JPH08284648A - Catalyst deterioration diagnosing device for internal combustion engine - Google Patents

Abstract

PURPOSE: To detect reduction of low temperature activator of a catalyst by an O2 sensor arranged downstream from the catalyst, and diagnose deterioration of the catalyst on the basis thereof. CONSTITUTION: When a catalyst 38 is deteriorated, the low temperature activity (activated temperature) thereof is reduced. As a result, rising start of a catalyst outlet gas temperature is delayed, and warming-up of a O2 sensor 46 arranged downstream from the catalyst 38 is also delayed, and finally, activator (rising start) of output of the O2 sensor 46 is delayed. The activating period of the O2 sensor 46 is measured, and it is judged that the catalyst 38 is deteriorated when the measured value is larger than a prescribed referential value. Deterioration of the catalyst 38 is correctly diagnosed regardless of change of an operating condition while taking a factor which is influenced by warming-up of the O2 sensor 46 in consideration.

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 diagnosis device) for diagnosing the degree of deterioration of a catalyst provided in an exhaust passage of an internal combustion engine (engine) to purify exhaust gas.

[0002]

2. Description of the Related Art Conventionally, in an engine for an automobile, as a measure for purifying exhaust gas, there have been three measures for simultaneously promoting the oxidation of unburned components (HC, CO) and the reduction of nitrogen oxides (NO _x ) in the exhaust gas. The original catalyst is used. In order to enhance the oxidation / reduction ability of such a three-way catalyst, it is necessary to control the air-fuel ratio (A / F), which indicates the combustion state of the engine, to near the stoichiometric air-fuel ratio. Therefore, in fuel injection control in the engine, an O ₂ sensor (oxygen concentration sensor) that detects the air-fuel ratio based on the residual oxygen concentration in the exhaust gas
Etc., an air-fuel ratio sensor is provided, and air-fuel ratio feedback control is performed to correct the fuel amount based on the sensor output.

In such air-fuel ratio feedback control, an O ₂ sensor for detecting the oxygen concentration is provided at a position as close to the combustion chamber as possible, that is, upstream of the catalytic converter. In recent years, however, the output characteristics of the O ₂ sensor have been changed. A double O ₂ sensor system has also been implemented in which a second O ₂ sensor is further provided downstream of the catalytic converter to compensate for variations. 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 downstream O ₂
The output of the sensor changes more slowly than the upstream O ₂ sensor, and therefore shows a rich / lean tendency of the entire mixture. The double O ₂ sensor system carries out sub air-fuel ratio feedback control by the catalyst downstream O ₂ sensor, in addition to main air-fuel ratio feedback control by the catalyst upstream O ₂ sensor, and performs 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 accuracy of air-fuel ratio control is improved.

Even if the above-mentioned precise air-fuel ratio control is carried out, sufficient exhaust gas purification performance cannot be obtained if the catalyst deteriorates due to the heat of exhaust gas or poisoning of lead or the like. . Therefore, various catalyst deterioration diagnosing devices have been conventionally proposed. The apparatus according to the first conventional example detects the decrease in the O ₂ storage effect (the function of holding excess oxygen and utilizing it for purification of unburned exhaust gas) after warm-up by the catalyst downstream O ₂ sensor. , To diagnose the deterioration of the catalyst. That is, the deterioration of the catalyst results in the deterioration of the purification performance after warming up, but this device estimates that the deterioration of the O ₂ storage effect is the deterioration of the purification performance and uses the output signal of the downstream O ₂ sensor. The deterioration of the catalyst is diagnosed by detecting the feedback frequency, the locus ratio, etc., and the deterioration of the O ₂ storage effect is detected (for example, see Japanese Patent Laid-Open No. Hei5-263686).

