JPH08338233A - Exhaust emission control device for engine - Google Patents

Abstract

PURPOSE: To raise a use temperature limit and to maintain high purifying performance for a bypass catalyst by actively restoring the bypass catalyst from deterioration. CONSTITUTION: A main catalyst 32 is arranged on the downstream side of an exhaust pipe 31, while a platinum group catalyst 34 is arranged in a bypass passage 33 which diverges on the upstream side of the exhaust pipe 31 and converges again on the upstream side of the main catalyst 32, and a valve 35, which is positioned in a divergent part or a convergent part in the bypass passage 33 and can switch the passage, is arranged. In this case, a determining means 36 determines if the platinum group catalyst 34 deteriorates or not, and in determination of deterioration in the platinum catalyst 34, the valve 35 is switched to the side, on which the bypass passage 33 is fully opened, in the deterioration restoring area consisting of an exhaust high temperature area and an area, in which an air-fuel ratio is richened, by means of a deterioration restoring means 37.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying device for an engine, and more particularly to an exhaust gas purifying device having two or more catalysts.

[0002]

2. Description of the Related Art There is one in which two catalysts are selectively used according to the exhaust gas temperature (see JP-A-57-210116).

This will be explained with reference to FIG. 13. When the temperature of the exhaust gas detected by the temperature sensor 22 is low, such as when the engine is started, the switching valve 6 shuts off the exhaust flow to the main passage 3A and bypasses all the exhaust gas. It is guided to the catalyst 23.
Since the bypass catalyst 23 is close to the engine body 1, the inlet temperature of the bypass catalyst 23 is high, and the high-temperature exhaust gas causes the bypass catalyst 23 to exhibit high purification performance. Further, the exhaust gas that has passed through the bypass catalyst 23 warms up the main catalyst 4.

On the other hand, when the exhaust gas temperature detected by the temperature sensor 22 becomes higher than a predetermined value, such as during acceleration, switching of the switching valve 6 shuts off the exhaust flow to the bypass passage 3B, and the entire amount of exhaust gas is exhausted from the main passage 3A. To reach the main catalyst 4. Although the position of the main catalyst 4 is far from the engine body 1, the catalyst temperature of the main catalyst 4 is raised by the above-mentioned warming up from the start of the engine, and the inlet temperature of the main catalyst 4 is also high at the time of high exhaust temperature, so The catalyst 4 exhibits an excellent purifying action.

If the exhaust temperature state is divided into two, that is, when the temperature is low and when it is high, the proportion of the exhaust gas that directly flows into the bypass catalyst 23 and the main catalyst 4 is evenly distributed, and the catalysts 4 and 23 have substantially the same amount. That is, the poisoning substance of 1 is attached, and only one catalyst is not extremely deteriorated.

[0006]

By the way, in the conventional device, since the deterioration recovery process of the bypass catalyst is not performed,
In order to prevent the bypass catalyst from deteriorating, the exhaust gas is allowed to flow through the bypass passage 3B in a region of a considerably low temperature (for example, 500 ° C.), but at this time, the chances of using the bypass catalyst are reduced, so that the exhaust gas purification performance is improved. Deteriorate.
On the contrary, if the bypass catalyst is used at a higher temperature in order to enhance the exhaust purification performance, the deterioration of the bypass catalyst progresses and the exhaust purification performance deteriorates eventually, or the capacity of the bypass catalyst increases to withstand the catalyst deterioration. It is necessary to increase the amount of precious metal supported, which is disadvantageous in terms of cost increase and mounting.

On the other hand, if the switching valve is fixed and exposed to high temperature exhaust gas for a long time, the switching valve is oxidized and sticks to the valve. On the other hand, when the exhaust temperature is high, the switching valve is driven to the side that fully closes the bypass passage.Therefore, if the valve is switched to open the bypass passage to prevent the valve from sticking, the bypass catalyst becomes hot exhaust gas. It is exposed and deteriorates.

Therefore, in the present invention, firstly, by positively recovering the deterioration of the bypass catalyst, the operating temperature limit of the bypass catalyst is increased (that is, it can be used even at a temperature of 500 ° C. or higher) and the Takai purification performance is maintained. Secondly, the valve is periodically switched when the exhaust temperature is high, and the air-fuel ratio is made rich when the bypass passage is opened by this valve switching, thereby preventing and recovering the deterioration of the bypass catalyst. It is also intended to prevent valve sticking.

[0009]

The first invention, as shown in FIG. 14, is a bypass passage 33 branched from a main passage 32 upstream of an exhaust pipe 31, and a platinum inserted in the bypass passage 33. A system catalyst 34, a valve 35 capable of switching the exhaust flow to the bypass passage 33 and the main passage 32, and means 36 for determining whether the platinum catalyst 34 has deteriorated.
When the deterioration of the platinum-based catalyst 34 is determined, a means 37 for switching the valve 35 to the side where the bypass passage 33 is fully opened in the deterioration recovery area, where the exhaust temperature is high and the air-fuel ratio is rich. And.

In a second aspect based on the first aspect, when the valve 35 is switched to the side where the bypass passage 33 is fully opened, the control period Δt is set to the exhaust temperature Tmp.
Means for calculating the recovery degree Kk of the platinum-based catalyst 34 by adding up the value multiplied by every control cycle, and the bypass passage 33 when the catalyst recovery degree Kk becomes equal to or higher than the deterioration recovery degree request value K. The valve 35 is provided on the side to be fully closed.
And means for returning.

