Optimized Tapered Roller Bearing Power Loss Equals Deep Groove Ball Bearings in Real-World Electric Vehicle Intermediate Shaft Tests 2024-01-2440
One often reported roadblock to consumer acceptance of electric vehicles is driving range, which is a function of powertrain efficiency and vehicle mass. Electric vehicle gearbox design often is based on multiple parallel shafts, thereby creating significant packaging constraints. Industry perception holds that deep groove ball bearings (DGBB) are more efficient than tapered roller bearings (TRB), and standard spin-loss testing confirms those beliefs. However, spin-loss efficiency testing does not accurately reproduce typical real-world driving. A more realistic comparison of bearing efficiency is required to properly select bearings during the powertrain design stage.
Recently completed testing focused on recreating application conditions (including bearing loads, speeds, misalignment, and load zones) for electric vehicle gearbox intermediate shafts. These conditions varied between TRB and DGBB as a result of application bearing setting and reaction load changes and were faithfully reproduced. Under light load conditions, power loss from a 35 mm DGBB was significantly lower than that of a 35 mm bore TRB, but the TRB power loss was significantly lower than the DGBB’s under heavier loads.
When the individual test conditions were weighted to represent a road-use cycle, weighted power loss was equivalent between the two bearing types at expected vehicle operating temperatures. The bearings had the same rated radial capacity, but the TRB had reduced width, outer diameter (OD), and mass. The TRB’s capability of exhibiting power loss equivalent to the DGBB but within a smaller required envelope size can significantly aid electric vehicle design engineers who are faced with fitting multiple parallel shafts in their applications. In addition, the reduced size of the TRB allows system mass reductions, increasing battery range to address consumer concerns.
