JP3218747B2 - Catalyst deterioration degree detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst deterioration detecting device, and more particularly to a catalyst deterioration detecting device for detecting the deterioration of a catalytic converter provided in an exhaust gas passage of an internal combustion engine based on the amount of oxygen that can be stored in the catalytic converter. The present invention relates to a degree detection device.

[0002]

2. Description of the Related Art A device disclosed in Japanese Patent Application No. 3-295565 is known as a device for detecting the degree of deterioration of a catalytic converter provided in an exhaust gas passage of an internal combustion engine. According to this device, it is possible to accurately detect the degree of deterioration of the catalytic converter based on the oxygen adsorption capacity of the catalytic converter.

[0003] In a vehicle-mounted internal combustion engine, a catalyst such as a three-way catalyst is disposed in an exhaust gas passage to purify exhaust gas. The three-way catalyst adsorbs and retains excess oxygen present in the exhaust gas when the air-fuel ratio of the air-fuel mixture supplied into the cylinder of the internal combustion engine becomes greater than the stoichiometric air-fuel ratio, that is, when the fuel becomes lean, and the air-fuel mixture becomes empty. It has a so-called O ₂ storage function of releasing adsorbed and held oxygen when the fuel ratio becomes smaller than the stoichiometric air-fuel ratio, that is, when the fuel becomes rich.

On the other hand, when the air-fuel mixture supplied to the cylinder of the internal combustion engine becomes fuel-lean, the exhaust gas contains nitrogen oxides (NO _x ) due to excess oxygen in the air-fuel mixture. When the air-fuel mixture becomes rich, exhaust gas containing unburned components such as carbon monoxide (CO) and hydrocarbons (HC) is emitted from the internal combustion engine.

Accordingly, if a three-way catalyst is provided in the exhaust gas passage and the exhaust gas flows through the catalytic converter, excess oxygen is adsorbed by the catalytic converter when the air-fuel mixture becomes fuel-lean. When NO _X is reduced and the air-fuel mixture becomes rich, the oxygen adsorbed in the catalytic converter is released to oxidize CO, HC, etc., so that unburned components contained in the exhaust gas can be efficiently purified. .

Incidentally, when the three-way catalyst is deteriorated, the exhaust gas purifying ability is reduced, and it is difficult to secure good exhaust emission. On the other hand, even if the catalytic converter is deteriorated, it is difficult to find it because there is no change in the kinetic performance of the vehicle. Since the purification of the exhaust gas is performed by the O ₂ storage function of the catalytic converter as described above, the deterioration of the catalytic converter in this case means a decrease in the O ₂ storage function.

[0007] The above-mentioned conventional catalyst deterioration degree detecting apparatus has been made to meet such a demand, and detects an amount of oxygen that can be adsorbed by a catalytic converter under a certain condition, and detects O ₂ storage from the amount of oxygen. It is intended to determine the deterioration of the function, that is, the deterioration of the catalytic converter.

When detecting the amount of oxygen that can be adsorbed by the catalytic converter in this device, first, an air-fuel mixture set on the fuel rich side (or fuel lean side) with respect to the stoichiometric air-fuel ratio is supplied to the internal combustion engine for a predetermined time. To cause the catalytic converter to release (or adsorb) oxygen sufficiently. Next, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is switched to fuel lean (or fuel-rich), and oxygen is adsorbed (or released) by the catalytic converter.

Here, paying attention to the air-fuel ratio of the exhaust gas downstream of the catalytic converter, the air-fuel ratio is maintained substantially near the stoichiometric air-fuel ratio while the amount of oxygen in the exhaust gas can be adjusted by the O ₂ storage function of the catalytic converter. If a fuel-lean (or fuel-rich) mixture continues to be supplied beyond the capacity of the O ₂ storage function, the air-fuel ratio is naturally supplied to the internal combustion engine, that is, the air-fuel ratio of the exhaust gas upstream of the catalytic converter. Becomes equal to the air-fuel ratio of the mixture.

At this time, excess oxygen in the exhaust gas flowing through the catalytic converter during this time is adsorbed by the catalytic converter (or the oxygen adsorbed to the full oxygen adsorption capacity of the catalytic converter becomes unburned component in the exhaust gas). Are all released to oxidize).

That is, after the air-fuel ratio of the air-fuel mixture is switched, the catalyst is kept lean (or fuel-rich) between the air-fuel ratio of the exhaust gas downstream of the catalytic converter and the air-fuel ratio of the air-fuel mixture. The excess oxygen amount (or insufficient oxygen amount) in the exhaust gas flowing through the converter corresponds to the oxygen adsorption capacity of the catalytic converter.

In view of the above, the conventional catalyst deterioration degree detecting device is provided with means for detecting the amount of gas flowing through the catalytic converter, and an air-fuel ratio sensor provided downstream of the catalytic converter to allow the catalytic converter to flow during the above period. The amount of excess oxygen (or the amount of insufficient oxygen) in the exhaust gas is detected, and the degree of deterioration of the catalytic converter is detected based on the detected value.

[0013]

However, as described above, the conventional catalyst deterioration degree detecting device determines the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine for a predetermined period of time when detecting the oxygen adsorption capacity of the catalytic converter. Must be kept rich or fuel lean. The period during which the air-fuel ratio of the air-fuel mixture is maintained at the air-fuel ratio is set to a time long enough to saturate the catalytic converter with oxygen or to release all the oxygen adsorbed by the catalytic converter. .

