JP5867357B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, which includes an exhaust gas purification catalyst for an internal combustion engine and an exhaust gas sensor installed downstream of the catalyst or in the middle of the catalyst.

In an exhaust gas purification system for an internal combustion engine, for example, as described in Patent Document 1 (Japanese Patent No. 3997599), an exhaust gas purification catalyst (for example, a three-way catalyst or a NO _x storage reduction catalyst) is provided in an exhaust pipe. ) And an exhaust gas sensor (air-fuel ratio sensor or oxygen sensor) for detecting the air-fuel ratio or rich / lean of the exhaust gas is installed upstream and downstream of the catalyst, and the air-fuel ratio is adjusted based on the output of the exhaust gas sensor. There is a type that improves the exhaust gas purification rate of the catalyst by feedback control.

  By the way, in exhaust gas sensors such as oxygen sensors, when the air-fuel ratio of exhaust gas changes between rich and lean, the actual situation is that the change in sensor output is delayed with respect to the actual change in air-fuel ratio, and the detection response There remains room for improvement in terms of sex.

  Therefore, for example, as described in Patent Document 2 (Japanese Patent Publication No. 8-20414), at least one auxiliary electrochemical cell is incorporated in a gas sensor such as an oxygen sensor, and the auxiliary electrochemical cell is incorporated into the gas sensor. By connecting to one of the electrodes and applying an applied current to the auxiliary electrochemical cell to perform ion pumping, the output characteristics of the gas sensor can be changed according to the applied current to improve detection response. There is something.

  Further, as described in Patent Document 3 (Japanese Patent Laid-Open No. 56-89051), a sensor element is configured by laminating a diaphragm layer, a reference electrode electron conduction layer, a solid electrolyte layer, and a measurement electrode electron conduction layer. In the oxygen sensor, oxygen ions are moved from the measurement electrode side to the reference electrode side by the current supplied from the DC power source, so that the oxygen partial pressure on the measurement electrode side is reduced to the oxygen in the exhaust gas (detected gas). There is also a system in which an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio can be detected by lowering the partial pressure [see FIG. 11 (a)].

Japanese Patent No. 3997599 Japanese Patent Publication No. 8-20414 JP 56-89051 A

  The air-fuel ratio of the exhaust gas flowing into the catalyst changes depending on the operating state of the internal combustion engine, and the air-fuel ratio of the exhaust gas downstream of the catalyst and in the catalyst also changes accordingly. However, since the exhaust gas purification system of Patent Document 1 does not have a function of changing the output characteristics of the exhaust gas sensor, the exhaust gas purification system is affected by a delay in sensor output change with respect to changes in the air-fuel ratio downstream of the catalyst or in the catalyst. As a result, the catalyst may not be used effectively, and exhaust emissions cannot be effectively reduced.

  Moreover, in the said patent document 2, although the technique which changes the output characteristic of a gas sensor is disclosed, in this technique, since it is necessary to incorporate an auxiliary electrochemical cell in the inside of a gas sensor, the auxiliary electrochemical cell is not provided. It is necessary to greatly change the sensor structure with respect to a general gas sensor, and in practical use, there are inconveniences such as a forced change in the design of the gas sensor and an increase in the manufacturing cost of the gas sensor.

Further, the technique of Patent Document 3 has the following problems.
The output E of the oxygen sensor can be expressed by the following basic equation (Nernst equation).
E = (R * T) / (4 * F) * ln (P1 / P2)
Here, R is a gas constant, T is an absolute temperature, F is a Faraday constant, P1 is an oxygen partial pressure on the atmosphere side (reference electrode side), and P2 is an oxygen partial pressure on the exhaust side (measurement electrode side).

  Therefore, in order to stabilize the output E of the oxygen sensor (to reduce variation in the output E), it is important to stabilize the oxygen partial pressure P1 on the reference electrode side by stabilizing the oxygen concentration on the reference electrode side. is there.

  However, the oxygen sensor of Patent Document 3 is configured so that the reference electrode side is not exposed to the atmosphere and oxygen is supplied from the measurement electrode side to the reference electrode side. As a result, the oxygen concentration on the reference electrode side may not be kept constant. For example, when an oxygen sensor is installed on the downstream side of the catalyst, the oxygen concentration of the exhaust gas detected by the oxygen sensor may be significantly reduced. In such a case, the oxygen concentration on the measurement electrode side is significantly reduced. There is a possibility that almost no oxygen can be supplied from the measurement electrode side to the reference electrode side, and the oxygen concentration on the reference electrode side cannot be kept constant [see FIG. 11B]. As a result, the output on the rich side of the oxygen sensor becomes unstable, and there is a problem that the detection accuracy of the oxygen sensor decreases.

  Further, the oxygen sensor of Patent Document 3 can shift the output characteristic line of the oxygen sensor to the lean side by flowing current so that oxygen is supplied from the measurement electrode side to the reference electrode side. Since the side is not exposed to the atmosphere and oxygen can hardly be supplied from the reference electrode side to the measurement electrode side, the output characteristic line of the oxygen sensor can hardly be shifted to the rich side [FIG. 11 (c). )reference].

  Therefore, an object of the present invention is to solve the above problems.

In order to solve the above problem, the invention according to claim 1 is a catalyst for purifying exhaust gas of an internal combustion engine (11) , wherein the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the catalyst is lean occluding NO _X in, NO _X occluding and reducing catalyst when the air-fuel ratio of the exhaust gas flowing into the catalyst a NO _X which is stored in the catalyst is reduced and purified to release when they become rich (19) If this _the NO _X storage reduction catalyst (19) disposed downstream or the _the NO _X storage reduction catalyst (19), the solid electrolyte body (32) is provided between the pair of sensor electrodes (33, 34) And an exhaust gas sensor (28) for detecting the concentration of a predetermined component in the exhaust gas by a sensor element (31) in which one of the pair of sensor electrodes (33, 34) is exposed to the atmosphere. In an internal combustion engine exhaust gas purification device equipped with A constant current supply means (27) for changing the output characteristics of the exhaust gas sensor (28) by passing a constant current between the sensor electrodes (33, 34) and a change request for changing the output characteristics of the exhaust gas sensor (28) or The direction of the constant current flowing between the sensor electrodes (33, 34) is determined according to the operating state of the internal combustion engine (11), and the constant current supply means (27) is controlled so that the constant current flows in the determined direction. Current control means (25), and the current control means (25) is a lean component of the exhaust gas sensor (28) during lean combustion control for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine (11) lean. The constant current supply means (27) is controlled so that the constant current flows in a direction to improve the detection response to the exhaust gas, and the exhaust gas is discharged during the rich combustion control in which the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine (11) is controlled to be rich. Gassen (28) is obtained by the configuration of controlling the constant current supplying means (27) so that a constant current flows in a direction to increase the detection responsiveness to rich components.

