JP2591006B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides an air-fuel ratio sensor (in this specification, an oxygen concentration sensor (O ₂ sensor)) on the upstream and downstream sides of a catalytic converter. O in addition the air-fuel ratio feedback control related to the air-fuel ratio control apparatus for an internal combustion engine which performs air-fuel ratio feedback control by the O ₂ sensor downstream by _two sensors.

[Conventional technology]

In simple air-fuel ratio feedback control (single O ₂ sensor system), an O ₂ sensor that detects oxygen concentration is provided at a point in the exhaust system as close as possible to the combustion chamber, that is, at the gathering portion of the exhaust manifold upstream of the catalytic converter. In addition, the variation in the output characteristics of the O ₂ sensor hinders the improvement of the air-fuel ratio control accuracy. Such O ₂ component variation variation and the fuel injection valve and the output characteristics of the sensor, to compensate for time or secular change, a second O ₂ sensor disposed downstream of the catalytic converter, by the upstream O ₂ sensor Downstream O ₂ in addition to air-fuel ratio feedback control
Double O ₂ with air-fuel ratio feedback control by sensor
Sensor systems have already been proposed (see:
-72647). In this double O ₂ sensor system,
O ₂ sensor provided downstream of the catalytic converter, compared with the upstream O ₂ sensor, but has a low response speed,
There is an advantage that the variation in output characteristics is small for the following reasons.

(1) Since the exhaust gas temperature is low downstream of the catalytic converter, there is little thermal effect.

(2) Downstream of the catalytic converter, various poisons are trapped in the catalyst, so that the amount of poisoning of the downstream O ₂ sensor is small.

(3) The exhaust gas is sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the exhaust gas is close to the equilibrium state.

Therefore, as described above, the air-fuel ratio feedback control based on the outputs of the two O ₂ sensors (double O ₂ sensor system), the variations in the output characteristic of the upstream O ₂ sensor can be absorbed by the downstream O ₂ sensor. Indeed, as shown in FIG. 2, the single O ₂ sensor system, when the output characteristic of the O ₂ sensor has deteriorated, compared to directly affect the exhaust emission characteristics, the double O ₂ sensor system, upstream even if the output characteristics of the side O ₂ sensor deteriorates, the exhaust emission characteristics are not deteriorated. That is, in the double O ₂ sensor system, good exhaust emissions are guaranteed as long as the downstream O ₂ sensor maintains stable output characteristics.

In the above-described double O ₂ sensor system, the required level related to the air-fuel ratio correction at the time of feedback control (hereinafter, “air-fuel ratio required level”) may be largely different from that at the time of non-feedback control. The following problem occurs at the time of starting the feedback in which the feedback control by the two O ₂ sensors is started. That is, in this case, usually, the air-fuel ratio feedback control speed by the downstream O ₂ sensor is set smaller than that in the air-fuel ratio feedback control speed by the upstream O ₂ sensor, air-fuel ratio feedback by the downstream O ₂ sensor It takes time for the air-fuel ratio control amounts controlled by the control, for example, the skip amounts RSR, RSL, to reach the required skip amount level, and, consequently, the air-fuel ratio reaches the required control level by the air-fuel ratio feedback control. It takes time, and as a result, insufficient correction occurs, which leads to deterioration of fuel efficiency, drivability, deterioration of emission, generation of catalyst exhaust odor, and the like.

Further, even during the air-fuel ratio feedback control, when the state of the engine transits to a different operating condition, the air-fuel ratio control level may also deviate from the air-fuel ratio required level, and in this case, insufficient correction occurs. This leads to deterioration of fuel economy, drivability, mission, deterioration of catalyst exhaust odor, and the like.

For example, due to the O ₂ storage effect of the catalyst, the gas amount is smaller in the low load area compared to the high load, the consumption of O ₂ stored in the catalyst is small, and the downstream O ₂ sensor has a longer time to indicate lean. As a result, the values of the air-fuel ratio control amounts RSR and RSL are shifted between the high load and the low load regions. This is particularly remarkable when a new catalyst having a large O ₂ storage effect is used. Therefore, when changing from the low load range to the high load range, the air-fuel ratio feedback cycle of the downstream O ₂ sensor is a relatively long time, so that the downstream O ₂ control delay occurs, the air-fuel ratio becomes over-rich, This leads to deterioration of emission and generation of catalytic odor.

For this reason, the applicant of the present application has already determined whether the load state of the engine, for example, the intake air amount, the intake air pressure, the throttle valve opening, the rotation speed, etc., belongs to any of the operating condition areas divided into a plurality of sections, When the load state of the engine belongs to the same operating condition area and the engine satisfies the learning condition,
The center value of the air-fuel ratio control amount is calculated, the center value of the air-fuel ratio control amount is stored for each operating condition area, and the operating conditions in which the engine state is different when the engine satisfies the air-fuel ratio feedback condition or after that are stored. At the point of transition to (1), block learning control using the air-fuel ratio control amount as the center value of the air-fuel ratio control amount stored in the current operation condition area is proposed (see Japanese Patent Application Laid-Open No. Sho 62-60941). According to this, downstream O
At the start of air-fuel ratio feedback control by _two sensors,
Starting from the central value of the stored air-fuel ratio control amount,
Thereafter, even when the state of the engine transits to a different operating condition area, the operation is started from the center value of the air-fuel ratio control amount stored for each operating condition.

