WO2018221528A1 - Gas sensor control device - Google Patents

Abstract

A gas sensor comprises: a pump cell which, by means of the application of a voltage, adjusts the oxygen concentration in a gas being detected that has been introduced into a gas chamber; a sensor cell which detects the concentration of a specific gas component in the gas chamber after the oxygen concentration has been adjusted by the pump cell; and a monitor cell which detects the residual oxygen concentration in the gas chamber. Each SCU 31-33 is provided with: a pump cell control unit (M11) which causes the pump cell to adjust the residual oxygen concentration in such a way as to control the output from the monitor cell to a target value; an acquiring unit (M12) which acquires an output from the sensor cell, in a state in which the residual oxygen concentration has been adjusted by the pump cell control unit; and a degradation determining unit (M13) which determines the state of degradation of the monitor cell on the basis of the output from the sensor cell, acquired by the acquiring unit.

Description

Gas sensor control device Cross-reference of related applications

This application is based on Japanese Patent Application No. 2017-107026 filed on May 30, 2017, the contents of which are incorporated herein by reference.

This disclosure relates to a gas sensor control device.

2. Description of the Related Art A NOx sensor that detects NOx (nitrogen oxide) concentration is known as a gas sensor that detects the concentration of a specific gas component in a gas to be detected such as exhaust gas from an internal combustion engine. The NOx sensor has a three-cell structure composed of a pump cell, a monitor cell, and a sensor cell as described in Patent Document 1, for example, and the pump cell discharges or pumps out oxygen in the exhaust gas introduced into the gas chamber. The monitor cell detects the residual oxygen concentration in the gas chamber after passing through the pump cell, and the sensor cell detects the NOx concentration from the gas after passing through the pump cell.

When the NOx sensor deteriorates, it becomes impossible to detect an accurate NOx concentration. As a result, when the NOx sensor is installed in an exhaust system of an automobile, there is a possibility that problems such as deterioration of exhaust emission may occur. Therefore, a NOx sensor deterioration diagnosis method has been proposed. For example, Patent Document 1 forcibly switches the applied voltage to the pump cell, and determines the deterioration of the NOx sensor based on the change amount of the sensor cell output at this time. A method for diagnosing is disclosed.

JP 2009-175013 A

Incidentally, in a gas sensor having a pump cell, a sensor cell, and a monitor cell, the concentration of the specific gas component is calculated by subtracting the monitor cell output from the sensor cell output. Here, when the monitor cell is deteriorated, the detection accuracy of the residual oxygen concentration by the monitor cell is lowered, and there is a concern that the detection of the concentration of the specific gas component may be affected. That is, in the configuration in which the concentration of the specific gas component is calculated based on the difference between the sensor cell output and the monitor cell output, there is a concern that the accuracy of detecting the concentration of the specific gas component may decrease with the deterioration of the monitor cell. In this respect, there is still room for improvement in the existing technology.

This indication is made in view of the above-mentioned subject, and the main purpose is to provide the gas sensor control device which can judge the deterioration state of a monitor cell appropriately in the gas sensor which has a pump cell, a sensor cell, and a monitor cell. is there.

In order to solve the above problems, this means
A pump cell that adjusts the oxygen concentration in the gas to be detected introduced into the gas chamber by applying a voltage, a sensor cell that detects the concentration of a specific gas component in the gas chamber after the oxygen concentration is adjusted by the pump cell, and a residual in the gas chamber A control device that is applied to a gas sensor having a monitor cell that detects an oxygen concentration and performs control related to the gas sensor,
A pump cell control unit for adjusting the residual oxygen concentration by the pump cell in order to control the output of the monitor cell to a target value;
In a state where the residual oxygen concentration is adjusted by the pump cell control unit, an acquisition unit that acquires the output of the sensor cell;
A deterioration determination unit that determines a deterioration state of the monitor cell based on the output of the sensor cell acquired by the acquisition unit;
Is provided.

In a gas sensor having a pump cell, a sensor cell, and a monitor cell, the residual oxygen concentration in the gas chamber is adjusted by the pump cell. After the adjustment, the concentration of the specific gas component is detected by the sensor cell, and the residual oxygen concentration is detected by the monitor cell. Here, if the concentration of the specific gas component is calculated from the difference between the sensor cell output and the monitor cell output, the detection accuracy of the residual oxygen concentration decreases with the deterioration of the monitor cell, which affects the detection of the concentration of the specific gas component. It is thought that it reaches. Therefore, it is considered important to grasp the deterioration state of the monitor cell.

In this regard, in the above configuration, the residual oxygen concentration is adjusted by the pump cell so as to control the output of the monitor cell to the target value, and the output of the sensor cell is acquired in a state where the residual oxygen concentration is adjusted. Based on the output of the sensor cell, the deterioration state of the monitor cell is determined. If the monitor cell has deteriorated, the residual oxygen concentration in the gas chamber becomes too large or too small in a state where the monitor cell output is controlled to the target value, and the sensor cell output fluctuates due to the influence. The state can be determined. As a result, it is possible to appropriately determine the deterioration state of the monitor cell in the gas sensor having the pump cell, the sensor cell, and the monitor cell.

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The drawing
FIG. 1 is a diagram showing a system configuration of an engine exhaust system. FIG. 2 is a cross-sectional view showing the configuration of the NOx sensor, FIG. 3 is a cross-sectional view showing a III-III cross section of FIG. FIG. 4 is a functional block diagram of the SCU and ECU. 5A is a diagram showing electromotive force characteristics of a monitor cell, FIG. 5B is a diagram showing electromotive force characteristics in a deteriorated state, and FIG. 5C is an enlarged view of an X portion of FIG. 5B. , FIG. 6 is a time chart showing changes in sensor cell current accompanying the start of electromotive force feedback control. FIG. 7 is a flowchart showing a processing procedure for sensor deterioration determination in the case of performing electromotive force feedback control. FIG. 8A is a diagram showing a relationship between the output ratio and the deterioration rate of the monitor cell, and FIG. 8B is a diagram showing a relationship between the output ratio and the deterioration rate of the sensor cell. FIG. 9 is a diagram showing current characteristics of the monitor cell, FIG. 10 is a time chart showing changes in sensor cell current accompanying the start of current feedback control. FIG. 11 is a flowchart showing a processing procedure for sensor deterioration determination when current feedback control is performed. FIG. 12 is a diagram showing a relationship between electromotive force feedback control and current feedback control, and monitor cell deterioration and sensor cell deterioration. FIG. 13 is a flowchart showing a processing procedure for sensor deterioration determination in the case of performing electromotive force feedback control and current feedback control. FIG. 14 is a diagram for explaining changes in the transient characteristics of the sensor cell output accompanying the deterioration of the sensor cell. FIG. 15 is a flowchart showing the deterioration determination process in the second embodiment. FIG. 16 is a cross-sectional view showing the configuration of another NOx sensor.

Hereinafter, embodiments will be described with reference to the drawings. This embodiment embodies a gas sensor control device that performs control related to a NOx sensor in a system in which exhaust gas discharged from an on-board diesel engine is detected gas and the NOx concentration in the exhaust gas is detected by a NOx sensor. It is said. In the following embodiments, parts that are the same or equivalent to each other are given the same reference numerals in the drawings, and the description of the same reference numerals is used.

(First embodiment)
As shown in FIG. 1, an exhaust gas purification system that purifies exhaust gas is provided on the exhaust side of an engine 10 that is a diesel engine. As an exhaust purification system configuration, an exhaust pipe 11 that forms an exhaust passage is connected to the engine 10, and an oxidation catalytic converter 12 and a selective catalytic reduction converter (hereinafter referred to as SCR) are connected to the exhaust pipe 11 in order from the engine 10 side. 13) (referred to as a catalytic converter). The oxidation catalyst converter 12 includes a diesel oxidation catalyst 14 and a DPF (Diesel Particulate Filter) 15. The SCR catalytic converter 13 has an SCR catalyst 16 as a selective reduction type catalyst. Further, a urea water addition valve 17 for adding and supplying urea water (urea aqueous solution) as a reducing agent into the exhaust pipe 11 is provided between the oxidation catalytic converter 12 and the SCR catalytic converter 13 in the exhaust pipe 11. ing.

