JP2015125035A - NOx MEASUREMENT DEVICE AND NOx MEASUREMENT METHOD - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device capable of detecting abnormality of an engine or an NOx sensor without being affected by humidity change even in a vehicle during running.SOLUTION: An NOx measurement device 1 comprises: an NOx sensor 2 attached to an exhaust pipe 7 of an engine 6 and capable of detecting NOx and oxygen in the exhaust pipe 7; and an NOx sensor control part 3 in which a detection value detected by the NOx sensor 2 is input and which calculates an NOx value and oxygen density based on the detection value. The NOx sensor control part 3 calculates humidity in atmosphere based on the calculated oxygen density, converts the calculated NOx value into an NOx value in a predetermined atmosphere condition based on the humidity and outputs the converted value. Even in a vehicle during running, it is therefore possible to determine whether the engine is operated in a normal state or not with high accuracy, and determination error is reduced.

Description

  The present invention relates to an apparatus for measuring NOx contained in exhaust gas such as an engine.

  It is known that the amount of NOx discharged from the engine is affected by humidity (for example, see Patent Document 1). For this reason, in the exhaust gas test method for testing whether or not the engine complies with exhaust gas regulations, the amount of NOx discharged from the engine is corrected by humidity.

JP 2008-286019 A

  However, even if a vehicle that is actually running has a NOx sensor that can measure the amount of NOx in the exhaust gas, the amount of NOx that is calculated under the same conditions as in the exhaust gas test method is unknown. For this reason, when the output value of the NOx sensor deviates from the reference value, it may not be possible to determine whether the cause is due to an abnormality in the engine or the NOx sensor or due to humidity in the atmosphere.

  The present invention has been made in view of the above problems, and an object of the present invention is to make it possible to detect an abnormality in an engine or a NOx sensor without being affected by a change in humidity even in a traveling vehicle.

  The present invention is attached to an exhaust pipe of an engine, and a NOx detection unit capable of detecting NOx and oxygen in the exhaust pipe, and a detection value detected by the NOx detection unit are input, and a NOx value based on the detection value And a control unit that calculates an oxygen concentration, wherein the control unit calculates humidity in the atmosphere based on the calculated oxygen concentration, and calculates the calculated NOx value, It converts into the NOx value in predetermined atmospheric conditions based on the humidity and outputs it.

  According to the present invention, the NOx measuring device outputs a value that takes into account changes in NOx emissions due to humidity in the atmosphere, so that the engine and NOx sensor are not affected by changes in humidity even in a running vehicle. It is possible to detect abnormalities.

It is a block diagram which shows the relationship between the NOx measuring device which concerns on embodiment of this invention, and an engine. It is a block diagram which shows the outline of a NOx sensor. It is a flowchart which converts NOx value based on the humidity in air | atmosphere. It is a block diagram which calculates the humidity in air | atmosphere from an air fuel ratio. It is a map which shows the relationship between the humidity in air | atmosphere, and an air fuel ratio. It is a map which shows the relationship between the humidity in air | atmosphere, and a NOx value. It is a flowchart of abnormality determination using the NOx value converted based on the humidity in the atmosphere.

  Hereinafter, a NOx measuring device 1 according to an embodiment of the present invention will be described with reference to the drawings.

  First, the configuration of the NOx measuring device 1 will be described with reference to FIG.

  The NOx measuring device 1 is a device that detects NOx (nitrogen oxide) in exhaust gas discharged from the engine 6 and outputs a NOx value. Here, the NOx value refers to the concentration of NOx (eg, ppm), the mass of NOx per unit time (eg, g / h), and the mass of NOx per unit time unit output (eg, g / kWh). Etc.) etc.

  An engine 6 to which the NOx measuring device 1 is mounted is mounted on a vehicle, burns a mixture of air and fuel in a cylinder (not shown), and rotates a crankshaft (not shown) by the combustion pressure. The rotation of the crankshaft is transmitted to a drive shaft that drives the wheels via a transmission or the like.