Incidentally, the present applicant, instead of operating conditions region of the load state of the above engine, block the learning control by the operating condition region of the inversion cycle of the output of the upstream O ₂ sensor is also proposed (see JP 61-241484).

[Problems to be solved by the invention]

However, in the above-described block learning control of the load state of the engine based on the operating condition area, the load fluctuates greatly even though the reversal cycle of the downstream O ₂ sensor requires a relatively long time. Since the time immediately after the stepping-in and the stepping-out of the pedal are changed and kept in the same load area is short, sufficient learning cannot be performed. FIG. 3 shows the relationship between the load, for example, the intake / intake amount Q / Ne per revolution, and the required level of the rich skip amount RSR. As described above, at the time of transition or when the accelerator pedal is depressed and released frequently, the load greatly fluctuates, and the above-mentioned operation condition area changes drastically. However, for example, information on the period affected by the transient is required to be excluded from the learning value calculation, and when learning is performed, sufficient time is required to detect the center value of the air-fuel ratio indicated by the engine. For this reason, a state where learning cannot be performed occurs, and if a learning value is obtained in a short period of time, an accurate center value cannot be learned due to the influence of a transient.
As a result, after the feedback control starts and during the feedback control, when the state of the engine transits to a different condition, there is a problem that fuel economy, drivability, and emission deteriorate.

An object of the present invention is to provide a block learning control system that sufficiently prevents deterioration of fuel efficiency, drivability, emission, and the like.

[Means for solving the problem]

The means for solving the above-mentioned problem is shown in FIG. That is, in the exhaust passage upstream of the three-way catalyst CC _RO provided in the exhaust passage of the internal combustion engine, an upstream air-fuel ratio sensor for detecting the air-fuel ratio of the engine is provided.
A downstream air-fuel ratio sensor that detects an air-fuel ratio of the engine is provided in an exhaust passage downstream of the _RO . The air-fuel ratio feedback condition determining means determines whether the engine satisfies a predetermined air-fuel ratio feedback condition. As a result, when the engine satisfies the air-fuel ratio feedback condition, the air-fuel ratio control amount calculating means It calculates an air-fuel ratio control amount according to the output V ₂ of the downstream air-fuel ratio sensor. The learning condition determining means determines whether the engine satisfies a predetermined learning condition. The vehicle speed detecting means is a vehicle speed of a vehicle on which the engine is mounted.
The SPD is detected, and the vehicle speed region determining means determines whether the vehicle speed SPD belongs to any of the regions divided into a plurality of sections. As a result, when the vehicle speed SPD belongs to the same region and the engine satisfies the learning condition, the learning means calculates the center value of the air-fuel ratio control amount, and calculates the center value of the air-fuel ratio control amount for each region. To memorize. The air-fuel ratio adjusting means outputs the output V ₁ of the upstream air-fuel ratio sensor.
And the air-fuel ratio of the engine is adjusted according to the air-fuel ratio control amount.
When the engine satisfies the air-fuel ratio feedback condition or when the vehicle speed SPD transits to a different region thereafter, the air-fuel ratio control amount is set to the center value of the air-fuel ratio control amount stored in the current region. .

(Operation)

The operation of the above means will be described with reference to FIGS. FIG. 4A shows a required level of the rich skip amount RSR when the vehicle speed SPD is kept constant within about one minute. That is, the vehicle speed SPD is a parameter that well represents the load, and the low speed region indicates a region where fuel cut is frequently used. Therefore, the fourth
As shown in the figure, O ₂ due to fuel cut by vehicle speed SPD
The shift of the rich skip amount RSR due to the storage effect can be obtained. FIG. 4B shows a required level of the rich skip amount RSR when the vehicle speed SPD is kept constant for 2 minutes or more. In this case, if the vehicle is driven at a constant speed for 2 minutes or more, the O ₂ stored in the catalyst at the time of fuel cut is consumed. Therefore, the deviation amount of the rich skip amount RSR between the low speed (low load) region and the high speed (high speed load) region becomes small. FIG. 5 is a diagram showing a problem with respect to learning control due to a change in vehicle speed SPD and load, and a difference between vehicle speed SPD and load Q / Ne. As shown in FIG. 5, when the area is divided by the load, in the area change due to the fluctuation of the load (the load fluctuates because the accelerator is depressed and depressed to maintain a constant speed), for example, the learning time is sufficient in the section T. Although it cannot be taken (causes erroneous learning), the fluctuation of the vehicle speed SPD is small and sufficient learning time can be taken, so that the rich skip amount RSR has a small difference between low speed and high speed as shown in FIG. 4B, and erroneous learning can be prevented. . In this manner, according to the block learning control based on the vehicle speed driving condition area, the number of area divisions can be reduced.

