sensores en el auto

Sensores y actuadores

JJVS - 2016

Ingenierıa en Sistemas Automotrices

Puebla, Pue., a 15 de febrero de 2017

JJVS - 2016 Ingenierıa en Sistemas Automotrices 1/39

Sensors in the vehicle

In developed countries, government transport policy placesincreasing emphasis on the efficient management of existing roadsand recognizes the difficulty of satisfying demand by building newroads.



Advanced sensing and control systems also offer the possibility ofsafely reducing the gaps between vehicles (the ”headway”), thusincreasing the number of vehicles that can use a particular stretchof road.



All telematic systems rely heavily on sensors and measurementtechniques, and this is especially true of those applications that aresafety critical.



As a rule of thumb, at 2005 prices, a vehicle manufacturer willnormally tolerate a ”measurement cost” of only around $10 permeasurand, including all the signal conditioning required.



Highway sensor costs are much higher than those of automotivedevices.



To succeed commercially, automotive sensors have to be veryrobust. They must tolerate an environment that includestemperatures from possible exposure to -40 to +140 ◦ C boilingwater, battery acid, fuel, hydraulic fluid, road salt, and so forth, aswell as very high shock and vibration loads, which can exceed 1000g on the unsprung side of the vehicle suspension.


Electronic measurement systems can be applied very widely withina motor vehicle, as shown in figure 1.1.


The complexity of the control task involved in powertrainmanagement is demonstrated by figure.



A typical automotive sensor has a design life of up to 10 years, andshould require no initial setting up or maintenance within thattime. Table 1.1 lists typical required specifications for thepowertrain sensors.


Ignition Control

The ignition timing sensors available at present normally use Halleffect or other electromagnetic transducers to detect the movementof a magnet or metallic projection attached to the flywheel.


Ignition Control

The pressure and speed signals provide inputs to a microprocessor,which is programmed to look up the optimum advance angle froma three-dimensional table relating speed, load, and advance anglestored in the microprocessor’s memory.


Manifold pressure sensor

There are devices based on capacitive, inductive, andpotentiometric techniques. The most widely used approach is toemploy a silicon diaphragm with integral silicon strain gauges, orto use a capacitive deflection sensing method.


Knock Sensing

When an ignition system with electronic advance control isoptimized for best performance and economy, it can, under someconditions, be set sufficiently far advanced to cause a conditionknown as ”knocking”. The frequency of knocking in normal-sizedengines is in the region of 8 kHz (a piezoelectric accelerometer).


Fuel Control : Veleta

The total quantity of fuel and the ratio of air mass to fuel injectedinto the engine are critical. Under these circumstances, the idealmeasurement to be made is the mass airflow into the enginemanifold.


Fuel Control : Hot-wire


Emission Control

The only way to meet the emissions regulations is to use aso-called three-way catalyst in the exhaust system to reduce thelevels of the critical pollutants of carbon monoxide (CO),hydrocarbons (HC ), and the oxides of nitrogen (NOx).For its correct operation, such a catalyst requires that the air-fuelratio supplied to the engine should always be as close as possibleto the optimum stoichiometric level of 14.7:1.


In-Cylinder Combustion Measurement

Three methods have been developed for meeting this requirement.The first approach is based on measurements of the pressurevariations within the combustion chamber. The second relies ondetecting the arrival time of the flame front by means of anionization detector, and the third technique assesses the opticaloutput from the combustion process (i.e., its color and intensity)by means of an optical sensor.


In-Cylinder Combustion Measurement

High-cost, laboratory-grade piezoelectric pressure sensors havebeen available to the engine developer for many years. Theproblem in applying them to production vehicles has been the needto reduce the price to a level that will permit the economic fittingof a pressure sensor in each combustion chamber of the engine inmass production.


Engine Speed and Torque Measurement

The engineer faced with the problem of measuring torque normallyuses a torque transducer, which has been made by applying straingauges to a shaft to measure the shear strain caused by torque.


TRANSMISSION CONTROL

The sensors required are for engine speed, transmission outputspeed, vehicle speed, and, assuming that the transmission ratio ishydraulically controlled, hydraulic valve position and hydraulic oilpressure. A pressure sensor based on etched-silicon technology islikely to be the best device from the standpoint of cost andreliability.


SUSPENSION CONTROL

With this approach either the vehicle springs or the dampers orboth are replaced by controllable devices with variablecharacteristics. There are two major types of controllablesuspension : Active suspension and adaptive damping.


Adaptive Damping System


SENSORS FOR ANTILOCK BRAKING AND TRACTIONCONTROL

Antilock brakes work by sensing whether, on braking, one wheelstarts to slow down towards a locked condition faster than theother wheel. When a wheel starts to speed up towards spin,braking is applied to that particular wheel, and backing off the(electronic) engine throttle through the engine control systemreduces engine power.


TIRE AND WHEEL SENSING

The wheels and particularly the tires of a road vehicle represent thefinal and probably the most critical link in the chain by whichengine power is used to create vehicle motion.With the exceptionof wind resistance and gravity, all external forces are transmittedthrough the tire-to-road contact patch.


TIRE AND WHEEL SENSING

Continuous monitoring of the coefficient of friction between thetire and road could enhance both vehicle safety and performance.Tire temperature could also be measured, and this has been shownto be a good predictor for tire blowouts. Work undertaken atSouthampton University demonstrated that most high-speed tireblowouts result from prolonged running on under-pressure tires.


