JP6927174B2 - 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, one 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 located on the downstream side, a current corresponding to the concentration of residual oxygen and nitrogen oxides contained in the exhaust gas after oxygen is discharged (hereinafter, the current is also referred to as "output current"). Flows. 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.

By the way, in an exhaust gas sensor having a plurality of cells, the relationship between the concentration of the component to be measured and the output current may change due to the deterioration of the cells. Therefore, in the gas sensor control device described in Patent Document 1 below, it is possible to determine the deterioration of the exhaust gas sensor. Specifically, after reducing the voltage applied to the first cell (pump cell) and temporarily increasing the amount of oxygen reaching the second cell (sensor cell), the second cell at that time Deterioration is determined based on the slope of the change in output current.

JP-A-2017-116438

The slope of the change in the output current from the second cell changes not only according to the degree of deterioration of the second cell, but also according to the oxygen concentration of the exhaust gas to be detected. For example, when the oxygen concentration in the exhaust gas is low, only a relatively small amount of oxygen reaches the second cell when the voltage applied to the first cell is reduced. Therefore, the slope of the change in the output current from the second cell is small even though the second cell has not deteriorated. As a result, it may be erroneously determined that the second cell has deteriorated.

In order to prevent such an erroneous determination, the above patent document 1 normalizes the above inclination by dividing it by the amount of change in the output current from the first cell, and deteriorates based on the inclination after normalization. Is to be determined. As a result, it is possible to accurately determine whether or not the second cell has deteriorated, regardless of the oxygen concentration of the exhaust gas at that time.

However, after the voltage applied to the first cell is reduced, it takes a certain amount of time for the fluctuation of the output current value (that is, the parameter for normalization) from the first cell to settle down. Similarly, after the voltage applied to the first cell is restored, it still takes a certain period of time for the fluctuation of the output current value from the first cell to settle down again. Therefore, there is a problem that it takes a relatively long time to accurately acquire the amount of change in the output current from the first cell and complete the deterioration determination based on the normalized slope.

An object of the present disclosure is to provide a control device capable of accurately determining whether or not a second cell of an exhaust gas sensor has deteriorated in a short time.

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 current having a magnitude corresponding to the concentration. This control device includes a first cell control unit (13) that controls the discharge of oxygen by the first cell, a current value acquisition unit (14) that acquires the value of the current output from the second cell, and a current value acquisition unit. A deterioration determination unit (15) for determining whether or not deterioration has occurred in the second cell based on the value of the current acquired by the unit is provided. The value of the current acquired by the current value acquisition unit is the first current at the first timing, which is the timing at which the first predetermined period has elapsed from the time when the oxygen discharge by the first cell is suppressed by the first cell control unit. When the value of the current acquired by the current value acquisition unit is set as the second current value in the second timing, which is the timing when the second predetermined period elapses from the first timing, the deterioration determination unit sets the value. Based on the ratio of the second current value to the first current value, it is determined whether or not the second cell has deteriorated. The deterioration determination unit determines that the second cell has deteriorated when the value obtained by dividing the second current value by the first current value falls below a predetermined threshold value.

The deterioration determination unit included in the control device is not based on the slope of the change in the current output from the second cell, but is measured at different timings from the two values of the current (second current value and first current). Based on the ratio of the value), it is determined whether or not the second cell has deteriorated.

According to the experiments conducted by the present inventors, the ratio of the second current value to the first current value as described above changes according to the degree of deterioration of the second cell, while the first cell to the first cell. It has been found that there is almost no change depending on the concentration of oxygen reaching the two cells.

Since the ratio of the second current value to the first current value is hardly affected by the oxygen concentration of the exhaust gas at that time, the deterioration determination can be performed accurately. Further, in performing the deterioration determination by the above method, the normalization as described in Patent Document 1 is not required, so that the deterioration determination can be completed in a relatively short time. Become.

According to the present disclosure, there is provided a control device capable of accurately determining whether or not the second cell of the exhaust gas sensor has deteriorated in a short time.

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 showing an example of time change of the pump cell voltage and the like. FIG. 6 is a diagram for explaining a method of determining deterioration in the first embodiment. FIG. 7 is a diagram showing the relationship between the first current value and the second current value. FIG. 8 is a flowchart showing a flow of processing executed by the control device according to the first embodiment. FIG. 9 is a diagram for explaining a method of determining deterioration in the second embodiment. FIG. 10 is a flowchart showing a flow of processing executed by the control device according to the second embodiment. FIG. 11 is a diagram schematically showing a configuration of a vehicle exhaust system provided with a control device and an exhaust gas sensor according to a third embodiment. FIG. 12 is a flowchart showing a flow of processing executed by the control device according to the third embodiment. FIG. 13 is a flowchart showing a flow of processing executed by the control device according to the fourth embodiment. FIG. 14 is a flowchart showing a flow of processing executed by the control device according to the fifth embodiment. FIG. 15 is a flowchart showing a flow of processing executed by the control device according to the sixth 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 its 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 one of the exhaust gas sensors 100 (the one with the reference numeral 101), and the configuration and the like for the other (the one with the reference numeral 102) the exhaust gas sensor 100. 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 formed in the solid electrolyte body 110, respectively, 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 current having a magnitude corresponding to the oxygen concentration of the exhaust gas. The control device 10 can acquire the oxygen concentration of the exhaust gas existing in the measurement chamber 121 based on the value of the current.

The voltage applied between the pump electrode 111 and the common electrode 114 is also hereinafter referred to as “pump cell voltage”. Further, the current flowing between the pump electrode 111 and the common electrode 114 when the pump cell voltage is applied is also referred to as "pump cell current" below.

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 amount of 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.

The voltage applied between the sensor electrode 112 and the common electrode 114 is also hereinafter referred to as “sensor cell voltage”. Further, the current flowing between the sensor electrode 112 and the common electrode 114 when the sensor cell voltage is applied is also hereinafter referred to as “sensor cell current”.

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 has a current having a magnitude 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 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.

The voltage applied between the monitor electrode 113 and the common electrode 114 is also hereinafter referred to as “monitor cell voltage”. Further, the current flowing between the monitor electrode 113 and the common electrode 114 when the monitor cell voltage is applied is also hereinafter referred to as “monitor cell current”.

As described above, the second cell in the present embodiment is a monitor cell that outputs a current having a magnitude 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 current of 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 sensor cell current indicates the concentration of nitrogen oxides and oxygen contained in the exhaust gas.

On the other hand, the magnitude of the monitor cell current indicates the concentration of oxygen contained in the exhaust gas. Therefore, the current value obtained by subtracting the monitor cell current value from the sensor cell current value 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. The control device 10 includes a concentration detection unit 11, an internal combustion engine control unit 12, a first cell control unit 13, a current value acquisition unit 14, and a deterioration determination unit 15 as functional control blocks. There is.

The concentration detection unit 11 is a portion that detects the concentration of nitrogen oxides contained in the exhaust gas based on each of the monitor cell current and the sensor cell current. 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 monitor cell current from the value of the sensor cell current.

