JP2814718B2 - Oxygen sensor deterioration detection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor deterioration detection device that is disposed in an exhaust system of an engine and detects deterioration of an oxygen sensor that detects oxygen concentration. .

[Conventional technology]

2. Description of the Related Art Conventionally, in a case where one oxygen sensor is disposed before and after a catalyst for purifying exhaust gas, in order to detect deterioration of an oxygen sensor before the catalyst (hereinafter, referred to as an upstream oxygen sensor), it is necessary to detect a deterioration after the catalyst. When the air-fuel ratio feedback constant calculated according to the output of the oxygen sensor (hereinafter referred to as the downstream oxygen sensor) becomes equal to or more than a predetermined value, the upstream oxygen sensor is determined to be deteriorated. (For example, see JP-A-62-147034.
No.). Further, there is a method in which when the period of a signal from the upstream oxygen sensor becomes equal to or longer than a predetermined value, deterioration of the upstream oxygen sensor is determined (for example, JP-A-64-3550).

[Problems to be solved by the invention]

However, when the upstream oxygen sensor determines that the deterioration has occurred when the period of the signal from the upstream oxygen sensor is equal to or longer than a predetermined value, the engine operates at a low load (the engine speed is small).
At times, the signal cycle from the upstream oxygen sensor is inevitably long, so that it may be erroneously determined that the upstream oxygen sensor is deteriorated.

Further, 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 equal to or less than a predetermined value, but the output signal period of the upstream oxygen sensor is increased. There is a problem that deterioration cannot be detected and emission deteriorates.

An object of the present invention is to provide an O ₂ sensor deterioration detection device that can reliably detect deterioration of an oxygen sensor in view of the above problems.

[Means for solving the problem]

As means for solving the above-mentioned problems, the present invention provides an upstream and downstream oxygen sensor for detecting the oxygen concentration in exhaust gas which is provided on the upstream and downstream sides of a catalyst provided in an exhaust system of an engine as shown in FIG. A sensor; a control constant calculating means for calculating an air-fuel ratio feedback control constant according to an output signal of the downstream oxygen sensor; and an air-fuel mixture supplied to the engine according to the output signal of the upstream oxygen sensor and the control constant. An engine control means for controlling the air-fuel ratio of the upstream oxygen sensor to near the stoichiometric air-fuel ratio; an inversion cycle detection means for detecting an inversion cycle of the output signal of the upstream oxygen sensor; an operation state detection means for detecting an operation state of the engine; First comparing means for outputting a predetermined signal when the inversion cycle is greater than a first predetermined value determined by the operating state; A second comparing means for outputting a predetermined signal when the predetermined signal is larger than a predetermined value, and the upstream oxygen sensor deterioration when either the first comparing means or the second comparing means outputs the predetermined signal. Provided with an oxygen sensor deterioration detecting device.

[Action]

Thus, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled near the stoichiometric air-fuel ratio in accordance with the output signal of the upstream oxygen sensor and the air-fuel ratio feedback constant corresponding to the output signal of the downstream oxygen sensor.

When the inversion cycle of the output signal from the upstream oxygen sensor is larger than a first predetermined value determined by the operation state of the engine, it is determined that the upstream oxygen sensor has deteriorated. Also, when the air-fuel ratio feedback constant according to the output signal from the downstream oxygen sensor is larger than the second predetermined value, it is determined that the upstream oxygen sensor has deteriorated.

〔The invention's effect〕

According to the present invention, when the air-fuel ratio feedback constant according to the output signal of the upstream oxygen sensor is larger than the second predetermined value, it is determined that the upstream oxygen sensor has deteriorated, and the operation state is changed from the inversion cycle of the output signal of the upstream oxygen sensor. Since the deterioration is determined in response, there is an excellent effect that the deterioration of the upstream oxygen sensor can be reliably determined without the need for a dedicated reference oxygen sensor for detecting the deterioration of the upstream oxygen sensor.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic configuration diagram of the present 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 intake air amount Q guided through the air cleaner 4. Further, the intake passage 2 is provided with a throttle valve 6 that opens and closes in accordance with a driver's operation amount of an accelerator 5 and adjusts an intake air amount 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 for each cylinder.

