Epicyclic traction transmission with truncated conical rolling elements

Abstract

An actuator comprises a sun wheel roller (104), a planet wheel roller (102), an auxiliary roller (103) and a fixed gear ring (101), the sun wheel roller (104) is located in the center, and the fixed gear ring (101) is located outside all elements. The auxiliary roller (103) is positioned between the planet wheel roller (102) and the fixed gear ring (101), and the planet wheel roller (102) is in contact with the sun wheel roller (104), the auxiliary roller (103) and the fixed gear ring (101), characterized in that the sun wheel roller (104), the planet wheel roller (102), the auxiliary roller (103) and the fixed gear ring (101) all have a truncated cone geometry or a truncated cone geometry. According to the invention, a transmission device is realized, which provides a simple method for changing the pre-tightening force on the rolling contact element, thereby providing an effective means for improving the torque density and the mechanical efficiency of the transmission device.

Description

TECHNICAL FIELD

[0001] As the title suggests, the object of the present invention is to provide a epicyclic traction drive with truncated conical rolling elements that enables to vary the pre-load on the rolling contact elements and thereby provide a method to improve the torque density and mechanical efficiency of the drive.

[0002] The present invention is characterized by the fact that each component element of the epicyclic gear has a special design and configuration that enables to vary the pre-load on the rolling contact elements and thereby provides an effective means to improve the torque density and mechanical efficiency of the drive.

[0003] Therefore, the present invention belongs to the technical field of epicyclic gear drives or planetary gear drives. BACKGROUND

[0004] Many systems employ epicyclic gear drives or planetary gear drives (PGTs) for their high mechanical efficiency and high torque density.

[0005] In some cases, a key factor limiting the application of traction units is their generally low specific torque (i.e. output torque or maximum torque per unit mass) and low torque density (torque output per unit volume). Industries are investing significant efforts and resources to develop traction drives with comparable torque density to planetary gear drives.

[0006] The service life of rolling contact components is greatly affected by the radius of the contact components. Therefore, the design of compact traction devices is challenging because the smaller the radius of the rolling components, the greater the contact stress and the shorter the fatigue life of the drive.

[0007] It is known in the art US 11473653 B2, which has a central roller that acts as a sun gear, three planetary rollers and a series of auxiliary rollers in rolling contact with a hollow planet wheel, which transmit the orbital motion of the planet wheel around the sun gear and the torque load to the planet carrier.

[0008] Unlike gear drives, in epicyclic traction drives with set pre-load lubrication, the maximum shear stress experienced by the rolling contact components varies by only 3-5% with the torque load. To operate the epicyclic traction drive properly, the pre-load must be set to ensure that the rollers transmit the given maximum torque without slipping. In practice, this means that in most operating environments of the traction drive, the pre-load is higher than actually needed, resulting in a shorter service life and lower mechanical efficiency of the drive.

[0009] To address this problem, agencies such as NASA have developed torque-dependent variable pre-load systems [1], [2], [3], [4]. These agencies act as extremely rigid torsional springs that increase or decrease the pre-load in proportion to the torque delivered by the device. These systems typically require the pre-load to be applied in the axial direction, although one or two proposed designs claim that their mechanisms can apply the pre-load in the radial direction [5].

[0010] [1] D. M. Williams and D. P. Kuban. (1989) Traction Drive Force Transmission For Telerobotic joints. NASA Technical Report.

[0011] [2] Montgomery, M. and Sherill, R. (2020) Angular Contact Ball Ramps for Driven Turbocharger. US 10,539,210 B2.

[0012] [3] Montgomery, M. and Sherill, R. (2010) Single Angular ball ramp for driven Turbocharger. US 10,655,711 B2.

[0013] [4] Petersen, R., Mockel, J., Lutz, A. and Hanke, S. (2016) Friction Roller Planetary Gearing and Speed-Changing and Differential gearing. US 9,341,245 B2.

[0014] [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), 498-506.

[0015] It is therefore the object of the present invention to overcome the drawbacks of the prior art, to avoid the use of a preloading system that leads to a reduced service life and a reduced mechanical efficiency of the transmission, and to develop a epicyclic traction transmission as described below, the core of which is set out in the independent claims. SUMMARY

[0016] The core of the present invention is set out in the independent claims, different embodiments are set out in the dependent claims.

