Patent Application
20110041488
The present invention relates to an exhaust system of an internal combustion engine.
An exhaust system of an internal combustion engine in which an extension chamber having a cross sectional area larger than the cross sectional area of an exhaust pipe is provided in the middle of the exhaust pipe upstream of an exhaust gas purification apparatus has been developed (see, for example, Patent Document 1 and 2).
In the above-mentioned prior art technology, the axis of the extension chamber and the axis of the exhaust pipe are arranged on substantially the same line. In consequence, the exhaust gas flowing from the exhaust pipe into the extension chamber tends to be partially localized to a certain portion (i.e. a certain portion in a cross sectional plane perpendicular to the direction of the exhaust gas flow) rather than dispersed with respect to radial directions. Such localization of the distribution of the exhaust gas flow rate is considered to become remarkable during the time of high speed operations in which the inertial force of the exhaust gas is large.
If the above-described localization of the distribution of the exhaust gas flow rate occurs, since the most part of the exhaust gas concentrates to a portion of the exhaust gas purification apparatus, the purification capability of the exhaust gas purification apparatus cannot be made use of efficiently.
In particular, in the exhaust system in which a reducing agent needs to be supplied to the exhaust gas purification apparatus, the inertial force of the reducing agent is larger than the inertial force of the exhaust gas, and consequently the reducing agent tends to concentrate to a portion of the exhaust gas purification apparatus. If the reducing agent concentrates to a portion of the exhaust gas purification apparatus, the purification capability of the exhaust gas purification apparatus cannot be fully made use of, and the reducing agent may fail to be consumed usefully.
The present invention has been made in view of the above described situations and has an object to provide a technology with which the purification capability of the exhaust gas purification apparatus can be effectively made use of.
To solve the above-described problem, according to the present invention, in an exhaust system of an internal combustion engine including an exhaust gas purification apparatus provided in an exhaust pipe of the internal combustion engine and a reducing agent supply apparatus that supplies a reducing agent to the exhaust gas before it flows into the exhaust gas purification apparatus, an extension chamber is provided downstream of the position at which the reducing agent supply apparatus supplies the reducing agent to the exhaust gas and upstream of the exhaust gas purification apparatus so that a plurality of flows are generated in the extension chamber.
Specifically, an exhaust system of an internal combustion engine according to the present invention comprises:
an exhaust gas purification apparatus disposed in an exhaust pipe of the internal combustion engine;
an extension chamber provided in the middle of the exhaust pipe upstream of the exhaust gas purification apparatus, the extension chamber having an exhaust gas channel with a cross sectional area larger than a cross sectional area of the passage of the exhaust pipe; and
a reducing agent supply apparatus that supplies a reducing agent to exhaust gas flowing into said extension chamber,
wherein said extension chamber is provided with a back step flow creating portion that creates a back step flow of exhaust gas in the interior space of said extension chamber and a swirling flow creating portion that changes the flow of exhaust gas flowing into the interior space of said extension chamber into a swirling flow.
As the reducing agent supplied by the reducing agent supply apparatus and the exhaust gas flow into the interior space of the extension chamber, a back step flow is created. When the back step flow is created in the interior space of the extension chamber, the exhaust gas and the reducing agent flowing in the vicinity of the inner wall surface of the exhaust pipe are diffused and dispersed toward the periphery of the extension chamber. This leads to a decrease in the degree of convergence of the stream containing the exhaust gas and the reducing agent. The exhaust gas and the reducing agent flowing into the interior of the extension chamber tend to flow basically straightly along the inflowing direction by inertia, but their flow is changed into a swirling flow by the swirling flow creating portion. The change of the flow of the exhaust gas and the reducing agent into the swirling flow promotes the mixing of the exhaust gas and the reducing agent. In addition, when the back step flow and the swirling flow cross or meet each other, turbulence occurs in the interior space of the extension chamber. In consequence, partial localization of the distribution of the flow rate of the exhaust gas is eliminated, and the exhaust gas and the reducing agent are mixed uniformly. Consequently, the exhaust gas and the reducing agent are likely to extend uniformly in the entire of the exhaust gas purification apparatus.
