JP2006083833A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system for an internal combustion engine, comprising particulate filters in exhaust passages for trapping PMs, wherein the trapped PMs are efficiently oxidized and removed. <P>SOLUTION: The exhaust emission control system for the internal combustion engine comprises the first and second particulate filters 17, 18 provided in the exhaust passages 11, 12 of the internal combustion engine 1 for trapping particulate materials in exhaust gas. The exhaust flow-out face of the first particulate filter 17 and the exhaust flow-out face of the second particulate filter 18 are joined to each other in the opposed condition via a connection passage 19 so that exhaust gas flows from the connection passage to an exhaust passage 13 on the downstream side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust purification system that purifies particulate matter contained in exhaust gas from an internal combustion engine.

  In order to collect particulate matter (hereinafter referred to as “PM”) contained in the exhaust, a particulate filter is provided in the exhaust passage of the internal combustion engine. However, if PM collection in the exhaust gas is continued by this particulate filter, the exhaust pressure loss increases. Therefore, by applying an exhaust flow opposite to the normal exhaust flow to the particulate filter provided in the exhaust passage, the PM collected in the particulate filter is peeled off once, and the exhaust pressure loss increases. A technique for solving this problem is disclosed (for example, see Patent Document 1).

In addition, the oxidizing agent is supported on the wall surface of the particulate filter provided in the exhaust passage, and PM is disturbed between the two wall surfaces to increase the chance of contact between PM and the oxidizing agent, so that the PM is oxidized. A technique for reducing the amount of PM removed and deposited on the particulate filter has been disclosed (see, for example, Patent Document 2).
JP 2000-234509 A JP 2001-342823 A JP 2004-52611 A JP 2002-266630 A

  In order to collect PM in the exhaust, a particulate filter is provided in the exhaust passage. However, the collection amount of the particulate filter is limited, and the exhaust pressure loss increases because the back pressure in the exhaust passage increases as the collection amount increases. Therefore, when a certain amount of PM is collected in the particulate filter, it is necessary to remove the oxidation to recover the collecting ability of the particulate filter. However, in order to oxidize and remove the collected PM, it is necessary to place the PM in a relatively high temperature atmosphere.

  In the present invention, in view of the problems described above, in an exhaust gas purification system for an internal combustion engine that includes a particulate filter that collects PM in an exhaust passage of the internal combustion engine, it is possible to more efficiently oxidize and remove the collected PM. Objective.

  In order to solve the above-described problems, the present invention provides a set of particulate filters in the exhaust passage of the internal combustion engine, and sets the exhaust outlet surfaces of the respective particulate filters to face each other. More specifically, the present invention is an internal combustion engine exhaust purification system in which a first particulate filter and a second particulate filter that collect particulate matter in exhaust gas are provided in an exhaust passage of the internal combustion engine. The exhaust outlet surface of the first particulate filter and the exhaust outlet surface of the second particulate filter are connected to each other by a connection passage in an opposed state, and exhaust gas flows from the connection passage to the downstream exhaust passage. .

That is, in the exhaust purification system described above, the exhaust discharged from the internal combustion engine flows into the first particulate filter and the second particulate filter, and the PM in the exhaust is collected by each. Then, the exhaust gas flowing out from each particulate filter flows into the common connection passage and is then sent to the exhaust passage on the downstream side.

  Here, exhaust pulsation due to the combustion order in the cylinders exists in the exhaust discharged from the internal combustion engine. Therefore, the exhaust gas flowing into the first particulate filter is oxidized to remove a part of the collected PM to become high-temperature exhaust gas, and also flows into the second particulate filter in an opposed state through the connection passage. . At this time, the exhaust gas that has flowed into the second particulate filter peels off the PM collected therein from the second particulate filter, thereby finely granulating the PM.

  By doing so, it is possible to avoid the state where PM is continuously deposited on the second particulate filter and is not easily removed by oxidation, and the PM is placed in a state where it is easily oxidized. Therefore, it is possible to remove the oxidized PM by oxidation. The same applies to PM collected by the first particulate filter.

