JPH08303280A - O2 sensor control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To prevent the occurrence of an error to control an engine owing to the generation of hydrogen at the initial stage of the use of a three- dimensional catalyst. CONSTITUTION: A control circuit 10 is provided to effect feedback control of an engine air-fuel ratio to a theoretical air-fuel ratio based on outputs from an O2 sensor 15 situated downstream from a catalyst 12 and an O2 sensor 13 situated upper stream therefrom. The control circuit 10 calculates a time in which an engine is run in a high exhaust gas temperature state after the starting of the use of a catalyst, and air-fuel ratio feedback control based on the output of the downstream O2 sensor is prohibited until the integrated time attains a given value. Since, at the initial stage of the use of a catalyst, hydrogen is generated at a catalyst during a high exhaust gas temperature state, an influence is exercised on the output characteristics of the downstream O2 sensor but since, during the generation of hydrogen, control by the output of the downstream O2 sensor is prohibited, no adverse influence is exercised on control of an engine air-fuel ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an O ₂ sensor control device for an internal combustion engine.

[0002]

_2. Description of the Related Art Conventionally, an exhaust gas manifold of an internal combustion engine is provided with an O ₂ sensor, and the air-fuel ratio of the engine is feedback-controlled to a target air-fuel ratio based on the output of the O ₂ sensor to exhaust the exhaust gas on the downstream side of the O ₂ sensor. There is known a technique for maintaining a high purification capacity of an exhaust purification catalyst provided in a passage.

Also, the O ₂ placed in the exhaust manifold
An O ₂ sensor (downstream O ₂ sensor) is further provided in the exhaust passage on the downstream side of the exhaust purification catalyst in order to compensate for variations over time in output characteristics of the sensor (upstream O ₂ sensor) and individual differences.
Is provided to correct the air-fuel ratio control based on the upstream O ₂ sensor output based on the downstream O ₂ sensor output.
_{A two-} sensor system is also commonly used (JP-A-61)
-286550).

Since the upstream O ₂ sensor is arranged close to the engine, the exhaust gas from each cylinder is not always uniformly mixed in the upstream O ₂ sensor portion. Further, the exhaust gas temperature is high in the upstream O ₂ sensor portion, and the O ₂ sensor itself is likely to deteriorate. Therefore, when the upstream O ₂ sensor is strongly affected by the exhaust gas from a specific cylinder or the O ₂ sensor is deteriorated, the air-fuel ratio feedback control is performed based on the upstream O ₂ sensor output. Therefore, accurate air-fuel ratio control may not be possible. On the other hand, at the position of the downstream O ₂ sensor, the exhaust gas is uniformly mixed when passing through the catalyst and the exhaust gas temperature is low. Therefore, in the double O ₂ sensor system, the air-fuel ratio feedback control based on the upstream O ₂ sensor output, by correcting on the basis of the downstream O ₂ sensor output, changes in the characteristics of the upstream O ₂ sensor is produced In this case, it is possible to perform accurate air-fuel ratio control.

Further, in the above double O ₂ sensor system, there is known a catalyst deterioration detecting device for judging the presence or absence of deterioration of the exhaust purification catalyst based on the fluctuation of the downstream O ₂ sensor output during the air-fuel ratio feedback control. (JP-A-5-
See Japanese Patent No. 263686). Normally, a three-way catalyst used as an exhaust purification catalyst adsorbs oxygen in the exhaust when the incoming exhaust air-fuel ratio becomes leaner than the theoretical air-fuel ratio, and the incoming exhaust air-fuel ratio becomes richer than the theoretical air-fuel ratio. performing an O ₂ storage operation which releases oxygen adsorbed when it becomes. Therefore, even if the exhaust air-fuel ratio flowing into the catalyst fluctuates between the lean side and the rich side, the air-fuel ratio fluctuation of the exhaust gas after passing through the catalyst decreases due to the absorption and release of oxygen due to the O ₂ storage action, and the downstream side Fluctuations in the O ₂ sensor output are reduced.

However, when the catalyst deteriorates, the O ₂ storage function of the catalyst decreases, and the amount of oxygen adsorbed on the catalyst decreases, so that the air-fuel ratio of the exhaust gas that has passed through the catalyst changes as in the upstream exhaust gas. Become. Japanese Patent Laid-Open No. 5-26368
In the device of Japanese Patent Laid-Open No. 6, the period in which the output of the downstream O ₂ sensor is reversed from rich to lean and lean to rich is measured during the air-fuel ratio feedback control, and it is determined from this period whether or not the catalyst has deteriorated. ing. That is, when the catalyst is normal and a sufficient O ₂ storage action is obtained, even if the exhaust air-fuel ratio on the upstream side of the catalyst fluctuates, the fluctuation of the exhaust air-fuel ratio after passing through the catalyst is reduced and _{2 The} sensor output inversion cycle becomes longer.

On the other hand, when the catalyst deteriorates and the O ₂ storage action decreases, the exhaust air-fuel ratio after passing through the catalyst also fluctuates like the exhaust air-fuel ratio on the upstream side of the catalyst.
₂ The inversion cycle between the rich side and the lean side of the sensor output becomes longer as the catalyst deterioration progresses. The above-mentioned JP-A-5-26
In the device disclosed in Japanese Patent No. 3686, the inversion cycle of the downstream O ₂ sensor output during the air-fuel ratio feedback control is calculated, and it is determined that the catalyst has deteriorated when the inversion cycle of the downstream O ₂ sensor output becomes larger than a predetermined value. I am trying to do it.

[0008]

However, in a system that controls based on the output of the O ₂ sensor arranged in the exhaust passage on the downstream side of the catalyst, such as the above-mentioned double O ₂ sensor system, a new three-way catalyst is used. Problems may occur at the start of use. The three-way catalyst is a catalyst for HC in exhaust gas,
Oxidation of CO and reduction of NO _x are carried out simultaneously to purify these harmful components at the same time. The catalytic activity for promoting the above-mentioned oxidation and reduction is high when the catalyst is new, and gradually decreases as the use time of the catalyst becomes longer. Therefore, since the catalytic activity is extremely strong at the start of use of a new three-way catalyst, a reduction reaction of water gas H ₂ O + CO → H ₂ + CO ₂ occurs at a relatively high exhaust temperature. H ₂ may be generated in the catalyst. Thus, the H ₂ the catalyst occurs is limited to a period of time immediately after the start of using the exhaust gas temperature is high and catalyst, the exhaust gas reaching the downstream O ₂ sensor when the H ₂ is generated at the catalyst Since the H ₂ component exists in the above, there arises a problem that the output characteristics of the downstream O ₂ sensor are affected.

