阅读说明：本技术 气体传感器控制装置 (Gas sensor control device ) 是由 小薮忠胜 村山勇树 加山龙三 长谷川明里 河本祐辅 于 2018-05-25 设计创作，主要内容包括：气体传感器具有泵单元与传感器单元。SCU(31～33)具备：电压切换部(M11),实施向增加气体室内的氧浓度一侧切换泵单元的施加电压(Vp)的第1电压切换,以及在该第1电压切换的实施后、向减少气体室内的氧浓度一侧切换施加电压的第2电压切换；输出变化计算部(M12),在实施了第1电压切换或者第2电压切换的状态中,对表示与该电压切换对应的传感器单元的输出变化的输出变化参数进行计算；浓度差计算部(M13),对于被检测气体中的氧浓度或者特定气体成分的浓度,对表示第1电压切换的实施前以及第2电压切换的实施后的浓度差的浓度差参数进行计算；以及劣化判定部(M14),基于通过输出变化参数以及浓度差参数,判定传感器单元的劣化状态。(The gas sensor has a pump unit and a sensor unit. The SCU (31-33) is provided with: a voltage switching unit (M11) for performing 1 st voltage switching for switching the applied voltage (Vp) of the pump unit to the side of increasing the oxygen concentration in the gas chamber and 2 nd voltage switching for switching the applied voltage to the side of decreasing the oxygen concentration in the gas chamber after the 1 st voltage switching is performed; an output change calculation unit (M12) that calculates an output change parameter indicating a change in the output of the sensor cell corresponding to the voltage switching, while the 1 st voltage switching or the 2 nd voltage switching is being performed; a concentration difference calculation unit (M13) that calculates a concentration difference parameter indicating a concentration difference between the concentration of oxygen in the gas to be detected and the concentration of the specific gas component before and after the 1 st voltage switching; and a deterioration determination unit (M14) that determines the deterioration state of the sensor cell based on the pass-through output variation parameter and the concentration difference parameter.)

1. A gas sensor control device (31-33, 35) applied to a gas sensor (21-23) having a pump means (41) for adjusting the oxygen concentration of a gas to be detected introduced into a gas chamber (61) by applying a voltage thereto and a sensor means (42) for detecting the concentration of a specific gas component from the gas to be detected whose oxygen concentration has been adjusted by the pump means, the gas sensor control device comprising:

a voltage switching unit that performs 1 st voltage switching for switching an applied voltage (Vp) of the pump unit to a side of increasing an oxygen concentration in the gas chamber and 2 nd voltage switching for switching the applied voltage to a side of decreasing the oxygen concentration in the gas chamber after the 1 st voltage switching is performed;

an output change calculation unit that calculates an output change parameter indicating an output change of the sensor cell according to the voltage switching in at least one of a state where the 1 st voltage switching is performed and a state where the 2 nd voltage switching is performed;

a concentration difference calculation unit that calculates a concentration difference parameter indicating a concentration difference between the concentration of the oxygen in the gas to be detected and the concentration of the specific gas component before the 1 st voltage switching and after the 2 nd voltage switching; and

and a deterioration determination unit that determines a deterioration state of the sensor unit based on the output change parameter calculated by the output change calculation unit and the concentration difference parameter calculated by the concentration difference calculation unit.

2. The gas sensor control device according to claim 1,

the concentration difference calculation unit calculates, as the concentration difference parameter, a difference between the outputs of the pump unit or the sensor unit before the 1 st voltage switching and after the 2 nd voltage switching,

the deterioration determination unit determines a deterioration state of the sensor unit based on the output change parameter calculated by the output change calculation unit and the output difference of the pump unit or the output difference of the sensor unit calculated by the concentration difference calculation unit.

3. The gas sensor control device according to claim 2,

the voltage switching unit sets the voltage applied to the pump cell to the same voltage as the voltage applied to the pump cell before the 1 st voltage switching is performed when the 2 nd voltage switching is performed.

4. The gas sensor control device according to any one of claims 1 to 3,

the deterioration determination unit determines whether or not the deterioration determination of the sensor unit is valid based on the concentration difference parameter calculated by the concentration difference calculation unit.

5. The gas sensor control device according to claim 4,

the deterioration determination unit performs the 1 st voltage switching and the 2 nd voltage switching again by the voltage switching unit when it is determined that the deterioration of the sensor cell is not effective, and determines the deterioration state of the sensor cell again based on the output change parameter calculated by the output change calculation unit and the concentration difference parameter calculated by the concentration difference calculation unit when the voltage switching is performed again.

6. The gas sensor control device according to any one of claims 1 to 5,

the deterioration determination unit corrects the deterioration determination result of the sensor cell based on the concentration difference parameter calculated by the concentration difference calculation unit.

7. The gas sensor control device according to claim 6,

when the concentration difference parameter corresponds to an increase in the oxygen concentration or the concentration of the specific gas component after the 2 nd voltage switching is performed and before the 1 st voltage switching is performed, the degradation determination unit corrects the degradation determination result of the sensor cell to a smaller degradation degree.

8. The gas sensor control device according to claim 6 or 7,

when the concentration difference parameter corresponds to a decrease in the oxygen concentration or the concentration of the specific gas component after the 2 nd voltage switching is performed and before the 1 st voltage switching is performed, the deterioration determination unit corrects the result of the deterioration determination of the sensor cell to a larger degree of deterioration.

9. The gas sensor control device according to any one of claims 1 to 8,

the voltage switching unit performs a voltage switching cycle including the 1 st voltage switching and the 2 nd voltage switching a plurality of times at predetermined time intervals,

the deterioration determination section determines a deterioration state of the sensor cell based on the output change parameter of the voltage switching cycle in which the density difference is smallest among the density difference parameters calculated by the density difference calculation section in each of the plurality of voltage switching cycles.

10. The gas sensor control device according to any one of claims 1 to 9, comprising:

a fluctuation determination unit that determines whether or not a steady state is reached in which a fluctuation amount per unit time is equal to or less than a predetermined value with respect to at least one of an oxygen concentration in the gas to be detected and a concentration of the specific gas component; and

and a permission unit that permits the 1 st voltage switching and the 2 nd voltage switching by the voltage switching unit, respectively, on the condition that it is determined that the steady state is achieved.

11. The gas sensor control device according to any one of claims 1 to 10,

the gas sensor is an exhaust gas sensor for detecting the concentration of the specific gas component in an exhaust gas, using the exhaust gas discharged from an internal combustion engine (10) as the gas to be detected,

the gas sensor control device is a gas sensor control device that can communicate with an engine control device (35) that performs control of the internal combustion engine or control related to an exhaust system of the internal combustion engine, and is provided with:

and an information transmitting unit that transmits a determination result of the degradation determining unit to the engine control device on the condition that the concentration difference parameter calculated by the concentration difference calculating unit corresponds to the concentration difference being smaller than a predetermined value.

12. The gas sensor control device according to any one of claims 1 to 10,

the gas sensor is an exhaust gas sensor for detecting the concentration of the specific gas component in an exhaust gas, using the exhaust gas discharged from an internal combustion engine (10) as the gas to be detected,

the gas sensor control device is a gas sensor control device that can communicate with an engine control device (35) that performs control of the internal combustion engine or control related to an exhaust system of the internal combustion engine, and is provided with:

and an information transmitting unit that transmits the determination result of the degradation determining unit and the information of the concentration difference parameter calculated by the concentration difference calculating unit to the engine control device.

Technical Field

The present application relates to a gas sensor control device.

Background

As a gas sensor for detecting the concentration of a specific gas component in a gas to be detected such as an exhaust gas of an internal combustion engine, an NOx sensor for detecting the concentration of NOx (nitrogen oxide) is known. For example, as described in patent document 1, the NOx sensor has a three-unit structure including a pump unit that discharges or draws out oxygen in exhaust gas in a gas chamber, a monitor unit that detects a residual oxygen concentration in the gas chamber after passing through the pump unit, and a sensor unit that detects a NOx concentration in the gas after passing through the pump unit.

If the NOx sensor deteriorates, accurate NOx concentration cannot be detected any more, and as a result, when the NOx sensor is installed in an exhaust system of an automobile, there is a concern that a problem such as deterioration of exhaust emission may occur. Therefore, a method of diagnosing deterioration of the NOx sensor has been proposed, and for example, patent document 1 discloses a method of forcibly switching the voltage applied to the pump unit and diagnosing deterioration of the NOx sensor based on the amount of change in the sensor unit output at that time.