Further, the distributor 9 is provided with a reference position sensor 10 for generating a reference position detection signal every 720 crank angles (° C.) and a crank angle sensor 11 for generating a crank angle detection signal every 30 ° C. ing.

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

On the other hand, in the exhaust system, a three-way catalyst 1 that simultaneously purifies harmful components (HC, CO, NOx) in exhaust gas is provided downstream of the exhaust manifold 14.
5 are provided. An upstream oxygen sensor (O ₂ sensor) 16 is provided on the upstream side of the three-way catalyst 15, that is, on the exhaust manifold 14, and an exhaust pipe 17 on the downstream side of the three-way catalyst 15 is provided.
Is provided with a downstream O ₂ sensor 18. As we all know,
These upstream and downstream O ₂ 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.

Reference numeral 19 denotes an alarm for issuing a warning to a driver when an electronic control unit (ECU) 20 described later determines that the three-way catalyst 15 has deteriorated.

The ECU 20 is configured as, for example, a microcomputer, and as is well known, an A / D converter 101, an I / O port 102, a CPU 103, a ROM
104, RAM 105, backup RAM 106, clock generation circuit 107
Etc. are provided.

The following describes the degradation detection method of the air-fuel ratio control method and the upstream O ₂ sensor 16 of the engine 1 with reference to a flowchart shown in FIG. 3 to 7 FIG.

FIG. 3 is a flowchart showing a fuel injection amount calculation routine for calculating the fuel injection amount TAU according to the detection signals from the various sensors described above. This routine is started and executed every predetermined period (for example, 360 ° C. in this embodiment).

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

 Tp ← K · Q / NE where K is a constant.

In the following step 103, the basic fuel injection amount Tp is subjected to various corrections such as air-fuel ratio feedback control described later, and the fuel injection amount TAU is calculated.

TAU ← Tp · FAF · F Here, FAF is an air-fuel ratio correction coefficient by air-fuel ratio feedback control, and F is various correction coefficients. Then, in step 104, the fuel injection amount calculated in step 103 described above.
A control signal corresponding to TAU is output to the fuel injection valve 8.

FIG. 4 shows a detection signal (upstream output value) V1 of the upstream O ₂ sensor 16.
Is an air-fuel ratio feedback control routine for setting an air-fuel ratio correction coefficient FAF. This routine is executed for a predetermined time (for example,
In this embodiment, it is started and executed every 4 msec).

In step 201, it is determined whether a condition (first execution condition) of the main air-fuel ratio feedback control is satisfied.
Here, the first execution condition, for example, in the present embodiment is such that the upstream O ₂ sensor 16 and after an engine start is active. 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 1.0 (FAF ← 1.
0), and terminates this routine.

On the other hand, when it is determined in step 201 that the first execution condition is satisfied, a feedback process based on the upstream output value V1 in step 203 and thereafter is executed.

In step 203, the upstream output value V1 is read. In the following step 204, the upstream output value V1 is changed to the first comparison voltage VR1 (for example,
In this embodiment, it is determined whether or not the pressure is 0.45 V or less, that is, whether the air-fuel ratio is rich or lean. Here, when the upstream output value V1 is equal to or lower than the first comparison voltage VR1, that is, when the air-fuel ratio is lean, the process proceeds to step 205. In step 205, it is determined whether or not the first delay counter CDLY1 has a positive value, that is, whether or not the upstream output value V1 has inverted from rich to lean at the current control timing. Here, the first delay counter CDLY1 is a counter for measuring the elapsed time from when the upstream output value V1 crosses the first comparison voltage VR1, and the elapsed time in the rich state is a positive value and the elapsed time in the lean state is Elapsed time is defined as a negative value.

If the first delay counter CDLY1 has a negative value in step 205, the process proceeds to step 207. If the first delay counter CDLY1 has a positive value in step 205, the process proceeds to step 206. In step 206, the first delay counter CDLY1 is reset (CDLY1 ← 0), and the process proceeds to step 207. In step 207, the value of the first delay counter CDLY1 is decremented. (CDLY1 ← CDLY1-1). In step 208, it is determined whether the value of the first delay counter CDLY1 is less than the first lean delay time TDL1. Here, the first lean delay time TDL1 is a count value corresponding to the delay time in the delay processing that holds the determination that the output signal of the upstream O ₂ sensor 16 is rich even when the output signal changes from rich to lean. And is defined by a negative value. If the first delay counter CDLY1 is equal to or longer than the first lean delay time TDL1 in step 208, the process proceeds to step 217.

