JPH066915B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using an air-fuel ratio sensor (in this specification, an oxygen concentration sensor (O ₂ )), and in particular, an air-fuel ratio feedback according to performance deterioration of the O ₂ sensor. Control improvements.

[Prior art]

Generally, the basic injection amount of the fuel injection valve is calculated according to the intake air amount (or intake air pressure) of the engine and the engine rotation speed, and the detection signal of a specific component in the exhaust gas of the engine, for example, the concentration of the oxygen component is detected. The basic injection amount is corrected according to the air-fuel ratio correction coefficient FAF calculated based on the detection signal of the O ₂ sensor, and the fuel amount actually supplied to the internal combustion engine is controlled according to the corrected injection amount. To do. By repeating this control, the air-fuel ratio of the engine is finally converged within a predetermined range. By such air-fuel ratio feedback control,
Since the air-fuel ratio can be controlled within a very narrow range near the theoretical air-fuel ratio, a three-way catalytic converter provided in the exhaust system, that is, three harmful components of CO, HC, and NOx contained in the exhaust gas are simultaneously purified. The purification performance of the catalytic converter can be kept high. In the air-fuel ratio feedback control (single O ₂ sensor system) described above, an O ₂ sensor for detecting the oxygen concentration is provided at a location in the exhaust system that is as close as possible to the combustion chamber, that is, at the exhaust manifold manifold upstream of the catalytic converter. However, the variation in the output characteristics of the O ₂ sensor hinders the improvement of the air-fuel ratio control accuracy. The causes of variations in the output characteristics of the O ₂ sensor are listed below. (1) Individual difference of O ₂ sensor itself, (2) Fuel injection valve and exhaust gas recirculation valve (EGR valve)
Non-uniform mixing of exhaust gas at the location where the O ₂ sensor is attached due to the tolerance of the assembly position of parts such as (3) Changes in the output characteristics of the O ₂ sensor over time or over time. In addition to the O ₂ sensor, the non-uniformity of the exhaust gas mixture changes and expands due to changes in the engine state such as the fuel injection valve, the exhaust gas recirculation flow rate, the tappet clearance, and the like over time, and manufacturing variations. Sometimes. A second O ₂ sensor is provided downstream of the catalytic converter in order to compensate for such variations in the output characteristics of the O ₂ sensor, variations in parts, and changes over time or over time, and the air-fuel ratio feedback control is performed by the upstream O ₂ sensor. In addition, a double O ₂ sensor system that performs air-fuel ratio feedback control using a downstream O ₂ sensor has already been proposed. For example, the first as well as calculating the air-fuel ratio correction coefficient FAF1, it calculates a second air-fuel ratio correction coefficient FAF2 in accordance with the output of the downstream O ₂ sensor in accordance with the output of the upstream O ₂ sensor,
The basic injection amount is corrected by these two air-fuel ratio correction coefficients FAF1 and FAF2. In this case, the O ₂ sensor provided on the downstream side of the catalytic converter has a lower response speed than the O ₂ sensor on the upstream side, but has an advantage that the variation in the output characteristics is small for the following reason. ing. (1) Downstream of the catalytic converter, the exhaust temperature is low, so there is little thermal effect. (2) Downstream of the catalytic converter, various poisons are trapped in the catalyst, so the amount of poisoning of the downstream O ₂ sensor is small. (3) The exhaust gas is sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the exhaust gas is close to the equilibrium state. Therefore, as described above, the first based on the outputs of the two O ₂ sensors, the air-fuel ratio feedback control for correcting the basic fuel injection quantity by the second air-fuel ratio correction coefficient (double O ₂ sensor system), the upstream O the variations in the output characteristics of the _second sensor can be absorbed by the downstream O ₂ sensor. Actually, as shown in FIG. 2, in the single O ₂ sensor system, when the output characteristic of the O ₂ sensor is deteriorated, the exhaust emission characteristic is directly affected, whereas the double O ₂ sensor system is directly affected.
The sensor system, even if the output characteristic of the upstream O ₂ sensor deteriorates, the exhaust emission characteristics are not deteriorated, that is, in the double O ₂ sensor system, downstream O ₂
Good exhaust emission is guaranteed as long as the sensor maintains stable output characteristics. On the other hand, stopped in the single O ₂ sensor system, comprising a deterioration detecting means for detecting the characteristic degradation due to aging or aging of the O ₂ sensor, air-fuel ratio feedback control when the characteristic deterioration of the O ₂ sensor is detected by the deterioration detecting means Air-fuel ratio control devices for performing open control have also already been proposed in JP-A-53-81826 and JP-A-57-13246. According to the above configuration, when the reliability of the O ₂ sensor output decreases due to characteristic deterioration and the air-fuel ratio feedback control is greatly deviated from the theoretical air-fuel ratio, the air-fuel ratio control can be switched to open control. It is possible to maintain the minimum air-fuel ratio control accuracy.