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 first cell control unit 13 is a portion that controls the discharge of oxygen by the pump cell 150, which is the first cell, by changing the pump cell voltage. When the nitrogen oxide concentration is detected by the exhaust gas sensor 100, that is, in a normal state, the first cell control unit 13 maintains the pump cell voltage at a substantially constant value. On the other hand, when the deterioration determination described later is performed, the first cell control unit 13 temporarily lowers the pump cell voltage.

The current value acquisition unit 14 is a portion that acquires the value of the current output from the second cell, specifically, the value of the sensor cell current or the value of the monitor cell current. The values of the sensor cell current and the monitor cell current acquired by the current value acquisition unit 14 are used for calculating the concentration of nitrogen oxides in a normal state. In addition, values such as sensor cell current are also used for deterioration determination, which will be described later.

The deterioration determination unit 15 is a unit that determines whether or not the sensor cell 160, which is the second cell, has deteriorated. The determination in the present embodiment is performed based on the value of the sensor cell current acquired by the current value acquisition unit 14.

When the sensor cell 160 is deteriorated, the value of the sensor cell current 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, the concentration cannot be accurately measured by the exhaust gas sensor 100. Therefore, the deterioration determination unit 15 periodically performs a process (that is, deterioration determination) for determining whether or not the sensor cell 160 has deteriorated.

The outline of the processing performed for deterioration determination will be described. FIG. 5A shows an example of a time change of the pump cell voltage when the deterioration determination is performed. FIG. 5 (B) shows an example of the time change of the pump cell current. FIG. 5C shows an example of the time change of the sensor cell current.

In the example shown in FIG. 5, 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 15 is started from time t0. ing. At time t0, the voltage applied to the pump cell 150 is changed from the initial VP1 to a lower VP0 (FIG. 5A). The process is performed by the first cell control unit 13. As a result, the discharge of oxygen by the pump cell 150 is suppressed after the time t0.

Along with this, the pump cell current has decreased from the initial IP0 to an IP1 lower than this (FIG. 5 (B)). This decrease in the pump cell current 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. 5C, the sensor cell current starts to increase from time t0, and finally becomes a substantially constant value.

At the subsequent time t1, the pump cell voltage is returned to the original value VP1 (FIG. 5 (A)). Along with this, the value of the pump cell current rises to IP2. IP2 may be equal to the original value of IP1, but it is often slightly different from IP1 due to changes in the state of the internal combustion engine up to that point.

After time t1, the amount of oxygen reaching the sensor cell 160 decreases. Along with this, the value of the sensor cell current decreases at time t1 (FIG. 5 (C)).

The line L10 in FIG. 5C shows the time change of the sensor cell current in the normal state in which the sensor cell 160 is not deteriorated. On the other hand, the line L11 in the figure shows the time change of the sensor cell current when the sensor cell 160 is deteriorated.

As is clear from comparing the line L10 and the line L11, the slope of the sensor cell current after the time t0 becomes smaller when the sensor cell 160 is deteriorated than in the normal state. Therefore, as described in Japanese Patent Application Laid-Open No. 2017-116438, it is conceivable to perform deterioration determination based on the magnitude of the inclination.

However, the slope of the time change of the sensor cell current not only changes according to the degree of deterioration of the sensor cell 160, but also changes according to the oxygen concentration of the exhaust gas to be detected. For example, when the oxygen concentration in the exhaust gas is low, only a relatively small amount of oxygen reaches the sensor cell 160 even after the time t0 when the pump cell voltage is reduced. Therefore, the slope of the time change of the sensor cell current may be as small as the line L11 even though the sensor cell 160 is not generated. As a result, it may be erroneously determined that the sensor cell 160 has deteriorated.

In order to prevent such erroneous determination, the slope of the time change of the sensor cell current is normalized by dividing by the amount of change of the pump cell current (ΔIP in FIG. 5B), and based on the slope after normalization. Deterioration may be determined. This makes it possible to accurately determine whether or not the sensor cell 160 has deteriorated, regardless of the oxygen concentration of the exhaust gas at that time.

However, as shown in FIG. 5B, the pump cell current temporarily fluctuates greatly for a while after the time t0 when the pump cell voltage is reduced, and then converges to a substantially constant value. Similarly, the pump cell current temporarily fluctuates greatly for a while after the time t1 when the pump cell voltage is returned to the original value, and then converges to a substantially constant value after the time t2.

In the example of FIG. 5B, the value of the pump cell current immediately before the time t0 is IP0, and the value of the pump cell current at the time t2 is IP2. The dotted line DL1 shown in the figure is a straight line showing the change when the value of the pump cell current changes from IP0 to IP2 with a constant slope in the period from time t1 to time t2. It can be said that the straight line indicates a change in the value of the pump cell current when the value of the pump cell voltage is kept constant at VP1. ΔIP, which is the amount of change in the pump cell current, is defined as the difference between the dotted line DL1 defined in this way and the value of the pump cell current (IP1) immediately before the time t1.

The state of the internal combustion engine and the like changes even after time t0, but if the inclination is normalized using ΔIP defined in this way, even if the oxygen concentration reaching the sensor cell 160 fluctuates, the effect will be affected. Deterioration can be accurately determined with almost no reception.

However, in order to calculate ΔIP as described above, it is necessary to wait from the time t0 when the pump cell voltage is reduced to the time t2 when the value of the pump cell current converges. That is, it takes a relatively long time to accurately acquire ΔIP, which is the amount of change in the pump cell current, and complete the deterioration determination based on the normalized slope.

Therefore, the deterioration determination unit 15 according to the present embodiment determines the deterioration of the sensor cell 160 by a method different from the above, based on the change in the sensor cell current after the time t0.

The deterioration determination method will be described with reference to FIG. FIG. 6 is a graph similar to FIG. 5 (C), showing an example of the time change of the sensor cell current after the time t0 when the pump cell voltage is reduced.

The time t10 shown in FIG. 6 is the time at which the preset first predetermined period TM1 has elapsed from the time t0. That is, it is the time when the first predetermined period TM1 has elapsed from the time when the oxygen discharge by the pump cell 150 is suppressed by the first cell control unit 13 (time t0). The first predetermined period TM1 is set in advance as a period shorter than the period until the sensor cell current rises and becomes constant after the time t0 when the pump cell voltage decreases. The time t10, which is the timing at which the first predetermined period TM1 has elapsed, corresponds to the “first timing” in the present embodiment.

The time t20 shown in FIG. 6 is a time at which a preset second predetermined period TM2 has further elapsed from the time t10. That is, it is the time at which the second predetermined period TM2 has elapsed from the time t10, which is the first timing. The second predetermined period TM2 is preset as a period shorter than the period until the sensor cell current rises and becomes constant after the time t10, which is the first timing. The time t20, which is the timing at which the second predetermined period TM2 has elapsed, corresponds to the “second timing” in the present embodiment.

