JPS6226337A - Air/fuel ratio controller for internalc-combustion engine - Google Patents

Abstract

PURPOSE:To permit the speedy judgement for the active or inactive state of the air/fuel ratio sensors by compulsorily making rich the air/fuel ratio of an engine when the downstream side sensor is in inactive state, when the air/fuel ratio sensors are installed onto the upstream and downstream sides of a catalytic converter. CONSTITUTION:The first and the second air/fuel ratio sensor means A and B which generate the lean signals in inactive state are installed onto the upstream and downstream sides of a catalytic converter installed into the exhaust system of an engine. The first air/fuel ratio control means C for controlling the air/fuel ratio according to the outputs of the sensors A and B is installed. The second air/fuel ratio control means D for compulsorily making the air/fuel ratio rich is installed. Further, a judging means E which judges the active or inactive state of the downstream side sensor means B from the fact that the output V2 of the means B becomes over a prescribed value or not is installed. Therefore, the air/fuel ratio is adjusted by selecting the first air/fuel ratio control means C when the downstream side sensor means B is in active and selecting the second air/fuel ratio control means D when said sensor is in active, by an air-fuel ratio adjusting means F.

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 02 sensor in addition to air-fuel ratio feedback control using an upstream 0□ sensor.

[Conventional technology]

-a, in the air-fuel ratio feedback system based on a single 02 sensor (single 0□ sensor system), 0
□The sensor is installed in the exhaust system as close as possible to the combustion chamber, that is, in the gathering part of the exhaust manifold upstream of the catalytic converter, but due to variations in the output characteristics of the 02 sensor, it is difficult to improve the accuracy of air-fuel ratio control. is occurring. The causes of variations in the output characteristics of the 02 sensor are listed below.

(t) Individual differences in the O2 sensor itself; (2) uneven mixing of exhaust gas at the O2 sensor location due to tolerances in the position of parts such as fuel injection valves and exhaust gas recirculation valves when assembled to the engine; 3) Changes in the output characteristics of the 0□ sensor over time or over time.

In addition, for sensors other than the 02 sensor, non-uniformity in the exhaust gas mixture may change and expand due to changes in engine conditions such as the fuel injection valve, exhaust gas recirculation flow rate, and tappet clearance over time, as well as manufacturing variations. There is.

In order to compensate for variations in the output characteristics of the 0□ sensor, variations in parts, and changes over time, a second Ot sensor is provided downstream of the catalytic converter, in addition to the air-fuel ratio feedback control by the upstream 0□ sensor. A double 02 sensor system that performs air-fuel ratio feedback control using a downstream 02 sensor has already been proposed. In this double 02 sensor system, although the 0□ sensor installed downstream of the catalytic converter has a lower response speed than the upstream 0□ sensor, 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 0□ sensor system) based on the outputs of the two 0□ sensors, variations in the output characteristics of the upstream 02 sensor can be absorbed by the downstream 0□ sensor. In fact, as shown in Figure 2, in a single 0□ sensor system, 02
If the output characteristics of the sensor deteriorate, it will directly affect the exhaust emission characteristics, but with the double 0□ sensor system, even if the output characteristics of the upstream 0□ sensor deteriorate,
Exhaust emission characteristics are not deteriorated. That is, double 0
In the □ 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, due to various manufacturing tolerances of fuel control system components, changes over time during use, etc., the controlled air-fuel ratio may remain on the rich side or lean side of the stoichiometric air-fuel ratio. For example, if a fuel injection valve is installed in the first cylinder that injects more fuel than other cylinders, and the upstream 02 sensor is strongly affected by the gas from the first cylinder, the upstream 0□ sensor Catalyst and downstream side 0□ by air-fuel ratio feedback control based on output
It becomes the gas line to the sensor. As a result, the downstream side is 0.
The sensor output remains at a lean signal (low level).

On the other hand, there is a sensor that determines whether the 02 sensor is activated or deactivated based on whether the output of the 02 sensor reaches a predetermined value or higher, or whether it once goes up or down.In this case, as mentioned above, the air-fuel ratio becomes lean and the output of the downstream 0□ sensor is held at a lean signal (low level), it is not possible to determine whether it is an inactive lean signal or an active lean signal.In other words, even if the downstream 02 sensor is activated. Even if the downstream side is 0, the activity of the sensor cannot be determined.

