JP2759821B2 - Catalyst purification efficiency diagnostic device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a catalyst purification efficiency diagnosis device for judging deterioration of a three-way catalyst for purifying exhaust gas of an internal combustion engine based on purification efficiency.

(Prior Art) In a fuel control apparatus for an internal combustion engine, a fuel injection amount is adjusted by multiplying a basic injection amount by various correction coefficients and calculating an air-fuel ratio correction coefficient according to air-fuel ratio information of the engine. ing. Furthermore, in the exhaust gas aftertreatment system of the exhaust system of the engine,
To obtain a non-gas purification action of the three-way catalyst used to effectively you'll need to maintain the exhaust gas in the range of the vicinity of the stoichiometric air-fuel ratio (window), O ₂ in order to obtain an air-fuel ratio information used in these control Uses sensors.

That is, in the conventional fuel control device of the internal combustion engine, an O ₂ sensor is provided upstream of the three-way catalyst, the output of the O ₂ sensor is received by the control means, and the air-fuel ratio of the exhaust gas is determined to be rich and lean around the stoichiometric air-fuel ratio. The air-fuel ratio correction coefficient is set so as to alternately swing between the widths, and feedback control is performed so that the fuel injection amount increases or decreases, whereby the three-way catalyst operates efficiently.

Here, in the O ₂ sensor, a platinum electrode is superimposed on a zirconia tube, and a gas having a different oxygen concentration is guided to both spaces facing the two electrodes, and a larger electromotive force is generated as the ratio of the oxygen concentration in both spaces is larger. Utilizing the characteristic of making it. When the O ₂ sensor receives an exhaust gas with a stoichiometric air-fuel ratio, the gas greatly changes its output before and after the stoichiometric air-fuel ratio, so when the gas is in a very narrow range (window) close to the change position, The exhaust gas is configured to be determined to be substantially at the stoichiometric air-fuel ratio.

(Problems to be Solved by the Invention) By the way, in the conventional device, the air-fuel ratio at that time is determined to be rich and lean before and after the stoichiometric air-fuel ratio based on the air-fuel ratio information of the O ₂ sensor on the upstream side of the three-way catalyst. Even if the three-way catalyst was controlled to swing alternately between the widths, it was not possible to confirm at what purification efficiency the three-way catalyst was actually operating at that time.

That is, even if the feedback control of the fuel supply amount is operating normally, if the three-way catalyst itself is deteriorated, the emission level of harmful substances in the exhaust gas may exceed the specified value. Yes, it is a problem.

Here, the exhaust gas with the air-fuel ratio swayed rich and lean flows into the upstream side of the three-way catalyst, and from the downstream side of the three-way catalyst, the amplitude of the air-fuel ratio is smoothed and kept almost at stoichio. If the condition that the exhaust gas flows out is maintained,
The three-way catalyst can be regarded as exhibiting a predetermined O ₂ storage capacity. That is, by looking at the ratio of the amplitudes of the air-fuel ratio on the upstream side and the downstream side of the three-way catalyst, the purification efficiency of the catalyst can be almost understood. Therefore, the air-fuel ratio on the downstream side of the three-way catalyst is detected,
It is presumed that it is possible to diagnose the purification efficiency by comparing the change width of the air-fuel ratio information with the upstream side.

An object of the present invention is to provide a catalyst purification efficiency diagnosis device capable of accurately determining catalyst deterioration.

To achieve (solutions for the problems) described above object, the present invention provides an O ₂ sensor mounted in an exhaust system with a three-way catalyst for purifying exhaust gas of an internal combustion engine, the output of the O ₂ sensor Based on the air-fuel ratio information to be performed, the air-fuel ratio of the engine is attached to an exhaust gas after-treatment system that performs feedback control of the fuel supply amount so as to match the stoichiometric air-fuel ratio. An air-fuel ratio sensor, and an air-fuel ratio feedback correction coefficient change width calculating means for taking in an air-fuel ratio feedback correction coefficient for the feedback control and calculating a change width thereof; and an equivalent based on an air-fuel ratio output from the air-fuel ratio sensor. An equivalence ratio change width calculating means for calculating a change width of the ratio, and catalyst deterioration information when the equivalence ratio change width with respect to the air-fuel ratio feedback correction coefficient change width exceeds a set value. And a catalyst deterioration determining unit that emits the catalyst.

