JP2712086B2 - 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 improve such a problem, when the load of the engine becomes high, a method of leaning the air-fuel mixture within a predetermined time period after a lapse of a predetermined time period (Japanese Patent Laid-Open No. 59-128,941) or a high-pressure method is used. When the load condition continues for more than a predetermined time,
A method for enriching an air-fuel mixture (JP-A-57-24435)
Is conventionally known.

(Problems to be Solved by the Invention) According to the above-mentioned conventional control method, for example, FIG.
(1) When the high-load operation is performed intermittently for a time shorter than the predetermined time, as shown in (1) (when the operation parameter for determining the high-load state is equal to or higher than the high-load determination critical value is indicated as a high-load state). In this case, since the air-fuel mixture is not enriched to the air-fuel ratio at which the effect of the fuel cooling appears, a situation occurs in which the exhaust gas temperature continues to rise (FIG. 13 (a)).
(2)). As a result, the exhaust temperature may exceed the continuous exhaust allowable temperature, and may further rise without exceeding the continuous exhaust allowable temperature within the allowable heat-resistant time of the engine to exceed the temperature limit, particularly provided in the exhaust system. There has been a problem that the catalyst temperature of the exhaust gas purification device may be excessively increased.

The present invention has been made in view of the above points, and appropriately controls the air-fuel ratio of an air-fuel mixture supplied to an engine in a high-load operation state of the engine to reduce CO, HC component emissions and reduce fuel consumption. It is an object of the present invention to provide a method for controlling an air-fuel ratio of an internal combustion engine, which is capable of preventing an excessive increase in the exhaust gas temperature and the catalyst temperature of the exhaust gas purification device while improving the exhaust gas temperature.

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine is feedback-controlled based on an output of an exhaust gas concentration sensor provided in an exhaust system of the engine. In addition, when the engine is operated in a predetermined high load state, the feedback control is stopped after the high load state continues for a predetermined time, and the air-fuel ratio control method of the internal combustion engine for enriching the air-fuel ratio of the air-fuel mixture is provided. The predetermined time is set according to a time during which the feedback control immediately before the engine enters a high load state and a time during which the high load state immediately before the feedback control is continued. .

Further, in the present invention, the predetermined high load state includes a first high load state and a second high load state which is higher than the first high load state.
When the engine is in the second high load state, the air-fuel ratio of the air-fuel mixture is immediately enriched to a first predetermined air-fuel ratio, and the engine is switched to the first predetermined air-fuel ratio. The air-fuel ratio of the air-fuel mixture is further made richer than the first predetermined air-fuel ratio after the lapse of the predetermined time from the high load state.

Embodiment 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 the angular position, and each of these signal pulses is supplied to the ECU 5.

The three-way catalyst 14 is arranged in an exhaust pipe 13 of the engine 1 is performed HC in the exhaust gas, CO, purification components such as NO _x.
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. 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 exhaust gas. Based on (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) where Ti is a reference value of the injection time T _OUT of the fuel injection valve 6, the engine speed Ne and the absolute value in the intake pipe. It is read from the Ti map set according to the pressure _PBA . K _WOT is a high load coefficient for enriching the air-fuel mixture when the throttle valve 3 'is almost fully opened, and is set by the 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, optimization of the properties of engine acceleration and the like 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, high load by applying interpolation coefficient C _WOT stored together with the reference value Ti of the fuel injection time in the Ti map according to the engine rotational speed Ne and the intake pipe pressure absolute pressure P _BA in the following equation (2) The increase coefficient K _WOT is calculated.

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 _WOT110 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 At the same time as 303), the second discrimination value T _WOT2 is _set to the same value as the first discrimination value T _WOT1 (step 304), 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). When the answer is negative (No), that is, when 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 equation (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 corrected by 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 by the determination circuit N _HSFE
(For example, 2,500 rpm), and if the answer is negative (No), that is, if Ne ≦ N _HSFE , step 304 is performed.
On the other hand, when the answer is affirmative (Yes), that is, when Ne> N _HSFE , whether or not the engine _coolant temperature T _W is lower than the second predetermined _coolant temperature T _WHSFE (for example, 100 ° C.) lower than the first predetermined _coolant temperature T _WWOTE is determined. Is determined (step 310). If this answer is negative (N
o), that is, when T _W ≧ T _WHSFE , the first discrimination value T _WOT1 is further subtracted and corrected by the second predetermined value 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 of the steps 309 and 310 are both affirmative (Yes), that is, Ne
> N _HSFE and T _W <T _WHSFE , the engine speed Ne
A second discrimination value T _WOT2 is retrieved from the T _WOT2 table in accordance with. 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 . Here, 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 =
When T _WOT24 , Ne ≧ N _WOT5 , N _WOT2 = T _WOT25
N _WOT3 <Ne <N _WOT4 or N
_{When WOT4} <Ne <N _WOT5 , it is calculated by interpolation calculation. 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) End this program.

