JPH04109051A - Oxygen sensor deterioration detecting device - Google Patents

Abstract

PURPOSE:To carry out positive discrimination by discriminating the deterioration of an upstream oxygen sensor when an air-fuel ratio feedback constant corresponding to the output signal of a downstream oxygen sensor is larger than the second specified value or when the reversal cycle of the output signal of the upstream oxygen sensor is larger than the specified value. CONSTITUTION:Oxygen sensors A, B are provided respectively on the upstream and downstream sides of a catalyst provided in an exhaust system, and an air-fuel ratio feedback control constant is computed by a control constant computing means C according to the output signal of the downstream oxygen sensor B. The air-fuel ratio of mixture is also controlled (D) to be in the vicinity of a theoretical air-fuel ratio according to the output signal of the upstream oxygen sensor A and the above-mentioned control constant. In this case, the reversal cycle of the output signal of the upstream oxygen sensor A is detected by a reversal cycle detecting means E. When this reversal cycle is larger than the first specified value determined by the operating state, a specified signal is outputted from a first comparing means F, and when the air-fuel ratio feedback control constant is larger than the second specified value, a specified signal is outputted from a second comparing means G. When the specified signal is outputted from either one of the comparing means F, G, the deterioration of the upstream oxygen sensor A is discriminated by a deterioration discriminating means H.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an oxygen sensor deterioration detection device that is installed in an engine exhaust system and detects deterioration of an oxygen sensor that detects oxygen concentration. .

[Conventional technology]

Conventionally, one oxygen sensor has been installed before and after a catalyst for purifying exhaust gas. Some devices determine that an upstream oxygen sensor has deteriorated when an air-fuel ratio feedback constant calculated according to the output of an oxygen sensor (hereinafter referred to as a downstream oxygen sensor) exceeds a predetermined value (for example, Japanese Patent Laid-Open No. 62 -1470
Publication No. 34). Furthermore, there is a method that determines whether the upstream oxygen sensor has deteriorated when the period of the signal from the upstream oxygen sensor exceeds a predetermined value (for example, Japanese Patent Laid-Open No. 64-3550).

[Problem to be solved by the invention]

However, in the case where the upstream oxygen sensor is determined to have deteriorated when the cycle of the signal from the upstream oxygen sensor is greater than a predetermined value, when the engine is operating at low load (engine speed is low), the upstream oxygen sensor inevitably Since the signal period becomes long, it may be erroneously determined that the upstream oxygen sensor has deteriorated.

In addition, in the case where the deterioration of the upstream oxygen sensor is determined only by the feedback constant of the downstream oxygen sensor, the feedback constant is less than a predetermined value, but the upstream oxygen sensor exhibits a symptom in which the output signal period of the upstream oxygen sensor becomes longer. There is a problem in that deterioration cannot be detected and emissions worsen.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide an 02 sensor deterioration detection device that can reliably detect deterioration of an oxygen sensor.

[Means to solve the problem]

As a means for solving the above problems, the present invention is shown in FIG.
Upstream and downstream oxygen sensors are provided on the upstream and downstream sides of the catalyst provided in the exhaust system of the engine to detect the oxygen concentration in the exhaust gas, and the air-fuel ratio is determined according to the output signal of the downstream oxygen sensor. control constant calculation means for calculating a feedback control constant; engine control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to be near the stoichiometric air-fuel ratio according to the output signal of the upstream oxygen sensor and the control constant; , an inversion period detection means for detecting an inversion period of an output signal of the upstream oxygen sensor; an operating state detection means for detecting an operating state of the engine; and the inversion period is greater than a first predetermined value determined by the operating state. a first comparing means that outputs a predetermined signal when the air-fuel ratio feedback control constant is larger than a second predetermined value; a second comparing means that outputs a predetermined signal when the air-fuel ratio feedback control constant is larger than a second predetermined value; The present invention provides an oxygen sensor deterioration detecting device comprising: deterioration determining means that determines that the upstream oxygen sensor has deteriorated when either one of the second comparing means outputs the predetermined signal.

