JP3303604B2 - Engine exhaust purification device - Google Patents

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 apparatus for an engine, and more particularly to an apparatus having two or more catalysts.

[0002]

2. Description of the Related Art There is one in which two catalysts are selectively used in accordance with the exhaust gas temperature (see Japanese Patent Application Laid-Open No. 57-210116).

Referring to FIG. 13, when the exhaust gas temperature detected by the temperature sensor 22 is low, such as when the engine is started, the flow of exhaust gas to the main passage 3A is cut off by the switching valve 6, and the entire amount of exhaust gas is bypassed. It is led 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 allows the bypass catalyst 23 to exhibit high purification performance. Further, the main catalyst 4 is warmed up by the exhaust gas that has passed through the bypass catalyst 23.

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, the flow of exhaust gas to the bypass passage 3B is cut off by switching the switching valve 6, and the entire amount of exhaust gas is reduced to the main passage 3A. And reaches 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 warming-up after the engine is started, and the inlet temperature of the main catalyst 4 is high at a high exhaust temperature. The catalyst 4 shows an excellent purifying action.

If the exhaust gas temperature state is roughly divided into a low temperature state and a high temperature state, the ratio of the exhaust gas directly flowing into the bypass catalyst 23 and the main catalyst 4 is evenly distributed. No poisoning substance adheres, and only one of the catalysts does not extremely deteriorate.

[0006]

By the way, in the conventional device, the deterioration recovery processing of the bypass catalyst is not performed.
In order to prevent the bypass catalyst from deteriorating, the exhaust gas is flown into the bypass passage 3B at a considerably low temperature (for example, 500 ° C.). become worse.
Conversely, if the bypass catalyst is used at a higher temperature in order to enhance the exhaust purification performance, the degradation of the bypass catalyst will progress, and eventually the exhaust purification performance will deteriorate. It is necessary to increase the amount of the noble metal carried, which is disadvantageous in terms of cost and mounting.

On the other hand, if the time during which the switching valve is exposed to high-temperature exhaust gas while the switching valve is fixed becomes longer, the switching valve is oxidized and causes sticking of the valve. However, when the exhaust gas is hot, the switching valve is driven to fully close the bypass passage, so if the valve is switched to open the bypass passage in order to prevent sticking of the valve, the bypass catalyst may generate high-temperature exhaust gas. Exposure deteriorates.

Accordingly, the present invention firstly raises the operating temperature limit of the bypass catalyst (that is, it can be used even at a temperature of 500 ° C. or more) by actively recovering the deterioration of the bypass catalyst, and maintains the Takai purification performance. Secondly, while the exhaust gas is at a high temperature, the valve is periodically switched, and by switching the valve, the air-fuel ratio is made rich when the bypass passage is opened, thereby preventing and recovering the deterioration of the bypass catalyst. Another object is to prevent the valve from sticking.

[0009]

According to a first aspect of the present invention, as shown in FIG. 14, a bypass passage 33 branched from a main passage 32 upstream of an exhaust pipe 31 and a platinum passage provided in the bypass passage 33 are provided. 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.
Means for switching the valve 35 to a side in which the bypass passage 33 is fully opened in the deterioration recovery region, using the high temperature region of the exhaust gas and the region where the air-fuel ratio is enriched as the deterioration recovery region when the deterioration of the platinum catalyst 34 is determined. And provided.

According to a second aspect of the present invention, in the first aspect, when the valve 35 is switched to the side where the bypass passage 33 is fully opened, the exhaust gas temperature Tmp is changed to a control cycle Δt.
Means for calculating the degree of recovery Kk of the platinum-based catalyst 34 by accumulating a value obtained by multiplying by a control cycle. The valve 35 on the side to be fully closed
And means for returning.

According to a third aspect of the present invention, in the first or second aspect, when the catalyst recovery degree Kk is out of the deterioration recovery range before reaching the required deterioration recovery degree value K, the deterioration recovery degree at that time is determined. A 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, the stored catalyst deterioration degree R1 is obtained.
A required value K of the degree of deterioration recovery is set according to 1.

As shown in FIG. 15, the fourth invention comprises a bypass passage 33 branched from a main passage 32 upstream of an 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 the sticking of the valve 35 is estimated based on the exhaust gas temperature Tmp; 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, the exhaust temperature Tmp is reduced 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. When the temperature becomes lower than the start temperature Tc, the time t at that time is stored, and thereafter, when the exhaust gas temperature Tmp becomes higher than the valve oxidation start temperature Tc, time measurement is started from the stored time. .

