WO2023121959A1 - High efficiency drivetrain - rolling element on tooth - Google Patents

Abstract

A gear drives with an additional floating rolling element may facilitate rolling friction and eliminates sliding friction. The floating rolling element is compressed between two gear teeth during meshing. This arrangement creates a gear drive of very high efficiency that is applicable to linear, circular, and conical gear drives through a wide range of gear ratios.

Description

HIGH EFFICIENCY DRIVETRAIN - ROLLING ELEMENT ON TOOTH

REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63/292,512, filed on December 22, 2021, and entitled HIGH EFFICIENCY DRIVETRAIN - ROLLING ELEMENT ON TOOTH, the content of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates generally to gears used to transmit power in a drivetrain.

BACKGROUND

[0003] A drivetrain such as a bicycle chain drive transmits power from an operator input at a crank sprocket to a driven sprocket on a wheel via a chain. During such transfer of power, the drivetrain suffers from power loss due to undesirable frictional losses, which reduces power transferred to the driven sprocket. As an example, while bicycle chain drives are heralded as highly efficient drivetrains, in practice, when the chain is engaging a gear that causes the chain to not be parallel to the bicycle centerline, the power loss is relatively high (e.g., 8% power loss or higher).

[0004] Several approaches have traditionally been utilized to try and minimize power loss.

[0005] One approach has been to use rollers that are substituted for fixed gear teeth. Commonly referred to as roller-teeth, examples of these inventions can be found in GB PatentNo. 191419772, US Patent No. 563,971, US Patent No. 608,8 21, US PatentNo. 5,247,847, and US Pub. No. 2008/0276739. With such roller-teeth, the axes of the rollers are a fixed distance from center axis of the gear. While these inventions may improve the efficiency (e.g., reduce power loss) compared to traditional non-roller fixed-teeth gearsets, roller-teeth have drawbacks. One such drawback is that because each roller must rotate about a fixed axis on a roller support during meshing, sliding friction will occur as the roller rotates on its axis on a bushing (typically) on the roller support.

[0006] Another approach has been to use a roller-tooth which can float and the axis of the roller is not fixed to the axis of the gear, such as described in CN110848333B and US Patent No. 4,6 21,586. However, these inventions continue to use roller support mechanisms and therefore still create rotating friction between the roller and the roller axial support mechanism.

[0007] Other approaches eliminate the need for roller axial load/bearing supports. For example, US Patent No. 609,314 uses only a floating ball/sphere. While this invention does use a bevel gearset (non-parallel axes gears), a ball is used as the floating rolling element because of the ball’s multidirectional roll capabilities to accommodate the nonlinear travel path of the meshing bevel teeth. The retainment of the balls causes significant sliding friction.

[0008] US Patent No. 2,070,777 describes another approach that uses a floating cylinder; however, this invention is only applicable to parallel axes gearsets. The split rows of teeth and straight cylinder would not allow this invention to work in a bevel application. [0009] DE4128302 describes an approach that uses a ball as the floating rolling element, with a traditional cylinder as an embodiment. This invention is specific to parallel-axes spur gears. The embodiment with the cylinder uses split rows of teeth which would not work in a bevel application.

[0010] In view of the limitations of prior approaches, there is still a need for a gearset with non-parallel gear axes, high load carrying capability, and/or extremely high efficiency.

SUMMARY

[0011] Described herein are gears used to transmit power in a drivetrain. More specifically, the embodiments provided herein may be gears that are capable of transmitting power with near 0% power loss by using a floating rolling element between gear teeth. The present invention can be used to change input and output speeds of a drive system like spur gears. Additionally or alternatively, the embodiments provided herein may be used to change drive angle like bevel gears.

[0012] The embodiments described herein (e.g., gears, gear drives, drivetrains, etc.) may be used in various applications and/or operating environments as desired, including but not limited to bicycle drivetrains, gearboxes, transmissions, combinations thereof, and/or various other uses or applications as desired. Thus, while the below description makes reference to bicycles, the embodiments of the invention are by no means limited to bicycles.

