JP3912488B2 - Air-fuel ratio control device for multi-cylinder internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control apparatus for a multi-cylinder internal combustion engine, and more particularly to an air-fuel ratio feedback control technique when a plurality of catalytic converters are provided in parallel in a dual exhaust manifold system.
[0002]
[Related background]
In an internal combustion engine (engine), output can be improved by reducing exhaust interference and utilizing exhaust pulsation. Therefore, for example, in a four-cylinder engine, four exhaust passages are combined into two exhaust passages from a group of cylinders whose combustion order is not continuous, and these two exhaust passages are further combined into one. A 2-1 type exhaust manifold system, that is, a 4-2-1 dual exhaust manifold system is known.
[0003]
On the other hand, exhaust purification technology using a catalytic converter is known for the purpose of reducing harmful substances (HC, CO, NOx, etc.) in the exhaust. Since such a catalytic converter does not function sufficiently unless a certain activation temperature is reached, it is required to be disposed as close to the engine as possible. For example, a catalytic converter (manifold catalyzer converter or front catalyzer converter, hereinafter referred to as MCC, An exhaust purification system in which FCC is abbreviated to the exhaust manifold is employed.
[0004]
When arranging the MCC or FCC in the 4-2-1 dual exhaust manifold system, considering that the MCC or the FCC is arranged in the vicinity of the engine as much as possible, for example, two MCCs are individually provided in the two exhaust passage portions. It is desirable to arrange.
[0005]
[Problems to be solved by the invention]
By the way, in order for the catalytic converter to effectively catalyze harmful substances in the exhaust gas, it is necessary to control the exhaust air-fuel ratio flowing into the catalytic converter in the vicinity of a predetermined air-fuel ratio. An exhaust sensor (λ sensor or the like) is provided, and air-fuel ratio feedback control is performed to adjust the combustion air-fuel ratio of the internal combustion engine, that is, the intake air amount and the fuel injection amount to an appropriate one based on the air-fuel ratio information from the exhaust sensor. I have to.
[0006]
However, when the exhaust sensors are arranged upstream of the catalytic converter in this way, when two MCCs are provided in the 4-2-1 dual exhaust system as described above, the exhaust sensors are arranged upstream of each MCC. This is not preferable because it leads to cost increase.
Therefore, it is conceivable that only one air-fuel ratio sensor is provided in a portion where the exhaust passages downstream of the MCC are gathered. However, the single air-fuel ratio sensor can be used to determine the combustion air-fuel ratio for each cylinder group. The challenge is to optimize the exhaust air-fuel ratio flowing into each catalytic converter.
[0007]
The present invention has been made to solve such problems, and the object of the present invention is to reduce the cost with a single air-fuel ratio sensor when a plurality of catalytic converters are provided in parallel in a dual exhaust manifold system. An object of the present invention is to provide an air-fuel ratio control device for a multi-cylinder internal combustion engine capable of leveling the exhaust air-fuel ratio flowing into each catalytic converter and appropriately performing air-fuel ratio feedback control.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a plurality of exhaust passages provided for each cylinder group consisting of a plurality of cylinders in which combustion does not continue among the cylinders of the multi-cylinder internal combustion engine, A plurality of catalytic converters respectively disposed in the exhaust passage; and an exhaust sensor that detects an exhaust air-fuel ratio provided at a collection portion of the plurality of exhaust passages downstream of the plurality of catalytic converters in the exhaust flow direction; Based on the exhaust air / fuel ratio information detected by the exhaust sensor, combustion air / fuel ratio control means for feedback correcting the combustion air / fuel ratio so that the average exhaust air / fuel ratio becomes a predetermined air / fuel ratio, and for each cylinder group according to the operating state, A cylinder resting means for closing the at least the exhaust valves of the plurality of cylinders and stopping the fuel supply to perform a cylinder resting operation, and a cylinder resting air for sequentially switching a cylinder group performing the cylinder resting operation by the cylinder resting means. When a feedback correction is performed by the group switching means and the combustion air-fuel ratio control means and a cylinder resting operation is performed by the cylinder resting means, the combustion air-fuel ratio of the combustion cylinder group feedback-corrected by the combustion air-fuel ratio control means is determined for each cylinder group. And a combustion air-fuel ratio learning means for storing and learning.
