JP7245149B2 - gas detector - Google Patents

Description

The present disclosure relates to a gas detection device mounted on a vehicle.

Vehicles having internal combustion engines are equipped with gas detection devices. A gas detection device is a device for detecting the concentration of various gases discharged from an internal combustion engine. Gases to be detected include, for example, nitrogen oxides contained in exhaust gas. In addition, in a vehicle in which a selective reduction catalyst is arranged in the path through which exhaust gas passes, ammonia also needs to be detected by the gas detection device.

A gas detection device is provided with a sensor for detecting the concentration of a gas to be detected. A sensor for detecting the concentration of nitrogen oxides is generally configured as a critical current sensor. A critical current sensor can relatively accurately measure the concentration of a gas to be detected, and electrodes and the like are less likely to deteriorate.

The concentration of some gases, such as ammonia, is difficult to detect with critical current sensors. Therefore, a sensor for detecting the concentration of ammonia or the like is configured as a mixed potential type sensor instead of a critical current type sensor. In a mixed potential sensor, an electrochemical oxidation reaction or reduction reaction occurs on a pair of electrodes, and the voltage between the electrodes changes according to the gas concentration. The voltage is output as a signal indicating the concentration of the gas to be detected.

However, it is known that in a mixed potential sensor, the output voltage fluctuates greatly due to deterioration of the electrodes. Therefore, in order to accurately obtain the concentration of ammonia or the like, it is necessary to appropriately correct the correspondence relationship between the signal output from the mixed potential sensor and the concentration.

A gas detection device described in Patent Document 1 below includes a NO _x sensor for detecting the concentration of nitrogen oxides and an ammonia sensor for detecting the concentration of ammonia. The _NOx sensor is configured as a critical current sensor, and the ammonia sensor is configured as a mixed potential sensor. This gas detection device corrects the concentration of ammonia obtained by the ammonia sensor by utilizing the fact that the output from the _NOx sensor also changes according to the concentration of ammonia.

Specifically, in a situation where ammonia passes through both the NO _x sensor and the ammonia sensor, the concentration of ammonia detected by the NO _x sensor is compared with the concentration of ammonia detected by the ammonia sensor. ing. The gas detection device described in Patent Document 1 below determines the correspondence between the signal output from the ammonia sensor and the concentration of ammonia by taking the concentration of ammonia detected by the _NOx sensor as a true value. Correcting.

JP 2016-223446 A

As described above, the gas detection device described in Patent Document 1 corrects the concentration of ammonia detected by the _NOx sensor as a true value. The concentration of ammonia is detected by the _NOx sensor because part of the ammonia contained in the exhaust gas is oxidized to nitrogen monoxide before it reaches the electrode of the _NOx sensor, and the concentration of the nitrogen monoxide is This is because a current corresponding to is output from the _NOx sensor.

However, the rate at which ammonia is oxidized until it reaches the electrodes of the _NOx sensor is not always constant, and changes according to the operating state of the internal combustion engine. For example, when the flow velocity of the exhaust gas discharged from the internal combustion engine increases, the rate at which ammonia is oxidized decreases. Therefore, even if correction is performed using the concentration of ammonia detected by the _NOx sensor as the true value as in the gas detection device described in Patent Document 1, the concentration of ammonia can be accurately obtained by the ammonia sensor. seems difficult to do.

An object of the present disclosure is to provide a gas detection device capable of accurately obtaining the concentration of a specific gas using a mixed potential sensor.

A gas detection device (10) according to the present disclosure is configured as a mixed potential type sensor, and includes a first sensor (81) for detecting the concentration of a specific gas contained in exhaust gas, and a critical current type sensor. A second sensor (82) for detecting the concentration of nitrogen oxides contained in the exhaust gas, and a concentration acquisition unit (21) for acquiring the concentration of the specific gas based on the signal from the first sensor. and a correction unit (22) that performs correction processing, which is processing for correcting the concentration of the specific gas acquired by the concentration acquisition unit. The correcting unit outputs a signal output from the first sensor according to the concentration of nitrogen oxides while the nitrogen oxides are passing through the first sensor and the second sensor, and Correction processing is performed based on each of the signals output from the second sensor.

In the gas detection device having such a configuration, the correction section performs correction processing while the nitrogen oxides are passing through the first sensor and the second sensor. The correction process is a process for correcting the concentration of the specific gas acquired by the concentration acquisition unit, and is a process for correcting the signal output from the first sensor according to the concentration of nitrogen oxides and the signal output according to the concentration of nitrogen oxides. and the signal output from the second sensor.

The second sensor is a sensor for detecting the concentration of nitrogen oxides contained in the exhaust gas, and is configured as a critical current sensor. Therefore, the signal output from the second sensor during execution of the correction process accurately indicates the concentration of nitrogen oxides contained in the exhaust gas, regardless of the operating conditions of the internal combustion engine. Furthermore, the signal output from the critical current type second sensor is less susceptible to deterioration of the electrodes and the like. Therefore, the signal output from the second sensor can be said to be a signal indicating the true value of the concentration of nitrogen oxides.

A 1st sensor is a sensor for detecting the density|concentration of the specific gas contained in exhaust gas. However, since the first sensor is configured as a mixed-potential sensor, it outputs a signal corresponding to the concentration of nitrogen oxides during execution of the correction process.

There is a correlation between the degree of deterioration of the sensitivity of the first sensor with respect to the concentration of the specific gas and the degree of deterioration of the sensitivity of the first sensor with respect to the concentration of nitrogen oxides. Therefore, in the gas detection device having the above configuration, when the nitrogen oxides are passing through the first sensor and the second sensor, for example, the signal output from the first sensor and the nitrogen oxides obtained by the second sensor By comparing with the true value of the density of , the above correction processing can be performed accurately. That is, the degree of deterioration of the sensitivity of the first sensor with respect to the concentration of nitrogen oxides is first calculated from the above comparison, and based on this degree of deterioration, the degree of deterioration of the sensitivity of the first sensor with respect to the concentration of the specific gas is calculated, Necessary corrections can be made.

