JPH0686830B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to an air-fuel ratio sensor (in this specification, an oxygen concentration sensor (O ₂ sensor)) upstream and downstream of a catalytic converter.
The provided, relates to an air-fuel ratio control apparatus for an internal combustion engine which performs air-fuel ratio feedback control by the O ₂ sensor downstream in addition to the air-fuel ratio feedback control by the O ₂ sensor in the upstream side.

[Conventional technology]

In simple air-fuel ratio feedback control (single O ₂ sensor system), an O ₂ sensor that detects the oxygen concentration is provided at a location in the exhaust system that is as close to the combustion chamber as possible, that is, at the collective portion of the exhaust manifold that is upstream from the catalytic converter. , O ₂ sensor's output characteristic variation hinders improvement of air-fuel ratio control accuracy. In order to compensate for such variations in the output characteristics of the O ₂ sensor, variations in parts such as the fuel injection valve, and changes over time or over time, a second O ₂ sensor is provided downstream of the catalytic converter and the upstream O ₂ sensor is used. A double O ₂ sensor system has already been proposed which performs air-fuel ratio feedback control by a downstream O ₂ sensor in addition to air-fuel ratio feedback control. In this double O ₂ sensor system, it was installed on the downstream side of the catalytic converter.
The O ₂ sensor has a lower response speed than the upstream O ₂ sensor, but has an advantage that the variation in output characteristics is small for the following reason.

(1) Since the exhaust gas temperature is low downstream of the catalytic converter, 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 the equilibrium state.

Therefore, as described above, the air-fuel ratio feedback control based on the outputs of the two O ₂ sensors (double O ₂ sensor system), the variations in the output characteristic of the upstream O ₂ sensor can be absorbed by the downstream O ₂ sensor. Actually, as shown in FIG. 2, in the single O ₂ sensor system, when the output characteristic of the O ₂ sensor deteriorates, the exhaust emission characteristic is directly affected, whereas in the double O ₂ sensor system, the upstream Even if the output characteristic of the side O ₂ sensor deteriorates, the exhaust emission characteristic does not deteriorate. That is, in the double O ₂ sensor system, good exhaust emission is guaranteed as long as the downstream O ₂ sensor maintains stable output characteristics.

[Problems to be solved by the invention]

However, double O ₂ sensor system (see the air-fuel ratio feedback control constant in the air-fuel ratio feedback control by the upstream O ₂ sensor is variable by the output of the downstream O ₂ sensor: JP 52-102934, JP 58-48756 , 55-375
62, 58-48755, 58-72647).
When the upstream O ₂ sensor is deteriorated or damaged, the air-fuel ratio feedback control by the upstream O ₂ sensor becomes open.In this case, even if the air-fuel ratio feedback control by the downstream O ₂ sensor is performed, the entire system is The air-fuel ratio feedback control of is substantially stopped. As a result, there is a problem in that the three-way catalyst is not effectively used, which causes deterioration of emission, deterioration of drivability, and the like.

[Means for solving problems]

An object of the present invention, even if the upstream O ₂ sensor is deteriorated or damaged, empty by the upstream O ₂ sensor instead of the output of the upstream O ₂ sensor using the output of the downstream O ₂ sensor in a specific operating condition By performing the fuel ratio feedback control, the three-way catalyst is effectively used to prevent deterioration of emission, deterioration of drivability, and the like, and its configuration is shown in FIG.

In FIG. 1, first and second air-fuel ratio sensors for detecting the concentration of a specific component in exhaust gas are provided upstream and downstream of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine, respectively. Has been. The control involvement constant computing means computes a constant involved in the air-fuel ratio feedback control, such as the rich skip amount RSR and the lean skip amount RSL, in accordance with the output of the downstream (second) air-fuel ratio sensor. The air-fuel ratio sensor normal / abnormality determining means determines whether the upstream (first) air-fuel ratio sensor is normal or abnormal, and the state detecting means determines whether the rich or lean cycle of the output of the downstream side air-fuel ratio sensor is the second one. It is indirectly or directly detected whether or not the response speed of the air-fuel ratio sensor is shorter than a predetermined value indicating that the response speed of the first air-fuel ratio sensor is about the same as the response speed of the first air-fuel ratio sensor under normal conditions. As a result,
The air-fuel ratio correction amount calculation means calculates the air-fuel ratio correction amount FAF according to the output of the upstream air-fuel ratio sensor and the constant RSR (RSL) involved in the air-fuel ratio feedback control when the upstream air-fuel ratio sensor is normal, and the other Output of the downstream side air-fuel ratio sensor when the upstream side air-fuel ratio sensor is abnormal and the rich or lean output of the downstream side air-fuel ratio sensor is indirectly or directly detected to be shorter than the above-mentioned predetermined value. Also, the air-fuel ratio correction amount FAF is calculated according to the constant RSR (RSL) involved in the air-fuel ratio feedback control. The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF.

