JP2007032544A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of prematurely activating a catalyst in an exhaust emission control system during the cold start of an internal combustion engine in the exhaust emission control system purifying exhaust gases from a plurality of groups of cylinders of the internal combustion engine. <P>SOLUTION: Exhaust gas passages 1, 51 from the groups of cylinders are branched into a plurality of branch passages 2a, 2b, 52a, 52b. During the cold start of the internal combustion engine, the flow amount of the exhaust gases in a part 2b, 52b of the plurality of branched exhaust gas passages is reduced to reduce discharged heat amount from the entire exhaust gases to the outside. Consequently, the temperature of the exhaust gases introduced into the exhaust emission control devices 4, 54 is maintained at a high temperature. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

The exhaust gas of an internal combustion engine contains harmful substances such as NOx. In order to reduce the emission of these harmful substances, it is known to provide an exhaust purification device including a NOx catalyst for purifying NOx in exhaust gas in an exhaust system of an internal combustion engine.

Here, the exhaust gas purification apparatus including the NOx catalyst can purify NOx in the exhaust gas in a state where the temperature is maintained at or above the activation temperature of the catalyst. Therefore, at the time of cold start of the internal combustion engine, the temperature of the exhaust purification device does not reach the activation temperature of the catalyst, and it becomes difficult to sufficiently purify NOx in the exhaust, and the emission may deteriorate. . Therefore, at the time of cold start of the internal combustion engine, it is necessary to raise the temperature of the exhaust purification catalyst at an early stage so as to be equal to or higher than the activation temperature of the catalyst so that NOx in the exhaust can be purified.

On the other hand, regarding the exhaust purification device as described above, when the internal combustion engine has a plurality of cylinder groups, a configuration in which the dual configuration exhaust purification device is arranged downstream from the junction where the exhaust from the plurality of cylinder groups merges. It is publicly known (for example, refer to Patent Document 1). Even in such an exhaust purification system, it is necessary to quickly raise the temperature of the dual configuration exhaust purification apparatus at the time of cold start.
JP 2002-364352 A

  An object of the present invention is to provide a technology capable of activating a catalyst in an exhaust purification system earlier in a cold start of the internal combustion engine in an exhaust purification system for purifying exhaust from a plurality of cylinder groups of the internal combustion engine. Is to provide.

  In order to achieve the above object, the present invention divides an exhaust passage from each cylinder group into a plurality of parts, and at the time of cold start of the internal combustion engine, the flow rate of exhaust gas for a part of the branched exhaust passages. The main feature is that the temperature of the exhaust gas introduced into the exhaust gas purification apparatus is maintained at a high temperature by reducing the amount of heat released to the outside as a whole exhaust gas.

More specifically, an exhaust passage through which exhaust discharged from a plurality of cylinder groups of the internal combustion engine passes,
One or more exhaust purification devices provided in the exhaust passage and purifying the exhaust;
An exhaust purification system for an internal combustion engine comprising:
The exhaust passage is
A cylinder group directly connected exhaust passage connected to each of the plurality of cylinder groups and having the same number of cylinder groups through which exhaust discharged from each cylinder group passes;
A branch passage for each cylinder group formed by dividing the cylinder group directly connected exhaust passage by the same number with respect to each of the cylinder group directly connected exhaust passages;
A single cylinder group is formed by merging one of a plurality of cylinder group branch passages branched from each of the cylinder group direct exhaust passages with respect to all the cylinder group direct exhaust passages. A mixed exhaust passage formed in the same number as the number of branch passages per cylinder group;
A combined mixed exhaust passage formed by joining all of the mixed exhaust passages;
An exhaust amount control means provided in at least one of the mixed exhaust passages for controlling the amount of exhaust gas passing through the mixed exhaust passage;
Have
Exhaust gas passing through the merged mixed exhaust passage is introduced into the exhaust gas purification device,
The exhaust amount control means reduces the amount of exhaust gas passing through at least one of the mixed exhaust passages for a predetermined period after the cold start of the internal combustion engine.

  That is, the exhaust discharged from each cylinder group of the internal combustion engine is branched and allowed to pass through a plurality of cylinder group branch passages, and when the internal combustion engine is cold started, the exhaust passing through some of the cylinder group branch passages is The amount of exhaust is reduced by the exhaust amount control means. As a result, the exhaust from the internal combustion engine intensively passes through the branch passages for each cylinder group in which the exhaust amount control means is not provided.

  If it does so, when it sees in the whole exhaust_gas | exhaustion from an internal combustion engine, when passing the branch passage for every cylinder group, the surface area of the surface which contacts the exterior can be made relatively small. As a result, the amount of heat radiation to the outside as the entire exhaust from the internal combustion engine can be reduced, and the temperature of the exhaust introduced into the exhaust purification device can be relatively increased. Therefore, the temperature of the exhaust emission control device can be raised at an early stage even during a cold start of the internal combustion engine, and deterioration of emissions can be suppressed.

