MINIATURE SPECTROMETER EMBARKS IN A MOTOR VEHICLE HAS DETECTING OF MEASUREMENT AND DETECTOR OF REFERS SINGLE

The present invention relates to the field of electronics on board motor vehicles. More specifically, the optoelectronic equipment. More specifically, it touches in spectrometry adapted to determining composition of a fluid.

The competition between the various automobile designers causes a search without renewed improved operating performance, mileage consumption degree and ecological characteristics. In the field of vehicles powered by an internal combustion engine, the composition of the fuel has a direct impact on engine performance. Therefore, the precise knowledge of the fuel composition provides for certain operating parameters of the engine to improve combustion and reduce pollution of the vehicle.

Furthermore, this knowledge may also detect false manipulations (filling a fuel tank with diesel or vice versa) potentially damaging to the engine, and prevent the driver, or of blocking the ignition to avoid irreparable damage. Similarly, detecting a non-legal meets the standards for quality.

Analogs The remarks apply to the engine oil, or the cooling liquid or other fluids whose properties effect the operation of the vehicle.

One means achieve this composition analysis of a fluid is to use technology spectrometers.

The biases that a spectrometer is a measuring instrument for determining the absorption of certain wavelengths of the spectrum (general light) by a sample to be analyzed. The wavelengths absorbed form peaks in the absorption spectrum, and characterize certain molecules or components present in the sample.

As defined in the scope of the present invention, an optical spectrometer is thus comprised mainly of a light source, of an optical assembly for shaping the light beam to form a parallel beam capable of passing through the sample, a wavelength filter for measurement in a certain wavelength range, and a light detector for measuring the intensity of light received in the wavelength.

Spectrometers working in the fields of light wavelengths ultraviolet, visible and near infrared are already in use on a daily basis in many fields. Among these domains include:

food technology (for example for monitoring the moisture content of the cereal grains, maturity fruit, grease in certain food, etc)

the biomedical (for example measurement of the blood sugar level without extraction, etc)

the production of fuels (monitoring the quality and the composition of the crude, quality control of the final products such as gasoline and diesel, etc)

All these fields of application use the same type of measuring instrument, whereof only vary the characteristics of size and portability. Such instruments, optionally using different technologies (Fourier transform, Filter, monochromator, diffraction gratings, etc), does not operate over a range of large temperature variation.

Indeed, for reasons related to the drift of their performance according to the temperature, they have rarely been used in environments having high temperature variations.

The are often laboratory-type equipment, or in any case requiring easy access to components thereof for maintenance of the sensor or of the light source (in which the service life is often short, and, in any case, lower than the fortnight of years required in the medium vehicle-mounted). Therefore, they are unsuitable for long-term installation in an environment substantially inaccessible for maintenance.

Finally, these spectrometers are not subjected to constraints, unit cost of production, and hence utilize often high-end components, e.g. lamps Tungsten halogen or filament, temperature-stable, but that are incompatible with a mass installation in motor vehicles.

Been that the questions, temperature drift, of reliability of the components, and therefore access for maintenance, and finally manufacturing cost, make these commercial spectrometers unsuitable for use in environments comparable to the automobile.

In an application such as domain control of automobile fluids, it is necessary to use components to very low unit cost and robust in time, so as to ensure continuous operation. One solution is to use as a light source light emitting diodes (LEDs, acronym to "Light Emitting Diode").

In effect, the light emitting diodes are components well known, highly reliable, very low cost because used in very high volume for a multitude of applications. They are today available in multiple versions of wavelength, for their use in a domain spectrum 300 nm (near ultraviolet) to 2500 nm (near infrared).

As shown on Figure 1, the LEDs typically have a large enough spectrum characterized by a full-width mi-height of 35 nm to more delOOnm. Therefore, it is possible, by using a combination of different characteristics more diodes, source has an emission spectrum very wide.

The characteristics of emission spectrum and optical power of the LEDs may vary significantly according to the current flowing therethrough, and the ambient temperature at which they are used (Figures 1.2, 3 and 4 for one example of measured value on a light emitting diode to 650 nm). Or the interpretation of the absorption measurement requires precisely detect the intensity at a given wavelength, of the light wave sent through the sample analyzed.

Their use as a light source for spectroscopy, in environments in which the temperature can vary significantly (e.g.

-40 °C to + 105 °C in automobiles), requires innovative solutions to compensate for the natural variation of their characteristics. More generally, these remarks all light sources of variations in performance with aging and temperature.

Are known spectrometry devices at low cost using a technology based on light emitting diodes. A plurality of such devices are currently proprietary and marketed.

One such device is sold by Zeltex and described in the Patent US 6,369 388 B2. It is a portable spectrometer working in the near infrared primarily intended for use in quality analysis of harvested seed. Various applications are contemplated for the device, from the biomedical field to food technology and fuels.

Applications proposed for the device, it is mentioned a measure of octane rating of a gasoline from a discrete spectrum obtained by measuring the absorption to 14 different wavelengths, this constraint corresponding to a legal standard quality of fuels distributed in the American service stations in a state.

The spectrometer Zeltex uses the same absorption measurements in its different uses, thus independently of the type of sample analyzed.

The operating temperature range providing a measure of reliability guaranteed ranges from to +55°C -20°C. Such operating range is incompatible with use by in-car, for which the sensors are to be sized for temperatures between -40 °C and + 105 °C.

Two methods are disclosed in the Patent US 6,369 388 B2 to account for the effect of the temperature.

A first proposed method uses a compensation of the measurement results spectral absorption according to the temperature measured by a sensor, and a compensation logic pre-stored. This method does not sought to combat the deformations or drift components related to the temperature, but to correct the measured values according to a predetermined correction curve.

A second method in the frame of the Zeltex uses a self calibration of the spectrometer. Are to be a true compensating variations in temperature and aging of the components of the measuring chain, and particularly light-emitting diodes.

In this method, prior to each acquisition of spectrum measurement, the measuring cell is emptied, a first measurement is performed with the light source off (light measuring 0) that characterizes the measurement noise due to electronics and sensor, which varies with the environmental conditions and the time. Then a second measurement is performed with the light being lit, always without sample in the cell, providing a measure of light 100, also impacted by the environmental conditions of the measurement.

These two successive measurements enable self-calibration of the spectrometer. But the stress of having to empty the cell in such a procedure is not compatible with an in-vehicle use, for example, and as easily designed, in the case of an installation permanently in a fuel tank or in the fuel distribution circuit.

Another device, designed and manufactured by the company Rikola , relates to a spectrometer for laboratory use. The spectrometer can also be implemented in an environment the temperature of which varies between 5 and 55 °C, too narrow to the constraints of the motor medium.

It provides a measure of the absorption for 32 wavelengths determined. For this purpose, it uses a wavelength filter monochromator type, source side of the spectrometer, and consisting of a diffraction grating and 32 of light emitting diodes (LEDs). These LEDs are placed at points selected for obtaining the desired wavelengths.

In account for best mimic the effect of temperature variations on the components of the spectrometer, and, leaving, on the quality of the measurements provided, the device of the company Rikola permits the light to light 0 and 100, without the presence of the sample to be analyzed. A calibration of the apparatus is thus obtained.

However, a temperature change results in a significant deformation of the materials and thus movement of the light emitting diodes, which causes a change in the wavelengths created by the array assembly and light emitting diodes.

Therefore, the spectrometer uses a Peltier device to provide a satisfactory measuring accuracy in the temperature range considered, of 5° to 55 °C, by controlling the temperature of the grating and light emitting diodes around 30 °C. This limits the conditions of use that are possible for the spectrometer.

Furthermore, and unlike the preceding device, the spectrometer is not associated with a processing algorithm of the measured spectrum.

A third spectrometer existing low cost has been developed by the company Sentelligence , and is for example described in the document W0 2003 030,621 A2.

The spectrometer, for mounting, is formed as an integrated component comprising a light source in the form of light emitting diodes, an optic having a frustoconical placed in contact with the sample to be analyzed, and a detector disposed substantially in the plane of the light source.