[0009]
That is, for example, a dual exhaust system is adopted for a multi-cylinder internal combustion engine (for example, a four cylinder engine), and a catalytic converter is provided in parallel in each of a plurality of exhaust passages of the dual exhaust system, so that a plurality of exhaust passages, that is, a cylinder group is provided. In the air-fuel ratio control apparatus for a multi-cylinder internal combustion engine that can be operated in a cylinder-free manner, only one exhaust sensor is provided at a collection portion of a plurality of exhaust passages, and the combustion air-fuel ratio is determined based on the exhaust air-fuel ratio information from the one exhaust sensor. Combustion cylinders that are feedback-corrected based on exhaust air-fuel ratio information from the one exhaust sensor while performing feedback correction and performing cylinder-cylinder operation for each cylinder group according to the operating state while switching the cylinder group that performs cylinder-cylinder operation The combustion air-fuel ratio is learned for each cylinder group based on the combustion air-fuel ratio of the group.
[0010]
As a result, in a dual exhaust system having a plurality of exhaust passages each having a catalytic converter in parallel, even if only one exhaust sensor is provided at a collection portion of the plurality of exhaust passages, the combustion air-fuel ratio for each cylinder group The exhaust air-fuel ratio flowing into each catalytic converter can be leveled reliably, and the air-fuel ratio feedback control can be properly performed as a whole.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of an air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to the present invention. The configuration of the air-fuel ratio control apparatus will be described below.
As shown in the figure, an engine main body (hereinafter simply referred to as an engine) 1 that is a multi-cylinder internal combustion engine, for example, in a compression stroke together with fuel injection in an intake stroke (intake stroke injection) by switching a fuel injection mode. An in-cylinder injection type spark ignition type 4-cycle 4-cylinder gasoline engine capable of performing the fuel injection (compression stroke injection) is employed. The in-cylinder injection type engine 1 can be operated at a rich air-fuel ratio (rich air-fuel ratio operation) or a lean air-fuel ratio operation (lean air-fuel ratio operation) in addition to the operation at the stoichiometric air-fuel ratio (stoichio). It is.
[0012]
As shown in the figure, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, so that fuel can be directly injected into the combustion chamber. .
An ignition coil 8 that outputs a high voltage is connected to the spark plug 4. Further, a fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe 7. More specifically, the fuel supply device is provided with a low pressure fuel pump and a high pressure fuel pump, whereby fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. Can be injected from the fuel injection valve 6 into the combustion chamber at a desired fuel pressure.
[0013]
An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected so as to communicate with each intake port. The intake manifold 10 is provided with an electromagnetic throttle valve 14 for adjusting the intake air amount.
Further, an exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of the exhaust manifold 20 is connected to communicate with each exhaust port. Here, as the exhaust manifold 20, a dual type exhaust manifold system as shown in FIG. 2 is employed.
[0014]
In the exhaust manifold 20 including the dual type exhaust manifold system, the exhaust passage 20a from the # 1 cylinder, the exhaust passage 20d from the # 4 cylinder, the exhaust passage 20b from the # 2 cylinder, and the exhaust passage 20c from the # 3 cylinder merge. (When the combustion order is # 1 → # 3 → # 4 → # 2). That is, the # 1 and # 4 cylinders that do not continue combustion are combined into one cylinder group (# 1, # 4 cylinder group), and the # 2 and # 3 cylinders that also do not continue combustion are combined with another cylinder group (# 2). , # 3 cylinder group). Thereby, in the exhaust manifold 20, as described above, the exhaust interference is reduced, and a large effect of exhaust inertia or exhaust pulsation can be obtained.
