JP5221053B2 - Urea concentration detector - Google Patents

Description

  The present invention relates to a urea concentration detection device applied to a urea SCR (Selective Catalytic Reduction) catalyst system of a diesel vehicle, and more specifically, a simple urea water concentration optimal for NOx purification can be obtained without deteriorating the fuel consumption of the vehicle. The present invention relates to a urea concentration detection device capable of measuring with high accuracy and responsiveness with a configuration.

  In recent years, a urea SCR catalyst system has been put into practical use as a technology for reducing NOx in exhaust from an engine in vehicles equipped with a diesel engine (hereinafter abbreviated as an engine) as an environmental measure, and a particulate matter (Particulate Matter): As a particulate matter) reduction technology, a catalyst regeneration type particulate filter system has been put into practical use.

  Among these, the urea SCR catalyst system includes a NOx reduction catalyst (selective reduction catalyst) having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen in the middle of an exhaust passage through which exhaust from the engine flows. It is a thing.

  That is, the urea SCR catalyst system adds a necessary amount of a reducing agent upstream of the NOx reduction catalyst and causes the reducing agent to undergo a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the NOx reduction catalyst. The NOx emission concentration is reduced by decomposing it into nitrogen. As this reducing agent, using non-toxic urea water has been put into practical use to reduce NOx with high efficiency.

  In order to spray the urea water on the catalyst, continuously maintain the decomposition of NOx, and increase the efficiency, it is preferable that the urea water is in a specific concentration range (for example, about 32.5%). Are known. For this reason, it has been desired to provide means for measuring and determining the urea water concentration optimum for NOx purification of diesel engine-equipped vehicles.

  For example, the following is known as a conventional technique for measuring the concentration of a liquid (see Patent Document 1). In other words, this prior art is an apparatus for measuring the concentration of the electrolyte solution of a lead storage battery. An electrolyte solution is interposed between the light emitting element and the light receiving element, and the amount of light received in the wavelength range that is easily absorbed by water It is configured to measure increase / decrease (electrolyte concentration).

  In addition, as a related prior art, a technique for determining an oil type using two light emitting elements that emit light in different wavelength ranges and a light receiving element that receives the light has been proposed (for example, see Patent Document 2). .

  Further, a technique has been proposed in which light having a high absorption rate is selected by a filter for each liquid to be measured and a liquid leak is detected (for example, see Patent Document 3).

  Further, a technique has been proposed in which light of a specific wavelength is selectively transmitted through a filter and the concentration of the liquid is measured (see, for example, Patent Document 4).

  In addition, a concentration detection unit having a heating element and a temperature sensing element, and a liquid temperature detection unit for measuring the temperature of the urea solution, the initial temperature and peak temperature of the temperature sensing element when the heating element generates heat A technique for obtaining the urea concentration from a voltage value corresponding to the difference has been proposed (see, for example, Patent Document 5).

JP 2005-17261 A JP 10-329899 A JP 2000-97850 A JP 2005-43069 A JP-A-2005-84026

  However, in the conventional techniques according to Patent Documents 1 to 4, specific means for applying to the urea SCR catalyst system of a diesel vehicle is not disclosed, and in particular, the urea water concentration (optimum for NOx purification ( For example, it has been desired to provide a means for measuring or determining 32.5%).

  Moreover, in the prior art which concerns on the said patent document 5, since it heat-generates a heat generating body (electrode), while being concerned about deterioration of a heat generating body, power consumption becomes large and it will worsen the fuel consumption of a vehicle. There was a problem. Furthermore, the urea aqueous solution concentration is changed by heat generation, and there is a possibility that the concentration cannot be measured with high accuracy, and there is a problem that measurement responsiveness is not good because heat is generated.

  The present invention has been made in view of the above, and a urea concentration detection device capable of measuring the urea water concentration optimal for NOx purification with a simple configuration with high accuracy and responsiveness without deteriorating the fuel consumption of the vehicle. The purpose is to provide.

