The conical involute gears have been applied to automotive parts such as 4WD transfer. The conical gear pair has characteristic large ease-off and this is equivalent to meshing of cylindrical gears which has large crowning for lead direction. Consequently, the trochoidal interference is thought to be caused because of tooth stiffness reduction. In this study, to clarify the influence of the tooth flank modification on the tooth surface damage, tooth surface endurance test with several tooth flank modification forms is experimented. As a result, the gear pair with crowning for tooth profile direction and reverse crowning for lead direction can extend the pitting fatigue life because of the edge load reduction of tip or root.

The conical involute gears have been applied to automotive parts such as FR-4WD transfer. To apply for automobile, high capacity, higher quietness and efficiency are required. However the tooth contact of conical gear pair is point contact, so the large ease off happens even though each tooth surface has no manufacture error. Also the tooth depth and thickness of conical involute gears change along the lead direction. These characteristics have to be considered for the tooth mesh analysis. We have already published the transmission error analysis and tooth surface durability analysis considering these peculiar characteristics. In this paper, we develop the mesh efficiency analysis and show the improvement method of mesh efficiency by tooth surface modification. From this investigation, it is found that the mesh efficiency of conical involute gears is better than same size cylindrical gears due to the peculiar ease off distribution.

Most transmissions that use a traction drive mechanism also have a gear train to transmit power to the outside. In these transmissions, traction oil is used both as the working fluid and gear lubricant. Since precedence is given to the performance of traction oil as a working fluid, its performance as a lubricant is generally inferior. The traction coefficient of traction oil is higher than that of automatic transmission fluids (ATFs), so it is thought that the power loss of meshing gears under traction oil will be larger than that under ATF. In this paper, we experimentally compare the power loss of meshing gears between use with traction oil and with ATF and show that the power loss with the former increases by approximately 0.5% compared with that found for ATF. And also, it is shown that the magnitude of the power loss depends on the gear dimensions and operating conditions. The one of authors proposed the new estimation formula of friction coefficient and confirmed the usefulness of this formula under ATFs. In this paper, the usefulness of proposed estimation formula is also confirmed under traction oil. * 原稿受付 2013 年 4 月 11 日 *1 正員，日産自動車 (株)総合研究所(〒243-0123 神奈川県厚木市森の里青山 1-1) *2 日産自動車 (株)総合研究所 *3 日産自動車 (株)パワートレイン開発本部 *4 正員，フェロー，早稲田大学 大学院情報生産システム研究科

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This paper presents the result of fatigue tests carried out with an ATF and two types of traction oil. Since the performance of these oils as working fluid is preferred, the performance as a lubricant is inferior. The pitting life is evaluated by the value of D computed by the surface roughness and EHL film thickness. The high traction coefficient causes the tooth surface temperature rise by frictional heat, and then the oil film thickness and pitting life are decreased. To evaluate the performance of these oils as lubricants, the tooth surface temperature at the pitting tests is measured and the EHL film thickness is calculated with it for computing the value of D precisely. All results of fatigue test with three types of oils are examined together and it is found out that they are evaluated by the value of D only. The experimental formula to estimate the pitting life is obtained. This procedure is useful to design the surface gear strength of the automotive ATs and CVTs.