JP2621066B2 - Air-fuel ratio control method for a vehicle 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 for a vehicle, and more particularly to an air-fuel ratio control method during acceleration or high load.

(Prior Art) Conventionally, as an air-fuel ratio control method for an internal combustion engine, when the fuel supply amount to the engine is smaller than a predetermined reference amount, the air-fuel ratio of the air-fuel mixture supplied to the engine in accordance with the oxygen concentration in the exhaust gas is determined. By performing the feedback control for correction, the supply air-fuel ratio is made to coincide with the stoichiometric mixture ratio to secure good exhaust gas characteristics and fuel consumption characteristics, etc., while the fuel supply amount is larger than the reference amount, An open-loop control for enriching the air-fuel ratio independently of the oxygen concentration in the air to improve the acceleration is disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 62-157252 by the present applicant. I have.

(Problems to be Solved by the Invention) The above-mentioned conventional control method is intended to improve acceleration in a high-speed and high-load region (WOT region) in which the stottle valve is almost fully opened. When the determination condition that is larger than the reference amount is satisfied, it is uniformly determined to be the WOT region and the air-fuel ratio enrichment correction is performed by the open loop control. There was a problem.

In other words, in city driving, deceleration and acceleration driving in the medium speed range of the vehicle (for example, when the vehicle speed is in the range of 25 to 50 km / h), such as when avoiding other vehicles or pedestrians or when starting from a traffic light. Therefore, the frequency of the air-fuel ratio enrichment correction by the open-loop control increases, while the time ratio at which the feedback control is performed in accordance with the oxygen concentration in the exhaust gas decreases. As a result, there has been a problem in that, when traveling in an urban area where better exhaust gas characteristics are required, the amount of CO emission increases and the purification performance of an exhaust gas purification device provided in the exhaust system of the engine decreases.

On the other hand, when traveling on an uphill road, the above-described determination condition is satisfied, that is, the high-load operation in the middle vehicle speed range in which the supplied fuel amount is larger than the reference amount continues for a long time. This would continue for a long time, causing the same problem as in the case of traveling in an urban area as described above.

The present invention has been made in order to solve the above problems, and can reduce the amount of CO emissions in exhaust gas in an operation state in which the acceleration operation frequency is high in a middle vehicle speed range, and can prevent the performance of the exhaust gas purification device from deteriorating. An object of the present invention is to provide an air-fuel ratio control method for a vehicle internal combustion engine.

(Means for Solving the Problems) In order to achieve the above object, the present invention detects an exhaust component concentration based on an output of an exhaust concentration sensor provided in an exhaust system of an internal combustion engine, and responds to the detected value signal. Air-fuel ratio control of an internal combustion engine for a vehicle that performs feedback control so that an air-fuel ratio of an air-fuel mixture supplied to the engine becomes a set value and stops the feedback control when the engine continues a predetermined high load state for a predetermined time. In the method,
The predetermined time is changed according to the vehicle traveling speed.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an overall configuration diagram of a fuel supply control apparatus to which the method of the present invention is applied. Reference numeral 1 denotes, for example, a 4-cylinder 4-cycle internal combustion engine, and the engine 1 has an intake pipe via an intake pipe collecting section 2a. 2 are connected. A throttle body 3 is provided upstream of the gathering portion of the intake pipe 2, and a throttle valve 3 'is provided therein. A throttle valve opening sensor (hereinafter referred to as “θ _TH sensor”) 4 is connected to the throttle valve 3 ′ to convert the valve opening of the throttle valve 3 ′ into an electric signal, and an electronic control unit (hereinafter “ECU”) is provided. 5).

A main fuel injection valve 6 is provided upstream of the throttle body 3 of the intake pipe 2. The main fuel injection valve 6 supplies fuel to all cylinders of the internal combustion engine 1 during an operation other than the idle operation of the internal combustion engine 1.

On the other hand, an auxiliary fuel injection valve 6a is provided on the downstream side of the throttle body 3 of the intake pipe 2, and when the internal combustion engine 1 is idling in a sufficiently warmed state, the engine 1
The fuel is supplied to all cylinders.

