JP2621067B2 - Air-fuel ratio feedback control method for an internal combustion engine - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an air-fuel ratio feedback control method for an internal combustion engine, and more particularly to a method of supplying an air-fuel ratio to an internal combustion engine when the load fluctuates, or when it fluctuates within a hollow fuel ratio feedback control operation region. The present invention relates to a control method for appropriately controlling an air-fuel ratio of an air-fuel mixture to be performed.

(Problems to be Solved by the Related Art and the Invention) Conventionally, during operation in an air-fuel ratio feedback control operation region of an engine, a coefficient that changes according to an output of an exhaust gas concentration detector arranged in an exhaust system of the engine has been calculated. An air-fuel ratio feedback control method for an internal combustion engine that controls the air-fuel ratio of an air-fuel mixture supplied to the engine using the same is known (JP-A-58-160528).

According to the conventional control method, an average value of the coefficients obtained during operation in the feedback control operation region is calculated,
When the operation state shifts from the operation region other than the feedback control operation region to the feedback control operation region, the feedback control in the transition destination region is performed by using a value obtained by multiplying or adding a predetermined value to the average value of the coefficient as the coefficient. Is started, the initial value of the coefficient at the start of the feedback control can be set to an appropriate value.

However, in the feedback control operation region, for example, at the time of deceleration such as when the engine shifts from a high load state to a low load state, the air-fuel ratio tends to be over-rich due to the effect of fuel adhering to the intake pipe wall and the like. Become. That is, due to the decrease in the absolute pressure in the intake pipe due to the deceleration, the adhering fuel is sucked into the combustion chamber, and the deceleration becomes overrich accordingly (this tendency becomes stronger when the high load state is continued and the deceleration is performed). As a result, the emission of CO components increases.

Therefore, as a countermeasure in such a case, in order to satisfy the emission characteristics, for example, control of the air-fuel ratio is shifted to the lean side, that is, lean bias is performed, and in addition, increase of NOx component emission due to leaning is prevented. For this purpose, the ignition timing is retarded (retarded). However, such a method of controlling the ignition timing by an increase in NOx results in a decrease in fuel consumption, and thus a decrease in fuel consumption. Without satisfying the emission characteristics.

In particular, in a dual point injection (DPI) type internal combustion engine having a fuel injection valve upstream and downstream of the throttle valve, respectively, the fuel injection valve to the combustion chamber from the multipoint injection (MPI) type is compared with the multipoint injection (MPI) type internal combustion engine. Since the distance is long, the amount of the adhering fuel becomes larger than the length of the intake pipe, so that it is more difficult to achieve both the emission characteristics and the fuel consumption characteristics described above, and the above problem becomes more remarkable.

The present invention has been made in view of the above points,
Feedback control The air-fuel ratio of an internal combustion engine that enables appropriate air-fuel ratio control at the transition of the operating state within the operating range, thereby improving emission characteristics and realizing this without deteriorating fuel efficiency. It is an object to provide a feedback control method.

(Means for Solving the Problems) In order to achieve the above object, the present invention is arranged in an exhaust system of an internal combustion engine during operation in an air-fuel ratio feedback control operation region that is set in accordance with the load of the engine. In a feedback control method for an air-fuel ratio of an internal combustion engine, wherein an air-fuel ratio of an air-fuel mixture supplied to the engine is feedback-controlled using a coefficient that varies according to an output of an exhaust gas concentration detector, an average value of the coefficient is calculated. When the engine operating state shifts from the low load region to the high load region in the plurality of regions, a value obtained by performing a predetermined enrichment correction on the average value as an initial value of the coefficient is used, When the air condition shifts from the low load region to the low load region, the air-fuel ratio fee is calculated using a value obtained by performing a predetermined leaning correction on the average value as an initial value of the coefficient. This is to start the feedback control.

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 (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, which is converted to an electronic control unit (hereinafter referred to as “ECU”) 5. Is to be sent.

A main fuel injection valve 6 for main injection 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 of the auxiliary fuel injection valve 6a of the intake pipe 2, an absolute pressure sensor ( _PBA sensor) in the intake pipe via a pipe 7 is provided.
An absolute pressure signal converted into an electric signal by the _PBA sensor 8 is supplied to the ECU 5. Further, the downstream mounted an intake air temperature sensor (T _A sensor) 17, which supplies an electrical signal corresponding the sensed intake air temperature to the ECU 5.