[0013] In some cases, in ideal conditions, the embodiments described herein reduce the power loss to near 0% due to the elimination of sliding friction. Additionally, the power loss does not increase with different gear ratios like a chain. [0014] In some embodiments, a gearset according to embodiments includes fixed teeth on both gears, and each gear may transfer and subsequently receive loads through a floating intermediate rolling element. In various embodiments, the floating intermediate rolling element does not have load bearing auxiliary supports, and while the opposing teeth create the opposing load bearing forces, an axis of rotation of the floating rolling element is able to translate relative to the gear axis and is not a fixed distance to either of the gearset axes during meshing and load transfer.

[0015] According to certain embodiments, a gear drive or gear train may include, but is not limited to, two gears and a floating rolling element compressed between meshing teeth of the gears. The two gears could be, but are not limited to, rack gears (linear), spur gears (circular), and bevel gears (conical), among others. The gears could be mounted directly to shafts or other hardware as desired using various suitable devices or mechanisms such as bearings, bushings, and/or other mechanisms as desired. The floating rolling element may have various shapes or profiles as desired. As some nonlimiting examples, the floating rolling element may be a constant width, a non-constant width, cylindrical, conical, spherical, oloid, sphericon, and/or as otherwise desired.

[0016] The embodiments of the present invention can be used in many drive types. As some non-limiting examples, the embodiments described herein may be used with a gear drive, a gear train, a friction drive, a drive shaft, a chain drive, and/or a belt drive. Moreover, the embodiments of the present invention can be used on various gear train types as desired, including, but not limited to, simple, compound, reverted, internal, and epicyclic (planetary). The tooth profile on each gear can take many shapes as desired, including, but not limited to, flat, convex, concave, and/or at many angles such as, but not limited to, radial, forming an acute root angle, and forming an obtuse root angle. [0017] The compressed floating rolling element is a concept not unlike the involute toothed gear. The involute toothed gear reduces sliding friction between opposing gear teeth by ‘rocking’ the meshing gear teeth against one another. However, the involute tooth shape does not completely eliminate sliding friction between meshing teeth, leading to frictional losses of 2% in ideal conditions for involute spur gears. Because the sliding friction (and therefore power losses) occurs at the entry and exit tooth contact patches during mesh, losses can be much higher for gears with a small number of teeth. The lower tooth count causes higher angular changes (arc of action) during meshing.

[0018] Embodiments of the present invention eliminate the sliding friction occurring during meshing, including at the tooth entry and exit contact path areas. In some embodiments, as the floating rolling element is compressed between the meshing teeth, such engagement allows ‘rocking’ to occur through the entirety of the tooth contact path. This feature of the present invention is possible because while the teeth are ‘rocking,’ the floating rolling element is translating with reference to tooth face it is constrained against. This translation takes the form of rolling to an outside observer. Certain embodiments of the present invention may include a flat radial tooth profile on both gears. During meshing action with such embodiments, the floating rolling element will roll towards the roots of both meshing teeth upon mesh engagement (arc of approach) and during first half of the contact path, and then roll back towards the tips of both meshing teeth in the second half of the contact path (arc of recess) concluding with mesh disengagement. The floating rolling element can be retained but floating on the driven or drive gears of a gear drive. The surface of the floating rolling elements and/or the teeth may have various shapes or profiles as desired, including but not limited to smooth, textured, knurled, ribbed, waffled, slotted, and/or dimpled. The present invention may also allow more than one rolling element per mesh, and there may be one or multiple rolling elements on both the driven and drive gear teeth.

[0019] With the elimination of the major cause of power loss in a gear drive only the minor contributors remain, for example Hertzian deformation or tooth deflection. These losses are typically fractions of a percent of total power loss, thus providing a substantial improvement compared to traditional drivetrains.

