JP2018084436A - Nox sensor inspection device and nox sensor inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an NOx sensor inspection device and an NOx sensor inspection method that improve the availability of vehicles by highly accurate inspection and prevent a non-defective NOx sensor from being replaced accidently.SOLUTION: An NOx sensor inspection device 10 includes a reference gas generation device 12, an installation pipe 13, a control cum data processing device 14, and a reference NOx sensor 15. Each of the NOx sensor 11 and reference NOx sensor 15 in a removed state is connected with the control cum data processing device 14 in the state of being inserted into the installation pipe 13, and detects each of a detection value Cβ and a reference detection value Cγ for each of actual NOx concentration Cα of a reference gas Gα flown into the installation pipe 13. The control cum data processing device 14 inspects the NOx sensor 11 according to an output characteristic Lβ based on them.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a NOx sensor inspection device and a NOx sensor inspection method, and more specifically, a NOx sensor inspection device for improving the operating rate of a vehicle by high-precision inspection and preventing erroneous replacement of a non-failing NOx sensor, and The present invention relates to a NOx sensor inspection method.

  In order to purify nitrogen oxides (NOx) in the exhaust gas, the diesel engine detects the NOx concentration in the exhaust gas with a NOx sensor disposed in the exhaust passage, and injects urea water based on the detected NOx concentration. Self-diagnosis such as quantity adjustment and catalyst.

  This NOx sensor has a problem that the element is poisoned by a metal component or hydrocarbon (HC) in the exhaust gas, or the element is cracked. When these problems occur, the output characteristics of the NOx sensor change, and the NOx concentration in the exhaust gas cannot be accurately detected.

  In this regard, an apparatus has been proposed in which air is supplied from an air pump to the exhaust passage while the engine is stopped, and the NOx sensor is inspected based on whether or not the detected value of the NOx sensor at that time exceeds a reference value. (For example, refer to Patent Document 1).

  However, this apparatus only checks whether or not the detected value of the NOx sensor is normal, and does not check the output characteristics of the NOx sensor. Therefore, the inspection accuracy is low, and there is a possibility that an erroneous replacement of a NOx sensor that has not failed occurs or a failure of the NOx sensor is missed.

JP 2009-145219 A

  The object of the present invention is to obtain the output characteristics of the NOx sensor in a short time and with high accuracy, and to improve the operating rate of the vehicle and prevent erroneous replacement of the NOx sensor that has not failed by high-precision inspection based on the output characteristics. An object of the present invention is to provide a NOx sensor inspection device and a NOx sensor inspection method that can be realized.

  The NOx sensor inspection device of the present invention that achieves the above object is a NOx sensor inspection device that inspects a NOx sensor inserted in an exhaust passage of an engine mounted on a vehicle, and adjusts the actual NOx concentration in a reference gas. A reference gas generating device, an installation pipe into which the reference gas generated by the reference gas generating device flows, a control and data processing device connected to the reference gas generating device, and a reference NOx maintaining a normal state Each of the NOx sensor and the reference NOx sensor removed from the exhaust passage is connected to the control and data processing device in a state of being inserted into the installation pipe, For each actual NOx concentration of the reference gas flowing into the installation pipe, the detected value is detected by the NOx sensor, and the detected reference value is detected by the reference NOx sensor. The control and data processing device, in accordance with the output characteristics based on their detected values and the reference detection value, is characterized in that it has the structure to inspect the NOx sensor.

  A NOx sensor inspection method of the present invention that achieves the above object is a NOx sensor inspection method for inspecting a NOx sensor inserted in an exhaust passage of an engine mounted on a vehicle, wherein the NOx sensor is connected to the exhaust passage. Removing from the exhaust passage, inserting the NOx sensor removed from the exhaust passage into an installation pipe in which a reference NOx sensor maintaining a normal state is inserted, and changing the actual NOx concentration of the reference gas, A step of sequentially flowing a reference gas into the installation pipe for each actual NOx concentration, a step of acquiring a detection value of the NOx sensor and a reference detection value of the reference NOx sensor for each actual NOx concentration of the reference gas, and Generating an output characteristic of the NOx sensor from the detected value and the reference detected value, and the NOx sensor according to the output characteristic. A step of checking the service, is a method which comprises a.

