JP2712089B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control method for an internal combustion engine, and more particularly to an air-fuel ratio control method for a high-load operation of an engine.

(Prior Art) When the load on the engine is relatively low, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to be close to the stoichiometric air-fuel ratio. Conventionally, the fuel ratio is made rich to prevent the engine temperature from excessively rising due to so-called fuel cooling. However, there have been disadvantages such as an increase in fuel consumption or deterioration in exhaust gas characteristics.

In order to remedy such a problem, when the engine operating state shifts to a predetermined high load operation region, a method of leaning the air-fuel mixture within a predetermined time than after a predetermined time has elapsed (Japanese Patent Application Laid-Open No. Sho 59-128941). Japanese Patent Application Laid-Open No. 57-24435 discloses a method of enriching the air-fuel mixture when a predetermined high load state continues for a predetermined time or longer.

(Problems to be Solved by the Invention) Generally, when the so-called feedback control region for feedback-controlling the air-fuel ratio to near the stoichiometric air-fuel ratio is expanded toward a high load side for the purpose of improving exhaust gas characteristics, the so-called feedback control region within the feedback control region is increased. During the partial load operation, the amount of air-fuel mixture supplied to the engine increases, and the amount of heat generated by the engine increases, resulting in a high exhaust gas temperature. However, according to the above-described conventional control method, the air-fuel mixture is enriched after a lapse of a predetermined time from the point of transition to the predetermined high-load operation region. When the operation shifts to the load operation region, the exhaust gas temperature becomes high before the predetermined time elapses, and there is a problem that the durability of the exhaust gas purification device is deteriorated.

The present invention has been made in view of the above points, and appropriately controls an air-fuel ratio of an air-fuel mixture supplied to an engine under a partial load and a high load operation state of an engine, and achieves an exhaust temperature and a catalyst temperature of an exhaust purification device. It is an object of the present invention to provide an air-fuel ratio control method for an internal combustion engine that can prevent an excessive increase in the air-fuel ratio.

(Means for Solving the Problems) In order to achieve the above object, the present invention detects an exhaust gas component concentration based on an output of an exhaust gas concentration sensor provided in an exhaust system of an internal combustion engine, and according to the detected value, An air-fuel ratio control method for an internal combustion engine that performs feedback control so that an air-fuel ratio of an air-fuel mixture supplied to an engine becomes a predetermined value.
A first engine load corresponding to a predetermined high load state;
The feedback control is performed when a state of exceeding a predetermined value and exceeding a second predetermined value corresponding to a predetermined high load region lower than the first predetermined value in an operation region in which the feedback control is performed continues for a predetermined period. The engine is stopped to enrich the air-fuel ratio of the air-fuel mixture supplied to the engine.

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 electronic control unit (hereinafter referred to as “ECU”) 5 outputs an electric signal corresponding to the opening of the throttle valve 3 ′.
To supply.

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. Each injection valve is connected to a fuel pump (not shown). And is electrically connected to ECU5
The valve opening time of fuel injection is controlled by a signal from the ECU 5.

On the other hand, an intake pipe absolute pressure (P _BA ) sensor 8 is provided immediately downstream of the throttle valve 3 ′ via a pipe 7. The absolute pressure signal converted into an electric signal by the absolute pressure sensor 8 is supplied to the ECU 5. Supplied to 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 signal pulse (hereinafter referred to as “TDC signal pulse”) at a predetermined crank angle position every time the crankshaft of the engine 1 rotates by 180 degrees, and the cylinder discriminating sensor 12 outputs a predetermined crank of a specific cylinder. A signal pulse is output at an angular position, and each of these signal pulses is supplied to the EUC5.

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 detects 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. An atmospheric pressure sensor 16 for detecting the atmospheric pressure is connected to the ECU 5, and a signal indicating the atmospheric pressure 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.

Based on the various engine parameter signals described above, the CPU 5b determines various engine operation states such as a feedback control operation area and an open loop control operation area according to the oxygen concentration in the gas distribution, and determines the next according to the engine operation state. Based on the equation (1), a fuel injection time _TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated.