In a third aspect of the present invention, in the first or second aspect, when the catalyst recovery degree Kk disappears in the deterioration recovery region before reaching the deterioration recovery degree request value K, the deterioration recovery degree at that time is eliminated. The catalyst deterioration degree R1 corresponding to the difference between the required value K and the catalyst recovery degree Kk is obtained and stored, and when the deterioration recovery area is reached thereafter, the stored catalyst deterioration degree R1.
The deterioration recovery degree request value K corresponding to 1 is set.

As shown in FIG. 15, a fourth aspect of the present invention includes a bypass passage 33 branched from the main passage 32 upstream of the exhaust pipe 31, a platinum catalyst 34 interposed in the bypass passage 33, and A valve 35 capable of switching the exhaust flow to the bypass passage 33 and the main passage 32, a means 51 for determining whether or not sticking of the valve 35 is estimated based on the exhaust gas temperature Tmp, and a valve 51 for judging the sticking of the valve. Means 52 for periodically switching the valve 35 and means 54 for enriching the air-fuel ratio when the bypass passage 33 is opened by this valve switching are provided.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, before the time t during which the exhaust temperature Tmp is equal to or higher than the valve oxidation start temperature Tc is equal to or longer than the estimated valve sticking time tc, the exhaust temperature Tmp is equal to or higher than the valve oxidation. When the temperature becomes lower than the start temperature Tc, the time t at that time is stored, and when the exhaust temperature Tmp becomes equal to or higher than the valve oxidation start temperature Tc thereafter, the time measurement is started from the stored time. .

A sixth aspect of the invention is the fuel cell system according to any one of the first to third aspects of the invention, in which the bypass passage 33 is fully opened in the deterioration recovery region when the catalyst deterioration degree R becomes equal to or higher than the deterioration determination value Rc. The fuel cut or the air-fuel ratio feedback control is prohibited when the valve 35 is switched to the operating side.

A seventh aspect of the present invention is the valve according to the fourth or fifth aspect, wherein when the time t during which the exhaust gas temperature Tmp is equal to or higher than the valve oxidation start temperature Tc is equal to or higher than the valve sticking estimated time tc. Disables fuel cut or air-fuel ratio feedback control when switching is periodically performed.

In an eighth aspect based on any one of the second to seventh aspects, the exhaust temperature Tmp is calculated from the engine speed and the engine load.

In a ninth aspect based on any one of the fourth, fifth, seventh and eighth aspects, the valve sticking determination means 51 determines that the exhaust temperature Tmp is equal to or higher than the valve oxidation start temperature Tc. The means for measuring the time t during which the valve is stuck is estimated when the measured time t is equal to or longer than the estimated valve sticking time tc by comparing the measured time t with the estimated valve sticking time tc. And a means for determining.

[0018]

The deterioration of the catalyst includes permanent deterioration caused by the sintering of the noble metal and deformation of the cocatalyst (ceria, zirconia, alumina, etc.) due to heat, and recoverable temporary deterioration caused by the adhesion of sulfur and the oxidation reduction of the noble metal. In this case, the platinum-based catalyst is mostly deteriorated temporarily by the oxidation of the precious metal, so it is significantly deteriorated at high lean exhaust temperature, and conversely, it is recovered from the deteriorated state at high rich exhaust temperature. It was discovered for the first time that this was possible through experiments (see Japanese Patent Application No. 6-42794).

In the first aspect of the present invention, the region where the air-fuel ratio is made rich in the high temperature region of the exhaust gas is predetermined as the deterioration recovery region, and when the deterioration of the platinum-based catalyst is judged, the valve is switched in the deterioration recovery region and the platinum-based catalyst is heated at a high temperature. Since exhaust gas in a rich atmosphere is flown, the platinum-based catalyst recovers from deterioration, which enhances exhaust gas purification performance, and can reduce the capacity of the platinum-based catalyst and the amount of noble metal supported by the amount capable of recovery from deterioration.

It has been found for the first time by experiments that the recovery of the platinum-based catalyst from deterioration can be performed faster as the exhaust gas in the deterioration recovery region is at a higher temperature, and that recovery can be performed according to the time in the deterioration recovery region. Because it is, the second
In the invention described above, the value obtained by multiplying the exhaust temperature Tmp by the control cycle Δt is added up for each control cycle to recover the platinum-based catalyst according to the exhaust temperature in the rich atmosphere and the time of exposure to the exhaust temperature. Since the degree Kk can be calculated, the deterioration recovery process can be accurately finished.

In the third aspect of the invention, the deterioration recovery degree request value K when the catalyst recovery degree Kk is not in the deterioration recovery area before reaching the deterioration recovery degree request value K and is again in the deterioration recovery area is deteriorated for the first time. Since the value is smaller than the value when the recovery processing is started, the time until the deterioration recovery processing is started is shortened, and thus it is possible to avoid duplication of the deterioration recovery processing.

On the other hand, if the valve is fixed and exposed to high temperature exhaust gas for a long period of time, the valve oxidizes and sticks to the valve. Since the engine is driven, if the valve is switched to open the bypass passage to prevent the valve from sticking, the bypass catalyst is exposed to high temperature exhaust gas and deteriorates. However, in the fourth invention, it is based on the exhaust gas temperature. When the valve 34 is estimated to be stuck, the valve is switched periodically, and the air-fuel ratio is enriched when the bypass passage is opened by switching the valve. Therefore, deterioration of the platinum-based catalyst is suppressed as much as possible, and the valve is stuck. Can be prevented.