[Means for solving problems]

An object of the present invention is to normally perform air-fuel ratio feedback control using an upstream air-fuel ratio sensor (O2 sensor) and a downstream air-fuel ratio sensor, but when the output of the downstream air-fuel ratio sensor holds an active lean signal, Another object of the present invention is to provide a double air-fuel ratio sensor (0□ sensor) system that enables air-fuel ratio feedback control using a downstream air-fuel ratio sensor. The first step is to detect the concentration of a specific component in the gas. Upstream of a catalytic converter for purifying exhaust gas, the second air-fuel ratio sensor means is provided in the exhaust system of the internal combustion engine;
Each is provided downstream. In addition, in this case, the first. It is assumed that the second air-fuel ratio sensor means generates a lean signal when inactive. The first air-fuel ratio control means each have a first air-fuel ratio control means.
The air-fuel ratio of the engine is controlled according to the outputs V, , V of the second air-fuel ratio sensor output, and the second air-fuel ratio control means forcibly makes the air-fuel ratio of the engine rich. The activation/deactivation determining means determines whether the second air-fuel ratio sensor is active or inactive based on whether the output v2 of the second air-fuel ratio sensor has exceeded a predetermined value or has once gone up or down. As a result, the air-fuel ratio adjusting means selects the first air-fuel ratio control means when the second air-fuel ratio sensor means is active, and selects the second air-fuel ratio control means when the second air-fuel ratio sensor means is inactive. The air-fuel ratio of the engine is adjusted by selecting the means.

1st. The present invention is also applicable to the case where the second air-fuel ratio sensor means generates a rich signal when it is inactive. In this case, the second air-fuel ratio control means forcibly makes the air-fuel ratio of the engine lean.

[For production]

According to the above means, when the air-fuel ratio is lean and it is unclear whether the output of the downstream air-fuel ratio sensor means is an active lean signal or an inactive lean signal, the air-fuel ratio is forcibly set to stoichiometric. The fuel ratio is on the richer side. Therefore, when the output of the downstream air-fuel ratio sensor means is a lean signal when activated, it is switched to a rich signal, and as a result, the downstream air-fuel ratio sensor means is determined to be activated. On the other hand, if the output of the downstream air-fuel ratio sensor means is a lean signal when inactive, it remains a lean signal, and as a result, the downstream air-fuel ratio sensor means is still determined to be inactive.

In addition, 1. When the second air-fuel ratio sensor means generates a rich signal when it is inactive, the above is reversed. In other words,
When the air-fuel ratio is rich and it is unclear whether the output of the downstream air-fuel ratio sensor means is an active rich signal or an inactive rich signal, the air-fuel ratio is forced to be leaner than the stoichiometric air-fuel ratio. .

Therefore, when the output of the downstream air-fuel ratio sensor means is a rich signal when activated, it is switched to a lean signal, and as a result, the downstream air-fuel ratio sensor means is determined to be activated. On the other hand, if the output of the downstream air-fuel ratio sensor means is the inactive rich signal, it remains the rich signal, and as a result, the downstream air-fuel ratio sensor means is still determined to be inactive.

〔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 throttle valve 16 of the intake passage 2 is provided with a throttle sensor 17 that generates an analog voltage according to its opening degree TA. The output signal of this throttle sensor 17 is also supplied to the A/D converter 101 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. Pulse signals from these crank angle sensors 5 and 6 are supplied to an input/output interface 102 of a control circuit 10, and the output of the crank angle sensor 6 is supplied to an interrupt terminal of a 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 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 TI
- Generates an analog voltage electrical signal according to the voltage. 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 the exhaust gas.

The exhaust manifold 11 includes a catalytic converter 1.
A first O2 sensor 13 is provided on the upstream side of the catalytic converter 12, and a second O2 sensor 15 is provided on the exhaust pipe 14 on the downstream side of the catalytic converter 12.

The 0□ sensor 13.15 generates an electrical signal according to the concentration of oxygen components in the exhaust gas. That is, 0□ sensor 13.
15 is a control circuit 10 which outputs different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio. A/D converter 1 via sensor output processing circuits 111 and 112
Occurs on 01.

Note that the 0□ sensor output processing circuits 111 and 112 normally have a flow-out type circuit configuration as shown in FIG. 4A, and their output characteristics are as shown in FIG. 4B, depending on the air-fuel ratio A/
When F is rich, as the element temperature rises, 02
The output of the sensor (rich signal) increases and stabilizes at a high level, while when the air-fuel ratio A/F is lean, it stabilizes at a low level as the element temperature increases. On the other hand, the Ot sensor output processing circuits 111 and 112
When the flow-in type circuit configuration as shown in the figure is used, as shown in Fig. 4B, when the air-fuel ratio A/F is rich, the output characteristics change to 0.0 as the element temperature rises. The output of the sensor (lean signal) stabilizes at the D-level as it falls, while on the other hand, when the air-fuel ratio A/F is rich, it stabilizes at a high level as the element temperature rises.

