Fluid coupling device

Claim 1

A fluid coupling device including a stationary main coupling body which has a cylindrical wall portion, means for retaining a rotary shaft to be rotatably supported in the main coupling body by at least one bearing, the rotary shaft extending through a cavity within the main coupling body and being formed with an internal fluid passage, a fluid being supplied from a fluid inlet in a first end of the main coupling body to a rear end of the fluid passage of the rotary shaft, the rotary shaft having an outer peripheral surface, and the main coupling body having an inner peripheral surface defining the cavity therein, the device comprising: the inner peripheral surface of the main coupling body having first, second and third internal portions arranged in order from the first end thereof, a rear end portion of the outer peripheral surface of the rotary shaft and the first internal portion of the inner surface of the main coupling body defining a first minute space therebetween, said first minute space in communication with the fluid inlet in the first end of the main coupling body; the outer peripheral surface of the rotary shaft and the second internal portion of the main coupling body defining a pressure reduction chamber in fluid communication with the first minute space; a drain hole formed through a wall portion of the main coupling body in fluid communication with the pressure reduction chamber; the outer peripheral surface of the rotary shaft and the third internal portion of the main coupling body defining a second minute space in communication with the pressure reduction chamber, the second minute space being positioned between the pressure reduction chamber and the bearing; and a pneumatic pressure inlet formed through the wall portion of the main coupling body in fluid communication with the second minute space.