JPS63117139A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent offensive smell of exhaust gas, by employing a control constant corresponding to a second O2 sensor arranged in the downstream of a catalyst, and controlling the air-fuel ratio to the lean side for a predetermined time if the second O2 sensor is rich during fuel increment, when feedback control is made through a first O2 sensor arranged in the upstream of the catalyst. CONSTITUTION:A control circuit 10 operates such as rich skip quantity, lean skip quantity corresponding to a value detected through a second O2 sensor 15 arranged in the downstream of a catalyst converter 12, so as to make feedback control of air-fuel ratio corresponding to the operating condition based on said control constant and a value detected through a first O2 sensor 13 arranged in the upstream of the catalyst converter 12. When synchronous increment is carried out during acceleration and the output from the second O2 sensor 15 exhibits rich, control to lean side is carried out for a predetermined time based on a value detected through the first O2 sensor 13 thereafter reset control to a theoretical air-fuel ratio is carried out.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides air-fuel ratio sensors (herein, oxygen concentration sensors (Ot sensors)) on the upstream and downstream sides of a catalytic converter.
), and relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using a downstream Ot sensor in addition to air-fuel ratio feedback control using an upstream 0□ sensor.

[Conventional technology]

In simple air-fuel ratio feedback control (single 0 sensor system), the Ot sensor that detects oxygen concentration is installed at a location in the exhaust system as close to the combustion chamber as possible, that is, at the collection point of the exhaust manifold upstream of the catalytic converter. Due to variations in the output characteristics of the 0□ sensor, it is difficult to improve the control accuracy of the air-fuel ratio. It takes 0
In order to compensate for variations in the output characteristics of the two sensors, variations in parts such as fuel injection valves, and changes over time or aging, a second 0□ sensor is provided downstream of the catalytic converter.
A double 0□ sensor system that performs air-fuel ratio feedback control using a downstream 0□ sensor in addition to air-fuel ratio feedback control using a downstream Ot sensor has already been proposed (see Japanese Patent Laid-Open No. 58-48756). In this tuple 0□ sensor system, the 0□ sensor provided downstream of the catalytic converter has a
Although it has a low response speed, it has the advantage of small variations in output characteristics for the following reason.

(1) Downstream of the catalytic converter, the exhaust gas temperature is low, so there is little thermal influence.

(2) Since various poisons are trapped in the catalyst downstream of the catalytic converter, the amount of poisoning of the downstream 0□ sensor is small.

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

Therefore, as mentioned above, the upstream side 0. Variations in sensor output characteristics can be absorbed by the downstream Oz sensor. In fact, as shown in Figure 2, in a single Ot sensor system, 0□
If the output characteristics of the sensor deteriorate, it will directly affect the exhaust emission characteristics, but with the double 02 sensor system, even if the output characteristics of the upstream 0□ sensor deteriorate,
Exhaust emission characteristics are not deteriorated. That is, double 0
In a two-sensor system, good exhaust emissions are guaranteed as long as the downstream Ot sensor maintains stable output characteristics.

On the other hand, in general, the average air-fuel ratio after control is determined under the following conditions: (1) the catalyst temperature is high; (2) the exhaust gas amount is small (that is, the intake air amount is small) in the light load region. It is said that when the exhaust gas becomes rich, the inside of the catalyst becomes a reducing atmosphere and an exhaust odor (lhs) is generated. For example, high speed driving (condition (1)
) during idling or garage driving (condition (2) met), due to variations in characteristics of the injection valve, O2 sensor, air flow meter, etc., increase in deceleration, increase in fuel when returning from fuel cut, asynchronous injection, etc. The average air-fuel ratio after control may become rich. For this reason, the single 0□ sensor system controls the air-fuel ratio slightly to the lean side only in special driving conditions, such as when the vehicle is idling, when the vehicle speed is below a predetermined value or for a predetermined period of time after stopping. Reduces exhaust odor that occurs when the engine stops (Reference: Japanese Patent Application Laid-Open No. 173533/1983)
.

[Problem that the invention seeks to solve]

However, the single Ot sensor system described above does not reliably detect the average air-fuel ratio flowing into the catalyst, and as a result, lean control cannot be reliably performed in the region where exhaust odor occurs, causing exhaust odor or , the air-fuel ratio is controlled to the lean side even in the operating range other than the range where exhaust odor occurs,
As a result, it becomes over-lean, and the drivability and N
There was a problem in that it caused deterioration of Ox emissions and the like.

