JP3395586B2 - Diagnosis device for exhaust purification system of multi-cylinder internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Type, horizontally opposed type, in which cylinders are divided into cylinder groups and arranged, and an exhaust passage extending from an exhaust port of each cylinder is collected for each cylinder group. .

[0002]

2. Description of the Related Art An air-fuel ratio sensor is arranged on each of an upstream side and a downstream side of an internal combustion engine, and feedback control is performed based on an output of the upstream side air-fuel ratio sensor so that the air-fuel ratio becomes a stoichiometric air-fuel ratio. A so-called double air-fuel ratio sensor system or a double O ₂ sensor system that corrects feedback control based on the upstream side air-fuel ratio sensor is known (see Japanese Patent Laid-Open No. 61-286550).

In such a double air-fuel ratio sensor system, the locus length L of the output of the upstream side air-fuel ratio sensor
A method has been developed for detecting catalyst deterioration from the ratio LVOS / LVOM between VOS and the locus length LVOMY of the downstream air-fuel ratio sensor. Further, in addition to the ratio of the locus lengths, the area A surrounded by the output of the upstream air-fuel ratio sensor and a predetermined reference value
A method of detecting catalyst deterioration from the ratio AVOS / AVOM of VOS and the output of the downstream side air-fuel ratio sensor and the area AVOM surrounded by a predetermined reference value has also been developed (Japanese Patent Laid-Open No. Hei 5).
See 163989).

Exhaust passages coming out of the exhaust ports of each cylinder, such as the V type and the horizontally opposed type, are collected for each cylinder group by the primary collecting exhaust pipe, and the primary collecting exhaust pipe is further constructed by the secondary collecting exhaust pipe. A double air-fuel ratio sensor system has also been proposed for those assembled and connected to a catalyst (see Japanese Patent Laid-Open No. 64-8332). In the device of the above publication, an upstream side air-fuel ratio sensor is arranged at the collecting portion of each primary collecting exhaust pipe on the upstream side of the catalyst, and a downstream side air-fuel ratio sensor is arranged at the exhaust pipe on the catalyst downstream side. Feedback control is performed so that the air-fuel ratio of each cylinder group becomes the theoretical air-fuel ratio based on the output of the side air-fuel ratio sensor, and the air-fuel ratio control of all cylinders is corrected based on the output of the downstream side air-fuel ratio sensor.

In the double air-fuel ratio sensor system of this type, the exhaust gas actually flowing into the catalyst is a mixture of exhaust gas from each cylinder group. Therefore, when determining the deterioration of the catalyst from the ratio of the locus lengths of the outputs of the air-fuel ratio sensors on the upstream side and the downstream side, or in addition, the area ratio, the air-fuel ratio of the exhaust gas actually flowing into the catalyst is
Since it does not match the output of any of the upstream side air-fuel ratio sensors, the deterioration of the catalyst cannot be accurately detected.

Therefore, from the average value of the outputs of the two upstream side air-fuel ratio sensors provided in the collecting portion of each primary collecting exhaust pipe, the air-fuel ratio immediately upstream of the collecting portion of the secondary collecting exhaust pipe, that is, the catalyst is determined. A method for estimating and deteriorating the catalyst based on this estimated value has been proposed (see JP-A-6-173661).

[0007]

However, in the device of the above publication, when one upstream air-fuel ratio sensor is deteriorated,
Alternatively, if the output characteristics of the air-fuel ratio sensors are different, the air-fuel ratio of the secondary collecting portion of the exhaust passage cannot be correctly estimated, and as a result, catalyst deterioration cannot be accurately determined.

In view of the above problems, the present invention is such that the exhaust passages from the exhaust ports of the cylinders are collected by the primary collecting exhaust pipe for each cylinder group, and the primary collecting exhaust pipes are further collected by the secondary collecting exhaust pipe. For those linked to the catalyst,
An object of the present invention is to provide an apparatus capable of accurately determining catalyst deterioration. Another object of the present invention is to provide an apparatus capable of detecting deterioration of one upstream air-fuel ratio sensor.

[0009]

According to the invention of claim 1, a primary collecting exhaust pipe for collecting exhaust gas emitted from an exhaust port of each cylinder for each cylinder group, and a combined outlet of each primary collecting exhaust pipe. A secondary collecting exhaust pipe that collects the exhaust gas emitted from the exhaust gas and guides it to the catalyst, and is arranged in the collecting part of each primary collecting exhaust pipe, and outputs a signal that linearly corresponds to the exhaust air-fuel ratio on the upstream side of the catalyst. An upstream air-fuel ratio sensor, a downstream air-fuel ratio sensor arranged in the exhaust pipe on the downstream side of the catalyst, and at least the air of each cylinder group based on the deviation between the output of each upstream air-fuel ratio sensor and the theoretical air-fuel ratio. Control means for performing feedback control so that the fuel ratio becomes the stoichiometric air-fuel ratio, and upstream-side air-fuel ratio sensor output trajectory length calculation means for computing the trajectory length of the output of each upstream-side air-fuel ratio sensor within a predetermined period during feedback control And each upstream side air-fuel ratio A representative upstream side air-fuel ratio sensor output locus length calculating means for calculating a representative upstream side air-fuel ratio sensor output locus length representing the locus length of the output of the upstream side air-fuel ratio sensor, and feedback control during feedback control. A downstream side air-fuel ratio sensor output locus length calculating means for calculating the locus length of the output of the downstream side air-fuel ratio sensor within a predetermined period, a representative upstream side air-fuel ratio sensor output locus length, and a downstream side air-fuel ratio sensor output locus length. A diagnostic device for an exhaust gas purification device for a multi-cylinder internal combustion engine, comprising: a catalyst deterioration detecting means for detecting catalyst deterioration based on the upstream air-fuel ratio. A locus length comparison calculation means for comparing and calculating the locus length of the output of the sensor, and a locus for correcting the short locus length to be the same as the long locus length when it is confirmed by the locus length comparison calculation that there is a short locus length. And correction means,
Of the exhaust gas purifying apparatus that calculates a representative upstream air-fuel ratio sensor output trajectory length from the trajectory length of the output of the upstream air-fuel ratio sensor that includes the trajectory length of the output of the upstream air-fuel ratio sensor that is corrected by the trajectory length correction means. A diagnostic device is provided.

In the diagnostic device thus constructed, the locus length of the output of the upstream side air-fuel ratio sensor is compared and calculated, and the locus length of the output of at least one of the upstream side air-fuel ratio sensors is corrected based on the result. . Then, the representative upstream air-fuel ratio sensor output trajectory length is calculated from the trajectory length of the output of the upstream air-fuel ratio sensor including the corrected trajectory length of the output of the upstream air-fuel ratio sensor, and the representative upstream air-fuel ratio sensor output trajectory length And the deterioration of the catalyst is detected based on the output trajectory length of the downstream air-fuel ratio sensor.