[0015]
An exhaust pipe 28 is connected to the other end of the exhaust manifold 20 via a collecting pipe 22, and the collecting pipe 22 is connected to the collecting pipe 22a and the exhaust passage 20b through which exhaust gas from the exhaust passage 20a and the exhaust passage 20d flows. It consists of two pipe lines (dual pipe lines) of the collecting pipe 22b through which the exhaust gas from the exhaust passage 20c flows. That is, in the collecting pipe 22, exhaust gas from one cylinder group consisting of # 1 cylinder and # 4 cylinder flows through the collecting pipe 22a, and exhaust gas from another cylinder group consisting of # 2 cylinder and # 3 cylinder is collected in the collecting pipe 22b. It is configured to flow through.
[0016]
The collecting pipe 22a is provided with a three-way catalyst (manifold catalyzer converter, hereinafter abbreviated as MCC) 24 as a front-stage catalytic converter. Similarly, the collecting pipe 22b has a three-way catalyst (hereinafter referred to as MCC) as a front-stage catalyst. (Not shown) 26 is interposed. When the MCCs 24 and 26 are interposed in the collecting pipe 22a and the collecting pipe 22b as described above, the MCCs 24 and 26 can be activated early even if the engine 1 is in a cold state because the MCCs 24 and 26 are located close to the engine 1. Therefore, it is possible to satisfactorily purify harmful substances (HC, CO, NOx, etc.) in the exhaust gas regardless of the operating state.
[0017]
A transition portion from the collecting pipe 22 to the exhaust pipe 28, that is, a collecting section 27 of the collecting pipe 22a and the collecting pipe 22b has a linear air-fuel ratio sensor (λ sensor, hereinafter abbreviated as LAFS) 29 as an exhaust sensor. One is provided.
Further, a three-way catalyst (underfloor catalyzer converter, hereinafter abbreviated as UCC) 30 is interposed in the exhaust pipe 28 as a post-stage catalytic converter. As described above, when the UCC 30 is further provided downstream of the MCCs 24 and 26, harmful substances (HC, CO, NOx, etc.) in the exhaust gas can be further purified.
[0018]
Further, the engine 1 is configured to be able to perform a cylinder resting operation for each cylinder group (# 1, # 4 cylinder group and # 2, # 3 cylinder group). That is, the engine 1 is configured to be able to stop the fuel supply from the fuel injection valve 6 while maintaining the exhaust valve of each cylinder in the closed state for each cylinder group (cylinder resting means). Specifically, the engine 1 has, for example, a variable cam mechanism in order to keep the exhaust valve in a closed state. However, the variable cam mechanism is well known, and the details thereof are omitted here. As a result, the fuel consumption can be improved by stopping the fuel supply to some of the cylinders at the time of low and medium load operation where a high output is not required.
[0019]
The electronic control unit (ECU) 60 includes an input / output device, a storage device (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like. Comprehensive control of the air-fuel ratio control device is performed.
In addition to the LAFS 29 described above, various sensors such as a crank angle sensor 62 are connected to the input side of the ECU 60, and detection information from these sensors is input. When the crank angle is detected by the crank angle sensor 62, the current combustion cylinder is determined based on the crank angle, and the engine speed Ne is detected.
[0020]
On the other hand, various output devices such as the fuel injection valve 6, the ignition coil 8, and the throttle valve 14 are connected to the output side of the ECU 60, and these various output devices are operated based on detection information from various sensors. The fuel injection amount, the fuel injection timing, the ignition timing, etc., are output, respectively, whereby an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and spark ignition is carried out at an appropriate timing by the spark plug 4 Is done.
[0021]
When the engine 1 is operating at the stoichiometric air-fuel ratio (stoichio), the combustion air-fuel ratio feedback correction (hereinafter referred to as F / B correction) is performed so that the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio (predetermined air-fuel ratio). (Combustion air-fuel ratio control means). Specifically, in the normal F / B correction, based on the exhaust air / fuel ratio information from the LAFS 29, the combustion air / fuel ratio is set in the order of the combustion cylinders (# 1) so that the exhaust air / fuel ratio becomes a predetermined air / fuel ratio (for example, the theoretical air / fuel ratio). → # 3 → # 4 → # 2) (see FIG. 4 described later). Note that the target predetermined air-fuel ratio may not be the stoichiometric air-fuel ratio, and may be, for example, a light lean or a light rich air-fuel ratio.