The O ₂ sensor has a structure in which platinum electrodes are arranged on both sides of a solid electrolyte such as zirconium, exhaust gas is brought into contact with one electrode side of this solid electrolyte, and atmospheric air is brought into contact with the other electrode side. . When the temperature of the solid electrolyte exceeds a predetermined temperature, oxygen in the atmosphere is ionized at the electrodes on the atmosphere side due to the difference in concentration of oxygen components between the atmosphere and the exhaust gas, and the solid electrolyte moves to the exhaust side. A current according to the concentration difference from the exhaust gas flows from the exhaust side electrode to the atmosphere side electrode, and a voltage corresponding to the oxygen concentration difference is generated between the electrodes. The O ₂ sensor detects the oxygen concentration in the exhaust gas by taking out the voltage as a signal.

However, when the exhaust gas has a certain concentration or more,
H₂If a component is present, the oxygen component in the exhaust gas is H₂To the ingredients
It is further blocked and it becomes difficult to reach the exhaust side electrode. others
H₂If the component is present, O₂The sensor output is the actual acid
An oxygen concentration signal lower than the elementary concentration is output. You
Nachi, O₂The sensor output signal on the rich air-fuel ratio side
Issue, O₂Overall sensor output characteristics
Is shifted to the lean air-fuel ratio side. (downstream
Side O₂The air-fuel ratio that the sensor recognizes as the theoretical air-fuel ratio is theoretical
The state is shifted to the lean side from the air-fuel ratio. ) Therefore, in the catalyst H₂When the ingredients come to life,
Downstream O₂The exhaust air-fuel ratio reaching the sensor is the theoretical air-fuel ratio
Even if it was O₂Rich air-fuel ratio from sensor
Since a signal is output, for example, double O₂Sensor system
On the downstream side O ₂The air-fuel ratio is lean based on the sensor output
Side, the stoichiometric air-fuel ratio cannot be maintained,
Deterioration of engine drivability and deterioration of exhaust emission
There's a problem.

Further, in such a state, the exhaust air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio.
The amount of oxygen adsorbed on the catalyst has reached the saturation amount, oxygen absorption and release by O ₂ storage action no longer occurs, and the exhaust air-fuel ratio on the downstream side of the catalyst is the same as the exhaust air-fuel ratio on the upstream side compared to the theoretical air-fuel ratio. The lean side will repeat the fluctuation. On the other hand, the output characteristic of the downstream O ₂ sensor is shifted to the lean side, and the value of a certain air-fuel ratio on the lean side of the stoichiometric air-fuel ratio is recognized as the stoichiometric air-fuel ratio, so the actual exhaust air-fuel ratio changes this air-fuel ratio to this lean air-fuel ratio. The output signal of the downstream O ₂ sensor is inverted every time it passes and goes up and down.

Therefore, when the downstream O ₂ sensor output characteristic shifts to the lean side due to the H ₂ component generated in the catalyst, the engine air-fuel ratio as a whole shifts to the lean air-fuel ratio side, and the air-fuel ratio of the exhaust gas flowing into the catalyst increases. In fact, no inversion occurs between lean and rich, so that the O ₂ storage action does not occur, and the air-fuel ratio on the downstream side of the catalyst also repeats the same variation as on the upstream side within the lean air-fuel ratio range. Further, as a result, the output of the downstream O ₂ sensor is inverted at the same cycle as the output of the upstream O ₂ sensor, so the inversion cycle becomes short and it is determined that the catalyst has deteriorated immediately after the start of use. Occurs.

[0013] The above has been described the control of the double O ₂ sensor system and catalyst deterioration detection, thus the deviation of the output characteristic of the downstream O ₂ sensor is produced, other control based on the downstream O ₂ sensor output If it is, the control will be hindered in the same manner. In view of the above problems, it is an object of the present invention to provide an O ₂ sensor control device capable of solving various problems that occur when the downstream O ₂ sensor output is adversely affected by the H ₂ component generated in the catalyst. .

[0014]

According to the invention as set forth in claim 1, an exhaust purification catalyst arranged in an exhaust passage of an internal combustion engine, and an exhaust purification catalyst arranged in a downstream exhaust passage of the exhaust purification catalyst,
Downstream O that outputs a signal according to the oxygen component concentration in the exhaust gas
₂ sensors, H ₂ detecting means for detecting the hydrogen component concentration in the exhaust gas on the downstream side of the exhaust purification, and H ₂ detecting means when a hydrogen component of a predetermined value or more is detected in the exhaust gas. There is provided an O ₂ sensor control device for an internal combustion engine, comprising: a prohibiting unit that prohibits control performed based on the output of the downstream O ₂ sensor.

According to the second aspect of the present invention, the control performed based on the output of the downstream O ₂ sensor is the downstream O 2.
The O ₂ sensor control device according to claim 1, which is air-fuel ratio control for performing feedback control of the engine air-fuel ratio to the target air-fuel ratio based on the output of the _two sensors. According to the invention described in claim 3, in the O ₂ sensor control device according to claim 1, the O ₂ sensor control device is further arranged in the exhaust passage upstream of the exhaust purification catalyst, and outputs a signal according to the concentration of oxygen component in the exhaust. The upstream O ₂ sensor, the output of the downstream O ₂ sensor and the upstream O _2
2. An air-fuel ratio control means for feedback-controlling an engine air-fuel ratio to a target air-fuel ratio based on _two sensor outputs.
An O ₂ sensor controller as described in 1. is provided.

According to the fourth aspect of the invention, the control performed based on the output of the downstream O ₂ sensor is the downstream O 2.
_2. The O ₂ sensor control device according to claim 1, wherein the catalyst deterioration detection control is for detecting whether or not the exhaust purification catalyst is deteriorated based on a change in the output of the ₂ sensor.

[0017]

In the O ₂ sensor control device according to the first aspect of the present invention, the H ₂ detection means causes the H _{2 having} a concentration of a predetermined value or more in the exhaust gas on the downstream side of the catalyst.
_{When the} presence of the _two components is detected, the prohibiting means prohibits the control based on the output of the downstream O ₂ sensor. As a result, the control based on the wrong downstream oxygen concentration is not executed, so that the problem due to the wrong control does not occur.

In the O ₂ sensor control device according to the _{second aspect} , the air-fuel ratio feedback control of the engine based on the output of the downstream O ₂ sensor is prohibited by the prohibiting means. Therefore, deterioration of drivability and exhaust emission due to lean engine air-fuel ratio do not occur. In the O ₂ sensor control device according to the third aspect, correction of the upstream O ₂ sensor output based on the downstream O ₂ sensor output in the double O ₂ sensor system is prohibited by the prohibiting means. Therefore, deterioration of drivability and exhaust emission due to lean engine air-fuel ratio do not occur.