Disclosure of Invention

However, the conventional deterioration diagnosis method described above is designed to intentionally change the residual oxygen concentration in the gas chamber by switching the pump cell applied voltage, and to perform the deterioration diagnosis of the sensor cell based on the transient response of the sensor cell accompanying the change in the residual oxygen concentration, but it is considered that, after the switching of the pump cell applied voltage, for example, the change in the oxygen concentration in the exhaust gas, the change in the NOx concentration, or the like occurs, and the change in the output of the sensor cell due to the change in the concentration occurs. In other words, in the periphery of the sensor unit, it is considered that the sensor unit is affected by an unplanned change generated as a gas atmosphere. In this case, there is a possibility that the deterioration diagnosis of the sensor unit is adversely affected.

The present application has been made in view of the above-described problems, and a main object thereof is to provide a gas sensor control device capable of appropriately determining a deterioration state of a sensor cell.

In order to solve the above problem, the present invention is a gas sensor control device applied to a gas sensor having a pump means for adjusting an oxygen concentration in a gas to be detected introduced into a gas chamber by voltage application and a sensor means for detecting a concentration of a specific gas component from the gas to be detected whose oxygen concentration has been adjusted by the pump means, the gas sensor control device including:

a voltage switching unit that performs 1 st voltage switching for switching the applied voltage of the pump unit to a side of increasing the oxygen concentration in the gas chamber and 2 nd voltage switching for switching the applied voltage to a side of decreasing the oxygen concentration in the gas chamber after the 1 st voltage switching is performed;

an output change calculation unit that calculates an output change parameter indicating an output change of the sensor cell corresponding to the voltage switching in at least one of a state in which the 1 st voltage switching is performed and a state in which the 2 nd voltage switching is performed;

a concentration difference calculation unit that calculates a concentration difference parameter indicating a concentration difference between the concentration of the oxygen in the gas to be detected and the concentration of the specific gas component before the 1 st voltage switching and after the 2 nd voltage switching; and

and a deterioration determination unit that determines a deterioration state of the sensor unit based on the output change parameter calculated by the output change calculation unit and the concentration difference parameter calculated by the concentration difference calculation unit.

In the above configuration, when the applied voltage of the pump unit is switched to the side of increasing the oxygen concentration in the gas chamber as the 1 st voltage or the applied voltage of the pump unit is switched to the side of decreasing the oxygen concentration in the gas chamber as the 2 nd voltage at the time of determining the deterioration of the sensor unit, a transient change in the output of the sensor unit occurs in accordance with the voltage switching. Therefore, the deterioration state of the sensor unit can be determined using the output variation parameter indicating the output variation of the sensor unit. However, if the oxygen concentration in the gas to be detected or the concentration of the specific gas component fluctuates during the period in which the output of the sensor cell changes, there is a concern that this will adversely affect the deterioration determination of the sensor cell based on the output change parameter of the sensor cell.

In this regard, according to the above configuration, the concentration difference parameter indicating the concentration difference between the concentration of the oxygen in the gas to be detected and the concentration of the specific gas component before the 1 st voltage switching and after the 2 nd voltage switching is performed is calculated, and the deterioration state of the sensor cell is determined based on the output variation parameter of the sensor cell and the concentration difference parameter. Thus, if the oxygen concentration in the gas to be detected or the concentration of the specific gas component (NOx concentration) fluctuates during the period in which the 1 st voltage is switched to the 2 nd voltage, the deterioration state of the sensor cell can be appropriately determined.

Drawings

The above and other objects, features and advantages of the present application will become more apparent with reference to the accompanying drawings and the following detailed description. The attached drawings are as follows:

FIG. 1 is a diagram showing a system configuration of an engine exhaust system,

FIG. 2 is a sectional view showing the constitution of a NOx sensor,

figure 3 is a cross-sectional view showing the III-III section of figure 2,

fig. 4 is a diagram for explaining a change in transient characteristics of the sensor cell output accompanying deterioration of the NOx sensor,

FIG. 5 is a view showing a start point and an end point used for calculation of a slope parameter,

FIG. 6 is a functional block diagram showing the SCU and the ECU,

fig 7 is a flowchart showing a processing procedure of the deterioration determination of the sensor unit,

FIG. 8 is a graph showing the relationship between the reaction rate ratio and the deterioration rate,

FIG. 9 is a timing chart showing the behavior when a voltage switching cycle is performed a plurality of times,

fig. 10 is a flowchart showing a procedure of a process of deterioration judgment of the sensor unit in embodiment 2,

figure 11 is a graph showing the relationship between the pump unit output difference deltaipx and the correction value KC,

fig. 12 is a flowchart showing a procedure of a process of deterioration judgment of the sensor unit in embodiment 3,

fig. 13 is a sectional view showing the configuration of another NOx sensor.

Detailed Description

Hereinafter, embodiments will be described based on the drawings. In the present embodiment, a gas sensor control device that performs control related to an NOx sensor is embodied in a system that detects a NOx concentration in exhaust gas discharged from a diesel engine mounted on a vehicle as a detected gas by the NOx sensor. In the following embodiments, the same or equivalent portions are denoted by the same reference numerals in the drawings, and the description thereof will be referred to for the portions denoted by the same reference numerals.

(embodiment 1)

As shown in fig. 1, an exhaust gas purification system for purifying exhaust gas is provided on an exhaust side of an engine 10 as a diesel engine. As a configuration of the exhaust gas purification system, an exhaust pipe 11 forming an exhaust passage is connected to the engine 10, and an oxidation catalyst converter 12 and a selective reduction catalyst converter (hereinafter, referred to as an SCR catalyst converter) 13 are provided in this exhaust pipe 11 in this order from the engine 10 side. The oxidation catalyst converter 12 has a diesel oxidation catalyst 14 and a dpf (diesel particulate filter) 15. The SCR catalyst converter 13 includes an SCR catalyst 16 as a catalyst for selective reduction. Further, in the exhaust pipe 11, 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 catalyst converter 12 and the SCR catalyst converter 13.

In the oxidation catalytic converter 12, the diesel oxidation catalyst 14 is mainly composed of a ceramic carrier, an oxide mixture containing alumina, ceria, and zirconia, 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 gas temperature by heat generated at the time of the catalytic reaction.

The DPF15 is formed of a honeycomb structure, and is configured by loading a platinum group catalyst such as platinum or palladium on porous ceramics. The DPF15 collects particulate matter contained in the exhaust gas by depositing it on the partition walls of the honeycomb structure. The accumulated particulate matter is oxidized and purified by combustion. This combustion utilizes a temperature increase in the diesel oxidation catalyst 14 and/or a reduction in the combustion temperature of the particulate matter by the additive.

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

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

SCUs (sensor Control units) 31, 32, and 33 are connected to the NOx sensors 21 to 23, respectively, and detection signals of the NOx sensors 21 to 23 are appropriately output to the SCUs 31 to 33 for each sensor. The SCUs 31-33 are electronic control devices having a microcomputer with a CPU, various memories, and peripheral circuits thereof, and the SCUs 31-33 calculate oxygen (O) in exhaust gas based on detection signals (limit current signals) of the NOx sensors 21-23₂) Concentration, NOx concentration as the concentration of a specific gas component, and the like.

The SCUs 31-33 are connected to a communication line 34 such as a CAN bus, and are connected to various ECUs (for example, an engine ECU35) via the communication line 34. In other words, the SCUs 31-33 and the engine ECU35 can transmit and receive information to and from each other using the communication line 34. The SCUs 31-33 transmit information on the oxygen concentration and NOx concentration in the exhaust gas to the engine ECU35, for example. The engine ECU35 is an electronic control device including a microcomputer having a CPU, various memories, and peripheral circuits thereof, and controls various devices of the engine 10 and the exhaust system. The engine ECU35 performs fuel injection control and the like based on, for example, the accelerator opening degree and the engine rotational speed.

The engine ECU35 also performs control of urea water addition by the urea water addition valve 17 based on the NOx concentrations detected by the NOx sensors 21 to 23. The engine ECU35 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 catalyst converter 13, and performs feedback correction on the urea water addition amount so that the NOx concentration detected by the NOx sensor 23 on the downstream side of the SCR catalyst converter 13 becomes a value as small as possible, while omitting the control of urea water addition. Then, the driving of the aqueous urea solution addition valve 17 is controlled based on the amount of the aqueous urea solution added.