  Here, the “normal state” means a state in which the difference between the actual NOx concentration of the reference gas flowing through the installation pipe and the reference detection value detected by the reference NOx sensor is within a preset error range. That is.

  The detected value of the NOx sensor and the detected reference value of the reference NOx sensor are the same as the reference value of the NOx sensor and the reference NOx sensor when the reference gas whose actual NOx concentration sequentially changes due to the generation of the reference gas sequentially flows into the installation pipe for each actual NOx concentration. This value is detected by the NOx sensor. Accordingly, these detection values and reference detection values are detected as a set each time the actual NOx concentration of the reference gas changes, and therefore the control and data processing device stores a plurality of sets of detection values and reference detection values. The

  The output characteristic indicates the detected value of the NOx sensor with respect to the actual NOx concentration of the reference gas. That is, the detected value of the NOx sensor with respect to the reference detected value of the reference NOx sensor is shown.

  According to the NOx sensor inspection device and the NOx sensor inspection method, the NOx sensor is removed from the exhaust passage, and is inserted into the installation pipe into which the reference gas whose actual NOx concentration varies together with the reference NOx sensor. Each detection value and reference detection value can be acquired. Thereby, the output characteristics of the NOx sensor can be acquired in a short time and with high accuracy based on the detected value and the reference detected value. Further, since the NOx sensor is inspected based on the output characteristics of the NOx sensor without determining only whether the detected value of the NOx sensor is normal or not, the accuracy of the inspection of the NOx sensor can be improved. .

  For example, the output characteristic when a crack occurs in the element of the NOx sensor has a higher detection value than when it is normal, and the output characteristic when the NOx sensor element is poisoned is compared with that when it is normal. The detection value becomes low. Thus, by checking the NOx sensor in accordance with the output characteristics of the NOx sensor, it is possible to determine the cause of the failure of the NOx sensor and repair the cause of the failure.

  Therefore, the above-described NOx sensor inspection device and the NOx sensor inspection method can determine and maintain both the failure of the NOx sensor and the cause of the failure by high-precision inspection based on the output characteristics of the NOx sensor. By avoiding re-entry due to poor maintenance, the operation rate of the vehicle can be improved. In addition, the maintenance cost can be reduced by preventing erroneous replacement of the NOx sensor that is not in failure.

It is a block diagram which illustrates the NOx inspection apparatus of embodiment of this invention. It is a block diagram which illustrates the control and data processing apparatus of FIG. It is an example of the output characteristic map based on the actual NOx density | concentration of a reference gas, and the detected value. It is a flowchart which illustrates the NOx inspection method of embodiment of this invention. It is a modification of an output characteristic map. It is a graph which illustrates the relationship between the elapsed time after energizing a sensor and the detected value.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 illustrates a NOx sensor inspection device 10 according to an embodiment of the present invention. This NOx sensor inspection device 10 inspects a NOx sensor 11 inserted in an exhaust passage of an engine mounted on a vehicle (not shown), and is provided in a vehicle inspection facility. In addition, as a vehicle inspection equipment, service stations, such as a gas station, can be illustrated.

  As shown in FIG. 1, the NOx sensor inspection device 10 includes a reference gas generator 12, an installation pipe 13, a control / data processing device 14, and a reference NOx sensor 15. A suction pump 16 is installed downstream of the installation pipe 13, and a purification device (not shown) is installed downstream thereof.

  In the following description, the reference gas flowing into the installation pipe 13 is Gα, the actual NOx concentration of the reference gas Gα (hereinafter referred to as the actual NOx concentration) is Cα, the detected value of the NOx sensor 11 is Cβ, and the reference NOx sensor 15 The reference detection value is Cγ.

  The reference gas generator 12 includes a plurality of cylinders 17a to 17d, a plurality of regulators 18a to 18d, a manifold 19 and an on-off valve 20.

