable Reluctance (VR) Sensors

Used mainly for speed and position

measurements of rotating members. ( Ex:crank shaft speed and position sensing)

The variable reluctance sensor is an electro-

magnetic device consisting of a permanentpermanent

magnetmagnet surrounded by a winding of wirewinding of wire.

The sensor is used in conjunction with a

ferrous target that either has notches or teeth.

Rotation of the target wheeltarget wheel near the tip of the

sensor chan eschan es the ma netic fluxma netic flux, creatin an


analog voltage signal in the sensor coil.

Though the voltage may vary depending on the

speed of rotating member, the frequencyfrequency is

used for measurement.

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A common method of

converting this signal into a

useful signaluseful signal for interfacinginterfacing

w o er g a c rcu s y

using a Schmitt triggerSchmitt trigger circuit.

Another method is by using a

quenched oscillator circuit as

shown in the figure. This circuit

has good resistance to


.


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Typical Applications:

Ignition system engine speedand position

Speed sensing for

e ectron ca y contro e

transmissions

Vehicle speed sensing

Wheel speed sensing for ABS

and traction control systems


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Hall Effect Transducers

Principle:

If a certain type of crystal is carrying acurrent in a transverse magnetic field,then a voltage will be produced at right

.

The magnitude of the voltagemagnitude of the voltage isproportional to the supply currentsupply current and tothe magnetic field strength.

With proper designproper design, the output of thisdevice is a square wave.

The principle is used in distributors andalso to detect the current flowing on a


ca e.


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Variable resistance

These sensors are mainly used for sensing larger changelarger change inpositionposition.

Example: The throttle position sensor, which is a

potentiometer.

It is supplied with a stablestable 5 Volts DC.

The wiper wiper is driven by the throttle shaftthrottle shaft. Thus , the voltage from

the wiper contact will be proportionalproportional to the throttle positionthrottle position.

In many cases,throttle potentiometer is used to indicate the raterate


.

implementing acceleration enrichment or over-run fuel cut-off.

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Available in clockwise and anti-clockwise


Printed Circuit Resistors


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Accelerator-pedal module


Function Registering the driver's wisheseman or torque)

Installation Passenger compartment

Sensing principle Hall effect orpotentiometer

Technical data Supply voltage: 5 V


easur ng range: cus omer-spec c pe a rave40 mm ... 80 mm

Temperature range: -40... +80C Output signal: analog

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Pressure sensor Application Engine management

Function Barometric pressure

Installation Printed circuit board(PCB)

Sensing principle Siliconmicromechanics with integratedevaluation circuit

Technical data

Measurin ran e: 60 kP


...115 kPa

Analog output: 2.37 V ...4.54 V

Temperature range: -40C ... +130C


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Low-pressure sensors for gaseous media


Function Registration of intake-manifold

ressure or atmos heric ressure

Installation Air-intake tract

Sensing principle Micromechanics with piezo-

resistive sensor element (MEMS based)

Technical data


upp y vo age:

Power consumption: 9 mA (typical)

Measuring range: < 400 kPa (absolute) Response time: < 1 ms

Temperature range: -40... +130C

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Acclerometers Piezoelectric accelerometers are generally used as knockknock

sensors.sensors.

A piezoelectric accelerometer is a seismic mass

accelerometer using a piezoelectric crystalpiezoelectric crystal to convert the

forceforce on the mass due to acceleration into an electricalelectrical

output signaloutput signal. The piezoelectric crystal acts not only as a

transducer but also as the suspension spring for the mass.

When used for knock detection, they also pick up other

vibrations, these are kept at minimum by looking for a


knock a few degrees before and after the TDC.a few degrees before and after the TDC.


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The signals from this type of

sensors are detected by charge

amplifiers.

The sensitivity of a vehicle

knock sensor is about 20mV/g (

g=9.81 m/s2).

MEMS accelerometers are

replacing conventional

accelerometers for


Knock sensing

Crash sensing

INS, etc

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Knock sensor


Function Registration of structure-borne vibrations(knocking). Knocking combustion can damage the engine.The data from the knock sensor enables counter-measuresto be undertaken.

Installation Engine block

Sensing principle Piezo-electrical

Technical data


Sensitivity at 5 kHz: 30 6 mV/g Linearity at 5-kHz value: 10 %

Frequency range: 3 kHz ...22 kHz

Temperature range: -40...+150C


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Application ESP

ABS

Safety (airbag systems)

the X, Y and Z axes

Installation Integration into circuit board (SMD)

Remote sensor

Sensing principle Surface mechanics(capacitive)


Technical data Measuring range (airbag) SMD element: 2 g...250 g

Peripheral sensor: 50 g...250 g

Sensor output: analog or digital

Temperature range: -40C...+120C

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Yaw-rate sensor

Application ESP Function Registration of the rotational movement of the

vehicle around its vertical axis

Installation Passenger compartment

Sensing principle Micromechanics, CAN interface

Technical data Yaw-rate sensor measuring range: 100/s

Acceleration sensor measuring range: 1.8 g

Initialization time:


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Air Flow Sensor

Air flow Sensor is another

example of variablevariable

resistanceresistance sensor.

