JPH076441B2 - 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 particularly to an air-fuel ratio suitable for any fuel even if fuels having different properties are used. Regarding control method.

(Prior Art and Problems Thereof) There are cases where the properties of the fuel used for the internal combustion engine are not constant depending on the region and time. In particular, countries such as countries in the process of switching from unleaded gasoline to unleaded gasoline have a demand to use all fuels having different octane numbers. The engine matched by assuming the use of fuel with a low octane number is set with a delayed ignition timing.Therefore, if a fuel with a high octane number is used for this, the output originally obtained by that fuel will be obtained. Absent. On the other hand, the engine matched by assuming the use of fuel with a high octane number is set with the ignition timing advanced, so if you use a fuel with a low octane number,
There is a risk of knocking and damaging the engine.

In order to avoid such inconvenience, an octane number select switch is provided, the octane number select switch is switched according to the octane number of the fuel to be used, and the basic ignition timing map corresponding to the octane number of the fuel to be used is selected and the knock sensor is set to the engine. Ignition timing control (knock control) suitable for the fuel used is performed so that the retard amount is determined according to the amount of mounting and knocking, and the basic ignition timing read out and calculated from the basic ignition timing map is corrected. Things are known.

On the other hand, when a fuel having a low octane number is used, if the ignition timing is set with a delay as described above, the exhaust temperature rises, which may damage the exhaust system components. Therefore, for the basic fuel injection amount map, switch the octane number select switch according to the octane number of the fuel to be used, select the basic fuel injection amount map corresponding to the octane number of the fuel to be used, and set the basic fuel injection amount to the low octane fuel. The value is set to the rich side and to the lean side for high octane fuel.

However, if the octane number select switch is operated manually (manual operation) to select the basic ignition timing map and the basic fuel injection amount map, it is easy to make a mistake in operating the switch or forget to do so, and the air-fuel ratio The following problems occur in control. That is, for example, when the low octane fuel is used when the high octane fuel is used and the octane number select switch is switched to the low octane side, the ignition timing control is
The knock control gradually shifts the ignition timing to the advanced side, and eventually the ignition timing is advanced until just before the knock sensor detects the knock occurrence, and it is possible to compensate for an operation error of the octane number select switch. . On the other hand, regarding air-fuel ratio control, since the air-fuel ratio has not been conventionally corrected by the knock sensor, an excessive amount of fuel is supplied to the engine due to an operation error in the octane number select switch. In this case, the air-fuel ratio for the low octane fuel is set to the rich side, so it will not damage the engine, but conversely, it is assumed that the high octane fuel is used when using the low octane fuel. Is switched to the high octane number side, the ignition timing is gradually switched to the retard side by the knock control, and the ignition timing is gradually retarded until the knock occurrence is not detected by the knock sensor. In this case, the air-fuel ratio is set to the lean side as if high-octane fuel is used, so if the ignition timing is retarded by knock control, the exhaust gas temperature rises and damages the exhaust system components. There is a risk. In particular, if high-speed traveling and high-load operation are continued, there is a high possibility of such damage.

The present invention has been made in order to solve such problems, and it is possible to use fuels having various properties with different octane numbers, and it is possible to perform optimal ignition timing control and air-fuel ratio control at the same time for the properties of the fuel used. SUMMARY OF THE INVENTION It is an object of the present invention to provide an air-fuel ratio control method for an internal combustion engine, which prevents knocking and prevents exhaust gas temperature rise.

(Means for Solving the Problems) According to the present invention in order to achieve the above object, the ignition advance value is sequentially corrected according to the knock generation amount detected at every predetermined crank angle rotation of the internal combustion engine. In the air-fuel ratio control method for an internal combustion engine, in which the ignition timing is electronically controlled based on the corrected ignition advance value, and fuel is injected and supplied by the fuel injection valve, at least the engine speed and the engine load. Are stored in advance according to
And a first suitable for use of a fuel having a second fuel property
And the basic ignition timing is read from the second basic ignition timing map in accordance with the engine speed detection value and the engine load detection value, and the ignition advance value is calculated from these two basic ignition timings in accordance with the knock generation amount detection value. Are sequentially corrected, and an air-fuel ratio correction map value suitable for use of the fuel having the first fuel property is stored in advance according to at least the engine speed and the engine load, and the engine speed is corrected from the air-fuel ratio correction map value. The air-fuel ratio correction value corresponding to the number detection value and the engine load detection value is read, and the air-fuel ratio correction value is
Correction is made according to the deviation between the basic ignition timing read out from the first basic ignition timing map according to the engine speed detection value and the engine load detection value and the corrected ignition advance value, and the corrected empty There is provided an air-fuel ratio control method for an internal combustion engine, characterized in that the fuel injection supply amount is corrected according to the fuel ratio correction value.

