JPH048284Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The invention provides an air-fuel ratio sensor (in this specification, an oxygen concentration sensor (O ₂ sensor)) on the upstream side of a catalytic converter and inside the converter, and 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 O ₂ sensor in a catalytic converter in addition to air-fuel ratio feedback control using an O ₂ sensor in a catalytic converter.

[Conventional technology]

Simple air-fuel ratio feedback control (single
_O2 sensor system) detects oxygen concentration
The O ₂ sensor is installed in the exhaust system as close to the combustion chamber as possible, that is, in the exhaust manifold assembly section upstream of the catalytic converter, but due to variations in the output characteristics of the O ₂ sensor, it is difficult to improve the accuracy of air-fuel ratio control. There is a problem. In order to compensate for variations in the output characteristics of the O ₂ sensor, variations in parts such as fuel injection valves, and changes over time or aging, a second O ₂ sensor is provided downstream of the catalytic converter, and the upstream O ₂ sensor A double O ₂ sensor system has already been proposed that performs air-fuel ratio feedback control using a downstream O ₂ sensor in addition to air-fuel ratio feedback control. this double
In the O ₂ sensor system, the O ₂ sensor installed downstream of the catalytic converter has a lower response speed than the upstream O ₂ sensor, but it has the advantage of less variation in output characteristics for 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 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 an equilibrium state.

Therefore, as mentioned above, air _- fuel ratio feedback control (double
O ₂ sensor system) allows variations in the output characteristics of the upstream O ₂ sensor to be absorbed by the downstream O ₂ sensor. In fact, as shown in Figure 2, in a single O ₂ sensor system, if the output characteristics of the O ₂ sensor deteriorate, it directly affects the exhaust emission characteristics, whereas in a double O ₂ sensor system, the upstream Even if the output characteristics of the side _O2 sensor deteriorate,
Exhaust emission characteristics are not deteriorated. In other words, in the double O ₂ sensor system, good exhaust emissions are guaranteed as long as the downstream O ₂ sensor maintains stable output characteristics.

[Problem that the invention attempts to solve]

However, in the double O ₂ sensor system described above, the O ₂ sensor is of the zirconia type, which requires a reference gas (generally atmospheric air), and therefore, in particular the downstream O ₂ sensor located downstream of the catalytic converter. However, when a vehicle drives through a river, swamp, pond, etc., water, mud, etc. flow into the reference gas side, resulting in a reduction in output. Furthermore, since the aforementioned downstream O ₂ sensor is located on the low temperature side, it is susceptible to the influence of unforeseen gas, and therefore there is a problem in that it cannot accurately detect the stoichiometric air-fuel ratio.

[Means for solving problems]

The purpose of this invention is to prevent water, mud, etc. from flowing in.
Without causing a decrease in the output of the O ₂ sensor, and
The purpose is to propose a double _O2 sensor system that can accurately detect the stoichiometric air-fuel ratio, and its configuration is as follows:
A semiconductor O ₂ sensor is used as the downstream O ₂ sensor, and this semiconductor O ₂ sensor is provided inside the catalytic converter on the high temperature side.

Note that installing a zirconia-type O ₂ sensor in the catalytic converter, especially in the center, requires a large element length, which causes thermal distortion.
In the case of automobiles, it cannot withstand the thermal shock of about 50℃/s, and the sealing material of the device, such as talc and Cu packing, is not heat resistant.
It's impossible.

[Effect]

Compared to zirconia-type sensors, semiconductor-type O ₂ sensors do not require a reference gas and have more freedom in determining the distance between the detection part and the sensor housing mounting part, so they can be installed inside the catalytic converter. As a result, there is no reduction in output even if water, mud, etc. enter, and the catalyst is easily activated by the influence of the catalyst temperature of the catalytic converter, thus making it possible to accurately detect the stoichiometric air-fuel ratio.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 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. 1, an air flow meter 3 is provided in an intake passage 2 of an engine body 1. As shown in FIG. air flow meter 3
The device directly measures the amount of intake air, and includes a built-in potentiometer to generate an analog voltage output signal proportional to the amount of intake air. This output signal is supplied to an A/D converter 101 with a built-in multiplexer of the control circuit 10. Distributor 4 has an axis whose axis is converted into a crank angle, for example.
The crank angle sensor 5 generates a reference position detection pulse signal every 720° and converts it into a crank angle.
A crank angle sensor 6 is provided that generates a reference position detection pulse signal every 30 degrees. The pulse signals of these crank angle sensors 5 and 6 are transmitted to the control circuit 10.
The output of the crank angle sensor 6 is supplied to the input/output interface 102 of the CPU 10.
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, the water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of cooling water. The water temperature sensor 9 generates an analog voltage electrical signal according to the temperature THW of the cooling water. This output is also from A/D converter 1
01.

