JP6900937B2 - Control device - Google Patents

Description

The present disclosure relates to a control device for an exhaust gas sensor.

The exhaust pipe of a vehicle having an internal combustion engine is provided with an exhaust gas sensor for measuring the concentration of a specific gas (for example, nitrogen oxide) contained in the exhaust gas. As such an exhaust gas sensor, a sensor having a plurality of cells in which electrodes are formed on both sides of a solid electrolyte layer is known. In the cell, a current having a magnitude corresponding to the concentration of the component to be measured flows in a state where a voltage is applied between the electrodes. The exhaust gas sensor measures the concentration of the component to be measured based on the value of the current.

For example, as the above-mentioned plurality of cells, an exhaust gas sensor having a configuration having a first cell and a second cell is known. In the exhaust gas sensor, oxygen contained in the exhaust gas is discharged in advance by the first cell arranged on the upstream side. In the second cell arranged on the downstream side, a current flows according to the concentration of residual oxygen and nitrogen oxides contained in the exhaust gas after the oxygen is discharged. In the exhaust gas sensor having such a configuration, the concentration of nitrogen oxides can be measured accurately by discharging oxygen in a larger amount than the nitrogen oxides from the exhaust gas in advance.

In the exhaust gas sensor having the above configuration, the magnitude of the current flowing through the second cell may change due to deterioration of the second cell on the downstream side. Therefore, for the purpose of detecting the deterioration of the second cell, the deterioration determination is performed periodically. In the deterioration determination, the amount of oxygen reaching the second cell is temporarily increased, for example, by lowering the voltage applied to the first cell. At that time, it can be determined whether or not the second cell has deteriorated based on the change in the current flowing through the second cell.

The magnitude of the current flowing through the cell changes according to the concentration of oxygen and the like reaching the cell, and also changes according to the temperature of the cell. Therefore, in Patent Document 1 below, it is proposed to perform deterioration determination during the aftermath after the internal combustion engine is stopped, that is, during the period when the temperature of the entire exhaust gas sensor is high.

Japanese Patent No. 4767621

In order to more accurately determine the deterioration of the second cell, it is necessary not only to maintain the entire exhaust gas sensor at a high temperature but also to accurately acquire the temperature of the second cell. Further, if the temperature of the second cell can be accurately acquired, not only the deterioration determination but also the concentration measurement in the normal state can be performed more accurately. However, if a temperature sensor or a measurement circuit for measuring the temperature of the second cell is separately provided, the cost of the entire system including the exhaust gas sensor increases, which is not preferable.

An exhaust gas sensor having a configuration capable of measuring the temperature of the first cell based on impedance is also known in order to enable temperature control of the built-in heater. Therefore, it is conceivable to estimate and acquire the temperature of the second cell based on the measured temperature of the first cell. However, due to heat conduction between the exhaust gas sensor and the exhaust pipe, the temperature of the first cell and the temperature of the second cell are often different from each other. Further, the temperature difference between the two is not constant and changes depending on the driving state of the vehicle and the like. Therefore, it is not easy to accurately estimate the temperature of the second cell based on the temperature of the first cell.

An object of the present disclosure is to provide a control device capable of acquiring the temperature of a cell of an exhaust gas sensor without separately providing a circuit for temperature measurement.

The control device according to the present disclosure is the control device (10) of the exhaust gas sensor (100). The exhaust gas sensor to be controlled is the first cell (150) that discharges oxygen from the exhaust gas generated by the internal combustion engine (EG), and the residual oxygen contained in the exhaust gas after the oxygen is discharged by the first cell. It has a second cell (160, 170) that outputs a signal having a magnitude corresponding to the density. This control device has a gas temperature acquisition unit (14) that acquires the temperature of the exhaust gas and a cell temperature estimation unit (14) that estimates the temperature of the second cell based on the temperature of the exhaust gas acquired by the gas temperature acquisition unit. 15) and. This control device further includes a deterioration determination unit (13) for determining whether or not deterioration has occurred in the second cell, and the temperature of the second cell estimated by the cell temperature estimation unit is within a preset appropriate temperature range. When it is out of the above range, the deterioration determination unit does not determine whether or not the second cell has deteriorated.

The temperature of the second cell changes according to the temperature of the exhaust gas flowing in the vicinity of the exhaust gas sensor. That is, there is a correlation between the temperature of the exhaust gas and the temperature of the second cell. Therefore, the control device having the above configuration estimates the temperature of the second cell based on the temperature of the exhaust gas acquired by the gas temperature acquisition unit. Vehicle exhaust piping is often provided with a temperature sensor for measuring the temperature of the exhaust gas. Therefore, by using the signal from the temperature sensor, it is possible to acquire the temperature of the second cell without separately providing a circuit for temperature measurement.

According to the present disclosure, there is provided a control device capable of acquiring the temperature of a cell of an exhaust gas sensor without separately providing a circuit for measuring the temperature.

FIG. 1 is a diagram schematically showing a configuration of a vehicle exhaust system provided with a control device and an exhaust gas sensor according to the first embodiment. FIG. 2 is a diagram schematically showing the configuration of the control device and the exhaust gas sensor according to the first embodiment. FIG. 3 is a cross-sectional view showing a section III-III of FIG. FIG. 4 is a diagram for explaining the measurement principle of the exhaust gas sensor. FIG. 5 is a diagram for explaining a method of acquiring the temperature of the pump cell. FIG. 6 is a diagram for explaining a method of determining deterioration of the sensor cell. FIG. 7 is a diagram for explaining a method of determining deterioration of the sensor cell. FIG. 8 is a diagram showing the relationship between the temperature of the sensor cell and the deterioration index. FIG. 9 is a diagram showing the relationship between the temperature of the exhaust gas and the temperature of the sensor cell. FIG. 10 is a flowchart showing a flow of processing executed by the control device according to the first embodiment. FIG. 11 is a diagram showing the time change of the temperature of the sensor cell and the temperature of the exhaust gas. FIG. 12 is a diagram showing the relationship between the temperature of the exhaust pipe and the temperature of the sensor cell. FIG. 13 is a diagram showing the relationship between the temperature of the exhaust gas and the temperature of the exhaust pipe. FIG. 14 is a flowchart showing a flow of processing executed by the control device according to the second embodiment. FIG. 15 is a flowchart showing a flow of processing executed by the control device according to the third embodiment. FIG. 16 is a flowchart showing a flow of processing executed by the control device according to the fourth embodiment.

Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components are designated by the same reference numerals as much as possible in each drawing, and duplicate description is omitted.

The first embodiment will be described. The control device 10 according to the present embodiment is configured as a device for controlling the exhaust gas sensor 100. FIG. 1 schematically shows an exhaust system of a vehicle provided with an exhaust gas sensor 100. As shown in the figure, an exhaust pipe 20 for guiding the exhaust gas discharged from the internal combustion engine EG to the outside is connected to the internal combustion engine EG of the vehicle. A plurality of exhaust gas sensors 100 are provided at positions in the middle of the exhaust pipe 20 for measuring the concentration of nitrogen oxides contained in the exhaust gas.

In addition to the exhaust gas sensor 100, an oxidation catalyst converter 22 and an SCR catalyst converter 23 are provided in the middle of the exhaust pipe 20.

The oxidation catalyst converter 22 purifies harmful substances contained in the exhaust gas. An oxidation catalyst (not shown) is housed inside the oxidation catalyst converter 22. The oxidation catalyst is mainly composed of a ceramic carrier, an oxide mixture containing aluminum oxide, cerium dioxide and zirconium dioxide as components, and a noble metal catalyst such as platinum, palladium and rhodium. The oxidation catalyst oxidizes and purifies hydrocarbons, carbon monoxide, nitrogen oxides, etc. contained in the exhaust gas. In addition to the above-mentioned oxidation catalyst, a particulate filter for capturing fine particles may be contained inside the oxidation catalyst converter 22.

The SCR catalyst converter 23 is a device for further purifying the exhaust gas after passing through the oxidation catalyst converter 22, and a selective reduction type catalyst (not shown) is housed therein. As the catalyst, a catalyst in which a noble metal such as Pt is supported on the surface of a base material such as zeolite or alumina is used. The catalyst reduces and purifies nitrogen oxides when the temperature is in the active temperature range and urea as a reducing agent is added. A urea addition injector 24 for adding urea is provided at a position on the exhaust pipe 20 on the upstream side of the SCR catalyst converter 23.

