JP3334453B2 - Catalyst deterioration detection 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 a device (catalyst deterioration detecting device) for detecting 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, although the deterioration of the catalyst results in a decrease in the purification performance after warm-up, this device estimates that the decrease in the O ₂ storage effect is a decrease in the purification performance, and uses the output signal of the downstream O ₂ sensor. , The length of the trajectory, the feedback frequency, and the like, and the deterioration of the O ₂ storage effect is detected to detect the deterioration of the catalyst. For example, the apparatus disclosed in Japanese Patent Application Laid-Open No. 5-98946 is an apparatus that obtains the trajectory length of the output of the downstream O ₂ sensor during feedback control to the stoichiometric air-fuel ratio, and detects catalyst deterioration based on the trajectory length.

On the other hand, in recent years, there has been developed an internal combustion engine that controls an air-fuel ratio so that a 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 utilize the O ₂ storage capacity effectively, the amount of oxygen stored in the catalyst must be adjusted so that the air-fuel ratio of the exhaust gas may be either rich or lean next. Predetermined amount (for example, half of the maximum oxygen storage amount)
In this case, a constant O ₂ adsorption / desorption action is always possible, and as a result, a constant oxidation / reduction capacity of the catalyst 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 (A / F) sensor (see FIG. 2) capable of linearly detecting the air-fuel ratio is used, and feedback control (F / B control) by proportional and integral operations (PI operations) is performed. In other words, the next time fuel correction amount = K _p * (difference this time of fuel) + K _s * Σ
(Fuel difference so far) However, fuel difference = (fuel amount actually burned in the cylinder)-(target cylinder fuel amount with stoichiometric intake air) fuel amount actually burned = air amount The detection value / 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, as shown in FIG. 3, when a lean gas is generated due to sudden acceleration or the like, the action of the integral term generates a rich gas, thereby canceling the effect of the lean gas generation. Such control for intentionally changing the air-fuel ratio in order to keep the O ₂ storage amount constant is called counter control.

[0008]

In the above-described O ₂ storage amount constant control system, an O ₂ sensor may be provided on the downstream side of the catalyst in order to compensate for variations in the output characteristics of the A / F sensor. Therefore, also in this case,
As in the double O ₂ sensor system, it is conceivable to detect deterioration of the catalyst by detecting a decrease in the O ₂ storage effect of the catalyst with the O ₂ sensor.

However, in the O ₂ storage amount constant control system, the counter control is executed at any time as described above. At the time of the execution, as shown in FIG.
The / F sensor output voltage VAF, that is, the air-fuel ratio greatly fluctuates (the air-fuel ratio of the gas actually entering the catalyst is within the window, so that the emission does not become rough).
Moreover, the sub feedback by O ₂ sensors, O ₂
Since the sensor output is controlled so as to be in the vicinity of stoichiometry (see FIG. 1), as shown in FIG. 4B, the output voltage VOS of the O ₂ sensor greatly changes with the air-fuel ratio fluctuation. Become. In addition, an over-response is caused by a sudden change in gas permeation to the O ₂ sensor. Therefore, when catalyst deterioration is determined based on the trajectory length of the O ₂ sensor output, an erroneous determination may be made.

In view of such circumstances, an object of the present invention is to provide an A /
It is an object of the present invention to establish a method for accurately executing catalyst deterioration determination by a catalyst downstream O ₂ sensor in an internal combustion engine of an O ₂ storage constant control system using an F sensor. Accordingly, an object of the present invention is to improve exhaust gas purification performance and contribute to prevention of air pollution.

[0011]

A first aspect of the present invention, which is devised to achieve the above object, is a catalyst deterioration determining apparatus for an internal combustion engine, which is provided in an exhaust passage of the internal combustion engine.
₍₂₎ a three-way catalyst having a storage capacity, an air-fuel ratio sensor provided upstream of the three-way catalyst and linearly detecting an air-fuel ratio, and, based on an output of the air-fuel ratio sensor, converting the air-fuel ratio to a stoichiometric air-fuel ratio. Air-fuel ratio feedback control means for calculating a feedback correction amount including a proportional term for convergence and an integral term for converging an air-fuel ratio deviation between the stoichiometric air-fuel ratio to zero, and a downstream side of the three-way catalyst An O ₂ sensor that detects whether the air-fuel ratio is rich or lean, and the ternary based on the trajectory length of the output of the O ₂ sensor during the air-fuel ratio feedback control by the air-fuel ratio feedback control means. A catalyst deterioration determining means for determining catalyst deterioration; and a performance of a trajectory length by the catalyst deterioration determining means for a predetermined period when an output of the air-fuel ratio sensor or a change amount of the output exceeds a set value. The locus length computing interruption means allowed to suspend comprises a.

