JPH07269330A - Catalyzer deterioration deciding device - Google Patents

Abstract

PURPOSE:To heighten the accuracy in deciding the degree of catalyzer deterioration by installing a front oxygen sensor and a rear oxygen sensor on the inlet side and on the outlet side of the catalyzer, respectively, and deciding the degree of deterioration based on a response delay, or a period from a time at which the output of the front oxygen sensor becomes lower than a standard value to another time at which the output of the rear oxygen sensor becomes lower than the standard value, taking almost one half the voltage value, or an amplitude, of each output signal as the standard value common to both sensors. CONSTITUTION:A front oxygen sensor 3 is installed in an exhaust pipe 2 on the inlet side of a catalyzer 1, which purifies exhaust gas from an engine, while a rear oxygen sensor 5 is installed in an exhaust pipe 4 on the outlet side. A catalyzer deterioration deciding device 6 is connected to both oxygen sensors 3, 5 so that the deterioration of the catalyzer can be decided from a response delay of both oxygen sensors. When the fuel supply to the engine is cut, the catalyzer deterioration is decided based on the response delay, or a period from a time at which the output of the front oxygen sensor becomes lower than a standard value to another time at which the output of the rear oxygen sensor becomes lower than the standard value, taking almost one half the voltage value, or an amplitude, of each output signal as the standard value common to both sensors. With this, arithmetic processing can be reduced and the accuracy can be hightened.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as a technique in the field of detecting a purification rate of a catalyst, a front oxygen sensor and a rear oxygen sensor are arranged in an exhaust pipe and an exhaust pipe of a catalyst, respectively. There is a method in which the purification rate of the catalyst is detected from the response delay time (for example, JP-A-51-55818). This catalyst is a three-way catalyst, and it contains carbon monoxide (CO) and hydrocarbons (H
Oxidation of C) and reduction of nitrogen oxides (NO _x ) are carried out simultaneously, and the three harmful gas components in the exhaust gas are converted into carbon dioxide (C
O ₂ ), water vapor (H ₂ O) and nitrogen (N ₂ ) are purified. This purification characteristic largely changes depending on the set air-fuel ratio of the engine. That is, when the air-fuel ratio is lean, the amount of oxygen increases even after combustion, and the oxidizing action becomes active and the reducing action becomes inactive. On the contrary, when the air-fuel ratio is rich, the oxidizing action becomes inactive and the reducing action becomes active. When this oxidation and reduction are well balanced (in the vicinity of the theoretical air-fuel ratio),
The three-way catalyst works most effectively.

The oxygen sensor may be a zirconia type oxygen sensor, and the zirconia type oxygen sensor is ZrO 2.
₂ is fired into a test tube, platinum electrodes are provided inside and outside, atmosphere is introduced into the inside to keep the oxygen concentration constant, and the outside air is exposed to the exhaust gas. When a difference in oxygen concentration occurs between both electrodes, oxygen ions flow from the side with a high oxygen concentration to the side with a low oxygen concentration, and an electromotive force (in the range of about 0 V to 1 V) is generated. This electromotive force outputs a small voltage in exhaust gas with a high oxygen partial pressure (combustion of a lean air-fuel mixture from the theoretical air-fuel ratio), and in exhaust gas with low oxygen partial pressure (combustion of a rich air-fuel mixture).
Outputs a large voltage.

By the way, the reduction of the purification rate of the catalyst means the deterioration of the catalyst. With the deterioration of the catalyst, the oxygen storage effect of the catalyst is reduced, and it is originally necessary for the catalyst to purify gases such as HC. Because the enzyme passes through,
The cycle of the rear oxygen sensor becomes shorter. That is, due to deterioration of the catalyst, the response delay time difference DT between the front oxygen sensor and the rear oxygen sensor changes so as to become shorter. The deterioration determining device for exhaust gas purification makes it possible to determine catalyst deterioration by utilizing the change in the response delay time difference DT.

