JP3232987B2 - Catalyst deterioration determination device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for determining catalyst deterioration of an internal combustion engine.

[0002]

2. Description of the Related Art A three-way catalyst is disposed in an engine exhaust passage, an upstream air-fuel ratio sensor is disposed in an engine exhaust passage upstream of the three-way catalyst, and a downstream air-fuel ratio is disposed in an engine exhaust passage downstream of the three-way catalyst. There is known an internal combustion engine in which sensors are arranged to determine whether or not the three-way catalyst has deteriorated based on the output signals of the upstream air-fuel ratio sensor and the downstream air-fuel ratio sensor (Japanese Patent Laid-Open No. 3-281960). Reference). When the deterioration of the three-way catalyst is determined based on the output signal of the air-fuel ratio sensor in this manner, the deterioration determination of the three-way catalyst is performed when the air-fuel ratio fluctuates, for example, during acceleration / deceleration operation of the engine. If this is done, the possibility of erroneously determining that the three-way catalyst has deteriorated even though the three-way catalyst has not deteriorated becomes extremely high. Therefore, in the above-described internal combustion engine, when the air-fuel ratio is stable in order to prevent such an erroneous determination, that is, during steady-state operation in which the engine speed and the engine load are within a predetermined range, the three-way catalyst is used. Deterioration is determined.

[0003]

However, in actual operation of the engine, there are many opportunities for acceleration / deceleration operation.
Therefore, if the determination of the deterioration of the three-way catalyst is made only during the steady operation, the chance of the deterioration determination decreases, and thus there is a problem that the deterioration of the three-way catalyst cannot be properly determined.

[0004]

According to the present invention, a catalyst for purifying exhaust gas and an air-fuel ratio sensor are arranged in an engine exhaust passage, and the catalyst is detected from an output signal of the air-fuel ratio sensor. An internal combustion engine which determines whether or not the engine has deteriorated includes an operating element which causes an increase or a decrease in engine output torque when the internal combustion engine is operated, and a command for operating the operating element when determining the deterioration of the catalyst. Is provided, there is provided an operating element control means for slowing down the operation of the operating element to the extent that deterioration of the catalyst can be accurately determined.
In other words, the operation of the operating element is slowed down to such an extent that the deterioration of the catalyst can be accurately determined when a command to operate the operating element is issued, so that the fluctuation of the air-fuel ratio is suppressed low. The deterioration of the catalyst is determined in a state where the fluctuation of the catalyst is kept low.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, reference numeral 1 denotes an engine body, 2 denotes a piston, 3 denotes a combustion chamber, 4 denotes an intake port, and 5 denotes an exhaust port. The intake port 4 is connected to a surge tank 7 via an intake branch pipe 6, and a fuel injection valve 8 for injecting fuel into the corresponding intake port 4 is attached to each intake branch pipe 6. The surge tank 7 is connected to an air cleaner 11 via an intake duct 9 and an air flow meter 10, and a throttle valve 12 is arranged in the intake duct 9. On the other hand, the exhaust port 5 is connected to an exhaust manifold 13, and the exhaust manifold 13 is configured to convert unburned HC and C in exhaust gas.
O and NO _X simultaneously through capable of reducing the three-way catalyst 14 catalytic converter 15 having a built-in is connected to the exhaust pipe 16. A secondary air supply conduit 17 is connected to the exhaust manifold 13, and a secondary air supply control valve 18 is disposed in the secondary air supply conduit 17. The throttle valve 12 is connected to an actuator 19 for driving the throttle valve 12. This actuator comprises a step motor or a DC motor.

The electronic control unit 30 is composed of a digital computer, and is connected to a ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, and a power source which are interconnected by a bidirectional bus 31. Backup RAM connected
35, an input port 36 and an output port 37. The air flow meter 10 generates an output voltage proportional to the amount of intake air, and this output voltage is
Is input to the input port 36 via the. Throttle valve 1
A throttle sensor 20 for generating an output voltage proportional to the throttle opening is attached to 2, and the output voltage of the throttle sensor 20 is input to an input port 36 via a corresponding AD converter 38.

The distributor 21 has, for example, a top dead center sensor 21a for generating a signal indicating that the first cylinder is at the intake top dead center, and a crank angle sensor 21b for generating an output pulse every time the crankshaft rotates 30 degrees. The output signal of the top dead center sensor 21a and the output pulse of the crank angle sensor 21b are input to the input port 36. In the CPU 34, the current crank angle and the current engine speed are calculated from the output signal of the top dead center sensor 21a and the output pulse of the crank angle sensor 21b. A temperature sensor 22 for generating an output voltage proportional to the engine cooling water temperature is attached to the engine body 1, and the output voltage of the temperature sensor 22 is input to an input port 36 via a corresponding AD converter 38.

In the exhaust manifold 13 upstream of the three-way catalyst 14, an air-fuel ratio sensor 23 for detecting an air-fuel ratio based on the oxygen concentration in the exhaust gas is disposed.
An air-fuel ratio sensor 24 that detects the air-fuel ratio from the oxygen concentration in the exhaust gas is also disposed therein. Hereinafter, the air-fuel ratio sensor 23 disposed upstream of the three-way catalyst 14 is referred to as an upstream O ₂ sensor, and the air-fuel ratio sensor 24 disposed downstream of the three-way catalyst 14 is referred to as a downstream O ₂ sensor. . These upstream O
Output signals of the _two sensors 23 and the downstream O ₂ sensor 24 are input to the input port 36 via the corresponding AD converter 38.

