JP4214766B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine having a variable valve mechanism capable of continuously and variably controlling an intake air amount by changing a valve lift characteristic of an intake valve, and more particularly to an air-fuel ratio control device thereof.
[0002]
[Prior art]
Patent Document 1 discloses a variable valve mechanism that can be continuously variably controlled by a lift amount and an operating angle of an intake valve previously proposed by the present applicant. According to this type of variable valve mechanism, it is possible to variably control the amount of air flowing into the cylinder without depending on the opening degree control of the throttle valve, and so-called throttleless operation, particularly in a small load region. Or, the operation with the throttle valve opening kept sufficiently large can be realized, and the pumping loss can be greatly reduced.
[0003]
Further, in Patent Document 2, in order to eliminate the variation in the air-fuel ratio between the cylinders, the temporal change of the detection signal of the air-fuel ratio sensor and the exhaust timing of each cylinder are collated to determine the air-fuel ratio of each cylinder. A technique for detecting and performing feedback correction of the injection amount for each cylinder is disclosed.
[0004]
[Patent Document 1]
JP 2002-89341 A
[0005]
[Patent Document 2]
JP-A-9-203337
[0006]
[Problems to be solved by the invention]
When controlling the intake air amount using the variable valve mechanism as described above, the intake valve lift amount (maximum lift amount) must be set to achieve a very small intake air amount as in idling. For example, the minimum lift is about 1 mm. In such a minimal lift state, the amount of air flowing into the cylinder varies relatively greatly due to a slight error in the lift amount of each cylinder, and the intake air amount itself is small, so that the air-fuel ratio variation among the cylinders varies. Is likely to occur.
[0007]
As described above, Patent Document 2 discloses feedback control of the air-fuel ratio for each cylinder. However, particularly in an internal combustion engine having a large number of cylinders, air-fuel ratio detection for each cylinder based on the exhaust timing is accurately performed. It is difficult.
[0008]
[Means for Solving the Problems]
This invention All cylinders in a multi-cylinder internal combustion engine The valve lift characteristics of the intake valve All at once A variable valve mechanism capable of continuously and variably controlling the intake air amount of the internal combustion engine by changing, a fuel supply means for supplying fuel to each cylinder, and an air-fuel ratio detection means provided in the exhaust system of the internal combustion engine And an air-fuel ratio control apparatus for an internal combustion engine comprising: a feedback control means for controlling the amount of fuel supplied by the fuel supply means based on the detection signal of the air-fuel ratio detection means. Above variable valve mechanism The valve lift characteristics of the intake valves for all cylinders The target air-fuel ratio is changed from the stoichiometric air-fuel ratio to the rich side and the lean side under a predetermined operation state controlled to the minimum lift state, and the in-cylinder pressure change of each cylinder accompanying each air-fuel ratio change is detected. Therefore, the variation in intake air amount of each cylinder is tested, and the correction amount stored for each cylinder is used to cancel the variation, and the fuel supply amount of each cylinder is corrected to increase or decrease during engine operation. Features.
[0009]
That is, according to the present invention, when the variable valve mechanism is operated in the minimal lift state in which the error between the cylinders is most noticeable, the presence or absence of variation in the intake air amount of each cylinder is tested. During normal operation, the fuel supply amount of each cylinder is corrected to increase or decrease so as to cancel out the variation detected during this test. Thereby, the actual air-fuel ratio of each cylinder more accurately matches the target air-fuel ratio, for example, the stoichiometric air-fuel ratio.
[0010]
More specifically, the above test is performed by changing the air-fuel ratio of each cylinder from the stoichiometric air-fuel ratio to the rich side and the lean side, and detecting the in-cylinder pressure change of each cylinder accompanying each air-fuel ratio change. be able to.