  In this configuration, the output characteristics of the exhaust gas sensor can be changed by causing a constant current to flow between the sensor electrodes by the constant current supply means. In this case, since it is not necessary to incorporate an auxiliary electrochemical cell or the like inside the exhaust gas sensor, the output characteristics of the exhaust gas sensor can be changed without causing a significant design change or cost increase of the exhaust gas sensor.

Further, the direction of the constant current flowing between the sensor electrodes is determined according to a change request for changing the output characteristics of the exhaust gas sensor or the operating state of the internal combustion engine, and a constant current supply means is provided so that the constant current flows in the determined direction. by controlling, by the operating state of the internal combustion engine NO _X storage reduction catalyst exhaust gas flowing into the state changes in the NO _X occluding and reducing catalyst downstream and NO of _X storage reduction catalyst the exhaust gas Even if the state changes, it is possible to improve the detection response by changing the output characteristics of the exhaust gas sensor accordingly. Utilization Thus, the _the NO _X storage reduction catalyst effectively without being much the delay effect of the sensor output change with respect to changes in the state of the exhaust gas on the downstream side and _the NO _X storage reduction type in the catalyst of the NO _X occluding and reducing catalyst Thus, exhaust emission can be effectively reduced.

In addition, since one sensor electrode (atmosphere side sensor electrode) is exposed to the atmosphere, the oxygen concentration on the atmosphere side sensor electrode side is always controlled regardless of the oxygen concentration on the other sensor electrode (exhaust side sensor electrode) side. constant even (if sometimes i.e. oxygen concentration of the exhaust gas detected by the exhaust gas sensor is significantly decreased) can be maintained (atmospheric equivalent), when installed the exhaust gas sensor downstream of the NO _X occluding and reducing catalyst The output of the exhaust gas sensor can be stabilized (variation in output can be reduced).

  Furthermore, by supplying an electric current so that oxygen is supplied from the exhaust side sensor electrode side to the atmosphere side sensor electrode side, the output characteristic line of the exhaust gas sensor can be shifted to the lean side, and the exhaust gas is discharged from the atmosphere side sensor electrode side. By flowing current so that oxygen is supplied to the side sensor electrode side, the output characteristic line of the exhaust gas sensor can be shifted to the rich side, and the output characteristic line of the exhaust gas sensor can be shifted to either the lean side or the rich side. There is also an advantage that can be shifted.

The present invention provides a system installed exhaust gas sensor on the downstream side or _the NO _X storage reduction catalyst of the NO _X occluding and reducing catalyst, the lean combustion control for controlling the air-fuel ratio of a mixture supplied to the internal combustion engine (11) to lean The constant current supply means (27) is controlled so that the constant current flows in a direction to increase the detection response to the lean component of the exhaust gas sensor (28), and the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine (11) is controlled. during the rich combustion control to control the rich so as to control the constant current supply means so constant current flows in a direction to increase the detection responsiveness to the rich component of the exhaust gas sensor (28) (27).

During lean combustion control, the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst becomes lean, and NO _X (lean component) in the exhaust gas is stored in the NO _X storage reduction catalyst. When _the NO _X storage amount of _X storage reduction catalyst increases, so NO _X in the exhaust gas is discharged to the downstream side of the NO _X storage reduction catalyst through the _the NO _X storage reduction catalyst. Thus, if to increase the lean responsiveness of the exhaust gas sensor during the lean combustion control (detection responsiveness to a lean component), an increasing number of _the NO _X storage amount of the NO _X occluding and reducing catalyst during the lean combustion control, when NO _X (the lean component) is ready to be discharged to the downstream side of the NO _X occluding and reducing catalyst, it is possible to detect at an early stage that state in the exhaust gas sensor. As a result, the lean combustion control can be stopped early when NO _X is discharged downstream of the NO _X storage reduction catalyst after the start of the lean combustion control, and the NO _X emission amount is reduced. Can be reduced.

During the rich combustion control is, NO _X occluding air-fuel ratio of the exhaust gas flowing into the catalytic reduction catalyst becomes rich, NO _X HC and CO (rich components of storage reduction catalyst NO _X which is stored in the in the exhaust gas ) by it is released is reduced and purified, _the NO _X storage reduction type when _the NO _X storage amount of the catalyst is reduced, _the NO _X storage reduction catalyst HC and CO in the exhaust gas passes through the _the NO _X storage reduction catalyst It is discharged to the downstream side. Thus, if to increase the rich responsiveness of the exhaust gas sensor during the rich combustion control (detection responsiveness to rich components), is less _the NO _X storage amount of the NO _X occluding and reducing catalyst during the rich combustion control, When HC and CO (rich components) are exhausted downstream of the NO _x storage reduction catalyst, the state can be detected early by the exhaust gas sensor. Thus, when the state in which HC and CO is discharged to the downstream side of the NO _X occluding and reducing catalyst after the start of the rich combustion control, it is possible to stop the rich combustion control early discharge of HC and CO The amount can be reduced.

FIG. 1 is a diagram showing a schematic configuration of an engine control system in Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing a cross-sectional configuration of the sensor element. FIG. 3 is an electromotive force characteristic diagram showing the relationship between the air-fuel ratio (excess air ratio λ) of exhaust gas and the electromotive force of the sensor element. FIG. 4 is a schematic view showing the state of gas components around the sensor element. FIG. 5 is a time chart for explaining the behavior of the sensor output. FIG. 6 is a schematic view showing the state of gas components around the sensor element. FIG. 7 is an output characteristic diagram of the oxygen sensor when the lean response / rich response is enhanced. FIG. 8 is a time chart for explaining an execution example of catalyst utilization control. FIG. 9 is a flowchart showing the flow of processing of the catalyst utilization control routine. FIG. 10 is a diagram for explaining the effect of the first embodiment. FIG. 11 is a diagram for explaining a problem of the prior art. FIG. 12 is a diagram showing a schematic configuration of an engine control system according to a second embodiment as a reference example related to the present invention . FIG. 13 is a flowchart showing the flow of processing of the sensor responsiveness control routine.

