JPH05248227A - Catalyst deterioration detecting device of internal combustion engine - Google Patents

Abstract

PURPOSE:To judge deterioration of a catalyst certainly even if O2 storage performance of the catalyst is changed according to a temperature. CONSTITUTION:In a CPU 15, a deterioration judging value corresponding to a catalyst temperature detected by a catalyst temperature sensor 13, is outputted, after being retrieved from, for example, a judging value table. In the CPU 15, deterioration of the catalyst is detected on the basis of output of O2 sensors (FS), (RS) and a retrieved judging value. It is thus possible to correct the judging value according to temperature characteristic of the catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst deterioration detecting device for an internal combustion engine provided in an exhaust system of the internal combustion engine to purify exhaust gas.

[0002]

As means for determining the deterioration of the Prior Art Catalysts for purifying exhaust gas of an internal combustion engine, the O ₂ sensor provided upstream and downstream of the catalyst, the upstream O output of the ₂ sensor and the downstream O ₂
It is known to measure the time from the reversal of the intake system supply air-fuel ratio to the reversal of the output of the downstream O ₂ sensor while adjusting the supply air-fuel ratio to the intake system according to the output of the sensor (for example, Japanese Patent Application Laid-Open Nos. 2-30915 and 2-3
3408, Japanese Patent Laid-Open No. 2-207159). Further, as a means for determining the deterioration of the catalyst, the upstream side O
A method of comparing the outputs of the ₂ sensor and the downstream O ₂ sensor, for example, the output ratio method (see JP-A-63-231252),
A response ratio method (see Japanese Patent Application Laid-Open No. 3-57862), a phase difference time measuring method (see Japanese Patent Application Laid-Open No. 2-310453), and the like have been proposed.

[0003] Also by the applicant, the fuel correction coefficient switching at constant frequency, the deterioration of the catalyst based on the area difference calculated from outputs of the downstream O ₂ sensor at the upstream side O ₂ sensor generated when the Judgment method (area difference method)
Have already been proposed by Japanese Patent Application No. 2-117890. Both of these approaches focus on the O ₂ storage capability possessed by the catalyst, by quantifying the O ₂ storage capability, is performed deterioration determination of the catalyst.

Moreover, applicant performs degradation determination using only the output of the downstream O ₂ sensor without using the output of the upstream O ₂ sensor, whereby Ya independent characteristics of the upstream O ₂ sensor A method for performing accurate catalyst deterioration determination based on the stable output of the downstream O ₂ sensor without being affected by the deviation of the control air-fuel ratio from the theoretical air-fuel ratio due to deterioration (Japanese Patent Application No. 3-271204). Is proposed. That is, in this method, when adjusting the air-fuel ratio of the engine in accordance with the output of the downstream O ₂ sensor, a skip amount that changes the fuel correction coefficient (Ko2) from the rich side to the lean side with respect to the theoretical air-fuel ratio is generated. It is determined that the catalyst has deteriorated when the time (TL) from when the output of the downstream O ₂ sensor is inverted from rich to lean with respect to the stoichiometric air-fuel ratio is shorter than a predetermined time. Furthermore, in this proposal, in order to prevent erroneous determination, a catalyst temperature sensor that detects the temperature of the catalyst is used,
There is provided means for prohibiting catalyst deterioration detection when the catalyst temperature deviates from a predetermined range (deterioration monitor temperature range).

[0005]

However, the above-mentioned O
_{2 The} storage capacity may change depending on the temperature of the catalyst (CAT). In such a case, the time from the rich output of the downstream O ₂ sensor to the lean inversion (T
L) changes depending on the temperature of the catalyst. Japanese Patent Application No. 3-
The deterioration determination device of No. 271204 does not consider this point, and there is room for solving the problem from the viewpoint of improving the accuracy of deterioration determination.

This point will be specifically described with reference to FIG.
FIG. 23 is a diagram showing changes in the catalyst O ₂ storage capacity (OSC) with respect to the catalyst temperature.

As shown in FIG. 23, a new catalyst is 30
0 O ₂ storage ability at temperatures in the vicinity ° C is saturated, O ₂ storage capability is stable without changing the temperature of the catalyst in the deterioration monitoring the temperature range after the saturation. However, good thermal deterioration of the catalyst is going proceeds from new, further becomes degraded products, the O ₂ storage ability is decreased, the O ₂ storage in the range of A~B in FIG (300 to 550 ° C) Capacity changes with the temperature of the catalyst.

In such a situation, the lower limit of the deterioration monitor temperature range is 3 in A in the figure according to a new catalyst.
When the temperature is set to 00 ° C, the catalyst temperature is AB in the figure.
When the deterioration determination is performed in the range of, the erroneous determination can be prevented for the new catalyst, but the erroneous determination may be performed for the good catalyst whose O ₂ storage capacity is lower than that of the new catalyst. Further, if the lower limit value of the deterioration monitor temperature range is set to 550 ° C. of B in the figure in accordance with a good product, it cannot be determined that the deteriorated product is deteriorated at a higher temperature, or the temperature of the catalyst is There was a risk that the deterioration judgment would not be performed because the deterioration monitor temperature range was not reached.

As described above, in order to prevent the erroneous judgment, the erroneous judgment can be prevented for the new catalyst only by the condition that the deterioration detection of the catalyst is prohibited when the catalyst temperature deviates from the deterioration monitor temperature range. It was not sufficient as a condition for preventing erroneous determination of a deteriorated catalyst.

In view of the above-mentioned conventional problems, the present invention provides a catalyst deterioration detecting device for an internal combustion engine, which can accurately judge the deterioration of the catalyst even when the O ₂ storage capacity of the catalyst changes with temperature. With the goal.

[0011]

In order to achieve the above object, a first aspect of the present invention is provided with a catalyst means attached to an exhaust system of an internal combustion engine for purifying harmful components in exhaust gas, and a catalyst means provided downstream of the catalyst means. A catalyst deterioration detecting device for an internal combustion engine, comprising: an oxygen concentration detecting means for detecting an oxygen concentration in exhaust gas; and detecting deterioration of the catalyst means based on an output of the oxygen concentration detecting means and a predetermined discriminant value, It is characterized in that it has a catalyst temperature detecting means for detecting the temperature of the means, and a discriminant value determining means for determining the discriminant value corresponding to the temperature of the catalyst means detected by the catalyst temperature detecting means.

A second aspect of the present invention is a catalyst means attached to an exhaust system of an internal combustion engine for purifying harmful components in the exhaust gas, and an upstream oxygen concentration attached to an upstream side of the catalyst means for detecting an oxygen concentration in the exhaust gas. A detection means and a downstream side oxygen concentration detection means attached to the downstream side of the catalyst means for detecting the oxygen concentration in the exhaust gas are provided, and the outputs of the upstream side and downstream side oxygen concentration detection means and a predetermined discriminant value are set. A catalyst deterioration detecting device for an internal combustion engine for detecting deterioration of the catalyst means based on the catalyst temperature detecting means for detecting the temperature of the catalyst means, and the catalyst temperature detecting means for detecting the temperature of the catalyst means detected by the catalyst temperature detecting means. A discriminant value determining means for determining a discriminant value.

