JPS63239333A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent exhaust emission from deteriorating,by discriminating the responsiveness of a downstream side sensor from a difference in lean mixture action of each air-fuel sensor installed at both up- and downstreams of catalytic converter rhodium at the time of a fuel cut, and at the time of discrimination of a response drop, stopping the air-fuel regulation made by the downstream side sensor. CONSTITUTION:Each of air-fuel ratio sensors 13 and 15 is installed at both up- and downstreams of catalytic converter rhodium 12 in an exhaust system, and the air-fuel ratio of an engine is regulated by a regulating device A according to each output of these sensors 13 and 15 at both upstream and downstream sides. And, there is provided with a discriminating device B which discriminates whether the engine is in a fuel-cut state or not, and when YES discrimination is the case, time ranging from the point when output of the upstream side sensor 13 showed its leanness to that when output of the downstream side sensor 15 showed its leanness is measured by a time measuring device C. And, the measured time is compared with the specified time set by driving state parameter as to the transport delay of exhaust gas, and when the measuring time is more than the specified time, air-fuel ratio regulation by the regulating device A is stopped by a stopping device E.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides air-fuel ratio sensors (herein, oxygen concentration sensors (Oz 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 0□ sensor in addition to air-fuel ratio feedback control using an upstream 0□ sensor.

(Prior art) In simple air-fuel ratio feedback control (single 0! sensor system), the 0□ sensor that detects oxygen concentration is installed at a point in the exhaust system as close to the combustion chamber as possible, that is, at a gathering point in the exhaust manifold upstream of the catalytic converter. However, due to variations in the output characteristics of the 02 sensor, it is difficult to improve the control accuracy of the air-fuel ratio.
In order to compensate for variations in sensor output characteristics, variations in parts such as fuel injection valves, and changes over time or aging, a second 02 sensor is sanded downstream of the catalytic converter.
A double 02 sensor system has already been proposed in which air-fuel ratio feedback control is performed by a downstream 02 sensor in addition to air-fuel ratio feedback control by an upstream 0□ sensor (see Japanese Patent Laid-Open No. 58-48756). In this double 02 sensor system, the 08 sensor installed downstream of the catalytic converter has a
Although it has a low response speed, it has the advantage of small variations in output characteristics for the following reason.

(1) Downstream of the catalytic converter, the exhaust gas temperature is low, so there is little thermal influence.

(2) Since various poisons are trapped in the catalyst downstream of the catalytic converter, the amount of poisoning of the downstream 02 sensor is small.

(3) The exhaust gas is sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the exhaust gas is close to an equilibrium state.

Therefore, as described above, by air-fuel ratio feedback control (double Ox 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, as shown in Figure 2, in a single Ot sensor system, 0
□If the output characteristics of the sensor deteriorate, it will directly affect the exhaust emission characteristics, whereas in the double Ox 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.

[Problem that the invention seeks to solve]

However, in the double 02 sensor system described above, the 0□ sensor usually has an element temperature of 300 to 450°C.
Although it is activated in the above cases, the response of the downstream 0□ sensor located downstream of the catalyst may deteriorate, especially when the sensor element temperature is low and poisonous substances adhere to the coating surface. big. Therefore, when the downstream 02 sensor deteriorates, the responsiveness does not increase, and as a result, the average air-fuel ratio deviates, resulting in a problem of deterioration of emissions, particularly NOx.

Therefore, an object of the present invention is to provide a double air-fuel ratio sensor system that prevents deterioration of emissions due to deterioration of the downstream air-fuel ratio sensor, that is, a decrease in responsiveness.

[Means for solving problems]

A means for solving the above-mentioned problems is shown in FIG. That is, an upstream air-fuel ratio sensor that detects the air-fuel ratio of the engine is provided in the exhaust passage upstream of the three-way catalyst CCR0 provided in the exhaust passage of the internal combustion engine, and the three-way catalyst CCR0 is provided in the exhaust passage of the internal combustion engine.
A downstream air-fuel ratio sensor that detects the air-fuel ratio of the engine is provided in the exhaust passage downstream of C++o. The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the output V of the upstream air-fuel ratio sensor and the output (2) of the downstream air-fuel ratio sensor.