A load sensor 26 for generating an output voltage proportional to the amount of depression of the accelerator pedal 25 is connected to the accelerator pedal 25, and the output voltage of the load sensor 26 is supplied to an input port via a corresponding AD converter 38. 36. Further, the operation switch 28 of the air conditioner 27 is connected to the input port 36. On the other hand, the output port 37 is connected to the fuel injection valves 8, 2 via the corresponding drive circuit 39.
The secondary air supply control valve 18, the actuator 19, an alarm device 29 such as a warning lamp and a warning buzzer, and an air conditioner 27 are connected.

In an embodiment according to the present invention, the fuel injection time TA
U is calculated based on the following equation. TAU = TP · FAF · K + γ Here, TP denotes a basic fuel injection time, FAF denotes a feedback correction coefficient, K denotes an increase coefficient, and γ denotes an invalid injection time. The basic fuel injection time TP is an injection time required for setting the air-fuel ratio to the stoichiometric air-fuel ratio. This basic fuel injection time TP
Is previously obtained by an experiment as a function of the engine load Q / N (intake air amount Q / engine speed N) and the engine speed N. As shown in FIG. It is stored in the ROM 32 in advance in the form of a map as a function.

The feedback correction coefficient FAF is changed based on the output signal of the upstream O ₂ sensor 23 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. The feedback correction coefficient FAF normally moves up and down around 1.0. are doing. That is, as shown in FIG. 3, the upstream O ₂ sensor 23 generates an output voltage of about 0.1 (V) when the air-fuel ratio is lean, and about 0.9 (V) when the air-fuel ratio is rich. Generates output voltage. When the air-fuel ratio from the output voltage of the upstream O ₂ sensor 23 is determined to be lean feedback correction coefficient FAF is made to increase, the air-fuel ratio is determined to be rich feedback correction coefficient FAF
Is reduced, whereby the air-fuel ratio is controlled to the stoichiometric air-fuel ratio.

In the embodiment according to the present invention, the feedback
The lock correction coefficient FAF is _TwoOutput of sensor 24
It is controlled based on the signal. That is, upstream of the three-way catalyst 14
That the center of fluctuation of the air-fuel ratio on the side deviates from the stoichiometric air-fuel ratio
The center of fluctuation of the air-fuel ratio upstream of the three-way catalyst 14
Feedback correction coefficient FA so as to approach the stoichiometric air-fuel ratio
F is downstream O_TwoIt is determined based on the output signal of the sensor 24.
It is. This downstream O_TwoThe sensor 24 is also as shown in FIG.
When the air-fuel ratio is lean, the output voltage is about 0.1 (V).
Pressure is generated, and when the air-fuel ratio is rich, about 0.9 (V)
Output voltage.

The increase coefficient K is usually fixed at 1.0, and is set to a value larger than 1.0 when the fuel should be increased, that is, when the air-fuel ratio should be made rich. Next, a control routine of the air-fuel ratio feedback performed based on the output signal of the upstream O ₂ sensor 23 will be described with reference to FIGS. This routine is executed by interruption every predetermined time, for example, every 4 ms.

Referring to FIGS. 4 and 5, first, at step 101, it is determined whether or not the feedback condition of the air-fuel ratio by the upstream O ₂ sensor 23 is satisfied. When the engine cooling water temperature is below the set value,
Immediately after start-up, during warm-up, during power increase,
It is determined that the feedback condition is not satisfied when the upstream O ₂ sensor 23 is not activated during the increase in the amount of fuel for preventing the catalyst from overheating, or when the fuel injection is stopped during the deceleration operation. If the feedback condition is not satisfied, the routine proceeds to step 125, where the feedback correction coefficient FAF is set to 1.0, and then at step 126, the air-fuel ratio feedback flag XMFB
Is set to “0”. On the other hand, when the feedback condition is satisfied, the routine proceeds to step 102.

In step 102, the upstream O ₂ sensor 2
3 output VOM is taken are converted A / D, the air-fuel ratio on the basis of step 103 VOM is on whether the comparison voltage V _R1 following either is rich or lean is determined.
This comparison voltage V _R1 is a voltage at the center of the amplitude of the output of the O ₂ sensor, and in this embodiment, V _R1 = 0.45V. Air-fuel ratio is lean in the step 103 (VOM ≦ V _R1)
If it is determined that the delay counter CDLY is positive, it is determined whether or not the delay counter CDLY is positive.
If Y> 0, CDLY is set to 0 in step 105, and then the process proceeds to step 106. In step 106, the delay counter CDLY is decremented by one,
Next, in steps 107 and 108, the delay counter CDLY is guarded by the minimum value TDL. in this case,
When the delay counter CDLY reaches the minimum value TDL, in step 109, the air-fuel ratio flag F1 is set to "0" (lean). Note that this minimum value TDL is a negative value.

