JPH08254146A - Fuel-air ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To facilitate the accurate control of a fuel-air ratio by obtaining an actual fuel-air ratio or an actual fuel supply quantity using a linear type fuel-air ratio sensor, and calculating deviations between their actual values and a target value, and integrating these deviations in every operating domain to compute a learning value. CONSTITUTION: A target fuel supply quantity computing means 13 computes a target fuel supply quantity according to an operating state so as to attain a target fuel-air ratio. An integrated value computing means 16 integrates a deviation between an actual fuel-air ratio based on the output of a linear type fuel-air ratio sensor 11 and a target fuel-air ratio, or a deviation between an actual fuel supply quantity and the target fuel supply quantity in every domain for computing an integrated value. In addition, a memory means 17 sets up and stores a learning value in every operating domain, and the computating renewal of the learning value in every domain is carried out on the integrated value in every domain by a learning value renewing means 18. The learning value which is computed and renewed on the integrated value and stored is reflexed in the case of computing the fuel supply quantity as a correction term for correcting the target fuel supply quantity by a fuel supply quantity computing means 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine, and more particularly, it controls the steady-state error of the fuel supply system control by using the output value of the air-fuel ratio sensor so as to reflect it in the fuel supply amount. The present invention relates to an air-fuel ratio control device for an internal combustion engine.

[0002]

2. Description of the Related Art Generally, an air-fuel ratio control system for an internal combustion engine is provided with an air-fuel ratio sensor in the exhaust system of the engine, and the air-fuel ratio sensor provides a ratio of the air amount to the fuel amount of the air-fuel mixture supplied into the cylinder of the engine. That is, the air-fuel ratio is detected, and the fuel injection amount according to the operating state of the engine is supplied to the engine so that the air-fuel ratio becomes the target air-fuel ratio. The output of the air-fuel ratio sensor has a Z characteristic in which the air-fuel mixture of the engine is inverted at a stoichiometric point where the stoichiometric air-fuel ratio is reached. That is, the air-fuel ratio of the air-fuel mixture is reversed from rich to smaller than the stoichiometric air-fuel ratio to lean larger than the stoichiometric air-fuel ratio or lean to rich. When reversing the output of this air-fuel ratio sensor, the air-fuel ratio of the engine is corrected by a proportional term called skip amount so that the air-fuel ratio before reversal is rich when the air-fuel ratio is rich and becomes rich when lean. Similarly, from the next to the next reversal, the correction is performed by gradually increasing or decreasing by the integral term. Further, since the lean-to-rich inversion of the air-fuel ratio sensor is better than the rich-to-lean inversion, a delay time is provided before the integration starts after the inversion, and the delay time is also corrected. The air-fuel ratio control device controls to supply to the engine a fuel injection amount obtained by multiplying the basic fuel injection amount according to the operating state of the engine by the air-fuel ratio correction coefficient FAF set as described above.

However, the air-fuel ratio control device may not perform feedback control based on the output of the air-fuel ratio sensor. At this time, the air-fuel ratio may deviate due to the individual difference of the engine or the change over time, so the average value of the correction amount by feedback is learned and the air-fuel ratio learning control is always performed to correct the fuel injection amount. For example, JP-A-60-45743
An air-fuel ratio control device, which is called an engine fuel control device disclosed in Japanese Patent Publication, uses a mean value of an air-fuel ratio correction coefficient FAF to calculate a learning value for each operating region of the engine, and takes in the learning value even during a transient operation. This improves the responsiveness of air-fuel ratio control during transient operation.

[0004]

However, the air-fuel ratio control device of Japanese Patent Laid-Open No. 60-45743 has the learning value updated for each operating region of the engine, but the air-fuel ratio correction coefficient FAF which is the basis of the learning value. Is based on the previous operating condition of the engine, that is, the value of another operating region of the engine. Therefore, the learning value for each operating region cannot be accurately calculated, and the air-fuel ratio of the air-fuel mixture of the engine deviates from the target air-fuel ratio, resulting in deterioration of the exhaust gas purifying performance of the engine. In order to solve the above problems, the present invention accurately calculates a learning value for each operating region, calculates a fuel injection amount so that the air-fuel ratio of the air-fuel mixture supplied to the engine becomes a target air-fuel ratio, and supplies the fuel injection amount to the engine. By doing so, it is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that improves the exhaust gas purifying performance of the engine. The present invention also provides
Another object is to bring the air-fuel ratio control into a normal state early by increasing the learning speed.