According to a sixth aspect of the present invention, in any one of the first to third aspects, the bypass passage 33 is fully opened in the deterioration recovery region when the catalyst deterioration degree R becomes equal to or greater than the deterioration determination value Rc. The fuel cut or air-fuel ratio feedback control is prohibited when the valve 35 is switched to the side to be operated.

According to a seventh aspect of the present invention, in the fourth or fifth aspect, 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 longer than the estimated valve sticking time tc, the valve 35 is set. Prohibits the fuel cut or the air-fuel ratio feedback control when periodically changing over.

In an eighth aspect based on any one of the second to seventh aspects, the exhaust temperature Tmp is calculated from an engine speed and an 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. This is a case in which the sticking of the valve is estimated when the measuring time t becomes equal to or longer than the estimated valve sticking time tc by comparing the measured time t with the valve sticking estimated time tc. Determining means.

[0018]

The deterioration of the catalyst includes permanent deterioration caused by sintering of the noble metal due to heat and deformation of the cocatalyst (ceria, zirconia, alumina, etc.) and recoverable temporary deterioration caused by sulfur deposition and redox of the noble metal. In this case, temporary deterioration due to oxidation of precious metals occupies most of the platinum-based catalyst, so that it deteriorates significantly at high temperatures of lean exhaust, and conversely, recovers from the deteriorated state at high temperatures of rich exhaust. It has been found for the first time by experiments (see Japanese Patent Application No. 6-42794).

In the first invention, the region where the air-fuel ratio is enriched in the high temperature region of the exhaust gas is predetermined as the deterioration recovery region, and when the deterioration of the platinum catalyst is determined, the valve is switched in the deterioration recovery region to switch the platinum catalyst to the high temperature. Since the exhaust gas in the rich atmosphere flows, the platinum-based catalyst recovers from the deterioration, thereby improving the exhaust gas purifying performance. In addition, the capacity of the platinum-based catalyst and the amount of the noble metal carried can be reduced by the extent that the deterioration can be recovered.

The recovery from the deterioration of the platinum-based catalyst can be carried out as soon as the exhaust gas in the deterioration recovery region is at a higher temperature, and it has also been found for the first time by an experiment that the recovery is made in accordance with the time in the deterioration recovery region. The second
In the invention of the present invention, a value obtained by multiplying the exhaust gas temperature Tmp by the control cycle Δt is integrated for each control cycle, thereby recovering the platinum-based catalyst according to the exhaust gas temperature in the rich atmosphere and the time of exposure to the exhaust gas temperature. Since the degree Kk can be calculated, the deterioration recovery processing can be completed with high accuracy.

According to the third aspect of the present invention, when the catalyst recovery degree Kk does not reach the deterioration recovery degree required value K before it falls out of the deterioration recovery area and then returns to the deterioration recovery area, the deterioration recovery degree required value K becomes the first time. Since the value is smaller than the value at the time of starting the recovery processing, the time until the start of the deterioration recovery processing is shortened, and thus the duplication of the deterioration recovery processing can be avoided.

On the other hand, if the time of exposure to high-temperature exhaust gas while the valve is fixed increases, the valve oxidizes and causes sticking of the valve. However, when the exhaust gas temperature is high, the valve closes the bypass passage completely. If the bypass catalyst is driven and the bypass passage is opened by switching the valve in order to prevent the valve from sticking, the bypass catalyst is exposed to high-temperature exhaust gas and deteriorates. When the valve 34 is estimated to be stuck, the valve is periodically switched, and when the bypass passage is opened by the valve switching, the air-fuel ratio is enriched. Can be prevented from occurring.

Even when the exhaust gas temperature Tmp temporarily falls below the valve oxidation start temperature Tc, if the time t is returned to 0 and the time measurement is restarted, the timing of starting the valve switching process is delayed by that much, and the valve sticking may occur. In the fifth invention, the time measured halfway in the previous high-temperature region where the exhaust temperature Tmp became equal to or higher than the valve oxidation start temperature is left as it is, and when the present high-temperature region is reached, Since the time measurement is performed from the remaining time, the time required to reach the estimated valve sticking time tc is shortened, thereby reliably preventing valve sticking even when the exhaust gas temperature Tmp temporarily falls below the valve oxidation start temperature Tc. can do.