On the other hand, if it is determined in step 103 that the air-fuel ratio is rich (VOM> V _R1 ), step 1 is executed.
Proceeding to 10, it is determined whether or not the delay counter CDLY is negative. If CDLY <0, CDLY is set to 0 in step 111, and then the process proceeds to step 112.
In step 112, the delay counter CDLY is incremented by one, and then in steps 113 and 114, the delay counter CDLY is guarded by the maximum value TDR. In this case, when the delay counter CDLY reaches the maximum value TDR, the air-fuel ratio flag F1 is set to "1" (rich) in step 115. This maximum value TDR is a positive value.

Next, at step 116, it is determined whether or not the sign of the air-fuel ratio flag F1 has been inverted. When the air-fuel ratio is inverted, the routine proceeds to step 117, where the air-fuel ratio flag F
From the value of 1, it is determined whether the inversion is from rich to lean or from lean to rich. If the transition is from rich to lean, in step 118 the FAF becomes FAF ←
FAF + RSR is increased in a skipping manner, whereas if the transition is from lean to rich, step 11
At 9, the FAF is skipped to FAF-FAF-RSL. That is, skip processing is performed.

On the other hand, when it is determined in step 116 that the sign of the air-fuel ratio flag F1 has not been inverted, integration processing is performed in steps 120, 121 and 122. That is, it is determined in step 120 whether or not F1 = "0". If F1 = "0" (lean), FAF ← FAF + KIR is determined in step 121, while F1 = "1" (rich). Step 1 if available
At 22, FAF ← FAF-KIL. Here, the integration constants KIR, KIL are the skip amounts RSR, RS
L is set sufficiently smaller than L, and KIR (KIL)
<RSR (RSL). By this integration processing, F1
When "0" (lean), the fuel injection amount is gradually increased, and when F1 = "1" (rich), the fuel injection amount is gradually reduced.

Next, in step 123, step 11
The feedback correction coefficient FAF calculated in 8, 119, 121, 122 is guarded by a minimum value, for example, 0.8, and guarded by a maximum value, for example, 1.2. Thus, when the feedback correction coefficient FAF becomes too large or too small for some reason, the fluctuation of the air-fuel ratio of the engine is suppressed, thereby preventing the air-fuel ratio from becoming over-rich or over-lean. . Next, at step 124, the air-fuel ratio feedback flag XMFB is set to "1".

FIG. 6 is a timing chart for explaining the operation according to the flowcharts of FIGS.
When the rich / lean discrimination air-fuel ratio signal A / F is obtained from the output VOM of the upstream O ₂ sensor 23 as shown in FIG. 6 (A), the delay counter CDLY becomes rich as shown in FIG. 6 (B). It counts up and counts down in a lean state. As a result, as shown in FIG. 6 (C), an air-fuel ratio signal A / F ′ (corresponding to the flag F1) subjected to the delay processing is formed. For example, the air-fuel ratio signal A / F at the time t ₁ is changed from lean to rich, the air-fuel ratio signal A / F 'is changed to rich at time t ₂ after being held lean only the rich delay time TDR. Also, be varied air fuel ratio signal A / F from the rich at time t ₃ in a lean, air-fuel ratio signal A / F 'is the time after being held rich only equivalent lean delay time (-TDL) t
Changes to lean at ₄ . However the air-fuel ratio signal A / F is the time t _5, t _6, Invert in a shorter period of time than the rich delay time TDR as the t ₇ delay counter CD
LY it takes time to reach the maximum value TDR, as a result, air-fuel ratio signal A / F 'is reversed at time t _8. That is, the delayed air-fuel ratio signal A / F 'is more stable than the delayed air-fuel ratio signal A / F before the delay processing. Based on the stable air-fuel ratio signal A / F 'after the delay processing, the feedback correction coefficient FAF shown in FIG.
Is obtained.

Next, the second air-fuel ratio feedback control by the downstream O ₂ sensor 24 will be described. The second air-fuel ratio feedback control includes a skip amount RS as a constant related to the first air-fuel ratio feedback control.
R, RSL, integration constants KIR, KIL, delay time TD
R, TDL or output VO of upstream O ₂ sensor 23
There are a system for controlling the M comparison voltage V _R1 and a system for introducing the second air-fuel ratio correction coefficient FAF2.

For example, when the rich skip amount RSR is increased, the control air-fuel ratio can be shifted to the rich side, and when the lean skip amount RSL is decreased, the control air-fuel ratio can be shifted to the rich side, while the lean skip amount RSL is increased. Then, the control air-fuel ratio can be shifted to the lean side, and even if the rich skip amount RSR is reduced, the control air-fuel ratio can be shifted to the lean side. Accordingly, the rich skip amount RSR and the lean skip amount RSL are determined according to the output of the downstream O ₂ sensor 24.
Is corrected, the air-fuel ratio can be controlled.
When the rich integration constant KIR is increased, the control air-fuel ratio can be shifted to the rich side, and when the lean integration constant KIL is decreased, the control air-fuel ratio can be shifted to the rich side. On the other hand, when the lean integration constant KIL is increased, the control air-fuel ratio can be shifted. The fuel ratio can be shifted to the lean side, and even if the rich integration constant KIR is reduced, the control air-fuel ratio can be shifted to the lean side. Therefore, it becomes possible to control the air-fuel ratio by correcting the rich integration constant KIR and the lean integration constant KIL in accordance with the output of the downstream O ₂ sensor 24. Also, the rich delay time TDR
The control air-fuel ratio can be shifted to the rich side by increasing the delay time (-TDL) or increasing the lean time (-TDL). On the other hand, the control air-fuel ratio can be increased by increasing the lean delay time (-TDL) or decreasing the rich delay time (TDR). Can move to the side. That is, it becomes possible to control the air-fuel ratio delay time in accordance with the output VOS of the downstream O ₂ sensor 24 TDR, by correcting the TDL. When the comparison voltage V _R1 is further increased, the control air-fuel ratio can be shifted to the rich side, and when the comparison voltage V _R1 is reduced, the control air-fuel ratio can be shifted to the lean side. Therefore, it becomes possible to control the air-fuel ratio by correcting the reference voltage V _R1 in accordance with the output VOS of the downstream O ₂ sensor 24.