[0005]

However, in the catalyst deterioration determination device, the oxygen storage capacity is obtained from the response delay time difference, and the purification rate of the catalyst is obtained from the oxygen storage capacity. Therefore, the catalyst deterioration is determined. Since the logic is complicated, the ECU (Electronic Control U
The calculation of (nit) becomes complicated. Further, if there is a variation in the operating state, the determination of catalyst deterioration depends on the operating state and is not reliable. That is, when driving in an urban area where the constant speed traveling is short, there is a problem that it is very difficult to determine the deterioration of the catalyst because the driving state varies and the variation of the response delay time difference increases.

Further, if the front oxygen sensor or the rear oxygen sensor itself is deteriorated, the response delay time difference is changed, which makes it impossible to obtain a highly accurate determination of catalyst deterioration. Therefore, in view of the above problems, the present invention is simple in calculation, does not depend on operating conditions, and can improve the accuracy of catalyst deterioration determination even when there is deterioration of the front oxygen sensor and the rear oxygen sensor. An object is to provide a deterioration determination device.

[0007]

In order to solve the above problems, the present invention provides a catalyst deterioration judging device having the following constitution. The catalyst deterioration determination device includes a front oxygen sensor and a rear oxygen sensor that are attached to each of an inlet side and an outlet side of a catalyst arranged in an exhaust pipe of an engine. When the fuel cut of the engine is performed, the output value of the front oxygen sensor is smaller than the reference value, with a common reference value being a voltage value that is approximately half the amplitude of each output signal of the front oxygen sensor and the rear oxygen sensor. After that, a response delay time difference, which is the time until the output of the rear oxygen sensor becomes smaller than the reference value, is obtained, and the catalyst deterioration is determined by comparing the response delay time difference and the degradation determination value.

Further, instead of the fuel cut, the response delay time difference may be obtained when the air is forced to flow into the exhaust pipe on the inlet side of the catalyst. Instead of the fuel cut, the fuel injection amount may be increased at least during acceleration to obtain the response delay time difference between the front oxygen sensor and the rear oxygen sensor.

Positions where upper and lower limit voltage values are set in the vicinity of the upper limit and the lower limit of the amplitudes of the front oxygen sensor and the rear oxygen sensor, respectively, and the outputs of the front oxygen sensor and the rear oxygen sensor cross the reference value. The respective tangents are determined, and the time difference between the positions where the tangent intersects the upper limit voltage value or the lower limit voltage value is defined as the response delay time difference.

[0010]

According to the catalyst deterioration determination device of the present invention, the deterioration determination of the catalyst is performed by determining the response delay time difference between the outputs of the front oxygen sensor and the rear oxygen sensor and using the response delay time difference for the catalyst deterioration determination. The logic of is simplified and the calculation processing is reduced.

Furthermore, by obtaining the response delay time difference between the front oxygen sensor and the rear oxygen sensor during fuel cut, a stable response delay time difference that does not depend on the operating condition can be detected. The response delay time difference between the front oxygen sensor and the rear oxygen sensor obtained by injecting air into the exhaust pipe on the inlet side of the catalyst was obtained, and the response delay time difference could be detected again well for an AT vehicle.

By obtaining the response delay time difference between the front oxygen sensor and the rear oxygen sensor obtained by increasing the fuel injection amount at the time of acceleration, the timing of detecting the response delay time difference in the city area is increased and the accuracy is improved. Can contribute.
The response delay time difference is that the upper limit voltage value or the lower limit voltage value is preset near the upper limit or the lower limit of the amplitude of the front oxygen sensor and the rear oxygen sensor, and the waveforms of the output signals of the front oxygen sensor and the rear oxygen sensor are the reference values. Even if the front oxygen sensor and the rear oxygen sensor are deteriorated, the accuracy is obtained by obtaining each tangent line at the position intersecting the value and obtaining the time difference between the positions at which each tangent line intersects the upper limit voltage value or the lower limit voltage value. The response delay time difference can be detected well.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a catalyst deterioration determination device according to an embodiment of the present invention. As shown in the figure, a front oxygen sensor 3 is provided on an exhaust pipe 2 on the inlet side of a catalyst 1 for purifying exhaust gas from an engine, and a rear oxygen sensor 5 is provided on an exhaust pipe 4 on the outlet side of the catalyst 1. Has been. The catalyst deterioration determination device 6 connected to the front oxygen sensor 3 and the rear oxygen sensor 5 determines the catalyst deterioration based on the response delay of both oxygen sensors. A method for determining catalyst deterioration will be described below.

