JPH066920B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention provides an air-fuel ratio sensor (an oxygen concentration sensor (O ₂ sensor) in this specification) on the upstream side and the downstream side of a catalytic converter, and O ₂ 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 sensor.

[Conventional technology]

Generally, the basic injection amount of the fuel injection valve is calculated according to the intake air amount (or intake air pressure) and the rotation speed of the engine,
The basic injection amount is corrected according to an air-fuel ratio correction coefficient FAF calculated based on a detection signal of an O ₂ sensor that detects the concentration of a specific component such as an oxygen component in the exhaust gas of the engine,
The amount of fuel actually supplied is controlled according to the corrected injection amount. By repeating this control, the air-fuel ratio of the engine is finally converged within the predetermined range. By such air-fuel ratio feedback control, the air-fuel ratio can be controlled within a very narrow range near the stoichiometric air-fuel ratio, so the three-way catalytic converter provided in the exhaust system, that is, CO, H contained in the exhaust gas
The catalytic converter's purifying ability to purify three harmful components of C and NO _x at the same time can be kept high.

In the above-mentioned air-fuel ratio feedback control (single O ₂ sensor system), an O ₂ sensor for detecting 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 a collective portion of the exhaust manifold that is upstream from the catalytic converter. However, the variation in the output characteristics of the O ₂ sensor hinders the improvement of the air-fuel ratio control accuracy. The causes of variations in the output characteristics of the O ₂ sensor are listed below.

(1) Individual difference of the O ₂ sensor itself, (2) Non-uniform mixing of exhaust gas at the O ₂ sensor location due to tolerance of assembly position of parts such as fuel injection valve and exhaust gas recirculation valve to the engine, (3) Changes in the output characteristics of the O ₂ sensor over time or over time.

In addition to the O ₂ sensor, the non-uniformity of the exhaust gas mixture changes and expands due to changes in the engine state such as the fuel injection valve, the exhaust gas recirculation flow rate, the tappet clearance, and the like over time, and manufacturing variations. Sometimes.

A second O ₂ sensor is provided downstream of the catalytic converter in order to compensate for such variations in the output characteristics of the O ₂ sensor, variations in parts, and changes over time or over time, and the air-fuel ratio feedback control is performed by the upstream O ₂ sensor. In addition, a double O ₂ sensor system that performs air-fuel ratio feedback control using a downstream O ₂ sensor has already been proposed. In this double O ₂ sensor system, the O ₂ sensor provided on the downstream side of the catalytic converter has a lower response speed than the upstream O ₂ sensor, but the variation in the output characteristics is small for the following reasons. Have advantages.

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

(2) Since various poisons are trapped in the catalyst downstream of the catalytic converter, the poisoning amount 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, it directly affects the exhaust emission characteristic, whereas in the double O ₂ sensor system, the exhaust emission characteristic deteriorates even if the output characteristic of the upstream O ₂ sensor deteriorates. do not do. 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.

Generally, the temperature characteristic of the oxygen concentration battery type O ₂ sensor is the third
As shown in FIG. A, when the air-fuel ratio A / F is rich,
The output (rich signal) of the O ₂ sensor rises and stabilizes at a high level as the element temperature rises. On the other hand, when the air-fuel ratio A / F is lean, at a low level as the element temperature rises. Stabilize. Note that FIG. 3A shows the case where the outflow type is used as the O ₂ sensor signal processing circuit, and when the inflow type is used as the O ₂ sensor output processing circuit, it becomes as shown in FIG. 3B. In the inactive state, both the rich and lean signals are at high level. In any case, the O ₂ sensor becomes inactive or active depending on the element temperature, and the usable area is limited.
Generally, the range of 400 to 700 ° C. is considered suitable. In this active state, it is possible to discriminate between rich and lean by comparing the output voltage of the O ₂ sensor with a constant comparison voltage VR, for example, about 0.45V.

[Problems to be solved by the invention]

However, the downstream _{O 2} sensor described above, the upstream _{O 2}
Compared to the sensor, it is more likely to suffer mechanical damage due to flying stones, water, mud, etc. As a result of this mechanical damage, if an outflow type signal processing circuit is used, the output of the downstream O ₂ sensor will be lean. Therefore, the air-fuel ratio is controlled to be overrich, which leads to deterioration of fuel consumption, deterioration of exhaust emission, and the like. On the other hand, when a flow-in type signal processing circuit is used, the downstream O ₂ sensor Output may lean toward the rich side, so the air-fuel ratio is controlled to be lean,
There is a problem in that drivability is deteriorated and exhaust emission is deteriorated.

[Means for solving problems]

An object of the present invention is to provide a double air-fuel ratio sensor system capable of detecting output deterioration or mechanical damage of a downstream side air-fuel ratio sensor (O ₂ sensor), and its means is shown in FIGS. 1A to 1D. As shown in the figure.

1A and 1B show a double air-fuel ratio sensor system using an outflow type signal processing circuit. In FIG. 1A,
First and second air-fuel ratio sensors for detecting the concentrations of specific components in the exhaust gas are provided upstream and downstream of a catalytic converter provided in the exhaust system of the internal combustion engine for purifying the exhaust gas. . The first and second outflow type signal processing circuits process the outputs of the first and second air-fuel ratio sensors. Then, the air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the outputs V ₁ and V ₂ of the first and second outflow type signal processing circuits. The active rich signal determination means determines whether or not the output V ₁ of the first outflow type signal processing circuit is an active rich signal. As a result, the output V _{1 of} the first outflow type signal processing circuit
Is determined to be a rich signal when activated, the lean signal determination means determines whether or not the output V _{2 of} the second outflow type signal processing circuit is a lean signal. The lean signal frequency determination means determines whether the frequency at which the output V ₂ of the second outflow type signal processing circuit is a lean signal is equal to or higher than a predetermined value. As a result, when the frequency of the lean signal is equal to or higher than the predetermined value, the stop means stops the air-fuel ratio adjustment according to the output V ₂ of the second outflow type signal processing circuit in the air-fuel ratio adjusting means.

In FIG. 1B, the second active rich signal discriminating means and releasing means are added to FIG. 1A.
That is, the second active-time rich signal determination means determines whether or not the output V _{2 of} the second outflow-type signal processing circuit is the active-time rich signal, and as a result, the second outflow-type signal processing circuit. The release means releases the stop means when the output V _{2 of} is a rich signal when active.

1C and 1D show a double air-fuel ratio sensor system using a flow-in type signal processing circuit. Note that, in FIGS. 1C and 1D, similar to FIGS. 1A and 1B, the first and second
Air-fuel ratio sensor is provided.

