US20030173148A1

US20030173148A1 - Muffler

Info

Publication number: US20030173148A1
Application number: US10/258,037
Authority: US
Inventors: Lars Andersson; Mikael Bergman; Hans Strom
Original assignee: Electrolux AB
Current assignee: Electrolux AB
Priority date: 2000-04-20
Filing date: 2001-04-18
Publication date: 2003-09-18
Also published as: SE0001465L; WO2001081738A1; SE0001465D0; AU2001248988A1

Abstract

A muffler (1) intended for portable working tools, preferably chain saws, in which the muffler is mounted directly to the exhaust gas outlet (3) of the cylinder (2). The muffler is provided with at least one upstream partition wall (4, 5) at the muffler's inlet (6) from the cylinder and arranged essentially laterally in relation to the engine's cylinder bore (7), so that the partition wall (4) separates an upper fraction (8) above it, i.e. in the direction towards the upper side of the cylinder, and a lower fraction below it, i.e. in the opposite direction, and this dividing into two or several fractions (8, 9, 10) is kept maintained through a great deal of the muffler from the inlet to a number of outlets (11, 12, 13).

Description

TECHNICAL FIELD

The subject invention refers to a muffler intended for portable working tools, preferably chain saws in which the muffler is mounted directly to the exhaust gas outlet of the cylinder.

BACKGROUND OF THE INVENTION

In portable working tools usually the muffler is mounted directly to the exhaust gas outlet of the cylinder in a way as compact as possible. For these tools there is a very strong demand for a low total weight and small size. This leads to a demand for a small and light muffler. In the same time it is important that the user does not get injured if he comes into contact with the tool's muffler or its exhaust gases, or that the exhaust gases cannot set fire to adjacent objects. This has lead to the existence of special legal requirements concerning the muffler's surface contact temperature and the exhaust gas temperature in its vicinity. The working tool is usually equipped with a cooling fan and various safety covers around the cylinder and partly around the muffler. These problems are particularly characteristic for mufflers equipped with a catalytic converter element, which results in a high development of energy at combustion of the exhaust gases. Furthermore, these problems are particularly significant for crankcase scavenged two-stroke engines provided with additional air to the upper part of their scavenging ducts for in this way reducing the scavenging losses of the engine. This additional air will press the exhaust gases out through the exhaust port and will itself follow through this. Thereby exhaust gases with a great oxygen surplus will be created, which might result in an after-oxidation in the muffler. This would result in that all combustible exhaust gas components are oxidized. Obviously the exhaust emissions will fall down towards zero, but at the same time the heat generation will become extremely strong. For practical reasons such an after-oxidation must as far as possible be prevented.

SAE-report 911848 shows that the gas structure and temperature are different for different components of the exhaust gases when these are divided into a number of fractions by means of a rotating valve at the exhaust port of the engine and to this valve connected longitudinal fixed partition walls in the exhaust duct. These partition walls are then located laterally in relation to the cylinder bore. The author has used this arrangement in order to separate an upper fraction, i.e. that fraction in the exhaust port that is located closest to the upper side of the cylinder, as well as a lower fraction in the opposite direction. The upper fraction was led to a burner of a sterling-engine, while the lower fraction after adding of atmospheric air was led to a catalytic converter element for usage in a three-way catalyzer. The applicant does not know of any one who has designed a muffler that utilizes the principle to separate different fractions at the exhaust port and lead into the muffler.

PURPOSE OF THE INVENTION

The purpose of the subject invention is to substantially reduce the above outlined problems.

SUMMARY OF THE INVENTION

The above purpose is achieved in a muffler in accordance with the invention having the characteristics appearing from the appended claims.

