JP2671877B2 - Catalyst deterioration determination device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is provided with an air-fuel ratio sensor (in this specification, an oxygen concentration sensor (O ₂ sensor)) downstream of a catalytic converter, and determines deterioration of a catalyst based on the output of this O ₂ sensor. The present invention relates to a catalyst deterioration discriminating device.

[0002]

2. Description of the Related Art In a simple air-fuel ratio feedback control (single O ₂ sensor system), an oxygen concentration detection O
_{The two} sensors are provided in a part of the exhaust system that is as close to the combustion chamber as possible, that is, in the exhaust manifold assembly part upstream of the catalytic converter. However, the variation in the output characteristics of the O ₂ sensor hinders the improvement of the air-fuel ratio control accuracy. Is occurring.
In order to compensate for such variations in the output characteristics of the O ₂ sensor, variations in parts such as the fuel injection valve, and changes over time or over time, a second O ₂ sensor is provided downstream of the catalytic converter and the upstream O ₂ sensor is used. A double O ₂ sensor system has already been proposed which performs air-fuel ratio feedback control by a downstream O ₂ sensor in addition to air-fuel ratio feedback control (see Japanese Patent Publication No. 7-26528 and Japanese Patent Laid-Open No. 63-97852). . In this double O ₂ sensor system, the O ₂ sensor provided on the downstream side of the catalytic converter has a lower response speed than the downstream O ₂ sensor, but the variation in the output characteristics is reduced due to the following reasons. .

(1) Since the exhaust gas temperature is low downstream of the catalytic converter, thermal influence is small. (2) Since various poisons are trapped in the catalyst downstream of the catalytic converter, the poisoning amount of the downstream O ₂ sensor is small. (3) The exhaust gas is sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the exhaust gas is close to the equilibrium state.

[0004] Thus, as described above, the air-fuel ratio feedback control based on the outputs of the two O ₂ sensors (double O ₂ sensor system), the variations in the output characteristic of the upstream O ₂ sensor can be absorbed by the downstream O ₂ sensor . Actually, as shown in FIG. 14, in the single O ₂ sensor system, when the O ₂ sensor output characteristic deteriorates, the exhaust emission characteristic is directly affected, whereas in the double O ₂ sensor system, the upstream O ₂ sensor system _{2 Even if} the output characteristics of the sensor deteriorate, the exhaust emission characteristics do not deteriorate. That is, in the double O ₂ sensor system, as long as the downstream O ₂ sensor maintains stable output characteristics,
Good exhaust emissions are guaranteed.

The catalyst of the above-mentioned catalytic converter is designed so that its function is not significantly deteriorated as long as the catalyst is used within the range of normally considered usage conditions of the vehicle. However, if the user mistakenly puts leaded gasoline in the fuel, or if the high tension coat comes off and causes misfire during use, the function of the catalyst may be significantly reduced. In the former case, the user does not notice at all, and in the latter case, since the high tension cord may be reinserted, the catalyst is rarely replaced. As a result, traveling may occur without the catalytic converter purifying exhaust gas sufficiently.

[0006] In the above double O ₂ sensor system, as described above, the function of the catalyst is deteriorated, the number of reversals of the output V ₂ of the downstream O ₂ sensor increases, as a result, the downstream O ₂ sensor As a result, the air-fuel ratio feedback control is disturbed by the engine, and a good air-fuel ratio cannot be obtained, resulting in deterioration of fuel efficiency, deterioration of drivability, HC, C
O, there is a problem that leads to deterioration of the NO _X emissions.

Therefore, in view of the difference in the output cycle of the downstream side O ₂ sensor between when there is no catalyst deterioration shown in FIG. 2 and when there is catalyst deterioration shown in FIG. comparison of the output inversion cycle side O ₂ sensor, or to determine the deterioration of the catalyst by output inversion cycle of the downstream O ₂ sensor (see Kokoku 7-26528 discloses), or downstream O ₂ per predetermined time It has been proposed that the catalyst deterioration is determined based on whether or not the number of output reversals of the sensor is a predetermined value or more (see Japanese Patent Laid-Open No. 63-98552).

[0008]

However, when detecting catalyst deterioration based on the output of the O ₂ sensor on the downstream side of the catalyst as described above, corrosion or cracks in the exhaust pipe on the upstream side of the downstream O ₂ sensor, Alternatively, when the connection portion is distorted, it may be erroneously determined that the normal catalyst is deteriorated.

For example, when a crack or the like occurs in the downstream O ₂ sensor mounting portion or the upstream side of the mounting portion, the outside air is sucked into the exhaust pipe from the crack portion in accordance with the pulsation of the exhaust flow in the exhaust pipe. become. Therefore, the downstream O ₂ sensor is periodically exposed to the exhaust gas whose oxygen concentration has increased due to the sucked air, and the downstream O ₂ sensor output is shown in FIG. Thus, lean and rich fluctuations are repeated in synchronization with the pulsation of exhaust gas.

