JP5007689B2 - Gas concentration detector - Google Patents

Description

  The present invention relates to a gas concentration detection device, and more particularly to a gas concentration detection device that detects the concentration of a specific gas in exhaust gas discharged from an engine.

  Conventionally, for example, as disclosed in Japanese Patent Application Laid-Open No. 2000-137018, a gas concentration sensor having a pump cell for detecting the oxygen concentration in exhaust gas and a sensor cell for detecting the NOx concentration in exhaust gas is provided. A gas concentration detection device used has been proposed. In this apparatus, the pump cell discharges surplus oxygen in the gas to be detected, and the sensor cell detects the NOx concentration in the gas after surplus oxygen is discharged.

  Further, in the conventional gas concentration detection device, when the oxygen concentration of the gas to be detected changes due to the pump cell discharging excess oxygen in the gas to be detected, the gas flows to the sensor cell based on the current value flowing through the pump cell. The current value is corrected. Thereby, even if the oxygen concentration in the gas to be detected changes, it is possible to avoid a situation in which the NOx concentration changes carelessly following this.

JP 2000-137018 A JP 2002-116180 A JP 2001-74692 A JP 2000-171436 A JP 2001-141696 A

  The value of the current flowing through the gas concentration detection cell varies depending on the oxidation state of the electrode of the gas concentration detection cell, in addition to the influence of the discharge of excess oxygen by the oxygen pump cell. That is, when the internal combustion engine is stopped and left as it is, the electrode of the gas concentration detection cell absorbs oxygen in the gas to be measured and oxidizes. Oxygen combined with the electrode is reduced and desorbed when a predetermined condition is satisfied after energization of the gas concentration detection cell is started. For this reason, current may flow through the gas concentration detection cell due to the desorbed oxygen, and the concentration of the specific gas in the gas to be measured may not be accurately detected.

  The present invention has been made to solve the above-described problems, and provides a gas concentration detection device capable of detecting the gas concentration with high accuracy by eliminating the influence of oxidation of the electrode of the gas concentration detection cell. The purpose is to provide.

In order to achieve the above object, a first invention is a gas concentration detection device,
Surplus oxygen removing means for removing surplus oxygen in the gas to be measured;
The gas side electrode exposed to the gas to be measured after the excess oxygen is removed by the excess oxygen removing means, the atmosphere side electrode exposed to the atmosphere, and interposed between the gas side electrode and the atmosphere side electrode A gas concentration detection cell having an electrolyte layer capable of transferring oxygen ions between the two,
A change amount calculating means for calculating a change amount of the cell output of the gas concentration detection cell every predetermined time;
During warm-up of the gas concentration detection cell, and during the execution of the excess oxygen removal means, timing the amount of change falls below the reference value (hereinafter, a first timing) and specific means that identifies a
Gas concentration detecting means for detecting the gas concentration of the specific gas component based on the cell output after the first time ;
Oxidation state estimation means for estimating an oxidation state of the gas side electrode;
Correction means for correcting the influence of oxygen reduced from the gas side electrode on the cell output based on the oxidation state;
It is characterized by providing.

According to a second invention, in the first invention,
Gas concentration estimating means for estimating the gas concentration of the specific gas component based on the operating state of the internal combustion engine,
The correction means includes a gas concentration at the first time detected by the gas concentration detecting means (hereinafter referred to as a first detected concentration), a gas concentration at the first time estimated by the gas concentration estimating means ( Hereinafter, the cell output is corrected based on the first estimated concentration) and the oxidation state.

According to a third invention, in the second invention,
It said correction means, said first detection density and the first estimated concentration and the correction value calculating unit operable to calculate a correction value that reflects the influence of the elapsed time from the oxidation state and the first time to the deviation of The cell output is corrected by subtracting the correction value from the cell output.

According to a fourth invention, in the third invention,
The correction value calculation means calculates so that the correction value becomes smaller as the elapsed time is longer.

A fifth invention is the third or fourth invention, wherein
5. The gas concentration detection device according to claim 3, wherein the correction value calculation means calculates the correction value so that the higher the oxidation state, the larger the correction value.

A sixth invention is the invention according to any one of the third to fifth inventions,
A stable time estimation means for estimating a time (hereinafter, a stable time) when the gas concentration detection cell detects a cell output in which the influence of oxidation of the gas side electrode is not superimposed;
Prohibiting means for prohibiting execution of the correcting means for the cell output at the stable time;
Is further provided.

A seventh invention is the sixth invention, wherein
7. The gas concentration detection device according to claim 6, wherein the stable time estimating means estimates a time when the correction value is 0 or less as the stable time.

According to an eighth invention, in any one of the first to seventh inventions,
The oxidation state estimation means estimates the oxidation state higher as the period from the start of energization to the gas concentration detection cell to the first time is longer.

According to a ninth invention, in any one of the first to eighth inventions,
Further comprising integrated value calculating means for calculating an integrated value of the cell output in a period from the start of energization to the gas concentration detection cell to the first time period,
The oxidation state estimation means estimates the oxidation state higher as the integrated value is larger .

In a tenth aspect of the present invention based on any one of the first to ninth aspects,
The oxidation state estimation means includes air-fuel ratio acquisition means for acquiring the air-fuel ratio of the gas under measurement at the previous stop of the internal combustion engine, and the oxidation state is estimated to be higher as the air-fuel ratio is leaner. It is characterized by.

An eleventh aspect of the invention is any one of the first to tenth aspects of the invention,
The oxidation state estimation means includes a leaving time acquisition means for acquiring a standing time from a previous stop of the internal combustion engine to a current start, and the oxidation state is estimated to be higher as the leaving time is longer. .

A twelfth aspect of the invention is any one of the first to eleventh aspects of the invention,
It further comprises an oxidation suppressing means for suppressing oxidation of the gas side electrode while the internal combustion engine is stopped.

In a thirteenth aspect based on the twelfth aspect,
The oxidation suppressing means controls the air-fuel ratio to be rich when the internal combustion engine is stopped.

In a fourteenth aspect of the present invention based on any one of the first to thirteenth aspects,
The surplus oxygen removing means includes an oxygen pump cell, and discharges surplus oxygen in the gas to be measured as a voltage is applied to the oxygen pump cell.

When the amount of change in the cell output of the gas concentration detection cell falls below the reference value (first time) , the surplus oxygen remaining in the gas under measurement affects the cell output of the gas concentration detection cell by the surplus oxygen removing means. It shows the time when it was removed to the extent that it was not given. That is, after the first period, the influence of surplus oxygen remaining from the cell output of the gas concentration detection cell is eliminated. Here, when the internal combustion engine equipped with the gas concentration detection device is stopped and left to stand, the gas side electrode of the gas concentration detection cell adsorbs oxygen in the gas to be measured and oxidizes. The oxygen combined with the gas side electrode is reduced and desorbed when a predetermined condition is satisfied after the energization of the gas concentration detection cell is started. For this reason, the influence of the desorbed oxygen is superimposed on the cell output of the gas concentration detection cell, and the specific gas concentration may not be detected accurately even after the first period .

