Development of Concave Conical Gear Used for Marine Transmissions : 2nd Report, Principal Normal Radii of Concave Conical Gear and Design of a Pair of Gears

Abstract

Conical involute gears used for marine transmissions are mostly helical conical involute gears. Besides these gears are not only intersecting axis gears but also nonintersecting-nonparallel axis gears. In this case the contact between tooth surfaces of a pair of gears is the point contact. Hence the tooth surface durability is generally small. In order to overcome this weak point, one of the authors invented a new type of conical gear, which is called "concave conical gear". Concave conical gear has higher tooth durability than the conventional conical involute gear. So we have already developed generating method of helical concave conical gear. In this paper, first the principal normal radii of the tooth surface generated by this method are expressed in terms of basic dimensions of gear and tool. The principal normal radii of test gears are measured. They are in good agreement with the theoretical ones. Secondly an allowable normal load of a pair of concave conical gear is obtained. Tooth bearing tests prove that the Heltzian contact ellipse is larger than that of the conventional conical gear. Thus it is proven that a designing method of a pair of concave conical gears is of practical use.