In the oxidation catalyst converter 12, the diesel oxidation catalyst 14 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 diesel oxidation catalyst 14 oxidizes and purifies hydrocarbons, carbon monoxide, nitrogen oxides and the like contained in the exhaust gas. Further, the diesel oxidation catalyst 14 raises the exhaust temperature by heat generated during the catalytic reaction.

The DPF 15 is formed of a honeycomb structure, and is configured by supporting a platinum group catalyst such as platinum or palladium on a porous ceramic. The DPF 15 collects particulate matter contained in the exhaust gas by depositing it on the partition walls of the honeycomb structure. The deposited particulate matter is oxidized and purified by combustion. For this combustion, a temperature increase in the diesel oxidation catalyst 14 or a decrease in the combustion temperature of the particulate matter due to the additive is used.

The SCR catalytic converter 13 is a device for reducing NOx to nitrogen and water as a post-treatment device for the oxidation catalytic converter 12, and the SCR catalyst 16 carries a noble metal such as Pt on the surface of a base material such as zeolite or alumina. The catalyst used is used. The SCR catalyst 16 reduces and purifies NOx by adding urea as a reducing agent when the catalyst temperature is in the activation temperature range.

In the exhaust pipe 11, there is a limit as a gas sensor on the upstream side of the oxidation catalytic converter 12, between the oxidation catalytic converter 12 and the SCR catalytic converter 13, upstream of the urea water addition valve 17, and downstream of the SCR catalytic converter 13. Current- type NOx sensors 21, 22, and 23 are provided, respectively. The NOx sensors 21 to 23 detect the NOx concentration in the exhaust gas at the respective detection positions. The position and number of NOx sensors in the engine exhaust system may be arbitrary.

SCUs (Sensor Control Units) 31, 32, and 33 are connected to the NOx sensors 21 to 23, and the detection signals of the NOx sensors 21 to 23 are appropriately output to the SCUs 31 to 33 for each sensor. The SCUs 31 to 33 are electronic control devices including a CPU and a microcomputer having various memories and peripheral circuits thereof, and oxygen (O2) in exhaust gas based on detection signals (limit current signals) of the NOx sensors 21 to 23. The concentration and the NOx concentration as the concentration of the specific gas component are calculated.

The SCUs 31 to 33 are connected to a communication line 34 such as a CAN bus, and are connected to various ECUs (for example, an engine ECU 35) via the communication line 34. That is, the SCUs 31 to 33 and the engine ECU 35 can exchange information with each other using the communication line 34. For example, information on oxygen concentration and NOx concentration in exhaust gas is transmitted from the SCUs 31 to 33 to the engine ECU 35. The engine ECU 35 is an electronic control device including a CPU, a microcomputer having various memories, and its peripheral circuits, and controls the engine 10 and various devices in the exhaust system. The engine ECU 35 performs fuel injection control and the like based on, for example, the accelerator opening and the engine speed.

Further, the engine ECU 35 performs urea water addition control by the urea water addition valve 17 based on the NOx concentration detected by each of the NOx sensors 21 to 23. Briefly describing the control of the urea water addition, the engine ECU 35 calculates the urea water addition amount based on the NOx concentration detected by the NOx sensors 21 and 22 on the upstream side of the SCR catalytic converter 13, and the SCR catalytic converter 13. The urea water addition amount is feedback-corrected so that the NOx concentration detected by the downstream NOx sensor 23 becomes as small as possible. Based on the urea water addition amount, the driving of the urea water addition valve 17 is controlled.

Next, the configuration of the NOx sensors 21 to 23 will be described. Each of the NOx sensors 21 to 23 has the same configuration, and the configuration of the NOx sensor 21 will be described here. 2 and 3 are views showing the internal structure of the sensor element 40 constituting the NOx sensor 21. FIG. In addition, the left-right direction of a figure is a longitudinal direction of the sensor element 40, and the left side of a figure is an element front end side. The sensor element 40 has a so-called three-cell structure including a pump cell 41, a sensor cell 42 and a monitor cell 43. The monitor cell 43 has a function of discharging oxygen in the gas, like the pump cell 41, and may be referred to as an auxiliary pump cell or a second pump cell.

The sensor element 40 includes a first main body 51 and a second main body 52 made of an insulator such as alumina, a solid electrolyte body 53 disposed between the main bodies 51 and 52, a diffusion resistor 54, and a pump cell. An electrode 55, a sensor cell electrode 56, a monitor cell electrode 57, a common electrode 58, and a heater 59 are provided. A gas chamber 61 that is a concentration meter side chamber is formed between the first main body 51 and the solid electrolyte body 53, and an atmospheric chamber 62 that is a reference gas chamber is formed between the second main body 52 and the solid electrolyte body 53. Is formed.

The pump cell 41 adjusts the oxygen concentration in the exhaust gas introduced into the gas chamber 61, and is formed by the pump cell electrode 55, the common electrode 58, and a part of the solid electrolyte body 53. The sensor cell 42 detects the concentration (NOx concentration) of a predetermined gas component in the gas chamber 61 based on an oxygen ion current flowing between the sensor cell electrode 56 and the common electrode 58. The sensor cell electrode 56 and the common electrode 58 And a part of the solid electrolyte body 53. The monitor cell 43 detects the residual oxygen concentration in the gas chamber 61 on the basis of the oxygen ion current flowing between the monitor cell electrode 57 and the common electrode 58, and one of the monitor cell electrode 57, the common electrode 58, and the solid electrolyte body 53. Part.

The solid electrolyte body 53 is a plate-like member and is made of an oxygen ion conductive solid electrolyte material such as zirconia oxide. The first main body 51 and the second main body 52 are arranged on both sides of the solid electrolyte body 53. The first main body 51 has a stepped shape on the solid electrolyte body 53 side, and a recess formed by the step is a gas chamber 61. One side surface of the concave portion of the first main body 51 is open, and the diffusion resistor 54 is disposed on the open side surface. The diffusion resistor 54 is made of a porous material or a material in which pores are formed. The speed of the exhaust gas introduced into the gas chamber 61 is regulated by the action of the diffusion resistor 54.

Similarly, the second main body portion 52 has a stepped shape on the solid electrolyte body 53 side, and a concave portion formed by the step is an atmospheric chamber 62. One side of the atmospheric chamber 62 is open. The gas introduced into the atmospheric chamber 62 from the solid electrolyte body 53 side is released to the atmosphere.

On the surface facing the gas chamber 61 of the solid electrolyte body 53, a pump cell electrode 55, a sensor cell electrode 56, and a monitor cell electrode 57 on the cathode side are provided. In this case, the pump cell electrode 55 is disposed on the inlet side of the gas chamber 61 close to the diffusion resistor 54, that is, on the upstream side in the gas chamber 61, and the sensor cell electrode 56 and the monitor cell electrode 57 have a diffusion resistance across the pump cell electrode 55. It is disposed on the opposite side of the body 54, that is, on the downstream side in the gas chamber 61. The pump cell electrode 55 has a larger surface area than the sensor cell electrode 56 and the monitor cell electrode 57. The sensor cell electrode 56 and the monitor cell electrode 57 are arranged side by side at positions close to each other and equivalent to the exhaust flow direction. The pump cell electrode 55 and the monitor cell electrode 57 are electrodes made of a noble metal such as Au—Pt that is inactive to NOx (electrodes that are difficult to decompose NOx), whereas the sensor cell electrode 56 is platinum Pt and rhodium that are active to NOx. It is an electrode made of a noble metal such as Rh.

A common electrode 58 on the anode side is provided on the surface of the solid electrolyte body 53 facing the atmospheric chamber 62 at a position corresponding to each of the electrodes 55 to 57 on the cathode side.