The response delay time TF from when the air-fuel mixture supplied to the engine changes from rich to lean until the output signal of the front oxygen sensor 3 changes from rich (1V) to lean (0V) is given by the following equation. expressed. TF = t1 + D1 (1) Here, t1 is the delay time of the exhaust gas until the exhaust gas reaches the front oxygen sensor 3 from the engine, and D1 is the response time of the front oxygen sensor 3.

On the other hand, the response delay time T of the rear oxygen sensor 5
R is expressed by the following equation. TR = t1 + t2 + VO2 / QO2 + t3 + D2 (2) Here, t2 is the delay time of the exhaust gas until the exhaust gas reaches the catalyst 1 from the front oxygen sensor 3, QO2 is the oxygen flow rate in the exhaust gas, and VO2 / QO2 is the oxygen storage capacity VO2. The time until the overflow occurs, t3 is the delay time of the exhaust gas from the catalyst reaching the rear oxygen sensor 5, and D2 is the response time of the rear oxygen sensor 5. The above formula (1),
From (2), the response delay time difference DT is expressed by the following equation.

DT = TR-TF = VO2 / QO2 + (D2-D1) + (t2 + t3) (3) Here, the response time difference (D2-D1) must be taken into consideration when variations and characteristics of the oxygen sensor itself are not taken into consideration. I won't. However, by detecting the response delay time difference DT during the fuel cut, the response time difference (D2-D1) becomes a stable value regardless of the operating state, and the relationship between the response delay time difference DT and the oxygen storage capacity VO2 is 1: 1. Corresponding to.

FIG. 2 is a diagram showing the relationship between the response delay time difference and the purification rate. As shown in this figure, the relationship between the response delay time difference DT of the front oxygen sensor 3 and the rear oxygen sensor 5 and the purification rate α is known in advance, and this response delay time difference DT
Corresponds to the oxygen storage capacity of the catalyst 1 as described above. Therefore, the catalyst deterioration determination device 6 determines that the catalyst has deteriorated when the response delay time difference is smaller than the deterioration determination value (predetermined value). Thus, the purification rate can be easily determined directly from the response delay time difference without obtaining the oxygen storage capacity as in the conventional case.

FIG. 3 is a diagram showing a first structural example of the catalyst deterioration determination device 6 of FIG. As shown in the figure, the catalyst deterioration determination device 6 includes gate circuits 61 and 62 that allow the output signals of the front oxygen sensor 3 and the rear oxygen sensor 5 to pass through for a fixed time when the fuel cut signal is input. The output signals of the front oxygen sensor 3 and the rear oxygen sensor 5 change in the amplitude range of 0V to 1V. further,
The comparator 63, which inputs the output signal of the gate circuit 61 to the inverting terminal, inputs the reference voltage of 0.45 V to the other non-inverting terminal. This reference voltage is made to correspond to approximately half the amplitude of the front oxygen sensor 3 and the rear oxygen sensor 5. Further, the comparator 64 which inputs the output signal of the gate circuit 62 to the non-inverting terminal inputs the reference voltage of 0.45 V to the other inverting terminal. The output signals of the comparators 63 and 64 are A
Input to the ND circuit 65. The output signal of the AND circuit 65 is input to the timer 66, and the timer 66 starts at the rising edge of the output signal of the AND circuit and stops at the falling edge. The response delay time difference DT between the front oxygen sensor 3 and the rear oxygen sensor 5 is obtained from the measurement time of the timer 66. The deterioration determination unit 67 determines the deterioration of the catalyst by comparing the response delay time difference DT and the deterioration determination value.