[Work]

According to the above configuration, even when the upstream side air-fuel ratio sensor is abnormal due to deterioration, damage, etc., the rich or lean cycle of the output of the downstream side air-fuel ratio sensor and the response speed of the second air-fuel ratio sensor When it is indirectly or directly detected that the value is shorter than a predetermined value indicating that the response speed of the first air-fuel ratio sensor is normal, the output of the downstream air-fuel ratio sensor is used. Since the correction amount FAF is calculated, the air-fuel ratio feedback control is substantially performed. That is, high rotation,
When the load is high, the response speed of the downstream side air-fuel ratio sensor becomes approximately the same as the response speed of the upstream side air-fuel ratio sensor, as described later. Therefore, in this case, when the upstream air-fuel ratio sensor becomes abnormal, the air-fuel ratio feedback control can be maintained by calculating the air-fuel ratio correction amount FAF from the output of the downstream air-fuel ratio sensor.

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

FIG. 3 is an overall schematic diagram showing an embodiment of an air-fuel ratio control system 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. The air flow meter 3 directly measures the intake air amount, has a built-in potentiometer, and generates an analog voltage output signal proportional to the intake air amount. This output signal is the A / D converter 101 with built-in multiplexer of the control circuit 10.
Is being supplied to.

The distributor 4 converts the shaft into, for example, a crank angle sensor 5 which generates a reference position detection pulse signal every 720 ° and a crank angle.
A crank angle sensor 6 for generating a reference position detecting pulse signal every 30 ° is provided. These crank angle sensors
The pulse signals 5 and 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 interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from the fuel supply system to the intake port for each cylinder.

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 the cooling water. The water temperature sensor 9 is the temperature of the cooling water THW
Generates an electric signal of analog voltage according to. 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 _x in the exhaust gas.

A first O ₂ sensor 13 is provided on the exhaust manifold 11, that is, on the upstream side of the catalytic converter 12, and a second O ₂ sensor 15 is provided on the exhaust pipe 14 on the downstream side of the catalytic converter 12. . The O ₂ sensors 13 and 15 generate electric signals according to the concentration of oxygen components in the exhaust gas. That is, the O ₂ sensor 13,1
5 generates a different output voltage in the A / D converter 101 via the O ₂ sensor output processing circuits 111 and 112 of the control circuit 10, depending on whether the air-fuel ratio is leaner or richer than the stoichiometric air-fuel ratio.

Note that the O ₂ sensor output processing circuits 111 and 112 usually have an outflow type circuit configuration as shown in FIG. 4A, and the output characteristic thereof is that the air-fuel ratio A / F is rich as shown in FIG. 4B. In the case of, the output (rich signal) of the O ₂ sensor rises and stabilizes at a high level as the element temperature rises, while
When the air-fuel ratio A / F is lean, it stabilizes at a certain low level as the element temperature rises.

Reference numeral 17 is a temperature sensor provided in the oxidation catalyst in the three-way catalytic converter 12, and its output is supplied to the A / D converter 101 of the control circuit 10.

Reference numeral 18 denotes an alarm such as a buzzer and a display, which is activated when the upstream O ₂ sensor 13 fails.

The control circuit 10 is configured as, for example, a microcomputer, and includes an A / D converter 101, an input / output interface 102, a C
In addition to PU 103, O ₂ sensor output processing circuit 111, 112, ROM 10
4, RAM 105, backup RAM 106, clock generator 1
07 etc. are provided.

Further, in the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110 are for controlling the fuel injection valve 7. That is, when the fuel injection amount TAU is calculated in the routine described later, the fuel injection amount T
The AU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, drive circuit 1
10 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts a clock signal (not shown) and finally its carry-out terminal becomes the "1" level, the flip-flop 109 is set and the drive circuit 110 causes the fuel injection valve 7 to operate. Stop energizing. That is, the above-mentioned fuel injection amount TA
Only U, the fuel injection valve 7 is energized, and therefore the fuel injection amount TAU
The amount of fuel corresponding to is sent to the combustion chamber of the engine body 1.

The CPU 103 generates an interrupt when the A / D conversion of the A / D converter 101 is completed, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6, the clock generation circuit 107.
When an interrupt signal from is received.

The intake air amount data Q and the cooling water temperature data THW of the air flow meter 3 are fetched by an A / D conversion routine executed every predetermined time and stored in a predetermined area of the RAM 105. That is, the data Q and THW in the RAM 105 are updated every predetermined time. The rotation speed data Ne is calculated by interruption of the crank angle sensor 6 every 30 ° CA and stored in a predetermined area of the RAM 105.

