JP2019074493A - Gas sensor controller - Google Patents

Abstract

To perform appropriate concentration detection after an oxygen concentration has increased for determination of degradation of a gas sensor.SOLUTION: A gas sensor of the present invention comprises a pump cell for adjusting an oxygen concentration in a gas chamber by voltage application, and a sensor cell for detecting the concentration of a specific gas component from the gas being detected after oxygen concentration adjustment by the pump cell. SCUs 31-33 comprise: a first voltage switching unit M11 for switching the pump cell application voltage from a first voltage to a second voltage lower than the first voltage; a degradation determination processing unit M12 which, when the pump cell application voltage is switched from the first voltage to the second voltage, acquires a degradation determination parameter for determining sensor degradation on the basis of output of the sensor cell, and determines the degradation of the gas sensor on the basis of the degradation determination parameter; and a second voltage switching unit M13 for switching the pump cell application voltage after degradation determination by the degradation determination processing unit M12 to a third voltage higher than the first voltage.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a gas sensor control device.

  As a gas sensor for detecting the concentration of a specific gas component in a gas to be detected such as exhaust gas of an internal combustion engine, a 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-cell structure consisting of a pump cell, a monitor cell, and a sensor cell, and the pump cell discharges or pumps out oxygen in the exhaust 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 is deteriorated, the accurate NOx concentration can not be detected. As a result, when the NOx sensor is installed in the exhaust system of a car, there is a possibility that problems such as deterioration of exhaust emission may occur. Therefore, conventionally, a method for diagnosing deterioration of the NOx sensor has been proposed. For example, in Patent Document 1, the voltage applied to the pump cell is forcibly switched, and deterioration of the NOx sensor is detected based on the amount of change in sensor cell output at this time. Techniques for diagnosing are disclosed.

JP, 2009-175013, A

  By the way, in the conventional degradation diagnosis method, the residual oxygen concentration in the gas chamber is intentionally increased by switching the pump cell applied voltage, and the degradation diagnosis of the sensor cell is performed based on the transient response of the sensor cell accompanying the change of the oxygen concentration. However, since the oxygen concentration in the gas chamber is excessive after the completion of the deterioration diagnosis, there is a concern that the detection accuracy may be adversely affected when the detection of the NOx concentration is started after the deterioration diagnosis. In addition, since it takes time to bring the gas chamber into the desired low oxygen concentration, it is feared that the start of detection of the NOx concentration will be delayed.

  The present invention has been made in view of the above problems, and a main object of the present invention is to provide a gas sensor control device capable of performing appropriate concentration detection after an increase in oxygen concentration for determining deterioration of a gas sensor. is there.

In order to solve the above problems, this means
A pump cell (41) for adjusting the oxygen concentration in the gas to be detected introduced into the gas chamber (61) by voltage application, and a concentration of a specific gas component from the gas to be detected after the oxygen concentration is adjusted by the pump cell A gas sensor control device (31 to 33, 35) that is applied to a gas sensor (21 to 23) having a sensor cell (42) for detecting
A first voltage switching unit configured to switch a pump cell applied voltage applied to the pump cell from a first voltage to a second voltage lower than the first voltage;
When the voltage applied to the pump cell is switched from the first voltage to the second voltage by the first voltage switching unit, a deterioration determination parameter for determining the deterioration of the gas sensor is acquired based on the output of the sensor cell, A deterioration determination processing unit that performs the deterioration determination of the gas sensor based on the deterioration determination parameter;
A second voltage switching unit configured to switch the voltage applied to the pump cell to a third voltage higher than the first voltage after processing for parameter acquisition or deterioration determination by the deterioration determination processing unit;
Equipped with

  In the above configuration, the pump cell applied voltage is switched from the first voltage to the second voltage lower than the first voltage in determining the deterioration of the gas sensor. Then, with the pump cell applied voltage switched from the first voltage to the second voltage, the deterioration determination parameter for determining the deterioration of the gas sensor is obtained based on the output of the sensor cell, and based on the deterioration determination parameter, The deterioration determination is performed. In such a case, when the voltage applied to the pump cell is switched to the low voltage side, the amount of pumped oxygen decreases and the oxygen concentration in the gas chamber increases. Therefore, after parameter acquisition or deterioration determination, if the gas chamber is in an oxygen excess state and concentration detection of a specific gas component is subsequently performed, there is a concern that the concentration detection will be adversely affected.

  In this respect, according to the above configuration, after the parameter acquisition or the deterioration determination process, the pump cell applied voltage is switched to the third voltage higher than the first voltage before the deterioration determination start. Therefore, after the parameter acquisition or deterioration determination processing, the oxygen excess state in the gas chamber is quickly resolved, and when the concentration detection of the specific gas component is performed after the processing, the detection accuracy decreases or the concentration detection start is excessive. It is possible to suppress the inconvenience of being late. As a result, it is possible to carry out appropriate concentration detection after the increase in oxygen concentration for determining the deterioration of the gas sensor.

  Note that “after processing of parameter acquisition or deterioration determination by the deterioration determination processing unit” is during parameter acquisition or sensor deterioration determination except after parameter acquisition is completed or after sensor deterioration determination is completed. And after the process was interrupted.

The figure which shows the system configuration of an engine exhaust system. Sectional drawing which shows the structure of a NOx sensor. Sectional drawing which shows the III-III cross section of FIG. The figure for demonstrating the change of the transient characteristic of the sensor cell output accompanying degradation of a NOx sensor. Functional block diagram of SCU and ECU. The flowchart which shows the processing procedure of deterioration decision of the sensor cell. The figure which shows the relationship between reaction rate ratio and a degradation rate. The time chart which shows change of sensor cell current accompanying switching of pump cell impressed voltage. (A) is a figure which shows relationship with change amount (DELTA) Ip of pump cell current, and 3rd voltage V3, (b) is a figure which shows relationship with change amount (DELTA) Ip of pump cell current, and voltage application time Ta. The time chart which shows change of pump cell impressed voltage at the time of degradation judging, and sensor cell current. Sectional drawing which shows the structure of another NOx sensor.