18 is an alarm, which is displayed when the downstream 02 sensor 15 is out of order.

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, an O□ sensor output processing circuit 111, 112, and a ROM 104 and a RAM.
105, a backup RAM 106, a clock generation circuit 107, and the like.

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 TAI
When J is calculated, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 10
9 is also set. As a result, drive diagram path 110 begins energizing the fuel injector 7. On the other hand, down counter 1
When 0B counts a clock signal (not shown) and finally its carrier terminal becomes "1" level, the flip-flop 109 is set and the drive circuit 110 stops energizing the fuel injection valve 7. do. That is, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body l.

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 of the air flow meter 3, the opening degree data TA of the throttle valve 16, and the cooling water temperature data TH- are taken in by an A/D conversion routine executed at predetermined intervals and stored in a predetermined area of the RAM 105. Ru. That is, the data Q and T)IW in the RAM 105 are updated at predetermined intervals. Also, rotation speed data N
e is calculated by an interrupt of the crank angle sensor 6 every 30'CA and stored in a predetermined area of the RAM 105.

FIG. 6 shows a first air-fuel ratio feedback control routine that calculates an air-fuel ratio correction coefficient FAF1 based on the output of the upstream 02 sensor 13, and is performed for a predetermined period of time, for example, 4 ms.
executed every time.

In step 601, it is determined whether the closed loop (feedback) condition of the air-fuel ratio by the upstream 02 sensor 13 is satisfied.0 During engine starting, during fuel increase operation after startup, during warm-up increase operation, power increase operation Medium, lean control,
The closed loop condition is not satisfied when the upstream 02 sensor 13 is in an inactive state, and the closed loop condition is satisfied in other cases. The active/inactive state of the upstream O2 sensor 13 can be determined by reading the water temperature data TH- from the RAM 105 and determining whether TH-≧70°C, or by reading the water temperature data TH- from the RAM 105 and determining whether TH-≧70°C or This is done by determining whether the output level has increased or decreased once. If the closed loop condition is not satisfied, the process proceeds to step 617 and the air-fuel ratio correction coefficient FAF 1 is set to 1.0.

On the other hand, if the closed loop condition is satisfied, the process proceeds to step 602.

In this way, step 601 is a means for determining whether the upstream 02 sensor 13 is active or inactive.

In step 602, the output vI of the upstream 02 sensor 13
is A/D converted and taken in, and in step 603, it is determined whether or not ■ is a comparison voltage ■□, for example, 0.45V or less.
In other words, it determines whether the air-fuel ratio is rich or lean. If lean (v r ≦ V Rl ), the first delay counter CDLY 1 is subtracted by 1 in step 604, and the first delay counter C
Guard DLY 1 with minimum value TDR1.

Note that the minimum value TDR1 is 0. The rich delay time is defined as a negative value of 1, which is used to maintain the determination that the sensor 13 output changes from lean to rich and is in a dust state. On the other hand, rich (V, >V□
), the first delay counter CDLY 1 is incremented by 1 in step 607, and the process proceeds to steps 608 and 609.
Set the first delay counter CDLY 1 to the maximum value TI
Guard with IL 1. Note that the maximum value TDL 1 is a lean delay time for maintaining the judgment that the rich state is present even if there is a change from rich to lean in the output of the upstream side 02 sensor 13, and is defined as a positive value. Ru.

Here, the reference for the first delay counter CDLY 1 is O, and when CDLY 1 > 0, the air-fuel ratio after the delay process is considered rich, and when CDLY 1≦O, the air-fuel ratio after the delay process is considered lean. shall be deemed.

In step 610, the first delay counter CDLY
It is determined whether the sign of 1 has been reversed, that is, it is determined whether the air-fuel ratio after the delay processing has been reversed. If the air-fuel ratio is reversed, it is determined in step 611 whether the reversal is from rich to lean or from lean to rich. If it is a reversal from rich to lean, step 612
In step 613, FAF 1 - FAFI + RS1 is increased in a skip manner. Conversely, if there is a reversal from lean to rich, in step 613, FAF 1 ← FAF 1 - R51 is decreased in a skip manner.

In other words, skip processing is performed.