  The plurality of cylinders 17a to 17d are containers for storing gases having different NOx concentrations. The cylinder 17a stores a gas Ga having a NOx concentration Cc, the cylinder 17b stores a gas Gb having a NOx concentration Cb, the cylinder 17c stores a gas Gc having a NOx concentration Cc, and the cylinder 17d stores a gas Gd having a NOx concentration Cd.

  The gases Ga to Gd are generated so as to have different NOx concentrations. For example, the NOx concentration Ca of the gas Ga is zero ppm, the NOx concentration Cb of the gas Gb is 100 ppm, the NOx concentration Cc of the gas Gc is 1000 ppm, and the NOx concentration Cd of the gas Gd is 2000 ppm.

  The reference gas generator 12 changes the actual NOx concentration Cα of the reference gas Gα flowing into the installation pipe 13 continuously or stepwise by combining any or some of these gases Ga to Gd.

  In this embodiment, the gas cylinders Ga to Gd having different NOx concentrations Ca to Cd are stored in the four cylinders 17a to 17d. However, the number of cylinders may be at least two, and the number is not limited. Further, the NOx concentration of the gas stored in the cylinder may be at least two of zero ppm and a value equal to or higher than the emission standard value of the Air Pollution Control Law (for example, 950 ppm to 1200 ppm in the case of a diesel engine).

  The regulators 18a to 18d are electronically controlled pressure regulators. The manifold 19 is connected to each outlet of the regulators 18a to 18d and collects the gases Ga to Gd. The on-off valve 20 is an electronically controlled valve that is interposed in the manifold 18 and opens and closes the manifold 18 to the installation pipe 13. The reference gas generator 12 may be configured to generate the reference gas Gα so that the actual NOx concentration Cα in the reference gas Gα can be adjusted, and is not limited to the above configuration. For example, a flow path control valve may be used instead of the regulators 18a to 18d. However, the reference gas generator 12 is limited to an apparatus in which the actual NOx concentration Cα of the reference gas Gα is automatically adjusted by the control and data processing device 14.

  The installation pipe 13 is interposed in the middle of the manifold 19 of the reference gas generator 12. The installation pipe 13 is a pipe into which the NOx sensor 11 removed from the engine exhaust passage and the reference NOx sensor 15 are inserted.

  The control and data processing device 14 includes a CPU that performs various processes, a ROM that temporarily stores programs used to perform the various processes, a RAM that can read and write processing results, and various interfaces including a display screen. Composed. The control and data processing device 14 is connected to the regulators 18a to 18d and the on-off valve 20 of the reference gas generator 12 via signal lines. The control / data processing device 14 adjusts the actual NOx concentration Cα of the reference gas Gα flowing from the reference gas generator 12 into the installation pipe 13. The control / data processing device 14 is connected to the NOx sensor 11 and the reference NOx sensor 15 which are inserted into the installation pipe 13 via signal lines. The control / data processing device 14 acquires the detection value Cβ of the NOx sensor 11 and the reference detection value Cγ of the reference NOx sensor 15 and stores them in the RAM.

  The reference NOx sensor 15 is electrically connected to the control and data processing device 14 while being inserted into the installation pipe 13. The reference NOx sensor 15 is a sensor that maintains a normal state. The normal state here is a state in which the difference between the actual NOx concentration Cα of the reference gas Gα and the reference detection value Cγ detected by the reference NOx sensor 15 is within a preset error range. It is preferable that the actual NOx concentration Cα and the reference detection value Cγ are equal. In this embodiment, it is assumed that the reference detection value Cγ of the reference NOx sensor 15 indicates the actual NOx concentration Cα of the reference gas Gα.

  The NOx sensor 11 is removed from the exhaust passage of the engine and is electrically connected to the control and data processing device 14 while being inserted into the installation pipe 13.

  FIG. 2 illustrates an outline of a program of the control / data processing apparatus 14. The control / data processing device 14 stores a density adjustment control program 21, an output characteristic generation program 22, and a pass / fail judgment program 23 as execution programs. These execution programs perform processes designated in advance by the CPU.