Hereinafter, an embodiment 2 of a reference example relating to the actual Example 1 and the present invention embodying the embodiments of the present invention.

A first embodiment of the present invention will be described with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.

  An intake pipe 12 of an engine 11 that is an internal combustion engine is provided with a throttle valve 13 whose opening is adjusted by a motor or the like, and a throttle opening sensor 14 that detects the opening (throttle opening) of the throttle valve 13. ing. Further, a fuel injection valve 15 that performs in-cylinder injection or intake port injection is attached to each cylinder of the engine 11, and a spark plug 16 is attached to the cylinder head of the engine 11 for each cylinder. The air-fuel mixture in the cylinder is ignited by the spark discharge of each spark plug 16.

On the other hand, the exhaust pipe 17 of the engine 11 is provided with a three-way catalyst 18 for purifying CO, HC, NO _{x and the} like in the exhaust gas, and the NO _x storage reduction catalyst 19 is provided downstream of the three-way catalyst 18. Is provided. This _the NO _X storage reduction catalyst 19, the air-fuel ratio of the exhaust gas flowing into the catalyst 19 occludes NO _X in the exhaust gas when the lean air-fuel ratio of the exhaust gas flowing into the catalyst 19 becomes rich Sometimes NO _x stored in the catalyst 19 is reduced and purified and released.

Further, exhaust gas sensors 20 and 21 for detecting the air-fuel ratio or rich / lean of the exhaust gas are installed on the upstream side and the downstream side of the three-way catalyst 18, respectively. As these exhaust gas sensors 20, 21, an air-fuel ratio sensor (linear A / F sensor) that outputs a linear air-fuel ratio signal corresponding to the air-fuel ratio of the exhaust gas, or the air-fuel ratio of the exhaust gas is richer than the stoichiometric air-fuel ratio. An oxygen sensor (O ₂ sensor) whose output voltage is inverted depending on whether it is lean or not is used. Further, an oxygen sensor 28 (O ₂ sensor) whose output voltage is inverted depending on whether the air-fuel ratio of the exhaust gas is rich or lean with respect to the stoichiometric air-fuel ratio is installed as an exhaust gas sensor on the downstream side of the NO _x storage reduction catalyst 19. Has been.

  In addition, this system includes a crank angle sensor 22 that outputs a pulse signal every time a crankshaft (not shown) of the engine 11 rotates by a predetermined crank angle, an air amount sensor 23 that detects an intake air amount of the engine 11, Various sensors such as a cooling water temperature sensor 24 for detecting the cooling water temperature of the engine 11 are provided. Based on the output signal of the crank angle sensor 22, the crank angle and the engine speed are detected.

  Outputs of these various sensors are input to an electronic control unit (hereinafter referred to as “ECU”) 25. The ECU 25 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium), so that the fuel injection amount and the ignition timing are determined according to the engine operating state. The throttle opening (intake air amount) and the like are controlled.

Next, the configuration of the oxygen sensor 28 will be described with reference to FIG.
The oxygen sensor 28 includes a sensor element 31 having a cup-shaped structure. In actuality, the sensor element 31 is configured so that the entire element is accommodated in a housing or an element cover (not shown). Arranged in the tube 17.

In the sensor element 31, the solid electrolyte layer 32 (solid electrolyte body) is formed in a cup shape in cross section, an exhaust side electrode layer 33 is provided on the outer surface, and an air side electrode layer 34 is provided on the inner surface. It has been. The solid electrolyte layer 32 is made of an oxygen ion conductive oxide that is formed by dissolving CaO, MgO, Y ₂ O ₃ , Yb ₂ O ₃ or the like as a stabilizer in ZrO ₂ , HfO ₂ , ThO ₂ , Bi ₂ O ₃ or the like. Consists of union. Each of the electrode layers 33 and 34 is made of a noble metal having high catalytic activity such as platinum, and the surface thereof is subjected to porous chemical plating or the like. These electrode layers 33 and 34 form a pair of counter electrodes (sensor electrodes). An internal space surrounded by the solid electrolyte layer 32 is an atmospheric chamber 35, and a heater 36 is accommodated in the atmospheric chamber 35. The heater 36 has a heat generation capacity sufficient to activate the sensor element 31, and the entire sensor element 31 is heated by the heat generation energy. The activation temperature of the oxygen sensor 28 is, for example, about 350 to 400 ° C. The atmosphere chamber 35 is maintained at a predetermined oxygen concentration by introducing the atmosphere, and the atmosphere-side electrode layer 34 is exposed to the atmosphere in the atmosphere chamber 35.

  In the sensor element 31, the outside of the solid electrolyte layer 32 (electrode layer 33 side) is an exhaust atmosphere, and the inside of the solid electrolyte layer 32 (electrode layer 34 side) is an air atmosphere. An electromotive force is generated between the electrode layers 33 and 34 in accordance with the difference in partial pressure. That is, the sensor element 31 generates different electromotive force depending on whether the air-fuel ratio is rich or lean. Thereby, the oxygen sensor 28 outputs an electromotive force signal corresponding to the oxygen concentration (that is, the air-fuel ratio) of the exhaust gas.

  As shown in FIG. 3, the sensor element 31 generates an electromotive force that varies depending on whether the air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio (excess air ratio λ = 1). 1) It has a characteristic that the electromotive force changes suddenly in the vicinity. Specifically, the sensor electromotive force when the fuel is rich is about 0.9V, and the sensor electromotive force when the fuel is lean is about 0V.

  As shown in FIG. 2, the exhaust-side electrode layer 33 of the sensor element 31 is grounded, and the microcomputer 26 is connected to the atmosphere-side electrode layer 34. When an electromotive force is generated in the sensor element 31 according to the air-fuel ratio (oxygen concentration) of the exhaust gas, a sensor detection signal corresponding to the electromotive force is output to the microcomputer 26. The microcomputer 26 is provided in the ECU 25, for example, and calculates the air-fuel ratio based on the sensor detection signal. The microcomputer 26 may calculate the engine rotation speed and the intake air amount based on the detection results of the various sensors described above.