Further, the catalyst deterioration diagnosing device according to the second conventional example is for diagnosing the catalyst deterioration by detecting the catalyst temperature by a temperature sensor and comparing the catalyst temperature with a judgment reference value. That is, catalyst deterioration results in a decrease in low-temperature activity, but this device diagnoses catalyst deterioration when the catalyst temperature falls below a predetermined value determined by operating conditions (for example, Japanese Patent Laid-Open No. 2- 27109 gazette).

[0006]

However, these catalyst deterioration diagnosing apparatuses according to the prior arts do not always guarantee accurate diagnosis. First, in the device according to the first conventional example described above, it is estimated that the reduction of the O ₂ storage effect results in the reduction of the purification performance, but the O ₂ storage amount of the catalyst and the purification performance do not have a one-to-one correspondence. There are cases. That is, even if the O ₂ storage amount is large, the purification performance is poor due to catalyst poisoning by lead, oil, or the like, or conversely, the O ₂ storage amount is small but the purification performance is not deteriorated (emission is deteriorated. In some cases, the deterioration of the catalyst cannot be uniquely diagnosed only by the O ₂ storage effect.

Further, in the catalyst deterioration diagnosing device according to the second conventional example described above, the catalyst temperature or the catalyst discharge gas temperature is measured by the temperature sensor. Therefore, accurate temperature may be measured, and accurate diagnosis may not be performed. In addition, in the exhaust system, the temperature sensor may have a high temperature of about 800 ° C. in some cases, and therefore, the temperature sensor is required to have reliability that can withstand high temperature conditions. However, a temperature sensor with high accuracy has not been developed yet. Furthermore, it goes without saying that there are cost disadvantages.

As can be seen from the above description, the deterioration of the catalyst is represented by a decrease in low temperature activity and a decrease in purification performance after warming up. Conventionally, the catalyst downstream O ₂ sensor has been utilized to detect a decrease in the O ₂ storage effect to detect the purification performance degradation after warm-up, by the catalytic downstream O ₂ sensor, the low-temperature activity If a decrease can be detected, a more accurate diagnosis will be possible without incurring an increase in cost, in combination with the conventional diagnosis based on the decrease in the O ₂ storage effect after warming up.

In view of the above situation, an object of the present invention is to provide a catalyst deterioration diagnosing device which detects a decrease in low temperature activity by a catalyst downstream O ₂ sensor and diagnoses catalyst deterioration based on the decrease, thereby warming up the catalyst. The deterioration of the catalyst can be diagnosed more accurately by combining with a conventional diagnostic device based on the subsequent reduction of the O ₂ storage effect, thereby improving the exhaust gas purification performance of the internal combustion engine and eventually preventing air pollution. To contribute.

[0010]

The present invention is described below based on the basic idea that a decrease in the low temperature activity of the catalyst can be detected based on the delay in the rise of the catalyst downstream O ₂ sensor. The above object is achieved by adopting such a technical configuration.

That is, the catalyst deterioration diagnosing device for an internal combustion engine according to the first aspect of the present invention includes a downstream side air-fuel ratio sensor provided in an exhaust passage downstream of a catalyst for purifying exhaust gas of the internal combustion engine, and the internal combustion engine. Period measurement means for measuring the period from the cold start of the engine until the downstream side air-fuel ratio sensor is activated, and the catalyst when the period measured by the period measurement means is larger than a predetermined reference value. Deterioration determining means for determining deterioration.

A catalyst deterioration diagnosing device for an internal combustion engine according to a second aspect of the present invention includes a downstream air-fuel ratio sensor provided in an exhaust passage downstream of a catalyst for purifying exhaust gas of the internal combustion engine, and the internal combustion engine. From the cold start of the engine, the count-up value according to one or more factors affecting the warm-up of the downstream side air-fuel ratio sensor is integrated in a predetermined cycle, and the downstream side air-fuel ratio sensor is Warm-up factor integrating means for obtaining an integrated value at the time of activation, and deterioration determining means for determining that the catalyst has deteriorated when the integrated value obtained by the warm-up factor integrating means is larger than a predetermined reference value. , Are provided.