The back step flow creating portion according to the present invention may be, for example, an inlet port that brings the interior of the exhaust pipe located upstream of the extension chamber and the interior space of said extension chamber into communication with each other through a step. In this case, since the cross sectional area of the channel of the exhaust gas increases abruptly by the step, the back step flow is created as the exhaust gas and the reducing agent pass through the step.
The swirling flow creating portion according to the present invention may be, for example, a guide wall surface that is oriented obliquely to the inflowing direction of the exhaust gas flowing into the extension chamber. The most part of the exhaust gas flowing from the exhaust pipe into the extension chamber (in particular, the exhaust gas flowing in the vicinity of the center axis of the exhaust pipe) travels substantially straightly in said inflowing direction and strikes the guide wall surface. Since the guide wall surface is oriented obliquely to said inflowing direction, the flow of the exhaust gas is then guided by the guide wall surface to change into a swirling flow.
The extension chamber according to the present invention may be disposed in such a way that the axis of the extension chamber is oriented obliquely to the inflowing direction of the exhaust gas flowing into the extension chamber. In this case, the inner wall surface of the extension chamber is oriented obliquely to the exhaust gas inflowing direction. In this case, the inner wall surface of the extension chamber can function as the aforementioned guide wall surface.
A projection or recess having a wall surface that is oriented obliquely to the inflowing direction of the exhaust gas flowing into the extension chamber may be provided on the inner wall surface of the extension chamber according to the present invention. In this case, the wall surface of the projection or recess can function as the aforementioned guide wall surface.
The aforementioned projection or recess may extend helically. In this case, the exhaust gas flowing into the extension chamber will swirl helically.
The inlet port of the extension chamber according to the present invention may be designed in such a way as to make the inner bottom surface of the exhaust pipe and the bottom surface of the interior space of the extension chamber continuous with each other without a step therebetween. In other words, the step of the inlet port may be provided only in the portion other than the portion by which the inner bottom surface of the exhaust pipe and the bottom surface of the interior space of the extension chamber are connected. Here, the bottom surface includes the surface that is located lowest when the exhaust gas purification system is mounted on a vehicle, and surfaces in the vicinity of this surface.
If a step is present between the inner bottom surface of the exhaust pipe and the bottom surface of the interior space of the extension chamber, liquid reducing agent that has not evaporated and condensed water may be stored on the step. In contrast, if the step is provided only in the portion other than the portion by which the inner bottom surface of the exhaust pipe and the bottom surface of the interior space of the extension chamber are connected, the above described problem can be prevented from occurring.
The distance along the direction of flow of the exhaust gas over which a back step flow(s) can be created is approximately equal to seven times the height of the step. Therefore, the distance from the upstream end of the interior space of the extension chamber to the downstream end thereof may be designed to be equal to or smaller than seven times the height of the step. In this case, back step flow(s) can be created in substantially the entire region in the interior space of the extension chamber from its upstream end to downstream end. Consequently, the diffusion of the exhaust gas and the reducing agent can be enhanced without an unduly large increase in the size of the extension chamber.
The extension chamber according to the present invention may be configured to have a hollow cylindrical shape. In this case, since the inner wall surface of the extension chamber is a curved surface, an increase in the pressure loss and an increase in the noise that will be caused when the exhaust gas strikes the inner wall surface of the extension chamber can be minimized. Furthermore, the extension chamber can be manufactured easily.
In the system according to the present invention, an outlet port that brings the interior space of the extension chamber into communication with the exhaust pipe disposed downstream of the extension chamber may be provided in such a way that the opening area of the outlet port is disposed at a position offset from the region defined by extending the opening area of the inlet port. This is because if at least a portion of the opening area of the outlet port overlaps the region defined by extending the opening area of the inlet port, a portion of the exhaust gas flowing into the extension chamber through the inlet port may travel straightly to the outlet port.
