Epicyclic traction power transmission device with truncated conical rolling elements

Abstract

An actuator comprising a sun roller (104), a planetary roller (102), an auxiliary roller (103), and a fixed crown (101), wherein the sun roller (104) is central, the fixed crown (101) is positioned outside all elements, the auxiliary roller (103) is positioned between the planetary roller (102) and the fixed crown (101), and the planetary roller (102) is in contact with the sun roller (104), the auxiliary roller (103), and the fixed crown (101), in an actuator, An actuator characterized in that the sun roller (104), planetary roller (102), auxiliary roller (103), and fixed crown (101) all have the geometry of a frustocone or truncated cone. A power transmission device is achieved that provides a simple method for changing the preload on the rolling contact elements, thereby providing a means to improve the torque density and mechanical efficiency of the power transmission device.

Description

Technical Field

[0001] Object of the Invention An object of the present invention is to provide a means for improving the torque density and mechanical efficiency of a power transmission device by enabling the change of preload on a rolling contact element, and is an epicyclic traction power transmission device provided with frustum-shaped rolling elements, as indicated by the name of the invention.

[0002] The present invention is characterized by the special design and configuration of all elements that are part of an epicyclic gear, which enables the change of preload on the rolling contact element, and as a result, improves the torque density and mechanical efficiency of the power transmission device.

[0003] Therefore, the present invention is included in the scope of an epicyclic gear power transmission device or a planetary gear power transmission device.

Background Art

[0004] Many systems use an epicyclic gear power transmission device or a planetary gear power transmission device (PGT) because of their high mechanical efficiency and high torque density. An important aspect that sometimes limits the use of a traction drive is typically its specific torque, that is, the output torque or maximum torque per unit mass is generally low, and its torque density, the torque output per unit volume is low. Considerable effort and resources have been invested in various industries to develop a traction drive having a torque density similar to that of a planetary gear power transmission device.

[0005] The life of a rolling contact component is greatly affected by the radius of the contact component. Therefore, the design of a compact traction unit is difficult because the smaller the radius of the rolling component, the higher the contact stress, and as a result, the fatigue life of the power transmission device becomes shorter.

[0006] Prior art known is U.S. Patent No. 11473653(B2), which has a central roller that functions as a sun, three planetary rollers, and a series of auxiliary rollers that roll in contact with these hollow planets and transmit the orbital motion and torque load of these planets around the sun to the planetary carrier.

[0007] Unlike geared power transmissions, the change in maximum shear stress experienced by rolling contact components in an epicyclic traction power transmission, lubricated with a set preload, due to torque load is only on the order of 3-5%. For an epicyclic traction drive to operate, the preload must be set so that the rollers transmit a given maximum torque without slipping. In practice, this means that in most operating envelopes of traction power transmissions, the preload is unnecessarily high, resulting in a shorter service life and reduced mechanical efficiency of the power transmission.

[0008] To solve this problem, NASA and others have developed torque-based variable preload systems [1, 2, 3, 4]. These mechanisms function as highly rigid torsional springs, increasing or decreasing the preload in proportion to the torque transmitted by the device. While these systems tend to require axial preloading, one or two design proposals advocate for mechanisms that apply radial preloading [5].

[0009] 1.DM Williams and DP Kuban. (1989)Traction Drive Force Transmission For Telerobotic joints. NASA Technical Note.

[0010] 2. Montgomery, M. and Sherill, R. (2020). U.S. Patent No. 10,539,210(B2), Angular Contact Ball Ramps for Driven Turbocharger.

[0011] 3. Montgomery, M. and Sherill, R. (2010). U.S. Patent No. 10,655,711(B2), Single Angular ball ramp for driven Turbocharger.

[0012] 4. Petersen, R., Mockel, J., Lutz, A., and Hanke, S. (2016). U.S. Patent No. 9,341,245(B2), Friction Roller Planetary Gearing and Speed-Changing and Differential Gearing.

[0013] 5. Chen, D., and Du, X. (2013). Development of self-adaptively loading for planetary roller traction-drive transmission. Journal of Chemical and Pharmaceutical Research, 5(9), pp. 498-506. [Overview of the project] [Problems that the invention aims to solve]

[0014] Therefore, the object of the present invention is to overcome the shortcomings of the prior art by developing an epicyclic traction power transmission device as described below, without using a pre-pressurized system and without reducing the service life and mechanical efficiency of the power transmission device, the essence of which is contained in the first claim. [Means for solving the problem]

[0015] The subject matter of the present invention is essentially contained in the independent claims, and different embodiments are contained in the dependent claims. The subject of the present invention is an epicyclic traction power transmission device in which rolling contact elements have a shape that allows for axial preloading. From a practical standpoint, this means that the rolling elements can be any combination of axially symmetric geometric shapes, and that the contact areas of these geometric shapes contact at an angle such that they are not aligned parallel to the axis of the power transmission device, but rather the resulting axial preload allows for a collectively applied normal load.

[0016] This key difference provides a simple method for changing the preload on rolling contact elements, thereby providing a means to improve the torque density and mechanical efficiency of the power transmission system. While this topology offers some improvements, it also introduces new problems. For example, in order for planetary rolling elements to maintain alignment even under high preload, they need to be restricted in some way in the axial direction. This has traditionally been done in roller bearings by providing small flanges at both ends of the inner and outer rings that slide against their end faces to keep the rollers properly aligned. In roller bearings where the coefficient of friction is very low due to lubrication, this results in a small and manageable decrease in mechanical efficiency. In traction power transmissions, where the coefficient of friction obtained with special traction lubricants can reach values ​​two orders of magnitude higher than in lubricated roller bearings, friction loss is not a small problem. Another problem that designers may face is that using a variable preload system in applications where positional accuracy is critical can introduce mechanical play, especially when the direction of movement changes.

[0017] Unless otherwise indicated, all technical and scientific elements used herein have meanings that are commonly understood by those skilled in the art to which the present invention pertains. In carrying out the present invention, procedures and materials similar or equivalent to those described herein may be used.

[0018] In this specification and in the claims, “comprise” and its variations are not intended to exclude other technical features, additives, components, or processes. Other purposes, advantages, and features of the present invention will be inferred to those skilled in the art, partly from this specification and partly from practices of the invention.

[0019] To supplement the description made herein and to aid in a better understanding of the features of the present invention, a set of drawings, as an integral part of the above description, are provided in accordance with a preferred practical embodiment, and these drawings illustrate, in an exemplary and non-limiting manner, the following: [Brief explanation of the drawing]

[0020] [Figure 1] This is a front view of the epicyclic traction power transmission system. [Figure 2] This is a diametrical cross-sectional view of the power transmission device. [Modes for carrying out the invention]

[0021] In view of the figures, preferred embodiments of the proposed invention will be described below. Figure 1 shows that the proposed invention comprises a solar roller (104), a planetary roller (102), an auxiliary roller (103), and a fixed crown (101), with the solar roller (104) in the center and the fixed crown (101) positioned outside all the elements, the auxiliary roller (103) positioned between the planetary roller (102) and the fixed crown (101), the planetary roller (102) in contact with the solar roller (104), the auxiliary roller (103), and the fixed crown (101), and that the solar roller (104), planetary roller (102), auxiliary roller (103), and fixed crown (101) all have a frustoconical geometric shape or a frustoconical shape.

[0022] The axes of all conical elements coincide at a point, and at this time, the end portions having the minimum diameter of each frustum-shaped conical element are located on the side closer to the point where the axis intersects. This configuration provides the most efficient rolling contact conditions between the conical elements compared to other configurations.

[0023] FIG. 2 more clearly shows that the cross-sections of the sun roller (104), the planetary roller (102), the auxiliary roller (103), and the fixed crown (101) have a frustum-shaped cross-section, and all of these can be preloaded by the resulting axial preload force.

[0024] The axes at both ends of the tapered auxiliary roller can be attached to the planetary carrier by rolling bearings. Therefore, the rollers are brought into contact with each other at an angle with respect to their axes, and as a result, they are preloaded by the axial resultant force, which makes it possible to change the preload of different rollers.

[0025] Although the nature of the present invention has been fully described together with the method of implementing the present invention, in essence, the present invention may be implemented in other embodiments that are different in details from those shown as examples, and here it is specified that the protection is equally applicable as long as the main principle is not modified, changed, or corrected.

Claims

1. In an epicyclic traction power transmission device, a sun roller (104), a planetary roller (102), an auxiliary roller (103), and a fixed crown (101) are provided, wherein the sun roller (104) is located in the center, the fixed crown (101) is positioned outside all the elements, the auxiliary roller (103) is positioned between the planetary roller (102) and the fixed crown (101), and the planetary roller (102) is in contact with the sun roller (104), the auxiliary roller (103), and the fixed crown (101). An epicyclic traction power transmission device characterized in that the solar roller (104), the planetary roller (102), the auxiliary roller (103), and the fixed crown (101) all have a frustoconical or truncated cone geometry.

2. The epicyclic traction power transmission device according to claim 1, characterized in that the shafts at both ends of the auxiliary roller (103) are connected to the planetary carrier by roller bearings.

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