JP2014169912A - Sensor system and gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lightweight and compact gas sensor and a sensor system using the gas sensor.SOLUTION: In a sensor system mounted on an engine exhaust gas purification system, a gas sensor for measuring an object to be measured includes a case having a measurement chamber, an introduction passage for supplying the object to the measurement chamber, a granular porous body which is stored in the measurement chamber and sucks the object; a deriving passage which discharges a gas passing through the measurement chamber; a heater which heats the porous body during non-measurement, a light source device 53 which irradiates the porous body with measurement light of a specific wavelength region, and a detection device 56 which detects absorption intensity in the specific wavelength region in response to the measurement light reflected and diffused in the porous body, to calculate concentration of the object.

Description

  The present invention relates to a gas sensor for measuring a concentration of a measurement substance and a sensor system using the gas sensor.

  2. Description of the Related Art Conventionally, detection devices that use spectroscopy are widely used to measure the concentration of a measurement substance. In this apparatus, for example, the transmitted light that has passed through the sample is detected by a detector, the substance contained in the sample is specified based on the wavelength of the light absorbed by the sample, and the absorption intensity (transmittance, absorbance) is calculated. Calculate the concentration of the substance.

  At the experimental level, existing devices such as FT-IR can be used, but these devices measure a wide range of substances and are compatible with various measurement methods, so that the interferometer is large and the optical path length is secured. Large and heavy. Therefore, it is not practical to use these devices as sensors mounted on a moving body such as an automobile.

  For example, Patent Document 1 discloses a portable NOx detection device as a sensor that is miniaturized. This NOx detection device secures the optical path length by providing an optical ring cell in which a closed optical path through which light can circulate by a large number of reflecting mirrors, and suppresses the enlargement of the device.

JP 2009-98135 A

  Although the above-described NOx detection device can be downsized by using an optical ring cell, it is expected to increase in weight because it is configured to provide a large number of optical ring cells. Therefore, when the NOx detection device is mounted on a vehicle, there is a possibility of adversely affecting fuel consumption. For this reason, there has been a demand for a small and lightweight gas sensor that does not significantly reduce fuel consumption even when mounted on a vehicle. Such problems are not limited to sensors mounted on vehicles, but are generally common to sensors used outside the laboratory.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a lightweight and small gas sensor and a sensor system using the gas sensor.

  A sensor system that solves the above problem is a sensor system that is mounted on an exhaust gas purification system of an engine. A gas sensor that measures a measurement substance supplies a case having a measurement chamber and a gas containing the measurement substance to the measurement chamber. An introduction path, a granular porous body accommodated in the measurement chamber and adsorbing the measurement substance, a lead-out path for discharging the gas that has passed through the measurement chamber, a heater for heating the porous body, and the porous A light source device that irradiates the measurement material in a specific wavelength range to the material, and diffused reflected light that is reflected by the porous material and diffused in the measurement chamber, detects the absorption intensity in the specific wavelength region, and calculates the concentration of the measurement substance And a detecting device.

  A gas sensor that solves the above problems includes a case having a measurement chamber, an introduction path for supplying a gas containing a measurement substance to the measurement chamber, and a granular porous body that is accommodated in the measurement chamber and adsorbs the measurement substance A discharge path for discharging the gas that has passed through the measurement chamber, a heater that heats the porous body during non-measurement, a light source device that irradiates the porous body with measurement light in a specific wavelength range, and the porous body And a detection device that receives the diffusely reflected light reflected from the body and diffused in the measurement chamber, detects the absorption intensity in a specific wavelength region, and calculates the concentration of the measurement substance.

  According to these aspects, the measurement light incident on the measurement chamber is diffused while being repeatedly reflected between the particles of the porous body adsorbing the measurement substance, so that the optical path of the measurement light becomes long. For this reason, since the length of the measurement chamber itself can be shortened compared with a gas sensor having the same detection concentration range and not containing a porous body, the space occupied by the gas sensor can be reduced. Further, the gas sensor includes a heater that desorbs the measurement substance and water adsorbed by heating the porous body at the time of non-measurement, so that it can be repeatedly measured by sequentially performing regeneration. Moreover, since the detection device detects the absorption intensity at the absorption wavelength inherent to the substance, for example, it is possible to detect the concentration of a specific substance contained in the exhaust gas or the concentration of ozone added to the exhaust passage.

  In the sensor system, the gas sensor is provided in a bypass passage having a start end and a termination end connected to the exhaust passage, the porous body made of zeolite is accommodated in the measurement chamber, and the light source device emits infrared measurement light. Preferably, the light is emitted to the measurement chamber, and the detection device receives the measurement light and detects the light intensity in the absorption wavelength region of ammonia or the absorption wavelength region of nitrogen dioxide.