Therefore, an object of the present invention is to provide a double 0□ sensor system that reliably detects the occurrence of abnormal exhaust odor, controls the air-fuel ratio to the lean side, and reduces the exhaust odor.

[Means for solving problems]

A means for solving the above-mentioned problems is shown in FIG.

In FIG. 1, the first section detects the concentration of a specific component in exhaust gas. A second air-fuel ratio sensor is provided upstream and downstream of a catalytic converter for purifying exhaust gas, which is provided in an exhaust system of an internal combustion engine. The control constant calculation means calculates an air-fuel ratio feedback control constant, for example, rich skip 1, according to the output v2 of the downstream (second) air-fuel ratio sensor.
Calculate lR3R and lean skip amount R3L. The amount increase determination means determines whether or not the engine is in the time of increase, and
When the engine is increasing and the downstream air-fuel ratio sensor output v
2 indicates rich, the timer means measures a predetermined time. As a result, while the timer means is measuring the predetermined time, the first air-fuel ratio correction amount calculation means controls the air-fuel ratio correction amount FAF according to the output V of the upstream air-fuel ratio sensor so that the air-fuel ratio moves towards the lean side. On the other hand, when the timer means is not measuring a predetermined time, the second air-fuel ratio correction amount calculating means adjusts the air-fuel ratio correction amount according to the air-fuel ratio feedback control constants R5R and RSL and the output V of the upstream air-fuel ratio sensor. A fuel ratio correction amount FAF is calculated so that the control air-fuel ratio approaches the stoichiometric air-fuel ratio. The air-fuel ratio adjustment means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF.

[For production]

According to the above-mentioned means, since the downstream side air-fuel ratio sensor is provided downstream of the catalytic converter, it is possible to detect the average air-fuel ratio including the 0□ storage amount of the catalyst. Therefore, the exhaust odor condition can be reliably detected by the rich output of the downstream side air-fuel ratio sensor immediately before the increase is executed, and therefore, in this case, the first air-fuel ratio correction amount calculation means can adjust the control air-fuel ratio toward the lean side. act.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 3 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. 3, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. As shown in FIG. The air flow meter 3 directly measures the intake air amount, has a built-in potentiometer, and generates an analog voltage output signal proportional to the intake air amount. This output signal is supplied to an A/D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose shaft generates a reference position detection pulse signal every 720° in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30' in terms of crank angle. A crank angle sensor 6 is provided. The pulse signals of these crank angle sensors 5.6 are supplied to the input/output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is sent to the CPU 1.
03 interrupt terminal.

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

Further, a water temperature sensor 9 for detecting the temperature of cooling water is provided in the water jacket 8 of the cylinder block of the engine body 1. Water temperature sensor 9 indicates cooling water temperature TH
Generates an analog voltage electrical signal according to W. This output is also supplied to the A/D converter 101.

The exhaust system downstream of the exhaust manifold 11 is provided with a catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three harmful components HC, Co, and NOx in the exhaust gas.

The exhaust manifold 11 includes a catalytic converter 1.
A first 02 sensor 13 is provided on the upstream side of the catalytic converter 12, and a second 0□ sensor 15 is provided on the exhaust pipe 14 on the downstream side of the catalytic converter 12.

The 0□ sensors 13 and 15 generate electrical signals corresponding to the concentration of oxygen components in the exhaust gas. That is, 0. Sensor 13
, 15, the control circuit 10 outputs different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
This occurs in the D converter 101. 16 is a throttle sensor provided in the throttle valve 17 of the intake passage 2. A signal from the throttle sensor 16 representing the throttle opening TA is supplied to the A/D converter 101 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 102, a CPU 103, and a ROM 104.
゜RAM 105, backup RAM 106,
A clock generation circuit 107 and the like are provided.

Further, in the control circuit 10, a down counter 108,
Flip-flop 109 and drive circuit 110 are for controlling fuel injection valve 7.

That is, in the routine described later, the fuel injection amount TAU
is calculated, the fuel injection amount TAtJ is preset in the down counter 108 and the flip-flop 10
9 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, the down counter 108
Finally, when the carrier voltage terminal reaches the 1" level based on a clock signal (not shown), the control circuit 110 activates the fuel injection valve 7. In other words, the above-mentioned fuel injection 1
The fuel injection valve 7 is energized by iTAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body 1.

