JPS61237858A - Control device for air-fuel ratio in internal-combustion engine - Google Patents

Abstract

PURPOSE:To prevent air-fuel ratio from being excessively corrected, by detecting the element temperature of a sensor in the downstream side and stopping a control of the air-fuel ratio in accordance with an output of said sensor when the element temperature is less than a fixed value, in the case of an engine respectively providing air-fuel ratio sensors in the upstream and the downstream sides of a catalytic converter. CONSTITUTION:An internal-combustion engine, providing in its exhaust system a catalytic converter, provides in its upstream and downstream sides respectively the first and second air-fuel ratio sensors A, B, and in accordance with outputs of these sensors A, B an air-fuel ratio regulating means C controls air-fuel ratio in the engine. While here an element temperature discriminating means D, detecting an element temperature of the downstream side sensor B, discriminates whether or not this element temperature is in a fixed value or more. And when the element temperature is less than the fixed value, a stopping means E stops a control of the air-fuel ratio in accordance with the downstream side sensor B in the air-fuel ratio regulating means C. In this way, the engine, correctly discriminating the downstream side sensor B to be active or inactive, prevents an overrich and overlean state of the actual air-fuel ratio.

Description

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

[Conventional technology]

Generally, the basic injection amount of the fuel injection valve is calculated according to the intake air amount (or intake air pressure) and rotational speed of the engine.
Detects the concentration of specific components, such as oxygen components, in engine exhaust gas. The basic injection amount is corrected according to the air-fuel ratio correction coefficient FAF calculated based on the detection signals of the two sensors, and the amount of fuel actually supplied is controlled according to the corrected injection amount. This control is repeated until the air-fuel ratio of the engine is finally converged within a predetermined range. With this kind of air-fuel ratio feedback control, the air-fuel ratio can be controlled within a very narrow range near the stoichiometric air-fuel ratio.
It is possible to maintain a high purification ability of the catalytic converter, which simultaneously purifies three harmful components: , IC, and NOx.

In the above-mentioned air-fuel ratio feedback control (single 02 sensor system), the 02 sensor that detects the oxygen concentration is installed at a location in the exhaust system as close to the combustion chamber as possible, that is, at the gathering part of the exhaust manifold upstream from the catalytic converter. Due to variations in the output characteristics of the 02 sensor, it is difficult to improve the control accuracy of the air-fuel ratio. The causes of variations in the output characteristics of the 02 sensor are listed below.

(1) Individual differences in the 02 sensor itself; (2) uneven mixing of exhaust gas at the location of the 02 sensor due to positional tolerances in the assembly of parts such as fuel injection valves and exhaust gas recirculation valves into the engine; 3) Changes in the output characteristics of the 02 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 02 sensor, variations in parts, and changes over time, a second O2 sensor is provided downstream of the catalytic converter, in addition to the air-fuel ratio feedback control by the upstream 02 sensor. A double 02 sensor system that performs air-fuel ratio feedback control using a downstream O2 sensor has already been proposed. In this double 02 sensor system, although the 02 sensor installed downstream of the catalytic converter has a lower response speed than the upstream O2 sensor, it has the advantage of less variation in output characteristics for the following reasons. are doing.

(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 O2 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 performing air-fuel ratio feed pack control (double 02 sensor system) based on the outputs of the two 02 sensors, variations in the output characteristics of the upstream 02 sensor can be absorbed by the downstream 02 sensor. In fact, the second
As shown in the figure, in a single 02 sensor system, 0
If the output characteristics of the O2 sensor on the upstream side deteriorate, the exhaust emission characteristics will be directly affected, whereas in the double 02 sensor system, even if the output characteristics of the upstream O2 sensor deteriorate, the exhaust emission characteristics will not deteriorate. In other words, in the double 02 sensor system, good exhaust emissions are guaranteed as long as the downstream 02 sensor maintains stable output characteristics.