  According to the first invention, the oxidation state of the gas side electrode of the gas concentration detection cell is estimated. Based on the oxidation state, the influence of oxygen reduced and desorbed from the gas side electrode on the cell output is corrected. For this reason, according to this invention, the influence of the oxidation of a gas side electrode is excluded, and the specific gas concentration in to-be-measured gas can be detected accurately.

According to the second invention, the specific gas at the first time estimated based on the gas concentration at the first time ( first detected concentration) detected by the gas concentration detecting means and the operating state of the internal combustion engine. The cell output of the gas concentration detection cell is corrected based on the gas concentration of the component ( first estimated concentration) and the oxidation state of the gas side electrode. The first period is a period when the influence of the surplus oxygen remaining in the measurement gas disappears from the cell output of the gas concentration detection cell. Therefore, according to the present invention, compared with the first detection density and the first estimated concentration, i.e., based on the concentration comparison on in which the influence of the excess oxygen remaining in the measurement gas, the gas Since the cell output of the concentration detection cell is corrected, the specific gas concentration in the gas to be measured can be detected with high accuracy.

According to the third invention, the deviation of the first detection density and the first estimated concentration, correction value that reflects the elapsed time from the oxidation state and the first time of the gas-side electrode is calculated. Then, the cell output is corrected by subtracting the correction value from the cell output of the gas concentration detection cell. For this reason, according to the present invention, cell output correction reflecting the oxidation state can be performed, so that the influence of oxygen combined with the gas side electrode by the oxidation reaction on the cell output can be effectively corrected. Can do.

According to the fourth aspect of the invention, the correction value is calculated so as to become smaller as the elapsed time after the first time appears is longer. The longer the elapsed time, the smaller the influence of oxidation of the gas side electrode, that is, the influence of oxygen desorbed from the gas side electrode. For this reason, according to the present invention, it is possible to calculate a correction value for effectively eliminating the influence due to the oxidation of the gas side electrode.

  According to the fifth invention, the correction value is calculated so as to increase as the oxidation state increases. The higher the oxidation state of the gas side electrode, the greater the influence of oxidation of the gas side electrode, that is, the influence of oxygen desorbed from the gas side electrode. For this reason, according to the present invention, it is possible to calculate a correction value for effectively eliminating the influence due to the oxidation of the gas side electrode.

  According to the sixth aspect of the present invention, the time (stable time) when the gas concentration detection cell detects the cell output in which the influence of the oxidation of the gas side electrode is not superimposed is estimated, and correction of the cell output at the stable time is prohibited. Is done. Therefore, according to the present invention, it is possible to effectively avoid a situation where an unnecessary correction is performed and an error occurs in the cell output.

  According to the seventh aspect, the time when the correction value is 0 or less is estimated as the stable time. The correction value indicates the output due to the effect of oxidation of the gas side electrode among the cell outputs detected by the gas concentration detection cell. For this reason, according to the present invention, the stable time can be accurately estimated based on the correction value.

According to the eighth invention, the oxidation state of the gas-side electrode, the time until the first time of cell output from the start of energization of the gas concentration detection cell (hereinafter, referred to as "arrival our time") is The longer it is, the higher it is estimated. Here, as the arrival time is longer, it can be determined the residual oxygen in the measurement gas before the supply is to have been a large amount. The more residual oxygen before energization, that is, the more the gas side electrode is exposed to more oxygen before energization, the higher the oxidation state of the gas side electrode. For this reason, according to this invention, the oxidation state of a gas side electrode can be estimated with high precision based on the said arrival time.

According to the ninth invention, the integrated value of the cell output of the gas concentration detection cell in arrival our time is calculated. And it is estimated that the oxidation state of a gas side electrode is so high that the said integrated value is large. Here, it can be determined that the greater the integrated value of the cell output, that is, the more oxygen is actively pumped in the gas concentration detection cell, the greater the amount of residual oxygen in the gas to be measured before energization. The more residual oxygen before energization, that is, the more the gas side electrode is exposed to more oxygen before energization, the higher the oxidation state of the gas side electrode. For this reason, according to this invention, the oxidation state of a gas side electrode can be estimated with high precision based on the integrated value of the sensor output in the said arrival time.

  According to the tenth aspect, the air-fuel ratio of the gas to be measured when the internal combustion engine is stopped is acquired. The leaner the air-fuel ratio is, the higher the oxidation state of the gas side electrode is estimated. Here, the leaner the air-fuel ratio of the gas to be measured, that is, the higher the oxygen concentration around the gas side electrode while the internal combustion engine is stopped, the higher the oxidation state of the gas side electrode. Therefore, according to the present invention, the oxidation state of the gas side electrode can be estimated with high accuracy based on the air-fuel ratio of the gas to be measured when the internal combustion engine is stopped.

  According to the eleventh aspect, the neglected time from the previous stop of the internal combustion engine to the current start is acquired. And it is estimated that the oxidation state of a gas side electrode is so high that the said leaving time is long. Here, the longer the standing time, that is, the longer the time required for the oxidation reaction of the gas side electrode, the higher the oxidation state of the gas side electrode. For this reason, according to the present invention, the oxidation state of the gas side electrode can be estimated with high accuracy based on the standing time.

  The higher the oxidation state of the gas side electrode, the more hindered the improvement in accuracy of concentration detection by the gas concentration detection cell. According to the twelfth aspect, since the oxidation reaction of the gas side electrode is suppressed while the internal combustion engine is stopped, the influence of the oxidation of the gas side electrode on the cell output can be minimized.

  According to the thirteenth invention, the air-fuel ratio when the internal combustion engine is stopped is controlled to be rich. For this reason, according to the present invention, the oxygen concentration of the gas to be measured can be reduced, so that the oxidation of the gas side electrode while the internal combustion engine is stopped can be effectively suppressed.

  According to the fourteenth invention, surplus oxygen in the gas to be measured can be discharged by applying a voltage to the oxygen pump cell.

  Several embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
First, the configuration of the gas concentration detection apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a diagram for explaining a configuration of a gas concentration detection apparatus 10 according to the first embodiment. A gas concentration detection device 10 shown in FIG. 1 is a NOx concentration detection device that detects the concentration of nitrogen oxides (NOx) in exhaust gas discharged from an internal combustion engine (engine), for example.