Next, the structure of the NOx sensors 21 to 23 will be explained. The NOx sensors 21 to 23 have the same configuration, and the configuration of the NOx sensor 21 will be described here. Fig. 2 and 3 are diagrams showing an internal structure of the sensor element 40 constituting the NOx sensor 21. The left-right direction of the drawing is the longitudinal direction of the sensor element 40, and the left side of the drawing is the element tip side. The sensor element 40 has a so-called three-unit configuration including a pump unit 41, a sensor unit 42, and a monitor unit 43. The monitor unit 43 has a function of discharging oxygen in the gas, and may be referred to as an auxiliary pump unit or a2 nd pump unit, as in the pump unit 41.

The sensor element 40 includes a1 st body portion 51 and a2 nd body portion 52 formed of an insulator such as alumina, a solid electrolyte body 53 disposed between the body portions 51 and 52, a diffusion resistor 54, a pump cell electrode 55, a sensor cell electrode 56, a monitor cell electrode 57, a common electrode 58, and a heater 59. A gas chamber 61 as a concentration measuring chamber is formed between the 1 st body 51 and the solid electrolyte body 53, and an atmospheric chamber 62 as a reference gas chamber is formed between the 2 nd body 52 and the solid electrolyte body 53.

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 of a predetermined gas component (NOx concentration) in the gas chamber 61 based on the oxygen ion current flowing between the sensor cell electrode 56 and the common electrode 58, and is formed by the sensor cell electrode 56, 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 based on the oxygen ion current flowing between the monitor cell electrode 57 and the common electrode 58, and is formed by the monitor cell electrode 57, the common electrode 58, and a part of the solid electrolyte body 53.

The solid electrolyte body 53 is a plate-like member, and is made of an oxygen-ion solid electrolyte material such as zirconia. The 1 st body part 51 and the 2 nd body part 52 are disposed on both sides of the solid electrolyte body 53. The solid electrolyte body 53 side of the 1 st main body 51 has a step shape, and a recess formed by the step shape serves as a gas chamber 61. One side surface of the recess of the 1 st body 51 is open, and the diffusion resistor 54 is disposed on the open side surface. The diffusion resistance member 54 is formed of a material in which a porous material or pores are formed. The velocity of the exhaust gas introduced into the gas chamber 61 is regulated by the action of the diffusion resistance body 54.

Similarly, the second body part 52 has a stepped shape on the solid electrolyte body 53 side, and a recess formed by the stepped shape serves as an atmospheric chamber 62. One side of the atmospheric chamber 62 is open. The gas introduced into the atmospheric chamber 62 from the side of the solid electrolyte body 53 is released into the atmosphere.

In the solid electrolyte body 53, a pump cell electrode 55, a sensor cell electrode 56, and a monitor cell electrode 57 are provided on the cathode side on the surface facing the gas chamber 61. 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, i.e., on the upstream side in the gas chamber 61, and the sensor cell electrode 56 and the monitor cell electrode 57 are disposed on the opposite side of the diffusion resistor 54, i.e., on the downstream side in the gas chamber 61, with the pump cell electrode 55 interposed therebetween. 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 at positions close to each other and at positions equivalent to each other with respect to the flow direction of the exhaust gas. The pump cell electrode 55 and the monitor cell electrode 57 are electrodes made of a noble metal such as Au — Pt which is inactive to NOx (electrodes which are hard to decompose NOx), while the sensor cell electrode 56 is an electrode made of a noble metal such as platinum Pt or rhodium Rh which is active to NOx.

In addition, in the solid electrolyte body 53, a common electrode 58 serving as an anode side is provided at a position corresponding to each of the electrodes 55 to 57 on the cathode side on a surface facing the atmospheric chamber 62.

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 by the pump cell electrode 55 on the cathode side. The oxygen ions move in the solid electrolyte body 53 toward the common electrode 58 on the anode side, and are discharged to the atmosphere chamber 62 as oxygen by discharging electric charges in the common electrode 58. Thereby, the gas chamber 61 is maintained in a predetermined low oxygen state.

The higher the applied voltage of the pump cell 41 (i.e., 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 unit 41, the smaller the amount of oxygen discharged from the exhaust gas by the pump unit 41. Therefore, by increasing or decreasing the applied voltage of the pump unit 41, the amount of residual oxygen in the exhaust gas flowing through the sensor unit 42 and the monitor unit 43 at the subsequent stage can be increased or decreased. In the present embodiment, the voltage applied to the pump cell 41 is a pump cell applied voltage Vp, and the current output in the voltage applied state of the pump cell 41 is a pump cell current Ip.

The monitor unit 43 detects the concentration of oxygen remaining in the gas chamber 61 in a state after the oxygen is discharged by the pump unit 41. At this time, the monitor unit 43 outputs a current signal generated as a result of 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 unit 43 is obtained as a monitor unit current Im or a monitor unit electromotive force Vm in the SCU31 to 33.

In the state where oxygen is discharged by the pump means 41, the sensor means 42 reduces and decomposes NOx in the exhaust gas with the application of voltage, and outputs current signals corresponding to the NOx concentration and the residual oxygen concentration in the gas chamber 61. The output of the sensor unit 42 Is obtained as a sensor unit current Is in the SCUs 31-33. In SCU31 ~ 33, the NOx concentration in the exhaust gas Is calculated by using sensor cell current Is.

However, in the sensor cell 42, due to the influence of aging or the like, even if the concentration of the gas to be detected in the exhaust gas Is the same, the transient response of the sensor cell current Is as its output tends to change. This trend is illustrated with reference to fig. 4. In fig. 4, (a) schematically shows the pump unit applied voltage Vp, (b) schematically shows the pump unit current Ip, and (c) schematically shows the time lapse of the sensor unit current Is. Here, the case where the 1 st voltage switching and the 2 nd voltage switching are performed is described, the 1 st voltage is switched to the switching pump cell application voltage Vp for increasing the residual oxygen concentration in the gas chamber 61, and the 2 nd voltage is switched to the switching pump cell application voltage Vp for decreasing the residual oxygen concentration in the gas chamber 61 after the 1 st voltage switching is performed.

In fig. 4, at time t1, the pump-unit applied voltage Vp is switched from Vp0 to Vp1 in a stepwise manner as the 1 st voltage switching (Vp0 > Vp 1). Thereby, the pump cell current Ip changes to the decreasing side, and the residual oxygen concentration in the gas chamber 61 increases. At this time, the pump cell current Ip changes from Ip0 with trailing (tailing), and converges to Ip 1. In the sensor cell 42, the sensor cell current Is increases to a steady-state value through a transient response in accordance with an increase in the residual oxygen concentration.

In fig. 4 (c), the transient response characteristic of the sensor cell current Is according to the decrease of the pump cell applied voltage Vp Is shown by two characteristics, that Is, a characteristic at the time of manufacturing the NOx sensor (initial characteristic) and a characteristic at the time of deterioration of the NOx sensor (post-deterioration characteristic). The solid line indicates the initial characteristic, and the dashed dotted line indicates the characteristic at the time of deterioration. Fig. 4 (c) shows that, when the exhaust gas supplied to the sensor cell 42 has the same oxygen concentration, a difference occurs between the initial characteristic of the sensor cell current Is and the characteristic at the time of deterioration. In this case, first, there is a tendency that the steady-state value of the characteristic at the time of degradation is lower than the steady-state value of the initial characteristic. Second, there is a tendency that the rise of the characteristic at the time of deterioration is later than the rise of the initial characteristic. For example, when the slope of the characteristic in the period Ta during transient change is observed, the slope a11 of the characteristic at the time of deterioration becomes gentler than the slope a10 of the initial characteristic. The period Ta is a period between the start point P1 and the end point P2 in the transient response accompanying the switching of the pump cell applied voltage Vp. These trends become significant as the deterioration of the sensor unit 42 progresses.

