JP4344940B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to a technique for adjusting an air-fuel ratio of an internal combustion engine by an exhaust sensor provided in an exhaust system of the internal combustion engine.

A catalyst is provided in the exhaust passage of the internal combustion engine mounted on the vehicle for the purpose of purifying substances such as HC, CO, and NOx discharged from the internal combustion engine.
In order to effectively use the catalyst, the average exhaust air-fuel ratio flowing into the catalyst needs to be close to the target air-fuel ratio (for example, stoichiometric), and in order to achieve this purpose, an O ₂ sensor is provided in the exhaust passage. A technology for adjusting the exhaust air-fuel ratio by rich / lean modulation (air-fuel ratio modulation) of the combustion air-fuel ratio of the internal combustion engine using the output of the exhaust sensor as a trigger has been developed.

By the way, the catalyst has a function of adsorbing O ₂ , HC and the like in the exhaust to the noble metal. From this, when the air-fuel ratio modulation is performed, the HC etc. adsorbed on the noble metal when the catalyst is in an oxidizing atmosphere (lean air-fuel ratio). While releasing NOx and suppressing NOx emission by adsorbing O ₂ and NOx in the exhaust, when in a reducing atmosphere (rich air-fuel ratio), O ₂ and NOx adsorbed on the noble metal are released and HC in the exhaust is removed. It is possible to suppress the discharge of HC and the like by adsorption.

However, when the air-fuel ratio modulation is performed, if the modulation period of the air-fuel ratio modulation is long, the adsorption amount (adsorption time) of the noble metal such as O ₂ , NOx, or HC to the noble metal is an adsorption capacity corresponding to the adsorption speed, that is, This exceeds the breakthrough amount (breakthrough time). In this case, there is a problem that NOx, HC, etc. cannot be sufficiently purified and the catalyst performance deteriorates.
This problem arises because the air-fuel ratio of the exhaust gas causes the air-fuel ratio fluctuation due to the air-fuel ratio modulation of the internal combustion engine. Therefore, in order to improve the catalyst performance, the air-fuel ratio fluctuation of the exhaust air-fuel ratio is inherently changed. The average exhaust air-fuel ratio may be eliminated and the target air-fuel ratio (for example, stoichiometric) may be maintained.

  For example, as shown in FIG. 11, when the modulation period of the combustion air-fuel ratio is shortened and the combustion air-fuel ratio is modulated at high speed, the exhaust air-fuel ratio does not follow this, and fluctuations in the air-fuel ratio of the exhaust air-fuel ratio are eliminated. From the above, it is considered that the combustion air-fuel ratio should be modulated at high speed in order to improve the catalyst performance by eliminating the air-fuel ratio fluctuation of the exhaust air-fuel ratio in the catalyst.

  However, in the conventional method of detecting the exhaust air / fuel ratio after the exhaust gas collected from the exhaust ports of a multi-cylinder internal combustion engine is generally adjusted and adjusting the air / fuel ratio, the air / fuel ratio modulation period is rich or lean. This is basically the same as the period of reversal, and is determined by the transport delay due to the volume of the exhaust system and the response delay of the exhaust sensor itself. It is difficult to improve.

For this reason, it has been considered that the combustion air-fuel ratio is forcibly modulated at high speed or no modulation (see Patent Document 1, etc.).
Further, a technology has been developed in which an exhaust sensor is provided at a position where exhaust gas collects, and an average air-fuel ratio in a specific section within one cycle is obtained by statistical processing over a plurality of cycles (see Patent Document 2).
Japanese Patent Laid-Open No. 6-200802 JP 2000-220492 A

However, in the case of the technique disclosed in Patent Document 1, an expensive air-fuel ratio sensor capable of outputting linear air-fuel ratio information must be used to detect the average exhaust air-fuel ratio after the exhaust gas has gathered. However, there is a problem that an inexpensive exhaust sensor such as an O ₂ sensor whose main output is rich / lean determination cannot sufficiently cope.
In the case of the technique disclosed in Patent Document 2, there is a problem that a certain amount of processing period is required to improve the accuracy of statistical processing, and the responsiveness is poor.

  The present invention has been made to solve such problems, and the object of the present invention is to provide an inexpensive and highly responsive exhaust air / fuel ratio that can be adjusted in the vicinity of a target air / fuel ratio (for example, stoichiometric) and a catalyst. An object of the present invention is to provide an air-fuel ratio control device for a multi-cylinder internal combustion engine capable of suppressing fluctuations in the air-fuel ratio of exhaust gas flowing in.

An air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to claim 1 , wherein the exhaust sensor is provided at a collecting portion of exhaust exhausted from at least two cylinders of the multi-cylinder, and detects and outputs a concentration of a predetermined exhaust component; The combustion air-fuel ratios of some cylinders of at least two or more cylinders and the combustion air-fuel ratios of the remaining cylinders are reversed with a predetermined value between them so that the output from the exhaust sensor fluctuates in a cycle within approximately one cycle of the internal combustion engine. And when the output from the exhaust sensor corresponding to the some cylinders is contrary to the combustion air-fuel ratio set for the some cylinders, the combustion air-fuel ratio for the remaining cylinders characterized in that the average value of the exhaust air-fuel ratio of the approximately 1 cycle at Rukoto is inverted with an exhaust air-fuel ratio adjusting means for adjusting towards the predetermined value.