In order to solve the above-described problems and achieve the object, a urea concentration detection device according to claim 1 of the present invention is installed in a urea water tank that stores urea water as a measurement target, and a light emitting means and a light receiving means. And the urea water is interposed between the light emitting means and the light receiving means, and the concentration of the urea water based on the relationship between the amount of light received by the light receiving means and the concentration of the urea water determined in advance. The light emitting means detects light in the first wavelength range and the second wavelength range in which the amount of change in transmittance calculated based on the amount of light received by the light receiving means is large. Formed to emit at least one of light, hermetically sealed as an outer shell and fixed to the urea water tank and housing the light emitting means and the light receiving means, and sealed and positioned with the housing Before A prism that guides the light from the light emitting means to the urea water and guides the light that has passed through the urea water to the light receiving means, and the urea water that is provided in the prism and that can enter to detect the concentration of the urea water A concave portion provided in the concave portion and guiding the light of the light-emitting means, and defining the optical path length of the light at the time of concentration detection so as to be movable by the flow of the urea water while maintaining the optical path length. It comprises the light guide member comprised, It is characterized by the above-mentioned.

  According to a second aspect of the present invention, there is provided a urea concentration detecting device according to the first aspect of the present invention, further comprising a concentration determining means for determining whether or not the detected urea concentration is a predetermined default value. It is characterized by that.

The urea concentration detecting device according to claim 3 of the present invention is the invention according to claim 1 or 2, wherein when the urea concentration is not a predetermined default value by the concentration determining means, that effect is provided. It is characterized by comprising notifying means for notifying of the above.
According to a fourth aspect of the present invention, there is provided the urea concentration detection device according to any one of the first to third aspects, wherein the light emitting means includes light in the first wavelength range and light in the second wavelength range. A first light emitting element configured to emit one of the lights and a second light emitting element configured to emit the other light are provided, and the light receiving element emits light from the first light emitting element. A first light receiving element that receives the emitted light and a second light receiving element that receives the light emitted from the second light emitting element, and the light guide member includes a step portion, The optical path length of the one light and the optical path length of the other light are defined.

  According to the urea concentration detection device of the present invention (Claim 1), it is possible to simply configure a light emitting diode with low power consumption as the light emitting means and a low power consumption photodiode as the light receiving means. Since there is no need to heat the urea water at the time, the responsiveness is good and the fuel consumption of the vehicle is not deteriorated. Further, by using at least one wavelength region, it is possible to accurately measure the urea water concentration optimum for NOx purification.

  Moreover, according to the urea concentration detection apparatus (claim 2) according to the present invention, it is possible to determine whether or not the urea concentration is optimal for NOx purification.

  Further, according to the urea concentration detection device according to the present invention (Claim 3), when there is an abnormality, that fact is notified and the user is instructed to perform a predetermined treatment (for example, inspection or replacement of urea water). You can call attention.

  Embodiments of a urea concentration detection device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  As will be described later, the present invention uses near infrared light having a wavelength of 1500 to 1900 nm or 2100 to 2300 nm where a difference in light transmittance characteristics between water and urea water (for example, 32.5%) is observed. The urea concentration is calculated from the attenuation amount of the transmittance of light that passes through the target urea water.

  First, a known urea SCR catalyst system to which the urea concentration detection device 20 according to the present invention is applied will be described with reference to FIG. Here, FIG. 2 is a block diagram showing a urea SCR catalyst system to which the urea concentration detection device is applied.

  As shown in FIG. 2, the exhaust passage 11 of the engine 10 is provided with an oxidation catalyst 12 on the upstream side and a urea SCR catalyst 13 on the downstream side. A urea water injection nozzle 16 for adding urea water is provided between the oxidation catalyst 12 and the urea SCR catalyst 13 in the exhaust passage 11.

  The urea water is supplied to the urea water injection nozzle 16 through a urea water supply passage 15 from a urea water tank 14 that stores urea water. The urea water addition system tank 17 is a control means for obtaining operation information of the engine 10 from an electronic control device (hereinafter referred to as ECU) (not shown) and optimally adding urea water in accordance with the engine output and the like. This ECU also functions as a concentration determination means for determining whether or not the urea concentration is a predetermined default value.