Even when the exhaust gas temperature Tmp is temporarily below the valve oxidation start temperature Tc, if the time t is returned to 0 and the time measurement is performed again, the timing for starting the valve switching process is delayed by that much, and the valve sticking is fixed. In the fifth aspect of the invention, the time measured halfway in the previous high temperature region where the exhaust gas temperature Tmp is equal to or higher than the valve oxidation start temperature is left as it is, and when the fifth high temperature region is reached, Since the time measurement is performed from the remaining time, the time until the estimated valve sticking time tc is reached is shortened, which reliably prevents the sticking of the valve even when the exhaust temperature Tmp is temporarily below the valve oxidation start temperature Tc. can do.

During the deterioration recovery process in which exhaust gas of high temperature and rich atmosphere in the deterioration recovery region is passed through the platinum-based catalyst, if fuel cut or air-fuel ratio feedback control is performed due to rapid deceleration, the air-fuel ratio becomes rich. If the air-fuel ratio enrichment process is not performed and the platinum-based catalyst deteriorates, the platinum-based catalyst deteriorates. However, in the sixth invention, the fuel cut and the air-fuel ratio feedback control are prohibited during the deterioration recovery process. Therefore, it is possible to prevent the deterioration of the platinum-based catalyst due to the fuel cut and the feedback control of the air-fuel ratio being performed during the deterioration recovery process.

When the valve is switched and the exhaust is flowing to the platinum-based catalyst during the valve sticking prevention process by periodically switching the valve, if fuel cut or feedback control of the air-fuel ratio due to rapid deceleration is performed. Since the exhaust gas in the lean atmosphere flows or may flow, the platinum-based catalyst deteriorates. In the seventh invention, however, the fuel cut and the air-fuel ratio feedback control are prohibited during the valve sticking prevention process. Of the exhaust gas does not flow to the platinum-based catalyst, which can prevent deterioration of the platinum-based catalyst due to fuel cut and feedback control of the air-fuel ratio during the valve sticking prevention process.

In the eighth aspect of the invention, a sensor for detecting the exhaust gas temperature is not required, so the cost does not increase.

According to the ninth aspect of the present invention, the determination as to whether or not the valve sticking is estimated is determined by both the valve oxidation start temperature and the valve sticking estimation time. Therefore, when the size and material of the valve are different, In response to this, the valve oxidation start temperature and the estimated valve sticking time may be changed,
This makes it possible to handle differences in valve size and material.

[0028]

EXAMPLE In FIG. 1, a main catalyst 4 which is a three-way catalyst is provided downstream of an exhaust pipe 3 connected to an exhaust manifold 2.
Is installed.

The exhaust pipe 3 branches into a main passage 3A and a bypass passage 3B immediately downstream of the exhaust manifold 2, and a bypass catalyst 5 consisting of a three-way catalyst mainly carrying platinum (Pt) is interposed in the bypass passage 3B. To be dressed.

A valve 6 for switching the flow of exhaust gas is provided at a branch portion between the bypass passage 3B and the main passage 3A, and the switching valve 6 is driven by a drive signal from the control unit 21. The switching valve 6 may be provided at the confluence of the bypass passage 3B and the main passage 3A.

A pair of O ₂ sensors 11 and 12 are provided immediately upstream and downstream of the bypass catalyst 5, and signals from these O ₂ sensors 11 and 12 are a sensor 13 for detecting the engine cooling water temperature Tw and an air flow meter. 14. Crank angle signal for each unit angle and reference position signal (Ref
Signal) and the signal from the crank angle sensor 15 that outputs the signal) to the control unit 21 and is composed of a microcomputer.
In No. 1, when the valve 6 is driven to the side where the bypass passage 3B is fully opened, the air-fuel ratio becomes a narrow range around the theoretical air-fuel ratio in the predetermined air-fuel ratio feedback control region based on the upstream O ₂ sensor output. Perform feedback control so that it fits.

In order to prevent the bypass catalyst 5 from deteriorating, the exhaust gas is allowed to flow in the bypass passage 3B in a region of a considerably low temperature (for example, 500 ° C.), but at this time, the opportunity to use the bypass catalyst 5 is reduced. Therefore, the exhaust purification performance becomes poor.

Further, the valve 6 is driven to the side where the bypass passage 3B is fully closed at the time of high temperature of exhaust gas, but in this state, when the valve 6 is fixed and exposed to high temperature exhaust gas for a long time, The valve 6 oxidizes and causes valve sticking. However, if the valve 6 is driven to open the bypass passage 3B in order to prevent the valve from sticking, the bypass catalyst 5 is exposed to high temperature exhaust gas and deteriorates.

In order to cope with this, in the present invention, the bypass catalyst 5, which is a platinum-based catalyst, is positively recovered from the deterioration to raise the operating temperature limit of the bypass catalyst 5 (that is, it can be used even at a temperature of 500 ° C. or higher). In addition to maintaining high exhaust gas purification performance, the valve 6 is periodically switched when the exhaust gas temperature is high, and the air-fuel ratio is made rich when the bypass passage 3B is opened by this valve switching, thereby degrading the bypass catalyst 5. Prevents valve recovery and prevents valve sticking.