  The gas concentration detection device 10 has a NOx sensor 1. The NOx sensor 1 is formed by sequentially stacking a spacer 3, a NOx sensor cell 4, a spacer 5, and a heater 6 below the oxygen pump cell 2.

The oxygen pump cell 2 has a function of removing surplus oxygen in the gas to be measured. The oxygen pump cell 2 includes a solid electrolyte body 21, and a first pump electrode 22 and a second pump electrode 23 arranged so as to sandwich the solid electrolyte body 21. Have. The solid electrolyte body 21 as an element has oxygen ion conductivity, and for example, ZrO ₂ , HfO ₂ , ThO ₂ , BiO ₃ or the like formed into a sheet shape is used. The 1st pump electrode 22 and the 2nd pump electrode 23 which are arrange | positioned so that this solid electrolyte body 21 may be pinched | interposed can be formed by methods, such as screen printing, for example.

  The first pump electrode 22 formed on the surface of the solid electrolyte body 21 is exposed in the space where the exhaust gas that is the gas to be measured exists, that is, in the exhaust passage of the engine. As the first pump electrode 22, for example, a porous cermet electrode containing a noble metal such as Pt can be used.

  On the other hand, the second pump electrode 23 formed on the back surface of the solid electrolyte body 21 so as to face the first pump electrode 22 is exposed to a first internal space 31 described later. As the second pump electrode 23, an electrode inert to a gas containing NOx, for example, a porous cermet electrode containing a Pt—Au alloy and ceramics such as zirconia or alumina can be used.

  In the oxygen pump cell 2, a pinhole 24 is formed as an introduction hole that penetrates the solid electrolyte body 21, the first pump electrode 22, and the second pump electrode 23. The hole diameter of the pinhole 24 is designed so that the diffusion speed of the exhaust gas introduced into the first internal space 31 described later through the pinhole 24 becomes a predetermined speed. The first internal space 31 communicates with the space where the gas to be measured exists through the pinhole 24 and the porous protective layer 7 described later.

  Further, the porous protective layer 7 is formed on the solid electrolyte body 21 on the first pump electrode 22 side so as to cover the surface of the first pump electrode 22 including the pinhole 24 and the periphery thereof. The porous protective layer 7 can be formed of, for example, porous alumina. The porous protective layer 7 can prevent the first pump electrode 22 from being poisoned and can prevent the pinhole 24 from being clogged with soot contained in the exhaust gas.

  The spacer 3 is formed with the first internal space 31 and the second internal space 32 described above. The spacer 3 can be formed of alumina or the like, for example. The two internal spaces 31 and 32 communicate with each other through a communication hole 33. The first internal space 31, the second internal space 32, and the communication hole 33 can be formed by providing a hole in the spacer 3.

  The NOx sensor cell 4 detects the NOx concentration from the amount of oxygen generated by NOx reductive decomposition. The NOx sensor cell 4 includes a solid electrolyte body 41 and a first detection electrode 42 and a second detection electrode 43 that are disposed so as to sandwich the solid electrolyte body 41. The first detection electrode 42 and the second detection electrode 43 can be formed by a method such as screen printing, for example.

  The first detection electrode 42 formed on the surface of the solid electrolyte body 41 is exposed in the second internal space 32. As the first detection electrode 42, for example, a porous cermet electrode containing a Pt—Au alloy and ceramics such as zirconia and alumina can be used.

  On the other hand, the second detection electrode 43 formed on the back surface of the solid electrolyte body 41 so as to face the first detection electrode 42 is exposed to the atmospheric duct 51 formed in the spacer 5. Air is introduced into the air duct 51. As this 2nd detection electrode 43, the porous cermet electrode containing noble metals, such as Pt, can be used, for example. The air duct 51 can be formed by providing a cutout in the spacer 5.

  The heater 6 includes sheet-like insulating layers 62 and 63 and a heater electrode 61 embedded between these insulating layers 62 and 63. The insulating layers 62 and 63 are made of ceramics such as alumina, for example. The heater electrode 61 is made of, for example, cermet of Pt and ceramics such as alumina.

  The gas concentration detection device 10 according to the first embodiment includes an ECU (Electronic Control Unit) 8 as a control device. The ECU 8 includes a pump cell control means 81, a sensor cell control means 82, and a heater control means 83. The ECU 8 may be configured separately from the engine control ECU or may be configured as a part of the engine control ECU.

  The pump cell control means 81 is connected to the first pump electrode 22 and the second pump electrode 23 in the oxygen pump cell 2. The pump cell control means 81 applies a voltage between the first pump electrode 22 and the second pump electrode 23 and detects the value of the current flowing through the oxygen pump cell 2 as an “oxygen pump cell output”.

  The sensor cell control means 82 is connected to the first detection electrode 42 and the second detection electrode 43 in the NOx sensor cell 4. The sensor cell control means 82 applies a voltage between the first detection electrode 42 and the second detection electrode 43 and detects the current value flowing through the NOx sensor cell 4 as “NOx sensor cell output”.

  The heater control means 83 is connected to the heater electrode 61. The heater control unit 83 supplies power to the heater electrode 61.

[Operation of Embodiment 1]
(NOx concentration detection principle)
Next, the principle of detection of NOx concentration by the gas concentration detector 10 will be described with reference to FIG. In the space around the protective layer 7, there is exhaust gas as a gas to be measured flowing through the exhaust passage of the engine. This exhaust gas contains O ₂ , NOx, CO ₂ , H ₂ O and the like. The exhaust gas is introduced into the first internal space 31 through the porous protective layer 7 and the pinhole 24. The amount of exhaust gas introduced into the first internal space 31 is determined by the diffusion resistance of the porous protective layer 7 and the pinhole 24.

Prior to the detection of the NOx concentration, power is first supplied from the heater control means 83 to the heater electrode 61, and the solid electrolyte bodies 21 and 41 are heated to the activation temperature. Next, the second pump exposed to the first internal space 31 when activity in the oxygen pump cell 2 is expressed and a voltage is applied between the first pump electrode 22 and the second pump electrode 23 from the pump cell control means 81. On the electrode 23, residual oxygen and oxygen in the exhaust gas are reduced to oxygen ions O ²⁻ . This oxygen ion O ²⁻ passes through the solid electrolyte body 21 by the pumping action and is discharged to the first pump electrode 22 side. At this time, the current value flowing through the oxygen pump cell 2 is detected by the pump cell control means 81 as an oxygen pump cell output. Excess oxygen is discharged by the oxygen pump cell 2, so that the oxygen concentration in the exhaust gas is lowered to a level that does not affect the NOx concentration detection by the NOx sensor cell 4. In addition, by increasing the applied voltage between the first pump electrode 22 and the second pump electrode 23 as much as possible, the pumping action of the oxygen ions O ²⁻ can be made more active, and the oxygen discharge amount can be increased.

