Muffler with catalytic converter

Muffler with catalytic converter (1) essentially arranged in direct connection with a combustion engine's exhaust port and especially intended for portable working tools such as chain saws. At least one partition (2) is embodied in the muffler, or instance in the form of a baffle (3), and the partition (2) comprises one or several apertures (9, 10), through which the exhaust flow passes in order to flow from one side of the partition to the other side, and the partition is at least partly coated with a catalyzing layer.

TECHNICAL FIELD 
The subject invention refers to a muffler with catalytic converter arranged 
basically in direct proximity to an exhaust port of a combustion engine 
and mainly intended for portable power equipment such as chain saws. 
BACKGROUND OF THE INVENTION 
Mufflers with catalytic converters for combustion engines are well-known 
since a very long time, especially for cars. For portable power equipment, 
such as chain saws, they have been available on the market to a small 
extent since the end of the 1980'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 equipment, have as a rule 
consisted of a converter element comprising coated, thin sheet metal 
strips. A pleated or corrugated metal strip can for instance be rolled 
together with a plane strip into a cylindrical element. Both strips are 
coated with a catalyzing layer, and the exhaust emissions are conducted 
through the axial cavities, which are formed between the strips, and are 
hereby cleaned. The catalytic converter element is relatively sensitive to 
vibrations and demands an elaborately designed mounting in order to get an 
acceptable length of life, seen from a purely mechanical point of view. 
The mounting itself demands additional details in the muffler, for 
instance a sleeve, which shall serve as an enclosure of the element. 
Furthermore, the muffler must be designed so that the catalytic converter 
element functions as a passage in the muffler, for instance located in an 
exhaust pipe out of the muffler. This implies certain restrictions for the 
muffler, since it is hardly reasonable from a cost point of view to use 
several smaller catalytic elements, which serve as parallel passages in 
the muffler. Thus, the usage of a converter element implies certain 
restrictions when designing the muffler, and this could bring about a 
reduced silencing effect. Both the converter element itself and its 
mounting are relatively costly, and this brings about a considerably more 
expensive muffler in total. When the converter element is used in a 
muffler for two-stroke engines, problems can also arise with a very high 
temperature in the converter element. This is due to the fact that the 
exhaust gases from the two-stroke engine contain a high content of 
unburned hydrocarbons, which are burned in the converter element. This 
partly leads to a very high heat generation in the converter element and 
partly to very hot exhaust gases. The converter element often reaches 
temperatures exceeding 1000 degrees C and must therefore be cooled down, 
for instance by means of heat dissipation. This must take place without 
the muffler's casing overheating anywhere, considering user-safety and 
legal requirements. The local heat generation in the converter element is 
consequently a problem. 
PURPOSE OF THE INVENTION 
The purpose of the subject invention is to substantially reduce the above 
outlined problems by creating a muffler with a catalytic converter, which 
achieves an effective reduction of the exhaust emissions without using a 
conventional converter element. 
SUMMARY OF THE INVENTION 
The above mentioned purpose is achieved in a muffler with catalytic 
converter in accordance with the invention having the characteristics 
appearing from the appended claims. 
The muffler with catalytic converter in accordance with the invention thus 
is essentially characterized in that at least one partition is embodied in 
the muffler in the shape of for instance a baffle or an inlet or outlet 
tube, and the partition is designed with one or several openings through 
which the exhaust gas flow passes in order to flow from one side of the 
partition to the other, and the partition is at least partly coated with a 
catalyzing layer. That implies that a number of partitions are embodied in 
the muffler and the exhaust gases pass each partition respectively through 
apertures. A baffle with a large number of holes can for instance be 
located in the muffler. The baffle is coated with a catalyzing layer and 
the exhaust gases are cleaned when they come into contact with the baffle. 