  According to this aspect, since zeolite with high adsorptivity is used as the porous body, even if ammonia or nitrogen dioxide contained in the exhaust gas has a low concentration, the amount of adsorption on the zeolite becomes large, so that measurement is possible. In addition, the detection device detects the light intensity in the specific absorption wavelength range based on the stretching motion of the ammonia molecule, the bending motion, the stretching motion of the nitrogen dioxide molecule, etc., so the ammonia contained in the exhaust gas Alternatively, the concentration of nitrogen dioxide can be detected individually.

  In the sensor system, the gas sensor is provided in a communication passage provided between the exhaust passage and an ozone generator for adding ozone to the exhaust passage, or a bypass passage that bypasses the communication passage, and is made of zeolite. A porous body is accommodated in the measurement chamber, the light source device emits ultraviolet measurement light to the measurement chamber, and the detection device receives the measurement light and detects light intensity in an absorption wavelength region of ozone. Is preferred.

  According to this aspect, since zeolite with high adsorptivity is used as the porous body, even if ozone is at a low concentration, the amount of adsorption on the zeolite becomes large, so that measurement is possible. Moreover, since a detection apparatus detects the intensity | strength in the absorption wavelength range peculiar to ozone, it can detect ozone concentration separately.

  In the sensor system, it is preferable that a bypass passage connected to the exhaust passage or a communication passage provided between the exhaust passage and the ozone generator is provided with an opening / closing valve for stopping gas supply to the measurement chamber. .

  According to this aspect, the porous body can be regenerated by closing the on-off valve and driving the heater of the gas sensor. For this reason, a gas sensor can be utilized continuously by repeating measurement and regeneration of a porous body.

  In the sensor system, the gas sensor includes a pair of light-transmitting window members in the case, the one window member allows measurement light to enter the porous body, and the other window member includes the one window member. It is preferable that the light diffused between the porous bodies is emitted out of the case.

  According to this aspect, since the pair of window members are provided in parallel, the detection device receives light transmitted through the case. That is, since the detection device does not receive diffusely reflected light, an optical system such as a reflection mirror that guides light from the case to the detection device is not necessary.

In the sensor system, it is preferable that the heater heats the porous body to 100 ° C. or higher at least in a measurement process.
According to this aspect, the porous body is heated to 100 ° C. or higher in the measurement process from the start of adsorption of the measurement substance until the absorption intensity is detected. For this reason, adsorption | suction of the water of a porous body can be suppressed.

The schematic diagram which shows the exhaust gas purification system of one Embodiment to which the sensor system in this invention is applied. The schematic diagram of the 1st and 2nd sensor unit which comprises the sensor system. The schematic diagram of the sensor main body of the sensor unit. The side view which shows typically the measurement part of the sensor main body. The schematic diagram of the 3rd sensor unit which comprises the sensor system. The schematic diagram of the sensor unit of the modification which actualized the sensor system in this invention.

  Hereinafter, an embodiment of a gas sensor and a sensor system will be described. In this embodiment, a gas sensor and a sensor system will be described as constituting a part of a vehicle exhaust purification system.

  As shown in FIG. 1, the engine 11 includes an intake passage 13 connected to an intake manifold, and a compressor 17 of a turbocharger 16 is provided in the intake passage 13. An exhaust passage 15 is connected to the exhaust manifold, and a turbine 18 of the turbocharger 16 is provided in the middle.

(Configuration of exhaust purification system)
An exhaust purification system 20 is provided downstream of the turbine 18 in the exhaust passage 15. The exhaust purification system 20 includes an oxidation catalyst that oxidizes NO and a DPF (Diesel Particulate Filter) that traps particulate matter (both not shown). The exhaust gas purification system 20 is provided with a selective reduction catalyst 21 that reduces NOx into _{N 2.} The selective reduction catalyst 21 is provided downstream of the oxidation catalyst and the DPF in the exhaust passage 15. The selective catalytic reduction catalyst 21 is a known catalyst, for example, a zirconia or the like supported on a honeycomb carrier.

The exhaust purification system 20 includes a first sensor unit 41 provided between the DPF and the selective reduction catalyst 21 in the exhaust passage 15. The first sensor unit 41 measures the concentration of nitrogen dioxide (NO ₂ ) contained in the exhaust. Further, the exhaust purification system 20 includes a NOx sensor 63 in the vicinity of the first sensor unit 41. The NOx sensor 63 is a sensor having a known configuration such as a resistance change type, and is a sensor that measures the total concentration of NO and NO ₂ .

The exhaust purification system 20 includes a urea water supply device 22, an ozone generation device 30, and an ECU 19 that drives these devices. The ozone generator 30 generates ozone from the air, and supplies the generated ozone to the upstream side of the selective reduction catalyst 21 in the exhaust passage 15. By adding ozone to the exhaust, an oxidation reaction from NO to NO ₂ can be promoted.