[0013]

When the catalyst deteriorates, its low temperature activity decreases.
If that happens, the rise of the catalyst outlet gas temperature will be delayed,
As a result, the warm-up of the air-fuel ratio sensor downstream of the catalyst is also delayed, and finally the activation (rise) of the output of the catalyst downstream-side air-fuel ratio sensor is delayed. In the catalyst deterioration diagnosis device according to the first aspect of the present invention configured as described above, the activation period of such a downstream side air-fuel ratio sensor is measured, and the catalyst is detected when the measured value is larger than a predetermined reference value. Is determined to have deteriorated.

Further, in the catalyst deterioration diagnosing device according to the second aspect of the present invention, since the factor affecting the warming-up of the downstream side air-fuel ratio sensor is further taken into consideration, a more accurate irrespective of the change of the operating state is achieved. A catalyst deterioration diagnosis will be made.

[0015]

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

FIG. 1 is an overall schematic view of an electronically controlled internal combustion engine equipped with a catalyst deterioration diagnosing device according to an embodiment of the present invention. Air required for combustion in 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 at the surge tank (intake manifold) 6. The intake air flow rate is adjusted by the throttle valve 5 provided on the throttle body 4 and measured by the air flow meter 40. Also,
The intake air temperature is detected by the intake air temperature sensor 43.
Further, the intake pipe pressure is detected by the vacuum sensor 41.

The opening of the throttle valve 5 is detected by the throttle opening sensor 42. When the throttle valve 5 is fully closed, the idle switch 52 is turned on, and the output of the throttle fully closed signal is active. In addition, an idle speed control valve (ISCV) 66 for adjusting the air flow rate during idling is provided in the idle adjust 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 the fuel pipe 12
Then, the fuel 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 the combustion chamber 21 of the engine body, that is, the cylinder 20 via the intake valve 24. In the combustion chamber 21, the air-fuel mixture is compressed by the piston and then ignited to explode and burn to generate power. In such ignition, 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. Made by.

The ignition distributor 64 includes:
Its axis is, for example, 720 ° converted to crank angle (CA)
A reference position detection sensor 50 that generates a reference position detection pulse for each CA and a crank angle sensor 51 that generates a position detection pulse for each 30 ° CA are provided. 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 the cooling water guided to the cooling water passage 22, and the temperature of the cooling water is detected by the water temperature sensor 44.

The combusted air-fuel mixture is discharged as exhaust gas to the exhaust manifold 30 via the exhaust valve 26, and is then guided to the exhaust pipe 34. The exhaust pipe 34 is provided with a first O ₂ sensor (catalyst upstream O ₂ sensor) 45 for detecting the oxygen concentration in the exhaust gas. Further, a catalytic converter 38 is provided in the exhaust system downstream thereof, and the catalytic converter 38 oxidizes unburned components (HC, CO) and reduces nitrogen oxides (NO _x ) in the exhaust gas. A three-way catalyst that simultaneously promotes and is housed. The exhaust gas thus purified by the catalytic converter 38 is discharged into the atmosphere.

This engine is a so-called double O engine.
_{The two-} sensor system is an engine that performs air-fuel ratio feedback control, and a second O ₂ sensor (catalyst downstream side O ₂ sensor) 46 is provided in the exhaust system downstream of the catalytic converter 38.

Engine electronic control unit (engine EC
U) 70 is a microcomputer system that executes fuel injection control, ignition timing control, idle speed control, etc., and its hardware configuration is shown in the block diagram of FIG. The central processing unit (CPU) 71 inputs signals from various sensors and switches through the A / D conversion circuit 75 or the input interface circuit 76 according to the programs stored in the read-only memory (ROM) 73 and various maps. Then, the arithmetic processing is executed based on the input signal, and the drive control circuits 77a ...
Control signals for various actuators are output via 77c. The random access memory (RAM) 74 is used as a temporary data storage location in the arithmetic / control processing process. Further, the backup RAM 79 is supplied with power by being directly connected to a battery (not shown), and stores data (for example, various learning values) to be held even when the ignition switch is off. Used for. Further, each component in these ECUs is connected by a system bus 72 including an address bus, a data bus, and a control bus.

