JP3075001B2 - Catalyst deterioration diagnosis 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 utilizes air-fuel ratio sensors disposed upstream and downstream of a catalytic converter.
The present invention relates to a catalyst deterioration diagnosis device for an internal combustion engine that diagnoses a deterioration state of a catalyst.

[0002]

It arranged an air-fuel ratio sensor, for example O ₂ sensor, respectively upstream and downstream of the catalytic converter of an internal combustion engine, and executes the air-fuel ratio feedback control by the main output signal of the upstream O ₂ sensor Japanese Patent Application Laid-Open Nos. 63-97852 and 63-97852 disclose a device for diagnosing catalyst deterioration based on a comparison between output signals of both sensors.
-205441.

[0003] That is, during execution of the air-fuel ratio feedback control, the fuel supply amount is controlled mainly by example pseudo proportional integral control based on the output signal of the upstream O ₂ sensor, the upstream O ₂ sensor The output signal of FIG.
As shown in (1), rich and lean inversions are repeated periodically. On the other hand, on the downstream side of the catalytic converter, the fluctuation of the residual oxygen concentration becomes very gentle due to the O ₂ storage capacity of the catalyst. Therefore, the output signal of the downstream O ₂ sensor is as shown in FIG. As shown in ( ₂₎ , the fluctuation width is smaller and the cycle is longer than in the upstream O2 sensor.

However, when the catalyst in the catalytic converter deteriorates, the oxygen concentration does not change much between the upstream side and the downstream side of the catalytic converter due to a decrease in the O ₂ storage capacity, and as a result, the output of the downstream O ₂ sensor is reduced. As shown in FIG. 7 (c), the signal repeats inversion at a cycle approximating the output of the upstream O ₂ sensor, and its fluctuation width also increases.

Therefore, in the device described in the above publication, the ratio (T) of the rich / lean inversion period T2 of the upstream O ₂ sensor to the rich / lean inversion period T2 of the downstream O ₂ sensor is determined.
1 / T2), and when this ratio exceeds a predetermined value,
It is determined that the catalyst has deteriorated.

[0006] Generally, such catalyst deterioration diagnosis is performed only when the operating conditions such as the engine speed and the load and the cooling water temperature satisfy predetermined diagnosis conditions.

The output signal of the downstream O ₂ sensor is used in addition to the above-mentioned catalyst deterioration diagnosis, for example, for learning correction of the air-fuel ratio bias in the air-fuel ratio feedback control based on the output signal of the upstream O ₂ sensor. It is generally used for

[0008]

The O ₂ storage capacity of the catalyst greatly depends on the temperature of the catalyst, and particularly in a low temperature state below the catalyst activation temperature, the O ₂ storage capacity is very low. That is, if the above-described catalyst deterioration diagnosis is performed in a state where the catalyst temperature is low, the deterioration may be erroneously determined as the deterioration even if the conversion performance of the catalyst remains. Therefore, in order to prevent such an erroneous determination in a low-temperature state, it is necessary to ensure that the catalyst is in a high-temperature state at the time of diagnosis on condition that high-speed high-load operation has continued for a certain period of time. There is. However, if the diagnostic conditions for performing the catalyst deterioration diagnosis are set strictly in this way, the frequency at which the diagnosis conditions are actually satisfied becomes very low. For example, there is a possibility that the catalyst deterioration diagnosis may be performed during one drive. Will be lower.

Conversely, if the diagnosis conditions are set loosely so that the catalyst deterioration diagnosis is performed relatively frequently, the catalyst temperature may not be sufficient and an erroneous determination may occur depending on conditions such as the outside air temperature. There is.

That is, it has been difficult to achieve both the reliable execution of the catalyst deterioration diagnosis during the short-time running and the prevention of erroneous determination.

