DE112021001278T5 - control device - Google Patents

Abstract

An exhaust gas sensor (100) has a first cell (150) which removes oxygen from exhaust gas generated by an internal combustion engine (EG) and a second cell (160) which supplies a current having a magnitude corresponding to the concentration of a residual in the exhaust gas Oxygen outputs after exhausting oxygen through the first cell. The control device further comprises a first cell control unit (13) which controls the exhaust of oxygen by the first cell, a current value obtaining unit (14) for obtaining a cell current value which corresponds to the value of current output from the second cell, and a Deterioration degree calculation unit (15) for calculating a deterioration degree corresponding to an index indicative of the deterioration degree of the exhaust gas sensor, the deterioration degree being calculated based on the cell current value. The degree of deterioration calculation unit is configured to calculate the degree of deterioration based on both a first slope and a second slope after the first cell is suppressed from purging oxygen by the first cell control unit, the first slope being the slope corresponds to the change in cell current value at a prescribed point in time, and the second slope corresponds to the slope of change in cell current value at a point in time after the first slope.

Description

Cross reference to related applications

This application is based on earlier Japanese patent application no. 2020-031804 , which was filed on February 27, 2020, the specification of which is incorporated herein by reference and claims priority therefrom.

technical field

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

General state of the art

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 contained in exhaust gas. The “specific gas” can be nitrogen oxides, for example. Such an exhaust gas sensor is known, which has a plurality of cells in which electrodes are formed on both sides of a solid electrolyte layer. A current flows in a cell whose magnitude corresponds to the concentration of the component to be measured when a voltage is applied between the electrodes. The exhaust gas sensor measures the concentration of the component to be measured based on the current value.

For example, there is known an exhaust gas sensor having a configuration in which a first cell and a second cell constitute the above-mentioned plurality of cells. In a pre-extraction, the oxygen contained in the exhaust gas is pre-extracted from the first cell, which is located in the exhaust gas flow upstream of the second cell. In the second cell, which is located downstream, a current flows depending on the concentration of oxygen and nitrogen oxides that are still contained in the exhaust gas after the oxygen has been removed. This current is also referred to below as the "output current". With an exhaust gas sensor having such a configuration, the concentration of nitrogen oxides in exhaust gas can be accurately measured when the rate of removal of oxygen from exhaust gas is larger than that of nitrogen oxides.

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 cell deterioration. With a gas sensor control device described in Patent Document 1 below, it is possible to calculate a degree of deterioration as an index indicating the degree of deterioration of the exhaust gas sensor. Specifically, the voltage applied to the first cell (the pump cell) is temporarily reduced, thereby temporarily increasing the amount of oxygen reaching the second cell (the sensor cell), and the degree of deterioration is determined based on the slope of the variation in the output current of the second cell at that time is calculated.

citation list

patent literature

Patent Document 1: JP 2017 - 116 438 A

Summary of the Invention

The slope of the variation in the output current from the second cell tends to decrease according to an increased degree of deterioration of the second cell. Therefore, when the slope of the change in the output current from the second cell becomes smaller than that in the normal state, it can be judged that the second cell has deteriorated, that is, the degree of deterioration of the exhaust gas sensor has increased.

However, 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 temperature of the second cell. For example, the slope of the change in output current from the second cell tends to be large when the temperature of the second cell is higher than usual. Therefore, if the temperature of the second cell is high, the slope of the change in the output current from the second cell will be approximately the same as in the normal case, so the degree of deterioration will be calculated as smaller than the actual value even if in the second cell actually deterioration occurs. As a result, it may be wrongly judged that the exhaust gas sensor has not deteriorated.

It is an object of the present disclosure to provide a control device capable of accurately calculating the degree of deterioration of an exhaust gas sensor.

The control device according to the present disclosure corresponds to a control device for an exhaust gas sensor. The exhaust gas sensor to be controlled has a first cell which removes oxygen from exhaust gas generated in the internal combustion engine, and a second cell which outputs a current whose magnitude corresponds to the concentration of oxygen contained in the exhaust gas Residual oxygen after the removal of oxygen by the first cell. The control device includes a first cell control unit that controls the exhaust of oxygen by the first cell, and a current value acquisition unit that acquires a cell current value corresponding to the value of the current output from the second cell. A degree of deterioration calculation unit is provided to calculate a degree of deterioration corresponding to an index indicating the degree of deterioration of the exhaust gas sensor. The degree of deterioration calculation unit is configured to calculate the degree of deterioration based on both a first slope and a second slope, the first slope corresponding to that of the change in the cell current value at a predetermined point in time or period after the point in time at which the purging of oxygen through the first cell is suppressed by the first cell control unit, and the second slope corresponds to that of the change in cell current value at a time or period subsequent to that of the first slope.

The inventors of the present invention have found that immediately after the first cell suppresses oxygen discharge, the slope of the change in cell current value fluctuates significantly only under the influence of cell temperature, with cell deterioration having little effect on the slope. On the other hand, it was found that the slope fluctuates later under both the influence of deterioration and temperature. Therefore, in the control device with the above configuration, the degree of deterioration of the exhaust gas sensor is calculated based on two slopes, that is, a first slope which is the slope of the change in cell current value at a predetermined time or period immediately after the oxygen purge is suppressed by the first cell, and a second slope, which corresponds to the slope of the change in cell current value at a time or period after the first slope. This makes it possible to accurately calculate the degree of deterioration while eliminating the influence of the temperature of the second cell on the slope of the change in cell current value.

The present disclosure thus provides a control device capable of accurately calculating the rate of deterioration of an exhaust gas sensor.

character list

• 1 12 is a diagram schematically showing the configuration of a vehicle exhaust system provided with a control device and an exhaust gas sensor according to a first embodiment;
• 2 12 is a diagram schematically showing a configuration of a control device and an exhaust gas sensor according to the first embodiment;
• 3 shows a sectional view through III-III in 2 ;
• 4 Fig. 14 is an illustration for explaining measurement principles of an exhaust gas sensor;
• 5 (A) , (B) and (C) are graphs showing an example of a variation of a pump cell voltage, etc. with the passage of time;
• 6 Fig. 14 is a graph showing changes in sensor cell current over time;
• 7 Fig. 14 is a graph showing changes in sensor cell current over time;
• 8th Fig. 12 is a map showing an example of a correspondence relationship among a first index, a second index and calculated values of the degree of deterioration;
• 9 12 is a flowchart showing a flow of processing executed by the control device according to the first embodiment;
• 10 Fig. 14 is a graph showing changes in sensor cell current over time;
• 11 Fig. 14 is a diagram showing a correspondence relationship between values of the second index and the degree of deterioration;
• 12 Fig. 14 is a diagram showing a correspondence relationship between the first index and a correction coefficient; and
• 13 14 is a flowchart showing a flow of processing executed by a control device according to a second embodiment.