(Operation) The basic ignition timing is read from the first and second basic ignition timing maps suitable for use of the fuel having the first and second fuel properties in accordance with the engine speed detection value and the engine load detection value, respectively. Then, the ignition advance value is sequentially corrected from these two basic ignition timings in accordance with the knock generation amount detection value.
Therefore, the fuel property of the fuel actually used is
And the ignition advance value is sequentially corrected according to the knock generation amount detection value regardless of the second fuel property, the ignition advance value suitable for the fuel used is set. . On the other hand, only the air-fuel ratio correction map value suitable for use of the fuel having the first fuel property is stored in advance, and each air-fuel ratio correction value stored in this air-fuel ratio correction map value corresponds to the corresponding first air-fuel ratio correction map value. A value suitable for each basic ignition timing of the basic ignition timing map is set. Then, an air-fuel ratio correction value corresponding to the engine speed detection value and the engine load detection value is read out from this air-fuel ratio correction map, and the air-fuel ratio correction value is detected from the first basic ignition timing map. The corrected air-fuel ratio correction value is corrected according to the deviation between the basic ignition timing read according to the value and the engine load detection value and the corrected ignition advance value. Therefore, the air-fuel ratio is controlled to an appropriate value according to the fuel property of the fuel actually used, and the exhaust temperature is prevented from rising.

(Example) Hereinafter, one example of the present invention will be described in detail with reference to the drawings.

First, the structure of an internal combustion engine controller for executing the method of the present invention will be described with reference to FIGS. 1 and 2. Reference numeral 10 in FIG. 1 denotes a multi-cylinder internal combustion engine, for example, a 4-cylinder gasoline engine, and reference numeral 12 denotes an intake passage connected to the intake port of each cylinder. An air cleaner 13 and a Karman vortex type air flow sensor 14 are attached to the open end of the intake passage 12 on the atmosphere side. The air flow sensor 14 is electrically connected to the input side of an electronic control unit (ECU) 16 and has a Karman vortex generation period signal f.
Is supplied to the electronic control unit 16. Intake passage 12
A throttle valve 18 is provided on the way, a fuel injection valve 20 is provided in each intake passage 12 in the vicinity of the intake port of each cylinder, and each fuel injection valve 20 is connected to the output side of the electronic control unit 16. It is driven by a new drive from the electronic control unit 16.

On the input side of the electronic control unit 16 various engine operating parameter sensors, such as the throttle valve 18
A throttle sensor 19 for detecting the valve opening θt of the engine, an intake air temperature sensor 21 installed in the air cleaner 13 for detecting the intake air temperature Ta, a predetermined crank angle position of each cylinder (for example, 75 ° before the top dead center of the intake stroke). The crank angle position sensor 22 for detecting, the engine water temperature sensor 23 for detecting the cooling water temperature Tw of the engine 10, the atmospheric pressure sensor 24 for detecting the atmospheric pressure Pa, the octane number of the fuel supplied to the engine 10 are manually operated. 2 position, eg premium octane number (eg
RON95) position and regular octane number (eg, RON91) position octane number select switch (OS
S) 25, mounted on a cylinder block of the engine 10 and connected with sensors such as a knock sensor 26 for detecting a knock generation level, which supplies detection signals to the electronic control unit 16.

A spark plug 30 is attached to each cylinder of the engine 10, and the spark plug 30 is connected to an input side of the electronic control unit 16 via a distributor 29 and an igniter device 28 that generates a secondary high voltage by an ignition coil. There is.
The igniter device 28 generates a secondary high voltage in response to an ignition signal from the electronic control unit 16, and the secondary high voltage is sequentially supplied to a spark plug 30 of each cylinder in a predetermined order by a distributor 29.

The electronic control unit 16 is a central processing unit (CPU) that calculates an ignition timing and a fuel injection amount, which will be described later, a ROM that stores various calculation programs that will be described later, a RAM that temporarily stores and stores data, and an engine 10 It is composed of a non-volatile RAM that stores and stores necessary data even after the operation is stopped and is backed up by a battery, an I / O interface, an A / D converter (neither is shown), a knock detection circuit 16a, and the like. The electronic control unit 16 calculates the ignition timing according to the procedure described later according to the engine operating parameter values detected by the various sensors described above, outputs the ignition signal based on the calculated ignition timing, and calculates the fuel injection amount. Then, a valve opening drive signal is output to the fuel injection valve 20.

