JP2024000576A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device for an internal combustion engine which can apply a correction associated with unevenness of hitting of gas to a catalyst caused by a degree of opening of a waste gate valve to an air-fuel ratio detected by an air-fuel ratio sensor located downstream of the catalyst, thus suppressing deterioration of emission characteristics.

SOLUTION: An air-fuel ratio control device for an internal combustion engine comprises a controller that controls a correction for setting an air-fuel ratio on a downstream side of catalyst to a prescribed air-fuel ratio. The controller comprises: air-fuel ratio detection means for detecting an air-fuel ratio in an exhaust passage at a downstream side via a downstream-side exhaust gas sensor arranged at the downstream side of the catalyst; suction air quantity detection means for detecting a suction air quantity Ga of intake air of the internal combustion engine; valve opening detection means for detecting a degree of opening of a waste gate valve; and air-fuel ratio correction means. The air-fuel ratio correction means makes a correction with a predefined feedback correction amount which is based on the suction air quantity Ga and the degree of opening.

SELECTED DRAWING: Figure 3

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to an air-fuel ratio control device for an internal combustion engine equipped with a supercharger, and particularly relates to an air-fuel ratio control device for an internal combustion engine equipped with an exhaust purification catalyst disposed downstream of a turbine of the supercharger.

Patent Document 1 describes an air-fuel ratio control device for an internal combustion engine for always maintaining optimal emission characteristics downstream of an exhaust purification catalyst. Specifically, main feedback control sets the fuel injection amount based on the output value of an air-fuel ratio sensor installed upstream of the catalyst (three-way exhaust gas purification catalyst) in the exhaust passage, and The fuel injection amount is also controlled by executing sub-feedback control that corrects deviations in main feedback control based on the output value of an oxygen sensor provided at a downstream location. In Patent Document 1, the deviation in main feedback control is focused on the amount of intake air, and in a region where the amount of intake air exceeds a predetermined value, the air-fuel ratio on the upstream side of the catalyst is adjusted based on the outputs of the upstream and downstream sensors. It is said that by controlling the fuel injection amount so that the air-fuel ratio is richer than the stoichiometric (stoichiometric air-fuel ratio), it is possible to achieve more stable and better emission characteristics than in the stoichiometric state.

Japanese Patent Application Publication No. 2005-351250

In the catalyst characteristic correction amount for an internal combustion engine described in Patent Document 1, by performing correction based on the amount of intake air, the catalyst is brought into a stoichiometric state and the emission characteristics are improved. However, when a turbocharger turbine is provided in the exhaust passage of a supercharged internal combustion engine, and a bypass passage that detours around the turbine is further provided, the catalyst characteristic correction amount cannot be corrected by only the above-mentioned intake air amount. There is a possibility that the emission characteristics cannot be sufficiently improved.

A specific reason why the emission characteristics cannot be sufficiently improved is that the flow of exhaust gas in the exhaust passage changes depending on the opening degree of the waste gate valve. In the exhaust passage, the combustion exhaust gas discharged from the combustion chamber is combined with the exhaust gas from the bypass passage and the exhaust gas from the turbine, and hits the inlet surface of the catalyst. The angle at which exhaust gas flows from the above-mentioned bypass passage changes between a state in which the opening degree of the waste gate valve is decreased and a state in which the opening degree is increased.

Furthermore, the temperature of the exhaust gas from the turbine is lower than that of the exhaust gas from the bypass passage, into which the combustion exhaust gas directly flows, because the turbine rotates and recovers thermal energy. The exhaust gas hits the entire surface of the catalyst. On the other hand, the flow of exhaust gas from the bypass passage has no stirring action or structure compared to the flow of exhaust gas from the turbine, so the flow has momentum and hits the catalyst in a locally concentrated manner. In other words, the angle at which exhaust gas flows changes depending on the opening degree of the wastegate valve, so when the flow of exhaust gas from the turbine and the flow of exhaust gas from the bypass passage merge, the amount of gas hitting the catalyst will be uneven. There are cases.

