Method and apparatus for controlling the air-fuel ratio of an internal combustion engine

Abstract

When exhaust gas purification is performed using the exhaust particulate filter 17A, which also functions as a three-way catalytic converter, the accumulation of exhaust particulate matter reduces the oxidation performance of the three-way catalytic converter. [Solution] An exhaust particulate filter 17A, on which a three-way catalyst with oxygen storage capacity is supported, is provided at the uppermost position of the exhaust passage 11 of the internal combustion engine 2, and an upstream air-fuel ratio sensor 31 is provided on the inlet side thereof. The air-fuel ratio of the internal combustion engine 2 is controlled so that the oxygen storage amount of the three-way catalyst becomes the target oxygen storage amount. In order to counteract the effects of exhaust particulate matter accumulation, the amount of exhaust particulate matter accumulation is estimated, and the target air-fuel ratio is corrected to the lean side according to this amount of accumulation.

Description

Technical Field

[0001] The present invention relates to an air-fuel ratio control of an internal combustion engine provided with an exhaust particulate filter in an exhaust passage for collecting exhaust particulates contained in the exhaust gas of the internal combustion engine, particularly an exhaust particulate filter having a three-way catalyst with oxygen storage capacity supported thereon.

Background Art

[0002] An exhaust particulate filter may be provided in the exhaust passage even in a spark ignition type internal combustion engine, so-called gasoline engine. And, as disclosed in Patent Document 1, by supporting a catalytic metal on the exhaust particulate filter, it is possible to achieve exhaust purification by catalytic action simultaneously with the collection of exhaust particulates.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a three-way catalyst is supported on an exhaust particulate filter, in order to achieve high-level compatibility between the oxidation of CO and HC and the reduction of NOx by catalytic action, it is important that the catalyst has so-called oxygen storage capacity to store and release oxygen.

[0005] Here, in the case of an exhaust particulate filter also serving as a three-way catalyst, as a result of exhaust particulates depositing on the surface of the catalyst layer, the surface area for oxygen adsorption decreases. Further, since the carbon component in the deposited exhaust particulates reacts with oxygen to consume oxygen, the oxygen storage capacity of the three-way catalyst or the actually adsorbed oxygen storage amount decreases as the deposition amount of exhaust particulates increases. Therefore, there is a problem that the atmosphere inside the catalyst layer shifts to the rich side as the deposition amount increases, and the original exhaust purification performance of the three-way catalyst cannot be exhibited. [Means for solving the problem]

[0006] This invention relates to an air-fuel ratio control method for an internal combustion engine, comprising an exhaust particulate filter having a three-way catalyst with oxygen storage capacity supported at the uppermost position of the exhaust passage, and an upstream air-fuel ratio sensor for detecting the exhaust air-fuel ratio located on the inlet side of the exhaust particulate filter, wherein the air-fuel ratio is controlled so that oxidation and reduction reactions are obtained in the three-way catalyst of the exhaust particulate filter. The amount of exhaust particulate matter deposited in the exhaust particulate filter described above is estimated, Depending on the amount of this deposit, the air-fuel ratio of the internal combustion engine is corrected in a direction that makes the exhaust air-fuel ratio on the exhaust particulate filter inlet leaner the larger the amount of deposit.

[0007] This correction offsets the impact on oxidation and reduction performance caused by the accumulation of exhaust particulate matter. [Effects of the Invention]

[0008] According to this invention, the exhaust gas purification effect of an exhaust particulate filter supported with a three-way catalyst can be appropriately obtained regardless of the amount of exhaust particulate matter deposited. [Brief explanation of the drawing]