The knock detection circuit 16a is a bandpass filter (BPF) 3
2, composed of a noise level detector 33, a comparator 34, an integrator 35, etc., the knock sensor 26 is connected to the input of the bandpass filter 32, and the output is connected to one input of the comparator 34. , Connected to the input of the noise level detector 33. The output of the noise level detector 33 is the comparator 34
Connected to the other. The output of the comparator 34 is connected to the input of the integrator 35, and the output of the integrator 35 is A /
It is connected to the input of the D converter.

Next, the operation of the control device for the internal combustion engine configured as described above will be described.

First, the method of detecting the knock level of the engine 10 by the knock sensor 26 and the knock detection circuit 16a will be described with reference to FIG. 3. The crank angle position sensor 22 determines the predetermined crank angle position of each cylinder (before the intake stroke top dead center). Each time (BTDC) 75 ° is detected, it is inverted to a high level and a predetermined crank angle position signal STG that holds the high level for a predetermined crank angle (for example, 70 ° C) is output (Fig. 3 ( a)
reference). The output signal of the knock sensor 26 which detects the vibration propagating through the cylinder block of the engine 10 is filtered by the bandpass filter 32 (FIG. 3 (c)). The output of the bandpass filter 32 is a mixture of a noise signal and a knock signal, and the comparator 34 separates the knock signal and the noise signal and outputs a high level signal while the knock signal having a predetermined threshold value or more is input. Is output (the third
Figure (d)). The integrator 35 detects the high level signal supplied from the comparator 34 at predetermined time intervals, generates a knock level signal Vn increasing to a constant value every time the high level signal is detected, and holds the signal level. To do. Since the integrator 35 is configured to be reset by the reset signal (FIG. 3 (f)) synchronized with the predetermined crank angle position signal STG, the knock level signal Vn of the integrator 35 is adjacent to the adjacent BTDC75.
Corresponds to the knock level of the knock that occurs between the ° positions. The output level of the integrator 35 is converted into a digital signal by the A / D converter when the predetermined crank angle position signal STG is generated and read by the CPU.

Next, the ignition timing control procedure executed by the electronic control unit 16 will be described with reference to FIGS. 4 to 11.

The program flow chart shown in FIG. 4 and FIG.
The procedure for calculating the optimum ignition timing for the properties of the fuel actually used and the operating state of the engine 10 is shown. The electronic control unit 16 uses this program to determine the crank angle position sensor 22 to the predetermined crank angle position (BTDC 75 °). Is executed every time is detected.

First, the electronic control unit 16 uses the signal values of the various sensors described above, that is, the Karman vortex generation period signal f, the throttle valve opening θt, the intake air temperature Ta, the cooling water temperature Tw, and the atmospheric pressure P.
a, The signal values after the knock level Vn are read, these values are stored in the storage device, and the on / off state of the octane number select switch 25 is detected and stored in the storage device (step 40). Next, in step 41, the engine speed Ne and the intake air amount A / N are calculated. The engine speed Ne is calculated from the time interval from the previous STG signal input generation to the current STG signal generation time, and the intake air amount A / N is the intake capacity flow rate obtained from the Karman vortex generation signal f and the engine speed Ne. Is multiplied by the air density obtained from the atmospheric pressure Pa and the intake air temperature Ta to obtain the mass flow rate per intake stroke. The engine speed Ne and the intake air amount A / N are stored and stored in the storage device RAM.

Next, the electronic control unit 16 determines whether or not the engine 10 is operating in the knocking possible operating region, that is, in the knocking control zone (step 43). The operating region representing the knock control zone is defined by the engine opening speed Ne and the parameter value representing the engine load such as the valve opening θt of the throttle valve 18 and the intake air amount A / N, and knock may occur during normal operation. This is a predetermined engine operating range. Step
If 43 of the determination result is negative (No), i.e., there is no fear of knocking when the engine 10 is operating in a region other than the regions mentioned above, the knock control amount theta _K to be described later 06
Set to (step 45). Step 64 in FIG. 5 described later
Proceed to.

If the determination result of step 43 is affirmative (Yes), that is, if the engine 10 is operating in the knock control zone, it is determined whether or not the knock level Vn is larger than a predetermined threshold value V _RTH (step 46). ). If the determination result is negative, the retard change amount θn (t) is set to 0 this time (step 48), and the process proceeds to step 54 described later.

If the determination result of step 46 is affirmative, the process proceeds to step 50, and the present retard change amount θn (t) is calculated by the following equation (1).