In the present embodiment, two exhaust gas sensors 100, which are the control targets of the control device 10, are provided in the exhaust pipe 20. The first exhaust gas sensor 100 (indicated by reference numeral 101 in FIG. 1) is provided at a position in the exhaust pipe 20 between the oxidation catalyst converter 22 and the SCR catalyst converter 23, and is located at that position. The concentration of nitrogen oxides in the exhaust gas in Japan is measured. The second exhaust gas sensor 100 (indicated by reference numeral 102 in FIG. 1) is provided at a position downstream of the SCR catalytic converter 23 in the exhaust pipe 20, and the exhaust gas at that position is provided. It measures the concentration of nitrogen oxides.

The concentration of nitrogen oxides measured by each exhaust gas sensor 100 is transmitted to the control device 10. The control device 10 performs various controls on the internal combustion engine EG based on the measured concentration of nitrogen oxides. The control includes, for example, a control for adjusting the ignition timing in the internal combustion engine EG, a control for adjusting the fuel injection amount, a control for adjusting the urea addition amount in the urea addition injector 24, and the like.

As described above, the control device 10 according to the present embodiment is configured as a device that controls the internal combustion engine EG in addition to the control of the exhaust gas sensor 100 described later. That is, the control device 10 also has a function as a so-called "engine ECU". Instead of such a mode, even if the control device 10 is configured as a dedicated device for controlling the exhaust gas sensor 100 and is a control device different from the engine ECU. Good. In this case, the control device 10 contributes to the control of the internal combustion engine EG performed by the engine ECU by communicating with the engine ECU.

Other configurations will be described. A gas temperature sensor 25 is provided at a position of the exhaust pipe 20 between the oxidation catalyst converter 22 and the SCR catalyst converter 23. The gas temperature sensor 25 is a sensor for measuring the temperature of the exhaust gas in the vicinity of the exhaust gas sensor 100. The temperature of the exhaust gas measured by the gas temperature sensor 25 is transmitted to the control device 10. A similar gas temperature sensor may be further provided in the exhaust pipe 20 at a position downstream of the SCR catalytic converter 23.

The configurations of the two exhaust gas sensors 100 provided in FIG. 1 are the same as each other. Further, the control performed by the control device 10 for measuring the nitrogen oxide concentration, determining deterioration, and the like is the same for the two exhaust gas sensors 100. Therefore, in the following, the configuration and the like will be described only for the exhaust gas sensor 100 of one side (the one with the reference numeral 101), and the configuration and the like of the exhaust gas sensor 100 of the other side (the one with the reference numeral 102). The explanation of is omitted.

A specific configuration of the exhaust gas sensor 100 will be described with reference to FIGS. 2 to 4. FIG. 2 schematically shows a cross section of a portion of the exhaust gas sensor 100 that is arranged inside the exhaust pipe 20. The left end (the side on which the diffusion resistor 140 is arranged) in FIG. 2 corresponds to the tip of the exhaust gas sensor 100 protruding inside the exhaust pipe 20.

The exhaust gas sensor 100 includes a solid electrolyte body 110 and main bodies 120 and 130.

The solid electrolyte body 110 is a plate-shaped member, and is made of a solid electrolyte material such as zirconia oxide. The solid electrolyte body 110 becomes oxygen ion conductive when it is in an active state of a predetermined temperature or higher. A pump cell 150, a sensor cell 160, and a monitor cell 170 are each formed in the solid electrolyte body 110, and these plurality of cells will be described later.

The main body portions 120 and 130 are both plate-shaped members, and are made of an insulator material containing alumina as a main component. The main bodies 120 and 130 are arranged so as to sandwich the above-mentioned solid electrolyte body 110 in between. Of the main body 120 arranged on one side of the solid electrolyte 110, a part of the surface on the solid electrolyte 110 side is recessed toward the side opposite to the solid electrolyte 110. As a result, a space is formed between the main body 120 and the solid electrolyte 110. The space is a space in which the exhaust gas to be measured is introduced. Hereinafter, the space is also referred to as “measurement chamber 121”.

A diffusion resistor 140 is arranged at the tip of the exhaust gas sensor 100. The measurement chamber 121 is open to the outside (that is, inside the exhaust pipe 20) via the diffusion resistor 140. The diffusion resistor 140 is made of a ceramic material such as alumina in which porous or pores are formed. By the action of the diffusion resistor 140, the flow rate of the exhaust gas drawn into the measuring chamber 121 is regulated. The exhaust gas that has flowed into the measurement chamber 121 through the diffusion resistor 140 is supplied to the pump cell 150, the sensor cell 160, and the monitor cell 170, which will be described later.

Of the main body 130 arranged on the other side of the solid electrolyte 110, a part of the surface on the solid electrolyte 110 side is recessed toward the side opposite to the solid electrolyte 110. As a result, a space is also formed between the main body 130 and the solid electrolyte 110. A part of the space (not shown) is open to the atmosphere outside the exhaust pipe 20. That is, the space is a space into which the atmosphere is introduced. Hereinafter, the space is also referred to as "atmosphere chamber 131".

A pump electrode 111, a sensor electrode 112, and a monitor electrode 113 are formed on the surface of the solid electrolyte body 110 that is in contact with the measurement chamber 121, respectively. The pump electrode 111 is formed at a position closer to the diffusion resistor 140 in the solid electrolyte 110. The sensor electrode 112 and the monitor electrode 113 are formed at positions of the solid electrolyte body 110 opposite to the diffusion resistor 140 with the pump electrode 111 sandwiched between them. The sensor electrode 112 and the monitor electrode 113 are arranged so as to be arranged along the depth direction of the paper surface in FIG. 2 (see FIG. 3).

The pump electrode 111 and the monitor electrode 113 are formed of a Pt-Au alloy (platinum-gold alloy). All of these are electrodes that are active with respect to oxygen and inactive with respect to nitrogen oxides. On the other hand, the sensor electrode 112 is formed of a noble metal such as Pt (platinum) or Rh (rhodium), and is an electrode that is active against oxygen and also active against nitrogen oxides.

A common electrode 114 is formed on the surface of the solid electrolyte body 110 that is in contact with the atmosphere chamber 131. The common electrode 114 is formed in a range that overlaps all of the pump electrode 111, the sensor electrode 112, and the monitor electrode 113 when viewed along the direction perpendicular to the solid electrolyte body 110 as shown in FIG. There is. The common electrode 114 is formed of a material containing Pt (platinum) as a main component.

When a voltage is applied between the pump electrode 111 and the common electrode 114 while the solid electrolyte body 110 is in a high temperature active state, oxygen contained in the exhaust gas of the measurement chamber 121 is decomposed in the pump electrode 111. It becomes oxygen ions and passes through the solid electrolyte 110. As a result, oxygen is discharged from the measurement chamber 121 to the atmosphere chamber 131. That is, the portion of the pump electrode 111, the common electrode 114, and the solid electrolyte 110 sandwiched between the pump electrode 111 and the common electrode 114 is a portion that functions as a pump cell 150 for discharging oxygen from the exhaust gas. It has become. The pump cell 150 corresponds to the "first cell" in this embodiment.

When the oxygen is discharged as described above, a current flows between the pump electrode 111 and the common electrode 114. The value of the current is a value proportional to the amount of oxygen discharged from the exhaust gas and a value proportional to the oxygen concentration of the exhaust gas. That is, it can be said that the pump cell 150 outputs a signal (the above-mentioned current) having a magnitude corresponding to the oxygen concentration of the exhaust gas. The control device 10 described later can acquire the oxygen concentration of the exhaust gas existing in the measurement chamber 121 based on the value of the current.

When a voltage is applied between the sensor electrode 112 and the common electrode 114 while the solid electrolyte body 110 is in a high temperature active state, oxygen and nitrogen oxides contained in the exhaust gas of the measurement chamber 121 are sensored. It is decomposed at the electrode 112, and all become oxygen ions and pass through the solid electrolyte 110. As a result, a current corresponding to the concentrations of oxygen and nitrogen oxides in the vicinity of the sensor electrode 112 flows between the sensor electrode 112 and the common electrode 114. The value of the current is acquired by the control device 10.

