JP2938288B2 - Catalyst deterioration detection device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine for detecting deterioration of a catalyst based on air-fuel ratio signals from two air-fuel ratio sensors provided before and after a catalytic converter (hereinafter simply referred to as a catalyst) in an exhaust pipe. More particularly, the present invention relates to a catalyst deterioration detection device for an internal combustion engine that suppresses variations in deterioration parameter values due to differences in output characteristics, operating conditions, and the like of an air-fuel ratio sensor and improves reliability of deterioration determination. .

[0002]

2. Description of the Related Art Generally, a fuel injection amount of an internal combustion engine is adjusted to a specific component (for example, O ₂ ) in an exhaust pipe so that an air-fuel ratio of an air-fuel mixture becomes an optimum value (for example, about 14.7) according to an operating state. Feedback control is performed by a signal from the air-fuel ratio sensor that detects the concentration.

Usually, the oxygen concentration in the exhaust gas air-fuel ratio of the mixture is reduced in the case of lower richer than 14.7, so increases in the case of lean, the output signal of the O ₂ sensor, air-fuel ratio In response to an oxygen concentration corresponding to 14.7, the voltage level varies between 0 and 1. For example, when the air-fuel ratio is rich, the voltage value of the output signal (air-fuel ratio signal) of the air-fuel ratio sensor increases as the oxygen concentration decreases.

Although a catalyst for purifying exhaust gas is inserted into the exhaust pipe, when a single air-fuel ratio sensor is provided only on the upstream side of the catalyst, the output characteristic (operating point) of the air-fuel ratio sensor is provided.
, The control accuracy is hindered. Therefore,
An air-fuel ratio control device has been proposed in which another air-fuel ratio sensor is provided also on the downstream side of the catalyst and performs feedback control based on the air-fuel ratio signal on the downstream side in addition to feedback control based on the air-fuel ratio signal on the upstream side of the catalyst.

In this case, the air-fuel ratio sensor on the downstream side of the catalyst detects the exhaust gas having the oxygen concentration averaged after the catalytic reaction, and the deterioration due to the exhaust gas is reduced.
High-precision air-fuel ratio feedback control is enabled, and it is possible to compensate for variations in the air-fuel ratio sensor and injectors (fuel injection valves) and changes over time in output characteristics. Such a dual air-fuel ratio sensor system is described, for example, in U.S. Pat.
No. 39,654.

[0006] On the other hand, the catalyst is designed so that its function does not significantly deteriorate as long as it is used within a normal vehicle condition range. However, in the case of misfire due to some abnormality, for example, it is exposed to unburned gas. Therefore, the function may be significantly reduced. As a result, the catalyst becomes to continue running without purify sufficient exhaust gas, HC, CO, the behavior of the output of the air-fuel ratio sensor on the downstream side under the influence of unburnt gas such as H ₂ changes. That is, the degree of change of the air-fuel ratio signal from the air-fuel ratio sensor on the downstream side becomes large, and the emission (exhaust gas purification performance) is reduced.

Therefore, it is important to detect the deterioration of the function due to the deterioration of the catalyst, and it is necessary to immediately alert the driver when the deterioration of the catalyst is detected. Conventionally, there has been proposed a catalyst deterioration detecting device as disclosed in Japanese Patent Application No. 3-264312 by the present applicant. That is, the air-fuel ratio signals from the sensors before and after the catalyst are compared with the respective reference values, the area (integral value) equivalent value δ of the figure formed by the deviation, the number n of times the reference value is crossed, the inversion period τ, or , 2
Period ratio γ [= of each inversion period τ for two air-fuel ratio signals
τ ₁ (upstream side) / τ ₂ (downstream side)] are calculated as deterioration parameter values, and these deterioration parameter values are compared with a predetermined value. When the deterioration parameter value exceeds a predetermined value, catalyst deterioration is determined. Can be determined.

FIG. 15 is a block diagram showing an example of a general catalyst deterioration detecting device for an internal combustion engine provided with air-fuel ratio sensors before and after the catalyst (upstream and downstream). In the figure, 1 is an internal combustion engine, that is, an engine, 2 is an intake pipe for supplying an air-fuel mixture to the engine 1, 3 is an air cleaner provided at an intake port on the upstream side of the intake pipe 2, 4 is a downstream side of the intake pipe 2 and the engine 1 is an intake manifold formed at a connection portion with 1, and 5 is an intake pipe 2
Is an injector for fuel injection provided upstream of the fuel injector.

6 is a pressure P in the intake manifold 4
, Which measures the amount of air taken into the engine 1 from the intake pipe 2 via the intake manifold 4 as a pressure P. Reference numeral 7 denotes a throttle valve provided on the downstream side of the injector 5 in the intake pipe 2.

Reference numeral 8 denotes a throttle sensor for detecting the throttle opening φ of the throttle valve 7, reference numeral 9 denotes an exhaust pipe for taking out exhaust gas after combustion from the engine 1, and reference numeral 10 denotes a three-way exhaust gas inserted into the exhaust pipe 9 to process the exhaust gas. The reference numeral 11 denotes a first air-fuel ratio sensor provided on the upstream side of the catalyst 10, and 12 denotes a second air-fuel ratio sensor provided on the downstream side of the catalyst 10.

Reference numeral 13 denotes an ignition coil comprising a step-up transformer, 14
Is an igniter composed of a power transistor for interrupting the primary winding of the ignition coil 13. Reference numeral 15 denotes an idle switch integrated with the throttle sensor 8, which detects an idling operation state and turns on when the throttle valve 7 is fully closed. Reference numeral 16 denotes a thermistor-type water temperature sensor for detecting a cooling water temperature T of the engine 1, reference numeral 17 denotes a battery serving as a power supply, reference numeral 18 denotes a key switch for starting power supply from the battery 17, and starting ignition, and reference numeral 19 denotes deterioration of the catalyst 10. It is an alarm generating means, that is, an alarm lamp, which is driven when an abnormality is detected such as at the time of detection.

Reference numeral 20 denotes an electronic control unit (ECU) for driving and controlling the injector 5, the alarm lamp 19, and the like in accordance with various operation states. The operation state signal Q from various sensors (not shown) is used as the operation state. , The throttle opening φ from the throttle sensor 8, the pressure P in the intake manifold 4 from the pressure sensor 6, the cooling water temperature T from the water temperature sensor 16, the idle signal D from the idle switch 15, and the cutoff of energization of the ignition coil 13. Based on the rotation signal R, the air-fuel ratio signals V1 and V2 from the air-fuel ratio sensors 11 and 12 are input.

The ECU 20 functions by being supplied with power from the battery 17 when the key switch 18 is closed, generates the fuel injection signal J for the injector 5 in response to the air-fuel ratio signals V1 and V2 and the operating state, and feeds back the air-fuel ratio. It includes an air-fuel ratio control means for controlling and a catalyst deterioration determining means for generating an abnormal signal E for the alarm lamp 19 when deterioration of the catalyst 10 is detected. The ignition signal for the igniter 14 is
It may be generated from the ECU 20.

FIG. 16 is a block diagram showing a specific functional configuration of the ECU 20, in which 21 is an input interface for shaping the waveform of the rotation signal R into an interrupt signal INT, and 22 is an air-fuel ratio signal.
V1, V2, pressure P, water temperature T and throttle opening φ input interface, input interface 23 for capturing idle signal D, output interface 24 for outputting abnormal signal E, fuel injection signal J, etc., 25 key switch
A power supply circuit connected to the battery 17 via 18, and a microcomputer 30 connected to the input interfaces 21 to 23, the output interface 24 and the power supply circuit 25.

