JP5155913B2 - Exhaust gas analyzer - Google Patents

Description

  The present invention relates to an exhaust gas analyzer and exhaust gas analysis method for automobiles and the like, and in particular, an exhaust gas analyzer that can be mounted in the exhaust path so that the components of the exhaust gas passing through the exhaust path can be accurately measured in real time. And an exhaust gas analysis method.

  Conventionally, as an exhaust gas analyzer of this type, Patent Document 1 describes an exhaust gas analyzer using a laser suction method that can improve the accuracy of exhaust gas analysis and can easily perform exhaust gas analysis in real time. The apparatus demultiplexes the output light of the laser light generating means into measurement light and reference light, and irradiates the measurement light to the exhaust gas flowing in the measurement cell, and between the optical demultiplexing means and the measurement cell. An optical attenuator disposed in the optical path, a light receiving element that receives measurement light and reference light transmitted through the exhaust gas, and a difference detector that detects a difference signal between the measurement light signal received by the light receiving element and the reference light signal The difference detector further calculates a feedback correction amount based on the measurement light signal and the reference light signal received by the light receiving element so as to make the light intensities of the measurement light and the reference light constant. To optical attenuator And it includes a circuit to power.

  In this type of exhaust gas analyzer, when background light (radiant light) from a measurement cell that is a measurement unit is input to a light receiving element for measurement light, an error based on background light is added to the difference between the measurement light signal and the reference light signal. Resulting in a measurement error.

  In Patent Document 2, in a gas concentration meter side device including a light source that oscillates laser light having an absorption wavelength unique to a gaseous substance to be measured, and means for receiving laser light that has passed through a measurement gas, It is described that a means for receiving background light (radiation light) is separately installed at a position off the optical axis of the laser, and the effect of background light is removed by subtracting the light reception output of the background light from the light reception output of the laser light. Has been.

  Further, in Patent Document 3, in order to detect the fuel concentration in the combustion chamber of the internal combustion engine with high accuracy, the light intensity after passing when the measurement light is incident is detected, and the detected value is obtained from the light source. Obtain the light intensity from which the influence of thermal radiation has been removed by correcting with the detected value that is similarly detected by the thermal radiation light in the combustion chamber when the measurement light is blocked by the shutoff valve, and calculate the fuel concentration from that signal It is described.

JP 2006-337326 A JP 2001-74653 A JP 2003-4633 A

  In the exhaust gas analyzer described in Patent Document 1, no particular mention is made of a measurement error due to background light (radiant light) from a measurement cell which is a measurement unit. In the gas concentration meter side device described in Patent Document 2, it is necessary to separately install a light receiving means for receiving background light at a position off the optical axis of the laser. Further, in the fuel concentration measuring device described in Patent Document 3, the detected value is corrected by the detected value similarly detected by the heat radiation light in the combustion chamber when the measuring light from the light source is blocked by the shut-off valve. In addition, since the measurement light is blocked by mechanical means called a shut-off valve, real-time measurement is difficult even if the technology is applied to an exhaust gas analyzer that requires a high-speed calculation within 1 ms.

  Further, as described in Patent Document 1, in order to balance the measurement signal and the reference signal, the light intensity of the measurement light and the reference light is feedback-controlled by an optical attenuator so as to receive light having a constant intensity. In order to eliminate the measurement error due to background light (radiant light), just subtracting the reference light signal from the measurement light signal as described in Patent Document 2 or Patent Document 3, as described later, correct measurement is performed. There is an inconvenience that cannot be done.

  The present invention has been made based on the background as described above. By eliminating the influence of background light (radiant light), measurement errors can be eliminated, and measurement can be performed in real time. It is an object of the present invention to disclose an improved exhaust gas analyzer.

