A short introduction to the common types of sensors used in modern automobiles and their functions. Please note this is only an overview, and does not include ultramodern sensors used in high end cars.

1. SENSORSusedin
Automobiles
BY:
SIJU K ABRAHAM
SMBS
VIT UNIVERSITY
CHENNAI

2. What is a sensor?
 Device which detects or measures a physical property
 Records or indicates the value proportional to the physical property
 Responds to the physical property

3. What physical properties?
 Temperature
 Pressure / Force
 Velocity / Flow
 Acceleration
 Position / Angle / Displacement
 Current / Voltage
 Magnetic flux
 pH value / Chemical properties
 Light / Optical Properties
 Proximity / Presence
 Ionization / Radiation
 Acoustics / Vibration

5. Temperature sensors
Thermocouple
◦ Two wires of different material joined at bot ends, both at different temperatures
◦ For high temperature applications like exhaust gas temperature and catalytic convertors
Thermistors
◦ PTC / NTC Semiconductors used in ECT
Resistance Temperature Detectors
◦ Positive Resistance Coefficient materials : Platinum
Integrated Silicon Temperature sensors
◦ Ambient temperature monitoring, air conditioning
Pyrometric Sensors
◦ Passenger / occupant detection, air conditioning, Disc and tire temperature
Thermal Imaging Cameras
◦ Obstacle detection

6. Engine Coolant Temperature sensor
(ECT)
To measure engine temperature
The readings from this sensor are then fed back to the Engine control
unit (ECU), which uses this data to adjust the fuel injection and ignition
timing.
To control the cooling fan
To provide data for temperature gauge on dashboard
Cold engine requires different injection and ignition timings compared
to hot conditions, in order to operate smoothly

7. Types of sensors
Thermistors
Negative temperature coefficient (NTC) sensors: - Internal
resistance will decrease as the temperature rises (and vice versa)
Positive temperature coefficient (PTC) sensor :- Resistance will
increase with rising temperature.
Most automotive coolant temperature sensors are NTC sensors.

8. Outside Air Temperature Sensor
(OAT)
RTDs or Integrated Silicon Temperature sensors (LM34 /LM35 etc)
Usually mounted inside or near the front bumper or in the side mirror
Automatic Climate controller uses this temperature to help control the
interior temperature of the vehicle
Provides the vehicle occupants with the outside temperature readings

9. Exhaust Gas Temperature sensor
EGT
Thermocouple based sensor
High temperature operation
Directly measures the temperature of exhaust gas

11. Pressure sensors
1. Gravitational transducer
a) Manometer
b) Dead weight tester
2. Elastic transducer
a) Bourdon tube pressure gauge
b) Elastic diaphragm pressure gauge
c) Bellows type pressure gauge
3. Electrical transducer
a) Variable resistance type
b) Strain gauge type
c) Variable capacitance type
d) LVDT type
4. Thermal transducer
5. Piezo- electric transducer

12. Manifold absolute pressure (MAP) sensor
Used to sense the load on the engine
Measures the amount of vacuum in the intake manifold
Amount of intake manifold vacuum is directly related to
engine load
The ECU uses this information to calculate the correct amount
of fuel to inject, when to ignite (ignition timing retard or
advance) and other functions.

13. Working
Piezo resistive type
A silicon chip is mounted inside a reference chamber.
One side of the chip is the reference pressure (Calibrated pressure, usually vacuum)
On the other side is the pressure to be measured.
The silicon chip changes its resistance with the change in pressure.
This change in resistance alters the voltage signal to the ECU ( 1V – 4.5V)

14. Tire pressure monitoring system (TPMS) employs capacitive or piezoresistive
sensors to measure the pressure of tire directly.
Some systems use vibration and sound sensors combined with the wheel speed
sensor to monitor the tire pressure