[0022]
By the way, the F / B correction can control the average exhaust air-fuel ratio to the stoichiometric air-fuel ratio as a whole, but actually the combustion air-fuel ratio varies for each cylinder, and therefore the collecting pipe having the MCCs 24 and 26 is provided. Exhaust air / fuel ratios in 22a and collecting pipe 22b are not exactly stoichiometric, but often vary. As described above, if the exhaust air-fuel ratio in the collecting pipe 22a and the collecting pipe 22b varies as described above, harmful substances in the exhaust cannot be effectively catalyzed in the MCCs 24 and 26, which is preferable. Absent.
[0023]
Therefore, in the air-fuel ratio control apparatus according to the present invention, in addition to the F / B correction, furthermore, variation in the exhaust air-fuel ratio in the collecting pipe 22a and the collecting pipe 22b is suppressed, and exhaust is performed from one cylinder group and another cylinder group. The air-fuel ratio of the exhaust gas is leveled.
Referring to FIG. 3, the control routine of the combustion group-by-cylinder group learning control of the combustion air-fuel ratio, that is, the cylinder group-by-cylinder group A / F learning control according to the present invention is shown in a flowchart, and will be described along the flowchart.
[0024]
First, in step S1, it is determined whether or not the F / B correction is being performed. If the determination result is false (No) and it is determined that the F / B correction is not being performed, the routine exits without doing anything, while the determination result is true (Yes) and the F / B If it is determined that correction is in progress, the process proceeds to step S10.
In step S10, it is determined whether the current mode is the cylinder deactivation control mode, that is, the exhaust valve for one of the one cylinder group (# 1, # 4 cylinder group) and the other cylinder group (# 2, # 3 cylinder group). Is closed and it is determined whether or not the fuel supply is stopped. Actually, when the engine load is relatively small, the cylinder resting operation is performed. Here, based on, for example, the accelerator opening degree, it is determined whether or not the engine load is equal to or less than a predetermined value. If the determination result is false (No), the routine is exited as it is. In this case, F / B correction is performed as usual. On the other hand, if the determination result is true (Yes) and it is determined that the cylinder resting control mode is currently in progress, the process proceeds to step S12.
[0025]
In step S12, it is determined whether or not the cylinder deactivation cylinder group in the cylinder deactivation operation performed last time is one cylinder group (# 1, # 4 cylinder group). If the determination result is true (Yes) and it is determined that the previous cylinder resting cylinder group is the # 1, # 4 cylinder group, the process proceeds to step S14. On the other hand, if the determination result is false (No) and it is determined that the previous cylinder-cylinder group is not # 1, # 4 cylinder group but # 2, # 3 cylinder group, the process proceeds to step S20. .
[0026]
That is, in step S12, the cylinder group in which the cylinder is deactivated is switched alternately (cylinderless cylinder group switching means).
In step S14, the cylinder resting operation is performed for the other cylinder groups (# 2, # 3 cylinder group). That is, the cylinder resting operation is performed for the # 2 and # 3 cylinder groups different from the cylinder group that has been previously deactivated, and the combustion operation is performed only for the # 1 and # 4 cylinder groups.
[0027]
In step S16, an error e # between the predetermined air-fuel ratio (theoretical air-fuel ratio) that is the target of the F / B correction and the current average exhaust air-fuel ratio, that is, the current average exhaust air-fuel ratio for the # 1 and # 4 cylinder groups. 1 and 4 are detected.
