JPS63176642A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce the exhaust emission by installing the air-fuel ratio sensors an the upstream and downstream sides of a catalyst and varying the comparison voltage of the second sensor on the downstream side according to the load and calculating the air-fuel ratio control quantity set according to the load, according to the result of the second comparison. CONSTITUTION:Air-fuel ratio sensors 13 and 15 are installed on the upstream and downstream sides of a catalytic converter 12 in an exhaust pipe 11. A controller 10 detects the engine load by receiving the signal of an air flow meter 3, and varies the comparison voltage of the second air-fuel ratio sensor 15 according to the load. Further, each air-fuel ratio control quantity which is provided according to the load is calculated according to the result of the comparison by the second comparator. The air-fuel ratio is controlled according to the result of the comparison by the first air-fuel ratio sensor and the air-fuel ratio control quantity corresponding to the load. Thus, the exhaust emission can be reduced.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides air-fuel ratio sensors (herein, oxygen concentration sensors (0□ 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 02 sensor.

[Conventional technology]

In simple air-fuel ratio feedbank control (single 02 sensor system), the 02 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 02 sensor is provided downstream of the catalytic converter, and the air-fuel ratio feed by the downstream 02 sensor is A double 02 sensor system that performs air-fuel ratio feedback control using a downstream 0□ sensor in addition to hack control has already been proposed (see Japanese Patent Laid-Open No. 58-48756). In this double 0° sensor system, although the 0□ sensor installed on the downstream side of the catalytic converter has a lower response speed than the 02 sensor on the upstream side, it has the advantage of less variation in output characteristics due to the following reasons. have.

(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 02 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 an equilibrium state.

Therefore, as described above, by air-fuel ratio feedback control (double 02 sensor system) based on the outputs of the two O2 sensors, variations in the output characteristics of the upstream 02 sensor can be absorbed by the downstream 02 sensor. In fact, as shown in Figure 2, in the single 02 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 02 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 0□ sensor maintains stable output characteristics.

[Problem that the invention seeks to solve]

However, in the double 02 sensor system described above, the downstream 02 sensor detects the stoichiometric air-fuel ratio (λ-1), and the downstream 02 sensor performs air-fuel ratio feed-hack control, so that the average air-fuel ratio is always kept close to the stoichiometric air-fuel ratio. Therefore, there is a problem in that it is not possible to obtain the optimum air-fuel ratio for reducing exhaust emissions and catalyst exhaust odor.

For example, at high speeds and high loads, NOx emissions increase, so it is necessary to change the air-fuel ratio to the Lynch side, and at low speeds and low loads, IC and CO emissions increase, as well as catalyst exhaust odor. , the air-fuel ratio needs to be on the lean side.

Therefore, an object of the present invention is to provide a double 0□ sensor system that can obtain an air-fuel ratio that is suitable for operating conditions.

[Means for solving problems]

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

In Fig. 1, the upstream and downstream sides of the catalytic converter for exhaust gas purification installed in the exhaust system are
First and second air-fuel ratio sensors are provided to detect the concentration of specific components in the exhaust gas.

The first comparison means compares the output V of the upstream side (first) air-fuel ratio sensor with the first comparison voltage VRI. Further, the load detection means detects the engine load, for example, the intake air amount Q,
The comparison voltage calculation means sets the second comparison voltage VH2 to the rich judgment side when the detected load Q1 is large, and sets the second comparison voltage VR to the rich judgment side when the detected load Q is small.
2 is calculated on the lean judgment side. As a result, the second comparison means compares the output V2 of the downstream (second) air-fuel ratio sensor with the second comparison voltage VR2. Further, the air-fuel ratio control amount calculating means calculates each air-fuel ratio control amount provided according to the detected load Q, such as skip amounts R3R8, R3L, according to the comparison result of the second comparing means, and, The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the comparison result of the first comparing means and the air-fuel ratio control amounts R5R, R3L corresponding to the detected load Q8.

