JPH06264726A - Catalyst deterioration diagnosing device of internal combustion engine - Google Patents

Abstract

PURPOSE:To enhance the reliability of deterioration diagnosis by providing air-fuel ratio sensors on the upstream side and the downstream side of a catalytic converter, performing the deterioration judgement on the basis of signals of the air-fuel ratio sensors when it is judged that an engine meets the diagnosis conditions, and raising the exhaust gas temperature through the process of forcibly delaying the ignition time. CONSTITUTION:A catalytic converter 17 is interposed in an air exhaust passage 13, and O2 sensors 18, 19 are provided as air-fuel ratio sensors on the upstream side and the downstream side so as to input signals into a control unit 23. The control unit 23 performs the catalyst deterioration diagnosis from output signals of the O2 sensors 18, 19 after judging the fact that the fixed diagnosis conditions are met from a water temperature sensor 11, a crank angle sensor 21, a car speed sensor 22, etc. At this time, the exhaust temperature is raised by delaying the injection amount control of a fuel injection valve 14 and delaying the ignition time later than the optimum ignition time. Thus, the temperature of the catalytic converter 17 can be kept high, and the reliability of the diagnosis is enhanced without decreasing the opportunity and the frequency of the catalyst deterioration diagnosis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes air-fuel ratio sensors arranged upstream and downstream of a catalytic converter,
The present invention relates to a catalyst deterioration diagnosing device for an internal combustion engine which diagnoses a catalyst deterioration state.

[0002]

2. Description of the Related Art An air-fuel ratio sensor, for example, an O ₂ sensor is provided on each of an upstream side and a downstream side of a catalytic converter of an internal combustion engine, and air-fuel ratio feedback control is executed mainly by using an output signal of the upstream side O ₂ sensor. An apparatus for diagnosing deterioration of a catalyst based on comparison of output signals of both sensors is disclosed in, for example, JP-A-63-97852 or JP-A-63-952.
-205441 publication.

[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 is (a) in FIG.
As shown in, the inversion of rich and lean is 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, so the output signal of the downstream O ₂ sensor is as shown in FIG. As shown in, the fluctuation range is smaller and the cycle is longer than that of the upstream O ₂ 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 the decrease in the O ₂ storage capacity, and as a result, the output of the downstream O ₂ sensor. As shown in (c) of FIG. 7, the signal repeats inversion at a cycle close to the output of the upstream O ₂ sensor, and its fluctuation range becomes large.

Accordingly, in the apparatus described in the above publication, the ratio of the upstream O ₂ sensor rich and lean inversion period T1 downstream O ₂ sensor rich and lean inversion period T2 (T
1 / T2) is obtained, and when this ratio is equal to or greater than a predetermined value,
It is determined that the catalyst has deteriorated.

Such catalyst deterioration diagnosis is generally carried out only when operating conditions such as engine speed and load, cooling water temperature and the like satisfy predetermined diagnosis conditions.

The output signal of the downstream O ₂ sensor is not only the above-described catalyst deterioration diagnosis but also learning correction of the deviation of the overall air-fuel ratio of the air-fuel ratio feedback control based on the output signal of the upstream O ₂ sensor. It is also commonly used for.

[0008]

The O ₂ storage capacity of the catalyst is greatly influenced by the temperature of the catalyst, and especially at low temperatures below the catalyst activation temperature, the O ₂ storage capacity is very low. That is, when the catalyst deterioration diagnosis described above is executed in the 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 the low temperature state, it is necessary to make sure that the catalyst is in the high temperature state at the time of diagnosis under the condition that the high-speed and high-load operation is continued for a certain period of time. There is. However, if the diagnostic condition for performing the catalyst deterioration diagnosis is set to be strict as described above, the frequency at which the diagnostic condition is actually satisfied becomes extremely low. For example, the catalyst deterioration diagnosis may be executed during one run. Will be low.