In the O ₂ sensor control apparatus according to the present invention, the catalyst deterioration detection control based on the downstream O ₂ sensor output is prohibited by the prohibiting means. Therefore, erroneous determination due to catalyst deterioration does not occur.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing an overall schematic configuration of an embodiment when the present invention is applied to an internal combustion engine for automobiles. FIG.
In the figure, 1 is an internal combustion engine body, 2a is an intake manifold connected to an intake port of each cylinder of the engine 1, and 11 is an exhaust manifold connected to an exhaust port of each cylinder.

The intake manifold 2a is connected to the intake passage 2 via a common surge tank 2b. Reference numeral 3 in FIG. 1 is an air flow meter for detecting the intake air amount of the engine 1. As the air flow meter 3, for example, a movable vane type with a built-in potentiometer is used, and generates a voltage signal proportional to the amount of intake air. The intake passage 2 is provided with a throttle valve 16 that opens according to the operation amount of the accelerator pedal by the driver.
An idle switch 17 is provided near 6 to generate an idle state signal (LL signal) when the throttle valve 16 is fully closed.

Reference numeral 7 in FIG. 1 indicates an intake manifold 2a.
Is a fuel injection valve disposed near the intake port of each cylinder. The fuel injection valve 7 is opened in response to a signal from the control circuit 10 to inject pressurized fuel into each intake port of each cylinder.
The fuel injection control from the fuel injection valve 7 will be described later.
The exhaust manifold 11 is connected to the catalytic converter 12 via a common exhaust pipe. The catalytic converter 12 has a built-in three-way catalyst and can simultaneously purify three components of HC, CO, and NO _x in the exhaust gas. Also, the catalytic converter 1
2, an upstream air-fuel ratio sensor 13 is provided in the exhaust manifold of the exhaust manifold 11, and a downstream air-fuel ratio sensor 15 is provided in the downstream exhaust pipe 14 of the catalytic converter 12. In this embodiment, the air-fuel ratio sensors 13, 1
An O ₂ sensor for generating a voltage signal according to the concentration of oxygen components in the exhaust is used as 5. Figure 2 shows the O ₂ sensor 1
It is a figure which shows the output characteristic of 3 and 15. As shown by the solid line in FIG. 2, the normal O ₂ sensor output changes abruptly at the stoichiometric air-fuel ratio, and different output voltages are generated on the rich air-fuel ratio side and the lean air-fuel ratio side. Therefore, the O ₂ sensor 1
From the outputs of 3 and 15, it can be determined whether the current air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio.

Reference numeral 18 in FIG. 1 denotes a secondary air introduction valve for introducing secondary air into the exhaust system. The secondary air introduction valve 18 is opened during engine deceleration, idle operation, etc. to introduce secondary air into the exhaust manifold 11 to reduce HC and CO emissions. Further, the ignition distributor 4 of the engine 1 is provided with two crank angle sensors 5 and 6 which generate a pulse signal each time the engine crankshaft rotates at a constant speed. In the present embodiment, the crank angle sensor 5 outputs a reference position detection pulse signal, for example, every time a specific cylinder reaches the compression top dead center (that is, every 720 ° of crank rotation angle), and the crank angle sensor 6 outputs, for example, the crank. A pulse signal for crank rotation angle detection is output for each rotation angle of 30 °.

The water jacket 8 of the cylinder block of the engine 1 is provided with a cooling water temperature sensor 9 which outputs an analog voltage according to the engine cooling water temperature. The control circuit 10 includes, for example, an input / output interface 102,
A microcomputer having a known structure in which a CPU 103, a ROM 104, and a RAM 105 are mutually connected by a bidirectional bus, and further includes a multiplexer built-in AD converter 10.
1. Backup RA that can be stored directly even if the engine ignition switch is off by being directly connected to the power supply
An M106, a clock generation circuit 107, etc. are provided.

The control circuit 10 performs basic control such as fuel injection control and ignition timing control of the engine, and in the present embodiment, the upstream O ₂ sensor 13 and the downstream O ₂ sensor 1 as will be described later.
The air-fuel ratio feedback control based on the output of No. 5 and the control at the time of detecting H ₂ generation at the start of use of the catalyst are performed.
In order to execute these controls, the control circuit 10 sends the engine intake air amount signal from the air flow meter 3, the cooling water temperature signal from the cooling water temperature sensor 9, and the O ₂ sensors 13 and 15 via the AD converter 101. In addition to the respective air-fuel ratio signals of 1, the pulse signals from the crank rotation angle sensors 5 and 6 and the idle signal from the idle switch 17 are input through the input / output interface 102.

The engine intake air amount signal and the cooling water temperature signal are taken in by an AD conversion routine executed at every constant crank rotation angle, and the engine intake air amount data Q and the cooling water temperature data are respectively stored in predetermined areas of the RAM 105. TH
Stored as W. Every time the pulse signal of the crank rotation angle sensor 6 is input, the engine rotation speed is calculated from the pulse interval by a routine (not shown).
The engine speed data Ne is stored in a predetermined area 05.

On the other hand, the control circuit 10 is connected to the fuel injection valve 7 via the input / output interface 102 and controls the fuel injection from the fuel injection valve 7. 1 in FIG.
Denoted at 09 and 110 are a down counter, a flip-flop, and a drive circuit for controlling the fuel injection amount from the fuel injection valve 7, respectively. That is, when the fuel injection amount (time) TAU is calculated in the routine described later, the fuel injection time TAU is preset in the down counter 108, the flip-flop 109 is set, and the drive circuit 110 causes the drive signal of the fuel injection valve 7 to be set. Is output. As a result, the fuel injection valve 7 is opened and fuel injection is started. The down counter 108 counts the clock signal of the clock 107 and outputs a set signal to the flip-flop 109 when the preset time TAU elapses. As a result, the flip-flop 109 is set, so that the drive circuit 110 stops the drive signal of the fuel injection valve 7, and the fuel injection valve 7 is closed. Therefore, the fuel injection valve 7 is opened for the time corresponding to the calculated fuel injection time TAU, and the fuel of the amount corresponding to TAU is injected from the fuel injection valve 7 to the engine 1.

Further, the control circuit 10 has an input / output interface.
The above-described secondary air introduction valve 18 and the
It is connected to Ram 19. In this embodiment, the upstream side O
₂Feedback control of air-fuel ratio based on sensor 13 output
Controlled and downstream O₂Based on the output of the sensor 15
Upstream O₂Correct the deviation of the output characteristics of the sensor 13
While performing control, during air-fuel ratio feedback control
Downstream of O₂Rich and lean output of sensor 15 output
The presence or absence of deterioration of the catalyst 12 is detected based on the inversion cycle between
It is controlled to output. As will be described later, catalyst 1
2 H in the catalyst after the start of use₂When the ingredients occur,
Downstream O ₂Because the output characteristics of the sensor 15 change
Side O₂Air-fuel ratio control that uses sensor 15 output
Will receive.