According to the invention of claim 2, in the invention of claim 1, the locus length comparison calculation means is a locus length ratio calculation means for calculating the ratio of the locus lengths of the outputs of the upstream side air-fuel ratio sensors. The length correction means includes a trajectory length correction availability determination means,
Based on the ratio of the locus lengths, the locus length correction feasibility determining means determines whether or not the locus lengths can be corrected and used. If it is determined that the locus lengths cannot be corrected and used, the catalyst Provided is a diagnostic device for an exhaust gas purification device in which deterioration detecting means does not detect deterioration of a catalyst.

In the diagnostic device thus constructed, the ratio of the locus lengths of the output of the upstream side air-fuel ratio sensor is calculated, and if the ratio is not within the range where it is judged that the locus length can be corrected from the ratio, the catalyst is used. It does not detect the deterioration of.

According to the third aspect of the present invention, the primary collecting exhaust pipe for collecting the exhaust gas emitted from the exhaust port of each cylinder for each cylinder group and the collecting portion of each primary collecting exhaust pipe are arranged upstream of the catalyst. The upstream side air-fuel ratio sensor that outputs a signal that linearly corresponds to the exhaust air-fuel ratio, and the air-fuel ratio of each cylinder group based on the deviation between the output of each upstream side air-fuel ratio sensor and the theoretical air-fuel ratio Control means for performing feedback control so that each of the upstream side air-fuel ratio sensor output trajectory length calculating means for calculating the trajectory length of the output of each upstream side air-fuel ratio sensor within a predetermined period during feedback control A trajectory length comparison calculation means for comparing and calculating the trajectory length of the output of the fuel ratio sensor, a sensor deterioration detection means for detecting deterioration of one upstream side air-fuel ratio sensor from the result of the trajectory length comparison calculation, and a deteriorated air Fuel ratio Comprises a gain correcting means for correcting so that the gain of the feedback control is increased for the cylinder group on the side where the support is disposed, a diagnostic device is provided in the exhaust purification apparatus.

In the diagnostic device thus constructed, the locus lengths of the outputs of the upstream side air-fuel ratio sensors are compared and calculated, and as a result, it is detected that one upstream side air-fuel ratio sensor has deteriorated, and further deterioration occurs. The feedback control gain for the cylinder group on the side where the air-fuel ratio sensor is arranged is corrected to be large.

[0015]

[0016]

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall schematic diagram showing an embodiment of an internal combustion engine to which a catalyst deterioration detecting device according to the present invention is applied. In FIG. 1, the cylinder of the engine body 1 is a V-shaped engine in which V-shaped cylinders are arranged in two banks, and an air flow meter 3 is provided in an intake passage 2 of the engine body 1.
Is provided. The air flow meter 3 directly measures the intake air amount, and has a built-in potentiometer to generate an output signal of an analog voltage proportional to the intake air amount. This output signal is supplied to the A / D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 is provided with, for example, a crank angle sensor 5 that generates a reference position detection pulse signal for each crank angle 720 ° and a crank angle sensor 6 that generates a reference position detection pulse signal for each crank angle 30 °. . 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 fuel injection valves 7A and 7B for supplying pressurized fuel from the fuel supply system to the intake port for each cylinder. 8A and 8B are spark plugs. Further, a water jacket (not shown) 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. Water temperature sensor 9
Generates an electric signal of an analog voltage according to the temperature THW of the cooling water. This output is also supplied to the A / D converter 101.

Exhaust manifolds 11A, 11 of the right bank (hereinafter, A bank) and the left bank (hereinafter, B bank)
The exhaust systems downstream of B are respectively provided with three-way catalysts 12A and 12B for simultaneously purifying three toxic components HC, CO and NOx in the exhaust gas. This catalyst 12A,
The 12B has a small capacity and is installed in the engine room so that the engine can be warmed up at the start in a short time.

An upstream air-fuel ratio sensor 13A is provided in the exhaust pipe 14A upstream of the catalyst 12A, and the catalyst 12B is also provided.
The upstream air-fuel ratio sensor 13B is connected to the exhaust pipe 14B on the upstream side of
Is provided. Furthermore, two exhaust pipes 14A, 14
B merges at a merging portion 15a downstream thereof, and a catalyst (main catalyst) 16 that accommodates a three-way catalyst is provided in the collective exhaust pipe 15 downstream of the merging portion 15a. Since this catalyst 16 is relatively large, it is provided under the floor of the vehicle body.

A downstream side air-fuel ratio sensor 17 is provided in the collective exhaust pipe on the downstream side of the catalyst 16. The upstream side air-fuel ratio sensors 13A and 13B and the downstream side air-fuel ratio sensor 17 generate an electric signal according to the oxygen component concentration in the exhaust gas. That is, the air-fuel ratio sensors 13A, 13B, 17 are
_{2 The} sensor produces a different output voltage depending on whether the air-fuel ratio is leaner or richer than the stoichiometric air-fuel ratio, while linearly corresponding to the oxygen component concentration in the exhaust gas, that is, the exhaust air An output signal corresponding to the fuel ratio is generated. That is, the normal O ₂ sensor outputs only a signal indicating whether the exhaust air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio, whereas the air-fuel ratio sensor of the present embodiment outputs an output linearly corresponding to the exhaust air-fuel ratio. It generates a signal.

There are several types of this type of air-fuel ratio sensor. FIG. 2 schematically shows the structure of a general air-fuel ratio sensor. The air-fuel ratio sensor 210 includes a solid electrolyte 213 such as zirconia between platinum electrodes 211 and 212.
And a diffusion rate controlling layer 214 made of a ceramic coating layer is provided on the surface of the cathode (exhaust side electrode) 212 to restrict the oxygen molecules in the exhaust gas from reaching the cathode.

In the air-fuel ratio sensor of FIG. 2, when a voltage is applied between the electrodes 211 and 212 at a certain temperature or higher, oxygen molecules are ionized on the cathode 212 side, and the ionized oxygen molecules pass through the solid electrolyte 213 inside the anode 211. Oxygen pump action is generated by moving toward the anode 211 to become oxygen molecules again. Due to this oxygen pump action, the electrodes 211, 2
An electric current that is proportional to the amount of oxygen molecules moved per unit time flows between 12. However, since the diffusion rate controlling layer 214 restricts the oxygen molecules from reaching the cathode, the output current is saturated at a certain constant value, and the current does not increase even if the voltage is increased.