On the other hand, if the diagnostic conditions are set so that the catalyst deterioration diagnosis is executed relatively frequently, the catalyst temperature may not be sufficient depending on the conditions such as the outside air temperature, resulting in erroneous determination. There is

That is, it has been difficult to achieve both reliable diagnosis of catalyst deterioration and prevention of erroneous determination while traveling for a short time.

[0011]

Therefore, according to the present invention,
When diagnosing the catalyst deterioration, the exhaust temperature is raised by retarding the ignition timing of the internal combustion engine so that the catalyst temperature can be reliably maintained above the activation temperature. That is, as shown in FIG. 1, an internal combustion engine catalyst deterioration diagnosing device according to the present invention includes an upstream air-fuel ratio sensor 1 arranged upstream of a catalytic converter interposed in an exhaust passage, and a catalytic converter. The downstream side air-fuel ratio sensor 2 arranged on the downstream side, a diagnostic condition determining means 3 for determining whether various conditions of the internal combustion engine satisfy predetermined diagnostic conditions, and the upstream side when the diagnostic conditions are satisfied. Diagnostic means 4 for diagnosing catalyst deterioration using the output signal of the side air-fuel ratio sensor 1 and the output signal of the downstream side air-fuel ratio sensor 2.
And an ignition timing control means 5 for setting the ignition timing of the internal combustion engine based on engine operating conditions, and a retard correction means 6 for forcibly retarding the ignition timing in the catalyst deterioration diagnosis. It has a feature.

[0012]

In normal operation without catalyst deterioration diagnosis, the ignition timing of the internal combustion engine is controlled by the ignition timing control means 5 to an optimum value according to the engine operating conditions.

During the engine operation, when the diagnostic condition determining means 3 determines that various conditions such as the operating region of the engine and the cooling water temperature satisfy predetermined diagnostic conditions, the diagnostic means 4 executes the catalyst deterioration diagnosis. To be done. This is diagnosed, for example, by comparing the inversion cycle of the output signal of the upstream side air-fuel ratio sensor 1 with the inversion cycle of the output signal of the downstream side air-fuel ratio sensor 2 accompanying the air-fuel ratio feedback control. Then, in this catalyst deterioration diagnosis, the ignition timing correction unit 6 forcibly corrects the ignition timing from the optimum ignition timing. The exhaust gas temperature rises as the ignition timing is retarded, and the temperature of the catalytic converter is kept high.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An 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 an embodiment of the present invention, in which 11 is an internal combustion engine, 12 is an intake passage thereof, 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 provided at an upstream collecting portion, and On the upstream side, for example, a hot wire type air flow meter 16 for detecting the intake air amount is provided.

A catalytic converter 17 using, for example, a three-way catalyst is provided in the exhaust passage 13, and
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 according to the residual oxygen concentration in the exhaust gas, and have a characteristic that the electromotive force suddenly changes stepwise at the theoretical air-fuel ratio. is doing.

Further, 20 is a water temperature sensor for detecting the cooling water temperature of the internal combustion engine 11, 21 is a crank angle sensor for outputting a pulse signal for each predetermined crank angle provided for detecting the engine speed, and 22 is a vehicle speed sensor. Shown respectively.

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
9 based on the injection amount control of the fuel injection valve 14, that is, the air-fuel ratio control by the feedback control method, and
The ignition timing of a spark plug (not shown) is controlled according to engine operating conditions. Further, the deterioration diagnosis of the catalyst as will be 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 (However, k is a constant), and various increase corrections and feedback corrections are added to this, and the drive pulse width Ti of the fuel injection valve 14 is calculated.
(Injection amount) is determined, and specifically, the pulse width Ti is obtained by the following equation.

Ti = Tp × COEF × α + Ts Here, COEF is various amount increase correction coefficients, and includes, for example, water temperature increase correction according to water temperature and 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 the dead time of the fuel injection valve 14.