  Hereinafter, embodiments will be described based on the drawings. In this embodiment, in a system in which exhaust gas discharged from a diesel engine mounted on a vehicle is used as a gas to be detected, and the concentration of NOx in the exhaust gas is detected by a NOx sensor, a gas sensor control device for implementing control related to the NOx sensor is embodied. And In addition, in the following each embodiment, the same code | symbol is attached | subjected to the mutually same or equal part in the figure, and the description is used about the part of the same code | symbol.

  As shown in FIG. 1, an exhaust gas purification system for purifying the exhaust gas is provided on the exhaust side of the engine 10 which is a diesel engine. As a configuration of the exhaust purification system, an exhaust pipe 11 forming an exhaust passage is connected to the engine 10, and an oxidation catalytic converter 12 and a selective reduction catalytic converter (hereinafter referred to as SCR) are connected to the exhaust pipe 11 sequentially from the engine 10 side. A catalytic converter 13) is provided. The oxidation catalytic 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 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 catalytic converter 12, the diesel oxidation catalyst 14 is mainly composed of a ceramic support, an oxide mixture containing aluminum oxide, cerium dioxide and zirconium dioxide as components, and a noble metal catalyst such as platinum, palladium, 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 the 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 the particulate matter on the partition walls of the honeycomb structure. The deposited particulate matter is oxidized and purified by combustion. For this combustion, the temperature rise in the diesel oxidation catalyst 14 and the combustion temperature fall of the particulate matter due to the additive are used.

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

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

  SCU (Sensor Control Unit) 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 to 33 are electronic control units comprising a microcomputer having a CPU and various memories and their peripheral circuits, and based on the detection signals (limit current signals) of the NOx sensors 21 to 23, oxygen in exhaust gas (O2) The concentration or NOx concentration as the concentration of the specific gas component is 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, the 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 of 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 unit equipped with a microcomputer having a CPU and various memories and its peripheral circuits, and controls the engine 10 and various devices of the exhaust system. The engine ECU 35 implements fuel injection control and the like based on, for example, the accelerator opening degree and the engine rotational speed.

  The engine ECU 35 also controls addition of urea water by the urea water addition valve 17 based on the NOx concentration detected by each of the NOx sensors 21-23. 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. The urea water addition amount is feedback corrected so that the NOx concentration detected by the NOx sensor 23 on the downstream side of the above becomes as small as possible. Then, the drive of the urea water addition valve 17 is controlled based on the urea water addition amount.

  In addition to the above, the engine ECU 35 performs fuel cut to stop fuel injection by the fuel injection valve when the vehicle decelerates, that is, when the accelerator is off, while automatically stopping and restarting the engine 10 according to the vehicle traveling state and the like. Perform so-called idling stop control. The fuel cut temporarily stops the fuel injection, and the automatic engine stop temporarily shuts down the engine 10. In the idling stop control, as is well known, the engine is automatically stopped by the establishment of a predetermined automatic stop condition for vehicle speed, accelerator operation and brake operation, and under the automatic stop state, predetermined restart conditions for accelerator operation and brake operation are The engine is restarted upon establishment.

  Next, the configurations 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. FIGS. 2 and 3 are views showing the internal structure of the sensor element 40 constituting the NOx sensor 21. FIG. The left and 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-cell structure including a pump cell 41, a sensor cell 42 and a monitor cell 43. The monitor cell 43, like the pump cell 41, has a function of discharging oxygen in gas, 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, which is a densitometer-side chamber, is formed between the first main body 51 and the solid electrolyte body 53, and an air chamber 62, which is a reference gas room, between the second main body 52 and the solid electrolyte body 53. Is formed.

  The pump cell 41 is for adjusting the oxygen concentration in the exhaust 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 the 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 based on 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. It is formed by the 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 portion 51 and the second main body portion 52 are disposed on both sides of the solid electrolyte body 53. The first main body portion 51 has a step shape on the side of the solid electrolyte body 53, 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 action of the diffusion resistor 54 regulates the speed of the exhaust introduced into the gas chamber 61.

  Similarly, in the second main body portion 52, the side of the solid electrolyte body 53 is in the form of a step, and the recess formed by the step is the air chamber 62. One side of the atmosphere chamber 62 is open. The gas introduced into the atmosphere chamber 62 from the solid electrolyte body 53 side is released to the atmosphere.

  A pump cell electrode 55 on the cathode side, a sensor cell electrode 56 and a monitor cell electrode 57 are provided on the surface of the solid electrolyte body 53 facing the gas chamber 61. In this case, the pump cell electrode 55 is disposed on the inlet side of the gas chamber 61 near 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 sandwich the pump cell electrode 55 and diffuse resistance. 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 large surface area as compared to the sensor cell electrode 56 and the monitor cell electrode 57. The sensor cell electrode 56 and the monitor cell electrode 57 are arranged close to each other and at the same position as the exhaust flow direction. While the pump cell electrode 55 and the monitor cell electrode 57 are electrodes made of noble metals such as Au-Pt inert to NOx (electrodes that are difficult to decompose NOx), the sensor cell electrode 56 is platinum Pt or rhodium active to NOx. It is an electrode made of a noble metal such as Rh.

  Further, on the surface of the solid electrolyte body 53 facing the atmosphere chamber 62, a common electrode 58 to be the anode side is provided 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 by 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 the charge is released from the common electrode 58 to be oxygen, which is discharged to the atmosphere chamber 62. Thus, the inside of the gas chamber 61 is maintained in a predetermined low oxygen state.

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

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

  In a state where oxygen is discharged by the pump cell 41, the sensor cell 42 reductively decomposes NOx in the exhaust gas with voltage application, and outputs a current signal according to the concentration of NOx and the concentration of residual oxygen 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 is calculated by the sensor cell current Is.

  In the sensor cell 42, the transient response of the sensor cell current Is, which is the output of the sensor cell 42, tends to change even if the concentration of the detection gas in the exhaust gas is the same, due to the influence of aging and the like. This tendency will be described with reference to FIG. FIG. 4 schematically shows temporal changes of (a) pump cell applied voltage Vp, (b) pump cell current Ip, and (c) sensor cell current Is.