Note that the interrupt generation of the CPU 103 is caused by the A/D converter 1.
When the A/D conversion of 01 is completed, the input/output interface 10
2 receives a pulse signal from the crank angle sensor 6, receives an interrupt signal from the clock generation circuit 107, etc.

The intake air amount data Q and cooling water temperature data THW of the air flow meter 3 are fetched by an A/D conversion routine executed at predetermined time intervals and stored in a predetermined area of the RAM 105. In other words, data Q in RAM 105
and THW are updated at predetermined intervals. Further, the rotational speed data Ne is calculated by an interrupt of the crank angle sensor 6 every 30'' CA, and is stored in a predetermined area of the RAM 105.

FIG. 4 shows an asynchronous injection routine, which is executed every predetermined period of time, for example, 12+ms. In step 401, the throttle opening degree TA is A/D converted and taken in, and in step 4
At step 02, the difference ΔTA from the previous captured value TAO is calculated by ΔTA4-TA-TAO. In step 403, ΔTA>X (
It is determined whether or not it is time to increase the amount of fuel at an accelerated rate depending on whether the amount is increased (a positive value) or not. As a result,
If ΔTA>X, proceed to step 404, and ΔTA≦X
If so, proceed directly to step 411. In addition, step 4
The determination of 02 is based on the amount of intake air per revolution Q / N e
The amount of change in the intake air pressure PM, the first differential value or the second differential value of the intake air pressure PM, a power switch, etc. may be used.

In step 404, the output Vi of the downstream sensor 15
is A/D converted and taken in, and in step 405, Vt is the comparison voltage ■. For example, it is determined whether the value is greater than 0.55. At step 406, v2>v,l! (rich), an acceleration increase flag FACC is set in step 407, and a predetermined value n is set in a counter CACC in step 408. Note that n is a value of about 1 to 63, and may be a constant value or may be variable depending on ΔTA.

In step 409, an asynchronous injection amount TAUA is calculated based on ΔTA, and in step 410, asynchronous injection is executed.

In step 411, TA is set as TAO in preparation for the next execution, and in step 412, this routine ends.

In this way, when the output vt of the downstream side 02 sensor 15 indicates lean during acceleration increase (asynchronous injection), HC is generated due to Ot accumulated in the catalyst.

Since CO is purified, there is less possibility of generating an exhaust odor (
, so the flag FACC is not sent. On the other hand, at the time of acceleration increase, the output of the downstream 0□ sensor 15 ■z
When the catalyst is rich, the 02 storage capacity of the catalyst is low (the HC and Co emissions that have increased due to the increase are not purified and are emitted as they are, and this continues, so there is a high possibility that an exhaust odor will occur. Flag FACC is set.

Although the amount is increased by asynchronous injection after the acceleration amount increase determination, the present invention can also be applied to the case where the synchronous injection amount TAU, which will be described later, is increased.

FIG. 5 shows a first air-fuel ratio feedback control routine that calculates an air-fuel ratio correction coefficient FAF based on the output of the upstream 02 sensor 13, and is executed every predetermined time, for example, 4 ms.

In step 501, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 02 sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value, while the engine is starting, during engine startup, during warm-up, and during acceleration.
During asynchronous injection), during power increase, upstream side 02 sensor 13
When the output signal of has never been inverted, during fuel cut,
The closed loop condition is not satisfied when the idle switch is turned on, and the closed loop condition is satisfied in other cases.

If the closed loop condition is not satisfied, the process proceeds to step 534 and the air-fuel ratio correction coefficient FAF is set to 1.0. In addition, F.A.
F may be a value immediately before the end of closed loop control. In this case, proceed directly to step 528. Alternatively, it may be a learned value (value of the backup RAM 106). On the other hand, if the closed loop condition is satisfied, the process proceeds to step 502.

In step 502, the output ■ of the upstream Ot sensor 13,
In step 503, it is determined whether or not (1) is less than the comparison voltage Vllll, for example, 0.45V, that is, it is determined whether the air-fuel ratio is rich or lean. If it is lean (V+≦Vm+), it is determined in step 504 whether the delay counter CDLY is positive or not, and the CD
If LY>0, CDLY is set to 0 in step 505 and the process proceeds to step 506. In steps 507 and 508, the delay counter CDLY is guarded at the minimum value TDL.
When reaching L, the air-fuel ratio flag Fl is set to "0" (lean) in step 509. In addition, the minimum value TDL
is a lean delay time for maintaining the determination that the state is in a rich state even if there is a change from rich to lean in the output of the upstream O2 sensor 13, and is defined as a negative value. On the other hand, if rich (V, > V□), step 5
At step 10, it is determined whether the delay counter CDLY is negative or not, and if CDLY<O, CDLY is set at step 511.
is set to 0, and the process proceeds to step 512. Step 513゜5
In step 514, the delay counter CDLY is guarded at the maximum value TDR. In this case, when the delay counter CDLY reaches the maximum value TDR, the air-fuel ratio flag F1 is set to "1" (rich) in step 515.