Meanwhile, the first delay counter CDLY1 is less than a first lean delay time TDL1 at step 208, that is, when the output signal of the upstream O ₂ sensor 16 has passed the aforementioned delay time or more from the Rinhe changed from rich to step 209 move on. Step 2
At 09, the first delay counter CDLY1 is set to the first lean delay time TDL1 (CDLY1 ← TDL1), and the routine proceeds to step 210. At step 210, the flag F1 indicating the state of the air-fuel ratio after the delay processing is reset (F1 ← 0), and the routine proceeds to step 217.
That is, when the flag F1 is in the reset state (F1 = 0), it indicates that the air-fuel ratio after the delay processing is lean.

Also, in step 204, the upstream output value V1 is changed to the first comparison voltage V1.
When it is larger than R1, that is, when the air-fuel ratio is rich, the process proceeds to step 211. In step 211, the first delay counter CD
LY1 is a negative value, that is, the upstream output value V
It is determined whether 1 has been inverted from lean to rich. Here, when the first delay counter CDLY1 is a positive value, the process proceeds to step 213.

On the other hand, if the first delay counter CDLY1 has a negative value in step 211, the process proceeds to step 212. In step 212, the first delay counter CDLY1 is reset (CDLY ← 0).
Then, the process proceeds to step 213.

In step 213, the value of the first delay counter CDLY1 is incremented (CDLY1 ← CDLY1 + 1). Next steps
At 214, it is determined whether the first delay counter CDLY1 is less than the first rich delay time TDR1. Here, the first rich delay time TDR1 corresponds to a delay time corresponding to the delay processing that holds the determination that the output signal of the upstream O ₂ sensor 16 is lean even when the output signal changes from lean to rich. Count value, defined as a positive value. If the first delay counter CDLY1 is equal to or longer than the first rich delay time TDR1 in step 214, the process proceeds to step 217.

On the other hand, if the first delay counter CDLY1 is larger than the first rich delay time TDR1 in step 214, that is, if the upstream O ₂
If a delay time described later has elapsed since the output signal of the sensor 16 changed from lean to rich, the process proceeds to step 215. At step 215, the first delay counter CDLY1 is set to the first
(CDLY1 ← TDR1), and the process proceeds to step 216. At step 216, a flag F1 indicating the state of the air-fuel ratio after the delay processing is set (F1 ← 1), and at step 217
Proceed to. That is, when the flag F1 is in the set state (F1 = 1), it indicates that the air-fuel ratio after the delay processing is rich.

In step 217, it is determined whether or not the flag F1 has been inverted, that is, whether or not the state of the air-fuel ratio after the delay processing has been inverted. Here, when the state of the air-fuel ratio after the delay processing is reversed, skip processing of steps 218 to 220 is performed. First,
At step 218, it is determined whether or not the flag F1 is in a reset state. If the flag F1 is in the reset state, that is, if the flag F1 is inverted from rich to lean, the process proceeds to step 219. At step 219, the air-fuel ratio correction coefficient FAF is increased by the first rich skip amount RSR1 (FAF ← FAF + RSR1), and the routine proceeds to step 224. If the flag F1 is in the set state in step 218, that is, if the flag F1 is inverted from lean to rich, the process proceeds to step 220. In step 220, the air-fuel ratio correction coefficient FAF
Is reduced by the first lean skip amount RSL1 (FAF ← FAF
-RSL1), proceed to step 224;

On the other hand, if the state of the air-fuel ratio after the delay processing is not inverted at step 217, the integration processing of steps 221 to 223 is performed. First, at step 221, it is determined whether or not the flag F1 is in a reset state, that is, whether or not the flag is lean. If it is lean, the process proceeds to step 222. Step 2
At 22, the air-fuel ratio correction coefficient FAF is increased by the first rich integration constant KIR1 (FAF ← FAF + KIR1), and the routine proceeds to step 224.
If it is rich in step 221, the process proceeds to step 223. At step 223, the air-fuel ratio correction coefficient FAF is reduced by the first lean integration constant KIL1 (FAF ← FAF-KIL1), and the routine proceeds to step 224.