In fig. 4, at time t2, the pump-unit applied voltage Vp is switched from Vp1 to Vp2 in a stepwise manner as the 2 nd voltage switching (Vp1 < Vp 2). Thereby, the pump cell current Ip changes to the increasing side, and the residual oxygen concentration in the gas chamber 61 decreases. At this time, the pump cell current Ip changes from Ip1 with tailing, and converges to Ip 2. In the sensor cell 42, the sensor cell current Is reduced to a steady-state value through a transient response in correspondence with the decrease in the residual oxygen concentration. In the case of performing the 2 nd voltage switching, a difference occurs between the initial characteristic of the sensor cell current Is and the characteristic at the time of deterioration. In this case, for example, when the slope of the characteristic in the period Tb during transient change is observed, the slope a21 of the characteristic at the time of degradation is gentler than the slope a20 of the initial characteristic. The period Tb is a period between the start point P3 and the end point P4 in the transient response accompanying the switching of the pump cell applied voltage Vp.

In the implementation of the 1 st voltage switching, the start point P1 and the end point P2 are timings included in a predetermined period after the switching of the pump cell applied voltage Vp and before the sensor cell current Is stabilized, and the timings set as the start point P1 and the end point P2 will be described below.

As shown in fig. 5, the starting point P1 is, for example, one of the following three points.

(a1) The timing of the trailing lowest point PL of the pump cell current Ip occurring in response to the switching of the pump cell applied voltage Vp (point P11 in FIG. 5)

(a2) Timing at which the amount of fluctuation of the sensor unit output generated in response to the switching of the pump unit applied voltage Vp reaches a prescribed value L1 (point P12 in FIG. 5)

(a3) Timing when a predetermined time E1 has elapsed after switching of the pump cell applied voltage Vp (point P13 in FIG. 5)

As shown in fig. 5, the end point P2 is, for example, one of the following two points.

(a4) Timing when a predetermined time E2 has elapsed after switching of the pump cell applied voltage Vp (point P21 in FIG. 5)

(a5) Timing at which the amount of fluctuation of the sensor unit output generated in response to the switching of the pump unit applied voltage Vp reaches a prescribed value L2 (point P22 in FIG. 5)

The predetermined value L1 Is a value obtained by adding a predetermined percentage (for example, any one of 5 to 30%) to a current value before voltage switching, assuming that the amount of current change of the sensor cell current Is when switching the same pump cell applied voltage Vp as this time (switching Vp0 → Vp1) Is 100% in the initial state of the NOx sensors 21 to 23. The predetermined value L2 is a value larger than the predetermined value L1, and is a value obtained by adding a predetermined percentage (for example, one of 50 to 95%) to the current value before switching the same voltage.

In consideration of performing the deterioration judgment as early as possible, it is preferable to set the starting point P1 and the end point P2 at the earliest possible timing, and in the above-described specific examples (a1) to (a5), it is preferable to set the starting point P1 to (a1) and the end point P2 to (a 4).

In the implementation of the 2 nd voltage switching, the start point P3 and the end point P4 are timings included in a predetermined period after the switching of the pump cell applied voltage Vp and before the sensor cell current Is stabilized, and the start point P3 and the end point P4 are set as follows. The setting method is based on the setting methods of the start point P1 and the end point P2, and therefore the following description is made for simplicity.

The starting point P3 is, for example, one of the following three points.

(b1) The timing at which the trailing maximum point of the pump cell current Ip occurs in response to the switching of the pump cell applied voltage Vp

(b2) Timing when the amount of variation in sensor unit output caused in response to switching of the pump unit applied voltage Vp reaches a predetermined value L3

(b3) Timing when a predetermined time E3 has elapsed after switching of the pump cell applied voltage Vp

The end point P2 is, for example, one of the following two points.

(b4) Timing when a predetermined time E4 has elapsed after switching of the pump cell applied voltage Vp

(b5) Timing when the amount of variation in sensor unit output caused in response to switching of the pump unit applied voltage Vp reaches a predetermined value L4

The predetermined values L3 and L4 may be determined by predetermined percentages based on the amount of change in the sensor cell current Is when the same pump cell applied voltage Vp Is switched this time (Vp1 → Vp2 switching) in the initial state of the NOx sensors 21 to 23, as in the predetermined values L1 and L2 (L3 > L4).

Here, in the deterioration determination of the sensor cell 42, the residual oxygen concentration in the gas chamber 61 changes with the switching of the pump cell applied voltage Vp, and the deterioration determination of the sensor cell 42 Is performed based on the transient response of the sensor cell 42 accompanying the change in the residual oxygen concentration, but after the switching of the pump cell applied voltage Vp, for example, when the oxygen concentration in the exhaust gas changes or the NOx concentration changes, the change in the sensor cell current Is due to the change in the concentration occurs. In other words, in the periphery of the sensor unit 42, an unplanned change is generated as a gas atmosphere, taking into account that the sensor unit 42 is affected by it. In this case, there is a fear that the deterioration judgment of the sensor unit 42 is adversely affected. For example, in fig. 4, when the oxygen concentration in the exhaust gas increases after the switching of the pump cell applied voltage Vp (after time t1), the amount of change in the sensor cell current Is due to the influence of the increase in the oxygen concentration increases, and there Is a possibility that the detection accuracy of the sensor cell current Is, which Is a parameter used for the deterioration determination, decreases.

Therefore, in the present embodiment, the concentration difference (i.e., the amount of change in concentration) between before the 1 st voltage switching is performed and after the 2 nd voltage switching is performed is calculated for the oxygen concentration in the exhaust gas, and the deterioration state of the sensor cell 42 is determined using the concentration difference, thereby suppressing a decrease in the accuracy of the deterioration determination of the sensor cell 42.

FIG. 6 is a functional block diagram illustrating the functions of the SCUs 31-33. Each SCU 31-33 includes: a voltage switching unit M11 for switching the pump cell applied voltage Vp by performing the 1 st voltage switching and the 2 nd voltage switching; an output change calculation unit M12 that calculates an output change parameter indicating an output change of the sensor cell 42 corresponding to the voltage switching in at least one of a state where the 1 st voltage switching is performed and a state where the 2 nd voltage switching is performed by the voltage switching unit M11; a concentration difference calculation unit M13 for calculating a concentration difference parameter indicating a concentration difference between the oxygen concentration in the exhaust gas before the 1 st voltage switching and after the 2 nd voltage switching; and a deterioration determination unit M14 that determines the deterioration state of the sensor cell 42 based on the output variation parameter calculated by the output variation calculation unit M12 and the density difference parameter calculated by the density difference calculation unit M13.

The voltage switching unit M11 performs 1 st voltage switching (voltage switching Vp0 → Vp1 in fig. 4) for applying the voltage Vp to the oxygen concentration side switching pump cell in the gas chamber 61 and 2 nd voltage switching (voltage switching Vp1 → Vp2 in fig. 4) for applying the voltage Vp to the oxygen concentration side switching pump cell in the gas chamber 61 after the 1 st voltage switching is performed. In other words, the voltage switching unit M11 performs a series of voltage switching cycles in which the pump cell applied voltage Vp is decreased and then increased. In the present embodiment, the pump unit applied voltage Vp is switched in a stepwise manner, but the voltage variation waveform may be a waveform other than a stepwise waveform. However, since the deterioration determination is performed by comparison with the initial characteristic, it is preferable that the initial characteristic be measured in the same manner as the voltage change waveform.

The output change calculator M12 calculates the slope (a 11 or a21 in fig. 4) of the transient change of the sensor cell current Is associated with the switching of the pump cell applied voltage Vp by the voltage switching unit M11. That Is, as the output change parameter, at the time of transient change of the sensor cell current Is, the slope of the transient change Is calculated from the change amount Δ Is of the sensor cell current Is with respect to the unit time Δ t. In the present embodiment, as the output change parameter, the slope (a 11 in fig. 4) at the time of transient change of the sensor cell current Is accompanying the 1 st voltage switching in the 1 st voltage switching (voltage switching Vp0 → Vp1 in fig. 4) and the 2 nd voltage switching (voltage switching Vp1 → Vp2 in fig. 4) Is calculated.

The concentration difference calculation unit M13 calculates the amount of change in the oxygen concentration of the exhaust gas in a series of voltage switching cycles, and calculates, as a concentration difference parameter, a pump cell output difference Δ Ipx, which is the difference between the pump cell current Ip0 before the 1 st voltage switching is performed and the pump cell current Ip2 after the 2 nd voltage switching is performed.

As the degradation determination process of the sensor cell 42, the degradation determination section M14 determines the degradation state of the sensor cell 42 based on basically the slope at the time of transient change of the sensor cell current Is. In this case, in the present embodiment, the deterioration rate C of the sensor cell 42 Is calculated based on the slope of the transient response of the sensor cell current Is calculated by the output change calculation unit M12 and the pump cell output difference Δ Ipx calculated by the concentration difference calculation unit M13, and the deterioration state Is determined from the deterioration rate C.