FIG. 4 shows a response delay time difference D between the front oxygen sensor 3 and the rear oxygen sensor 5 according to the first configuration example of FIG.
It is a signal waveform diagram explaining that T is derived. As shown in this figure, the cycle of the output waveform A7 of the front oxygen sensor 3 is set to the rear oxygen sensor 5 due to the storage effect of the catalyst 1.
Is shorter than that of the output waveform A8. If there is a fuel cut during deceleration of the engine, there is a high probability that the front oxygen sensor 3 has
And the output signal of the rear oxygen sensor 5 is a reference voltage (0.45
It may be larger than V). In such a case, the output waveforms of the front oxygen sensor 3 and the rear oxygen sensor 5 head toward the lean state (0V). At this time, the output waveforms of the front oxygen sensor 3 and the rear oxygen sensor 5 are the reference voltage (0.
The points intersecting 45 V) are designated as A9 and A10. The time difference DT between the intersections A9 and A10 becomes the response delay time difference between the front oxygen sensor 3 and the rear oxygen sensor 5. The response delay time difference DT is obtained and, as described above, this is compared with the catalyst deterioration determination value.

Therefore, even if the constant speed running in the city area is not ensured, an accurate response delay time difference can be obtained in the fuel cut during deceleration of the engine without depending on the operating condition, so that the catalyst deterioration even during the city running. The accuracy of judgment can be improved. FIG. 5 is a diagram showing a modification of the first configuration example of FIG. The output signals of the front oxygen sensor 3 and the rear oxygen sensor 5 may be digitized, and the catalyst deterioration determination device 6 may perform the processing shown in this figure.

In step S1, it is determined whether or not there is a fuel cut signal. In step S2, if there is a fuel cut signal in the above determination, it is determined whether the voltage of the output signal of the front oxygen sensor 3 has become smaller than 0.45V. In step S3, the above determination is “Y
In the case of "ES", the timer is started when the voltage of the output signal of the front oxygen sensor 3 becomes smaller than 0.45V.

In step S4, the rear oxygen sensor 5
It is determined whether the voltage of the output signal of is smaller than 0.45V. In step S5, the above judgment is “YE
In the case of "S", the timer is stopped when the voltage of the output signal of the rear oxygen sensor 5 becomes smaller than 0.45V. The time measured by this timer is the response delay time difference DT.

In step S6, the response delay time difference is compared with the deterioration judgment value to judge the deterioration of the catalyst. In the above example, the response delay time difference DT changes depending on the degree of deterioration of the front oxygen sensor 3 and the rear oxygen sensor 5, and in this case, it is difficult to obtain an accurate catalyst deterioration determination. However, the oxygen sensor is characterized in that the response becomes slower as it deteriorates and the output waveform has a gentler slope. A solution using this feature will be described below.

FIG. 6 is a diagram for explaining the calculation of the response delay time difference DT when the front oxygen sensor 3 and the rear oxygen sensor 5 are deteriorated. As shown in FIG. 6, the tangent lines A11 and A12 are drawn at points A9 and A10 where the output waveform A7 of the front oxygen sensor 3 and the output waveform A8 of the rear oxygen sensor 5 intersect the line A15 of the reference voltage (0.45 V). . The tangent lines A11 and A12 intersect the line A16 having an output of 1.0 V, which is near the upper limit of the oxygen sensor, at points A13 and A1. Point A1
3, the time difference DT of A14 is the catalyst 1 as the response delay time difference.
It is used to judge the deterioration of. It will be explained below that the accuracy is improved by doing so.