The muffler according to the invention is thus essentially characterized in that it is provided with at least one upstream partition wall at the muffler's inlet from the cylinder, and arranged essentially laterally in relation to the engine's cylinder bore, so that the partition wall separates an upper fraction above it, i.e. in the direction towards the upper side of the cylinder, and a lower fraction below it, i.e. in the opposite direction, and this dividing into two or several fractions is kept maintained through a great deal of the muffler from the inlet to a number of exhaust gas outlets. Owing to the fact that several fractions can be separated these fractions can be treated separately. For, research-work has shown that the fractions have different gas structure and different temperature. The upper fraction usually has a higher temperature and greater contents of oxygen than the lower fraction. Consequently, by treating two or several fractions separately through a large part of the muffler a number of advantages can be achieved. Particularly, this enables that an uncontrolled combustion of the exhaust gases under extremely high heat generation essentially can be avoided. By the dividing into fractions these can be cooled each one separately without being mixed with each other, and then be treated in a catalytic converter, which then treats all the fractions or only some of these. A number of measures can be taken to improve the cooling of the different fractions, or by other means trying to prevent them from reacting. Further characteristics and advantages of the invention will be apparent from the detailed description of preferred embodiments and with the support of the drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in closer detail in the following by way of various embodiments thereof with reference to the accompanying drawing figures. [0007]
FIG. 1 shows schematically in a cross-sectional view a muffler in accordance with the invention. It is connected to the outlet of an imagined cylinder. The figure shows a first embodiment of the invention. [0008]
FIG. 2 shows a second embodiment of the invention provided with a reinforced cooling of the exhaust gases, and a partition wall which extends out into the cylinder's exhaust gas outlet. [0009]
FIG. 3 shows a third embodiment of the invention, in which a dividing into three fractions has been made, and a half intermediate wall has been used. [0010]
FIG. 4 shows a fourth embodiment of the invention where two fractions after passing an intermediate wall will join together and then run out through a common exhaust gas outlet, possibly via a catalytic converter element. [0011]
FIG. 5 shows a fifth embodiment of the invention where an intermediate wall separates an upstream partition wall from a downstream partition wall. The intermediate wall is partly composed of a catalytic converter element. [0012]
FIG. 6 shows a sixth embodiment in which the upstream partition wall is variable vertically, so that the amount of each fraction can be varied. [0013]
FIG. 7 shows a partition wall, which to a great extent is arranged as a house-shaped body located inside the muffler. [0014]
FIG. 8 shows an embodiment with an internally located house-shaped body for one fraction, and an intermediate wall with a catalytic converter for the other fraction.[0015]

