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Torque Losses
Associated with Pumping ATF
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SwRI Project: |
03-6138 |
Client: |
Industrial Confidential |
Project Brief
The pumping of automatic transmission fluid (ATF) through a transmission may represent more than 40% of the total energy losses for the transmission assembly. Transmission manufacturers have addressed this type of energy consumption by incorporating fluid recirculation loops, multiple pumping systems, variable orifice effects, improved fixed displacement gear tooth forms, asnd variable displacement pumps.
A characteristic of all of the above modifications is the fluid viscosity effects associated with pumping ATF. To gain even more efficiency from whatever hardware enhancements are incorporated, lowering the viscosity of the ATF should be considered. This may be accomplished chemically or through operation at elevated temperature.
For a typical current production ATF blend, the difference between operating an internal-external crescent-type fixed displacement gear pump at 2,500 rpm and 60 psig between 100 and 250°F will provide the following percentage reductions in pumping torque:
ATF Temperature |
Percent Reduction in Torque |
100°F |
Baseline |
200°F |
23.6% |
250°F |
27.4% |
For an ideal hydraulic pump, pumping is a function of the pressure drop across the pump, mechanical friction and viscous drag of the fluid. Viscous drag of the fluid is directly proportional to the viscosity of the fluid as shown in the relationship below:
Dv = f(CdDpµNp)
where
Dv = viscous drag (in.-lb)
cd = viscous drag coefficient (unitless)
Dp = pump displacement (in.³/rev)
µ = fluid viscosity (lb-sec/in.²)
Np = speed of delivery (rev/min)
For the above pump, overall and mechanical efficiency improves due to a reduction of the viscosity drag coefficients and the fluid viscosity, while volumetric efficiency decreases due to increased leakage which also results from decreased fluid viscosity as follows:
Overall Efficiency, % |
Volumetric Efficiency, % |
Mechanical Efficiency, % |
Flow, gpm |
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100°F |
25.9 |
95.1 |
27.2 |
14.97 |
200°F |
31.6 |
93.5 |
33.8 |
14.58 |
250°F |
34.4 |
90.0 |
38.2 |
14.18 |
For more information about our drivetrain engineering capabilities and past performance briefs, or how you can contract with SwRI, please contact Douglas Fussner at dfussner@swri.org or (210) 522-3972.
Contact Information |
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Drivetrain Design and Development (210) 522-3972 |
Related Terminology |
transmission test transmission testing automatic
drivetrain database drivetrain |
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| Design and Development | Engine, Emissions & Vehicle Research Division | SwRI Home |
Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.
December 28, 2012