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

During the valve sticking prevention process by periodically switching the valve, when the valve is switched and the exhaust gas is flowing through the platinum-based catalyst, if the fuel cut or the air-fuel ratio feedback control accompanying the rapid deceleration is performed. Since the exhaust gas in the lean atmosphere flows or may flow, the platinum-based catalyst is deteriorated. However, in the seventh invention, the fuel cut and the air-fuel ratio feedback control are prohibited during the valve sticking prevention processing. The exhaust gas does not flow to the platinum-based catalyst, thereby preventing deterioration of the platinum-based catalyst due to the fuel cut or the feedback control of the air-fuel ratio during the valve sticking prevention processing.

According to the eighth aspect, since a sensor for detecting the exhaust gas temperature is not required, the cost does not increase.

According to the ninth aspect of the present invention, whether or not the sticking of the valve is estimated is determined by both the valve oxidation start temperature and the estimated sticking time of the valve. In response to this, the valve oxidation start temperature and the estimated valve sticking time may be changed.
This makes it possible to cope with differences in valve size and material.

[0028]

1, a main catalyst 4 as a three-way catalyst is provided downstream of an exhaust pipe 3 connected to an exhaust manifold 2.
Is interposed.

The exhaust pipe 3 is branched immediately downstream of the exhaust manifold 2 into a main passage 3A and a bypass passage 3B. In the bypass passage 3B, a bypass catalyst 5 composed of a three-way catalyst mainly carrying platinum (Pt) is interposed. Be mounted.

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

A pair of O ₂ sensors 11, 12 are provided immediately upstream and downstream of the bypass catalyst 5, and a signal from these O ₂ sensors 11, 12 is provided by a sensor 13 for detecting a cooling water temperature Tw of the engine, an air flow meter. 14. A signal for each unit angle of the crank angle and a reference position signal (Ref
), Together with a signal from the crank angle sensor 15 that outputs a signal to the control unit 21.
In 1, the air-fuel ratio is set to a narrow range centered on the stoichiometric air-fuel ratio in a predetermined air-fuel ratio feedback control region based on the output of the upstream O ₂ sensor when the valve 6 is driven to the side where the bypass passage 3B is fully opened. Feedback control is performed to make it fit.

Now, in order to prevent the bypass catalyst 5 from deteriorating, exhaust gas flows through the bypass passage 3B at a considerably low temperature (for example, 500 ° C.). At this time, the opportunity to use the bypass catalyst 5 is reduced. As a result, the exhaust purification performance deteriorates.

When the temperature of the exhaust gas is high, the valve 6 is driven to fully close the bypass passage 3B. In this state, if the time for which the valve 6 is fixed and exposed to high-temperature exhaust gas is extended, The valve 6 is oxidized to cause sticking of the valve. However, if the valve 6 is driven to open the bypass passage 3B 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 operating temperature limit of the bypass catalyst 5 is increased (that is, it can be used even at a temperature of 500 ° C. or more) by actively recovering the bypass catalyst 5 which is a platinum catalyst from deterioration. In addition to maintaining high exhaust purification performance, the valve 6 is periodically switched when the exhaust gas is at a high temperature, and when the bypass passage 3B is opened by this valve switching, the air-fuel ratio is enriched, thereby deteriorating the bypass catalyst 5. Prevention and recovery while preventing valve sticking.

More specifically, catalyst deterioration includes permanent deterioration caused by sintering (sintering) of a noble metal by heat and deformation of a cocatalyst, and recoverable temporary deterioration caused by sulfur deposition and redox of a noble metal. There is. In this case, temporary deterioration due to oxidation of precious metals occupies most of the platinum-based catalyst, so that it deteriorates significantly at high temperatures of lean exhaust, and conversely, recovers from the deteriorated state at high temperatures of rich exhaust. It has been found for the first time by an experiment that it recovers with time (Japanese Patent Application No. 6-42).
No. 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 and the bypass catalyst 5 is not exposed to the exhaust gas as before, but it is determined whether the catalyst 5 has deteriorated. Only when it is determined, in order to recover from the deterioration, the valve 6 is switched after enriching the air-fuel ratio in a predetermined high temperature region of the exhaust gas, and the exhaust gas having a high temperature and rich atmosphere is caused to flow through the bypass catalyst 5.