T _OUT = Ti × K ₁ × K _WOT × K _TW × K _O2 + K ₂ (1) Here, Ti is a reference value of the injection time T _OUT of the fuel injection valve 6, and the engine speed Ne and the intake pipe It is read from the Ti map set according to the absolute pressure _PBA . K _WOT is a high load increase coefficient for enriching the air-fuel mixture when the throttle valve 3 'is almost fully opened, and is set by a method shown in FIG. K _TW is a fuel increase coefficient for enriching the air-fuel mixture when the engine water temperature T _W is equal to or lower than a predetermined value. K _O2 is an air-fuel ratio feedback correction coefficient, which is set according to the oxygen concentration in the exhaust gas during feedback control, and is included in each of a plurality of specific operating regions (open-loop control operating regions) where no feedback control is performed. It is a coefficient set according to.

K ₁ and K ₂ are other correction coefficients and correction variable computed according to various engine parameter signals, so that the fuel consumption characteristic according to engine operating conditions, the optimization of various properties such as the engine acceleration characteristics can be achieved Is determined to be a predetermined value.

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 shows a flowchart of a subroutine for calculating a high load increase coefficient K _WOT . This program is executed in synchronization with each generation of a TDC signal pulse.

In step 201, the reference value T of the fuel injection time is stored in the Ti map in accordance with the engine speed Ne and the intake pipe absolute pressure _PBA.
The high load increase coefficient K _WOT is calculated by applying the interpolation coefficient C _WOT stored together with i to the following equation (2).

K _WOT = 1 + C _WOT / 32 (2) In step 202, the T _WOT subroutine shown in FIG. 3 is executed. This T _WOT subroutine calculates a discrimination value T _WOT for discriminating an engine operation region (hereinafter, referred to as “WOT region”) in which a high load increase is to be performed.

First, in step 301, T is set according to the engine speed Ne.
The first determination value T _WOT1 is searched from the _WOT1 table. This T
For example, as shown in FIG. 5, the _WOT1 table stores a first determination value T _WOT10 for a predetermined engine speed N _{WOT0 to} N _WOT5 .
~ T _WOT15 are respectively set. Engine speed Ne
_{Is in} the range of Ne <N _WOT0 or Ne> N _WOT5 , T _WOT1
= T _WOT10 or T _WOT15 , and when N _WOT0 <Ne <N _WOT5 , the first discrimination value T _WOT1 is calculated by interpolation for rotation _speeds other than the predetermined rotation speeds N _{WOT1 to} N _WOT4. calculate.

In step 302, the engine speed Ne becomes the first predetermined speed N
_It is determined whether it is higher than _WOT0 (for example, 600 rpm), and if the answer is negative (No), that is, Ne ≦ N _WOT0 , the first determination value T _WOT1 is set to the value calculated in step 301 (step 303). Next, the second determination value T _WOT2 is _changed to the first determination value.
The same value as T _WOT1 (step 304), and a third discrimination value
T _WOT3 is set to a value _obtained by subtracting the predetermined value ΔT _WOT3 from the second discrimination value T _WOT2 (step 314), and the program ends.

If the answer in step 302 is affirmative (Yes), that is, Ne> N _WOT0
In this case, it is determined whether the engine _coolant temperature T _W is lower than a first predetermined _coolant temperature T _WWOTE (for example, 114 ° C.) (step 30).
Five). If the answer is negative (No), that is, if T _W ≦ T _WWOTE , the first discrimination value T _WOT1 calculated in step 301 is subtracted and corrected by a first predetermined amount ΔT _WOTE (step 306). move on. When the fuel injection time T _OUT calculated by the above-described formula (1) exceeds the determination values T _WOT1 and T _WOT2 , the determination is made in the WOT region. Therefore, the first determination value T _WOT1 is _set to the first value.
WOT by subtracting and correcting by the predetermined amount ΔT _WOTE
The area is enlarged. In the WOT region, an engine cooling effect is obtained by enriching the air-fuel mixture, so that an excessive increase in the engine temperature can be prevented by expanding the WOT region.

If the answers of steps 302 and 305 are both affirmative (Yes),
When Ne> N _WOT0 and T _W <of T _WWOTE from [Delta] T _WOTPA table according to the atmospheric pressure P _A, and calculates an atmospheric pressure correction value ΔT _WOTPA. For example, as shown in FIG. 7, this ΔT _WOTPA table has ΔT _WOTPA = ΔT _WOTPA1 in the range of P _A <P _ATWOT1 (predetermined pressure corresponding to high altitude), and P _A > P _ATWOT0 (predetermined pressure corresponding to low altitude). the range) is set to the ΔT _WOTPA = ΔT _WOTPA0, in the range of _{P ATWOT1 <P a <P ATWOT0} , atmospheric pressure
[Delta] T _WOTPA with increasing P _A is set so as to decrease.