The value of this saturation current is substantially proportional to the oxygen concentration in the exhaust gas. Therefore, by appropriately setting the applied voltage, it is possible to obtain an output current approximately proportional to the oxygen concentration. In the present embodiment, this output current is converted into a voltage signal and supplied to the A / D converter 101 of the control circuit 10. Since there is a one-to-one correlation between the oxygen concentration in the exhaust gas and the air-fuel ratio, the above output voltage linearly corresponds to the exhaust air-fuel ratio,
The exhaust air-fuel ratio can be known from the output current.

The control circuit 10 in FIG. 1 is configured as, for example, a microcomputer, and has an A / D converter 10
1. Input / output interface 102, CPU 103, ROM 104, RAM 105, backup RAM
106, a clock generation circuit 107, etc. are provided.
Further, the throttle valve 18 of the intake passage 2 is provided with an idle switch 19 for detecting whether or not the throttle valve 18 is fully closed. This output signal is supplied to the input / output interface 102 of the control circuit 10. It

Further, 20A and 20B are secondary air introducing intake valves, which supply the secondary air to the exhaust manifolds 11A and 11B at the time of deceleration or idling, and HC and C.
This is for reducing the emission of O 2. Also,
In the control circuit 10, the down counter 108A, the flip-flop 109A, and the drive circuit 110A are for controlling the fuel injection valve 7A in the A bank, and the down counter 108B, the flip-flop 109B, and the drive circuit 110B are in the B bank. It controls the fuel injection valve 7B.

That is, when the fuel injection amount TAUA (TAUB) is calculated in the routine described later, the fuel injection amount TAUA (TAUB) is reduced by the down counter 108A (1).
08B) and flip-flop 1
09A (109B) is also set. As a result, the drive circuit 110A (110B) starts energizing the fuel injection valve 7A (7B). On the other hand, the down counter 108A (108
B) counts a clock signal (not shown), and when the carry-out terminal finally becomes "1" level, the flip-flop 109A (109B) is set and the drive circuit 110A (110B) injects fuel. The energization of the valve 7A (7B) is stopped. That is, the above-mentioned fuel injection amount TAUA
(TAUB) only fuel injection valve 7A (7B) is energized,
Therefore, the amount of fuel corresponding to the fuel injection amount TAUA (TAUB) is sent to the fuel chambers of banks A and B of the engine body 1.

Incidentally, the interrupt generation of the CPU 103 is A /
For example, when 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, when the interrupt signal from the clock generation circuit 107 is received, and the like. Intake air amount data Q of the air flow meter 3, cooling water temperature data THW, air-fuel ratio sensor 13
The outputs V _1A , V _1B and V ₂ of A, 13B and 17 are taken in by an A / D conversion routine executed every predetermined time and R
It is stored in a predetermined area of the AM 105. That is, RAM1
The data Q and THW in 05 are updated every predetermined time. The rotation speed data Ne is calculated by interruption every 30 degrees of the crank angle sensor 6 and is stored in the RAM 1
05 is stored in a predetermined area.

Next, (1) first air-fuel ratio feedback control based on the upstream side air-fuel ratio sensor output, and (2) second air-fuel ratio feedback control based on the downstream side air-fuel ratio sensor output, which are executed by the control circuit 10. , Will be described.

(1) First Air-Fuel Ratio Feedback Control As described above, in the present embodiment, the air-fuel ratios of both banks of the engine 1 are independent of each other based on the outputs of the upstream side air-fuel ratio sensors 13A, 13B. And it is feedback controlled. FIGS. 3, 4, and 5 are first air-fuel ratio feedbacks for calculating the A-bank and B-bank air-fuel ratio correction coefficients FAFA, FAFB based on the outputs V _1A , V _1B of the upstream side air-fuel ratio sensors 13A, 13B. The control routine is executed every predetermined time, for example, every 4 ms.

In step 301 in FIG. 3, it is determined whether or not the feedback control execution condition of the air-fuel ratio by the upstream side air-fuel ratio sensors 13A and 13B is satisfied. For example, when the cooling water temperature is equal to or lower than a predetermined value, during engine start, during post-start increase, during warm-up increase, during power increase, during OTP increase for catalyst overheat prevention, upstream side air-fuel ratio sensors 13A, 13
When the output signal of B has never changed, during the fuel cut, the feedback control condition is not satisfied, and in other cases, the feedback control condition is satisfied. When the feedback control condition is not satisfied, the routine proceeds to step 312, where the air-fuel ratio feedback control flag XM
FB is set to "0", and the routine ends in step 313.

If the feedback control condition is satisfied in step 301, the flag Xw is determined in step 302.
Is reset (= “0”) and the process proceeds to step 303. The flag Xw is a flag indicating a cylinder bank for which feedback control is to be performed. Xw = “0” is the A bank, and Xw =
"1" means B bank. Steps 303-306
Then, the address of the RAM 105 is set according to the value of the flag Xw. That is, if Xw = "0", the address of the RAM 105 is set for the A bank, and the parameters for the subroutine executed in step 307 are those for the A bank (in this case, the parameters in the following explanation of the subroutine are used). (The subscript "i" means "A".) Similarly, when Xw = "1", the address of the RAM 105 is set for the B bank. In this case, the subscript "i" of the parameter in the following explanation of the subroutine means "B". )

Next, at step 307, the air-fuel ratio correction coefficient FAFi (in this case, Xw = "0", FAFi
Means a FAFA, that is, an air-fuel ratio correction coefficient for bank A). A calculation subroutine (described later) is executed. Then, in step 309, it is determined whether or not Xw is 1, and Xw ≠
In case of 1, Xw is set in step 310 (= "1")
Then, the process returns to step 303. If Xw = "1", the air-fuel ratio feedback control flag XMFB is set to "1" to indicate that the air-fuel ratio feedback control is being performed in step 311, and then the routine is ended in step 313. That is, when this routine is executed, first, the air-fuel ratio correction coefficient FAFA of Bank A is calculated,
Then, the B-bank air-fuel ratio correction coefficient FAFB is calculated.

Next, the air-fuel ratio correction coefficient FAFA, FAFB calculation subroutine of step 307 of FIG. 3 will be described with reference to FIGS.
Is shown in. The letter i in the following description represents A or B depending on the value of the flag Xw. At step 401, the output V _{1i of} the upstream air-fuel ratio sensor 13i
Is A / D converted and taken in, and it is determined in step 402 whether V _1i is equal to or higher than the comparison voltage V _R1 . Here, the comparison voltage V
_R1 is the output voltage corresponding to the stoichiometric air-fuel ratio. That is, in step 402, it is determined whether the air-fuel ratio is rich or lean.