In FIG. 1C, first and second inflow type signal processing circuits process the outputs of the first and second air-fuel ratio sensors. Then, the air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the outputs V ₁ and V ₂ of the _first and _second inflow type signal processing circuits. The active lean signal determination means determines whether or not the output V ₁ of the first flow-in type signal processing circuit is an active lean signal. As a result, the output V _{1 of} the first flow-in type signal processing circuit
Is determined to be a lean signal when activated, the rich signal determination means determines whether or not the output V _{2 of} the second flow-in type signal processing circuit is a rich signal. The rich signal frequency determination means determines whether or not the frequency at which the output V ₂ of the second flow-in type signal processing circuit is a rich signal is a predetermined value or more. As a result, when the frequency of the rich signal is equal to or higher than the predetermined value, the stopping means stops the air-fuel ratio adjustment according to the output V ₂ of the second flow-in type signal processing circuit in the air-fuel ratio adjusting means.

In FIG. 1D, second active lean signal discriminating means and releasing means are added to FIG. 1C.
That is, the second active lean signal determination means determines whether or not the output V _{2 of the second} inflow type signal processing circuit is the active lean signal, and as a result, the second inflow type signal processing circuit. The release means releases the stop means when the output V _{2 of} is a lean signal when active.

[Action]

According to the above means, for example, when the outflow type signal processing circuit is used, the output V _{1 of} the first outflow type signal processing circuit based on the output of the upstream side air-fuel ratio sensor is at a high level (that is, active). If the downstream side air-fuel ratio sensor is active during the time rich signal), the output V _{2 of} the second outflow type signal processing circuit is also expected to be at a high level (that is, the active rich signal). Utilizing this fact, the activity of the downstream air-fuel ratio sensor is determined. As a result, when it is determined that the downstream side air-fuel ratio sensor is inactive (failure), the air-fuel ratio adjustment based on the output of the downstream side air-fuel ratio sensor, that is, the air-fuel ratio feedback control is stopped. On the other hand, when the downstream side air-fuel ratio sensor is inactivated by water, the downstream side air-fuel ratio sensor returns to the activated state (non-fault state) when the water is dried. Therefore, the air-fuel ratio adjustment based on the downstream side air-fuel ratio sensor is stopped by determining whether or not the output V _{2 of} the second outflow type signal processing circuit has become the high level (that is, the active rich signal). Is canceled.

Similarly, when the flow-in type signal processing circuit is used, when the output V _{1 of} the first flow-in type signal processing circuit based on the output of the upstream side air-fuel ratio sensor is at a low level (that is, the lean signal during activation). If the downstream air-fuel ratio sensor is active,
The activity of the downstream side air-fuel ratio sensor is determined by utilizing the fact that the output V _{2 of} the second flow-in type signal processing circuit is also expected to be at the low level (that is, the lean signal during activation). As a result, when it is determined that the downstream side air-fuel ratio sensor is inactive (failure), the air-fuel ratio adjustment based on the output of the downstream side air-fuel ratio sensor, that is, the air-fuel ratio feedback control is stopped. On the other hand, the output V of the second outflow type signal processing circuit
The stop of the air-fuel ratio adjustment based on the downstream side air-fuel ratio sensor is released by determining whether ₂ has become the low level (that is, the lean signal when activated).

〔Example〕

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

FIG. 4 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. 4, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. The air flow meter 3 directly measures the intake air amount, 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 supplied to the A / D converter 101 with a built-in multiplexer in the control circuit 10. In Distributor 4,
For example, a crank angle sensor 5 whose axis generates a reference position detection pulse signal every 720 ° converted into a crank angle and a crank angle sensor which generates a reference position detection pulse signal converted every 30 ° into a crank angle 6 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, of which 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 TH of the cooling water.
An electric signal having an analog voltage corresponding to W is generated. This output is also supplied to the A / D converter 101.

An 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.

The exhaust manifold 11 includes the catalytic converter 1
A first O ₂ sensor 13 is provided on the upstream side of 2, 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 oxygen component concentration in the exhaust gas. That is, the O ₂ sensors 13 and 15 output different output voltages via the signal 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. 1
Occurs on 01.

The signal processing circuit 111 (112) is roughly divided into the outflow formation and the inflow form as described above. The spill formation has a grounded resistor R ₁ and a buffer OP, as shown in FIG. 5A, and thus the O ₂ sensor 13 (15).
Is in the inactive state, its output voltage disappears, and as a result, due to the sink current flowing through the resistor R ₁ , rich,
The input of the signal processing circuit 111 (112) takes a low level regardless of the lean state, and thus the output V ₁ (V ₂ ) becomes a low level. That is, as shown in FIG. 3A, if the presence of a high level signal (rich signal during activation) can be confirmed, the active state of the corresponding O ₂ sensor can be determined.

On the other hand, the flow-in type, as shown in FIG. 5B, has a resistor R ₂ and a buffer OP connected to the power source V _cc , so that if the O ₂ sensor 13 (15) is in the inactive state. , Its output voltage disappears, and as a result, the input of the signal processing circuit 111 (112) becomes high level regardless of the active or inactive state by the source current flowing from the power source V _cc to the resistor R ₂ , and therefore the output V ₁ (V ₂ ) becomes high level. That is, as shown in FIG. 3B, if the presence of a low level signal (lean signal when active) can be confirmed, the corresponding O ₂
The active state of the sensor can be determined.

In the following description, the outflow type is used as the signal processing circuit 111 (112).

Reference numeral 16 is an alarm, which is displayed when the downstream O ₂ sensor 15 is determined to be inactive (failed) according to the present invention.

The control circuit 10 is configured as a microcomputer, for example, and includes an A / D converter 101, an input / output interface.
102, CPU 103, signal processing circuits 111, 112, ROM 104, RA
An M 105, a backup RAM 106, a clock generation circuit 107, etc. are provided.

Further, in the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110 include the fuel injection valve 7
Is for controlling. That is, when the fuel injection amount TAU is calculated in the routine described later, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is also set. As a result,
The drive circuit 110 starts energizing the fuel injection valve 7. On the other hand,
When the down counter 108 counts a clock signal (not shown) and finally its carry-out terminal becomes "1" level, the flip-flop 109 is set and the drive circuit 110 activates the fuel injection valve 7. To stop. That is, the fuel injection valve 7 is biased by the above-mentioned fuel injection amount TAU, and accordingly, the amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

It should be noted that the interrupt generation of the CPU 103 is caused by the A / D converter 101 A / D
For example, when the D conversion is completed, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6, or when the interrupt signal from the clock generation circuit 107 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. Further, the rotation speed data Ne is calculated by interruption of the crank angle sensor 6 every 30 ° CA and is stored in a predetermined area of the RAM 105.

The operation of the control circuit shown in FIG. 4 will be described below.

FIG. 6 is a routine for determining a failure of the downstream O ₂ sensor 15, which is executed every predetermined time, for example, 4 ms.
The flag FSF and the counters T, K, L and M are cleared by an initial routine (not shown).

In step 601, whether or not the downstream O ₂ sensor 15 is currently in failure is determined by the flag FSF. In addition, FSF
= “0” indicates that the downstream O ₂ sensor 15 has no failure, and F
SF = “1” indicates that the downstream O ₂ sensor 15 is in failure.