[0009] [Figure 1] Diagram illustrating the configuration of a series hybrid vehicle. [Figure 2] Diagram illustrating the configuration of the intake and exhaust systems of an internal combustion engine. [Figure 3] A flowchart illustrating the process for setting the target air-fuel ratio. [Figure 4] A characteristic diagram showing the relationship between exhaust particulate matter accumulation and the target air-fuel ratio. [Figure 5] A flowchart illustrating the process for setting the target oxygen storage capacity. [Figure 6] A characteristic diagram showing the relationship between exhaust particulate matter accumulation and target oxygen storage capacity. [Figure 7] A flowchart illustrating an example of sediment volume estimation. [Figure 8] A characteristic diagram showing the relationship between the exhaust air-fuel ratio difference and the amount of exhaust particulate matter deposited. [Figure 9] A flowchart illustrating another example of sediment volume estimation. [Figure 10] A characteristic diagram showing the relationship between the time difference in air-fuel ratio change and the amount of exhaust particulate matter accumulation. [Figure 11] A flowchart illustrating the temperature control of an electrically heated exhaust particulate filter. [Figure 12] A characteristic diagram showing the relationship between exhaust particulate matter accumulation and target temperature. [Modes for carrying out the invention]

[0010] Hereinafter, an embodiment of this invention will be described in detail with reference to the drawings. Figure 1 schematically shows the configuration of a series hybrid vehicle as an example of a vehicle to which this invention is applied. The series hybrid vehicle is configured to include a power generation motor generator 1 that mainly operates as a generator, an internal combustion engine 2 used as a power generation internal combustion engine that drives the power generation motor generator 1 according to power demands, a drive motor generator 4 that mainly operates as a motor to drive the drive wheels 3, and a battery 5 that stores the generated electricity. The electricity obtained by the internal combustion engine 2 driving the power generation motor generator 1 is stored in the battery 5 via an inverter device (not shown). The drive motor generator 4 is driven and controlled using the power from the battery 5. The electricity generated during regeneration by the drive motor generator 4 is also stored in the battery 5 via an inverter device (not shown).

[0011] The operation of motor generators 1 and 4, the charging and discharging of battery 5, and the operation of internal combustion engine 2 are controlled by controller 6. Controller 6 consists of multiple controllers connected to each other so as to be able to communicate with one another, including motor controller 7 which controls motor generators 1 and 4, engine controller 8 which controls internal combustion engine 2, and battery controller 9 which manages battery 5. Information such as the opening of the accelerator pedal (not shown) and vehicle speed is input to controller 6. Battery controller 9 also determines the State of Charge (SOC) of battery 5 based on the voltage and current of battery 5. When the SOC drops to a predetermined lower limit level, the internal combustion engine 2 is started via engine controller 8 and power generation is performed. Even if the SOC is above the lower limit level, if the vehicle's required driving force is relatively large, the internal combustion engine 2 is driven, resulting in driving accompanied by power generation. Therefore, while the vehicle's main switch is on, the internal combustion engine 2 repeatedly cycles between combustion operation and combustion operation stoppage.

[0012] Figure 2 shows the configuration of the intake and exhaust systems of the internal combustion engine 2. The internal combustion engine 2 in one embodiment is a four-stroke cycle spark-ignition internal combustion engine (a so-called gasoline engine), and is a so-called direct-injection type internal combustion engine in which, for example, a fuel injector directly injects fuel into the cylinder. A port injection type configuration is also possible.

[0013] An electronically controlled throttle valve 21 is positioned in the intake passage 12 of the internal combustion engine 2, which is equipped with an air cleaner 28, to control the amount of intake air. The throttle valve 21 consists of a conventional butterfly valve with a circular valve body, and its opening degree is controlled by the engine controller 8.

[0014] An upstream catalyst converter 17 is disposed in an exhaust passage 11 of an internal combustion engine 2. An exhaust muffler 19 is provided downstream of the upstream catalyst converter 17, and the exhaust passage 11 is open to the atmosphere via the exhaust muffler 19. The upstream catalyst converter 17 is a so-called manifold catalyst attached to the outlet of an exhaust manifold 11a within the engine room of the vehicle. As shown by the phantom line, a downstream catalyst converter 18 disposed under the vehicle floor may be provided between the upstream catalyst converter 17 and the exhaust muffler 19. The downstream catalyst converter 18 is composed of, for example, a three-way catalyst using a monolithic ceramic carrier.