〔Example〕

FIG. 6 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 6, an air flow meter 3 is provided in an intake passage 2 of an engine body 1. The air flow meter 3 directly measures the amount of intake air, and has a built-in potentiometer to generate an analog voltage output signal proportional to the amount of intake air. This output signal is supplied to the A / D converter 101 with built-in multiplexer of the control circuit 10. Distributor 4 has
For example, a crank angle sensor 5 which generates a reference position detecting pulse signal every 720 ° when converted into a crank angle and a crank angle sensor which generates a reference position detecting pulse signal every 30 ° when converted into a crank angle 6 are provided. The pulse signals of the crank angle sensors 5 and 6 are supplied to an input / output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to an interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to an intake port for each cylinder.

The water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of the cooling water. The water temperature sensor 9 detects the temperature THW of the cooling water.
Generates an electric signal of an analog voltage corresponding to. This output is also supplied to the A / D converter 101.

The exhaust system downstream of the exhaust manifold 11, a catalytic converter 12 is provided to accommodate the three harmful components HC in the exhaust gas, CO, a three-way catalyst that simultaneously purifies NO _X.

The exhaust manifold 11 includes a catalytic converter 12
A first O ₂ sensor 13 is provided on the upstream side, and a second O ₂ sensor 15 is provided on the exhaust pipe 14 downstream of the catalytic converter 12. The O ₂ sensors 13 and 15 generate an electric signal corresponding to the concentration of the oxygen component in the exhaust gas. That is, the O ₂ sensor 1
A / D converters 3 and 15 output different output voltages using the control circuit 10A depending on whether the air-fuel ratio is leaner or richer than the stoichiometric air-fuel ratio.
Occurs at 101.

Reference numeral 18 denotes a vehicle speed sensor such as a permanent magnet and a reed switch, the output of which is sent to a vehicle speed forming circuit 111 of the control circuit 10.

The control circuit 10 is configured as a microcomputer, for example, and includes an A / D converter 101, an input / output interface 10
2. In addition to the CPU 103 and the vehicle speed forming circuit 111, a ROM 104, a RAM 105, a backup RAM 106, a clock generating circuit 107, and the like are provided.

In the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110
Is to control the That is, when the fuel injection amount TAU is calculated in a routine described later, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts a clock signal (not shown) and the carry-out terminal finally becomes "1" level, the flip-flop 109 is set and the drive circuit 110 sets the fuel injection valve 7 Stop energizing. That is, the fuel injection valve 7 is energized by the above-described fuel injection amount TAU, so that fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

Note that the CPU 103 generates an interrupt when the A / D conversion of the A / D converter 101 ends, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6,
When an interrupt signal from 7 is received, and so on.

The intake air amount data Q and the cooling water temperature data THW of the air flow meter 3 are fetched by an A / D conversion routine executed every predetermined time and stored in a predetermined area of the RAM 105.
That is, the data Q and THW in the RAM 105 are updated every predetermined time. The rotation speed data Ne is calculated by an interrupt every 30 ° CA of the crank angle sensor 6 and is calculated by RA
It is stored in a predetermined area of M105.

Figure 7 is a first air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF based on the output of the upstream O ₂ sensor 13 is executed at a predetermined time, for example, 4ms each.

In step 701, the air-fuel ratio of the closed loop by the upstream O ₂ sensor 13 (feedback) condition is determined whether or not satisfied. For example, when the cooling water temperature is equal to or lower than a predetermined value, during engine start, during increase after start, during warm-up, during power increase,
During OTP boost for the catalyst overheat prevention, when the output signal of the upstream O ₂ sensor 13 is not also inverted once, also a closed loop condition any fuel cut secondary is is not satisfied, otherwise it is a closed loop condition is satisfied. When the closed loop condition is not satisfied, the routine proceeds to step 727, where the air-fuel ratio correction coefficient FAF is set to 1.0. Note that FAF may be set to a value immediately before the end of the closed loop control. In this case, proceed directly to step 728. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 702.

