DE112018002725T5 - GAS SENSOR CONTROL DEVICE - Google Patents

Abstract

A gas sensor has the following: a pump cell that adjusts an oxygen concentration in a detection target gas introduced into a gas chamber by the application of voltage; a sensor cell that detects a concentration of a certain gas component in the gas chamber after the oxygen concentration is set by the pump cell; and a monitor cell that detects a residual oxygen concentration in the gas chamber. Each of the SCUs 31 to 33 includes: a voltage switching unit (M11) that switches an applied voltage of a pump cell; a detection unit (M12) that detects an output of the sensor cell and an output of the monitor cell when the applied voltage is switched by the voltage switching unit; and a deterioration determination unit (M13) that determines a deterioration state of the sensor cell based on the output of the sensor cell and the output of the monitor cell detected by the detection unit.

Description

[Cross-reference to an associated application]

This registration is based on the one filed on May 26, 2017 Japanese Patent Application No. 2017-104901 , the description of which is incorporated herein by reference.

Technical field

The present disclosure relates to a gas sensor control device.

State of the art

As a gas sensor that detects the concentration of a specific gas component in a detection target gas, such as exhaust gas from an internal combustion engine, a NOx sensor is known that detects the concentration of NOx (nitrogen oxides). The NOx sensor has a three-cell structure, which is formed from a pump cell, a monitor cell and a sensor cell, as described for example in PTL 1. The pump cell discharges or conveys the oxygen from the exhaust gas introduced into a gas chamber. The monitor cell detects the concentration of the residual oxygen in the gas chamber after passing through the pump cell. The sensor cell detects the NOx concentration of the gas after passing through the pump cell.

The deteriorated NOx sensor cannot accurately detect the NOx concentration. Therefore, when the NOx sensor is installed in the exhaust system of an automobile, there is a possibility that the exhaust system suffers from a failure such as reduced exhaust gas emission. For example, there have been conventionally proposed methods for diagnosing deterioration of a NOx sensor. For example, PTL 1 discloses a method by which a voltage applied to the pump cell is forcibly switched and the deterioration of the NOx sensor is diagnosed based on the amount of a change in the sensor cell power output at that time.

List of citations

patent literature

[PTL 1] JP 2009-175013 A

SUMMARY OF THE INVENTION

According to the aforementioned conventional deterioration diagnosis method, the concentration of the residual oxygen in the gas chamber is deliberately changed by switching the voltage applied to the pump cell, and the deterioration diagnosis of the sensor cell is carried out based on a transient reaction of the sensor cell together with a change in the residual oxygen concentration. After switching the applied voltage of the pump cell, however, if the residual oxygen concentration in the gas chamber is not set correctly, the change in the output of the sensor cell can be influenced. In this case, the accuracy of the deterioration diagnosis of the sensor cell may decrease.

The present disclosure has been prepared with the foregoing in mind. A main object of the present disclosure is to provide a gas sensor control device that properly determines the deterioration state of the sensor cell.

In order to solve the aforementioned problems, the present means is a control device applied to a gas sensor, comprising: a pump cell that adjusts an oxygen concentration in a detection target gas introduced into a gas chamber by voltage application; a sensor cell that detects or detects a concentration of a specific gas component in the gas chamber after the oxygen concentration has been set by the pump cell; and a monitor cell that detects a residual oxygen concentration in the gas chamber, wherein the control device performs a control connected to the gas sensor. The control device includes: a voltage switching unit that switches an applied voltage to the pump cell; a detection unit that detects, when the applied voltage is switched by the voltage switching unit, an output of the sensor cell and an output of the monitor cell; and a deterioration determination unit that determines a deterioration state of the sensor cell based on the output of the sensor cell and the output of the monitor cell detected by the detection unit.

In a gas sensor, when a deterioration determination of a sensor cell is carried out based on the output reaction of the sensor cell, the deterioration determination of the sensor cell based on the output change of the sensor cell corresponding to the residual oxygen concentration in the gas chamber after the pump cell is switched on under voltage. In this connection, according to the above configuration, when the applied voltage is switched by the voltage switching unit, the sensor cell output and the monitor cell output are detected, and the deterioration state of the sensor cell is determined based on the sensor cell output and the monitor cell output. In this case, the Determination of deterioration of the sensor cell can be carried out after the residual oxygen concentration in the gas chamber has been correctly detected from the output of the monitor cell. This makes it possible to correctly determine the deterioration state of the sensor cell.

list of figures

• 1 ist ein Diagramm, das eine Systemkonfiguration eines Motorabgassystems veranschaulicht;
• 2 ist eine Querschnittsansicht einer Konfiguration eines NOx-Sensors;
• 3 ist eine Querschnittsansicht von 2 entlang der Linie III-III;
• 4 ist ein Diagramm zur Beschreibung von Änderungen der transienten Eigenschaften des Ausgangs einer Sensorzelle aufgrund einer Verschlechterung des NOx-Sensors;
• 5 ist ein Diagramm, das einen Startpunkt und einen Endpunkt veranschaulicht, die bei der Berechnung eines Gradientenparameters verwendet werden;
• 6 ist ein Funktionsblockdiagramm einer SCU und eines Steuergeräts;
• 7 ist ein Flussdiagramm eines Prozesses zur Verschlechterungsbestimmung der Sensorzelle;
• 8 ist ein Diagramm, das eine Beziehung zwischen einer Änderungsmenge eines Pumpzellenstroms und einem Konvergenzwert des Monitorzellenstroms veranschaulicht;
• 9 ist ein Diagramm, das eine Beziehung zwischen dem aktuellen Konvergenzwert der Monitorzelle und einem Anfangsgradienten veranschaulicht;
• 10 ist ein Diagramm, das eine Beziehung zwischen einem Reaktionsgeschwindigkeitsverhältnis, einem aktuellen Konvergenzwert der Sensorzelle und einer Verschlechterungsrate darstellt;
• 11 ist ein Flussdiagramm eines Prozesses zur Verschlechterungsbestimmung einer Sensorzelle in einer zweiten Ausführungsform;
• 12 ist ein Diagramm, das eine Beziehung zwischen einer Änderungsmenge eines Pumpzellenstroms und einem anfänglichen Gradienten veranschaulicht;
• 13 ist ein Flussdiagramm eines Prozesses zur Verschlechterungsbestimmung einer Sensorzelle in einer dritten Ausführungsform;
• 14 ist ein Diagramm, das eine Beziehung zwischen einem Monitorzellenstrom und einem Sensorzellenstrom veranschaulicht;
• 15 ist ein Flussdiagramm eines Prozesses zur Verschlechterungsbestimmung einer Sensorzelle in einer vierten Ausführungsform; und
• 16 ist eine Querschnittsansicht einer Konfiguration eines anderen NOx-Sensors.

The foregoing and other objects, features, and advantages of the present disclosure are explained in more detail by the following detailed descriptions with reference to the accompanying drawings. The drawings are as follows:

• 1 12 is a diagram illustrating a system configuration of an engine exhaust system;
• 2 12 is a cross-sectional view of a configuration of a NOx sensor;
• 3 is a cross-sectional view of FIG 2 along the line III-III;
• 4 Fig. 11 is a diagram for describing changes in the transient properties of the output of a sensor cell due to deterioration of the NOx sensor;
• 5 Fig. 12 is a diagram illustrating a start point and an end point used in calculating a gradient parameter;
• 6 Fig. 4 is a functional block diagram of an SCU and a controller;
• 7 FIG. 14 is a flowchart of a process for determining deterioration of the sensor cell;
• 8th FIG. 12 is a diagram illustrating a relationship between a change amount of a pump cell current and a convergence value of the monitor cell current;
• 9 Fig. 12 is a graph illustrating a relationship between the current convergence value of the monitor cell and an initial gradient;
• 10 Fig. 12 is a graph showing a relationship between a response speed ratio, a current convergence value of the sensor cell, and a deterioration rate;
• 11 10 is a flowchart of a process for determining deterioration of a sensor cell in a second embodiment;
• 12 Fig. 12 is a graph illustrating a relationship between a change amount of a pump cell current and an initial gradient;
• 13 10 is a flowchart of a process for determining deterioration of a sensor cell in a third embodiment;
• 14 FIG. 12 is a diagram illustrating a relationship between a monitor cell current and a sensor cell current;
• 15 11 is a flowchart of a process for determining deterioration of a sensor cell in a fourth embodiment; and
• 16 13 is a cross-sectional view of a configuration of another NOx sensor.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments are described with reference to the drawings. In the present embodiments, in a system in which the exhaust gases emitted from a vehicle diesel engine as a detection target gas and the NOx concentration in the exhaust gas is detected by a NOx sensor, a gas sensor control device is implemented to control NOx Sensor to perform. Identical or equivalent components in the following embodiments are shown with the same reference numerals in the drawings, and descriptions of the components with the same reference numbers are incorporated by reference.