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 Ne ≦ 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.

Returning to FIG. 2, in step 203, the F _HSFE shown in FIG.
Perform 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 the fuel injection time T _OUT calculated by the above equation (1) is greater than the second determination value T _WOT2 , and the answer is affirmative (Yes), that is, T
_When the engine in which _OUT > T _WOT2 is established is in the WOT region, the count value of the t _WOT2 timer is equal to the reference time T _BASE (for example,
30 seconds) is determined (step 402).
When the answer to step 402 is affirmative (Yes), that is, when t _WOT2 <T _BASE , the t _WOT2 timer is counted up (step 4).
03) After that, the answer in step 402 is negative (No), that is, t _WOT2 ≧ T
_{In the case of BASE,} the process immediately proceeds to step 404. Step 401
In the WOT region where T _OUT > T _WOT2 is satisfied by _{403403, the} t _WOT2 timer is counted up until the reference time T _BASE is reached.

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 0 when the answer to step 401 is negative (No), that is, T _OUT ≦ T _WOT2 is satisfied and the engine is in a region other than the WOT region. When the answers of steps 401 and 404 are both affirmative (Yes), it means that the state is immediately after the transition from the area other than the WOT area to the WOT area.

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

t _WOTX = t _WOTX- (t _WOT2RAM- t _PT ) = t _WOTX + (t _PT- t
( _WOT2RAM) … (3) This accumulated time t _WOTX was in the area other than the WOT area last time (T _OUT ≦ T _WOT2 was satisfied) and was previously in the WOT area from time t _PT (T _OUT > T _WOT2 was satisfied) ) Time t _This is the sum of the time _obtained by subtracting _WOT2RAM .

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) If the answer is negative (No), that is, t _WOTX ≦ T _BASE , the process immediately proceeds to step 408, and if the answer is affirmative (Yes), that is, t _WOTX > T _BASE , the accumulated time t _WOTX is set to the reference time T.
_After setting to _BASE (step 407), the process proceeds to step 408. So that a reference time T _BASE the maximum value of the integrated time t _WOTX in step 406 and 407. Next, the second flag F _PT is set to a value of 1 (step 408),
t _Set the count value of the _PT timer to the value 0 (step 409),
It is determined whether or not the value of the t _WOT2 timer is equal to or greater than the accumulated time t _WOTX (step 410). The answer is affirmative (Yes), ie t
_{When WOT2} ≧ t _WOTX , the first flag F _HSFE is set to a value of 1 (step 411), while the answer is affirmative (No),
That is, when t _WOT2 <t _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 WOT2} is satisfied and the engine is in a region other than the WOT region, the count value of the t _PT timer is equal to the reference time T _BASE.
It is determined whether or not it is smaller (step 412). If the answer to step 412 is affirmative (Yes), that is, if t _PT <T _BASE , then t
_After counting up the _PT timer (step 413), if the answer to step 412 is negative (No), that is, if t _PT ≧ T _BASE , the process proceeds to step 414. According to steps 401, 412, 413, WO
In regions other than the T region, the t _PT timer is set to the reference time T
_It counts up until it reaches _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 the engine was in the WOT area last time, the count value of the t _WOT2 timer is stored in the RAM of the storage means 5c as t _WOT2RAM (step 415), and the second flag F Set _PT to value 0 (step 41
6) Go to step 417. In step 417, the count value of the t _WOT2 timer is set to a value of 0, the first flag F _HSFE is set to a value of 0 (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 second discrimination value T _{WOT2 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 _WOT2 to T _OUT
It is calculated immediately after the transition to the state of> T _WOT2 (transition to the WOT area), that is, at times t ₁ , t ₃ , t ₆ , t ₈ , and t ₁₀ in FIG. Accumulation at these times time t _WOTX1 ~t _WOTX5 is as shown in FIG. (C). The T ₁ through T ₉ of FIG. (C) is a time shown in FIG. 6 (a), for example, T ₁ is a time until t ₁ through T _2, in this example is set to 15 seconds.