In step 702, capture, is V ₁ at step 703 to determine whether the comparison voltage V _R1 for example 0.45V below the output V ₁ of the upstream O ₂ sensor 13 as the A / D conversion, i.e., the air-fuel ratio is rich or lean to determine, that is, if the air-fuel ratio is lean (V ₁ ≦ V _R1), the delay counter CDLY is to determine positive or not at step 704, if CDLY> 0 step
At 705, CDLY is set to 0, and the routine proceeds to step 706. Step 70
In step 6, the delay counter CDLY is decremented by 1 and step 70
At 7,708, guard the delay counter CDUY with the minimum value TDL. In this case, when the delay counter CDLY reaches the minimum value TDL, in step 709, the first air-fuel ratio flag F1
To “0” (lean). In addition, the minimum value TDL is the upstream O ₂
This is a lean delay state for maintaining the determination of the rich state even when the output of the sensor 13 changes from rich to lean, and is defined by a negative value. On the other hand, if rich (V ₁ > V _R1 ), it is determined at step 710 whether or not the delay counter CDLY is negative.
At 711, CDLY is set to 0, and the routine proceeds to step 712. Step 71
In step 2, the delay counter CDLY is incremented by 1, and steps 713 and 7
At 14, guard the delay counter CDLY with the maximum value TDR. In this case, when the delay counter CDLY reaches the maximum value TDR, the first air-fuel ratio flag F1 is determined in step 715.
To “1” (rich). Note that the maximum value TDR is the upstream O ₂
This is a rich delay time for maintaining the determination of the lean state even when the output of the sensor 13 changes from lean to rich, and is defined as a positive value.

In step 716, it is determined whether or not the sign of the first air-fuel ratio flag F1 has been inverted, that is, whether or not the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is inverted, it is determined in step 717 whether the air-fuel ratio is inverted from rich to lean or from lean to rich, based on the value of the first air-fuel ratio flag F1. In the case of inversion from rich to lean, in step 718, FAF ← FAF + RSR is increased in a skipping manner. Conversely, in the case of inversion from lean to rich, in step 719, FAF ← FAF−RSL is skipped. Decrease.
That is, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted at step 712, the integration processing is performed at steps 720, 721, and 722. That is, in step 720, it is determined whether or not F1 = "0". If F1 = "0" (lean), the FAF is determined in step 721.
← FAF + KIR. On the other hand, if F1 = “1” (rich), in step 722, FAF ← FAF−KIL. Where the integration constant KI
R and KIL are set sufficiently smaller than the skip amounts RSR and RSL, that is, KIR (KIL) <RSR (RSL). Therefore, step 721 gradually increases the fuel injection amount in the lean state (F1 = "0"), and step 722 sets the rich state (F1 =
In “1”), the fuel injection amount is gradually reduced.

The air-fuel ratio correction coefficient FAF calculated at steps 718, 719, 721, 722 is guarded at steps 723, 724 at a minimum value, for example, 0.8, and at steps 725, 726, at a maximum value, for example.
Guarded at 1.2. Thus, if the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled with that value to prevent over-rich or over-lean.

The FAF calculated as described above is stored in the RAM 105, and this routine ends in step 728.

FIG. 8 is a timing chart for supplementarily explaining the operation according to the flowchart of FIG. Rich As shown in Figure 8 by the output of the upstream O ₂ sensor 13 (A), when the air-fuel ratio A / F is obtained, the delay counter CDLY is
As shown in FIG. 8 (B), the count is incremented in the rich state and is counted down in the lean state. As a result, as shown in FIG. 8 (C), a delayed air-fuel ratio signal A / F '(corresponding to the flag F1) is formed. For example, 'also is changed from lean to rich, the air-fuel ratio signal A / F which is delayed processed' air-fuel ratio signal A / F at time t ₁ is the time t ₂ after being held lean only the rich delay time TDR It changes richly at. Also the air-fuel ratio signal A / F from the rich at time t ₃ is changed to the lean, the delayed air-fuel ratio signal A /
F 'is changed to the lean at time t ₄ after being held rich only equivalent lean delay time (-TDL). However, when the air-fuel ratio signal A / F ′ is inverted during a short period of the rich delay time TDR as at times t ₅ , t ₆ , and t ₇ , the delay counter CDLY reaches the maximum value TD.
Takes time to reach the R, Consequently, the air-fuel ratio signal A / F after the delay is reversed at time t _8. That is, the air-fuel ratio signal A / F ′ after the delay processing is the air-fuel ratio signal A / F ′ before the delay processing.
Stable compared to / F. In this way, the air-fuel ratio correction coefficient FAF shown in FIG. 8D is obtained based on the stable air-fuel ratio signal A / F 'after the delay processing.

Next, a description will be given of the second air-fuel ratio feedback control by the downstream O ₂ sensor 15. As the second air-fuel ratio feedback control, the skip amounts RSR, RSL, the integration constants KIR, KIL, the delay times TDR, TDL, or the output V ₁ of the upstream O ₂ sensor 13 as the first air-fuel ratio feedback control constant are determined. There are a system that makes the comparison voltage V _R1 variable, and a system that introduces the second air-fuel ratio correction coefficient FAF2.