DESCRIPTION OF EMBODIMENTS

In FIG. 1 [0016] numeral reference 1 designates a muffler, which is mounted directly to the exhaust gas outlet 3 of the cylinder 2. In the conventional way the muffler is composed of an inner half 30 and an outer half 31 assembled at a parting plane 32. The muffler can be either permanently or detachably assembled. The characteristic feature is that an upstream partition wall 4 is located inside the muffler, e.g. it can be welded at the inner muffler half 30. The partition wall 4 has preferably approximately the same angle as the engine's exhaust gas outlet. It reaches all the way up to the muffler's inlet 6 and is located somewhere in the middle of this. Hereby it separates an upper gas fraction 8 and a lower gas fraction 9. The partition wall 4 does not have to be gas-tight mounted around the walls of the muffler. Rather it could be an advantage if there is a certain leakage along the walls, so that a compensation of pressure can occur. Obviously, this leakage along a wall will be cooled substantially by the wall, resulting in decreased reactivity of the gas. The partition wall 4 is at its lower side provided with a catalytic layer 28, so that a combustion of exhaust emissions can take place for the lower fraction 9, but not for the upper fraction 8. In another application with another gas structure the relation would of course be reversed. The upper fraction 8 has an exhaust gas outlet 11 located on the upper side 25 of the muffler. It can be designed so that a great deal of the exhaust gases will flow in the lateral direction of the muffler, which can not be apparent from the figure. The fraction 9 has in a corresponding way an exhaust gas outlet 12 located in the front side 24 of the muffler.
FIG. 2 shows an embodiment that among other features is different from the previous one in that the [0017] upstream partition wall 4 runs out through the exhaust gas outlet 3 of the cylinder up to the cylinder bore 7 of the engine, so that the dividing of the fractions 8 and 9 takes place at an early stage. This is an advantage since thereby the risk that the fractions will mix with each other can be minimized. As earlier mentioned the partition wall 4 separates the muffler into two parts. An upper duct section 22, preferably designed as an upside-down U, is located above the partition wall 4 and connects to the inlet 6 of the muffler and has approximately the same width as this. Thereby the duct section encloses the fraction 8 within itself and forwards this fraction with comparatively unreduced speed. The closed duct section is thus created by the open U in combination with the partition wall 4. The fraction 8 will deflect towards the inner surface of the front side 24 of the muffler and will become cooled by it. In a similar way the lower duct section 23, preferably designed as an up-right U, will together with the partition wall 4 create a closed duct, which ends up close to the mer wall of the front side 24. Hereby the exhaust gas flow of the two duct sections will be cooled substantially. Consequently, in this embodiment the duct sections direct their flow towards the front side 24 of the muffler, however, they could as well be shorter and be directed towards an intermediate wall 21, compare the following figures. Furthermore, the duct sections could also be curved so that they direct their flow towards the upper side 25 of the muffler, or towards a side surface 26 or 27, or maybe towards the bottom side 33 of the muffler. Furthermore, the one, or perhaps both duct sections, could be sub-divided into a number of sub duct sections having a small cross-sectional size. When the cross-section dimensions are in the size of approximately 1-2 millimeters, all reactions within each sub duct section will be efficiently prevented. For, using a duct width of about this size ignition of the gas fraction will be prevented.
FIG. 3 shows a muffler where dividing into three different fractions takes place, the [0018] upper fraction 8, the lower fraction 9, as well as a mid fraction 10. This is effected in that a second upstream partition wall 5 is located below the first upstream partition wall 4. In the shown case these two partition walls separate three fractions completely through the whole muffler. The mid fraction 10 has thus its own outlet 13. The outlet 12 for the lower fraction 9 and the outlet 13 share the same cover 34, which directs the exhaust gas flow along the front side 24 of the muffler. The direction can be upwards, as shown, or sideways, or both, or possibly even downwards. The duct section 22 connects to the inlet of the muffler and encloses the fraction 8 until it is released towards the cooled front side 24. A half intermediate wall 21 connects to the second partition wall 5, so that the fraction 9 must pass through this half intermediate wall. Owing to the fact that the duct section 22 is used to take care of the upper fraction 8, this fraction will be particularly strongly cooled in connection with its expanding. Thereby there will be a reduced risk of combustion reactions in the fraction 8. Since the upper exhaust gas fraction usually has the highest temperature it might be preferable to let this get the most intense cooling. However, obviously the duct section 22 could also or instead be used for some or any of the other both fractions. The intermediate wall 21 can be provided with a catalytic layer for cleaning of the fraction 9. The half intermediate wall 21 can be mounted into either one of the muffler halves 30, 31, or be clamped between these in the conventional way. In the latter case the intermediate wall can extend into the joint between the parts also on the upper side of the muffler even if this is not shown. As becomes apparent from the cross-section B-B the duct section 22 has been given a sub-division into a number of sub duct sections with small cross-sectional dimensions in order to complicate or prevent reactions in the gas fraction before it has had time to get cooled.
FIG. 4 shows a muffler with an [0019] intermediate wall 21 and one to this wall attached upstream partition wall 4, which separates two fractions 8, 9. The intermediate wall is preferably clamped between the muffler halves 30 and 31 in the conventional way. In this embodiment the two fractions are not kept separated through the whole muffler but are allowed to join together after the intermediate wall. However, when joining together they have already had time to be cooled by the outer walls of the muffler as well as by the intermediate wall 21. In order to reach the inlet 34 of the catalytic converter element 14 the exhaust gases must also get cooled against the inner wall of the front side 24 of the muffler. When the exhaust gases have passed through the catalytic converter element they flow in an outlet duct 35 out of the muffler.
FIG. 5 shows a muffler with a complete [0020] intermediate wall 21 and to this wall an upstream partition wall 4 as well as a downstream partition wall 19 are connected. Hereby the two gas fractions are kept separated through the whole muffler since it is provided with two separate exhaust outlets 11, 12. The upstream partition wall 4 is preferably mounted to the inlet 6 of the muffler in order to provide an exact position of its upstream section, which separates the two fractions. The exhaust gas outlet can also have grooves in its side, which are formed in the moulding process, so that the partition wall can be guided by these grooves in order to provide a particularly exact position. At its lower end the intermediate wall 21 is provided with a catalytic layer 28 and a number of apertures in order to let the gas fraction 9 pass through. In this case the fraction 9 has been considered as the most preferable to burn in a controlled way. However, in another application perhaps instead the upper fraction 8 had been more preferable to convert in a catalyzer. In this case the catalytic layer would instead had been present on the upper part of the intermediate wall 21.