FIG. 5 shows a first air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF based on the output of the upstream O ₂ sensor 13, which is executed every predetermined time, for example, 4 ms.

In step 501, it is determined whether or not the closed loop (feedback) condition of the air-fuel ratio by the upstream O ₂ sensor 13 is satisfied. During engine start, during fuel increase operation after start, during warm-up increase operation, during power increase operation, during lean control, upstream side
When the O ₂ sensor 13 is inactive, the closed loop condition is not satisfied, and in other cases, the closed loop condition is satisfied. In order to determine the active / inactive state of the upstream O ₂ sensor 13, the water temperature data THW is read from RAM 105 and once THW ≧ 70 ° C.
Or whether the upstream side O ₂ sensor
This is done by determining whether the output level of 13 has once risen or falled. When the closed loop condition is not satisfied, the routine proceeds to step 533, where the air-fuel ratio correction coefficient FAF is set to a constant value, for example
Set to 1.0. In this case, the air-fuel ratio correction coefficient FAF may be a value immediately before the air-fuel ratio feedback control is stopped, or an average value. On the other hand, if the closed loop condition is satisfied, step
Proceed to 502.

In step 502, it is determined whether the upstream O ₂ sensor 13 is normal or abnormal depending on whether the first diagnostic flag DFG 1 calculated in the diagnostic routine shown in FIG. 10 described later is “1”. If the upstream O ₂ sensor 13 is normal (DFG 1 = “0”), the process proceeds to step 503, where the output V ₁ of the upstream O ₂ sensor 15 is A / D converted and captured, while the upstream O ₂ sensor ₂ If the sensor 13 is abnormal (DFG 1 =
“0”), the process proceeds to step 504.

In step 504, the rotational speed data Ne is read from the RAM 105 to determine whether Ne> N _H (constant value). In step 505, the intake air amount data Q is read from the RAM 105 and Q> Q _H (constant). Value) or not. As a result, only when Ne> N _H and Q> Q _H , that is, only when high rotation and high load, step
Proceeding to 506, the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and taken in, and in step 507 V ₁ ← V ₂ is set. That is, downstream side O
Use the output V ₂ of the ₂ sensor 15 as an output V ₁ of the upstream O ₂ sensor 13.

On the other hand, in step 504 or 505, Ne ≦ N _H or Q
If ≦ Q _H , the process proceeds to step 533 and the open control is performed.

In step 508, it is determined whether or not V ₁ is the comparison voltage V _R1 or less, for example 0.45V. That is, it is determined whether the air-fuel ratio is rich or lean. If lean (V ₁ ≦ V _R1 ), then step 509
At step 510, it is determined whether or not the first delay counter CDLY1 is positive. If CDLY1> 0, at step 510 the first delay counter CDLY1 is set to zero. In step 511, the first delay counter CDLY1 is decremented, and in step 512 CDLY
Determine if 1 <TDL 1 or not. Note that when TDL 1 is via the output V ₁ of the upstream O ₂ sensor 13 (step 504 to 507) is even changes from rich to lean is the output V ₂₎ of the downstream O ₂ sensor 15 It is a lean delay time for holding the determination that the state is rich, and is defined by a negative value. Therefore, only when CDLY <TDL 1 in step 507, CDLY ← TDL 1 is set in step 508, and the air-fuel ratio flag F1 is set to “0” (lean state) in step 509. On the other hand,
If it is rich (V ₁ > V _R1 ) in step 508, step
At 515, it is determined whether the first delay counter CDLY1 is negative. If CDLY1 <0, at step 516 the first delay counter CDLY1 is set to 0. In step 517, the first delay counter CDLY1 is incremented, and in step 518 CDLY1.
1> Determine if TDR 1 or not. Note that when TDR 1 is via the output V ₁ (step 504 to 507 of the upstream O ₂ sensor 13,
It is the rich delay time for holding the judgment that the lean state is maintained even when the output V ₂ ) of the downstream O ₂ sensor 15 changes from lean to rich, and is defined by a positive value. Therefore, only when CDLY> TDR 1 in step 518,
In step 519, CDLY ← TDR 1 is set, and in step 520, the air-fuel ratio flag F1 is set to “1” (rich state).

In step 521, 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 process has been inverted. If the air-fuel ratio is reversed, the routine proceeds to step 522, where learning control is performed.

In the learning control, as shown in FIG. 6, in step 601, the average value FAFAV of the air-fuel ratio correction coefficient FAF is set to (FAF ₀ is the previous FAF value) and calculated in step 602
Determine whether FAFAV is 1.02 or more, and go to step 603 FAFAV
Is 0.98 or less, and as a result, when FAFAV ≧ 1.02, the learning value KG is increased by a constant value ΔKG, while FA
When FAV ≦ 0.98, the learning value KG is decreased by a constant value ΔKG. In step 606, FAF ₀ ← FAF is set to prepare for the next execution, and in step 607, the learning routine ends.
In this way, for example, even during high altitude operation, even if the air-fuel ratio correction coefficient FAF decreases, the learning control absorbs this decrease, so the air-fuel ratio control coefficient FAF is always controlled with a constant value of 1.0. As a result, high altitude compensation is performed, and deterioration of drivability can be prevented.