Further, on the downstream side from the auxiliary fuel injection valve 6a of the intake pipe 2, an intake pipe absolute pressure sensor (hereinafter referred to as "P _BA sensor") through a conduit 7 8 is provided, the P _BA sensor 8
The absolute pressure signal converted into an electric signal by the above is supplied to the ECU 5.

Further, an engine speed sensor (hereinafter, referred to as a “Ne sensor”) 11 is mounted around a camshaft (not shown) of the engine 1 or around a crankshaft. The Ne sensor 11 is located at a predetermined crank angle position every 180 ° rotation of the crankshaft of the engine 1, that is, at a crank angle position that is a predetermined crank angle before the top dead center (TDC) at the start of the intake stroke of each cylinder. It outputs a signal (hereinafter, referred to as “TDC signal”), and this TDC signal is sent to the ECU 5.

A three-way catalyst 13 is disposed in an exhaust pipe 12 of the engine 1 and purifies components such as HC, CO, and NOx in exhaust gas. O ₂ sensor 14 as exhaust gas concentration sensor is a three-way catalyst of exhaust pipe 12
The sensor is mounted upstream of 13 and detects the oxygen concentration in the exhaust gas, outputs a signal corresponding to the detected value, and supplies the signal to the ECU 5. Further, the ECU5 atmospheric pressure for detecting the atmospheric pressure (P _A) sensor 15, and vehicle speed (V) sensor 16 for detecting a vehicle speed is connected, these detection signals are 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 drive signals to the main fuel injection valve 6, and the auxiliary fuel injection valve 6a, respectively. .

The CPU 5b responds to the various engine parameter signals described above,
Based on a control program (FIG. 2) to be described later, various engine operating states such as a feedback control area and an open control area are determined, and the main fuel injection is synchronized with the TDC signal in accordance with the determined engine operating state. The fuel injection time T _OUTM for opening the valve 6 is calculated based on the following equation (1).

T _OUTM = Ti _M × K _O2 × K _WOT × K _LS × K ₁ + K ₂ (1) Here, Ti _M indicates a basic fuel injection time of the main fuel injection valve 6, for example, an intake pipe absolute pressure P _BA and Engine speed Ne
Is determined according to K _O2 is set according to the output of the O ₂ sensor 14 when the engine 1 is in the feedback control range, that is, according to the actual oxygen concentration in the exhaust gas. When the engine 1 is in the feedback operation range,
A O ₂ feedback correction coefficient set average value K _REF) of the applied K _O2 value generation of each TDC signal.

K _WOT is the _enrichment coefficient set to a predetermined value larger than 1.0 when the engine 1 is in the throttle valve fully open range (WOT range), that is, in the high load operation state, and _KLS is the engine 1
Is in the lean region, that is, in the low-load operation state, the value 1.0
Is a leaning coefficient set to a predetermined value less than or equal to.

K ₁ and K ₂ are other correction coefficients and correction variables calculated according to various engine parameter signals, respectively, and are required values for optimizing fuel consumption characteristics, engine acceleration characteristics, etc. according to the engine operating state. Is set to

The CPU 5b supplies a drive signal for opening the main fuel injection valve 6 to the main fuel injection valve 6 via the output circuit 5d based on the fuel injection time T _OUTM obtained as described above.

The CPU 5b controls the fuel supply from the auxiliary fuel injection valve 6a during the idling operation of the engine 1, but the description is omitted.

FIG. 2 is a flowchart of a control program showing an execution procedure of the control method of the present invention.
Executed every time the C signal is generated.

First, when the engine speed Ne is equal to the predetermined engine speed N _LOP (for example, 60
0 rpm) is determined (step 201). This determination is for determining whether the engine 1 is in the low-speed open loop control operation region. If the answer to this question is affirmative (Yes), that is, when the engine 1 is in the low rotational open-loop control regions proceeds to step 235, performs open-loop control is set to O ₂ feedback correction coefficient C _O2 value 1.0, terminating the Purogumamu I do. The steps
If the answer to 201 is negative (No), it is determined whether or not the engine speed Ne is higher than a predetermined speed N _HOP (for example, 3500 rpm) (step 202). This determination is for determining whether or not the engine 1 is in the high-speed open loop control operation region. When this answer is affirmative (Yes), that is, when the engine 1 is in the high-speed open loop control operation region, it is determined whether or not the leaning coefficient _KLS is smaller than 1.0, that is, when the engine 1 is in the leaning region (low-load operation region). Is determined (step 203). When the answer is negative (No), that is, when the engine 1 is in the high-speed open-loop control operation region other than the lean region, the routine proceeds to the step 235. When the answer to step 203 is affirmative (Yes), that is, when the engine 1 is in the lean range, the routine proceeds to step 204. Also, when the answer to step 202 is negative (No), the process proceeds to step 204.