Therefore, before describing the control when H _{2 is} generated in the catalyst, the air-fuel ratio control of this embodiment will be briefly described first. FIG. 3 is a flowchart showing a fuel injection amount calculation routine of this embodiment. This routine is executed by the control circuit 10
Is executed every fixed crank rotation angle (for example, every 360 °). In the routine of FIG. 3, the fuel injection amount, that is, the fuel injection time TAU of the fuel injection valve 7, the intake air amount Q / Ne per engine revolution, and the air-fuel ratio correction coefficient F described later.
It is calculated based on AF and.

That is, in the routine of FIG. 3, the intake air amount data Q and the rotation speed data Ne are read from a predetermined area of the RAM 105, and the intake air amount Q / N per engine revolution is read.
In addition to calculating e (step 301), the basic fuel injection time TAUP is calculated as TAUP = α × Q / Ne (step 302). Here, the basic fuel injection time TAUP is a fuel injection time required to make the air-fuel mixture supplied to the combustion chamber have a stoichiometric air-fuel ratio, and α
Is a constant.

The actual fuel injection time TAU is calculated as TAU = TAUP × FAF × β + γ, which is a value obtained by correcting the above TAUP with the air-fuel ratio correction coefficient FAF (step 303). Where β, γ
Are constants determined according to the engine operating state. Further, when the fuel injection time TAU is calculated as described above, the time TAU is reduced by the down counter 10 in step 304.
8 is set, and the amount of fuel corresponding to the time TAU is injected from the fuel injection valve 7.

Next, in step 303, the air-fuel ratio correction coefficient F
The calculation of AF will be described. The air-fuel ratio correction coefficient FAF is the first air-fuel ratio feedback control based on the output of the upstream O ₂ sensor 13 and the _second air-fuel ratio correction control based on the output of the downstream O ₂ sensor 15.
Of the air-fuel ratio feedback control. 4 and 5 are flowcharts showing the first air-fuel ratio feedback control based on the output of the upstream O ₂ sensor 13.
This routine is executed by the control circuit 10 at regular time intervals (for example, every 4 ms).

In this routine, the output VOM of the upstream O ₂ sensor 13 is compared with the comparison voltage V _R1 (the theoretical air-fuel ratio equivalent voltage), and the exhaust air-fuel ratio on the downstream side of the catalytic converter is richer than the theoretical air-fuel ratio (VOM> When V _R1 ), the air-fuel ratio correction amount FAF is decreased, and when lean (VOM ≦ V _R1 ), FAF is increased. The O ₂ sensor outputs a voltage signal of, for example, 0.9 V when the exhaust air-fuel ratio is richer than the theoretical air-fuel ratio, and outputs a voltage signal of, for example, about 0.1 V when the exhaust air-fuel ratio is leaner than the theoretical air-fuel ratio. Output voltage signal. In this embodiment, the comparison voltage V _R1 is 0.45.
It is set to about bolts. As described above, the air-fuel ratio correction amount F
By increasing / decreasing AF according to the exhaust air-fuel ratio, the engine air-fuel ratio can be accurately brought close to the stoichiometric air-fuel ratio even if there are some errors in the devices of the fuel supply system such as the air flow meter 3 and the fuel injection valve 7. Will be fixed.

The flow charts of FIGS. 4 and 5 will be briefly described below. Step 401 shows whether or not the feedback control execution condition is satisfied. The feedback control execution conditions are, for example, that the O ₂ sensor is activated, that the engine warming up is completed, that a predetermined time has elapsed after returning from the fuel cut, and that the secondary air introduction valve 18 has two The FAF calculation in and after step 402 is performed only when the execution condition is satisfied because the next air is not introduced. If the feedback control execution condition is not satisfied, the routine proceeds to step 425 in FIG. 5, sets the value of the flag XMFB to 0, and ends the routine. The flag XMFB is a flag indicating whether or not the first air-fuel ratio feedback control is being executed,
XMFB = 0 means that the first air-fuel ratio feedback control is stopped.

Steps 402 to 415 show the determination of the air-fuel ratio. Flag F1 shown in steps 409 and 415
Indicates that the engine air-fuel ratio is rich (F1 = 1) or lean (F1 =
0) is an air-fuel ratio flag indicating that F1 = 0 to F1 =
When switching from 1 (lean to rich), the upstream O ₂ sensor 13 continues for a predetermined time (TDR) or longer and the rich signal (V
OM > V _R1 ) is output (steps 403, 4)
10 to 415), and switching from F1 = 1 to F1 = 0 (rich to lean) is continued by the upstream O ₂ sensor 13 for a predetermined time (−TDL) or longer and the lean signal (VOM). ≤
This is performed when V _R1 ) is output (steps 403 to 409). CDLY is a counter for determining the air-fuel ratio flag switching timing.

In steps 416 to 423 in FIG. 5, the FAF is increased or decreased according to the value of the flag F1 set as described above. That is, the value of F1 at the time of executing this routine is compared with the value of F1 at the time of executing the previous routine, and it is determined whether the value of F1 has changed, that is, whether the air-fuel ratio has reversed from rich to lean or lean to rich. Yes (Step 4
16). The current value of F1 is F1 = 0 (lean)
In the case of, first, a relatively large value RSR is obtained immediately after changing (reversing) from F1 = 1 to F1 = 0 (rich to lean).
Increase FAF in a skip manner (step 417,
418), and thereafter, while F1 = 0, the FAF is gradually increased by a relatively small value KIR each time the routine is executed (steps 420 and 421). Similarly, when the current value of F1 is F1 = 1 (rich), first, F1 = 0 to F
Immediately after reversing from 1 to 1 (from lean to rich), the FAF is decreased by RSL (steps 417 and 419), and thereafter, while F1 = 1, the FAF is gradually decreased by KIL for each routine execution (step 420). 422).
Further, the value of FAF calculated as described above is the maximum value (FAF = 1.2 in this embodiment) and the minimum value (FAF in this embodiment).
= 0.8) so as not to exceed the range defined by (step 423), the value of the flag XMFB is set to 1 (step 424), and this routine ends.

