I would like to briefly discuss some thoughts on ball bearing efficiency specifically in terms of applied load and resulting stress. I don’t want to trivialize this subject; there are textbooks written on the subjects of electrohydrodynamic lubrication (EHL), octahedral subsurface shear stress and friction losses due to elastic hysteresis. This is a just a high-level discussion on the importance of individual bearing stress on efficiency. 

It seems like everyone is jumping into the electric gearbox market. Even Schaeffler is in the electric drive module (EDM) market now with their own 800v system. With all these new entries, some companies are satisfied with following traditional bearing arrangements while some want new and unique solutions or some combination of both. There is heavy debate over which styles are the best. In this article, we will talk about the different types of 2-bearing arrangements for each shaft with the pros and cons of each for a simple three shaft, single speed parallel axis gearbox (ala Tesla style).

Welcome back to Part 2 of our inner ring and creep discussion. We left off with our creep calculation resulting in a 10.5 µm minimum inner ring fit to avoid creep. For the sake of making clean dimensions, let’s call it 10 µm on the lower end and the upper end is simply whatever your manufacturer can hold.

I think I spend more time talking about ball bearings today than at any other time in my career. Ball bearings have always had a large place in automotive, but not typically in high demand positions—other than a few niche areas. High demand positions, such as axles and planetaries, were typically reserved for tapers, needles and cylindricals. The landscape is changing quickly.

This article is Part III in a series of articles on speed rating of bearings. Part I appeared in the September 2022 issue ("Ball Bearing Limiting Speeds"), and Part II appeared in the October 2022 issue ("Ball Bearing Thermal Speed Rating"). Bearings with Norm examines the latest in bearing technology and design. 

Electrification has really brought ball bearings back into focus as the primary bearing in our drive systems. Some boxes have tapers on the slower shafts for stiffness and others are using a ball/cylindrical combo for efficiency. Regardless, we all face the same challenge on the primary shaft in dealing with the potential of 18,000–20,000+ rpm speeds coming out of the motor. Plenty of applications run 20,000 rpm; what makes the automotive motor unique is, in addition to speed, we are driving huge torques, frequent torque reversals and a huge range of temperatures both internally and geographically. Of course, this all needs to be suited for high-volume manufacturing as well. Adding full ceramic balls, a PEEK cage and a high precision classification is a really easy way to run greater than 20,000 rpm all day but is an expensive option. One bearing alone could hurt the cost competitiveness of your gearbox. In the case where a single bearing can change the landscape of your project, it is worth taking a little time to understand exactly what the drivers of our speed limitations are.