Abstract:
A muffler with catalytic converter ( 1 ) in which at least one catalytic converter element ( 2 ) is located in the muffler so that an essential part of all exhaust gases ( 3 ) from the engine are forced to pass through the element ( 2 ) and be converted there into cleaned exhaust gases ( 4 ). The element is designed as an essentially self-supporting body of catalytic material, which is hollow or partly concave and has inner and outer surfaces ( 6, 7 ), e.g. the body is shaped as a circular or non-circular sleeve, or possibly even as a narrowing sleeve ( 8 ), a dome-shaped or angular bowl-shaped body ( 5 ), and the element is, either directly or via intermediary elements, mounted to a dividing part inside the muffler, such as a partition wall ( 10 ), an outlet duct ( 11 ) or an inlet duct ( 12 ), and the mounting is so arranged that at least one end surface ( 13, 14 ) is kept fixed at the same time as the element is supported at the outer surface ( 7 ) by at least one part ( 10, 18, 23, 24 ), while the inner surface is essentially free.

Description:
TECHNICAL FIELD 
     The subject invention refers to a muffler with catalytic converter, in which at least one catalytic converter element is located in the muffler, so that an essential part of all exhaust gases from the engine are forced to pass through the element and there be converted into cleaned exhaust gases. 
     BACKGROUND OF THE INVENTION 
     Catalytic mufflers for internal combustion engines are well-known since a very long time, and have mainly been intended for cars. For portable working tools, such as chain saws, they have been available on the market to a small extent since the end of the 1980&#39;s. Demands for low weight, size and cost have contributed towards the fact that catalytic converter technology was put into practice considerably later within this field. The catalytic mufflers which have been used for portable working tools, generally included a catalytic converter element built-up of coated thin sheet metal strips, e.g. a pleated or corrugated metal strip could be rolled together with a plane strip into a cylindrical element. Both strips are coated with a catalytic layer and the exhaust gases are conducted through the axial cavities which are created between the strips and in this manner the exhaust gases are converted. This type of catalytic converter element is comparatively expensive at the same time as it is sensible to vibrations and it therefore requires an elaborately designed mounting in order to obtain an acceptable lifetime, seen from a pure mechanical point of view. 
     Catalytic converter elements composed of a thread-formed material are known for a long time. These catalytic converter elements are generally designed like plates or cylindrical elements of different lengths. They are usually made of a stainless steel wire material which has been crochetted into a plane sheet, which then has been folded a couple of times, or, rolled together into a homogeneous cylinder. DE 3024491 also describes some examples of elements where a sheet has been rolled up to be a tubular element. This tubular element is mounted along an inner diameter. The mufflers described were mainly intended for use in cars. As far as the applicant knows no muffler with a thread-formed catalytic converter element has reached the market before. Since these catalytic converter elements generally can be manufactured at a low cost compared with other types of catalytic converter elements, probably the lifetime of these elements has been considered as unsatisfactory from a mechanical point of view. For, the heat generation in a catalytic converter element is high, especially in elements intended for two-stroke engines. In such an element temperatures of overbearingly 1000 degrees centigrade can occur. In the tests made by the applicant of such a muffler the mounting as well as the design of the catalytic converter element have turned out to be utmost important in order to achieve an adequate lifetime. 
     DE 19514828 and DE 19643191 are showing examples of catalytic mufflers where a catalytic material with an extremely limited stability has been used. The catalytic material is a fibre material which is enclosed between close-meshed nets on both sides. Consequently, the catalytic material is not composed of a self-supporting body but is completely dependent on support from essentially all sides. In order to achieve enough durability the close-meshed nets must therefore lie close to each other meaning that the catalytic converter element is small in thickness. Naturally this means that the duration of the flow passing through the element is short. It will therefore be difficult to achieve a high conversion ratio in the catalytic converter at the same time as the total design of the conversion unit will be relatively complicated and expensive. 