Steps 602 to 615 are for detecting a failure of the downstream O ₂ sensor 15, and when the failure is detected, the flag FSF is set. On the other hand, steps 616 to 625 are for detecting the recovery of the failure of the downstream O ₂ sensor 15, and when the failure is detected, the flag FSF is reset.

The steps 602-615 will be described. In step 602, it is determined whether or not the counter T is less than the predetermined value T ₀ . As a result, when T <T _0, the counter T is incremented in step 603, and the upstream O ₂ is counted in step 604.
The output V _{1 of the} sensor 13 (to be precise, the output of the signal processing circuit 111, but hereinafter referred to as the output of the upstream O ₂ sensor 13) is A / D converted and taken in, and the average value thereof is calculated in step 605. (Smoothed value) Calculate with. Then, in step 606, the downstream O ₂
The output V _{2 of the} sensor 15 (to be precise, the output of the signal processing circuit 112, but hereinafter referred to as the output of the downstream O ₂ sensor 15) is A / D converted and taken in, and the average value thereof is calculated in step 607. (Smoothed value) ₂ Calculate with. Then, it proceeds to step 626.

When the counter T reaches T ₀ by repeating the routine of steps 603 to 607, the flow of step 602 is step 6
It flows to 08. As a result, the counter T is cleared in step 608, and it is determined in step 609 whether ₁ > ₁₀ . Here, ₁₀ is, for example, 0.45V. That is, in step 609, it is determined whether or not the output V ₁ of the upstream O ₂ sensor 13 is the active rich signal.
_{If 1} > ₁₀ , proceed to step 610.

At step 610, it is judged if ₂ < ₂₀ . Here, ₂₀ is, for example, 0.3V. That is, step 610 determines whether the output V ₂ of the downstream O ₂ sensor 15 is a lean signal. ₁ <
Only when it is _20, the process proceeds to step 611 and the counter K is incremented. The counter K indicates the frequency at which the output V ₂ of the downstream O ₂ sensor 15 is a lean signal.

It determines whether K> _{K 0} in step 612, when K> _{K 0,} Step regarded downstream _{O 2} sensor 15 is a failure
The flag FSF is set at 613 (FSF = "1"),
The counter K is cleared at step 614, then the alarm 16 is displayed at step 615, and the routine proceeds to step 626.

In this way, when the flag FSF is set, the flow in step 601 proceeds to step 616, and steps 616-6
25 will be executed.

In step 616, it is determined whether the counter L is less than the predetermined value L ₀ . As a result, when L <L ₀ , the step
At 617, the counter L is counted up, at step 618 the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and taken in, and at step 619 its average value (smoothed value) ₂ is obtained. Calculate with. The alarm 16 continues to be displayed in step 615, and the flow advances to step 626.

When the routine of steps 617 to 619,615 is repeated and the counter L reaches L ₀ , the flow of step 616 flows to step 620. As a result, the counter L is cleared in step 620, and it is determined in step 621 whether ₂ > ₂₀ . So step 621 is step
The output V _{2 of the} downstream O ₂ sensor 15 that is the opposite of 610
Is a rich signal when activated. ₂ > ₂₀
Only in this case, the process proceeds to step 622 and the counter M is incremented. The counter M is the downstream O ₂ sensor 15
Of the output V ₂ is a rich signal when active.

It is determined whether or not M> _{M 0} at step 623, M> when _{M 0,} and resets the flag FSF step 624 considers the recovery failure of the downstream _{O 2} sensor 15 (FSF
= “0”), clear the counter M in step 625,
Go to step 626.

In this way, when the flag FSF is reset, the flow in step 601 proceeds to step 602 and step 60
2 to 615 will be executed again.

As described above, when the average value of the output V ₁ of the upstream O ₂ sensor 13 is the active rich signal, the frequency K at which the average value of the output V ₂ of the downstream O ₂ sensor 15 is the lean signal.
When the frequency K exceeds a predetermined value K ₀ , it is considered that the downstream O ₂ sensor 15 has failed, and when it fails, the average value of the output V ₂ of the downstream O ₂ sensor 15 is calculated. Is counted as a rich signal when activated, and this frequency M
Is considered to have recovered from the failure of the downstream O ₂ sensor 15 when the value exceeds a predetermined value M ₀ .

If the signal processing circuit 111 (112) is of a flow type, step 609 may be ₁ < ₁₀ , step 610 may be ₂ > _20, and step 621 may be ₂ ≦ ₂₀ . In this case, when the average value of the output V ₁ of the upstream O ₂ sensor 13 is the active lean signal, the frequency K at which the average value of the output V ₂ of the downstream O ₂ sensor 15 is the rich signal is counted and regarded as the downstream O ₂ sensor 15 when the frequency K exceeds a predetermined value K ₀ has failed, further, in case of failure, the output V of the downstream O ₂ sensor 15
_The frequency M in which the average value of _{2 is} a lean signal when activated is counted,
When the frequency M exceeds the predetermined value M ₀ , it is considered that the failure of the downstream O ₂ sensor 15 has been recovered.

FIG. 7A is a modified example of steps 604 and 605 of FIG.
FIG. 7B is a modification of step 609 in FIG. That is, in step 701, V ₁ <V ₁₀ where V ₁₀ is the output of the upstream O ₂ sensor 13 at the time of the previous execution. If V ₁ <V ₁₀ (negative slope), step
At 702, it is determined whether or not the inclination flag F = “1” (positive inclination). If F = “1”, it means that the voltage V ₁ has changed from the positive slope to the negative slope. That is, the voltage V ₁
It means that the maximum value of is detected. Therefore, in this case, in step 703, the average value _r of the maximum values of the voltage V ₁ is
(Smoothed value) To update. In step 704, the inclination flag F is reset, and in step 706, V ₁₀ ← V ₁ to prepare for the next execution. On the other hand, in step 702, the inclination flag F =
If it is “0”, the voltage V ₁ has a negative slope, and therefore the process proceeds directly to step 706. Also, in step 701, V ₁
If ≧ V ₁₀ (positive inclination), the inclination flag F is set at step 705 and the routine proceeds to step 706.

On the other hand, in step 707 of FIG. 7B, _{r 2} > V _r0 , where V _r0 is a predetermined value and it is determined whether or not it is 0.7 V, for example.

As described above, using FIGS. 7A and 7B, when the average value of the maximum values of the output V ₁ of the upstream O ₂ sensor 13 is a predetermined value or more, the output of the downstream O ₂ sensor 15 V ₂
The frequency K that is an average value of the lean signals is counted, and when the frequency K exceeds a predetermined value K ₀ , it is considered that the downstream O ₂ sensor 15 has failed. ₂ Count the frequency M that the average value of the output V ₂ of the sensor 15 is the active rich signal, and consider that the failure of the downstream O ₂ sensor 15 is recovered when this frequency M exceeds a predetermined value M _0. become.

