Air Bag Sensors: For Protection in Cars

AIR BAG SENSORS
FOR PROTECTION
IN CARS
A.V.S. NARASIMHAM(Y7EE318)
S.VENU(Y7EE320)
K.RAMKUMAR(L8EE332)
INTRODUCTION
 An airbag is a vehicle safety device. It is an occupant
restraint consisting of a flexible envelope designed to inflate
rapidly in an automobile collision, to prevent vehicle
occupants from striking interior objects such as the steering
wheel or window
 Because of no action by the vehicle occupant is required to
activate or use the airbag, so it is thus considered as a passive
safety device. This is in contrast to seat belts, which are
considered active safety devices .Terminological confusion
can arise from the fact that passive safety devices and systems
— those requiring no input or action by the vehicle occupant
— can themselves operate in an active manner; an airbag is
one such device.
INSIDE AIRBAG SENSOR…….
 The goal of an airbag is to slow the passenger's forward
motion as evenly as possible in a fraction of a second. There
are three parts to an airbag that help to accomplish this feat:
1. The bag itself is made of a thin, nylon fabric, which is
folded into the steering wheel or dashboard or, more
recently, the seat or door.
2. The sensor is the device that tells the bag to inflate.
Inflation happens when there is a collision force equal to
running into a brick wall at 10 to 15 miles per hour (16 to
24 km per hour). A mechanical switch is flipped when
there is a mass shift that closes an electrical contact, telling
the sensors that a crash has occurred. The sensors receive
information from an accelerometer built into a microchip.
3.The airbag's inflation system reacts sodium aside
(NaN3) with potassium nitrate (KNO3) to produce nitrogen
gas. Hot blasts of the nitrogen inflate the airbag
WORKING
 Airbags are inflated by gas produced in a chemical reaction
 Gas inflates the airbag with velocities of up to 320km/h
 The entire process happens in 20-30 milliseconds
 The chemical reaction is triggered by an

ACU(AirbagControlUnit)
 The ACU has to decide whether or not to deploy the airbag
once the sensors
 located throughout the car report a collision
 The circuit has to be very reliable; no room for error is

allowed
 The ACU has to make the decision really fast; in less time
than it takes for a collision to occur
 The ACU is programmed to deploy different airbags (front,
side, knee etc.) depending on
 the different combinations of data received from sensors. For
instance, if the on-board
 gyroscope detects that the vehicle has flipped over, the front
airbags may not necessarily
 have to be deployed. However, side airbags will need to be
activated because the person
 will likely fall on their side.
The following flow chart shows how the information is received and processed by the ACU
 Sensors are very small devices and the signals they produce
are relatively weak.
 The signal has to be amplified in order to analyze it.
 However, amplification may interfere with the signal, so the
signal must be filtered as well.
 The signals are then sent to the Multiplexer.
 The Multiplexer receives numerous signals and presents them
to the ACU in orderly fashion, because the ACU can only
process one signal at a time.
 Prior to that, the signal has to go through the ADC (Analog-
to-Digital Converter).
 The ACU is a digital device and can only accept digital
signals communicated using machine code, whereas the
electric pulses from sensors are examples of an analog signal.
 Thus they need to be converted first
 The following circuit diagram describes the circuit we built to implement the block diagram
 AC Voltage Source (1) models the output signal of a sensor
 High Pass Filer (2) filters the output signal.
 741 Operational Amplifier (3) amplifies the filtered signal.
 Wheatstone bridge (4) is used to change the amplified AC
signal into DC; this mimics the function of ADC (Analog-to-
Digital Converter).
 Comparator (5) compares the received DC signal with the
base 5V signal and depending on the difference in voltages,
sends current to either the green LED (NO AIRBAG) or the
red LED (YES ARIBAG). Comparator models the behaviour
of the ACU by deciding which light should light up; similarly
to how the ACU decides whether or not the airbag should be
deployed.
ACCELEROMETER
 An accelerometer is a device
that measures proper
acceleration, the acceleration
experienced relative to freefall.
 Single- and multi-axis models
are available to detect
magnitude and direction of the
acceleration as a vector quantity,
and can be used to sense
orientation, vibration and shock.
Micro machined accelerometers
are increasingly present in
portable electronic devices and
video game controllers, to detect
the orientation of the device or
provide for game input
IMPACT SENSORS
 The side impact sensor, installed in the B-pillar or C-pillar on
the side of a vehicle, detects a side collision instantaneously.
When the sensor detects the collision, it sends a signal to the
airbag ECU which deploys the side airbag or curtain airbag.
 Impact sensor is so small, it can be installed on the narrow top

portion of the vehicle pillar, resulting in precise detection of a
collision even with high-height vehicles, such as an SUVs.
WHEEL TACHOMETERS
A wheel tachometer minimizes
variances in the rate of revolution
detected by the wheel velocity
sensors of the tachometer due to
assembling errors and improves
the accuracy of the operation of
driving force allocation.
Sinusoidal wheel velocity signals

vF and vR representing the rates
of revolution of the front and rear
wheels are produced respectively
by front and rear wheel
revolution sensors are subjected
to wave shaping to obtain the rate
of revolution of the front wheels
nF and that of the rear wheels nR.
GYROSCOPES
 A gyroscope is a device for measuring or maintaining orientation,
based on the principles of conservation of angular momentum. A
mechanical gyroscope is essentially a spinning wheel or disk whose
axle is free to take any orientation. This orientation changes much less
in response to a given external torque than it would without the large
angular momentum associated with the gyroscope's high rate of spin.
Since external torque is minimized by mounting the device in
gimbals, its orientation remains nearly fixed, regardless of any motion
of the platform on which it is mounted. Solid state devices also exist,
such as the ring laser gyroscope.
 Applications of gyroscopes include navigation (INS) when magnetic
compasses do not work (as in the Hubble telescope) or are not precise
enough (as in ICBMs) or for the stabilization of flying vehicles like
Radio-controlled helicopters or UAVs. Due to higher precision,
gyroscopes are also used to maintain direction in tunnel mining
 A gyroscope exhibits a number of behaviors including precession
and nutation. Gyroscopes can be used to construct gyrocompasses
which complement or replace magnetic compasses (in ships, aircraft
and spacecraft, vehicles in general), to assist in stability (bicycle,
Hubble Space Telescope, ships, vehicles in general) or be used as
part of an inertial guidance system.
 Gyroscopic effects are used in toys like tops,boomerangs,yo-yos,

and Powerballs. Many other rotating devices, such as flywheels,
behave gyroscopically although the gyroscopic effect is not used.
BRAKE PRESSURE SENSORS
 Brake pressure sensing is used in a Dynamic Brake Control (DBC)
system which improves brake effectiveness in emergency "panic
stop" situations.
 In an emergency stop the brake pressure will be distributed to any or
all of the wheels in a manner designed to retain directional stability
of the car
 The system also helps to maintain directional stability when braking
while cornering.
 A brake pressure sensor records the magnitude and speed of the
brake pressure change and the sensor communicates these values to
the DBC control unit. The control unit compares the values to its
stored DBC activation thresholds. DBC will activate only if certain
predefined criteria are met. DBC deactivates when the driver releases
the brake pedal or if the vehicle slows down below a minimum
speed.

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AIR BAG SENSORS

 The entire process happens in 20-30 milliseconds

 The chemical reaction is triggered by an

 The circuit has to be very reliable; no room for error is

 Impact sensor is so small, it can be installed on the narrow top

Sinusoidal wheel velocity signals

 Gyroscopic effects are used in toys like tops,boomerangs,yo-yos,

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