  Exhaust gas generated by combustion in the cylinder of the engine 6 is released to the atmosphere through an exhaust pipe 7 connected to the engine 6. A catalyst 8 is disposed in the exhaust pipe 7 to purify NOx, HC (hydrocarbon), and CO (carbon monoxide) in the exhaust gas. As the catalyst 8, a known catalyst such as an oxidation catalyst, a three-way catalyst, a NOx storage reduction catalyst, or a NOx selective reduction catalyst may be used alone or in combination.

  The NOx measuring device 1 includes a NOx sensor 2 as a NOx detection unit that detects NOx and oxygen, and a NOx sensor control unit 3 as a control unit connected to the NOx sensor 2 via a harness.

  The NOx sensor 2 is attached to the exhaust pipe 7 on the downstream side of the catalyst 8 and has a structure in which the gas in the exhaust pipe 7 is guided to the inside as will be described later.

  The NOx sensor control unit 3 controls a voltage supplied to the NOx sensor 2 and detects a voltage value and a current value in the NOx sensor 2, and a value detected by the sensor control unit 4 and an engine control device 9 (hereinafter referred to as “ECU”), and a calculation unit 5 that calculates a NOx value and the like based on the value of the parameter relating to the engine operating state. Specific functions of the sensor control unit 4 and the calculation unit 5 will be described later.

  The ECU 9 is composed of a microcomputer having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an I / O interface (input / output interface). The RAM stores data in the processing of the CPU, the ROM stores a control program of the CPU in advance, and the I / O interface is used for input / output of information with the connected device.

  The ECU 9 has a program and a map necessary for controlling the engine 6, and various sensors (accelerator opening sensor, intake air amount sensor, intake air pressure sensor, intake air temperature sensor, atmospheric pressure) related to engine control (not shown). Output from a sensor, an engine speed sensor, etc.) and a signal for operating the amount of fuel supplied to the engine 6, the supply timing, and the like.

  The ECU 9 and the NOx sensor control unit 3 are connected via a CAN (controller area network) and a harness, and transmit and receive values calculated in each. Electric power is supplied to the ECU 9 and the NOx measuring device 1 from a battery (not shown).

  Next, a schematic configuration of the NOx sensor 2 will be described with reference to FIG.

  Inside the NOx sensor 2, there are an oxygen concentration detection chamber 20 that communicates with the inside of the exhaust pipe 7 through the first communication passage 22, and a NOx concentration detection chamber 21 that communicates with the oxygen concentration detection chamber 20 through the second communication passage 23. It is formed.

  An inner reference electrode 25 and a first inner electrode 27 are provided in the oxygen concentration detection chamber 20. An outer reference electrode 26 is disposed outside the oxygen concentration detection chamber 20 via a partition wall 24 made of a solid electrolyte having oxygen ion conductivity, at a position facing the inner reference electrode 25. A first outer electrode 28 is disposed at a position facing the first inner electrode 27.

  A second inner electrode 29 is provided in the NOx concentration detection chamber 21, and is opposed to the second inner electrode 29 on the outer side of the NOx concentration detection chamber 21 through a partition wall 24 made of a solid electrolyte having oxygen ion conductivity. The second outer electrode 30 is disposed at a position to be performed.

  The outer reference electrode 26 and the first outer electrode 28 disposed outside the oxygen concentration detection chamber 20 and the second outer electrode 30 disposed outside the NOx concentration detection chamber 21 are exposed to the atmosphere.

  The first inner electrode 27 preferably contains a metal having an oxidation function, for example, platinum. The second inner electrode 29 preferably contains a metal having a function of reducing NOx, for example, rhodium.

  As shown in the flowchart of FIG. 3, the NOx measuring device 1 configured as described above calculates the air-fuel ratio and the NOx value, calculates the atmospheric humidity, and calculates the calculated atmospheric humidity. The NOx value converted into a NOx value under a predetermined atmospheric condition is output.

  Next, each step will be described with reference to FIG.

  In steps S1 and S2, the NOx measuring device 1 acquires the atmospheric pressure and the atmospheric temperature from the ECU 9. In addition, it is good also as a structure which provides an atmospheric pressure sensor and atmospheric temperature sensor in the NOx measuring device 1, and acquires atmospheric pressure and atmospheric temperature from these sensor outputs. In this case, the NOx measuring device 1 can convert the NOx value independently.