If lean (V _1i ≧ V _R1 ), it is judged at step 403 whether or not the delay counter CDLYi is positive. If CDLYi> 0, at step 404 CD
LYi is set to 0 and the process proceeds to step 405. Step 40
In 5, the delay counter CDLYi is decremented by 1, and in steps 406 and 407, the delay counter CDLYi is guarded by the minimum value TDL.

In this case, when the delay counter CDLYi reaches the minimum value TDL, the air-fuel ratio flag F1i is set to "0" (lean) at step 408. It should be noted that the minimum value TDL is a lean delay state for holding the determination that the output state of the upstream side air-fuel ratio sensor 13i is in the rich state even if there is a change from rich to lean, and is defined as a negative value. It

On the other hand, if rich (V _1i <V _R1 ), it is determined in step 409 whether or not the delay counter CDLYi is negative. If CDLYi> 0, CDLYi is set to 0 in step 410, and step 411. Proceed to. In step 411, the delay counter CDLYi is incremented by 1,
Delay counter CDLY in steps 412 and 413
i is guarded by the maximum value TDR.

In this case, when the delay counter CDLYi reaches the maximum value TDR, the air-fuel ratio flag F1i is set to "1" (rich) in step 414. The maximum value TDR is a rich delay state for holding the determination that it is in the lean state even if there is a change from lean to rich in the output of the upstream side air-fuel ratio sensor 13i, and is defined as a positive value. It

Next, proceeding to FIG. 5, at step 415, it is judged if the sign of the air-fuel ratio flag F1i is reversed, that is, if the air-fuel ratio after the delay processing is reversed. If the air-fuel ratio is reversed, it is determined in step 416 whether the air-fuel ratio is changed from rich to lean or lean to rich, depending on the value of the air-fuel ratio flag F1i.
If it is inversion from rich to lean, in step 417 the rich skip amount RSR is read from the RAM 105,
FAFi ← FAFA + RSR and skip-like increase,
On the other hand, if it is the reverse from lean to rich, step 4
At 18, the lean skip amount RSL is read from the RAM 105, and skipped as FAFi ← FAFi−RSL. That is, skip processing is performed. Here, the skip amount RSR is calculated by a routine (FIGS. 7 and 8) described later, and the skip amount RSL is calculated by, for example, RSL = 10% −RSR.

If the sign of the air-fuel ratio flag F1i is not inverted in step 415, steps 419, 420,
At 421, integration processing is performed. That is, in step 419, it is determined whether or not F1i = "0", and F1i = "0".
If it is (lean), FAFi ← FA in step 420
Fi + KIR, and if F1i = “1” (rich), FAFi ← FAFi−KIL in step 421.
And

Here, the integration constants KIR and KIL are set sufficiently smaller than the skip amounts RSR and RSL,
That is, KIR (KIL) <RSR (RSL).
Therefore, step 420 is in the lean state (F1i =
"0") gradually increases the fuel injection amount, and the step 42
1 is a rich state (F1i = “1”) and gradually decreases the fuel injection amount.

Next, in step 422, step 41
The air-fuel ratio correction coefficient FAFi calculated at 7, 418, 420, 421 is guarded at a minimum value of 0.8,
Also, the maximum value, for example 1.2, is guarded. As a result, when the air-fuel ratio correction coefficient FAFi becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled by that value to prevent overrich or over lean. The guarded FAFi is stored in the RAM 105, and the subroutine ends.

As described above, since this subroutine is executed alternately for the A bank and the B bank according to the value of the flag Xw, FAFA and FAFB are calculated individually, and the air-fuel ratios of the banks are independent of each other. Controlled by.

FIG. 6 is a timing chart for supplementarily explaining the operation according to the flow chart of FIG. 4, showing, for example, the A bank. When an air-fuel ratio signal A / F for rich / lean discrimination is obtained from the output V _1A of the upstream side air-fuel ratio sensor 13A as shown in FIG. 6 (A), the delay counter CDLYA changes as shown in FIG. 6 (B). , It counts up in the rich state and counts down in the lean state. As a result, as shown in FIG. 6C, the delayed air-fuel ratio signal A / F '(corresponding to the flag F1A) is formed.

For example, at time t _{1, the} air-fuel ratio signal A / F
Even if 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. Time t ₃
Even if the air-fuel ratio signal A / F changes from rich to lean at time t, the delayed air-fuel ratio signal A / F 'is held rich for a lean delay time (-TDL) and then at time t.
Change to lean at ₄ .

However, the air-fuel ratio signal A / F 'changes from time t ₅ to time t ₅ .
_When inverted in a short period of the rich delay time TDR such as ₆ and t ₇ , it takes time for the delay counter CDLY to reach the maximum value TDR. As a result, at the time t _{8, the} delayed air-fuel ratio signal A / F 'is inverted. That is, the air-fuel ratio signal A / F ′ after the delay processing becomes more stable than the air-fuel ratio signal A / F before the delay processing. In this way, the air-fuel ratio correction coefficient FAFA shown in FIG. 6D is obtained based on the stable air-fuel ratio signal A / F 'after the delay processing.

(2) Second air-fuel ratio feedback control Next, the second air-fuel ratio filter by the downstream side air-fuel ratio sensor 17
The feedback control will be described. Second air-fuel ratio fee
As the feedback control, the first air-fuel ratio feedback system
Skip amount RSR, RSL as a constant, integration constant K
IR, KIL, delay time TDR, TDL, or upstream
Output V of the side air-fuel ratio sensors 13A, 13B _1A,V_1Bcomparison
Voltage V_R1And a second air-fuel ratio compensator
There is a system that introduces several FAF2.

These skip amount, integration constant, delay time,
Each of the advantages of making the comparison voltage variable by the downstream side air-fuel ratio sensor 17 has its advantages. For example, the delay time allows very delicate adjustment of the air-fuel ratio, and the skip amount enables control with good response without lengthening the feedback cycle of the air-fuel ratio like the delay time.
Therefore, these variable amounts can naturally be used in combination of two or more.

Here, a double air-fuel ratio sensor system in which the skip amount as the air-fuel ratio feedback control constant is made variable will be described. Rich skip amount RS
If R is increased, the control air-fuel ratios of both banks A and B can be shifted to the rich side, and even if the lean skip amount RSL is decreased, the control air-fuel ratios of both banks A and B can be shifted to the rich side, while When the lean skip amount RSL is increased,
The control air-fuel ratios of both banks A and B can be shifted to the lean side, and the control air-fuel ratios of both banks A and B can be shifted to the lean side even if the rich skip amount RSR is reduced. Therefore, the air-fuel ratio can be controlled by correcting the rich skip amount RSR or the lean skip amount RSL according to the output V ₂ of the downstream side air-fuel ratio sensor 17.