Therefore, in the above-described conventional apparatus, near the end of the period in which the air-fuel ratio is kept rich or lean, the catalytic converter cannot be purified by the catalytic converter.
O, HC or NO _X will be released downstream of the catalytic converter, ie into the atmosphere. As described above, the conventional catalyst deterioration degree detection device has a problem that the exhaust emission is temporarily deteriorated when detecting the catalyst deterioration degree.

The present invention has been made in view of the above points, and detects the degree of deterioration of the catalyst during the period in which the fuel supply to the internal combustion engine is stopped, that is, during the fuel cut. It is an object of the present invention to provide a catalyst deterioration degree detecting device which suppresses deterioration of exhaust emission in the above.

[0016]

FIG. 1 shows a principle diagram of a catalyst deterioration degree detecting device for achieving the above object. In FIG. 1, reference numeral 1 denotes an internal combustion engine provided with a catalyst deterioration detection device according to the present invention. A catalytic converter 11 is provided in the exhaust gas passage of the internal combustion engine 1. An air-fuel ratio sensor 18 is arranged downstream of the catalytic converter 11. The air-fuel ratio sensor 18 detects the air-fuel ratio in the exhaust gas flowing through the catalytic converter 11.

The fuel cut detecting means M1 monitors the state of fuel supply to the internal combustion engine 1, and detects the stop of fuel supply when the fuel supply is stopped under a predetermined operating condition. The air-fuel ratio switching means M2 is a fuel cut detection means M
If 1 detects the suspension of fuel supply for a predetermined time,
The air-fuel mixture supplied to the internal combustion engine 1 is switched to a predetermined air-fuel ratio set on the rich side with respect to the stoichiometric air-fuel ratio for a predetermined period .

Further, the deterioration degree detecting means M3 switches the air-fuel ratio of the gas supplied upstream of the catalytic converter 11 to the fuel rich state by the air-fuel ratio switching means M2.
Exhaust gas flowing through the catalytic converter 11 during a period until the air-fuel ratio sensor 18 outputs a signal indicating fuel rich is
Calculate the total amount and switch to the total amount of exhaust gas and fuel rich
During the above period, based on the obtained air-fuel ratio and
The amount of oxygen released from the converter 11 into the exhaust gas is
The deterioration degree of the catalyst is detected as the oxygen adsorption capacity of the medium converter 11 .

[0019]

In the device for detecting the degree of deterioration of the catalyst, the fuel cut detecting means M1 is provided when the fuel supply is stopped when the fuel supply to the internal combustion engine 1 is unnecessary, such as during deceleration.
The fuel cut is detected. Here, the fuel cut in the internal combustion engine is a process that is performed only when fuel supply is unnecessary, and thus is executed only when the throttle valve 9 provided in the intake duct 6 is fully closed.

During the period from when the fuel cut is performed to when the air-fuel ratio is switched to fuel rich by the air-fuel ratio switching means M2, air containing no fuel flows through the catalytic converter 11, and finally the catalytic converter 11 The oxygen corresponding to the oxygen adsorbing capacity is adsorbed, and the air-fuel ratio sensor 18 outputs a signal indicating that the air-fuel ratio is fuel-lean. At this time, since the exhaust gas contains no fuel, oxides such as NO _X are not discharged downstream of the catalytic converter 11.

The internal combustion engine 1 is controlled by the air-fuel ratio switching means M2.
When the air-fuel ratio of the air-fuel mixture supplied to the fuel cell is switched to fuel-rich, the catalytic converter 11
A small amount of fuel-rich exhaust gas flows in response to full closure. As a result, the oxygen adsorbed by the catalytic converter 11 is gradually released in order to compensate for the lack of oxygen in the exhaust gas.

At this time, the air-fuel ratio sensor 18 outputs a signal indicating the stoichiometric air-fuel ratio while the amount of oxygen in the exhaust gas can be compensated for by the oxygen adsorbed by the catalytic converter 11. When all the oxygen in the catalytic converter 11 is released, the atmosphere downstream of the catalytic converter 11 becomes fuel-rich thereafter, and the air-fuel ratio sensor 18 outputs a signal indicating the fuel-rich. During the period from when the air-fuel ratio of the air-fuel mixture is switched to fuel rich to when the air-fuel ratio sensor 18 outputs a signal indicating fuel rich, the catalytic converter 11
A length corresponding to the O ₂ storage amount. Therefore, the deterioration degree detecting means M3 sets the catalytic converter during this period.
The total amount of exhaust gas flowing through the
Based on the air-fuel ratio of the exhaust gas supplied to the
Released into the exhaust gas from the catalytic converter during the period
The amount of released oxygen is calculated, and the amount of released oxygen is
The deterioration degree of the catalyst is detected based on the oxygen adsorption capacity of the catalyst. Here, the catalytic converter 1
The flow rate of the exhaust gas flowing through 1 is small, and at the end of the predetermined period, the air-fuel ratio switching means M2 switches again to the fuel cut state. Therefore, the unburned components such as CO and HC released into the atmosphere after releasing all oxygen are suppressed to a very small amount. In this case, the unburned component is further suppressed by setting the predetermined period as a period until the air-fuel ratio sensor 18 outputs a signal indicating fuel rich.