As a result, even if the catalytic converter is normal, the reversal cycle of the downstream O ₂ sensor output is short and the number of reversals is large, which causes a problem that the normal catalyst is erroneously determined to be deteriorated. Of. The present invention has been made in view of the above problems, and an object thereof is to provide a catalyst deterioration determination device capable of preventing a catalyst deterioration erroneous determination when an abnormality such as air leakage occurs in an exhaust pipe.

[0011]

According to the first aspect of the present invention, is the exhaust air-fuel ratio provided in the exhaust passage downstream of the three-way catalyst disposed in the exhaust passage of the internal combustion engine, and is the exhaust air-fuel ratio lean? An air-fuel ratio sensor that generates a signal of a different output level depending on whether it is rich, a constant calculation means that calculates a constant used for air-fuel ratio feedback control based on the output of the air-fuel ratio sensor, and an engine based on the constant. In a catalyst deterioration determination device comprising an air-fuel ratio feedback control means for feedback controlling an air-fuel ratio to a theoretical air-fuel ratio, and a catalyst deterioration determination means for determining deterioration of the three-way catalyst based on the air-fuel ratio sensor output, Exhaust passage abnormality detecting means for detecting abnormality in the exhaust passage upstream of the air-fuel ratio sensor based on the output of the air-fuel ratio sensor; And inhibiting means for inhibiting the catalyst deterioration determination by the deterioration determining means, the catalyst deterioration determination apparatus characterized by comprising a are provided.

That is, according to the first aspect of the invention, the prohibiting means prohibits the catalyst deterioration determination by the catalyst deterioration determining means when an abnormality in the exhaust passage is detected. Therefore, the catalyst deterioration determination is likely to be erroneous. Deterioration determination execution is prevented. Further, according to the invention described in claim 2, it is provided in the exhaust passage downstream of the three-way catalyst arranged in the exhaust passage of the internal combustion engine, and the exhaust air-fuel ratio is lean or rich. Air-fuel ratio sensors that generate signals of different output levels, constant calculation means that calculates a constant used for air-fuel ratio feedback control based on the output of the air-fuel ratio sensor, and the air-fuel ratio of the engine to the theoretical air-fuel ratio based on the constants. In a catalyst deterioration determination device including an air-fuel ratio feedback control means for feedback control and a catalyst deterioration determination means for determining deterioration of the three-way catalyst based on the output of the air-fuel ratio sensor, a constant used for the air-fuel ratio feedback control. Deterioration of the catalyst, the prohibition means for prohibiting the catalyst deterioration determination by the catalyst deterioration determination means when the value of is reached to a predetermined guard value. Another device is provided.

That is, in the second aspect of the present invention, the constant calculating means calculates the constant used for the air-fuel ratio feedback control based on the output of the air-fuel ratio sensor. Therefore, for example, air leakage in the exhaust passage upstream of the air-fuel ratio sensor or other Due to the cause
When the output of the air-fuel ratio sensor repeats a variation that is biased to the lean side or the rich side, the value of the above constant becomes a value that greatly deviates from the normal variation range, and it is provided to prevent an excessive change in the air-fuel ratio. Reached the guard value. The prohibition means prohibits the deterioration determination by the catalyst deterioration determination means when the above constant reaches the guard value, that is, when the output of the air-fuel ratio sensor is deviated to the lean side or the rich side. As a result, the catalyst deterioration determination is prevented from being performed in a state where an error is likely to occur in the catalyst deterioration determination.

[0014]

1 is an overall schematic view showing an embodiment of an air-fuel ratio control system for an internal combustion engine according to the present invention. In FIG. 1, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. The air flow meter 3 directly measures the amount of intake air, and for example, incorporates a potentiometer and generates an output signal of an analog voltage proportional to the amount of intake air. This output signal is provided to the A / D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose axis generates, for example, a reference position detection pulse signal every 720 ° in terms of crank angle, and a reference position detection pulse signal in every 30 degrees which is converted into crank angle. A generated crank angle sensor 6 is provided. The pulse signals of the crank angle sensors 5 and 6 are supplied to the input / output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to the interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from the fuel supply system to the intake port for each cylinder. The water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of the cooling water. The water temperature sensor 9 generates an analog voltage electric signal corresponding to the cooling water temperature THW. This output is also supplied to the A / D converter 101.