[Problems to be Solved by the Invention]

Even in the case of the double O ₂ sensor system from the above-mentioned conventional technique, deterioration detection means is provided in both the upstream and downstream O ₂ sensors,
When the deterioration of each O ₂ sensor is detected, the deteriorated O ₂ sensor is detected.
It is possible to stop the air-fuel ratio feedback control by the _two sensors. However, as described above, in the double O ₂ sensor system, even if the upstream O ₂ sensor deteriorates, the downstream O ₂ sensor can compensate the deviation of the air-fuel ratio, so that the upstream O ₂ sensor is substantially The weight of detecting deterioration is low. Further, if the upstream O ₂ sensor deteriorates and the air-fuel ratio feedback control by the upstream O ₂ sensor is stopped, the air-fuel ratio feedback control by only the downstream O ₂ sensor will be performed. Since the downstream O ₂ sensor has a lower control response speed than the upstream O ₂ sensor, it is difficult to maintain the air-fuel ratio at the stoichiometric air-fuel ratio only by the air-fuel ratio feedback control using only the downstream O ₂ sensor. Further, the deterioration detecting means needs to dispose two O ₂ sensors at the same location or store the maximum value and the minimum value of the output of the O ₂ sensor within a predetermined time, which is generally costly. Therefore, if both the upstream and downstream O ₂ sensors are equipped with deterioration detecting means, the cost of the entire air-fuel ratio control device will increase considerably. An object of the present invention is to realize the air-fuel ratio control according to the performance deterioration of the O ₂ sensor without unnecessarily increasing the cost by determining whether or not the deterioration detection means is equipped depending on the importance of the deterioration detection. .

[Means for Solving the Problems]

The above-mentioned problems are solved by the following means in the present invention as shown in FIG. First and second air-fuel ratio sensors provided upstream and downstream of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine to detect a concentration of a specific component in the exhaust gas; An air-fuel ratio controller for adjusting the air-fuel ratio of the internal-combustion engine according to each output of the second air-fuel ratio sensor, the air-fuel ratio controller for the internal-combustion engine being provided only for the second air-fuel ratio sensor. Deterioration detecting means for detecting characteristic deterioration of the second air-fuel ratio sensor, and outputs of the first and second air-fuel ratio sensors when deterioration of the second air-fuel ratio sensor is not detected by the deterioration detecting means. According to the above, the air-fuel ratio of the internal combustion engine is adjusted by the air-fuel ratio adjusting means, and when deterioration of the second air-fuel ratio sensor is detected, the air-fuel ratio adjusting means according to the output of the second air-fuel ratio sensor. by Air-fuel ratio control system for an internal combustion engine, characterized in that it comprises a control means for stopping the adjustment of the air-fuel ratio of the serial engine.

[Action]

According to the above configuration, characteristic deterioration of only the second air-fuel ratio sensor, which has a high importance for deterioration detection, is constantly monitored by the deterioration detecting means, and when the second air-fuel ratio sensor deteriorates, the second air-fuel ratio sensor immediately. The adjustment of the air-fuel ratio of the internal combustion engine due to is stopped. On the other hand, the characteristic deterioration of the first air-fuel ratio sensor is not detected.