Next, the first determination value T _WOT1 calculated in step 301
_Is subtracted with the atmospheric pressure correction amount ΔT _WOTPA (step
309). As a result, the WOT region expands as the atmospheric pressure decreases.

In step 309, the engine speed Ne is determined as the determined engine speed N.
_It is determined whether or not the answer is higher than _HSFE (for example, 2,500 rpm). If the answer is negative (No), that is, Ne ≦ N When _HSFE is _satisfied , the process proceeds to step 304, while the answer is affirmative (Yes), ie, Ne> N.
_{In the case} of _HSFE, the engine _coolant temperature T _W is _equal to the first predetermined _coolant temperature T.
_It is determined whether the temperature is lower than a second predetermined water temperature T _WHSFE (for example, 100 ° C.) lower than _WWOTE (step 301). If this answer is negative (No), that is, if T _W ≦ T _WHTFE , the first determination value T
_WOT1 is further subtracted and corrected by the second predetermined amount ΔT _WOTHS (step 311), and the _routine proceeds to step 304. This subtraction correction is also intended to prevent an excessive rise in the engine temperature, as in the case of step 306.

If the answers in steps 309 and 310 are both affirmative (Yes),
When Ne> N _HSFE and T _W <T _WHSFE , the engine speed N
A second discrimination value T _WOT2 is retrieved from the T _WOT2 table according to e. The T _WOT2 table is set, for example, as shown by a broken line in FIG. 6 for a range in which the engine speed Ne is higher than the determination engine speed N _HSFE . Where the second discrimination value
T _WOT2 when the engine speed Ne is in the range of _{N HSFE <Ne ≦ N WOT3,} T WOT2 = T WOT23, Ne = the N _WOT4 T _WOT2 = T
_{When WOT24} , Ne ≧ N _WOT5 , T _WOT2 = T _WOT25 is set, and N _WOT3 <Ne <N _WOT4 or N
_{When WOT4} <Ne <N _WOT5 , it is calculated by interpolation. As is apparent from FIG. 6, the table setting value of the second determination value T _WOT2 is smaller than the table setting value of the first determination value T _WOT1 corresponding to the same engine speed.

Next, the second determination value T _WOT2 calculated in step 312 is subtracted and corrected by the atmospheric pressure correction amount ΔT _WOTPA (step 31).
3), proceed to step 314.

According to the T _WOT subroutine described above, the engine coolant temperature T _W
Is lower than the second predetermined water temperature T _WHSFE , the first and second discrimination values when the engine speed Ne is in the range of Ne> N _HSFE
T _WOT1 and T _WOT2 are set to different values (T _WOT1 > T _WOT2 )
In the range of e ≦ N _HSFE , T _WOT1 and T _WOT2 are set to the same value. If the engine water temperature is equal to or higher than the second predetermined water temperature T _WHSFE , T _WOT2 = T _WOT1 is always set regardless of the engine speed Ne. Further, the third discrimination value T _WOT3 is set to a value smaller by a predetermined value ΔT _WOT3 than the second discrimination value T _WOT2 , as shown by a dashed line in FIG.

Returning to FIG. 2, in step 203, the F _HSFE shown in FIG.
Execute a subroutine. This F _HSFE subroutine
A first flag F used to switch the degree of fuel increase in the WOT region in steps 217 and 220 described below.
_{This is} for setting the _HSFE .

In step 401 of FIG. 4, it is determined whether or not the fuel injection time T _OUT calculated by the above equation (1) is greater than the second determination value T _WOT3 , and the answer is affirmative (Yes), that is, T
_{When OUT} > T _WOT3 holds, it is determined whether or not the count value of the t _WOT3 timer is smaller than a reference time T _BASE (for example, 30 seconds) (step 402). If the answer in step 402 is negative (Yes), that is, if t _WOT3 <T _BASE , the t _WOT3 timer is counted up (step 403), and if the answer in step 402 is negative (No), ie, t _WOT3 ≧ T _BASE Proceed immediately to step 404. T _OUT > T by steps 401 to 403
_{When WOT3} is established, t until the reference time T _BASE is reached
_WOT3 counts up the timer.