(Operation) The air-fuel ratio feedback correction coefficient change width calculating means takes in the air-fuel ratio feedback correction coefficient for feedback control, calculates the change width, and the equivalent ratio change width calculating means calculates the equivalent based on the air-fuel ratio output from the air-fuel ratio sensor. The change width of the ratio is calculated, and the catalyst deterioration determination means can issue catalyst deterioration information when the equivalent ratio change width with respect to the air-fuel ratio feedback correction coefficient change width exceeds a set value.

(Embodiment) The catalyst purification efficiency diagnosing device of FIG. 1 is installed in an exhaust gas aftertreatment system S of an engine E.

The exhaust gas after-treatment system S is provided with an electronic control unit (hereinafter simply referred to as ECU1), and is configured to turn on and off a warning lamp R (see FIG. 2) for indicating catalyst deterioration.

Here, an intake passage 2 is connected to a combustion chamber B of the engine E via an intake valve 4, and an exhaust passage 3 is connected via an exhaust valve 5.

The intake passage 2 is provided with an air cleaner 6, a throttle valve 7 connected to an accelerator pedal operated by a driver, and an electromagnetic fuel injection valve (hereinafter simply referred to as an electromagnetic valve) 8 in this order from the upstream side. 3 is provided with a three-way catalyst 9 for purifying exhaust gas and a muffler (not shown) in order from the upstream side.

With such a configuration, the air sucked through the air cleaner 6 according to the opening degree of the throttle valve 7 is mixed with the fuel from the solenoid valve 8 at the intake manifold portion so as to have an appropriate air-fuel ratio, and ignited in the combustion chamber B. By igniting the plug at an appropriate timing, it is burned to generate engine torque, and then the air-fuel mixture is discharged as exhaust gas to the exhaust passage 3, and the three-way catalyst 9 causes CO, HC, NOx in the exhaust gas.
After purifying these three harmful components, the muffler silences them and releases them to the atmosphere.

Further, in order to control the air-fuel ratio and the like of the engine E,
Various sensors are provided.

First, on the intake path 2 side, an air flow sensor 11 for detecting an intake air amount from Karman vortex information and an intake air temperature sensor 1 for outputting intake air temperature information are provided at a portion where the air cleaner 6 is provided.
2, and an atmospheric pressure sensor 13 for outputting atmospheric pressure information is provided. A potentiometer type throttle sensor 14 for outputting opening degree information of the throttle valve 7 is provided at a portion where the throttle valve 7 is provided, and an idling state is output. An idle switch 15 is provided, and these are connected to the ECU 1.

Further, an O ₂ sensor 17 for detecting the oxygen concentration in the exhaust gas is provided in the exhaust manifold of the exhaust path 3.
An air-fuel ratio sensor 18 of a full area type is provided on the outlet side of the canning container for storing the air-fuel ratio.

Here, the all-area air-fuel ratio sensor 18 can output air-fuel ratio information over the entire area from rich to lean, and the sensor cell,
A pump cell, a heater and the like, for example, those disclosed in the specification and drawings of Japanese Patent Application No. 60-262982 by the present applicant are used.

Further, as other sensors, a water temperature sensor 19 that outputs engine cooling water temperature information, a crank angle sensor that outputs crank angle information (can output rotation speed information as an engine rotation sensor) 21, and outputs top dead center information of the first cylinder. TDC
A sensor 22 (see FIG. 2) and the like are provided.

Here, the hardware configuration of the ECU 1 is as shown in FIG. 2, where the ECU 1 includes a CPU 23, which includes an intake air temperature sensor 12, an atmospheric pressure sensor 13, a throttle sensor 14, and an O ₂ sensor.
17, the outputs from the air-fuel ratio sensor 18 and the water temperature sensor 19 of the full range type are input through the input interface 25 and the A / D converter 26, and the output of the idle switch 15 is input through the input interface 27, and the air flow Sensor 11,
Outputs from the crank angle sensor 21 and the TDC sensor 22 are directly input to the input port.

Further, the CPU 23 connects via a bus line a ROM 28 for storing various control program data and preset fixed value data, a RAM 29 which is updated and sequentially rewritten, and the like.