On the other hand, since the air-fuel ratio detection sensor placed downstream of the catalyst is installed in a position off the center of the catalyst outlet in the exhaust passage, the amount of gas hitting the catalyst due to the opening degree of the waste gate valve mentioned above is reduced. Due to this bias, the detection by the air-fuel ratio detection sensor at the catalyst outlet becomes susceptible to influence.

For example, suppose the bypass passage outlet is provided at the bottom of the vehicle in the vertical direction in the exhaust passage, the waste gate valve is opened at a certain opening degree, and the air-fuel ratio detection sensor at the catalyst outlet is located at the top of the vehicle in the vertical direction. Let's assume that when the system is installed, the amount of fuel injection is controlled to burn a richer mixed gas due to a change in operating conditions, and the richer exhaust gas flows into the exhaust passage. Rich exhaust gas from the bypass passage with high temperature and flow through the wastegate valve is concentrated locally at the lower part of the inlet face of the catalyst, passes through the catalyst, and exits from the lower part of the outlet face of the catalyst. come. Since the catalyst outlet air-fuel ratio detection sensor installed at the top of the catalyst outlet surface detects the air-fuel ratio of the exhaust gas near the sensor, the sensor is located at the bottom of the catalyst outlet surface where rich exhaust gas is concentrated. Therefore, the detected air-fuel ratio value is detected to be lean exhaust gas compared to the lower part, and there is a possibility that the fuel injection amount is controlled to make it even richer. By making the fuel richer than necessary, harmful substances such as hydrocarbons are likely to be emitted, and there is a risk that emission characteristics may deteriorate.

On the other hand, let us assume a case where the waste gate valve is in a state where the opening degree is decreased from a certain predetermined opening degree and rich exhaust gas flows into the exhaust passage. The rich exhaust gas from the bypass passage with high temperature and flow through the wastegate valve is blown to the upper part by reducing the valve opening of the wastegate valve, and the rich exhaust gas is blown to the upper part of the inlet surface of the catalyst. It hits the catalyst in a concentrated manner, passes through the catalyst, and emerges from the upper part of the exit surface of the catalyst. Since the catalyst outlet air-fuel ratio detection sensor is attached to the upper part of the catalyst outlet surface where rich exhaust gas is concentrated, the detected air-fuel ratio value indicates that the exhaust gas is richer than the lower part. Therefore, it is determined that the detected air-fuel ratio satisfies the requirements, but the lower part of the catalyst is not sufficiently exposed to exhaust gas, and exhaust gas containing nitrogen oxides that could not be purified comes out from the catalyst outlet. is likely to be emitted, and the emission characteristics may deteriorate.

In particular, in the case where the distance between the turbine and the catalyst is relatively short and the catalyst is placed close to each other, the flow characteristics of the exhaust gas from the turbine, the exhaust gas from the bypass passage, and the exhaust gas due to the opening degree of the waste gate valve will affect the catalyst. The bias per gas may become even larger.

This invention has been made with a focus on the above-mentioned technical problem, and is based on the air-fuel ratio detected by the air-fuel ratio sensor located downstream of the catalyst. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can suppress deterioration of emission characteristics by making corrections due to the bias in .

In order to achieve the above object, the present invention provides a supercharger having a turbine provided in an exhaust passage of an internal combustion engine, a catalyst provided downstream of the turbine in the exhaust passage, and a catalyst provided downstream of the turbine in the exhaust passage. a bypass passage that branches from the exhaust passage upstream, bypasses the turbine and joins the exhaust passage upstream of the catalyst; and a waste gate valve whose flow cross-sectional area of the bypass passage can be changed by a valve opening degree. An air-fuel ratio control device for an internal combustion engine, comprising: a controller that controls correction for adjusting an air-fuel ratio downstream of the catalyst to a predetermined air-fuel ratio, the controller disposed downstream of the catalyst. air-fuel ratio detection means for detecting the air-fuel ratio on the downstream side of the exhaust passage by a downstream exhaust gas sensor; intake air amount detection means for detecting the intake air amount of the intake air of the internal combustion engine; It further includes a valve opening degree detection means for detecting a valve opening degree, and an air-fuel ratio correction means, and the air-fuel ratio correction means corrects it by a predetermined feedback correction amount based on the intake air amount and the valve opening degree. It is characterized in that it is configured to.