For example, if the rich skip amount RSR is increased, the control air-fuel ratio can shift to the rich side, and even if the lean skip amount RSL is reduced, the control air-fuel ratio can shift to the rich side, while the lean skip amount RSL increases. Then, the control air-fuel ratio can be shifted to the lean side, and even if the rich skip amount RSR is reduced, the control air-fuel ratio can be shifted to the lean side. Accordingly, the air-fuel ratio can be controlled by correcting the rich skip amount RSR and the lean skip amount RSR in accordance with the output of the downstream O ₂ sensor 15. Also, the rich integration constant KIR
By increasing the control air-fuel ratio, it is possible to shift the control air-fuel ratio to the rich side, and even if the lean integration constant KIL is reduced, the control air-fuel ratio can be shifted to the rich side. The control air-fuel ratio can shift to the lean side even when the rich integration constant KIR is reduced. Accordingly, the air-fuel ratio can be controlled by correcting the rich integration constant KIR and the lean integration constant KIL in accordance with the output of the downstream O ₂ sensor 15. Rich delay time TDR
> Lean delay time (-TDL), the control air-fuel ratio can shift to the rich side. Conversely, the lean delay time (-TDL)
If L)> rich delay time (TDR) is set, the control air-fuel ratio can shift to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay time TDR, the TDL in accordance with the output of the downstream O ₂ sensor 15. Furthermore, it shifts the control air-fuel ratio by increasing the comparison voltage V _R1 to the rich side, also, possible shifts the control air-fuel ratio by decreasing the reference voltage V _R1 to the lean side. Therefore, according to the output of the downstream O ₂ sensor 15, the comparison voltage
The air-fuel ratio can be controlled by correcting _VR1 .

These skip amount, integration constant, the delay time, to a variable comparison voltage by the downstream O ₂ sensor has an advantage in, respectively. For example, the delay time enables very delicate arbitration of the air-fuel ratio, and the skip amount enables control with good response without extending the feedback cycle of the air-fuel ratio unlike the delay time. Therefore, these variable amounts can be used in combination of two or more.

Next, a description will be given double O ₂ sensor system in which the skip amounts as an air-fuel ratio feedback control constant to a variable.

Figure 9 is skip amount based on the output of the downstream O ₂ sensor 15 RSR, a second air-fuel ratio feedback control routine for calculating the RSL, is executed at predetermined time, for example 152ms. In step 901 to 905, it is determined whether or not the closed loop condition by the downstream O ₂ sensor 15. For example, downstream O ₂
Failure of closed loop condition by sensor 13 (step 901)
In addition, when the cooling water temperature THW is equal to or lower than a predetermined value (for example, 70 ° C.) (step 902), the throttle valve 16 is fully opened (LL =
“1”) (step 903), and light load (Q / Ne <X
₁₎ (step 904), when the downstream O ₂ sensor 15 is not activated (step 905) and the closed loop condition is not satisfied, otherwise it is a closed loop condition is satisfied. If it is not a closed loop condition, the process proceeds to steps 928 and 929.

If the closed loop condition is satisfied, the process proceeds to step 906. That is, the vehicle speed SPD data SP
D is taken and n ← SPD / ΔSPD where ΔSPD is a constant value. Note that n is an integer, and the decimal part of SPD / ΔSPD is rounded down. In this way, the vehicle speed SPD It is determined whether or not it belongs to any one of. Step 90
The vehicle speed SPD at 6 may be the average value.

In step 907, it is determined whether or not the current operation condition area n is the same as the previous operation condition area no. If they are the same (n = no), the process proceeds to step 908.

On the other hand, when the region n of the vehicle speed SPD is shifted or when the closed loop is not satisfied by the downstream O ₂ sensor 15, the process proceeds to step 928 and 929, the rich skip amount RSR and the lean skip amount RSL, the learned value of the corresponding area n RSRG (n ) And RSLG (n).

In step 908, takes in the output V ₂ of the downstream O ₂ sensor 15 is converted A / D, V ₂ at step 909 it is determined whether or not the comparison voltage V _R2 eg 0.55V or less. That is, it is determined whether the air-fuel ratio is rich or lean. The comparison voltage V _R2 is determined by comparing the upstream O ₂ with the comparison voltage V _R1 of the output of the sensor 13 in consideration of the difference in output characteristics due to the influence of raw gas and the deterioration rate at the upstream and downstream of the catalytic converter 14. Set higher. As a result, if V ₂ ≦ VR ₂ (lean), the second air-fuel ratio flag F2 is set to “0” in step 910, while V 2
_{If 2} > _VR2 (rich), the second air-fuel ratio flag F2 is set to "1" in step 911. Next, in step 912, it is determined whether or not the second air-fuel ratio flag F2 has been inverted. At a result, if the inverted or learning condition is satisfied (the learning execution flag F _G = "1") at step 913 whether determined, if the learning condition is satisfied step 914 Perform learning control. The learning execution flag F _G and learning steps
914 will be described later.

