JP2864699B2 - Catalyst deterioration diagnosis device for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine that diagnoses a deterioration state of a catalyst by using air-fuel ratio sensors disposed upstream and downstream of a catalytic converter. A catalyst deterioration diagnosis device.

Disposed upstream and the air-fuel ratio sensor, for example O ₂ sensor, respectively at the downstream side of the catalytic converter of the prior art internal combustion engine, upstream O ₂
An apparatus that performs air-fuel ratio feedback control mainly based on sensor output signals and diagnoses catalyst deterioration based on a comparison between output signals from both sensors is disclosed in, for example,
No. -20541.

That is, during execution of the air-fuel ratio feedback control,
Since the fuel supply amount is mainly controlled based on the output signal of the upstream O ₂ sensor by, for example, pseudo proportional integral control, the output signal of the upstream O ₂ sensor is as shown in FIG. , And the 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, so that the output signal of the downstream O ₂ sensor is the fifth signal.
As shown in (b) of FIG, small variation width as compared with the upstream O ₂ sensor, and the period is lengthened.

However, the catalyst in the catalytic converter deteriorates, the reduction of O ₂ storage capability, the oxygen concentration in the catalytic converter upstream side and the downstream side is not changed so, as a result, the output signal of the downstream O ₂ sensor, FIG. 5 (c)
As shown in ( ₂₎ , the reversal is repeated at a cycle approximating the output of the upstream O2 sensor, and the fluctuation width increases.

Accordingly, in the apparatus described in the above publication, the upstream O ₂ sensor rich, lean inversion period T1 and the downstream O ₂ sensor rich, the ratio of the lean inversion period T2 (T1 / T2) determined, the ratio When is equal to or more than a predetermined value, it is determined that the catalyst has deteriorated.

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

Invention compared try to challenge, however the output of the downstream O ₂ sensor and the output of the upstream O ₂ sensor as described above resolved to accurately diagnose the deterioration of the catalyst, as a premise, the air-fuel ratio feedback The actual air-fuel ratio provided by the control must be controlled with very high precision around the logical air-fuel ratio.
That is, when the actual air-fuel ratio due to aging or the like of the upstream O ₂ sensor is repeatedly periodically reversed in a state of leaning to the rich side or the lean side, the effect is the inversion period of the downstream O ₂ sensor Therefore, diagnosis based on a certain level cannot be performed accurately.

Means for Solving the Problems Therefore, in the present invention, the learning correction of the air-fuel ratio feedback control using the output signal of the downstream air-fuel ratio sensor is performed, provided that the learning has sufficiently proceeded.
Diagnosis of catalyst deterioration is performed. That is, the apparatus for diagnosing catalyst deterioration of an internal combustion engine according to the present invention is provided with an upstream air-fuel ratio sensor 1 provided upstream of a catalytic converter interposed in an exhaust passage and a downstream side of the catalytic converter. A downstream air-fuel ratio sensor 2, basic fuel injection amount setting means 3 for setting a basic fuel injection amount according to operating conditions of the internal combustion engine,
A correction coefficient calculating means 4 for calculating a feedback correction coefficient based on the output of the upstream air-fuel ratio sensor 1 and a learning value assigned to each of a plurality of sections of the operating region using at least the engine speed and the load as parameters are stored. A storage means 5, a learning correction means 6 for correcting the feedback correction coefficient using the learning value of each section, a fuel injection amount correction means 7 for correcting the basic fuel injection amount using the feedback correction coefficient, and an engine When the operating condition remains in any of the sections for a predetermined period, the downstream air-fuel ratio sensor 2
In an internal combustion engine comprising a learning updating means 8 for correcting and updating the learning value in the storage means based on the output of the storage means and a learning number counting means 9 for counting the number of times of updating for each section, the air-fuel ratio feedback A deterioration determining means for comparing the output of the upstream air-fuel ratio sensor with the output of the downstream air-fuel ratio sensor during control to determine the deterioration of the catalyst; And a determination prohibition unit for prohibiting the deterioration determination.

Operation In the above configuration, the feedback correction coefficient is obtained based on the output of the upstream air-fuel ratio sensor 1, and the fuel injection amount is feedback-controlled using the feedback correction coefficient. Here, a learning value is obtained based on the output of the downstream air-fuel ratio sensor 2, and the feedback correction coefficient is corrected by the learning value. That is, as a result of the air-fuel ratio feedback control, if the air-fuel ratio is still offset, the offset is removed by the learning correction by the downstream air-fuel ratio sensor 2.