It enables the measurement of the absorption for different wavelengths. This is different from a spectrometer in transmission for the other two spectrometers as mentioned, but a spectrometer by reflection. It therefore useful for characterizing of the components in the sample a measurement of the reflection spectrum of said sample subjected to a known light source, and without its absorption spectrum. A selection technology in reflection spectrometer is envisaged for products relatively opaque, highly absorbent light rays (soot etc).

The light source is formed by a combination of light emitting diodes each selected according to one of the wavelengths which it is desired to measure the reflection by the sample to be analyzed. Filters installed on the side of the light source, to limit the beam which passes through the test sample to a certain band of optical wavelengths, and the level of the emission intensity is optionally controlled by a photodiode (reference detector), placed on an optical path independent of the sample to be analyzed.

The light measurements 0 (light-up for measuring the electronic noise) and light 100 (light being lit) can be performed without that the sample to be analyzed is removed from the measuring cell.

This is carried out by correcting the measured intensity on the photodiode to calculate an intensity that theoretically would receive the measuring sensor, if the sample was absent.

By allowing a calibration of the measuring sensor by a reference detector is not influenced by the sample to be analyzed, and in order to take into account a drift of the light source, for example according to the temperature, the system is compatible with an application within the field of the measurement in a harsh environment.

However, such a mass spectrometer has its cost determined by the number of light emitting diodes installed, which is directly related to the number of wavelengths to be measured. If this number is substantially greater than six, it becomes too expensive for installation on a vehicle.

Additionally, a source created by juxtaposition of a large number of light emitting diodes can no longer be considered point, resulting in errors of measurement sensors (problem of parallax).

Furthermore, the device of the company Sentelligence is to be adapted during the design to each particular application, thereof require measurements at certain wavelengths specific to the type of sample to be analysed.

These spectrometers do not allow for high-precision spectral measurement as required by some applications in the automotive field, i.e. for example a measure of the absorption at a given wavelength ± 5 nm with an accuracy of 1% on the absorption value given. They do not use on a wide temperature range.

These various restrictions make them unsuitable for use in embedded applications on motor such that the measurement of the chemical composition of a fuel or its properties accurate combustion.

The invention presented to, therefore, to provide a concept of mini spectrometer responsive to size constraints, of reliability and performance compatible with applications of the automotive type.

A second object of the invention is to allow an inexpensive realisation realistic rendering its use on motor vehicle.

A third goal is to provide an on-board spectrometer operable to more applications to different fluids, without hardware modification.

To this end, the present invention relates, firstly a device for measuring a spectrum of a light beam, in a wavelength range of preselected, said spectrum is generated by a sample to be analyzed, the measuring device comprising:

at least one light source,

a measuring cell,

a measuring sensor placed on a measurement optical path, said measurement optical path is achieved by a optical measurement beam from the light source and meeting with the measuring cell, means for self-calibration to account for possible drift of the light source, due to environmental conditions or use, independently of the presence or absence of a sample to be analyzed into the measuring cell, said means for self calibration comprising:

o means create a reference optical path, through which a optical reference beam, from the light source and does not encounter the measuring cell,

o a reference detector.

The measurement device is remarkable in that it is designed to be installed on board a motor vehicle and that it comprises means for selectively mixing the optical measurement beam and the optical reference beam and in that the measuring sensor also acts as a reference detector.

Preferably, the device measures an absorption spectrum of the light beam by the sample to be analyzed.

In another embodiment, the device measures a reflection spectrum of the light beam by the sample to be analyzed.

In a preferred embodiment, the device also comprises at least one wavelength filter associated with the reference detector, said wavelength filter is a variable filter Fabry-Perot interferometric cavity.

Advantageously in this case, the device also comprises means of transforming the light beam from the light source into a parallel beam.

In a particular embodiment, the measuring cell comprises means for returning the optical measurement beam in a direction substantially opposite its original direction.

According to an advantageous embodiment, the means for returning the optical beam for measuring comprises two facets, oriented at 90° from each other, placed on a side face of said measuring cell.

In the case of an absorption spectrometer, advantageously the facets form a generally concave surface within the vein for circulating fluid in the measuring cell and are mirrored by metallization.

In the case of a spectrometer in reflection, the facets form advantageously surface within the vein for circulating fluid in the measuring cell, and are transparent in the wavelength range of interest.

Been that this arrangement corresponds to the special case of reflection for spectrometer which the light beams reflect simply on the sample locking of the reference beam,

measuring, for each selected wavelength, by the detector for measuring the intensity of light received in the wavelength,

and, at predetermined intervals,

o passage of the reference beam and mixture in the second divider, o measuring, for each selected wavelength, by the detector for measuring the intensity received in the combined light wavelength,

transmitting to the computer measurements of the absorption spectrum of the fluid to be analysed and measurements of the combined spectrum,

comparison by the computer of the measurement and the combined value,

determination by the computer absorption due to the sample contained in the measuring cell,

determining, based on a calculation logic or a chart stored in memory, by the computer, at regular intervals, changes of engine operating parameters.

Been that the functions of the computer are realized either by the engine control, or by electronics associated with the sensor-the transmission to the motor computer then directly corresponding to the value of the parameter of the fluid.

The invention also relates to software adapted to perform the method set forth.

The aim of the invention is under yet another aspect a vehicle using a device as set forth, or a process as set forth.

Goals and advantages of the invention will become better understood upon reading of the description and drawings of a particular embodiment, given by way of non-limiting example and for which the drawing is:

figure 1 illustrates the spectral characteristics of a light emitting diode (LED) as a function of the temperature, by highlighting the offset of the emission spectrum in wavelength and transmit power;

figure 2 illustrates the wavelength shift peak of a light emitting diode according to the temperature and the current flowing through the light emitting diode;

figure 3 illustrated the same peak width at mi-height of the spectrum of the light emitting diode according to the temperature and the current flowing through the light emitting diode;

figure 4 shows the emitted light power according to various values of current through the light emitting diode between -40 °C and about + 95 °C;

figure 5 is a schematic representation of a spectrometer for functional mini environment difficult in the invention, in plan view;

figure 6 is a view in isometric perspective of the same spectrometer;

figure 7 illustrates schematically the operation of the spectrometer, in the case where the shutter is opened;

figure 8 illustrates the emission spectra of three light emitting diodes different in the near infrared (700,1050 nm);

figure 9 illustrates the addition of the three normalized spectra of Figure 8;

figure 10 illustrates the integration of a spectrometer of the invention on a fuel circuit of motor vehicle;

figure 11 illustrates schematically the principle of design of a detector combined with a filter activatable on command.

As shown on Figure 10 in the case of application of a device for measuring absorption spectrum according to the invention to a fuel system of an automotive vehicle, such a mass spectrometer 1 can advantageously be provided on a fuel pipe 2, downstream of the reservoir 3 and the fuel pump 4, also downstream of the fuel filter 5 (to reduce measurement errors), but upstream of the injection pump 6 and the motor 7.

The spectrometer 1 is connected to a control computer 8, which is also connected to the injection pump or to the motor which it is capable of driving individual adjustments. Note that the control computer 8 may be either the motor computer, conventionally present in motor vehicles, is an electronic control of the spectrometer, which sends directly to the motor computer the values of the parameters of the sample fluid.

The device according to the invention is as shown in Figures 5 to 7.

The spectrometer 1 according to the invention is arranged about a measuring cell 9 in which the fluid circulates to be analyzed, such as fuel.

Is defined for the rest of the description a longitudinal axis X corresponding to the direction of circulation of the fluid in the measuring cell 9.

The load cell 9 is herein shown in the form of a tube segment of rectangular cross-section (Figure 6), oriented substantially along the longitudinal axis X.

It comprises on one of its two side faces (left side in Figure 5) two glass panes 10, coplanar 11, rectangular, and substantially identical dimensions.

These can be produced for example glass or plastic, their material to be chemically neutral to the sample fluid, dimensionally stable as a function of the temperature, and transparent in the wavelength range used to measure (herein the near infrared, but wavelength ranges U-V./ visible are also usable, without modification of the device).

The attachment of the panes 10, 11 in the wall of the measuring cell 9 is made by gluing or otherwise known means.

