DE102005031177A1 - Vehicle passenger compartment gas mixture constituent measurement procedure uses electrically filtered infrared radiation passed twice through sample holder using mirror on window heat sink - Google Patents

Abstract

A vehicle passenger compartment gas mixture constituent measurement procedure uses electrically filtered infrared radiation passed twice through the sample holder (4) from transmitter (10) to a receiver (11) via a reflector (8) thermally coupled to a window or windscreen as heat sink : Independent claims are included equipment using the procedure.

Description

The The present invention relates to a method and an apparatus for measuring at least one constituent of a gas mixture, in particular of certain components of the air in a vehicle interior.

To Numerous methods and devices are known in the art in which a gas mixture in a sample carrier or a cuvette in a measuring space is introduced or penetrates and the gas mixture in the sample carrier penetrated by a transmitter from radiation in an infrared range , wherein the radiation is subsequently detected in a receiver and the result finally is evaluated.

Here occurs, however, just in an application in the interior of a motor vehicle with its characteristic temperature range at least during the cold season the problem on that any form of an optical Measurement, for example by non-dispersive IR spectroscopy (NDIR) or related methods utilizing optical effects Fog or condensation must not be impaired. Otherwise false readings are delivered. Therefore, known sensors depending Often the ambient conditions only after a longer switch-on unadulterated Deliver measurement results. These measurement errors can be subordinated by one connected electronics, which also has a signal conditioning Perform calibration can not be compensated.

It is the object of the present invention, a method and a Device for a reliable one Temperature measurement to create the compact even in the interior a motor vehicle can be used.

These The object is solved by the features of the independent claims. Accordingly, points a method according to the invention the steps, after which the sample carrier so in a beam path arranged that the radiation from the transmitter to a sample carrier Reflector back and then from the reflector again through the sample carrier to the recipient along its longest Passage extends essentially twice completely. Here is the reflector with a heat sink thermally coupled, in particular a window or a windshield. Through this process, one of the radiation interacts with the gas mixture available standing free optical path maximized, thus by law Lambert-Beer improved device sensitivity is reached. At the same time, however, the procedure is also used to carry out a Deworming investigation used by the thermal coupling the reflector an early Condensation is targeted.

by virtue of the general temperature dependence of known sensors is in a measuring range, a temperature measuring device provided. As a result, in addition to a correction of the temperature response the sensor also a validation of a moisture or condensation signal carried out, which was obtained by a method according to the invention.

A inventive device for measuring at least one constituent of a gas mixture, in particular the air in a passenger compartment of a vehicle in which the investigating gas mixture independently and essentially continuously arranged interchangeably in a substantially elongated sample carrier is, wherein the sample carrier with a transmitter for penetrating radiation in an infrared range and with a receiver for detecting the radiation and with means for evaluation in connected optical optical path lying, points to the implementation of a inventive method accordingly a sample carrier on, at an open end area with at least one reflector and at a second open end region with a transmitter and a receiver so closed is the radiation on its way from the transmitter to the receiver the sample carrier passes twice, with a reflector for forming a Betauungssensors with a window or a windshield is thermally coupled.

advantageous versions are the subject of the respective subclaims. Accordingly, the radiation from the reflector to the concentration of optical information contained on the receiver bundled or focused reflected.

advantageously, the gas mixture or the air in the sample carrier is adjustable slowly replaced in time. This is preferably achieved by that openings in the sample carrier outward covered by a material of specific pore opening width or filled with this are. here we can u. a. single or multi-layered membrane or filter foils as air intakes and air outlet are used, as in technical applications find as pressure equalization application.

In a preferred embodiment of the invention, the radiation is optically filtered after leaving the transmitter and / or before hitting the receiver in at least one way. there For example, at least one optical parameter of the filtering can be set electrically, in particular for the selective wavelength adjustment of a subsequent measurement. In one embodiment of the invention, at least one filter is arranged in front of a sensor, which is preferably electrically adjustable in its optical properties and / or the transmitter is electrically tuned in its radiation frequency, in particular temporally in steps over a predetermined range and / or specific frequency points , different measurements can be carried out in parallel or consecutively according to this method and in a corresponding device. In one embodiment of the invention, the sample carrier to a reference channel for determining a humidity while cooling the reflector on the windshield. Further, in the sample carrier, a measuring channel for measuring a gas component contained in the air is provided with extensive thermal insulation.

As in the following embodiments still running is, so is a measurement and analysis of the carbon dioxide content in the interior air of a motor vehicle of particular importance.