  The urea concentration detection apparatus 20 according to the first embodiment is installed, for example, in the urea water tank 14, and its tip (detection unit) is immersed in urea water and measures its concentration. The urea concentration detection device 20 will be described in more detail based on FIGS. 1, 3, and 4. Here, FIG. 1 is a sectional view showing a urea concentration detection device according to Embodiment 1 of the present invention, FIG. 3 is a plan view showing the urea concentration detection device, and FIG. 4 shows a light guide member of the urea concentration detection device. It is a perspective view shown.

  As shown in FIG. 1, the urea concentration detection device 20 is hermetically formed with cylindrical casings 21 and 22 as main outer shells, and is configured to accommodate each member described later. That is, the housing 21 is screwed to the housing 22 by the screw portion 21 a and is sealed by the seal member 29. Further, the housing 22 and a prism 40 described later are sealed by a seal member 29.

  The holder 24 is for fixing and holding a light emitting element (light emitting means) 30, a light receiving element (light receiving means) 34 and a substrate 25, which will be described later, and is fixed to the housing 22 by pins 26. The housing 22 can be fixed to the urea water tank 14 with screws or the like using the mounting holes 22c.

  The light emitting element 30 is an element that emits near-infrared light having a wavelength of 1500 to 1900 nm (first wavelength range) or 2100 to 2300 nm (second wavelength range). For example, the light emitting element 30 has high reliability and low power consumption. An inexpensive light emitting diode (LED) can be used. The reason why the wavelength range of the light beam by the light emitting element 30 is selected as described above is as follows.

  That is, it has been confirmed by experiments that the relationship between the light transmittance (hereinafter referred to as “transmittance” where appropriate) and the measured concentration varies with the optical path length. For example, it was found that when the optical path length is long, the change in transmittance is small in the high concentration region, but is large in the low concentration region, and the detection accuracy is increased.

  As described above, in the urea SCR catalyst system, it is important that the urea water concentration is accurately measured at around 32.5%. For this reason, as shown in FIG. 5, it is important to pay attention to the wavelength region where the difference in transmittance between urea water and water is remarkable.

  That is, it can be seen that the concentration can be measured with high accuracy in the wavelength range of 1500 to 1900 nm and 2100 to 2300 nm. Here, FIG. 5 is a graph showing transmittance characteristics of water and urea water, and shows a case where the optical path length is 1 mm and the urea water concentration is 32.5%. Note that the graph shown in FIG. 5 shows the same tendency in the above two wavelength ranges for other optical path lengths.

  For the above reason, in the first embodiment, the light-emitting element 30 that emits near-infrared light in the wavelength range of 1500 to 1900 nm or 2100 to 2300 nm is used.

  As a result of the experiment, for example, the relationship between the transmittance and the urea concentration when the optical path length is 0.5 mm and the wavelength is 2200 nm is as shown in the map of FIG. Further, the relationship between the transmittance and the urea concentration when the optical path length is 2 mm and the wavelength is 1650 nm is as shown in the map of FIG. Here, FIG. 6 is a map showing the relationship between the transmittance and the urea concentration when the optical path length is 0.5 mm and the wavelength is 2200 nm, and FIG. 7 is the transmittance when the optical path length is 2 mm and the wavelength is 1650 nm. It is a map which shows the relationship with a urea concentration.

  Therefore, in the first embodiment, for example, an interval between gaps 45 to be described later, which is an optical path length, is set to 0.5 mm, and a light emitting element 30 having a wavelength of 2200 nm is used, or an interval between gaps 45 is set to 2 mm. And a light emitting element 30 having a wavelength of 1650 nm can be used.

  The light receiving element 34 is for receiving a light beam emitted from the light emitting element 30 and then attenuated by passing through urea water. For example, a photodiode can be used.