     Purpose of the Invention 
     The purpose of the subject invention is to substantially reduce the above outlined problems. 
     SUMMARY OF THE INVENTION 
     The above mentioned purpose is achieved in that the catalytic muffler in accordance with the invention having the characteristics appearing from the appended claims. 
     The catalytic muffler according to the invention is thus essentially characterized in that the element is designed as an essentially self-supporting body made of catalytic material, which is hollow, or partly concave, and has inner and outer surfaces, e.g. the body is shaped as a circular or non-circular or possibly even as a narrowing sleeve, a dome-shaped or angular bowl-shaped body, and the element is, directly or via intermediary elements, mounted to a deviding part inside the muffler, such as a partition wall or an outlet or inlet pipe, and the mounting is arranged so that at least one end surface is kept fixed at the same time as the element is supported at the outer surface by at least one part while the inner surface is essentially free. The element is thus designed as an essentially self-supporting body made of catalytic material. It means that the element does not have to be encased on all sides but certain surfaces can be left free. Since the element is essentially self-supporting the surfaces which have to be provided with inlet or outlet openings can be made with considerably fewer and larger holes. This results in a more simple and efficient design at the same time as it enables saving of costs. 
     The shape as well as the mounting of the catalytic element are of great importance for its lifetime. A hollow or partly concave shape is especially advantageous. It could be a sleeve or a bowl-shaped body, and these are normally circular or dome-shaped, but could also have a polygonal angular form. All these shapes described have in common that the element can have a great form stability and that the wires in the element can run around the element, e.g. a sleeve-shaped element can be created from a crochetted tube-shaped sleeve in that the ends of the sleeve are being folded into themselves and the sleeve is being pressed in an axial direction between an inner and an outer tool. In this manner a cylindrical or conical or possibly an angular sleeve can be created. The element consists of a number of closed threads extending around the element and this in turn of course creates a very great stability, which is advantageous considering the very high temperatures the element is being exposed to. 
     The mounting of the catalytic converter element into the muffler is extremely important since it affects the stability as well as the cooling of the element. As for an element formed as a sleeve it has turned out to be especially advantageous to hold both ends fixed and support the element at its outer surface. Preferably the ends are kept fixed in that they are inserted into adapted depressions in the surrounding parts. This creates a stable mounting of the ends, which will stable the whole element. This is particularly true if the element has a relatively limited length. To support the element at the outer surface is advantageous. Since the element becomes warmer than its own housing it tends to expand against the outer surface and in this manner it will get an improved support. The outer surface is larger than the inner surface and hereby the cooling of the outer surface can be more effective. Furthermore, as a rule the untreated exhaust gases from the engine have better access to the outer surface and its enclosure than to the inner surface. This contributes highly to a better cooling of the outer surface. From many points of view it is thus advantageous to support the outer surface and left the inner surface essentially free. This reasoning is also valid for a bowl-shaped body. Such a body has only one end surface. Preferably this end surface is kept fixed while the outer surface is supported and the inner surface is essentially left free. These and other characteristic features and advantages will become more apparent from the detailed description of various embodiments with the support of the annexted drawing. 
    
    
     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. 
     FIG. 1 shows in perspective a catalytic muffler according to the invention. Its parts are shown in an exploded view-manner to make the construction and functioning of the muffler more clear. 
     FIG. 2 shows straight from the front a partition wall with a catalytic converter element and cover plate according to FIG.  1 . 
     FIG. 3 shows in a cross-sectional view and seen from the side another embodiment of the catalytic muffler according to the invention. Also this embodiment is provided with a partition wall. 
     FIG. 4 shows a catalytic muffler, which is similar to that in FIG. 3, but without a partition wall. 
     FIG. 5 shows a catalytic muffler provided with a bowl-shaped catalytic converter element. 
     FIG. 6 shows a catalytic muffler in which the catalytic converter element is connected to an inlet pipe in the muffler. Exhaust gases will flow radially outwards through the sleeve-shaped element. 