According to this invention, the air-fuel ratio detection value detected by the exhaust gas sensor on the downstream side of the catalyst is corrected by adding a predetermined feedback correction amount based on the intake air amount and the opening degree of the waste gate valve. Accordingly, it is possible to determine an appropriate air-fuel ratio by correcting the imbalance in the amount of gas hitting the catalyst due to the opening degree of the waste gate valve. Therefore, a mixture with a stable air-fuel ratio is burned and discharged without excess or deficiency of fuel for the requested air-fuel ratio, and exhaust gas with an appropriate air-fuel ratio passes through the catalyst, suppressing deterioration of emission characteristics. can do.

FIG. 1 is a schematic diagram for explaining the configuration of an embodiment of the present invention. FIG. 2 is a block diagram for explaining an example of a control device in an embodiment of the invention. FIG. 3 is a schematic diagram for explaining feedback correction of an air-fuel ratio control device for an internal combustion engine in an embodiment of the present invention. 1 is a flowchart for explaining a control example of an air-fuel ratio control device for an internal combustion engine in an embodiment of the present invention.

An example of an air-fuel ratio control device for an internal combustion engine according to an embodiment of the present invention will be described with reference to FIG. A supercharged internal combustion engine (hereinafter referred to as engine) 1 shown in FIG. The exhaust gas passage 4 includes an intake passage 3 in which the fuel and air are combusted, and an exhaust passage 4 in which exhaust gas generated by burning a mixture of fuel and air flows.

An air cleaner 5 is provided upstream of the intake passage 3 shown in FIG. A throttle valve 6 is provided. This throttle valve 6 can be used in the same configuration as a conventional throttle valve. That is, it can be configured by an electronically controlled throttle valve that can determine the load required of the engine based on the amount of accelerator operation by the driver, and control the opening degree according to the load.

On the downstream side of the throttle valve 6, an intake manifold 7 is provided for supplying air to a plurality of cylinders, similar to a conventional engine. That is, the downstream side of the intake passage 3 is branched into a number corresponding to the number of cylinders, and the tips thereof are connected to the cylinder block 2.

An exhaust passage 4 is connected to the cylinder block 2 for outputting exhaust gas generated by burning the air-fuel mixture. Specifically, the upstream portion of the exhaust passage 4 is provided with an exhaust manifold 8 that is branched into a number corresponding to the number of cylinders and connected to each cylinder, similar to a conventional engine. That is, exhaust gas discharged from each cylinder is combined via the exhaust manifold 8.

A three-way exhaust gas purification catalyst (hereinafter simply referred to as catalyst) 9 is provided downstream of the exhaust passage 4 to remove substances such as hydrocarbons, carbon monoxide, and nitrogen oxides contained in the exhaust gas. ing. The catalyst 9 is made of, for example, porous ceramic and has a large number of passages in a lattice pattern, and the porous body has holes on the inlet side and holes on the outlet side that are alternately closed, and holes on the inlet side that are open. The structure is such that the exhaust gas entering the open passage passes through a partition wall that separates the passages and escapes to the passage whose exit side is open. Then, the purified exhaust gas is discharged outside the vehicle via the catalyst 9. Note that another catalytic converter (not shown) may be added downstream of the catalyst 9 in order to further purify the exhaust gas that has passed through the catalyst 9.

In the exhaust passage 4 and on the downstream side of the catalyst 9, an air-fuel ratio sensor 10 is installed as an exhaust gas sensor. Output. Note that the air-fuel ratio sensor is arranged at least on the downstream side of the catalyst 9, and for example, the air-fuel ratio sensor is further arranged in addition to the air-fuel ratio sensor 10 on the upstream side of the catalyst 9, and is arranged on the downstream side of the catalyst 9. The air-fuel ratio is adjusted by controlling the fuel injection amount of an injector (not shown) based on the air-fuel ratio detection value of the air-fuel ratio sensor 10, and the exhaust gas entering the catalyst 9 is controlled by the air-fuel ratio sensor (not shown) provided upstream of the catalyst 9. The air-fuel ratio may also be detected.

