Patent Application
20110237384
1. Field of the Invention
This invention generally relates to a planetary gear mechanism for a bicycle internal hub transmission. More specifically, the present invention relates to planetary gear mechanism that includes a stepped planetary gear.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle.
One aspect is to provide a planetary gear mechanism with a stepped planetary gear that includes two sets of helical gear teeth.
Another aspect is to provide a stepped planetary gear that includes two sets of helical gear teeth, where the helical gear teeth are provided with relative helical angles that make the planetary gear less expensive to manufacture with fewer manufacturing steps.
In view of the state of the known technology, a planetary gear mechanism for a bicycle internal hub transmission is provided with at least one stepped planetary gear having a plurality of first helical gear teeth with a first outer diameter and a plurality of second helical gear teeth with a second outer diameter that is greater than the first outer diameter. The first helical gear teeth have a first helix angle and the second gear teeth have a second helix angle. The first and second helix angles are angled such that for a given amount of rotation of the stepped planetary gear corresponding travel points on the first and second helical gear teeth move the same axial amount with respect to the rotational axis of the stepped planetary gear.
Referring now to the attached drawings which form a part of this original disclosure:
Selected embodiments will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
Referring initially to
As shown in
With reference again to
As best shown in
The first pawl mechanism 36 is disposed on portions of the driver 34 and serves as a one-way clutch that selectively transmits torque to the planetary gear mechanism 14.
The shifting section 38 is a conventional shifting mechanism that operates in the same manner as the shifting mechanism in either U.S. Pat. Nos. 5,928,103 and/or 6,607,464 (both assigned to Shimano Inc.). The shifting section 38 engages and disengages certain elements within the internal hub transmission 12 in order to select one of a plurality of torque transmission paths. Specifically, when the driver 34 is rotated, the driver 34 transmits torque to either the first pawl mechanism 36 or directly to a portion of the planetary gear mechanism 14, in a conventional manner. Since operation of the shifting section 38 and the various torque transmission paths of internal hub transmissions are conventional, further description is omitted for the sake of brevity.
The planetary gear mechanism 14 includes a ring gear 54 having a first end 56 (
The second planetary gear mechanism 42 is a conventional planetary gear mechanism and therefore further description is omitted for the sake of brevity.
The second pawl mechanism 44 transmits torque from the second planetary gear mechanism 42 to the hub shell 46 in a conventional manner, depending upon which torque transmission path has been engaged by the shifting section 38.
A description of the stepped planetary gear 16 is now provided with specific reference to
The stepped planetary gear 16 includes a plurality of first helical gear teeth 70 and a plurality of second helical gear teeth 72. The first helical gear teeth 70 are configured to mesh with the sun gear 50. The second helical gear teeth 72 mesh with the internal helical gear teeth 62 of the second end 60 of the ring gear 54.
As best shown in
The first helical gear teeth 70 have a first helix angle α1 and the second gear teeth 72 have a second helix angle α2, as shown in
As shown in
Each of the first helical gear teeth 70 has an axial end 74 with a beveled edge. The beveled edge of the axial ends 74 are angularly offset from a line normal to a rotational axis A of the stepped planetary gear 16, as shown in
Similarly, each of the second helical gear teeth 72 has an axial end 76 with a beveled edge. The beveled edge of the axial ends 76 are also angularly offset from a line normal to the rotational axis A of the stepped planetary gear 16, as shown in
It should be understood from the drawings and the description herein that the first helix angle α1 and the second helix angle α2 can be any of a range of angles where the first helix angle α1 is between 15 and 30 degrees. The second helix angle α2 is determined based upon criteria described in greater detail below.
Specifically, the first helix angle α1 and the second helix angle α2 identified in
To better understand the relationship between the first helix angle α1 and the second helix angle α2, the following explanation is provided. A stationary plane represented by the line L1 in
Thus, as the stepped planetary gear 16 rotates, the travel points P1 and P2 move along the corresponding ones of the first helical gear teeth 70 and the second helical gear teeth 72, and eventually move from tooth to tooth.
As indicated in
More specifically, the distance between travel point P1 and the travel location P1′ is equal to the distance β for the angular displacement angle α5. As well, the distance between travel point P2 and the travel location P2′ is also equal to the distance β for the angular displacement angle α5.
Thus, for the stepped planetary gear 16, the relationship between the first helix angle α1 and the second helix angle α2, the corresponding diameters D1 and D2, and the number of gear teeth on each of the first and second helical gear teeth 70 and 72 are determined such that the pair of corresponding travel points P1 and P2 on the first helical gear teeth 70 and the second helical gear teeth 72 move the same axial amount β with respect to the rotational axis A.
In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Also, the terms “part,” “section,” “portion,” “member” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts. As used herein to describe the above embodiment(s), the following directional terms “forward”, “rearward”, “above”, “downward”, “vertical”, “horizontal”, “below” and “transverse” as well as any other similar directional terms refer to those directions of a bicycle equipped with the planetary gear mechanism for a bicycle internal hub transmission. Accordingly, these terms, as utilized to describe the planetary gear mechanism for a bicycle internal hub transmission should be interpreted relative to a bicycle equipped with the planetary gear mechanism for a bicycle internal hub transmission as used in the normal riding position. Finally, terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed.
While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. For example, the size, shape, location or orientation of the various components can be changed as needed and/or desired. Components that are shown directly connected or contacting each other can have intermediate structures disposed between them. The functions of one element can be performed by two, and vice versa. The structures and functions of one embodiment can be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). Thus, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