On the other hand, the fuel cut state determining means determines whether or not the engine is in the fuel cut state, and when the engine is in the fuel cut state, the time measuring means determines when the output ■1 of the upstream air-fuel ratio sensor indicates lean. The time A from when the output vt of the downstream air-fuel ratio sensor indicates lean is measured. The comparison means compares this measured time A with a predetermined time B determined by operating state parameters relating to the exhaust gas transport delay. As a result, when the measured time A is equal to or longer than the predetermined time 8, the stopping means stops the air-fuel ratio adjustment by the downstream air-fuel ratio sensor in the air-fuel ratio adjusting means.

[For production]

According to the above-mentioned means, the responsiveness of the downstream air-fuel ratio sensor is determined from the difference (time) between the lean operation of the upstream air-fuel ratio sensor and the lean operation of the downstream chamber and fuel ratio sensor during fuel cut. As a result, when it is determined that the responsiveness of the downstream air-fuel ratio sensor has decreased, the operation of the downstream air-fuel ratio sensor is stopped.

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

FIG. 3 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 3, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. As shown in FIG. The airflow meter 3 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. The distributor 4 includes a crank angle sensor 5 whose shaft generates a pulse signal for detecting a reference position every 7200 inches in terms of crank angle, and a crank angle sensor 5 which generates a pulse signal for detecting a reference position every 30 inches in terms of crank angle. The pulse signals of these crank angle sensors 5.6 are supplied to the input/output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to 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 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 l. Water temperature sensor 9° indicates cooling water temperature T
Generates analog voltage electrical signals according to HW. This output is also supplied to the A/D converter 101.

The exhaust system downstream of the exhaust manifold 11 is provided with a catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three harmful components IC, CO, and NO in the exhaust gas.

The exhaust manifold 11 is provided with a first 08 sensor 13 on the upstream side of the catalytic converter 12, and the exhaust pipe 14 on the downstream side of the catalytic converter 12 is provided with a second 08 sensor 13.
A sensor 15 is provided.

The Ot sensors 13 and 15 generate electrical signals depending on the concentration of oxygen components in the exhaust gas. That is, Ot sensor 13
, 15 is an A/D 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.
occurs in converter 101.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 for detecting whether the throttle valve 16 is fully closed, and this output signal is supplied to the input/output interface 102 of the control circuit 10. Ru. moreover,
Reference numeral 18 is an alarm for indicating deterioration in responsiveness of the downstream OR sensor 15.

The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, an input/output interface 102 . In addition to the CPt 1103, there is a ROM 104.

A ROM 105, a backup RAl' 1106, a clock generation circuit 107, and the like are provided.

In addition, in the control circuit IO, 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, 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, the down counter 108 receives the clock signal (
(not shown), and finally the carrier terminal is “
1" level, the flip-flop 109 is set and the drive circuit 110 stops energizing the fuel injection valve 7. In other words, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TAU, and therefore , 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 CPt1103 is caused by 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 cooling water temperature data THW of the air flow meter 3 are fetched 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 THW in RAM 105 are updated at predetermined time intervals. Further, the rotational speed data Ne is calculated by an interrupt every 30'CA of the crank angle sensor 6 and stored in a predetermined area of the RAM 105.

The operation of the control circuit shown in FIG. 3 will be explained below.

FIG. 4 shows a fuel cut setting routine, which is executed every predetermined period of time, for example, every 4 ms. This routine is for setting the fuel cut flag XFC as shown in FIG. In FIG. 5, N indicates the fuel cut rotation speed and N indicates the fuel cut return rotation speed, both of which are updated by the engine cooling water temperature T) (W).

