JPH04116239A - Catalystic deterioration diagnostic device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent decrease in diagnostic accuracy caused by deviation of a rear air-fuel ratio and deviation of a judging standard by inhibiting deterioration diagnosis of catalyst in the case renewal of learning compensation which uses a downstream air-fuel ratio sensor is not performed enough. CONSTITUTION:A catalyst converter 27 is interposed at an exhaust passage 23 in an internal combustion engine 21, and an upstream oxygen sensor 28 is arranged above the catalyst converter 27, and a downstream oxygen sensor 29 is arranged downstream. A feedback compensation coefficient is calculated based on output of the oxygen sensor 28 in a control unit 32, and the feedback compensation coefficient is corrected by a learning value based on the output of the oxygen sensor 29. When the number of renewal of the learning value based on the output of the oxygen sensor 29 is at a specified value or more, the deviation in the air-fuel ratios is seldom happened, and deterioration diagnosis of the catalyst converter 27 is performed by comparing the outputs of the oxygen sensors 28, 29 each other. Consequently, the deterioration diagnosis is performed accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an internal combustion engine in which the deterioration state of a catalyst is diagnosed using air-fuel ratio sensors disposed on the upstream and downstream sides of a catalytic converter. The present invention relates to a catalyst deterioration diagnostic device.

BACKGROUND OF THE INVENTION Air-fuel ratio sensors, for example 0.0. A sensor is installed on the upstream side
For example, Japanese Patent Application Laid-Open No. 63-205441 discloses a device that executes air-fuel ratio feedback control mainly using the output signal of a sensor and diagnoses deterioration of a catalyst by comparing the output signals of both sensors. ing.

That is, during execution of air-fuel ratio feedback control, the fuel supply amount is controlled mainly by pseudo proportional-integral control based on the output signal of the upstream O sensor, so the output signal of the upstream O sensor is As shown in FIG. 5(a), it is rich periodically.

Repeat lean reversals. On the other hand, on the downstream side of the catalytic converter, the fluctuation in the residual oxygen concentration is very gradual due to the O storage capacity of the catalyst, so the output signal of the downstream O sensor is ), the fluctuation range is smaller and the period is longer than that of the upstream Ot sensor.

However, as the catalyst in the catalytic converter deteriorates, 0. Due to the decrease in storage capacity, the oxygen concentration does not change much between the upstream and downstream sides of the catalytic converter, and as a result, the output signal of the downstream O sensor becomes as shown in (c) in Figure 5.
), the upstream side 0. Inversions begin to repeat at a period similar to the sensor output, and the range of variation becomes large.

Therefore, in the device described in the above publication, the ratio (TI/T2) of the upstream side 0, sensor rich, lean inversion period TI and the downstream side O, sensor rich, lean inversion period T2 is determined, and this ratio When the value exceeds a predetermined value, it is determined that the catalyst has deteriorated.

In addition, downstream O! In addition to diagnosing catalyst deterioration as described above, the output signal of the sensor is generally used for learning correction of the overall air-fuel ratio bias in air-fuel ratio feedback control based on the output signal of the upstream oxygen sensor. It is.

Problems to be Solved by the Invention However, in order to accurately diagnose catalyst deterioration by comparing the output of the upstream O sensor and the output of the downstream O sensor as described above, air-fuel ratio feedback is a prerequisite. The actual air-fuel ratio provided by the control must be controlled with fairly high precision around the stoichiometric air-fuel ratio. In other words, upstream side 0. If the actual air-fuel ratio is biased toward the rich or lean side due to aging of the sensor and repeats periodic reversals, the reversal period of the downstream O and sensor will be affected, so it is necessary to maintain a constant level. Diagnosis based on the standard cannot be performed with high accuracy.

Means for Solving the Problems Therefore, the present invention learns and corrects air-fuel ratio feedback control using the output signal of a downstream air-fuel ratio sensor, and performs catalyst deterioration diagnosis on the condition that the learning has sufficiently progressed. I decided to do this. That is, 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 interposed in an exhaust passage, and an upstream air-fuel ratio sensor 1 disposed downstream of the catalytic converter. A correction unit that calculates a feedback correction coefficient based on the output of the downstream air-fuel ratio sensor 2, the basic fuel injection amount setting means 3 that sets the basic fuel injection amount according to the operating conditions of the internal combustion engine, and the output of the upstream air-fuel ratio sensor l. Coefficient calculation means 4, and storage means 5 for storing learning values respectively assigned to a plurality of sections of an operating region having at least engine speed and load as parameters.
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; Learning and updating means 8 corrects and updates the learning value in the storage means based on the output of the downstream air-fuel ratio sensor 2 when the user stays in one of the compartments for a predetermined period of time; In an internal combustion engine, the deterioration of the catalyst is determined by comparing the output of the upstream air-fuel ratio sensor 1 and the output of the downstream air-fuel ratio sensor 2 during air-fuel ratio feedback control. The present invention is characterized in that it includes a deterioration determination means IO that performs the above-mentioned update, and a determination prohibition means 11 that prohibits the deterioration determination described above when the number of updates of the learned value is equal to or less than a predetermined number of times.