[Effect]

As a result, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to be close to the stoichiometric air-fuel ratio according to the output signal of the upstream oxygen sensor and the air-fuel ratio phytback constant corresponding to the output signal of the downstream oxygen sensor.

Further, when the inversion period of the output signal from the upstream oxygen sensor is larger than a first predetermined value determined by the operating state of the engine, it is determined that the upstream oxygen sensor has deteriorated. Furthermore, it is also determined that the upstream oxygen sensor has deteriorated when the air-fuel ratio feedback constant corresponding to the output signal from the downstream oxygen sensor is larger than the second predetermined value.

(Effects of the Invention) According to the present invention, it is determined that the upstream oxygen sensor has deteriorated when the air-fuel ratio feedback constant corresponding to the output signal of the downstream oxygen sensor is larger than a second predetermined value, and furthermore, the inversion period of the output signal of the upstream oxygen sensor Since the deterioration is also determined according to the operating condition, there is an excellent effect that it is possible to reliably determine the deterioration of the upstream oxygen sensor.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a schematic configuration diagram of this embodiment. An air flow meter 3 is provided in an intake passage 2 of the engine 1. The air flow meter 3 directly measures the amount of intake air Q guided through the air cleaner 4. Furthermore, in the intake passage 2,
A throttle valve 6 is provided that opens and closes in response to the amount of operation of the accelerator 5 by the driver to adjust the amount of intake air Q supplied to the engine 1. Further, each cylinder of the engine 1 is provided with a fuel injection valve 8 for supplying pressurized fuel from a fuel supply system 7 to an intake port.

The distributor 9 is also provided with a reference position sensor 10 that generates a reference position detection signal every 720 crank angles ('CA) and a crank angle sensor 11 that generates a crank angle detection signal every 30° CA. It is being

Furthermore, the water jacket 12 of the cylinder block of the engine 1 is provided with a water temperature sensor 13 for detecting the cooling water temperature Thw.

On the other hand, the exhaust system is provided downstream of the exhaust manifold 14 with a three-way catalyst 15 that simultaneously purifies harmful components (HC, CO, NOx) in the exhaust gas.

An upstream oxygen sensor (02 sensor) 16 is provided on the upstream side of the three-way catalyst 15, that is, on the exhaust manifold 14, and a downstream 0□ sensor 18 is provided on the fJl trachea 17 on the downstream side of the three-way catalyst 15. It is being As is well known, these upstream and downstream 0□ sensors 16 and 18 generate different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.

In addition, 19 is an electronic control device (Ti CtJ) which will be described later.
This is an alarm for issuing a warning to the driver when it is determined that the three-way catalyst 15 has deteriorated at 20.

The ECU 20 is configured, for example, as a microphone D combination eater, and as is well known, the ECU 20 is configured as a microphone D combination eater, and as is well known, the ECU 20 is an A/D converter 11! ! device 101110 port 102. CPU103. ROMIO4, RAMIO3
, Hank Asop RAM 106° Clock generation circuit 107
etc. are provided.

The air-fuel ratio control force method for the engine 1 and the deterioration detection method for the upstream 0□ sensor 16 will be described below using flowcharts shown in FIGS. 3 to 7.

FIG. 3 is a flowchart showing a fuel injection amount calculation routine for calculating the fuel injection amount TAU in accordance with detection signals from the various sensors described above. This routine is activated and executed at predetermined intervals (eg, 360° CA in this embodiment).

In step 101, detection signals such as intake air amount Q and rotational speed NE are read. In step 102, basic fuel injection mTp is calculated using the following equation.

Tp-ni-Q/NE Here, K is a constant.

[Subsequent Step] In step 03, the basic fuel injection amount Tp is subjected to various corrections such as air-fuel ratio feedback control, which will be described later, and the fuel injection amount 'T''AU is calculated.

TAU←Tp-FAF-F Here, FAF is an air-fuel ratio correction coefficient based on air-fuel ratio feedback control, and F is various correction coefficients.

