US Patent 9010210 Internal circulation ball screw

An internal circulation ball screw includes a threaded shaft, a nut having a receiving space, a circulation member mounted to the receiving space and having a first circulation groove and a second circulation groove, and a plurality of rolling members running between the threaded shaft and the nut. The first circulation groove defines a first front section, a first rear section, and a first curved section communicating with the first front section and the first rear section separately. The second circulation groove defines a second front section, a second rear section, and a second curved section communicating with the second front section and the second rear section separately. The first and second curved sections define a predetermined included angle with respect to the threaded shaft radially. Therefore, the wall between the circulation channels is uniform to enhance the durability of the ball screw.