An engine cooling water temperature sensor (Tw sensor) 10 is provided in the engine 1 main body. The Tw sensor 10 is composed of a thermistor or the like, is inserted into the peripheral wall of the engine cylinder filled with cooling water, and supplies a detected water temperature signal to the ECU 5. Further, an engine speed sensor (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. Signal (hereinafter "TDC
Signal), and this TDC signal is E
Sent to CU5.

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, and the like. .

The CPU 5b responds to the various engine parameter signals described above,
Based on a control program (FIGS. 2 to 5) to be described later, a plurality of air-fuel ratio feedback control regions set according to the engine load, for example, an O ₂ feedback (F / B) region as shown in FIG. In addition to determining various engine operating states such as the areas II ₁ and II ₂ and the open control area when divided into _two areas II ₁ and II ₂ according to the load, The fuel injection time for opening the main fuel injection valve 6 and the auxiliary fuel injection valve 6a in synchronization with the TDC signal is calculated.

The fuel injection time T _OUTM of the main fuel injection valve 6 is calculated based on the following equation (1).

T _OUTM = T _iM × K _O2 × K _WOT × K _LS × K _TW × K _AST × K ₁ + K ₂ (1) Here, T _iM indicates the basic fuel injection time of the main fuel injection valve 6. Intake pipe absolute pressure _PBA 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 region (region III in FIG. 6), that is, in the high load operation state, and _KLS is the engine 1 lean. A region (region VI in FIG. 6), that is, a leaning coefficient that is set to a predetermined value less than 1.0 when in the low-load operation state.

K _TW is a water temperature increase coefficient set in accordance with the actual engine cooling water temperature Tw, and K _AST is a post-start increase coefficient applied after the engine 1 is started.

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 set to the required value.

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 idle operation of the engine 1 (during the operation in the region I in FIG. 6). The fuel injection time of the auxiliary fuel injection valve 6a is also calculated according to a predetermined calculation formula, and based on this, the injection of the auxiliary fuel injection valve 6a is controlled.

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, the intake pipe absolute pressure P _BA is determined whether or not larger than the predetermined value P _BACAT (step 201). This determination is for determining whether the engine 1 is in the throttle valve fully open area. This answer is negative (No), that is, P _{BA ≤P BACAT}
Consists of a down counter at low load where
The t _WOTCAT timer is set to a first predetermined time t _WOTCAT and started (step 202), and the process proceeds to step 205 described later.

If the answer in step 201 is affirmative (Yes), that is, P _BA > P
_{When BACAT} is established, it is determined whether or not the count value of the t _WOTCAT timer started in step 202 is equal to 0 (step 203). That is, the state in which the intake pipe absolute pressure P _BA is larger than the predetermined value P _BACAT is the first predetermined time t _WOTCAT
It is determined whether or not the above has been continued. This determination is disengaged P _BA> P _BACAT becomes state at the throttle valve fully open zone, i.e., by the fuel to determine the length of time that adhered easily state continues into the intake pipe wall or the like, the engine 1 is a throttle valve fully open area This is for determining whether or not a large amount of fuel is attached to the intake pipe wall or the like when performing the operation.

The answer to the above step 203 is affirmative (Yes), that is, the state of high load P _BA > P _BACAT continues for the first predetermined time t _WOTCAT or more, and therefore, a large amount of fuel adheres to the intake pipe wall or the like. T _CAT consisting of a down counter
The timer is set to a second predetermined time t _CAT and started, and the first and second flags F _CAT1 and F _CAT2 applied to the determination in step 206 or step 216 described below are each set to a value of 0 (step 204), and proceed to step 205. If the answer in step 203 is negative (No), that is, P _BA > P
_When the state of _BACAT does not continue for the first predetermined time t _WOTCAT or more, and therefore it is not estimated that a large amount of fuel is attached to the intake pipe wall or the like, the process skips step 204 and proceeds directly to step 205.

In step 205, it is determined whether or not the leaning coefficient _KLS is smaller than a value of 1.0, that is, whether or not the engine 1 is in a leaning region (low load operation state). If the answer is negative (No), that is, if the engine 1 is not in the lean range, it is determined whether or not the first flag F _CAT1 is equal to the value 1 (step 2).
06), if the answer is affirmative (Yes), the second flag F _CAT2 is set to a value of 1 (step 207), and negative (No)
In the case of, the second flag F _CAT2 is set to the value 0 (step 208), and the routine proceeds to step 209.