When a voltage is applied between the pump cell electrode 55 and the common electrode 58, oxygen contained in the exhaust gas in the gas chamber 61 is ionized at the pump cell electrode 55 on the cathode side. Then, oxygen ions move in the solid electrolyte body 53 toward the common electrode 58 on the anode side, and electric charges are released from the common electrode 58 to become oxygen, which is discharged into the atmospheric chamber 62. Thereby, the inside of the gas chamber 61 is maintained in a predetermined low oxygen state.

The higher the applied voltage of the pump cell 41 (that is, the applied voltage between the pump cell electrode 55 and the common electrode 58), the greater the amount of oxygen discharged from the exhaust gas by the pump cell 41. Conversely, the lower the applied voltage of the pump cell 41, the smaller the amount of oxygen discharged from the exhaust by the pump cell 41. Therefore, by increasing or decreasing the applied voltage of the pump cell 41, the amount of residual oxygen in the exhaust gas flowing through the sensor cell 42 and the monitor cell 43 in the subsequent stage can be increased or decreased. In the present embodiment, a voltage applied to the pump cell 41 is a pump cell applied voltage Vp, and a current output when the pump cell 41 is in a voltage applied state is a pump cell current Ip.

The monitor cell 43 detects the oxygen concentration remaining in the gas chamber 61 in a state where oxygen is exhausted by the pump cell 41. At this time, the monitor cell 43 outputs a current signal generated with voltage application or an electromotive force signal corresponding to the residual oxygen concentration in the gas chamber 61 as a residual oxygen concentration detection signal. The output of the monitor cell 43 is acquired by the SCUs 31 to 33 as the monitor cell current Im or the monitor cell electromotive force Vm.

The sensor cell 42 reduces and decomposes NOx in the exhaust gas according to voltage application in a state where oxygen is exhausted by the pump cell 41, and outputs a current signal corresponding to the NOx concentration and the residual oxygen concentration in the gas chamber 61. The output of the sensor cell 42 is acquired as the sensor cell current Is in the SCUs 31 to 33. In the SCUs 31 to 33, the NOx concentration in the exhaust gas is calculated from the sensor cell current Is.

Incidentally, in the detection of the NOx concentration by the NOx sensors 21 to 23 having the pump cell 41, the sensor cell 42 and the monitor cell 43, the NOx concentration in the exhaust gas is calculated by subtracting the monitor cell current Im from the sensor cell current Is. In such a case, if the monitor cell 43 deteriorates, the accuracy of the monitor cell current Im decreases, and there is a concern that the NOx concentration detection may be affected. Therefore, in this embodiment, the deterioration determination is performed with the monitor cell 43 as a determination target. Each of the SCUs 31 to 33 provided for each of the NOx sensors 21 to 23 has the same function.

FIG. 4 is a functional block diagram for explaining the functions of the SCUs 31 to 33 and the engine ECU 35. The SCUs 31 to 33 adjust the residual oxygen concentration in the gas chamber 61 by the pump cell 41 and the residual oxygen concentration by the pump cell control unit M11 in order to control the monitor cell outputs (Vm, Im) to the target values. In a state in which is adjusted, an acquisition unit M12 that acquires the sensor cell output (Is) and a deterioration determination unit M13 that determines the deterioration state of the monitor cell 43 based on the sensor cell output acquired by the acquisition unit M12 are provided. Yes. In this embodiment, the NOx sensors 21 to 23 generate the monitor cell electromotive force Vm corresponding to the residual oxygen concentration in the gas chamber 61 as the monitor cell output, and the voltage applied to the monitor cell 43 in the gas chamber 61 It is possible to generate a monitor cell current Im corresponding to the residual oxygen concentration. In the SCUs 31 to 33, the monitor cell electromotive force Vm, the monitor cell current Im, the sensor cell current Is, the pump cell current Ip, and the like are appropriately detected. Then, the deterioration determination unit M13 performs the deterioration determination of the NOx sensors 21 to 23 with the monitor cell 43 or the monitor cell 43 and the sensor cell 42 as determination targets.

The pump cell control unit M11 causes the pump cell 41 to adjust the residual oxygen concentration by performing electromotive force feedback control (VmF / B control) for controlling the monitor cell electromotive force Vm to the target value Vmtg. At this time, the pump cell control unit M11 sets the pump cell applied voltage Vp based on the deviation between the actual monitor cell electromotive force Vm and the target value Vmtg, and performs voltage application at the pump cell applied voltage Vp.

Moreover, the pump cell control unit M11 causes the pump cell 41 to adjust the residual oxygen concentration by performing current feedback control (ImF / B control) for controlling the monitor cell current Im to the target value Imtg. At this time, the pump cell control unit M11 sets the pump cell application voltage Vp based on the deviation between the actual monitor cell current Im and the target value Imtg, and performs voltage application to the pump cell 41 with the pump cell application voltage Vp. The residual oxygen concentration is appropriately adjusted in the pump cell 41 by controlling the pump cell applied voltage Vp. The electromotive force feedback control corresponds to “electromotive force control”, and the current feedback control corresponds to “monitor cell current control”.

The acquisition unit M12 acquires the sensor cell current Is that changes in response by the electromotive force feedback control as the sensor cell output in a state where the residual oxygen concentration is adjusted by the electromotive force feedback control. In addition, as the sensor cell output in a state where the residual oxygen concentration is adjusted by the current feedback control, the sensor cell current Is that changes in response by the current feedback control is acquired.

The degradation determination unit M13 determines degradation of the monitor cell 43 and the sensor cell 42 using at least one of the sensor cell current Is acquired when the electromotive force feedback control is performed and the sensor cell current Is acquired when the current feedback control is performed. To implement. For example, the deterioration determination unit M13 calculates the deterioration rate Cm of the monitor cell 43 based on the response change amount ΔIs of the sensor cell current Is, while calculating the deterioration rate Cs of the sensor cell 42 based on the response change amount ΔIs of the sensor cell current Is. To do.

Further, the engine ECU 35 has an abnormality determination unit M21 that determines abnormality due to emission deterioration based on the deterioration determination results of the SCUs 31 to 33. The abnormality determination unit M21 determines an abnormality in engine emission based on the deterioration rate Cm of the monitor cell 43 and the deterioration rate Cs of the sensor cell 42 calculated by the deterioration determination unit M13 of each of the SCUs 31 to 33. In addition to the deterioration rates Cm and Cs, the emission abnormality is determined by comprehensively considering the outputs of the NOx sensors 21 to 23, various sensor information from other sensors, the engine operating state, and the like. May be.

Both the deterioration determination and the emission abnormality determination regarding the NOx sensors 21 to 23 may be performed by the SCUs 31 to 33, or both may be performed by the engine ECU 35. Since it is desirable that the emission abnormality determination is performed using elements other than the degree of deterioration of the NOx sensors 21 to 23, it is preferable that the emission abnormality determination is performed by the engine ECU 35.

Next, the electromotive force feedback control and the current feedback control will be described, and the deterioration determination of the monitor cell 43 and the sensor cell 42 performed together with each feedback control will be described.

First, the electromotive force feedback control of the monitor cell 43 will be described. The monitor cell 43 has an electromotive force characteristic (so-called Z characteristic) that generates a monitor cell electromotive force Vm corresponding to the oxygen concentration (excess air ratio). More specifically, as shown in FIG. 5A, the monitor cell 43 has a monitor cell electromotive force Vm substantially zero in a region where the oxygen concentration> 0, and a monitor cell electromotive force Vm in a region where the oxygen concentration <0. It has an electromotive force characteristic in which the monitor cell electromotive force Vm changes suddenly in the region where the oxygen concentration = 0. In terms of the excess air ratio instead of the oxygen concentration, the monitor cell electromotive force Vm is substantially zero in the region where the excess air ratio> 1, and the monitor cell electromotive force Vm is a predetermined value (for example, about 0 in the region where the excess air ratio <1). .9V), and the monitor cell electromotive force Vm has an electromotive force characteristic that changes suddenly in a region near the excess air ratio = 1.