The exhaust gas from which excess oxygen has been removed to a low oxygen concentration is introduced into the second internal space 32 through the communication hole 33. When the NOx sensor cell 4 is activated and a voltage is applied between the first detection electrode 42 and the second detection electrode 43 by the sensor cell control means 82, NOx, which is a specific component in the exhaust gas, is detected by the first detection electrode 42. It is decomposed above to generate oxygen ions O ²⁻ . More specifically, NOx is decomposed into NO at one end (single gasification) and then further decomposed into oxygen ions O ²⁻ . The oxygen ions O ²⁻ pass through the solid electrolyte body 41 and are discharged from the second detection electrode 43 to the air duct 51. At this time, the current flowing through the NOx sensor cell 4 is detected by the sensor cell control means 82 as the NOx sensor cell output, that is, the NOx concentration output of the gas to be measured.

(NOx sensor activation judgment operation)
Next, the activity determination operation of the NOx sensor 1 will be described with reference to FIGS. In order to accurately detect the NOx concentration described above, it is necessary that the NOx sensor 1 has reached an active state. The “active state” of the present invention means that the NOx sensor cell output can be used for various controls at the time when the NOx sensor output without the influence of the residual oxygen is detected, that is, without being influenced by the residual oxygen. This shows the state (hereinafter the same).
Therefore, if the activation determination of the NOx sensor 1 can be performed at an early stage, the NOx sensor cell output can be quickly used for various controls to reduce emissions.

  Here, in the NOx sensor using the element made of the solid electrolyte body like the NOx sensor 1, the element temperature is heated to a predetermined activation temperature by energizing the heater in order to obtain normal characteristics. There is a need to. It is known that the activity determination of the gas concentration sensor is performed based on element impedance, power supplied to the heater, heater resistance, or the like. However, element impedance, heater supply power, and the like vary among sensors. For this reason, it is difficult to quickly and accurately grasp the active state of the sensor based on these parameters.

  Therefore, in the first embodiment, the determination of the activity of the NOx sensor 1 is performed early and with high accuracy by the method described below. FIG. 2 is a diagram showing changes in the output of the oxygen pump cell and the NOx sensor cell output when the NOx sensor is warmed up. The chain line Lp shown in FIG. 2 indicates the change in the oxygen pump cell output, and the solid line Ls indicates the change in the NOx sensor cell output.

  As shown in FIG. 2, at time t0, warming up of the NOx sensor 1 is started as the engine starts. More specifically, energization from the heater control means 83 to the heater electrode 61 is started. By this energization operation, the temperatures of the oxygen pump cell 2 and the NOx sensor cell 4, that is, the temperatures of the solid electrolyte bodies 21 and 41 are gradually increased. At this time t0, oxygen in the atmosphere remains in the first internal space 31 in the vicinity of the oxygen pump cell 2 and the second internal space 32 in the vicinity of the NOx sensor cell 4.

  Thereafter, when the temperature of the solid electrolyte body 41 in the NOx sensor cell 4 reaches a predetermined temperature at time t1, a NOx sensor cell output is obtained. After the time t1, the NOx sensor cell output increases as the activity of the NOx sensor cell 4 (solid electrolyte body 41) increases. This is not because NOx introduced into the second internal space 32 in the vicinity of the NOx sensor cell 4 is decomposed on the first detection electrode 42, but oxygen remaining in the second internal space 32 is generated on the first detection electrode. It is because it is decomposed. Thereafter, at time t3, the NOx sensor cell output reaches the upper limit value, that is, the upper limit value of the oxygen concentration detectable by the NOx sensor cell 4.

  On the other hand, when the temperature of the solid electrolyte body 21 of the oxygen pump cell 2 reaches a predetermined temperature at time t2 after time t1, an oxygen pump cell output is obtained. After the time t2, the amount of oxygen remaining in the first internal space 31 near the oxygen pump cell 2 increases as the activity of the oxygen pump cell 2 (solid electrolyte body 21) increases. For this reason, the oxygen pump cell output increases with time.

  As the activity of the oxygen pump cell 2 increases, the amount of oxygen discharged from the first internal space 31 increases. Further, the amount of exhaust gas introduced into the first internal space 31 becomes large. As a result, the residual oxygen concentration in the first internal space 31 becomes low, and the amount of oxygen supplied from the first internal space 31 to the second internal space 32 becomes small. For this reason, as the activity of the oxygen pump cell 2 increases, the residual oxygen concentration in the second internal space 32 gradually decreases. As a result, the NOx sensor cell output decreases after time t4.

  Thereafter, at time t5 when the residual oxygen in the second internal space 32 is almost removed, an inflection point, that is, a point where the curve of the NOx sensor cell output changes greatly appears in the NOx sensor output. More specifically, the NOx sensor cell output before the inflection point appears is mainly the pumping action of oxygen ions using oxygen remaining in the second internal space 32. For this reason, the NOx sensor cell output curve during this period is dominated by the oxygen concentration in the second internal space 32, that is, the activity of the oxygen pump cell 2.

  On the other hand, the NOx sensor cell output after the inflection point appears is mainly the pumping of oxygen ions using NOx in the second internal space 32 due to the decrease in residual oxygen. For this reason, the NOx sensor cell output curve in such a period is dominated by the NOx concentration in the second internal space 32, that is, the activity of the NOx sensor cell 4. For this reason, it can be understood that oxygen remaining in the first internal space 31 and the second internal space 32 before the warming-up of the NOx sensor 1 is substantially removed at time t5 when the inflection point appears. Therefore, after the time t5 when the inflection point appears, the NOx concentration can be accurately detected by the NOx sensor cell 4 without being affected by the residual oxygen.

  Therefore, in the first embodiment, the NOx sensor 1 is determined to be active at time t5 when an inflection point appears in the NOx sensor cell output. Thus, the NOx sensor 1 can be activated at the time when the NOx sensor cell 4 starts to detect the NOx concentration without being affected by the residual oxygen, so that the demand for early activation of the NOx sensor 1 is maximized. Can be satisfied.

Next, with reference to FIG. 3, the operation for specifying the inflection point described above will be described. FIG. 3 is a diagram for explaining a method for specifying the inflection point of the NOx sensor cell output. As shown in this figure, first, the NOx sensor cell output N is acquired at every predetermined time, and the change amount ΔN of the NOx sensor cell output is calculated at each time. Here, the amount of change ΔN (t) at time t can be calculated according to the following equation (1). When the calculated change amount ΔN (t) becomes smaller than a predetermined reference value ΔNth, the NOx sensor cell output N (t) at the time t is specified as the inflection point.
ΔN (t) = N (t−1) −N (t) (1)

  In the example shown in FIG. 3, the NOx sensor cell output N decreases from time t10 to time t14. For this reason, at each time t11 to time t14, the change amounts ΔN (t11) to ΔN (t14) calculated by the above equation (1) all take positive values. The change amounts ΔN (t11) to ΔN (t13) are equal to or greater than a predetermined reference value ΔNth, but the change amount ΔN (t14) is smaller than the reference value ΔNth. For this reason, the NOx sensor cell output N (t14) at time t14 is specified as the inflection point. Therefore, the activation determination of the NOx sensor 1 is performed at time t14 when an inflection point appears in the NOx sensor cell output.