The learning value is updated when it stays in any of the sections of the driving area for a predetermined period, so that the greater the number of updates, the higher the reliability. Therefore, if the number of updates is equal to or more than a certain value, it is considered that there is almost no deviation of the air-fuel ratio, and the feedback control periodically changes the air-fuel ratio in a relatively narrow range around the stoichiometric air-fuel ratio.

Thus, by comparing the output of the upstream air-fuel ratio sensor 1 and the output of the downstream air-fuel ratio sensor 2 in such a state, the catalyst deterioration diagnosis can be performed with high accuracy.

Hereinafter, an embodiment of the present invention will be described 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, wherein 21 is an internal combustion engine, 22 is an intake passage thereof, 23
Indicates an exhaust passage. In the intake passage 22, a fuel injection valve 24 for supplying fuel to each intake port is provided for each cylinder, and a throttle valve 25 is interposed. For example, a hot-wire type air flow meter 26 for detecting the temperature is provided.

To the exhaust passage 23, for example, with a catalytic converter 27 using a three-way catalyst is interposed, the upstream O ₂ sensor 28 to the upstream position than the catalyst converter 27, the downstream O ₂ sensor downstream position 29 are arranged respectively. O ₂ sensor 28, 29 as the air-fuel ratio sensor is for generating an electromotive force corresponding to the residual oxygen concentration in the exhaust gas, in particular, the electromotive force changes suddenly bordering the stoichiometric air-fuel ratio, excessive than the stoichiometric air-fuel ratio High level (about 1V) on the dark side (rich side), lean side (lean side)
At low level (about 100mV).

Reference numeral 30 denotes a water temperature sensor for detecting a cooling water temperature of the internal combustion engine, and reference numeral 31 denotes a crank angle sensor provided for detecting the engine speed and emitting a pulse signal at every predetermined crank angle.

The control unit 32 to which the detection signals of the various sensors described above are input uses a so-called microcomputer system, and the fuel injection valve 24 based on the O ₂ sensors 28 and 29 is used.
In addition to executing the injection amount control, that is, the air-fuel ratio control by the feedback control method, the deterioration diagnosis of the catalyst as described later is performed, and when it is determined that the deterioration is equal to or more than the predetermined level, the warning lamp 33 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, a basic pulse width Tp (basic injection amount) is calculated from the intake air amount Q detected by the air flow meter 26 and the engine speed N detected by the crank angle sensor 31 as Tp = Q / N, and The drive pulse width Ti (injection amount) of the fuel injection valve 24 is determined by adding various increase corrections and feedback corrections to this. 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, an air-fuel ratio correction at a high speed and a high load, and the like. 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 24.

Further, alpha is mainly feedback correction coefficient is calculated based on the detection signal of the upstream O ₂ sensor 28. That is, the output signal of the upstream O ₂ sensor 28 is compared with a predetermined slice level (corresponding to the logical 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.

Of FIG. 6 (a) shows an example of an output signal of the upstream O ₂ sensor 28, shows (b) the change of the feedback correction coefficient α corresponding thereto. The feedback correction coefficient α is obtained by pseudo proportional integral control as described above. When the output of the upstream O ₂ sensor 28 crosses a predetermined slice level and reverses from rich to lean, the correction coefficient α α constant proportional amount P _L is added to, and integral amount in inclination by a predetermined integral constant I _L is gradually being added gradually. Since the feedback correction coefficient α is multiplied by the basic fuel injection amount Tp as described above, the actual air-fuel ratio gradually increases. When the next output of the upstream O ₂ sensor 28 is inverted from the lean side to the rich side, certain proportional portion P _R from the correction coefficient α is subtracted, and the integral component with a slope by a predetermined integral constant I _R is gradually Going to be subtracted. By repeating such an operation, the actual air-fuel ratio is maintained in the vicinity of the stoichiometric air-fuel ratio while changing at a cycle of about 1 to 2 Hz.

Note that the feedback correction coefficient α is clamped to 1 at the time of low water temperature, high speed, high load, or fuel cut during deceleration, where it is necessary to perform some fuel increase.
In effect, open loop control is performed.