A third invention is characterized in that, in the first and second inventions, the catalyst temperature detecting means is attached to a part of the catalyst means and detects a temperature of a central portion of the catalyst means. ..

According to a fourth aspect of the present invention, there is provided catalyst means which is attached to an exhaust system of an internal combustion engine to purify harmful components in the exhaust gas, and oxygen concentration detection means which is installed downstream of the catalyst means and detects the oxygen concentration in the exhaust gas. A catalyst deterioration detecting device for an internal combustion engine that detects deterioration of the catalyst means based on an output of the oxygen concentration detecting means and a predetermined discriminant value, and an operating state detecting means for detecting an operating state of the engine; Catalyst temperature estimating means for estimating the temperature of the catalyst means according to the operating state of the engine detected by the operating state detecting means, and the discriminant value is determined according to the temperature of the catalyst means estimated by the catalyst temperature estimating means. And a discriminant value determining means for performing the determination.

According to a fifth aspect of the present invention, there is provided catalytic means for purifying harmful components in exhaust gas, which is mounted in an exhaust system of an internal combustion engine, and upstream oxygen concentration for detecting oxygen concentration in exhaust gas, which is mounted upstream of the catalytic means. A detection means and a downstream side oxygen concentration detection means attached to the downstream side of the catalyst means for detecting the oxygen concentration in the exhaust gas are provided, and the outputs of the upstream side and downstream side oxygen concentration detection means and a predetermined discriminant value are set. A catalyst deterioration detecting device for an internal combustion engine that detects deterioration of the catalyst means based on an operating state detecting means for detecting an operating state of the engine, and the catalyst according to the operating state of the engine detected by the operating state detecting means. A catalyst temperature estimating means for estimating the temperature of the means, and a discriminant value determining means for determining the discriminant value according to the temperature of the catalyst means estimated by the catalyst temperature estimating means. It is characterized in.

In a sixth aspect based on the fourth or fifth aspect, the operating state detecting means detects the engine speed and the load of the engine, or the amount of intake air drawn into the engine as the operating state of the engine. However, the catalyst temperature estimating means estimates the temperature of the catalyst means on the basis of the engine speed and the engine load, or the amount of intake air taken into the engine.

[0017]

According to the first and second aspects of the present invention, the discriminant value determining means determines the discriminant value corresponding to the temperature of the catalyst detected by the catalyst temperature detecting means by searching, for example, the discriminant value table. Then, the deterioration of the catalyst means is detected based on the output of the oxygen concentration detection means and the retrieved judgment value. As a result, the judgment value can be corrected according to the temperature characteristic of the catalyst means.

According to the third invention, since the catalyst temperature detecting means detects the temperature of the central portion of the catalyst means, the catalyst temperature sensor can be placed in a stable gas flow.

According to the fourth and fifth aspects of the invention, the catalyst temperature estimating means estimates the catalyst temperature according to the operating state of the internal combustion engine detected by the operating state detecting means by calculation or the like. The discriminant value determining means retrieves and determines a discriminant value corresponding to the estimated catalyst temperature from, for example, a discriminant value table.
Deterioration of the catalyst means is determined based on the retrieved determination value and the output of the oxygen concentration detection means. As a result, the determination value corresponding to the temperature characteristic of the catalyst is corrected without using the catalyst temperature detecting means such as the catalyst temperature sensor.

According to the sixth aspect of the present invention, the catalyst temperature estimating means calculates, for example, at least the rotational speed of the internal combustion engine, the load of the internal combustion engine, and the air-fuel ratio supplied to the internal combustion engine by the operation state detecting means. Since the catalyst temperature is estimated, highly accurate temperature estimation is possible.

[0021]

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

FIG. 1 is an overall configuration diagram of a fuel supply control device to which a catalyst deterioration detecting device for an internal combustion engine according to a first embodiment of the present invention is applied. A throttle body 2 is provided, and a throttle valve 3 is arranged inside the throttle body 2. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3 and supplies an electric signal corresponding to the opening θTH of the throttle valve 3 to an electronic control unit (hereinafter referred to as “ECU”) U.

The fuel injection valve 5 is provided for each cylinder between the engine E and the throttle valve 3 and slightly upstream of the intake valve 6, and each fuel injection valve 5 is connected to a fuel pump (not shown). With. It is electrically connected to the ECU
A signal from the CU controls the valve opening time of fuel injection.

On the other hand, an intake pipe absolute pressure (Pb) sensor 7 is provided immediately downstream of the throttle valve 3, and the absolute pressure Pb detected by this absolute pressure sensor 7 is converted into an electric signal and supplied to the ECU. To be done. An intake air temperature (Ta) sensor 8 is attached downstream thereof, and the intake air temperature Ta detected by the intake air temperature sensor 8 is converted into an electric signal and supplied to the ECU.

The cooling water temperature (Tw) sensor 9 mounted on the body of the engine E is composed of a thermistor or the like,
Is detected and a corresponding electric signal is supplied to the ECU. The engine speed (Ne) sensor 10 is mounted around a cam shaft or a crank shaft (not shown) of the engine E,
A pulse (hereinafter referred to as "TDC signal pulse") is output at a predetermined crank angle position of the crank shaft and supplied to the ECU. The ECU has a vehicle speed (Vh) sensor 1 for detecting the vehicle speed.
1 is connected and an electric signal indicating the vehicle speed Vh is supplied.

At an upstream position of the catalyst C in the exhaust pipe 12, an upstream O ₂ sensor FS as an exhaust component concentration detector is provided.
Is mounted, and a downstream O ₂ sensor RS is mounted downstream of the catalyst C to detect the oxygen concentration in the exhaust gas, and to detect an electric signal (F) corresponding to the detected value.
V ₀₂ , RV ₀₂ ) is supplied to the ECU. Further, the catalyst C is equipped with a catalyst temperature (TCAT) sensor 13 that detects the temperature, and an electric signal corresponding to the detected catalyst temperature TCAT is supplied to the ECU.

As shown in FIGS. 2 (a) and 2 (b), the catalyst C is composed of independent two beds C1 and C2 arranged in series at a predetermined interval (for example, 25 mm). , The catalyst temperature sensor 13 between the beds C1 and C2.
Is mounted, and the thermistor 13a, which is the temperature detecting portion thereof, is located substantially in the center of the catalyst C in the radial direction.

The ECU forms input signal waveforms from various sensors, corrects a voltage level to a predetermined level, converts an analog signal value into a digital signal value, and the like, a central processing circuit (hereinafter referred to as a central processing unit). "CPU") 15, ROM 16 in which various calculation programs and various reference values used for calculation in CPU 15 are stored, RAM 17 in which the detected various engine parameter signals and calculation results are temporarily stored, and It is composed of an output circuit 18 and the like for supplying a drive signal to the fuel injection valve 5.

Based on the above-mentioned various engine parameter signals, the CPU 15 determines various engine operating states in a feedback control region and a plurality of specific operating regions (hereinafter referred to as "open loop control region") in which feedback control is not performed, as will be described later. The TD is determined based on the following equation (1) according to the determined engine operating state.
Fuel injection time T of the fuel injection valve 5 synchronized with the C signal pulse
Calculate OUT.