Then, in step 104, a control signal corresponding to the fuel injection amount TAU calculated in step 103 described above is output to the fuel injection valve 8.

Figure 4 shows the detection signal of the upstream 0□ sensor 16 (upstream output value)
Main air-fuel ratio feedback control performed based on Vl,
That is, this is an air-fuel ratio feedback control routine for setting the air-fuel ratio correction coefficient FAF.

This routine lasts for a predetermined period of time (for example, 4m5 in this example).
ec) is started and executed every time.

In step 201, the main air-fuel ratio feedback control conditions (
It is determined whether or not the first execution condition) is satisfied. Here, the first execution condition is, for example, that the upstream 02 sensor 16 is in an active state after the engine is started in this embodiment.

If it is determined in step 201 that the first execution condition is not satisfied, the process proceeds to step 202.

In step 202, the air-fuel ratio correction coefficient FAF is set to 1. Set to O (FAF←1.0) L, and end this routine.

On the other hand, if it is determined in step 201 that the first execution condition is satisfied, the upstream output value from step 203 onward is
1. Execute the feedback process according to 1.

In step 203, the upstream output value Vl is read.

In the following step 204, it is determined whether the upstream output value V1 is less than or equal to the first comparison voltage VRI (for example, 0.45 V in this embodiment), that is, whether the air-fuel ratio is rich or lean. Here, if the upstream output value Vl is less than or equal to the first comparison voltage VRI, that is, if the air-fuel ratio is lean, the process proceeds to step 205.

In step 205, it is determined whether the first delay counter CDLYI has a positive value, that is, whether the upstream output value Vl has reversed from rich to lean at the current control timing. Here, the first delay counter CDLY 1 is the upstream output value ■
1 is a counter for measuring the elapsed time after crossing the first comparison voltage VRI, and the elapsed time in a rich state is defined as a positive value, and the elapsed time in a lean state is defined as a negative value.

If the first delay counter CDLYI is a negative value in step 205, the process advances to step 207. Further, if the first delay counter CDLY_l is a positive value in step 205, the process advances to step 206. Step 20
6 resets the first delay counter CDLYI (C
DLYI←0) and proceeds to step 207. Step 2
At step 07, the value of the first delay counter CDLYI is decremented (CDLYI←CDLYI-1). In the following step 208, the first delay counter CDLYl is set to the first delay counter CDLYl.
It is determined whether or not the lean delay time TDLI is less than the lean delay time TDLI. Here, the first lean delay time TDL1 is upstream 0. This is a count value corresponding to a delay time in a delay process that maintains the judgment that the output signal of the sensor 16 is rich even if it changes from rich to lean, and is defined as a negative value. In step 208, the first delay counter CDLYl
is equal to or greater than the first lean delay time TDL1, the process advances to step 217.

On the other hand, in step 208, the first delay counter CDL
Y1 is less than the first lean delay time TDL1, that is, upstream 0
If the aforementioned delay time or more has elapsed since the output signal of the second sensor 16 changed from rich to lean, step 209
Proceed to. In step 209, the first delay counter CD
Set LYI to the first lean delay time TDLI (CDL
YI←TDLI)L, proceed to step 210. In step 210, the flag F1 indicating the state of the air-fuel ratio after the delay processing is reset (Fl←0), and the process proceeds to step 217. That is, when the flag F1 is in the reset state (Fl-◯), it indicates that the air-fuel ratio after the delay processing is lean.

Further, if the upstream output value ■1 is larger than the first comparison voltage VRI in step 204, that is, if the air-fuel ratio is rich, the process proceeds to step 211. In step 211, it is determined whether the first delay counter CDLYI has a negative value, that is, whether the upstream output value (1) has reversed from lean to rich at the current control timing. Here, the first delay counter CD
If LYI is a positive value, the process advances to step 213.

On the other hand, in step 211, the first delay counter CDL
If Y1 is a negative value, the process advances to step 212. In step 212, the first delay counter CDLYI is reset (CDLY←0), and the process proceeds to step 213.