[0011]
In a state where the plurality of cylinders are controlled to the stoichiometric air-fuel ratio, a certain cylinder is rich (for convenience, this is referred to as a rich cylinder), and another cylinder is lean (similarly, this is lean). It is assumed that the remaining cylinders are correctly the stoichiometric air-fuel ratio (also referred to as stoichiometric cylinders). Note that these variations in the air-fuel ratio are mainly caused by variations in the lift amount due to the variable valve mechanism. In addition, since the stoichiometric air-fuel ratio is the whole of the plurality of cylinders, normally, if there are rich cylinders, there are lean cylinders at the same time. From this state, for example, when the fuel supply amount is increased and the air-fuel ratio of the plurality of cylinders is changed to the rich side, sufficient air is present in the lean cylinder. , Torque increases. That is, an in-cylinder pressure higher than that at the stoichiometric air-fuel ratio is detected. On the other hand, in the stoichiometric cylinder and the rich cylinder, there is no excess air, so that the cylinder pressure does not increase even if the fuel supply amount is increased. On the other hand, if the intake air amount is increased from the stoichiometric air-fuel ratio, for example, and the air-fuel ratio of the plurality of cylinders is changed to the lean side, there is sufficient fuel in the rich cylinder. As the amount increases, the torque increases. That is, an in-cylinder pressure higher than that at the stoichiometric air-fuel ratio is detected. On the other hand, in the stoichiometric cylinder and the lean cylinder, there is no excess fuel, so even if the air amount is increased, the in-cylinder pressure does not increase.
[0012]
In this way, by executing the forced rich operation and the lean operation for a short time, it is possible to easily determine the lean cylinder and the rich cylinder.
[0013]
【The invention's effect】
According to the air-fuel ratio control apparatus for an internal combustion engine according to the present invention, in the internal combustion engine provided with the variable valve mechanism that can continuously and variably control the intake air amount, each variable attributed to the variation in the lift amount by the variable valve mechanism. The variation in the air-fuel ratio of the cylinders can be reduced, and the deterioration of the drivability and the emission due to the variation in the air-fuel ratio of each cylinder can be avoided, and the fuel efficiency can be further improved.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0015]
FIG. 1 is a system configuration diagram showing an air-fuel ratio control apparatus for an internal combustion engine according to the present invention. An internal combustion engine 1 comprising a spark ignition gasoline engine has an intake valve 3 and an exhaust valve 4, and the intake air A variable valve mechanism 2 described later is provided as a valve mechanism on the valve 3 side. The valve operating mechanism on the exhaust valve 4 side is a direct acting type that drives the exhaust valve 4 by the exhaust camshaft 5, and its valve lift characteristic is always constant.
[0016]
The outlet side of the exhaust manifold 6 that collects the exhaust of each cylinder is connected to the catalytic converter 7, and an air-fuel ratio sensor 8 for detecting the air-fuel ratio is provided at an upstream position of the catalytic converter 7. . A second catalytic converter 10 and a silencer 11 are further provided on the downstream side of the catalytic converter 7. The air-fuel ratio sensor 8 may be an oxygen sensor that detects only the rich or lean air-fuel ratio, or may be a wide-area air-fuel ratio sensor that can provide an output corresponding to the value of the air-fuel ratio.
[0017]
A fuel injection valve 12 is disposed so as to inject and supply fuel to each cylinder toward the intake port of each cylinder. A branch passage 15 is connected to each intake port, and upstream ends of the plurality of branch passages 15 are connected to a collector 16. An intake inlet passage 17 is connected to one end of the collector 16, and an electronically controlled throttle valve 18 is provided in the intake inlet passage 17. The electronically controlled throttle valve 18 includes an actuator 18a made of an electric motor, and its opening degree is controlled by a control signal supplied from an engine control unit 19. A sensor 18b for detecting the actual opening of the throttle valve 18 is integrally provided, and the throttle valve opening is closed-loop controlled to the target opening based on the detection signal. An air flow meter 20 that detects the intake air flow rate is disposed upstream of the throttle valve 18, and an air cleaner 21 is further disposed upstream.
[0018]
A crank angle sensor 22 is provided for the crankshaft in order to detect the engine rotation speed and the crank angle position. In the present embodiment, the change in the crankshaft angular velocity is obtained from the detection signal of the crank angle sensor 22, and the change in the cylinder pressure in the cylinder in the explosion stroke is detected. That is, an in-cylinder pressure sensor that directly detects the in-cylinder pressure of each cylinder is not provided. Further, an accelerator opening sensor 23 for detecting an accelerator pedal opening (depression amount) operated by the driver is provided. These detection signals are input to the engine control unit 19 together with detection signals from the air flow meter 20, the air-fuel ratio sensor 8, and the like. In the engine control unit 19, based on these detection signals, the injection amount and injection timing of the fuel injection valve 12, the ignition timing by the ignition plug 24, the valve lift characteristics by the variable valve mechanism 2, the opening of the throttle valve 18, etc. To control.