[For production]

According to the above-mentioned means, the comparison voltage V R2 of the downstream air-fuel ratio sensor changes according to the engine load, and therefore the average air-fuel ratio changes according to the engine load. Further, when the engine load changes to a different range, the air-fuel ratio is adjusted by the air-fuel ratio control amount corresponding to each load, and the air-fuel ratio immediately shifts to the optimum air-fuel ratio corresponding to each load.

〔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 degrees in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30 degrees in terms of crank angle. A crank angle sensor 6 is provided. The pulse signals of these crank angle sensors 5 and 6 are supplied to the input/output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is
3 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 IC, CO, and NOx in exhaust gas.

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

The 02 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 on the lean side or the lean side with respect to the stoichiometric air-fuel ratio.
This occurs in the D converter 101.

In addition, each 02 sensor 13, 15 is connected to a heater 13a, 15.
a is built in, and thereby the element temperature of the 02 sensor is raised to, for example, 350 to 40.0° C. or higher for activation.

16 is a starter switch, the output of which is supplied to the input/output interface 102 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 . In addition to CPL1103, ROM104
.

A RAM 105, a back amplifier RAM 106, a clock generation circuit 107, and the like are provided.

Further, in the control circuit 10, a down counter 108,
The flip-flop 109 and the drive circuit 110 to which the battery voltage (3) is applied are for controlling the fuel injection valve 7. That is, in the routine described later, when the fuel injection amount TAU is calculated, the fuel injection amount TAU is preset in the down counter 10B and the flip-flop 109 is also set. As a result, drive circuit 1
10 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts the clock signal (not shown) and finally its carrier terminal reaches the "1" level, the flip-flop 109 is set and the drive circuit 1
10 stops the energization of the fuel injection valve 7. That is, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TA, U, and therefore, an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body 1.

Further, the drive circuit 111 to which the battery voltage ■8 is applied
The heaters 13a and 15a of the 02 sensors 13 and 15 are driven simultaneously.

Note that the interrupt generation of the CPU 103 is caused by the A/D converter 10.
1, the input/output interface 102
When the controller receives a pulse signal from the crank angle sensor 6, when it receives an interrupt signal from the clock generation circuit 107, etc.

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

FIG. 4 shows a first air-fuel ratio feed puncture control routine for calculating an air-fuel ratio correction coefficient FAF based on the output of the upstream 0□ sensor 13, and is executed every predetermined period of time, for example, every 4 ms.

In step 401, it is determined whether a closed loop (feed hack) 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 post-starting, during warm-up increase, or during acceleration increase (
Asynchronous injection), power increase, upstream O, sensor 13
When the output signal of is never inverted, the closed loop condition is not satisfied in any case such as fuel cut, and the closed loop condition is satisfied in other cases. If the closed loop condition is not satisfied, the process proceeds to step 427 and the air-fuel ratio correction coefficient FAF is determined.
is set to 1.0. Note that FAF may be set to a value immediately before the end of closed loop control. In this case, proceed directly to step 428. Also, the learning value (value of backup RAM 106)
You can also use it as On the other hand, if the closed loop condition is satisfied, the process proceeds to step 402.

In step 402, the output V of the upstream 02 sensor 13,
In step 403, it is determined whether vl is less than the comparison voltage (2), +, for example, 0.45V, that is, it is determined whether the air-fuel ratio is rich or lean. If lean (■1≦VRI), it is determined in step 404 whether the delay counter CDLY is positive or not, and CDLY is
If >0, CDLY is set to 0 in step 405 and the process proceeds to step 406. In Ste Nobu 407.408,
Guard the delay counter CDLY with the minimum value TDL,
In this case, when the delay counter CDLY reaches the minimum value TDL, the air-fuel ratio flag F is set by the steering knob 409.
1 is 0'' (lean).The minimum value TDL is the lean delay time to maintain the judgment that the state is rich even if there is a change from rich to lean in the output of the upstream 0□ sensor 13. and is defined as a negative value.