[0015] The upstream catalyst converter 17 is configured such that an electrically heated exhaust particulate filter (hereinafter referred to as an EGPF) 17A is housed within a casing. The EGPF 17A of one embodiment is composed of a porous honeycomb-type monolith filter formed in a cylindrical shape using a ceramic material having conductivity such as SiC. The monolith filter made of a ceramic material has a number of fine passages, that is, a number of cells, along the axial direction, and the ends of these cells are alternately plugged, and is configured as a so-called wall flow type filter. And, a catalyst layer containing a three-way catalyst material is coated on the entire surface including the inner surface of the cell, and it also serves as a catalyst for exhaust purification. In the present invention, it is not limited to a filter made of ceramic, and for example, a configuration in which a catalyst is supported on a metal filter may be used. Further, it may be a simple exhaust particulate filter not provided with electric heating means.

[0016] The upstream catalyst converter 17 does not include another three-way catalyst or the like other than the EGPF 17A carrying the three-way catalyst, and the purification of emissions discharged from the internal combustion engine 2 is basically carried out by the EGPF 17A.

[0017] In the claims, "the upstream position in the exhaust passage" does not refer to a physical distance, but rather to the position where exhaust gas flows in without passing through other exhaust purification devices (such as catalysts or exhaust particulate filters). If no other exhaust purification devices are provided besides EGPF17A, EGPF17A will always be at the upstream position. If other exhaust purification devices are provided, EGPF17A will be positioned relatively upstream.

[0018] An upstream air-fuel ratio sensor 31 is positioned upstream of the upstream catalytic converter 17, that is, upstream of the upstream catalytic converter 17, to detect the exhaust air-fuel ratio of the exhaust gas discharged by the internal combustion engine 2 (in other words, the exhaust air-fuel ratio of the exhaust gas flowing into the EGPF 17A). This upstream air-fuel ratio sensor 31 is a so-called wide-range air-fuel ratio sensor that provides an output corresponding to the exhaust air-fuel ratio. Furthermore, a downstream air-fuel ratio sensor 32 is positioned downstream of the upstream catalytic converter 17, either on the outlet side or downstream of the EGPF 17A, to detect the exhaust air-fuel ratio of the exhaust gas flowing out of the EGPF 17A. The downstream air-fuel ratio sensor 32 is a wide-range air-fuel ratio sensor that provides an output corresponding to the exhaust air-fuel ratio, similar to the upstream air-fuel ratio sensor 31.

[0019] The engine controller 8 in Figure 1 receives detection signals from numerous sensors, either directly or via other controllers, although these are not shown in detail. These sensors include an air flow meter for detecting intake air volume, the aforementioned air-fuel ratio sensors 31 and 32 for detecting exhaust air-fuel ratio, a crank angle sensor for detecting engine rotational speed, a water temperature sensor for detecting coolant temperature, an accelerator pedal position sensor for detecting accelerator pedal depression, an atmospheric pressure sensor for detecting atmospheric pressure, and an ambient temperature sensor for detecting ambient temperature. Based on these detection signals and requests from other controllers, the engine controller 8 optimally controls the fuel injection amount and timing, ignition timing, throttle valve 21 opening, EGPF 17A temperature, and the like.