The maximum value TDR is a rich delay time for maintaining the determination that the engine is in a lean state even if there is a change from lean to rich in the output of the upstream Ot sensor 13, and is defined as a positive value. .

In step 516, the acceleration increase flag FACC is “1”
Determine whether or not. If FACC="1°, proceed to step 517 and thereafter, perform lean control (λ>1), and
If CC="0", the process proceeds to step 523 and thereafter, and the stoichiometric air-fuel ratio side m (λ=1) is performed.

First, to explain lean control, step 517
, decrease the counter CACC by 1'$i, and proceed to step 5.
18, the counter CACC is guarded at the minimum value O at 519. At this time, when the counter CACC becomes less than 0, the flag FACC is reset in step 518. In other words, if the flag FACC is "1",
The flow proceeds to step 521 for a time corresponding to the predetermined value n. In step 521, the air-fuel ratio flag F
1 is "1" or not. Only when F1="1' (rich), the process proceeds to step 522, where KIL is a lean integral constant used in stoichiometric air-fuel ratio feed control, and k is a value between 2 and 5. Then, in steps 532 and 533, the FAF is guarded at a minimum value of 0.8, for example, and the process proceeds to step 535.

In addition, lean control makes the rich side delay time and the lean side delay time asymmetric by making the rich side integral and the lean side integral asymmetrical, thereby making the rich side skip and the lean side skip asymmetrical. It can also be carried out by this method or by a combination of these methods.

Next, stoichiometric air-fuel ratio control (λ=1) will be explained.

In step 523, it is determined whether the sign of the air-fuel ratio flag F1 has been inverted, that is, it is determined whether the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is reversed, then in step 524, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the air-fuel ratio flag F1. If it is a reversal from rich to lean, it is increased in a skip manner as FAF -FAF+R3R in step 525, and conversely, if it is a reversal from lean to rich, it is increased in a skip manner as FAF←FAF-RSL in step 526. reduce In other words, skip processing is performed. If the sign of the air-fuel ratio flag F1 is not inverted in step 523, step 527. 528. Integration processing is performed at 529. That is, in step 527, F1="
0” or not, and if F1=“0” (lean), set FAF −FAF+KIR in step 528,
On the other hand, if F1="1" (rich), step 52
In step 9, FAF←FAF-KIL. Here, the integral constant KIR (KIL) is set sufficiently small compared to the skip constants RSR and RSL, that is, KTR (KI
L) < lll5R(RSL). Therefore, step 528 gradually increases the fuel injection amount in the lean state (F1="0"), and step 529 gradually increases the fuel injection amount in the rich state [(F1="0").
="1") to gradually reduce the fuel injection amount. The air-fuel ratio correction coefficient FAF calculated in steps 525, 526, 528, and 529 is calculated in step 530. In step 531, the maximum value, for example 1.2, is set to garr', and in step 5
32 and 533 are guarded at a minimum value of 0.8, for example. As a result, for some reason, the air-fuel ratio correction coefficient FAF
When becomes too small or too large,
This value controls the engine's air-fuel ratio to prevent it from becoming over-lean or over-rich.

F A F -t-RAM 1 calculated as described above
05, and the routine ends at step 535.

FIG. 6 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream 07 sensor 13 as shown in FIG. 6(A), the delay counter CD
As shown in FIG. 6(B), LY is counted up in a rich state and counted down in a lean state.

As a result, as shown in FIG. 6(C), a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed. For example, time 1. Even if the air-fuel ratio signal A/F changes from lean to rich, the delayed air-fuel ratio signal A/F changes from lean to rich.
Fl' is maintained lean for the rich delay time TDR and then changes to rich at time t2. Even if the air-fuel ratio signal A/F changes from rich to lean at time t, the delayed air-fuel ratio signal A/F 'return delay time (-T
DL) After being held rich by a considerable amount, it changes to lean at time t4. However, the air-fuel ratio signal A/F at time tS
.