In the present embodiment, in particular, the deterioration determination unit M14 determines whether or not the deterioration determination of the sensor cell 42 is effective based on the pump cell output difference Δ Ipx calculated by the concentration difference calculation unit M13. Specifically, if the pump unit output difference Δ Ipx is smaller than a predetermined value, the deterioration determination of the sensor unit 42 is validated, and if the pump unit output difference Δ Ipx is equal to or larger than the predetermined value, the deterioration determination of the sensor unit 42 is invalidated. When the degradation determination unit M14 determines that the degradation determination of the sensor cell 42 is not valid, the voltage switching unit M11 performs the 1 st voltage switching and the 2 nd voltage switching again, and when the voltage is switched again, the degradation state of the sensor cell 42 is determined again based on the output change parameter calculated by the output change calculation unit M12 and the density difference parameter calculated by the density difference calculation unit M13.

Incidentally, the sensor cell 42 detects the sensor cell current Is at the nA level during normal NOx concentration detection, and detects the sensor cell current Is at the μ a level as the residual oxygen concentration increases during switching of the pump cell applied voltage Vp for degradation determination. In this case, in either case, in order to improve the resolution of current detection, the current processing range of the a/D conversion in the SCU31 to 33 may be switched between at the time of NOx concentration detection and at the time of deterioration determination. In the deterioration determination, the current processing range can be expanded compared to that in the NOx concentration detection.

The engine ECU35 also has an abnormality determination unit M21 that determines an abnormality due to emission degradation based on the degradation determination results of the SCUs 31-33. The abnormality determination unit M21 determines an abnormality in engine emissions based on the degradation rate C of the sensor unit 42 calculated by the degradation determination unit M14 of each SCU 31-33. Further, the exhaust abnormality may be 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 in addition to the deterioration rate C of the sensor unit 42.

Both the deterioration determination and the emission abnormality determination for the NOx sensors 21 to 23 may be performed by the SCUs 31 to 33, or both the determinations may be performed by the engine ECU 35. Further, since it is desirable that the emission abnormality determination be performed using an element other than the degree of deterioration of the NOx sensors 21 to 23, it is preferable that the engine ECU35 perform the determination.

Next, a process procedure of the deterioration determination of the sensor unit 42 will be described with reference to the flowchart of fig. 7. The processing shown in fig. 7 is arithmetic processing for realizing the functions of the SCUs 31 to 33 shown in fig. 6, and is performed for each SCU31 to 33, for example, at every predetermined cycle.

In step S10, it is determined whether or not the conditions for performing the degradation determination are satisfied. The present implementation condition includes, for example, an authorization signal for authorizing implementation of the deterioration determination received from engine ECU 35. The engine ECU35 transmits the permission signal when the gas environment in the exhaust pipe 11 is stable in a predetermined environment. Specifically, engine ECU35 transmits the permission signal when engine 10 is in a predetermined operating state and the amount of exhaust gas is relatively stable, when fuel cut is underway, when the ignition switch is turned off (immediately after IG is turned off), or when engine ECU35 is started by a breakthrough timer. In particular, it is preferable to use the conditions immediately after the IG is turned off. This is because immediately after the IG is turned off, the deterioration determination can be performed in a state where the gas environment is stable because the engine is stopped and no exhaust gas flows. If the implementation condition of the degradation determination is satisfied, the process proceeds to the subsequent step S11, and if the implementation condition is not satisfied, the process is ended.

In step S11, it is determined whether or not the 1 st voltage switching, that is, the switching of the voltage Vp applied to the pump cell on the side of increasing the residual oxygen concentration in the gas chamber 61 is performed. At this time, each SCU31 to 33 judges that the amount of fluctuation per unit time of the oxygen concentration and the NOx concentration in the exhaust gas has become a stable state of a predetermined value or less, and permits the 1 st voltage switching to be performed on the condition that the judgment is that the stable state has been made. Specifically, before the 1 st voltage switching Is performed, it Is determined whether or not the variation per unit time of the pump cell current Ip Is equal to or less than a predetermined value, and it Is determined whether or not the variation per unit time of the sensor cell current Is equal to or less than a predetermined value. If it is determined that the state is stable, the routine goes to step S12, following step S11. In this case, the concentration stabilization determination process can be omitted.

Each of the SCU31 to 33 may determine that the amount of fluctuation per unit time has become a steady state of a predetermined value or less with respect to either the oxygen concentration or the NOx concentration in the exhaust gas. In this case, if the oxygen concentration in the exhaust gas has become a steady state or the NOx concentration in the exhaust gas has become a steady state, the 1 st voltage switching is permitted. In the case where the exhaust pipe 11 is provided with an a/F sensor, it is also possible to determine that the oxygen concentration in the exhaust gas has reached a steady state based on the detection value of the a/F sensor.

Further, the 1 st voltage switching may be permitted on the condition that the oxygen concentration in the exhaust gas falls within a predetermined concentration range and the NOx concentration falls within a predetermined concentration range. In this case, the determination that the oxygen concentration and the NOx concentration in the exhaust gas have stabilized may be performed instead of or in addition to the determination that the oxygen concentration and the NOx concentration have entered the predetermined concentration ranges.

In step S11, in addition to the above conditions, the condition that there is no failure history (dialogue information) relating to the engine exhaust system and that the power supply voltage (battery voltage) is equal to or greater than a predetermined value may be used to permit the 1 st voltage switching. Further, if the power supply voltage is less than a predetermined value, the energization of the sensor heater becomes insufficient, and the NOx sensors 21 to 23 cannot be maintained in an appropriate active state, and there is a concern that the accuracy of the deterioration determination may be lowered.

For example, when the deterioration determination is performed immediately after the IG is turned off, the SCUs 31 to 33 may start acquiring the detection signals of the NOx sensors 21 to 23 at the timing when the engine stop signal is received from the engine ECU35 before the permission signal is received from the engine ECU 35. In this case, by quickly acquiring the sensor detection signal, it is possible to determine that the oxygen concentration in the exhaust gas has become a stable state as soon as possible, and thus it is possible to quickly start the deterioration determination of the sensor unit 42.

When the 1 st voltage switching is performed, in step S12, a pump cell current Ip0 is detected, and the pump cell current Ip0 is a pump cell output before the pump cell applied voltage Vp is switched to Vp1 (before the 1 st voltage switching is performed), that is, in a state where the pump cell applied voltage Vp is Vp 0.

Thereafter, in step S13, the pump cell application voltage Vp is switched from Vp0 to Vp 1. In the timing chart of fig. 4, this processing is performed at time t 1. Thereafter, in step S14, the sensor cell current Is1 at the start point P1 and the sensor cell current Is2 at the end point P2 in the 1 st voltage switching are detected. In step S15, the pump cell output, i.e., the pump cell current Ip1 after the pump cell applied voltage Vp is switched to Vp1 is detected. The pump cell current Ip1 is detected at the timing when a predetermined time has elapsed since the voltage switching (time t1), that is, at the timing when the pump cell current Ip is stabilized. The order of detection of the sensor cell currents Is1, Is2, and the pump cell current Ip1 may be arbitrary.

Then, in step S16, the slope a11 at the time of transient change of the sensor cell current Is calculated based on the current change amount Δ Is1 (Is 2-Is 1), which Is the difference between the sensor cell currents Is1 and Is2 at the start point P1 and the end point P2, and the time difference Δ t1 between the start point P1 and the end point P2, using the following expression (1), for example.

A11＝ΔIs1/Δt1…(1)

The slope a10 in the initial characteristic shown in fig. 4 is also calculated using the above expression (1).

In step S17, a slope B11 is calculated by normalizing the slope a 11. In this case, using the following equation (2), the normalized slope B11 Is calculated based on the slope a11 at the time of the transient change in the sensor cell current Is and the change amount Δ Ip1 (Ip 0-Ip 1) of the pump cell current Ip accompanying the switching of the pump cell applied voltage Vp.

B11＝A11/ΔIp1…(2)

In step S21, it is determined whether or not the 2 nd voltage switching, that is, the switching of the voltage Vp applied to the pump cell on the side of reducing the residual oxygen concentration in the gas chamber 61 is performed. In the case of performing the 2 nd voltage switching, the process proceeds to step S22, and the pump cell applied voltage Vp is switched from Vp1 to Vp 2. In the timing chart of fig. 4, this processing is performed at time t 2. In the present embodiment, Vp2 is Vp 0.