In the exhaust system downstream of the exhaust manifold 11, a catalytic converter 12 containing a three-way catalyst for simultaneously purifying three toxic components HC, CO and NO _x in the exhaust gas.
Is provided. The first O ₂ sensor 1 is provided on the exhaust manifold 11, that is, on the upstream side of the catalytic converter 12.
3, the exhaust pipe 1 on the downstream side of the catalytic converter 12.
4 is provided with a _second O ₂ sensor 15. The O ₂ sensors 13 and 15 generate electric signals according to the oxygen component concentration in the exhaust gas. That is, the O ₂ sensors 13 and 15 output different output voltages depending on whether the air-fuel ratio is leaner or richer than the stoichiometric air-fuel ratio.
Occurs at 01. The control circuit 10 is configured as, for example, a microcomputer, and in addition to the A / D converter 101, the input / output interface 102, the CPU 103, the RA
M104, ROM 105, backup RAM 106,
A clock generation circuit 107 and the like are provided.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 for generating a signal LL indicating whether or not the throttle valve 16 is fully closed. The idle state output signal LL is supplied to the input / output interface 102 of the control circuit 10. Reference numeral 18 denotes a secondary air introduction intake valve for supplying secondary air to the exhaust pipe 11 during deceleration or idling to reduce HC and CO emissions.

Reference numeral 19 is a catalyst deterioration alarm, and 20 is an exhaust pipe abnormality alarm. Further, in the control circuit 10, the down counter 108, the flip-flop 109,
The drive circuit 110 is for controlling the fuel injection valve 7. That is, when the fuel injection amount TAU is calculated in a routine described later, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is set. As a result, the drive circuit 11
0 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts a clock signal (not shown) and the terminal finally becomes the “1” level, the flip-flop 109 is set and the drive circuit 110 energizes the fuel injection valve 7. To stop. That is, the above-mentioned fuel injection amount TA
The fuel injection valve 7 is energized by U, and therefore the fuel injection amount T
The amount of fuel corresponding to AU is sent to the fuel chamber of the engine body 1.

The CPU 103 generates an interrupt at A /
After the A / D conversion of the D converter 101 is completed, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6, the interrupt signal from the clock generation circuit 107, and the like. The intake air amount data Q and the cooling water temperature data THW of the air flow sensor 3 are fetched by an A / D conversion routine executed at a predetermined time or every predetermined crank angle, and stored in a predetermined area of the RAM 105.
That is, the data Q and THW in the RAM 105 are updated every predetermined time. Also, the rotation speed data N
e is calculated by interruption of the crank angle sensor 6 every 30 ° CA and is stored in a predetermined area of the RAM 105.

5 and 6 show a first air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF based on the output of the upstream O ₂ sensor 13, which is executed every predetermined time, for example, 4 ms. In step 501, it is determined whether or not the closed loop (feedback) condition of the air-fuel ratio by the upstream O ₂ sensor 13 is satisfied. For example,
When the cooling water temperature is below the specified value, the output signal of the upstream O ₂ sensor 13 is inverted even once during engine startup, during startup increase, during warm-up increase, power increase, OTP increase for catalyst overheat prevention. When not, the closed loop condition is not satisfied during the fuel cut, and in other cases, the closed loop condition is satisfied. When the closed loop condition is not satisfied, the process directly proceeds to step 526. The air-fuel ratio correction coefficient FAF is 1.
It may be set to 0. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 502.

In step 502, the upstream O ₂ sensor 1
The output V ₁ of _No. 3 is A / D converted and fetched, and step 503
In step 504, it is determined whether V ₁ is the comparison voltage V _R1 or less, for example, 0.45 V or less, that is, whether the air-fuel ratio is rich or lean, that is, if lean (V ₁ ≦ V _R1 ). It is determined whether or not the delay counter CDLY is positive. If CDLY> 0, the CDL is determined in step 505.
Y is set to 0, and the process proceeds to step 506. In step 506, the delay counter CDLY is decremented by 1, and step 5
At 07 and 508, the delay counter CDLY is set to the minimum value T.
Guard with DL. In this case, the delay counter CDL
When Y reaches the minimum value TDL, the air-fuel ratio flag F1 is set to "0" (lean) in step 509. In addition,
The minimum value TDL is a lean delay state for holding the determination that it is in the rich state even if the output of the upstream O ₂ sensor 13 changes from rich to lean, and is defined as a negative value. On the other hand, if lean (V ₁ > V _R1 ), it is determined in step 510 whether the delay counter CDLY is negative, and if CDLY <0, step 511.
Then, CDLY is set to 0, and the routine proceeds to step 512. In step 512, the delay counter CDLY is incremented by 1, and in steps 513 and 514, 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 515. Note that the maximum value TDR is a rich delay state for maintaining the determination that the output is the lean state even when the output of the upstream O ₂ sensor 13 changes from lean to rich, and is defined as a positive value. You.

In step 516 of FIG. 6, the air-fuel ratio flag F
It is determined whether or not the sign of 1 is inverted, that is, it is determined whether or not the air-fuel ratio after the delay process is inverted. If the air-fuel ratio is reversed, at step 517, the air-fuel ratio flag F1
Depending on the value of, it is determined whether the reversal from rich to lean or the reversal from lean to rich. If it is the reverse from rich to lean, in step 518 FAF ← FAF + RS
If R is reversed from lean to rich, FAF ← FAF− in step 519.
Decrease on RSL and skip. That is, skip processing is performed.