     FIG. 7 shows a catalytic muffler, in which the exhaust gases are flowing radially outwards through the sleeve-shaped element. This embodiment has a partition wall with an associated outlet pipe. 
     FIG. 8 shows a catalytic muffler, in which a partition wall with catalytic element separates a corner of the muffler provided with an exhaust gas outlet. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the schematical FIG. 1 numeral reference  1  designates a catalytic muffler. It has two mutually demountable housing parts, i.e. a rear housing part  9  and a front housing part  25 . A partition wall  10  is clamped between the both housing parts. A catalytic converter element  2  is clamped between the partition wall  10  and a cover plate  18 , which is mounted to the partition wall, e.g. by means of spot welding. The catalytic converter element is in this case a sleeve  8  having a cylindrical form. But it could also have a conical form. It has an inner surface  6  and an outer surface  7  as well as end surfaces  13 ,  14 . The element is kept fixed in that the rear end surface  14  is resting in an adapted depression  15  in the partition wall  10  at the same time as the front end surface  13  is resting in an adapted depression  16  in the cover plate  18 . Thus, in this case the sleeve  8  is round, but it could also be non-circular and have three or several side-surfaces. The adapted depressions  15  and  16  will of course get the equivalent form. 
     The muffler is fastened with screws directly to the exhaust port of the cylinder, said screws are not shown here. These screws extend through apertures  31  and  32  in the rear housing part  9 . The former aperture is concealed. An exhaust port  26  in the rear housing part connects towards the very exhaust port of the cylinder. Distance pipes  27  and  28  are lead through the front housing, the cover plate and the partition wall in order to support against the rear housing part  9  around the apertures  31  and  32 . The distance pipe  27  is lead through an aperture  29  in the front housing, an aperture  29 ′ in the cover plate and an aperture  29 ″ in the partition wall. The distance pipe  28  is lead through an aperture  30  in the front housing, a recess  30 ′ in the cover plate and an aperture  30 ″ in the partition wall. Screws, which are not shown here, are then inserted through the distance pipes and tightened to the cylinder. This is a conventional arrangement and will therefore not be commented on in any further detail. 
     Exhaust gases  3  from the exhaust port are flowing out through at least one aperture  33  in the partition wall  10 . The exhaust gases will then turn their direction and flow in through at least one inlet opening  21  arranged inside the adapted depression  16  in the cover plate  18 . Thereafter the gases are flowing radially outwards through the element  2 . The cover plate  18  is provided with a duct  34 , which connects to the outer surface  7  of the sleeve  8 . The duct  34  is formed through an immersed part in the cover plate. The immersed part is not as deep as the adapted depression  16 . Thereby the front end surface  13  is kept fixed around its whole circumference. The partition wall  10  is provided with a corresponding duct  35 . The cleaned exhaust gases  4  flow through the both ducts  34  and  35  away from the sleeve  8 . The sleeve  8  is thus kept fixed at both of its end surfaces  13 ,  14  while a great part of its outer surface  7  is free, so that the exhuast gases can flow out through the element. 
     By comparing FIG.  1  and FIG. 2, which is a cross-section through the cover plate  18  and the sleeve, you can see that the ducts  34 ,  35  are not reaching all the way around the whole sleeve  8 , but approximately 90 degrees of angular section is saved, as shown in the lower part of the figure. It means that the sleeve  8  is supported at its outer surface  7  along its entire length within this section of approximately 90 degrees. The sleeve is thus having a particularly good support in this section. It also means that the catalytic converter element is in principle shut off in this section. A wart  23  is arranged in the duct  35  in the partition wall. The wart  23  is thus arising from the duct  35  adjacent the adapted depression  15 . It supports the outer surface  7 . A corresponding wart  24  is arranged in the cover plate  18 . It is placed in a position corresponding to the wart  23 , and the both warts are almost reaching each other. It means that the sleeve  8  is supported along its entire length, on the one hand at the previously mentioned section downwards in the FIGS. 1 and 2, and on the other hand at the warts  23  and  24 . As for the rest the both end surfaces are kept fixed in that they are immersed into the adapted depressions  15 ,  16 . The cleaned exhaust gases  4  are flowing out into the ducts  34 ,  35 . An outlet opening  22  connects to the duct  35 . This outlet opening is embodied as a collared hole in which an outlet pipe  11  is connected. The cleaned exhaust gases  4  are thus flowing out through the outlet opening  22  and through the outlet pipe  11 . The other end of the outlet pipe  11  is connected to an aperture  36  which is arranged on the upper side of the rear housing  9 . The cleaned exhaust gases are conducted through an exhaust gas outlet  37  which is arranged on the upper side of the rear housing. 