The engine control processing of the ECU 70 executed in the internal combustion engine (engine) having the above hardware structure will be described below. Basically, the fuel injection control is performed based on the intake air amount per engine revolution calculated from the intake air flow rate measured by the air flow meter 40 and the engine rotation speed obtained from the crank angle sensor 51. A fuel injection amount that achieves an air-fuel ratio, that is, an injection time by the fuel injection valve 60 is calculated, and the fuel injection valve 60 is controlled via the drive control circuit 77a so as to inject fuel when a predetermined crank angle is reached. Is. The intake air amount per engine revolution may be estimated from the intake pipe pressure obtained from the vacuum sensor 41 and the engine rotation speed. When the fuel injection amount is calculated, basic correction based on signals from the throttle opening sensor 42, the intake air temperature sensor 43, the water temperature sensor 44, and the like, the O ₂ sensor 4 is performed.
Air-fuel ratio feedback correction based on signals from 5, and 46, and air-fuel ratio learning correction for making the median of the feedback correction values the theoretical air-fuel ratio are added.

In the ignition timing control, the engine state is comprehensively determined by the engine speed obtained from the crank angle sensor 51 and signals from other sensors.
The optimum ignition timing is determined and an ignition signal is sent to the igniter 62 via the drive control circuit 77b.

In the idle speed control, the idle state is detected by the throttle fully closed signal from the idle switch 52 and the vehicle speed signal from the vehicle speed sensor 53, and a target determined by the engine cooling water temperature from the water temperature sensor 44 and the like. The rotation speed is compared with the actual engine rotation speed, the control amount is determined according to the difference so that the target rotation speed is obtained, and the ISC is passed through the drive control circuit 77c.
By controlling V66 and adjusting the air amount, the optimum idle rotation speed is maintained.

The catalyst deterioration diagnosis according to the present invention will be described in detail below. First, a first embodiment according to the first invention will be described. In the first aspect of the invention, as described above, when the catalyst deteriorates, the activation (rise) of the output of the catalyst downstream side air-fuel ratio sensor is finally delayed, so that the downstream side air-fuel ratio from the cold start of the internal combustion engine. The period until the sensor is activated is measured, and when the measured period is larger than a predetermined reference value, it is determined that the catalyst has deteriorated.

Specifically, first, the diagnostic condition determination routine shown in FIG. 3 is configured to be executed at a predetermined cycle. In this routine, first, in a predetermined self-failure diagnosis routine that is separately executed, is a failure code indicating that an abnormality has been detected in the past regarding the catalyst downstream side O ₂ sensor 46 left in the backup RAM 79? It is determined whether or not (step 102). When such a failure code remains, this routine is ended.

If there is no such abnormality with respect to the catalyst downstream side O ₂ sensor 46, it is next determined whether or not a diagnosis completion flag, which will be described later, is already set to 1 (step 104). The diagnosis completion flag is reset to 0 by a predetermined initialization routine executed when the ignition switch (not shown) is turned on and the ECU 70 is powered on accordingly. When the diagnosis completion flag has already been set to 1, this routine ends.

When the diagnosis completion flag is 0, it is judged whether or not a predetermined diagnosis start flag is already set to 1 (step 106). This diagnosis start flag is also initially reset to 0 in the initialization routine, similarly to the diagnosis completion flag described above. If the diagnosis start flag has already been set to 1, this routine ends.