7 and 8 show a second air-fuel ratio feedback control routine based on the output V ₂ of the downstream side air-fuel ratio sensor 17, which is executed every predetermined time, for example, 512 ms. In steps 701 to 706, it is determined whether or not the feedback control condition of the downstream air-fuel ratio sensor 17 is satisfied. For example, when the feedback control condition by the upstream air-fuel ratio sensor 13 is not satisfied (XMFB ≠ “1” in step 701) and the cooling water temperature THW is a predetermined value (for example, 70 ° C.) or less (step 702), the throttle valve 16 Is fully closed (LL = "1") (step 703), the rotation speed N _e , the vehicle speed, the idle switch 1
When the secondary air is introduced based on the signal LL of 9, the cooling water temperature THW, etc. (step 704) and when the load is light (Q / N _e <X ₁ ) (step 705), the downstream side air-fuel ratio sensor 17 Is not activated (Step 70
6), etc., the feedback control condition is not satisfied, and in other cases, the feedback control condition is satisfied. If the feedback control condition is not satisfied, the routine proceeds to step 719, where the air-fuel ratio feedback flag XSFB is reset (“0”), and if the feedback control condition is satisfied, the routine proceeds to step 708, where the air-fuel ratio feedback flag XS.
Set FB (“1”).

At step 709, the output V ₂ of the downstream side air-fuel ratio sensor 17 is A / D converted and fetched, and step 7
At 10, it is determined whether V ₂ is equal to or higher than the comparison voltage V _R2 , that is, it is determined whether the air-fuel ratio is rich or lean. The comparison voltage V _R2 is the comparison voltage V _R of the output of the upstream side air-fuel ratio sensor 13 in consideration of the difference in output characteristics due to the influence of raw gas and the deterioration rate on the upstream side and the downstream side of the catalyst 16.
_Although it is set lower than _R1 , this setting may be arbitrary.

As a result, if V ₂ ≧ V _R2 (lean), the process proceeds to steps 711, 712 and 713, where V ₂ <V
_{If R2} (rich), steps 714, 715, 716
Proceed to.

That is, in step 711, RSR ←
RSR + ΔRS (constant value), that is, the rich skip amount RSR is increased to shift the air-fuel ratio to the rich side,
In steps 712 and 713, RSR is set to the maximum value MAX.
(= 7.5%), on the other hand, in step 714, RSR ← RSR−ΔRS is set, that is, the rich skip amount RSR is decreased to shift the air-fuel ratio to the lean side,
In steps 715 and 716, RSR is set to the minimum value MIN (=
2.5%).

The minimum value MIN is a value at which transient followability is not impaired, and the maximum value MAX is a value at which drivability does not deteriorate due to air-fuel ratio fluctuations.

At step 717, the lean skip amount R
Let SL be RSL ← 10% −RSR. That is, RSR + RSL = 10%. In step 718, the skip amounts RSR and RSL are stored in the RAM1.
05, and the process proceeds to step 720 (FIG. 7) to end the routine.

FIG. 9 is a routine for calculating the fuel injection amount TAUA, TAUB of each bank using the air-fuel ratio correction coefficients FAFA, FAFB calculated by FIGS. 3, 4, 5, 7, and 8. Every predetermined crank angle, for example 360
It is executed every ° C. In step 901, the RAM 10
The intake air amount data Q and the rotation speed data Ne are read from 5 and the basic injection amount TAUP is set to TAUP ← α · Q / Ne
(Α is a constant). The basic injection amount TAU
P is a fuel injection amount for obtaining the stoichiometric air-fuel ratio, and α is a constant.

In step 902, the final injection amount TAUA for bank A is set to TAUA ← TAUP.FAFA.β + γ.
(Β and γ are correction amounts determined by other operating state parameters).

Next, at step 903, the injection amount TA
The UA is set to the A bank down counter 108A and the flip-flop 109A is set to start fuel injection. Similarly, in step 904, the final injection amount TAUB for B bank is set to TAUB ← TAUP.FAF
Calculate by B · β + γ. Next, at step 905, the injection amount TAUB is set to the B bank down counter 108.
B is set and flip-flop 109B is set to start fuel injection. And step 906
Then, this routine ends.

As described above, when the time corresponding to the injection amount TAUA or TAUB elapses, the flip-flop 109A or 109B is reset by the carry-out signal of the down counter 108A or 108B, and the fuel injection ends.

The above is the description of the operation of the exhaust purification system in the present embodiment. The contents of the above-described diagnostic device for the exhaust gas purification device including the characteristic portion according to the present invention will be described below. First, I will explain the idea. Figure 2
Outputs V of the upstream-side air-fuel ratio sensor 13A on the side of (A) Bank A during steady running and during acceleration / deceleration are respectively 0, 21, and 22.
_1A (B) Output V of the upstream air-fuel ratio sensor 13B on the B bank side
_1B (C) Output V of the upstream air-fuel ratio sensor 13A on the A bank side
Output V _1B of upstream side air-fuel ratio sensor 13B on bank _1A and bank _B
The average value of V _M = (V _1A + V _1B ) / 2 is shown.

FIG. 20 shows a case where both sensors are normal, FIG. 21 shows a case where the upstream side air-fuel ratio sensor 13B on the B bank side is deteriorated but its degree is not large, and FIG. 22 is shown. Upstream air-fuel ratio sensor 13 on the B bank side
The case where B is deteriorated and its degree is large is shown.

In FIG. 21, the output V _1B of the upstream side air-fuel ratio sensor 13B on the B bank side has no phase shift with respect to the output V _1A of the upstream side air-fuel ratio sensor 13A on the A bank side, and the average value is obtained. V _M does not occur the shift of the phase with respect to also V _1A. Therefore, in the present embodiment, in the case of FIG. 21, the trajectory length of the output of the deteriorated air-fuel ratio sensor is corrected, and the corrected value is calculated from the value and the trajectory length of the undegraded one. An average value is obtained as a representative value of the locus lengths of the two sensors, and the deterioration of the catalyst is determined from that value and the locus length of the output of the downstream side air-fuel ratio sensor.

On the other hand, in FIG. 22, the output V _1B of the upstream air-fuel ratio sensor 13B on the B bank side is out of phase with the output V _1A of the upstream air-fuel ratio sensor 13A on the A bank side. The average value V _M also has a phase shift with respect to V _1A . In such a case, it is inappropriate to correct the path length of the output of the air-fuel ratio sensor that is deteriorated as described above and use it to determine the deterioration of the catalyst.

