Up to now, a torque measuring device has been proposed in, for example, Patent Literature 1. In the torque measuring device, a strain gauge for detecting a strain of a torque sensor shaft is fitted to an outer surface of the torque sensor shaft. Specifically, a configuration has been proposed in which when the torque sensor shaft is twisted and strained, the strain gauge detects the strain, and outputs an electric signal corresponding to a change in electric resistance attributable to the stain, and a torque value is calculated according to the electric signal.
The strain gauge is configured in such a manner that a metal resistive element is formed on a thin insulator, and stuck onto the torque sensor shaft by adhesive. Therefore, even if the strain gauge undergoes the strain of the torque sensor shaft, the strain gauge is flexibly deformed. For that reason, the strain gauge does not crack due to the deformation of the torque sensor shaft.
In this example, when not the strain gauge but a torque sensor of the SAW type is employed as device for detecting the strain, the torque sensor is configured as a sensor chip of a hard piezoelectric body. Therefore, the hard piezoelectric body is fixed directly to the torque sensor shaft by adhesive. For that reason, when the adhesive is crept or deteriorated, the strain of the torque sensor shaft is not transmitted to the hard torque sensor of the SAW type, resulting in such a problem that a detection precision of the strain decreases.