Catalyst-attached muffler for internal combustion engine

Abstract

A catalyst-installed muffler includes an expansion chamber (25), and a gas-permeable exhaust gas-purifying catalyst (30), wherein exhaust gas blown out of the exhaust port (10) of an internal combustion engine is introduced into the expansion chamber (25) through the catalyst (30). The catalyst (30) may be cylindrical in configuration. An outer circumferential cross-sectional configuration of the catalyst (30) is made identical with an inner circumferential cross-sectional configuration of the outer end portion (10a) of the exhaust port (10), so that one end portion (exhaust gas introducing side 30a) of the catalyst (30) is enabled to fit in an outer end portion (10a) of the exhaust port (10). According to this muffler, it is made possible to utilize the purifying capacity of the catalyst to a maximum extent.

Description

FIELD

The present invention relates to a muffler with catalytic converter which is provided with an expansion chamber and with an exhaust gas-purifying catalyst. In particular, the present invention relates to a muffler with catalytic converter which is suited for use in a small air-cooled two-stroke gasoline engine for use in a portable power working machine such as a brush cutter or a chain saw.

BACKGROUND INFORMATION

In recent years, even in an internal combustion engine such as a small air-cooled two-stroke gasoline engine to be employed in a portable power working machine such as a brush cutter or a chain saw, it is strongly demanded, as in the case of on-vehicle engine, to minimize the quantity of hydrocarbon (HC), carbon monoxide (CO), etc. in the exhaust gas. Accordingly, it has been proposed to mount an exhaust gas-purifying catalyst inside the muffler installed on the exhaust gas system of the engine so as to enable the exhaust gas to pass through the catalyst, thereby purifying (minimizing HC, CO, etc.) the exhaust gas (see JP Laid-open Patent Publication (Kokai) No.9-184418 (1997) and International Patent Publication No.9-507898 (1997)).

FIG. 4 illustrates, together with part of internal combustion engine 1′, one example of the conventional catalyst-installed muffler which is constructed as described above. The internal combustion engine 1′ shown in FIG. 4 is a small air-cooled two-stroke gasoline engine of Schnürle type scavenging system which can be mounted as a power source on a portable power working machine such as a brush cutter or a chain saw. The displacement of the engine 1′ may be about 23 to 45 mL for example. This engine 1′ is provided with a cylinder 2′ having a domed combustion chamber 5′. The cylinder 2′ is provided with a large number of cooling fins 6′ on the outer circumference thereof Moreover, as shown in FIG. 5, the cylinder 2′ is provided with an exhaust port 10′ which is rectangular in cross-section having nearly rounded corners and which is tapered in configuration, i.e. the cross-sectional area of the exhaust port 10′ is gradually increased from the inner end (cylinder bore 2a′ side) to the outer end thereof. Although not shown in the drawing, the cylinder 2′ is further provided with an air-intake port and a scavenging port which are disposed in the known manner along the inner circumferential wall of the cylinder bore 2a′.

On the outer side of the exhaust port 10′ of the cylinder 2′, there is attached a muffler 20′. This muffler 20′ is provided with a couple of outer wall panels 21′ and 22′, i.e. a left side outer wall panel 21′ and a right side outer wall panel 22′, which are hermetically jointed together with each other by means of flat lock seam, thereby defining an expansion chamber 25′. The left side outer wall panel 21′ located on the exhaust port 10′ side is provided with an opening 21a′ having approximately the same configuration as the outer end portion 10a′ of the exhaust port 10′. A reinforcing plate 28′ is fixedly mounted along the opening 21a′ by means of welding, etc. Further, the right side outer wall panel 22′ is provided with a recessed portion 22a′ which is located just in front of the exhaust port 10′. A closed-end cylindrical catalyst holder 40′ is interposed between the recessed portion 22a′ and the reinforcing plate 28′ so as to interconnect the recessed portion 22a′ and the reinforcing plate 28′. A heat-insulating/shock-absorbing plate 27′ is interposed between the catalyst holder 40′ and the recessed portion 22a′.

At an inner end portion 41′ (on the exhaust port 10′ side) of the catalyst holder 40′, there is provided a mounting hole 40a′ for fitting and fixedly holding (by means of welding, etc.) a short cylindrical exhaust gas-purifying catalyst 30′. At an outer end portion 42′ (on the recessed portion 22a′ side) of the catalyst holder 40′, there are provided a suitable number of exhaust gas-passing holes 43′. The catalyst 30′ is formed of an oxidation catalyst comprising a gas-permeable metallic carrier and enclosed by a cylindrical shell 32′. This catalyst 30′ is held by the catalyst holder 40′ in such a manner that the central axis “O” of catalyst 30′ extending along the passing direction of exhaust gas is approximately aligned with the central line of the exhaust port 10′ (i.e. the outer end portion 10a′ thereof) and also with the central line of the catalyst holder 40′.