  In addition, the specific method of an inflection point is not restricted to the method mentioned above. That is, for example, the NOx sensor cell output N at the time when the NOx sensor cell output N has started to increase may be specified as the inflection point. This is because when the NOx concentration in the exhaust gas increases, the increase can be detected by the NOx sensor cell 4. Further, even when the change amount ΔN of the NOx sensor cell output N is larger than the reference value ΔNth, when the NOx sensor cell output N becomes smaller than the reference value Nth, the NOx sensor cell output N is specified as an inflection point. May be. This is because it means that the remaining oxygen has been removed prior to completion of warm-up of the NOx sensor 1.

[Characteristic operation of the first embodiment]
Next, characteristic operations of the present embodiment will be described with reference to FIGS. As described above, at the time when the inflection point appears, it can be grasped that oxygen remaining in the first internal space 31 and the second internal space 32 before the NOx sensor 1 is warmed up is almost removed. Therefore, after the time when the inflection point appears, the NOx concentration can be detected by the NOx sensor cell 4 without being affected by the residual oxygen.

  However, the NOx sensor cell output varies depending on the oxidation state of the first detection electrode 42 in the NOx sensor cell 4 in addition to the influence of residual oxygen. That is, the oxidation of the first detection electrode 42 occurs when oxygen remaining in the second internal space 32 reacts with the first detection electrode 42 while the engine is stopped and left (during soak). In particular, when rhodium (Rh) is contained in the first detection electrode 42, the oxidation reaction is more likely to proceed.

  In the oxidized first detection electrode 42, the reduction reaction proceeds as the warm-up of the NOx sensor 1 proceeds. For this reason, the NOx sensor cell output fluctuates due to the influence of oxygen desorbed by the reduction reaction, and there is a possibility that the NOx concentration cannot be detected accurately. In particular, in the electrode containing rhodium (Rh) described above, since it takes time until the oxidized rhodium is reduced, the period during which the NOx concentration cannot be accurately detected may be prolonged.

  That is, the time from when the inflection point appears until the output of the NOx sensor cell is stabilized (hereinafter referred to as “output stabilization time”), that is, the period until the influence of the oxidation of the first detection electrode 42 is eliminated, is the NOx sensor 1. It changes depending on the oxidation state of the first detection electrode 42 in FIG. FIG. 4 is a diagram for explaining the relationship between the oxygen partial pressure around the first detection electrode 42 in the soak and the sensor output stabilization time. As shown in this figure, it can be seen that the higher the oxygen partial pressure in the second internal space 32 in the soak, the longer the output stabilization time. That is, the higher the oxygen partial pressure in the second internal space 32, the more the oxidation of the first detection electrode proceeds. For this reason, the time until the reduction reaction at the first detection electrode 42 is completed is prolonged, and as a result, the output stabilization time is prolonged.

  FIG. 5 is a diagram for explaining the relationship between the soak time and the sensor output stabilization time. As shown in this figure, it can be seen that the longer the soak time, the longer the output stabilization time. That is, the longer the soak time, the more the oxidation of the first detection electrode 42 proceeds. For this reason, the time until the reduction reaction of the first detection electrode 42 is completed is prolonged, and as a result, the output stabilization time is prolonged.

  As described above, the output stabilization time varies depending on the oxidation state of the first detection electrode 42. Therefore, in the first embodiment, the oxidation state of the first detection electrode 42 is estimated, and correction is performed to eliminate the influence of oxidation of the first detection electrode 42 from the NOx sensor cell output. As a result, the NOx concentration can be accurately detected using the NOx sensor cell output after the inflection point appears. Hereinafter, the oxidation state estimation operation and the NOx sensor cell output correction operation will be described in detail.

(Oxidation state estimation operation)
Next, an operation for estimating the electrode oxidation state of the NOx sensor cell 4 will be described with reference to FIGS. As described above, in the first detection electrode 42 in the soak, the higher the oxygen partial pressure in the second internal space 32 and the longer the soak time, the higher the oxidation state. FIG. 6 shows a map for specifying the oxidation state of the first detection electrode 42. The correlation value K reflecting the oxidation state of the first detection electrode 42 becomes smaller as the oxidation state is higher. Therefore, the correlation value K is specified, for example, according to the map shown in FIG. More specifically, the correlation value K is specified as a smaller value as the soak time is longer. Further, the leaner the air-fuel ratio when the engine is stopped, that is, the air-fuel ratio of the exhaust gas remaining in the second internal space 32 is specified as a smaller value. Thus, by specifying the oxidation state correlation value K according to the map shown in FIG. 6, the oxidation state based on the situation where the first detection electrode 42 in the soak is placed can be reflected in the correlation value K. it can.

  Further, the correlation value K of the oxidation state can be estimated based on the NOx sensor cell output after the NOx sensor 1 starts to warm up. FIG. 7 shows a map for specifying the oxidation state of the first detection electrode 42. In this figure, the horizontal axis indicates the time from the start of warming-up of the NOx sensor 1 until the inflection point appears in the NOx sensor cell output (hereinafter referred to as “inflection point arrival time”). The longer the inflection point arrival time is, the more oxygen remains in the first internal space 31 and the second internal space 32. For this reason, it can be determined that the oxidation state of the first detection electrode 42 is higher as the inflection point arrival time is longer. Therefore, the correlation value K is specified as a smaller value as the inflection point arrival time is longer, as shown in FIG.

  The oxidation state correlation value K may be estimated by appropriately combining the above-described methods, or may be estimated by other methods. For example, the integrated value of the NOx sensor cell output up to the inflection point can be used instead of the inflection point arrival time described above. Moreover, it is good also as estimating based on a NOx sensor cell output, and good also as estimating based on the ratio of the rising speed of NOx sensor cell output, and falling speed.