  In FIG. 4, before time t1, the pump cell applied voltage Vp is the first voltage V1, and oxygen is pumped out by the pump cell 41, so that the inside of the gas chamber 61 is in a predetermined low oxygen concentration state. This state is a state in which the NOx concentration can be detected.

  Then, at time t1, the pump cell applied voltage Vp is switched in a step-like manner from the first voltage V1 to the second voltage V2 which is lower than that (V1> V2). As a result, the pump cell current Ip changes to a decreasing side, and the residual oxygen concentration in the gas chamber 61 is increased. At this time, the pump cell current Ip changes from Ip1 along with tailing and converges to Ip2. In the sensor cell 42, the sensor cell current Is increases to a steady value through a transient response according to the increase of the residual oxygen concentration.

  In FIG. 4C, the transient response characteristics of the sensor cell current Is according to the reduction of the pump cell applied voltage Vp are the characteristics at the time of manufacturing the NOx sensor (initial characteristics) and the characteristics at the time of NOx sensor deterioration (post-deterioration characteristics). Are shown in two types. The solid line indicates the initial characteristic, and the dashed line indicates the deterioration characteristic. FIG. 4C shows that when the exhaust gas supplied to the sensor cell 42 has the same oxygen concentration, a difference occurs between the initial characteristic and the deterioration characteristic of the sensor cell current Is. In this case, first, the steady-state value of the deterioration characteristic tends to be smaller than the steady-state value of the initial characteristic. Second, there is a tendency for the rise time of the deterioration characteristics to be later than that of the initial characteristics. For example, when looking at the slope of the characteristic during the predetermined period during the transient change, the slope A1 of the characteristic at the time of deterioration becomes looser than the slope A0 of the initial characteristic. These tendencies become more remarkable as the deterioration of the sensor cell 42 progresses.

  As described above, when the sensor cell 42 is deteriorated from the initial characteristics, the above tendency appears in the output value. Therefore, in the present embodiment, the deterioration determination of the sensor cell 42 is performed based on the output value. The deterioration state of the sensor cell 42 is confirmed based on the deterioration determination. And thereby, the accuracy of NOx concentration detection can be improved, and the deterioration of exhaust emission can be suppressed.

  Here, at the time of the deterioration determination of the sensor cell 42, the pump cell applied voltage Vp is switched to the side where the oxygen concentration in the gas chamber 61 is increased, that is, the low voltage side. Therefore, after the deterioration determination, the inside of the gas chamber 61 is in an oxygen excess state, and when the detection of the NOx concentration is subsequently performed, there is a concern that the concentration detection may be adversely affected. Therefore, in the present embodiment, after the deterioration determination of the sensor cell 42, the pump cell applied voltage Vp is switched to a voltage (third voltage V3) higher than the voltage (first voltage V1) before the voltage switching for the deterioration determination. Thus, the oxygen excess state in the gas chamber 61 can be quickly resolved after the deterioration determination, and the appropriate concentration detection can be started early.

  FIG. 5 is a functional block diagram for explaining the functions of each of the SCUs 31 to 33. As shown in FIG. Each of the SCUs 31 to 33 switches the pump cell applied voltage Vp from the first voltage V1 to the second voltage V2 lower than the first voltage V1, and the pump cell applied voltage Vp by the first voltage switch M11. When the voltage is switched from the first voltage V1 to the second voltage V2, the deterioration determination parameter for the sensor deterioration determination is acquired based on the sensor cell current Is, and the NOx sensors 21 to 23 are deteriorated based on the sensor cell current Is. A deterioration determination processing unit M12 that performs determination, and a second voltage switching unit M13 that switches the pump cell applied voltage Vp to a third voltage V3 higher than the first voltage V1 after the deterioration determination by the deterioration determination processing unit M12; Have. In the present embodiment, the deterioration determination of the sensor cell 42 is performed as the deterioration determination of the NOx sensors 21 to 23.

  The first voltage switching unit M11 is configured to increase the oxygen concentration in the gas chamber 61 when the deterioration determination of the sensor cell 42 is performed, the pump cell application voltage Vp is a first voltage V1 to a second voltage lower than the first voltage V1. Implement processing to switch to V2. In the present embodiment, the pump cell application voltage Vp is switched in a step-like manner, but the voltage change waveform may be other than the step waveform. However, since deterioration determination is performed by comparison with the initial characteristics, it is preferable to make the voltage change waveform the same as when measuring the initial characteristics.

  The deterioration determination processing unit M12 determines the deterioration rate C of the sensor cell 42 based on the slope of the transient change of the sensor cell current Is accompanying the switching of the pump cell applied voltage Vp by the first voltage switching unit M11 as the deterioration determination process of the sensor cell 42. calculate. In the present embodiment, as the deterioration determination parameter of the sensor cell 42, the slope of the transient change is calculated from the current change amount ΔIs with respect to the unit time Δt. In addition, it is also possible to use another parameter as the deterioration determination parameter, for example, it is possible to use (the current after convergence) the current change amount ΔIs within a predetermined period of transient change or the sensor cell current Is after current convergence. It is.

  Incidentally, the sensor cell 42 detects the sensor cell current Is at the nA order level at the time of normal NOx concentration detection, while at the time of switching of the pump cell applied voltage Vp for deterioration determination, the residual oxygen concentration increases. The sensor cell current Is is detected. In this case, it is preferable that the current processing range of A / D conversion in the SCUs 31 to 33 be switched between the time of NOx concentration detection and the time of deterioration determination in order to enhance the resolution of current detection. At the time of the deterioration determination, the current processing range may be expanded as compared with the time of the NOx concentration detection.

  Further, after the deterioration determination of the sensor cell 42 is completed, the second voltage switching unit M13 reduces the pump cell application voltage Vp from the second voltage V2 to the first voltage V1 (first switching process) to reduce the oxygen concentration in the gas chamber 61. The process of switching to the third voltage V3 higher than the voltage of. By this voltage switching, oxygen in the gas chamber 61 is quickly exhausted after the deterioration determination.