θn (t) = (Vn−V _RTH ) × K1 (1) Here, K1 is a predetermined coefficient. The present retard change amount θn (t) calculated by the equation (1) is a predetermined allowable maximum value θ.
_RMAX1 is compared (step 51), and if it is _smaller than the predetermined allowable maximum value θ _RMAX1 , nothing is done to the step 54, and if it is larger, the predetermined allowable maximum value θ _RMAX1
(Step 52) and proceed to step 54. Rapidly changing the retard amount is not preferable in terms of drivability, and an upper limit is set to regulate this.

In step 54, the present retard amount θ _R (t) is calculated by the following equation (2).
Calculate with.

θ _R (t) = θ _R (t−1) + θ _n (t) (2) where θ _R (t−1) is the previous retard amount calculated when the program was executed last time, and the present retard amount Is a value obtained by adding the retard change amount θn (t) of this time to the previous retard amount θ _R (t−1).

Next, the routine proceeds to step 55, where it is judged if a predetermined time τ (for example, 0.2 to 1.0 seconds) has elapsed since the step 56 described later was executed. If the predetermined time τ has not elapsed, that is, if the determination result is negative, the process proceeds to step 58 without changing the present retard amount θ _R (t) set in step 54, and the determination result of step 55 Is affirmative,
After this much by subtracting this retard amount set theta from _{R (t)} predetermined minute retard amount [Delta] R _R re set this as a retard amount θ _{R (t)} in step 54, the process proceeds to step 58.

[theta] _R (t) = [theta] _R (t)-[Delta] _RR ... (3) In steps 58 to 61, the current retard amount [theta] _R set in this way is set.
It is determined whether (t) is within a predetermined range. That is,
In step 58, it is determined whether or not the upper limit value θ _RMAX2 or less, and in step 60, it is determined whether or not the lower limit value 0 or more. And
If the retard amount θ _R (t) exceeds the upper limit value θ _RMAX2 this time, the upper limit value θ _RMAX2 is _reset , and if it is lower than the lower limit value 0, the lower limit value 0 is reset (steps 59 and 61). Is stored in the storage device as a knock control amount θ _K.

θ _K = θ _R (t) (4) The electronic control unit 16 uses the knock control amount θ _K set as described above, and calculates the ignition timing θ _A by the following equation (5) (step 64). ).

θ _A = θ _B + θ _AT −θ _K (5) Here, θ _B is the basic ignition timing, and its setting method will be described later. θ _AT is a correction value set according to the intake air temperature Ta detected by the intake air temperature sensor 21, the engine cooling water temperature Tw detected by the engine water temperature sensor 23, and the like. FIG. 6 shows a relationship between the intake air temperature Ta and the correction value θ _AT when the correction value θ _AT is set only by the intake air temperature Ta, for example, and the intake air temperature Ta is equal to or lower than a predetermined temperature Tao (for example, −15 ° C.). in the case of,
Alternatively, when the temperature is equal to or higher than the predetermined temperature Ta1 (for example, 35 ° C.), the correction value θ _AT for advancing the ignition timing is set.

The basic ignition timing θ _B is set by the following equation (6).

θ _B = K _NK · θ _P + (1-K _NK ) · θ _R (6) where θ _P and θ _R are premium octane gasoline (hereinafter simply referred to as “RON 95”) and regular octane gasoline ( These are the ignition timings that are read out from the ignition timing maps prepared for "RON 91"). FIG. 7 shows an ignition timing map for RON 95 stored in the storage device of the electronic control unit 16, for example, using the known 4-point interpolation method, the engine speed Ne calculated and stored in the step 41. And the ignition timing θ _P corresponding to the intake air amount A / N is read out and calculated. The ignition timing map for RON 91 (not shown) is also shown in FIG.
The ignition timing map is similar to the ignition timing map for the engine, and the ignition timing θ _R corresponding to the engine speed Ne and the intake air amount A / N is read out from the ignition timing map for the RON 91 stored in the storage device in the same manner as the ignition timing θ _P. To be done. Straight, ignition timing map for RON 95 and
The values corresponding to the same engine speed Ne and intake air amount A / N in the ignition timing map for RON 91 are larger than the values read from the ignition timing map for RON 95. That is, it is set to a value on the more advanced side.

K _NK is a knock learning correction value, which is a learning correction value K _NK described later.
It is set to a value in the range of 0 to 1.0 by the setting routine.
As the value of this knock learning correction value K _NK increases, the basic ignition timing θ _B calculated by the equation (6) is closer to the value read from the ignition timing map for RON 95, that is, the value on the more advanced side. Will be set to.