According to the present invention, the purification capability of an exhaust gas purification apparatus provided in an exhaust pipe of an internal combustion engine can be efficiently made use of.
1: internal combustion engine
2: upstream exhaust pipe
3: extension chamber
4: downstream exhaust pipe
5: exhaust gas purification apparatus
6: reducing agent addition valve (reducing agent supply apparatus)
30: cylindrical member
31: inner circumferential wall surface (swirling flow creating portion)
32: upstream end wall
33: inlet port (back step flow creating portion)
34: downstream end wall
35: outlet port
36: projection
37: projecting pipe
38: projecting pipe
39: annular projection
40: stepped portion
41: ridge portion
42: resonator
43: communication hole
44: bottom surface
50: inner wall surface
51: inlet port
60: extension chamber
61: cylindrical member
In the following, specific embodiments of the present invention will be described with reference to the drawings.
A first embodiment of the present invention will be firstly described with reference to
In
The aforementioned exhaust gas purification apparatus 5 has any one of a configuration in which an NOx storage reduction catalyst is housed in a casing, a configuration in which an NOx storage reduction catalyst and a particulate filter are housed in a casing, and a configuration in which an oxidation catalyst and a particulate filter are housed in a casing.
A reducing agent addition valve 6 that supplies a reducing agent to the exhaust gas flowing in the upstream exhaust pipe 2 is attached to the upstream exhaust pipe 2. The reducing agent addition valve 6 is an embodiment of the reducing agent supply apparatus according to the present invention.
The reducing agent addition valve 6 adds a reducing agent such as fuel or urea to the exhaust gas when NOx stored in the exhaust gas purification apparatus 5 is to be removed by reduction, when SOx stored in the exhaust gas purification catalyst 5 is to be removed by reduction, or when PM trapped in the exhaust gas purification apparatus 5 is to be removed by oxidation.
The distribution of the flow rate of the exhaust gas and the reducing agent tends to be partially localized to a portion in a cross section perpendicular to the direction of flow of the exhaust gas. For example, the distribution of the flow rate of the exhaust gas tends to concentrate to a central portion of the aforementioned cross section. On the other hand, the reducing agent tends to flow on the inner bottom surface of the exhaust pipe. If the distribution of the flow rate of the exhaust gas and the distribution of the flow rate of the reducing agent are partially localized to a portion, there arises a situation in which the distribution of the flow rate of the exhaust gas concentrate to a central portion of the exhaust gas purification apparatus and the distribution of the flow rate of the reducing agent concentrate to the bottom portion of the exhaust gas purification apparatus.
A conceivable method of preventing this situation from occurring would be to provide a dispersing plate in the flow channel upstream of the exhaust gas purification apparatus so as to uniformly mix the exhaust gas and the reducing agent and to eliminate partial localization of the distribution of the flow rate of the exhaust gas and the reducing agent. However, since the dispersing plate provides a resistance against the flow of the exhaust gas and the reducing agent, it may cause a rise in the back pressure.
An alternative conceivable method would be to provide the exhaust pipe with an extension chamber with an interior space having a cross sectional area larger than the cross sectional area of the passage in the exhaust pipe, at a certain position upstream of the exhaust gas purification apparatus. However, in the case where the axis of the exhaust pipe and the axis of the extension chamber are aligned on the same line, the partial localization of the distribution of the flow rate of the exhaust gas may fail to be eliminated when the inertial force of the exhaust gas is large, as is the case when the internal combustion engine is operating at high speed. This problem may be solved by increasing the length and/or cross sectional area of the extension chamber, but this solution will lead to a deterioration in the in-vehicle mountability.
In view of the above, the exhaust system of an internal combustion engine according to this embodiment is designed in such a way that back step flow and a swirling flow of the exhaust gas are generated in the interior of the extension chamber 3. By this feature, the uniform mixing of the exhaust gas and the reducing agent can be facilitated, and the partial localization of the distribution of the flow rate can be eliminated without an increase in the size of the extension chamber 3.