[0020] Various other benefits and advantages may be realized with the systems and methods provided herein, and the aforementioned advantages should not be considered limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The principles of the embodiments described herein show the structure and operation of several examples used to illustrate the disclosure. It should be understood that the drawings are diagrammatic and schematic representations of such example embodiments and, accordingly, are not limiting the scope of the present invention, nor are the drawings necessarily drawn to scale.

[0022] FIG. 1 illustrates a gear drive with a floating rolling element according to embodiments.

[0023] FIG. 2 illustrates rolling and meshing of the gear drive of FIG. 1.

[0024] FIG. 3 illustrates another gear drive with a floating rolling element according to embodiments.

[0025] FIG. 4 illustrates rolling and meshing of the gear drive of FIG. 3. [0026] FIGS. 5A-B illustrate a portion of a gear drive with a floating rolling element during operation when the floating rolling element is not in an operating position according to embodiments.

[0027] FIG. 6 illustrates the core design principles for bevel gears according to embodiments.

DETAILED DESCRIPTION

[0028] Described herein are gear drives with floating rolling elements. In certain embodiments, the gear drives provided herein may be used to transmit power in a drivetrain. In some embodiments, gear drives with floating rolling elements provided herein may be capable of transmitting power with near 0% power loss by using the floating rolling element between gear teeth. As used herein, “near 0% power loss” means a power loss of less than or equal to 2% power loss, such as less than or equal to 1.5% power loss, such as less than or equal to 1% power loss, such as less than or equal to 0.5% power loss, such as less than 0.5% power loss. As used herein, a “rolling element” or “roller” refers to any suitable structure that is rotatable about at least one axis. In some non-limiting embodiments, the rolling elements may be elongated structures with various shapes or profiles as desired (e.g., conical, cylindrical, etc.), although in other non-limiting embodiments the rolling element need not be elongated (e.g., it may be spherical and/or as otherwise desired).

[0029] FIGS. 1 and 2 illustrate an example of a gear drive 10 according to embodiments. The gear drive 10 generally includes a first gear 12 having a first plurality of teeth 14 and a second gear 16 having a second plurality of teeth 18. The number of teeth 14 and teeth 18 illustrated in FIGS. 1 and 2 should not be considered limiting. In the embodiment illustrated, the first gear 12 and the second gear 16 are both spur gears; however, they need not be spur gears in other embodiments. In the embodiment of

FIGS. 1 and 2, each of the teeth 14 and the teeth 18 are flat radial teeth; however, in other embodiments, the teeth 14 and/or the teeth 18 need not be flat radial teeth.

[0030] Referring to FIG. 1, in addition to the teeth 18, the second gear 16 includes a plurality of floating rolling elements 20. In the embodiment of FIGS. 1 and 2, and as best illustrated in FIG. 2, the floating rolling elements 20 are cylindrical. However, the shape of the rolling elements 20 should not be considered limiting, and in other embodiments the floating rolling elements 20 need not be cylindrical. In some embodiments, each floating rolling element 20 includes an engagement portion 28 that may be used to retain the floating rolling element 20 relative to the second gear 16. In the embodiment illustrated, the engagement portion 28 is a pin 30; however, in other embodiments, other types of engagement portions 28 may be utilized as desired, and in some embodiments, engagement portions 28 may be omitted.

[0031] As illustrated in FIGS. 1 and 2, a containment feature 22 may be utilized to retain the floating rolling elements 20 relative to the teeth 18 while allowing the floating rolling elements 20 to float or otherwise move relative to the teeth 18. The containment feature 22 may be various devices or mechanisms for retaining the floating rolling elements 20 relative to the second gear 14 while allowing for floating of the rolling elements 20. As some non-limiting examples, the containment feature 22 may be devices or mechanisms including but not limited to a geometric constraint (e.g., a male with mating female surface), other physical constraints, a magnetic device (permanent, electro, or electro permanent), and/or other features or combination of features as desired. In some embodiments, containment feature 22 may be an extension of the second gear 16 and/or monolithically or integrally formed with the second gear 16. In other embodiments, the containment feature 22 may be a separate structure that is joined and/or otherwise attached or connected to second gear 16 using various mechanisms or devices as desired. As mentioned, the containment feature 22 may retain the floating rolling elements 18 as desired, including physically restraining the floating rolling elements, using magnetic forces, and/or as otherwise desired.