Next, the second air-fuel ratio feedback control based on the output of the downstream O ₂ sensor 15 will be described. 6 and 7 show a second air-fuel ratio feedback control routine. In this routine, the control circuit 10 causes the control circuit 10 to perform a predetermined interval longer than the first air-fuel ratio feedback control (for example, 5).
Every 00 ms). In this routine, the downstream side O
₂ The output VOS of the sensor 15 is compared with the comparison voltage V _R2 (theoretical air-fuel ratio equivalent voltage, for example, 0.45 V), and the exhaust air-fuel ratio on the downstream side of the catalytic converter is richer than the theoretical air-fuel ratio (VOS > V _R2 ), the correction amount RSR used in the first air-fuel ratio feedback control (step 418 in FIG. 5)
And RSL (step 419 in FIG. 5) are increased. Further, it performs an operation of reducing the RSL with increasing correction amount RSR is when the exhaust gas air-fuel ratio of the catalytic converter downstream leaner than the stoichiometric air-fuel ratio (VOS ≦ V _R2). As a result, when the exhaust air-fuel ratio is rich on the downstream side of the catalytic converter, the FAF value is generally set to be small in the first air-fuel ratio feedback control, and conversely, the exhaust air-fuel ratio on the downstream side is set to be small. FA in case of rich
The value of F is generally set to be large. Therefore, even if the output of the upstream O ₂ sensor 13 deviates from the actual exhaust air-fuel ratio due to the deterioration of the upstream O ₂ sensor 13 or the strong influence of the exhaust gas of a specific cylinder, the value of FAF is set to the downstream. Since it is corrected based on the output of the side O ₂ sensor 15, the engine air-fuel ratio is accurately maintained at the stoichiometric air-fuel ratio.

Below, the flowcharts of FIGS. 6 and 7 are simplified.
6 steps 600, 601, 602
Judgment of whether or not the feedback control execution condition is satisfied
Shows the fixed value. In step 600, H₂
Flag XH indicating the occurrence or non-occurrence ₂Determines whether the value of is 0
It Flag XH₂The value of the
H at 12₂H is generated when₂Has occurred
Set to 0 when not in use. Hula in step 600
Gu XH₂= 1, that is, H in the catalyst 12₂Is occurring
If it is determined that the downstream O₂Based on sensor 15 output
The second air-fuel ratio feedback control is not executed and the step
Go to step 603 and set the value of the flag XFB to 0
The routine ends as it is. Flag XSFB is the second air-fuel
This is a flag that indicates whether or not ratio feedback control is being executed.
Therefore, when XSFB = 0, the second air-fuel ratio feedback control is
It means that it has been stopped. As a result, the catalyst 12
And H₂Is occurring downstream O₂Sensor 15 out
The force-based second air-fuel ratio feedback control is stopped.
It

Further, the judgment condition of step 601 is as shown in FIG.
It is similar to that of step 401. Further, in step 602, it is determined whether or not the first air-fuel ratio feedback control is being executed, and the control is being executed (flag XMFB).
= 1) only, the control from step 604 onward is executed. When the control is not executed (XMFB ≠
1) In step 603, the value of the flag XSFB is set to 0, and the routine ends.

If the first air-fuel ratio feedback control is being executed in step 602, the value of the flag XSFB is set to 1 in step 604, and then the exhaust air-fuel ratio detected by the downstream O ₂ sensor 15 is An operation of increasing or decreasing the values of the correction amounts RSR and RSL is performed depending on whether or not it is rich. That is, in step 605 of FIG. 7, the output VOS of the downstream O ₂ sensor 15 is AD-converted and read, and in step 606 it is determined whether or not VOS is the lean air-fuel ratio equivalent value (VOS ≦ V _R2 ), and the value of VOS is If it is the lean air-fuel ratio equivalent value, the RSR value is increased by a constant amount ΔRS in step 607, and the increased RSR does not exceed a predetermined maximum value MAX (MAX = 0.09 in this embodiment). (Steps 608 and 609). Further, when the VOS value is the rich air-fuel ratio equivalent value (VOS> V _R2 ) in step 606, the RSR value is changed by a constant amount Δ in step 610.
Only the RS is reduced, and the reduced RSR is a predetermined minimum value MI.
Guarding is performed so as not to become smaller than N (MIN = 0.01 in this embodiment) (steps 611 and 612).

Further, using the RSR value calculated above, in step 613, the value of RSL (step 419 in FIG. 5) used in the first air-fuel ratio feedback control routine is calculated as RSL = 0.1-RSR. . That is, the sum of RSR and RSL is always held at a constant value (0.1) in this embodiment, and when RSR increases, RS
When L decreases and RSR decreases, RSL increases.

By executing the second air-fuel ratio feedback control routine, when the exhaust air-fuel ratio detected by the downstream O ₂ sensor 15 is rich, RSR is decreased and RSL is increased, and the exhaust air-fuel ratio is lean. In this case, RSR is increased and RSL is decreased at the same time. FIG. 8 shows a case where the first air-fuel ratio feedback control of FIGS. 4 and 5 is performed.
Counter CDLY (same (B)), flag F1 (same (C)), air-fuel ratio correction coefficient FAF (same) for changes in the air-fuel ratio (A / F) detected by the upstream O ₂ sensor 13 (FIG. 8A). (D))
Shows the change. As shown in FIG. 8 (A), even if the A / F changes from lean to rich, the air-fuel ratio flag F1
The value in (Fig. 8 (C)) does not change from 0 to 1 immediately, and is kept at 0 during the time (Fig. 8 (C) T ₁ ) until the value of the counter CDLY increases from 0 to TDR. Then, after the lapse of T ₁ , it changes from 0 to 1. Also, when the A / F changes from rich to lean, the value of F1 is the time during which the value of the counter CDLY decreases from 0 to TDL (TDL is a negative value) (T _{2 in} FIG. 8C). Is maintained as 1 and changes from 1 to 0 after T ₂ . Therefore, as indicated by N in FIG. 8 (A), even if the output of the upstream O ₂ sensor 13 changes in a short cycle due to disturbance or the like, the value of the flag F1 does not follow and the air-fuel ratio changes. Control is stable.

As a result of the first air-fuel ratio feedback control,
The value of the air-fuel ratio correction coefficient FAF repeatedly increases and decreases as shown in FIG. 8 (D), and the engine air-fuel ratio alternates between the rich air-fuel ratio and the lean air-fuel ratio. Further, as described with reference to FIG. 3, when the value of FAF increases, the fuel injection time TAU increases, and when the value of FAF decreases, the fuel injection time TAU also decreases.

As can be seen from FIG. 8 (D), when RSR increases and RSL decreases due to the second air-fuel ratio feedback control (FIGS. 6 and 7), the swing range to the rich air-fuel ratio side increases. The air-fuel ratio shifts to the rich air-fuel ratio side as a whole. Conversely, when RSR decreases and RSL increases, the swing range of the engine air-fuel ratio to the lean air-fuel ratio side increases, and the air-fuel ratio shifts to the lean air-fuel ratio side as a whole.