That is, the portion of the sensor electrode 112, the common electrode 114, and the solid electrolyte 110 sandwiched between the sensor electrode 112 and the common electrode 114 corresponds to the concentration of residual oxygen and nitrogen oxides contained in the exhaust gas. It is a part that functions as a sensor cell 160 that outputs a large signal (the above current) in a state where a voltage is applied. The exhaust gas whose concentration of nitrogen oxides and residual oxygen is measured by the sensor cell 160 is the exhaust gas after the oxygen is discharged in the pump cell 150. The sensor cell 160 corresponds to one of the "second cells" in this embodiment.

When a voltage is applied between the monitor electrode 113 and the common electrode 114 while the solid electrolyte body 110 is in a high temperature active state, oxygen contained in the exhaust gas of the measurement chamber 121 is decomposed in the monitor electrode 113. It becomes oxygen ions and passes through the solid electrolyte 110. As a result, a current corresponding to the concentration of oxygen in the vicinity of the monitor electrode 113 flows between the monitor electrode 113 and the common electrode 114. The value of the current is acquired by the control device 10.

That is, the portion of the monitor electrode 113, the common electrode 114, and the solid electrolyte 110 sandwiched between the monitor electrode 113 and the common electrode 114 is a signal having a size corresponding to the concentration of residual oxygen contained in the exhaust gas. It is a part that functions as a monitor cell 170 that outputs (the above current). The exhaust gas whose residual oxygen concentration is measured by the monitor cell 170 is the exhaust gas after the oxygen is discharged in the pump cell 150. The monitor cell 170, together with the sensor cell 160 described above, corresponds to one of the "second cells" in the present embodiment.

As described above, the second cell in the present embodiment is a monitor cell that outputs a signal having a size corresponding to the concentration of residual oxygen contained in the exhaust gas after oxygen is discharged by the pump cell 150 (first cell). It includes 170 and a sensor cell 160 that outputs a signal having a magnitude corresponding to the concentration of residual oxygen and nitrogen oxides contained in the exhaust gas after oxygen is discharged by the pump cell 150.

The exhaust gas that has flowed into the measurement chamber 121 through the diffusion resistor 140 flows along the pump cell 150 and then is supplied to each of the sensor cell 160 and the monitor cell 170. In FIG. 4, such an exhaust gas flow is schematically shown by a plurality of arrows. The arrow AR10 indicates the flow of oxygen discharged by the pump cell 150 after flowing into the measuring chamber 121 through the diffusion resistor 140. In the pump cell 150, most of the oxygen contained in the exhaust gas is removed, but it is difficult to completely remove the oxygen. Therefore, a small amount of oxygen reaches each of the sensor cell 160 and the monitor cell 170. The arrow AR11 indicates the flow of oxygen reaching the sensor cell 160, and the arrow AR12 indicates the flow of oxygen reaching the monitor cell 170.

As described above, the pump electrode 111 and the monitor electrode 113 are both electrodes that are inactive with respect to nitrogen oxides. Therefore, the nitrogen oxide contained in the exhaust gas flowing into the measurement chamber 121 is not discharged by the pump cell 150 or the monitor cell 170, and reaches the sensor electrode 112 of the sensor cell 160 as it is. The arrow AR20 indicates the flow of nitrogen oxides thus reaching the sensor cell 160.

As shown in FIG. 4, both nitrogen oxides (arrow AR20) and residual oxygen (arrow AR11) reach the sensor cell 160. Therefore, the magnitude of the current flowing through the sensor cell 160 indicates the concentration of nitrogen oxides and oxygen contained in the exhaust gas.

On the other hand, the magnitude of the current flowing through the monitor cell 170 indicates the concentration of oxygen contained in the exhaust gas. Therefore, the current value obtained by subtracting the value of the current flowing through the monitor cell 170 from the value of the current flowing through the sensor cell 160 indicates the concentration of nitrogen oxides only. With such an exhaust gas sensor 100, it is possible to suppress the influence of oxygen contained in the exhaust gas and accurately measure the concentration of nitrogen oxides.

As shown in FIG. 2, a heater 180 is embedded in the main body 130. The heater 180 generates heat inside the main body 130 to heat each of the pump cell 150, the sensor cell 160, and the monitor cell 170. The heater 180 keeps the solid electrolyte 110 at a temperature at which it becomes active. The output (calorific value) of the heater 180 is adjusted by the control device 10.

The configuration of the control device 10 will be described with reference to FIG. The control device 10 is configured as a computer system having a CPU, ROM, RAM, and the like. As a functional control block, the control device 10 includes a concentration detection unit 11, an internal combustion engine control unit 12, a deterioration determination unit 13, a gas temperature acquisition unit 14, a cell temperature estimation unit 15, and a cell current acquisition unit 16. And a pipe temperature acquisition unit 17 and a heater control unit 18.

The concentration detection unit 11 is a portion that detects the concentration of nitrogen oxides contained in the exhaust gas based on the signals (current in this embodiment) output from each of the monitor cell 170 and the sensor cell 160. As described above, the concentration detection unit 11 detects the concentration of nitrogen oxides based on the current value obtained by subtracting the value of the current flowing through the monitor cell 170 from the value of the current flowing through the sensor cell 160.

The internal combustion engine control unit 12 is a portion that controls the internal combustion engine EG based on the concentration of nitrogen oxides detected by the concentration detection unit 11. The internal combustion engine control unit 12 adjusts the fuel injection amount of the internal combustion engine EG and the like so that the concentration of nitrogen oxides detected by the exhaust gas sensor 100 approaches zero. As described above, the control device 10 may be configured as a dedicated device for controlling the exhaust gas sensor 100, and may be a control device different from the engine ECU. In this case, the internal combustion engine control unit 12 is configured as a part of the engine ECU.

The deterioration determination unit 13 is a unit that determines whether or not the sensor cell 160 (second cell) has deteriorated. When the sensor cell 160 is deteriorated, the value of the current flowing through the sensor cell 160 becomes smaller than that in the normal state even when the concentration of nitrogen oxides contained in the exhaust gas is the same. As a result, it becomes impossible to accurately measure the concentration by the exhaust gas sensor 100. Therefore, the deterioration determination unit 13 periodically performs a process for determining whether or not the sensor cell 160 has deteriorated. The specific content of the process will be described later.

The gas temperature acquisition unit 14 is a portion that performs a process of acquiring the temperature of the exhaust gas. The gas temperature acquisition unit 14 acquires the temperature of the exhaust gas passing in the vicinity of the exhaust gas sensor 100 in the exhaust pipe 20 based on the signal from the gas temperature sensor 25 shown in FIG.

The cell temperature estimation unit 15 is a part that performs a process of estimating the temperature of the sensor cell 160 (second cell). The cell temperature estimation unit 15 estimates the temperature of the sensor cell 160 based on the temperature of the exhaust gas acquired by the gas temperature acquisition unit 14. The estimation method will be described later.

The cell current acquisition unit 16 is a portion that performs a process of acquiring the value of the current flowing through the sensor cell 160 (second cell). The value of the current acquired by the cell current acquisition unit 16 is used for the calculation of the deterioration index described later.

The pipe temperature acquisition unit 17 is a portion of the exhaust pipe 20 that performs a process of acquiring the temperature in the vicinity of the portion to which the exhaust gas sensor 100 is attached. The acquisition method will be described later.

The heater control unit 18 is a portion that controls the heater 180. The heater control unit 18 measures the temperature of the pump cell 150, and adjusts the calorific value of the heater 180 so that the temperature becomes a predetermined target temperature. As a result, the solid electrolyte body 110 of the exhaust gas sensor 100 is kept in an active state.

A method of acquiring the temperature by the heater control unit 18 will be described with reference to FIG. FIG. 5 shows an example of a time change of the applied voltage applied between the pump electrode 111 and the common electrode 114. When detecting the temperature of the pump cell 150, the heater control unit 18 temporarily increases the applied voltage. In the example of FIG. 5, the applied voltage increases from V0 to V10 in the period from time t1 to time t2.