【Example】

 First, O of the three-way catalyst_TwoExplain storage effect
It The three-way catalyst purifies NOx, CO, and HC at the same time.
Therefore, the purification rate η is as shown by the alternate long and short dash line in FIG.
On the rich side of the theoretical air-fuel ratio (λ = 1), the purification of NOx is
The conversion rate is large, and the purification rate of CO and HC is large on the lean side.
(HC is not shown, but has the same tendency as CO). This
As a result, the required purification rate η₀Controllable air fuel
The ratio window w is very narrow (w = w₁), Therefore,
The air-fuel ratio feedback control for the air-fuel ratio is also essentially
This range (w₁) Must be done in. But,
The three-way catalyst is O when the air-fuel ratio is lean._TwoCapture
Take in CO and HC when the air-fuel ratio becomes rich
O which was taken in when lean_TwoWhen you react with
Say O_TwoHas storage effect, air-fuel ratio feedback
Control like this_TwoActively use storage effect
In order to control the air-fuel ratio with the optimum frequency and amplitude.
I am sorry. As a result, as shown by the solid line in FIG.
During air-fuel ratio feedback control, the purification rate η improves and
The controllable air-fuel ratio window w is substantially wide (w =
w_Two)Become. In this case, O provided upstream of the three-way catalyst_TwoSE
The output of the sensor is, for example, a frequency of 2H as shown in FIG. 4A.
It changes with z. However, O_TwoWhen the sensor deteriorates, oxygen_TwoSE
It becomes difficult to enter the sirconia element of the sensor, and as a result,
When the gas changes from rich to lean
Is O_TwoChange the sensor output from rich signal to lean signal.
Is delayed, that is, O_TwoMaximum to minimum sensor output
The change time to becomes longer. At this time, the output voltage is low enough
The air-fuel ratio becomes rich before lowering. As a result, Fig. 4B
As shown in, the control air-fuel ratio frequency decreases and
O_TwoThe storage effect is also small. Like this, O
_TwoThe air-fuel ratio controllable when the storage effect becomes small.
Window w becomes narrower, for example w = w₁(1H at frequency
z) and O_TwoThe sensor output amplitude also becomes smaller. Note that FIG. 5 shows the air-fuel ratio window w and the control air-fuel ratio frequency.
The relationship with f is shown. The deterioration detecting means in this embodiment has such O_TwoSensor
By detecting the magnitude of the output amplitude of_TwoSensor
The deterioration is detected. FIG. 6 shows an embodiment of an air-fuel ratio control system for an internal combustion engine according to the present invention.
It is an overall outline figure showing an example. In Figure 6, the institution book
An air flow meter 3 is provided in the intake passage 2 of the body 1.
ing. The air flow meter 3 directly measures the intake air amount.
Intake air with a built-in potentiometer
Generate an analog voltage output signal proportional to the quantity. this
The output signal is an A / D converter with a multiplexer in the control circuit 10.
It is supplied to the converter 101. To distributor 4
Indicates that its axis is converted into a crank angle, for example, every 720 °.
Crank angle sensor that generates a reference position detection pulse signal
The standard position is detected every 30 ° converted to the crank angle and crank angle.
The crank angle sensor 6 for generating the output pulse signal is provided.
Has been. Pulse signals of these crank angle sensors 5 and 6
Is supplied to the input / output interface 102 of the control circuit 10.
Of these, the output of the crank angle sensor 6 is the CPU 1
03 interrupt terminal. Further, the intake passage 2 is pressurized from the fuel supply system for each cylinder.
A fuel injection valve 7 is provided for supplying fuel to the intake port.
Has been. In addition, the water jacket of the cylinder block of the engine body 1
The water temperature sensor 9 for detecting the temperature of the cooling water
Is provided. The water temperature sensor 9 is the cooling water temperature THW.
Generates an electric signal of analog voltage according to. This output
Is also supplied to the A / D converter 101. Exhaust gas in the exhaust system downstream from the exhaust manifold 11
Purifies three harmful components HC, CO, and NOx at the same time
A catalytic converter 12 that accommodates a three-way catalyst is provided.
It The exhaust manifold 11 includes a catalytic converter 12
Upstream of the first O_TwoA sensor 13 is provided and the catalyst
The exhaust pipe 14 on the downstream side of the inverter 12 has a second O_TwoSen
Service 15 is provided. O_TwoExhaust for sensors 13 and 15
An electric signal corresponding to the oxygen component concentration in the gas is generated. You
Nachi, O_TwoFrom the sensors 13 and 15, the air-fuel ratio is the theoretical air-fuel ratio.
Different output power depending on the lean side or rich side of the ratio
The pressure is input to the A / D converter 101 of the control circuit 10. The control circuit 10 is, for example, a microcomputer.
A / D converter 101, input / output interface
CPU 103, ROM 104, RAM in addition to memory 102
105, a clock generation circuit 106 and the like are provided. In the control circuit 10, the down counter 107,
Flip-flop 108 and drive circuit 109 are fuel
It is for controlling the injection valve 7. That is, later
In the routine, the fuel injection amount TAU is
Flip-flop 1 as well as preset in the data 107
08 is also set. As a result, the drive circuit 109
Energization of the injection valve 7 is started. On the other hand, down counter 10
7 counts the clock signal (not shown) and finally the key
When the carry-out terminal becomes "1" level, the