     Obviously the partition wall and the cover plate could change place. It means that the inlet opening  21  could instead be arranged in the partition wall and the outlet opening  22  could instead be arranged in the cover plate. Both openings could also be arranged in one of the parts. Naturally the ducts  34  and  35  could also be placed only in one part and not in the other. In the described embodiment the outlet opening  22  is arranged outside the adapted depression in the partition wall, or in the cover plate. The fastening of the sleeve&#39;s both end surfaces  13 ,  14  is substantially contributing to the stability of the sleeve. It is therefore advantageous if its axial length is less than its outer diameter, preferably the length of the sleeve is less than half of the outer diameter. In the shown embodiment the inner- and outer surfaces  6 ,  7  are curving in at least one direction and the body is formed like a cylindrical sleeve  8 . But it could also be formed like a conical sleeve. The adapted depressions are arranged partly in the partition wall and partly in the cover plate, which fastens the element between the partition wall and itself. 
     FIG. 3 shows a catalytic converter element in the shape of a cylindrical sleeve, which is clamped between a partition wall  10  and a cover plate  18 . However, the partition wall  10  inside the adapted depression  15  is connected to an outlet pipe  11 . Apertures  19  are arranged on the outside  20  of the cover plate  18 , which supports the outer surface  7  of the element. In this manner exhaust gases  3  will flow radially inwards through the apertures  19  and through the element  2  in order to then flow out through the outlet pipe  11 , in the same way as earlier described In this case the outside  20  of the cover plate is supporting the outer surface of the element, except for the apertures  19 . Consequently, the element is here supported along most part of its outer surface  7 . The figure is partly cross-sectional and it thus becomes apparent how very well the end surfaces  13  and  14  are being kept fixed into the adapted depressions  15 ,  16 . 
     FIG. 4 shows an embodiment which is similar to that in the FIG.  3 . The partition wall  10  is here missing, which implies a certain simplification, but at the same time it could result in a reduced silencing effect. The adapted depression  15  is here arranged in a mounting part  17 , which fastens the element onto the outlet pipe  11 , in the same way as the partition wall  10  was connected to the outlet pipe  11 , according to FIG.  3 . 
     FIG. 6 shows an embodiment which is quite similar to that in the FIG. 4 in many respects. In this embodiment the mounting part  17  connects to an inlet pipe  12 . In this manner exhaust gases  3  will flow radially outwards through the element  2  and out through the apertures  19 . The mounting part  17  could be replaced by a partition wall  10 . 
