Ring-Drive Methods for In-Wheel Motors  

Paper #:
  • 2018-01-0459

Published:
  • 2018-04-03
Author(s):
Affiliated:
Abstract:
In electric vehicles, in-wheel motors have heretofore required copper windings be coiled about the central axis of a wheel, yielding both a 1:1 ratio and a formula necessary to meet torque and mass specifications that dictate the number, volume and ultimately the weight of copper windings.   While sound in principle, this methodology in practice results typically in a performance penalty and specifically an increase in weight as compared to conventional wheels, which has sidelined this otherwise promising technology.   if the weight problem of in-wheel motors could be solved, various mechanical systems could be lightened to decrease cost, weight and complexity of electric and hybrid drivetrains, leading to increased profitability in electric vehicles, and lower sticker prices.   A “ring-drive” wheel configuration is one such solution for reducing wheel weight. In a so-called ring-drive, the hub is separated from the rim, such that the rim orbits the now stationary hub. A motor positioned within the stationary hub may then drive a ring-gear located within the interior circumference of the rim.   While seeming counterintuitive, given the inefficiencies arising from mechanical gearing methods, including the friction and noise that result from gear meshing, the higher maintenance required of various moving parts, bearings, etc. (which of course are the principle arguments for utilizing non-geared wheel motors in the first place), the result is an in-wheel motor with equivalent weight to conventional, non-motorized wheels. It is the contention of this author that the net-net benefits of ring-drives far outweigh the aforementioned compromises.   And while the comparative inefficiency between non-geared in-wheel motors and geared in-wheel motors may be as high as 30%, the potential for in-wheel motors that match the weight of conventional non-powered wheels foster other opportunities such as low-cost torque vectoring, all-wheel-drive, and overall improvements in real-world operating performance of electric and hybrid electric vehicles.
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