The exhaust system downstream of the exhaust manifold 11 contains three harmful components in the exhaust gas: HC, CO,
A catalytic converter 12 is provided that houses a three-way catalyst that simultaneously purifies NOx.

A first O 2 sensor 13 is provided in the exhaust manifold 11, that is, on the upstream side of the catalytic converter 12, and a second O ₂ sensor 13 is provided in the catalytic converter 12.
An O ₂ sensor 14 is provided. _O2 sensor 13,
Reference numeral 15 generates an electric signal according to the concentration of oxygen components in the exhaust gas. That is, O ₂ sensors 13, 15
The control circuit 10 generates different output voltages in the A/D converter 101 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.

Here, the upstream O ₂ sensor 13 uses a zirconia type, and the in-catalyst O ₂ sensor 14 uses a semiconductor type. Note that the in-catalyst O ₂ sensor 14 is provided with a heater in order to keep its element temperature within a usable range.

The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, an input/output interface 102, a CPU 103, and
ROM104, RAM105, backup RAM
106, a clock generation circuit 107, etc. are provided.

Further, in the control circuit 10, a down counter 108, a flip-flop 109, and a drive circuit 110 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 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts the clock signal (not shown) and finally its carry out terminal reaches the "1" level, the flip-flop 109 is set and the drive circuit 110 activates the fuel injector 7. stop. In other words, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TAU,
Therefore, an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body 1.

Furthermore, in the control circuit 10, 111 is a drive circuit that energizes the heater of the catalyst O ₂ sensor 14, and for example, when the element temperature of the catalyst O ₂ sensor 14 is low, the output signal is at a low level. The heater is energized when the output level of the in-catalyst O ₂ sensor 14 is low level.

Note that the CPU 103 generates an interrupt when the A/D converter 101 finishes A/D conversion, when the input/output interface 102 receives the pulse signal from the crank angle sensor 6, and when the interrupt signal from the clock generation circuit 107 is generated. When received, etc.

The intake air amount data Q and cooling water temperature data THW of the air flow meter 3 are taken in by an A/D conversion routine executed at predetermined intervals and stored in the RAM.
105 in a predetermined area. In other words, RAM
Data Q and THW in 105 are updated at predetermined intervals. Also, rotation speed data Ne
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. 3 is an external view of the in-catalyst O ₂ sensor 14 shown in FIG. 1, and FIG. 4 is a sectional view thereof. The in-catalyst O ₂ sensor 14 will be explained with reference to FIGS. 3 and 4.
An oxide semiconductor element 141 as a detection part and a heater (not shown) are inserted into a hollow cylindrical housing 142 having an external sensor mounting flange 142a and a gas exchange hole 142b, and an inorganic adhesive 143 is used. Fix it. Then, wires 144, 145, 146 connected to the output terminal of the detection section, the heater terminal, and the ground are connected to the housing 142 through a ceramic insulator tube 147.
It is pulled out from the outside. These wires 14
4,146 is connected to the control circuit 10, and the wire 1
45 is connected to a grounded object. Such a semiconductor type O ₂ sensor is described in, for example, Japanese Patent Laid-Open No. 124057/1982, and as mentioned above, compared to the zirconia type, it does not require a reference gas, and also
This has the advantage that there is a degree of freedom in determining the distance between the detection section and the housing mounting section of the sensor.

5 to 7 are for explaining the mounting arrangement of the in-catalyst O ₂ sensor 14. In addition, the fifth
6 is an external view of the catalytic converter 12, FIG. 6 is an external view of the catalytic converter 12 as seen from the rear, and FIG. 7 is an internal view of the catalytic converter 12. In this case, it is assumed that the catalytic converter 12 is equipped with a single bed monolith catalyst. In this way, the tip of the in-catalyst O ₂ sensor 14 is located at the center of the monolithic catalyst. In this case, a catalyst temperature CCo sensor is also built-in.

