Internal-combustion engines – Vibration compensating device – Balancing arrangement
Reexamination Certificate
1999-07-30
2001-10-16
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Vibration compensating device
Balancing arrangement
Reexamination Certificate
active
06302077
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to balancer systems for motorcycle engines.
BACKGROUND
Piston reciprocation in internal combustion engines often causes the engine to vibrate. More specifically, the motion of an engine's pistons within their respective cylinder bores causes vibrations because the pistons' movement is started and stopped twice during each rotation of the engine's crankshaft. The inertial effects of each piston cause primary vibrations along the axis of that piston.
One known method of damping or offsetting primary vibrations is to mount one or more counterweights to the crankshaft. The counterweights are most effective when they are spaced radially from the crankshaft axis of rotation, with the crankshaft axis of rotation intermediate the crankpin and the counterweights. Although the counterweights orbit about the crankshaft axis of rotation in a generally circular path, the counterweights move generally opposite the direction of travel of the linearly-reciprocating pistons.
While it is possible to offset most or all primary vibrations of the piston with such counterweights, movement of the counterweights causes further vibrations that may not be aligned with the primary vibrations. Thus, as the mass of the counterweights is increased to further offset the primary vibrations of the pistons, the moving counterweights create higher-order vibrations.
The vibration environment becomes even more complex in a V-twin, single-crankpin engine. In that type of engine, the pistons are interconnected with the same crankpin, and are oriented at a 45° angle with respect to each other. Therefore, the pistons do not start and complete their respective strokes in unison. The resultant combined primary vibration acts generally vertically and transverse to the crankshaft axis of rotation.
It is known to provide one or more balancer shafts in combination with crankshaft-mounted counterweights to substantially offset primary vibrations. One known configuration includes a pair of balancer shafts disposed on opposite sides of the crankshaft, and rotating in timed sequence with the crankshaft.
Typically, no balancing system is perfect, and there will often exist higher order vibrations that cannot practically be dampened. Such vibrations may resonate in the engine's crankcase and be amplified by the same.
SUMMARY
The present invention provides a motorcycle including a crankcase having a left side and a right side mounted on a motorcycle frame, a crankshaft, and a balancer shaft mounted for rotation within the crankcase and supported substantially by only one of the sides of the crankcase. Because the balancer shaft is supported substantially by only one of the sides of the crankcase, vibrations are substantially isolated from the other side of the crankcase, and there is believed to be less amplification and noise.
The balancer shaft is driven by a drive member, such as a gear, belt, or chain, that interconnects the balancer shaft with the crankshaft. Sprockets or gears may be mounted on the balancer shaft and crankshaft to transfer force from the crankshaft to the drive member, and from the drive member to the balancer shaft. The balancer shaft thus rotates in response to rotation of the crankshaft.
Preferably, the motorcycle includes two balancer shafts that are disposed on opposite sides of the crankshaft. One end of each balancer shaft can be supported by a bearing in a first side of the crankcase, and the other end can be supported by a bearing in a bearing housing that is also mounted to the first side of the crankcase. Preferably, the bearing housings are joined together with a guide bracket. The guide bracket provides a substantially rigid connection between the bearing housings that permits the free ends of the bearing housings to oscillate in unison. The guide bracket also provides at least one tensioner (e.g., a hydraulic tensioner) for the drive member.
In one embodiment, the engine also includes a flywheel that includes a counterweight portion. In a V-twin single-crankpin engine, two flywheels may be mounted on opposite sides of the connecting rods, with the ends of the crankpin supported by the respective flywheels. The flywheel is configured to cooperate with the balancer shafts to more effectively offset piston-induced vibrations.
The invention also includes an interconnect seal providing fluid communication between an oil passage extending through one side of the crankcase and a hydraulic passage in the guide bracket. An oil pump provides pressurized oil to the hydraulic tensioner through the interconnect seal. The interconnect seal includes a central portion that is thicker than the opposite end portions. In this regard, the interconnect seal initially yields relatively easily as the sides of the crankcase are brought together, and then increasingly resists being compressed as the sides come together. Compression tends to drive the sealing edges out radially. The interconnect seal is therefore believed to permit a quality seal between the side of the crankcase and the guide bracket without causing the guide bracket to unacceptably deflect. The interconnect seal also allows for some misalignment and motion between the sides of the crankcase and the guide bracket.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.
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Dennert R. Bruce
Enright Bernard F.
Safarik David A.
Troxler Paul
Vandenhoeven Bernardus G. H.
Ali Hyder
Harley-Davidson Motor Company
Michael & Best & Friedrich LLP
Yuen Henry C.
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