Patent ID: 6923294

Claim:
A lockable wheel which comprises an axle; a ground-engaging hollow casing that is mounted for rotation on the axle; and a resetable locking mechanism that is mounted on the axle and housed in the casing, the locking mechanism comprising: a locking element which is axially displaceable in the casing between a first position in which it permits rotation of the casing with respect to the axle and a second position in which it releasably engages with the axle and the casing to lock the casing against rotation with respect to the axle; biasing means for biasing the locking element towards the second position; and metering means for metering the number of revolutions of the casing after the locking mechanism has been reset from a locked condition wherein the locking element is in its second position to an unlocked condition wherein the locking element is in its first position and releasing the locking element for displacement to the second position when a predetermined number of revolutions of the casing has taken place, the metering means comprising a train of at least three gear wheels housed in the hollow casing, with a first of the gear wheels being advanced by each revolution of the casing, and a second of the gear wheels being advanced by each revolution of the first gear wheel and a third of the gear wheels being advanced by each revolution of the second gear wheel.