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Automotive - 2021-06-14

NSK’s ball bearing for EV motors

NSK has developed a third-generation ultra-high speed ball bearing for electric vehicle (EV) motors that is capable of operating at over 1.8 million dmN(1). The new bearing is in fact the world's fastest grease-lubricated deep groove ball bearing for EV applications, enabling longer vehicle range and higher energy economy. Additionally, the bearing facilitates motor and component downsizing for space gains within vehicle interiors.

In line with consumer and environmental demands, automakers are pursuing smaller and lighter automotive components to help extend the range achievable on a single charge. EV OEMs are also developing faster, higher output motors operating with better efficiencies. Accordingly, bearings used in powertrains, especially in electric motors, must meet the demand for increasingly higher speeds and performance.

The previous (second) generation of ultra-high speed ball bearings for EV motors offered 1.4 million dmN and significant advances in cage and anti-seizure technology. However, with the third-generation product, NSK has aligned its solution with the need for bearings capable of even higher speeds.

Aside from its rotational performance of 1.8 million dmN (a 28.5% increase), the new bearing features the world’s first cage to leverage the benefits of topology optimisation. By using this process, it was possible to optimise the material layout inside the design space with the goal of maximising product performance.

For the new bearing, topology optimisation helped to maximise strength and minimise weight by eliminating parts that did not contribute to cage durability or rigidity, while also serving to derive the optimal cage shape for high-speed rotation. The development time of the cage was very short by using leading-edge simulation technology to verify cage performance and production considerations.

The cage makes use of a new high-rigidity resin material that is more effective at suppressing deformation during high-speed rotation than conventional materials. As a further point of note, NSK fills the bearing with a proprietary grease that reduces lubricant churning resistance and any subsequent heat generation, prolonging both grease and bearing life, and reducing the risk of seizure. It is the combination of special NSK grease and newly developed cage that enables this high-performance deep groove ball bearing to operate at over 1.8 million dmN.

Having a bearing of this capability enables customers to develop and implement electric motors that operate at significantly higher speeds. Higher motor output contributes to greater efficiency (reducing power consumption per unit distance), extended vehicle range and enhanced user comfort. Higher speeds also facilitate the utilisation of smaller motors, thus reducing vehicle weight and increasing the amount of space available for other components, more battery cells, or a larger vehicle interior.

(1) dmN: A measure of bearing rotational performance. The product of bearing pitch diameter (dm) and rotational speed (N).

 

Picture 1): It is the combination of proprietary grease and newly developed cage that enables NSK’s latest-generation ball bearing for EV motors to operate at over 1.8 million dmN

Picture 2): The design steps taken by NSK to optimise the cage of the new bearing. 1: Issue: Potential deformation of bearing cage due to centrifugal force, 2: Working shape: Maximise strength and minimise weight of cage. Remove parts not contributing to durability or rigidity. 3: Final shape: Verification of performance and production consideration. Optimal design and ease of manufacturing

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