Now, focusing only on the well-known fuel injection control using the air-fuel ratio information and the purification efficiency diagnosis control of the catalyst, the ECU 1 takes in the air-fuel ratio feedback correction coefficient for feedback control as the air-fuel ratio feedback correction coefficient change width calculating means. The change width is calculated, the equivalent ratio change width calculation means calculates the change width of the equivalent ratio based on the air-fuel ratio output from the air-fuel ratio sensor, and the catalyst deterioration determination means calculates the equivalent ratio change with respect to the air-fuel ratio feedback correction coefficient change width. Each function is provided to issue catalyst deterioration information when the width exceeds the set value.

Here, from the CPU 23, an injection control signal having a time width corresponding to the fuel injection amount calculated based on a program described later is sequentially output to the solenoid valve 8 of each cylinder via the driver 30 according to the stroke phase. Is done. Furthermore, from CPU23,
A catalyst deterioration display signal based on the catalyst purification efficiency calculated based on a program described later is output to the alarm lamp R via the driver 31.

The catalyst purification efficiency calculation map (see FIG. 3) for calculating the catalyst purification efficiency from the ratio of the equivalent ratio change width _{Δφ REAR to} the air-fuel ratio feedback correction coefficient change width ΔK _FB is shown.
It is stored in ROM28.

The injection control signal is obtained by loading a basic drive time data set according to the intake air amount with a correction value according to each operation state such as air-fuel ratio information, and the basic drive time data is The solenoid valve driving routine (see FIG. 8) is executed by using the crank angle signal from the crank angle sensor 21 as an interrupt. On the other hand, each correction data is obtained by the main routine when the program is not executed by the interrupt. . Here, the main routine, the catalyst upstream amplitude calculation routine, the catalyst downstream amplitude calculation routine, and the solenoid valve driving routine will be described.

As shown in FIG. 5, in the main routine, first, when a terminal of a battery (not shown) is turned off, a step is performed.
Otherwise go directly to step a3. At step a2, a warning lamp extinguishing process is performed.

At step a3, each address in the RAM 29 is initialized. Subsequently, the detection information of each sensor is read, that is, the water temperature correction value is obtained from the output of the water temperature sensor 19.
Kwt is set based on the intake air temperature correction coefficient Kat from the output of the intake air temperature sensor 12, the atmospheric pressure correction coefficient Kap from the output of the atmospheric pressure sensor 13, the acceleration correction coefficient Kac from the output of the throttle sensor 14, and the output of the battery sensor 21. The battery voltage correction amount TD as the invalid time data is read and input to each address.

When the process reaches step a5, it is determined whether or not the warning lamp R is on. If the warning lamp R is on, the process proceeds to step a6. In step a6, after confirming that the lamp is
Return to a4. In step a7, a later-described catalyst upstream amplitude calculation routine and a later-described air-fuel ratio feedback correction coefficient change width ΔK _FB and an equivalent ratio change width Δφ _REAR obtained in the catalyst downstream amplitude calculation routine are called, and the ratio Δφ _REAR /
ΔK _FB is calculated, and the data of the predetermined area is updated with this value. Here, ΔK _FB and Δφ _REAR are both averaged values, and when the average equivalent ratio φ _REAR is correctly controlled to 1.0, the difference between Δφ _REAR / ΔK _FB and the catalyst purification efficiency is shown in FIG. A substantially first-order relationship as shown in FIG.

In step a8, Δφ _REAR / ΔK _FB is called, and at the same time, this value and the specified value α for determining that the catalyst purification efficiency is catalyst deterioration.
It is determined whether or not this value is larger than a threshold value in a region where the catalyst purification efficiency falls below β% considered as catalyst deterioration. Then, if the catalyst is deteriorated, that is, if it exceeds, the process proceeds to step a9, and if the catalyst is normal, the process directly returns to step a4. In step a9, display indicating catalyst deterioration, that is, lighting driving of the warning lamp R is performed, the driver is notified of the catalyst abnormality, and the process returns to step a4.

Next, as shown in FIG. 6, the catalyst upstream amplitude calculation routine is executed by a timer interruption every predetermined time width.