[0020] Next, the air-fuel ratio control, which is the core of the present invention, will be described. As one of the various controls of the internal combustion engine 2, the engine controller 8 controls the air-fuel ratio so that oxidation and reduction can be achieved in the three-way catalyst, in order to optimize the exhaust gas purification performance of the three-way catalyst equipped with the EGPF 17A. In the air-fuel ratio control of one embodiment, feedback correction of the target air-fuel ratio of the internal combustion engine 2 is performed so that the oxygen storage amount of the three-way catalyst is maintained at the target oxygen storage amount. That is, the fuel injection amount is controlled so that the exhaust air-fuel ratio detected by the upstream air-fuel ratio sensor 31 (hereinafter referred to as the upstream exhaust air-fuel ratio) is in line with the target air-fuel ratio, but the target air-fuel ratio is corrected so that the oxygen storage amount of the three-way catalyst estimated from the upstream exhaust air-fuel ratio matches the target oxygen storage amount. For example, if the estimated oxygen storage amount is greater than the target oxygen storage amount, the target air-fuel ratio is corrected to the rich side, and conversely, if the estimated oxygen storage amount is less than the target oxygen storage amount, the target air-fuel ratio is corrected to the lean side. Therefore, the oxygen storage capacity of the three-way catalyst is basically maintained near the target oxygen storage capacity.

[0021] Here, the engine controller 8 corrects the target air-fuel ratio according to the amount of exhaust particulate matter deposited in the EGPF17A in order to improve the accuracy of air-fuel ratio control. In the EGPF17A supported by the three-way catalytic converter, exhaust particulate matter is deposited as it functions as a filter, and oxygen is consumed for the oxidation of this deposited exhaust particulate matter. In other words, as carbon-containing exhaust particulate matter is deposited on the surface of the catalyst layer, reactions such as "C + O2 → CO2" and "C + NO → CO2 + N2" are relatively increased, and oxygen is consumed. As a result, the greater the amount of exhaust particulate matter deposited, the lower the oxidation performance of CO and HC.

[0022] The flowchart in Figure 3 shows the process flow for setting the target air-fuel ratio. In step 1, the temperature of the three-way catalyst, i.e., the temperature of the EGPF17A, is determined. The temperature of the EGPF17A may be measured by installing a temperature sensor on the EGPF17A, but in a preferred embodiment, the temperature of the EGPF17A can be determined by a known method that estimates the temperature by accumulating the temperature change per minute unit time based on the amount of electricity supplied to the EGPF17A and the energy received from the exhaust gas. Next, in step 2, the amount of exhaust particulate matter deposited in the EGPF17A is determined. This can be determined, for example, by estimation based on the pressure difference before and after the EGPF17A, or by estimation based on the exhaust air-fuel ratio, which will be described later.

[0023] Next, in step 3, the target air-fuel ratio is set according to the relationship shown in Figure 4, which was prepared in advance, based on the temperature of EGPF17A and the amount of exhaust particulate matter deposited.

[0024] The relationship shown in Figure 4 has been determined in advance through experiments or simulations to offset the effects of exhaust particulate matter deposition and temperature, which are involved in the actual oxidation and reduction performance of the three-way catalyst, and is provided to the engine controller 8, for example, in the form of a map. As shown in Figure 4, the larger the exhaust particulate matter deposition, the leaner the target air-fuel ratio becomes. The final air-fuel ratio control based on the target oxygen storage amount described above is performed based on the target air-fuel ratio determined in step 3. Therefore, the decrease in oxidation performance due to the deposition of exhaust particulate matter described above can be offset. Note that the higher the catalyst temperature, the higher the oxygen storage capacity and the higher the oxygen absorption and desorption rate, so the characteristics of the target air-fuel ratio in Figure 4 are determined taking this effect into consideration.

[0025] Next, we will explain the correction of the target oxygen storage amount in response to the accumulation of exhaust particulate matter, based on Figures 5 and 6.

[0026] In the case of an exhaust particulate filter that also functions as a three-way catalyst, exhaust particulate matter accumulates on the surface of the catalyst layer, reducing the surface area on which oxygen can be adsorbed. Furthermore, the carbon components in the accumulated exhaust particulate matter react with oxygen and consume it, causing the oxygen storage capacity of the three-way catalyst to decrease as the amount of accumulated exhaust particulate matter increases. Therefore, if the target oxygen storage amount is constant (e.g., 50%), the control center will be shifted from an appropriate position relative to the actual oxygen storage capacity, reducing the robustness of the control. Accordingly, in a preferred embodiment, the target oxygen storage amount is corrected or set according to the amount of accumulated exhaust particulate matter (in other words, the effective oxygen storage capacity).

