Sealing Shielding

Clutch Sealing for Today's Automatic Transmissions

Clutch Sealing for Today's Automatic TransmissionsThe competitive landscape, combined with government regulations, are driving technology in today's automotive market for improved efficiency and fuel economy. Any incremental improvement in fuel economy is strongly considered. Just a half mile per gallon may seem to be insignificant, but these projects are all taken very seriously. The entire vehicle is being examined for efficiency improvements; not just the engine. Anything that reduces weight or eliminates friction is a prime target for investigation. 

Recently, technological advances in the automatic transmission have been a big step in improving fuel economy. The "old" 5 and 6 speed transmissions are being replaced with more efficient 8, 9, and even 10 speed transmissions. The theory behind these new designs is providing the optimum gear ratio for the current acceleration condition. 

Increasing the number of speeds, however, also increases the number of clutches, components, fluid circuits, and potential friction locations within the transmission. Combined with the fact that the available space under the vehicle does not change, means all this has to be done within the same size transmission case. This has resulted in packaging challenges for the additional clutch packages within the transmission.

One critical component within the clutch assembly is the clutch piston itself. These pistons are energized by hydraulic fluid pressure with the assistance of elastomeric sealing elements. In addition to being a critical component in the function of the unit, each of these sealing elements is a source of friction in the transmission, thus directly impacting the overall efficiency of the vehicle. 

As important to the application of the clutch when needed, is the ability of the clutch to release when not in use. Return springs are used to retract these pistons. Lower force springs are being implemented to reduce the energy needed to apply the clutch, therefore lower drag seals are required to assure smooth, quick response time for the apply and retract cycles of the piston. These smaller springs also reduce weight and the space utilized. 

Automatic transmission clutch pistons are typically made from either steel stampings or cast aluminum. The configuration of these pistons and corresponding sealing elements are dictated by the available space within the mating components:

O-Rings Clutch Sealing for Today's Automatic Transmissions, O-Ring, O-Ring & Engineered Seals Division

  • bi-directional radial compression seal,

  • simplest assembly, and

  • minimal use of radial space.

D-RingsClutch Sealing for Today's Automatic Transmissions, D-Ring

  • bi-directional radial compression seal,

  • minimal use of axial space, and

  • reduced drag force compared to O-rings.

Low Drag D-RingsClutch Sealing for Today's Automatic Transmission, Low Drag D-Ring

  • bi-directional radial compression seal,

  • minimal use of radial space, and

  • significant drag reduction compared to D-rings.

Lip SealClutch Sealing for Today's Automatic Transmissions, Lip Seal

  • unidirectional deflection seal,

  • energized by fluid pressure, and

  • lower drag than compression seal designs.

Bonded Piston Seal Clutch Sealing for Today's Automatic Transmissions, Bond Piston Seal

  • elastomeric sealing lips bonded directly to the piston stamping,   

  • steel stamping reduces the overall size of the piston,

  • single piece assembly, and

  • low drag deflection lips.


Parker Hannifin has the engineering design and manufacturing expertise to supply all clutch sealing configuration. Please contact one of our Applications Engineers to evaluate your specific needs and provide the optimal sealing solution for your application needs.


Clutch Sealing for Today's Automatic Transmissions, Scott Van Luvender



This blog was contributed by Scott Van Luvender, applications engineering manager, Automotive.






Related content:

Advancements in Automotive Transmissions

O-Rings and Seals for Automotive Transmission Fluid

Seals and Vehicle Evaporative Emissions

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