[0005]

FIG. 1 is a basic configuration diagram of a first embodiment of an air-fuel ratio control device according to the present invention. An air-fuel ratio control device for an internal combustion engine according to the present invention which solves the above-mentioned problem is a linear type air-fuel ratio sensor 11 provided in an exhaust system of the engine 10.
And a target air-fuel ratio of the air-fuel mixture supplied to the engine 10 is set, and a target fuel supply amount calculation means for calculating the target fuel supply amount supplied to the engine 10 based on the target air-fuel ratio and the operating state of the engine 10. In the air-fuel ratio control device for an internal combustion engine, the actual air-fuel ratio or the actual fuel supply amount is calculated based on the output of the air-fuel ratio sensor 11 for each operating region in which the operating state of the engine 10 is divided into a plurality of sections. An integral value calculating means 16 for calculating an integral value of the deviation between the actual air-fuel ratio and the target air-fuel ratio or the deviation between the actual fuel supply amount and the target fuel supply amount,
A storage unit 17 that stores a learning value for the integrated value of the deviation for each operating region, and a learning value updating unit that updates the learning value stored in the storage unit 17 according to the integrated value calculated by the integral value calculating unit 16. 19, and a fuel supply amount calculation means 15 for calculating the fuel supply amount based on the target fuel supply amount and the learned value.

The air-fuel ratio control apparatus for an internal combustion engine according to the present invention further comprises update amount changing means 19 for changing the update amount of the learning value according to the magnitude of the integral value.

[0007]

The target fuel supply amount calculation means 13 calculates the target fuel supply amount in accordance with the operating condition, for example, the intake air amount, the water temperature, etc., so that the target air-fuel ratio is set. The actual air-fuel ratio V based on the output of the linear type air-fuel ratio sensor 11 provided in the exhaust system, which sets the operating region in which the operating region is divided into a plurality of areas and the integral value calculating means 16 can linearly output the value of the air-fuel ratio
Integrating deviation [Delta] V A _{/ F} of the _{A / F} and the target air-fuel ratio V _{A / FS,} or the actual fuel supply amount fc and deviation between the target fuel supply amount fcr calculated from the actual air-fuel ratio and the intake air amount for each of the areas And the integrated value is calculated. The storage unit 17 sets and stores the learned value for each of the operation areas. The learning value updating means 18 updates and calculates the learning value for each area based on the integral value for each area. The learned value calculated and updated based on the integrated value and stored is reflected in the calculation of the fuel supply amount fi as a correction term for correcting the target fuel supply amount by the fuel supply amount calculation means 15.

Since the update amount of the learning value can be changed by the update changing means according to the magnitude of the integral value, the learning speed can be increased.

[0009]

FIG. 2 shows an air-fuel ratio control device according to the present invention, which is a V-type 6
It is the whole schematic diagram showing the example when applied to a cylinder engine. It goes without saying that the present invention is naturally applicable to in-line cylinder engines other than V-type engines.

In FIG. 2, reference numeral 21 denotes a main body of a V-type 6-cylinder engine in which three cylinders are arranged in two rows in a V-shape. An air flow meter 23 is provided in the intake passage 22 of the engine body 21. Air flow meter 2
Reference numeral 3 is a device for directly measuring the intake air amount. For example, a movable vane type air flow meter having a built-in potentiometer is used to generate an output signal of an analog voltage proportional to the intake air amount. This output signal is input to the A / D converter 101 with a built-in multiplexer of the control circuit 30. The distributor 24 has a crank angle sensor 25A whose axis generates a reference position detection pulse signal every 720 ° converted into a crank angle, and a crank detection pulse signal every 30 ° converted into a crank angle. A crank angle sensor 25B for generating each is provided. The pulse signals of the crank angle sensors 25A and 25B are supplied to the input / output interface 102 of the control circuit 30, and the output of the crank angle sensor 25B is C
It is supplied to the interrupt terminal of the PU 103.

An intake pressure sensor 26 for detecting the pressure in the intake pipe is provided in the intake pipe of the engine 21. The intake pressure sensor 26 generates an electric signal of an analog voltage proportional to the intake pressure, and its output is also A. It is supplied to the / D converter 101. Further, the intake passage 22 is provided with fuel injection valves 27A and 27B for supplying the pressurized fuel from the fuel supply system to the intake port for each cylinder. In addition, the engine body 21
Cylinder block water jacket (not shown)
Is provided with a water temperature sensor 29 for detecting the temperature of the cooling water. The water temperature sensor 29 generates an electric signal of analog voltage according to the temperature of the cooling water. This output is also A /
It is supplied to the D converter 101.

The exhaust systems downstream of the exhaust manifolds 31A and 31B of the right bank (hereinafter referred to as A bank) and the left bank (hereinafter referred to as B bank) of the engine 21 respectively have three harmful components HC and CO in the exhaust gas. , A catalytic converter 32A containing a three-way catalyst for purifying NO _x at the same time,
32B is provided. The catalytic converters (start catalysts) 32A and 32B have a relatively small capacity and are provided in the engine room so that the catalyst can be warmed up when starting the engine in a short time.

In the exhaust manifold 31A of the A bank,
That is, the exhaust pipe 34A on the upstream side of the catalytic converter 32A
Is provided with an air-fuel ratio sensor 33A for bank A, and the exhaust manifold 31B of bank B, that is, the exhaust pipe 34B on the upstream side of the catalytic converter 32B is similarly provided with B.
An air-fuel ratio sensor 33B for the bank is provided.