In step 209, it is determined whether or not the engine speed Ne is lower than a predetermined speed _NLOP for determining whether or not the engine speed is in a low-speed open loop control region (region IV in FIG. 6). In step 211, it is further determined whether or not the rotational speed is higher than a predetermined rotational speed N _HOP for determining whether or not the rotational open loop control region (region V in FIG. 6).
It is determined whether or not the _enrichment coefficient K _WOT is a value of 1.0. If either of the answers in step 209 or 210 is affirmative (Yes), or the answer in step 211 is negative (No)
In the case of ( ₂₎ , the O2 feedback correction coefficient is set to a value of 1.0 (step 212), and open control is performed. If both of the answers at the steps 209 and 210 are negative (No) and the answer at the step 211 is affirmative (Yes), a step 220 described later is performed.
Proceed to the following. After step 220, feedback control is performed under certain conditions, as described later.

When the answer to step 205 is affirmative (Yes), that is, when K _LS <1.0 holds, and thus the engine 1 is in the lean range, it is determined whether or not the count value of the aforementioned t _CAT timer is equal to 0 ( Step 213). If this answer is negative (No),
That is, after the count value is not equal to 0 and the state of P _BA > P _BACAT continues for the first predetermined time t _WOTCAT or more in the throttle valve fully open area and the engine 1 leaves the throttle valve fully open area, the second state is established. If the predetermined time t _CAT has not elapsed, at step 214 the vehicle speed V becomes the predetermined value V
Whether it is greater than _CAT (eg 19.2km / h), step 215
At a predetermined value N _CAT (for example, 2,800r
pm) is determined. The determination in steps 214 and 215 determines whether the temperature of the three-way catalyst 13 is high. If the answer at steps 214 and 215 is both affirmative (Yes), that is, V> V _CAT and Ne
When> N _CAT is satisfied, it is determined that the three-way catalyst 13 is in the high temperature state, and it is determined whether or not the second flag F _CAT2 is equal to the value 1 (step 216). If the answer is negative (No), the t _CAT timer is reset to the second predetermined time t _CAT and restarted, and the first flag F _CAT1 is set to a value of 1 (step 217). . If the answer to step 216 is affirmative (Yes), step 217
Skip to step 220 directly.

Since the feedback control is performed in the processing after step 220, as described above, the state where P _BA > P _BACAT is _satisfied for the first predetermined time t in the throttle valve fully open area.
Continued over _WOTCAT, and after the engine 1 has left the throttle valve fully open area, when the transition to lean zone before the second predetermined time t _CAT has elapsed, even the feedback control in the lean region is performed The Rukoto.

In this case, when the engine 1 shifts from the throttle valve fully open range to the lean range through the feedback control range, the execution of steps 204, 206 and 208
Since the second flag F _CAT2 is set to the value 0 and the execution and execution of steps 216 and 217 repeat the setting and start of the t _CAT timer, the answer in step 213 is negative as long as the engine 1 stays in the lean region ( 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, the engine 1 temporarily shifts from the lean region to the feedback control region and returns to the lean region again. The first flag F _CAT1 is set to the value 1 by the execution, and the second flag F _CAT2 is set to the value 1 by the execution of the steps 206 and 207 in the feedback control area. The answer to step 216 is affirmative (Yes), and step 217 is not executed. Therefore, after the vehicle leaves the lean region, the feedback control is continued until the second predetermined time t _CAT elapses. Also at this time, it is possible to prevent the air-fuel ratio from being over-rich.

If the answer at step 214 is affirmative (Yes), that is, t _CAT
= 0 holds, therefore, in the fully open throttle valve range
When the state of P _BA > P _BACAT has not continued for the first predetermined time t _WOTCAT or more, or when the engine 1 has left the throttle valve fully open area and the second predetermined time t _CAT or more has elapsed, the process proceeds to step 218 and thereafter. Open control is performed, and the air-fuel ratio is controlled to be lean using the lean coefficient _KLS .

That is, the count value of the _tCAT tie is set to 0 (step 218), and then the main fuel injection valve 6 and the auxiliary fuel injection valve 6a
Mean value K as O ₂ feedback correction coefficient K _O2 is applied to the calculation of the fuel injection time, which is calculated as described below
Open control is performed by setting _REF1 and _KREF0 (step 219), and this program ends.

If the answer to step 214 or 215 is negative (No), that is, if V ≦ V _CAT or Ne ≦ N _CAT holds, the three-way catalyst 13
Is not in a high temperature state, and there is little possibility that afterfire will occur. Therefore, in this case as well, step 218 and subsequent steps are executed, and lean control of the air-fuel ratio is performed by open control using the lean coefficient _KLS .

