Exhaust gas muffler for an internal combustion engine

Abstract

An exhaust gas muffler for an internal combustion engine is provided, especially for a portable implement. The muffler has a housing with at least two parts, an inlet for exhaust gas issuing from the engine, and an outlet for discharge of processed exhaust gas. A partition is disposed within the housing between the inlet and outlet and divides the housing into two chambers. The partition is provided with a first opening in which a catalyzer is mounted, and at least one bypass opening. The muffler also has a respective valve member for each bypass opening. Below a specified temperature the bypass opening is closed. The valve member is controlled by the temperature in the muffler in such a way that when a prescribed operating temperature is exceeded, the bypass opening is opened.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an exhaust gas muffler for an internal combustion engine, especially for a portable implement.

[0002] U.S. Pat. No. 4,890,690 discloses an exhaust gas muffler for a power chain saw; the muffler is secured directly to the exhaust gas outlet of the cylinder of the two-cycle engine of the chain saw. The housing of the muffler is comprised of two shell-like housing portions that are detachably joined together at a separating plane of the housing. A partition is disposed in the muffler parallel to the separating plane. The partition divides the muffler into two chambers. A catalyzer is disposed in a break-out of the partition, and exhaust gases from the engine flow through the catalyzer. A bypass opening in the partition ensures that an undesirably high throttling effect of the catalyzer is avoided. During the oxidation and also the reduction of the exhaust gases in the conversion process of the catalyzer, the latter is heated to approximately 1000° C. It is in particular possible for new catalyzers to overheat under these conditions, thereby adversely affecting their ability to last.

[0003] It is therefore an object of the present invention to improve an exhaust gas muffler of the aforementioned general type in such a way as to extensively avoid temperature fluctuations of the catalyzer due to conversion variations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] This object, and other objects and advantages of the present invention, will appear more clearly from the following specification in conjunction with the accompanying schematic drawings, in which:

[0005] FIG. 1 is a longitudinal cross-sectional view through one exemplary embodiment of an inventive exhaust gas muffler;

[0006] FIG. 2 shows a further exemplary embodiment of an inventive exhaust gas muffler; and

[0007] FIG. 3 is a view of a partition having a circular opening for the catalyzer.

SUMMARY OF THE INVENTION

[0008] The exhaust gas muffler of the present invention comprises a housing having at least two parts, an inlet for exhaust gas issuing from the internal combustion engine, and an outlet for a discharge of processed exhaust gas to the atmosphere; a partition disposed within the housing between the inlet and outlet and dividing the housing into two chambers, wherein the partition is provided with an opening and at least one bypass opening; a catalyzer mounted in the opening of the partition; and a respective valve member for the bypass opening, wherein below a specified temperature the bypass opening is closed and wherein the valve member is controlled by the temperature in the muffler such that when a prescribed operating temperature therein is exceeded, the bypass opening is opened.

[0009] The exhaust gas muffler is formed from a housing having two pan or shell-shaped parts. The housing of the muffler is divided by a partition into two chambers, whereby the partition is provided with an opening in which a catalyzer is held. The exhaust gases from the internal combustion engine flow though the catalyzer, which at a temperature of about 600° C. converts the exhaust gases issuing from the internal combustion engine by oxidation into energy poor gases. During the conversion process the catalyzer is heated up.

[0010] To regulate the operating temperature of the catalyzer and to keep the operating temperature approximately constant, it is proposed, pursuant to the present invention, to provide the bypass openings that are disposed in the partition with a valve member, or to bring a valve member into engagement with the bypass openings. The valve member is controlled by the temperature of the catalyzer in such a way that the bypass opening opens if the temperature of the catalyzer exceeds a prescribed operating temperature; the bypass opening is closed below a specified temperature.