When the diagnosis start flag is 0, the current intake air temperature TH is detected based on the output signal from the intake air temperature sensor 43.
A is within a predetermined range (a ≤ THA that is recognized as a cold start
Check if ≦ b) (step 1)
08). Such a check is performed when the engine is started in a very low temperature range (THA <a) where a false diagnosis may occur or in a high temperature range (b <THA) where the fuel injection amount is small during cold increase. This is because it is necessary to suppress the execution of catalyst deterioration diagnosis. When the intake air temperature THA is not within the predetermined range, this routine is ended.

When the intake air temperature is within the above-described predetermined range, the current engine cooling water temperature THW is further determined based on the output signal from the water temperature sensor 44 within a predetermined range (c≤ It is checked whether THW ≦ d) (step 110). The purpose of this check is the same as the purpose of checking the intake air temperature THA described above. When the water temperature THW is not within the predetermined range, this routine ends.

If the water temperature THW is also within the predetermined range, the diagnosis start flag is set to 1 (step 112). By doing so, the processes after step 108 are executed only once in each trip (one run from when the ignition switch is turned on until when the ignition switch is turned off) (except at the time of high temperature start). ). Next, a predetermined determination reference value TR is obtained by searching the map shown in FIG. 4 based on the current water temperature THW (step 114). It should be noted that this determination reference value TR represents the time required for the catalyst downstream side O ₂ sensor 46 to be naturally activated when the catalyst is not deteriorated when the starting water temperature THW is at a certain value. There is. The content is determined by experiments and the like and is stored in the ROM 73 in advance. Further, it may be a two-dimensional map in which the intake air temperature THA is added to the water temperature THW. The judgment reference value TR obtained by such a diagnosis condition judgment routine is used in the catalyst deterioration diagnosis routine described next.

FIG. 5 is a flow chart showing the processing procedure of the catalyst deterioration diagnosis routine according to the first embodiment. In this routine, first, it is judged whether or not the diagnosis completion flag is already set to 1 (step 202), and when the diagnosis completion flag is 1, this routine is ended. On the other hand, when the diagnosis completion flag is still 0, it is determined whether or not the diagnosis start flag is set to 1 (step 204). When the diagnosis start flag is 0, this routine ends.

On the other hand, when the diagnosis start flag is 1, it is determined whether or not the cold increase is currently being executed in the fuel injection control (step 206). In general,
Immediately after the cold start, the vaporization of the fuel is poor, the amount of the fuel adhering to the wall surface of the intake system is large, and the air-fuel mixture contributing to the combustion tends to be lean. This cold increase is to increase the fuel injection amount in order to prevent it. If the cold amount increase is not being executed, this routine ends.

When it is determined in step 206 that the cold increase is being executed, the value of the predetermined activation period counter TUP is incremented by 1 (step 210). The value of the counter TUP is cleared to 0 in the initialization routine executed when the power is turned on. Next, by comparing the output voltage VSO of the catalyst downstream side O ₂ sensor 46 with the rich / lean determination threshold value VR (for example, 4.5 V), the sensor is rich (VSO ≧ VSO).
R) or lean (VSO <V
R), that is, whether or not the sensor has been activated (step 212). When VSO <VR, that is, when the catalyst downstream side O ₂ sensor 46 is not activated yet, this routine is ended.

The reason why the activation of the O ₂ sensor can be determined in this way will be described. When the element temperature is low (about 400 ° C. or less), the O ₂ sensor is in an inactive state, that is, it is in a state in which a sufficient electromotive force corresponding to the oxygen concentration cannot be generated because the internal resistance is large.
That is, in this state, even if the air-fuel ratio is rich, the O ₂ sensor cannot generate an output voltage of about 1 V, VSO <VR, and it is determined to be lean. Since the air-fuel ratio is rich during the cold increase, it is possible to determine that the O ₂ sensor is activated if it is actually determined that VSO ≧ VR, that is, rich.