Returning to the routine of FIG. 5, in step 523, it is determined whether the reversal from rich to lean (F1 = "0") or the reversal from lean to rich (F1 = "1"). If it is inversion from rich to lean, step 524 increases FAF ← FAF + RSR in a skip-like manner. Conversely, if it is inversion from lean to rich, skips FAF ← FAF−RSL in step 525. Reduce. That is, skip processing is performed.

If the sign of the air-fuel ratio flag F1 is not inverted in step 521, integration processing is performed in steps 526, 527 and 528. That is, in step 526, it is determined whether or not F1 = "0", and F1
If ＝ “0” (lean), in step 527 FAF ← FAF + K
I, and if F1 = "1" (rich), step 528.
Then FAF ← FAF ← KI. Here, the integration constant KI is set sufficiently smaller than the skip constants RSR, RSL, that is, KI <RSR (RSL). Therefore, in step 527, the fuel injection amount is gradually increased in the lean state (F1 = "0"),
In step 528, the fuel injection amount is gradually reduced in the rich state (F1 = "1").

The air-fuel ratio correction coefficient FAF calculated in steps 524, 525, 527, 528 is guarded in steps 529 to 532 with a minimum value, for example 0.8, and a maximum value, for example 1.2, which causes the air-fuel ratio correction coefficient FAF to become too large for some reason, or When it becomes too small, the air-fuel ratio of the engine is controlled by that value to prevent overrich or over lean.

The FAF calculated as described above is stored in the RAM 105, and this routine ends at step 534.

FIG. 7 is a timing chart for supplementarily explaining the operation according to the flowchart of FIG. Output V of upstream O ₂ sensor 13
₁ (Downstream O ₂ sensor 1 if steps 504-507
The output V _{2 of} 5 is rich as shown in FIG.
When the lean-determined air-fuel ratio signal A / F is obtained, the first delay counter CDLY1 is counted up in the rich state and counted down in the lean state as shown in FIG. 7 (B). As a result, as shown in FIG. 7 (C),
The delayed air-fuel ratio signal A / F 'is formed. For example, even if the air-fuel ratio signal A / F changes from lean to rich at time t ₁ , the delayed air-fuel ratio signal A / F ′ is held lean for the rich delay time (TDR 1) and then It changes to rich at t ₂ . 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 ′ changes to lean at time t ₄ after being held rich for a lean delay time TDL 1. However, when the air-fuel ratio signal A / F is inverted 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 the maximum value TDL 1 or the minimum value TDL 1. It takes time to do so, and as a result, the delayed air-fuel ratio signal A / F ′ is inverted at time t ₈ . That is, the air-fuel ratio signal A / F ′ after the delay processing becomes more stable than the air-fuel ratio signal A / F before the delay processing. In this way, the stable air-fuel ratio signal after delay processing is
Based on A / F ', the air-fuel ratio correction coefficient F shown in Fig. 7 (D)
AF is obtained.

Next, the second air-fuel ratio feedback control by the downstream O ₂ sensor 15 will be described. As the second air-fuel ratio feedback control, a system that introduces a second air-fuel ratio correction coefficient FAF 2 and delay times TDR 1, TDL 1 and skip amount RS as constants involved in the first air-fuel ratio feedback control
R, RSL, integration constant KI (in this case, the rich integration constant KIR and lean integration constant KIL are set separately), or a system that makes the comparison voltage V _R1 of the output V ₁ of the upstream O ₂ sensor 13 variable However, the invention applies to the latter system.

For example, if rich delay time (TDR 1)> lean delay time (TDL 1) is set, the control air-fuel ratio can shift to the rich side, and conversely, lean delay time (TDL 1)> rich delay time (TDR 1) If set, the control air-fuel ratio can shift to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay times TDR 1 and TDL 1 according to the output of the downstream O ₂ sensor 15. Also, if the rich skip amount RSR is increased,
The control air-fuel ratio can be shifted to the rich side, and the control air-fuel ratio can be shifted to the rich side even if the lean skip amount RSL is reduced, while the control air-fuel ratio can be shifted to the lean side by increasing the lean skip amount RSL. , Also rich skip amount
The control air-fuel ratio can be shifted to the lean side even if RSR is reduced. Therefore, the air-fuel ratio can be controlled by correcting the rich skip amount RSR and the lean skip amount RSL according to the output of the downstream O ₂ sensor 15. Furthermore, if the rich integration constant KIR is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean integration constant KIL is decreased, the control air-fuel ratio can be shifted to the rich side, while if the lean integration constant KIL is increased, The control air-fuel ratio can be shifted to the lean side, and the control air-fuel ratio can be shifted to the lean side even if the rich integration constant KIR is reduced. Therefore, the air-fuel ratio can be controlled by correcting the rich integration constant KIR and the lean integration constant KIL according to the output of the downstream O ₂ sensor 15. Furthermore, the comparison voltage
If V _R1 is increased, the control air-fuel ratio can shift to the rich side,
Further, the control air-fuel ratio can be shifted to the lean side by decreasing the comparison voltage V _R1 . Therefore, the air-fuel ratio can be controlled by correcting the comparison voltage V _R1 according to the output of the downstream O ₂ sensor 15.