[0032] In the embodiment of FIGS. 1 and 2, the containment feature 22 is a cage 24 with cage sides 26A-B that overlap the floating rolling elements 20 on opposing sides of the second gear 16. In FIG. 2, the cage side 26A is omitted for clarity of the figure such that floating rolling elements 20 are visible. In the embodiment of FIGS. 1 and 2, each cage side 26A-B includes a slot 32 for receiving an engagement feature 28 of a particular floating rolling element, and the positioning of the engagement feature 28 within the slot 32 retains the floating rolling element 20 while allowing the floating rolling element 20 to “float.” As mentioned, the retention of the floating rolling elements 20 facilitates simultaneous ‘rocking’ of the teeth 14, 18 and ‘rolling’ of the floating rolling elements 20 compressed between the teeth 14, 18. In another embodiment the floating rolling elements 20 may not actually roll or translate in relation to the second gear 16 but only facilitate ‘rocking’ of the teeth 14, 18.

[0033] FIG. 2 depicts the movement of the floating rolling elements 20 when meshing with the teeth 14, 18 as the gears 12, 16 rotate (represented by arrows 36 and 38). In this embodiment, rotation of the second gear 12 applies a centrifugal force on the floating rolling elements 20, and this centrifugal force positions the floating rolling element 20 associated with unmeshed teeth 18 at the end of the slot 32. See, e.g., the topmost floating rolling element 20 in FIG. 2. This positioning may facilitate the ‘rocking’ and ‘rolling’ of the teeth during meshing. Referring to the middle floating rolling element 20 in FIG. 2, meshing of the teeth 14, 18 may result in a tooth 14 of the first gear 12 contacting the floating rolling element 20 and moving the floating rolling element 20 inwards as represented by arrow 40. In some embodiments, such contact may also cause rotation of the floating rolling element 20 as represented by arrow 42. Referring to the bottom floating rolling element 20 in FIG. 2, as the teeth 14, 18 become unmeshed, the floating rolling element 20 may be moved outwards again due to the centrifugal force and/or contact with the tooth 14. In the embodiment illustrated in FIG. 2, only one pair of teeth 14, 18 mesh at a time; however, in other embodiments, a plurality of pairs of teeth 14, 18 are meshing at any given moment.

[0034] FIGS. 3 and 4 illustrate another example of a gear drive 110 according to embodiments. Similar to the gear drive 10, the gear drive 110 includes a first gear 112 and a second gear 116. The gears 112, 116 are similar to the gears 12, 16 except that the gears 112, 116 are beveled gears. In addition, and as illustrated in FIGS. 3 and 4, compared to the gears 12, 16, the gears 112, 116 each include teeth 114, 118 that are bevel flat teeth. The angle of the bevel teeth 114, 118 is not limited to the angle illustrated in FIGS. 3 and 4, and the number of teeth 114, 118 likewise should not be considered limiting.

[0035] Similar to the second gear 16, the gear 116 includes the floating rolling elements 120 and a containment feature 122 retaining the rolling elements 120 to the gear 116. Compared to the gear drive 10, the floating rolling elements 120 of the gear drive 110 are conical. Similar to the rolling elements 20, the rolling elements 120 include engagement features 128 that are pins 130 in the embodiment of FIGS. 3 and 4.