(First embodiment)

As in 1 is shown on the exhaust side of an engine 10 , which is a diesel engine for purifying the exhaust gas, an exhaust gas purification system is provided. The emission control system is configured so that the engine 10 with an exhaust pipe 11 is connected, which forms an exhaust gas path, and the exhaust pipe 11 is with an oxidation catalyst 12 and a selective catalyst (hereinafter referred to as SCR catalyst) 13 in this order from the side of the engine 10 Mistake. The oxidation catalyst 12 has a diesel oxidation catalyst 14 and a diesel particulate filter (DPF) 15 on. The selective SCR catalyst 13 has an SCR catalyst 16 as a selective reduction catalyst. The exhaust pipe 11 is with an aqueous urea addition valve 17 provided to aqueous urea (aqueous urea solution) as a reducing agent in the exhaust pipe 11 between the oxidation catalyst 12 and the SCR catalyst 13 supply.

In the oxidation catalyst 12 there is the diesel oxidation catalyst 14 Mainly 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 or rhodium. The diesel oxidation catalyst 14 oxidizes and cleans hydrocarbon, carbon monoxide, nitrogen oxide and others Substances containing exhaust gas. The diesel oxidation catalyst 14 also increases the exhaust gas temperature by generating heat at the time of the catalytic reaction.

The DPF 15 is formed from a honeycomb structure in which a platinum group catalyst such as platinum or palladium is carried in porous ceramic. The DPF 15 collects the particles contained in the exhaust gas by collecting them on the partitions of the honeycomb structure. The accumulated particulate matter is oxidized and cleaned by combustion. The combustion takes place using the temperature increase of the diesel oxidation catalyst 14 and the reduction in the combustion temperature of the particulates caused by an additive.

The SCR catalytic converter 13 is an aftertreatment device of the oxidation catalyst 12 that reduces NOx to nitrogen and water. The SCR catalytic converter 16 is, for example, a catalyst in which a noble metal such as Pt is carried on the surface of a base material such as zeolite or aluminum oxide. If the catalyst temperature is in an active temperature range, the SCR catalyst reduces and cleans 16 NOx with the addition of urea as a reducing agent.

The exhaust pipe 11 is with limit current NOx sensors 21 . 22 and 23 as gas sensors upstream of the oxidation catalyst 12 , upstream of the aqueous urea addition valve 17 between the oxidation catalyst 12 and the SCR catalyst 13 and downstream of the SCR catalyst 13 Mistake. The NOx sensors 21 to 23 detect the NOx concentration in the exhaust gas at their respective detection positions. The positions and number of NOx sensors in the engine exhaust system can be set as required.

The NOx sensors 21 to 23 are each with the sensor control units (SCUs) 31 . 32 and 33 connected. Detection signals from the NOx sensors 21 to 23 may be sent to the appropriate SCUs 31 to 33 output. The SCUs 31 to 33 are electronic control devices, each of which contains a microcomputer with a CPU and various memories and their peripheral circuits and which oxygen ( O2 ) Concentration and calculate the NOx concentration as the concentration of a specific gas component in the exhaust gas, based on the detection signals (limit current signals) of the NOx sensors 21 to 23 ,

The SCUs 31 to 33 are on the communication line 34 with a communication line 34 such as the CAN bus and with various control units (e.g. the engine ECU 35 ) connected. That is, the SCUs 31 to 33 and the engine control unit 35 can over the communication line 34 send and receive each other information. For example, the SCUs transmit 31 to 33 Information about the oxygen concentration and the NOx concentration in the exhaust gas to the engine control unit 35 , The engine ECU 35 is an electronic control device with a microcomputer with a CPU and various memories and their peripheral circuits that drive the motor 10 and controls various devices in the exhaust system. The engine control unit 35 performs fuel injection control and others based, for example, on accelerator opening and engine speed.

In addition, the engine control unit controls 35 the addition of aqueous urea with the aqueous urea addition valve 17 based on that from the NOx sensors 21 to 23 detected NOx concentration. The control of the addition of aqueous urea is briefly described. The engine control unit 35 calculates the additive amount of aqueous urea based on the NOx concentration by the NOx sensors 21 and 22 upstream of the SCR catalyst 13 is detected, and performs a feedback correction on the additive amount of aqueous urea so that the value of the NOx concentration obtained from the NOx sensor 23 downstream of the SCR catalyst 13 is captured as small as possible. Then the engine-ECU controls 35 driving the aqueous urea additive valve 17 based on the amount of additive aqueous urea.

Next is a configuration of the NOx sensors 21 to 23 described. The NOx sensors 21 to 23 are the same in configuration, therefore here the configuration of the NOx sensor 21 described. The 2 and 3 are diagrams showing an internal structure of a sensor element 40 represent that the NOx sensor 21 forms. The longer side of the sensor element 40 extends along the right / left direction in the drawing, and the front end of the sensor element 40 is on the left side of the drawing. The sensor element 40 has a three-cell structure that is a pump cell 41 , a sensor cell 42 and a monitor cell 43 includes. The monitor cell 43 has the function both from a gas and from the pump cell 41 Deriving oxygen and can also be referred to as an auxiliary pump cell or second pump cell.

The sensor element 40 includes a first main body part 51 and a second main body part 52 a solid electrolyte body from an insulator such as aluminum oxide 53 between the main body parts 51 and 52 is arranged, a diffuse resistance 54 , a pump cell electrode 55 , a sensor cell electrode 56 , a monitor cell electrode 57 , a common electrode 58 and a heater 59 , Between the first main body part 51 and the solid electrolyte body 53 is a gas chamber 61 formed as a concentration measuring chamber, and between the second main body part 52 and the solid electrolyte body 53 is an air chamber 62 designed as a standard gas chamber.

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

The solid electrolyte body 53 is a plate-shaped element which is formed from an oxygen ion-conducting solid electrolyte material such as zirconium oxide. The first main body part 51 and the second main body part 52 are on both sides of the solid electrolyte body 53 arranged. The first main body part 51 is on the side of the solid electrolyte body 53 entered, and the step forms a concave section, which is the gas chamber 61 forms. A side surface of the concave portion in the first main body part 51 is opened, and the diffuse resistance 54 is arranged on one open side surface. The diffused resistance 54 consists of a porous material or a material with fine pores. The speed of the gas chamber 61 Exhaust gas introduced is diffused by the effect of resistance 54 regulated.

Likewise, the second main body part 52 to the side of the solid electrolyte body 53 entered, and the step forms a concave section, which is the air chamber 62 forms. One side face of the air can 62 is opened. That from the side of the solid electrolyte body 53 in the air chamber 62 The gas introduced is released into the atmosphere.

The cathode-side pump cell electrode 55 , the sensor cell electrode 56 and the monitor cell electrode 57 are on the gas chamber 61 facing surface of the solid electrolyte body 53 intended. In this case, the pump cell electrode 55 on the entrance side of the gas chamber 61 near the diffuse resistance 54 , i.e. upstream of the gas chamber 61 , arranged. The sensor cell electrode 56 and the monitor cell electrode 57 are on the opposite side of the diffuse resistance 54 with the pump cell electrode 55 in between, ie downstream of the gas chamber 61 , arranged. The pump cell electrode 55 has a larger surface area than that of 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 which are close to each other and are the same 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 that is inactive towards NOx like Au-Pt (electrodes that are less able to decompose NOx), while the sensor cell electrode 56 is an electrode made of a noble metal active against NOx, such as platinum Pt or rhodium Rh.

