Patent ID: 7478567

Claim:
A device for sensing a torque applied through a shaft having a longitudinal axis of rotation, the device comprising: a magnetoelastic ring press-fitted on the shaft whose torque is measured; an excitation coil placed in close proximity to the magnetoelastic ring with a longitudinal excitation axis of said excitation coil radially aligned with said axis of rotation at a selected radial position on an outer circumferential surface of the magnetoelastic ring, the excitation coil driven by an oscillator for inducing localized eddy currents inside the material of the magnetoelastic ring; a coupling sleeve disposed between the shaft and the magnetoelastic ring to minimize hysteresis effects of the shaft upon the magnetoelastic ring during induction of said localized eddy currents; a sensing coil placed in close proximity to the magnetoelastic ring with a longitudinal sensing axis of said sensing coil radially aligned with said axis of rotation at a radial position on the outer circumferential surface of the magnetoelastic ring and in close proximity to the excitation coil for sensing the magnetic field generated by the induced eddy currents inside the magnetoelastic ring; an electrical circuit configured to receive signals from said sensing coil to detect changes in the magnetoelastic ring's electrical conductivity and magnetic permeability responsive to applied torque forces in the shaft.