A double O ₂ sensor system in which the skip amount as a constant involved in the air-fuel ratio feedback control is variable will be described with reference to FIGS. 8 and 9.

FIG. 8 shows a second air-fuel ratio feedback control routine for calculating the skip amounts RSR, RSL based on the output of the downstream O ₂ sensor 15, which is executed every predetermined time, for example, every 1 s. In step 801, it is determined whether or not the closed loop condition by the downstream O ₂ sensor 15 is satisfied. For example, when the cooling water temperature is equal to or lower than a predetermined value and the output signal of the downstream O ₂ sensor 15 is never inverted, the second operation calculated by the routine of FIG.
When it is determined by the failure flag DFG 2 that the downstream O ₂ sensor 15 is broken, the closed loop condition is not satisfied during the transient operation, and the closed loop condition is satisfied in other cases. If it is not the closed loop condition, the process proceeds to steps 831 and 832, and the skip amounts RSR and RSL are set to constant values RSR ₀ and RSL ₀ , for example, RSR ₀ = 5% RSL ₀ = 5%. In this case, the value immediately before the air-fuel ratio feedback control is stopped or the average value may be used. Step 80
If the closed loop condition is satisfied in step 2, the output CC ₀ of the temperature sensor 17 is A / D converted in step 802, and it is determined in step 803 whether CC ₀ > 400 ° C. As a result, CC ₀ ≤ 400 ° C
If so, proceed to steps 831 and 832 to set open control CC ₀
Only when> 400 ° C., the routine proceeds to step 804, where the air-fuel ratio feedback control by the downstream O ₂ sensor 15 is performed. As a result, when the downstream O ₂ sensor 15 becomes cold and becomes inactive,
By stopping the air-fuel ratio feedback control by the downstream side O ₂ sensor 15, deterioration of emission and deterioration of drivability due to lean control are prevented. In this case, the temperature sensor 17 may be in the vicinity of the downstream O ₂ sensor 15 even if it is not in the oxidation catalyst in the catalytic converter 12.

In step 804, the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and captured, and in step 805, V ₂ is compared voltage V _R2
It is determined whether it is 0.55V or less, that is, whether the air-fuel ratio is rich or lean. Note that the comparison voltage V _R2 takes into consideration that output characteristics due to the influence of raw gas are different upstream and downstream of the catalytic converter 14 and that the deterioration rate is different,
It is set higher than the comparison voltage V _R1 of the output of the upstream O ₂ sensor 13.

Steps 806 to 817 are for performing delay processing, as in steps 509 to 520 in FIG. Here, the rich delay time is TDR2 and the lean delay time is TDL2. As a result, if the air-fuel ratio after the delay processing is rich, the air-fuel ratio flag F2 is set to "1", and if it is lean, the air-fuel ratio flag F2 is set. "0"
It is what

Next, at step 818, it is judged if the air-fuel ratio flag F2 is "0". As a result, if F2 = "0", the air-fuel ratio is judged to be lean and the routine proceeds to steps 819 to 824, while on the other hand, F2 If = "1", it is determined that the air-fuel ratio is rich and the routine proceeds to steps 825-830.

In step 819, RSR ← RSR + ΔRS (a constant value, for example, 0.0
8%), that is, the rich skip amount RSR is increased to shift the air-fuel ratio to the rich side. R in steps 820, 821
Guard SR with maximum value MAX, for example 6.2%. further,
In step 822, RSL ← RSL−ΔRS is set, that is, the rich skip amount RSL is decreased and the air-fuel ratio is shifted to the rich side. In steps 823 and 824, RSL is set to the minimum value MIN, for example.
Guard at 2.5%.

On the other hand, when rich (V ₂ > V _R2 ), in step 825
RSR ← RSR−ΔRS, that is, the rich skip amount RSR is decreased and the air-fuel ratio is shifted to the lean side. Step 82
In 6,827, RSR is guarded by the minimum value MIN. further,
In step 828, 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. In steps 829 and 830, RSL is set to the maximum value MA.
Guard at X.