If the signal processing circuit 111 (112) is of a flow-in type, step 701 sets V ₁ > V ₁₀ and step 707 sets _r <V _ro ′, where V _ro ′ is 0.3 V, for example. There is. In this case, _r is the average value of the minimum values of the voltage V ₁ . Therefore, when the average value of the minimum values of the output V ₁ of the upstream O ₂ sensor 13 is less than or equal to a predetermined value, the frequency K at which the average value of the output V ₂ of the downstream O ₂ sensor 15 is a rich signal is counted. When the frequency K exceeds a predetermined value K ₀ , it is considered that the downstream O ₂ sensor 15 has failed, and when it fails, the average value of the output V ₂ of the downstream O ₂ sensor 15 is active. The frequency M which is a lean signal is counted, and when the frequency M exceeds a predetermined value M ₀ , it is considered that the failure of the downstream O ₂ sensor 15 has been recovered.

FIG. 8A is another modified example of steps 604 and 605 of FIG. 6, FIG. 8B is another modified example of step 609 of FIG. 6, and FIG. 9 is a timing diagram supplementarily explaining FIG. 8A. is there. Here, as shown in FIG. 9, the rich counter CR
Is a rich state (V ₁ > V _R1 : V _R1 is a comparison voltage, for example, 0.
45V), and the lean counter CL measures the duration of the lean state (V ₁ ≤V _R1 ). That is, in step 801, V ₁ ≦ V
_It is determined whether or not _{R1, and} if V ₁ > V _R1 (rich), it is determined at step 802 whether or not the lean counter CL = 0, and thereby whether or not it is the change point from lean to rich. If it is a change point from lean to rich (CL ≠
0), the lean duration CLE is set to CL in step 803, and the counter CL is cleared in step 804. Next, at step 805, the rich counter CR is incremented. On the other hand, if it is not the change point from lean to rich in step 802 (CL = 0), the process directly proceeds to step 805 and the rich counter CR is counted up.

On the other hand, if V ₁ ≦ V _R1 (lean) in step 801, then it is determined in step 806 whether or not the rich counter CR = 0, thereby determining whether or not the change point is from rich to lean. If it is a change point from rich to lean (CR ≠
0), the rich duration CRE is set to CR in step 807, and the counter CR is cleared in step 808. Next, at step 809, the lean counter CL is counted up. On the other hand, if it is not the change point from rich to lean at step 806 (CR = 0), the routine proceeds directly to step 809 to count up the lean counter CL.

In this way, the lean duration CLE and the rich duration CRE are constantly updated. Then step
At 810, rich duration CRE and lean duration CL
The sum TT of E and TT is calculated by TT ← CRE + CLE, then the duty ratio DRI is calculated by step 811 by DRI ← CRE / TT, and then the average value of the duty ratio DRI is calculated by step 812. Value) () Calculate with.

On the other hand, in step 813 of FIG. 8B, < ₀ , where ₀ is a constant value is determined.

As described above, using FIGS. 8A and 8B, when the average value of the duty ratios of the rich signals of the output V ₁ of the upstream O ₂ sensor 13 is equal to or less than a predetermined value, the downstream O ₂ sensor The frequency K at which the average value of the output V ₂ of 15 is a lean signal
When the frequency K exceeds a predetermined value K ₀ , it is considered that the downstream O ₂ sensor 15 has failed, and when it fails, the average value of the output V ₂ of the downstream O ₂ sensor 15 is calculated. Is counted as a rich signal when activated, and this frequency M
When the value exceeds a predetermined value M ₀ , it is considered that the failure of the downstream O ₂ sensor 15 has been recovered.

If the signal processing circuit 111 (112) is of a flow-in type, step 811 may be DRI ← CLE / TT. In this case, when the average value of the duty ratio of the lean signal of the output V ₁ of the upstream O ₂ sensor 13 is less than or equal to a predetermined value, the average value of the output V ₂ of the downstream O ₂ sensor 15 is a rich signal. Counting a certain frequency K, this frequency K
There regarded as downstream O ₂ sensor 15 when exceeding the predetermined value K ₀ has failed, further, in case of failure, the downstream O
₂ Count the frequency M that the average value of the output V ₂ of the sensor 15 is a lean signal at the time of activation, and consider that the failure of the downstream O ₂ sensor 15 is recovered when this frequency M exceeds a predetermined value M _0. become.

Incidentally, the determination of the recovery of the failure of the downstream _{O 2} sensor 15 in step 616 to 625 of FIG. 6, the downstream _{O 2} sensor 15
Can be performed by the output V ₂ of the above has passed the comparison voltage V _R1 by a predetermined number.

Air-fuel ratio feedback control is performed by the flag FSF set as described above.

The air-fuel ratio feedback control will be described below.

FIG. 10 shows a first air-fuel ratio feedback control routine for calculating the air-fuel ratio correction count FAF1 based on the output of the upstream O ₂ sensor 13, which is executed every predetermined time, for example, 4 ms.

In step 1001, 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,
The closed loop condition is not satisfied during the warm-up increase operation, the power increase operation, the lean control, the inactive state of the upstream O ₂ sensor 13, and the closed loop condition is satisfied in other cases. The determination of the active / inactive state of the upstream O ₂ sensor 13 is performed by reading the water temperature data THW from the RAM 105 and once determining whether THW ≧ 70 ° C. or by the output of the upstream O ₂ sensor 13. It is performed by determining whether or not the level once goes up or down. When the closed loop condition is not satisfied, the routine proceeds to step 1017, where the air-fuel ratio correction coefficient FAF1 is set to 1.0. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 1002.

In step 1002, the output V ₁ of the upstream O ₂ sensor 13 is A / D converted and taken in, and in step 1003, it is determined whether or not V ₁ is the comparison voltage V _R1, for example, 0.45 V or less. That is,
Determine whether the air-fuel ratio is rich or lean. Lean (V ₁ ≦
If it is V _R1 ), the first delay counter CDLY1 is decremented by 1 in step 1004, and the first delay counter CDLY1 is guarded by the minimum value TDR1 in steps 1005 and 1006. It should be noted that the minimum value TDR1 is a rich delay time for holding the determination that the output is the lean state even if the output of the upstream O ₂ sensor changes from lean to rich, and is defined by a negative value. . On the other hand, if rich (V ₁ > V _R1 ),
At step 1007, the first delay counter CDLY1 is incremented by 1, and at steps 1008 and 1009, the first delay counter CDLY1 is guarded with the maximum value TDL1. The maximum value TDL1
Is a lean delay time for holding the determination that the state is rich even if there is a change from rich to lean in the output of the upstream O ₂ sensor 13, and is defined by a positive value.

Here, the reference of the first delay counter CDLY1 is set to 0, the air-fuel ratio after delay processing is considered rich when CDLY1> 0, and the air-fuel ratio after delay processing is considered lean when CDLY1 ≦ 0. To do.