[0023]

[0024]

FIG. 2 is a block diagram showing an embodiment of a catalyst deterioration detecting device according to the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals.

In FIG. 2, reference numeral 1 denotes an internal combustion engine equipped with the catalyst deterioration detecting device of the present embodiment. 2 and 3 in FIG.
1 shows an intake port and an exhaust port of the internal combustion engine 1, respectively. Each intake port 2 of the internal combustion engine 1 is connected to a surge tank 5 via a corresponding branch pipe 4, and the surge tank 5 is connected to an air cleaner 8 via an intake duct 6 and an air flow meter 7.

In the intake duct 6, a throttle valve 9 is arranged. On the other hand, the exhaust port 3 is the exhaust manifold 1
0, it is connected to a catalytic converter 11 containing a three-way catalyst corresponding to the above-mentioned catalyst. Further, each branch pipe 4 connected to the intake port 2 has a fuel injection valve 12 controlled based on an output signal of the electronic control unit 20.
Is arranged.

The electronic control unit 2 which is a main part of this embodiment
Numeral 0 includes a read only memory (ROM) 22, a random access memory (RAM) 23, a central processing unit (CPU) 24, an input port 25, and an output port 26, which are interconnected by a bidirectional bus 21.

The air flow meter 7 generates an output voltage corresponding to the amount of intake air, and supplies the output voltage to the input port 25 via the A / D converter 27. The throttle valve 9 is provided with an idle switch 13 which is turned on when the throttle valve 9 is at the idling position and supplies an output signal thereof to the input port 25.

The internal combustion engine 1 is provided with a water temperature sensor 14 for generating a voltage signal corresponding to the cooling water temperature.
The output voltage is supplied to the input port 25 via the D converter 28. Further, to the input port 25, an output signal of the rotation speed sensor 15 for generating a pulse representing the rotation speed of the internal combustion engine is supplied.

A first air-fuel ratio sensor 16 is disposed in the exhaust manifold 10 upstream of the catalytic converter 11, and a second air-fuel ratio sensor corresponding to the above-described air-fuel ratio sensor is disposed in the exhaust passage 17 downstream of the catalytic converter 11. An air-fuel ratio sensor 18 is provided. These first and second air-fuel ratio sensors 16,
Reference numeral 18 is connected to the input port 25 via the corresponding current-voltage conversion circuits 29, 30 and A / D converters 31, 32, respectively. The output port 26 is connected to a display device 35 for displaying the degree of deterioration of the fuel injection valve 12 and the catalyst via drive circuits 33 and 34, respectively.

First and second air-fuel ratio sensors 16, 18
Has a structure in which an anode is formed on the inner surface of a cylindrical body made of, for example, zirconia, a cathode is formed on the outer surface, and the outside of the cathode is covered with a porous layer. A current I according to the air-fuel ratio of the atmosphere flows between the anode and the cathode as shown in FIG.

This current I is converted into a voltage V as shown in FIG. 3B in the corresponding current-voltage conversion circuits 29 and 30. That is, the output voltage V corresponding to the air-fuel ratio is supplied to the A / D converters 31 and 32, and the electronic control unit 20 detects the air-fuel ratio based on the output voltage V.

In this embodiment, the fuel injection time TAU from the fuel injection valve 12 is calculated based on the following equation.

TAU = TP.FAF.GA.CM Here, TP: basic fuel injection amount FAF: feedback correction coefficient GA: learning coefficient C: increase coefficient M: air-fuel ratio setting coefficient The basic fuel injection time TP is the internal combustion engine. Is the fuel injection time required to make the air-fuel ratio of the mixture supplied to the engine a stoichiometric air-fuel ratio, and is a function of the load Q / N (intake air amount Q / engine speed N) of the internal combustion engine and the engine speed N. Is stored in the ROM 22 in advance.

The feedback correction coefficient FAF is controlled based on the output signal of the first air-fuel ratio sensor 16 upstream of the catalytic converter 11 so as to fluctuate around 1.0 in order to maintain the air-fuel ratio at the target air-fuel ratio. The learning coefficient GA is a coefficient for changing the feedback correction coefficient FAF around 1.0.

The increase coefficient C is a coefficient for increasing the fuel injection amount during warm-up or acceleration, and is 1.
It is set to 0. The air-fuel ratio setting coefficient M is a coefficient for obtaining a predetermined target air-fuel ratio according to the operating state of the internal combustion engine. When the target air-fuel ratio is the stoichiometric air-fuel ratio, 1.0 is set.
Becomes

Next, the feedback correction coefficient FAF and the learning coefficient GA will be briefly described with reference to FIGS. It should be noted that the air-fuel ratio setting coefficient M represents the target air-fuel ratio (A
/ F) _O, it is represented by the theoretical air-fuel ratio / (A / F) _O.

FIG. 4 shows a routine executed by interruption every predetermined time. When the routine shown in FIG. 4 starts, first in step 50, the routine shown in FIG.
From the relationship shown in (B), the output signal of the first air-fuel ratio sensor 16 corresponding to the target air-fuel ratio (A / F) _O , that is, the target voltage value E of the current-voltage conversion circuit 29 is calculated.

