Planetary gear transmission systems or components – Planetary gearing or element
Patent
1997-12-17
1999-09-28
Marmor, Charles A
Planetary gear transmission systems or components
Planetary gearing or element
475342, 475344, F16H 5708
Patent
active
059578041
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a planetary gear having a driven sun wheel, two internally toothed hollow wheels of which one is fixedly mounted and the other is rotatably mounted and forms the output. Several planetary wheels are provided which are mounted upon planet axles of a planet carrier. The planetary wheels are in permanent tooth contact with the sun wheel and the hollow wheels.
Many tasks in the transmission technology require the obtention of extreme transmission ratios. Planetary gears are especially well suited to combine high transmission ratios with a compact design. The Wolfrom coupling gear, which with a high transmission ratio still has good efficiency, constitutes such a planetary gear. The Wolfrom gear is designed as a specially simple coupling gear. The input is connected with a sun wheel which interacts with a planetary wheel block. The planetary wheel rests on the internally toothed hollow wheel which is fixed to the housing. A web runs along idly as a planet carrier. The motion is passed on via the planet carrier and the planetary wheel(s) (step planet). The planetary wheel, for its part, meshes again with an internally toothed hollow wheel which forms the output. The arrangement described is adequate for a compact design which, in a narrow space, makes high transmission densities possible (see Klein: Theoretical Principles for the Design of Wolfrom Coupling Gears, in Maschinenmarkt 1982, pages 341 to 344).
It is especially in handling engineering that, for power transmission of high-speed prime movers, strongly reducing gears are needed. A case of utilization is constituted by industrial robots in which planetary gears are used. Primary importance is attached to the planetary gear for the precision of an industrial robot. Precise motion sequences, with the highest repetitive accuracy, must be ensured. For such a planetary gear the following criteria are of special importance: small, adjustable torsional play, great rigidity, high efficiency, low heat development, slight vibration and a high noise level. The overall efficiency is also a decisive criterion for the fitness of the planetary gear. Locked-up stresses have a serious effect upon the overall efficiency due to the elevated inner rolling activity that results.
U.S. Pat. No. 4,106,366 has disclosed a planetary gear where an internally toothed hollow wheel is pressed upon the conically made planet wheels by means of compression springs. On account of the elevated tooth rolling activity, due to locked-up stresses, the overall efficiency is inadmissibly reduced here.
A planetary gear with planet wheels which have a continuous straight toothing is also known from U.S. Pat. No. 5,242,336. The disadvantage of this gear is that a relatively large contact-free axial intermediate space is required between both of the hollow wheels in order to compensate for the relatively great difference in the number of teeth of the two hollow wheels without extreme distortions of the contact ratios. Also said axial intermediate space naturally increases the axial length of the gear and reduces the rigidity thereof. Of considerable disadvantage is also the increase in drag torque since the planets and the planet carrier clearly become heavier due to said intermediate space. The dynamic properties of this drive are impaired by said construction, especially when the planet wheels and the planet carrier rotate at high speeds. Were it desired to eliminate said axial intermediate space, then considerable distortions of the contact ratios would be inevitable. Extreme values in the addendum modification coefficient of the hollow wheels result in pointed tooth gaps in the hollow wheels which also have an unfavorable effect upon the toothed tools. In addition, extreme values in the working pressure angle would cause noise, friction torque and abrasion problems.
From European patent application 0 627 575 has become known a Wolfrom planetary gear in which the planet wheels are distributed axially in two differently toothed areas. The pitch diameter of both toothed are
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Schulz Horst
Somschor Bernd
Marmor Charles A
Pang Roger
ZF Friedrichshafen AG
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