Improved reliability and robustness.
Higher pressures, up to 2000 psi.
Higher operating temperatures, up to 150
Low-temperature materials for synthetic fluids.
Improved lubricant compatibility.
Lower friction, by as much as 20%.
Higher speeds, up to 8000 rpm.
Manufacturers of manual transmissions for large trucks are faced with essentially the same
challenges as are bearing manufacturers power density and durability. Although the product
envelope has not changed in size since the 1960s, power requirements have increased from 300
to 800 horsepower, and warranty periods are at 750,000 miles and moving to 1,000,000 miles.
The increasing power density causes surface fatigue (pitting and wear) on the gears, which
results in noisy gears, tooth breakage, and lower efficiency.
Methods to solve those problems include use of premium steels, improved lubrication, and
surface treatments such as smoothing and coatings. Affordability has been a key concern with
Continued improvements in engineered surface would allow improved fuel efficiencies through
friction reduction, enhanced gear life through increased resistance to pitting and wear, lower
operating temperatures, and cost savings in steel consumption and cutting tools.
An important factor affecting the efficiency of an automatic transmission is the amount of oil
that it contains. Increases of efficiency between 1 and 5% could be obtained by reducing oil
flow, and up to 10% if the transmission could run totally dry. While these approaches are
theoretically possible, heat dissipation becomes a problem at low oil flow rates, and new friction
materials also might be needed. A systematic approach to transmission design will be required
to solve these problems. The approach should include:
Generic studies of the factors that affect torque capacity.
Generic studies on efficient heat dissipation at low oil flow.
Generic studies of factors that affect drag losses in friction systems.
Analyses to optimize the above phenomena.
The studies should be based on an experimental and practical approach supported by theoretical
analyses of the friction interface and the surrounding environment. The entire system of friction
material, automatic-transmission fluid, and separator plates should be considered in an integrated