Toy vehicle wheels are each mounted on an axle having a gear with each of the wheels having a pair of diametrically opposed arcuate segments. Each of the arcuate segments includes an inwardly extending member with each member including a rack that is kept in engagement with an opposed toothed side of...http://www.google.com.tw/patents/US5102367?utm_source=gb-gplus-share專利 US5102367 - Toy vehicle wheel and axle assembly