The drive circuit 109 is burned when the flip-flop 108 is reset.
The energization of the fuel injection valve 7 is stopped. That is, the above-mentioned fuel injection
The fuel injection valve 7 is energized by the amount TAU, and therefore the fuel injection valve 7 is
The amount of fuel corresponding to the injection amount TAU is sent to the combustion chamber of the engine body 1.
Will be involved. It should be noted that the interrupt generation of the CPU 103 is caused by the A / D converter 1
Input / output interface 10 when A / D conversion of 01 is completed
When 2 receives the pulse signal of the crank angle sensor 6,
Received an interrupt signal from the lock generation circuit 106
Time, etc. Intake air amount data Q of the air flow meter 3 and cooling water
The temperature data THW is the A / D conversion rule that is executed every predetermined time.
Captured in the RAM 105 and stored in a predetermined area of the RAM 105.
Is stored. That is, the data Q and
And THW are updated every predetermined time. Also rotation
The speed data Ne is obtained for each 30 ° CA of the crank angle sensor
Calculated by an interrupt and stored in a predetermined area of RAM 105
Is stored. The operation of the control circuit of FIG. 6 will be described with reference to the flow charts of FIGS.
The chart will be described. FIG. 7 shows the air-fuel ratio feedback control flags F1 and F2.
This is a routine for making a decision, which is a predetermined time, for example, 4
It is executed every ms. In step 701, the air-fuel ratio is closed.
Loop control (feedback control) conditions are met
Or not. Fuel increase operation during engine start and after start
Medium, during warm-up increase operation, during power increase operation, lean control
Medium, O_TwoClosed loop control in all cases such as sensor inactivity
Condition is not satisfied, otherwise closed-loop control condition
It is approved. In addition, O_TwoDetermining the active / inactive state of the sensor
Another is to read the water temperature data THW from the RAM 105 and
Whether to determine whether the THW ≧ 70 ° C. or
O_TwoDetermine whether the output level of the sensor has been inverted once
It is done by When the closed loop condition is not satisfied
In step 721, the upstream side O_TwoOn the sensor 13
According to the air-fuel ratio feedback control flag F1 (hereinafter,
The F / B flag F1) is set to "0", and step 7 is performed.
Proceed to 22 and go downstream O_TwoAir-fuel ratio fee by sensor 15
The feedback control flag F2 (hereinafter, the sub F / B flag F
2) is set to "0" and the process proceeds to step 726. That is, air fuel
Do not perform ratio feedback control at all. other
On the other hand, if the closed loop condition is satisfied, the process proceeds to step 702. At step 702, the main F / B flag F1 is set to "1".
And upstream O_TwoAir / fuel ratio feedback sensor 13
Control. In step 703, the rotation speed data is read from the RAM 105.
Read out Ne and 1000 rpm ≤ Ne ≤ 4000 rp
It is determined whether or not m, 1000 rpm ≦ Ne ≦ 4000r
Only when it is pm, the process proceeds to step 704. That is, the rotation speed
If Ne is too small, O_TwoThe response speed of the sensor is small
On the other hand, if the rotation speed Ne is too high, in the high rotation range
Has a region where the fuel injection amount is increased to make it rich.
Increase amount increase area and other areas near the set rotation speed
Causes hunting, and the air-fuel ratio changes drastically.
O_TwoBecause the operation of the sensor becomes unstable, the downstream side O_Two
The determination of the deterioration of the sensor 15 is stopped. Also, step 7
In 04, the intake air amount data Q is read from the RAM 105.
10m out³/ h ≦ Q ≦ 120m³/ h or not,
10m³/ h ≦ Q ≦ 120m³Step 70 only when / h
Go to 5. That is, the intake air amount Q as well as the rotation speed Ne
Is too small, O_TwoThe response speed of the sensor decreases,
On the other hand, if the intake air amount Q is too large, the engine speed N
e is in the high speed range, and the fuel injection amount is increased in the high speed range.
There is a region to make fuel rich, and the fuel increase start setting rotation speed
In the vicinity, hunting occurs in the increase area and other areas.
However, the air-fuel ratio changes drastically._TwoSensor operation
Becomes unstable, so the downstream side O_TwoDetermining deterioration of sensor 15
Cancel another. Note that steps 402 and 403 are both
Either one may be omitted, and the upper limit of the rotation speed Ne
Value, lower limit, and upper and lower limits of intake air amount Q are required.
Not changed as needed. In step 705, the downstream side O_TwoOutput V of sensor 15_TwoTo
A / D converted and imported, and steps 706 and 707
The minimum level V_L, Maximum level V_HCompare with. Na
Oh, V_L, V_HIs the comparison voltage V as an initial value_R2For example
0.55V is set in the initial routine
And As a result, V_L≤V_Two≤V_HIf so, the minimum
Bell V_L, Maximum level V_HBoth remain unchanged, V_Two<V
_LIf so, V_L← V_TwoAs the minimum level V_LUpdate
And then V_Two> V_HThen V_H← V_TwoAs the maximum level V
_HTo update. Thus, steps 706-70
In 9, the downstream side O_TwoThe minimum level V of the output of the sensor 15_L
And the maximum level V_HAnd are calculated. In step 710, the counter C is incremented by +1 to
In step 711, the counter C is C ≧ C₀Determine whether
It The counter C is cleared by the initial routine.
It is assumed that Therefore, steps 701 and 70
If the conditions 3 and 704 are satisfied, step 70
Flow from 5 to 709 is C₀Repeated 71 times
Go to 2. That is, C <C₀If so, go to step 726.
Proceed directly and hold flag F2 and state before alarm