At time t _1, since t ₁ is previously T _OUT ≦ T _WOT2 a a time is the reference time T _BASE (e.g. 30 seconds), the integrated time t _WOTX1 = T _BASE at time t _1.

At time t _3, the previous value t _WOTX1, previous WOT region to a time T ₁ and (= t _WOT2RAM), previous WOT region time was in the region other than T ₂ (t _PT) and the formula (3 ) To calculate the integrated time _tWOTX2 . At this time, since t _WOTX2 = 25 seconds, the flag F _HSFE of 1 is changed from 0 to 1 at time t ₄ after 25 seconds (= T ₃ ) from time t ₃ (see steps 410, 411, and 418 in FIG. 4). ). When the T _OUT <T _WOT2 in the subsequent time t _5, the first flag F _HSFE is changed from the value 1 to 0.

At time t ₆ , the time previously in the WOT area is T ₃ + T
₄ = 45 seconds, but since the maximum count value of the t _WOT2 timer is the reference time T _BASE , the integrated time at time t ₆ is replaced with the time (T ₃ + T ₄ ) actually in the WOT area. It is calculated using the reference time T _BASE .

At times T ₈ and t ₁₀ , the accumulated time t
_WOtX4 and _tWOtX5 are calculated. Integration time at time t ₁₀
Since t _WOtX5 is 15 seconds, the value of the first flag F _HSFE is changed from 0 to 1 at time t ₁₁ after 15 seconds (= T ₁₀ ) from time t ₁₀ .

Note that if the time in the WOT region is shorter than the integrated time _{t WOtX (T 1, T 6} , T 8 of FIG. 8 (a)), the first flag F
_HSFE is maintained at the value 0.

As described above, according to the program shown in FIG. 4, when the engine is not in the WOT region and during the period from the transition to the WOT region to the lapse of the integration time _tWOtX calculated at that time, the first flag F _HSFE Is set to a value of 0, while it is set to a value of 1 while the engine is in the WOT region after _{tWOtX has} elapsed.

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 _WOT1
It is determined whether or not it is higher than N _{WOT0 in the} table) (step 204), and the answer is affirmative (Yes), that is, Ne> N.
_{When WOT0} , the engine _coolant temperature T _W is _equal to the first predetermined _coolant temperature.
It is determined whether it is lower than _TWWOTE (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 to step 206 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
In this case (region IIb in FIG. 10), a predetermined time t _WOT1 (for example, 10 seconds) is set in a t _WOT1 timer described later and started (step 209). Next, high load increase coefficient K
_WOT is set to a value of 1.0 (uncorrected value) (step 211), and a third flag F _WOT is set to a value of 0 (step 212) to indicate that K _WOT = 1.0, and t _EXM described later.
A predetermined time t _EXM (for example, 5 minutes) is set in the timer and started (step 213), 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 negative (N
o), that is, when t _WOT1 > 0 and the predetermined time t _WOT1 has not elapsed after the transition from the region IIb to the region 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 substantially fully opened, or when the answer to step 210 is affirmative (Yes), that is, when t _WOT1 = 0 and a predetermined time has elapsed after shifting from the region IIb to the region Ib in FIG. The process proceeds to step 216 to be described later.

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 IIc in FIG. 10), the _routine proceeds to step 211, where the high load increase coefficient K _WOT is set to a value.
While setting to 1.0, the answer in step 215 is affirmative (Yes),
That is, when T _OUT > T _WOT2 , it is further determined whether or not the fuel injection time T _OUT is greater than the first determination value T _WOT1 (step 216).

If the answer to step 215 is affirmative (Yes) and the answer to step 216 is negative (No), that is, if T _WOT2 <T _OUT ≦ T _WOT1 (region I _{C2 in} FIG. 10), the first flag F _It is determined whether _HSFE is equal to the value 1 (step 217). 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). If the answer is affirmative (Yes), that is, if K _TW > K _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 255). 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 a range of <T _WWOT0 or T _W> T _WWOT3 is set to X _WOT0 or _{X WOT3, T WWOT0 <T w} <
For range T _WWOT1 or T _WWOT2 other T _W of T _WWOT3 is calculated by interpolation calculation.