On the other hand, when VSO ≧ VR, that is, when it is determined that the catalyst downstream-side O ₂ sensor 46 is activated, the determination reference value TR already obtained by the above-mentioned diagnostic condition determination routine and the time point at that time. Counter T
The value of UP is compared (step 214). And T
When UP ≧ TR, the time required to activate the catalyst downstream-side O ₂ sensor 46 is abnormally long, so it is determined that the catalyst has deteriorated, and a predetermined catalyst abnormality flag is set to 1 (step 216). ), And stores it in the backup RAM 79. The fact that the catalyst abnormality flag is set to 1 is recognized by a predetermined process executed separately, and is notified to the user by an appropriate means. On the other hand, TUP
When <TR, the catalyst downstream-side O ₂ sensor 46 is normally activated, so it is determined that the catalyst has not deteriorated, and the catalyst abnormality flag is set to 0 (step 218).

In step 220 executed after step 216 or 218, the above-mentioned diagnosis completion flag is set to 1. As a result, the catalyst deterioration diagnosis is suppressed until the next trip, as shown in step 104 (diagnosis condition determination routine of FIG. 3) or step 202. Thus, the catalyst deterioration diagnosis in this trip is completed.

Next, a second embodiment according to the second invention will be described. While the first embodiment considers only the sensor activation time, this second embodiment further considers the factors that affect the warm-up of the catalyst downstream side O ₂ sensor 46 to change the operating state. It is intended to perform a more accurate catalyst deterioration diagnosis that is not affected by.

FIG. 6 is a flow chart showing the processing procedure of the diagnostic condition judging routine according to the second embodiment. Steps 302 to 312 are the same as steps 102 to 112 (FIG. 3) of the diagnostic condition determination routine according to the first embodiment, so description thereof will be omitted. And the final step 3
In 14, the predetermined determination reference value FR is obtained by searching the map shown in FIG. 7 based on the current water temperature THW.
Ask for. The determination reference value FR is such that the catalyst has deteriorated at the time when the sensor is activated, when the factors that affect the warm-up of the sensor are integrated from the start when the water temperature THW has a certain value. If not, the integrated value naturally represents a value that is less than that. As such factors, in this embodiment, the intake air amount Q and the intake air temperature T are
HA and vehicle speed SPD are adopted. The contents of the map are those determined by experiments and the like, and are stored in the ROM 7 in advance.
Stored in 3.

FIG. 8 is a flow chart showing the processing procedure of the catalyst deterioration diagnosis routine according to the second embodiment. Steps 402 to 406 are steps 202 to 2 of the first embodiment.
It is the same as 06. When it is determined in step 406 that the cold amount is being increased, a predetermined warm-up factor integration counter FUP is set.
In order to obtain the count-up amount of the intake air, the factors that affect the warm-up of the sensor
Based on A and the vehicle speed SPD, the maps shown in FIGS. 9, 10, and 11 are searched to obtain the basic count-up amount FB, the intake temperature correction coefficient KA, and the vehicle speed correction coefficient KS, respectively (step 408). ).

As shown in FIG. 9, as the intake air amount Q increases, the basic count-up amount FB also increases because the intake air amount increases, the exhaust gas amount increases, and the O ₂ sensor warms up faster. This is because they are punished. The value of the basic count-up amount FB depends on the vehicle weight, the catalyst position,
Since it depends on the catalyst size, speed change mechanism, etc., it is determined by testing. Further, as shown in FIG. 10, it is necessary to correct the intake air temperature correction coefficient KA as the intake air temperature THA rises, and thus to increase the basic count-up amount FB. This is because the higher the temperature, the higher the exhaust temperature, and the warming up of the O ₂ sensor is promoted. In addition, as shown in FIG. 11, the vehicle speed SP
The vehicle speed correction coefficient KS decreases as D increases,
Therefore, it is necessary to correct the basic count-up amount FB in the direction of decreasing it because the higher the vehicle speed SPD is, the more the traveling wind cools the O ₂ sensor and the warm-up thereof is delayed. Note that these maps are stored in the ROM 73 in advance.