  In step S3, the NOx measuring device 1 calculates an air-fuel ratio. A method for calculating the air-fuel ratio will be described mainly with reference to FIG.

The exhaust gas discharged from the engine 6 flows through the exhaust pipe 7, and a part thereof flows into the oxygen concentration detection chamber 20 through the first communication path 22 of the NOx sensor 2. When the exhaust gas flows into the oxygen concentration detection chamber 20, the distance between the inner reference electrode 25 and the outer reference electrode 26 depends on the difference between the oxygen concentration D ₁ in the exhaust gas flowing in and the oxygen concentration D ₀ in the atmosphere. An electromotive force is generated. The sensor control unit 4 of the NOx sensor control unit 3 adjusts the oxygen concentration in the atmosphere so that the electromotive force becomes a predetermined voltage V ₀ , that is, the oxygen concentration in the oxygen concentration detection chamber 20 is a reference. A voltage V ₁ is applied between the first inner electrode 27 and the first outer electrode 28 so that the target oxygen concentration D ₂ is lower by a predetermined concentration than D ₀ .

Specifically, if the oxygen concentration D ₁ in the exhaust gas is higher than the target oxygen concentration D ₂ , the oxygen in the oxygen concentration detection chamber 20 is discharged into the atmosphere through the first inner electrode 27 and the first outer electrode 28. As described above, the voltage V ₁ is applied between the first inner electrode 27 and the first outer electrode 28. On the other hand, if the oxygen concentration D ₁ in the exhaust gas is lower than the target oxygen concentration D ₂ , the oxygen is taken in from the atmosphere outside the oxygen concentration detection chamber 20 through the first inner electrode 27 and the first outer electrode 28. A voltage V ₁ is applied between the first inner electrode 27 and the first outer electrode 28.

In this manner, the sensor control unit 4, the oxygen concentration of the oxygen concentration detection chamber 20 is controlled to be a predetermined target oxygen concentration D _2. At this time, the first inner electrode 27 a current value A ₁ flowing between the first outer electrode 28 is correlated with the discharged oxygen amount or incorporated amount of oxygen. Therefore, the calculation unit 5 calculates the oxygen concentration D ₁ of the exhaust gas based on the current value A _1. Calculation unit 5 calculates an air-fuel ratio based on the oxygen concentration D ₁ of the exhaust gas is calculated.

  In step S4, the NOx measuring device 1 calculates a NOx value. A method for calculating the NOx value will be described with reference to FIG.

In step S <b> 3, the exhaust gas in the oxygen concentration detection chamber 20 whose oxygen concentration is controlled to be constant in order to measure the oxygen concentration in the exhaust gas flows into the NOx concentration detection chamber 21 through the second communication path 23. Oxygen in the exhaust gas flowing into the NOx concentration detection chamber 21 becomes oxygen ions when a predetermined voltage V ₂ is applied between the second inner electrode 29 and the second outer electrode 30, and the second inner electrode 29 and the second outer electrode 30 to be discharged into the atmosphere.

When the oxygen concentration in the NOx concentration detection chamber 21 decreases, NOx in the exhaust gas undergoes a reduction reaction at the second inner electrode 29 and is decomposed into oxygen and nitrogen. Oxygen generated by the reduction reaction of NOx becomes oxygen ions and is discharged into the atmosphere through the second inner electrode 29 and the second outer electrode 30. At this time, the current value A ₂ flowing between the second inner electrode 29 and the second outer electrode 30 is generated by the reduction reaction between the oxygen concentration (target oxygen concentration D ₂ ) remaining in the exhaust gas and NOx. This is the value required to discharge the oxygen concentration to the atmosphere. Therefore, the calculation unit 5 can calculate the NOx value in the exhaust gas on the basis of the current value A ₂ at the target oxygen concentration D ₂ current A ₃ minus the corresponding minute.

  Subsequently, in step S5, it is determined whether or not a condition for calculating atmospheric humidity is satisfied. If the condition for calculating the atmospheric humidity is satisfied, the process proceeds to step S6, and the atmospheric humidity is calculated.

  Here, two methods will be described as methods for calculating the humidity used for the conversion of the NOx value in the NOx measuring device 1.