Proceeding from step 211 or step 217 or step 216 to step 220, it is determined here whether or not the activation of the O ₂ sensor 14 has been completed, and the answer is negative (No), that is, the O ₂ sensor When 14 is inactive, a _tTX timer consisting of a down counter is set to a predetermined time _tTX and started (step 221), and the above-mentioned step 219 is executed and the present program ends.

If the answer to step 220 is affirmative (Yes), that is, the O ₂ sensor
When the activation in step 14 is completed, it is determined whether or not the count value of the _tTX timer started in step 221 is equal to 0 (step 222). If the answer is negative (No), step 219 is performed. When the answer is affirmative (Yes) while the open control is continued, the following step 223 is performed.
It is determined whether or not the engine cooling water temperature Tw is higher than a predetermined temperature _TWO2 .

If the answer to step 233 is negative (No) and the water temperature is low, step 219 is executed and the program ends. Thus, the answer is affirmative (Yes) and therefore Tw> T _WO2
Is satisfied, the feedback control is executed by performing the following processing, and the program is terminated. That is, K including the initialization process of the O ₂ feedback correction coefficient K _O2
O2 calculation processing is performed (step 224), K _O2 is calculated in accordance with the output of the O ₂ sensor 14, and the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is controlled so as to become a set value.
It calculates an average value K _REF of _O2 (step 225).

FIG. 3 is a diagram showing the steps in the main routine of FIG. 2;
5 shows a flowchart of a K _O2 calculation subroutine including a K _O2 initialization process executed in 224.

First, it is determined whether or not the previous control was feedback control (step 301), and the answer to step 301 is negative (No), that is, the previous control is open loop control,
Therefore, when the current loop is the first loop immediately after shifting from the open loop control area to the feedback control area, the process proceeds to step 302.

In this step 302, it is determined whether or not this time is within the operating range (region I in FIG. 6) (AUX range) of the auxiliary fuel injection valve 6a, and the answer is affirmative (Yes), that is, the current loop is controlled by the open loop control. In the first loop immediately after shifting to the operation range of the auxiliary fuel injection valve 6a in the feedback control region from the region, the initial value of the correction coefficient _KO2 is calculated in the operation range of the auxiliary injection valve 6a as described later. Auxiliary injection valve 6a
Product K of the average value K _REED and a predetermined coefficient C _RO of K _O2 for operation range of
Set _REFO × C _RO (step 303), then executes the integration control by the addition process of the well known integral term (I term) (step 304), followed by terminating the program.

When the answer to the step 302 is negative (No), that is, when the current loop is the first loop immediately after shifting from the open loop control area to the operation area of the main fuel injection valve 6 in the feedback control area, the previous time the fuel cut is performed. It is determined whether or not the answer has been made (step 305).
In the case of o), the initial value of the correction coefficient K _O2 is
_Is set to the average value K _REF1 of K _O2 for the operation range (main range) of the main fuel injection valve 6 calculated as described later in the operation range (step 306).

Next, integral control of step 304 and subsequent steps is performed. Thus, even when the engine shifts from the open loop control region to the operation range of the main fuel injection valve 6 in the feedback control region, the correction coefficient K _O2 is quickly set to a value suitable for the operation range of the main fuel injection valve 6. Can be set, and the excessive cotton responsiveness at this time can be improved.

If the answer to step 305 is affirmative (Yes), the initial value of the correction coefficient K _O2 is set to the product K of the average value K _REF1 and the predetermined coefficient C _R1.
REF1 × C _R1 is set (step 307), then step 30
Execute 4 to end this program. Immediately after the end of the fuel cut, the air-fuel mixture tends to be substantially lean due to the effect of the fuel adhering to the intake pipe 2 or the like. Therefore, the air-fuel mixture should be enriched by an amount corresponding to the _enrichment coefficient C _R1. Thus, the above-described substantial leaning is prevented.

When the answer to the step 301 is affirmative (Yes), that is, when the previous control is the feedback control, it is determined whether or not the last time was in the operating range (AUX range) of the auxiliary fuel injection valve 6a (step 308). The answer to step 308 is affirmative (Yes)
In this case, it is determined whether or not this time is within the operating range of the auxiliary fuel injection valve 6a as in the case of step 302 (step 30).
9) If the answer is affirmative (Yes), that is, if the engine is in the operating range of the auxiliary fuel injection valve 6a both last time and this time, it is determined whether or not the output VO ₂ level of the O ₂ sensor 14 has been inverted (step 310). ).