[0011]

Accordingly, in the present invention,
When it is diagnosed that the catalyst has deteriorated, the operation is further performed with the ignition timing of the internal combustion engine forcibly retarded, and the exhaust gas temperature is raised to make sure that the catalyst temperature is maintained at or above the activation temperature. To do. That is, as shown in FIG. 1, the catalyst deterioration diagnosis device for an internal combustion engine according to the present invention includes an upstream air-fuel ratio sensor 1 disposed upstream of a catalytic converter disposed in an exhaust passage, and a catalytic converter. A downstream air-fuel ratio sensor 2 disposed downstream; a first diagnostic condition determining means 3 for determining whether various conditions of the internal combustion engine satisfy a first diagnostic condition; A first diagnostic means for diagnosing deterioration of the catalyst using an output signal of the upstream air-fuel ratio sensor and an output signal of the downstream air-fuel ratio sensor when the diagnostic conditions are satisfied; And a retard correction means 5 for forcibly delaying the ignition timing of the internal combustion engine when it is diagnosed that the catalyst has deteriorated, and that the engine has been operated in the retarded state for a predetermined period in the retarded state.
Second diagnostic condition determining means 6 for determining whether a second diagnostic condition included in one of the cases is satisfied, and an output signal of the upstream air-fuel ratio sensor 1 when the second diagnostic condition is satisfied. A second diagnostic means for finally determining the deterioration of the catalyst by using the output signal of the downstream air-fuel ratio sensor.

[0012]

[Action] at the time of the normal that has not been the catalyst deterioration diagnosis operation, the optimal value of the ignition timing of the internal combustion engine in accordance with the machine SekiHakobu rolling conditions
The engine is operated in this state.
Various conditions such as a region and a cooling water temperature are predetermined first diagnostic conditions.
Is satisfied by the first diagnostic condition determining means 3
Then, the catalyst deterioration diagnosis by the first diagnosis means 4 is executed.
Is done. This is due to, for example, air-fuel ratio feedback control.
The inversion cycle of the output signal of the upstream air-fuel ratio sensor 1 and the downstream side
By comparing the output signal of the air-fuel ratio sensor 2 with the inversion cycle,
Is diagnosed.

[0013] The first diagnostic means 4 uses the catalyst.
When it is diagnosed that the battery has deteriorated, the ignition timing is corrected by the retard correction means 5.
Is forcibly retarded from the optimal ignition timing,
The internal combustion engine is operated in the state. With this ignition timing retard
The exhaust gas temperature rises and the temperature of the catalytic converter rises.
During operation in this state, the operating range of the engine,
If each condition satisfies a predetermined second diagnostic condition, a second
The second diagnostic condition is determined by the diagnostic condition determining means 6.
The catalyst deterioration diagnosis by the means 7 is executed. This is the first
As in the case of the diagnosis means 4, for example, the air-fuel ratio feedback system
Control cycle of the output signal of the upstream air-fuel ratio sensor 1
Compare the output signal of the downstream side air-fuel ratio sensor 2 with the inversion cycle.
It is diagnosed by This second diagnostic means 7 allows the catalyst
If the deterioration is diagnosed, it is finally determined that the catalyst is deteriorated.
You.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 2 is a structural explanatory view showing a mechanical structure of one embodiment of the present invention, wherein 11 is an internal combustion engine, 12 is an intake passage, and 13 is an exhaust passage. In the intake passage 12, a fuel injection valve 14 for supplying fuel to each intake port is provided for each cylinder, and a throttle valve 15 is interposed in an upstream gathering portion. On the upstream side, for example, a hot-wire type air flow meter 16 for detecting the intake air amount is provided.

The exhaust passage 13 is provided with a catalytic converter 17 using a three-way catalyst, for example.
An upstream O ₂ sensor 18 is provided at a position upstream of the catalytic converter 17, and a downstream O ₂ sensor 19 is provided at a downstream position. The O ₂ sensors 18 and 19 as the air-fuel ratio sensors generate an electromotive force in accordance with the concentration of residual oxygen in the exhaust gas. doing.

Reference numeral 20 denotes a water temperature sensor for detecting a cooling water temperature of the internal combustion engine 11, reference numeral 21 denotes a crank angle sensor which is provided for detecting the engine speed and emits a pulse signal at every predetermined crank angle, and reference numeral 22 denotes a vehicle speed sensor. Each is shown.

The control unit 23 detects signals of various sensors described above is input, one using a so-called microcomputer systems, O ₂ sensor 18, 1
While controlling the injection amount of the fuel injection valve 14 based on No. 9, that is, the air-fuel ratio control by the feedback control method,
The ignition timing of an unillustrated spark plug is controlled according to the engine operating conditions. Further, a catalyst deterioration diagnosis as described later is performed, and when it is determined that the deterioration is equal to or higher than a predetermined level, the warning lamp 24 is turned on.