By the way, when the engine 11 is operated, the actual air-fuel ratio of the exhaust gas changes sequentially, and may change repeatedly, for example, between rich and lean. When the actual air-fuel ratio changes, if the detection response of the oxygen sensor 28 is low, there is a concern that the engine performance may be affected. For example, when the engine 11 is operating at a high load, the amount of NO _x in the exhaust gas increases more than intended.

The detection response of the oxygen sensor 28 when the actual air-fuel ratio changes between rich and lean will be described. When the actual air-fuel ratio (the actual air-fuel ratio downstream of the NO _x storage reduction catalyst 19) changes in rich / lean in the exhaust gas discharged from the engine 11, the component composition of the exhaust gas changes. At this time, due to the residual exhaust gas component immediately before the change, the change in the output of the oxygen sensor 28 relative to the air-fuel ratio after the change (that is, the response of the sensor output) is delayed. Specifically, at the time of the change from rich to lean, as shown in FIG. 4 (a), immediately after the lean change, HC or the like, which is a rich component, remains in the vicinity of the exhaust-side electrode layer 33. the reaction of the lean component of the electrode (NO _X, etc.) is prevented. As a result, the responsiveness of the lean output as the oxygen sensor 28 decreases. Further, at the time of the change from lean to rich, as shown in FIG. 4B, immediately after the rich change, NO _x or the like that is a lean component remains in the vicinity of the exhaust-side electrode layer 33, and this lean component causes the sensor electrode to Reaction of the rich component (HC, etc.) As a result, the responsiveness of rich output as the oxygen sensor 28 decreases.

  The output change of the oxygen sensor 28 will be described with reference to the time chart of FIG. In FIG. 5, when the actual air-fuel ratio changes between rich and lean, the sensor output (the output of the oxygen sensor 28) changes between the rich gas detection value (0.9 V) and the lean gas detection value (0 V) according to the change in the actual air-fuel ratio. Change. However, in this case, the sensor output changes with a delay with respect to the change in the actual air-fuel ratio. In FIG. 5, the sensor output changes with a delay of TD1 with respect to the change of the actual air-fuel ratio when changing from rich to lean, and the sensor output is delayed with respect to the change of the actual air-fuel ratio when changing from lean to rich. It has come to change.

  Therefore, in the first embodiment, as shown in FIG. 2, a constant current circuit 27 as a constant current supply means is connected to the atmosphere side electrode layer 34, and the constant current Ics supplied by the constant current circuit 27 is supplied by the microcomputer 26. By controlling the current to flow between the pair of sensor electrodes (between the exhaust-side electrode layer 33 and the atmosphere-side electrode layer 34) in a predetermined direction, the output characteristics of the oxygen sensor 28 are changed to change the detection response. I try to let them. In this case, the microcomputer 26 sets the direction and amount of the constant current Ics flowing between the pair of sensor electrodes, and controls the constant current circuit 27 so that the set constant current Ics flows.

  Specifically, the constant current circuit 27 supplies the constant current Ics to the atmosphere-side electrode layer 34 in either the forward or reverse direction, and the constant current amount can be variably adjusted. That is, the microcomputer 26 variably controls the constant current Ics by PWM control. In this case, in the constant current circuit 27, the constant current Ics is adjusted in accordance with the duty signal output from the microcomputer 26, and the constant current Ics whose current amount is adjusted is provided between the sensor electrodes (the exhaust side electrode layer 33 and the atmosphere side electrode). (Between the layers 34).

  In this embodiment, the constant current Ics that flows in the direction from the exhaust side electrode layer 33 to the atmosphere side electrode layer 34 is a negative constant current (−Ics), and the constant current Ics flows in the direction from the atmosphere side electrode layer 34 to the exhaust side electrode layer 33. The constant current Ics is a positive constant current (+ Ics).

For example, in order to increase the detection response (lean sensitivity) at the time of change from rich to lean, as shown in FIG. 6A, the atmosphere side electrode layer 34 through the exhaust side electrode layer 33 through the solid electrolyte layer 32. A constant current Ics (negative constant current Ics) is supplied so that oxygen is supplied to. In this case, by supplying oxygen from the atmosphere side to the exhaust side, the oxidation reaction is promoted with respect to the rich component (HC) existing (residual) around the exhaust side electrode layer 33, and accordingly, the rich component is promptly removed. Can be removed. As a result, the lean component (NO _x ) easily reacts in the exhaust-side electrode layer 33, and as a result, the response of the lean output of the oxygen sensor 28 is improved.

Further, in the case where the detection responsiveness (rich sensitivity) at the time of change from lean to rich is increased, as shown in FIG. 6B, the exhaust-side electrode layer 33 through the atmosphere-side electrode layer 34 through the solid electrolyte layer 32. Is supplied with a constant current Ics (positive constant current Ics). In this case, by supplying oxygen from the exhaust side to the atmosphere side, the reduction reaction is promoted with respect to the lean component (NO _x ) existing (residual) around the exhaust side electrode layer 33, and accordingly, the lean component is reduced. It can be removed quickly. As a result, the rich component (HC) easily reacts in the exhaust-side electrode layer 33, and as a result, the responsiveness of the rich output of the oxygen sensor 28 is improved.

  FIG. 7 is a diagram showing output characteristics (electromotive force characteristics) of the oxygen sensor 28 when increasing the detection responsiveness (lean sensitivity) at the time of lean change and when increasing the detection responsiveness (rich sensitivity) at the time of rich change. is there.

  In the case of increasing the detection responsiveness (lean sensitivity) at the time of lean change, the negative constant current Ics is set so that oxygen is supplied from the atmosphere-side electrode layer 34 to the exhaust-side electrode layer 33 through the solid electrolyte layer 32 as described above. When the current flows (see FIG. 6A), as shown in FIG. 7A, the output characteristic line shifts to the rich side (more specifically, shifts to the rich side and the electromotive force decreasing side). In this case, the sensor output becomes a lean output even if the actual air-fuel ratio is in the rich region near the stoichiometric range. This means that the detection response (lean sensitivity) at the time of a lean change is enhanced as the output characteristic of the oxygen sensor 28.