If the sign of the air-fuel ratio flag F1 is not reversed in step 512, steps 520, 521, 5
At 22, an integration process is performed. That is, in step 520, it is determined whether or not F1 = "0". If F1 = "0" (lean), in step 521 FAF ← FAF + KI.
R, and if F1 = “1” (rich), then at step 522, FAF ← FAF-KIL. here,
The integration constants KIR and KIL are set sufficiently smaller than the skip amounts RSR and RSL, that is, KIR (KI
L) <RSR (RSL). Therefore, step 52
1 is the lean state (F1 = “0”) and gradually increases the fuel injection amount, and step 522 is the rich state (F1 =
In “1”), the fuel injection amount is gradually reduced.

Further, step 52 is performed for each skip processing.
At 3, 524, the air-fuel ratio correction coefficient FAF is learned. You
That is, in step 523, the learning condition is satisfied.
It is determined whether or not For example, the intake air from RAM105
Read the volume data Q, Q <Q ₀(Q₀Is a constant value)
Is determined. Q ≧ Q₀If so, go directly to step 525.
Proceed and do not perform learning control. This is because the intake air amount Q is large.
When learning control is performed when the threshold is reached, learning is performed due to the effect of evaporative
The learning (overcorrection) of the value FGHAC may be performed.
This is because that. On the other hand, if the learning conditions are met, the
At 524, the air-fuel ratio correction coefficient FAF is learned.
U. The learning step 524 will be described later.

Next, steps 518, 519, 521,
The air-fuel ratio correction coefficient FAF calculated at 522 is guarded at step 525 with a minimum value of 0.8 and a maximum value of 1.2, for example. As a result, when the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled at the maximum value or the minimum value to prevent the air-fuel ratio from becoming rich or over lean. .

The FAF calculated as described above is stored in the RAM 1
05, and this routine ends at step 526. FIG. 7 is a detailed flowchart of the learning step 524 of FIG. 6, and as described above, under the air-fuel ratio feedback control by the upstream O ₂ sensor 13, when the learning condition is satisfied, the air-fuel ratio correction is performed. It is executed every time the coefficient FAF is skipped.

That is, in step 601, the average value FAFAV of the air-fuel ratio correction coefficient FAF is calculated by FAFAV ← (FAF + FAFO) / 2, where FAFO is the FAF value immediately after the previous skip, and in step 602, FAF is calculated. In preparation for the next calculation, FAFO ← FAF. Next, in step 603, ΔFAF ← FAFAV-1.0 is calculated.

Next, at step 604, ΔFAF> 0.
If ΔFAF> 0 as a result, the learning correction amount FGHAC is increased by FGHAC ← FGHAC + ΔFGHAC in step 605, and the maximum value, for example 1.05, is guarded in steps 606 and 607. On the other hand, if ΔFAF ≦ 0, the learning correction amount FGHAC is decreased by FGHAC ← FGHAC−ΔFGHAC in step 608, and the minimum correction value 0.90 is guarded in steps 609 and 610. Note that | ΔFAF |>
The FGHAC may be updated only when K (a positive value). In this way, according to the learning control, the learning correction amount FGHAC is increased or decreased so that the center of variation of the air-fuel ratio correction coefficient FAF converges to 1.0.

FIG. 8 is a timing diagram for supplementarily explaining the operation according to the flowcharts of FIGS. Upstream O ₂
When the air-fuel ratio signal A / F for the rich / lean determination is obtained from the output of the sensor 13 as shown in FIG. 8A, the delay counter CDLY is counted up in the rich state as shown in FIG. 8B. Countdown in the lean state. As a result, as shown in FIG. 8C, the delayed air-fuel ratio signal A / F '(corresponding to the flag F1).
Is formed. For example, at time t _{1, the} air-fuel ratio signal A /
Even when F ′ changes from lean to rich, the delayed air-fuel ratio signal A / F ′ changes to rich at time t ₂ after being held lean for the rich delay time TDR. Even the air-fuel ratio signal A / F at time t ₃ is changed from rich to lean, the delayed air-fuel-fuel ratio signal A / F 'is the time after being held rich only equivalent lean delay time (-TDL) t It changes to lean at ₄ . However, the air-fuel ratio signal A / F '
Is the rich delay time TDR at times t ₅ , t ₆ , and t _7.
Invert a short period of, delay counter CDLY it takes time to reach the maximum value TDR, a result, the air-fuel ratio signal A / F of the delayed at time t ₈ 'is reversed. That is, the air-fuel ratio signal A / F 'after the delay processing is more stable than the air-fuel ratio signal A / F before the delay processing. The air-fuel ratio correction coefficient FAF shown in FIG. 8D is obtained based on the stable air-fuel ratio signal A / F 'after the delay processing.