  The urea water supply device 22 stores urea water as a urea-based fluid and supplies urea water to the upstream side of the selective reduction catalyst 21 in the exhaust passage 15. The urea water is hydrolyzed by the heat of the exhaust to become ammonia. As shown in the following formula, the hydrolyzed ammonia reacts with nitrogen monoxide and nitrogen dioxide contained in the exhaust gas to reduce the nitrogen monoxide and nitrogen dioxide to nitrogen.

NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O
In the reaction represented by the above formula, when the concentration ratio of NO: NO ₂ approaches 1: 1, reduction to N ₂ is promoted. Therefore, the ECU 19 calculates a ratio of NO: NO ₂ based on each measurement signal received from the first sensor unit 41 and the NOx sensor 63, and adds ozone according to this ratio.

(Urea water supply device)
The urea water supply device 22 connects a urea water tank 23 that stores urea water, a urea water supply nozzle 24 that adds urea water upstream of the selective reduction catalyst 21, a urea water tank 23, and a urea water supply nozzle 24. A urea water supply path 25 is provided. In the middle of the urea water supply path 25, a pump 26 that pumps urea water from the urea water tank 23 to the urea water supply nozzle 24 and a flow rate adjustment valve 27 that adjusts the supply amount of the urea water are provided. The ECU 19 drives the pump 26 and controls the opening degree of the flow rate adjustment valve 27. Further, the ECU 19 applies a drive pulse to the urea water supply nozzle 24. Upon receipt of the drive pulse, the urea water supply nozzle 24 opens and injects urea water into the exhaust passage 15.

A second sensor unit 42 for measuring the ammonia concentration downstream of the nozzle 24 is provided downstream of the urea water supply nozzle 24 in the exhaust passage 15. The second sensor unit 42 transmits the NH ₃ concentration to the ECU 19. The ECU 19 adjusts the urea water supply amount based on the received NH ₃ concentration or the like.

(Ozone generator)
Next, the ozone generator 30 will be described. The ozone generator 31 that constitutes the ozone generator 30 is an apparatus having a known configuration, and a silent discharge type, an electron beam irradiation type, a radiation irradiation type, a light irradiation type, an electrolytic type, or the like can be used. When the ozone generator 31 is a silent discharge type, the ozone generator 31 includes a pair of electrode plates provided through an ozone generation space, a dielectric interposed between the electrode plates, an AC high-voltage power source, and the like. Ozone is generated from oxygen in the ozone generation space by applying a high voltage between the electrodes by an AC high voltage power source.

  An air introduction path (not shown) is connected to the upstream side of the ozone generator 31, and its starting end is opened to the atmosphere to suck in external air. A compressor, a dryer, etc. (not shown) are provided in the middle of the air introduction path.

  An ozone supply path 33 is provided downstream of the ozone generator 31, and a flow rate adjusting valve 34 is provided in the middle of the ozone supply path 33. The ECU 19 adjusts the amount of ozone supplied to the exhaust passage 15 by controlling the opening degree of the flow rate adjusting valve 34, the air flow rate supplied to the ozone generator 31, and the like. An ozone supply nozzle 32 is provided at the tip of the ozone supply path 33. The discharge port of the ozone supply nozzle 32 is provided upstream of the urea water supply nozzle 24 in the exhaust passage 15. The ECU 19 applies a drive pulse to the ozone supply nozzle 32, and the ozone supply nozzle 32 that has received the drive pulse opens to supply ozone to the exhaust passage 15.

  A third sensor unit 43 that measures the ozone concentration is provided in the middle of the ozone supply path 33. Ozone is easily self-decomposing and its concentration is likely to change according to temperature changes. For this reason, ozone concentration is measured by the 3rd sensor unit 43, and ECU19 adjusts the air flow rate etc. of the ozone generator 31 based on a measured value.

  Further, the ECU 19 receives a pressure measurement signal and a temperature measurement signal from a pressure sensor 61 and a temperature sensor 62 provided on the upstream side of the selective reduction catalyst 21 in the exhaust passage 15. The pressure sensor 61 and the temperature sensor 62 measure the pressure and temperature in the exhaust passage 15, respectively.

(Configuration of sensor unit)
Next, the structure of each sensor unit 41-43 is demonstrated. Since the first sensor unit 41 that measures the NO ₂ concentration and the second sensor unit 42 that measures the NH ₃ concentration have the same configuration, only the configuration of the first sensor unit 41 will be described.

As shown in FIG. 2, the first sensor unit 41 is provided in a bypass passage 15 a that branches from the exhaust passage 15. The first sensor unit 41 includes a sensor body 50 that measures NO ₂ , a suction pump 51, and a pressure sensor 52. Since the bypass passage 15a has a smaller inner diameter than the exhaust passage 15, driving the suction pump 51 can stabilize the amount of exhaust flowing into the bypass passage 15a. The pressure sensor 52 measures the pressure in the bypass passage 15 a and transmits the pressure measurement value to the ECU 19. Based on this pressure measurement value, the ECU 19 drives the suction pump 51 to bring the pressure in the bypass 15a close to the target pressure. For this reason, the pressure in the bypass 15a is maintained at the target pressure or a pressure close thereto.