In step 404, it is determined whether or not the second flag F _PT is equal to the value 0. If the answer is negative (No), that is, if F _PT = 1, the process immediately proceeds to step 409, while the answer is affirmative (Yes). ), That is, when F _PT = 0, the routine proceeds to step 405.
Here, the second flag F _PT is a flag that is set to a value of 0 when the answer of step 401 is negative (No), that is, when T _OUT ≦ T _WOT3 is satisfied, and the answers of steps 401 and 404 are both affirmative ( If Yes), it means that it is immediately after the transition from the state where T _OUT ≦ T _WOT3 holds to the state where T _OUT > T _WOT3 holds.

In step 405, the integration time T _{WOTX is calculated} by the following equation (3).
Is calculated.

t _WOTX = t _WOTX − (t _WOT3RAM −t _PT ) = t _WOTX + (t _PT −t _WOT3RAM ) (3) This accumulated time t _WOTX is the time when T _OUT ≦ T _WOT3 was last established.
It is obtained by integrating the time _obtained by subtracting the time t _{WOT3RAM at} which the last time T _WOT3 was established from t _PT .

Then, integration time t _WOTX calculated in step 405 it is determined whether or not larger than the reference period T _BASE (Step 40
6), the answer is negative (No), i.e. t _WOTX ≦ T proceeds immediately step 408 when the _BASE, the answer is affirmative (Yes), i.e. t _WOTX> T _BASE reference time integration time t _WOTX when the T _BASE
After setting (step 407), the process proceeds to step 408. Steps 406 and 407 _determine the maximum value of the accumulated time t _WOTX as the reference time
T _BASE . Next, the second flag F
_PT is set to a value of 1 (step 408), and the count value of the t _PT timer is set to a value of 0 (step 409), and it is determined whether or not the value of the t _WOT3 timer is equal to the accumulated time t _WOTX (step 410). . The answer is affirmative (Yes), that is, t _WOT3 ≧ t _WOTX
In the case of, the first flag F _HSFE is set to a value of 1 (step 411), while the answer is negative (No), that is, t _WOT3 <t
_{In the case} of _WOTX , the first flag F _HSFE is set to a value of 0 (step 418), and this program ends.

On the other hand, if the answer in step 401 is negative (No), that is, T _OUT
When ≦ T _WOT3 is satisfied, it is determined whether or not the count value of the t _PT timer is smaller than the reference time T _BASE (step 412). If the answer to step 412 is negative (Yes), that is, t _PT <
At the time of T _BASE , after counting up the t _PT timer (step 413), the answer at step 412 is negative (No), that is, t _PT
When ≧ T _BASE, the process proceeds to step 414. Step 401,41
According to 2,413, when T _OUT ≦ T _WOT3 holds, the t _PT timer is counted up until it reaches the reference time T _BASE .

In step 414, it is determined whether or not the second flag F _PT is equal to a value 0. If the answer is affirmative (Yes), that is, if F _PT = 0, the process immediately proceeds to step 417, while the answer is negative (N
o), that is, when F _PT = 1 and T _OUT > T _WOT2 is satisfied last time, the count value of the t _WOT3 timer is stored in the RAM of the storage means 5c as t _WOT3RAM (step 415),
Set the second flag F _PT to the value 0 (step 416),
Proceed to step 417. In step 417, the count value of the t _WOT3 timer is set to a value of 0, and the first flag F _HSFE is set to a value of 0.
Is set (step 418), and the program ends.

FIG. 8 is a diagram for explaining the operation of the program shown in FIG. 4. The solid line in FIG. 8 (a) indicates that the fuel injection time T _OUT is _{close to} the third discrimination value T _{WOT3 as} time elapses. It shows an operating state that goes up and down. Here, the accumulated time t
_{WOTX changes} the fuel injection time T _OUT from T _OUT ≦ T _WOT3 to T _OUT
> T _WOT3 immediately after the transition to the state, that is, at time t ₁ ,
It is calculated at t ₃ , t ₆ , t ₈ , and t ₁₀ . Accumulation at these times time t _WOTX1 ~t _WOTX5 is as shown in FIG. (C). T ₁ through T ₉ in figure (c) is a time shown in FIG. 6 (a), for example, T ₁ in the time from time t ₁ to t _2, in this example
15 seconds.