The current value acquisition unit 14 acquires the value of the sensor cell current at the first timing as the first current value IS1. Further, the value of the sensor cell current at the second timing is acquired as the second current value IS2.

After that, the deterioration determination unit 15 determines whether or not the sensor cell 160 has deteriorated based on the ratio of the second current value IS2 and the first current value IS1. Specifically, when the value (IS2 / IS1) obtained by dividing the second current value IS2 by the first current value IS1 is lower than the predetermined threshold value TH1, the sensor cell 160 is deteriorated. Is determined.

According to the experiments conducted by the present inventors, it has been confirmed that the ratio of the second current value IS2 to the first current value IS1 as described above changes according to the degree of deterioration of the sensor cell 160. Specifically, it has been confirmed that the greater the degree of deterioration of the sensor cell 160, the smaller the value obtained by IS2 / IS1. On the other hand, it has also been confirmed that the ratio of the second current value IS2 to the first current value IS1 hardly changes depending on the concentration of oxygen contained in the exhaust gas.

FIG. 7 shows the relationship between the first current value IS1 (horizontal axis) and the second current value IS2 (vertical axis) when the sensor cell 160 is not deteriorated. As shown in the figure, the graph showing the relationship between the first current value IS1 and the second current value IS2 is a linear graph that rises to the right. As the sensor cell voltage increases, each of the first current value IS1 and the second current value IS2 increases accordingly, but the relationship between the two itself hardly changes. Further, as the oxygen concentration contained in the exhaust gas increases, each of the first current value IS1 and the second current value IS2 increases accordingly, but the relationship between the two itself hardly changes.

When the sensor cell 160 is normal and the sensor cell voltage and oxygen concentration are changed, the points showing the measured values of the first current value IS1 and the second current value IS2 are as shown in FIG. 7. It will be plotted on a straight line rising to the right.

Therefore, when the value obtained by IS2 / IS1 is substantially equal to the slope of the graph shown in FIG. 7 (specifically, when IS2 / IS1 ≧ TH1), it is determined that the sensor cell 160 has not deteriorated. can do. On the other hand, when the value obtained by IS2 / IS1 is smaller than the slope of the graph shown in FIG. 7 (specifically, in the case of IS2 / IS1 <TH1), it is determined that the sensor cell 160 has deteriorated. can do.

The specific contents of the processing performed by the control device 10 will be described with reference to FIG. The series of processes shown in FIG. 8 is a process that is repeatedly executed by 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 diagnostic conditions are satisfied. The "diagnostic condition" is set in advance as a condition necessary for the deterioration determination of the sensor cell 160 to be performed. In the present embodiment, the above-mentioned diagnostic condition is set that the ignition switch (not shown) of the vehicle is immediately turned off by the driver. Instead of such an aspect, for example, the stable operating state of the internal combustion engine may be set as a diagnostic condition.

If the diagnostic conditions are not satisfied, the series of processes shown in FIG. 8 is terminated. If the diagnostic conditions are satisfied, the process proceeds to step S02. In step S02, the process of lowering the pump cell voltage is performed by the first cell control unit 13. The process corresponds to the process started at time t0 in FIGS. 5 (C) and 6 (C). After the process of step S02 is performed, the oxygen discharge by the pump cell 150 is suppressed, and the pump cell current gradually increases.

In step S03 following step S02, whether or not TM1 has elapsed for the first predetermined period from the time when the process of step S02 is performed, that is, the time when the oxygen discharge by the pump cell 150 is suppressed by the first cell control unit 13. Is determined. If TM1 has not yet elapsed for the first predetermined period, the process of step S03 is repeatedly executed. When the first predetermined period TM1 has elapsed, the process proceeds to step S04. Therefore, the timing for shifting to step S04 is the above-mentioned first timing (time t10 in FIG. 6).

In step S04, the process of acquiring the first current value IS1 is performed by the current value acquisition unit 14. The acquired first current value IS1 is stored in a storage device (not shown) included in the control device 10.

In step S05 following step S04, it is determined whether or not the second predetermined period TM2 has elapsed from the time when the process of step S04 is performed, that is, from the first timing. If the second predetermined period TM2 has not yet elapsed, the process of step S05 is repeatedly executed. When the second predetermined period TM2 has elapsed, the process proceeds to step S06. Therefore, the timing for shifting to step S06 is the above-mentioned second timing (time t20 in FIG. 6).

In step S06, the process of acquiring the second current value IS2 is performed by the current value acquisition unit 14. The acquired second current value IS2 is stored in a storage device (not shown) included in the control device 10.

In step S07 following step S06, it is determined whether or not the value (IS2 / IS1) obtained by dividing the second current value IS2 by the first current value IS1 is below the threshold value TH1. The threshold value TH1 is a preset threshold value as a lower limit value in the range of IS2 / IS1 that can be calculated when the sensor cell 160 is not deteriorated. The determination is made by the deterioration determination unit 15.

If the value of IS2 / IS1 is below the threshold value TH1, the process proceeds to step S08. In step S08, the deterioration determination unit 15 determines that the sensor cell 160 has deteriorated. The term "deterioration of the sensor cell 160" as used herein means, for example, a situation in which it is necessary to turn on a warning light for urging the replacement or repair of the sensor cell 160 to notify the driver. Means that.

On the other hand, if the value of IS2 / IS1 is equal to or higher than the threshold value TH1 in step S07, the process proceeds to step S09. In step S09, the deterioration determination unit 15 determines that the sensor cell 160 has not deteriorated.

After the processing of step S08 or step S09 is performed, the process proceeds to step S10. In step S10, the first cell control unit 13 performs a process of returning the pump cell voltage to a voltage before the time t0. The process corresponds to the process performed at time t1 in FIG. As a result, the process for determining deterioration is completed.

As described above, in the control device 10 according to the present embodiment, the deterioration determination unit 15 deteriorates into the sensor cell 160, which is the second cell, based on the ratio of the second current value IS2 and the first current value IS1. Is configured to determine whether or not is occurring. Since the ratio of the second current value IS2 to the first current value IS1 is hardly affected by the oxygen concentration of the exhaust gas at that time, the normalization as explained with reference to FIG. 5 is not required. However, deterioration determination can be performed accurately. Further, since normalization is not required, it is possible to complete the deterioration determination within a relatively short time without waiting until the time t2 shown in FIG. 5 (B). Therefore, since the change in the operating state of the internal combustion engine during the deterioration determination is relatively small, it is possible to prevent an erroneous determination due to the change.

In the example shown in FIG. 8, in step S07, the deterioration determination is performed by directly comparing the value of IS2 / IS1 with the threshold value TH1. Instead of such an embodiment, another index indicating the degree of deterioration of the sensor cell 160 may be calculated based on IS2 / IS1 and the deterioration determination may be performed by comparing the index with a predetermined threshold value. As such an index, for example, a "deterioration rate" that changes in the range of 0% (initial state without deterioration) to 100% (state in which deterioration has progressed and becomes unusable) can be used. In this case, the smaller the calculated IS2 / IS1 is, the larger the deterioration rate is, and when the deterioration rate is larger than the threshold value, it is determined that the sensor cell 160 is deteriorated. The relationship between IS2 / IS1 and the above index (deterioration rate, etc.) may be stored in the control device 10 as a map in advance.