  The concentration adjustment control program 21 causes the reference gas generator 12 to change the actual NOx concentration Cα of the reference gas Gα continuously or stepwise, and causes the reference gas Gα to flow into the installation pipe 13 in order for each actual NOx concentration Cα. It is a control program that executes a procedure.

  In addition, it is preferable that this density | concentration adjustment control program 21 is comprised so that the procedure which operates from the regulator 18a to the regulator 18d in order may be implemented. With this configuration, the actual NOx concentration Cα of the reference gas Gα is increased continuously or stepwise, and sequentially from the reference gas Gα having a lower actual NOx concentration Cα toward the reference gas Gα having a higher actual NOx concentration Cα. It can flow into the installation pipe 13. If the reference gas Gα having a high actual NOx concentration Cα is caused to flow into the installation pipe 13 first, the NOx may remain in the installation pipe 13 and the subsequent change in the actual NOx concentration Cα may become dull. On the other hand, if the reference gas Gα is caused to flow into the installation pipe 13 in the order of the low actual NOx concentration Cα to the high actual NOx concentration Cα, the actual NOx concentration Cα of the reference gas Gα can be reliably changed continuously or stepwise. Can do. This is advantageous in improving the generation accuracy of the output characteristic Lβ of the NOx sensor 11 described later.

  The output characteristic generation program 22 is a program that reads the detection value Cβ and the reference detection value Cγ stored in the RAM as a set and generates the output characteristic Lβ of the NOx sensor 11 based on them. Note that the output characteristic Lβ of the NOx sensor 11 here indicates a detection value Cβ with respect to the actual NOx concentration Cα of the reference gas Gα. That is, in this embodiment, the detection value Cβ with respect to the reference detection value Cγ is shown.

  The control and data processing device 14 has an output characteristic map M1 in which the horizontal axis is the actual NOx concentration Cα and the vertical axis is the detected value Cβ. The output characteristic Lβ of the NOx sensor 11 generated by the output characteristic generation program 22 is plotted on the preset output characteristic map M1. The output characteristic map M1 on which the output characteristic Lβ is plotted is preferably output on the display screen of the control and data processing device 14. By doing in this way, the mechanic can visually confirm the output characteristic Lβ of the NOx sensor 11, so that the NOx sensor 11 can be inspected with higher accuracy.

  The pass / fail determination program 23 compares the reference output characteristic Lα set in the output characteristic map M1 in advance with the output characteristic Lβ of the NOx sensor 11 generated by the output characteristic generation program 22, and outputs the output characteristic Lβ of the NOx sensor 11. This is a program for judging whether the product is good or bad.

  The reference output characteristic Lα is an output characteristic when the NOx sensor 11 is normal, and this normal case is when the actual NOx concentration Cα is equal to the detected value Cβ. Therefore, the output characteristic of the reference NOx sensor 15 can be used as the reference output characteristic Lα.

  FIG. 3 illustrates an output characteristic map M1. Hereinafter, the quality determination of the output characteristic Lβ of the NOx sensor 11 in the quality determination program 23 will be described with reference to FIG.

  The output characteristic map M1 is set with a reference output characteristic Lα, an upper limit output characteristic Lu indicating a high detection value with respect to the reference output characteristic Lα, and a lower limit output characteristic Ll indicating a low detection value.

  For example, the upper limit output characteristic Lu is +20 ppm or less with respect to the reference output characteristic Lα in the vicinity of 0 ppm, and becomes + 20% or less with respect to the reference output characteristic Lα at a predetermined concentration or more sufficiently exceeding 0 ppm. Further, the lower limit output characteristic Ll is, for example, −20 ppm or more with respect to the reference output characteristic Lα in the vicinity of 0 ppm, and −20% or more with respect to the reference output characteristic Lα at a predetermined concentration or more.

  The pass / fail judgment program 23 determines that the output characteristic Lβ of the NOx sensor 11 is in a range where the output characteristic Lβ is within the range A (shaded area in the figure) surrounded by the upper limit output characteristic Lu and the lower limit output characteristic Ll. Judge as good. On the other hand, in other cases, it is determined that the output characteristic Lβ of the NOx sensor 11 is defective.