  First, the first method will be described with reference to FIG.

  In the NOx sensor 2 as described above, a predetermined voltage is applied between the electrodes in order to detect the oxygen concentration. When the voltage is increased, the moisture in the detection chamber is decomposed, and oxygen generated by the decomposition of the moisture is also detected. It is known that it will be detected by a part.

  On the other hand, the humidity in the atmosphere is defined by the moisture contained in the air. Therefore, in the first method, moisture in the air is calculated using the NOx sensor 2, and humidity is calculated based on the amount of moisture.

  Specifically, first, the sensor control unit 4 determines whether or not the engine 6 is in a fuel cut state based on a parameter value indicating the engine state provided from the ECU 9. When the sensor control unit 4 determines that the engine 6 is in the fuel cut state, the sensor control unit 4 detects the oxygen concentration of the gas flowing into the oxygen concentration detection chamber 20. When the engine 6 is in the fuel cut state, the air sucked into the engine 6 is released into the atmosphere as it is through the exhaust pipe 7 without being mixed with the fuel, so that there is no exhaust gas in the oxygen concentration detection chamber 20. Air flows in without.

The sensor control unit 4 adjusts the electromotive force generated between the inner reference electrode 25 and the outer reference electrode 26 to a predetermined predetermined humidity measurement voltage V _H , that is, oxygen in the oxygen concentration detection chamber 20. A first discharge voltage V ₃ is applied between the first inner electrode 27 and the first outer electrode 28 so that the concentration becomes a predetermined humidity measurement oxygen concentration D ₃ . Thereby, oxygen in the oxygen concentration detection chamber 20 is discharged out of the oxygen concentration detection chamber 20 through the first inner electrode 27 and the first outer electrode 28. Since the current value A ₃ that flows between the first inner electrode 27 and the first outer electrode 28 correlates with the amount of oxygen that has been exhausted, the calculation unit 5 can enter the NOx sensor 2 based on the current value A _3. it is possible to calculate the oxygen concentration D ₄ of inflow air. By setting as possible humidity during measurement of oxygen concentration D ₃ low oxygen concentration D ₄ is extremely close to the oxygen concentration D ₀ in the atmosphere.

Subsequently, the sensor control unit 4 applies a second discharge voltage V ₄ higher than the first discharge voltage V ₃ between the first inner electrode 27 and the first outer electrode 28 in order to measure moisture in the air. Apply. The second discharge voltage V _4, the moisture in the air is set to a value enough to produce oxygen is decomposed. Current A ₄ taken in order to discharge the oxygen from the oxygen concentration-detecting chamber 20 at this time is correlated with the combined amount of oxygen and oxygen water oxygen in the air in the air has been generated is decomposed. For this reason, since the difference between the current value A ₄ and the current value A ₃ correlates with the moisture content in the air, the calculation unit 5 calculates the moisture content in the air based on this difference, Humidity is calculated based on the amount of moisture.

  When calculating the atmospheric humidity by this method, the humidity calculation condition in step S5 is that the engine 6 is in a fuel cut state.

  Next, the second humidity calculation method will be described mainly with reference to FIGS.

As described above, the calculation unit 5, and calculates the air-fuel ratio based on the oxygen concentration D ₁ of the exhaust gas. Here, the target oxygen concentration D ₂ as a reference for calculating the oxygen concentration D _1, because is set based on the oxygen concentration D ₀ in the atmosphere, where the oxygen concentration D ₀ in the atmosphere is changed according to the humidity also changes similarly target oxygen concentration D _2.

However, when calculating an air-fuel ratio in the arithmetic unit 5, the oxygen concentration D ₀ of the atmosphere it has always been assumed to have an oxygen concentration of the standard atmospheric conditions (e.g., 21%). For this reason, the air-fuel ratio calculated by the calculation unit 5 becomes smaller as the humidity is higher. Here, if viewed in reverse, the air-fuel ratio calculated by the calculation unit 5 and the same atmospheric state as the exhaust gas test method, so-called standard atmospheric conditions (for example, atmospheric pressure 100 kPa, atmospheric temperature 25 ° C., relative humidity 30%) It is understood that the difference between the air-fuel ratio when the engine 6 is operated (hereinafter referred to as a standard operating air-fuel ratio) and the humidity in the atmosphere. Therefore, in the second method, the humidity in the atmosphere is calculated using this correlation.