[0011] It can be expedient to control the valve member thermoelectrically with the aid of a thermocouple and an external electrical adjustment member. The valve member is preferably embodied as a bimetal strip and preferably overlaps the bypass opening on that side of the partition that faces the inlet of the muffler. The bimetal strip is expediently approximately linear and planar and is comprised of two metal bands that are rolled together or are welded to one another, whereby the metal bands have thermal expansion coefficients that are as different as possible. It can be advantageous to connect the metal band or layer of the bimetal strip having the higher thermal expansion coefficient with the catalyzer, and in particular with the housing of the catalyzer. To reduce the temperature that is present at the bimetal, it is expedient to fix the bimetal to the housing of the catalyzer, or to the partition, with, for example, a steel tongue. The bimetal strip bends when a prescribed operating temperature of the catalyzer is exceeded. The selection of the thermal expansion coefficients of the metal bands determines the prescribed operating temperature from which the bimetal strips bend. The bypass opening is released and exhaust gases flow through. This prevents an overheating of the catalyzer.

[0012] It is expedient to expedient to dispose the valve member or the bimetal strips on that side of the partition that faces the inlet. It can also be expedient to dispose a plurality of bypass openings in the partition.

[0013] Further specific features of the present invention will be described in detail subsequently.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0014] Referring now to the drawings in detail, FIG. 1 is a schematic longitudinal cross-sectional view through an exhaust gas muffler 1 for an internal combustion engine 8, especially for a portable implement. The muffler 1 is essentially formed from a housing 2, which in turn is formed from a pan or shell-shaped first housing portion 3, which is disposed close to the cylinder 7 of the internal combustion engine 8, and a second housing portion 4. The rims of the housing portions 3 and 4 are placed against one another, so that a separating plane 18 is formed in the middle of the housing 2. An inlet 5 for the exhaust gas 9 is provided in the first housing portion 3, and an outlet 6 for the exhaust gas 9 is disposed on a side wall of the second housing portion 4.

[0015] Disposed in the housing 2 is a catalytic converter or catalyzer 14, which converts at least the hydrocarbons contained in the exhaust gas 9 extensively to carbon dioxide and water. This conversion process, which essentially represents an oxidation, is exothermic, whereby the exhaust gases that generally enter the muffler 1 at approximately 600° C. can be heated up. The catalyzer 14 is disposed in an opening 13 in a partition 10. The catalyzer 14 is connected on the outside all the way around, in the opening 13, with the partition 10 in such a way via a weld seam 19 that a gas tight connection or seal is provided. The partition 10 is advantageously secured in the second housing portion 4, whereby the outer rim of the partition 10 is fused or flanged in a gas tight manner with the wall of the second housing portion 4. The partition 10 is disposed transverse to the direction of flow of the exhaust gases 9.

[0016] In the illustrated embodiment, two bypass openings 15 are disposed in the partition 10 above and below the catalyzer 14. Each of the bypass openings 15 is provided with a respective valve member 16 that is mechanically or thermo-electrically controlled by the temperature of the catalyzer 14. If the temperature of the catalyzer 14 exceeds the desired set operating temperature &dgr;, the valve member 16 is raised from the bypass opening 15. The open bypass openings 15 permit exhaust gases 9 to flow through, thereby bypassing the passage through the catalyzer 14. The temperature of the catalyzer 14 can thereby again drop, and an approximate constant operating temperature &dgr; of the catalyzer 14 is established. Depending upon the configuration of the valve member, the opening process of the bypass openings can also occur without temperature hysteresis. After achieving the operating temperature, a nearly linear temperature gradient of the catalyzer is established.