  Further, in the case where the detection responsiveness (rich sensitivity) at the time of rich change is enhanced, a positive constant current is supplied so that oxygen is supplied from the exhaust-side electrode layer 33 to the atmosphere-side electrode layer 34 through the solid electrolyte layer 32 as described above. When Ics flows (see FIG. 6B), the output characteristic line shifts to the lean side (more specifically, to the lean side and the electromotive force increasing side, as shown in FIG. 7B). ). In this case, the sensor output becomes a rich output even if the actual air-fuel ratio is in the lean region near the stoichiometric range. This means that the detection response at the time of rich change (rich sensitivity) is enhanced as the output characteristic of the oxygen sensor 28.

In the first embodiment, the ECU 25 (or the microcomputer 26) executes a catalyst utilization control routine of FIG. 9 to be described later, so that the sensor electrodes (exhaust-side electrode layer 33 and atmosphere-side electrode layer) are arranged according to the operating state of the engine 11. The constant current circuit 27 is controlled so that the constant current Ics flows in the determined direction. Accordingly, even after changing the state of the exhaust gas downstream of the NO _X storage reduction state of the exhaust gas flowing into the catalyst 19 changes _the NO _X storage reduction catalyst 19 by operating conditions of the engine 11, accordingly Thus, the output response of the oxygen sensor 28 can be changed to improve the detection response.

Specifically, as shown in the time chart of FIG. 8, when a predetermined lean operation execution condition is satisfied during engine operation, the air-fuel ratio of the air-fuel mixture supplied to the engine 11 is set to the stoichiometric air-fuel ratio (λ = 1). ) To perform lean combustion control for lean combustion by controlling leaner than. During the lean combustion control, NO _x (lean component) is discharged downstream of the NO _x storage reduction catalyst 28 at time t1 when the output of the oxygen sensor 28 becomes a predetermined lean determination threshold value (eg, 0.45 V) or less. When it is determined that the combustion has started, the lean combustion control is stopped, and the rich combustion control for rich combustion is performed by controlling the air-fuel ratio of the air-fuel mixture supplied to the engine 11 to be richer than the theoretical air-fuel ratio (λ = 1). . During the rich combustion control, at the time t2 when the output of the oxygen sensor 28 becomes equal to or higher than a predetermined rich determination threshold value (for example, 0.45 V), HC and CO (rich components) are present downstream of the NO _x storage reduction catalyst 28. It is determined that the exhaust has started, rich combustion control is stopped, and lean combustion control is executed. In this way, lean combustion control and rich combustion control are executed alternately.

  At that time, during the lean combustion control, the constant current circuit 27 is controlled so that the constant current Ics flows in a direction in which the lean sensitivity of the oxygen sensor 28 is increased to increase the lean response (detection response to the lean component). In this case, the constant current circuit 27 is controlled so that the constant current Ics (negative constant current Ics) flows in a direction in which oxygen is supplied from the atmosphere-side electrode layer 34 to the exhaust-side electrode layer 33. On the other hand, during the rich combustion control, the constant current circuit 27 is controlled so that the constant current Ics flows in a direction in which the rich sensitivity of the oxygen sensor 28 is increased to increase the rich response (detection response to the rich component). In this case, the constant current circuit 27 is controlled so that the constant current Ics (positive constant current Ics) flows in the direction in which oxygen is supplied from the exhaust side electrode layer 33 to the atmosphere side electrode layer 34.

During lean combustion control, the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst 19 becomes lean, and NO _X (lean component) in the exhaust gas is stored in the NO _X storage reduction catalyst 19. When _the NO _X storage amount of the NO _X occluding and reducing catalyst 19 is increased, so that NO _X in the exhaust gas is discharged to the downstream side of the NO _X occluding and reducing catalyst 19 through the _the NO _X storage reduction catalyst 19 become. Therefore, if the lean response of the oxygen sensor 28 (detection response to the lean component) is increased during the lean combustion control, the NO _X storage amount of the NO _X storage reduction catalyst 19 increases during the lean combustion control. Thus, when the NO _X (lean component) is discharged downstream of the NO _X storage reduction catalyst 19, the state can be detected early by the oxygen sensor 28. As a result, the lean combustion control can be stopped at an early stage when NO _X is exhausted downstream of the NO _X storage reduction catalyst 19 after the start of the lean combustion control. compared to a system that does not have a function of changing the (see a broken line in FIG. 8), it is possible to reduce the emissions of nO _X.

On the other hand, during the rich combustion control is, NO _X air-fuel ratio of the exhaust gas flowing into the occlusion-reduction catalyst 19 becomes rich, Ya _the NO _X storage reduction type HC of the NO _X which the catalyst 19 has been occluded in the exhaust gas Although it is reduced and purified by CO (rich component) and released, when the NO _X storage amount of the NO _X storage reduction catalyst 19 decreases, HC and CO in the exhaust gas pass through the NO _X storage reduction catalyst 19. The NO _x storage reduction catalyst 19 is discharged downstream. Thus, if to increase the rich responsiveness of the oxygen sensor 28 during the rich combustion control (detection responsiveness to rich components), _the NO _X storage amount of the NO _X storage reduction catalyst 19 during the rich combustion control is getting low Thus, when HC and CO (rich components) are exhausted downstream of the NO _x storage reduction catalyst 19, the state can be detected early by the oxygen sensor 28. As a result, the rich combustion control can be stopped at an early stage when HC and CO are discharged downstream of the NO _x storage reduction catalyst 19 after the rich combustion control is started. Compared with a system that does not have a function of changing characteristics (see the broken line in FIG. 8), the amount of HC and CO emissions can be reduced.

  Hereinafter, the processing content of the catalyst utilization control routine of FIG. 9 executed by the ECU 25 (or the microcomputer 26) in the first embodiment will be described.

  The catalyst utilization control routine shown in FIG. 9 is repeatedly executed at a predetermined cycle during the power-on period of the ECU 25, and serves as current control means in the claims. When this routine is started, first, at step 101, it is determined whether a lean operation execution condition is satisfied. Here, the lean operation execution condition is to satisfy all of the following conditions (1) to (3), for example.