As the applied voltage increases, so does the current flowing between the pump electrode 111 and the common electrode 114. The heater control unit 18 calculates the impedance of the pump cell 150 by dividing the amount of increase in the applied voltage during the period from time t1 to time t2 by the amount of increase in the current during the same period.

There is a correlation between the impedance of the pump cell 150 and the temperature of the pump cell 150, and the relationship between the two is measured in advance and stored as a map. The heater control unit 18 acquires the temperature of the pump cell 150 by referring to the impedance calculated as described above and the map.

In the example of FIG. 5, the applied voltage is V20, which is smaller than V0, in the period from time t2 to time t3. After that time t3, the applied voltage is returned to the original V0. In the present embodiment, by temporarily setting the applied voltage at the time of temperature acquisition to V20, it is possible to prevent the electric charge from accumulating in the pump cell 150 with the passage of time.

The period during which the applied voltage changes for temperature measurement (the period from time t1 to time t3 in the example of FIG. 5) is very short, and is on the order of microseconds. Since the change in current due to the change in applied voltage is very small and negligible, it has almost no effect on the measurement of oxygen concentration by the monitor cell 170, the measurement of nitrogen oxide concentration by the sensor cell 160, and the like.

The outline of the process performed by the deterioration determination unit 13, that is, the process for determining whether or not the sensor cell 160 has deteriorated will be described. FIG. 6 (A) shows the time change of the voltage applied to the pump cell 150. What is shown in FIG. 6 (B) is the time change of the current flowing through the pump cell 150. FIG. 6C shows the time change of the current flowing through the sensor cell 160.

In the example shown in FIG. 6, the normal control (that is, the process for measuring the nitrogen oxide concentration) is temporarily stopped at time t0, and the deterioration determination by the deterioration determination unit 13 is started from time t0. ing. At time t0, the voltage applied to the pump cell 150 _{is changed from the initial VP} 2 to a lower _VP 1 (FIG. 6 (A)).

Along with this, the current flowing through the pump cell 150 has _{decreased from the initial I P} 2 to a lower I _P 1 (FIG. 6 (B)). This decrease in the current flowing through the pump cell 150 means that the amount of oxygen passing through the pump cell 150 and reaching the sensor cell 160 has increased after time t0. Therefore, as shown by the line L10 in FIG. 6C, the current flowing through the sensor cell 160 starts to increase from time t0, and finally becomes a substantially constant value.

The amount of increase in the current flowing through the sensor cell 160 is roughly proportional to the amount of increase in oxygen reaching the sensor cell 160. Therefore, if the sensor cell 160 is normal and the amount of decrease in the current flowing through the pump cell 150 ( _IP 2- _IP 1) is constant, the current flowing through the sensor cell 160 is always the line L10 in FIG. 6 (C). Should change like this.

However, when the sensor cell 160 is deteriorated, the current flowing through the sensor cell 160 becomes small even if the amount of decrease in the current flowing through the pump cell 150 is the same. The line L11 in FIG. 6C shows an example of a time change of the current flowing through the sensor cell 160 when the sensor cell 160 is deteriorated.

The time change of the current flowing through the sensor cell 160 differs depending on the deterioration mode of the sensor cell 160. For example, when deterioration occurs in the sensor cell 160 due to aggregation of the sensor electrodes 112, the time change of the current becomes a graph as shown by line L11 in FIG. 6 (C). On the other hand, in the sensor cell 160, when poisoning by gold moved from the pump electrode 111 occurs, the time change of the current becomes a graph as shown in the line L110 of FIG. 6C. .. That is, the current becomes lower than the value (normal value) shown on the line L10 for a while from the time t0, while the final current value after the lapse of time is almost the same as the value shown on the line L10. It becomes a value.

In any case, the value of the current flowing through the deteriorated sensor cell 160 is lower than the normal value for a while from the time t0. The deterioration determination unit 13 determines whether or not the sensor cell 160 has deteriorated based on the value of the current flowing through the sensor cell 160.

The time change of the current flowing through the sensor cell 160 changes according to the degree of deterioration of the sensor cell 160 and also changes according to the temperature of the sensor cell 160. As is well known, the higher the temperature of the sensor cell 160, the larger the current flowing through the sensor cell 160. The line L12 in FIG. 6C shows the time change of the current flowing through the sensor cell 160 when the temperature of the sensor cell 160 is higher than usual.

The deterioration determination unit 13 determines whether or not the sensor cell 160 has deteriorated, taking into consideration that the value of the current flowing through the sensor cell 160 changes depending on the temperature.

A specific determination method by the deterioration determination unit 13 will be described. The deterioration determination unit 13 calculates the deterioration index using the value of the current acquired by the cell current acquisition unit 16, that is, the value of the current flowing through the sensor cell 160, and determines the deterioration based on the deterioration index. The "deterioration index" in the present embodiment is a value obtained by dividing the amount of change in the value of the current acquired by the cell current acquisition unit 16 by the amount of change in the value of the current flowing through the sensor cell 160 in the normal state. That is.

The method of calculating the deterioration index will be described with reference to FIG. 7. The lines L10, L11, and L12 shown in FIG. 7 are all enlarged views of the line L10 and the like shown in FIG. The time t10 shown in FIG. 7 is a time after a predetermined fixed period has elapsed from the time t0 at which the deterioration determination was started. The time t20 shown in FIG. 7 is a time after a predetermined fixed period has elapsed from the time t10.

In the period from time t10 to time t20, the current value indicated by line L10 is increased by [Delta] I _S 0. This amount of increase corresponds to "the amount of change in the value of the current flowing through the sensor cell 160 in the normal state", is acquired in advance by an experiment or the like, and is stored in a storage device (not shown) provided in the control device 10. ..

The value of the current flowing the current value represented by line L11, i.e., the sensor cell 160 deterioration has occurred in the period from time t10 to time t20 is increased by [Delta] I _S 1. The increase is less than the amount increased in the normal (ΔI _S 0).

Further, the current value indicated by the line L12, i.e., the value of the current flowing through it and sensor cells 160 to a high temperature, it is increased by [Delta] I _S 2 during the period from time t10 to time t20. This increase is greater than the increase in the amount in the normal (ΔI _S 0).

The value of the obtained current by the cell current acquisition unit 16, when a change as line L10 in FIG. 7, deterioration index to be calculated ΔI _S 0 / ΔI _S 0, that is, 1. That is, when the sensor cell 160 has not deteriorated, the calculated deterioration index is 1.

The value of the obtained current by the cell current acquisition unit 16, when a change as line L11 in FIG. 7, deterioration index to be calculated becomes a value smaller than ΔI _S 1 / ΔI _S 0, namely 1 .. That is, when the sensor cell 160 is deteriorated, the calculated deterioration index is a value smaller than 1. Further, the larger the degree of deterioration, the smaller the calculated deterioration index.

After calculating the deterioration index as described above, the deterioration determination unit 13 determines that the sensor cell 160 has deteriorated when the deterioration index is smaller than the predetermined lower limit TH (see FIG. 8). .. A value smaller than 1 is set as the lower limit value TH.

As described above, the deterioration determination unit 13 in the present embodiment sets the value of the current acquired by the cell current acquisition unit 16 (specifically, the amount of change thereof in the period from time t10 to time t20) in the normal state. Using the value obtained by dividing by the value of the current flowing through the sensor cell 160 (specifically, the amount of change in the period from time t10 to time t20), a deterioration index indicating the degree of deterioration of the sensor cell 160 is obtained. It is configured to calculate and determine whether or not the sensor cell 160 has deteriorated based on the deterioration index.

In the present embodiment, the current value obtained by dividing the value of the current acquired by the cell current acquisition unit 16 by the value of the current flowing through the sensor cell 160 in the normal state is defined as the "current ratio". The ratio itself is used as the degradation index. Instead of such an embodiment, the value obtained by subjecting the current ratio to a predetermined conversion may be used as the deterioration index. For example, a value such that 100% when the current ratio is 0 and 0% when the current ratio is 1 may be used as the deterioration index. In this case, when the calculated deterioration index exceeds a predetermined upper limit value, it is determined that the sensor cell 160 has deteriorated.