According to a second aspect of the present invention, there is provided an apparatus for determining catalyst deterioration in an internal combustion engine, comprising:
₍₂₎ a three-way catalyst having a storage capacity, an air-fuel ratio sensor provided upstream of the three-way catalyst and linearly detecting an air-fuel ratio, and, based on an output of the air-fuel ratio sensor, converting the air-fuel ratio to a stoichiometric air-fuel ratio. Air-fuel ratio feedback control means for calculating a feedback correction amount including a proportional term for convergence and an integral term for converging an air-fuel ratio deviation between the stoichiometric air-fuel ratio to zero, and a downstream side of the three-way catalyst An O ₂ sensor that detects whether the air-fuel ratio is rich or lean, and the ternary based on the trajectory length of the output of the O ₂ sensor during the air-fuel ratio feedback control by the air-fuel ratio feedback control means. a catalyst deterioration determining means for determining deterioration of the catalyst, the during the determination processing by the catalyst deterioration determining means, integral term system for setting an upper limit to the absolute value or the gain of the integral term of the integral term Comprising a means, a.

According to a third aspect of the present invention, there is provided a catalyst deterioration determining device for an internal combustion engine, comprising:
₍₂₎ a three-way catalyst having a storage capacity, an air-fuel ratio sensor provided upstream of the three-way catalyst and linearly detecting an air-fuel ratio, and, based on an output of the air-fuel ratio sensor, converting the air-fuel ratio to a stoichiometric air-fuel ratio. First air-fuel ratio feedback control means for calculating a feedback correction amount including a proportional term for converging and an integral term for converging an integral value of a deviation between an air-fuel ratio and a stoichiometric air-fuel ratio to zero; An O ₂ sensor that is provided downstream of and detects whether the air-fuel ratio is rich or lean, and a second air-fuel ratio feedback control unit that corrects the output of the air-fuel ratio sensor based on the output of the O ₂ sensor. Catalyst deterioration determining means for determining deterioration of the three-way catalyst based on the length of the trajectory of the output of the O ₂ sensor during a period during the air-fuel ratio feedback control by the first air-fuel ratio feedback control means And an air-fuel ratio sensor output correction suppression unit that suppresses the output correction of the air-fuel ratio sensor by the second air-fuel ratio feedback control unit during the determination process by the catalyst deterioration determination unit.

[0014]

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

FIG. 5 is an overall schematic diagram of an electronically controlled internal combustion engine provided with a catalyst deterioration detecting device according to one embodiment of the present invention. The air required for combustion of the engine 20 is filtered by the air cleaner 2, passes through the throttle body 4, and is distributed to the intake pipe 7 of each cylinder by the surge tank (intake manifold) 6. 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. Also,
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 20 is cooled by cooling water guided to the cooling water passage 22, and the temperature of the cooling water is detected by a water temperature sensor 44.

The burned air-fuel mixture is discharged as an exhaust gas through an exhaust valve 26 to an exhaust manifold 30 and then guided to an 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 a sub air-fuel ratio feedback control in order to compensate for variations in the output characteristics of the engine, and an O ₂ sensor 46 is provided in an exhaust system downstream of the catalytic converter 38.

Engine electronic control unit (engine EC
U) 70 is a microcomputer system that executes catalyst deterioration detection according to the present invention in addition to fuel injection control, ignition timing control, idle speed control, and the like, and its hardware configuration is shown in the block diagram of FIG. It is. A central processing unit (CPU) 71 according to a program and various maps stored in a read only memory (ROM) 73.
Inputs signals from various sensors and switches via an A / D conversion circuit 75 or an input interface circuit 76, executes arithmetic processing based on the input signals, and drives control circuits 77a to 77d based on the arithmetic results. And outputs control signals for various actuators via the. The random access memory (RAM) 74 is used as a temporary data storage place in the operation / control processing. The backup RAM 79 is provided with a battery (not shown).
Is directly connected to the power supply, and 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.

The engine control process of the ECU 70 executed in the internal combustion engine having the above-described 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 the other sensors. The engine condition is comprehensively determined, the optimum ignition timing is determined, and the drive control circuit 77b is controlled. The ignition signal is sent to the igniter 62 through the igniter 62.

In the idle speed control, the 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.

