This paper presents a study on the friction and wear characteristics of gears in high vacuum. A power-circulating-type gear testing machine with a vacuum chamber was developed, in which the coefficient of friction between the contacting tooth surfaces, and the temperatures of the gear tooth and the shaft can be measured simultaneously under various running conditions, The running tests for S 45 C, SUS 440 C and MoS2-coated SUS 440 C gears were carried out in high vacuum and air environments by using the gear testing machine, and the coefficient of friction between the contacting tooth surfaces, the wear of the gear teeth, and temperature changes of the gear teeth, the shaft, etc. were measured. On the basis of these results, the friction and wear characteristics of gears in high vacuum were determined.
