Variable tooth worm

Details Variable tooth worm Variable tooth worm

1998-07-15

2001-01-23

Fenstermacher, David (Department: 3682)

Machine element or mechanism

Gearing

Directly cooperating gears

C074S458000

Reexamination Certificate

active

06176148

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a component of a worm gear set used for a gear transmission mechanism.
BACKGROUND OF THE INVENTION
According to the classification of the helicoid shape of thread teeth on worm shaft bodies, the known worms in the prior art can mainly be classified as involute helicoid worms, prolate-involute helicoid worms and Archimedes worms, etc. Both the tip surface (outer envelope) and the reference circle (tooth flank) of this type of worms are a cylinder. Moreover, in recent years there appear K-form cylindrical worms and hollow flank worms, etc. They are all constructed as cylindrical worms. They have the advantages of a lower heat value (i.e., heat generated) and lower requirements for the assembly and adjustment of the center distance and axial position because of a lower number of teeth which are simultaneously meshing, but they have the disadvantages of lower loading capacity and lower transmission efficiency. Therefore, toroidal worm and worm gear transmissions have been proposed which also consist of a shaft body with thread teeth. The tip surface and reference circle of the toroidal worm are not a cylinder, but a concave circular-arc revolution which is formed by a sector of a concave circular-arc rotating around the worm axis. The tip surface therefore has a concave face as disclosed, for example, in the Japanese Patents Nos. 7-42813 and 5-196115. As compared with normal cylindrical worm transmissions, the toroidal worm transmissions have the advantages of less wear, higher transmission efficiency, more simultaneously-meshing teeth and larger loading capacity as well as the ability to bear impact loads. However, these toroidal worm transmissions have some disadvantages such as a greater meshing heat value, the requirement of a housing with a larger volume and more lubricating oil volume as well as more radiating (cooling) ribs. The service life of the associated bearings becomes shorter due to a higher oil temperature. The worm gear sets are sensitive to center distance and axial assembly position. Therefore, they require higher accuracy in center distance and axial position, thus increasing the manufacturing cost.
SUMMARY OF THE INVENTION
Therefore, a principal object of the present invention is to provide a variable tooth worm which possesses the advantages of the above two types of worms such as lower heat value, lower requirements of assembly and adjustment for center distance and axial position, larger loading capacity, higher transmission efficiency and easier manufacture as well as better economy so as to avoid the shortcomings in the prior art.
The variable tooth worm provided herein comprises a shaft body with thread teeth having a tooth flank. In accordance with the present invention, the tip surface of the teeth is a cylinder or crowning surface, while the reference circle of the tooth flank is a revolution generated by a section of curved line. With this arrangement, the worm products are available with a variable tooth thickness and variable tooth height.
Whether the tip surface of the teeth is a cylinder or a crowning surface, the teeth at two ends along the length of the variable tooth worm are the thickest and the shortest, and gradually vary towards the middle portion, where the tooth is the thinnest and the highest. The performance of the variable tooth worm according to the present invention is between that of cylindrical worms and toroidal worms. It possesses the advantages of the above two types of worms, but avoids their disadvantages.
Under the conditions of meeting with the above-mentioned structure requirements, the helicoid shape of thread teeth on the shaft body of variable tooth worms, the practical structure of other parts such as the module, starts, rotating direction and complete dimension may all be designed according to the given practical situation. They do not affect the useful performance of the variable tooth worms.
As is the case with worms in the prior art, the worm gears can be machined by using a hob corresponding to the shape of variable tooth worms.


REFERENCES:
patent: 73095 (1868-01-01), Harrigan et al.
patent: 264428 (1882-09-01), Albro
patent: 493493 (1893-03-01), Fowler
patent: 3106103 (1963-10-01), Smith
patent: 3728907 (1973-04-01), Stade
patent: 4047449 (1977-09-01), Popov
patent: 4685346 (1987-08-01), Brackett
patent: 5605071 (1997-02-01), Buchanan, Jr.
patent: 602620 (1948-05-01), None
patent: 715462 (1954-09-01), None
patent: 513833 (1954-09-01), None
patent: 5-196115 (1993-08-01), None
patent: 7-42813 (1995-02-01), None

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