Date:         Sat, 3 Apr 2010 15:18:34 -0700
Reply-To:     Alistair Bell <albell@SHAW.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Alistair Bell <albell@SHAW.CA>
Subject:      more on vc humping
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed

Its been stated that the tiny burrs produced when the internal plates
of the viscous coupling are pierced during manufacture play some role
in torque transfer. The mechanism has not been explained, until,
perhaps, now.

I found this abstract (no full text, sorry) and it states that the
burrs are involved with the asymmetric forces that force the plates
together (humping, or STA- self induced torque amplification) in the
100% torque transfer state. Its just another bit of the puzzle.

Unfortunately :) the abstract mentions, at the end, a temperature
dependent viscosity change model, I still believe this is not the
phenomenon involved in the vw vc

alistair


Title:

Numerical analysis of torque augmentation in viscous couplings
Authors:

Pan, Chen
Affiliation:

AA(SYRACUSE UNIVERSITY)
Publication:

Thesis (PhD). SYRACUSE UNIVERSITY, Source DAI-B 59/07, p. 3659, Jan
1999, 153 pages.
Publication Date:

00/1998
Category:

Engineering: Mechanical, Applied Mechanics, Physics: Fluid and Plasma
Origin:

UMI
Abstract Copyright:

(c) 1998: UMI Company
Comment:

Publication Number: 9842398; Advisor: Lewalle, Jacques
Bibliographic Code:

1998PhDT.......126P
Abstract

The humping phenomenon in viscous couplings is investigated by the
finite element method. The possible destabilizing factors suggested
by the experimental results are divided in two groups: fluid
properties and plate geometry. A simple two-dimensional model capable
of including these factors was devised. Both Newtonian flow and Non-
Newtonian flow in the viscous coupling were solved by our Finite
Element Method code. The finite element formulation based on the
variational principle is discretized by the mixed interpolation
functions. Within each triangular element, velocities were
approximated with a quadratic function and the pressure was
represented with a linear function. The non-linear system of
equations resulting from the discretization process were solved by
Gaussian elimination and iteration procedures. As a result, several
routes to humping in viscous couplings are documented. The plate
permeability associated with the perforations was found to have no
significant effect on the humping scenario. The initial loss of
symmetry can be provided by random fluctuations of the axial location
of the inner plates, or by the presence of burrs. Once the symmetry
is broken, the left side burrs at the leading edge of the inner
plates can initiate humping with a preferred direction of motion
toward the burrs side of the inner plate. It was found that viscous
coupling have an ability to recover from the plate torsion. The fluid
properties of the silicone oil are also associated with the humping.
After examining the power law model, the visco-pseudoplastic model
and the temperature-dependent viscosity model for the variable
viscosity, it was found that only visco-pseudoplastic model and the
temperature-dependent viscosity model can be used to explain the
humping. For some transition shear rate (233.3</bar Str<816.5) in the
visco- pseudoplastic model, the axial forces will increase the given
asymmetry and initiate the humping. For the temperature-dependent
viscosity model, the axial force initially stabilized the inner
plate, after passing the transition time (0.028 sec), the axial force
will destabilize the inner plate and initiate the humping.