In step 213, the first delay counter CDLYIO
Increment the value (CDLYI←CDLY1+1
). In the following step 214, the first delay counter CD
It is determined whether LY 1 is less than the first rich delay time TDR1. Here, the first rich delay time TDRI is
This is a count value corresponding to a delay time corresponding to a delay process that maintains the determination that the output signal of the upstream 02 sensor 16 is lean even if it changes from lean to rich, and is defined as a positive value. If the first delay counter CDLYI is equal to or greater than the first rich delay time TDR1 in step 214, the process advances to step 217.

On the other hand, in step 214, the first delay counter CDL
If Y1 is larger than the first rich delay time TDRl,
That is, if a delay time described below has elapsed since the output signal of the upstream O sensor 16 changed from lean to rich, the process proceeds to step 215.

In step 215, the first delay counter CDLY1 is set to the first rich delay time TDRI (CDLYl-T
DR1')L, proceed to step 216.

In step 216, a flag F1 indicating the state of the air-fuel ratio after the delay processing is set (Fl←1), and the process proceeds to step 217. That is, when the flag F1 is set (Fl-1), it indicates that the air-fuel ratio after the delay process is rich.

In step 217, it is determined whether the flag F1 has been inverted, that is, whether the state of the air-fuel ratio after the delay processing has been inverted.

Here, if the state of the air-fuel ratio after the delay processing is reversed,
Skip processing from step 218 to step 220 is performed. First, in step 218, it is determined whether the flag Fl is in a reset state.

Here, if the flag F1 is in a reset state, that is, if it is inverted from rich to lean, the process advances to the steering knob 219. In step 219, the air-fuel ratio correction coefficient FAF is increased by the first rich skip amount R3R1 (FAF-FAF
10R3R1), step.

Proceed to 224. Further, if the flag F1 is set in step 218, that is, if there is a reversal from lean to rich, the process proceeds to step 220. In step 220, the air-fuel ratio correction coefficient FAF is decreased by the first linear skip amount R3L1 (FAF-FAF-R3LI), and in step 2
Proceed to 24.

On the other hand, if the state of the air-fuel ratio after the delay processing has not been reversed in step 217, the integral processing of steps 221 to 223 is performed. First, in step 221, it is determined whether the flag F1 is in a reset state, that is, in a lean state. Here, if it is lean, the process advances to step 222. In step 222, the air-fuel ratio correction coefficient FAF is increased by the first rich integral constant KIRI (FAF 4 - FAF
+KIRI), proceed to step 224. Further, if it is determined in step 221 that the amount is rich, the process proceeds to step 223. In step 223, the air-fuel ratio correction coefficient F A F is decreased by the first lean integral constant KILI (FAF 4 - FAF
- K I L 1 ), step 224 - Proceed.

The air-fuel ratio coefficient FAF set as described above in step 224 is within a predetermined range (for example, 0.8 to 1 in this embodiment).
．． 2), the guard process is performed and this routine ends.

Figure 5 shows the output value (downstream output value) of the downstream 0□ sensor 18
2 in the main air-fuel ratio feedback control based on
rich step amount R3RI, first lean skip 1
2 is a flowchart showing a sub air-fuel ratio feedback control routine for correcting lR3L1. This routine is activated and executed at predetermined time intervals (for example, 1 sec in this embodiment).

First, in step 301, it is determined whether the air-fuel ratio feedback condition (second execution condition) is satisfied, that is, whether or not the auxiliary air-fuel ratio feedback control is to be executed. Here, the second execution condition is, for example, in this embodiment, the first execution condition is satisfied, that is, the main air-fuel ratio feedback control is being performed.

For example, the downstream 0□ sensor 18 is in an active state.

If the second execution condition is not satisfied in step 301, the process advances to step 302. In step 302, the first rich skip 1R3R1 is set to a predetermined rich skip 1iR3.
Set to Ro. In the following step 303, the first lean skip 1R3L1 is adjusted to a predetermined lean skip amount R3LO.
, and end this routine.