To be done. Value C₀Can be constant, for example 30, and in FIG. 8A
As shown, the engine load such as the intake air amount Q or
It may be changed according to the rotation speed Ne. That is, the eighth
In Figure A, as the load decreases, the downstream side O_TwoSensor
Since the response speed of 15 decreases, the value C₀To increase
It In step 712, the maximum level V_HAnd the minimum level V_L
Let w be the difference between_H-V_L In step 713, w ≧ w₀Or not. this
Value w₀May be constant, for example, 0.4V, and 8B
As shown in the figure, if the engine load such as intake air amount Q
Alternatively, it may be changed according to the rotation speed Ne. That is,
In FIG. 8B, when the load decreases, the downstream side O_TwoSensor
Exhaust gas transportation delay time to 15 becomes large, and this result
Fruit, O_TwoSince the sensor output amplitude increases, the value w₀Larger
However, if the load becomes smaller (for example, eye
Dollar state), O_TwoThe sensor is cooled and its output amplitude is small.
Considering that it will get worse. In step 713, w ≧ w₀If so, downstream side O_TwoSE
It is assumed that the output of the sensor 15 has not deteriorated (characteristic deterioration) yet.
Then, in step 714, the sub F / B flag F2 is set together.
Set to "1", so two O's_TwoBy the sensors 13 and 15
To perform air-fuel ratio feedback control. Furthermore
Then, in step 715, the alarm is released (however,
(If currently displayed), and the process proceeds to step 718. In step 713 w <w₀If so, step 716
And the sub F / B flag F2 is set to "0".
Upstream O_TwoAir-fuel ratio feedback by sensor 13 only
Get control. Further, in step 717,
The alarm is displayed and the process proceeds to step 718. That is, the predetermined
Time C₀Maximum level V within_HAnd the minimum level V_LDifference from
Is a predetermined value w₀If less than O_TwoSensor 15
To consider that output deterioration (characteristic deterioration) has occurred
Done O_TwoIt is a deterioration detecting means of the sensor. Steps 718 to 720 are for initialization. One
In steps 718 and 719, the minimum level V_L,
Maximum level V_HTogether with the comparison voltage V_R2(0.55V)
Then, in step 720, the counter C is cleared. On the other hand, one of the judgment results in steps 703 and 704
If no, go to step 723 to display the alarm
Or not. As a result, in the alarm display
If so, go directly to step 726. In other words, this place
In this case, the main F / B flag F1 is "1", and the sub F / B
The B flag F2 is "0", and therefore the downstream side O_TwoSen
The air-fuel ratio feedback control by the server 15 is stopped and the
Flow side O_TwoOf the air-fuel ratio feedback control by the sensor 13
Mika is done. If no alarm is being displayed in step 723, the sub
F / B flag F2 is set to "1" and two O_TwoSensor 1
To perform air-fuel ratio feedback control by 3 and 15
Then, in step 725, the counter C is cleared.
Then, the process proceeds to step 726. In this way, the downstream side O_TwoMaximum output of sensor 15
Bell V_HAnd the minimum level V_LDifference w is a predetermined value w₀Less than
If there is, downstream O_TwoDeterioration of output on the sensor 15 (characteristic
(Deterioration) is considered to have occurred, and the sub F / B flag F2
Is set to “0”. Note that the alarm display was once performed in step 717.
Sometimes downstream O_TwoNote that the alarm display was once performed in step 717.
Sometimes downstream O_TwoFor the purpose of checking the sensor 15,
In order to prevent the display of the alarm from disappearing, the control circuit 10
By storing in a backup RAM (not shown),
You can also keep a history of alarm displays. Fig. 9 shows upstream O_Two1st based on the output of the sensor 13
For calculating the air-fuel ratio correction coefficient FAF1 of
This is a feedback control routine for a predetermined time, for example, 4
It is executed every ms. In step 901, the route shown in FIG.
Whether the main F / B flag F1 set by Chin is "1"
Determine whether. When F1 = "0", step 913
Go to and set FAF1 = 1.0, and when F1 = “1”
Advances to step 902, and the air-fuel ratio feedback correction is performed.
To do. In step 902, O_TwoOutput voltage V of sensor 13₁To
A / D conversion and import, V₁Is the comparison voltage V_R1For example
It is determined whether it is 0.45 V or less. In other words, the air-fuel ratio
Or not (rich). And lean
(V₁≤V_R1), In step 903, the first
Determine if lean or not, that is, from rich to lean
It is determined whether or not it is a change point. As a result, the first lean
Then, in step 904, FAF1 = FAF1 + A
Up, and otherwise, in step 905, FA
F1 is increased by a constant value a. That is, step 9
05 is fuel injection when the lean signal is continuously output
Integral processing is performed to gradually increase the amount.
By repeating this routine, FAF
1 is increased by a. The skip amount A is a
It is set sufficiently larger. That is, A >> a. Finally in step 904 or step 905
The calculated first air-fuel ratio correction coefficient FAF1 is calculated in step 90.
At 6,907, the maximum value of 1.2 is guarded. On the other hand, in step 902, (V₁> V_R1)
If it is, whether or not it is the first rich in step 908
(Lean or not), that is, from lean to rich
It is determined whether or not it is a change point. As a result, the first rich
Then, in step 909, FAF1 = FAF1-A
FA in step 910
F1 is decreased by a constant value a. That is, step 9
10 is fuel injection when the output of the rich signal continues
The integration process is performed to gradually decrease the amount.
By repeating this routine, FAF
1 is decreased by a. The first determined finally in steps 909 and 910.
The air-fuel ratio correction coefficient FAF1 is set in steps 911 and 912.
