Use of Electronics In The Automobile, Antilock Brake Systems, (ABS), Electronic steering control, Power steering, Traction control, Electronically controlled suspension

Automotive electronics

1. SYLLABUS
UNIT II: AUTOMOTIVE INSTRUMENT CONTROL
Sampling, Measurement and signal conversion of various parameters.
Sensors and Actuators, Applications of sensors and actuators

2. SAMPLING THEOREM
Denition
A continuous time signal can be represented in its samples and can be
recovered back when sampling frequencyfsis greater than or equal to the
twice the highest frequency component of message signal i.e.
fs>= 2fm

3. SAMPLING THEOREM
Proof.
Consider a continuous time signal x(t).
The spectrum of x(t) is a band limited tofmHz i.e. the spectrum of
x(t) is zero forjwj>wm.
Sampling of input signal x(t) can be obtained by multiplying x(t) with
an impulse train (t) of periodTs.
The output of multiplier is a discrete signal called sampled signal
which is represented with y(t).

4. SAMPLING THEOREM
Figure:

5. SAMPLING THEOREM
Figure:

6. Type of SAMPLING
There are mainly three type of sampling
1
Impulse Sampling
2
Natural Sampling
3
Flip Flop Sampling
1
Impulse Sampling
Figure:
i

7. Type of SAMPLING
1
Natural Sampling
Figure:

8. Type of SAMPLING
1
Flip Flop Sampling
Figure:

9. Sensors and Transducers
Sensor
It is dened as an element which produces signal relating to the
quantity being measured
Output is usually an electrical quantity and measurand is a physical
quantity
Transducer
A device which convert a signal from one form of energy to another
form
A wire of Constantan alloy can be called as sensor because variation in
mechanical displacement can be sensed as change in electrical
resistance
This wire become a transducer with appropriate electrodes and
input-output mechanism attached with it.

10. Sensor Characteristics
Range
Span
Error
Accuracy
Sensitivity
Non-Linearity
Hysteresis
Resolution
Stability
Repeatability
Response Time

11. Sensor Specication
Range
Range of a sensor indicates the limit between which the input can vary
eg:- A thermocouple for temperature measurement might have a range
of 25225
0
C
Span
The span is the dierence between the maximum and minimum values
of the input
eg:-A thermocouple for temperature measurement might have a range
of 25225
0
C, therefore span is 200
0
C
Error
Error is the dierence between the result of the measurement and the
true value of the quantity being measured
A sensor might give a displacement reading of 29.9mm, when the
actual displacement had been 30 mm, then error is0:1mm

12. Sensor Specication
Accuracy
Accuracy denes the closeness of the agreement between the actual
measurement result and a true value of the measurand.
It is often expressed as a percentage of the full range output or full
scale deection
Sensitivity
It is the ratio of change in output value of a sensor to the per unit
change in input value that causes the output change
Eg:- a general purpose thermocouple may have a sensitivity of
41V=
0
C

13. Sensor Specication
Non-Linearity
Non-Linearity indicates the maximum deviation of the measured curve
of a sensor from the ideal curve
Linearity is often specied in terms of percentage of non-linearity
Nonlinearity (%)=Maximum deviation in input/ Maximum full scale
input
Figure:

14. Sensor Specication
Hysteresis
Hysteresis is an error of a sensor, which is dened as the maximum
dierence in output at any measured value within the sensor's specied
range when approaching the point rst with increasing and then with
decreasing the input parameters.
Hysteresis error might have occurred during the measurement of
temperature using a thermocouple is shown below.
Figure:

15. Sensor Specication
Resolution
It is the smallest detectable incremental change of input parameter
that can be detected in the output signal
It can be expressed either as a portion of the full scale reading or in
absolute terms
Eg:-In LVDT, a sensor measures displacement upto 20mm and it
provides an output as a number between 1 and 100 then the resolution
is 0.2mm
Stability
Stability is the ability of a sensor device to give same output when used
to measure a constant input over a period of time.
The term Drift is used to indicate the change in output that occurs
over a period of time.

16. Sensor Specication
Repeatability
Ability of a sensor to measure same output for a repeated application
of same input value
Repeatability=(maximum-minimum value)100=fullrange
Response Time
Speed of change in the output on a step-wise change of the measurand.
It is always specied with an indication of input step and the output
range for which the response time is dened
Dead Time
Dead Time/Band is the range of input values for which there is no
output.
The dead time of a sensor device is the time duration from the
application of an input until the output begins to respond or change.