TOUT = Ti × K ₀₂ × KLS × K ₁ + K ₂ (1) Here, Ti is the basic fuel injection time of the fuel injection valve 5, and it corresponds to the engine speed Ne and the intake pipe absolute pressure Pb. It is determined.

K ₀₂ is an O ₂ feedback correction coefficient (hereinafter, simply referred to as “correction coefficient”), which is obtained in accordance with the oxygen concentration in the exhaust gas during feedback control. It is set accordingly.

KLS is set to a predetermined value (for example, 0.95) less than 1.0 when the engine E is in the lean region or the fuel cut region of the open loop control region, that is, the predetermined deceleration operation region. Is the leaning coefficient.

K ₁ and K ₂ are correction coefficients and correction variables calculated according to various engine parameter signals, respectively, so that various characteristics such as fuel consumption characteristics and engine acceleration characteristics can be optimized according to engine operating conditions. To a predetermined value.

The CPU 15 supplies a drive signal for opening the fuel injection valve 5 to the fuel injection valve 5 via the output circuit 18 based on the fuel injection time TOUT obtained as described above.

3 and 4, it is determined whether the engine E is in a feedback control region or a plurality of open loop control regions, and a correction coefficient K ₀₂ is set according to the determined operation state. The flowchart of the program to be performed is shown. This program is executed in synchronization with the generation of the TDC signal pulse.

First, at step 101, flag n _{02 is set.}
Is determined to be equal to the value 1. The flag n ₀₂ is for determining whether or not the upstream O ₂ sensor FS and the downstream O ₂ sensor RS are in the activated state, and when the answer to step 101 is (Yes), that is, both When it is determined that the O ₂ sensors FS and RS are in the activated state, it is determined in step 102 whether the cooling water temperature Tw is higher than the predetermined water temperature TW ₀₂ . When the answer is (Yes), that is, when Tw> Tw ₀₂ is satisfied and the engine E has finished warming up, it is determined in step 103 whether the flag FLGWOT is equal to the value 1. This flag FLGWOT
Is set to a value of 1 when it is determined by a program (not shown) that the engine E is in the high load region in which the amount of supplied fuel should be increased.

When the answer to step 103 is (No), that is, when the engine E is not in the high load region, it is determined in step 104 whether the engine speed Ne is higher than a predetermined speed NHOP on the high speed side, This answer is (No)
If it is, the engine speed Ne is further determined in step 105.
Is greater than the predetermined rotation speed NLOP on the low rotation side. The answer is (Yes), that is, NLOP <Ne ≦ NH
When OP is satisfied, it is determined in step 106 whether the lean coefficient KLS is less than 1.0, that is, the engine E.
Is in a predetermined deceleration operation range. If the answer to step 106 is (No), step 10
In step 7, it is determined whether the engine E is performing fuel cut. When the answer is (No), it is determined that the engine E is in the feedback control region, and further, in step 108, it is determined whether or not the engine operating state is the state in which the monitoring of the catalyst C is permitted. This answer is (Ye
s), ie, if the monitor is allowed, step 109
Then, the correction coefficient K ₀₂ is controlled on the basis of the output voltage RV ₀₂ of the downstream O ₂ sensor RS, the deterioration of the catalyst C is monitored, and the program ends.

On the other hand, the answer to step 108 is (N
o) That is, when the monitoring of the catalyst C is not permitted, it is determined in step 110 whether the previous monitoring is being performed. If the answer is (No), that is, if the monitoring is not continuously performed, then in step 111, the outputs FV ₀₂ , R of the upstream O ₂ sensor FS and the lean side O ₂ sensor RS are obtained.
While controlling the correction coefficient K ₀₂ based on V ₀₂ ,
The average value KREF of the correction coefficient K ₀₂ is calculated, and this program ends.

When the answer to step 105 is (No), that is, when Ne ≦ NLOP is satisfied and the engine E is in the low speed region, the answer to step 106 is (Yes), that is, the engine E is in the predetermined deceleration operation region. If so, or if the answer to step 107 is (Yes), that is, if the engine E is executing fuel cut, the routine proceeds to step 112. In this step 1112, it is judged whether or not the loop has continued for a predetermined time tD, and if the answer is (No), the correction coefficient K ₀₂ is held at the value immediately before the transition to the loop in step 113, while If the answer is (Yes), the correction coefficient K is calculated in step 114.
₀₂ is set to the value 1.0 and open loop control is performed, and this program ends. That is, the step 105
When the engine E shifts from the feedback control region to the open loop control region by any of the conditions from 1 to 107, the correction coefficient K ₀₂ is calculated during the feedback control immediately before the shift until a predetermined time tD elapses after the shift. On the other hand, the value is set to 1.0 after the predetermined time tD has elapsed.

The answer to step 102 is (No), that is, when the engine E has not finished warming up, the answer to step 103 is (Yes), that is, when the engine E is in the high load region, or When the answer to step 104 is (Yes), that is, when the engine E is in the high rotation speed region, the routine proceeds to step 114, where the open loop control is executed and the present program is terminated.

The answer to step 101 is (No), that is, when it is determined that both O ₂ sensors FS and RS are inactive, and the answer to step 110 is (Yes
s), that is, when the monitor is not permitted for the first time this time, the routine proceeds to step 115, where it is judged if the engine E is in the idle region. This determination is performed, for example, by determining whether the engine speed Ne is equal to or lower than a predetermined speed and the throttle valve opening degree θTH is equal to or lower than a predetermined opening degree. If the answer to step 115 is (Yes), that is, if the engine E is in the idle region, the correction coefficient K ₀₂ is set to the average value KRE for the idle region in step 116.
Set to F0, execute open loop control, and terminate this program.

When the answer to step 115 is (No), that is, when the engine E is in the operating region other than the idle region (hereinafter referred to as "off idle region"), the routine proceeds to step 117, where the correction coefficient K _{02 is set} for the off idle region. Set to the average value KREF1 of.

Next, the deterioration of the catalyst will be described.

As described above, in the flowchart of FIG. 3, when the catalyst C is not permitted to be monitored in step 108, the output voltage FV ₀₂ of the upstream O ₂ sensor FS and the output voltage RV _{02 of the} downstream O ₂ sensor RS. Based on and, feedback control is performed. On the other hand, the step 10
If the monitoring of the catalyst C is permitted in step 8, the monitoring mode of the catalyst C is executed in step 109. The contents will be described in detail below with reference to the flowcharts of FIGS.

The feedback control for monitoring the deterioration of the catalyst C is performed by the output voltage RV of the downstream O ₂ sensor RS.
Based on ₀₂ only. Then, the time TL from the occurrence of the special P term PLSP for skipping the correction coefficient K ₀₂ from the rich side to the lean side with respect to the theoretical air-fuel ratio to the confirmation of the O ₂ concentration rich → lean inversion is TL. From the occurrence of the special P term PRSP, which is detected and causes the correction coefficient K ₀₂ to be skipped from the lean side to the rich side with respect to the theoretical air-fuel ratio, until the inversion of lean → rich of the O ₂ concentration is confirmed. Of time TR is detected, and the deterioration of the catalyst C is determined based on these times TL and TR.

The schematic structure of the catalyst deterioration monitor will be described with reference to the flowchart of FIG.