Next, the second air-fuel ratio feedback control by the downstream O ₂ sensor 15 will be described. As the second air-fuel ratio feedback control, the skip amount RSR as a constant used in the first air-fuel ratio feedback control,
RSL, integration constants KIR, KIL, delay time TDR, T
There are DL and a system that makes the comparison voltage V _R1 of the output V ₁ of the upstream O ₂ sensor 13 variable, and a system that introduces the second air-fuel ratio correction coefficient FAF2.

For example, the rich skip amount RSR is increased.
The control air-fuel ratio can be shifted to the rich side by increasing the
Even if the lean skip amount RSL is reduced, the control air-fuel ratio
Can be shifted to the high side, while the lean skip amount RSL is increased.
The control air-fuel ratio can be shifted to the lean side by changing the
Even if the switch skip amount RSR is reduced, the control air-fuel ratio is
You can move to the computer side. Therefore, the downstream side O_TwoSensor 15
Rich skip amount RSR and lean according to the output of
The air-fuel ratio can be controlled by correcting the KIP amount RSL.
You. Also, if the rich integration constant KIR is increased, the control
The air-fuel ratio can be shifted to the rich side, and the lean integration constant K
Even if IL is reduced, the control air-fuel ratio can be shifted to the rich side,
On the other hand, if the lean integration constant KIL is increased, control air-fuel
The ratio can be shifted to the lean side, and the rich integration constant KIR
The control air-fuel ratio can be shifted to the lean side even if is decreased. Obedience
O downstream_TwoRich integration according to the output of the sensor 15
Correcting the constant KIR and the lean integration constant KIL
The air-fuel ratio can be controlled by. Large rich delay time TDR
Kiku or lean delay time (-TDL) is set small
If so, the control air-fuel ratio can shift to the rich side, and conversely
Delay time (-TDL) is large or rich delay
If the interval (TDR) is set small, the control air-fuel ratio becomes lean.
Can move to the side. That is, the downstream side O_TwoOutput of sensor 15
By correcting the delay times TDR and TDL according to
The air-fuel ratio can be controlled. Furthermore, the comparison voltage V_R1The big
The control air-fuel ratio can be shifted to the rich side by changing the
Voltage V _R1When is decreased, the control air-fuel ratio can be shifted to the lean side.
Wear. Therefore, the downstream O_TwoThe ratio depends on the output of the sensor 15.
Reference voltage V_R1The air-fuel ratio can be controlled by correcting

The skip amount, integration constant, delay time,
Making the comparison voltage variable by the downstream O ₂ sensor has its own advantages. For example, the delay time allows very fine adjustment of the air-fuel ratio, and the skip amount is
Control with good response is possible without lengthening the feedback cycle of the air-fuel ratio like the delay time. Therefore, these variable amounts can be used in combination of two or more.

Next, a double O ₂ sensor system in which the skip amount as a constant used for the air-fuel ratio feedback control is variable will be described. FIG. 9 shows a second air-fuel ratio feedback control routine based on the output of the downstream O ₂ sensor 15, which is executed every predetermined time, for example, 512 ms. In steps 801 to 806, it is determined whether or not the closed loop condition by the downstream O ₂ sensor 15 is satisfied. For example,
In addition to the closed loop condition not being satisfied by the upstream O ₂ sensor 13 (step 801), when the cooling water temperature THW is below a predetermined value (for example, 70 ° C.) (step 802), the throttle valve 16 is fully closed (LL = “1”). ) (Step 8
03), when the secondary air is not introduced based on the rotation speed Ne, the vehicle speed, the signal LL of the idle switch 17, the cooling water temperature THW, etc. (step 804), when the load is light (Q / Ne <X ₁ ) ( In step 805), the closed loop condition is not satisfied when the downstream O ₂ sensor 15 is not activated (step 806), and in other cases, the closed loop condition is satisfied. If it is not a closed loop condition, step 8
If the condition is a closed loop condition, the process proceeds to step 807.

In step 807, the downstream O ₂ sensor 1
The output V ₂ of 5 is A / D converted and fetched, and step 80
At 9, it is determined whether V ₂ is equal to or less than the comparison voltage V _R2, for example, 0.55 V, that is, it is determined whether the air-fuel ratio is rich or lean. Note that the comparison voltage V _R2 is calculated from the comparison voltage V _R1 of the output of the upstream O ₂ sensor 13 in consideration of the fact that the output characteristics due to the influence of the raw gas and the degradation speed differ upstream and downstream of the catalytic converter 12. Although set high, this setting may be arbitrary. As a result, V ₂ ≤V
_{If R2} (lean), steps 809, 810, 811
If V ₂ > V _R2 (rich), proceed to step 81.
Proceed to 2, 813, 814. That is, step 809
Then, RSR ← RSR + ΔRS (constant value), that is, the rich skip amount RSR is increased to shift the air-fuel ratio to the rich side, and in steps 810 and 811, RSR is executed.
Is protected by the maximum value MAX (= 7.5%), while RSR ← RSR−ΔRS is set in step 812, that is, the rich skip amount RSR is decreased to shift the air-fuel ratio to the lean side, and step 813 , 814 guards RSR with the minimum value MIN (= 2.5%). Note that the minimum value MIN is a value at a level at which the transient followability is not deteriorated, and the maximum value MAX is a value at a level at which the drivability does not deteriorate due to the air-fuel ratio fluctuation.