That is, the combustion air-fuel ratios of some cylinders and the combustion air-fuel ratios of the remaining cylinders are set in opposite directions (eg, rich air-fuel ratio and lean air-fuel ratio) with a predetermined value (eg, stoichiometric) in between, and some cylinders And by changing the output of the exhaust sensor provided in the exhaust gas gathering portion from the remaining cylinders in a cycle within approximately one cycle, the output of the exhaust sensor changes in a short cycle.
Further, when the output from the exhaust sensor corresponding to some cylinders is contrary to the combustion air-fuel ratio set for some cylinders, the combustion air-fuel ratio for the remaining cylinders is reversed to set the average value of the exhaust air-fuel ratio to a predetermined value. By adjusting toward, the average value of the exhaust air / fuel ratio is adjusted toward a predetermined value with high response even when an inexpensive exhaust sensor such as an O ₂ sensor is used. Specifically, when the combustion air-fuel ratio of some cylinders is set to a lean air-fuel ratio and the combustion air-fuel ratio of the remaining cylinders is set to a rich air-fuel ratio, for example, from an exhaust sensor originally corresponding to some cylinders Even if the output should be the lean air-fuel ratio information, even if the rich air-fuel ratio information is obtained due to an error or the like, the remaining air-fuel ratio is reversed instead of the rich air-fuel ratio to reverse the lean air-fuel ratio. By setting to, the average value of the exhaust air / fuel ratio is adjusted toward a predetermined value with high response while using an inexpensive exhaust sensor such as an O ₂ sensor.

The air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to claim 2 , wherein the exhaust air-fuel ratio adjusting means adjusts the combustion air-fuel ratio of at least two cylinders by the same amount or the same ratio with the predetermined value interposed therebetween. To do.
As a result, the average value of the exhaust air-fuel ratio is adjusted to a predetermined value.

According to the air-fuel ratio control apparatus for a multi-cylinder internal combustion engine 請 Motomeko 1, a predetermined value the combustion air-fuel ratio of the combustion air-fuel ratio and the balance cylinder of some of the cylinders (e.g., stoichiometric) interposed therebetween reverse (e.g., Rich air-fuel ratio and lean air-fuel ratio), and the output of the exhaust sensor provided in the exhaust collecting part from some cylinders and the remaining cylinders is changed in a short cycle within approximately one cycle, so that the catalyst is provided in the exhaust passage. In this case, the catalyst performance (purification efficiency) can be improved by minimizing the air-fuel ratio fluctuation of the exhaust air-fuel ratio in the catalyst.

Further, when the output from the exhaust sensor corresponding to some cylinders is contrary to the combustion air-fuel ratio set for some cylinders, the combustion air-fuel ratio for the remaining cylinders is reversed to set the average value of the exhaust air-fuel ratio to a predetermined value. (For example, stoichiometric adjustment), even when an inexpensive exhaust sensor such as an O ₂ sensor is used, the average value of the exhaust air / fuel ratio can be adjusted to a predetermined value with high response, and the catalyst performance (purification) Efficiency).

According to the air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to claim 2 , the combustion air-fuel ratio of each cylinder is adjusted by the same amount or the same ratio with a predetermined value interposed therebetween. Alternatively, it is possible to satisfactorily adjust the average value of the exhaust air / fuel ratio to a predetermined value while preventing an overrich air / fuel ratio.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
First, the first embodiment will be described.
Referring to FIG. 1, there is shown a schematic configuration diagram of an air-fuel ratio control device for a multi-cylinder internal combustion engine according to the present invention mounted on a vehicle. Hereinafter, the configuration of the air-fuel ratio control device will be described.
As shown in the figure, an intake pipe injection (MPI) 4-cylinder gasoline engine is adopted as an engine body (hereinafter simply referred to as an engine) 1 that is an internal combustion engine.

A spark plug 4 is attached to each cylinder of the cylinder head 2 of the engine 1, and an ignition coil 8 that outputs a high voltage is connected to the spark plug 4.
In the cylinder head 2, an intake port is formed for each cylinder, and one end of an intake manifold 10 is connected so as to communicate with each intake port. An electromagnetic fuel injection valve 6 is attached to the intake manifold 10, and a fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe 7. .

  An electromagnetic throttle valve 14 for adjusting the amount of intake air is provided upstream of the fuel injection valve 6 of the intake manifold 10 and a throttle position sensor (for detecting the valve opening θth of the throttle valve 14). TPS) 16 is provided. Further, an air flow sensor 18 for measuring the intake air amount is interposed upstream of the throttle valve 14. A Karman vortex airflow sensor is used as the airflow sensor 18.

The cylinder head 2 has an exhaust port for each cylinder, and one end of an 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.
In the exhaust manifold 20 comprising 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, exhaust interference is reduced, and a great effect of exhaust inertia or exhaust pulsation can be obtained.

An O ₂ sensor (exhaust sensor) 32 for detecting the concentration of oxygen (predetermined exhaust component) is provided at the junction of the exhaust passage 20a from the # 1 cylinder and the exhaust passage 20d from the # 4 cylinder. .
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.

