NSK Hybrid vehicles: low-torque ball bearings

NSK Ltd has developed new low-torque ball bearings for hybrid vehicles featuring a 50–65 per cent improvement in frictional loss compared to conventional bearings. NSK designed the new product specifically for use in hybrid vehicles — a growing market due to improvements in fuel efficiency and rising environmental awareness — and expects annual sales of more than 3 billion yen by 2013. 

In recent years, demand for hybrid vehicles has been rising rapidly, thanks to the low fuel consumption and low emissions realised through a more efficient integration of the engine and electric motor. In order to further improve fuel efficiency, there is a growing need to reduce torque loss in the bearings used in the transmissions (drive-trains) of new generation hybrid cars. NSK expects growing sales to automobile manufacturers of hybrid vehicles in and outside Japan. The new product will be featured first in Toyota’s latest Prius. 

Despite this, NSK has found a way to cut torque by 50–65 per cent compared with existing product by implementing the solutions described below. 

1. Optimisation of internal design.The number of balls has been dramatically reduced, and ball diameters, race dimensions, and clearances have been optimized utilizing analysis technology, which has allowed rolling friction losses to be minimized. Another key factor in this success was NSK’s development of new manufacturing processes that overcame conventional hurdles to significantly decrease the number of balls. 

2. Introduction of low-torque cages. Losses have been reduced dramatically by agitating lubrication oils during operation via the introduction of specially shaped cages made of resin. 

NSK has achieved compactness, lightness and low torque for automobiles via its four core technologies (tribology, materials, analysis and mechatronics), which it has cultivated for 90 years, and is determined to push forward with the development of products that will improve the fuel efficiency of automobiles in the future.