Guarded to a minimum of 0.8. The steps 906, 907, 911, and 912
The air-fuel ratio correction coefficient FAF1 is large for some reason.
The value when it gets too small or too small
Control the air-fuel ratio of the engine with
This is to prevent it from becoming a ghost. Store FAF1 in RAM 105 at step 914
Then, in step 915, this routine ends. Fig. 10 shows O on the downstream side_TwoBased on the output of the sensor
The second air-fuel ratio fee for calculating the air-fuel ratio correction coefficient FAF2
This is a feedback control routine for a predetermined time, for example, 1 s.
It is executed every time. In step 1001, the route shown in FIG.
Whether the sub F / B flag F2 set by Chin is "1"
To determine. When F2 = "0", step 1013
Go to and set FAF2 = 1.0, and when F2 = "1"
Proceeds to step 1002, and air-fuel ratio feedback correction
I do. In step 1002, O_TwoOutput voltage V of sensor 15_Two
A / D conversion and import, V_TwoIs the comparison voltage V_R2for example
For example, it is determined whether it is 0.55V or less. That is, the air-fuel ratio is
It is determined whether it is lean or not (rich). In addition, in FIG.
The value obtained in step 705 is stored in the RAM 105 in advance.
It may be stored and read out. Also step
Comparison voltage V at 1002_R2On the catalytic converter 12
O downstream_TwoStep 902 due to different sensor characteristics
Comparison voltage V_R1Set higher. And lean
(V_Two≤V_R2), First in step 1003
Is lean, that is, from rich to lean
It is determined whether or not the change point of As a result, in the first lean
If so, in step 1004, FAF2 = FAF2 + B.
Increase in a skip manner, otherwise go to step 1005
Then, FAF2 is increased by a constant value b. That is,
Up 1005 is when the lean signal is continuously output.
Integral processing to gradually increase the fuel injection amount
Is. By repeating this routine
FAF2 is increased by b. In addition, skip
The quantity B is set to be sufficiently larger than b. That is, B >> b
Is. Final in step 1004 or step 1005
The second air-fuel ratio correction coefficient FAF2 obtained in
The maximum value of 1.2 is guarded at 1006 and 1007. On the other hand, in step 1002, (V_Two> V_R2) Is determined
If it is, whether or not it is the first rich in step 1008
Or lean, that is, from lean to rich
It is determined whether or not the change point of As a result, in the first rich
If so, FAF2 = FAF2-B in step 1009.
Decrease in skips, otherwise go to step 1010
FAF2 is decreased by a constant value b. That is,
Up 1010 is when the rich signal output continues.
Integral processing to gradually reduce the fuel injection amount
Is. By repeating this routine
FAF2 is reduced by b. The number finally obtained in steps 1009 and 1010
The air-fuel ratio correction coefficient FAF2 of 2 is 1011 and 1012.
Guarded to a minimum of 0.8. Note that steps 1006, 1007, 1011, 101
The guard at 2 is for some reason the air-fuel ratio correction coefficient FAF
When 2 becomes too large or too small
And control the air-fuel ratio of the engine with that value to overrich,
This is to prevent becoming over lean. Store FAF2 in RAM 105 at step 1014
Then, in step 1015, this routine ends. FIG. 11 shows an injection amount calculation routine in which a predetermined crank
It is executed every corner, for example, every 360 ° CA. Step 1
In 101, the intake air amount data Q and
And the rotation speed data Ne are read to obtain the basic injection amount TAUP
Is calculated. For example, TAUP ← KQ / Ne (K is constant
Number). Cool down from RAM 105 in step 1102.
The discharge water temperature data THW is read out and stored in the ROM 104.
The warm-up increase value FWL is interpolated by the one-dimensional map
It As shown in the figure, this warm-up increase value FWL is
Set to decrease as the wastewater temperature THW rises
Has been done. In step 1103, the final injection amount TAU is calculated by TAU ← TAUP · FAF1 · FAF2 · (1 + FWL + α) + β. Note that α and β are other operating state parameters.
The correction amount is determined by the
Is it a signal from the rottle position sensor or an intake air temperature sensor?
The amount of correction determined by the signal from the
These are also stored in the RAM 105. Next
Then, in step 1104, the injection amount TAU is reduced.
Flip-flop 10
Set 8 to start fuel injection. And step
At step 1105, this routine ends. Note that the above
Thus, when the time corresponding to the injection amount TAU elapses,
Uncounter 107 carrier flip
The rop 108 is reset and the fuel injection ends. FIG. 12 shows the flow chart of FIG. 9 and FIG.
First and second air-fuel ratio correction coefficients FAF1 and FA obtained by
FIG. 11 is a timing chart for explaining F2. Upstream O_Two
Output voltage V of sensor 13₁Is shown in Fig. 12 (A)
If the comparison result in step 902 in FIG.
This is as shown in FIG. 12 (B). As a result, Fig. 12
As shown in (C), when switching between rich and lean
FAF1 skips only A. On the other hand, downstream side O_TwoSen
Output voltage V_TwoChanges as shown in Fig. 12 (D).
Then, the comparison result in step 1002 of FIG. 10 is
As shown in FIG. 12 (E). As a result, Fig. 12
As shown in (F), when switching between rich and lean
Then FAF2 skips only B. If the main F / B flag F1 is "0", FIG.
The control of FAF1 shown in (C) is stopped, and for example, FA
F1 = 1.0 is held, while the sub F / B flag F2 is
If it is "0", control of FAF2 shown in FIG.
Is stopped and held at FAF2 = 1.0, for example. The integration constant a of the first air-fuel ratio correction coefficient FAF1 is
2 is larger than the integration constant b of the air-fuel ratio correction coefficient FAF2.
It is set to a predetermined value, for example, a: b = 1000: 1. In other words, the air-fuel ratio feedback control