Further, α is a feedback correction coefficient which is calculated mainly based on the detection signal of the upstream O ₂ sensor 18. That is, a value obtained by comparing the output signal of the upstream O ₂ sensor 18 with a predetermined slice level (corresponding to the theoretical air-fuel ratio) and quasi proportional integral control based on the inversion of the lean side and the rich side. If it is 1 or more, the air-fuel ratio is controlled to the rich side, and if it is 1 or less, the air-fuel ratio is controlled to the lean side. Therefore, as a result of this proportional-plus-integral control, the output signal of the upstream O ₂ sensor 18 changes at a cycle 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 not only for diagnosing the deterioration of the catalyst which will be described later, but also for correcting the overall deviation of the feedback control by the upstream O ₂ sensor 18. That is, the downstream O ₂ sensor 1
The output signal of 9 is also subjected to pseudo proportional-plus-integral control based on the rich / lean inversion, and the second correction coefficient αi is obtained. Then, the second correction coefficient α
i is used to learn and correct the proportional amount of the above-described feedback correction coefficient α in the proportional-plus-integral control. still,
As a result, the output signal of the downstream O ₂ sensor 19 repeats rich / lean inversion with a relatively long cycle as shown in FIG. 7B unless the catalyst is deteriorated.

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

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

FIG. 3 is a main flow chart showing the overall flow of the catalyst deterioration diagnosis. First, in step 1 (abbreviated as S1 etc. in the figure), a diagnosis completion flag indicating whether or not the catalyst deterioration diagnosis has been completed. It judges based on. The diagnosis end flag is reset when the operation of the internal combustion engine 11 is completed, 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
Subsequently, it is sequentially determined whether or not various conditions of the internal combustion engine 11 satisfy predetermined diagnostic conditions. The diagnostic condition is
It is roughly divided into a diagnosis permission condition that defines conditions that are prerequisites for diagnosis and a diagnosis region condition that defines an operation region in which diagnosis is performed. Steps 2 to 4 are diagnostic permission conditions, and steps 5 to 7 are diagnostics. 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, the water temperature sensor 2
0, crank angle sensor 21, and vehicle speed sensor 22 are all 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 the catalyst temperature point P described later is equal to or higher than a predetermined value.

Further, in step 5, whether the engine speed N at that time is greater than or equal to a predetermined value, and in step 6, whether the load (for example, basic injection amount Tp) is greater than or equal to 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 the conditions are satisfied, the process proceeds to step 8 and the 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 the subroutine shown in FIG.

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

There are various methods for diagnosing the catalyst deterioration in step 8, but, for example, as shown in FIG. 7, the rich / lean inversion period T1 of the output signal of the upstream O ₂ sensor 18 and the downstream O ₂ are detected. The ratio (T2 / T1) of the rich / lean inversion period T2 of the output signal of the ₂ sensor 19 is obtained within an appropriate period, and this is used as a value indicating the O ₂ storage capacity.

When the calculation of the ratio of the inversion period is completed in step 9, the process proceeds to step 10 and it is determined whether or not the detected O ₂ storage capacity is equal to or more than a predetermined value. Specifically, it is determined whether or not the ratio of the inversion period described above is equal to or greater 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, it is determined that the catalyst is normal, and the diagnosis end flag is set in step 17, and the ignition timing retard flag described later is cleared. Then, a series of processing is ended.

On the other hand, when it is determined in step 10 that the O ₂ storage capacity is lower than the predetermined value, step 12
Then, the process proceeds to step S23 and compares with the value of the O ₂ storage capacity measured last time to determine whether or not the value has decreased by a predetermined value or more. Here, in the case of NO, the routine proceeds to step 13, where it is judged that the catalyst has deteriorated, and the warning lamp 24 is turned on.

In step 12, when the value of the O ₂ storage capacity is sharply decreased as compared with the previous value, it is highly possible that the catalyst temperature at the time of measurement was not sufficient, not deterioration over time. Therefore, the routine proceeds to steps 14 and 15, and the ignition timing retard flag is set. And step 16
Then, after clearing the catalyst temperature point P described above, a series of catalyst deterioration diagnosis is executed again.

