Variable face width gearing

Details Variable face width gearing Variable face width gearing

1999-04-30

2001-05-15

Herrmann, Allan D. (Department: 3682)

Machine element or mechanism

Gearing

Teeth

Reexamination Certificate

active

06230578

ABSTRACT:

I. BACKGROUND OF THE INVENTION
A. Field of the Invention
This invention relates to the design of gear teeth. Specifically, it relates to gearing having characteristics that reduce the self-excited component of dynamic load. As a consequence, this gearing is quieter and exhibits greater power density than conventional gearing. The invention discloses a gear form that achieves these desirable performance characteristics in a way that is less costly and, in many commonly encountered circumstances, more robust than previously disclosed gear forms.
B. Related Art
It is well known in the art that, as a pair of gears rotates, the effective stiffness of the gear mesh varies as a function of mesh cycle position. This periodic variation in mesh stiffness gives rise to what has been referred to in the art as the “dynamic increment” of load. In addition to serving as the primary excitation for gear noise, this “dynamic increment” serves to reduce effective torque capacity. Any means that can be employed to reduce this self-excited component of dynamic load will have the effect of reducing gear noise and increasing power density.
U.S. Pat. Nos. 5,083,474, 5,341,699 and 5,485,761, disclose an elastic means for reducing mesh stiffness variation that is effective at all operating loads. This desirable mesh stiffness characteristic is achieved by introducing different forms and amounts of lead crowning at different positions along the length of the gear tooth. The introduction of this “differential crowning” serves to decrease the elastic stiffness of gear teeth in the portion of the mesh cycle having the greater number of tooth pairs in contact. While effective in reducing mesh stiffness variation, this approach, which frequently concentrates loads over a small area, can lead to excessive contact pressures and stresses, potentially compromising performance in high-speed or high-load applications. Furthermore, the manufacture of gears having different forms and amounts of crowning at different roll angle positions often requires special cutting tools and/or manufacturing processes.
U.S. Pat. No. 5,315,790 discloses a method of using finite element analysis to calculate a tooth topology that compensates for load-induced tooth deflections. Similar in effect to conventional tip relief, and unlike the means disclosed in the present application, this type of modification uses initial separation to reduce mesh stiffness variation; as a consequence, it is effective only in the vicinity of a particular design load. In addition, this particular type of modification can be difficult and expensive to produce. U.S. Pat. No. 5,802,921 discloses the use of “liminal cross-modification” for reducing dynamic loading and tooth impact in helical and spiral bevel gearing only. Although this approach does not lead to an increase in contact pressure, the means used to achieve this end are markedly different from and typically more expensive than those prescribed by the present invention.
II. SUMMARY OF THE INVENTION
An advantage of the present invention is to provide a novel shape of gear teeth that reduces the self-excited component of dynamic load in a way that is less costly and more robust than previously disclosed gear forms. Specifically, what is disclosed is the use of different gear tooth face widths along the tooth height to elastically reduce mesh stiffness variation.
This invention embodies the use of different face widths along the tooth height to change both the geometric properties of the tooth and the load distribution or concentration. The change in geometric properties directly affects the bending stiffness and the change in load distribution directly affects the compressive stiffness of the tooth pair. In this manner, a favorable proportion of a change in bending stiffness and a change in compressive stiffness can be used to reduce mesh stiffness variation. The advantage of this is evident by contrasting with U.S. Pat. Nos. 5,083,474, 5,341,699 and 5,485,761. Due to the effective use of the bending component of tooth pair stiffness, gears embodying this invention will exhibit lower compressive pressures and stresses than those embodying the above referenced patents, while achieving a comparable mesh stiffness characteristic. Therefore, in high speed and high load applications, the reduced compressive pressures and stresses will be advantageous.
In contrast to U.S. Pat. Nos. 5,083,474, 5,341,699 and 5,485,761, the use of no crowning or a constant crowning curve throughout the tooth height may not provide an ideal solution at all loads. However, compared to those types of modifications that use initial separation to reduce mesh stiffness variation such as that of U.S. Pat. No. 5,315,790, the herein disclosed invention still affords a significant performance improvement across a range of loads by elastically modifying the tooth pair stiffness characteristic.
While the discussion has concentrated on reducing mesh stiffness variation through a mesh cycle, another advantage of this form of gearing is the ability to reduce weight without compromising gear noise or power density. As such, a method of choosing the appropriate face width at specific roll angles to achieve numerous design objectives is disclosed.
Another advantage of gears embodying this invention, specifically in contrast with known gear forms requiring topological modifications such as those of the above referenced patents, is the simplicity of manufacture. That is, gears embodying the present invention can be manufactured using conventional machines with conventional tools by any process currently used to make gears. The only difference from a manufacturing viewpoint is the blank design and fabrication, which can be carried out using any conventional lathe with conventional tooling. This can represent a significant cost savings in comparison with those gear forms requiring topological modifications.
These and other advantages of the present invention will be clarified in the detailed description of the preferred embodiments taken together with the attached figures wherein like reference numerals represent like elements throughout.


REFERENCES:
patent: Re. 28696 (1976-01-01), Rouverol
patent: Re. 29115 (1977-01-01), Rouverol
patent: 1194904 (1916-08-01), Wagner
patent: 1613702 (1927-01-01), Hammar
patent: 1690931 (1928-11-01), Hammar
patent: 1766153 (1930-06-01), Trbojevich
patent: 2453656 (1948-11-01), Bullard, III
patent: 2764034 (1956-09-01), Hotine
patent: 3184988 (1965-05-01), Osplack et al.
patent: 3206997 (1965-09-01), Hardy
patent: 3881364 (1975-05-01), Rouverol
patent: 3937098 (1976-02-01), Rouverol
patent: 3938865 (1976-02-01), Rouverol
patent: 3946621 (1976-03-01), Rouverol
patent: 3982444 (1976-09-01), Rouverol
patent: 3982445 (1976-09-01), Rouverol
patent: 4108017 (1978-08-01), Rouverol
patent: 4140026 (1979-02-01), Rouverol
patent: 4149431 (1979-04-01), Rouverol
patent: 4259875 (1981-04-01), Rouverol
patent: 4276785 (1981-07-01), Rouverol
patent: 4324441 (1982-04-01), Rouverol
patent: 4464138 (1984-08-01), Decker
patent: 4589300 (1986-05-01), Rouverol
patent: 4644814 (1987-02-01), Rouverol
patent: 4651588 (1987-03-01), Rouverol
patent: 4899609 (1990-02-01), Nagata
patent: 5083474 (1992-01-01), Rouverol
patent: 5271289 (1993-12-01), Baxter, Jr.
patent: 5315790 (1994-05-01), Kish et al.
patent: 5341699 (1994-08-01), Rouverol
patent: 5485761 (1996-01-01), Rouverol
patent: 5802921 (1998-09-01), Rouverol
patent: 5946975 (1999-09-01), Yun
patent: 741376 (1955-11-01), None
Product Brochure, Stealth® Planetary Gearhead, Bayside Precision Gearheads; two pages.

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