  The engine ECU 35 also has an abnormality determination unit M21 that determines an abnormality due to emission deterioration based on the deterioration determination results of the SCUs 31 to 33. The abnormality determination unit M21 determines the abnormality of the engine emission based on the deterioration rate C of the sensor cell 42 calculated by the deterioration determination processing unit M12 of each of the SCUs 31 to 33. In addition to the deterioration rate C of the sensor cell 42, the output abnormality of the NOx sensors 21 to 23, the various sensor information from other sensors, the engine operation state, etc. are comprehensively considered to determine the emission abnormality. It is also good.

  Both the deterioration determination and the emission abnormality determination regarding the NOx sensors 21 to 23 may be performed by the SCU 31 to 33, or both may be performed by the engine ECU 35. It is desirable that the emission abnormality determination be performed using an element other than the degree of deterioration of the NOx sensors 21-23. Therefore, it is preferable to send the information on the deterioration determination of the SCUs 31 to 33 to the engine ECU 35, and combine the information on the deterioration determination with the various sensor information described above, the engine operating condition, etc.

  Next, the process procedure of the deterioration determination of the sensor cell 42 will be described with reference to the flowchart of FIG. The process shown in FIG. 6 is an arithmetic process for realizing the functions of the SCUs 31 to 33 described in FIG. 5 and is performed, for example, at predetermined intervals in each of the SCUs 31 to 33.

  In step S11, it is determined whether an execution condition of the deterioration determination is satisfied. The present implementation condition includes, for example, that a permission signal for permitting execution of the deterioration determination is received from the engine ECU 35. The engine ECU 35 transmits a permission signal when the gas environment in the exhaust pipe 11 is stable under a predetermined environment. Specifically, when the engine 10 is in a predetermined operation state and the amount of exhaust is relatively stable, the engine ECU 35 turns off the ignition switch when fuel cut is in progress or when the engine 10 is automatically stopped. When it is immediately after (immediately after IG off) or when the engine ECU 35 is being started by the soak timer, the permission signal is transmitted. If the implementation condition of the deterioration determination is satisfied, the process proceeds to the subsequent step S12, and if the implementation condition is not satisfied, the present process ends. In addition, step S11 is affirmed also when performing again after degradation determination is implemented.

  In step S12, it is determined whether or not the pump cell application voltage Vp is before switching from the first voltage V1 to the second voltage V2 before performing the first voltage switching. And if it is before implementation of 1st voltage switching, it will progress to step S13, and if it is not before implementation of 1st voltage switching, it will progress to step S16. In step S12, it is determined whether the oxygen concentration or NOx concentration in the exhaust gas is in a predetermined stable state, and if it is not in the stable state, the process may be ended as it is. . Specifically, it is determined whether the fluctuation amount per unit time of the oxygen concentration or NOx concentration in the exhaust gas is less than or equal to a predetermined value, and whether the oxygen concentration or NOx concentration in the exhaust gas is within a predetermined concentration range. Good to be done.

  In step S13, the detection of the NOx concentration by the NOx sensors 21 to 23 (NOx sensors to be subjected to voltage switching) is prohibited. Thereafter, in step S14, a pump cell current Ip1 which is a pump cell output before the first voltage switching, that is, in a state where the pump cell applied voltage Vp is the first voltage V1, is detected. In step S15, the pump cell applied voltage Vp is switched from the first voltage V1 to the second voltage V2.

  After performing the first voltage switching, in step S16, it is determined whether or not the current pump cell applied voltage Vp is the second voltage V2. Then, if the pump cell applied voltage Vp is the second voltage V2, the process proceeds to step S17, and it is determined whether or not the deterioration determination is ended. Specifically, when any one of the following conditions (conditions 1 and 2) is satisfied, it is determined that it is a timing to end the deterioration determination.

  (Condition 1) A predetermined deterioration determination period (processing period) has elapsed after switching to the second voltage V2. The deterioration determination period is, for example, about 10 seconds.

  (Condition 2) A request for interrupting the deterioration determination has occurred. The request for interrupting the deterioration determination occurs based on the fact that the fuel cut is stopped, that is, the fuel injection is resumed when the deterioration determination is being performed along with the fuel cut, and the deterioration determination is performed along with the automatic engine stop. Occurs when the engine restart is performed.

  Step S17 is affirmed when either of the above (condition 1) and (condition 2) is established first. And when step S17 is denied, it progresses to step S18, and when step S17 is affirmed, it progresses to step S22.

In step S18, when the sensor cell current Is transiently changes with the switching of the pump cell applied voltage Vp using the following equation (1), the amount of change ΔIs of the sensor cell current Is in the predetermined period during the transient change and the predetermined period The slope A1 of the sensor cell current Is at transient change is calculated on the basis of the time difference ΔT1.
A1 = ΔIs / ΔT1 (1)
Thereafter, in step S19, a pump cell current Ip2 which is a pump cell output after the pump cell applied voltage Vp is switched to the second voltage V2 is detected. The pump cell current Ip2 is detected at a timing when a predetermined time has elapsed since the voltage switching, that is, at a timing when the pump cell current Ip is stabilized.

In step S20, the slope B1 is calculated by normalizing the slope A1. In this case, using the following equation (2), normal based on the slope A1 at the time of transient change of the sensor cell current Is and the change amount ΔIp (= Ip1−Ip2) of the pump cell current Ip accompanying switching of the pump cell applied voltage Vp. Calculate the converted inclination B1.
B1 = A1 / ΔIp (2)
In step S21, the deterioration rate C (%) of the sensor cell 42 is calculated using the slope B1 calculated in step S20. At this time, the ratio (B1 / B0) of the slope B1 to the slope B0 of the initial characteristic is calculated as a reaction rate ratio, and the deterioration rate of the sensor cell 42 based on the reaction rate ratio B1 / B0 using, for example, the relationship of FIG. Calculate C. The reaction rate ratio B1 / B0 is determined as the ratio of the reaction rate to the oxygen supplied to the sensor cell 42. The slope B0 representing the initial characteristic is stored in advance in the memory in the SCUs 31 to 33. In FIG. 7, a relationship is defined in which the deterioration rate C increases as the reaction speed ratio B1 / B0 decreases, that is, as the difference between the deterioration characteristic of the sensor cell 42 and the initial characteristic increases. A large deterioration rate C means that the degree of deterioration of the sensor cell 42 is large. In step S21, the deterioration rate C of the sensor cell 42 is transmitted to the engine ECU 35.