In step S18, the supplied fuel amount of the # 1, # 4 cylinder group (# 1 cylinder and # 4 cylinder) is corrected based on the error e # 1, 4 thus detected, and the corrected supplied fuel is corrected. The quantity, that is, the combustion air-fuel ratio is stored and learned (combustion air-fuel ratio learning means).
[0028]
On the other hand, in step S20, the cylinder resting operation is performed for one cylinder group (# 1, # 4 cylinder group). That is, the cylinder resting operation is performed for the # 1 and # 4 cylinder groups that are different from the cylinder group that was previously deactivated, and the combustion operation is performed only for the # 2 and # 3 cylinder groups.
In step S22, an error e # 2, 3 between the predetermined air-fuel ratio that is the target of F / B correction and the current average exhaust air-fuel ratio, that is, the current average exhaust air-fuel ratio for the # 2 and # 3 cylinder groups is detected. To do.
[0029]
In step S24, the supplied fuel amount of the # 2, # 3 cylinder group (# 2 cylinder and # 3 cylinder) is corrected based on the error e # 2, 3 detected in this way, and the corrected supplied fuel is corrected. The quantity, that is, the combustion air-fuel ratio is stored and learned (combustion air-fuel ratio learning means).
That is, referring to FIG. 4, the output value of LAFS 29 in the order of combustion cylinders (for example, # 1 → # 4 or # 2 → # 3) when F / B correction is performed and cylinder resting operation is performed (ie, The time variation of the exhaust air / fuel ratio is shown in a time chart, in which the target predetermined air / fuel ratio (theoretical air / fuel ratio) is indicated by a solid line, and the average exhaust air / fuel ratio before learning is indicated by a broken line. However, the difference between the predetermined air-fuel ratio (solid line) and the average exhaust air-fuel ratio (broken line) is obtained as an error e # 1, 4 (or error e # 2, 3), and the error e # 1,4 Based on (or error e # 2, 3), the amount of supplied fuel is corrected for each cylinder group (# 1, # 4 cylinder group and # 2, # 3 cylinder group). Then, the corrected supplied fuel amount, that is, the combustion air-fuel ratio is stored and learned for each cylinder group.
[0030]
As a result, the exhaust air-fuel ratio in the collecting pipe 22a corresponding to the # 1, # 4 cylinder group and the exhaust air-fuel ratio in the collecting pipe 22b corresponding to the # 2, # 3 cylinder group become appropriate, and the cylinder groups The exhaust air-fuel ratio flowing into the MCCs 24 and 26 can be leveled while reducing the cost by one LAFS 29. Therefore, in the MCCs 24 and 26, the harmful substances in the exhaust can always be effectively catalyzed and purified. In addition, since the air-fuel ratio feedback control can be always properly performed as a whole, the engine output can be stabilized and the fuel consumption can be improved.
[0031]
Referring to FIG. 5, a control routine for cylinder group-specific A / F learning control according to another embodiment of the present invention is shown in a flowchart, and the other embodiments will be described below along the flowchart. Note that the same steps as those in FIG. 3 are denoted by the same reference numerals and description thereof is omitted, and only portions different from the above embodiment are described here.
[0032]
In step S12a through step S1 and step S10, it is determined whether or not the cylinder rest duration t # 2, 3 for the other cylinder groups (# 2, # 3 cylinder group) is equal to or shorter than a predetermined time t1. If the determination result is true (Yes), that is, if the idle cylinder group is the # 2, # 3 cylinder group and the idle cylinder continuation time t # 2, 3 is equal to or shorter than the predetermined time t1, the process proceeds to step S14 '. . On the other hand, when the determination result is false (No), that is, when the idle cylinder group is not the # 2, # 3 cylinder group, or when the idle cylinder group is the # 2, # 3 cylinder group, the idle cylinder continuing time t # If 2, 3 exceeds the predetermined time t1, the process proceeds to step S12b.