The common electrode on the anode side 58 is on the air chamber 62 facing surface of the solid electrolyte body 53 at a position corresponding to the electrodes on the cathode side 55 to 57 intended.

If there is a voltage between the pump cell electrode 55 and the common electrode 58 is created, it is in the exhaust gas in the gas chamber 61 contained oxygen through the cathode-side pump cell electrode 55 ionized. Then the oxygen ions move in the solid electrolyte body 53 towards the common electrode on the anode side 58 , and the oxygen ions in the common electrode 58 release electrical charge and become oxygen. The oxygen is in the air chamber 62 issued. Accordingly, the gas chamber 61 kept in a predetermined low-oxygen state.

Because the to the pump cell 41 applied voltage (ie the applied voltage between the pump cell electrode 55 and the common electrode 58 ) is higher, that of the pump cell 41 the amount of oxygen released from the exhaust gas is greater. Conversely, since the pump cell 41 Applied voltage is lower, the amount of oxygen released by the pump cell 41 is released from the exhaust gas, smaller. Therefore, increasing or decreasing the pump cell enables 41 applied voltage to increase or decrease the amount of residual oxygen in the exhaust gas entering the subsequent sensor cell 42 and monitor cell 43 flows. In the present embodiment, the pump cell 41 applied voltage referred to as pump cell applied voltage Vp, and that of the pump cell 41 Current output in the voltage-applied state is referred to as pump cell current Ip.

The monitor cell 43 detects the concentration of residual oxygen in the gas chamber 61 . after the oxygen through the pump cell 41 was dissipated. At this point the monitor cell is there 43 as a detection signal of the residual oxygen concentration, a current signal generated by the application of the voltage or an electromotive signal corresponding to the residual oxygen concentration in the gas chamber 61 out. The output of the monitor cell 43 is used by the SCUs 31 to 33 as monitor cell current Im or as electromotive force Vm of the monitor cell.

After the oxygen through the pump cell 41 has been removed, the sensor cell undergoes 42 the NOx in the exhaust gas together with the voltage application of a reductive decomposition and gives a current signal corresponding to the NOx concentration and the residual oxygen concentration in the gas chamber 61 out. The output of the sensor cell 42 is the sensor cell current Is from the SCUs 31 to 33 detected. The SCUs 31 to 33 calculate the NOx concentration in the exhaust gas from the sensor cell current Is.

In the sensor cell 42 Even if the concentration of the detection target gas in the exhaust gas is the same, the transient reactivity of the sensor cell current Is tends to be the output of the sensor cell 42 to vary with time or the like under the influence of deterioration. This tendency is related to 4 described. 4 schematically illustrates transitions with time from (a) the applied voltage Vp of the pump cell, (b) the current Ip of the pump cell, (c) the current Is of the sensor cell and (d) the current Im of the monitor cell. In the following, the case of carrying out a first voltage circuit is described in which the applied voltage Vp of the pump cell for increasing the residual oxygen concentration in the gas chamber 61 is switched, and a second voltage circuit in which the applied voltage Vp of the pump cell to reduce the residual oxygen concentration in the gas chamber 61 is switched after performing the first voltage switching.

With reference to 4 , at time t1, the applied voltage vp the pump cell gradually from vp0 on Vp1 as the first voltage circuit ( vp0 > Vp1 ) switched. Accordingly, the pump cell current Ip changes and decreases, thereby reducing the residual oxygen concentration in the gas chamber 61 to increase. At this time, the current Ip of the pump cell changes with the lagging of ip0 and converges on Ip1 , In the sensor cell 42 and the monitor cell 43 the sensor cell current Is and the monitor cell current Im increase due to a transient reaction corresponding to the increase in the residual oxygen concentration to a stationary value.

4 (c) illustrates two types of transient response of the sensor cell current according to the decrease in applied voltage vp the pump cell, ie the properties at the time of manufacture of the NOx sensor (initial properties) and the properties with the NOx sensor deteriorate (post-deterioration properties). In 4 (c) the initial characteristics are represented by a solid line and the deterioration time characteristics by a single-point chain line. 4 (c) shows that a difference occurs between the initial characteristics and the deterioration characteristics of the current of the sensor cell even if that of the sensor cell 42 supplied exhaust gas has the same oxygen concentration. In this case, the stationary value of the deterioration time characteristics tends to be smaller than the stationary value of the original characteristics. Second, the increase in the deterioration time characteristics tends to be slower than the increase in the original characteristics. For example, in the case of gradients of the features in a period Ta during a transient change, there is a gradient A11 the deterioration time characteristics are less than a gradient A10 of the initial characteristics. The period Ta refers to a period between a starting point P1 and an end point P2 the transient response to the switching of the pump cell with applied voltage Vp. These tendencies become apparent as the sensor cell deteriorates 42 more and more clearly.

With reference to 4 , at time t2, the applied voltage Vp of the pump cell is gradually increased from Vp1 on Vp2 as a second voltage circuit ( Vp1 < Vp2 ) switched. The current Ip of the pump cell increases accordingly, thereby increasing the residual oxygen concentration in the gas chamber 61 to reduce. In addition, the sensor cell current Is and the monitor cell Im change and decrease in accordance with the reduction in the residual oxygen concentration to their respective stationary values.

When the first voltage changeover is carried out, the starting point refers P1 and the end point P2 at times in a predetermined period after switching the pump cell with the voltage applied vp and lie before the stabilization of the sensor cell current Is. The as a starting point P1 and end point P2 set times are described below.

1. (1) einen Zeitpunkt, mit dem das durch das Schalten der angelegte Spannung Vp der Pumpzelle verursachte Nachlaufen des Pumpzellenstroms Ip einen Nachlauftiefpunkt PL erreicht (ein in 5 dargestellter Punkt P11);
2. (2) einen Zeitpunkt, mit dem eine Sensorzellenausgangsfluktuationsmenge, die durch das Schalten der Pumpzellenanlegte Spannung Vp verursacht wird, einen vorbestimmten Wert L1 erreicht (ein Punkt P12, der in 5 dargestellt ist); und
3. (3) ein Timing, mit dem eine vorbestimmte Zeit E1 nach dem Schalten der an die Pumpzelle angelegten Spannung Vp vergeht (ein in 5 dargestellter Punkt P13).

Wie in 5 dargestellt, ist der Endpunkt P2 beispielsweise einer der beiden folgenden Punkte:

• (4) ein Timing, mit dem eine vorbestimmte Zeit E2 nach dem Schalten der an die Pumpzelle angelegten Spannung Vp (ein Punkt P21, dargestellt in 5) vergeht; und
• (5) einen Zeitpunkt, mit dem die Schwankungsbreite der Sensorzellenausgabe, die durch das Schalten der angelegte Spannung Vp der Pumpzelle verursacht wird, einen vorbestimmten Wert L2 erreicht (ein in 5 veranschaulichter Punkt P22).

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

1. (1) a point in time at which the after-running of the pumping cell current Ip caused by the switching of the applied voltage Vp of the pumping cell reaches a lagging low point PL (an in 5 represented point P11 );
2. (2) a time at which a sensor cell output fluctuation amount caused by switching the pump cell applied voltage Vp becomes a predetermined value L1 reached (one point P12 who in 5 is shown); and
3. (3) a timing at which a predetermined time E1 after switching the voltage Vp applied to the pump cell (an in 5 represented point P13 ).

As in 5 is the end point P2 for example one of the following two points:

• (4) a timing at which a predetermined time E2 after switching the voltage applied to the pump cell vp (one point P21 , shown in 5 ) passes; and
• (5) a time point at which the fluctuation range of the sensor cell output caused by the switching of the applied voltage Vp of the pump cell becomes a predetermined value L2 reached (one in 5 illustrated point P22 ).

The default value L1 is a value obtained by increasing the current value before the voltage switching by a predetermined percentage (for example, one of 5 to 30%), the current change amount of the sensor cell current at the time of switching the voltage applied by the pump cell vp (Toggle from vp0 on Vp1 ) is set to 100%, in the same way as this time in the initial states of the NOx sensors 21 to 23 , The default value L2 is greater than the specified value L1 , which is obtained by increasing the current value before the voltage changeover by a predetermined percentage (for example selected from 50 to 95%).