At step 815, the lean skip amount R
Let SL be RSL ← 0.1-RSR. That is, RSR + RSL = 0.1. In step 816, it is determined whether the catalyst is deteriorated or the exhaust pipe is abnormal. Then, in step 817, this routine ends.

Next, the determination of catalyst deterioration and exhaust pipe abnormality executed in step 816 will be described. In the present embodiment, the presence or absence of an exhaust pipe abnormality is detected based on the change in the rich skip amount RSR determined by the second air-fuel ratio feedback control based on the output of the downstream O ₂ sensor 15 described above. The principle of this detection method will be described below with reference to FIGS. 2, 3, and 4. That is, as shown in FIG. 3, when the catalyst is deteriorated, the lean output and the rich output are alternately repeated with substantially the same length, although the output inversion cycle of the downstream side air-fuel ratio sensor is shortened. Therefore, the update of the skip amount RSR calculated according to the output of the downstream side air-fuel ratio sensor and the update of the skip amount RSR in the decreasing direction occur repeatedly, and the amount of change of the skip amount RSR within a predetermined time period. ΔRSR becomes very small.

On the other hand, as shown in FIG. 2, when there is no catalyst deterioration, the output inversion cycle of the downstream side air-fuel ratio sensor is long,
The skip amount RSR calculated according to the output of the downstream side air-fuel ratio sensor changes greatly, and the change amount ΔRSR of the skip amount RSR within a predetermined time becomes a large value. Further, as shown in FIG. 4, when there is air leakage, the downstream side air-fuel ratio sensor is reversed due to the influence of exhaust pulsation, but the lean output increases due to the influence of air leakage, and the rich output extremely decreases. . As a result, the skip amount RSR calculated according to the output of the downstream air-fuel ratio sensor becomes large. Further, the calculation of the skip amount RSR is performed for a relatively long time, for example, every 512 ms because the output of the downstream side air-fuel ratio sensor changes relatively slowly due to the O ₂ storage result of the catalyst. If the timing and the update timing of the skip amount RSR match, the RSR is made smaller, but as described above, since the rich output is extremely small, there is no opportunity to update the skip amount RSR in the decreasing direction, and therefore the skip amount RSR is skipped. The quantity RSR is updated in the increasing direction and eventually clings to the upper limit guard MAX.

Therefore, as can be seen from FIGS. 2, 3 and 4, when the exhaust pipe is abnormal, the skip amount RSR sticks to the guard value, so that it is possible to detect that the exhaust pipe is abnormal. On the other hand, as is clear from a comparison between FIG. 2 and FIG. 3, when the catalyst deteriorates (FIG. 3), the change amount ΔRSR of the skip amount RSR within a predetermined time becomes a small value, so the catalyst deterioration is detected. be able to.

In FIGS. 2, 3, and 4, Q indicates the intake air amount. 10 and 11 are detailed flowcharts of the above-described catalyst deterioration / exhaust pipe abnormality determination executed in step 816 of FIG. That is, step 90
1 and 902, the learning value FGH calculated in FIG.
The abnormality of the fuel injection valve 7 is determined by determining whether the AC is stuck at the lower limit 0.90 or the upper limit 1.05. Further, in step 903, it is determined whether or not the steady state is present, for example, by whether or not the intake air change amount is a fixed value or less, or the load Q / Ne change amount is a fixed value or less. When the fuel injection valve is abnormal or in an unsteady state, the skip amount RSR does not become a normal value, so step 92
1, the counters C1 and C2 are cleared, and the process proceeds to step 922 in FIG. In this case, the catalyst deterioration / exhaust pipe abnormality is not substantially discriminated. Further, only in other cases, the process proceeds to step 904 in FIG.

At step 904, the rich skip amount R
It is determined whether SR sticks to the maximum value MAX, that is, whether RSR = MAX, and as a result, RSR
If ≠ MAX, the process proceeds to steps 905 to 913. Conversely, if RSR = MAX, steps 914 to 9 are performed.
Go to 20. The flow of steps 905 to 913 is shown in FIG.
It is determined whether there is no catalyst deterioration shown in FIG. 3 or there is catalyst deterioration shown in FIG. That is, at step 905, the counter C1 for measuring the determination period C1 ₀ shown in FIGS. 2 and 3 is incremented by +1 while the counter C2 for measuring the exhaust pipe abnormality determination period C2 ₀ shown in FIG. 4 is set. clear. In step 907, the change amount (amplitude) ΔRSR of the rich skip amount RSR is calculated. Step 907 will be described later. Then, step 90
8 determining period C1 _0, it is determined whether or not the elapsed at this result, until after determining period proceeds directly to step 921, after determining period proceeds to step 909-913.