Then, based on the basic count-up amount FB, the intake air temperature correction coefficient KA and the vehicle speed correction coefficient KS thus obtained, the warm-up factor integration counter FUP is counted up as shown in the following equation ( Step 41
0). FUP ← FUP + FB * KA * KS The value of the counter FUP is initialized to 0 by the initialization routine executed at power-on. Of the subsequent steps 412 to 420, step 4 is different from steps 212 to 220 (FIG. 5) of the first embodiment.
Only 14 That is, in step 414, the catalyst deterioration is determined by comparing the value of the warm-up factor integration counter FUP with the determination reference value FR obtained in the above-mentioned diagnostic condition determination routine. Thus, according to the second embodiment,
Since factors that affect the warm-up of the catalyst downstream side O ₂ sensor 46 are taken into consideration, more accurate catalyst deterioration diagnosis can be performed regardless of changes in the operating state.

Finally, a heater control method when the present invention is applied to the case where the O ₂ sensor has a heater will be described. That is, on the downstream side of the catalyst,
Since the exhaust temperature becomes low, a heater is provided in the downstream O ₂ sensor to maintain the element temperature of the downstream O ₂ sensor in an active state (especially during idle operation or light load), and the heater is supplied according to the operating state. In some cases, the electric power to be controlled is controlled to keep the O ₂ sensor element temperature constant.

In this case, at the time of cold start, since the temperature of the O ₂ sensor element is low, a large electric power is supplied to the heater,
The warm-up of the O ₂ sensor is controlled to be accelerated. However, in the present invention, the deterioration of the catalyst is diagnosed based on the period until the activation of the downstream O ₂ sensor. Therefore, when the present invention is applied in such a case, power supply to the heater of the O ₂ sensor with a heater is stopped at the time of deterioration diagnosis, the downstream O ₂ sensor is warmed up only by the catalyst outlet gas temperature, and after the deterioration diagnosis is completed. Start power supply to the heater.

FIG. 12 shows a specific heater control processing procedure. This routine is executed every predetermined time. As shown in this figure, "diagnosis start flag =
1 and the diagnosis completion flag = 0 ", that is, when the deterioration diagnosis is being executed, the power supply to the heater is stopped (steps 502, 504, 506). Then, when the deterioration diagnosis is not being executed, it is determined whether or not the heater is in an operating state in which the heater should be energized (step 508). When the operating state is in which the heater is energized, the electric power determined according to the operating state is supplied to the heater. (Step 508).

In some cases, the catalyst upstream side O₂SE
A heater may also be provided in the sensor. In that case,
It may be controlled as follows. That is, the heater on the upstream side
Instantly supplies power to activate the catalyst and
That the air-fuel ratio of the exhaust gas supplied to the
To see. The reason is the downstream O₂The sensor has not deteriorated
At least, if the air-fuel ratio is lean, the downstream side O₂Sensor
Does not show rich output, so activation period or warm-up factor
This is because the integrated value becomes large and there is a possibility of erroneous diagnosis.
It In other words, in the present invention, catalyst deterioration is diagnosed during cold increase.
Although the fuel injection valve is blocked,
Therefore, the actual air-fuel ratio may be lean,
In case of, it is necessary to prevent misdiagnosis. for that reason
Is the upstream O ₂The sensor monitors that the air-fuel ratio is rich.
While watching, the downstream side O₂To detect sensor activation
do it.