  The light quantity monitoring light receiving element 36 is provided in the vicinity of the light emitting element 30 (the same environmental temperature condition as the light emitting element 30) in order to cancel the influence of the environmental temperature change and correct the light quantity of the light emitting element 30. For example, a photodiode can be used.

  That is, the relationship between the monitor light quantity Im (V) obtained based on the output of the light quantity monitor light receiving element 36 and the light emission quantity Io (V) of the light emitting element 30 is expressed as a map or a predetermined relational expression as shown in FIG. The light amount Io (V) of the light emitting element 30 can be calculated from the monitor light amount Im (V) output at the time of light amount correction and this map. Here, FIG. 8 is a map showing the relationship between the monitor light quantity Im of the light receiving element for monitoring the light quantity and the light emission quantity Io of the light emitting element.

  The prism 40 guides the light beam from the light emitting element 30 to the urea water that is the liquid to be inspected, and guides the light beam that has passed through the urea water to the light receiving element 34. The prism 40 is also positioned with respect to the housing 22 by the pin 26.

  As shown in FIGS. 1 and 4, the rectangular parallelepiped light guide member 43 is provided in the concave portion 41 of the prism 40, sets the optical path length by the gap 45, and maintains the optical path length with urea water. It is configured so that it can be moved by the flow of the liquid and so that the contamination on the detection surface can be automatically removed. Further, as shown in FIGS. 1 and 3, the light guide member 43 is prevented from dropping from the recess 41 by the retaining member 47 via the fixing member 46.

  The thermistor 38 thermally protects the light emitting element 30, the light receiving element 34, and the light quantity monitoring light receiving element 36, and therefore energizes these members when the environmental temperature inside the urea concentration detector 20 exceeds the operating temperature. It is for blocking as necessary.

  The substrate 25 fixes the light emitting element 30, the light receiving element 34, the light quantity monitoring light receiving element 36, the thermistor 38, and the like, and is provided with a drive circuit for the light emitting element 30, an amplifier circuit for the light receiving element 34, and the like.

  The connector 23 is connected to the light emitting element 30, the light receiving element 34, the light quantity monitoring light receiving element 36, the thermistor 38, and the like through the wiring 23 a, and supplies power to them, and from the light receiving element 34 and the light quantity monitoring light receiving element 36. This signal is for outputting to the ECU (not shown). This connector 23 is fixed to the housing 21.

  The heat radiating fin portion 22a of the housing 22 is provided to suppress heat accumulation in the urea concentration detection device 20 and to protect the light emitting element 30, the light receiving element 34, the light amount monitoring light receiving element 36, and the like from thermal deterioration. It is a thing.

  Next, a control method of the urea concentration detection device 20 will be described with reference to FIG. Here, FIG. 9 is a flowchart showing a control method of the urea concentration detection device 20. The following control is executed at appropriate timing by the ECU.

  As shown in FIG. 9, first, the light emitting element 30 is energized (step S10). As a result, the light emitting element 30 emits light, and as shown in FIG. 1, the light beam passes through the urea water existing in the gap 45 by the prism 40 and the light guide member 43 and attenuates a predetermined amount of light before receiving the light. Guided to element 34.

  Since an output signal corresponding to the amount of transmitted light is output by the light receiving element 34, the transmitted light amount I (V) of urea water is calculated based on the output (step S20).

  Since the light beam of the light emitting element 30 emitted in step S10 is also received by the light quantity monitoring light receiving element 36, the monitor light quantity Im is calculated based on the output of the light quantity monitoring light receiving element 36 (step S10). S30).

  When the monitor light amount Im is calculated, the light emission amount Io (a value in which the light amount is not attenuated by urea water) of the light emitting element 30 can be calculated by using the map shown in FIG. 8 (step S40). .

  Next, the light transmittance T is calculated based on the transmitted light amount I calculated in step S20 and the light emission amount Io calculated in step S40 (step S50). As described above, since the optical path length and wavelength are known, the urea concentration can be easily calculated based on the light transmittance T using the corresponding map shown in FIG. 6 or FIG. 7 (step S60). ).