In step 610, the first delay counter CDLY
If the sign of 1 is not reversed, steps 614, 61
5. Integration processing is performed at 616. That is, step 61
4, determine whether CDLY 1≦0, and
If 1≦0 (lean), FAF in step 615
1← Set 11 to FAF 1 +, and on the other hand, CDLY 1
> 0 (rich), in step 616 FAF
1-FAF 1-Kl 1. Here, the constant of integration K
II is set sufficiently smaller than the skip constant RSI, that is, Kll<RSI. Therefore, step 615 gradually increases the fuel injection amount in the lean state (CDLY l≦0), and step 616 gradually increases the fuel injection amount in the rich state (CDLY l≦0).
DLY 1 > 0), the fuel injection amount is gradually decreased.

The air-fuel ratio correction coefficient FAF 1 calculated in steps 612, 613, 615, and 616 shall be guarded at a minimum value such as 0.8 and a maximum value such as 1.2. When FAPI becomes too large or too small, the air-fuel ratio of the engine is controlled using that value to prevent over-rich or over-lean conditions.

The FAF 1 calculated as described above is stored in the RAM 105, and the routine ends at step 618.

FIG. 7 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 6. When the air-fuel ratio signal A/Fl for rich/lean discrimination is obtained from the output of the upstream 02 sensor 13 as shown in FIG. 7(A), the first delay counter CDLY 1 is activated as shown in FIG. 7(0). As in, it counts up when it is in a rich state and counts down when it is in a lean state. As a result, a delayed air-fuel ratio signal A/Fl' is formed as shown in FIG. 7(C). For example, even if the air-fuel ratio signal A/Fl changes from lean to rich at time 1°, the delayed air-fuel ratio signal ^/F
1' is maintained lean for a rich delay time (-TDRI) and then changes to rich at time t2. Even if the air-fuel ratio signal ^/Fl changes from rich to lean at time t3, the delayed air-fuel ratio signal A/Fl' is held rich for an amount equivalent to the lean delay time TDL l before reaching time t.
Changes to lean at 4. However, the air-fuel ratio signal A/PI
is the rich delay time (-T
DRI) is reversed in a shorter period of time.

Then, it takes time for the first delay counter CDLY 1 to cross the reference value 0, and as a result, the air-fuel ratio signal A/Fl' after the delay process is inverted at time t.

In other words, the air-fuel ratio signal A/Fl' after the delay process is more stable than the air-fuel ratio signal A/Fl before the delay process.

In this way, the stable air-fuel ratio signal A/Pi after the delay processing
Based on ', the air-fuel ratio correction coefficient PA shown in Figure 7 (b)
PI is obtained.

Next, the second air-fuel ratio feedback control by the downstream Ot sensor 15 will be explained. As the second air-fuel ratio feedback control, the second air-fuel ratio correction coefficient FAF 2
and the delay times TDRI, TDLI, and the skip amount RSI as the first air-fuel ratio feedback control constants (in this case, the rich skip amount from lean to rich RS I R and the lean skip from rich to lean fiRs I set L separately),
integral constant KII (in this case, Ricci integral constant KIIR
and the lean integral constant KILL separately), or the comparison voltage of the output V of the upstream O2 sensor 13■□
There is a system that makes it variable.

For example, if you set rich delay time (-TDRI) > lean delay time (TDLI), the control air-fuel ratio can shift to the rich side, and conversely, if you set lean delay time (TDLI) > rich delay time (-TDRI). Then, the controlled air-fuel ratio can be shifted to the lean side. In other words, downstream side 0□sensor 1
The air-fuel ratio can be controlled by correcting the delay times TDR1 and TDLI in accordance with the output of 5. Furthermore, if the rich skip amount R5IR is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean skip 1lRs I L is decreased, the control air-fuel ratio can be shifted to the rich side. If it is increased, the control air-fuel ratio can be shifted to the lean side, and the rich skip amount 1? S
Even if the IR is reduced, the control air-fuel ratio can be shifted to the lean side. Therefore, downstream side 0. Depending on the output of the sensor 15, the rich skip amount RS I R and the lean skip amount RS I R
The air-fuel ratio can be controlled by correcting IL. Furthermore, by increasing the rich integral constant KIIR, the control air-fuel ratio can be shifted to the rich side, and the lean integral constant KIIL
The control air-fuel ratio can be shifted to the rich side even if the lean integral constant KILL is made small, and on the other hand, the control air-fuel ratio can be shifted to the lean side by increasing the lean integral constant KILL.
The control air-fuel ratio can be shifted to the lean side even if the ratio is made smaller. Therefore, the air-fuel ratio can be controlled by correcting the rich integral constant KIIR and the lean integral constant KIIL according to the output of the downstream 0□ sensor 15. Furthermore, by increasing the comparison voltage vR, 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, by correcting the comparison voltage VRI according to the output of the downstream 02 sensor 15, the air-fuel ratio can be controlled.