Further, if the second execution condition is satisfied in step 301, the sub air-fuel ratio feedback process based on the downstream output value (2) from step 304 onwards is executed. First, in step 304, the downstream output value ■2 is read. In step 305, it is determined whether the downstream output value 2 is less than or equal to the second comparison voltage VR2 (for example, in this embodiment, it is set to 0.45 V, which is the same as the first comparison voltage VRI), that is, whether the air-fuel ratio is rich or not. Determine whether

Here, the downstream output value ■2 is lower than the second comparison voltage VR2,
That is, if the air-fuel ratio is lean, the process advances to step 306. In step 306, the second delay counter CDLY2
is a positive value, that is, the downstream output value ■2 at the current control timing
Determine whether or not it has reversed from rich to lean. Here, the second delay counter CDLY2 is a counter for measuring the elapsed time after the downstream output value 2 crosses the second comparison voltage VR2, similar to the first delay counter CDLYI described above, and is a counter for measuring the elapsed time after the downstream output value 2 crosses the second comparison voltage VR2. The elapsed time in a state is defined as a positive value, and the elapsed time in a lean state is defined as a negative value.

If the second delay counter CDLY2 is a negative value in step 306, the process advances to step 308. Further, if the second delay counter CDLY2 is a positive value in step 306, the process advances to step 307. Step 307
to reset the second delay counter CDLY2 (CD
LY2←0) and proceeds to step 308.

In step 308, the value of the second delay counter CDLY2 is decremented (CDLY2←CDLY2-1)
. In the following step 309, the second delay counter CDL
It is determined whether Y2 is less than the second lean delay time TDL2. Here, the second lean delay time TDL2 is a count value corresponding to a delay time in a delay process that maintains the judgment that the output signal of the downstream 02 sensor 18 is rich even if it changes from rich to lean. Yes, defined as a negative value. If the second delay counter CDLY2 is equal to or greater than the second lean delay time TDL2 in step 309, the process advances to step 318.

On the other hand, in step 309, the second delay counter CDL
Y2 is less than the second lean delay time TDL2, that is, downstream 0
□If the aforementioned delay time or more has elapsed since the output signal of the sensor 18 changed from rich to lean, step 310
Proceed to. In step 310, the second delay counter CD
Set LY2 to the second lean delay time TDL2 (CDL
Y2←TDL2)L, proceed to step 311. In step 311, the flag F2 indicating the state of the air-fuel ratio after the delay processing is reset (F2←0), and the process proceeds to step 318. That is, when the flag F2 is in the reset state (F2=0), it indicates that the air-fuel ratio after the delay process is lean.

Further, in step 305, if the downstream output value ■2 is larger than the second comparison voltage VR2, that is, if the air-fuel ratio is rich, the process proceeds to step 312. In step 312, it is determined whether the second delay counter CDLY2 has a negative value, that is, whether the downstream output value (2) has reversed from lean to rich at the current control timing. Here, the second delay counter CD
If LY2 is a positive value, the process advances to step 314.

Meanwhile, in step 312, the second delay counter CDL
If Y2 is a negative value, the process advances to step 313. In step 313, the second delay counter CDLY2 is reset (CDLY2←0), and the process proceeds to step 314.

In step 314, the value of the second delay counter CDLY2 is incremented (CDLY2←CDLY2+1
). In the following step 315, the second delay counter CD
It is determined whether LY2 is less than the second rich delay time TDR2. Here, the second rich delay time TDR2 is a count corresponding to a delay time corresponding to a delay process that maintains the determination that the output signal of the downstream 02 sensor 18 is lean even if it changes from lean to rich. value and is defined as a positive value. If the second delay counter CDLY2 is equal to or greater than the second rich delay time TDR2 in step 315, the process advances to step 318.

On the other hand, in step 315, the second delay counter CDL
If Y2 is greater than the second rich delay time TDR2, that is, if the aforementioned delay time or more has elapsed since the output signal of the downstream 02 sensor 18 changed from lean to rich, the process proceeds to step 316. In step 316, the second delay counter CDLY2 is set to the second rich delay time TDR2 (
CDLY2←TDR2)L, proceed to step 317. In step 317, a flag F2 indicating the state of the air-fuel ratio after the delay processing is set (F2←1), and the process proceeds to step 318.