On the other hand, if it is rich (V+ > VRI), it is determined in step 410 whether the delay counter CDLY is negative or not, and if CDLY<0, in step 411 CDLY is
is set to 0, and the process proceeds to step 412. Step 413゜4
In step 14, 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 415.

The maximum value TDR is a slope/notch delay time for maintaining the determination that the lean state is present even if the output of the upstream 0□ sensor 13 changes from lean to rich, and is defined as a positive value. be done.

In step 416, 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, in step 417, 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 to FAF 4-FAF+R5R in step 418, and conversely, if it is a reversal from lean to rich, it is skipped to FAF 4-FAF-R5L in step 419. decrease. In other words, skip processing is performed. If the sign of the air-fuel ratio flag F1 is not inverted in step 416, integration processing is performed in steps 420, 421, and 422. That is, in step 420, F1="
If Fl-“0” (lean), FAF 4-FAF+KTR is set in step 421, and if F1=“1” (rich), the process goes to step 422. FAF 4-FAF-KIL.Here, the integral constant KIR(KTL) is the skip constant R5R,
It is set sufficiently small compared to R5L, that is, KI
R(KrL)<R3R(R3L). Therefore, step 421 gradually increases the fuel injection amount in the lean state (F1="0"), and step 422 gradually increases the fuel injection amount in the rich state a (F1="0").
1-1"). The air-fuel ratio correction coefficient FAF calculated in steps 418, 419 and 42L422 is guarded at a maximum value, for example 1.2, in steps 423 and 424, and , step 425.4
26 is guarded at a minimum value, for example, 0.8. As a result, if the air-fuel ratio correction coefficient FAF becomes too small or too large for some reason, the air-fuel ratio of the engine is controlled using that value to prevent over-lean or over-rich conditions.

The FAF calculated as described above is expressed as l? The data is stored in AM 105, and the routine ends at step 428.

FIG. 5 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 4. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream O2 sensor 13 as shown in FIG. 5(A), the delay counter CD
As shown in FIG. 5(B), LY is counted up in a rich state and counted down in a lean state.

As a result, as shown in FIG. 5(C), a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed. For example, even if the air-fuel ratio signal A/F changes from lean to rich at time t, 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 t3, the air-fuel ratio signal A/F' subjected to the delay processing is delayed by the lean 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 js
+t6+jff, when inverted in a period shorter than the rich delay time TDR, it takes time for the delay counter CDLY to reach the maximum value TDR, and as a result, time t8
The air-fuel ratio signal A/F' after the delay processing is inverted at .

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 manner, the air-fuel ratio correction coefficient FAF shown in FIG. 5(D) is obtained based on the stable air-fuel ratio signal A/F' after the delay processing.

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 R3R, R3L, integral constants KIR, KTL, and delay times TDR, TDL as first air-fuel ratio feedback control constants.

Or the comparison voltage V of the output V of the upstream side 02 sensor 13
A system that makes RI variable and a second air-fuel ratio correction coefficient F
There is a system that introduces AF2.

For example, if the rich skip amount R3R is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean skip amount R3L is decreased, the control air-fuel ratio can be shifted to the rich side. Then,
The control air-fuel ratio can be shifted to the lean side, and even if the rich skip amount R3R is decreased, 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 amount R3R and the lean skip amount R3L in accordance with the output of the downstream 02 sensor 15. Also, the Ricci integral constant K
If IR is increased, the controlled air-fuel ratio can be shifted to the rich side, and even if the lean integral constant KTL is decreased, the controlled air-fuel ratio can be shifted to the rich side.
If KIR is increased, the controlled air-fuel ratio can be shifted to the lean side, and even if the rich integral constant KIR is decreased, the controlled air-fuel ratio can be shifted to the lean side. Therefore, downstream side 02 sensor 15
The air-fuel ratio can be controlled by correcting the rich integral constant KIR and the lean integral constant KIL according to the output of .