Description of the embodiments

Embodiments are described below with reference to the attached figures. In order to facilitate the understanding of the description, components that are identical in the respective figures are given the same references in each figure as much as possible numbers, with no duplicate description.

A first embodiment will be described. The control device 10 according to the present embodiment is configured as a device for controlling an exhaust gas sensor 100 . 1 FIG. 12 schematically shows the exhaust system of a vehicle provided with an exhaust gas sensor 100. FIG. As shown in the figure, an exhaust pipe 20 is connected to the internal combustion engine EG to lead the exhaust gas discharged from the internal combustion engine EG to the outside. The exhaust gas sensor 100 is for measuring the concentration of nitrogen oxides contained in the exhaust gas and is provided at an intermediate position in the exhaust pipe 20 . In the present embodiment, the component to be detected by the exhaust gas sensor 100 is nitrogen oxides as described above, but it is equally conceivable that the component is other than nitrogen oxides, such as ammonia.

In addition to the exhaust gas sensor 100, an oxidation catalyst converter 22 is provided in the middle of the exhaust pipe 20 to remove pollutants contained in the exhaust gas. In the oxidation catalyst converter 22, an oxidation catalyst (not shown in the figure) is accommodated. The oxidation catalyst consists mainly of a ceramic support, an oxide mixture containing alumina, ceria and zirconia, and a noble metal catalyst such as platinum, palladium or rhodium. The oxidation catalytic converter oxidizes and purifies hydrocarbons, carbon monoxide, nitrogen oxides and the like contained in the exhaust gas. In addition to the oxidation catalyst mentioned above, the oxidation catalyst converter 22 may include a particulate filter for capturing fine particulates.

The exhaust gas sensor 100, which corresponds to the control target of the control device 10, is provided in the exhaust pipe 20 at a position downstream of the oxidation catalyst converter 22, and measures the concentration of nitrogen oxides in the exhaust gas at this position.

The concentration of nitrogen oxides measured by exhaust gas sensor 100 is transmitted to control device 10 . The control device 10 performs various controls on the internal combustion engine EG based on the measured nitrogen oxide concentration. The control processes include, for example, adjusting the ignition timing of the internal combustion engine EG.

The control device 10 according to the present embodiment is configured to control the internal combustion engine EG in addition to controlling the exhaust gas sensor 100 as described below. That is, the control device 10 also serves as a known engine ECU. However, it is also possible that the control device 10 is configured as a dedicated device for controlling the exhaust gas sensor 100, that is, as a separate control device from the engine ECU. In this case, the control device 10 would contribute to the control of the internal combustion engine EG performed by the engine ECU by communicating with the engine ECU.

A specific configuration of the exhaust gas sensor 100 is described with reference to FIG 2 until 4 described. 2 1 schematically shows a cross section of a part of the exhaust gas sensor 100, which is arranged within the exhaust pipe 20. FIG. The left side in 2 , that is, the side on which the diffusion resistor 140 is arranged corresponds to the tip of the exhaust gas sensor 100, which protrudes into the interior of the exhaust pipe 20.

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

The solid electrolyte 110 corresponds to a plate-shaped member made of a solid electrolyte material such as zirconia. The solid electrolyte 110 becomes conductive to oxygen ions when it is in an active state by being above a predetermined temperature. A pump cell 150, a sensor cell 160 and a monitor cell 170, which will be described later, are formed in the solid electrolyte 110, respectively.

Portions of the main bodies 120 and 130 both correspond to plate-shaped members made of an insulating material containing alumina as a main component. The main bodies 120 and 130 are arranged to sandwich the solid electrolyte 110 therebetween. From the sides of the main body 120, part of the surface of the side that lies on the solid electrolyte 110 is recessed toward the opposite side. Consequently, a space is formed between the main body 120 and the solid electrolyte 110 . This space corresponds to an area into which the exhaust gas to be measured is introduced. This space is also referred to below as the "measuring chamber 121".

A diffusion resistor 140 is arranged at the tip of exhaust gas sensor 100 . The measuring chamber 121 opens via the diffusion resistance faced 140 to the outside (that is, to the inside of the exhaust pipe 20). The diffusion resistance 140 consists of a ceramic material, such as. B. alumina in which pores are formed.

The flow rate of the exhaust gas sucked into the measuring chamber 121 is regulated by the action of the diffusion resistance 140 . The exhaust gas that has flowed into the measurement chamber 121 through the diffusion resistance 140 is supplied to a pump cell 150, a sensor cell 160, and a monitor cell 170, which will be described later.

From the sides of the main body 130 located on the other side of the solid electrolyte 110 , a part of the surface of the side on the solid electrolyte 110 is recessed toward the opposite side of the main body 130 . Consequently, a space is also formed between the main body 130 and the solid electrolyte 110 . Part of this space (not shown in the figure) is open to the atmosphere outside the duct 20. In other words, atmospheric air is introduced into this space. This space is also referred to below as the “atmosphere chamber 131”.

A pumping electrode 111, a sensor electrode 112 and a monitor electrode 113 are respectively formed on the surface of the body of the solid electrolyte 110 in contact with the measuring chamber 121. FIG. Of these, the pumping electrode 111 is formed on the body of the solid electrolyte 110 at the position closest to the diffusion resistance 140 . The sensor electrode 112 and the monitor electrode 113 are formed on the body of the solid electrolyte 110 at positions opposite to the diffusion resistor 140 with the pumping electrode 111 sandwiched between them and the diffusion resistor 140 . The sensor electrode 112 and the monitor electrode 113 are in 2 arranged along the depth direction of the paper surface (see 3 ).

The pumping electrode 111 and the monitor electrode 113 are formed of Pt-Au alloy (platinum-gold alloy). Both electrodes are active against oxygen and inactive against 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 active against both oxygen and nitrogen oxides.

On the surface of the body of the solid electrolyte 110 which is in contact with the atmosphere chamber 131, a common electrode 114 is formed. The common electrode 114 is formed in a region which overlaps with all of the pumping electrode 111, the sensor electrode 112 and the monitor electrode 113 when viewed along a direction perpendicular to the body of the solid electrolyte 110 as shown in FIG 3 to see. The common electrode 114 is formed of a material containing Pt (platinum) as a main component.

When a voltage is applied between the pumping electrode 111 and the common electrode 114 while the body of the solid electrolyte 110 is in a high-temperature active state, oxygen contained in the exhaust gas of the measurement chamber 121 is decomposed into oxygen ions at the pumping electrode 111 . The oxygen ions permeate the body of the solid electrolyte 110 and consequently oxygen is discharged from the measurement chamber 121 into the atmosphere chamber 131 . That is, the parts of the pumping electrode 111, the common electrode 114 and the solid electrolyte 110 sandwiched between the pumping electrode 111 and the common electrode 114 form a portion serving as a pumping cell 150 to discharge oxygen from the exhaust gas. The pump cell 150 corresponds to “first cell” in the present embodiment.