FIG. 7 is a diagram for explaining the improvement of the accuracy of the response delay time difference DT. As shown in the figure, for example, when the front oxygen sensor 3 deteriorates, the output thereof changes from a solid line A23 to a broken line A24 so that the response becomes gradually slower. Therefore, the intersection A25 on the solid line A23 before deterioration and the reference voltage line A15 greatly changes to the intersection A26 with the broken line A24 according to the deterioration of the front oxygen sensor 3. However, the points A29 and A31 at which the tangent lines A27 and A28 of the points A25 and A26 intersect the line A16 having the output of 1.0 V are substantially the same. Therefore, the response delay time difference DT obtained from FIG. 6 is hardly affected by the deterioration of the front oxygen sensor 3 and the rear oxygen sensor 5, and a stable judgment can be made with respect to the deterioration of the catalyst. The achievement means will be described in detail below.

FIG. 8 is a diagram for explaining a second configuration example of the catalyst deterioration determination device 6 of FIG. As shown in this figure, when the fuel cut signal is input, the catalyst deterioration determination device 6 allows the gate circuits 61 and 62 to pass the output signals of the front oxygen sensor 3 and the rear oxygen sensor 5 for a certain period of time.
It is equipped with. Further, comparators 71 and 72 for inputting the output signal of the gate circuit 61 to the non-inverting terminal and the inverting terminal, respectively.
Is 0.4V to the other inverting terminal and non-inverting terminal,
Input 0.5V. Comparators 73 and 74 for inputting the output signal of the gate circuit 62 to the non-inverting terminal and the inverting terminal, respectively.
Is 0.4V to the other inverting terminal and non-inverting terminal,
Input 0.5V. The AND circuit 75 inputs the outputs of the comparators 71 and 72. The AND circuit 76 inputs the outputs of the comparators 73 and 74. The AND circuit 77 is the comparator 72
And the inverted output of the comparator 74 are input. Timers 78, 79, 8 connected to AND circuits 75, 76, 77
0 starts at the rising edge of each of the output signals of the AND circuits 75, 76 and 77 and stops at the falling edge to measure the time. The response delay time difference forming unit 81, which receives the output signals of the timers 75, 76, 77, is
The output signals of 6 and 77 are processed to obtain the response delay time DT of the front oxygen sensor 3 and the rear oxygen sensor 5. Based on this result, the deterioration determination unit 67 determines the deterioration of the catalyst in the same manner as described above.

FIG. 9 is a diagram for explaining the processing contents in the response delay time difference forming section 81 in FIG. As shown in the figure, the output waveform A7 of the front oxygen sensor 3 is 0.4 V and 0.
Points A20, A1 intersecting the 5V output lines A17, A18
The line segment formed by 9 can be approximated to the tangent line at the point A9. Similarly, a point A22 at which the output waveform A8 of the rear oxygen sensor 5 intersects the output lines A17 and A18 of 0.4 V and 0.5 V,
The line segment formed by A21 can be approximated to the tangent line at the point A10. The line segment formed by the points A13 and A14 where these tangents intersect the 1.0V output line A16 is the response delay time difference DT between the front oxygen sensor 3 and the rear oxygen sensor 5.

The times of A19 and A20 are TF1 and TF1, respectively.
Assuming TF2, the output of the timer 78 is TF2-TF1. The time of A21 and A22 is set to TR1 and TR2, respectively.
Then, the output of the timer 79 is TR2-TR1.
The output of the timer 80 is TR1-TF1.

In the response delay time difference forming section 81, the timer 7
The points A19 and A1 shown in FIG.
3 time difference DDT1, time difference DDT between points A21 and A14
2 is calculated as follows. DDT1 = {(TF2-TF1) / (0.5-0.4)} * (1.0-0.5) (4) DDT2 = {(TR2-TR1) / (0.5-0.4) )} × (1.0-0.5) (5) Using the data of the timer 80, the response delay time difference DT = TR1-TF1 + DDT1-DDT2 (6). After all, the values to be detected are TF1, TF2, TR
Therefore, the calculation of the response delay time difference DT can be realized very easily.

