Internal-combustion engines – Vibration compensating device – Balancing arrangement
Reexamination Certificate
1999-12-28
2001-09-25
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Vibration compensating device
Balancing arrangement
C123S197400
Reexamination Certificate
active
06293243
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine for a work tool, especially for a portable work tool, such as a motor chainsaw, etc. wherein the internal combustion engine is comprised of a cylinder having a combustion chamber and a reciprocating piston moving in the cylinder. The piston is connected by a connecting rod to the crankshaft of the engine which is rotatably mounted in a crankcase. The crankshaft has at least one bearing pin with a mounting end that is secured in a receiving bore of a crank web, and the assembled crankshaft is rotatably supported by the bearing pin in the crankcase. The connecting rod is connected to the crank pin which is mounted with its mounting end in a further receiving bore of the crank web. The longitudinal center axis of the crank pin is arranged at a stroke spacing to the parallel extending rotational axis of the crankshaft.
An internal combustion engine suitable for hand-held portable work tools is especially a single cylinder two-stroke engine which is of a simple design and provides a minimal weight in comparison to its output. Due to the size of the work tool it must be ensured that the internal combustion engine requires only a minimal mounting space so that the work tool is of a small size and can be easily manipulated.
Because of more favorable exhaust gas behavior, single cylinder four-stroke motors are also becoming more popular in hand-guided, portable work tools wherein the four-stroke motor is of a much larger size because of the intake and exhaust valves and the required valve drives. In order to be able to mount four-stroke motors in portable, hand-guided work tools, a size reduction is required. From U.S. Pat. No. 5,207,120 an assembled crankshaft for an internal combustion engine is known in which the crank pins and the bearing pins are positive-lockingly secured by press fit in the crank webs. The mounting ends of the crank pins and bearing pins have a smaller diameter than the hardened regions of its running surfaces. The resulting step in the diameter is mechanically greatly stressed and must therefore be properly sized. This results in a stroke spacing between the longitudinal center axis of the crank pin and of the rotational axis of the crankshaft that cannot be reduced.
It is therefore and object of the present invention to provide an internal combustion engine of the aforementioned kind for small-sized work tools having a constructive length in the direction of the vertical cylinder axis that is reduced as much as possible.
SUMMARY OF THE INVENTION
According to the present invention, this is solved in that the stroke spacing is substantially identical or smaller than the sum of the radii of the mounting ends of the crank pin and the bearing pin measured in the plane of the crank web.
Inventively, the stroke spacing is identical to and preferably smaller, than the sum of the radii of the mounting ends of the crank pin and the bearing pin when measured in the plane of the crank web so that the total stroke of the piston is reduced. Accordingly, the size of the cylinder can be reduced. The required displacement can be realized by enlarging the bore diameter of the combustion chamber so that, despite the stroke reduction, the displacement is unchanged.
The reduced stroke spacing is achieved in a crankshaft comprised of individual components such that the circumferential circles of the receiving bores provided within the crank web intercept one another. When the receiving bores are separated from one another by a stay, at least one mounting end is provided with a flattened portion, especially a flat surface which rests without play at the counter abutment of the stay. The flattened portion is provided preferably at the mounting end of the bearing pin of the crankshaft so that the required fixed connection to the crank web can be simply realized with positive-locking engagement.
When the receiving bores are connected to one another (communicate with one another) within the interception area, a substantially Figure 8-shaped opening is provided within the crank web. This makes it possible to secure positive-lockingly the mounting ends of the bearing pin and of the crank pin relative to the crank web or relative to one another. This positive-locking engagement fixedly secures the bearing pin and the crank pin within the crank web. In this manner it is also possible to distribute great drive output securely onto the crankshaft.
The material of the crank web itself no longer must provide the rotationally fixed connection for the drive forces but must only provide simple securing forces for the positive-lockingly arranged mounting ends of the bearing pin and of the crank pin by acting as a securing bracket. Accordingly, it is possible to employ a material of reduced quality for the crank web. It must only have a sufficient load capability, respectively, stiffness in order to act as a bracket.
The inventive design of the crankshaft allows stamping of the crank web itself and also of the receiving openings for the mounting ends of the bearing pin and the crank pin.
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patent: 4356741 (1982-11-01), Schopf et al.
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patent: 4867007 (1989-09-01), Krotky
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patent: 5203230 (1993-04-01), Distelrath
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patent: 6164159 (2000-12-01), Saker
Brunner Michael
Köder Ingo
Otterbach Horst
Andreas Stihl AG & Co.
Becker R. W.
Huynh Hai
Kamen Noah P.
R. W. Becker & Associates
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