  Here, the predetermined period is a period during which it is determined that the exhaust purification device can be brought to a high temperature sufficiently early by reducing the amount of exhaust passing through at least one of the mixed exhaust passages by the exhaust amount control means. Therefore, a value experimentally obtained as a constant value in advance may be used, or a different value may be selected depending on the initial water temperature and the operating state of the internal combustion engine. Alternatively, the predetermined period may be a period until the warm-up of the exhaust gas purification apparatus ends, and during that period, the amount of exhaust gas passing through at least one of the mixed exhaust passages may be continuously reduced.

  Here, examples of the exhaust amount control means include valve devices such as an exhaust throttle valve and a three-way valve, as well as a shutter device.

In the present invention, the integrated intake air amount or the integrated fuel injection amount after the cold start of the internal combustion engine is estimated,
The predetermined period is a period from the start of cold start until the estimated value of the integrated intake air amount or the integrated fuel injection amount exceeds a predetermined value,
The exhaust amount control means may increase the amount of exhaust gas passing through the mixed exhaust passage after the predetermined period has elapsed since the cold start of the internal combustion engine.

  Here, in the case where the cumulative intake air amount after the cold start of the internal combustion engine is estimated, the predetermined value is the time when the air is sucked in after this start of the cold start of the internal combustion engine. This is the integrated intake air amount as a threshold at which it can be determined that the exhaust purification device has sufficiently warmed up and has been warmed up. On the other hand, when the integrated fuel injection amount is estimated in the same manner, the predetermined value means that the exhaust purification device is sufficiently raised when such an amount of fuel is injected after the cold start of the internal combustion engine is started. This is the integrated fuel injection amount as a threshold value that can be determined as warming up and warming up completed.

  That is, according to the above, during the period until the temperature of the exhaust purification device sufficiently rises, the exhaust amount control means continues to reduce the amount of exhaust passing through the mixed exhaust passage provided with the exhaust control means. . Therefore, the temperature of the exhaust purification device can be raised efficiently. Further, since the exhaust amount control means does not reduce the amount of exhaust gas passing through the mixed exhaust passage for an unnecessarily long period, it does not unnecessarily limit the exhaust flow rate of the internal combustion engine, and the operating state and output that the internal combustion engine can take Can be restricted.

In the present invention, the exhaust amount control means is an exhaust throttle valve provided in at least one of the mixed exhaust passages, and passes through at least one of the mixed exhaust passages when the exhaust throttle valve opens and closes. Increase or decrease the amount of exhaust,
An air-fuel ratio sensor capable of detecting the air-fuel ratio of the exhaust in a state activated by heating on the upstream side and / or downstream side of the exhaust purification device;
When the exhaust throttle valve opens during the predetermined period, heating of the air-fuel ratio sensor may be stopped.

Here, in order to efficiently purify NOx in the exhaust purification device, it is desirable to accurately control the air-fuel ratio of the exhaust from the internal combustion engine. For this purpose, the present invention further includes an air-fuel ratio sensor capable of detecting the air-fuel ratio of the exhaust while being activated by heating, on the upstream side and / or downstream side of the exhaust purification device. The exhaust amount control means is an exhaust throttle valve provided in at least one of the mixed exhaust passages, and controls the amount of exhaust gas passing through the mixed exhaust passage by opening and closing the exhaust throttle valve.

  In such a case, considering only the exhaust gas temperature rising effect, the exhaust throttle valve is ideally closed in the entire period of the predetermined period when the internal combustion engine is cold-started. It is preferable to open the exhaust throttle valve. However, in that case, during the period when the exhaust throttle valve is closed, the exhaust blocked by the exhaust throttle valve may be cooled and condensed water may be generated in the mixed exhaust passage. When the exhaust throttle valve is opened in the presence of such condensed water, the condensed water is scattered downstream by the exhaust that has started to flow and adheres to the air-fuel ratio sensor. There was a case where it was damaged.

  On the other hand, in the present invention, the heating of the air-fuel ratio sensor is stopped when the exhaust throttle valve is opened, so that the temperature of the air-fuel ratio sensor is at the time when the condensed water is scattered downstream. It is falling. Therefore, damage to the air-fuel ratio sensor due to thermal shock when condensed water adheres can be suppressed.

  In this case, the exhaust throttle valve may be opened after a lapse of a predetermined delay time after the heating of the air-fuel ratio sensor is stopped. By doing so, the temperature of the air-fuel ratio sensor can be more reliably lowered when the exhaust throttle valve is opened, and damage to the air-fuel ratio sensor due to thermal shock can be more reliably suppressed.

  In the present invention, at least part of the predetermined period, the exhaust throttle valve is opened and the heating is stopped, and the exhaust throttle valve is closed and the heating is started. You may make it repeat alternately.

  Then, exhaust gas can be made to flow gradually through the mixed exhaust passage provided with the exhaust throttle valve even during the predetermined period, and the temperature of the mixed exhaust passage in the vicinity of the exhaust throttle valve can be increased. Then, even during the predetermined period, the temperature of the mixed exhaust passage in the vicinity of the exhaust throttle valve can be set near or above the dew point temperature. As a result, adhesion of condensed water to the air-fuel ratio sensor when the exhaust throttle valve is opened can be more reliably suppressed.