In step 224, guard processing is performed so that the air-fuel ratio coefficient FAF set as described above falls within a predetermined range (for example, 0.8 to 1.2 in the present embodiment), and the routine ends.

FIG. 5 is a sub air-fuel ratio feedback control for correcting the first rich step amount RSR1 and the first lean skip amount RSL1 in the main air-fuel ratio feedback control based on the output value (downstream output value) V2 of the downstream O ₂ sensor 18. It is a flowchart which shows a routine. This routine is started and executed every predetermined time (for example, 1 second in this embodiment).

First, at step 301, it is determined whether or not the air-fuel ratio feedback condition (second execution condition) is satisfied, that is, whether or not to execute the sub-air-fuel ratio feedback control. Here, the second execution condition is, for example, in the present embodiment, the first execution condition is satisfied, that is, the main air-fuel ratio feedback control is being performed. Downstream O ₂ sensor 18 is equal in the active state.

If the second execution condition is not satisfied in step 301, the process proceeds to step 302. In step 302, the first rich skip amount RSR1 is set to a predetermined rich skip amount RSR0.
In the next step 303, the first lean skip amount RSL1 is set to a predetermined lean skip amount RSL0, and this routine ends.

If the second execution condition is satisfied in step 301, the sub air-fuel ratio feedback processing based on the downstream output value V2 in step 304 and thereafter is executed. First, step 304
Reads the downstream output value V2. In step 305, the downstream output value V
It is determined whether or not 2 is equal to or lower than a second comparison voltage VR2 (for example, 0.45 V which is the same as the first comparison voltage VR1 in this embodiment), that is, whether the air-fuel ratio is rich or lean. Here, the downstream output value V2
Is equal to or lower than the second comparison voltage VR2, that is, when the air-fuel ratio is lean, the routine proceeds to step 306. In step 306, it is determined whether the second delay counter CDLY2 has a positive value, that is, whether or not the downstream output value V2 has been inverted from rich to lean at the current control timing. Here, the second delay counter CDLY2 has the same downstream output value V as the first delay counter CDLY1.
Reference numeral 2 denotes a counter for measuring an elapsed time after the second reference voltage VR2 is crossed. The elapsed time in the rich state is defined by a positive value, and the elapsed time in the lean state is defined by a negative value.

If the second delay counter CDLY2 has a negative value in step 306, the process proceeds to step 308. If the second delay counter CDLY2 has a positive value in step 306, the process proceeds to step 307. In step 307, the second delay counter CDLY2 is reset (CDLY2 ← 0), and the process proceeds to step 308.

In step 308, the value of the second delay counter CDLY2 is decremented (CDLY2 ← CDLY2-1). Next step 30
At 9, it is determined whether the value of the second delay counter CDLY2 is less than the second lean delay time TDL2. Here, the second lean delay time TDL2 is a count value corresponding to the delay time in the delay processing that holds the determination that the output signal of the downstream O ₂ sensor 18 is rich even when the output signal changes from rich to lean. And is defined by a negative value. If the second delay counter CDLY2 is not equal to the second lean delay time TDL2 in step 309, the process proceeds to step 318.

On the other hand, the step when the second delay counter CDLY2 in step 309 less than the second lean delay time TDL2, i.e. the output signal of the downstream O ₂ sensor 18 has passed over the delay time of the above after changing from rich to lean Proceed to 310. In step 310, the second delay counter CDLY2 is set to the second lean delay time TDL2 (CDLY2 ← TDL2), and the process proceeds 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 routine 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 processing is lean.

Also, in step 305, the downstream output value V2 is changed to the second comparison voltage V2.
When it is larger than R2, that is, when the air-fuel ratio is rich, the process proceeds to step 312. In step 312, the second delay counter CD
LY2 is a negative value, that is, the downstream output value V
It is determined whether or not 2 is inverted from lean to rich. Here, if the second delay counter CDLY2 is a positive value, the process proceeds to step 314.

On the other hand, if the second delay counter CDLY2 has a negative value in step 312, the process proceeds to step 313. In step 313, the second delay counter CDLY2 is reset (CDLY2 ← 0).
Then, the process proceeds to step 314.