In step 401, the output signal L of the idle switch 5 is
It is determined whether or not L is 1", that is, whether or not there is an idle state. If it is a non-idle state, the process proceeds to step 404;
On the other hand, if it is in the idle state, the process advances to step 402.

In step 402, the rotation speed N is read from the RAM 105 and compared with the fuel cut rotation speed Nc, and in step 403, it is compared with the fuel cut return rotation speed N8.

As a result, if N, ≦NR, the fuel cut flag
1''. When N H < No < N, the flag XFC is held at its previous state.

The routine then ends at step 412.

FIG. 6 shows a routine for calculating the air-fuel ratio feedback control execution flag X5FB by the downstream side 02 sensor 15, and is executed at predetermined time intervals, for example, every dma.

Steps 601 to 605 are for detecting the fuel cut start point. In addition, the fuel cut start flag fF
(="1") indicates that the fuel cut start time has been detected, and is assumed to have been cleared in an initial routine (not shown). Therefore, the flow in step 601 proceeds to step 602, where the rotational speed data N is sequentially outputted from the RAM 106, and it is determined whether or not No > N (up to a fixed value). Data Q is read and it is determined whether Q>Qo (constant value). Then, proceed to step knob 604 only when N>No and Q>QO, otherwise proceed to step 6.
Proceed to step 27.

That is, N, > N and Q > Q, both 0□ sensor 13
, 15 activation conditions. In addition, both 02 sensor 13
, 15 is not limited to this. In step 604, it is determined whether or not the fuel cut is I-(XFC="1"). As a result, only when XFC="12", a fuel cut start flag fF is set ("1") in step 605. In this way, when the engine shifts from the fuel injection state to the fuel cut state, the fuel cut start flag f
F is set. Once the fuel cut start flag fF is set, the flow in step 601 is changed to step 6.
Proceed to 06-611.

In other words, the present invention predicts that when a fuel cut is performed, if the responsiveness of both 0□ sensors 13 and 15 is normal, these outputs will be delayed by the exhaust gas transport time and become lean. Deterioration in the responsiveness of the downstream 0□ sensor 15 is determined by determining whether there is a lean output from the downstream 0□ sensor after a predetermined period of time after the lean output from the downstream 0□ sensor.

In step 606, the output of the upstream 02 sensor 13 is
is A/D converted and imported, and in step 607, V, <0
, 2V or not. Note that here, the value 0.2 V is a level indicating that the output (1) of the upstream side 02 sensor 13 is sufficiently lean. Therefore, if V+<0.2V, it is determined that the output V of the upstream 0□ sensor 13 has become lean, and the time counter A is incremented by +1 in step 608. Next, in step 609, it is determined whether the time counter A is less than or equal to the maximum value A_man.

As a result, if A≧A,□, the downstream side 0□ sensor 15
It is assumed that the responsiveness has decreased significantly, and in this case, in step 617, the downstream air-fuel ratio feedback control execution flag X5FB is immediately reset (to "0"). On the other hand, if A < A m a X, step 610
, 611, it is determined whether the output V2 of the downstream side 02 sensor 15 has become sufficiently lean (Vz<0.2V). Only when V,<0.2V, proceed to step 612;
Otherwise, proceed to step 9, step 628. in this way,
The time counter A measures the time from the time when the output 1 of the upstream side 02 sensor 13 becomes sufficiently lean to the time when the output v2 of the downstream side 02 sensor 15 becomes sufficiently lean after the start of fuel cut. be. Normally, this time A is the transport time of the exhaust gas from the position of the upstream 0□ sensor 13 to the position of the downstream 0□ sensor 15, and this transport time is determined by engine load parameters such as Q, Q
/N, ,N, depends on intake pipe pressure and throttle valve opening TA. Therefore, in step 612, time B corresponding to the transportation time is calculated according to the load parameter, for example, Q/N, and in step 613, it is determined whether or not it is A2B. As a result, if it is A2B, the responsiveness of the downstream 0□ sensor 15 is considered to be low (deteriorated), and steps 614 to 619
Prepare to stop downstream air-fuel ratio feedback control execution. On the other hand, if A<B, the responsiveness of the downstream 02 sensor 15 is considered normal, and if the downstream air-fuel ratio feedback control is stopped (XSPB="O"), the control is stopped in steps 620 to 624. Prepare for reopening.