Further, the two exhaust pipes 34A and 34B are joined together at a downstream side thereof in a collecting portion 35a, and a catalytic converter (main catalyst) 36 for accommodating a three-way catalyst is provided in the exhaust pipe downstream of the collecting portion 35a. Are arranged. The catalytic converter 36 has a relatively large capacity and is installed under the floor of the vehicle body. Catalytic converter 36
A collective exhaust pipe 35 is connected to the downstream side of the.

In this embodiment, the air-fuel ratio sensors 33A, 33A
B is a linear global air-fuel ratio sensor (A) that produces an output signal that corresponds one-to-one with the oxygen component concentration in the exhaust gas over a wide air-fuel ratio range.
/ F sensor) is used. Air-fuel ratio sensor 33A,
33B generates an output voltage substantially proportional to the oxygen concentration contained in the exhaust gas of the engine 21, and this output voltage is the control circuit 3
0 to the A / D converter 101.

In the present embodiment, the control circuit 30 is configured as, for example, a microcomputer, and the A / D converter 1 is used.
01, input / output interface 102, CPU 103, ROM 104, RAM 105, backup RA
An M106, a clock generation circuit 107, etc. are provided. The control circuit 30 performs basic control such as fuel injection control and ignition timing control of the engine 21, and also has the target fuel supply amount calculation means 13, the subtractor 14, the fuel supply amount calculation means 15, and the integration described with reference to FIG. It has a function as a value calculation means 16, a storage means 17, a learning value update means 18, and an update amount change means 19, and controls the air-fuel ratio of the engine 21.

Further, the throttle valve 38 of the intake passage 22 is provided with an idle switch 39 for generating a signal indicating whether or not the throttle valve 38 is fully closed, that is, an XIDL signal. The idle state output signal XIDL is supplied to the input / output interface 102 of the control circuit 30.

Further, 40A and 40B are secondary air introduction intake valves, which exhaust secondary air from an air source such as an air pump (not shown) during deceleration or idling.
It is for supplying to A and 31B to reduce HC and CO emissions.

Further, in the control circuit 30, the down counter 108A, the flip-flop 109A, and the drive circuit 110A are for controlling the fuel injection valve 27A of the A bank, and the down counter 108B, the flip-flop 109B, and the drive circuit 110B. Is for controlling the fuel injection valve 7B of the B bank. That is,
In the routine described later, the fuel injection amount (injection time) fi
_{When (A)} (fi _(B) ) is calculated, the injection time fi
_(A) (fi _(B) ) is the down counter 108A (108
B) preset and flip-flop 109
A (109B) is also set. As a result, the drive circuit 1
10A (110B) starts energizing the fuel injection valve 27A (27B). On the other hand, the down counter 108A (108
B) counts the clock signal (not shown), and when the output terminal finally becomes the "1" level, the flip-flop 109A (109B) is set and the drive circuit 11
0A (110B) stops energizing the fuel injection valve 27A (27B). That is, the fuel injection time fi _(A) (f
i _(B) ), the fuel injection valve 27A (27B) is energized,
The fuel corresponding to the time fi _(A) (fi _(B) ) is supplied to the engine 21.
Will be sent to the A bank (B bank) combustion chamber. Note that the interrupt of the CPU 103 is caused by the A / D converter 10
After the A / D conversion of 1 is completed, the input / output interface 102
When the pulse signal of the crank angle sensor 25B is received,
Etc.

The intake air amount data of the air flow meter 23, the intake pressure data of the intake pressure sensor 26, and the cooling water temperature data of the water temperature sensor 29 are fetched by an A / D conversion routine which is executed every predetermined time or every predetermined crank angle. It is stored in a predetermined area of the RAM 105. That is, RA
The intake air amount data, the intake pressure data, and the cooling water temperature data in M105 are updated every predetermined time. The rotation speed data is 30 ° of the crank angle sensor 25B.
RA is calculated by an interrupt for each CA (crank angle)
It is stored in a predetermined area of M105.