That is, when the flag F2 is set (F2=1), it indicates that the air-fuel ratio after the delay process is rich.

In step 318, it is detected whether the flag F2 is in a reset state, that is, whether the air-fuel ratio after the delay processing is lean or rich. Here, if the flag F2 is in the reset state, that is, the air-fuel ratio has returned after the delay processing, step 31
Proceed to 9. In step 319, the first rich skip amount R
8R1 is increased by a predetermined value R3 (R3RI←R3R1
+R3), proceed to step 320. At step 320, the first lean skip amount R3L1 is decreased by a predetermined value R3 (R3LI←R3L1-R3), and at step 323
Proceed to.

On the other hand, if the flag F2 is set in step 318, that is, the air-fuel ratio after the delay process is rich, step 32
Go to 1. In step 321, the first rich skip lid R is
3R1 is decreased by a predetermined value R3 (R3RI←R3RI
-R3), proceed to step 322. In step 322, the first lean skip amount R3Ll is increased by a predetermined value R3 (R3L14-R3L1+R3), and the process proceeds to step 323.

The first rich skip amount R3R1 and the first lean skip 1R3 set as described above in step 323.
Skip 1t to ensure that L1 is within a predetermined range.
It is determined whether R3R1 and R3LI exceed a predetermined range, and if they do, guard processing is performed.

Next, the process proceeds to step 324, and in step 323, it is determined whether or not the skip amount R3R1 or R3LI exceeds a predetermined range and guard processing is performed.

When guard processing is performed, guard processing determination flag X5
FBG is set (XSFBG←1), and if guard processing is not performed, the guard processing determination flag X5FBG is reset in step 326 (XSFBG←0), and this routine ends.

FIG. 6 is a flowchart showing the process of determining the reversal period of the upstream output value 1, which is the detection signal of the upstream 02 sensor 16, and comparing it with the deterioration judgment period according to the operating state C. For example, start every 8 m5ec: ),
executed.

At step 401, it is determined whether the engine 1 is in a steady state based on, for example, the throttle opening, the throttle opening change rate, etc. If it is not in a steady state, step 402
Proceed to and reset the counter CT. This counter C
T is a counter for measuring the reversal cycle detection time of the upstream output value ■. Next, in step 403, the counter COx
will also be reset. This counter COX is for measuring the number of times the detection signal V is inverted. Thereafter, in an unsteady state, the counters CT and COX are reset and this routine is ended.

If the steady state is determined in step 401, step 4
Increment the counter CT at 04 (CT=CT+1
)do. Next, in step 405, it is detected whether the upstream output value {circle around (2)} is higher than the comparison voltage VRI, that is, whether the air-fuel ratio is lean or rich. Here, if the upstream output value ■1 is less than the comparison voltage ■R1, that is, if the air-fuel ratio is lean, the process advances to step 406. In step 406, the flag F3 indicating the state of the air-fuel ratio is reset (F3←0), and the process proceeds to step 408. If the upstream output value ■1 is larger than the comparison voltage ■R1, that is, the air-fuel ratio is rich, the flag F3 is set (F3←1) in step 407, and the process proceeds to step 408.

In step 408, it is detected whether the flag F3 has been inverted, that is, whether the air-fuel ratio has changed. Here, flag F3
If is not reversed, skip step 409 and
Proceed to step 110. If the flag F3 is inverted, the flag COx for counting the number of inversions is incremented (COX-COX+1) in step 409. In the next step 111, it is determined whether the counter CT for measuring the reversal period detection time has reached α. If α has not been reached, this routine ends. When α has been reached, proceed to step 111 and reset the counter CT (
CT←0), and in step 112, the deterioration judgment frequency fmn corresponding to the operating state (engine speed, intake M) is set to the eighth
Calculated from the map shown in the figure.

The map shown in FIG. 8 is stored in the ROM 104,
The deterioration determination frequency fmn is determined by the engine rotational speed NE and the intake air amount Q.