  In FIG. 3, since the output characteristic Lβ1 is within the range A, it is determined to be good. As a result, the NOx sensor 11 need not be replaced. On the other hand, since the output characteristic Lβ2 is not within the range A, it is determined to be defective. As a result, the NOx sensor 11 needs to be replaced because it is out of order.

  The NOx sensor inspection method by the NOx sensor inspection device 10 will be described below based on the flowchart shown in FIG. It is assumed that the NOx sensor 11 is inserted into an exhaust passage of an engine (not shown) at the start. In the flowchart described below, α, β, and γ are treated as variables, and the values of these variables are set to zero at the start.

  When the vehicle enters the vehicle inspection facility, in step S10, the mechanic removes the NOx sensor 11 inserted in the engine exhaust passage. Next, in step S20, the removed NOx sensor 11 is inserted into the installation pipe 13 and installed.

  Next, when the maintenance engineer starts the program of the control and data processing device 14, in step S <b> 30, the concentration adjustment control program 21 causes the reference gas generator 12 to perform a procedure for causing the reference gas Gα to flow into the installation pipe 13.

  Next, in step S40, the NOx sensor 11 acquires the detection value Cβ in the reference gas Gα, and the reference NOx sensor 15 acquires the reference detection value Cγ in the reference gas Gα. Next, in step S50, the control and data processing device 14 sets the detection value Cβ of the NOx sensor 11 and the reference detection value Cγ of the reference NOx sensor 15 as a set and stores them in the RAM.

  Next, in step 60, the variables α, β, and γ are changed. Next, in step S70, the concentration adjustment control program 21 determines whether or not the actual NOx concentration Cα of the reference gas Gα is the maximum value Cmax. The maximum value Cmax is the maximum value of the actual NOx concentration Cα of the reference gas Gα flowing into the installation pipe 13 from the reference gas generator 12. In this embodiment, the NOx concentration Cd of the gas Gd stored in the cylinder 17d is set. If the actual NOx concentration Cα is less than the maximum value Cmax in step S60, the process returns to step S30. On the other hand, if the actual NOx concentration Cα is greater than or equal to the maximum value Cmax, the concentration adjustment control program 21 ends, the output characteristic generation program 22 starts, and the process proceeds to step S80.

  By repeatedly performing the above steps S30 to S70, the reference gas Gα in which the actual NOx concentration Cα increases continuously or stepwise flows into the installation pipe 13 in the order of concentration. Specifically, in the first step S30 from the start, the gas Ga of NOx concentration Ca is caused to flow into the installation pipe 13 as the reference gas Gα. Thereafter, the gas Gb having the NOx concentration Cb is introduced as the reference gas Gα in the second time, the gas Gc having the NOx concentration Cc in the third time, and the gas Gd having the NOx concentration Cd in the fourth time. In the second and subsequent times, a new regulator may be opened without closing the regulator that has been opened. The NOx sensor 11 and the reference NOx sensor 15 detect the detection value Cβ and the reference detection value Cγ for each actual NOx concentration Cα, and these are stored in the control / data processing device 14 as a set.

  Next, in step S80, the output characteristic generation program 22 reads a plurality of sets of detection values Cβ and reference detection values Cγ stored in the RAM. Next, in step S90, the output characteristic generation program 22 generates the output characteristic Lβ of the NOx sensor 11. Next, in step S100, the output characteristic Lβ generated by the output characteristic generation program 22 is plotted on the output characteristic map M1. When the generated output characteristic Lβ is plotted on the output characteristic map M1 in step S100, the output characteristic generation program 22 is terminated and the pass / fail determination program 23 is started.

  Next, in step S110, the pass / fail determination program 23 compares the output characteristic Lβ with a preset normal output characteristic Lα to determine the pass / fail of the output characteristic Lβ, thereby completing the inspection method.