If rich delay time TDR>lean delay time (-TDL) is set, the control air-fuel ratio can be shifted to the rich side, and conversely,
Lean delay time (-TDL) > Rich delay time (TDR
), the control 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, if the comparison voltage V B 1 is increased, the control air-fuel ratio can be shifted to the rich side, and the comparison voltage V H
If 1 is made smaller, the controlled air-fuel ratio can be shifted to the lean side.

Therefore, by correcting the comparison voltage V□1 according to the output of the downstream 02 sensor 15, the air-fuel ratio can be controlled.

Making these skip amount, integral constant, delay time, and comparison voltage variable by the downstream 02 sensor has its own advantages. For example, the delay time allows very delicate adjustment of the air-fuel ratio, and the skip amount can be controlled with good response without lengthening the feed-hack cycle of the air-fuel ratio unlike the delay time. Therefore, naturally, 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 feedhack control constant is made variable will be described with reference to FIG.

FIG. 6 shows a second air-fuel ratio feedback control routine that calculates skip amounts R5R and R3L based on the output of the downstream 02 sensor 15, and is executed at predetermined intervals, for example, every IS. In step 601, it is determined whether the downstream 0□ sensor 15 is in a closed loop condition. for example,
In addition to the failure of the closed loop condition by the upstream side 02 sensor 13, the closed loop condition is not satisfied when the output signal of the downstream side 02 sensor 15 has never been inverted, and in other cases, the closed loop condition is satisfied. If it is not a closed loop condition, proceed to step 63L632 and skip 1iR3R.
.

Let R5L be a constant value R3R,, R5Lo. for example,
R3RQ=5% R3Lo-5% Note that the skip amounts R5R and R3L can also be held at values immediately before the end of the closed loop. In this case, step 631
Proceed directly to. Also, skip ill? sl? , I? S
l, can also be used as a learning value (value of the backup RAM 106).

If the closed loop condition is satisfied by the downstream 02 sensor 15, the intake air amount Q is determined in steps 603 to 605. That is, the intake air amount Q is read from the RAM 105, Q≦25 i/h, 25 bo/h<Q≦50 m/h, 50
r+(/h<Q≦8On?/h, 80n?/h<
Q≦12On? /h, Q>120m/h. In addition, Q≦25%/
Since the element temperature of the downstream 02 sensor 15 decreases in the region of h, and in the region of Q > 120 m/h,
For the TP increase area, proceed to steps 631 and 632;
Open loop control is used.

On the other hand, in the low intake air amount region (25 i/h<Q≦50rrr
/h), proceed to steps 606 to 613,
If it is in the medium intake air amount region (50r+?/h<Q≦80m/h), proceed to steps 614 to 621, and if it is in the high intake air amount region (80r+?/h<Q≦12Or+?/h), Proceed to steps 622 to 629, and skip amount R3 for each corresponding
R+ 1R5LI; R3R2, R5L2; R5R31
Update R5I-s.

Note that the above skip amounts R3R1, R3L+ (i =
The updates 1 to 3) may be prohibited until the change in the intake air amount Q is stabilized, taking into account the delay in transport of exhaust gas and the reaction delay due to the 0□ storage effect of the three-way catalyst. Now, to explain the 0□ storage effect of the three-way catalyst,
The three-way catalyst purifies NOx, Go, and HC at the same time, and as shown in Figure 7, the purification rate η is large on the rich side of the stoichiometric air-fuel ratio (λ-1), and the purification rate of NOx is large on the rich side compared to the stoichiometric air-fuel ratio (λ-1). On the side, the purification rate of Go and HC is large. At this time, the three-way catalyst is 0 when the air-fuel ratio is lean.
□ is taken in, and when the air-fuel ratio becomes rich, Co,
It produces an 02 storage effect by taking in the IC and making it react with the 02 taken in when it is lean.