Effect: In the above configuration, a feedback correction coefficient is determined based on the output of the upstream air-fuel ratio sensor l, and the fuel injection amount is feedback-controlled using this coefficient. Here, a learned value is determined based on the output of the downstream air-fuel ratio sensor 2, and the feedback correction coefficient is corrected using the learned value. That is, if the air-fuel ratio is still biased as a result of the air-fuel ratio feedback control, the bias is removed by the learning correction by the downstream air-fuel ratio sensor 2.

The above learned value is updated when the vehicle remains in any section of the driving region for a predetermined period of time, so the greater the number of updates, the higher the reliability.

Therefore, if the number of updates exceeds a certain value, it is considered that there is almost no deviation in the air-fuel ratio, and the air-fuel ratio changes periodically within a relatively narrow range around the stoichiometric air-fuel ratio due to feedback control.

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

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 2 is a structural explanatory diagram showing the mechanical structure of an embodiment of the present invention, in which 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 boat is arranged for each cylinder, and a throttle valve 25 is interposed, and on the upstream side thereof, a hot wire type, for example, for detecting the amount of intake air is installed. An air flow meter 26 is also provided.

A catalytic converter 27 using, for example, a three-way catalyst is interposed in the exhaust passage 23, and an upstream 0 sensor 28 is located upstream of the catalytic converter 27, and a downstream sensor 28 is located downstream of the catalytic converter 27. 29 are arranged respectively. The O sensors 28 and 29, which act as air-fuel ratio sensors, generate an electromotive force according to the residual oxygen concentration in the exhaust gas. High level (about 1V) on the rich side (about 1V), low level (about 100!V) on the lean side
becomes.

Further, 30 indicates a water temperature sensor that detects the temperature of the cooling water of the internal combustion engine, and 31 indicates a crank angle sensor that is provided to detect the engine rotational speed and generates 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 micro combi coater system, and controls the injection amount of the fuel injection valve 24 based on the Ot sensors 28 and 29, that is, the air-fuel ratio is controlled by a feedback control method. At the same time, a deterioration diagnosis of the catalyst is performed as will be described later, and if it is determined that the deterioration has exceeded a predetermined level, a warning light 33 is turned on.

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

First, an outline of air-fuel ratio control will be explained. This air-fuel ratio control is performed based on the intake air amount Q detected by the air flow meter 26 and the engine rotation speed N detected by the crank angle sensor 31.
/N to calculate the basic pulse width Tp (basic injection amount),
Further, various increase corrections and feedback corrections are added to this to determine the drive pulse width Ti (injection amount) of the fuel injection valve 24. Specifically, the pulse width T1 is determined by the following equation.

T i =TpXCOEFXα+Ts Here, C0EF is various increase correction coefficients, such as water temperature increase correction according to water temperature, air-fuel ratio correction at high speed and high load, etc. 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, α is a feedback correction coefficient calculated mainly based on the detection signal of the upstream side O and the sensor 28. That is, the value obtained by comparing the output signal of the upstream O sensor 28 with a predetermined slice level (corresponding to the stoichiometric air-fuel ratio) and performing pseudo proportional-integral control based on its reversal to the lean side and 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.

(a) of FIG. 6 shows the upstream side 0. An example of the output signal of the sensor 28 is shown, and (b) shows the corresponding change in the feedback correction coefficient α. The feedback correction coefficient α is obtained by pseudo-proportional-integral control as described above, and when the output of the upstream O sensor 28 crosses a predetermined slice level and reverses from the rich side to the lean side, the correction coefficient α A constant proportional bone PL is added to α, and an integral is gradually added with a slope according to a predetermined integral constant IL. This feedback correction coefficient α is multiplied by the basic fuel injection amount 'rp as described above, so
The actual air-fuel ratio gradually enriches.

Then, when the output of the upstream Ot sensor 28 is reversed from the lean side to the rich side, a constant proportional bone PR is subtracted from the correction coefficient α, and the integral is gradually subtracted with a slope according to a predetermined integral constant IR. Go. By repeating such actions, the actual air-fuel ratio is maintained approximately near the stoichiometric air-fuel ratio while changing at a period of about 1 to 2 Hz.

