JP3156582B2 - Catalyst deterioration determination device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus (catalyst deterioration judging apparatus) for judging the presence or absence of deterioration of a catalyst provided in an exhaust passage of an internal combustion engine (engine) for purifying exhaust gas.

[0002]

2. Description of the Related Art Conventionally, as a measure for purifying exhaust gas, an automobile engine simultaneously promotes oxidation of unburned components (HC, CO) and reduction of nitrogen oxides (NO _x ) in exhaust gas. A raw catalyst is used. In order to increase the oxidation / reduction capacity of such a three-way catalyst, it is necessary to control the air-fuel ratio (A / F) indicating the combustion state of the engine to be close to the stoichiometric air-fuel ratio (window). for that reason,
In fuel injection control in an engine, an O ₂ sensor (oxygen concentration sensor) that detects whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio based on the concentration of residual oxygen in exhaust gas.
(See FIG. 1), and air-fuel ratio feedback control for correcting the fuel amount based on the sensor output is performed.

In this air-fuel ratio feedback control, an O ₂ sensor for detecting the oxygen concentration is provided as close to the combustion chamber as possible, that is, upstream of the catalytic converter, but the variation in output characteristics of the O ₂ sensor is compensated. For this reason, a double O ₂ sensor system further provided with a _second O ₂ sensor downstream of the catalytic converter has also been realized. That is, in the downstream side of the catalyst, the exhaust gas is sufficiently stirred, by which is in near equilibrium state by action of the oxygen concentration the three-way catalyst, the output of the downstream O ₂ sensor, the upstream O ₂ sensor Also changes slowly, thus indicating a rich / lean tendency for the entire mixture. The double O ₂ sensor system performs the sub air-fuel ratio feedback control by the catalyst downstream O ₂ sensor in addition to the main air-fuel ratio feedback control by the catalyst upstream O ₂ sensor, and performs the air-fuel ratio correction by the main air-fuel ratio feedback control. By correcting the coefficient based on the output of the downstream O ₂ sensor, variations in the output characteristics of the upstream O ₂ sensor are absorbed, and the air-fuel ratio control accuracy is improved.

[0004] Even if the above-described precise air-fuel ratio control is performed, sufficient exhaust gas purification performance cannot be obtained if the catalyst is deteriorated due to the action of heat of the exhaust gas or poisoning of lead or the like. . Therefore, various catalyst deterioration detection devices have been conventionally proposed. One of them is to detect the deterioration of the O ₂ storage effect (the function of retaining excess oxygen and using it for purifying unburned exhaust gas) after the warm-up by the O ₂ sensor on the downstream side of the catalyst, thereby reducing the deterioration of the catalyst. It is to diagnose. That is, the deterioration of the catalyst results in a decrease in the purification performance after warm-up. As a result, this apparatus estimates that the decrease in the O ₂ storage effect is a decrease in the purification performance, and outputs the output signal of the downstream O ₂ sensor. It is used to determine the locus length, feedback frequency, etc., to detect a decrease in the O ₂ storage effect, and to detect catalyst deterioration.

For example, an apparatus disclosed in Japanese Patent Publication No. 7-26578 is an apparatus for detecting deterioration of the O ₂ storage effect and determining catalyst deterioration. That is, the device
In the double O ₂ sensor system, when the rich / lean inversion cycle of the downstream O ₂ sensor output during the air-fuel ratio feedback control becomes shorter than a predetermined value, it is determined that the catalyst has deteriorated. The catalyst deterioration determination is performed only when the intake air amount is within a predetermined deterioration determination execution area.

Generally, even if the level of the O ₂ storage capacity of the catalyst is the same, the amount of O ₂ adsorbed and released by the catalyst changes according to the exhaust gas flow rate. That is, if the exhaust gas flow rate is large, the amount of O ₂ adsorbed and released by the catalyst per unit time will also be large. Therefore, the excessive state exhaust flow rate, even normal catalyst O ₂ storage capability is not reduced in a short time will be exhausted to release O ₂ while the inflow exhaust air-fuel ratio is oscillated at the rich side , Then O
₂ can no longer be released. Similarly, when the exhaust gas flow rate is excessively large, even if the O ₂ storage capacity of the normal catalyst is not reduced, the O ₂ adsorption amount can be reduced in a short time while the inflow exhaust air-fuel ratio swings to the lean side. Saturation occurs, after which O ₂ cannot be adsorbed. Therefore, in a state where the exhaust gas flow rate is excessive, even if the catalyst is normal, the downstream O ₂ sensor output fluctuates similarly to the upstream O ₂ sensor output, and it is erroneously determined that the catalyst is deteriorated. there is a possibility.