  A three-way catalyst 30 is interposed in the exhaust pipe 28. The three-way catalyst 30 has at least one of copper (Cu), cobalt (Co), silver (Ag), platinum (Pt), rhodium (Rh), palladium (Pd) as a noble metal, and an exhaust air-fuel ratio (exhaust gas). When A / F) is in the vicinity of stoichiometric (theoretical air-fuel ratio), HC and CO can be satisfactorily oxidized and NOx can be satisfactorily reduced.

The ECU (electronic control unit) 40 includes an input / output device, a storage device (ROM, RAM, etc.), a central processing unit (CPU), a timer counter, and the like. The ECU 40 controls the air-fuel ratio control device including the engine 1. Overall control is performed.
Various sensors such as a crank angle sensor 42 for detecting the crank angle of the engine 1 are connected to the input side of the ECU 40 in addition to the TPS 16, the air flow sensor 18 and the O ₂ sensor 32 described above. Detection information is input. The engine speed Ne is detected based on the crank angle information of the crank angle sensor 42.

  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 40. These various output devices are operated based on detection information from various sensors. The fuel injection amount, fuel injection timing, ignition timing, etc., are output. Specifically, the combustion air-fuel ratio (combustion A / F) in each cylinder is set to an appropriate target air-fuel ratio (target A / F) based on detection information from various sensors, and an amount corresponding to the target A / F. The fuel is injected from the fuel injection valve 6 at an appropriate timing, the throttle valve 14 is adjusted to an appropriate opening degree, and the spark plug 4 performs spark ignition at an appropriate timing.

  Referring to FIG. 3, the control routine of the combustion A / F control according to the first embodiment of the present invention is shown in a flowchart, and the combustion A / F according to the first embodiment of the present invention will be described below based on the flowchart. A control procedure of control will be described. Here, the combustion order of the engine 1 is in the order of # 1 → # 3 → # 4 → # 2, and the initial values of the combustion A / F of the # 1, # 3 cylinders are rich A / F, # 2, # The initial value of the combustion A / F for the four cylinders is set to lean A / F. The rich A / F and the lean A / F may be reversed.

First, in step S10, it is determined whether the exhaust gas detected by the O ₂ sensor 32 is from the # 1 cylinder or the # 4 cylinder. Specifically, since the O ₂ sensor 32 is provided in the exhaust manifold 20 and is located very close to the exhaust port, the cylinder currently in the exhaust stroke is # 1 based on the information from the crank angle sensor 42. It is determined whether the cylinder is a cylinder or # 4 cylinder. Note that the transport delay of exhaust gas in the exhaust manifold 20 may be taken into account.

If it is determined in step S10 that the exhaust gas detected by the O ₂ sensor 32 is from the # 1 cylinder, the process proceeds to step S12.
In step S12, it is determined whether the output of the O ₂ sensor 32 is a value corresponding to the rich air-fuel ratio (rich A / F) or a value corresponding to the lean air-fuel ratio (lean A / F). If it is determined that the output of the O ₂ sensor 32 is a value corresponding to rich A / F, the process proceeds to step S14.

In step S14, the combustion A / F of the # 4 cylinder is set to lean A / F (combustion air-fuel ratio setting means).
If it is determined in step S10 that the exhaust gas detected by the O ₂ sensor 32 is from the # 4 cylinder, the process proceeds to step S18, and the output of the O ₂ sensor 32 is still rich A / It is determined whether the value corresponds to F or the value corresponding to lean A / F.

As described above, since the combustion A / F of the # 4 cylinder is set to the lean A / F, normally, the output of the O ₂ sensor 32 relating to the exhaust gas from the # 4 cylinder corresponds to the lean A / F. Value and proceeds to step S22.
In step S22, the combustion A / F of the # 1 cylinder is set to rich A / F (combustion air-fuel ratio setting means).

Specifically, the combustion A / F may be set individually. Here, however, the lean degree of the combustion A / F of the # 4 cylinder set to the lean A / F as described above and the stoichiometry (the target A / F) The combustion A / F of the # 1 cylinder is set to the rich A / F with the same amount or the same degree of enrichment across the predetermined value). Further, the output of an exhaust sensor (not shown) installed downstream of the three-way catalyst 30 based on the ratio (variation ratio) of the rich output period and lean output period of the output of the O ₂ sensor 32 or the correlation value thereof. The degree of leaning and the degree of enrichment are corrected based on the above (exhaust air / fuel ratio adjusting means). As a result, the exhaust A / F can be favorably held in the vicinity of the stoichiometry.

Here, for the # 3 cylinder, which is the next to the # 1 cylinder, for example, the combustion A / F is the same as the # 1 cylinder, and for the # 2 cylinder, which is the next to the # 4 cylinder, for example, Same combustion A / F as # 4 cylinder.
As described above, when the combustion A / F of the # 4 cylinder is set to the lean A / F and the combustion A / F of the # 1 cylinder is set to the rich A / F, the determination result of step S12 is thereafter the rich A / F. As long as the determination result in step S18 is lean A / F, the combustion A / F of the # 1 cylinder is rich A / F, while the combustion A / F of the # 4 cylinder is lean A / F. . That is, the combustion A / F is alternately made rich A / F and lean A / F in the cycle (two rotations) of the engine 1, and the combustion A / F is modulated at high speed around the stoichiometric in a very short cycle. .