17. Sensor- Classications
Sensors can be classied into various groups according to the factors
such as measurand, application eld,conversion principles, energy
domain of the measurand and thermodynamic considerations.
Classied into groups based on
Displacement, Position and Proximity Sensors
Motion and Velocity Sensors
Force Sensors
Liquid Flow/Level Sensors
Temperature Sensors

18. Sensor-Classications
Displacement, Position and Proximity Sensors
Potentiometer
Strain Gauge
Capacitive Element
Dierential Transformers
Eddy Current Proximity Sensor
Inductive Proximity Sensor
Optical Encoders
Pneumatic Sensor
Proximity Switches(magnetic)
Hall Eect Sensors

19. Sensor Classications
Velocity and Motion Sensors
Incremental Encoder
Tachogenerator
Pyroelectric sensors
Force Sensor
Strain Gauge Load Cell
Fluid Pressure Sensors
Diaphragm Pressure Gauge
Piezoelectric Sensors
Tactile Sensors
Capsules, Bellows, Pressure Tubes

20. Sensor Classications
Liquid Flow Sensors
Orice Plate
Turbine meter
Liquid Level Sensors
Floats
Dierential Pressure
Temperature Sensors
Bimetallic Strip
Resistance Temperature detector
Thermistors
Thermocouple
Light Sensor
Photo Diode
Photo Transistor
Photo Resisor

21. Displacement Sensors
1
Potentiometer Sensor
2
Strain Gauge
3
Capacitive Element Based Sensor
4
LVDT

22. Displacement Sensors
1
Potentiometer Sensors
The below gure shows the construction of a rotary type potentiometer
sensor for linear displacement measurement.
It can be linear or angular type
It works on the principle of conversion of mechanical displacement into
an electrical signal
The sensor has a resistive element and sliding contact
Figure:

23. Displacement Sensor
2
Strain Gauge
A ratio of change in length in the direction of applied load to the
original length of an element.
The strain gauge changes the resistance R of the element
Widely used in experimental stress analysis and diagnosis on machines
and failure analysis and safety in automobiles
Figure:

24. Displacement Sensor
3
Capacitive element based Sensor
It is of non-contact type sensor and used to measure linear
displacement in few millimeter to hundreds of millimeter.
It comprises of three plates with upper pair forming one capacitor and
lower pair forming another.
Figure:

25. Displacement Sensor
4
LVDT(Linear Variable Dierential Transformer)
LVDT is a primary transducer used for measurement of linear
displacement with an input range of about2mmto400mm
It has a nonlinearity error of0:25% of full range
It has three coils symmetrically spaced along an insulated tube.
Central coil is primary coil and other two are secondary coil
Secondary coils are connected in series in such a way that their output
oppose each other.
A magnetic core attached to the element of which displacement is to
be monitored is placed inside the insulated tube
Figure:

26. Displacement Sensor
Figure:

27. Displacement Sensor
LVDT Application
To provide displacement feedback for hydraulic cylinder
To control weight and thickness of mechanical products
For automatic inspection of nal dimensions of products being packed
for dispatch

28. Proximity Sensors
1
Eddy Current Proximity
2
Inductive Proximity
3
Optical Encoder
4
Hall Eect Sensors

29. Proximity Sensors
1
Eddy Current Proximity Sensor
It is used to detect non-magnetic but conductive materials
It comprise of a coil, an oscillator, a detector and a triggering circuit
When an alternative current is passed through the coil, an alternative
magnetic eld is generated
If a metal object comes in the close proximity of the coil, then eddy
currents are induced in the object due to the magnetic eld.
Eddy current creates their own magnetic eld which distorts the
magnetic eld responsible for this generation
As a result, impedance of the coil changes and so the amplitude of
alternating current.
Inexpensive, available in small size, highly reliable and highly sensitive

30. Proximity Sensors
Application
Machine tool monitoring
Automation requiring precise location
Final assembly of precision equipment such as disk drives
Drive shaft monitoring
Vibration measurement
Figure:

31. Proximity Sensors
2
Inductive Proximity Sensor
Inductive proximity switches are basically used for detection of metallic
objects.
An AC current is supplied to the coil which generates a magnetic eld
When a metal object comes closed to the end of the coil,inductance of
the coil changes
This is continuously monitored by a circuit which triggers a switch
which a present value of inductance change is occurred.
Figure:

32. Proximity Sensor
3
Optical Encoder
Optical encoder provide a digital output as a result of linear/angular
displacement.
Figure:

33. Proximity Sensor
It is widely used in servo motors to measure the rotation of shafts
It comprise of a disc with three concentric tracks of equally spaced
holes.
The light sensors are employed to detect the light passing through the
holes.
These sensors produces electric pulses which give the angular
displacement of the mechanical element eg:-shaft on which the optical
encoder is mounted
The inner track has just one hole which is used to locate the home
position of the disc
Hole on the middle track oset from the holes of the outer track by
one-half of the width of the hole.
This arrangement provides the direction of rotation to be determined.
When disc rotates in clockwise direction, the pulses in the outer track
lead those in the inner; in counter clockwise direction they lag behind.