By the way, the magnitude of the sensor cell current is not the same for all the exhaust gas sensors 100, and usually varies from individual to individual exhaust gas sensor 100. Therefore, even if the conditions such as the sensor cell voltage and the oxygen concentration of the exhaust gas are the same, the magnitude of the sensor cell current acquired at that time will be a different value for each individual exhaust gas sensor 100. Further, if the conditions such as the sensor cell voltage and the oxygen concentration of the exhaust gas are different, the degree of variation in the sensor cell current also changes.

Therefore, when the deterioration judgment of the sensor cell 160 is performed by the conventional method, the value of the initial characteristic (that is, the value of the sensor cell current in the normal state) which is the reference for the deterioration judgment is set to a plurality of values including the sensor cell voltage and the oxygen concentration. It was necessary to individually acquire each exhaust gas sensor 100 in advance for each condition.

On the other hand, in the present embodiment, only the relationship between the first current value IS1 and the second current value IS2 as shown in FIG. 7 is determined for each exhaust gas sensor 100 as an initial characteristic that serves as a reference for deterioration determination. It is only necessary to obtain them individually in advance. That is, if only the value of IS2 / IS1 when the sensor cell 160 is normal is acquired as the initial characteristic and the threshold value TH1 is appropriately set based on this, the subsequent deterioration determination can be performed accurately. It will be possible. Therefore, in the present embodiment, there is also an advantage that the initial characteristics of each individual of the exhaust gas sensor 100 can be acquired relatively easily.

In the example described above, the second cell to be determined for deterioration is the sensor cell 160. However, the second cell to be determined for deterioration may be the monitor cell 170 instead of the sensor cell 160. Even in this case, it can be determined whether or not the monitor cell 170 has deteriorated by the same method as the method described above.

The second embodiment will be described. The second embodiment is different from the first embodiment only in the content of the processing performed for the deterioration determination. 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.

The outline of the process performed for determining the deterioration of the present embodiment will be described with reference to FIG. Each graph shown in FIG. 9 is an example of the time change of the sensor cell current after the time t0 when the pump cell voltage is reduced.

The line L20 shows the time change of the sensor cell current when the sensor cell 160 is not deteriorated. Further, what is indicated by the line L21 is the time change of the sensor cell current when the sensor cell 160 is deteriorated. When the sensor cell 160 is deteriorated, the sensor cell current after time t0 gradually increases as compared with the normal time (line L20). As a result, the calculated IS2 / IS1 value is smaller than that in the normal state.

By the way, the value of the sensor cell current tends to increase as the temperature of the sensor cell 160 increases. What is shown by the line L22 in FIG. 9 is the time change of the sensor cell current when the sensor cell 160 is not deteriorated and the temperature of the sensor cell 160 is higher than that in the normal state. In this case, the sensor cell current rises more rapidly than the line L20 after time t0, then its slope gradually becomes gentle, and finally converges to the same value as the line L20.

Therefore, the value of IS2 / IS1 when the sensor cell current changes as in line L22 may be smaller than the value of IS2 / IS1 when the sensor cell current changes as in L20. That is, when the temperature of the sensor cell 160 is high, the value of IS2 / IS1 may be calculated to be small even though the sensor cell 160 has not deteriorated. If IS2 / IS1 falls below the threshold value TH1, it is erroneously determined that the sensor cell 160 has deteriorated.

Therefore, the deterioration determination unit 15 according to the present embodiment does not determine whether or not the sensor cell 160 has deteriorated when the temperature of the sensor cell 160 is high.

The reference value ST1 shown in FIG. 9 is the first acquired at the first timing (time t10) when the sensor cell 160 has not deteriorated and the temperature of the sensor cell 160 is a normal temperature. This is the value of the current value IS1.

As shown by the line L21, when the sensor cell 160 is deteriorated, the value of the first current value IS1 acquired at the first timing is smaller than the reference value ST1. On the other hand, as shown by the line L22, when the sensor cell 160 has not deteriorated and the sensor cell 160 has a high temperature, the value of the first current value IS1 acquired at the first timing is The value is larger than the reference value ST1.

Therefore, the deterioration determination unit 15 according to the present embodiment does not determine whether or not the sensor cell 160 has deteriorated when the acquired first current value IS1 is larger than the reference value ST1. It is said. This makes it possible to prevent the above-mentioned erroneous determination.

As shown in FIG. 9, at the time t30, which is the timing when a sufficient time has passed from the time t0, the sensor cell current converges to a substantially constant value. The value of the sensor cell current at this time is the same value for all of the lines L20, L21, and L22. As shown in FIGS. 6 and 9, the value of the sensor cell current that converges at time t30 is also hereinafter referred to as “third current value IS3”.

The time t30 is a timing after the time t20, which is the second timing, and corresponds to the “third timing” in the present embodiment. The above-mentioned third current value IS3 can be said to be the value of the sensor cell current acquired by the current value acquisition unit 14 at the third timing after the second timing.

The value of the third current value IS3 is not always the same value, but changes depending on the oxygen concentration of the exhaust gas and the like. When the value of the third current value IS3 becomes large, the above-mentioned reference value ST1 also becomes large. Therefore, when making the above determination, it is preferable to set the reference value ST1 which is the reference of the determination to an appropriate value in advance according to the value of the third current value IS3.

In the present embodiment, a plurality of candidates for the reference value ST1 for the first current value IS1 in the normal state in which the sensor cell 160 is not deteriorated are stored in advance corresponding to the plurality of third current values IS3. That is, the value of the sensor cell current that should be acquired at the first timing when no deterioration has occurred is stored in advance for each of the various third current values IS3 as candidates for the reference value ST1.

The deterioration determination unit 15 according to the present embodiment acquires the third current value IS3 at time t30, and then selects and sets the corresponding reference value ST1 from the above candidates. After that, the set reference value ST1 is compared with the first current value IS1 acquired in advance at the first timing, and if the latter is larger, it is determined whether or not the sensor cell 160 has deteriorated. Do not do.

The specific contents of the processing performed by the control device 10 will be described with reference to FIG. The series of processes shown in FIG. 10 is a process executed in place of the series of processes shown in FIG. This process is a process in which steps S11 to S14 are added between steps S06 and S07 in the series of processes shown in FIG.

After the process of acquiring and storing the second current value IS2 is performed in step S06, the process proceeds to step S11 in the present embodiment. In step S11, it is determined whether or not the third predetermined period TM3 has elapsed from the time when the process of step S06 is performed, that is, from the second timing. The third predetermined period TM3 is preset as a period required for the value of the sensor cell current acquired by the current value acquisition unit 14 to stabilize after the second timing. The third predetermined period TM3 corresponds to the period from time t20 to time t30 in the example shown in FIG.