In FIG. 5, first, at step 201, it is judged if the precondition for detecting the deterioration of the catalyst is satisfied or not. If the answer is (No), then the step 20 is executed.
2, NTL (TL measurement count, that is, the time T
L is the total number of times measured, nTR (the number of TR measurements, that is, the total number of times the time TR was measured), TLSUM
(TL total value, that is, total time of TL measured a plurality of times) and TRSUM (TR total value, that is, total time of TR measured a plurality of times) are set to zero. Then, in step 203, the above-mentioned normal feedback control is performed. If the precondition is not satisfied during the deterioration monitoring of the catalyst C, KREF is set as the initial value of the feedback control.
Is used.

When the answer to step 201 is (Yes), that is, when the precondition for monitoring the deterioration of the catalyst C is satisfied, at step 204 the TR measurement number nTR is reached.
Is determined to be equal to or greater than a predetermined value. If the answer to step 204 is (Yes), it is considered that the data for determining the deterioration of the catalyst C has been prepared, the deterioration determination process B of step 205 is executed, the monitoring is ended in step 206, and normal feedback is performed. Return to control. Also in this case, KREF is used as the initial value of the feedback control.

When the answer to step 204 is (No), the following steps 207 to 213 are executed on the assumption that the data for determining the deterioration of the catalyst C has not been prepared. That is, first, at step 207, it is judged whether the first special P terms PLSP, PRSP have occurred since the monitor was permitted. If the monitor has not started yet, the answer is (No), and the monitor start process is executed in step 208. On the other hand, the answer to step 207 is (Yes), and the first special P term PLSP, P has already been reached.
If RSP has occurred, it is determined in step 209 whether the output voltage RV ₀₂ of the downstream O ₂ sensor RS has been inverted. If the answer to step 209 is (Yes), step 21
When 0, RV ₀₂ inversion processing, that is, increment of TL measurement number nTL or TR measurement number nTR, lean delay timer tLD (measures time from RV ₀₂ inversion to generation of special P term PRSP) or rich delay The timer tRD (measurement of the time from when RV ₀₂ is inverted until the special P term PLSP is generated) is started, and the special P terms PLSP and PRSP are generated.

On the other hand, the answer to step 209 is (No).
In this case, the deterioration determination process A is started in step 214, the normality of the catalyst C is confirmed in the following step 215, and if the answer is (Yes), that is, the normality of the catalyst C is confirmed, the process proceeds to step 206. Migrate and exit monitoring. on the other hand,
If the answer to step 215 is (No) and normality cannot be confirmed, the process proceeds to step 211.

In step 211, it is judged whether or not the output voltage RV _{02 of the} downstream side O ₂ sensor RS has been inverted even once after the monitor is permitted. If the answer in step 211 is (No), that is, if the first inversion is performed after the monitor is permitted, the inversion waiting process after the start is performed in step 212, while the answer in step 211 is ( In the case of Yes), that is, after one or more inversions after the start, the RV ₀₂ inversion waiting process is executed in step 213. These steps 212, 213
Then, in each case, the special I term I with respect to the correction coefficient K ₀₂
RSP is added or special I term IRSP is decremented. However, in step 213, the time TL, T
While R is measured, it is not measured in step 212. This is because the duration of waiting for reversal after the start depends on the timing at which the monitor is permitted, and it is meaningless to measure the times TL and TR.

FIG. 6 shows the pre-monitoring condition of step 201 in the flow chart of FIG.
At 01, the operating state of the engine E for starting monitoring is confirmed. That is, the output Ta of the intake air temperature sensor 8 is 60 ° C.
Is in the range of up to 100 ° C., or the output T of the cooling water temperature sensor 9
w is in the range of 60 ° C. to 100 ° C., or the output Ne of the engine speed sensor 10 is 2800 rpm to 3200 rp
m range or output P of the absolute pressure sensor 7 in the intake pipe
b is in the range of -350 mmHg to -250 mmHg, or the output Vh of the vehicle speed sensor 11 is 32 km / h to 80 k.
m / h range, output of catalyst temperature sensor 13 TCA
It is checked whether T is in the range of 350 ° C to 800 ° C. Next, at step 302, is the vehicle speed constant?
That is, the fluctuation of the output Vh of the vehicle speed sensor 11 is 0.8 km.
It is determined whether the state of / sec or less continues for a predetermined time (for example, 2 seconds). Next, at step 303, it is judged if the feedback control has been performed for a predetermined time (for example, 10 seconds) before the monitor is permitted. Further step 30
At 4, it is determined whether a predetermined time (for example, 2 seconds) has elapsed.

If all the answers in the above steps 301 to 304 are (Yes), the monitor is permitted in step 305, and the process proceeds to step 204 in the flowchart of FIG. 5, and any answer is (No). If, then step 30
In step 6, the monitor is not permitted, and the process proceeds to step 202 in the flowchart of FIG.

Next, the monitor start processing of step 208 in the flow chart of FIG. 5 will be described. Downstream O ₂
When the O ₂ concentration detected by the sensor RS is in the lean state, proportional control is performed in which the special P term PRSP is added to the immediately preceding value of the correction coefficient Ko ₂ , whereby the air-fuel ratio is stepped to the rich side. To increase. When the O ₂ concentration detected by the downstream O ₂ sensor RS is in a rich state, proportional control for subtracting the special P term PLSP from the immediately preceding value of the correction coefficient Ko ₂ is performed, thereby making the air-fuel ratio lean. Decrease in steps.

Step 21 in the flow chart of FIG.
The reversal waiting process after the start of 2 is performed as follows. This process is executed subsequently to the monitor start process described above. When the O ₂ concentration detected by the downstream O ₂ sensor RS is in the lean state, integral control is performed to add the special I term IRSP to the immediately preceding value of the correction coefficient Ko ₂ , whereby the air-fuel ratio is set to the rich side. Increase in stages. On the other hand, when the O ₂ concentration detected by the downstream O ₂ sensor RS is in a rich state, integral control is performed to subtract the special I term ILSP from the immediately preceding value of the correction coefficient Ko ₂ , thereby making the air-fuel ratio lean. Reduce gradually.

Step 21 of the flow chart of FIG.
The downstream O ₂ sensor inversion waiting process of No. 3 is performed as follows. This processing is performed by the output voltage RVo of the downstream O ₂ sensor RS.
The reversal of ₂ is executed as before. First, it is determined whether the rich delay timer tRD is counting down or timed up. The rich delay timer tRD is composed of a subtraction counter and starts counting down at the moment when the output voltage RVo _{2 of the} downstream O ₂ sensor RS changes from lean to rich with respect to the stoichiometric air-fuel ratio, and the time is up when a predetermined time has elapsed. Then, the count value becomes zero. When the rich delay timer tRD is counting down, integral control for adding the special I term IRSP to the immediately preceding value of the correction coefficient Ko ₂ is performed, thereby gradually increasing the air-fuel ratio to the rich side.

