JP2623473B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a feedback control method of an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine, and particularly to a method in which a throttle valve shifts from a substantially fully closed state to an open state. The present invention relates to an air-fuel ratio feedback control method for an internal combustion engine in a vehicle.

(Prior Art) In a general internal combustion engine in an accelerating operation state, a technique is known in which a fuel increase is performed to prevent a change in the air-fuel ratio or to make the air-fuel ratio rich to improve drivability.
(For example, JP-A-60-1346, JP-A-62-49641 and JP-A-59-200031) Also, conventionally, when the engine is operated in the air-fuel ratio feedback control operation region, the engine is disposed in the exhaust system of the engine. An air-fuel ratio feedback control method for an internal combustion engine that controls an air-fuel ratio of an air-fuel mixture supplied to the engine by using a coefficient that changes in accordance with an output of an exhaust gas concentration detector is known. JP-A-60-1341).

This conventional control method detects whether the engine is operated in a feedback control operation region or in any region other than the feedback control operation region,
An average value of the coefficients obtained at the time of operation in the feedback control operation region is calculated, and when the operating state shifts from an operation region other than the feedback control operation region to the feedback control operation region, the average of the coefficients is used as the coefficient. It is characterized in that feedback control in the transition destination area is started using a value obtained by multiplying or adding a predetermined value to a value, whereby the initial value of the coefficient at the start of feedback control is set to an appropriate value. By setting, for example, enriching the air-fuel ratio in the transition destination area, NOx is particularly reduced.

(Problems to be Solved by the Invention) However, a general fuel increase at the time of acceleration is to enrich the air-fuel ratio supplied to the cylinder of the engine during the acceleration period in order to improve drivability, or to increase the parameter representing the intake air amount. The present invention does not consider the problem that the coefficient fluctuates at the time of acceleration in a state where the air-fuel ratio feedback control is continued, in order to prevent the fluctuation of the air-fuel ratio due to the detection delay or the like. Also, the conventional air-fuel ratio feedback control method is as follows:
Since the predetermined value to be multiplied or added to the average value of the coefficient is set regardless of the throttle valve opening and the engine temperature, there is room for improvement in performing control according to changes in the throttle valve opening and the engine temperature. Was leaving. For example,
In the feedback control operation region, when deceleration is continued with the throttle valve slightly opened from the fully opened state, the amount of fuel that has increased according to the engine temperature and adhered to the inner wall of the intake pipe is drawn into the cylinder of the engine by the negative pressure in the intake pipe. And
Since the air-fuel ratio is enriched, the coefficient also changes in the direction to make the air-fuel ratio lean according to the engine temperature by the feedback control. When gradually opening the throttle valve in order to shift from such a deceleration state to acceleration or low-speed traveling, this time, due to the difference in the specific gravity between the revenue air and fuel,
Since the increased intake air by opening the throttle valve reaches the cylinder before the increased fuel, the air-fuel ratio temporarily becomes lean. In addition, at this time, the feedback control is started from the value at which the air-fuel ratio is made lean as described above, and the air-fuel ratio of the air-fuel ratio is reduced due to a delay until the correction value of the feedback control is reversed in a direction to become rich. Since it is inevitable to temporarily make the vehicle lean, not only the acceleration performance of the vehicle deteriorates, but also the NOx emission increases. In particular, when the engine temperature is low, since the viscosity of the fuel is higher than at the time of high temperature, a large amount of fuel adheres to the inner wall of the intake pipe, and the air-fuel ratio becomes even leaner, which promotes the above-mentioned problem.

The present invention has been made in order to solve the above-described problems of the related art, and when the throttle valve shifts from a substantially fully closed state to an open state in a feedback control region,
It is an object of the present invention to provide an air-fuel ratio feedback control method for an internal combustion engine that prevents deterioration of the acceleration performance of a vehicle at both a high temperature and a low engine temperature, and that can obtain good exhaust gas characteristics.

(Means for Solving the Problems) In order to achieve the above object, the present invention supplies an air-fuel ratio to an internal combustion engine based on an air-fuel ratio correction value set according to an output signal of an exhaust gas sensor for detecting an exhaust gas concentration of the internal combustion engine. In the method for controlling the air-fuel ratio of an internal combustion engine for a vehicle, the amount of fuel to be fed back is controlled by detecting an opening of a throttle valve and an engine temperature of the engine, and the opening of the throttle valve of the engine is set to a predetermined opening during the feedback control. When it is detected that the value has changed from the following value to a value equal to or more than the predetermined opening, the initial value of the air-fuel ratio correction value is corrected by the enrichment coefficient corresponding to the engine temperature to increase the fuel amount. Things.

