JP2008240525A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device wherein the temperature retaining performance of a temperature retaining container is improved so that an exhaust emission control catalyst reaches an activating temperature earlier at cold starting. <P>SOLUTION: The exhaust emission control device 1 comprises the exhaust emission control catalyst 2 mounted in an exhaust pipe 3. The exhaust pipe 3 has a heat storage material 5 mounted around the exhaust emission control catalyst 2 mounted therein. Furthermore, the exhaust pipe 3 has the temperature retaining container 4 mounted around the exhaust emission control catalyst 2 mounted therein. The temperature retaining container 4 has an introduction port 4a opened downward, and an delivery port 4b. The exhaust pipe 3 is introduced into the temperature retaining container 4 through the introduction port 4a in the perpendicular direction and delivered therefrom through the delivery port 4b in the perpendicular direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an improvement of an exhaust purification device that purifies exhaust gas discharged from an engine (internal combustion engine).

  Conventionally, various exhaust purification apparatuses for purifying engine exhaust gas and improving emission have been proposed. Among these exhaust purification apparatuses, there are proposals aimed at prematurely warming the catalyst at the start of the engine and improving the heat retention, for example, Patent Document 1. Patent Document 1 discloses the following exhaust purification device. The exhaust emission control device disclosed in Patent Document 1 inserts an inner tube into an outer tube to form a passage between the outer tube and the inner tube, and arranges a carrier carrying a catalyst in the inner tube, By passing the exhaust gas through the passage, the heat retaining property of the catalyst is improved.

JP-A-6-101465

  Here, referring to FIG. 4 and FIG. 5, the positional relationship between the exhaust pipe and the exhaust purification catalyst, which has been generally adopted conventionally, as well as the proposal of Patent Document 1, and the positional relationship between the inner pipe and the outer pipe are referred to. I will explain.

  An exhaust purification catalyst 101 in the exhaust purification apparatus 100 is mounted inside the exhaust pipe 102. The exhaust pipe 102 is provided with a heat retaining container 103 around the exhaust purification catalyst 101. The heat retaining container 103 is provided with an inlet 103a and an outlet 103b of the exhaust pipe 102 on the side of the container. That is, both the inlet 103a and the outlet 103b are so-called side openings. The exhaust pipe 102 is introduced from the side in a state of being almost horizontal with respect to such a heat insulating container 103, and is led out while being maintained in a substantially horizontal state. A heat retaining shield 104 made of ceramic honeycomb is disposed at the position of the exhaust pipe 102 corresponding to the inlet 103a and outlet 103b.

  The heat transfer in the vicinity of the inlet 103a and the outlet 103b in the exhaust purification apparatus 100 having such a configuration will be described with reference to FIG. Normally, the heat distribution forms a temperature gradient along the top and bottom direction. Therefore, also in the exhaust gas purification apparatus 100, the high temperature part is formed on the top side and the low temperature part is formed on the ground side in the exhaust pipe 102. Thus, when attention is paid to the inside of the exhaust pipe 102 accommodated in the heat insulating container 103, a temperature gradient is formed. On the other hand, when the temperature inside the exhaust pipe 102 is compared between the inside and outside of the heat insulating container 103, the temperature is naturally lower on the outside of the heat insulating container 103.

  The heat transfer in such a state is actively performed at a position indicated by A in FIG. In other words, the heat transfer is performed more actively as the temperature difference is larger. When heat transfer occurs, the density of the air changes, and the presence of air having a different density causes convection. Once convection occurs, heat transfer becomes active, and the temperature decreases more and more. A similar phenomenon occurs on the outlet 103b side.

  As described above, in the conventional exhaust purification apparatus, even if the structure is provided with the heat insulation container, the temperature in the heat insulation container is lowered due to the movement of heat at the inlet and the outlet. When the temperature in the heat retaining container is lowered, it is difficult to achieve further improvement in environmental performance because the exhaust purification catalyst reaches the activation temperature later.

  Therefore, an object of the present invention is to provide an exhaust emission control device in which the heat insulation performance of the heat insulation container is improved so that the exhaust emission purification catalyst reaches the activation temperature early at the time of cold start.

  In order to solve such a problem, an exhaust purification device of the present invention includes an exhaust pipe, an exhaust purification catalyst mounted in the exhaust pipe, and a heat insulation container covering a mounting position of the exhaust purification catalyst, The introduction port and the discharge port of the exhaust pipe of the heat insulation container are downwardly opened (Claim 1). For example, it can be set as the structure which provided the said inlet and the outlet in the lower surface side of the said heat retention container (Claim 2). With such a configuration, it is difficult for the temperature in the heat insulating container to decrease due to a temperature gradient formed in the exhaust pipe at the inlet and outlet. That is, since the portion where the temperature gradient is low comes into contact with the outside of the heat insulating container, the temperature difference in the portion is small and the amount of heat transfer can be reduced. Thereby, the heat retention of a heat retention container can be improved.

  In such an exhaust purification device, it is possible to adopt a configuration in which a heat retaining means is provided around the place where the exhaust purification catalyst is mounted (Claim 3). Furthermore, it can be set as the structure which has arrange | positioned the heat insulation shield in the vicinity of the said inlet and / or outlet. By adopting such a configuration, it is possible to improve the heat retention of the exhaust catalyst in combination with the arrangement of the inlet and outlet of the heat retaining container and the opening direction.

