Frictional heating from rolling and sliding contacts of gear teeth is of extreme importance for monitoring the health of a gear transmission under its continuing operation. The surface temperature holds the critical information about a gear's health condition. A new power circulating gear test rig with a multichannel computer data acquisition system has been built to develop various sensor technologies for surface temperature evaluation of gear teeth. In this paper, the surface temperature monitoring of gear tooth will be presented by using miniature thermocouples. Five miniature type-K thermocouples of 125 μm in diameter have been embedded underneath the tooth surface of a spur gear, and real-time surface temperature variations from a wide range of operating conditions were measured. The various effects of load, rotating speed, and meshing point on the surface temperature are discussed. The results attained in this study indicate that the maximum temperature rise occurs on the dedendum, close to the dedendum circle, and the maximum surface temperature difference at the various contact points along the tooth profile was 13°C. Among the various temperature monitoring techniques, the thermocouple is a very reliable and practical mean for gear health monitoring.
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