JPH0726578B2 - 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 that performs air-fuel ratio feedback control by a downstream O ₂ sensor in addition to air-fuel ratio feedback control (see JP-A-58-58).
48756 publication). In this double O ₂ sensor system, the O ₂ sensor provided downstream of the catalytic converter is
Although it has a low response speed as compared with the O ₂ sensor, it has an advantage that 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]

The catalyst of the catalytic converter is designed so that its function is not significantly deteriorated as long as the vehicle is used within the range of conditions normally considered. However, if the user mistakenly uses leaded gasoline as fuel, or if the high tension cord is pulled out and misfires during use, the function of the catalyst may be significantly reduced. In the former case, the user does not notice at all, and in the latter case, since the high tension cord may be reinserted, the catalyst is rarely replaced. As a result, the catalytic converter may run without sufficiently purifying the exhaust gas.

However, in the above-mentioned double O ₂ sensor system, when the function of the catalyst deteriorates, as described above, HC, CO, H ₂
Due to the influence of unburned gas, the output reversal cycle of the downstream O ₂ sensor becomes short. Therefore, it is possible to determine that the three-way catalyst is deteriorated because the reversal period is shortened (reference: Japanese Patent Application No. 60-127121). However, this reversal cycle becomes shorter as the amount of intake air increases, that is, as the time it takes for the burned gas to reach the downstream O ₂ sensor is shortened, and therefore the catalyst deteriorates immediately because the reversal cycle becomes shorter. If you judge that, you will make a wrong judgment. That is, in order to determine whether or not the catalyst has deteriorated based on the inversion cycle, the inversion cycle must be detected in a predetermined specific operating state, and the deterioration of the catalyst must be determined based on this inversion cycle. It will have to be done.

[Means for solving problems]

According to the present invention, a first method for accurately determining deterioration of a catalyst is provided.
As shown in the configuration diagram of the invention of the figure, it is provided on each of the upstream side and the downstream side of a catalytic converter for purifying exhaust gas provided in the exhaust system of an internal combustion engine, and detects the concentration of a specific component in the exhaust gas. The first and second air-fuel ratio sensors, and the second
Air-fuel ratio control amount calculation means for calculating an air-fuel ratio control amount according to the output of the air-fuel ratio sensor, and air-fuel ratio adjustment for adjusting the air-fuel ratio of the engine according to the output of the first air-fuel ratio sensor and the air-fuel ratio control amount. Means, an operating area determination means for determining whether or not the operating area of the engine is within a predetermined specific operating area, and a second air-fuel ratio when the operating area of the engine is within the specific operating area. It is provided with a detecting means for detecting the inversion cycle of the output of the sensor, and a catalyst deterioration judging means for judging that the catalyst of the catalytic converter has deteriorated when the inversion cycle becomes shorter than a predetermined cycle.

[Work]

Whether or not the catalyst has deteriorated is determined from the inversion cycle of the output of the second air-fuel ratio sensor when the operating region of the engine is within the specific operating region.

〔Example〕

 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, and has a built-in potentiometer to generate an output signal of an analog voltage 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 includes a crank angle sensor 5 whose axis generates a reference position detecting pulse signal every 720 ° converted into a crank angle, and a reference position detecting pulse signal every 30 ° converted into a crank angle. A crank angle sensor 6 for generating is provided. The pulse signals of the crank angle sensors 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 vapor.

Further, the walk 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 NOx 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 is an A / D converter 101 that outputs different output voltage by the control circuit 10 depending on whether the air-fuel ratio is lean or rich with respect to the theoretical air-fuel ratio.
Occurs in.

Reference numeral 16 is an alarm that is activated when the catalyst of the catalytic converter 12 deteriorates.

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
A ROM 104, a RAM 105, a backup RAM 106, a clock generation circuit 107, and the like are provided outside the PU 103.