Therefore, in this embodiment, as shown in FIG.
In the case of 2, the deterioration of the catalyst is not judged. Then, the feedback control F of the deteriorated sensor is performed.
Correct the AF to bring it closer to the output of the sensor that has not deteriorated, or correct the amplitude of the output of the sensor that has deteriorated (displacement from the stoichio value) to bring it closer to the output of the sensor that has not deteriorated. Prevents deterioration of exhaust emission. The corrected output is shown by the dotted line in FIG.

Based on the above idea, the embodiment of the present invention operates as follows. (1) The locus length of each upstream air-fuel ratio sensor in bank A and bank B and the locus length of each downstream air-fuel ratio sensor are calculated. (2) The ratio of the locus lengths of the upstream air-fuel ratio sensor (hereinafter referred to as the upstream air-fuel ratio sensor locus length ratio) is calculated.

(3) It is determined from the upstream side air-fuel ratio sensor locus length ratio whether or not it is within the detectable range. (4) When the upstream side air-fuel ratio sensor locus length ratio is within the detectable range, the locus length of the smaller locus length is corrected so that the ratio of 4a−the locus length becomes 1. 4b-The representative trajectory length of the upstream side air-fuel ratio sensor is obtained from the corrected trajectory length and the other uncorrected trajectory length.

4c-Deterioration of the catalyst is judged from the ratio of the representative locus length of the upstream side air-fuel ratio sensor and the locus length of the downstream side air-fuel ratio sensor. (5) If the upstream air-fuel ratio sensor trajectory length ratio is not within the detectable range, 5a-correct the feedback gain of the feedback control. In another embodiment, the output of the 5a′-sensor is corrected.

The details of the operation will be described below with reference to the flow charts shown in FIGS. In step 1001, it is judged whether or not the execution condition is satisfied. The catalyst deterioration detection condition is, for example, that the air-fuel ratio feedback control based on the output of the upstream side air-fuel ratio sensor is being executed (XMFB = "1") and that the air-fuel ratio feedback control based on the output of the downstream side air-fuel ratio sensor is being executed. (Flag XSFB = "1") and the like. If any of these conditions is not satisfied, the steps following step 1002 are not executed and step 1023 of FIG.
To end the routine.

When the catalyst deterioration detection condition is satisfied in step 1001, in step 1002, the locus length L of the upstream side air-fuel ratio sensor 13A on the bank A side is calculated by the following equation.
VMA and the trajectory length LVMB of the upstream air-fuel ratio sensor 13B on the B bank side are calculated. _{LVMA ← LVMA + | V 1A -V} 1A (n-1) | LVMB ← LVMB + | V 1B -V 1B (n-1) | Further, in step 1003, by the following equation, the locus length LVS of the downstream air-fuel ratio sensor Calculate FIG. 14 is a diagram for explaining the above calculation.

[0070] _{LVST ← LVST + | V 2 -V} 2 (n-1) | where the subscript, n-1 indicates a value calculated at the previous execution of the routine.

Next, at step 1004, the upstream side air-fuel ratio sensor locus length ratio R _AB is calculated by the following equation. R _AB ← LVMB / LVMA Next, in step 1005, it is determined whether the upstream side air-fuel ratio sensor locus length ratio R _AB is within the detectable range.

Here, the determination in step 1005 will be described with reference to FIG. In FIG. 15, the horizontal axis represents the locus length LV of the upstream air-fuel ratio sensor 13A on the bank A side.
MA, and the vertical axis represents the upstream side air-fuel ratio sensor 13 on the B bank side.
It is the graph which made the locus length LVMB of B.

R _AB = LVMB / LVMA on this graph
Plotting, if both are equal, then R _AB is 45
It is on the RNORM line of degrees of inclination. However, when the upstream air-fuel ratio sensor 13B on the B bank side is normal, but when the upstream air-fuel ratio sensor 13A on the A bank side deteriorates and its locus length LVMA becomes small, R _AB is the RNORM line. Come to the upper left side of. On the contrary, when the upstream air-fuel ratio sensor 13A on the bank A side is normal, but the upstream air-fuel ratio sensor 13B on the bank B side is deteriorated and the locus length LVMB becomes small, R _AB is equal to RNORM. Come to the lower right side of the line.

The greater the degree of deterioration and the shorter the trajectory length, the greater the deviation from the RNORM line. Conversely, if R _AB differs greatly from R NORM, then one of the air-fuel ratio sensors has deteriorated considerably. More specifically, R _AB
If it is considerably smaller than RNORM, the upstream side air-fuel ratio sensor 13B on the B bank side has deteriorated, and R _AB is RNOR.
If it is much larger than M, it means that the upstream side air-fuel ratio sensor 13A on the bank A side is considerably deteriorated.

In the present invention, as described above, the deterioration of the catalyst is judged by correcting the path length of the deteriorated sensor.
There is a possibility that an unacceptable error will occur if the one with a large degree of deterioration is corrected, so in such a case, the deterioration judgment of the catalyst is not performed. Therefore, a threshold value RDTRA smaller than RNORM and a threshold value RDTRB larger than RNORM are set in advance, and if R _AB is smaller than RDTRA or larger than RDTRB, catalyst deterioration determination is not performed. To
This is the operation performed in step 1005.

If a positive determination is made in step 1005 and catalyst deterioration determination may be performed, that is, in FIG.
In the case where R _AB is between RDTRA and RDTRB, the routine proceeds to step 1006, where the size of R _AB and RNORM is compared and calculated, and whether the upstream side air-fuel ratio sensor 13A on the A bank side is deteriorated, It is determined whether the upstream air-fuel ratio sensor 13B on the B bank side is deteriorated. When a negative determination is made in step 1005, the process returns without performing the subsequent steps.

At step 1006, R _AB ≧ RNORM
Since it is determined whether or not, if a positive determination is made, A
Since the upstream air-fuel ratio sensor 13A on the bank side has deteriorated, the routine proceeds to step 1007, and the locus length LVMA of the upstream air-fuel ratio sensor 13A on the bank A becomes large,
Multiply the correction value K _A. On the contrary, if a negative determination is made in step 1006, the upstream side air-fuel ratio sensor 13 on the B bank side
Since B has deteriorated, the routine proceeds to step 1008, and the correction value K _B is multiplied so that the locus length LVMB of the upstream air-fuel ratio sensor 13B on the B bank side becomes large. The correction values K _A and K _B are stored as values shown in FIG.