Furthermore, when the catalytic converter 12 is equipped with a _double bed monolith catalyst, as shown in FIG. The tip of the in-catalyst O ₂ sensor 14 is placed in the center of the catalytic converter 12 .

In this way, by installing the tip of the in-catalyst O ₂ sensor 14 in the center of the catalytic converter 12, early activation of the in-catalyst O ₂ sensor 14 is achieved.
That is, as shown in Figure 9, for example, from 0 to 60
This is because when the vehicle is traveling steadily for Km/h, there are differences in the degree of temperature rise at points a, b, and c in the catalytic converter 12, and the temperature rise at point a, which is the central portion, is the fastest. Therefore, the in-catalyst O ₂ sensor 14 whose tip is provided in the center of the catalytic converter 12
is activated early, making it possible to accurately detect the stoichiometric air-fuel ratio.

Furthermore, as shown in FIG. 10, upstream of the catalytic converter 12, there is an influence of unburned gases such as H ₂ , CO, and HC, so the output characteristics of the upstream O ₂ sensor 13 are determined by the accurate stoichiometric air-fuel ratio (λ =1) cannot be detected, but since there is no influence of gas near or downstream of the catalytic converter 12, the output characteristics of the in-catalyst O ₂ sensor 14 are maintained well, and an accurate stoichiometric air-fuel ratio can be detected.

FIG. 11 shows a first air-fuel ratio feedback control routine for calculating an air-fuel ratio correction coefficient FAF based on the output of the upstream O ₂ sensor 13, and is executed every predetermined period of time, for example, every 4 ms.

In step 1101, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream O ₂ sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value, when the engine is starting, when increasing the amount after starting, when increasing the amount during warm-up, when increasing the power, when the output signal of the upstream O ₂ sensor 13 has never been reversed, when the fuel is cut off, etc. The closed-loop condition is not satisfied in all cases, and the closed-loop condition is satisfied in all other cases.
If the closed loop condition is not satisfied, step 1127
Proceed directly to. On the other hand, if the closed loop condition is met, the process advances to step 1102.

In step 1102, the output V ₁ of the upstream O ₂ sensor 13 is A/D converted and taken in, and in step 1103 it is determined whether or not V ₁ is lower than the comparison voltage V _R1 , for example, 0.45V. Determine whether it is rich or lean. If it is lean (V ₁ ≦ V _R1 ), it is determined in step 1104 whether the first delay counter CDLY1 is positive or not, and if CDLY1>0, the step
At 1105, the first delay counter CDLY1 is set to 0. In step 1106, the first delay counter CDLY1 is decremented by 1, and in step 1107, the first delay counter CDLY1 is decremented by 1.
Determine whether CDLY1<TDL1. In addition,
TDL1 is a lean delay time for maintaining the determination that the fuel is in a rich state even if the output of the upstream O ₂ sensor 13 changes from rich to lean, and is defined as a negative value. Therefore, the steps
Only when CDLY<TDL1 at 1107, step
In step 1108, CDLY←TDL1 is set, and in step 1109, the air-fuel ratio flag F1 is set to "0" (lean state). On the other hand, at step 1103, rich (V ₁ > V _R1 )
If so, in step 1110 it is determined whether the first delay counter CDLY1 is negative or not, and CDLY1>0.
If so, the first delay counter CDLY1 is set to 0 in step 1111. In step 1112, the first
The delay counter CDLY1 of is incremented by 0, and in step 1113 it is determined whether CDLY1>TDR1. Note that TDR1 is a rich delay time for maintaining the determination that the engine is in a lean state even if the output of the upstream O ₂ sensor 13 changes from lean to rich, and is defined as a positive value. Therefore, only when CDLY>TDR1 in step 1113, CDLY←TDR1 is set in step 1115, and the air-fuel ratio flag F1 is set to "1" (rich state) in step 1115.

In step 1116, 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, the process proceeds to step 1117, where it is determined whether the reversal is from rich to lean (F1="0") or from lean to rich (F1="1").
If reversing from rich to lean, step
In step 1118, FAF←FAF+RSR is increased in a skip manner, and conversely, if there is a reversal from lean to rich, in step 1119, FAF←FAF+RSL is decreased in a skip manner. In other words, skip processing is performed.