  In step S22, it is determined whether or not the pump cell applied voltage Vp is to be switched to the third voltage V3, that is, whether or not the second voltage switching is to be performed, after the end of the deterioration determination. Specifically, when any of the following conditions (conditions 3 to 5) is satisfied, it is determined that the pump cell applied voltage Vp is switched to the third voltage V3. The processing of this step corresponds to the concentration detection determination unit, the reexecution determination unit, and the suitability determination unit.

  (Condition 3) Subsequent to the end of the current deterioration determination, the NOx concentration detection by the NOx sensors 21 to 23 is performed. For example, when the first voltage switching and the deterioration determination are performed along with the fuel cut or the automatic engine stop, the combustion is temporarily stopped and the combustion is restarted thereafter, so after the deterioration determination It is determined that NOx concentration detection is to be performed. When the NOx concentration detection is performed after the deterioration determination, step S22 is affirmed.

  (Condition 4) In the case where the first voltage switching of the pump cell applied voltage Vp and the subsequent deterioration determination are repeatedly performed n times, the nth (final) deterioration determination is completed. When the n-th deterioration determination is completed, that is, when the second voltage switching and the deterioration determination are not performed again, step S22 is affirmed. In addition, if the nth deterioration determination is not completed, the first voltage switching and the deterioration determination are performed again.

  (Condition 5) Deterioration determination based on the sensor cell current Is is properly performed. In this case, if the deterioration determination is not properly performed, the first voltage switching and the deterioration determination are performed again. The propriety of the deterioration determination is determined based on the change of the sensor cell current Is in the state where the second voltage V2 is applied as the pump cell applied voltage Vp. Specifically, as shown in FIG. 8, after the pump cell applied voltage Vp is switched from the first voltage V1 to the second voltage V2, if the sensor cell current Is converges to a certain value, it is determined that the deterioration determination is properly performed. (See Is1 in the figure). On the other hand, if the sensor cell current Is does not converge after switching the pump cell applied voltage Vp from the first voltage V1 to the second voltage V2, it is assumed that the deterioration determination is not properly performed (see Is2 and Is3 in the figure). . The change in the sensor cell current Is is considered to occur due to the change in concentration in the gas chamber 61. When the deterioration determination is properly performed, that is, when the second voltage switching and the deterioration determination are not performed again, step S22 is affirmed.

  When it is determined that the pump cell applied voltage Vp is to be switched to the third voltage V3, the process proceeds to step S23, and when it is not determined to switch the pump cell applied voltage Vp to the third voltage V3, the process proceeds to step S26. .

  In steps S23 to S25, a process related to the application of the third voltage V3 is performed. That is, in step S23, the third voltage V3 is set based on the amount of change .DELTA.Ip of the pump cell current Ip generated as the pump cell applied voltage Vp is switched from the first voltage V1 to the second voltage V2. At this time, the third voltage V3 may be set using, for example, the relationship shown in FIG. In step S24, a voltage application time Ta for applying the third voltage V3 is set based on the change amount ΔIp of the pump cell current Ip. At this time, for example, the voltage application time Ta may be set using the relationship shown in FIG. In FIGS. 9A and 9B, in consideration of the fact that the oxygen concentration in the gas chamber 61 is higher as the change amount ΔIp of the pump cell current Ip is larger, the change amount ΔIp of the pump cell current Ip is larger. The voltage V3 and the voltage application time Ta are set to large values. Then, in step S25, the pump cell applied voltage Vp is switched from the second voltage V2 to the third voltage V3.

  The third voltage V3 and the voltage application time Ta may be set based on the value of the pump cell current Ip or the value of the sensor cell current Is instead of the change amount ΔIp of the pump cell current Ip. In this case, for example, as the sensor cell current Is (Is convergence value) in the state where the second voltage V2 is applied as the pump cell applied voltage Vp is larger, the third voltage V3 and the voltage application time Ta are set to larger values. It is good. It is also possible to variably set one of the third voltage V3 and the voltage application time Ta.

  As described above, in step S17, deterioration occurs in response to the passage of the predetermined deterioration determination period after switching to the second voltage V2 (condition 1) or the occurrence of the request for interruption of the deterioration determination (condition 2). Although the determination is ended, in step S23, it is preferable that the third voltage V3 be set in accordance with which one of the conditions 1 and 2 is satisfied. That is, in the situation where the pump cell applied voltage Vp is switched to the second voltage V2 with the fuel cut or the engine automatic stop, the SCUs 31 to 33 deteriorate with the restart of the fuel injection or the engine restart before the deterioration determination period elapses. When the determination is ended, the third voltage V3 is set higher than when the deterioration determination is ended with the passage of the deterioration determination period.

  In step S26, the pump cell application voltage Vp is switched from the second voltage V2 to the first voltage V1 (Vp before performing the first voltage switching). Thereafter, in step S27, it is determined whether to perform the first voltage switching and deterioration determination again. Here, if it is determined that the first voltage switching and the deterioration determination are to be performed again by the determination shown in (Condition 4) above, step S27 is affirmed. That is, in the case where the first voltage switching and the deterioration determination are repeated n times, it is determined that the second voltage switching and the deterioration determination are to be performed again if the nth deterioration determination is not completed. When it is determined that the first voltage switching and the deterioration determination are to be performed again by the determination shown in (Condition 5) above, step S27 is affirmed. That is, if the deterioration determination based on the sensor cell current Is is not properly performed, it is determined that the second voltage switching and the deterioration determination are to be performed again.

  If step S27 is affirmed, it will progress to step S28. In step S28, execution of the second voltage switching and deterioration determination again is permitted. If step S27 is negative, the process proceeds to step S31. In step S31, detection of the NOx concentration by the NOx sensors 21 to 23 is permitted.

  In addition, after the pump cell applied voltage Vp is switched from the second voltage V2 to the third voltage V3, step S16 is denied and the process proceeds to step S29. In step S29, it is determined whether or not the voltage application time Ta has elapsed after switching to the third voltage V3. Then, if the voltage application time Ta has elapsed, the present process is once ended, and if the voltage application time Ta has not elapsed, the process proceeds to step S30.