In step 606, the output ■2 of the downstream 0° sensor 15
is A/D converted and taken in, and in step 607 it is determined whether v2 is less than the comparison voltage VR2, in this case 0.2V, that is, it is determined whether the air-fuel ratio is on the rich side or the lean side. In this case, the output characteristic of the 0□ sensor is as shown in FIG. 8, so the comparison voltage VR2 is set small so that the average air-fuel ratio is on the lean side. As a result, ■2≦VR2(
lean side), in step 608, RAM10
5, the rich skip amount R3R for low intake air amount is successively outputted, and R5R, -1? SR, ten ΔI? 5R (constant directness)
In other words, the rich skip amount R5R+ is increased to shift the air-fuel ratio to the rich side, and in step 609, the lean skip I for low intake air amount is stored in the RAM 105.
Read R3L, R5L, -R5L, -ΔR3L
(a constant value), that is, the rich skip amount R3L+ is decreased to shift the air-fuel ratio to the Sochi side. Conversely, if V2 > VH2 (rich side), step 61
At 0, R3R,4-R5I? , -ΔR3R, that is, rich skip iil? sR, to shift the air-fuel ratio to the lean side, and in step 611, R
3L, ←R3L, +ΔR3L, that is, the lean skip amount R5L is increased to shift the air-fuel ratio to the lean side. Then, in steps 612 and 613, R
5R4-R5R,, R3I, ←R3L.

Similarly, in step 614, the output ■2 of the downstream 0□ sensor 15 is A/D converted and taken in, and in step 615, it is determined whether or not ■2 is less than the comparison voltage VR2, in this case 0.5V. In other words, it determines whether the air-fuel ratio is rich or lean. In this case, the comparison voltage ■8□ is set so that the average air-fuel ratio becomes the stoichiometric air-fuel ratio (λ-1). As a result, V2≦VR
2 (lean), in step 615, RAM1
From 05 onwards, the rich skip 1iR3R, for medium intake air amount is successively set to R3R2''R3R, +ΔR5R, that is, the rich skip amount R5Rz is increased to shift the air-fuel ratio to the rich side, and in step 617, R ^Old 0
5, the lean skip amount R5L for the medium intake air amount is successively determined to be R5L□・−R3L2−ΔR3L, that is,
The rich skip amount R5L is decreased to shift the air-fuel ratio to the rich side. Conversely, if V2 > VH2 (rich), in step 618, R3R2←R3R
2-ΔR3R, that is, the rich skip amount R5R2
In step 619, R5L2-R3L2+ΔR5I is set, that is, the lean skip amount R5L2 is increased to shift the air-fuel ratio to the lean side. And step 6
At 20.621 R3R←R5R,, R3L←R5L2
shall be.

Similarly, in step 622, the output V2 of the downstream O2 sensor 15 is A/D converted and taken in, and it is determined whether or not 7Vz is the comparison voltage VR2, 0.8V or less in the case 7623, that is, Determine whether the air-fuel ratio is rich or lean. In this case, the comparison voltage vR
4, the rich skip amount R3R for high intake air amount is successively output from the RAM 105, and R5Rz'-R5Rt+ΔR
3R, that is, increase the rich skip amount R3Ra to shift the air-fuel ratio to the rich side, and step 62
5, lean skip itl for higher intake air amount than RAM105? sL, and then R5L3←R5L3−Δ
R5L, that is, the rich skip amount R3L is decreased to shift the air-fuel ratio to the rich side. On the contrary, V2
>V, □ (rich side), at step 626,
R3R: 1-R5R, -ΔR5R, that is, the rich skip amount R3R3 is decreased to shift the air-fuel ratio to the lean side, and in step 627, R5L3←R5I
, 3+ΔR3L, that is, the lean skip amount R3
L3 is increased to shift the air-fuel ratio to the lean side. Then, at steps 628 and 629, R5R-R5R
3, R5I, ←R5L3.

The skips 1iR5R and R5L calculated as described above are guarded at step 630 by a maximum value of, for example, 7.5% and a minimum value of, for example, 2.5%.

l? calculated as above? sR, R3L is RAM10
5, the routine ends at step 633.