Taking into account the early implementation of the deterioration determination, both the starting point P1 as well as the end point P2 preferably set as early as possible. In the above concrete examples (1) to (5), it is preferable to use the starting point P1 on (1) and the end point P2 to put on (4).

When performing the deterioration determination of the sensor cell 42 the residual oxygen concentration in the gas chamber changes 61 by switching the pump cell with applied voltage Vp, and determining the deterioration of the sensor cell 42 is based on the transient response of the sensor cell 42 to change the residual oxygen concentration. However, the determination of the deterioration can correspond to the residual oxygen concentration in the gas chamber 61 after switching the pump cell with applied voltage Vp. For example, with reference to 4 the residual oxygen concentration in the gas chamber 61 after switching the pump cell voltage vp (after time t1) is greater than an assumed value, the detection accuracy of the sensor cell current Is can decrease as a parameter for the aging determination.

Thus, in the present embodiment, when the pump cell voltage Vp is switched, the sensor cell current Is and the monitor cell current Im are detected and the deteriorated state of the sensor cell 42 based on the sensor cell current Is and the monitor cell Im, thereby reducing the accuracy of the wear determination of the sensor cell 42 to suppress.

6 is a functional block diagram for describing the functions of the SCUs 31 to 33 , Each of the SCUs 31 to 33 includes: a voltage switch unit M11 that the applied voltage vp the pump cell switches; a registration unit M12 that when switching the applied voltage vp detects the sensor cell current Is and the monitor cell current Im; and a deterioration determination unit M13 that the deterioration state of the sensor cell 42 based on the sensor cell current Is and the monitor cell current Im.

The voltage switch unit M11 performs the first voltage switching at which the applied voltage Vp of the pumping cell increases the oxygen concentration in the gas chamber 61 (the voltage switching of vp0 on Vp1 in 4 ) and the second voltage circuit, in which the applied voltage Vp of the pump cell to reduce the oxygen concentration in the gas chamber 61 is switched (the voltage switching of Vp1 on Vp2 in 4 ). That is, the voltage switching unit M11 performs a voltage switching cycle in which the applied voltage Vp of the pump cell is reduced and then increased. In the present embodiment, the voltage applied by the pump cell vp switched in stages. However, the voltage change waveform may differ from a stepped waveform. However, the waveform of the voltage change is preferably the same as that at the time of measuring the initial properties because the deterioration determination is made compared to the initial properties.

The registration unit M12 detects the sensor cell current Is as the sensor cell current convergence value Isx under the condition that the change of the monitor cell current Im after the switching of the pump cell voltage Vp by the voltage switching unit M11 converges, and detects a gradient of the transient change in the sensor cell current Is before the convergence of the change in the monitor cell current Im as a gradient parameter. The registration unit M12 also detects a monitor cell current convergence value Imx.

The deterioration determination unit M13 determines the deterioration state of the sensor cell 42 based on the sensor cell current convergence value Isx and the gradient of the sensor cell current Isx by the detection unit M12 is recorded. In the present embodiment, the deterioration determination unit calculates M13 as the deterioration process, the deterioration rate C of the sensor cell 42 based on the sensor cell current convergence value Isx and the slope of the sensor cell current Is. In this case, the sensor cell current convergence value Isx is the sensor cell current Is after the convergence of the change in the monitor cell current Im since the switching of the pump cell voltage vp of vp0 on Vp1 detected. In addition, the gradient of the sensor cell current Is has a value which is calculated from a current change amount ΔIs per unit time Δt during the transient change in the sensor cell current. Is on switching the voltage applied to the pump cell vp due.

In short, if the voltage switching unit M11 the applied voltage Vp of the pump cell switches, determines the deterioration determination unit M13 the deterioration of the sensor cell 42 based on the sensor cell current Is and the monitor cell current Im.

The deterioration determination unit M13 includes a monitor cell output determination unit that determines whether the monitor cell current Im has a normal value using correlation data that shows a relationship between the pump cell current ip and define the monitor cell current Im at least before or after the voltage switchover. If the monitor cell output determination unit does not determine that the monitor cell current Im has a normal value, the deterioration determination unit invalidates M13 the determination of the deterioration of the sensor cell 42 , The correlation data define a relationship between a change amount ΔIp of the pump cell current Ip between before and after the first voltage circuit has been carried out and the convergence value Imx of the monitor cell current. In addition, the correlation data can be data that shows a relationship between the pump cell current ip0 before performing the first voltage switching and the monitor cell current convergence value Imx, or data defining a relationship between the pump cell current Ip1 Define Imxm after performing the first voltage switching and the monitor cell current convergence value. In either case, the correlation data preferably defines a relationship corresponding to the residual oxygen concentration in the gas chamber 61 ,

The sensor cell 42 detects the sensor cell current Is at the time of the general NOx concentration detection in an nA order level, but detects the sensor cell current Is due to the residual oxygen concentration at the time of switching the pump cell due to the voltage Vp applied at the time of switching the pump cell for the aging determination in a µA order level , In both cases, the A / D conversion current processing area in the SCUs 31 to 33 preferably switched between the time of the NOx concentration detection and the time of the deterioration determination. At the time of the deterioration determination, the current processing range is preferably expanded compared to that at the time of the NOx concentration determination.

The engine control unit 35 has an anomaly determination unit M21 an anomaly due to emission changes based on the results of the deterioration determination by the SCUs 31 to 33 certainly. The anomaly determination unit M21 determines engine emission anomalies based on the deterioration rate C of the sensor cell 42 by the deterioration determination units M13 of the SCUs 31 to 33 is calculated. The anomaly determination unit M21 can be configured to detect an emission anomaly based not only on the rate of deterioration C of the sensor cell 42 to determine, but also in a comprehensive view of the outputs of the NOx sensors 21 to 23 , various types of sensor information from other sensors, engine operating status and others.

The determination of deterioration in relation to the NOx sensors 21 to 23 and the determination of the emission variance can be done by both the SCUs 31 to 33 as well as from the engine control 35 be performed. The engine ECU preferably determines the emission deviation 35 carried out, since the determination of the emission deviation preferably with elements other than the degree of deterioration of the NOx sensors 21 to 23 is carried out.

Next is a method for determining the deterioration of the sensor cell 42 with respect to that in 7 described flowchart described. The in 7 process shown is an arithmetic processing to implement the in 6 described functions of the SCUs 31 to 33 , for example, by the SCUs 31 to 33 is performed in any given cycle.

In step S10 each of the SCUs determines whether a condition for performing the deterioration determination is satisfied. The execution condition includes, for example, receiving an approval signal to perform the deterioration determination from the engine control unit 35 to enable. The engine control unit 35 transmits the approval signal when the gas environment in the exhaust pipe 11 is a predetermined stable environment. In particular, the engine control unit transmits 35 the approval signal when the engine 10 is in a predetermined operating condition with a relatively stable amount of emissions, or when a fuel is turned off, or immediately after the ignition switch is turned off (immediately after the ignition switch is turned off), or when the engine control unit 35 is started by a soak timer. In particular, the execution condition is expediently set to the time immediately after the IG shutdown. Immediately after the IG shutdown, the exhaust gas flow is stopped by switching off the engine and the deterioration determination can be carried out in the stable gas environment. If the condition for performing the deterioration determination is met, the SCU goes to the next step S11 about. If the condition for performing the deterioration determination is not met, the SCU ends this process.

In step S11 the SCU determines whether the first voltage switching, ie switching the voltage Vp applied to the pumping cell, to increase the residual oxygen concentration in the gas chamber 61 , should be carried out. At this point, each of the SCUs determines 31 to 33 whether the oxygen concentration and the NOx concentration in the exhaust gas are in a stable state in which the fluctuation quantities per unit of time are equal to or less than predetermined values. Provided that these concentrations are in a stable state, the SCU allows the first voltage switching to be carried out. In particular, the SCU determines whether the fluctuation amount of the pump cell current Ip per time unit is equal to or less than a predetermined value and the fluctuation amount of the sensor cell current Is per time unit is equal to or less than a predetermined value before the first voltage circuit is carried out. When these concentrations are stable, the SCU takes a step S11 make a confirmatory determination and go to the next step S12 about. However, the process of determining concentration stability can be omitted.