After the RSR and RSL calculated as described above are stored in the RAM 105, this routine ends at step 833.

FAF, RSR, RS calculated during air-fuel ratio feedback
L can be once converted into other values FAF ′, RSR ′, RSL ′ and stored in the backup RAM 106, which is also useful for improving drivability at the time of restart. The minimum value MIN in FIG. 8 is a value at which the transient followability is not impaired, and the maximum value MAX is a value at which driveability does not deteriorate due to air-fuel ratio fluctuations.

As described above, according to the routine of FIG. 8, when the output of the downstream O ₂ sensor 15 is lean, the rich skip amount RSR is gradually increased and the lean skip amount RSL is gradually decreased, which results in , The air-fuel ratio is shifted to the rich side.
Further, if the output of the downstream O ₂ sensor 15 is rich, the rich skip amount RSR is gradually reduced and the lean skip amount RSL is gradually increased, whereby the air-fuel ratio is shifted to the lean side.

FIG. 9 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, every 360 ° CA. RA in step 901
The intake air amount data Q and the rotation speed data Ne are read from M105 to calculate the basic injection amount TAUP. For example TAUP ← KQ
/ Ne (K is a constant). In step 902, the cooling water temperature data THW is read from the RAM 105, and the warm-up increase value FWL is interpolated by the one-dimensional map stored in the ROM 104. In step 903, the operating state parameter, for example, the throttle valve opening TA is read from the RAM 105, and the power increase value FPOWR is calculated only when TA ≧ 70 °. The power increase value FPOWE
R is to increase the output under high load. Further, in step 904, the intake air amount data Q is read from the RAM 105.
And the rotation speed data Ne is read out to calculate the OTP increase value FOTP. The OTP increase value FOTP is for preventing the catalytic converter, the exhaust pipe, and the like from being heated when the load is high. Then, in step 905, the final injection amount TAU is calculated as TAU ← TAUP ・ FAF ・ KG (I + FWL + FPOWER + FOTP + γ) +
Calculate with δ. Note that γ and δ are correction amounts that are determined by other operating state parameters. Then step 90
At 6, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 907, this routine ends.

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

FIG. 10 is a routine for determining a failure of the upstream O ₂ sensor 13 and the upstream O ₂ sensor 15, which is executed as part of the main routine or at predetermined time intervals or at predetermined crank angle intervals.

In step 1001, similarly to step 501 in FIG. 5, it is determined whether or not the closed loop condition of the air-fuel ratio by the upstream O ₂ sensor 13 is satisfied, and in step 1002, the water temperature data TH
Determine whether the condition of W ≧ 70 ° has been maintained for 60 s or more. That is, in steps 1001 and 1002, it is determined whether or not the activation condition of the downstream O ₂ sensor 15 is satisfied. Only when these conditions are satisfied, the process proceeds to step 1003, and in other cases, the counters C ₁ and C ₂ are cleared in steps 1019 and 1020, and the routine ends in step 1021.

In step 1003, it is determined whether or not the upstream O ₂ sensor 13 has been activated. For example, activation is determined by whether V ₁ > 0.45 V is satisfied at least once or whether V ₁ once rises and falls. When it is determined that the upstream O ₂ sensor 13 is still inactive, the process proceeds to step 1010 and the counter C ₁ is cleared.

In step 1004, it is determined whether or not the fuel is in the fuel increase state based on the fuel increase value (coefficient). For example, the FOTP increment value FOTP is 0
It is determined whether or not the power increase value FPOWER is not 0. Of course, in this case, other increment values may be used. If the fuel amount is increased (FOTP
≠ 0), the routine proceeds to step 1005, increments the duration counter C ₁ of the fuel increase state by +1, and at step 1006, it is determined whether or not C ₁ > α (predetermined value). Note that α is determined in consideration of the gas transfer delay. As a result, if the fuel increase state continues for a predetermined time (C> α), it is determined in step 1007 whether the upstream O ₂ sensor 13 is active or inactive. In other words, in this state, it is expected that the vicinity of the upstream O ₂ sensor 13 is in a rich atmosphere, and therefore, if the upstream O ₂ sensor 13 is normal, its output will output a rich signal (V ₁ > V _R1 ). If so, and if it fails, the output is expected to produce a lean signal (V ₁ ≤V _R1 ). Therefore, if V ₁ ≦ V _R1 in step 1007, it is considered that the upstream O ₂ sensor 13 has failed, and step 1008
The alarm 18 is displayed at and the first failure flag DFG1 is set at step 1009. Similarly, step
In 1011, it is determined whether or not the downstream O ₂ sensor 15 has been activated. For example, activation is determined by whether V ₂ > 0.45 V is satisfied at least once, or whether V ₂ once rises or falls. When it is determined that the downstream O ₂ sensor 15 is still inactive, the process proceeds to step 1018 and the counter C ₂ is cleared.

