JP2007198288A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain exhaust control performance by an air-fuel ratio controller of an internal combustion engine even if fuel with a high sulfur content is used. <P>SOLUTION: The controller has a three-way conversion catalyst including a primary catalyst (noble metel) and an auxiliary catalyst. The auxiliary catalyst is judged to be deteriorated when all the conditions of (maximum oxygen occlusion value Cmax)<(threshold value), (travel distance)<(threshold value) and no thermal deterioration influence history are judged to be established (Step 100). If such a judgment is made, the controller shifts the center of target air-fuel ratio control to a lean-side value in relation to the stoichiometry in order to restrict the air-fuel ratio control toward the rich side (Step 102). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio control apparatus suitable as an apparatus for controlling an internal combustion engine having a three-way catalyst in an exhaust passage.

  Conventionally, for example, Patent Literature 1 discloses an air-fuel ratio control apparatus for an internal combustion engine. This conventional apparatus detects a decrease (deterioration) in oxygen storage capacity due to sulfur poisoning of a catalyst disposed in an exhaust system of an internal combustion engine, distinguishing it from deterioration due to secular change. More specifically, when the maximum output value of the oxygen sensor disposed on the downstream side of the catalyst (three-way catalyst) becomes equal to or less than a predetermined value, it is determined that the sulfur is poisoned. And in the said conventional apparatus, when it determines with the catalyst being sulfur poisoning, the desulfurization process of a catalyst is performed by enriching an air fuel ratio over a fixed period.

JP-A-8-144746 JP 2002-97938 A JP 2002-36441 A JP 2004-76681 A

  The above-described conventional air-fuel ratio control apparatus performs control (desulfurization) in response to the result that sulfur poisoning has occurred in the catalyst, and in terms of exhaust purification measures during use of fuel with a high sulfur concentration. There was still room for improvement.

  The present invention has been made to solve the above-described problems, and is an air-fuel ratio control device for an internal combustion engine that can maintain good exhaust purification performance even when a fuel having a high sulfur concentration is used. The purpose is to provide.

A first invention is an air-fuel ratio control apparatus for an internal combustion engine comprising a three-way catalyst including a main catalyst and a co-catalyst,
A deterioration determining means for determining deterioration of the main catalyst and deterioration of the promoter;
An air-fuel ratio control limiting means for limiting air-fuel ratio control to the rich side with respect to the stoichiometric air-fuel ratio when the deterioration determining means determines that the promoter is deteriorated;
It is characterized by providing.

The second invention is the first invention, wherein the oxygen storage capacity acquisition means for acquiring the oxygen storage capacity of the three-way catalyst;
Temperature information acquisition means for acquiring temperature information of the three-way catalyst,
The deterioration determining means determines that the promoter is deteriorated when the oxygen storage capacity is lowered and the three-way catalyst is not exposed to a high temperature.

The third invention is the first or second invention, wherein the oxygen storage capacity acquisition means for acquiring the oxygen storage capacity of the three-way catalyst;
Further comprising aging information acquisition means for acquiring aging information of the three-way catalyst,
The deterioration determining means determines that the promoter is deteriorated when it is determined that the oxygen storage capacity is reduced and the three-way catalyst has not changed over time.

The fourth invention further comprises feedback means for correcting the fuel injection amount so that the target air-fuel ratio in the exhaust passage becomes the stoichiometric air-fuel ratio in any of the first to third inventions,
The restriction by the air-fuel ratio control restricting means shifts the control center of the target air-fuel ratio to the lean side with respect to the theoretical air-fuel ratio.

The fifth invention further comprises feedback means for correcting the fuel injection amount so that the target air-fuel ratio in the exhaust passage becomes the stoichiometric air-fuel ratio in any of the first to third inventions,
The restriction by the air-fuel ratio control restricting means speeds up the corrected response speed of the fuel injection amount when the target air-fuel ratio swings to the rich side with respect to the theoretical air-fuel ratio compared to when the target air-fuel ratio swings to the lean side. It is characterized by being.