A turbine housing 11 is provided between the exhaust manifold 8 and the catalyst 9 in the exhaust passage 4, and a turbine impeller 12 that rotates as exhaust gas flows is provided inside the turbine housing 11. This turbine impeller 12 can have a similar configuration to a turbine impeller configuring a conventional supercharger.

One end of a connecting shaft 13 is connected to the rotation center axis of the turbine impeller 12 so as to be integrally rotatable, and a compressor impeller 14 is connected to the other end of the connecting shaft 13 so as to be integrally rotatable. ing.

The compressor impeller 14 is housed in a compressor housing 15 provided between the air cleaner 5 and the throttle valve 6 in the intake passage 3. Therefore, the turbine impeller 12 is rotated by the exhaust gas, and the compressor impeller 14 is rotated in conjunction with the turbine impeller 12. As a result, the air flowing through the intake passage 3 is fed under pressure, thereby increasing the supercharging pressure.

In order to control the amount of exhaust gas flowing into the turbine housing 11 , a bypass passage 16 is provided on the upstream and downstream sides of the turbine housing 11 in the exhaust passage 4 and communicates with the turbine housing 11 , bypassing the turbine housing 11 . is provided with a waste gate valve 17 that controls the cross-sectional area of the flow path. This waste gate valve 17 is a normally open type valve that is always open, and is configured to adjust the cross-sectional area of the flow path by an opening sensor 18 installed near the waste gate valve when there is a request for supercharging. has been done. In addition, when reducing the flow path cross-sectional area by changing the opening degree of the waste gate valve 17, the opening degree of the waste gate valve 17 is not limited to being set to a fully closed state, but an intermediate opening degree that can be set to an appropriate opening degree is used. may be provided.

By providing the waste gate valve 17 in this way, the exhaust gas discharged from the cylinder is once branched into the bypass exhaust gas 19, which is the exhaust gas from the bypass passage 16, and the turbine exhaust gas 20, which is the exhaust gas from the turbine. They merge in the exhaust passage 4 on the upstream side.

Next, an electronic control unit (ECU) 21 for controlling the engine 1 is provided. This ECU 21 corresponds to the "controller" in the embodiment of the present invention, and is mainly composed of a microcomputer. FIG. 2 is a block diagram for explaining an example of the configuration of the ECU 21. As shown in FIG.

The ECU 21 is configured to receive data from various sensors mounted on the vehicle, and output command signals based on the input data and pre-stored maps, calculation formulas, and the like. An example of data input to the ECU 21 is shown in FIG. 2, which includes a signal from an air-fuel ratio sensor 10 that detects the air-fuel ratio, a signal from an accelerator opening sensor that detects the operating amount of an accelerator pedal (not shown), and the rotational speed of the engine 1. Data such as a signal from a sensor that detects the opening of the waste gate valve 17 and an opening sensor 18 that detects the opening of the waste gate valve 17 are input to the ECU 21 .

The ECU 21 shown in FIG. 2 includes at least an air-fuel ratio detection means 22, an intake air amount detection means 23, a valve opening detection means 24, and an air-fuel ratio correction means 25 as a functional configuration.

The air-fuel ratio detection means 22 has a function of detecting the air-fuel ratio after passing through the catalyst 9 based on the air-fuel ratio sensor 10.

The intake air amount detection means 23 has a function of calculating the intake air amount Ga of the engine 1 based on the engine speed and the accelerator opening. Alternatively, it may be determined based on an intake air amount map stored in advance in the ECU 21.

The valve opening detection means 24 has a function of detecting the opening of the waste gate valve 17 based on the opening sensor 18.