Is defined for the rest of the description a transverse axis Y normal to the two glass panes 10, 11.

On the side opposite side (right side in Figure 5), an area of reflecting light, comprising two reflective facets 27, 29, oriented at 90° from each other enables returning an incoming light beam by a first window 10 (thus in a direction oriented according to the axis-Y), to the second pane 11 (in a direction along the axis + Y). The two reflective facets 27, 29 are in the present example formed from planar surfaces, oriented to the first to 45° in the XY mark, and for the second to 135° in the marking.

They are separated by a facet 28, substantially planar and parallel to the longitudinal axis X.

The two reflective facets 27.29 are sized to return entirely a light beam emerging from the first pane to the second pane 11 10.

Their reflective character is, in the present invention, obtained by polishing and local metallization of the surface (for example by chromium) forming the side face of the measuring cell 9, process which is carried out by means known to those in the art. These facets can also be formed by a bonding of mirrors on the faces oriented at 45° and 135 °, or by any other suitable means.

The measuring cell 9 is made of metal or rigid plastic, so that the two glass panes 10, 11 remain coplanar independently of environmental conditions (in particular temperature), and that the two reflective facets 27, 29 remain oriented at 90° from each other, in order to maintain the path of a light beam passing through the measuring cell 9, and thus in order to avoid the creation of measurement errors.

The measuring cell 9 is connected at its two open ends, by means known to those in the art, to a circulation line for pre-existing fuel in the vehicle.

To perform the measurement of absorption spectrum, the two glass panes 10, 11 are penetrated, and the fluid contained in the measuring cell 9, by a light beam, which is reflected in the reflecting facets of the measuring cell.

The light beam is created by a light source 12, whose emission spectrum naturally corresponds to the wavelength range of interest for the fluid to be analyzed.

Here in no way limiting, the light source 12 is formed of three light emitting diodes (LEDs) arranged in the triangle and tighter possible, on a same support, perpendicular to the transverse axis Y (facing the measuring cell 9), so as to minimize the offsets linked measurement to the distance between the three light emitting diodes.

Their emission peaks are located respectively around 850 nm, 950 nm and 900 nm. As shown on Figure 8 that illustrates the emission spectra respective 25 °C, each one light-emitting diode has an emission spectrum extending to mi-height to about 100 nm.

The superimposition of the three spectra, shown in Figure 9, shows the spectrum equivalent to the complete source. The light source 12 effective to cover a wavelength range of 825 to 975 nm (near infrared).

It is clear that other diodes can be used, or for the evolution of the technique with diodes low unit cost but wider spectrum, either for the purpose of creating a spectrum in another wavelength range.

Been selected that the light-emitting diodes are commercial products, very low unit cost. It has thus created a light source 12 equivalent, based on existing components and very inexpensive, in order to minimize the overall cost of the spectrometer 1. Furthermore, the light emitting diodes are known to have a life (duration before the transmit power has been divided by two) of several tens of thousands of hours, thus compatible with the lifetime requested to-board equipment on motor vehicle.

These three light emitting diodes, whose combined power does not exceed a few tenths of a watt, are energized by known means and not detailed herein.

The light beam created by the light source 12 is generally conical, set angle by the LEDs selected, and in this example the order of a few tens of degrees.

This beam is optionally restricted to a circular beam (or shape preselected) of smaller width in the space, by a diaphragm, for example a mechanical device of known type.

After passing through the diaphragm, the light beam, conical always there, is transformed into a parallel beam, of cylindrical section, by a collimating lens 14. The collimator lens 14 is of the type known (such as plane/convex) and can be made of glass or plastic material of good optical quality in the wavelengths being measured. Its dimensions as to enable creating a beam of one to several tens of cm² .

The collimating the light, which renders its parallel rays, is particularly useful for the quality of the measurement, particularly in the case of using technology type "interference filter", it will be shown further.

The spectrometer according to the invention comprises, downstream of the collimating lens 14, a beam splitter 15, for separating the light beam (shown by the segment 32 in Figure 7) in, on the one hand, a measuring beam according to a measurement optical path cm, parallel to the transverse axis Y (segment 33 in Figure 7), and, on the other hand, a reference beam according to a reference optical path CR, generally parallel to the longitudinal axis X (segment 39 in Figure 7).

The beam splitter 15 is an optical component allowing example 50% of the light and reflecting 50% in a direction at 90° relative to the original beam. It is such as optical cube having on its diagonal plane, oriented at 45° in the XY mark, a half mirror 16. It has thus created herein two beams, considered to be same spectrum (wavelengths and transmit power in each wavelength). The light transmitted through the mirror is directed to the measuring cell 9. Its mode of manufacture is known to those skilled in the art and therefore not detailed herein. It may also be a birefringent mirror.

The beam splitter 15 is placed immediately adjacent to, or directly in contact with the first pane 10 of the measuring cell 9 to minimize the path of the optical beam out of the fluid of interest.

The measurement beam, as shown clearly in Figure 7, through the first window 10, a thickness of the fluid to be examined which depends on the width/of the measuring cell according to the transverse axis Y and the distance d between the ends of the reflective facets, according to formula 2 /+ d.

After this optical path (shown by the segments 34, 35 and 36 in Figure 7 for a ray of light situated at the centre of the beam) within the sample fluid in the measuring cell 9, the light beam spring of said measuring cell 9 through the second pane 11. Upon path within the sample fluid, certain wavelengths of the emission spectrum of the light source 12 are attenuated due to the absorption of photons of these wavelengths by molecules present in the fluid.

The measurement beam, whose spectrum is modified by the fluid flow therethrough, and from the measuring cell 9 according to the transverse axis Y, flows through a second beam splitter 31, placed immediately adjacent to, or directly in contact with the second glass sheet 11 of the measuring cell 9 is again to minimize the path of the optical beam out of the fluid of interest.

The second beam splitter 31 herein is for mixing the measuring beam that has seen the measurement optical path cm (segments 33 to 37 in Figure 7), and the reference beam that has seen a reference optical path CR (segments 39 and 40 in Figure 7) in a single light beam (segment 38 in Figure 7).

The second beam splitter 31 is an optical component similar to the first beam splitter 15, allowing example 50% of the light and reflecting 50% in a direction at 90° relative to the original beam. It is such as optical cube having on its diagonal plane, oriented at 135° XY in the reference frame, a half mirror 41.

The includes that the second beam splitter 31 is disposed at the intersection of the measurement optical path cm and the reference optical path CR. In the present example It is aligned with the first divider 15 according to the longitudinal axis X. The distance between the centers of the semi-reflecting mirrors 16, 41 is substantially equal to the distance between the centers of the reflective facets 27, 29 of the measuring cell 9.

The device also comprises, placed on the optical path of reference CR between the two beam splitters 15, 31, a beam shutter 30 of a type known per se and activatable on command by electrical means. The beam shutter 30 aperture passes or not the reference beam (segment 39 in Figure 7) to the second beam splitter 31 (segment 40 in Figure 7 when the shutter 30 is open), and, in a controlled manner.

The shutter is an electromechanical actuator or electro-optical (e.g. liquid crystals), the selecting is for example, according to the environmental conditions in which the spectrometer is to be used.

The light beam 38, from the second beam splitter 31, and comprising either the single measurement light beam, and the combination of the measuring and reference beam, is finally picked up by a measuring sensor 17 equipped with a wavelength filter.

The filters are in the preferred embodiment and described herein, Fabry-Perot interferometric cavities-and in which case the wavelength capable of the bushing is, in a known manner, dependent on the width of the cavity thus the angle of attack of the light rays. Been that it is desirable, for accurate measurement, that the light rays are actually parallel. This justifies the use of the collimating lens 13.

The measuring sensor 17 is equipped with a variable filter 26, Fabry-Perot cavity for example, of the type presented in the document " Infrared dectector Tunable with Integrated micromachined Fabry-Perot filter (Neumann, Ebermann, Hiller, Kurth, MOEMS jan 2007), and shown in Figure 11.