According to the present disclosure, there is provided a gas detection device capable of accurately obtaining the concentration of a specific gas using a mixed potential type sensor.

FIG. 1 is a diagram schematically showing the configuration of the gas detection device according to the first embodiment. FIG. 2 is a diagram showing the correspondence relationship between the concentration of ammonia and the signal output from the first sensor. FIG. 3 is a diagram showing the correspondence relationship between the concentration of nitrogen oxides and the signal output from the first sensor. FIG. 4 is a diagram showing the correspondence relationship between the sensitivity of the first sensor to the concentration of nitrogen oxides and the sensitivity of the second sensor to the concentration of ammonia. FIG. 5 is a diagram showing the correspondence relationship between the first tilt and the second tilt. FIG. 6 is a diagram showing the correspondence relationship between the concentration of nitrogen oxides and the signal output from the first sensor for each concentration of oxygen. FIG. 7 is a flow chart showing the flow of processing executed by the control device of the gas detection device according to the first embodiment. FIG. 8 is a flow chart showing the flow of processing executed by the control device of the gas detection device according to the first embodiment. FIG. 9 is a diagram schematically showing the configuration of the gas detection device according to the second embodiment. FIG. 10 is a diagram schematically showing the configuration of the gas detection device according to the third embodiment. FIG. 11 is a diagram schematically showing the configuration of the gas detection device according to the fourth embodiment. FIG. 12 is a flow chart showing the flow of processing executed by the control device of the gas detection device according to the fifth embodiment.

Hereinafter, this embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same constituent elements in each drawing are denoted by the same reference numerals as much as possible, and overlapping descriptions are omitted.

A first embodiment will be described. A gas detection device 10 according to the present embodiment is mounted on a vehicle MV and configured as a device for detecting the concentration of each component in exhaust gas discharged from an internal combustion engine 110 of the vehicle MV. Before describing the gas detection device 10, the configuration of the vehicle MV will be described.

FIG. 1 schematically shows the configuration of an exhaust system of a vehicle MV. As shown in the figure, the vehicle MV includes an internal combustion engine 110, an exhaust pipe 100, an oxidation catalyst 120, a filter 130, and a selective reduction catalyst 140.

The internal combustion engine 110 is a so-called engine. Internal combustion engine 110 burns fuel to generate driving force for running vehicle MV. In this embodiment, the internal combustion engine 110 is configured as a diesel engine, and light oil is used as fuel. The exhaust pipe 100 is a pipe for discharging the exhaust gas generated by the combustion of the internal combustion engine 110 to the outside.

The oxidation catalyst 120 is a catalyst for oxidizing and purifying the exhaust gas flowing through the exhaust pipe 100 . The oxidation catalyst 120 is provided at a position in the middle of the exhaust pipe 100 . In the oxidation catalyst 120, carbon monoxide and hydrocarbons contained in the exhaust gas are oxidized into carbon dioxide and water.

Filter 130 is a filter for collecting particulate matter contained in the exhaust gas. The filter 130 is provided in the exhaust pipe 100 at a position downstream of the oxidation catalyst 120 along the flow of the exhaust gas. The filter 130 is also called a DPF (Diesel Particulate Filter). The filter 130 is constructed by forming a large number of grid-like passages in porous ceramics and alternately blocking the entrance side and the exit side.

The selective reduction catalyst 140 is a catalyst for purifying nitrogen oxides contained in the exhaust gas. The selective reduction catalyst 140 is provided in the exhaust pipe 100 at a position downstream of the filter 130 along the flow of the exhaust gas.

An injector 60 is arranged in the exhaust pipe 100 at a position between the filter 130 and the selective reduction catalyst 140 . The injector 60 is an on-off valve for injecting urea and supplying it to the selective reduction catalyst 140 . When urea is injected from the injector 60, the urea is hydrolyzed in the selective reduction catalyst 140 and changed into ammonia. In the selective reduction catalyst 140, the nitrogen oxides contained in the exhaust gas are reduced by the above-mentioned ammonia and changed to nitrogen gas and water vapor. The opening/closing operation of the injector 60 is controlled by the control device 20, which will be described later.

As shown in FIG. 1, the position where the selective reduction catalyst 140 and the injector 60 are arranged is a position upstream of a multi-gas sensor 80, which will be described later, along the flow path of the exhaust gas.

A temperature sensor 70 is provided in the selective reduction catalyst 140 . The temperature sensor 70 is a sensor for measuring the temperature of the selective reduction catalyst 140, and is a thermistor, for example. The temperature of selective reduction catalyst 140 measured by temperature sensor 70 is transmitted to control device 20 .

Other configurations will be described. A NO _X sensor 50 is provided in the exhaust pipe 100 at a position between the filter 130 and the selective reduction catalyst 140 . The NO _X sensor 50 is a sensor for detecting the concentration of nitrogen oxides contained in the exhaust gas at a position upstream of the selective reduction catalyst 140 . The NO _X sensor 50 constitutes part of the gas detection device 10 .

The NO _X sensor 50 is configured as a so-called "critical current type" sensor. As is well known, in the critical current type NO _x sensor 50, a predetermined voltage is applied between a pair of electrodes formed on both sides of the solid electrolyte layer. At this time, a current flows between the electrodes according to the concentration of nitrogen oxides contained in the exhaust gas. The current is output from the _NOx sensor 50 as a signal corresponding to the concentration of nitrogen oxides. Since a known structure can be adopted as the structure of the NO _X sensor 50, the specific illustration and description thereof will be omitted.