Hereinafter, detection of catalyst deterioration according to the present invention will be described in detail together with fuel injection control. As described above, the present invention intends to execute the catalyst deterioration determination by the catalyst downstream O ₂ sensor in the O ₂ storage amount constant control system using the A / F sensor while preventing the erroneous determination accompanying the counter control. It is. Hereinafter, three embodiments will be described.

First, a first embodiment according to the first invention will be described. In the first embodiment, as shown in FIG. 7, the output absolute value of the A / F sensor 45 exceeds the limit value (upper limit a, lower limit b) at which the O ₂ sensor 46 responds excessively. In this case, taking into account the distance between the two sensors (the delay time from when the gas reaches the O ₂ sensor from the A / F sensor), the data (output VOS of the O ₂ sensor 46) for determining the catalyst deterioration for a certain period of time is obtained This is to interrupt the accumulation.

FIG. 8 is a flowchart showing the processing procedure of the in-cylinder air amount estimation and target in-cylinder fuel amount calculation routine according to the first embodiment. 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) times MC _i and FCR _i are (i +
1) The previous MC _{i + 1} and FCR _{i + 1} are set (step 1)
02). This is because, as shown in FIG. 9, and stores the data of past n times of the in-cylinder air amount MC _i and target cylinder fuel amount FCR _i in RAM 74, new MC ₀ and FCR time
_{This is} for calculating ₀ .

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, the engine rotation speed NE, and the 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 74 as the latest data obtained this time, as shown in FIG.

FIG. 10 is a flowchart showing a processing procedure of a main air-fuel ratio feedback control routine according to the first embodiment. This routine is executed at a predetermined time period. 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, during engine start, during start-up increase,
During an increase in warm-up, when there is no change in the output signal of the A / F sensor 45, during fuel cut, etc., the feedback condition is not satisfied, and in other cases, the condition is satisfied. When the condition is not satisfied, the fuel correction amount DF by the feedback control is set to 0 (step 220), and this routine ends.

When the feedback condition is satisfied, the fuel amount difference (difference between the actually burned fuel amount and the target in-cylinder fuel amount) F obtained by the previous running of this routine F
Update _Di. That is, the i-th (i = 0, 1,..., M
-1) times the previous FD _i (i + 1) th time and before the FD _{i + 1} (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). Next, the current air-fuel ratio ABF is determined by referring to the characteristic diagram of FIG. 2 based on the corrected VAF (step 210). The characteristic diagram of FIG. 2 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.
_{Based on n} and the target in-cylinder fuel amount FCR _n (see FIG. 9), the difference between the actually burned fuel amount and the target in-cylinder fuel amount is obtained by the calculation FD ₀ ← MC _n / ABF-FCR _n (Step 212). In addition,
The reason why the adopting n times before the cylinder air amount MC _n and target cylinder fuel amount FCR _n is because in consideration of the time difference between the actual combustion fuel ratio which is detected by the current A / F sensor is there. In other words, the in-cylinder air amount M for the past n times
It is because of such a time difference that C _i and the target in-cylinder fuel amount FCR _i need to be stored.

Next, the proportional term of the proportional-integral control (PI control) is calculated by an operation of DFP ← K _fp * FD ₀ (step 214). Note that K _fp is a proportional term gain. Next, an integral term of PI control is calculated by an operation of DFS ← K _fs * ΣFD _i (step 216). Note that K _fs is an integral term gain. Finally, the fuel correction amount DF by the main air-fuel ratio feedback control is determined by the calculation of DF ← DFP + DFS (step 218).

FIG. 11 is a flowchart showing the processing procedure of the sub air-fuel ratio feedback control routine according to the first embodiment. 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 condition is not satisfied, the A / F sensor output voltage correction amount DV
Is set to 0 (step 312), and this routine ends.

When the feedback condition is satisfied, the voltage difference (target O)
The difference between the actually detected O ₂ sensor output voltage and the _second sensor output voltage) to update the VD _i. That is, the i-th (i =
0,1, ..., p-1) times the previous VD _i (i + 1) th time and 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, based on the VOS and the target O ₂ sensor output voltage VT (for example, 0.5 V), the latest voltage difference VD ₀ is obtained by executing the calculation of VD ₀ ← VT−VOS (step 308).

[0039] 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. The correction amount DV thus obtained is used for compensating for variations in the output characteristics of the A / F sensor in the main air-fuel ratio feedback control routine, as described above.