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 of the air flow meter 3 and the cooling water temperature data THW 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. Further, the rotation speed data Ne is calculated by the interrupt of the crank angle sensor 6 every 30 ° CA and is calculated by the RAM1.
It is stored in the predetermined area of 05.

FIG. 4 is 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 401, 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. For example, when the cooling water temperature is equal to or lower than a predetermined value, during engine start, during starting increase, during warm-up increase, during power increase, when the output signal of the upstream O ₂ sensor 13 has never been reversed,
The closed loop condition is not satisfied during the fuel cut, and the closed loop condition is satisfied in other cases. When the closed loop condition is not satisfied, the routine proceeds to step 427, where the air-fuel ratio correction coefficient FAF is set to 1.0. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 402.

In step 402, the output V ₁ of the upstream O ₂ sensor 13 is A / D converted and captured, and in step 403 V ₁ is the comparison voltage V _R1
It is determined whether 0.45V or less, that is, whether the air-fuel ratio is rich or lean. If the air-fuel ratio is lean (V ₁ ≤V _R1 ), the first delay counter CDLY1 is determined in step 404.
Is determined to be positive. If CDLY1> 0, CDLY1 is set to 0 in step 405, and the routine proceeds to step 406. Step 407, 40
At 8, the first delay counter CDLY1 is guarded by the minimum value TDL1, and in this case, when the first delay counter CDLY1 reaches the minimum value TDL1, the first air-fuel ratio flag F1 is set to “0” (at step 609). Lean). The minimum value TD
L1 is a lean delay time for holding the determination that the output of the upstream O ₂ sensor 13 is in the rich state even if there is a change from rich to lean, and is defined by a negative value. On the other hand, if rich (V ₁ > V _R1 ), it is determined in step 410 whether the first delay counter CDLY1 is negative, and C
If DLY1 <0, CDLY1 is set to 0 in step 411, and the process proceeds to step 412. In steps 413 and 414, the first delay counter CDLY1 is guarded with the maximum value TDR1. In this case, when the first delay counter CDLY1 reaches the maximum value TDR1, the first air-fuel ratio flag F1 is set to "1" in step 415.
(Rich) The maximum value TDRY1 is the rich delay time for holding the determination that the output is upstream from the upstream O ₂ sensor 13 is in the lean state even if there is a change from lean to rich, and is defined as a positive value. It

In step 416, it is determined whether or not the sign of the first 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,
At step 417, according to the value of the first air-fuel ratio flag F1,
Determine whether the reversal from rich to lean or from lean to rich. If it is a reversal from rich to lean,
In step 418, FAF ← FAF + RSR is increased in a skip manner, and conversely, in the case of reversal from lean to rich, in step 419, FAF ← FAF−RSL is reduced in a skip manner. That is, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 412, integration processing is performed in steps 420, 421 and 422. That is, in step 420, it is determined whether or not F1 = "0". If F1 = "0" (lean), in step 421 FAF ←
If FAF + KIR, on the other hand, if F1 = "1" (rich), then in step 422 FAF ← FAF-KIL. Where the integration constant KI
R (KIL) is set sufficiently smaller than the skip constants RSR and RSL, that is, KIR (KIL) <RSR (RSL).
Therefore, step 421 gradually increases the fuel injection amount in the lean state (F1 = "0"), and step 422 increases the rich state (F1).
1 = "1") to gradually reduce the fuel injection amount.

The air-fuel ratio correction coefficient FAF calculated at steps 418, 419, 421, 422 is guarded at the minimum value, for example 0.8, at steps 423, 424, and at the maximum value, for example, at steps 425, 426.
Guarded at 1.2. Thus, when the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled by that value to prevent overrich or over lean.

The FAF calculated as described above is stored in the RAM 105, and in step 428, this routine ends.

