PEMP
AEL2501
Automotive Sensors & Actuators
Lecture delivered by:
Prof. Ashok C.Meti
MSRSAS--Bangalore
MSRSAS
M.S Ramaiah School of Advanced Studies - Bangalore
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Session Objectives
• On completion of this session the delegates
would have understood :
– Th
The various
i
sensors andd actuators that
h are usedd
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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Automotive Electronics - Introduction
• Over the past 30 years, vehicle electronic systems have
changed significantly.
• Mechanical systems are continue to be controlled with
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.
y
design
g is
• The overall ggoal of electronic embedded system
to balance production costs with development time and
cost.
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Automotive Sensors & Actuators
• Automotive manufacturers are continuously increasing
the use of electronics systems to– improve vehicle performance
– Safety
– passenger comfort.
• Sensors and actuators integrated with automotive control
computers help optimize vehicle performance while
improving
p
g reliability
y and durability.
y
Sensor-- Input
Sensor
Microcontroller
Actuator-- Output
Actuator
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Measurement System
ELECTRICAL
OUTPUT
MEASURED
QUANTITY
SENSOR
SIGNAL
CONDITIONING
SERIAL
OR
PARALLEL
VOLTAGE
A/D
CPU
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Selection Criteria
• What is to be measured
• Magnitude, range, dynamics
of measured quantity
• Required resolution, accuracy
• Cost
• Environment
• Interface Requirements:
– Output quantity (voltage,
current, resistance,…)
– Sensitivity
– Signal conditioning
– A/D requirements (#bits, data
rate)
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Thermistors
• Commonly used for temperature measurement
on vehicles.
• They are made out of semiconductor materials
such as cobalt or nickel oxides.
• Change in temperature causes change in
resistance of the thermistor.
• Most of the thermistors are of the negative
temperature coefficient (NTC) type
• Resistance range – Several Kilo Ohms at 0oC
to a few hundred Ohms at 100o C. Thus it can
be more sensitive.
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• Important factors for accurate
measurements:
– Supply must be constant
– Current through the thermistor
should be negligible ( I.e. No heating
effect)
• These devices are commonly used as
sensors for–
–
–
–
Air intake
Battery
Engine and transmission temperature
Air conditioning and internal/external
environmental temperature
– Oil and gas temperatures.
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Temperature sensor
• Application Engine management
• Function Registration of temperature of
coolants,
l
fuel
f l andd air
i
• Installation Engine block, coolant
circuit, air-intake tract
• Sensing principle NTC technology (hot
conductor, negative temperature
coefficient)
• Technical data
– Temperature range: -40°C...+150°C
– Time constant: 5 s...44 s (depending on type)
– Accuracy: ± 0.8 K at 100°C ±1.5 K at 20°C
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Thermocouples
• When two dissimilar metals are joined together, the
thermocouple junction is formed.
• Among the two junctions used, one of the junctions is kept
at a constant known
kno n temperature
temperat re where
here as the other at the
temperature to be measured.
• Ex: 70% platinum & 30% rhodium alloy known as B Type
, Has a range of 0 15000C.
• Used for measuring Exhaust Gas and turbocharger
temperatures in a vehicle.
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Magnetic Sensors
Variable Reluctance (VR) Sensors
• Used mainly for speed and position
measurements of rotating members.
( Ex:
crank shaft speed
p
and position
p
sensing)
g)
• The variable reluctance sensor is an electromagnetic device consisting of a permanent
magnet surrounded by a winding of wire.
wire
• The sensor is used in conjunction with a
ferrous target that either has notches or teeth.
• Rotation of the target wheel near the tip of the
sensor changes
g the magnetic
g
flux, creatingg an
flux,
analog voltage signal in the sensor coil.
• Though the voltage may vary depending on the
speed of rotating member, the frequency is
used for measurement.
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• A common method of
converting this signal into a
useful signal for interfacing
with
ith other
th di
digital
it l circuit
i it is
i by
b
using a Schmitt trigger circuit.
• Another method is by using a
quenched oscillator circuit as
shown in the figure. This circuit
has good resistance to
interference
interference.
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• Typical Applications:
– Ignition system engine speed
and position
– Speed sensing for
electronically
l t i ll controlled
t ll d
transmissions
– Vehicle speed sensing
– Wheel speed sensing for ABS
and traction control systems
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Hall Effect Transducers
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Principle:
• If a certain type of crystal is carrying a
current in a transverse magnetic field,
then a voltage will be produced at right
angles to the supply current.
current
• The magnitude of the voltage is
proportional to the supply current and to
the magnetic field strength.
• With proper design,
design the output of this
device is a square wave.
• The principle is used in distributors and
also to detect the current flowing on a
cable.
bl
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Variable resistance
• These sensors are mainly used for sensing larger change in
position.
position
– Example: The throttle position sensor, which is a
potentiometer.
• It is supplied with a stable 5 Volts DC.