In the present invention, an air-fuel ratio sensor is provided on the upstream side and the downstream side of the exhaust purification device,
When heating of the air-fuel ratio sensor upstream of the exhaust purification device is stopped, the air-fuel ratio control of the internal combustion engine may be performed using the output of the air-fuel ratio sensor downstream of the exhaust purification device. .

  That is, in the state where the heating of the air-fuel ratio sensor upstream of the exhaust purification device is stopped, the air-fuel ratio of the exhaust gas introduced into the exhaust purification device cannot be accurately detected. Therefore, in this state, the air-fuel ratio of the exhaust gas in the internal combustion engine is controlled using the output of the air-fuel ratio sensor downstream of the exhaust purification device. Here, since the above-mentioned condensed water is hardly scattered on the downstream side of the exhaust purification device, the heating of the air-fuel ratio sensor on the downstream side of the exhaust purification device can be continued regardless of opening and closing of the exhaust throttle valve.

  Thereby, control of the air-fuel ratio of the internal combustion engine can be continued regardless of the open / closed state of the exhaust throttle valve, and the deterioration of the emission of the internal combustion engine can be suppressed.

  Further, in the present invention, when the temperature of the mixed exhaust passage provided with the exhaust throttle valve becomes a dew point temperature or higher while the heating of the upstream air-fuel ratio sensor is stopped, the exhaust purification device The heating of the upstream air-fuel ratio sensor may be started, and the air-fuel ratio control of the internal combustion engine may be performed using the output of the upstream air-fuel ratio sensor of the exhaust purification device.

  That is, when the temperature of the mixed exhaust passage provided with the exhaust throttle valve becomes equal to or higher than the dew point temperature, the air-fuel ratio sensor upstream of the exhaust purification device is heated regardless of whether the exhaust throttle valve is open or closed. However, since the condensed water itself does not exist, the air-fuel ratio sensor is not damaged. On the other hand, from the viewpoint of air-fuel ratio control of the internal combustion engine, it is desirable to perform air-fuel ratio control using the output of the air-fuel ratio sensor on the upstream side of the exhaust gas purification device with less detection delay with respect to changes in the air-fuel ratio.

  Therefore, even when the heating of the upstream air-fuel ratio sensor is stopped, if the temperature of the mixed exhaust passage provided with the exhaust throttle valve becomes equal to or higher than the dew point temperature, the upstream side of the exhaust purification device The heating of the air-fuel ratio sensor may be started and the air-fuel ratio control of the internal combustion engine may be performed using the output of the air-fuel ratio sensor upstream of the exhaust purification device. Then, in the situation where condensed water does not exist, the air-fuel ratio control can be performed using the upstream air-fuel ratio sensor preferentially, and the air-fuel ratio can be controlled more accurately.

In the present invention, the exhaust amount control means is an exhaust throttle valve provided in at least one of the mixed exhaust passages, and the amount of exhaust gas that passes through the mixed exhaust passage when the exhaust throttle valve opens and closes Increase or decrease
An air-fuel ratio sensor capable of detecting the air-fuel ratio of the exhaust in a state activated by heating on the upstream side and / or downstream side of the exhaust purification device;
Immediately after the start of cold start of the internal combustion engine in the predetermined period, the exhaust throttle valve is opened, and heating of the air-fuel ratio sensor is stopped,
When the temperature of the mixed exhaust passage provided with the exhaust throttle valve becomes a dew point temperature or higher during the predetermined period, the upstream air-fuel ratio sensor is heated and the exhaust throttle valve is closed. May be.

  Then, since the upstream air-fuel ratio sensor is heated after the temperature of the mixed exhaust passage becomes equal to or higher than the dew point temperature, it is possible to more reliably suppress the condensed water from adhering to the upstream heater.

  In the present invention, each of the plurality of cylinder groups may form each of a plurality of banks provided in the internal combustion engine. If it does so, the said invention can be applied suitably with respect to the exhaust_gas | exhaustion from each bank in a V-type internal combustion engine, for example.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  In the present invention, in the exhaust purification system that purifies exhaust from a plurality of cylinder groups of the internal combustion engine, the catalyst in the exhaust purification system can be activated earlier when the internal combustion engine is cold started.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of an exhaust purification system according to the present embodiment. In FIG. 1, an exhaust purification system for a V-type internal combustion engine, for example, having two banks, a right bank and a left bank, is assumed. Exhaust gas from a right bank (not shown) flows into the right first-stage exhaust gas purification device 10 in FIG. 1 to purify the exhaust gas when it is cold. Similarly, exhaust gas from a left bank (not shown) flows into the left first-stage exhaust gas purification device 50, and exhaust gas is purified when it is cold. In addition, the exhaust gas that has passed through the right first-stage exhaust purification device 10 flows into the right exhaust pipe 1 in FIG. Further, the exhaust that has passed through the left first-stage exhaust purification device 50 flows into the left exhaust pipe 51. The right exhaust pipe 1 branches into two right branch pipes 2a and 2b on the way, and similarly the left branch pipe 51 branches into two left branch pipes 52a and 52b.