Regarding the above, since the valve sticking occurs when the exhaust high temperature state has passed a predetermined time while the valve 6 is fixed, the time during which the exhaust high temperature state continues while the valve 6 is fixed is measured. The valve is prevented from sticking by switching the valve 6 every time when a predetermined time is set with a margin. At this time, when the valve 6 is switched to the side where the bypass passage 3B is opened by utilizing the property of deterioration and recovery of the catalyst 5 which is a platinum-based catalyst,
By making the air-fuel ratio rich, 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
Can be recovered from the deterioration.

In this manner, both the positive recovery from the deterioration of the catalyst 5 and the prevention of sticking of the valve 6 at high exhaust temperatures are performed.

The contents of the 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, where it is determined whether or not the catalyst 5 is in the deterioration diagnosis area. The diagnosis area is determined by checking each of the following items one by one. 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 a predetermined range, it is determined that the region is a 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 is calculated in step 5 as the inversion frequency ratio Fr. .

In the diagnostic region, the valve 6 is driven to open the bypass passage 3B fully, and the fuel supply amount is controlled by pseudo proportional integral control based on the output of the upstream O ₂ sensor. The output of the upstream O ₂ sensor periodically repeats rich and lean. In contrast, the variation of the residual oxygen concentration by the O ₂ storage capability of the catalyst 5 becomes very gentle in the catalyst 5 downstream, the downstream O ₂ sensor output, compared to the upstream O ₂ sensor output Therefore, the fluctuation width is small and the cycle is long. On the other hand, when the catalyst 5 deteriorates, due to the decrease of the O ₂ storage capability of the catalyst 5, the oxygen concentration is not much different between the upstream side and the downstream side of the catalyst 5, close to the upstream O ₂ sensor output period As a result, the output of the downstream O ₂ sensor repeats reversal, and the fluctuation width increases. Therefore, the value of the reversal frequency ratio Fr before catalyst deterioration is substantially zero.
It indicates that the degree of deterioration increases as the value of Fr approaches 1.

In step 6, the inversion frequency ratio Fr is calculated from FIG.
Is obtained with reference to a table having the following contents.

In step 7, the deterioration recovery processing flag (initial value is "0") is checked. If the deterioration recovery processing has not been performed yet, the deterioration recovery processing flag is set to 0, so the routine proceeds to step 8, where the catalyst deterioration degree R is compared with the deterioration determination value Rc. In order to execute the recovery processing, the deterioration recovery processing flag is set to “1” in step 9.

The flowchart of FIG. 4 is for performing a process for recovering the deterioration of the catalyst 5, and is executed at a constant period (Δt).

In step 11, the deterioration recovery processing flag is checked. If this flag is “1”, step 12 is executed in step 12.
See if this is the first time you have gone 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. During the deterioration recovery process in which high-temperature exhaust gas in the deterioration recovery region is caused to flow through the bypass catalyst 5, when fuel cut or feedback control of the air-fuel ratio is performed due to rapid deceleration, exhaust gas in a lean atmosphere flows through the catalyst 5,
Alternatively, since the catalyst 5 may be degraded due to the flow, the fuel cut and the air-fuel ratio feedback control are prohibited during the degradation 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 with reference to a table containing the contents shown in FIG.

In step 15 in FIG. 4, the deterioration recovery area flag (initial value is "0") is checked. If it is the first time that the process has proceeded to step 15 after the deterioration recovery processing flag has become “1”, since the deterioration recovery region flag has become “0”, the process proceeds to step 16 and the engine speed N and the basic injection pulse width Tp From FIG. 6 to N and Tp.
It is determined whether the operating point to which the operation 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 shown by the broken line as a boundary.

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

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

By setting the deterioration recovery area flag to "1", in the next control cycle, steps 13 and 14 are skipped, and the process proceeds to steps 15 and 19, where it is determined whether or not it is in the deterioration recovery area. View. If it is in the deterioration recovery region, it is continuously in the deterioration recovery region. Therefore, the routine proceeds to step 20, in which the exhaust gas temperature Tmp is obtained from N and Tp by referring to the map shown in FIG. In the using step 21, the degree of recovery (initial value: 0) Kk of the catalyst 5 is determined by the following equation: Kk ← Kk + Δt × Tmp.