The SCUs 31 to 33 perform electromotive force feedback control so that the monitor cell electromotive force Vm generated according to the residual oxygen concentration in the gas chamber 61 matches the target value Vmtg. At this time, as shown in FIG. 5A, the target value Vmtg is within a sudden change region where the monitor cell electromotive force Vm changes suddenly in the electromotive force characteristics of the monitor cell 43, and the oxygen concentration is larger than 0 (ie, excess air). The rate may be determined as monitor cell electromotive force Vm. By performing the electromotive force feedback control, the residual oxygen concentration is controlled to 1000 ppm, for example (A1 in the figure).

Here, if the monitor cell 43 is deteriorated, the electromotive force characteristic changes as the sensitivity decreases, as shown by the solid line in FIG. In FIG. 5 (b), the initial characteristic before deterioration is indicated by a one-dot chain line, and the characteristic after deterioration is indicated by a solid line. In the characteristic after deterioration, a region where the oxygen concentration is <0 (the excess air ratio <1) in accordance with the characteristic change. In the region, the monitor cell electromotive force Vm is small. Therefore, the actual residual oxygen concentration in the gas chamber 61 deviates from the target oxygen concentration under the state where the electromotive force feedback control is performed. Specifically, as shown in FIG. 5C in which the portion X in FIG. 5B is enlarged, the residual oxygen concentration decreases from A1 to A2 when the electromotive force feedback control is performed.

The SCUs 31 to 33 determine the deterioration of the monitor cell 43 by utilizing the change in the responsiveness of the sensor cell current Is according to the change in the residual oxygen concentration accompanying the deterioration of the monitor cell 43 during the electromotive force feedback control. To implement. The outline will be described with reference to the time chart of FIG.

In FIG. 6, electromotive force feedback control is started at time t1. At this time, the residual oxygen concentration in the gas chamber 61 is extremely low before time t1, and oxygen supply to the monitor cell 43 and the sensor cell 42 is started with the start of the electromotive force feedback control. That is, in the electromotive force feedback control, the oxygen concentration is adjusted so that the residual oxygen concentration increases. In this case, in the initial state where the deterioration of the monitor cell 43 has not occurred, the sensor cell current Is changes transiently as indicated by the alternate long and short dash line, whereas when the deterioration of the monitor cell 43 occurs, the residual oxygen concentration becomes lower than expected. As a result, the sensor cell current Is changes transiently as indicated by a solid line. That is, the response change amount ΔIs1 of the sensor cell current Is decreases with respect to the initial value of the response change amount of the sensor cell current Is calculated in advance under the same conditions as the current electromotive force feedback control (hereinafter referred to as the initial change amount ΔIsini1). Due to the difference in the change in the sensor cell current Is, the deterioration of the monitor cell 43 can be determined.

FIG. 7 is a flowchart showing a processing procedure for determining the deterioration of the NOx sensors 21 to 23 when the electromotive force feedback control (VmF / B control) is performed. The processing shown in FIG. 7 is arithmetic processing for realizing the functions of the SCUs 31 to 33 shown in FIG. 4, and is executed in each of the SCUs 31 to 33, for example, at predetermined intervals.

In step S11, it is determined whether or not an execution condition for deterioration determination is satisfied. The implementation condition includes, for example, receiving an permission signal from the engine ECU 35 to permit the execution of the deterioration determination. The engine ECU 35 transmits a permission signal when the gas environment in the exhaust pipe 11 is in a predetermined environment that is stable. Specifically, the engine ECU 35 is in a state where the engine 10 is in a predetermined operation state and the amount of exhaust is relatively stable, in the case of fuel cut, immediately after the ignition switch is turned off (immediately after the IG is turned off), Alternatively, the permission signal is transmitted when the engine ECU 35 is being activated by the soak timer. In particular, it is desirable that the condition is immediately after the IG is turned off. This is because immediately after the IG is turned off, the exhaust flow disappears when the engine is stopped, so that it is possible to determine the deterioration in a stable gas environment. If the execution condition for the deterioration determination is satisfied, the process proceeds to the subsequent step S12. If the execution condition is not satisfied, the present process is terminated.

In step S12, electromotive force feedback control is performed. At this time, the target value Vmtg of the monitor cell electromotive force Vm is set, and the pump cell applied voltage Vp is feedback-controlled based on the deviation between the target value Vmtg and the actual monitor cell electromotive force Vm. Thereby, the monitor cell electromotive force Vm is controlled to the target value Vmtg, and the residual oxygen concentration in the gas chamber 61 is adjusted to an oxygen concentration corresponding to the target value Vmtg.

Thereafter, in step S13, a response change amount ΔIs1 of the sensor cell current Is is calculated after the start of the electromotive force feedback control. At this time, based on the fact that the amount of change per unit time of the sensor cell current Is is less than a predetermined value, it is considered that the change in the sensor cell current Is has converged, and the sensor cell current Is after the convergence and the electromotive force feedback control The response change amount ΔIs1 is calculated from the difference from the sensor cell current Is before the start.

In step S14, using the following equation (1), the output ratio β1 is calculated from the response change amount ΔIs1 and the initial change amount ΔIsini1 of the sensor cell current Is calculated this time. The output ratio β1 is calculated as a ratio of the response change amount ΔIs1 to the initial change amount ΔIsini1. The initial change amount ΔIsini1 is stored in advance in the memories in the SCUs 31 to 33.
β1 = ΔIs1 / ΔIsini1 (1)
In a succeeding step S15, it is determined whether or not the output ratio β1 is smaller than a predetermined value TH1. Note that 0 <TH1 <1. And if step S15 is YES, it will consider that the monitor cell 43 has deteriorated and will progress to step S16.

The processing of step S15 is to determine whether or not the output ratio β1 calculated this time has occurred due to deterioration of the monitor cell 43. That is, comparing the case where the response change amount ΔIs1 of the sensor cell current Is decreases with the deterioration of the monitor cell 43 and the case where the response change amount ΔIs1 of the sensor cell current Is decreases with the deterioration of the sensor cell 42, the former is more responsive. There is a tendency that the degree of decrease of the change amount ΔIs1 increases (ΔIs1 tends to be a small value). This is because when the monitor cell 43 is deteriorated, a current drop occurs due to a shift in the residual oxygen concentration. From this difference, it is possible to specify that the cause of deterioration is the monitor cell 43.

In step S16, for example, the deterioration rate Cm of the monitor cell 43 is calculated based on the output ratio β1 using the relationship L1 in FIG. According to the relationship L1, the deterioration rate Cm is calculated as a larger value as the output ratio β1 is smaller than 1, that is, as the difference from the initial characteristic is larger. A large deterioration rate Cm means that the degree of deterioration of the monitor cell 43 is large. In FIG. 7, the step S15 can be omitted.

Next, the current feedback control of the monitor cell 43 will be described. The monitor cell 43 has the current characteristics shown in FIG. 9 as the relationship between the oxygen concentration and the monitor cell current Im. The SCUs 31 to 33 perform current feedback control so that the monitor cell current Im generated according to the residual oxygen concentration in the gas chamber 61 matches the target value Immtg.

In FIG. 9, the initial characteristics before deterioration are indicated by a one-dot chain line, and the characteristics after deterioration are indicated by solid lines. In the characteristics after deterioration, the reaction sensitivity to oxygen is reduced as the characteristics change. Therefore, the actual residual oxygen concentration in the gas chamber 61 deviates from the target oxygen concentration under the state where the current feedback control is performed. Specifically, as shown in FIG. 9, the residual oxygen concentration increases from A3 to A4 when the current feedback control is performed.

When the residual oxygen concentration changes with the deterioration of the monitor cell 43 during the current feedback control, the SCUs 31 to 33 determine the deterioration of the monitor cell 43 using the change in the response of the sensor cell current Is accordingly. To implement. The outline will be described with reference to the time chart of FIG.