34. Proximity Sensor
4
Hall Eect Sensor
When a beam of charge particles passes through a magnetic eld,
forces act on the particles and the current beam is deected from its
straight line path.
Thus one side of the disc become negatively charged and the other side
will be positive charge
This separation generates a potential dierence which is the measure of
distance of magnetic eld from the disc carrying current.
Figure:

35. Velocity, Motion, Force and Pressure Sensors
1
Tachogenerator
2
Strain Gauge as force sensor
3
Fluid Pressure
4
Tactile Sensor
5
Piezoelectric Sensor

36. Velocity,Motion, Force and Pressure Sensors
1
Tachogenerator
It works on the principle of variable reluctance.
It consist of an assembly of a toothed wheel and a magnetic circuit.
Toothed wheel is mounted on the shaft or the element of which
angular motion is to be measured.
Magnetic circuit comprising of a coil wounded on a ferromagnetic
material core.
Figure:

37. Velocity,Motion, Force and Pressure Sensors
As the wheel rotates, the air gap between wheel tooth and magnetic
core changes which results in cyclic change in ux linked with the coil.
The alternating emf generated is the measure of angular motion.
A pulse shaping signal conditioner is used to transform the output into
a number of pulses which can be counted by a counter
An Alternating current generator can also be used as a tachogenerator
Comprises of a rotor coil which rotates with the shaft.
Rotor rotates in the magnetic eld produced by a stationary permanent
magnet or electromagnet.
During this process, an alternating emf is produced which is the
measure of the angular velocity of the rotor.

38. Velocity,Motion, Force and Pressure Sensors
2
Strain Gauge as Force Sensor
Worked on the principle of change in electrical resistance.
When, a mechanical element subjects to a tension or a compression the
electric resistance of the material changes.
This is used to measure the force acted upon the element.
Figure:

39. Velocity,Motion, Force and Pressure Sensors
It comprise of a cylindrical tube to which strain gauges are attached.
A load applied on the top collar of the cylinder compress the strain
gauge element which changes its electric resistance.
Generally it can measure force up to 10MN.

40. Velocity,Motion, Force and Pressure Sensors
3
Fluid Pressure
Various types of instruments such as diaphragms, capsules and bellows
are used to monitor the uid pressure
Specially designed strain gauges doped in diaphragms are generally
used to measure the inlet manifold pressure in application such as
automobiles.
Figure:

41. Velocity,Motion, Force and Pressure Sensors
4
Tactile Sensor
Tactile sensors are used to sense the contact of ngertips of a robot
with an object.
They are also used in manufacturing of ' touch display' screens of
visual display units of CNC machine tools.
Figure:

42. Velocity,Motion, Force and Pressure Sensors
It has two PVDF layers separated by a soft lm which transmits the
vibrations.
An alternating current is applied to lower PVDF layer which generates
vibrations due to reverse piezoelectric eect.
These vibrations are transmitted to the upper PVDF layer via soft lm.
These vibrations cause alternating voltage across the upper PVDF
layer.
When some pressure is applied on the upper PVDF layer the vibrations
gets aected and the output voltage changes.
This triggers a switch or an action in robots or touch displays.

43. Velocity,Motion, Force and Pressure Sensors
5
Piezoelectric Sensor
Application:- measure pressure, acceleration,oscillation, impact or high
speed compression or tension.
It contains piezoelectric ionic crystal material such as Quartz,
application of force or pressure these materials get stretched or
compressed.
During this process, the charge over the material changes and
redistributes , One end of the material becomes positively charged and
the other negatively charged.
Figure:

44. Temperature Sensors
Temperature conveys the state of a mechanical system in terms of
expansion or contraction of solids, liquids or gases, change in electrical
resistance of conductors, semiconductors and thermo-electric emfs.
1
Bimetallic Strips
2
Resistance Temperature Detectors(RTD)
3
Thermistor
4
Thermocouple

