Ball screw apparatus

A ball screw apparatus comprising:

• a ball nut including an inner periphery, a ball track formed in the inner periphery, and a second stopper, wherein the second stopper includes a second recessed portion formed in the inner periphery of the ball nut,
• a ball screw shaft including an outer periphery and a ball track formed in the outer periphery, the ball screw shaft being inserted through the ball nut;
• a ball train including a plurality of main balls housed in a raceway formed between the ball track of the ball nut and the ball track of the ball screw shaft;
• a second coil spring including a first end that engages with a second end of the ball train and a second end supported by the second stopper and housed in the raceway;
• and
• a second stopper ball held in the raceway and interposed between the second recessed portion and the second end of the coil spring and having a larger diameter than the main balls,
• wherein the second recessed portion holds the second stopper ball such that the second stopper ball is sandwiched between the second recessed portion and the ball track of the ball screw shaft to regulate movement of the second stopper ball with respect to the ball nut,
• wherein the second recessed portion is elongated along an axial direction of the ball screw shaft and has a length corresponding to a width of a plurality of tracks of the ball track of the ball nut, and
• wherein the second recessed portion is shaped as a circular arc, a diameter of the circular arc being larger than a diameter of the second stopper ball.