In step 915, it is determined whether or not the second air-fuel ratio flag F2 is "0". As a result, if F2 = "0" (lean), the process proceeds to steps 916 to 921, while F2 = "1" ( If it is rich, the process proceeds to steps 922 to 927.

In step 916, RSR ← RSR + ΔRS (a constant value, for example,
0.08%), that is, the air-fuel ratio is shifted to the rich side by increasing the rich skip amount RSR. Step 917,918
Then, the RSR is guarded at the maximum value MAX, for example, 7.5%.
Further, at step 919, RSL ← RSL−ΔRS, that is, the rich skip amount RSL is reduced to shift the air-fuel ratio to the rich side. In steps 920 and 921, the RSL is set to the minimum value MI.
Guard at 2.5% N, for example.

On the other hand, when F2 = "1" (rich), step 922
RSR ← RSL−ΔRS, that is, the rich skip amount RS
R is decreased to shift the air-fuel ratio to the lean side. In steps 923 and 924, the RSR is guarded at the minimum value MIN. Further, at step 925, RSL ← RSL + ΔRS, that is, the lean skip amount RSL is increased to shift the air-fuel ratio to the lean side. In steps 926 and 927, the RSL is guarded at the maximum value MAX.

In step 930, the area n is set to n _O in preparation for the next execution.

After the RSR and RSL calculated as described above are stored in the RAM 105, the routine ends in step 930.

Next is a description of a 9 learning execution flag of Figure F _G and learning control step 914.

Figure 10 is a routine for setting a learning execution flag F _G, is executed at predetermined time, for example 512ms or a predetermined crank angle for example, every 180 ° CA. Step 100
Steps 1 to 1005 are the same corresponding to steps 901 to 905 in FIG. 9, respectively, but differ only in step 1002. That is,
In step 1002, it is determined whether the cooling water temperature THW is within a predetermined range, for example, 70 ° C <THW <90 ° C. That is, a stable cooling water temperature is determined.

The process proceeds to step 1006 only when all the conditions of steps 1001 to 1005 are satisfied.

In step 1006, it is determined whether or not the variation ΔQ of the intake air amount data Q per time or crank angle is less than a constant value A. As a result, when ΔQ ≧ A, the counter C _ΔQ is cleared in step 1009, Delta] Q <when a is a counter C _{Delta] Q} is incremented at step 1007, C _{Delta] Q} in step _1008> flag F _G learning executed in viewing step 1010 when the B (constant value) to "1", otherwise, the learning execution flag F _G in step 1011 to "0". Note that the counter C _ΔQ is guarded at a certain maximum value. Then, this routine ends in step 1012.

As described above, under the condition that the air-fuel ratio feedback control by the upstream O ₂ sensor 13 and the air-fuel ratio feedback control by the downstream O ₂ sensor 15 are performed,
Limiting the conditions by THW, only as "1" to the learning execution flag F _G, so that the learning control is executed when the addition amount of intake air change ΔQ is a constant value A is smaller than a stable state was maintained constant time .

FIG. 11 is a detailed flowchart of the learning step 914 in FIG. This routine, as described above, the output signal of the downstream O ₂ sensor 15 which is delayed by a when inverted, is executed when the learning condition is satisfied. In this learning step, a learning value is calculated for each area n and stored in the backup RAM 106 as shown in the table below.

In step 1101, the average value of the current rich skip amount RSR and the previous rich skip amount RSRO is calculated, ie, ▲ ▼ ← (RSR + RSRO) / 2, and in step 1102, the rich skip of the current region n is calculated. The quantity learning value RSRG (n) is calculated by the average value ▲ ▼. That is, And Then, in step 1103, the learning value RSRG (n)
Is stored in the corresponding area of the backup RAM 106.

Similarly, in step 1104, the current lean skip amount RS
Average value of L and previous lean skip amount RSLO ▲ ▼
Is calculated, that is, ▲ ▼ ← (RSL + RSRO) / 2, and in step 1105, the learning value RSLG (n) of the lean skip amount of the current area n is calculated as the average value ▲ ▼. That is, And Then, at step 1106, the learning value RSRG (n)
Is stored in the corresponding area of the backup RAM 106.

In steps 1107 and 1108, RSR is set to RSRO in preparation for the next execution.
The RSL is set to RSLO, and this routine ends in step 1109.

FIG. 12 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360 ° CA. In step 1201, the intake air amount data Q and the rotational speed data Ne are read from the RAM 105 to calculate the basic injection amount TAUP. For example
TAUP ← α · Q / Ne (α is a constant). In step 1202
The cooling water temperature data THW is read from the RAM 105, and the warm-up increase value FWL is calculated by interpolation using a one-dimensional map stored in the ROM 104. As shown in the figure, the warm-up increase value FWL is set so as to decrease as the current cooling water temperature THW increases. In step 1203, the final injection amount TAU is calculated from TAU ← TAUP · FAF · (FWL + β) + γ.
Here, β and γ are correction amounts determined by other operating state parameters, for example, correction amounts determined by a signal from a throttle position sensor (not shown), a signal from an intake air temperature sensor, a battery voltage, and the like.
It is stored in M105. Next, in step 1204, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 1205, this routine ends. As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carry-out signal of the down counter 108, and the fuel injection ends.

