Efficiency losses in a gearbox are originated
from several sources including gear mesh sliding
and rolling friction, windage, oil churning, and
bearing friction [34]. When gears are loaded, a gear
contact under load experiences combined sliding
and rolling, both of which result in frictional losses.
The amount of sliding frictional loss is directly related
to the coefficient of friction, normal tooth load and
relative sliding velocity of the surfaces while the
rolling friction occurs due to the deformation of the
two contacting surfaces. When the contact is
lubricated, rolling frictional losses are originated from
the formation of the EHL film [35]. Efficiency can be
improved by reducing the coefficient of friction via
precision manufacturing and smoothening the
contact surfaces and enhancement of lubricant
properties. Existing approaches of improving
efficiency are based mostly on experimental trialand-
error type procedures focusing on such
parameters, while the predictive capabilities have
been limited.
The main objective of this study is to develop a
mechanical efficiency model for hypoid gears. The
model allows an analysis of both face-hobbed and
face-milled hypoid gears. The efficiency model will
allow two methods of calculating μ , i.e. published
empirical formulae and a thermal EHL formulation.
The differences amongst these approaches will be
described. Parametric studies will be performed to
investigate the influence of several relevant
parameters such as speed, load, surface roughness,
lubricant temperature as well as the assembly errors
on the mechanical efficiency of hypoid gears. This
study is focused primarily on the mechanical
efficiency losses related to tooth friction, including
sliding and rolling friction, while it relies on the
published studies in terms of losses associated with
windage, oil churning and bearings [34,35,64-69]
when necessary.