With reference to FIGS. 8 to 10, the second air-fuel ratio correction coefficient FA
A double 0□ sensor system incorporating F2 will be explained.

FIG. 8 shows the second
This is a second air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF2, and is executed every predetermined period of time, for example, every 1 second. In step 801, the downstream Ot
It is determined whether the sensor 15 is in a closed loop condition. This step is substantially the same as step 601 in FIG.

Therefore, step 801 is a means for determining whether the downstream O2 sensor 15 is active or inactive. If the condition is not a closed loop condition, the process proceeds to step 817 to set FAF 2 = 1.0, and if the condition is a closed loop condition, the process proceeds to step 802.

In step 802, the output ■2 of the downstream O2 sensor 15
is A/D converted and taken in, and in step 803 v2 is the comparison voltage ■. For example, it is determined whether the voltage is 0.55V or less, that is, it is determined whether the air-fuel ratio is rich or lean. Note that the comparison voltage V+tZ is set higher than the comparison voltage Vl11 of the output of the upstream side 02 sensor 13, taking into account that the output characteristics are different due to the influence of raw gas and the deterioration rate is different between upstream and downstream of the catalytic converter 14. Ru. Lean (
v2≦vR□), the second delay counter CDLY2 is counted by 1'$i in step 804, and the second delay counter CDLY2 is counted in steps 805 and 806.
2 is guarded with the minimum value TDR2. In addition, the minimum value TD
R2 is a rich delay time for maintaining a lean state even when there is a change from lean to rich, and is defined as a negative value. On the other hand, if it is rich (Vz > Viz),
In step 807, the second delay counter CDLY
2 is incremented by 1, and in steps 808 and 809, the second delay counter CDLY2 is guarded at the maximum value TDL2.

Note that the maximum value TDL 2 is a lean delay time for maintaining a rich state even when there is a change from rich to lean, and is defined as a positive value.

Here again, the reference for the second delay counter CDLY 2 is set to 0, and when CDLY 2 > 0, the air-fuel ratio after the delay process is considered rich, and when CDLY 2 ≦ 0, the air-fuel ratio after the delay process is considered lean. shall be deemed.

In step 810, a second delay counter CDLY
It is determined whether the sign of No. 2 has been reversed, that is, it is determined whether the air-fuel ratio after the delay processing has been reversed. If the air-fuel ratio is reversed, it is determined in step 811 whether the reversal is from rich to lean or from lean to rich. If it is a reversal from rich to lean, step 812
In step 813, FAF 2←FAF2+RS2 is increased in a skip manner, and conversely, if the change is from lean to rich, in step 813, FAF 2←FAF 2 to R32 is decreased in a skip manner.

In other words, skip processing is performed.

In step 810, the second delay counter CDLY2
If the sign of is not reversed, step 814゜815
, 816 performs integration processing. That is, step 814
, determine whether CDLY 2 < O or not, and
2〈0 (lean), FA in step 815
F 2 ← FAF 2 + KI 2, and on the other hand, CDLY
If 2>0 (rich), FAF in step 816
2←FAP 2-KI 2. Here, the constant of integration K
I2 is set sufficiently small compared to the gap constant RS2, that is, KI2<R52. Therefore, step 815 gradually increases the fuel injection amount in a lean state (CDLY 2≦0), and step 816 gradually increases the fuel injection amount in a rich state (CDLY 2≦0).
CDLY 2 > 0), the fuel injection amount is gradually decreased.

The air-fuel ratio correction coefficient FAF 2 calculated in steps 812, 813, 815, and 816 shall be guarded at a minimum value such as 0.8 and a maximum value such as 1.2. When FAF2 becomes too large or too small, the air-fuel ratio of the engine is controlled using that value to prevent over-rich or over-lean conditions.

The FAF 2 calculated as described above is stored in the RAM 105, and the routine ends in step 818.

In this way, the second air-fuel ratio correction coefficient FAF2 is calculated based on the delayed output of the downstream 02 sensor 15.

As mentioned above, F calculated during air-fuel ratio feedback
AF 1 and FAF 2 are temporarily changed to other values FAF1'.

Convert to FAF2' and bank up RAM RAM 106
The engine can also be stored in the engine, which helps improve drivability during restarts, etc.

