A spindle motor for use in a disk drive having a rotor assembly and a stator
assembly.
The rotor assembly has a hub and a rotating shaft with an outer diameter, the hub
being mounted for rotation on the rotating shaft. The stator assembly has a bearing
sleeve with a bottom opening, the rotating shaft being inserted into the bearing
sleeve for rotation. A counter-plate is inserted into the bottom opening of the
bearing sleeve thereby closing the bottom opening. A thrust plate is mounted on
the rotating shaft in opposing relationship with the counter-plate, the thrust
plate having an outer diameter. A fluid dynamic thrust bearing is formed between
the counter-plate and the thrust plate. A ratio between the outer diameter of the
shaft to the outer diameter of the thrust plate is reduced to reduce spindle motor's
power consumption.