[0019]
The variable valve mechanism 2 on the intake valve 3 side is known, for example, from the aforementioned Japanese Patent Application Laid-Open No. 2002-89341, and as shown in FIG. 2, the lift / operating angle of the intake valve 3 is continuously increased. The lift / operating angle variable mechanism 51 that is variably controlled and the phase variable mechanism 52 that continuously advances or retards the phase of the center angle of the lift (phase with respect to the crankshaft) are combined. Thus, according to the variable valve mechanism that combines the lift / operating angle variable mechanism 51 and the phase variable mechanism 52, both the intake valve opening timing and the intake valve closing timing can be arbitrarily controlled independently. At the same time, by reducing the lift amount (maximum lift amount) in the low load range, it is possible to limit the intake air amount according to the load. In the region where the lift amount is large to some extent, the air amount flowing into the cylinder is mainly determined by the opening / closing timing of the intake valve 3, whereas in the state where the lift amount is sufficiently small, the air amount is mainly determined by the lift amount. .
[0020]
The outline of the lift / operating angle variable mechanism 51 will be described together with the operation explanatory diagram of FIG. 3. The lift / operating angle variable mechanism 51 is rotatably supported by the cylinder head and rotates in conjunction with the crankshaft. A hollow drive shaft 53, an eccentric cam 55 fixed to the drive shaft 53, a rotatable control shaft 56 disposed in parallel above the drive shaft 53, and an eccentric cam of the control shaft 56 A rocker arm 58 that is swingably supported by the portion 57 and a swing cam 60 that contacts the tappet 59 at the upper end of each intake valve 3 are provided. The eccentric cam 55 and the rocker arm 58 are linked by a link arm 61, and the rocker arm 58 and the swing cam 60 are linked by a link member 62. The link arm 61 has an annular portion 61 a rotatably fitted on the outer peripheral surface of the eccentric cam 55. Further, the extension portion 61 b of the link arm 61 is linked to one end portion of the rocker arm 58, and the upper end portion of the link member 62 is linked to the other end portion of the rocker arm 58. The eccentric cam portion 57 is eccentric from the axis of the control shaft 56, and accordingly, the rocking center of the rocker arm 58 changes according to the angular position of the control shaft 56.
[0021]
The swing cam 60 is fitted to the outer periphery of the drive shaft 53 and is rotatably supported, and the lower end portion of the link member 62 is linked to the end portion 60a extending to the side. On the lower surface of the swing cam 60, a base circle surface 64a that forms a concentric arc with the drive shaft 53, and a cam surface 64b extending in a predetermined curve from the base circle surface 64a to the end portion 60a, Are formed continuously. The base circle surface 64a is a section where the lift amount becomes zero, and as the swing cam 60 swings and the cam surface 64b contacts the tappet 59 as shown in FIG. become.
[0022]
The rotational position of the control shaft 56 is controlled by a lift / operating angle control actuator 65 formed of, for example, an electric motor provided at one end.
[0023]
For example, when the eccentric cam portion 57 is in the upper position as shown in FIG. 3A by the actuator 65, the rocker arm 58 is positioned upward as a whole, and the end portion 60a of the swing cam 60 is relatively lifted upward. It becomes a state. That is, the initial position of the swing cam 60 is inclined in the direction in which the cam surface 64 b is separated from the tappet 59. Therefore, when the swing cam 60 swings with the rotation of the drive shaft 53, the base circle surface 64a continues to contact the tappet 59 for a long time, and the period during which the cam surface 64b contacts the tappet 59 is short. Therefore, the lift amount is reduced as a whole, and the angle range from the opening timing to the closing timing, that is, the operating angle is also reduced.