FIG. 13 is a timing chart showing an example of the rich skip amount RSR and the lean skip amount RSL obtained from FIG. 9, FIG. 10, and FIG. In FIG. 13, it is assumed that the air-fuel ratio feedback control by the downstream O ₂ sensor starts at time t _O. At this time, when the vehicle speed SPD changes as shown in FIG. 13 (B), the area n also changes, and accordingly, the required level of the rich skip amount RSR and the lean skip amount RSL also changes from the required level I → the required level II → the required level. Level III
→ It changes as required level IV. As a result, the rich skip amount RSR and the lean skip amount RSL are feedback-controlled so as to approach each required level. Further, the learning control is executed in each of the learning periods I, II, III, and IV, and the learning values of the rich skip amount RSR and the lean skip amount RSL are obtained.
RSRG and RSLG updates are performed. Here, the required level I and the required level III belong to the same vehicle speed region n = k,
Required level III and required level IV are in the same vehicle speed area n = k
At the transition point from the required level II to the required level III, the rich skip amount RSR and the lean skip amount RSL are the learning values RSRG (k) and RSLG (k) obtained in the learning period I. Using the initial value, at the transition point from requirement level III to requirement level IV,
The rich skip amount RSR and the lean skip amount RSL are the learning values RSRG (k + 1) and RS obtained in the learning period II.
LG (k + 1) uses the initial value. Therefore, even during the air-fuel ratio feedback control, the rich skip amount RSR and the lean skip amount RSL immediately approach the required levels even if the inversion cycle region transitions. Of course, even when a transition from the open control in the air-fuel ratio feedback control by the downstream O ₂ sensor 15, since using a learned value belonging to the corresponding region as the rich skip amount RSR and the lean skip amount RSL, the rich skip amount RSR and the lean skip amount The RSL will soon approach the required level.

Incidentally, essential as conventional, even vehicle speed region is changed, changing the air-fuel ratio feedback control by the downstream O ₂ sensor 15 rich skip amount RSR and the lean skip amount RSR, the time to reach the required level And the arrow D ₁ , D
_As shown in FIG. ₂ , a control delay occurs, which leads to deterioration of fuel efficiency, drivability, emission, and the like.

In addition, it is not necessary to divide each vehicle speed area at equal intervals by the fixed value ΔSPD, and may be unequal interval divisions.

Further, as described above, in the block learning control based on the vehicle speed SPD, as shown in FIGS. 4 and 5, the required level of the air-fuel ratio control amount, for example, the rich skip amount RSR, changes little in accordance with the vehicle speed SPD. In consideration of the case where a catalyst having a large O ₂ storage effect is used, the number of regions of the vehicle speed SPD can be set to two. For example, it is divided into a low vehicle speed region (SPD ≦ 50 km / h) and a high vehicle speed region (SPD> 50 km / h). In this case, in FIG.
Steps 1401, 1402, and 1403 shown in FIG. 14A are used instead of, and step 1404 shown in FIG. 14B is used instead of step 930. In this case, FIG. 13 becomes as shown in FIG.

Further, in the above-described embodiment, the case where one catalytic converter is provided in the exhaust system is shown. However, the present invention is applicable to the case where two catalytic converters 121 and 122 shown in FIG.
The present invention is also applicable to a case having three catalytic converters 121a, 122b, 122 shown in FIG. In this case, the downstream O ₂ sensor 15
Is provided at any of the positions P1, P2, and P3 in FIG. 16 and at any of the positions P4 and P5 in FIG. In such a case where a plurality of catalytic converters, the influence of the O ₂ storage effect in response to a position downstream O ₂ sensor is provided,
For example, as shown in FIG. 18, it is greatly different, and the present invention is effective when such an O ₂ storage effect is large.

Also, the first air-fuel ratio feedback control is performed every 4 ms,
Also, the second air-fuel ratio feedback control is performed every 512 ms because the air-fuel ratio step feedback control is mainly performed by the upstream O ₂ sensor having good responsiveness, and the downstream O ₂ sensor having poor responsiveness. This is for performing the control according to.

Further, other control constants in the air-fuel ratio feedback control by the upstream O ₂ sensor, such as a delay time, an integration constant, and a comparison voltage of the upstream O ₂ sensor (refer to Japanese Patent Laid-Open No. 55-3756)
The present invention can also be applied to a double O ₂ sensor system that corrects the output of the downstream O ₂ sensor or the like, or a double O ₂ sensor system that introduces a second air-fuel ratio correction coefficient.

Further, instead of an air flow meter, a Karman vortex sensor, a heat wire sensor, or the like can be used as the intake air amount sensor.

