Machine element or mechanism – Gearing – Teeth
Patent
1988-03-18
1990-02-13
Herrmann, Allan D.
Machine element or mechanism
Gearing
Teeth
F16H 5500
Patent
active
048996092
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates generally to gears, and more particularly to gears having a tooth-profile with a smaller relative curvature at a contact point.
DESCRIPTION OF THE PRIOR ART
As a tooth-profile of power transmitting gears, an involute tooth-profile is typically employed, but other tooth-profiles are also utilized, for example a cycloid tooth-profile, a circular arc tooth-profile, or a combination thereof.
In these gear's art tooth-profiles except for the circular arc tooth-profile, a radius of curvature is monotonously and continuously varied. Also, in the circular arc tooth-profiles of gears having a finite number of gear teeth, the radius of curvature thereof is continuously varied. It is impossible, therefore, to retain or maintain the relative curvatures between two adjacent tooth-profiles at a smaller value or a constant value during their engagement.
Further, the strength of the tooth-profile has an upper limit determined by a bending stress therein and another upper limit determined by the tooth surface pressure stress. Generally in an involute gear, however, since the limit determined by the bending stress is higher than the limit determined by the tooth surface pressure stress, it is necessary to increase the limit (named the K value) determined by the tooth surface pressure stress.
In order to increase the K value, however, it is required to decrease the relative curvature between tooth surfaces at the point of engagement thereof, because the Hertz stress is affected by the relative curvature.
As an example of a tooth-profile having a smaller relative curvature, there is a tooth-profile of the Wildhaver-Novikov type, but in order to use this tooth-profile for power transmitting gears, the gears must be a helical gear with a large width, since this tooth-profile is a point contact type (contact interval=0) in which the tooth-profiles engagement with each other only at a single point thereon.
DISCLOSURE OF THE INVENTION
The present invention was made from the above view point. It is an object of the present invention to provide gears wherein the relative of curvature between tooth-surfaces is brought near to that of Wildhaver-Novikov type tooth-profile, its contact interval is more than one, the operating pressure angle is decreased to thereby prevent the surface pressure and the bearing stress from being increased, and the relative curvature between two tooth-surfaces is maintained at a lower level to thereby markedly increase the strength of the tooth-profile.
Specifically, according to the present invention, the radius of curvature of the tooth-profile is repeatedly increased and decreased from a pitch line in the direction of addendum and dedendum of a tooth without monotonously changing as in the prior art. And, preferably at the point where the radius of curvature is minimum, the center of the radius of curvature is positioned on the pitch line. In this case, the relative curvature between tooth-profiles at this point becomes zero, but in the gears according to the present invention, a plurality of the points at which the relative curvature becomes zero periodically appear in one pitch. In these points, of course, the specific sliding is also zero.
The present invention is intended to provide a complete tooth-profile obtained through many trials and errors on various tooth-profiles formerly proposed.
The above object of the present invention is accomplished by providing a tooth-profile wherein the curvature of the tooth-profile curve is a function which is not monotonously varied and is continuous and capable of being differentiated, and a locus of the center of curvature forms a series of continuous curves which exist generally near a pitch circle.
In this case, the center of curvature corresponding to the point of relative of curvature being zero is preferably positioned on a pitch line.
Also, it is preferred that a locus of the centers of curvature is a series of curves which is formed by alternately connecting a small arc having its center within
REFERENCES:
patent: Re29115 (1977-01-01), Rouverol
patent: 4149431 (1979-04-01), Rouverol
patent: 4644814 (1987-02-01), Rouverol
Standard Handbook for Mechanical Engineers (9th Edition), 1951, pp. 80-90 to 80-107.
Hall William D.
Herrmann Allan D.
Kyouiku Haguruma Kogko Kabushiki-Kaisha
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