Planetary Traction Drive for Submarine Application withTapered Rollers

Abstract

Fundamental contributions of this research include: • Demonstrate scaling potential of traction drives for larger power scales (on the order of 80MW) • Creation, modeling, and testing verification of a tapered traction drive that uses axial thrust to provide operational preload to maximize fatigue lifetime with variable preloading • Demonstrate water’s feasibility as a traction fluid Within demonstrating scaling potential, the stresses generated in a traction roller are modeled and applied to a case study of the Emma Maersk suggesting that a 3.5m hub inner diameter with a transmission ratio of 3 is within infinite lifetime operation of a highstrength bearing steel traction drive at 81MW and 100rpm output power and rotation speed respectively. Variable preloading can be produced from the thrust force of a propeller pushing into tapered roller planetary transmission and provide enough preload to sustain its entire operational range if a non-dimensional slope parameter is less than [formula]. Here θ is the taper angle of the sun roller, µ is the coefficient of traction between rolling surfaces, rₛ is the sun roller radius, ϕ is the transmission ratio of the drive, k_q is the torque coefficient of the propeller, kₜ is the thrust coefficient of the propeller, and D is the diameter of the propeller. If instead the slope parameter is greater than one, extra initial axial preload is needed for the propeller’s thrust to sustain its operation and can be calculated with [formula]. Water has the potential to be comparable to, and even surpass, existing traction fluids in traction performance because it can transform into Ice VI under pressures in the elastohydrodynamic layer leading to a potential 0.24 effective coefficient of traction between rolling surfaces compared to a maximum of 0.13 for traction oils. To confirm the theory, more testing is needed to measure actual rheological properties. A dynamic rheometer test would require sufficient surface speeds to entrain water into a traction drive’s contact zones against the large pressure gradient. An example system with a rotation element of 5in radius and a rotation speed of 2000rpm is theorized to work. For water to be effectively used in a traction drive system, faster roller surface speeds, larger system sizes, better surface roughness specifications, or some combination of these would be necessary.