Conversely, if the exhaust gas flow rate is small, the amount of O ₂ adsorbed and released by the catalyst per unit time will also be small. Therefore, in a state where the exhaust gas flow rate is too small, even if the deteriorated catalyst has a reduced O ₂ storage capacity, it is difficult to reach a state in which oxygen is exhausted while the inflow exhaust air-fuel ratio swings to the rich side. On the other hand, it is difficult to reach a state where the O ₂ adsorption amount is saturated while the inflow exhaust air-fuel ratio swings to the lean side. Therefore, in a state where the exhaust gas flow rate is too small, even if the catalyst is deteriorated, the fluctuation of the output of the downstream O ₂ sensor becomes small, and it may be erroneously determined that the catalyst is not deteriorated. Above 7-265
The device disclosed in Japanese Patent Publication No. 78 prevents the erroneous determination by performing the catalyst deterioration determination only when the intake air amount substantially proportional to the exhaust flow rate is within a predetermined deterioration determination execution region.

[0008]

On the other hand, in recent years, an internal combustion engine has been developed which controls the air-fuel ratio so that the three-way catalyst can always exhibit a constant and stable purification performance.
That is, the O ₂ storage capacity purifies the exhaust gas by adsorbing excess oxygen when the exhaust gas is lean and releasing insufficient oxygen when the exhaust gas is rich. However, such capabilities are finite. Therefore, in order to effectively use the O ₂ storage capacity, the air-fuel ratio of the exhaust gas may be either a rich state or a lean state next.
It is important to maintain the amount of oxygen stored in the catalyst at a predetermined amount (for example, half of the maximum oxygen storage amount), and if it is maintained, a constant O ₂ adsorption / desorption effect is always maintained. Is possible, and as a result, a certain amount of oxidation
Reducing ability is always obtained.

In order to maintain the purification performance of the catalyst as described above, O
_{(2) In} an internal combustion engine that controls the storage amount constant,
An air-fuel ratio sensor (A / F sensor) (see FIG. 2) capable of linearly detecting the air-fuel ratio is used, and a proportional and integral operation (PI
Operation) performs feedback control (F / B control). In other words, the next time fuel correction amount = K _p * (difference this time of fuel) + K _s * Σ
(Fuel difference up to now) Fuel difference = (Actual amount of fuel actually burned in the cylinder)-(Target in-cylinder fuel amount with stoichiometric intake air) Fuel amount actually burned in the cylinder = Air flow detection value /
The air-fuel ratio detection value K _p = proportional term gain K _s = integral term gain By the calculation, the feedback fuel correction amount is calculated.

As can be seen from the above equation for calculating the fuel correction amount, the proportional term is a component that acts to maintain the air-fuel ratio at stoichiometry, as in the feedback control by the O ₂ sensor. It is a component that acts to eliminate the deviation (offset). That is, the action of the integral term results in that the O ₂ storage amount in the catalyst is kept constant. For example, when lean gas is generated due to sudden acceleration or the like, the action of the integral term generates rich gas, and the effect of lean gas generation is offset.

In such a constant O ₂ storage amount control system, an O ₂ sensor may be provided downstream of the catalyst in order to compensate for variations in the output characteristics of the A / F sensor. Therefore, also in this case, similarly to the double O ₂ sensor system, the decrease in the O ₂ storage effect of the catalyst is reduced by O _2.
It is conceivable to detect catalyst deterioration by detecting with a sensor. Also in this case, as disclosed in Japanese Patent Publication No. Hei 7-26578, the catalyst deterioration determination is performed only when the intake air amount substantially proportional to the exhaust gas flow is within a predetermined deterioration determination execution area. Thus, it is preferable to prevent erroneous determination. However, at that time, erroneous detection may occur due to the following factors.

