MUFFLER

MUFFLER

s Technical field

The subject invention refers to a muffler for portable working tools, particular¬ ly chain saws at which the muffler is directly mounted to the exhaust gas outlet of ^- cylinder. 0

Background of the invention

The muffler for portable working tools is usually directly mounted to the cylin¬ der^'s exhaust gas outlet as compactly 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 5 small and light muffler, which at the same time gives a satisfactory silencing function. It is also important that the user does not get injured if he comes into con¬ tact with the tool^'s muffler or its exhaust gases. Furthermore, it is obviously impor¬ tant that the exhaust gases do not set fire to adjacent objects, for example grass or twigs in the case of a chain saw. This has lead to the existence of special legal requi- 0 rements concerning the muffler^'s surface contact temperature and the exhaust gas temperature in the vicinity. The working tool is usually supplied with a cooling fan and various safety covers around the cylinder and partly around the muffler. It is de¬ sirable to achieve a good mix of the exhaust gases in the cooling-air to reduce the temperature. However, in reality this is hard to achieve due to lack of space and with 5 regard to weight.

Purpose of the invention

The purpose of the subject invention is to substantially reduce the above outli¬ ned 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 in accordance with the invention is thus essentially characterized in that the muffler^'s exhaust gas outlet is located on an upper side of the muffler, i.e. a side which is turned in the same direction as the upper side of the cylinder, i.e. tur¬ ned away from the engine^'s crankcase. Furthermore, the muffler's exhaust gas outlet is supplied with a deflecting device, for instance a bent tube, which deflects the ex- haust gas flow, so that it leaves the muffler in a plane which is relatively parallel to the upper side of the muffler. By locating the exhaust gas outlet on the upper side of the muffler it is made possible to take advantage of the large amount of cooling air. which usually blows over the upper sides of the cylinder and muffler. Hereby an ef¬ fective mix of exhaust gases and cooling-air can take place, assuming that a deflec- ting device directs the exhaust gases relatively parallel to the upper side of the muffler. Problems with space and temperature have most likely lead to that this so¬ lution has not previously been used, as far as the applicant is aware of. According to a further development of the preferred embodiment of the invention the exhaust gas outlet is shaped and directed so that a substantial part of the exhaust gases flow side- ways across the muffler^'s upper side. This contributes to a good mix of exhaust ga¬ ses and cooling-air and to a lower temperature around the tool. Further characteristics and advantages of the invention will be apparent from the ensuing 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 va¬ rious embodiments thereof with reference to the accompanying drawing figures.

Figure 1 shows a chain saw schematically seen from above. The saw^'s guide bar and chain as well as various safety covers have been removed, to more clearly show the muffler and its cooling. Figure 2 shows the muffler in figure 1 from above, although in a larger scale and in more detail.

Figure 3 shows the muffler in figure 2 from the front.

5 Figure 4 shows a cross section of the muffler in the previous figures seen from the side along line A-A in figure 3.

Figure 5 shows a further preferred embodiment of a muffler according to the invention.

n Description of embodiments

In figure 1, numeral reference 1 designates a muffler, which is directly moun¬ ted to the cylinder^'s 16 exhaust gas outlet 3. We see the chain saw straight from abo¬ ve down towards the cylinder^'s 16 upper side with spark plug 17. Next to the cylinder a carburetor 18 is located, on the opposite side of the muffler 1. The chain 5 saw 2 is air-cooled and its cylinder 16 has suitably square cooling fins, as illustrated in the figure. The upper side of the cylinder 16 and the muffler 1 are approximately on the same level. A cooling fan 19 blows cooling air around and over the cylinder 16. The air flow is steered by protective covers, which are not shown here. That me¬ ans that a protective cover on the upper side covers the cylinder and a part of the 0 muffler.

