JP2006337326A - Apparatus and method for analyzing exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas analyzer, capable of enhancing the analyzing precision of an exhaust gas, and of easily performing the analysis of exhaust gas in real time and of analyzing at low cost. <P>SOLUTION: The exhaust gas analyzer 10 is equipped with a light attenuator 34 for irradiating the exhaust gas discharged from an engine 2 with laser beams, which are emitted by applying a drive pulse to laser diodes LD1-LD5 through an optical fiber 24, and detecting the laser beams transmitted through the exhaust gas by a detector 25 to measure the concentration or temperature of the components of the exhaust gas, on the basis of the detected transmitted laser beams to adjust the intensities of the laser beams; and the light attenuator 34 is subjected to feedback control, by calculating feedback correction quantity on the basis of the detected transmitted laser beams with a differential photodetector 40. A drive pulse 50 is equipped with a current main scanning section 52 that is changed in the current value with the elapse of time and with a current-constant section 51 continuing to the current main scanning section 52 and becoming constant in the current value and is preferably equipped with a finished current-constant section 53. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas analyzer for an automobile or the like and an exhaust gas analysis method, and in particular, by mounting in an exhaust path, the concentration and temperature of exhaust gas passing through the exhaust path can be accurately measured in real time, and the cost is low. TECHNICAL FIELD The present invention relates to an exhaust gas analysis apparatus capable of analyzing exhaust gas with a gas exhaust method and an exhaust gas analysis method.

  Conventionally, as this type of exhaust gas analyzer, there is an in-vehicle HC measuring device described in Patent Document 1. This measuring apparatus includes an NDIR (non-dispersive infrared spectroscopy) gas analyzer for continuously measuring the concentration of HC (hydrocarbon) in exhaust gas flowing through an exhaust pipe connected to an engine, and exhaust gas flowing through the exhaust pipe. Exhaust gas flow meter that continuously measures the flow rate of gas, and calculation processing that calculates the THC (total hydrocarbons) amount in the exhaust gas continuously by calculating the output of each of the NDIR gas analyzer and the exhaust gas flow meter The circuit can be installed in the vehicle.

  In the NDIR (Non-Dispersive Infrared Analyzer) non-dispersive infrared spectroscopy described in Patent Document 1 and the like, an infrared light source for irradiating infrared light is provided in a cell to which a sample gas is supplied. .

  In addition, there are various exhaust gas measurement devices and analysis devices using the non-dispersive infrared spectroscopy, FID (Frame Ionization Detector) method, CLD (Chemical Luminescence Detector) method, etc. In all measurement principles, a reference gas for calibration and an auxiliary gas for use in analysis are required. Further, in the measurement by the infrared absorption method, the driving pulse applied to the infrared laser light generating means uses a triangular driving pulse to sweep the wavelength.

JP 2004-117259 A

  By the way, in-vehicle type HC measuring devices of the above structure and other exhaust gas analyzers require reference gas and auxiliary gas for measurement as described above, and the entire analyzer including facilities such as reference gas becomes large. A great running cost is necessary. In addition, in order to carry out these chemical analyses, it is necessary to perform measurement after removing moisture and dirt (soot) in the exhaust gas. The exhaust gas to be analyzed is sampled and subjected to analysis such as dilution. Therefore, real-time analysis of exhaust gas is not possible.

  Furthermore, in the measurement by the infrared absorption method, the drive pulse applied to the laser light generating means usually uses a triangular wave as described above. For example, the triangular drive pulse P has a shape as schematically shown in FIG. 12, and a pulse having a frequency band of about several Hz to several tens Hz is used. In FIG. 12, the horizontal axis indicates time t, and the vertical axis indicates the current value A. When this triangular wave drive pulse P is applied to the laser light generating means, laser light having a peak in a predetermined frequency band can be generated, and the component gas concentration can be measured by matching the frequency band to the component gas in the exhaust gas. .

  However, the laser light generated in this way has a problem that it is difficult to make the peak light intensity constant, and when performing exhaust gas analysis, the peak portion is buried by noise and accurate gas concentration measurement cannot be performed. . The noise includes, for example, optical noise and electrical noise due to engine start vibration. In addition, in order to make the light intensity of the laser light constant, the light intensity of the laser light is measured and feedback controlled, but it is difficult to make the dispersion of the light intensity constant. Furthermore, the measuring device described in Patent Document 1 cannot measure component gases other than HC.

  The present invention has been made in view of such problems, and the object of the present invention is to stabilize the light intensity of the laser beam that passes through the exhaust gas, to eliminate noise and to improve the accuracy of exhaust gas analysis. It is an object to provide an exhaust gas analysis apparatus and an exhaust gas analysis method that can improve the quality of the exhaust gas. It is another object of the present invention to provide an exhaust gas analysis apparatus and an exhaust gas analysis method that can easily perform an exhaust gas analysis in real time without using a reference gas and can analyze various component gases at a low cost. It is another object of the present invention to provide an exhaust gas analyzing apparatus and an exhaust gas analyzing method that are simple in configuration, can be miniaturized, and can be mounted on a vehicle.

  As a result of intensive studies on laser light generating means for making the light intensity of the laser light used in the exhaust gas analyzer constant, the present inventors have completed the present invention having the following characteristics. That is, the exhaust gas analyzer according to the present invention irradiates the exhaust gas discharged from the engine with a laser beam generated by applying a drive pulse to the laser beam generating means, receives the laser beam transmitted through the exhaust gas, An apparatus for analyzing the exhaust gas by measuring the concentration and temperature of the components of the exhaust gas based on the received laser light, and this apparatus is an optical attenuator for adjusting the light intensity of the laser light generated from the laser light generating means The optical attenuator is feedback-controlled based on the received laser light, and the drive pulse applied to the laser light generating means includes a current scanning section in which a current value changes with time, and a current scanning section. And a constant current section where the current value is constant.