  Here, the right exhaust pipe 1 and the left exhaust pipe 51 correspond to a cylinder group direct connection exhaust passage. The right branch pipes 2a and 2b and the left branch pipes 52a and 52b correspond to branch paths for each cylinder group.

  On the downstream side of the exhaust purification system, the right branch pipe 2a and the left branch pipe 52a merge to form the right mixing pipe 3. On the other hand, the right branch pipe 2b and the left branch pipe 52b merge to form the left mixing pipe 53. Further, on the further downstream side, the right mixing tube 3 and the left mixing tube 53 are once joined together to form a joining and mixing tube 5. The right main exhaust purification device 4 and the left main exhaust purification device 54 are provided for the right second mixing tube 6 and the left second mixing tube 56 from which the merging and mixing tube 5 is branched again. Here, the right mixing pipe 3 and the left mixing pipe 53 correspond to a mixed exhaust passage. The merging / mixing pipe 5 corresponds to a merging / mixing exhaust passage.

The right first-stage exhaust purification device 10 and the left first-stage exhaust purification device 50 in the present embodiment include a three-way catalyst. Here, the three-way catalyst is a catalyst that converts CO, HC, NO _x in the exhaust gas burned near the stoichiometric air-fuel ratio to CO ₂ , H ₂ O and N ₂ , for example, a mixture of Pt and Rh, or Pt And Pd
And a mixture of Rh can be used as those supported on alumina.

  On the other hand, the right main exhaust purification device 4 and the left main exhaust purification device 54 in the present embodiment include an NOx storage reduction catalyst. This NOx storage reduction catalyst uses alumina as a carrier, and on the carrier, at least selected from alkali metals such as K, Na and Li, alkaline earth metals such as Ba and Ca, and rare earths such as La and Y. One and a noble metal such as Pt are supported.

Further, the merging and mixing pipe 5 on the upstream side of the right main exhaust purification device 4 and the left main exhaust purification device 54 is heated by energizing the heater, and the oxygen concentration is detected in a state where the internal sensor element is activated. A possible upstream O ₂ sensor 8 is provided. Similarly, a downstream O ₂ sensor 9 is provided at the downstream junction of the right main exhaust purification device 4 and the left main exhaust purification device 54. Further, the left mixing pipe 53 is provided with an exhaust throttle valve 7 that controls the amount of exhaust gas passing through the left mixing pipe 53 by an opening / closing operation. Here, the upstream sensor 8 and the downstream sensor 9 correspond to an air-fuel ratio sensor, and the exhaust throttle valve 7 corresponds to an exhaust amount control means.

In the exhaust purification system, an A / F sensor (not shown) is provided in the vicinity of the right front exhaust purification device 10 and the left front exhaust purification device 50. The air-fuel ratio of the exhaust gas from the right bank and the left bank is determined based on the main feedback control using the output of the A / F sensor and the sub feedback control using the output of the upstream O ₂ sensor 8 or the downstream O ₂ sensor 9. And is controlled by.

Here, the temperature range in which NOx can be efficiently stored in the right main exhaust purification device 4 and the left main exhaust purification device 54 is approximately 350 ° C. to 450 ° C. On the other hand, when the internal combustion engine is cold-started, the temperature of the right main exhaust purification device 4 and the left main exhaust purification device 54 is lower than the above temperature range, so that the NOx purification efficiency may be reduced and the emission may deteriorate. there were.

Therefore, in the present embodiment, the exhaust throttle valve 7 is closed when the NOx purification efficiency of the right main exhaust purification device 4 and the left main exhaust purification device 54 is low after the start of the cold start of the internal combustion engine. did. If it does so, exhaust_gas | exhaustion cannot pass through the right branch pipe 2b and the left branch pipe 52b, and the exhaust which should have passed through them will pass through the right branch pipe 2a and the left branch pipe 52a intensively. Then, the surface area of the exhaust passage through which the entire exhaust from the internal combustion engine passes is reduced, and the exhaust heat released to the outside of the exhaust passage is reduced. As a result, the exhaust temperature can be maintained at a high temperature, and the temperatures of the right main exhaust purification device 4 and the left main exhaust purification device 54 can be raised early.

  FIG. 2 is a time chart showing the control during the cold start of the exhaust purification system described above. The upper side shows the change in the catalyst warm-up completion flag before and after the start of the internal combustion engine, and the lower side shows the opening / closing operation of the exhaust throttle valve 7. Here, the catalyst warm-up completion flag is a flag that is turned on when the integrated intake air amount after the start of the internal combustion engine reaches the warm-up completion air amount. The warm-up completion air amount is an integrated value of the intake air amount at which it can be determined that the temperatures of the right main exhaust purification device 4 and the left main exhaust purification device 54 have sufficiently increased and sufficient exhaust purification efficiency can be obtained. Yes, determined experimentally in advance. Note that the warm-up completion air amount corresponds to a predetermined value when the integrated intake air amount after the cold start of the internal combustion engine is estimated.