Further, the right side outer wall panel 22′ is provided, at a lower portion thereof, with an outlet port 29′ for discharging exhaust gas out of the muffler 20′. Although not shown in the drawing, a spark arrester screen, an exhaust gas-guiding member for regulating the discharge direction of exhaust gas, etc. may be mounted at this outlet port 29′.

In the muffler constructed as described above, the exhaust gas to be blown out of the exhaust port 10′ at nearly the sound velocity is guided, through the inner end portion 41′ of the catalyst holder 40′ positioned in the muffler 20′, to the catalyst 30′ and forced to pass through the interior of catalyst 30′ as shown by a solid arrow in FIG. 4. As the exhaust gas passes through the catalyst 30′, the quantities of HC, CO, etc. in the exhaust gas are minimized by the catalyst 30′. The exhaust gas that has passed through the catalyst 30′ is blown into the expansion chamber 25′ through the exhaust gas-passing holes 43′ of the catalyst holder 40′ and forced to expand and diffuse. As a result, the exhaust sound can be attenuated. The exhaust gas thus expanded and diffused in the expansion chamber 25′ is then permitted to move downward and discharged out of the muffler 20′ through the outlet port 29′.

In the case of the conventional catalyst-installed muffler 20′ however, since the cross-sectional configuration of the catalyst 30′ differs from the shape of opening of the exhaust port 10′ and from the cross-sectional configuration of the catalyst holder 40′ (i.e. the inner end portion 41′ thereof) as shown in FIG. 5, most of the exhaust gas is caused to pass through a central portion of the catalyst 30′, so that the catalyst 30′ existing at the peripheral portion thereof is substantially kept away from the flow of exhaust gas. Additionally, since the catalyst 30′ is located far away from the outer end portion 10a′ of the exhaust port 10′, it is impossible to take in the exhaust gas of higher temperature. Thus, the conventional catalyst-installed muffler 20′ is accompanied with the problem that the purifying capacity of the catalyst 30′ is not sufficiently utilized.

The present invention has been made in view of overcoming the aforementioned problem, and therefore an object of the present invention is to provide a catalyst-attached muffler for internal combustion engine, which is capable of utilizing the purifying capacity of catalyst as much as possible.

BRIEF SUMMARY OF THE INVENTION

With a view to realize the aforementioned object, the catalyst-installed muffler according to the present invention is basically constructed such that it comprises an expansion chamber, and a gas-permeable exhaust gas-purifying catalyst, that exhaust gas blown out of the exhaust port of an internal combustion engine is introduced into the expansion chamber through the catalyst, and that one end portion of the catalyst is fitted in an outer end portion of the exhaust port.

Preferably, the catalyst is cylindrical or prismatic in configuration, and an outer circumferential cross-sectional configuration of the catalyst is identical with an inner circumferential cross-sectional configuration of the outer end portion of the exhaust port.

Preferably, the catalyst is an oxidation catalyst formed of metallic carrier.

Preferably, the exhaust port is tapered in configuration, wherein the cross-sectional area thereof is expanded gradually from the inner end to the outer end thereof.

Preferably, the engine is a small air-cooled two-stroke gasoline engine.

According to the catalyst-installed muffler of the present invention, since the exhaust gas-purifying catalyst is cylindrical or prismatic in configuration, and an outer circumferential cross-sectional configuration of the catalyst is made identical with an inner circumferential cross-sectional configuration of the outer end portion of the exhaust port, it is possible to enable one end portion of the catalyst (i.e. the exhaust gas-introducing side thereof) to fit substantially hermetically in an outer end portion of the exhaust port, thereby making it possible to make the entire region of the catalyst available for the purification of the exhaust gas. As a result, it is now possible to utilize the purifying capacity of the catalyst to a maximum extent and hence to greatly enhance the exhaust gas purifying performance of the catalyst.

Further, since part of the catalyst is introduced into the exhaust port, the temperature of exhaust gas to be introduced into the catalyst can be kept higher as compared with the conventional muffler. As a result, the reactive capacity (activation) of catalyst can be enhanced, thus making it possible to further enhance the exhaust gas purifying capacity of the catalyst.