In step 314, the value of the second delay counter CDLY2 is incremented (CDLY2 ← CDLY2 + 1). Next steps
At 315, it is determined whether the value of the second delay counter CDLY2 is less than the second rich delay time TDR2. Here, the second rich delay time TDR2 corresponds to the delay time the output signal of the downstream O ₂ sensor 18 which corresponds to the delay processing for holding a judgment that even if there is a change from lean to rich is lean Count value, defined as a positive value. If the second delay counter CDLY2 is equal to or longer than the second rich delay time TDR2 in step 315, the process proceeds to step 318.

On the other hand, the step when the second delay counter CDLY2 in step 315 is greater than the second rich delay time TDR2, i.e. the output signal of the downstream O ₂ sensor 18 has passed the aforementioned delay time or more changes from the lean to rich Proceed to 316. In step 316, the second delay counter CDLY2 is set to the second rich delay time TDR2 (CDLY2 ← TDR2).
Proceed to. At step 317, the flag F2 indicating the state of the air-fuel ratio after the delay processing is set (F2 ← 1), and the routine proceeds to step 318. That is, when the flag F2 is set (F2 = 1), it indicates that the air-fuel ratio after the delay processing 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, when the flag F2 is in the reset state, that is, when the air-fuel ratio after the delay processing is lean, the process proceeds to step 319. In step 319, the first rich skip amount RSR1 is increased by a predetermined value RS (RSR1 ← RSR1 + RS), and the process proceeds to step 320. In step 320, the first lean skip amount RSL1 is reduced by a predetermined value RS (RSL1 ← RSL1-RS), and step 323 is performed.
Proceed to.

On the other hand, if the flag F2 is set in step 318, that is, if the air-fuel ratio after the delay processing is rich, the process proceeds to step 321. In step 321, the first rich skip amount RSR1 is reduced by a predetermined value RS (RSR1 ← RSR1-RS), and in step 322.
Proceed to. In step 322, the first lean skip amount RSL1 is increased by a predetermined value RS (RSL1 ← RSL1 + RS), and step 32
Proceed to 3.

In step 323, the skip amounts RSR1 and RSL1 are set so that the first rich skip amount RSR1 and the first lean skip amount RSL1 set as described above fall within a predetermined range.
Is determined to be outside a predetermined range, and if so, guard processing is performed.

Next, proceed to step 324, and in step 323, the skip amount
It is determined whether guard processing has been performed on RSR1 or RSL1 beyond a predetermined range. If the guard processing has been performed, the guard processing determination flag XSFBG is set (XSFBG ← 1). If the guard processing has not been performed, the guard processing determination flag XSFBG is reset (XSFBG ← 0) in step 326, and End the routine.

Figure 6 obtains the inversion period of the upstream output value V1 is the detection signal of the upstream O ₂ sensor 16 is a flowchart illustrating a process of comparing the degradation determination period corresponding to the operation state, the process for a predetermined time (for example It is started and executed every 8 msec).

First, in step 401, it is determined whether or not the engine 1 is in a steady state based on, for example, a throttle opening, a throttle opening change rate, and the like. If it is not in the steady state, the process proceeds to step 402, where the counter CT is reset. The counter CT is a counter for measuring the inversion period detection time of the upstream output value V _1. Next, in step 403, the counter COX is also reset. The counter COX is used to measure the number of reversals of the detection signal V _1. Above, the counter CT, COX
Is reset and this routine ends.

If it is determined in step 401 that the state is a steady state, step 404
Increments the counter CT (CT ← CT + 1). Then upstream output value V ₁ at step 405 whether the comparison voltage VR1 higher, that is, the air-fuel ratio is detected whether lean or rich. Here, when the upstream output value V1 is equal to or lower than the comparison voltage VR1, that is, when the air-fuel ratio is lean, the process proceeds to step 406. Step 4
At 06, the flag F3 indicating the state of the air-fuel ratio is reset (F3 ← 0)
Then, the process proceeds to step 408. When the upstream output value V1 is larger than the comparison voltage VR1, that is, when the air-fuel ratio is rich, the flag F3 is set (F3 ← 1) in step 407, and
Go to 08.