As shown in FIG. 3, the sensor body 50 is a single beam type device, and includes a light source device 53, a spectroscope 54, a measurement unit 55, and a detection device 56. The light source device 53 provided in the first sensor unit 41 and the second sensor unit 42 is a known light source that can emit light having a wavelength in the infrared region, and includes, for example, a ceramic light source and a tungsten lamp. The spectroscope 54 is a small and light one, and is a known spectroscope configured by combining, for example, a grating and a slit. The wavelength range of the light that can be emitted by the light source device 53 and the spectroscope 54 only needs to include at least one absorption wavelength based on energy level transitions such as stretching motion and bending motion of NO ₂ molecules, Other wavelength ranges may not be supported. In addition, arrangement | positioning of the light source device 53, the spectrometer 54, the measurement part 55, and the detection apparatus 56 which are shown in FIG. 3 is an example, Comprising: It is not limited to the said arrangement | positioning pattern.

For example, in the first sensor unit 41, light source device 53 and the spectroscope ^{54, 4672nm (2140cm -1), 6042~6116nm} (1655~1653cm -1), at least one 10695~11049nm (935~905cm ^-1) It suffices if measurement light in the wavelength region can be emitted. Further, in the second sensor unit 42, the light source device 53 and the spectroscope 54 are 3030 to 3300 nm (3300 to 3030 cm ⁻¹ ) and 4545 to 5882 nm (2200 to 1700 cm) corresponding to the absorption band of NH ₃ in the infrared wavelength region. ^-1 ), measuring light in at least one wavelength region of 6993-7194 nm (1430-1390 cm ^-1 ) may be emitted. These wavelength ranges (wave number ranges) vary depending on the specifications of the apparatus.

  As shown in FIG. 4, the measurement unit 55 includes a rectangular parallelepiped case 55a. The case 55a includes an upper wall portion 55b, a lower wall portion 55c, side wall portions 55d and 55e, a front wall portion 55f, and a back wall portion (not shown), and a measurement chamber 55g is provided inside each of the wall portions 55b to 55f. A compartment is formed. The upper wall 55b and the lower wall 55c are provided with an introduction path 55h and a lead-out path 55i connected to the upstream side and the downstream side of the bypass path 15a. The introduction path 55h and the lead-out path 55i communicate with the measurement chamber 55g, and supply and discharge exhaust gas from the bypass path 15a to the measurement chamber 55g.

The measurement chamber 55g is filled with a porous body 60. The porous body 60 is made of a material having a large NO ₂ adsorption amount, and is made of, for example, zeolite. Zeolite has pores on the surface and inside, and is highly adsorbable to molecules such as water. Regarding NOx, zeolites often have higher adsorptivity to NO ₂ than NO. The porous body 60 is formed in a granular shape, and the particle size is such that the measurement light can pass through the measurement chamber 55g in a state where the entire measurement chamber 55g is filled with the porous body 60. The particle size is approximately several mm to several tens of mm. If the porous body 60 is a powder, the amount of light transmission decreases, and the porous body 60 may be discharged together with the exhaust from the lead-out path 55i, and the pressure loss increases. The exhaust introduced into the measurement chamber 55g from the introduction passage 55h is discharged from the lead-out passage 55i while passing through the gap of the porous body 60. At this time, the porous body 60 adsorbs not only NO _{2 in} the exhaust gas but also other substances such as water.

The front wall portion 55f and the back wall portion of the case 55a are constituted by a window material W made of a light-transmitting material having heat resistance such as quartz glass. These window members W are provided in parallel, the incident side window member W transmits measurement light, and the emission side window member W transmits light that has passed through the measurement chamber 55g. The measurement light incident on the measurement chamber 55g is reflected on the surface of the porous body 60 and diffuses in the measurement chamber 55g by reentering the gap of the porous body 60 or the surface of another porous body 60. Go. For this reason, when NO ₂ is adsorbed on the porous body 60, a part of the measurement light is absorbed by NO ₂ in the process of repeated reflection, and is emitted as transmitted light from the back wall to the detection device 56 side. As described above, since the transmitted light in which light of a specific wavelength is repeatedly absorbed by NO ₂ is obtained from the measurement unit 55, the NO ₂ concentration can be detected by the detection device 56 even if the optical path length is short.

The side walls 55d and 55e also serve as the heater H. The heater H has a configuration in which a heating element is embedded in a plate-like insulator, for example, and is driven by the ECU 19. The case 55a is provided with a temperature sensor 55t. The ECU 19 drives the heater H to a predetermined temperature based on the temperature measured by the temperature sensor 55t. For example, the heater H heats the porous body 60 to 100 ° C. in the measurement process, and reduces the amount of water adsorbed on the porous body 60 as much as possible. Further, by heating the porous body 60 at a regeneration temperature of 100 ° C. or more, desorption of NO ₂ adsorbed on the porous body 60 is promoted.