In step 1012, it is determined whether or not the fuel is in the fuel increase state based on the fuel increase value (coefficient). For example, the FOTP increment value FOTP is 0
It is determined whether or not the power increase value FPOWER is not 0. Of course, also in this case, other increase values can be used. If you are in the fuel increase state,
(FOTP ≠ 0), the routine proceeds to step 1013, increments the duration counter C ₂ of the fuel increase state by −1, and at step 1014 C ₂ >.
It is determined whether or not β (predetermined value). Note that β is also determined in consideration of the gas transfer delay. As a result, if the fuel increase state continues for a predetermined time (C> β), in step 1015 it is determined whether the downstream O ₂ sensor 15 is active or inactive. In other words, in this state, it is expected that the vicinity of the downstream O ₂ sensor 15 is in a rich atmosphere, and therefore, if the downstream O ₂ sensor 15 is normal, its output will be a rich signal (V ₂ > V _R2 ). If so, and if it fails, the output is expected to generate a lean signal (V ₂ ≤V _R2 ). Therefore, in step 1015, V ₂ ≤
If it is V _R2 , it is considered as a failure of the downstream O ₂ sensor 15, the alarm 18 is displayed in step 1016, and the step
At 1017, the second failure flag DFG2 is set. And
At step 1021, this routine ends.

It should be noted that the alarm 18 may separately display the failure display of the upstream O ₂ sensor 13 and the failure display of the downstream O ₂ sensor 15.

11 and 12 are FIG. 5, FIG. 6, FIG. 8 and FIG.
FIG. 11 is a timing chart for supplementarily explaining the operation according to the flowchart of FIG. Here, FIG. 11 shows the upstream O ₂ sensor.
13 shows a case where the engine is normal and is in a low rotation and low load state, and FIG. 12 shows a case where the upstream O ₂ sensor 13 is abnormal and is in a high rotation and high load state.

When the upstream O ₂ sensor 13 is normal and its output V ₁ changes as shown in FIG. 11 (A), the comparison result at step 508 in FIG. 5 becomes as shown in FIG. 11 (B), and The comparison result is delayed and becomes as shown in FIG. 11C (corresponding to the flag F1). As a result, the air-fuel ratio correction coefficient FAF is calculated based on the result of this delay processing, and changes as shown in FIG. 11 (D). On the other hand, in the low rotation and low load state, the output V ₂ of the downstream O ₂ sensor 15 changes slowly as shown in FIG. 11 (E). As a result, the comparison result in step 805 in FIG. 8 changes as shown in FIG. 11 (F), and the comparison result is delayed and becomes as shown in FIG. 11 (G) (flag F2 is set). Equivalent). As a result, as shown in FIG. 11 (H), the rich skip amount RSR increases and the lean skip amount RSL decreases in the lean state, while on the other hand, as shown in FIG. 11 (I), in the rich state. If so, the rich skip amount RSR decreases and the lean skip amount RSL increases. At this time, RSR and RSL change from MAX to MIN.

In the above-mentioned state, even if the downstream O ₂ sensor 15 is normal, if the upstream O ₂ sensor 13 becomes abnormal, for example, if V ₁ is maintained at a low level, the air-fuel ratio correction coefficient FA
Although the calculation of F is stopped and the open control (FAF = 1.0) is performed, according to the present invention, even if the upstream O ₂ sensor 13 becomes abnormal, the calculation of the air-fuel ratio correction coefficient FAF at high rotation and high load is performed. Is performed to substantially maintain the air-fuel ratio feedback control. Of course, in this case, it goes without saying that the downstream O ₂ sensor 15 is normal. That is,
As shown in FIG. 12 (A), the output V _{1 of the} upstream O ₂ sensor 13
Is maintained at a low level, the output V ₂ of the downstream O ₂ sensor 15 has a high response speed at the time of high rotation and high load as shown in FIG. 12 (F). Therefore, the calculation of the air-fuel ratio correction coefficient FAF is performed based on the output V ₂ of the downstream O ₂ sensor 15. That is, in this case, the comparison result of step 508 in FIG. 5 is as shown in FIG. 12 (B), and further,
After the delay processing, the result is as shown in FIG. As a result, the air-fuel ratio correction coefficient FAF is calculated as shown in FIG. 12 (D), and the air-fuel ratio feedback control is performed. At the same time, for the output V _{2 of} the downstream O ₂ sensor 15, the comparison result in step 805 of FIG. 8 changes as shown in FIG. 12 (F) by the routine of FIG. The comparison result is delayed and becomes as shown in FIG. 12 (G) (corresponding to the flag F2). As a result, as shown in FIG. 12 (H), the rich skip amount RSR increases and the lean skip amount RSL decreases in the lean state, while the lean skip amount RSR decreases in the rich state as shown in FIG. 12 (I). If so, the rich skip amount RSR decreases and the lean skip amount RSL increases, but the repetition cycle thereof becomes faster.