Next, referring to FIG. 1 and FIG.
A first embodiment of the air-fuel ratio control device according to the present invention based on D control will be described. As a first embodiment of the air-fuel ratio control device according to the present invention, a PI based on a linear air-fuel ratio sensor output is used.
An example was adopted in which learning control based on the integral value of the air-fuel ratio deviation was added to the air-fuel ratio feedback control of the classical control method using the D (proportional integral derivative) term. In the control circuit 30 in the first embodiment, the output V of the air-fuel ratio sensor 33A or 33B
_A target air-fuel ratio set by the target air-fuel ratio setting means so that the air-fuel ratio of the air-fuel mixture of the engine 21 becomes the stoichiometric air-fuel ratio according to the operating state of the _{A / F} and the engine 21, that is, the reference value _{VA / FS} equivalent to stoichiometry. And the deviation (V _{A / F} −V _{A / FS} = ΔV _{A / FS} ) from the air-fuel ratio feedback correction amount ΔV _{A / F of the} fuel injection amount.
Is calculated as follows. ΔV _{A / F} = KP ・ ΔV _{A / FS} + KI ・ SUM (Δ
V _{A / FS} ) + KD · d (ΔV _{A / FS} ) where KP is a constant proportional coefficient, and SUM (ΔV _{A / FS} ) is the integrated value of the deviation ΔV _{A / FS} (SUMΔ
V _{A / FS} = ΣΔV _{A / FS} ), KI is a constant integration coefficient, d (Δ
V _{A / FS} ) represents the change rate (differential value) of ΔV _{A / FS} , and KD represents a constant differential coefficient.

That is, the air-fuel ratio feedback correction amount ΔV _{A / F} of the fuel injection amount is a reference corresponding to the output of the air-fuel ratio sensor when the air-fuel ratio sensor output V _{A / F} and the mixture of the engine have the stoichiometric air-fuel ratio. P based on the deviation ΔV _{A / FS from the} value V _{A / FS}
It is determined by ID (proportional, integral, differential) processing. Here, KP, KI, and KD are feedback gain constants, which are determined by experiments or the like.

Here, the proportional term KP · ΔV _{A / FS} and the differential term KD · (dΔV _{A / FS} ) are for correcting transient fluctuations of the air-fuel ratio, and the integral term KI · (SUMΔV
_{A / FS} ) is for correcting a steady deviation of the air-fuel ratio, for example, a steady deviation caused by the secular change of the reference output.

Further, the control circuit 30 controls the correction amount ΔV.
_The fuel injection amount correction term Δfi is converted using _{A / F,} and the fuel injection amount fi of the engine is calculated as fi = fim + Δfi. Next, a method of calculating the integrated value of the deviation ΔV _{A / FS} will be described.

FIG. 3 is a flow chart of the air-fuel ratio control routine of the first embodiment. This routine is executed by the control circuit 30 based on the PID control every constant rotation of the crankshaft (for example, every 360 degrees). When this routine starts, in steps 301 to 303, the value of the flag i is changed from the value at the time of executing the previous routine. Here, the value of the flag i represents the cylinder bank from which the fuel injection amount is to be calculated, i = 0 represents the A bank, and i = 1 represents the B bank.
When the value of the flag i is set in steps 301 to 303, R is set according to the value of the set flag i in the following calculation.
The address of the AM 105 is set, and the calculation is performed according to each bank. That is, when i = 0, the address of the RAM 105 is set for the bank A, and the fuel injection amount is calculated using the air-fuel ratio sensor 33A for the bank A (in this case, steps 307 and 308).
The subscript “(i)” described in () shall mean “A”). Further, when i = 1, RA for B bank is similarly set.
The address of M105 is set, and the fuel injection amount is calculated using the B-bank air-fuel ratio sensor 33B (in this case, the subscript "(i) described in steps 307 and 308).
"Means" B ".) As a result, fuel injection valves in banks A and B are alternately calculated once during one cycle of the engine (crankshaft 720 degrees rotation).

The conditions for executing the air-fuel ratio feedback control based on the outputs of the air-fuel ratio sensors 33A and 33B are, for example, that the cooling water temperature is equal to or higher than a predetermined value, that the start of the engine is completed, the amount of increase after start and the warm-up are increased. Fuel increase such as machine increase, power increase, OTP increase for catalyst overheat prevention, etc. is not being executed, and a predetermined time has elapsed since the above fuel increase was completed, fuel cut is not being executed, and fuel That a predetermined time has passed since the cutting was completed,
After the engine is started, it is determined that the air-fuel ratio sensors 33A and 33B are activated, etc., and steps 304 to 310 are executed only when all of these conditions are satisfied.

At step 304, the air-fuel ratio sensor output V
The deviation of _{A / F from} the reference output V _{A / FS} , ΔV _{A / FS} , is calculated as ΔV _{A / FS} = V _{A / F} −V _{A / FS} . In addition, upstream A / F of both A and B banks
The sensor output V _{A / F (i)} is output at regular intervals (for example, 8 times) by a routine (not shown ₎ executed by the control circuit 30 separately.
The data is AD-converted and read every ms, and the latest data is always stored in the RAM 105. Next, at step 305, by using the value of the [Delta] V A _{/ FS,} the integral value of ΔV A _{/ FS} SU
MΔV _{A / FS} is calculated.

Next, in step 306, the amount of change in ΔV _{A / FS} from when the previous routine was executed to when this routine was executed,
That is, the differential value dΔV A _{/ FS} of ΔV A _{/ FS,} calculated as _{dΔV A / FS = ΔV A /} FS (K) -ΔV A / FS (K-1). Here, ΔV _{A / FS (K-1)} indicates the amount of change in ΔV _{A / FS (K)} during the execution of the previous routine.

