Power wrench with magnetic sleeves for variable torque output

Claim 1

A power wrench having a variable torque output, comprising: a motor; an output shaft; reduction gear means and a magnetic clutch means rotatably coupling said motor to said output shaft, said magnetic clutch means being arranged to release the output shaft from the motor when the torque transmitted therethrough reaches a predetermined value, said magnetic clutch means comprising: a driven shaft having a permanent-magnetic sleeve affixed thereon; and a driving sleeve means comprising two intercoupled sleeves each having a permanent-magnetic sleeve affixed therein, said driving sleeve means having a predetermined radial clearance to the magnetic sleeve on the driven shaft, said permanent-magnetic sleeves being radially magnetized so that their annular surfaces toward said clearance form a plurality of axially extended and circumferentially distributed pole surfaces; said two intercoupled sleeves of said driving sleeve means being turnable relative to each other and interlockable in preselected relative angular positions so that the pole surfaces of the permanent-magnetic sleeves of said two sleeves of said driving sleeve means coact or counteract in selective amounts in their magnetic couplings to said permanent-magnetic sleeve of said driven clutch member to thereby vary the torque output of the power wrench.