More specifically, the deterioration of the catalyst includes permanent deterioration caused by sintering (sintering) of the noble metal due to heat and deformation of the co-catalyst and recoverable temporary deterioration caused by adhesion of sulfur and redox of the noble metal. There is. In this case, the platinum-based catalyst is mostly deteriorated temporarily by the oxidation of the precious metal, so it is significantly deteriorated at high lean exhaust temperature, and conversely, it is recovered from the deteriorated state at high rich exhaust temperature. It was found for the first time by experiments that recovery was achieved according to the time (Japanese Patent Application No. 6-42).
794). Therefore, when the temperature of the exhaust gas is high when the catalyst 5 is not deteriorated, the bypass passage 3B is not fully closed as in the conventional case to expose the bypass catalyst 5 to the exhaust gas, but it is judged that the catalyst 5 is deteriorated depending on whether it is deteriorated. Only when the judgment is made, in order to recover from the deterioration, the valve 6 is switched after the air-fuel ratio is made rich in a predetermined exhaust high temperature region, and the exhaust gas in a high temperature and rich atmosphere is flown to the bypass catalyst 5.

With respect to the above, since the valve sticking occurs when the exhaust gas high temperature state has passed a predetermined time with the valve 6 fixed, the time during which the exhaust high temperature state is maintained with the valve 6 fixed is measured. The valve sticking is prevented by switching the valve 6 every time when a predetermined time has a margin with respect to the predetermined time. Also at this time, when the valve 6 is switched to the side that opens the bypass passage 3B by utilizing the property of deterioration and recovery of the catalyst 5 which is a platinum-based catalyst,
By enriching the air-fuel ratio, deterioration of the catalyst 5 is suppressed as much as possible. At this time, if a certain high temperature can be obtained, the catalyst 5
It is possible to recover from deterioration.

By doing so, both active recovery from deterioration of the catalyst 5 and prevention of sticking of the valve 6 under high exhaust temperature are performed.

The contents of this control executed by the control unit 21 will be described with reference to the following flowchart.

The flowchart of FIG. 2 is for calculating the degree of deterioration of the catalyst 5, and is executed in synchronization with the Ref signal.

In step 1, the cooling water temperature Tw and the predetermined value T1
If Tw ≧ T1, it is determined that the warm-up is completed, and the process proceeds to step 2 to check whether it is in the deterioration diagnosis region of the catalyst 5. The diagnosis area is determined by checking the following items one by one, and when all of the items are satisfied, the diagnosis area is determined. That is, (1) the air-fuel ratio feedback control range, (2) the vehicle speed is within a predetermined range, (2) the engine speed N is within a predetermined range,
(3) When the basic injection pulse width Tp is within the predetermined range, it is determined to be in the diagnostic region, and the process proceeds to step 3 and subsequent steps.

In Steps 3 and 4, the inversion frequency F1 of the output of the upstream O ₂ sensor and the inversion frequency F2 of the output of the downstream O ₂ sensor are read, and the ratio F2 / F1 thereof is calculated in Step 5 as the inversion frequency ratio Fr. .

In the diagnosis area, the valve 6 is driven to the side where the bypass passage 3B is fully opened, and the supplied fuel amount is controlled by pseudo proportional-plus-integral control based on the upstream O ₂ sensor output. The output of the upstream O ₂ sensor periodically repeats rich and lean. On the other hand, on the downstream side of the catalyst 5, the fluctuation of the residual oxygen concentration becomes very gentle due to the O ₂ storage capacity of the catalyst 5, so that the downstream O ₂ sensor output is different from the upstream O ₂ sensor output. The fluctuation range is small and the cycle is long. On the other hand, when the catalyst 5 deteriorates, the oxygen concentration of the upstream side and the downstream side of the catalyst 5 do not change so much due to the decrease of the O ₂ storage capacity of the catalyst 5, so the cycle close to the output of the upstream O ₂ sensor is obtained. Then, the output of the downstream O ₂ sensor is repeatedly inverted, and its fluctuation range becomes large. Therefore, the value of the reversal frequency ratio Fr before catalyst deterioration is almost 0.
That is, the closer the Fr value is to 1, the greater the degree of deterioration.

In step 6, from the inversion frequency ratio Fr, as shown in FIG.
The catalyst deterioration degree R is obtained by referring to the table having the contents of.

In step 7, the deterioration recovery processing flag (initial value is "0") is checked. When the deterioration recovery process is not yet performed, the deterioration recovery process flag is set to 0. Therefore, the process proceeds to step 8, the catalyst deterioration degree R and the deterioration determination value Rc are compared, and when R ≧ Rc, the deterioration is performed. In order to execute the recovery process, the deterioration recovery process flag is set to "1" in step 9.

The flowchart of FIG. 4 is for carrying out the deterioration recovery process of the catalyst 5, and is executed at a constant cycle (Δt).

In step 11, the deterioration recovery processing flag is checked. If it is "1", step 12 is followed by step 12
See if it is the first time to proceed to.