[0036] Similar to the containment feature 22 of the gear drive 10, the containment feature 122 of the gear drive 110 is a cage 124 with cage sides 126A-B; however, compared to the cage 124, the cage sides 126A-B of the cage 124 are asymmetrical (e.g., the size of the cage side 126A is less than the size of the cage side 126B). As illustrated in FIG. 3, similar to the cage 24, each cage side 126A-B of the cage 124 includes a slot 132 for receiving the engagement features 128. In FIG. 4, the cage sides 126A-B are omitted for clarity of the figure. In certain embodiments, the asymmetric cage 124 shown in FIG. 3 does not support or guide the rolling elements 120 during meshing. In certain embodiments, and referring to FIG. 4, a spherical roller or ball would not be possible without introducing sliding friction via a retainment method. Bevel gears work on the principle of cones as depicted in FIG. 6. If a ball was used, the ball would not return to the starting point. Said another way, the ball will roll in and out like the floating rolling elements 120, however it will also roll towards the projected cone tips. This means the retainment for a ball would need to restrict the drift towards the cone tips, this would introduce frictional losses of the ball sliding against the retainment device. In another embodiment of the present invention a ball is used, however, a tooth profile that is not flat will be required for the ball to track back to its starting position through the meshing stage.

[0037] FIG. 4 illustrates depicts the floating rolling elements 120 meshing with the teeth 114, 118. In certain embodiments, the slots 132 and pins 130 of the gear drive 110 are designed to accommodate the fact that the conical floating rolling elements 120 do not roll the same distance along the face of the teeth over the contact length of the conical floating rolling elements 120. In one embodiment, the gear drive 110 is designed so that the flat surfaces of both gear teeth 114, 118 and the conical floating rolling element 120 all intersect at the same projected point (see, e.g., the middle floating rolling element 120 in FIG. 4). In embodiments, the gear teeth 114, 118 and conical floating rolling elements 120 need not coincide. In certain embodiments and as illustrated in FIG. 4, the teeth 114, 118 and floating rolling elements 120 mate flush across the entire length of the floating rolling elements 120 throughout the contact path. Such flush contact may allow for a better distribution of contact stresses and may encourage rolling of the floating rolling elements 120 against the teeth 114, 118 rather than sliding.

[0038] FIGS. 5A-B depict a portion of another gear drive 210 according to embodiments. The gear drive 210 includes gears 212, 216 that each include teeth 214, 216. A floating rolling element 220 is provided. In certain embodiments, the gears 212, 216, the teeth 214, 216, and the floating rolling element 220 may be substantially similar to the gear drive 10, although it need not be in other embodiments.

[0039] FIGS. 5A-B illustrate the gear drive 210 in different stages of operation. In certain embodiments, because the floating rolling element 220 is floating, when the gear drive 210 is not operating the floating rolling element 220 sometimes may be positioned closer to the root of the tooth 218 (see FIG. 5 A). As the gear drive 210 increases speed, centrifugal force on the floating rolling element 220 moves the floating rolling element 220 into its optimal operating location (see FIG. 5B, with movement represented by arrow 544 in FIG. 5B). During the speed up phase of the gear derive 210, efficiency may be similar to conventional gear drives. In some embodiments, the containment feature (not illustrated in FIGS. 5A-B) may the limit of the outermost radial position of the floating rolling element 220 (e.g., the position of the floating rolling element 220 in FIG. 5B) and/or may define a range of radial movement from a minimum position (e.g., FIG. 5A) to a maximum position (e.g., FIG. 5B). The minimum and maximum positions illustrated in FIGS. 5A-B should not be considered limiting.

