Automotive sensors

Abstract.

This paper will provide a review of past, present and future automotive

sensors. Today’s vehicles have become highly complex sophisticated electronic

control systems and the majority of innovations have been solely achieved through

electronics and the use of advanced sensors. A range of technologies have been

used over the past twenty years including silicon micro engineering, thick film,

capacitive, variable reluctance, optical and radar. The automotive sensor market

continues to grow with respect to vehicle production level in recognition of the

transition to electronically controlled electrically actuated systems. The environment

for these sensors continues to be increasingly challenging with respect to

robustness, reliability, quality and cost.

Introduction

Today’s vehicles are pervaded with a diverse range of sensors providing

critical data for performance, safety, comfort and convenience functions. The

measurement of inlet manifold absolute pressure in early ignition and fuelling control

systems was one of the first and most successful automotive applications of sensors,

and continues to this day to be an important parameter. Many other sensors

including crankshaft position, knock, air mass flow, exhaust gas and temperature

sensors have been subsequently used to enhance powertrain performance.

The trend towards ever increasing use of electronically controlled electrically

actuated systems on vehicles (for example, electrically powered steering, semi-

active ride control, slip control systems and adaptive cruise control) has created new

challenges and opportunities for sensor developers. Traditional sensors have been

complemented by the addition of new sensors for new applications, for example,

long range radar, optical steering torque sensors, tyre pressure monitoring systems

and yaw rate sensors. Sensor cost continues to be a significant factor in the

selection criteria of automotive system designers, recognising the reward of large

production volumes if successful. In addition, sensor suppliers must also deliver the

robustness and quality targets demanded of this automotive market. Figure 1

provides some examples of sensors used on today’s vehicles.

Hybrid & Fuel Cell Vehiclese.g. Hydrogen Leak DetectionCurrent MonitoringPressureFlowTemperatureMotor Speed & Position

Vehicle Controle.g. Hydraulic PressureLat/Long AccelerationWheel SpeedYaw RateRide Height PositionSteering Torque & Position

Engine Sensorse.g. Inlet Manifold PressureCamshaft PositionAir TemperatureFuel TemperatureFuel PressureKnockCoolant TemperatureEGR Valve PositionAir Mass FlowOxygen

Crash Avoidancee.g. Adaptive Cruise Control RadarParking SensorsLane Departure WarningDriver Monitoring

Passenger Comforte.g. HVAC TemperatureHumidityAir Vent PositionsSeat PositionWindow Position

Passenger Conveniencee.g. Remote Keyless EntryAutomatic Rain WipersAutomatic HeadlampsWasher Fluid LevelHeadlamp Levelling

Safety & Securitye.g. Theft PreventionOccupant Airbag SystemsSeat Belt Pre-tensionersTyre Pressure MonitoringOccupant DetectionPredestrian Detection

Figure 1. Examples of Automotive Sensor Applications

Sensors & their Applications

A typical top-of-the-range vehicle will comprise over 30 electrical/electronic systems and more than 100 sensors. Although some sensor applications have been dominated by one specific technology, e.g. accelerometers and silicon microengineering, a number of sensor technologies do co-exist and compete within a given application.From this task,we are about to explain only 3 sensors from hundreds of sensors in Automotive industries which are:

a) Tyre Pressure sensorb) Parking sensorc) Automatic rain wipers

Parking sensor

Parking sensors are proximity sensors for road vehicles designed to alert the driver

to obstacles while parking. These systems, which use either electromagnetic or

ultrasonic sensors, are marketed variously by vehicle manufacturers under

proprietary brand names

Description.

This simple circuit can be used as an aid for sensing the distance between the rear

bumper of the car and any obstacle behind the car. The distance can be understood

from the combination of the LEDs (D5 to D7) glowing. At 25cm D7 will glow, at 20 cm

D7&D6 will glow and at 5cm D7, D6 and D5 will glow. When the obstacle is beyond

25 cm none of the above LEDs will glow.

Two ICs are used in the circuit. The IC1 (NE555) is wired as an astable multivibrator

for driving the IR Diode D1 to emit IR pulses. The operating frequency of the

transmitter is set to be 120Hz.The IR pulses transmitted by D1 will be reflected by

the obstacle and received by the D2 (IR photo diode).The received signal will be

amplified by IC2a.The peak of the amplified signal will be detected by the diode D4

and capacitor C4.R5 and R6 compensates the forward voltage drop of D4.The

output voltage of the peak detector will be proportional to the distance between car’s

bumper and obstacle. The output of peak detector is given to the inputs of the other

three comparators IC2b,IC2c and IC2d inside the IC2 (LM324).The comparators

switch the status LEDs according to the input voltage their inverting inputs and

reference voltages at their non inverting inputs. Resistances R7 to R10 are used to

set the reference voltages for the comparators.

Circuit diagram with Parts list.