At time t ₁ , the time T _OUT ≦ T _WOT3 before t ₁ is equal to or longer than the reference time T _BASE (for example, 30 seconds), so that the integration time t _WOTX1 = T _{BASE at} time t ₁ .

At time t _3, the previous value t _WOTX1, the last time T _OUT> T
_The time T _{1 when WOT3} was established (= t _WOT3RAM ) and the previous time T _OUT ≦ T
_WOT3 is by applying a time established T ₂ (= t _PT) to (3), it calculates a cumulative time t _WOTX2. At this time, t _WOTX2 =
Since it is 25 seconds, the time after 25 seconds (= T ₃ ) has passed since time t ₃
The flag F _HSFE at t ₄ is changed from the value 0 to 1 (see Fig. 4 step 410,411,418). Then time t ₅
When T _OUT <T _WOT3 , the first flag F _HSFE is changed from the value 1 to 0.

At time t ₆ , the time when T _OUT > T _WOT3 was last established is T ₃ + T ₄ = 45 seconds. However, _since the maximum count value of the t _WOT3 timer is the reference time T _BASE , the integration time at time t ₆ Is the time when T _OUT > T _WOT3 is actually established (T ₃ +
It is calculated using the reference time T _{BASE instead} of T ₄ ).

At times t ₈ and T ₁₀ , the accumulated time t
_WOTX4 and _tWOTX5 are calculated. Integration time t at time t ₁₀
Since _WOTX5 is a 15 sec, at time t ₁₁ from the time t ₁₀ 15 seconds (= T ₁₀₎ after the first flag F _HSFE is changed from a value 0 to 1.

When the time when T _OUT > T _WOT3 is shorter than the integration time t _WOtX (T ₁ , T ₆ , T _{8 in} FIG. 8A), the first flag F _HSFE is maintained at 0. Is done.

Thus, according to the program of FIG. 4, T _OUT ≦ T
When _WOT3 is established and T _OUT> T time _WOT3 from the transition point to the state established until that time has been accumulated time t _WOtX course calculation, while the first flag F _HSFE is set to 0 while the T _OUT> T _WOT3 is established after lapse of t _WOtX it is set to the value 1.

Returning to FIG. 2, after executing the F _HSFE subroutine,
When the engine speed Ne is equal to the first predetermined speed N _WOT0 (the T
_It is determined whether it is higher than the same as N _{WOT0 in the WOT1} table (step 204), and the answer is affirmative (Yes), that is, Ne>
When the N _WOT0 the engine water temperature T _W is determined whether or not lower than the first predetermined temperature T _WWOTE (step 205).
If the answer to this question is affirmative (Yes), ie if T _W <T _WWOTE determines whether the engine speed Ne is higher than the determination number of revolutions N _HSFE (step 206). If the answer in step 20 is negative (N
o), that is, when Ne ≦ N _HSFE , the throttle valve opening θ _TH
Is smaller than a predetermined opening θ _WOT1 (for example, 50 °) (step 207). This answer is affirmative (Yes), that is, θ
_{When TH} <θ _WOT1 , it is determined whether the fuel injection time T _OUT is greater than the first determination value T _WOT1 (step 20).
8). The answer to step 208 is negative (No), that is, T _OUT ≦ T _WOT1
At this time (region _{IIb in} FIG. 10), a predetermined time t _WOT1 (for example, 10 seconds) is set in a t _WOT1 timer described later, and these are started (step 209). Next, the high load increase coefficient K _WOT is set to a value of 1.0 (uncorrected value) (step 211).
At the same time, the third flag F _WOT is set to a value 0 to indicate that K _WOT = 1.0 (step 212), and the program ends. Thus, in the region IIb in FIG. 10, the high load increase coefficient K _WOT is set to the value 1.0, and the high load increase correction is not performed.

If the answer in step 208 is affirmative (Yes), that is, T _OUT > T
_{In the case} of _WOT1 (region Ib in FIG. 10), the aforementioned step 209
It is determined whether or not the count value of the t _WOT1 timer started in step is equal to the value 0 (step 210). The answer is undefined (N
o), that is, if t _WOT1 > 0 and the predetermined time t _WOT1 has not elapsed after the transition from the area _IIb to the area Ib in FIG.

