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.