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
The count value of the _WOT1 timer was set to 0 (step 23
1) Thereafter, it is determined whether or not the engine speed Ne is higher than a second predetermined speed N _EXM (step 232). When the answer is negative (No), that is, when Ne ≦ N _EXM , the process proceeds to step 213. On the other hand, when the answer is affirmative (Yes), that is, when Ne> N _EXN , the count of the t _EXM timer started in step 213 is counted. Determine whether the value is equal to the value 0 (step
233). The answer to step 233 is affirmative (Yes), that is, t _EXM = 0.
When the predetermined time t _{EXM has} elapsed since the engine speed Ne became higher than the second predetermined speed N _EXM , the high load increase coefficient K _WOT becomes the rich predetermined value K _WOTH (for example, the air-fuel ratio A /F=11.0) is determined (step 234). When the answer of step 233 or 234 is negative (No), that is, when t _EXM > 0 or K _WOT ≧ K _WOTH , the program is immediately terminated, while the answer of step 234 is affirmative (Yes), that is, when K _WOT <K _WOTH At times, the K _WOT value is set to the _enrichment predetermined value K _WOTH (step 235), and this program ends.

According to steps 232 to 235, the high engine speed (Ne
> N _EXM ) for more than the predetermined time t _EXM , the high load increase coefficient K _WOT is made _richer than the predetermined value K _WOTH to enhance the engine cooling effect of the fuel, and cracks in the exhaust pipe.
It prevents distortion and the like from occurring.

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 2).
20). The answer to step 220 is affirmative (Yes), that is, F _HSFE = 1
If the answer is negative (No), that is, if F _HSFE = 0, the high load increase coefficient K _WOT calculated in step 201 is _replaced with 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 _WOT2 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, if T _OUT ≦ T _WOT1 (region IIa in FIG. 10), the process proceeds to step 219, while step 22
When the answer to 3 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 22
Four). The answer to step 224 is negative (No), ie if T _W ≦ T _WWOT0, while proceeding to the step 218, the answer to step 224 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) Area IIa, IIb, IIc in Fig. 10 (area other than WOT area)
, K _WOT = 1.0 (uncorrected 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 Ib in FIG. 10, as shown in FIG.
i) from the time t ₂₁ which has shifted to the region Ib to time t ₂₂ which has passed the predetermined time t _WOT1 is a K _WOT = 1.0, ii) the time t ₂₂ after the first flag F _HSFE from value 0 to 1 during the changing to the (from time t ₂₁ the integration time t _WOTX elapsed) time t ₂₃ is a _{K WOT = K WOT1 = K WOT0} × X WOTL × X WOT, i
ii) the time t ₂₃ after that, are _{K WOT = K WOT2 = K WOT0} × X WOT.

(4) In the region I _C2 (first high load state) in FIG. 10, the solid line in FIG. 12 (a) and the solid lines in FIG. 12 (b), (c),
As shown in (1), i) the first flag F _HSFE has the value 0
From changes in 1 to (from time t ₃₁ which has shifted to the region I _c2 integrated time t _WOTX elapsed) time t ₃₃ is the K _WOT = 1.0, i
i) a time t ₃₃ after that, it is K _WOT = K _WOT2.

(5) In the region I _{C1 in} FIG. 10 (high load state in FIG. 2), the broken line in FIG. 12 (a) and FIGS.
As shown in (2), i) from the time t ₃₂ which has shifted to the region I _C1, the time the first flag F _HSFE changes from a value 0 to 1 t
K _WOT = K _WOT1 until ₃₃ , and ii) K _WOT after time t ₃₃
= K _WOT2 .

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 respectively the air-fuel ratio A / F = 13.5 (first predetermined air-fuel ratio), It is set to a value of about 12.5.

In the case of the K _WOT = 1.0, i.e. when the engine is operating in a region of FIG. 10 IIa, IIb, the IIc, and the region I _C2
When the first flag F _HSFE = 0, the air-fuel ratio feedback control is performed by the air-fuel ratio feedback correction coefficient K _O2 which is set according to the oxygen concentration in the exhaust gas, and good exhaust gas characteristics are maintained. You. In other cases, that is, when the engine operating state is in the area I _C1 of FIG. 10 and in the area I _C2 , the first flag F _HSFE = 1
, The air-fuel ratio feedback correction coefficient K _O2 is 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, for example, as shown in FIG. 13 (b) (1), a case where the high load operation which continues for a relatively short time is intermittently repeated. _However , the integrated time _tWOTX described above _indicates that the engine operating state was in the WOT region before _{tWOTX was} calculated (T
_OUT > T _wot2 ) is a value corresponding to the ratio of the time and the time in the area where the feedback control is performed (see FIG. 8). That is, if the time in the WOT area is relatively long, the accumulated time t _WOTX Is shortened, so that the air-fuel ratio for the purpose of cooling the fuel is enriched appropriately. As a result, even if the exhaust gas temperature exceeds the continuous exhaust allowable temperature, the exhaust gas temperature becomes equal to or lower than the allowable temperature within the allowable heat resistant time, and the state is continued thereafter (FIGS. 13 (b) and (2)). The catalyst temperature can be prevented from excessively rising, and the durability of the catalyst can be improved.