On the other hand, for the first time this time, the rich delay timer t
When the count value of RD becomes zero, the measurement of TL is started and the special P term P from the correction coefficient Ko ₂ is started.
The air-fuel ratio is reduced stepwise toward the lean side by performing proportional control by subtracting LSP. In addition, the rich delay timer t
If TL is being measured when the count value of RD is continuously zero, the correction coefficient Ko ₂ to the special I term ILSP
The air-fuel ratio is gradually reduced to the lean side by performing integral control for subtracting.

When the lean delay timer tLD is counting down, integral control for subtracting the special I term ILSP from the immediately preceding value of the correction coefficient Ko ₂ is performed, whereby the air-fuel ratio is gradually reduced to the lean side. Let

Furthermore, when the count value of the lean delay timer tLD becomes zero for the first time this time, the measurement of TR is started and the proportional control for adding the special P term PRSP to the correction coefficient Ko ₂ is performed to change the air-fuel ratio. Increase stepwise on the rich side. Further, during the measurement of TR when the count value of the lean delay timer tLD is continuously zero, integral control for adding the special I term IRSP to the correction coefficient Ko ₂ is performed to gradually increase the air-fuel ratio to the rich side. To increase.

Step 21 of the flow chart of FIG.
The process of inverting the O ₂ sensor on the downstream side of 0 is performed as follows. This process is executed after the downstream O ₂ sensor RS is inverted. First, when the previous TL was being measured, T
The measurement of L is stopped, the TL measured this time is added to the TL total value TLSUM, and the TL measurement number nTL is incremented.

On the other hand, when the previous TR measurement is in progress when the previous TR measurement is in progress, the TR measurement is stopped and T
The TR measured this time is added to the R total value TRSUM, and the TR measurement number nTR is incremented.

Then, nTR is 1 and nTL is 0.
, Then TRSUM is set to zero. This is to cancel the TR if the TR is measured first because the measurement is performed in the order of TL → TR.

Then, the output voltage RVo ₂ is changed to the reference voltage VREF.
When it is less than, the lean delay timer tLD is started to count down, and the integral control is performed to subtract the special I term ILSP from the immediately preceding value of the correction coefficient Ko ₂ , whereby the air-fuel ratio is gradually reduced to the lean side. Let

On the other hand, when the output voltage RVo ₂ is equal to or higher than the reference voltage VREF, the rich delay timer tRD starts counting down, and the integral control for adding the special I term IRSP from the value immediately before the correction coefficient Ko ₂ is performed. This gradually increases the air-fuel ratio to the rich side.

FIG. 7 shows the subroutine of step 214 in FIG. 5. First, at step 401, it is judged if the limit time tSTRG has elapsed without the next inversion after the special P term is generated. Where the limit time tSTRG
The average value of TL and TR (TL
+ TR) / 2 is used. And this average value (TL
If + TR) / 2 is longer than the limit time tSTRG, it is determined that the O ₂ storage capacity of the catalyst C is large, and the catalyst C is a good product in step 402 without executing the deterioration determination processing device B described above. Is determined.

The reason why it is possible to determine that the catalyst C is a good product in the deterioration determination process A is as follows. That is, a small degree of deterioration of the catalyst C higher O ₂ storage capability, the downstream O ₂ sensor RS when performing the feedback control using only the output signal of the downstream O ₂ sensor RS
The inversion period of is extended. Therefore, the downstream O ₂ sensor R
If the average value of the times TL and TR until S is reversed is larger than the limit time tSTRG, it can be determined that the catalyst C is a good product. Further, it is known that if the catalyst C is a good product and the inversion period is long, the drivability is deteriorated and harmful substances in the exhaust gas are increased. Therefore, when the catalyst C is a non-defective product, the inconvenience can be avoided by immediately stopping the monitor mode and switching the normal feedback control.

FIG. 8 shows a characteristic part of the present invention, and FIG.
21 shows the deterioration determination process B in step 205 of the flowchart of FIG. 7, and this flow is executed when the TR measurement number nTR exceeds a predetermined number. First, step 5
In 01, the determination value TCHKG corresponding to the catalyst temperature detected by the catalyst temperature sensor 13 is searched by the determination value table shown in FIG. Here, the judgment value table of FIG.
For example, it is created according to the temperature characteristic of the catalyst as shown in FIG.
It has a slope that rises to the right in the range of T1 (for example, 600 ° C.). Next, in step 502, the value obtained by dividing the TL total value by the TL measurement number (TLSUM / nTL) and the TR total value are TR.
The time TCHK is calculated by calculating the average value of the values (TRSUM / nTR) divided by the number of measurements.

Then, at step 503, the time TCHK
Is larger than the judgment value TCHKG retrieved in step 501, and if the answer is (Yes), the O ₂ storage capacity of the catalyst C is above the reference, and in step 504. It is determined that the exhaust gas purification system is normal. On the other hand, when the answer to step 503 is (No), it is determined that the O ₂ storage capacity of the catalyst C is below the reference, and it is determined in step 505 that the exhaust gas purification system is abnormal.

By using the judgment table in this way, the deterioration judgment value can be corrected in accordance with the temperature characteristic of the catalyst,
Erroneous determination can be prevented by monitoring deterioration at any catalyst temperature.
Further, as shown by A to B in FIG.
_{2 If the} catalyst temperature region where deterioration of the storage capacity is easily discriminated is limited and the region is used as the deterioration monitor region and the deterioration judgment value is corrected, the deterioration judgment can be made with higher accuracy.

Further, in this embodiment, the catalyst temperature sensor 13
Since the temperature measuring part of _{No. 2} was mounted between the beds C ₁ and C ₂ of the catalyst C,
It has the following advantages.

As shown in FIG. 11 (a), the catalyst temperature sensor used conventionally is used as an exhaust temperature warning light sensor for the purpose of detecting an abnormal temperature rise of the catalyst. In the case of a two-bed type catalyst in which the front bed C1 and the rear bed C2 are arranged in series at a predetermined interval, the exhaust temperature warning light sensor 13-1 is provided in the end cone portion C3 immediately after the rear bed. It is general.

As described above, when the catalyst temperature sensor is provided in the end cone portion C3 immediately after the rear bed, as shown in FIG.
As shown in (b), as the temperature of the catalyst bed increases,
The error between the actual temperature of the catalyst bed and the temperature detected by the sensor 13-1 tends to increase. Further, as is clear from the exhaust gas temperature distribution in the radial direction in the encoding section C3 shown in FIG. 12, the temperature gradient changes when the engine load changes. That is, reference numerals A to D in FIG. 12 are temperature measurement points in the end cone portion C3, and these temperature measurement points A to
The temperature difference between the temperature measured at D and the floor temperature of the front bed C1 is, for example, 35 km / h, 80 km / h, 1
When the load is changed to 10 km / h and 140 km / h, the temperature changes as shown in the figure.

Thus, in the case where the catalyst temperature sensor is provided in the end cone portion C3 immediately after the rear bed,
There is a problem that the accuracy of the exhaust temperature detected due to the influence of the exhaust gas flow due to the shape of the end cone portion C3 and the influence of the gas flow due to the exhaust pulsation becomes low. If the detected exhaust temperature is not accurate, an error will occur in the above-mentioned deterioration determination value, and it will not be possible to make a highly accurate catalyst deterioration determination.Therefore, the catalyst temperature sensor will make a highly accurate catalyst deterioration determination. It becomes an important factor.