As illustrated by the cooling air arrows 20, some of the cooling air flows aro¬ und the cylinder 16 and also between the cylinder and the muffler 1. A large portion of the cooling air flows across the cylinder 16 and further towards the muffler 1. The muffler^'s exhaust gas outlet 4 is located on an upper side 5 of the muffler, 5 i.e. a side which is turned in the same direction as the cylinder^'s 16 upper side. i.e. turned away from the engine^'s crankcase. The muffler^'s exhaust gas outlet 4 has a deflecting device 6, for instance a bent tube, which deflects the exhaust gas flow 7. so that it leaves the muffler in a plane which is relatively parallel to the muffler s up¬ per side 5. The amount of cooling air is approximately 10 times greater than the amount of exhaust gas and it is important to achieve a good mix of exhaust gas and cooling air. The exhaust gas outlet 4 is located close to a corner 8 of the muffler situated close to the cylinder. The corner 8, which is closest to the cooling fan 19, is suitably chosen. The exhaust gas outlet is shaped and directed so that a considerable part of the exhaust gas flows sideways over the muffler^'s upper side 5, i.e. across the direc¬ tion of the cylinder^'s exhaust gas outlet 3. The deflecting device 6 is designed so that it expands sideways and consequently spreads the exhaust gases sideways. This de- vice is designed so that the exhaust gases spread in a sector from 60 to 120 degrees and preferably around 90 degrees. In the illustrated embodiment the spread is around 90 degrees, but even the amount of exhaust gases vary in the different directions. For, the deflecting device 6 has a throttling 9 in the outlet 4. This throttling varies si¬ deways and it is larger in the muffler^'s longitudinal direction than in its sideways di- rection. Consequently a larger amount of exhaust gas flows in the muffler's sideways direction than in its longitudinal direction. This is suitable considering the mix of exhaust gases in the cooling air 20.

When using the saw practically it is important that the exhaust gases do not set fire to for instance twigs in the vicinity, or cause any injuries to the user. Formally there are also existing legal requirements both concerning the surface contact tempe¬ rature and the maximum temperature of the exhaust gas in the so called roll plane. The easiest way to understand the term roll plane is to imagine that the chain saw, without guide bar and chain, is driven and held against a plane surface in a large number of different angles. Figure 1 shows an example of roll plane 24. In this case the saw is partly supported against its spiked bumper 23 and partly against a so cal¬ led bumper 22 on the muffler 1. The bumper 22 is mounted in a strategic position on the front of the muffler, in order to move the roll plane outwards in many cases. The handle 21 of the chain saw as well as the spiked bumper 23 and the bumper 22 will in many cases constitute contact points against the roll plane. During the measurement the chain saw, in a specified condition without guide bar and chain, is rolled over a plane measuring table, after which measuring of maximum temperature takes place. Current legal requirements state that the maximum temperature of the exhaust gas must not exceed 247 degrees Celsius, which is hard to meet. Current le¬ gal requirements for surface contact temperatures is a maximum of 288 degrees C, which applies to points that come into contact with the roll plane, for example the bumper 22. These legal requirements applies in parts of the USA, Canada and Aust¬ ralia. As illustrated in figure 1 the majority of the exhaust gas flows sideways relati- ve to the muffler and is mixed with cooling air 20. In this direction it is always far to the roll plane, even when it is at its closest. Only a minor amount of exhaust gas flows in the muffler^'s longitudinal direction, which is the direction in which the roll plane comes closest to the exhaust gas outlet.