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram of a fuel supply control device to which the control method of the present invention is applied. A throttle body 3 is provided in the middle of an intake pipe 2 of an engine 1, and a throttle valve 3 'is provided therein. Is arranged. A throttle valve opening (θ _TH ) sensor 4 is connected to the throttle valve 3 ′.
An electric signal corresponding to the opening of the throttle valve 3 is output and supplied to an electronic control unit (hereinafter referred to as “ECU”) 5.

The fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of the intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). Is electrically connected to ECU5 together with the EC
The valve opening time of fuel injection is controlled by a signal from U5.

On the other hand, an absolute pressure (P _BA ) sensor 8 in the intake pipe is provided immediately downstream of the throttle valve 3 via a pipe 7, and the absolute pressure signal converted into an electric signal by the absolute pressure sensor 8 is sent to the ECU 5. Supplied. Further, the downstream mounted an intake air temperature (T _A) sensor 9 is supplied to the ECU5 outputs an electric signal indicative of the sensed intake air temperature T _A.

The engine water temperature (Tw) sensor 10 mounted on the main body of the engine 1 is composed of a thermistor or the like, detects the engine water temperature (cooling water temperature) Tw, outputs a corresponding temperature signal, and supplies it to the ECU 5. The engine speed (Ne) sensor 11 and the cylinder discrimination (CYL) sensor 12 are mounted around a camshaft (not shown) of the engine 1 or around a crankshaft. The engine speed sensor 11 outputs a pulse (hereinafter referred to as “TDC signal pulse”) at a predetermined crank angle position every time the crankshaft of the engine 1 rotates 180 degrees, and the cylinder discriminating sensor 12 outputs a predetermined crank angle of a specific cylinder. A signal pulse is output at the position, and each of these signal pulses is supplied to the ECU 5.

The three-way catalyst 14 is disposed in the exhaust pipe 13 of the engine 1 and purifies components such as HC, CO, and NOx in the exhaust gas.
O ₂ sensor 15 as an exhaust gas concentration detector outputs a three-way catalyst 14 is mounted on the upstream side of the signal corresponding to the detected value by detecting the oxygen concentration in the exhaust gas in the exhaust pipe 13 ECU 5 To supply. The ECU 5 has an atmospheric pressure sensor 16 for detecting the atmospheric pressure,
An engine ignition switch 17 and an air conditioner switch 19 are connected to supply a signal from the atmospheric pressure sensor 16 and a signal indicating whether the ignition switch 17 and the air conditioner switch 19 are on or off.

Further, a battery 18 is connected to the ECU 5, and an ECU operating voltage is supplied.

The ECU 5 shapes input signal waveforms from various sensors, corrects a voltage level to a predetermined level, and converts an analog signal value to a digital signal value. The input circuit 5a has a function of a central processing unit (hereinafter referred to as a “CPU”). 5b), a storage means 5c for storing various calculation programs executed by the CPU 5b, calculation results, and the like, an output circuit 5d for supplying a drive signal to the fuel injection valve 6, and the like.

The CPU 5b determines various engine operation states such as a feedback control operation area and an open loop control operation area based on the above-described various engine parameter signals, and according to the engine operation state, calculates the TDC based on the following equation (1). The fuel injection time _TOUT of the fuel injection valve 6 synchronized with the signal pulse is calculated.

T _OUT = Ti × (K _TA · K _TW · K _WOT · K _LS · K _DR · K _CAT · K _AST · K _O2 ) + (Tv + ΔTv) ... (1) where Ti is the injection time of the fuel injection valve 6. a reference value of T _OUT, is determined according to the engine rotational speed Ne and the intake pipe absolute pressure P _BA. K _TA is an intake temperature correction coefficient, and K _TW is an engine water temperature correction coefficient, which are determined according to the intake air temperature T _A and the engine water temperature Tw, respectively. K _WOT , K _LS , and K _DR are coefficients, K _WOT is the air-fuel mixture _enrichment coefficient when the throttle valve is fully open, K _LS is the air-fuel mixture lean coefficient, and K _DR is the process of rapid acceleration from the idle range. The enrichment coefficient is applied for the purpose of improving the operation performance of the engine 1 in the low-speed open control region that passes.