FIG. 10 is a diagram showing a modification of the second configuration example of FIG. Front oxygen sensor 3 and rear oxygen sensor 5
The output signal of the catalyst is digitized, and the catalyst deterioration determination device 6
May perform processing as shown in the figure. In step S11, it is determined whether or not there is a fuel cut signal. In step S12, if there is a fuel cut signal in the above judgment, it is judged whether the voltage of the output signal of the front oxygen sensor 3 has become smaller than 0.5V.

In step S13, the above judgment is "Y.
In the case of "ES", the first timer and the second timer are started when the voltage of the output signal of the front oxygen sensor 3 becomes smaller than 0.5V. In step S14, the voltage of the output signal of the front oxygen sensor 3 is 0.4V.
To determine if it has become smaller than.

In step S15, the above judgment is "Y.
In the case of "ES", the first timer is stopped when the voltage of the output signal of the front oxygen sensor 3 becomes smaller than 0.4V. DDT1 is obtained from the measurement time of the first timer. In step S16, it is determined whether the voltage of the output signal of the rear oxygen sensor 5 has become smaller than 0.5V.

In step S17, the above judgment is "Y
In the case of "ES", when the voltage of the output signal of the rear oxygen sensor 5 becomes smaller than 0.5 V, the second timer is stopped and the third timer is started. The measurement time of the second timer is set to TR1-TF1. In step S18, it is determined whether the voltage of the output signal of the rear oxygen sensor 5 has become smaller than 0.4V.

In step S19, the above judgment is "Y
In the case of "ES", the third timer is stopped when the voltage of the output signal of the rear oxygen sensor 5 becomes smaller than 0.4V. DDT2 is obtained from the measurement time of the third timer. In step S20, steps S15, S17,
According to the measurement time obtained in 19, based on the above equation (6),
The response delay time difference DT is obtained.

In step S21, the deterioration of the catalyst is judged from the response delay time difference DT. Next, the following experiment was performed to show how excellent the catalyst deterioration determination method using the response delay time difference DT as a determination value is. 11 is a diagram showing an experimental system for confirming the accuracy of catalyst deterioration determination according to the present embodiment. As shown in the figure, regarding the positional relationship between the front oxygen sensor 3 and the rear oxygen sensor 5 attached to the exhaust pipe 32 and the catalyst 1, the distance A33 from the engine 30 to the front oxygen sensor 3 is 1000 mm. The distance A34 from the front oxygen sensor 3 to the catalyst 1 having a capacity of 1700 cc and a length of 320 mm is 75 mm, and further, the distance A3 from the catalyst 1 to the rear oxygen sensor 5.
5 is 125 mm. The engine speed of the engine 30 is 200
The intake pressure is kept constant at 0 rpm and -200 mmHg, the throttle is fully closed there and the fuel is cut, and the value of the response delay time difference DT at that time is examined. The catalyst 1 is prepared as a new product, a deteriorated product, and a product without catalyst support. Here, the catalyst-free product is more deteriorated than the deteriorated product.

12 and 13 show a combination of the front oxygen sensor 3 and the rear oxygen sensor 5 for a new product, a deteriorated product, and a product without catalyst loading in the first configuration example of FIG. 2 and the second configuration example of FIG. It is a figure which shows the response delay time difference obtained in the case of. As can be seen by comparing the response delay time differences in FIGS. 12 and 13, it can be seen that the second configuration example according to FIG. 13 has a stable response delay time difference value without being significantly affected by the deterioration of the oxygen sensor. .