These skip amounts, integration constants, delay times,
Controlling the comparison voltage by the downstream O ₂ sensor 24 has an advantage in, respectively. For example, by controlling the delay time, very fine adjustment of the air-fuel ratio can be performed, and by controlling the skip amount, control with good response can be performed without lengthening the feedback cycle of the air-fuel ratio. It should be noted that two or more of these control amounts can be used in combination.

Next, a description will be given of a double O ₂ sensor system which controls the skip amount as a constant involved in the air-fuel ratio feedback control. 7 and 8
Is a second air-fuel ratio feedback control routine based on the output VOS of the downstream O ₂ sensor 24, which is executed by interruption every predetermined time, for example, every 512 ms. In steps 201 to 206, it is determined whether the feedback condition by the downstream O ₂ sensor 24 is satisfied. For example, in addition to the failure of the feedback condition by the upstream O ₂ sensor 23 (step 201), when the cooling water temperature THW is equal to or lower than a set value (for example, 70 ° C.) (step 202), the throttle valve 22 opens the idling opening (LL).
= "1") (step 203), when secondary air is being introduced based on the engine speed, vehicle speed, a signal from the throttle sensor 20, the cooling water temperature THW, and the like (step 20).
4) At light load (Q / N <X ₁ ) (step 20)
5), when the downstream O ₂ sensor 24 is not activated (step 206) is determined feedback condition unsatisfied, it is determined that the feedback condition is established otherwise. When the feedback condition is not satisfied, the routine proceeds to step 208, where the air-fuel ratio feedback flag XSFB is reset (“0”). When the feedback condition is satisfied, the routine proceeds to step 207, where the air-fuel ratio feedback flag XSB is set (“1”). Then, the process proceeds to step 209.

In step 209, the downstream O ₂ sensor 24
The output VOS is A / D converted and taken in, and in step 210, the VOS is compared with the comparison voltage V _R2 (for example, V _R2 =
0.55 V) or less, that is, whether the air-fuel ratio is rich or lean. In step 210, VOS ≦ V
_If it is determined that _R2 (lean), step 21
Proceed to 1, 212, 213, and when it is determined that VOS> V _R2 (rich), steps 214, 215, ₂
Proceed to 16. That is, in step 211, RSR ← RSR
+ ΔRS (constant value), that is, the rich skip amount RSR
Is increased, and the air-fuel ratio is shifted to the rich side.
The RSR is the maximum value MAX (= 7.5) at 12,213.
%). On the other hand, in step 214, R
SR ← RSR−ΔRS, that is, the rich skip amount RS
R is decreased to shift the air-fuel ratio to the lean side, and in steps 215 and 216, the RSR has the minimum value MIN (= 2.
5%).

Next, at step 217, the lean skip amount RSL is set to RSL ← 10% -RSR. That is, R
SR + RSL = 10%. Then step 218
In, the skip amounts RSR and RSL are stored in the RAM 33. FIG. 9 shows a fuel injection control routine, which is executed, for example, by interruption every certain crank angle.

Referring to FIG. 9, first, in step 3
At 01, the basic fuel injection time TP is calculated from the map shown in FIG. Next, at step 302, the value of the correction coefficient K determined by the operating state of the engine is calculated. Next, at step 303, it is determined whether or not the value of the correction coefficient K is 1.0. Step 3 when K = 1.0
Jump to 05. On the other hand, when K is not 1.0, the routine proceeds to step 304, where the feedback correction coefficient FAF is fixed at 1.0, and then proceeds to step 305. In step 305, the fuel injection time TAU (= TP
FAF · K + γ) is calculated.

Next, a basic method of determining deterioration of the three-way catalyst 14 used in the present invention will be described with reference to FIGS. FIG. 10A shows the output voltage VOM of the upstream O ₂ sensor 23 when the air-fuel ratio feedback control is being performed, and FIG.
Shows the output voltage VOS of the downstream O ₂ sensor 24 when the feedback control of the air-fuel ratio is performed. The concept that the area of the output of the trajectory length and each O ₂ sensors 23 and 24 outputs of the O ₂ sensors 23 and 24 are introduced in the three-way catalyst 14 deterioration determination method as used in the present invention. Here, the trajectory length of each of the O ₂ sensors 23 and 24 means the output voltages VOM and VOS on the ordinate and the output voltage VOM when the time is on the abscissa as shown in FIGS. 10 (A) and 10 (B). , VOS.