The application of the voltage between the electrodes of the NO _X sensor 50 and the acquisition of the current flowing between the electrodes are performed by the NO _X sensor control device 30 . The NO _X sensor control device 30 is a device for controlling the NO _X sensor 50 and constitutes a part of the gas detection device 10 together with the NO _X sensor 50 . The NO _X sensor control device 30 sends a signal output from the NO _X sensor 50 according to the value of the current flowing between the electrodes of the NO _X sensor 50, that is, the concentration of nitrogen oxides contained in the exhaust gas, to the control device 20. and send.

A multi-gas sensor 80 is provided in the exhaust pipe 100 at a position downstream of the selective reduction catalyst 140 along the flow of the exhaust gas. The multi-gas sensor 80 is a sensor for detecting the concentration of nitrogen oxides contained in the exhaust gas and the concentration of ammonia contained in the exhaust gas at a position downstream of the selective reduction catalyst 140 . The multi-gas sensor 80 constitutes part of the gas detection device 10 .

The multi-gas sensor 80 has an NH ₃ sensor section 81 and an NO _X sensor section 82 . The NH ₃ sensor part 81 is a part configured as a so-called "mixed potential type" sensor, and is a part for detecting the concentration of ammonia (NH ₃ ) contained in the exhaust gas.

As is well known, the NH ₃ sensor unit 81, which is a mixed-potential sensor, has a detection electrode and a reference electrode (both not shown). All of these are electrodes composed of platinum and gold, but differ from each other in the content ratio of platinum and gold. On the surface of each electrode, ammonia contained in the exhaust gas is electrochemically oxidized and oxygen contained in the exhaust gas is electrochemically reduced. As a result, a potential difference, that is, a voltage is generated between these electrodes according to the concentrations of ammonia and oxygen contained in the exhaust gas. The voltage is output from the NH ₃ sensor section 81 as a signal corresponding to the concentration of ammonia.

The NH ₃ sensor unit 81 corresponds to the "first sensor" in this embodiment. Further, ammonia detected by the first sensor corresponds to the "specific gas" in this embodiment.

Acquisition of the voltage generated between the electrodes of the NH ₃ sensor unit 81 and the like are performed by the multigas sensor control device 40 . The multigas sensor control device 40 is a device for controlling the multigas sensor 80 and forms a part of the gas detection device 10 together with the multigas sensor 80 . The multigas sensor control device 40 sends a signal output from the NH ₃ sensor section 81 according to the value of the voltage generated between the electrodes of the NH ₃ sensor section 81, that is, the concentration of ammonia contained in the exhaust gas, to the control device 20. and send.

The NO _X sensor section 82 is a section configured as a so-called "critical current type" sensor, and is a section for detecting the concentration of nitrogen oxides (NO _X ) contained in the exhaust gas. The structure of the NO _X sensor section 82 is substantially the same as that of the NO _X sensor 50 described above. That is, in the critical current type NO _x sensor section 82, a predetermined voltage is applied between a pair of electrodes formed on both sides of the solid electrolyte layer. At this time, a current flows between the electrodes according to the concentration of nitrogen oxides contained in the exhaust gas. The current is output from the NO _X sensor section 82 as a signal corresponding to the concentration of nitrogen oxides.

The NO _X sensor section 82 corresponds to the "second sensor" in this embodiment. In this embodiment, the NH ₃ sensor section 81 as the first sensor and the NO _X sensor section 82 as the second sensor are configured as a multi-gas sensor 80 integrated with each other. As the configuration of such a multi-gas sensor 80, for example, a known configuration as described in JP-A-2016-223446 can be adopted. Therefore, specific illustration and description thereof will be omitted.

The multi-gas sensor control device 40 performs the application of voltage between the electrodes of the NO _X sensor section 82, the acquisition of the current flowing between the electrodes, and the like. The multi-gas sensor control device 40 outputs a signal output from the NO _X sensor section 82 according to the value of the current flowing between the electrodes of the NO _X sensor section 82, that is, the concentration of nitrogen oxides contained in the exhaust gas. Send to Thus, the multi-gas sensor control device 40 is configured as a device for controlling each of the NH ₃ sensor section 81 and the NO _X sensor section 82 .

Due to its structure, the NO _X sensor section 82 has a function of detecting the concentration of oxygen contained in the exhaust gas in addition to the function of detecting the concentration of nitrogen oxides contained in the exhaust gas. The control device 20 can also detect the concentration of oxygen contained in the exhaust gas based on the signal from the NO _x sensor section 82 obtained via the multigas sensor control device 40 . As a specific configuration or the like for detecting the concentration of oxygen, a known configuration such as that described in Japanese Unexamined Patent Application Publication No. 2016-223446 can be employed. Therefore, specific illustration and description thereof will be omitted.

The configuration of the gas detection device 10 will be described with continued reference to FIG. The gas detection device 10 includes a control device 20 in addition to the _NOx sensor 50, the _NOx sensor control device 30, the multigas sensor 80, and the multigas sensor control device 40 described so far. The control device 20 is a computer system having a CPU, ROM, RAM, etc., and is configured as a device for controlling the gas detection device 10 as a whole. The control device 20 includes a density acquisition section 21, a correction section 22, a storage section 23, and an abnormality determination section 24 as functional control blocks.

The concentration acquisition unit 21 is a part that acquires the concentration of ammonia, which is the specific gas, based on the signal output from the NH ₃ sensor unit 81, which is the first sensor. The correspondence relationship between the concentration of ammonia contained in the exhaust gas and the signal (voltage in this case) output from the NH ₃ sensor section 81 is pre-stored as a map in the storage section 23, which will be described later.

FIG. 2 shows an example of the correspondence relationship. The horizontal axis of the graph shown in FIG. 2 indicates the concentration of ammonia along a logarithmic scale. The vertical axis of the graph indicates the magnitude of the voltage output from the NH ₃ sensor section 81 . Assuming that the concentration of ammonia is x and the magnitude of the voltage output from the NH ₃ sensor unit 81 is y, the correspondence relationship between the two is expressed by y=A×ln(x). The slope is represented by the straight line of A. A line L1 in the figure indicates the corresponding relationship. Line L2 will be described later.