  The exhaust gas analyzer of the present invention configured as described above is obtained by forming a constant current section having a constant current value in the drive pulse supplied to the laser light generating means, and fixing the wavelength in the constant current section. For example, the optical attenuator inserted on the measurement light side is adjusted by feedback control so that the optical balance between the signal light and the measurement light can be kept constant, so that the balance between the signal light and the measurement light can be accurately maintained. For this reason, even if the balance is lost due to thermal fluctuation due to exhaust gas, deviation of the optical axis between the laser beam and the light receiving part, dirt on the mirror that reflects the laser beam, etc., the optical attenuator is adjusted to provide feedback to the laser beam generating means. By applying, the balance can be returned to the initial state, and the exhaust gas analysis with high accuracy becomes possible. Moreover, since this exhaust gas analyzer does not require a reference gas, it can easily analyze exhaust gas in real time and can analyze various component gases at low cost.

  Moreover, as a preferable specific aspect of the exhaust gas analyzer according to the present invention, the drive pulse has a constant start current section that is constant at the current value on the start end side of the current scanning section, and a straight line from the constant start current section. And the current scanning section in which the current increases. According to this configuration, by applying a drive pulse having a current scanning period in which the current increases linearly from a constant starting current constant section where the current value is constant to the laser light generating means, overshoot is prevented and laser light is emitted. It can be generated stably. That is, by providing a constant start current section on the start side, the possibility of noise on the waveform at the start of oscillation can be eliminated.

  Furthermore, as another preferred specific aspect of the exhaust gas analyzer according to the present invention, the drive pulse is continuous with the current scanning section, and the end current is constant with the current constant at the current value at the end of the current scanning section. It is characterized by further comprising a section. According to this configuration, since the start current constant section is provided in the front stage of the current scanning section in which the current value changes with time and the end current constant section is provided in the subsequent stage, the laser current can be changed by changing the intermediate current value over time. By sweeping the wavelength of light, the wavelength range including the absorption wavelength can be fixed at a constant wavelength without absorption, and the wavelength stability can be improved.

  As another aspect, a sensor unit is formed that includes an irradiation unit that irradiates the laser beam to the through-hole through which the exhaust gas passes, and a light receiving unit that receives the laser beam that has passed through the exhaust gas, and the sensor unit is configured to exhaust the exhaust gas. It is preferable to install in the path and irradiate the exhaust gas with laser light from the irradiation unit, and then receive the laser light transmitted through the exhaust gas with the light receiving unit to analyze the exhaust gas. In particular, it is preferable to install the sensor units at a plurality of locations in the exhaust path. With this configuration, it is possible to measure the concentration and temperature of the exhaust gas component at an intermediate position in the exhaust path of the exhaust gas discharged from the engine. For example, the concentration of the exhaust gas component before and after passing through the catalyst device can be measured in real time. Can be detected. In addition, since the device configuration can be simplified and the size can be reduced, the vehicle can be mounted on the vehicle.

  In the exhaust gas analysis method according to the present invention, a driving pulse including a current scanning interval in which a current value changes with time and a constant current interval in which the current value is constant is continuous to the laser light generating unit. Laser light is generated, and the laser light is split into signal laser light and measurement laser light, and the measurement laser light is irradiated to the exhaust gas through an optical attenuator to transmit the laser light transmitted through the exhaust gas. Calculates a feedback correction amount for correcting the optical attenuator based on the received transmitted laser light and the signal laser light, and inputs the feedback correction amount to the optical attenuator to obtain the light intensity of the measurement laser light. And the concentration and temperature of exhaust gas components are calculated based on the signal laser beam and the transmitted laser beam. This feedback correction amount is preferably calculated from the optical balance between the transmitted laser beam and the signal laser beam by inputting the transmitted laser beam to the differential photodetector. According to this configuration, the light intensity of the laser light generated from the laser light generating means is adjusted based on the laser light transmitted through the exhaust gas, and the signal laser light and the transmitted laser light are adjusted by the laser light having the adjusted light intensity. By controlling the light balance, it is possible to cope with environmental changes in the exhaust path of the engine or the like, and to perform exhaust gas analysis with high accuracy.

  According to the exhaust gas analyzer and the exhaust gas analysis method of the present invention, the drive pulse applied to the means for generating the laser light has a current scanning interval in which the current changes linearly, the current scanning interval is continuous, and the current value is constant. By using a shape having a constant current section, laser light can be generated without overshoot, and wavelength stability of the laser light can be improved. Further, by adjusting the light intensity of the laser light generated from the laser light generating means using this drive pulse, the balance between the signal light and the measurement light is improved, and the exhaust gas analysis with high accuracy can be performed. Furthermore, the concentration of exhaust gas components can be accurately detected at low cost without using a reference gas by using the laser light having high wavelength stability. In addition to measuring the final form from the end of the exhaust pipe, various types of component gases can be measured in the middle of the exhaust path, and measurement at high temperatures is possible, so high-temperature exhaust gas immediately after discharge can be measured. It can also measure the concentration of components.

  Hereinafter, an embodiment of an exhaust gas analyzer according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a main part configuration diagram in which the exhaust gas analyzer according to the present embodiment is mounted on a vehicle, FIG. 2 is a main part configuration diagram in a state where the exhaust gas analyzer of FIG. 1 is installed on an engine bench, and FIG. FIG. 4 is a block diagram showing an overall configuration of an exhaust gas analyzer including a personal computer as a signal analysis unit and a main configuration of the laser oscillation / light reception controller.

  In FIG. 1, an exhaust gas analyzer 10 of this embodiment is an apparatus that analyzes exhaust gas discharged from an engine 2 installed in an automobile 1. Moreover, as shown in FIG. 2, it is an apparatus which analyzes the exhaust gas of the engine 2 installed in the engine bench 1A. 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 through the muffler 7 to the exhaust pipe 8. From the atmosphere. 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, and the exhaust gas discharged from the engine 2 is converted into the first catalyst device 5. Then, after purifying with the second catalyst device 6, the muffler 7 mute and reduce the pressure and release it into the atmosphere. The muffler may have two main mufflers and sub mufflers.