Incidentally, at low water temperatures, at high speeds and high loads, or at times of fuel cut during deceleration, etc., when it is necessary to increase the amount of fuel in some way, the feedback correction coefficient α is clamped to 1, essentially resulting in oven loop control.

On the other hand, the output signal of the downstream side O sensor 29 can be used for diagnosing catalyst deterioration, which will be described later. It is used for learning correction of overall bias in feedback control by the sensor 28.

That is, if the air-fuel ratio as a whole tends to be rich as a result of the feedback control by the upstream side Ot sensor 28 described above, the downstream side 0. The output signal of the sensor 29 is continuous on the rich side. Further, if the air-fuel ratio as a whole tends to be lean, the output signal of the downstream side 0 and the sensor 29 will be continuous on the lean side. Therefore, depending on the overall tendency of the air-fuel ratio to be biased, a learned value is set in advance for each operating region.
Assign the proportional bone PL when reversing from rich to lean.
and the proportional bone PII at the time of lean-rich reversal are respectively corrected as P t,=PL+LPPR=PtaLP. In detail, as shown in Fig. 3, engine speed N and load (for example, basic fuel injection amount Tp)
Divide the operating region into multiple (n) sections using as a parameter, and calculate the learned values LP, -LPn corresponding to each section.
is stored in read/write memory backed up by the vehicle's on-board battery. Then, among the learned values, a value corresponding to the operating conditions at that time is read out, and the proportional bones PL and PR are corrected as described above.

Incidentally, it is also possible to correct the integral constants 1t, , I++ instead of or in addition to the proportional bones PL and Pl.

The learned value LP is corrected and updated when the engine operating condition remains within each section of the operating range for a certain period of time. In other words, the downstream side is 0. If the output signal of the sensor 29 is still on the rich side, the predetermined amount ΔL is reduced from the learned value LP.
P* is subtracted and the stored contents are updated as a new learned value LP. Similarly, if the output signal of the sensor 29 on the downstream side O is still on the lean side, the learning value LP is increased by a predetermined amount ΔLP
L is added and the stored contents are updated as a new learned value LP.

Therefore, upstream side 0. The overall air-fuel ratio deviation due to aging of the sensor 28 and individual differences in each part is corrected with higher accuracy and responsiveness, and the feedback correction coefficient α becomes α=
It changes periodically around 1.

In addition, for each section of the above-mentioned operation region, the above-mentioned learned value LP
A learning counter is provided that is incremented each time learning is updated, and the value L CNT is used to determine whether learning has progressed sufficiently, especially whether sufficient learning has been performed within that section. It is possible to distinguish.

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

First, in step 1, it is determined whether a diagnosis permission condition is satisfied. The conditions for this are: (1) the water temperature at the time of lateral start is above a predetermined value, (2) a predetermined time has elapsed after engine warm-up was completed, and (2) downstream side 0. There are three conditions: that the sensor 29 is activated (this is determined from the output level of the sensor 29), and only when all the conditions are met does the process proceed to step 2. In step 2, the operating state at that time is within the range where air-fuel ratio feedback control is performed;
And it is determined whether or not it is in a steady state.

In other words, ■ Vehicle speed ■ SP is within a predetermined range, ■ Change amount ΔVSP in vehicle speed VSP is less than or equal to a predetermined value, ■ Engine speed N is within a predetermined range, ■ Engine load, e.g. basic fuel injection. The condition is that the amount 'rp is within a predetermined range, and if all of these conditions are met, the process proceeds to step 3 as being within the diagnostic range. In step 3, furthermore, the learning counter LCNT in the corresponding section at that time is
It is determined whether the value of is less than or equal to a predetermined value LCNTO.

Here, if the learning counter value LCNT is less than or equal to the predetermined value LCNTO, learning in that section has not progressed sufficiently, and the air-fuel ratio changes periodically around a value somewhat distant from the stoichiometric air-fuel ratio during feedback control. Deterioration diagnosis is not performed because there is a possibility that it may change.

If the learning counter value LCNT is larger than the predetermined value LCNTO, it is considered that the actual air-fuel ratio is maintained fairly accurately near the stoichiometric air-fuel ratio, so the process proceeds to step 4 and subsequent steps for diagnosis.