  It is assumed that the internal combustion engine is started at time t1 in FIG. At that time, the exhaust throttle valve 7 is closed. Further, from that time point, detection of the integrated intake amount of the internal combustion engine is started. If the catalyst warm-up completion flag is turned on at time t2, the exhaust throttle valve 7 is opened at that time.

  According to the present embodiment, the exhaust throttle valve 7 is closed until the temperatures of the right main exhaust purification device 4 and the left main exhaust purification device 54 are sufficiently raised and sufficient exhaust purification efficiency is obtained. I speak. Therefore, the passage through which the exhaust from the internal combustion engine passes can be concentrated on the right branch pipe 2a and the left branch pipe 52a among the right branch pipes 2a and 2b and the left branch pipes 52a and 52b. Then, the amount of heat released from the exhaust to the outside of each branch pipe can be relatively reduced, and the exhaust can be maintained at a high temperature. As a result, the temperatures of the right main exhaust purification device 4 and the left main exhaust purification device 54 can be increased efficiently. In the present embodiment, the period from time t1 to time t2, that is, the period from the start of the cold start of the internal combustion engine until the catalyst warm-up completion flag is turned on corresponds to the predetermined period.

Next, a second embodiment of the present invention will be described. In the present embodiment, an example will be described in which warm-up of the exhaust purification device is promoted and the O ₂ sensor is prevented from being damaged by being wet when the internal combustion engine is cold-started.

  FIG. 3 is a time chart showing control at the time of cold start of the exhaust purification system according to the present embodiment.

  In FIG. 3, it is assumed that the start of the internal combustion engine is started at time t3. Then, as in the first embodiment, the exhaust throttle valve 7 is closed and the detection of the integrated intake air amount is started. Further, in the present embodiment, detection of the intake air amount is started in order to estimate the depression amount of the accelerator. In this embodiment, when the detected intake air amount exceeds the valve closing limit air amount, the exhaust throttle valve opening flag is turned ON. The valve closing limit air amount is the amount of intake air that is determined that if the intake air amount exceeds this value, the output of the internal combustion engine is limited or the exhaust gas becomes too hot when the exhaust throttle valve 7 is closed. Value, which is experimentally determined in advance.

Next, energization to the heater for heating the sensor element of the upstream O ₂ sensor 8 is turned on at time t4. As a result, the sensor element of the upstream O ₂ sensor 8 is activated and the oxygen concentration can be detected.

  Next, it is assumed that the exhaust throttle valve opening flag is turned ON by suddenly depressing the accelerator at time t5. In this case, if the exhaust throttle valve 7 remains closed, the above-described problem may occur, so the exhaust throttle valve 7 is opened.

However, in this embodiment, even if the exhaust throttle valve opening flag is turned on, the exhaust throttle valve 7 is not immediately opened. First, power supply to the heater of the upstream O ₂ sensor 8 is turned off. After providing the time delay Δt, the exhaust throttle valve 7 is opened after the temperature of the upstream O ₂ sensor 8 has sufficiently decreased. Next, when the exhaust throttle valve opening flag is turned off at time t6, the exhaust throttle valve 7 is closed and energization of the heater of the upstream O ₂ sensor 8 is turned on at the same time. Here, Δt is a time required for the temperature of the upstream O ₂ sensor 8 to sufficiently decrease after the energization of the heater of the upstream O ₂ sensor 8 is turned off, and a predetermined delay time. It corresponds to.

Next, when the catalyst warm-up completion flag is turned on at t7, the exhaust throttle valve 7 is opened as in the first embodiment. At the time when the catalyst warm-up completion flag is turned ON, the temperature in the vicinity of the exhaust throttle valve 7 in the left mixing pipe 53 is already high, or the exhaust throttle valve 7 has been opened or closed before this time. It can be judged that there is hardly any. Therefore, at this time, the energization of the heater of the upstream O ₂ sensor 8 is not turned off.

Thus, in this embodiment, when the exhaust throttle valve 7 is opened while the catalyst warm-up completion flag is OFF, the energization to the heater of the upstream O ₂ sensor 8 is always turned OFF. . Therefore, scattered with the opening of the condensate exhaust throttle valve 7 that has accumulated in the left mixing tube 53, even if attached to the upstream O ₂ sensor 8, it is possible to suppress the upstream O ₂ sensor 8 is damaged .

Next, another aspect related to the control of the opening / closing of the exhaust throttle valve 7 and the energization of the heater of the upstream O ₂ sensor 8 in this embodiment will be described.

In this embodiment, while the catalyst warm-up completion flag is OFF, the exhaust throttle valve 7 is opened and the energization to the heater of the upstream O ₂ sensor 8 is turned OFF, and the exhaust throttle valve 7 is closed. A description will be given of the control for repeatedly executing the operation of turning on the energization to the heater of the upstream O ₂ sensor 8 while performing the valve operation.