Therefore, when the values of RSR and RSL are increased or decreased by the second air-fuel ratio feedback control, the engine air-fuel ratio changes to the rich side or the lean side. It should be noted that in this embodiment, RSR and RSL are controlled by the second air-fuel ratio feedback control.
However, the engine air-fuel ratio can also be changed by setting another correction amount in the first air-fuel ratio control in the second air-fuel ratio feedback control.

For example, KIR, KIL (step 4 in FIG. 5)
21 and 422) or the values of TDR and TDL (steps 407 and 413 in FIG. 4) based on the second air-fuel ratio feedback control, the engine air-fuel ratio can be similarly changed. Or upstream O
It is also possible to change the engine air-fuel ratio in the same manner by setting the value of the comparison voltage V _R1 (step 403 in FIG. 4) of the ₂ sensor 13 based on the second air-fuel ratio feedback control. Next, the control when H _{2 is} generated in the catalyst 12 of this embodiment will be described. As described above, H ₂ is generated in the catalyst at the beginning of using the catalyst. Also, H when _two components are present, the output characteristic of the O ₂ sensor for arrival of oxygen in the exhaust to the O ₂ sensor electrodes are prevented from changes in the exhaust. The dotted line in FIG. 2 shows the output characteristics of the O ₂ sensor when there is a certain concentration of H ₂ component in the exhaust gas. As shown by the dotted line in FIG. 2, in the presence of the H ₂ component, O ₂
The sensor actually outputs a rich output even at the stoichiometric air-fuel ratio or the lean air-fuel ratio, so the output characteristics are shifted to the lean air-fuel ratio side as compared to the normal state (solid line in Fig. 2). become. Therefore, the downstream O ₂ sensor 1
In No. 5, when the exhaust air-fuel ratio reaches a certain value on the lean side of the stoichiometric air-fuel ratio (for example, the air-fuel ratio indicated by ST 'in FIG. 2), the stoichiometric air-fuel ratio equivalent output is generated. Thus, the downstream O ₂ sensor 15 even if the actual exhaust air-fuel ratio by the first air-fuel ratio feedback control based on the upstream O ₂ sensor 13 output is controlled to the stoichiometric air-fuel ratio to generate a rich air-fuel ratio corresponding output By the second air-fuel ratio feedback control, RSR is reduced and RSL is increased, and the engine air-fuel ratio gradually shifts to the lean side from the theoretical air-fuel ratio. For this reason, during the period in which H ₂ is generated after the use of a new catalyst, a decrease in the engine output due to the lean air-fuel ratio and a decrease in the NO _x purification capacity of the catalyst are likely to occur.

As described above, the reduction reaction of water gas (H ₂ O + CO → H ₂ + CO ₂ ) occurs in the catalyst 12 only in a state where the catalyst activity is very strong after the start of use of the catalyst, If the catalyst activity is slightly reduced by use, H ₂ will not be generated even in an operating state where the exhaust gas temperature is high. Therefore, in the present embodiment, the second air-fuel ratio feedback control based on the downstream O ₂ sensor 15 is performed while H ₂ of a concentration that affects the downstream O ₂ sensor 15 is generated after the start of use of the catalyst. It is prohibited to prevent the air-fuel ratio from becoming lean.

FIG. 9 is a flow chart showing a routine for prohibiting the second air-fuel ratio feedback control when the above H _{2 is} generated in this embodiment. This routine is executed by the control circuit 10 at regular intervals. In this routine, it is determined whether or not H ₂ is generated by the catalyst based on the total time during which the engine is operated in a state where the exhaust gas temperature is high after the predetermined condition is satisfied. When exposed to hot exhaust gas,
Since the activity of the catalyst gradually decreases, when the operation at high exhaust temperature continues for a predetermined time, the activity of the catalyst becomes O ₂ on the downstream side.
This is because it can be considered that the concentration of H ₂ affecting the sensor 15 is reduced to such an extent that it does not occur.

After the catalyst is started to be used, if the catalyst activity is gradually reduced due to use at a high exhaust temperature, the amount of H ₂ generated during the high exhaust temperature operation is also gradually reduced. Therefore, if the operation is continued in a state where the exhaust gas temperature is high, such as during high-load operation, immediately after the start of use of the catalyst, the H ₂ component concentration in the exhaust gas is high, so the output characteristic of the downstream O ₂ sensor 15 may shift to the lean side. Although it is large, the concentration of H ₂ component in the exhaust also decreases as the operating time elapses,
The shift of the output characteristic of the downstream O ₂ sensor 15 to the lean side also becomes small.

Therefore, the high exhaust gas temperature immediately after the start of use of the catalyst
At the time of turning, exhaust air is exhausted by the first air-fuel ratio feedback control.
The fuel ratio is regularly rich around the theoretical air-fuel ratio as shown in Fig. 8.
Even if the reversal of lean and lean is repeated, the downstream side O
₂The sensor 15 output stays on the rich side and goes to the lean side.
No force is generated. On the other hand, the high exhaust temperature operating state continues to some extent.
The catalytic activity gradually decreases and H in the exhaust gas₂Of component concentration
Downstream O for reduction ₂The output characteristics of the sensor 15 gradually
When approaching at normal times, the downstream side O₂Sensor 15 output is
Reverse between rich and lean air-fuel ratio output
Like

In this embodiment, the downstream side O ₂
The integrated value of the time when the engine is operated in the high temperature state from the time when the output of the sensor 15 stays on the rich side and then the reversal starts to be obtained, and the second value is calculated until the integrated time becomes a predetermined value or more. The air-fuel ratio feedback control is stopped. Since the initial activity of the catalyst may vary from one catalytic converter to another, erroneous determination may occur if the presence or absence of H ₂ is simply determined by the high temperature operating time after the start of use. On the other hand, the time from when the catalytic activity starts to decrease to when the catalytic activity decreases to such an extent that the downstream O ₂ sensor 15 is not affected is substantially uniform regardless of variations in the initial activity. For this reason, in this embodiment, it is detected that the downstream O ₂ sensor 15 output has started reversing that the catalyst activity has begun to decrease, and it is determined whether H _{2 is} generated in the catalyst by the subsequent high temperature operation time. It is something that is done.

When the routine starts in FIG. 9,
In step 901, it is determined whether the current exhaust gas temperature is equal to or higher than a predetermined temperature. Exhaust temperature judgment is
Although it is possible to directly measure the temperature by providing a temperature sensor in the exhaust passage, in the present embodiment, the determination is made based on the engine load (that is, the intake air amount Q / N per engine revolution). That is, in step 901,
When the Q / N value is equal to or higher than a predetermined value (Q / N) _C , it is determined that the engine exhaust temperature is equal to or higher than the predetermined value.