Considering this point, in this embodiment, the catalyst temperature sensor 13 is mounted between the catalyst beds C1 and C2 as described above. As a result, the catalyst temperature sensor can be placed in a stable gas flow, so that the catalyst bed temperature can be detected stably and accurately even when the load or the like changes. Moreover, the thermistor 13 which is the temperature detecting portion of the catalyst temperature sensor 13
Since a is located substantially in the center of the catalyst C in the axial direction, the influence of the gas flow due to exhaust pulsation is small, and stable and highly accurate temperature detection can be performed. This point is shown in FIG. 13 and FIG.
It is also clear from 4. That is, FIG. 13 shows the exhaust gas temperature distribution in the radial direction (temperature measuring points A to G) between the beds C1 and C2 of the catalyst C, in which the temperature gradient is small even if the engine load changes. The closer to the temperature measurement points (for example, D and E) near the top and center, the smaller the temperature difference between the temperature measured there and the floor temperature of the front bed C1. In addition, FIG. 14 is a graph showing the floor temperature of the front bed C1 in FIG.
3 is a diagram showing a gas temperature difference (temperature difference from the bed temperature of the front bed C1) at each of the temperature measurement points A to E of FIG. 3, and the front bed B1 becomes closer to a temperature measurement point (eg, D, E) near the center. The difference in the gas temperature difference with respect to the change in the bed temperature becomes small.

Further, in this embodiment, the bet interval C
Since the distance between 1 and C2 is set to 25 mm, the influence of heat drawing (lowering the exhaust gas temperature at the temperature measuring point when the outside air is low) is eliminated, and more accurate temperature detection becomes possible. This point is made clear by FIG. That is, FIG.
Shows a gas temperature difference with respect to the bed temperature of the front bed C1 in a state where the space between the beds is 25 mm and the catalyst is not covered with a cover, a state where the space between the beds is 45 mm in which the cover and the heat insulating material are mounted on the catalyst b, and It is the figure which compared with the state c which the space | interval was 45 mm and the cover was not attached to the catalyst.
It can be seen that the state a is stable with the least variation in the gas temperature difference.

Next, a second embodiment of the present invention will be described.

In this embodiment, instead of using the catalyst temperature sensor 13 to detect the catalyst temperature as in the first embodiment, the catalyst temperature is estimated and obtained according to the operating condition of the engine. ..

First, in step 601, the equilibrium catalyst temperature Tb is calculated by the following equation (2).

[0079]

[Equation 1] Here, Ne is the engine speed and TOUT is the fuel injection valve 5.
Fuel injection time and A / F represent the air-fuel ratio, and K, a,
Both b and c are constants experimentally determined.

Further, in the following step 602, the equilibrium catalyst temperature Tb calculated in step 601 is averaged by the following equation (3) to calculate the current catalyst temperature TCATn.

[0081]

[Equation 2] Here, CREFT is the average value (TCATn
-1) weighting coefficient, which is set to an appropriate value from 1 to 2 ¹⁶ .

By calculating the catalyst temperature in this way, the same effect as that of the first embodiment can be obtained without providing the catalyst temperature sensor 13. That is, in the first embodiment, since the temperature of the catalyst C is directly detected by the catalyst temperature sensor 13, there is an advantage that the temperature detection accuracy is relatively high, but it is expensive as the accuracy and responsiveness are pursued. It is necessary to add a sensor, and improvement in cost is desired.
Further, the catalyst temperature sensor 13 is often attached to the underfloor portion of the vehicle body, and it is necessary to take into account water splashes, flying stones, etc., which is problematic in terms of durability and reliability of the sensor. From this point of view, in the present embodiment which does not use the catalyst temperature sensor, it is possible to realize an inexpensive catalyst deterioration determination device adapted to the temperature characteristics of the catalyst.

FIG. 17 is a diagram showing an outline of the area difference method of the third embodiment of the present invention, and the outline of the present embodiment will be described below with reference to this drawing.

First, when the two O ₂ sensors FS and RS are normal and activated and the engine E is in the normal operation mode after the start operation mode, the fuel cut is performed.
(F / C) Average value VCHKF of output values FVo ₂ and RVo ₂ of the O ₂ sensors FS and RS on the upstream and downstream sides of the catalyst C during operation
L, and respectively calculates VCHKRL, also high-load (WOT) O ₂ sensor FS during operation, RS output value FVO _2, RVO ₂ of average VCHKFH, respectively calculating VCHKRH (Figure 17b,
c).

[0085] The cruising of the vehicle continues for a predetermined time, the engine executes the perturbation of the air-fuel ratio correction coefficient Ko ₂ when in a predetermined operating condition, for example, the value of the coefficient Ko _2, the average value of the coefficient Ko ₂ Change ± 4 to 10% around 0.
Invert every 5 seconds (Fig. 17a). Due to this perturbation, exhaust gas from which the oxygen concentration has fluctuated steadily is discharged from the engine E, which is the O ₂ sensor F.
It is detected by S and RS (FIGS. 17b and 17c).

Output values FVo ₂ and RVo _{2 of} the O ₂ sensors FS and RS thus obtained and the average values VCHKFL and VCHKR.
Based on L, VCHKFH, VCHKRH, a predetermined time tMES from the time when the coefficient Ko ₂ rises substantially during the perturbation.
(Figure 17d), FVo _2, VCHKFL, the area of the portion surrounded by the VCHKFH SQRF and RVo _2, VCHKRL, area SQRR of the portion surrounded by the respective calculated by VCHKRH (Figure 17e,
f). The area calculation is repeated during the perturbation.

If the output value FVo _{2 of the} upstream O ₂ sensor FS is between the upper and lower limit values VCHKFH and VCHKFL, the following equation (4)
Based on the above, the upstream side area SQRF is calculated.

SQRF ← SQRF + Vo ₂ F−VCHKFL (4) On the other hand, the output value FVo _{2 of the} upstream O ₂ sensor FS is the upper limit value VC.
If it is HKFH or more, the upstream side area SQRF is calculated based on the following equation (5).

SQRF ← SQRF + VCHKFH−VCHKFL (5) It should be noted that SQRF on the right side of the equations (4) and (5) is given an initial value 0, and is based on the equations (4) and (5) up to the previous time, respectively. It is the calculated upstream area. On the other hand, if the output value FVo _{2 of} the upstream O ₂ sensor FS is not less than the upper limit value VCHKFH, the upstream area SQRF is calculated based on the following equation (5).

SQRF ← SQRF + VCHKFH−VCHKFL (5) It should be noted that SQRF on the right side of the equations (4) and (5) is given an initial value of 0 and is based on the equations (4) and (5) up to the previous time, respectively. It is the calculated upstream area.

On the other hand, the output value RVo of the downstream O ₂ sensor RS
_{If 2} is between the upper and lower limit values VCHKRH and VCHKRL, the upstream area SQRR is calculated based on the following equation (6).

SQRR ← SQRR + Vo ₂ R−VCHKRL (6) Further, the output value RVo _{2 of the} downstream O ₂ sensor RS is the upper limit value VC.
If it is HKRH or more, the upstream area SQRR is calculated based on the following formula (7).