[0041] That is, in step 909, the change amount DerutaRSR the rich skip amount RSR is determined whether or not less than the predetermined value X _2, as a result, determines that the catalyst deterioration shown in FIG. 3, if DerutaRSR <X _2, Step catalyst deterioration alarm 19
On the other hand, if ΔRSR ≧ X ₂ , it is determined that there is no catalyst deterioration shown in FIG. 2, and the catalyst deterioration alarm 19 is turned off in step 911. Then, in step 912, the counter C1 is cleared and initialized, and in step 9
In 13, the upper limit value RSR used in step 907
U, the lower limit value RSRL, and the change amount ΔRSR are initialized as RSRU ← RSR RSRL ← RSR ΔRSR ← 0, respectively.

The flow of steps 914 to 920 is to determine whether the exhaust pipe is abnormal as shown in FIG. That is, in step 914, the counter C1 is cleared, +1 increases the counter C2 for the exhaust pipe abnormality determining period C2 ₀ measured in step 915. In step 916, it is determined whether or not the determination period C2 ₀ has elapsed, and if C2> C2 _{0 as a} result, it is determined that the rich skip amount RSR has been enriched due to an exhaust pipe abnormality, and the process proceeds to step 917. The exhaust pipe abnormality alarm 20 is turned on, and the catalyst deterioration alarm 19 is turned off in step 918. That is, when the exhaust pipe abnormality is detected, the catalyst deterioration determination is not substantially performed. Then, in step 919, the counter C2 is cleared and initialized, and in step 920, the rich skip amount RSR is set to an initial value, for example, 0.05.

Then, this routine ends at step 922 in FIG. FIG. 12 is a detailed flowchart of the change amount ΔRSR calculation step 907 in FIG. 11, in which the upper limit value RSRU and the lower limit value RSRL are initialized to RSR in advance (see step 913 in FIG. 11). Step 10
In 01 and 1002, the current rich skip amount RSR is compared with the upper limit value RSRU, and the upper limit value RSRU is updated only when RSR> RSRU. Also, step 100
In 3 and 1004, the current rich skip amount RSL is compared with the lower limit value RSRL, and the lower limit value RSRL is updated only when RSR <RSRL. And step 10
At 05, the change amount ΔRSR is calculated by ΔRSR ← RSRU−RSRL, and at step 1006, this routine ends.

FIG. 13 shows an injection amount calculation routine, which is executed at a predetermined crank angle, for example, at 360 ° CA. In step 1101, the intake air amount data Q and the rotation speed data Ne are read out from the RAM 105 to obtain the basic injection amount TAU.
Calculate P. For example, TAUP ← α · Q / Ne (α is a constant). At step 1102, the final injection amount TA
U is TAU ← TAUP ・ (FAF + FAHAC) ・ β
Computed by + γ. Note that β and γ are correction amounts that are determined by other operating state parameters. Next, at step 1103, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 1104, this routine ends.

As described above, when the time corresponding to the injection amount TAU elapses, the flip-flop 109 is reset by the signal of the down counter 108 and the fuel injection ends. Note that, in the above-described embodiment, the control of the rich skip amount RSR is continued even when the catalyst deterioration is determined, but the RSR may be fixed to a constant value in the routine of FIG. 9.

Further, the first air-fuel ratio feedback control is
Every 4 ms, the second air-fuel ratio feedback control is 5
Air-fuel ratio feedback control is performed every 12ms.
Responsive upstream O_TwoMainly controlled by sensors
O, which has poor responsiveness_TwoDepends on the control by the sensor
To do so. Also, upstream side O_TwoAir-fuel by sensor
Other constants used for ratio feedback control, such as slow
Delay time, integration constant, etc._TwoDepending on the sensor output
Double O to correct_TwoThe sensor system also has a second
Double O that introduces air-fuel ratio correction coefficient _TwoFor sensor systems
The present invention can also be applied. Also, skip amount, delay time,
Control by controlling two of the integration constants at the same time
You can improve the property. Further skip amount RSR, RSL
It is also possible to fix one of the two and make only the other variable during delay.
One of TDR and TDL is fixed and the other is variable
Alternatively, the rich integration constant KIR, lean
It is also possible to fix one of the integration constants KIL and make the other variable.
It is possible.

Further, as the intake air amount sensor, a Karman vortex sensor, a heat wire sensor or the like can be used instead of the air flow meter. Further, in the above-described embodiment, the fuel injection amount is calculated according to the intake air amount and the engine rotation speed. However, the fuel injection amount is calculated according to the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may be calculated.