Figures 2-4 show the muffler according to figure 1 enlarged and in more detail. Its main parts are illustrated in figure 2 seen from above. As illustrated in the figure the deflecting device 6 is designed in the form of a housing shaped body 10, which has an unbroken roof and walls supplied with outlet 4 for the exhaust gases. The housing shaped body 10 lacks flooring to certain extent, and is mounted to the muff¬ ler^'s upper side 5. This is supplied with a corresponding aperture 11, through which the exhaust gases penetrate into the deflecting device 6. The housing shaped body 10 is suitably manufactured by pressing in a tool. Along all edges but one, the plate is shaped so that it is adapted to the muffler's upper side 5. Thus along three sides, the housing shaped body touches the muffler's upper side, while it has an opening on the fourth side next to a pocket which is embodied between the body 10 and the muffler's upper side 5. A structure 12 comprising a spark arrester screen, is designed so that it can be inserted into the pocket. This implies that the exhaust gas flow 7 exits the aperture 1 1 on the upper side 5 of the muffler, thence passes the spark ar¬ rester screen and deflects in the housing shaped body 10 in order to flow out of its exhaust gas discharge 4. Figures 2 and 3 show that the exhaust gas outlet 4 has a height which varies side¬ ways and this height is smallest in the longitudinal direction and largest in the side¬ ways direction. The outlet throttles the exhaust gases and the throttling is consequently higher in the muffler^'s longitudinal direction than in the sideways di¬ rection. The structure 12 is normally called a spark arrester screen. It partly contains a fastening device and partly a wire mesh or net. The fastening device can comprise a plate folded around a wire mesh. This plate is supplied with a fastening hole in which a fastening screw 25 is inserted and screwed tightly onto the muffler's upper side 5. A number of stampings 26 are embodied in the fastening device, in order to join this with the wire mesh or net in a safer way. Obviously, even the housing sha¬ ped body 10 could have an alternative primary form than the illustrated rectangular one and the aperture into the pocket can naturally take up a larger or smaller part than one side of its surrounding edge. Figure 3 shows the muffler from the front and figure 4 in cross section from the side along the line A-A. By comparing these two illustrations the muffler^'s construc¬ tion becomes more clear. The bumper 22 is located on the highest part of the front, which previously has been described. As illustrated in figure 4, it consists of a profi¬ led plate, which has been spot welded and /or soldered onto the muffler. Beneath there are two holes 27 and 28, which extends straight through the muffler and exits on both sides of the cylinder^'s exhaust gas outlet 3. Two distance tubes 29 and 30 surround these holes. The distance tubes are soldered onto both sides inside the muffler. When screws are inserted into the holes and screwed down tightly in the corresponding screw holes on both sides of the cylinder^'s exhaust gas outlet 3, the distance tubes prevent the muffler from being deformed. They further prevent ex¬ haust gases from leaking out of the front. Far down the front 14 there are two holes 31 and 32. On the inside of these holes there are nuts which are fastened by means of welding and /or soldering. These fastening holes are used for attaching a support bracket onto the muffler by means of screws. As illustrated in figure 4 the muffler is supplied with a baffle 35 which divides the total muffler volume into two parts. The exhaust gases exit the exhaust gas outlet 3 into the following part and consequently pass through apertures out into the next part of the muffler. From there the exhaust gases flow through a tube 36 to the muffler^'s deflecting device. The tube 36 is partly attached to the baffle 35 and partly to the muffler^'s upper side 5. The arrangement of having a baffle 35 and tube 36 is not necessary, but contributes to an improved noise reduction. The muffler's main parts are joined together at a joint 37 where the parts have been soldered together in a gas-proof sealed manner.

As illustrated in figures 3 and 4, the transition from the upper side 5 to a verti- cal side 13, 14 is designed with an unusually large radius for these types of mufflers. The radius is suitably 5 to 15 mm and preferably about 10 mm. Hereby a well adap¬ ted spreading effect of the exhaust gas flow is obtained. A portion of the exhaust gas flow simply deflects and follows the radius transition fractionally downwards. By choosing a well adapted radius this spreading effect becomes optimal. If the radius is made even larger, the entire exhaust gas flow could then easily be deflected and if it is smaller, the exhaust gas flow is hardly deflected at all. This adapted rounding of the transition from the upper side to the vertical side contributes to reduce the ex¬ haust gas temperature in the roll plane.

Within the scope of the invention, the muffler with its special exhaust gas out- let can be designed in many ways. As mentioned, the muffler can be short of a baffle 35 and it can be detachable so that firstly the inner part is screwed onto the cylin¬ der's exhaust gas outlet 3 and after that, the outer part is screwed onto the inner part. Furthermore, the muffler can be equipped with a catalytic converter element to redu¬ ce the exhaust gas emissions. This could for instance be located in the illustrated tu- be 36, but also in many other ways.

Figure 5 illustrates a somewhat different embodiment of the invention than the one previously described. Also in this case, the muffler^'s exhaust gas outlet 4 is located on the upper side 5 of the muffler and supplied with a deflecting device 6, so that the exhaust gas flow leaves the muffler in a plane relatively parallel to the muff- ler's upper side 5. The muffler^'s exhaust gas outlet is also positioned close to a corner 8 of the muffler, situated close to the cylinder, suitably the corner which is closest to the cooling fan 19. However, in this case the deflecting device 6 is desig¬ ned and directed in a way so that it discharges a relatively concentrated exhaust gas 5 flow in a sideways direction over the muffler. The deflecting device 6 is even in this case designed as a housing shaped body 10, but here it has a more oblong shape and exhaust gas outlet 4 only along one of the short sides. Along the remaining sides the body 10 is mounted to the upper side 5 of the muffler. An aperture 1 1 on the upper side 5 of the muffler leads the exhaust gases up into the housing shaped body 10. 10 This aperture 11 connects close to the short side of the body 10, which is opposite the exhaust gas outlet 4. Through these measures a concentrated exhaust gas flow 7 is created. By the housing shaped body being directed so that its aperture 4 points sideways relative to the muffler, the exhaust gases flow in this direction.