Responsive upstream O_TwoMainly control by the sensor 13
The downstream side with poor responsiveness_TwoControl by sensor 15
Is to be followed. According to the above embodiment, the downstream O_TwoCharacteristics of sensor 15 only
The deterioration consists of steps 705 to 720 in FIG.
Always monitored by the detection means_TwoSensor 15
Immediately after deterioration, O downstream_TwoWithin the sensor 15
The adjustment of the air-fuel ratio of the fuel engine is stopped. On the other hand, upstream O_TwoNo detection of characteristic deterioration of the sensor 13 is performed.
I don't know. As a result, the upstream side O_TwoIf the characteristics of the sensor 13 are deteriorated
Even upstream O_TwoThe adjustment of the air-fuel ratio by the sensor 13 is stopped
Not downstream O_TwoWhen the characteristic deterioration of the sensor 15 is detected
If not, upstream side O_TwoEmpty due to deterioration of sensor 13 characteristics
The difference in fuel ratio is set to the downstream side O_TwoCompensated by sensor 15, downstream
Side O_TwoThe adjustment of the air-fuel ratio using only the sensor 15
Therefore, the air-fuel ratio can be maintained at the stoichiometric air-fuel ratio. Also, the downstream side O_TwoWhen the characteristic deterioration of the sensor 15 is detected
In the case of O_TwoWhether the characteristics of the sensor 13 have deteriorated
Regardless of this, the air-fuel ratio will deviate from the theoretical air-fuel ratio.
Therefore, downstream side O_TwoThe adjustment of the air-fuel ratio by the sensor 15 is stopped.
And upstream O_TwoAir-fuel due to deterioration of sensor 13 characteristics
Deviation of ratio is downstream O_TwoIncreased due to deterioration of sensor 15 characteristics
It will not be done. Further, the deterioration detecting means is the downstream side O_TwoOnly for sensor 15
Is a low-cost air-fuel ratio controller.
There is. Incidentally, in the above-mentioned embodiment, the downstream side O_TwoCharacteristics of sensor 15
If deterioration is detected, upstream O_TwoThe sensor 13 is special
O upstream regardless of deterioration_TwoSensor 1
3 continues to adjust the air-fuel ratio, but the downstream side O_TwoSE
When the characteristic deterioration of the sensor 15 is detected, the upstream side O_TwoSen
The adjustment of the air-fuel ratio by the server 13 may also be stopped. That is, the downstream side O_TwoThe characteristic deterioration of the sensor 15 is detected.
In case of_TwoAdjustment of air-fuel ratio by sensor 13
Whether or not to stop is determined by the entire air-fuel ratio control device for the internal combustion engine.
Closed loop control of air-fuel ratio, which can be determined by all characteristics
Accuracy is low, air-fuel without feedback control
Of the air-fuel ratio control device that cannot maintain the accuracy of the ratio control sufficiently
In case of upstream O_TwoDeterioration of the characteristics of the sensor 13
Even if it is better to continue the air-fuel ratio feedback control
is there. Further, in the above-described embodiment, the two air-fuel ratio correction factors FAF
1, FAF2 is introduced, and each is upstream O_TwoSensor
13 is calculated according to each output, but one air-fuel ratio supplement
Positive coefficient O upstream_TwoSensor 13 and downstream O_TwoSensor
The same applies when the calculation is performed according to both outputs of 15. further,
Upstream O_TwoAir-fuel ratio feedback control by sensor 13
Control constants, such as proportional control constants and integral control constants
Number, skip control constant, upstream O_TwoComparative voltage of sensor 13
Pressure (Reference: Japanese Patent Laid-Open No. 55-37562), delay time
(Reference: JP-A-55-37562, JP-A-58-58)
No. 72647), etc._TwoComplemented by sensor 15
Double O to correct_TwoThe present invention can also be applied to a sensor system.
It Also, as an intake air amount sensor, replace the air flow meter.
Instead, use Karman vortex sensor, heat wire sensor, etc.
You can also Furthermore, in the above-described embodiment, the intake air amount and the engine speed are
The fuel injection amount is calculated according to the rolling speed, but the intake air
Pressure and engine speed, or throttle valve opening
And calculate the fuel injection amount according to the engine speed.
Yes. Further, in the above-described embodiment, the fuel injection valve is used to connect to the intake system.
I showed an internal combustion engine that controls the fuel supply of
The present invention can be applied to an internal combustion engine. For example,
With the Ktrick Bleed Air Control Valve
Adjust the air bleed amount of the
And control the air-fuel ratio by introducing air into the slow passage
Things, adjust the amount of secondary air sent to the exhaust system of the engine
The present invention can be applied to such things. In this case,
Basic fuel equivalent to basic injection amount TAUP in UP 1101
The rate of supply is determined by the carburetor itself, i.e.
Depending on the intake pipe negative pressure according to the amount of incoming air and the rotation speed of the engine
Determined and final fuel injection amount TAU in step 1103
The amount of supply air corresponding to is calculated. Further, in the above-described embodiment, the air-fuel ratio sensor is O_TwoSE
Sensor was used, but CO sensor, lean mixture sensor
Etc. can also be used. In addition, CO sensor, lean
The gesture sensor is also O_TwoHas the same output deterioration characteristics as the sensor
To do. Moreover, the above-described embodiment is a microcomputer
Although it is composed of digital circuits,
It can also be constituted by a road.