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

[0050]

As described above, according to the present invention,
There is provided a catalyst deterioration diagnosing device which detects a decrease in low temperature activity by a catalyst downstream side air-fuel ratio sensor and diagnoses catalyst deterioration based on the decrease. By combining the conventional diagnostic device based on the deterioration of the O ₂ storage effect after warming up with the diagnostic device of the present invention, it becomes possible to more accurately diagnose the deterioration of the catalyst. Therefore, the present invention promotes the improvement of the exhaust gas purification performance of the internal combustion engine, and eventually contributes to the prevention of air pollution.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram of an electronically controlled internal combustion engine equipped with a catalyst deterioration diagnosis device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a hardware configuration of an engine ECU according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a processing procedure of a diagnostic condition determination routine according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a map for obtaining a catalyst deterioration determination reference value TR according to the first embodiment based on an engine starting water temperature THW.

FIG. 5 is a flowchart showing a processing procedure of a catalyst deterioration diagnosis routine according to the first embodiment of the present invention.

FIG. 6 is a flowchart showing a processing procedure of a diagnostic condition determination routine according to the second embodiment of the present invention.

FIG. 7 is a diagram showing a map for obtaining a catalyst deterioration determination reference value FR according to the second embodiment based on an engine starting water temperature THW.

FIG. 8 is a flowchart showing a processing procedure of a catalyst deterioration diagnosis routine according to the second embodiment of the present invention.

9 is a diagram showing a map for obtaining a basic count-up amount FB of a warm-up factor integration counter FUP based on an intake air amount Q. FIG.

FIG. 10 is a diagram showing a map for obtaining an intake air temperature (THA) correction coefficient KA for the basic count-up amount FB.

FIG. 11: Water temperature (T for basic count-up amount FB)
It is a figure which shows the map for calculating | requiring (HW) correction coefficient KW.

FIG. 12 is a flowchart showing a heater control processing procedure when the present invention is applied in the case where the catalyst downstream-side O ₂ sensor has a heater.

[Explanation of symbols]

2 ... Air cleaner 4 ... Throttle body 5 ... Throttle valve 6 ... Surge tank (intake manifold) 7 ... Intake pipe 8 ... Idle adjust passage 10 ... Fuel tank 11 ... Fuel pump 12 ... Fuel pipe 20 ... Engine body (cylinder) 21 ... Combustion Chamber 22 ... Cooling water passage 24 ... Intake valve 26 ... Exhaust valve 30 ... Exhaust manifold 34 ... Exhaust pipe 38 ... Catalytic converter 40 ... Air flow meter 41 ... Vacuum sensor 42 ... Throttle opening sensor 43 ... Intake temperature sensor 44 ... Water temperature sensor 45 ... catalyst upstream O ₂ sensor 46 ... catalyst downstream O ₂ sensor 50 ... reference position detection 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 ... Idle speed control valve (ISCV) 70 ... Engine ECU 71 ... CPU 72 ... System bus 73 ... ROM 74 ... RAM 75 ... A / D conversion circuit 76 ... Input interface circuit 77a, 77b, 77c ... Drive control circuit 79 ... Backup RAM

Claims (2)

[Claims] 1. A downstream side air-fuel ratio sensor provided in an exhaust passage downstream of a catalyst for purifying exhaust gas of an internal combustion engine, and the downstream side air-fuel ratio sensor is activated from a cold start of the internal combustion engine. Of the internal combustion engine, which comprises a period measuring means for measuring the period up to, and a deterioration determining means for determining that the catalyst has deteriorated when the period measured by the period measuring means is larger than a predetermined reference value. Catalyst deterioration diagnosis device. 2. A downstream side air-fuel ratio sensor provided in an exhaust passage downstream of a catalyst for purifying exhaust gas of an internal combustion engine, and warming up of the downstream side air-fuel ratio sensor from a cold start of the internal combustion engine. Warm-up factor accumulating means for accumulating count-up values according to one or two or more factors that affect the above in a predetermined cycle to obtain an integrated value at the time when the downstream side air-fuel ratio sensor is activated, A catalyst deterioration diagnosing device for an internal combustion engine, comprising: deterioration judging means for judging that the catalyst has deteriorated when the integrated value obtained by the warm-up factor integrating means is larger than a predetermined reference value.