That is, when it is determined that the responsiveness of the downstream side 02 sensor 15 has deteriorated, in step 61'4, the downstream side air-fuel ratio feedback control is currently being executed (XSFB
If the execution is in progress, the downstream air-fuel ratio feedback stop counter S is incremented by +1, and in step 616 it is determined whether or not it has reached a predetermined value S6. If the result is S≦80, step 62
6, reset the fuel cut start flag XFC to “0”.
”), the time counter A is cleared in step 627, and the process proceeds to step 628. In other words, the fuel power is reset again.
Wait for throat status. Therefore, after the fuel cut is started 80 times or more (but within the limit that is not cleared in step 624), the downstream side 0. When the response deterioration determination (A2B) of the sensor 15 has been made 80 times, the downstream air-fuel ratio feedback execution flag X is set in step 617.
5FB should be reset (10"), and step 618
At step 619, the downstream side air-fuel ratio feedback restart counter C is cleared, and at step 619, the alarm 18 is activated to indicate a failure of the downstream side Ch sensor 15. Note that even after flag X5PB is reset, step 6
If it is A2B in step 13, the flow proceeds directly to step 625, so the flag X5FB (="0"), counter C (=O), and alarm display are retained.

Furthermore, once the flag X5FB is reset, if A<B (normal) at step 613,
Proceed to steps 620-625. In other words, downstream side 0□
When it is determined that the responsiveness of the sensor 15 has recovered to normal, the flow in step 613 is changed to step 620.
The process proceeds to step 621, where the downstream air-fuel ratio feedback restart counter C is incremented by +1, and it is determined in step 622 whether or not it has reached a predetermined value C0.

As a result, if C≦00, the fuel cut start flag Therefore, after the fuel cut has been started 00 times or more (but within the limit that is not cleared in step 618), the normality determination of the responsiveness of the downstream 0□ sensor 15 (A<
B) 00 times, the downstream air-fuel ratio feedback execution flag X5FB is set to "1" in step 621, and the downstream air-fuel ratio feedback stop counter S is cleared in step 624. At 625, the alarm 18 is deenergized and the downstream side is set to 0□
The failure indication of the sensor 15 is stopped. In addition, once the flag
Even after 5FB is set, A<
If B, the flow goes directly to step 625, so
Flag X5FB, (= “1”) Counter 5 (=
O), the alarm release is retained.

In this way, in step 613, the downstream Ot sensor 15
If there is a deterioration or recovery in responsiveness, the downstream air-fuel ratio feed bank control execution flag The air-fuel ratio feedback control execution flag X5FB is changed, thereby stabilizing the air-fuel ratio feedback control.

FIG. 7 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 02 sensor 13, and is executed every predetermined period of time, for example, every dma.

In step 701, as one of the closed loop (feedback) conditions for the air-fuel ratio by the upstream Ot sensor 13, it is determined whether fuel is being cut (XFC="1"). If the fuel is not being cut (X F C = "01"), it is determined in step 702 whether other closed loop conditions are satisfied.For example, if the cooling water temperature is a predetermined value (for example, 60°C
) In the following cases, while starting the engine, increasing fuel after starting, increasing fuel during warm-up,
During acceleration increase (non-service injection), during power increase, upstream side 02
When the output signal of the sensor 13 never crosses the reference voltage, etc., the closed loop condition is not satisfied.
In other cases, the closed loop condition is met. If the closed loop condition is not met, the process proceeds directly to step 729. That is, the air-fuel ratio correction coefficient FAF is set to the value immediately before the end of the closed loop control. Note that FAF may be a constant value, an average value before the end of the closed loop, or a learned value (value of the backup RAM 106).