[0040] In some embodiments, the containment feature may facilitate positioning of the floating rolling element 220 radially with reference to the face of the tooth 218 during mesh initiation to a mesh initiation position. In some embodiments, the mesh initiation position optionally is the maximum position illustrated in FIG. 5B. In certain embodiments, positioning the floating rolling element 220 at the mesh initiation position may facilitate and/or increase the likelihood that the floating rolling element 220 rolls throughout meshing while minimizing potential slippage. In some embodiments, such positioning optionally ensures that the floating rolling element 220 and does not slip. The floating rolling element 220 may be moved into this initiation position via centrifugal force and/or as otherwise desired. In other embodiments, a spring, a magnet, a track, rail or slide, and/or other various devices or mechanisms may be used to move the floating rolling element 220 into the mesh initiation position. In other embodiments, the floating rolling element 220 need not be in the mesh initiation position and/or any other predetermined radial position prior to initial meshing, and the gear drive system may have a plurality of possible starting positions for the floating rolling element 220 and/or the gear drive system may be able to maximize rolling while minimizing slippage regardless of the position of the floating rolling element 220.

[0041] A collection of exemplary embodiments is provided below, including at least some explicitly enumerated as “Embodiments” providing additional description of a variety of example embodiments in accordance with the concepts described herein. These embodiments are not meant to be mutually exclusive, exhaustive, or restrictive; and the disclosure not limited to these example embodiments but rather encompasses all possible modifications and variations within the scope of the issued claims and their equivalents.

[0042] Embodiment 1. A gear drive, comprising: a first gear with teeth profiled to mesh with a rolling element; a second gear with teeth profiled to mesh with a rolling element; a structure attached to said second gear which retains and locates the floating rolling element; a rolling element positioned between a tooth of the first gear and a tooth of the second gear designed to mesh with said first and second gear to cause rolling contact.

[0043] Embodiment 2. The gear drive of any of the preceding or subsequent embodiments or combination of embodiments, wherein the rolling element is a floating rolling element that is independently movable in a radial direction and is independently rotatable.

[0044] Embodiment 3. The gear of any of the preceding or subsequent embodiments or combination of embodiments, wherein the rolling element is elongated.

[0045] Embodiment 4. A drivetrain comprising the gear drive of any of the preceding or subsequent embodiments or combination of embodiments.

[0046] Embodiment 5. The gear drive of any of the preceding or subsequent embodiments or combination of embodiments, wherein the rolling element is conical, cylindrical, or spherical.

[0047] Embodiment 6. A gear for a gear drive, the gear comprising: at least one tooth; a floating rolling element; and a containment feature retaining the rolling element relative to the at least one tooth, wherein the floating rolling element is independently movable relative to the at least one tooth.

[0048] Embodiment 7. A drivetrain comprising the gear of any of the preceding or subsequent embodiments or combination of embodiments.

[0049] Embodiment 8. A gear drive comprising: a first gear comprising at least one first tooth; a second gear comprising at least one second tooth; and a floating rolling element configured to be compressed between the at least one first tooth and the at least one second tooth during meshing, wherein meshing transmits power between the gears with a power loss of less than or equal to 2% power loss. [0050] Embodiment 9. The gear drive of any of the preceding or subsequent embodiments or combination of embodiments, wherein the power loss is less than or equal to 0.5% power loss.

[0051] Embodiment 10. The gear drive of any of the preceding or subsequent embodiments or combination of embodiments, wherein the power loss is less than or equal to 1.0% power loss.

[0052] Embodiment 11. A gear drive, comprising: a first gear with a first plurality of teeth; a second gear with a second plurality of teeth; a floating rolling element; and a containment feature with the second gear, the containment feature retaining the floating rolling element relative to the second gear while enabling floating movement of the floating rolling element, wherein, during a meshing of a tooth of the first plurality of teeth and a tooth of the second plurality of teeth, the rolling element is positioned between the two teeth such that contact of the teeth with the floating rolling element causes rolling contact.

[0053] Embodiment 12. A gear for a gear drive, the gear comprising: a tooth; a rolling element; and a containment feature retaining the rolling element relative to the tooth, wherein the rolling element is radially movable and rotatable while retained by the containment feature.