Assuming that the air-fuel ratio setting coefficient M is the stoichiometric air-fuel ratio / (A / F) _O and the fuel injection time is TP · M, the air-fuel ratio becomes substantially the target air-fuel ratio (A / F) _O ,
Therefore, the current-voltage conversion circuit 2 of the first air-fuel efficiency sensor 16
9 is almost equal to the target output voltage E.

When the target output voltage E is calculated in step 50, the process proceeds to step 51, where the current-voltage conversion circuit 2
9 whether the output voltage V is higher than the target output voltage E,
That is, it is determined whether or not the air-fuel ratio of the exhaust gas to which the first air-fuel ratio sensor 16 is exposed is leaner than the target air-fuel ratio (A / F) _O.

When V> E, that is, when the target air-fuel ratio (A /
F) If it is leaner than _O , the routine proceeds to step 52, where it is determined whether or not it was lean at the time of the previous interruption. If it is not lean at the time of the previous interruption, it is determined that the state has changed from rich to lean, and the routine proceeds to step 53.

In step 53, the feedback correction coefficient FAF at this time is stored as FAFR. Then, the process proceeds to a step 54, wherein the skip value S is added to the FAF.
Is added and the routine proceeds to step 55. On the other hand, the integral value K to the FAF proceeding to Step 56 if it is determined that also lean side at the time of the previous interruption (K <S) is added at step 52, then the routine proceeds to step 55.

Therefore, as shown in FIG. 5, when the air-fuel ratio of the exhaust gas to which the air-fuel ratio sensor 16 is exposed changes from rich to lean, the feedback correction coefficient FAF is sharply increased by the skip value S. , Gradually increases as the integral value K is added.

On the other hand, if V> E is not satisfied in step 51, that is, if it is determined that the air-fuel ratio of the exhaust gas to which the air-fuel ratio sensor 16 is exposed is rich relative to the target air-fuel ratio, The process proceeds to step 57, where it is determined whether or not the state was rich at the time of the previous interruption. If it was not rich at the time of the previous interruption, it is determined that the state has changed from lean to rich, and the process proceeds to step 58.

In step 58, the feedback correction coefficient FAF at this time is stored as FAFL. Then, the process proceeds to a step 59, wherein the skip value S is obtained from the FAF.
, And then the routine proceeds to step 55. On the other hand, if it is determined in step 57 that the air condition is rich even at the time of the previous interruption, the process proceeds to step 60, where the integral value K (K <S) is subtracted from FAF, and the process proceeds to step 55.

Therefore, as shown in FIG. 5, when the air-fuel ratio of the exhaust gas to which the air-fuel ratio sensor 16 is exposed changes from lean to rich, the feedback correction coefficient FAF is rapidly reduced by the skip value S. , Gradually decreases as the integral value K is subtracted.

In step 55, the average value of FAFL and FAFR is set as the learning coefficient GA. Therefore, for example, when the feedback correction coefficient FAF is leaned toward the lean side, the learning coefficient GA becomes larger than 1.0. Therefore, the fuel injection time T
AU becomes longer, and the feedback correction coefficient FAF is corrected to the rich side.

When the feedback correction coefficient FAF is biased toward the rich side, the learning coefficient GA becomes smaller than 1.0.
Therefore, the fuel injection time TAU becomes short, and the feedback correction coefficient FAF is corrected to the lean side. in this way,
The correction coefficient FAF in the present embodiment is varied around 1.0 by the action of the learning coefficient GA.

The feedback correction coefficient FAF shown in FIG.
Is the same even if the target air-fuel ratio (A / F) _O changes. For example, even if the target air-fuel ratio (A / F) _O is the stoichiometric air-fuel ratio, the FAF is varied around 1.0. Therefore, when the target air-fuel ratio (A / F) _O is the stoichiometric air-fuel ratio, that is, when the air-fuel ratio setting coefficient M is 1.0, if the FAF is fixed to 1.0, that is, if the air-fuel ratio feedback control is stopped, the air-fuel ratio becomes The stoichiometric air-fuel ratio will be maintained.

Similarly, when the target air-fuel ratio (A / F) _O is not the stoichiometric air-fuel ratio, the air-fuel ratio setting coefficient M is changed to the target air-fuel ratio (A
/ F) _O , and if the FAF is fixed at 1.0, the air-fuel ratio is maintained at the target air-fuel ratio (A / F) _O. Therefore, in order to set the air-fuel ratio to the target air-fuel ratio (A / F) _O , the air-fuel ratio setting coefficient M may be set to a value corresponding to the target air-fuel ratio (A / F) _O , and the FAF may be fixed to 1.0. Will be.

Next, referring to FIG.
A method of detecting the amount of oxygen adsorbed and held in the first embodiment will be described. In FIG. 6 solid line indicates the air-fuel ratio detected by the first air-fuel ratio sensor 16, and a broken line shows the air-fuel ratio detected by the second air-fuel ratio sensor 18.

FIG. 6 shows that the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine at the time t ₁ is determined by the lean air-fuel ratio (A / F) _L
From the rich air-fuel ratio (A / F) _R is forcibly switched, mixed air-fuel ratio rich air-fuel ratio of air-fuel at the time t ₂ is supplied to the internal combustion engine (A / F) lean from _R-fuel ratio (A / F)
_This shows a case where the mode is forcibly switched to _L.