  As shown in FIG. 4, the calculation unit 5 includes an air-fuel ratio calculation block 41 that calculates an air-fuel ratio based on the output of the NOx sensor 2, an air-fuel ratio estimation block 42 that estimates a standard operating air-fuel ratio, and an air-fuel ratio calculation block. A humidity calculation block 43 for calculating the humidity in the atmosphere from the calculated air-fuel ratio calculated in 41 and the standard operating air-fuel ratio estimated in the air-fuel ratio estimation block 42.

In the air-fuel ratio calculation block 41, the calculated air-fuel ratio _RC is calculated based on the detection value of the NOx sensor 2 as described above.

In the air-fuel ratio estimation block 42, the standard operating sky when the engine 6 is operated under the same atmospheric conditions as the exhaust gas test method, so-called standard atmospheric conditions (for example, atmospheric pressure 100 kPa, atmospheric temperature 25 ° C., relative humidity 30%). A map in which the fuel ratio is mapped to the accelerator opening, the intake air amount, the engine speed, and the like, which are parameters indicating the operating state of the engine 6 is stored. In the air-fuel ratio estimation block 42, the standard operating air-fuel ratio _RR is estimated based on the parameter value indicating the current engine state supplied from the ECU 9.

The humidity calculation block 43 stores a map showing the correlation between the difference between the calculated air-fuel ratio _RC and the standard operating air-fuel ratio _RR and the humidity in the atmosphere as shown in FIG. 5, the horizontal axis represents the humidity of the atmosphere, and the vertical axis represents the difference between the calculated air-fuel ratio R _C and the standard operating air-fuel ratio R _R. The calculated air-fuel ratio _RC is smaller than the standard operating air-fuel ratio R _R , indicating that the humidity is higher. At humidity calculation block 43, based on the calculated air-fuel ratio is input R _C and standard operating air-fuel ratio R _R, humidity in the atmosphere is calculated.

  When calculating the atmospheric humidity by this method, the humidity calculation condition in step S5 is that the engine 6 is in a steady operation state in which the rotational speed and load are stable, and the air-fuel ratio is in a stable state.

  The calculated humidity is stored in the calculation unit 5. The humidity is calculated when the calculation condition is satisfied after the key switch is turned on, and the calculated humidity is stored until the humidity is next calculated. The frequency of calculating the humidity may be performed at least once after the key switch is turned on, but may be performed a plurality of times. When the humidity is calculated a plurality of times, the calculation accuracy can be improved by calculating the humidity from the average value.

  In step S7, the NOx value calculated in step S4 is converted into a NOx value in a predetermined atmospheric condition by the humidity calculated in step S6, as will be described later. If the condition is not satisfied in step S5, the conversion of the NOx value is performed based on the previously calculated humidity. The method for calculating the humidity is not limited to the above-described method, and any method may be used as long as the humidity can be obtained using the output value of the NOx sensor 2. Moreover, it is good also as a structure which uses the average value of the humidity calculated by the several calculation method. In this case, the humidity calculation accuracy is improved, and the NOx value can be converted more accurately.

  Here, a method for converting the NOx value into a NOx value under a predetermined atmospheric condition in accordance with the humidity in step S7 will be described.

  As shown in FIG. 6, the calculation unit 5 shows how the NOx value discharged from the engine changes when the atmospheric humidity is changed as a map for each engine speed and engine load. Stored. In FIG. 6, the horizontal axis represents the humidity in the atmosphere, and the vertical axis represents the NOx value. The solid line indicates the NOx value measured by the engine test, and the NOx value discharged from the engine decreases as the humidity in the atmosphere increases. The broken line indicates the NOx value when the humidity is humidity (for example, 30%) under a predetermined atmospheric condition. From the difference between the solid line and the broken line at the calculated humidity, a conversion coefficient for converting the calculated NOx value into the NOx value under a predetermined atmospheric condition is obtained.