  According to the first invention, the cocatalyst is deteriorated due to a decrease in oxygen storage capacity, but when it is determined that the activity of the main catalyst is not deteriorated, the air-fuel ratio control to the rich side is limited. As a result, the time during which the air-fuel ratio is controlled to the rich side can be shortened. For this reason, even when it is judged that the promoter has deteriorated, such as when fuel with a high sulfur concentration is used, it ensures good purification of HC and CO and improves the three-way activity. Can be maintained.

  According to the second invention, it is possible to accurately determine that the promoter has deteriorated based on the oxygen storage capacity and temperature information of the three-way catalyst.

  According to the third invention, it is possible to accurately determine that the promoter has deteriorated based on the oxygen storage capacity of the three-way catalyst and the aging information.

  According to the fourth aspect of the present invention, air-fuel ratio control without removing the purification window can be realized even in a situation where it is determined that the promoter is deteriorated.

  According to the fifth aspect of the invention, air-fuel ratio control that does not remove the purification window can be realized even in a situation where it is determined that the promoter has deteriorated. Then, according to the present invention, such air-fuel ratio control is performed, while suppressing the deterioration of the NOx purification performance when the target air-fuel ratio swings to the lean side, as compared with the fourth invention, Can be realized.

Embodiment 1 FIG.
[Configuration of Device of Embodiment 1]
FIG. 1 is a diagram for explaining a configuration of an air-fuel ratio control apparatus according to Embodiment 1 of the present invention. As shown in FIG. 1, the apparatus of this embodiment includes an upstream catalyst (S / C) 12 and a downstream catalyst (U / F) 14 disposed in an exhaust passage 10 of the internal combustion engine. The upstream catalyst 12 and the downstream catalyst 14 are all three-way catalysts that can simultaneously purify CO, HC, and NOx.

A main air-fuel ratio sensor 16 and a sub O ₂ sensor (oxygen sensor) 18 are disposed upstream and downstream of the upstream catalyst 12, respectively. The main air-fuel ratio sensor 16 is a sensor that emits a substantially linear output with respect to the air-fuel ratio A / F of the exhaust gas flowing into the upstream catalyst 12. On the other hand, the sub O ₂ sensor 18 generates a rich output (for example, 0.8 V) when the exhaust gas flowing out from the upstream catalyst 12 is rich with respect to the stoichiometric air-fuel ratio, and the exhaust gas is lean. In this case, the sensor generates a lean output (for example, 0.2 V).

The output of the main air-fuel ratio sensor 16 and the output of the sub O ₂ sensor 18 are respectively supplied to an ECU (Electronic Control Unit) 20. The ECU 20 is further connected to various sensors such as an air flow meter 22, a crank angle sensor 24, a throttle position sensor 26, and an accelerator position sensor 28 for detecting the operating state of the internal combustion engine, and a fuel injection valve 30 and the like. Yes. The air flow meter 22 is a sensor that detects an intake air amount Ga of the internal combustion engine. The crank angle sensor 24 is a sensor that generates an output corresponding to the engine speed Ne. The throttle position sensor 26 and the accelerator position sensor 28 are sensors that generate outputs corresponding to the opening degree of the throttle valve and the depression amount of the accelerator pedal, respectively. The fuel injection valve 30 is an electromagnetic valve for injecting fuel into the intake port of the internal combustion engine.

FIG. 2 is a graph showing the conversion efficiency characteristics of HC and the like with respect to the air-fuel ratio in the three-way catalyst. Here, the simultaneous purification of the three components HC, CO, and NOx is referred to as “three-way activity”. In order to simultaneously purify the three components HC, CO, and NOx discharged from the cylinder of the internal combustion engine with high conversion efficiency, it is necessary to control the air-fuel ratio within the range of the purification window near the stoichiometry shown in FIG. . For this reason, in the system shown in FIG. 1 configured as described above, main feedback control is executed based on the output of the upstream main air-fuel ratio sensor 16, while the downstream side sub-O ₂ sensor 18 Sub feedback control is executed based on the output.

In the main feedback control, the fuel injection amount is controlled so that the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 12 matches the target air-fuel ratio with the stoichiometric air-fuel ratio (stoichiometric) as the control center. In the sub-feedback control, more specifically, a sub O ₂ sensor disposed downstream of the upstream catalyst 12 so that the air-fuel ratio of the exhaust gas flowing out downstream of the upstream catalyst 12 becomes the stoichiometric air-fuel ratio. The content of the main feedback control is corrected so that the output of 18 becomes a stoichiometric output. According to these controls, the fuel injection amount is appropriately corrected as needed, the air-fuel ratio downstream of the upstream catalyst 12 can be accurately maintained at a value close to the stoichiometric value, and excellent exhaust purification performance can be obtained.