This occurs to a particularly great extent in the area around each hole, 
when the exhaust gases pass through each hole respectively. Thereby the 
heat generation takes place in a number of different places in the 
muffler, and this makes it easier to conduct the heat to the muffler's 
casing in an even and controlled way. The muffler can be supplied with 
several different partitions, and this further increases the possibility 
of dissipating the heat in an even and controlled manner. Furthermore, the 
partitions can be designed in an effective way from a noise reduction 
point of view. The partition parts are simple and inexpensive to produce 
at the same time as they are mechanically durable and easy to mount in the 
muffler. The baffle can also be made from several details so that a number 
of cavities are formed in the baffle and hereby the exhaust gases get an 
effective contact with the walls in the cavities. A number of measures can 
be taken in order to create an effective contact between exhaust gases and 
the coated, partitioning parts in the muffler. The muffler's casing parts 
can also be coated on the inside and in different ways come into contact 
with the exhaust gases. These and other characteristics and advantages of 
the invention will be more apparent in connection with the description of 
the preferred embodiments, and with full support of the drawing figures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION 
In the schematic FIG. 1 numeral reference 1 designates a catalytic muffler 
in accordance with the invention and 2 designates a partition, which is 
embodied in the muffler in the shape of a baffle 3. In this case, the 
muffler consists of a rear half 13, which is directly mounted to the 
combustion engine's exhaust port, and a front half 14. Both halves are 
attached by means of the rear half having a seam into which the front half 
fits. The baffle 3 is located between the two halves, so that it is firmly 
clamped between them. The halves can be detachably mounted to each other 
with for instance a screw, but they can also be firmly mounted through 
welding or soldering. The baffle 3 is designed with a basic part 6 and at 
least one covering plate 7, which covers a section of or the entire 
baffle. At least one of the basic part 6 or the covering plate 7 is 
profiled, so that at least one cavity 8 is formed between the basic part 6 
and the covering plate 7. At least one aperture 9 connects the cavity 8 
with the space upstream the baffle and at least one aperture 10 connects 
the cavity 8 with the space downstream the baffle. FIG. 1 clarifies how 
the exhaust gases 15 flow in through the aperture 9 and through the cavity 
8 and out through the aperture 10. The baffle 3 is at least partly coated 
with a catalyzing layer C. Naturally, the entire baffle can be coated, but 
it is also possible that, for instance, only the surfaces which include 
the cavity 8 are coated with a catalyzing layer. It is above all these 
surfaces on the inside which come into contact with the exhaust gases. The 
cavity 8 is designed so that satisfactory contact is created between 
exhaust gases and walls coated with a catalyzing layer. This is apparent 
from FIGS. 2 and 3. 
Thus, FIG. 2 shows the baffle 3 seen from the front. It consists of two 
profiled plates 6, 7, which have an interactive profiling, so that at 
least one cavity 8 is formed between them when they have been joined 
together. The two plates are in this case profiled in the same way, so 
that they each form half of the depth of the cavity 8. However, this can 
naturally vary within wide limits. One of the plates can for instance be 
completely plane and the other have the entire profiling. Furthermore, a 
number of smaller cover plates 7 can be used. Two holes 16 and 17 are made 
through the two plates. They are used for fastening the muffler with 
screws in a conventional way. The two plates 6, 7 are plane from their 
outer edges and inwards. In this case one of the plates is larger than the 
other, and the smaller plate does not quite extend to the edges. However, 
this can naturally vary, so that the two plates are of the same size. The 
cavity 8 is here created by means of the two plates being profiled out 
from each other. This profiling is made with curved sides in the flow 
direction in order to increase the turbulence in the exhaust gas flow. 
Furthermore, a number of islands 18-24 are embodied in the cavity 8. This 
also increases the turbulence in the flow as well as it creates an 
improved contact between the walls and the gas flow. The islands are 
created by means of local stampings in the plates so that these meet each 
other or almost reach each other. For the sake of clarity, the cross 
section A--A has been located beside the islands 18-20. As appears from 
FIGS. 2 and 3, the profiling is elongated so that two ducts 11, 12 are 
formed between the plates. In order to illustrate this principle the gas 
flow is shown in one 12 of the two ducts. Naturally, the baffle can be 
designed so that only one duct is formed or so that more ducts than two 
are formed. The basic desire is to create a satisfactory contact between 
exhaust gases and sidewalls in each duct respectively in order to enable a 
satisfactory exhaust gas conversion rate. Of course, several upstream 
apertures 9 can be used as well as several downstream apertures 10. The 
sides of the apertures can be collared as here or straight. By means of 
collaring, a somewhat improved contact can be created with the gas flow. 
As mentioned, FIG. 3 shows a cross section along line B--B. For the sake 
of clarity, the cross section has been located beside the islands 20, 22. 
Thus, these islands serve as obstacles in the gas flow and interacts with 
profilings in the outer sides of the cavity. This will be apparent by 
studying the gas flow, marked with broken lines, in FIG. 2. 