  The plurality of members constituting the exhaust path are basically pipe-like tube members, and are connected by bolts or the like with the flange portions in contact with each other. For example, the first catalyst device 5 has exhaust pipe portions connected upstream and downstream of a large-diameter main body portion, and flange portions F and F are fixed to the end portions of these exhaust pipe portions by welding or the like. The second catalyst device 6 also has an exhaust pipe connected to the upstream and downstream sides of the large-diameter main body, and flanges F and F are fixed to the ends of these exhaust pipes to connect the flanges. Thus, an exhaust path is configured. The exhaust pipe 8 at the end is fixed directly to the muffler 7 by welding or the like.

  The exhaust gas analyzer 10 of the present embodiment includes a plurality of sensor units 11 to 14 attached to a plurality of locations in the exhaust path. The first sensor unit 11 is installed between the exhaust pipe 4 on the engine side upstream of the first catalyst device 5, the second sensor unit 12 is installed on the downstream side of the first catalyst device 5, and the third The sensor unit 13 is installed on the downstream side of the second catalyst device 6. The fourth sensor unit 14 is installed in the exhaust pipe 8 downstream of the muffler 7. The sensor unit 14 may be installed in the middle of the exhaust pipe or may be installed by being inserted into the opening at the end of the exhaust pipe. The first sensor unit 11 may be configured to be installed in the exhaust pipe of each cylinder before joining the exhaust manifold 3.

  As shown in FIG. 3, the exhaust pipe 4, the first catalyst device 5, the second catalyst device 6, and the muffler 7 are connected by tightening flange portions F and F with bolts (not shown). The sensor parts 11, 12, 13 installed between the members constituting the are installed in a state of being sandwiched between the flange parts F, F. The flange portions F and F are formed at both end portions of the member constituting the exhaust path, and the joint surfaces of the flange portions intersect at right angles to the center line of the exhaust path. As a result, the sensor parts 11 to 13 are installed so as to cross the exhaust path between the flange parts F and F. The fourth sensor unit 14 performs analysis immediately before the exhaust gas is released into the atmosphere, and may be installed between the flanges F and F in the middle of the exhaust pipe 8 protruding from the muffler 7. In addition, what is necessary is just to set the number of installation of a sensor part arbitrarily.

  The sensor units 11 to 14 attached in the exhaust path have substantially the same configuration, and one sensor unit 11 will be described in detail with reference to FIGS. The sensor portion has a sensor base 21 formed of a plate material having a predetermined thickness of, for example, about 5 to 20 mm, and a through hole 22 having a diameter substantially the same as the inner diameter of the exhaust pipe portion is formed in the center portion. The exhaust gas passing through the exhaust passage passes through the through hole 22. The shape of the through hole 22 is preferably a circle having the same diameter as the inner diameter of the exhaust pipe portion so as not to disturb the exhaust flow. A metal plate or a ceramic plate is used as the plate, but the material is not particularly limited. The sensor base 21 is formed with two sensor holes 21a and 21b penetrating from the outer peripheral surface toward the through hole. A collimator 23 for condensing laser light is fixed to one sensor hole 21a, an optical fiber 24 for irradiating the laser light is connected to the collimator, and a detector such as a photodiode for receiving the laser light is connected to the other hole 21b. 25 is fixed.

  In the through hole 22 of the sensor base 21, two upper and lower reflecting plates 26 and 27 are fixed facing each other. The two reflecting plates are fixed in a parallel state, and the infrared laser light condensed and emitted from the irradiation-side optical fiber 24 through the collimator 23 is first reflected upward by the lower reflecting plate 27, and then the upper The light is reflected downward by the reflection plate 26 and is alternately reflected by the two reflection plates 26 and 27 so as to reach the detector 25 on the light receiving side. In this manner, the transmission distance of the laser light in the exhaust gas is set to be long.

The reflectors 26 and 27 are preferably formed of materials that do not deteriorate due to exhaust gas. A thin film such as gold or platinum is formed on a base plate material, and a thin film of MgF ₂ or SiO ₂ is formed thereon as a protective layer. What is done is preferable. Further, it is desirable that the reflector has a high reflectance so that infrared laser light can be efficiently reflected. Since the reflector is exposed to the exhaust gas during engine startup and becomes contaminated, it is preferable to remove the sensor base 21 from the flange portions F and F for cleaning as necessary. By wiping the protective layer covering the reflective surface, the attached dirt can be easily cleaned, and the reflectance can be improved.

  The sensor base 21 is fixed in a state of being sandwiched between the flange portions F, F, and a bolt, a nut, etc., not shown in the state of having the gaskets 28, 28 sandwiched between the flange portions F, F and the sensor base 21. It is fixed by. The gasket 28 is made of asbestos or the like, and has a through hole having the same diameter as the inner diameter of the exhaust pipe. With this configuration, even if the exhaust path is connected with the sensor base 21 sandwiched between the flange portions F and F, the exhaust gas does not leak in the middle, and the increase in the length of the exhaust path is small. In FIG. 3, between the flange portion F welded to the downstream end of the exhaust pipe 4 and the flange portion F welded to the end portion of the exhaust pipe portion 5a on the upstream side of the first catalyst device 5, the gaskets 28, In this configuration, the sensor base 21 is fixed with 28 interposed therebetween.

  An optical fiber 24 that supplies laser light to the sensor unit 11 and a detector 25 that receives laser light that has passed through the exhaust gas by the sensor unit 11 and outputs an electrical signal are connected to a laser oscillation / light reception controller 30. That is, infrared laser light emitted from a laser diode (to be described later) of the laser oscillation / light reception controller 30 is irradiated into the through hole 22 through the sensor hole 21a of the sensor base 21 through the optical fiber 24 and reflected by the reflection surfaces 26 and 27. The infrared laser light thus received is received by the detector 25 on the light receiving side through the sensor hole 21 b, and an electric signal output from the detector 25 is input to the laser oscillation / light receiving controller 30 via the cable 29.