[0027] The flowchart in Figure 5 shows the process flow for setting the target oxygen storage amount. In step 11, the temperature of the three-way catalyst, i.e., the temperature of EGPF17A, is determined, similar to step 1 described above. In step 12, the amount of exhaust particulate matter accumulation in EGPF17A is determined, similar to step 2 described above. Next, in step 13, the target oxygen storage amount is set according to the relationship shown in Figure 6, which was created in advance, based on the temperature of EGPF17A and the amount of exhaust particulate matter accumulation. Then, in step 14, air-fuel ratio feedback control is performed to achieve this target oxygen storage amount.

[0028] The relationship shown in Figure 6 has been determined in advance through experiments or simulations to offset the effects of exhaust particulate matter deposition and temperature, which are involved in the actual oxygen storage capacity of the three-way catalyst, and is provided to the engine controller 8, for example, in the form of a map. As shown in Figure 6, the larger the exhaust particulate matter deposition, the smaller the target oxygen storage capacity. Therefore, despite the decrease in effective oxygen storage capacity due to the aforementioned accumulation of exhaust particulate matter, the control center can be maintained in an appropriate position, improving the robustness of the control.

[0029] Next, we will explain two methods for estimating the amount of exhaust particulate matter accumulation in EGPF17A by utilizing the effect of exhaust particulate matter accumulation on the air-fuel ratio, as described above.

[0030] The flowchart shown in Figure 7 illustrates the first method of estimating the amount of deposit. In step 21, the temperature of the three-way catalyst, i.e., the temperature of EGPF17A, is determined. In step 22, it is determined whether the temperature of this three-way catalyst is above a predetermined temperature. If it is below the predetermined temperature, the amount of deposit is not estimated. If the temperature of the three-way catalyst is relatively high, the effective oxygen storage capacity changes according to the amount of deposit, but at low temperatures, the change in oxygen storage capacity according to the amount of deposit is small. Therefore, in order to ensure estimation accuracy, the amount of deposit estimation is permitted only if the temperature is above the predetermined temperature.

[0031] In step 23, the upstream exhaust air-fuel ratio (indicated as AFRfr in the figure) detected by the upstream air-fuel ratio sensor 31 is read, and in step 24, the downstream exhaust air-fuel ratio (indicated as AFRrr in the figure) detected by the downstream air-fuel ratio sensor 32 is read. In step 25, the difference A between the two (A = AFRfr - AFRrr) is calculated. Then, in step 26, the amount of exhaust particulate matter accumulation is calculated based on the air-fuel ratio difference A, according to the relationship shown in Figure 8, which was created in advance. The relationship shown in Figure 8 has been determined in advance by experiment or simulation, and is provided to the engine controller 8, for example, in the form of a map.

[0032] As mentioned above, the greater the amount of exhaust particulate matter accumulation, the lower the oxidation performance of the three-way catalyst, and the downstream exhaust air-fuel ratio, which responds to the gas that has passed through EGPF17A, shifts relatively towards the rich side. Therefore, it is possible to estimate the amount of exhaust particulate matter accumulation based on the difference A between the upstream exhaust air-fuel ratio and the downstream exhaust air-fuel ratio.

[0033] The flowchart shown in Figure 9 illustrates the second method for estimating the amount of deposit. In step 31, the temperature of the three-way catalyst, i.e., the temperature of EGPF17A, is determined. In step 32, it is determined whether the temperature of the three-way catalyst is above a predetermined temperature and whether the operating state of the internal combustion engine 2 is immediately after recovery (resumption of fuel injection) from a fuel cut. If the temperature is below the predetermined temperature, the amount of deposit is not estimated. This is for the same reasons as the first method described above. Recovery from a fuel cut means that the gas flowing into EGPF17A changes from air to exhaust gas, or in other words, the exhaust air-fuel ratio of the gas flowing into EGPF17A changes stepwise. Therefore, the amount of deposit is only allowed immediately after recovery from a fuel cut. Note that fuel cut and recovery may be actively performed for the purpose of estimating the amount of deposit.