When the oxygen is purged as described above, a current flows between the pumping electrode 111 and the common electrode 114. The value of the current is proportional to the rate at which the oxygen is purged from the exhaust gas and is proportional to the oxygen concentration of the exhaust gas. Thus, it can be said that the pumping cell 150 delivers a current whose magnitude corresponds to the oxygen concentration of the exhaust gas. Based on the value of this current, the control device 10 obtains the oxygen concentration of the exhaust gas residing in the measurement chamber 121 .

The voltage applied between the pumping electrode 111 and the common electrode 114 is hereinafter referred to as “pump cell voltage”. Furthermore, 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” hereinafter.

When a voltage is applied between the sensor electrode 112 and the common electrode 114 while the solid electrolyte 110 is in a high-temperature active state, oxygen and nitrogen oxides contained in the exhaust gas of the measuring chamber 121 are decomposed at the electrode 112 into oxygen ions, which pass through the solid electrolyte 110. Consequently, flows between the sensor electrode 112 and the common electrode 114 a current which corresponds to the concentrations of oxygen and nitrogen oxides in the vicinity of the sensor electrode 112 . The value of this current is obtained from the control device 10 .

That is, the parts 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 form a part serving as a sensor cell 160 which generates a current upon application of a voltage emits, the magnitude of the current corresponding to the concentration of residual oxygen and nitrogen oxides in the exhaust gas. The exhaust gas whose concentration of nitrogen oxides and residual oxygen is measured by the sensor cell 160 corresponds to the gas which remains in the pump cell 150 after oxygen has been discharged. The sensor cell 160 corresponds to the “second cell” of the present embodiment.

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

When a voltage is applied between the monitor electrode 113 and the common electrode 114 while the solid electrolyte 110 is in a high-temperature active state, the oxygen contained in the exhaust gas of the measuring chamber 121 is decomposed at the monitor electrode 113 and converted into oxygen ions, which are separated by the solid electrolyte 110 go through. Consequently, a current having a value corresponding to the oxygen concentration in the vicinity of the monitor electrode 113 flows between the monitor electrode 113 and the common electrode 114 .

That is, the parts 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 form a part serving as a monitor cell 170. FIG. The monitor cell 170 outputs a current whose magnitude corresponds to the concentration of residual oxygen in the exhaust gas. The exhaust gas whose residual oxygen concentration is measured by the monitor cell 170 corresponds to the gas remaining in the pump cell 150 after oxygen has been purged.

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

In this way, a monitor cell 170 and a sensor cell 160 are arranged at positions on the downstream side of the pump cell 150 . The monitor cell 170 outputs a current whose magnitude corresponds to the concentration of oxygen remaining in the exhaust gas after oxygen has been purged by the pumping cell 150, and the sensor cell 160 outputs a current whose magnitude corresponds to the concentration of oxygen and nitrogen oxides which remain in the exhaust gas after the pumping cell 150 has purged oxygen.

The exhaust gas that has flowed into the measurement chamber 121 through the diffusion resistance 140 flows along the pump cell 150 and is then supplied to the sensor cell 160 and the monitor cell 170, respectively. This exhaust stream is in 4 represented schematically by a plurality of arrows. Arrow AR10 indicates the flow of oxygen discharged from pump cell 150 after flowing through diffusion resistance 140 into measurement chamber 121 . Most of the oxygen contained in the exhaust gas is removed in the pump cell 150, but it is difficult to remove the oxygen completely, and therefore a small amount of oxygen reaches each of the sensor cell 160 and the monitor cell 170. The arrow AR11 indicates the oxygen flow , which reaches the sensor cell 160, and the arrow AR12 indicates the oxygen flow, which reaches the monitor cell 170.

As described above, both the pumping electrode 111 and the monitor electrode 113 are inactive to nitrogen oxides. Therefore, the nitrogen oxides contained in the exhaust gas flowing into the measurement chamber 121 are not discharged from the pump cell 150 or the monitor cell 170 and reach the sensor electrode 112 of the sensor cell 160 as they are. Arrow AR20 indicates the flow of nitrogen oxides reaching sensor cell 160 in this manner.

As in 4 shown, both the nitrogen oxides (arrow AR20) and the residual oxygen (arrow AR11) reach the sensor cell 160. The size of the The sensor cell current therefore indicates the concentration of the 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 only the concentration of nitrogen oxides. With such an exhaust gas sensor 100, therefore, it is possible to suppress the influence of oxygen contained in the exhaust gas and accurately measure the concentration of nitrogen oxides.

As in 2 1, a heater 180 is embedded in the main body 130. As shown in FIG. The heater 180 generates heat inside the main body 130 and heats 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 heating output or the heating power of the heater 180 is adjusted by the control device 10 .

The configuration of the control device 10 is described with reference to FIG 2 described. The control device 10 is configured as a computer system including a CPU, ROM, RAM, and so on. Block elements representing respective functions of the control device 10 are composed of a concentration detection unit 11, an internal combustion engine control unit 12, a first cell control unit 13, a current value obtaining unit 14, a deterioration degree calculation unit 15, and a storage unit 16.

The concentration detection unit 11 detects the concentration of nitrogen oxides contained in the exhaust gas based on the values of the monitor cell current and the sensor cell current. As described above, the detection of the concentration of nitrogen oxides by the concentration detection unit 11 is performed based on the current value obtained by subtracting the value of the monitor cell current from that of the sensor cell current.

The internal combustion engine control unit 12 controls the internal combustion engine EG based on the concentration of nitrogen oxides detected by the concentration detection unit 11, and performs operations including adjusting fuel injection amounts of the internal combustion engine EG so that the concentration of nitrogen oxides detected by the exhaust gas sensor 100 approaches zero goes. As described above, the control device 10 may be configured as a dedicated device for controlling the exhaust gas sensor 100, that is, a control device other than the engine ECU. In this case, the internal combustion engine control unit 12 is configured as part of the engine ECU.

The first cell control unit 13 controls the discharge of oxygen by the pump cell 150, which corresponds to the first cell, by changing the pump cell voltage. When the concentration of nitrogen oxides 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 degree of deterioration is calculated as described below, the first cell control unit 13 lowers the pump cell voltage temporarily.

The current value obtaining unit 14 obtains the value of the current output from each cell, specifically, the values of the pump cell current, the sensor cell current, and the monitor cell current. In the normal state, the values of the sensor cell current etc. obtained by the current value obtaining unit 14 are used for calculating the concentration of nitrogen oxides. The values of the sensor cell current, etc. are also used to calculate the degree of degradation, as described below.