In step 204, it is determined whether or not the throttle valve opening θ _TH is larger than a predetermined opening θ _WT (for example, 60 degrees), that is, whether or not the throttle valve 3 ′ is in a high opening state (substantially fully open state). Then, in the subsequent step 205, it is determined whether or not the fuel injection time T _OUTM of the main fuel injection valve 6 calculated by the equation (1) is _longer than a reference time (reference amount) T _WOT (for example, 8 msec). When the answer to both steps 204 and 205 is affirmative (Yes), that is, when the driver's acceleration request is clear (θ _TH > θ _WT ) and the fuel supply amount to the engine 1 is larger than the reference amount ( T _OUTM > T _WOT ), it is determined that the engine 1 is in the high-speed high-load region (WOT region), and the _routine proceeds to the next step 206, where the _enrichment coefficient K _WOT is set to a value X larger than 1.0.
Set to _WOT1 . X _WOT1 may be set to a fixed value, for example, 1.18, or may be determined according to the engine speed Ne and the throttle valve opening θ _TH . Then step
Proceeds to 235, stops the feedback control of the O ₂ feedback correction coefficient K _O2 is applied to the formula (1) as the value 1.0, the program is finished.

As described above, when it is determined that the engine 1 is in the WOT region, the O ₂ feedback correction coefficient K _O2 is set to a value of 1.0.
The O ₂ feedback control is stopped to perform open loop control, and the _enrichment coefficient K _WOT applied to the above equation (1) is 1.
The value is set to a value X _WOT1 larger than 0, and the air-fuel ratio of the air-fuel mixture is corrected for _enrichment .

If any of steps 204 and 205 is negative (No), the process proceeds to steps 207 to 209. That is, in the engine 1 in the previous execution of the present program 0 ₂ whether the feedback control is performed (step 207), the atmospheric pressure P _A is whether or not a predetermined greater than the atmospheric pressure P _AA2L (e.g. 710MmHg), i.e., atmospheric pressure Whether you are driving on a level terrain (step 20)
8) and determine whether or not the vehicle speed V is higher than a predetermined vehicle speed V _TMT (for example, 32 km / h), that is, whether or not the vehicle speed V is higher than a vehicle speed region where emphasis is placed on starting acceleration of the vehicle (step 209). I do. If any of the answers in steps 207 to 209 is negative (No), the process proceeds to step 212, in which it is determined whether the fuel injection time T _OUTM calculated by the equation (1) is longer than the reference time T _WOT. Determine. If this answer is affirmative (Yes), that is, if any of the answers in steps 207 to 209 is negative (N
o), and when the fuel supply amount to the engine 1 is larger than the reference amount, it is determined that the engine 1 is in the WOT region, and the process proceeds to the subsequent steps 206 and 235 to perform open loop control and supply to the engine 1 The mixture to be enriched. If the answer in step 212 is negative (No), the process proceeds to step 213.

On the other hand, if all of the answers at the steps 207 to 209 are affirmative (Yes), the process proceeds to step 210, and
Similarly to 2, it is determined whether the fuel injection time T _OUTM is longer than the reference time T _WOT . When the answer is negative (No), the process also proceeds to step 213. Therefore, when T _OUTM > T _WOT is not satisfied, steps 213 to 217 are executed irrespective of the determination results of steps 207 to 209.

In step 213 through 217, the vehicle speed V predetermined vehicle speed V ₁ (e.g., 32km / h) and the given vehicle speed V ₂ of the V ₁ greater than (eg if 64
miles / h) compared to (step 213, 215), the V ≦ V ₁ if step _{214, V 1 <V ≦ V} 2 if step 216, V> V ₂ If step 217 counts down based on the clock pulse tDLY The timer has a predetermined time tDLY ₁ , tDlY
₂ and tDLY ₃ are set respectively, and the timer is started.