  On-off valves 57 and 58 are provided upstream and downstream of the measurement unit 55, respectively. When measurement is performed by transmitting light to the measurement chamber 55g, the on-off valves 57 and 58 are temporarily closed to suppress noise caused by fluctuations in the concentration of the measurement substance in the measurement chamber 55g and gas flow.

  As the detection device 56, a known detector such as a photomultiplier tube that converts transmitted light into an electrical signal, a semiconductor element, or the like can be used. The detection device 56 converts the light intensity in the specific wavelength region into an electrical signal and outputs the electrical signal to the ECU 19. The ECU 19 receives the measurement signal from the detection device 56 and calculates the transmittance or absorbance as the absorption intensity.

The ECU 19 stores background data and a calibration map for calculating the NO ₂ concentration and the NH ₃ concentration. The background data is data measured by flowing dry air or the like through the measurement unit 55, for example, and reflects the light absorption intensity of the zeolite itself. By comparing the data and the measurement signal received from the detection device 56, the absorption intensity of the substance contained in the exhaust gas is calculated. In addition, the calibration map is a map of a calibration curve that associates, for example, the transmittance with the NO ₂ concentration, and the calibration curve is obtained in advance by experiments or the like under the same temperature conditions and pressure conditions. The ECU 19 also includes the same background data and calibration map for the second sensor unit 42 and the third sensor unit, respectively.

  Next, the configuration of the third sensor unit 43 will be described. As shown in FIG. 5, the third sensor unit 43 includes a sensor body 50 and an orifice plate 59. The sensor main body 50 has the same configuration as the sensor main body 50 provided in the first and second sensor units 41 and 42. The measuring unit 55 is communicated with a bypass path 33 a branched from the ozone supply path 33. The start and end of the bypass path 33 a are connected to the ozone supply path 33. The light source device 53 and the spectroscope 54 of the third sensor unit 43 have substantially the same configuration as the first sensor unit 41, but differ from the first sensor unit 41 in that light in the ultraviolet region is emitted.

The orifice plate 59 is provided between the start end and the end of the bypass passage 33 a in the ozone supply passage 33. A circular through hole 59 a is formed in the center of the orifice plate 59. While ozone generated by the ozone generator 31 is supplied to the ozone supply path 33 at a positive pressure, the orifice plate 59 increases the flow resistance of the ozone supply path 33, so that ozone can be stably supplied to the bypass path 33a. Can be supplied. The wavelength range of the light that can be emitted by the light source device 53 and the spectroscope 54 is at least one absorption wavelength based on energy level transitions such as stretching and bending motions of O ₃ molecules, such as 200 nm to 300 nm. It may be included, and it does not need to correspond to other wavelength ranges.

(Operation)
Next, the operation of the exhaust purification system 20 will be described. The ECU 19 performs measurement by driving the sensor units 41 to 43 at predetermined sampling intervals or the like. The measurement timings of the sensor units 41 to 43 are preferably synchronized.

  Further, the ECU 19 regenerates the porous body 60 by driving the heaters H of the first to third sensor units 41 to 43 every predetermined period or immediately after the measurement is completed. At this time, the ECU 19 drives the suction pump 51 to discharge the desorbed material. The regeneration of the porous body 60 is performed with the driving of the light source device 53 and the detection device 56 stopped. At this time, only the upstream opening / closing valve 57 is closed, the downstream opening / closing valve 58 is opened, and the substance desorbed from the porous body 60 is discharged from the measurement unit 55. When the regeneration is completed, the suction pump 51 is stopped and the on-off valves 57 and 58 are closed to suppress the adsorption of moisture or the like to the porous body 60. For this reason, the inside of the measurement chamber 55g is in a negative pressure state.

The measurement is performed in a state where the regeneration of the porous body 60 is completed. At this time, the ECU 19 drives the heater H, opens the on-off valves 57 and 58, and supplies exhaust gas to the measurement chamber 55g. Since the measurement chamber 55g has a negative pressure and the moisture in the porous body 60 is small, NO ₂ is adsorbed on the porous body 60. The ECU 19 receives the pressure measurement value and the temperature measurement value from the pressure sensor 52 and the temperature sensor 55t. Then, the suction pump 51 is driven to bring the pressure in the bypass passage 15a close to the target pressure, and the heater H is driven to heat the porous body 60 to 100 ° C.