When the combustion A / F is modulated at high speed, as shown in FIG. 11, the air-fuel ratio fluctuation of the exhaust A / F is almost eliminated in the three-way catalyst 30, and the exhaust A / F is held near the stoichiometric. Thus, the catalyst performance (purification efficiency) of the three-way catalyst 30 can be improved.
On the other hand, despite the fact that the combustion A / F of the # 1 cylinder is set to rich A / F, the output of the O ₂ sensor 32 corresponds to the lean A / F in the determination of step S12 due to various factors such as errors. If it is determined to be a value, the process proceeds to step S16.

In step S16, the combustion A / F of the # 4 cylinder is set to rich A / F. That is, when the exhaust A / F of the exhaust gas from the # 1 cylinder is lean A / F against the combustion A / F, the average value of the exhaust A / F is greatly biased toward the lean A / F side from the stoichiometry. The combustion A / F of the other # 4 cylinder that detects the exhaust A / F by the O ₂ sensor 32 is reversed and set to rich A / F (exhaust air / fuel ratio adjusting means).

When the combustion A / F of the # 4 cylinder is set to the rich A / F, normally, the output of the O ₂ sensor 32 relating to the exhaust gas from the # 4 cylinder is a value corresponding to the rich A / F. The process proceeds to step S20 via S18.
In step S20, the combustion A / F of the # 1 cylinder is set to lean A / F. That is, when the combustion A / F of the other # 4 cylinder is inverted and set to rich A / F, the combustion A / F of the other # 1 cylinder is similarly inverted and set to lean A / F. (Exhaust air / fuel ratio adjusting means). In this case as well, the # 1 cylinder has the same amount or the same lean ratio as the richness of the combustion A / F of the # 4 cylinder set to rich A / F and the stoichiometry which is the target A / F. The combustion A / F is set to lean A / F. Further, lean based on the ratio of the rich output period and lean output period of the output of the O ₂ sensor 32 or a correlation value thereof, or based on the output of an exhaust sensor (not shown) installed downstream of the three-way catalyst 30. The degree of enrichment and the degree of enrichment are corrected (exhaust air / fuel ratio adjusting means).

As described above, when the combustion A / F of the # 4 cylinder is reversed and set to the rich A / F, and the combustion A / F of the # 1 cylinder is reversed and set to the lean A / F, the lean A / F is greatly increased from the stoichiometry. It is expected that the average value of the exhaust A / F that is biased toward the F side is immediately returned to the vicinity of the stoichiometry.
As a result, as long as the determination result in step S12 is lean A / F and the determination result in step S18 is rich A / F, the combustion A / F of the # 1 cylinder is lean A / F, while # The combustion A / F of the four cylinders is rich A / F, and the high speed modulation of the combustion A / F can be maintained with high responsiveness. High performance (purification efficiency) can be maintained.

Although not described here, the output of the O ₂ sensor 32 is determined to be a value corresponding to the rich A / F even though the combustion A / F of the # 4 cylinder is set to the lean A / F. In the case where the output of the O ₂ sensor 32 is determined to be a value corresponding to the rich A / F even though the combustion A / F of the # 1 cylinder is set to the lean A / F as described above, The same applies to the case where the output of the O ₂ sensor 32 is determined to be a value corresponding to the lean A / F even though the combustion A / F of the # 4 cylinder is set to the rich A / F.

Next, a second embodiment will be described.
In the second embodiment, as shown in FIG. 4, an O ₂ sensor 32 is disposed at the junction of the exhaust passage 20b from the # 2 cylinder and the exhaust passage 20c from the # 3 cylinder.
In this case, only the # 1 cylinder and the fourth cylinder in the first embodiment are replaced with the # 3 cylinder and the # 2 cylinder, respectively. Therefore, the same effect as in the first embodiment is achieved. It will be.

Next, a third embodiment will be described.
In the third embodiment, as shown in FIG. 5, the junction of the exhaust passage 20a from the # 1 cylinder and the exhaust passage 20d from the # 4 cylinder, and the exhaust passage 20b from the # 2 cylinder and the # 3 cylinder The O ₂ sensor 32 is disposed at both of the junctions with the exhaust passage 20c.
Referring to FIGS. 6 and 7, the control routine of the combustion A / F control according to the third embodiment of the present invention is shown by a flowchart. Hereinafter, the combustion A / F control according to the third embodiment based on the flowchart. The control procedure will be described. As in the case of FIG. 3, the combustion order here is the order of # 1 → # 3 → # 4 → # 2.

First, the case where the initial values of the combustion A / F of the # 1 and # 4 cylinders are rich A / F and the initial value of the combustion A / F of the # 2 and # 3 cylinders is lean A / F will be described. The rich A / F and the lean A / F may be reversed.
In step S30, it is determined in the same manner as described above whether the exhaust gas detected by the O ₂ sensor 32 is any of the # 1, # 2, # 3, and # 4 cylinders.

If it is determined in step S30 that the exhaust gas detected by the O ₂ sensor 32 is from the # 1 cylinder, the process proceeds to step S32.
In step S32, it is determined whether the output of the O ₂ sensor 32 is a value corresponding to rich A / F or a value corresponding to lean A / F. If it is determined that the output of the O ₂ sensor 32 is a value corresponding to the rich A / F, the process proceeds to step S34.