FIG. 3 shows the predetermined times tDLY _{1 to} tDLY ₃ according to the vehicle speed V.
A table for setting a set in V ≦ V ₁ to tDLY ₁ to the value t ₁ (e.g. 1.0 seconds), the V ₁ <V ≦ V ₂ In tDLY ₂
Set t ₂ (for example, 3.0 seconds) larger than t ₁ and V> V ₂
Then, tDLY ₃ is set to the value t ₁ . The tDLY _3, less than the value t _2, may be set to different another value from the value t _1. It reads a predetermined time tDLY ₁ to tDLY ₃ in accordance with the vehicle speed V from the table, sets the tDLY timer.

As described above, the fuel injection time T _OUTM of the main fuel injection valve 6
Is less than or equal to the reference time T _WOT (the answer of 212 is negative (No) in steps 210 and others), the tDLY timer is set to the predetermined time tDLY _{1 to} tDL ₁
Set in one of the Y _3, the engine 1 after the start
It is determined that it is not in the WOT area, and the routine proceeds to step 218, where the _enrichment coefficient K _WOT is set to a value of 1.0, and the _routine proceeds to step 219.

On the other hand, when the answer to step 210 is affirmative (Yes), the process proceeds to step 211, where the timer value of the tDLY timer set and started in any of steps 214, 216 and 217 is set.
It is determined whether or not tDLY is zero. That is, T _OUTM > T _WOT
State, during any time predetermined time tDLY ₁ to tDLY _3, determines whether to continue. If the answer to step 211 is affirmative (Yes), it is determined that the engine 1 is in the WOT range, and the process proceeds to steps 206 and 235 to perform open loop control to enrich the mixture supplied to the engine 1. On the other hand, if the answer to step 211 is negative (No), the process proceeds to step 218. That is, even when the fuel supply amount is larger than the reference amount (the answer to step 210 is affirmative (Yes)), this is the case where the O ₂ feedback control is executed also at the previous execution of this program (the answer to step 207 is Affirmative (Yes)) and when the vehicle is traveling on level ground (the answer to step 208 is affirmative (Yes)), and furthermore, the vehicle speed V is higher than the vehicle speed range where emphasis is placed on the starting acceleration of the vehicle. In the speed range, when the vehicle is in a traveling speed range that includes high-speed driving, such as traveling in an urban area where the frequency of acceleration operation is high and easily emitting CO, or traveling on an uphill road where CO emission can be easily performed with continued high-load driving (step 209). If the answer is affirmative (Yes), the _duration of the T _OUTM > T _WOT state is the predetermined time tDLY ₁ , tDLY ₂
Alternatively, the engine 1 is not in the WOT region until tDLY ₃ and the enrichment coefficient K _WOT is set to a value of 1.0.

As described above, the mixture supplied to the engine 1 is supplied to the engine 1 when the vehicle 1 is traveling on a highland where an uphill road continues for a long time or when the vehicle 1 is in a low vehicle speed range where the acceleration of the vehicle is important. _Enriches immediately, but even when the fuel supply is greater than the reference amount (T _OUTM > T _WOT ), when traveling on vehicles, on flat _terrain , and traveling on urban areas and uphill roads where CO emissions are easy to emit State, and when the O ₂ feedback control is being continuously executed, the predetermined time tDLY ₁ , tDLY
During LY ₂ or tDLY ₃ , the mixture is not enriched. Therefore O ₂
The time ratio for performing the feedback control increases, and the amount of CO emitted from the engine 1 can be reduced.