  Next, the structures of the upstream catalyst 12 and the downstream catalyst 14 that are three-way catalysts will be described with reference to FIG. More specifically, FIG. 3 (A) is a diagram showing a cross section of the catalyst 12 and the like, and FIG. 3 (B) is a conceptual diagram in which a portion of the catalyst layer 34 shown in FIG. 3 (A) is enlarged. .

As shown in FIG. 3A, the three-way catalyst 12 or the like includes a ceramic carrier 32 configured in a cell shape. The ceramic carrier 32 has a function of holding the catalyst layer 34. As shown in FIG. 3B, the catalyst layer 34 includes a noble metal (main catalyst) 36 such as platinum Pt and a promoter 38 such as ceria CeO ₂ .

  The three-way catalyst 12 or the like configured as described above has an oxygen storage capacity, and can store oxygen within the range. This oxygen storage capacity (maximum oxygen storage amount Cmax value) can be a criterion for detecting deterioration of the catalyst. The maximum oxygen storage amount Cmax value decreases as the catalyst is deteriorated by being exposed to high heat or by aging of the catalyst.

Further, it has been conventionally known that the maximum oxygen storage amount Cmax value of the catalyst decreases with deterioration due to so-called poisoning even when a fuel having a high sulfur concentration is used. However, even if the maximum oxygen storage amount Cmax value is reduced due to the use of fuel with a high sulfur concentration, the catalyst is not exposed to high heat or the catalyst has not changed over time. It is considered that noble metals are not sintered (grain growth). Therefore, in such a case, it can be determined that the activity of the noble metal as the main catalyst is not deteriorated, and the oxygen absorption / release site of the ceria CeO _{2 as} the promoter is deteriorated (or hindered). .

In the region on the richer side than stoichiometric, the oxygen in the exhaust gas is insufficient. For this reason, in order to sufficiently oxidize HC and CO in the rich region, the oxygen storage capacity of ceria CeO ₂ is essential. However, as described above, when a fuel having a high sulfur concentration is used and the oxygen absorption / release site of the ceria CeO ₂ as a co-catalyst deteriorates, the oxidation rate of HC and CO in the rich side region. Will fall. As a result, it becomes difficult to control the air-fuel ratio within the range of the purification window in the rich region.

  Therefore, in the present embodiment, even when a fuel having a high sulfur concentration is used, the ECU 20 is shown in FIG. 4 below in order to maintain good exhaust purification performance without removing the purification window. The routine is executed every predetermined time.

[Specific Processing in Embodiment 1]
FIG. 4 is a flowchart of a routine executed by the ECU 20 in the first embodiment to achieve the above object. In the routine shown in FIG. 4, first, it is determined whether or not the catalyst 12 or the like has deteriorated, and if it has deteriorated, whether or not the main catalyst or the promoter has deteriorated. (Step 100). Specifically, in this step 100, whether or not the maximum oxygen storage amount Cmax value is smaller than a predetermined threshold value, whether or not the mileage of the vehicle is smaller than a predetermined threshold value, the history of thermal deterioration influence on the catalyst 12 such as misfire. A determination is made based on whether there is any.

  If it is determined in step 100 that the maximum oxygen storage amount Cmax value <threshold value is not satisfied, it can be determined that the catalyst 12 or the like has not deteriorated due to heat or sulfur poisoning. Note that the maximum oxygen storage amount Cmax value can be obtained, for example, by a method disclosed in Japanese Patent Application Laid-Open No. 2004-76681. If it is determined that the travel distance <threshold value is not satisfied, that is, if the vehicle has already traveled more than the specified distance, it can be determined that the catalyst 12 or the like has deteriorated due to secular change. In addition, when the misfire counter of the ECU 20 recognizes that a certain ratio or more of misfire has occurred, or when the vehicle travels in a high load state or a high vehicle speed state, there is a history of the heat deterioration effect on the catalyst. When it is recognized that there is, it can be determined that thermal degradation has occurred in the catalyst 12 or the like. In any of these cases, the process of the current routine is immediately terminated. The ECU 20 always calculates the maximum oxygen storage amount Cmax value. Further, the ECU 20 acquires the travel distance based on the output of the wheel speed sensor provided in the vehicle, and the thermal deterioration influence history using the misfire counter.

