Internal-circulation-type ball screw

An internal-circulation-type ball screw, comprising:

• a nut, having an internal-thread groove;
• a screw shaft, rotatably passing through the nut and having axially a returning channel, the screw shaft having and outer surface provided with an external-thread groove and two opposite receiving recesses, the external-thread groove corresponding the internal-thread groove of the nut so as to form a helix channel therebetween, each said receiving recess extending form the external-thread groove radially along the screw shaft so as to get communicated with the returning channel;
• two returning members, being received in the receiving recesses of the screw shaft and each having a redirecting channel, and the redirecting channel having one end connected to the helix channel and having an opposite end connected to the returning channel of the screw shaft;
• and
• a plurality of balls, being rollably received in the helix channel, the redirecting channel, and the returning channel;
• wherein the redirecting channel forms a first returning path and a second returning path the first returning path having one end connected to one end of the second returning path, the first returning path having an opposite end connected to the helix channel, and the second returning path having an opposite end connected to the returning channel;
• wherein the first returning path is greater than a semicircle defining a path of greater than 180°, and the second returning path is a quartered circle.