  The signal analysis unit is a signal analysis unit in which the emission intensity of the signal light of the infrared laser light emitted from the laser oscillation / light reception controller 30 and the light reception intensity of the measurement light (transmission laser light) transmitted through the exhaust gas and received by the detector 25 The computer 45 is configured to measure and analyze the concentration and temperature of exhaust gas components with a personal computer. Thus, the exhaust gas analyzer 10 includes a plurality of sensor units 11 to 14, the laser oscillation / light reception controller 30, and the personal computer 45. The exhaust gas analyzer 10 introduces exhaust gas discharged from the engine into the through hole 22 of the sensor unit, irradiates the exhaust gas with laser light through the optical fiber 24, and receives the laser light transmitted through the exhaust gas with the detector 25. In this apparatus, the concentration and temperature of exhaust gas components are measured and analyzed based on the received laser beam.

  Here, the laser oscillation / light reception controller 30 will be described with reference to FIG. The laser oscillation / light reception controller 30 supplies a plurality of frequency signals from a signal generator 31 such as a function generator to a plurality of laser diodes LD1 to LD5 as a laser beam generating means for generating infrared laser beams having a plurality of wavelengths. The laser diodes LD1 to LD5 respectively generate infrared laser beams having a plurality of wavelengths corresponding to the respective frequencies. Signals of a plurality of frequencies output from the signal generator 31 of the laser oscillation / light reception controller 30 are supplied to the laser diodes LD1 to LD5 to generate laser light. For example, LD1 has a wavelength of about 1300 to 1330 nm, and LD2 has a wavelength of 1330 to It is set to generate an infrared laser beam having a wavelength band such that the wavelength band in which the peak wavelength of the component gas to be detected exists, such as 1360 nm, continues.

The wavelength of the infrared laser beam that passes through the exhaust gas is set in accordance with the exhaust gas component to be detected. Carbon monoxide (CO), carbon dioxide (CO ₂ ), ammonia (NH ₃ ), methane (CH ₄ ), water When detecting (H ₂ O), infrared laser beams having five wavelengths are used. For example, the wavelength suitable for detecting ammonia is 1530 nm, the wavelength suitable for detecting carbon monoxide is 1560 nm, and the wavelength suitable for detecting carbon dioxide is 1570 nm. The wavelength suitable for detecting methane is 1680 nm, and the wavelength suitable for detecting water is 1350 nm. As described above, it is preferable to use a laser beam obtained by combining a plurality of types of single wavelength laser beams as the infrared laser beam transmitted through the exhaust gas. Furthermore, when detecting the concentration of other exhaust gas components, infrared laser beams having different wavelengths are used in accordance with the number of exhaust gas components. Since the concentration of exhaust gas components can be measured using different wavelengths even with the same components, measurement may be performed by selecting an appropriate wavelength. Thus, the laser diodes LD1 to LD5 constitute a single laser light generating means (single light source) having a plurality of types of wavelength bands.

  The laser light generated from each of the laser diodes LD1 to LD5 is divided into signal light and measurement light by optical fibers 32. The measurement laser beams divided by the five demultiplexers 33 are multiplexed by the multiplexer 36 through the optical fiber 35A in which an optical attenuator 34 is installed on the way, and the sensor units 11 to 14 pass through the optical fiber 24. The light is guided to the irradiating unit and irradiated into the through hole 22 through the collimator 23. Further, the signal laser light divided by the five demultiplexers 33 is multiplexed by the multiplexer 37 through the optical fiber 35B. The laser beam for measurement and signal is an infrared laser beam obtained by combining laser beams having a plurality of wavelengths in accordance with a plurality of component gases of exhaust gas.

  In the present embodiment, the measurement laser light demultiplexed by the demultiplexer 33 as described above is configured to be multiplexed through the optical attenuator 34. The optical attenuator 34 has a function of adjusting the intensity of the measurement laser beam that transmits the exhaust gas by controlling the light intensity of the measurement laser beam. That is, a feedback correction amount is calculated based on the light intensity of the transmitted laser light that has passed through the exhaust gas and the light intensity of the signal laser light, and this correction amount is input to the optical attenuator 34 to input the light of the measurement laser light. Adjust the strength. The optical attenuator 34 is provided with a filter capable of changing the transmittance in the optical path of the laser light, adjusting the light intensity by changing the amount of transmitted light, and placing a mirror in the optical path, and changing the reflection angle of the mirror. The thing of appropriate forms, such as what adjusts light intensity, can be used. The optical attenuator may be configured to adjust the demultiplexed signal laser beam, or may be configured to adjust both the signal laser beam and the measurement laser beam.

  The driving pulse 50 output from the signal generator 31 and supplied to the laser diodes LD1 to LD5 includes a starting current constant section 51 as shown in FIGS. 5 and 6, and a current scanning section 52 continuous to the starting current constant section. In addition, a constant end current section 53 continuous with the current scanning section is formed. More specifically, the drive pulse 50 according to the present embodiment includes a start current constant section 51 in which the current is constant at the current value on the start end side of the current scanning section 52 in which the current value changes with time, and a continuous start current section. And a current scanning section 52 in which the current value increases linearly with time, and an end current constant section 53 that is continuous with the current scanning section and that makes the current constant at the current value at the end of the current scanning section. Composed. As an example, the time width of one pulse is set to about 30 to 100 μS, and the maximum current value is set to about several hundred to 400 mA.

  FIG. 5 shows drive pulses when two laser diodes are used. For example, the upper drive pulse corresponds to the laser diode LD1, and the lower drive pulse corresponds to the laser diode LD2. In the case of five laser diodes, although not shown, five drive pulses are sequentially shifted in time. The horizontal axis in FIG. 5 indicates time t, and the vertical axis indicates the current value A. In addition, the triangular wave shown with the broken line in a figure has overlapped and shown the triangular wave P shown in FIG. 12 which is a conventional drive pulse.