1. 1. When the delay counter CDLY is reversed in a period shorter than the rich delay time TDR, the delay counter CDLY reaches the maximum value TD.
It takes time to reach R, and as a result, the air-fuel ratio signal A/F' after the delay process is inverted at time t8. In other words, the air-fuel ratio signal A/F' after the delay process is more stable than the air-fuel ratio signal A/F before the delay process. In this way, based on the stable air-fuel ratio signal A/F' after the delay processing, the sixth
The air-fuel ratio correction coefficient FAF shown in Figure (D) is obtained.

Next, the second air-fuel ratio feedback control by the downstream 02 sensor 15 will be explained. The second air-fuel ratio feedback control includes skip amounts RSR and RSL as the first air-fuel ratio feedback control constants, and an integral constant K.
IR, KIL, delay time TDR.

There is a system in which TDL or the comparison voltage V□ of the output V1 of the upstream 02 sensor 13 is made variable, and a system in which a second air-fuel ratio correction coefficient FAF2 is introduced.

For example, if you increase rich skip fiR3R,
The control air-fuel ratio can be shifted to the rich side, and even if the lean skip [RSL is reduced, the control air-fuel ratio can be shifted to the rich side.On the other hand, if the lean skip amount R3L is increased,
The control air-fuel ratio can be shifted to the lean side, and even if the rich skip @R5R is reduced, the control air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich skip fiR3R and the lean skip amount R3L according to the output of the downstream 02 sensor 15. In addition, by increasing the rich integral constant KIR, the control air-fuel ratio can be shifted to the rich side, and even if the lean integral constant KIL is made smaller, the control air-fuel ratio can be shifted to the rich side;
By increasing L, the control air-fuel ratio can be shifted to the lean side,
Further, even if the rich integral constant KIR is made smaller, the controlled air-fuel ratio can be shifted to the lean side. Therefore, downstream side 0□sensor 1
The air-fuel ratio can be controlled by correcting the rich integral constant KIR and the rich integral constant KIL according to the output of 5. Rich delay time TDR > Lean delay time (-TDL)
If set, the control air-fuel ratio can be shifted to the rich side, and conversely, if lean delay time (-TDL) > rich delay time (TD
R), the controlled air-fuel ratio can be shifted to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay times TDR and TDL according to the output of the downstream 02 sensor 15. Furthermore, by increasing the comparison voltage Vll, the controlled air-fuel ratio can be shifted to the rich side, and by decreasing the comparison voltage V, the controlled air-fuel ratio can be shifted to the lean side. Therefore, depending on the output of the downstream 0□ sensor 15, the comparison voltage
By correcting the air-fuel ratio, the air-fuel ratio can be controlled.

Making the skip amount, integral constant, delay time, and comparison voltage variable by the downstream 0□ sensor has its own advantages. For example, the delay time allows for very delicate air-fuel ratio adjustments, and the skip amount does not lengthen the air-fuel ratio feedback cycle (which allows for control with good response), unlike the delay time. Of course, two or more of these variable amounts can be used in combination.

A double 02 sensor system in which the skip amount as an air-fuel ratio feedback control constant is made variable will be described with reference to FIG.

FIG. 7 shows a second air-fuel ratio feedback control routine that calculates the skip amounts R3R and RSL based on the output of the downstream 02 sensor 15, and is executed every predetermined period of time, for example, every 1 second. In step 701, downstream 0! It is determined whether the sensor 15 is in a closed loop condition. for example,
In addition to the failure of the closed loop condition by the upstream 02 sensor 13, the closed loop condition is not satisfied when the output signal of the downstream 0□ sensor 15 has never been inverted, and in other cases, the closed loop condition is satisfied. . If it is not a closed loop condition, step 716. Proceed to 717, skip amount R5
Let R and RSL be constant values RSR (1, RSLo. For example, RS Ro -5% R3Ls=5% Note that it is also possible to hold the skip amounts RSR and RSL at the values immediately before the end of the closed loop. In this case, step 718
Proceed directly to. Further, the skip amounts RSR and RSL can also be set as learned values (values of the backup RAM 106).