45. Temperature Sensor
1
Bimetallic Strips
Bimetallic strips are used as thermal switch in controlling the
temperature or heat in a manufacturing process or system.
It contains two dierent metal strips bonded together having dierent
coecient of expansion
On heating the strip bend into curved strips with the metal with higher
coecient of expansion on the outside of the curve.
As the strips bend, the soft iron comes in closer proximity of the small
magnet and further touches.
The electric circuit completes and generate an alarm
In this way bimetallic strip help to protect the desired application from
heating above the pre-set value of temperature

46. Temperature Sensors
The below gure shows a typical arrangement of a bimetallic strip
with a setting-up magnet.
Figure:

47. Temperature Sensors
2
Resistance Temperature Detectors ( RTDs)
RTDs work on the principle that the electric resistance of a metal
changes due to change in its temperature.
On heating up metals, their resistance increases and follows a linear
relationship as given below
Rt=R0(1 +T)
Rt= resistance at temperatureT(
0
C)
R0is the temperature at 0
0
C
is the constant for the metal termed as temperature coecient of
resistance/
The sensor is usually mage to have a resistance of 100at0
0
C

48. Temperature Sensor
Figure:Figure:

49. Temperature Sensor
It has a resistor element connected to Wheatstone Bridge.
The element and the connection leads are insulated and protected by
sheath.
A small amount of current is continuously passing through the coil.
As the temperature changes the resistance of the coil changes which is
detected at the Wheatstone Bridge
Application
Air conditioning and refrigeration servicing
Food processing
Stoves and grills
Exhaust gas temperature measurement

50. Temperature Sensor
3
Thermistor
It follows the principle of decrease in resistance with increase in
temperature
The material used in thermistor is a semiconductor material such as
sintered metal oxide or doped poly-crystalline ceramics and other
compounds.
As the temperature of the semiconductor material increases the
number of electrons increases and reduced resistance.
Thermistors are available in the form of a bead, probe or chip as shown
in gure.
Figure:

51. Temperature Sensor
Application of Thermistors
To monitor the coolant temperature and/or oil temperature inside the
engine.
To monitor the temperature of an incubator
Thermistors are used in modern digital thermostats
To monitor the temperature of battery packs while charging
To monitor temperature of hot ends of 3D printers
To maintain correct temperature in the food handling and processing
industry equipment.
To control the operations of consumer appliances such as toasters,
coee makers, refrigerators, freezers, hair dryers etc.

52. Temperature Sensors
4
Thermocouple
Thermocouple works on the fact that when a junction of dissimilar
metals heated, it produces an electric potential related to temperature.
As per Thomas Seebeck:- When two wires composed of dissimilar
metals are joined at both ends and one of the ends is heated, then
there is a continuous current which ows in the thermo-electric circuit.
The net open circuit voltage is a function of junction temperature and
composition of two metals.
VAB=T
where is Seebeck coecient i.e. coecient of proportionality.

53. Temperature Sensors
Figure:

54. Temperature Sensors
Figure:

55. Temperature Sensors
To monitor temperature and chemistry throughout the steel making
process
Testing temperature associated with process plants e.g. Chemical
Production and petroleum reneries
Testing of heating appliance safety
Temperature proling in ovens, furnaces and kilns
Temperature measurement of gas turbine and engine exhausts
Monitoring of temperature throughout the production and smelting
process in the steel, iron and aluminium industry.

56. Light Sensors
Light Sensors is a device that is used to detect light
Dierent types of Light Sensors are
1
Photo Resistors
2
Photo Diodes
1
Photo Resistors
It is also called Light Dependent Resistor(LDR)
It has a resistor whose resistance decrease with increasing incident light
intensity.
It is made of a high resistance semiconductor material, Cadmium
Sulde(CdS)
The resistance of CdS photo-resistor varies inversely to the amount of
light incident upon it
Photo-resistor follows the principle of photo-conductivity which results
from the generation of mobile carriers when photons are absorbed by
the semiconductor material.

57. Light Sensors
The CdS resistor coil is mounted on a ceramic substrate.
This assembly is encapsulated by a resin material.
The sensitive coil electrodes are connected to the control system
through lead wires.
On incidence of high intensity light on the electrodes, the resistance of
resistor coil decreases which will be used further to generate the
appropriate signal by the microprocessor via lead wires
Figure:

58. Light Sensors
2
Photo Diodes
It is a solid state device which converts incident light into an electric
current.
It consist of a shallow diused p-n junction, normally a p-on-n
conguration.
When photons of energy greater than 1.1eV fall on the device, they are
absorbed and electron hole pairs are created.
The depth at which the photons are absorbed depends upon their
energy
The lower the energy of the photons, the deeper they absorbed.
Then the electron hole pairs drift apart.
When a minority carriers reach the junction, they are swept across by
electric eld and an electric current establishes.