  When the laser diode is driven using such a driving pulse 50, as shown in FIG. 6, since the current value is constant in the constant start current section 51 of T1 to T2, the wavelength is fixed at the constant wavelength λ1, and at the start of oscillation. The possibility of noise on the waveform can be reduced. In the current scanning section 52 of T2 to T3, the wavelength is swept with the change of the current, and the absorption intensity of the exhaust gas appears as the peak wavelength λ2 in the wavelength region including the absorption wavelength, and the concentration of the exhaust gas component is measured. be able to. Further, since the current value is constant in the end current constant section 53 from T3 to T4, the wavelength is fixed to the constant wavelength λ3. In this way, the light intensity at the peak wavelength is stabilized because the wavelength is fixed and the light intensity is constant in the constant start current section 51 and the constant end current section 53 where the current value is constant. As a result, the optical attenuator 34 is feedback-controlled via the feedback line 41 from the differential photodetector 40, which will be described later, based on the laser light intensity balance, and the light intensity of the signal laser light can be adjusted in a stable state. it can. In the current scanning section 52 where the current value increases linearly, the concentration and temperature of the exhaust gas component can be accurately measured from the light intensity at the peak wavelength corresponding to the exhaust gas component gas.

  The drive pulse is a start current constant section 61a in which the current is constant at the current value on the start end side of the current scanning section 61b, like the drive pulse 61 in FIG. 7b, instead of the drive pulse 50 in FIG. You may comprise from the current scanning area 61b from which a current value changes with time continuously from the starting current fixed area. Further, like the drive pulse 62 in FIG. 7c, a constant start current section 62a in which the current is constant at the current value on the start end side of the current scan section 62b, and a current scan in which the current value decreases linearly continuously. You may comprise from the area 62b and the end current constant area 62c which made the electric current constant with the electric current value of a termination | terminus succeeding this. Further, as in the drive pulse 63 of FIG. 7d, a constant start current section 63a in which the current is constant at the current value on the start end side of the current scan section 63b, and a current scan in which the current value decreases linearly continuously. It can also consist of the section 63b. As described above, the drive pulse may have any shape as long as it has at least one of the current scanning period and the constant starting current period and the constant ending current period continuous to the current scanning period.

  Since any of the drive pulses 50, 61, 62, and 63 has a constant start current section where the current value is constant, the wavelength of the laser light is fixed at a constant wavelength that is not absorbed by the gas component, and oscillation starts. It is possible to eliminate the possibility of noise and to perform feedback control of the adjustment of the light intensity balance of the laser light with high accuracy. Further, the wavelength can be swept in the current scanning section where the current value changes with time, and the concentration of the exhaust gas component can be detected using the light intensity of the peak wavelength matched to the absorption of the exhaust gas by the component gas. In particular, when there is a constant start current interval and a constant end current interval on both sides of the current scanning interval, the light intensity balance can be further stabilized and the measurement accuracy of the concentration of exhaust gas components and the like can be improved. be able to.

  In FIG. 4, the electrical signal output from the detector 25 fixed to the light receiving unit of the sensor unit 11 is supplied to the differential photodetector 40 via the cable 29. The signal laser beam supplied from the signal light multiplexer 37 through the optical fiber 38 is input to the differential photodetector 40 and converted into an electric signal by a photoelectric converter such as a photodiode. The differential optical detector 40 provides feedback to make the light intensity of the measurement light constant based on the electrical signal of the measurement laser light that has passed through the exhaust gas and the electrical signal of the signal laser light that has not passed through the exhaust gas. The correction amount is calculated and input to the optical attenuator 34 disposed in front of the measuring light multiplexer 36 through the feedback line 41.

  The feedback correction amount is calculated for each component gas, supplied to the optical attenuator 34 for each measurement light of the laser diode that generates the peak wavelength of the component gas, and adjusts and controls the light intensity of the measurement light. The differential photodetector 40 inputs the electrical signals output from the plurality of sensor units to a personal computer 45 as a signal analysis unit that calculates the concentration and temperature of the exhaust gas components. Note that the signal light may not be directly input to the differential photodetector, but may be input after being converted into an electrical signal via a photodiode or the like.

  The optical attenuator 34 controls the laser diodes LD1 to LD5 so that the laser light generated from the laser diode is attenuated based on the supplied feedback correction amount so that the light intensity of the signal light and the measurement light becomes constant. To do. An electrical signal corresponding to the difference between the signal light and the measurement light calculated by the differential photodetector 40 is amplified by, for example, a preamplifier (not shown), and is passed through an A / D converter and is a personal computer 45 serving as a signal analysis unit. In the personal computer, the data from the differential photodetector is converted into a concentration value to calculate the concentration of the exhaust gas component and the exhaust gas temperature.

  In place of the detector 25 fixed to the sensor base 21 as the light receiving part of the sensor parts 11 to 14, a light receiving optical fiber is fixed to the sensor base 21, and the received laser light is separated by a demultiplexer for each gas component. Alternatively, the output voltage for each gas component may be detected by a photodiode or the like, and the concentration of the exhaust gas component may be calculated by the personal computer 45 from the measurement light and the signal light.

  The exhaust gas analyzer 10 of the present invention transmits, for example, infrared laser light into the exhaust gas, calculates the concentration of exhaust gas components based on the intensity of incident light and the intensity of transmitted light after passing through the exhaust gas, Is to analyze. That is, the concentration C of the exhaust gas component is calculated from the following formula (1).

C = −ln (I / I ₀ ) / kL (1)

In Equation (1), I is the transmitted light intensity, I ₀ is the incident light intensity, k is the absorptance, and L is the transmission distance. Therefore, the concentration C of the exhaust gas component is calculated based on the ratio of the transmitted light intensity (I) to the incident light intensity (I ₀ ), which is signal light, and the signal intensity (I / I ₀ ). The transmitted light intensity I passes through the exhaust gas through the optical fiber 24 and is output from the detector 25, and the incident light intensity I ₀ is input from the multiplexer 37 through the optical fiber 38 to the differential optical detector 40 and is shown in the figure. Output from a non-photodiode. In the present embodiment, the signal light intensity that does not pass through the exhaust gas is used as the incident light intensity I ₀ .