On one end wall 32 of the aforementioned cylindrical member 30 is provided an inlet port 33 that allows the exhaust gas to flow from the upstream exhaust pipe 2 into the interior of the cylindrical member 30. On the other end wall 34 of the aforementioned cylindrical member 30 is provided an outlet port 35 that allows the exhaust gas to flow from the interior of the cylindrical member 30 into the downstream exhaust pipe 4. In the following, the end wall 32 on which the inlet port 33 is provided will be referred to as the upstream end wall 32, and the end wall 34 on which the outlet port 35 is provided will be referred to as the downstream end wall 34.
The inlet port 33 has a step by which an inner diameter equal to that of the upstream exhaust pipe 2 is stepped up substantially vertically to an inner diameter equal to that of the extension chamber 3. This step corresponds to the back step flow creating portion according to the present invention.
The outlet port 35 is connected with the downstream exhaust pipe 4. The outlet port 35 has a step by which an inner diameter equal to that of the extension chamber 3 is stepped down substantially vertically to an inner diameter equal to that of the downstream exhaust pipe 4.
With the exhaust system of an internal combustion engine having the above-described construction, as the reducing agent added through the reducing agent addition valve 6 and the exhaust gas flow from the upstream exhaust pipe 2 into the extension chamber 3 through the inlet port 33, there are created back step flows Fb by which the exhaust gas and the reducing agent flowing in the vicinity of the inner wall surface of the upstream exhaust pipe 2 are diffused and dispersed in radial directions after passing through the step of the inlet port 33 as shown in
The exhaust gas and the reducing agent having been flowing in the vicinity of the center axis of the upstream exhaust pipe 2 strike the inner wall surface 31 of the extension chamber 3 obliquely to create a swirling flow Fs that swirls upward. The swirling flow Fs promotes the uniform mixing of the exhaust gas and the reducing agent. In particular, the reducing agent flowing in the bottom portion in the upstream exhaust pipe 2 is diffused and dispersed as it is brought upward by the aforementioned swirling flow Fs.
Furthermore, as the aforementioned swirling flow and the aforementioned back step flows cross or meat each other, turbulence occurs in the extension chamber 3. The turbulence further promotes the uniform mixing of the reducing agent and the exhaust gas, and eliminates the partial localization of the distribution of the flow rate of the exhaust gas and the reducing agent.
In consequence, the gas flowing out of the outlet port 35 of the extension chamber 3 into the downstream exhaust pipe 4 contains the exhaust gas and the reducing agent that are mixed uniformly, and a stream free from the partial localization of the distribution of the flow rate is created. Therefore, the exhaust gas and the reducing agent will extend uniformly in the entire of the exhaust gas purification apparatus 5. Consequently, the purification capability of the exhaust gas purification apparatus 5 can be efficiently made use of.
According to the exhaust system of an internal combustion engine of this embodiment, since it is not necessary to make the size of the extension chamber 3 unduly large, a deterioration in the in-vehicle mountability can be prevented. Furthermore, according to the exhaust system of an internal combustion engine of this embodiment, the pressure loss across the extension chamber 3 will not become unduly large.
Effective back step flow and swirling flow may fail to be created only by arranging the cylindrical member 30 constituting the extension chamber 3 obliquely with respect to the upstream exhaust pipe 2.
For example, as shown in
Therefore, it is preferred that the region R defined by extending the opening area of the inlet port 33 include only the inner circumferential wall surface 31 of the cylindrical member 30. To meet this condition, the extension chamber 3 may be designed in such a way as to satisfy the following formula (1):
α≧sin−1(C+D)/A (1).
In formula (1) presented above, A is the length of the interior space of the cylindrical member 30 along the axial direction, C is the inner diameter of the upstream exhaust pipe 2 (i.e. the diameter of the opening area of the inlet port 33), D is the height of the step of the inlet port 33, and α is the inclination angle of the cylindrical member 30 with respect to the upstream exhaust pipe 2 (i.e. the angle of intersection of the aforementioned virtual lines L1 and L2) (see
With the above-described design of the extension chamber 3, the quantity of the exhaust gas traveling straightly from the inlet port 33 to the outlet port 35 can be made as small as possible. In other words, substantially the entire portion of the exhaust gas flowing through the inlet port 33 into the cylindrical member 30 strikes the inner circumferential wall surface 31 obliquely to create the swirling flow.