If the sign of the air-fuel ratio flag F1 is not inverted in step 1116, integration processing is performed in steps 1120, 1121, and 1122. In other words, at step 1120,
Determine whether F1="0" or not, and if F1="0" (lean), at step 1121 FAF←FAF+KL
On the other hand, if F1="0" (rich), then in step 1122 FAF←FAF+KI is set. here,
The integral constant KI is set sufficiently small compared to the skipping constants RSR and RSL, that is, KI<RSR
(RSL). Therefore, step 1121 gradually increases the fuel injection amount in the lean state (F1="0"), and step 1122 gradually decreases the fuel injection amount in the rich state (F1="1").

The air-fuel ratio correction coefficient FAF calculated in steps 1118, 1119, 1121, and 1122 is guarded at a minimum value of 0.8 in steps 1123 and 1124, and is guarded at a maximum value of 1.2 in steps 1125 and 1126. Ru. As a result, if the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled using that value to prevent over-rich or over-lean conditions.

The FAF calculated as described above is stored in the RAM 105, and the routine ends at step 1127.

FIG. 12 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 11. upstream side
When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the O ₂ sensor 13 as shown in FIG. 12A, the first delay counter CDLY1 is
As shown in FIG. 12B, it returns to 0 at the time of change from rich to lean or vice versa, counts up in the rich state, and counts down in the lean state.

As a result, a delayed air-fuel ratio signal A/F' is formed as shown in FIG. 12C. For example, even if the air-fuel ratio signal A/F changes from lean to rich at time _t1 , the delayed air-fuel ratio signal A/F' remains lean for the rich delay time TDR1 and then changes to rich at time _t2 . It becomes richer. time
Even if the air-fuel ratio signal A/F changes from rich to lean at time t ₃ , the delayed air-fuel ratio signal A/F' remains rich for an amount equivalent to the lean delay time TDL1, and then changes to lean at time t ₄ . Changes to However, when the air-fuel ratio signal A/F reverses in a period shorter than the rich or lean delay time as at times t ₅ , t ₆ , and t ₇ , the first delay counter CDLY1 reaches its maximum value.
It takes time to reach TDR1 or the minimum value TDL1, and as a result, the air-fuel ratio signal A/F' after the delay process is inverted at time _t8 . In other words, the air-fuel ratio signal A/F' after the delay process is more stable than the air-fuel ratio signal A/F before the delay process. In this way, based on the stable air-fuel ratio signal A/F' after the delay processing, the first
The air-fuel ratio correction coefficient FAF shown in FIG. 2D is obtained.

Next, the second air-fuel ratio feedback control using the in-catalyst O ₂ sensor 14 will be explained. The second air-fuel ratio feedback control includes a skip amount as a first air-fuel ratio feedback control constant.
RSR, RSL, delay times TDR1, TDL1, integral constant KI (in this case, set Ritch integral constant KI1R and lean integral constant KI1R separately), or comparison voltage V _R1 of output V ₁ of upstream O ₂ sensor 13. Variable system and second air-fuel ratio correction coefficient
There is a system that introduces FAF2.

For example, by increasing the richness skip amount RSR, the control air-fuel ratio can be shifted to the rich side, and
Even if the lean skip amount RSL is decreased, the control air-fuel ratio can be shifted to the rich side.On the other hand, if the lean skip amount RSL is increased, the control air-fuel ratio can be shifted to the lean side, and even if the rich skip amount RSR is decreased, the control air-fuel ratio can be shifted to the rich side. can be shifted to the lean side.
Therefore, the rich skip amount RSR and the lean skip amount are determined according to the output of the in-catalyst O ₂ sensor 14.
The air-fuel ratio can be controlled by correcting RSL.
Also, rich delay time TDR1 > lean delay time
If TDL1 is set, the controlled air-fuel ratio can be shifted to the rich side, and conversely, if the lean delay time (TDL1) is set to be greater than the rich delay time (TDL1), the controlled air-fuel ratio can be shifted to the lean side. In other words, inside the catalyst
Depending on the output of the O ₂ sensor 14, the delay time TDR1,
The air-fuel ratio can be controlled by correcting TDL1. Furthermore, by increasing the rich integral constant KI1R, the control air-fuel ratio can be shifted to the rich side, and even by decreasing the lean integral constant KI1L, 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 the Ritzch integral constant KI1R
The control air-fuel ratio can be shifted to the lean side even if the ratio is made smaller. Therefore, depending on the output of the in-catalyst O ₂ sensor 14, the Rich integral constant KI1R and the Lean integral constant
The air-fuel ratio can be controlled by correcting KI1L. Furthermore, by increasing the comparison voltage V _R1 , the control air-fuel ratio can be shifted to the rich side;
By reducing V _R1 , the control air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the comparison voltage V _R1 according to the output of the in-catalyst O ₂ sensor 14.

