Motor-incorporated spindle head unit

A motor-incorporated spindle head unit adapted to be mounted in a machine tool, comprising:

• a housing means provided as an outer framework of the unit and having therein a mounting space;
• a spindle extending centrally axially in said mounting space of said housing means and having front and rear end parts thereof, said front end part having a spindle nose to receive a tool or workpiece holder;
• a drive motor for said spindle, incorporated in said mounting space and including a rotor assembly rotatably fixed on said spindle and a stator assembly arranged to be fixed to said outer housing around said rotor assembly;
• a bearing means supporting said spindle at said front and rear end parts;
• and
• an annular insulating means for reducing heat transfer from said drive motor to said bearing means, including a fluid passage means arranged in said mounting space located between said stator assembly of said drive motor and said bearing means supporting said front end part of said spindle, said fluid passage means extending radially from adjacent said spindle to the outer circumference of said housing with a fluid inlet and a fluid outlet spaced remotely from said inlet, and said annular insulating means being enclosed by a partition plate member in said mounting space constituting a part of an inside wall of said housing means and being made of a heat insulating material.