The knock learning correction value K _NK is calculated and set by the learning correction value K _NK setting routine shown in FIG. 8, and the electronic control unit 16 first sets the knock learning correction precision K _NK to a new value in step 80 of FIG. It is determined whether or not the learning condition to be updated is satisfied. This learning condition is the engine
It is necessary for the operation of 10 to be stable and for the engine 10 to be operated in the knocking-prone operating region. Whether or not this learning condition is satisfied is determined by, for example, an engine water temperature sensor.
The cooling water temperature detected by 23 is a predetermined value (for example, 80
℃) or more, and the intake air amount A / N, throttle valve opening θt, engine speed Ne detected by the air flow sensor 14, the throttle sensor 19, the crank angle position sensor 22, etc.
From the above, it is determined whether or not the engine 10 is operating in a predetermined knocking operation region. If the above learning conditions are not satisfied, the routine is ended without doing anything.

On the other hand, when the determination result of step 80 is affirmative and the learning condition is satisfied, the routine proceeds to step 81, where the present retard amount θ _R (t) set in FIGS. 4 and 5 is equal to or more than the predetermined upper limit value θ _R2 . It is determined whether or not there is, and if the result of this determination is negative, the routine proceeds to step 83, where the retard amount θ
_R (t) is a predetermined lower limit value θ smaller than the predetermined upper limit value θ _R2
It is determined whether or not _R1 or less. When this determination result is also negative, that is, when the present retard amount θ _R (t) shows a value between the upper and lower limits (before the time t1 shown in FIG. 9A), the knock learning correction value K _NK is The routine is terminated without making any changes.

Knock occurred in the engine 10 and the retard amount θ this time
_{When R} (t) exceeds the predetermined upper limit value θ _R2, that is, when the determination result of step 81 is affirmative, the routine proceeds to step 82, where the determination result of step 81 is affirmative and the first execution from this step is performed. It is determined whether or not the predetermined integration time interval τ1 of 1 has elapsed. If the predetermined time interval τ1 has not yet passed, the knock learning correction value K _NK is not changed and the previous value is held. Then, if the state in which the determinations in steps 80 and 81 are both positive, continues,
The determination of 82 is repeatedly executed, and the routine proceeds to step 86 every time the predetermined time interval τ1 has elapsed, and the previous value of the knock learning correction value.
A value smaller than the previous value is subtracted from K _NK (t-1) to the first predetermined cumulative gain G _K1, and a new current knock learning correction value is set.
_Let K _NK (t) (between t1 and t2 in FIG. 9 (b)).

Then, again, the present retard amount θ _R (t) is the upper limit value θ.
When showing a value between _R2 and the lower limit value θ _R1 (shown in Fig. 9 (a))
Between time t2 and time t3), the knock learning correction value K _NK is again held at the previous value (between time t2 and time t3 shown in FIG. 9B). If the engine 10 continues to knock,
As described above, the present retard amount θ _R (t) is gradually reduced to a smaller value by being subtracted to the predetermined minute retard amount ΔR _R every predetermined time τ, and eventually falls to the predetermined lower limit value θ _R1 or less, and the step 81 The determination result of is negative, and the determination result of step 83 is affirmative.

If the determination result of step 83 is affirmative, the electronic control unit 16 executes step 84, and this time step 83
When the determination result of is positive and the step 84 is first executed, it is determined whether or not the second predetermined integration time interval τ2 has elapsed. If the predetermined time interval τ2 has not yet passed, the knock learning correction value K _NK is not changed and the previous value is held. Then, when the conditions in which the determination results of steps 80 and 83 are both positive and the determination result of step 81 is negative continue, the determination of step 84 is repeatedly executed, and step 88 is performed every time the predetermined time interval τ2 elapses. Then, the value of the previous knock learning correction value N _NK (t-1) is added to the second predetermined integrated gain G _K2 , and a value larger than the previous value is set as the new knock learning correction value K _NK (t). (Between t3 and t4 in FIG. 9 (b)). Then, when the present retard amount θ _R (t) again indicates a value between the upper limit value θ _R2 and the lower limit value θ _R1 (after time t4 shown in FIG. 9A), the knock learning correction value K _NK is again set. It is held at the previous value (after time t4 shown in FIG. 9B). Knock learning correction value K _NK
Is stored and stored in the above-mentioned nonvolatile RAM incorporated in the electronic control unit 16, and the stored value is retained even when the engine 10 is stopped.