     FIG. 7 shows an embodiment which is quite similar to both that shown in FIG.  3  and to that in FIG.  6 . As in the latter embodiment the exhaust gases  3  are flowing radially outwards through the element  2  and out through the apertures  19 . As in the embodiment according to FIG. 3 the catalytic converter element is mounted onto a partition wall  10 . The only difference is that the outlet pipe  11  connects to an aperture  33  located beside the catalytic converter element with its housing. Compare FIG.  3 . Instead the untreated exhaust gases are now flowing into the aperture  38 , which is embodied in the partition wall  10 , and connects to the middle of the catalytic converter element. A flow directed outwards could be advantageous since the cylindrical sleeve  8  has a better support outwards than inwards. In the shown embodiment the outlet pipe  11  is being reflushed by the untreated exhaust gases  3 . These have a lower temperature than the cleaned exhaust gases  4 . In this manner the exhaust gases  3  will cool down the outlet pipe  11 , which is advantageous. But obviously the outlet pipe  11  could also be connected to the partition wall in other positions outside the catalytic converter element. This could lead to a reduced cooling effect as well as a shorter outlet pipe. In the shown embodiment the cooling effect is especially substantial since the outlet pipe  11  is here located directly downstreams the exhaust gases which are flowing out from the exhaust port. 
     FIG. 8 shows a particularly simple solution where the outlet pipe  11 , or the inlet pipe  12 , is missing. This is achieved by placing the partition wall  10  with the catalytic converter element, so that it separates a corner of the muffler provided with an exhaust gas outlet. The partition wall is placed completely into one part of the muffler, i.e. in the figure to the left of the vertical line  39 , which illustrates the partition between the both housing parts. Obviously this location is very advantageous considering the mounting of the partition wall  10 . The both housing parts could be either detachably or undetachably mounted to each other in a conventional way. In the shown embodiment the partition wall  10  extends between the both opposite sides of the housing. Hereby a more simple and distinct figure is achieved. However, in a real case it is often preferable to let the partition wall  10  extend from a side-wall of the muffler and connect to the upper side of the muffler so that it separates only one back corner of the muffler and not as in the shown case separates two back corners of the muffler. The separated part of the muffler will become very hot owing to the very high temperature of the cleaned exhaust gases  4 . It is therefore preferable to separate only one back corner of the muffler and to choose a corner having a particularly good external cooling. In the shown embodiment the untreated exhaust gases  3  are flowing radially inwards through the catalytic converter element. But obviously the catalytic coverter element could be turned right about, so that the untreated exhaust gases  3  instead are flowing in at the middle of the catalytic converter element and then flow radially outwards through the apertures  19 . Consequently, in this case the apertures are instead located within the separated part of the muffler, which connects to the exhaust gas outlet. 
     FIG. 5 shows an embodiment where the catalytic converter element is composed of a bowl-shaped body  5 . In the shown example it forms part of a sphere, but it could also be a semi-sphere or a similar kind of rotary-symmetric body. Consequently, in this case the body  5  has dome-shaped inner- and outer surfaces  6 ,  7 . But it could also have angular surfaces, even if this is not as advantageous. The cover plate  18  is designed with a number of apertures  19 , through which the exhaust gases  3  are flowing in order to continue in through the element. The body  5  is kept fixed in that its end surface  13  is resting against the mounting part  17  at the same time as the body is supported on the outer surface  7  of the cover plate  18  with the apertures  19 . The mounting part  17  fastens the element onto the outlet pipe  11 . In the same way as in the preceding embodiments the mounting part could be replaced by the partition wall  10 . In the shown example no depression is made for the end surface into the mounting part  17 . In this case the adjacent part of the cover plate will keep the end surface  13  fixed. If instead a semi-sphere should be used, it would be preferable to have an adapted depression in the mounting part  17 , or in the partition wall when such a wall is used. The end surface  13  would then be kept fixed both on its inside as well on its outside. Owing to the bowl-shape of the body  5  a large through flow area is achieved. And at the same time the cover plate  18  will have a large area, which is advantageous, since the cover plate will be cooled down by the untreated exhaust gases  3 . For, these have considerably lower temperature than the cleaned exhaust gases  4 . Preferably the catalytic body  5  is produced in that round sheets are being crochetted. Depending on the thickness of the sheets one or several sheets are being calibration-pressed together, so that the desired bowl-shape is achieved. In the shown examples only one catalytic converter element is used. But several elements could be piled axially. Preferably adapted washers are then used to hold each end surface fixed.