The degree of deterioration calculation unit 15 performs processing for calculating the degree of deterioration of the exhaust gas sensor 100 . The “degree of deterioration” corresponds to an index expressing the degree of deterioration of the exhaust gas sensor 100, and is calculated as a value that increases as the deterioration of the exhaust gas sensor 100 progresses. In this embodiment, the degree of deterioration is calculated as a value in the range of 0% to 100%. The degree of deterioration calculation unit 15 calculates the degree of deterioration based on the value of the sensor cell current, that is, the cell current value. A specific calculation method is described below.

The degree of deterioration calculated by the degree of deterioration calculation unit 15 is used, for example, as an index for determining whether the exhaust gas sensor 100 is normal. When the calculated degree of deterioration exceeds a predetermined value, a warning lamp provided on the vehicle may be turned on to motivate the occupants to take measures such as replacing parts. The degree of deterioration can also be used to correct the value of the concentration of nitrogen oxides obtained from the exhaust gas sensor 100 .

The memory unit 16 is a non-volatile memory device provided in the control device 10, in particular a flash memory. In the storage unit 16, the information necessary for the calculation of the degree of deterioration is stored in advance. Specific contents of the information are described below.

An outline of the processing performed to calculate the degree of deterioration will be described. 5 (A) Fig. 12 shows an example of the change in pump cell voltage with time when the degree of deterioration is calculated. 5 (B) shows an example of the change in pump cell current over time, and 5 (c) shows an example of the change in sensor cell current over time.

in the in 5 In the examples shown, the normal control, that is, the processing for measuring the concentration of nitrogen oxides, is temporarily stopped at time t0, and the processing for calculating the degree of deterioration is started. Specifically, the first cell control unit 13 changes the voltage applied to the pump cell 150 from the initial value VP1 to a lower value VP0 ( 5 (A) ). As a result, the discharge of oxygen by the pump cell 150 is temporarily suppressed from time t0.

At the same time, the pump cell current drops from the initial value IP0 to a lower value of IP1 ( 5 (B) ). This decrease in pump cell current means that the rate at which oxygen is passing through pump cell 150 and reaching sensor cell 160 has increased after time t0. As with the line L10 in 5 (c) shown, the sensor cell current therefore begins to increase from time t0 and eventually reaches a substantially constant value.

Subsequently, at time t4, the pump cell voltage is restored to the original value VP1 ( 5 (A) ) returned. As a result, the value of the pump cell current increases to IP2. IP2 may be equal to the initial value of IP0, but often differs slightly from IP0 due to changes in the engine state up to that point.

After time t4, the amount of oxygen reaching the sensor cell 160 decreases. Along with this, the value of the sensor cell current decreases after time t4 ( 5 (c) ). As described above, when the degree of deterioration is calculated, the discharge of oxygen by the pump cell 150 is temporarily suppressed. In 5 the period in which the discharge of oxygen by the pump cell 150 is temporarily suppressed is referred to as “TM0”.

The line L10 in 5 (c) 12 shows the change in sensor cell current with time in the normal state, that is, in which the sensor cell 160 is not deteriorated. On the other hand, the line L11 in 5 (c) the change in sensor cell current over time when the sensor cell 160 has degraded.

As can be seen by comparing lines L10 and L11, the slope of the change in cell current value after time t0 when the sensor cell 160 has deteriorated is smaller than that in the normal state. In addition, as the degree of deterioration of the sensor cell 160 increases, the slope of the change in the cell current value tends to decrease. Therefore, the degree of deterioration can be calculated based on the slope of the change in cell current value after time t0. For example, when the correspondence relationship between the slope of change in cell current value and the degree of deterioration is expressed as a map in advance, the degree of deterioration can be calculated based on the slope of change in cell current value with reference to the map.

However, the slope of the change in cell current value changes not only according to the degree of deterioration of the sensor cell 160 but also according to the temperature of the sensor cell 160. For example, the slope of the change in cell current value tends to be large when the temperature of the sensor cell 160 is higher than usual. In the example of 5 (c) As the temperature of the sensor cell 160 becomes high, the slope of the line L11 increases, so that the line L11 approaches the line L10. Therefore, when the sensor cell 160 has a high temperature, the slope of the change in cell current value becomes almost equal to that in the normal state even if the sensor cell 160 is actually deteriorated. Therefore, the degree of deterioration is calculated to be smaller than its actual value. Consequently, it may be wrongly judged that the exhaust gas sensor 100 has not deteriorated.

Therefore, in the control device 10 according to the present embodiment, the influence of the temperature of the sensor cell 160 on the calculated degree of deterioration by developing a method of calculating the degree of deterioration based on the value of the sensor cell current.

6 FIG. 12 is an enlarged diagram of the change in sensor cell current, showing part of FIG 5 (c) indicates. In the diagram of 6 an initial area surrounded by the broken line R1 and a subsequent area surrounded by the broken line R2 lie within the period TM0.

In the initial phase of the period TM0, within the area surrounded by the broken line R1, there is little difference between the line L10 expressing the change in cell current value during normal operation and the line L11 expressing the change at expresses a deterioration. That is, in the initial phase of the period TM0, the change over time in the cell current value is less susceptible to deterioration as described above.

As can be seen from the area surrounded by the broken line R2, after some time elapsed from the start of the period TM0, a large difference arises between the line L10, which expresses the change in cell current value during the normal operation, and the line L11 , which expresses the change with deterioration. That is, within the range surrounded by the broken line R2 and subsequent to the range surrounded by the broken line R1, the change with time of the sensor cell current is easily affected by deterioration as described above.

However, when the temperature of the sensor cell 160 changes, the slope of the change in the sensor cell current changes within the two areas surrounded by the broken line R1 and the broken line R2 under the influence of the temperature change.

In this way, the slope of the change in cell current immediately after the pump cell 150 suppresses oxygen discharge is hardly influenced by deterioration of the sensor cell 160 and is generally influenced only by the temperature of the sensor cell 160 . On the other hand, it is found that the slope thereafter is affected by both degradation and temperature. For this reason, the deterioration degree calculation unit 15 of the present embodiment obtains the slope of the change in the value of the sensor cell current at each of two time points at which the temperature of the sensor cell 160 has a different influence, respectively. The degree of deterioration is then calculated while removing the influence of the temperature of the sensor cell 160 as much as possible by using the two slopes obtained.

A specific method of calculating the degree of deterioration by the degree of deterioration calculation unit 15 will be described. 7 FIG. 14 is a diagram showing an example of the change in cell current value during the period TM0 as shown in FIG 5 (c) , indicates. In the time period TM0, the control device 10 acquires a plurality of cell current values, such as those in FIG 7 shown values "IS 11" and "IS3".

the inside 7 The value “IS3” shown is the value to which the cell current value converges after the oxygen exhaust is suppressed. In the present embodiment, the period TM0 is set so that the cell current value immediately before the end of the period TM0 at time t4 becomes IS3 defined as described above. The length of the period TM0 is preferably set in the range of 3 seconds to 10 seconds. That is, IS3 corresponds to the cell current value obtained at a time (time t4) after a predetermined period of time ranging from 3 to 10 seconds has elapsed since the pump cell 150 started to suppress oxygen discharge (at time t0).

the inside 7 The value IS 11 shown corresponds to a cell current value set as a predetermined proportion of IS3. In 7 the time when the cell current value reaches IS11 is shown as time t1. The point P1 corresponding to time t1 is also on the graph of 7 shown.