The operation of the exhaust gas analyzer 10 of the present embodiment configured as described above will be described below. When analyzing the exhaust gas by measuring the concentration of the components of the exhaust gas, the signal generator 31 of the laser oscillation / light receiving controller 30 is operated to apply the drive pulse 50 as shown in FIG. 5 to each of the laser diodes LD1 to LD5. Thus, infrared laser light having a predetermined wavelength is generated from each of the laser diodes LD1 to LD5. The infrared laser light generated from each of the laser diodes LD1 to LD5 reaches the splitters 33 through the optical fibers 32, where it is split into measurement light and signal light. The measurement light demultiplexed by each demultiplexer is multiplexed by a multiplexer 36 through an optical attenuator 34 and an optical fiber 35A to become a measurement laser beam, and is guided through the optical fiber 24 to the irradiation portions of the sensor units 11-14. Lighted. Further, the signal light demultiplexed by each of the demultiplexers 33... Is multiplexed by the multiplexer 37 through the optical fiber 35B to become signal laser light, and is measured as the incident light intensity I ₀ by the differential photodetector 40. The

  The drive pulse 50 output from the signal generator 31 has a constant start current section 51 as shown in FIG. 5, a current scanning section 52 in which the current value increases linearly, and a constant end current section 53. In addition, since the wavelength of the emitted laser light does not change during the constant current period before and after, and the wavelength changes only during the intermediate current scanning period, stable laser light with less noise can be generated. That is, as shown in FIG. 6, the wavelength is swept by fixing the wavelength λ1 with no absorption in the constant starting current section 51 and changing the current value with time in the intermediate current scanning section to include the absorption wavelength. By measuring the absorption intensity of the laser beam, the peak wavelength can be stabilized, the noise component can be reduced, and the S / N ratio can be improved. In the constant end current section 53, the wavelength is fixed at a constant wavelength λ3.

And the laser beam for a measurement irradiated to the sensor parts 11-14 from the optical fiber 24 is irradiated into the through-hole 22 through which the exhaust gas passes. The laser beam for measurement reaches the detector 25 of the light receiving unit by being repeatedly reflected by the reflecting surfaces 26 and 27. The measurement laser light attenuated through the exhaust gas is received as the transmitted light intensity I by the detector 25 which is a light receiving unit, converted into an electric signal, and input to the differential photodetector 40. The laser beam for measurement is repeatedly reflected to increase the distance transmitted through the exhaust gas, and the attenuation is increased by increasing the transmission distance L in the formula (1). It is possible to measure the concentration. Thus, the signal intensity which is the ratio (I / I ₀ ) between the light intensity I ₀ of the signal laser light and the transmitted light intensity I of the measurement laser light is calculated, and the component of the exhaust gas is calculated based on this signal intensity ratio. The concentration of is calculated. The light intensity received by the detector 25 is preferably 30% or more with respect to the light intensity irradiated from the optical fiber 24. This is because if it is less than 30%, it is difficult to distinguish the noise.

  In the differential optical detector 40, an optical attenuator 34 is used to calculate a feedback correction amount from the measurement laser light that has been transmitted and attenuated through the exhaust gas and adjust the light intensity of the laser diodes LD1 to LD5 corresponding to each wavelength. Feedback control. The optical attenuator 34 adjusts the light intensity for each laser diode and calibrates the measurement laser light. For example, when the measurement light intensity decreases due to a disturbance, the light intensity can be increased by automatically detecting and reducing the attenuation rate, and a balance equivalent to the initial state can be maintained. Note that. The signal light has no disturbing elements from the generation to the reception of the laser light, and the signal laser light intensity does not change unless the laser output changes. Therefore, it is possible to adjust the measurement laser light intensity with an optical attenuator to achieve a balance. preferable.

Further, the differential photodetector 40 takes a difference between the signal laser beam and the measurement laser beam and supplies a signal to the personal computer 45 for signal analysis. The personal computer 45 calculates the ratio (I / I ₀ ) between the light intensity of the signal laser light and the light intensity of the peak wavelength of the measurement laser light attenuated by passing through the exhaust gas, and the sensor unit is installed. The concentration of the exhaust gas component at a position in the exhaust path is calculated. Moreover, the relative change in the concentration of the components of the exhaust gas at a plurality of locations in the exhaust path can be analyzed by the sensor units 11 to 14 installed at the plurality of locations.

  In this embodiment, the several sensor parts 11-14 are installed in the exhaust path, and the density | concentration and temperature of the component of the exhaust gas in the position of each sensor part are measured. For this reason, the concentration and temperature of the exhaust gas component in the downstream portion of the exhaust manifold 3 and the concentration and temperature of the exhaust gas component on the upstream side and downstream side of the first catalyst device 5 can be measured. For example, the performance of the catalyst devices 5 and 6 is evaluated based on the temperature after passing through the catalyst devices 5 and 6 and the concentration of the exhaust gas components, and the temperature before processing in the catalyst devices 5 and 6 and the concentration of the exhaust gas components. In addition, the deterioration of the catalyst device due to, for example, aging can be detected.

  The output of the detector 25 used when measuring the concentration and temperature of the components of the exhaust gas is easily affected by noise due to disturbances such as vibration. If noise is superimposed on the output pattern, accurate measurement is not possible. FIG. 8 shows an output pattern diagram of the detector 25 of the exhaust gas analyzer, and FIG. 8a shows a stable output with little noise output from the detector of the present embodiment. On the other hand, in FIG. 8b, optical noise or the like is superimposed and the signal is unstable. Since the output of the detector 25 of the exhaust gas analyzer of the present embodiment is configured to have a section in which the current value is constant in the drive pulse for driving the laser light generating means, a stable output pattern is obtained as shown in FIG. 8a. It is possible to accurately measure the concentration and temperature of exhaust gas components in response to environmental changes in the exhaust path. In FIG. 8, the horizontal axis indicates time t, and the vertical axis indicates output voltage V.