In the embodiment according to the present invention, the accumulated value of the change amounts of the output voltages VOM and VOS of the respective O ₂ sensors 23 and 24 per fixed time is used as a value representative of the locus length. That is, the trajectory length ΣLM of the upstream O ₂ sensor 23 is as shown in FIG.
Represented by the accumulated value _{| VOM i -VOM i-1 |} 0 absolute value of the difference between the output voltage VOM _i of the output voltage VOM _i-1 and the time i at time i-1, as shown in (A) ,
The trajectory length ΣLS of the downstream O ₂ sensor 24 is, as shown in FIG. 10B, the output voltage VOS _i−1 at time i−1.
Absolute value | V of the difference between output voltage VOS _{i at} time i
OS _i −VOS _{i− 1} |.

On the other hand, the area of the output of each O ₂ sensor 23, 24 is defined as the output voltage VOM, VOS on the vertical axis and the time on the horizontal axis, as shown in FIGS. 10 (A) and 10 (B). the output voltage VOM, refers to the area indicated by hatching surrounded by the comparative voltage V _R1, V _R2 and VOS. In the embodiment according to the present invention, the accumulated value of the difference between the output voltages VOM and VOS of the respective O ₂ sensors 23 and 24 and the comparison voltages V _R1 and V _{R2 at} certain time intervals is used as a value representative of the area. That is, the area ΣAM of the output of the upstream O ₂ sensor 23 is shown in FIG.
The output voltage VOM at each time as shown in FIG.
The absolute value | VOM _i −V _R1 | of the difference between _i and the comparison voltage V _R1 is represented by the accumulated value. The area ΔAS of the output of the downstream O ₂ sensor 24 is, as shown in FIG. the absolute value of the difference between the output voltage VOS _i with the comparison voltage V _R2 at time | VO
It is represented by the cumulative value of S _i -V _R2 |.

[0031] is further defined ratio between the locus length ShigumaLM the output of the downstream O ₂ sensor output of 24 trajectory length ShigumaLS upstream O ₂ sensor 23 (ΣLS / ΣLM) is the locus length ratio, the downstream O ₂ sensor The ratio (ΣAS / ΣAM) of the output area ΣAS of the output 24 and the area ΣAM of the output of the upstream O ₂ sensor 23 is defined as the area ratio. Using these trajectory length ratios and area ratios, the ordinate represents the trajectory length ratio (ΣLS /
ΣLM) and the area ratio (ΣAS / ΣAM) on the horizontal axis, the three-way catalyst 14 is basically not deteriorated in the region below the broken line W shown in FIG. In the upper region, it can be determined that the three-way catalyst 14 has deteriorated. Next, this will be described with reference to FIG.

The curve X shown in FIG. 12 (A) shows the change in the output voltage VOM of the upstream O ₂ sensor 23 when the upstream O ₂ sensor 23 is not deteriorated, the curve X shown in FIG. 12 (B) and curve X in FIG. 12 (C) downstream O ₂ sensor 24
4 shows a change in the output voltage VOS of the downstream O ₂ sensor 24 when the three-way catalyst 14 has not deteriorated and the three-way catalyst 14 has not deteriorated. Thus, any of the O ₂ sensors 23, ₂
It is assumed that the relationship between the area ratio and the trajectory length ratio when the number 4 is not deteriorated and the three-way catalyst 14 is not deteriorated is represented by a point a in FIG.

Now, assuming that the upstream O ₂ sensor 23 has deteriorated, the amplitude of the output voltage VOM of the upstream O ₂ sensor 23 decreases as shown by the curve Y in FIG. At this time, as can be seen from the curves X and Y in FIG. 12A, the trajectory length ΣLM decreases and the area ΣAM decreases in proportion thereto. Therefore, as the ratio of the trajectory length increases, the area ratio increases in proportion to the ratio, and at this time, the point a in FIG. 11 moves to the point a '.

On the other hand, if the downstream O ₂ sensor 24 is deteriorated, the amplitude of the output voltage VOS of the downstream O ₂ sensor 24 becomes small as shown by the curve Y in FIG. At this time, as can be seen from the curves X and Y in FIG. 12B, the trajectory length ΣLS decreases and the area 小 さ く AS decreases in proportion thereto. Accordingly the area ratio in proportion thereto with locus length ratio is small at this time is also reduced, a point in FIG. 11 this time is moved in a "point and thus. Thus O ₂ sensor 23, When 24 deteriorates, the point representing the relationship between the trajectory length ratio and the area ratio is the origin 0
Move on a straight line A passing through.

On the other hand, when the three-way catalyst 14 deteriorates, O_TwoStrike
Oxidation of unburned HC and CO based on storage function and N
O_XOf the three-way catalyst
14 also fluctuates in a short cycle.
You. In this case, as the three-way catalyst 14 deteriorates, the downstream O_Two
The fluctuation cycle of the output voltage VOS of the sensor 24 becomes shorter,
If the three-way catalyst 14 is completely deteriorated, the downstream O_TwoSen
The output voltage VOS of the power supply 24 is_TwoOutput of sensor 23
It fluctuates with the same cycle as the voltage VOM. Figure
A curve Y of 12 (C) shows a time when the three-way catalyst 14 has deteriorated.
It can be seen from the curves X and Y in FIG.
When the three-way catalyst 14 deteriorates, the downstream O _TwoSensor 24
The fluctuation period becomes shorter.