When the answer to the step 309 is negative (No), that is, when the current loop is the first loop immediately after the engine shifts from the operation range of the auxiliary fuel injection valve 6a to the operation range of the main fuel injection valve 6, the vehicle speed V becomes lower. It is determined whether or not it is smaller than a predetermined value V ₁ (for example, 15 km / h) (step 311), and the answer is affirmative (Ye
s), that is, when the vehicle speed is low, the initial value of the correction coefficient K _O2 is changed from the operation range of the auxiliary fuel injection valve 6a to the operation range of the main fuel injection valve 6 within a predetermined time after the shift of the main fuel injection valve 6 _Is set to the average value K _REF2 of K _O2 calculated as described later in the operating range of, the t _FBTH timer comprising a down counter is reset to a predetermined time (for example, 2.5 seconds), and started (step 312). ), Execute step 304 and terminate the program.

If the answer to step 311 is negative (No) and the vehicle speed is high, steps 306 and 304 are executed, and the program ends.

If the answer to step 308 is negative (No), it is determined whether or not the current time is within the operating range (main range) of the main fuel injection valve 6 (step 313), and the answer to step 313 is negative (N
o), that is, when the current loop is the first loop immediately after the engine has shifted from the operation range of the main fuel injection valve 6 to the operation range of the auxiliary fuel injection valve 6a, the steps 303 and 304 are executed to execute this program. To end.

On the other hand, when the answer of step 313 is affirmative (Yes), ie if the engine is in the operating area of the main fuel injection valve 6 with the previous and current proceeds to step 314, similarly to the step 310, O ₂
It is determined whether or not the output VO ₂ level of the sensor 14 has been inverted.

Here, when the answer of step 314 is negative (No),
Proceeding to step 315, using a predetermined increase / decrease coefficient C _R2 ,
When the O ₂ feedback area is divided into a plurality of areas according to the load, the K _O2 is initialized at the time of transition from one area to another area.

FIG. 4 is a flowchart showing a subroutine for the above-described _KO2 initialization processing including the _CR2 selection processing executed in step 315.

First, in step 401, it is determined whether or not the count value of the t _FBTH timer is equal to 0. If the answer is negative (No), the O ₂ feedback region is set in the high load region as shown in FIG. In the case of dividing into the (II ₁ ) and the low load area (II ₂ ), the initialization processing of _KO2 to be executed at the time of transition from one area to the other area is not performed (step 402), and this program ends. I do. That is, the t _FBTH timer is a K _REF2 calculation timer for a K _REF2 value to be applied as an initial value when switching from the operation range of the auxiliary fuel injection valve 6a to the operation range of the main fuel injection valve 6, and accordingly, K _REF2 During the calculation period of, the initialization of the _KO2 value according to this program is stopped.

When the answer to step 401 is affirmative (Yes), that is, when the t _FBTH timer is not operating, the operating state of the engine 1 has shifted from the high load region to the low load region in the feedback control region, or has changed from the low load region to the high load region. The processing of step 403 and subsequent steps is executed to see whether or not the processing has shifted to the load area.

That is, the previous operating condition, the intake pipe absolute pressure P _BA is determined whether or not a to a predetermined discrimination value P _BO2H (e.g. 500 mmHg) is greater than the state (step 403), the answer is affirmative (Ye
s), that is, when P _BA > P _BO2H is satisfied and the previous time was a high load, it is determined whether or not the current operating state is the intake pipe absolute pressure P _BA is smaller than the determination value P _BO2H (step 40).
4) If the answer to step 404 is affirmative (Yes), that is, if the load is low this time, it is determined that the vehicle is in a deceleration state, and the initial value of the correction coefficient K _O2 is made lean with the average value K _REF1 . A product K _REF × C _R20 with a predetermined correction coefficient C _R20 (for example, 0.96) is set (step 405), and the program ends.

As a result, when shifting from the high load region to the low load region, the feedback control of the air-fuel ratio is performed using the value K _REF1 × C _R20 obtained by performing the lean correction on the calculated K _REF1 as the initial value of K _O2. Is started, and it is possible to prevent the air-fuel ratio from being enriched due to the suction of the fuel attached to the intake pipe wall during the transition,
The generation of CO and HC can be reduced. That is, when the transition from a high load to a low load, easily a large amount of adhering fuel is drawn into the combustion chamber by a reduction in the intake pipe absolute pressure P _BA,
Although the air-fuel mixture becomes darker during deceleration, by performing the initialization of K _O2 as described above by the intake pipe absolute pressure P _BA, it is possible to alleviate the tendency of such deceleration over rich.