Here is first fuel control device determines whether the air-fuel ratio feedback control, when starting, transition and returns to the main during other non-feedback control as, during feedback control, the output of the O ₂ sensor 17 (4th (See FIG. (C)) and fetch it into a predetermined area. At this time,
The three-way catalyst inlet is an air-fuel ratio supplied exhaust gas that has been swung to (showed equivalence ratio phi _BX that is the reciprocal of the air-fuel ratio in this case) as shown in FIG. 4 (b). And based on the output and the current output of the step b3 taken last O ₂ sensor 17, O ₂ sensor output is determined whether inverted from rich to lean, step noninverting to step b4 in inverted b5
Proceed to. In step b4, the air-fuel ratio feedback correction coefficient (K _FB ) at the time of inversion from rich to lean (this value is
The value calculated in the solenoid valve driving routine performed by the ECU and stored in a predetermined area can be used in the storage area (K _FB ) _MIN of the air-fuel ratio feedback correction coefficient of the minimum value, and the process returns to the main routine.

On the other hand, at the time of non-inversion from rich to lean, the process reaches step b5, where it is determined whether or not the inversion from lean to rich is performed based on the output of the O ₂ sensor 17 previously taken and the current output. In the case of inversion, the process returns to step b6 in the case of non-inversion, that is, when the lean or rich state continues. In this step b6, the air-fuel ratio feedback correction coefficient (K _FB ) at the time of inversion from lean to rich
This value is taken into the maximum value air-fuel ratio feedback correction coefficient storage area (K _FB ) _MAX .

Thereafter, in step b7, the deviation between the maximum value and the minimum value of the air-fuel ratio feedback correction coefficient, (K _FB ) _MAX − (K _FB ) _MIN
Is calculated, and the calculated value is taken into the storage area (ΔK _FB ) of the air-fuel ratio feedback correction coefficient change width. Thereafter, an averaged value (ΔK _FB ) _AV of the air-fuel ratio feedback correction coefficient change width ΔK _FB is obtained by the calculation of the following formula, and sequentially updated.
Return to main.

(ΔK _FB ) _AV = k (ΔK _FB ) _AV + (1−k) (ΔK _FB ) where k is the averaging capture ratio.

Next, as shown in FIG. 7, the catalyst downstream amplitude calculation routine is also executed by a timer interrupt every predetermined time width.

Here, first, it is determined whether or not the fuel control device is performing the air-fuel ratio feedback control. When the feedback control is not performed, the process returns to the main process. Otherwise, the process proceeds to step c2.
Here, the reciprocal of the latest air-fuel ratio of the full-range type air-fuel ratio sensor 18 is calculated as the equivalence ratio φ (= 14.7 / A / F) and taken into a predetermined area φ _REAR .

In step a3, it is determined whether or not the detected equivalence ratio φ _REAR is higher than the maximum value φ _RMAX up to then, and if it is higher, φ _RMAX is updated with the detected equivalence ratio φ _REAR ,
Proceed to step c7, otherwise proceed to step c5.
In step c5, it is determined whether or not the detected equivalence ratio φ _REAR is lower than the previous minimum value φ _RMIN.If it is lower, φ _RMIN is _updated with the detected equivalence ratio φ _REAR , and the process proceeds to step c7. Otherwise, if it is moving in the maximum / minimum intermediate range, it proceeds directly to step c7.

In step c7, the current count (COUNT) is decremented by one.
Thereafter, it is determined whether or not the count (COUNT) has reached 0. If the count (COUNT) has reached 0, the process returns to step c9.

In step c9, the maximum value (maximum value) φ _RMAX and the minimum value (minimum value) φ _RMIN during the time width defined by the count value (COUNT) are fetched. For example, the maximum value φ _RMAX and the minimum value φ _RMIN in the time width T0 in FIG. Then, the minimum value φ _RMIN is subtracted from the maximum value φ _RMAX ,
_{Find the} equivalent ratio change width Δφ _REAR . Thereafter, an average value (Δφ _REAR ) _AV of the equivalent ratio change width Δφ _REAR is obtained by the calculation of the following expression, and the process proceeds to step c11.

(Δφ _REAR ) _AV ) = k (Δφ _REAR ) _AV + (1−k) (Δφ _REAR ) Here, k is an averaging capture ratio.