As can be seen from FIG. 6, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine at time t ₁ is a lean air-fuel ratio (A
/ F) When the air-fuel ratio is switched from _L to the rich air-fuel ratio (A / F) _R , the air-fuel ratio detected by the first air-fuel ratio sensor 16 quickly changes to the rich air-fuel ratio (A / F) _R. Similarly, when the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is switched from the rich air-fuel ratio (A / F) _R to the lean air-fuel ratio (time t _{2 in} FIG. 6), the first air-fuel ratio sensor The air-fuel ratio detected at 16 immediately changes to the lean air-fuel ratio (A / F) _L.

On the other hand, the air-fuel ratio detected by the second air-fuel ratio sensor 18 is the first air-fuel ratio as shown by the broken line in FIG.
It changes with a behavior different from the air-fuel ratio detected by the air-fuel ratio sensor 16. That is, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine at the time t ₁ in FIG. 6 is a lean air-fuel ratio (A / F).
_{When the} air-fuel ratio changes from _L to the rich air-fuel ratio (A / F) _R , the air-fuel ratio detected by the second air-fuel ratio sensor 18 first changes from the lean air-fuel ratio (A / F) _L to the stoichiometric air-fuel ratio, and then ΔT _R After the stoichiometric air-fuel ratio is maintained for the time, the rich air-fuel ratio (A / F) _R is obtained.

On the other hand, when the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine changes from the rich air-fuel ratio (A / F) _R to the lean air-fuel ratio (A / F) _L at time t ₂ , the second air-fuel ratio sensor 18 is the rich air-fuel ratio (A
/ F) _R first changes to the stoichiometric air-fuel ratio, and then is maintained at the stoichiometric air-fuel ratio for ΔT _L time, after which the lean air-fuel ratio (A /
F) It becomes _L.

When the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is thus switched, the second air-fuel ratio sensor 18
Is maintained at the stoichiometric air-fuel ratio during the period ΔT _R or ΔT _L because the catalytic converter 11
Due to the O ₂ storage function of the is.

That is, when the air-fuel ratio of the air-fuel mixture is lean, excess oxygen present in the exhaust gas is adsorbed by the catalytic converter 11, and the air-fuel ratio of the air-fuel mixture becomes rich at the time t ₁ (A / F). _R , CO, H in the exhaust gas
When unburned components such as C come to be contained, the oxygen adsorbed in the catalytic converter 11 is consumed to oxidize these unburned components.

While the unburned components in the exhaust gas are being oxidized by the oxygen adsorbed on the catalytic converter 11, that is, the period indicated by ΔT _R in FIG. The stoichiometric air-fuel ratio is maintained at the stoichiometric air-fuel ratio, and when all of the oxygen adsorbed and held in the catalytic converter 11 is consumed, the oxidizing action of the unburned components is no longer performed. The air-fuel ratio becomes a rich air-fuel ratio (A / F) _R.

Next, when the fuel efficiency of the air-fuel mixture changes to the lean air-fuel ratio (A / F) _L at time t ₂ , the catalytic converter 11 starts to adsorb excess oxygen. The air-fuel ratio detected by the second air-fuel ratio sensor 18 is maintained at the stoichiometric air-fuel ratio while oxygen is being adsorbed, that is, while indicated by ΔT _L in FIG. When the adsorption capacity of the catalytic converter 11 is saturated with oxygen, oxygen is no longer
The air-fuel ratio detected by the second air-fuel ratio sensor 18 without being adsorbed to 1 becomes a lean air-fuel ratio (A / F) _L.

During the oxygen adsorption operation,
Since oxygen in the exhaust gas is lost to the catalytic converter, oxides such as NO _X contained in the exhaust gas is reduced. The adsorption capacity of the catalytic converter 11 concurrently with the saturation, so that the oxide such as NO _X is discharged from the downstream of the catalytic converter 11.

There is an upper limit to the amount of oxygen that can be adsorbed and held by the catalytic converter 11. Then, naturally the amount of oxides of the NO _X, etc. may be the amount and the reduction of the unburned components of the CO, HC, etc. the amount of oxygen capable of oxidizing the more capable of attracting and holding is increased, the purification rate of the exhaust gas is high . However, the upper limit of the amount of oxygen that can be adsorbed by the catalytic converter 11, that is, the oxygen adsorption capacity tends to decrease with time, and the exhaust gas purification rate of the catalytic converter 11 tends to deteriorate with this decrease.

As described above, since the exhaust gas purification rate of the catalytic converter 11 and the oxygen adsorbing ability are closely related, if the oxygen adsorbing ability of the catalytic converter 11 can be detected, the detected value is used as a basis. Thus, the degree of deterioration of the exhaust gas purification rate of the catalytic converter 11 can be detected.

Incidentally, the rich air-fuel ratio (A / A
F) _{Assuming that} the mixture of _R is supplied only by G ₀ , the insufficient amount of air can be expressed by the following equation.