As the current ratio, a current ratio different from the above may be used. For example, the current ratio may be calculated based on the current value after a sufficient time has elapsed from the time t0 and the time has become substantially constant. That is, the value of the current acquired by the cell current acquisition unit 16 (current value after becoming constant) is the value of the current flowing through the sensor cell 160 in the normal state (current value after becoming constant in the normal state). The divided product may be calculated as a current ratio, and the deterioration index may be calculated using the current ratio.

However, as described above, depending on the deterioration mode of the sensor cell 160, the final current value after a lapse of time may become the same as the current value in the normal state. Therefore, as in the present embodiment, the sensor cell 160 is deteriorated based on the change in the current value in the period immediately after the voltage applied to the pump cell 150 is changed (the period from time t10 to time t20). It is preferable that the determination as to whether or not it is performed is performed.

The value of the obtained current by the cell current acquisition unit 16, when a change as line L12 in FIG. 7, deterioration index to be calculated becomes a value larger than ΔI _S 2 / ΔI _S 0, namely 1 .. That is, when the temperature of the sensor cell 160 is higher than the normal temperature, the calculated deterioration index becomes a larger value than when the temperature is low.

Therefore, even if the sensor cell 160 is deteriorated and the deterioration index is originally smaller than 1, if the temperature of the sensor cell 160 at that time is high, the deterioration index rises to 1. It will be approaching. Therefore, the calculated deterioration index may exceed the lower limit value TH, and it may be erroneously determined that the sensor cell 160 has not deteriorated. In order to prevent erroneous determination, it is necessary to correct the calculated deterioration index according to the temperature of the sensor cell 160.

The correction method will be described with reference to FIG. The graph shown in FIG. 8 shows the correspondence between the temperature (horizontal axis) of the sensor cell 160 and the calculated deterioration index (vertical axis) when the sensor cell 160 is not deteriorated.

“T0” shown in FIG. 8 is a preset reference temperature of the sensor cell 160. When the temperature of the sensor cell 160 matches this reference temperature and the sensor cell 160 has not deteriorated, the calculated deterioration index is 1. On the other hand, when the temperature of the sensor cell 160 becomes higher than the reference temperature, the calculated deterioration index becomes a value larger than 1. When the temperature of the sensor cell 160 becomes lower than the reference temperature, the calculated deterioration index becomes a value smaller than 1. As shown in FIG. 8, the graph showing the correspondence between the temperature of the sensor cell 160 and the calculated deterioration index is a linear graph rising to the right. This correspondence relationship has been acquired in advance by an experiment or the like, and is stored in a storage device (not shown) included in the control device 10.

By using this correspondence, it is possible to acquire the calculated deterioration index fluctuation amount PR1 when the temperature of the sensor cell 160 is a specific value (for example, T1 in FIG. 8). The fluctuation amount PR1 is a value obtained by subtracting 1 from the calculated deterioration index, and can be expressed as a function of the temperature of the sensor cell 160.

That is, by using the correspondence relationship shown in FIG. 8, it is possible to acquire the fluctuation amount PR1 corresponding to the temperature of the sensor cell 160 acquired by the cell temperature estimation unit 15. If the correction is performed by subtracting the fluctuation amount PR1 from the calculated deterioration index, the deterioration index excluding the fluctuation due to the influence of temperature can be obtained. The deterioration determination unit 13 determines whether or not deterioration has occurred in the sensor cell 160 by comparing the deterioration index after such correction with the lower limit value TH.

As described above, the deterioration determination unit 13 in the present embodiment corrects the deterioration index based on the temperature of the sensor cell 160 (second cell) estimated by the cell temperature estimation unit 15, and based on the corrected deterioration index. , It is configured to determine whether or not the sensor cell 160 has deteriorated. As a result, even when the temperature of the sensor cell 160 is higher or lower than the reference temperature, it is possible to accurately determine whether or not the sensor cell 160 has deteriorated.

Depending on how the period for calculating the deterioration index (the period from the time t10 to the time t20 shown in FIG. 7) is set, the graph shown in FIG. 8 may be a downward-sloping graph. Even in this case, the deterioration index calculated can be corrected by the fluctuation amount PR1 by the same method as described above.

The temperature estimation method by the cell temperature estimation unit 15 will be described with reference to FIG. The graph shown in FIG. 9 shows the correspondence between the temperature of the exhaust gas acquired by the gas temperature acquisition unit 14 (horizontal axis) and the temperature of the sensor cell 160 (vertical axis). As shown in the figure, the higher the temperature of the exhaust gas acquired by the gas temperature acquisition unit 14, the higher the temperature of the sensor cell 160 at that time tends to be.

As shown in FIG. 9, the graph showing the correspondence relationship between the temperature of the exhaust gas and the temperature of the sensor cell 160 is a linear graph rising to the right. This correspondence relationship has been acquired in advance by an experiment or the like, and is stored in a storage device (not shown) included in the control device 10. By referring to this correspondence, the cell temperature estimation unit 15 can estimate the temperature of the sensor cell 160 corresponding to the temperature of the exhaust gas acquired by the gas temperature acquisition unit 14. After that, the deterioration index as described above is corrected based on the estimated temperature of the sensor cell 160.

The flow of processing executed by the control device 10 in order to realize the deterioration determination of the sensor cell 160 (second cell) as described above will be described with reference to FIG. The series of processes shown in FIG. 10 is repeatedly executed mainly by the deterioration determination unit 13 of the control device 10 every time a predetermined control cycle elapses.

In the first step S01 of the process, it is determined whether or not the determination condition is satisfied. The "determination condition" is preset as a condition necessary for the deterioration determination unit 13 to perform the deterioration determination. In the present embodiment, it is set as a determination condition that the timing is after the internal combustion engine EG is stopped and before 3 seconds have elapsed after the internal combustion engine EG is stopped.

The reason why the determination conditions are set as described above will be described with reference to FIG. FIG. 11A is a graph showing the time change of the temperature of the exhaust gas in the exhaust pipe 20. FIG. 11B is a graph showing the time change of the temperature of the sensor cell 160. In the example shown in FIG. 11, the internal combustion engine EG is operating in the period before the time t30, and the internal combustion engine EG is stopped in the period after the time t30.

As shown in FIG. 11A, after the time t30 when the internal combustion engine EG is stopped, the high temperature exhaust gas is not discharged from the internal combustion engine EG, so that the temperature of the exhaust gas in the exhaust pipe 20 gradually decreases. go. In the configuration of the present embodiment, the temperature of the exhaust gas is lowered by about 100 ° C. within 100 seconds.

On the other hand, even after the time t30 when the internal combustion engine EG was stopped, the temperature of the sensor cell 160 was hardly lowered (FIG. 11 (B)). In the configuration of the present embodiment, the temperature of the sensor cell 160 decreased by only about 5 ° C. within 100 seconds. It is considered that this is because substantially the entire exhaust gas sensor 100 shown in FIG. 2 is covered with a cover (not shown), and the thermal resistance between the sensor cell 160 and the exhaust gas is increased.

As described above, after the time t30 when the internal combustion engine EG is stopped, the temperature of the exhaust gas gradually decreases, while the temperature of the sensor cell 160 hardly decreases. Therefore, after a while from the time t30, the correspondence shown in FIG. 9 is broken, and the temperature of the sensor cell 160 cannot be accurately estimated by the cell temperature estimation unit 15. Therefore, in the present embodiment, the determination conditions are set as described above, and the deterioration determination is started at a timing before 3 seconds elapse after the internal combustion engine EG is stopped.

The explanation will be continued by returning to FIG. If it is determined in step S01 that the determination condition is not satisfied, the series of processes shown in FIG. 10 is terminated without performing the deterioration determination by the deterioration determination unit 13. If it is determined that the determination condition is satisfied, the process proceeds to step S02.

In step S02, the gas temperature acquisition unit 14 performs a process of acquiring the temperature of the exhaust gas. In step S03 following step S02, the cell temperature estimation unit 15 performs a process of estimating the temperature of the sensor cell 160. As described above, the cell temperature estimation unit 15 estimates the temperature of the sensor cell 160 based on the temperature of the exhaust gas earned in step S02 and the correspondence shown in FIG.

