Machine element or mechanism – Gearing – Rotary bodies
Reexamination Certificate
1998-02-02
2001-04-10
Bucci, David A. (Department: 3682)
Machine element or mechanism
Gearing
Rotary bodies
C074S415000, C074S460000
Reexamination Certificate
active
06212967
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to transmission gear assemblies, and is particularly concerned with a variable gear assembly for producing a variable transmission ratio.
Gear assemblies are known which have a constant angular velocity or transmission ratio for transmitting power from one shaft to another shaft. These gear assemblies have two gears of constant diameter which are in meshing engagement via teeth or the like. U.S. Pat. No. 5,247,847 of Gu describes a cam gear assembly in which a cam gear of a first, constant diameter has a series of teeth defining a lobular periphery and a roller gear of a second, constant diameter is in meshing engagement with the cam gear. Both gears are of constant diameter. The roller gear has a plurality of rotatably mounted rollers around its perimeter for meshing engagement with the gear teeth, and the second diameter is smaller than the first diameter. This provides a constant angular velocity ratio. The provision of a roller gear instead of mating conventional gears with meshing teeth reduces the risk of damage to the gear teeth and possible failure of the transmission.
Variable ratio gear transmissions employ at least one pair of non-circular gears to provide a continuously variable transmission ratio. One such variable gear arrangement is described in U.S. Pat. No. 4,685,348 of Takami. At least one pair of non-circular gears have intermeshing gear teeth to produce a continuously variable transmission. U.S. Pat. Nos. 5,381,766 and 5,405,300 of Sakita describe a rotary piston engine in which piston assemblies are connected to the engine output shaft through non-circular gear sets. Each non-circular gear set includes a heart shaped gear and a teardrop shaped gear with intermeshing teeth. The teeth on the teardrop shaped gear may be replaced with rollers. However, this gear has a relatively large number of rollers and the engagement of the rollers in the recesses between adjacent teeth may give rise to some instability.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a new and improved variable assembly.
According to one aspect of the present invention, a variable gear assembly is provided which comprises a first, roller gear having a plurality of rotatable rollers and rotatable about a first rotation axis, each roller being at a predetermined distance from the first rotation axis, and a second, cam gear having a plurality of teeth for engagement with the rollers as the roller gear rotates, each tooth having opposing first and second sides, and an apex between the first and second sides, and the arrangement being such that, as the roller gear rotates through a cycle of 360°, the rollers engage successive active teeth along the second cam gear, and a pair of adjacent rollers engage at least one active tooth at any time during a complete cycle of said roller gear, the roller gear and cam gear being arranged to provide mechanical communication at a variable angular velocity ratio.
In a preferred embodiment of the invention, at least the roller gear is of variable diameter. The cam gear may also be rotatable about a second rotation axis and be of variable diameter. The rollers are preferably at variable angular spacings from each other and at varying distances from the roller gear rotation axis. The roller gear may engage the outer periphery of the cam gear, or the cam gear may be a ring gear with teeth on its inner periphery. A single pair of opposing gears may be provided, or two or more stacked pairs of gears may be used. The cam gear may be a rack with spaced teeth, with the roller gear comprising a pinion for rotatable engagement with the teeth on the rack, the rack or the roller gear moving in a linear direction as the roller gear rotates, for converting rotational motion to linear motion, or vice versa.
In one embodiment of the invention, each tooth on the cam gear is relatively large as compared to the varying radius of the cam gear, and a relatively small number of cam gear teeth are provided, which may be of varying sizes.
A large number of different variable gear relationships may be provided using this arrangement, and the arrangement permits use of the entire range of motion of the gears. The arrangement is also such that there is no slack between the gears, regardless of their relative position, and the variable gear assembly is smoother in operation than previous variable transmission arrangements.
REFERENCES:
patent: 3818747 (1974-06-01), Van Riemsdijk
patent: 4416165 (1983-11-01), Kramer et al.
patent: 4685348 (1987-08-01), Takami
patent: 4765195 (1988-08-01), Takami
patent: 5247847 (1993-09-01), Gu
patent: 5381766 (1995-01-01), Sakita
patent: 5405300 (1995-04-01), Sakita
patent: 1566-124 (1990-05-01), None
Brown Martin Haller & McClain LLP
Bucci David A.
Hansen Colby
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