In addition, FAP, R calculated during air-fuel ratio feedback
5I? , R3L are once changed to other values FAF', R3R'
, R5L' and stored in the hack-up RAM 106. This is also useful for improving maneuverability when restarting, etc. Further, the minimum value at step 630 in FIG. 6 is a value at which transient followability is not impaired, and the maximum value is at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

Also, the skip amount R5R, R5! , are divided into blocks according to the load, for example, the intake air amount Q, so when the intake air amount Q changes to a different region, the skip amount R5R+, R5L1 (i = 1 to 3) suitable for that region is determined.
for each skip amount R5l1. Since it is used as R5L, the required skip amounts R3R and R5L can be obtained immediately.

In addition, in the above embodiment, the number of block divisions by Q is 3.
However, it goes without saying that it can be done with other numbers. Further, the block division intervals may be either irregular intervals or equal intervals. Furthermore, the correction amount ΔR of the skip amount once in each area
It is also possible to improve controllability by setting 5R and ΔR3L to different values. For example, step 608.61 in FIG.
Set ΔR3R of 0 to ΔR3RI, step 609. 6
11 is set as ΔRSLI, and step 616
．． Set ΔR5R of 618 to ΔR3R2, and step 617
．． Set ΔR5L of 619 to ΔR3L2, and step 62
4. Set ΔR3R of 626 to ΔR5R3, and step 6
25. Let ΔR5L of 627 be ΔR3L3, ΔR3RI <ΔR5I'12 <ΔR3R3ΔR3L
It may be done as I < ΔR3L2 < ΔR3L3, etc.

FIG. 9 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, 360° CA.

In step 901, the intake air amount data Q and rotational speed data Ne are read from the RAM 105, and the basic injection amount TA is read out.
Calculate UP. For example, TAUP←α・Q/N
Let it be e (α is a constant). At step 902, RAM10
Read the cooling water temperature data THW from 5 and get 170M104.
The warm-up increase value FWL is calculated by interpolation using the one-dimensional map stored in the . In step 903, final injection 1 (TAU
, TAU 4-TAtlP -FAF ・(FW
Calculate by L + β + 1) + γ. In addition,
β and T are correction amounts determined by other operating state parameters. Next, in step 904, the injection amount TAU is input to the down counter 108 and the flip-flop 109 is input to start fuel injection. This routine then ends in step 905. In addition,
As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carrier signal of the down counter 108, and the fuel injection ends.

In this way, the comparison voltage VR□
changes, and therefore, the average air-fuel ratio changes depending on the intake air amount Q. Furthermore, it is divided into blocks according to the intake air MQ and the amount of air is divided into blocks R5R.

and lean skip amount R3Li (i = 1 to 3
) are calculated and used as the lean skip amount R5R and lean skip (iR5L), so the average air-fuel ratio corresponding to the intake air amount Q can be obtained immediately.

In order to accurately detect the air-fuel ratio, the element temperature of the 0□ sensor needs to be 350 to 400°C or higher.

As shown in FIGS. 10 and 11, the element temperature of the 0□ sensor increases as it is located upstream in the exhaust system.

However, if the upstream 0□ sensor 13 is placed further upstream in the exhaust system, problems arise in terms of durability and characteristic changes in high speed and high load ranges. On the other hand, if the downstream side 02 sensor 15 is placed further downstream in the exhaust system, there will be a problem in that the element temperature will drop and damage will be caused by flying stones, water, etc. from the outside.

Therefore, the 0□ sensors 13 and 15 are placed at appropriate locations above and downstream of the catalytic converter 12, but as described above, it is preferable to ensure the target element temperature using a built-in heater. In addition, since the capacity of the heaters t3a and tsa also affects the exhaust gas temperature exposed to each 02 sensor, the capacity of each heater 13a and 15a is
The capacities of are set to different values. Furthermore, the relationship between the heater supply power and the element temperature or heater temperature depends on the engine rotational speed N e (or load), as shown in FIG. 12 or FIG. 13. Therefore, in the present invention,
The heaters 13a and 15 are
Control a. Hereinafter, heater control will be explained with reference to FIG. 14.