Thereafter, in step S23, a pump cell current Ip2 is detected, which is the pump cell output after the pump cell applied voltage Vp is switched to Vp2 (after the 2 nd voltage switching is performed), that is, in a state where the pump cell applied voltage Vp is Vp 2. The pump cell current Ip2 is detected at the timing when a predetermined time has elapsed since the voltage switching (time t2), that is, at the timing when the pump cell current Ip is stabilized.

Then, in step S24, a pump cell output difference Δ Ipx (Δ Ipx — Ip 2-Ip 0) which is the difference between the pump cell currents Ip0 and Ip2 detected in steps S12 and S23 is calculated. The pump cell output difference Δ Ipx is a concentration difference parameter indicating the difference between the oxygen concentrations before the 1 st voltage switching is performed and after the 2 nd voltage switching is performed.

Thereafter, in step S25, it is determined whether the absolute value of the pump unit output difference Δ Ipx is smaller than a predetermined threshold value TH. When | Δ Ipx | < TH, the deterioration determination of the sensor unit 42 is validated, and the process proceeds to the subsequent step S26.

In step S26, the slope B11 calculated in step S17 is used to calculate the degradation rate C (%) of the sensor unit 42. At this time, the ratio (B11/B10) of the slope B11 to the slope B10 of the initial characteristic is calculated as a reaction rate ratio, and the deterioration rate C of the sensor unit 42 is calculated based on the reaction rate ratio B11/B10, for example, using the relationship of fig. 8. The reaction rate ratio B11/B10 is determined as a ratio of the reaction rate of oxygen supplied to the sensor cell 42. In addition, a slope B10 representing the initial characteristic is stored in advance in a memory in the SCUs 31-33. In fig. 8, it is decided that the smaller the reaction rate ratio B11/B10, that is, the larger the difference between the characteristic at the time of deterioration of the sensor cell 42 and the initial characteristic, the larger the relationship of the deterioration rate C. The larger degradation rate C means that the degree of degradation of the sensor unit 42 is larger.

Thereafter, in step S27, the degradation rate C of the sensor unit 42 is transmitted to the engine ECU 35. At this time, in step S25, deterioration rate C, which is the result of deterioration determination of sensor unit 42, is transmitted to engine ECU35 on the condition that pump unit output difference Δ Ipx is smaller than predetermined threshold TH.

In step S25, if | Δ Ipx | ≧ TH, the deterioration determination of the sensor unit 42 is invalidated, and the process returns to step S11 to perform the redetermination. That is, the SCU31 to 33 perform the 1 st voltage switching again to acquire the output variation parameter (steps S12 to S17), and then perform the 2 nd voltage switching again to acquire the density difference parameter (steps S22 to S24). Then, the deterioration state of the sensor unit 42 is re-determined based on the output variation parameter and the density difference parameter (step S26).

In step S27, together with the degradation rate C of the sensor unit 42, information indicating that the absolute value of the pump unit output difference Δ Ipx is smaller than the predetermined threshold TH, that is, that the present degradation determination has been normally performed, may be transmitted to the engine ECU 35. If no in step S25 and the degradation determination is to be performed again, information indicating that the determination is to be performed again may be transmitted to engine ECU 35.

Fig. 9 is a timing chart showing the behavior of the case where the voltage switching cycle is performed a plurality of times. Two voltage switching cycles are shown in fig. 9. In fig. 9, it is assumed that the pump cell applied voltage Vp is switched from Vp0 to Vp1 in the 1 st voltage switching, and from Vp1 to Vp0 in the 2 nd voltage switching.

In fig. 9, the 1 st voltage switching and the 2 nd voltage switching are performed at times t11 and t12, respectively. At this time, if the oxygen concentration in the exhaust gas fluctuates during the period from t11 to t12, it is determined that the absolute value of the pump cell output difference Δ Ipx is equal to or greater than the predetermined threshold TH after the time t 12. This makes it possible to determine that the deterioration determination in the present voltage switching cycle is invalid. Then, at times t21 and t22, the 1 st voltage switching and the 2 nd voltage switching are performed again, and when it is determined that the deterioration determination in the voltage switching cycle is valid, the deterioration determination of the sensor unit 42 is performed.

In step S25, if | Δ Ipx | ≧ TH, the present processing may be terminated as it is. When the present process is ended, the subsequent process is not performed, thereby invalidating the deterioration determination of the sensor unit 42.

After the deterioration rate C of the sensor cell 42 Is calculated, the SCUs 31 to 33 correct the sensor cell current Is by the deterioration rate C for each of the NOx sensors 21 to 23 when the NOx concentration Is detected by the NOx sensors 21 to 23, and calculate the NOx concentration based on the corrected sensor cell current Is. In this case, the current sensor cell characteristics are returned to the initial characteristics, and the sensor cell current Is corrected.

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

If the oxygen concentration in the exhaust gas fluctuates during the period in which the output of the sensor cell 42 changes as the pump cell applied voltage Vp is switched, there is a concern that this will adversely affect the deterioration determination of the sensor cell based on the output change parameters (slopes a11, a21) of the sensor cell 42. In this regard, in the above configuration, a concentration difference parameter (pump cell output difference Δ Ipx) indicating a concentration difference between the oxygen concentration in the exhaust gas before the 1 st voltage switching is performed and the oxygen concentration after the 2 nd voltage switching is performed is calculated, and the deterioration state of the sensor cell 42 is determined based on the output change parameter of the sensor cell 42 and the concentration difference parameter. Accordingly, if the oxygen concentration in the exhaust gas fluctuates during the period from the 1 st voltage to the 2 nd voltage, the deterioration state of the sensor cell 42 can be appropriately determined.

By calculating the pump cell output difference Δ Ipx before the 1 st voltage switching is performed and after the 2 nd voltage switching is performed, it is possible to appropriately grasp the variation in the oxygen concentration in the exhaust gas during the period from the 1 st voltage switching to the 2 nd voltage switching. This enables the deterioration state of the sensor unit 42 to be appropriately determined.

In a situation where the oxygen concentration in the exhaust gas does not fluctuate during the abnormality determination period for switching from the 1 st voltage to the 2 nd voltage, the pump cell applied voltage Vp Is set to be the same before the 1 st voltage switching Is performed and after the 2 nd voltage switching Is performed, and the pump cell current Ip and the sensor cell current Is are not changed during the abnormality determination period. In this regard, since the pump cell applied voltage Vp0 before the 1 st voltage switching Is performed and the pump cell applied voltage Vp2 after the 2 nd voltage switching Is performed are the same, it Is possible to appropriately determine whether or not there Is a variation in the oxygen concentration and the NOx concentration in the exhaust gas based on the pump cell current Ip and the sensor cell current Is.

The deterioration judgment of the sensor unit 42 is determined to be valid or invalid based on the pump unit output difference Δ Ipx, which is a concentration difference parameter. Specifically, when the concentration difference of the oxygen concentration in the exhaust gas is equal to or greater than a predetermined value, the deterioration determination of the sensor unit 42 is invalidated. This can suppress the deterioration state of the erroneous determination sensor unit 42.

When it is determined that the deterioration determination of the sensor unit 42 is not valid, the 1 st voltage switching and the 2 nd voltage switching are performed again, and the deterioration determination of the sensor unit 42 is performed again. By performing the deterioration determination of the sensor unit 42 again in this manner, an appropriate deterioration determination result can be obtained even if the deterioration determination of the previous time is inaccurate. Further, when the deterioration determination of the sensor unit 42 is effective, repeated deterioration determination (voltage switching) is not necessary, and therefore, the time required for the deterioration determination can be shortened.

The control device is configured to determine a stable state in which a fluctuation amount per unit time of at least one of an oxygen concentration and an NOx concentration in the exhaust gas is equal to or less than a predetermined value, and to permit switching of the pump cell applied voltage Vp (implementation of the 1 st voltage switching and the 2 nd voltage switching) on the condition that the determination is made that the stable state is achieved. With this, the deterioration determination of the sensor unit 42 can be performed in a state where the oxygen concentration NOx in the exhaust gas is stable after the engine is stopped, and the determination accuracy can be improved.