Moreover, this deterioration judgment frequency fmn is the engine rotation speed NE
It is set so that the larger the value is, and the larger the intake air amount QN is, the larger the value becomes.

In step 112, the deterioration judgment period fmn according to the operating state
After calculating COX, the process proceeds to step 113, where the counter COX
and the deterioration determination frequency fmn. Here, the value of the counter COX is the number of times the upstream output (1) is reversed during the α time, and this corresponds to the frequency.

When the counter COX is larger than the deterioration determination frequency fmn, it means that the upstream 02 sensor 16 has deteriorated, and in step 114, the deterioration determination flag XMFBG is set (XMFBG
G←1), and when the counter COS is smaller than the deterioration determination frequency fmn, the deterioration determination flag XMF is set in step 114.
Reset BG (XMFBG←0). Then, in step 116, reset the counter COS (COX←0)
to end this routine.

FIG. 7 shows a routine for determining deterioration of the upstream 02 sensor 16.

First, in step 501, it is determined whether a deterioration detection condition is satisfied. Here, the deterioration detection conditions include, for example, in this embodiment, the aforementioned main/auxiliary chamber fuel ratio feedback control is being performed, the engine 1 is in a steady state, etc. If the deterioration detection condition is not satisfied in step 501, this routine ends.

On the other hand, if the deterioration condition is satisfied in step 501, deterioration detection processing from step 502 onwards is executed. First, in step 502, guard processing determination flag X5FBC;
Determine whether or not is set. Above flag X5FB
When G is set (XSFBG=1), that is, the fifth
In the sub-feedback control shown in the figure, the skip amount R
When 3R1 or R3L1 exceeds a predetermined range and guard processing is performed, it is determined in step 506 that the upstream 02 sensor is abnormal, and a warning light is turned on in step 507.

Further, if it is determined in step 502 that the guard processing discrimination flag is not set, the process advances to step 503, and
It is determined whether the deterioration determination flag XMFBG is set. When it is set (XMFBG=1), that is, in the flow shown in FIG. 6, when it is determined that the frequency of upstream output 0
The sensor 16 is determined to be abnormal and a warning light is turned on.

When the deterioration determination flag XMFBG is not set in step 503, that is, the guard processing determination flag X5FB
If both G and the deterioration determination flag XMFBG are not set, the process advances to step 504, where it is determined that the upstream 0□ sensor is normal, and the warning light is turned off at step 505.

[Brief Description of the Drawings] Fig. 1 is a diagram corresponding to claims, Fig. 2 is a schematic configuration diagram of an embodiment to which the present invention is applied, Figs. 3 to 7 are flowcharts for explaining the operation of the embodiment; FIG. 8 is a map of predetermined values determined depending on the operating conditions in the embodiment. 1...Engine, 8...Injector, ]5...
Three-way catalyst, 16...Upstream oxygen sensor, 18...Downstream oxygen sensor, 20...ECU. Figure 1: Patent attorney Takashi Okabe (one idiot) Figure 1: Patent attorney (rpm)

Claims (1)

[Scope of Claims] Upstream and downstream oxygen sensors that are respectively provided on the upstream and downstream sides of a catalyst provided in the exhaust system of an engine and detect oxygen concentration in exhaust gas; and an output signal of the downstream oxygen sensor. control constant calculation means for calculating an air-fuel ratio feedback control constant according to the output signal of the upstream oxygen sensor and the control constant; controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to be near the stoichiometric air-fuel ratio; an engine control means for detecting the reversal period of the output signal of the upstream oxygen sensor; an operating state detecting means for detecting the operating state of the engine; a first comparing means that outputs a predetermined signal when the air-fuel ratio feedback control constant is larger than a second predetermined value; a second comparing means that outputs a predetermined signal when the air-fuel ratio feedback control constant is larger than a second predetermined value; An oxygen sensor deterioration detection device comprising: deterioration determining means for determining that the upstream oxygen sensor has deteriorated when either the comparing means or the second comparing means outputs the predetermined signal.