If the third predetermined period TM3 has not yet elapsed, the process of step S11 is repeatedly executed. When the third predetermined period TM3 has elapsed, the process proceeds to step S12. Therefore, the timing of shifting to step S12 is the above-mentioned third timing (time t30 in FIGS. 6 and 9).

In step S12, the process of acquiring the third current value IS3 is performed by the current value acquisition unit 14. The acquired third current value IS3 is stored in a storage device (not shown) included in the control device 10.

In step S13 following step S12, a process of setting the reference value ST1 is performed. As already mentioned, here, from among the candidates of the plurality of reference values ST1 stored in advance,
The one corresponding to the third current value IS3 acquired in step S12 is selected, and this is set as the reference value ST1.

In step S14 following step S13, it is determined whether or not the first current value IS1 acquired in step S04 is equal to or less than the reference value ST1 set in step S13. If the first current value IS1 is equal to or less than the reference value ST1, the process proceeds to step S07. After that, it is determined whether or not the sensor cell 160 has deteriorated by the same method as described for the first embodiment.

In step S14, when the first current value IS1 exceeds the reference value ST1, the series of processes shown in FIG. 10 is terminated without determining whether or not the sensor cell 160 has deteriorated.

As described above, in the present embodiment, the value of the sensor cell current is acquired as the third current value by the current value acquisition unit 14 at the third timing (time t30) after the second timing (time t20). Will be done. Regarding the first current value IS1, a plurality of reference values ST1, which are values in the normal state where deterioration has not occurred in the sensor cell 160, are stored in advance corresponding to the plurality of third current values IS3.

When the first current value IS1 acquired by the current value acquisition unit 14 is larger than the reference value ST1 corresponding to the third current value IS3 acquired by the current value acquisition unit 14, the deterioration determination unit 15 causes the sensor cell. It is configured so as not to determine whether or not the 160 has deteriorated. This prevents erroneous determination that the second cell has deteriorated when the temperature of the sensor cell 160 is high.

In the example described above, the value of the first current value IS1 is compared with the reference value (ST1), and if the value of the first current value IS1 is larger, the deterioration determination is not performed. Instead of such an embodiment, the value of the second current value IS2 may be compared with the reference value instead of the first current value IS1.

The control in such a modification will be described. The reference value ST2 shown in FIG. 9 is acquired at the second timing (time t20) when the sensor cell 160 has not deteriorated and the temperature of the sensor cell 160 is the normal temperature. This is the value of the current value IS2.

As shown by the line L21, when the sensor cell 160 is deteriorated, the value of the second current value IS2 acquired at the second timing is smaller than the reference value ST2. On the other hand, as shown by the line L22, when the sensor cell 160 has not deteriorated and the sensor cell 160 has a high temperature, the value of the second current value IS2 acquired at the second timing is The value is larger than the reference value ST2.

Therefore, when the value of the second current value IS2 is larger than the reference value ST2, the deterioration determination unit 15 in this modification does not determine whether or not the sensor cell 160 has deteriorated. This makes it possible to prevent erroneous determination at high temperatures.

The value of the third current value IS3 is not always the same value, but changes depending on the oxygen concentration of the exhaust gas and the like. When the value of the third current value IS3 becomes large, the above-mentioned reference value ST2 also becomes large. Therefore, in making the above determination, it is preferable to set the reference value ST2, which is the reference for the determination, to an appropriate value in advance according to the value of the third current value IS3.

In this comparative example, a plurality of candidates for the reference value ST2 for the second current value IS2 in the normal state in which the sensor cell 160 is not deteriorated are stored in advance corresponding to the plurality of third current values IS3. That is, the value of the sensor cell current that should be acquired at the second timing when no deterioration has occurred is stored in advance for each of the various third current values IS3 as candidates for the reference value ST2.

The deterioration determination unit 15 according to the present embodiment acquires the third current value IS3 at time t30, and then selects and sets the corresponding reference value ST2 from the above candidates. After that, the set reference value ST2 is compared with the second current value IS2 acquired in advance at the third timing, and if the latter is larger, it is determined whether or not the sensor cell 160 has deteriorated. Do not do.

Specific processing for realizing this is to replace the first current value IS1 with the second current value IS2 and replace the reference value ST1 with the reference value ST2 in steps S11 to S14 of FIG. equal. Therefore, the description of the specific processing contents will be omitted.

As described above, in this comparative example, the value of the sensor cell current is acquired as the third current value by the current value acquisition unit 14 at the third timing (t30) after the second timing (time t20). NS. Regarding the second current value IS2, a plurality of reference values ST2, which are normal values without deterioration in the sensor cell 160, are stored in advance corresponding to the plurality of third current values IS3.

When the second current value IS2 acquired by the current value acquisition unit 14 is larger than the reference value ST2 corresponding to the third current value IS3 acquired by the current value acquisition unit 14, the deterioration determination unit 15 determines the sensor cell. It is configured so as not to determine whether or not the 160 has deteriorated. This prevents erroneous determination that the second cell has deteriorated when the temperature of the sensor cell 160 is high.

In the second embodiment and its modification described above, the time t30, which is the third timing, is after the oxygen discharge by the pump cell 150 is suppressed by the first cell control unit 13, and the current value acquisition unit. It is set as the timing after the value of the sensor cell current acquired by 14 becomes stable. However, the time t30, which is the third timing, may be set as a timing different from the above as long as the timing is later than the time t20. For example, a third timing may be set as a timing before the value of the sensor cell current stabilizes. Also in this case, the reference value ST1 and the reference value ST2 are set corresponding to the third current value IS3 acquired at the third timing.

A third embodiment will be described. In the third embodiment, the configuration of the control device 10 and the content of the processing performed for determining the deterioration are each modified from the above-mentioned second embodiment. In the following, the points different from the second embodiment will be mainly described, and the points common to the second embodiment will be omitted as appropriate.

As shown in FIG. 11, the control device 10 in the present embodiment further includes a temperature estimation unit 16. The temperature estimation unit 16 is a part that estimates the temperature of the sensor cell 160, which is the second cell. The temperature of the sensor cell 160 estimated by the temperature estimation unit 16 is used, for example, to correct the concentration of nitrogen oxides measured by the exhaust gas sensor 100.

The process executed to estimate the temperature of the sensor cell 160 will be described with reference to FIG. In the present embodiment, each time the series of processes shown in FIG. 10 is executed, the series of processes shown in FIG. 12 is subsequently executed. The series of processes shown in FIG. 12 is executed by the temperature estimation unit 16 described above.

In the first step S21 of the process, a process of calculating a value obtained by dividing the first current value IS1 by the reference value ST1 (that is, IS1 / ST1) is performed. The first current value IS1 used for this calculation is the value of the sensor cell current acquired by the current value acquisition unit 14 at the first timing, and was acquired in step S04 of FIG. Further, the reference value ST1 used for the calculation is the reference value ST1 corresponding to the third current value IS3 acquired by the current value acquisition unit 14, and is set in step S13 of FIG.