In step S34, the combustion A / F of the # 3 cylinder with the next combustion order is set to lean A / F. Specifically, the combustion A / F may be set individually, but here, the richness of the combustion A / F of the # 1 cylinder determined as rich A / F and the stoichiometry which is the target A / F are determined here. The combustion A / F of the # 3 cylinder is set to lean A / F with the same amount or lean degree of sandwiching. Further, lean based on the ratio of the rich output period and lean output period of the output of the O ₂ sensor 32 or a correlation value thereof, or based on the output of an exhaust sensor (not shown) installed downstream of the three-way catalyst 30. The degree of enrichment and the degree of enrichment are corrected.

If it is determined in step S30 that the exhaust gas detected by the O ₂ sensor 32 is from the # 3 cylinder, the process proceeds to step S38, and the output of the O ₂ sensor 32 is still rich A /. It is determined whether the value corresponds to F or the value corresponding to lean A / F.
As described above, since the combustion A / F of the # 3 cylinder is set to the lean A / F, the output of the O ₂ sensor 32 relating to the exhaust gas from the # 3 cylinder normally corresponds to the lean A / F. Value and proceeds to step S42.

In step S42, the combustion A / F of the # 4 cylinder having the next combustion order is set to rich A / F. Specifically, the rich A / F setting is performed in the same manner as the lean A / F setting performed in step S34. In other words, the combustion A / F of the # 4 cylinder is set to the same amount or the same degree of enrichment across the stoichiometry that is the target A / F and the leaning degree of the combustion A / F of the # 3 cylinder set to lean A / F. Set to rich A / F. Further, lean based on the ratio of the rich output period and lean output period of the output of the O ₂ sensor 32 or a correlation value thereof, or based on the output of an exhaust sensor (not shown) installed downstream of the three-way catalyst 30. The degree of enrichment and the degree of enrichment are corrected.

If it is determined in step S30 that the exhaust gas detected by the O ₂ sensor 32 is from the # 4 cylinder, the process proceeds to step S44, and the output of the O ₂ sensor 32 is still rich A /. It is determined whether the value corresponds to F or the value corresponding to lean A / F.
As described above, since the combustion A / F of the # 4 cylinder is set to the rich A / F, the output of the O ₂ sensor 32 related to the exhaust gas from the # 4 cylinder normally corresponds to the rich A / F. Value and proceeds to step S46.

In step S46, the combustion A / F of the # 2 cylinder with the next combustion order is set to lean A / F. Also in this case, the combustion A / F of the # 2 cylinder is set with the same amount or the same degree of leaning across the stoichiometric degree and the richness of the combustion A / F of the # 4 cylinder set to the lean A / F as described above. Set to lean A / F.
If it is determined in step S30 that the exhaust gas detected by the O ₂ sensor 32 is from the # 2 cylinder, the process proceeds to step S50, and the output of the O ₂ sensor 32 is still rich A /. It is determined whether the value corresponds to F or the value corresponding to lean A / F.

As described above, since the combustion A / F of the # 2 cylinder is set to the lean A / F, the output of the O ₂ sensor 32 related to the exhaust gas from the # 2 cylinder normally corresponds to the lean A / F. Value and proceeds to step S54.
In step S54, the combustion A / F of the # 1 cylinder having the next combustion order is set to rich A / F. Also in this case, the combustion A / F of the # 1 cylinder is set to the same amount or the same degree of enrichment across the stoichiometric degree of the leanness of the combustion A / F of the # 2 cylinder set to the lean A / F as described above. The rich A / F is set, and the lean degree and the rich degree are corrected as described above.

  As described above, when the combustion A / F of the # 2 cylinder and the # 3 cylinder is set to the lean A / F and the combustion A / F of the # 1 cylinder and the # 4 cylinder is set to the rich A / F, step S32 is performed thereafter. As long as the determination result of step S44 is rich A / F and the determination result of step S38 and step S50 is lean A / F, the combustion A / F of the # 1 cylinder and # 4 cylinder is rich A / F. The combustion A / F of the # 2 cylinder and # 3 cylinder is set to lean A / F. That is, in the case of the third embodiment, the combustion A / F is alternately made rich A / F and lean A / F in the half cycle period (one rotation) of the engine 1, and the combustion A / F in an extremely short period. Is modulated at high speed with a focus on stoichiometry.

As a result, the exhaust A / F can be held in the vicinity of the stoichiometry, and the catalytic performance (purification efficiency) of the three-way catalyst 30 can be improved.
On the other hand, despite the fact that the combustion A / F of the # 1 cylinder is set to rich A / F, the output of the O ₂ sensor 32 corresponds to the lean A / F in the determination of step S32 due to various factors such as errors. If it is determined to be a value, the process proceeds to step S36.

In step S36, the combustion A / F of the # 3 cylinder is set to rich A / F. That is, when the exhaust A / F of the exhaust gas from the # 1 cylinder is lean A / F against the combustion A / F, the average value of the exhaust A / F is greatly biased toward the lean A / F side from the stoichiometry. The combustion A / F of the next # 3 cylinder in the combustion order is reversed and set to rich A / F.
When the combustion A / F of the # 3 cylinder is set to the rich A / F, normally, the output of the O ₂ sensor 32 relating to the exhaust gas from the # 3 cylinder is a value corresponding to the rich A / F. The process proceeds to step S40 via S38.