If the closed loop condition is satisfied by the downstream side 02 sensor 15, the process proceeds to step 702, where the output v2 of the downstream side 02 sensor 15 is A/D converted, and at step 703, the output v2 is
It is determined whether or not the comparison voltage VII□ is, for example, 0.55V or less, that is, it is determined whether the air-fuel ratio is rich or lean. Note that the comparison voltage ■4□ is upstream of the catalytic converter 12,
The upstream side 02 sensor 13
It is set higher than the comparison voltage V,ll of the output of , but it may be set arbitrarily.

If v2≦V*z (lean) in step 703, the process proceeds to steps 704 to 709; on the other hand, vz>v+tz(
rich), the process advances to steps 710-715.

In step 704, RSR←RSR+ΔRSR (constant value) is set, that is, rich skip @R8R is increased to shift the air-fuel ratio to the rich side. step 705,
At 706, the RSR is guarded at a maximum value MAX, for example, 6.2%. Furthermore, in step 707, RSL-R
SL-ΔRS direct-direct value is set, that is, the rich skip 11R5L is decreased to shift the air-fuel ratio to the rich side. Step 708. 709, RSL is set to the minimum value MI
Guard at N, for example 2.5%.

On the other hand, when V, > V, □ (rich), step 7
At step 10, RSR4-RSR-ΔRSR is set, that is, rich skip 1iR3R is decreased to shift the air-fuel ratio to the lean side. In steps 711 and 712, RSR
is guarded at the minimum value MIN. Furthermore, step 71
In step 3, RSL is set to -R5L+ΔRSL, that is, the lean skip amount R3L is increased to shift the air-fuel ratio to the lean side. Step 714. At 715, the RSL is guarded at the maximum value MAX.

RSR and RSL calculated as described above are stored in RAM 10.
5, the routine ends at step 718.

Note that FAF calculated during air-fuel ratio feedback,
RSR,l? sL is once changed to another value FAF', R3
R'.

It can also be converted into RSL' and stored in the bank-up RAM 106, which is useful for improving maneuverability when restarting, etc. The minimum value MIN in FIG. 8 is a value at a level that does not impair transient followability, and the maximum value MAX is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

As described above, according to the routine shown in FIG. 7, if the output of the downstream side 02 sensor 15 is lean, the rich skip amount R
5R and the lean skip amount R3L are reduced relatively quickly, and as a result, the air-fuel ratio is relatively quickly shifted to the rich side.Furthermore, if the output of the downstream 0□ sensor 15 is rich, the rich skip amount R3R is reduced relatively quickly. And the lean skip amount R3L is increased relatively slowly, thereby shifting the air-fuel ratio to the lean side relatively slowly.

FIG. 8 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, 360°C. Step 801
Then, the intake air amount data Q and the rotational speed data Ne are read out from the RAM 105 to calculate the basic injection amount PAUP. For example, assume TAUU-α·Q/Ne (α is a constant). At step 802 , the coolant temperature data THW:g: is read out from the RAM 105 and a one-dimensional map stored in the ROM 104 is used to interpolate and calculate the warm-up increase value FWL.

In step 803, the final injection amount TAU is determined by TAU - TAUP - FAF - (FWL + β) + γ
Calculate by Note that β and T are correction amounts determined by other operating state parameters. Then, in step 80
At step 4, the final injection amount TAtJ is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. The routine then ends at step 805.

FIG. 9 is a timing diagram for explaining the air-fuel ratio correction coefficient FAF obtained by the flowchart of FIG. The output voltage V of the upstream Ox sensor 13 is shown in FIG. 9(A).
, the comparison result at step 503 in FIG. 5 changes as shown in FIG. 9(B), and the air-fuel ratio flag F1, which is the delayed result, changes as shown in FIG. 9(C). .

Here, before the acceleration increase time is determined (FACC=“
0"), as shown in FIG. 9(D), the air-fuel ratio correction coefficient FAF is determined by the skip amounts R5R, RSL and the integral constant K.
It changes around a certain value (equivalent to the stoichiometric air-fuel ratio) depending on IR and KIL, but when increasing the amount during acceleration, the downstream side 02 sensor 15
When the output Vt of is a rich output, FIG. 9(D)
As shown in , the air-fuel ratio correction coefficient FAF changes to the lean integral constant -KIL (the rich integral constant is 0) for a predetermined period.
is controlled to the lean side.

Note that the first air-fuel ratio feedback control is performed every 4 ms.
Further, the second air-fuel ratio feedback control is performed for each IS because the air-fuel ratio feedback control is performed on the upstream side 0.001, which has good responsiveness. This is because control by the sensor is performed primarily, and control by the downstream 02 sensor, which has poor responsiveness, is performed secondary.