IS 12 and IS21, the in 7 shown are cell current values set as respective predetermined portions of IS3. In 7 the time when the cell current value IS reaches 12 and IS21 is shown as time t2, and the point P2 on the graph corresponding to time t2 is also shown.

the inside 7 The value IS22 shown corresponds to a cell current value set as a predetermined proportion of IS3. In 7 the time when the cell current value reaches IS22 is shown as time t3, and the point P3 on the graph corresponding to time t3 is also shown.

The time TM1 that elapses when the cell current value changes from IS 11 to IS 12 becomes Calculation of the first slope A1 is used, which is described below. In order to set such a length of time, the aforementioned “predetermined proportion” of IS3 set for each of IS11 and IS12 is preferably a value in the range of 0% to 50%. That is, it is preferable that each of IS11 and IS12 can be set as any value within the range of 0% to 50% of IS3 (where IS11 is smaller than IS12).

Likewise, the period TM2 from IS21 to IS22 of the cell current value corresponds to a period for calculating the second slope A2, which will be described later. In order to set such a length of time, the aforementioned “predetermined rate” set for each of IS21 and IS22 is preferably a value in the range of 30% to 100%. That is, it is preferable that each of IS21 and IS22 can be set as any value in the range of 30% to 100% of IS3 (where IS21 is smaller than IS22).

The period of time TM1 from time t1 to time t2, in the range included in 6 surrounded by the broken line R1 corresponds to a period in which the slope of the change in cell current value is not easily affected by deterioration. The slope of the change in cell current value in this period TM1 is calculated as the “first slope A1”. The first slope A1 corresponds to the slope of a straight line connecting points P1 and P2 and is calculated using the following equation: $$\text{A1}=\left(\text{IS12}-\text{IS11}\right)/\left(\text{t2}-\text{t1}\right)$$

The first slope A1 corresponds to the slope of the change in cell current value in the period TM1 after the first cell control unit 13 suppresses the oxygen discharge by the pumping cell 150 .

The period of time TM2 from time t2 to time t3, in the range shown in 6 surrounded by the broken line R2 corresponds to a period in which the slope of the change in cell current value is susceptible to deterioration of the sensor cell. The slope of the change in cell current value in this period TM2 is calculated as the “second slope A2”. The second slope A2 corresponds to the slope of a straight line connecting points P2 and P3 and is calculated using the following equation: $$\text{A2}=\left(\text{IS22}-\text{IS21}\right)/\left(\text{t3}-\text{t2}\right)$$

The second gradient A2 corresponds to the gradient of the change in the cell current value in the time period TM2 following the first gradient A1 described above.

The storage unit 16 included in the control device 10 has a map stored therein in advance, which is used for calculating the degree of deterioration based on the first slope A1 and the second slope A2 in combination. 8th shows an example of such a map.

Shown along the horizontal axis of the graph are “first index” values obtained by dividing values of the first slope A1 by a reference value of A1. The “reference value of A1” corresponds to a value of the first slope A1 obtained when the exhaust gas sensor 100 has not deteriorated and the sensor cell 160 has a predetermined reference temperature. That is, the reference value of A1 corresponds to a value of the first slope A1 obtained when the exhaust gas sensor 100 is normal and the sensor cell 160 is normal in temperature.

When the temperature of the sensor cell 160 becomes higher than usual, the value of the first slope A1 becomes large, so that the first index, which is the horizontal axis in 8th corresponds to becomes greater than 1.0. On the other hand, when the temperature of the sensor cell 160 becomes lower than usual, the value of the first slope A1 becomes smaller, so that the first index becomes smaller than 1.0. Since the first index defined as described above changes its value based on the value of the first slope A1, it can be said to correspond to an index based on the value of the first slope A1.

The greater the degree of suppression of oxygen discharge by the pump cell 150 in the period TM0, that is, the greater the magnitude of ΔIP in 5 (B) is, the larger both the "first gradient A1" and the "reference value of A1" become. Therefore, the correspondence relationship between ΔIP and the reference value of A1 is also stored in advance in the storage unit 16 of the control device 10. In calculating the above first index, the control device 10 uses the “reference value of A1”, which corresponds to the measured ΔIP. In this way, the calculated first index is prevented from fluctuating according to the magnitude of ΔIP.

Along the vertical axis of the chart in 8th Illustrated are "second index" values obtained by dividing values of the second slope A1 by a reference value of A2 will. The “reference value of A2” corresponds to a value of the second slope A2 obtained when the exhaust gas sensor 100 has not deteriorated and the sensor cell 160 has a predetermined reference temperature. That is, the reference value of A2 corresponds to the value of the second slope A2 obtained when the exhaust gas sensor 100 is normal and the sensor cell 160 is at a normal temperature.

When the temperature of the sensor cell 160 becomes higher than usual or when the sensor cell 160 deteriorates, the value of the second slope A2 becomes large, and thus the second index whose values along the vertical axis are in 8th are shown are greater than 1.0. When the temperature of the sensor cell 160 is lower than usual and no deterioration has occurred in the sensor cell 160, the value of the second slope A2 becomes smaller, so that the second index becomes smaller than 1.0. Since the second index defined as described above changes its value based on the value of the second slope A2, it can be said to correspond to an index based on the value of the second slope A2.

The greater the degree of suppression of oxygen discharge by the pump cell 150 in the period TM0, that is, the greater the magnitude of ΔIP in 5 (B) is, the larger the “second slope A2” and the “reference value of A2” become. Therefore, the correspondence relationship between ΔIP and the reference value of A2 is also stored in the storage unit 16 of the control device 10 in advance. In the calculation of the second index described above, the control device 10 uses the “reference value of A2” corresponding to the measured ΔIP. This prevents the calculated second index from fluctuating according to the magnitude of ΔIP.

In the present embodiment, areas expressing respective combinations of the first index (horizontal axis) and the second index (vertical axis) are divided into a set of 4 × 4 areas as shown in FIG 8th shown so that there are a total of 16 areas. A corresponding calculated value of the degree of deterioration is set for each of these areas. in the in 8th In the area labeled “D0”, the calculated value of the degree of deterioration is set to 0%. In the area labeled “D1”, the calculated value of the degree of deterioration is set to 20%. In the area labeled “D2”, the calculated value of the degree of deterioration is set to 50%. In the area labeled “D4”, the calculated value of the degree of deterioration is set to 80%.

