PRE-LOAD VARIABLE TYPE SPINDLE UNIT

PROBLEM TO BE SOLVED: To slide a sleeve in a housing smoothly irrespective of operating conditions. SOLUTION: Between a spindle 1 and the housing 2, two angular bearings 3, 4 supporting the spindle 1 rotatably, the sleeve 5 giving a pre-load to the bearing 3, a positioning ring 6 contacted with and separated from the sleeve 5, and a regulating member 7 regulating the axial movement of the sleeve 5 are assembled. A helical groove 21 filled with pressure oil lubricating the sliding surface 24 of the sleeve 5 is formed. Wall surfaces on both sides of this helical groove 21 are made inclined axially outward to the sliding surface 24, and the angle of the inclination of the inclined surface 25 is set to be 20°-40° relative to the sliding surface 24. By this configuration, a force pressing the inclined surface 25 of the helical groove 21 axially inward is applied by the wedge effect of the filled pressure oil when the sleeve 5 slides. This prevents the open rim of the helical groove from biting into the sliding surface of the other member, and permits the sleeve 5 to be slid smoothly in the housing 2. COPYRIGHT: (C)2008,JPO&INPIT