The microcomputer 30 calculates an air-fuel ratio signal V
A CPU 31 that calculates an air-fuel ratio feedback control amount (hereinafter, simply referred to as an air-fuel ratio control amount) according to 1 and V2 and the like;
A free-running counter 32 that measures the rotation cycle of the engine 1 based on the rotation signal R, that is, the interrupt signal INT, via the input interface 21, a timer 33 that performs timekeeping for various controls, and an input interface 22. AD converter 34 that converts the analog signals (the air-fuel ratio signals V1, V2, the pressure P, the water temperature T, and the throttle opening φ) into digital signals.
An input port 35 for taking in an idle signal D via the input interface 23, a RAM 36 used as a work memory of the CPU 31, a ROM 37 storing an operation program of the CPU 31, and various control signals via the output interface 24. Output port 38 for outputting E and J
And a common bus 39 that couples each of the elements 32-38 to the CPU 31.

When an interrupt signal INT is input via the input interface 21, the CPU 31 reads the value of the counter 32 and calculates the rotation cycle of the engine 1 from the difference between the current value of the counter 32 and the previous value. Stored in the RAM 36.
The output interface 24 amplifies the control signal from the output port 38 and outputs it as an abnormal signal E and a fuel injection signal J.

FIG. 17 is a functional block diagram schematically showing the air-fuel ratio control means of the microcomputer 30.
A first PI controller that performs PI (proportional integration) control on the air-fuel ratio signal V1 from the air-fuel ratio sensor 11 is a second PI controller that performs PI control on the air-fuel ratio signal V2 from the air-fuel ratio sensor 12. It is a PI controller.

Each of the PI controllers 41 and 42 constitutes computing means for computing each of the air-fuel ratio control amounts C1 and C2 based on each of the air-fuel ratio signals V1 and V2. Acts as a correction amount for the first air-fuel ratio control amount C1. Further, the first air-fuel ratio control amount C1 corresponds to the air-fuel ratio correction amount, whereby the final fuel injection signal J to the injector 5 is feedback-controlled, and the second air-fuel ratio signal
V2 is made to coincide with the second target value VR2.

VR1 and VR2 are air-fuel ratio signals V1 and V2, respectively.
The first and second target values for air-fuel ratio control are set in advance, and both are set to voltage values substantially corresponding to the optimal air-fuel ratio 14.7, but the second target value VR2 is First
May be set to a voltage value slightly higher than the target value VR1 (corresponding to the rich side, that is, an air-fuel ratio smaller than 14.7).

FR is a basic fuel amount calculated from a pressure P corresponding to an intake air amount, CF is a fuel correction amount corresponding to an acceleration / deceleration state based on a water temperature T and a throttle opening φ, and KF is an injector 5 for a target fuel amount. Injection time correction coefficient,
Q is a dead time correction amount for the driving time of the injector 5.

Reference numeral 43 denotes a subtractor for obtaining a deviation ΔV2 between the second target value VR2 and the air-fuel ratio signal V2 and inputting the difference ΔV2 to the second PI controller 42. Reference numeral 44 denotes a second air-fuel ratio control for the first target value VR1. Quantity C2
Is a subtractor that calculates a deviation ΔV1 between the correction target value VT1 and the air-fuel ratio signal V1 and inputs the deviation ΔV1 to the first PI controller 41. Adder 44
Constitutes a correction means for correcting the air-fuel ratio control amount C1 calculated by the first PI controller 41.

A target fuel amount F1 is obtained by multiplying an air-fuel ratio control amount C1 from the first PI controller 41 by a basic fuel amount FR.
, And 47 is a fuel correction amount C for the target fuel amount F1.
F is a multiplier that generates the corrected fuel amount F by multiplying F, 48 is a multiplier that generates the drive time G of the injector 5 by multiplying the corrected fuel amount F by the injection time correction coefficient KF, and 49 is a wasteful drive time G. This is an adder that adds the time correction amount Q to generate a final fuel injection signal J for the injector 5. The multipliers 46 to 48 and the adder 49 constitute control amount conversion means for converting the air-fuel ratio control amount C1 into the fuel injection signal J.

Next, the air-fuel ratio control operation and the catalyst deterioration judgment operation by the microcomputer 30 will be described with reference to the waveform diagrams of FIGS. 18 to 21 together with FIGS.
First, the subtractor 43 in the air-fuel ratio control means compares the second air-fuel ratio signal V2 on the downstream side of the catalyst 10 with the second target value VR2 to generate a deviation ΔV2 (= VR2−V2), The second PI controller 42 calculates the air-fuel ratio control amount C2 by performing PI control on the deviation ΔV2.

On the other hand, the adder 44 adds the air-fuel ratio control amount C2, that is, the correction amount, to the first target value VR1, and the first air-fuel ratio sensor
A correction target value VT1 (= VR1 + C2) for 11 is generated.
Further, the subtractor 45 outputs the first air-fuel ratio signal V on the upstream side of the catalyst 10.
1 and the correction target value VT1 to compare the deviation ΔV1 (= VT1−V
1), and the first PI controller 41 performs PI control on the deviation ΔV1 to calculate the air-fuel ratio control amount C1 for feedback.

In this way, the air-fuel ratio control amount C1 based on the first air-fuel ratio signal V1 is corrected by the second air-fuel ratio control amount C2 to become the final air-fuel ratio control amount. From FIG. 18, it can be seen that the air-fuel ratio control amount C1 is substantially equal to the number and cycle of crossing the correction target value VT1.

Next, the intake air amount is detected based on the pressure P from the pressure sensor 6, and the basic fuel amount FR is calculated from the intake air amount. The target fuel amount F1 is obtained by multiplying FR.

Subsequently, a correction amount corresponding to the warm-up state of the engine 1 is calculated based on the water temperature T from the water temperature sensor 16 and acceleration / deceleration is performed based on this correction amount and the throttle opening φ from the throttle sensor 8. The state is detected, and a fuel correction amount CF is calculated from a correction amount or the like corresponding to the acceleration / deceleration state. Then, the multiplier 47 multiplies the target fuel amount F1 by the fuel correction amount CF to obtain a corrected fuel amount F corresponding to the final fuel injection amount.

Further, the multiplier 48 multiplies the correction fuel amount F by an injection time correction coefficient KF to calculate the driving time G of the injector 5.
The adder 49 adds the dead time correction amount Q to the driving time G to obtain a final fuel injection signal J for the injector 5.

As described above, by correcting the target value VR1 for the first air-fuel ratio sensor 11 using the air-fuel ratio signal V2 from the second air-fuel ratio sensor 12, the air-fuel ratio signal on the downstream side of the catalyst 10 is corrected. The air-fuel ratio feedback control is performed so that V2 becomes the second target value VR2.

That is, if the air-fuel ratio signal V2 on the downstream side of the catalyst 10 indicates the lean side (the air-fuel ratio is larger than 14.7), the fuel injection signal J is set long, and the air-fuel ratio is controlled to the rich side.
If the air-fuel ratio signal V2 on the downstream side of the catalyst 10 indicates the rich side (the air-fuel ratio is smaller than 14.7), the fuel injection signal J is set short, and the air-fuel ratio is controlled to the lean side.