The recovery from the deterioration of the catalyst 5 can be performed faster as the temperature of the exhaust gas in the deterioration recovery area becomes higher, and the recovery can be made in accordance with the time in the deterioration recovery area (the longer the residence time is, the more the recovery is made). Control cycle Δt
Is multiplied by the exhaust temperature Tmp for each control cycle, thereby obtaining a catalyst recovery degree Kk corresponding 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, and 32 will be described later.

Next, at step 22 in FIG. 4, the catalyst recovery degree Kk is compared with the required degree of deterioration recovery K, and if Kk> K, the state returns to step 11 if the catalyst 5 has not yet recovered to the required value. Repeat the process. Steps 11, 12, 15, 19, 20, 2
The processing of steps 1 and 22 is repeated, and when the catalyst recovery degree Kk eventually becomes equal to or greater than the deterioration recovery degree required value K, post-processing of steps 23, 24 and 25 is performed.

In steps 23, 24, and 25, the deterioration recovery area flag, the deterioration recovery processing flag, and the deterioration recovery halfway flag are all returned to "0" to terminate the deterioration recovery processing. 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 area is no longer in the deterioration recovery area during the deterioration recovery processing, the processing proceeds from step 19 to step 2 in FIG.
Go to 6-29. First, in step 26, the deterioration recovery area flag is returned to "0", and the deterioration recovery middle flag (initial value is "0") is set to "1". In steps 27 and 28, the catalyst deterioration degree R1 in the middle of the deterioration recovery processing is obtained from the value (K-Kk) obtained by subtracting the catalyst recovery degree Kk from the deterioration recovery degree required value K by referring to the table shown in FIG. After storing this in the 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, step 1
From steps 1, 12, 30 to steps 31, 32, the value of R1 stored in the memory is transferred to the catalyst deterioration degree R,
Based on the transferred catalyst deterioration degree R, the deterioration recovery degree required degree K is obtained by referring to the table having the contents shown in FIG. 5, and then the processing from step 15 is executed.

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

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

In step 41, the exhaust gas temperature Tmp is determined from the engine speed N and the basic injection pulse width Tp by referring to the map shown in FIG. 6, and the exhaust gas temperature Tmp is compared with the catalyst deterioration temperature TR. TR is predetermined as a temperature at which the catalyst 5 deteriorates.
When it is lower, it is determined that the catalyst 5 does not deteriorate much,
Proceeding to step 43, it is determined whether Tmp ≦ TR is satisfied for the first time. If this is the first time, the valve 6 is switched to fully open the bypass passage 3 </ b> B, and the exhaust gas flows through the catalyst 5. On the other hand, even when the exhaust gas temperature Tmp becomes higher than TR, when the exhaust gas flows through the catalyst 5, the catalyst 5 starts to deteriorate.
If it is not the first time that p has exceeded TR, the valve 6 is switched to the side where the bypass passage 3B is fully closed in step 46.

As described above, when the exhaust gas is at a low temperature, the bypass catalyst 5 and the main catalyst 4 purify the exhaust gas. When the exhaust gas reaches a predetermined high temperature range, it is determined that the main catalyst 4 is sufficiently activated. Further, exhaust gas is not flown into the bypass catalyst 5 in order to prevent the deterioration of the bypass catalyst 5.

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

First, at step 51, the engine speed N
The exhaust temperature Tmp is determined by referring to the map shown in FIG. 6 from the basic injection pulse width Tp and the basic injection pulse width Tp, and the 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 based on Tmp ≧ Tc, in step 53, the time (initial value is 0) t is compared with the estimated valve sticking time tc. tc is the estimated time until the valve sticks, and when Tmp ≧ Tc for the first time, t <tc, so that step 53 to step 5
Proceeding to 4, the time t is increased by the control period Δt. t
Measures the time during which the exhaust temperature Tmp is equal to or higher than Tc.
Is determined to be stuck, and the process proceeds from step 53 to step 55 to periodically switch the valve 6.

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

In step 55, a valve switching flag (initial value is "0") is checked. At the first time, the process proceeds to step 56 from the valve switching flag = 0, and sets the valve switching flag 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. In step 60, the valve 6 is switched to the side where the bypass passage 3B is fully opened. In order to prevent sticking, the valve 6 is switched. When the valve 6 is switched to the side where the bypass passage 3B is fully opened with this valve switching, fuel cut or air-fuel ratio feedback control is performed, and the catalyst 5 leans. If the exhaust gas of the atmosphere flows, or may flow, the catalyst 5 is deteriorated. Therefore, when the bypass passage 3B is opened, the catalyst 5
The exhaust gas in a rich atmosphere is supplied to the catalyst 5 in order to prevent the deterioration of the catalyst.

