Planetary gear

Details Planetary gear Planetary gear

1999-09-27

2001-04-24

Marmor, Charles A (Department: 3681)

Planetary gear transmission systems or components

Planetary gearing or element

Coaxial teeth around planet pinion engage axially spaced...

C475S342000, C475S344000, C475S348000

Reexamination Certificate

active

06220984

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a planetary gear having a sun gear connected with a driven central shaft, a geared wheel, a group of first stepped planetary gears, a group of second stepped planetary gears, wherein all stepped planetary gears are supported on a common planet carrier, the number of the second stepped planetary gears corresponds to half the number of the first stepped planetary gears, the large step wheels of the second planetary gears engage the sun gear, the small step wheels of the second stepped planetary gears simultaneously engage one pair of adjoining large step wheels of the first stepped planetary gear and all small step wheels of the first stepped planetary gear engage the ring gear.
A planetary gear of this type has been described in the applicant's not published international application PCT/EP97/00288. The gear is designed as a so-called Wolfrom gear and, in particular, is very adequate for the production of very high total speed ratios with a good utilization of installation space. It further stands out by a high transmission quality, high efficiency and relatively low inertia moment, and by easy assemblage and low production costs.
U.S. Pat. No. 1,499,762 has disclosed a Wolfrom gear with stepped planetary gears in which the geared wheels have conical design and the planetary axles extend radially inclined toward the gear main axle.
Wolfrom gears are distinguished above all by high speed ratios with a very compact type of construction, but Wolfrom gears also have a few disadvantage basically conditioned. On the teeth (ring gears and the planets engaging the geared wheels) at the output are under a high torque load, elevated rotation speeds and relative speeds. This leads to elevated idle power requirements, reduced efficiency and under certain operating conditions to problems with vibration and noise. The planet carrier moving at relatively high rotational speed contributes to a substantial inertia moment of the gear. A high inertia moment produces high reaction torques in the event of abrupt changes in rotational speed.
Although compared to the Wolfrom gears, spur gear drives have more efficiency; they do not attain the great space and moment compactness of planetary gears. Other disadvantages of spur gear drives, compared to planetary gears, are that they are not well-suited to coaxial arrangement of input and output, and that pitch errors in the teeth of each wheel of a gear chain fully affect the transmission quality between input and output.
With conventional one-step planetary gears only with limitations, is it possible to implement very high speed ratios, due to problems with the tooth geometry in the very small gears needed therefor.
Already known planetary gears with several planet steps, connected in series, have a great number of parts and a large axial space.
The problem to be solved by the invention is to obtain high speed ratios with great space and moment compactness, to clearly improve the transmission quality and efficiency and at the same time to reduce the inertia moment and the tendency to vibration. In addition, the gear must be favorably produced and require no great assemblage expenditure.
SUMMARY OF THE INVENTION
The problem is solved by a planetary gear having a sun gear (
2
) connected with a driven central shaft (
20
), a ring gear (
12
), a group of first stepped planetary gears (
8
,
10
), a group of second stepped planetary gears (
4
,
6
) wherein all stepped planetary gears are supported in a common planet carrier (
24
), the number of the second stepped planetary gears (
4
,
6
) corresponding to half the number of the first stepped planetary gears (
8
,
10
), the large step wheels (
4
) of the second stepped planetary gears engage the sun gear (
2
), the small step wheels (
6
) of the second stepped planetary gears engage simultaneously one pair of adjacent large step wheels (
8
) of the first stepped planetary gears, all small step wheels (
10
) of the first stepped planetary gears engage the ring gear (
12
), the planet carrier (
24
) being the gear output and the ring gear (
12
) the supporting element. Advantageous developments and other embodiments of the invention are given in the sub-claims.
The input torque is distributed by the sun gear; first among several large step wheels of the second stepped planetary gears. After the speed ratio by the second stepped planetary gears, the torque is again distributed by the small step wheels of the second stepped planetary gears among double the number of tooth engagements than with the first stepped planetary gears. According to the speed ratio step, as the torque increases so does advantageously increase the number of tooth engagements to which said torque is distributed. A very uniform load distribution is achieved.
The gear parts, loaded with high torque, which rotate slowly because of their necessary dimension, take a high portion on the total transmission volume. No gear parts, moving at high speed, are exposed to a high torque load and, therefore, are accordingly lightly constructed. For the gear, a very low inertia moment altogether results therefrom.
Low peripheral speeds on the teeth make possible the use of compact, quick revolving prime movers.
In addition, the arrangement by pairs of the first stepped planetary gears results in an easy adaptation to different torques to be transmitted with many equal parts. For higher torques, one other pair of first stepped planetary gears with another pair of second stepped planetary gears are simply placed on the planet carrier.
A gear, according to the invention, has the advantage of making possible high speed ratios in a narrow space with small internal rolling outputs. Thereby it has a high degree of efficiency. Starting and other friction torques remain small. Besides, the low rolling outputs have a positive effect on the noise characteristic, as does the stability of the slight gear play during the service life.
In the embodiment as planetary gear, the further advantage obtained in the substantially horizontal position of the gear main axle, with a partial oil filling of the gear, is that the stepped planetary gears are regularly immersed in oil while the planet carrier rotates. All teeth and planetary bearings are in this manner optimally lubricated.
In the alternative embodiment, the gear has a total speed ratio higher by 1. In this embodiment, the input and output shafts rotate in the same direction.
By virtue of advantageous development, wherein the connecting lines (
14
,
16
) from the wheel central point of a small step wheel (
6
) of a second stepped planetary gears to the wheel central points of the two adjacent large step wheels (
8
) of the first stepped planetary gears form an angle (
18
) of between 180° and 195°, there results extensively weighed off teeth forces on the small step wheels of the second stepped planetary gears whereby the support thereof is easier and simpler. The exact angle for the arrangement of the second stepped planetary gears can be selected according to the assemblage conditions.
A ring gear of conical design, combined with an axial adjustability of the ring gear in relation to the first stepped planetary gears along the gear main axle, makes good adjustability of the play between teeth of the small step wheels of the first stepped planetary and the ring gear possible.
With the development according to claim
5
, the advantage is obtained that an axial play of the bearings of the first stepped planetary gears does not affect the total play of the gear. An exact axial position is not required. The adjustment expenditure is thus reduced and a small gear play is attained.
Another advantageous possibility of the small step wheels to the conicity of the geared, wheel is wherein the small step wheels (
10
) of the first stepped planetary gears have a conical design and the axles of rotation of the first stepped planetary gears are parallel to the main axle of the gear. In this case, the planet carrier is easier to make since no inclined planetary axles ar

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