Electric power steering apparatus

An electric power steering apparatus, comprising a casing, a steering shaft, a planetary roller nut, and a motor, wherein:

• the casing, having a first casing and a second casing, the first casing being a hollow tubular body;
• the second casing being a hollow tubular body with multi-order tube diameters, an accommodating space being formed inside one end of a larger tube diameter of the second casing, and a first waterproof ring being embedded at a selected position inside the accommodating space;
• the steering shaft, disposed in the casing in an axially reciprocal manner, two ends thereof respectively extending from the first casing and the second casing, and a body of the steering shaft having a rack portion and a screw portion;
• the planetary roller nut, assembled in the casing and screwed to the screw portion of the steering shaft, the planetary roller nut being supported and accommodated in the accommodating space of the second casing through a bearing, and the planetary roller nut and the first waterproof ring being matched with each other;
• the planetary roller nut being provided with a driver flange on one side end, and a second waterproof ring being embedded in a center of an outer end of the driver flange;
• the motor, disposed in the second casing;
• the motor having a hollow-shaped motor stator and an external rotor, and the motor stator being assembled with a set of coils pierced through by a hollow seat tube;
• the motor stator allowing the steering shaft to pass through the hollow seat tube, and the hollow seat tube of the motor stator and the second waterproof ring being matched with each other;
• one end of the external rotor being coupled to the planetary roller nut to drive the planetary roller nut to rotate, further driving the steering shaft to axially reciprocate within the casing.