[0024]
Conversely, if the eccentric cam portion 57 is positioned downward as shown in FIG. 3B, the rocker arm 58 is positioned downward as a whole, and the end portion 60a of the swing cam 60 is pushed downward relatively. It will be in the state. That is, the initial position of the swing cam 60 is inclined in the direction in which the cam surface 64 b approaches the tappet 59. Therefore, when the swing cam 60 swings with the rotation of the drive shaft 53, a large lift amount is obtained and the operating angle is also expanded.
[0025]
Since the initial position of the eccentric cam portion 57 can be continuously changed, the valve lift characteristic changes continuously as shown in FIG. That is, the lift and the operating angle can be continuously expanded and contracted simultaneously.
[0026]
Next, as shown in FIG. 2, the phase variable mechanism 52 relatively connects the sprocket 71 provided at the front end portion of the drive shaft 53 and the sprocket 71 and the drive shaft 53 within a predetermined angle range. And a hydraulic actuator 72 for phase control that is rotated to the right. The sprocket 71 is linked to the crankshaft via a timing chain or timing belt (not shown). Therefore, by the hydraulic control to the phase control hydraulic actuator 72, the sprocket 71 and the drive shaft 53 rotate relatively, and the lift center angle is retarded as shown in FIG. That is, the lift characteristic curve itself does not change, and the whole advances or retards.
[0027]
The lift / working angle variable mechanism 51 and the phase variable mechanism 52 may be controlled by providing a sensor for detecting the actual lift / working angle or phase and performing closed loop control, or depending on the operating conditions. It is also possible to simply perform open loop control.
[0028]
In the above configuration, the intake air amount is controlled so that the required torque determined by the accelerator pedal opening is obtained. The opening of the electronically controlled throttle valve 18 is basically the exhaust gas recirculation, etc. Is controlled so that the minimum negative pressure required is generated in the collector 16. The variable valve mechanism 2 is controlled so that the amount of air flowing into the cylinder is optimized under the negative suction pressure close to the atmospheric pressure.
[0029]
Here, as described above, in a low load region such as during idling, the lift amount of the intake valve 3 becomes a minimal lift of about 1 mm by the lift / operating angle variable mechanism 51 and is limited to an air amount corresponding to the lift amount. Therefore, the air amount of each cylinder varies relatively large due to slight variations in the lift amount of each cylinder due to the dimensional error or assembly error of the components of each cylinder in the variable valve mechanism 2. End up. The fuel injection amount of each cylinder is controlled so as to be the target air-fuel ratio (for example, the theoretical air-fuel ratio) in all the cylinders based on the detection signal of the air-fuel ratio sensor 8 in the exhaust system. Therefore, if there is a variation in the air amount between the cylinders, the actual air-fuel ratio of each cylinder is shifted from the target air-fuel ratio to the rich side or the lean side.
[0030]
In the present invention, in order to reduce the influence of the variation in the air amount due to the variable valve mechanism 2, the intake of each cylinder is performed under a predetermined operation state in which the variable valve mechanism 2 is controlled to a minimum lift. The variation in the air amount is tested, and the fuel injection amount of each cylinder is corrected so as to cancel out the variation.
[0031]
The flowchart of FIG. 6 shows the flow of processing for the variation test of the intake air amount. First, in step 1, it is determined whether or not the conditions for performing the test are satisfied. In this embodiment, as an example applied to the internal combustion engine 1 equipped with an automatic transmission, the automatic transmission is in a normal travel range (so-called D range) and the vehicle is stopped by a driver's brake operation. That is, when the traveling range idle condition is satisfied, the variation test is executed. By performing the test while the vehicle is stopped in this way, even if a change in the in-cylinder pressure occurs during the test, the passenger is less likely to feel uncomfortable. In addition, during idling with the automatic transmission in the neutral range, the combustion of the internal combustion engine 1 is relatively unstable, so that the in-cylinder pressure is likely to fluctuate due to factors other than variations in the lift amount. The traveling range idle condition in which a slight load is applied can more accurately detect the in-cylinder pressure change of each cylinder associated with the test described later. For the same reason, for example, when a test is performed in a neutral state in an internal combustion engine with a manual transmission, it is desirable that the test be performed under idle conditions in which a load of an air conditioner compressor is applied.