SQRR ← SQRR + VCHKRH−VCHKRL (7) It should be noted that SQRR on the right side of the equations (6) and (7) is given an initial value of 0, and is based on the equations (6) and (7) up to the previous time, respectively. It is the calculated downstream area.

When the deviation between the areas SQRF and SQRR thus obtained is smaller than the predetermined reference value, it is determined that the exhaust gas purification performance of the catalyst C is deteriorated.

As described above, the average values VCHKFL, VCHKRL of the output values of the O ₂ sensors FS, RS on the upstream and downstream sides of the catalyst C during the fuel cut operation are calculated, and the O ₂ sensor during the high load operation is calculated. The average value VCHKFH of the output values of FS and RS,
VCHKRH is calculated, and the area SQR is calculated based on these average values.
By calculating F, SQRR, the deviation of the area is eliminated, that is, corrected by the influence of individual difference in the performance of the O ₂ sensors FS, RS, and therefore the performance deterioration of the catalyst C is determined by O _2. It becomes possible to perform accurately by eliminating the influence of the individual difference of the sensor.

Next, the catalyst deterioration determination routine of this embodiment will be described with reference to FIG.

First, at step 701, the reference value VCHKFH,
Using VCHKFL, VCHKRH, and VCHKRL, the following equations (8), (9)
The fluctuation range DELTA of the output value of the upstream O ₂ sensor FS based on
The fluctuation range DELTAR of the output value of F and the downstream O ₂ sensor RS is calculated.

DELTAF ← VCHKFH−VCHKFL (8) DELTAR ← VCHKRH−VCHKRL (9) The area SQRR obtained by the above equation (7) is calculated based on the following equation (10) using these calculated fluctuation ranges. Correct and calculate the change value SQRRARE (step 602)

[0099]

[Equation 3] The SQRRARE calculated as described above can be said to be a value obtained by removing the individual difference between the output values of the upstream and downstream O ₂ sensors FS and RS included in SQRR. The above formula
In (10), the downstream area SQRR is corrected by the fluctuation width ratio, but the upstream area SQRF may be corrected by the reciprocal of the fluctuation width ratio.

In the next step 703, step 702
The deviation SQR DIF is calculated based on the following equation (11) using the downstream area change value SQRRARE calculated in step (4) and the upstream area SQRF calculated in equation (5).

SQRDIF ← SQRF-SQRARE (11) In step 704, the deterioration determination value SQRLMT corresponding to the catalyst temperature detected by the catalyst temperature sensor 13 is set as shown in FIG.
Search using the judgment value table shown in. This judgment value table is created in accordance with the temperature characteristics of the catalyst as shown in FIG.
It has a slope rising to the right in the range of TO (eg 350 ° C.) to TCAT1 (eg 600 ° C.).

Deviation SQRDI calculated by the above equation (11)
F is the deterioration determination reference value SQRL retrieved in step 704.
Step 7: Check if it is smaller than MT (eg 2.0 Vsec)
Judge with 05. If this answer is negative (No), that is, S
If QRDIF is equal to or higher than SQRLMT, it is determined that the performance of the catalyst C is not deteriorated, and the program of this routine is ended. On the other hand, if the answer to step 705 is affirmative (Yes), the process proceeds to step 706.

At step 706, it is judged if the temperature TCAT of the catalyst C detected by the catalyst temperature sensor 13 is higher than the first judgment value TCATLMT ₁ . This first discriminant value TCATLMT
₁ is set to the temperature (for example, 560 ° C.) of the catalyst C when the HC purification rate ηHC of the catalyst C is 50%. If the answer to step 706 is affirmative (Yes), that is, the catalyst temperature TCAT is higher than the first determination value TCATLMT _1, step 705 is performed.
If the answer is affirmative, it is determined that an abnormality has occurred in the purification performance of the catalyst C, and the flag F-C indicating the abnormality by 1 is given.
ATNG is set to 1 (step 707), and based on the setting, for example, an LED is turned on to issue an alarm, and the program of this routine ends.

On the other hand, the answer to step 706 is negative (No).
Then, it is determined whether or not the catalyst temperature TCAT is lower than the second determination value TCATLMT ₂ (step 708). This second discriminant value TCATLMT ₂ is a value that is set according to the engine speed Ne and the intake pipe absolute pressure PBA based on the table shown in FIG. 20, and the higher the engine speed Ne, the more the absolute pressure PBA increases. The larger the value, the larger the value set. If the answer to this step 708 is affirmative (Yes), that is, the catalyst temperature T
If CAT is lower than the catalyst temperature TCATLMT ₂ that should be under the engine load condition at that time, it is determined that the purification performance of the catalyst C is deteriorated, and the process proceeds to step 707, while if the answer to step 708 is negative (No), That is, the catalyst temperature TCA
If T is so low that the HC purification rate ηHC 50% cannot be secured (the answer in step 706 is negative) and the catalyst temperature that should be under the engine load condition at that time is reached, even if the answer in step 705 is positive, the catalyst C It is judged that there is no abnormality in performance, and the program of this routine is terminated without setting the flag F-CATNG to 1.

In this embodiment, since the deterioration judgment value SQRLMT is searched from the judgment value table of FIG.
It has the following advantages.

As described above, the O ₂ storage capacity of the catalyst C changes depending on the catalyst temperature TCAT. When the O ₂ storage capacity decreases, the inversion cycle of the downstream O ₂ sensor RS becomes short and the downstream area SQRR becomes large. Therefore, the difference between the downstream area SQRR and the upstream side SQRR becomes small, and the catalyst temperature TCAT must be set in order to make a highly accurate deterioration determination.
It is necessary to decrease the deterioration determination value SQRLMT as the value decreases. In the present embodiment, this is realized by the discriminant value table shown in FIG. 19, so that highly accurate deterioration determination can be performed.

The present invention is not limited to the illustrated embodiment, but various modifications can be made. Examples of such modifications include the following.

[0108] (1) In the above embodiment, were subjected to deterioration determination without using the output of the upstream O ₂ sensor FS using only the output of the downstream O ₂ sensor RF, both O ₂ sensor FS,
The present invention can also be applied to a method of determining deterioration based on the output of RS.

(2) In the above embodiment, the judgment value of the O ₂ storage capacity is decided by the table.
The determination value can be calculated based on the catalyst temperature. It is also possible to correct the detected O ₂ storage capacity by the catalyst temperature, and in this case also, the same effect as in the above embodiment can be obtained.

(3) The catalyst C used in the above embodiment is composed of the beds C1 and C2 having substantially the same size. However, as shown in FIG. 21, for example, the size of the bed C1 is larger than that of the bed C2. Any catalyst may be used. Further, as shown in FIG. 22, the beds C1 having substantially the same size are provided.
You may use the catalyst comprised by C2 and C3.

(4) The present invention can be applied to all methods for detecting catalyst deterioration based on the O ₂ storage capacity of the catalyst.

[0112]

As described above, the first and second
According to the invention, since the judgment value corresponding to the temperature of the catalyst is used, the judgment value corresponding to the temperature characteristic of the catalyst can be corrected, and erroneous judgment can be prevented regardless of which catalyst temperature the deterioration is monitored. Further, if the catalyst temperature region where it is easy to determine the deterioration of the O ₂ storage capacity due to the catalyst deterioration is defined and the region is set as the deterioration monitor region, the judgment can be performed with higher accuracy.