On the other hand, when it is determined in step 100 that all conditions that the maximum oxygen storage amount Cmax value <threshold value, the travel distance <threshold value, and the absence of the thermal deterioration influence history are satisfied. As described above, it can be determined that the activity of the noble metal that is the main catalyst has not deteriorated, and the oxygen absorption / release site of the ceria CeO ₂ that is the cocatalyst has been deteriorated (or hindered). .

  Therefore, in this case, the control center of the target air-fuel ratio is shifted to a value on the lean side with respect to stoichiometry (step 102). More specifically, when the target air-fuel ratio is switched alternately between the rich side and the lean side, the limit value on the rich side is shifted to the stoichiometric position without changing the limit value on the lean side in the purification window shown in FIG. Thus, the air-fuel ratio is controlled so as to be within the limits.

  According to the routine shown in FIG. 4 described above, it is possible to determine the deterioration of the main catalyst 36 and the deterioration of the co-catalyst 38 under the situation where the maximum oxygen storage amount Cmax value of the catalyst 12 or the like is decreasing. According to the processing of the above routine, when the fuel having a high sulfur concentration is used, the co-catalyst 38 is deteriorated due to the decrease in oxygen storage capacity, but the activity of the main catalyst 36 is not deteriorated. When it is determined that the air-fuel ratio control to the rich side is limited, the time during which the air-fuel ratio is controlled to the rich side can be shortened. For this reason, even in a situation where it is determined that the co-catalyst 38 has deteriorated, air / fuel ratio control without removing the purification window can be realized while ensuring good purification of HC and CO, and three-way activation Can be maintained well.

In the first embodiment described above, the ECU 20 executes the process of step 100, so that the “deterioration determination unit” in the first invention executes the process of step 102. Each of the “air-fuel ratio control limiting means” in the present invention is realized.
Further, when the ECU 20 calculates the maximum oxygen storage amount Cmax value, the “oxygen storage capacity acquisition means” in the second or third invention acquires the thermal deterioration influence history using the misfire counter provided in the ECU 20. Thus, the “temperature information acquisition means” in the second aspect of the invention is realized.
Further, the “aging change information acquisition means” in the third aspect of the present invention is realized by acquiring the travel distance based on the output of the wheel speed sensor provided in the vehicle of the ECU 20.
Further, the “feedback means” in the fourth aspect of the present invention is realized by the ECU 20 performing the main feedback control and the sub feedback control.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG.
The system of the present embodiment can be realized by causing the ECU 20 to execute a routine shown in FIG. 5 described later instead of the routine shown in FIG. 4 using the hardware configuration shown in FIG.

[Specific Processing in Second Embodiment]
FIG. 5 is a flowchart of a routine executed by the ECU 20 in the second embodiment. In FIG. 5, the same steps as those shown in FIG. 4 in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 5, if it is determined in step 100 that the promoter 38 has deteriorated due to a decrease in the oxygen storage capacity, then the rich side is controlled in order to limit the air-fuel ratio control to the rich side. The corrected response speed is increased (step 200).

In the above-described sub feedback control, more specifically, the correction amount for correcting the content of the main feedback control is calculated by PID control. This correction amount includes a proportional term and an integral term. The proportional term is set as a value obtained by multiplying the output deviation between the output of the sub O ₂ sensor 18 and the target voltage (stoichiometric output) of the sub feedback by a predetermined proportional term gain. The integral term is set as a value obtained by multiplying the integrated value of the output deviation by a predetermined integral term gain.

  In the routine shown in FIG. 5, the values of the proportional term gain and the integral term gain are the same before the start of the control of step 200, regardless of whether the target air-fuel ratio fluctuates on the rich side or the lean side. Is set.

  On the other hand, when the processing of this step 200 is executed, the values of the proportional term gain and the integral term gain are set to the values before the control start of this step 200 while the control center of the target air-fuel ratio is controlled as it is. It is changed for each. More specifically, the values of the proportional term gain and the integral term gain used when the target air-fuel ratio fluctuates to the rich side are changed to larger values than the values used when the target air-fuel ratio fluctuates to the lean side.