In step S04 following step S03, it is determined whether or not the temperature of the sensor cell 160 estimated in step S03 is within a predetermined appropriate temperature range. The "optimal temperature range" is preset as a temperature range of the sensor cell 160 suitable for determining deterioration. When the temperature of the sensor cell 160 is out of the optimum temperature range, the series of processes shown in FIG. 10 is completed without performing the deterioration determination by the deterioration determination unit 13.

When the temperature of the sensor cell 160 is extremely higher than the reference temperature (T0 shown in FIG. 8) or extremely lower than the reference temperature, the current flowing through the sensor cell 160 changes significantly, which is shown in FIG. The linearity of the graph is broken. As a result, the deterioration index cannot be calculated or corrected accurately. Therefore, in the present embodiment, the optimum temperature range is set as the range including the reference temperature, and the deterioration determination is performed only when the temperature of the sensor cell 160 is within the optimum temperature range.

As described above, when the temperature of the sensor cell 160 (second cell) estimated by the cell temperature estimation unit 15 is out of the preset appropriate temperature range, the deterioration determination unit 13 according to the present embodiment sets the sensor cell 160. It is configured so as not to determine whether or not deterioration has occurred. As a result, it is possible to prevent the deterioration determination unit 13 from performing the deterioration determination in a situation where it is difficult to accurately perform the deterioration determination.

If the temperature of the sensor cell 160 is within the appropriate temperature range in step S04, the process proceeds to step S05. In step S05, the cell current acquisition unit 16 performs a process of acquiring the value of the current flowing through the sensor cell 160. Here, in a predetermined period after the timing when the internal combustion engine EG is stopped (at least, a period including the period from time t10 to time t20 in FIG. 7), the value of the current flowing through the sensor cell 160 is a plurality of times. It will be sampled.

In step S06 following step S05, the deterioration determination unit 13 performs a process of calculating the deterioration index. The method of calculating the deterioration index is as described above with reference to FIG. 7.

In step S07 following step S06, a process of correcting the deterioration index calculated in step S06 using the temperature of the sensor cell 160 estimated in step S03 is performed. The method for correcting the deterioration index is as described above with reference to FIG.

In step S08 following step S07, it is determined whether or not the corrected deterioration index obtained in step S07 is equal to or higher than the lower limit value TH. If the deterioration index is equal to or higher than the lower limit value TH, the process proceeds to step S09. In step S09, it is determined that the sensor cell 160 has not deteriorated.

If the deterioration index is less than the lower limit value TH in step S08, the process proceeds to step S10. In step S10, it is determined that the sensor cell 160 has deteriorated. In this case, for example, a process is performed to notify the occupants of the vehicle by, for example, lighting an LED, that the nitrogen oxide concentration cannot be accurately measured by the exhaust gas sensor 100. Instead of such an embodiment, a process of correcting the measured value of the nitrogen oxide concentration by the exhaust gas sensor 100 according to the degree of deterioration of the sensor cell 160 may be performed.

As described above, the control device 10 according to the present embodiment is configured to estimate the temperature of the sensor cell 160 based on the temperature of the exhaust gas and determine the deterioration of the sensor cell 160 based on the estimated temperature of the sensor cell 160. Has been done.

By the way, the temperature of the pump cell 150 is acquired by the heater control unit 18 as described above. Further, the sensor cell 160 is formed near the pump cell 150. Therefore, based on the temperature of the pump cell 150 acquired by the heater control unit 18, it seems that the temperature of the sensor cell 160 can be accurately acquired. For example, it is conceivable to use the acquired temperature of the pump cell 150 as it is as the temperature of the sensor cell 160, or to use the temperature shifted by a predetermined temperature from the acquired temperature of the pump cell 150 as the temperature of the sensor cell 160.

However, while the sensor cell 160 is arranged near the wall surface of the exhaust pipe 20, the pump cell 150 is arranged at a position inside the exhaust pipe 20. Therefore, a temperature difference occurs between the pump cell 150 and the sensor cell 160 due to heat conduction between the exhaust gas sensor 100 and the exhaust pipe 20. Further, the temperature difference is not always constant and changes according to the driving state of the vehicle and the like. Therefore, it is not easy to accurately estimate the temperature of the sensor cell 160 based on the temperature of the pump cell 150.

On the other hand, in the present embodiment, the temperature of the sensor cell 160 itself, which is the target of the deterioration determination, is estimated by the cell temperature estimation unit 15, and then the deterioration determination of the sensor cell 160 is performed based on the temperature. This makes it possible to perform more accurate deterioration determination than before.

Further, since it is not necessary to separately provide a temperature sensor or a measurement circuit for acquiring the temperature of the sensor cell 160, the cost of the entire system including the exhaust gas sensor 100 does not increase.

The deterioration determination unit 13 in the present embodiment uses a value (current ratio) obtained by dividing the value of the current acquired by the cell current acquisition unit 16 by the value of the current flowing through the sensor cell 160 in the normal state. Then, a deterioration index indicating the degree of deterioration of the sensor cell 160 is calculated. Further, based on the deterioration index, it is determined whether or not the sensor cell 160 has deteriorated.

Further, the deterioration determination unit 13 corrects the deterioration index based on the temperature of the sensor cell 160 estimated by the cell temperature estimation unit 15, and determines whether or not the sensor cell 160 has deteriorated based on the corrected deterioration index. It is configured to determine. This makes it possible to accurately determine whether or not the sensor cell 160 has deteriorated based on the sensor cell 160.

The second embodiment will be described. In the following, the points different from the first embodiment will be mainly described, and the points common to the first embodiment will be omitted as appropriate.

In this embodiment, the temperature estimation method by the cell temperature estimation unit 15 is different from that in the first embodiment. The cell temperature estimation unit 15 according to the present embodiment estimates the temperature of the sensor cell 160 based on the temperature of the exhaust pipe 20.

The graph shown in FIG. 12 shows the correspondence between the temperature (horizontal axis) in the vicinity of the portion of the exhaust pipe 20 to which the exhaust gas sensor 100 is attached and the temperature (vertical axis) of the sensor cell 160. As shown in the figure, the higher the temperature of the exhaust pipe 20, the higher the temperature of the sensor cell 160 at that time tends to be.

As shown in FIG. 12, the graph showing the correspondence relationship between the temperature of the exhaust pipe 20 and the temperature of the sensor cell 160 is a linear graph rising to the right. This correspondence relationship has been acquired in advance by an experiment or the like, and is stored in a storage device (not shown) included in the control device 10. The cell temperature estimation unit 15 can estimate the temperature of the sensor cell 160 corresponding to the temperature of the exhaust pipe 20 by referring to this correspondence relationship. After that, the deterioration index as described above is corrected based on the estimated temperature of the sensor cell 160.

A method of acquiring the temperature of the exhaust pipe 20 will be described. The graph shown in FIG. 13 shows the correspondence between the temperature of the exhaust gas passing through the inside of the exhaust pipe 20 (horizontal axis) and the temperature of the exhaust pipe 20 (vertical axis). As shown in the figure, the higher the temperature of the exhaust gas, the higher the temperature of the exhaust pipe 20 at that time tends to be.

As shown in FIG. 13, the graph showing the correspondence relationship between the temperature of the exhaust gas and the temperature of the exhaust pipe 20 is a linear graph rising to the right. This correspondence relationship has been acquired in advance by an experiment or the like, and is stored in a storage device (not shown) included in the control device 10. The pipe temperature acquisition unit 17 can estimate the temperature of the exhaust pipe 20 corresponding to the temperature of the exhaust gas by referring to this correspondence relationship.

It should be noted that a plurality of correspondences shown in FIG. 13 may be stored according to parameters other than the temperature of the exhaust gas. For example, a plurality of correspondences shown in FIG. 13 are stored according to the temperature of the air supplied to the internal combustion engine EG from the air supply pipe (not shown), the load status of the internal combustion engine EG, the continuous operation time of the internal combustion engine EG, and the like. It may be done. In this case, the pipe temperature acquisition unit 17 selects a correspondence relationship according to the situation at that time, and then exhaust pipes based on the correspondence relationship and the temperature of the exhaust gas acquired by the gas temperature acquisition unit 14. The temperature of 20 will be estimated.