Furthermore, in the above embodiment, the internal combustion engine in which the fuel injection amount to the intake system is controlled by the fuel injection valve has been shown, but the present invention can be applied to a carburetor type internal combustion engine.
For example, an electric air control valve (EACV) is used to adjust the intake air amount of the engine to control the air-fuel ratio, and an electric bleed air control valve is used to adjust the air bleed amount of the carburetor to control the main system passage and The present invention can be applied to, for example, the one in which the air-twisting ratio is controlled by introducing the atmosphere into the slow passage, the one in which the 2 o'clock air amount sent to the exhaust system of the engine is adjusted, and the like. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 1101 is determined by the carburetor itself, that is, in accordance with the intake pipe negative pressure according to the intake air amount and the rotational speed of the engine.
At 02, the supply air amount corresponding to the final fuel injection amount TAU is calculated.

Further, in the above-mentioned embodiment, the O ₂ sensor is used as the air-fuel ratio sensor, but a CO sensor, a lean mixture sensor or the like may be used. In particular, when a TiO ₂ sensor is used as the upstream air-fuel ratio sensor, control responsiveness is improved, and overcorrection due to the output of the downstream air-fuel ratio sensor can be prevented. Furthermore, although the above-described embodiment is configured by a microcomputer, that is, a digital circuit, it may be configured by an analog circuit.

[0050]

As described above, according to the present invention, the catalyst deterioration determination is prohibited when an abnormality occurs in the upstream exhaust passage of the catalyst downstream side air-fuel ratio sensor. It is possible to prevent erroneous determination of.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram showing an embodiment of a catalyst deterioration determination device for an internal combustion engine according to the present invention.

FIG. 2 is a diagram illustrating the principle of catalyst deterioration determination in the embodiment of FIG.

FIG. 3 is a diagram illustrating the principle of catalyst deterioration determination in the embodiment of FIG.

FIG. 4 is a diagram for explaining the principle of exhaust pipe abnormality determination in the embodiment of FIG.

FIG. 5 is a part of a flowchart illustrating first air-fuel ratio feedback control. It is.

FIG. 6 is a part of a flowchart illustrating first air-fuel ratio feedback control. It is.

FIG. 7 is a flowchart illustrating air-fuel ratio learning control.

FIG. 8 is a timing diagram for supplementarily explaining the flowcharts of FIGS. 5 and 6.

FIG. 9 is a flow chart illustrating second air-fuel ratio feedback control.

FIG. 10 is a part of a flowchart for explaining a catalyst deterioration and exhaust pipe abnormality determination operation.

FIG. 11 is a part of a flowchart for explaining a catalyst deterioration and exhaust pipe abnormality determination operation.

FIG. 12 is a flowchart illustrating parameter calculation of the routines of FIGS.

FIG. 13 is a flowchart illustrating a fuel injection amount calculation operation.

FIG. 14: Single O ₂ sensor system and double O ₂
It is a figure explaining the exhaust emission characteristic of a _two- sensor system.

[Explanation of symbols]

1 ... Engine body 2 ... Air flow meter 4 ... Distributor 5, 6 ... Crank angle sensor 10 ... Control circuit 12 ... Catalytic converter 13 ... Upstream O ₂ sensor 15 ... Downstream O ₂ sensor 17 ... Idle switch

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F01N 7/00 F01N 7/00 A

Claims (2)

(57) [Claims] 1. A signal, which is provided in an exhaust passage downstream of a three-way catalyst arranged in an exhaust passage of an internal combustion engine and generates a signal having a different output level depending on whether the exhaust air-fuel ratio is lean or rich. An air-fuel ratio sensor, a constant calculation means for calculating a constant used for air-fuel ratio feedback control based on the output of the air-fuel ratio sensor, and an air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the engine to the stoichiometric air-fuel ratio based on the constant. And a catalyst deterioration determining device that determines deterioration of the three-way catalyst based on the output of the air-fuel ratio sensor, and a catalyst deterioration determining device comprising: Exhaust passage abnormality detecting means for detecting abnormality of the passage, and prohibiting catalyst deterioration determination by the catalyst deterioration determining means when abnormality of the exhaust passage is detected Catalyst deterioration determination apparatus characterized by comprising a stop means. 2. A signal, which is provided in an exhaust passage downstream of a three-way catalyst arranged in an exhaust passage of an internal combustion engine and generates a signal having a different output level depending on whether the exhaust air-fuel ratio is lean or rich. An air-fuel ratio sensor, a constant calculation means for calculating a constant used for air-fuel ratio feedback control based on the output of the air-fuel ratio sensor, and an air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the engine to the stoichiometric air-fuel ratio based on the constant. In the catalyst deterioration determination device including a catalyst deterioration determination unit that determines deterioration of the three-way catalyst based on the output of the air-fuel ratio sensor, a constant value used for the air-fuel ratio feedback control is a predetermined guard value. A catalyst deterioration determination device, comprising: a prohibition unit that prohibits catalyst deterioration determination by the catalyst deterioration determination unit when it reaches.