On the other hand, the output signal of the downstream O ₂ sensor 29 is used for, in addition to the catalyst deterioration diagnosis described later, learning correction of the overall deviation of the feedback control by the upstream O ₂ sensor 28.

That is, as a result of the feedback control by the upstream O ₂ sensor 28 described above, if the rich tendency as a whole air-fuel ratio, the output signal of the downstream O ₂ sensor 29 become continuous at the rich side. Further, if the lean tendency as a whole air-fuel ratio, the output signal of the downstream O ₂ sensor 29 become continuous with the lean side. Therefore, in accordance with the overall bias tendency of the air-fuel ratio, a learning value LP is assigned in advance to each operation region, and the proportional component P _L at the time of rich → lean inversion and the lean →
The proportional amount P _R of the rich inversion time, respectively, of correcting as _{P L = P L + LP P} R = P R -LP. Specifically, as shown in FIG. 3, the operating range is divided into a plurality of (n) sections by using the engine speed N and the load (for example, the basic fuel injection amount Tp) as parameters, and the learning value corresponding to each section is obtained. LP ₁ ~LP _n is stored in the vehicle battery backed-up writable memory. Then, a value corresponding to the operating condition at that time among the learning values is read out, whereby the proportional components P _L and P _R are corrected as described above.

Incidentally, the proportional component P _L, P instead of _R, or integral constant I _L In addition to this, it is also possible to correct the I _R.

Then, the learning value LP is corrected and updated when the engine operating condition has been within each section of the operating region for a certain period. That is, if the output signal is still rich side of the downstream O ₂ sensor 29, subtracts the predetermined amount DerutaLP _R from the learning value LP, and updates the stored contents as a new learning value LP. Similarly, if the output signal is still lean side of the downstream O ₂ sensor 29, by adding a predetermined amount DerutaLP _L to the learning value LP, and updates the stored contents as a new learning value LP.

Therefore, the deviation of the overall air-fuel ratio due to the aging of the upstream O ₂ sensor 28 and the individual difference of each part is corrected with higher accuracy and responsiveness, and the feedback correction coefficient α becomes α = 1.
At the center.

Further, for each section of the above-described operation region, the learning value LP
A learning counter that is incremented each time learning is updated is provided, and the value LCNT is used to determine whether the learning has progressed sufficiently, particularly whether the learning has been sufficiently performed in the section. Has become.

Next, FIG. 4 is a flowchart showing a program for catalyst deterioration diagnosis executed in the control unit 32, which will be described below. This routine is repeatedly executed at regular intervals, for example.

First, in step 1, it is determined whether a diagnosis permission condition has been satisfied. As this condition, the water temperature at engine starting is a predetermined value or more, it has passed a predetermined time after engine warm-up completion, it downstream O ₂ sensor 29 is activated (which is the sensor 29 (Determined from the output level of the above), and the process proceeds to step 2 only when all the conditions are satisfied. In step 2, it is determined whether or not the operation state is within a region where the air-fuel ratio feedback control is performed and is in a steady state. In other words, vehicle speed VS
P is within a predetermined range, the change amount ΔVSP of the vehicle speed VSP is equal to or less than a predetermined value, the engine speed N is within a predetermined range, an engine load, for example, a basic fuel injection amount Tp is within a predetermined range. When all of these conditions are satisfied, the process proceeds to step 3 within the diagnostic area. In step 3, it is further determined whether or not the value of the learning counter LCNT in the corresponding section at that time is equal to or smaller than a predetermined value LCNTO. Here, the learning counter value LCNT is a predetermined value.
If it is less than LCNTO, the learning is not sufficiently advanced in that section, and the possibility that the air-fuel ratio changes periodically around the value slightly different from the stoichiometric air-fuel ratio during feedback control remains. Not performed.

If the learning counter value LCNT is larger than the predetermined value LCNTO, it is considered that the actual air-fuel ratio is kept fairly close to the stoichiometric air-fuel ratio.