FIG. 14 shows a heater control routine, which is executed at predetermined time intervals. In step 1401, it is determined whether the starter switch 16 is on (STA-"1") or not. As a result, when the starter switch 16 is on (STA-"1"), the process proceeds to step 1408 to turn off the heaters 13a and 15b. That is, at the time of starting the engine, the amount is increased at the time of starting regardless of the output of the O2 sensor, so the heater energization control is stopped. Also, step 14o
In step 2, the panteri voltage (2) is A/D converted and taken in, and in step 14o3, it is determined whether (1)8≧11.5V. As a result, if VB<11.5V, step 1
Proceed to 408 and turn off the heaters 13a and 15a. That is, when the battery voltage V is low, the heater energization control is stopped to prevent the battery voltage V from decreasing.

In step 1404, the cooling water temperature data THW is read from the RAM 105 and it is determined whether THW≧60°C.

In other words, it estimates whether the exhaust gas temperature is high or low. If the exhaust gas temperature is high (THW≧60°C), the heater 13a
, the on/off switching point of 15a is set to Q-50m/h, and conversely, if the exhaust gas temperature is low (THW<60°C)
, the on/off switching point of heaters 13a and 15a is Q=70.
Let it be rd/h. That is, if THW≧60°C, the process proceeds to step 1405, where the intake air amount data Q is read from the RAM 105 and it is determined whether Q≦50d/h. As a result, if Q≦50m/h, step 1407 Turn on heaters 13a and 15a at Q>50m/h
If so, the heater 13a and tsa are turned off in step 1408. Similarly, if THW<60°C, proceed to step 1406, read the intake air amount data Q from the RAM 105, determine whether Q≦70m+/h, and if the result is Q≦70i/h. In step 1407, heaters 13a and 15a are turned on, and 0>79rd/h
If so, the heaters 13a and 15a are turned off in step 1408.

This routine then ends in step 1409.

In this manner, according to the routine shown in FIG. 14, the heaters 13a and 15a of the 02 sensors 13 and 15 having different capacities are controlled to be turned on and off simultaneously in accordance with the load, for example, Q.

FIG. 15 shows a modification of FIG. 14, in which heaters 13a,
This is a case where the capacity of 15a is made the same. In this case,
On/off conditions for the heater 13a and on/off conditions for the heater 15a,
The OFF conditions are changed to increase the energization time of the heater 15a of the downstream 0□ sensor 15, which tends to get cold. That is, if THW<60°C, both heaters 13a and 15a are turned on, but if THW≧60°C, different heaters 13a and 15a are turned on and off depending on the intake air amount Q. In other words, Q≦4On? /h, heater 1
3a.

15a are both turned on, and 40〈Q≦7On? /h, the heater 13a is turned off and the heater 15a is turned on; if q>70rrr/h, the heater 13a is turned on.

15a are both turned off.

In this way, according to the modified example of FIG. 15, the heater 13a
, 15a have the same capacity, the load is controlled to turn on and off according to Q, but the heaters 13a, 15a
By changing the on/off control conditions, the same effect as in the case of FIG. 14 can be obtained.

Note that the first air-fuel ratio feedback control is performed every 4 mS.
In addition, the second air-fuel ratio feedback control is performed every 1 second, because the air-fuel ratio feed hack control is mainly performed by the upstream 02 sensor, which has good responsiveness, and is controlled by the downstream 02 sensor, which has poor responsiveness. This is to follow.

In addition, the double 0□ sensor system corrects other control constants in air-fuel ratio feedback control by the upstream 0□ sensor, such as integral constant, delay time, comparison voltage VRI of the upstream 0□ sensor, etc., using the output of the downstream 02 sensor. The present invention can also be applied to a double 0° sensor system that introduces a second air-fuel ratio correction factor. Moreover, controllability can be improved by simultaneously controlling two of the skip amount, integral constant, and delay time. Furthermore, the skip amount R
It is also possible to fix one of 5R and R5L and make only the other variable, or to fix one of the integral constants KIR and KIL and make only the other variable, or to change the delay time T.
It is also possible to fix one of DR and TDL and make the other variable.