• The wiper is driven by the throttle shaft
shaft. Thus , the voltage from
the wiper contact will be proportional to the throttle position.
position
• In many cases,throttle potentiometer is used to indicate the rate
of change of throttle position
position. This information is used in
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
• Application Engine management
• Function Registering the driver's wishes
(d
(demand
d for
f torque))
• Installation Passenger compartment
• Sensing principle Hall effect or
potentiometer
• Technical data
– Supply voltage: 5 V
– Measuring
M
i range: customer-specific
t
ifi pedal
d l travel
t
l
40 mm ... 80 mm
– Temperature range: -40°... +80°C
– Output signal: analog
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Pressure sensor
• Application Engine management
• Function Barometric pressure
measurement
• Installation Printed circuit board
(PCB)
• Sensing principle Silicon
micromechanics with integrated
evaluation circuit
• Technical data
– Measuring range: 60 kP...
kP
115 kPa
– Analog output: 2.37 V ...
4.54 V
– Temperature range: 40°C ... +130°C
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Low-pressure sensors for gaseous media
• Application Engine management
• Function Registration of intake-manifold
pressure or atmospheric pressure
• Installation Air-intake tract
• Sensing principle Micromechanics with piezoresistive sensor element (MEMS based)
• Technical data
– Supply
S
l voltage:
lt
5V
– Power consumption: 9 mA (typical)
– Measuring range: < 400 kPa (absolute)
– Response time: < 1 ms
– Temperature range: -40°... +130°C
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Acclerometers
• Piezoelectric accelerometers are generally used as knock
sensors.
• A piezoelectric accelerometer is a seismic mass
accelerometer using a piezoelectric crystal to convert the
force on the mass due to acceleration into an electrical
output signal.
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.
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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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AEL2501
Knock sensor
• Application Engine management
• Function Registration
g
of structure-borne vibrations
(knocking). Knocking combustion can damage the engine.
The data from the knock sensor enables counter-measures
to 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°...+150°C
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Acceleration sensor
AEL2501
• Application
– ESP®
– ABS
– Safety (airbag systems)
• Function Registration of accelerations in
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: -40°C...+120°C
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Yaw-rate sensor
AEL2501
• 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: <= 1.0 s
Temperature range: -40°C...+85°C
Supply voltage: 8.2
8 2 V...16
V 16 V
Nominal voltage: 12 V
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Air Flow Sensor
• Air flow Sensor is another
example of variable
resistance sensor.
• When air flows in to the
sensor, exerts a force on the
flap which is counteracted by
a calibrated spring
spring. This
ensures that movement of the
flap is proportional to the
volume of air passing
through the sensor.
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AEL2501
• 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 voltage
is proportional to the quantity of induced air.
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Hot wire air flow sensor
• This measures air mass flow.
flow
• The basic principle is that as air passes over a hot wire it
tries to cool the wire down. A circuit is created that tends
to increase the current through the wire.
wire This current will
be proportional 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 loop
feedback for the engine management
system to control the air fuel ratio.
ratio
• The amount of oxygen sensed is directly
related to the mixture strength or air-fuel
ratio.
• Normalized air-fuel ratio(λ) = Current air-
OBD II Requirement
Sensor – 1 – Air/Fuel Ratio
Sensor – 2 – Catalytic Converter Efficiency
fuel ratio / Stoichiometric air-fuel ratio
• The air-fuel
air fuel ratio 14.7:1
14 7:1 by mass is
known as a Lambda ((λλ) value of one.
one
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• The sensor operates reliably above 3000C.
• The EGO – Exhaust Gas Oxygen sensors are
placed in the exhaust manifold ensure adequate
heating.
• In some cases, a heating element is used to bring
the temperature to the working level quickly.
• These heating element do not operate all the time.
(>8500C – Damage)
• These are called HEGO.
HEGO
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• The main active component in most of
the sensors is Zirconium dioxide,
dioxide ZrO2
• This ceramic material is housed in gas
permeable electrodes of platinum.
platinum
• At temperatures above 3000C, the
zirconium dioxide will conduct negative
oxygen ions.
ions
• The sensor is designed to be responsive
very close to a Lambda value of 1.
• Greater quantity of oxygen ions will be
present near one of the electrode which
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 charge
charge.
• 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 one
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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Actuators
• ‘Actuator’ is a general term to describe a control mechanism.
• An actuator is part of an open
open--loop or closed
closed--loop control
system which connects the electronic unit with the process.
• 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
• Some of the actuators are:
–
–
–
–
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 current
resembles a bar magnet so that a moveable core
(armature) is drawn into (pulled
(pulled--in) the coil when a
currentt flows.
flows
fl
• 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 compresses a
spring.
• On power-off, the armature returns back to its normal
position.
ii
• 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:
–
–
–
–
–
–
–
–
–
–
Stroke
Force or Torque
Voltage
Current / Power
Duty Cycle
Temperature
p
Operating Time / Speed
Environmental
AC / DC
Life
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• One of the examples of solenoid actuator
is the one used in Fuel injector.
injector
• A typical fuel injector solenoid has the
follo ing:
following:
– Stroke: 0.1mm
– Open period range: 1.5 to 10.0 ms.