FIG. 4 is a time chart showing the control at the time of cold start of the exhaust purification system according to this aspect. It is assumed that the internal combustion engine starts to be started at time t8 in FIG. Next, energization to the heater of the upstream O ₂ sensor 8 is turned on at time t9. At time t10, the energization of the heater of the upstream O ₂ sensor 8 is turned off, and the exhaust throttle valve 7 is opened after a time delay Δt. Next, at time t11, energization to the heater of the upstream O ₂ sensor 8 is turned on and the exhaust throttle valve 7 is closed. Further, at time t12, energization to the heater of the upstream O ₂ sensor 8 is turned off, and the exhaust throttle valve 7 is opened after a time delay Δt.

When the catalyst warm-up completion flag is turned on at time t13, it can be determined that condensed water does not already exist in the vicinity of the exhaust throttle valve 7 of the left mixing pipe 53, so the open state of the exhaust throttle valve 7 is maintained. At the same time, energization of the heater of the upstream O ₂ sensor 8 is turned on.

Thus, in this embodiment, during the period when the catalyst warm-up completion flag is OFF, the energization to the heater of the upstream O ₂ sensor 8 is turned OFF and the exhaust throttle valve 7 is opened after the time delay Δt. The operation and the operation of turning on the energization of the heater of the upstream O ₂ sensor 8 and closing the exhaust throttle valve 7 are repeated.

  Then, even when the right exhaust purification device 4 and the left exhaust purification device 54 are warmed up, the exhaust gas can be made to flow through the left mixing pipe 53 little by little, and the temperature in the vicinity of the exhaust throttle valve 7 is reduced to the dew point temperature. It can be raised quickly.

Next, a third embodiment of the present invention will be described. In the present embodiment, an example will be described in which the air-fuel ratio of the internal combustion engine is controlled using the downstream O ₂ sensor 9 during a period when the heater of the upstream O ₂ sensor 8 is not energized. In the first embodiment, it is assumed that the catalyst warm-up completion flag is turned on earlier than when the temperature near the exhaust throttle valve 7 reaches the dew point temperature by closing the exhaust throttle valve 7 immediately after starting. It is said.

FIG. 5 is a time chart showing control during cold start of the exhaust purification system according to the present embodiment. In the present embodiment, starting of the internal combustion engine is started at time t14, and thereafter, energization of the heaters of the upstream O ₂ sensor 8 and the downstream O ₂ sensor 9 is turned ON at time t15. Further, after the warm-up of the right front exhaust purification device 10 and the left front exhaust purification device 50 is completed, the sub-feedback control of the air-fuel ratio is started at time t16.

At this time, since the heater of the upstream O ₂ sensor 8 is energized, the sub-feedback control of the air-fuel ratio is performed using the output of the upstream O ₂ sensor 8. Next, it is assumed that a catalyst warm-up completion flag (not shown) is turned on at time t17. At this time, it is not necessary to close the exhaust throttle valve 7. However, in this embodiment, the temperature in the vicinity of the exhaust throttle valve 7 in the left mixing pipe 53 does not reach the dew point temperature even at this time, so that when the exhaust throttle valve 7 is opened, the condensed water becomes upstream O ₂ sensor 8. The upstream O ₂ sensor 8 may be damaged. Accordingly, the energization of the heater of the upstream O ₂ sensor is first turned off, and the exhaust throttle valve 7 is opened after a time delay Δt.

Further, in this embodiment, at this time, the sub feedback is switched using the output of the downstream O ₂ sensor 9. Thereby, even after the energization of the heater of the upstream O ₂ sensor 8 is turned off, it becomes possible to continue the control of the exhaust air / fuel ratio of the internal combustion engine using the output of the downstream O ₂ sensor 9.

Next, it is assumed that the dew point temperature flag is turned on at t18. This dew point temperature flag is a flag indicating that the temperature of the exhaust gas passing through the left mixing pipe 53 has become equal to or higher than the dew point temperature, and this may also be estimated from the integrated value of the intake air amount or the fuel injection amount. This dew point temperature flag is O
When N, the condensed water cannot be present in the left mixing pipe 53, so the energization to the heater of the upstream O ₂ sensor 8 is turned on. At the same time, the sub feedback control is switched to control using the output of the upstream O ₂ sensor 8. Then, energization of the heater of the downstream O ₂ sensor 9 is turned off.

As described above, in this embodiment, the sub-feedback control is continued using the output of the downstream O ₂ sensor 9 while the energization of the heater of the upstream O ₂ sensor 8 is OFF. Therefore, the control of the exhaust air / fuel ratio of the internal combustion engine can be continued regardless of the warm-up state of the right main exhaust purification device 4 and the left main exhaust purification device 54, the exhaust temperature, and the opening / closing of the exhaust throttle valve 7.