The value of IS1 / ST1 calculated in this way can be said to be a parameter indicating the degree of deviation of the first current value IS1 from the reference value ST1. As described above with reference to FIG. 9, since the first current value IS1 becomes larger as the temperature of the sensor cell 160 becomes higher, the calculated value of IS1 / ST1 also becomes larger. When the sensor cell 160 is not deteriorated, the value of IS1 / ST1 becomes a value corresponding to the temperature of the sensor cell 160.

In a storage device (not shown) included in the control device 10, the correspondence relationship between the value of IS1 / ST1 and the temperature of the sensor cell 160 when the sensor cell 160 is not deteriorated is stored as a map.

In step S22 following step S21, the temperature of the sensor cell 160 is estimated by referring to the value of IS1 / ST1 calculated in step S21 and the above map.

If the sensor cell 160 is deteriorated, the correspondence between the value of IS1 / ST1 and the temperature of the sensor cell 160 changes, so that the temperature of the sensor cell 160 may not be estimated accurately. Therefore, the process of FIG. 12 may be performed only when the process of FIG. 10 shifts from step S07 to step S09, that is, when it is determined that the sensor cell 160 has not deteriorated.

As described above, the temperature estimation unit 16 divides the first current value IS1 acquired by the current value acquisition unit 14 by the reference value ST1 corresponding to the third current value IS3 acquired by the current value acquisition unit 14. The temperature of the sensor cell 160 is estimated based on the value obtained by the above.

In the example described above, the temperature of the sensor cell 160 is estimated based on the value of the first current value IS1. Instead of such an embodiment, the temperature of the sensor cell 160 may be estimated based on the value of the second current value IS2 instead of the first current value IS1.

The control in such a modification will be described. In this modification, instead of step S21 in FIG. 12, a process of calculating a value obtained by dividing the second current value IS2 by the reference value ST2 (that is, IS2 / ST2) is performed. The second current value IS2 used for this calculation is the value of the sensor cell current acquired by the current value acquisition unit 14 at the second timing, and was acquired in step S06 of FIG. Further, the reference value ST2 used for the calculation is the reference value ST2 corresponding to the third current value IS3 acquired by the current value acquisition unit 14, and in the modified example of the second embodiment, in step S13 of FIG. It was set.

The IS2 / ST2 value calculated in this way can be said to be a parameter indicating the degree of deviation of the second current value IS2 from the reference value ST2. As described above with reference to FIG. 9, the higher the temperature of the sensor cell 160, the larger the second current value IS2, so that the calculated IS2 / ST2 value also increases. When the sensor cell 160 is not deteriorated, the value of IS2 / ST2 becomes a value corresponding to the temperature of the sensor cell 160.

In a storage device (not shown) included in the control device 10, the correspondence relationship between the IS2 / ST2 value and the temperature of the sensor cell 160 when the sensor cell 160 is not deteriorated is stored as a map.

In this modification, the temperature of the sensor cell 160 is estimated by referring to the IS2 / ST2 value calculated as described above and the map described above in step S22.

If the sensor cell 160 is deteriorated, the correspondence between the IS2 / ST2 value and the temperature of the sensor cell 160 changes, so that the temperature of the sensor cell 160 may not be estimated accurately. Therefore, the temperature of the sensor cell 160 is estimated as described above only when the process of FIG. 10 shifts from step S07 to step S09, that is, when it is determined that the sensor cell 160 has not deteriorated. , May be.

As described above, the temperature estimation unit 16 in this modified example uses the second current value IS2 acquired by the current value acquisition unit 14 as a reference value corresponding to the third current value IS3 acquired by the current value acquisition unit 14. The temperature of the sensor cell 160 is estimated based on the value obtained by dividing by ST2.

The temperature estimation unit 16 may estimate the temperature of the monitor cell 170 instead of the sensor cell 160 by performing the same processing as in the second embodiment and its modification as described above.

A fourth embodiment will be described. The fourth embodiment is different from the first embodiment only in the content of the processing performed for the deterioration determination. 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, instead of the series of processes shown in FIG. 8, the series of processes shown in FIG. 13 is executed. The process is a process in which the processes between steps S06 and steps S08 and S09 in the series of processes shown in FIG. 8 are replaced with steps S31 to S33.

After the process of acquiring and storing the second current value IS2 is performed in step S06, the process proceeds to step S31 in the present embodiment. In step S31, a process of calculating ΔIS, which is the difference between the two, is performed by subtracting the value of the first current value IS1 acquired in step S04 from the value of the second current value IS2 acquired in step S06. Will be. ΔIS can be said to be a parameter indicating the magnitude of the slope of the change in the sensor cell current in the second predetermined period TM2 of FIG. When the sensor cell 160 is deteriorated, the calculated value of ΔIS becomes smaller according to the degree of deterioration.

In step S32 following step S31, ΔIS (hereinafter, also referred to as “normal ΔIS”) when the sensor cell 160 is not deteriorated is calculated.

In the storage device (not shown) included in the control device 10, the ratio of the first current value IS1 to the second current value IS2 and the first current value IS1 at that time when the sensor cell 160 is not deteriorated. (Specifically, IS2 / IS1) and the correspondence relationship are stored as a map. The control device 10 calculates the value of the second current value IS2 when the sensor cell 160 is not deteriorated by referring to the value of the first current value IS1 acquired in step S04 and the map. After that, by subtracting the value of the first current value IS1 acquired in step S04 from the calculated value of the second current value IS2, the normal ΔIS which is the difference value between the two is calculated.

In step S33 following step S32, a value obtained by dividing ΔIS calculated in step S31 by the normal ΔIS calculated in step S32 (that is, ΔIS / normal ΔIS) is calculated, and the value falls below the threshold TH2. Whether or not it is determined.

When the sensor cell 160 is deteriorated, the calculated value of ΔIS / normal ΔIS becomes smaller according to the degree of deterioration. The threshold value TH2 is a preset threshold value as a lower limit value in the range of ΔIS / normal ΔIS that can be calculated when the sensor cell 160 is not deteriorated.

If the value of ΔIS / normal ΔIS is less than the threshold value TH2, the process proceeds to step S08, and it is determined that the sensor cell 160 has deteriorated. When the value of ΔIS / normal ΔIS is equal to or higher than the threshold value TH2, the process proceeds to step S09, and it is determined that the sensor cell 160 has not deteriorated. Subsequent processing is the same as that of the first embodiment shown in FIG.

Also in this embodiment, the deterioration determination unit 15 determines whether or not the sensor cell 160, which is the second cell, has deteriorated based on the ratio of the second current value IS2 and the first current value IS1. However, the deterioration is not determined by directly comparing the ratio of the second current value IS2 to the first current value IS1 (for example, IS2 / IS1) with the threshold value, but the second current value IS2 and the first current value IS1 are used. Deterioration is determined by comparing the value (ΔIS / normal ΔIS) calculated using the ratio with the threshold value TH2.