On the other hand, if the closed loop condition is satisfied, the process proceeds to step 703.

In step 703, the output of the upstream 0□ sensor 13 is
In step 704, it is determined whether 1'' is less than the comparison voltage VRI, for example 0.45V.In other words, it is determined whether the air-fuel ratio is rich or lean.Lean (V+ ≦V R1 ), in step 705 it is determined whether the delay counter CDLY is positive or not, and CDL
If Y>0, set CDLY to 0 in step 706,
Proceed to step 707. In steps 708 and 709, the delay counter CDLY is guarded at the minimum value TDL.
When the air-fuel ratio flag F is reached, the air-fuel ratio flag F is set in step 710.
Let l be “0” (lean). Note that the minimum value TDL is a lean delay time for maintaining the judgment that the state is rich even if there is a change from rich to lean in the output of the upstream 0□ sensor 13, and is defined as a negative value. Ru. On the other hand, if it is rich (V+ > V, lt), it is determined in step 711 whether the delay counter CDLY is negative or not, and if CDLY<O, in step 712 the CD
Set LY to 0 and proceed to step 713. Step 714
At ゜715, the delay counter CDLY is set to the maximum value TD.
In this case, when the delay counter CDLY reaches the maximum value TDR, the air-fuel ratio flag F1 is set to "1" (rich) in step 716.

The maximum value TDR is a rich delay time for maintaining the determination that the engine is in a lean state even if there is a change from lean to rich in the output of the upstream 02 sensor 13, and is defined as a positive value. .

In step 717, it is determined whether the sign of the air-fuel ratio flag Fl 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, then in step 718, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the air-fuel ratio flag Fl. If it is a reversal from rich to lean, it is increased in a skip manner as PAP←FAF +R3R in step 719, and conversely, if it is a reversal from lean to rich, it is increased in a skip manner as FAF-FAF-R5L in step 720. decrease to In other words, skip processing is performed. If the sign of the air-fuel ratio flag F1 is not inverted in step 717, integration processing is performed in steps 721, 722, and 713. That is, in step 721, it is determined whether Fl-0'' or not, and if F1="0" (lean), PAP-FAF +KIR is set in step 722, and on the other hand, F
If 1="1" (rich), F at step 723.
AF 4-PAF-KIL. Here, the constant of integration K
rR (KIL) is set sufficiently small compared to the skip constants R5R and RSL, that is, K IR (K IL
) < RSR (RSL). Therefore, step 7
Step 22 gradually increases the fuel injection amount in a lean state (F1="'0"), and step 723 gradually increases the fuel injection amount in a rich state (F1="'0").
1") to gradually reduce the fuel injection amount. Step 71
The air-fuel ratio correction coefficient FAF calculated at 9°720.722, 723 is guarded at the maximum value, for example, 1.2 at steps 724 and 725, and is guarded at a maximum value of 1.2, for example, at steps 726 and 725.
727 and is guarded at a minimum value of 0.8, for example. As a result, if the air-fuel ratio correction coefficient FAF becomes too small or too large for some reason, the air-fuel ratio of the engine is controlled using that value to prevent over-lean or over-rich conditions.

The FAF calculated as described above is stored in the RAM 105, and the routine ends in step 729.

FIG. 8 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 7. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream 02 sensor 13 as shown in FIG. 8(A), the delay counter CD
As shown in FIG. 8(B), LY is counted up in a rich state and counted down in a lean state.

As a result, as shown in FIG. 8(C), a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed. For example, even if the air-fuel ratio signal A/F changes from lean to rich at time 1, the delayed air-fuel ratio signal A/F
' is maintained lean for the rich delay time TDR and then changes to rich at time t2. Even if the air-fuel ratio signal A/F changes from rich to lean at time t3, the air-fuel ratio signal A/F' subjected to the delay processing is delayed by the lean delay time (-TD
L) After being kept rich for a considerable amount, it changes to lean at time t4. However, the air-fuel ratio signal A/F at time jS
+j&+t, when inverted in a period shorter than the rich delay time TDR, it takes time for the delay counter CDLY to reach the maximum value TDR, and as a result, the air-fuel ratio signal A after the delay processing at time t. /F' is inverted. In other words, the air-fuel ratio signal A/F' after the delay process is more stable than the air-fuel ratio signal A/F before the delay process. In this manner, the air-fuel ratio correction coefficient FAF shown in FIG. 8CD) is obtained based on the stable air-fuel ratio signal A/F' after the delay processing.