A double O ₂ sensor system in which the skip amount as an air-fuel ratio feedback control constant is made variable will be described with reference to FIGS. 13 and 14.

FIG. 13 shows a second air-fuel ratio feedback control routine for calculating the skip amounts RSR and RSL based on the output of the in-catalyst O ₂ sensor 14, and is executed every predetermined period of time, for example, every 1 second. Step 1301
Now, it is determined whether the in-catalyst O ₂ sensor 14 is in a closed loop condition. For example, when the cooling water temperature is below a predetermined value, when the output signal of the catalyst O ₂ sensor 14 has never reversed, when the catalyst O ₂ sensor 14 is malfunctioning, or during transient operation, the loop is closed. The condition is not true, and the other cases are closed-loop conditions. Step if not closed loop condition
Proceed directly to 1329.

If the closed loop condition is satisfied in step 1301, the output V ₂ of the in-catalyst O ₂ sensor 14 is A/D converted and taken in in step 1302, and the process is carried out in step 1303.
It is determined whether V ₂ is lower than the comparison voltage V _R2 , for example, 0.55V. In other words, it determines whether the air-fuel ratio is rich or lean. Note that the comparison voltage V _R2 is a comparison voltage of the output of the in-catalyst O ₂ sensor 14, taking into account that the output characteristics are different due to the influence of raw gas and the deterioration rate is different between the upstream and downstream of the catalytic converter 12.
V is set higher than _R1 .

Steps 1304 to 1315 are step 1104 in FIG.
Similar to ~1115, this is for delaying the air-fuel ratio determination result. In other words, the rich delay time
The air-fuel ratio flag F2 is set based on TDR2 and lean delay time TDL2.

At step 1316, the air-fuel ratio after the delay process is determined based on the air-fuel ratio flag F2. As a result, F2=
If F2 is "0" (lean), the process proceeds to steps 1317-1322, while if F2="1" (rich), the process proceeds to steps 1323-1328.

In step 1317, RSR←RSR+ΔRS (constant value, for example, 0.08%) is set, that is, the rich skip amount RSR is increased to shift the air-fuel ratio to the rich side. Steps 1318 and 1319 set RSR to the maximum value.
Guard at MAX, for example 6.2%. Furthermore, in step 1320, RSL←RSL−ΔRS, that is,
Decrease the rich skip amount RSL to shift the air-fuel ratio to the rich side. In steps 1321 and 1329,
Guard RSL at minimum value MIN, for example 2.5%.

On the other hand, when F2="1" (rich), RSR←RSR−ΔRS is set in step 1323, that is,
Decrease the richness skip amount RSR to shift the air-fuel ratio to the lean side. In steps 1324 and 1325,
Guard RSR at minimum value MIN. Further, in step 1326, RSL←RSL+ΔRS (constant value) is set, that is, the lean skip amount RSL is increased to shift the air-fuel ratio to the lean side. step
In 1327 and 1328, RSL is guarded at the maximum value MAX.

RSR and RSL calculated as above are RAM1
05, the routine ends at step 1326.

In addition, the air-fuel ratio calculated during air-fuel ratio feedback
FAF, RSR, and RSL are temporarily changed to other values FAF′, RSR′,
It is also possible to convert it to RSL' and store it in the backup RAM 106, which is useful for improving drivability when restarting, etc. The minimum value MIN in FIG. 13 is a value at which transient followability is not impaired, and the maximum value MAX is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

As described above, according to the routine shown in FIG. 13, if the output of the in-catalyst O ₂ sensor 14 is lean, the rich skip amount RSR is gradually increased and the lean skip amount RSL is gradually decreased. The fuel ratio is shifted to the rich side. Further, if the output of the in-catalyst O ₂ sensor 14 is rich, the rich skip amount RSR is gradually decreased and the lean skip amount RSL is gradually increased, thereby shifting the air-fuel ratio to the lean side.