Next, the operation of the above embodiment will be described.

First, the outline of the air-fuel ratio control will be described. In this air-fuel ratio control, the basic pulse width Tp (basic injection amount) is calculated from the intake air amount Q detected by the air flow meter 16 and the engine speed N detected by the crank angle sensor 21 as follows: Tp = (Q / N) × k (Where k is a constant), and various increase corrections and feedback corrections are added thereto to obtain the drive pulse width Ti of the fuel injection valve 14.
(Injection amount) is determined. Specifically, the pulse width Ti is obtained by the following equation.

Ti = Tp × COEF × α + Ts Here, COEF is a various increase correction coefficient, and includes, for example, a water temperature increase correction according to the water temperature, and an air-fuel ratio correction at high speed and high load. Ts is a voltage correction coefficient added according to the battery voltage so as to compensate for the invalid time of the fuel injection valve 14.

Α is a feedback correction coefficient which is calculated mainly based on the detection signal of the upstream O ₂ sensor 18. That is, the output signal of the upstream O ₂ sensor 18 is compared with a predetermined slice level (corresponding to the stoichiometric air-fuel ratio), and a value obtained by pseudo proportional integral control based on the inversion to the lean side and the rich side. If the value is 1 or more, the air-fuel ratio is controlled to the rich side, and if the value is 1 or less, the air-fuel ratio is controlled to the lean side. Accordingly, as a result of this proportional integration control, the output signal of the upstream O ₂ sensor 18 changes at a period of about 1 to 2 Hz as shown in FIG.

On the other hand, the output signal of the downstream O ₂ sensor 19 is used for correcting the overall deviation of the feedback control by the upstream O ₂ sensor 18 in addition to the catalyst deterioration diagnosis described later. That is, the downstream O ₂ sensor 1
Similarly, pseudo proportional integral control is performed on the output signal of No. 9 based on the inversion of rich and lean, and the second correction coefficient αi is obtained. Then, the second correction coefficient α
Using i, the proportional component of the feedback correction coefficient α in the proportional integral control is learned and corrected. still,
As a result, as long as the catalyst is not deteriorated, the output signal of the downstream O ₂ sensor 19 repeats the inversion of rich and lean at a relatively long cycle as shown in FIG. 7B.

On the other hand, the ignition timing of the internal combustion engine 11 is sequentially set based on an ignition advance value map using the engine speed N and the basic injection amount Tp as parameters.

Next, the catalyst deterioration diagnosis will be described with reference to the flowcharts of FIGS. Note that the routines shown in the flowcharts are repeatedly executed at predetermined intervals.

FIG. 3 is a main flowchart showing the overall flow of the catalyst deterioration diagnosis. First, in step 1 (abbreviated as S1 in the figure), a diagnosis end flag is used to determine whether the catalyst deterioration diagnosis has been completed. Is determined based on The diagnosis end flag is reset when the operation of the internal combustion engine 11 ends, that is, when the key is turned off. If the diagnosis is not completed, that is, if the diagnosis end flag is 0, step 2
Proceeding to the subsequent steps, it is sequentially determined whether various conditions of the internal combustion engine 11 satisfy predetermined diagnostic conditions. The diagnostic conditions are
Diagnosis permission conditions that prescribe the conditions premised on the diagnosis and diagnosis region conditions that prescribe the operation region in which the diagnosis is to be performed are roughly classified. Steps 2 to 4 are the diagnosis permission conditions, and steps 5 to 7 are the diagnosis permission conditions. It corresponds to each area condition.
Specifically, in step 2, each sensor, that is, the upstream O ₂ sensor 18, the downstream O ₂ sensor 19, and the water temperature sensor 2
0, it is determined whether or not all of the crank angle sensor 21 and the vehicle speed sensor 22 are normal. Next, in step 3, it is determined whether or not the water temperature TW detected by the water temperature sensor 22 is equal to or higher than a predetermined value. Then, in step 4, it is determined whether or not a later-described catalyst temperature point P is equal to or more than a predetermined value.