FIG. 4 shows a further design of a partitioning baffle 3. Just as in the 
previous design, the baffle is located in a divisible muffler housing 
consisting of a rear half 13 and a front half 14. These are similar to the 
halves in the previous design, but can also be identical. For the sake of 
clarity, the halves are shown in a partly exploded view. In this case, the 
baffle 3 consists of one single plate, and this is shaped in a way that it 
to a great extent follows the shape of the muffler's one half 13, 14 on 
the inside, so that a space of 1 to 20 mm is created between the baffle 3 
and the muffler half 13. Thus, in this case the baffle is located in the 
rear muffler half 13, but it could also be located in the front half 14. A 
baffle can also be used in each half, as well as several baffles in each 
half. In the illustrated design the baffle 3 has no contact with the front 
half 14, but it could also be clamped between the halves in the same way 
as in the embodiment in FIG. 1. In the illustrated design, the baffle 3 
can rest on a number of local stampings in the rear half 13 and be fixed 
by other local stampings. Naturally, it can also be fixed in other ways. 
In the illustrated design the baffle 3 closely follows the shape of the 
muffler's one half, in this case the rear one, so that a space of 1 to 10 
mm is created between the baffle 3 and the muffler half 13. The space is 
on average approximately 6 mm and hereby a flow along the baffle's 
upstream side is created before the exhaust gases pass in through a number 
of small holes 25. By means of this flow a satisfactory contact is created 
between the baffle's upstream side and the exhaust gases. This is 
advantageous considering the exhaust gas conversion rate. Furthermore, it 
is advantageous using a number of small holes 25, which the exhaust gases 
pass in order to flow from one side of the partition to the other. The 
total surface area of the holes becomes large. Furthermore, the holes have 
been collared, so that the surface area of each hole has increased 
considerably. All of this lead to a more effective exhaust gas conversion 
rate. The entire baffle 3 is suitably coated with a catalyzing layer C. 
However, it is especially important that the upstream side and the holes 
are coated, since these have most contact with the exhaust gases. The 
holes can also be collared in the opposite direction. This would create a 
substantial turbulence on the upstream side of the baffle 3, which 
possibly could increase the conversion rate. Naturally, it is also 
possible to use non-collared holes and a greater or lesser number than 
those illustrated. This will to a certain extent influence the conversion 
rate. Naturally, the insides of the muffler halves 13 and 14 can also be 
coated with a catalyzing layer. In the illustrated design, this probably 
has the greatest effect in the case of the rear muffler half 13. However, 
by making an elaborate choice of the apertures' 25 size and preferably 
several collared holes, it is possible to create a number of exhaust gas 
jets, which hit the wall of the front muffler half 14, so that the exhaust 
gases get a satisfactory contact with the wall and consequently 
contributes to a satisfactory conversion rate. 
FIGS. 5 and 6 shows another type of partition than those apparent from the 
previous embodiments. The exhaust gases 15 flow straight into an inlet 
tube 4. The inlet tube extends from one side of the muffler across to 
another side of it, in this case from the side which is connected to the 
engine's exhaust port and across to the opposite side. All communication 
out of the inlet tube 4 occurs by means of transverse apertures 26, seen 
in the inlet tube's axial direction. FIG. 6 shows in perspective the inlet 
tube 4 with apertures 26. Thus, the inlet tube 4 is open in both ends and 
these apertures are sealed by means of the inlet tube being clamped 
between the rear muffler half 13 and the front one 14. The inlet tube 4 
surrounds the engine's exhaust port in the rear muffler half 13. The inlet 
tube has a profiled shape and is supplied with a number of apertures 26, 
through which the exhaust gases 15 flow out from the inlet tube. The 
profiling of the inlet tube can to a certain extent improve the exhaust 
gas conversion rate. The two indentations at the tube's two short sides 
are on the other hand mainly intended for creating space for two fastening 
screws, which extend straight through the muffler, and are intended for 
fastening it to the engine's cylinder. An outlet tube 5 is here integrated 
with the inlet tube 4, so that they form an assembled unit. This can for 
instance be punched from one single plate, which then is pressed so that 
it is given the desired appearance. Obviously, it can also consist of 
several units, which have been fastened together into an integrated or 
assembled unit. In the illustrated design, the outlet tube 5 partly has a 
large aperture at its end 28 and partly transverse apertures 27 seen in 
the outlet tube's axial direction. Thus, the exhaust gases 15 can flow 
partly into the outlet tube's 5 end and partly at its periphery through 
apertures 28 and 27 respectively. Naturally, it is also possible to equip 
the end of the outlet tube with a closure, so that all of the inflowing 
gases pass through the apertures 27. Furthermore, outlet tube 5 can be 
lacking entirely, so that only the inlet tube 4 is used or vice versa, 
i.e. so that only the outlet tube 5 is used and the inlet tube 4 is 
lacking. In this case the outlet tube extends from one side of the muffler 
across to another side of the muffler and all communication into the 
outlet tube 5 takes place by means of transverse apertures 27. 