If the current engine exhaust temperature is lower than the predetermined value in step 901, this routine ends. Further, when it is determined in step 901 that the exhaust temperature is equal to or higher than the predetermined value, the operations in step 903 and thereafter are executed. That is, in step 903, it is determined whether or not the value of the flag XR is set to 1. If XR ≠ 1, the value of the clock counter CCAT is set to a constant value M in step 905. When XR = 1, the value of the counter CCAT is decremented by 1.

Here, XR is the lean air-fuel ratio equivalent output after the output of the downstream O ₂ sensor 15 continues to output the rich air-fuel ratio equivalent output for a predetermined time or more under a predetermined high temperature condition by the routine of FIG. 10 described later. Is a flag that is set to 1 when occurs. That is, the flag XR indicates that the activity has begun to decrease after the use of the catalyst. As a result, the value of the counter CCAT is maintained at the constant value M until the initial activity of the catalyst starts to decrease, and after the activity starts to decrease, as long as the exhaust temperature condition of step 903 is satisfied,
Each time this routine is executed, the countdown will be one by one.

Further, in step 908, the current value of the counter CCAT is stored in a predetermined area of the backup RAM 106, and the value of CCAT is held even if the condition of step 901 is temporarily not satisfied. As a result, the value of CCAT becomes a value corresponding to the cumulative time that the engine was operated under high temperature conditions. In step 909, it is determined whether the value of the counter CCAT is a positive value. CCAT
If it is> 0, it means that the integrated value of the time during which the engine has been operating in the high exhaust temperature state has not reached the predetermined value M since the activity of the catalyst started to decrease. Since there is a possibility that the concentration of H ₂ affecting the side O ₂ sensor 15 is generated, the value of the flag XH ₂ is set to 1 and the routine is ended. As a result, in step 600 of FIG. 6, the second air-fuel ratio feedback control based on the output of the downstream O ₂ sensor 15 is prohibited, so that leaning of the engine air-fuel ratio is prevented. The CCAT determination value M is determined in advance by experiments or the like according to the type and capacity of the catalyst.

If CCAT ≦ 0 in step 909, the engine has been operating in the high exhaust temperature state for a sufficiently long time since the activity of the catalyst began to decrease.
The activity of the catalyst has decreased, and the downstream O ₂ sensor 1 is no longer in use.
Since it can be considered that the concentration of H ₂ that affects 5 is not generated, the flag XH is determined in step 913.
Set the value of ₂ to 0 and terminate the routine. Thus, in FIG. 6 step 601 following the downstream O ₂ sensor 1
Execution of the second air-fuel ratio feedback control based on the 5-output is permitted.

FIG. 10 is a flow chart showing a routine for setting the flag SR. This routine is performed by the control circuit 10
Is executed every fixed time. When the routine starts in FIG. 10, it is determined in step 1001 whether or not the first air-fuel ratio feedback control based on the output of the upstream O ₂ sensor 13 is currently executed from the value of the flag XMFB (see steps 424 and 425 in FIG. 5). To be judged.

Further, in step 1003, it is determined whether or not the catalyst temperature has risen sufficiently after the start of engine operation by flag HC.
It is determined from the value of. HC is a flag that is set to 1 when the catalyst warm-up is completed. In this embodiment, a separately executed routine (not shown) determines that the catalyst warm-up is completed when the integrated value of the engine intake air amount after the engine is started reaches a predetermined value or more, and sets the value of the flag HC to 1 Is set to. This is because the engine intake air amount is almost proportional to the heat amount generated in the engine, and therefore the integrated value of the intake air amount corresponds to the heat amount given to the catalyst from the exhaust gas.

Further, in step 1005, as in step 901 of FIG. 9, it is determined from the value of Q / N whether the engine exhaust temperature is equal to or higher than a predetermined value. Step 1 above
If any one of the conditions 001 to 1005 is not satisfied, this routine immediately ends, and step 100
7 and below are not executed. Here, the condition that the first air-fuel ratio feedback control is being executed (step 1001) is the condition that the downstream O ₂ sensor 15 output is detected to start reversing in step 1009, which will be described later. Since the value of XR is set to 1, it is necessary that the engine air-fuel ratio be in a state in which reversal between the rich air-fuel ratio and the lean air-fuel ratio is repeated as shown in FIG. The machine is complete (step 100
The condition 3) and that the exhaust gas temperature is equal to or higher than a predetermined temperature (step 1005) are because the condition that H ₂ is generated in the catalyst must be satisfied.

If all of the above conditions are satisfied, at step 1007, the output VOS of the downstream O ₂ sensor 15 continuously outputs a rich air-fuel ratio equivalent output for a predetermined time or more by the time the previous routine is executed. Whether or not (VOS> _VR2
Is established for a predetermined time or more) is determined. If the condition of step 1007 is satisfied,
Proceeding to step 1009, the current downstream O ₂ sensor 15
Whether or not the output VOS is a lean air-fuel ratio equivalent output (VOS ≦ V
_R2 ) is judged. If the conditions of steps 1007 and 1009 are satisfied, after the output of the downstream O ₂ sensor 15 remains on the rich air-fuel ratio side, inversion is started between the lean air-fuel ratio and the rich air-fuel ratio, That is, since it means that the activity of the catalyst has started to decrease, in step 1011 the value of the above-mentioned flag XR is set to 1,
After storing this value in a predetermined area of the backup RAM 106, the routine ends. The initial value of the flag XR is set to 0, and once all the conditions in FIG.
When set to = 1 it will not be reset to 0 again.

As described above, in the present embodiment, the air-fuel ratio feedback control based on the output of the downstream O ₂ sensor 15 is prohibited during the period when H ₂ is generated after the start of use of the catalyst. It is possible to prevent a decrease in engine output and deterioration of exhaust emission due to leaning. Incidentally, in the state where the downstream O ₂ sensor output characteristic with H ₂ generation catalyst as described above is shifted to the lean side, the downstream side O ₂ in addition to the air-fuel ratio feedback control
A problem arises when performing control based on the sensor output.
For example, as described above, when the presence or absence of catalyst deterioration is determined based on the inversion cycle of the downstream O ₂ sensor output, the O ₂ storage action of the catalyst cannot be exhibited due to the shift of the output characteristics. The inconvenience arises that the new catalyst is erroneously determined to be deteriorated. Therefore, in the present embodiment, when the value of the flag XH ₂ is set to 1, similarly, the deterioration determination of the catalyst based on the output of the downstream O ₂ sensor 15 is prohibited to prevent erroneous determination. ing.

11 to 12 show a flow chart of the catalyst deterioration determination routine of this embodiment. In this embodiment, as in the above-mentioned JP-A-5-263686, the upstream side O
The presence or absence of catalyst deterioration is determined based on the inversion cycle of the output of the downstream O ₂ sensor 15 during execution of the air-fuel ratio feedback control based on the output of the ₂ sensor 13. Hereinafter, FIG. 11 and FIG.
The routine will be briefly described.

