Analytical Model Tool Development
for the Lubrication
of an Automatic Transmission, 03-R9602
Principal Investigator
Glenn
R. Wendel
Inclusive Dates: 01/01/06 – 12/31/06
Background - Automatic transmissions are complex mechanisms which, when designed well, provide very smooth operation with good efficiency and durability. A key element of an automatic transmission design that is often not optimized because it is not well defined is the fluid lubrication circuit. The circuit is a complex network of flow paths that serve to provide lubrication and cooling flow to clutch packs, bearings, gears, torque converter and shift control module. Excessive flow through the circuit can cause excessive power loss, and insufficient flow in any part of the transmission can result in poor durability and can affect shift performance. The automotive industry continues to increase its reliance on math-based tools for design and analysis, but still relies heavily on road and lab testing. Commercially available software tools have been developed for fluid flow networks; however, accurate and easy to use modeling tools for analyzing the complex flow paths and restrictions typical of an automatic transmission are not currently available.
Approach - The purpose of this project is to develop analytical tools for modeling critical flow areas within an automatic transmission. Computational fluid dynamics (CFD) analysis software will be applied to model selected key flow areas that cannot be easily modeled using traditional modeling techniques. The flow characteristics will be evaluated for a variety of operating conditions, including speeds, pressures, fluid temperature, air entrainment, and dimensional parameters. The analytical tools will be developed using physics-based modeling techniques by applying coefficients derived from the flow characteristics observed from CFD analysis results. These analytical tools can be incorporated into library elements of commercial flow network analysis software packages and integrated into a network of other standard library elements to represent the more complete transmission lubrication flow network. The CFD analysis results will be correlated, and the software tools will be validated by running laboratory tests.
Accomplishments - CFD analysis was performed for a matrix of conditions for flow through a rotating shaft with a variety of radial lubricating holes and for flow past roller bearings. A special test fixture was built to replicate these same flow paths, and pressure and flow measurements were made. Software tools were developed, and the tools correlated well with the laboratory test results and the CFD analysis results. The expected benefits of this program are that the transmission design and analysis capabilities of SwRI are greatly enhanced, which will support future transmission design projects and open up new opportunities for analysis and testing of transmission lubrication.
