Critical Analysis of Achievements and Missing Links in Gear and Bearing Tribology in Relation to Power Envelopes,

Power envelopes provide a convenient and informative basis of comparison for the development of gear transmissions towards higher power densities. Each such envelope consists of a sequence of segments representing power barriers due to a variety of critical phenomena. Most of these phenomena and barriers are tribologically affected. They may be exemplified by the occurrence of contact between the rubbing surfaces whenever a fully separating lubricant film can no longer be maintained and, further, by fitting and scubbing. For every gear transmission at least two power envelopes have to be considered in conjunction, i.e. for the most vulnerable pair of gears and rolling-element bearing, respectively. The trends of these two envelopes, as well as their mutual position, depend on the configuration of the major elements in the transmission concerned and on certain tribological characteristics of the solid rubbing materials and the lubricant. The present paper concentrates upon those segments of the two paper envelopes that are called contact barriers in that they relate to the occurrence of contact. In fact, the fundamentals of the other tribologically affected barriers, that of pitting and the one of scuffing, have already been dealt with fairly thoroughly in literature and therefore will here be treated only concisely.