Next, the second air-fuel ratio feedback control by the downstream 02 sensor 15 will be explained. The second air-fuel ratio feedback control includes skip amounts RSR and RSL as the first air-fuel ratio feedback control constants, and an integral constant K.
IR, KIL, delay time TDR.

TDL or the output V of the upstream O2 sensor 13.

There are systems that make the comparison voltages V and II variable, and systems that introduce a second air-fuel ratio correction coefficient FAF2.

For example, if the rich skip amount R3R is increased, the controlled air-fuel ratio can be shifted to the rich side, and even if the lean skip amount R3L is decreased, the controlled air-fuel ratio can be shifted to the rich side.On the other hand, if the lean skip amount R3L is increased, The control air-fuel ratio can be shifted to the lean side, and even if the rich skip IR3R is reduced, the control air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich skip fR8R and the lean skip amount R3L according to the output of the downstream 0□ sensor 15. Also, the Ricci integral constant KI
By increasing R, the control air-fuel ratio can be shifted to the rich side,
In addition, the control air-fuel ratio can be shifted to the rich side even if the lean integral constant KIL is decreased, and on the other hand, the control air-fuel ratio can be shifted to the lean side by increasing the lean integral constant KIL. The controlled air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich integral constant KTR and the lean integral constant KIL according to the output of the downstream 0□ sensor 15. Rich delay time TDR> IJ-on delay time (-TD
L), the control air-fuel ratio can be shifted to the rich side,
Conversely, lean delay time (-TDL) > rich delay time (
TDR), the controlled air-fuel ratio can be shifted to the lean side. That is, by correcting the delay times TDR and TDL according to the output of the downstream 02 sensor 15, the air-fuel ratio can be controlled. Furthermore, if the comparison voltage Vj11 is increased, the controlled air-fuel ratio can be shifted to the rich side. , the control i air-fuel ratio can be shifted to the lean side by decreasing the comparison voltage ■□. Therefore, the comparison voltage V□ is corrected according to the downstream side O, the output of the sensor 15]. : The air-fuel ratio is controlled by 2・ζ-! It is possible to make these skip concealment, integral constant, delay time, and comparison voltage variable by the downstream 02 sensor (there are some advantages. For example, the delay time can be adjusted very delicately to adjust the air-fuel ratio. In addition, the skip amount can be controlled with good response without lengthening the air-fuel ratio feedback cycle like the delay time.Therefore, these variable amounts are naturally used in combination on the 2nd parameter. obtain.

A double Ot sensor system in which the skip amount as an air-fuel ratio feedback control constant is made variable will be explained with reference to FIG. A second air-fuel ratio feedback control routine that calculates
6 Stesob 9) to 905 performed every 12 fertilizers,
Downstream side 0. It is determined whether the sensor 15 is closed or not. For example, in addition to the failure of the closed loop condition determined by the upstream sensor 13 (step 901), when the cooling water temperature T'HW is below a predetermined value (for example, 70'C) (step 902), the throttle valve 16 is When fully closed (LL="1") (snap 903), downstream (F
l! Has the output VZ of 02 sensor 15 ever been used? $ voltage is not crossed (i.e. downstream 02 sensor 1
The closed-loop condition is not satisfied in cases such as when Q5 is not activated (step 904), when the load is light (Q/N, <X+) (step 905), and in other cases, the closed-loop condition is not satisfied.