In general, the amount of O ₂ adsorbed and released by the catalyst depends on the exhaust gas flow rate as described above, and also on the fluctuation range of the air-fuel ratio (or the absolute value of the displacement of the engine air-fuel ratio from the stoichiometric air-fuel ratio). I do. In other words, even with the same exhaust flow rate, when the fluctuation width of the air-fuel ratio is large, O ₂ adsorption and emission as compared to when the variation width is small, increases. Therefore, even for the same exhaust flow rate, as the fluctuation width of the air-fuel ratio is large, the amount of intake air O ₂ storage capacity reaches the limit can be reduced, that.

FIG. 3 shows the relationship between the fluctuation range of the air-fuel ratio and the amount of intake air at which the O ₂ storage capacity of the catalyst reaches its limit, for a normal catalyst (curve C1) and for a deteriorated catalyst (curve C2). FIG. In the region of the intake air amount exceeding the curve C1, even if the catalyst is normal, it is erroneously determined that the catalyst has deteriorated. In other words, the curve C2 represents the amount of intake air in which the O ₂ storage effect appears in the deteriorated catalyst. In the region of the amount of intake air lower than the curve C2, even if the catalyst is actually deteriorated, the catalyst is not deteriorated. An incorrect determination is made.

In the case of a double O ₂ sensor system, a constant fuel injection amount correction is performed irrespective of the amount of intake air, depending on whether the O ₂ sensor indicates rich or lean, thereby achieving a constant value. Since the control for changing the air-fuel ratio is performed, the control range is, as shown in FIG.
₀ the narrow range indicated by a ₁ from. Therefore, the region of the intake air amount in which the catalyst deterioration determination should be performed can be set to a certain range with b ₀ shown in the figure as a lower limit and b _{1 shown} as an upper limit.

However, in the air-fuel ratio feedback control based on the output voltage of the A / F sensor, control is performed such that the larger the deviation between the output voltage and the target voltage (stoichiometric equivalent voltage), the larger the fuel correction amount. The fluctuation width of the air-fuel ratio greatly changes depending on the running state. Therefore, it is extremely difficult to limit the region of the intake air amount for which the catalyst deterioration determination is to be performed to a certain region in order to prevent erroneous detection. Even if a certain region can be set, it is extremely difficult. This is a narrow range, which significantly reduces the chance of detecting catalyst deterioration.

In view of the above circumstances, an object of the present invention is to provide an A / F sensor having an output characteristic substantially proportional to the oxygen concentration in exhaust gas on the upstream side of the exhaust gas purification catalyst, and to provide an A / F sensor based on the output of the A / F sensor. in an internal combustion engine is feedback controlled so that the air-fuel ratio becomes the stoichiometric air-fuel ratio on the basis of a deviation between the air-fuel ratio and the stoichiometric air-fuel ratio which is, in the case of performing the catalyst deterioration diagnosis based on the output of the catalyst downstream O ₂ sensor, the An object of the present invention is to achieve both an improvement in diagnostic accuracy and an increase in diagnostic opportunities. Accordingly, an object of the present invention is to improve exhaust gas purification performance and contribute to prevention of air pollution.

[0017]

According to the present invention, the region of the intake air amount in which the catalyst deterioration determination is to be performed is made variable in accordance with the air-fuel ratio fluctuation width (that is, the displacement of the engine air-fuel ratio from the stoichiometric air-fuel ratio). Based on the basic idea of the above, the above object is achieved by adopting a technical configuration as described below.

That is, the device for determining catalyst deterioration of an internal combustion engine according to the present invention is provided on the upstream side of an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine, and has output characteristics substantially proportional to the oxygen concentration in exhaust gas. An upstream air-fuel ratio sensor having
A downstream air-fuel ratio sensor provided downstream of the exhaust purification catalyst, and air-fuel ratio feedback control means for performing feedback control so that an engine air-fuel ratio becomes a stoichiometric air-fuel ratio based on at least an output of the upstream air-fuel ratio sensor. An intake air amount detecting means for detecting an engine intake air amount; and, during execution of the air-fuel ratio feedback control, when the engine intake air amount is within a predetermined determination execution region, at least the downstream air-fuel ratio sensor Catalyst deterioration determining means for determining whether or not the exhaust purification catalyst has deteriorated based on the output; and the engine intake air amount according to a deviation between an output of the upstream air-fuel ratio sensor and a target output corresponding to a stoichiometric air-fuel ratio. And an area setting means for setting a determination execution area related to the area.