FIG. 5 is a timing diagram for supplementarily explaining the operation according to the flowchart of FIG. When the rich-lean air-fuel ratio signal A / F is obtained as shown in FIG. 5 (A) from the output of the upstream O ₂ sensor 13, the first delay counter CDLY1
Is counted up in the rich state and counted down in the lean state as shown in FIG. 5 (B). As a result, as shown in FIG. 5 (C), the delayed air-fuel ratio signal A / F '(corresponding to the flag F1) 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 1 ′ is held lean for the rich delay time TDRY 1 and then at time t ₂ . Change to rich. 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
F ′ changes to lean at time t ₄ after being held rich for a lean delay time (−TDL1). However, the air-fuel ratio signal A / F is the time t _5, t _6, t ₇ rich delay time as the TDR1
When inverted in a shorter period, the first delay counter CD
It takes time for LY1 to reach the maximum value TDR1, 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 air-fuel ratio correction coefficient FAF shown in FIG. 5 (D) 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 O ₂ sensor 15 will be described. As the second air-fuel ratio feedback control, skip amounts RSR, RSL as the first air-fuel ratio feedback control constants, integration constants KIR, KIL delay time
There is a system in which the comparison voltage V _R1 of TDR1, TDL1 or the output V ₁ of the upstream O ₂ sensor 13 is variable.

For example, if the rich skip amount RSR is increased, the control air-fuel ratio can be shifted to the rich side, and the lean skip amount
Even if RSL is reduced, the control air-fuel ratio can be shifted to the rich side,
On the other hand, if the lean skip amount RSL is increased, the control air-fuel ratio can be shifted to the lean side, and the rich skip amount RSR
The control air-fuel ratio can be shifted to the lean side even if is decreased. 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. Also, 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. If rich delay time TDR1> lean delay time (-TDL1) is set, the control air-fuel ratio can shift to the rich side, and conversely, if lean delay time (-TDL1)> rich delay time (TDR1) is set, control can be performed. The air-fuel ratio can shift to the lean side.

That is, the delay time TDR depends on the output of the downstream O ₂ sensor 15.
1, the air-fuel ratio can be controlled by correcting TDL1. Furthermore, if the comparison voltage V _R1 is increased, the control air-fuel ratio can be shifted to the rich side, and if the comparison voltage V _R1 is decreased, the control air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the comparison voltage V _R1 according to the output of the downstream O ₂ sensor 15.

Each of these skip amount, integration constant, delay time, and comparison voltage can be made variable by the downstream O ₂ sensor. For example, the delay time allows very delicate adjustment of the air-fuel ratio, and the skip amount enables control with good response without lengthening the feedback cycle of the air-fuel ratio like the delay time. Therefore, these variable amounts can naturally be used in combination of two or more.

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 FIG.

FIG. 6 is 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, and is executed every predetermined time, for example, every 1 s. In step 601, it is determined whether or not the closed loop condition by the downstream O ₂ sensor 15 is satisfied. For example, the closed loop condition is not satisfied when the cooling water temperature is equal to or lower than a predetermined value, the transient operation is performed, the air-fuel ratio feedback control condition is not satisfied by the upstream O ₂ sensor 13, and the closed loop condition is satisfied in other cases. If it is not a closed loop condition, the process proceeds to steps 830 and 831 to set the skip amounts RSR and RSL to a value stored in the RAM 105 or a fixed value such as 5%, or the backup RAM 106.
The value stored in.

If the closed loop condition is satisfied in step 601, the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and taken in in step 602, and in step 603 V ₂ is compared voltage V _R2, for example 0.55.
It is determined whether it is V or less, that is, whether the air-fuel ratio is rich or lean. It should be noted that the comparison voltage V _R2 is set on the upstream side in consideration of the difference in the output specification due to the influence of raw gas and the deterioration speed on the upstream and downstream sides of the catalytic converter 12.
It is set higher than the comparison voltage V _R1 of the output of the O ₂ sensor 13.

Steps 604-615 are similar to steps 404-415 of FIG.
This is for delaying the air-fuel ratio determination result. That is, the second air-fuel ratio flag F2 is set based on the rich delay time TDR2 and the lean delay time TDL2.