[0034] In step 33, the upstream exhaust air-fuel ratio AFRfr detected by the upstream air-fuel ratio sensor 31 is repeatedly read, and in step 34, the downstream exhaust air-fuel ratio AFRrr detected by the downstream air-fuel ratio sensor 32 is repeatedly read. In step 35, the time T1 from recovery until the upstream exhaust air-fuel ratio AFRfr falls below the stoichiometric air-fuel ratio is determined, in step 36, the time T2 from recovery until the downstream exhaust air-fuel ratio AFRrr falls below the stoichiometric air-fuel ratio is determined, and in step 37, the time difference ΔT (ΔT = T2 - T1) between the two is determined. Then, in step 38, the amount of exhaust particulate matter accumulation is determined based on the above time difference ΔT, according to the relationship shown in Figure 10 which was created in advance. The relationship shown in Figure 10 has been determined in advance by experiment or simulation, etc., and is provided to the engine controller 8 in the form of a map, for example.

[0035] During fuel cut-off, oxygen-containing air flows into the EGPF17A, causing the oxygen storage capacity of the three-way catalytic converter to reach saturation. The actual oxygen storage capacity decreases as the amount of exhaust particulate matter accumulation increases. When the exhaust air-fuel ratio changes stepwise upstream of the EGPF17A, if the amount of oxygen storage is large, the time T2 until the downstream exhaust air-fuel ratio AFRrr falls below the stoichiometric air-fuel ratio is long. Conversely, as the amount of oxygen storage decreases due to the decrease in oxygen storage capacity, the time T2 decreases. Therefore, it is possible to estimate the amount of exhaust particulate matter accumulation based on the time difference ΔT.

[0036] Here, even if the three-way catalyst is degraded, the time difference ΔT will be shorter. Therefore, if the time difference ΔT in the exhaust particulate matter deposition estimation shown in Figure 9 is below a certain threshold (which is set to a relatively small value), it is desirable to perform forced regeneration and removal of the accumulated exhaust particulate matter, and then perform a degradation diagnosis of the three-way catalyst using the same process as in Figure 9. The reliability of the subsequent estimation of exhaust particulate matter deposition will be increased by confirming that there is no degradation through the degradation diagnosis.

[0037] The EGPF17A, which also functions as a three-way catalytic converter, is preferably energized to maintain a target temperature during operation of the internal combustion engine 2. In one embodiment, the target temperature is corrected according to the amount of exhaust particulate matter accumulation in order to compensate for the reduction in effective oxygen storage capacity due to the accumulation of exhaust particulate matter as described above.

[0038] Figure 11 is a flowchart showing the temperature control of the EGPF17A. In the first step 41, the temperature of the EGPF17A is determined. In step 42, the amount of exhaust particulate matter deposited in the EGPF17A is determined, similar to step 2 described above. Next, in step 43, the target temperature is determined based on the amount of exhaust particulate matter deposited, according to the relationship shown in Figure 12, which was created in advance. Then, in step 44, the energization of the EGPF17A is controlled to achieve the target temperature. As shown in Figure 12, the larger the amount of exhaust particulate matter deposited, the higher the target temperature is set. By increasing the temperature of the EGPF17A, the oxygen storage capacity is relatively increased, and the effect of exhaust particulate matter deposition is reduced, at least partially.