Each of the SCUs 31 to 33 can determine whether either the oxygen concentration or the NOx concentration in the exhaust gas is in the stable state in which the fluctuation amount per unit time is equal to or less than a predetermined value. In this case, when the oxygen concentration in the exhaust gas is in the stable state, or when the NOx concentration in the exhaust gas is in the stable state, the SCU allows the first voltage switching to be carried out. If the exhaust pipe 11 is equipped with an AC current sensor, the SCU can determine whether the oxygen concentration in the exhaust gas is in a stable state based on the detection value of the AC current sensor.

Alternatively, the SCU can allow the first voltage switching to be carried out under the condition that the oxygen concentration in the exhaust gas is within a predetermined concentration range or the NOx concentration in the exhaust gas is within a predetermined concentration range. In this case, instead of or in addition to determining whether the oxygen concentration or the NOx concentration in the exhaust gas is stable, the SCU preferably carries out a determination as to whether the oxygen concentration or the NOx concentration is within a predetermined concentration range.

In step S11 In addition to the aforementioned conditions, the SCU can allow the first voltage switching to be carried out on the condition that there is no failure history (dialog information) with respect to the engine exhaust system or that the power voltage (battery voltage) is equal to or greater than a predetermined value. If the power voltage is lower than a predetermined value, the current distribution to the sensor heater is not sufficient, so that the NOx sensors 21 to 23 cannot be kept in a properly active state, resulting in a decrease in the accuracy of the deterioration determination.

If the first voltage switching is carried out, the SCU detects in step S12 a pump cell current ip0 voltage Vp applied as the pump cell output before switching the pump cell Vp1 , ie in the state in which the pump cell applied voltage Vp vp0 is.

Then the SCU switches in step S13 the applied voltage Vp of the pump cell from vp0 on Vp1 , With reference to the in 4 shown timing diagram, this step becomes at time t1 carried out. The SCU then detects in step S14 a sensor cell current Is 1 at the starting point P1 and a sensor cell current Is 2 at the end point P2 in the first voltage circuit. In step S15 the SCU recognizes or detects the current Ip1 of the pump cell as the output of the pump cell after switching on the applied voltage Vp of the pump cell Vp1 , The SCU detects the pump cell current Ip1 with a timing when a predetermined time has elapsed since the voltage switchover (time t1), ie with a timing when the pump cell current Ip becomes stable. The order of detection of the sensor cell currents Is 1 and Is 2 and the pump cell current Ip1 is freely adjustable.

The SCU then records in step S16 the sensor cell current Is and the monitor cell current Im at the time of the convergence of the change in the monitor cell current Im after switching the pump cell with applied voltage Vp, as the sensor cell current convergence value Isx and the monitor cell current convergence value Imx, respectively. In this case, when the amount of change in the monitor cell current Im per unit time becomes smaller than a predetermined value, the SCU considers that the change in the monitor cell current Im has converged, and detects the current convergence value of the sensor cell Isx and the current convergence value of the monitor cell Imx after the convergence , With reference to the in 4 shown time diagram, the current convergence value of the sensor cell Isx and the current convergence value of the monitor cell Imx are recorded at time t11.

In step S17 The SCU determines whether the monitor cell current Im has a normal value by using the correlation data that defines the relationship between the pump cell current Ip and the monitor cell current Im. The correlation data are predefined as the ratio between the change amount ΔIp (= ip0 - Ip1 ) of the pump cell current Ip and the convergence value Imx of the monitor cell current, as for example in 8th shown. In step S17 the SCU determines whether the convergence value of the monitor cell Imx with the in 8th shown relationship matches.

More specifically, referring to 8th , the standard value of the monitor cell current convergence value Imx becomes Imsd according to the change amount ΔIp of the pump cell current ip determined, and a predetermined allowable range RA is determined according to the standard value Imsd. The SCU determines whether the convergence value of the monitor cell current convergence Imx is within the allowable range RA lies according to the current change value of the pump cells ΔIp is determined. When the monitor cell current convergence value Imx is in the allowable range RA lies, determines the SCU that the monitor cell current Im has a normal value and when the monitor cell current convergence value Imx is outside the allowable range RA lies, determines the SCU that the monitor cell current Im has no normal value. If the monitor cell current Im has a normal value, the goes SCU to the next step S18 over, and if the monitor cell current Im has no normal value, the goes SCU to step S17a about. In step S17a determines the SCU that the monitor cell 43 is abnormal, and then ends this process. That is, if the monitor cell current Im has no normal value, the deterioration determination of the sensor cell 42 invalid this time.

In step S18 calculates the SCU with the following equation (1) the gradient A11 of the sensor cell current Is at the time of a transient response based on a current change amount ΔIs1 (= Is2-Is1) as the difference between the sensor cell currents Is 1 and Is 2 at the starting point P1 and end point P2 and on a time difference Δt1 between the starting point P1 and the end point P2 : $$\text{A11}=\Delta \text{Is 1 /}\Delta \text{t1}$$

The SCU also calculates the gradient A10 in the in 4 initial features shown using equation (1) above.

In step S19 calculates the SCU a gradient B11 by changing the gradient A11 normalized. In this case, the SCU the normalized gradient from the following equation (2) B11 based on the gradient A11 of the sensor cell current Is at the time of the transient change and the change amount ΔIp1 (= ip0 - Ip1 ) of the pump cell current Ip by switching the pump cell applied voltage Vp: $$\text{B11}=\text{A11 /}\Delta \text{Ip1}$$

Then the SCU sets in step S20 an initial gradient B10 of the sensor cell current Is as a determination criterion value, which is a criterion for determining the deterioration of the sensor cell 42 based on the monitor cell current convergence value Imx. The initial gradient B10 gives the initial properties of the sensor cell 42 which, for example, about the in 9 shown relationship is set. With reference to 9 , since the current convergence value of the monitor cell Imx is larger, the initial gradient becomes B10 set to a larger value.

The SCU then calculates in step S21 the rate of deterioration C (%) of the sensor cell 42 based on the gradient B10 and B11 and the current convergence value Isx of the sensor cell. At this point the SCU the Ratio of the gradient B11 to the initial gradient B10 (B11 / B10) as the reaction speed ratio and calculates the deterioration rate C of the sensor cell 42 based on the reaction speed ratio B11 / B10 and the current convergence value Isx of the sensor cell using the in 10 for example depicted relationship. The reaction rate ratio B11 / B10 is called the ratio of reaction speed to that of the sensor cell 42 supplied oxygen determined.

10 illustrates the relationship between the reaction speed ratio B11 / B10 and the rate of deterioration C at which, since the reaction speed ratio B11 / B10 is small, ie because of the difference between the deterioration time characteristics and the initial characteristics of the sensor cell 42 is greater, the rate of deterioration C gets higher. 10 also illustrates the relationship between the current convergence value of the sensor cell isx and the rate of deterioration C , when if the current convergence value of the sensor cell isx is smaller, the rate of deterioration C gets lower. It is therefore assumed that with a smaller convergence value, the sensor cell current Isx is the range of change of the residual oxygen concentration in the gas chamber 61 by switching the pump cell with the voltage applied vp becomes smaller and the transient reaction of the sensor cell current Is slows down. Therefore, the relationship between the current convergence value of the sensor cell Isx and the rate of deterioration C at which, since the convergence value of the sensor cell Isx is smaller, the rate of deterioration C is defined lower to suppress a wrong determination that the degree of deterioration is too high even though the current convergence value of the sensor cell Isx is small. The high wear rate C means the degree of wear of the sensor cell 42 is high.

The SCU then transmits in step S22 the rate of deterioration C of the sensor cell 42 to the engine-ECU 35 ,

In step S23 determines the SCU whether the second voltage switching should be carried out, ie switching the voltage Vp applied to the pump cell by the residual oxygen concentration in the gas chamber 61 to reduce. In the case of performing the second voltage switching, the SCU to step S24 over to the applied voltage Vp of the pump cell from Vp1 on Vp2 to switch. With reference to the in 4 shown timing diagram, this process is carried out at time t2. In the present embodiment, Vp2 = Vp0. When the applied voltage Vp the pump cell on Vp2 ( vp0 ) is switched, the series of steps in the deterioration determination is ended.