(NOx sensor cell output correction operation)
Next, the NOx sensor cell output correction operation will be described with reference to FIG. As described above, the correlation value K reflecting the oxidation state of the first detection electrode 42 can be estimated based on the soak state or the inflection point arrival time. Therefore, in the first embodiment, the NOx sensor cell output N after the inflection point is corrected using the correlation value K of the oxidation state. More specifically, first, the output difference Nm between the NOx sensor cell output Nb at the inflection point and the estimated value of NOx concentration at the inflection point (hereinafter referred to as “estimated NOx value”) Np is determined according to the following equation (2). calculate. The estimated NOx value Np can be estimated based on, for example, the engine operating state (intake air amount, EGR amount, etc.) at the inflection point.
Nm = Nb−Np (2)

Next, in order to correct the influence of the output difference Nm at the inflection point, the final NOx sensor cell output correction value Na is calculated according to the following equation (3).
Na = N− (Nm−Kt) (3)

  Here, the correction term (Nm−Kt) in the above equation (3) is a value reflecting the time change of the oxidation state of the first detection electrode 42 in the output difference Nm. That is, the higher the oxidation state of the first detection electrode 42, the longer the output stabilization time. For this reason, in the above equation (3), the smaller the correlation value K of the oxidation state, the smaller the attenuation of the correction term. Thereby, the influence by the oxidation of the 1st detection electrode 42 superimposed on the NOx sensor cell output N after an inflection point can be correct | amended effectively.

  FIG. 8 is a diagram for comparing the NOx concentration before correction with the NOx concentration after correction. In this figure, the chain line in (a) indicates the actual NOx concentration of the gas to be measured, the thin line in (b) indicates the detected NOx concentration value before correction, the solid line in (c) indicates the detected NOx concentration value after correction, Each is shown. As shown in this figure, it can be seen that the corrected NOx detection value is closer to the actual NOx concentration than the corrected NOx detection value.

  When the correction term (Nm−Kt) in the above equation (3) is 0 or less, it can be estimated that the NOx sensor cell 4 is detecting a stable NOx sensor cell output N (stable time). . For this reason, the execution of the correction is terminated when the condition of (Nm−Kt) ≦ 0 is satisfied. Thereby, it is possible to effectively avoid a situation where unnecessary correction is made to the NOx sensor cell output N.

[Specific Processing in First Embodiment]
Next, specific processing of the first embodiment will be described with reference to FIGS. 9 and 10. FIG. 9 is a flowchart illustrating a routine in which the ECU 8 performs the activity determination of the NOx sensor 1 in the first embodiment. This routine is started at predetermined intervals. This predetermined interval corresponds to, for example, the interval from time t10 to time t11, the interval from time t11 to time t12, and the like shown in FIG.

  In the routine shown in FIG. 8, it is first determined whether or not the NOx sensor 1 is warming up (step 100). Specifically, it is determined whether or not the NOx sensor 1 is warmed up when the engine is started, or when returning from a long-time fuel cut. As a result, when it is determined that the NOx sensor 1 is not warming up, it is determined that the NOx sensor cell output as shown in FIG. 2 cannot be obtained, and this routine is immediately terminated.

  On the other hand, if it is determined in step 100 that the NOx sensor 1 is warming up, the process proceeds to the next step, and the NOx sensor cell output N (t) is acquired (step 102). Next, a change amount ΔN (t) is calculated (step 104). Specifically, the amount of change ΔN (t) is calculated by substituting the NOx sensor cell outputs N (t) and N (t−1) acquired in step 102 into the above equation (1). .

  Next, it is determined whether or not the change amount ΔN (t) is greater than 0 (step 106). As a result, when the change amount ΔN (t)> 0 is recognized, it is determined that the change amount ΔN (t) in this routine is smaller than the change amount ΔN (t−1) in the previous routine. Then, the process proceeds to the next step, and it is determined whether or not the change amount ΔN (t) is smaller than the reference value ΔNth (step 108). As a result, when it is recognized that the change amount ΔN (t) <reference value ΔNth is established, the process proceeds to the next step, and the NOx sensor cell output N (t) is specified as the inflection point (step 110). In the example shown in FIG. 3, since the change amount ΔN (t14) is smaller than the reference value ΔNth, the NOx sensor cell output N (t14) at time t14 is specified as the inflection point. Then, it is determined that the time when the inflection point appears is the activation time of the NOx sensor cell 4 (step 112), and this routine is ended.

  On the other hand, when the change amount ΔN (t)> 0 is not established in step 106, the change amount ΔN (t) in this routine is equal to or greater than the change amount ΔN (t−1) in the previous routine. If it is determined that there is, the process proceeds to the next step, and it is determined whether or not the amount of change ΔN (t−1) in the previous routine is greater than zero (step 114). Specifically, it is determined whether or not the change amount ΔN (t−2) in the last routine is greater than the change amount ΔN (t−1) in the previous routine. As a result, when the change amount ΔN (t−1)> 0 is not established, the NOx sensor cell output N is rising toward the upper limit value, so that an inflection point has not yet appeared. As a result, this routine is immediately terminated.

  On the other hand, when the change amount ΔN (t−1)> 0 is recognized in step 114, the change amount ΔN (t−2) in the previous routine is changed to the change amount ΔN (t in the previous routine. -1). In this case, it is determined that an increase in the NOx concentration in the exhaust gas has been detected this time, the process proceeds to step 110, and the NOx sensor cell output N (t) is specified as the inflection point.

  If it is not found in step 108 that the change amount ΔN (t) <reference value ΔNth, the process proceeds to the next step, and whether the NOx sensor cell output N (t) is smaller than the reference value ΔNth. Is determined (step 116). As a result, if the establishment of NOx sensor cell output N (t) <reference value ΔNth is not recognized, it is determined that an inflection point has not yet appeared in the NOx sensor cell output N, and this routine is immediately terminated. .

  On the other hand, if it is determined in step 116 that NOx sensor cell output N (t) <reference value ΔNth is established, the routine proceeds to step 110 where the NOx sensor cell output N (t) is specified as an inflection point. .

  FIG. 9 is a flowchart showing a routine in which the ECU 8 corrects the NOx sensor cell output N in the first embodiment. This routine is started at predetermined intervals in parallel with the routine shown in FIG. In the routine shown in FIG. 9, first, the activation determination of the NOx sensor 1 is executed (step 200). Here, specifically, whether or not the activity determination is made in the routine shown in FIG. 8 executed in parallel with this routine, that is, whether or not the NOx sensor 1 is determined in the above step 112. Is determined. As a result, when the activation determination of the NOx sensor 1 is not performed, this routine is immediately terminated.

  On the other hand, when the activation determination of the NOx sensor 1 is performed in step 200, it is determined that the inflection point of the NOx sensor output has been specified, and the process proceeds to the next step, where the NOx sensor cell output at the inflection point is determined. Nb is acquired (step 202). Specifically, the NOx sensor cell output N (t) specified as the inflection point in step 110 of the routine shown in FIG. 8 is acquired as the NOx sensor cell output Nb at the inflection point in this routine.

