Freudenberg Sealing Technologies presented a new generation of low-friction transmission seals at the recent 5th International CTI symposium, a meeting place for transmission experts.
The supplier said its Levitas seal rings are suited for installation in all forms of automated transmissions. A special seal design produces a hydrodynamic oil film between the seal ring and its dynamic counter surface, which reduces friction to the point that merely replacing conventional transmission seals in an automatic transmission reduces the vehicle's CO2 emissions by 0.8g/km. If 1m new vehicles were equipped with these seals, the total emissions over their entire operating life would decline by 192,000 tonnes, Freudenberg claimed.
Automatic, double-clutch or continuously variable, the transmission is one main determinant of the efficiency of a vehicle's powertrain so every transmission manufacturer is working on minimising frictional losses. Seals are responsible for about one-quarter of all the lost mechanical energy in automatic transmissions, as they keep the oil pressure in the transmission at the prescribed level, making it possible to shift gears perfectly. The key is to keep the amount of oil that flows past the seal very low.
"Today, low leakage and minimal friction are the most important target conflicts in the development of new seals," said Hikaru Tadano of Freudenberg Sealing Technologies' Advanced Development. "Up until now, the problem has been handled by giving the sealing rings a T-shaped profile. The reduced contact surface between a shaft that is rotating and the stationary seal rings already decreases friction significantly. This solution has proven to be successful but it is no longer possible to further reduce friction by even smaller contact surfaces."
With the Levitas line, Freudenberg is now pursuing a completely new approach: during operation, the seal floats on a hydrodynamic oil film that it generates itself. Small pockets are incorporated across the entire circumference of the ring seal. When the shaft begins to rotate, the dynamic pressure in the pockets generate axial forces, creating the oil film.
As no physical contact remains between the shaft and the seal ring, only fluid friction remains, causing torque levels to decline by up to 70%, depending on the application's conditions. Since the pockets are bi-directional, the effect occurs irrespective of the shaft's rotational direction. This makes installation easier and more secure for the transmission manufacturer.
Volume production of the new seals begins in 2017.
"The technology also appeals to European car and transmission manufacturers due to increasingly strict CO2 limits," said Eberhard Bock, director of strategic product development at Freudenberg Sealing Technologies. "With the combination of Levitas and the friction-free Levitex seals for internal combustion engines, we are demonstrating the potential for further CO2 reduction in conventional powertrains."
Levitex seals for engines operate on a similar principle, but ambient air functions as the 'lubricant' instead of oil. This nearly reduces frictional torque to zero. The production of Levitex engine seals for a European customer is also due to begin in 2017.
Both Levitas and Levitex are products of Freudenberg's LESS initiative. The acronym stands for Low Emission Sealing Solutions.