The muffler according to FIG. 6 has a very similar [0021] intermediate wall 21, but with the difference that the lower part of the intermediate wall has been made as a separate part. Thereby it will be simpler to provide it with a catalytic layer since it can be coated entirely, preferably on both sides, although this in not shown in the figure. Such a plate that is entirely coated does not have to be provided with any shielding at the coating. Furthermore, the catalyticly coated plate will be subjected to greater thermal loads than the non-coated one. Thereby the non-coated intermediate wall 21 can be manufactured in a simpler and cheaper plate material. The downstream partition wall 19 is attached to the intermediate wall 21. On the other hand it is not attached to the inside of the front side 24 of the muffler, but there is a gap left. This is deliberate since through this gap a pressure-compensation can take place between the different parts. By providing this gap a determined length the character of said pressure-compensation can also be affected. The exhaust gases that will flow between the partition wall 19 and the outer wall will be cooled substantially and thereby be less inclined to react. Both the upper fraction 8 and the lower fraction 9 are passing through an intermediate wall, which is advantageous considering the silencing ability of the muffler. The upstream partition wall 4 is at least partly variable in height, so that the amounts of the fractions either above or below it can be varied, based on at least one engine parameter, such as flow speed, temperature, pressure or rotational speed. This is achieved in that a part of the partition wall, or the whole partition wall, is pivotably mounted to the pivot 36 in relation to the remaining part of the partition wall. Preferably only that part of the partition wall that represents a direct prolongation of the part that protrudes out through the exhaust gas outlet 3 is pivoted. A spring 37 holds this part against an abutment, in this case upwards. A wing profile is located on the bottom side of the movable part of the intermediate wall. At increasing speed of the onflowing gases the downward directed force generated by the wing profile will increase, and at a certain flow speed this force will overcome the spring, so that the relevant part of the partition wall will deflect downwards. Thereby the amount of the fraction 8 will increase, while the amount of the fraction 9 will decrease. Hereby the amount that goes through the catalyzer will decrease, e.g. this could be preferable for avoiding overheating. However, the movable part of the partition wall could also be maneuvered by a temperature sensitive element 40, which is shown as a bimetal element, so that the same effect would be achieved at increasing temperature. In both these cases there are no need for any external connection for maneuvering the pivoted part of the partition wall. However, obviously a link controlled from the outside should be able to handle this maneuvering, so that an external control means would maneuver the partition wall part based on a number of engine parameters, such as flow speed, temperature, pressure or rotational speed.
The muffler has an [0022] exhaust gas outlet 11 arranged in connection to its upper side, but could after a certain adjustment of the intermediate wall 21 and the downstream partition wall 19 as well have two exhaust gas outlets arranged at the upper side 25. This is a favorable positioning of an exhaust gas outlet considering the strong cooling air stream 38 that usually sweeps over the upper side of the cylinder 2. This cooling effect can be reinforced in that protective cover 29 is located above a great deal of the upper side 25 of the muffler. In the shown case the safety cover is angled around the corner between the upper side and the front side, so that it also covers a great deal of the front side 24 of the muffler. Hereby a very favorable cooling air stream is created, following both the upper side and the front side of the muffler. The protective cover 29 could also be drawn downwards along one or both side surfaces 26, 27 of the muffler. In the shown case the protective cover is drawn down so that it covers approximately half of these two sides. Consequently, it covers completely or partly four of the muffler's six sides. Two advantages are achieved in that the protective cover is covering large parts of the muffler. In the first place cooling air will be captured and be forced to follow several of the muffler's sides. In the second place, owing to the protective cover an outer protection around the muffler is created. As air is circulating between this cover and the muffler the temperature of the cover will be considerably lower than that of the muffler. It means that in case the muffler should achieve extremely high temperatures, e.g. by an occasional after-oxidation, the risks that the tool might be damaged by these high temperatures, or that the user will be injured, would be minimized. In case a protective cover 29 is used preferably the plastic covers that normally cover a part of the muffler will be shortened, so that this function instead will be taken over by the protective cover, which obviously is considerably more heat resistant.
FIG. 7 shows a muffler with a very characteristic [0023] upstream partition wall 4. Partly it has been given a shape like a housing body, which well corresponds to the shape of the upper muffler part. Hereby the upper fraction 8 will be forced to flow between the partition part 4 and the internal surfaces of the upper side 25 of the muffler, the side surfaces 26, 27 and its front side 24. This is valid only for the upper part of the muffler. Consequently, hereby the upper fraction 8 will be cooled particularly strong. On the other hand it is not considered that the housing-shaped body will separate the inner space completely into two pieces. Instead this has been made according to the further developed solution according to FIG. 8. In this case a complementary partition wall 4′ is connected to the upstream partition wall 4 and is extended to essentially seal against the inner sides of the muffler. Apertures 3.9 are arranged in the trough-shaped part of the partition wall 4. They are preferably located close to the front side 24 of the muffler. Hereby the partition wall 4 will also serve as an intermediate wall and thereby contribute to the silencing of the muffler. The exhaust gases will leave the muffler through an outlet 11 connecting to the upper side of the muffler. The lower fraction 9 passes a catalytic converter element 14 located in a half intermediate wall 21 connecting to the complementary partition wall 4′. The lower fraction will then continue out through the exhaust gas outlet 12 at the front side 24 of the muffler.
A number of various embodiments have been described regarding mufflers utilizing the principle of dividing the exhaust gases into fractions for special treatment in the most appropriate way of these fractions through at least a part of the muffler. The different embodiments can be combined with each other so that a number of variants can be achieved. E.g. the protective cover as shown in FIG. 6 can also be combined with any one of the solutions as shown in the other FIGS. [0024] 1-8, or variants that are combinations of these.