When air flows in to the

sensor, exerts a forceforce on the

flapflap which is counteracted by

a calibrated springcalibrated spring. This

ensures that movement of the

flap is proportional to the


through the sensor.

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A slider potentiometer is connected to the flap shaft.

The resistive material used for the track is a ceramic metal

mixture which is burnt into a ceramic plate at a very high

temperature.

The potentiometer is calibrated such that the output voltageoutput voltage

is proportional to the quantity of induced air.quantity of induced air.



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Hot wire air flow sensor

This measures air mass flowair mass flow. The basic principle is that as air passesair passes over a hot wirehot wire it

tries to cool the wire down. A circuit is created that tends

to increaseincrease the current through the wirecurrent through the wire. This current will

be proportionalproportional to the air flow.

The hot-wire:

Material - Platinum

Few mm long

Dia about 70 microns.


Time constant very short (Small size)

Current range 0.5 to 1.2 A

Dirt problem Burn-off cycle at power-on or power-off.

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By-pass hot wire air flow meter


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Oxygen Sensor

The oxygen sensor provides a closed loopclosed loopfeedbackfeedback for the engine management

system to control the air fuel ratioair fuel ratio.i

The amount of oxygenamount of oxygen sensed is directly

related to the mixture strengthmixture strength or air-fuel

ratio.

Normalized air-fuel ratio() = Current air-

fuel ratio/Stoichiometric air-fuel ratio

i

Sensor 1 Air/Fuel Ratio

Sensor 2 Catalytic Converter Efficiency


- .

known as a Lambda (Lambda () value of one) value of one.

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The sensor operates reliably above 300above 30000CC.

The EGO Exhaust Gas Oxygen sensors are

heating.

In some cases, a heating elementheating element is used to bring

the temperature to the working level quickly.

These heating element do not operatedo not operate all the time.0


These are called HEGOHEGO.


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The main active component in most ofthe sensors is Zirconium dioxideZirconium dioxide, ZrO2

This ceramic material is housed in gasgas.

At temperatures above 3000C, thezirconium dioxide will conduct negativenegativeoxygen ionsoxygen ions.

The sensor is designed to be responsiveresponsivevery close to a Lambda value of 1.very close to a Lambda value of 1.

Greater quantity of oxygen ions will be


is exposed to reference atmospheric air.

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Through electrolytic action these ions permeate the electrode and

migrate through the electrolyte. This builds up the chargecharge.

The magnitude of the charge is dependent on the oxygen % in the

exhaust.

A voltage of 400mV is the normal value at lambda value of onelambda value of one.

Most lambda sensors will cycle from rich to lean in about 50 to 100

milliseconds, and from lean to rich in 75 to 150 milliseconds. This is

referred to as the "transition" time. If the O2 sensor is taking

significantly longer to reverse readings, this too is an indication that it

is getting sluggish and may need to be replaced.



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Actuator is a general term to describe a control mechanism. An actuator is part of an openopen--looploop or closedclosed--loop controlloop control

systemsystem which connects the electronic unitelectronic unit with the process.process.

Actuators

The actuator consists of a transformer and a final-control

element.

Each positioning signals are converted to mechanical output.


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A wide variety of actuators are used in control

loops in an automobile

Solenoids

DC Motors

Stepper motors

Piezo Actuators and so on..



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Solenoid Actuators A solenoid is defined as a coil of wire commonly in the

form of a long cylinder that when carrying a currentresembles a bar magnet so that a moveable core

(armature) is drawn into (pulleddrawn into (pulled--in)in) the coil when a

curren owscurren ows.

A more simple definition is that a solenoid is a coil and

a moveable iron core used to convert electrical energy

into mechanical energy.

Normally, the movement of the core compressescompresses a

spring.

On power-off, the armature returns back to its normal


pos t on.

The stroke of the armature varies from fraction of a mm

to several mm depending on application. There are two main categories of solenoids:

Rotary rotary motion of the armature

Linear linear motion of the armature

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Important considerations when designing a

solenoid for an application:

Force or Torque

Voltage

Current / Power

Duty Cycle

Temperature


Operating Time / Speed

Environmental

AC / DC

Life


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One of the examples of solenoid actuatoris the one used in Fuel injectorFuel injector.

A typical fuel injector solenoid has theo ow ng: Stroke: 0.1mm

Open period range: 1.5 to 10.0 ms.

Coil resistance : 16

Time taken by an injector to open andclose is critical in fuel injection.

The induction of the coil la s an


important role in the reaction time for thesolenoid. (Higher inductance -> longer reaction time,

ballast resistors)

Another application of solenoid actuatoris for door locksdoor locks.

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RelaysElectromagnetic switches



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DC Motors

Permanent magnet motors are commonly used inautomobiles as they are versatile.