  Next, in order to determine whether or not the urea concentration is optimal for NOx purification, it is determined whether or not the urea concentration calculated in step S60 is a predetermined value near 32.5% (step S70). ).

  If the urea concentration is a predetermined value (Yes at step S70), the control is terminated. If the urea concentration is not a predetermined value (No at Step S70), the fact that it is abnormal is notified by a notification means such as a voice or a display means (Step S80), and a predetermined treatment (for example, inspection or replacement of urea water) is performed. Alert the user to do so.

  As described above, the urea concentration detection apparatus 20 according to the first embodiment has the following effects. That is, the light emitting element 30, the light receiving element 34, and the light quantity monitoring light receiving element 36 can be measured in a non-contact manner, have good responsiveness, consume very little power, and do not deteriorate the fuel consumption of the vehicle.

  In addition, by using the predetermined wavelength range, it is possible to measure only urea water with a simple configuration, and it is possible to accurately measure the urea water concentration optimum for NOx purification. Further, when the concentration is measured, an extra step such as heating urea water, which is necessary in the prior art, is unnecessary.

  In the first embodiment, a light emitting diode (LED) is used as the light emitting element 30. However, the present invention is not limited to this. For example, an LD (laser diode) having a larger amount of light can be used.

  In addition, the light amount monitoring light receiving element 36 has been described as being provided. However, the present invention is not limited to this, and a light receiving element corresponding to the light amount monitoring light receiving element 36 is built in the light emitting element 30 to form one package. The size may be reduced.

  Although the said Example 1 demonstrated the case where the light emitting element 30 which emits the near-infrared light of the wavelength range of either 1500-1900nm or 2100-2300nm was used, in this Example 2, both these wavelength ranges are demonstrated. Thus, it is configured so that a more accurate density measurement can be performed using two sets of light emitting / receiving elements capable of emitting and receiving light in each wavelength region.

  10 is a cross-sectional view showing a urea concentration detection device according to Embodiment 2 of the present invention, FIG. 11 is a perspective view showing a light guide member of the urea concentration detection device, and FIG. 12 shows a detection unit of the urea concentration detection device. It is sectional drawing expanded and shown. In the following description, the same or corresponding parts as those already described or the step numbers are denoted by the same reference numerals, and redundant description is omitted or simplified.

  As shown in FIGS. 10 to 12, the light guide member 43 includes a stepped portion 43 a and is configured to be able to form two types of optical path lengths L <b> 1 and L <b> 2 in the gap portion 45. For example, the optical path length L1 is set to 0.5 mm, and the optical path length L2 is set to 2 mm.

  As shown in FIG. 10, the first light emitting element (light emitting means) 30a is configured such that the optical path length corresponds to the above L1 and the wavelength is 2200 nm, and the second light emitting element (light emitting means) 30b The length is configured to correspond to the L2 and the wavelength of 1650 nm.

  The first light receiving element (light receiving means) 34 a is provided so as to receive light emitted from the first light emitting element 30 a and passing through the light guide member 43 and the gap 45. Similarly, the second light receiving element (light receiving means) 34 b is provided so as to receive light emitted from the second light emitting element 30 b and passing through the light guide member 43 and the gap 45.

  Although not shown, the light quantity monitoring light receiving element corresponding to the light quantity monitoring light receiving element 36 described in the first embodiment is built in the first light emitting element 30a and is adjacent to the first light emitting element 30a. By monitoring the light amount of the second light emitting element 30b, the influence of the environmental temperature change can be canceled and the light amount can be corrected. Other configurations are the same as those in the case of the first embodiment, and a duplicate description is omitted.

  Next, a control method of the urea concentration detection device 20 will be described with reference to FIG. Here, FIG. 13 is a flowchart showing a control method of the urea concentration detection device 20. The following control is executed at appropriate timing by the ECU.