The air-fuel ratio correction means 25 has a function of determining an air-fuel ratio feedback correction amount based on data obtained by the air-fuel ratio detection means 22, the intake air amount detection means 23, and the valve opening detection means 24. There is. Then, the air-fuel ratio after passing through the catalyst 9 is corrected based on data such as the air-fuel ratio feedback correction amount inputted to the ECU 21.

As described above, depending on the opening degree of the waste gate valve 17, it is necessary to take into consideration the uneven distribution of the exhaust gas flow to the catalyst 9 and the strength of the contact with the catalyst 9, that is, the variation in the flow velocity of the exhaust gas. Therefore, the air-fuel ratio feedback correction amount determined based on the variation in the flow velocity of exhaust gas on the inlet surface of the catalyst 9, etc., for correcting the value of the air-fuel ratio detected by the air-fuel ratio sensor 10 will be specifically explained.

FIG. 3 is a schematic diagram for explaining feedback correction of an air-fuel ratio control device for an internal combustion engine in an embodiment of the present invention. As a method for determining the air-fuel ratio feedback correction amount, first, based on the detected values of the intake air amount Ga and the opening degree of the waste gate valve 17, the uneven distribution of exhaust gas concentration near the inlet of the catalyst 9 and the inlet of the catalyst 9 are determined. Changes in the flow velocity of exhaust gas on the surface are verified and calculated in advance using computational fluid dynamics (CFD), and a two-dimensional array map (2D map) is created based on the verification data. The air-fuel ratio feedback correction amount is determined from the variation in exhaust gas concentration depending on the opening degree of the valve 17 and the relationship between the flow velocity of the exhaust gas and the position of the air-fuel ratio sensor 10, and is stored in the ECU 21.

Here, two examples of verification data by CFD are given: calculation by grid point division (a) and calculation by sensor unit (b). In calculation (a) using lattice point division in FIG. 3, first, the intake air amount Ga and the opening degree of the waste gate valve 17 are input. Next, looking at the cells formed in a lattice of the catalyst 9 from the front, each cell of the catalyst 9 is divided into a lattice, and the flow velocity and concentration of exhaust gas at each lattice point (intersection of each lattice) are analyzed. Verify and calculate the required air-fuel ratio. Since each grid point of the catalyst 9 is analyzed, a highly accurate correction amount can be determined.

Next, in the calculation (b) by the sensor section in FIG. 3, the intake air amount Ga and the opening degree of the waste gate valve 17 are first input, similar to the calculation (a) by grid point division. Then, looking at the grid-shaped cells of the catalyst 9 from the front, the overall flow velocity and concentration of exhaust gas at the tip 10' of the air-fuel ratio sensor 10 are analyzed and verified, and the required air-fuel ratio is calculated. . In order to verify the flow rate and concentration of exhaust gas at the tip 10' of the air-fuel ratio sensor by comparing the entire catalyst 9, the amount of information input is reduced compared to calculation (a) using grid point division to reduce the amount of calculation. That is, the processing time can be shortened.

Therefore, a two-dimensional array map is created based on the verification data obtained by the calculation by grid point division (a) or the calculation by the sensor section (b), and is stored in the ECU 21. Then, when the air-fuel ratio correction means 25 is executed, the air-fuel ratio after passing through the catalyst 9 is corrected based on data such as a predetermined air-fuel ratio feedback correction amount.

Further, the air-fuel ratio control device for an internal combustion engine in the embodiment of the present invention described above is configured to execute the control described below. FIG. 4 is a flowchart for explaining an example of the control, and the control shown in these flowcharts is repeatedly executed by the ECU 21 while the engine 1 is being operated. First, the air-fuel ratio is detected (step S1). The air-fuel ratio is determined by the air-fuel ratio detection means 22. Specifically, the air-fuel ratio after passing through the catalyst 9 is detected based on the air-fuel ratio sensor 10.

Next, the intake air amount Ga is detected (step S2). The intake air amount Ga is determined by the intake air amount detection means 23. Specifically, the intake air amount Ga of the engine 1 is calculated based on the engine speed and the accelerator opening.

Following this, the opening degree of the waste gate valve 17 is detected (step S3). The opening degree of the waste gate valve 17 is determined by the valve opening detection means 24. Specifically, the opening degree of the waste gate valve 17 is detected based on the opening degree sensor 18 .