Each of the SCUs 31 to 33 is configured to transmit a result of determination of deterioration of the sensor unit 42 to the engine ECU35 on the condition that the difference in concentration of oxygen in the exhaust gas before the implementation of the 1 st voltage switching and after the implementation of the 2 nd voltage switching is smaller than a predetermined value. Thus, in engine ECU35, the exhaust system abnormality diagnosis can be performed based on the highly accurate deterioration determination result of sensor unit 42, and the reliability of the abnormality diagnosis can be improved.

Hereinafter, other embodiments will be described mainly focusing on differences from embodiment 1.

(embodiment 2)

In embodiment 2, the deterioration determination unit M14 corrects the deterioration determination result of the sensor cell 42 based on the density difference parameter calculated by the density difference calculation unit M13. Specifically, the SCUs 31 to 33 perform the degradation determination process of fig. 10 instead of the degradation determination process of fig. 7 described above. Fig. 10 is a diagram in which a part of fig. 7 is changed, and the same process as that of fig. 7 is assigned with the same step number.

In fig. 10, in step S24, after calculating the pump unit output difference Δ Ipx (Δ Ipx — Ip 2-Ip 0) as the density difference parameter, the process advances to step S41. Then, in step S41, the degradation rate C of the sensor unit 42 is calculated using the slope B11 calculated in step S17. The calculation process of the degradation rate C is in accordance with step S26 of fig. 7.

Thereafter, in step S42, the degradation rate C is corrected based on the pump cell output difference Δ Ipx. At this time, if the pump cell output difference Δ Ipx Is a positive value (i.e., Ip2 > Ip0), the oxygen concentration in the exhaust gas increases during the 1 st voltage switching to the 2 nd voltage switching, and the slope of the response change of the sensor cell current Is considered to be increased. Therefore, in order to correct the increase in the oxygen concentration, the deterioration rate C is corrected to be decreased. In contrast, if the pump cell output difference Δ Ipx Is negative (i.e., Ip2 < Ip0), the oxygen concentration in the exhaust gas decreases during the 1 st voltage switching to the 2 nd voltage switching, taking into account the smaller slope of the response change of the sensor cell current Is caused thereby. Therefore, in order to correct the decrease in the oxygen concentration, the deterioration rate C is corrected to be increased.

Specifically, the SCUs 31 to 33 calculate a correction value KC based on the pump cell output difference Δ Ipx using the relationship of fig. 11, for example, and calculate the corrected degradation rate C by the product of the correction value KC and the degradation rate C. In fig. 11, the dead zone F in which the correction value KC is zero is provided in the vicinity of Δ Ipx being 0, or the dead zone F may not be provided.

The configuration may be such that only the pump unit output difference Δ Ipx is assumed to be a positive value or a negative value. In this case, in step S42, only one of the process of correcting to the side of decreasing the degradation rate C on the condition that the pump cell output difference Δ Ipx is a positive value and the process of correcting to the side of increasing the degradation rate C on the condition that the pump cell output difference Δ Ipx is a negative value is performed.

Thereafter, in step S43, the deterioration rate C of the sensor unit 42 and correction information of the deterioration rate C are transmitted to the engine ECU 35. At this time, the SCUs 31 to 33 transmit, as correction information, information of the pump unit output difference Δ Ipx, which is density difference information, and the correction value KC based on the pump unit output difference Δ Ipx to the engine ECU 35.

In the present embodiment described above, the deterioration rate (deterioration determination result) of the sensor cell 42 is corrected based on the pump cell output difference Δ Ipx, which is a concentration difference parameter. Accordingly, even if the oxygen concentration in the exhaust gas fluctuates during the period from the 1 st voltage switching to the 2 nd voltage switching before the 1 st voltage switching is performed, the deterioration state of the sensor cell 42 can be appropriately determined.

When the pump cell output difference Δ Ipx is a positive value, that is, when the oxygen concentration in the exhaust gas increases during the switching from the 1 st voltage to the 2 nd voltage, the deterioration rate C is corrected to a smaller value in order to correct the increase in the oxygen concentration. In addition, when the pump cell output difference Δ Ipx is a negative value, that is, when the oxygen concentration in the exhaust gas decreases during the 1 st voltage switching to the 2 nd voltage switching, the deterioration rate C is corrected to increase in order to correct the decrease in the oxygen concentration. Thereby, the deterioration rate C can be appropriately calculated in accordance with the change in the oxygen concentration in the exhaust gas in the voltage switching cycle.

Each of the SCUs 31 to 33 is configured to transmit the result of the deterioration determination of the sensor unit 42 and the concentration difference information used in the deterioration determination to the engine ECU 35. Thus, when engine ECU35 performs an exhaust system abnormality diagnosis based on the deterioration determination result of sensor unit 42, the abnormality diagnosis can be rationalized.

As described with reference to fig. 7, the deterioration determination of the sensor unit 42 may be invalidated when | Δ Ipx | ≧ TH, while the deterioration rate C may be corrected based on the pump unit output difference Δ Ipx when | Δ Ipx | < TH.

(embodiment 3)

In embodiment 3, the voltage switching unit M11 performs a voltage switching cycle including the 1 st voltage switching and the 2 nd voltage switching a plurality of times at predetermined time intervals. The deterioration determination unit M14 determines the deterioration state of the sensor cell 42 based on the output variation parameter of the voltage switching cycle in which the density difference is the smallest among the density difference parameters calculated by the density difference calculation unit M13 in the plurality of voltage switching cycles.

Specifically, the SCUs 31 to 33 perform the degradation determination process of fig. 12 instead of the degradation determination process of fig. 7 described above. Fig. 12 is a diagram in which a part of fig. 7 is changed, and the same process as that of fig. 7 is assigned with the same step number.

In fig. 12, in step S24, the pump unit output difference Δ Ipx (Δ Ipx — Ip 2-Ip 0) is calculated as the density difference parameter, and the process advances to step S51. Then, in step S51, it is determined whether or not a voltage switching cycle including the 1 st voltage switching and the 2 nd voltage switching is performed n times. n is2 or more, for example, n-2 or n-3. If step S51 is negative, the process returns to step S11. That is, the SCU31 to 33 perform the 1 st voltage switching again to acquire the output variation parameter (steps S12 to S17), and then perform the 2 nd voltage switching again to acquire the density difference parameter (steps S22 to S24).

If step S51 is affirmative, the process proceeds to step S52, and the voltage switching cycle with the minimum pump cell output difference Δ Ipx (density difference) among the n voltage switching cycles is selected. In subsequent step S53, the degradation rate C of the sensor cell 42 is calculated using the slope B11 (output variation parameter) in the voltage switching cycle in which the pump cell output difference Δ Ipx is minimum. The calculation process of the degradation rate C is in accordance with step S26 of fig. 7.

Thereafter, in step S54, the degradation rate C of the sensor unit 42 is transmitted to the engine ECU 35. At this time, information of the concentration difference parameter of the voltage switching cycle, which is finally used in the calculation of the degradation rate C, may be transmitted to the engine ECU35 together with the degradation rate C.

In the present embodiment described above, the deterioration state of the sensor cell 42 is determined based on the output change parameter of the sensor cell 42 in the voltage switching cycle in which the pump cell output difference Δ Ipx, which is the density difference parameter, is the smallest among the plurality of voltage switching cycles. Thus, even if the oxygen concentration in the exhaust gas fluctuates during a certain voltage switching cycle from the 1 st voltage switching to the 2 nd voltage switching before the 1 st voltage switching is performed, the determination result of the voltage switching cycle can be excluded, and the deterioration state of the sensor cell 42 can be appropriately determined.

In the case where the voltage switching cycle is performed three or more times, for example, the output variation parameter in the voltage switching cycle with the smallest density difference and the output variation parameter in the voltage switching cycle with the second smallest density difference may be used. In the case of using the output variation parameter in the plurality of voltage switching cycles, for example, the average value of the degradation rates C may be set as the final degradation rate C. In short, the deterioration state of the sensor unit 42 may be determined using the output variation parameter in the voltage switching cycle in which the density difference is the smallest. When the voltage switching cycle is performed a plurality of times (two or more times), the concentration difference may be smaller than the predetermined total concentration difference.

(other embodiments)

The above embodiment may be modified as follows, for example.