All in all results from an inventive arrangement under implementation a method according to the invention according to the developments described above, a gas measuring device, which on the one hand enables high measuring accuracy, but on the other hand also reliable across from condensation-related incorrect measurements is. The device builds by using the reflector is very compact and is also against EMC sources of interference largely insensitive. A post-processing of the sensor output signals contained gas information is also easy in the form of digital data possible.

Beyond of the present exclusively treated use case in passenger cars, is so too an insert of a measuring device according to the invention possible with any type of gas analysis.

Further Advantages of a device according to the invention will be described below with reference to the illustration of embodiments closer to the drawing described. In a schematic representation:

1 FIG. 2 is a sectional view of a first embodiment of a measuring device in an installed position and FIG

2 A second embodiment of a device according to the invention analogous to the illustration of FIG 1 ,

In the individual representations of embodiments are in the drawing uniformly the same components and components throughout with provide the same reference numerals.

For measuring a component of the air within a passenger compartment of a vehicle, in the embodiments described below with reference to the drawing, a device 1 on a windshield 2 arranged as a heat sink or coldest place within a passenger compartment. When used in the interior of a motor vehicle with its characteristic temperature range, at least during the cold season, the problem often arises that any form of optical measurement, for example by non-dispersive IR spectroscopy (NDIR) or related methods using optical effects, by fog or condensation should not be affected. Otherwise, incorrect measurement results will be delivered. Therefore, known sensors can often deliver unadulterated measurement results only after a longer switch-on time, depending on the respective ambient conditions. These measurement errors can not be compensated by a downstream connected electronics. In the device 1 to 1 On the other hand, early condensation is deliberately enforced so that appropriate countermeasures can be taken. This can be a targeted activation of a ventilation for heating the air in the vehicle interior and / or an air conditioning system for dehumidifying the indoor air.

The present invention will be described below without restricting the scope of application and use in the following background solely with reference to the use in a vehicle interior with a particular focus on a measurement of a respective CO ₂ concentration: In particular, on cold winter days an air conditioning system in a motor vehicle via a Setting a desired internal temperature even when dehumidifying the interior. As a result, the air conditioning contributes significantly to keep the windows fog-free. For these reasons, modern motor vehicles are now almost all equipped with air conditioning. Since in motor vehicles but so far a powerful electrical power supply z. B. is missing on the basis of a 42V supply network, an electrical operation of the compressor of the air conditioning is currently not possible. The realized by V-belt mechanical drive directly through the motor vehicle engine requires a shaft bushing and a use of oscillatory hoses between the compressor and the heat exchangers. Accordingly, air conditioners also have significant disadvantages: Since the air conditioning operates under constant pressure of up to about 140 bar, their components are subjected to a natural wear process. Even hoses and seals can age, dry out and become leaky. This leads to the volatilization of the refrigerant and reduced cooling capacity.

• – Wellendichtung des Kompressors: 10–30 g
• – flexible Schlauchleitungen: 10–20 g
• – pro O-Ring an Bauteilanschlüssen: 2–3 g.

In some air conditioning systems, up to about 5% of refrigerant evaporates through the hose lines per year alone. Based on the average capacity of the air conditioners, this means a normal refrigerant loss of around 52 g per year. This loss usually goes unnoticed by a user, as car manufacturers dictate leeway for the loss of refrigerant through seals and hoses, within which a car air conditioning system is accepted as "leakproof". For such as densely defined car air conditioning systems, the users are regularly given by the car manufacturer no maintenance intervals. According to the specifications of the car manufacturers, the refrigerant losses per year must be within the following limits:

• - Shaft seal of the compressor: 10-30 g
• - flexible hose lines: 10-20 g
• - per O-ring on component connections: 2-3 g.

