Electric power steering apparatus

An electric power steering apparatus for assisting to steer steered wheels with a steering wheel, comprising:

• a housing;
• a rack shaft for steering the steered wheels, said rack shaft having a first rack and a second rack provided separately axially thereof;
• a supported part whereby said rack shaft is supported on the housing by means of intervening bearings, and a rack formation part where said first and second racks are formed, being disposed on said rack shaft;
• said rack formation part having an axis and a reference pitch line and said supported part having a diameter, wherein when a circular section perpendicular to the axis of said rack formation part is equal in diameter to the diameter of said supported part, and a distance from the center of said circular section to the reference pitch line is set to a specific dimension, said rack formation part having an actual tooth width greater than a second rack tooth width determined by the specific dimension;
• a first rack-and-pinion mechanism, including said first rack, for transferring a steering torque produced by turning a steering wheel to said rack shaft;
• an electric motor for producing an assist torque in accordance with the steering torque;
• and
• a second rack-and-pinion mechanism, including a pinion and said second rack, for transferring via a gear reduction mechanism the assist torque to said rack shaft,
• said pinion and said second rack of said second rack-and-pinion mechanism both being helical gears, one of said helical gears having a tooth profile wherein at least an addendum is a circular arc of which the radius of the arc of the addendum is generally centered on a reference pitch line, the other of said helical gears having a tooth profile wherein at least a dedendum is a circular arc of which the radius of the arc of the dedendum is generally centered on the reference pitch line, the circular arcs of the addendum and the dedendum of the tooth profile of each of the helical gears is point symmetrical with respect to the reference pitch line.