Patent ID: 8813598

Claim:
A ball screw, comprising: a screw defined on its outer periphery with a helical groove; a nut being inserted on the screw and defined with a helical groove which cooperates with the helical groove to form a load path; at least one return assembly being disposed on the nut and defined with a return passage which is connected to the load path to form a circulation path; a chain received in the circulation path and comprising a plurality of partition portions and a connecting portion for connecting the partition portions, a plurality of rolling elements being retained in the chain in such a manner that between each two neighboring partition portions is arranged a rolling element, each of the rolling elements being partially in contact with the return passage of each of the return assembly; characterized in that: a cross section of the return passage is a closed and complete elliptical shape and includes a first axis and a second axis which is shorter than the first axis, a central portion of the return passage is provided for passage of the rolling elements, an outer diameter of the rolling elements is equal to a length of the second axis, and a length of the first axis is larger than the outer diameter of the rolling elements, so that two semilunar receiving spaces will be formed between an inner surface of the return passage at both ends of the first axis and each of the rolling elements, and the connecting portion of the chain is movably accommodated in the receiving spaces.