FIG. 12 is a flowchart showing a processing procedure of a fuel injection control routine according to the first embodiment. 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. 13 and 14 are flowcharts showing the processing procedure of the catalyst deterioration detection routine according to the first embodiment. This routine is executed at a predetermined time period. First, it is detected whether or not the output voltage VAF of the A / F sensor 45 is equal to or higher than the upper limit value a or equal to or lower than the lower limit value b (step 502). When VAF ≧ a or VAF ≦ b,
A predetermined value A is set in a predetermined monitor disable counter CMDIS (step 504), and this routine ends.

If a <VAF <b, it is determined whether the content of the monitor disable counter CMDIS is positive (step 506). If CMDIS> 0, the process proceeds to step 508, and if CMDIS ≦ 0, Step 5
Proceed to 12. At step 508, CMDIS is decremented. At next step 510, it is determined whether or not CMDIS is 0. If not, this routine is terminated.
If it is 0, the process proceeds to step 512. In step 512, it is determined whether or not a monitor condition for deterioration determination is satisfied. If the monitor condition is not satisfied, the present routine ends, and if the monitor condition is satisfied, the process proceeds to step 514 and subsequent steps.

In step 514, the trajectory length LVAF of the output VAF of the A / F sensor 45 is calculated by the following formula: LVAF ← LVAF + | VAF−VAFO | In the next step 516, VAFO ← VAF is set in preparation for the next execution.

In step 518, the trajectory length LVOS of the output VOS of the O ₂ sensor 46 is calculated by the following equation: LVOS ← LVOS + | VOS−VOSO |. In the next step 520, VOSO ← VOS is set in preparation for the next execution.

[0045] Next, incrementing a predetermined counter CTIME (step 522), determines whether or not exceeded the predetermined value C ₀ (step 524). CTIME> C
When it is _0, the process proceeds to step 526, and CTIME ≦ C ₀
In this case, this routine ends. In step 526, to determine the more deterioration determination reference value L _ref LVAF. It should be noted that the deterioration criterion value L _ref is A / F when the catalyst deterioration judgment is performed based on the trajectory length LVOS of the output VOS of the O ₂ sensor 46 for discriminating between a normal product and a deteriorated product. The path length LVA of the output VAF of the sensor 45
F, the determination reference value is set to LVAF
Is determined in accordance with
73. Next, at step 528,
Trajectory length LVOS of the output VOS of the O ₂ sensor 46 determines whether the deterioration determination reference value L _ref more. LVOS ≧
In the case of L _ref , it is considered that the catalyst has deteriorated, and the predetermined alarm flag ALM is set to 1 (step 53).
0), the alarm lamp 68 (see FIGS. 5 and 6) is turned on (step 532). LVOS <when L _ref is regarded as no catalyst deterioration, the alarm flag ALM is set to 0 (step 534). The alarm flag ALM is stored in the backup RAM 79 so that it can be collected at the time of repair and inspection (step 536). Finally, CTIME, LVAF, and LVOS are cleared in preparation for the next catalyst deterioration determination (step 538).

According to the first embodiment, the section where the output variation of the O ₂ sensor is large is masked, and the accuracy of the catalyst deterioration diagnosis is improved. In the first embodiment, masking is performed when the output voltage VAF of the A / F sensor 45 is equal to or more than the upper limit value a or equal to or less than the lower limit value b. As a modification, the absolute value | ΔVAF of the amount of change in VAF is used. | May be obtained and masked when the value exceeds a predetermined value.

Next, a second embodiment according to the second invention will be described. In the first embodiment, the specific section and the trajectory length calculation are masked on the side of the catalyst determination processing. On the other hand, the second embodiment restricts the counter control when determining the catalyst deterioration. That is, by providing an upper limit to the absolute value of the integral term in the fuel correction amount, O ₂
The return of the sensor output to the stoichiometric state is made gentle as shown in FIG. 15 to prevent over-response.

In the second embodiment, the in-cylinder air amount estimation and target in-cylinder fuel amount calculation routine, the sub air-fuel ratio feedback control routine, and the fuel injection control routine are the same as those in the first embodiment. The catalyst deterioration determination routine and the main air-fuel ratio feedback control routine are the first routine.
Modifications are made to the embodiment.

FIGS. 16 and 17 are flowcharts showing the processing procedure of the catalyst deterioration detection routine according to the second embodiment. Explaining only the differences from FIGS. 13 and 14 according to the first embodiment, first, steps 502 to 510 of the condition determination regarding the A / F sensor output voltage are deleted. Steps 604 and 606 are added after step 602 for determining the monitoring condition. That is, when the monitor condition is not satisfied, the monitor execution flag MONEX is set to 0, and when the monitor condition is satisfied, MONEX is set to 1. Steps 608 to 630 are the same as steps 514 to 536 of the first embodiment. In step 632, processing for clearing the monex is added to step 538. Thus, in the second embodiment, the VAF
Is determined, the monitoring execution flag MONEX is set to 1 during execution.