In step 617, the air-fuel ratio after the delay processing is determined by the second air-fuel ratio flag F2. As a result, F2 = "0" (lean)
If so, the process proceeds to steps 618 to 623, while if F2 = "1" (rich), the process proceeds to steps 624 to 629.

At step 618, RSR ← RSR + ΔRS (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 619,620
Guard SR with maximum value MAX, for example 6.2%. further,
In step 621, RSL ← RSL−ΔRS is set, that is, the lean skip amount RSL is decreased to shift the air-fuel ratio to the rich side. In steps 622 and 623, RSL is set to the minimum value MIN, for example
Guard at 2.5%.

On the other hand, when F2 = "1" (rich), RSR ← RSR−ΔRS is set in step 624, that is, the rich skip amount RSR
Is reduced to shift the air-fuel ratio to the lean side. Step
In 625 and 626, RSR is guarded by the minimum value MIN. Further, in step 627, RSL ← RSL + ΔRS, that is, the lean skip amount RSL is increased to shift the air-fuel ratio to the lean side. In steps 628 and 629, RSL is guarded with the maximum value MAX.

After the RSR and RSL calculated as described above are stored in the RAM 105, this routine ends at step 632.

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 also helps improve drivability at the time of restarting. The minimum value MIN in FIG. 6 is a value at which transient followability is not impaired, and the maximum value MAX is a value at which drivability does not deteriorate due to air-fuel ratio fluctuations.

As described above, according to the routine of FIG. 6, 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. 7 shows a catalyst deterioration determination routine, which is executed every predetermined time, for example, every 4 ms. In step 701, the rotation speed data Ne is read from the RAM 105 and N ₁ ≤Ne ≤N ₂ For example, 1000 rpm
It is determined whether or not the range is ≦ Ne ≦ 3000 rpm, and in step 702, the intake air amount data Q is read from the RAM 105 and Q ₁ ≦ Q ≦
Q ₂ For example, it is determined whether or not the range is 0.5 / rev ≦ Q / Ne ≦ 1.0 / rev. That is, only the steady state excluding the idle state, the acceleration / deceleration state, the fuel increase region, etc., is advanced to step 703. Otherwise, proceed directly to step 713.

In step 703, the timer counter CT is incremented by 1,
Predetermined time CT ₀ × 4ms depending on whether CT ≤ CT _{0 in} step 704
It is determined whether or not it has passed.

1000 rpm ≤ Ne ≤ 3000 rpm and 0.5 / rev ≤ Q / Ne ≤ 1.0 / rev
If the state of is maintained before the predetermined time has elapsed (CT ≤ CT ₀ ),
Proceeding to steps 705 and 706, the number of inversions of the output V ₂ of the downstream O ₂ sensor 15 is counted by the number counter CS. That is,
In step 705, it is determined whether or not the second air-fuel ratio flag F2 is reversed, and the number-of-times counter CS is incremented by 1 every time the second air-fuel ratio flag F2 is reversed.

Next, 1000 rpm ≤ Ne ≤ 3000 rpm and 0.5 / rev ≤ Q / Ne ≤ 1.0
When the state of / rev has passed the predetermined time (CT> CT ₀ ), the flow of step 704 proceeds to step 707. As a result, in step 707, the inversion count CS of the downstream O ₂ sensor 15 is set to a predetermined value CS _0.
It is determined whether or not the above. If CS <CS ₀ , it is determined that there is no catalyst deterioration, the alarm is stopped (or canceled) in step 708, and the alarm flag F is determined in step 709.
_{Set ALM} to “0”. On the other hand, if CS ≧ CS ₀ , it is determined that the catalyst has deteriorated, the alarm 16 is activated in step 710, and
In step 711, the alarm flag F _{ALM is set} to "1". Then, in step 712, the counters CT and CS are both cleared and the process proceeds to step 713. The alarm flag F _ALM is stored in the backup RAM 106. Therefore, the catalyst deterioration can be known by reading the alarm flag F _ALM with a special reading device, and the catalyst can be replaced accordingly.