FIG. 5 shows an ignition timing control subroutine. In step 31, the ignition timing corresponding 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 to step 33, the ignition timing is forcibly retarded by a predetermined crank angle.

Therefore, when the catalyst deterioration diagnosis is performed again through steps 15 and 16, since the operation is performed with the ignition timing retarded, the exhaust gas temperature rises and the catalytic converter 17
Can be actively heated. In particular, step 16
By once clearing the catalyst temperature point P, 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. However, since the exhaust gas temperature in each region is increased due to the retard of the ignition timing, at the stage (step 4) when the catalyst temperature point P reaches a predetermined value, the temperature is definitely higher than the catalyst activation temperature. Become.

Therefore, in the catalyst deterioration diagnosis to be executed again, there is no risk of erroneous diagnosis due to the low catalyst temperature, and it can be surely judged whether the deterioration has occurred. That is, if the O ₂ storage capacity is equal to or higher than the predetermined value with the catalyst temperature thus raised (step 10), it is determined that the catalyst has not deteriorated (step 11). Even if the catalyst temperature is raised in this way, if the O ₂ storage capacity is not more than the predetermined value, the process proceeds to step 13 through steps 12 and 14, and it is determined that the catalyst has deteriorated.

By clearing the ignition timing retard flag in step 17, the forced retardation of the ignition timing is released, and the control returns to the optimum ignition timing control.

As described above, in the above embodiment, when the catalyst is suspected to be deteriorated at the time of the first diagnosis, the ignition timing is forcibly retarded, the catalytic converter 17 is actively heated, and then the diagnosis is executed again. The erroneous determination is surely prevented. Even 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 traveling.

In the above embodiment, the diagnosis is performed under the normal ignition timing prior to the diagnosis accompanied by the forced retardation of the ignition timing, and when the O ₂ storage capacity is sufficient,
Since the diagnosis is settled at that time, it is possible to minimize the deterioration of the fuel consumption due to the retard of the ignition timing.

[0040]

As is apparent from the above description, according to the catalyst deterioration diagnosing device for an internal combustion engine according to the present invention, the catalytic converter is positively heated by the rise in exhaust temperature due to the ignition timing retard. It is possible to prevent erroneous diagnosis when the catalyst temperature is low. In particular, since the catalyst temperature can be increased without excessively strict diagnosis conditions such as the operating region, the reliability of the deterioration diagnosis can be improved without reducing the opportunity and frequency of the catalyst deterioration diagnosis.

[Brief description of drawings]

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

FIG. 2 is a structural explanatory view showing a mechanical structure of an 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 catalyst temperature points P.

FIG. 5 is a flowchart showing a subroutine of ignition timing correction.

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Upstream side air-fuel ratio sensor 2 ... Downstream side air-fuel ratio sensor 3 ... Diagnostic condition determination means 4 ... Diagnostic means 5 ... Ignition timing control means 6 ... Delay angle correction means

Claims (1)

[Claims] 1. An upstream air-fuel ratio sensor disposed upstream of a catalytic converter interposed in an exhaust passage, a downstream air-fuel ratio sensor disposed downstream of the catalytic converter, and various internal combustion engines. Diagnostic condition determining means for determining whether or not the condition of (1) satisfies a predetermined diagnostic condition, and when the diagnostic condition is satisfied, using the output signal of the upstream side air-fuel ratio sensor and the output signal of the downstream side air-fuel ratio sensor. Diagnosis means for diagnosing deterioration of the catalyst, ignition timing control means for setting ignition timing of the internal combustion engine based on engine operating conditions, and retard correction means for forcibly retarding the ignition timing in the catalyst deterioration diagnosis. A catalyst deterioration diagnosis device for an internal combustion engine, comprising: