<div>The axle, or differential, flange is understood to be a large source of vehicle
driveline imbalance, or unbalance, through defining the center of rotation of a
driveshaft. The tolerances and methods of manufacturing and assembly are
therefore very important. The aim of the current investigation, is to understand
and quantify the imbalance contributions from flange radial and axial runout,
along with location error between the driveshaft and axle flange. An overview of
the measured radial and axial runouts from a population of 100 axle assemblies
is presented, including correlation of the imbalance amplitude distributions to
some standard probability density functions. It was found from the
investigation, that it is important to understand the nature of any source of
runout, relative to any subassembly/component-level balancing, in modeling the
transfer function from runout to imbalance loading. Methods for calculating the
imbalance of an assembled driveline are presented, which include the mass levels
of important driveline components in their calculation. Two methods of
quantifying the weight contribution are given—the “distributed weight” method
and the “hung mass” method. The latter is known to be used in some parts of the
industry. The “distributed weight” method led to an improved estimate of the
contribution from the driveshaft tube mass on the imbalance force at the axle
flange. Two methods of dealing with the radial and axial runout of an axle
flange are discussed—the industry-standard “CFRO” method (combined flange run
out) and the “IIRA” (individual imbalance forces from radial and axial runout)
method. The CFRO method tended to lead to overestimation of the level of runout
imbalance. The contribution of imbalance due to location error between the
driveshaft and axle flange is identified and quantified with results, for the
100 axle assemblies of measured data, given. It is hoped and intended to be a
useful guide to the NVH engineer doing the calculation of imbalance loading from
axle runout.</div>