In FIG. 10, current feedback control is started at time t2. At this time, before time t2, the residual oxygen concentration in the gas chamber 61 is extremely low, and oxygen supply to the monitor cell 43 and the sensor cell 42 is started with the start of the current feedback control. That is, in the current feedback control, the oxygen concentration is adjusted so that the residual oxygen concentration increases. In this case, in the initial state where the deterioration of the monitor cell 43 has not occurred, the sensor cell current Is changes transiently as indicated by the alternate long and short dash line, whereas when the deterioration of the monitor cell 43 occurs, the residual oxygen concentration becomes higher than expected. As a result, the sensor cell current Is changes transiently as indicated by a solid line. That is, the response change amount ΔIs2 of the sensor cell current Is increases with respect to the initial value of the response change amount of the sensor cell current Is calculated in advance under the same conditions as the current feedback control (hereinafter referred to as the initial change amount ΔIsini2). Due to the difference in the change in the sensor cell current Is, the deterioration of the monitor cell 43 can be determined.

FIG. 11 is a flowchart showing a processing procedure for determining the deterioration of the NOx sensors 21 to 23 when the current feedback control (ImF / B control) is performed. The process shown in FIG. 11 is an arithmetic process for realizing each function of the SCUs 31 to 33 shown in FIG. 4, and is executed in each SCU 31 to 33, for example, at predetermined intervals.

In step S21, it is determined whether or not an execution condition for deterioration determination is satisfied. However, since this process is the same as step S11 of FIG. 7, detailed description thereof is omitted. If the execution condition for the deterioration determination is satisfied, the process proceeds to the subsequent step S22. If the execution condition is not satisfied, the present process is terminated.

In step S22, current feedback control is performed. At this time, the target value Imtg of the monitor cell current Im is set, and the pump cell applied voltage Vp is feedback-controlled based on the deviation between the target value Imtg and the actual monitor cell current Im. As a result, the monitor cell current Im is controlled to the target value Imtg, and the residual oxygen concentration in the gas chamber 61 is adjusted to an oxygen concentration corresponding to the target value Immtg.

Thereafter, in step S23, the response change amount ΔIs2 of the sensor cell current Is is calculated after the start of the current feedback control. At this time, based on the fact that the amount of change per unit time of the sensor cell current Is is less than a predetermined value, it is considered that the change in the sensor cell current Is has converged, and the sensor cell current Is after the convergence and the start of current feedback control. The response change amount ΔIs2 is calculated based on the difference from the previous sensor cell current Is.

Thereafter, in step S24, the difference between the response change amount ΔIs2 calculated in step S23 and the initial change amount ΔIsini2 is calculated as α1 (α1 = ΔIsini2−ΔIs2). In step S25, it is determined whether or not the difference α1 is smaller than the negative predetermined value TH2. In step S26, it is determined whether or not the difference α1 is larger than the positive predetermined value TH3. Note that the initial change amount ΔIsini2 is stored in advance in the memories in the SCUs 31 to 33. TH2 <0 and TH3> 0.

The processing of steps S24 to S26 is to determine whether the difference α1 between the response change amount ΔIs2 calculated this time and the initial change amount ΔIsini2 is caused by the deterioration of the monitor cell 43 or the sensor cell 42. . In other words, when the current feedback control is performed, in the state where the monitor cell 43 is deteriorated, the residual oxygen concentration is shifted to a larger side (see FIG. 9), but the sensor cell 42, not the monitor cell 43, is deteriorated. In this state, the residual oxygen concentration is adjusted to an appropriate value. In this case, when the monitor cell 43 is deteriorated, the residual oxygen concentration becomes higher than expected, so that the response change amount ΔIs2 of the sensor cell current Is is larger than the initial change amount ΔIsini2, whereas when the sensor cell 42 is deteriorated, Due to the decrease in response of the sensor cell 42, the response change amount ΔIs2 of the sensor cell current Is becomes smaller than the initial change amount ΔIsini2. Therefore, it is possible to determine whether the deterioration of the monitor cell 43 or the deterioration of the sensor cell 42 occurs depending on whether the response change amount ΔIs2 of the sensor cell current Is increases or decreases with respect to the initial change amount ΔIsini2. It has become.

If step S25 is YES, the monitor cell 43 is regarded as degraded and the process proceeds to step S27. If step S26 is YES, the sensor cell 42 is regarded as degraded and the process proceeds to step S28.

In step S27, the deterioration determination of the monitor cell 43 is performed based on the response change amount ΔIs2 of the sensor cell current Is. At this time, using the following equation (2), the output ratio β2 is calculated from the response change amount ΔIs2 and the initial change amount ΔIsini2 of the sensor cell current Is calculated this time.
β2 = ΔIs2 / ΔIsini2 (2)
Then, for example, using the relationship L2 in FIG. 8A, the deterioration rate Cm of the monitor cell 43 is calculated based on the output ratio β2. According to the relationship L2, the deterioration rate Cm is calculated as a larger value as the output ratio β2 is larger than 1, that is, as the difference from the initial characteristic is larger.

In step S28, the deterioration of the sensor cell 42 is determined based on the response change amount ΔIs2 of the sensor cell current Is. At this time, using the following equation (3), the output ratio β3 is calculated from the response change amount ΔIs2 and the initial change amount ΔIsini2 of the sensor cell current Is calculated this time.
β3 = ΔIs2 / ΔIsini2 (3)
For example, the deterioration rate Cs of the sensor cell 42 is calculated based on the output ratio β3 using the relationship L3 in FIG. 8B. According to the relationship L3, the deterioration rate Cs is calculated as a larger value as the output ratio β3 is smaller than 1, that is, as the difference from the initial characteristic is larger.

In FIG. 11, instead of steps S24 to S26, the output ratio β2 is calculated prior to steps S27 and S28, and whether the output ratio β2 is greater than a predetermined value TH4 or the output ratio β2 However, it may be determined whether the monitor cell 43 is deteriorated or the sensor cell 42 is deteriorated by determining whether it is smaller than the predetermined value TH5. That is, when the output ratio β2 is larger than the predetermined value TH4, it is determined that the monitor cell 43 is deteriorated. When the output ratio β2 is smaller than the predetermined value TH5, it is determined that the sensor cell 42 is deteriorated. Then, based on each determination result, it progresses to Step S27 and Step S28. The predetermined value TH4> 1 and the predetermined value TH5 <1.

It is also possible to omit steps S24 to S26 and S28. In this case, in FIG. 11, as the deterioration determination of the NOx sensors 21 to 23, the deterioration determination is performed only for the monitor cell 43.

Degradation determination process when the SCUs 31 to 33 perform electromotive force feedback control (VmF / B control) (FIG. 7) and deterioration determination process when current feedback control (ImF / B control) is performed (FIG. 11) The structure which implements only any one of these may be sufficient. In addition, each of these determination processes may be performed at different execution opportunities. For example, one of the determination processes may be performed for each drive cycle, one determination process may be performed immediately after the current IG is turned off, and the other determination process may be performed immediately after the next IG is turned off.

Next, both the electromotive force feedback control (VmF / B control) and the current feedback control (ImF / B control) are performed, and based on the deterioration information obtained in the implementation state of each feedback control, the monitor cell 43 and the sensor cell An example of performing the deterioration determination of 42 will be described.

FIG. 12 shows the relationship between the response change of the sensor cell current Is when the monitor cell deteriorates and the response change of the sensor cell current Is when the sensor cell deteriorates when the electromotive force feedback control and the current feedback control are executed. Are shown together. In FIG. 12, the initial characteristics are indicated by a one-dot chain line, and the deteriorated characteristics are indicated by a solid line.

Here, there are the following tendencies when the monitor cell 43 is deteriorated and when the sensor cell 42 is deteriorated.
(1) When the deterioration of the monitor cell 43 proceeds, the response change amount ΔIs1 of the sensor cell current Is decreases when the electromotive force feedback control is performed, and the response change amount ΔIs2 of the sensor cell current Is increases when the current feedback control is performed. .
(2) When deterioration of the sensor cell 42 proceeds, the response change amount ΔIs1 of the sensor cell current Is decreases when the electromotive force feedback control is performed, and the response change amount ΔIs2 of the sensor cell current Is decreases when the current feedback control is performed. .