In the prior art, when storing ΔIS, it is necessary to acquire the first current value IS1 and the second current value IS2 at a plurality of points in consideration of the oxygen concentration, and to store the ΔIS corresponding to each oxygen concentration. However, in the present embodiment, as described in the first embodiment, the normal ΔIS is obtained by obtaining IS2 based on the ratio of the second current value IS2 and the first current value IS1 which are less affected by the oxygen concentration. Therefore, the deterioration determination can be performed relatively easily and accurately. Further, the ratio of the absolute value of the second current value IS2 in the normal state calculated from the ratio of the second current value IS2 and the first current value IS1 to the absolute value of the second current value IS2 acquired in step S06. It is also possible to determine the deterioration by calculating and comparing with the threshold value, but by calculating the ratio of the difference as in this embodiment, the degree of deterioration from the normal state becomes clearer and the accuracy becomes clearer. Deterioration judgment can be performed well.

In step S32, the normal ΔIS was calculated based on the actually acquired value of the first current value IS1 and the value of the second current value IS2 obtained by referring to the map. The normal ΔIS may be calculated by a method different from the above. For example, the normal state ΔIS may be calculated based on the value of the second current value IS2 actually acquired in step S06 and the value of the first current value IS1 obtained by referring to the map. The map in this case shows the correspondence between the value of the second current value IS2 when the sensor cell 160 is not deteriorated and the ratio of the second current value IS2 and the first current value IS1 at that time. It only needs to be remembered.

A fifth embodiment will be described. The fifth embodiment is different from the first embodiment only in the content of the processing performed for the deterioration determination. 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, instead of the series of processes shown in FIG. 8, the series of processes shown in FIG. 14 is executed. Hereinafter, differences from the series of processes shown in FIG. 8 will be described.

After it is determined in step S03 that the first predetermined period TM1 has elapsed, the process proceeds to step S41 in the present embodiment. In step S41, the value of the sensor cell current and the value of the monitor cell current at the first timing are acquired, respectively. All of these correspond to the "first current value" in the present embodiment.

The value of the sensor cell current acquired at the first timing is hereinafter referred to as "first sensor cell current value IS1". Further, the value of the monitor cell current acquired at the first timing is hereinafter referred to as "first monitor cell current value IM1". That is, the "first current value" in the present embodiment includes the first monitor cell current value IM1 output from the monitor cell 170 and the first sensor cell current value IS1 output from the sensor cell 160.

In step S05 following step S41, the same processing as described with reference to FIG. 8 is performed. If it is determined in step S05 that the second predetermined period TM2 has elapsed, the process proceeds to step S42 in the present embodiment. In step S42, the value of the sensor cell current and the value of the monitor cell current at the second timing are acquired, respectively. All of these correspond to the "second current value" in the present embodiment.

The value of the sensor cell current acquired at the second timing is hereinafter referred to as "second sensor cell current value IS2". Further, the value of the monitor cell current acquired at the second timing is hereinafter referred to as "second monitor cell current value IM2". That is, the "second current value" in the present embodiment includes the second monitor cell current value IM2 output from the monitor cell 170 and the second sensor cell current value IS2 output from the sensor cell 160.

In step S43 following step S42, the first ratio and the second ratio are calculated, respectively.

The above-mentioned "first ratio" is a value obtained by dividing the second sensor cell current value IS2 calculated in step S42 by the first sensor cell current value IS1 calculated in step S41.

Further, the above-mentioned "second ratio" is a value obtained by dividing the second monitor cell current value IM2 calculated in step S42 by the first monitor cell current value IM1 calculated in step S41. ..

When the temperature of the sensor cell 160 becomes high, the waveform of the sensor cell current changes from line L20 in FIG. 9 to line L22. Therefore, the higher the temperature of the sensor cell 160, the smaller the first ratio tends to be. Similarly, the higher the temperature of the monitor cell 170, the smaller the second ratio tends to be.

Since the sensor cell 160 and the monitor cell 170 are arranged at positions close to each other in the exhaust gas sensor 100, their respective temperatures are substantially equal to each other. According to the experiments conducted by the present inventors, when the temperature of the sensor cell 160 and the temperature of the monitor cell 170 rise by the same degree, the amount of decrease in the second ratio is larger than the amount of decrease in the first ratio. It has been confirmed to be large. It is considered that this is because the monitor cell current tends to be more susceptible to the temperature due to the difference in the manufacturing methods of the sensor cell 160 and the monitor cell 170.

In step S44 following step S43, it is determined whether or not the difference obtained by subtracting the second ratio from the first ratio is equal to or less than the threshold value TH3. The threshold value TH3 is preset as an upper limit value in the range of values that the above difference can take when the sensor cell 160 is not deteriorated and the temperature of the sensor cell 160 or the like is not higher than usual. It is a thing.

When the above difference exceeds the threshold value TH3, the temperatures of the sensor cell 160 and the monitor cell 170 are higher than those in the normal state, and as a result, the waveforms of the sensor cell current value and the monitor cell current value change from the normal waveforms. It is presumed that it is doing. Therefore, in this case, the series of processes shown in FIG. 14 is completed without determining whether or not the sensor cell 160 has deteriorated.

In step S44, when the above difference is equal to or less than the threshold value TH3, it is presumed that the temperature of the sensor cell 160 and the monitor cell 170 is the normal temperature. Therefore, in this case, the process proceeds to step S07, and thereafter, the same processing as that described in the first embodiment is performed.

As described above, the deterioration determination unit 15 in the present embodiment determines whether or not the sensor cell 160 is deteriorated only when the first ratio and the second ratio satisfy predetermined predetermined conditions. It is configured to make a determination. The "predetermined condition" in the above means that the difference between the first ratio and the second ratio is equal to or less than a predetermined value (threshold value TH3). As a result, it is possible to prevent an erroneous determination as to whether or not deterioration has occurred due to the temperature rise of the sensor cell 160 or the like.

The sixth embodiment will be described. The fifth embodiment is different from the above-mentioned fifth embodiment only in the content of the processing performed for the deterioration determination. In the following, the points different from the fifth embodiment will be mainly described, and the points common to the fifth embodiment will be omitted as appropriate.

In the present embodiment, instead of the series of processes shown in FIG. 14, the series of processes shown in FIG. 15 is executed. This process is a process in which step S44 in FIG. 14 is replaced with step S45.

After the first ratio and the second ratio are calculated in step S43, the process proceeds to step S45 in the present embodiment. In step S45, it is determined whether or not the value obtained by dividing the first ratio by the second ratio (hereinafter, the value is also referred to as “ratio ratio”) is equal to or less than the threshold value TH4. .. The threshold value TH4 is preset as an upper limit of a range of values that the above ratio ratio can take when the sensor cell 160 has not deteriorated and the temperature of the sensor cell 160 or the like is not higher than usual. Is what it is.