FIG. 9 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360° CA. Step 90
1, the RAM 105 reads intake air amount data Q and rotational speed data Ne to calculate the basic injection amount TAUP. For example, TAUP←KQ/Ne (K is a constant). In step 902, the cooling water temperature data TOW is read from the RAM 105, and a warm-up increase value FWL is calculated by interpolation using the one-dimensional map stored in the ROM 10°4. As shown in the figure, this warm-up increase value FWL is set to decrease as the current cooling water temperature TFIW increases. In step 903, the final injection amount TAU
, TAU -TAUP -FAF 1 ・FA
Calculate by F 2 · (FWL+ α) + β. Note that α and β are correction amounts determined by other operating state parameters, such as a signal from a throttle sensor (not shown), a signal from an intake air temperature sensor, battery voltage, etc. R
It is stored in AM 105.

Steps 904 to 911 are for determining whether the downstream 0□ sensor 15 is active or inactive. In step 904, similarly to step 601 in FIG.
It is determined whether the state of 70° C. lasted for 60 seconds or more. In other words, steps 904 and 905 are performed on the downstream side 02 sensor 1.
It is determined whether or not the activation condition No. 5 is satisfied. Only when these conditions are satisfied, the downstream side 02 sensor 1
Step 906 is executed to determine whether No. 5 is active or inactive.

In step 906, it is determined whether the downstream side 02 sensor 15 has been activated. For example, activation is determined based on (2) whether 0.45V has been increased by at least one concave groove or whether V2 has once gone up or down. Downstream side 0□sensor 1
If it is determined that 5 is still inactive, the process advances to step 907.

In step 907, it is determined whether the change ΔTA in the throttle opening data TA is greater than or equal to a predetermined value, for example, 2°/16m5. In other words, it is determined whether or not the vehicle is in an accelerated state. In the acceleration state, the fuel injection amount TAU is increased by 10% in steps 908 to 910 to confirm the activation of the downstream 02 sensor 15.
Increase the amount. This amount increase operation is performed up to five times, but if it is determined in step 906 that the downstream side 02 sensor 15 is activated before then, this amount increase is stopped. On the other hand, if activation is not determined in step 906 even after performing this increase operation five times, it is assumed that the downstream 02 sensor 15 has failed.
In step 911, an alarm is displayed.

In addition, upstream side 0□ sensor 13 and downstream side 02 sensor 1
If the air-fuel ratio feedback control in step 910 is the first air-fuel ratio control, then the fuel increase in step 910 can be said to be the second air-fuel ratio control.

Next, in step 912, the injection [TAU is set in the down counter 108 and the flip-flop 10 is
Set 9 to start fuel injection. This routine then ends in step 913.

As described above, when the time corresponding to the injection amount TAII has elapsed, the flip-flop 109 is reset by the carrier signal of the down counter 108, and the fuel injection ends.

Note that if the 02 sensor output processing circuits 111 and 112 are of the flow-in type, step 907 is omitted and step 910 is performed to determine the fuel reduction, for example, TAυ-TAtl
, 9 are performed.

FIG. 10 shows the first step obtained by the flowcharts of FIGS. 6 and 8. second air-fuel ratio correction coefficient FAPI,
FIG. 3 is a timing diagram for explaining FAF2. When the output voltage V of the upstream O2 sensor 13 changes as shown in FIG. 10 (8), the comparison result at step 603 in FIG. ) is processed as shown in Fig. 10 (C). As a result, as shown in Fig. 10 (D), at the time of delayed rich and lean switching, FAF 1 is R
Skip only 5I. On the other hand, when the output voltage ■2 of the downstream 0□ sensor 15 changes as shown in FIG. 10(E), the comparison result at step 803 in FIG.
), and when the delay processing is further performed, the result becomes as shown in FIG. 10(G). Second air-fuel ratio correction coefficient Fig. 10 (
When the calculation is performed based on the delayed comparison result of G), the result is as shown in FIG. 10(H).

Next, with reference to FIGS. 11 and 12, the air fuel
A double 02 sensor system in which the delay time as a ratio feedback control constant is made variable will be described.

FIG. 11 shows a second air-fuel ratio feedback control routine that calculates the delay times TDRI and TOLL based on the output of the downstream 02 sensor 15, and is executed at predetermined intervals, for example, every IS. In step 1101, the eighth
Similar to step 801 in the figure, it is determined whether the closed loop condition of the air-fuel ratio is satisfied.

If the closed loop condition is not satisfied, step 1123.