Subsequently, the air-fuel ratio is corrected (step S4). The air-fuel ratio feedback correction amount is determined based on the data obtained by the air-fuel ratio detection means 22, the intake air amount detection means 23, and the valve opening detection means 24, and the air-fuel ratio feedback correction amount input into the ECU 21, etc. Based on the data, the air-fuel ratio after passing through the catalyst 9 is corrected. Once the air-fuel ratio has been corrected, the routine shown in FIG. 4 is temporarily terminated.

By determining the air-fuel ratio feedback correction amount and correcting the air-fuel ratio, exhaust gas with an appropriate air-fuel ratio can pass through the catalyst 9. Specifically, a predetermined air-fuel ratio feedback correction amount based on the intake air amount Ga and the opening degree of the waste gate valve 17 is added to the air-fuel ratio detection value detected by the air-fuel ratio sensor on the downstream side of the catalyst 9. By performing the correction, it is possible to correct the imbalance in the amount of gas hitting the catalyst 9 due to the opening degree of the waste gate valve 17, and to determine an appropriate air-fuel ratio. Therefore, the air-fuel mixture with a stable air-fuel ratio is burned and discharged without excess or deficiency of fuel relative to the requested air-fuel ratio, and exhaust gas with an appropriate air-fuel ratio passes through the catalyst 9, thereby preventing deterioration of emission characteristics. Can be suppressed.

Note that this invention is not limited to the embodiments described above, and can be implemented with appropriate modifications within the scope of the objective of this invention. Furthermore, the present invention is not limited to the configuration of the flowchart described above. For example, the order of step S1 and step S2 may be changed, and two examples of methods for determining the air-fuel ratio feedback correction amount are calculation by grid point division (a) and calculation by the sensor unit (b). However, it is not limited to these. The intake air amount Ga and the opening degree of the waste gate valve 17 are input, and the variation in the flow velocity of exhaust gas at the inlet face of the catalyst 9 is analyzed and calculated to correct the air-fuel ratio of the catalyst 9 (catalyst stoichiometric state). If so, the analysis and calculation methods are not particularly limited.

1 Engine 2 Cylinder block 3 Intake passage 4 Exhaust passage 5 Air cleaner 6 Throttle valve 7 Intake manifold 8 Exhaust manifold 9 Catalyst 10 Air-fuel ratio sensor 10' Tip part 11 Turbine housing 12 Turbine impeller 13 Connection shaft 14 Compressor impeller 15 Compressor housing 16 Bypass passage 17 Waste gate valve 18 Opening sensor 19 Bypass exhaust gas 20 Turbine exhaust gas 21 ECU
22 Air-fuel ratio detection means 23 Intake air amount detection means 24 Valve opening detection means 25 Air-fuel ratio correction means Ga Intake air amount

Claims (1)

A supercharger having a turbine provided in an exhaust passage of an internal combustion engine, a catalyst provided downstream of the turbine in the exhaust passage, and a supercharger branching from the exhaust passage upstream of the turbine and bypassing the turbine. An air-fuel ratio control device for an internal combustion engine, comprising: a bypass passage that merges with the exhaust passage upstream from the catalyst; and a wastegate valve that can change the cross-sectional area of the bypass passage by changing the valve opening. ,
A controller that controls correction for adjusting the air-fuel ratio downstream of the catalyst to a predetermined air-fuel ratio,
The controller includes:
air-fuel ratio detection means for detecting an air-fuel ratio on the downstream side of the exhaust passage by a downstream exhaust gas sensor disposed downstream of the catalyst; and intake air amount detection means for detecting the intake air amount of intake air of the internal combustion engine. , further comprising a valve opening detection means for detecting the valve opening of the wastegate valve, and an air-fuel ratio correction means,
An air-fuel ratio control device for an internal combustion engine, wherein the air-fuel ratio correction means is configured to perform correction using a predetermined feedback correction amount based on the intake air amount and the valve opening degree.

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