For example, if the temperature of the sensor cell 160 is lower than usual, the first index becomes less than 1.0. At this time, if the sensor cell 160 has not deteriorated, the second index is also reduced. For example, when both the first index and the second index are approximately 0.3, this corresponds to the area D0, and thus the degree of deterioration is calculated as 0%. The same is true when the temperature of the sensor cell 160 is higher than usual and both the first index and the second index are approximately 1.7.

On the other hand, when the temperature of the sensor cell is higher than usual and the sensor cell 160 has deteriorated, the first index becomes larger than 1.0 while the second index becomes smaller than that of a normal sensor cell. Consequently, the range specified by the first index and the second index is in 8th below the area D0. This is because although the first index is less prone to deterioration and is only affected by temperature, the second index is affected by both deterioration and temperature.

Further, when the pump cell 150 has deteriorated, the amount of oxygen reaching the downstream side increases in the period TM0. As a result, the second slope A2 becomes larger than in the normal state, so that the range indicated by the first subscript and the second subscript is in 8th is above the range D0. In this case as well, the degree of deterioration is calculated as a value greater than 0% as in the case where deterioration has occurred in the sensor cell 160 .

The subdivision arrangement in 8th is presented only as an example, and the areas indicated by the first index and the second index can be divided into smaller areas, each of the divided areas being assigned a value of a degree of deterioration. In this case everyone would 8th The area D0 shown in FIG. Likewise, each area D1 could be further subdivided, with the subdivided areas being assigned, for example, respective values of a degree of deterioration in the range of 10% to 30%, each area D2 could be further subdivided, with the subdivided areas being assigned, for example, respective values of a degree of deterioration in the range from 30% to 60% can be assigned, and each area D3 could be further divided, the divided areas having, for example, respective values of a degree of deterioration in the range of 60% to 100% are assigned.

In this way, the degree of deterioration calculation unit 15 of the present embodiment is configured to calculate the degree of deterioration based on both a first slope A1 and a second slope A2, where A1 corresponds to the slope of the change in cell current value within a prescribed period TM1 and A2 corresponds to the slope of the change in cell current value within a period of time TM2 following the first slope A1. This enables the degree of deterioration of the exhaust gas sensor 100 to be calculated accurately, while the influence of the temperature of the sensor cell 160 is eliminated.

The length of time TM1 used to calculate the first slope A1 and the length of time TM2 used to calculate the second slope A2 can be set as lengths of time that are continuous with each other as in the present embodiment, but it is the same possible to set these as durations having some degree of mutual overlap. For example, time period TM2 may begin before time period TM1 ends. In this case, in the example of 7 IS21 must be set as a smaller value than IS12.

Alternatively, time period TM2 may begin after some time has elapsed since the end of time period TM1. In this case, in the example of 7 IS21 must be set as a larger value than IS 12.

In the present embodiment, both the first gradient A1 and the second gradient A2 are calculated as gradients within a predetermined period of time. However, it would be equally possible for at least one of the first gradient A1 and the second gradient A2 to be calculated as a gradient at a predetermined point in time. For example, a slope at a predetermined time corresponds to a differential coefficient at a specific time in a graph of the variation in cell current value. That is, the first slope A1 and/or the second slope A2 may be calculated with the length of the above “predetermined period of time” made as close to zero as possible.

The degree of deterioration calculation unit 15 of the present embodiment is configured to calculate the degree of deterioration using a correspondence relationship between the first index based on the value of the first slope A1, the second index based on the value of the second slope A2, and the calculated degree of deterioration. That is, the degree of deterioration is determined with reference to the map of FIG 8th calculated, which is stored in the memory unit 16. Thus, the degree of deterioration can be easily and accurately calculated according to the temperature of the sensor cell 160 . It should be noted that such a correspondence relation may be stored as a mathematical equation instead of a map as well.

As mentioned above, the pumping electrode 111 of the pumping cell 150 is made of a Pt-Au alloy containing gold. Since gold has a relatively low melting point, as the temperature of the pump cell 150 increases, part of the gold may evaporate and adhere to the sensor electrode 112 of the sensor cell 160 on the downstream side. When such Au poisoning occurs, the sensor cell 160 deteriorates and the slope of the cell current change becomes small.

Since Au poisoning is particularly likely to occur in an exhaust gas sensor 100 having such a configuration that the electrode of the sensor cell 160 contains gold, resulting in deterioration of the sensor cell 160, the application of the deterioration degree calculation method using the deterioration degrees described above is necessary -Calculation unit 15 particularly advantageous. In this case, the deterioration degree calculation unit 15 can accurately calculate the deterioration degree even if deterioration caused by aggregation of metal of the sensor electrode 112 occurs due to the effects of temperature.

In the exhaust gas sensor 100 according to the present embodiment, the pump electrode 111 of the pump cell 150 and the sensor electrode 112 of the sensor cell 160 are arranged within the same measurement chamber 121 . That is, these are arranged in the same room. Here, "arranged in the same space" means that there is no structure, such as a porous body, that separates the space where the pumping electrode 111 is arranged and the space where the sensor electrode 112 is arranged. forms.

In the exhaust gas sensor 100 having such a configuration, a poisonous substance such as Au vaporized in the pump cell 150 can easily reach the electrode of the sensor cell 160 located downstream of the pump cell 150, and this tends to deteriorate the sensor cell 160 lead. Hence the Application of the deterioration degree calculation method using the deterioration degree calculation unit 15 described above is particularly advantageous.

A specific flow of processing executed by the control device 10 for calculating the degree of deterioration as described above will be explained with reference to FIG 9 described. the inside 9 The flow of processing illustrated is repeatedly executed by the control device 10 in a predetermined control cycle.

In the first step S01, a decision is made as to whether the ignition switch of the vehicle is on or off. When the ignition switch is turned on, the in 9 The flow of processing shown above ends without calculating the degree of deterioration.

When the ignition switch is turned on and exhaust gas is exhausted from the internal combustion engine EG, the oxygen concentration around the exhaust gas sensor 100 may fluctuate. Under such circumstances, the slope of the change in cell current value changes due to factors other than the degree of deterioration and the temperature of the sensor cell 160. Therefore, it will be difficult to accurately calculate the degree of deterioration based on the slope of change in the cell current value. For this reason, in the present embodiment, the calculation of the degree of deterioration is prohibited while the ignition switch is turned on.

When it is judged in step S01 that the ignition switch is off, the processing proceeds to step S02 to judge whether predetermined environmental conditions are satisfied. The "environmental conditions" are set in advance as conditions required for the calculation of the degree of deterioration. In the present embodiment, these environmental conditions are that the value of the oxygen concentration around the exhaust gas sensor 100 is within a predetermined range and that the magnitude of the fluctuation range of the oxygen concentration is not more than a prescribed value. The “oxygen concentration around the exhaust gas sensor 100” can be obtained based on the value of the pump cell current.