In view of these tendencies, the SCUs 31 to 33 (degradation determination unit M13) have a response change amount ΔIs1 when the electromotive force feedback control is performed smaller than the initial change amount ΔIsini1 that is the first reference value, and the current Based on the fact that the response change amount ΔIs2 when the feedback control is performed becomes larger than the initial change amount ΔIsini2 that is the second reference value, it is determined that the monitor cell 43 is deteriorated. Further, the response change amount ΔIs1 when the electromotive force feedback control is performed is smaller than the initial change amount ΔIsini1, and the response change amount ΔIs2 when the current feedback control is performed is smaller than the initial change amount ΔIsini2. Based on the above, it is determined that the sensor cell 42 has deteriorated.

FIG. 13 is a flowchart showing a processing procedure for determining the deterioration of the NOx sensors 21 to 23 when performing electromotive force feedback control (VmF / B control) and current feedback control (ImF / B control). The process shown in FIG. 13 is an arithmetic process for realizing each function of the SCUs 31 to 33 shown in FIG. 4, and is executed in each SCU 31 to 33, for example, at predetermined intervals. The processing in FIG. 13 is performed instead of the processing in FIG. 7 and FIG.

In step S31, it is determined whether or not an execution condition for deterioration determination is satisfied. However, since this process is the same as step S11 of FIG. 7, detailed description thereof is omitted. If the execution condition for the deterioration determination is satisfied, the process proceeds to the subsequent step S32. If the execution condition is not satisfied, the present process is terminated.

In steps S32 and S33, electromotive force feedback control is performed, and the response change amount ΔIs1 of the sensor cell current Is is calculated (same as steps S12 and S13 described above). In steps S34 and S35, current feedback control is performed, and the response change amount ΔIs2 of the sensor cell current Is is calculated (same as steps S22 and S23 described above).

Thereafter, in step S36, it is determined whether or not the response change amount ΔIs1 has decreased with respect to the initial change amount ΔIsini1, and in step S37, whether or not the response change amount ΔIs2 has increased with respect to the initial change amount ΔIsini2. Determine. And when both step S36 and S37 are YES, it progresses to step S38 and the deterioration determination of the monitor cell 43 is implemented. Moreover, when step S36 is YES and step S37 is NO, it progresses to step S39 and the deterioration determination of the sensor cell 42 is implemented.

It should be noted that the calculation process of the response change amount ΔIs1 in steps S32 and S33 and the calculation process of the response change amount ΔIs2 in steps S34 and S35 can be performed discontinuously, that is, at different execution opportunities. For example, the processing may be performed for each drive cycle, the response change amount ΔIs1 may be calculated immediately after the current IG is turned off, and the response change amount ΔIs2 may be calculated immediately after the next IG is turned off. Then, when the response change amounts ΔIs1 and ΔIs2 are calculated, the deterioration determination of either the monitor cell 43 or the sensor cell 42 is performed.

According to the embodiment described above in detail, the following excellent effects can be obtained.

In the above configuration, in order to control the monitor cell output (Vm, Im) to the target value, the residual oxygen concentration is adjusted by the pump cell 41, and based on the sensor cell output acquired in the state where the residual oxygen concentration is adjusted, the monitor cell 43 deterioration states were determined. Here, if the monitor cell 43 is deteriorated, the residual oxygen concentration in the gas chamber 61 becomes excessive or low in a state where the monitor cell output is controlled to the target value, and the sensor cell output fluctuates due to the influence thereof. The deterioration state of the monitor cell 43 can be determined using As a result, the deterioration state of the monitor cell 43 can be properly determined in the NOx sensors 21 to 23 having the pump cell 41, the sensor cell 42, and the monitor cell 43.

Further, in the configuration in which the monitor cell output (Vm, Im) is controlled to the target value, the residual oxygen concentration in the gas chamber 61 is kept constant, so that the deterioration determination of the monitor cell 43 can be performed under a condition where the oxygen concentration is constant. For this reason, it is possible to increase the degradation determination accuracy.

The electromotive force feedback control for adjusting the monitor cell electromotive force Vm to the target value is performed to adjust the residual oxygen concentration by the pump cell 41 (FIG. 7). In this case, if the monitor cell 43 is deteriorated, the actual residual oxygen concentration in the gas chamber 61 is the target oxygen in the state where the electromotive force feedback control is performed due to the change in the electromotive force characteristic due to the sensitivity decrease. Deviation from concentration. Thereby, since the response change amount ΔIs1 of the sensor cell current Is deviates from a predetermined reference value (initial change amount ΔIsini1), it can be appropriately determined that the monitor cell 43 has deteriorated.

In a state where the monitor cell 43 is deteriorated, the residual oxygen concentration is shifted to a smaller side by performing the electromotive force feedback control. In this case, as the residual oxygen concentration shifts, the response change amount ΔIs1 of the sensor cell current Is becomes smaller than a predetermined reference value (initial change amount ΔIsini1). Based on this, the deterioration state of the monitor cell 43 is appropriately set. Can be determined.

When the electromotive force feedback control is performed, if the residual oxygen concentration shifts to a smaller side due to the deterioration of the monitor cell 43, the response change amount ΔIs1 of the sensor cell current Is according to the deviation of the residual oxygen concentration. However, even if the monitor cell 43 has not deteriorated and the sensor cell 42 has deteriorated, the response change amount ΔIs1 of the sensor cell current Is similarly decreases. However, comparing the case where the response change amount ΔIs1 of the sensor cell current Is decreases with the deterioration of the monitor cell 43 and the case where the response change amount ΔIs1 of the sensor cell current Is decreases with the deterioration of the sensor cell 42, the former is more responsive. There is a tendency that the degree of decrease in the change amount ΔIs1 increases. This is because when the monitor cell 43 is deteriorated, a current drop occurs due to a shift in the residual oxygen concentration. Therefore, it is possible to identify the deterioration of the monitor cell 43 based on the magnitude of the ratio between the response change amount ΔIs1 and the initial change amount ΔIsini1 of the sensor cell current Is, and the ratio of the response change amount ΔIs1 to the initial change amount ΔIsini1 is predetermined. It is appropriately determined that the monitor cell 43 has deteriorated among the monitor cell 43 and the sensor cell 42 based on being smaller than the value, that is, the degree of decrease in the response change amount ΔIs1 with respect to the initial change amount ΔIsini1 is large. Can do.

Further, current feedback control is performed so that the monitor cell current Im matches the target value, and the residual oxygen concentration by the pump cell 41 is adjusted (FIG. 11). In this case, if the monitor cell is deteriorated, the actual residual oxygen concentration in the gas chamber 61 is changed from the target oxygen concentration in the state where the current feedback control is performed due to the change in the monitor cell current characteristic due to the sensitivity reduction. Shift. Thereby, since the response change amount ΔIs2 of the sensor cell current Is deviates from a predetermined reference value (for example, the initial change amount ΔIsini2), it can be appropriately determined that the monitor cell 43 is deteriorated.

In the state where the monitor cell 43 is deteriorated, the residual oxygen concentration is shifted to the side by increasing the current feedback control. In this case, as the residual oxygen concentration shifts, the response change amount ΔIs2 of the sensor cell current Is becomes larger than a predetermined reference value (initial change amount ΔIsini2). Based on this, the deterioration state of the monitor cell 43 is appropriately set. Can be determined.

When the current feedback control is performed, the residual oxygen concentration is adjusted to an appropriate value if the monitor cell 43 is in a normal state rather than a deteriorated state. In such a case, if the sensor cell 42 is deteriorated, the response change amount ΔIs2 of the sensor cell current Is is smaller than a predetermined reference value (initial change amount ΔIsini2) due to a decrease in response due to the deterioration. . Therefore, the deterioration state of the sensor cell 42 can be appropriately determined based on the decrease in the response change amount ΔIs.