When the three-way catalyst 14 is deteriorated in this manner, the fluctuation cycle of the downstream O ₂ sensor 24 becomes shorter, so that the trajectory length Σ
LS increases. On the other hand, even if the fluctuation cycle of the downstream O ₂ sensor 24 changes, the area ΔAS within a certain period hardly changes. Therefore, when the three-way catalyst 14 deteriorates, the locus length ratio increases, but the area ratio hardly changes, so that the point a in FIG. 11 moves to the point b. If the O ₂ sensors 23 and 24 deteriorate in a state where the three-way catalyst 14 is deteriorated, the point representing the relationship between the trajectory length ratio and the area ratio moves on the straight line B passing through the origin 0. Therefore, as described above, basically, the point representing the relationship between the trajectory length ratio and the area ratio is the origin 0
Is located above the straight line W passing through the three-way catalyst 1
4 can be determined to have deteriorated.

In practice, however, especially the downstream O ₂ sensor 2
4 does not change with clean waveforms as shown in FIGS. 12 (B) and 12 (C).
2 (B) and 2 (C) show a shape in which fine vibrations are superimposed on the curves X and Y. Such fine vibration does not significantly affect the area ΣAM of the output voltage VOM of the downstream O ₂ sensor 24, but has a greater effect on the trajectory length ΣLS as the trajectory length ratio (ΣLS / ΣLM) becomes smaller. Will be. That is, if the trajectory length ΣLS is increased by a fixed amount due to the fine vibrations superimposed on the curves X and Y, the smaller the trajectory length ratio, the greater the trajectory length ratio increases. Therefore, when it is determined that the three-way catalyst 14 has deteriorated because the straight line W has been exceeded, the three-way catalyst 14 is not deteriorated when the trajectory length ratio is small even though the three-way catalyst 14 has not deteriorated. There is a risk of misjudging that the battery has deteriorated.

Therefore, in the embodiment according to the present invention, as shown in FIG.
h a is the area locus length ratio and the area ratio is to some extent larger leave the-threshold level Th ₁ that matches a straight line is W, the-threshold level Th ₂ in the region locus length ratio and the area ratio is small as a constant locus length ratio I have. Therefore, in the embodiment according to the present invention, if the point indicating the relationship between the trajectory length ratio and the area ratio is located in the region above the set value in FIG. 11, that is, the threshold levels Th ₁ and Th ₂ , the three-way catalyst 14 has deteriorated. I try to judge. Note that-threshold level Th ₂ is defined so as not to erroneously determine empirically rather than withers guide beauty from theory.

Next, a routine for determining the deterioration of the three-way catalyst 14 will be described with reference to FIGS. In addition,
This routine is executed by interruption every predetermined time. Referring to FIGS. 13 and 14, first, at step 401, it is determined whether or not a determination completion flag indicating that the deterioration determination has been completed is set. If the determination completion flag is set, the processing cycle is immediately completed. On the other hand, when it is determined that the determination completion flag has not been set, the routine proceeds to step 402, where the air-fuel ratio feedback flag XMFB indicating that the air-fuel ratio feedback control by the upstream O ₂ sensor 23 is being performed is set ( = “1”) is determined. Air-fuel ratio feedback flag XMFB
If is not set (= "0"), step 4
Jump to 16. On the other hand, when it is determined that the air-fuel ratio feedback flag XMFB is set (= "1"), the routine proceeds to step 403.

In step 403, the downstream O ₂ sensor 24
It is determined whether or not an air-fuel ratio feedback flag XSB indicating that the air-fuel ratio feedback control is being performed is set (= “1”). When the air-fuel ratio feedback flag XSFB is not set (= “0”), the process jumps to step 416. When the air-fuel ratio feedback flag XSB is set (= “1”), the process proceeds to step 404. Step 40
At 4, it is determined whether another determination condition is satisfied. For example, the warm-up of the engine is completed, that is, the engine cooling water temperature is equal to or higher than the set temperature, and the accelerator pedal 25 is rapidly depressed based on the output signal of the load sensor 26, or the accelerator pedal 25 is depressed. When it is determined that the vehicle is not suddenly released, it is determined that another determination condition is satisfied. When the other determination conditions are not satisfied, the process jumps to step 416, and when the other determination conditions are satisfied, the process proceeds to step 405 to start the deterioration determination.

At step 405, the flag under determination is set. Next, at step 406, a process of integrating the trajectory length ΣLM of the output voltage VOM of the upstream O ₂ sensor 23 is performed based on the following equation. _{ΣLM = ΣLM + | VOM i -VOM} i-1 | then accumulation process area ΣAM the output voltage VOM of the upstream O ₂ sensor 23 based on the following equation at step 407 is performed.