[0019]

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

FIG. 4 is an overall schematic diagram of an electronically controlled internal combustion engine equipped with a catalyst deterioration determination device according to one embodiment of the present invention. The air required for engine combustion is air cleaner 2
And is distributed to an intake pipe 7 of each cylinder by a surge tank (intake manifold) 6 through a throttle body 4. The intake air flow rate is adjusted by a throttle valve 5 provided on the throttle body 4 and is measured by an air flow meter 40. The intake air temperature is detected by an intake air temperature sensor 43. Further, the intake pipe pressure is detected by a vacuum sensor 41.

The opening of the throttle valve 5 is detected by a throttle opening sensor 42. When the throttle valve 5 is in the fully closed state, the idle switch 52 is turned on, and the throttle fully closed signal output from the idle switch 52 becomes active. An idle speed control valve (ISCV) 66 for adjusting the air flow during idling is provided in the idle adjustment passage 8 that bypasses the throttle valve 5.
Is provided.

On the other hand, the fuel stored in the fuel tank 10 is pumped up by the fuel pump 11 and
Is injected into the intake pipe 7 by the fuel injection valve 60.

In the intake pipe 7, air and fuel are mixed,
The air-fuel mixture is sucked into a combustion chamber 21 of an engine body, that is, a cylinder 20 via an intake valve 24. In the combustion chamber 21, the air-fuel mixture is compressed by the piston 23, ignited, exploded and burned to generate power.
Such ignition depends on the igniter 62 receiving the ignition signal.
Controls the energization and interruption of the primary current of the ignition coil 63, and the secondary current is supplied to the spark plug 65 via the ignition distributor 64.

The ignition distributor 64 includes:
Its axis is, for example, 720 ° in terms of crank angle (CA).
A reference position detection sensor 50 for generating a reference position detection pulse for each CA and a crank angle sensor 51 for generating a position detection pulse for each 30 ° CA are provided. Note that the actual vehicle speed is detected by a vehicle speed sensor 53 that generates an output pulse representing the vehicle speed. The engine body (cylinder) 20 is cooled by cooling water guided to a cooling water passage 22, and the temperature of the cooling water is measured by a water temperature sensor 4.
4 detected.

The burned air-fuel mixture is discharged as exhaust gas to the exhaust manifold 30 via the exhaust valve 26, and then guided to the exhaust pipe 34. The exhaust pipe 34 has an A / F that linearly detects the air-fuel ratio based on the oxygen concentration in the exhaust gas.
A sensor 45 is provided. Further, a catalytic converter 38 is provided downstream of the exhaust system, and the catalytic converter 38 has an unburned component (H
A three-way catalyst that simultaneously promotes the oxidation of (C, CO) and the reduction of nitrogen oxides (NO _x ) is accommodated. The exhaust gas thus purified in the catalytic converter 38 is discharged into the atmosphere.

The engine is provided with an A / F sensor 45.
The engine performs sub air-fuel ratio feedback control to compensate for variations in the output characteristics of the A / F sensor 45 by changing the control center of the air-fuel ratio feedback control by _Two sensors 46 are provided.

Engine electronic control unit (engine EC
U) 70 is a microcomputer system that executes catalyst deterioration determination processing in addition to fuel injection control (air-fuel ratio control), ignition timing control, idle rotation speed control, and the like. The hardware configuration thereof is a block diagram of FIG. Is shown in
According to the programs stored in the read-only memory (ROM) 73 and various maps, the central processing unit (CP)
U) 71 converts signals from various sensors and switches into A /
Input through the D conversion circuit 75 or the input interface circuit 76, and execute arithmetic processing based on the input signal;
Various actuator control signals are output via the drive control circuits 77a to 77d based on the calculation results. The random access memory (RAM) 74 is used as a temporary data storage place in the operation / control processing. The backup RAM 79 is supplied with power by being directly connected to a battery (not shown),
It is used to store data (for example, various learning values) to be held even when the ignition switch is off. Each component in the ECU is connected by a system bus 72 including an address bus, a data bus, and a control bus.

An engine control process of the ECU 70 executed in the internal combustion engine (engine) having the above hardware configuration will be described below.