In step 1010, it is determined whether or not the sign of the first delay counter CDLY1 is inverted, that is, it is determined whether or not the air-fuel ratio after the delay process is inverted. If the air-fuel ratio is reversed, it is determined in step 1011 whether rich-to-lean reversal or lean-to-rich reversal is performed. If it is the reverse from rich to lean, in step 1012 FAF1 ← FA
F1 ＋ RS1 is increased in a skip manner, and conversely, if lean to rich, then in step 1013 FAF1 ← FAF1−
RS1 and skip. That is, skip processing is performed.

If the sign of the first delay counter CDLY1 is not inverted in step 1010, integration processing is performed in steps 1014, 1015 and 1016. That is, in step 1014, CDLY1 ≦
It is determined whether or not 0, and if CDLY1 ≦ 0 (lean), FAF1 ← FAF1 + KI1 is set in step 1015, while CDLY1> 0.
If it is (rich), in step 1016 FAF1 ← FAF1-KI1
And Here, the integration constant KI1 is set sufficiently smaller than the skip constant RS1, that is, KI1 << RS1. Therefore, step 1015 is in the lean state (CDLY1 ≦
0), the fuel injection amount is gradually increased, and step 1016 gradually reduces the fuel injection amount in the rich state (CDLY1> 0).

The air-fuel ratio correction coefficient FAF1 calculated in steps 1012, 1013, 1015, and 1016 is guarded at the minimum value, for example, 0.8 and the maximum value, for example, 1.2. When becomes too large or too small, the air-fuel ratio of the engine is controlled by that value to prevent overrich or over lean.

The FAF1 calculated as described above is stored in the RAM 105, and this routine ends at step 1018.

FIG. 11 is a timing diagram for supplementarily explaining the operation according to the flowchart of FIG. When the rich / lean air-fuel ratio signal A / F1 is obtained by the output of the upstream O ₂ sensor 13 as shown in FIG. 11 (A), the first delay counter CDLY1 is shown in FIG. 11 (B). As described above, the rich state is counted up, and the lean state is counted down. As a result, as shown in FIG. 11C, the delayed air-fuel ratio signal A / F1 'is formed. For example, the time after the air-fuel ratio signal A / F1 at time t ₁ is also changed from lean to rich, the air-fuel ratio signal A / F1 delayed processed 'is held lean only the rich delay time (-TDR1) It changes to rich at t ₂ . Time t ₃
Change change the air-fuel ratio signal A / F1 is from rich to lean, at time t ₄ after the air-fuel ratio signal A / F1 delayed processed 'is held in the rich only equivalent lean delay time TDL1 lean at To do. However, when the air-fuel ratio signal A / F1 is reversed in a shorter period of time than the rich delay time (-TDR1) as the time _{t 5, t 6, t 7} , the first delay counter CDLY
1 takes time to cross a reference value 0, the result, the air-fuel ratio signal A / F1 after the delay process at time t ₈ 'is reversed. That is, the air-fuel ratio signal A / F1 'after the delay processing is more stable than the air-fuel ratio signal A / F1 before the delay processing. In this way, the air-fuel ratio correction coefficient FAF1 shown in FIG. 11D is obtained based on the stable air-fuel ratio signal A / F1 '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, a system that introduces a second air-fuel ratio correction coefficient FAF2, delay times TDR1 and TDL1 as the first air-fuel ratio feedback control constants, and a skip amount RS1 (in this case, from lean to rich) To the rich skip amount RS1R and the lean skip amount RS1L from rich to lean are set separately, and the integration constant KI1 (also in this case, the rich integration constant
KI1R and lean integration constant KI1L are set separately), or the comparison voltage V _R1 of the output V ₁ of the upstream O ₂ sensor 13
There is a system that makes variable.

For example, rich delay time (-TDR1)> lean delay time (TD
If set to (L1), the control air-fuel ratio can shift to the rich side,
Conversely, lean delay time (TDL1)> rich delay time (-TDR
If set to 1), 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 TDR1 and TDL1 according to the output of the downstream O ₂ sensor 15. If the rich skip amount RS1R is increased, the control air-fuel ratio can be shifted to the rich side, and the lean skip amount can be increased.
Even if RS1L is reduced, the control air-fuel ratio can be shifted to the rich side,
On the other hand, if the lean skip amount RS1L is increased, the control air-fuel ratio can be shifted to the lean side, and the rich skip amount RS1R
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 RS1R and the lean skip amount RS1R according to the output of the downstream O ₂ sensor 15. Furthermore, if the rich integration constant KI1R is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean integration constant KI1L is decreased, the control air-fuel ratio can be shifted to the rich side, while the lean integration constant KI1L is increased. Then, 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 lean integration constant KI1R is reduced. Therefore, depending on the output of the downstream O ₂ sensor 15, the rich integration constant KI1R and the lean integration constant KI1R
The air-fuel ratio can be controlled by correcting KI1L. 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.

Second air-fuel ratio correction coefficient FA with reference to FIG. 12 to FIG.
A double O ₂ sensor system incorporating F2 will be described.

FIG. 12 shows a second air-fuel ratio feedback control routine for calculating the second air-fuel ratio correction coefficient FAF2 based on the output of the downstream O ₂ sensor 15, which is for a predetermined time, for example, 1 s.
It is executed every time. In step 1201, it is determined whether or not the flag FSF calculated as described above is "1". FSF
If “1”, the downstream O ₂ sensor 15 is regarded as a failure, and the process proceeds to step 1218. In Step 1202, the downstream side O
_It is determined whether or not the closed loop condition by the _two- sensor 15 is satisfied. This step is almost the same as step 1001 in FIG. If it is not a closed loop condition, proceed to step 1218 and FAF2
= 1.0, and when the closed loop condition is satisfied, the routine proceeds to step 1203.

In step 1203, the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and captured, and in step 1204, it is determined whether or not V ₂ is the comparison voltage V _R2, for example, 0.55 V or less, that is,
Determine whether the air-fuel ratio is rich or lean. The comparison voltage V _R2 is the comparison voltage V _R1 of the output of the upstream O ₂ sensor 13 in consideration of the difference in output characteristics due to the influence of raw gas and the deterioration speed on the upstream side and the downstream side of the catalytic converter 14. Set higher. If lean (V ₂ ≦ V _R2 ), the second delay counter CDLY 2 is determined in step 1205.
Is subtracted by 1, and in steps 1206 and 1207, the second delay counter CDLY2 is guarded by the minimum value TDR2. The minimum value
TDR2 is a rich delay time for maintaining a lean state even when there is a change from lean to rich, and is defined by a negative value. On the other hand, if rich (V ₂ > V _R2 ), the second delay counter CDLY2 is incremented by 1 in step 1208, and the second delay counter CD is added in steps 1209 and 1210.
Guard LY2 with maximum value TDL2. The maximum value TDL2 is a lean delay time for maintaining the rich state even when there is a change from rich to lean, and is defined by a positive value.

