Rotating seal deflects dirt and debris

Dearborn, MI--Primary radial shaft seals function to seal engine crankcase oil internally while preventing external contaminant ingress. Anyone who owns a high-mileage vehicle has probably encountered the familiar oil spots on the driveway that result from failed seals.

Prior to production, Ford bench-tests, dynamometer-tests, and fleet-tests new engine designs. "Routine fluid-leak inspection surveys conducted on higher-mileage vehicle fleets revealed instances of rear main-oil-seal failure," says Joseph Gutierrez, Ford's section supervisor for engine sealing components.

During engine tear-down analysis, Ford engineers found heavy seal contamination from the environment. Dusty regions, such as the Southwest, exhibited significantly increased seal contamination.

In 1993, Ford started the project to eliminate environmental seal contamination on fleet-tested 4.6-, 5.4-, and 6.8-liter engines. These engines employ a deep-skirt block design with no half-round. This design re-quires a retainer to hold the primary oil seal.

Analysis revealed two main sources of contamination to the rear of the engine. First, the engine's top-end open-valley design accumulated dirt and debris. Eventually contamination fell through the block-cleanout hole to the flywheel area, and into the primary seal lip. Another contamination source was road splash and slurry. Engineers closed the rear top end of the engine with only token improvements.

Next, engineers considered industry's standard auxiliary-lip (A-lip) design. Bench tests, designed to apply contamination to the seal, revealed the A-lip's non-contacting design was only partially effective.

Engineers designed a separately installed secondary seal. This contacting radial-lip slinger seal solved the problem. The metal inner lip, pressed onto the crankshaft flange journal, rotates with the crankshaft, while an integral molded-rubber lip deflects contamination away from the primary oil seal retainer. Slinger rotation provides a barrier between the internal primary oil seal and the external environment.

Ford's universal sealing strategy enables a common slinger seal design to mount on three different engines. Bench tests proved the spinning radial-lip slinger seal increases the primary seal's life six-fold.

There were two major design challenges. First engineers succeeded in mounting the slinger seal within tight packaging constraints by increasing the retainer's width 2 mm. Pressure differential between the primary and secondary seals caused by the slinger's angular velocity was the second problem. Vacuum produced by seal rotation pulled engine oil into the cavity between the seals. Ford engineers solved the problem by venting the slinger seal's ID.

Ford teamed component and reliability engineers with seal supplier Chicago Rawhide, Elgin, IL, to develop and manufacture the slinger seal.

Additional details...Contact Tom Sochacki, CR Industries, 2611 Evergreen, Suite 303, Southfield, MI 48076, (810)799-3405.