When the routine starts in FIG. 11, in steps 1101 to 1103, it is determined whether or not the catalyst deterioration determination execution condition is satisfied. These conditions are that the first air-fuel ratio feedback control based on the output of the upstream O ₂ sensor 13 is executed (step 1101), and the output of the upstream O ₂ sensor 13 has not been stuck to the lean side for a predetermined time or longer. (Step 110
2) It is determined that the output of the upstream O ₂ sensor 13 has not been stuck to the rich side for a predetermined time (step 1103). The condition is required because the exhaust air-fuel ratio flowing into the catalyst needs to regularly fluctuate between the rich side and the lean side in order to determine the catalyst deterioration. If any of the above conditions is not satisfied, the routine proceeds to step 1116 of FIG. 12 and ends the routine.

Next, in step 1104, it is judged whether or not the value of the above-mentioned flag XH ₂ is set to 1. If XH ₂ = 1 then H ₂ is generated in the catalyst, so the downstream If the catalyst deterioration is determined based on the output of the side O ₂ sensor 15, an erroneous determination may occur. Therefore, similarly, the routine proceeds to step 1116 in FIG. 12 to end the routine. That is, catalyst deterioration detection is not performed.

When all of the above execution conditions are satisfied, the catalyst deterioration determination of step 1105 onward in FIG. 12 is performed. In FIG. 12, the downstream side O is reached until a predetermined period elapses after the execution conditions of FIG. 11 are satisfied (steps 1105 and 1106).
_{2 The} number CS of outputs of the sensor 15 output VOS is inverted (steps 1107 and 1108), and after a lapse of a predetermined time, it is determined whether or not the number of inversions is a predetermined value CS ₀ or more (step 1109). When the number of reversals CS of the output VOS of the downstream O ₂ sensor 15 within a predetermined time is equal to or greater than a predetermined value CS ₀ , that is, the reversal cycle of the output of the downstream O ₂ sensor 15 is short, and the catalyst deteriorates. It is determined that the alarm has been set and the alarm flag ALM is set to 1, and a deterioration alarm (indicated by 19 in FIG. 1) is turned on (step 11).
10, 1111). If the number of inversions is less than the predetermined value in step 1109, the alarm flag ALM is reset and the alarm 19 is turned off (steps 1112 and 1113). The value of the alarm flag is stored in the backup RAM 106 so that it can be prepared for the next repair or inspection.

According to the embodiments shown in FIGS. 11 and 12, when H ₂ is generated in the catalyst and the downstream O ₂ sensor output characteristic is shifted to the lean side, the catalyst deterioration determination is prohibited. As a result (step 1104 in FIG. 11), the problem of erroneously determining that the new catalyst is deteriorated is prevented. In addition,
In the above embodiment has been described taking examples of the air-fuel ratio feedback control and catalyst deterioration detection control as an example of control based on the downstream O ₂ sensor output, control based on the downstream O ₂ sensor output to other row In the case where H ₂ is generated in the catalyst, it is preferable to prohibit the control execution in the same manner as above to prevent erroneous control.

[0067]

According to the inventions described in the claims, the control based on the output of the downstream O ₂ sensor is performed while the output characteristic of the downstream O ₂ sensor is affected by the hydrogen generation at the initial stage of catalyst use. Since it is prohibited, there is a common effect that erroneous control of the engine can be prevented when hydrogen is generated by the catalyst.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment in which the present invention is applied to an automobile engine.

FIG. 2 is a diagram illustrating a change in output characteristics of an O ₂ sensor due to an influence of H ₂ component in exhaust gas.

FIG. 3 is a flowchart illustrating a fuel injection amount calculation routine of the engine of FIG.

FIG. 4 is a part of a flowchart showing an example of first air-fuel ratio feedback control based on an upstream air-fuel ratio sensor output.

FIG. 5 is a part of a flowchart showing an example of first air-fuel ratio feedback control based on an upstream air-fuel ratio sensor output.

FIG. 6 is a part of a flowchart showing an example of second air-fuel ratio feedback control based on a downstream side air-fuel ratio sensor output.

FIG. 7 is a part of a flowchart showing an example of second air-fuel ratio feedback control based on a downstream side air-fuel ratio sensor output.

FIG. 8 is a timing diagram supplementarily explaining the flowcharts of FIGS. 4 to 7.

FIG. 9 is a flowchart showing an H ₂ generation determination routine in the catalyst.

10 is a flowchart showing a setting operation of a flag used in the routine of FIG.

FIG. 11 is a part of a flowchart showing a catalyst deterioration determination routine.

FIG. 12 is a part of a flowchart showing a catalyst deterioration determination routine.

[Explanation of symbols]

1 ... Engine body 3 ... Air flow meter 4 ... Distributor 5, 6 ... Crank rotation angle sensor 7 ... Fuel injection valve 10 ... Control circuit 12 ... Catalytic converter 13 ... Upstream O ₂ sensor 15 ... Downstream O ₂ sensor

Claims (4)

[Claims] 1. An exhaust purification catalyst arranged in an exhaust passage of an internal combustion engine, and a downstream O ₂ arranged in a downstream exhaust passage of the exhaust purification catalyst for outputting a signal according to an oxygen component concentration in exhaust gas. A sensor, an H ₂ detection unit that detects the hydrogen component concentration in the exhaust gas on the exhaust purification downstream side, and a H ₂ detection unit that detects a hydrogen component of a predetermined value or more in the exhaust gas, An O ₂ sensor control device for an internal combustion engine, comprising: a prohibiting unit that prohibits control performed based on the output of the downstream O ₂ sensor. 2. A control performed on the basis of the downstream O ₂ sensor output, according to claim 1 wherein the air-fuel ratio control for feedback control to the target air-fuel ratio of the engine air-fuel ratio on the basis of the downstream O ₂ sensor output O ₂ sensor controller. 3. The O ₂ sensor control device according to claim 1, further comprising an upstream O ₂ sensor which is arranged in the exhaust passage on the exhaust purification catalyst upstream side and which outputs a signal according to the concentration of oxygen component in the exhaust gas. , The downstream O ₂ sensor output and the upstream O
_2. An air-fuel ratio control means for feedback-controlling an engine air-fuel ratio to a target air-fuel ratio based on _two sensor outputs.
O ₂ sensor control device described in 1. 4. A control performed on the basis of the downstream O ₂ sensor output, claim a catalyst deterioration detection control for detecting the presence or absence of deterioration of the exhaust purification catalyst based on the fluctuation of the downstream O ₂ sensor output 1. The O ₂ sensor control device described in 1.