When a predetermined time required for NO ₂ adsorption elapses, the upstream side open / close valve 57 and the downstream side open / close valve 58 are closed. For this reason, changes in NO ₂ concentration due to inflow of exhaust gas and noise due to gas flow can be eliminated as much as possible. The ECU 19 drives the light source device 53 and the detection device 56. If the spectroscope 54 has a moving mirror or the like, the spectroscope 54 is also driven. The measurement light emitted from the light source device 53 is diffused through the measurement unit 55, then emitted from the window material W, and enters the detection device 56. The detection device 56 converts the light intensity into a measurement signal and outputs it to the ECU 19. When the measurement is completed, the heater H and the suction pump 51 are driven again, and the substance adsorbed on the porous body 60 is desorbed and regenerated. When the regeneration of the porous body 60 is completed and a waiting time is provided until the next measurement, the on-off valves 57 and 58 are kept closed. The heater H is not driven when the on-off valves 57 and 58 are kept closed, and the porous body 60 is heated to 100 ° C. when the on-off valves 57 and 58 are opened.

On the other hand, the ECU 19 starts driving the ozone generator 30 based on the exhaust temperature. For example, when the exhaust gas temperature acquired from the temperature sensor 62 is a low temperature of 200 ° C. or lower, the ECU 19 drives the ozone generator 30, and stops the ozone generator 30 when the exhaust gas temperature is a high temperature exceeding 200 ° C. This is because when the exhaust gas temperature exceeds 200 ° C., NOx reacts with ammonia in the selective catalytic reduction catalyst 21 and is quickly reduced to N ₂ without converting a part of NO contained in the exhaust gas to NO _2. is there. Therefore, the ECU 19 stops driving the first sensor unit 41 and the third sensor unit 43 when the exhaust gas temperature exceeds 200 ° C.

The ECU 19 calculates the NO ₂ concentration in the sensor body 50 as described above based on the measurement signal received from the first sensor unit 41, the background data, and the calibration map. Further, the ECU 19 calculates the NO: NO ₂ ratio based on the calculated NO ₂ concentration and the measurement signal received from the NOx sensor 63. The pressure of the bypass passage 15a, NO pressure, calculated received from the pressure sensor 61 provided in the exhaust passage 15: on the basis of the NO _2, and calculates the flow rate of NO in the exhaust passage 15. Then, the ECU 19 calculates, as the ozone supply amount, the same amount as the NO flow rate or an amount larger than the NO flow rate by a predetermined amount. The ECU 19 sets discharge conditions such as an air flow rate and output power supplied to the ozone generator 31 based on the ozone supply amount.

The ECU 19 obtains the air flow rate of the ozone generator 31 and receives a measurement signal from the detection device 56 of the third sensor unit 43. Then, the ECU 19 calculates the ozone concentration using the calibration map after obtaining the absorption intensity based on the measurement signal. Furthermore, the ECU 19 determines whether the ozone supply amount calculated based on the NO: NO ₂ ratio is excessive or insufficient. If the ozone supply amount is insufficient, the discharge condition is changed, for example, the discharge condition is changed or the cooling of the ozone generator 31 is promoted, and if the ozone supply amount is excessive, the pulse frequency is reduced. As a result, NO: ratio of NO ₂ is 1: approaches 1.

The ECU 19 calculates the urea water supply amount based on a load sensor or the like (not shown). At the same time, the ECU 19 receives the measurement signal from the detection device 56 of the second sensor unit 42 and calculates the NH ₃ concentration. At this time, the ECU 19 may adjust the urea water supply amount so that the NH ₃ concentration approaches a target concentration corresponding to twice the NO flow rate calculated based on the first sensor unit 41. Or if the second sensor unit 42 is provided in the vicinity selective reduction catalyst 21, since the consumption state of the NH ₃ in the NH ₃ concentration can be predicted, when NH ₃ concentration is equal to "0", The adjustment may be performed while slightly increasing the urea water supply amount. When the urea water supply amount is determined, the ECU 19 drives the pump 26 and controls the opening of the flow rate adjusting valve 27 according to the injection amount, and applies a drive pulse to the urea water supply nozzle 24. As a result, the urea water supply nozzle 24 opens according to the drive pulse, and urea water is injected into the exhaust passage 15.

As described above, according to the sensor system of the present embodiment, the effects listed below can be obtained.
(1) According to the above embodiment, the porous body 60 accommodated in the measurement unit 55 of the sensor body 50 is granular, and thus allows measurement light to pass through while adsorbing a measurement substance. That is, the measurement light incident on the measurement chamber 55g of the sensor main body 50 is diffused while being repeatedly reflected between the particles of the porous body 60 that has adsorbed the measurement substance, so that the optical path traveled by the measurement light becomes long. For this reason, the length of the measurement chamber itself can be shortened compared to a sensor in which the same detection concentration range is set and the porous body 60 is not accommodated. In other words, the lower limit value of the detectable concentration can be reduced as compared with a sensor having the measurement unit 55 of the same size and not containing the porous body 60. Therefore, the space occupied by the gas sensor in a limited space around the engine can be reduced. Furthermore, since the sensor main body 50 includes the heater H that heats the porous body 60, it is possible to suppress the adsorption of water to the porous body 60 and to perform regeneration. Moreover, since the detection apparatus 56 detects the light intensity in the absorption wavelength intrinsic | native to a substance, it can detect the density | concentration of the specific substance contained in exhaust gas.