FIG. 7 shows a further embodiment of the invention. The muffler's main 
parts are shown in an exploded view in order to make the flow inside the 
muffler more apparent. The embodiment has a number of similarities with 
the embodiment in accordance with FIGS. 1-3, but also shows a few 
differences. A partition or baffle 2, 3 is clamped between the housing 
parts 13, 14, exactly as in the previous embodiment. Two plate parts 6, 7 
follow each other, seen in the flow direction of the exhaust gases. Part 6 
is substantially profiled, while part 7 is relatively plane and only 
equipped with a few stiffening stampings 34. When the parts are joined 
together a cavity 8 is formed between part 6 and 7. For, part 6, which 
also can be called the basic part, has a depressed part 29, which is 
partitioned by surrounding edges 30. Furthest out there is a plane flange 
part 31. A number of apertures 9 are made in the depressed part 29. The 
apertures and the surrounding plate surface are designed so that they make 
the gas flow obliquely in relation to the plate part's surface. This is 
carried out by means of the aperture having been given a gill shape or 
similar. The plate part 6 is entirely or partly coated with a catalyzing 
layer C. The apertures' 9 gill shape is used in order to make the gas flow 
15 out of the engine come into contact with the catalyzing layer of part 6 
as effectively as possible. This takes place in a number of ways. Firstly, 
the surface area is large in each aperture 9 by means of the gill shape. 
Secondly, the gill shape directs the gas flow in a desirable direction. A 
number of gills are positioned around the depressed part's 29 outer 
periphery. These gills are turned towards the surrounding edges 30, so 
that the exhaust gases spray against these edges and are there redirected. 
Hereby they get a satisfactory contact with the catalyzing coating on the 
edges. The remaining gills have been turned in a diagonal direction, so 
that the exhaust gases spray in a direction away from the outlet hole 10 
in the connecting plate 7. This contributes to an increase of the exhaust 
gases' 15 residence time in the cavity 8 between the plates 6 and 7. Thus, 
the aperture 10, which connects the cavity 8 with the space downstream the 
cavity, is located near one of the plate's 7 corners. Plate 7 can either 
be coated with a catalyzing layer or non-coated. The coating makes the 
plate considerably more expensive and in this case a non-coated plate has 
been chosen. Notice that through its presence the non-coated plate 7 makes 
sure that the exhaust gases come into contact with plate 6 to a greater 
extent than they would have done if plate 7 had been lacking. Thus, the 
non-coated plate 7 increases the usage of the plate 6. If an increased 
conversion rate is desired, it is suitable to locate an additional plate 
downstream plate 7 and let this plate be coated. It could be designed in 
much the same way as plate 6, but its profiling would then be turned away 
from plate 7, so that a cavity is formed between the downstream plate and 
plate 7. Apertures 9 shaped as gills, with the same orientation as for 
plate 6, is suitably used in order to create, in this case as well, as 
good a contact as possible between the exhaust gases 15 and the coated 
downstream plate. In this case the exhaust gases 15 are directed to an 
exhaust gas outlet 35 which is located in the outer muffler half 14. The 
exhaust gas outlet 35 is so designed that the greater amount of the 
exhaust gases flow across the muffler's outside, and certain amounts flow 
obliquely out through slits somewhat upstream the exhaust outlet 35. The 
holes 16, 17 which are embodied in the parts 6, 7 and 14 are used for 
fastening the muffler with screws in a conventional manner. In this case, 
the plate parts 6 and 7 consist of two separate plates, having the same 
width and height. For, plate 7 has a flange part 33 which comes into 
contact with the flange part 31 in the plate 6 when the plates are clamped 
together. One or several similar plates could in the same way be piled 
together in order to give a more effective exhaust gas conversion rate, as 
already mentioned. However, it is also possible that certain plate parts 
have reduced outer dimensions and are located inside the other plate 
parts, in order to avoid too many flange parts 31, 33 being piled on top 
of each other. Furthermore, several plate parts can be created by means of 
folding one plate once or several times, so that thereby one single plate 
can be shaped so that it functions as several plate parts following each 
other. Such a plate could for instance be immersed into an immersed part 
of another plate.