If the closed loop condition is not met, the process goes directly to the step/button 14. If the closed loop condition is met by the downstream 02 sensor 15, the process goes to step 90G, where the downstream air-fuel ratio feed bank control phase calculated in the routine of FIG. Execution flag X5
Determine whether PB is "1' or not. As a result, XSl'B
="1", the downstream side O and the output V of the sensor 15 in the flow of steps 907 to 913.

This essentially performs air-fuel ratio feedback control.

That is, in step 907, the downstream side 0! The output v2 of the sensor 15 is A/D converted and taken in, and in step 908 it is determined whether or not V2 is less than the comparison voltage Vll, for example 0.55V. In other words, it determines whether the air-fuel ratio is rich or lean. As a result, in step 908 v2≦V112(
lean), proceed to step 909;
>VRl (rich), the process advances to step 910.

In step 909, the rich skip amount RSR is read from the backup RAM 106, and RSR=R3R+ΔR
5 (constant value), that is, the rich skip amount R5R is increased to shift the air-fuel ratio to the rich side, and further, in step 910, the lean skip amount R3L is read from the backup RAM 106, and R5L←R5L-ΔR5, that is, , the rich skip amount R3L is decreased to shift the air-fuel ratio to the rich side.

On the other hand, when Vt>V, □ (rich), step 9
Rich skip amount 1 from backup RAM 106 at 11? Read SR, R5I? −RSR−ΔR5,
.

In other words, Rich Skip! RR8R is decreased to shift the air-fuel ratio to the lean side, and further, in step 912, the lean skip amount R3L is read from the bank-up RAM 106, and RSL 4-1? SL +ΔR5, that is, lean skip 1iR3L is increased to shift the air-fuel ratio to the lean side.

Step 913 is the RSR calculated as described above.

It performs RSL guard processing, for example, maximum value M A X = 7.5%, minimum value M I N = 2
．． It is guarded at 5% and stored in the backup RAM 106. Note that the minimum value MIN is a value at a level that does not impair transient followability, and the maximum value MAX is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

The routine of FIG. 9 then ends at step 914.

Note that the skip amount R5R and the RSL update rate ΔR3 in steps 909 to 912 in FIG. 9 can be made variable according to the value of A obtained in FIG. 6.

At that time, ΔR3 used in steps 909, 910, 911, and 912 are respectively ΔR3i, ΔR32, and ΔR.
33°ΔI? As S4, it is also possible to consider a system in which these are independently used as functions of A to compensate for the response delay of the downstream 02 sensor 15. In this case, the larger A obtained, the larger ΔR3I and ΔR52, and ΔR33°Δl? All you have to do is make s4 smaller.

FIG. 10 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, 360'' CA.

It is determined whether or not the fuel cuff flag Proceed to. In step 1002, R
The basic injection 1TAUP is calculated by reading the intake air amount data Q and the rotational speed data N0 from the AM105. For example, assume that TAtlP←α·Q/N (α is a constant). At step 1003, cooling water temperature data T is stored in RAM 105.
HW is read out and a warm-up increase value FWL is calculated by interpolation using the one-dimensional map stored in the RO old 04. step 100
4, the final injection 1iTAU, TAU 6-TAuP
Calculate by -FAF ・(F rotation + β + 1) + T. Note that β and T are correction amounts determined by other operating state parameters. Next, in step 1005, the injection fiTAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. The routine then ends at step 1006. As described above, when the time corresponding to the injection ff1TAU has elapsed, the flip-flop 109 is reset by the carrier-out signal of the down counter 10B, and the fuel injection ends.

Note that the first air-fuel ratio feedback control is performed every 4 ms.
Also, the second air-fuel ratio feedback control is 512 ff
The reason why the air-fuel ratio feedback control is performed every 15 is that the air-fuel ratio feedback control is primarily performed by the upstream 0□ sensor, which has good responsiveness, and is secondary to the control by the downstream 02 sensor, which has poor responsiveness.