□ Furthermore, instead of an 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, an electric air control valve (EACV) adjusts the intake air amount of the engine to control the air-fuel ratio, and an electric bleed air control valve adjusts the amount of air bleed from the carburetor to control the main system passage and The present invention can be applied to devices that control the air-fuel ratio by introducing atmospheric air into the slow system passage, devices that adjust the amount of secondary air sent to the exhaust system of an engine, and the like. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 901 is determined by the carburetor itself,
That is, it is determined according to the intake pipe negative pressure corresponding to the intake air amount and the rotational speed of the engine, and in step 903, the supplied air amount corresponding to the final fuel injection amount TAU is calculated.

Further, in the above-described embodiment, a 0□ sensor was used as the air-fuel ratio sensor, but a CO sensor, a lean mixture sensor, etc. may also be used.

Furthermore, the above-mentioned embodiment is based on the microcombi 1. -Although it is constructed from a digital circuit, it can also be constructed from an analog circuit.

〔Effect of the invention〕

As explained above, according to the present invention, the average air-fuel ratio is changed depending on the engine load, that is, when the load is high, the average air-fuel ratio is set to the lean side, and when the load is low, the average air-fuel ratio is set to the lean side. This is useful for reducing engineering work and catalyst exhaust odor, and since the air-fuel ratio control amount, for example, R5R and R5L, is divided into blocks according to the engine load, it is possible to reduce engine load transitions to different regions. Sometimes the required air-fuel ratio can be quickly approached,
As a result, it is possible to prevent deterioration in fuel efficiency, drivability, and emissions due to control delays.

[Brief explanation of the drawing]

Figure 1 is an overall block diagram for explaining the present invention in detail, Figure 2 is a single 02 sensor system and a double 02 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. 6, Fig. 9, Fig. 14; , Figure 15 is a flowchart to explain the operation of the control circuit in Figure 3, Figure 5 is a timing diagram to supplement the flowchart in Figure 4, Figure 7 is the exhaust emission characteristics of the three-way catalyst. Figure 8 is a graph showing the output characteristics of the 02 sensor, Figure 10 is an overview of the engine showing the placement position of the 02 sensor, and Figure 11 shows the element temperature corresponding to the placement position of Figure 10. FIG. 12 is a graph showing the relationship between heater supply power and element temperature, and FIG. 13 is a graph showing the relationship between heater supply power and heater temperature. ■...Engine body, 3...Air flow meter, 4...Distributor, 5.6...Crank angle sensor, 10...Control circuit, I2...Catalytic converter, 13..."Second class Side (first) O2 sensor, 15.
...Downstream (second) 0□ sensor, 16...Starter switch. Figure 1 - d≧, -. Figure 9 Figure 10 Figure 11 Heater supply power (W) Figure 12 Heater supply power (W) Figure 13 Figure 14

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 first comparing means for comparing the output of the first air-fuel ratio sensor with a first comparison voltage; a load detecting means for detecting the load of the engine; and the detected load. a comparison voltage calculation means that calculates a second comparison voltage to make a rich judgment side when the detected load is large, and a comparison voltage calculation means to make the second comparison voltage a lean judgment side when the detected load is small; a second comparison means for comparing the output of the fuel ratio sensor with the second comparison voltage; and a second comparison means for comparing each air-fuel ratio control amount provided according to the detected load according to the comparison result of the second comparison means. an air-fuel ratio control amount calculation means for calculating, and an air-fuel ratio adjustment means for adjusting the air-fuel ratio of the engine according to the comparison result of the first comparison means and the air-fuel ratio control amount corresponding to the detected load. An air-fuel ratio control device for an internal combustion engine.