Patent ID: 7456536

Claim:
An electric motor comprising: a casing; a rotor shaft that is arranged in said casing and has a hollow bore which is formed through said rotor shaft in coaxial relation therewith and through which pressurized and cooled lubricating oil is caused to flow; a rotor that is fixedly secured to said rotor shaft in coaxial relation therewith and is arranged in said casing so as to be rotatable about an axis of said rotor shaft; a stator that is supported by said casing so as to surround said rotor; a pair of bearings that each have an inner race and an outer race, and are mounted on said rotor shaft at axially opposite sides of said rotor with said inner races being fitted over said rotor shaft; a pair of bearing fixing parts that are arranged in said casing at the axially opposite ends of said rotor shaft, with said individual outer races of said one pair of bearings being fitted into said bearing fixing parts, respectively, thereby to rotatably support said rotor shaft; bearing cooling devices that each have a cylindrical heat dissipation portion fixedly secured to said rotor shaft in a fitted-over state so as to be in contact with either one of end faces of said individual inner races of said one pair of bearings, said cylindrical heat dissipation portion extending from said one end face of each of said inner races to a side opposite to said bearings; spaces that are formed between rotor side end faces of said one pair of bearings and said bearing fixing parts, respectively; ring gaps that are formed between said heat dissipation portion and said rotor shaft, and each have an opening at a side opposite to said bearings, respectively; first communication holes that are formed through said rotor shaft in a radial direction thereof to provide communication between said hollow bore and said spaces; second communication holes that are formed through said rotor shaft in a radial direction thereof to provide communication between said hollow bore and said ring gaps, wherein said heat dissipation portion extends in the axial direction of said rotor shaft so as to cover the second communication holes; said first communication holes are formed so that lubricating oil can flow from said hollow bore of said rotor shaft through said first communication holes and through said bearings to provide lubrication and cooling; and said second communication holes are formed so that lubricating oil can flow from said hollow bore of said rotor shaft through said second communication holes and through the bearing cooling devices to provide lubrication and cooling.