VEHICLE-BASED EXTERNAL SENSORS FOR DRIVERSUPPORT

The term used by the automotive industry for driver supportequipment is Integrated Driver Support (IDS). The first commercialapplication of IDS is the autonomous cruise control (ACC) system.Other IDS systems likely to appear in the next decade are targetedat making the roads safer for both vehicle occupants and otherroad users.


Sensors for Adaptive Cruise Control (ACC) and CollisionAvoidance

ACC is capable of maintaining a cruising speed at a preset level,but is also able to adjust the speed to maintain a safe distancefrom the vehicle in front.Quite apart from being seen as a convenience feature, ACCappears to be able to help reduce traffic congestion by keeping thetraffic moving.Most of the proposed systems adopt a pulsed mode of operationand use infrared to achieve better penetration in mist or rain.


Sensors for the Vehicle Environment

Visibility of the road around a vehicle has always been problematiceven on bright and sunny days. A number of vehicle manufacturersare studying the idea of replacing mirrors with video cameras toeliminate blind spots.

ULTRASOUND, are restricted in their application tolow-speed maneuvering and other applications where therelative velocity is low.

VISION AND IMAGE-BASED SYSTEMS,

PIR camera uses an array of detectors to image the radiationof a warm body, which can be significantly higher than thebackground temperature

CAPACITIVE PROXIMITY SENSORS, They have also beenconsidered for detecting obstacles in low-speed maneuverssuch as parking.


Figura: Crash sensor operation curve.


Crash switch

Applications:

Fuel cutoffBattery disconnectSeat belt pretensionersActivation of hazardwarning lights

Mobile phone distressbeacons

Door lock releases

Antitheft devices


Rollover switches

Some crashes do not result in a deceleration severe enough totrigger inertia switches of the types described above. Rolloverswitches has been developed with the purpose of firing airbags,switching off fuel pumps, and so forth in the event of this type ofaccident occurring.


VEHICLE-HIGHWAY SYSTEMS

The major telematic products currently under development by theroad transport industry include the following:

Others in their immediate environment, normally using somecombination of radar, image processing, laser rangefinders,ultrasound, and vehicle-vehicle communications.

Highway operators use a variety of sensing techniques tomonitor traffic flow and detect incidents (breakdowns andaccidents).

Many navigation and traffic congestion warning systems usehighway sensors to monitor and collect information, which isthen used to optimize the driver’s route choice in the light ofprevailing traffic conditions.

So-called drive-by-wire systems are becoming widespread inautomotive engineering.

Convoy driving involves setting up electronic ”trains” ofvehicles, which run close together under autonomous control.


Loop detector

f =

√1

LC− R2

L2

Magnetic and eddycurrents are induced in thevehicle, which oppose themain field of the coil andtherefore reduce the loopinductance.

The magnetic flux density

increases because of theiron content of the vehicle,which increases the loopinductance.

The loop capacitanceincreases due to theproximity of the vehicle.


INFRARED DETECTORS

IR detectors can only detect movement within their zone ofcoverage, while loop detectors sense the presence of a vehicle. IRdetectors can only detect movement within their zone of coverage,while loop detectors sense the presence of a vehicle.Active IR detectors can also be used for speed measurement asshown in figure. The normal arrangement is for two detectionzones per lane to be used. The time at which a target vehicleenters each zone is noted, and the vehicle speed can then readilybe calculated as long as the installation geometry is known.


MICROWAVE DETECTORS

They operate by radiating a microwave beam in the X (10.587GHz) or K (24.2 GHz) frequency bands. When the beam strikes amoving metallic object, a reflection is returned at a slightlydifferent frequency (the Doppler effect). Some studies of MVDshave shown that their performance can be erratic.


PIEZOELECTRIC DETECTORS AND VIDEO IMAGEPROCESSING

Piezoelectric cable uses the well-known piezoelectric effect [32], inwhich lateral compression of a cable made from a piezoelectricplastic material such as PVdF (Poly-vinylidene fluoride) results inthe generation of a small charge that can be amplified anddetected.Video image processing techniques are increasingly being appliedto detect the presence and speed of vehicles in real time, as well asfor vehicle identification through number-plate recognition.


CONCLUSIONS AND FUTURE DEVELOPMENTS

Is show the breadth of sensing and transduction techniquescurrently in use for automotive telematics.Drive-by-wire systems are replacing mechanical links betweendriver and vehicle will be partially or completely d by electricalconnections.The electronic systems currently incorporated in a motorvehicle account for 30 % of the cost of building the vehicle. Alarge part of this increase will be the result of increased sensoruse (and the associated signal conditioning systems).The advent of silicon micromachining techniques has meantthat much greater intelligence can be incorporated within asensor, with many of the signal conditioning and compensationcircuits being fabricated on the same wafer as the sensor.The society tolerates the fact that human drivers causeseveral hundred deaths a month in Europe—but there wouldbe an enormous outcry if it were found that systems werecausing even one fatality a year! The hardware/softwareinteractions will require particularly close scrutiny.Convoy driving systems are the logical extension of theAutonomous Cruise Control (ACC) systems now beingdeployed.However, the safety of convoy driving in the event offull or partial systems or mechanical failure on one of theconvoy vehicles has not been examined in depth, and furtherresearch in this area is urgently required.


sensores en el auto

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