  Further, when the oxidation catalyst is supported on the first particulate filter and / or the second particulate filter, the collected PM is disturbed by the high-temperature exhaust gas flowing from the opposite particulate filter, and the oxidation is performed. Increases the chance of contact with the catalyst. Therefore, PM can be oxidized and removed more efficiently.

  Here, in the exhaust gas purification system for an internal combustion engine, the central axis of the exhaust outlet surface of the first particulate filter and the central axis of the exhaust outlet surface of the second particulate filter are substantially on the same axis. May be. By making them substantially on the same axis, the exhaust from the first particulate filter can easily enter the second particulate filter through the connection passage, and conversely, the exhaust from the second particulate filter passes through the connection passage. This is because it becomes easier to enter smoothly by the first particulate filter.

  In the exhaust gas purification system for an internal combustion engine, the cylinders of the internal combustion engine are divided into two cylinder groups having common exhaust, and the first particulate filter is provided in one of two exhaust passages connected to each cylinder group. The second particulate filter may be provided in the other exhaust passage.

  In other words, due to the structure of the internal combustion engine, etc., exhaust from all cylinders is not concentrated in one exhaust passage, but is divided into two exhaust passages, thereby securing piping space and avoiding exhaust interference, etc. Therefore, the cylinders of the internal combustion engine may be divided into two cylinder groups that share exhaust. In such a case, more efficient oxidation of PM can be achieved by providing the above-described first particulate filter and second particulate filter in each exhaust passage connected to each cylinder group in a state where the exhaust outlet surfaces face each other. Removal is possible.

  As an example in which the cylinders of the internal combustion engine are divided into two cylinder groups having a common exhaust, the internal combustion engine is a V-type engine or a horizontally opposed engine having two banks, each of the two banks. May be connected to each of the two exhaust passages, the first particulate filter may be provided in one exhaust passage, and the second particulate filter may be provided in the other exhaust passage. .

  Further, the above is a case where the cylinders of the internal combustion engine are divided into two common cylinder groups, but the exhaust passage extending from the internal combustion engine branches into two, and the first exhaust passage is divided into the first exhaust passage. One particulate filter may be provided, and the second particulate filter may be provided in the other exhaust passage. This also makes it possible to remove PM more efficiently by oxidation.

  Here, in the exhaust gas purification system for an internal combustion engine up to the above, in the case where a supercharger that performs supercharging by exhaust gas flowing through the exhaust passage is provided, the first particulate filter and the second particulate filter are obtained from the supercharger. You may make it provide in an upstream exhaust passage. By providing the first particulate filter and the second particulate filter in the exhaust passage on the upstream side of the supercharger, it becomes possible to set the exhaust temperature flowing into each of these particulate filters to a relatively high temperature state, It is possible to greatly contribute to the oxidation removal of PM collected by the particulate filter.

  However, if the first particulate filter and the second particulate filter are provided upstream of the turbocharger, the pressure loss increases, and therefore, when supercharging is required particularly during sudden acceleration of the internal combustion engine. In this case, it is difficult to quickly generate the required supercharging, and the torque exerted by the internal combustion engine may be reduced.

  Therefore, in the exhaust gas purification system for an internal combustion engine, a required torque calculation means for calculating a torque required for a vehicle on which the internal combustion engine is mounted, and an actual torque calculation means for calculating a torque actually exhibited by the internal combustion engine; A torque assisting means for applying an assist torque to the torque of the internal combustion engine when the exerted torque calculated by the exerted torque calculating means is lower than the required torque calculated by the required torque calculating means. It may be.

  That is, when steep supercharging is required, when the torque that can be exhibited by the internal combustion engine due to pressure loss due to the first and second particulate filters is less than the required torque required for the vehicle The torque assisting means provides the insufficient torque as the torque of the internal combustion engine. When the internal combustion engine is a so-called hybrid vehicle equipped with both the internal combustion engine and the electric motor, the electric motor can be used as the auxiliary torque means.