15. Mass Air Flow Sensor (MAF)
 Used to find the mass flow rate of air entering the engine
 The MAF data is used by the ECU to deliver the correct fuel mass to the engine for
providing the exact air fuel ratio required.
 The air density varies with the ambient temperature, altitude and the use of forced
induction.
 Two types of MAF – Vane type and Hot wire
 The Vane type sensor measures the air flow into the engine with a spring-loaded air
vane (flap/door) attached to a variable resistor (potentiometer).
 The vane moves in proportion to the airflow.
 A voltage is applied to the potentiometer and a proportional voltage appears on the
output terminal of the potentiometer in proportion to the angle the vane rotates

16. Hot Air Mass Meter

17. To provide precise pilot control of the air-fuel ratio, it is essential for the supplied air
mass to be exactly determined in the respective operating status.
 The wire's electrical resistance increases as the wire’s temperature increases, which
varies the electrical current flowing through the circuit, according to Ohm's law.
When air flows past the wire, the wire cools, decreasing its resistance, which in turn
allows more current to flow through the circuit, since the supply voltage is a constant.
As more current flows, the wire’s temperature increases until the resistance reaches
equilibrium again. The current increase or decrease is proportional to the mass of air
flowing past the wire

18. Hall Effect Sensor
Varies its output voltage in response to a magnetic field
 When a current carrying conductor is placed in a magnetic field, the electrons will
be deflected from a straight path
Consequently, one plane of the conductor will become negatively charged and the
opposite side will become positively charged
 The voltage between these planes is called Hall voltage
This type of sensors are non contact sensors and are used in speed measurement of
rotating parts, position sensing, etc

19. Torque sensor
1 Torsion rod (twisting area internal)
2 Input shaft (from the steering wheel)
3 Housing for the coil spring making
the electrical connections
4 Sensor module with Magneto
resistive sensor chip and signal
amplification
5 Steering pinion/ balancer shaft
6 Magnetic multipole wheel

20. Passive Wheel Speed Sensor

21. Active wheel speed sensor

22. Working

23. Exhaust Gas Sensor – O2 sensor
Monitor the concentration of residual oxygen within the exhaust gases
Reduce engine emissions
Best economy and performance
The ideal ratio of air to fuel to achieve complete combustion is 14.7:1
The term Lambda refers to the ratio of air to fuel; this chemically
correct air/fuel ratio is known as a stoichiometric ratio or Lambda (λ)
=1.0.
 A fuel rich mixture would have a lower value e.g. 0.8 and a fuel lean
mixture would have a higher value e.g. 1.2.
Lambda sensor works on closed-loop control system

24. Working

25. “Knocking” occurs when the air-fuel mixture self-ignites prematurely. Sustained
knocking combustion causes damage primarily to the cylinder head gasket and
cylinder head.
Damage to pistons, rings, and exhaust valves can result if sustained heavy knock
occurs
The knock sensor is mounted on the crankcase and measures the structure-borne
noise using a piezoelectric measuring element. Knocking is discernible by its higher
sound frequencies.
Knock Sensor

26. Working
A piezo-electric element is translating the vibrations into an electric signal
proportional to the acceleration
Due to the vibration, a counter weight inside the sensor is applying pressure on the
piezo element, this pressure creates an electric charge in the piezo element
This is the output signal of the sensor.
For a knock application on a gasoline engine, the ECU adjusts the spark timing and
on a diesel application the ECU controls the pilot injection quantity.

27. Throttle Position Sensor
Senses the position of the butterfly valve in the throttle body
Contact type – Potentiometer type
Non contact type – Hall effect or inductive or magnetoresistive
 A magnet/inductive loop is mounted on the throttle spindle
 The change in the magnetic field is sensed by the sensor and the voltage generated is
given as the input to the ECU

28. Crank Position sensor
Senses the position of the crankshaft
This is very important for adjusting the ignition and injection timing
Non contact type sensor
Hall effect sensor
Crank angle encoder

29. Thank You