FIG. 10 shows the retard amount θ _R (t) and the integrated time interval τ 1,
The relationship between τ2 and the integrated gains G _K1 and G _K2 is shown. In this embodiment, the absolute values of the integration gains G _K1 and G _K2 are set to the same value, and the integration time interval τ2 set when the retard amount θ _R (t) is the lower limit value θ _R1 or less is the upper limit value θ _R2. Is set to a value larger than the integration time interval τ1 set in the above case,
The correction gain is changed by setting the time interval for adding the integration gain G _K2 longer than the time interval for subtracting the integration gain G _K1 . Further, when the retard amount θ _R (t) is a value between the upper and lower limit values θ _R2 and θ _R1, there is a dead zone in which the knock learning correction value K _NK is held at the previous value, which improves the control stability. I am trying.

It should be noted that the method of changing the correction gain is not limited to the above-described embodiment, and if the integrated time intervals τ1 and τ2 are set to the same value and the G _K2 value of the integrated gain is set to a value smaller than the G _K1 value. For example, the same effect as described above can be obtained. Further, in the above embodiment, the dead zone is provided, and when the present retard amount θ _R (t) is a value between the predetermined upper and lower limit values θ _R2 and θ _R1 , the knock learning correction value K
_{Although NK} is retained, this dead zone may not be provided in some cases.

The initial value of the knock learning correction value K _NK described above is set by the switching position of the OSS 25 when the octane number select switch (OSS) 25 is switched. More specifically with reference to FIG. 11, the electronic control unit 16 first,
It is determined whether the OSS 25 is switched and the output of the OSS 25 is inverted (step 90). If the determination result is negative, the knock learning correction value K _NK is not rewritten and the current value is held. If the result of the determination in step 90 is affirmative, it is determined whether or not the OSS 25 is in the on state (step 91). If affirmative, that is, in the on state, the knock learning correction value K _NK is set to the initial value of the premium octane number. Set the value 1 which means that gasoline is used (step 92). on the other hand,
When the determination result of step 91 is negative, that is, when the OSS 25 is in the off state, the knock learning correction value K _NK is set to an initial value of 0, which means that regular octane gasoline is used (step 94). . The initial value of the knock learning correction value K _NK is stored in the nonvolatile RAM.

It should be noted that, in the determination in step 91 described above, when the on or off state continues for a predetermined time (for example, 1 second)
It may be determined that S25 is in the on or off state. or,
For example, if the non-volatile RAM battery backup line is removed during maintenance, the same OS as above is used when connecting the non-volatile RAM battery backup line.
The initial value of the knock learning correction value K _NK may be set by determining the on / off state of S25.

Thus, the basic addition timing θ _B is set to the optimum value for the property of the fuel used by the knock learning correction value K _NK .

Returning to step 64 in FIG. 5, the electronic control unit
16 outputs an ignition signal to the exciter 28 based on the ignition timing θ _A calculated and set as described above, and ignites the mixed cut at the crank angle position corresponding to the ignition timing θ _A.

Next, an air-fuel ratio control method according to the present invention will be described with reference to FIGS. 12 to 14. The flowchart of FIG. 12 shows the calculation procedure of the valve opening drive time T _INJ of the fuel injection valve 20, and the electronic control unit 16 first determines the air-fuel ratio by the knock control amount θ.
It is determined whether or not the vehicle is operating in an operating region in which the enrichment correction should be performed according to _K and the knock learning correction value K _NK (step 100). FIG. 13 shows the above-described enriched operation region. Whether the engine 10 is operating in this enriched operation region depends on whether the detected engine speed Ne is a predetermined number of revolutions.
It is determined whether the engine load is N _AFR or more and the engine load is a predetermined value or more.

When the engine 10 is operating in this rich operating region, the routine proceeds to step 101, where a deviation Δθ described below is set to a value 0, and when it is operating in the rich operating region, the routine proceeds to step 102 and the deviation is Δθ is calculated by the following equation (7) (step 102).

Δθ = θ _K + (θ _P −θ) −θ _AF (7) Here, θ _K is the knock control amount set in step 63 of FIG. 5 described above, and θ _P is the ignition timing map for RON95 described above. The read-out calculated ignition timing, θ _AF, is a predetermined threshold value. θ is a lead angle correction amount that reflects the knock learning correction value K _NK , and is obtained by the following equation (8) similar to the above equation (5).

θ = θ _B + θ _AT = K _NK · θ _P + (1-K _NK ) · θ _R + θ _AT (8) Therefore, in the above formula (7), (θ _P −θ) is set for premium octane gasoline. It represents the difference between the ignition timing θ _P and the ignition timing learning value θ that should actually be advanced. In the above formula (7), Δθ is set to 0 when Δθ becomes a negative number. That is, the Δθ value is set to 0 when the first and second terms (θ _K + (θ _P −θ)) on the right side of the equation (7) are smaller than the threshold θ _AF . This threshold θ _AF
Corresponds to the provision of a dead zone in which the air-fuel ratio is not corrected according to the ignition timing control amount.