  That is, the conversion coefficient increases as the difference between the calculated humidity and the humidity under a predetermined atmospheric condition increases. Further, when the calculated humidity is higher than the humidity under the predetermined atmospheric condition, the calculated NOx value is converted in an increasing direction, and when the calculated humidity is lower than the humidity under the predetermined atmospheric condition, the calculated NOx value is calculated. The NOx value is converted in a decreasing direction.

  As a result, the calculated NOx value is based on the calculated humidity, for example, the same atmospheric state as the exhaust gas test method, so-called standard atmospheric conditions (for example, atmospheric pressure 100 kPa, atmospheric temperature 25 ° C., relative humidity 30%. ) Is converted into a value corresponding to when the engine 6 is operated. The predetermined atmospheric condition is not limited to the same atmospheric condition as the exhaust gas test method, and can be arbitrarily set. In converting the NOx value into the NOx value under a predetermined atmospheric condition depending on the humidity, a known NOx value conversion formula can also be used.

  In general, since the output value of the NOx sensor or air-fuel ratio sensor has an error depending on the humidity, the air-fuel ratio calculated in step S3 and the step S4 are calculated before the NOx value is converted in step S7. It is preferable that the NOx value thus corrected is corrected by the humidity calculated in step S6 to eliminate the output error of the NOx sensor 2 due to the humidity.

NOx value _{E H,} which is converted by humidity in step S7, in step S8, is output from the NOx measuring device 1 to the ECU 9, in terms of NOx values due to humidity in the atmosphere is completed. The NOx value E _H, which is converted by humidity in the atmosphere as is used abnormality to determine at ECU9 in the vehicle during running.

Hereinafter, a method for determining an abnormality in a running vehicle using the NOx value E _H converted by humidity will be described with reference to FIG.

In step S _< b> 11, the ECU 9 obtains the NOx value E _H converted by the humidity from the NOx measuring device 1. In steps S12 and S13, the ECU 9 corrects the NOx value E _H converted by the humidity with the atmospheric pressure and the atmospheric temperature based on the output values of the atmospheric pressure sensor and the intake air temperature sensor. In addition, in the calculating part 5 of the NOx measuring device 1, steps S12 and S13 are not executed when the NOx value has already been corrected based on the atmospheric pressure and the atmospheric temperature.

In step S14, it is determined whether or not NOx value E _H, which is converted by the humidity is fixed to a constant value. If the value does not change over a predetermined time despite the change in engine load and rotation speed, it is determined that the value is fixed, and the process proceeds to step S15 where it is determined as abnormal.

Whether NOx value E _H, which is converted by the humidity when it is determined not to be fixed to a certain value, the process proceeds to step S16, NOx value E _H, which is converted by the humidity exceeds the upper limit or the lower limit value Determine whether. The upper limit value and the lower limit value are set to values that cannot be generated under normal engine operating conditions. If NOx value E _H, which is converted by the humidity exceeds the upper limit or the lower limit value, it is determined that an abnormality process proceeds to step S15, if not exceeded, the process proceeds to step S17.

In step S17, it derives the NOx values predicted from the operating state of the engine 6, and the compared the NOx value E _H converted by derived predicted NOx value E _P and humidity, and calculates the difference. The derivation of predicted NOx value _{E P,} reference NOx value map stored in ECU9 is used. The reference NOx value map is the NOx value emitted when the engine 6 is operated in the same atmospheric condition as the exhaust gas test method, so-called standard atmospheric condition (for example, atmospheric pressure 100 kPa, atmospheric temperature 25 ° C., relative humidity 30%). Is mapped to the accelerator opening, intake air amount, engine speed, and the like, which are parameters indicating the operating state of the engine 6.

  In step S18, it is determined whether or not the difference calculated in step S17 is greater than a threshold value. The threshold value is set in consideration of variations in the NOx value due to individual differences of the engine 6, the allowable range of the NOx value with respect to the legal regulation value, and the like. If the difference is larger than the threshold, the process proceeds to step S15, where it is determined to be abnormal. If the difference is less than the threshold, the process proceeds to step S19, where it is determined to be normal, and the determination ends.

