Mathematical Model of Drag Torque with Surface Tension in Single-Plate Wet Clutch

Abstract

Reduction of drag torque in disengaged wet clutches is essential for transmission research because it is one of the potentials of efficiency improvement. Aeration of oil film between two closely rotating plates promotes the decrease of drag torque at high speed region. The effects of surface tension and static contact angles during aeration are nonnegligible showed by test results. The traditional lubrication model does not adequately predict the experimental results with different surface tension and contact angles during aeration. Hence, in this present paper, contact angles between Aluminum and Teflon materials were firstly measured, and the drag torques under two different contact angles were examined experimentally. An improved lubrication model of drag torque based on Navier-Stokes equations at the gas-liquid interface was built. The lubrication boundary condition was modified to introduce the effects of surface tension and contact angle. The model shows that the effects at the beginning of aeration of oil film are significant. These effects almost occur at stationary plate due to low Reynolds number and Weber number. The model shows that an increase in the surface tension promotes aeration, but does not affect the peak drag torque. Increasing contact angle also promotes the aeration, and accelerates the decrease of drag torque. The larger contact angle is, the smaller the peak drag torque will be. A computational fluid dynamics (CFD) model based on volume of fluid (VOF) method was presented to validate the interface shape when aeration occurs. The model prediction has a good agreement with experimental observations for Aluminum plates and Teflon plates. The modified lubrication model of drag torque gives a convenient description of the effects of surface tension and contact angel, and lays down a frame to understand the beginning of aeration.

A methodology for data-driven modeling and prediction of the drag losses of wet clutches

“…Basically, existing models are either based on analytical or numerical calculation methods. The numerical CFD simulation represents a modern tool to calculate the drag torque and has therefore been used in various research studies [9,11,20,[27][28][29][30][31][32][33]. CFD simulations can be performed in the early development phase, do not require prototype parts or even series parts, and enable targeted optimization of the clutch design and the operating parameters.…”

“…A high correspondence of simulation and measurement can be achieved with a high-resolution 3D CFD model [27]. To model the heterogenous phase distribution in the two-phase flow, the Volume of Fluid (VOF) model [35] is commonly used [11,[27][28][29][30][31]. However, the simulations usually require high computational resources [2,11].…”

Theoretical and experimental study on drag torque of wet clutch considering surface tension and shrinkage of oil film

“…Mahmud et al 12 considered the effect of oil inflow and outflow behavior on the drag torque in the process of improving the simulation model. Peng and Yuan 13 established an improved model by introducing the influence of surface tension and contact angle to modify the lubrication boundary conditions. The above-improved models have obtained good prediction results in the lower speed range (usually less than 5000 r/min), but it has not yet been able to explain the sharp increase of drag torque in the high speed range, for which some scholars proposed the following explanations: including the increase of mechanical friction caused by the unstable swing vibration of the friction disk, 14 the large vacuum force caused by the static pressure drop at the oil outlet 15,16 and the rigid body impact caused by the increase in the lubricating oil flow.…”

Detailed CFD transient heat transfer modelling in a brake friction system

“…In both the systems there is a coupling between rotating and non rotating elements and a disengage/engage that leads to high power dissipation due to relative rotation and friction between the elements in contact. Lot of studies were performed to find relations during the disengage event and the torque calculation also with means of analytic studies ( [1], [2], [3], [4], [5], [6], [7]). Unfortunately, the analytic approach results in good agreement with the measurements only for simplified geometries, while for more complex geometries like the realistic grooves patterns of the rotating discs deviations are obtained from the test measurements.…”

“…Mainly executed with means of Simcenter STAR-CCM+ and ANSYS mainly, the simplest studies generally involve single phase models ( [8], [9]), but doing so the lubricating oil distribution tend to lead to over simplistic results while the temperature field distribution gives generally good agreement with the experiments. More accurate studies were realized considering twophase models ( [10], [11], [12], [13], [7]) of the oil/air mixture, implementing the Volume of Fluid method mainly. Then, most of the current studies focus mainly on single discs analysis or single steel-disc coupling ( [14], [15], [16], [17], [18]), where the influence of the different geometric pattern was demonstrated to be a fundamental parameter ( [19], [20], [21]) , while few exist that investigated more elaborated geometries ( [22], [23], [24]).…”