Patent ID: 7509825

Claim:
An automatic balancing device for counterbalancing an out-of-balance mass present in a rotating body, comprising: a chamber having an outer wall and an axis, and which rotates with the rotating body, first and second counterbalancing masses spaced along the axis and constrained to move freely in a circular path about the axis and within the chamber such that, when the device is in use, the first counterbalancing mass leads the second counterbalancing mass, a viscous fluid provided in the chamber so as to provide viscous coupling between the outer wall of the chamber and each of the counterbalancing masses when the device is in use, and a constraint operating at all speeds of rotation when the device is in use to prevent the first counterbalancing mass from leading the second counterbalancing mass by more than substantially 180Â° at all speeds of rotation when the device is in use, wherein the first counterbalancing mass and the second counterbalancing mass are spaced along the axis such that the first counterbalancing mass is spaced further from a side of the chamber than the second counterbalancing mass such that the viscous coupling between the first counterbalancing mass and the outer wall of the chamber is higher than the viscous coupling between the second counterbalancing mass and the outer wall of the chamber.