  In step S40, the combustion A / F of the # 4 cylinder is set to lean A / F. That is, when the combustion A / F of the # 3 cylinder is reversed and set to the rich A / F, the combustion A / F of the next # 4 cylinder is similarly reversed and set to the lean A / F. To do. Also in this case, the combustion A / F of the # 4 cylinder is set to the same amount or the lean ratio of the same ratio with the stoichiometric ratio between the richness of the combustion A / F of the # 3 cylinder set to the rich A / F as described above. The lean A / F is set, and the lean degree and the rich degree are corrected in the same manner as described above.

When the combustion A / F of the # 4 cylinder is set to the lean A / F, normally, the output of the O ₂ sensor 32 relating to the exhaust gas from the # 4 cylinder is a value corresponding to the lean A / F. The process proceeds to step S48 via S44.
In step S48, the combustion A / F of the # 2 cylinder is set to rich A / F. That is, when the combustion A / F of the # 4 cylinder is inverted and set to lean A / F, the combustion A / F of the next # 2 cylinder is similarly inverted and set to rich A / F. To do. Also in this case, the combustion A / F of the # 2 cylinder is set to the same amount or the same degree of enrichment with the same amount or the same ratio of the leanness of the combustion A / F of the # 4 cylinder set to the lean A / F as described above. Set to rich A / F.

When the combustion A / F of the # 2 cylinder is set to the rich A / F, the output of the O ₂ sensor 32 relating to the exhaust gas from the # 2 cylinder is normally a value corresponding to the rich A / F. The process proceeds to step S52 via S50.
In step S52, the combustion A / F of the # 1 cylinder is set to lean A / F. That is, when the combustion A / F of the # 2 cylinder is reversed and set to the rich A / F, the combustion A / F of the next # 1 cylinder is similarly reversed and set to the lean A / F. To do. Also in this case, the combustion A / F of the # 1 cylinder is set with the same amount or the same degree of leaning across the stoichiometric degree and the richness of the combustion A / F of the # 2 cylinder set to the rich A / F as described above. The lean A / F is set, and the lean degree and the rich degree are corrected in the same manner as described above.

In this way, the combustion A / F of the # 2 and # 3 cylinders is inverted to set to rich A / F, and the combustion A / F of the # 1 and # 4 cylinders is inverted to set to lean A / F. Then, it is expected that the average value of the exhaust A / F that is largely deviated from the stoichiometric side toward the lean A / F side is immediately returned to the stoichiometric vicinity.
As a result, as long as the determination results of step S32 and step S44 are lean A / F and the determination results of step S38 and step S50 are rich A / F, the combustion A / F of the # 1 cylinder and # 4 cylinder Is a lean A / F, while the combustion A / F of the # 2 and # 3 cylinders is a rich A / F, so that high-speed modulation of the combustion A / F can be maintained with high responsiveness, and the exhaust A / F Can always be maintained in the vicinity of the stoichiometry, and the catalytic performance (purification efficiency) of the three-way catalyst 30 can be maintained high.

Although not described, in this regard, as in the case of the first embodiment, the output of the O ₂ sensor 32 is output even though the combustion A / F of the # 3 cylinder is set to lean A / F. When it is determined that the value corresponds to the rich A / F, the output of the O ₂ sensor 32 is a value corresponding to the lean A / F even though the combustion A / F of the # 4 cylinder is set to the rich A / F. When the determination is made, the same applies to the case where the output of the O ₂ sensor 32 is determined to be a value corresponding to the rich A / F even though the combustion A / F of the # 2 cylinder is set to the lean A / F. is there.

The case where the initial values of the combustion A / F of the # 1 and # 3 cylinders are rich A / F and the initial value of the combustion A / F of the # 2 and # 4 cylinders is lean A / F will be described. The rich A / F and the lean A / F may be reversed.
In this case, the combination of the first embodiment and the second embodiment is nothing but the combustion A / F is alternately rich A / F and lean A / F in the cycle (two revolutions) of the engine 1. The combustion A / F is modulated at high speed around the stoichiometric cycle with an extremely short period. As a result, the same effects as those of the first and second embodiments are obtained.

Next, a fourth embodiment will be described.
In the fourth embodiment, as shown in FIG. 8, an O ₂ sensor 32 is disposed at the junction of the collecting pipe 22a and the collecting pipe 22b.
Referring to FIG. 9, a control routine for combustion A / F control according to the fourth embodiment of the present invention is shown in a flowchart. Hereinafter, control of combustion A / F control according to the fourth embodiment is based on the flowchart. The procedure will be described. Here, the combustion order is in the order of # 1 → # 3 → # 4 → # 2, and the initial values of the combustion A / F of the # 1, # 4 cylinders are the rich A / F, # 2, # 3 cylinders. The initial value of the combustion A / F is set to lean A / F. The rich A / F and the lean A / F may be reversed.

In step S60, it is determined in the same manner as described above whether the exhaust gas detected by the O ₂ sensor 32 is from the # 1, # 4 cylinder or the # 2, # 3 cylinder.
If it is determined in step S60 that the exhaust gas detected by the O ₂ sensor 32 is from the # 1 and # 4 cylinders, the process proceeds to step S62.
In step S62, it is determined whether the output of the O ₂ sensor 32 is a value corresponding to rich A / F or a value corresponding to lean A / F. If it is determined that the output of the O ₂ sensor 32 is a value corresponding to rich A / F, the process proceeds to step S64.