Moreover, since switching to control using the output of the upstream O ₂ sensor 8 sub feedback control at the time the temperature reaches the dew point temperature of the exhaust throttle valve 7 near the left mixing tube 53, a state where the upstream O ₂ sensor 8 can be used In this case, since the control is performed preferentially using the output of the upstream O ₂ sensor 8, the accuracy of the sub feedback control can be improved as much as possible.

  Next, another aspect of the present embodiment will be described. In this mode, as described later, by opening the exhaust throttle valve 7 immediately after the start of the cold start, the timing at which the catalyst warm-up completion flag is turned on is later than the timing at which the dew point temperature flag is turned on. It is an example of control about the case where becomes.

FIG. 6 is a time chart showing control at the time of cold start of the exhaust purification system according to this aspect. In this aspect, the start of the internal combustion engine starts at time t20. At this time, the exhaust throttle valve 7 is open. Then, since there is a possibility that the condensed water is wetted, the heater of the upstream O ₂ sensor 8 is not energized. Instead, energization of the heater of the downstream O ₂ sensor 9 is turned ON at time t21. Then, the sub feedback control is started at time t22. At this time, sub-feedback control is performed using the output of the downstream O ₂ sensor 9.

  Then, it is assumed that the dew point temperature flag is turned ON at time t23, that is, the temperature near the exhaust throttle valve 7 of the left mixing pipe 53 has reached the dew point temperature. Then, the exhaust throttle valve 7 is closed at that time. This is to complete the warm-up of the right main exhaust purification device 4 and the left main exhaust purification device 54 as soon as possible.

At this time, since the condensed water cannot already exist in the left mixing pipe 53, energization to the heater of the upstream O ₂ sensor 8 is turned on. Further, at this time, the sub feedback control is switched to control using the output of the upstream O ₂ sensor 8. At time t24, when the catalyst warm-up completion flag is turned on, it is not necessary to close the exhaust throttle valve 7, so the exhaust throttle valve 7 is opened.

Also in this embodiment, since the sub feedback control is continued using the output of the downstream O ₂ sensor 9 while the energization to the heater of the upstream O ₂ sensor 8 is OFF, the right main exhaust purification device 4 and Control of the exhaust air / fuel ratio of the internal combustion engine can be continued regardless of whether the left exhaust gas purification device 54 is warmed up, the exhaust temperature, or the exhaust throttle valve 7 is opened or closed.

Further, the priority in the case for switching to control using the output of the upstream O ₂ sensor 8 sub feedback control when the temperature of the left mixing tube 53 has reached the dew point temperature is a state where the upstream O ₂ sensor 8 can be used Since the control is performed using the output of the upstream O ₂ sensor 8, the accuracy of the sub-feedback control can be improved as much as possible.

Further, in this aspect, from the start of the start until the dew point temperature flag is turned ON, the exhaust throttle valve 7 is opened and the energization to the heater of the upstream O ₂ sensor 8 is turned OFF. Therefore, until the temperature in the vicinity of the exhaust throttle valve 7 of the left mixing pipe 53 reaches the dew point temperature, the generation of condensed water itself is suppressed and the upstream O ₂ sensor 8 is suppressed from becoming high temperature. Accordingly, it is possible to more reliably prevent the upstream O ₂ sensor 8 from being damaged due to water.

  In the embodiment described above, two exhaust pipes from the two cylinder groups of the internal combustion engine are branched into four branch pipes in total, and two branch pipes are joined together to form two mixing pipes. A 2-4-2 type exhaust system has been described. In addition, the 2-4-2-1-2 type exhaust system in which two mixing tubes are joined and further branched into two second mixing tubes has been described.

  However, the type of exhaust system to which the present invention is applied is not limited to these. That is, for example, an exhaust system such as a 2-6-3 type, a 2-6-3-1 type, or a 2-6-3-1-3 type may be used.

  In the above embodiment, the case where the internal combustion engine has two banks and controls the air-fuel ratio and the amount of exhaust discharged from the two banks has been described. However, the cylinder group in the present invention includes only the banks. I don't mean. For example, the present invention may be applied to a case where one cylinder block row is divided into a plurality of cylinder groups and the air-fuel ratio and the operation state are controlled for each cylinder group.

It is a figure which shows schematic structure of the exhaust gas purification system in Example 1 of this invention. It is a time chart shown about the control at the time of the cold start of the internal combustion engine which concerns on Example 1 of this invention. It is a time chart shown about the control at the time of the cold start of the internal combustion engine which concerns on Example 2 of this invention. It is a time chart shown about another aspect of the control at the time of the cold start of the internal combustion engine which concerns on Example 2 of this invention. It is a time chart shown about the control at the time of the cold start of the internal combustion engine which concerns on Example 3 of this invention. It is a time chart shown about another aspect of the control at the time of the cold start of the internal combustion engine which concerns on Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Right exhaust pipe 2a, 2b ... Right branch pipe 3 ... Right mixing pipe 4 ... Right main exhaust purification device 5 ... Confluence mixing pipe 6 ... Right 2nd mixing pipe 7. ..Exhaust throttle valve 8 ... Upstream O ₂ sensor 9 ... Downstream O ₂ sensor 10 ... Right front exhaust purification device 50 ... Left front exhaust purification device 51 ... Left exhaust pipe 52a, 52b ... Left branch pipe 53 ... Left mixing pipe 54 ... Left main exhaust purification device 56 ... Left second mixing pipe