In addition, other control constants in the air-fuel ratio feedback control by the upstream Ot sensor, such as an integral constant, delay time, and upstream 0! The double 02 sensor system that corrects the sensor comparison voltage VRI, etc. using the output of the downstream 02 sensor also has a double 02 sensor system that introduces a second air-fuel ratio correction coefficient.
The present invention can also be applied to sensor systems. Moreover, controllability can be improved by simultaneously controlling two of the skip amount, integral constant, and delay time. Furthermore, Skip I
It is possible to fix one of RSR and R5L and make only the other variable, or to fix one of the integral constants KIR and KIL and make only the other variable, or to change one of the delay times TDR and TDL. It is also possible to have one fixed and 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.

Further, in the above embodiment, an internal combustion engine is shown in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, but the present invention can also be applied to a carburetor type internal combustion engine. For example, an electric air control valve (EACV) adjusts the intake air amount of the engine to control the air-fuel ratio, and an electric bleed air control valve adjusts the amount of air bleed from the carburetor to control the main system passage and The present invention can be applied to devices that control the air-fuel ratio by introducing atmospheric air into the slow system passage, and devices that adjust the amount of secondary air sent to the exhaust system of an engine. In this case, the basic injection ITAt! in step 1001! P
A corresponding basic fuel injection amount is determined by the carburetor itself, that is, depending on the intake pipe negative pressure depending on the intake air amount and the engine rotational speed, and in step 1003, the supply air corresponding to the final fuel injection amount TAU is determined. The quantity is calculated.

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

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

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to detect deterioration in the responsiveness of the downstream air-fuel ratio sensor, and in this case,
Since the air-fuel ratio feedback control by the downstream air-fuel ratio sensor is stopped, this is useful for reducing NOx emissions, etc.

[Brief explanation of drawings]

Fig. 1 is an overall bronch diagram for explaining the present invention in detail, Fig. 2 is a single 0□ sensor system and a double 02 sensor system.
Fig. 3 is an overall schematic diagram showing an embodiment of the air-fuel ratio and control device for an internal combustion engine according to the present invention; Figs. 4, 6, 7, and 9; Figure 10 is a flowchart to explain the operation of the control circuit in Figure 3, Figure 5 is a timing diagram to supplement the flowchart in Figure 4, and Figure 8 is a supplementary flowchart in Figure 7. FIG. 2 is a timing diagram for explanation. 1... Engine body, 3... Air flow meter,
4... Distributor, 5.6... Crank angle sensor, 10... Control circuit, 12... Catalytic converter, 13... Upstream side (first) 02 sensor, 15...
Downstream side (second) 0□ sensor, 17... Idle switch, 18... Alarm. 00...The worst single 0□ system ■...Double 02 system Figure 4 Figure 8 Figure 10

Claims (1)

[Claims] 1. A three-way catalyst provided in an exhaust passage of an internal combustion engine; and an upstream air-fuel ratio sensor provided in the exhaust passage upstream of the three-way catalyst to detect the air-fuel ratio of the engine. , a downstream air-fuel ratio sensor that is provided in the exhaust passage downstream of the three-way catalyst and detects the air-fuel ratio of the engine; an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine; a fuel-cut state determining means for determining whether the engine is in a fuel-cut state; and an upstream air-fuel ratio sensor when the engine is in a fuel-cut state. a time measuring means for measuring the time from the point in time when the output of the downstream side air-fuel ratio sensor indicates lean to the point in time when the output of the downstream air-fuel ratio sensor indicates lean; Comparing means for comparing with a determined predetermined time; and stopping means for stopping air-fuel ratio adjustment by the downstream air-fuel ratio sensor in the air-fuel ratio adjusting means when the measured time is equal to or greater than the predetermined time. Air-fuel ratio control device for internal combustion engines. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, which displays a failure of the downstream air-fuel ratio sensor when the air-fuel ratio adjustment by the downstream air-fuel ratio sensor is stopped. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, which restarts air-fuel ratio adjustment by the downstream air-fuel ratio sensor when the measured time is less than the predetermined time.