  As shown in FIG. 13, first, the first and second light emitting elements 30a and 30b are energized (step S110). As a result, the first and second light emitting elements 30a and 30b emit light, and as shown in FIG. 10, the light rays pass through the urea water present in the corresponding gap 45 by the prism 40 and the light guide member 43, and After a predetermined amount of light is attenuated, the light is guided to the first and second light receiving elements 34a and 34b.

  Since output signals corresponding to the amount of the transmitted light are output by the first and second light receiving elements 34a and 34b, the transmitted light amounts I1 and I2 (V) of the urea water are calculated based on the outputs (step S120). .

  Further, the light beams of the first and second light emitting elements 30a and 30b emitted in the step S110 are also received by a light quantity monitoring light receiving element (not shown) built in the first light emitting element 30a. Each monitor light amount Im is calculated based on the output of the light receiving element for light (step S130).

  When each of the monitor light amounts Im is calculated, the light emission amounts I1o and I2o of the first and second light emitting elements 30a and 30b (the light amount is attenuated by urea water) by using the map shown in FIG. It is possible to calculate a value that has not been performed (step S140).

  Next, light transmittances T1 and T2 are calculated based on the transmitted light amounts I1 and I2 calculated in step S120 and the light emission amounts I1o and I2o calculated in step S140 (step S150).

  Next, it is determined using the map shown in FIG. 14 whether there is any abnormality in the light transmittances T1 and T2 calculated in step S150 (step S155). Here, FIG. 14 is a map showing the relationship between the transmittances in the two wavelength ranges with respect to a certain concentration of urea water, and the light transmittance T2 when the wavelength is 1650 nm and the wavelength when it is 2200 nm. The relationship with the transmittance | permeability T1 is shown.

  That is, if the calculated transmittances T1 and T2 are on the graph shown in FIG. 14, it can be determined that the aqueous urea solution has a predetermined concentration (no abnormality). It can be determined that there is an abnormality.

  Therefore, if there is no abnormality (Yes in step S155), the optical path length and wavelength are known, so the urea concentration can be easily determined based on these light transmittances T1 and T2 using a map corresponding to FIG. 14 prepared in advance. (Step S160).

  On the other hand, if there is an abnormality (No at Step S155), the user is informed of the abnormality (Step S180) and alerts the user to perform a predetermined treatment (for example, inspection or replacement of urea water).

  Next, in order to determine whether or not the urea concentration is optimal for NOx purification, it is determined whether or not the urea concentration calculated in step S160 is a predetermined value near 32.5% (step S170). ).

  If the urea concentration is a predetermined value (Yes at step S170), the control is terminated. If the urea concentration is not the predetermined value (No at Step S170), the fact that it is abnormal is notified (Step S180), and the user is alerted to perform a predetermined treatment (for example, inspection or replacement of urea water).

  As described above, according to the urea concentration detection apparatus 20 according to the second embodiment, since the two wavelength regions are configured using the two sets of light emitting / receiving elements, the same effect as the first embodiment can be obtained. In addition to this, it is possible to measure the concentration with higher accuracy.

  In addition, when an abnormality is found in the measurement result, the user is notified of this, so that it is possible to respond quickly thereafter.

  Further, the light quantity monitoring light receiving element corresponding to the light quantity monitoring light receiving element 36 described in the first embodiment is built in the first light emitting element 30a, and the first and second light emitting elements are provided by the one light quantity monitoring light receiving element. Since the light amount correction of the elements 30a and 30b can be performed, the entire apparatus can be reduced in size.

  In the first embodiment and the second embodiment, the optical path length and the wavelength are limited for the convenience of description. However, the optical path length and the wavelength are not limited to the above, and other optical path lengths or It may be a wavelength.

  As described above, the urea concentration detection device according to the present invention is useful for a urea SCR catalyst system of a diesel vehicle, and particularly has a simple configuration with a urea water concentration optimum for NOx purification without deteriorating the fuel consumption of the vehicle. It is suitable for a urea concentration detection device aiming at measuring with high accuracy and responsiveness.