If these environmental conditions are not satisfied, it is difficult to accurately calculate the degree of deterioration based on the slope of the change in cell current value. Therefore, in this case, the in 9 The flow of processing shown ends without calculating the degree of deterioration. If the environmental conditions are satisfied, the processing proceeds to step S03.

In step S<b>03 , processing for obtaining the value of the pump cell current is performed by the current value obtaining unit 14 . The value of the pump cell current obtained here corresponds to the value immediately before the pump cell 150 starts to suppress the oxygen discharge, that is, the value IP0 in 5 (B) .

In step S<b>04 subsequent to step S<b>03 , the first cell control unit 13 starts to suppress the pump cell 150 from exhausting oxygen. At this time, as described above, the pump cell voltage is changed from the original value VP1 to a lower value VP0. Thereby, the time period TM0 starts, and thereafter the current value obtaining unit 14 samples the waveform of the variation in the sensor cell current and the waveform of the variation in the pump cell current at respective prescribed periods.

This sampling is performed throughout the period from time t0 to time t5 as shown in FIG 5 (B) shown. Time t5 is preset as a time when the value of the pump cell current is stabilized after the period TM0 ends and the value of the pump cell voltage is returned to VP1. In the present embodiment, the length of time period TM0 from time t0 to time t4 is set in the range of 3 seconds to 10 seconds, and the length of time period from time t0 to time t5 is in the range of 15 Seconds set to 30 seconds. That is, in the present embodiment, the sampling of the waveforms of the pump cell current and the sense cell current is continued beyond the period TM0.

After the processing has proceeded to step S04 and the above sampling period has elapsed, the sampling is stopped and the processing proceeds to step S05. In step S05, the in 5 (B) shown values of IP1 and IP2 are obtained from the waveform of the sampled pump cell current variation. IP1 corresponds to the value of the pump cell current just before the end of the period TM0.

In addition, the respective values of IS11, IS 12, IS21, IS22 and IS3 contained in 7 are obtained in step S05 from the waveform of the change in the sampled sensor cell current. The meaning of each of these stats and the time at which each stat is acquired is how above with reference to 7 described.

In step S06 following step S05, the process for calculating the in 5 (B) shown ΔIP performed. In the 5 (B) The dashed straight line DL1 shown shows the change in the pump cell current if the current were to change with a constant gradient from IP0 to IP2 in the period from time t0 to time t5.

The straight line expresses, so to speak, the change in the pump cell current if the value of the pump cell voltage were kept constant at VP1. ΔIP, which corresponds to the variation amount of the pump cell current, is calculated as the difference between the value of the pump cell current expressed by the broken line DL1 defined above and the value of the pump cell current immediately before time t4 (that is, the value IP1). This value ΔIP corresponds to the purge amount of oxygen by the pump cell 150, which is suppressed. It can also be said that ΔIP corresponds to the increase amount of oxygen reaching the sensor cell 160 at the beginning of the period TM0.

In step S07 following step S06, processing is performed to calculate the reference values of A1 and A2, respectively. As described above, the “reference value of A1” corresponds to a value of the first slope A1 set in association with the measured value of ΔIP and obtained at a time when the exhaust gas sensor 100 has not deteriorated and the sensor cell 160 has has predetermined reference temperature. Likewise, the “reference value of A2” corresponds to a value of the second slope A2 that is set in association with the measured value of ΔIP and that is obtained when the exhaust gas sensor 100 has not deteriorated and the sensor cell 160 has a predetermined reference temperature.

$$\text{A2}=\left(\text{IS22}-\text{IS21}\right)/\left(\text{t3}-\text{t2}\right).$$

In step S08 following step S07, the respective values of the first slope A1 and the second slope A2 are calculated based on the values calculated in step S05. As described above, these values are calculated using the following equations: $$\text{A1}=\left(\text{IS12}-\text{IS11}\right)/\left(\text{t2}-\text{t1}\right)$$

$$\text{A2}=\left(\text{IS22}-\text{IS21}\right)/\left(\text{t3}-\text{t2}\right).$$

The first index and the second index are calculated in step S09 subsequent to step S08. The first index is calculated by dividing the first slope A1 by the reference value of A1. The second index is calculated by dividing the second slope A2 by the reference value of A2.

In step S10 subsequent to step S09, a process of calculating the degree of deterioration with reference to the first index, the second index and the in 8th shown map, which are calculated as described above. The degree of deterioration is thereby calculated accurately with the influence of the temperature of the sensor cell 160 being eliminated.

A second embodiment is described below. The control device according to the second embodiment differs from the first embodiment only in the method of calculating the degree of deterioration by the degree of deterioration calculation unit 15. The following will mainly describe points that differ from the first embodiment, with the points that are common to are the same as in the first embodiment are omitted where appropriate.

10 FIG. 12 shows an example of a change in the cell current value during the period TM10. The line L20 in 10 corresponds to a graph showing an example of the change in cell current value actually obtained in a state where the temperature of the sensor cell 160 was relatively high. The line L21 from 10 corresponds to a hypothetical graph of the change in cell current value that would be obtained when the temperature of the sensor cell 160 is at a normal temperature if the degree of deterioration of the sensor cell 160 is the same as in the case of the line L20. That is, the line L21 corresponds to a graph showing the change in a virtual cell current value that would be obtained if the influence of the temperature of the sensor cell 160 were eliminated and only the influence of the deterioration of the sensor cell 160 was applied.

Also in the example of 10 the first slope A1 and the second slope A2 of the line L20 defined in the same manner as described above can be calculated as described above. The first slope A1 and the second slope A2 of the line L21 can be calculated in a similar way. The first slope A1 and the second slope A2 calculated in the case of the line L21 are hereinafter referred to as the “first slope A1''' and the "second slope A2''', respectively.

The second slope A2' corresponds to the slope of the change in cell current value when the effects of the temperature of the sensor cell 160 are excluded, so that only the effects of the deterioration of the sensor cell 160 remain. Therefore, the degree of deterioration can be accurately calculated based on the second slope A2' if the second slope A2' can be estimated by any method.

In the present embodiment, the second slope A2' is first calculated by a method described below, and the degree of deterioration is then calculated based on the second slope A2' using the in 11 illustrated map or the characteristic calculated. The values along the horizontal axis of 11 are obtained by dividing the value of the second slope A2' by the “reference value A2”, that is, the second index described above. The values along the vertical axis of 11 are degrees of deterioration corresponding to the respective values of the second index. The correspondence relationship between the second index and the deterioration degree values is expressed in advance as a map, which is stored in the storage unit 16 of the control device 10 . It would be equally possible to express the correspondence relation as a mathematical equation instead of a map.