  Next, the operation for measuring the temperature using the exhaust gas analyzer of the present embodiment will be described. Each gas has its own absorption wavelength band, and many absorption lines exist in the absorption wavelength band, for example, as shown in FIG. FIG. 9a shows the signal intensity at the low temperature (= number of molecules), and FIG. 9b shows the signal intensity at the high temperature. Thus, since the signal intensity changes depending on the temperature, the temperature of the exhaust gas at the time of measurement can be calculated by measuring the signal intensity ratio. In FIG. 9, the horizontal axis indicates the wavelength λ, and the vertical axis indicates the signal intensity. The temperature of the exhaust gas thus calculated can also be measured with high accuracy because the infrared laser light irradiated to the exhaust gas is stable.

  Next, another embodiment of the present invention will be described in detail with reference to FIG. FIG. 10 is a block diagram showing an overall configuration including a main configuration and a signal analysis unit of a laser oscillation / light reception controller 30A of another embodiment of the exhaust gas analyzer according to the present invention. In addition, this embodiment is characterized in that the signal laser light generated from the laser light generating means is detected by a photodetector and the laser light generating means is calibrated from the detection result. Other substantially equivalent configurations are denoted by the same reference numerals, and detailed description thereof is omitted.

  The laser oscillation / light reception controller 30A of this embodiment includes a configuration device 70 that calibrates the laser light generation means. The calibration device 70 is installed on an optical fiber 38 that is output from the signal laser beam multiplexer 37 and input to the differential photodetector 40 via a splitter 71 such as a beam splitter, and is used for the split signal. A part of the laser light is supplied. The calibration device 70 includes a demultiplexer 72 that demultiplexes part of the signal laser beam into two, a detector 73 that receives one of the laser beams divided by the demultiplexer, and a filter that filters the other laser beam. A detector 75 input through 74 and a wavelength controller 76 for controlling the wavelength of the laser light generating means based on the results of the two detectors are provided. The laser diodes LD1 to LD5 are respectively supplied to control the output.

  The filter 74 used in the calibration device 70 is a filter having wavelength dependency. The filter 74 has a characteristic that the light transmittance changes linearly with respect to the wavelength. For example, as shown in FIG. 11A, a filter whose transmittance increases linearly as the wavelength becomes longer is used. The ratio between the wavelength of the laser beam output from one detector 73 and the wavelength of the laser beam output from the other detector 75 through the filter 74 is constantly monitored, and the laser diodes LD1 to LD5 are feedback-controlled. In addition, you may use the filter which has a transmittance | permeability as the filter which has wavelength dependence becomes long when a wavelength becomes long.

  That is, as shown in FIG. 11b, one laser beam output from the detector 73 is set to a constant light intensity I1 in a predetermined wavelength band, and the other laser beam output from the other detector 75 is wavelength-dependent. The light intensity I2 linearly changes in a predetermined wavelength band by the filter 74 having a characteristic. One laser beam with a constant light intensity and the other laser light with a linearly changing light intensity intersect on the monitor, so when this intersection is shifted from a predetermined wavelength λ5 to λ6, for example, the drive pulse It can be adjusted to a predetermined wavelength by increasing or decreasing the current.

  Thus, since the calibration device 70 can easily calibrate the light output (light emission amount) of the laser diode, the exhaust gas analyzer 10 can accurately measure the concentration and temperature of the components of the exhaust gas. For example, the output of the laser diode is adjusted by changing the current of the driving pulse for driving the laser diode. When this calibration device 70 is used, calibration maintenance using a tester for laser light generation means such as a laser diode becomes unnecessary, and labor and cost for exhaust gas analysis can be reduced.

  As described above, the exhaust gas analyzer 10 of the present embodiment performs the drive pulse 50 applied to the laser light generating means in the current scanning period and at least one of the continuous start current constant period and the constant end current period. By using the pattern, the laser beam overshoot can be prevented, the optical balance between the measurement light and the signal light is detected by fixing the wavelength in a constant current interval, and the measurement laser light is detected by the optical attenuator by feedback control. Therefore, it is possible to analyze the exhaust gas with high accuracy. In addition, since the concentration and temperature of exhaust gas components can be measured at a plurality of locations in the exhaust path and the concentration of exhaust gas components in the exhaust path can be analyzed, it is also possible to evaluate catalyst devices and the like. .

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed. For example, nitrogen oxide (NOx) can be measured as a component gas of exhaust gas. In this case, as a matter of course, a wavelength (for example, 1800 nm) suitable for NOx is used as the infrared laser beam that passes through the exhaust gas. The laser light emitted from the irradiation unit is not limited to infrared laser light, and may be visible laser light or ultraviolet laser light.

  An example was shown in which a laser beam irradiation unit was attached to the sensor base of the sensor unit via an optical fiber, and a photodiode was fixed to the sensor base to serve as a light receiving unit. And it is good also as a laser beam irradiation part. Alternatively, the detector that is the light receiving unit may not be directly fixed to the sensor base, but the optical fiber may be fixed and guided to the detector. The optical attenuator may be installed not on the measurement laser beam side but on the signal laser beam side.

Moreover, although the example which forms the thin film of gold | metal | money or platinum as a reflective surface was shown, thin films, such as a titanium oxide, may be formed, and if it is excellent in heat resistance and can be mirror-finished, a material will not be specified. The reflecting surface may be formed directly on the inner surface of the through hole through which the exhaust gas flows without using a reflecting plate such as a mirror. In this case, after reflecting the inner peripheral surface of the through hole, the reflection surface may be formed by a technique such as plating or vapor deposition. The reflecting surface may be a gold or platinum thin film formed by polishing the inner peripheral surface of the through-hole without using a mirror or the like, and a MgF ₂ or SiO ₂ thin film is formed thereon as a protective layer. Also good. Thereby, the structure of a reflective surface can be simplified.