After calculating the deterioration rate C of the sensor cell 42 corrects each of the SCUs 31 to 33 the sensor cell current Is by the deterioration rate C for each of the NOx sensors 21 to 23 at the time the NOx concentration is detected by the NOx sensors 21 to 23 and calculates the NOx concentration based on the corrected sensor cell current Is. In this case, the SCU corrects the current of the sensor cell to reset the properties of the current sensor cell to the original properties.

• Im Falle der Durchführung der Verschlechterungsbestimmung der Sensorzelle 42 basierend auf der Ausgangsreaktion der Sensorzelle 42 in den NOx-Sensoren 21 bis 23 kann die durchzuführende Verschlechterungsbestimmung der Sensorzelle 42 basierend auf einer Änderung des Sensorzellenstroms Is gemäß der Restsauerstoffkonzentration in der Gaskammer 61 nach dem Schalten der Pumpzelle mit Spannung Vp negativ beeinflusst werden. In diesem Zusammenhang werden gemäß der vorstehenden Konfiguration beim Schalten der Pumpzellenanlegte Spannung Vp der Sensorzellenstrom Is und der Monitorzellenstrom Im erfasst und der Verschlechterungszustand der Sensorzelle 42 basierend auf dem Sensorzellenstrom Is und dem Monitorzellenstrom Im bestimmt. In diesem Fall kann die Verschlechterungsbestimmung der Sensorzelle 42 durchgeführt werden, nachdem die Restsauerstoffkonzentration in der Gaskammer 61 aus dem Strom der Monitorzelle Im korrekt ermittelt wurde. Dadurch ist es möglich, den Verschlechterungszustand der Sensorzelle 42 richtig zu bestimmen.

According to the present embodiment described in detail above, the following excellent effects can be achieved:

• In the case of performing the deterioration determination of the sensor cell 42 based on the output response of the sensor cell 42 in the NOx sensors 21 to 23 can determine the deterioration of the sensor cell 42 based on a change in sensor cell current Is according to the residual oxygen concentration in the gas chamber 61 after switching the pump cell with voltage Vp. In this connection, according to the above configuration, when the pump cell voltage Vp is switched, the sensor cell current Is and the monitor cell current Im and the deteriorated state of the sensor cell are detected 42 based on the sensor cell current Is and the monitor cell current Im. In this case, the determination of the deterioration of the sensor cell 42 be carried out after the residual oxygen concentration in the gas chamber 61 from the current of the monitor cell Im was determined correctly. This makes it possible to determine the deterioration state of the sensor cell 42 to determine correctly.

After switching the pump cell voltage Vp, the sensor cell current Is with the convergence of the change in the monitor cell current Im is recorded as the sensor cell current convergence value Isx, the change gradient of the sensor cell current Is before the convergence of the change in the monitor cell current Im as a gradient parameter, and the deterioration or wear condition of the sensor cell 42 based on the sensor cell current convergence value Isx and the gradient of the sensor cell current Is. This makes it possible to determine the deterioration of the sensor cell 42 considering both the fact that the stationary value of the deterioration time characteristics (the convergence of the sensor cell current Isx) becomes lower than the stationary value of the initial characteristics, and the fact that the The increase in the deterioration time characteristics (the gradient of the sensor cell current Is) becomes slower than that of the initial characteristics together with the progress of the deterioration of the sensor cell 42 ,

The determination criterion value as a criterion for determining the deterioration of the sensor cell 42 (the initial gradient B10 in the present embodiment) is set based on the current convergence value Imx of the monitor cell. This enables the rate of deterioration C by comparison between the gradients B11 the existing properties and the initial gradient B10 for use in determining the deterioration of the sensor cell 42 to calculate under the same conditions and thereby to increase the calculation accuracy of the deterioration rate C, that is, the deterioration determination accuracy.

When the residual oxygen concentration in the gas chamber 61 by applying a voltage to the pump cell 41 is set, the value of the current, which can be taken as the monitor cell current Im, can be assumed based on the pump cell current Ip before and after the voltage switchover. With this point in mind, the correlation data defining the relationship between the pump cell current Ip before and after the voltage switch and the monitor cell current convergence value Imx is used to determine whether the monitor cell current convergence value Imx is a normal value in this relationship. If it is determined that the current convergence value of the monitor cell Imx is not a normal value, the deterioration determination of the sensor cell becomes 42 invalidated. This suppresses a decrease in the accuracy of the deterioration determination of the sensor cell 42 caused by an anomaly in the monitor cell 43 is caused.

In the above embodiment, the deterioration state of the sensor cell 42 based on the current convergence value of the sensor cell Isx and the gradient of the sensor cell current Is. However, this configuration can be changed so that between the current convergence value of the sensor cell isx and the gradient of the sensor cell current ix only the current convergence value of the sensor cell isx or only the gradient of the sensor cell current Is to determine the deterioration state of the sensor cell 42 is used. When using only the sensor cell current convergence value isx can be the initial convergence value Isx0 as sensor cell current convergence value isx can be set in the initial properties of the sensor cell based on the monitor cell current convergence value Imx, and the deterioration rate C can be determined from the relationship between the sensor cell current convergence value isx can be calculated in the current properties and the initial convergence value Isx0. Even after this configuration, it is possible to determine the deterioration of the sensor cell 42 taking into account the residual oxygen concentration in the gas chamber 61 to perform properly.

In the following, further embodiments are described which mainly focus on differences from the first embodiment.

(Second embodiment)

In the second embodiment, as in 6 shown includes a deterioration determination unit M13 a monitor cell output determination unit that uses correlation data that establishes a relationship between a pump cell current Ip ( ΔIp . ip0 or Ip1 ) define at least before or after the voltage switchover and a monitor cell current Im to determine whether the monitor cell current Im has a normal value in this regard. When determining that the monitor cell current Im has a normal value, the deterioration determination unit sets M13 a determination criterion value (an initial gradient B10 ) the sensor cell deterioration based on a monitor cell current convergence value IMx and determines the deterioration state of a sensor cell 42 using the determination criterion value. When determining that the monitor cell current Im has no normal value, the deterioration determination unit sets M13 the determination criterion value (the initial gradient B10 ) based on the pump cell current ip at least before or after the voltage switchover and determines the deterioration state of the sensor cell 42 based on the determination criterion value. That is, if the monitor cell current Im has no normal value, the deterioration determination unit performs M13 the determination of deterioration with the pump cell current ip instead of the monitor cell current Im through.

In the present embodiment, the SCUs perform 31 to 33 through a deterioration determination process, which in 11 instead of in 7 described deterioration determination process is provided. The in 11 process is partially compared to that in 7 changed process, following the same steps as in 7 with the same step numbers as in 7 shown.

With reference to 11 , recorded in step S16 each of the SCUs has a sensor cell current convergence value Isx and the monitor cell current convergence value Imx. In the next step S18 the SCU calculates a gradient A11 of the sensor cell current Is at the time of the transient change and calculated in step S19 a gradient B11 by normalizing the gradient A11 , After that, the SCU used in step S31 the correlation data (see 8th ) to define a relationship between the amount of change ΔIp of the pump cell current Ip and the monitor cell current convergence value Imx to determine whether the monitor cell current Im has a normal value. This step is the same as the step S17 who in 7 is described, and thus a detailed description thereof is omitted.

If the monitor cell current Im has a normal value, the SCU goes to step S32 about. In step S32 the SCU provides the initial gradient B10 of the sensor cell current. Based on the convergence value Imx of the monitor cell current. This step is the same as the step S20 who in 7 and thus the detailed description is omitted.