The ignition timing control is based on the engine speed obtained from the crank angle sensor 51 and other signals from other sensors, and comprehensively determines the state of the engine, determines the optimal ignition timing, and controls the drive control circuit 77b. The ignition signal is sent to the igniter 62 through the igniter 62.

In the idle speed control, an idle state is detected by a throttle fully closed signal from an idle switch 52 and a vehicle speed signal from a vehicle speed sensor 53, and a target determined by an engine coolant temperature from a water temperature sensor 44 and the like. The engine speed is compared with the actual engine speed, and a control amount is determined according to the difference so as to attain the target engine speed.
By controlling the V66 to adjust the amount of air, the optimum idle rotation speed is maintained.

In the following, in order to describe in detail the air-fuel ratio control (fuel injection control) and the catalyst deterioration determination processing according to the present invention, the procedures of related processing routines will be shown in order.

FIG. 6 is a flowchart showing the processing procedure of the in-cylinder air amount estimation and target in-cylinder fuel amount calculation routine. This routine is executed every predetermined crank angle. First updates the cylinder air amount MC _i and target cylinder fuel amount FCR _i is obtained by the running up to the previous routine. That is, the i-th (i = 0, 1,..., N−1) -th previous MC _i and FCR _i are replaced by the “i + 1” -th previous MC _{i
i + 1} and FCR _{i + 1} (step 102). This is, as shown in FIG. 7, the in-cylinder air amount M for the past n times.
The data of C _i and the target in-cylinder fuel amount FCR _i are stored in the RAM 74.
Stored within, in order to newly calculate the MC ₀ and FCR ₀ time.

Next, based on the outputs from the vacuum sensor 41, the crank angle sensor 51, and the throttle opening sensor 42, the current intake pipe pressure PM, engine speed NE, and throttle opening TA are obtained (step 1).
04). Then, these PM, NE, and from TA data, to estimate the amount of air MC ₀ supplied to the cylinder (step 106). In general, the in-cylinder air amount can be estimated from the intake pipe pressure PM and the engine rotational speed NE. However, in this embodiment, a transient state is detected from a change in the value of the throttle opening TA, and even in the transient state. A precise air volume is calculated.

Next, based on the in-cylinder air amount MC ₀ and the stoichiometric air-fuel ratio AFT, a calculation of FCR ₀ ← MC ₀ / AFT is executed, and the target fuel to be supplied into the cylinder to make the air-fuel mixture stoichiometric. The quantity FCR ₀ is calculated (step 108). The in-cylinder air amount MC ₀ and the target in-cylinder fuel amount FCR ₀ thus calculated are stored in the RAM in the form shown in FIG.
It is stored in 74.

FIG. 8 is a flowchart showing the processing procedure of the main air-fuel ratio feedback control routine. This routine is executed every predetermined crank angle. First, it is determined whether a condition for executing feedback is satisfied (step 202). For example, when the cooling water temperature is equal to or lower than a predetermined value, the feedback condition is not satisfied when the engine is started, during the increase after the start, during the warm-up, when there is no change in the output signal of the A / F sensor 45, during the fuel cut, and the like. In the case of, the condition is satisfied. When the condition is not satisfied, the fuel correction amount DF by the feedback control is set to 0 (step 216), and this routine ends.

The feedback condition at the time of establishment, updating the FD _i (the difference between the actual amount of fuel that is burned in the cylinder and target cylinder fuel amount) fuel amount difference is obtained by the running up to the previous routine . That is, the i-th (i = 0, 1,
.., M−1) times the FD _i before the “i + 1” th times FD _{i
i + 1} is set (step 204). This is to store data of the past m times the fuel amount difference FD _i in RAM 74, calculates a new fuel amount difference FD ₀ time.

Next, the output voltage value V of the A / F sensor 45
AF is detected (step 206). Next, A calculated by the sub air-fuel ratio feedback control described later.
The A / F sensor output voltage VAF is corrected by executing a calculation of VAF ← VAF + DV based on the / F sensor output voltage correction amount DV (step 208). By such a correction, the center of the air-fuel ratio fluctuation is gradually shifted until the target voltage is reached in the sub-air-fuel ratio feedback control. Then, based on the VAF after such correction, FIG.
The current air-fuel ratio ABF is determined by referring to the characteristic diagram (step 210). The characteristic diagram of FIG.
The data is mapped and stored in the ROM 73 in advance.