(1) The cooling water temperature of the engine 11 is equal to or higher than a predetermined temperature.
(2) The NO _X storage reduction catalyst 19 is in an active state (for example, the estimated temperature or the detected temperature of the catalyst 19 is equal to or higher than the active temperature, or the elapsed time after engine start is equal to or longer than a predetermined time. about)
(3) There is no abnormality in each part of the system (for example, fuel system and exhaust system)

  If all the conditions (1) to (3) are satisfied, the lean operation execution condition is satisfied. If any one of the conditions (1) to (3) is not satisfied, the lean operation execution condition is satisfied. The operation execution condition is not satisfied.

  If it is determined in step 101 that the lean operation execution condition is satisfied, the processes of steps 102 to 108 are repeatedly executed. First, the routine proceeds to step 102, where lean combustion control is performed in which lean combustion is performed by controlling the air-fuel ratio of the air-fuel mixture supplied to the engine 11 to be leaner than the stoichiometric air-fuel ratio (λ = 1).

  Thereafter, the routine proceeds to step 103, and during the lean combustion control, the constant current circuit 27 is controlled so that the constant current Ics flows in a direction to improve the lean responsiveness of the oxygen sensor 28. That is, the constant current circuit 27 is controlled so that the constant current Ics (negative constant current Ics) flows in a direction in which oxygen is supplied from the atmosphere-side electrode layer 34 to the exhaust-side electrode layer 33. Thereby, the lean responsiveness of the oxygen sensor 28 is enhanced.

  Thereafter, the process proceeds to step 104, where it is determined whether or not the output of the oxygen sensor 28 is equal to or lower than the lean determination threshold (for example, 0.45V), and it is determined that the output of the oxygen sensor 28 is higher than the lean determination threshold. Therefore, the process returns to step 102, and the lean combustion control is continued and the control for increasing the lean responsiveness of the oxygen sensor 28 is continued (steps 102 and 103).

Thereafter, when it is determined in step 104 that the output of the oxygen sensor 28 is equal to or less than the lean determination threshold value, it is determined that NO _X (lean component) has started to be discharged to the downstream side of the NO _X storage reduction catalyst 19. Then, the routine proceeds to step 105, where the lean combustion control is stopped, and the rich combustion control for performing rich combustion by controlling the air-fuel ratio of the air-fuel mixture supplied to the engine 11 to be richer than the theoretical air-fuel ratio (λ = 1) is executed. .

  Thereafter, the routine proceeds to step 106, and during the rich combustion control, the constant current circuit 27 is controlled so that the constant current Ics flows in a direction to improve the rich response of the oxygen sensor 28. That is, the constant current circuit 27 is controlled so that the constant current Ics (positive constant current Ics) flows in the direction in which oxygen is supplied from the exhaust side electrode layer 33 to the atmosphere side electrode layer 34. Thereby, the rich responsiveness of the oxygen sensor 28 is improved.

  Thereafter, the process proceeds to step 107, and when it is determined that the output of the oxygen sensor 28 is lower than the rich determination threshold depending on whether the output of the oxygen sensor 28 is equal to or higher than the rich determination threshold (eg, 0.45V). Returning to step 105, the rich combustion control is continued, and the control for increasing the rich response of the oxygen sensor 28 is continued (steps 105, 106).

Thereafter, when it is determined in step 107 that the output of the oxygen sensor 28 is greater than or equal to the rich determination threshold value, it is determined that HC and CO (rich components) have started to be discharged downstream of the NO _x storage reduction catalyst 19. Then, the process proceeds to step 108 and the rich combustion control is stopped.

  On the other hand, if it is determined in step 101 that the lean operation execution condition is not satisfied, the routine proceeds to step 109 where the air-fuel ratio of the air-fuel mixture supplied to the engine 11 is controlled to the stoichiometric air-fuel ratio (stoichiometric). Execute stoichiometric combustion control for burning. Thereafter, the process proceeds to step 110, and a control that does not change the detection response of the oxygen sensor 28 with respect to the reference response, that is, a control for setting the constant current Ics = 0 is performed.

In the first embodiment described above, in the system in which the oxygen sensor 28 is installed on the downstream side of the NO _x storage reduction catalyst 19, a constant current is caused to flow between the sensor electrodes by the constant current circuit 27 provided outside the oxygen sensor 28. As a result, the output characteristics of the oxygen sensor 28 can be changed on-board to improve lean responsiveness and rich responsiveness. In addition, since it is not necessary to incorporate an auxiliary electrochemical cell or the like in the oxygen sensor 28, the output characteristics of the oxygen sensor 28 can be changed without causing a significant design change or cost increase.

Further, during the lean combustion control, the constant current circuit 27 is controlled so that the constant current Ics flows in the direction of increasing the lean responsiveness of the oxygen sensor 28, so that the downstream side of the NO _X storage reduction catalyst 19 is provided. When the NO _x (lean component) is discharged, the state is detected early by the oxygen sensor 28, and the lean combustion control can be stopped early, thereby reducing the amount of NO _x discharged. be able to. On the other hand, during the rich combustion control, the constant current circuit 27 is controlled so that the constant current Ics flows in a direction in which the rich response of the oxygen sensor 28 is increased, so that the downstream side of the NO _X storage reduction catalyst 19 is controlled. When HC and CO (rich components) are exhausted, the state can be detected early by the oxygen sensor 28, and rich combustion control can be stopped early, and the HC and CO emissions can be reduced. Can be reduced. As a result, the NO _X storage reduction catalyst 19 can be effectively used without being affected by the delay of the sensor output change with respect to the change in the exhaust gas state downstream of the NO _X storage reduction catalyst 19. Exhaust emissions can be effectively reduced.

Incidentally, the output E of the oxygen sensor 28 can be expressed by the following basic equation (Nernst equation).
E = (R * T) / (4 * F) * ln (P1 / P2)
Here, R is a gas constant, T is an absolute temperature, F is a Faraday constant, P1 is an oxygen partial pressure on the atmosphere side electrode layer 34 side, and P2 is an oxygen partial pressure on the exhaust side electrode layer 33 side.

  Therefore, in order to stabilize the output E of the oxygen sensor 28 (to reduce the variation in the output E), the oxygen concentration on the atmosphere side electrode layer 34 side is stabilized and the oxygen partial pressure P1 on the atmosphere side electrode layer 34 side is set. It is important to stabilize.