  An exhaust gas analyzer according to the present invention is basically an exhaust gas analyzer that irradiates exhaust gas emitted from an engine with laser light and analyzes components of the exhaust gas from an absorption line of signal light transmitted through the exhaust gas. A laser beam irradiation timing chart, a laser beam generator having a timing signal generator for selecting a time zone in which the laser beam is not irradiated, and the measurement light and the reference beam separated by the output light of the laser beam generator Optical demultiplexing means for irradiating the exhaust gas flowing in the measurement cell, an optical attenuator disposed in an optical path between the optical demultiplexing means and the measurement cell, the measurement light transmitted through the exhaust gas, and the reference A light receiving element that receives light, a difference detector that detects a difference signal between a measurement light signal received by the light receiving element and a reference light signal, and a laser beam based on a signal from the timing signal generating means A memory that stores a radiation light signal received by the light receiving element of the measurement light when it is not irradiated, a subtraction circuit that subtracts the radiation light signal from the measurement signal, and a signal after the subtraction is fed back to the optical attenuator. And an optical attenuator control circuit.

  Further, the exhaust gas analysis method according to the present invention irradiates the exhaust gas discharged from the engine with the measurement light demultiplexed from the output light of the laser light generating means through the optical attenuator, and the measurement light and the reference light transmitted through the exhaust gas. Is an exhaust gas analysis method for detecting a difference signal between a measurement light signal and a reference light signal and analyzing an exhaust gas component based on the difference signal, wherein the exhaust gas analysis method is irradiated with laser light. Obtained by subtracting the radiant light signal from the measurement light signal received by the measurement light receiving means when the laser light is irradiated and stored in the memory. Control is provided to bring the measured light level excluding radiation into a set value by feeding back the signal to the optical attenuator.

  Hereinafter, characteristic items of the exhaust gas analyzer and the exhaust gas analysis method of the present invention will be described. In the gas analysis method using the difference method described in Patent Document 1 described above, when the drive pulse applied to the laser light generating means is a drive pulse having a current scanning section in which the current value changes with time, background light ( In the state where there is no radiation light signal (radiation light), as shown in FIG. 1 (a), the difference in signal level between the measurement light signal passing through the exhaust gas and the reference light signal passing through the exhaust gas is taken and this is amplified. By differentially amplifying the signal, an absorption waveform of the differential signal as shown in FIG. 1B is obtained, and gas analysis is performed based on this intensity. The difference amplification is necessary because the difference between the measurement signal and the reference signal is extremely weak. Here, since it is necessary to balance the measurement signal (excluding the absorber) and the reference signal, the received light intensity of the measurement light and reference light is feedback-controlled by the optical attenuator as described above. , Always receive light of constant intensity.

  If the method of simply subtracting the reference light signal and the radiation light signal from the measurement light signal is applied to this method in order to eliminate an error due to the radiation light, correct measurement cannot be performed for the following reason.

(A) Since the contribution to the measurement light due to radiation is low in wavelength dependence, it can be considered to be almost constant in the region measured by the difference method. Therefore, the measurement signal is compared with the reference signal as shown in FIG. Thus, it is equal to the value obtained by adding the amount of radiation.
(A) When this is differentially amplified, if the radiation light is sufficiently larger than the difference signal before the difference, the difference signal after radiation may be saturated, and measurement becomes impossible.
(C) Furthermore, when the value with the getter in (a) is superimposed on the measurement signal, in order to restore the balance between the measurement signal and the reference signal, the attenuation factor of the measurement optical system is manipulated to increase the intensity of the measurement light. Lower and balance. At this time, the measurement signal is discounted at a constant ratio. As a result, as shown in FIG. 2B, a difference occurs in the gradient of the measurement signal / reference signal. By amplifying the difference, the slope is amplified, and as shown in FIG. 2 (c), a part of the difference signal is saturated in the measurement system, resulting in an area where the signal cannot be measured. Problems with measurement.

  In the present invention, in order to eliminate the above-described inconvenience, in the present invention, the radiation light signal is deleted from the measurement light signal before the measurement signal / reference signal is balanced. That is, as shown in FIG. 3A, the signal obtained by superimposing the radiation light on the measurement light is subtracted from the radiation light signal obtained simultaneously with the measurement light shown in FIG. Feedback control is performed so that the measurement signal / reference signal becomes a constant value. The measurement light signal and the reference light signal thus obtained have the same inclination as shown in FIG. 3C, and the difference between the two signals is amplified by the differential amplifier circuit, so that FIG. As shown in FIG. 5, a difference signal without error can be obtained in real time. The obtained difference signal is sent to a conventionally known analysis system to analyze the exhaust gas.