Claims

1. A muffler (1) intended for portable working tools, preferably chain saws, in which the muffler (1) is mounted directly to an exhaust gas outlet (3) of a cylinder (2), characterized in that the muffler is provided with at least one upstream partition wall (4, 5) at the muffler's inlet (6) from the cylinder, and arranged essentially laterally in relation to the engine's cylinder bore (7), so that the partition wall (4) separates an upper fraction (8) above it, i.e. in the direction towards the upper side of the cylinder, and a lower fraction (9) below it, i.e. in the opposite direction, and that this dividing into two or several fractions (8, 9, 10) is kept maintained through a great deal of the muffler from the inlet (6) to a number of outlets (11, 12, 13), so that the separated fractions (8, 9, 10), with different gas structure and different temperature can be treated separately essentially to avoid uncontrolled combustion of the exhaust gases under extremely high heat generation.

2. A muffler (1) according to claim 1, characterized in that one or several upstream partition walls (4, 5) are drawn out into the exhaust gas outlet (3) of the cylinder and up to the cylinder bore (7), so that the dividing into fractions (8, 9, 10) will take place at an early stage.

3. A muffler (1) according to claim 1 or 2, characterized in that at least one catalytic converter element (14) is arranged so that it comes into contact with one or several (8,9; 9,10) of the fractions (8, 9, 10).

4. A muffler (1) according to claim 3, characterized in that the catalytic converter element (14) is arranged so that it comes into contact with one or several (8,9; 9,10) but not all the fractions (8, 9, 10).

5. A muffler (1) according to any one of the preceding claims, characterized in that at least one upstream partition wall is at least partly variable in height, so that the amount of the fraction (8, 9, 10), above and below it, can be varied based on at least one engine parameter, such as flow speed, temperature, pressure or rotational speed.

6. A muffler (1) according to any one of the preceding claims, characterized in that it is provided with at least one intermediate wall (21), which at least partly divides the muffler into a number of upstream volumes (15, 16) and a number of downstream volumes (17, 18), and separates the partition walls into upstream partition walls (4, 5) and downstream partition walls (19, 20).

7. A muffler (1) according to any one of the preceding claims, characterized in that it is provided with a number of duct sections (22, 23), which connect to the inlet (6) of the muffler and have approximately the same width as this, so that each duct section within itself encloses preferably one fraction (8, 9, 10) and forwards this fraction with comparatively unreduced speed.

8. A muffler (1) according to claim 7, characterized in that it has a subdivision into a number of sub duct sections of small cross sectional dimensions.

9. A muffler (1) according to patent claim 8 or 9, characterized in that the duct sections (22, 23) are drawn so that they direct their exhaust gas flow towards at least one cooled surface, such as the muffler's front side (24), an upper side (25), a side surface (26, 27) or an intermediate wall (21), so that the exhaust gas flow of the duct section is cooled.

10. A muffler (1) according to any one of the preceding claims, characterized in that it has at least one catalytic converter element (14) arranged in that at least one part of a partition wall (4, 5, 19, 20), or an intermediate wall (21), is coated with a catalytic layer (28) on one or both sides.

11. A muffler (11) according to any one of the preceding claims, characterized in that it has at least one exhaust gas outlet (11, 12, 13) arranged in connection to its upper side (25).

12. A muffler (1) according to claim 11, characterized in that it has at least one more exhaust gas outlet (11, 12, 13) arranged in connection to its front side (24).

13. A muffler (1) according to any one of the preceding claims, characterized in that it has a protective cover (29) located above a large part of the upper side (25) of the muffler.

14. A muffler (1) according to claim 13, characterized in that the protective cover (29) is curved around the corner between the upper side and the front side, so that it also covers a great deal of the front side (24) of the muffler.