Next, the electronic control unit 16 calculates the A / F correction coefficient K _AF by the following equation (9) (step 104).

K _AF = K _AFP + Δθ · K _AFK (9) where K _AFP is premium octane gasoline (RON9
It is the A / F correction coefficient that is read out and calculated from the A / F correction map prepared for 5). FIG. 14 shows the A / A for RON 95 stored in the storage device of the electronic control unit 16.
The F correction map is shown, and the engine speed Ne calculated and stored in step 41 of FIG. 4 is calculated using a known 4-point interpolation method.
And the A / F correction coefficient K _AFP corresponding to the intake air amount A / N is read out and calculated.

As can be seen from equations (7) to (9), the A / F correction coefficient K _AF
Is the A / F correction factor K _AFP applied to RON95 gasoline Δ
θ ・ K _AFK term is used for _enrichment correction, and Δθ ・
K _AFK term is the ignition timing θ _P applied to RON95 gasoline
Is set as a reference in accordance with the deviation between this value θ _P and the advance value θ corrected by the advance angle learning correction value and corrected by the intake air temperature Ta, and the knocking amount that changes in real time. Since it is set based on the value obtained by adding the knock control amount θ _K , the ignition timing set value is accurately corresponded. Therefore, the knock control amount θ _K , the knock learning correction value K _{NK, and the} like used for the ignition timing control can be directly applied to the air-fuel ratio control, and it is not necessary to recalculate the air-fuel ratio enrichment correction. Can be simplified.

As is clear from the equations (7) to (9), the A / F correction coefficient K _AF is the A / F correction coefficient K applied to gasoline for RON95.
Only the _AFP map needs to be stored in the storage device of the electronic control unit 16, and A / F for gasoline for RON91
It is not necessary to store the correction coefficient map separately,
Since only one correction coefficient map is required, the program required for the air-fuel ratio control can be made compact.

The A / F correction coefficient K _AF calculated by equation (9) is
The upper limit is checked by 106. That is, step 1
At 06, it is determined whether or not the A / F correction coefficient value K _AF is _{equal to} or higher than a predetermined upper limit value K _AFMAX.
The process proceeds to step 108 without changing the value of the A / F correction coefficient K _AF , and if it is more than that, the A / F correction coefficient value K _AF is _reset to the upper limit value K _AFMAX in step 107 and then the step 108 is _executed.
Proceed to.

In step 108, the valve opening drive time T _INJ of the fuel injection valve 20 is calculated by the following equation (10) using the A / F correction coefficient K _AF set as described above.

T _INJ = T _B · K _AF · K2 + Tb (10) Here, T _B is the basic drive time, and from the basic drive time map stored in the storage device ROM of the electronic control unit 16, the engine speed Ne and the intake air A read operation is performed according to the amount A / N. K2 is another correction coefficient such as engine cooling water temperature correction, O ₂ feedback correction, acceleration correction, etc.
Is an injection valve operation dead time correction value set according to the battery voltage or the like.

The electronic control unit 16 outputs a drive signal to the fuel injection valve 20 based on the valve opening drive time T _INJ thus calculated and injects into the engine 10 the fuel amount corresponding to the optimum air-fuel ratio for the retard amount of the ignition timing. Can be supplied.

Incidentally, in the above-mentioned embodiment, the A / F correction coefficient K _AF is a correction for enrichment of the A / F correction coefficient K _AFP applied to gasoline for _RON95 by the Δθ · K _AFK term. RON9
_{R based} on the ignition timing θ _R applied to gasoline for 1
Prepare the A / F correction map applied to gasoline for ON91,
The A / F correction coefficient K _AFR corresponding to the engine speed detection value Ne and the intake air amount detection value A / N is read from this map, and this A / F correction coefficient K _AFR is set to the value θ _R and the advance learning correction value. To reflect
Moreover, the lean correction may be performed by the value Δθ · K _AFK ′ according to the deviation from the advance angle value θ corrected by the intake air temperature Ta or the like.