If the current of the monitor cell Im has an abnormal value, the runs SCU with step S33 continued. In step S33 determines the SCU that the monitor cell 43 is abnormal. Then the SCU in step S34 the initial gradient B10 of the sensor cell current. Based on the pump cell current Ip at least before or after the voltage switchover. The SCU represents the initial gradient B10 with the help of a relationship that is in 12 is shown for example. With reference to 12 because the change set ΔIp of the pump cell current ip is greater, the initial slope B10 set to a larger value. Alternatively, the initial gradient B10 based on the current of the pump cell ip0 or Ip1 can be set. In both cases the initial gradient becomes B10 according to the residual oxygen concentration in the gas chamber 61 set.

The SCU then calculates in step S21 a rate of deterioration C based on the gradients B10 and B11 and the current convergence value Isx of the sensor cell 42 , and in the next step S22 sends the SCU the rate of deterioration C ,

In the above embodiments, the relationship between the pump cell current Ip and the monitor cell current Im before and after the voltage switch is referred to determine whether the monitor cell current Im has a normal value. If the monitor cell current Im is normal, the initial gradient becomes B10 of the sensor cell current Is set based on the convergence value Imx of the monitor cell current. If the monitor cell current Im is not normal, the initial gradient becomes B10 of the sensor cell current Is is set based on the pump cell current Ip. This makes it possible to decrease the accuracy of the deterioration determination of the sensor cell 42 due to an abnormality in the monitor cell 43 to suppress.

(Third embodiment)

In a third embodiment, a deterioration determination unit includes M13 instead of the monitor cell output determination unit, a correlation determination unit that uses correlation data defining a relationship between a monitor cell current Im and a sensor cell current Is at the time of switching a pump cell applied voltage Vp to determine whether the relationship between the monitor cell current Im and the sensor cell current Is at the time of the actual voltage switching matches the correlation data. If the correlation determination unit determines that the actual relationship does not match the correlation data, the deterioration determination unit sets M13 the determination of the deterioration of a sensor cell 42 inoperative.

In the present embodiment, the SCUs perform 31 to 33 one in 13 depicted deterioration determination process instead of the one shown in 7 shown deterioration determination process by. The in 13 process is partially compared to that in 7 changed process, following the same steps as in 7 with the same step numbers as in 7 shown.

With reference to 13 captured each of the SCU in step S16 a current convergence value of the sensor cell Isx and then moves to step S41 continued. In step S41 the SCU uses the correlation data defining a relationship between the monitor cell current Im and the sensor cell current Is to determine whether the actual relationship between the monitor cell current Im and the sensor cell current Is corresponds to the correlation data. The correlation data are predefined, for example in 14 shown. In step S41 the SCU determines whether a relationship between a monitor cell current convergence value Imx and the sensor cell current convergence value Isx with the in 14 shown relationship matches.

In particular, referring to 14 a standard value of the sensor cell current Is as Issd according to the monitor cell current Im and a predetermined permissible range B according to the default value ISSD certainly. Then determines the SCU whether the current convergence value of the sensor cell isx with respect to the current convergence value of the monitor cell Imx within the permissible range RB lies. If the current convergence value of the sensor cell isx within the allowable range RB lies, determines the SCU that the correlation is normal and if the current convergence value of the sensor cell Isx is outside the allowable range RB , the SCU determines that the correlation is not normal. If the correlation is normal, it goes SCU to the next step S18 over, and if the correlation is not normal, the SCU to step S42 about. In step S42 determines the SCU that the monitor cell 43 is abnormal and ends this process. That is, if the correlation is not normal, the SCU overrides the current deterioration determination of the sensor cell 42 on. step S18 and the subsequent steps are as described above.

If the sensor cell 42 and the monitor cell 43 in the NOx sensors 21 to 23 are normal, there is a predetermined correlation between the monitor cell current Im and the sensor cell current Is at the time of the voltage switchover. In the present embodiment, the correlation data between the monitor cell current Im and the sensor cell current Is at the time of the voltage switchover is used. If the relationship between the monitor cell current Im and the sensor cell current Is does not match the correlation data, the deterioration determination of the sensor cell is made 42 invalid. This suppresses a decrease in the accuracy of the deterioration determination of the sensor cell 42 caused by an anomaly in the monitor cell 43 is caused.

Fourth Embodiment

In a fourth embodiment, a deterioration determination unit includes M13 instead of the monitor cell output determination unit or the correlation determination unit, an output difference calculation unit which has a first output difference ΔIX1 calculated as the difference between a sensor cell current Is and a monitor cell current Im before switching a pump cell voltage Vp and a second output difference ΔIX2 calculated as the difference between the sensor cell current Is and the monitor cell current Im after switching. The deterioration determination unit M13 determines the deterioration state of the sensor cell 42 based on a comparison between the first output difference ΔIX1 and the second output difference ΔIX2 which is calculated by the output difference calculation unit.

In the present embodiment, the SCUs perform 31 to 33 one in 15 depicted deterioration determination process instead of the one shown in 7 shown deterioration determination process by. The in 15 process is partially compared to that in 7 changed process, following the same steps as in 7 with the same step numbers as in 7 shown.

With reference to 15 does that SCU after acquiring a current convergence value of the sensor cell Isx in step S16 to step S51 about. In step S51 calculates the SCU a difference between the sensor cell current Is and the monitor cell current Im as the first output difference ΔIX1 in a state in which the applied voltage of the pump cell Vp vp0 and calculates a difference between the sensor cell current Is and the monitor cell current Im as the second output difference ΔIX2 in a state in which the applied voltage vp the pump cell Vp1 is switched. The SCU calculates the first output difference ΔIX1 from the in a state where the tension vp0 is applied, recorded current values (Is and Im) and calculates the second output difference ΔIX2 from the in a state where the tension Vp1 is created, recorded current convergence values (Isx and Imx).

Then the SCU in step S52 whether the first output difference ΔIX1 and the second output difference ΔIX2 to match. In particular, the SCU whether a difference between the first output difference ΔIX1 and the second output difference ΔIX2 is less than a predetermined value. If ΔIX1 and ΔIX2 match, that goes SCU to the next step S18 about and if ΔIX1 and ΔIX2 do not match, that goes SCU to step S53 about. In step S53 determines the SCU that a monitor cell 43 is abnormal, and then ends this process. That is, if ΔIX1 and ΔIX2 do not match, highlights the SCU the current deterioration determination of the sensor cell 42 on or invalidates them. step S18 and the subsequent steps are as described above.

When the applied voltage of the pump cell vp in the NOx sensors 21 to 23 is switched, the sensor cell current Is and the monitor cell current Im each change in the sensor cell 42 and the monitor cell 43 along with a change in the residual oxygen concentration in a gas chamber 61 , In this case, if the sensor cell 42 and the monitor cell 43 are normal, the first output difference is correct ΔIX1 before switching the voltage and the second output difference ΔIX2 largely match after switching the voltage. In the present embodiment, using this fact, it is determined whether the first output difference ΔIX1 and the second output difference ΔIX2 match, and if it is determined that there is no match, the deterioration determination of the sensor cell 42 overridden or invalidated. This suppresses a decrease in the accuracy of the Determination of deterioration of the sensor cell 42 caused by an anomaly in the monitor cell 43 is caused.

(Other embodiments)

The aforementioned embodiments can be changed, for example, as described below.

When determining the deterioration of the sensor cell 42 can when switching the pump cell voltage vp to increase the oxygen concentration in the gas chamber 61 (during the first voltage switchover) the pump cell voltage Vp are switched to zero, that is to say are put into a state without voltage application. Otherwise, the applied voltage vp the pump cell can be switched to a negative voltage. In both cases the oxygen concentration in the gas chamber 61 by switching the applied voltage, and the deterioration can be determined by the transient behavior of the sensor cell 42 be done at this time.

In the above embodiments, the gradient of the transient change becomes the current change amount ΔIs per unit of time .delta.t calculated in the transient period of the sensor cell current Is as the "gradient parameter" of the sensor cell current Is. Alternatively, the current change amount ΔIs can be used as gradient parameters in a predetermined time. Otherwise, the duration of the time required to generate a predetermined amount of current change can be used as the gradient parameter. In short, the gradient of the sensor cell current Is or a value correlating with it is preferably calculated as a gradient parameter.