Further, in the above description, the response delay time difference is obtained at the time of fuel cut, but if the throttle is rapidly returned during running, the same result as above can be obtained even at the time of fuel cut. FIG. 14 is a diagram showing the characteristics of the oxygen sensor. As shown in this figure, the output of the oxygen sensor changes rapidly in the vicinity of the stoichiometric air-fuel ratio (A / F). Therefore, the oxygen sensor output B1 changes the response to the lean state B2 by only slightly increasing the oxygen concentration of the exhaust gas. Show. Therefore, the output waveform of the oxygen sensor as when all cylinders are in the fuel cut state can be obtained by only performing the fuel cut when decelerating only one cylinder.

In the above embodiment, the responsiveness of the oxygen sensor at the time of fuel cut is utilized, but AT (Automatic Trans
mission) In vehicles, the problem is that the fuel cut timing decreases. Therefore, in order to solve the above problem, an embodiment will be described below in which the oxygen sensor is forcibly provided with an environment such as during fuel cut. FIG. 15 is a diagram showing another example of the present invention, in which the output of the oxygen sensor during fuel cut is reproduced by forcibly changing the oxygen concentration in the exhaust gas. As shown in the figure, it is possible to reproduce the output of the oxygen sensor at the time of fuel cut by injecting air into the exhaust pipe 32 using the air pump 36. Since the output of the oxygen sensor can be arbitrarily set to the lean state by opening / closing the valve 37, the response delay time difference between the front oxygen sensor 3 and the rear oxygen sensor 5 can be obtained.

Although the above-described embodiment at the time of deceleration and the like uses the lean response of the oxygen sensor, even if the rich response of the oxygen sensor accompanying the increase in the fuel injection amount at the time of acceleration is utilized,
Deterioration of the catalyst can be determined as follows. FIG.
FIG. 8 is a diagram showing another example of the present invention, in which the response delay time difference is obtained by utilizing the rich response of the oxygen sensor associated with the fuel injection amount increase during acceleration or the like. As shown in the figure, in the output waveforms A7 and A8 of the front oxygen sensor 3 and the rear oxygen sensor 5 at the time of acceleration, the response delay time DT is obtained from the intersections A9 and A10 with the reference voltage from the direction opposite to that of FIG. You may Furthermore, the tangent line at the intersection of the front oxygen sensor 3 and the rear oxygen sensor 5 is shown in FIG.
, The time difference D near the output 0 V, which is the lower limit of the front oxygen sensor 3 and the rear oxygen sensor 5,
T is used for determining the deterioration of the catalyst as a response delay time difference when the front oxygen sensor and the rear oxygen sensor 5 are deteriorated.

[0040]

As described above, according to the present invention, the response delay time difference between the outputs of the front oxygen sensor and the rear oxygen sensor is obtained without using the oxygen storage capacity and is used for the catalyst deterioration determination. Processing is reduced. Since the response delay time difference between the front oxygen sensor and the rear oxygen sensor at the time of fuel cut is obtained, the response delay time difference can be obtained without depending on the operating state, and therefore, the response delay time difference can be accurately detected. The response delay time difference between the front oxygen sensor and the rear oxygen sensor obtained by injecting air into the exhaust pipe on the inlet side of the catalyst was obtained, and the response delay time difference could be detected again well for an AT vehicle. Since the response delay time difference is the time difference between the tangent line at the reference voltage of the output waveforms of the front oxygen sensor and the rear oxygen sensor and the voltage value near the upper limit value or the lower limit value of the output waveform, the response delay time difference is set, and thus the oxygen sensor deteriorates. Also, the response delay time difference can be accurately detected.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a catalyst deterioration determination device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a deviation of a response delay time difference and a purification rate.

3 is a diagram showing a first configuration example of a catalyst deterioration determination device 6 of FIG.

FIG. 4 is a signal waveform diagram for explaining that a response delay time difference DT between the front oxygen sensor 3 and the rear oxygen sensor 5 is derived in the first configuration example of FIG.

FIG. 5 is a diagram showing a modification of the first configuration example of FIG.