The electromotive force feedback control of the monitor cell 43 is performed to calculate the response change amount ΔIs1 of the sensor cell current Is at that time, while the current feedback control is performed to calculate the response change amount ΔIs2 of the sensor cell current Is at that time. Based on the response change amounts ΔIs1 and ΔIs2, the monitor cell 43 and the sensor cell 42 are subjected to deterioration determination (FIG. 13). In the deterioration determination with electromotive force feedback control and the deterioration determination with current feedback control, the deterioration of the NOx sensors 21 to 23 is mainly caused by the deterioration of the monitor cell 43 or the deterioration of the sensor cell 42. Since the mode of the response change of the sensor cell current Is changes depending on whether or not the sensor cell 43 or the sensor cell 42 is deteriorated, it can be suitably determined.

Note that the characteristic change of the sensor cell current Is when the electromotive force feedback control and the current feedback control are performed differs between the state in which the monitor cell 43 is deteriorated and the state in which the sensor cell 42 is deteriorated as shown in FIG. Therefore, it is distinguished whether the deterioration of the NOx sensors 21 to 23 is the deterioration of the monitor cell 43 or the sensor cell 42. As a result, the NOx sensors 21 to 23 can appropriately determine the deterioration state of the monitor cell 43 and the deterioration state of the sensor cell 42, respectively.

When the electromotive force feedback control is performed, the monitor cell electromotive force within the sudden change region where the monitor cell electromotive force Vm suddenly changes in the electromotive force characteristics of the monitor cell 43 and the oxygen concentration is greater than 0 (the excess air ratio is greater than 1). Vm is set as a target value, and the oxygen concentration is adjusted by the pump cell 41 based on the target value. As a result, in the deterioration state of the monitor cell, a shift in the residual oxygen concentration is likely to occur according to the deterioration state, so that the deterioration state of the monitor cell can be accurately determined.

The NOx sensors 21 to 23 have a one-chamber structure in which each electrode (cathode) of the pump cell 41, the sensor cell 42, and the monitor cell 43 is provided in the same gas chamber 61. In this configuration, the gas atmosphere of the monitor cell 43 and the sensor cell 42 can be switched at an early stage by adjusting the oxygen concentration of the pump cell applied voltage Vp, so that deterioration can be determined in a shorter time compared to a configuration having a plurality of chambers. .

In the first embodiment, it is also possible to use the slope of the sensor cell current Is during a transient change instead of the response change amount ΔIs of the sensor cell current Is as a parameter for determining deterioration.

(Second Embodiment)
In the following, the second embodiment will be described with a focus on differences from the first embodiment. In the second embodiment, the SCUs 31 to 33 have a function of switching the pump cell applied voltage Vp to a predetermined value and determining the deterioration state of the sensor cell 42 based on a change in the sensor cell current Is accompanying the voltage switching. The SCUs 31 to 33 (degradation determination unit M13) determine the deterioration state of the monitor cell 43 based on the response change amount ΔIs of the sensor cell current Is in the state where the electromotive force feedback control is performed and the deterioration determination result of the sensor cell 42. judge.

Here, the deterioration determination of the sensor cell 42 performed by switching the pump cell applied voltage Vp will be briefly described with reference to FIG. In FIG. 14, at time t3, the pump cell applied voltage Vp is switched from Vp0 to Vp1 stepwise (Vp0> Vp1). Along with this, the pump cell current Ip is changed to a decreasing side, and the residual oxygen concentration in the gas chamber 61 is increased. In the sensor cell 42, the sensor cell current Is increases to a steady value (convergence value) through a transient response as the residual oxygen concentration increases. In this case, when the initial state in which the sensor cell 42 is not deteriorated is compared with the state after deterioration, the steady state value decreases from the steady state value of the initial characteristic and the rise is increased after the deterioration. Slower than the ones. Based on these, the SCUs 31 to 33 perform the deterioration determination of the sensor cell 42.

FIG. 15 is a flowchart showing the deterioration determination process in the present embodiment. This process is performed by the SCUs 31 to 33, for example, at a predetermined cycle.

In step S31, it is determined whether or not an execution condition for deterioration determination is satisfied. However, since this process is the same as step S11 of FIG. 7, detailed description thereof is omitted. If the execution condition for the deterioration determination is satisfied, the process proceeds to the subsequent step S42. If the execution condition is not satisfied, the present process is terminated.

In step S42, the pump cell applied voltage Vp is switched from Vp0 to Vp1. Vp1 is a predetermined value. Thereafter, in step S43, an output change amount of the sensor cell current Is after voltage switching is calculated. Here, for example, the response change amount ΔIs3 (see FIG. 14) is calculated from the sensor cell current Is after the current change converges. Instead of this, as the output change amount of the sensor cell current Is, it is also possible to calculate the slope at the time of the transient change of the sensor cell current Is.

Thereafter, in step S44, the response change amount ΔIs3 is compared with the initial value of the response change amount of the sensor cell current Is calculated in advance under the same conditions as the current voltage switching (hereinafter, referred to as the initial change amount ΔIsini3). Deterioration judgment is performed. In this case, the deterioration determination may be performed by calculating the output ratio (ΔIs3 / ΔIsini3) based on the ratio between the response change amount ΔIs3 and the initial change amount ΔIsini3 and calculating the deterioration rate based on the output ratio.

In steps S45 and S46, electromotive force feedback control is performed to calculate the response change amount ΔIs1 of the sensor cell current Is (same as steps S12 and S13 described above).

Thereafter, in step S47, the deterioration of the monitor cell 43 is determined. At this time, the deterioration rate Cm of the monitor cell 43 is calculated based on the response change amount ΔIs1 and the initial change amount ΔIsini1 of the sensor cell current Is while taking into consideration the determination result in step S44 (the deterioration state of the sensor cell 42). For example, the deterioration rate Cm of the monitor cell 43 is calculated on the condition that no deterioration has occurred in the sensor cell 42 (the deterioration rate of the sensor cell 42 is less than a predetermined value). In this case, if the sensor cell 42 is in a deteriorated state, the deterioration determination of the monitor cell 43 is not performed.

Alternatively, the deterioration rate Cm of the monitor cell 43 is corrected based on the deterioration rate (degradation degree) of the sensor cell 42. For example, when performing electromotive force feedback control, the response change amount ΔIs of the sensor cell current Is tends to decrease both when the monitor cell 43 is deteriorated and when the sensor cell 42 is deteriorated. Based on this, the deterioration rate Cm of the monitor cell 43 is corrected to the decreasing side. That is, the correction is made to reduce the degree of deterioration.

In steps S45 and S46, current feedback control can be performed instead of the electromotive force feedback control, and the response change amount ΔIs2 of the sensor cell current Is can be calculated (same as the above-described steps S22 and S23). In this case, in step S47, the deterioration rate Cm of the monitor cell 43 is calculated based on the response change amount ΔIs2 and the initial change amount ΔIsini2 of the sensor cell current Is while taking the determination result in step S44 (deterioration state of the sensor cell 42) into account. calculate. The specific contents are the same as described above. However, when the current feedback control is performed, since the increase / decrease in the response change amount ΔIs is reversed between the deterioration of the monitor cell 43 and the deterioration of the sensor cell 42, the deterioration of the monitor cell 43 is determined based on the deterioration rate of the sensor cell 42. The rate Cm may be corrected to the increasing side. That is, the correction is made so that the degree of deterioration becomes larger.

When the pump cell applied voltage Vp is intentionally switched, the sensor cell current Is changes with a change in the residual oxygen concentration due to the voltage switching, and the deterioration state of the sensor cell 42 can be determined based on the change in the sensor cell current Is. In such a configuration, the deterioration state of the monitor cell 43 is determined based on the sensor cell current Is acquired with the execution of the electromotive force feedback control while taking into account the deterioration determination result of the sensor cell 42. In this case, the transient change of the sensor cell current Is depends on the deterioration state of both the monitor cell 43 and the sensor cell 42, but it is possible to appropriately determine the deterioration state of the monitor cell 43 by performing the deterioration determination individually. Become.

(Other embodiments)
You may change the said embodiment as follows, for example.

