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Research Papers: Applications

# The Influence of Grooves on the Fully Wetted and Aerated Flow Between Open Clutch Plates

[+] Author and Article Information
Chinar R. Aphale1

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48105caphale@umich.edu

William W. Schultz

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48105schultz@umich.edu

Steven L. Ceccio

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48105ceccio@umich.edu

1

Corresponding author. Present address: 3833 Cummins Street, Houston, TX 77027.

J. Tribol 132(1), 011104 (Dec 10, 2009) (7 pages) doi:10.1115/1.3195037 History: Received October 04, 2007; Revised July 09, 2009; Published December 10, 2009; Online December 10, 2009

## Abstract

In a disengaged or open clutch mode, one plate rotates while the other is stationary. This speed difference between the two plates (on the order of 1000 rpm) and the small clearance between them (on the order of $100 μm$) results in large velocity gradients. Transmission fluid is passed between clutches since during reengagement; this oil provides lubrication and carries heat away. However, during the disengaged mode the shearing of this oil as it passes between the plates results in viscous drag that wastes power. Introduction of air between the two plates during the disengaged mode, referred to as aeration, is the most significant way of reducing this friction drag due to low viscosity of air compared with oil. Open clutch drag reduction is enhanced by providing grooves on one of the plates since they are known to promote aeration. Yet, a continuous supply of lubrication oil is necessary, even during disengagement. This study examines the underlying processes responsible for the oil flow between grooved disks and possible aeration through a combination of experiments and numerical computations. A two-dimensional model of the three-dimensional, single-phase flow between a stationary and a rotating clutch plate is presented, which is capable of describing pressures and shear stress distribution for plates with radial grooved geometries. The computational fluid dynamics code FLUENT ® is used to examine the single-phase and aerated flows between the plates. These results are compared with accompanying experimental observations. We also examine new groove designs to study their efficiency in promoting aeration. Finally, we propose reasons for grooves promoting aeration in clutches.

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## Figures

Figure 1

Block diagram of overall experimental configuration. The circulation pump maintains a steady oil flow with nearly constant temperature. The syringe pump is used to deliver a fixed flow rate of oil. St. P: stationary plate; RP: rotating plate; TA: torque arm; T: thermocouple; M: motor; PG: Pressure gauge; SG: strain gauge; DB: driving belt; SP: syringe pump; OS: oil sump; CP: circulation pump.

Figure 2

Repeatability study of the drag torque measurement. The repeated data are for 80 grooves, 100 μm clearance.

Figure 3

Hour-glass and Inclined plate grooves. The angle of inclination of the grooves was 60 deg from the radial line.

Figure 4

Geometry of the model. The groove extends between x=2nl and x=l. The faces at x=0,l are modeled as periodic.

Figure 5

Pressure comparisons between model and FLUENT ® for a two step geometry with periodic boundary conditions. The groove extends from X=0.4 to X=1.0.

Figure 6

Comparison of analytic model, FLUENT ® three-dimensional single phase and experimental data at low rotation rates to ensure that the flow is single phased. The comparisons are for a plate with 40 radial grooves with 200 μm clearance and 100 ml/min.

Figure 7

Experimental results for 200 μm clearance and 100 ml/min. The sharp drop in the curves indicate the onset of aeration.

Figure 8

Visual images of aerating clutch taken with a high speed camera. The flow rate is reduced at a constant rotation rate in the five frames to induce aeration.

Figure 9

Comparison of hour-glass and inclined groove plate drag torque profiles. The inclined grooves has significantly different aeration onset conditions depending on the direction of rotation.

Figure 10

Comparison between FLUENT ® and the experiments for 40 radial grooves with 200 μm clearance and a 200 μm depth and inclined grooves plate at 100 ml/min

Figure 11

Path lines of fluid motion in a grooved geometry. The oil in between the pads moves in a tangential direction, whereas grooves push the oil radially outwards. The different thicknesses of the lines in the pad region denote different depths, with the bolder line closer to the top, rotating plate.

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