Further, in the above-described embodiment, the fuel injection amount is calculated according to the intake air amount and the engine speed. However, the fuel injection amount is calculated according to the intake air pressure and the engine speed, or the throttle valve opening and the engine speed. The fuel injection amount may be calculated.

Further, in the above-described embodiment, the internal combustion engine in which the fuel injection valve controls the fuel injection amount to the intake system is described. However, the present invention can be applied to a carburetor-type internal combustion engine. For example, one that controls the air-fuel ratio by adjusting the intake air amount of the engine with an electric air control valve (EACV),
Electric bleed air control valve adjusts the air bleed amount of the carburetor to control the air-fuel ratio by introducing air into the main passage and the slow passage, and controls the amount of secondary air sent to the exhaust system of the engine. The present invention can also be applied to a device to be adjusted. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 1201 is determined by the carburetor itself, that is, determined in accordance with the intake pipe negative pressure according to the intake air amount and the engine speed, and step 1203. At the final fuel injection amount TAU
Is calculated.

Furthermore, in the above-described embodiment, the O ₂ sensor is used as the air-fuel ratio sensor, but a CO sensor, a lean mixture sensor, or the like may be used.

Further, although the above-described embodiment is constituted by a microcomputer, that is, a digital circuit, it may be constituted by an analog circuit.

〔The invention's effect〕

As described above, according to the present invention, since the variation of the learning area is reduced by adopting the block learning control using the vehicle speed as a parameter, it is possible to perform sufficient learning in each area,
As a result, it is possible to prevent deterioration of fuel consumption, drivability, emission, catalyst exhaust odor, and the like.

[Brief description of the drawings]

FIG. 1 is an overall block diagram for explaining the configuration of the present invention, FIG. 2 is an exhaust emission characteristic diagram for explaining a single O ₂ sensor system and a double O ₂ sensor system, and FIG. 3 is a conventional air-fuel ratio control amount. 4A and 4B are graphs showing the required level of the air-fuel ratio control amount according to the present invention, FIG. 5 is a timing chart explaining the problem of the present invention, and FIG. 6 is the present invention. FIG. 7, FIG. 9, FIG. 10, FIG. 11, and FIG. 12 are diagrams for explaining the operation of the control circuit shown in FIG. 6, showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. 8, FIG. 8 is a timing chart for supplementary explanation of the flowchart of FIG. 7, FIG. 13 and FIG. 15 are timing charts for explaining the effect of the present invention, FIG. 14A, FIG. FIG. 16 is a flowchart showing a modification example of FIG. 9, and FIG. FIG. 18 is a layout diagram of a catalytic converter showing a modified example of the diagram. FIG. 18 is a graph showing the degree of influence of the O ₂ storage effect at each position in FIG. 1 ...... engine body, 3 ...... air flow meter, 4 ...... distributor, 5,6 ...... crank angle sensor, 10 ...... control circuit, 12 ...... catalytic converter, 13 ...... upstream O ₂ sensor, 15 ...... downstream O ₂ sensor, 17 ...... idle switch.

Claims (4)

(57) [Claims] A three-way catalyst provided in an exhaust passage of an internal combustion engine; and an upstream air-fuel ratio sensor provided in an exhaust passage upstream of the three-way catalyst for detecting an air-fuel ratio of the engine. 13), a downstream air-fuel ratio sensor (15) provided in an exhaust passage downstream of the three-way catalyst and detecting an air-fuel ratio of the engine, and whether the engine satisfies a predetermined air-fuel ratio feedback condition. Air-fuel ratio feedback condition determining means for determining whether or not the air-fuel ratio control amount is calculated according to the output of the downstream air-fuel ratio sensor when the engine satisfies the air-fuel ratio feedback condition. Computing means; learning condition determining means for determining whether or not the engine satisfies predetermined learning conditions; vehicle speed detecting means for detecting a vehicle speed of a vehicle on which the engine is mounted; Area divided into A vehicle speed region determining means for determining whether the vehicle belongs to the same region, and calculating a center value of the air-fuel ratio control amount when the engine belongs to the same region and the engine satisfies the learning condition. Learning means for storing a central value of the control amount for each of the regions; and air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the output of the upstream air-fuel ratio sensor and the air-fuel ratio control amount. When the engine satisfies the air-fuel ratio feedback condition or when the vehicle speed transitions to a different region thereafter, the internal combustion engine uses the air-fuel ratio control amount as a central value of the air-fuel ratio control amount stored in the current region. Engine air-fuel ratio control device. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the number of sections is two. 3. The internal combustion engine according to claim 1, wherein the air-fuel ratio control amount is set to a center value of the air-fuel ratio control amount stored in a current area even when the engine does not satisfy the air-fuel ratio feedback condition. Air-fuel ratio control device. 4. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein said vehicle speed is an average value.