  In an exhaust gas purification system for an internal combustion engine that includes a particulate filter that collects PM in the exhaust passage of the internal combustion engine, it becomes possible to more efficiently remove the oxidized PM that has been collected.

  Here, an embodiment of an exhaust gas purification system for an internal combustion engine according to the present invention will be described based on the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of an exhaust purification system of an internal combustion engine 1 to which the present invention is applied and a control system thereof. The internal combustion engine 1 is an internal combustion engine having four cylinders 2, and # 1, # 2, # 3, and # 4 in the figure are cylinder numbers for identifying each cylinder. An intake branch pipe 7 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 7 is connected to a combustion chamber via an intake port. The intake branch pipe 7 is connected to the intake pipe 8. An air flow meter 9 for detecting the flow rate of intake air flowing through the intake pipe 8 is provided upstream of the intake pipe 8, and an air cleaner 6 is provided immediately upstream thereof. An intake throttle valve 10 that adjusts the flow rate of intake air flowing through the intake pipe 8 is provided downstream of the air flow meter 9.

Here, an exhaust branch pipe 11 and an exhaust branch pipe 12 are connected to the internal combustion engine 1. Exhaust from the second cylinder 2 # 2 and third cylinder 2 # 3 flows into the exhaust branch pipe 11, and exhaust from the first cylinder 2 # 1 and fourth cylinder 2 # 4 flows into the exhaust branch pipe 12 It has become. That is, the cylinder 2 is divided into two cylinder groups (a group of cylinders 2 # 1 and 2 # 4 and a group of cylinders 2 # 2 and 2 # 3) that share the same exhaust gas. The branch pipe 11 and the exhaust branch pipe 12 are connected. This is because the order of combustion in the cylinder 2 of the internal combustion engine 1 is # 1 → # 4 → # 2 → # 3.

  The exhaust branch pipe 11 and the exhaust branch pipe 12 are connected to each other by a connection passage 19 on the downstream side, and PM in the exhaust is collected immediately upstream of the connection portion with the connection passage 19 of each exhaust branch pipe. A particulate filter is provided. Specifically, the exhaust branch pipe 12 is provided with a first particulate filter 17, and the exhaust branch pipe 11 is provided with a second particulate filter 18. Further, the exhaust outlet surfaces of the first particulate filter 17 and the second particulate filter 18 are opposed to each other, and the center axis of each exhaust outlet surface is substantially on the same axis so that each particulate filter The position of is adjusted. An exhaust pipe 13 extends from the connection passage 19.

  Here, the intake pipe 8 on the downstream side of the intake throttle valve 10 is provided with a compressor side 16a of a supercharger 16 that operates using exhaust energy as a drive source, and the exhaust pipe 13 is provided with a turbine side of the turbocharger 16. 16b is provided. The supercharger 16 is a so-called variable capacity supercharger. The supercharger 16 has a movable nozzle vane therein, and the supercharging pressure by the supercharger 16 is controlled by adjusting the opening degree of the nozzle vane. . The intake pipe 8 downstream of the supercharger 16 is provided with an intercooler 15 for cooling the intake air that has been pressurized by the supercharger 16 and has reached a high temperature. Moreover, the turbine side 16b of the supercharger 16 is connected to the exhaust pipe 13, and is connected to the muffler on the downstream side. In the middle of the exhaust pipe 13, a NOx catalyst 14 of a so-called storage reduction type NOx catalyst is provided.

  Further, the internal combustion engine 1 is provided with an EGR device. The EGR device recirculates a part of the exhaust gas flowing through the exhaust pipe 13 to the intake pipe 8. The EGR device mainly includes an intake pipe 8 (downstream) located between the intake throttle valve 10 and the compressor side 16a of the supercharger 16 from an exhaust pipe 13 (upstream side) located between the upstream side of the NOx catalyst 14. The EGR passage 22 extending to the EGR passage 22, an EGR valve 24 for adjusting the flow rate of EGR gas provided in order from the upstream side on the EGR passage 22, and an EGR cooler 23 for cooling the EGR gas.