  According to the exhaust purification apparatus of the present invention, since the inlet and outlet of the heat insulation container covering the exhaust purification catalyst are opened downward, the low temperature portion of the temperature gradient formed in the exhaust pipe is connected to the outside of the heat insulation container. Since it comes into contact, the temperature difference in the part is small, and the amount of heat transfer can be reduced. Thereby, the heat retention of a heat retention container can be improved.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing a schematic configuration of an exhaust emission control device 1 of the present invention. The exhaust purification catalyst 2 in the exhaust purification apparatus 1 is made of Pt (platinum) / zeolite and is mounted inside the exhaust pipe 3. The exhaust purification catalyst 2 can also use other Cu (copper) / zeolite. The exhaust pipe 3 is provided with a heat storage material 5 corresponding to the heat retaining means in the present invention around the exhaust purification catalyst 2. As the heat storage material 5, NaF—SnF ₂ , NaOH—NaNO ₂ , NaOH—NaNO ₃ , LiNO ₃ , SnF ₂ or the like can be used as appropriate.

  Further, the exhaust pipe 3 is provided with a heat retaining container 4 around the exhaust purification catalyst 2. The heat retaining container 4 is provided with an inlet 4a and a outlet 4b that are downwardly opened. That is, the inlet 4a and the outlet 4b are provided on the lower surface side of the container. The exhaust pipe 3 is introduced into the heat insulating container 4 from the introduction port 4a in the vertical direction, and is led out from the outlet port 4b in the vertical direction. A heat insulating shield 6 made of ceramic honeycomb is disposed at the position of the exhaust pipe 3 corresponding to the inlet 4a and outlet 4b of the heat insulating container 4. Note that the portion where the exhaust purification catalyst 2 is mounted is maintained in a substantially horizontal state.

  The heat transfer in the vicinity of the inlet 4a and the outlet 4b in the exhaust emission control device 1 having such a configuration will be described with reference to FIG. Since the vicinity of the inlet 4a and the vicinity of the outlet 4b are in the same state, the vicinity of the inlet 4a is enlarged in FIG. 2 to explain the heat transfer in the vicinity of the inlet 4a. To do. Normally, the heat distribution forms a temperature gradient along the top and bottom direction. Therefore, also in the exhaust gas purification apparatus 1, a high temperature part is formed on the top side and a low temperature part is formed on the ground side in the exhaust pipe 3. That is, in FIG. 2, point A has the highest temperature, point B, point C, point D, point E, and the temperature in the up and down direction decrease, and point F has the lowest temperature. . FIG. 2 also shows the relationship between the temperature at each point and the heat retention time, but naturally the heat retention at point A near the center of the heat retaining container 4 is high.

  In addition, a layer having a low temperature contacts the outside of the heat insulating container 4. For this reason, the air in the exhaust pipe 3 comes into contact with the temperature layer having the smallest temperature difference from the outside of the heat retaining container 4. As a result, the amount of heat transfer is reduced. In addition, since convection hardly occurs in the vicinity of the inlet 4a, the heat transfer from the inside of the heat insulating container 4 can be suppressed, and the heat insulating property is improved.

  As described above, the exhaust purification device 1 has improved heat retention, and can maintain the temperature in the heat insulation container 4 for a long time even after the engine is stopped. As a result, even when the engine is restarted, the exhaust purification catalyst 2 can be immediately heated to the activation temperature, and the deterioration of emissions can be suppressed.

  Here, the heat retention effect of the exhaust emission control device 1 of the present embodiment will be described in comparison with a conventional example. What was compared was an exhaust purification device provided with no heat retention means for the exhaust purification catalyst, such as a heat storage material, or an exhaust purification device provided with a heat storage material. The exhaust gas purification apparatus provided with the heat storage material includes a heat retaining container, but the inlet and the outlet are provided on the side of the container.

  In an exhaust gas purification apparatus that does not have any heat retaining means, the temperature of the catalyst rapidly decreases with time. In comparison with this, in the exhaust emission control device provided with the heat storage material, the temperature decrease once stops at the temperature at which the heat storage material functions. Thereafter, when the phase change of the heat storage material is completed and the function as the heat storage material cannot be exhibited, the temperature gradually decreases therefrom. In comparison with this, it can be confirmed that the exhaust gas purification apparatus 1 of the present embodiment has a moderate temperature drop to the temperature at which the heat storage material 5 functions, and maintains heat retention for a long time. Thus, the exhaust emission control device 1 of the present embodiment has high heat retention.

  The above-described embodiments are merely examples for carrying out the present invention, and the present invention is not limited thereto. Various modifications of these embodiments are within the scope of the present invention. It is apparent from the above description that various other embodiments are possible within the scope.

It is the schematic diagram which showed schematic structure of the exhaust gas purification apparatus of an Example. It is explanatory drawing which expanded and showed the external temperature distribution while showing the introduction port vicinity of a heat retention container expanded. It is explanatory drawing which showed the heat retention effect of the exhaust gas purification apparatus of an Example compared with the prior art example. It is explanatory drawing which showed schematic structure of the conventional exhaust gas purification apparatus. It is explanatory drawing which shows the temperature gradient formed in the introduction port vicinity of the conventional heat retention container.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust purification device 2 Exhaust purification catalyst 3 Exhaust pipe 4 Thermal insulation container 5 Thermal storage material 6 Thermal insulation shield

Claims (4)

An exhaust pipe,
An exhaust purification catalyst mounted in the exhaust pipe;
A heat retaining container covering the mounting position of the exhaust purification catalyst;
With
An exhaust emission control device characterized in that the inlet and outlet of the exhaust pipe of the heat retaining container are downwardly opened. The exhaust emission control device according to claim 1,
An exhaust emission control device, wherein the introduction port and the discharge port are provided on a lower surface side of the heat insulating container. The exhaust emission control device according to claim 1,
An exhaust emission control device, characterized in that a heat retaining means is disposed around a place where the exhaust purification catalyst is mounted. The exhaust emission control device according to claim 1,
An exhaust emission control device, wherein a heat insulation shield is disposed in the vicinity of the inlet and / or outlet.

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