A protective cover 15, suitably of metal, is mounted onto the muffler so that it 15 extends above mainly the whole width of the upper side 5 and extends above the ex¬ haust gas outlet 4. As illustrated in figure 5 the protective cover 15 is fastened at the same corner 8 as the deflecting device 6. It extends straight across the muffler and also down along the opposite side wall. As illustrated in the figure, cooling air 20 can blow between the protective cover 15 and the muffler 1 along the vertical side 20 1 of the muffler. Along the upper side 5 of the muffler, the protective cover is sui¬ tably designed so that cooling air 20 can pass in between the protective cover and the muffler on the side of the protective cover 15, which is closest to the cylinder. The opposite side of the protective cover can on the other hand be more or less clo¬ sed in order to fit different applications.

2 In the embodiment according to figure 5 the protective cover extends down outside the side wall 13. towards which the exhaust gas outlet is directed. However, the protective cover 15 could also be so large that it covers the entire upper side 5 and extends down even along the front side 14. It could then even replace the bum¬ per 22. Thus, the protective cover could extend downwards outside the side wall(s)

30 against which the exhaust gas outlet is directed. Such a protective cover, with greater or lesser extension (figure 5), could also be used in combination with a muffler according to figures 1 to 4.

A great advantage with the muffler according to the invention is that it facilita- tes a very effective mix of the exhaust gases with the cooling air 20. especially with the substantial cooling air flow which passes above the cylinder 16 and the muffler^'s upper side 5. Since it is usually very tight between the protective cover, which ex¬ tends over the upper side of the cylinder and the muffler, other solutions are neces¬ sary in this case. This is due to the fact that the protective cover is usually made of temperature sensitive plastic material. One solution is to equip the muffler with the protective cover 15, as described above. The protective cover can of course be equipped with insulating material on its upper side to reduce the surface temperatu¬ re. When the protective cover 15 is used, the normal plastic protective cover over the cylinder and muffler is shortened , so that it just reaches the muffler or extends only fractionally beyond the muffler. The chain saw is supplied with a front hand guard, which is not illustrated in the schematic figure 1. This front hand guard is positioned in front of the handle 21 and above the muffler 1. This front hand guard is suitably supplied with a protective part, which begins where the shortened plastic engine co¬ ver ends. Hereby the muffler according to figures 1 to 4, can be used without pro- blems. The front hand guard is also usually made of plastic, but it is located at a greater distance from the muffler, which is favourable. Such a front hand guard can obviously also be used in combination with a muffler according to figure 5 or si¬ milar, i.e. supplied with the protective cover 15. This is possible, but hardly necessary. The muffler is supplied with an aperture 1 1 in the muffler^'s 1 upper side 5 or in a side wall 13, 38 and at least one deflecting device 6, 15, for instance a bent tube, is connected to the aperture 1 1 and deflects the engine^'s exhaust gas flow 7, so that it leaves the muffler in a plane which is relatively parallel with the muffler^'s 1 upper side 5. and thereby the muffler^'s exhaust gas outlet 4 is essentially arranged on an upper side 5 of the muffler. For instance, the aperture 1 1 can be positioned in a side wall 13, 38 and be supplied with a deflecting device in the form of a bent tube, which makes the exhaust gases flow along the side wall 13, 38 up towards the upper side 5. A protective cover 15, suitably made of metal, is mounted on the muffler, so that it extends above the exhaust gas outlet 4 at the mouth of the bent tube. Thus, the protective cover 15 extends relatively parallel with the side wall 13. 38 around the corner to the upper side 5 and relatively parallel with this, along the entire or a por¬ tion of its width. Thus, in this case, the protective cover 15 also functions as a de¬ flecting device. The bent tube can of course also be drawn around the corner to the upper side 5. Preferably, the distance from the aperture 1 1 to the upper side 5 is small and the side wall 13, 38 leans upwards, i.e. the angle between these sides exce¬ eds 90 degrees. On the contrary', it is unsuitable to locate the aperture 1 1 in the side, which is turned towards the cylinder. This would result in a substantial heating of the deflecting device and consequently the cylinder.