FIG. 18 is a flowchart showing a processing procedure of a main air-fuel ratio feedback control routine according to the second embodiment. Explaining only the differences from FIG. 10 according to the first embodiment, the only difference is that steps 718 and 720 are added. That is, after the integral term DFS of the fuel correction amount DF is calculated in step 716,
If the catalyst deterioration determination is being executed (MONEX = 1), the absolute value | DFS | of the integral term is limited to a predetermined value B or less.

By doing so, the fluctuation of the air-fuel ratio is suppressed, the output of the O ₂ sensor returns to the stoichiometric mode slowly, and there is no over-response, and the diagnostic accuracy is improved. In addition,
As a modified example of the second embodiment, the gain K _fs of the integral term DFS is
May be reduced during execution of the catalyst deterioration determination.

Finally, a third embodiment according to the third invention will be described. In the third embodiment, the output correction of the A / F sensor 45 based on the output of the O ₂ sensor 46 is suppressed during the execution of the catalyst deterioration determination, as in the second embodiment.
The return of the O ₂ sensor output to the stoichiometric state is made gentle to prevent an over-response. In the third embodiment, the in-cylinder air amount estimation and target in-cylinder fuel amount calculation routines are the same as in the first and second embodiments, the main air-fuel ratio feedback control routine is the same as in the first embodiment, and the fuel injection control routine is The same as in the first and second embodiments, the catalyst deterioration determination routine is the same as in the second embodiment, and only the sub air-fuel ratio feedback control routine is modified.

FIG. 19 is a flowchart showing a processing procedure of a sub air-fuel ratio feedback control routine according to the third embodiment. Explaining only the differences from FIG. 11 according to the first embodiment, the only difference is that step 804 is added. That is, the catalyst deterioration determination is being executed (MONEX = 1)
If so, the A / F sensor output voltage correction amount DV is set to 0, and no correction is made to the output voltage VAF of the A / F sensor 45. By doing so, the output of the O ₂ sensor returns to the stoichiometric state slowly, and there is no over-response, and the diagnostic accuracy is improved.

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

[0055]

As described above, according to the present invention,
In O ₂ storage amount constant control system using an A / F sensor, it is prevented erroneous determination due to counter control, so that the catalyst deterioration determination by the catalyst downstream O ₂ sensor is performed.

[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 diagram for explaining counter control.

FIG. 4A is a time chart illustrating an A / F sensor output voltage VAF, and FIG. 4B is a time chart illustrating an O ₂ sensor output voltage VOS responding to the VAF.

FIG. 5 is an overall schematic diagram of an electronically controlled internal combustion engine including a catalyst deterioration detection device according to one embodiment of the present invention.

FIG. 6 is a block diagram illustrating a hardware configuration of an engine ECU according to one embodiment of the present invention.

FIG. 7 is a diagram for explaining the principle of the first embodiment.

FIG. 8 is a flowchart showing a processing procedure of a cylinder air amount estimation and target cylinder fuel amount calculation routine according to the first embodiment.

FIG. 9 is a diagram for explaining a storage state of an estimated in-cylinder air amount and a calculated target in-cylinder fuel amount.

FIG. 10 is a flowchart showing a processing procedure of a main air-fuel ratio feedback control routine according to the first embodiment.

FIG. 11 is a flowchart illustrating a processing procedure of a sub air-fuel ratio feedback control routine according to the first embodiment.

FIG. 12 is a flowchart illustrating a processing procedure of a fuel injection control routine according to the first embodiment.

FIG. 13 is a flowchart (1/2) showing a processing procedure of a catalyst deterioration detection routine according to the first embodiment.

FIG. 14 is a flowchart (2/2) showing a processing procedure of a catalyst deterioration detection routine according to the first embodiment.

FIG. 15 is a diagram for explaining the principle of the second embodiment.

FIG. 16 is a flowchart (1/2) showing a processing procedure of a catalyst deterioration detection routine according to the second embodiment.

FIG. 17 is a flowchart (2/2) showing a processing procedure of a catalyst deterioration detection routine according to the second embodiment.

FIG. 18 is a flowchart illustrating a processing procedure of a main air-fuel ratio feedback control routine according to the second embodiment.