At step 408, it is detected whether or not the flag F3 has been inverted, that is, whether or not the air-fuel ratio has changed. Here, if the flag F3 is not inverted, the process goes through the step 409 and proceeds to the step 110. Step 4 if the flag F3 is inverted
Increment the flag COX that counts the number of reversals at 09 (C
OX ← COX + 1). Next, in step 110, it is determined whether or not the counter CT for measuring the inversion cycle detection time has reached α. If it has not reached α, this routine ends. If it has reached α, the routine proceeds to step 111, where the counter CT is reset (CT ← 0), and in step 112, the deterioration determination frequency fmn corresponding to the operating state (engine speed, intake air amount) is set to It is calculated from the map shown.

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

Further, the deterioration determination frequency fmn is set so as to increase as the engine speed NE increases and as the intake air amount QN increases.

When the deterioration determination cycle fmn according to the operation state is calculated in step 112, the process proceeds to step 113, where the counter COX is compared with the deterioration determination frequency fmn. Here, the value of the counter COX is the inverse number of upstream output V ₁ in the α times, which is equivalent to the frequency.

When the counter COX deterioration determination frequency fmn greater than the upstream O ₂ sensor 16 will be deteriorated, the deterioration determination flag XMFBG set (XMFBG ← 1) at step 114, the counter
If COS is smaller than the deterioration determination frequency fmn, step 114
Resets the deterioration determination flag XMFBG (XMFBG ← 0).
Then, in step 116, the counter COS is reset (COX ←
0) and end this routine.

7 is a routine for determining the deterioration of the upstream O ₂ sensor 16.

First, in step 501, it is determined whether a deterioration detection condition is satisfied. Here, as the deterioration detection condition, for example, in the present embodiment, the main / sub air-fuel ratio feedback control is being performed, and the engine 1 is in a steady state. 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 in step 502 and thereafter is executed. First, in step 502, it is determined whether the guard processing determination flag XSFBG is set. If the flag XSFBG is set (XSFBG = 1), that is, if the skip amount RSR1 or RSL1 exceeds the predetermined range and the guard processing is performed in the sub-feedback control shown in FIG.
It determines that the upstream O ₂ sensor abnormality in 506, a warning lamp is turned on at step 507.

If it is determined in step 502 that the guard processing determination flag has not been set, the process proceeds to step 503, where it is determined whether the deterioration determination flag XMFBG has been set. When set (XMFBG = 1) i.e. when the frequency of the upstream output V ₁ is is determined that the deterioration determination frequency fmn larger in accordance with the operating conditions in the flow shown in FIG. 6 upstream O ₂ proceeds to step 506 and 507 The sensor 16 is determined to be abnormal, and the warning light is turned on.

When the deterioration determination flag XMFBG is not set in step 503, that is, when both the guard processing determination flag XSFBG and the deterioration determination flag XMFBG are not set,
Upstream O ₂ sensor proceeds to step 504 determines that the normal, turns off the warning lamp 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, and FIG. 5 is a map of a predetermined value determined by the operation state in FIG. 1… Engine, 8… Injector, 15… Three-way catalyst, 16
…… Upstream oxygen sensor, 18 …… Downstream oxygen sensor, 20 …… EC
U.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02D 41/00-45/00

Claims (1)

(57) [Claims] An upstream and downstream oxygen sensor for detecting an oxygen concentration in exhaust gas is provided upstream and downstream of a catalyst provided in an exhaust system of an engine, respectively, and an output signal of the downstream oxygen sensor is provided. Control constant calculating means for calculating an air-fuel ratio feedback control constant in accordance with the control signal; and controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to a value close to the stoichiometric air-fuel ratio in accordance with the output signal of the upstream oxygen sensor and the control constant. Engine control means, inversion cycle detection means for detecting an inversion cycle of the output signal of the upstream oxygen sensor, operation state detection means for detecting an operation state of the engine, and a first inversion cycle determined by the operation state. First comparing means for outputting a predetermined signal when the air-fuel ratio feedback control constant is larger than a second predetermined value; A second comparing means, and a deterioration judging means for judging the upstream oxygen sensor deterioration when one of the first comparing means and the second comparing means outputs the predetermined signal. An oxygen sensor deterioration detection device characterized by the above-mentioned.