In this case as well, the reference of the second delay counter CDLY2 is set to 0, the air-fuel ratio after delay processing is considered rich when CDLY2> 0, and the air-fuel ratio after delay processing is considered lean when CDLY2 ≦ 0. To do.

In step 1211, it is determined whether or not the sign of the second delay counter CDLY2 is inverted, that is, it is determined whether or not the air-fuel ratio after the delay process is inverted. If the air-fuel ratio is reversed, it is determined in step 1212 whether the reversal from rich to lean or the reversal from lean to rich. If it is the reverse from rich to lean, in step 1213 FAF2 ← FA
F2 + RS2 is increased in a skip manner, and conversely, if lean-to-rich reversal, then in step 1214 FAF2 ← FAF2-
Reduce with RS2 in a skip manner. That is, skip processing is performed.

If the sign of the second delay counter CDLY2 is not inverted in step 1211, integration processing is performed in steps 1215, 1216 and 1217. That is, in step 1215, CDLY2 <
It is determined whether 0 or not. If CDLY <0 (lean), in step 1216, FAF2 ← FAF2 + KI2, and on the other hand, CDLY2> 0.
If it is (rich), in step 1217 FAF2 ← FAF2 ＋ KI2
And Here, the integration constant KI2 is set sufficiently smaller than the skip constant RS2, that is, KI2 <RS2. Therefore, step 1216 is in the lean state (CDLY2 ≦
0), the fuel injection amount is gradually increased, and step 1217 gradually decreases the fuel injection amount in the rich state (CDLY2> 0).

The air-fuel ratio correction coefficient FAF2 calculated in steps 1213, 1214, 1216, and 1217 is guarded at the minimum value, for example, 0.8 and the maximum value, for example, 1.2, so that the air-fuel ratio correction coefficient FAF2 becomes large for some reason. If it becomes too small or too small, the air-fuel ratio of the engine is controlled by that value to prevent overrich or over lean.

The FAF2 calculated as described above is stored in the RAM 105, and this routine ends at step 1219.

In this way, the second air-fuel ratio correction coefficient FAF2 is calculated based on the output of the downstream side O ₂ sensor 15 that has been subjected to the delay processing.

As described above, FA calculated during air-fuel ratio feedback
F1 and FAF2 can be once converted into other values FAF1 ′ and FAF2 ′ and stored in the backup RAM RAM 106, which is useful for improving drivability at the time of restart or the like.

FIG. 13 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, every 360 ° CA. In step 1301, the RAM 105 reads the intake air amount data Q and the rotation speed data Ne to calculate the basic injection amount TAUP. For example, TAUP ← KQ / Ne (K is a constant). Step 13
At 02, read the cooling water temperature data THW from RAM 105 and ROM
Warm-up increase value FWL based on the one-dimensional map stored in 104
Is calculated by interpolation. This warm-up increase amount FWL is set to decrease as the current cooling water temperature THW increases, as shown in the figure.

In step 1303, the final injection amount TAU is set to TAU ← TAUP ・ F
Calculate with AF1, FAF2, (FWL + α) + β. In addition,
α and β are correction amounts determined by other operating state parameters, and are correction amounts determined by, for example, a signal from a throttle position sensor (not shown), a signal from an intake air temperature sensor, a battery voltage, or the like.
It is stored in. Next, at step 1304, 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 1305, 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. 14 shows the first and second air-fuel ratio correction factors FAF1 and FAF2 obtained by the flowcharts of FIGS. 10 and 12.
FIG. 6 is a timing chart for explaining the above. When the output voltage V ₁ of the upstream O ₂ sensor 13 changes as shown in FIG. 14 (A), the comparison result in step 1003 in FIG.
It becomes like Fig. 4 (B). If the comparison result of FIG. 14 (B) is delayed, it becomes as shown in FIG. 14 (C). As a result, as shown in FIG. 14 (D), FAF1 skips only RS1 at the time of switching the delayed rich and lean.
On the other hand, when the output voltage V ₂ of the downstream O ₂ sensor 15 changes as shown in FIG. 14 (E), step 1204 in FIG.
The comparison result at is as shown in Fig. 14 (F).
When the delay processing is performed, it becomes as shown in FIG. When the second air-fuel ratio correction coefficient FAF2 is calculated based on the delayed comparison result of FIG. 14 (G), it becomes as shown in FIG. 14 (H).

Next, a double O ₂ sensor system in which the delay time as a constant involved in the air-fuel ratio feedback control is variable will be described with reference to FIGS. 15 and 16.

FIG. 15 is a second air-fuel ratio feedback control routine for calculating the delay times TDR1 and TDL1 based on the output of the downstream O ₂ sensor 15, which is executed every predetermined time, for example, every 1 s. In step 1501, it is determined whether or not the flag FSF "1" calculated as described above. FSF = "1"
If so, the downstream O ₂ sensor 15 is regarded as a failure and the process proceeds to steps 1524 and 1525. In step 1502, the first
Similar to step 1202 in FIG. 2, it is determined whether the closed loop condition of the air-fuel ratio is satisfied. If the closed loop condition is not satisfied, the process proceeds to step 1524. In steps 1524 and 1525, the rich delay time TDR1 and the lean delay time TDL1 are set to constant values. For example, TDR1 ← -12 (equivalent to 48 ms) TDL1 ← 6 (equivalent to 24 ms). Here, the reason to set the rich delay time (-TDR1) greater than the lean delay time TDL1, the comparison voltage V _R1
Is set to a low value such as 0.45 V on the lean side.

If FSF = "0" and the closed loop condition is satisfied, the process proceeds to step 1502.

Steps 1503 to 1510 correspond to steps 1203 to 1210 in FIG. In other words, rich / lean discrimination is a step
Although it is done in 1504, the result of this determination is step 1505 ~
Delayed at 1510. Then, the rich / lean discrimination that has been delayed is performed in step 1511.

In step 1511, the second delay counter CDLY2 is set to CDLY.
It is determined whether or not 2 ≦ 0. As a result, if CDLY2 ≦ 0, the air-fuel ratio is determined to be lean and the process proceeds to steps 1512 to 1517. On the other hand, if CDLY2> 0, the air-fuel ratio is determined to be rich. Proceed to steps 1518-1532.

In step 1512, TDR1 ← TDR1-1 is set, that is, the rich delay time (-TDR1) is increased, the change from rich to lean is further delayed, and the air-fuel ratio is shifted to the rich side. In steps 1513 and 1514, TDR1 is guarded by the minimum value T _R1 . Here, T _R1 is also a negative value, so
(-T _R1 ) means the maximum value rich delay time. Further, in step 1515, TDL1 ← TDL1-1 is set, that is, the lean delay time TDL1 is reduced, the delay of the change from lean to rich is reduced, and the air-fuel ratio is shifted to the rich side.
In steps 1516 and 1517, TDL1 is guarded with the minimum value T _L1 . Here, T _L1 is a positive value, so T _L1 means the minimum lean delay time.

