Internal-combustion engines – Cooling – Air-cooled
Reexamination Certificate
1999-07-23
2001-11-13
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Cooling
Air-cooled
C423S041000, C423S041000
Reexamination Certificate
active
06314922
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a hand-held working tool, especially a motor chainsaw etc., comprising an internal combustion engine arranged in a housing and having a crankshaft for driving a tool and a fan wheel. The fan wheel is arranged in a fan housing and conveys through an air inlet cooling air to the internal combustion engine. Combustion air is axially guided through an outlet opening in the housing bottom via a combustion air channel to the air filter of the internal combustion engine.
U.S. Pat. No. 3,994,076 discloses a motor chainsaw in which an air-cooled internal combustion engine is arranged in a housing. The crankshaft of the internal combustion engine supports at one end the drive member for the tool, i.e., a saw chain circulating on a guide bar. The other end drives a fan wheel which is arranged within a fan housing and takes in cooling air through an air inlet for supplying the cooling air to the combustion engine. A portion of the intake air of the fan wheel is guided as combustion air to the air filter of the internal combustion engine. The combustion air is supplied via an outlet opening, provided in the bottom of the fan housing and covered by the fan wheel, in the axial direction and is guided via a combustion air channel to the air filter. The known arrangement with axially directed air removed from a chamber that is delimited by the fan housing bottom and the end face of the fan wheel and that contains centrifuged suction air will provide substantially dust-free combustion air to the dirt chamber of the air filter.
The outlet opening in the known device is arranged centrally within the bottom of the fan housing, i.e., adjacent to the crankshaft bearing within the crankshaft housing of the internal combustion engine. The combustion air channel connected to the outlet opening must have over its entire length a sufficiently large flow cross-section for supplying the required combustion air amount. In the known arrangement the combustion air channel connection between the outlet opening at the housing bottom and the air filter as well as, in the flow direction, the connection downstream to the carburetor of the internal combustion engine requires great constructive expenditures. The complicated channel design of the combustion air channel increases the size of the working tool so that its ease of manipulation and operating comfort are impeded.
It is therefore an object of the present invention to provide a working tool of the aforementioned kind with which a simple guiding of clean combustion air in combination with a compact design of the hand-held working tool is possible.
SUMMARY OF THE INVENTION
Expediently, the combustion air channel is delimited by the bottom of the fan housing and by a channel wall portion that covers partially the bottom of the fan housing so as to form a double-walled bottom.
In another embodiment, the combustion air channel is provided within a hollow support of the working tool that is supports the drive unit including the internal combustion engine.
When providing a combustion air channel which is embodied by a channel wall covering the bottom of the fan housing as a double-walled bottom of the fan housing, the air can be guided on the shortest possible path, i.e., perpendicularly to the direction of extension of the crankshaft, to the air filter. The combustion air channel may extend about a large radial portion of the fan housing bottom so that a sufficiently large flow cross-section is achieved already with a minimal depth of the double-walled bottom while the entire arrangement is space-saving. An especially compact construction for the shortest extension of the combustion air channel is provided when the combustion air channel at the level of the combustion air outlet in the fan housing bottom is completely positioned at the end face of the fan housing and includes a tangential portion of the channel wall extending in the flow direction past the periphery of the bottom and at least partially in the circumferential direction of the fan housing. The channel wall is connected to the circumferential wall of the fan housing, covering the fan wheel, spaced from the plane of the fan housing bottom. This arrangement defines a circumferential portion of the combustion air channel at the outer side of the circumferential wall. The respective flow cross-section of the end face portion of the combustion air channel covering the fan housing bottom is reduced in the flow direction, and the required flow cross-section is provided by an increasing widening of the circumferential portion of the combustion air channel.
Advantageously, the combustion air channel, respectively, its end section at the air filter or the air filter dirt chamber can be positioned entirely on the side of the plane of the fan housing bottom opposite the end face portion so that, due to the minimal axial extension of the arrangement, the fan housing can be positioned in the vicinity of the crankshaft housing of the internal combustion engine. This arrangement provides a compact design of the working tool.
A minimal size of the drive unit of the hand-held working tool can also be provided by supplying the combustion air through a hollow support beam of the working tool. The support beam has connected thereto the drive unit as well as guide and support elements and optionally further components of the working tool. The combustion air channel extends through the hollow support beam whereby an inlet opening in the wall of the support beam coincides with the combustion air outlet at the bottom of the fan housing. The air-conducting connection for introducing the combustion air, axially removed from the fan housing, into the support beam is preferably provided by a connecting channel member which is made of elastic material and is formed-lockingly connected to the respective openings and in addition provides vibration dampening.
Expediently, the combustion air channel branches substantially tangentially to the rotational direction of the fan wheel away from the fan housing and extends substantially straight to the air filter so that the flow path of the combustion air is kept short and the flow resistance of the combustion air channel is reduced. The inlet area of the combustion air channel is delimited by the housing bottom and a channel wall that forms a double-walled bottom with the housing bottom of the fan housing so that the assembly of fan housing and combustion air channel is of a small size in the axial direction relative to the crankshaft axis. The fan housing can be mounted adjacent to the internal combustion engine or its crankcase so that the drive unit of the working tool is of a compact design.
When the flow cross-section of the combustion air channel widens in the flow direction, a sufficient amount of air reaches the air filter box of the internal combustion engine without any flow resistance at any operational state of the engine. Pulsation events in the combustion air stream due to cyclical operation of the combustion engine are prevented by the small length but relatively wide flow cross-section of the combustion air channel. The air filter box and the fuel metering or mixture forming devices of the combustion engine can be arranged directly adjacent to the combustion engine because, due to the inventive design, these components are not subject to vibrations. The combustion air channel is of an especially flat design in the inlet area whereby the combustion air channel wall forming the double-walled bottom of the fan housing can be positioned in close proximity to the combustion engine. The assembly comprised of fan housing and combustion air channel can be realized in an especially flat design when the widening of the flow cross-section is realized by a widening of the inlet area parallel to the housing bottom. Expediently, the combustion air channel has a rectangular cross-section so that the side facing the combustion engine has a large surface area. The fan housing can thus be slipped onto the drive pin of the cranksh
Durr Bernhard
Geyer Werner
Klimmek Axel
Nickel Hans
Schliemann Harald
Andreas Stihl AG & Co.
Becker Robert W.
Benton Jason
Robert W. Becker & Associates
Wolfe Willis R.
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