Analytical Model Tool Development
for the Lubrication of an
Automatic Transmission, 03-R9602
Principal Investigator
Glenn R. Wendel
Inclusive Dates: 01/01/06 – Current
Background - Automatic transmissions are complex mechanisms which, when designed well, provide very smooth operation with good efficiency and durability. One of the key elements of an automatic transmission design that is often not optimized because it is not well defined is the fluid lubrication circuit. It is a complex network of flow paths that serve to provide lubrication and cooling flow to clutch packs, bearings, gears, torque converter and to 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 to 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 a 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. Pressure and flow will be measured through selected key flow areas of an automatic transmission for which the software tools were developed.
Accomplishments - CFD analysis has been completed for a matrix of conditions for flow through a rotating shaft with a variety of radial lubricating holes, and the analysis is continuing for the analysis of flow past roller bearings and clutch hubs. A special test fixture has been built to replicate these same flow paths from which pressure and flow measurements are being made which would not be possible in a complete transmission. These results are being evaluated and are being used to develop the math based relationships for the fluid flow.