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

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 or not a predetermined time has elapsed while the valve is fixed to the side where the bypass passage 3B is fully opened. If not, the process returns to step 51 to repeat the processing. That is, the apparatus stands by in that state until the predetermined time elapses. When the predetermined time has elapsed, from step 61 to steps 62 and 6
4 and the valve 6 is moved to the side where the bypass passage 3B is fully closed.
To stop the enrichment of the air-fuel ratio. If it is determined in step 63 that the vehicle is in the KMR zone, 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 of the rich atmosphere is caused to flow through the catalyst 5 for a predetermined time. After continuing, bypass passage 3B
The operation of once returning the valve 6 to the side in which is fully closed is repeatedly performed.

As described above, even when the exhaust gas is at a high temperature, the valve 6 is periodically switched while the deterioration of the catalyst 5 is suppressed as much as possible, whereby the sticking of the valve 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. If the valve switching process flag = 1, the valve switching process is terminated. In step, the valve switching flag is returned to “0” to clear the time t.

On the other hand, when Tmp <Tc and the valve switching flag = 0, steps 52 and 65 to step 6
Proceeding to 9, the time t is stored in the memory. Steps 68 and 70 will be described later.

The reason that t has a value other than 0 in step 69 in FIG. 10 is that the condition of Tmp ≧ Tc is satisfied once and the measurement of the time t is started, but before the time t reaches the estimated valve sticking time tc. Tmp <Tc (that is, the valve switching processing flag is not set to “1”). In this case, when the condition of Tmp ≧ Tc is satisfied again, the time measurement in step 54 in FIG. 10 is performed using the value stored in the memory as an initial value.

This is because, as shown in FIG. 12, even when the exhaust gas temperature Tmp temporarily falls below Tc, it is necessary to return the time t to 0 and repeat the time measurement (see the second broken line). The timing of starting the valve switching process is delayed by that much, which may lead to valve sticking.
In order to reliably prevent valve sticking even when p temporarily falls below Tc, the time measured halfway in the previous exhaust high temperature region is left as it is, and when the present exhaust high temperature region is reached, the remaining time , The time is measured (see the solid line in the second row).

In step 68 of FIG. 10, it is determined whether or not the valve 6 has been operated at least once by another control (the basic switching process of FIG. 9). 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, the exhaust gas purifying performance can be improved, and the capacity of the platinum-based catalyst and the amount of the noble metal carried can be reduced by the extent that the deterioration can be recovered.

According to the second aspect of the present invention, the degree of recovery of the catalyst can be calculated in accordance with the exhaust temperature of the platinum-based catalyst in a rich atmosphere and the time of exposure to the exhaust temperature. Can be terminated.

According to the third aspect of the present invention, when the catalyst recovery degree does not reach the deterioration recovery degree required value before reaching the deterioration recovery degree required value, the time until the deterioration recovery area is started when the deterioration recovery area starts thereafter is reduced. As a result, duplication of the deterioration recovery processing can be avoided.

According to the fourth aspect of the present invention, it is possible to prevent valve sticking while minimizing deterioration of the platinum-based catalyst.

According to the fifth aspect, even when the exhaust gas temperature temporarily falls below the valve oxidation start temperature, the sticking of the valve can be reliably prevented.

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

According to the seventh aspect of the invention, it is possible to prevent the platinum-based catalyst from deteriorating due to the fuel cut or the feedback control of the air-fuel ratio being performed during the valve sticking prevention processing.

According to the eighth aspect, a sensor for detecting the exhaust gas temperature is not required, and the cost is not increased.

According to the ninth aspect, when the engine model is different, the valve oxidation start temperature and the estimated sticking time may be changed correspondingly, whereby it is possible to cope with the difference in the engine model.

[Brief description of the drawings]

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

FIG. 2 is a flowchart for explaining calculation of a degree of deterioration of a 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 illustrating a deterioration recovery process.

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

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

FIG. 7 is a graph showing a difference (K−
FIG. 7 is a characteristic diagram of a catalyst deterioration degree R1 with respect to Kk).