In the present embodiments, the gradient becomes B11 by normalizing the gradient A11 of the sensor cell current Is and the wear rate C through the gradient B11 calculated. However, this configuration can be changed. For example, the rate of deterioration C with the slope A11 be calculated.

In the above embodiments, as the determination of the deterioration rate of the sensor cell 42 the deterioration rate C (%) as a ratio between the present properties and the initial properties of the sensor cell 42 calculated. However, the present disclosure is not limited to this configuration. For example, the difference in the gradient of the sensor cell current Is can be used as a deterioration determination parameter for the sensor cell 42 , a correlated value or the amount of current change ΔIs after the convergence of the sensor cell current Is can be calculated from the initial value, and the degree of deterioration of the sensor cell 42 can be captured based on the difference. Otherwise the comparison cannot be carried out with the initial value, but with a predefined standard value. The degree of deterioration can be determined by an index represented as "100 - the deterioration rate C". In this case, after the index, the value of the characteristics is initially shown as 100% and decreases with the progress of the deterioration. In both cases, the deterioration state, ie the degree of wear, is based on the characteristic change in the sensor cell 42 certainly.

In the above embodiments, the sensor element has 40 the individual solid electrolyte body 53 and the single gas chamber 61 on. However, this configuration can be changed. For example, the sensor element 40 a variety of solid electrolyte bodies 53 and a variety of gas chambers 61 have, and the pump cell 41 and the sensor cell 42 can in the various solid electrolyte bodies 53 and opposite the different gas chambers 61 be provided. 16 shows an example of this configuration.

An in 16 sensor element shown 40 has two opposite solid electrolyte bodies 53a and 53b and gas chambers 61a and 61b between the solid electrolyte bodies 53a and 53b on. The gas chamber 61a communicates with an exhaust gas inlet opening 53c , and the gas chamber 61b communicates with the gas chamber 61a over a drawn section 71 , The pump cell 41 has a pair of electrodes 72 and 73 on, and an electrode 72 is the inside of the gas chamber 61a exposed. The sensor cell 42 has an electrode 74 and a common electrode 76 opposite on. The monitor cell 43 has an electrode 75 and the common electrode 76 opposite on. The sensor cell 42 and the monitor cell 43 are arranged side by side. The electrodes are in these cells 74 and 75 on one side the inside of the gas chamber 61b exposed. Depending on the configuration in which the pump cell 41 and the sensor cell 42 also in the different gas chambers 61a and 61b are provided, it is possible to implement the functions in the aforementioned embodiments such as the deterioration determination cheaply.

The specific gas component to be detected may differ from NOx. For example, the gas sensor can be used specifically to detect HC or CO in the exhaust gas. In this case, the gas sensor preferably conducts oxygen in the exhaust gas through the pump cell and decomposes HC or CO from the gas after the emission of the Oxygen to detect the HC concentration or the CO concentration. Otherwise, the gas sensor can detect the concentration of ammonia in the detection target gas.

The present disclosure can also be embodied as a gas sensor control device aimed at a gas sensor used in other types of engines, such as a gas sensor provided in the intake path of an internal combustion engine or a gasoline engine other than a diesel engine. The gas sensor may be aimed at a detection target gas other than the exhaust gas or used for purposes other than automobiles.

The present disclosure has been described in accordance with the embodiments so far, but it should be understood that the present disclosure is not limited to the aforementioned embodiments or structures. The present disclosure includes various changes and additions to an equivalent scope. In addition, various combinations and modes and other combinations and modes that include only one element of the aforementioned combinations and modes are less or more than the one element included in the scope and conceptual scope of the present disclosure.

QUOTES INCLUDE IN THE DESCRIPTION

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

Patent literature cited

• JP 2017104901 [0001]
• JP 2009175013 A [0005]

Claims (8)

A gas sensor control device (31 to 33, 35) applied to a gas sensor (21 to 23), the gas sensor control device (31 to 33, 35) comprising: a pump cell (41) that sets an oxygen concentration in a detection target gas that is introduced into a gas chamber (61) by applying a voltage; a sensor cell (42) that detects a concentration of a certain gas component in the gas chamber after the oxygen cell is adjusted by the pump cell; and a monitor cell (43) that detects a residual oxygen concentration in the gas chamber, the gas sensor control device performs control with respect to the gas sensor, and the gas sensor control device comprises: a voltage switching unit that switches a voltage (Vp) applied to the pump cell; a detection unit which, when the applied voltage is switched by the voltage switching unit, detects an output (Is) of the sensor cell and an output (Im) of the monitor cell; and a deterioration determination unit that determines a deterioration state of the sensor cell based on the output of the sensor cell and the output of the monitor cell detected by the detection unit. Gas sensor control device after Claim 1 , under the condition that a change in the output of the monitor cell after the switching of the applied voltage has converged by the voltage switching unit, the detection unit detects the output of the sensor cell as a convergence value of the sensor cell output; and the deterioration determination unit determines the deterioration state of the sensor cell based on the convergence value of the sensor cell output detected by the detection unit. Gas sensor control device after Claim 2 , wherein the detection unit detects the convergence value of the output signal of the sensor cell after switching the applied voltage by the voltage switching unit and detects a gradient of the output change of the sensor cell before converging the output change of the monitor cell as a gradient parameter, and the deterioration determination unit detects the deterioration state of the sensor cell based on the convergence value the sensor cell output and the gradient parameter detected by the detection unit. Gas sensor control device according to one of the Claims 1 to 3 , wherein the detection unit receives a convergence value of the monitor cell output after convergence of the output change of the monitor cell since the applied voltage is switched by the voltage switching unit, and the deterioration determination unit sets a determination criterion value as a criterion for determining the deterioration of the sensor cell based on the convergence value of the monitor cell output and using the deterioration state of the sensor cell of the determination criterion value. Gas sensor control device according to one of the Claims 1 to 4 , wherein the deterioration determination unit includes a monitor cell output determination unit that uses correlation data that defines a relationship between the output of the pump cell and the output of the monitor cell at least before or after the voltage switching by the voltage switching unit to determine whether the output of the monitor cell has a normal value , and when the monitor cell output determination unit determines that the output of the monitor cell has no normal value, the deterioration determination unit invalidates the deterioration determination of the sensor cell. Gas sensor control device according to one of the Claims 1 to 3 , wherein the detection unit receives a convergence value of the monitor cell output after convergence of the output change of the monitor cell since the applied voltage is switched by the voltage switching unit, and the deterioration determination unit includes a monitor cell output determination unit that uses correlation data that uses a relationship between the output of the pump cell and the output of the monitor cell Define at least before or after the voltage switching by the voltage switching unit to determine whether the output of the monitor cell has a normal value, if the monitor cell output determination unit determines that the output of the monitor cell has a normal value, the deterioration determination unit sets a determination criterion value as a criterion for the Determination of deterioration of the sensor cell based on the monitor cell output convergence value and determines the deterioration state of the sensor cell using the determination criterion value, and if the monitor cell output determination unit determines that the output of the monitor cell has no normal value, the deterioration determination unit sets a determination criterion value as a criterion for the deterioration determination of the sensor cell on the output of the pump cell at least before or after the voltage switchover and determines the deterioration state of the sensor cell on the basis of the determination criterion value. Gas sensor control device according to one of the Claims 1 to 4 , wherein the deterioration determination unit includes a correlation determination unit that uses correlation data that defines a relationship between the output of the monitor cell and the output of the sensor cell at a time of voltage switching by the voltage switch unit to determine whether an actual relationship between the output of the monitor cell and the Output of the sensor cell at a time of the actual voltage switching corresponds to the correlation data, and if the correlation determination unit determines that the actual relationship does not match the correlation data, the deterioration determination unit invalidates the deterioration determination of the sensor cell. Gas sensor control device according to one of the Claims 1 to 4 , wherein the deterioration determination unit includes an output difference calculation unit that calculates a first output difference as the difference between the output of the sensor cell and the output of the monitor cell before the voltage switchover by the voltage switching unit and a second output difference as the difference between the output of the sensor cell and the output of the monitor cell after the voltage switchover is calculated, and the deterioration determination unit determines the deterioration state of the sensor cell based on a comparison between the first output difference and the second output difference calculated by the output difference calculation unit.

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