  Here, the vehicle on which the internal combustion engine 1 is mounted is a so-called hybrid vehicle, and includes an electric motor 20 in addition to the internal combustion engine 1 as a drive source. In the hybrid vehicle, the motive power from the internal combustion engine 1 and the motive power from the electric motor 20 are transmitted to the power split mechanism 21, and finally the drive wheels 22 of the vehicle are rotated.

  The internal combustion engine 1 is provided with an electronic control unit (hereinafter referred to as “ECU”) 30 for controlling the internal combustion engine 1 and the like. The ECU 30 includes a CPU, a ROM, a RAM, and the like that store various programs and maps to be described later, and controls the operating conditions of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 and the driver's request. Unit.

  Here, the ECU 30 is electrically connected to the above-described electric motor 20, the power split mechanism 21, and the like, and each is controlled in accordance with a command from the ECU 30. Further, an accelerator opening sensor 31 is electrically connected to the ECU 30, and the ECU 30 receives a signal corresponding to the accelerator opening and calculates an engine load required for the internal combustion engine 1 based on the signal. Further, the crank position sensor 32 is electrically connected to the ECU 30, and the ECU 30 receives a signal corresponding to the rotation angle of the output shaft of the internal combustion engine 1 and calculates the engine rotational speed and the like of the internal combustion engine 1.

  Further, the ECU 30 and the air flow meter 9 are electrically connected, and the intake flow rate flowing through the intake pipe 8 is measured. In addition to this, various sensors and control devices are electrically connected to the ECU 30, but the description thereof is omitted because the relevance to the present invention is low.

In the exhaust purification system of the internal combustion engine 1 configured as shown in FIG. 1, PM in the exhaust discharged from the cylinders 2 # 1 and 2 # 4 is collected by the first particulate filter 17, and the second particulate filter 18 collects PM in the exhaust discharged from the cylinders 2 # 2 and 2 # 3. The exhaust heat from the cylinders 2 # 1 and 2 # 4 is partly removed by oxidation of the PM collected by the first particulate filter 17, so that the exhaust temperature rises and becomes higher than that. The exhaust gas flows into the second particulate filter 18 through the connection passage 19. As a result, the PM collected and accumulated in the second particulate filter 18 is peeled off, and the PM is finely divided in the exhaust branch pipe 11 to be separated from the cylinders 2 # 2, 2 # 3 again. Will be exposed to the exhaust heat of

  Thus, since the PM collected by the second particulate filter 18 is exposed to a high-temperature atmosphere by the high-temperature exhaust from the opposing first particulate filter 17, the collected PM Oxidation removal is promoted. In particular, when the amount of PM accumulated on the second particulate filter 18 is large, it is difficult to sufficiently remove the accumulated PM by simply flowing exhaust from the cylinders 2 # 2, 2 # 3. It is. Therefore, as shown in FIG. 1, the arrangement in which the exhaust outlet surfaces of the first particulate filter 17 and the second particulate filter 18 face each other is useful for efficient PM removal.

  In the above description, the oxidation removal of the PM collected by the second particulate filter 18 has been described. Similarly, the PM collected by the first particulate filter 17 is also the second particulate filter 18. The PM is efficiently oxidized and removed by the high-temperature exhaust gas flowing from the exhaust gas.

  Further, by connecting the cylinders and the exhaust branch pipes in consideration of the combustion order in the cylinder 2, the exhaust from the first cylinder 2 # 1 and the fourth cylinder 2 # 4 is sent to the first particulate filter 17 and the second particulate filter. After reaching the order of the curative filter 18, the exhaust from the second cylinder 2 # 2 and the third cylinder 2 # 3 arrives in the order of the second particulate filter 18 and the first particulate filter 17. In other words, the exhaust pulsation in the exhaust passage is fully utilized to more efficiently remove the PM collected by each particulate filter.