  In this way, the NOx sensor 11 is removed from the exhaust passage and inserted into the installation pipe 13 into which the reference gas Gα in which the actual NOx concentration Cα changes together with the reference NOx sensor 15, so that a plurality of sets for each actual NOx concentration Cα is obtained. Detection value Cβ and reference detection value Cγ can be acquired. Thereby, the output characteristic Lβ of the NOx sensor 11 can be acquired in a short time and with high accuracy based on the detection value Cβ and the reference detection value Cγ. The inspection accuracy of the NOx sensor 11 is checked by checking the NOx sensor 11 based on the output characteristic Lβ of the NOx sensor 11 without checking whether the detected value Cβ of the NOx sensor 11 is normal. Can be improved.

  For example, by referring to the output characteristic map M1 on which the output characteristic Lβ is plotted and comparing the reference output characteristic Lα set in the output characteristic map M1 with the output characteristic Lβ, the quality of the output characteristic Lβ is determined with high accuracy. Can be determined.

  Further, the cause of the failure of the NOx sensor 11 can be grasped by comparing the reference output characteristic Lα and the output characteristic Lβ. For example, the output characteristic Lβ when a crack occurs in the element of the NOx sensor 11 has a detection value Cβ higher than the reference output characteristic Lα, and the output characteristic Lβ when the element of the NOx sensor 11 is poisoned is The detection value Cβ is lower than the reference output characteristic Lα. In this way, by comparing the reference output characteristic Lα and the output characteristic Lβ, it is possible not only to perform a simple check on whether or not a failure has occurred, but also to determine the cause of the failure. It can also be repaired.

  That is, according to the NOx sensor inspection device 10 and the NOx sensor inspection method, both the failure of the NOx sensor 11 and the cause of the failure are identified and maintained by high-precision inspection based on the output characteristic Lβ of the NOx sensor 11. This makes it possible to avoid re-entry due to poor maintenance and improve the operation rate of the vehicle. In addition, the maintenance cost can be reduced by preventing erroneous replacement of the NOx sensor 11 that has not failed.

  FIG. 5 is a modification of the output characteristic map M1. As shown in FIG. 5, it is desirable to set a plurality of failure output characteristics Lδ1 to Lδ3 corresponding to the failure pattern of the NOx sensor 11 in the output characteristic map M1. In accordance with this, the pass / fail determination program 23 of the control and data processing device 14 is configured to determine the cause of the failure of the NOx sensor 11 by comparing the output characteristic Lβ and the failure output characteristics Lδ1 to Lδ3. It is desirable.

  There are various failure patterns in the failure of the NOx sensor 11. As one of the failure patterns, for example, a pattern in which a crack occurs in the element of the NOx sensor 11 can be exemplified. Cracks often occur in the measurement chamber of the element of the NOx sensor 11, and in principle, the output characteristic Lβ is higher than the reference output characteristic Lα when oxygen is supplied from the crack. Thus, when a crack occurs in the element of the NOx sensor 11, the NOx sensor 11 needs to be replaced because the output characteristic Lβ of the NOx sensor is not recoverable. In addition, the cause of cracks in the element includes moisture on the element and heating of the heater of the NOx sensor 11. Therefore, by checking the source of water vapor in the exhaust gas, the heating control of the heater, etc., failure due to cracks in the NOx sensor after replacement can be prevented.

  Further, as one of the failure patterns, for example, a pattern in which the NOx sensor 11 is poisoned by a metal component or the like in the exhaust gas can be exemplified. The poisoning by the metal component is caused by the metal component in the exhaust gas adhering to the electrode of the NOx sensor 11 and the detection of NOx is inhibited, so that the output characteristic Lβ is inclined with respect to the reference output characteristic Lα. Becomes smaller. Thus, in the case of poisoning of the metal component, the NOx sensor 11 needs to be replaced because the output characteristic Lβ of the NOx sensor is not recoverable. In addition, by checking the source of the metal component in the exhaust gas (for example, engine oil), poisoning due to the metal component of the NOx sensor after replacement can be prevented.