FIG. 8 is a waveform chart for explaining a deterioration recovery process.

FIG. 9 is a flowchart illustrating a basic switching process of the valve 6;

FIG. 10 is a waveform chart for explaining valve sticking prevention processing.

FIG. 11 is a waveform chart for explaining valve sticking prevention processing.

FIG. 12 is a waveform chart for explaining valve sticking prevention processing when the exhaust gas temperature Tmp temporarily falls 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 the claims of the first invention.

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

[Explanation of symbols]

Reference Signs List 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-based catalyst 35 switching valve 36 Catalyst deterioration determination means 37 Deterioration recovery means 51 Valve sticking determination means 52 Valve periodic switching means 53 Air-fuel ratio enrichment means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI F01N 3/24 ZAB F01N 3/24 ZABR F02D 41/04 305 F02D 41/04 305Z 41/14 310 41/14 310B (56) Reference Document JP-A-5-340238 (JP, A) JP-A-6-88518 (JP, A) JP-A-5-312026 (JP, A) JP-A-57-210116 (JP, A) JP-A-7-210 247829 (JP, A) Japanese Utility Model 63-128221 (JP, U) Japanese Utility Model 3-108813 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08-3 / 36 F02D 41/04 F02D 41/14

Claims (9)

(57) [Claims] A bypass passage branched from a main passage upstream of an exhaust pipe; a platinum catalyst interposed in the bypass passage; a valve capable of switching exhaust flow to the bypass passage and the main passage; Means for determining whether or not the platinum-based catalyst has deteriorated; and when the platinum-based catalyst has been determined to be deteriorated, the exhaust high temperature region and the region where the air-fuel ratio is enriched are set as the deterioration recovery region, and the bypass passage is fully opened in the deterioration recovery region. Means for switching the valve on the side of the exhaust gas purifying apparatus. 2. When the valve is switched to a side where the bypass passage is fully opened, the recovery degree of the platinum catalyst is calculated by integrating a value obtained by multiplying the exhaust gas temperature by a control cycle for each control cycle. 2. The apparatus according to claim 1, further comprising: means for calculating, and means for returning the valve to a side on which the bypass passage is fully closed when the degree of catalyst recovery is equal to or greater than a required value of the degree of deterioration recovery. Engine exhaust purification device. 3. If the catalyst recovery degree does not reach the deterioration recovery area before reaching the deterioration recovery degree required value, the catalyst deterioration degree corresponding to the difference between the required deterioration recovery degree value and the catalyst recovery degree at that time is determined. 3. The method according to claim 1, further comprising: determining and storing a deterioration recovery degree required value corresponding to the stored catalyst deterioration degree when the deterioration recovery area is reached. Engine exhaust purification device. . A bypass passage branched from the main passage upstream of the exhaust pipe; a platinum catalyst interposed in the bypass passage; a valve capable of switching an exhaust flow to the bypass passage and the main passage; Means for determining whether the sticking of the valve is estimated based on the exhaust gas temperature; means for periodically switching the valve at the time of determining the sticking of the valve; and means for opening the bypass passage by switching the valve. Means for enriching the air-fuel ratio. 5. If the exhaust gas temperature is lower than the valve oxidation start temperature before the time when the exhaust gas temperature is equal to or 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 purifying apparatus for an engine according to claim 4, wherein when the exhaust gas temperature becomes equal to or higher than the valve oxidation start temperature, time measurement is started from the stored time. 6. A fuel cut or air-fuel ratio feedback control is prohibited when the valve is switched to a side where the bypass passage is fully opened in the deterioration recovery region when the degree of catalyst deterioration becomes equal to or more than the deterioration determination value. The exhaust gas purification device for an engine according to any one of claims 1 to 3, 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 gas temperature is equal to or higher than the valve oxidation start temperature is equal to or longer than the valve sticking estimated time. The exhaust gas purifying apparatus for an engine according to claim 4 or 5, wherein: 8. The exhaust gas purifying 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 judging means includes means for measuring a time during which the exhaust gas temperature is equal to or higher than the valve oxidation start temperature, and measuring the valve sticking time by comparing the measured time with the valve sticking estimated time. Means for judging a case in which the sticking of the valve is estimated when the sticking estimation time or more has elapsed.
An exhaust gas purification device for an engine according to any one of claims 7 and 8.