[0017] It is expedient to embody the valve member 16 as a bimetal strip 17. The function of a bimetal strip is known per se. Two metal bands of different materials having different thermal expansion coefficients are connected with one another. Due to the heating effect, the metal bands expand differently, thereby effecting a bending and curvature of the bimetal strip. A metal band 20 having a higher thermal expansion coefficient than a second metal band 21 are nearly linearly connected with one another. A portion 22 of the bimetal strip 17 in FIG. 1 overlaps the bypass opening 15 and effects a sealing of the bypass opening. The metal band 20 with the greater expansion coefficient is preferably connected with the housing 23 of the catalyzer 14 in a thermally conducting manner. If the housing 23 of the catalyzer 14 is heated to a prescribed operating temperature, the metal band 20 expands to a greater degree than does the metal band 21, which effects a gradual bending of the bimetal strip 17 away from the bypass opening 15 (see the top of FIG. 1). The bypass opening 15 is thereby opened and a portion of the exhaust gas 9 can flow to the outlet 6 without passing through the catalyzer 14. This reliably avoids a thermal overstressing of the catalyzer 14 and a greater wear of the catalyzer, especially with new catalyzers. When the bypass openings close, for example during a cold start, the entire conversion capacity of the catalyzer is available.

[0018] FIG. 2 shows a modified embodiment of the exhaust gas muffler 1, and has a comparable basic construction to that of the embodiment of FIG. 1, so that for components having the same function, the same reference numerals are used as in FIG. 1. In this embodiment, disposed downstream of the catalyzer 14 and of the partition 10 is an exhaust gas chamber 25 that is delimited by a sheet cover 33 that is secured to the partition 10. The catalyzer 14 has a cylindrical shape and is held in a circular opening 26 in the partition 10.

[0019] The partition 10 is illustrated as an individual component in FIG. 3. A channel 28 leads approximately radially relative to the longitudinal axis 27 from the exhaust gas chamber 25 into an exhaust final stage conduit 29. The conduit 29, together with its end 30 that is remote from the catalyzer 14, forms the outlet 6 for the exhaust gases 9. In the illustrated embodiment, the outlet 6 is embodied as the nozzle 31. The cross-sectional configuration of the nozzle 1 changes from circular to oval. In a side wall portion 32 of the nozzle 31 that is oriented approximately parallel to the plane of the partition 10, the bypass opening 15 with a circular cross-sectional configuration, is guided through this side wall portion 32. The bypass opening 15 is covered and sealed by a bimetal strip 17 that is fixed in position on the side wall portion 32. The functioning of this catalyzer arrangement with a controllable bypass corresponds to that described in detail previously in conjunction with the embodiment of FIG. 1.

[0020] The specification incorporates by reference the disclosure of German priority document DE 100 42 145.8 of Aug. 26, 2000.

[0021] The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.

Claims

1. An exhaust gas muffler for an internal combustion engine comprising:

a housing having at least two parts an inlet for exhaust gas issuing from said internal combustion engine, and an outlet for a discharge of processed exhaust gas to the atmosphere;

a partition disposed within said housing between said inlet and said outlet and dividing said housing into two chambers, wherein said partition is provided with a first opening and at least one bypass opening;

a catalyzer mounted in said first opening of said partition; and

a respective valve member for said at least one bypass opening, wherein below a specified temperature said at least one bypass opening is closed and wherein said valve member is controlled by the temperature in said muffler such that when a prescribed operating temperature therein is exceeded, said at least one bypass opening is opened.

2. An exhaust gas muffler according to claim 1, wherein said valve member is thermoelectrically controlled.

3. An exhaust gas muffler according to claim 1, wherein said valve member is a bimetal strip.

4. An exhaust gas muffler according to claim 1, wherein said valve member is disposed on a side of said partition that faces said inlet of said housing.

5. An exhaust gas muffler according to claim 1, wherein a plurality of bypass openings are disposed in said partition.

6. An exhaust gas muffler according to claim 1, wherein said valve member can assume two operating positions, and wherein upon reaching a prescribed temperature said valve member is brought from a position where said at least one bypass opening is completely closed into a position in which said at least one bypass opening is completely opened.

7. An exhaust gas muffler according to claim 1, wherein after a predetermined temperature threshold said valve member partially opens said at least one bypass opening, and during a further increase in temperature said valve member increases a passage cross section of said at least one bypass opening.