In the embodiment described above, it is indirectly determined whether the rich or lean cycle of the output of the downstream O ₂ sensor is shorter than a predetermined value by detecting the state of high rotation and high load.
Alternatively, the output may be directly determined from the output of the downstream O ₂ sensor.

Further, the first air-fuel ratio feedback control is performed every 4 ms, and the second air-fuel ratio feedback control is performed every 1 s because the air-fuel ratio feedback control has an excellent responsive upstream side.
This is because the control by the O ₂ sensor is mainly performed, and the control by the downstream O ₂ sensor, which has poor response, is performed as the _secondary control.

Further, in a double O ₂ sensor system that corrects constants related to other air-fuel ratio feedback control in the air-fuel ratio feedback control by the upstream O ₂ sensor, such as delay time and integration constant, by the output of the downstream O ₂ sensor. The present invention can be applied.

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

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

Further, although the internal combustion engine in which the fuel injection amount is controlled by the fuel injection valve is shown in the above-mentioned embodiment, the present invention can 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, an electric bleed air control valve adjusts the air bleed amount of the carburetor, and the main system passage and The present invention can be applied to those that control the air-fuel ratio by introducing the atmosphere into the slow passage and those that adjust the amount of secondary air sent into the exhaust system of the engine. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 901 is determined by the carburetor itself, that is, the intake pipe negative pressure according to the intake air amount and the rotation speed of the engine. At, the supply air amount corresponding to the final fuel injection amount TAU is calculated.

Furthermore, in the above-mentioned embodiment, the O ₂ sensor is used as the air-fuel ratio sensor, but a CO sensor, a lean mixture sensor or the like can be used.

Further, although the above-mentioned embodiment is constituted by a microcomputer, that is, a digital circuit, it may be constituted by an analog circuit.

〔The invention's effect〕

As described above, according to the present invention, even if the upstream side air-fuel ratio sensor (O ₂ sensor) is abnormal, the air-fuel ratio feedback control is performed under a specific operating condition, so that the emission is deteriorated. It is possible to prevent deterioration of drivability.

[Brief description of drawings]

FIG. 1 is an overall block diagram for explaining the configuration of the present invention, FIG. 2 is an exhaust emission characteristic diagram for explaining a single O ₂ sensor system and a double O ₂ sensor system, and FIG. 3 is an internal combustion engine according to the present invention. FIG. 4A is a circuit diagram of the O ₂ sensor output processing circuit of FIG. 3, and FIG. 4B is an output characteristic of the O ₂ sensor output processing circuit of FIG. 3. 5, FIG. 6, FIG. 6, FIG. 8, FIG. 9, and FIG. 10 are flowcharts for explaining the operation of the control circuit of FIG. 3, and FIG. 7 is a supplementary explanation of the flowchart of FIG. 11 and 12 are timing charts for supplementary explanation of the flowcharts of FIGS. 5, 6, 8, 9, and 10. 1 ... Engine main 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, 15 …… Downstream (second) O ₂ sensor, 18 …… Alarm.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 61-210242 (JP, A) JP-A 61-212643 (JP, A) JP-A 55-37562 (JP, A) JP-A 57- 13246 (JP, A) JP-A-62-157254 (JP, A)

Claims (1)

[Claims] 1. First and second air-fuel ratio sensors for respectively detecting the concentrations of specific components in the exhaust gas on the upstream side and the downstream side of a catalytic converter for purifying the exhaust gas provided in the exhaust system of an internal combustion engine. , A control-related constant calculating means for calculating a constant involved in the air-fuel ratio feedback control according to the output of the second air-fuel ratio sensor, and an air-fuel ratio sensor normal for determining whether the first air-fuel ratio sensor is normal or abnormal / Abnormality determination means, the rich and lean cycles of the output of the second air-fuel ratio sensor, the response speed of the second air-fuel ratio sensor is about the same as the normal response speed of the first air-fuel ratio sensor. Status detecting means for indirectly or directly detecting whether or not the value is shorter than a predetermined value indicating that there is an output of the first air-fuel ratio sensor and the air-fuel ratio when the first air-fuel ratio sensor is normal. Involved in feedback control It is indirect that the first air-fuel ratio sensor is abnormal and the rich or lean cycle of the output of the second air-fuel ratio sensor is shorter than the predetermined value. The second when detected directly or directly
Air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount according to the output of the air-fuel ratio sensor and a constant involved in the air-fuel ratio feedback control, and adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio adjusting means.