In step 1518, TDR1 ← TDR1 + 1 is set, that is, the rich delay time (-TDR1) is reduced, the delay of the change from rich to lean is reduced, and the air-fuel ratio is shifted to the lean side. In step 1519 and 1520 the TDR1 is guarded by a maximum value T _R2. Here, T _{R2 is} also a negative value, so (−T
_R2 ) means the minimum rich delay time. Further, in step 1521, TDL1 ← TDL1 + 1 is set, that is, the lean delay time TDL1 is increased, the change from lean to rich is further delayed, and the air-fuel ratio is shifted to the lean side. Step 15
In 22 and 1523, TDL1 is guarded by the maximum value T _L1 . Here, T _L1 is a positive value, so T _L2 means the maximum lean delay time.

After the TDR1 and TDL1 calculated as described above are stored in the RAM 105, this routine ends at step 1526.

FAF1, TDR calculated during air-fuel ratio feedback
1, TDL1 can be temporarily converted into other values FAF1 ', TDR1', TDL1 'and stored in the backup RAM 10, which is useful for improving drivability at the time of restart.

FIG. 16 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, every 360 ° CA. In step 1601, the intake air amount data Q and the rotation speed data Ne are read from the RAM 105 to calculate the basic injection amount TAUP. For example
TAUP ← KQ / Ne (K is a constant). In step 1602, the cooling water temperature data THW is read from the RAM 105 and the RAM 104 is read.
The warm-up increase value FWL is interpolated by the one-dimensional map stored in.

In step 1603, the final injection amount TAU is calculated by TAU ← TAUPFAF1 (FWL + α) + β. Note that α and β are correction amounts that are determined by other operating state parameters.

Next, at step 1604, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. And step 1605
Then, this routine ends.

FIG. 17 is a timing chart of the delay times TDR1 and TDL1 obtained by the flow charts of FIGS.
As shown in FIG. 17 (A), when the output voltage V _{2 of the} downstream O ₂ sensor 15 changes, as shown in FIG. 17 (B), if the lean state (V ₂ ≦ V _R2 ), the delay time TDR1 ，
Both TDL1 are increased, while the delay times TDR1 and TDL1 are both decreased in the rich state. At this time, TDR1 is T _R1
Vary from through T _R2, TDL1 varies from T _L1 through T _L2.

If the flag FSF = "1" or the closed loop condition of the downstream O ₂ sensor 15 is not satisfied, TDR1 in FIG. 17 (B),
Control of TDL1 is stopped, eg TDR1 = -12 and TD
It is held at L1 = 6.

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. The main reason for the air-fuel ratio feedback control is the upstream O ₂ sensor with good responsiveness. This is because the control is performed by the downstream O ₂ sensor, which has poor responsiveness.

In addition, other constants related to the air-fuel ratio feedback control by the upstream O ₂ sensor, such as the skip amount, the integration constant,
The present invention can also be applied to a double O ₂ sensor system that corrects a comparison voltage of the upstream O ₂ sensor (see Japanese Patent Laid-Open No. 55-37562) by the output of the downstream O ₂ sensor.

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. However, depending on 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 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 steps 1301 and 1601 is determined by the carburetor itself, that is, determined according to the intake pipe negative pressure according to the intake air amount and the rotation speed of the engine, In steps 1303 and 1603, the supply air amount corresponding to the final fuel injection amount TAU is calculated.

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

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

〔The invention's effect〕

As described above, according to the present invention, it is possible to detect output deterioration or mechanical damage of the downstream side air-fuel ratio sensor.

[Brief description of drawings]

1A to 1D are overall block diagrams for explaining the configuration of the present invention, and FIG. 2 is a single O ₂ sensor system and a double O ₂ sensor system.
FIG. 3A and FIG. 3B are graphs showing output characteristics of a signal processing circuit of an O ₂ sensor, and FIG. 4 is an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. An overall schematic diagram showing an example, FIGS. 5A and 5B are circuit diagrams of the signal processing circuit of FIG. 4, FIG. 6, FIG. 7A, FIG. 7B, FIG. 8A, FIG. 8B, and FIG. 12, FIG. 13, FIG. 15, and FIG. 16 are flow charts for explaining the operation of the control circuit of FIG. 4, and FIG. 9 is a timing chart for supplementary explanation of the flow chart of FIG. 8A. FIG. 11 is a timing chart for supplementary explanation of the flowchart of FIG. 10, FIG. 14 is a timing chart for supplementary explanation of the flowchart of FIG. 10 and FIG. 12, and FIG. 17 is FIG. 10 and FIG. Supplement the flowchart of It is a timing diagram for a light. DESCRIPTION OF SYMBOLS 1 ... Engine main body, 3 ... Air flow meter, 4 ... Distributor, 5, 6 ... Crank angle sensor, 10 ... Control circuit, 12 ... Catalytic converter, 13 ... Upstream (first) O ₂ sensor, 15 ... Downstream ( Second) O ₂ sensor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshinari Nagai 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (56) References JP-A-59-96451 (JP, A) JP-A-52-77931 (JP, A)

Claims (24)