In step 4, the reversal frequency ratio H2RATE between the upstream side O, sensor 28 and the downstream side O, sensor 29 is calculated. Specifically, using the rich/lean reversal frequency f of the upstream O sensor 28 and the lip/lean reversal frequency f of the downstream O sensor 29 associated with air-fuel ratio feedback control, H2RATE=f2/f.

Find it as. When the deterioration of the catalyst in the catalytic converter 27 progresses, the downstream side O, the inversion frequency f of the sensor 29,
becomes high, so the above-mentioned inversion frequency ratio HzRATE becomes large. Of course, it is also possible to measure the reversal period of each sensor 28, 29 and calculate the reversal frequency ratio HzRATE from this.

Then, in step 5, the above reversal frequency ratio HzRATE is compared with a predetermined determination reference value CNGH2.

Here, the reversal frequency ratio HzRATE is the judgment reference value CNGH2
If it is less than that, it is determined that the catalyst has not deteriorated, and the warning light 23 is not turned on. In addition, the counter CCA described later
Clear the value of TNG (step 6.7) On the other hand, the reversal frequency ratio HzRATE is the judgment reference value CN.
If it is GH2 or more, the value of the counter CCATNG is incremented and compared with a predetermined number of determinations CCATJ (step 8.9). Then, a predetermined number of times CCA
If TJ is reached, that is, H2RAT continues for a predetermined number of times.
When a state of E≧CNGHz is detected, it is determined that the catalyst has deteriorated, and the warning light 23 is turned on (step 10).

In this way, in the above embodiment, the upstream side O, the sensor 28 and the downstream side 0. When diagnosing catalyst deterioration using the ratio of the number of reversals of the sensor 29, it is necessary to check that the learning using the downstream O sensor 29 has progressed sufficiently, that is, the actual air-fuel ratio is maintained accurately near the stoichiometric air-fuel ratio. Since the diagnosis is started in the current state, stable judgments can always be made at a constant level.

Effects of the Invention As is clear from the above explanation, the catalyst deterioration diagnosis device for an internal combustion engine according to the present invention compares the outputs of the upstream air-fuel ratio sensor and the downstream air-fuel ratio sensor of the catalytic converter to detect catalyst deterioration. When making a determination, if the learning correction using the downstream air-fuel ratio sensor has not been updated sufficiently,
Since such diagnosis is prohibited, it is possible to prevent a decrease in diagnostic accuracy due to deviation of the actual air-fuel ratio itself and to prevent variations in the determination criteria, and it is possible to perform catalyst deterioration diagnosis with high reliability.

[Brief explanation of the drawing]

Fig. 1 is a claim correspondence diagram showing the structure of the present invention, Fig. 2 is an explanatory view of the structure showing an embodiment of the invention, Fig. 3 is an explanatory drawing showing the relationship between the operating range and the learned value, and Fig. 4 is FIG. 5 is a flowchart showing a program for diagnosing catalyst deterioration in this embodiment. FIG. 6 is a waveform chart showing a comparison of the output signal of the sensor and the downstream side O, and FIG. 6 is a waveform chart showing a comparison of the output signal of the upstream side O, the sensor, and the feedback correction coefficient. L... 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 correction means, 8...Learning update means, 9...Learning frequency coefficient means, 10...Deterioration determination means, II...Judgment prohibition means. Fig. 2 3] Fig. 3 1'P→ Fig. 4

Claims (1)

[Claims] (1) The upstream air-fuel ratio sensor installed upstream of the catalytic converter installed in the exhaust passage, the downstream air-fuel ratio sensor installed downstream of the catalytic converter, and the internal combustion engine operating conditions. basic fuel injection amount setting means for setting a basic fuel injection amount accordingly; correction coefficient calculation means for calculating a feedback correction coefficient based on the output of the upstream air-fuel ratio sensor;
storage means for storing learned values assigned to a plurality of sections of an operating range in which at least engine speed and load are parameters; learning correction means for correcting the feedback correction coefficient using the learned values for each section; a fuel injection amount correction means that corrects the basic fuel injection amount using the feedback correction coefficient; and a fuel injection amount correction means that corrects the basic fuel injection amount using the feedback correction coefficient; In an internal combustion engine comprising learning updating means for correcting and updating the learning value in the storage means, and learning number counting means for counting the number of updates for each section, an upstream air-fuel ratio is provided during air-fuel ratio feedback control. Deterioration determination means for determining deterioration of the catalyst by comparing the output of the sensor and the output of the downstream air-fuel ratio sensor, and determination prohibition means for prohibiting the deterioration determination when the number of updates of the learned value is less than or equal to a predetermined number of times. A catalyst deterioration diagnostic device for an internal combustion engine, comprising: