Eccentric planetary gearing

Details Eccentric planetary gearing Eccentric planetary gearing

2002-03-25

2003-10-14

Marmor, Charles A (Department: 3682)

Planetary gear transmission systems or components

Planet periphery surrounds axis of interacting gear

Gear has plural circumferential tooth sets

C475S181000

Reexamination Certificate

active

06632152

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority from PCT application Ser. No. PCT/BG00/00025 filed on Sep. 27, 2000, which in turn claims priority from Bulgarian patent application Ser. No. 103769 filed on Sep. 29, 1999.
BACKGROUND OF THE INVENTION
This invention relates to an eccentric planetary gearing and can find commercial application first and foremost if implemented as a gear-type speed reducer in the driving systems of industrial machines and equipment.
In the present description, in correspondence with the International Patent Classification, Seventh Edition, Subclass F16H 1/32, by eccentric planetary gearing is meant a planetary gearing in which, as distinct from other planetary gearings, the central axis of the gearing lies inside the periphery of at least one planetary gear.
An eccentric planetary gearing, comprising two internally toothed gears, a double-ring externally toothed planetary gear and a planet carrier, is known in the prior art. The double-ring externally toothed planetary gear has the design of a cluster gear comprising two externally toothed gear rings of different diameters coaxially aligned and consecutively disposed relative to one another. The internally toothed gears are coaxially aligned and consecutively disposed relative to one another and their common axis is central axis of the gearing. One of the internally toothed gears is mounted for a rotation, and the other is held in a fixed position and does not rotate. The planet carrier is mounted for rotation about the central axis of the gearing. The double-ring externally toothed planetary gear is rotatably mounted on the planet carrier. The axis of the double-ring externally toothed planetary gear is parallel to and offset from the central axis of the gearing, and the respective eccentricity is less than the outside radius of the double-ring externally toothed planetary gear so that the central axis of the gearing lies inside the periphery of the double-ring externally toothed planetary gear. Each of the internally toothed gears is in meshing engagement with a respective gear ring of the double-ring externally toothed planetary gear.
Usually, the planet carrier is constructed as an eccentric shaft, the latter being integral with a high-speed shaft of the gearing. The rotatable internally toothed gear is secured to a slow-speed shaft of the gearing. The high-speed and the slow-speed shafts of the gearing are coaxially aligned and their common axis is coincident with the central axis of the gearing. An eccentric planetary gearing of such design, comprising two counterweights secured to the eccentric shaft, is described, for example, in U.S. Pat. No. 4,014,224. The counterweights are disposed on both sides of the double-ring externally toothed planetary gear. The eccentric shaft, the double-ring externally toothed planetary gear and the counterweights constitute a system which is statically and dynamically balanced in respect to the central axis of the gearing.
In addition to the above-described eccentric planetary gearing, some modifications of its should be considered herein as background of the invention. For example, the planet carrier can be constructed as a built-up crankshaft of composite and collapsible design. A planet carrier of a similar design is described, for example, in U.S. Pat. No. 2,481,627. It is supposed in the present description that such a modification of the above-described eccentric planetary gearing can be classified as a combination of known gear designs, such combination being obvious to those skilled in the art.
Yet another modification of the above-described eccentric planetary gearing should be considered herein as background of the invention. This modification is characterized in that the corresponding planet carrier is composed of support means for providing the rotatable mounting of the planet carrier itself and the rotatable mounting of the double-ring externally toothed planetary gear, said support means being integrated into a rigid member through an interjacent crescent-shaped section disposed within the space between the double-ring externally toothed planetary gear and the internally toothed gears. A planet carrier of a similar design is described, for example, in U.S. Pat. No. 4,825,726. It is supposed in the present description that such a modification of the above-described eccentric planetary gearing can be classified as a combination of known gear designs, such combination being obvious to those skilled in the art.
Depending on the specific design of the planet carrier, the above-described eccentric planetary gearing and its modifications can have various advantages and disadvantages.
When the planet carrier is constructed as an eccentric shaft, the eccentric planetary gearing is characterized by relatively high torque-transmitting capacity, but at the same time it has low mechanical efficiency in operation and the frictional losses are much higher than for ordinary gearings. In Kudriavtzev V. N. et al.,
Planetary transmissions, Handbook
, Mashinostroenie Publishing House, Leningrad, 1977, in Russian, at page 36-43, it is stated that if the eccentric planetary gearing operates as a gear-type speed reducer, the following functional relation should be valid:
E
=
1
1
+
&LeftBracketingBar;
R
-
1
&RightBracketingBar;
⁢
L
P
(
1
)
wherein E is the mechanical efficiency, R is the gear ratio, and L
P
is a provisional dimensionless parameter, equal to the coefficient of frictional losses with which the gearing would operate should the planet carrier be fixed in a stationary position and the housing accordingly released. Supposing such an imaginary experiment is conducted, the eccentric planetary gearing would then be transformed into an ordinary gearing with fixed axes of rotation of all gears and with a total gear ratio close to 1.00, and then the respective coefficient of frictional losses would accordingly be of the order of less than one percent. For the purpose of clarification of formula (1) it should be specified that if, for example, R=101 and L
P
=0.0025, then E=0.80. The coefficient of frictional losses of a gearing is the sum total of the coefficients of frictional losses in the meshing and in the bearings, as well as of the coefficient of frictional losses caused by the hydraulic resistance of the lubricating liquid. The methods for estimating the coefficient of frictional losses in the meshing, known from the existing references and discussed, for example, at page 36-43 of the above-referenced handbook, are confined to the implementation of simple calculation schemes and are represented by functional relations of a limited number. These methods for estimating the coefficient of frictional losses in the meshing are inappropriate when referring to the eccentric planetary gearings because the meshing in the real gearing, in this case, differs substantially from the theoretic one. This is due to the fact that the difference between the number of teeth of the gears in meshing engagement of internal gearset is usually too small in this case, and this peculiarity, in combination with the inevitable errors in the gearing and with the elastic deformation of the teeth in mesh, is the reason why the number of tooth pairs simultaneously in mesh is considerably greater than the theoretic one. That is why, in this case, estimating the coefficient of frictional losses in the meshing requires the elaboration of complex computer models and the implementation of appropriate calculation methods, such as Simulation and Finite Element Analyses. The experience suggests that, as a rule, the decrease in the absolute value of the gear ratio of an eccentric planetary gearing result in an increase in the corresponding mechanical efficiency. At the same time, when designing eccentric planetary gearing in which the planet carrier is constructed as an eccentric shaft, there are certain limitations in the case of decreasing the absolute value of the gear ratio. In this case, as stated at page 13-15 of the above-referenced handbo

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