Generally, the temperature characteristics of the oxygen concentration battery type 02 sensor are
As shown in diagram A, when the air-fuel ratio A/F is rich,
As the element temperature rises, the output of the 02 sensor (rich signal) rises and stabilizes at a certain high level.On the other hand, when the air-fuel ratio A/F is lean, as the element temperature rises, the output of the 02 sensor (rich signal) rises and remains at a certain low level. Stabilize. Note that Figure 3A shows the case where the flow-in type is used as the O2 sensor output processing circuit, and if the flow-in type is used as the O22 sensor output processing path, the result will be as shown in Figure 3B, and the circuit will be in an inactive state. If so, both the rich and lean signals will be at high level. In any case, the 02 sensor becomes inactive or active depending on the element temperature, and the usable area is limited.
A range of 400 to 700°C is considered appropriate. In this active state, richness and leanness can be determined by comparing the output voltage of the 02 sensor using a constant comparison voltage VIIEF, for example, about 0.45V.

[Problem that the invention seeks to solve]

However, since the downstream 02 sensor is located at a lower temperature than the upstream 02 sensor, it takes time to activate it. Therefore, if activation is not sufficient, if the outflow type is used as the 02 sensor output processing circuit, downstream IIJ
Even if the atmosphere at the O2 sensor is rich, it may be determined to be lean, and as a result, air-fuel ratio feedback control is performed by the downstream O2 sensor, resulting in the actual air-fuel ratio becoming overrich, resulting in poor fuel efficiency. , CO, and HC emissions. Conversely, if a flow-in type is used as the 02 sensor output processing circuit, even if the downstream 02 sensor atmosphere is lean, it may be determined to be rich. , air-fuel ratio feedback control is performed by the downstream 02 sensor, and therefore the actual air-fuel ratio becomes over-lean, leading to deterioration of drivability, deterioration of NOx emissions, etc.

Note that whether the 02 sensor is active or inactive is normally determined by checking whether the output voltage of its output processing circuit once goes up or down, but this method does not accurately determine whether the 02 sensor is active or inactive. Even if the 02 sensor is activated, if the air-fuel ratio of the engine is lean or rich, activation will not be determined and the advantage of the double 02 sensor system cannot be utilized. Even if the temperature of the compound decreases, it is not considered inactive.

[Means for solving problems]

The purpose of the present invention is to prevent the actual air-fuel ratio from becoming over-rich or over-lean by accurately determining whether the downstream air-fuel ratio sensor (02 sensor) is active or inactive, thereby reducing fuel consumption and drivability. The purpose is to prevent the deterioration of the energy consumption, the deterioration of the emissions, etc., and the means thereof are shown in FIGS. 1A, 1B, 1C, and 1D.

In FIG. 1A, the first step detects the concentration of a specific component in the exhaust gas. Second air-fuel ratio sensors are provided upstream and downstream of a catalytic converter for purifying exhaust gas, which is provided in the exhaust system of the internal combustion engine. The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to each output of the upstream and downstream air-fuel ratio sensors.

The element temperature determining means detects the element temperature of the downstream (second) air-fuel ratio sensor, and determines whether or not this element temperature is equal to or higher than a certain value. As a result, when the element temperature is less than a certain value, the stopping means stops the air-fuel ratio adjustment according to the downstream air-fuel ratio sensor in the air-fuel ratio adjusting means.

In FIG. 1B, instead of the element temperature determining means in FIG. 1A, a catalytic converter temperature determining means is provided that detects the temperature of the catalytic converter and determines whether the temperature is equal to or higher than a certain value. As a result, the stopping means stops the air-fuel ratio adjustment according to the output of the downstream air-fuel ratio sensor when the catalytic converter temperature is below a certain value.

In FIG. 1C, instead of the element temperature determining means of FIG. 1A, exhaust temperature determining means is provided for detecting the exhaust gas temperature of the engine and determining whether or not the exhaust gas temperature is equal to or higher than a certain value. As a result, the stopping means stops the air-fuel ratio adjustment according to the output of the downstream air-fuel ratio sensor when the exhaust gas temperature is less than a certain value.

In FIG. 1D, instead of the element temperature determining means in FIG. 1A, there is provided a cooling water temperature determining means for detecting the engine cooling water temperature and determining whether or not the cooling water temperature is equal to or higher than a certain value.

As a result, the stopping means stops the air-fuel ratio adjustment according to the output of the downstream air-fuel ratio sensor when the cooling water temperature is less than a certain value.