[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, first and second outflow type signal processing circuits for processing the outputs of the first and second air-fuel ratio sensors, and each of the first and second outflow type signal processing circuits Air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the output; active rich signal determining means for determining whether the output of the first outflow type signal processing circuit is an active rich signal; Lean signal discriminating means for discriminating whether or not the output of the second outflow type signal processing circuit is a lean signal when the output of the first outflow type signal processing circuit is determined to be an active rich signal; The output of the second outflow signal processing circuit is a lean signal Lean signal frequency determining means for determining whether or not a certain frequency is a predetermined value or more, and an output of the second outflow type signal processing circuit in the air-fuel ratio adjusting means when the frequency of the lean signal is a predetermined value or more. An air-fuel ratio control device for an internal combustion engine, comprising: stop means for stopping the corresponding air-fuel ratio adjustment. 2. The active rich signal determination means determines the active rich signal by determining that an average value of output signal levels of the first outflow type signal processing circuit is equal to or more than a predetermined value. The air-fuel ratio control device for an internal combustion engine according to claim 1. 3. The active rich signal when the active rich signal determining means determines that the average value of the output signal maximum value levels of the first outflow type signal processing circuit is not less than a predetermined value. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein 4. The activation-time rich signal determining means determines that the average value of the duty ratios of the rich signals of the output signals of the first outflow type signal processing circuits is less than or equal to a predetermined value. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the time rich signal is discriminated. 5. The lean signal determination means determines the lean signal by determining that the average value of the output signal levels of the second outflow type signal processing circuit is less than or equal to a predetermined value. The air-fuel ratio control device for an internal combustion engine according to item 1. 6. 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, first and second outflow type signal processing circuits for processing the outputs of the first and second air-fuel ratio sensors, and each of the first and second outflow type signal processing circuits Air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the output, and first active rich signal determining means for determining whether the output of the first outflow type signal processing circuit is an active rich signal. And a lean signal discriminating means for discriminating whether or not the output of the second outflow type signal processing circuit is a lean signal when the output of the first outflow type signal processing circuit is determined to be a rich signal when activated. And the output of the second outflow signal processing circuit is A lean signal frequency determining means for determining whether the frequency of the signal is a predetermined value or more, and a lean signal frequency determining means of the second outflow type signal processing circuit in the air-fuel ratio adjusting means when the frequency of the lean signal is a predetermined value or more. Stop means for stopping the air-fuel ratio adjustment according to the output; second active rich signal determination means for determining whether or not the output of the second outflow type signal processing circuit is an active rich signal; 2. An air-fuel ratio control device for an internal combustion engine, comprising: a release means for releasing the stop means when the output of the outflow type signal processing circuit 2 is a rich signal when activated. 7. The first active rich signal discriminating means comprises:
7. The internal combustion engine according to claim 6, wherein the active rich signal is determined by determining that the average value of the output signal levels of the first outflow type signal processing circuit is equal to or greater than a predetermined value. Air-fuel ratio control device. 8. The first active rich signal discriminating means comprises:
7. The active rich signal is discriminated by discriminating that the average value of the output signal maximum value levels of the first outflow type signal processing circuit is not less than a predetermined value.
Item 3. An air-fuel ratio control device for an internal combustion engine according to item. 9. The first active-time rich signal discriminating means,
The active rich signal is determined by determining that the average value of the duty ratios of the rich signals of the output signals of the first outflow type signal processing circuit is less than or equal to a predetermined value. An air-fuel ratio control device for an internal combustion engine as described. 10. The lean signal discrimination means discriminates the lean signal by discriminating that the average value of the output signal levels of the second outflow type signal processing circuit is not more than a predetermined value. An air-fuel ratio control device for an internal combustion engine according to the sixth aspect. 11. The active-time rich signal determining means determines that the average value of the output signal levels of the second outflow-type signal processing circuit is equal to or more than a predetermined value, thereby determining the active-time period. The air-fuel ratio control device for an internal combustion engine according to claim 6, which determines a rich signal. 12. The active rich signal is determined by the second active rich signal determining means by determining that the output signal level of the second outflow type signal processing circuit has passed a predetermined comparison voltage a predetermined number of times. The air-fuel ratio control device for an internal combustion engine according to claim 6, which determines a signal. 13. 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, first and second flow-in type signal processing circuits for processing outputs of the first and second air-fuel ratio sensors, and each of the first and second flow-in type signal processing circuits Air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the output; active lean signal determining means for determining whether the output of the first flow-in type signal processing circuit is an active lean signal; Rich signal discriminating means for discriminating whether or not the output of the second pouring type signal processing circuit is a rich signal when the output of the first pouring type signal processing circuit is discriminated to be a lean signal when active; The output of the second inflow signal processing circuit is rich Rich signal frequency determining means for determining whether the frequency is equal to or higher than a predetermined value, and the output of the second flow-in type signal processing circuit in the air-fuel ratio adjusting means when the frequency of the rich signal is equal to or higher than a predetermined value. An air-fuel ratio control device for an internal combustion engine, comprising: stop means for stopping the adjustment of the air-fuel ratio according to. 14. The active lean signal determining means determines the active lean signal by determining that an average value of output signal levels of the first flow-in type signal processing circuit is equal to or less than a predetermined value. The air-fuel ratio control device for an internal combustion engine according to claim 13. 15. The active lean signal is determined by the active lean signal determining means determining that the average value of the output signal minimum value levels of the first flow-in type signal processing circuit is not more than a predetermined value. The air-fuel ratio control device for an internal combustion engine according to claim 13, wherein 16. The active lean signal determining means determines that the average value of the duty ratios of the lean signals of the output signals of the first flow-in type signal processing circuits is equal to or less than a predetermined value. The air-fuel ratio control device for an internal combustion engine according to claim 13, which determines an hourly lean signal. 17. The rich signal discriminating means discriminates the rich signal by discriminating that the average value of the output signal levels of the second flow-in type signal processing circuit is not less than a predetermined value. The air-fuel ratio control device for an internal combustion engine according to Item 13. 18. 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, first and second flow-in type signal processing circuits for processing outputs of the first and second air-fuel ratio sensors, and each of the first and second flow-in type signal processing circuits Air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the output, and first active lean signal determining means for determining whether or not the output of the first flow-in type signal processing circuit is an active lean signal. And a rich signal discriminating means for discriminating whether or not the output of the second pouring type signal processing circuit is a rich signal when the output of the first pouring type signal processing circuit is discriminated as a lean signal when active. And the output of the second flow-in type signal processing circuit is A rich signal frequency determining means for determining whether or not the frequency of the H signal is a predetermined value or more, and the second flow-in type signal processing circuit in the air-fuel ratio adjusting means when the frequency of the rich signal is a predetermined value or more. Stop means for stopping the adjustment of the air-fuel ratio according to the output of the second active-time lean signal determination means for determining whether or not the output of the second flow-in type signal processing circuit is the active lean signal. An air-fuel ratio control apparatus for an internal combustion engine, comprising: a release means for releasing the stop means when the output of the second flow-in type signal processing circuit is a lean signal when activated. 19. The active lean signal is determined by the first active lean signal determining means by determining that the average value of the output signal levels of the first flow-in type signal processing circuit is not more than a predetermined value. Claim 18 for determining a signal
Item 3. An air-fuel ratio control device for an internal combustion engine according to item. 20. The active lean signal discriminating means discriminates that the average value of the output signal minimum value levels of the first flow-in type signal processing circuit is equal to or less than a predetermined value. The air-fuel ratio control device for an internal combustion engine according to claim 18, wherein the lean signal is discriminated. 21. The first active lean signal determining means determines that the average value of the duty ratios of the lean signals of the output signals of the first flow-in type signal processing circuits is not more than a predetermined value. 19. The air-fuel ratio control device for an internal combustion engine according to claim 18, wherein the lean signal during activation is determined by: 22. The rich signal discrimination means discriminates the rich signal by discriminating that the average value of the output signal levels of the second flow-in type signal processing circuit is not less than a predetermined value. Item 18. An air-fuel ratio control device for an internal combustion engine according to item 18. 23. The active lean signal is determined by the second active lean signal determining means by determining that the average value of the output signal levels of the second flow-in type signal processing circuit is not more than a predetermined value. Claim 18 for determining a signal
Item 3. An air-fuel ratio control device for an internal combustion engine according to item. 24. The active lean signal determination means determines that the output signal level of the second flow-in type signal processing circuit has passed a predetermined comparison voltage a predetermined number of times, and thereby the active lean signal is detected. The air-fuel ratio control device for an internal combustion engine according to claim 18, which determines a signal.