– Coil resistance : 16 Ω
• Time taken by an injector to open and
close is critical in fuel injection.
• The induction of the coil pplays
y an
important role in the reaction time for the
solenoid. (Higher inductance -> longer reaction time,
ballast resistors)
• Another application of solenoid actuator
is for door locks.
locks
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Relays
Electromagnetic switches
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DC Motors
• Permanent magnet motors are commonly used in
automobiles as they are versatile.
– The rotary speed (RPM) of the motor which is usually high is
suitably
i bl modified
difi d through
h
h gearing
i down
d
(i
(increase
in
i torque)) or
other mechanisms to get the desired rotary or linear motion.
• For applications such as power electric steering, the
options available are :
– Brushless DC (BLDC)
– Switched-reluctance motors (SRM)
– The BLDC motor has permanent magnets that are susceptible to
high temperature complications (automotive temperatures -40 to
125°C.)
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• Typical Specifications of a DC
Motor:
– Voltage: 12V DC
– No load speed: 9000r/min±
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 feedback.
feedback If required, one has to use variable
resistor
i
sensor to get the
h necessary feedback.
f db k
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• Ex:
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Windows Motors
Cable Window Lift Systems
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Actuators for climate control
Systems
EPB Actuator
Actuators for Locking Systems
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Stepper Motors
• Stepping motors:
– Permanent magnet Type
• Permanent magnet motors
usually
ll have
h
two
t
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 common
return.
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• Angular resolution:
AEL2501
– The coarsest motors typically turn 90 degrees per
step
– High resolution permanent magnet motors are
commonly able to handle 1.8 or even 0.72
degrees per step.
– With an appropriate
i t controller,
t ll mostt permanentt
magnet and hybrid motors can be run in halfsteps, and some controllers can handle smaller
fractional steps or microsteps.
• For both permanent magnet and variable
reluctance stepping motors, if just one
winding of the motor is energized, the rotor
(under no load) will snap to a fixed angle
and then hold that angle until the torque
exceeds the holding torque of the motor, at
which point, the rotor will turn, trying to
hold at each successive equilibrium point.
• They do not have high starting torque
torque.
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• Applications:
–
–
–
–
Idle speed air by-pass
Electronic Throttle control
Speedometer display drives
Adaptive Front-lighting
(AFS) system, etc.
Adaptive Front-lighting System
Digital Instrument Cluster
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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 by
a few hundredths of millimeters when voltage is
applied.
• One of the automotive applications of the Piezo
actuators is in Diesel Unit Injection Systems.
• Example:
– Stacked actuator
•
•
•
•
Motion up to 100 µm
Maximum load 3500 N
Very high stiffness up to 200 N/µm
Voltage -10...150V (multi-layer)
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A Case Study: HONDA City Engine
Throttle Body
Master Cylinder
Battery
Engine (Transverse mounted)
Air Filter
Alternator
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HONDA City Engine sensors
IAT Sensor
MAP Sensor
• Manifold Air Temperature
p
sensor
– measures the temperature of
incoming air.
• Manifold Absolute Pressure
sensor – measures the –ve
pressure in the inlet manifold.
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HONDA City Engine sensors
Purge Control Solenoid
Throttle Body
Wiring Harness
TPS
ISC Solenoid
• Purge Control Valve
– part of the
evaporative
emission control
system.
• TPS- Throttle
Position Sensor
measures the throttle
valve opening.
• ISC Solenoid –
Idlingg speed
p
control
solenoid controls the
flow of air during
idling of engine to
control the speed of
engine within the
specified range.
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HONDA City Engine sensors
MAP Sensor
Ignition Coils (on plug)
Starter Motor
Fuel Injector
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HONDA City Engine sensors
• One of the important
sensors mounted on
engine.
• Senses the coolant
temperature
surrounding the engine
cylinder in the engine
block.
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HONDA City Engine sensors
Master Cylinder
A/C system Pressure Sensor
Brake Fluid Level 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 cam
shaft.
• It is a Hall effect transducer which generates an electrical
signal 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 accelerometer which generates an
electrical signal that is proportional to the vibration of
the cylinder block.
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Crank shaft position / Speed sensor
Fly wheel
• Crankshaft
position/speed sensor
is mounted near the
flywheel.
• The flywheel will have
projections that
generate the pulses.
• These pulses are
handled by the ECU to
generate the necessary
information.
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Oxygen Sensors
• The oxygen sensors are
also known as the
Lambda Sensors.
Sensors
• They
Th are located
l t d in
i the
th
exhaust gases leaving
the cylinder.
• They measure the
amount of oxygen
present in the exhaust
p
gases.
• This information is used
to control the emission
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Summary
• Various types of automotive sensors and
actuators have been discussed in terms of
working
ki principles,
i i l applications
li ti
in
i
automotive electronic systems.
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