1. Field of the Invention
The invention relates to a bearing device that supports, for example, a main shaft of a machine tool that rotates at a high speed.
2. Description of the Related Art
A typical mode of lubrication for a bearing includes grease lubrication and oil lubrication. A bearing device that provides the oil lubrication is described in Japanese Patent Application Publication No. 2002-130303 (JP-A-2002-130303).
More specifically, the bearing device transfers lubricating oil from an outside into a ball bearing by compressed air to lubricate raceway surfaces and balls of the ball bearing. In such lubrication, lubricating oil having a relatively low temperature is supplied from an outside to actively cool the ball bearing from an inside thereof. By so doing, it is possible to form a sufficient lubricating oil film inside the ball bearing.
However, in the bearing device according to the related art, because lubricating oil is transferred from an outside into the ball bearing by compressed air, there is a problem that lubricating oil splashes around the ball bearing to deteriorate its usage environment.
On the other hand, the grease lubrication lubricates a raceway surface, and the like, with grease sealed in the bearing, so that the above problem does not occur; however, there is another problem that the agitation resistance of grease lubrication is larger than that of oil lubrication to cause a large increase in temperature, and the service life of grease is relatively short, so that periodic maintenance is required. Therefore, it is difficult to use grease lubrication for a bearing of a machine tool that rotates at a high speed.