K _CAT is an enrichment coefficient applied for the purpose of preventing burnout of the three-way catalyst 14 in FIG. 1 in the high rotation range of the engine (high rotation open loop control range). Is set to

K _AST is a post-start fuel increase coefficient applied immediately after the start of the engine for the purpose of preventing engine stall and the like.

K _O2 is an O ₂ feedback correction coefficient, which is obtained by the control program of FIG. 3 according to the oxygen concentration in the exhaust gas at the time of feedback control. It is a coefficient set according to. Tv and ΔTv are variables corresponding to the battery voltage and their correction variables.

The CPU 5b outputs a drive signal for opening the fuel injection valve 6 based on the fuel injection time T _OUT obtained as described above in an output circuit.
The fuel is supplied to the fuel injection valve 6 via 5d.

FIG. 2 is a flowchart showing a procedure for implementing the control method of the present invention. This program is executed in synchronization with each generation of a TDC signal pulse.

First, it is determined whether or not a predetermined time to ₂ seconds has elapsed after the ignition switch 17 is turned on (ON) (step 29). When the answer is negative (No), the correction coefficient K _{O2 is set} to a value K described later. open-loop control is performed by setting the _PRO (step 40), when the affirmative (Yes), determines whether the activation of the O ₂ sensor 15 is completed (step 30). The answer to step 30 is negative (No), that is, when the activation of the O ₂ sensor 15 has not been completed to determine whether the operating region is in the idle region (step 45).

The determination as to whether or not the vehicle is in the idle region is performed as shown in FIG. That is, the engine speed Ne is the idle speed.
It is determined whether or not it is lower than N _IDL (for example, 1200 rpm) (step 401). If the answer is affirmative (Yes), it is determined whether or not the air conditioner, which is the engine load, is operating (step 402). . When the answer to step 402 is negative (No), the intake pipe absolute pressure P _BA is equal to the first predetermined intake pipe absolute pressure P _BAIDL (for example, 460 mmHg) when the air conditioner is not operating and the engine is in the idle range. ) Is determined (step 403). Step 402
Is affirmative (Yes), the intake pipe absolute pressure P _BA is larger than the first predetermined intake pipe absolute pressure P _BAIDL when the air conditioner is operating and the engine is in the idle range. Absolute pressure P _{BAIDLHAC in} intake pipe (for example, 510mm
Hg) is determined (step 404). When the answer to step 403 or step 404 is affirmative (Yes), it is determined that the engine is in the idling operation range (step 406). If the answer of step 403 or step 404 is negative (N
In the case of o), it is determined that the engine is out of the idle operation range (steps 405 and 407). The determination as to whether or not the vehicle is in the idling operation region is performed in the control program of FIG.

Returning to FIG. 2, when the answer to step 45 is negative (No), the correction coefficient K _O2 for O ₂ feedback is set to K _PRO (step 40). This K _PRO value, when the O ₂ sensor 15 is inactive,
At the time of low water temperature and at the time of high load, it is applied in each specific operation area.By applying it alone or together with the correction coefficient specific to the target area, the optimum value of each of these areas is obtained. A value that gives an air-fuel ratio, usually
It is set to 1.0 or its approximate value.

Each of the above-mentioned specific operation regions has considerably different operation conditions as compared with the feedback control region in which the average value K _{REF of} K _O2 is obtained. Therefore, if the K _REF value is directly applied to these specific operation regions, the obtained air-fuel ratio may be considerably different from the respective required predetermined values.

Therefore, in such an area, the coefficient K _PRO is used instead of K _REF.
Apply Specifically, in the engine production line, a _KPRO value that can be controlled to an air-fuel ratio that can obtain various characteristics such as optimal driving performance, exhaust gas characteristics, and fuel efficiency for an engine to be applied to each production lot is obtained. Set within.

The K _PRO value is set in the ECU 5 so as to be used as an initial value of the average value K _REF of K _O2 when the fuel supply control device is newly assembled to the engine. This is because K _REF is the average value of K _O2 during the past operation and has not yet been obtained when the engine was shipped.

When the answer to step 45 is affirmative (Yes), that is, when the operating region is in the idling region, the value of the correction coefficient K _O2 is set to K _O2IDL (step 46), and open loop control is performed.
The value K _{O2IDL at} this time is a value slightly larger than 1.0 to _{enrich the} air-fuel ratio.

