Ball screw device

Abstract

A ball screw apparatus is provided which is less likely to increase dynamic friction torque even when a nut is contracted by cooling, and in which cooling effect is made as high as possible and which does not invite excessive machining efficiency droop and increase in pressure loss. The ball screw apparatus includes a screw shaft, a nut screwed with the screw shaft via a plurality of balls, and a cooling section cooling the nut. The plurality of balls to which preload is applied in a two-point contact state, with a preload direction as a tensile direction, are disposed between a screw groove of the screw shaft and a screw groove of the nut. Or, a ratio of the axial length L of the through hole axially formed in the nut and the diameter D of the through hole axially formed in the nut is given by an equation “10≦L/D≦60”.

Dependencies are inferred from the claim text.