The loss of coolant must be supplemented by regular inspections every two years or so. Only in this way can the efficiency and operational readiness of the air conditioning system be maintained. The existing ozone depletion potential due to emitted refrigerants from car air conditioning systems was only mitigated with the transition to the replacement refrigerant R134a. The refrigerants used in the compression heat pumps are often indicated with abbreviations, such as the aforementioned R134a. This nomenclature refers to the chemical composition of the substances. The numbers or letters following the letter "R" as an abbreviation for refrigerant or refrigerant represent the atomic composition of the refrigerant. The first digit indicates the number of carbon atoms minus 1. The second digit denotes the number of hydrogen atoms plus 1. The third digit contains the number of fluorine atoms. The remaining free valence electrons must form bonds with chlorine atoms. The term "a" stands for asymmetric and denotes an isomer. Thus it can be seen that even the refrigerant R134a, which is presented as modern and climate-friendly as C ₂ H ₂ F ₄ or tetrafluoroethane, pollutes the environment as it is not completely CFC-free. Since compression air conditioning systems are not leak-free by design and the alternative refrigerant R134a has an ozone destruction potential ODP of 0, but has greenhouse effect, results in addition to the indirect direct greenhouse effect, in the form of the parameter value of the global greenhouse potential GWP relative to the 1 normalized greenhouse effect of CO ₂ can be stated at a time horizon of 100 years. For R134a and C ₂ H ₂ F ₄ , the GWP is 0.26 and 26%, respectively, in 100 years.

in the Order of the Federal Environmental Agency was determined that vehicle air conditioners an average of about 86 g of refrigerant per year and thus almost 8.2% their total filling quantity to lose. That means that at present in Germany per year to 1,140 t of refrigerant exit from car air conditioners. A value that increases with the Number of air-conditioned vehicles continues to rise rapidly.

Today's air conditioners usually use the refrigerant R134a. To reduce the global greenhouse effect, a replacement of this refrigerant is also discussed. Propane / butane-based refrigerants have a lower global warming potential and have proven themselves in domestic refrigerators under the name "Greenfreeze". Due to their risk of fire and explosion in case of leakage, however, they are not used in motor vehicles. Thus, in the coming years, the comparatively more environmentally friendly carbon dioxide CO _{2 will be} replaced. Since the use of CO _{2 has} a higher pressure in the heat pump circuit of the air conditioner, the use of flexible metal pipes is currently being tested as an alternative to reduce the leakage losses, which should withstand about four times the pressure compared to rubber hoses.

Furthermore occurs even in such air conditioners in addition to systemic leaks, the risk of leakage. In the event of a defect, leakage of the refrigerant into the passenger compartment can never be ruled out. In contrast to other refrigerants, CO _{2 is} always present in the natural air composition and is therefore fundamentally harmless within certain limits. Also, CO _{2 is contained} in the breath of all living things. However, at concentrations of 1 to about 4% in an air mixture generated by additional refrigerant leakage, a driver may not notice the deterioration in air quality and become fatigued. It may even become unconscious due to the toxicity of CO ₂ . These effects do not occur when using previously used, but climate-damaging refrigerant. For safety reasons, it is therefore necessary to provide a reliable CO ₂ sensor in each passenger compartment of a motor vehicle provided with a CO ₂ -driven air conditioning system. Such a CO ₂ sensor has to monitor the air composition, in particular with regard to the CO ₂ content. If exceeded ei Safety and countermeasures, such as short-term opening of the windows, adding fresh air via the air-conditioning system itself and / or issuing a warning as information to the driver, are automatically to be taken at a predetermined level.

Since CO _{2 has} chemically almost inert properties, its concentration is not using simple gas sensors, such as. As Lundström-FET or semiconducting metal oxide sensors to detect. Essentially, an absorption measurement in the infrared region of the CO ₂ characteristic wavelength of 4.2 μm is used. However, such measurements require undisturbed by condensation or fog beam path to provide reliable measurement results can.

As shown in the picture of 1 a structure is proposed with which a condensation of the optical channel or beam path is detected at low cost for the early initiation of countermeasures. The device 1 comprises a substantially elongated sample carrier 4 , in which the gas mixture to be examined or here the air 5 is arranged independently and substantially continuously interchangeable. The sample carrier 4 is at an open end area 7 with a reflector 8th and at a second open end area 9 with a transmitter 10 and a receiver 11 locked. This structure is one of the transmitter 10 emitted infrared or IR radiation on their way to the receiver 11 forced the sample carrier 4 to go through twice. According to Bouger-Lambert-Beer's law, often referred to as Lambert-Beer's law, there is one between broadcasters 10 and receiver 11 to be measured absorption of IR radiation by a particular substance on the concentration of this absorbing substance and on the distance traveled by the radiation in the sample carrier dependent. Due to the selected structure of the sample holder 4 with reflector 8th So an improved sensitivity to a sample carrier is achieved with end sides opposite transmitter and receiver units by doubling or multiplying the free path.