FIG. 14 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360° CA.
In step 1401, the intake air amount data Q and rotational speed data Ne are read from the RAM 105 to calculate the basic injection amount TAUP. For example, TAUP←
Let KQ/Ne (K is a constant). At step 1402
Cooling water temperature data THW is read from RAM 105 and a warm-up increase value FWL is calculated by interpolation using a one-dimensional map stored in ROM 104. Step 1403
Then, the final injection amount TAU is TAU←TAUP・FAF・(1+FWL+
Calculate by α) + β. Note that α and β are correction amounts determined by other operating state parameters. Then,
At step 1404, the injection amount TAU is set in the down counter 108 and the flip-flop 1 is set.
09 to start fuel injection. The routine then ends at step 1405.

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

The first air-fuel ratio feedback control is 4ms.
Also, the second air-fuel ratio feedback control
The reason why the air-fuel ratio feedback control is performed every 1 second is that the air-fuel ratio feedback control is mainly performed by the upstream O ₂ sensor, which has a good response, and is controlled by the in-catalyst O ₂ sensor, which has a poor response.

In addition, a double O ₂ sensor system in which other control constants such as delay time, integral constant, etc. in the air-fuel ratio feedback control by the upstream O ₂ sensor is corrected by the output of the in-catalyst O ₂ sensor is also used. Double _O2 introducing air-fuel ratio correction factor
The present invention can also be applied to sensor systems. Also,
Controllability can be improved by simultaneously controlling two of the skip amount, delay time, and integral constant.
Furthermore, it is also possible to fix one of the skip amounts RSR and RSL and make only the other variable.
It is also possible to fix one of TDR1 and TDL1 and make only the other variable, or use the Ritzch integral constant.
It is also possible to fix one of KIR and lean integral constant KIL and make the other variable.

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

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

Furthermore, although the above-described embodiment shows an internal combustion engine in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, 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;
A bleed air control valve that controls the air-fuel ratio by adjusting the amount of air bleed from the carburetor and introducing atmospheric air into the main system passage and slow system passage, which is sent to the engine's exhaust system.
The present invention can be applied to devices that adjust the amount of air. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 1401 is determined by the carburetor itself, that is, it is determined according to the intake pipe negative pressure according to the intake air amount and the engine rotation speed, At step 1403, the amount of supplied air corresponding to the final fuel injection amount TAU is calculated.

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

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

〔Effect of the invention〕

As explained above, according to the present invention,
The O ₂ sensor does not decrease its output even when water, mud, etc. enter, and is easily activated by the influence of the catalyst temperature of the catalytic converter, making it possible to accurately detect the stoichiometric air-fuel ratio.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic diagram showing one embodiment of an air-fuel ratio control device for an internal combustion engine according to 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, and FIG. The figure is an external view of the in-catalyst O ₂ sensor shown in Fig. 1, Fig. 4 is a sectional view of Fig. 3, Fig. 5 is an external view of the catalytic converter shown in Fig. 1, and Fig. 6 is a view from the rear of Fig. 5. Figures 7 and 8 are diagrams showing the inside of Figure 5, Figure 9 is a graph showing the temperature characteristics inside the catalytic converter of Figure 1, and Figure 10 is the output characteristic of the O ₂ sensor. The graphs shown in Figures 11, 13, and 14 are
FIG. 12 is a flowchart for explaining the operation of the control circuit shown in the figure, and FIG. 12 is a timing diagram for supplementary explanation of the flowchart in FIG. 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) O ₂ sensor, 1
4... In-catalyst (second) O ₂ sensor.

Claims (1)

[Claims for Utility Model Registration] 1. First and second air-fuel ratio sensors are provided upstream of and within the catalytic converter for purifying exhaust gas provided in the exhaust system of an internal combustion engine, respectively. , at least the second air-fuel ratio sensor is configured with a semiconductor air-fuel ratio sensor,
An air-fuel ratio control device for an internal combustion engine, wherein air-fuel ratio feedback control is performed by the second air-fuel ratio sensor as well as air-fuel ratio feedback control by the first air-fuel ratio sensor. 2. The air-fuel ratio control device according to claim 1, wherein the second air-fuel ratio sensor is provided in the center of the catalytic converter.