[0029] In step 307, [Delta] V _{A / FS} calculated by the, SUMΔV _{A / FS,} using the values of dΔV _{A / FS,} the air-fuel ratio feedback correction amount of the fuel injection amount [Delta] V
_{A / F (i)} , ΔV _{A / F (i)} = KP · ΔV _{A / FS} + KI · (SUMΔV
Calculate as _{A / FS} ) + KD · (dΔV _{A / FS} ).

Next, at step 308, a jump learning correction coefficient FKG is calculated to a learning routine which will be described later. In step 309, the fuel injection amount fi _(i) is calculated using the Δfi and a learning correction coefficient FKG calculated from a learning value described later.
Is calculated as fi _(i) = fim _(i) × FKG + Δfi _(i) . Here, fi m _(i) is the basic fuel injection amount. In step 310, the time fi _(i) is set in the down counter 108 (i) of the control circuit 30 by a fuel injection routine (not shown) executed separately. As a result, the fuel injection valve 27 (i) is driven by the drive circuit 110 (i).
From the fuel is injected in an amount corresponding to fi _(i) .

4 to 6 are flowcharts of the learning routine for the integral value. This routine is executed by the control circuit 30 every constant rotation of the crankshaft (for example, every 360 degrees) or every predetermined time. First, a routine for discriminating the eight operating regions (j = 0 to 7) of the engine 21 shown in FIGS. 4 and 5 will be described. In step 401, the rotational speed NE of the engine 21, the intake pressure PM, and the idle state signal XIDL of the idle switch 39 are fetched. In step 402, it is determined whether or not the idle state signal XIDL is on, and when it is on, it is regarded as an idle state and the process proceeds to step 403. When it is off, it is determined that it is not in the idle state and the process proceeds to step 406. In step 403, the engine speed NE of the engine 21 is 500.
It is determined whether or not ≦ NE <1000 (RPM), and Y
If ES, the process proceeds to step 404, and if NO, the process proceeds to step 421. In step 404, it is determined whether or not the intake pressure PM of the engine 21 is 173 (mmHg) ≦ PM. If YES, the process proceeds to step 405, the operating region is set to j = 0, the process proceeds to step 422, and NO. If it is, the process proceeds to step 421.

Next, at step 406, it is judged if the rotational speed NE of the engine 21 is 1000≤NE≤3200 (RPM), and if YES, the routine proceeds to step 407,
If NO, the process proceeds to step 421. In step 407, it is determined whether or not the intake pressure PM of the engine 21 is PM <173 (mmHg). If YES, then the process proceeds to step 421, and if NO, then the process proceeds to step 408. Next, at step 408, the intake pressure PM of the engine 21 is 173 ≦ PM <
It is determined whether or not it is 251 (mmHg), and if YES, the process proceeds to step 409, the operating region is set to j = 1 and the process proceeds to step 422, and if NO, step 410.
Go to. Similarly, in steps 410 to 420, depending on the intake pressure PM of the engine 21, j = 2 when 251 ≦ PM <329 and j = 3 when 329 ≦ PM <407,
When 407 ≦ PM <485, j = 4, 485 ≦ PM <
When 563, j = 5, when 563 ≦ PM <641, j = 6, and when 641 ≦ PM, j = 7. When the determination result in step 403, 404, 406 or step 407 is NO, it is considered that the air-fuel ratio feedback condition is not satisfied, and the routine proceeds to step 421, where the operating region is set to j = FF (hexadecimal number).

FIG. 6 is a flow chart showing a routine for learning the integrated value for each operating region determined and set in steps 401 to 421. First, in step 422, j
Is determined to be FF. If YES, this routine is ended, and if NO, the routine proceeds to step 423. Next, in step 423, the integrated value is sum (j) = Sum (j) + {V _{A / F} (k) −V _{A / FS}
(K)} is calculated. Here, j is an integer of 0 to 7, V
_{A / F} (k) indicates the output of the air-fuel ratio sensor 33 (i) in the current processing cycle, and _{VA / FS} (k) indicates the air-fuel ratio sensor 33 when the air-fuel mixture supplied to the engine 21 has the theoretical air-fuel ratio. Shows the output from (i). The initial value of the integrated value Sum (j) is 0.

Next, in step 424, the RAM 1
Integrated value Sum for each operating region of the engine 21 stored in 05
The learning update amount Δkg (j) is read from the map of the learning update amount Δkg (j) for (j). Step 424
The value 1/512 is assigned to the LSB shown in FIG. As shown in this map, the learning update amount Δkg (j) decreases as the integrated value Sum (j) increases.
Next, at step 425, the learning value KG (j) is calculated and updated as KG (j) = KG (j) + Δkg (j).