[0042] _{ΣAM = ΣAM + | VOM i -V} R1 | then integration processing of the locus length ΣLS output voltage VOS of the downstream O ₂ sensor 24 based on the following equation at step 408 is performed. ΣLS = ΣLS + │VOS _i -VOS _i-1 │ Next, at step 409, an integration process of the area ΣAS of the output voltage VOS of the downstream O ₂ sensor 24 is performed based on the following equation.

ΣAS = ΣAS + │VOS _i -V _R2 │ Next, at step 410, the count value C is incremented by one, and then at step 411, the count value C
There whether exceeds the set value C ₀ is determined. When C ≦ C ₀ , the processing cycle is completed. On the other hand, C> C
_{When the value} becomes ₀ , that is, when a certain period of time has elapsed since the start of the deterioration determination, the process proceeds to step 412.

In step 412, the trajectory length ratio ΣLS / ΣL
M and the area ratio ΣAS / ΣAM are calculated. Next, at step 413, it is determined from the relationship shown in FIG. 11 whether or not the three-way catalyst 14 has deteriorated. When it is determined that the three-way catalyst 14 has not deteriorated, the routine proceeds to step 415, where a determination completion flag is set. On the other hand, when it is determined that the three-way catalyst 14 is
Proceeding to 14, the alarm device 29 is activated, then proceeding to step 415. Next, in step 416, the determination flag is reset, and then, in step 417, various values related to the deterioration determination are cleared.

As described above, in the embodiment according to the present invention, when the depression amount of the accelerator pedal 25 is suddenly increased or decreased rapidly, the deterioration judgment is not performed, but the depression amount of the accelerator pedal 25 is not so rapid. The deterioration determination is performed during the acceleration operation and during the deceleration operation in which the depression amount of the accelerator pedal 25 is not so rapid.
That is, in the embodiment according to the present invention, when an actuation command is issued to an actuation element which, when actuated, causes an increase or decrease in engine output torque, for example, an actuation command is issued to the throttle valve 12 by the accelerator pedal 25. When the valve opening speed or the valve closing speed of the throttle valve 12 is not so high, the deterioration determination is performed.

In this case, even if the opening speed or closing speed of the throttle valve 12 is not so high, if the throttle valve 12 performs the opening operation or the closing operation, the air-fuel ratio fluctuates. Erroneous judgment is made about the deterioration of Therefore, in the first embodiment of the present invention, when the deterioration determination is started and the determination flag is set, the opening and closing operations of the throttle valve 12 are slowed down.

Next, the first embodiment will be described with reference to a control routine for the throttle valve 12 shown in FIG. This routine is executed by interruption every predetermined time. Referring to FIG. 15, first, step 5
At 01, a target value TA of the opening of the throttle valve 12 is calculated. As shown in FIG. 16A, the target value TA is previously determined as a function of the depression amount L of the accelerator pedal 25,
It is stored in M32. Next, at step 502, the difference between the throttle opening at the time of the previous interruption and the current throttle valve opening, that is, the opening / closing speed ΔTA of the throttle 12,
Is calculated. Next, in step 503, it is determined whether or not a determination flag indicating that deterioration is being determined is set. When the determination flag is not set, the target value TA of the throttle opening is set to the actual target throttle opening TAE, and then in step 508, the actuator 19 is driven so that the throttle opening becomes the target throttle opening TAE. You. On the other hand, when the determination flag is set, the steps 503 to 50 are performed.
4 and the absolute value of the opening / closing speed ΔT of the throttle valve 12 |
It is determined whether ΔT | is smaller than a fixed value X. |
When ΔTA | <X, that is, when the opening of the throttle valve 12 does not change or when the opening / closing speed ΔT is extremely small, the process proceeds to step 507. On the other hand, when | ΔTA | ≧ X, the routine proceeds to step 505, where the value of the smoothing coefficient n is calculated. As shown in FIG. 16B, the value of the annealing coefficient n is the absolute value | ΔT of the opening / closing speed of the throttle valve 12.
It becomes smaller as A | becomes larger. The relationship shown in FIG. 16B is also stored in the ROM 32. Next, at step 506, the target throttle opening TAE is calculated based on the following equation.

TAE = TAE _i−1 + (TA−TAE _i−1 ) / n Here, TAE _i−1 indicates the target throttle opening at the time of the previous interruption. FIGS. 17A and 17B show the relationship between the target throttle opening TA determined by the depression amount L of the accelerator pedal 25 and the actual target throttle opening TAE. FIG. 17A shows a case where | ΔTA | is small and therefore the value of the annealing coefficient n is large, and FIG. 17B shows a case where | ΔTA | is large and the value of the annealing coefficient n is small. Shows the case. FIG. 17 (A)
As can be seen from (B) and (B), the change in the actual throttle opening indicated by TAE is made slower than the change in the target value TA determined by the amount of depression of the accelerator pedal 25, and | ΔTA | The greater the coefficient n, the more slowly the actual throttle opening TAE is changed. As described above, when the deterioration of the three-way catalyst 14 is determined, the change in the air-fuel ratio becomes small because the actual throttle opening change is slowed down. Therefore, it is possible to accurately determine whether the three-way catalyst 14 has deteriorated. Can be determined.

