Planetary gear transmission systems or components – Electric or magnetic drive or control
Reexamination Certificate
2000-11-21
2002-09-03
Wright, Dirk (Department: 3681)
Planetary gear transmission systems or components
Electric or magnetic drive or control
C475S183000, C310S083000, C310S103000
Reexamination Certificate
active
06443868
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a frictional transmission (or tractional) apparatus which comprises a simple planetary roller mechanism having friction (or traction) rollers including a sun roller, a planetary roller (or rollers), and a ring roller, and a brake mechanism for braking rotation of these friction rollers. The invention also relates to a frictional transmission type rotational driving apparatus having the frictional transmission apparatus and a motor in combination, a series of the same, and a method of fabricating the frictional transmission apparatus.
2. Description of the Related Art
Conventionally, frictional transmission apparatuses comprising a simple planetary roller mechanism are known widely.
FIG. 8
schematically shows an example of such a conventional frictional transmission apparatus. This frictional transmission apparatus
1
comprises a simple planetary roller mechanism
10
arranged in an outer casing
9
(general view omitted). The simple planetary roller mechanism
10
has friction rollers including a sun roller
2
, a planetary roller
6
, and a ring roller
8
. The planetary roller
6
makes rolling contact with the outer periphery of the sun roller
2
and with the inner periphery of the ring roller
8
. The ring roller
8
is restricted in its rotation. Besides, a supporting pin is inserted through the planetary roller
6
so as to couple a carrier
4
to this simple planetary roller mechanism
10
.
In this frictional transmission apparatus
1
, the sun roller
2
and the carrier
4
make input/output elements, and the ring roller
8
a fixed element. Making the input element out of the sun roller
2
provides a speed reducing function, and making the output element out of the sun roller
2
a speed increasing function. Here, the ring roller
8
is fixed onto the part of the outer casing
9
.
FIG. 9
shows the embodiment of the structure in
FIG. 8
, or a rotational driving apparatus
100
of frictional transmission type devised by the present inventors (not yet known publicly as of this point of application). This rotational driving apparatus
100
comprises a simple planetary roller mechanism
28
and a motor
126
. The simple planetary roller mechanism
28
has friction rollers consisting of a sun roller
30
, a planetary roller (or rollers)
34
, and a ring roller
36
. The planetary roller
34
is retained by a carrier
32
, and makes rolling contact with the outer periphery of the sun roller
30
and with the inner periphery of the ring roller
36
. The ring roller
36
is restricted in its rotation. The motor
126
is coupled to the sun roller
30
to drive this sun roller
30
.
Specifically, a motor shaft
126
A of the motor
126
is coupled to the sun roller
30
via a parallel key. The motor
126
itself is fixed to a flange portion
38
B of a casing
38
which accommodates the simple planetary roller mechanism
28
.
This casing
38
has a ring-shaped fixing portion
38
A projected radially inward from its inner-peripheral side. The ring roller
36
is fixed to this fixing portion
38
A by a bolt
40
.
In the simple planetary roller mechanism
28
, the sun roller
30
makes an input element, the carrier
32
an output element, and the ring roller
36
a fixed element. The entire mechanism thus has a speed reducing function. That is, this rotational driving apparatus
100
has a structure of transmitting rotational power of the motor
126
to the sun roller
30
and outputting the same from the part of the carrier
32
with a predetermined reduction ratio.
The simple planetary roller mechanism
28
transmits the rotational power from the motor
126
by means of frictional forces or oil shearing forces (tractional forces) occurring between the respective contact surfaces of the friction rollers (tractional transmission). This allows smoother, quieter operation as compared with geared and other transmission structures.
Accordingly, in order to secure a predetermined transmission capability (transmittable torque) from the simple planetary roller mechanism
28
, sufficient frictional forces need to be produced between the individual friction rollers. The frictional forces are generally given by making the inside diameter of the ring roller
36
smaller than the sum of twice the diameter of the planetary roller
34
and the diameter of the sun roller
30
, i.e., applying a squeezing force to the ring roller
36
for elastic deformation. The larger the squeezing force, the larger the frictional forces between the friction rollers become, and these frictional forces in turn increase the transmittable torque of the simple planetary roller mechanism
28
. In contrast, smaller squeezing forces lower the transmittable torque. Incidentally, when the transmittable torque is higher (the squeezing forces are larger), the individual friction rollers increase in rotational resistance. This can lower the transmission efficiency of the rotational driving apparatus
100
and produce a low-durability problem of the simple planetary roller mechanism
28
due to rolling fatigue.
The rotational driving apparatus
100
mainly receives two merits from the adoption of the above-described simple planetary roller mechanism
28
. First, as stated already, power transmission can be performed more smoothly and quietly than in geared and other transmission structures. The result is that the efficiency of the rotational power transmission is enhanced to suppress the power consumption of the motor
126
, contributing to so-called “energy saving.” Second, since the friction rollers are relatively easy to fabricate as compared with gears and the like, the fabrication costs are reduced to make the entire rotational driving apparatus
100
“low-priced.”
Meanwhile, the adoption of this frictional transmission type simple planetary roller mechanism
28
brings about the following demerit. That is, due to the structure of transmitting rotational power by means of frictional forces, the respective contact surfaces of the rotating friction,rollers always bear some slight slips therebetween. This precludes a “strict” reduction ratio being maintained between the revolution speed of the sun roller
30
and the revolution speed of the carrier
32
all the time. Therefore, as long as this point is concerned, geared and other transmission structures are superior.
Considering actual use situations of such a motor in a reduction mechanism (rotational driving apparatus), however, the induction motor adopted involves a certain slip between its rotor and rotating field in the first place. Therefore, a strict reduction ratio need not be required of the reduction mechanism itself. That is, maintaining a coupled mating machine at a predetermined revolution speed typically requires measuring the mating machine or the like for revolution speed and performing feedback control onto the motor. Thus, “energy-saving” and “low-priced” simple planetary roller mechanisms better fit the current market needs than geared reduction mechanisms which are expensive through strict in reduction ratio.
Conventionally, there are many gear transmission type rotational driving apparatuses (so-called geared motors) with a brake mechanism added to their motor and the like. To the present inventors' knowledge, however, neither a frictional transmission type rotational driving apparatus with a brake mechanism exists on the market, nor a proposal to add a brake mechanism has been made under current conditions. The reason for this seems that there actually exist a number of difficulties as follows.
To be more specific, frictional transmission apparatuses with a simple planetary roller mechanism transmit power by means of frictional forces occurring between the respective contact surfaces of their friction rollers, and therefore a large rotational load applied thereto can easily produces a “slip” on the contact surfaces. Meanwhile, brake mechanisms in common use convert kinetic energy into thermal energy by means of friction between their brake ring and brake shoes. In
Minegishi Kiyoji
Tamenaga Jun
Arent Fox Kintner Plotkin & Kahn
Sumitomo Heavy Industrie's, Ltd.
Wright Dirk
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