  More specifically, in the present invention, the laser light generation means includes a laser light irradiation timing chart and a timing signal generation means for selecting a time zone in which the laser light is not irradiated. According to the timing chart, as shown in FIG. 4, the laser light generating means repeats a time zone a in which the laser is not irradiated and a time zone b in which the laser is irradiated. As a result, the signal intensity having the waveform as shown in FIG. 3B is obtained from the light receiving element that receives the measurement light. That is, in FIG. 3B, the signal intensity in the time zone “a” where the laser is not irradiated is caused by the radiation light, and the signal intensity in the time zone “b” where the laser is irradiated includes the contribution of the radiation light. Signal strength.

  The laser light generating means further includes timing signal generating means for selecting a time zone in which the laser light is not irradiated, and when the laser light is not irradiated based on the signal from the timing signal generating means, the light receiving element for the measurement light is The received radiation light signal is stored in the memory. The subtraction circuit subtracts the radiation light signal from the measurement light signal, and the signal subtracted by the subtraction circuit is sent to the optical attenuator control circuit and fed back to the optical attenuator on the measurement light side.

  On the reference light side, the signal is sent to the optical attenuator control circuit and fed back to the optical attenuator on the reference light side.

  The measurement signal and the reference signal that are feedback-controlled so that the measurement signal / reference signal has a constant value and a constant inclination are sent to a differential detector having a differential amplifier circuit. A differentially amplified differential signal is formed. The signal is sent to the analysis system, and the exhaust gas is analyzed in real time by a conventionally known analysis method as described in Patent Document 1, for example.

  In the present invention, it is desirable to remove the signal component resulting from the radiation light from the input signal to the differential amplifier circuit, and this can be done by an appropriate method. As an example, a bandpass filter provided in the difference detector can be used. That is, the spectrum of the radiant light is flat and can be treated as a constant bias within the range of the wavelength sweep width in the spectroscopic analysis performed by the laser absorption method as described in Patent Document 1. Therefore, for example, by using a band pass filter of 7 k to 2 MHz, it is possible to remove a radiation light signal as a DC component.

  According to the present invention, in the exhaust gas analysis apparatus and method using the laser suction method, real-time signal processing that eliminates the influence of background light (radiant light) generated in the measurement cell is possible, and exhaust gas analysis with a high degree of measurement can be performed in real time. Can be performed.

The figure which shows typically the signal processing state in the state without a radiant light signal in the exhaust gas analysis using a difference method. The figure which shows typically the signal processing state in case the radiation light contributes in the exhaust gas analysis using a difference method. The figure which shows typically the signal processing state which concerns on this invention. The figure which shows an example of the laser beam irradiation timing chart in the laser beam generation means which concerns on this invention. The figure which shows the whole structure of one Embodiment of the exhaust gas analyzer which concerns on this invention. The principal part block diagram of one Embodiment which mounted the exhaust gas analyzer which concerns on this invention in the vehicle. The principal part block diagram at the time of mounting the exhaust gas analyzer which concerns on this invention in an engine bench.

  Hereinafter, an embodiment of an exhaust gas analyzer according to the present invention will be described with reference to the drawings. FIG. 5 is a block diagram showing the overall configuration of the exhaust gas analyzer. In FIG. 5, the exhaust gas analyzer 30 includes a laser light generating unit 31, and a driving pulse having a current scanning section in which the current value changes with time is applied to the laser light generating unit 31. The laser light generating means 31 includes a laser light irradiation timing chart 32 and a timing signal generating means 33 for selecting a time zone during which no laser light is irradiated. The output light P (having a waveform as shown in FIG. 4) of the laser light generating means 31 is demultiplexed into the measurement light P1 and the reference light P2 by a known demultiplexer 34. The measurement light P1 and the reference light P2 pass through a known optical attenuator (VOA) 35, respectively.