(Effects of the Invention) As described in detail above, according to the air-fuel ratio control method for an internal combustion engine of the present invention, it is stored in advance in accordance with at least the engine speed and the engine load, and each of the first and second fuel properties is stored. The basic ignition timings are read out from the basic ignition timing maps shown in FIGS. 1 and 2 which are suitable for use with fuels having the following values, respectively, and knocks are generated from these two basic ignition timings. The ignition advance value is sequentially corrected according to the amount detection value, and at least according to the engine speed and the engine load, an air-fuel ratio correction map value suitable for use of the dye having the first fuel property is stored in advance, An air-fuel ratio correction value corresponding to the engine speed detection value and the engine load detection value is read from the air-fuel ratio control map value, and the air-fuel ratio correction value is read as the first basic ignition timing map. Is corrected according to the deviation between the basic ignition timing read according to the engine speed detection value and the engine load detection value from the corrected ignition advance value, and the fuel injection is performed according to the corrected air-fuel ratio correction value. Since the supply amount is corrected, even if various fuels with different properties are used, the optimum ignition timing is set for the properties of the fuel used, and at the same time, the fuel injection supply amount is optimized for the properties of the fuel. A value corresponding to the fuel ratio can be set, engine knock can be prevented, and an increase in exhaust gas temperature caused by retard of ignition timing can be reliably prevented. Further, the air-fuel ratio correction map need only be one corresponding to the fuel having the first fuel property, and the air-fuel ratio control program can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of an internal combustion engine control apparatus for carrying out the air-fuel ratio control method for an internal combustion engine according to the present invention, and FIG. 2 is a knock incorporated in the electronic control unit 16 shown in FIG. FIG. 3 is a block diagram showing the configuration of the detection circuit 16a, and FIG. 3 is a knock detection circuit 16a shown in FIG.
4 and 5 are timing charts for explaining the operation of the electronic control unit 16 shown in FIG.
FIG. 6 is a flowchart for explaining the ignition timing setting procedure, which is executed by the intake air temperature and ignition timing correction value θ _AT.
FIG. 7 is a graph showing the relationship between the basic ignition timing map for premium octane gasoline in which the basic ignition timing θ _P is read according to the engine speed Ne and the intake air amount A / N, and FIG. A flowchart of the correction value K _NK setting routine, FIG. 9 is a timing chart showing the relationship between the retard control amount θ _R (t) and the knock learning correction value K _NK , and FIG. 10 is the retard control amount θ _R (t ) And the cumulative time intervals τ1, τ2 and the cumulative gains G _K1 , G _K2 , FIG. 11 is a program flowchart showing the procedure for setting the initial value of the knock learning correction value K _NK , and FIG. 12 is the electronic control unit. 16 performed by the fuel injector 20
Is a flow chart for explaining the procedure for setting the valve opening drive time T _INJ , FIG. 13 is a graph showing the air-fuel ratio correction operation region,
FIG. 14 is a configuration diagram of a premium octane gasoline A / F correction map in which the A / F correction coefficient K _AFP is read according to the engine speed Ne and the intake air amount A / N. 10 …… Internal combustion engine, 14 …… Air flow sensor, 16 ……
Electronic control unit, 16a ... Knock detection circuit, 2
0 …… Fuel injection valve, 22 …… Crank angle position sensor, 25
...... Octane number select switch, 26 …… knock sensor, 28 …… igniter device, 30 …… spark plug, 33 …… noise level detector, 34 …… comparator, 35 …… integrator.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area F02P 5/153

Claims (3)

[Claims] 1. An ignition advance value is sequentially corrected according to a knock generation amount detected at every predetermined crank angle rotation of an internal combustion engine, and an ignition timing is electronically controlled based on the corrected ignition advance value. In the air-fuel ratio control method for an internal combustion engine, in which fuel is injected and supplied by a fuel injection valve, fuel having a first and a second fuel property stored in advance in accordance with at least the engine speed and the engine load. The basic ignition timings are read from the first and second basic ignition timing maps suitable for use in accordance with the engine speed detection value and the engine load detection value, respectively, and the knock generation amount detection value is determined from these two basic ignition timings. The ignition advance value is sequentially corrected accordingly, and is suitable when using the fuel having the first fuel property in accordance with at least the engine speed and the engine load. Previously stored air-fuel ratio correction map value,
From this air-fuel ratio correction map value, read the air-fuel ratio correction value according to the engine speed detection value and the engine load detection value,
The air-fuel ratio correction value is corrected according to the deviation between the basic ignition timing read from the first basic ignition timing map according to the engine speed detection value and the engine load detection value and the corrected ignition advance value. An air-fuel ratio control method for an internal combustion engine, wherein the fuel injection supply amount is corrected according to the corrected air-fuel ratio correction value. 2. The initial value of the ignition advance value is the first and second values.
2. The basic ignition timing read according to the engine speed detection value and the engine load detection value from a map artificially selected from the basic ignition timing map of FIG. An air-fuel ratio control method for an internal combustion engine as set forth. 3. The ignition advance value is set according to at least one of engine operating parameters including an intake air temperature and an engine cooling water temperature together with a knock generation amount. 2. An air-fuel ratio control method for an internal combustion engine according to claim 1.