It is sectional drawing which shows the urea concentration detection apparatus which concerns on Example 1 of this invention. It is a block diagram which shows the urea SCR catalyst system to which a urea concentration detection apparatus is applied. It is a top view which shows a urea concentration detection apparatus. It is a perspective view which shows the light guide member of a urea concentration detection apparatus. It is a graph which shows the transmittance | permeability characteristic of water and urea water. It is a map which shows the relationship between the transmittance | permeability and urea concentration in case an optical path length is 0.5 mm and a wavelength is 2200 nm. It is a map which shows the relationship between the transmittance | permeability and urea concentration in case an optical path length is 2 mm and a wavelength is 1650 nm. It is a map which shows the relationship between the monitor light quantity Im of the light receiving element for light quantity monitoring, and the light emission quantity Io of a light emitting element. It is a flowchart which shows the control method of a urea concentration detection apparatus. It is sectional drawing which shows the urea concentration detection apparatus which concerns on Example 2 of this invention. It is a perspective view which shows the light guide member of a urea concentration detection apparatus. It is sectional drawing which expands and shows the detection part of a urea concentration detection apparatus. It is a flowchart which shows the control method of a urea concentration detection apparatus. It is a map which shows the relationship of the transmittance | permeability in two types of wavelength ranges with respect to arbitrary urea water density | concentrations.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 11 Exhaust passage 12 Oxidation catalyst 13 Urea SCR catalyst 14 Urea water tank 15 Urea water supply passage 16 Urea water injection nozzle 17 Urea water addition system tank 20 Urea concentration detectors 21 and 22 Case 24 Holder 25 Substrate 30 Light emitting element ( (Light emitting means)
30a First light emitting element (light emitting means)
30b Second light emitting element (light emitting means)
34 Light receiving element (light receiving means)
34a First light receiving element (light receiving means)
34b Second light receiving element (light receiving means)
36 Light receiving element for light intensity monitoring (light receiving means)
38 Thermistor 40 Prism 41 Concave portion 43 Light guide member 43a Step portion 45 Clearance portion

Claims (4)

The urea water tank that stores the urea water to be measured has a light emitting means and a light receiving means, the urea water is interposed between the light emitting means and the light receiving means, A urea concentration detection device that detects the concentration of the urea water based on the relationship between the amount of light received by the light receiving means and the concentration of the urea water,
The light emitting means is formed to emit at least one of light in a first wavelength range and light in a second wavelength range that has a large amount of change in transmittance calculated based on the amount of light received by the light receiving means. ,
A housing that is hermetically formed as an outer shell and is fixed to the urea water tank and contains the light emitting means and the light receiving means,
A prism that is positioned sealed with the housing and guides the light beam from the light emitting means to the urea water and guides the light beam that has passed through the urea water to the light receiving means;
A recess provided in the prism and into which the urea water can enter in order to detect the concentration of the urea water;
A light guide that is provided in the recess and guides the light of the light emitting means and is configured to be movable by the flow of the urea water while defining the optical path length of the light at the time of concentration detection and maintaining the optical path length. A urea concentration detection device comprising an optical member .   The urea concentration detection device according to claim 1, further comprising concentration determination means for determining whether or not the detected urea concentration is a predetermined default value.   The urea concentration detection device according to claim 1, further comprising a notification unit that notifies the fact that the concentration determination unit does not provide a predetermined predetermined value for the urea concentration.   As the light emitting means, a first light emitting element configured to emit one of the light in the first wavelength band and the light in the second wavelength band, and a second configured to emit the other light. A light emitting element, and
  As the light receiving element, a first light receiving element that receives the light emitted from the first light emitting element and a second light receiving element that receives the light emitted from the second light emitting element are provided,
  The said light guide member is provided with the step part, The optical path length of said one light and the optical path length of said other light are prescribed | regulated as an optical path length, The any one of Claim 1 to 3 characterized by the above-mentioned. The urea concentration detection apparatus described in 1.

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