If it is the first time, the process proceeds to the preprocessing of steps 13 and 14. In step 13, both fuel cut and air-fuel ratio feedback control (abbreviated as F / B control in the figure) are prohibited. If fuel cut or feedback control of the air-fuel ratio accompanying rapid deceleration is performed during the deterioration recovery process in which the hot exhaust gas in the deterioration recovery region is passed through the bypass catalyst 5, exhaust gas in a lean atmosphere flows to the catalyst 5,
Alternatively, the catalyst 5 may flow due to the flow, and the catalyst 5 deteriorates. Therefore, the fuel cut and the air-fuel ratio feedback control are prohibited during the deterioration recovery process.

In step 14, in order to determine how much deterioration recovery should be performed, a deterioration recovery degree required value K corresponding to the catalyst deterioration degree R is obtained by referring to the table having the contents of FIG.

In step 15 of FIG. 4, the deterioration recovery area flag (initial value is "0") is checked. If it is the first time that the process proceeds to step 15 after the deterioration recovery processing flag becomes "1", the deterioration recovery region flag = 0, so the process proceeds to step 16 and the engine speed N and the basic injection pulse width Tp are set. To N and Tp with reference to the map containing the contents of FIG.
Check whether the operating point to which the belongs belongs to the deterioration recovery area.
In FIG. 6, the deterioration recovery region is on the higher load and higher rotation side with the curve indicated by the broken line as the boundary.

FIG. 6 also shows a KMR zone (a region where the air-fuel ratio feedback control is stopped and the mixture ratio increasing coefficient KMR acts), and in this KMR zone, the air-fuel ratio is made richer than the stoichiometric air-fuel ratio. In other words, a region in which the temperature necessary for recovery from deterioration is equal to or higher than a predetermined value and the air-fuel ratio is in the rich atmosphere is the deterioration recovery region. Note that FIG. 6 also shows a map of the exhaust temperature Tmp, which will be described later, in an overlapping manner.

When it is judged that the deterioration recovery region is reached, in steps 17 and 18 of FIG. 4, the valve 6 is switched to the side where the bypass passage 3B is fully opened to flow all the exhaust gas to the catalyst 5, and the deterioration recovery region flag is set to "1". Set to.

By setting the deterioration recovery area flag to "1", in the next control cycle, steps 11 and 12 are skipped and steps 13 and 14 are skipped to flow to steps 15 and 19, where it is determined whether the area is in the deterioration recovery area. View. If it is in the deterioration recovery region, it is continuously in the deterioration recovery region, so the routine proceeds to step 20, where the exhaust temperature Tmp is obtained from N and Tp by referring to the map having the contents of FIG. 6, and this Tmp and the control cycle Δt are calculated. In step 21 of use, the recovery degree Kk of the catalyst 5 (initial value is 0) Kk is calculated by the following equation: Kk ← Kk + Δt × Tmp.

The higher the temperature of the exhaust gas in the deterioration recovery region, the faster the recovery from the deterioration of the catalyst 5 can be performed, and the recovery can be performed according to the time in the deterioration recovery region (the longer the stay time, the higher the recovery time). Since it is early), the control cycle Δt
Is multiplied by the exhaust temperature Tmp for each control cycle to obtain the catalyst recovery degree Kk according to the exhaust temperature of the catalyst 5 in a rich atmosphere and the time of exposure to the exhaust temperature.
Can be calculated. The skipped steps 30, 31, 32 will be described later.

Next, at step 22 in FIG. 4, the catalyst recovery degree Kk is compared with the deterioration recovery degree request value K. If Kk> K, the catalyst 5 has not yet recovered to the required value, and the process returns to step 11. Repeat the process. As long as it continues to the degradation recovery area, steps 11, 12, 15, 19, 20, 2
The processes of 1 and 22 are repeated, and when the catalyst recovery degree Kk eventually becomes equal to or higher than the deterioration recovery degree request value K, the post-processing of steps 23, 24 and 25 is performed.

In steps 23, 24 and 25, since the deterioration recovery process is completed, the deterioration recovery region flag, the deterioration recovery process flag and the deterioration recovery in-progress flag are all returned to "0", and the catalyst deterioration degree R and the catalyst recovery degree Kk are set. The value is cleared and the valve 6 is switched to the side where the bypass passage 3B is fully closed.

On the other hand, when the deterioration recovery area is no longer in the middle of the deterioration recovery process, steps 19 to 2 in FIG.
Go to 6-29. First, in step 26, the deterioration recovery area flag is returned to "0", and the deterioration recovery midway flag (initial value is "0") is set to "1". In steps 27 and 28, the catalyst deterioration degree R1 during the deterioration recovery process is obtained from the value (K-Kk) obtained by subtracting the catalyst recovery degree Kk from the deterioration recovery degree request value K with reference to the table having the contents of FIG. After storing this in memory, the value of Kk is cleared. Further, in step 29, the valve 6 is switched to the side where the bypass passage 3B is fully closed. In this case, follow step 1
From 1, 12, 30 to steps 31, 32, the value of R1 stored in the memory is transferred to the catalyst deterioration degree R,
From the transferred catalyst deterioration degree R, the deterioration recovery degree request degree K is obtained by referring to the table having the contents of FIG. 5, and then the processing of step 15 and thereafter is executed.

In this case (that is, deterioration recovery intermediate flag = 1)
Also, the deterioration recovery degree request value K (when the deterioration recovery area flag = 1) is smaller than the value when the deterioration recovery process is started for the first time (see the left half of FIG. 8), as shown in the right half of FIG. Therefore, the time until the catalyst recovery degree Kk reaches the deterioration recovery degree required value K in this case is shortened. The catalyst deterioration degree R is reduced by the amount of recovery even halfway and stored, and when the deterioration recovery region is reached thereafter, the required value K corresponding to the stored deterioration degree R is set, This avoids duplication of deterioration recovery processing.