Next, the on / off state of the idle state signal XIDL is discriminated. When XIDL = 1, the process proceeds to step 427 and KGX = KG (0) is set and the process proceeds to step 433. When XIDL = 0, the process proceeds to step 428. move on. In step 428, it is determined whether j ≦ 1. If YES, the process proceeds to step 429, KGX = KG (1) is set, and the process proceeds to step 433. If NO, the process proceeds to step 430. In step 430, it is determined whether 7 ≦ j. If YES, the process proceeds to step 431, KGX = KG (7) is set, and the process proceeds to step 433. If NO, the process proceeds to step 432.
In step 432, KGX of 1 <j <7 is obtained by interpolation calculation between KG (j) and KG (j-1). Step 4
In 33, the KGX is compared with the lower limit guard value KKGMN,
If KKGMN ≤ KGX, proceed to step 435, where K
When KGMN> KGX, the process proceeds to step 434 and KGX
Set KKGMN to step 437. In step 435, KGX is compared with the upper limit guard value KKGMX. When KGX ≦ KKGMX, the routine proceeds to step 437, and when KXG> KKKGMX, the routine proceeds to step 436, where KGXM is set to KGX and the routine proceeds to step 437.
At step 437, 1 is added to the learning value KGX to calculate the learning correction coefficient FKG and the learning correction coefficient FKG is stored in the RAM 105, and this learning routine is ended.

The air-fuel ratio control apparatus for an internal combustion engine according to the present invention further comprises update amount changing means for changing the update amount of the learning value according to the magnitude of the integrated value. This means can be executed by changing the learning value Δkg (j) according to the magnitude of the value of SUM (j) in step 424 described above by changing the value of LSB. The smaller the value of LSB, the faster the learning speed.

In addition to the air-fuel ratio control method described above, there are various air-fuel ratio control methods based on the output signal of the air-fuel ratio sensor. From this, in order to maximize the O ₂ storage action of the three-way catalyst, the engine combustion air-fuel ratio should be set equal to the theoretical air-fuel ratio while keeping in mind that the amount of oxygen adsorbed (stored) in the three-way catalyst is maintained at a predetermined amount. An example in which the present invention is applied to an air-fuel ratio control method based on modern control, which enables highly accurate convergence in a short time, will be described below. The applicant of the present application has already proposed this air-fuel ratio control method in Japanese Patent Application No. 5-68391.

FIG. 7 is a basic configuration diagram of the second embodiment of the air-fuel ratio control device according to the present invention. As a second embodiment of the air-fuel ratio control device according to the present invention, a modern control type air-fuel ratio feedback control using a PI (proportional integral) term based on the output of a linear type air-fuel ratio sensor is used, which is based on an integrated value of a deviation of a fuel supply amount. An example with learning control is adopted. The air-fuel ratio control device in the second embodiment detects the rotational speed NE of the internal combustion engine 730 from the crank angle sensor 25A and the intake air amount ma into the cylinder from the air flow meter 23, and the air-fuel ratio sensor 730.
The air-fuel ratio α of the air-fuel mixture supplied to the internal combustion engine 730 is calculated from the output of A. Next, the in-cylinder air amount estimating means 731 estimates the in-cylinder air amount mc from the map of the intake air amount ma and the rotational speed NE. The actual fuel amount estimating means 732 estimates the fuel amount fc actually supplied into the cylinder from the air-fuel ratio α of the air-fuel mixture and the in-cylinder air amount mc. The target fuel amount setting means 733 sets the target fuel amount fcr that becomes the stoichiometric air-fuel ratio from the cylinder air amount mc. Subtractor 734 is fc
A difference between the fuel amount fc estimated by the actual fuel amount estimating means 732 and the target fuel amount fcr is calculated by subtracting -fcr. The integral value calculating means 735 calculates the integral value of the deviation fc-fcr for each operating region in which the operating state of the engine 730 is divided into a plurality of sections. However, since the amount of fuel injected into the intake pipe and the amount of fuel actually supplied into the cylinder are not necessarily the same, the adhesion rate r adhering to the wall surface inside the intake pipe and the cylinder remaining attached to the wall surface inside the intake pipe. It is necessary to predict the residual rate p of the adhered fuel that is not supplied into the cylinder and to estimate the amount of fuel that is supplied into the cylinder from the fuel injection amount fi. Therefore, the basic fuel injection amount calculation means 736 estimates and calculates the basic fuel injection amount fim based on the target fuel amount fcr.

The storage means 737 stores a learning value kg for the integrated value of the deviation fc-fcr for each operating region. The learning value updating means 738 is the integral value calculating means 73.
The deviation fc-fcr calculated for each operating region by
Learning value k stored in the storage means 737 according to the integral value of
Update g. The fuel injection amount calculation means 740 reads the learning value kg from the storage means 737 and reads it as a correction coefficient FKG, and the correction coefficient FKG and the basic fuel injection amount fi.
The fuel injection amount fi supplied to the engine 730 is calculated using m.