According to the third invention, since the catalyst temperature detecting means detects the temperature of the central portion of the catalyst means, the catalyst temperature sensor can be placed in a stable gas flow, so that the engine load or the like changes. Even then, the bed temperature of the catalyst can be detected stably and accurately.

According to the fourth and fifth inventions, instead of detecting the catalyst temperature by using the catalyst temperature detecting means as in the first to third inventions, the catalyst temperature is estimated according to the operating state of the engine. As a result, the judgment value corresponding to the temperature characteristic of the catalyst can be corrected without using the catalyst temperature sensor, and an inexpensive catalyst detection device suitable for the temperature characteristic of the catalyst can be realized.

According to the sixth aspect of the invention, the temperature of the catalyst is estimated based on at least the engine speed, the load of the engine, and the air-fuel ratio supplied to the engine, so that the temperature can be estimated with high accuracy.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a fuel supply device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a catalyst C in FIG.

FIG. 3 is a flowchart of a program for setting a correction coefficient Ko2.

FIG. 4 is a flowchart of a program for setting a correction coefficient Ko2.

FIG. 5 is a flowchart for explaining a schematic configuration of a catalyst deterioration monitor.

FIG. 6 is a flowchart showing processing of pre-monitoring conditions in FIG.

FIG. 7 is a flowchart showing deterioration determination processing A in FIG.

FIG. 8 is a flowchart showing deterioration determination processing B in FIG.

9 is a diagram showing a determination value table used in deterioration determination processing B in FIG.

FIG. 10 is an explanatory diagram for explaining the effect of the first embodiment.

FIG. 11 is another explanatory diagram for explaining the effect of the first embodiment.

FIG. 12 is another explanatory diagram for explaining the effect of the first embodiment.

FIG. 13 is another explanatory diagram for explaining the effect of the first embodiment.

FIG. 14 is another explanatory diagram for explaining the effect of the first embodiment.

FIG. 15 is another explanatory diagram for explaining the effect of the first embodiment.

FIG. 16 is a flowchart showing a CAT temperature calculation process according to the second embodiment of the present invention.

FIG. 17 is a diagram showing an outline of an area difference method according to a third embodiment of the present invention.

FIG. 18 is a diagram illustrating a catalyst deterioration determination routine according to a third embodiment of this invention.

FIG. 19 is a diagram showing a judgment value table used in FIG. 17;

20 is a diagram showing a table of a judgment value TCATLMT2 in FIG.

FIG. 21 is a view showing a modified example of the catalyst C.

FIG. 22 is a diagram showing another modification of the catalyst C.

FIG. 23 is a diagram showing OSC with respect to CAT temperature.

[Explanation of symbols]

13 catalyst temperature sensor (catalyst temperature detection means) C catalyst E engine FS upstream O ₂ sensor (upstream oxygen concentration detection means) RS downstream O ₂ sensor (downstream oxygen concentration detection means) 15 CPU (discrimination value determination means, Operating state detection means, catalyst temperature estimation means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location F02D 45/00 360 C 7536-3G G01M 15/00 Z 7324-2G (72) Inventor Toshihiko Sato Saitama 1-4-1 Chuo, Wako-shi, Waka Prefectural Honda R & D Co., Ltd. (72) Inventor Makoto Kobayashi 1-4-1 Chuo, Wako-shi, Saitama Inside Honda R & D Co., Ltd.

Claims (6)

[Claims] 1. A catalyst means installed in an exhaust system of an internal combustion engine for purifying harmful components in exhaust gas, and an oxygen concentration detection means installed downstream of the catalyst means for detecting oxygen concentration in the exhaust gas. In a catalyst deterioration detecting device for an internal combustion engine, which detects deterioration of the catalyst means based on an output of the oxygen concentration detecting means and a predetermined discriminant value, a catalyst temperature detecting means for detecting a temperature of the catalyst means, and the catalyst temperature detecting means. A catalyst deterioration detecting device for an internal combustion engine, comprising: a discriminant value determining means for determining the discriminant value in accordance with the temperature of the catalyst means detected by. 2. A catalyst means attached to an exhaust system of an internal combustion engine to purify harmful components in exhaust gas, and an upstream oxygen concentration detection means attached to an upstream side of the catalyst means to detect oxygen concentration in the exhaust gas. A downstream side oxygen concentration detecting means attached to a downstream side of the catalyst means for detecting an oxygen concentration in exhaust gas, and the catalyst means based on outputs of the upstream side and downstream side oxygen concentration detecting means and a predetermined discriminant value. In a catalyst deterioration detecting device for an internal combustion engine for detecting deterioration of the catalyst, the catalyst temperature detecting means for detecting the temperature of the catalyst means, and the discriminant value corresponding to the temperature of the catalyst means detected by the catalyst temperature detecting means are determined. And a discriminant value deciding means for operating the catalyst deterioration detecting device for an internal combustion engine. 3. The catalyst deterioration detection for an internal combustion engine according to claim 1, wherein the catalyst temperature detection means is attached to a part of the catalyst means and detects the temperature of the central portion of the catalyst means. apparatus. 4. A catalyst means installed in an exhaust system of an internal combustion engine for purifying harmful components in exhaust gas, and an oxygen concentration detection means installed downstream of the catalyst means for detecting oxygen concentration in the exhaust gas. In a catalyst deterioration detecting device for an internal combustion engine, which detects deterioration of the catalyst means based on an output of an oxygen concentration detecting means and a predetermined discriminant value, an operating state detecting means for detecting an operating state of the engine, and the operating state detecting means. Catalyst temperature estimating means for estimating the temperature of the catalyst means according to the operating state of the engine detected by, and determination value determination for determining the determination value according to the temperature of the catalyst means estimated by the catalyst temperature estimating means And a catalyst deterioration detecting device for an internal combustion engine. 5. A catalyst means attached to an exhaust system of an internal combustion engine to purify harmful components in exhaust gas, and an upstream oxygen concentration detection means attached to an upstream side of the catalyst means to detect oxygen concentration in the exhaust gas. A downstream side oxygen concentration detecting means attached to a downstream side of the catalyst means for detecting an oxygen concentration in exhaust gas, and the catalyst means based on outputs of the upstream side and downstream side oxygen concentration detecting means and a predetermined discriminant value. In a catalyst deterioration detection device for an internal combustion engine that detects the deterioration of, the operating state detecting means for detecting the operating state of the engine, and the temperature of the catalyst means according to the operating state of the engine detected by the operating state detecting means. It has a catalyst temperature estimating means for estimating and a discriminant value determining means for determining the discriminant value according to the temperature of the catalyst means estimated by the catalyst temperature estimating means. A catalyst deterioration detection device for an internal combustion engine. 6. The operating condition detecting means detects an engine speed and an engine load, or an intake air amount drawn into the engine as an operating condition of the engine, and the catalyst temperature estimating means detects the engine speed. 6. The catalyst deterioration detecting device for an internal combustion engine according to claim 4, wherein the temperature of the catalyst means is estimated based on the number of the engine, the load of the engine, or the amount of intake air taken into the engine.