Drive motor for use in variable valve operating device for internal combustion engine

Abstract

An actuator of a variable valve operating device includes an electric motor for varying the distance by which an intake valve of an internal combustion engine is lifted. The electric motor has a hollow cylindrical magnet assembly disposed around a hollow cylindrical holder, and a shaft rotatably supported in a housing, with a hollow region being defined between the shaft and the holder. The magnet assembly is skew-magnetized at a predetermined angle to the axis of the magnet assembly.

1 . A drive motor for use in a variable valve operating device disposed in a cylinder head of an internal combustion engine for controlling an angular displacement of a camshaft which is angularly movably supported in the cylinder head, comprising:
 a housing;   a rotor including a shaft rotatably supported in said housing and a hollow cylindrical magnet assembly disposed around said shaft; and   a stator disposed around said rotor and including a wound coil;   said magnet assembly comprising a Nd—Fe—B magnet.   
   
   
       2 . A drive motor according to  claim 1 , wherein said magnet assembly has skewed magnetic poles. 
   
   
       3 . A drive motor according to  claim 2 , wherein said rotor has a hollow region defined between said magnet assembly and said shaft. 
   
   
       4 . A drive motor according to  claim 3 , wherein said hollow region is defined between a holder disposed around said shaft and holding said magnet assembly and a slender shaft portion of said shaft which faces said holder. 
   
   
       5 . A drive motor according to  claim 4 , wherein said holder has a breather hole through which said hollow region is held in fluid communication with the exterior of said holder. 
   
   
       6 . A drive motor according to  claim 2 , wherein said magnet assembly comprises a pair of magnets held by said holder, said magnets being arrayed along an axial direction of said holder. 
   
   
       7 . A drive motor according to  claim 6 , wherein said magnets are skew-magnetized at a predetermined angle to an axis of the magnets. 
   
   
       8 . A drive motor according to  claim 7 , wherein said predetermined angle is 15°.