[0039] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications are possible. For example, although an electrically heated exhaust particulate filter is used in the above embodiment, an exhaust particulate filter that does not have an electrically heated function may also be used, as mentioned above. Furthermore, the present invention is not limited to internal combustion engines for series hybrid vehicles, but can also be similarly applied to internal combustion engines that serve as a driving source. [Explanation of Symbols]

[0040] 1…Power generation motor generator 2…Internal combustion engine 4…Drive motor generator 5… Battery 8…Engine controller 17…Upstream catalytic converter 17A…EGPF 31…Upstream air-fuel ratio sensor 32… Downstream air-fuel ratio sensor

Claims

1. An air-fuel ratio control method for an internal combustion engine, comprising an exhaust particulate filter having a three-way catalyst with oxygen storage capacity supported at the uppermost position of the exhaust passage, and an upstream air-fuel ratio sensor for detecting the exhaust air-fuel ratio at the inlet side of the exhaust particulate filter, wherein the air-fuel ratio is controlled so that oxidation and reduction reactions are obtained in the three-way catalyst of the exhaust particulate filter, The amount of exhaust particulate matter deposited in the exhaust particulate filter described above is estimated, Depending on the amount of this deposit, the air-fuel ratio of the internal combustion engine is corrected in a direction that makes the exhaust air-fuel ratio on the exhaust particulate filter inlet leaner the larger the amount of deposit. A method for controlling the air-fuel ratio of an internal combustion engine.

2. The above exhaust particulate filter is an electrically heated exhaust particulate filter whose temperature rises when electricity is applied. The air-fuel ratio control method for an internal combustion engine according to claim 1.

3. The target air-fuel ratio of the internal combustion engine is adjusted to be leaner as the amount of the above-mentioned deposit increases. The air-fuel ratio control method for an internal combustion engine according to claim 1.

4. Based on the exhaust air-fuel ratio and exhaust flow rate detected by the upstream air-fuel ratio sensor, the amount of oxygen stored in the three-way catalyst is estimated, and the target air-fuel ratio is feedback-corrected so that this oxygen storage amount becomes the target storage amount. The above target storage amount is reduced as the above accumulation amount increases. The air-fuel ratio control method for an internal combustion engine according to claim 3.

5. Determine the catalyst temperature, The higher the catalyst temperature, the more it corrects the air-fuel ratio of the internal combustion engine toward the lean side. The air-fuel ratio control method for an internal combustion engine according to claim 1.

6. The exhaust particulate filter described above is equipped with a downstream air-fuel ratio sensor on the outlet side, The amount of accumulation is estimated based on the fact that the exhaust air-fuel ratio at the outlet of the exhaust particulate filter, as detected by the downstream air-fuel ratio sensor, is relatively richer than the exhaust air-fuel ratio at the inlet of the exhaust particulate filter, as detected by the upstream air-fuel ratio sensor. The air-fuel ratio control method for an internal combustion engine according to claim 1.

7. During operation of the internal combustion engine, the power supply is controlled to maintain the temperature of the electric heated exhaust particulate filter at the target temperature. The target temperature of this electrically heated exhaust particulate filter is increased as the amount of deposit increases. The air-fuel ratio control method for an internal combustion engine according to claim 2.

8. An air-fuel ratio control device for an internal combustion engine, comprising: an exhaust particulate filter provided at the uppermost position of the exhaust passage of the internal combustion engine, on which a three-way catalyst having oxygen storage capacity is supported; an upstream air-fuel ratio sensor provided on the inlet side of the exhaust particulate filter for detecting the exhaust air-fuel ratio; and a controller that controls the air-fuel ratio based on the detected exhaust air-fuel ratio so that oxidation and reduction reactions are obtained in the three-way catalyst in the exhaust particulate filter, The above controller is The amount of exhaust particulate matter deposited in the exhaust particulate filter described above is estimated, Depending on the amount of this deposit, the air-fuel ratio of the internal combustion engine is corrected in a direction that makes the exhaust air-fuel ratio on the exhaust particulate filter inlet leaner the larger the amount of deposit. Air-fuel ratio control device for internal combustion engines.

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