As described above, the catalyst deterioration determining means in the microcomputer 30 determines whether each of the air-fuel ratio signals V1 and V2
Δ, the number of output inversions n, the inversion period τ, or the inversion period ratio γ obtained by comparing the target values VT1 and VR2 with
Based on the above, when each deterioration parameter value exceeds a predetermined value, deterioration of the catalyst 10 is determined.

At this time, the behavior of the air-fuel ratio signals V1 and V2 output from the air-fuel ratio sensors 11 and 12 is as shown in FIG. 19 when the catalyst 10 is normal, and as shown in FIG. 20 when the catalyst 10 is deteriorated. . That is, as shown in FIGS. 19 and 20, the first air-fuel ratio signal V1 changes at an appropriate cycle with respect to the correction target value VT1 by the air-fuel ratio feedback control regardless of the state of the catalyst 10.

On the other hand, when the catalyst 10 is normal, the second air-fuel ratio signal V2 becomes substantially constant due to the purifying action of the catalyst 10 as shown in FIG. 19, and when the catalyst 10 is deteriorated, as shown in FIG. Since the purifying action of the catalyst 10 is reduced, it largely changes following the first air-fuel ratio signal V1. Therefore, the integral value δ when comparing the second air-fuel ratio signal V2 with the target value VR2,
The deterioration of the catalyst 10 can be determined based on the number of inversions n or the inversion period τ.

Furthermore, when the reversal period ratio γ is used as the deterioration parameter value, the reversal period ratio γ changes as shown in FIG. 21, and when the reversal period ratio γ exceeds the deterioration determination value γo (about 50%). The deterioration of the catalyst 10 can be determined.

However, since the first air-fuel ratio sensor 11 disposed on the upstream side of the catalyst 10 is easily deteriorated and the output characteristics vary widely, the downstream air-fuel ratio also varies due to the air-fuel ratio feedback control error. Affect. Therefore, for example, as shown by the broken line in FIG.
2 is shifted so that it does not cross the second target value VR2. In this case, even if the catalyst 10 deteriorates as shown in FIG. 20, there is a possibility that the second air-fuel ratio signal V2 does not cross the target value VR2, and the integral value δ, the number of reversals n and the reversal period τ cannot be calculated. There is a risk.

The air-fuel ratio signals V1 and V2 are also affected by variations in various operating conditions and the like, and therefore, the calculation results of the integral value δ, the inversion period T, and the inversion period ratio γ also vary, and the catalyst 10 However, there is a risk that the deterioration may be determined even though is not deteriorated.

[0037]

As described above, the conventional catalyst deterioration detecting device for an internal combustion engine has a deterioration parameter value δ due to a difference in the output characteristics and operating conditions of the first and second air-fuel ratio sensors 11 and 12. , N, τ or γ will be different,
There is a problem that the deterioration of the catalyst 10 cannot be accurately determined.

The present invention has been made in order to solve the above-mentioned problems, and a catalyst deterioration detecting device for an internal combustion engine which suppresses a variation in a deterioration parameter value due to a difference in output characteristics or operating state of each air-fuel ratio sensor. The purpose is to obtain.

[0039]

According to a first aspect of the present invention, there is provided a catalyst deterioration detecting device for an internal combustion engine, comprising: an operating state determining means for determining an operating state of the internal combustion engine; and a filter processing for a second air-fuel ratio signal. a first comparison operation means for generating a filter processing means for generating a filtered signal, a first comparison result of the second air-fuel ratio signal is compared with a filtered signal Te,
The first air-fuel ratio signal is compared with a target value, and the second comparison result is obtained.
Generating second comparison operation means, and first and second comparison results;
A third comparison operation for comparing results to generate a third comparison result
Means for comparing the deterioration parameter value based on the third comparison result with a predetermined value in accordance with the operating state, and when the deterioration parameter value exceeds the predetermined value, determines deterioration of the catalyst. It is.

[0040]

[0041] Furthermore, catalyst deterioration detection device for an internal combustion engine according to claim 2 of the present invention, the degradation determination means according to claim 1, compared to a predetermined value the deterioration parameter value when the operating condition is within the predetermined range Things.

According to a third aspect of the present invention, there is provided a catalyst deterioration detecting device for an internal combustion engine, wherein the deterioration judging means of the first or second aspect compares a predetermined value which differs depending on an operation state with a deterioration parameter value. Is what you do.

According to a fourth aspect of the present invention, there is provided an apparatus for detecting deterioration of a catalyst for an internal combustion engine, wherein the time constant of the filter processing means according to any one of the first to third aspects is set to 100 ms to 300 ms. It is.

According to a fifth aspect of the present invention, there is provided a catalyst deterioration detecting device for an internal combustion engine according to any one of the first to fourth aspects, wherein the filter processing signal responds to the magnitude of the second air-fuel ratio signal. , Has a hysteresis that is increased or decreased by a predetermined noise removal amount.

Further, according to a sixth aspect of the present invention, there is provided a catalyst deterioration detecting device for an internal combustion engine, wherein the deterioration parameter value according to any one of the first to fifth aspects is obtained by combining the second air-fuel ratio signal and the filter processing signal. This is an integral operation value of the deviation.

[0046] Further, the internal combustion engine for a catalyst deterioration detection device according to claim 7 of the invention, the target value of claim 1, is increased or decreased by a predetermined noise removal amount in response to the magnitude to the first air-fuel ratio signal It has such hysteresis.

[0047]

[0048] Furthermore, catalyst deterioration detection device for an internal combustion engine according to claim 8 of the present invention, the deterioration parameter value filtering
Filtering to generate filtering parameter values
Means for determining deterioration of the catalyst when a state in which the filter processing parameter value exceeds a predetermined value continues for a predetermined time.

According to a ninth aspect of the present invention, there is provided a catalyst deterioration detecting device for an internal combustion engine, wherein the comparing and judging means according to the eighth aspect is configured such that when the deviation between the previous value and the current value of the filter processing parameter value is equal to or less than an allowable upper limit value. Then, a comparison is made between the filter processing parameter value and a predetermined value.

[0050]

According to the first aspect of the present invention, the first comparison is performed by comparing the second air-fuel ratio signal with its filtered signal.
By comparing the result with the first air-fuel ratio signal and its target value
The catalyst is compared with the second comparison result, and the deterioration of the catalyst is determined using the deterioration parameter value based on the obtained third comparison result.

[0051]

Further, in claim 2 of the present invention,
In the item (1) , the deterioration determining means performs the deterioration determination only when the vehicle is in a predetermined operation state.

According to a third aspect of the present invention, in any one of the first and second aspects, the deterioration judging means judges the deterioration of the catalyst using a predetermined value corresponding to the operating state.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the filter processing time constant is set to 100 ms to 300 ms.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the filter processing signal is provided with hysteresis by a noise removal amount.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the integrated value of the deviation is used as the deterioration parameter value.

Further, in claim 7 of the present invention,
In item 1 , the target value is provided with hysteresis by the amount of noise removal.

[0058]

[0059] Further, in claim 8 of the present invention determines that the catalyst has deteriorated when the state where filtering parameter value exceeds a predetermined value continues for a predetermined time.

[0060] In the ninth aspect of the invention, wherein
In item 8 , comparison with a predetermined value is performed only when the variation of the filter processing parameter value is within an allowable range.

[0061]

[Embodiment 1] Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG.
FIG. 3 is a functional block diagram schematically showing deterioration determination means relating to the first embodiment of the present invention, wherein 30A corresponds to the microcomputer 30, and 5, 11, 12, and 19 are the same as those described above. . In addition, the configuration of the entire device (not shown), the ECU, the air-fuel ratio control means 20a, and the like are as shown in FIGS.

Reference numeral 20a denotes air-fuel ratio control means having the functional configuration shown in FIG. 17, and is configured in the microcomputer 30A together with catalyst deterioration determination means described later. Numeral 50 denotes a filtering means for filtering the second air-fuel ratio signal V2 to generate a filtered signal Vf2. The filtering time constant is not several milliseconds for removing extraneous noise, but a deterioration parameter value. 100 ms to suppress the variation of
It is set to about 300 ms.

Numeral 51 denotes comparison operation means for comparing the second air-fuel ratio signal V2 with the filtered signal Vf2, and outputs a deviation ΔVf2 between the second air-fuel ratio signal V2 and the filtered signal Vf2 as a comparison result.

Reference numeral 52 denotes operating state determining means for determining an operating state based on an operating state signal Q (including a water temperature T, a throttle opening φ, etc.). When it is determined that the operating state is within a predetermined range, a steady operation is performed. Generate a signal Q '. The steady operation state is determined, for example, when the engine speed is within a predetermined range and the engine load is within a predetermined range.

An AND gate 53 passes the deviation ΔVf2 of the second air-fuel ratio signal V2 in response to the steady operation signal Q '.
Numeral 54 denotes a deterioration judging means for judging deterioration of the catalyst 10 when the deviation ΔVf2 exceeds a predetermined value. The filter processing means 50 to the deterioration determination means 54 constitute catalyst deterioration determination means, and are included in the microcomputer 30 together with the air-fuel ratio control means 20a.

Next, the general operation of the catalyst deterioration detecting device shown in FIG. 1 will be described. First, the air-fuel ratio control means 20a
Generates the fuel injection signal J based on the air-fuel ratio signals V1 and V2 as described above, and optimally controls the fuel injection amount from the injector 5, that is, the air-fuel ratio.

On the other hand, the filter processing means 50 of the catalyst deterioration determining means generates a filtered signal Vf2 of the second air-fuel ratio signal V2, and the comparison calculating means 51 generates the filtered signal Vf2 and the second air-fuel ratio signal V2. Is generated.

The operating state determining means 52 determines, based on the rotation signal R, the throttle opening φ, and the like, if the rotation speed temperature load and the like are within a predetermined range, a steady operation suitable for determining deterioration is performed. The signal Q 'is generated to open the AND gate 53, and the deviation ΔVf2 is input to the deterioration determining means 54. As the predetermined operation state, a state where the exhaust gas temperature and the intake air amount are equal to or more than a predetermined value may be selected.

Therefore, the deterioration determining means 54 determines that the deviation ΔVf2 is a predetermined value (deterioration criterion) when the operating state allows deterioration determination.
Is determined, and when it exceeds a predetermined value, an abnormal signal E is generated and the alarm lamp 19 is driven. As a result, the driver recognizes that the catalyst 10 has deteriorated, and can immediately stop the operation and take measures.

Next, the processing operation of the catalyst deterioration judging means in FIG. 1 will be specifically described with reference to the flowchart in FIG. First, the air-fuel ratio signal V2 from the second air-fuel ratio sensor 12 is read (step S1).
The filter processing signal Vf2 from 50 is read (step S2).

Subsequently, a comparison operation is performed between the second air-fuel ratio signal V2 and the filtered signal Vf2 (step S3), and a comparison result, that is, a deviation ΔVf2 is generated. Next, it is determined whether or not the operation state is a predetermined operation state based on the presence or absence of the steady operation signal Q '(step S4). If the operation state is the predetermined operation state (steady operation state), the comparison result ΔVf2 in step S3 is a predetermined value. It is determined whether the value is larger than the value A (step S5).

The operation state judgment step S4 is executed by the operation state judgment means 52 and the AND gate 53, and the comparison result judgment step S5 is executed by the deterioration judgment means 54.
If ΔVf2 ≦ A, that is, “NO” in step S5, it is determined that the catalyst 10 is normal (step S6), and the abnormal signal E is not generated. Therefore, the alarm lamp 19
Is turned off (step S7), and the process returns.

On the other hand, in step S5, ΔVf2> A,
That is, if “YES”, it is determined that the catalyst 10 has deteriorated (step S8), and an abnormal signal E is generated. Therefore, the alarm lamp 19 is turned on (step S9), and the process returns. Further, in the operation state determination step S4, if it is out of the predetermined operation state, that is, if “NO”, it is an operation state in which the deterioration cannot be determined.

Next, the flowchart of FIG.
5 and the waveform diagram of FIG.
Will be described. FIG.
Is executed, for example, every 10 ms. First, the air-fuel ratio signal V2 from the second air-fuel ratio sensor 12
Is read (step S11), and it is determined whether or not this is the first reading after the power is turned on (step S12).

If it is determined in step S12 that this is the first reading, the air-fuel ratio signal V2 is initialized as the current filtered signal Vf2 (n) (step S13), and the filtering process is terminated and the process returns. . At this time, the current filtered signal Vf2 (n) is
Updated and registered as f2 (n-1).

On the other hand, if it is determined in step S12 that this is not the first reading, the current filtered signal Vf2
(n) is set by a primary filter operation as in the following equation (1) (step S14).

Vf2 (n) = (1−Ks) × Vf2 (n−1) + Ks × V2 (1)

However, in the equation (1), Ks is a filter operation coefficient, and is set to a value within a range of 0 <Ks <1. The current filtered signal Vf2 calculated by equation (1)
Based on (n), the second air-fuel ratio signal V2 is
Response time is delayed by the filter processing time constant of 0 ms,
The signal is converted into a filtered signal Vf2 that can be reliably determined for deterioration, and is input to the comparison operation means 51.

At this time, when the function of the catalyst 10 is normal, the waveform of the filtered signal Vf2 is as shown by the broken line in FIG. 4, and when the catalyst 10 is deteriorated and the purification performance is reduced, the broken line in FIG. It becomes as shown by.

That is, when the catalyst 10 is normal, the second air-fuel ratio signal V2 almost follows the second air-fuel ratio signal V2 even if the level of the second air-fuel ratio signal V2 shifts as shown by the solid line a to b in FIG. A filtered signal Vf2 (broken line) is obtained. Since the time constant of the filtered signal Vf2 at this time is as large as 100 msec to 300 msec, it has a waveform almost coincident with the second air-fuel ratio signal V2.

On the other hand, when the catalyst 10 has deteriorated, the second air-fuel ratio signal V2 having a large amplitude as indicated by the broken line in FIG.
Since there is a response delay with respect to the (solid line), the level difference from the second air-fuel ratio signal V2 increases, and a filtered signal Vf2 having a waveform that intersects periodically is obtained. As a result, the filtered signal Vf2 always corresponding to the second air-fuel ratio signal V2
Is generated as a comparison reference instead of the second target value VR2.

Accordingly, if the comparison result of the comparison operation means 51, that is, the deviation ΔVf2, is normal if the catalyst 10 is normal, the solid line b in FIG.
Even if the second air-fuel ratio signal V2 shifts to such an extent that the second air-fuel ratio signal V2 does not cross the second target value VR2 as described above, the second air-fuel ratio signal V2 always has a small level equal to or less than the predetermined value A regardless of the variation of the second air-fuel ratio signal V2. . If the catalyst 10 has deteriorated as shown in FIG. 5, the level of the deviation ΔVf2 becomes larger than the predetermined value A.

As described above, by using the filtered signal Vf2 of the second air-fuel ratio signal V2 as the comparison reference value, the deviation ΔVf2 which is not affected by the variation of the second air-fuel ratio signal V2 from the comparison calculation means 51 can be obtained. Generated. Deterioration determination means
54 can accurately determine the deterioration of the catalyst 10 based on the deviation ΔVf2 only in the steady operation state in which the deterioration can be determined. Therefore, the deterioration of the catalyst 10 cannot be determined,
Deterioration is not erroneously determined even though it is normal.

In the above device , the comparison operation means 51 outputs the deviation ΔVf2 between the second air-fuel ratio signal V2 and the filtered signal Vf2 as a comparison result, and the operation state judgment means 52 judges the steady operation state, and The deviation ΔVf2 is made effective only when 53 is in the steady operation state, and the deterioration determination means 54 compares the deviation ΔVf2 with a predetermined value. However, another calculation value may be used as the deterioration parameter value.

For example, deterioration can be determined when the number n of inversions in which the second air-fuel ratio signal V2 crosses the filtered signal Vf2 during a steady state operation exceeds a predetermined number.
In this case, the comparison operation means for counting the number of times of crossover inversion of each signal includes the operation state determination means 52 and the AND gate 53 in FIG.
Function will be included.

[0086] Next, with reference to FIG. 6, the fruit of the present invention
Comparison operation processing of the comparison operation means according to the first embodiment (reversal number n
The operation will be specifically described. First, it is determined whether or not the second air-fuel ratio signal V2 is greater than the filtered signal Vf2 (step S21). If V2> Vf2, the current flag is set to 1 (step S22), and the second flag is set. It is assumed that the air-fuel ratio signal V2 indicates a slightly rich state.
If V2 ≦ Vf2, the current flag is reset to 0 (step S23).

When the state of the current flag is determined in step S22 or S23, it is determined whether or not the first comparison has been performed since the power was turned on (step S24). Initialize by setting to the value of the previous flag (step S25), and if not the first comparison, step S25
To skip.

Subsequently, it is determined whether or not the operating state is a predetermined steady state (step S26). If not, the counter CN is reset to 0 (step S27). The reset step S27 is skipped.

Next, it is determined whether or not the current flag is 1 (step S28). If 1 is set, then it is determined whether or not the previous flag is 0 (step S2).
9) If the flag is not set to 1 this time (0
Then, it is determined whether or not the previous flag is 1 (step S30).

That is, in steps S29 and S30,
It is determined whether the current flag and the previous flag are different from each other, that is, whether the second air-fuel ratio signal V2 has crossed the filtered signal Vf2 and the current flag and the previous flag have been inverted.

If "Y" in step S29 or S30
If it is determined to be "ES" (crossed), the counter CN is incremented (step S31), and the number of times the second air-fuel ratio signal V2 crosses the filtered signal Vf2 is counted. or,
If "NO" is determined in the step S29 or S30, the step S31 is skipped.

Next, it is determined whether or not a predetermined time has elapsed in the steady operation state (step S32). If the predetermined time has elapsed, the value of the counter CN is set as a comparison result, and the counter CN is reset to 0. Reset (step S33) and return. If it is determined in step S32 that the predetermined time has not elapsed, step S33 is skipped and the process returns.

As a result, the number of reversals n is input to the deterioration determining means as a deterioration parameter value, and the deterioration determining means can determine the deterioration of the catalyst 10 when the number of reversals n exceeds a predetermined number.

Embodiment 2 FIG. In the first embodiment , the number of inversions n
Is calculated, and the number of inversions n is input to the deterioration determination means as a deterioration parameter value. However, the same effect can be obtained when the inversion period τ is calculated as the deterioration parameter value. in this case,
The measurement of the inversion cycle can be realized by a timer function in the microcomputer 30A.

Embodiment 3 FIG. Further, in order to reliably detect the deviation of the air-fuel ratio on the downstream side of the catalyst 10, the comparison operation means may calculate the integral value (area equivalent value δ) of the deviation ΔVf2 as the deterioration parameter value. Next, referring to the flowchart of FIG.
The operation of the comparison operation (operation of the integral value δ) of the comparison operation means according to the third embodiment ( corresponding to claim 6 ) will be described. In the figure, S21, S24, S26 and S32 are the same steps as in FIG.

First, the second air-fuel ratio signal V2 is compared with the filtered signal Vf2 (step S21). If V2> Vf2, the deviation ΔVf2 is calculated from V2-Vf2 (step S4).
1) The degree of the second air-fuel ratio signal V2 is slightly rich. Also, if V2 ≦ Vf2, the deviation ΔV is obtained by Vf2−V2.
f2 is calculated (step S42).

Subsequently, if it is determined in step S24 that the comparison is the first comparison after the power is turned on, the deviation ΔV calculated this time is used.
f2 is initially set as the integral value δ (step S43), and if not the first comparison, step S43 is skipped. If it is determined in step S26 that the vehicle is not in the predetermined operation state,
The integral value δ is reset to 0 (step S44), and if it is determined that the vehicle is in the predetermined operation state, step S44 is skipped. next,
The current integral value δ (n) is calculated by the following equation (2) (step S45).

Δ (n) = δ (n−1) + ΔVf2 (2)

In equation (2), δ (n−1) is the previous integral value, and ΔVf2 is the present deviation. Finally, after confirming that the predetermined operation state has continued for the predetermined time in step S32, the integral value δ is set as a comparison result, and then the integral value δ is reset to 0 (step S46).

Embodiment 4 FIG. Further, in each of the above embodiments, the filtered signal Vf2 calculated according to the second air-fuel ratio signal V2 is used as it is for the comparison calculation, but it is considered that noise is superimposed on the second air-fuel ratio signal V2. Then, the filtered signal V
Hysteresis may be given to f2 (corresponding to claim 5 ).

That is, if V2> Vf2, the amount of noise removal is subtracted from the filtered signal Vf2, and V2 ≦ Vf2
Then, the noise removal amount may be added to the filtered signal Vf2 to increase the deviation ΔVf2 so as not to be affected by noise. As a result, a margin for external noise can be provided, and more accurate deterioration detection can be performed.

Embodiment 5 FIG. Further, in each of the above embodiments, the catalyst deterioration determination function is enabled during the predetermined steady operation state, but the predetermined value to be compared with the deterioration parameter value in the deterioration determination means 54 is changed according to the operation state. (Corresponding to claim 3 ). In this case, the range of the operating state in which the deterioration can be determined is widened, and the reliability of the deterioration determination is further improved even within the predetermined operating state range.

Embodiment 6 FIG. In each of the above embodiments, the deterioration of the catalyst 10 is determined based only on the second air-fuel ratio signal V2. However, depending on the operating state, the air-fuel ratio control state using the first air-fuel ratio signal V1 changes. As a result, the amount of change in the second air-fuel ratio signal V2 increases, which may hinder deterioration determination.

Therefore, it is desirable to make a deterioration judgment using not only the second air-fuel ratio signal V2 but also the first air-fuel ratio signal V1, and suppress the air-fuel ratio control error to perform a more reliable deterioration detection. . Next, a catalyst deterioration detecting device according to a sixth embodiment of the present invention ( corresponding to claim 1 ) will be described with reference to a functional block diagram of FIG.

Reference numeral 55 denotes the first air-fuel ratio signal V1 as a target value V
R1 is a second comparison operation means for comparing the deviation Δ between the first air-fuel ratio signal V1 and a target value VR1 (rich lean determination value).
V1 is generated as a second comparison result. Reference numeral 56 denotes a third comparison / calculation means for comparing the deviation ΔVf2 (first comparison result) from the first comparison / calculation means 51 with the deviation ΔV1 (second comparison result) from the second comparison / calculation means 55. Yes, deviation ratio ε (= Δ
V1 / ΔVf2) is generated as a third comparison result. Second
The comparison calculation means 55 and the third comparison calculation means 56 are configured in the microcomputer 30B together with the air-fuel ratio control means 20a to the deterioration determination means 54.

In this case, the deterioration determining means 54 compares the third comparison result, that is, the deviation ratio ε, as a deterioration parameter value with a predetermined value in accordance with the operating state. When the deterioration parameter value exceeds the predetermined value, the catalyst Is determined. At this time, since the deviation ratio ε reflects the state of the air-fuel ratio control means 20a, it is possible to suppress the influence of the first air-fuel ratio signal V1, that is, the influence of the change in the state of the air-fuel ratio control. It is possible to make a judgment on deterioration.

Embodiment 7 FIG. Also, in the case of the sixth embodiment , similarly to the fourth embodiment ,
If the target value VR1 of the first air-fuel ratio signal V1 is provided with hysteresis, the influence of extraneous noise superimposed on the first air-fuel ratio signal V1 can be suppressed (corresponding to claim 8). Further, the deviation ΔV1 is used as the deterioration parameter value from the second comparison / calculation means 55.
Of the air-fuel ratio signal V1 may cross over the target value VR1, the number of reversals, the cycle or the integral value may be used. Has the same effect.

Embodiment 8 FIG. In each of the above embodiments, the deterioration of the catalyst 10 is determined based on the calculated deterioration parameter value regardless of the level of the second air-fuel ratio signal V2.
The purification rate of 10 is the ideal air-fuel ratio 1 where the oxidation-reduction reaction is likely to occur.
Since it becomes the highest near 4.7, when the air-fuel ratio largely deviates from the ideal value, even if the catalyst 10 is normal, the purification rate may be reduced and the deterioration may be erroneously determined.

[0109] Therefore, means for determining the air-fuel ratio state, when the air-fuel ratio is further provided with means for inhibiting the deterioration determination when outside the predetermined range, for example, the second air-fuel ratio signal V2 of the O ₂ sensor output It is determined whether the voltage level is within the range of 0.1 V to 0.8 V. If the voltage level is 0.1 V or lower or 0.8 V or higher, the air-fuel ratio is deemed to be out of the predetermined range, and the deterioration determination is prohibited. It may be. Thus, the deterioration determination is performed only when the air-fuel ratio is within the predetermined range, and the reliability of the deterioration determination of the catalyst 10 is further improved.

Embodiment 9 FIG. Further, in each of the above embodiments, the second air-fuel ratio signal V2 is filtered, but a deterioration parameter value calculated based on at least the second air-fuel ratio signal V2 may be filtered. Hereinafter, the functional block diagram of FIG . 9, FIG. 10, FIG. 11, and FIG.
A ninth embodiment ( corresponding to claim 8 ) of the present invention will be described with reference to a flowchart of FIG. 13 and a waveform diagram of FIG.

In FIG. 9, reference numeral 60 denotes a deterioration parameter value γ at every predetermined time based on at least the second air-fuel ratio signal V2.
And outputs, for example, a ratio γ of a reversal period τ between each of the air-fuel ratio signals V1 and V2 and the target values VR1 and VR2 as a deterioration parameter value.

Reference numeral 61 denotes filter processing means for filtering the deterioration parameter value γ every time the deterioration parameter value γ is calculated to generate a filter processing parameter value γf. 62
Is a comparing and judging means for comparing the filter processing parameter value γf with a predetermined value. When the filter processing parameter value γf exceeds a predetermined value, it judges deterioration of the catalyst and generates an abnormal signal E. These deterioration parameter calculation means 60 to comparison determination means 62 are configured in the microcomputer 30C.

Next, the operation of the catalyst deterioration determination processing related to the ninth embodiment of the present invention will be specifically described with reference to the flowchart of FIG. Note that in FIG.
S9 is the same step as in FIG.

First, the deterioration parameter calculating means 60 determines whether the first
Period tau ₁ of the air-fuel ratio signal V1 crosses the target value VR1 and the second
Is calculated as a deterioration parameter value with a period ratio γ (τ ₁ / τ ₂ ) with respect to a period τ _{2 at} which the air-fuel ratio signal V2 crosses the target value VR2,
The filter processing means 61 filters the deterioration parameter value γ to generate a filter processing parameter value γf.

The comparison determining means 62 reads the filter processing parameter value γf (step S51), and determines whether the filter processing parameter value γf is larger than a predetermined value A ′ (step S52).

If the determination result is "NO" (γf ≦ A ′), the catalyst 10 is recognized as normal (step S6), and the alarm lamp 19 is turned off without generating the abnormal signal E (step S6).
7). If the determination result is “YES” (γf> A ′),
The catalyst 10 is recognized as being deteriorated (step S8), and an abnormal signal E is generated to turn on the alarm lamp 19 (step S9).

FIG. 11 shows a filter processing routine of the filter processing means 61, which is executed every time, for example, every 10 seconds, required for calculating the deterioration parameter value (period ratio) γ. First, the deterioration parameter value γ is read (step S61), and it is determined whether or not this is the first reading after the power is turned on, that is, whether or not the deterioration parameter value γ is calculated for the first time (step S62).

If this is the first reading, the read deterioration parameter value γ is initialized as the current filtering parameter value γf (n) (step S63), and the filtering process ends and returns. At this time, the current filter processing parameter value γf (n) is updated and registered as the previous filter processing parameter value γf (n-1).

On the other hand, if it is determined in step S62 that the reading is not the first reading, the current filtering parameter value γf (n) is set by a primary filter operation as shown in the following equation (3) (step S64).

Γf (n) = (1−Kt) × γf (n−1) + Kt × γ (3)

However, in the equation (3), Kt is a filter operation coefficient, and is set to a value within the range of 0 <Kt <1. By this filter operation coefficient Kt, the current filter processing parameter value γf (n) is set to be stable when the same deterioration parameter value γ is calculated several times.

As a result, the filter processing parameter value γf
Is smoothed as shown by the broken line in FIG. 12, and the variation in the calculation of the deterioration parameter value γ due to the influence of various operating conditions and the like is absorbed. Therefore, even if the level of the deterioration parameter value γ temporarily fluctuates as shown by the solid line, if the catalyst 10 is normal, the filter processing parameter value γf does not exceed the predetermined value A ′, and the comparison determination means 62 Erroneous determination of deterioration is prevented and reliability is improved.

Here, the filter processing parameter value γf
When the value exceeds a predetermined value A ′, the deterioration of the catalyst 10 is determined.
If the value temporarily exceeds the predetermined value A ', an erroneous determination may still occur.

[0124] Therefore, in order to filter parameter values γf is prevented from determining temporarily erroneous degradation when exceeding the predetermined value A ', it determines the degradation when exceeded continuously for a predetermined time Is desirable . FIG. 13 shows an embodiment of the present invention.
10 is a flowchart showing a deterioration determination process according to Example 9 ( corresponding to claim 8 ), wherein S51 and S52 are the same steps as in FIG.

In this case, a timer counter C for measuring time
T has been added, and the result of the determination in step S52 is “N
If "O" (γf ≦ A ′), the counter CT is reset to 0 and initialized (step S53), and the routine returns.

When the result of the determination in step S52 is "YES",
If (γf> A ′), the counter CT is incremented (step S54), and it is determined whether or not the value of the counter CT exceeds a predetermined value B (step S55). In addition, the increment step S54 is performed with the filter processing parameter value γ.
The time during which f continuously exceeds the predetermined value A 'is measured, and the predetermined value B in the determination step S55 is set to a value corresponding to the predetermined time (for example, five times).

If the decision result in the step S55 is "NO",
If (CT ≦ B), the step of recognizing the catalyst 10 as normal
Proceeding to S6, if "YES"(CT> B), proceed to step S8 for recognizing that the catalyst 10 has deteriorated. As a result, the deterioration of the catalyst 10 can be determined only when the filter processing parameter value γf exceeds the predetermined value A ′ for a predetermined time, and the reliability is further improved.

Embodiment 10 FIG. In the ninth embodiment , the deterioration of the catalyst 10 is determined when the filter processing parameter value γf equal to or more than the predetermined value continues for the predetermined time. As another means for this purpose, means for calculating the amount of change in the filter processing parameter value may be provided.

FIG. 14 is a functional block diagram showing a catalyst deterioration detecting device according to the tenth embodiment ( corresponding to claim 9 ) of the present invention. Reference numeral 62A denotes a comparison operation means corresponding to 62 in FIG.
Reference numeral 63 denotes a filter processing value change amount calculating means for calculating a change amount Δγf of the filter processing parameter value γf, and is configured in the microcomputer 30D together with the deterioration parameter calculating means 60 to the comparison calculating means 62A.

The filter processing value change amount calculating means 63 calculates the following value based on the difference between the present value γf (n) and the previous value γf (n-1) of the filter processing parameter value γf from the filter processing means 61. The change amount Δγf is calculated as in equation (4).

Δγf = | γf (n) −γf (n−1) | (4)

The comparison operation means 62A takes in the change amount Δγf together with the filter processing parameter value γf, and obtains the change amount Δγf
Is equal to or less than the allowable upper limit, the filter processing parameter value γ
It is determined that f is not a temporary calculation result, and the filter processing parameter value γf at that time is compared with a predetermined value A ′.

When the variation Δγf exceeds the allowable upper limit value, it is regarded as a temporary calculation variation and the deterioration determination is prohibited. As a result, it is possible to absorb the variation in the calculation of the filter processing parameter value γf, and the reliability of the catalyst deterioration determination is further improved. Further, by combining the ninth and tenth embodiments , it is possible to further absorb the variation in the calculation of the filter processing parameter value γf. Further, Example 9 and
In the tenth embodiment , the period ratio γ is used as the deterioration parameter value. However, it goes without saying that the same effect can be obtained by using another deterioration parameter value.

[0134]

As described above, according to the first aspect of the present invention, the operating state determining means for determining the operating state of the internal combustion engine and the second air-fuel ratio signal are filtered to generate a filtered signal. Filtering means for comparing the second air-fuel ratio signal with the filtered signal to generate a first comparison result
A first comparison operation means, and a first air-fuel ratio signal as a target value.
Second comparison operation means for comparing and generating a second comparison result
And a third comparison result by comparing the first and second comparison results.
And a third comparison operation means for generating a value, which compares the deterioration parameter value based on the third comparison result with a predetermined value in accordance with the operating state, and determines whether the catalyst has deteriorated when the deterioration parameter value exceeds the predetermined value. Since the determination is made, there is an effect that a catalyst deterioration detecting device for an internal combustion engine with improved reliability by suppressing the variation of the deterioration parameter value due to the difference in the output characteristics and the operation state of the air-fuel ratio sensor is obtained.

[0135]

According to claim 2 of the present invention,
In 1 , the deterioration parameter value is compared with the predetermined value and the deterioration determination is performed only when the operation state is within the predetermined range, so that the deterioration parameter value variation due to the difference in the output characteristics of the air-fuel ratio sensor and the operation state. While suppressing
This has the effect of providing a catalyst deterioration detection device for an internal combustion engine that prevents erroneous determinations due to variations in operating conditions.

According to the third aspect of the present invention, in the first or second aspect , the deterioration is determined by comparing a predetermined value different from the deterioration parameter value according to the operating state. Effect of Obtaining a Catalyst Deterioration Detector for Internal Combustion Engines that Reduces Variations in Deterioration Parameter Values Due to Differences in Output Characteristics and Operating Conditions of Fuel Ratio Sensors, Expands the Operating State Range in Which Deterioration Determination is Possible, and Improves Determination Reliability There is.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the time constant of the filter processing means is set to 100 msec to 300 msec. In addition, it is possible to obtain a catalyst deterioration detection device for an internal combustion engine that suppresses variations in deterioration parameter values due to differences in operation state and operating conditions, and reliably absorbs variations in the air-fuel ratio signal to improve determination reliability.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the noise reduction amount is increased or decreased by a predetermined noise removal amount in response to the magnitude of the second air-fuel ratio signal. Hysteresis is given to the filter processing signal, so that the variation in the deterioration parameter value due to the difference in the output characteristics and the operating state of the air-fuel ratio sensor is suppressed, and the erroneous determination due to the superposition of noise on the air-fuel ratio signal is prevented. There is an effect that a deterioration detection device can be obtained.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the deterioration parameter value is determined by calculating an integral operation value of a deviation between the second air-fuel ratio signal and the filtered signal. As a result, there is an effect that a catalyst deterioration detecting device for an internal combustion engine can be obtained in which variation in deterioration parameter values due to differences in output characteristics and operating conditions of the air-fuel ratio sensor is suppressed and determination reliability is improved.

According to claim 7 of the present invention, claim
In 1 , the target value has a hysteresis that is increased or decreased by a predetermined amount of noise removal in response to the magnitude of the first air-fuel ratio signal. There is an effect that a catalyst deterioration detecting device for an internal combustion engine in which the variation in the values is suppressed can be obtained.

[0142]

According to the eighth aspect of the present invention, there is provided a filter processing means for filtering the deterioration parameter value to generate a filter processing parameter value, wherein the comparing and judging means determines that the filtering parameter value exceeds a predetermined value. The deterioration of the catalyst is determined when the exhausted state continues for a predetermined period of time, so that the variation in the deterioration parameter value due to the difference in the output characteristics of the air-fuel ratio sensor and the operating state is suppressed, and the temporary This has the effect of obtaining a catalyst deterioration detection device for an internal combustion engine that absorbs calculation variations and prevents erroneous determination.

Further, according to claim 9 of the present invention, claim
In step 8 , when the deviation between the previous value and the current value of the filter processing parameter value is equal to or smaller than the allowable upper limit, the filter processing parameter value is compared with a predetermined value. In addition, it is possible to obtain a catalyst deterioration detecting device for an internal combustion engine that suppresses variation in the deterioration parameter value due to the difference and absorbs the temporary calculation variation in the filter processing parameter value to prevent erroneous determination.

[Brief description of the drawings]

FIG. 1 is a functional block diagram schematically showing catalyst deterioration determination means in a microcomputer (ECU) by a device according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating a deterioration determination processing operation performed by the apparatus according to the first embodiment of the present invention.

FIG. 3 is a flowchart illustrating a filtering process performed by the apparatus according to the first embodiment of the present invention;

[4] relating to the first embodiment of the present invention when the catalyst is normal
It is a waveform diagram which shows the 2nd air-fuel ratio signal V2 and the filtered signal Vf2 by the connected apparatus .

[5] related to the first embodiment of the present invention when the catalyst is deteriorated
It is a waveform diagram which shows the 2nd air-fuel ratio signal V2 and the filtered signal Vf2 by the connected apparatus .

FIG. 6 is a flowchart illustrating a comparison operation processing operation according to the first embodiment of the present invention.

FIG. 7 is a flowchart illustrating a comparison operation processing operation according to a third embodiment of the present invention.

FIG. 8 is a functional block diagram schematically showing catalyst deterioration determination means in a microcomputer according to Embodiment 6 of the present invention.

FIG. 9 is a functional block diagram schematically showing catalyst deterioration determining means in a microcomputer by an apparatus according to Embodiment 9 of the present invention.

FIG. 10 is a flowchart illustrating a deterioration determination processing operation performed by an apparatus according to Embodiment 9 of the present invention;

FIG. 11 is a flowchart illustrating a filtering process performed by a device according to a ninth embodiment of the present invention;

FIG. 12 is a waveform chart showing a deterioration parameter value (period ratio) γ and its filtering parameter value γf by an apparatus according to Embodiment 9 of the present invention.

FIG. 13 is a flowchart showing a deterioration determination processing operation according to Embodiment 9 of the present invention.

FIG. 14 is a functional block diagram schematically showing catalyst deterioration determination means in a microcomputer according to Embodiment 10 of the present invention.

FIG. 15 is a configuration diagram illustrating a general catalyst deterioration detection device for an internal combustion engine.

16 is a block diagram showing the functional configuration of the ECU in FIG.

FIG. 17 is a functional block diagram schematically showing an air-fuel ratio feedback control calculation operation by a conventional catalyst deterioration detection device for an internal combustion engine.

FIG. 18 is a waveform chart for explaining an air-fuel ratio feedback control operation by a general catalyst deterioration detection device for an internal combustion engine.

FIG. 19: General first and second when the catalyst is normal
FIG. 6 is a waveform chart showing output characteristics of the air-fuel ratio signal of FIG.

FIG. 20 is a waveform chart showing output characteristics of the first and second air-fuel ratio signals when the catalyst has deteriorated.

FIG. 21 is a waveform chart showing output characteristics when a period ratio γ is used as a deterioration parameter value.

[Explanation of symbols]

Reference Signs List 1 engine 9, exhaust pipe, 10 catalyst, 11 first air-fuel ratio sensor, 12 second air-fuel ratio sensor, 19 alarm lamp, 20 ECU, 30A to 30D microcomputer, 50, 61 filter processing means, 51 first Comparison operation means, 52 operation state judgment means, 53 AND gate, 54 deterioration judgment means, 55 second comparison operation means, 56 third comparison operation means, 60 deterioration parameter operation means, 62, 62A comparison judgment means, 63 filter Processing value change amount calculating means, A 'predetermined value, E abnormal signal,
Q operation state signal, Q 'steady operation signal, V1 first air-fuel ratio signal, V2 second air-fuel ratio signal, Vf2 filter processing signal, ΔVf2 deviation (first comparison result), ΔV1
Deviation (second comparison result), ε deviation ratio (third comparison result), γ cycle ratio (deterioration parameter value), γf filter processing parameter value, Δγf change amount (deviation) .

Claims (9)

(57) [Claims] 1. A first air-fuel ratio sensor provided upstream of an exhaust gas purifying catalyst inserted into an exhaust system of an internal combustion engine and detecting a specific component concentration of the exhaust gas as a first air-fuel ratio signal. A second air-fuel ratio sensor provided downstream of the catalyst and detecting a specific component concentration of the exhaust gas as a second air-fuel ratio signal; and at least a second air-fuel ratio signal of the catalyst based on the second air-fuel ratio signal. An internal combustion engine catalyst deterioration detection device comprising: a deterioration determination unit that determines deterioration; and an alarm generation unit that generates an alarm when the deterioration of the catalyst is determined. In the operation state, the operation state of the internal combustion engine is determined. Determining means; filtering means for filtering the second air-fuel ratio signal to generate a filtered signal; and generating the first comparison result by comparing the second air-fuel ratio signal with the filtered signal. You That a first comparison operation means, second comparison binding compared to a target value of the first air-fuel ratio signal
A second comparison operation means for generating a result, and a third comparison result by comparing the first and second comparison results.
And a third comparison operation means for generating a comparison parameter, wherein the deterioration determination means compares a deterioration parameter value based on the third comparison result with a predetermined value according to the operation state,
A catalyst deterioration detection device for an internal combustion engine, wherein the deterioration of the catalyst is determined when the deterioration parameter value exceeds the predetermined value. 2. The deterioration determining means according to claim 1 , wherein said operating state is a predetermined
When the value is within the predetermined range, the deterioration parameter value is
2. The catalyst deterioration detecting device for an internal combustion engine according to claim 1, wherein the detected value is compared with a constant value . 3. The deterioration determining means according to the operating state .
3. The catalyst deterioration detecting device for an internal combustion engine according to claim 1 , wherein the predetermined parameter value and the deterioration parameter value are compared with each other. 4. The time constant of said filtering means is 10
Claims characterized in that the time is set from 0 ms to 300 ms.
The catalyst deterioration detecting device for an internal combustion engine according to any one of claims 1 to 3 . 5. The method according to claim 5, wherein the filtered signal is the second empty signal.
A certain amount of noise removal in response to the magnitude of the fuel ratio signal
It has a hysteresis that is increased or decreased only by
The catalyst deterioration detection device for an internal combustion engine according to any one of claims 1 to 4 . 6. The method according to claim 1, wherein the deterioration parameter value is the second empty value.
Integral operation value of deviation between fuel ratio signal and the filter processing signal
The catalyst deterioration detecting device for an internal combustion engine according to any one of claims 1 to 5 , wherein: 7. The method according to claim 6, wherein the target value is obtained by adding the first air-fuel ratio signal to the first air-fuel ratio signal.
The noise is increased or decreased by a predetermined amount in response to
Claims having a hysteresis such as
1 is a catalyst deterioration detection device for an internal combustion engine. 8. Exhaust gas inserted into an exhaust system of an internal combustion engine
The exhaust gas is provided upstream of a purifying catalyst to identify the exhaust gas.
First air-fuel detecting component concentration as a first air-fuel ratio signal
A ratio sensor, and a specific component of the exhaust gas provided downstream of the catalyst.
The second air-fuel ratio sensor detects the concentration as a second air-fuel ratio signal.
At least every predetermined time based on at least the second air-fuel ratio signal.
Parameter calculating means for calculating the deterioration parameter value
When the determination deterioration of the catalyst on the basis of the degradation parameter values
Comparing and judging means, and an alarm for issuing an alarm when deterioration of the catalyst is judged.
For detecting deterioration of a catalyst for an internal combustion engine provided with a generator
Te, the deterioration parameter value filtering to filter
Filter processing means for generating a parameter value is provided, and the comparing and judging means sets the filter processing parameter value to
When the state exceeding the predetermined value continues for a predetermined time,
A catalyst deterioration detection device for an internal combustion engine, which determines catalyst deterioration. 9. The filter processing device according to claim 1 , wherein
The deviation between the previous value and the current value of the parameter value is less than the allowable upper limit
When the filter processing parameter value and the predetermined value
9. The catalyst deterioration detecting device for an internal combustion engine according to claim 8, wherein a comparison is made with the following .