(2) According to the above embodiment, the exhaust purification system 20 includes the first sensor unit 41 that measures NO ₂ and the second sensor unit that measures NH ₃ . In addition, since each sensor main body 50 uses zeolite with high adsorptivity as the porous body 60, even if the NH ₃ and NO ₂ contained in the exhaust gas are low in concentration, the amount of adsorption in the zeolite becomes large and can be measured. Become. The detection device 56, and detects the intensity of the NH ₃ specific absorption wavelength range or NO ₂ intrinsic absorption wavelength region can be detected independently concentration of NH ₃ or NO ₂ contained in the exhaust.

(3) According to the above embodiment, the exhaust purification system 20 includes the third sensor unit 43 that measures O ₃ . Moreover, since zeolite with high adsorptivity is used as a porous body, even if ozone is low concentration, since the amount of adsorption in zeolite becomes large, measurement becomes possible. Moreover, since a detection apparatus detects the intensity | strength in the absorption wavelength range peculiar to ozone, it can detect ozone concentration independently.

  (4) According to the above embodiment, the on-off valves 57 and 58 for stopping the gas supply to the measurement chamber 55g and the gas discharge from the measurement chamber 55g are provided on the upstream side and the downstream side of the sensor body 50. For this reason, by closing the on-off valves 57 and 58, exhaust gas can be temporarily sealed in the measurement chamber 55g to stabilize the measurement conditions. Further, the porous body 60 can be regenerated by closing the upstream opening / closing valve 57 and driving the heater H. For this reason, a sensor can be utilized continuously by repeating measurement and regeneration of a porous body.

  (5) According to the embodiment, the sensor body 50 includes the pair of window materials having translucency in the case 55a. One window material allows measurement light to enter the porous body 60, and the other window material is provided in parallel with the one window material, and emits light diffused between the porous bodies 60 out of the case. For this reason, since the detection device 56 does not measure the reflected light from the measurement unit 55, an optical system such as a reflection mirror becomes unnecessary.

In addition, the said embodiment can also be suitably changed and implemented as follows.
In the above embodiment, the window material W of the case 55a of the sensor body 50 is provided in parallel so that the measurement light enters from one window material W and exits from the other window material W. In addition to this, a window member may be provided only on one surface of the rectangular parallelepiped case 55a, and measurement light may be incident from the window member and light diffusely reflected in the measurement chamber 55g may be emitted. In this case, an optical system for adjusting the angle of incident light or the angle of reflected light is required on the incident side or the reflection side with respect to the case 55a.

  In the above embodiment, the sensor body 50 is a single beam type sensor, but may be a double beam type sensor. In the case of the double beam type, a reference cell is required, and therefore a sensor main body 50 for supplying exhaust gas and the like and a reference sensor main body 50 are provided. In the case of the double beam type, it becomes easy to eliminate the influence of heat and vibration as much as possible.

  In the above embodiment, when the regeneration of the porous body 60 is completed and a standby time is provided until the next measurement, the on-off valves 57 and 58 are kept closed, but the control pattern for regeneration and measurement is It is not limited. For example, except during regeneration, exhaust gas may be supplied to the measurement unit 55 for a predetermined time while the on-off valves 57 and 58 are opened, and the exhaust gas amount may be added during that time.

In the above embodiment, the NO: NO ₂ ratio is calculated using the first sensor unit 41 and the NOx sensor 63, but a sensor unit that detects the NO concentration may be provided instead of the NOx sensor 63. This sensor unit may have the same configuration as the sensor units 41 to 42 or may be different.

  In the above embodiment, the sensor body 50 measures the concentration of the measurement substance under a constant temperature condition and pressure condition, but may be measured in a situation where the temperature and pressure change. In this case, the ECU 19 stores a calibration map in which the calibration curve is changed according to temperature and pressure.

  In the above embodiment, the heater H constantly heats the porous body 60 to 100 ° C. in the measurement process, but the heating of the heater H may be stopped during the measurement. In this case, noise due to heat can be reduced as much as possible.

  As shown in FIG. 6, the sensor main body 50 may have a configuration in which one on-off valve 57 is provided. Even with this configuration, the porous body 60 can be regenerated by closing the on-off valve 57.

  -The light source device 53, the spectroscope 54, the measurement part 55, and the detection apparatus 56 are not limited to the arrangement pattern of FIG. 3, as mentioned above. For example, the light source device 53 and the spectroscope 54 and the measurement unit 55 may be in contact with each other, or the measurement unit 55 and the detection device 56 may be in contact with each other. In this case, it is preferable to provide a cooler or a heat insulating material between the spectroscope 54, the detection device 56, and the like in order to reduce the influence of heat of the measurement unit 55.