If the answer to step 207 is negative (No), that is, θ _TH ≧ θ
_{When WOT1} is established and the throttle valve is almost fully opened, or the answer in step 210 is affirmative (Yes), that is, t _WOT1 = 0, and a predetermined time has elapsed after shifting from the area _IIb to the area Ib in FIG. In some cases, the process proceeds to step 216 described below.

If the answer in step 206 is affirmative (Yes), that is, Ne> N _HSFE
, The engine coolant temperature T _W is equal to the second predetermined coolant temperature T.
_It is determined whether it is lower than _WHSFE (step 214). If the answer is affirmative (Yes), that is, if T _W <T _WHSFE , it is determined whether the fuel injection time T _OUT is greater than the second determination value T _WOT2 (step 215). If the answer to step 215 is negative (No), that is, if T _OUT ≦ T _WOT2 (region II _C1 or II _{C2 in} FIG. 10), the process proceeds to step 211, where the high load increase coefficient K _WOT is set to a value of 1.0. On the other hand, if the answer to step 215 is affirmative (Yes), that is, if T _OUT > T _WOT2 , it is further determined whether the fuel injection time T _OUT is greater than the first determination value T _WOT1 (step 216).

When the answer in step 215 is affirmative (Yes) and the answer in step 216 is negative (No), that is, when T _WOT2 <T _OUT ≦ T _WOT1 (the tenth
In the region I _C2 ), the first _flux F _HSFE has a value of 1
Step (217) to determine whether or not is equal to. If the answer to step 217 is negative (No), that is, if F _HSFE = 0, the _routine proceeds to step 211, where the high load increase coefficient K _WOT is set to a value of 1.0, while if the answer to step 217 is affirmative (Yes), It is determined whether or not the value of the engine water temperature increase coefficient K _TW is larger than the value of the high load increase coefficient K _WOT calculated in step 201 (step 218). This answer is affirmative (Yes), that is, K _TW > K
_At the time of _WOT , the count value of the t _WOT1 timer is set to a value of 0 (step 219), and the _routine proceeds to step 211. Thus, low engine temperature, when K _TW value is greater than the K _WOT value, increase of the fuel by the high-load increase coefficient K _WOT as K _WOT = 1.0 are not performed.

If the answer to step 218 is negative (No), that is, if K _TW ≦ K _WOT , the X _WOT table is searched according to the engine coolant temperature T _W to calculate the _enrichment coefficient X _WOT (step 225). X _WOT multiplies and corrects the K _WOT value calculated in step 201 (or step 221 described later) (step 2
26). X _WOT table, for example, the ninth predetermined as shown in FIG engine coolant temperature T _WWOT0 ~T _WWOT3 relative (e.g. 90 ° C. to 110 ° C.), the enrichment factor X as the engine coolant temperature T _W is increased
_Enrichment coefficient values X _{WOT0 to} X _WOT3 (for example, _{1.0 to} 1.25) are set so that _WOT increases. Engine water temperature T _W is T
_W enrichment factor X _WOT when in range of <T _WWOT0 or T _W> T _WWOT3 is set to X _WOT0 or _{X WOT3, T WWOT0 <T W} <T
It is calculated by interpolation calculation for a range of _WWOT3 T _WWOT1 or T _WWOT2 other T _W.

When the engine temperature is high according to steps 225 and 226, K
_{The WOT} value is further increased and corrected by the _enrichment coefficient X _WOT to enhance the engine cooling effect by fuel and protect the radiator.

Next, at step 227, it is determined whether or not the value of the high load increase coefficient K _WOT corrected at step 226 is larger than an upper limit value K _WOTX (for example, 1.25), and the answer is negative (No), that is, K
_{When WOT} ≦ K _WOTX, the process immediately proceeds to step 229, and when the answer is affirmative (Yes), that is, when K _WOT > K _WOTX , the K _WOT value is set to the upper limit value K _WOTX (step 228).
Proceed to. In step 229, the engine water temperature increase coefficient K _TW is set to a value.
1.0 (no correction value) and then the third flag F
Set _WOT to a value of 1 (step 230), and
_Set the count value of the _WOT1 timer to 0 (step 23
1) End this program.

