Thesis-2010-DelaCruz.pdf (19.46 MB)
The influence of transient thermo-elastohydrodynamic conjunctions on automotive transmission rattle
thesis
posted on 2011-02-16, 17:20 authored by Miguel De la CruzAutomotive transmission rattle is the noise generated due to impacts between manual
transmissions meshing gear teeth in the presence of backlash. It is considered to be a Noise,
Vibration and Harshness (NVH) phenomenon and is originated due to combustion
irregularities (engine order vibrations), especially in diesel vehicles. This thesis focuses in the
case of creep rattle for the MMT6 Ford Getrag transmission (six speeds plus reverse) with a
DW10b, 4-cylinder, 4-stroke, 2.0 litres diesel engine. This particular rattle condition is
fundamentally similar to any other where an engaged gear is pertained (drive, over-run or
float), with the 1st or 2nd gear engaged at a very low engine speed.
The numerical models include an initial single degree of freedom (DoF) simulation. It
comprises either of the engaged gear pair under Hertzian contact conditions or of a loose
gear pair under hydrodynamic regime of lubrication. Once the validity of this model is
established and correlated with the results obtained from a single gear pair test rig,
simulations of increasing complexity can be envisaged. A 7 DoF numerical model is,
therefore, developed. The Hertzian contact model still prevails for the engaged gear pair,
whereas an analytical hydrodynamic solution is implemented for the remaining 6 loose gear
wheels and Petrov s law is applied to the needle bearings retaining the gear wheels.
With the aim of accommodating a fully lubricated model of all the tribological conjunctions,
an analytical elastohydrodynamic (EHL) Grubin type algorithm is employed. Also, the
energy equation is analytically solved for hydrodynamic and elastohydrodynamic
conjunctions, based on the assumptions dictated by the Peclet number. Therefore, under
hydrodynamic conditions, the energy equation is governed by viscous heating and
convective cooling, whereas in the EHL conjunctions the governing terms are viscous and
compressive heating, together with conductive cooling. The retaining needle bearings follow
the same heat generation mechanism as journal bearings.
The effective viscosity, as obtained from the Houpert s equation accounting for pressure and
thermal effects, is fundamental for the study of the friction in the contact. The hydrodynamic
contacts are only governed by viscous friction, whereas EHL conjunctions exhibit asperity
iv
interactions as well as viscous effects. The results obtained from this new 7 DoF model are
then compared to the experimental measurements taken from the vehicle tests and various
purpose-built drivetrain rigs.
A metric named Impulsion Ratio is hereby introduced, aiming to shed some light into the
predictions obtained by the various models presented. This metric is the ratio of driving over
resistive forces acting on each individual gear wheel. Its use is tested to predict single or
double-sided rattle scenarios and, therefore, ascertaining higher and lower rattle levels. The
13 DoF model from which these conclusions were obtained includes shafts planar
translation and rocking moments. The rolling element bearings supporting the shafts are,
therefore, modelled to capture the inherent frequencies arising from their motion.
The final model introduces the effects of transient thermo-elastohydrodynamics. This 7 DoF
dynamic model accounts for a numerical solution of Reynolds equation with Elrod s
cavitation algorithm for simultaneous teeth in mesh. The results obtained validate the
previously used Grubin assumption by comparing the predicted central film thickness along
the full mesh of one tooth. Also, the effect of starved input conditions and thermal and isothermal
solutions are studied.
History
School
- Mechanical, Electrical and Manufacturing Engineering
Publisher
© Miguel Angel De la Cruz López-OsornioPublication date
2011Notes
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.EThOS Persistent ID
uk.bl.ethos.594426Language
- en