  Here, in the exhaust purification system of the internal combustion engine 1 shown in FIG. 1, a first particulate filter 17 and a second particulate filter 18 are provided in the exhaust passage upstream of the supercharger 16. Therefore, a pressure loss occurs, and there is a possibility that the supercharging pressure in the intake pipe 8 and the intake branch pipe 7 may be insufficient particularly when the supercharger 16 performs supercharging sharply.

  Therefore, it is preferable to perform control related to torque assist (hereinafter referred to as “torque assist control”) when the supercharging pressure is insufficient as shown in FIG. The torque assist control will be described based on the flowchart of FIG. The torque assist control in the present embodiment is a routine that is repeatedly executed by the ECU 30 at a constant cycle.

  In S <b> 101, a torque required for acceleration of the vehicle is calculated based on a signal from the accelerator opening sensor 31 from a driver of the vehicle on which the internal combustion engine 1 is mounted. Specifically, a torque transition (increase from torque T1 to torque T2) indicated by line L1 in FIG. 3 is required. In FIG. 3, the horizontal axis represents time, and the vertical axis represents torque. When the process of S101 ends, the process proceeds to S102.

In S102, a torque that is shared and exhibited by each of the internal combustion engine 1 and the electric motor 20 with respect to the torque requested in S101 is calculated. Since the first particulate filter 17 and the second particulate filter 18 are provided in the exhaust branch pipes 11 and 12, pressure loss occurs. Therefore, the internal combustion engine 1 has the maximum torque indicated by the line L2 in FIG. This is the torque that can be exerted. The torque that can be exhibited to the maximum of the internal combustion engine 1 is estimated based on the accelerator opening signal from the accelerator opening sensor 31, the engine speed from the crank position sensor 32, and the like, and this becomes the engine torque Te. .

  Therefore, since the internal combustion engine 1 can exhibit only the acceleration torque represented by the line L2 with respect to the acceleration torque L1 represented by the line L1 required by the operator, the acceleration torque that is insufficient (indicated by the diagonal lines in FIG. 3). The acceleration torque in the region shown) is assisted by the electric motor 20, and this becomes the motor torque Tm. When the process of S102 ends, the process proceeds to S103.

  In S103, the intake air flow rate into the cylinder 2 is calculated based on the signal from the air flow meter 9. When the process of S103 ends, the process proceeds to S104.

  In S104, the engine maximum torque TL that can be exhibited by the internal combustion engine 1 is calculated based on the intake air flow rate calculated in S103. That is, the maximum torque that can be exhibited by the internal combustion engine 1 in a range where smoke does not occur is calculated as TL in accordance with the intake air flow rate. When the process of S104 ends, the process proceeds to S105.

  In S105, it is determined whether or not the engine torque Te calculated in S102 is greater than the engine maximum torque TL calculated in S104. That is, as shown in FIG. 3, even if the torque is to be exerted by the internal combustion engine 1, smoke is generated when the intake air flow rate is small, so it is determined whether it is difficult to exert sufficient torque. Is. It is determined that the engine torque Te is larger than the engine maximum torque TL. If the engine torque Te (torque indicated by the line L2) according to FIG. Therefore, in such a case, the process proceeds to S106. On the other hand, if it is determined that the engine torque Te is not greater than the engine maximum torque TL, the process proceeds to S107 because the occurrence of smoke is avoided.

In S106, in response to the determination in S105, the values of the engine torque Te and the motor torque Tm calculated in S102 are corrected. That is, in consideration of the fact that smoke can be generated when the internal combustion engine 1 exerts torque along the line L2 in FIG. 3, the maximum engine torque at which the smoke should be avoided from the initial Te is determined. Reduce to torque TL. On the other hand, the reduced torque is added to the motor torque Tm that is the torque generated by the electric motor 20. Therefore, the motor torque Tm is finally expressed by the following equation.
Tm = (original Tm) + (Te−TL)
When the process of S106 ends, the process proceeds to S107.