59. Light Sensors
Photo-diodes are on of the types of Photo-detector, which convert light
into either current or voltage.
These are regular semiconductor diodes except that they may be either
exposed to detect vacuum UV or X-rays or packaged with opening or
optical bre connection to allow light to reach the sensitive part of the
device.
Figure:

60. Light Sensors
It is constructed from a single crystal silicon wafers.
It is a P-N junction device.
The upper layer is P layer, is very thin and formed by thermal diusion
or ion implantation of doping material such as boron.
Depletion region is narrow and is sandwiched between P layer and bulk
type layer of Silicon
Light irradiates at front surface, anode, while the back surface cathode.
The incidence of light on anode generates a ow of electron across the
P-N junction which is the measure of light intensity
Applications
Camera:- Light meter, Shutter Control, Auto focus, ash control
Automotive:- Headlight Dimmer, Twilight Detectors, Climate Control
Other:- CAT scanner, X Ray, Bar code scanner, Brightness control,
Smoke Detectors etc.

61. Sensors used in Automobiles
1
Mass airow sensor
2
Engine Speed Sensor
3
Oxygen Sensor
4
Spark Knock Sensor
5
Coolant Sensor
6
Manifold Absolute Pressure Sensor
7
Fuel Temperature Sensor
8
Camshaft Position Sensor
9
Throttle Position Sensor
10
Vehicle Speed Sensor

62. Sensors used in Automobiles
1
Mass Airow Sensor
The Mass Air Flow sensor (MAF) is one of the key components of an
electronic fuel injection system in your car.
It is installed between the air lter and the intake manifold of the
engine
The mass air ow sensor measures the amount of air entering the
engine or the air ow.
In modern cars, an intake air temperature or IAT sensor is built in the
mass air ow sensor.
The commonly used MAF hot-wire type.
Figure:

63. Sensors used in Automobiles
How a hot-wire air ow sensor works
A hot-wire mass air ow sensor has a small electrically heated wire (hot
wire).
A temperature sensor installed close to the hot wire measures the
temperature of the air near the hot wire.
When the engine is idling, a small amount of air ows around the hot
wire, so it takes a very low electric current to keep the wire hot.
When you press the gas,the throttle opens allowing more air to ow
over the hot wire.
The passing air cools the wire down.
The more air ows over the wire, the more electrical current is needed
to keep it hot.

64. Sensors used in Automobiles
The electric current is proportional to the amount of air ow.
A small electronic chip installed inside the air ow sensor translates the
electric current into a digital signal and sends it to the engine computer
(PCM).
The PCM uses the air ow signal to calculate how much fuel to inject.
The goal is to keep the air/fuel ratio at the optimal level.
In addition, the PCM uses air ow readings to determine the shift
points of the automatic transmission.
If the air ow sensor doesn't work properly, the automatic transmission
might shift dierently too.
A bad mass air ow sensor causes various driveability problems,
including a no-start, stalling, lack of power, poor acceleration, Check
Engine and Service Engine Soon light to come on.

65. Sensors used in Automobiles
MAF Sensor Problems
The sensor element could get contaminated or damaged.
For example, in some engines, a failed mass air ow sensor could cause
the engine to crank but not to start.
An improperly installed or collapsed air lter and Over-soaking a
washable air lter can also cause problems with the air ow sensor.
MAF Sensor Testing
In modern cars, the only way to test the mass air ow sensor is with a
scan tool.
Mechanics measure the amount of air ow (mass air ow sensor
readings) at dierent RPMs.
They compare the readings to the specications or to the readings of a
known-good mass airow sensor.

66. Sensors used in Automobiles
2
Engine Speed Sensors / Crankshaft Speed Sensors
Crankshaft speed sensors, also called speed sensors, are used to
measure crankshaft speed; determine the position of the crankshaft (or
even the position of the engine cylinder).
The rotational speed is calculated by the time period of the sensor
signals, following the passage of the gear teeth.
The signal of the rotational speed sensor is one of the most important
values for an electronic control system for diesel engine operation.
The sensor is mounted directly opposite the ferromagnetic pulsed wheel
(ywheel) xed on the knee-shaft and is separated from it by an air
gap ( about 2mm gap).
The sensor contains a soft iron core (pole tip), which is surrounded by
an inductor.
The pole tip is connected to a permanent magnet
The magnetic eld passes through the pole tip inside the pulse wheel.