  Next, the estimated NOx value Np at the inflection point is acquired (step 204). Specifically, the estimated NOx value Np of the exhaust gas is estimated based on the engine operating state at the inflection point, that is, the intake air amount, the EGR amount, and the like.

  Next, the correlation value K of the oxidation state is acquired (step 206). Specifically, first, the time from when the engine is started until the NOx sensor cell output reaches the inflection point is acquired. And the correlation value K of an oxidation state is specified according to the map (refer FIG. 7) which prescribed | regulated the relationship between the inflection point arrival time and the correlation value K. FIG.

  Next, the NOx sensor cell output N after the inflection point is acquired (step 208). Next, a correction term for correcting the NOx sensor cell output N acquired in step 208 is calculated (step 210). Here, specifically, first, the NOx sensor cell output Nb at the inflection point obtained at step 202 and the estimated NOx value Np obtained at step 204 are substituted into the above equation (2), The output difference Nm at the inflection point is calculated. Next, a correction term (Nm−Kt) is calculated based on the output difference Nm, the correlation value K of the oxidation state acquired in step 206, and the elapsed time t from the inflection point.

  Next, the NOx sensor cell output correction value Na t seconds after the inflection point is calculated (step 212). Here, specifically, the NOx sensor cell output N acquired in step 208 and the correction term (Nm−Kt) acquired in step 210 are substituted into the above equation (3).

  Next, it is determined whether or not the NOx sensor cell output N has stabilized (step 214). Specifically, it is determined whether or not the correction term (Nm−Kt) in the above equation (3) calculated in step 212 has a value of 0 or less. As a result, if the establishment of (Nm−Kt) ≦ 0 is not recognized, it is determined that the NOx sensor cell output N has not yet been stabilized, and the process returns to step 208 again to acquire the NOx sensor cell output N again. Is done.

  On the other hand, if it is determined in step 214 that (Nm−Kt) ≦ 0 is established, it is determined that the NOx sensor cell output N has stabilized, and the correction in step 212 is forcibly terminated ( Step 216), the routine ends.

  As described above, according to the first embodiment, it is possible to effectively correct the influence of the oxidation of the first detection electrode 42 superimposed on the NOx sensor cell output N after the inflection point. The demand for early activation can be met.

  Further, according to the first embodiment described above, when it is determined that the NOx sensor cell output N has been stabilized, the correction operation of the NOx sensor cell output is forcibly terminated, so unnecessary output correction is performed. A situation in which the NOx sensor cell output is shifted can be effectively eliminated.

  Moreover, in Embodiment 1 mentioned above, inflection point arrival time is used in order to specify the correlation value K of an oxidation state, However, The identification method of the correlation value K is not restricted to this. That is, the correlation value K may be specified based on the above-described state in the soak, that is, the air-fuel ratio of the exhaust gas remaining in the NOx sensor 1 during the soak, the soak time, and the like. May be combined. Further, instead of the inflection point arrival time described above, the integrated value of the NOx sensor cell output up to the inflection point, the NOx sensor cell output, the ratio of the rising speed and the falling speed of the NOx sensor cell output, or the output of the oxygen pump cell 2 The correlation value K may be specified based on the above. When the accuracy requirement of the system is low, the correlation value K may be a constant.

In the first embodiment described above, the oxygen pump cell 2 is the “surplus oxygen removing means” in the first invention, and the NOx sensor cell 4 is the “gas concentration detection cell” in the first invention. The electrode 42 is the “gas side electrode” in the first invention, the second detection electrode 43 is the “atmosphere side electrode” in the first invention, and the solid electrolyte body 41 is the “electrolyte layer” in the first invention. Furthermore, the NOx sensor cell output corresponds to the “cell output” in the first invention, and the time t14 at which the inflection point appears corresponds to the “first time” in the first invention . Further, ECU 8 is, by executing the process of step 110, the "specific means" in the first aspect of the present invention, by executing the process in step 208, "the gas concentration detected in the first aspect of the present invention The “means” executes the process of step 206, and the “oxidation state estimating means” in the first invention executes the process of step 212, thereby “correcting means” in the first invention. Are realized.

In the first embodiment described above, the NOx sensor cell output Nb is the “ first detected concentration” in the second invention, the estimated NOx value Np is the “ first estimated concentration in the second invention” . Respectively. Further, the “gas concentration estimating means” in the second aspect of the present invention is realized by the ECU 8 executing the processing of step 204 described above.

  In the first embodiment described above, the output difference Nm corresponds to the “deviation” in the third aspect of the invention, and the ECU 8 executes step 210 described above, whereby “ "Correction value calculating means" is realized.

  In the first embodiment described above, the ECU 8 executes the step 214, whereby the “stable time estimation means” in the sixth invention executes the step 216. “Prohibiting means” is realized.

Embodiment 2. FIG.
[Features of Embodiment 2]
In the first embodiment described above, the influence of the oxidation of the first detection electrode 42 is corrected to improve the accuracy of the NOx concentration after the inflection point appears in the NOx sensor cell output. For this reason, in order to improve the accuracy of the NOx concentration, it is desirable to make the oxidation state of the first detection electrode 42 as low as possible. Therefore, in the second embodiment, the following control is executed in order to suppress oxidation of the first detection electrode 42.

(Heater control)
In the second embodiment, the heater electrode 61 in FIG. 1 described in the first embodiment is improved. More specifically, the heater electrode 61 according to the second embodiment includes a first heater pattern for heating the vicinity of the pump cell 2 and a second heater pattern for heating the vicinity of the NOx sensor cell 4. Have. The heater control means 83 can individually control the first heater pattern and the second heater pattern.

  When the engine in which the gas concentration detection device 10 having such a configuration is mounted is stopped, first, the heater control means 83 is controlled so that the input power to the second heater pattern in the heater electrode 61 is reduced. The The first detection electrode 2 is most easily oxidized when heated to about 300 ° C. to 400 ° C. For this reason, it is possible to suppress oxidation of the first detection electrode by quickly setting the first detection electrode to a low temperature as the engine stops.

  At the same time, the supply of power to the first heater pattern in the heater electrode 61 is continued. Thereby, since the discharge operation of oxygen in the oxygen pump cell 2 is continued, the oxygen concentration in the first internal space 31 and the second internal space 32 can be reduced. Therefore, the amount of oxidation of the first detection electrode 42 in the soak can be effectively suppressed.

(Air-fuel ratio control)
In the second embodiment, in addition to the heater control described above, the oxidation of the first detection electrode 42 can be suppressed by air-fuel ratio control. More specifically, the air-fuel ratio when the engine is stopped is controlled to the fuel rich side as compared with the normal time. As a result, the oxygen concentration in the first internal space 31 and the second internal space 32 before the temperature of the first detection electrode 42 decreases, particularly during the soak, can be reduced, so the oxidation amount of the first detection electrode 42 can be reduced. It can be effectively suppressed.