In addition, the predetermined time period tDLY _{1 to} tDLY ₃ depends on the vehicle speed V.
In particular, in the predetermined vehicle speed range (V ₁ ≦ V <V ₂ ) defined by the predetermined vehicle speeds V ₁ and V ₂ , the predetermined time tDLY ₁ and the predetermined time tDLY ₁ applied in the low and high vehicle speed regions outside the vehicle speed range are selected. A predetermined time period tDLY ₂ set to a value longer than tDLY ₃ is selected, and the mixture supplied to the engine 1 is not enriched during the selected predetermined time period. Driving in a city that is easy to emit, or traveling on an uphill road on flat ground, that is, there is no problem even if the engine output is not increased because the uphill road does not last for a long time, but rather on a flat ground where you want to reduce the CO emission due to continuous high load operation In particular, CO emissions can be reduced in a predetermined vehicle speed range corresponding to a traveling speed range such as traveling on an uphill road.

Further, a predetermined time tDLY applied in a low vehicle speed range (V ≦ V ₁ )
₁ is a predetermined time t applied in a predetermined vehicle speed range (V ₁ <V ≦ V ₂ )
By setting the length to be shorter than DLY _{2, the} air-fuel mixture can be enriched quickly when the vehicle starts, and the starting performance of the vehicle can be improved. Further, by setting the predetermined time tDLY ₃ applied in the high vehicle speed range (V> V ₂ ) to be shorter than the predetermined time tDLY ₂ applied in the predetermined vehicle speed range, it is possible to improve the acceleration performance of the vehicle at high speed running. it can.

Also, the fuel injection time (T
_OUT ), the mixture between the O ₂ feedback control region and the WOT open loop control region is determined, so that the air-fuel mixture can be appropriately enriched in accordance with the engine output required for the engine, and the engine can be used at high load. Output characteristics can be improved.

FIG. 4 shows t applied to the determination in step 224 described later.
It is a flowchart of an operation subroutine of a _CAT timer. This subroutine is executed in synchronization with the generation of the TDC signal when the engine 1 is in the WOT area.

First, it is determined whether or not the state in which the intake pipe absolute pressure P _BA is greater than the predetermined value P _BACAT has continued for a first predetermined time t _WOTCAT or more (step 401). This determination is made in the WOT area.
By determining the length of time _during which the state of P _BA > P _BACAT , that is, the state in which fuel easily adheres to the intake pipe wall, is determined,
This is for determining whether a large amount of fuel has adhered to the intake pipe wall or the like when the engine 1 leaves the WOT region.

FIG. 5 is a _PBACAT table for setting the predetermined value _PBACAT , wherein the predetermined value _PBACAT contains the engine speed Ne and the atmospheric pressure.
It is set according to P _A. That predetermined value P _BACAT is relative to the reference value Ne ₁ ～Ne ₅ of 5 points of the engine speed Ne, the P _BACAT1 the atmospheric pressure P _A 5-point when the first predetermined value or more P _A1, atmospheric pressure
When P _A is equal to or less than a second predetermined value P _A2 , the P _BACAT1
Each of the five larger P _BACAT2 is the engine speed N
e is set so becomes more and larger value larger when the engine speed Ne is the reference value Ne ₁ ~Ne ₅ other value seek P _BACAT1 or P _BACAT2 by interpolation calculation for the engine rotational speed Ne . When the atmospheric pressure P _A is between the first and second predetermined values P _A1 and P _A2 , the predetermined value P _BACAT is obtained by interpolation calculation with respect to the atmospheric pressure P _A.

As described above, the predetermined value P _BACAT is set to a larger value as the engine speed Ne is larger. This is because the larger the engine speed Ne, the higher the flow velocity of the intake air, and the more difficult it is for fuel to adhere to the intake pipe wall and the like. Further, as the atmospheric pressure P _A is smaller, i.e. as to set larger the predetermined value P _BACAT at high altitude, low weight of the intake air at high altitude,
As a result, the region where the temperature of the three-way catalyst rises tends to shift to the high load side as compared with the lowland, and this is to correct this.

If the answer in step 401 is affirmative (Yes), that is, P _BA > P
_{When it is estimated that} the state of _BACAT continues for the first predetermined time t _WOTCAT or more, and therefore that a large amount of fuel has adhered to the intake pipe wall or the like, the t _CAT timer including the down counter is set to the second predetermined time t _CAT. To start (step
402), and proceed to step 404 described below. The answer to step 401 is negative (No), that is, the state of P _BA > P _BACAT has not continued for the first predetermined time t _WOTCAT or more, and therefore a large amount of fuel has adhered to the intake pipe wall or the like. If it is not estimated, the count value of the _tCAT timer is set to 0 (step 403). Next, the first and second flags Ft _CAT1 and Ft _CAT2 applied to the determination of step 220 or step 227 of the control program of FIG. 2 are each set to a value of 0 (step 404), and this subroutine ends.