Next, the cylinder air amount MC already calculated by the cylinder air amount estimation and target cylinder fuel amount calculation routines.
_n and the target in-cylinder fuel amount FCR _n (see FIG. 7), the calculation of FD ₀ ← MC _n / ABF-FCR _{n is used to} calculate the difference between the fuel amount actually burned in the cylinder and the target in-cylinder fuel amount. The difference is obtained (step 212).
The reason for thus adopting n times before the cylinder air amount MC _n and target cylinder fuel amount FCR _n is consideration of the time difference between the actual combustion fuel ratio which is detected by the current A / F sensor Because he did. In other words, there is necessary to store the cylinder air amount MC _i and target cylinder fuel amount FCR _i for the past n times are for such a time difference.

Next, the fuel correction amount DF by the proportional / integral control (PI control) is determined by the calculation of DF ← K _fp * FD ₀ + K _fs * ΣFD _i (step 214). In addition,
The first term on the right side is a proportional term of PI control, and _Kfp is a proportional term gain. The second term on the right side is an integral term of PI control, and K _fs is an integral term gain.

FIG. 9 is a flowchart showing a processing procedure of a sub air-fuel ratio feedback control routine. This routine is executed at a predetermined time period longer than that in the main air-fuel ratio feedback control routine. First, similarly to the case of the main air-fuel ratio feedback, it is determined whether or not a condition for executing the sub air-fuel ratio feedback control is satisfied (step 302). If the conditions are not satisfied, the A / F sensor output voltage correction amount DV is set to 0 (step 312), and this routine ends.

[0041] During satisfied feedback condition, updates the VD _i (the difference between the actually detected O ₂ sensor output voltage and the target O ₂ sensor output voltage) voltage difference is obtained by the running up to the previous routine. That is, the i-th (i =
0,1, ..., a p-1) times before VD _i the "i + 1" times the previous VD _{i + 1} (step 304). This is the past p
Storing data batch voltage difference VD _i in the RAM 74,
This is for newly calculating the voltage difference VD ₀ this time.

Next, the output voltage VOS of the O ₂ sensor 46
Is detected (step 306). Next, the VOS and the target O ₂ sensor output voltage VOST (for example, 0.5 V)
, The latest voltage difference VD ₀ is obtained by executing an operation of VD ₀ ← VOS−VOST (step 308).

[0043] Finally, DV ← by _{K vp * VD 0 + K vs} * ΣVD it becomes operational, determining the A / F sensor output voltage correction amount DV by PI control (step 310). Note that K _vp
And K _vs are the gains of the proportional and integral terms, respectively. As described above, the correction amount DV thus obtained is used to change the control center voltage of the feedback control by the A / F sensor in the main air-fuel ratio feedback control routine.

FIG. 10 is a flowchart showing the processing procedure of the fuel injection control routine. This routine is executed every predetermined crank angle. First, based on the in-cylinder air amount estimation and the target in-cylinder fuel amount FCR ₀ calculated in the target in-cylinder fuel amount calculation routine and the feedback correction amount DF calculated in the main air-fuel ratio feedback control routine, FI ← The fuel injection amount FI is determined by executing the calculation of FCR ₀ * α + DF + β (step 402). Note that α and β are a multiplication correction coefficient and an addition correction amount determined by other operation state parameters. For example, α is the intake air temperature sensor 43, the water temperature sensor 4
4 includes a basic correction based on a signal from each sensor, and β includes a correction based on a change in the amount of fuel adhering to the wall surface (which changes with a change in the intake pipe pressure in a transient operation state). include. Finally, the obtained fuel injection amount FI is set in the drive control circuit 77a of the fuel injection valve 60 (step 404).

FIGS. 11 and 12 are flowcharts showing the processing procedure of the catalyst deterioration determination routine. This routine is executed at a predetermined time period. First, step 50
In step 2, it is determined whether or not a general monitoring condition for deterioration determination is satisfied. If the monitoring condition is not satisfied, this routine ends. If the monitoring condition is satisfied, step 504 is executed.
Proceed to. The monitoring condition is, for example, the A / F sensor 45
A main air-fuel ratio feedback control is being based on the output that it is sub air-fuel ratio feedback control is being based on the output of the O ₂ sensor 46, it is such that the engine load is higher than a predetermined value.