  In step S30, the pump cell applied voltage Vp is switched from the third voltage V3 to the first voltage V1. Then, in the subsequent step S31, the detection of the NOx concentration by the NOx sensors 21 to 23 is permitted.

  After the deterioration rate C of the sensor cell 42 is calculated, the SCUs 31 to 33 correct the sensor cell current Is with the deterioration rate C for each of the NOx sensors 21 to 23 when detecting the NOx concentration by the NOx sensors 21 to 23 It is preferable to calculate the NOx concentration based on the corrected sensor cell current Is. In this case, the sensor cell current Is is corrected such that the current sensor cell characteristic is returned to the initial characteristic.

  FIG. 10 is a time chart showing changes in the pump cell applied voltage Vp and the sensor cell current Is at the time of the deterioration determination. In this example, two deterioration determinations are performed in succession.

  In FIG. 10, at time t11, the pump cell applied voltage Vp is switched from the first voltage V1 to the second voltage V2, and in the period from time t11 to t12, deterioration determination (calculation of deterioration rate C) is made based on the sensor cell current Is. To be implemented. Although the first deterioration determination is completed at time t12, the pump cell applied voltage Vp is switched to the original first voltage V1 instead of the third voltage V3 because the second deterioration determination is performed thereafter. Thereafter, at time t13, the pump cell applied voltage Vp is again switched to the second voltage V2, and in the period from time t13 to t14, the deterioration determination (calculation of the deterioration rate C) is performed again based on the sensor cell current Is. At time t14, the second deterioration determination is ended, and the pump cell applied voltage Vp is switched to the third voltage V3 accordingly.

  Thereafter, at time t15 when the voltage application time Ta has elapsed since the switching to the third voltage V3, the pump cell applied voltage Vp is switched to the first voltage V1. Further, after time t15, detection of the NOx concentration is permitted.

  Here, the period of time t11 to t12 and the period of time t13 to t14 are both high oxygen concentration periods in which the pump cell applied voltage Vp is reduced, and the pump cell applied voltage Vp is switched to the high voltage side with the end of the deterioration determination. Then, oxygen removal is performed, but at time t12, the pump cell applied voltage Vp is switched to the first voltage V1 in anticipation of performing the deterioration determination again. At time t14, the pump cell applied voltage Vp is switched to the third voltage V3 in anticipation of the execution of the NOx concentration detection.

  When the deterioration determination is performed a plurality of times as shown in FIG. 10, the average value of the determination results (the deterioration rate C) may be set as the final determination result. In addition, when there is superiority or inferiority in a plurality of determination results (deterioration rate C), the superior determination result may be used as the final determination result.

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

  In the deterioration determination of the NOx sensors 21 to 23, after the deterioration determination of the sensor cell 42 is performed in a state where the pump cell applied voltage Vp is switched from the first voltage V1 to the second voltage V2 on the low voltage side, the pump cell applied voltage Vp is determined as a deterioration The third voltage V3 is switched to the third voltage V3 higher than the first voltage V1 before the start. Therefore, after the deterioration determination, the oxygen excess state in the gas chamber 61 is quickly resolved, and when the NOx concentration detection is performed after the deterioration determination, the detection accuracy is reduced, or the concentration detection start is delayed excessively. Can be suppressed. As a result, it is possible to carry out concentration detection that is appropriate after the deterioration determination of the NOx sensors 21-23.

  After the deterioration determination, the third voltage V3 is set based on the pump cell current Ip or the sensor cell current Is in a state where the pump cell applied voltage Vp is switched to the second voltage V2, and switching to the third voltage V3 is performed. It was composition. As a result, the third voltage V3 can be properly applied according to the oxygen concentration in the state where the oxygen concentration in the gas chamber 61 is increased. In this case, appropriate oxygen removal can be achieved while saving power.

  After the deterioration determination, the voltage application time Ta for applying the third voltage V3 is set based on the pump cell current Ip or the sensor cell current Is in a state where the pump cell applied voltage Vp is switched to the second voltage V2, and the voltage application is applied. The third voltage V3 is applied at time Ta. As a result, the third voltage V3 can be properly applied according to the oxygen concentration in the state where the oxygen concentration in the gas chamber 61 is increased. In this case, appropriate oxygen removal can be achieved while saving power.

  The pump cell applied voltage Vp is switched to the third voltage V3 on the condition that it is determined that the NOx concentration detection by the NOx sensors 21 to 23 is performed after the sensor deterioration determination. In this case, the NOx concentration can be detected promptly and properly after the sensor deterioration determination.

  When the deterioration determination of the sensor cell 42 is performed at the time of fuel cut or automatic stop of the engine 10, the fuel cut or the automatic stop of the engine is temporary, and at the subsequent restart of the fuel injection or restart of the engine 10, From the beginning, it is desirable that the NOx concentration be properly detected. In this respect, when the sensor deterioration determination (parameter acquisition) is performed along with the fuel cut or the engine automatic stop, it is considered that the NOx concentration detection is performed by the NOx sensors 21 to 23 after the deterioration determination, and the pump cell applied voltage The configuration is such that Vp is switched to the third voltage V3. Thereby, at the time of resumption of fuel injection or restart of the engine 10, the detection of the NOx concentration can be carried out promptly and properly.

  In the situation where the pump cell applied voltage Vp is switched to the second voltage V2 due to the fuel cut or the automatic engine stop, in the case where engine restart or resumption of fuel injection is required before the deterioration determination period has elapsed, the deterioration determination period It is desirable that NOx concentration detection be optimized earlier than when engine restart or resumption of fuel injection is required after lapse of time. In this respect, the third voltage V3 is higher than the case where the deterioration determination is ended along with the passage of the deterioration judgment period when the deterioration judgment is ended along with the restart of the fuel injection or the engine restart before the passage of the deterioration judgment period. Therefore, the third voltage V3 can be properly applied while aiming to start the NOx concentration detection early.