Proceeding to step 1124, the rich delay time TDR1 and lean delay time TDL1 are set to constant values. For example, TDR1=
12 (equivalent to 48 ras) TDL 1 =
6 (equivalent to 24ms). Here, the reason why the rich delay time (-TDRI) is set larger than the lean delay time TDL 1 is because the comparison voltage ■□ is set to a low value, for example, 0.
This is because the voltage is set at 45V on the lean side.

If the closed loop condition is satisfied, the process advances to step 1102.

Steps 1102 to 1109 are step 802 in FIG.
~809 is supported. In other words, rich/lean discrimination is performed in step 1103, but this discrimination result is delayed in steps 1104 to 1109. Then, the delayed rich/lean discrimination is performed in step 11.
It will be held at 10.

In step 1110, the second delay counter CDLY
2 is CDLY 2≦0, and as a result, C
If DLY2≦0, the air-fuel ratio is determined to be lean and the process proceeds to steps 1111 to 1116;
> If it is 0, the air-fuel ratio is determined to be rich and step 1 is started.
Proceed to steps 117-1122.

In step 1111, TDR1←TDR1-1,
That is, the rich delay time (-TDRI) is increased, the change from rich to lean is further delayed, and the air-fuel ratio is shifted to the rich side. Step 1112.

At 1113, TDR1 is guarded with the minimum value TRI.

Here, TR1 is also a negative value, so (-TRI
) means the maximum rich delay time. Furthermore, in step 1114, TOL 1←TDL 1-1 is set, that is, the lean delay time TDL 1 is decreased, the delay in changing from lean to rich is reduced, and the air-fuel ratio is shifted to the rich side. In steps 1115 and 1115, TDL
1 is guarded at the minimum value TLI. Here, TLl
is a positive value, therefore TLl means the minimum lean delay time.

In step 1117, TDR1←TDR1+1 is set, that is, the delay time (-T[)R1) is decreased, and the
The air-fuel ratio is shifted to the lean side by reducing the delay in changing from 7-inch to lean. In steps 1118 and 1119, TDR1 is guarded at the maximum value TR2. Here T,
□ is also a negative value, so (-'r*z) means the minimum rich delay time. Furthermore, in step 1120, TDL 1←TDL 1 + 1 is set, that is, the lean delay time TDL 1 is increased, the change from lean to rich is further delayed, and the air-fuel ratio is shifted to the lean side. In steps 1121 and 1122, TDL 1 is guarded at the maximum value TLI. Here, TLI is a positive value, so T'Lz means the maximum lean delay time.

TDR1 and TOLL calculated as above are stored in RAM1.
05, the routine ends at step 1125.

In addition, FAFI calculated during air-fuel ratio feedback
, TDRI, TDLI are once changed to other values FAF1
'.

It can also be converted into TDRI', TDLI' and stored in the backup RAM 106, which is useful for improving drivability during restarts and the like.

FIG. 12 shows an injection amount calculation routine, which is almost the same as the predetermined routine shown in FIG. That is, step 903' differs from step 903 in FIG.
U ←TAUP -FAFI ・(FWL+ (X)
Calculated using +β.

FIG. 13 is a timing diagram of the delay times TDRI and TDLI obtained by the flowcharts of FIGS. 6 and 11. As shown in Fig. 13(A), the downstream side 02
When the output voltage ■2 of the sensor 15 changes, Fig. 13 (B
), if the lean B CV2≦■, I2), both the delay times TDRI and TDLI are increased. On the other hand, if it is in a rich state, the delay time TDRI,
TDLI is reduced together. At this time, TDR1 is 'r
Changes in the range of +tt to TR1, TDL 1 is TL1%
It changes within the range of TL2.

Note that the first air-fuel ratio feedback control is performed every 4 ms.
The second air-fuel ratio feedback control is performed every ls because the air-fuel ratio feedback control is mainly performed by the upstream 0□ sensor, which has good responsiveness, and is controlled by the downstream 02 sensor, which has poor responsiveness. This is to follow.

In addition, other control constants in air-fuel ratio feedback control by the upstream 0□ sensor, such as skip amount, integral constant, upstream 0. Comparison voltage of sensor (Reference: JP-A-55-
The present invention can also be applied to a double 02 sensor system that corrects the output of the downstream 02 sensor.

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 capretor 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 is determined in step 903 (903'
), the supplied air amount corresponding to the final fuel injection amount TAU is calculated.