  In S107, the engine torque Te and the motor torque Tm calculated in S102, or the combustion control including the fuel injection in the internal combustion engine 1 and the torque assist of the motor so that the engine torque Te and the motor torque Tm corrected in S106 are exhibited. Control is performed. After the process of S107, this control is terminated.

  According to this control, as described above, the first particulate filter 17 and the second particulate filter 18 can oxidize and remove PM more efficiently, and these particulate filters can be disposed upstream of the supercharger 16. It is possible to perform torque assistance for the pressure loss generated by being provided on the side by the electric motor 20, and it is possible to respond to an instantaneous acceleration request or the like of the vehicle operator.

It is a figure showing the schematic structure of the exhaust gas purification system of the internal combustion engine which concerns on the Example of this invention. 5 is a flowchart relating to torque assist control for assisting torque of the internal combustion engine in the exhaust gas purification system for the internal combustion engine according to the embodiment of the present invention. It is a figure which shows the torque which an internal combustion engine can exhibit when the sudden acceleration request | requirement is performed in the exhaust gas purification system of the internal combustion engine which concerns on the Example of this invention, and its shortage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 .... Internal combustion engine 2 .... Cylinder 7 .... Intake branch pipe 8 .... Intake pipe 9 .... Air flow meter 11 .... Exhaust branch pipe 12 .... Exhaust branch Pipe 13 ... Exhaust pipe 16 ... Supercharger 17 ... First particulate filter 18 ... Second particulate filter 19 ... Connection passage 20 ... Electric motor 30 .... ECU
31 ··· Accelerator position sensor

Claims (7)

An exhaust purification system for an internal combustion engine in which an exhaust passage of the internal combustion engine is provided with a first particulate filter and a second particulate filter that collect particulate matter in the exhaust,
The exhaust outflow surface of the first particulate filter and the exhaust outflow surface of the second particulate filter are connected by a connection passage in a state of being opposed to each other, and exhaust flows from the connection passage to the downstream exhaust passage. An exhaust gas purification system for an internal combustion engine.   2. The exhaust gas of an internal combustion engine according to claim 1, wherein the central axis of the exhaust outlet surface of the first particulate filter and the central axis of the exhaust outlet surface of the second particulate filter are substantially on the same axis. Purification system.   The cylinders of the internal combustion engine are divided into two cylinder groups having common exhaust, the first particulate filter is provided in one of two exhaust passages connected to each cylinder group, and the second particulate filter is provided in the other exhaust passage. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2, wherein a filter is provided.   The internal combustion engine is a V-type engine or a horizontally opposed engine having two banks, and a cylinder group in each of the two banks is connected to each of the two exhaust passages, and the one exhaust passage has the The exhaust gas purification system for an internal combustion engine according to claim 3, wherein a first particulate filter is provided, and the second particulate filter is provided in the other exhaust passage.   An exhaust passage extending from the internal combustion engine branches into two, the first particulate filter is provided in one exhaust passage, and the second particulate filter is provided in the other exhaust passage. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2. A supercharger that performs supercharging by exhaust gas flowing through the exhaust passage;
The internal combustion engine according to any one of claims 1 to 5, wherein the first particulate filter and the second particulate filter are provided in an exhaust passage upstream of the supercharger. Exhaust purification system. Requested torque calculating means for calculating torque required for a vehicle equipped with the internal combustion engine;
Exerted torque calculating means for calculating torque actually exerted by the internal combustion engine;
Torque assisting means for applying auxiliary torque to the torque of the internal combustion engine when the exerted torque calculated by the exerted torque calculating means is lower than the required torque calculated by the required torque calculating means;
An exhaust purification system for an internal combustion engine according to claim 6, comprising:

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