Patent Application
20080164092
The invention relates to a silencer for a working tool, in particular a motor chain saw with a housing with a housing wall which has at least one opening for exhaust gases and a hood extending outside the housing through at least one opening, with a hood opening pointing to one side from which exhaust gases flowing from an interior of the housing are guided to the outside through the at least one opening in an exhaust gas jet.
Silencers are sufficiently known in the state of the art. Furthermore, exhaust gas outlets of the silencer in different forms are known.
An exhaust device for internal combustion engines is described in DE 25 39 516 A1. Here the silencer has three exhaust ports which comprise wall sections overlapping them and installed on the outside.
DE 28 22 966 C2 describes a hood-like outlet, also with walls projecting on the outside from the silencer.
DE 78 10 865 U1 describes an exhaust silencer for an exhaust device for internal combustion engines. It gives a description of a device similar to the aforementioned publication with outwardly projecting, inclined hoods.
The exhaust silencer should be designed so that during operation the formation of hot spots at contact points on the motor chain saw is prevented as it rolls off onto a roll-off surface. For the same reasons the heat of the exhaust gas jet on an envelope clamped through the contact points from exceeding a predetermined limit temperature.
The disadvantage of the silencers known in the state of the art is that the exhaust jet either bears against the outer silencer wall, heats and follows its contour, or can be directed sharply from the outer silencer in order to avoid the above disadvantage.
The object of this invention is to make available a silencer for a working tool which overcomes the advantages mentioned.
The object is achieved by a silencer with the features of claim 1.
The aforementioned silencer has a housing with a housing wall with at least one opening for exhaust gases and a hood extending outside the housing through the at least one opening, with a hood opening, pointing to one side, from which exhaust gases flowing from an interior of the housing are guided to the outside in an exhaust jet through the at least one opening. It has been shown that a fin arranged on the at least one opening and directed against the direction of flow of the exhaust jet predetermines, more precisely positions and focuses the exhaust jet escaping from the hood. This therefore prevents the exhaust jet from bearing against the housing wall on the outside.
For this purpose the at least one fin is preferably directed towards a hood roof, and it gives the exhaust gases escaping from the housing through the at least one opening a direction towards one inside of the hood roof. Directing the exhaust gas towards the inside of the hood roof provides the exhaust gas with a defined tear-off edge so that exhaust jet does not come into contact on the outside with the housing wall of the silencer.
The fin is arranged to oppose the direction of flow of the exhaust jet. The fin is preferably arranged at an angle to the hood roof so that exhaust gases are opposed to the direction of flow of the exhaust jet in at least one direction component after passing through the at least one opening. The angle is advantageously smaller than 90°, preferably smaller than 70°.
The advantage mentioned is particularly evident in a working tool in which the silencer according to the invention is installed and in which the hood opening must guide the exhaust jet along a housing wall of the silencer over the longest possible distance to an envelope formed by spacing surfaces. The envelope is formed by the spacing surfaces clamped through the contact points of the working tool—e.g. the chain saw without blade. The spacing surfaces therefore correspond to the shortest distance from the flat bottom, which can be ignited by the growth of moss, for example, to the working tool lying on it in a corresponding position.
The distance along the exhaust jet between the hood opening and the envelope is preferably the maximum distance. After escaping from the hood opening, the exhaust jet cools considerably as the distance increases. The cooling is of the order of 30° C./cm. The exhaust jet may be guided onto an extremely small region by the predetermination according to the invention. The exhaust temperature in the region must be kept as low as possible.
The silencer is normally mounted on a crankcase on a side of the internal combustion engine facing away from the user. Undesirable deflection of the exhaust jet by bearing against the crankcase is prevented by the silencer according to the invention, and additional heating of the housing wall of the silencer and adjacent components is avoided.
It has proved advantageous for each of the at least one fin to extend in the interior of the housing through exactly one opening. In principle, however, it is also conceivable to arrange at least one fin outside the housing and inside the hood through exactly one opening. The fin can even be guided through the opening.
The plane formed by the at least one fin opening is preferably arranged essentially perpendicularly to the housing wall. As a result of this arrangement the exhaust gas is forced particularly far into the region distant from the hood opening inside the hood. The exhaust jet may then bear particularly well against the hood roof on the inside and is able to escape from the hood in a focussed manner.
The at least one opening advantageously has a straight edge on one side and an arc-shaped edge on the opposite side. In this case the fin can be connected along the arc-shaped edge to the housing wall in a gas-tight manner. The straight edge of the opening, together with the open fin edge, forms the fin opening that is open on one side. The admission cross-section thus formed, which is essentially in the shape of a circle segment, has proved particularly favourable for focussing the exhaust jet.
In a particularly preferred further development of the silencer according to the invention a plurality of openings, arranged in a row pointing from one side to the opposite side, are provided in the housing wall. Here the shape of the openings is advantageously the same for each, and each of the openings is covered on the inside by exactly one fin. In particular, the fins may be of the same construction. The plurality of fins additionally focuses the exhaust jet and enlarges the admission cross-section.
The exhaust gas is largely prevented from bearing on the outside against the housing wall by a hood roof running obliquely to the housing wall and rising towards the hood opening opposite the housing wall if the exhaust jet bears on the inside against the hood roof. Preferably the hood roof is designed flat and is inclined at a slight angle of approximately 5 to 30 degrees to the housing wall. The hood roof forms a tear-off edge on the hood opening. The hood should, in the case of a plurality of openings, extend with its hood roof across all the openings.
A hood roof that widens towards the hood opening is also conceivable in order to disperse the exhaust jet in parallel with the housing wall.
The hood is advantageously formed in an essentially L-shaped cross-section that runs approximately centrally and perpendicularly through the hood opening from one side to the opposite side. The long L-leg then runs in the hood roof and the short L-leg runs in the hood wall
Working tools, particularly hand-guided working tools such as motor chain saws, parting-off grinders and hedge shears, preferably have the silencer according to the invention. The silencer is then provided on the exhaust port of an internal combustion engine.
The invention is described in seven figures with reference to an exemplary embodiment, in a purely diagrammatically representation.
The three fins 3, unlike hood 2, are provided on the inside of the silencer housing but are open on the same side as hood 2. Each of the three fins 3 opens into an opening 16 in housing wall 8. Each fin 3 is arranged completely straight along the section running centrally from one side to the opposite side perpendicularly to housing wall 8, and is inclined at an angle of approximately 45°, so that it projects on the inside from silencer wall 8. Each of fins 3 forms a fin opening 17 pointing to one side on the inside.
Hood 2 is designed to have an essentially L-shaped cross-section according to
| Number | Date | Country | Kind |
|---|---|---|---|
| DE 202006013280.5 | Aug 2006 | DE | national |