  The measurement light P1 passes through the exhaust gas discharged from the engine flowing in the measurement cell 36, and then is received by the light receiving element 37 such as a photodiode (PD) in a state including radiation light. The reference light P2 is received by the same light receiving element 38 as it is.

  The measurement light signal from the light receiving element 37 and the reference light signal from the light receiving element 38 are input to the differential signal device 40. In this example, the difference signal device 40 passes the amplifier 41 and the band pass of the 7 k to 2 MHz band corresponding to the measurement light signal from the light receiving element 37 and the reference light signal from the light receiving element 38, respectively. A filter (BPF) 42 is provided, and two signals that have passed through the band-pass filter 42 are sent to a known differential amplifier circuit 43.

  By passing through the band-pass filter 42, a DC component is removed from the measurement light signal and the reference light signal. In particular, the radiation light signal component is removed from the measurement light signal. The measurement light signal and the reference light signal from which the DC component has been removed are subjected to differential amplification in the differential amplifier circuit 43, and a differential signal as shown in FIG. 3D is output. The waveform of the difference signal depends on the component of the exhaust gas flowing in the measurement cell 36, and is sent to the computer 44 that constitutes the analysis system, using a conventionally known method as described in Patent Document 1 described above. An exhaust gas analysis is performed.

  In the exhaust gas analyzer 30 according to the present invention, the measurement light signal is partially branched in front of the bandpass filter 42, and the measurement light signal including the branched radiation light component is controlled by the analog memory 45 and the optical attenuator control. It is sent to the circuit 46. The analog memory 45 is supplied with a signal for turning on a time zone during which no laser beam is irradiated from the timing signal generating unit 33 provided in the laser beam generating unit 31, and the memory update timing control is performed. The analog memory 45 stores the measurement light signal including the radiation component when the signal is ON. Here, the actually stored signal intensity is in a time zone in which the laser beam is not irradiated, and is a signal intensity caused by background light in the measurement cell 36, that is, radiation light.

  The signal intensity of the signal stored in the analog memory 45 is subtracted from the signal intensity of the measurement light signal including the radiation component transmitted at the next timing in the adder (subtraction circuit) 47, and the signal after the subtraction Is sent to the optical attenuator control circuit 46 described above. The processed feedback signal is sent to the optical attenuator (VOA) 35 and feedback-controlled by the optical attenuator control circuit 46, and the optical intensity of the measurement light is controlled to approach the set value.

  Similarly, the reference light P2 is subjected to feedback control by the optical attenuator control circuit 46 so that the light intensity of the reference light approaches the set value. Thereby, the balance of the measurement signal / reference signal is achieved.

  As described above, in the exhaust gas analyzer according to the present invention, in the region surrounded by (a) in FIG. 5, the process of removing the radiant light from the measurement light is performed, and in the region surrounded by (a), Feedback control for the optical attenuator (VOA) is performed by the signal component excluding the radiated light component, and the light intensity of the measurement light is controlled to approach the set value. Therefore, in the exhaust gas analysis apparatus and method using the laser suction method, real-time signal processing that eliminates the influence of background light (radiant light) generated in the measurement cell 36 is possible, and exhaust gas analysis with a high degree of measurement is performed in real time. It becomes possible. In the illustrated example, the bandpass filter 42 removes a direct current component from the measurement light signal and the reference light signal in the area of the difference detector surrounded by (c). There is also an advantage that a bandpass filter provided in a known difference detector can be used as it is. In FIG. 5, SV represents a light amount setting value.

  Although not shown, it is possible to take out a group of measurement light and reference light shown in FIG. 5 from the branching filter 34 and perform gas analysis at a plurality of locations at the same time. In that case, laser beams having the same frequency may be used in a plurality of systems, or signals of a plurality of frequencies output from the signal generator may be used in each system. In the former case, for example, by installing the above-described exhaust gas analyzer before and after the exhaust gas catalyst, the change in the exhaust gas component can be known by the catalyst. In the latter case, it is possible to analyze a plurality of kinds of gas components contained in the exhaust gas.