When the above ratio ratio exceeds the threshold value TH4, the temperatures of the sensor cell 160 and the monitor cell 170 are higher than those in the normal state, so that the waveforms of the sensor cell current value and the monitor cell current value are different from the waveforms in the normal time. It is presumed that it is changing. Therefore, in this case, the series of processes shown in FIG. 15 is completed without determining whether or not the sensor cell 160 has deteriorated.

In step S45, when the ratio ratio is equal to or less than the threshold value TH4, it is presumed that the temperature of the sensor cell 160 and the monitor cell 170 is the normal temperature. Therefore, in this case, the process proceeds to step S07, and thereafter, the same processing as that described in the first embodiment is performed.

As described above, the deterioration determination unit 15 in the present embodiment determines whether or not the sensor cell 160 is deteriorated only when the first ratio and the second ratio satisfy predetermined predetermined conditions. It is configured to make a determination. The "predetermined condition" in the above means that the ratio obtained by dividing the first ratio by the second ratio is equal to or less than a predetermined value (threshold value TH4). As a result, it is possible to prevent an erroneous determination as to whether or not deterioration has occurred due to the temperature rise of the sensor cell 160 or the like.

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, etc. is not limited to the illustrated one, 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.

EG: Internal combustion engine 10: Control device 13: First cell control unit 14: Current value acquisition unit 15: Deterioration determination unit 100: Exhaust gas sensor 150: Pump cell (first cell)
160: Sensor cell (second cell)
170: Monitor cell (second cell)

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 current of a magnitude corresponding to the above.
The first cell control unit (13) that controls the discharge of oxygen by the first cell, and
A current value acquisition unit (14) that acquires the value of the current output from the second cell, and
A deterioration determination unit (15) for determining whether or not deterioration has occurred in the second cell based on the current value acquired by the current value acquisition unit is provided.
The value of the current acquired by the current value acquisition unit is set at the first timing, which is the timing at which the first predetermined period has elapsed from the time when the oxygen discharge by the first cell is suppressed by the first cell control unit. Let it be the first current value
When the value of the current acquired by the current value acquisition unit is set as the second current value in the second timing, which is the timing at which the second predetermined period has elapsed from the first timing,
The deterioration determination unit
Based on the ratio of the second current value to the first current value, it is determined whether or not the second cell has deteriorated .
The deterioration determination unit controls to determine that the second cell has deteriorated when the value obtained by dividing the second current value by the first current value falls below a predetermined threshold value. Device. 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 current of a magnitude corresponding to the above.
The first cell control unit (13) that controls the discharge of oxygen by the first cell, and
A current value acquisition unit (14) that acquires the value of the current output from the second cell, and
A deterioration determination unit (15) for determining whether or not deterioration has occurred in the second cell based on the current value acquired by the current value acquisition unit is provided.
The value of the current acquired by the current value acquisition unit is set at the first timing, which is the timing at which the first predetermined period has elapsed from the time when the oxygen discharge by the first cell is suppressed by the first cell control unit. Let it be the first current value
When the value of the current acquired by the current value acquisition unit is set as the second current value in the second timing, which is the timing at which the second predetermined period has elapsed from the first timing,
The deterioration determination unit
Based on the ratio of the second current value to the first current value, it is determined whether or not the second cell has deteriorated.
When the value of the current acquired by the current value acquisition unit is set to the third current value in the third timing after the second timing,
Regarding the first current value, a plurality of reference values, which are normal values without deterioration in the second cell, are stored in advance corresponding to the plurality of the third current values.
The first current value acquired by the current value acquisition unit is
When it is larger than the reference value corresponding to the third current value acquired by the current value acquisition unit,
The deterioration determining unit, had control apparatus perform the determination of whether the degradation in the second cell is generated. A temperature estimation unit (16) for estimating the temperature of the second cell is further provided.
The temperature estimation unit
Based on the value obtained by dividing the first current value acquired by the current value acquisition unit by the reference value corresponding to the third current value acquired by the current value acquisition unit. The control device according to claim 2 , wherein the temperature of the second cell is estimated. 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 current of a magnitude corresponding to the above.
The first cell control unit (13) that controls the discharge of oxygen by the first cell, and
A current value acquisition unit (14) that acquires the value of the current output from the second cell, and
A deterioration determination unit (15) for determining whether or not deterioration has occurred in the second cell based on the current value acquired by the current value acquisition unit is provided.
The value of the current acquired by the current value acquisition unit is set at the first timing, which is the timing at which the first predetermined period has elapsed from the time when the oxygen discharge by the first cell is suppressed by the first cell control unit. Let it be the first current value
When the value of the current acquired by the current value acquisition unit is set as the second current value in the second timing, which is the timing at which the second predetermined period has elapsed from the first timing,
The deterioration determination unit
Based on the ratio of the second current value to the first current value, it is determined whether or not the second cell has deteriorated.
When the value of the current acquired by the current value acquisition unit is set to the third current value in the third timing after the second timing,
With respect to the second current value, a plurality of reference values, which are normal values without deterioration in the second cell, are stored in advance corresponding to the plurality of the third current values.
The second current value acquired by the current value acquisition unit is
When it is larger than the reference value corresponding to the third current value acquired by the current value acquisition unit,
The deterioration determining unit, had control apparatus perform the determination of whether the degradation in the second cell is generated. A temperature estimation unit for estimating the temperature of the second cell is further provided.
The temperature estimation unit
Based on the value obtained by dividing the second current value acquired by the current value acquisition unit by the reference value corresponding to the third current value acquired by the current value acquisition unit. The control device according to claim 4 , wherein the temperature of the second cell is estimated. The third timing is
Any of claims 2 to 5 , which is the timing after the discharge of oxygen by the first cell is suppressed by the first cell control unit and then the value of the current acquired by the current value acquisition unit stabilizes. The control device according to item 1. The second cell is
A monitor cell (170) that outputs a current having a magnitude corresponding to the concentration of residual oxygen contained in the exhaust gas after oxygen is discharged by the first cell, and
Claims 1 to 1, wherein the sensor cell (160) that outputs a current 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 is included. The control device according to any one of 6. The first current value includes a first monitor cell current value output from the monitor cell and a first sensor cell current value output from the sensor cell.
The second current value includes a second monitor cell current value output from the monitor cell and a second sensor cell current value output from the sensor cell.
The value obtained by dividing the second sensor cell current value by the first sensor cell current value is defined as the first ratio.
When the value obtained by dividing the second monitor cell current value by the first monitor cell current value is taken as the second ratio,
The deterioration determination unit
The control according to claim 7 , wherein it is determined whether or not the second cell is deteriorated only when the first ratio and the second ratio satisfy predetermined predetermined conditions. Device. The control device according to claim 8 , wherein the condition is that the difference between the first ratio and the second ratio is equal to or less than a predetermined value. The control device according to claim 8 , wherein the condition is that the value obtained by dividing the first ratio by the second ratio is equal to or less than a predetermined value.

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