  Note that the determination of abnormality may be performed by the NOx measuring device 1 instead of the ECU 9. In this case, the determination result is transmitted from the NOx measuring device 1 to the ECU 9.

  Moreover, as a NOx value used for determination of abnormality, an instantaneous value may be used or an integrated value in a predetermined period may be used.

  Further, the NOx measuring device 1 may be arranged upstream rather than downstream of the catalyst 8. In this case, it is not necessary to consider the change in the NOx value due to the deterioration of the catalyst 8.

  According to the above embodiment, there exists an effect shown below.

  Conventionally, a vehicle that is actually running has a NOx sensor that can measure the amount of NOx in exhaust gas, but the amount of NOx that is calculated under the same conditions as in the exhaust gas test method is unknown. For this reason, when the output value of the NOx sensor deviates from the reference value, it may not be possible to determine whether the cause is due to an abnormality in the engine or the NOx sensor or due to humidity in the atmosphere.

  On the other hand, the NOx measuring device 1 outputs the NOx value converted by the humidity in the atmosphere, so that the engine is in a normal state even in the traveling vehicle based on the converted NOx value. Whether or not the vehicle is in operation can be determined with high accuracy, and erroneous determination can be reduced.

  Moreover, since the NOx value output from the NOx measuring device 1 is converted into the NOx value under a predetermined atmospheric condition, for example, the NOx value of the engine alone measured under the same conditions as the exhaust gas test method is determined as an abnormality. Therefore, it can be used as a reference for comparison.

  Conventionally, in order to measure the humidity in the atmosphere, a humidity sensor must be provided separately. However, since the humidity in the atmosphere is calculated based on the value detected by the NOx sensor, a humidity sensor is provided separately. There is no need and the cost is reduced. In addition, when a humidity sensor is provided separately, it is necessary to determine whether or not the humidity sensor is abnormal, but this is not necessary because a NOx sensor that has been conventionally attached is used.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

DESCRIPTION OF SYMBOLS 1 NOx measuring device 2 NOx sensor (NOx detection part)
3 NOx sensor control unit (control unit)
4 Sensor Control Unit 5 Arithmetic Unit 6 Engine 7 Exhaust Pipe 8 Catalyst 9 Engine Control Device 20 Oxygen Concentration Detection Chamber 21 NOx Concentration Detection Chamber 25 Inner Reference Electrode 26 Outer Reference Electrode 27 First Inner Electrode 28 First Outer Electrode 29 Second Inner Electrode 30 Second outer electrode

Claims (5)

A NOx detector attached to the exhaust pipe of the engine and capable of detecting NOx and oxygen in the exhaust pipe;
A NOx measuring device comprising: a control unit that receives a detection value detected by the NOx detection unit and calculates a NOx value and an oxygen concentration based on the detection value;
The control unit calculates humidity in the atmosphere based on the calculated oxygen concentration, and converts the calculated NOx value into a NOx value in a predetermined atmospheric condition based on the humidity and outputs the NOx value. NOx measuring device characterized by this.   When the control unit determines that the engine is in a fuel cut state, the control unit calculates an oxygen concentration based on the detection value detected by the NOx detection unit, and based on the calculated oxygen concentration, humidity in the atmosphere The NOx measuring device according to claim 1, wherein the NOx measuring device is calculated.   The control unit calculates an air-fuel ratio in the exhaust gas based on the calculated oxygen concentration, derives a standard operating air-fuel ratio from the operating state of the engine, and derives the calculated air-fuel ratio from the calculated air-fuel ratio. The NOx measuring device according to claim 1, wherein the humidity is calculated based on a difference from the standard operating air-fuel ratio.   The control unit compares the NOx value in a predetermined atmospheric condition converted based on the humidity with a reference NOx value derived from the operating state of the engine, and the difference is equal to or greater than a predetermined value. The NOx measuring device according to any one of claims 1 to 3, wherein it is determined that there is an abnormality. The NOx value and the oxygen concentration are calculated from the detection value detected by the NOx detection unit, the atmospheric humidity is calculated based on the calculated oxygen concentration, and the calculated NOx value is determined based on the humidity. A NOx measuring method, wherein the NOx value is converted into a NOx value under atmospheric conditions.

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