[0033]
In step S12b, it is determined whether or not the cylinder deactivation duration t # 1,4 for one cylinder group (# 1, # 4 cylinder group) is equal to or shorter than a predetermined time t1. If the determination result is true (Yes), that is, if the idle cylinder group is # 1, # 4 cylinder group, and the idle cylinder continuation time t # 1, 4 is equal to or less than the predetermined time t1, the process proceeds to step S20 ′. . On the other hand, if the determination result is false (No), the process proceeds to step S14 ′.
[0034]
That is, in these steps S12a and S12b, the cylinder group in which the cylinder is idled is switched between the # 1, # 4 cylinder group, and the # 2, # 3 cylinder group at every predetermined time t1 (the cylinder cylinder is deactivated). Group switching means).
In step S14 ′, the cylinder resting operation is performed for the other cylinder groups (# 2 and # 3 cylinder groups). Thereafter, in the same manner as described above, in step S16, the predetermined air-fuel ratio (theoretical Fuel ratio) and the average exhaust air-fuel ratio before learning for the # 1, # 4 cylinder group is detected, and in step S18, # 1, # 4 are determined based on the error e # 1,4. The supply fuel amount of the cylinder group (# 1 cylinder and # 4 cylinder) is corrected, and the corrected supply fuel amount, that is, the combustion air-fuel ratio is stored and learned (combustion air-fuel ratio learning means). In step S14 ', at the first execution (immediately after t # 1,4 = t1), the cylinder resting durations t # 1,4 of the # 1 and # 4 cylinder groups are reset, and the next ## 1. Prepare for cylinder deactivation in the # 4 cylinder group.
[0035]
On the other hand, in step S20 ′, the cylinder resting operation is performed for one cylinder group (# 1, # 4 cylinder group), and thereafter, in the same manner as described above, in step S22, the predetermined air-fuel ratio which is the target of F / B correction and # 2 , The error e # 2,3 with respect to the average exhaust air-fuel ratio before learning for the # 3 cylinder group is detected, and in step S24, based on the error e # 2,3, the # 2, # 3 cylinder group (# 2 Cylinder and # 3 cylinder) are corrected, and the corrected supply fuel amount, that is, the combustion air-fuel ratio is stored and learned (combustion air-fuel ratio learning means). As in step S14 ′, in step S20 ′, when the first execution is performed (immediately after t # 2,3 = t1), the cylinder suspension durations t # 2,3 of the # 2, # 3 cylinder groups are set. Reset to prepare for the next cylinder suspension operation of the # 2, # 3 cylinder group.
[0036]
That is, in the other embodiment, the dead cylinder period of the # 1, # 4 cylinder group and the dead cylinder period of the # 2, # 3 cylinder group, that is, the # 1, # 4 cylinder group and the # 2, # 3 cylinder group. Each learning period is secured in a balanced manner.
As a result, as described above, the exhaust air-fuel ratio in the collecting pipe 22a corresponding to the # 1, # 4 cylinder group and the exhaust air-fuel ratio in the collecting pipe 22b corresponding to the # 2, # 3 cylinder group become appropriate. The variation in the exhaust air-fuel ratio among the cylinder groups is suppressed, and the exhaust air-fuel ratio flowing into the MCCs 24, 26 can be leveled while reducing the cost by one LAFS 29. The harmful substances in the exhaust gas in the MCCs 24, 26 can be achieved. Can always be effectively catalyzed and purified.
[0037]
The description of the embodiment is finished as above, but the present invention is not limited to the above embodiment.
For example, in the above embodiment, the LAFS 29 is used as the exhaust sensor, but an O ₂ sensor may be used.
In the above embodiment, a cylinder injection type spark ignition type four-cycle four-cylinder gasoline engine is used as the engine 1, but an intake pipe injection type gasoline engine, a two-cycle gasoline engine, a multi-cylinder engine other than the four-cylinder engine, etc. Even so, the present invention can be applied satisfactorily.
[0038]
In the above-described embodiment, the # 1, # 4 cylinder group and the # 2, # 3 cylinder group are alternately rested, but only one of them may be rested. In this case, although the learning accuracy is lowered, only one type of cylinder resting system is required, and an advantage of cost reduction is obtained.