Furthermore, in the above embodiment, the 02 sensor was used as the air-fuel ratio sensor, but a CO sensor, 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 the output of the air-fuel ratio sensor on the downstream side of the outflow type process is a lean signal, the air-fuel ratio is forcibly set to 0. When the output of the fuel ratio sensor is a rich signal, the air-fuel ratio is forcibly made lean to determine whether it is activated or not.

If the inactivation determination timing becomes earlier and the downstream air-fuel ratio sensor is activated, the air-fuel ratio feedback control by the sensor can be started earlier. In addition, there is no need for special hardware configuration compared to those that determine activation or inactivity by reading the resistance value of the air-fuel ratio sensor, and there are fewer misjudgments compared to those that determine activation or deactivation based only on water temperature. It also has this effect.

[Brief explanation of drawings]

Fig. 1 is an overall block diagram for explaining the present invention in detail, Fig. 2 is a single 0□ sensor system and a 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; Figs. 4A and 5A are the 02 sensor output of Fig. 3; The circuit diagram of the processing circuit, Figures 4B and 5B are the output characteristic diagrams of the 0□ sensor output processing circuit in Figure 3, Figures 6, 8, 9, 11 and 12 are Flowchart for explaining the operation of the control circuit in FIG. 3; FIG. 7 is a timing diagram for supplementary explanation of the flowchart in FIG. 6; FIG. 10 is a supplementary explanation for the flowcharts in FIGS. 6 and 8. FIG. 13 is a timing diagram for supplementary explanation of the flowcharts of FIGS. 6 and 11. 1... Engine body, 3... Air flow meter,
4...Distributor, 5.6...Crank angle sensor, 10...Control circuit, 12...Catalytic converter, 13...Upstream side (first) 0□ sensor, 15...Downstream Side (second) 0□ sensor, 17... Throttle sensor, 18... Alarm.

Claims (1)

[Claims] 1. Provided respectively upstream and downstream of a catalytic converter for purifying exhaust gas provided in the exhaust system of an internal combustion engine,
first and second air-fuel ratio sensor means that generate a lean signal when inactive and detect the concentration of a specific component in the exhaust gas when activated; and according to the outputs of the first and second air-fuel ratio sensor means. a first air-fuel ratio control means for controlling the air-fuel ratio of the engine; a second air-fuel ratio control means for forcibly making the air-fuel ratio of the engine rich; and an activation or non-activation of the second air-fuel ratio sensor means. Activation/inactivation determining means for determining activation based on whether the output of the second air-fuel ratio sensor means exceeds a predetermined value or once increases or decreases; when the first air-fuel ratio control means is selected, and when the second air-fuel ratio sensor means is inactive, the second air-fuel ratio control means is selected to adjust the air-fuel ratio of the engine. An air-fuel ratio control device for an internal combustion engine, comprising: a fuel ratio adjusting means; 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein an alarm is displayed when the activation/inactivation determining means determines that the second air-fuel ratio sensor means is inactive. 3. The activation/inactivation determining means determines whether the engine is active or inactive when the engine cooling water temperature remains at a predetermined value or higher for a predetermined period of time. Air-fuel ratio control device for internal combustion engines. 4. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the second air-fuel ratio control means forcibly makes the air-fuel ratio of the engine rich only when the engine accelerates. 5. Provided respectively upstream and downstream of a catalytic converter for exhaust gas purification provided in the exhaust system of an internal combustion engine,
first and second air ratio sensor means that generate a rich signal when inactive and detect the concentration of a specific component in the exhaust gas when activated; and according to the output of each of the first and second air ratio sensor means a first air-fuel ratio control means for controlling the air-fuel ratio of the engine; a second air-fuel ratio control means for forcibly making the air-fuel ratio of the engine lean; and an activation or non-activation of the second air-fuel ratio sensor means. Activation/inactivation determining means for determining activation based on whether the output of the second air-fuel ratio sensor means exceeds a predetermined value or once increases or decreases; when the first air-fuel ratio control means is selected, and when the second air-fuel ratio sensor means is inactive, the second air-fuel ratio control means is selected to adjust the air-fuel ratio of the engine. An air-fuel ratio control device for an internal combustion engine, comprising: a fuel ratio adjusting means; 6. The air-fuel ratio control device for an internal combustion engine according to claim 5, wherein an alarm is displayed when the activation/inactivation determining means determines that the second air-fuel ratio sensor means is inactive. 7. According to claim 5, the activation/inactivation determining means determines whether the engine is active or inactive when the cooling water temperature of the engine continues to be at a predetermined value or higher for a predetermined period of time. Air-fuel ratio control device for internal combustion engines.