Further, as one of the failure patterns, for example, a pattern in which the NOx sensor 11 is poisoned by hydrocarbons in exhaust gas can be exemplified. When the NOx sensor 11 is poisoned by hydrocarbons, the NOx is lost by being decomposed into nitrogen and oxygen by the hydrocarbons inside the sensor operating at a high temperature, so that the output characteristic Lβ becomes lower than the reference output characteristic Lα. . Some of the poisoning by hydrocarbons has a returnability in the output characteristic Lβ of the NOx sensor 11. Thus, in the case of poisoning by hydrocarbons, the maintenance cost is reduced by not replacing the NOx sensor 11 when the output characteristic Lβ has reversibility, and replacing the NOx sensor 11 when there is no reversibility. it can. In addition, by checking the source of hydrocarbons in the exhaust gas, poisoning of the NOx sensor after replacement by hydrocarbons can be prevented.

  In FIG. 5, a failure output characteristic Lδ1 is set as a failure pattern in which a crack is generated, a failure output characteristic Lδ2 is set as a failure pattern of metal poisoning, and a failure output characteristic Lδ3 is set as a failure pattern of hydrocarbon poisoning.

  Since the output characteristic Lβ1 is within the range A based on the reference output characteristic Lα in more detail as compared with the reference output characteristic Lα, the output characteristic Lβ1 is determined to be good. On the other hand, when compared with the failure output characteristic Lδ2, it can be seen that the characteristic is similar. Therefore, it can be seen that the NOx sensor 11 having this output characteristic Lβ1 is in the range where the characteristic is still judged to be good, but the poisoning by the metal component is in progress. In such a case, preventive and maintenance measures such as inspecting a portion that may be a poisoning source can be taken so as not to promote further progress of poisoning.

  The output characteristic Lβ2 is determined to be defective. Then, it can be seen that the characteristics are similar when compared with the failure output characteristics Lδ1. Therefore, it can be seen that the NOx sensor 11 having this output characteristic Lβ2 has cracks in the element.

  As described above, a plurality of failure output characteristics Lδ1 to Lδ3 corresponding to the failure pattern of the NOx sensor 11 are set in the output characteristic map M1, and the failure output characteristics Lδ1 to Lδ3 are compared with the output characteristics Lβ. Both the failure of the NOx sensor 11 and the cause of the failure can be accurately identified, and maintenance is performed together, thereby avoiding re-entry due to poor maintenance and improving the operation rate of the vehicle.

  FIG. 6 illustrates the relationship between the elapsed time from the start of energization and the detected value Cβ. As described above, in the case of poisoning with hydrocarbons, the output characteristic Lβ of the NOx sensor 11 may be recoverable.

  Therefore, in the NOx sensor inspection device 10 described above, the pass / fail judgment program 23 of the control / data processing device 14 changes the detected value Cβ at the elapsed time t after the NOx sensor 11 is energized and the reference NOx sensor 15. It is desirable that the output characteristic Lβ is determined to be good or bad by comparing with a change in the reference detection value Cγ at an elapsed time t after energization.

  When energization of the reference NOx sensor 15 is started, a heater (not shown) starts preheating at time t1. Next, the heater raises the temperature to a temperature suitable for measurement at time t2. At this time, the reference NOx sensor 15 detects a value Ce that is temporarily different from the NOx concentration of the reference gas (in FIG. 6, an example of a value larger than the reference gas concentration) as the reference detection value Cγ. Thereafter, the reference detection value Cγ converges to the reference gas concentration.

  At time t3, the reference gas generator 12 causes the gas Gb having the NOx concentration Cb to flow into the installation pipe 13 as the reference gas Gα. At this time, the reference NOx sensor 15 detects the actual NOx concentration Cα as the reference detection value Cγ.

Compared with the reference NOx sensor 15, the NOx sensor 11 having the output characteristic Lβ3 has a slower convergence of the detected value Cβ and does not approach the actual NOx concentration Cα even if the elapsed time t has elapsed. On the other hand, the NOx sensor 11 having the output characteristic Lβ4 has a slow convergence of the detection value Cβ, but approaches the actual NOx concentration Cα at time t4. For this reason, the NOx sensor 11 having the output characteristic Lβ4 is poisoned by hydrocarbons, but the poisoning is reversible and does not need to be replaced.

