Planetary gear transmission systems or components – Planetary gearing or element – Coaxial teeth around planet pinion engage axially spaced...
Reexamination Certificate
2000-04-28
2002-02-19
Marmor, Charles A (Department: 3681)
Planetary gear transmission systems or components
Planetary gearing or element
Coaxial teeth around planet pinion engage axially spaced...
Reexamination Certificate
active
06348022
ABSTRACT:
1. FIELD OF THE INVENTION
This invention relates to a planetary gear transmission apparatus and particularly to a planetary reduction gear that is able to reduce high speed motor rotation and to increase torque.
2. BACKGROUND OF THE INVENTION
Motor rotation transmission usually uses a gear set for reducing or increasing rotation speed. The planetary gear transmission has high variable speed ration and is widely used in many different type of mechanical transmission application.
FIGS. 1 and 2
illustrate a conventional gear transmission device
10
which includes a sun gear
11
, a first inner gear ring
12
, a second inner gear ring
13
and a planetary gear set
14
consisting of a plurality of planetary gears
141
.
The first and second inner gear ring
12
and
13
have respectively a plurality of teeth
121
and
131
formed therein. The first inner gear ring
12
has a circular space with an inside diameter slightly larger than the outside diameter of the second inner gear ring
13
for housing the second inner gear ring
13
therein and forming a hollow compartment within the first and second inner gear ring. The planetary gear set
14
has a pair of planetary gears
141
each being held between a pair of gear racks
142
by a pin
143
, and engages respectively with the first and second inner gear ring
12
and
13
. The assembled planetary gear set
14
is held in the hollow compartment. When in use, a sun gear
11
engages with the planetary gears
141
at a left half portion thereof which in turn engages with the first inner gear ring
12
(shown in
FIG. 2
) for driving the planetary gears
141
. As the first inner gear
12
is usually serving as a power input ring, the rotating planetary gears
141
then drive the second inner gear ring
13
rotating for output power at reduced speed. The teeth number of the first inner gear ring
12
usually is less than the second inner gear ring
13
. Hence the crown and root circles of the first inner gear ring
12
are smaller than those of the second inner gear ring
13
. For the planetary gears
141
to engage both with the first and second inner gear rings
12
and
13
, the teeth profile of the planetary gears
141
should be made in a step manner to match different size of crown and root circles. For instance, the left half portion of the planetary gears
141
has a lower teeth profile for engaging with the first inner gear ring
12
while the right half portion has a higher teeth profile for engaging with the second inner gear ring
13
. The design and fabrication of the planetary gears
141
thus become more complicated and expensive. The high profile teeth has narrower teeth crown which tends to produce noise and is prone to rupture.
Furthermore, the sun gear
11
engages with only a half section of the axial length of the planetary gears
141
. The axial positioning and alignment between the gears is difficult to attain at precise level and may result in vibration and noise production. The high speed rotation also tends to create vibration result from torque and may result in high friction and temperature, lower transmission efficiency, accelerated wearing and lower durability.
Moreover heat treatment during fabrication of the planetary gears
141
will have high stress concentration happened at the comer section like the juncture of step teeth which may result in teeth rupture under high speed or high work load condition.
In order to remedy the problems set forth above, the components of the gear transmission device
10
have to be made of higher strength steel at a greater size. Hence it is mostly used in large size transmission means such as premixture concrete truck, heavy truck and the like. It rarely being used in smaller size apparatus such as electric power hand-tools in which gear transmission means are mostly made by lower cost powder metallurgy technique.
There is another problem for the conventional transmission device
10
. The friction contact (other than teeth bearing surface) between the rotating elements is usually plane contact which has high friction coefficient. A slight deviation between the contact surface may result in vibration. Friction induced temperature is high and easily reaches above 100° C., and may result in poorer lubrication effect. Hence transmission efficiency of the conventional gear transmission device is usually lower than 0.9. There is still a room for improvement.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a planetary gear transmission apparatus, which is lower cost to fabricate and assemble, has lower noise during operation, has longer durability and may be used in small size devices.
It is another object of this invention to provide a planetary gear transmission apparatus that has lower friction and operation temperature and enhanced transmission efficiency.
In one aspect, the transmission apparatus of this invention includes a sun gear, a first inner gear ring, a second inner gear ring and a planetary gear set consisting of a plurality of planetary gears. The first inner gear ring has an increased tooth root circle, larger tooth space and smaller teeth thickness. The second inner gear ring has a reduced tooth root circle, smaller tooth space and larger tooth thickness. The first and second inner gear rings have substantially same size of tooth root circle. The planetary gear has uniform teeth profile on a barrel type member. Hence stress concentration may be avoided. The apparatus may be made smaller size at lower cost. The friction contact surface between the rotation elements are formed in a curved plane so that friction loss and heat may be reduced.
In another aspect, the teeth of the inner gear ring is fabricated by gear rack cutting. For the first inner gear ring, the tooth crown height is increased by about 20-35% than regular value (e.g., the value for making the conventional tooth as which illustrated in FIGS.
1
and
2
). The tooth root height is reduced by about 10-25% and the tooth thickness is increased by about 2-10% than regular value. For the second inner gear ring, the tooth crown height is reduced by about 1-5% tooth root height is increased by about 1-5% and tooth thickness is reduced by about 1-8% than regular value.
Each planetary gear is held between a pair of gear racks by a pin with about 0.1-0.15 mm of tolerance between the gear and the rack for the gear to rotate smoothly between the racks. The contact surface between the gear ring and the rack has a curvature of about 20-50 times of the gear diameter.
REFERENCES:
patent: 3675510 (1972-07-01), Duggar
patent: 4429594 (1984-02-01), Heller
patent: 4850247 (1989-07-01), Yu
patent: 4942781 (1990-07-01), Hiri
patent: 226941 (1985-09-01), None
patent: 6388346 (1988-04-01), None
patent: 4131542 (1992-05-01), None
Ho Ha
Marmor Charles A
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