Furthermore, since the catalyst is positioned close to the exhaust port (combustion chamber), the distance between the distal end (exhaust gas discharging side) of the catalyst and the exhaust outlet port of muffler can be elongated. As a result, the temperature of exhaust gas at the exhaust outlet port of muffler can be much lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating one embodiment of the catalyst-installed muffler according to the present invention together with part of the internal combustion engine to which this muffler is applied;

FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1;

FIG. 3 is an enlarged view showing the exhaust port and peripheries thereof in the internal combustion engine shown in FIG. 1;

FIG. 4 is a cross-sectional view schematically illustrating one example of the conventional catalyst-installed muffler together with part of the internal combustion engine to which this muffler is applied; and

FIG. 5 is a cross-sectional view taken along the line V-V in FIG. 4.

DETAILED DESCRIPTION

Next, one embodiment of the muffler according to the present invention will be explained with reference to the drawings.

Just like the conventional internal combustion engine shown in FIG. 4, an internal combustion engine 1 shown in FIG. 1 is a small air-cooled two-stroke gasoline engine of Schnürle type scavenging system which can be mounted as a power source on a portable power working machine such as a brush cutter or a chain saw. The displacement of the engine 1 may be about 23 to 45 mL for example. This engine 1 is provided with a cylinder 2 having a domed combustion chamber 5. The cylinder 2 is provided with a large number of cooling fins 6 on the outer circumference thereof. Moreover, the cylinder 2 is provided with an exhaust port 10 which is circular in cross-section as shown in FIG. 2 and generally tapered in configuration (bell-like), i.e. the cross-sectional area of the exhaust port 10 is gradually increased from the inner end (cylinder bore 2a side) to the outer end thereof, excepting the outer end portion 10a of the exhaust port 10 whose inner circumferential cross-section is made cylindrical (having an inner diameter of Φx as shown in FIG. 3). Although not shown in the drawing, the cylinder 2 is further provided with an air-intake port and a scavenging port, both of which are disposed in the known manner along the inner circumferential wall of the cylinder bore 2a.

On the outer side of the exhaust port 10 of the cylinder 2, there is attached a muffler 20. This muffler 20 is provided with a couple of outer wall panels 21 and 22, i.e. a left side outer wall panel 21 and a right side outer wall panel 22, which are hermetically jointed together with each other by means of flat lock seam, thereby defining an expansion chamber 25. The left side outer wall panel 21 located on the exhaust port 10 side is provided with an opening 21a having approximately the same configuration as the outer end portion 10a of the exhaust port 10. Further, the right side outer wall panel 22 is provided with a recessed portion 22a which is located just in front of the exhaust port 10. A closed-end cylindrical catalyst holder 40 is interposed between the recessed portion 22a and a terminal fringe portion of the opening 21a of the left side outer wall panel 21 so as to interconnect the recessed portion 22a and the terminal fringe portion of the opening 21a. A heat-insulating/shock-absorbing plate 27 is interposed between the catalyst holder 40 and the recessed portion 22a.

At an inner end portion 41 (on the exhaust port 10 side) of the catalyst holder 40, there is mounted a short cylindrical exhaust gas-purifying catalyst 30 in such a manner that one end portion 30a thereof is substantially hermetically introduced into the interior of the outer end portion 10a of the exhaust port 10 and the other end portion 30b thereof (exhaust gas discharging side) is inserted into the inner end portion 41 of the catalyst holder 40 and fixedly secured thereto by means of welding for example. At an outer end portion 42 (on the recessed portion 22a side) of the catalyst holder 40, there are provided a suitable number of exhaust gas-passing holes 43. The catalyst 30 is formed of an oxidation catalyst comprising a gas-permeable metallic carrier and enclosed by a cylindrical shell 32. This catalyst 30 is held by the catalyst holder 40 in such a manner that the central axis “O” of catalyst 30 extending along the passing direction of exhaust gas is approximately aligned with the central line of the exhaust port 10 (i.e. the outer end portion 10a thereof) and also with the central line of the catalyst holder 40.

Further, the right side outer wall panel 22 is provided, at a lower portion thereof, with an outlet port 29 for discharging exhaust gas out of the muffler 20. Although not shown in the drawing, a spark arrester screen, an exhaust gas-guiding member for regulating the discharge direction of exhaust gas, etc. may be mounted at this outlet port 29.

In the muffler constructed as described above, the exhaust gas to be blown out of the exhaust port 10 at nearly the sound velocity is guided to the catalyst 30 which is partially inserted into the exhaust port 10 and forced to pass therethrough along the central axis “O” as shown by a solid arrow in FIG. 1. As the exhaust gas passes through the catalyst 30, the quantities of HC, CO, etc. in the exhaust gas are minimized by the catalyst 30. The exhaust gas that has passed through the catalyst 30 is blown into the expansion chamber 25 through the exhaust gas-passing holes 43 of the catalyst holder 40 and forced to expand and diffuse. As a result, the exhaust sound can be attenuated. The exhaust gas thus expanded and diffused in the expansion chamber 25 is then permitted to move downward and discharged out of the muffler 20 through the outlet port 29.