[0054] Embodiment 13. A gear for a gear drive, the gear comprising: a tooth; and a rolling element supported relative to the tooth, wherein the rolling element is radially movable and rotatable relative to the tooth.

[0055] Embodiment 14. A drivetrain with a gear drive, wherein the gear drive is configured to have less than 2% power loss during meshing of gears of the gear drive. [0056] The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. It should be appreciated that the various elements of concepts from the figures may be combined without departing from the spirit or scope of the invention.

[0057] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Directional references such as “up,” “down,” “top,” “bottom,” “left,” “right,” “front,” and “back,” among others, are intended to refer to the orientation as illustrated and described in the figure (or figures) to which the components and directions are referencing. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, or gradients thereof, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0058] As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. All ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more, e.g. 1 to 6.1, and ending with a maximum value of 10 or less, e.g., 5.5 to 10.

[0059] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. The invention is susceptible to various modifications and alternative constructions, and certain shown exemplary embodiments thereof are shown in the drawings and have been described above in detail. Variations of those preferred embodiments, within the spirit of the present invention, may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, it should be understood that there is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. [0060] The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Claims

What is claimed is:

1. A gear drive, comprising: a first gear with teeth profiled to mesh with a rolling element; a second gear with teeth profiled to mesh with a rolling element; a structure attached to said second gear which retains and locates the floating rolling element; a rolling element positioned between a tooth of the first gear and a tooth of the second gear designed to mesh with said first and second gear to cause rolling contact.

2. The gear drive of claim 1, wherein the rolling element is a floating rolling element that is independently movable in a radial direction and is independently rotatable.

3. The gear of claim 1, wherein the rolling element is elongated.

4. A drivetrain comprising the gear drive of claim 1.

5. The gear drive of claim 1, wherein the rolling element is conical, cylindrical, or spherical.

6. A gear for a gear drive, the gear comprising: at least one tooth; a floating rolling element; and a containment feature retaining the rolling element relative to the at least one tooth, wherein the floating rolling element is independently movable relative to the at least one tooth. ear of claim 6, wherein the floating rolling element is independently movable in a radial direction and is independently rotatable. ear of claim 6, wherein the floating rolling element is elongated. vetrain comprising the gear of claim 6. gear of claim 6, wherein the rolling element is conical, cylindrical, or spherical. ear drive comprising: a first gear comprising at least one first tooth; a second gear comprising at least one second tooth; and a floating rolling element configured to be compressed between the at least one first tooth and the at least one second tooth during meshing, wherein meshing transmits power between the gears with a power loss of less than or equal to 2% power loss. gear drive of claim 11, wherein the power loss is less than or equal to 0.5% power loss. gear drive of claim 11, wherein the power loss is less than or equal to 1.0% power loss. ear drive, comprising: a first gear with a first plurality of teeth; a second gear with a second plurality of teeth; a floating rolling element; and a containment feature with the second gear, the containment feature retaining the floating rolling element relative to the second gear while enabling floating movement of the floating rolling element, wherein, during a meshing of a tooth of the first plurality of teeth and a tooth of the second plurality of teeth, the rolling element is positioned between the two teeth such that contact of the teeth with the floating rolling element causes rolling contact. gear of claim 14, wherein the floating rolling element is independently movable in a radial direction and is independently rotatable. gear of claim 14, wherein the floating rolling element is elongated. ear for a gear drive, the gear comprising: a tooth; a rolling element; and a containment feature retaining the rolling element relative to the tooth, wherein the rolling element is radially movable and rotatable while retained by the containment feature.

18. A gear for a gear drive, the gear comprising: a tooth; and a rolling element supported relative to the tooth, wherein the rolling element is radially movable and rotatable relative to the tooth.

19. The gear or gear drive of claim 18, wherein the rolling element is conical, cylindrical, or spherical.

20. A drivetrain with a gear drive, wherein the gear drive is configured to have less than

2% power loss during meshing of gears of the gear drive.

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