Claims (9)

An exhaust passage through which exhaust discharged from a plurality of cylinder groups of the internal combustion engine passes;
One or more exhaust purification devices provided in the exhaust passage and purifying the exhaust;
An exhaust purification system for an internal combustion engine comprising:
The exhaust passage is
A cylinder group directly connected exhaust passage connected to each of the plurality of cylinder groups and having the same number of cylinder groups through which exhaust discharged from each cylinder group passes;
A branch passage for each cylinder group formed by dividing the cylinder group directly connected exhaust passage by the same number with respect to each of the cylinder group directly connected exhaust passages;
One cylinder group is formed for one cylinder group by joining one of the plurality of cylinder group branch passages branched from each of the cylinder group direct exhaust passages with respect to all the cylinder group direct exhaust passages. Mixed exhaust passages formed in the same number as the number of branch passages per cylinder group,
A combined mixed exhaust passage formed by joining all of the mixed exhaust passages;
An exhaust amount control means provided in at least one of the mixed exhaust passages for controlling the amount of exhaust gas passing through the mixed exhaust passage;
Have
Exhaust gas passing through the merged mixed exhaust passage is introduced into the exhaust gas purification device,
An exhaust purification system for an internal combustion engine, wherein the exhaust amount control means reduces the amount of exhaust passing through at least one of the mixed exhaust passages for a predetermined period after the cold start of the internal combustion engine. Estimating the cumulative intake air amount or cumulative fuel injection amount after the cold start of the internal combustion engine,
The predetermined period is a period from the start of cold start until the estimated value of the integrated intake air amount or the integrated fuel injection amount exceeds a predetermined value,
2. The internal combustion engine according to claim 1, wherein the exhaust amount control means increases the amount of exhaust gas passing through the mixed exhaust passage after the predetermined period has elapsed since the cold start of the internal combustion engine. Exhaust purification system. The exhaust amount control means is an exhaust throttle valve provided in at least one of the mixed exhaust passages, and increases or decreases the amount of exhaust passing through at least one of the mixed exhaust passages when the exhaust throttle valve opens and closes Let
An air-fuel ratio sensor capable of detecting the air-fuel ratio of the exhaust in a state activated by heating on the upstream side and / or downstream side of the exhaust purification device;
The exhaust purification system for an internal combustion engine according to claim 1 or 2, wherein heating of the air-fuel ratio sensor is stopped when the exhaust throttle valve opens during the predetermined period.   The internal combustion engine according to claim 3, wherein when the exhaust throttle valve opens during the predetermined period, the exhaust throttle valve opens after a predetermined delay time has elapsed since the heating stopped. Engine exhaust purification system.   The operation of opening the exhaust throttle valve and stopping the heating and the operation of closing the exhaust throttle valve and starting the heating are alternately repeated in at least a part of the predetermined period. The exhaust gas purification system for an internal combustion engine according to claim 3 or 4. Provided with an air-fuel ratio sensor upstream and downstream of the exhaust purification device,
When heating of the air-fuel ratio sensor upstream of the exhaust purification device is stopped, the air-fuel ratio control of the internal combustion engine is performed using the output of the air-fuel ratio sensor downstream of the exhaust purification device. The exhaust gas purification system for an internal combustion engine according to claim 3.   When the temperature of the mixed exhaust passage provided with the exhaust throttle valve becomes equal to or higher than the dew point temperature while heating of the upstream air-fuel ratio sensor is stopped, the upstream air-fuel ratio sensor of the exhaust gas purification device 7. The exhaust gas purification system for an internal combustion engine according to claim 6, wherein the air fuel ratio control of the internal combustion engine is performed using the output of the air fuel ratio sensor upstream of the exhaust gas purification device while starting heating. The exhaust amount control means is an exhaust throttle valve provided in at least one of the mixed exhaust passages, and increases or decreases the amount of exhaust passing through the mixed exhaust passage by opening and closing the exhaust throttle valve,
An air-fuel ratio sensor capable of detecting the air-fuel ratio of the exhaust in a state activated by heating on the upstream side and / or downstream side of the exhaust purification device;
Immediately after the start of cold start of the internal combustion engine in the predetermined period, the exhaust throttle valve is opened, and heating of the air-fuel ratio sensor is stopped,
When the temperature of the mixed exhaust passage provided with the exhaust throttle valve becomes a dew point temperature or higher during the predetermined period, the air-fuel ratio sensor on the upstream side of the exhaust purification device is heated, and the exhaust throttle valve is 3. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the exhaust gas purification system is closed.   9. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein each of the plurality of cylinder groups forms each of a plurality of banks provided in the internal combustion engine. 10.

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