Returning to the control program of FIG. 2, in step 219 following step 218, it is determined whether the leaning coefficient _KLS is smaller than 1.0 in lean 219, that is, whether the engine 1 is in a leaning region (low load operation state). It is determined whether or not. When this answer is negative (No), that is, when the engine 1 is not in the lean region and therefore in the feedback control region, the first
It is determined whether or not the flag Ft _CAT1 is equal to the value 1 (step 220). When the answer is affirmative (Yes), the second flag Ft _CAT2 is set to the value 1 (step 221), and the negative (N)
In the case of o), the second flag Ft _CAT2 is set to the value 0 (step 222), and the process proceeds to step 223.

In this step 223, feedback control is executed, and this program ends. That is, to calculate the O ₂ feedback coefficient Ko ₂ in response to the output of the O ₂ sensor 14, and controls so that the air-fuel ratio of a mixture supplied to the engine 1 becomes a predetermined set value, the the coefficient Ko ₂ Calculate the average value K _REF .

When the answer to the step 219 is affirmative (Yes), that is, when K _LS <1.0 is satisfied and the engine 1 is in the lean range, it is determined whether or not the count value t _CAT of the aforementioned t _CAT timer is equal to 0. (Step 224). If this answer is negative (N
o), that is, the count value t _CAT is not equal to 0, and therefore the state of P _BA > P _BACAT in the WOT region continues for the first predetermined time t _WOTCAT or more, and after the engine 1 leaves the WOT region, If the predetermined time t _CAT has not elapsed, the vehicle speed V is increased to a predetermined value V _CAT (for example, 1
In step 226, it is determined whether the engine speed Ne is larger than a predetermined value N _CAT (for example, 2,800 rpm). Steps 225 and 226
Is to determine whether or not the temperature of the three-way catalyst 13 is high. If the answers of steps 225 and 226 are both affirmative (Yes), that is, if V> V _CAT and Ne> N _CAT hold, it is determined that the three-way catalyst 13 is at a high temperature and the second flag Ft _CAT2 is set to the value 1 Is determined (step 227). If the answer is negative (No), the t _CAT timer is reset to the second predetermined time t _CAT and restarted (step 228), and then the first flag Ft _CAT1 is set to the value 1 (step 229). Then, the above-mentioned step 223 is executed, feedback control is performed, and this program is terminated.

As described above, when the throttle valve is fully opened, P _BA > P
_{After the} state of _BACAT has continued for a first predetermined time t _WOTCAT or more and the engine 1 has left the WOT region, a second predetermined time t
If the vehicle shifts to the lean region before _CAT elapses, the feedback control is also performed in the lean region, so that the fuel adhering to the intake pipe wall or the like is sucked into the combustion chamber, causing the air-fuel ratio to exceed. Enrichment can be reliably prevented.

In this case, when the engine 1 shifts from the WOT region to the leaning region via feedback control, the second flag Ft _CAT2 is set to a value by executing step 404 of the subroutine of FIG. 4 and steps 220 and 222 of the present control program. 0 and execution of steps 227 and 228 results in t
_Since the setting and start of the _CAT timer are repeated,
As long as the engine 1 remains in the lean region, the answer to step 224 is negative (No), and the feedback control is repeatedly executed.

Further, as in the case where the accelerator pedal is depressed for a short time in the lean region, when the engine 1 temporarily shifts from the lean region to the feedback control region and returns to the lean region again, when the engine 1 returns to the lean region, the routine proceeds to step 229 in the lean region. The first flag Ft _CAT1 is set to the value 1 by the execution, and the second flag Ft _CAT2 is set to the value 1 by the execution of the steps 220 and 221 in the feedback control area. Since the answer to step 227 is affirmative (Yes) and step 228 is not executed, the feedback control is continued until the second predetermined time t _CAT elapses after the vehicle leaves the lean area. This also prevents the air-fuel ratio from becoming over-rich.