When the answer to step 30 is affirmative (Yes), that is, when the O ₂ sensor 1
When the activation of 5 is completed, it is determined whether or not the engine water temperature Tw is lower than a predetermined temperature T _WO2 (for example, 40 ° C.) (step 31), and the engine performs feedback based on the output of the O ₂ sensor 15. It is determined whether or not the area is present. That is, in step 31, it is determined whether or not the engine _coolant temperature Tw is lower than the predetermined temperature _TWO2 , and the answer is affirmative (Ye
In the case of s), the process proceeds to step 40, and in the case of negative (No), the process proceeds to step 32.

Determine whether the low rotational open-loop control region in the step 32, when the answer is affirmative (Yes), i.e. the average value K to K _O2 when the engine speed Ne is lower than a predetermined rotational speed N _{LOP REF} is set (step 41). The average value K _REF is an average value of K _O2 obtained in the feedback area.

If the answer to step 32 is negative (No), the fuel injection time
It is determined whether T _OUT is longer than a predetermined fuel injection time T _WOT (step 33), and the answer to step 33 is affirmative (Yes).
In the case of, the process proceeds to step 47, and in the case of negative (No), it is determined whether or not the engine speed Ne is in a high-speed open loop region (step). When the answer to step 34 is affirmative (Yes), that is, when the engine speed Ne is equal to the predetermined speed N
When the value is higher than the _HOP , the process proceeds to step 41, and a negative (N
In the case of o), it is determined whether or not the correction coefficient K _LS of the mixture lean region is smaller than 1.0, that is, the engine is in the intake pipe absolute pressure P _BA
It is determined whether or not the engine is in a mixture lean region (K _LS <1.0) determined by the engine speed Ne and the engine speed Ne (step 3).
Five).

Step when the answer to the question of the step 33 is affirmative when the (Yes), and continues the loop comprising the steps 33 determines whether a predetermined time has passed t ₀ seconds (step 47), the answer is affirmative (Yes) Proceeding to 40, open loop control is performed, and if not (No), proceeding to step 43, the correction coefficient K just before leaning or just before fuel cut.
Open loop control is performed while holding _O2 .

The answer to step 35 is affirmative (Yes) to continue the loop comprising the steps 35 when the it is determined whether or not a predetermined time has elapsed t ₀ seconds (step 42), the current fuel cut when negative (No) (Fuel It is determined whether or not (interruption) is being performed (step 36). If the answer to step 36 is affirmative (Yes), the process proceeds to step 42. If the answer to step 42 is affirmative (Ye
In the case of s), the process proceeds to step 41, and in the case of negative (No), the leaning coefficient _KLS is 1.0 or less, that is, the value of the coefficient value K _O2 immediately before leaning or immediately before fuel cut is held (step 43). If the answer to step 36 is negative (N
In the case of o), it is determined that the engine is in the O ₂ sensor feedback range, and the engine water temperature correction coefficient K _TW and the post-start fuel increase coefficient K
_AST is set to a value of 1.0 (step 37), and the O ₂ feedback correction coefficient K _O2 in the feedback loop is set.
And an average value K _REF of K _O2 is calculated (step 44).

That, O ₂ determines whether the sensor feedback area in step 32-36, the engine water temperature correction factor K _TW is when in the feedback region, the correction coefficient of the after-start fuel increase coefficient K _AST values less than 1.0 and If so, the values of these coefficients are forcibly set to 1.0 and the feedback control is started. Accordingly, in this feedback control, the engine water temperature correction and the post-start fuel increase correction based on the engine water temperature correction coefficient K _TW and the post-start fuel increase coefficient K _AST are not performed.

The calculation of the correction coefficient K _O2 in step 44 is performed according to the flowchart shown in FIG.

First, the intake pipe absolute pressure P _BA , engine speed Ne, engine coolant temperature Tw, and throttle valve opening θ _TH are read (step 301). Next, it is determined whether or not the previous control was a feedback loop control (step 302). When the answer is negative (No), it is determined whether or not the previous time was the holding mode of the correction coefficient K _O2 , that is, FIG. It is determined whether or not step 43 has been executed (step 314). If the answer to step 314 is affirmative (Yes), the process proceeds to step 320, in which the correction coefficient K _O2 is set by the integral control, and the program ends. If the answer to step 314 is negative (No), it is determined whether or not the current operation area is in the idle area (step 315). If the answer to step 315 is affirmative (Yes),
The initial value of the correction coefficient K _O2 is set to the average value K _REFO of the idle area K _O2 calculated in the idle area as described later (step 316), and then the integration control of step 320 is performed. Exit this program. Step 315
If the answer is negative (No), the process proceeds to step 311 and below to set an initial value of the correction coefficient K _O2 .