The gas mixture or the air 5 in the sample carrier 4 is slowly exchangeable in a structurally adjustable way. These are openings 13 in the sample carrier 4 outwardly through a shell 14 covered by a membrane, such as. B. semipermeables stretched polytetrafluoroethylene. Such film are z. B. from technical measures for producing a pressure equalization and is available with adjustable parameters. This is the interior of the sample holder 4 on the one hand, on the life of the device 1 protected against contamination, on the other hand, an adjustment of the in the sample carrier 4 contained sample of the air-gas mixture 5 is guaranteed to a respective composition in the passenger compartment.

In the embodiment of 1 is the sample carrier 4 divided into two with respect to their central axis aligned parallel cavities: In the sample carrier 4 is in a reference channel 15 a humidity while cooling the reflector 8th on the windshield 2 and in a measuring channel 16 the composition of the air 5 or the content of a component of the air is measured with substantial thermal insulation. This is the reflector 8th divided into two and only in a region A to form a Betauungssensors with a windshield 2 thermally coupled. In the other area B is the reflector 8th opposite the windshield 2 thermally insulated. This is to ensure that a Betau always always first in the reference channel 15 or on its reflector element 8th , Area A, occurs before it is in the measurement channel 16 can occur. Now find in the reference channel 15 condensation takes place, the amplitude of the reception sensor for the reference channel drops sharply. This information is evaluated in a manner not shown taking into account each prevailing ambient temperature and provided via an interface to the air conditioner available. By activating the blower countermeasures can be initiated in the form of a "defrost ventilation". Optical or capacitive sensors, which are usually additionally used as stand-alone sensors for detecting condensation, can thus be dispensed with.

The reflector 8th is also in the area A, B for focusing or focusing the radiation on the respective receiver 10 educated. This can be an associated receiver sensor 11 or detector designed to be small. Due to the bundling, an increased sensitivity is achieved. In addition, it is independent of the material of the sample carrier 4 a coupling of reflected radiation from the reference channel 15 into the measuring channel 16 and vice versa largely excluded.

According to the embodiment of 2 is the device 1 as a gas sensor designed so that the sample carrier 4 has only a single channel. These are at the free end 9 of the sample carrier 4 the transmitter 10 and the receiver 11 no longer spatially one behind the other, but arranged side by side. Further, in front of the receiver 11 or detector sensor a filter 18 arranged to select the wavelengths of the receiver 11 incident reflected radiation is used. This allows a broadband receiver working 11 also be designed as a low-cost semiconductor element. The required selectivity of the system is through the filter 18 reached.

Corresponding filters 18 are also in the embodiment of 1 already in front of each of the two recipients 11 provided separately for the reference channel 15 and the measuring channel 16 are provided. In an alternative embodiment of the invention not shown, the filters 18 in front of broadband stations 10 arranged to select a specific frequency band. This is also achieved here that cheaper components lower narrowband and reduced spectral purity can be used. Of course, the transmitters 10 with the receivers 11 for adding the effects described above, each in common with only one filter 18 be provided.

In the embodiment of 1 are the filters 18 for the reference channel 15 and the measuring channel 16 set differently: in the measuring channel 16 becomes a CO ₂ content of the air 5 determined by absorption measurement in the wavelength range of 4.2 microns, while in the reference channel 15 A humidity measurement is performed that is about the water content of the air 5 in a wavelength range of 1.4 microns and / or 1.9 microns or in the case of condensation on the reflector 8th can be performed at 4.2 microns.

So that both measurements in the device 1 to 2 can be performed before the sensor 11 and / or the transmitter 10 at least one filter 18 arranged, electrically via contacts or electrical lines 19 is adjustable in its optical properties. As a result, a wavelength of 4.2 μm in the filter can then be used to examine a respective CO ₂ content 18 be set, wherein temporally preceding or subsequently a water content of the air 5 by absorption measurement in a wavelength range of 1.4 microns and / or 1.9 microns is determined. By a voltage-controlled adjustment of the optical properties of the filter 18 over the respective electrical lines 19 So the complexity of the structure of the entire device 1 significantly reduced. Of course, with reference to the figures, the two are the 1 and 2 described devices 1 Also combined with each other, for example by the reference channel 15 the device 1 from 1 according to the embodiment of the 2 is formed with the result that a moisture determination is redundant.

Across all embodiments of the invention is a device according to the invention 1 designed to extend the radiation path with focused on the respective sensor reflection and thus has a high sensitivity. The receiver-sensor element itself can consist of a semiconductor element that is particularly sensitive in the infrared range, such as a semiconductor diode. In the present embodiment, the sensor element 11 but designed as a thermocouple, namely in the form of so-called. Thermopiles, pyroelectric sensors or bolometers.

A selection of certain frequency bands in the IR range is determined by tuning the upstream filter 18 and / or the radiation transmitter 10 performed. This principle is also applicable to the measurement of other gas constituents by a compact device 1 applicable.

1

contraption

2

Windshield

4

sample carrier

5

air

7

first end

8th

reflector

9

second end

10

transmitter

11

receiver

13

opening

14

shell

15

reference channel

16

measuring channel

18

filter

19

electrical Contacts / lines

A

Area

B

Area

Claims (14)

Method for measuring at least one constituent of a gas mixture, in particular of the air in a passenger compartment of a vehicle, in which the gas mixture penetrates into a sample carrier and the gas mixture in the sample carrier is penetrated by radiation in an infrared range from a transmitter, the radiation subsequently detected in a receiver and the result is finally evaluated, characterized in that the radiation the sample carrier ( 4 ) from the transmitter ( 10 ) to a reflector ( 8th ) and then from the reflector ( 8th ) again through the sample carrier ( 4 ) through to the receiver ( 11 ) substantially completely passes twice, wherein the reflector ( 8th ) with a heat sink, in particular a window or a windshield ( 2 ) is thermally coupled. Method according to the preceding claim, characterized in that the radiation from the reflector ( 8th ) to the recipient ( 11 ) is focused or focused. Method according to one of the preceding claims, characterized in that the gas mixture in the sample carrier ( 4 ) in adjustable white time is slowly exchanged. Method according to one of the preceding claims, characterized in that the radiation after leaving the transmitter ( 10 ) and / or before impacting the recipient ( 11 ) is optically filtered in at least one way. Method according to the preceding claim, characterized characterized in that at least one optical parameter of the filtering is set electrically, in particular for selective wavelength adjustment a subsequent measurement. Method according to one of the preceding claims, characterized in that the transmitter ( 10 ) is electrically tuned in its radiation frequency, in particular temporally in steps over a predetermined range and / or certain frequency points away. Method according to one of the preceding claims, characterized in that temporally parallel or successively humidity and CO ₂ content of the gas mixture in one or more channels ( 15 . 16 ) of the sample carrier ( 4 ) are measured. Method according to one of the preceding claims, characterized in that in the sample carrier ( 4 ) in a reference channel ( 15 ) a humidity while cooling the reflector ( 8th ) on the windshield ( 2 ) and in a measuring channel ( 16 ) the air ( 5 ) under extensive thermal isolation with respect to at least one constituent. Device for measuring at least one constituent of a gas mixture, in particular of the air ( 5 ) in a passenger compartment of a vehicle, in which the gas mixture to be examined is autonomously and substantially continuously exchangeable in a substantially elongate sample carrier ( 4 ), the sample carrier ( 4 ) with a transmitter ( 10 ) for the penetration of radiation in an infrared range and with a receiver ( 11 ) for detecting the radiation and is connected to means for evaluation, characterized in that the sample carrier ( 4 ) at an open end area ( 7 ) with a reflector ( 8th ) and at a second open end area ( 9 ) with a transmitter ( 10 ) and a receiver ( 11 ) is closed in such a way that the radiation on its way from the transmitter ( 10 ) to the receiver ( 11 ) the sample carrier ( 4 ) passes twice and the reflector ( 8th ) for forming a dew sensor with a window or a windshield ( 2 ) is thermally coupled. Device according to the preceding claim, characterized in that the reflector ( 8th ) for focusing or focusing the radiation on the receiver ( 11 ) is trained. Device according to one of the preceding claims, characterized in that in front of a receiver sensor ( 11 ) and / or a transmitter ( 10 ) at least one filter ( 18 ), which is preferably electrically adjustable in its optical properties. Device according to one of the preceding claims, characterized in that in the sample carrier ( 4 ) a reference channel ( 15 ) for determining a humidity while cooling the reflector ( 8th ) on the windshield ( 2 ) and a measuring channel ( 16 ) for measuring one in the air ( 5 ) gas component is provided with extensive thermal insulation. Device according to one of the preceding claims, characterized in that the gas mixture ( 5 ) in the sample carrier ( 4 ) is temporally slowly replaceable in an adjustable manner, in particular by opening ( 13 ) in the sample carrier ( 4 ) to the outside through a material ( 14 ) are covered. Device according to one of the preceding claims, characterized in that the device ( 1 ) is formed as an optical gas sensor for at least one gas with a combined condensation detector.