Patent ID: 7351180

Claim:
An automatic speed changing device, comprising: a hub unit including a hub shaft with both ends supported by a frame and with a sun gear formed at the center thereof, and a hub shell surrounding the sun gear and having a first ratchet ring and an inner gear formed on an inner peripheral surface of one side of the hub shell rotatably secured on the hub shaft; a first travel unit including a driver for rotating the hub shell while closing the other side of the hub shell and being rotatably secured on the hub shaft, and a driven sprocket for rotating the driver by receiving power from a driving sprocket; a second travel unit including a first carrier disposed within the hub shell and mounted at one side thereof with a plurality of planetary gears engaged with the sun gear and the inner gear to rapidly rotate the hub shell, and a second carrier extending from the other side of the first carrier to the driver; and a conversion unit including a second ratchet ring interposed between the driver and the second carrier to transmit rotational force from the rotating driver to the second carrier and the planetary gears of the first carrier.