In the air-fuel ratio control method based on the modern control shown in FIG. 7, the amount of air sucked into the cylinder per one revolution of the engine (in-cylinder air amount) mc is calculated from the output of the air flow meter and the engine speed. , Output of air-fuel ratio sensor V
_The combustion air-fuel ratio α _(i) is obtained from _{A / F (i),} and the fuel amount fc _(i) actually supplied into the cylinder is calculated from these as fc _(i) = mc
Calculate as / α _(i) . Similarly, the theoretical air-fuel ratio αr
The target fuel amount fcr _(i) required to make the combustion air-fuel ratio the stoichiometric air-fuel ratio is calculated by fcr _(i) = mc / αr
The fuel injection amount fi _(i) is determined so that the difference fc _(i) −fcr _(i) and the time integrated value x1 _(i) thereof are simultaneously zero. Further, since a part of the fuel injected from the fuel injection valve adheres to the wall surface of the intake port, the injection amount from the fuel injection valve and the fuel amount supplied to the cylinder do not necessarily match, but the fuel injection amount fi _(i)
This fuel adhesion is taken into consideration in the determination of. In this way, by controlling the fuel injection amount fi _(i) so that the deviation between the target value fcr _(i) and the actual fuel supply amount fc _(i) and the time integral value thereof are simultaneously made zero, three A predetermined amount of oxygen is always stored in the source catalyst, and the responsiveness of air-fuel ratio control can be enhanced.

FIG. 8 is a flow chart of the air-fuel ratio control method shown in FIG.
It is a chart. This routine is executed by the control circuit 30.
It is executed every constant rotation of the crankshaft (for example, every 360 degrees).
Be done. When the routine starts in FIG.
In 801, the output V of the air-fuel ratio sensor 33 (i)_{A / F (i)}To
The linear output characteristics of the air-fuel ratio sensor 33 (i) (Fig.
(Not shown) to air-fuel ratio α_(i)Is calculated. Then step
In 802 and 803, the air-fuel ratio α obtained above is calculated._(i)When
Obtained from the output of the air flow meter 23 and the engine speed
Intake air amount mc per engine revolution and theory
It was actually supplied into the cylinder from the air-fuel ratio αr (constant).
Fuel quantity fc_{(k) (i)}And the target fuel amount fcr_{(k) (i)}And
calculate. In step 804, the above fc_{(k) (i)}
And fcr _{(k) (i)}Deviation δfc from_{(k) (i)}And δfc_{(k) (i)}= Fc_{(k) (i)}-Fcr_{(k) (i)} Calculate as

In step 805, the fuel injection amount fi_(i)
Nominal value of_(i)The fim_{(k) (i)}= {Fcr_{(k) (i)}-(1-P) fwm
_{(k) (i)}} / (1-R). In the second embodiment, the fuel injection amount fi
_(i), Of the injected fuel adheres to the wall surface of the intake port, etc.
Fuel quantity fw_(i), Fuel quantity fc supplied to the cylinder _(i)
Are nominal values fim_(i), Fwm_(i), Fc
m_(i)And the deviation δfi_(i), Δfw_(i), Δfc_(i)When
Is expressed as the sum of fi_(i)= Fim_(i)+ Δfi_(i) fw_(i)= Fwm_(i)+ Δfw_(i) fc_(i)= Fcm_(i)+ Δfc_(i)

Further, it is assumed that the following model formula is established between them. fw _{(k + 1) (i)} = Pfw _{(k) (i)} + Rfi _{(k) (i)} fc _{(k) (i)} = (1-P) fw _{(k) (i)} + (1-R) f
i _{(k) (i)} fwm _{(k + 1) (i)} = Pfwm _{(k) (i)} + Rfim _{(k) (i)} fcm _{(k) (i)} = (1-P) fwm _{(k) (i) )} + (1-R)
fim _{(k) (i)} fcm _{(k) (i)} = fcr _{(k) (i)} where the subscript k is the value at the time of execution of this routine, (k-
1) indicates the value at the time of executing the previous routine. Further, in this embodiment, P and R are constants. By modifying the above model equation, in step 805, the nominal value fim _(i) is obtained in the above form.

[0044] Next, at step 806, and calculates? Fc _{(i) is} the time integration value x1 _(i) of, as _{x1 (k) (i) =} x1 (k-1) (i) + δfc (k) (i).

In step 807, the integral value is learned in the same manner as described with reference to FIGS. 4 to 6 in the first embodiment,
The learning correction coefficient FKG is obtained and stored in the RAM. However,
It is assumed that step 423 in FIG. 6 is replaced with the following equation. Sum (j) = Sum (j) + {fc (k) -fcr
(K)} (where j = 0 to 7), that is, the deviation between the actual in-cylinder fuel amount and the target in-cylinder fuel amount is integrated. Since the in-cylinder fuel amount fc is calculated as the ratio mc / α of the intake air amount mc and the air-fuel ratio α, even if the deviation of the air-fuel ratio is small, the deviation of the fuel amount becomes large, and particularly in the region where the intake air amount is large Therefore, the larger the large intake amount region in which the absolute amount of fuel increases, the higher the accuracy of the deviation calculation, and the better the learning accuracy.