In step S64, the combustion A / F of the # 2 and # 3 cylinders is set to lean A / F.
If it is determined in step S60 that the exhaust gas detected by the O ₂ sensor 32 is from the # 2 and # 3 cylinders, the process proceeds to step S68, and the output of the O ₂ sensor 32 is also output. It is determined whether the value corresponds to the rich A / F or the value corresponding to the lean A / F.

As described above, since the combustion A / F of the # 2 and # 3 cylinders is set to lean A / F, normally, the output of the O ₂ sensor 32 regarding the exhaust gas from the # 2 and # 3 cylinders is lean. The value corresponds to A / F, and the process proceeds to step S72.
In step S72, the combustion A / F of the # 1 and # 4 cylinders is set to rich A / F. Specifically, the combustion A / F may be set individually, but here, the lean degree of the combustion A / F of the # 2 and # 3 cylinders set to the lean A / F as described above and the target A / F The combustion A / Fs of the # 1 and # 4 cylinders are set to rich A / F with the same amount or the same degree of enrichment across a certain stoichiometry, and the lean degree and rich degree are corrected in the same manner as described above.

  As described above, when the combustion A / F of the # 2 and # 3 cylinders is set to lean A / F and the combustion A / F of the # 1 and # 4 cylinders is set to rich A / F, the determination in step S62 is performed thereafter. As long as the result is rich A / F and the determination result in step S68 is lean A / F, the combustion A / F of the # 1, # 4 cylinders is rich A / F, while the # 2, # 3 cylinders The combustion A / F is defined as lean A / F. That is, as in the case of the third embodiment, the combustion A / F is alternately made rich A / F and lean A / F in the half cycle period (one rotation) of the engine 1, and the combustion A / F is performed in a very short period. F is modulated at high speed around the stoichiometry.

As a result, the exhaust A / F can be held in the vicinity of the stoichiometry, and the catalytic performance (purification efficiency) of the three-way catalyst 30 can be improved.
On the other hand, despite the fact that the combustion A / F of the # 1 and # 4 cylinders is set to rich A / F, the output of the O ₂ sensor 32 becomes lean A / F in the determination of step S62 due to various factors such as errors. If it is determined that the value corresponds to, the process proceeds to step S66.

In step S66, the combustion A / F of the # 2 and # 3 cylinders is set to rich A / F. That is, when the exhaust A / F of the exhaust gas from the # 1 and # 4 cylinders is lean A / F contrary to the combustion A / F, the average value of the exhaust A / F is greatly increased from the stoichiometric side. The combustion A / Fs of the other # 2, # 3 cylinders that detect the exhaust A / F by the O ₂ sensor 32 are reversed and set to rich A / F.

When the combustion A / F of the # 2 and # 3 cylinders is set to rich A / F, the output of the O ₂ sensor 32 relating to the exhaust gas from the # 2 and # 3 cylinders is usually a value corresponding to the rich A / F. In this case, the process proceeds to step S70 via step S68.
In step S70, the combustion A / F of the # 1 and # 4 cylinders is set to lean A / F. That is, the combustion A / F of the other # 2 and # 3 cylinders is reversed and set to rich A / F, and the combustion A / F of the other # 1 and # 4 cylinders is similarly reversed and lean. Set to A / F. Also in this case, the richness of the combustion A / F of the # 2 and # 3 cylinders set to the rich A / F as described above and the leaning degree of the same amount or the same ratio with the stoichiometric ratio are # 1, # 4 The combustion A / F of the cylinder is set to lean A / F, and the lean degree and rich degree are corrected as described above.

As described above, when the combustion A / F of the # 2 and # 3 cylinders is inverted to be set to rich A / F, and the combustion A / F of the # 1 and # 4 cylinders is inverted to be set to lean A / F, It is expected that the average value of the exhaust A / F that is largely biased toward the lean A / F side from the stoichiometry is immediately returned to the stoichiometric vicinity.
As a result, as long as the determination result in step S62 is lean A / F and the determination result in step S68 is rich A / F, the combustion A / F of the # 1 and # 4 cylinders is lean A / F. On the other hand, the combustion A / F of the # 2 and # 3 cylinders is rich A / F, so that high-speed modulation of the combustion A / F can be maintained with high responsiveness, and the exhaust A / F is always kept near the stoichiometric range. The catalytic performance (purification efficiency) of the three-way catalyst 30 can be maintained high.

Although explanation is omitted, in this respect, as in the case of the first embodiment, the O ₂ sensor 32 is set despite the fact that the combustion A / F of the # 2 and # 3 cylinders is set to lean A / F. The same applies to the case where the output is determined to be a value corresponding to the rich A / F.
Next, a fifth embodiment will be described.
In the fifth embodiment, instead of the dual type exhaust manifold system, as shown in FIG. 10, a normal exhaust manifold system is adopted, and the exhaust passage 20a from the # 1 cylinder and the exhaust passage 20b from the # 2 cylinder and # 3 are used. An O ₂ sensor 32 is disposed at the junction of the exhaust passage 20c from the cylinder and the exhaust passage 20d from the # 4 cylinder.

In the fifth embodiment, the exhaust A / F detected by the two O ₂ sensors 32 in the third embodiment using the dual type exhaust manifold system is detected by one O ₂ sensor 32. It is none other than.
Therefore, when the initial values of the combustion A / F of the # 1, # 4 cylinders are rich A / F and the initial value of the combustion A / F of the # 2, # 3 cylinders is lean A / F, the combustion A / F The / F control is the same as the flowcharts of FIGS. 6 and 7 of the third embodiment. The rich A / F and the lean A / F may be reversed.