The measuring sensor 17 is placed on the measurement optical path cm in output of the variable filter 26. It is a pyroelectric type in the present example, and thus, has a very short response time, but it can be replaced by a filter type LVF (of the acronym English "Linear Variable Filter") or by one or more optical filters associated with a CCD array (of the acronym English "charge Coupled Device") or CMOS (of the acronym English "conventional Complementary Metal Oxide Semiconductor").

In operation, if the computer 8 associated with the spectrometer 1 has been initialized for a type of fluid to be analyzed (selecting wavelengths to be observed), the computers causes ignition of the light source 12 at regular intervals, the spacing has been previously selected.

After a time adapted to take account of the normal operation of said light source, the computer controls the potential difference between the plates of filters Fabry-Perot interferometric (or pilot the means for varying the value of the variable filter) to adjust said filters successively on the different wavelengths forming a series necessary for determining the composition of the sample fluid, these wavelengths is previously stored in a memory of said computer 8.

The calculator 8 then causes closing of the shutter 30, and thus the locking of the reference beam along the optical pathway CR. Only the light beam passing through the measuring cell 9 is collected through the measuring sensor 17.

For each wavelength A selected, the measuring sensor 17 outputs a measure characterizing the light intensity received in that wavelength. The spectrometer 1 transmits at regular intervals to the computer 8 measurements of the absorption spectrum of the fluid to be analyzed.

The measurement is then defined by the equation

lreceiver_ob (A) ~ A IlED (4) Ctp_ue i (A) (EQ.1)

wherein:

A is the attenuation experienced on the measurement optical path cm flowing through the segments 32 to 38 (loss due to the collimating lens 14, to the beam splitter 15, to the measuring cell 9, the second beam splitter 31).

A is the wavelength of interest,

has_Fue i₍ A) is absorption of a known thickness (21 + d) of the analyzed fluid in this wavelength,

Iled (A) is the intensity of the light source in this wavelength,

læceiver_ob (λ) is the intensity measured by the detector in that wavelength.

Furthermore, at predetermined intervals,

The calculator causes the opening of the shutter 30, and thus the passage of the reference beam along the optical pathway CR reference, and subsequent mixing in the second divider 31 with the measurement beam along the optical pathway measuring cm,

At this time, the measuring sensor 17 relates to, for each wavelength λ selected, the combined light intensity received in this wavelength, and transmits the intensity measurement to the computer 8.

This measure is then defined by the equation

Ireceiver_Nob (λ) = A IlED (λ)* 0*_Fue i (λ) + B * l_LED (λ) (Eq. 2)

wherein:

A is the attenuation experienced on the measurement optical path cm, and B is the attenuation experienced on the reference optical path CR (path not passing through the sample fluid) through the segments 32, 39, 40, 38 (loss due to the collimating lens 14, to the beam splitter 15, the second beam splitter 31),

Note that the influence of the temperature and the aging is a priori negligible on the attenuation values A and S, which are known as manufactured the spectrometer and remain fixed in time.

The calculator 8 compares the measurement value and the combined value and derives, by first subtracting the two equations the term B * l_LED (λ), and thus, B being known, the luminous intensity provided by the light emitting diode in said wavelength in these environmental conditions and aging the LED, and then, by reintroducing that intensity on the equation Eq 1 absorption. has_Fuel( A) due to the sample contained in the measuring cell 9 for said wavelength in these environmental conditions.

Based on a calculation logic or a chart stored in memory, the computer 8 determines, at regular intervals, of changes of parameters of operation of the engine 7, for example according to the fuel suitable for operation of the engine, controlling the spark advance, injection variation andc.

The processing of the signal from the spectrometer according to the invention exits the frame of the present invention, and thus is not further detailed herein.

The first advantage of the spectrometer according to the invention is the use of a single detector used for both the reference beam, and for the measuring beam, through the use of a reflector in the cell, and a beam shutter on the reference optical path.

This enables a decrease in the cost of the sensor, the sensor associated with its variable filter one hand very significant component of the overall cost of said sensor. Furthermore, this design provides increased performance since the two signals (+ measuring and reference measurement) which are compared are measured by the same sensor, thereby eliminating systematic errors due to the detector optionally. Finally, the electronic control of the sensor is also simplified, since it controls a single sensor instead of two, thus contributing to trust the system and lower a cost.

A second advantage of the device is to group the optical and optoelectronic components on the same side of the measuring cell. Therefore, the spectrometer may be organized into two separate functional blocks. Furthermore, this realizes electronic card smaller dimensions, one of the faces of the measuring cell requiring no connection.

A third advantage of the present invention is the use of a reference optical path. This compensates for the effects of aging and changes in environmental conditions of on the diodes constituting the light source. Furthermore, the measuring cell does not have to be emptied for obtaining a reference measure, which can be performed at any time.

Applications can be considered to the spectrometer as described above, can be naturally include a on-board sensor quality onboard fuel, oil, coolant, or urea.

And more generally, a device such as suggested by the invention is applicable to all fluid quality measurements to perform in harsh environments (temperature, physical access etc.)

The scope of the present invention is not limited to details of the embodiments considered above example, but extends on the contrary to changes within the reach of the skilled in the art.

The description that processes a spectrometer by transmission, for which the measured spectrum is the spectrum of the light that has passed through the sample. The principle described is also applicable to a spectrometer in reflection, measuring light reflected from a sample.

In this case, the reflecting facets 27, 29, oriented at 90° from each other, form a surface within a vein fluid circulation, instead of a generally concave shape, as described above. They are naturally more metallized, but instead transparent in the wavelength range of interest, to measure the reflection spectrum of the fluid flowing in the measuring cell 9.

Been that the spectrometer as described consists of two main blocks, with the light source, the beam splitters and the detectors of a side forming the measuring instrument, and the measuring cell with its reflective facets on the other side. These two blocks can be embodied on parts manufactured separately and subsequently assembled.

In this manner, the choice of a mode of operation in transmission spectrometer (case described above), or in reflection spectrometer, can be made at the last moment. It is even possible to provide the measuring block with two blocks forming different measuring cells, adapted to the two modes of operation, the user choosing to install the block cell meter adapted to need.

Alternatively the two reflective facets 27, 29 can be replaced by any device reflecting the light back to 180° of its original direction, and, for example, by a parabolic reflector, or by a surface formed of a number of reflective facets greater than two.

Similarly, the two reflective facets 27, 29 may have a common edge, by suppressing the intermediate surface 28.

Alternatively, the shaping optics (collimating lens) 14 is located in the vicinity of the detector, instead of being placed immediately after the light source 12 (and optionally the diaphragm 13). The arrangement maintains the parallelism of the light rays into the detector 17.

In still another aspect, the first beam splitter 15 can be activated on command (e.g. mirror birefringent liquid crystal 16 or electric), and replaces therefore the shutter 30. When not activated, the light beam follows the measurement optical path cm and passes through the measuring cell 9. Instead, when the mirror activatable on command 16, is activated, the light beam is divided by the first divider 15 in an optical beam and optical reference beam, and these beams are recombined by the second divider 31. The operation of the spectrometer is generally unchanged.

Alternatively, the measuring cell 9 has no faceted reflector 27, 29, and the light passes through the measuring cell 9 right through. A light reflection device, external to the measuring cell 9, allows returning the measuring beam to the detector 17. Herein The operation of the device remains substantially unchanged.

Alternatively light source 12, thereof is formed of four light emitting diodes (LEDs) arranged in a square and the tighter possible.

The present invention relates to the field of electronics on board motor vehicles. More specifically, the optoelectronic equipment. More specifically, it touches in spectrometry adapted to determining composition of a fluid.

The competition between the various automobile designers causes a search without renewed improved operating performance, mileage consumption degree and ecological characteristics. In the field of vehicles powered by an internal combustion engine, the composition of the fuel has a direct impact on engine performance. Therefore, the precise knowledge of the fuel composition provides for certain operating parameters of the engine to improve combustion and reduce pollution of the vehicle.

Furthermore, this knowledge may also detect false manipulations (filling a fuel tank with diesel or vice versa) potentially damaging to the engine, and prevent the driver, or of blocking the ignition to avoid irreparable damage. Similarly, detecting a non-legal meets the standards for quality.