67. Sensors used in Automobiles
The intensity of the magnetic ux passing through the coil depends on
what is opposite the sensor:The tooth or the gap between the teeth of
the impulse wheel.
Now the tooth causes amplication, and the gap, on the contrary,
weakens the intensity of the magnetic ux.
These changes induced in the coil an electromotive force(EMF)
expressed in a sinusoidal output voltage which is proportional to the
rotational speed of the crankshaft.
Figure:

68. Sensors used in Automobile
3
Oxygen Sensor
An oxygen sensor is available in the exhaust system of an automobile.
The size and shape of this sensor look like a spark plug.
Based on its arrangement in regard to the catalytic converter, this
sensor can be arranged before (upstream) or after (downstream) the
converter.
Modern automobiles include upstream downstream o2 sensors.
The oxygen sensors used in automobiles are one sensor is arranged in
front of the catalytic converter one is arranged in every exhaust
manifold of the automobile.
Most of the vehicles have 4-sensors
Figure:

69. Sensors used in Automobiles
Working Principle
The working principle of the o2 sensor is to check the oxygen amount
within the exhaust.
Firstly, this oxygen was added to the fuel for good ignition.
The communication of this sensor can be done with the help of a
voltage signal.
So the oxygen status in the exhaust will be decided by the computer of
the car.
The computer regulates the mixture of fuel or oxygen delivered to the
car engine.
The arrangement of the sensor before after the catalytic converter
permits to maintain the hygiene of the exhaust check the converter's
eciency.

70. Sensors used in Automobiles
There are mainly two type of Oxygen Sensors
1
Binary Exhaust Gas Sensor
When at operating temperature (from 350°C), the binary sensor
generates a change in electric voltage depending on the oxygen level in
the exhaust.
It compares the residual oxygen content in the exhaust with the oxygen
level of the ambient air and identies the transition from a rich mixture
(lack of air) to a lean mixture (excess air) and vice versa.
2
Universal Exhaust Gas Sensor
The universal exhaust gas oxygen sensor is extremely accurate when
measuring both a rich and lean air/fuel ratio.
It has a greater measuring range and is also suitable for use in diesel
and gas engines.

71. Sensors in Automobiles
Signs of faulty sensor
Breakdown to exceed the emissions analysis
Fuel mileage can be decreased
The engine light will be o
Performance is poor, stalling and rough idling
Code checker recognizing sensor failure

72. Sensors used in Automobiles
4
Spark Knock Sensor
The knock sensor is one kind of sensor used to detect the ash knock.
This ash is the state within the engine of the automobile where the
fuel starts burning because of the pre-ignition, detonation, otherwise
pinging.
The main function of this sensor is to monitor the ignition process
inside the engine. Its indication assists the engine control to stop
knocking ignition and thus guard the motor or engine control.
Figure:

73. Sensors used in Automobiles
Construction Working
Piezoelectric elements involves the transmission of an electrical current
in response to detecting a change in pressure or vibration by these
elements.
The piezoelectric element inside the knock sensor is tuned to detect
the engine knock/detonation frequency.
The knock sensor is made up of piezocrystals (piezoelectric elements),
a shunt resistor and a thread at one end of the knock sensor, which
allows for the device to be threaded into the block near the pistons.
During combustion, a knock in the combustion chamber sends a
vibration to the silicone rings attached to the piezoelectric crystals in
the knock sensor (in the form of mechanical stress), accelerating the
silicon ring, forcing this sensor to generate an electrical voltage and a
pressure wave through the cylinder block.
Voltage output from the knock sensor will be high during a knock to
the ignition system.

74. Sensors used in Automobiles
Signs of faulty sensor
Engine power can be reduced
Fuel consumption can be increased
Warning light of the engine will be ON
Slow acceleration
Causes
Rust
The short circuit inside the engine
Damage of wiring
Wiring short circuit
Mechanical injury

75. Sensors used in Automobiles
5
Coolant Sensor
A coolant temperature sensor is conned to the engine of a vehicle and
measures the temperature of the vehicle's engine coolant.
The sensor feeds this information back in the form of an electrical
current to the engine control unit (ECU).
The ECU then responds to a change in the temperature dierence and
readjusts the engine's fuel injection
Figure:

76. Sensors used in Automobiles
A coolant sensor is similar to a thermistor, based on the working
principle that a change in electrical resistance will be the direct
product of a change in the temperature of a wire carrying current.
With a coolant temperature sensor, the full sensor is located in a
coolant passage that sits before a thermostat and is connected to the
engine control and monitoring unit.
The coolant temperature sensor is fastened to the intake manifold of
an engine coolant and is often referred to as a negative temperature
coecient type of sensor.
In terms of resistance capacity, this coolant sensor has 20,000 ohms
at 248 degrees Fahrenheit.
There is an inverse relationship between the electrical resistance and
the engine coolant
i.e. when the engine coolant temperature increases, the electrical
resistance decreases and this also causes a voltage drop in the sensor.