The predetermined value CS ₀ of step 707 may be variable according to the operating condition parameter, for example, the load.

That is, normally, the output V ₁ of the upstream O ₂ sensor 13 has a high response speed (frequency) as shown in FIG. 8 (A), but the output V ₂ of the downstream O ₂ sensor 15 is shown in FIG. 8 (B). ) Has a low response speed, but as the catalyst of the catalytic converter 12 deteriorates, the O ₂ storage effect decreases and the downstream O ₂
The response speed of the output V ₂ of the sensor 15 increases, and the response speed increases as the intake air amount Q increases. According to the routine of FIG. 7, the deterioration of the catalyst is detected by detecting such a high response speed of the downstream O ₂ sensor 15.

FIG. 9 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, every 360 ° C. 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 ← α
Q / Ne (α 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 final injection amount TAU is calculated by TAU ← TAUP · FAF · (FWL + β) + γ. The correction amount is determined by other operating state parameters such as β and γ. Next, at step 904, the injection amount TAU is set in the down counter 108 and the flip-flop 1
Set 09 to start fuel injection. Then, in step 905, 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.

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.
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, a constant involved in other control in the air-fuel ratio feedback control by the upstream O ₂ sensor, for example, an integration constant,
Delay time, the downstream O ₂ the comparison voltage V _RI, etc. of the upstream O ₂ sensor
The present invention can be applied to a double O ₂ sensor system that corrects by the output of the sensor and also to a double O ₂ sensor system that introduces a second air-fuel ratio correction coefficient. In addition, controllability can be improved by simultaneously controlling two of the skip amount, the integration constant, and the delay time. In addition, the skip amount RSR,
One of the RSLs can be fixed and only the other can be made variable, or one of the integration constants KIR, KIL can be fixed and only the other can be made variable, or one of the delay times TDR1, TDL1 can be fixed and the other It is also possible to make variable.

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 speed. 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 particularly 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 engine speed, and step 903 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, the deterioration of the catalyst can be detected more reliably.

[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. 4, FIG. 6, FIG. 7, FIG. 9, and FIG. 9 are flowcharts for explaining the operation of the control circuit shown in FIG. 3, and FIG. FIG. 8 is a timing chart for supplementary explanation of the flowchart of FIG. 4, and FIG. 8 is a timing chart for supplementary explanation of the flowchart of FIG. 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.

Claims (3)

[Claims] 1. A first and a second detector, which are respectively provided on the upstream side and the downstream side of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine, for detecting a concentration of a specific component in the exhaust gas. An air-fuel ratio sensor, an air-fuel ratio control amount calculating means for calculating an air-fuel ratio control amount according to the output of the second air-fuel ratio sensor, and an output of the first air-fuel ratio sensor and the air-fuel ratio control amount Air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine, operating area determining means for determining whether the operating area of the engine is within a predetermined specific operating area, and the operating area of the engine is the specific area Detecting means for detecting a reversal cycle of the output of the second air-fuel ratio sensor when the reversal cycle is shorter than a predetermined cycle, and the catalyst of the catalytic converter deteriorates. Deteriorated catalyst Air-fuel ratio control system for an internal combustion engine and a cross section. 2. The catalyst deterioration determination means for detecting the number of times the output of the second air-fuel ratio sensor has been inverted per predetermined time when the operating region of the engine is within the specific operating region. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the means determines that the catalyst has deteriorated when the number of times of inversion exceeds a predetermined number. 3. An operating area determining means for determining whether or not the rotational speed of the engine is within a predetermined range, and a means for determining whether or not the load of the engine is within a predetermined range. Claims, wherein the operating range of the engine is determined to be within the specific operating range when the rotational speed of the engine is within a predetermined range and the load of the engine is within a predetermined range. An air-fuel ratio control device for an internal combustion engine according to item 1.