(Theoretical air-fuel ratio− (A / F) _R ) · G ₀ (1) Here, when the proportion of oxygen in the deficient air amount is α, the deficient oxygen amount is as follows: Can be expressed as

Α · (Theoretical air-fuel ratio− (A / F) _R ) · G ₀ (2) Then, assuming that K = α · (A / F) _R , the equation (2) becomes as follows. Become.

K · (Theoretical air-fuel ratio / (A / F) _R −1) · G ₀ (3) Here, the exhaust gas flowing through the catalytic converter 11 during the time indicated by ΔT _R in FIG. If the amount is G ₀ , this ΔT _R
During this period, the amount of oxygen released from the catalytic converter 11 should be the same as the amount of oxygen deficiency shown in the above equation (3).
That is, the oxygen adsorbing ability of the catalytic converter 11 is eventually changed from G ₀ in the above equation (3) to the catalytic converter 1 during ΔT _R time.
It can be detected by calculating 1 as the flow rate of the circulated exhaust gas.

In this embodiment, as shown in FIG. 2, an air flow meter 7 is used to detect the amount of intake air. The air flow meter 7 generates an output voltage proportional to the intake air amount Ga supplied to the internal combustion engine per unit time. Therefore, the air flow meter 7
Is multiplied by ΔT _R , Ga · ΔT _R is the amount of air supplied to the internal combustion engine during the ΔT _R time, that is, the catalytic converter 1 during the ΔT _R time.
1 represents the flow rate of the exhaust gas.

Therefore, the detection value G by the air flow meter 7
When a is used, the amount of oxygen that can be adsorbed and held in the catalytic converter 11 can be expressed by the following equation.

K · (Theoretical air-fuel ratio / (A / F) _R −1) · Ga · ΔT _R (4) By the way, as described above, the oxygen adsorbing ability of the catalytic converter 11 is saturated with oxygen. When the lean exhaust gas continues to flow, oxides such as NO _X contained in the exhaust gas are released into the atmosphere without being completely absorbed by the catalytic converter 11. Further, if all the oxygen adsorbed in the catalytic converter 11 is released and the flow of the rich exhaust gas continues,
Unburned components such as CO and HC in the exhaust gas are released into the atmosphere.

That is, in order to ensure good exhaust emissions, it is necessary to minimize the amount of oxides and unburned components discharged as described above. Therefore, in the present embodiment, the lean air-fuel ratio (A / F) _L state (time t ₁ earlier state) in FIG. 6, it was decided to create during fuel cut.

The fuel cut in the internal combustion engine, that is, the stop of the fuel supply from the fuel injection valve 12 to the internal combustion engine is executed when it is determined that the fuel supply to the internal combustion engine is not necessary while the vehicle is running. The case where the fuel supply is unnecessary means a case where the engine does not stop even if the fuel supply is stopped and the driver does not intend to accelerate. Is equal to or higher than a predetermined rotational speed, and the idle switch 13 for detecting that the throttle valve 9 is in the idle position is on.

That is, when the fuel cut is operating, only the air containing no fuel is supplied to the internal combustion engine. Thus, the exhaust gas flowing through the catalytic converter 11 also does not include the fuel, that is, the air free of oxides such as NO _X flows. Therefore, according to the present embodiment, even if the catalytic converter 11 is saturated with oxygen while the air-fuel ratio of the exhaust gas is set to the lean air-fuel ratio (A / F) _L , the NO
Oxides such as _X are not released into the atmosphere.

Further, while the fuel cut is being performed as described above, the throttle valve is always at the idling position. Therefore, if a rich air-fuel ratio (A / F) _R state is to be created during execution of the fuel cut, the flow rate of the exhaust gas flowing through the catalytic converter 11 at this time will be a small amount corresponding to the flow rate at the time of idling. Becomes

Therefore, the exhaust gas having the rich air-fuel ratio (A / F) _R is circulated to consume the oxygen adsorbed on the catalytic converter 11, and the unburned components in the exhaust gas are discharged to the atmosphere. , The amount of unburned components discharged is suppressed to a small amount because the flow rate of the exhaust gas is small.

Hereinafter, the processing executed in the electronic control unit 20 of this embodiment will be described in detail with reference to the flowcharts shown in FIGS. This routine is an interrupt routine that is started every predetermined time Δt.

As shown in FIG. 7, when this routine is started, first, at step 101, it is determined whether or not the fuel cut is being executed. This is because, in the present embodiment, the detection of the degree of catalyst deterioration is performed at the time of fuel cut as described above. If it is determined that the fuel cut is being executed, the process proceeds to step 102 to detect the degree of deterioration of the catalyst, and it is determined whether or not a predetermined time T _(sec) has elapsed since the start of the fuel cut. Step 101 corresponds to the fuel cut detection means described above.

If it is determined in step 101 that the fuel cut is not being executed, the detection of the degree of deterioration of the catalyst is not performed because there is a possibility that the exhaust emission may deteriorate as described above. Therefore, in this case, the routine proceeds to step 103, where the O ₂ storage amount O _2st described later is reset to “0”, and the flag flg indicating that the degree of catalyst deterioration is being detected is set to “0”. A command to execute the injection control is issued, and the process ends.

In step 102, the time T _(sec) is still
Is determined not to have elapsed, it is considered that oxygen has not yet been sufficiently adsorbed in the catalytic converter 11, and the current process is terminated. If it is determined that a predetermined time T _(sec) set in advance that sufficient oxygen is adsorbed to the extent that the catalytic converter 11 is saturated has elapsed, the process proceeds to step 105.