Further, the longer the time in the feedback control region is, the longer the integration time _tWOTX is (the maximum value is the reference time T _BASE , for example, 30 seconds). The proportion of time for enriching the air-fuel ratio for the purpose of cooling the fuel is reduced, so that the emission of HC and CO components can be reduced and the fuel efficiency can be improved.

According to the result of a statistical investigation of the duration of high-load operation during general user travel, the duration is approximately 80% when the duration is 30 seconds or less.
In many seconds, the enrichment of the air-fuel ratio for the purpose of cooling the fuel is not performed in most high-load operations, and the generation of CO and HC components can be greatly reduced.

(Effect of the Invention) As described in detail above, according to the air-fuel ratio control method of the first aspect of the present invention, the mixing supplied to the internal combustion engine based on the output of the exhaust gas concentration sensor provided in the exhaust system of the engine is performed. When the engine is operated under a predetermined high load state, the feedback control is stopped after the high load state continues for a predetermined time, and the air-fuel ratio of the air-fuel mixture is enriched. In the air-fuel ratio control method for an internal combustion engine, the predetermined time is set according to a time during which the feedback control immediately before the engine enters a high load state and a time when the high load state immediately before the feedback control is continued. Therefore, it is possible to estimate the exhaust gas temperature and the exhaust gas purification device and the catalyst temperature with higher accuracy, prevent the catalyst temperature from excessively rising, and improve the durability of the catalyst. In both cases, CO and HC emissions can be reduced and fuel efficiency can be improved.

Further, according to the air-fuel ratio control method of the second aspect, the predetermined high load state is set to a first high load state and a second high load state that is higher in load than the first high load state. When the engine is in the second high load state, the air-fuel ratio of the mixture is immediately enriched to a first predetermined air-fuel ratio, and the engine is brought into the first high load state. After the elapse of the predetermined time, the air-fuel ratio of the air-fuel mixture is further made richer than the first predetermined air-fuel ratio. As a result, a sufficient engine output is ensured, and after a lapse of a predetermined period, the air-fuel ratio is further enriched, and an excessive rise in the catalyst temperature can be prevented to improve the durability of the catalyst.

[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. The figure shows the area in Figure 10.
FIG. 13 is a diagram showing a setting example of a high load increase coefficient (K _WOT ) in I _C1 and I _C2 , and FIG. 13 is a diagram showing a change in exhaust gas temperature when the high load operation of the engine is intermittently continued. 1: Internal combustion engine, 5: Electronic control unit (EC
U), 13 ... exhaust pipe, 15 ... O ₂ sensor (exhaust concentration sensor).

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-128941 (JP, A) JP-A-57-24435 (JP, A) JP-A-64-77731 (JP, A) JP-A-63-1988 201348 (JP, A) JP-A-62-87635 (JP, A) JP-A-61-232353 (JP, A)

Claims (2)

(57) [Claims] An air-fuel ratio of an air-fuel mixture supplied to the engine is feedback-controlled based on an output of an exhaust gas concentration sensor provided in an exhaust system of the internal combustion engine, and the engine is operated under a predetermined high load state. When the high load state continues for a predetermined time, the feedback control is stopped to enrich the air / fuel ratio of the air-fuel mixture. An air-fuel ratio control method for an internal combustion engine, wherein the air-fuel ratio control method is set according to a time during which the immediately preceding feedback control is continued and a time during which the high load state immediately before the feedback control is continued. 2. The predetermined high-load state is set to a first high-load state and a second high-load state that is higher in load than the first high-load state. Immediately after the high load state, the air-fuel ratio of the air-fuel mixture is enriched to a first predetermined air-fuel ratio, and after the predetermined time elapses after the engine enters the first high load state, 2. The air-fuel ratio control method according to claim 1, wherein the air-fuel ratio of the air-fuel mixture is further made richer than the first predetermined air-fuel ratio.