[For production]

According to the above-mentioned means, since the element temperature of the downstream side air-fuel ratio sensor is detected directly or indirectly to determine whether it is activated or not, the determination result is accurate, and moreover, the downstream side air-fuel ratio sensor during operation is accurate. It is also possible to determine whether the air-fuel ratio sensor is inactive.

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

FIG. 4 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. 4, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. 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 has already been supplied to the multiplexer built-in Δ/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 7200 degrees in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30 degrees in terms of crank angle. A crank angle sensor 6 is provided. The pulse signals of these crank angle sensors 5 and 6 are supplied to the input/output interface 102 of the control circuit 1°, and the output of the crank angle sensor 6 is cPυ10.
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 boat 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 analog voltage electrical signals according to IH. This output is also supplied to the A/D converter 101.

The exhaust system downstream of the exhaust manifold 11 is provided with a catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three harmful components HC, CO, and NO in the exhaust gas. Further, the catalytic converter 12 has a built-in catalytic converter temperature sensor 13a for detecting the catalytic converter temperature.

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

The 02 sensors 13 and 15 generate electrical signals corresponding to the concentration of oxygen components in the exhaust gas. That is, the o2 sensor 13
, 15 of the 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.
The signal is generated at the A/D converter 101 via sensor output processing circuits 111 and 112. The downstream side 02 sensor 15 has a built-in element temperature sensor 15a at its tip for detecting the element temperature. Note that the 02 sensor output processing circuit 111, 1
12 can be broadly divided into outflow type and inflow type,
When the 02 sensor is in the active state, both generate outputs at almost the same level, but in the inactive state, the former generates a high-level output and the latter generates a low-level output (
(See Figure 3A, Figure 3B).

Further, the exhaust manifold 11 is provided with an exhaust temperature sensor 17 for detecting the temperature of exhaust gas.

The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, an input/output interface 102, a CPU 103, and a ROM 104.
, RAM 105 , backup RAM 106 ,
A clock generation circuit 107 and the like are provided. Note that the backup RAM 106 is directly connected to a battery (not shown), so even if the ignition switch (not shown) is turned off, the stored contents will not be erased.

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

That is, in the routine described later, the fuel injection amount TAU
is calculated, the fuel injection amount TAU is counted down by the down counter 1.
08 and 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 carrier terminal reaches the "1" level, the flip-flop 109 is set and the drive circuit 110 controls the fuel injection valve 7. Stop biasing. In other words, the above fuel injection amount TA
The fuel injection valve 7 is energized by XI, so that an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body 1.

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

The intake air amount data Q and the cooling water temperature data TIIW of the air flow meter 3 are taken in by an A/D conversion routine executed at predetermined time intervals and stored in a predetermined area of the RAM 105. That is, data Q and TIIW in RAM 105 are updated at predetermined intervals. In addition, the rotational speed data Ne is 30° of the crank angle sensor 6.
It is calculated by an interrupt for each CA and stored in a predetermined area of the RAM 105.

The operation of the control circuit shown in FIG. 5 will be explained with reference to the flowcharts shown in FIGS. 5, 7, and 8.

FIG. 4 shows a first air-fuel ratio feedback control routine that calculates an air-fuel ratio correction (number FAF) based on the output of the upstream 02 sensor 13, and is executed every predetermined time, for example, 4 ms. Determines whether the air-fuel ratio closed loop (feedback) condition is established using the side 02 sensor.During engine startup, during fuel increase operation after engine start, during warm-up increase operation, during power increase operation, lean control, etc. In all cases, the closed-loop condition is not satisfied, and in other cases, the closed-loop condition is satisfied.When the closed-loop condition is not satisfied, the process proceeds to step 517 and the air-fuel ratio correction coefficient FAF is set to 1.0.On the other hand, when the closed-loop condition is satisfied The process proceeds to step 502.