In the above embodiment, the first to third sensor units 41 to 43 are provided in the exhaust purification system 20, but it is sufficient that at least one sensor unit is provided. For example, since the NO: NO ₂ ratio can be calculated only by the first sensor unit 41, the ozone supply amount can be optimized.

In the above embodiment, the measurement object is NO ₂ , NH ₃ , O ₃ , but other substances may be used as long as they can be adsorbed on the porous body 60. For example, volatile organic compounds such as formaldehyde and toluene, amine compounds, and the like may be used. Or you may utilize as a sensor and sensor system which measure the moisture content in gas.

In the above embodiment, the gas sensor and the sensor system are mounted on the engine and used for the purpose of measuring the content of exhaust gas. However, the present invention is not limited to this application, and may be mounted on other devices or moving bodies.
The third sensor unit 43 may be provided directly in the ozone supply path 33.

In the above embodiment, the urea water supply device 22 is configured to add urea water. However, the urea water supply device 22 may be configured to include a urea water reformer that converts the urea water into mist and then converts it to ammonia.
In the above embodiment, the sensor system is applied to the exhaust purification system 20 of the engine 11, but may be provided in another mechanism.

  In the above embodiment, the sensor system is mounted on an engine with a turbocharger. However, the sensor system may be applied to a naturally aspirated engine or an engine with a supercharger, and the configuration of the engine is particularly limited. Not. Moreover, although the engine to which the sensor system is applied is the engine of the vehicle, it may be an engine of a ship or an aircraft.

  DESCRIPTION OF SYMBOLS 11 ... Engine, 15 ... Exhaust passage, 15a, 33a ... Bypass passage, 20 ... Exhaust purification system, 31 ... Ozone generator, 33 ... Ozone supply passage as communication passage, 41 ... 1st sensor unit which comprises a sensor system, 42 ... a second sensor unit constituting the sensor system, 43 ... a third sensor unit constituting the sensor system, 53 ... a light source device, 55a ... a case, 55e ... a heater, 55g ... a measurement chamber, 55h ... an introduction path, 55i ... a derivation. Road, 56 ... detecting device, 57, 58 ... open / close valve, 60 ... porous body, W ... window material.

Claims (7)

In the sensor system installed in the engine exhaust purification system,
The gas sensor that measures the measurement substance is
A case having a measurement chamber;
An introduction path for supplying a gas containing a measurement substance to the measurement chamber;
A granular porous body accommodated in the measurement chamber and adsorbing the measurement substance;
A lead-out path for discharging the gas that has passed through the measurement chamber;
A heater for heating the porous body;
A light source device that irradiates the porous body with measurement light in a specific wavelength range; and
A sensor system comprising: a detection device that receives diffusely reflected light reflected by the porous body and diffused in the measurement chamber to detect an absorption intensity in a specific wavelength region and calculate a measurement substance concentration. The gas sensor
A starting end and a terminating end are provided in a bypass path connected to the exhaust passage of the engine;
The porous body made of zeolite is accommodated in the measurement chamber,
The light source device emits measurement light in the infrared region to the measurement chamber,
The sensor system according to claim 1, wherein the detection device receives the measurement light and detects light intensity in an absorption wavelength region of ammonia or an absorption wavelength region of nitrogen dioxide. The gas sensor
Provided in a communication passage provided between an exhaust passage of the engine and an ozone generator for adding ozone to the exhaust passage, or a bypass passage that bypasses the communication passage;
The porous body made of zeolite is accommodated in the measurement chamber,
The light source device emits ultraviolet measurement light to the measurement chamber,
The sensor system according to claim 1, wherein the detection device receives the measurement light and detects light intensity in an absorption wavelength region of ozone.   The on-off valve which stops supply of the gas to the said measurement chamber was provided in the bypass path connected to an exhaust passage, or the communicating path provided between the exhaust passage and the ozone generator. 2. The sensor system according to item 1. The gas sensor
The case includes a pair of light-transmitting window members, the one window member makes measurement light incident on the porous body, and the other window member is provided in parallel with the one window member, The sensor system according to claim 1, wherein light diffused between the porous bodies is emitted out of the case.   The sensor system according to claim 1, wherein the heater heats the porous body to 100 ° C. or higher at least in a measurement process. A case having a measurement chamber;
An introduction path for supplying a gas containing a measurement substance to the measurement chamber;
A granular porous body accommodated in the measurement chamber and adsorbing the measurement substance;
A lead-out path for discharging the gas that has passed through the measurement chamber;
A heater for heating the porous body during non-measurement;
A light source device that irradiates the porous body with measurement light in a specific wavelength range; and
A gas sensor comprising: a detection device that receives diffusely reflected light reflected on the porous body and diffused in the measurement chamber to detect an absorption intensity in a specific wavelength range and calculate a measurement substance concentration.

Images