[0032]
If the test conditions in step 1 are satisfied, the process proceeds to steps 2 and 3, and the cylinder pressure Pi (cylinder effective average pressure) of each cylinder is set while performing the operation with the target air-fuel ratio being the theoretical air-fuel ratio (ie, λ = 1). Measure each. That is, the fuel injection amount is feedback-controlled based on the detection signal of the air-fuel ratio sensor 8 and held in the state of λ = 1. Then, the change in the angular velocity of the crankshaft corresponding to the explosion stroke of each cylinder is obtained based on the detection signal of the crank angle sensor 22, and the in-cylinder pressure Pi of the corresponding cylinder is obtained. This is performed continuously for about 10 seconds, for example, and the in-cylinder pressure Pi is obtained as an average value of a plurality of cycles (for example, about 50 cycles) during that period.
[0033]
Next, proceeding to steps 4 and 5, the fuel injection amount is increased by a certain amount (for example, about 5 to 10% of the injection amount when λ = 1), and the air-fuel ratio is changed to the rich side. In-cylinder pressure Pi (cylinder effective average pressure) of each cylinder is measured. This is similarly performed continuously for about 10 seconds, and the in-cylinder pressure Pi is obtained as an average value of a plurality of cycles (for example, about 50 cycles) during that period. When enriching in this way, it is sufficient to stop the air-fuel ratio feedback control and perform the open loop control. However, the target air-fuel ratio is changed to the rich side while continuing the air-fuel ratio feedback control. May be.
[0034]
Next, proceeding to Steps 6 and 7, the intake air amount is increased from the stoichiometric air-fuel ratio by a certain amount (for example, about 5 to 10% of the air amount when λ = 1), and the air-fuel ratio is set to the lean side. The in-cylinder pressure Pi (cylinder effective average pressure) of each cylinder at that time is measured. This is similarly performed continuously for about 10 seconds, and the in-cylinder pressure Pi is obtained as an average value of a plurality of cycles (for example, about 50 cycles) during that period. The increase in the intake air amount can be realized by the control of the variable valve mechanism 2. However, the intake air amount is increased by temporarily increasing the opening of the electronic control throttle valve 18 to increase the pressure in the collector 16. This is more preferable because the minimum lift of the variable valve mechanism 2 can be maintained as it is.
[0035]
Next, in step 8, the rich cylinder and the lean cylinder are determined from the change in the in-cylinder pressure Pi of each cylinder under each air-fuel ratio. First, the in-cylinder pressure Pi when λ = 1 is compared with the in-cylinder pressure Pi at the time of fuel increase, and it is determined that the cylinder in which the in-cylinder pressure Pi has increased is a lean cylinder. More specifically, if the stoichiometric cylinder in which fuel and air are present in an amount of “one to one” when λ = 1, the amount of fuel increases, for example, an amount of “1.1 to 1”. Since only the work amount corresponding to “1” is generated, the work amount does not increase as compared to when λ = 1, that is, the in-cylinder pressure Pi does not increase. Even in a rich cylinder in which fuel and air exist in an amount of, for example, “1 to 0.9” when λ = 1, the amount of work does not increase due to the increase in fuel. On the other hand, in the lean cylinder in which the fuel and air are present in an amount of, for example, “1 to 1.1” when λ = 1, the fuel and air are, for example, “1.1 to 1.1” due to the increase in fuel. Therefore, the work amount, that is, the in-cylinder pressure Pi, increases as compared with the case of λ = 1.
[0036]
Further, the in-cylinder pressure Pi when λ = 1 is compared with the in-cylinder pressure Pi when the air amount is increased, and the cylinder having the increased in-cylinder pressure Pi is determined to be a rich cylinder. More specifically, if the stoichiometric cylinder in which fuel and air are present in an amount of “one to one” when λ = 1, the amount of air becomes, for example, “1 to 1.1”. However, the work amount does not increase, that is, the in-cylinder pressure Pi does not increase. Even in a lean cylinder in which fuel and air exist in an amount of, for example, “1 to 1.1” when λ = 1, the amount of work does not increase due to the increase in the air amount. In either case, the work amount corresponding to “1” remains unchanged. On the other hand, in the case of a rich cylinder in which fuel and air exist in an amount of, for example, “1 to 0.9” when λ = 1, only a work amount corresponding to “0.9” occurs when λ = 1. Therefore, when the fuel and air become an amount of “one to one” due to the increase in the amount of air, for example, a work amount corresponding to “1” is obtained, so that the work amount, that is, the in-cylinder pressure Pi is compared to when λ = 1. Will increase.