In step 502, the output ■1 of the upstream side 02 sensor 13
is A/D converted and taken in, and in step 503 it is determined whether or not (1) is less than the comparison voltage VRI, for example 0.45V, that is, it is determined whether the air-fuel ratio is rich or rich. If lean (V1≦VRI), the delay counter CDLY is decremented by 1 in step 504, and step 505;
At 506, the delay counter CDLY is guarded with the minimum value TDR. Note that the minimum value TDR is the upstream side 02 sensor 1.
The rich delay time is defined as a negative value to maintain the determination that the lean state is present even if there is a change from lean to rich in the output of No. 3. On the other hand, Rich (V
l>VR,), the delay counter CDLY is incremented by 1 in step 507, and steps 508 and 50
At step 9, the delay counter CDLY is guarded at the maximum value TDL. The maximum value TDL is a lean delay time for maintaining the determination that the engine is in a rich state even if the output of the upstream 02 sensor changes from rich to lean, and is defined as a positive value.

Here, the reference of the delay counter CDLY is set to 0, and C
When DLY≧0, the air-fuel ratio after the delay process is considered rich, and when CDLY<0, the air-fuel ratio after the delay process is considered lean.

In step 510, it is determined whether the sign of the delay counter CDLY 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, it is determined in step 511 whether the reversal is from rich to lean or from lean to rich. If it is a reversal from rich to lean, in step 512 FAF
-PAP+RS, and on the other hand, if it is a reversal from lean to rich, step 77"513 skips and decreases FAF4-FAF-RS.

In other words, skip processing is performed.

If the sign of the delay counter CDLY is not inverted in step 510, steps 514, 515, 516
Integration processing is performed at . In other words, step 514,
Determine whether CDLY < O or not, and if CDLY < O (lean), at step 515 FAF-FAF +K
On the other hand, if CDLY≧0 (rich), then in step 516 FAF-FAF-Kl is set. Here, the integral constant Kl is set sufficiently small compared to the skip constant R5, that is, Kl (R3). Therefore, step 515 gradually increases the fuel injection amount in a lean state (CDLY < 0). , step 516 gradually reduces the fuel injection amount in a rich state (CDLY≧0).

The air-fuel ratio correction coefficient FAF calculated in steps 512 to 516 has a minimum value such as 0.8 and a maximum value such as 1.
．． If the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, the air-fuel ratio of the engine will be controlled using that value and the engine will become over-rich or over-lean. prevent.

The FAF calculated as described above is stored in the RAM 105, and the routine ends in step 518.

FIG. 6 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the 02 sensor 13 as shown in FIG. 6(A), the delay counter CDLY counts in the rich state as shown in FIG. 6(B). It is counted down in a lean state. As a result, as shown in FIG. 6(C), the delayed air-fuel ratio signal A/l? ' is formed. For example, even if the air-fuel ratio signal A/F changes from lean to rich at time t1, the air-fuel ratio signal A/F' that has undergone the delay processing will be delayed by the rich delay time (-
After being kept lean by TDR), it changes to rich at time t2. Even if the air-fuel ratio signal ^/F changes from rich to lean at time t3, the delayed air-fuel ratio signal A
/F' is held rich for an amount equivalent to the lean delay time TDL, and then changes to lean at time t4. However, when the air-fuel ratio signal A/F is reversed in a period shorter than the rich delay time (-TDR) as at time j5-j6 #j7, it takes time for the delay counter CDLY to cross the reference value 0, 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 manner, the air-fuel ratio correction coefficient FIAP' shown in FIG. 6(D) is obtained based on the stable air-fuel ratio signal A/F' after the delay processing.

Further, by appropriately setting the delay times TDR and TOL, the air-fuel ratio controlled by the air-fuel ratio feedback control by the upstream 02 sensor 13 can be shifted to the rich side or the lean side.

For example, if you set rich delay time (-TDR) > lean delay time (TDL), the control air-fuel ratio can shift to the rich side, and conversely, if you set lean delay time (TDL) > rich delay time (-TDR). For example, the controlled air-fuel ratio can be shifted to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay times TDR and TDL according to the output of the downstream 02 sensor 15.

FIG. 7 shows a second air-fuel ratio feedback control routine that calculates delay times TDR and TOL based on the output of the downstream 02 sensor 15, and is executed every predetermined period of time, for example, every 1 second. In step 701, it is determined whether the closed loop condition of the air-fuel ratio by the 02 sensor on the downstream side is satisfied.