FIG. 19 is a flowchart illustrating a processing procedure of a sub air-fuel ratio feedback control routine according to a third embodiment.

[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

Claims (4)

(57) [Claims] 1. A provided in an exhaust passage of an internal combustion engine, O ₂
A three-way catalyst having a storage capacity, and an air-fuel ratio provided upstream of the three-way catalyst for linearly detecting the air-fuel ratio.
And air-fuel ratio sensor output, based on the output of the air-fuel ratio sensor, the theoretical air-fuel fuel ratio
Proportional term to converge to the ratio and the stoichiometric air-fuel ratio
Consisting of an integral term for converging the integral of the deviation of to zero
Air-fuel ratio feedback to calculate feedback correction amount
A control means provided downstream of the three-way catalyst for controlling whether the air-fuel ratio is rich or not.
And O ₂ sensor for detecting whether over emissions, the air-fuel ratio fee by the air-fuel ratio feedback control means
Of the output of the O ₂ sensor during the period during the feedback control.
A catalyst deterioration judgment for judging deterioration of the three-way catalyst based on a trace length
Determining means and the output of the air-fuel ratio sensor or the amount of change in the output correspond to a set value.
If it exceeds, the gauge is determined by the catalyst deterioration determining means for a predetermined period.
Comprising a locus length computing interruption means allowed to interrupt the operation of the mark length, a, the predetermined period of operation is interrupted in the locus length by the locus length computing interruption means, between the O ₂ sensor and the air-fuel ratio sensor A catalyst deterioration detection device for an internal combustion engine, which is determined in consideration of the distance of the engine. Wherein disposed in an exhaust passage of an internal combustion engine, O ₂
A three-way catalyst having a storage capacity, and an air-fuel ratio provided upstream of the three-way catalyst for linearly detecting the air-fuel ratio.
And air-fuel ratio sensor output, based on the output of the air-fuel ratio sensor, the theoretical air-fuel fuel ratio
Proportional term to converge to the ratio and the stoichiometric air-fuel ratio
Consisting of an integral term for converging the integral of the deviation of to zero
Air-fuel ratio feedback to calculate feedback correction amount
A control means provided downstream of the three-way catalyst for controlling whether the air-fuel ratio is rich or not.
And O ₂ sensor for detecting whether over emissions, the air-fuel ratio fee by the air-fuel ratio feedback control means
Of the output of the O ₂ sensor during the period during the feedback control.
A catalyst deterioration judgment for judging deterioration of the three-way catalyst based on a trace length
Determining means and the output of the air-fuel ratio sensor or the amount of change in the output correspond to a set value.
If it exceeds, the gauge is determined by the catalyst deterioration determining means for a predetermined period.
Comprising a locus length computing interruption means allowed to interrupt the operation of the mark length, a, the set value for the change in the output or the output of the air-fuel ratio sensor is determined the O ₂ sensor as a limit value such that excessive response A device for detecting catalyst deterioration of an internal combustion engine. Wherein disposed in an exhaust passage of an internal combustion engine, O ₂
A three-way catalyst having a storage capacity; an air-fuel ratio sensor provided upstream of the three-way catalyst and detecting an air-fuel ratio linearly; converging the air-fuel ratio to a stoichiometric air-fuel ratio based on an output of the air-fuel ratio sensor A first air-fuel ratio feedback control means for calculating a feedback correction amount comprising a proportional term for causing the air-fuel ratio and an integral value of a deviation between the stoichiometric air-fuel ratio and the stoichiometric air-fuel ratio to converge to zero; An O ₂ sensor that is provided on the downstream side and detects whether the air-fuel ratio is rich or lean; a second air-fuel ratio feedback control unit that corrects the output of the air-fuel ratio sensor based on the output of the O ₂ sensor; determining catalyst deterioration determining the O ₂ degradation of the three-way catalyst based on the trajectory length of the output of the sensor in a period of the air-fuel ratio feedback control by the first air-fuel ratio feedback control means And the step, during the determination process by the catalyst deterioration determining means, the second
A catalyst deterioration detection device for an internal combustion engine, comprising: an air-fuel ratio sensor output correction suppression unit that suppresses an air-fuel ratio sensor output correction by the air-fuel ratio feedback control unit. Wherein said air-fuel ratio sensor output correction inhibiting means,
The catalyst deterioration detection device for an internal combustion engine according to claim 3, wherein the output correction value is set to 0 when suppressing the output correction of the air-fuel ratio sensor.