Design of planetary gear sets is more involved than the design of their counter-shaft counterparts as it involves simultaneous design of a set of internal and external gear meshes while complying with a large number of systems and gear mesh related requirements for assembly, durability, noise, and efficiency. A manual iterative design process often results in suboptimal designs that fail to meet all these requirements simultaneously. In this paper, a methodology for an automated design search of single and double-planet planetary gear sets is proposed. With the input of a number of system-level constraints associated with the spacing and phasing of the planets, and acceptable ranges of basic geometric design parameters, this methodology defines a large design space in that a large number of geometric design concepts are identified and checked for any interferences. The external and internal meshes of these concepts are evaluated by using computationally efficient loaded gear tooth contact analysis model to predict their performance metrics such as transmission error amplitudes and contact and root stresses. They are then rank-ordered based on their performance metrics to identify balanced planetary gear set designs meeting all requirements equally well. At the end, results of an example design search were presented to demonstrate the effectiveness of the proposed methodology in defining a balanced solution that is acceptable in terms of all of its requirements.
Mechanical (load-dependent) power losses of a planetary gear set occurs primarily along its lubricated rolling-sliding interfaces at the external and internal gear meshes, and planet bearings. The gear mesh originated portion of these losses are influenced by all key gear parameter, tooth profile correction and other parameters dictating the fluid film formation. In this study, a systematic planetary gear design search algorithm is combined with an efficiency formulation to (i) quantify the sensitivity of gear mesh mechanical losses of planetary gear sets to the basic gear design parameters and (ii) investigate the compromise that must take place between the mechanical efficiency and other functional attributes associated with durability and noise performance of the gear set. An example design study is presented at the end to demonstrate both of these points.
In the recent automotive industries, automotive technologies for improving fuel efficiency have focused on the developments of reducing power losses in a transmission. As a well-developed and conventional power transmitting system, an automatic transmission is still widely used in many automotive vehicles. The automatic transmission is co-axially designed with several planetary gear sets and other mechanical parts. The co-axial arrangements and gear helix angles make the transmission necessarily include bearings for supporting loads and allowing relative rotations. In this study, the influences of thrust loads yielded by helix angle directions of planetary gear sets on bearing power losses are presented by performing the structural and power loss analysis. Bearing power losses consist of mechanical and spin power losses. For calculating thrust loads and bearing rotations, a complete transmission model is constructed by using an example structure, and structural analysis is performed for the combinations of helix angle directions of the gear sets. Finally, bearing power losses are computed by using the bearing power loss model, and the results of the entire combinations of helix angle directions are discussed.
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