If the closed loop condition is not satisfied, steps 718 and 719
Proceed to rich delay time TDR, lean delay time TDL
Set to a constant value. For example, TDR ← −12 (equivalent to 48 ms) TDL ← 6 (equivalent to 24+ms). Here, the rich delay time (-TDR') is defined as the lean delay time TD
The reason why the comparison voltage VR is set larger than L is because each 02 sensor is located before and after the catalyst, so the comparison voltage VR
This is because I is set to a value lower than the comparison voltage VR2, for example 0.45V, on the lean side.

If the closed loop condition is satisfied, the process advances to step 702. In step 702, the element temperature of the downstream side 02 sensor 15 is taken in by A/D converting the output of the element temperature sensor 15a, and in step 703, the element temperature is set to a constant value, e.g.
Determine whether the temperature is above 0°C.

It is determined that the downstream side 02 sensor 15 is in the active state when the element temperature≧−a certain value.

Note that in steps 702 and 703, the temperature of the catalytic converter 12 is determined by changing the output of the catalytic converter temperature sensor 12a to 4.
It is also possible to determine whether the catalytic converter temperature is above a certain value, for example 350°C, by converting the output of the exhaust temperature sensor 17 into 7 ports. The temperature is a constant value, for example 400.
It is also possible to determine whether or not the temperature is above ℃.Furthermore, it is also possible to take in the cooling water temperature by A/D converting the output of the water temperature sensor 9, and to determine whether the cooling water temperature is above a certain value, for example, 50 ℃. .

When the downstream O2 sensor 15 is determined to be active in steps 702 and 703, the process proceeds to step 704, and on the other hand, when it is determined to be inactive, the process proceeds to steps 718 and 719.

In step 704, the output v2 of the downstream O2 sensor 15 is
is A/D converted and taken in, and in step 705, the output voltage (2) of the 02 sensor 15 is equal to the comparison voltage VR or, for example, 0.
It is determined whether the voltage is 55V or less. In other words, it is determined whether the air-fuel ratio is rich or lean.

When lean (V2≦VR2), TDR-TDR-1 is set in step 706, that is, rich delay time (
-TDR) to further delay the change from rich to lean and shift the air-fuel ratio to the rich side. In steps 707 and 708, TDR is guarded to the minimum value TRI. Here, TRI is also a negative value, so
(-TRI) means the maximum rich delay time. Further, in step 709, TDL -TDL -1 is set, that is, the lean delay time TDL is decreased, the delay from lean to rich is reduced, and the air-fuel ratio is shifted to the rich side. In steps 710 and 711, TDL is set to the minimum value TL
Guard with I. Here, TLI is a positive value,
Therefore, TLI means minimum lean delay time.

On the other hand, when rich (V2>VR2), step 7
In step 12, TDR-TDR+1 is set, that is, the rich delay time (-TDR) is decreased, the delay in changing from rich to lean is reduced, and the air-fuel ratio is shifted to the lean side.

In steps 713 and 714, TDR is set to increase value TR2
Guard at. Here, TR2 is also a negative value, so (-TRY) means the minimum rich delay time.

Furthermore, in step 715, TDL - TDL + 1 is set, that is, the lean delay time TDL is increased, the change from lean to rich is further delayed, and the air-fuel ratio is shifted to the lean side.

In steps 716 and 717, TDL is set to the maximum value TLI.
Guard at. Here, TLI is a positive value, so TL2 means the maximum lean delay time.

The TDR and TDL calculated as described above are stored in RAM 10.
5, the routine ends at step 720.

In other words, TDL is controlled within the range of TLI≦TDL≦TL2, and TDR is controlled within the range of (-TRI)≦(-TDR)≦(-TRY
) is controlled within the range.

Note that the air-fuel ratio correction coefficient FAF and the delay times TDR and TDL during feedbank are once changed to FAF' and TDR'.
, Backup RAM RAM 10 after setting TDL'
6, which is useful for improving drivability during restarts, etc.

FIG. 8 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 3609 CA. Step 80
1, the RAM 105 reads intake air amount data Q and rotational speed data Ne to calculate the basic injection amount TAUP. For example, TAIJP4-K Q/N e
(K is a constant). At step 802, RAM 10
Read the cooling water temperature data T11- from ROM 10
The warm-up increase value PWL is calculated by interpolation using the one-dimensional map stored in step 4. As shown in the figure, this warm-up increase value PWL is set to decrease as the current cooling water temperature TIIW increases.