  When the deterioration determination (parameter acquisition) is not performed again after the deterioration determination of the NOx sensors 21 to 23, switching of the pump cell applied voltage Vp to the third voltage V3 is performed, and the deterioration determination (parameter acquisition) is performed again. When carrying out, it was set as the structure which does not switch the pump cell applied voltage Vp to the 3rd voltage V3 (it switches to the original 1st voltage V1). Therefore, when the deterioration determination is not performed again, that is, when the processing of the deterioration determination is completed, the oxygen concentration in the gas chamber 61 is reduced early in preparation for the next NOx concentration detection. Thereby, the NOx concentration in the exhaust can be properly detected. Further, when the deterioration determination is performed again, that is, when the processing of the deterioration determination is not completed, the pump cell applied voltage Vp is switched to the first voltage V1 without requiring the highly accurate NOx concentration detection. Thus, it is possible to suppress the energy consumption accompanying the increase of the applied voltage.

  In the determination of deterioration of the NOx sensors 21 to 23, it is determined whether or not the determination of deterioration is properly performed. If it is determined that the determination of deterioration is not appropriate, the deterioration determination is performed again. In this case, the reliability of the deterioration determination can be improved by re-doing the deterioration determination.

  If the sensor cell current Is does not converge and does not stabilize in the state where the second voltage V2 is applied as the pump cell applied voltage Vp, the oxygen concentration or NOx concentration in the gas chamber 61 fluctuates, and the deterioration determination parameter is correct It can not be acquired, and there is a possibility that the deterioration determination may not be properly performed. In this point, since the propriety of the sensor degradation determination is determined based on the change of the sensor cell current Is, it is possible to properly execute the degradation determination again.

  When the third voltage V3 is applied as the pump cell application voltage Vp during the sensor deterioration and after the sensor deterioration determination, the NOx concentration detection by the NOx sensors 21 to 23 is prohibited. Thereby, in the state where the oxygen concentration in the gas chamber 61 is fluctuating, it is possible to prevent the erroneous detection of the NOx concentration.

(Other embodiments)
The above embodiment may be modified, for example, as follows.

  · When the pump cell applied voltage Vp is switched to the side to increase the oxygen concentration in the gas chamber 61 (when performing the first voltage switching) in determining the deterioration of the sensor cell 42, the pump cell applied voltage Vp is zero, ie, no voltage is applied It may be configured to switch to the state. Alternatively, the pump cell applied voltage Vp may be switched to a negative voltage. In any case, by increasing the oxygen concentration in the gas chamber 61 by switching the applied voltage, the deterioration determination can be performed by the transient response of the sensor cell 42 at that time.

  The configuration may also be configured to determine that the deterioration determination is not appropriate based on, for example, that the difference from the previously calculated deterioration rate C is a predetermined value or more as the appropriateness determination of whether or not the deterioration determination of the sensor cell 42 is properly performed. Good. Then, based on the determination result that the deterioration determination is not appropriate, the first voltage switching and the deterioration determination are performed again.

  In the above embodiment, the slope A1 of the sensor cell current Is is normalized to calculate the slope B1, and the deterioration rate C is calculated using the slope B1. However, this may be changed. For example, the deterioration rate C may be calculated using the slope A1.

  In the above embodiment, the deterioration rate C (%), which is the ratio between the current characteristic of the sensor cell 42 and the initial characteristic, is calculated as the determination of the deterioration state of the sensor cell 42. However, the present invention is not limited thereto. For example, the difference from the initial value is calculated for the inclination of the sensor cell current Is as the deterioration determination parameter of the sensor cell 42, the value correlated with it, and the current change amount ΔIs after the convergence of the sensor cell current Is. The configuration may be such that the degree of deterioration of 42 is grasped. Moreover, comparison with a predetermined standard value may be performed instead of comparison with the initial value. The configuration may be such that the degree of deterioration is determined based on the index of "100-deterioration rate C". In this case, in the index, the initial characteristic is represented by 100%, and is represented by a smaller value as the deterioration progresses. In any case, any deterioration state based on the change in the characteristics of the sensor cell 42, that is, one that can determine the degree of deterioration may be used.

  -In the degradation determination processing unit M12, parameter acquisition and degradation determination are not continuously performed within the degradation determination period, but are performed at timings at which these parameter acquisition and degradation determination become discontinuous (that is, different periods) The configuration may be In this case, the deterioration determination processing unit M12 (SCU31 to 33) acquires the deterioration determination parameter in a state where the pump cell applied voltage Vp is switched from the first voltage V1 to the second voltage V2, and after acquiring the parameter, determines the deterioration The pump cell applied voltage Vp is switched to the third voltage V3 without performing. The deterioration determination may be appropriately performed at a timing later than the parameter acquisition.

  In addition, similarly to conditions 1 and 2 described above, the determination of completion of parameter acquisition is performed based on the passage of a predetermined processing period after switching to the second voltage V2 and the generation of a request for interrupting parameter acquisition. Good to be done. Then, similarly to the above, the third voltage V3 may be set in accordance with the termination condition. Further, it may be determined that whether or not parameter acquisition has been properly performed is performed, and if it is determined that the parameter acquisition is not appropriate, voltage switching and parameter acquisition are performed again.

  In the above embodiment, the deterioration of the sensor cell 42 is determined as the deterioration determination of the NOx sensors 21 to 23. However, this may be changed. If the pump cell 41 is deteriorated, it is conceivable that a desired change in oxygen concentration can not be obtained when the pump cell applied voltage Vp is switched, and the change in the sensor cell current Is becomes different from that in normal. Therefore, the deterioration determination of the NOx sensors 21 to 23 may be performed including the deterioration of the pump cell 41.

  In the above embodiment, the sensor element 40 is configured to include the single solid electrolyte body 53 and the single gas chamber 61. However, 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 different gas chambers 61. It may be configured to be provided. An example of such a configuration is shown in FIG.

  The sensor element 40 shown in FIG. 11 has two solid electrolyte bodies 53a and 53b disposed 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 gas inlet 53c, and the gas chamber 61b communicates with the gas chamber 61a via the narrowed portion 71. The pump cell 41 has a pair of electrodes 72 and 73, one of which 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 disposed opposite to each other, and the monitor cell 43 has an electrode 75 and a common electrode 76 disposed opposite to each other. The sensor cell 42 and the monitor cell 43 are provided adjacent to each other. In each of those cells, one electrode 74, 75 is provided to be exposed in the gas chamber 61b. As described above, even in the configuration in which the pump cell 41 and the sensor cell 42 are provided in different gas chambers 61a and 61b, each function such as the deterioration determination of the above embodiment can be suitably implemented.