The concentration acquisition unit 21 acquires the concentration of ammonia from the magnitude of the voltage output from the NH ₃ sensor unit 81 based on the correspondence shown in FIG. However, the correspondence relationship in FIG. 2 is not always the same, and may be changed by the correction unit 22 described below.

The correction unit 22 is a part that performs processing for correcting the concentration of the specific gas acquired by the concentration acquisition unit 21 . This process is hereinafter also referred to as "correction process". As correction processing, the correction unit 22 performs processing for appropriately updating the correspondence relationships in FIG. 2 stored in the storage unit 23 . As a result, the concentration of ammonia acquired by the concentration acquisition unit 21 is corrected. Specific contents of the correction processing will be described later.

The storage unit 23 is a nonvolatile storage device that the control device 20 has. As already described, the correspondence relationship shown in FIG. 2 is stored in the storage unit 23 . Other information stored in the storage unit 23 will be described later.

The abnormality determination unit 24 is a part that performs processing for determining whether or not the NH ₃ sensor unit 81, which is the first sensor, is abnormal. The determination method will be described later.

When the vehicle MV is running, the control device 20 performs a process of adjusting the injection amount of urea from the injector 60 so that the selective reduction catalyst 140 properly purifies the exhaust gas. Control device 20 sets a target value for the injection amount of urea according to the concentration of nitrogen oxides detected by NO _X sensor 50, and controls the operation of injector 60 according to the target value. In parallel with this, the control device 20 adjusts the target value of the injection amount of urea so that the concentration of nitrogen oxides and the concentration of ammonia detected by the multigas sensor 80 are approximately zero. As a result, the amounts of nitrogen oxides and ammonia passing through the selective reduction catalyst 140 can be suppressed to approximately zero.

By the way, it is known that in a mixed potential type sensor such as the NH ₃ sensor section 81, the output voltage fluctuates greatly as the electrode deteriorates. That is, even if the concentration of ammonia contained in the exhaust gas is constant, the voltage output from the NH ₃ sensor section 81 changes depending on the degree of deterioration of the electrodes of the NH ₃ sensor section 81 . Therefore, in the present embodiment, the correction unit 22 performs correction processing so that the concentration acquisition unit 21 can always acquire the concentration of ammonia accurately. As will be described below, in the correction process, the correspondence shown in _FIG .

An outline of correction processing will be described. The NH ₃ sensor unit 81, which is a mixed potential type sensor, outputs a voltage according to the concentration of ammonia contained in the exhaust gas, and also outputs a voltage according to the concentration of nitrogen oxides contained in the exhaust gas. In other words, the NH ₃ sensor unit 81 is a sensor that is sensitive not only to ammonia, which is the specific gas to be detected, but also to nitrogen oxides. Such characteristics of the NH ₃ sensor unit 81 are common characteristics of mixed potential type sensors. The correction process is a process that utilizes such characteristics of the NH ₃ sensor section 81 .

FIG. 3 shows an example of the correspondence relationship between the concentration of nitrogen oxides contained in the exhaust gas and the signal (voltage in this case) output from the NH ₃ sensor section 81 . The horizontal axis of the graph shown in FIG. 3 indicates the concentration of nitrogen oxides along a logarithmic scale. The vertical axis of the graph indicates the magnitude of the voltage output from the NH ₃ sensor section 81 . If x is the concentration of nitrogen oxides and y is the magnitude of the voltage output from the NH ₃ sensor unit 81, the correspondence relationship between the two is expressed by y=B×ln(x), and the semilogarithmic graph of FIG. , the slope is represented by the straight line of B. A line L11 and a line L12 in the figure show an example of the corresponding relationship.

When deterioration occurs in the electrodes of the NH ₃ sensor section 81, the voltage output from the NH ₃ sensor section 81 decreases according to the degree of deterioration. A line L11 in FIG. 3 indicates the correspondence relationship in the initial state where the electrodes of the NH ₃ sensor section 81 are not deteriorated. A line L12 in FIG. 3 indicates the above correspondence when deterioration occurs in the electrodes of the NH ₃ sensor section 81 . Comparing the cases where the concentration of nitrogen oxides is the same, the voltage output from the NH ₃ sensor unit 81 tends to decrease as the deterioration degree of the electrode increases. In other words, the slope of the graph shown in FIG. 3 tends to decrease as the degree of electrode deterioration increases. Therefore, it can be said that the slope of each graph shown in _FIG .

It should be noted that the same can be said for the correspondence relationship shown in FIG. A line L1 in FIG. 2 represents the correspondence relationship between the concentration of ammonia contained in the exhaust gas and the voltage output from the NH ₃ sensor unit 81 in the initial state where the electrode of the NH ₃ sensor unit 81 is not deteriorated. is shown. A line L2 in FIG. 2 indicates the corresponding relationship when the electrode of the NH ₃ sensor unit 81 is deteriorated. As in the case of FIG. 3, the slope of the graph shown in FIG. 2 tends to decrease as the degree of electrode deterioration increases. Therefore, it can be said that the slope of each graph shown in _FIG .

The horizontal axis of the graph shown in FIG. 4 represents the magnitude of the voltage output from the NH ₃ sensor unit 81 when the concentration of nitrogen oxides around the NH ₃ sensor unit 81 is a specific value, that is, The sensitivity of the NH ₃ sensor section 81 to nitrogen oxides is shown. As the degree of deterioration of the electrodes of the NH ₃ sensor unit 81 increases, the sensitivity decreases and shifts to the left in FIG.

The vertical axis of the graph shown in FIG. 4 represents the magnitude of the voltage output from the NH ₃ sensor unit 81 when the concentration of ammonia around the NH ₃ sensor unit 81 is a specific value, that is, the The sensitivity of the NH ₃ sensor section 81 is shown. As the degree of deterioration of the electrodes of the NH ₃ sensor unit 81 increases, the sensitivity decreases and shifts downward in FIG.