77. Sensors used in Automobiles
A basic functional principle to a coolant temperature sensor begins
with the ignition switch.
When the ignition switch is `on', a voltage passes through the resistor
and heats it up.
The resistor is connected to an electrical grid that behaves like a data
logger measuring the temperature dierence of the resistor.
When air traveling through a vehicle engine, which can come as a
result of heavy acceleration, the resistor to the sensor starts to cool
down and drops its resistance charge.
To control and maintain a balance in the engine temperature, the
coolant sensor detects the drop in electrical resistance and emits a
voltage to the resistor, a process that is completed in the space of a
millisecond.

78. Sensors used in Automobiles
It is important to monitor engine temperature as this will determine
exactly how much fuel is to be injected into the engine.
The engine control and monitoring unit assists in controlling the
temperature of the engine by supplying 5 volts to the circuitry
connected to the coolant temperature sensor, which allows for a
measurement of change in the voltage drop between the resistor and
the coolant temperature sensor.
Signs of faulty sensor
Higher idle speed
Increased fuel consumption
Poor starting behaviour

79. Sensors used in Automobiles
6
Manifold Absolute Pressure Sensor (MAP Sensor)
The sensor is used in electronic control systems for fuel consumption of
an engine.
The engines which use a MAP sensor are basically injected by fuel.
The various pressure sensors provide instant pressure data to the
electronic control unit (ECU) of an engine.
The data can be used to evaluate air density decide the air mass ow
rate of an engine that decides the necessary fuel metering for best
combustion.
An engine with fuel injected may use an alternate sensor namely MAF
sensor which is named as a mass airow sensor for detecting the intake
ow of air.

80. Sensors used in Automobiles
Figure:

81. Sensors used in Automobiles
Working Principle
The MAP sensor is an input sensor which detects an engine load and
provides a signal which is proportional to the sum of vacuum.
After that, an engine computer utilizes this data to alter explosion
timing fuel enhancement.
Whenever the engine works hard, ingestion vacuum falls because of the
throttle releases wide.
The engine utilizes more air or more fuel to maintain the air or the fuel
ratio instability.
Once the computer examines a load signal from the sensor, it makes
the blend of fuel go somewhat richer than regular thus the engine can
generate extra power.

82. Sensors used in Automobiles
Signs of faulty sensor
Fuel ratio of lean air and rich air
Surging
The economy of Poor fuel
Engine power problem
Stalling
Misre Detonation

83. Sensors used in Automobiles
7
Engine Temperature Sensor
The engine temperature sensor is a type of sensor that changes its
resistance with temperature.
Many critical engine functions such as selection of air-fuel ratio, fuel
injection timing, ignition timing etc. depend on the engine's
temperature.
This is because a cold engine requires a rich air-fuel mixture; whereas
the engine running at optimum operating temperature requires a lean
mixture.
The engine temperature sensor informs the engine's ECU about the
current ongoing variations in the engine temperature.
ECU, in turn, adjusts and regulates the fuel quantity ignition timing.
The data from the engine temperature sensor provides readings for
engine temperature gauge on the dashboard.
Based on this data, the ECU also controls the additional functions such
as switching on / o the engine cooling fan

84. Sensors used in Automobiles
The engine temperature sensor connects either to the temperature
gauge or to the temperature indicator in the dashboard.
In modern cars, you will notice that there is no separate engine
temperature gauge. Instead, there is a tiny `light' symbolizing the
engine temperature; which is integrated with rpm-meter/instrument
cluster.
Figure:

85. Sensors in Automobiles
8
Camshaft Position Sensor
The camshaft position sensor monitors the rotation of the camshaft,
specically targeting when valves open and close.
Most camshaft sensors are mounted just above a notched ring on the
camshaft.
It uses a magnet to produce or vary an AC electronic signal that is used
in conjunction with a crankshaft position sensor to determine when a
position approaches top dead center (TDC) on the compression stroke.
This information will help to ne tune spark timing and injector pulse.
In consecutive fuel injection systems, ECU must determine which
cylinder to re next.
This information is provided from the cylinder identication sensor.
During the engine rotation the sensor sends a signal to the onboard
controller whenever the rst cylinder is at the top dead center (TDC).