[0039]
【The invention's effect】
As described above in detail, according to the air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to claim 1 of the present invention, for example, a dual exhaust manifold system is adopted for a multi-cylinder internal combustion engine (for example, a 4-cylinder engine). In an air-fuel ratio control apparatus for a multi-cylinder internal combustion engine in which a catalytic converter is provided in parallel in each of a plurality of exhaust passages of an exhaust manifold system and a cylinder-cylinder operation can be performed for each of the plurality of exhaust passages, that is, for each cylinder group, a set of a plurality of exhaust passages A single exhaust sensor is provided in the unit, and the feedback correction of the combustion air-fuel ratio is performed based on the exhaust air-fuel ratio information from the one exhaust sensor, and the cylinder group that performs the cylinder resting operation is switched for each cylinder group according to the operating state. A cylinder idle operation is performed, and at this time, based on the combustion air-fuel ratio of the combustion cylinder group that is feedback-corrected by the exhaust air-fuel ratio information from the one exhaust sensor. Since the combustion air-fuel ratio is learned for each cylinder group, the combustion air-fuel ratio for each cylinder group is optimized even if only one exhaust sensor is provided in the aggregate portion of the plurality of exhaust passages. Thus, the exhaust air / fuel ratio flowing into each catalytic converter can be leveled reliably, and the air / fuel ratio feedback control can be properly performed as a whole. As a result, in each catalytic converter provided in the plurality of exhaust passages of the dual exhaust manifold system, harmful substances in the exhaust can always be effectively catalyzed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to the present invention.
FIG. 2 is a diagram showing a dual type exhaust manifold system according to the present invention.
FIG. 3 is a flowchart showing a control routine of A / F learning control by cylinder group according to the present invention.
FIG. 4 shows LAFS output values (ie, exhaust air-fuel ratio) in the order of combustion cylinders (for example, # 1 → # 4 or # 2 → # 3) when F / B correction is performed and cylinder resting operation is performed. It is a time chart which shows the time change of.
FIG. 5 is a flowchart showing a control routine of A / F learning control by cylinder group according to another embodiment of the present invention.
[Explanation of symbols]
1 Engine 6 Fuel Injection Valve 20 Exhaust Manifolds 22a and 22b Collecting Pipes (Multiple Exhaust Paths)
24, 26 Three-way catalyst (MCC)
27 Aggregation part 29 Linear air-fuel ratio sensor (exhaust sensor, LAFS)
30 Three-way catalyst (UCC)
60 Electronic control unit (ECU)
62 Crank angle sensor

Claims (1)

A plurality of exhaust passages provided for each cylinder group consisting of a plurality of cylinders in which combustion does not continue among the cylinders of the multi-cylinder internal combustion engine;
A plurality of catalytic converters respectively disposed in the plurality of exhaust passages;
An exhaust sensor that detects an exhaust air-fuel ratio, provided in a collective portion of the plurality of exhaust passages downstream from the plurality of catalytic converters in the exhaust flow direction;
Combustion air-fuel ratio control means for feedback correcting the combustion air-fuel ratio based on the exhaust air-fuel ratio information detected by the exhaust sensor so that the average exhaust air-fuel ratio becomes a predetermined air-fuel ratio;
A cylinder resting means for closing the at least the exhaust valves of the plurality of cylinders for each cylinder group according to the operating state and stopping the fuel supply to perform the cylinder resting operation;
A cylinder-cylinder group switching unit that sequentially switches cylinder groups that perform cylinder-cylinder operation by the cylinder-stopping unit;
When the feedback correction is performed by the combustion air-fuel ratio control means and the cylinder resting operation is performed by the cylinder resting means, the combustion air-fuel ratio of the combustion cylinder group feedback-corrected by the combustion air-fuel ratio control means is stored and learned for each cylinder group. Combustion air-fuel ratio learning means;
An air-fuel ratio control apparatus for a multi-cylinder internal combustion engine.

Images