Analogs The remarks apply to the engine oil, or the cooling liquid or other fluids whose properties effect the operation of the vehicle.

One means achieve this composition analysis of a fluid is to use technology spectrometers.

The biases that a spectrometer is a measuring instrument for determining the absorption of certain wavelengths of the spectrum (general light) by a sample to be analyzed. The wavelengths absorbed form peaks in the absorption spectrum, and characterize certain molecules or components present in the sample.

As defined in the scope of the present invention, an optical spectrometer is thus comprised mainly of a light source, of an optical assembly for shaping the light beam to form a parallel beam capable of passing through the sample, a wavelength filter for measurement in a certain wavelength range, and a light detector for measuring the intensity of light received in the wavelength.

Spectrometers working in the fields of light wavelengths ultraviolet, visible and near infrared are already in use on a daily basis in many fields. Among these domains include:

food technology (for example for monitoring the moisture content of the cereal grains, maturity fruit, grease in certain food, etc)

the biomedical (for example measurement of the blood sugar level without extraction, etc)

the production of fuels (monitoring the quality and the composition of the crude, quality control of the final products such as gasoline and diesel, etc)

All these fields of application use the same type of measuring instrument, whereof only vary the characteristics of size and portability. Such instruments, optionally using different technologies (Fourier transform, Filter, monochromator, diffraction gratings, etc), does not operate over a range of large temperature variation.

Indeed, for reasons related to the drift of their performance according to the temperature, they have rarely been used in environments having high temperature variations.

The are often laboratory-type equipment, or in any case requiring easy access to components thereof for maintenance of the sensor or of the light source (in which the service life is often short, and, in any case, lower than the fortnight of years required in the medium vehicle-mounted). Therefore, they are unsuitable for long-term installation in an environment substantially inaccessible for maintenance.

Finally, these spectrometers are not subjected to constraints, unit cost of production, and hence utilize often high-end components, e.g. lamps Tungsten halogen or filament, temperature-stable, but that are incompatible with a mass installation in motor vehicles.

Been that the questions, temperature drift, of reliability of the components, and therefore access for maintenance, and finally manufacturing cost, make these commercial spectrometers unsuitable for use in environments comparable to the automobile.

In an application such as domain control of automobile fluids, it is necessary to use components to very low unit cost and robust in time, so as to ensure continuous operation. One solution is to use as a light source light emitting diodes (LEDs, acronym to "Light Emitting Diode").

In effect, the light emitting diodes are components well known, highly reliable, very low cost because used in very high volume for a multitude of applications. They are today available in multiple versions of wavelength, for their use in a domain spectrum 300 nm (near ultraviolet) to 2500 nm (near infrared).

As shown on Figure 1, the LEDs typically have a large enough spectrum characterized by a full-width mi-height of 35 nm to more delOOnm. Therefore, it is possible, by using a combination of different characteristics more diodes, source has an emission spectrum very wide.

The characteristics of emission spectrum and optical power of the LEDs may vary significantly according to the current flowing therethrough, and the ambient temperature at which they are used (Figures 1.2, 3 and 4 for one example of measured value on a light emitting diode to 650 nm). Or the interpretation of the absorption measurement requires precisely detect the intensity at a given wavelength, of the light wave sent through the sample analyzed.

Their use as a light source for spectroscopy, in environments in which the temperature can vary significantly (e.g.

-40 °C to + 105 °C in automobiles), requires innovative solutions to compensate for the natural variation of their characteristics. More generally, these remarks all light sources of variations in performance with aging and temperature.

Are known spectrometry devices at low cost using a technology based on light emitting diodes. A plurality of such devices are currently proprietary and marketed.

One such device is sold by Zeltex and described in the Patent US 6,369 388 B2. It is a portable spectrometer working in the near infrared primarily intended for use in quality analysis of harvested seed. Various applications are contemplated for the device, from the biomedical field to food technology and fuels.

Applications proposed for the device, it is mentioned a measure of octane rating of a gasoline from a discrete spectrum obtained by measuring the absorption to 14 different wavelengths, this constraint corresponding to a legal standard quality of fuels distributed in the American service stations in a state.

The spectrometer Zeltex uses the same absorption measurements in its different uses, thus independently of the type of sample analyzed.

The operating temperature range providing a measure of reliability guaranteed ranges from to +55°C -20°C. Such operating range is incompatible with use by in-car, for which the sensors are to be sized for temperatures between -40 °C and + 105 °C.

Two methods are disclosed in the Patent US 6,369 388 B2 to account for the effect of the temperature.

A first proposed method uses a compensation of the measurement results spectral absorption according to the temperature measured by a sensor, and a compensation logic pre-stored. This method does not sought to combat the deformations or drift components related to the temperature, but to correct the measured values according to a predetermined correction curve.

A second method in the frame of the Zeltex uses a self calibration of the spectrometer. Are to be a true compensating variations in temperature and aging of the components of the measuring chain, and particularly light-emitting diodes.

In this method, prior to each acquisition of spectrum measurement, the measuring cell is emptied, a first measurement is performed with the light source off (light measuring 0) that characterizes the measurement noise due to electronics and sensor, which varies with the environmental conditions and the time. Then a second measurement is performed with the light being lit, always without sample in the cell, providing a measure of light 100, also impacted by the environmental conditions of the measurement.

These two successive measurements enable self-calibration of the spectrometer. But the stress of having to empty the cell in such a procedure is not compatible with an in-vehicle use, for example, and as easily designed, in the case of an installation permanently in a fuel tank or in the fuel distribution circuit.

Another device, designed and manufactured by the company Rikola , relates to a spectrometer for laboratory use. The spectrometer can also be implemented in an environment the temperature of which varies between 5 and 55 °C, too narrow to the constraints of the motor medium.

It provides a measure of the absorption for 32 wavelengths determined. For this purpose, it uses a wavelength filter monochromator type, source side of the spectrometer, and consisting of a diffraction grating and 32 of light emitting diodes (LEDs). These LEDs are placed at points selected for obtaining the desired wavelengths.

In account for best mimic the effect of temperature variations on the components of the spectrometer, and, leaving, on the quality of the measurements provided, the device of the company Rikola permits the light to light 0 and 100, without the presence of the sample to be analyzed. A calibration of the apparatus is thus obtained.

However, a temperature change results in a significant deformation of the materials and thus movement of the light emitting diodes, which causes a change in the wavelengths created by the array assembly and light emitting diodes.

Therefore, the spectrometer uses a Peltier device to provide a satisfactory measuring accuracy in the temperature range considered, of 5° to 55 °C, by controlling the temperature of the grating and light emitting diodes around 30 °C. This limits the conditions of use that are possible for the spectrometer.

Furthermore, and unlike the preceding device, the spectrometer is not associated with a processing algorithm of the measured spectrum.

A third spectrometer existing low cost has been developed by the company Sentelligence , and is for example described in the document W0 2003 030,621 A2.

The spectrometer, for mounting, is formed as an integrated component comprising a light source in the form of light emitting diodes, an optic having a frustoconical placed in contact with the sample to be analyzed, and a detector disposed substantially in the plane of the light source.

It enables the measurement of the absorption for different wavelengths. This is different from a spectrometer in transmission for the other two spectrometers as mentioned, but a spectrometer by reflection. It therefore useful for characterizing of the components in the sample a measurement of the reflection spectrum of said sample subjected to a known light source, and without its absorption spectrum. A selection technology in reflection spectrometer is envisaged for products relatively opaque, highly absorbent light rays (soot etc).

The light source is formed by a combination of light emitting diodes each selected according to one of the wavelengths which it is desired to measure the reflection by the sample to be analyzed. Filters installed on the side of the light source, to limit the beam which passes through the test sample to a certain band of optical wavelengths, and the level of the emission intensity is optionally controlled by a photodiode (reference detector), placed on an optical path independent of the sample to be analyzed.

The light measurements 0 (light-up for measuring the electronic noise) and light 100 (light being lit) can be performed without that the sample to be analyzed is removed from the measuring cell.

This is carried out by correcting the measured intensity on the photodiode to calculate an intensity that theoretically would receive the measuring sensor, if the sample was absent.