As shown in the graph of FIG. 4, the sensitivity of the NH ₃ sensor unit 81 to nitrogen oxides (horizontal axis) and the sensitivity of the NH ₃ sensor unit 81 to ammonia (vertical axis) correspond one-to-one. , there is a positive correlation between them. Therefore, the slope of the graph shown in FIG. 2 and the slope of the graph shown in FIG. 3 also have a one-to-one correspondence. FIG. 5 shows the correspondence relationship between the respective inclinations.

The horizontal axis of the graph _shown in FIG. 5 represents the slope of the graph shown in FIG. shows the slope of the graph showing the relationship between This tilt is hereinafter also referred to as a “first tilt”.

The vertical axis of the graph shown in FIG. 5 represents the slope of the graph shown in FIG. 2, that is, the relationship between the concentration of ammonia contained in the exhaust gas and the signal output from the NH ₃ sensor unit 81, which is the first sensor. shows the slope of the graph showing The inclination is hereinafter also referred to as a "second inclination". The graph shown in FIG. 5 shows the correspondence relationship between the first slope and the second slope. Such a correspondence relationship is measured in advance and stored in the storage unit 23 as a map.

In the correction process, the correspondence shown in FIG. 2 is updated based on the correspondence shown in FIG. Specifically, first, only nitrogen oxides pass through the exhaust pipe 100 . After that, the concentration of nitrogen oxides contained in the exhaust gas is acquired based on the signal from the NO _X sensor section 82, which is the second sensor. Since the NO _x sensor unit 82 is a critical current type sensor, it is possible to accurately obtain the concentration of nitrogen oxides without being affected by deterioration or the like.

Subsequently, the slope of the correspondence shown in _FIG . is calculated. Incidentally, when the concentration of nitrogen oxides is 0, the voltage output from the NH ₃ sensor section 81 is also 0. Therefore, if the voltage output from the NH ₃ sensor unit 81 and the nitrogen oxide concentration obtained as described above are known, the correspondence relationship in FIG. will be determined as

Thereafter, a process of acquiring a second tilt is performed based on the first tilt calculated as described above and the correspondence shown in FIG. For example, when the calculated first slope is C1 in FIG. 5, C2 is acquired as the second slope.

The correspondence shown in FIG. 2 is updated using the second inclination obtained as described above, and stored in the storage unit 23 again. When the concentration of ammonia is 0, the voltage output from the NH ₃ sensor section 81, which is the first sensor, is also 0. Therefore, the correspondence relationship in FIG. 2 is uniquely determined once the value of the second slope is determined. After that, the concentration acquisition unit 21 acquires the concentration of ammonia based on the correspondence relationship in _FIG .

In this way, the correction unit 22 according to the present embodiment provides the voltage output from the NH ₃ sensor unit 81 and _{the NO} By comparing the true value of the nitrogen oxide concentration obtained by _{the X} sensor unit 82, correction processing is performed. In other words, the degree of deterioration (specifically, the first slope) of the sensitivity of the NH ₃ sensor unit 81 with respect to the concentration of nitrogen oxides is first calculated from the above comparison. It is possible to calculate the degree of deterioration of the sensitivity of the NH ₃ sensor unit 81 with respect to the concentration (specifically, the second slope) and correct the correspondence relationship in FIG. As a result, even after the electrode of the NH ₃ sensor unit 81 has deteriorated, the concentration acquisition unit 21 can accurately acquire the concentration of ammonia.

As is well known, the correspondence shown in FIG. 3 changes depending on the degree of deterioration of the electrodes of the NH ₃ sensor unit 81, and also changes depending on the concentration of oxygen contained in the exhaust gas. Line L21 in FIG. 6 shows the correspondence relationship between the concentration of ammonia contained in the exhaust gas and the signal output from the NH ₃ sensor unit 81, which is the first sensor, when the concentration of oxygen is 5%. is a semilogarithmic graph showing in a manner similar to that of FIG. Similarly, the line L22 is a semilogarithmic graph showing the above correspondence when the oxygen concentration is 10%, and the line L23 is a graph when the oxygen concentration is 15%. is a semilogarithmic graph showing the above correspondence relationship, and the line L24 is a semilogarithmic graph showing the above correspondence relationship when the oxygen concentration is 20%.

In this manner, the correspondence relationship in FIG. 3 changes according to the concentration of oxygen. Therefore, the correspondence relationship between the first slope and the second slope shown in FIG. 5 is the correspondence relationship when the concentration of oxygen contained in the exhaust gas is a specific value. Therefore, in this embodiment, the storage unit 23 stores a plurality of correspondence relationships shown in FIG. 5 corresponding to a plurality of oxygen concentration ranges contained in the exhaust gas. The correction unit 22 selects one of these correspondence relationships (that is, the correspondence relationship between the first slope and the second slope) that corresponds to the concentration of oxygen measured by the NO _X sensor unit 82, This is used to calculate the second slope.

A specific flow of processing executed by the control device 20 will be described with reference to the flowchart of FIG. A series of processes shown in FIG. 7 are repeatedly executed by the control device 20 each time a predetermined control period elapses.

In the first step S01 of the process, it is determined whether or not the multi-gas sensor 80 is active. That is, it is determined whether or not the temperature of the solid electrolyte layer (not shown) of the multi-gas sensor 80 is equal to or higher than the activation temperature. The determination may be made based on whether the temperature of the exhaust gas passing through the exhaust pipe 100 has reached or exceeded a predetermined temperature, and may be based on whether a predetermined time has elapsed since the internal combustion engine 110 was started. may be done. If it is determined that the multigas sensor 80 is not yet activated, the process of step S01 is executed again. When it is determined that the multigas sensor 80 is active, the process proceeds to step S02.