In step c11, φ _{RMAX is set} to 0.0, and in step c12, φ
_RMIN is _rewritten to 2.0, and each area is reset to detect the next maximum and minimum. Thereafter, the predetermined value XCOUNT is reset in the count area (COUNT), and the process returns to the main.

If there is a crank pulse interruption every 180 ° in such a main routine, a solenoid valve driving routine is executed.

First, in step d1, based on the number of Kalman pulses generated between the previous crank pulse and the present pulse and the cycle data between the Kalman pulses, information Qer (Q / N) on the amount of intake air per crank angle of 180 ° is set. I do.

Then, in the next step d2, the basic drive time Tb of the solenoid valve is set according to this Qer. Then, in step d3, the solenoid valve drive time Tinj (= Tb · Kwt · Kat · Kap · Kac · K _FB + T
Perform the operation of _D ). In this case, each correction coefficient such as the air-fuel ratio feedback correction coefficient K _FB and the battery voltage correction amount T _D
Is the one calculated in the main routine.

When reaching step d4, after setting this Tinj in the injection timer, the injection timer is triggered in step d5.
Thereby, fuel is injected from the solenoid valve 8 only for the time Tinj, and the process returns to the main.

(Effects of the Invention) As described above, according to the present invention, an all-range air-fuel ratio sensor is provided downstream of the three-way catalyst, the variation range of the equivalence ratio based on the air-fuel ratio is calculated, and the air-fuel ratio feedback correction is performed. The equivalent ratio change width with respect to the coefficient change width is obtained, and when this exceeds a set value, catalyst deterioration information is issued, so that catalyst deterioration can be quantitatively grasped, and catalyst replacement can be performed properly,
Useful for environmental protection. Moreover, when using the average air-fuel ratio,
Since it does not depend on the air-fuel ratio control accuracy, catalyst deterioration can be accurately determined, and unnecessary catalyst replacement can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an exhaust gas after-treatment system to which a catalyst purification efficiency diagnostic device according to one embodiment of the present invention is attached, FIG. 2 is a block diagram showing hardware of a control system of the device, and FIG. The figure shows the characteristic diagram of the catalyst purification efficiency-Δφ _REAR / ΔK _FB as a map used in the control system of the above equipment.
FIGS. 5 (a), 5 (b), 5 (c), and 5 (d) are waveform diagrams showing operating characteristics at different parts of the above-mentioned device, and FIGS.
The drawings are different flowcharts each showing a control flow used in a control system of the above device. 1 ... ECU, 3 ... Exhaust passage, 9 ... Three-way catalyst, 17 ... O ₂
Sensor, 18: full-range air-fuel ratio sensor, E: engine, S: exhaust gas aftertreatment system.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-231252 (JP, A) JP-A-1-203633 (JP, A) JP-A-2-207159 (JP, A) JP-A-1- 216009 (JP, A) JP-A-2-33408 (JP, A) JP-A-2-310453 (JP, A) JP-A-3-57862 (JP, A) JP-A-3-121240 (JP, A) JP-A-3-249320 (JP, A) JP-A-3-249357 (JP, A) JP-A-3-279645 (JP, A) JP-A-3-281960 (JP, A) JP-A-3-293544 (JP, A) JP-A-3-293548 (JP, A)

Claims (1)

(57) [Claims] 1. A a O ₂ sensor mounted in an exhaust system with a three-way catalyst for purifying exhaust gas of an internal combustion engine, based on the air-fuel ratio information output of the O ₂ sensor, the air-fuel ratio of the engine to the stoichiometric air-fuel ratio In a catalyst purification efficiency diagnosis device attached to an exhaust gas after-treatment system that feedback-controls a fuel supply amount so as to match, a full-range air-fuel ratio sensor is provided downstream of the three-way catalyst, and the feedback control for the feedback control is performed. Air-fuel ratio feedback correction coefficient change width calculating means for taking in the air-fuel ratio feedback correction coefficient and calculating the change width thereof,
An equivalence ratio change width calculating means for calculating a change width of the equivalence ratio based on the air-fuel ratio output from the air-fuel ratio sensor, and catalyst deterioration information when the equivalence ratio change width with respect to the air-fuel ratio feedback correction coefficient change width exceeds a set value. And a catalyst deterioration determining means for generating a catalyst deterioration.