On the other hand, if the answer in step 216 is affirmative (Yes), that is, T _OUT
If> T _WOT1 (region I _{C1 in} FIG. 10), it is determined whether the first flag F _HSFE is equal to the value 1 (step 220). The answer to step 220 is affirmative (Yes), ie, F _HSFE =
If it is 1, the process proceeds to step 218, while step 220
Is negative (No), that is, when F _HSFE = 0, the high load increase coefficient K _WOT calculated in step 201 is changed to the leaning coefficient X
Multiplication correction by _WOTL (for example, 0.93) (Step 22
1), proceed to step 218.

If any one of the steps 204, 205, ₂₁₄ is negative (No), that is, Ne ≦ N _WOT0 or T _W ≧ T _WWOTE or T _W ≧ T
_{When WHSFE} is established, the count value of the t _WOT3 timer (see FIG. 4) is set to the reference time T _BASE (step 222), and whether the fuel injection time T _OUT is greater than the first determination value T _WOT1 is determined. Is determined (step 223). Step 223
Is negative (No), that is, when T _OUT ≦ T _WOT1 (region _IIa in FIG. 10), the process proceeds to step 219, while step 2
When the answer to 23 is affirmative (Yes), that is, when T _OUT > T _WOT1 (region Ia in FIG. 10), it is determined whether or not the engine _coolant temperature T _W is higher than the predetermined _coolant temperature T _{WWOT0 in the} X _WOT table. (Step
224). The answer to step 224 is negative (No), that is, T _W ≦ T _WWOT0
In the case of, while proceeding to step 218, step 224
Answer is affirmative (Yes), ie if T _W> T _WWOT0, the process proceeds to step 225.

According to the program of FIG. 2 described above, the high load increase coefficient K _WOT is determined when the engine _coolant temperature T _W is extremely high (the answer to the above step 205 or 214 is negative (No), ie, T _W ≧ T _WOTE or T _W
Except when ≧ T _WHSFE holds), it is set as follows.

(1) region II a in Fig. 10, II b, in II _C1, II _C2 (region other than the WOT region) is a K _WOT = 1.0 (no correction value).

(2) In the region Ia of FIG. 10, K _WOT = K _WOT0 × X _WOT
It is said. Here, K _WOT0 is the K calculated in step 201.
_WOT value.

(3) In the region I b of FIG. 10, 11 as shown in FIG, i) region I b the predetermined time from the time t ₂₁ the transition to t
_WOT1 until time t ₂₂ has elapsed is the K _WOT = 1.0, ii) time
t ₂₂ after the first flag F _HSFE changes from a value 0 to 1 (T _OUT = T _WOT3 and since the time t ₂₀ the integration time from t
_WOTX elapsed) until the time t ₂₃ is, K _WOT = K _WOT1 = K
Is a _{WOT0 × X WOTL × X WOT,} iii) the time t ₂₃ Thereafter, K _WOT
= K _WOT2 = K _WOT0 × X _WOT

(4) In the area _IC2 in FIG. 10, as shown by the solid line in FIG. 12 (a) and FIGS. 12 (b), (c) (1), i) the first flag F _HSFE is 0 To 1 (T _OUT = T
Cumulative time from the time t _30, which became the _WOT3 t _WOTX elapsed) time
K _WOT = 1.0 until t ₃₃ , ii) K _WOT after time t ₃₃
= K _WOT2 .

(5) In the region I _C1 of FIG. 10, the broken line and the drawing of Figure 12 (a) (b), (c) (2) as shown in the time t ₃₂ the process moves to i) regions I _c1 from to time t ₃₃ the first flag F _HSFE changes from a value 0 to 1 is the K _WOT = K _WOT1, ii) the time t ₃₃ after that, are K _WOT = K _WOT2.

Note that when the _enrichment correction according to the engine temperature is not performed (when X _WOT = 1.0), the above K _WOT1 and K _WOT2 are set to values where the air-fuel ratio A / F = 13.5 and 12.5, respectively. You.

In the case of the K _WOT = 1.0, i.e., the region of engine operating conditions Figure 10 _{II a, II b, II c1} , II when there _c2, and the first flux F _HSFE = 0 In the region I _C2 In the case of, the air-fuel ratio feedback control is performed by the air-fuel ratio feedback correction coefficient _KO2 set in accordance with the oxygen concentration in the exhaust gas, and good exhaust gas characteristics are maintained. In other cases, that is, when the engine operating state is in the region I _C1 of FIG. 10 and in the region I _C2 and the first flag F _HSFE = 1, the air-fuel ratio feedback correction coefficient K _O2 is It is set to 1.0 (no correction value), and the feedback control according to the oxygen concentration in the exhaust gas is not performed.