In step 1009, the locus length LVMA of the upstream air-fuel ratio sensor 13A on the bank A side and the locus length LVMB of the upstream air-fuel ratio sensor 13B on the bank B side corrected in steps 1007 and 1008 as described above. The representative air-fuel ratio sensor locus length LVM is calculated by addition calculation.

In step 1010, the value of the counter CT is incremented by +1 and step 1011 is executed.
Then, it is determined whether CT has exceeded a predetermined value C ₀ .
Note that, here, C ₀ is 2 in this embodiment.
This is the number of executions of the routine corresponding to 0 seconds. Step 1
If the affirmative judgment is made in 011, C is carried out in step 1012.
When T is cleared, step 1013 and the following steps are executed to determine the catalyst deterioration. That is, in the present embodiment, the catalyst deterioration determination is performed every 20 seconds.

In step 1013, determination of catalyst deterioration is executed based on the map shown in FIG. If it is determined in step 1013 that the catalyst has deteriorated, the alarm flag ALM is set (= “1”) in step 1014, and the catalyst deterioration alarm is activated in step 1015 to indicate that the catalyst has deteriorated. To inform.
If it is determined that the catalyst has not deteriorated, in step 1016 the alarm flag ALM is reset (=
"0") is performed, and the catalyst deterioration alarm is deactivated in step 1017. Further, in step 1018 after completion of these operations, the alarm flag ALM is stored in the backup RAM RAM 106 in preparation for the next repair or inspection.

In step 1019, the parameters LVMA and LVM are prepared for the next catalyst deterioration detection operation.
B, LVM, LVS, AVS, R _AB, etc. are cleared.

On the other hand, if a negative decision is made in step 1005, the process jumps to step 1020. Step 1020
Then, it is determined whether or not R _AB is larger than RDTRA. If the determination is affirmative, the upstream side air-fuel ratio sensor 13A on the A bank side has deteriorated in step 1021, so the control coefficient FAFA of the feedback control of the upstream side air-fuel ratio sensor 13A on the A bank side is multiplied by the correction value M _A. If the determination is negative, the upstream side air-fuel ratio sensor 13B on the B bank side has deteriorated in step 1022, so the control value FAFB of the feedback control of the upstream side air-fuel ratio sensor 13B on the B bank side is corrected to M _B. The correction values are calculated by multiplying by, and these correction values M _A and M _B can be obtained from the map shown in FIG.

In this way, in the present embodiment,
Upstream air-fuel ratio sensor 13A on the bank A side, or B
When one of the upstream air-fuel ratio sensors 13B on the bank side is deteriorated with respect to the other, and the degree of deterioration is small, that is, in FIG. 15, R _AB is equal to RDTRA and R
When it is between DTRB, the path length of the deteriorated air-fuel ratio sensor is corrected by the correction value K _A or K _B shown in FIG. 16, and the corrected path length is also used to make the upstream. Obtain the representative value LVM of the trajectory length of the side air-fuel ratio sensor
From M and the locus length LVS of the downstream side air-fuel ratio sensor, FIG.
The deterioration of the catalyst is judged based on the above.

Further, when one is deteriorated with respect to the other and the degree of deterioration is large, that is, when R _AB is not between RDTRA and RDTRB in FIG. 15, feedback control control is performed. The coefficient FAFA or FAFB is corrected by the correction value M _A or M _B to ensure controllability and prevent deterioration of exhaust emission.

If one is deteriorated with respect to the other,
And the degree of deterioration is large, the feed bar
Instead of correcting the control coefficient of the
It is also possible to correct the sensor output itself.
13 is a flowchart for that case. A
When the upstream air-fuel ratio sensor 13A on the bank side is deteriorated
In this case, the step corresponding to step 1021 in FIG.
In 1021a, the output V is calculated by the following equation. ₁Correct A
To do.

[0086] When the _{V 1A ← (V 1A -V S} ) × N A + V S B bank side of the upstream-side air-fuel ratio sensor 13B has deteriorated, at step 1022a corresponding to step 1022 of FIG. 12, the following The output V _1B is corrected by the following equation. Here _{V 1B ← (V 1B -V S} ) × N B + V S, V S is the output when the stoichiometric. Correction value N
_A, N _B is determined from the map shown in FIG. 19.

In the above-described embodiment, the case where the present invention is applied only to the internal combustion engine having two cylinder groups has been described. However, the present invention also applies to an internal combustion engine having three or more cylinder groups. Applicable. Further, in the present embodiment, the downstream side air-fuel ratio sensor 17 is also an air-fuel ratio sensor that produces a linear output with the exhaust air-fuel ratio, but the output of this downstream side air-fuel ratio sensor is reversed at the theoretical air-fuel ratio. Alternatively, an O ₂ sensor having a so-called Z characteristic may be used.

[0088]

According to the first and second aspects of the present invention, the exhaust gas emitted from the exhaust port of each cylinder is collected by the primary collecting exhaust pipe for each cylinder group and discharged from the combined outlet of each primary collecting exhaust pipe. The exhaust gas is reassembled by the secondary collecting exhaust pipe and guided to the catalyst, and the output of the upstream side air-fuel ratio sensor arranged at each outlet of the primary collecting exhaust pipe and the downstream side of the catalyst are arranged. The feedback control is performed for each cylinder group by the downstream side air-fuel ratio sensor and the output, and the deterioration of the catalyst is determined from the trajectory length of the output of the upstream air-fuel ratio sensor and the trajectory length of the output of the downstream air-fuel ratio sensor. In an exhaust gas purifying device for an internal combustion engine, if the outputs of the air-fuel ratio sensors on the upstream sides are not equal and there is a locus length shorter than the others, the ratio to the other is corrected within a predetermined range. If it is determined that you can Performs a correction, the representative value of the trajectory length of the output of the air-fuel ratio sensor including corrected those upstream side is determined, the deterioration determination of the catalyst is performed by using it. Therefore, it is possible to prevent the upstream air-fuel ratio of the catalyst from deviating from the actual air-fuel ratio, improve the accuracy of the catalyst deterioration determination, and prevent the chance of deterioration determination from decreasing.

Further, according to the invention of claim 3, it is possible to specify the air-fuel ratio sensor whose output is deteriorated by comparing the locus lengths of the upstream side air-fuel ratio sensors, and the deteriorated air-fuel ratio sensor is provided. Since the gain of the feedback control for the cylinder group on the operating side is increased, the deterioration of the controllability of the feedback control of the engine is recovered and the deterioration of the exhaust emission is prevented.

[Brief description of drawings]

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

FIG. 2 is a diagram schematically showing the structure of a general air-fuel ratio sensor.

FIG. 3 is a flowchart illustrating an air-fuel ratio feedback control operation of the control circuit of FIG.

