4. An idealized model was developed to understand the mechanism of
thermoelastic instability in two-conductor friction systems. This model
takes into account the effect of thermal contact resistance at the
interface. The simulations show that the critical speed increases when
the system has the symmetry of material properties and geometry. The
difference in material properties and geometry of two conducting bodies
influences the critical speed significantly.
5. In wet clutches, hydrodynamic pressure is developed inside the
friction material as well as the fluid film due to the porous
paper-based friction material. Moreover, ATF exudes from the friction
material due to developed hydrodynamic pressure. Considering the
continuity of Darcian flow, hydrodynamic pressure and exuding velocity
were included in the analysis.
6. To make realistic predictions of TEI in wet clutches the
analysis also takes into account the deformation of the core plate that
the friction material is bonded on. The analysis shows that the
deformation of the core plate improves the critical speed.
7. An idealized model was developed to investigate the growth rate
of the perturbed temperature. The governing equations were modified to
compute the growth rate at a given operating speed. The growth rate
increases with increasing operating speed. Determination of the growth
rate allows one to investigate the heat concentration and the
penetration depth.
Analytical solutions were based on the assumption that the system
consists of two disks and temperature and pressure variations in radial
direction are neglected. The three-dimensional problem can be solved by
the numerical analysis. However, such an analysis requires considerable
amounts of time and effort to develop and generally requires extensive
computation. It was also assumed that the operating speed remains
constant during the engagement. However, wet clutch systems are
designed to reduce the relative speed of two sliding surfaces and,
therefore, they are transient in operation. It follows that the
unperturbed pressure and temperature distributions should be considered
in the analysis. Our future work aims at developing the finite element
model, including the three-dimensional effect and transient effect.
Since there are a large number of interacting parameters involved,
developing a transient 3-D TEI model of a wet clutch is not a simple
task. Moreover, in order to apply the analytical results to the design
process, the result should be verified by the experiments. Experiments
allow one to verify the analytical model that can be used to determine
the conditions that are likely to initiate the formation of hot spots.
Journal Publications
Jang,
J. Y. and Khonsari, M. M., 1999, “Thermal Characteristics of a Wet
Clutch,” ASME Journal of Tribology, V. 121, pp. 610-617.
Jang, J. Y. and Khonsari, M. M., 1999, “Thermoelastic Instability
Including Surface Roughness Effects,” ASME Journal of Tribology, V.
121, pp. 648-654.
Jang, J. Y. and Khonsari, M. M., 2000, “Thermoelastic Instability with
Consideration of Surface Roughness and Hydrodynamic Lubrication,” ASME
Journal of Tribology, V. 122, pp. 725-732.
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