Internal-combustion engines – Cooling – Air-cooled
Reexamination Certificate
1999-07-28
2001-02-27
Dolinar, Andrew M. (Department: 3747)
Internal-combustion engines
Cooling
Air-cooled
C123S1950HC, C030S381000
Reexamination Certificate
active
06192840
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a drive unit of a portable handheld work apparatus such as a motor-driven chain saw.
BACKGROUND OF THE INVENTION
German patent publication 4,011,929 discloses a motor-driven chain saw wherein the drive unit includes an internal combustion engine. The crankshaft of the engine carries a chain sprocket at one end of the crankcase for driving a saw chain which moves around a guide bar. Furthermore, the crankshaft drives a fan wheel which is held on a drive pin of the crankshaft on the opposite side of the crankcase within a fan housing. The crankcase of the engine is made of a metal material and is configured of two parts. The axis of the crankshaft lies in the partition plane of the crankcase parts which can be connected to each other. The crankcase is rigidly connected to the cylinder of the engine. The upper part of the crankcase is cast with the cylinder as one piece and is unified with the lower part of the crankcase holding the piston.
The housing of the known drive unit includes a connecting base having a recess in which the engine can be seated with the crankcase in advance from above and can be tightly clamped to a flange-like configured receptacle part of the connecting base. The connecting base for the engine is seated in the handle frame in the known motor-driven chain saw. The handle frame is made of plastic which has a low weight while having high strength and excellent vibration damping characteristics. The total weight of the portable handheld work apparatus to be carried by the operator is intended to be low with respect to the best possible manipulability. The connecting base for accommodating the engine is used in the known motor-driven chain saw in order to facilitate assembly. The connecting base imparts the required stiffness to the force loaded total assembly; however, the component as an additional part increases the weight and the manufacturing costs.
SUMMARY OF THE INVENTION
It is an object of the invention to reduce the weight and the manufacturing costs of the work apparatus and especially the drive unit.
The drive unit of the invention is for a portable handheld work apparatus including a chain saw. The drive unit includes: an internal combustion engine having a cylinder including an upper crankcase half and a crankshaft defining a crankshaft axis; a work tool operatively connected to the crankshaft so as to be driven thereby; the crankshaft having a drive pin; a fan wheel attached to the drive pin; a fan housing made of plastic and being configured for accommodating the fan wheel therein; a metallic chassis including a crankcase sump as a lower crankcase half; the crankcase sump of the metallic chassis and the upper crankcase half conjointly defining a partition plane where the upper and lower crankcase halves are joined to each other; the metallic chassis having a flange surface lying essentially perpendicular to the crankshaft axis; the crankcase sump having an exposed end defining at least a portion of the flange surface; and, the fan housing having a housing base attached to the flange surface.
A metal chassis of the drive unit includes a crankcase sump as one of the two crankcase halves and supports the engine. The dynamic forces, which are generated by the crankshaft and the engine during operation, are taken up by the chassis with the known excellent material characteristics of the metal material. The fan housing is necessary for the operation of the engine but is not subjected to force. The fan housing is made of plastic and is attached with an end face thereof to a flange surface of the metal chassis so as to be in contact therewith. The end face lies essentially perpendicular to the crankshaft axis. In this way, the total weight of the drive unit is reduced by the high portion made of plastic. The plastic parts can be connected to the flange surface with only little complexity and the flange surface is configured essentially so as to be planar. The crankcase sump is configured as one piece with the metal chassis and purposefully lies opposite the cylinder with reference to the partition plane of the crankcase. The cylinder with the upper crankcase half cast thereon can be seated in the metal chassis during assembly of the drive unit and be joined to the crankcase sump. A seal is mounted in the flange plane between the metal chassis and the plastic housing.
The metal chassis advantageously includes a connecting anchor for attaching a guide element of the tool. The forces and torques, which occur during use of the portable work apparatus, and the torques are taken up by the metal chassis for mounting the engine and are directed to the carrying handle of the work apparatus so that no further heavy components are required herefor. The fan housing is advantageously connected to the chassis with threaded fasteners. The fastener heads are accessible from the fan housing to make a simple and rapid assembly possible.
A space for lubricant for the work tool is delimited in the chassis. The lubricant space is arranged close to the drive pin of the crankshaft for the tool of the work apparatus. A simple maintenance and filling is possible when the lubricant space is open in the flange plane and can be closed with a cover held with threaded fasteners. If the cover is made of plastic, then the total weight of the work apparatus is further reduced. The cover is advantageously made of plastic and is configured as one piece with the fan housing.
A savings of material and therefore a reduction of weight is possible when the fan housing is guided with a projection in the axial direction of the crankshaft below the metal chassis and lies against the housing wall. The metal housing wall can, as required, be configured with a thin wall because the housing wall is additionally supported by the contiguous plastic part. A cropped camshaft rotates in the region of the crankcase sump. Radial steps are formed in the wall of the chassis in this region and the plastic fan housing engages in the radial steps for further support of the crankcase sump.
REFERENCES:
patent: 4285309 (1981-08-01), Johansson
patent: 4700480 (1987-10-01), Rangert et al.
patent: 4872308 (1989-10-01), Nagai et al.
patent: 5029393 (1991-07-01), Nagashima et al.
patent: 5533869 (1996-07-01), Garrison et al.
patent: 4011929 (1990-10-01), None
Durr Bernhard
Klopfer Karl-Heinz
Andreas Stihl AG & Co.
Dolinar Andrew M.
Huynh Hai
Ottesen Walter
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