86. Sensors used in Automobiles
Function of Camshaft position sensor
To determine which cylinder is in its power stroke, while the car's
computer (for example) monitors the rotating position of the camshaft
which is relative to the crankshaft position using a camshaft position
(CMP) sensor. It will use this information to adjust the spark timing
and the operation of the fuel injectors
The CAM sensor or camshaft position sensor's role is to signal the
ECM the camshaft position. The crank and cam sensor operates in
sync with eachother. The CAM sensor is frequently used in
determining which injector to re in a sequential system and for the
COP or coil on-plug ignition systems coil ring event.

87. Sensors used in Automobiles
Figure:

88. Sensors used in Automobiles
9
Throttle Position Sensor
Throttle system present in the automobiles monitors and controls the
uid ow in the engine.
The power of the vehicle engine can be controlled by changing the
air-fuel ratio of the engine which is done by constrictions of the
Throttle.
The throttle is known as accelerator pedal in cars, thrust lever in
aircraft, and as a regulator in steam-powered engines.
Modern automobiles operate on the drive-by-wire system
In automobiles, the speed of the engine can be controlled by varying
the amount of fuel and air supplied to the engine.
For this throttle system is used. .

89. Sensors used in Automobiles
Working
This sensor is usually mounted on the throttle body.
It senses the position of the throttle valve or buttery valve and
transmits the information to the Engine control unit.
This sensor monitors how far down the accelerometer pedal is pushed
and gives the output current determining the position of the pedal.
The position of the pedal controls the airow of the engine.
If the valve is wide opened, a large amount of air is supplied to the
engine and vice-versa.
The output given by this sensor, along with other sensors is
transmitted to the engine control unit, which decides the amount of
fuel to be injected into the engine accordingly.

90. Sensors used in Automobiles
This sensor is a three wired potentiometer.
Through the rst wire, a 5V power is supplied to the sensors resistive
layer.
The second wire is used as ground whereas the third wire is connected
to the potentiometer wiper and provides input to the Engine control
system.
Based on its construction, there are three types of throttle position
sensors.
They are the throttle position sensors with built-in end switches also
known as Closed Throttle Position Sensor, the potentiometer type and
the combination of both these types

91. Sensors used in Automobiles
10
Vehicle Speed Sensor
The Vehicle Speed Sensor (VSS) is connected to a speedometer cable
and positioned between the axle and the wheel of a vehicle.
The most common types of VSS operate from a magnet connected at
the back of the transmission housing behind the speedometer.
The top of the VSS senses the output of the transmission.
Its opposite side is connected to a rotating magnet, which generates a
voltage.
This voltage is then transmitted to a computational device that
calculates the speed proportional to the moving vehicle.
During a vehicle's movement, the VSS will generate four pulses in
response to one rotation of the magnet.

92. Sensors used in Automobiles
Types of VSS
1
Hall Eect VSS
2
Reed Switch type VSS

93. Sensors used in Automobiles
1
Hall Eect VSS
This type of sensor is located on the dierential gear housing and
monitors the output speed of the transaxle.
On average, these sensors have 12-volts of sensor power.
Unlike typical speed sensors, a Hall-Eect sensor employs its own
reference voltage signal and is used for anti-lock braking systems in
vehicles, by timing the speed of the wheel and the shaft.
These sensors are made up of an internal transistor, which is activated
by the moving relcutor ring.
As the reluctor (the 'ngers' on the brake-disk) moves against the Hall
Eect sensor, it creates a magnetic eld that generates a voltage.
This voltage activates the transistor on the Hall Eect sensor
The voltage is then transmitted through a conductor to the processing
unit of the anti-lock brake system, which counts the voltage peaks and
divides them by the time duration, to measure the velocity of the
moving vehicle.
The voltage signal only drops to zero when the 'ngers' on the
brake-disk pass and have no contact with the sensor.

94. Sensors used in Automobiles
2
Reed Switch Type VSS
These sensors consist of a magnet and reed switch.
In comparison to the Hall Eect sensor, a magnet (powered by a
speedometer cable) is required to mechanically turn the reed switch on
and o (approximately four times per one complete rotation of the
magnet).
This allows the calculation of pulse numbers per second and therefore,
the measurement of vehicle speed.
Reed switch-type sensors are active and generate a voltage in response
to the continuous rotation of a magnet in close contact with a probe.
The voltage generated is directly proportional to the speed at which
the magnet rotates.

95. Sensors used in Automobiles
Figure:

96. Sensors used in Automobiles
Figure: