JP2990394B2 - Catalyst deterioration judgment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to determination of deterioration of a catalyst provided in an exhaust system of an engine for purifying exhaust gas.

[0002]

2. Description of the Related Art As means for judging deterioration of a catalyst for purifying exhaust gas of an engine, O _{2 is provided} upstream and downstream of the catalyst.
The time from when the sensor is provided and the air-fuel ratio supplied to the engine is changed until the output of the downstream O ₂ sensor changes from lean to rich with respect to the stoichiometric air-fuel ratio or from rich to lean with respect to the stoichiometric air-fuel ratio How to measure (for example,
JP-2-30915, JP-A No. 2-33408, JP-see Japanese Patent Laid-Open No. 2-207159), the output of the upstream O ₂ sensor after changing the air-fuel ratio of the engine and the downstream O ₂ sensor output Measuring the time difference between when the stoichiometric air-fuel ratio changes from lean to rich or when the stoichiometric air-fuel ratio changes from rich to lean (Japanese Patent Laid-Open No. 2-310)
No. 453) is known. Most of the methods for judging the deterioration of the catalyst based on the time when the output of the O ₂ sensor changes from lean to rich with respect to the stoichiometric air-fuel ratio or from rich to lean with respect to the stoichiometric air-fuel ratio, the variation in the judgment results is large. Sum of the time (or time difference) when the output of the O ₂ sensor changes from lean to rich with respect to the stoichiometric air-fuel ratio and the time (or time difference) when the output changes from rich to lean with respect to the stoichiometric air-fuel ratio Alternatively, the deterioration of the catalyst is determined by taking an average.

[0003]

[SUMMARY OF THE INVENTION Incidentally, any of the above technologies, by indirectly measuring the O ₂ storage capability of the catalyst based on the output of the O ₂ sensor, and determines the deterioration of the catalyst. Therefore, it is important to accurately grasp the characteristics of the O ₂ storage capacity of the catalyst and accurately measure the O ₂ storage capacity in order to prevent the dispersion of the determination result.

The present invention has been made in view of the above circumstances.
And the catalyst O_TwoO storage capacity _TwoResponse to sensor output
In the measurement method, the O_TwoStorage capacity
High-precision catalyst deterioration judgment considering characteristics
Aim.

[0005]

In order to achieve the above-mentioned object, the present invention has a configuration shown in a claim correspondence diagram of FIG.

That is, the present invention relates to an exhaust gas purification system for an engine in which a catalyst is disposed in an exhaust system, an upstream O ₂ sensor provided in an exhaust passage on the upstream side of the catalyst for detecting an air-fuel ratio of the engine, and a downstream of the catalyst. Provided in the exhaust passage on the side
And the downstream O ₂ sensor for detecting the air-fuel ratio of the engine, the air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine in response to at least one of the output of the upstream O ₂ sensor and the downstream O ₂ sensor, air-fuel ratio adjusting means from the time of changing from the rich side to the lean side with respect but stoichiometric air fuel ratio, the downstream O ₂
A first method of repeatedly measuring a time required for the output of the sensor to reverse from rich to lean with respect to the stoichiometric air-fuel ratio a predetermined number of times
From the time when the time measuring means and the air-fuel ratio adjusting means change the air-fuel ratio from the lean side to the rich side with respect to the stoichiometric air-fuel ratio,
A second time measuring means for output of the downstream O ₂ sensor is rich in measuring meter <br/> repeated for a predetermined number of times the time to inverted from lean against the stoichiometric air-fuel ratio, repetition thereof a predetermined number of times
A catalyst deterioration determining means for determining the catalyst has deteriorated when the sum or the average of the time measured for the following predetermined time Te, the air-fuel
The ratio adjusting means sets the air-fuel ratio from the rich side with respect to the stoichiometric air-fuel ratio.
Change to lean side, or change from lean side to switch side
When the reversal does not occur even after the limit time
Is judged to be good, and the catalyst deterioration judgment is forcibly terminated.
And a catalyst deterioration determining device for causing the catalyst deterioration determining device to determine whether the catalyst deterioration determining device has the time measured by the first time measuring device and the second time measuring device subsequent to the time measured by the first time measuring device. The first feature is that the catalyst deterioration is determined based on the sum or average of the measured times.

The present invention also relates to an exhaust gas purification system for an engine in which a catalyst is disposed in an exhaust system, wherein the upstream O is provided in an exhaust passage upstream of the catalyst and detects an air-fuel ratio of the engine.
₂ sensors, a downstream O ₂ sensor provided in the exhaust passage downstream of the catalyst and detecting the air-fuel ratio of the engine, and an upstream O ₂ sensor.
Changes from the rich side to the lean side air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine, the air-fuel ratio adjusting means with respect to the stoichiometric air-fuel ratio in accordance with at least one output of the _second sensor and the downstream O ₂ sensor after the time difference between the inverted from rich to lean against the output stoichiometric air-fuel ratio of the upstream O ₂ sensor, to the output of the downstream O ₂ sensor is inverted from rich to lean against the stoichiometric air-fuel ratio Repeat a predetermined number of times
After the first time measuring means for returning and measuring, and the air-fuel ratio adjusting means change the air-fuel ratio from the lean side to the rich side with respect to the stoichiometric air-fuel ratio, the output of the upstream O ₂ sensor is changed with respect to the stoichiometric air-fuel ratio. A time difference from when the output of the downstream O ₂ sensor is inverted from lean to rich with respect to the stoichiometric air-fuel ratio is repeatedly measured a predetermined number of times after the output is inverted from lean to rich.
A catalyst deterioration determining means for determining that the catalyst has deteriorated when the sum or average of the time differences repeatedly measured a predetermined number of times is equal to or less than a predetermined time; and an air-fuel ratio adjusting means.
The stage sets the air-fuel ratio from rich side to lean side with respect to the stoichiometric air-fuel ratio.
To the limit after changing from the lean side to the switch side
Even after a lapse of time, the output of the downstream O ₂ sensor is inverted.
If not, the catalyst is judged to be good, and the catalyst
A deterioration determination device for a catalyst having a catalyst normality determination means for terminating another forcibly, and the catalyst deterioration determining means, and time difference first time measuring means has measured the following the time difference A second feature is that the catalyst deterioration is determined based on the sum or average of the time differences measured by the second time measuring means.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 2 is an overall configuration diagram of a fuel supply control device to which the catalyst deterioration determination device of the present invention is applied. A throttle body 2 is provided in the middle of an intake pipe 1 of an engine E, and a throttle body 2 is provided therein. Is provided with a throttle valve 3. A throttle valve opening (θ _TH ) sensor 4 is connected to the throttle valve 3, and supplies an electric signal corresponding to the opening θ _TH of the throttle valve 3 to the electronic control unit U.

A 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. Each fuel injection valve 5 is connected to a fuel pump (not shown). Is electrically connected to the electronic control unit U, and the valve opening time of fuel injection is controlled by a signal from the electronic control unit U.

On the other hand, an absolute pressure (Pb) sensor 7 in the intake pipe is provided immediately downstream of the throttle valve 3, and the absolute pressure Pb detected by the absolute pressure sensor 7 is converted into an electric signal to be converted into an electronic control unit. U. Further, 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 electronic control unit U.

A cooling water temperature (Tw) sensor 9 mounted on the main body of the engine E is composed of a thermistor or the like.
w and supplies a corresponding electrical signal to the electronic control unit U. The engine speed (Ne) sensor 10 is mounted around a camshaft (not shown) or around a crankshaft of the engine E, and outputs a pulse (hereinafter, referred to as a “TDC signal pulse”) at a predetermined crank angle position of the crankshaft. To the electronic control unit U. The electronic control unit U is connected to a vehicle speed (Vh) sensor 11 for detecting the vehicle speed, and is supplied with an electric signal indicating the vehicle speed Vh.

An upstream O ₂ sensor FS as an exhaust gas component concentration detector is provided at a position upstream of the catalyst C in the exhaust pipe 12.
Is attached, and the downstream O
₂ sensors RS are installed, each of which detects the oxygen concentration in the exhaust gas and outputs an electric signal (FV _O2 , R
V _O2 ) is supplied to the electronic control unit U. Catalyst C
_Has a catalyst temperature (T _CAT ) sensor 13 for detecting the temperature.
Is mounted, and an electric signal corresponding to the detected catalyst temperature T _CAT is supplied to the electronic control unit U.

The electronic control unit U forms an input signal from various sensors, corrects a voltage level to a predetermined level, and converts an analog signal value into a digital signal value. Circuit (hereinafter "C
PU1), a ROM 1 for storing various calculation programs and various reference values used for calculation in the CPU 15
6, a RAM 17 for temporarily storing the detected various engine parameter signals and calculation results, an output circuit 18 for supplying a drive signal to the fuel injection valve 5, and the like.

Based on the various engine parameter signals described above, the CPU 15 determines various engine operating states in a feedback control area and a plurality of specific operating areas in which feedback control is not performed (hereinafter referred to as an "open loop control area"). 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 .

T _OUT = Ti × K _O2 × K _LS × K ₁ + K ₂ (1) where Ti is the basic fuel injection time of the fuel injection valve 5, the engine speed Ne and the absolute pressure in the intake pipe. It is determined according to Pb.

K _O2 is an O ₂ feedback correction coefficient (hereinafter, simply referred to as “correction coefficient”), which is obtained according to the oxygen concentration in the exhaust gas during feedback control. It is set according to.

[0018] K _LS Among engine E is open-loop control regions, set in a lean region or the fuel cut region, namely the predetermined value of less than a value 1.0 when in a predetermined decelerating region (e.g., 0.95) Is the leaning factor to be used.

K ₁ and K ₂ are correction coefficients and correction variables calculated according to various engine parameter signals, respectively, to optimize various characteristics such as fuel consumption characteristics and engine acceleration characteristics according to the engine operating state. Such a predetermined value is determined.

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 T _OUT obtained as described above.

FIGS. 3 and 4 determine whether the engine E is in a feedback control area or a plurality of open loop control areas, and set a correction coefficient K _O2 according to the determined operating state. 4 shows a flowchart of a program. This program is executed in synchronization with the generation of a TDC signal pulse.

First, in step 101, the flag n _O2
Is determined to be equal to the value 1. The flag n _O2 is for determining whether the upstream O ₂ sensor FS and the downstream O ₂ sensor RS are in the activated state.
01 is (Yes), that is, both O ₂ sensors F
When it is determined that S and RS are in the activated state, it is determined in step 102 whether the cooling water temperature Tw is higher than a predetermined water temperature _TWO2 . This answer is (Yes), that is, Tw> T
_{When WO2} is established and the engine E has completed warming-up, it is determined in step 103 whether the flag FLG _WOT is equal to the value 1. This flag FLG _WOT is set to a value of 1 when it is determined by a program (not shown) that the engine E is in a high load region where the supplied fuel amount should be increased.

[0023] If the answer to the question of the step 103 (No), i.e. if the engine E is not in the high load region, determines whether the engine speed Ne is larger than the predetermined rotational speed N _{HO P} of high-rotation in step 104 When the answer is (No), it is further determined at step 105 whether or not the engine speed Ne is higher than a predetermined low speed _NLOP . If the answer is (Yes), that is, if N _LOP <Ne ≦ N _HOP holds, then at step 106, the leaning coefficient K _LS
Is smaller than 1.0, that is, whether the engine E is in a predetermined deceleration operation region. If the answer to this step 106 is (No), it is determined in a step 107 whether or not the engine E is executing fuel cut. If the answer is (No), it is determined that the engine E is in the feedback control area, and
At 8, it is determined whether or not the engine operating state is in a state in which the monitoring of the catalyst C is permitted. If the answer is (Yes), that is, if the monitoring is permitted, the correction coefficient K _O2 is controlled in step 109 by a second air-fuel ratio adjusting means described later based on the output voltage RV _O2 of the downstream O ₂ sensor RS. At the same time, the deterioration of the catalyst C is monitored, and this program ends.

On the other hand, the answer at the step 108 is (No),
That is, when the monitoring of the catalyst C is not permitted, it is determined at step 110 whether or not the monitoring is being performed last time. The answer is (No), that is, when the continuously monitored is not performed, the output FV _O2 of the upstream O ₂ sensor FS and the downstream O ₂ sensor RS by the first air-fuel ratio adjusting means which will be described later in step 111, said correction coefficient based on the RV _O2 K _O2
, The average value K _REF of the correction coefficient K _O2 is calculated, and the program ends.

If the answer to step 105 is (No), that is, if Ne ≦ N _LOP is satisfied and the engine E is in the low speed region, the answer to step 106 is (Yes), that is, if the engine E is in the predetermined deceleration operation region. , Or when the answer to step 107 is (Yes), that is, when the engine E is executing fuel cut, the routine proceeds to step 112. In this step 112, it is determined whether or not the loop has been continued for a predetermined time t _{D. When the} answer is (No), the correction coefficient K _O2 is held at the value immediately before shifting to the loop in step 113. If the answer is (Yes), the correction coefficient K _O2 is set to a value of 1.0 in step 114 to perform open loop control, and the program ends. That is, when the engine E shifts from the feedback control area to the open loop control area according to any of the conditions in steps 105 to 107, the correction coefficient K
_O2 until the predetermined time t _D after the migration has elapsed while being held to a value that is calculated during the feedback control immediately before the transition, after the predetermined time t _D has elapsed is set to the value 1.0.

If the answer to step 102 is (No), that is, if the engine E has not completed warming up, the answer to step 103 is (Yes), that is, if the engine E is in the high load region, or The answer of 104 is (Ye
s), that is, when the engine E is in the high rotation range,
Proceeding to step 114, open loop control is executed, and this program ends.

If the answer in step 101 is (No), that is, if it is determined that both O ₂ sensors FS and RS are in the inactive state, and if the answer in step 110 is (Yes), that is, the monitor is disabled for the first time. When the permission is given, the routine proceeds to step 115, where it is determined whether or not the engine E is in an idle region. This determination is made, for example, by determining whether or not the engine speed Ne is equal to or less than a predetermined speed and the throttle valve opening θ _TH is equal to or less than a predetermined opening. If the answer to this step 115 is (Yes), that is, if the engine E is in the idle region, then in a step 116, the correction coefficient K _O2 is set to the average value K _REF0 for the idle region, open loop control is executed, and this program is executed. finish.

If the answer to step 115 is (No), that is, if the engine E is in an operating range other than the idle range (hereinafter referred to as "off idle range"), step 1 is executed.
Proceeding to 17, the correction coefficient K _O2 is set to the average value K _REF1 for the off-idle region.

FIGS. 5 and 6 show the correction coefficient K executed in step 111 of FIG. 3 during the feedback control.
₄ shows a flowchart of a subroutine for calculating _O2 .

First, at step 201, it is determined whether or not the previous control was an open loop control, and the answer is (Ye
In the case of s), it is determined in step 202 whether or not the value of the correction coefficient K _O2 in the previous control is held by executing step 113 in FIG. When this answer is (Yes)
In step 203, the value of the correction coefficient K _O2 is continuously held, and the integral control (I-term control) in step 223 and later described later is performed. If the answer in step 202 is (No), that is, if the value of the correction coefficient K _O2 has not been held in the previous control, it is determined in step 204 whether or not the engine E is in the idle region. If the answer is (Yes), that is, if the engine E is in the idle region,
At 5, the value of the correction coefficient K _O2 is changed to the average value K _REFO for the idle region.
And the integral control of the step 223 and subsequent steps is performed.

When the answer to step 204 is (No), that is, when the engine E is in the off-idle range, in step 206, the throttle valve opening θ _TH
Is greater than the idle throttle valve opening θ _IDL . If the answer is (Yes), go to step 2
07, the correction coefficient K _{O2 is changed} to the average value K for the off-idle region.
_REF1 is set, and the integral control of step 223 and _subsequent steps is performed.

If the answer to step 206 is (No), that is, if θ _TH ≤θ _IDL was established in the previous control, then at step 208, the current throttle valve opening θ
_It is determined whether or not _TH is larger than the idle throttle valve opening θ _IDL . This answer is (Yes), that is, the previous θ _TH ≤
when it becomes a time θ _TH> θ _IDL in theta _IDL is set the correction coefficient K _O2 at step 209, the product C _R × K _REF1 between the average value K _REF1 and enrichment predetermined value C _R for the off-idle region Then, the integral control of step 223 and subsequent steps is performed. Here, enrichment predetermined value C _R is intended to be set to the value greater than 1.0.

If the answer to step 208 is (No), that is, if θ _TH ≦ θ _IDL holds, then at step 210 the engine cooling water temperature Tw is reduced to a predetermined temperature T _WCL (for example, 70 °
C) It is determined whether or not it is larger. If the answer is (Yes), that is, if Tw> T _WCL is satisfied, and therefore the engine cooling water temperature Tw is not in the low temperature range, the aforementioned step 205
Proceed to.

If the answer to step 210 is (No), that is, if Tw ≦ T _WCL holds, and therefore the engine cooling water temperature is in the low temperature range, the correction coefficient K
The _O2, and set to the product C _L × K _REF0 between the average value K _REF0 and lean predetermined value C _L for the idle region, the step 2
23 or less integral control is performed. Here, lean predetermined value C
_L is set to a value smaller than 1.0.

When the answer to step 201 is (No), that is, when the previous control was feedback control,
In step 212, it is determined whether or not the throttle valve opening θ _TH was larger than the idle throttle valve opening θ _IDL in the previous control. If the answer is (No), it is further determined at step 213 whether or not the current throttle valve opening θ _TH is larger than the idle throttle valve opening θ _IDL . If the answer is (Yes), then go to step 20
In the same manner as when the answer to 8 is (Yes), the process proceeds to step 209, and the correction coefficient K _O2 is set to the average value K for the off-idle region.
Set to the product C _R × K _REF1 and _REF1 and enrichment predetermined value C _R.

The answer in step 212 is (Yes), that is, when θ _TH > θ _IDL is satisfied in the previous control, or when the answer in step 213 is (No), that is, this time θ
_{If TH} ≦ θ _IDL holds, it is determined in step 214 whether the output level of the upstream O ₂ sensor FS has been inverted. By the time the answer is (No), the correction term [Delta] K _R to be described later, the [Delta] K _L calculated in step 215, step 223
The following integral control is performed.

Now, if the answer to step 214 is (Yes),
That is, when the output level of the upstream O ₂ sensor FS is inverted, proportional control (P term control) is performed. First step 2
16 upstream O ₂ output voltage FV _O2 sensor FS is determined whether or not lower than the reference voltage value V _REF as described above, the answer to this question is (Yes), ie if the FV _O2 <V _REF is established,
In step 217 based on the output voltage RV _O2 of the downstream O ₂ sensor RS shown in FIG. 19 retrieves the correction term P _R, the proportional control is performed for adding the correction term P _R in step 218 the correction coefficient K _O2 . On the other hand, the answer of step 216 is (N
when o), like searching correction term P _L based on the output voltage RV _O2 of the downstream O ₂ sensor RS shown in FIG. 19 at step 219, subtracted from the correction coefficient K _O2 said correction term P _L in step 220 Proportional control is performed.

[0038] The correction term P _R when the output FV _O2 of the upstream O ₂ sensor FS is inverted from rich to lean against the stoichiometric air-fuel ratio, the air-fuel ratio by increasing the correction coefficient K _O2 stepwise intended to shift to the rich side, the output voltage RV _O2 of the downstream O ₂ sensor RS is referred to when the said correction term P _R decreases enough to the output voltage RV _O2 are offset to the rich side , the output voltage RV _O2 reversed is set as the correction term P _R is increased enough that offset to the lean side. Also, the correction term P _L when the output FV _O2 of the upstream O ₂ sensor FS is inverted from lean to rich with respect to the theoretical air-fuel ratio, the correction coefficient K _O2 is decreased stepwise lean side air-fuel ratio intended for shifting to, where the output voltage RV _O2 of the downstream O ₂ sensor RS is referred to, the correction term P _L becomes larger as the output voltage RV _O2 are offset to the rich side, opposite Output voltage RV _O2
Is set so that the correction term P _L becomes smaller as the deviation toward the lean side. Thus, the upstream O ₂ sensor F
Output voltage RF of S output FV _O2 and downstream O ₂ sensor RS
Fine proportional control of the correction coefficient K _O2 is performed based on both _{O 2} (see the normal F / B mode in FIGS. 17 and 18).

Next, at step 221, step 21 is executed.
Correction coefficient K set at 8 or 220_O2Limit Che
Do a check. That is, the correction coefficient K_O2Is within the specified range
Check if there is, and if not within the predetermined range,
Correction coefficient K to the lower limit or lower limit _O2Hold. And last
In step 222, the correction coefficient K_O2Average value of K_REFIs calculated
And exit this program.

Next, the integration control in step 223 and subsequent steps will be described. Output voltage FV _O2 of the upstream O ₂ sensor FS is determined whether or not the reference voltage value V _REF is less than or first, in step 223, the answer is (Yes), i.e. FV _O2 <
When V _REF is satisfied, the value 2 is added to the count number N _IL every time this step is executed in step 224, and the count number N _IL is increased to a predetermined value N _{I in} step 225.
Is determined. If the answer is (No), the correction coefficient K _O2 is held at the immediately preceding value in step 226. If the answer is (Yes), the correction term ΔK _R is added to the correction coefficient K _O2 in step 227. At the same time, in step 228, the count number N _IL is reset to 0, and every time N _IL reaches N _I , the correction coefficient K _O2 becomes a predetermined value ΔK
Add _R.

Thus, the upstream O_TwoOutput of sensor FS
Voltage FV_O2Is the reference voltage value V_REFSmaller state
That is, when the air-fuel ratio lean state continues, the correction
Number K _O2Is the count number N_ILIs a predetermined value N_IEvery time
Predetermined value ΔK_RTo increase the air-fuel ratio
Is controlled.

On the other hand, the answer of step 223 is (No),
That is, when FV _O2 ≧ V _REF is satisfied, the count number N is set each time this step is executed in step 229.
_The value 2 is added to _IH.
IH it is determined whether or not reached a predetermined value N _I. If the answer is (No), the above-described step 226 is executed to hold the correction coefficient K _O2 at the immediately preceding value. If the answer is (Yes), the correction term ΔK _L is subtracted from the correction coefficient K _{O2 in} step 231. At the same time, at step 232, the counted number N _IH
Was Risseto to 0, the count N _{the IH} subtracts a predetermined value [Delta] K _L from the correction coefficient K _O2 per reaches a predetermined value N _I.

[0043] Thus, the upstream O ₂ output voltage FV _O2 sensor FS is equal to or higher than the reference voltage value V _REF state, that is, when the rich state of the air-fuel ratio continues, the correction coefficient K
_O2 is the count number N _{the IH} is reduced by a predetermined value [Delta] K _L each reaches a predetermined value N _I, is controlled in the direction of lean air-fuel ratio.

The correction terms ΔK _L and ΔK _R are determined in consideration of the output voltage RVO ₂ of the downstream O ₂ sensor RS as shown in FIG. That is, the correction term [Delta] K _R is after the output FV _O2 of the upstream O ₂ sensor FS is inverted from rich to lean against the stoichiometric air-fuel ratio, a rich-side air-fuel ratio is increased stepwise the correction coefficient K _O2 but is intended for shifting to, the output voltage RV _O2 of the downstream O ₂ sensor RS is referred to when its output voltage RV _O2 decreases said correction term [Delta] K _R enough that deviate to the rich side Conversely, the more the output voltage RV _{O2 shifts} to the lean side, the more the correction term ΔK
_R is set to be large. The correction term ΔK
_L is after the output FV _O2 of the upstream O ₂ sensor FS is inverted from lean to rich with respect to the stoichiometric air-fuel ratio, for the purpose of shifting the correction coefficient K _O2 stepwise decreasing the air-fuel ratio to the lean side However, at this time, the downstream O ₂ sensor RS
The reference output voltage RV _O2, the correction term higher the output voltage RV _O2 is the correction term [Delta] K _L becomes large enough that deviate to the rich side, the output voltage RV _O2 conversely is offset to the lean side ΔK _L is set to be small. Thus, the output FV _O2 of the upstream O ₂ sensor FS and the downstream O ₂
By referring to both the output voltage RF _O2 of the sensor RS, fine integration control of the correction coefficient K _O2 is performed (see the normal F / B mode in FIGS. 17 and 18).

Next, the catalyst deterioration monitor will be described.

[0046] As described above, in the flowchart of FIG. 3, when the catalyst C of the monitor permission is not made in step 108, the output voltage of the output voltage FV _O2 and downstream O ₂ sensor RS of the upstream O ₂ sensor FS RV _O2 Based on the above, feedback control is performed by the first air-fuel ratio adjusting means (see flowcharts in FIGS. 5 and 6). On the other hand, if the monitoring of the catalyst C is permitted in step 108, the monitoring mode of the catalyst C is executed in step 109. Hereinafter, the contents will be described in detail with reference to the flowcharts of FIGS.

The monitoring of the deterioration of the catalyst C is performed by the second air-fuel ratio adjusting means. At this time, the feedback control by the first air-fuel ratio adjusting means makes the output voltage FV _{O2 of the} upstream O ₂ sensor FS and the downstream while was done based on both the output voltage RV _O2 side O ₂ sensor RS, the feedback control by the second air-fuel ratio adjusting means based on only the output voltage RV _O2 of the downstream O ₂ sensor RS Done. The time TL from the occurrence of the special P term P _LSP for skipping the correction coefficient K _O2 from the rich side to the lean side with respect to the stoichiometric air-fuel ratio until the inversion of the O ₂ concentration from rich to lean is confirmed. Is detected,
The time TR from the occurrence of the special P term P _RSP for skipping the correction coefficient K _O2 from the lean side to the rich side with respect to the stoichiometric air-fuel ratio until the inversion of the O ₂ concentration from lean to rich is confirmed is TR. The deterioration of the catalyst C is determined based on the detected times TL and TR.

First, the schematic configuration of the catalyst deterioration monitor will be described with reference to the flowchart of FIG. 7, and then the subroutine of each step will be described in detail.

In FIG. 7, first, at step 301, the touch
Whether the preconditions are met for the detection of medium deterioration
If the answer is (No), step 302
Where n_TL(The number of TL measurements, ie, the time TL
Is the total number of times that has been measured), n _TR(TR measurement times,
(The total number of times the time TR has been measured), TL_SUM(T
L total value, that is, the total time of TL measured multiple times
Interval), TR_SUM(TR total value, that is, measured multiple times
Is set to zero. Then
In step 303, the first air-fuel ratio adjusting means described above
Normal feedback control is performed. The catalyst C
If the prerequisites are not met during the degradation monitoring of
K as the initial value of feedback control_REFIs used.

When the answer to step 301 is (Yes),
That is, when the precondition for monitoring the deterioration of the catalyst C is satisfied, it is determined in step 304 whether the TR measurement count n _TR is equal to or greater than a predetermined value. If the answer to step 304 is (Yes), it is determined that the data for determining the deterioration of the catalyst C has been prepared, and the deterioration determination process B is executed in step 305. Return to control. Also in this case, K _REF is used as an initial value of the feedback control.

When the answer to step 304 is (No)
Indicates that data for determining deterioration of the catalyst C is not prepared.
The following steps 307 to 315 are executed
You. That is, first, in step 307, monitoring is permitted.
First special P item P _LSP, P_RSPThere has occurred
Is determined. If the monitor has not yet started
The answer is (No), and the monitor star
Is executed. On the other hand, the answer of step 307 is
(Yes) and already the first special P item P_LSP, P
_RSPHas occurred, in step 309, the downstream O_TwoC
Output voltage RV of the sensor RS_O2Is reversed.
If the answer to step 309 is (Yes), step 310
In RV_O2Processing at the time of inversion, that is, the number of TL measurements n_TLis there
Or TR measurement count n_TRIncrement, lean dire
Timer_LD(RV_O2Is reversed and special P term P
_LSPMeasure the time to generate
Relay timer t_RD(RV_O2Special P after reversing
Term P_RSPStart measuring)
And special P term P_LSP, P_RSPThe occurrence of
You.

On the other hand, if the answer in step 309 is (No), the deterioration judgment processing A is started in step 314, and if the answer in step 315 is (Yes) and normality is confirmed, the process proceeds to step 306. Move and exit the monitor. On the other hand, if the answer at the step 315 is (No), and normality cannot be confirmed, the routine goes to a step 311. Step 311
In the output voltage RV _O2 monitors Permitted downstream O ₂ sensor RS even once from whether inverted or not. If the answer to the above step 311 is (No), that is, if the first inversion is performed after the monitoring is permitted, the inversion waiting process after the start is executed in the step 312, while the answer in the step 311 is for (Yes), that is, if after passing through one or more reverse the after start, RV _O2 inversion waiting process is performed in step 313. In these steps 312 and 313, the correction coefficient K _O2
, The special I term I _LSP is added or the special I term I _RSP is reduced. However, while the times TL and TR are measured in step 313, the measurements are not performed in step 312. This is because the continuation time of the reversal wait after the start depends on the timing at which monitoring is permitted.
This is because it is meaningless to measure L and TR.

Next, steps 301, 308, 312, 313, 310, and 300 in the flowchart of FIG.
The subroutines 314 and 305 will be sequentially described in detail.

FIG. 8 shows a subroutine (pre-monitoring condition) of step 301 in the flowchart of FIG. 7. First, in step 401, the operating state of the engine E for starting monitoring is confirmed. That is, the intake air temperature sensor 8
Is in the range of 60 ° C. to 100 ° C., the output Tw of the cooling water temperature sensor 9 is in the range of 60 ° C. to 100 ° C., or the output Ne of the engine speed sensor 10 is 2
It is in the range of 800 rpm to 3200 rpm, or the output Pb of the absolute pressure sensor 7 in the intake pipe is -350 mmHg to-
Whether it is in the range of 250 mmHg, the output Vh of the vehicle speed sensor 11 is in the range of 32 km / h to 80 km / h, or the output T _CAT of the catalyst temperature sensor 13 is 400 ° C. to 800 °
It is checked whether it is in the range of C. Then step 4
02, the vehicle speed is in a constant state, that is, the vehicle speed sensor 1
It is determined whether the state where the fluctuation of the output Vh of No. 1 is 0.8 km / sec or less has continued for a predetermined time (for example, 2 seconds). Next, in step 403, it is determined whether the feedback control has been performed for a predetermined time (for example, 10 seconds) before monitoring is permitted. Further, at step 404, a predetermined time (for example, 2
Second) has elapsed.

If all of the answers in steps 401 to 404 are (Yes), monitoring is permitted in step 405 and the process proceeds to step 304 in the flowchart of FIG. 7, and any one of the answers is (No). In this case, the monitor is rejected in step 406, and the process proceeds to step 302 in the flowchart of FIG.

FIG. 9 is a flowchart showing the steps in the flowchart of FIG.
Shows the subroutine (monitor start processing) of step 308
First, at step 501, the downstream O_TwoOf sensor RS
Output voltage RV_O2Is the reference voltage V_REFAnd the answer is
(Yes) and the output voltage RV _O2Is the reference voltage V_REFBelow
In other words, the downstream O_TwoDetection of sensor RS
O_TwoIf the concentration is lean, step 50
Correction coefficient K by 2_O2Special P term P to the value immediately before_RSPAdd
The proportional control is performed to calculate the air-fuel ratio on the rich side.
To increase stepwise. On the other hand, step 501
Is (No) and the output voltage RV_O2Is the reference voltage V_REF
In other words, the downstream O_TwoDetection of sensor RS
O_TwoIf the density is rich, step 5
03 and correction coefficient K_O2Special P term P from the previous value of_LSP
Proportional control is performed to reduce the air-fuel ratio.
To the step side.

FIG. 10 shows a subroutine of step 312 of the flowchart of FIG. 7 (reversal wait processing after start), and this flow is executed subsequently to the above-described flow of FIG. 9 (monitor start processing). Things. First, at step 601, the downstream O ₂ sensor RS
Compared output voltage RV _O2 is the reference voltage V _REF of, O ₂ the answer is the output voltage RV _O2 A (Yes) when below the reference voltage V _REF, i.e. it detects the downstream O ₂ sensor RS If the concentration is lean, step 6
At 02, integral control is performed to add the special I term I _RSP to the value immediately before the correction coefficient K _O2 , thereby gradually increasing the air-fuel ratio to the rich side. On the other hand, when the answer to step 601 is (No) and the output voltage RV _O2 is equal to or higher than the reference voltage V _REF , that is, when the O ₂ concentration detected by the downstream O ₂ sensor RS is in a rich state, step 60
At 3, integral control is performed to subtract the special I term I _LSP from the immediately preceding value of the correction coefficient K _O2 , thereby gradually reducing the air-fuel ratio to the lean side.

FIGS. 11 and 12 show the subroutine of step 313 (waiting process for inverting the downstream O ₂ sensor) in the flowchart of FIG. 7. This flow is the inversion of the output voltage RV _O2 of the downstream O ₂ sensor RS. Is executed as before. First, at step 701, it is determined whether the rich delay timer t _RD is counting down or after time-up. Rich delay timer t _RD
Consists subtraction counter, downstream O ₂ output voltage RV _O2 sensor RS starts counting down at the moment when inverted from lean to rich with respect to the stoichiometric air-fuel ratio, the count value and the time up when a predetermined time elapses Is zero. When the count value of the rich delay timer t _RD if the answer to the question of the step 701 (No) is not zero, that is, when the rich delay timer t _RD is in countdown, Special immediately prior value of the aforementioned correction coefficient K _O2 at step 702 Integral control for adding the I term I _RSP is performed, thereby gradually increasing the air-fuel ratio to the rich side.

On the other hand, if the answer at the step 701 is (Yes)
If there is, in step 703 the previous rich dera
Im t_RDIs determined whether the count value is not zero, and the answer is
(Yes), that is, the first rich delay
Timer t_RDWhen the count value of
In step 704, measurement of TL is started, and
The correction coefficient K at 705_O2Special P from P_LSPSubtract
The air-fuel ratio to the lean side by performing proportional control
Decrease. In addition, the answer to step 703 is (No).
The rich delay timer t_RDCount
If the value is continuously zero, step 706 is further performed.
It is determined whether the TL is being measured and the answer is (Yes)
In this case, in step 707, the correction coefficient K_O2Specialist from
Le I term I _LSPThe air-fuel ratio is reduced by performing integral control to subtract
And gradually decrease to the side.

[0060] Subsequently, whether or not the output signal FV _O2 of the upstream O ₂ sensor FS is inverted is determined in step 708,
If the answer is (Yes), it is determined in step 709 whether or not a time difference DL described later is being measured. The answer is (N
If o), the measurement of the time difference DL is started in step 710.

In the following step 711, it is determined whether the count value of the lean delay timer t _LD is zero, and if the answer is (No), that is, if the lean delay timer t _LD is counting down, In step 712, the special I term I from the immediately preceding value of the correction coefficient K _O2
Integral control for subtracting _LSP is performed, thereby gradually decreasing the air-fuel ratio to the lean side.

On the other hand, if the answer in step 711 is (Yes), it is determined in step 713 whether the count value of the previous lean delay timer t _LD is not zero, and if the answer is (Yes), that is, When the count value of the lean delay timer t _LD becomes zero for the first time this time, measurement of TR is started in step 714, and proportional control for adding the special P term P _RSP to the correction coefficient K _O2 is performed in step 715, and the idle control is performed. The fuel ratio is increased stepwise to the rich side. When the answer in step 713 is (No), that is, when the count value of the lean delay timer t _LD is continuously zero, it is further determined in step 716 whether TR is being measured or not. If yes, in step 717, the correction coefficient K _{O2 is set} to the special I
The air-fuel ratio is gradually increased toward the rich side by performing integral control for adding the term I _RSP .

[0063] Subsequently, whether or not the output signal FV _O2 of the upstream O ₂ sensor FS is inverted is determined in step 718,
If the answer is (Yes), it is determined in step 719 whether or not a time difference DR described later is being measured. The answer is (N
If o), measurement of the time difference DR is started in step 720.

FIGS. 13 and 14 show a subroutine of Step 310 (processing at the time of inversion of the downstream O ₂ sensor) of the flowchart of FIG.
_This is executed after the inversion of the _two sensors RS. First,
At step 801, it is determined whether or not the TL was being measured last time. If the answer is (Yes), the process proceeds to step 80.
In step 803, the TL measured this time is added to the TL total value TL _SUM.
The measurement number n _Tl is incremented.

Subsequently, in step 804, the measurement of the time difference DL started in step 710 in FIG. 11 is terminated, and in step 805, the DL measured this time is added to the DL total value DL _SUM , and the DL measurement number n Increment _Dl .

On the other hand, when the answer in step 801 is (No), that is, when the previous TL measurement was not being performed, it is determined in step 806 whether or not the previous TR was being measured, and the answer is (Yes). ), The measurement of TR is stopped in step 807, and the TR measured this time is added to the TR total value TR _SUM in step 808.
The TR measurement number n _TR is incremented.

Subsequently, in step 809, the measurement of the time difference DR, the measurement of which has been started in step 720 of FIG. 12, is terminated, and in step 810, the currently measured DR is added to the DR total value DR _SUM , and the DL measurement number n Increment _DR .

If n _TR is 1 in step 811 and n _Tl is 0 in step 812, TR _SUM is set to zero in step 813. This is T
This is because, in order to perform measurement in the order of L → TR, if TR is measured first, the TR is canceled.

Subsequently, at step 814, the output voltage RV _O2 of the downstream O ₂ sensor RS is compared with the reference voltage V _REF ,
Reference voltage V the answer is the output voltage RV _O2 A (Yes)
When it is below _REF , the countdown of the lean delay timer t _LD is started in step 815,
In step 816, integral control for subtracting the special I term I _LSP from the immediately preceding value of the correction coefficient K _O2 is performed, thereby gradually decreasing the air-fuel ratio to the lean side.

On the other hand, if the answer of the above step 814 is (No)
Output voltage RV_O2Is the reference voltage V _REFIf it is over
In step 817, the rich delay timer t_RDCow
Start down and correct in step 818
Coefficient K_O2Special I term I to the value immediately before_RSPThe product to add
Minute control is performed, thereby gradually increasing the air-fuel ratio to the rich side.
To increase.

FIG. 15 shows a subroutine (deterioration determination processing A) of step 314 in FIG.
At 001, it is determined whether or not the limit time t _STRG has elapsed without the next inversion since the occurrence of the special P term. Here, the above-mentioned average value (TL + TR) / 2 of TL and TR is used as the time T to be compared with the limit time t _STRG . If the average value (TL + TR) / 2 is longer than the limit time t _STRG, it is determined that the O ₂ storage capacity of the catalyst C is large, and the process proceeds to step 1002 without executing the above-described deterioration determination processing B. It is determined that the catalyst C is good. The measurement of the limit time t _STRG is shown in FIG.
And in the right column of the table in FIG.

The reason why the catalyst C can be determined to be good in the deterioration determination processing A is as follows. That is, the higher the O ₂ storage capability degree is small deterioration of the catalyst C, extends the inversion period of the downstream O ₂ sensor RS when the feedback control was performed in the second air-fuel ratio adjusting means. Therefore, if the average value of the times TL and TR until the downstream O ₂ sensor RS is inverted is larger than the limit time t _STRG, it can be determined that the catalyst C is good. When the catalyst C is good and the reversal period is long,
It is known that drivability deteriorates and harmful substances in exhaust gas increase. Therefore, when the catalyst C is good, the monitor mode is immediately stopped, and the inconvenience can be avoided by switching from the second air-fuel ratio adjusting means to the first air-fuel ratio adjusting means.

This will be described with reference to the graph of FIG. 21. A limit time t _STRG capable of preventing deterioration of drivability and increase of harmful substances in exhaust gas is set, and the average value of the TL and TR (TL + TR) is set. If / 2 exceeds the limit time t _STRG , it is determined that the catalyst C is good, and the monitor mode is stopped. From this graph, it is understood that the non-defective product of the catalyst C can be accurately identified using the limit time t _STRG .

FIG. 16 shows a subroutine (deterioration determination processing B) of step 305 in the flowchart of FIG. 7, and this flow is executed when the TR measurement number _nTR exceeds a predetermined number. First, in step 901, a value obtained by dividing the TL total value by the number of TL measurements (TL _SUM / n _Tl )
And the value obtained by dividing the TR total value by the TR measurement number (TR _SUM / n
_The time T _CHK is obtained by calculating the average value of _TR ).

Subsequently, at step S902, the time T
_CHKIs greater than a predetermined value, and the answer is
(Yes), the catalyst C_TwoStorage capacity
Assuming that the value exceeds the standard, the exhaust gas purification is performed in step 903.
Is determined to be normal. On the other hand,
When the answer to step S902 is (No), the catalyst C
O _TwoIf the storage capacity is below the standard,
In step 904, it is determined that the exhaust gas purification system is abnormal.
You.

At step 905, the DL total value is
The time D _CHK is obtained by calculating an average value of a value (DL _SUM / n _DL ) divided by the number of measurements and a value (DR _SUM / n _DR ) obtained by dividing the total DR value by the number of DR measurements.

Subsequently, at step S906, the time D
_CHK it is determined whether or not larger than a predetermined value, when the answer is (Yes), the O ₂ storage capability of the catalyst C is higher than the reference, it is normal exhaust gas purification system in step 907 Is determined. On the other hand, if the answer to the question of the step S906 is (No), the catalyst C O ₂
If storage capacity is below standard, step 9
At 08, it is determined that the exhaust gas purification system is abnormal.

FIG. 17 shows the operation of the catalyst C deterioration monitor.
Further description will be made with reference to the time chart of FIG.

At time (1) in FIG.
When the operation state of the vehicle satisfies a predetermined condition, the first air-fuel ratio adjustment is performed.
The means is switched to the second air-fuel ratio adjusting means and the catalyst C
Enter monitor mode. At this time, the downstream side indicated by the solid line
O_TwoOutput voltage RV of sensor RS_O2Is the reference voltage V_REFLess than
(Lean state), special P item P_RSPBy
Fuel correction coefficient K_O2Increases stepwise, followed by
Special I term I in region (2) and region (4)_RSPTo
More fuel correction coefficient K_O2Increases step by step. On the way
At time (3), the downstream O_TwoOutput voltage of sensor RS
RV_O2Changes from lean to rich with respect to the stoichiometric air-fuel ratio
Then, the rich delay timer t_RDIs set
Start down. Rich delay timer t_RDIs time
When the time is up in (5), this time special
P term P_LSPThe fuel correction coefficient K _O2Decreases in steps
Then, in the area (6) and the area (8),
Call I_LSPThe fuel correction coefficient K_O2Decreases gradually
I do. And the rich delay timer t_LDIs time
The TL measurement is started at time (5) when the
L is measured at time (7) at the output voltage RV._O2Is reasonable
It ends when the air-fuel ratio is reversed from rich to lean.
Complete. Similarly, at time (9), the lean
Timer_LDStarted measuring when time expired
TR is the output voltage RV_O2Is theoretically empty at time (11)
Measure when the fuel ratio changes from lean to rich
finish. In the area (2), lean
Ray timer t_LDIs not operating, TR measurement is not
I can't.

The upstream O shown by a broken line_TwoSensor FS
Output voltage FV_O2Is the downstream O indicated by the solid line._TwoOutput of sensor RS
Force voltage RV_O2The phase shifts with the phase advanced. Soshi
And upstream O_TwoOutput voltage FV of sensor FS_O2Is theoretical air-fuel
Measurement starts at the moment when the ratio is reversed from rich to lean.
The started time difference DL is the downstream O_TwoOutput voltage of sensor RS
RV_O2Is the output voltage FV_O2The stoichiometric air-fuel ratio
Corresponding to the time it takes to switch from rich to lean
Both are upstream O_TwoOutput voltage FV of sensor FS _O2Is the theory
Measured at the moment when air-fuel ratio is reversed from lean to rich
Time difference DR at which the downstream O_TwoOutput of sensor RS
Voltage RV_O2Is the output voltage FV_O2To the stoichiometric air-fuel ratio
The time from lean to rich reversal
You.

[0081] the time chart of FIG. 18 shows an example in which entered the monitor mode of the catalyst C at the output voltage RV _O2 of the downstream O ₂ sensor RS is higher than the reference voltage V _REF (rich state). In this example, the time T in the region (2)
The measurement of R is not performed because this is programmed in advance so that the first measurement is started from time TL and then the time TR is measured (step 811 in the flowchart of FIG. 13). Step 813). Therefore, the time difference DL and DR for which the measurement is started during the measurement at the time TL and TR are also measured first, and subsequently the time difference DR is measured.
Will be measured. Other points in the time chart of FIG. 18 are substantially the same as those of the above-described time chart of FIG.

The time TL measured as described above is
Fuel correction coefficient K to shift air-fuel ratio to lean side_O2To
Special P item P_LSPInstantaneously reduced by
From between, actually downstream O_TwoOutput voltage RV of sensor RS_O2
Changes from rich to lean with respect to the stoichiometric air-fuel ratio
Is equivalent to the delay time. Also, the time TR is a time when the air-fuel ratio is
Fuel correction coefficient K to shift to_O2Special P
Term P_RSPFrom the moment of step increase by
Downstream O_TwoOutput voltage RV of sensor RS_O2Is the stoichiometric air-fuel ratio
The delay time from the lean to rich reversal
Equivalent to. Similarly, the time difference DL shifts the air-fuel ratio to the lean side.
The upstream O_TwoOutput voltage of sensor FS
FV_O2From the moment when is changed from rich to phosphorus,
_TwoOutput voltage RV of sensor RS_O2Of the stoichiometric air-fuel ratio
It is equivalent to the delay time from the switch to lean.
Time TR is determined by shifting the air-fuel ratio to the rich side.
More upstream O_TwoOutput voltage FV of sensor FS_O2Is theoretical air-fuel
From the moment when the ratio reverses from lean to rich,
Side O_TwoOutput voltage RV of sensor RS_O2Is stoichiometric air-fuel ratio
Is equivalent to the delay time from the lean to rich reversal.
By the way, when the air-fuel ratio shifts to the lean side, the catalyst C
Oxidizing gas (O _TwoAnd NO_XAction to take in)
There is that O_TwoAnd NO_XWhen the import is finished
Downstream O_TwoOutput voltage RV of sensor RS_O2Is the theoretical air-fuel ratio
On the other hand, it changes from rich to lean. Catalyst C is air-fuel
When the ratio shifts to the rich side, the reducing gas (CO
And HC) and already taken O_TwoAnd N
O_XTo react with CO, and the removal of CO and HC
Is completed, the downstream O_TwoOutput voltage RV of sensor RS
_O2Changes from lean to rich with respect to the stoichiometric air-fuel ratio.
Therefore, the length of the time TL, TR and the time difference
The length of DL and DR is O of catalyst C._TwoLarge storage capacity
Time TL, TR or
The catalyst C having deteriorated lengths of the time differences DL and DR, ie, O
_TwoA parameter for discriminating the catalyst C having reduced storage capacity.
It can be used as a parameter.

The time TL, that is, O ₂ in the exhaust gas
And the time until NO _X is completely taken into the catalyst C, and the time TR, that is, the already taken O ₂ and NO ₂
The time until _X completely reacts with the next incorporated CO and HC is closely related. Therefore, the first measured time TL and the subsequently measured time TR are combined, and the catalyst C is calculated using the average value T _CHK of the TL and TR.
By measuring the O ₂ storage capacity of the catalyst C, it is possible to make a very precise determination of the deterioration of the catalyst C. Similarly, reversal of the output voltage FV _O2 of the upstream O ₂ sensor FS is for interlocking with a relatively short time delay and change in the air-fuel ratio, the time difference DL, the same is true with the above applies DR. Therefore, by combining the first measured time difference DL and the subsequently measured time difference DR, and measuring the O ₂ storage capacity of the catalyst C using the average value D _CHK of the DL and DR, extremely precise measurement can be performed. The deterioration of the catalyst C can be determined.

FIG. 22 shows TL measured continuously.₁, TR
₁, TL_Two, TR_Two, TL_Three, TR _Three, ... value and its flat
It shows the average. Here, the prescribed order (TL → TR
TL measured consecutively in order₁And TR₁Average A of
₁And in the same prescribed order (TL → TR)
Measured TL_TwoAnd TR_TwoAverage A of_TwoAre almost the same
This shows that highly accurate detection of catalyst C deterioration can be performed.
ing. However, out of the prescribed order (TR → T
L order) TR measured₁And TL_TwoAverage B of₁And the same
Measured differently from the prescribed order (TR → TL)
TR_TwoAnd TL_ThreeAverage B of_TwoHas large variations up and down
And that the detection accuracy is degraded.
You. Regarding the time differences DL and DR, the prescribed order (DL → D
Use the average of the time differences DL and DR measured in the order of R)
It is possible to detect the deterioration of the catalyst C with high accuracy.
Wear.

In addition, instead of using the average value of TL and TR or the average value of DL and DR as the time for determining the deterioration of the catalyst C, the sum of TL and TR measured in the specified order or the specified order The sum of the measured DL and DR can be used.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various small design changes can be made without departing from the present invention described in the appended claims. It is possible to do.

[0087]

As described above, according to the first aspect of the present invention, the time measured by the first time measuring means, that is, the time when the air-fuel ratio changes from the rich side to the lean side with respect to the stoichiometric air-fuel ratio. From the time when the output of the downstream O ₂ sensor is inverted from rich to lean with respect to the stoichiometric air-fuel ratio, and the time measured by the second time measuring means, that is, the air-fuel ratio is from the lean side with respect to the stoichiometric air-fuel ratio. The first time measuring means is used to determine the deterioration of the catalyst based on the time from when the output of the downstream O ₂ sensor changes from rich to rich with respect to the stoichiometric air-fuel ratio after the change to the rich side. The measured time,
After that time, the catalyst deterioration determining means makes the catalyst deterioration determination based on the sum or average of the times measured by the second time measuring means, so that the closely related catalysts are O ₂ and NO. _Both the time for adsorbing _X and the subsequent time for the catalyst to adsorb CO and HC are properly considered. As a result, it is possible to accurately detect the O ₂ storage capacity of the catalyst and to accurately determine the deterioration of the catalyst. Moreover, the air-fuel ratio adjusting means sets the air-fuel ratio to the stoichiometric air-fuel ratio.
From the rich side to the lean side or from the lean side
The reversal occurs even if the limit time elapses after changing to
If the catalyst is not good, the catalyst is judged to be good, and the deterioration of the catalyst is determined.
The catalyst normality judgment means for forcibly terminating
Therefore, the second air-fuel ratio adjusting means having a long air-fuel ratio inversion cycle is
Avoiding working longer than necessary, and as a result
Deterioration of drivability and increase of harmful substances in exhaust gas
Is prevented.

According to the second feature of the present invention, after the time difference measured by the first time measuring means, that is, the air-fuel ratio changes from rich to lean with respect to the stoichiometric air-fuel ratio,
And time difference from rich to reversed to the lean against the upstream O ₂ downstream O ₂ outputs the stoichiometric air-fuel ratio sensor from inverted from the rich to the lean output with respect to the theoretical air-fuel ratio sensor, the second After the time difference measured by the time measuring means, that is, the air-fuel ratio changes from the lean side to the rich side with respect to the stoichiometric air-fuel ratio, the output of the upstream O ₂ sensor is inverted from lean to rich with respect to the stoichiometric air-fuel ratio. The time difference measured by the first time measuring means and the time difference measured when the catalyst deterioration is determined based on the time difference from when the output of the downstream O ₂ sensor changes from lean to rich with respect to the stoichiometric air-fuel ratio. Subsequently, since the catalyst deterioration determining means performs the catalyst deterioration determination based on the sum or the average of the time differences measured by the second time measuring means, the closely related catalysts determine O ₂ and NO _X. Sucking Time to, subsequent catalytic both time to adsorb CO and HC are properly considered. As a result, it is possible to accurately detect the O ₂ storage capacity of the catalyst and to accurately determine the deterioration of the catalyst.
Moreover, the air-fuel ratio adjusting means resets the air-fuel ratio to the stoichiometric air-fuel ratio.
From lean to lean, or from lean to lean
The reversal does not occur even if the limit time elapses after changing
The catalyst is good and make a strong determination of catalyst deterioration.
By providing the catalyst normality determination means for
Therefore, a second air-fuel ratio adjusting means having a long air-fuel ratio inversion cycle is necessary.
Operation for an unnecessarily long time is avoided, and as a result
Deterioration of liability and increase of harmful substances in exhaust gas
Is prevented.

[Brief description of the drawings]

[Fig. 1] Claim correspondence diagram

FIG. 2 is an overall configuration diagram of a fuel supply control device.

FIG. 3 is a first partial diagram of a flowchart of a program for setting a correction coefficient K _O2 ;

FIG. 4 is a second partial diagram of a flowchart of a program for setting a correction coefficient K _O2 ;

FIG. 5 is a first partial diagram of a flowchart of a program of a first air-fuel ratio adjusting unit.

FIG. 6 is a second diagram of the flowchart of the program of the first air-fuel ratio adjusting means.

FIG. 7 is a flowchart of a program of a second air-fuel ratio adjusting unit.

FIG. 8 is a flowchart showing a subroutine of step 301 in FIG. 7;

FIG. 9 is a flowchart showing a subroutine of step 308 in FIG. 7;

FIG. 10 is a flowchart showing a subroutine of step 312 in FIG. 7;

FIG. 11 is a first partial diagram of a flowchart showing a subroutine of step 313 in FIG. 7;

FIG. 12 is a second partial diagram of a flowchart showing a subroutine of step 313 in FIG. 7;

13 is a first branch diagram of a flowchart showing a subroutine of step 310 in FIG. 7;

14 is a second partial diagram of a flowchart showing a subroutine of step 310 in FIG. 7;

FIG. 15 is a flowchart showing a subroutine of step 314 in FIG. 10;

FIG. 16 is a flowchart showing a subroutine of step 305 in FIG. 10;

FIG. 17 is a time chart showing a change in a correction coefficient K _O2 ;

FIG. 18 is a time chart showing a change in a correction coefficient K _O2 .

FIG. 19 is a graph showing a relationship between an output voltage RV _O2 and correction terms _RR and _RL.

FIG. 20 is a graph showing the relationship between output voltage RV _O2 and correction terms ΔK _R , ΔK _L

FIG. 21 is a graph showing a relationship between a catalyst purification rate and a measurement time T.

FIG. 22 is a graph showing times TL and TR and their average values.

[Explanation of symbols]

M1 fuel ratio adjusting means M2 first time measuring means M3 second time measuring means M4 catalyst deterioration determining means M5 catalyst normality determination unit FS upstream O ₂ sensor RS downstream O ₂ sensor FV _O2 output of the upstream O ₂ sensor Voltage RV _O2 Output voltage of downstream O ₂ sensor TL First time TR Second time DL First time difference DR Second time difference C Catalyst E Engine

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Maruyama 1-4-1 Chuo, Wako-shi, Saitama Pref. Honda Technical Research Institute Co., Ltd. (56) References JP-A-2-207159 (JP, A) JP-A 2-310453 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) F02D 41/22 305 F01N 3/20 F02D 41/14 310

Claims (2)

(57) [Claims] 1. An exhaust purification system for an engine (E) in which a catalyst (C) is disposed in an exhaust system, wherein the upstream is provided in an exhaust passage on an upstream side of the catalyst (C) and detects an air-fuel ratio of the engine (E). Side O ₂ sensor (FS)
And a downstream O ₂ sensor (RS) provided in the exhaust passage downstream of the catalyst (C) and detecting the air-fuel ratio of the engine (E).
And an upstream O ₂ sensor (FS) and a downstream O ₂ sensor (R
S) that adjusts the air-fuel ratio of the engine (E) in accordance with at least one of the outputs (FV _O2 , RV _O2 ), and that the air-fuel ratio adjustment means (M1) sets the stoichiometric air-fuel ratio From the rich side to the lean side with respect to the downstream O ₂
A predetermined time (TL) until the output (RV _O2 ) of the sensor (RS) is inverted from rich to lean with respect to the stoichiometric air-fuel ratio is determined.
A first time measuring means (M2) for measuring repeatedly a number of times
From the time when the air-fuel ratio adjusting means (M1) changes the air-fuel ratio from the lean side to the rich side with respect to the stoichiometric air-fuel ratio, from the downstream O ₂
Predetermined time (TR) until the output (RV _O2 ) of the sensor (RS) reverses from lean to rich with respect to the stoichiometric air-fuel ratio
Second time measuring means (M3) for repeating and counting the number of times
When they predetermined repeat count measured time (TL, T
When the sum or average of R) is less than a predetermined time, the catalyst (C)
The catalyst deterioration determining means (M4) for determining that the fuel has deteriorated and the air-fuel ratio adjusting means (M1) determine the air-fuel ratio with respect to the stoichiometric air-fuel ratio.
Rich side to lean side, or lean side to touch side
The reversal occurs even if the limit time elapses after changing to
When there is no catalyst (C), it is judged that the catalyst (C) is good and the catalyst (C)
Catalyst normality determining means (M
5), a deterioration determination device of a catalyst wherein the catalyst deterioration determining means (M4) is a first time measuring means (M2) time was measured as (TL), the time (TL)
The deterioration of the catalyst (C) is determined based on the sum or average of the time (TR) measured by the second time measuring means (M3). Judgment device. 2. An exhaust purification system for an engine (E) in which a catalyst (C) is disposed in an exhaust system, wherein the upstream is provided in an exhaust passage on an upstream side of the catalyst (C) and detects an air-fuel ratio of the engine (E). Side O ₂ sensor (FS)
And a downstream O ₂ sensor (RS) provided in the exhaust passage downstream of the catalyst (C) and detecting the air-fuel ratio of the engine (E).
And an upstream O ₂ sensor (FS) and a downstream O ₂ sensor (R
S) that adjusts the air-fuel ratio of the engine (E) in accordance with at least one of the outputs (FV _O2 , RV _O2 ), and that the air-fuel ratio adjustment means (M1) sets the stoichiometric air-fuel ratio after changing from the rich side to the lean side with respect to, the inverted from rich to lean relative to the output (FV _O2) is the stoichiometric air-fuel ratio of the upstream O ₂ sensor (FS), the downstream O ₂ sensor ( R
The time difference (DL) until the output (RV _O2 ) of S) changes from rich to lean with respect to the stoichiometric air-fuel ratio is repeated a predetermined number of times.
The first and the time measuring means (M2) for measuring return, after the air-fuel ratio adjusting means (M1) has changed from the lean side to the rich side air-fuel ratio relative to stoichiometric air-fuel ratio, the upstream O ₂ sensor (FS from inverted from lean to rich with respect to the output (FV _O2) is the stoichiometric air-fuel ratio) of the downstream O ₂ sensor (R
The time difference (DR) until the output (RV _O2 ) of S) reverses from lean to rich with respect to the stoichiometric air-fuel ratio is repeated a predetermined number of times.
Returns the second time measuring means for measuring and (M3), the measured time difference by repeating them a predetermined number of times (DL, D
When the sum or average of R) is less than a predetermined time, the catalyst (C)
The catalyst deterioration determining means (M4) for determining that the fuel has deteriorated and the air-fuel ratio adjusting means (M1) determine the air-fuel ratio with respect to the stoichiometric air-fuel ratio.
Rich side to lean side, or lean side to touch side
To the downstream O ₂ cell
When the inversion of the output (RV _O2 ) of the sensor (RS) does not occur
The catalyst (C) is judged to be good, and the deterioration of the catalyst (C) is judged.
Catalyst normality determining means (M5) for forcibly terminating the other;
A deterioration determination device of a catalyst wherein the catalyst deterioration determining means (M4) is a first time measuring means (M2) is the time difference measured with (DL), the subsequent to the time difference (DL) 2 Time difference (D3) measured by the time measuring means (M3)
A catalyst deterioration judging device, characterized in that it is configured to judge the deterioration of the catalyst (C) based on the sum or the average with R).