In step 105, the catalytic converter 11
In order to release oxygen adsorbed on the internal combustion engine, a fuel injection amount Fi is calculated to make the air-fuel mixture supplied to the internal combustion engine have a predetermined rich air-fuel ratio (A / F) _R. The fuel injection amount Fi is obtained by dividing the flow rate of air supplied to the internal combustion engine at the time of fuel cut, that is, the flow rate Ga of air flowing through the catalytic converter 11, by the rich air-fuel ratio (A / F) _R. . Steps 102 and 105, together with step 112 described later, constitute the above-described air-fuel ratio switching means.

[0080] Thus Once switched mixture supplied to the internal combustion engine to a rich air-fuel ratio (A / F) _R, the first and second air-fuel ratio sensor 16, 18 and the air flow proceeds to step <br/> 106 The detected value Ga of the meter 7 is read. Then, those values are used as the air-fuel ratios (A / F) _in and (A / F) of the exhaust gas existing upstream and downstream of the catalytic converter 11, respectively.
_out and the exhaust gas flow rate Ga flowing through the catalytic converter 11 at the time of fuel cut.

Subsequently, in step 107 shown in FIG. 8, it is checked whether (A / F) _out read in step 106 is near the stoichiometric air-fuel ratio. Here, step 105
In the case where the air-fuel mixture switched to the rich air-fuel ratio (A / F) _R in the above-described case flows through the catalytic converter 11 and reaches the downstream thereof, (A / F) _out indicates that the catalytic converter 11
Is adjusted near the stoichiometric air-fuel ratio by the oxygen released from the fuel cell (corresponding to the period ΔT _R in FIG. 6).

That is, the reason why (A / F) _out is close to the stoichiometric air-fuel ratio is that the oxygen released from the catalytic converter 11 compensates for the oxygen deficiency in the exhaust gas discharged from the internal combustion engine. . Therefore, if the amount of exhaust gas flowing through the catalytic converter 11 and the amount of oxygen deficiency in the exhaust gas can be detected during the period in which (A / F) _out is determined to be near the stoichiometric air-fuel ratio, during that period, The amount of oxygen released from the catalytic converter 11, that is, the catalytic converter 1 which was saturated with oxygen at the start of the period.
This means that the amount of oxygen adsorbed on 1 can be detected.

Therefore, in step 107, (A /
F) When _out is determined to be near the stoichiometric air-fuel ratio,
Proceeds to step 108 to execute the O ₂ storage measurement execution flag f.
Set the lg (flg ← 1), followed Death step 109
, The amount of oxygen O released from the catalytic converter 11
_2st is calculated based on the following equation, and the current process ends.

O _2st ← O _2st + Ga · (Theoretical air-fuel ratio /
(A / F) _in −1) · Δt Here, Ga · (theoretical air-fuel ratio / (A / F) _in −1) · Δ
In t, the detection value (A / F) _in of the first air-fuel ratio sensor 16 is substituted for (A / F) _R in the above equation (4), and Δt, which is the activation cycle of this routine, is substituted for ΔT _R. , Where the constant K is omitted for simplicity. That is, O _2
Every time step 109 is executed, the amount of oxygen deficiency in the exhaust gas flowing through the catalytic converter 11 is accumulated in the storage amount O _2st from the execution of the previous routine to the execution of this routine.

On the other hand, in step 107, (A
/ F) _out proceeds to step 110 if it is not determined to be the stoichiometric air-fuel ratio O ₂ storage measurement execution flag fl
Check if g is set to "1".

If step 108 has been executed, that is, if the release of oxygen from the catalytic converter 11 has been started, flg has been set and the routine proceeds to step 111. Also, immediately after the air-fuel mixture is switched to the rich air-fuel ratio (A / F) _R , if the (A / F) _out has not yet reached the stoichiometric air-fuel ratio, flg remains "0". Therefore, the process is terminated as it is to prepare for the next startup.

In step 111, (A / F) _out and (A
/ F) Compare with _R to see if both values are approximately equal. Here, if the values are not equal, it is determined that oxygen is still being released from the catalytic converter 11, and the routine proceeds to step 109, where O
_{The 2nd} accumulation processing is continued and the processing ends.

On the other hand, here, (A / F) _out and (A / F)
_{When R} is the same value, it is determined that the oxygen adsorbed by the catalytic converter 11 has been almost consumed, and the routine proceeds to step 112. In step 112, the fuel injection amount Fi is set to "0" to end the fuel injection for achieving the rich air-fuel ratio (A / F) _R.

In the following step 113, the O ₂ storage amount O _2st at the present time is
Recognized as the oxygen adsorption capacity, to detect the catalyst deterioration degree by referring to a table showing the relationship between the oxygen adsorption capacity and the catalyst deterioration degree of the catalytic converter 11 shown in FIG. 9 with O _2st. This step 113 corresponds to the above-mentioned deterioration degree detecting means.

