High reduction planetary gear with intermediate shafts

Details High reduction planetary gear with intermediate shafts High reduction planetary gear with intermediate shafts

1998-06-25

2000-09-26

Marmor, Charles A

Planetary gear transmission systems or components

Planetary gearing or element

Coaxial teeth around planet pinion engage axially spaced...

475338, 475336, F16H 5708

Patent

active

061236403

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a planetary gear of the type described in more detail below.


BACKGROUND OF THE INVENTION

Planetary gears of this type are generally known. The planet wheels each have two sets of teeth for permanent meshing with two ring gears. They thus form a so-called Wolfrom coupling gear. The speed ratio of the planet carrier to the ring gear provided for the output is designated the Wolfrom ratio. In the planetary gears known already, the central sun wheel meshes directly with the planet wheels and forms a preliminary ratio with the planet wheels and the stationary ring gear of the two ring gears. The Wolfrom ratio, multiplied by the preliminary ratio, results in the total ratio.
Many tasks for such planetary gears, especially in robot technology, require high ratios with, for example, i=170 or still higher. But it is often desirable that the diameter of the central sun wheel not be too small since, for example, it may be provided with a hollow shaft for accommodating a shaft end of an engine or for conveying robot parts. Besides, it is often desirable to limit the Wolfrom ratio. But it is disadvantageous that moderate values regarding tooth rolling activity, noise, efficiency, heating and inertia result only from a limitation of the speeds of the planet carrier. On the other hand, with a limited Wolfrom ratio it also becomes difficult also to achieve elevated total ratios.
Since the driving central sun wheel is directly engaged with the planet wheels, in the formerly known planetary gear designs, it must be equal to them in module and other toothing data.
In the solutions known already, the obtention of high ratios brings, along with the above mentioned disadvantages, the further disadvantage that in cases having a maximum number of three planetary wheels, a weak torque tightness exists and problems can result regarding the uniformity of the output torque. The small number of sun wheel teeth needed for a sufficiently high total ratio brings, together with the problems associated with the parts of a robot environment, the added disadvantages relating to tooth shape, such as undercut or pointed tips. A further disadvantage is that this requires a relatively high number of teeth on ring gears having relatively small modules, and the torque tightness disadvantages resulting therefrom.
Therefore, the problem on which this invention is based is to obtain high ratios with a good utilization of installation space (torque tightness) while, as far as possible, overcoming the above mentioned disadvantages or at least clearly reducing them. In addition, transmission quality is to be improved, that is, vibrations and angular transmission errors must be minimized. Also, the planetary gear must have favorable production characteristics and require no elevated assembly cost.


SUMMARY OF THE INVENTION

The development of the planetary gear, in accordance with the invention, makes possible high preliminary ratios whereby a moderate Wolfrom ratio can be selected in spite of a high total ratio. In addition, internal tooth rolling activity, noise, efficiency, heating and inertia remain within advantageous limits. This means that good conditions exist for the gear play to have a long lasting stability. By virtue of the moderate Wolfrom ratio it is also possible to use additional planetary wheels in the number of 4, 6 or in pairs, when needed. Also, as a rule, a moderate or lesser Wolfrom ratio means greater optional differences in the number of teeth of the two ring gears. As result of assembly conditions, the number of planet wheels is generally in direct relationship with the difference in the number between teeth of the two ring gears.
In addition, a high number of planet wheels results in a good torque tightness. The intermediate shafts can be accommodated in the planet carrier practically without requiring additional space. Further, it is advantageous that the central sun wheel can be designed to have a hollow shaft depending on the desired total ratio, since the diameter of the sun wheel teeth can alway

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