[0037]
Accordingly, it is possible to distinguish between the stoichiometric cylinder, the lean cylinder, and the rich cylinder by a series of tests. In the test, there is no problem even if the order is changed so that leaning is performed first and then enriching is performed.
[0038]
In step 8, if there are no lean cylinder and rich cylinder, all the cylinders are stoichiometric cylinders, so this variation test is terminated. On the other hand, if there are lean cylinders and rich cylinders, the routine proceeds to step 9 where the correction amount of the fuel injection amount for the lean cylinder and the rich cylinder is set and the fuel injection amount is actually corrected in step 10. Return to Step 1 again and repeat the test. The correction amount is substantially equal to the increase amount during enrichment and leaning in the above test. That is, for a lean cylinder that is considered to have a relatively large amount of air flowing into the cylinder, a fuel amount equal to the fuel increase during the above-described enrichment is added as a correction amount. Further, for a rich cylinder that is considered to have a relatively small amount of air flowing into the cylinder, the same fuel amount is subtracted as a correction amount. In other words, the correction is made so that the air-fuel ratio becomes about 5 to 10%.
[0039]
In the test of the present embodiment, the degree of lean and rich in the lean cylinder and the rich cylinder is not measured, so that the test is performed again after correcting the fuel injection amount for the lean cylinder and the rich cylinder as described above. . In this state, if there are still lean cylinders and rich cylinders, the same correction amount is given in steps 9 and 10 in another step. Finally, if a lean cylinder and a rich cylinder are not found, a series of tests are completed in step 8. The value of the correction amount obtained for each cylinder in this way is stored until it is updated by the next variation test and used during the subsequent operation.
[0040]
Here, in the subsequent operation, the correction amount is given in the form of addition / subtraction to the basic fuel injection amount of each cylinder. That is, a fixed amount of fuel is added or subtracted regardless of the load. This corresponds to the fact that the influence of the variation in the intake air amount by the variable valve mechanism 2 becomes very small when the lift / operating angle is large. If correction of the variation between the cylinders is performed by multiplying by a correction coefficient, overcorrection will occur on the high load side where the lift / operation angle is large. For the same reason, when the lift / operating angle is controlled to be larger than a certain value, the injection amount correction for correcting the variation among the cylinders may not be performed. This is advantageous particularly in reducing the calculation load of the control circuit in the high speed range.
[0041]
On the other hand, in the present invention, the variation in the intake air amount of each cylinder by the variable valve mechanism 2 is not corrected, and the fuel injection amount corresponding to this is given. There is a possibility that the variation in the in-cylinder pressure Pi between the cylinders becomes significant in the region of the low-speed and low-load side. Therefore, in an operating condition such as an idle in which variation in the in-cylinder pressure Pi is a problem in terms of vibration noise, etc., the ignition timing is retarded for the cylinder having a relatively large fuel injection amount simultaneously with the correction of the fuel injection amount. It is desirable that the in-cylinder pressure Pi be equal to that of the other cylinders.
[0042]
If the variation in the lift amount is not extreme, it is generally considered that the cylinders are substantially aligned with the stoichiometric air-fuel ratio with the above-mentioned one-step correction. It is also possible to simplify the processing by detecting the cylinder and the rich cylinder only once.
[0043]
In the above embodiment, forced enrichment is performed by increasing the fuel amount, and forced leaning is performed by increasing the air amount. Accordingly, in either case, the lean cylinder or the rich cylinder appears in the form of an increase in the in-cylinder pressure Pi, and does not cause a stall or instability of combustion due to a decrease in the in-cylinder pressure Pi. However, on the contrary, the lean cylinder and the rich cylinder can be specified even when the forced enrichment is performed by limiting the air amount and the forced leaning is performed by reducing the fuel.