  -Of the pair of electrodes constituting the pump cell 41, one of the electrodes may be provided so as to be exposed to the exhaust gas space instead of the air chamber 62 as a reference gas chamber. That is, one of the pair of electrodes is provided at a position exposed to the exhaust gas, and the other electrode is provided so as to be exposed in the gas chamber 61. In this case, by applying a voltage to the pump cell 41, oxygen ions are moved from the gas chamber 61 to the exhaust gas space to discharge oxygen into the exhaust gas. When this configuration is employed, the solid electrolyte body on which the one electrode is provided is further provided with an insulating layer provided with a hole by boring out a portion where the one electrode is disposed. And the porous protective layer is provided in the said hole so that the said one electrode may be covered. It is preferable to protect one of the electrodes by doing this.

  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 gas. In this case, it is preferable that oxygen in the exhaust gas is discharged by the pump cell, and HC and CO are decomposed from the gas after the oxygen discharge by the sensor cell to detect HC concentration and CO concentration. Besides, the concentration of ammonia in the gas to be detected may be detected.

  The present invention can be embodied as a gas sensor control device for gas sensors provided in an intake passage of an internal combustion engine, and gas sensors used for engines of other types such as a gasoline engine other than a diesel engine. The gas sensor may use a gas other than the exhaust gas as a gas to be detected, and may be used in applications other than automobiles.

  21 to 23 NOx sensor (gas sensor) 31 to 33 SCU (gas sensor control device) 35 engine ECU (gas sensor control device) 41 pump cell 42 sensor cell 61 gas chamber.

Claims (9)

A pump cell (41) for adjusting the oxygen concentration in the gas to be detected introduced into the gas chamber (61) by voltage application, and a concentration of a specific gas component from the gas to be detected after the oxygen concentration is adjusted by the pump cell A gas sensor control device (31 to 33, 35) that is applied to a gas sensor (21 to 23) having a sensor cell (42) for detecting
A first voltage switching unit configured to switch a pump cell applied voltage applied to the pump cell from a first voltage to a second voltage lower than the first voltage;
When the voltage applied to the pump cell is switched from the first voltage to the second voltage by the first voltage switching unit, a deterioration determination parameter for determining the deterioration of the gas sensor is acquired based on the output of the sensor cell, A deterioration determination processing unit that performs the deterioration determination of the gas sensor based on the deterioration determination parameter;
A second voltage switching unit configured to switch the voltage applied to the pump cell to a third voltage higher than the first voltage after processing for parameter acquisition or deterioration determination by the deterioration determination processing unit;
A gas sensor control device comprising:   The second voltage switching unit sets the third voltage based on an output of the pump cell or an output of the sensor cell in a state where the pump cell applied voltage is switched to the second voltage by the first voltage switching unit. The gas sensor control device according to claim 1, wherein switching to the third voltage is performed.   The second voltage switching unit applies the third voltage based on the output of the pump cell or the output of the sensor cell in a state where the pump cell applied voltage is switched to the second voltage by the first voltage switching unit. The gas sensor control device according to claim 1 or 2, wherein the voltage application time to be set is set, and the third voltage is applied at the voltage application time. The concentration detection / determination unit is configured to determine whether or not the concentration detection of the specific gas component is performed by the gas sensor after the processing by the deterioration determination processing unit.
The second voltage switching unit switches the pump cell applied voltage to the third voltage on the condition that the concentration detection determination unit determines that the concentration detection of the gas sensor is performed. The gas sensor control device according to item 1. The gas sensor is an exhaust sensor that uses the exhaust gas discharged from the internal combustion engine (10) as the detection target gas and detects the concentration of a specific gas component in the exhaust gas,
The voltage switching by the first voltage switching unit and the parameter acquisition by the deterioration determination processing unit are performed when the internal combustion engine is temporarily stopped or when fuel injection is temporarily stopped.
The concentration detection determination unit performs voltage switching by the first voltage switching unit and parameter acquisition by the deterioration determination processing unit as the temporary operation stop of the internal combustion engine or the temporary stop of fuel injection is performed. 5. The gas sensor control device according to claim 4, wherein it is determined that the concentration detection of the specific gas component is performed by the gas sensor after the processing by the deterioration determination processing unit. The deterioration determination processing unit performs parameter acquisition within a predetermined processing period,
In the situation where the voltage applied to the pump cell is switched to the second voltage with the temporary stop of the internal combustion engine or the temporary stop of the fuel injection, the operation restart of the internal combustion engine before the elapse of the processing period The gas sensor according to claim 5, wherein, when the parameter acquisition is ended with resumption of the fuel injection, the third voltage is made higher than when the parameter acquisition is ended with the passage of the processing period. Control device. The voltage switching by the first voltage switching unit and the parameter acquisition by the deterioration determination processing unit can be performed a plurality of times consecutively.
It includes a re-execution determination unit that determines whether to perform voltage switching by the first voltage switching unit and parameter acquisition by the deterioration determination processing unit again after processing by the deterioration determination processing unit,
The second voltage switching unit switches the pump cell applied voltage to the third voltage on the condition that the re-execution determination unit determines that the re-execution is not to be performed again. The gas sensor control device according to claim 1. An appropriateness determination unit that determines whether the deterioration determination processing unit acquires the deterioration determination parameter or whether the deterioration determination based on the parameter is properly performed.
The gas sensor control device according to claim 7, wherein the re-execution determination unit determines that the re-execution is to be performed when it is determined that the parameter acquisition or the deterioration determination by the deterioration determination processing unit is not appropriate.   The appropriateness determination unit determines whether the parameter acquisition or the deterioration determination by the deterioration determination processing unit is properly performed based on a change in the output of the sensor cell in a state where the second voltage is applied as the pump cell applied voltage. The gas sensor control device according to claim 8, wherein

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