Lubrication of gear tooth is necessary for cooling as well as reducing friction losses. It is, however, difficult for rather high speed gear because both rotation of the gear itself and associated aero motion interferes the lubrication. In Addition lubrication consumes excess energy due to such kind of churning.

To realize efficient lubrication it is worthy to feed lubricant from both ends of tooth in axial direction by the aid of sucking action of tooth spaces just after meshing. This probably make possible that the oil can reach the tooth surface as earlier as possible.

Authors investigated the action of air due to pumping action of a spur gear pair by means of both pressure measurement and the hot wire anemometry at the bottom of tooth space to get fundamental data to asses the feasibility of the proposed way. It has been revealed that the behavior is mostly governed by geometric characteristics around the mesh area rather than operational speed, i.e., temporal response of the pressure and flow velocity is proportional to the speed of gear. It has been also found that pressure variation precedes the flow velocity. Sucking phenomena begins when the backlash space passes through the pitch point whereas the pressure is readily negative due to the mass inertia effect of air getting out of the tooth space.

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