The flowchart of FIG. 9 is for performing a basic switching process of the valve 6, and is executed at a constant cycle.
This is the same as the conventional one.

In step 41, the exhaust temperature Tmp is obtained from the engine speed N and the basic injection pulse width Tp by referring to the map shown in FIG. 6, and this exhaust temperature Tmp is compared with the catalyst deterioration temperature TR. TR is predetermined as a temperature at which the catalyst 5 deteriorates, and the exhaust temperature Tmp is the temperature TR.
When it is lower, it is judged that the catalyst 5 does not deteriorate much,
Proceed to step 43 to see if it is the first time that Tmp ≦ TR. If it is the first time, the valve 6 is switched to fully open the bypass passage 3B, and the exhaust gas is passed through the catalyst 5. On the other hand, even when the exhaust gas temperature Tmp becomes higher than TR, the catalyst 5 begins to deteriorate when the exhaust gas flows through the catalyst 5, so in this case, the routine proceeds to step 45, where the exhaust gas temperature Tm
If it is the first time for p to exceed TR, then in step 46 the valve 6 is switched to the side where the bypass passage 3B is fully closed.

Thus, when the exhaust gas is at a low temperature, the bypass catalyst 5 and the main catalyst 4 purify the exhaust gas, and when the exhaust gas reaches a predetermined high temperature range, it is judged that the main catalyst 4 is sufficiently activated, Further, in order to prevent the deterioration of the bypass catalyst 5, the exhaust gas does not flow through the bypass catalyst 5.

The flowchart of FIG. 10 is for preventing the valve 6 from sticking, and is executed at a constant cycle (Δt).

First, at step 51, the engine speed N
Then, the exhaust temperature Tmp is obtained from the basic injection pulse width Tp by referring to the map having the contents of FIG. 6, and this exhaust temperature Tmp and the valve oxidation start temperature Tc are compared in step 52. When it is determined that the oxidation of the valve 6 is started from Tmp ≧ Tc, the time (initial value is 0) t is compared with the estimated valve sticking time tc in step 53. tc is an estimated time until the valve sticks, and when Tmp ≧ Tc for the first time, t <tc. Therefore, step 53 to step 5
4, the time t is increased by the control cycle Δt. t
Measures the time during which the exhaust temperature Tmp is above Tc, and when t is above tc, the valve 6
Is determined to be fixed, and the process proceeds from step 53 to step 55 to the periodic switching of the valve 6.

The above valve oxidation start temperature Tc is T
Since the temperature is set to R (the temperature at which the catalyst 5 deteriorates) or a temperature higher than this, when the condition of Tmp ≧ Tc is satisfied before starting the sticking prevention processing of the valve 6, the valve 6 completely removes the bypass passage 3B. It is on the closed side.

At step 55, the valve switching processing flag (initial value is "0") is checked. When it is the first time, the process proceeds from step 0 to step 56, and the valve switching process flag is set to "1".

In steps 57 and 59, the fuel cut and the air-fuel ratio feedback control are prohibited, and the air-fuel ratio is made richer than the stoichiometric air-fuel ratio. Then, in step 60, the valve 6 is switched to the side where the bypass passage 3B is fully opened. The valve 6 is switched to prevent sticking. With this valve switching, when the valve 6 is switched to the side where the bypass passage 3B is fully opened, fuel cut or air-fuel ratio feedback control is performed and the catalyst 5 leans. When the exhaust gas in the atmosphere flows or may flow, the catalyst 5 deteriorates. Therefore, when opening the bypass passage 3B, the catalyst 5
Therefore, exhaust gas in a rich atmosphere is passed through the catalyst 5 in order to prevent deterioration of the catalyst.

When N and Tp are in the KMR zone shown in FIG. 6 in step 58, the enrichment of the air-fuel ratio in step 59 is skipped. This is because when the operating condition is in the KMR zone, the air-fuel ratio has already become rich due to the action of KMR, so it is not necessary to make it richer than that.

Even in the next control cycle, Tmp ≧ Tc and t ≧ t
When the condition of c is satisfied, the process proceeds from step 55 to step 61 in FIG. 10, and it is determined whether the predetermined time has elapsed with the valve fixed on the side where the bypass passage 3B is fully opened, and the predetermined time is determined. If it has not elapsed, the process returns to step 51 and is repeated. It waits as it is until a predetermined time elapses. When the predetermined time has elapsed, steps 61 to 62, 6
4 and the valve 6 on the side where the bypass passage 3B is fully closed.
To stop the enrichment of the air-fuel ratio. If it is in the KMR zone in step 63, step 64 is skipped. That is, when the conditions of Tmp ≧ Tc and t ≧ tc continue, as shown in FIG. 11, the valve 6 is fixed to the side where the bypass passage 3B is fully opened and the exhaust gas in the rich atmosphere is allowed to flow to the catalyst 5 for a predetermined time. After continuing, bypass passage 3B
The operation of returning the valve 6 to the fully closed side is repeated.

In this way, even if the temperature of the exhaust gas is high, the valve 6 can be periodically switched while suppressing the deterioration of the catalyst 5 as much as possible, so that the valve sticking can be prevented.