  FIG. 6 shows a case where the exhaust gas analyzer 30 according to the present invention is installed in the automobile 1, and FIG. 7 shows a case where it is installed on the engine bench 1A. In any case, the exhaust gas discharged from each cylinder of the engine 2 is merged in the exhaust manifold 3, introduced into the first catalyst device 5 through the exhaust pipe 4, further introduced into the second catalyst device 6, and then the muffler 7. Through the exhaust pipe 8 to the atmosphere. In this example, the exhaust path is formed by joining the exhaust manifold 3, the exhaust pipe 4, the first catalyst device 5, the second catalyst device 6, the muffler 7, and the exhaust pipe 8. After purification by the first catalyst device 5 and further purification by the second catalyst device 6, the muffler 7 silences and depressurizes it and releases it to the atmosphere.

  The above-described measurement cells 36 in the exhaust gas analyzer 30 according to the present invention are attached to a plurality of locations in such an exhaust path, and the above-described analysis system is arranged for each measurement cell 36, and these signals are detected by their respective differences. The difference signal is output to the device 40. These differential signals are sent to a computer 44 constituting an analysis system for exhaust gas analysis. As described above, by providing the plurality of measurement cells 36, exhaust gas analysis at various locations in the exhaust path can be performed simultaneously and in real time.

P: Output light of the laser light generating means,
P1: Measuring light,
P2: Reference light,
30 ... exhaust gas analyzer,
31 ... Laser light generating means,
32. Timing chart of laser beam irradiation,
33 ... Timing signal generating means for selecting a time zone in which the laser beam is not irradiated,
35. Optical attenuator (VOA),
36 ... measurement cell,
37, 38: a light receiving element such as a photodiode (PD),
40. Difference signal device,
41 ... Amplifier,
42: Band pass filter (BPF),
43 ... differential amplifier circuit,
44. Computer constituting analysis system,
45 ... Analog memory,
46: Optical attenuator control circuit,
47: Adder (subtraction circuit).

Claims (4)

An exhaust gas analyzer that irradiates exhaust gas emitted from an engine with laser light and analyzes components of the exhaust gas from an absorption line of signal light that has passed through the exhaust gas, the exhaust gas analyzer comprising:
A laser light generating means comprising a laser light irradiation timing chart and a timing signal generating means for selecting a time zone in which the laser light is not irradiated;
Optical demultiplexing means for demultiplexing the output light of the laser light generating means into measurement light and reference light and irradiating the measurement light on the exhaust gas flowing in the measurement cell;
An optical attenuator disposed in an optical path between the optical demultiplexing means and the measurement cell;
A light receiving element that receives the measurement light and the reference light transmitted through the exhaust gas;
A difference detector for detecting a difference signal between the measurement light signal and the reference light signal received by the light receiving element;
A memory for storing a radiation light signal received by the light receiving element of the measurement light when the laser light is not irradiated based on a signal from the timing signal generating unit;
A subtracting circuit for subtracting the radiation light signal from the measurement light signal;
And an optical attenuator control circuit that feeds back the signal after the subtraction to the optical attenuator.   The exhaust gas analyzer according to claim 1, wherein the difference detector further includes a band-pass filter that removes a DC component from the measurement light signal and the reference light signal. The exhaust gas discharged from the engine is irradiated with measurement light demultiplexed from the output light of the laser light generating means through the optical attenuator, and the measurement light signal and reference light signal transmitted through the exhaust gas are received and the measurement light signal and reference light signal are received. And an exhaust gas analysis method for analyzing a component of exhaust gas based on the difference signal,
In the exhaust gas analysis method, the radiation light signal received by the measurement light receiving means when the laser light is not irradiated is stored in the memory, and the measurement light signal received by the measurement light receiving means when the laser light is emitted. Exhaust gas analysis, including a control for bringing a measurement light level excluding radiation close to a set value by feeding back a signal obtained by subtracting the radiation light signal from the optical attenuator Method.   The exhaust gas analysis method according to claim 3, wherein the difference signal is obtained after removing a direct current component from the measurement signal and the reference signal using a band-pass filter.

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