The distance along the axial direction of the cylindrical member 30 over which back step flows can be created is approximately equal to seven times the height D of the step. Therefore, the length A of the interior of the cylindrical member 30 along the axial direction may be designed to be equal to or smaller than seven times the height D of the step (A≦7D).
In this case, the back step flows can be created in substantially the entire region inside the cylindrical member 30 from its upstream end to downstream end. Consequently, the diffusion of the exhaust gas and the reducing agent can be enhanced without an unnecessary increase in the size of the extension chamber 3.
Furthermore, the inventors of the present invention have found that the maximum distance that the back step flows can reach with respect to the vertical direction is approximately equal to three times the inner diameter C of the upstream exhaust pipe 2. Therefore, if the inner diameter B of the cylindrical member 30 is designed to be larger than three times the inner diameter C of the upstream exhaust pipe 2, a pressure loss may occur. On the other hand, if the inner diameter B of the cylindrical member 30 is designed to be excessively small, the back step flows may merge into the mainstream of the exhaust gas (i.e. the stream traveling along the axis of the upstream exhaust pipe 2) to disappear. Therefore, the inner diameter of the cylindrical member 30 may be designed in such a way that the following formula (2) be satisfied:
3C≧B≧1.2C (2).
If the inner diameter of the cylindrical member 30 is designed as above, an unnecessary increase in the size of the extension chamber 3, an increase in the pressure loss, and the disappearance of the back step flows can be prevented.
Since a large distance from the outlet port 35 of the extension chamber 3 to the exhaust gas purification apparatus 5 may cause partial localization of the distribution of the exhaust gas flow rate again, it is preferred that the distance between the outlet port 35 of the extension chamber 3 and the exhaust gas purification apparatus 5 be made as small as possible. In view of this, the exhaust gas purification apparatus 5 may be provided in the neighborhood of the outlet port 35 in the interior of the cylindrical member 30 as shown in
A second embodiment of the present invention will be described with reference to
With the extension chamber 3 having the above-described construction, the exhaust gas flowing from the upstream exhaust pipe 2 into the cylindrical member 30 through the inlet port 33 strikes the inner circumferential wall surface 31 of the cylindrical member 30, and consequently a swirling flow Fv that helically swirls around the axis of the cylindrical member 30 is created as shown in
The same effect can also be achieved by making the inflowing angle of the exhaust gas flowing from the upstream exhaust pipe 2 into the cylindrical member 30 skew as shown in
Alternatively, the effect similar to that of the construction shown in
A third embodiment of the present invention will be described with reference to
The outlet port 35 has a cylindrical projecting pipe 37 that projects into the interior of the cylindrical member 30. The inner diameter of the projecting pipe 38 is equal to the inner diameter of the downstream exhaust pipe 4. The length of projection of the projecting pipe 38 is larger in its lower portion than in its upper portion.
With the extension chamber 3 having the above-described construction, a swirling flow can be created more reliably because the projecting pipes 37, 38 hinder the exhaust gas from flowing straightly from the inlet port 33 to the outlet port 35.
In this embodiment, a case in which the inlet port 33 is arranged at a position lower than the outlet port 35 (in other words, a case in which the upstream end wall 32 of the cylindrical member 30 is arranged to be lower than the downstream end wall 34) has been described by way of example. In the case where the inlet port 33 is arranged at a position higher than the outlet port 35 (see
Instead of the projecting pipes 37, 38, an annular projection 39 may be provided on the inner circumferential wall surface 31 of the cylindrical member 30 (see
A fourth embodiment of the present invention will be described with reference to
With the extension chamber 3 having the above-described construction, the length of the inner circumferential wall surface 31 from its upstream end to downstream end increases, and therefore evaporation of the reducing agent in the extension chamber 3 can be facilitated.