By setting the high load increase coefficient K _WOT as described above, even when the high load operation that continues for a relatively short time is continuously repeated, the air-fuel ratio enrichment timing, that is, the first the integration time t _WOTX to determine when the flag F _HSFE as 0 → 1, said t _WOTX calculated previously in the fuel injection time T _OUT> time T _WOT3 is satisfied and T _OUT ≦ T _WOT3
(See FIG. 8), that is, if the time when T _OUT > T _WOT3 is relatively long, the accumulated time t _WOTX becomes short, so that the purpose of fuel cooling is reduced. The enrichment of the air-fuel ratio is appropriately performed. And third
Since the discrimination value T _WOT3 is set to a value smaller than the second discrimination value T _WOT2 , the motion state in which the fuel injection time T _{OUT rises} and _falls near the third discrimination value T _WOT3 as shown in FIG. In other words, after the operation on the high load side in the air-fuel ratio feedback control area (for example, the operation in the area II _C1 in FIG. 10) is continued, the state shifts to the WOT area (T _OUT > T _WOT2 ). the case, enrichment is started in a relatively short period (Figure 8 time t _11), the exhaust gas generated during operation at high load side of the air-fuel ratio feedback control region (partial load operation) The air-fuel ratio is enriched in consideration of the effect of the temperature rise. As a result, an excessive rise in the temperature of the three-way catalyst 14 can be prevented with higher accuracy, and the durability of the catalyst can be improved.

(Effects of the Invention) As described in detail above, according to the present invention, that is, according to the air-fuel ratio control method of the first aspect, the second predetermined value corresponding to the predetermined high load region in the air-fuel ratio feedback control region. When the engine load exceeds a first predetermined value corresponding to a predetermined high load state at a point in time when the state of exceeding the predetermined period continues for a predetermined period, feedback control of the air-fuel ratio is stopped to enrich the air-fuel ratio, In other words, the high-load operation state measurement timer counts taking into account the increase in exhaust gas temperature that occurs during air-fuel ratio feedback control (during operation at A / F = 14.7) in the partial load range. Can be prevented from increasing excessively with higher accuracy, and the durability of the catalyst can be improved.

[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 of a program for setting a high load increase coefficient (K _WOT ), and FIG. 3 is a program of FIG. 4 is a flowchart of a program for setting a discrimination value (T _WOT ) to be used, FIG. 4 is a flowchart of a program for setting a flag (F _HSFE ) used in the program of FIG. 2, and FIG. 5 is a first discrimination value. FIG. 6 shows a table for calculating (T _WOT1 ), FIG. 6 shows a table for calculating a second determination value (T _WOT2 ), and FIG. 7 shows an atmospheric pressure correction amount (ΔT _WOTPA ). FIG. 8 shows a table for calculating the operation of the program of FIG. 4, FIG. 9 shows a table for calculating the _enrichment coefficient (X _WOT ), FIG. The figure shows the engine speed (N
e) shows a region set according to the fuel injection time (T _OUT ). FIG. 11 shows a setting example of a high load increase coefficient (K _WOT ) in a region Ib of FIG. FIG. 12 is a diagram showing a setting example of the high load increase coefficient (K _WOT ) in the regions I _C1 and I _C2 of FIG. 1 ...... internal combustion engine, 5 ...... electronic control unit (ECU), 13 ...... exhaust pipe, 15 ...... O ₂ sensor (exhaust concentration sensor).

Claims (1)

(57) [Claims] An exhaust component concentration is detected based on an output of an exhaust concentration sensor provided in an exhaust system of an internal combustion engine, and an air-fuel ratio of an air-fuel mixture supplied to the engine becomes a predetermined value according to the detected value. In the air-fuel ratio control method for an internal combustion engine that performs feedback control as described above, the load of the engine exceeds a first predetermined value corresponding to a predetermined high load state, and the first predetermined value within an operation range in which the feedback control is performed. The feedback control is stopped and the air-fuel ratio of the air-fuel mixture supplied to the engine is enriched when a state exceeding a second predetermined value corresponding to a lower predetermined high load region continues for a predetermined period. Control method for an internal combustion engine.