Further, when the initial values of the combustion A / F of the # 1 and # 3 cylinders are rich A / F and the initial value of the combustion A / F of the # 2 and # 4 cylinders is lean A / F, the first It can be considered as a combination of the embodiment and the second embodiment. The rich A / F and the lean A / F may be reversed.
In this case, only the exhaust gas from the # 1 cylinder and the # 4 cylinder can be detected by the O ₂ sensor 32 and the combustion A / F can be set for the # 1 cylinder and the # 4 cylinder. Similar to the example. Further, only the exhaust gas from the # 2 cylinder and the # 3 cylinder can be detected by the O ₂ sensor 32, and the combustion A / F can be set for the # 2 cylinder and the # 3 cylinder. In this case, the second embodiment It is the same.

Further, in this case, only the exhaust gas from the # 2 cylinder and the # 3 cylinder can be detected by the O ₂ sensor 32, and the combustion A / F can be set for the # 1 cylinder and the # 4 cylinder having the next combustion order, respectively. Similarly, when the initial values of the combustion A / F of the # 1 and # 2 cylinders are rich A / F and the initial value of the combustion A / F of the # 3 and # 4 cylinders is lean A / F, the # 1 cylinder Further, only the exhaust gas from the # 4 cylinder can be detected by the O ₂ sensor 32, and the combustion A / F can be set for the # 3 cylinder and the # 2 cylinder having the next combustion order.

As a result, the fifth embodiment also achieves the same effects as those of the above embodiments.
This is the end of the description of the embodiment of the air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to the present invention, but the embodiment is not limited to the above.
For example, in the above embodiment, an inexpensive O ₂ sensor 32 can be applied as an exhaust sensor, which can reduce the cost. However, as an exhaust sensor, a linear A / F sensor (such as LAFS) or a NOx sensor can be used. Can also be applied.

In the above embodiment, the target A / F is stoichiometric. However, the target A / F may be a value near the stoichiometric value, and may be a rich A / F value or a lean A / F value. Also good.
Further, when the combustion A / F is modulated at high speed as described above, the exhaust A / F in the three-way catalyst 30 is not stoichiometric but biased toward the rich A / F side or lean A / F side, and the noble metal of the three-way catalyst 30 There is a case where reductive poisoning in which HC or the like remains adsorbed or oxidative poisoning in which oxygen remains adsorbed may occur. In such a case, reductive poisoning or oxidative poisoning is eliminated. It is effective to perform lean spike control and rich spike control as much as possible.

  In the above embodiment, a four-cylinder gasoline engine is used as the engine 1, but the engine 1 may be an engine of any cylinder as long as it has multiple cylinders.

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 mounted on a vehicle. It is a figure which shows the exhaust manifold and exhaust sensor which concern on 1st Example. It is a flowchart which shows the control routine of the combustion A / F control which concerns on 1st Example. It is a figure which shows the exhaust manifold and exhaust sensor which concern on 2nd Example. It is a figure which shows the exhaust manifold and exhaust sensor which concern on 3rd Example. It is a part of flowchart which shows the control routine of the combustion A / F control which concerns on 3rd Example of this invention. FIG. 7 is the remaining part of the flowchart that shows the control routine for the combustion A / F control according to the third embodiment of the present invention, following FIG. 6. It is a figure which shows the exhaust manifold and exhaust sensor which concern on 4th Example. It is a flowchart which shows the control routine of the combustion A / F control which concerns on 4th Example of this invention. It is a figure which shows the exhaust manifold and exhaust sensor which concern on 5th Example. It is a figure which shows the relationship between a modulation period and catalyst performance (purification efficiency).

Explanation of symbols

1 Engine Body 6 Fuel Injection Valve 20 Exhaust Manifold 30 Three-way Catalyst 32 O ₂ Sensor (Exhaust Sensor)
40 ECU (Electronic Control Unit)

Claims (2)

An exhaust sensor that is provided at a collecting portion of exhaust discharged from at least two cylinders of the multi-cylinder and detects and outputs a concentration of a predetermined exhaust component;
The combustion air-fuel ratios of some cylinders of at least two or more cylinders and the combustion air-fuel ratios of the remaining cylinders are reversed with a predetermined value therebetween so that the output from the exhaust sensor fluctuates in a cycle within approximately one cycle of the internal combustion engine. Combustion air-fuel ratio setting means for setting the direction,
Wherein when the output from the exhaust gas sensor is contrary to the combustion air-fuel ratio set in a part of the cylinder the said substantially one cycle Rukoto invert the combustion air-fuel ratio for the cylinders of the balance corresponding to the part of the cylinder Exhaust air-fuel ratio adjusting means for adjusting the average value of the exhaust air-fuel ratio in the predetermined value,
An air-fuel ratio control apparatus for a multi-cylinder internal combustion engine, comprising: The exhaust air-fuel ratio adjusting means may be adjusted by at least two or more equal amounts or the same rate across said predetermined value the combustion air-fuel ratio of the cylinders, the air-fuel ratio of a multicylinder internal combustion engine according to claim 1 Symbol placement Control device.

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