In this way, the pipe temperature acquisition unit 17 is configured to acquire the temperature of the exhaust pipe 20 to which the exhaust gas sensor 100 is attached, at least based on the temperature of the exhaust gas acquired by the gas temperature acquisition unit 14. There is. Further, the cell temperature estimation unit 15 in the present embodiment is configured to estimate the temperature of the sensor cell 160 (second cell) based on the temperature of the exhaust pipe 20 acquired by the pipe temperature acquisition unit 17.

The series of processes shown in FIG. 14 is a process executed by the control device 10 according to the present embodiment, and is executed in place of the series of processes shown in FIG. In this process, step S03 in FIG. 10 is replaced with step S13, and then a new step S12 is inserted between steps S02 and S13.

In step S02, after the process of acquiring the temperature of the exhaust gas is performed by the gas temperature acquisition unit 14, the process proceeds to step S12 in the present embodiment. In step S12, the pipe temperature acquisition unit 17 performs a process of acquiring the temperature of the exhaust pipe 20. The acquisition method is as described above with reference to FIG.

In step S13 following step S12, the cell temperature estimation unit 15 performs a process of estimating the temperature of the sensor cell 160. Here, a process of estimating the temperature of the sensor cell 160 is performed based on the temperature of the exhaust pipe 20 acquired in step S12. The estimation method is as described above with reference to FIG.

As described above, the control device 10 according to the present embodiment acquires the temperature of the exhaust pipe 20 based on at least the temperature of the exhaust gas, and estimates the temperature of the sensor cell 160 based on the temperature of the exhaust pipe 20. It is configured. Even in such an embodiment, the same effect as that described in the first embodiment is obtained.

The third embodiment will be described. In the following, the points different from the first embodiment will be mainly described, and the points common to the first embodiment will be omitted as appropriate.

In the present embodiment, not only the sensor cell 160 but also the monitor cell 170 is configured to estimate the temperature and determine the deterioration thereof. That is, in the present embodiment, the cell temperature estimation unit 15 is configured to estimate the temperature of the sensor cell 160 and the temperature of the monitor cell 170, respectively. Further, the deterioration determination unit 13 is configured to determine the deterioration of the monitor cell 170 based on the temperature of the monitor cell 170 in addition to the deterioration determination of the sensor cell 160 based on the temperature of the sensor cell 160.

The series of processes shown in FIG. 15 is a process executed by the control device 10 according to the present embodiment, and is executed in parallel with the series of processes shown in FIG. In this process, steps S03 to S10 in FIG. 10 are replaced with steps S23 to S30. In the present embodiment, the deterioration determination of the sensor cell 160 is performed by the series of processes shown in FIG. 10, and the deterioration determination of the monitor cell 170 is performed by the series of processes shown in FIG.

In the process shown in FIG. 15, after the temperature of the exhaust gas is acquired in step S02, the process proceeds to step S23. In step S23, the cell temperature estimation unit 15 performs a process of estimating the temperature of the monitor cell 170. The estimation method is the same as the method for estimating the temperature of the sensor cell 160. A storage device (not shown) included in the control device 10 stores a correspondence relationship between the temperature of the exhaust gas and the temperature of the monitor cell 170, that is, a correspondence relationship similar to that shown in FIG. The cell temperature estimation unit 15 estimates the temperature of the monitor cell 170 based on the temperature of the exhaust gas earned in step S02 and the corresponding relationship.

In step S24 following step S23, it is determined whether or not the temperature of the monitor cell 170 estimated in step S23 is within a predetermined appropriate temperature range. The "optimal temperature range" referred to here is the same as the optimum temperature range used for the determination in step S04 of FIG. The optimum temperature range for the monitor cell 170 may be set as a range different from the optimum temperature range for the sensor cell 160. When the temperature of the monitor cell 170 is out of the appropriate temperature range, the series of processes shown in FIG. 15 is completed without performing the deterioration determination by the deterioration determination unit 13.

If the temperature of the monitor cell 170 is within the appropriate temperature range in step S24, the process proceeds to step S25. In step S25, the cell current acquisition unit 16 performs a process of acquiring the value of the current flowing through the monitor cell 170. The method of acquiring the value of the current is the same as the method of acquiring the value of the current flowing through the sensor cell 160 in step S04 of FIG.

In step S26 following step S25, the deterioration determination unit 13 performs a process of calculating the deterioration index for the monitor cell 170. The method for calculating the deterioration index is the same as the method for calculating the deterioration index for the sensor cell 160 (the method described with reference to FIG. 7).

In step S27 following step S26, a process of correcting the deterioration index calculated in step S26 using the temperature of the monitor cell 170 estimated in step S23 is performed. The method for correcting the deterioration index is the same as the method for correcting the deterioration index for the sensor cell 160 (the method described with reference to FIG. 8).

In step S28 following step S27, it is determined whether or not the corrected deterioration index obtained in step S27 is equal to or higher than the lower limit value TH. The "lower limit value TH" referred to here is the same as the lower limit value TH used for the determination in step S08 of FIG. The lower limit value TH of the monitor cell 170 may be set as a value different from the lower limit value TH of the sensor cell 160. If the deterioration index is equal to or higher than the lower limit value TH, the process proceeds to step S29. In step S29, it is determined that the monitor cell 170 has not deteriorated.

If the deterioration index is less than the lower limit value TH in step S28, the process proceeds to step S30. In step S30, it is determined that the monitor cell 170 has deteriorated. In this case, for example, a process is performed to notify the occupants of the vehicle by, for example, lighting an LED, that the nitrogen oxide concentration cannot be accurately measured by the exhaust gas sensor 100. Instead of such an embodiment, a process of correcting the measured value of the nitrogen oxide concentration by the exhaust gas sensor 100 according to the degree of deterioration of the monitor cell 170 may be performed.

As described above, in the control device 10 according to the present embodiment, the cell temperature estimation unit 15 is configured to estimate both the temperature of the monitor cell 170 and the temperature of the sensor cell 160, respectively. Further, the deterioration determination unit 13 in the present embodiment is configured to calculate and correct the deterioration index for each of the monitor cell 170 and the sensor cell 160, which are the second cells.

Specifically, the deterioration determination unit 13 corrects the deterioration index calculated for the monitor cell 170 based on the temperature of the monitor cell 170 estimated by the cell temperature estimation unit 15, and is estimated by the cell temperature estimation unit 15. It is configured to correct the deterioration index calculated for the sensor cell 160 based on the temperature of the sensor cell 160. This makes it possible to accurately determine deterioration not only of the sensor cell 160 but also of the monitor cell 170.

The cell temperature estimation unit 15 may estimate only the temperature of the monitor cell 170, and the deterioration determination unit 13 may only determine the deterioration of the monitor cell 170 based on the temperature.

A fourth embodiment will be described. In the following, the points different from the first embodiment will be mainly described, and the points common to the first embodiment will be omitted as appropriate.

In the present embodiment, similarly to the third embodiment described above, the deterioration determination unit 13 is configured to perform deterioration determination for each of the sensor cell 160 and the monitor cell 170. However, each deterioration determination is performed based on the temperature of the sensor cell 160 estimated by the cell temperature estimation unit 15.

The series of processes shown in FIG. 16 is a process executed by the control device 10 according to the present embodiment, and is executed in parallel with the series of processes shown in FIG. In this process, steps S05 to S10 in FIG. 10 are replaced with steps S35 to S40. In the present embodiment, the deterioration determination of the sensor cell 160 is performed by the series of processes shown in FIG. 10, and the deterioration determination of the monitor cell 170 is performed by the series of processes shown in FIG.

In the process shown in FIG. 16, when it is determined in step S04 that the temperature of the sensor cell 160 is within an appropriate range, the process proceeds to step S35. In step S35, the cell current acquisition unit 16 performs a process of acquiring the value of the current flowing through the monitor cell 170. The method of acquiring the value of the current is the same as the method of acquiring the value of the current flowing through the sensor cell 160 in step S04 of FIG.