In the above embodiment, when the difference in oxygen concentration between before and after switching of the pump cell applied voltage Vp is equal to or greater than the predetermined value (when | Δ Ipx | ≧ TH at step S25), the calculation of the degradation rate C based on the output variation parameter acquired in the voltage switching cycle is not performed (degradation determination), and the degradation determination is invalidated by not performing the calculation of the degradation rate C, but it may be changed. For example, when the 1 st voltage switching is performed, the deterioration rate C may be calculated based on the output variation parameter associated with the voltage switching, and then the deterioration rate C calculated this time may be invalidated on the condition that the difference in oxygen concentration between before and after switching of the pump cell applied voltage Vp is equal to or greater than a predetermined value.

In the above embodiment, the concentration difference calculation unit M13 is configured to calculate the concentration difference (pump cell output difference Δ Ipx) between before the 1 st voltage switching and after the 2 nd voltage switching with respect to the oxygen concentration in the exhaust gas, but it may be modified. For example, the concentration difference calculation unit M13 may be configured to calculate the concentration difference (sensor cell output difference Δ Isx) between before the 1 st voltage switching and after the 2 nd voltage switching, with respect to the NOx concentration in the exhaust gas. In this case, the SCUs 31 to 33 calculate the sensor cell output difference Δ Isx using the difference between the sensor cell current Is before the 1 st voltage switching Is performed and the sensor cell current Is after the 2 nd voltage switching Is performed. Then, if the absolute value of the sensor cell output difference Δ Isx is smaller than a predetermined value, the deterioration determination of the sensor cell 42 is validated, and if the absolute value of the sensor cell output difference Δ Isx is equal to or larger than the predetermined value, the deterioration determination of the sensor cell 42 is invalidated. Further, the deterioration rate C may be corrected based on the sensor cell output difference Δ Isx.

The concentration difference calculation unit M13 may be configured to calculate the monitor cell output difference as the oxygen concentration difference between the monitor cell current Im before the 1 st voltage switching and the monitor cell current Im after the 2 nd voltage switching, using the difference between the monitor cell current Im before the 1 st voltage switching and the monitor cell current Im after the 2 nd voltage switching.

In the above embodiment, the slope a11 at the time of transient change of the sensor cell current Is associated with the implementation of the 1 st voltage switching Is calculated as the output change parameter at the time of the deterioration determination of the sensor cell 42, and the deterioration determination Is implemented using the slope a11 (specifically, the slope B11 obtained by normalizing the slope a11), but it may be modified. For example, the slope a21 at the time of transient change of the sensor cell current Is associated with the implementation of the 2 nd voltage switching may be calculated, and the degradation determination may be performed using the slope a 21.

Further, as the output change parameters, the slope a11 at the time of transient change of the sensor cell current Is accompanying the implementation of the 1 st voltage switching and the slope a21 at the time of transient change of the sensor cell current Is accompanying the implementation of the 2 nd voltage switching may be calculated, and the deterioration determination of the sensor cell 42 may be performed based on the slopes a11 and a 21. For example, the degradation determination is performed using the larger (or smaller) of the slopes a11 and a 21. Alternatively, the deterioration determination is performed using the average value of the slopes a11, a 21.

In the above-described embodiment, the steady state in which the amount of change per unit time of the oxygen concentration and the NOx concentration in the exhaust gas Is equal to or less than the predetermined amount Is determined by monitoring the changes in the pump cell current Ip and the sensor cell current Is after the engine Is stopped, or the like. For example, it may be configured to determine that the oxygen concentration and the NOx concentration in the exhaust gas have reached a stable state by the elapsed time after the engine stop. In this case, the SCU31 to 33 measure the elapsed time from the engine stop (IG off), and determine that the oxygen concentration and the NOx concentration in the exhaust gas have reached the steady state based on the elapsed time reaching a predetermined time (for example, several minutes).

When the pump cell applied voltage Vp is switched to the side of increasing the oxygen concentration in the gas chamber 61 (when the 1 st voltage switching is performed) at the time of determining the deterioration of the sensor cell 42, the pump cell applied voltage Vp may be set to zero, that is, switched to a state where no voltage is applied. Alternatively, the pump cell applied voltage Vp may be switched to a negative voltage. In either case, the oxygen concentration in the gas chamber 61 is increased as the applied voltage is switched, and the deterioration determination can be performed by the transient response of the sensor unit 42 at that time.

In the above-described embodiment, the slope of the transient change Is calculated using the amount of current change Δ Is per unit time Δ t in the transient period of the sensor cell current Is as the "slope parameter" of the sensor cell current Is, but instead of this, the amount of current change Δ Is within a predetermined time may be used as the slope parameter. Alternatively, the time width required to generate a predetermined current change amount may be used as the slope parameter. That Is, as the slope parameter, the slope of the sensor cell current Is, or a value related thereto, may be calculated.

In the above embodiment, the slope a11 of the sensor cell current Is normalized to calculate the slope B11, and the degradation rate C Is calculated using the slope B11. For example, the degradation rate C may be calculated using the slope a 11.

The degradation rate C of the sensor cell 42 can also be calculated using a value other than the slope (slope parameter) of the sensor cell current Is. For example, a value at which the change in the sensor cell current Is converges after the switching of the pump cell applied voltage Vp may be calculated as the sensor cell current change amount Δ Is, and the deterioration rate of the sensor cell 42 may be calculated using the current change amount Δ Is.

In the above-described embodiment, the deterioration rate C (%) which is the ratio between the current characteristic and the initial characteristic of the sensor unit 42 is calculated as the determination of the deterioration state of the sensor unit 42. For example, the slope of the sensor cell current Is, a value related to the slope, and the amount of current change Δ Is after convergence of the sensor cell current Is, which are degradation determination parameters of the sensor cell 42, may be configured to calculate a difference from an initial value, and grasp the degradation degree of the sensor cell 42 based on the difference. Further, the comparison may be made with a predetermined standard value, not with an initial value. The degree of degradation may be determined by using an index of "100-degradation rate C". In this case, in the index, the initial characteristic is represented by 100%, and the more the deterioration progresses, the smaller the value is represented. In any case, the index may be any index as long as the index can determine the deterioration state, that is, the degree of deterioration, based on the characteristic change of the sensor unit 42.

In the above embodiment, the sensor element 40 has the configuration of the single solid electrolyte body 53 and the single gas chamber 61, but it may be modified. For example, the sensor element 40 may have a plurality of solid electrolyte bodies 53 and a plurality of gas chambers 61, and the pump unit 41 and the sensor unit 42 may be configured to be different solid electrolyte bodies 53 and to face different gas chambers 61. Fig. 13 shows an example of such a configuration.

The sensor element 40 shown in fig. 13 includes 2 solid electrolyte bodies 53a and 53b arranged to face each other, and gas chambers 61a and 61b provided between the solid electrolyte bodies 53a and 53 b. The gas chamber 61a communicates with the exhaust gas inlet 53c, and the gas chamber 61b communicates with the gas chamber 61a via the throttle portion 71. The pump unit 41 has a pair of electrodes 72 and 73, and one electrode 72 is provided so as to be exposed to the inside of the gas chamber 61 a. The sensor unit 42 has an electrode 74 and a common electrode 76 that are disposed to face each other, and the monitor unit 43 has an electrode 75 and a common electrode 76 that are disposed to face each other. The sensor unit 42 is disposed adjacent to the monitor unit 43. In each of the sensor unit 42 and the monitor unit 43, one of the electrodes 74 and 75 is provided so as to be exposed to the inside of the gas chamber 61 b. In this way, in the configuration in which the pump unit 41 and the sensor unit 42 are provided in the different gas chambers 61a and 61b, respectively, it is possible to suitably perform each function such as the deterioration determination of the above-described embodiment.

As the sensor elements 40 of the NOx sensors 21 to 23, a sensor element having a two-unit structure including a pump unit and a sensor unit can be used.

The specific gas component to be detected may be a component other than NOx. For example, a gas sensor may be used which detects HC and CO in the exhaust gas. In this case, the device may be configured to discharge oxygen in the exhaust gas by the pump unit and to decompose HC and CO in the gas after discharge of oxygen by the sensor unit to detect the HC concentration and the CO concentration. Further, the apparatus may be a device for detecting the concentration of ammonia in the gas to be detected.

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

The present application has been described with reference to the embodiments, but it should be understood that the present application is not limited to the embodiments and the configurations. The present application also includes various modifications and modifications within the equivalent range. Further, the various combinations and forms may include only one element, and other combinations and forms not less than the element are also within the scope and spirit of the present invention.