In step 504, the output voltage VAF of the A / F sensor 45 and the output voltage VOS of the O ₂ sensor 46 are detected, and the intake air amount QA (volume flow rate) is detected based on the output of the air flow meter 40. Next, in step 506, based on the detected VAF and the A / F sensor target voltage (that is, the stoichiometric air-fuel ratio equivalent voltage) VAFT (for example, 3.3 V), an operation of ΔVAF ← | VAF−VAFT | Output voltage VAF and target voltage VAF
A deviation (absolute value) ΔVAF from T is obtained.

Next, in step 508, the upper limit value QAH and the lower limit value QAL for determining the catalyst deterioration are determined in accordance with the difference ΔVAF by referring to the map shown in FIG. 13 based on ΔVAF. This map is stored in the ROM 73 in advance. As described above with respect to FIG. 3, the QAH curve represents the amount of intake air at which O ₂ storage reaches its limit in a normal catalyst, while the QAL curve represents the amount of intake air at which O ₂ storage appears in a deteriorated catalyst. When QAH is exceeded, it is erroneously determined that the catalyst is deteriorated even if it is actually a normal catalyst, and when it is lower than QAL, there is no catalyst deterioration even if it is actually a deteriorated catalyst. Is incorrectly determined. Therefore, in step 510, it is determined whether or not the intake air amount QA is within the deterioration determination execution region, that is, whether or not QAL ≦ QA ≦ QAH is satisfied. If the intake air amount condition is not satisfied, Ends this routine, and if it is satisfied, the routine proceeds to step 512.

In step 512, the VAF locus length LV
The AF is updated by the calculation of LVAF ← LVAF + | VAF−VAFO |. Next, at step 514, the trajectory length LVOS of the VOS is updated by an operation of LVOS ← LVOS + | VOS−VOSO |. Next, at step 516, VAFO ← VAF VOSO ← VOS is set for the next execution. In the calculation of the trajectory length LVAF of the A / F sensor, if the difference (amplitude) between the maximum value and the minimum value of the A / F sensor output instantaneously exceeds the threshold value, the integration of the trajectory lengths LVAF and LVOS is stopped. (The integrated value is held), and the integration may be restarted when the integrated value becomes equal to or less than the threshold value.

Next, at step 518, a counter CTIME for measuring the monitoring time is incremented. At step 520, the value of the counter is set to a predetermined value C.
_It is determined whether or not ₀ has been exceeded. When CTIME> C _0, the routine proceeds to step 522, and when CTIME ≦ C ₀ , this routine ends. In step 522, LVA
By referring to a map as shown in FIG. 14 based on the value of F, the deterioration determination reference value L corresponding to the value of LVAF is determined.
Determine _ref . In addition, this map is RO
It is stored in M73. As shown in the figure, this L _ref is a reference value that increases as LVAF increases.

[0050] Then, in step 524, O ₂ sensor output trajectory length LVOS determines whether the deterioration determination reference value L _ref more. When LVOS ≧ L _ref , it is considered that the catalyst has deteriorated, and the predetermined alarm flag ALMCC is set to 1
(Step 526) and the alarm lamp 6
8 (see FIG. 4) is turned on (step 528). LVO
When S <L _ref , it is considered that the catalyst has not deteriorated, and the alarm flag ALMCC is set to 0 (step 530). The alarm flag ALMCC is stored in the backup RAM 79 so that it can be collected at the time of repair (step 532). In the last step 534, CTIME, LVAF, LV
The OS is cleared.

Although the embodiments of the present invention have been described above, the present invention is of course not limited to these embodiments, and it will be easy for those skilled in the art to devise various embodiments.

[0052]

As described above, the O ₂ storage amount of the catalyst is affected by the exhaust gas flow rate and the displacement of the engine air-fuel ratio from the stoichiometric air-fuel ratio. Since the catalyst deterioration determination execution area for the intake air amount to be changed is changed based on the current air-fuel ratio displacement,
It is possible to achieve both improvement in diagnosis accuracy and increase in diagnosis opportunities in the catalyst deterioration diagnosis processing. That is, the present invention enhances exhaust gas purification performance and contributes to prevention of air pollution.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between an air-fuel ratio and an O ₂ sensor output voltage.