When the answer to step 302 is affirmative (Yes), it is determined whether or not the previous operation range was the idle range (step 303).

When the answer to step 303 is affirmative (Yes), it is determined whether or not the current operating region is an idle region (step 30).
Four). If the answer to step 304 is negative (No), the process proceeds to step 311 and the subsequent steps to set the initial value of the correction coefficient K _O2 . If the answer to step 304 is affirmative (Yes), it is determined whether or not the previous throttle valve opening was fully closed (step 305). If the answer to step 305 is affirmative (Yes), it is determined whether the current throttle valve opening is fully closed (step 306). If the answer in step 306 is negative (No),
That is, when the throttle valve is not fully closed this time, for example, the count value of a T _FBTH timer composed of a down counter is set to a predetermined time T _FBTH (for example, 4 seconds) and started (step 307), and then the correction coefficient K _{O2 Is} set to the average value K _REF2 of the off-idle range K _O2 calculated in a region other than the idle range as described later (step 308), and the integral control is executed in the step 320 to execute this program. To end.

If the answer in step 303 or step 305 is negative (N
o) Or, if the answer to the step 306 is affirmative (Yes), it is determined whether or not the count value T _FBTH of the down counter started at the step 307 is equal to 0 (step 309). When the answer to step 309 is affirmative (Yes), that is, when a predetermined time T _{FBTH has} elapsed after the throttle valve has shifted from the fully closed state to the open state, it is determined whether or not the flag F _THCH is equal to the value 1 (step 310). ). Flag F _THCH
Is set or cleared under the conditions shown in FIG.

First, it is determined whether or not the feedback loop control is being performed (step 501). When the answer is affirmative (Yes), the previous throttle valve opening θ _TH is smaller than the predetermined value _THCH (for example, 2 °). Is determined (step 50
2). If the answer to step 402 is affirmative (Yes), it is determined whether the current throttle valve opening θ _TH is greater than the predetermined value THCH (step 503). If the result of step 503 is affirmative (Yes), that is, if the throttle valve opening θ _TH is smaller than the previous predetermined value THCH and larger than the current predetermined value THCH during the feedback loop control, the flag F _THCH is set to 1 (step). 504).

If any one of the steps 501, 502, 503 is negative (N
In the case of o), the flag F _THCH is cleared to 0 (step 505). Accordingly, during the feedback loop control, the flag F _THCH is set to a value of 1 when the throttle valve opening θ _TH shifts from a state below the predetermined value THCH to a state exceeding the predetermined value THCH, and otherwise to a value of 0.
Is cleared.

Returning to FIG. 3, the answer to step 310 is affirmative (Ye
In the case of s), it is determined whether or not the engine _coolant temperature Tw is higher than a predetermined temperature T _WO2CR (for example, 60 ° C.) (step 31).
1). The answer to step 311 is affirmative (Yes), that is, Tw> T _WO2CR
Therefore, when the engine coolant temperature is not in the low temperature range, the initial value of the correction coefficient K _O2 is set to the value for the off-idle range calculated in a region other than the idle range as described later.
The average value K _{REF1 of} K _O2 and the first _enrichment predetermined value C _R1H (for example,
1.0) is set to the product K _REF1 × C _R1H (step 312), and the _{routine proceeds} to step 320, where the integral control is executed and the present program ends. If the answer in step 311 is negative (No), that is, Tw
When ≦ T _WO2CR is satisfied and the engine _coolant temperature is in the low temperature range, the initial value of the correction coefficient K _O2 is set to the average value K _REF1 of the off-idle range K _O2 and the second _enrichment predetermined value C _R1L.
(For example, 1.1) and set the product K _REF1 × C _R1L
At 320, the integral control is executed and the program ends. Here, the second _enrichment predetermined value C _R1L is set to a value larger than the first _enrichment predetermined value C _R1H , and the initial value of the correction coefficient K _O2 at this time is that the engine water temperature is not in a low temperature range. It is richer than when. This allows the flag
When F _THCH is set to the value 1, that is, when the throttle valve opening shifts from the state below the predetermined value THCH to the state exceeding the predetermined value THCH, the initial value of the correction coefficient K _O2 becomes larger as the engine water temperature becomes lower. Because the air-fuel ratio becomes lean when the throttle valve is opened, it not only prevents a decrease in the acceleration performance of the vehicle and an increase in the amount of NOx emission, but also especially when the engine water temperature is in a low temperature range. Lean air-fuel ratio due to fuel adhering to the inner wall of the intake pipe can be further prevented.