  In the above-described embodiment, the configuration in which the sensor unit is installed on the downstream side of the exhaust manifold is shown, but the sensor unit may be installed between the exhaust manifold and the cylinder block of the engine. If comprised in this way, the density | concentration and temperature of the component of the exhaust gas for every cylinder of an engine can be measured, for example, the cause of engine malfunction etc. can be judged for every cylinder. In particular, since the exhaust gas analyzer of the present invention detects the concentration of exhaust gas components using laser light transmission without using a reference gas or the like, it has a feature that can be measured even at high temperatures. Measurement of the concentration of the exhaust gas component at a high temperature of about 800 ° C. can be performed with high accuracy.

  As an application example of the present invention, this exhaust gas analyzer can be used for exhaust gas analysis of a combustion apparatus such as a boiler, and it can also be applied to exhaust gas analysis of an internal combustion engine used in ships etc. in addition to automobile exhaust gas analysis it can.

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 of embodiment which mounted the exhaust gas analyzer which concerns on this invention in the engine bench. The disassembled perspective view which shows the principal part structure of a sensor part. The block diagram which shows the whole structure of the exhaust gas analyzer containing the principal part structure and signal analysis part of a laser oscillation and light reception controller. The current pattern figure of the drive pulse which drives the laser beam generation means used with the exhaust gas analyzer of this invention. FIG. 6 is an operation explanatory diagram of the drive pulse of FIG. The pattern diagram of other embodiment of a drive pulse. The output of the detector which received a laser beam is shown, (a) is an output pattern figure with little noise, (b) is an output pattern figure with much noise. The influence of the temperature of an absorption spectrum is shown, (a) is explanatory drawing of signal intensity at the time of low temperature, (b) is explanatory drawing of signal intensity at the time of high temperature. The block diagram which shows the whole structure including the principal part structure and signal analysis part of the laser oscillation and light reception controller of other embodiment of the exhaust gas analyzer which concern on this invention. (A) is a figure which shows the characteristic of the filter of the calibration apparatus used in embodiment of FIG. 10, (b) is explanatory drawing of calibration operation | movement. The current pattern figure of the drive pulse which drives the laser beam generation means used with the conventional exhaust gas analyzer.

Explanation of symbols

  1: automobile, 1A: engine bench, 2: engine, 3: exhaust manifold (exhaust path), 4: exhaust pipe (exhaust path), 5: first catalyst device (exhaust path), 6: second catalyst device (exhaust gas) Path), 7: muffler (exhaust path), 8: exhaust pipe (exhaust path), 10: exhaust gas analyzer, 11-14: sensor unit, 24: optical fiber (irradiation unit), 25: detector (light receiving unit), 30, 30A: Laser oscillation / light reception controller, 31: Signal generator, 33: Demultiplexer, 34: Optical attenuator, 36, 37: Multiplexer, 40: Differential photodetector, 41: Feedback line, 45 : Personal computer (signal analysis unit), 50: drive pulse, 51: constant start current interval, 52: current scan interval, 53: constant end current interval, 61, 62, 63: drive pulse, 61a, 62a, 63a Starting current constant interval, 61b, 62b, 63b: the current scan interval, 62c: End current constant interval, LD1 to LD5: a laser diode (laser light generating means)

Claims (7)

The exhaust gas discharged from the engine is irradiated with laser light generated by applying a drive pulse to the laser light generating means, the laser light transmitted through the exhaust gas is received, and the exhaust gas based on the received transmitted laser light A device for analyzing exhaust gas by measuring the concentration and temperature of the components of
The apparatus further includes an optical attenuator for adjusting the light intensity of the laser light generated from the laser light generating means, and the optical attenuator is feedback-controlled based on the received transmitted laser light. ,
The drive pulse applied to the laser light generating means includes a current scanning section in which a current value changes with time, and a current constant section that is continuous with the current scanning section and has a constant current value. Exhaust gas analyzer.   The drive pulse includes a start current constant section that is constant at a current value on a start end side of the current scan section, and the current scan section in which current increases linearly from the start current constant section. The exhaust gas analyzer according to claim 1.   3. The exhaust gas analysis according to claim 1, wherein the driving pulse further includes an end current constant section that is continuous with the current scanning section and has a constant current at a current value at a terminal end of the current scanning section. apparatus.   A sensor unit is formed that includes an irradiation unit that irradiates the laser beam to the through-hole through which the exhaust gas passes and a light receiving unit that receives the laser beam that has passed through the exhaust gas, and the sensor unit is installed in the exhaust gas exhaust path. The exhaust gas according to any one of claims 1 to 3, wherein the exhaust gas is analyzed by irradiating the exhaust gas from the irradiation unit with laser light and then receiving the laser beam transmitted through the exhaust gas in the light receiving unit. Analysis equipment.   The exhaust gas analyzer according to claim 4, wherein the sensor unit is installed at a plurality of locations in the exhaust path.   A laser pulse is generated by applying a driving pulse having a current scanning interval in which the current value changes with time and a constant current interval in which the current value is constant to the laser beam generating means, The laser beam is demultiplexed into a signal laser beam and a measurement laser beam, and the measurement laser beam is irradiated to the exhaust gas through an optical attenuator to receive the laser beam transmitted through the exhaust gas, and the received transmitted laser beam And calculating a feedback correction amount for correcting the optical attenuator based on the signal laser light and inputting the feedback correction amount to the optical attenuator to adjust the light intensity of the measurement laser light, and the signal An exhaust gas analysis method characterized in that the concentration and temperature of exhaust gas components are calculated based on the laser beam for transmission and the transmitted laser beam.   The exhaust gas analysis method according to claim 6, wherein the feedback correction amount is calculated from an optical balance between the transmitted laser beam and the signal laser beam by inputting the transmitted laser beam to a differential photodetector.

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