  As a result, the correction response speed of the air-fuel ratio when the target air-fuel ratio swings to the rich side can be increased compared to the case where the target air-fuel ratio swings to the lean side. As the gain value after the change in step 200, a value adapted to the calculated target air-fuel ratio within a range where hunting does not occur is used.

  According to the routine shown in FIG. 5 described above, when the fuel having a high sulfur concentration is used, the co-catalyst 38 is deteriorated due to a decrease in the oxygen storage capacity, but the activity of the main catalyst 36 is deteriorated. When it is determined that the air-fuel ratio is not, the air-fuel ratio control to the rich side is limited by increasing the correction response speed on the rich side. For this reason, it is possible to realize air-fuel ratio control without removing the purification window even under a situation where it is determined that the co-catalyst 38 is deteriorated.

  Further, according to the routine shown in FIG. 5, unlike the above-described first embodiment, even if it is determined that the promoter 38 has been deteriorated due to a decrease in oxygen storage capacity, the target air-fuel ratio is determined. The air-fuel ratio control to the rich side can be limited without changing the control center from stoichiometric. For this reason, it is possible to suppress deterioration of the NOx purification performance when the target air-fuel ratio fluctuates to the lean side as compared with the control in the first embodiment described above.

It is a figure for demonstrating the structure of the air fuel ratio control apparatus in Embodiment 1 of this invention. It is a figure which shows the conversion efficiency characteristics, such as HC, with respect to the air fuel ratio in a three-way catalyst. It is a figure for demonstrating the structure of the upstream catalyst which is a three way catalyst, and a downstream catalyst. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a flowchart of the routine performed in Embodiment 2 of this invention.

Explanation of symbols

10 Exhaust passage 12 Upstream catalyst 14 Downstream catalyst 16 Main air-fuel ratio sensor 18 Sub O ₂ sensor 20 ECU (Electronic Control Unit)
32 Ceramic carrier 34 Catalyst layer 36 Main catalyst (noble metal)
38 Cocatalyst
Cmax maximum oxygen storage capacity

Claims (5)

An air-fuel ratio control device for an internal combustion engine comprising a three-way catalyst including a main catalyst and a promoter,
A deterioration determining means for determining deterioration of the main catalyst and deterioration of the promoter;
An air-fuel ratio control limiting means for limiting air-fuel ratio control to the rich side with respect to the stoichiometric air-fuel ratio when the deterioration determining means determines that the promoter is deteriorated;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: Oxygen storage capacity acquisition means for acquiring the oxygen storage capacity of the three-way catalyst;
Temperature information acquisition means for acquiring temperature information of the three-way catalyst,
2. The deterioration determining unit determines that the promoter is deteriorated when the oxygen storage capacity is reduced and the three-way catalyst is not exposed to a high temperature. An air-fuel ratio control apparatus for an internal combustion engine. Oxygen storage capacity acquisition means for acquiring the oxygen storage capacity of the three-way catalyst;
Further comprising aging information acquisition means for acquiring aging information of the three-way catalyst,
The deterioration determining means determines that the promoter is deteriorated when it is determined that the oxygen storage capacity is reduced and the three-way catalyst has not changed over time. Item 3. The air-fuel ratio control apparatus for an internal combustion engine according to Item 1 or 2. Feedback means for correcting the fuel injection amount so that the target air-fuel ratio in the exhaust passage becomes the stoichiometric air-fuel ratio,
4. The restriction according to claim 1, wherein the restriction by the air-fuel ratio control restricting means shifts the control center of the target air-fuel ratio to the lean side with respect to the theoretical air-fuel ratio. An air-fuel ratio control apparatus for an internal combustion engine. Feedback means for correcting the fuel injection amount so that the target air-fuel ratio in the exhaust passage becomes the stoichiometric air-fuel ratio,
The restriction by the air-fuel ratio control restricting means speeds up the corrected response speed of the fuel injection amount when the target air-fuel ratio swings to the rich side with respect to the theoretical air-fuel ratio compared to when the target air-fuel ratio swings to the lean side. The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 3, wherein

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