In step 4, the upstream O ₂ sensor 28 and the downstream O ₂ sensor
Calculate the inversion frequency ratio HZRATE of 29. For more information, with rich upstream O ₂ sensor 28 associated with the air-fuel ratio feedback control, rich lean reversal frequency f ₁ and the downstream O ₂ sensor 29, a lean and reversal frequency f _2, HZRATE = f ₂ / determined as f _1. The deterioration of the catalyst in the catalytic converter 27 progresses, the inversion frequency f ₂ of the downstream O ₂ sensor 29 becomes higher, the number of reversals ratio HZRATE becomes larger. The inversion cycle of each of the sensors 28 and 29 was measured, and the inversion frequency ratio HZRAT
It is of course possible to ask for E.

Then, in step 5, the above inversion frequency ratio HZRATE is compared with a predetermined judgment reference value CNGHZ. Where the reversal ratio HZRAT
If E is less than the reference value CNGHZ, it is determined that the catalyst has not deteriorated, and the warning lamp 23 is not turned on. Further, the value of a counter CCANTG described later is cleared (steps 6 and 7).

On the other hand, if the inversion frequency ratio HZRATE is equal to or greater than the determination criterion CNGHZ, the value of the counter CCATNG is incremented and compared with a predetermined determination frequency CCATJ (step 8,
9). When the predetermined number of times CCATJ is reached, that is, when the state of HZRATE ≧ CNGHZ is detected continuously for a predetermined number of times, it is determined that the catalyst has deteriorated, and the warning lamp 23 is turned on (step 10).

Thus, in the above embodiment, when diagnosing catalyst deterioration using the reversing speed ratio of the upstream O ₂ sensor 28 and the downstream O ₂ sensor 29, learning using the downstream O ₂ sensor 29 sufficiently proceeds. The diagnosis is started in a state in which the diagnosis is performed, that is, in a state in which the actual air-fuel ratio is accurately maintained in the vicinity of the stoichiometric air-fuel ratio, so that a stable determination can be always performed at a constant level.

Advantageous Effects of the Invention As is apparent from the above invention, in the catalyst deterioration diagnosis device for an internal combustion engine according to the present invention, the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor of the catalytic converter are compared to determine the deterioration of the catalyst. When the determination is made, if the learning correction using the downstream air-fuel ratio sensor has not been sufficiently updated, the diagnosis is prohibited. Can be prevented, and a more reliable catalyst deterioration diagnosis can be performed.

[Brief description of the drawings]

FIG. 1 is a claim correspondence diagram showing a configuration of the present invention, FIG. 2 is a configuration explanatory diagram showing one embodiment of the present invention, FIG. 3 is an explanatory diagram showing a relationship between an operation range and a learning value, and FIG. FIG. 5 is a flowchart showing a program for diagnosing catalyst deterioration in this embodiment. FIG. 5 shows an upstream O ₂ sensor and a downstream side of a catalytic converter.
FIG. 6 is a waveform diagram showing the output signal of the O ₂ sensor in comparison, and FIG. 6 is a waveform diagram showing the output signal of the upstream O ₂ sensor in comparison with the feedback correction coefficient. 1 ... upstream air-fuel ratio sensor, 2 ... downstream air-fuel ratio sensor, 3 ... basic fuel injection amount setting means, 4 ... correction coefficient calculation means, 5 ... storage means, 6 ... learning correction means, 7 ......
Fuel injection amount correcting means 8, learning updating means 9, learning number coefficient means 10, deterioration determining means 11, determination prohibiting 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 operation of an internal combustion engine. Basic fuel injection amount setting means for setting a basic fuel injection amount according to conditions; correction coefficient calculating means for calculating a feedback correction coefficient based on an output of an upstream air-fuel ratio sensor; and at least engine speed and load as parameters. Storage means for respectively storing learning values assigned to a plurality of sections of the driving region, learning correction means for correcting the feedback correction coefficient using the learning values of the sections, and the basic A fuel injection amount correcting means for correcting the fuel injection amount, and an output of the downstream air-fuel ratio sensor when the engine operation condition is within a certain period for a predetermined period. The learning update means for correcting and updating the learning value in the storage means, and the learning number counting means for counting the number of times of updating for each section, the upstream side during the air-fuel ratio feedback control. A deterioration determining means for comparing the output of the air-fuel ratio sensor with the output of the downstream air-fuel ratio sensor to determine the deterioration of the catalyst; and a determination for prohibiting the deterioration determination when the number of updates of the learning value is equal to or less than a predetermined number. An apparatus for diagnosing catalyst deterioration of an internal combustion engine, comprising prohibiting means.