By allowing a calibration of the measuring sensor by a reference detector is not influenced by the sample to be analyzed, and in order to take into account a drift of the light source, for example according to the temperature, the system is compatible with an application within the field of the measurement in a harsh environment.

However, such a mass spectrometer has its cost determined by the number of light emitting diodes installed, which is directly related to the number of wavelengths to be measured. If this number is substantially greater than six, it becomes too expensive for installation on a vehicle.

Additionally, a source created by juxtaposition of a large number of light emitting diodes can no longer be considered point, resulting in errors of measurement sensors (problem of parallax).

Furthermore, the device of the company Sentelligence is to be adapted during the design to each particular application, thereof require measurements at certain wavelengths specific to the type of sample to be analysed.

These spectrometers do not allow for high-precision spectral measurement as required by some applications in the automotive field, i.e. for example a measure of the absorption at a given wavelength ± 5 nm with an accuracy of 1% on the absorption value given. They do not use on a wide temperature range.

These various restrictions make them unsuitable for use in embedded applications on motor such that the measurement of the chemical composition of a fuel or its properties accurate combustion.

The invention presented to, therefore, to provide a concept of mini spectrometer responsive to size constraints, of reliability and performance compatible with applications of the automotive type.

A second object of the invention is to allow an inexpensive realisation realistic rendering its use on motor vehicle.

A third goal is to provide an on-board spectrometer operable to more applications to different fluids, without hardware modification.

To this end, the present invention relates, firstly a device for measuring a spectrum of a light beam, in a wavelength range of preselected, said spectrum is generated by a sample to be analyzed, the measuring device comprising:

at least one light source,

a measuring cell,

a measuring sensor placed on a measurement optical path, said measurement optical path is achieved by a optical measurement beam from the light source and meeting with the measuring cell, means for self-calibration to account for possible drift of the light source, due to environmental conditions or use, independently of the presence or absence of a sample to be analyzed into the measuring cell, said means for self calibration comprising:

o means create a reference optical path, through which a optical reference beam, from the light source and does not encounter the measuring cell,

o a reference detector.

The measurement device is remarkable in that it is designed to be installed on board a motor vehicle and that it comprises means for selectively mixing the optical measurement beam and the optical reference beam and in that the measuring sensor also acts as a reference detector.

Preferably, the device measures an absorption spectrum of the light beam by the sample to be analyzed.

In another embodiment, the device measures a reflection spectrum of the light beam by the sample to be analyzed.

In a preferred embodiment, the device also comprises at least one wavelength filter associated with the reference detector, said wavelength filter is a variable filter Fabry-Perot interferometric cavity.

Advantageously in this case, the device also comprises means of transforming the light beam from the light source into a parallel beam.

In a particular embodiment, the measuring cell comprises means for returning the optical measurement beam in a direction substantially opposite its original direction.

According to an advantageous embodiment, the means for returning the optical beam for measuring comprises two facets, oriented at 90° from each other, placed on a side face of said measuring cell.

In the case of an absorption spectrometer, advantageously the facets form a generally concave surface within the vein for circulating fluid in the measuring cell and are mirrored by metallization.

In the case of a spectrometer in reflection, the facets form advantageously surface within the vein for circulating fluid in the measuring cell, and are transparent in the wavelength range of interest.

Been that this arrangement corresponds to the special case of reflection for spectrometer which the light beams reflect simply on the sample being analyzed, in contrast to the previous work corresponding to an absorption spectrometer, wherein the light rays are transmitted through the sample to be analyzed.

In an advantageous embodiment, the means for creating a reference optical path comprise a first beam splitter, in that the means for selectively mixing the optical measurement beam and the optical reference beam comprises a second beam splitter and a beam shutter activatable on command, said beam shutter being disposed on the optical reference beam between the two beam splitters.

More particularly, in this case, the two beam splitters are optical cube comprising, on the diagonal plane, a half mirror.

In another embodiment, the means for creating a reference optical path comprise a first beam splitter activatable on command, in that the means for selectively mixing the optical measurement beam and the optical reference beam comprises a second beam splitter and means for controlling the activation of the first beam splitter.

In an advantageous embodiment, the spectrometer is made in two separable blocks, a first block of the light source, the beam splitters, the beam shutter and the detectors and thereby forming the measuring instrument, and a second block comprising the measuring cell with its facets of returning the optical measurement beam in a direction substantially opposite its original direction.

The aim of the invention is in a second aspect a fuel quality sensor, oil, coolant, or urea, to be permanently installed in a vehicle.

In third a method for controlling at least one operating parameter of a vehicle engine, said vehicle having a sensor such as exposed, and a control computer connected to said sensor,

characterized in that it comprises the steps of:

selecting the type of fluid to be analyzed,

ignition at regular intervals from the light source,

waiting for a delay adapted to take account of the normal operation of said light source,

control of the variable filter for adjusting said filter successively on the different wavelengths forming a series necessary for determining the composition of the sample fluid, these wavelengths is previously stored in a memory of said computer for each type of fluid that can be analysed by the sensor,

locking of the reference beam,

measuring, for each selected wavelength, by the detector for measuring the intensity of light received in the wavelength,

and, at predetermined intervals,

o passage of the reference beam and mixture in the second divider, o measuring, for each selected wavelength, by the detector for measuring the intensity received in the combined light wavelength,

transmitting to the computer measurements of the absorption spectrum of the fluid to be analysed and measurements of the combined spectrum,

comparison by the computer of the measurement and the combined value,

determination by the computer absorption due to the sample contained in the measuring cell,

determining, based on a calculation logic or a chart stored in memory, by the computer, at regular intervals, changes of engine operating parameters.

Been that the functions of the computer are realized either by the engine control, or by electronics associated with the sensor-the transmission to the motor computer then directly corresponding to the value of the parameter of the fluid.

The invention also relates to software adapted to perform the method set forth.

The aim of the invention is under yet another aspect a vehicle using a device as set forth, or a process as set forth.

Goals and advantages of the invention will become better understood upon reading of the description and drawings of a particular embodiment, given by way of non-limiting example and for which the drawing is:

figure 1 illustrates the spectral characteristics of a light emitting diode (LED) as a function of the temperature, by highlighting the offset of the emission spectrum in wavelength and transmit power;

figure 2 illustrates the wavelength shift peak of a light emitting diode according to the temperature and the current flowing through the light emitting diode;

figure 3 illustrated the same peak width at mi-height of the spectrum of the light emitting diode according to the temperature and the current flowing through the light emitting diode;

figure 4 shows the emitted light power according to various values of current through the light emitting diode between -40 °C and about + 95 °C;

figure 5 is a schematic representation of a spectrometer for functional mini environment difficult in the invention, in plan view;

figure 6 is a view in isometric perspective of the same spectrometer;

figure 7 illustrates schematically the operation of the spectrometer, in the case where the shutter is opened;

figure 8 illustrates the emission spectra of three light emitting diodes different in the near infrared (700,1050 nm);

figure 9 illustrates the addition of the three normalized spectra of Figure 8;

figure 10 illustrates the integration of a spectrometer of the invention on a fuel circuit of motor vehicle;

figure 11 illustrates schematically the principle of design of a detector combined with a filter activatable on command.

As shown on Figure 10 in the case of application of a device for measuring absorption spectrum according to the invention to a fuel system of an automotive vehicle, such a mass spectrometer 1 can advantageously be provided on a fuel pipe 2, downstream of the reservoir 3 and the fuel pump 4, also downstream of the fuel filter 5 (to reduce measurement errors), but upstream of the injection pump 6 and the motor 7.

The spectrometer 1 is connected to a control computer 8, which is also connected to the injection pump or to the motor which it is capable of driving individual adjustments. Note that the control computer 8 may be either the motor computer, conventionally present in motor vehicles, is an electronic control of the spectrometer, which sends directly to the motor computer the values of the parameters of the sample fluid.

The device according to the invention is as shown in Figures 5 to 7.

The spectrometer 1 according to the invention is arranged about a measuring cell 9 in which the fluid circulates to be analyzed, such as fuel.

Is defined for the rest of the description a longitudinal axis X corresponding to the direction of circulation of the fluid in the measuring cell 9.

The load cell 9 is herein shown in the form of a tube segment of rectangular cross-section (Figure 6), oriented substantially along the longitudinal axis X.

It comprises on one of its two side faces (left side in Figure 5) two glass panes 10, coplanar 11, rectangular, and substantially identical dimensions.

These can be produced for example glass or plastic, their material to be chemically neutral to the sample fluid, dimensionally stable as a function of the temperature, and transparent in the wavelength range used to measure (herein the near infrared, but wavelength ranges U-V./ visible are also usable, without modification of the device).

The attachment of the panes 10, 11 in the wall of the measuring cell 9 is made by gluing or otherwise known means.

Is defined for the rest of the description a transverse axis Y normal to the two glass panes 10, 11.

On the side opposite side (right side in Figure 5), an area of reflecting light, comprising two reflective facets 27, 29, oriented at 90° from each other enables returning an incoming light beam by a first window 10 (thus in a direction oriented according to the axis-Y), to the second pane 11 (in a direction along the axis + Y). The two reflective facets 27, 29 are in the present example formed from planar surfaces, oriented to the first to 45° in the XY mark, and for the second to 135° in the marking.

They are separated by a facet 28, substantially planar and parallel to the longitudinal axis X.

The two reflective facets 27.29 are sized to return entirely a light beam emerging from the first pane to the second pane 11 10.

Their reflective character is, in the present invention, obtained by polishing and local metallization of the surface (for example by chromium) forming the side face of the measuring cell 9, process which is carried out by means known to those in the art. These facets can also be formed by a bonding of mirrors on the faces oriented at 45° and 135 °, or by any other suitable means.

The measuring cell 9 is made of metal or rigid plastic, so that the two glass panes 10, 11 remain coplanar independently of environmental conditions (in particular temperature), and that the two reflective facets 27, 29 remain oriented at 90° from each other, in order to maintain the path of a light beam passing through the measuring cell 9, and thus in order to avoid the creation of measurement errors.

The measuring cell 9 is connected at its two open ends, by means known to those in the art, to a circulation line for pre-existing fuel in the vehicle.

To perform the measurement of absorption spectrum, the two glass panes 10, 11 are penetrated, and the fluid contained in the measuring cell 9, by a light beam, which is reflected in the reflecting facets of the measuring cell.

The light beam is created by a light source 12, whose emission spectrum naturally corresponds to the wavelength range of interest for the fluid to be analyzed.

Here in no way limiting, the light source 12 is formed of three light emitting diodes (LEDs) arranged in the triangle and tighter possible, on a same support, perpendicular to the transverse axis Y (facing the measuring cell 9), so as to minimize the offsets linked measurement to the distance between the three light emitting diodes.

Their emission peaks are located respectively around 850 nm, 950 nm and 900 nm. As shown on Figure 8 that illustrates the emission spectra respective 25 °C, each one light-emitting diode has an emission spectrum extending to mi-height to about 100 nm.

The superimposition of the three spectra, shown in Figure 9, shows the spectrum equivalent to the complete source. The light source 12 effective to cover a wavelength range of 825 to 975 nm (near infrared).

It is clear that other diodes can be used, or for the evolution of the technique with diodes low unit cost but wider spectrum, either for the purpose of creating a spectrum in another wavelength range.

Been selected that the light-emitting diodes are commercial products, very low unit cost. It has thus created a light source 12 equivalent, based on existing components and very inexpensive, in order to minimize the overall cost of the spectrometer 1. Furthermore, the light emitting diodes are known to have a life (duration before the transmit power has been divided by two) of several tens of thousands of hours, thus compatible with the lifetime requested to-board equipment on motor vehicle.

These three light emitting diodes, whose combined power does not exceed a few tenths of a watt, are energized by known means and not detailed herein.

The light beam created by the light source 12 is generally conical, set angle by the LEDs selected, and in this example the order of a few tens of degrees.

This beam is optionally restricted to a circular beam (or shape preselected) of smaller width in the space, by a diaphragm, for example a mechanical device of known type.

After passing through the diaphragm, the light beam, conical always there, is transformed into a parallel beam, of cylindrical section, by a collimating lens 14. The collimator lens 14 is of the type known (such as plane/convex) and can be made of glass or plastic material of good optical quality in the wavelengths being measured. Its dimensions as to enable creating a beam of one to several tens of cm² .

The collimating the light, which renders its parallel rays, is particularly useful for the quality of the measurement, particularly in the case of using technology type "interference filter", it will be shown further.

The spectrometer according to the invention comprises, downstream of the collimating lens 14, a beam splitter 15, for separating the light beam (shown by the segment 32 in Figure 7) in, on the one hand, a measuring beam according to a measurement optical path cm, parallel to the transverse axis Y (segment 33 in Figure 7), and, on the other hand, a reference beam according to a reference optical path CR, generally parallel to the longitudinal axis X (segment 39 in Figure 7).

The beam splitter 15 is an optical component allowing example 50% of the light and reflecting 50% in a direction at 90° relative to the original beam. It is such as optical cube having on its diagonal plane, oriented at 45° in the XY mark, a half mirror 16. It has thus created herein two beams, considered to be same spectrum (wavelengths and transmit power in each wavelength). The light transmitted through the mirror is directed to the measuring cell 9. Its mode of manufacture is known to those skilled in the art and therefore not detailed herein. It may also be a birefringent mirror.

The beam splitter 15 is placed immediately adjacent to, or directly in contact with the first pane 10 of the measuring cell 9 to minimize the path of the optical beam out of the fluid of interest.

The measurement beam, as shown clearly in Figure 7, through the first window 10, a thickness of the fluid to be examined which depends on the width/of the measuring cell according to the transverse axis Y and the distance d between the ends of the reflective facets, according to formula 2 /+ d.

After this optical path (shown by the segments 34, 35 and 36 in Figure 7 for a ray of light situated at the centre of the beam) within the sample fluid in the measuring cell 9, the light beam spring of said measuring cell 9 through the second pane 11. Upon path within the sample fluid, certain wavelengths of the emission spectrum of the light source 12 are attenuated due to the absorption of photons of these wavelengths by molecules present in the fluid.

The measurement beam, whose spectrum is modified by the fluid flow therethrough, and from the measuring cell 9 according to the transverse axis Y, flows through a second beam splitter 31, placed immediately adjacent to, or directly in contact with the second glass sheet 11 of the measuring cell 9 is again to minimize the path of the optical beam out of the fluid of interest.

The second beam splitter 31 herein is for mixing the measuring beam that has seen the measurement optical path cm (segments 33 to 37 in Figure 7), and the reference beam that has seen a reference optical path CR (segments 39 and 40 in Figure 7) in a single light beam (segment 38 in Figure 7).

The second beam splitter 31 is an optical component similar to the first beam splitter 15, allowing example 50% of the light and reflecting 50% in a direction at 90° relative to the original beam. It is such as optical cube having on its diagonal plane, oriented at 135° XY in the reference frame, a half mirror 41.

The includes that the second beam splitter 31 is disposed at the intersection of the measurement optical path cm and the reference optical path CR. In the present example It is aligned with the first divider 15 according to the longitudinal axis X. The distance between the centers of the semi-reflecting mirrors 16, 41 is substantially equal to the distance between the centers of the reflective facets 27, 29 of the measuring cell 9.

The device also comprises, placed on the optical path of reference CR between the two beam splitters 15, 31, a beam shutter 30 of a type known per se and activatable on command by electrical means. The beam shutter 30 aperture passes or not the reference beam (segment 39 in Figure 7) to the second beam splitter 31 (segment 40 in Figure 7 when the shutter 30 is open), and, in a controlled manner.

The shutter is an electromechanical actuator or electro-optical (e.g. liquid crystals), the selecting is for example, according to the environmental conditions in which the spectrometer is to be used.

The light beam 38, from the second beam splitter 31, and comprising either the single measurement light beam, and the combination of the measuring and reference beam, is finally picked up by a measuring sensor 17 equipped with a wavelength filter.