In step S02, a process of acquiring the temperature of the selective reduction catalyst 140 by the temperature sensor 70 is performed. In step S03 following step S02, it is determined whether or not the acquired temperature of the selective reduction catalyst 140 is equal to or lower than a predetermined threshold temperature. This threshold temperature is a temperature set in advance as the lower limit of the temperature range of the selective reduction catalyst 140 that enables purification of exhaust gas, or a temperature lower than that. If the temperature of the selective reduction catalyst 140 exceeds the threshold value, the series of processes shown in FIG. 7 are terminated. If the temperature of the selective reduction catalyst 140 is equal to or lower than the threshold, the process proceeds to step S04.

The fact that the process has moved to step S04 means that the temperature of the selective reduction catalyst 140 is low, so that the selective reduction catalyst 140 does not purify the exhaust gas. It means that you can pass through. Further, even if urea does not change to ammonia in the selective reduction catalyst 140 and existing ammonia exists, the ammonia remains adsorbed to the selective reduction catalyst 140 . Therefore, the exhaust gas reaching the multi-gas sensor 80 generally contains only oxygen and nitrogen oxides. In other words, while oxygen and nitrogen oxides reach the NH ₃ sensor section 81, which is the first sensor, and the NO _X sensor section 82, which is the second sensor, respectively, ammonia, which is the specific gas, does not reach them. state.

In step S04, a process of acquiring various signals output from the multi-gas sensor 80 is performed. Specifically, the voltage value output from the NH ₃ sensor unit 81 according to the concentrations of nitrogen oxides and oxygen contained in the exhaust gas, and the NO _x A process of obtaining the current value output from the sensor section 82 and the current value output from the NO _X sensor section 82 according to the concentration of oxygen contained in the exhaust gas is performed.

In step S05 following step S04, the correction unit 22 performs the above-described processing of calculating the first inclination. Specifically, based on the value of the current output from the NO _x sensor unit 82, the concentration of nitrogen oxides is obtained, and based on the concentration and the value of the voltage output from the NH ₃ sensor unit 81, , a process of calculating a first slope, which is the slope of the graph in FIG.

In step S06 following step S05, the absolute value of the difference between the first slope calculated in step S05 and the initial value is calculated, and it is determined whether or not the absolute value is equal to or less than a predetermined value α. The "initial value" mentioned above is the value of the first slope calculated in the initial state where the electrode of the NH ₃ sensor section 81 is not deteriorated. Therefore, the above-mentioned "absolute value" can be said to be the amount of change from the initial value of the first slope calculated by the correction unit 22 in step S05.

If the absolute value is less than or equal to the predetermined value α, it means that the degree of deterioration of the electrodes of the NH ₃ sensor section 81 is small. Therefore, in this case, the series of processes shown in FIG. 7 ends without performing the correction process. If the absolute value exceeds the predetermined value α, the process proceeds to step S07, and the correction unit 22 executes correction processing.

The flowchart of FIG. 8 shows a specific flow of the correction process executed in step S07 of FIG. In the first step S11 of the process, it is determined whether or not the above absolute value is equal to or less than a predetermined value β. This predetermined value β is set in advance as a value greater than the predetermined value α described above. If the absolute value is equal to or less than the predetermined value β, the process proceeds to step S12.

In step S12, as the correspondence relationship between the first slope and the second slope as shown in FIG. is selected. The "current oxygen concentration" is the oxygen concentration obtained based on the signal output from the NO _X sensor section 82 in step 04 of FIG.

In step S13 following step S12, a second tilt corresponding to the first tilt obtained in step S05 of FIG. 7 is obtained by referring to the correspondence obtained in step S12.

After that, based on the second slope acquired as described above, the correspondence shown in FIG. 2 stored in the storage unit 23 is updated. Acquisition takes place.

In step S11, when the absolute value exceeds the predetermined value β, the process proceeds to step S14. In this case, since the value of the first slope has changed significantly from the initial value, there is a high possibility that the NH ₃ sensor section 81 is malfunctioning. Therefore, in step S14, the abnormality determination section 24 determines that the NH ₃ sensor section 81, which is the first sensor, is abnormal. In this case, for example, by turning on a warning light provided in the vehicle MV, a process of informing the occupant that an abnormality has occurred is also performed.

As described above, the correction unit 22 of the gas detection device 10 according to the present embodiment allows nitrogen oxides to pass through the NH ₃ sensor unit 81 (first sensor) and the NO _X sensor unit 82 (second sensor). based on the signal output from the NH ₃ sensor unit 81 according to the concentration of nitrogen oxides and the signal output from the NO _X sensor unit 82 according to the concentration of nitrogen oxides when Perform correction processing. Specifically, the correction unit 22 calculates the first slope based on the concentration of nitrogen oxides acquired by the NO _X sensor unit 82, and stores the second slope corresponding to the first slope in the storage unit 23. Correction processing is performed by obtaining based on the correspondence relationship shown in FIG.

With such a configuration, even if the electrode of the NO _X sensor unit 82, which is a mixed potential sensor, deteriorates, it is possible to continue to accurately acquire the concentration of ammonia, which is the specific gas. .

The NO _X sensor section 82, which is the second sensor, also has a function of detecting the concentration of oxygen contained in the exhaust gas. The correction unit 22 selects the correspondence relationship between the first slope and the second slope corresponding to the concentration of oxygen detected by the NO _X sensor unit 82 in step 12 of FIG. 8, and uses the selected correspondence relationship. Then, the correction process is performed. As a result, the concentration of ammonia can be accurately obtained without being affected by the concentration of oxygen contained in the exhaust gas.

When the amount of change from the initial value of the first slope calculated by the correction unit 22 exceeds the predetermined value β, that is, when the determination in step S11 of FIG. 8 is No, the abnormality determination unit 24 , the NH ₃ sensor unit 81 is determined to be abnormal. As a result, it is possible to prevent a situation in which the concentration of ammonia is erroneously obtained while the NH ₃ sensor unit 81 is in an abnormal state.