Further, in step 5, it is determined whether or not the engine speed N at that time is not less than a predetermined value, and in step 6, whether the load (for example, the basic injection amount Tp) is not less than a predetermined value,
In step 7, it is determined whether or not the vehicle speed is within a predetermined range. If any one of these conditions is NO, the catalyst deterioration diagnosis is not performed. Then, only when all of the conditions are satisfied, the routine proceeds to step 8, where a catalyst deterioration diagnosis is executed.

The catalyst temperature point P in step 4 serves as an index for estimating the catalyst temperature, and is sequentially obtained by a subroutine shown in FIG.

That is, when the engine speed N is equal to or more than the predetermined value N1 (step 21) and the basic injection amount Tp corresponding to the load is set.
Is greater than or equal to a predetermined value Tp1 (step 22),
Proceeding to step 23, the catalyst temperature point P is incremented. If the area is other than that, step 24
Then, the catalyst temperature point P is decremented. This takes into account whether the catalytic converter 17 is heated or cooled by the flow of exhaust gas, and as shown in FIG.
The high-speed, high-load region where the heating effect of the exhaust gas can be expected is defined as the addition region of the catalyst temperature point P. Conversely, the low-speed region and the low-load region where the catalytic converter 17 may be cooled by the flow of the exhaust gas. The region is a subtraction region of the catalyst temperature point P. Therefore, this catalyst temperature point P
By constantly repeating the addition and subtraction, the catalyst temperature at that time can be roughly estimated.

There are various methods for diagnosing the catalyst deterioration in step 8; for example, as shown in FIG. 7, the output signal of the upstream O ₂ sensor 18 is rich / lean inversion cycle T1 and the downstream O 2 the output signals of the _two sensors 19 rich, so that calculated in the lean appropriate period ratio (T2 / T1) between the inversion period T2 of, used as a value indicating the this O ₂ storage capability.

[0031] Then, at step 9, upon completion of calculation of the ratio of the inversion period as described above, the process proceeds to step 10, the detected O ₂ storage capability is determined whether more than a predetermined value. Specifically, it is determined whether or not the above-mentioned ratio of the inversion cycle is equal to or more than a predetermined value. Here, if the O ₂ storage capacity is equal to or greater than the predetermined value, the process proceeds to step 11, where it is determined that the catalyst is normal, and in step 17, a diagnosis end flag is set, and an ignition timing retard flag described later is cleared. To terminate a series of processing.

On the other hand, if it is determined in step 10 that the O ₂ storage capacity is lower than the predetermined value,
Then, it is determined whether or not the value of the O ₂ storage capacity has decreased by a predetermined value or more by comparing with the value of the O ₂ storage capacity measured last time. If the determination is NO, the process proceeds to step 13, where it is determined that the catalyst has deteriorated, and the warning lamp 24 is turned on.

If the value of the O ₂ storage capacity is sharply reduced as compared with the previous value in step 12, it is highly likely that the catalyst temperature at the time of measurement was not sufficient, not due to deterioration over time. Therefore, the process proceeds to steps 14 and 15, and the ignition timing retard flag is set. And step 16
Then, after the catalyst temperature point P is cleared, a series of catalyst deterioration diagnosis is executed again.

FIG. 5 shows a subroutine for ignition timing control. In step 31, the ignition timing according to the engine speed N and the basic injection amount Tp is obtained from the ignition advance value map as described above. Then, when the ignition timing retard flag is cleared, the ignition timing obtained in step 31 is used as it is. On the other hand, if the ignition timing retard flag is set to 1, step 3
From 2, the process proceeds to step 33 to forcibly retard the ignition timing by a predetermined crank angle.

Therefore, when the catalyst deterioration diagnosis is performed again through steps 15 and 16, the operation is performed with the ignition timing delayed, so that the exhaust gas temperature rises and the catalytic converter 17
Can be heated positively. In particular, step 16
By clearing the catalyst temperature point P once, the execution of the catalyst deterioration diagnosis is waited until the catalyst temperature point reaches the predetermined value again by the subroutine shown in FIG. 4, but the addition area and the subtraction area shown in FIG. Are the same, the exhaust gas temperature in each region rises due to the retardation of the ignition timing. Therefore, when the catalyst temperature point P reaches a predetermined value (step 4), the exhaust gas temperature surely exceeds the catalyst activation temperature. Become.