FIG. 2 is a characteristic diagram showing a relationship between an air-fuel ratio and an A / F sensor output voltage.

FIG. 3 is a characteristic diagram showing a relationship between an air-fuel ratio fluctuation width and an intake air amount at which the O ₂ storage capacity of a catalyst reaches a limit in a case of a normal catalyst (curve C1) and a case of a deteriorated catalyst (curve C2). .

FIG. 4 is an overall schematic diagram of an electronically controlled internal combustion engine including a catalyst deterioration determination device according to an embodiment of the present invention.

FIG. 5 is a block diagram showing a hardware configuration of an engine ECU according to one embodiment of the present invention.

FIG. 6 is a flowchart showing a processing procedure of an in-cylinder air amount estimation and a target in-cylinder fuel amount calculation routine.

FIG. 7 is a diagram for explaining a storage state of an estimated in-cylinder air amount and a calculated target in-cylinder fuel amount;

FIG. 8 is a flowchart showing a processing procedure of a main air-fuel ratio feedback control routine.

FIG. 9 is a flowchart showing a processing procedure of a sub air-fuel ratio feedback control routine.

FIG. 10 is a flowchart showing a processing procedure of a fuel injection control routine.

FIG. 11 is a flowchart (1/2) showing a processing procedure of a catalyst deterioration determination routine.

FIG. 12 is a flowchart (2/2) showing a processing procedure of a catalyst deterioration determination routine.

FIG. 13 shows A / F sensor output voltage VAF and target voltage VA.
FIG. 9 is a diagram showing a map for determining an upper limit value QAH and a lower limit value QAL for an intake air amount for catalyst deterioration determination in accordance with a deviation ΔVAF from FT.

14 is a diagram showing a map for determining the deterioration criteria for the O ₂ sensor output voltage trajectory length LVOS value L _ref in accordance with the A / F sensor output voltage trajectory length LVAF.

[Explanation of symbols]

2 ... Air cleaner 4 ... Throttle body 5 ... Throttle valve 6 ... Surge tank (intake manifold) 7 ... Intake pipe 8 ... Idle adjustment passage 10 ... Fuel tank 11 ... Fuel pump 12 ... Fuel pipe 20 ... Engine body (cylinder) 21 ... Combustion Chamber 22 ... Cooling water passage 23 ... Piston 24 ... Intake valve 26 ... Exhaust valve 30 ... Exhaust manifold 34 ... Exhaust pipe 38 ... Catalyst converter 40 ... Air flow meter 41 ... Vacuum sensor 42 ... Throttle opening degree sensor 43 ... Intake air temperature sensor 44 ... water temperature sensor 45 ... A / F sensor 46 ... O ₂ sensor 50 ... reference position sensor 51 ... crank angle sensor 52 ... idle switch 53 ... vehicle speed sensor 60 ... fuel injection valve 62 ... igniter 63 ... ignition coil 64 ... ignition distributor 65 ... Spark plug 66… A Dollar rotation speed control valve (ISCV) 68 alarm lamp 70 engine ECU 71 CPU 72 system bus 73 ROM 74 RAM 75 A / D conversion circuit 76 input interface circuit 77a, 77b, 77c, 77d drive Control circuit 79 ... Backup RAM

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F01N 3/08-3/38 F01N 9/00-11/00 F02D 41/00-41/40 F02D 43 / 00-45/00

Claims (1)

(57) [Claims] An upstream air-fuel ratio sensor provided upstream of an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine and having an output characteristic substantially proportional to an oxygen concentration in exhaust gas; A downstream air-fuel ratio sensor provided on the downstream side, air-fuel ratio feedback control means for performing feedback control so that an engine air-fuel ratio becomes a stoichiometric air-fuel ratio based on at least an output of the upstream air-fuel ratio sensor, and an engine intake air amount Intake air amount detecting means for detecting, during the execution of the air-fuel ratio feedback control, when the engine intake air amount is within a predetermined determination execution region,
Catalyst deterioration determining means for determining the presence or absence of deterioration of the exhaust purification catalyst based on at least the output of the downstream air-fuel ratio sensor; and a deviation between an output of the upstream air-fuel ratio sensor and a target output corresponding to a stoichiometric air-fuel ratio. And a region setting means for setting a determination execution region relating to the engine intake air amount in response thereto.