NSK develops tensioner with ball bearing

NSK developed the tensioner bearings for the idler pulley used in the auxiliary machine belt. By improving the seals, both high speed resistance and high sealing performance are achieved.

The idler pulley is one of the pulleys of the auxiliary machine belt for the automotive engine. Usually, neither the rotating part nor the rotating part of the idler pulley is used. Most of the pulleys are also used as the tensioner for giving the auxiliary machine belt tension. In general, the inner wheel is fixed and the outer wheel is directly connected to the pulley, thereby achieving the rotation. The bearing has a seal that prevents water and dust from entering. In the past, most of them were equipped with high-speed seals and high-seal seals, and they were selected by customers according to their needs.

Now all manufacturers are reducing the engine's displacement to improve fuel efficiency, and the idler's tensioner diameter also becomes smaller. At this time, due to the increased speed, high speed seals are used on the bearings. The shape of the previous high-speed seals can suppress the influence of increased centrifugal force under high-speed rotation. However, this shape has high rigidity and large variation in reaction force, which easily leads to gaps in the lip of the seal, and there is a problem of insufficient sealability. 

On the other hand, the demand for cars in emerging market countries is increasing. The environment in which these areas are used is harsh and most of the engines are contaminated with water and dust. The tensioner is located in front of the engine room and requires high tightness. High sealing seals are used. In order to improve the followability and sealability of the original high-sealing seals, the lip of the seal is relatively soft. However, when rotating at a high speed, the reaction force will greatly change, and the seal lip will be easily damaged.

The seals developed by NSK at this time put a lot of effort in the center of gravity of the lip of the seal. Even if the centrifugal force increases due to the high-speed rotation, the seal lip will not be greatly affected. In this way, the lip of the seal becomes more stable, so that it can withstand high-speed rotation, ensuring the same high-speed resistance as the original high-speed seal.

In addition, the lip of the seal used this time has a highly flexible shape and suppresses the change in reaction force. With this measure, the contact state of the lip of the seal is improved and foreign matter intrusion is prevented. In addition, a labyrinth is formed between the seal and the bearing member (inner wheel) to prevent foreign matter from invading from the outside. By these means, the sealability has been more than double that of previous high-sealing seals. (Reporter: Shinoda Yoshihiko, "Nikkei Auto")