If the answer to this step 224 is affirmative (Yes), that is, t _CAT
= 0, and therefore P _BA > P _BACAT in the WOT area
When the state has not continued for more than the first predetermined time t _WOTCAT or when the engine 1 has left the WOT region and has passed the second predetermined time t _CAT or more, a large amount of fuel has adhered to the intake pipe wall or the like. Since there is no such situation, the process proceeds to step 230 and thereafter, where open control is performed, and the air-fuel ratio is controlled to be lean by the lean coefficient _KLS .

First, in step 230, the first and second flags Ft _CAT1 ,
Ft _CAT2 is set to a value of 0, and then the count value of the t _CAT timer is set to 0 (step 231). Then this loop to determine whether passed continuously for a predetermined time period t _D in step 232, held at the value obtained the O ₂ feedback correction coefficient Ko ₂ in the previous loop when the answer is negative (No) And
While executing the open control (step 233), affirmative (Y
In the case of es), the open control is performed by setting the O ₂ feedback correction coefficient Ko ₂ to the average value K _REF calculated at the time of the feedback control (step 234), and the program ends. When the O ₂ feedback correction coefficient Ko ₂ is set to the average value K _REF , the predetermined waiting time t _D is provided because the air-fuel ratio is transient when the engine 1 shifts from the feedback control range to the open control range. This is in order to prevent a significant change.

If the answer in step 225 or 226 is negative (No), that is, V ≦
V three-way catalyst 13 when _CAT or the Ne ≦ N _CAT is established without a high temperature condition, since the less likely after-fire occurs, executes the step 230 follows, lean coefficient K _LS
The lean control of the air-fuel ratio is performed by the open control to which is applied.

(Effects of the Invention) As described in detail above, the present invention detects an exhaust component concentration based on the output of an exhaust concentration sensor provided in an exhaust system of an internal combustion engine, and supplies the exhaust component concentration to the engine in accordance with the detected value signal. The air-fuel ratio control method for an internal combustion engine for a vehicle, wherein the feedback control is performed such that the air-fuel ratio of the air-fuel mixture is set to a set value and the feedback control is stopped when the engine continues a predetermined high load state for a predetermined time. Since the predetermined time is changed according to the vehicle speed, traveling speeds such as city driving where the frequency of accelerated driving is high and CO is easy to emit and uphill road driving where CO is easy to emit with continuous high load driving In particular, it is possible to reduce CO emissions in the region.

[Brief description of the drawings]

1 is an overall configuration diagram of a fuel supply control device for an internal combustion engine for a vehicle to which the method of the present invention is applied, FIG. 2 is a flowchart of a control program showing an execution procedure of the control method of the present invention, and FIG. table for setting the predetermined time tDLY ₁ to tDLY ₃ in response to V, Figure 4 is a flowchart of the operation subroutine t _CAT timer, Fig. 5 a predetermined value P _BACAT an engine is applied to the subroutine of FIG. 4 it is a graph showing a table of the relationship between the rotational speed Ne and the atmospheric pressure P _a. 1: Internal combustion engine, 4: Throttle valve opening (θ _TH )
Sensor, 5 ... Electronic control unit (ECU), 8
…… Absolute pressure (P _BA ) sensor in the intake pipe, 12 …… Exhaust pipe, 14
…… O ₂ sensor (exhaust gas concentration sensor).

Claims (3)

(57) [Claims] An exhaust gas concentration sensor 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. In the air-fuel ratio control method for an internal combustion engine for a vehicle, the feedback control is performed so that the feedback control is stopped and the feedback control is stopped when the engine continues a predetermined high load state for a predetermined time. An air-fuel ratio control method for an internal combustion engine for a vehicle, comprising: 2. The air-fuel ratio of an internal combustion engine for a vehicle according to claim 1, wherein when the running speed of the vehicle is lower than a predetermined speed, the predetermined time is set longer than when the running speed is higher than the predetermined speed. Control method. 3. The engine has a fuel injection device, and the predetermined high load state is a state in which a fuel supply amount from the fuel injection device is larger than a predetermined reference amount. The method for controlling an air-fuel ratio of an internal combustion engine for a vehicle according to claim 1.