・ Deterioration determination (calculation of deterioration rate) described in FIG. 7, FIG. 11, FIG. 13, and FIG. It is good also as a structure which implements determination. Thereby, the determination accuracy can be increased.

In the above embodiment, the initial value calculated in advance under the same conditions is used as the reference value used when performing the deterioration determination of the monitor cell 43 or the deterioration determination of the sensor cell 42, but the degree of deterioration over time can be grasped. Any other value may be used. For example, a predetermined value other than the initial value, a predetermined value determined according to the number of years of use, or the like can be used.

In the above embodiment, the sensor element 40 has a single solid electrolyte body 53 and a single gas chamber 61 (one-chamber structure), but this may be changed. For example, the sensor element 40 has a plurality of solid electrolyte bodies 53 and a plurality of gas chambers 61, and the pump cell 41 and the sensor cell 42 are different solid electrolyte bodies 53 and face the other gas chambers 61. The structure provided so that it may be sufficient. An example of such a configuration is shown in FIG.

The sensor element 40 shown in FIG. 16 has two solid electrolyte bodies 53a and 53b arranged opposite to each other, and gas chambers 61a and 61b provided between the solid electrolyte bodies 53a and 53b. The gas chamber 61a communicates with the exhaust introduction port 53c, and the gas chamber 61b communicates with the gas chamber 61a via the throttle portion 71. The pump cell 41 has a pair of electrodes 72 and 73, and one of the electrodes 72 is provided so as to be exposed in the gas chamber 61a. The sensor cell 42 has an electrode 74 and a common electrode 76 that are arranged to face each other, and the monitor cell 43 has an electrode 75 and a common electrode 76 that are arranged to face each other. The sensor cell 42 and the monitor cell 43 are provided adjacent to each other. In each of these cells, one electrode 74, 75 is provided so as to be exposed in the gas chamber 61b. Thus, even in the configuration in which the pump cell 41 and the sensor cell 42 are provided in separate gas chambers 61a and 61b, each function such as the deterioration determination of the above-described embodiment can be suitably performed.

· The specific gas component to be detected may be other than NOx. For example, it may be a gas sensor that detects HC or CO in the exhaust. In this case, it is preferable that oxygen in exhaust gas is discharged by the pump cell, and HC and CO are decomposed from the gas after oxygen discharge by the sensor cell to detect the HC concentration and CO concentration. In addition, the concentration of ammonia in the gas to be detected may be detected.

∙ It can also be embodied as a gas sensor control device for a gas sensor provided in an intake passage of an internal combustion engine or a gas sensor used for other types of engines such as a gasoline engine in addition to a diesel engine. The gas sensor may use a gas other than exhaust as a gas to be detected, or may be used for applications other than automobiles.

Although the present disclosure has been described based on the embodiments, it is understood that the present disclosure is not limited to the embodiments and structures. The present disclosure includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more or less, are within the scope and spirit of the present disclosure.

Claims (10)

1. A pump cell (41) for adjusting the oxygen concentration in the gas to be detected introduced into the gas chamber (61) by applying a voltage, and a sensor cell for detecting the concentration of a specific gas component in the gas chamber after the oxygen concentration is adjusted by the pump cell. (42) and a control device (31-33, 35) which is applied to a gas sensor (21-23) having a monitor cell (43) for detecting the residual oxygen concentration in the gas chamber and performs control relating to the gas sensor. And
   A pump cell controller for adjusting the residual oxygen concentration by the pump cell in order to control the output (Vm, Im) of the monitor cell to a target value;
   An acquisition unit for acquiring the output (Is) of the sensor cell in a state where the residual oxygen concentration is adjusted by the pump cell control unit;
   A deterioration determination unit that determines a deterioration state of the monitor cell based on the output of the sensor cell acquired by the acquisition unit;
   A gas sensor control device comprising:
2. The gas sensor generates a monitor cell electromotive force (Vm) corresponding to a residual oxygen concentration in the gas chamber as an output of the monitor cell,
   The pump cell control unit performs adjustment of the residual oxygen concentration by the pump cell by performing electromotive force control for controlling the monitor cell electromotive force to a target value.
   The gas sensor control device according to claim 1, wherein the deterioration determination unit determines a deterioration state of the monitor cell based on an output change amount (ΔIs1) of the sensor cell generated by the execution of the electromotive force control.
3. 3. The deterioration determination unit according to claim 2, wherein the deterioration determination unit determines the deterioration state of the monitor cell based on a ratio of the output change amount of the sensor cell to the output change amount in an initial state before deterioration being smaller than a predetermined value. Gas sensor control device.
4. The gas sensor generates, as an output of the monitor cell, a monitor cell current (Im) corresponding to a residual oxygen concentration in the gas chamber in a state where a voltage is applied to the monitor cell.
   The pump cell control unit performs adjustment of the residual oxygen concentration by the pump cell by performing monitor cell current control for controlling the monitor cell current to a target value,
   2. The gas sensor control device according to claim 1, wherein the deterioration determination unit determines a deterioration state of the monitor cell based on an output change amount (ΔIs2) of the sensor cell caused by the execution of the monitor cell current control.
5. The gas sensor control device according to claim 4, wherein the deterioration determination unit determines a deterioration state of the monitor cell based on an output change amount of the sensor cell being larger than a predetermined reference value.
6. The gas sensor control device according to claim 4 or 5, wherein the deterioration determination unit determines a deterioration state of the sensor cell based on an output change amount of the sensor cell being smaller than a predetermined reference value.
7. A gas sensor control device that switches an applied voltage (Vp) of the pump cell to a predetermined value and determines a deterioration state of the sensor cell based on an output change of the sensor cell accompanying the voltage switching,
   The said deterioration determination part determines the deterioration state of the said monitor cell based on the output of the said sensor cell acquired by the said acquisition part, and the deterioration determination result of the said sensor cell. Gas sensor control device.
8. The gas sensor generates, as an output of the monitor cell, a monitor cell electromotive force (Vm) corresponding to the residual oxygen concentration in the gas chamber, and according to the residual oxygen concentration in the gas chamber in a state where a voltage is applied to the monitor cell. It is possible to generate a monitor cell current (Im),
   The pump cell control unit performs the electromotive force control for controlling the monitor cell electromotive force to a target value, thereby allowing the pump cell to adjust the residual oxygen concentration, while controlling the monitor cell current to the target value. By performing the control, the residual oxygen concentration is adjusted by the pump cell,
   The deterioration determination unit, based on the output change amount (ΔIs1) of the sensor cell caused by the execution of the electromotive force control and the output change amount (ΔIs2) of the sensor cell caused by the execution of the monitor cell current control, The gas sensor control device according to claim 1, wherein the deterioration determination is performed on the monitor cell and the sensor cell.
9. The deterioration determination unit
   The output change amount of the sensor cell is smaller than a predetermined first reference value (ΔIsini1) when the electromotive force control is performed, and a predetermined second reference value when the monitor cell current control is performed. Determining a degradation state of the monitor cell based on becoming larger than (ΔIsini2);
   The output change amount of the sensor cell becomes smaller than the first reference value (ΔIsini1) when the electromotive force control is performed, and becomes the second reference value (ΔIsini2) when the monitor cell current control is performed. The gas sensor control device according to claim 8, wherein a deterioration state of the sensor cell is determined based on an increase in size.
10. The gas sensor has an electromotive force characteristic of the monitor cell in which the monitor cell electromotive force is substantially zero in a region where the excess air ratio> 1, the monitor cell electromotive force becomes a predetermined value in the region where the excess air ratio <1, and the excess air ratio = 1. The monitor cell electromotive force has a characteristic that changes suddenly in the area of
    When the electromotive force control is performed, the pump cell control unit sets a monitor cell electromotive force within a sudden change region where the monitor cell electromotive force suddenly changes in the electromotive force characteristics of the monitor cell and an excess air ratio is greater than 1. The gas sensor control device according to any one of claims 2, 3, 8, and 9, wherein an oxygen concentration is adjusted by the pump cell based on the target value.

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