Patent ID: 7560849

Claim:
An AC generator for a vehicle, comprising a field winding that is wound on a rotor iron core, a rotor shaft having said rotor iron core mounted thereon, a negative polarity slip ring and a positive polarity slip ring which are each formed of an identical material and are mounted on a circumference of said rotor shaft and respectively electrically connected to opposite ends of said field winding, a negative polarity brush and a positive polarity brush that are held in sliding contact with respective outer circumferences of said negative polarity slip ring and positive polarity slip ring, a negative polarity spring for applying a predetermined amount of force acting to urge said negative polarity brush into contact with said negative polarity slip ring circumference, and a positive polarity spring for applying a predetermined amount of force acting to urge said positive polarity brush into contact with said positive polarity slip ring circumference, with each of said negative polarity brush and positive polarity brush having an operating life that is determined by a degree of wear which occurs due to said sliding contact; wherein said negative polarity spring is configured to apply a lower level of force to said negative polarity brush than a level of force applied to said positive polarity brush by said positive polarity spring, for rendering said operating lives of said negative polarity brush and positive polarity brush substantially identical to one another.