1. Field of the Invention
The present invention relates to a motor for suppressing the entry of a foreign matter.
2. Description of the Related Art
Some motors are used in environments where foreign matters are scattered. For example, the spindle head of a machine tool is arranged in a machining chamber for machining workpieces. The spindle head is used in an environment where foreign matters such as chips and cutting fluid are scattered during cutting. The spindle head includes a motor that rotates a spindle. The entry of the foreign matter into the motor may cause a failure of the insulation on windings or a deterioration of the function of a bearing.
The motor includes a rotor having a rotary shaft connected to another member and a housing surrounding the rotor. The rotary shaft rotates around the rotation axis. Since the rotary shaft cannot be fixed to the housing, the motor preferably has a mechanism for suppressing the entry of the foreign matter between the housing and the rotary shaft.
Conventionally, structures for suppressing the entry of the foreign matter between the rotary shaft and the housing have been examined. In the related art, the provision of an oil seal between the rotary shaft and the housing is known (for example, Japanese Unexamined Patent Publication No. 2004-36798A). The oil seal is fixed to the housing and is formed such that a lip part on the end part of the oil seal slides on the outer circumferential surface of the rotary shaft.
Moreover, a motor having a sealing structure is known. The structure has the function of the oil seal when the rotary shaft rotates at low speed, whereas the structure has the function of a labyrinth seal when the rotary shaft rotates at high speed (for example, Japanese Unexamined Patent Publication No. 7-55012A and Japanese Unexamined Patent Publication No. 9-28053A).
In addition to the oil seal and the labyrinth seal, a mechanical seal is known as a structure for suppressing a liquid flow to the outside from the inside of a casing (for example, Japanese Unexamined Patent Publication No. 2013-96568A).