  In that respect, as shown in FIG. 10, the oxygen sensor 28 of the first embodiment has the atmosphere side electrode layer 34 exposed to the atmosphere, so that the oxygen side is not affected by the oxygen concentration on the exhaust side electrode layer 33 side. The oxygen concentration on the electrode layer 34 side can always be kept constant (equivalent to the atmosphere), and when the oxygen sensor 28 is installed on the downstream side of the catalyst 19 (that is, the oxygen concentration of the exhaust gas detected by the oxygen sensor 28 is significantly reduced). Even in such a case, the output of the oxygen sensor 28 can be stabilized (variation in output can be reduced).

  Furthermore, by supplying a current so as to supply oxygen from the exhaust side electrode layer 33 side to the atmosphere side electrode layer 34 side, the output characteristic line of the oxygen sensor 28 can be shifted to the lean side, and the atmosphere side electrode layer By flowing current so as to supply oxygen from the 34 side to the exhaust side electrode layer 33 side, the output characteristic line of the oxygen sensor 28 can be shifted to the rich side, and the output characteristic line of the oxygen sensor 28 is set to the lean side. There is also an advantage that it can be shifted in any direction on the rich side.

In the first embodiment, a configuration was installed oxygen sensor 28 on the downstream side of the NO _X occluding and reducing catalyst 19, the position in of the NO _X occluding and reducing catalyst 19 (for example, the catalyst 19 inlet and outlet A configuration may be adopted in which the oxygen sensor 28 is installed at an intermediate position.

Next, a second embodiment as a reference example related to the present invention will be described with reference to FIGS. However, description of substantially the same parts as those in the first embodiment will be omitted or simplified, and different parts from the first embodiment will be mainly described.

In the second embodiment, as shown in FIG. 12, a three-way catalyst 37 for purifying CO, HC, NO _{x and the} like in the exhaust gas is also provided on the downstream side of the three-way catalyst 18. Further, an exhaust gas sensor 20 (air-fuel ratio sensor or oxygen sensor) for detecting the air-fuel ratio or rich / lean of the exhaust gas is installed on the upstream side of the three-way catalyst 18, and downstream of the three-way catalyst 18 (the three-way catalyst 18). And the three-way catalyst 37) is provided with an oxygen sensor 28 whose output voltage is inverted depending on whether the air-fuel ratio of the exhaust gas is rich or lean with respect to the stoichiometric air-fuel ratio.

  Furthermore, in the second embodiment, a sensor responsiveness control routine of FIG. 13 described later is executed by the ECU 25 (or the microcomputer 26).

  The sensor responsiveness control routine shown in FIG. 13 is repeatedly executed at a predetermined cycle during the power-on period of the ECU 25. In this routine, in steps 201 to 203, it is determined whether or not there is a change request for changing the detection responsiveness of the oxygen sensor 28. In steps 204 to 207, constant current control is performed based on the determination result of the change request. Thus, the detection responsiveness of the oxygen sensor 28 is changed.

  When this routine is started, first, at step 201, it is determined whether or not the engine 11 is in a cold state at the time of starting, for example, one of the following conditions (1) to (3): Judgment is made according to whether or not one is satisfied.

(1) The coolant temperature of the engine 11 is below a predetermined temperature.
(2) The oil temperature (lubricating oil temperature) of the engine 11 is below a predetermined temperature.
(3) The fuel temperature in the fuel path is below the specified temperature.

  If it is determined in step 201 that the engine 11 is in the cold state, it is determined that there is a change request for increasing the rich responsiveness (detection responsiveness at the time of rich change). In this case, the process proceeds to step 204, and the supply of the constant current Ics is controlled based on the change request for increasing the rich responsiveness. Specifically, “positive constant current Ics” is set as the constant current of the constant current circuit 27. At this time, the constant current circuit 27 is controlled by the microcomputer 26, and the constant current Ics (positive constant current Ics) flows in the direction in which oxygen is supplied from the exhaust side electrode layer 33 to the atmosphere side electrode layer 34. Thereby, when the engine 11 is in a cold state, the rich responsiveness of the oxygen sensor 28 is enhanced. Note that the constant current amount is preferably a predetermined value.

  On the other hand, when it is determined in step 201 that the engine 11 is not in the cold state, the process proceeds to step 202 to determine whether or not the engine 11 is in the high load operation state, for example, the following (4) Judgment is made based on whether any one of the conditions (6) to (6) is satisfied.

(4) The amount of air charged into the cylinder is greater than or equal to the specified amount
(5) Combustion pressure in the cylinder is above a specified value
(6) The accelerator opening must be greater than or equal to the specified value.

  If it is determined in step 202 that the engine 11 is in a high-load operation state, it is determined that there is a change request for improving lean responsiveness (detection responsiveness at the time of lean change). In this case, the process proceeds to step 205, and the supply of the constant current Ics is controlled based on the change request for improving the lean responsiveness. Specifically, “negative constant current Ics” is set as the constant current of the constant current circuit 27. At this time, the constant current circuit 27 is controlled by the microcomputer 26, and the constant current Ics (negative constant current Ics) flows in the direction in which oxygen is supplied from the atmosphere side electrode layer 34 to the exhaust side electrode layer 33. Thereby, when the engine 11 is in a high load operation state, the lean responsiveness of the oxygen sensor 28 is enhanced. Note that the constant current amount is preferably a predetermined value.

  Here, assuming the above-described high load operation, the high load operation period includes a transient time when the engine load changes to an increasing side and a high load steady time when the load increases due to the load increase. It is. In this case, both the transient response and the high load steady state can improve the lean response, but in order to increase the detection response, the response level required as the detection response is required for the transient and high load steady state. It is better to make them different.

Specifically, the response level at the time of transition is set to be higher than the response level at the time of steady high load. That is, when it is determined that the engine 11 is in a high load operation state, it is further determined whether the engine 11 is in a transient state or a high load steady state. It is determined to be the transient, even while increasing lean responsiveness, it is determined that the response level relatively large Kusuru change request (high load constant magnitude than during Kusuru) there in particular equivalent, it is determined that the high load steady state, while increasing lean responsiveness, there is a change request of the relatively small Kusuru the response level (Kusuru smaller than the transient) Is equivalent to being determined. Then, the supply of the constant current Ics is controlled based on the change request in each of the transition time and the high load steady time.