【effect】

As described above, according to the present invention, regardless of whether the characteristics of the upstream O ₂ sensor have deteriorated, if the characteristics of the downstream O ₂ sensor have not deteriorated, the output of the upstream O ₂ sensor is used. The adjustment of the air-fuel ratio (air-fuel ratio feedback control) is continued. Therefore, unless the downstream O ₂ sensor does not characteristic deterioration, an air-fuel ratio of the upstream O ₂ sensor and the downstream O ₂ adjustment of the air-fuel ratio in response to both the output of the sensor (air-fuel ratio feedback control) is performed by an internal combustion engine Can be accurately controlled to the stoichiometric air-fuel ratio. Further, since it is not necessary to confirm whether or not the characteristics of the upstream O ₂ sensor have deteriorated, deterioration detecting means for the upstream O ₂ sensor becomes unnecessary, and a low-cost air-fuel ratio control device can be realized.

[Brief description of drawings]

FIG. 1 is an overall block diagram for explaining the configuration of the present invention.

FIG. ₂ is an exhaust emission characteristic diagram illustrating a single O ₂ sensor system and a double O ₂ sensor system.

FIG. 3 is a graph explaining the storage effect of a three-way catalyst.

[FIGS. 4A and 4B] Timing charts showing an example of output waveforms of the O ₂ sensor.

FIG. 5 is a graph showing the relationship between the control air-fuel ratio frequency and the air-fuel ratio window.

FIG. 6 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention.

7 and 9 to 11 are flowcharts for explaining the operation of the control circuit of FIG.

[FIGS. 8A and 8B] Predetermined value C ₀ and step 7 in step 711 of FIG.
Graph illustrating the predetermined value _{w 0} of 13.

FIG. 12 is a timing chart for explaining changes in air-fuel ratio correction coefficients FAF1 and FAF2. DESCRIPTION OF SYMBOLS 1 ... Engine main body, 3 ... Air flow meter, 4 ... Distributor, 5, 6 ... Crank angle sensor, 10 ... Control circuit, 12 ... Catalytic converter, 13 ... Upstream (first) O ₂ sensor, 15 ... Downstream ( Second) O ₂ sensor,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takatoshi Masui 1 Toyota-cho, Toyota-shi, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Toshiyasu Katsuno 1-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (72) Inventor Toshio Tanahashi 1 Toyota Town, Toyota City, Aichi Toyota Motor Co., Ltd.

Claims (1)

[Claims] 1. A first and a second detector, which are provided respectively upstream and downstream of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine to detect a concentration of a specific component in the exhaust gas.
An air-fuel ratio control device for adjusting the air-fuel ratio of the internal combustion engine according to the outputs of the first and second air-fuel ratio sensors. A second air-fuel ratio sensor provided only in the second air-fuel ratio sensor to detect characteristic deterioration of the second air-fuel ratio sensor; and when the deterioration detection means does not detect deterioration of the second air-fuel ratio sensor, the first, The air-fuel ratio of the internal combustion engine is adjusted by the air-fuel ratio adjusting means according to each output of the second air-fuel ratio sensor, and when deterioration of the second air-fuel ratio sensor is detected, An air-fuel ratio control apparatus for an internal combustion engine, comprising: a control unit that stops adjustment of the air-fuel ratio of the internal combustion engine by the air-fuel ratio adjusting unit according to output.