4 is a part of a flowchart illustrating an air-fuel ratio feedback control operation of the control circuit of FIG.

5 is a part of a flowchart illustrating an air-fuel ratio feedback control operation of the control circuit of FIG.

FIG. 6 is a timing diagram for supplementarily explaining the operation according to the flowcharts of FIGS. 4 to 6.

7 is a part of a flowchart illustrating an air-fuel ratio feedback control operation of the control circuit of FIG.

8 is a part of a flowchart illustrating an air-fuel ratio feedback control operation of the control circuit of FIG.

9 is a flowchart showing a fuel injection amount control operation of the control circuit of FIG.

10 is a part of a flowchart showing a catalyst deterioration detection operation of the control circuit of FIG.

11 is a part of a flowchart showing a catalyst deterioration detection operation of the control circuit of FIG.

12 is a part of a flowchart showing a catalyst deterioration detection operation of the control circuit of FIG.

13 is a part of a flowchart showing a catalyst deterioration detection operation of the control circuit of FIG. 2 in a modified example.

FIG. 14 is a diagram showing definitions of a trajectory length and an area of an air-fuel ratio sensor output.

FIG. 15 is a diagram for explaining sensor deterioration based on the relationship between the locus length of the output of the upstream air-fuel ratio sensor on the A bank side and the locus length of the output of the upstream air-fuel ratio sensor on the B bank side.

FIG. 16 is a diagram showing a correction coefficient for correcting the path length of the deteriorated upstream side air-fuel ratio sensor.

FIG. 17 is a map for determining catalyst deterioration from the locus length of the output of the upstream air-fuel ratio sensor and the locus length of the output of the downstream air-fuel ratio sensor.

FIG. 18 is a diagram showing a correction coefficient for correcting the air-fuel ratio feedback control coefficient.

FIG. 19 is a diagram showing a correction coefficient for correcting the output voltage of the air-fuel ratio sensor.

FIG. 20 is a diagram showing a relationship between an upstream side air-fuel ratio sensor output of each bank and a combined output thereof (when neither bank is deteriorated).

FIG. 21 is a diagram showing a relationship between an upstream air-fuel ratio sensor output of each bank and a combined output thereof (when the air-fuel ratio sensor of bank B is deteriorated but the deterioration degree is not large).

FIG. 22 is a diagram showing a relationship between an upstream side air-fuel ratio sensor output of each bank and a combined output thereof (when the air-fuel ratio sensor of bank B is deteriorated and the deterioration degree is large).

[Explanation of symbols]

5, 6 ... Crank angle sensor 7A, 7B ... Fuel injection valve 8A, 8B ... Spark plug 10 ... Control circuit 13A, 13B ... Upstream air-fuel ratio sensor 16 ... Catalyst 17 ... Downstream air-fuel ratio sensor

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F01N 3/08-3/38 F01N 9 / 00,11 / 00 F02D 41/00-45/00

Claims (3)

(57) [Claims] 1. A primary collecting exhaust pipe that collects exhaust gas emitted from an exhaust port of each cylinder for each cylinder group, and an exhaust gas that exits from the combined outlet of each primary collecting exhaust pipe is guided to a catalyst. A secondary collecting exhaust pipe, an upstream air-fuel ratio sensor that is installed at the collecting part of each primary collecting exhaust pipe, and outputs a signal that linearly corresponds to the exhaust air-fuel ratio on the upstream side of the catalyst, and the exhaust gas on the downstream side of the catalyst. Feedback control is performed so that the air-fuel ratio of each cylinder group becomes the stoichiometric air-fuel ratio, based on the downstream side air-fuel ratio sensor arranged in the pipe and at least the deviation between the output of each upstream side air-fuel ratio sensor and the theoretical air-fuel ratio. Control means, upstream air-fuel ratio sensor output locus length calculation means for calculating the locus length of the output of each upstream air-fuel ratio sensor within a predetermined period during feedback control, and locus length of the output of each upstream air-fuel ratio sensor From the upstream air-fuel ratio Representative upstream air-fuel ratio sensor output locus length representative of the sensor output locus length, representative upstream air-fuel ratio sensor output locus length calculation means, and downstream air-fuel ratio sensor output within a predetermined period during feedback control Downstream air-fuel ratio sensor output trajectory length calculation means for calculating the trajectory length of the catalyst, catalyst deterioration detection means for detecting catalyst deterioration based on the representative upstream air-fuel ratio sensor output trajectory length, and downstream air-fuel ratio sensor output trajectory length Is a diagnostic device for an exhaust gas purification device of a multi-cylinder internal combustion engine, characterized in that the representative upstream air-fuel ratio sensor output trajectory length calculation means compares and calculates the trajectory length of the output of the upstream air-fuel ratio sensor. A path length correction means for correcting the short path length to be the same as the long path length when it is confirmed by the path length comparison operation that the short path length is included. Diagnosis of an exhaust gas purification device characterized by calculating a representative upstream air-fuel ratio sensor output trajectory length from the upstream trajectory of the output of the upstream air-fuel ratio sensor including the trajectory length of the output of the upstream air-fuel ratio sensor corrected by the stage apparatus. 2. The locus length comparison calculation means is a locus length ratio calculation means for calculating the ratio of the locus lengths of the outputs of the upstream side air-fuel ratio sensors, and the locus length correction means includes locus length correction feasibility determining means, The long-correction determination means determines whether or not the trajectory length can be corrected for use from the ratio of the trajectory lengths. If it is determined that the trajectory length cannot be corrected for use, catalyst deterioration is determined. The exhaust gas purification device diagnostic device according to claim 1, wherein the detection means does not detect deterioration of the catalyst. 3. A primary collecting exhaust pipe that collects exhaust gas emitted from an exhaust port of each cylinder for each cylinder group, and a primary collecting exhaust pipe is provided at a collecting portion of each primary collecting exhaust pipe. Feedback control is performed so that the air-fuel ratio of each cylinder group becomes the stoichiometric air-fuel ratio based on the deviation between the output of each upstream air-fuel ratio sensor and the theoretical air-fuel ratio Control means, an upstream air-fuel ratio sensor output trajectory length calculation means for calculating the trajectory length of the output of each upstream air-fuel ratio sensor within a predetermined period during feedback control, and the trajectory length of the output of the upstream air-fuel ratio sensor. A locus length comparison calculation means for comparing and calculating, a sensor deterioration detection means for detecting deterioration of one upstream air-fuel ratio sensor from the locus length comparison calculation result, and an deteriorated air-fuel ratio sensor are arranged. ~ side And a gain correction unit that corrects the feedback control gain for the cylinder group so that the gain becomes larger.