Incidentally, by providing two or more different predetermined temperature instead of a single predetermined temperature T _WO2CR, it may set the enrichment predetermined value C _R1 3 or more.

If the answer of the step 309 is negative (No) or the step 3
Answer 10 when negative (No), the output level of the O ₂ sensor 15 is determined whether or not inverted (Step 317). If the answer to step 317 is negative (No), step 320
To execute the integral control and terminate the program.
If the answer to step 317 is affirmative (Yes), _KO2 is set by proportional control (step 318).

Using the value of the correction coefficient K _O2 set in step 318, the average value K _REF of K _O2 is calculated based on the following equation (2) (step 319), stored in the memory, and the program ends. This average value K _REF is used when the current loop corresponds to a feedback control operation region other than the idle operation region.
K _REF1 or K _REF2 is calculated, and K _REF0 is calculated when it corresponds to the idle operation region.

K _REF = Cn × K _O2P + (1−Cn) × K _REF ′ (2) Here, the value K _O2P is the value of K _O2 immediately before or immediately after the operation of the proportional term (P term), and Cn is for each operation region. To an experimentally appropriate value (0
The variable set to <Cn <1), K _REF ′, is the average value of K _O2 obtained up to the previous time in the operation region corresponding to the current loop.

Depending on the value of the variable Cn, the ratio of K _O2P to K _REF at the time of each P term operation changes, that is, the calculation speed of the average value K _REF changes, so that this Cn value is used as the target air-fuel ratio feedback control device and By setting an appropriate value according to the specifications of the engine, etc., the optimum K _REF (K _REF0 , K _REF1 or
K _REF2 ) can be obtained.

(Effects of the Invention) As described above in detail, the present invention provides a method for controlling an amount of fuel supplied to an internal combustion engine based on an air-fuel ratio correction value set in accordance with an output signal of an exhaust gas sensor for detecting an exhaust gas concentration of the internal combustion engine. In an air-fuel ratio control method for a vehicle internal combustion engine that performs feedback control, an opening degree and an engine temperature of a throttle valve of the engine are detected, and the opening degree of the throttle valve of the engine is determined from a value equal to or less than a predetermined opening degree during the feedback control. When it is detected that the value has changed to a value equal to or more than the predetermined opening, the initial value of the air-fuel ratio correction value is corrected according to the engine temperature or by a richening coefficient so as to increase the fuel amount. The air-fuel ratio at the time of shifting from the almost fully closed state to the valve open state is appropriately set over a wide range of engine temperatures, and thus when the engine temperature is high. In both the low and low temperatures, it is possible to prevent the acceleration performance of the vehicle from deteriorating and to reduce the emission of NOx components.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a fuel supply control device to which the control method of the present invention is applied, FIG. 2 is a flowchart showing a procedure for implementing the control method of the present invention, and FIG. 3 is a correction coefficient K _{O2 in} FIG. FIG. 4 is a flowchart showing an idle determination subroutine of FIGS. 2 and 3, and FIG. 5 is a flag F _{THCH of} FIG.
9 is a flowchart showing the conditions under which is set or cleared. 1 ... internal combustion engine, 4 ... throttle valve opening sensor,
5 ... Electronic control unit (ECU), 8 ... Absolute pressure sensor in intake pipe, 10 ... Engine water temperature sensor, 11 ...
An engine speed sensor, 13 ...... exhaust pipe, 15 ...... O ₂ sensor (exhaust gas concentration detector).

Claims (2)

(57) [Claims] An air-fuel ratio of a vehicular internal combustion engine for feedback controlling an amount of fuel supplied to the internal combustion engine based on an air-fuel ratio correction value set according to an output signal of an exhaust gas sensor for detecting an exhaust gas concentration of the internal combustion engine. In the control method, the opening degree and the engine temperature of the throttle valve of the engine are detected, and during the feedback control, the opening degree of the throttle valve of the engine changes from a value equal to or less than a predetermined opening to a value equal to or more than a predetermined opening. Detecting an air-fuel ratio correction value, correcting an initial value of the air-fuel ratio correction value with an enrichment coefficient corresponding to the engine temperature. 2. An air-fuel ratio control method for an internal combustion engine according to claim 1, wherein an initial value of said air-fuel ratio correction value is obtained by multiplying an average value during said feedback control by said enrichment coefficient.