When the determination in step S03 of FIG. 7 is Yes, that is, when the temperature of the selective reduction catalyst 140 arranged upstream of the multi-gas sensor 80 is equal to or lower than the predetermined threshold temperature, the correction unit 22 It is configured to perform correction processing at certain times. In other words, the correction unit 22 is configured to perform correction processing when ammonia, which is the specific gas, reaches neither the NH ₃ sensor unit 81 nor the NO _X sensor unit 82 . As a result, it is possible to prevent a situation in which the voltage output from the NH ₃ sensor unit 81 fluctuates under the influence of ammonia and the correction process is performed incorrectly.

As described above, in the present embodiment, the correspondence relationship between the first slope and the second slope as shown in FIG. remembers several. Instead of such a mode, the correspondence relationship between the first slope and the second slope stored in the storage unit 23 may be only one corresponding to a specific oxygen concentration. In this case, the correction process of FIG. 8 may be executed only when the concentration of oxygen acquired in step S04 of FIG. 7 is the above-mentioned "specific oxygen concentration" or a value in the vicinity thereof. .

In this embodiment, the specific gas detected by the mixed potential type first sensor is ammonia. Instead of such a mode, the specific gas detected by the first sensor may be a gas other than ammonia, such as nitrogen dioxide (NO ₂ ). Nitrogen dioxide is known to be discharged from the selective reduction catalyst 140 when deterioration of the selective reduction catalyst 140 progresses excessively. Even in such a mode, correction processing similar to that described above can be performed.

A second embodiment will be described. This embodiment differs from the first embodiment in the configuration of the first sensor and the second sensor. In the following, points different from the first embodiment will be mainly described, and descriptions of points common to the first embodiment will be omitted as appropriate.

As shown in FIG. 9, in this embodiment, the multi-gas sensor 80 and the multi-gas sensor control device 40 are not provided, and instead, the NH ₃ sensor 810, the NH ₃ sensor control device 410, and the NO _x sensor 820 and NO _x sensor controller 420 are provided.

The NH ₃ sensor 810 is configured as a mixed potential sensor and is a sensor for detecting the concentration of ammonia contained in the exhaust gas. The NH ₃ sensor 810 is arranged in the exhaust pipe 100 at a position downstream of the selective reduction catalyst 140 along the flow of the exhaust gas. A specific configuration of the NH ₃ sensor 810 is the same as the configuration of the NH ₃ sensor section 81 in the first embodiment. The NH ₃ sensor 810 corresponds to the "first sensor" in this embodiment.

NH ₃ sensor control device 410 is a device for controlling NH ₃ sensor 810 . The function of the NH ₃ sensor control device 410 is the same as the function of controlling the NH ₃ sensor section 81 among the functions of the multigas sensor control device 40 in the first embodiment.

The NO _X sensor 820 is configured as a critical current sensor and is a sensor for detecting the concentration of nitrogen oxides contained in the exhaust gas. The NO _X sensor 820 is arranged in the exhaust pipe 100 at a position downstream of the selective reduction catalyst 140 along the flow of the exhaust gas. A specific configuration of the NO _X sensor 820 is the same as the configuration of the NO _X sensor section 82 in the first embodiment. The NO _X sensor 820 corresponds to the "second sensor" in this embodiment.

NO _X sensor control device 420 is a device for controlling NO _X sensor 820 . The function of the NO _X sensor control device 420 is the same as the function of controlling the NO _X sensor section 82 among the functions of the multi-gas sensor control device 40 in the first embodiment.

As described above, in this embodiment, the NH ₃ sensor 810, which is the first sensor, and the NO _X sensor 820, which is the second sensor, are configured as sensors separate from each other. Even in such a configuration, the same effects as those described in the first embodiment are obtained.

However, in this embodiment, the position where the NH ₃ sensor 810 as the first sensor is arranged and the position where the NO _X sensor 820 as the second sensor are arranged are different from each other. Due to such a configuration, the concentration of nitrogen oxides at each sensor location may not be the same, resulting in inaccurate correction processing. Therefore, in view of the possibility of the above problems occurring, it is preferable that the first sensor and the second sensor are integrated with each other as in the first embodiment. As a result, it is possible to prevent the concentration of nitrogen oxides from becoming inconsistent between the position of the first sensor and the position of the second sensor.

A third embodiment will be described. As shown in FIG. 10 , in the present embodiment, a selective reduction catalyst 150 is provided at a position downstream of the selective reduction catalyst 140 in the exhaust pipe 100 . The configuration of the selective reduction catalyst 150 is the same as the configuration of the selective reduction catalyst 140 .

Further, a multi-gas sensor 80A is provided at a position further downstream than the selective reduction catalyst 150 in the exhaust pipe 100 . The configuration of the multigas sensor 80A is the same as the configuration of the multigas sensor 80. FIG. In FIG. 10, the portion of the multigas sensor 80A corresponding to the NH ₃ sensor section 81 is denoted by "81A", and the portion corresponding to the _NOx sensor section 82 is denoted by "82A". there is

Furthermore, in this embodiment, a multigas sensor control device 40A is provided as a device for controlling the multigas sensor 80A. The configuration of the multigas sensor control device 40A is the same as the configuration of the multigas sensor control device 40 .

With such a configuration, even if nitrogen oxides leak downstream from the selective reduction catalyst 140 , the nitrogen oxides can be purified by the selective reduction catalyst 150 . This makes it possible to further reduce the amount of nitrogen oxides discharged from the vehicle MV to the outside.

A fourth embodiment will be described. As shown in FIG. 11, this embodiment has a configuration in which an injector 61 is added to the third embodiment shown in FIG. The injector 61 is provided at a position between the selective reduction catalyst 140 and the selective reduction catalyst 150 in the exhaust pipe 100 . The injector 61 is the same as the injector 60 and is an on-off valve for injecting urea and supplying it to the selective reduction catalyst 140 . The opening/closing operation of the injector 61 is controlled by the control device 20 . In such a configuration, by injecting urea also from the injector 61, it becomes possible to purify nitrogen oxides in the selective reduction catalyst 150 on the downstream side more appropriately.