Further, in step 808, by the last time
Sought fi_(i), Δfc_(i), X1 _(i)Using values such as
Deviation δfi_(i)And δfi_{(k) (i)}= F1 · δfi_{(k-1) (i)}+ F2 · δfc
_{(k-1) (i)} + F3 · x1_{(k) (i)}+ F4 · x1_{(k-1) (i)}+ F5 · x
1_{(k-2) (i)} Calculate as. Here, f1 to f5 are constants.

In step 809, the fuel injection amount fi _(i) is calculated using the nominal value fim _(i) , the deviation δfi _(i) and the learning correction coefficient FKG of the fuel injection amount obtained as described above, as fi _{(k) ( i)} = FKG.multidot.fim _{(k) (i)} +. delta.fi _{(k) (i)} .

In step 810, in preparation for the next routine execution, the nominal value of the amount of fuel adhering to the wall surface is set to fwm _{(k + )} by using the values of fwm _(i) and Rfim _(i) at the time of execution of this routine. _{1) (i)} = Pfwm _{(k) (i)} + Rfim _{(k) (i)} .

As described above, the fuel injection amount fi _(i) obtained above is set in the corresponding down counter 108 _(i) of the control circuit 30 as described in step 310 of FIG. Be seen. As a result, highly accurate air-fuel ratio control becomes possible.

[0050]

As described above, according to the present invention, the actual air-fuel ratio or the actual fuel supply amount is calculated every moment by using the linear air-fuel ratio sensor in the calculation update of each learning value for each operating region. Deviations between these actual values and target values are sequentially calculated, the deviations thus calculated are integrated for each operating region to form an integrated value for each operating region, and a learning value is calculated from the integrated value. Since the deviation is an independent value that does not have the influence before and after the deviation is calculated, the value of the adjacent operation area is dragged when integrating the deviation in each operation area for each operation area. It is possible to calculate as an independent integrated value for each operating region without any need, and thus the learning value can also not be influenced by the adjacent operating regions. Therefore, each learned value becomes a correct learned value in each operating region, which enables accurate air-fuel ratio control and improves exhaust gas purification.

According to the update changing means of the present invention, since the update amount of the learning value can be changed according to the magnitude of the integral value, the learning speed can be increased.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a first embodiment of an air-fuel ratio control device according to the present invention.

FIG. 2 is an overall schematic diagram showing an embodiment when the air-fuel ratio control device according to the present invention is applied to a V-type 6-cylinder engine.

FIG. 3 is a flowchart of an air-fuel ratio control method of the first embodiment.

FIG. 4 is a flowchart of an integrated value learning routine.

FIG. 5 is a flowchart of an integral value learning routine.

FIG. 6 is a flowchart of an integrated value learning routine.

FIG. 7 is a basic configuration diagram of a second embodiment of the air-fuel ratio control device according to the present invention.

FIG. 8 is a flowchart of an air-fuel ratio control method of a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine 11 ... Air-fuel ratio sensor 13 ... Target fuel supply amount calculation means 14 ... Subtractor 15 ... Fuel supply amount calculation means 16 ... Integral value calculation means 17 ... Storage means 18 ... Learning value updating means 19 ... Update amount changing means 21 ... Engine main body 22 ... Intake passage 23 ... Air flow meter 27A, 27B ... Fuel injection valve 30 ... Control circuit 32A, 32B ... Catalytic converter 33A, 33B ... Air-fuel ratio sensor

Claims (2)

[Claims] 1. A linear type air-fuel ratio sensor provided in an exhaust system of an engine and a target air-fuel ratio of an air-fuel mixture supplied to the engine are set, and based on the target air-fuel ratio and an operating state of the engine. A target fuel supply amount calculation means for calculating a target fuel supply amount to be supplied to the engine, and an air-fuel ratio control device for an internal combustion engine, comprising: The actual air-fuel ratio or the actual fuel supply amount is calculated based on the output of the fuel ratio sensor, and the deviation between the actual air-fuel ratio and the target air-fuel ratio or the integrated value of the deviation between the actual fuel supply amount and the target fuel supply amount is calculated. Integrated value calculation means, storage means for storing a learned value for the integrated value of the deviation for each of the operating regions, and a learned value stored in the storage means according to the integrated value calculated by the integrated value calculation means Learning value update hand to update An air-fuel ratio control device for an internal combustion engine, comprising: a stage; and a fuel supply amount calculation means for calculating a fuel supply amount based on the target fuel supply amount and the learned value. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, further comprising update amount changing means for changing the update amount of the learned value according to the magnitude of the integrated value.