Wherein when the answer to step 404 is negative (No), i.e. if the previous nor the intake pipe absolute pressure P _BA is equal to or higher than the determination value P _BO2H state this time, followed by terminating the program executes the step 402. That is, since it is not a transition from the high load state to the low load state, the initialization processing using the coefficient _CR20 is not performed.

On the other hand, if the answer in step 403 is negative (No), that is, P _BA ≦
If P _BO2H is established, and thus the previous P _BA value is less than or equal to P _BO2H , in a succeeding step 406, the previous P _BA value is _reduced to a predetermined discrimination value smaller than the discrimination value P _BO2H.
Compared to P _BO2L (e.g. 470mmHg), P _BA value該判specific value P
_It is determined whether or not the state is smaller than _BO2L . If the answer is negative (No), the program executes the aforementioned step 402 and terminates the program, while the answer to step 406 is affirmative (Ye
s), that is, when P _BA <P _BO2L holds and the previous time was a low load, it is determined whether or not the current operating state is that the intake pipe absolute pressure P _BA is larger than the determination value P _BO2L (step 40).
7), when the answer to the step 407 is affirmative (Yes), that is, when the load is high this time, the initial value of the correction coefficient K _O2 is changed to the average value K _REF1 and the predetermined coefficient C _R21 ( (For example, 1.03) is set to K _REF1 × C _R21 (step 40
8) End this program.

As described above, when the engine 1 shifts from the low load region to the high load region in the feedback control region, contrary to the above, the _enrichment correction is performed on the calculated K _REF1 as the initial value of K _O2 . Feedback control is started using the value K _REF1 × C _R21 , which prevents the air-fuel ratio from leaning due to fuel supply delay when shifting from low load to high load, and reduces the generation of NOx. it can. That is, when the accelerator is depressed to increase the opening of the throttle valve 3 'to accelerate, the air is very light, so the air enters immediately, but the fuel is delayed compared to this, and it is easy to lean. Lean air-fuel ratio due to such a delay in fuel supply can also be avoided.

The answer is negative at step 407 (No), i.e. if the last time also in the following state intake pipe absolute pressure P _BA is the discriminant value P _BO2L this time, similarly to the step 404, a high load from a low load state If not at the time of transition to the state
Step 402 is executed, and the initialization process using the coefficient C _R21 is not performed. Therefore, initialization of K _O2 using the increase / decrease coefficient C _R2 is as follows.
Under the condition that the count value of the t _FBTH timer is 0, it is performed only at the time of transition from one of the at least two areas divided and set according to the load in advance, and from the high load state or the low load state, respectively. Average K _O2 value _REF1 corresponding to transition
_Is multiplied by a coefficient C _R20 or C _R21 and applied as an initial value of K _O2 .

As described above, it is possible to perform appropriate initialization of deceleration of K _O2, On the other hand, during acceleration, K _O2 initialized at the time of acceleration for the proper air-fuel ratio during acceleration from the proper air-fuel ratio at the time of deceleration Can also be performed. That is, in order to prevent an increase in NOx due to a lean air-fuel ratio during K _O2 initialization during deceleration, when the load changes from a low load state to a high load state, K _REF1
Is multiplied by a coefficient _CR21 for _enrichment correction, and appropriate initialization of K _O2 at the time of acceleration is performed, thereby improving emission characteristics.

Moreover, in this case, the control of the air-fuel ratio is shifted to the lean side as in the countermeasure method described above, and the NOx
In order to prevent an increase in fuel consumption, the ignition timing is sent, and the fuel consumption is not reduced. Therefore, emission characteristics can be improved by reducing CO and the like, and this can be realized without lean biasing the air-fuel ratio control and delaying the ignition timing. That is, both the emission characteristic and the fuel consumption characteristic can be satisfied simultaneously.

Furthermore, as the initial value, because using the value obtained by increasing or decreasing with respect to the average value K _REF1, i.e. where the average value K _REF1 is the learning value and is used for correcting an error of the entire system, such an average value Since K _REF1 is used to increase or decrease this, it is also possible to correct the setting variation of the fuel supply system.

Returning to FIG. 3, if the initialization process has been performed as described above in step 315, the product value K
_The integration control described above is executed with _REF1 × C _R20 or K _REF1 × C _R21 as an initial value, and the program ends.