When Tmp <Tc, the process proceeds from step 52 to step 65 in FIG. 10, and the valve switching process flag is checked. When the valve switching process flag = 1, the valve switching process is terminated, so steps 66 and 67 are executed. At, the valve switching flag is returned to "0" and the time t is cleared.

On the other hand, when Tmp <Tc and the valve switching process flag = 0, steps 52 and 65 to step 6 are executed.
Proceed to step 9 to store the time t in the memory. Note that steps 68 and 70 will be described later.

In step 69 of FIG. 10, t has a value other than 0 because once the condition of Tmp ≧ Tc is satisfied and the time t is measured, the time t reaches the estimated valve sticking time tc. Is Tmp <Tc (that is, the valve switching process flag is not set to "1"). In this case, when the condition of Tmp ≧ Tc is satisfied again thereafter, the value stored in the memory is used as the initial value and the time measurement in step 54 of FIG. 10 is performed.

As shown in FIG. 12, even if the exhaust temperature Tmp is temporarily below Tc, the time t may be reset to 0 and the time measurement may be restarted (see the second broken line). However, the timing for starting the valve switching process is delayed by that much, which may lead to valve sticking.
Even if p is temporarily below Tc, in order to reliably prevent valve sticking, the time measured halfway in the previous exhaust high temperature region is left as it is, and when the current exhaust high temperature region is reached, the remaining time From then on, the time is measured (see the solid line in the second row).

In step 68 of FIG. 10, it is determined whether the valve 6 has been operated even once by other control (the basic switching process of FIG. 9). If the valve 6 is operated even once, the sticking is prevented. This time t is cleared.

In the embodiment, the control cycle of FIG. 4 and the control cycle Δt of FIG. 10 are the same, but they may be different.

[0075]

According to the first aspect of the present invention, not only the exhaust gas purification performance is enhanced, but also the capacity of the platinum-based catalyst and the amount of the noble metal supported can be reduced by the amount capable of recovery from deterioration.

In the second aspect of the present invention, it is possible to calculate the catalyst recovery degree according to the exhaust gas temperature in a rich atmosphere of the platinum-based catalyst and the time of exposure to this exhaust gas temperature. Can be finished.

According to the third aspect of the invention, when the catalyst recovery degree is no longer within the deterioration recovery area before reaching the deterioration recovery degree required value, the time until the deterioration recovery process is started when the catalyst recovery degree is subsequently reached This speeds up the process, thereby avoiding duplication of deterioration recovery processing.

In the fourth aspect of the present invention, it is possible to prevent the valve sticking while suppressing the deterioration of the platinum-based catalyst as much as possible.

In the fifth aspect, even if the exhaust temperature is temporarily below the valve oxidation start temperature, the valve sticking can be reliably prevented.

In the sixth aspect of the invention, it is possible to prevent deterioration of the platinum-based catalyst due to feedback control of fuel cut and air-fuel ratio during deterioration recovery processing.

In the seventh aspect of the present invention, it is possible to prevent the deterioration of the platinum-based catalyst due to the fuel cut and the feedback control of the air-fuel ratio being performed during the valve sticking prevention process.

In the eighth aspect of the invention, the sensor for detecting the exhaust gas temperature is not required and the cost does not increase.

In the ninth aspect of the invention, when the engine model is different, the valve oxidation start temperature and the estimated sticking time may be changed correspondingly, and thus the engine model can be coped with.

[Brief description of drawings]

FIG. 1 is a control system diagram of an embodiment.

FIG. 2 is a flowchart for explaining calculation of the degree of deterioration of the catalyst 5.

FIG. 3 is a characteristic diagram of a catalyst deterioration degree R with respect to an inversion frequency ratio Fr.

FIG. 4 is a flowchart for explaining deterioration recovery processing.

FIG. 5 is a characteristic diagram of a deterioration recovery degree required value K with respect to a catalyst deterioration degree R.

FIG. 6 is a characteristic diagram of a deterioration recovery region and a KMR zone.

FIG. 7 shows a difference (K− between the required degree of deterioration recovery and the catalyst recovery Kk.
It is a characteristic view of the catalyst deterioration degree R1 with respect to Kk).

FIG. 8 is a waveform diagram for explaining deterioration recovery processing.

FIG. 9 is a flowchart for explaining a basic switching process of the valve 6.

FIG. 10 is a waveform diagram for explaining a valve sticking prevention process.

FIG. 11 is a waveform diagram for explaining a valve sticking prevention process.

FIG. 13 is a control system diagram of a conventional example.

FIG. 14 is a diagram corresponding to claims of the first invention.

FIG. 15 is a diagram corresponding to claims of the fourth invention.

[Explanation of symbols]

3 Exhaust pipe 3A Main passage 3B Bypass passage 4 Main catalyst 5 Bypass catalyst 6 Switching valve 11 Upstream O ₂ sensor 12 Downstream O ₂ sensor 21 Control unit 31 Exhaust pipe 32 Main passage 33 Bypass passage 34 Platinum catalyst 35 Switching valve 36 Catalyst deterioration determination means 37 Degradation recovery means 51 Valve sticking determination means 52 Valve periodic switching means 53 Air-fuel ratio enrichment means

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] October 27, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a control system diagram of an embodiment.