The filters are in the preferred embodiment and described herein, Fabry-Perot interferometric cavities-and in which case the wavelength capable of the bushing is, in a known manner, dependent on the width of the cavity thus the angle of attack of the light rays. Been that it is desirable, for accurate measurement, that the light rays are actually parallel. This justifies the use of the collimating lens 13.

The measuring sensor 17 is equipped with a variable filter 26, Fabry-Perot cavity for example, of the type presented in the document " Infrared dectector Tunable with Integrated micromachined Fabry-Perot filter (Neumann, Ebermann, Hiller, Kurth, MOEMS jan 2007), and shown in Figure 11.

The measuring sensor 17 is placed on the measurement optical path cm in output of the variable filter 26. It is a pyroelectric type in the present example, and thus, has a very short response time, but it can be replaced by a filter type LVF (of the acronym English "Linear Variable Filter") or by one or more optical filters associated with a CCD array (of the acronym English "charge Coupled Device") or CMOS (of the acronym English "conventional Complementary Metal Oxide Semiconductor").

In operation, if the computer 8 associated with the spectrometer 1 has been initialized for a type of fluid to be analyzed (selecting wavelengths to be observed), the computers causes ignition of the light source 12 at regular intervals, the spacing has been previously selected.

After a time adapted to take account of the normal operation of said light source, the computer controls the potential difference between the plates of filters Fabry-Perot interferometric (or pilot the means for varying the value of the variable filter) to adjust said filters successively on the different wavelengths forming a series necessary for determining the composition of the sample fluid, these wavelengths is previously stored in a memory of said computer 8.

The calculator 8 then causes closing of the shutter 30, and thus the locking of the reference beam along the optical pathway CR. Only the light beam passing through the measuring cell 9 is collected through the measuring sensor 17.

For each wavelength A selected, the measuring sensor 17 outputs a measure characterizing the light intensity received in that wavelength. The spectrometer 1 transmits at regular intervals to the computer 8 measurements of the absorption spectrum of the fluid to be analyzed.

The measurement is then defined by the equation

lreceiver_ob (A) ~ A IlED (4) Ctp_ue i (A) (EQ.1)

wherein:

A is the attenuation experienced on the measurement optical path cm flowing through the segments 32 to 38 (loss due to the collimating lens 14, to the beam splitter 15, to the measuring cell 9, the second beam splitter 31).

A is the wavelength of interest,

has_Fue i₍ A) is absorption of a known thickness (21 + d) of the analyzed fluid in this wavelength,

Iled (A) is the intensity of the light source in this wavelength,

læceiver_ob (λ) is the intensity measured by the detector in that wavelength.

Furthermore, at predetermined intervals,

The calculator causes the opening of the shutter 30, and thus the passage of the reference beam along the optical pathway CR reference, and subsequent mixing in the second divider 31 with the measurement beam along the optical pathway measuring cm,

At this time, the measuring sensor 17 relates to, for each wavelength λ selected, the combined light intensity received in this wavelength, and transmits the intensity measurement to the computer 8.

This measure is then defined by the equation

Ireceiver_Nob (λ) = A IlED (λ)* 0*_Fue i (λ) + B * l_LED (λ) (Eq. 2)

wherein:

A is the attenuation experienced on the measurement optical path cm, and B is the attenuation experienced on the reference optical path CR (path not passing through the sample fluid) through the segments 32, 39, 40, 38 (loss due to the collimating lens 14, to the beam splitter 15, the second beam splitter 31),

Note that the influence of the temperature and the aging is a priori negligible on the attenuation values A and S, which are known as manufactured the spectrometer and remain fixed in time.

The calculator 8 compares the measurement value and the combined value and derives, by first subtracting the two equations the term B * l_LED (λ), and thus, B being known, the luminous intensity provided by the light emitting diode in said wavelength in these environmental conditions and aging the LED, and then, by reintroducing that intensity on the equation Eq 1 absorption. has_Fuel( A) due to the sample contained in the measuring cell 9 for said wavelength in these environmental conditions.

Based on a calculation logic or a chart stored in memory, the computer 8 determines, at regular intervals, of changes of parameters of operation of the engine 7, for example according to the fuel suitable for operation of the engine, controlling the spark advance, injection variation andc.

The processing of the signal from the spectrometer according to the invention exits the frame of the present invention, and thus is not further detailed herein.

The first advantage of the spectrometer according to the invention is the use of a single detector used for both the reference beam, and for the measuring beam, through the use of a reflector in the cell, and a beam shutter on the reference optical path.

This enables a decrease in the cost of the sensor, the sensor associated with its variable filter one hand very significant component of the overall cost of said sensor. Furthermore, this design provides increased performance since the two signals (+ measuring and reference measurement) which are compared are measured by the same sensor, thereby eliminating systematic errors due to the detector optionally. Finally, the electronic control of the sensor is also simplified, since it controls a single sensor instead of two, thus contributing to trust the system and lower a cost.

A second advantage of the device is to group the optical and optoelectronic components on the same side of the measuring cell. Therefore, the spectrometer may be organized into two separate functional blocks. Furthermore, this realizes electronic card smaller dimensions, one of the faces of the measuring cell requiring no connection.

A third advantage of the present invention is the use of a reference optical path. This compensates for the effects of aging and changes in environmental conditions of on the diodes constituting the light source. Furthermore, the measuring cell does not have to be emptied for obtaining a reference measure, which can be performed at any time.

Applications can be considered to the spectrometer as described above, can be naturally include a on-board sensor quality onboard fuel, oil, coolant, or urea.

And more generally, a device such as suggested by the invention is applicable to all fluid quality measurements to perform in harsh environments (temperature, physical access etc.)

The scope of the present invention is not limited to details of the embodiments considered above example, but extends on the contrary to changes within the reach of the skilled in the art.

The description that processes a spectrometer by transmission, for which the measured spectrum is the spectrum of the light that has passed through the sample. The principle described is also applicable to a spectrometer in reflection, measuring light reflected from a sample.

In this case, the reflecting facets 27, 29, oriented at 90° from each other, form a surface within a vein fluid circulation, instead of a generally concave shape, as described above. They are naturally more metallized, but instead transparent in the wavelength range of interest, to measure the reflection spectrum of the fluid flowing in the measuring cell 9.

Been that the spectrometer as described consists of two main blocks, with the light source, the beam splitters and the detectors of a side forming the measuring instrument, and the measuring cell with its reflective facets on the other side. These two blocks can be embodied on parts manufactured separately and subsequently assembled.

In this manner, the choice of a mode of operation in transmission spectrometer (case described above), or in reflection spectrometer, can be made at the last moment. It is even possible to provide the measuring block with two blocks forming different measuring cells, adapted to the two modes of operation, the user choosing to install the block cell meter adapted to need.

Alternatively the two reflective facets 27, 29 can be replaced by any device reflecting the light back to 180° of its original direction, and, for example, by a parabolic reflector, or by a surface formed of a number of reflective facets greater than two.

Similarly, the two reflective facets 27, 29 may have a common edge, by suppressing the intermediate surface 28.

Alternatively, the shaping optics (collimating lens) 14 is located in the vicinity of the detector, instead of being placed immediately after the light source 12 (and optionally the diaphragm 13). The arrangement maintains the parallelism of the light rays into the detector 17.

In still another aspect, the first beam splitter 15 can be activated on command (e.g. mirror birefringent liquid crystal 16 or electric), and replaces therefore the shutter 30. When not activated, the light beam follows the measurement optical path cm and passes through the measuring cell 9. Instead, when the mirror activatable on command 16, is activated, the light beam is divided by the first divider 15 in an optical beam and optical reference beam, and these beams are recombined by the second divider 31. The operation of the spectrometer is generally unchanged.

Alternatively, the measuring cell 9 has no faceted reflector 27, 29, and the light passes through the measuring cell 9 right through. A light reflection device, external to the measuring cell 9, allows returning the measuring beam to the detector 17. Herein The operation of the device remains substantially unchanged.

Alternatively light source 12, thereof is formed of four light emitting diodes (LEDs) arranged in a square and the tighter possible.