If the answer to step 314 is affirmative (Yes), that is, the O ₂ sensor 14
Is inverted, the well-known proportional term (P
(Step 31)
6), end this program. Step 310
Negative answer is (No), i.e. O ₂ sensor 14 when the engine is in the operating region of the auxiliary fuel injection valve 6a with the previous and current
If the output level of
Step 304 is executed to terminate the program, while if the answer is affirmative (Yes), the step 316 is executed to terminate the program.

The average value K _{REF of} K _O2 is calculated in step 225 of FIG. 2 using the value of the correction coefficient K _O2 calculated by the subroutine of FIG. 3 as described above, and is stored in the memory.

In this case, the average value K _REF is calculated for each area based on a K _REF calculation subroutine (FIG. 5) described later according to the feedback control area to which the current loop corresponds.
Calculation of K _RF0 , K _REF1 or K _REF2 is performed, and K _REF0 and K _{REF0
For REF1} , K _{REF (i)} (i = 0,1) according to the following equation (2).
There calculating of _{r also} is calculated for K _REF2 according to the following equation (3).

K _{REF (i)} = K _O2P · (C _{REF (i)} / A) + K _{REF (i) (n−1)} · (A−C _{REF (i)} ) / A (2) K _REF2 = K _{O2P / I} · (C _REF2 / A) + K _{REF2 (n−1)} (A−C _REF2 ) / A (3) As described later, the average value K according to the above equation (2)
Immediately after _REF0 and K _REF1 comparison section (P term) operation, i.e. O ₂ is only calculated when reversing the output level of the sensor 14, while the average value K _REF2 is for each TDC signal pulse generation, that is, calculated across.

That is, in the above, the value K _O2P is K _O2 immediately after the proportional term operation.
, The value K _{O2P / I} is the value of K _O2 every time, A is a constant, C _{REF (i)} and C _REF2 are variables that are experimentally set for each region and are 1 to A Of these, an appropriate value is set. K _{REF (i) (n-1)} and K _{REF2 (n-1)} are the K _O2 obtained up to the previous time in the operation region where the current loop is applicable.
Is the average value.

Depending on the values of variables C _{REF (i)} and C _REF2 ,
Since the ratio of the _KO2 value changes, by setting the value of such a variable to an appropriate value in the range of 1 to A in accordance with the specifications of the target air-fuel ratio feedback control device, engine, etc. K _REF (K _REF0 , K _REF1 or K _REF2 ) can be obtained.

Next, the processing procedure of the K _REF calculation subroutine executed in step 225 of FIG. 2 will be described in detail with reference to the flowchart shown in FIG.

In FIG. 5, in step 501, it is determined whether or not the intake air temperature T _A is lower than a predetermined intake air temperature determination value T _REFTA (for example, 80 ° C.).
Whether step 502 the O ₂ feedback region, lean coefficient K _LS at step 503 whether the value 1.0 or less is determined, respectively. If any of the answers of the above steps 501 and 502 is negative (No), or step 50
If the answer to 3 is affirmative (Yes) and K _LS <1.0 holds, this program is terminated as it is, and the calculation of the average value K _REF is stopped, while the answer to the above steps 501 and 502 is affirmative (Yes).
When the answer to step 503 is negative (No), that is, when the intake air temperature is low and feedback control is being performed and the engine 1 is not in the lean range, the count value of the t _FBTH timer is set to 0. It is determined whether they are equal (step 504).

When the answer to step 504 is negative (No), the average value K _REF2 of K _O2 is calculated based on the above equation (3) (step S 504).
505), end this program. That is, the average value of K _O2 K
_REF2 is calculated when the engine shifts from the operation range of the auxiliary fuel injection valve 6a to the operation range of the main fuel injection valve 6, and is calculated only until a predetermined time t _FBTH elapses after the shift.

If the answer in step 504 is affirmative (Yes), that is, t _FBTH = 0
Holds, the proportional term (P
Item) It is determined whether or not the control has been executed (step 50)
6) If the answer is negative (No), that is, if the proportional term control is not executed in the current loop, the program is terminated as it is, and the calculation of the average value K _REF is not performed. On the other hand, if the answer to step 506 is affirmative (Yes), that is, if the proportional term control is
At 507, it is determined whether or not the current loop is in the operating range of the main fuel injection valve 6, and if the answer is affirmative (Yes), the K for the operating range of the main fuel injection valve 6 is determined based on the equation (2). _O2
Is calculated (step 508), and this program ends. That is, the average value K _REF1 of K _O2 is calculated except when the engine is in the operating range of the main fuel injection valve 6 and the average value K _REF2 is calculated.