  In a gasoline engine having a variable valve mechanism, the variable valve mechanism is controlled so that the exhaust valve is opened during the compression stroke when the engine is stopped. Thereby, the amount of unburned gas contained in exhaust gas increases. These unburned gases combine with oxygen and burn in the exhaust system. For this reason, the oxygen concentration of the exhaust gas that reaches the gas concentration detection device 10 can be effectively reduced. Further, in the cylinder injection engine, by injecting the fuel in the exhaust stroke, the unburned gas contained in the exhaust gas can be increased, so that the same effect as the above variable valve control can be obtained.

  In the second embodiment described above, the “oxidation suppressing means” according to the twelfth aspect of the present invention is realized by the ECU 8 executing the heater control described above. Further, the “oxidation suppressing means” according to the thirteenth aspect of the present invention is realized by the ECU 8 performing the above-described air-fuel ratio control.

It is a figure for demonstrating the structure of the gas concentration detection apparatus 10 used in Embodiment 1 of this invention. It is a figure which shows the change of the oxygen pump cell output at the time of NOx sensor warming-up, and the change of NOx sensor cell output. It is a figure for demonstrating the method of specifying the inflection point of a NOx sensor cell output. It is a figure for demonstrating the relationship between the oxygen partial pressure around the 1st detection electrode 42 in a soak, and sensor output stabilization time. It is a figure for demonstrating the relationship between soak time and sensor output stabilization time. 4 is a map for specifying the oxidation state of the first detection electrode 42; 4 is a map for specifying the oxidation state of the first detection electrode 42; It is a figure for comparing the NOx density | concentration before correction | amendment with the NOx density | concentration after correction | amendment. 4 is a flowchart illustrating a routine that is executed by the ECU 8 in the first embodiment. 4 is a flowchart illustrating a routine that is executed by the ECU 8 in the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 NOx sensor 2 Oxygen pump cell 3 Spacer 4 NOx sensor cell 5 Spacer 6 Heater 7 Porous protective layer 8 ECU (Electronic Control Unit)
DESCRIPTION OF SYMBOLS 10 Gas concentration detection apparatus 21 and 41 Solid electrolyte body 22 1st pump electrode 23 2nd pump electrode 24 Pinhole 31 1st internal space 32 2nd internal space 33 Communication hole 42 1st detection electrode 43 2nd detection electrode 51 Atmospheric duct 61 Heater electrodes 62, 63 Insulating layer 81 Pump cell control means 82 Sensor cell control means 83 Heater control means K Correlation value N NOx sensor cell output Na NOx sensor cell output correction value Nb Sensor cell output (inflection point)
Np estimated NOx value (inflection point)
Nm output difference

Claims (14)

Surplus oxygen removing means for removing surplus oxygen in the gas to be measured;
A gas side electrode exposed to the gas to be measured after the excess oxygen is removed by the excess oxygen removing means, an atmosphere side electrode exposed to the atmosphere, and interposed between the gas side electrode and the atmosphere side electrode. A gas concentration detection cell having an electrolyte layer capable of transferring oxygen ions between the two,
A change amount calculating means for calculating a change amount of the cell output of the gas concentration detection cell every predetermined time;
During warm-up of the gas concentration detection cell, and during the execution of the excess oxygen removal means, timing the amount of change falls below the reference value (hereinafter, a first timing) and specific means that identifies a
Gas concentration detecting means for detecting the gas concentration of the specific gas component based on the cell output after the first time ;
Oxidation state estimation means for estimating an oxidation state of the gas side electrode;
Correction means for correcting the influence of oxygen reduced from the gas side electrode on the cell output based on the oxidation state;
A gas concentration detection device comprising: Gas concentration estimating means for estimating the gas concentration of the specific gas component based on the operating state of the internal combustion engine,
The correction means includes a gas concentration at the first time detected by the gas concentration detecting means (hereinafter referred to as a first detected concentration), a gas concentration at the first time estimated by the gas concentration estimating means ( The gas concentration detection device according to claim 1, wherein the cell output is corrected based on the first estimated concentration and the oxidation state. It said correction means, said first detection density and the first estimated concentration and the correction value calculating unit operable to calculate a correction value that reflects the influence of the elapsed time from the oxidation state and the first time to the deviation of The gas concentration detection device according to claim 2, wherein the cell output is corrected by subtracting the correction value from the cell output. 4. The gas concentration detection apparatus according to claim 3, wherein the correction value calculation means calculates the correction value to be smaller as the elapsed time is longer. 5. The gas concentration detection device according to claim 3, wherein the correction value calculation means calculates the correction value so that the higher the oxidation state, the larger the correction value. A stable time estimation means for estimating a time (hereinafter, a stable time) when the gas concentration detection cell detects a cell output in which the influence of oxidation of the gas side electrode is not superimposed;
Prohibiting means for prohibiting execution of the correcting means for the cell output at the stable time;
The gas concentration detection device according to claim 3, further comprising:   7. The gas concentration detection device according to claim 6, wherein the stable time estimating means estimates a time when the correction value is 0 or less as the stable time. The oxidation state estimation means estimates the oxidation state higher as the period from the start of energization to the gas concentration detection cell to the first time is longer. The gas concentration detection apparatus according to claim 1. Further comprising integrated value calculating means for calculating an integrated value of the cell output in a period from the start of energization to the gas concentration detection cell to the first time period,
9. The gas concentration detection device according to claim 1, wherein the oxidation state estimation unit estimates the oxidation state higher as the integrated value is larger.   The oxidation state estimation means includes air-fuel ratio acquisition means for acquiring the air-fuel ratio of the gas under measurement at the previous stop of the internal combustion engine, and the oxidation state is estimated to be higher as the air-fuel ratio is leaner. The gas concentration detection device according to claim 1, wherein the gas concentration detection device is a gas concentration detection device.   The oxidation state estimation means includes a leaving time acquisition means for acquiring a standing time from a previous stop of the internal combustion engine to a current start, and the oxidation state is estimated to be higher as the leaving time is longer. The gas concentration detection apparatus according to any one of claims 1 to 10.   The gas concentration detection device according to any one of claims 1 to 11, further comprising an oxidation suppression unit that suppresses oxidation of the gas side electrode while the internal combustion engine is stopped.   13. The gas concentration detection device according to claim 12, wherein the oxidation suppressing means controls the air-fuel ratio to be rich when the internal combustion engine is stopped.   14. The surplus oxygen removing means includes an oxygen pump cell, and discharges surplus oxygen in the gas to be measured as a voltage is applied to the oxygen pump cell. Gas concentration detector.

Images