In step 803, the final injection amount TAU is set to TAtl-
Calculate by TAIIP - FAF (1+FWL + α) + β. Note that α and β are correction amounts determined by other operating state parameters, such as a signal from a throttle position sensor (not shown), a signal from an intake air temperature sensor, battery voltage, etc. These are also correction amounts determined by the RAM 105. is stored in. Then,
At step 804, the injection amount TAU is counted down by 1.
08 and also sets the flip-flop 109 to start fuel injection. And step 805
This routine ends. As described above, when the time corresponding to 11 TAU of injection has elapsed, the flip-flop 109 is reset by the carrier signal of the down counter 108, and the fuel injection ends.

FIG. 9 is a timing diagram of delay times TDR and TDL obtained by the flowcharts of FIGS. 5 and 7. As shown in FIG. 9(A), when the output voltage ■2 of the downstream side 02 sensor 15 changes, as shown in FIG. 9(B), if it is in a lean state (V2≦VR2), the delay time TDR,
TOL is both increased, while in a rich state, both delay times TDR and TDL are decreased. At this time, T.D.
R varies in the range of TRI'''TR2 and TDR is TLI
~Tu.

If the downstream side 02 sensor 15 is not in a closed loop condition, the ninth
The control of TDR and TDL in FIG. 3B is stopped, and is maintained at, for example, TDR=-12 and TDL-6.

Note that the first air-fuel ratio feedback control is performed every 4 ms, and the second air-fuel ratio feedback control is performed for each IS, but this is because the air-fuel ratio feedback control is controlled by the upstream 02 sensor with good response. The control is performed primarily by the downstream 02 sensor, which has poor response, and is controlled by the downstream 02 sensor, which has poor responsiveness.

In addition, in the above-mentioned embodiment, a double 02 sensor system (see Japanese Patent Laid-Open No. 55-37562
(Japanese Patent Application Laid-open No. 58-72647),
The present invention uses other control constants, such as a proportional control constant, an integral control constant, a skip control constant, a comparison voltage of the upstream 02 sensor (see Japanese Patent Application Laid-open No. 55-37562! 13), etc. to the output of the downstream 02 sensor. The present invention can also be applied to a double 02 sensor system corrected by Furthermore, while fixing the control constant, two air-fuel ratio correction coefficients FAF 1 ,
The present invention can also be applied to a double 02 sensor system in which FAF 2 is introduced and each is calculated according to the re-outputs of the upstream 02 sensor and 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, and devices that adjust the amount of secondary air sent to the exhaust system of an engine. In this case, the basic fuel injection amount corresponding to the basic injection amount TAIIP in step 801 is determined by the carburetor itself, that is, it is determined in accordance with the intake pipe negative pressure depending on the intake air amount and the rotational speed of the engine, and the basic fuel injection amount corresponding to the basic injection amount TAIIP in step 803 is determined. 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〕

FIG. 10 is a timing diagram illustrating the present invention in detail. 10(A) and (B) show the output voltage VipV2 of the two 02 sensors 13 and 15 after the cold start at time to. Upstream 02 sensor 13
enters the active state relatively quickly, and the downstream 02 sensor 15
enters the active state relatively late. That is, at time t1, the first oven loop control is switched to the first air-fuel ratio feedbank control by the upstream side 02 sensor 13, whereas at time t2, the second oven loop control is switched to the downstream II
Switching is made to the second air-fuel ratio feedback control using the O2 sensor 15. In other words, from time t1 to t2, upstream side 0
Only the first air-fuel ratio feedback control using the second sensor 13 is performed. The switching point t2 between the second oven loop control and the second air-fuel ratio feedback control is shown in FIG.
At the point when the element temperature shown in C) reaches a certain value, the temperature shown in FIG. 10 (
When the temperature of the catalytic converter reaches a certain value shown in D), when the exhaust gas temperature reaches a certain value shown in Fig. 10 (E), or when the cooling water temperature reaches a certain value shown in Fig. 10 (F) That's when it happened. In this way, if the element temperature of the downstream III O2 sensor 15 is detected directly or indirectly and whether or not the downstream O2 sensor 15 is activated or inactive is determined based on whether or not this temperature exceeds a certain value, the 10th As shown by the dotted line in FIG. If so, it is accurately determined that it is active. Therefore, in this case, air-fuel ratio feedback control by the downstream 02 sensor is performed early. Furthermore, if the temperature of the downstream 02 sensor drops during operation due to a long period of idling, etc., it can be determined that the sensor is inactive.