If the answer to the question of the step 507 is negative (No), the vehicle speed V is determined whether or not the predetermined value V ₁ is smaller than (step
509) If the answer is negative (No), the program ends as it is, while if the answer is affirmative (Yes),
That is, when the current loop is in the operating range of the auxiliary fuel injection valve 6a and in the low vehicle speed state, the average value K _REF0 of K _O2 for the operating range of the auxiliary fuel injection valve 6a is calculated based on the above equation (2). (Step 510), the program ends.

The average value K _REF is calculated in each region as described above, and when the engine 1 shifts from one region to the other region in the feedback control charge region,
The K _REF1 value calculated and stored in 508 and the predetermined coefficient C described above
Initialization processing of _KO2 is performed using _R2, and the air-fuel ratio supplied to the engine 1 at the time of transition is appropriately controlled.

In the above embodiment, the case where the present invention is applied to a DPI type engine in which a fuel injection valve is provided on the upstream side of a throttle valve upstream of an intake pipe assembly is described, but the present invention does not prevent application to a normal MPI engine. . In particular, when applied to the DPI type, the effect of the attached fuel due to the long distance from the fuel injection valve to the combustion chamber is eliminated, and there is a great effect by improving the accuracy of the air-fuel ratio control in the DPI type.

(Effects of the Invention) According to the present invention, during operation in an air-fuel ratio feedback control operation region that is set in plurality according to the load of an internal combustion engine, the operation is performed in accordance with the output of an exhaust gas concentration detector disposed in the exhaust system of the engine. A feedback control of an air-fuel ratio of an air-fuel mixture supplied to the engine by using a coefficient that varies according to an average value of the coefficient. When shifting from the low load region to the high load region, a value obtained by performing a predetermined enrichment correction on the average value as an initial value of the coefficient is used, and when shifting from the high load region to the low load region, The air-fuel ratio feedback control may be started using a value obtained by performing a predetermined leaning correction on the average value as an initial value of the coefficient. Therefore, when shifting from a low load to a high load, it is possible to prevent the air-fuel ratio from leaning due to a delay in fuel supply and reduce the generation of NOx. It is possible to prevent the enrichment of the air-fuel ratio due to the suction of the adhering fuel and reduce the generation of CO and HC.Also, it is also possible to correct the setting variation of the fuel supply system by increasing or decreasing the average value as an initial value. it can.

[Brief description of the drawings]

1 is an overall configuration diagram of a fuel supply control device for an internal combustion engine 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. 3 is FIG. FIG. 4 is a flowchart showing a K _O2 calculation subroutine including a K _O2 initialization process executed in the program of FIG. 4. FIG. 4 is a flowchart showing a procedure of K _O2 initialization using the coefficient CR ₂ in the program of FIG. 5
FIG. 6 is a flowchart showing a K _REF calculation subroutine executed in the program of FIG. 2, and FIG. 6 is a diagram showing an operating region of the engine. 1 ... internal combustion engine, 2a ... intake pipe collecting part, 3 '... throttle valve, 5 ... electronic control unit (EC
U), 6 ...... main fuel injection valve, 8 ...... intake pipe absolute pressure (P _BA) sensor, 12 ...... exhaust pipe, 14 ...... O ₂ sensor.

Claims (2)

(57) [Claims] When an operation is performed in an air-fuel ratio feedback control operation region that is set in plurality according to a load of an internal combustion engine, a coefficient that changes according to an output of an exhaust gas concentration detector disposed in an exhaust system of the engine is used. An air-fuel ratio feedback control method for an internal combustion engine, wherein the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled.
The average value of the coefficient is calculated, and when the engine operation state shifts from the low load region to the high load region in the plurality of regions, a predetermined enrichment correction is performed on the average value as an initial value of the coefficient. Using the performed value, when shifting from the high load region to the low load region, feedback control of the air-fuel ratio is started using a value obtained by performing a predetermined leaning correction on the average value as an initial value of the coefficient. An air-fuel ratio feedback control method for an internal combustion engine. 2. The air-fuel ratio feedback of an internal combustion engine according to claim 1, wherein the engine includes a plurality of cylinders, and a fuel injection valve is provided upstream of a throttle valve upstream of an intake pipe assembly. Control method.