FIG. 2 is a flowchart for explaining calculation of the degree of deterioration of the catalyst 5.

FIG. 3 is a characteristic diagram of a catalyst deterioration degree R with respect to an inversion frequency ratio Fr.

FIG. 4 is a flowchart for explaining deterioration recovery processing.

FIG. 5 is a characteristic diagram of a deterioration recovery degree required value K with respect to a catalyst deterioration degree R.

FIG. 6 is a characteristic diagram of a deterioration recovery region and a KMR zone.

FIG. 7 shows a difference (K− between the required degree of deterioration recovery and the catalyst recovery Kk.
It is a characteristic view of the catalyst deterioration degree R1 with respect to Kk).

FIG. 8 is a waveform diagram for explaining deterioration recovery processing.

FIG. 9 is a flowchart for explaining a basic switching process of the valve 6.

FIG. 10 is a waveform diagram for explaining a valve sticking prevention process.

FIG. 11 is a waveform diagram for explaining a valve sticking prevention process.

FIG. 12 is a waveform diagram for explaining a valve sticking prevention process when the exhaust temperature Tmp is temporarily below the valve oxidation start temperature Tc.

FIG. 13 is a control system diagram of a conventional example.

FIG. 14 is a diagram corresponding to claims of the first invention.

FIG. 15 is a diagram corresponding to claims of the fourth invention.

[Explanation of symbols] 3 Exhaust pipe 3A Main passage 3B Bypass passage 4 Main catalyst 5 Bypass catalyst 6 Switching valve 11 Upstream O ₂ sensor 12 Downstream O ₂ sensor 21 Control unit 31 Exhaust pipe 32 Main passage 33 Bypass passage 34 Platinum system Catalyst 35 Switching valve 36 Catalyst deterioration determination means 37 Degradation recovery means 51 Valve sticking determination means 52 Valve periodic switching means 53 Air-fuel ratio enrichment means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location F01N 3/24 ZAB F01N 3/24 ZABR F02D 41/04 305 F02D 41/04 305Z 41/14 310 41 / 14 310B

Claims (9)

[Claims] 1. A bypass passage branched from a main passage upstream of an exhaust pipe, a platinum-based catalyst interposed in the bypass passage, and a valve capable of switching an exhaust flow to the bypass passage and the main passage. A means for determining whether or not the platinum-based catalyst has deteriorated, and when the deterioration of the platinum-based catalyst is judged, the exhaust passage is fully opened in this deterioration recovery area with the exhaust high temperature range and the region where the air-fuel ratio is enriched as the deterioration recovery area. An exhaust emission control device for an engine, characterized in that a means for switching the valve is provided on the side of the engine. 2. When the valve is switched to the side where the bypass passage is fully opened, the recovery degree of the platinum-based catalyst is calculated by adding up a value obtained by multiplying the exhaust temperature by a control cycle for each control cycle. The means for calculating, and the means for returning the valve to the side where the bypass passage is fully closed when the catalyst recovery degree becomes equal to or higher than the deterioration recovery degree request value, are provided. Engine exhaust purification device. 3. When the catalyst recovery degree is not within the deterioration recovery area before reaching the deterioration recovery degree required value, the catalyst deterioration degree according to the difference between the deterioration recovery degree required value and the catalyst recovery degree at that time is set. 3. The deterioration recovery degree demand value according to the stored catalyst deterioration degree is set when it is obtained and stored, and then the deterioration recovery area is reached. Engine exhaust purification device. . 4. A bypass passage branched from the main passage upstream of the exhaust pipe, a platinum catalyst interposed in the bypass passage, and a valve capable of switching the exhaust flow to the bypass passage and the main passage. Means for determining whether or not the valve sticking is estimated based on the exhaust temperature, means for periodically switching the valve when the valve sticking is judged, and means for opening the bypass passage by the valve switching. An exhaust emission control device for an engine, comprising: means for enriching an air-fuel ratio. 5. If the exhaust temperature is lower than the valve oxidation start temperature before the time when the exhaust temperature is higher than the valve oxidation start temperature is longer than the estimated valve sticking time, the time at that time is stored. The exhaust gas purification apparatus for an engine according to claim 4, wherein after that, when the exhaust gas temperature becomes equal to or higher than the valve oxidation start temperature, the time measurement is started from the stored time. 6. When the catalyst deterioration degree is equal to or higher than the deterioration judgment value, the fuel cut or the air-fuel ratio feedback control is prohibited when the valve is switched to the side where the bypass passage is fully opened in the deterioration recovery region. The exhaust emission control device for an engine according to any one of claims 1 to 3, which is characterized in that. 7. A fuel cut or air-fuel ratio feedback control is prohibited when the valve is periodically switched when the time when the exhaust temperature is equal to or higher than the valve oxidation start temperature is equal to or higher than the valve sticking estimated time. The exhaust emission control device for an engine according to claim 4 or 5, wherein 8. The exhaust gas purification apparatus for an engine according to claim 2, wherein the exhaust gas temperature is calculated from an engine speed and an engine load. 9. The valve sticking determination means measures the time during which the exhaust gas temperature is equal to or higher than the valve oxidation start temperature, and compares the measured time with the valve sticking estimated time to measure the valve time. 6. A unit for determining that the valve sticking is estimated when the sticking time is longer than the estimated sticking time.
7. An engine exhaust emission control device according to any one of 7 and 8.