  As described above, it is not necessary to replace the NOx sensor 11 by checking whether or not the output characteristic Lβ of the NOx sensor 11 is recoverable based on the change in the detected value Cβ at the elapsed time t after the NOx sensor 11 is energized. The NOx sensor 11 is not replaced, and maintenance costs can be reduced.

  In the NOx sensor inspection device 10, the actual NOx concentration Cα of the reference gas Gα generated from the reference gas generator 12 is accurately controlled by the concentration adjustment control program 21 of the control / data processing device 14 without sensing. If possible, the reference NOx sensor 15 may not be provided. However, considering the influence of the surrounding environment at the time of inspection, providing the reference NOx sensor 15 is advantageous for high-precision inspection.

  Further, in the NOx sensor inspection device 10, the date and time when the electronic computer 14 inspected the NOx sensor 11 and the number of times thereof may be stored. Thereby, by referring to the data at the time of past inspection, the progress of poisoning of the NOx sensor 11 and the like become clear, which is advantageous for pursuing the cause of the failure of the NOx sensor 11.

10 NOx sensor inspection device 11 NOx sensor 12 Reference gas generator 13 Installation pipe 14 Control and data processing device 15 Reference NOx sensor Cα Actual NOx concentration Cβ Detection value Cγ Reference detection value Gα Reference gas Lβ Output characteristics

Claims (6)

A NOx sensor inspection device for inspecting a NOx sensor inserted in an exhaust passage of an engine mounted on a vehicle,
A reference gas generator for adjusting the actual NOx concentration in the reference gas, an installation pipe into which the reference gas generated by the reference gas generator flows, and a control and data processing device connected to the reference gas generator; A reference NOx sensor that maintains a normal state,
Each of the NOx sensor and the reference NOx sensor removed from the exhaust passage is connected to the control and data processing device while being inserted into the installation pipe,
For each actual NOx concentration of the reference gas flowing into the installation pipe, a detection value is detected by the NOx sensor, and a reference detection value is detected by the reference NOx sensor,
The NOx sensor inspection device, wherein the control and data processing device is configured to inspect the NOx sensor according to output characteristics based on the detected value and the reference detected value.   The control / data processing apparatus has an output characteristic map based on an actual NOx concentration of the reference gas and a detected value, and the output characteristic map is plotted on the output characteristic map. NOx sensor inspection device. In the output characteristic map, a reference output characteristic in which the actual NOx concentration is equal to the detected value is set,
The NOx sensor inspection device according to claim 2, wherein the control / data processing device compares the reference output characteristic with the output characteristic to determine whether the output characteristic is good or bad. In the output characteristic map, a plurality of failure output characteristics according to the failure pattern of the NOx sensor are set,
The NOx sensor inspection device according to claim 2 or 3, wherein the control / data processing device is configured to determine the cause of the failure of the NOx sensor by comparing the failure output characteristic and the output characteristic.   The control and data processing device compares the change in the detected value after the energization of the NOx sensor with the change in the reference detection value during the elapse of time since the energization of the reference NOx sensor. The NOx sensor inspection device according to any one of claims 1 to 4, wherein the output characteristic is determined to be good or bad. A NOx sensor checking method for checking a NOx sensor inserted in an exhaust passage of an engine mounted on a vehicle,
Removing the NOx sensor from the exhaust passage;
Inserting the NOx sensor removed from the exhaust passage into an installation pipe into which a reference NOx sensor maintained in a normal state is inserted;
Changing the actual NOx concentration of the reference gas and flowing the reference gas into the installation pipe in order for each actual NOx concentration;
Obtaining a detection value of the NOx sensor and a reference detection value of the reference NOx sensor for each actual NOx concentration of the reference gas;
Generating an output characteristic of the NOx sensor from the detected value and the reference detected value;
And a step of inspecting the NOx sensor according to its output characteristics.