On the other hand, at step 202, if the engine 11 is determined not to be high-load operation state, the process proceeds to a step 203, the present time is a just return to the fuel injected from the fuel cut, the both catalysts 18, 37 It is determined whether or not rich injection control for neutralization is being performed. In this rich injection control, when the engine 11 returns from the fuel cut, based on the detection result of the oxygen sensor 28, the air-fuel ratio is adjusted so as to eliminate the excessive oxygen state (extremely lean atmosphere) of the two catalysts 18, 37. This is air-fuel ratio control that is temporarily enriched. In this rich injection control, the atmosphere of both the catalysts 18 and 37 is neutralized (the state is maintained near the stoichiometric state) by enriching the fuel injection amount. Then, at the timing when the output of the oxygen sensor 28 shifts from the lean value to the rich value after returning from the fuel cut, the rich injection control is terminated. In this embodiment, when this rich injection control is performed, the detection responsiveness at the time of rich change is lowered.

  If it is determined in step 203 that the rich injection control is being performed, it is determined that there is a change request for reducing the rich responsiveness (detection responsiveness at the time of rich change). In this case, the process proceeds to step 206, and the supply of the constant current Ics is controlled based on the change request for reducing the rich responsiveness. Specifically, “negative constant current Ics” is set as the constant current of the constant current circuit 27 (the same as the case where the lean responsiveness is enhanced). At this time, the constant current circuit 27 is controlled by the microcomputer 26, and the constant current Ics (negative constant current Ics) flows in the direction in which oxygen is supplied from the atmosphere side electrode layer 34 to the exhaust side electrode layer 33. Thereby, the rich responsiveness is lowered when the rich injection control is performed. Note that the constant current amount is preferably a predetermined value.

  If all the determinations in steps 201 to 203 are “No”, the process proceeds to step 207, in which the detection responsiveness of the oxygen sensor 28 is not changed with respect to the reference responsiveness, that is, the constant current Ics = 0. Implement control.

  In the routine of FIG. 13, processing for increasing the rich response of the oxygen sensor 28 when the engine 11 is cold (steps 201 and 204), and lean of the oxygen sensor 28 when the engine 11 is in a high load operation state. The process of increasing the responsiveness (steps 202 and 205) and the process of reducing the rich responsiveness of the oxygen sensor 28 when the rich injection control is performed (steps 203 and 206) are all performed. It is not limited and you may make it implement any one or two.

  In the second embodiment described above, in the system in which the oxygen sensor 28 is installed on the downstream side of the three-way catalyst 18, it is determined whether there is a change request for changing the detection responsiveness of the oxygen sensor 28, and the change request is determined. Since the constant current control is performed based on the result and the detection responsiveness of the oxygen sensor 28 is changed, the three-way catalyst 18 can be effectively used to reduce the exhaust emission.

  In the second embodiment, the oxygen sensor 28 is installed on the downstream side of the three-way catalyst 18, but the oxygen sensor is located at a position in the three-way catalyst 18 (for example, an intermediate position between the inlet and the outlet of the catalyst 18). It is good also as a structure which installed 28.

  In the first and second embodiments, the constant current circuit 27 is connected to the atmosphere-side electrode layer 34 of the oxygen sensor 28 (sensor element 31). However, the present invention is not limited to this. For example, the oxygen sensor 28 ( The constant current circuit 27 may be connected to the exhaust side electrode layer 33 of the sensor element 31), or the constant current circuit 27 may be connected to both the exhaust side electrode layer 33 and the atmosphere side electrode layer 34. .

  In each of the first and second embodiments, the present invention is applied to a system using the oxygen sensor 28 having the sensor element 31 having a cup-type structure. However, the present invention is not limited to this. You may apply this invention to the system using the oxygen sensor which has.

Further, the present invention is not limited to an oxygen sensor. For example, other than an oxygen sensor such as an air-fuel ratio sensor that outputs a linear air-fuel ratio signal corresponding to an air-fuel ratio, an HC sensor that detects HC concentration, or an NO _X sensor that detects NO _X concentration. The present invention may be applied to this gas sensor.

11 ... engine (internal combustion engine), 17 ... exhaust pipe, 18 ... three-way catalyst, 19 ... NO _X storage reduction catalyst, 25 ... ECU (current control means), 26 ... microcomputer, 27 ... constant current circuit (constant current supply Means), 28 ... oxygen sensor (exhaust gas sensor), 31 ... sensor element, 32 ... solid electrolyte layer (solid electrolyte body), 33 ... exhaust side electrode layer (sensor electrode), 34 ... atmosphere side electrode layer (sensor electrode), 37. Three-way catalyst

Claims (1)

A catalyst for purifying exhaust gas of an internal combustion engine (11), which stores NO _x in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the catalyst is lean , and generates exhaust gas flowing into the catalyst and the air-fuel ratio is the NO _X which is stored in the catalyst is reduced and purified to release when they become rich _the NO _X storage reduction catalyst (19), downstream of the _the NO _X storage reduction catalyst (19) or The NO _x storage-reduction catalyst (19 ) is provided, and a solid electrolyte body (32) is provided between the pair of sensor electrodes (33, 34) and one of the pair of sensor electrodes (33, 34). In an exhaust gas purifying apparatus for an internal combustion engine, comprising an exhaust gas sensor (28) for detecting a concentration of a predetermined component in the exhaust gas by a sensor element (31) having a sensor electrode (34) exposed to the atmosphere.
Constant current supply means (27) for changing the output characteristics of the exhaust gas sensor (28) by passing a constant current between the sensor electrodes (33, 34);
The direction of the constant current flowing between the sensor electrodes (33, 34) is determined according to a change request for changing the output characteristics of the exhaust gas sensor (28) or the operating state of the internal combustion engine (11), and the determined direction Current control means (25) for controlling the constant current supply means (27) so that the constant current flows in
The current control means (25) increases the detection responsiveness to the lean component of the exhaust gas sensor (28) during the lean combustion control for leanly controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine (11). The exhaust gas sensor (28) is controlled during the rich combustion control in which the constant current supply means (27) is controlled so that the constant current flows through the exhaust gas and the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine (11) is controlled to be rich. The exhaust gas purifying device for an internal combustion engine , wherein the constant current supply means (27) is controlled so that the constant current flows in a direction to improve the detection responsiveness to the rich component .

Images