As described above, the slope of the change in the cell current value immediately after the start of the period TM10 is not significantly affected by deterioration of the sensor cell 160 and changes substantially only depending on the temperature. Therefore, the first slope A1' of the line L21 is substantially identical to the slope obtained when the exhaust gas sensor 100 has not deteriorated and the sensor cell 160 has a predetermined reference temperature, that is, substantially identical to the "reference value of A1 “.

As described above, the reference value of A1 can be calculated based on the measured value of ΔIP in 5 be calculated. Therefore, the result of dividing the actually measured value of the first slope A1 by the "reference value of A1" calculated as described above can be referred to as an index expressing the extent to which the graph shown by the line L20 changes or the curve of the cell current value would change to the graph shown by the line L21 due to the temperature influence, as indicated by the arrow AR1 in FIG 10 specified. That is, the arrow AR1 can be referred to as an index showing the degree of change of the graph.

In the present embodiment, a correction coefficient is calculated based on the value obtained by dividing the value of the first slope A1 by the "reference value of A1", and this correction coefficient is multiplied by the second slope A2 to obtain the second slope A2' to calculate.

The value obtained by dividing the value of the first slope A1 by the "reference value of A1" corresponds to the first index described above and expresses the extent to which the line L21 is changed to become the line L20, as indicated by the arrow AR1 in 10 specified. Further, by multiplying the second slope A2 of the line L20 by the correction coefficient described above, the second slope A2 is changed to the second slope A2' as indicated by the arrow AR2 in FIG 10 specified.

As in 12 shown, there is a fixed correspondence relation between the value (arrow AR1 in 10 ), which is obtained by dividing the value of the first slope A1 by the "Reference value of A1", and the value (arrow AR2 in 10 ) of the above correction coefficient. Such a correspondence relationship is stored in advance as a characteristic map in the storage unit 16 of the control device 10 . It would be equally possible to store the correspondence relation as a mathematical equation instead of a map.

In summary, according to the present embodiment, the deterioration degree calculation unit 15 calculates the first slope A1 and the second slope A2, respectively, based on an obtained graph of cell current values. Next, the value of the first slope A1 is divided by the “reference value of A1”, and a correction coefficient is calculated using the division result and the map of 12 calculated. The second slope A2' is then calculated by multiplying the second slope A2 calculated as described above by the correction coefficient. Finally, the degree of deterioration is calculated using the second slope A2' and the map of FIG 11 calculated.

In this way, according to the present embodiment, the degree of deterioration calculation unit 15 is configured to calculate the correction coefficient based on the first slope A1, correct the second slope A2 using the calculated correction coefficient, and calculate the degree of deterioration based on the corrected second slope A2 (that is, based on the second slope A2'). Also in this embodiment, the degree of deterioration of the exhaust gas sensor 100 can be accurately calculated while whereby the effects of the temperature of the sensor cell 160 are eliminated.

A specific flow of processing executed by the control device 10 to realize the above-described deterioration degree calculation will be described with reference to FIG 13 described. In the 13 The processing sequence shown is executed by the control device 10 instead of the one shown in FIG 9 processing sequence shown is executed every time a predetermined control period elapses. The processes from step S01 to step S08 in 13 are identical to the corresponding processes in 9 .

After the respective values of the first slope A1 and the second slope A2 are calculated in step S08, the process proceeds to step S21. In step S21, the correction coefficient is calculated based on the first slope A1 calculated in step S08 and the “reference value of A1” using the map of FIG 12 calculated.

In step S22 following step S21, the second slope A2' is calculated by multiplying the correction coefficient calculated in step S21 by the second slope A2 calculated in step S08.

In step S23 following step S22, the degree of deterioration is calculated based on the second slope A2' calculated as described above and the "reference value of A2" using the map of FIG 11 calculated. The degree of deterioration is thereby accurately calculated while eliminating the effects of the temperature of the sensor cell 160 .

The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. The scope of the present disclosure includes these specific examples, with corresponding design changes made by those skilled in the art given the features of the present disclosure. Each element included in each of the above-mentioned specific examples, its arrangement, conditions, shape, etc. are not limited to those shown and can be changed as appropriate. The combinations of the elements included in each of the above-mentioned specific examples can be changed as appropriate unless technical inconsistencies arise.

The control devices and control methods described in the present disclosure may be implemented by one or more dedicated computers provided by configuring a processor that includes one or more dedicated hardware logic circuits programmed to perform one or more functions implemented by a computer program. The control devices and control methods described in the present disclosure may be implemented by one or more dedicated computers provided by configuring a processor that includes one or more dedicated hardware logic circuits. The control devices and control methods described in the present disclosure may be implemented by one or more dedicated computers provided by configuring a combination of a processor and memory programmed to perform one or more functions, and a processor that performs one or more Includes hardware logic circuits. The computer program may be stored on a computer-readable non-transitory recording medium as instructions to be executed by the computer. The dedicated hardware logic circuits and the hardware logic circuits can be realized by digital circuits including a plurality of logic circuits or by analog circuits.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• JP 2020031804 [0001]
• JP 2017116438 A [0006]

Claims (5)

Control device (10) of an exhaust gas sensor (100), wherein the exhaust gas sensor includes a first cell (150) which removes oxygen from exhaust gas generated by an internal combustion engine (EG), and a second cell (160) which detects a current having a magnitude corresponding to a concentration of oxygen remaining in the exhaust gas after removing outputs oxygen through the first cell, has the control device has: a first cell control unit (13) which controls the purging of oxygen through the first cell, a current value obtaining unit (14) for obtaining a cell current value corresponding to a value of a current output from the second cell, and a degree of deterioration calculation unit (15) for calculating a degree of deterioration corresponding to an index indicative of a degree of deterioration of the exhaust gas sensor, the degree of deterioration being calculated based on the cell current value; whereby the deterioration degree calculation unit is configured to calculate the deterioration degree based on either of the following: a first slope which corresponds to the slope of the change in the cell current value at a point of time or within a period of time after the first cell is suppressed from purging oxygen by the first cell control unit; and a second slope, which corresponds to the slope of the change in the cell current value at a point in time or within a period of time after the first slope. control device claim 1 , further comprising: a storage unit (16) storing a correspondence relationship between a first index, a second index and calculated values of the degree of deterioration, the first index being based on the value of the first slope and the second index being based on the value of the second slope ; wherein the deterioration degree calculation unit calculates the deterioration degree based on the correspondence relationship. control device claim 1 , wherein the deterioration degree calculation unit is configured to: calculate a correction coefficient based on the first slope, correct the second slope using the calculated correction coefficient, and calculate the deterioration degree based on the corrected second slope. Control device according to one of Claims 1 until 3 , where the electrode of the first cell contains gold. Control device according to one of Claims 1 until 4 wherein the exhaust gas sensor includes a first cell electrode and a second cell electrode respectively disposed within a common space.

Images