[Brief explanation of drawings]

Figure 1 is an overall block diagram for explaining the present invention in detail, Figure 2 is a single 02 sensor system and a double 02 sensor system.
FIG. 3A and FIG. 3B are graphs explaining the output characteristics of the 02 sensor. FIG. 4 is an overall diagram showing an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention. Schematic diagrams; Figures 5, 7, and 8 are flowcharts for explaining the operation of the control circuit in Figure 6; Figure 6 is a timing diagram for supplementary explanation of the flowchart in Figure 5; The figure is a timing diagram supplementary to the flowcharts of FIGS. 5 and 7, and FIG. 10 is a timing diagram for explaining the present invention in detail. 1: ta seki body 3: air flow meter, 4
: Distributor, 5.6: Crank angle sensor, 10: Control circuit, 12: Catalytic converter, 1
2a: Catalytic converter temperature sensor, 13: Upstream side (first) 02 sensor, 15: Downstream side (second) 02 sensor, 15a: Element temperature sensor, 17: Exhaust temperature sensor. Fig. 1A Fig. 18 Fig. 1C Fig. 1D Fig. 2
Double 02 system Figure 3A Figure 3B Element temperature (6C) Figure 6 Figure 8

Claims (1)

[Scope of Claims] 1. First and second catalytic converters for detecting the concentration of specific components in exhaust gas, which are respectively provided upstream and downstream of a catalytic converter for purifying exhaust gas provided in the exhaust system of an internal combustion engine. an air-fuel ratio sensor configured to detect an element temperature of the second air-fuel ratio sensor; , an element temperature determination means for determining whether or not the element temperature is above a certain value; An air-fuel ratio control device for an internal combustion engine, comprising: a stop means for stopping fuel ratio adjustment. 2. First and second air-fuel ratio sensors that detect the concentration of specific components in exhaust gas, which are respectively provided upstream and downstream of a catalytic converter for exhaust gas purification that is installed in the exhaust system of an internal combustion engine. , an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to each output of the first and second air-fuel ratio sensors, and detecting the temperature of the catalytic converter and determining whether or not the temperature is above a certain value. catalytic converter temperature discrimination means for determining; and stopping means for stopping air-fuel ratio adjustment according to the output of the second air-fuel ratio sensor in the air-fuel ratio adjustment means when the catalytic converter temperature is less than the certain value. An air-fuel ratio control device for an internal combustion engine. 3. First and second air-fuel ratio sensors that detect the concentration of specific components in exhaust gas, which are respectively provided upstream and downstream of a catalytic converter for purifying exhaust gas that is installed in the exhaust system of the internal combustion engine. , an air-fuel ratio adjustment means for adjusting the air-fuel ratio of the engine according to each output of the first and second air-fuel ratio sensors; and an air-fuel ratio adjusting means for detecting the exhaust gas temperature of the engine and determining whether the exhaust gas temperature is equal to or higher than a certain value. and stopping means for stopping air-fuel ratio adjustment according to the output of the second air-fuel ratio sensor in the air-fuel ratio adjusting means when the exhaust gas temperature is less than the certain value. Air-fuel ratio control device for internal combustion engines. 4. First and second air-fuel ratio sensors that detect the concentration of specific components in exhaust gas, which are respectively provided upstream and downstream of a catalytic converter for purifying exhaust gas that is installed in the exhaust system of the internal combustion engine. , an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to each output of the first and second air-fuel ratio sensors; and detecting a cooling water temperature of the engine, and determining whether the cooling water temperature is equal to or higher than a certain value. and a stopping means for stopping air-fuel ratio adjustment according to the output of the second air-fuel ratio sensor in the air-fuel ratio adjusting means when the cooling water temperature is less than the certain value. Air-fuel ratio control device for internal combustion engines.