In step S36 following step S35, the deterioration determination unit 13 performs a process of calculating the deterioration index for the monitor cell 170. The method for calculating the deterioration index is the same as the method for calculating the deterioration index for the sensor cell 160 (the method described with reference to FIG. 7). However, in step S36, the deterioration index for the monitor cell 170 is calculated after the temperature of the sensor cell 160 estimated in step S03 is used as the temperature of the monitor cell 170 at this time.

In step S37 following step S36, a process of correcting the deterioration index calculated in step S36 is performed. The method for correcting the deterioration index is the same as the method for correcting the deterioration index for the sensor cell 160 (the method described with reference to FIG. 8). However, in step S37, the temperature of the sensor cell 160 estimated in step S03 is set to the temperature of the monitor cell 170 at this time, and the deterioration index of the monitor cell 170 is corrected. In other words, in this embodiment, the deterioration index for the monitor cell 170 is corrected based on the estimated temperature of the sensor cell 160.

In step S38 following step S37, it is determined whether or not the corrected deterioration index obtained in step S37 is equal to or higher than the lower limit value TH. The "lower limit value TH" referred to here is the same as the lower limit value TH used for the determination in step S08 of FIG. The lower limit value TH of the monitor cell 170 may be set as a value different from the lower limit value TH of the sensor cell 160. If the deterioration index is equal to or higher than the lower limit value TH, the process proceeds to step S39. In step S39, it is determined that the monitor cell 170 has not deteriorated.

If the deterioration index is less than the lower limit value TH in step S38, the process proceeds to step S40. In step S40, it is determined that the monitor cell 170 has deteriorated. In this case, for example, a process is performed to notify the occupants of the vehicle by, for example, lighting an LED, that the nitrogen oxide concentration cannot be accurately measured by the exhaust gas sensor 100. Instead of such an embodiment, a process of correcting the measured value of the nitrogen oxide concentration by the exhaust gas sensor 100 according to the degree of deterioration of the monitor cell 170 may be performed.

As described above, the deterioration determination unit 13 according to the present embodiment corrects the deterioration index calculated for the monitor cell 170 and calculates the sensor cell 160 based on the temperature of the sensor cell 160 estimated by the cell temperature estimation unit 15. It is configured to perform each of the corrections of the deterioration index. Even in such an embodiment, the same effect as that described with respect to the first embodiment can be obtained.

Instead of the above aspect, the deterioration determination unit 13 corrects the deterioration index calculated for the monitor cell 170 and calculates the sensor cell 160 based on the temperature of the monitor cell 170 estimated by the cell temperature estimation unit 15. It may be a mode configured to perform each of the correction of the deterioration index.

The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Those skilled in the art with appropriate design changes to these specific examples 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 of the above-mentioned specific examples, its arrangement, conditions, shape, and the like are not limited to those illustrated, and can be changed as appropriate. The combinations of the elements included in each of the above-mentioned specific examples can be appropriately changed as long as there is no technical contradiction.

10: Control device 14: Gas temperature acquisition unit 15: Cell temperature estimation unit 100: Exhaust gas sensor 150: Pump cell 160: Sensor cell 170: Monitor cell EG: Internal combustion engine

Claims (10)

It is a control device (10) of the exhaust gas sensor (100).
The exhaust gas sensor includes a first cell (150) that discharges oxygen from the exhaust gas generated by the internal combustion engine (EG), and a concentration of residual oxygen contained in the exhaust gas after the oxygen is discharged by the first cell. It has a second cell (160, 170) that outputs a signal having a magnitude corresponding to the above.
Gas temperature acquisition unit (14) that acquires the temperature of exhaust gas,
A cell temperature estimation unit (15) that estimates the temperature of the second cell based on the temperature of the exhaust gas acquired by the gas temperature acquisition unit is provided .
A deterioration determination unit (13) for determining whether or not the second cell has deteriorated is further provided.
When the temperature of the second cell estimated by the cell temperature estimation unit is out of the preset optimum temperature range,
The deterioration determination unit is a control device that does not determine whether or not the second cell has deteriorated. A cell current acquisition unit (16) for acquiring the value of the current flowing through the second cell is further provided.
The deterioration determination unit
Deterioration indicating the degree of deterioration of the second cell by using the value obtained by dividing the value of the current acquired by the cell current acquisition unit by the value of the current flowing through the second cell under normal conditions. calculating the index based on the deterioration index, determines whether the degradation in the second cell occurs, the control device according to claim 1. The deterioration determination unit
The deterioration index is corrected based on the temperature of the second cell estimated by the cell temperature estimation unit, and it is determined whether or not the second cell is deteriorated based on the corrected deterioration index. The control device according to claim 2. The deterioration determination unit
The deterioration index is calculated using the value obtained by dividing the amount of change in the value of the current acquired by the cell current acquisition unit by the amount of change in the value of the current flowing through the second cell under normal conditions. The control device according to claim 2 or 3. A pipe temperature acquisition unit (17) for acquiring the temperature of the exhaust gas to which the exhaust gas sensor is attached is further provided based on the temperature of the exhaust gas acquired by the gas temperature acquisition unit.
The cell temperature estimation unit
The control device according to any one of claims 1 to 4 , which estimates the temperature of the second cell based on the temperature of the exhaust pipe acquired by the pipe temperature acquisition unit. The second cell is
A monitor cell (170) that outputs a signal having a magnitude corresponding to the concentration of residual oxygen contained in the exhaust gas after oxygen is discharged by the first cell, and
A sensor cell (160) that outputs a signal having a magnitude corresponding to the concentration of residual oxygen and nitrogen oxides contained in the exhaust gas after oxygen is discharged by the first cell, according to claims 1 to 1. 5. The control device according to any one of 5. The control device according to claim 6 , wherein the cell temperature estimation unit estimates at least one of the temperature of the monitor cell and the temperature of the sensor cell. It is a control device (10) of the exhaust gas sensor (100).
The exhaust gas sensor includes a first cell (150) that discharges oxygen from the exhaust gas generated by the internal combustion engine (EG), and a concentration of residual oxygen contained in the exhaust gas after the oxygen is discharged by the first cell. It has a second cell (160, 170) that outputs a signal having a magnitude corresponding to the above.
Gas temperature acquisition unit (14) that acquires the temperature of exhaust gas,
A cell temperature estimation unit (15) that estimates the temperature of the second cell based on the temperature of the exhaust gas acquired by the gas temperature acquisition unit is provided.
The second cell is
A monitor cell (170) that outputs a signal having a magnitude corresponding to the concentration of residual oxygen contained in the exhaust gas after oxygen is discharged by the first cell, and
It includes a sensor cell (160) that outputs a signal having a magnitude corresponding to the concentration of residual oxygen and nitrogen oxides contained in the exhaust gas after oxygen is discharged by the first cell.
The cell temperature estimation unit estimates at least one of the temperature of the monitor cell and the temperature of the sensor cell.
A deterioration determination unit that determines whether or not deterioration has occurred in the second cell,
A cell current acquisition unit for acquiring the value of the current flowing through the second cell is further provided.
The deterioration determination unit
The degree of deterioration of the second cell is indicated by using the value obtained by dividing the value of the current acquired by the cell current acquisition unit by the value of the current flowing through the second cell under normal conditions. The deterioration index is calculated, and based on the deterioration index, it is determined whether or not the second cell has deteriorated.
The deterioration index is corrected based on the temperature of the second cell estimated by the cell temperature estimation unit, and it is determined whether or not the second cell is deteriorated based on the corrected deterioration index. Is configured to
The deterioration calculation and correction of the deterioration index by the determination unit, the monitor cell and performed Ru control device for each of said sensor cells. The cell temperature estimation unit estimates the temperature of the monitor cell and the temperature of the sensor cell, respectively.
The deterioration determination unit
Based on the temperature of the monitor cell estimated by the cell temperature estimation unit, the deterioration index calculated for the monitor cell is corrected.
The control device according to claim 8 , wherein the deterioration index calculated for the sensor cell is corrected based on the temperature of the sensor cell estimated by the cell temperature estimation unit. The deterioration determination unit
Correction of the deterioration index calculated for the monitor cell based on one of the temperature of the monitor cell and the temperature of the sensor cell estimated by the cell temperature estimation unit, and the deterioration index calculated for the sensor cell. The control device according to claim 8 , which is configured to perform each of the amendments.

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