According to the catalyst-installed muffler 20 of this embodiment, since the exhaust gas-purifying catalyst 30 is cylindrical in configuration and an outer circumferential cross-sectional configuration (circular) of the catalyst 30 (the shell 32) is made identical with an inner circumferential cross-sectional configuration (circular) of the outer end portion 10a of the exhaust port, it is possible to enable one end portion of the catalyst (i.e. the exhaust gas-introducing side thereof) to fit substantially hermetically in an outer end portion 10a of the exhaust port 10, thereby making it possible to make the entire region of the catalyst available for the purification of the exhaust gas. As a result, it is now possible to utilize the purifying capacity of the catalyst 30 to a maximum extent and hence to greatly enhance the exhaust gas purifying performance of the catalyst 30.

Further, since part of the catalyst 30 is introduced into the exhaust port 10, the temperature of exhaust gas to be introduced into the catalyst 30 can be kept higher as compared with the conventional muffler. As a result, the reactive capacity (activation) of catalyst can be enhanced, thus making it possible to further enhance the exhaust gas purifying capacity of the catalyst.

Furthermore, since the catalyst 30 is positioned close to the exhaust port 10 (combustion chamber), the distance between the distal end (exhaust gas discharging side) of the catalyst 30 and the exhaust outlet port 29 of muffler 20 can be elongated. As a result, the temperature of exhaust gas at the exhaust outlet port 29 of muffler 20 can be much lowered.

While, in the foregoing description, one embodiment of the present invention has been explained in details for the purpose of illustration, it will be understood that the construction of the device can be variously modified without departing from the spirit and scope of the invention claimed in claims attached herewith.

For example, the muffler of the present invention can be also applied likewise to a four-stroke engine other than the air-cooled two-stroke gasoline engine which is employed in the aforementioned embodiment.

Further, with respect to the exhaust gas-purifying catalyst, it is also possible to employ a catalyst in the form of a foamed molded body or a ceramic carrier, other than the aforementioned example (oxidation catalyst formed of metallic carrier).

Claims

1. A muffler capable of cooperating with an exhaust port of an internal combustion engine, the muffler comprising:

an expansion chamber, and

a gas-permeable exhaust gas-purifying catalyst capable of allowing exhaust gas from the exhaust port to flow through the catalyst and be introduced into the expansion chamber,

wherein one end portion of the catalyst is positioned in an outer end portion of the exhaust port.

2. The muffler of claim 1 wherein the catalyst is cylindrical or prismatic in configuration, and an outer circumferential cross-sectional configuration of the catalyst is substantially identical with an inner circumferential cross-sectional configuration of the outer end portion of the exhaust port.

3. The muffler of claim 1 wherein the catalyst is an oxidation catalyst formed of a metallic carrier.

4. The muffler of claim 2 wherein the catalyst is an oxidation catalyst formed of a metallic carrier.

5. The muffler of claim 1 wherein the exhaust port is tapered in configuration and the cross-sectional area thereof gradually increases from an inner end to the outer end thereof.

6. The muffler of claim 4 wherein the exhaust port is tapered in configuration and the cross-sectional area thereof gradually increases from an inner end to the outer end thereof.

7. The muffler of claim 1 wherein the engine is a small air-cooled two-stroke gasoline engine.

8. The muffler of claim 6 wherein the engine is a small air-cooled two-stroke gasoline engine.

9. A muffler capable of cooperating with an exhaust port of an internal combustion engine, the muffler comprising:

an expansion chamber, and

a gas-permeable exhaust gas-purifying catalyst capable of allowing exhaust gas from the exhaust port to flow through the catalyst and be introduced into the expansion chamber,

wherein the catalyst is cylindrical or prismatic in configuration, and an outer circumferential cross-sectional configuration of the catalyst is substantially identical with an inner circumferential cross-sectional configuration of an outer end portion of the exhaust port.

10. The muffler of claim 9 wherein the catalyst is an oxidation catalyst formed of a metallic carrier.

11. The muffler of claim 9 wherein the exhaust port is tapered in configuration and the cross-sectional area thereof gradually increases from an inner end to the outer end thereof.

12. The muffler of claim 10 wherein the exhaust port is tapered in configuration and the cross-sectional area thereof gradually increases from an inner end to the outer end thereof.

13. The muffler of claim 9 wherein the engine is a small air-cooled two-stroke gasoline engine.

14. The muffler of claim 12 wherein the engine is a small air-cooled two-stroke gasoline engine.