In addition, the double 02 sensor system corrects other control constants in the air-fuel ratio feedback control by the upstream Ot sensor, such as the integral constant, delay time, comparison voltage Vll of the upstream 02 sensor, etc., using the output of the downstream 08 sensor. Also, double 02 introduces a second air-fuel ratio correction coefficient.
The present invention can also be applied to sensor systems. Moreover, controllability can be improved by simultaneously controlling two of the skip amount, integral constant, and delay time. Furthermore, one of the skip amounts RSR and RSL may be fixed and only the other variable, one of the integral constants KIR and KIL may be fixed and only the other variable, or the delay time TDR, It is also possible to have one of the TDLs fixed and the other variable.

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

Furthermore, in the above embodiment, the fuel injection amount is calculated according to the intake air amount and the engine rotation speed, but the fuel injection amount is calculated according to the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may also be calculated.

Further, in the above embodiment, an internal combustion engine is shown in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, but the present invention can also be applied to a carburetor type internal combustion engine. For example, Electric Air Control Pulp (EACV)
The electric bleed air control valve adjusts the air bleed amount of the carburetor and introduces atmospheric air into the main system passage and slow system passage to control the air-fuel ratio. The present invention can be applied to things such as those that control the exhaust system of an engine, and those that adjust the amount of secondary air sent into the exhaust system of an engine. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 801 is determined by the carburetor itself, that is, it is determined according to the intake pipe negative pressure depending on the intake air amount and the engine rotation speed, and in step 803 The supplied air amount corresponding to the final fuel injection amount TAU is calculated.

Further, in the above embodiment, an O2 sensor is used as the air-fuel ratio sensor, but a CO sensor, a lean mixture sensor, etc. may also be used.

Furthermore, although the embodiments described above are constructed using a microcomputer, that is, a digital circuit, they may also be constructed using an analog circuit.

〔Effect of the invention〕

As explained above, according to the present invention, when performing an asynchronous fuel increase, the rich output of the immediately downstream air-fuel ratio sensor reliably detects the region where exhaust odor occurs, and feedback control is performed to direct the air-fuel ratio toward the lean side. Therefore, exhaust odor can be reliably reduced, and deterioration of drivability, emissions, etc. can also be suppressed.

[Brief explanation of the drawing]

Figure 1 is an overall block diagram for explaining the present invention in detail, Figure 2 is a single O2 sensor system and double O2 sensor system.
Fig. 3 is an overall schematic diagram showing an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention; Fig. 4, Fig. 5, Fig. 7, Fig. 8; is a flowchart for explaining the operation of the control circuit in FIG. 3, FIG. 6 is a timing diagram for supplementary explanation of the flowchart in FIG. 5, and FIG. 9 is a flowchart for explaining the operation of the control circuit in FIG. FIG. 3 is a timing diagram for supplementary explanation of the flowchart. 1... Engine body, 3... Air flow meter,
4...Distributor, 5.6...Crank angle sensor, IO...Control circuit, 12...Catalytic converter,
13... Upstream side (first) 02 sensor, 15... Downstream side (second) 0□ sensor, 16... Throttle sensor. Mouth, 0... Worst na single o2 system■,...
・Tuple o2 system Figure 2, b...Kufunk moon sensor 16...Throttle sensor Figure 4, Figure 6, Figure 8

Claims (1)

[Scope of Claims] 1. A first catalytic converter installed on the upstream side and downstream side of a catalytic converter for purifying exhaust gas provided in the exhaust system of an internal combustion engine, and configured to detect the concentration of a specific component in the exhaust gas. a second air-fuel ratio sensor; a control constant calculation means for calculating an air-fuel ratio feedback control constant according to the output of the second air-fuel ratio sensor; and an increase-time determination means for determining whether or not the engine is at an increase-rate time. , timer means for measuring a predetermined time when the engine is increasing and the output of the second air-fuel ratio sensor indicates rich; and when the timer means is measuring the predetermined time, the first air-fuel ratio sensor first air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount according to the output of the air-fuel ratio sensor so that the control air-fuel ratio leans toward the lean side; a second air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount in accordance with a fuel ratio feedback control constant and the output of the first air-fuel ratio sensor so that the controlled air-fuel ratio moves toward the stoichiometric air-fuel ratio; An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the amount of air-fuel ratio. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the increase determination means determines whether or not an asynchronous increase is in progress.