[0044]
In the above embodiment, the cylinder pressure Pi of each cylinder is detected by using the crank angle sensor 22 without adding a special sensor. However, a known washer-type cylinder pressure sensor that is mounted together with a spark plug is known. It is also possible to detect the in-cylinder pressure Pi using other types of in-cylinder pressure sensors.
[0045]
The present invention is not limited to a combination of the lift / operating angle variable mechanism and the phase variable mechanism as described above as the variable valve mechanism, and the lift amount is a minimum lift at least in a low load region. In the configuration including the mechanism to be applied, it can be similarly applied to correct the variation.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a configuration of an embodiment of the present invention.
FIG. 2 is a perspective view showing a main part of a variable valve mechanism.
FIG. 3 is an operation explanatory diagram of a lift / operating angle variable mechanism.
FIG. 4 is a characteristic diagram showing changes in lift / operating angle characteristics by a variable lift / operating angle mechanism;
FIG. 5 is a characteristic diagram showing a phase change of a valve lift characteristic by a phase variable mechanism.
FIG. 6 is a flowchart showing a flow of processing of an intake air amount variation test;
[Explanation of symbols]
1. Internal combustion engine
2… Variable valve mechanism
3 ... Intake valve
8 ... Air-fuel ratio sensor
18 ... Electronically controlled throttle valve
51. Lift / operating angle variable mechanism
52. Phase variable mechanism

Claims (9)

A variable valve mechanism capable of continuously and variably controlling the intake air amount of the internal combustion engine by simultaneously changing the valve lift characteristics of the intake valves of all the cylinders in the multi-cylinder internal combustion engine, and fuel for supplying fuel to each cylinder Supply means, air-fuel ratio detection means provided in the exhaust system of the internal combustion engine, and feedback for controlling the fuel supply amount by the fuel supply means based on the detection signal of the air-fuel ratio detection means so as to reach the target air-fuel ratio An air-fuel ratio control apparatus for an internal combustion engine comprising:
Under a predetermined operating state in which the valve lift characteristics of the intake valves of all the cylinders are controlled to a minimal lift state by the variable valve mechanism, the target air-fuel ratio is changed from the stoichiometric air-fuel ratio to the rich side and the lean side, respectively. By detecting the in-cylinder pressure change of each cylinder accompanying each air-fuel ratio change, the variation in intake air amount of each cylinder is tested, and using the correction amount stored for each cylinder so as to offset this variation, An air-fuel ratio control apparatus for an internal combustion engine, wherein the fuel supply amount of each cylinder is corrected to increase or decrease during engine operation.   The air-fuel ratio is changed to a rich side by increasing the fuel supply amount, and the cylinder whose cylinder pressure has increased at that time is determined to be a relatively lean cylinder in the cylinder group. An air-fuel ratio control device for an internal combustion engine according to claim 1.   The air-fuel ratio is changed to a lean side by increasing the intake air amount, and the cylinder whose cylinder pressure has increased at that time is determined to be a relatively rich cylinder in the cylinder group. Or the air-fuel ratio control apparatus for an internal combustion engine according to 2;   The predetermined driving state in which the test is performed is a driving range idle state in which the automatic transmission of the vehicle is in a driving range and the vehicle is stopped by a brake operation. An air-fuel ratio control device for an internal combustion engine according to claim 1.   The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the fuel supply amount of each cylinder is corrected to increase or decrease by adding or subtracting a constant amount of fuel supply regardless of the load.   5. The fuel supply amount increase / decrease correction of each cylinder is not performed when the operating angle of the intake valve is controlled to be larger than a predetermined value by the variable valve mechanism. An air-fuel ratio control apparatus for an internal combustion engine.   The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the ignition timing of a cylinder having a relatively large fuel supply amount is retarded by correcting the increase or decrease of the fuel supply amount of each cylinder. .   2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein a change in the cylinder pressure of each cylinder accompanying a change in the air-fuel ratio is detected using a detection signal of a crank angle sensor that detects the rotation angle of the crankshaft. .   2. An air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein a change in the cylinder pressure in each cylinder accompanying the change in the air-fuel ratio is detected using an in-cylinder pressure sensor provided in each cylinder.

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