FIG. 18 shows another embodiment of the throttle valve control routine. In this embodiment, when the deterioration of the three-way catalyst 14 is determined, the opening / closing operation of the throttle valve 12 is temporarily stopped. That is, referring to FIG. 18, first, at step 601, the target value TA of the throttle opening is calculated from the relationship shown in FIG. 16A. Next, at step 602, it is determined whether or not the determination flag is set. When the determination flag is not set, the routine proceeds to step 603, where the target value TA is set to the actual target throttle opening TAE. Then, at step 604, the actuator is set so that the opening of the throttle valve 12 becomes the target throttle opening TAE. 19 is controlled. On the other hand, if the determination flag is set, the process jumps from step 602 to step 604. At this time, the opening of the throttle valve 12 is maintained at the target throttle opening TAE immediately before the determination flag is set.

The increase or decrease of the engine output torque is caused not only when the opening degree of the throttle valve 12 changes, but also when the external load applied to the engine changes, for example, when the air conditioner 27 is operated and the operation is stopped. It also occurs when it is done. That is, when the air conditioner 27 is also operated, it constitutes an operating element that increases or decreases the engine output torque.

FIG. 19 shows a routine for controlling the air conditioner 27. Referring to FIG. 19, first, in step 701, it is determined whether or not the operation switch 28 of the air conditioner 27 has been switched from off to on. When the operation switch 28 is off, the process jumps to step 704. When the operation switch 28 is on, the process proceeds to step 702. Step 702
In, it is determined whether or not the determination flag is set. When the determination flag is not set, the routine proceeds to step 703, where the air conditioner 27 is operated. On the other hand, when the determination flag is set, the routine jumps to step 704. That is, even if the operation switch 28 is turned on, the air conditioner 27 is not operated when the determination flag is set, and the air conditioner 27 is operated after the deterioration determination is completed and the determination flag is reset. Can be Accordingly, the fluctuation of the output torque during the deterioration determination is prevented, and thus the deterioration of the three-way catalyst 14 can be accurately determined.

Next, at step 704, it is determined whether or not the operation switch 28 of the air conditioner 27 has been switched from on to off. When the operation switch 28 is on, the processing cycle is completed, and when the operation switch 28 is off, the process proceeds to step 705. In step 705, it is determined whether or not the determination flag is set.
Step 7 when the determination flag is not set
Proceeding to 05, the operation of the air conditioner 27 is stopped. On the other hand, when the determination flag is set, the processing cycle is completed. That is, even if the operation switch 28 is turned off, when the determination flag is set, the operation of the air conditioner 27 is not stopped, and after the deterioration determination is completed and the determination flag is reset, the air conditioner 27 is stopped. Operation is stopped. Therefore, the fluctuation of the output torque during the deterioration judgment is prevented,
Thus, the deterioration of the three-way catalyst 14 can be accurately determined.

[0053]

According to the present invention, it is possible to increase the chances of the deterioration judgment while securing the accurate deterioration judgment of the catalyst.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing a map of a basic fuel injection time TP.

FIG. 3 is a diagram showing an output voltage of an O ₂ sensor.

FIG. 4 is a flowchart for performing air-fuel ratio feedback control.

FIG. 5 is a flowchart for performing air-fuel ratio feedback control.

FIG. 6 is a time chart showing changes in values related to feedback control.

FIG. 7 is a flowchart for performing a second air-fuel ratio feedback control.

FIG. 8 is a flowchart for performing a second air-fuel ratio feedback control.

FIG. 9 is a flowchart for controlling fuel injection.

FIG. 10 is a diagram for explaining the locus length and area of the output voltage of the O ₂ sensor.

FIG. 11 is a diagram showing a deteriorated region of a catalyst.

FIG. 12 is a diagram showing a change in an output voltage of an O ₂ sensor.

FIG. 13 is a flowchart for determining deterioration of the three-way catalyst.

FIG. 14 is a flowchart for determining deterioration of a three-way catalyst.

FIG. 15 is a flowchart for controlling a throttle valve.

FIG. 16 is a view showing a target value TA of a throttle opening and the like.

FIG. 17 is a diagram showing changes in a target value TA of the throttle opening and an actual target throttle opening TAE.

FIG. 18 is a flowchart for controlling a throttle valve.

FIG. 19 is a flowchart for controlling an air conditioner.

[Explanation of symbols]

3: Combustion chamber 13: Exhaust manifold 14: Three-way catalyst 23: Upstream O ₂ sensor 24: Downstream O ₂ sensor

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F02D 41/14 ZAB F02D 41/14 ZAB G01M 15/00 ZAB G01M 15/00 ZABZ (58) Investigated field (Int.Cl. ⁷ , DB name) F01N 3/20 F01N 3/24 F02D 41/14

Claims (1)

(57) [Claims] 1. An internal combustion engine in which an exhaust gas purifying catalyst and an air-fuel ratio sensor are arranged in an engine exhaust passage, and an output signal of the air-fuel ratio sensor determines whether the catalyst has deteriorated. When the operation of the operating element is performed when a catalyst deterioration determination is performed, the operation of the operating element is performed to the extent that the deterioration of the catalyst can be accurately determined. An apparatus for determining catalyst deterioration of an internal combustion engine, comprising an operating element control means for slowing down the operation of an operating element.