As the reducing agent in a liquid state flows from the upstream exhaust pipe 2 into the interior of the cylindrical member 30, the liquid reducing agent may flow on the inner circumferential wall surface 31. The liquid reducing agent evaporates as it flows on the circumferential wall surface 31 from its upstream end to downstream end, wherein the larger the length of the inner circumferential wall surface 31 from its upstream end to downstream end is, the larger the amount of the evaporation will be.
Therefore, the amount of evaporated reducing agent can be increased by providing the aforementioned stepped portions 40 to increase the length of the inner circumferential wall surface 31 from its upstream end to downstream end.
Furthermore, back step flows of the exhaust gas are created at the stepped portions 40, whereby the above-described evaporation of the liquid reducing agent is promoted. Even in cases where the flow speed of the exhaust gas is low as is the case when the internal combustion engine 1 is operating at low speed, the mixing of the exhaust gas and the reducing agent can be promoted by the back step flows created at the stepped portions 40.
In cases where the swirling flow is to be enhanced when the flow speed of the exhaust gas is low, ridge portions 41 as shown in
A fifth embodiment of the present invention will be described with reference to
With the extension chamber 3 having the above-described construction, noises generated when the exhaust gas strikes the inner circumferential wall surface 31 of the cylindrical member 30 can be attenuated.
The resonator 42 may be provided all along the circumference of the cylindrical member 30 as shown in
A sixth embodiment of the present invention will be described with reference to
If a step is present between the bottom surface inside the upstream exhaust pipe 2 and the bottom surface inside the cylindrical member 30, liquid reducing agent that has not evaporated and condensed water are expected to be stored on the aforementioned step. In contrast, if a step is not present between the bottom surface inside the upstream exhaust pipe 2 and the bottom surface inside the cylindrical member 30, liquid reducing agent and condensed water are prevented from being stored in the interior of the cylindrical member 30.
In this embodiment, a case in which the inlet port 33 is arranged at a position lower than the outlet port 35 (in other words, a case in which the upstream end wall 32 of the cylindrical member 30 is arranged to be lower than the downstream end wall 34) has been described by way of example. In the case where the inlet port 33 is arranged at a position higher than the outlet port 35 (see
A seventh embodiment of the present invention will be described with reference to
With the extension chamber 3 having the above-described construction, portions of the exhaust gas flowing from the upstream exhaust pipe 2 into the cylindrical member 30 through the inlet port 33 create back step flows Fb through the step of the inlet port 33 as shown in
In consequence, the gas flowing out of the outlet port 35 of the extension chamber 3 into the downstream exhaust pipe 4 contains the exhaust gas and the reducing agent that are mixed uniformly, and a stream free from partial localization of the distribution of the flow rate is created. Therefore, the exhaust gas and the reducing agent will extend uniformly in the entire of the exhaust gas purification apparatus 5. Consequently, the purification capability of the of the exhaust gas purification apparatus 5 can be efficiently made use of.
As shown in
Although cases in which the extension chamber is defined by a hollow cylindrical member have been discussed in the above description of the first to seventh embodiments, the shape of the extension chamber is not limited to this as a matter of course. The extension chamber may have any shape, on condition that it has an inner wall surface 50 with which the virtual line L2 drawn by extending the axis of the upstream exhaust pipe 2 crosses obliquely, and that it has an inlet port 51 having a step by which the cross sectional area abruptly increases from the interior of the upstream exhaust pipe 2 to the interior of the extension chamber, for example as shown in
It is not necessary that the inner wall surface of the extension chamber be flat, but it may be curved in the direction of swirling of the swirling flow, or curved in a direction that is oblique to or perpendicular to the direction of swirling of the swirling flow. For example, as shown in
The features described in the descriptions of the first to seventh embodiments may be adopted in any possible combination.
The present invention may be used in a vehicle equipped with an exhaust system in which a reducing agent is supplied to an exhaust gas purification apparatus.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-214902 | Aug 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/064720 | 8/19/2008 | WO | 00 | 2/17/2010 |