A fifth embodiment will be described. This embodiment differs from the first embodiment in the content of processing performed by the control device 20 . Differences from the first embodiment will be mainly described below, and descriptions of common points with the first embodiment will be omitted as appropriate.

A series of processes shown in FIG. 12 is executed by the control device 20 according to the present embodiment instead of the series of processes shown in FIG. This process is obtained by adding step S110 to the process of FIG.

When it is determined in step S01 that the multigas sensor 80 is active, the process proceeds to step S110 in this embodiment. In step S110, a process of stopping the supply of urea from the injector 60 is performed. After that, the process moves to step S02. Subsequent processes are the same as those described in the first embodiment.

Therefore, the correction unit 22 in the present embodiment performs correction processing when the supply of urea from the injector 60 to the selective reduction catalyst 140 is stopped. As described above, the correction process is performed when the determination in step S03 is Yes, that is, when the temperature of the selective reduction catalyst 140 is low, exhaust gas is not purified in the selective reduction catalyst 140. , At this time, even if urea is supplied from the injector 60 to the selective reduction catalyst 140, the urea does not change to ammonia. Therefore, in the present embodiment, by stopping the supply of urea from the injector 60 prior to the correction process, wasteful consumption of urea can be prevented.

Note that when the supply of urea from the injector 60 is stopped prior to the correction process as in the present embodiment, the determination in step S03 of FIG. 7 may not be performed. In this case, the correction process is performed even if the temperature of the selective reduction catalyst 140 is equal to or higher than the threshold temperature. is never reached. Therefore, the correction process can be appropriately performed without being affected by ammonia.

The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Design modifications to these specific examples by those skilled in the art are also included in the scope of the present disclosure as long as they have the features of the present disclosure. Each element included in each specific example described above and its arrangement, conditions, shape, etc. are not limited to those illustrated and can be changed as appropriate. As long as there is no technical contradiction, the combination of the elements included in the specific examples described above can be changed as appropriate.

The control apparatus and control method described in the present disclosure are provided by one or more dedicated processors provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. It may be implemented by a computer. The control apparatus and control method described in this disclosure may be implemented by a special purpose computer provided by configuring a processor including one or more special purpose hardware logic circuits. The control apparatus and control method described in the present disclosure are configured by a combination of a processor and memory programmed to perform one or more functions and a processor including one or more hardware logic circuits. It may be implemented by one or more special purpose computers. The computer program may be stored as computer-executable instructions on a computer-readable non-transitional tangible storage medium. Dedicated hardware logic circuits and hardware logic circuits may be implemented by digital circuits containing multiple logic circuits or by analog circuits.

MV: Vehicle 10: Gas detector 21: Concentration acquisition unit 22: Correction unit 81: NH ₃ sensor unit 82: NO _X sensor unit

Claims (8)

A gas detection device (10) mounted on a vehicle (MV),
a first sensor (81) configured as a mixed potential type sensor for detecting the concentration of a specific gas contained in the exhaust gas;
a second sensor (82) configured as a critical current sensor for detecting the concentration of nitrogen oxides contained in the exhaust gas;
a concentration acquisition unit (21) for acquiring the concentration of the specific gas based on a signal from the first sensor;
a correction unit (22) that performs correction processing for correcting the concentration of the specific gas acquired by the concentration acquisition unit;
The correction unit is
when nitrogen oxides are passing through the first sensor and the second sensor,
The correction processing is performed based on the signal output from the first sensor according to the concentration of nitrogen oxides and the signal output from the second sensor according to the concentration of nitrogen oxides. There is
The slope of the graph showing the relationship between the concentration of nitrogen oxides and the signal output from the first sensor is defined as a first slope,
When the slope of the graph showing the relationship between the concentration of the specific gas and the signal output from the first sensor is defined as the second slope,
further comprising a storage unit (23) that stores a correspondence relationship between the first tilt and the second tilt;
The correction unit is
The correction is performed by calculating the first slope based on the concentration of nitrogen oxides obtained by the second sensor and obtaining the second slope corresponding to the first slope based on the correspondence relationship. A gas detection device that processes . The second sensor also has a function of detecting the concentration of oxygen contained in the exhaust gas,
The correction unit is
2. The gas detection device according to claim 1 , wherein the correction process is performed using, as the correspondence relationship, a relationship corresponding to the concentration of oxygen detected by the second sensor. Further comprising an abnormality determination unit (24) for determining whether the first sensor is abnormal,
When the amount of change from the initial value of the first slope calculated by the correction unit exceeds a predetermined value,
The gas detection device according to claim 1 or 2 , wherein said abnormality determination unit determines that said first sensor is abnormal. The correction unit is
The gas detection device according to any one of claims 1 to 3 , wherein the correction process is performed when the specific gas reaches neither the first sensor nor the second sensor. The gas detection device according to any one of claims 1 to 4 , wherein the specific gas is ammonia. A selective reduction catalyst (140) for purifying nitrogen oxides contained in the exhaust gas is arranged at a position upstream of the first sensor and the second sensor along the flow path of the exhaust gas. ,
The gas detection device according to claim 5 , wherein the correction unit performs the correction process when the temperature of the selective reduction catalyst is equal to or lower than a predetermined threshold temperature. A selective reduction catalyst for purifying nitrogen oxides contained in the exhaust gas, and a urea and an injector (60) for supplying
The gas detection device according to claim 5 , wherein the correction unit performs the correction process when supply of urea from the injector to the selective reduction catalyst is stopped. A gas detection device according to any one of the preceding claims, wherein the first sensor and the second sensor are configured as an integral sensor (80).

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