Therefore, in the catalyst deterioration diagnosis to be executed again, there is no possibility of erroneous diagnosis due to a low catalyst temperature, and it is possible to reliably determine whether or not the catalyst has deteriorated. That is, if the O ₂ storage capability state where the enhanced catalyst temperature Rarere obtained above a predetermined value (step 10), the catalyst is judged to be not deteriorated (step 11). In addition, even if the catalyst temperature is raised in this way, if the O ₂ storage capacity is equal to or less than a predetermined value, the process proceeds to Step 13 via Steps 12 and 14, and it is determined that the catalyst has deteriorated.

When the ignition timing retard flag is cleared in step 17, the compulsory retardation of the ignition timing is released, and the control returns to the control of the optimum ignition timing.

As described above, in the above embodiment, when there is a suspicion that the catalyst has deteriorated at the time of the first diagnosis, the ignition timing is forcibly retarded, and the diagnosis is executed again after the catalytic converter 17 is actively heated. Erroneous determination is reliably prevented. Also in this case, since the catalyst temperature point P itself is determined under normal conditions, the chance of diagnosis does not decrease, and the catalyst deterioration diagnosis can be reliably performed during normal driving.

In the above-described embodiment, the diagnosis is performed under the normal ignition timing prior to the diagnosis with the compulsory retardation of the ignition timing. If the O ₂ storage capacity is sufficient,
Since the diagnosis is determined at that time, it is possible to minimize deterioration of fuel efficiency and the like due to retardation of the ignition timing.

[0040]

As is apparent from the above description, according to the apparatus for diagnosing catalyst deterioration of an internal combustion engine according to the present invention, the catalytic converter is actively heated by the rise of the exhaust gas temperature accompanying the retardation of the ignition timing. This can prevent erroneous diagnosis when the catalyst temperature is low. In particular, since the catalyst temperature can be increased without setting the diagnostic conditions such as the operation region too strict, the reliability of the deterioration diagnosis can be increased without reducing the opportunity and frequency of the catalyst deterioration diagnosis.

[Brief description of the drawings]

FIG. 1 is a claim correspondence diagram showing a configuration of a catalyst deterioration diagnosis apparatus according to the present invention.

FIG. 2 is a configuration explanatory view showing a mechanical configuration of one embodiment of the present invention.

FIG. 3 is a main flowchart showing the overall flow of catalyst deterioration diagnosis.

FIG. 4 is a flowchart showing a subroutine for counting a catalyst temperature point P;

FIG. 5 is a flowchart showing a subroutine for correcting an ignition timing.

FIG. 6 is a characteristic diagram showing an addition area and a subtraction area of a catalyst temperature point P.

FIG. 7 is a waveform diagram showing output signals of an upstream O ₂ sensor and a downstream O ₂ sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Upstream air-fuel ratio sensor 2 ... Downstream air-fuel ratio sensor 3 ... 1st diagnostic condition determination means 4 ... 1st diagnostic means 5 ... retard angle correction means 6 ... 2nd diagnostic condition determination means 7 ... 2nd Diagnostic means

Claims (1)

(57) [Claims] 1. An upstream air-fuel ratio sensor disposed upstream of a catalytic converter disposed in an exhaust passage, a downstream air-fuel ratio sensor disposed downstream of a catalytic converter, and various types of internal combustion engines. First diagnostic condition determining means for determining whether or not the above condition satisfies a first diagnostic condition; and when the first diagnostic condition is satisfied, an output signal of the upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor First diagnosing means for diagnosing deterioration of the catalyst by using the output signal of the first control means, and retard correction means for forcibly retarding the ignition timing of the internal combustion engine when the first diagnosing means diagnoses the deterioration of the catalyst. After driving in this retarded state,
A second diagnostic condition determining means for determining whether or not a second diagnostic condition including one of the conditions that the vehicle has been operated for a period of time, and the upstream air-fuel ratio sensor when the second diagnostic condition is satisfied And a second diagnosis means for finally determining the deterioration of the catalyst using the output signal of the first air-fuel ratio sensor and the output signal of the downstream air-fuel ratio sensor.