Lubricating oil is used for providing the lubrication between a spindle and a bearing when the spindle is rotating so as to reduce the wear caused by friction. Therefore, how to prevent the lubricating oil from leaking out is a primary topic in improving friction wear.
Conventionally, the way to prevent the lubricating oil from leaking out is to dispose an oil seal or pad on the two ends of the bearing having oil respectively. However, such way only can achieve a limited effect because when the spindle rotates at high speed, the lubricating oil moves upward continuously according to the rotation of the spindle, then exudes out from the gap between the spindle and the oil seal or pad, and finally slips off the spindle due to the centrifugal force caused by the rotation of the spindle. Therefore, such way only can block the lubricating oil from leaking out passively, but can not retain the lubricating oil actively. To improve the above-mentioned shortcoming, an oil retaining structure of a spindle is disclosed in ROC (Taiwan) Patent Publication No. 573710 entitled “Improved Spindle”, as shown in FIG. 1.
Referring to FIG. 1, a spindle 10 is provided with a plurality of annular grooves 11 that are perpendicular to the axial direction thereof. A plurality of oil retaining gaps are formed between the inner wall of the bearing 12 and the spindle 10. When the spindle 10 rotates, the oil retaining gaps are filled with the lubricating oil that provides the lubrication between the spindle 10 and the bearing 12.
Although the above-mentioned oil retaining structure can provide the lubrication between the spindle 10 and the bearing 12 having oil, it can not completely prevent the lubricating oil from leaking out. The reason is that when the spindle 10 rotates at high speed, the lubricating permeates into the gaps between the bearing 12 and the portion that are not the oil retaining gaps of the spindle 10 due to the capillary action, which forms a thin oil film that moves upwardly according to the rotation of the spindle 10, then exudes out from the gap between the top end of the spindle 10 and the oil seal or pad, and finally slips off the spindle 10 due to the centrifugal force caused by the rotation of the spindle 10. Accordingly, the above-mentioned oil retaining structure only can delay the speed of the lubricating oil leaks.
Consequently, there is a need for a new oil retaining structure that not only improves the above-mentioned problem of leaking of the lubricating oil but also makes the lubricating oil distribute evenly on the spindle so as to avoid wear of the spindle and the bearing, reduce noise, and extend operation life of the spindle motor.