The rotary speed (RPM) of the motor which is usually high is

su ta y mo e t roug gear ng owngear ng own ncrease n torque or

other mechanisms to get the desired rotaryrotary or linearlinear motion.

For applications such as power electric steering, the

options available are :

Brushless DC (BLDC)

Switched-reluctance motors (SRM)


high temperature complications (automotive temperatures -40 to

125C.)

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Typical Specifications of a DC

Motor:

Voltage: 12V DC

10%

No load current:4A

Load: 7650r/min 10%,

0.226Nm, 19A

Rotation direction:

clockwise



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Some of the automotive applications: Windscreen and head light washers & wipers.

Power windows and mirrors.

Fuel pumps

Head light lifts.

Electronic Parking Brake (EPB)

Ventilation fans and so on..

One of the draw backs of a DC motor is non-availability of

direct feedbackdirect feedback. If required, one has to use variable


res stor sensor to get t e necessary ee ac .

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Ex:



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Windows Motors


Cable Window Lift Systems

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Actuators for cl imate control

Systems

EPB Actuator


Actuators for Locking Systems


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Stepper Motors

Stepping motors: Permanent magnetType

Permanent magnet motors

usua y ave wo

independent windings, with

or without center taps.

Center-tapped windings are

used in unipolar permanent

magnet motors.

Variable reluctance Type

Variable reluctance motors


usually have three

(sometimes four or five)

windings, with a commonreturn.

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Angular resolution:

The coarsest motors typically turn 90 degrees perstep

High resolution permanent magnet motors arecommonly able to handle 1.8 or even 0.72degrees per step.

an appropr a e con ro er, mos permanenmagnet and hybrid motors can be run in half-steps, and some controllers can handle smallerfractional steps or microsteps.

For both permanent magnet and variablereluctance stepping motors, if just oneonewindingwinding of the motor is energized, the rotor


and then holdhold that angle until the torqueexceeds the holding torqueholding torque of the motor, atwhich point, the rotor will turn, trying tohold at each successive equilibrium point.

They do not have high starting torquestarting torque.


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Applications: Idle speed air by-pass

Speedometer display drives

Adaptive Front-lighting

(AFS) system, etc. Digital Instrument ClusterAdaptive Front-lighting System


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Piezo Actuators A piezo actuator enables response times of just a

few Tenth of a millisecond.

It consists of many crystal layers that expand bya few hundredths of millimeters when volta e isapplied.

One of the automotive applications of the Piezoactuators is in Diesel Unit Injection Systems.

Example:

Stacked actuator

Motion up to 100 m

Maximum load 3500 N


Voltage -10...150V (multi-layer)


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A Case Study: HONDA CityA Case Study: HONDA City EngineEngine

Battery

Throttle Body

Master Cylinder

Engine (Transverse mounted)


Air Filter

Alternator

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HONDA City Engine sensors

IAT Sensor

Manifold Air TemperatureManifold Air Temperature sensor


measures the temperature ofincoming air.

Manifold Absolute PressureManifold Absolute Pressure

sensor measures the ve

pressure in the inlet manifold.


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Purge Control Valve

part of the

evaporative

emission control

Throttle BodyPurge Control Solenoid


system.

TPS- Throttle

Position Sensor

measures the throttle

valve opening.

ISC Solenoid

Idling speed control

TPS

Wiring Harness


solenoid controls the

flow of air during

idling of engine tocontrol the speed of

engine within the

specified range.

ISC Solenoid

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MAP SensorHONDA City Engine sensors


Fuel Injector

Starter Motor


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sensors mounted on

engine.

Senses the coolant

temperature

surroundin the en ine


cylinder in the engine

block.

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Master CylinderHONDA City Engine sensors

Brake Fluid Level sensor

A/C system Pressure Sensor



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Completely assembled Porsche engine

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Cam shaft position sensor

CAM Shaft

Cam shaft sensor mounting


The cam shaft sensor is mounted on the engine near the camshaft.

It is a Hall effect transducer which generates an electricalsignal that is proportional to the rotation of the cam shaft.


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Knock Sensor

Knock sensor mounting


The knock sensor is mounted on the engine block.

It is essentially an accelerometeraccelerometer which generates anelectrical signal that is proportional to the vibration ofthe cylinder block.

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Crank shaft position / Speed sensor

Crankshaft

position/speed sensor

is mounted near the

Fly wheel

flywheel.

The flywheel will have

projections that

generate the pulses.


handled by the ECU to

generate the necessary

information.


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Oxygen Sensors

The oxygen sensorsoxygen sensors are

also known as theLambda SensorsLambda Sensors.

ey are oca e n eexhaust gases leavingthe cylinder.

They measure theamount of oxygen

present in the exhaust


gases.

This information is usedto control the emission

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Summary Various types of automotive sensors and

actuators have been discussed in terms of

wor ng pr nc p es, app ca ons n

automotive electronic systems.


Automotive Sensors and Actuators

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