FIG. 6 is a diagram illustrating the calculation of a response delay time difference DT when the front oxygen sensor 3 and the rear oxygen sensor 5 are deteriorated.

FIG. 7 is a diagram illustrating an improvement in accuracy of a response delay time difference DT.

FIG. 8 is a diagram showing a second configuration example of the catalyst deterioration determination device 6 of FIG.

FIG. 9 is a diagram for explaining processing contents in the response delay time difference forming unit 81 in FIG.

FIG. 10 is a diagram showing a modification of the second configuration example of FIG.

FIG. 11 is a diagram showing an experimental system for confirming the accuracy of catalyst deterioration determination according to the present embodiment.

FIG. 12 is a diagram showing a response delay time difference obtained when the front oxygen sensor 3 and the rear oxygen sensor 5 are combined with a new product, a deteriorated product, and a product without catalyst loading in the first configuration example of FIG. 2.

13 is a diagram showing a response delay time difference obtained when the front oxygen sensor 3 and the rear oxygen sensor 5 are combined with a new product, a deteriorated product, and a product without catalyst loading in the second configuration example of FIG.

FIG. 14 is a diagram showing characteristics of an oxygen sensor.

FIG. 15 is a diagram showing another example of the present invention in which the output of the oxygen sensor during fuel cut is reproduced by forcibly changing the oxygen concentration in the exhaust gas.

FIG. 16 is a diagram showing another example of obtaining the response delay time difference by utilizing the rich response of the oxygen sensor accompanying the increase in the fuel injection amount during acceleration or the like, which is another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Catalyst 2 ... Exhaust pipe on catalyst inlet side 3 ... Front oxygen sensor 4 ... Exhaust pipe on catalyst outlet side 5 ... Rear oxygen sensor 6 ... Catalyst deterioration determination device 30 ... Engine 32 ... Exhaust pipe 36 ... Air pump 37 ... Valve

Front page continued (72) Inventor Yoshihiko Watanabe 14 Iwatani Shimohakaku-cho, Nishio-shi, Aichi Japan Auto Parts Research Institute, Inc. (72) Inventor Yasushi Kawabe 14 Iwatani Shimohakaku-cho, Nishio-shi, Aichi Japan Automobile Co., Ltd. Inside Parts Research Laboratory (72) Inventor Kennori Kato 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Hirokazu Usui 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd.

Claims (4)

[Claims] 1. A front oxygen sensor and a rear oxygen sensor, each of which is attached to each of an inlet side and an outlet side of a catalyst disposed in an exhaust pipe of an engine, are provided, and when a fuel cut of the engine is performed, a front oxygen sensor is provided. The voltage value of approximately half the amplitude of each output signal of the oxygen sensor and the rear oxygen sensor is used as a common reference value, and after the output of the front oxygen sensor becomes smaller than the reference value, the output of the rear oxygen sensor is less than the reference value. A catalyst deterioration determination device that determines a response delay time difference, which is the time until it becomes smaller, and compares the response delay time difference with a deterioration determination value to determine catalyst deterioration. 2. The catalyst deterioration determination device according to claim 1, wherein the response delay time difference is obtained when air is forced to flow into the exhaust pipe on the inlet side of the catalyst instead of during the fuel cut. 3. The catalyst deterioration determination device according to claim 1, wherein instead of the fuel cut, the fuel injection amount is increased at least during acceleration to obtain a response delay time difference between the front oxygen sensor and the rear oxygen sensor. 4. An upper limit voltage value or a lower limit voltage value is set in the vicinity of the upper limit or the lower limit of the amplitudes of the front oxygen sensor and the rear oxygen sensor, respectively, and the outputs of the front oxygen sensor and the rear oxygen sensor cross the reference value. The catalyst according to any one of claims 1, 2 and 3, wherein each tangent of each position is determined, and a time difference between respective positions where the tangent intersects the upper limit voltage value or the lower limit voltage value is defined as a response delay time difference. Deterioration determination device.