As described above, according to the present embodiment, in addition to detecting the degree of catalyst deterioration at the time of fuel cut when the exhaust gas flow rate is small, the catalyst converter 11
When it is determined that the oxygen adsorbed on the fuel cell is almost consumed, the fuel injection is immediately terminated in step 112. Therefore, unburned components such as HC and CO released into the atmosphere when detecting the degree of catalyst deterioration are significantly reduced as compared with the conventional apparatus.

In the above steps, the process of detecting the degree of deterioration of the catalyst is ended, and both O _2st and flg are reset to “0” in step 114 in preparation for the start of the present and subsequent routines, and the current process is ended.

In the above embodiment, the first air-fuel ratio sensor 16 is provided upstream of the catalytic converter 11, and the O ₂ storage amount O _2st is calculated based on the detected value (A / F) _in (the above step). 109), the first air-fuel ratio sensor 16 may be omitted by calculating the air-fuel ratio (A / F) _R of the air-fuel mixture.

In the above embodiment, the time when the detection value (A / F) _out of the second air-fuel ratio sensor 18 reaches the stoichiometric air-fuel ratio is set as the measurement start time of the O ₂ storage amount O _2st (see the above step). 107) However, the present invention is not limited to this, and may be configured to start on the condition that the air-fuel ratio of the air-fuel mixture is switched to the rich air-fuel ratio (A / F) _R by executing step 105.

[0094]

As described above, according to the present invention, since the lean air-fuel ratio state for detecting the degree of catalyst deterioration is generated at the time of fuel cut, even if the fuel-lean exhaust gas is continuously discharged, At that time, unburned components such as NO _X are not released into the atmosphere.

Since the flow rate of the exhaust gas is small because the fuel is cut and the fuel injection is terminated immediately when the air-fuel ratio downstream of the catalyst becomes rich, the internal combustion engine is used to calculate the oxygen adsorption capacity of the catalyst. The amount of unburned components such as CO and HC discharged to the atmosphere after switching the air-fuel mixture supplied to the fuel-rich to the fuel-rich state is dramatically reduced as compared with the conventional apparatus.

As described above, the apparatus for detecting the degree of deterioration of the catalyst according to the present invention can detect the degree of deterioration of the catalyst with high accuracy based on the oxygen adsorbing ability of the catalyst, and always has good detection of the degree of deterioration of the catalyst. It has the feature that it can secure a high exhaust emission.

[Brief description of the drawings]

FIG. 1 is a principle diagram of a catalyst deterioration degree detecting device according to the present invention.

FIG. 2 is an overall view illustrating a configuration of an embodiment of a catalyst deterioration degree detection device according to the present invention.

FIG. 3 is a diagram illustrating output characteristics of an air-fuel ratio sensor used in the present embodiment.

FIG. 4 is a flowchart of an air-fuel ratio feedback control routine executed by the electronic control unit in the embodiment.

FIG. 5 is a time chart showing changes in an air-fuel ratio feedback correction coefficient.

FIG. 6 is a diagram showing a change in a detection value of a first air-fuel ratio sensor and a detection value of a second air-fuel ratio sensor in the present embodiment.

FIG. 7 is a flowchart (part 1) of a process executed by the electronic control unit to detect deterioration of the catalyst in the embodiment.

FIG. 8 is a flowchart (part 2) of a process executed by the electronic control unit to detect deterioration of the catalyst in the embodiment.

FIG. 9 is a table showing the relationship between the oxygen adsorption capacity of a catalyst and the degree of catalyst deterioration.

[Description of Signs] M1 fuel cut detection means M2 air-fuel ratio switching means M3 deterioration degree detection means 1 internal combustion engine 6 intake duct 7 air flow meter 9 throttle valve 11 catalytic converter 12 fuel injection valve 13 idle switch 16 first air-fuel ratio sensor 17 Exhaust passage 18 Second air-fuel ratio sensor

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F01N 3/20-3/24 F02D 41/12-41/14 F02D 41/22 330

Claims (2)

(57) [Claims] 1. An exhaust gas supplied to a catalytic converter provided in an exhaust gas passage of an internal combustion engine is switched from a lean to a rich fuel to a stoichiometric air-fuel ratio. Exhaust gas flowing through the catalytic converter during a period until the output signal of the air-fuel ratio sensor disposed downstream of the catalytic converter becomes a signal indicating fuel rich.
The total amount of gas supplied to the catalytic converter during the period.
During the period based on the exhaust gas air-fuel ratio
Calculate the amount of oxygen released into the exhaust gas from the converter
The amount of oxygen is regarded as the oxygen adsorption capacity of the catalytic converter.
A deterioration degree detecting means for detecting the degree of deterioration of the catalytic converter based on the oxygen adsorption capacity; and Fuel cut detection means for detecting the stop of the fuel supply; and when the fuel cut detection means continuously detects the stop of the fuel supply for a predetermined time, the air-fuel mixture supplied to the internal combustion engine is enriched with respect to the stoichiometric air-fuel ratio for a predetermined time. An air-fuel ratio switching unit for switching to a predetermined air-fuel ratio set on the side of the catalyst. 2. The catalyst deterioration degree detecting device according to claim 1,
And The air-fuel ratio switching means outputs an output signal of the air-fuel ratio sensor.
When the signal becomes a signal indicating fuel rich, the predetermined
Inferior catalyst characterized by stopping switching to air-fuel ratio
Chemical degree detection device.