[0017] It is the object of the present invention to provide an epicyclic traction transmission in which the shape of the rolling contact elements enables an axial application of the preloading force. In practice, this means that the rolling elements can be a combination of any axisymmetric geometry whose contact area is not aligned parallel to the axis of the transmission, but is contacted at an angle, so that it can generally be loaded jointly by a resultant axial preloading force.

[0018] This key difference provides a simple way to change the preloading force on the rolling contact elements, which in turn provides a way to increase the torque density and mechanical efficiency of the transmission.

[0019] While this topology brings certain improvements, it also brings new problems. For example, to ensure that the planetary rolling elements remain aligned under high preloading forces, they need to be axially limited in some way. Traditionally, in a roller bearing, this is achieved by providing small flanges on each end of the inner and outer raceways, which are in sliding contact with the end faces of the rollers to maintain their correct alignment. In a roller bearing where the lubrication provides an extremely low coefficient of friction, this will only result in a small and controllable loss of mechanical efficiency. In a traction transmission, however, the specialized traction lubricant can provide a coefficient of friction that is about two orders of magnitude higher than in a lubricated roller bearing, at which point the frictional losses become non-negligible. Another problem that designers can encounter is that for applications where the positional accuracy is high, the use of a variable preloading system can create mechanical play, especially when the direction of motion changes.

[0020] Unless otherwise defined, all technical and scientific terms used in this specification have the meaning commonly understood by one of ordinary skill in the art to which this invention belongs. Methods and materials similar or equivalent to those described herein can be used in the practice of the present invention.

[0021] In the description and claims of the application, the terms "comprise" and "comprising" are not intended to exclude other technical features, additives, components, or steps. Other objects, advantages and features of the present invention will be in part apparent and in part pointed out by the specification, and by the practice of the invention. BRIEF DESCRIPTION OF DRAWINGS

[0022] To complement the description made herein and to help better understand the features of the present invention, according to the preferred practical embodiment of the invention, a set of drawings is attached to the present specification, which illustrates, by way of example and without limitation, the following: Figure 1 A front view of the epicyclic traction transmission is shown.

[0023] Figure 2 A radial section view of the transmission is shown. DETAILED DESCRIPTION

[0024] With reference to the drawings, the preferred embodiment of the invention is described below.

[0025] Figure 1 It is shown that the epicyclic traction transmission has a sun roller 104, planet rollers 102, an auxiliary roller 103 and a fixed ring gear 101, wherein the sun roller 104 is located in the center; the fixed ring gear 101 is located outside all the elements; the auxiliary roller 103 is located between the planet rollers 102 and the fixed ring gear 101, and the planet rollers 102 are in contact with the sun roller 104, the auxiliary roller 103 and the fixed ring gear 101; the sun roller 104, the planet rollers 102, the auxiliary roller 103 and the fixed ring gear 101 all have a truncated cone body geometry or a truncated cone shape.

[0026] Figure 2 It is shown more clearly that the sun roller 104, the planet rollers 102, the auxiliary roller 103 and the fixed ring gear 101 have a truncated cone section, and all these components can be pre-tensioned by a synthetic axial pre-tensioning force.

[0027] The shaft at either end of the conical auxiliary roller can be connected to the planet carrier by a roller bearing.

[0028] Therefore, the rollers contact each other at an angle to their own axis, being pre-tensioned by an axial resultant force, which allows the pre-tensioning force of the different rollers to be varied.

[0029] After fully describing the essence and the embodiment of the invention, it is declared that, in essence, the invention can be implemented by other embodiments that differ from the exemplary ones shown in the details, but as long as the main principles are not changed, altered or modified, they are also protected.

Claims

1. Epicyclic traction drive comprising: - a sun roller (104), - a planet roller (102), - an auxiliary roller (103), and - a fixed ring gear (101), wherein the sun roller (104) is located in the center, the fixed ring gear (101) is located outside all elements, the auxiliary roller (103) is located between the planet roller (102) and the fixed ring gear (101), and the planet roller (102) is in contact with the sun roller (104), the auxiliary roller (103), and the fixed ring gear (101), characterized in that the sun roller (104), the planet roller (102), the auxiliary roller (103), and the fixed ring gear (101) each have a truncated cone geometry or a truncated cone body geometry.

2. The epicyclic traction drive of claim 1, wherein, The shaft at either end of the auxiliary roller (103) is connected to the planet carrier via roller bearings.

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