Self-calibrating torque measuring system

Abstract

A universal torque measuring system for hollow drive shafts which automatically compensates for variations in wall thickness exhibited by different drive shafts having the same nominal dimensions. During a calibration procedure, the drive shaft is subjected to a first predetermined torque which causes a certain amount of twist dependent upon its wall thickness. At this time, target indicia are positioned and affixed to the drive shaft to produce an initial phase shift relative to indicia on a reference shaft. Thereafter, when the drive shaft is incorporated into an engine and rotated under load subjecting it to a second predetermined torque less than the first predetermined torque, there is a resulting second phase shift. This second phase shift and the second predetermined torque define a second operating condition of the drive shaft. In turn, the first and second operating conditions define a characteristic relationship between torque and phase shift for the drive shaft. A sensor is positioned to detect deviations in phase shift of the first and second target teeth from the initial phase shift and generates a signal proportional to such deviations. A microprocessor is responsive to the signal from the sensor for automatically deriving a value of torque being experienced by the drive shaft as a function of each such deviation according to the characteristic relationship.