Assembly in Action: Roller Thrust Bearings Solve Car Seat Challenge
January 28, 2010
Engineers at bearing manufacturer Hartford Technologies helped GM improve the drive gear assembly for a seat adjuster.
Hartford Technologies manufactures a wide variety of custom bearings for automotive, off-highway and medical device manufacturers. The company makes drawn-cup needle roller bearings; sealed, drawn-cup needle roller bearings; and drawn-cup, full-complement needle roller bearings.
Hartford was recently approached by a division of General Motors Co. regarding a design issue on an automotive seat mechanism. The problem was in the drive gear assembly for the seat adjuster. Excessive friction from the motor to the screw drive mechanism, which adjusts the seat, had resulted in heat buildup that caused the plastic housing to degrade. The result was failure of the seat unit.
A GM engineer consulted with Hartford material and manufacturing specialists to see what solutions could be identified. Standard thrust bearings were considered, but no standard size would fit within the housing, so a custom bearing was developed. A related issue regarded the fact that thrust bearings consist of three parts: two washers and a retainer of balls or rollers.
During assembly, the operator had to carefully position the retainer between the two washers for it to perform correctly. If the parts were placed in incorrect order, a major failure of the unit was inevitable. To streamline the assembly process and eliminate scrap, a specially designed, cage-style thrust bearing was developed by Hartford engineers.
The custom-caged thrust bearing encapsulates the two washers within the cage that holds the retainer, and keeps them in place during assembly. This allows the operator to rapidly insert the bearing into the assembly without concern over the direction of insertion, or correct orientation.
The solution also allows the cage to sit below the face of the washers, so that loading can extend beyond the edges of the washers. This creates a larger, more convenient loading surface area that is not constrained by the diameter of the thrust bearing.
This custom bearing was distinctive in several ways. Unlike conventional encapsulated thrust bearings, the Hartford retainer held the assembly together and did not interfere with the bearing surface. The cage-style assembly allowed for increased productivity and reduction in scrap rates.
For more information on bearings, click www.hartfordtechnologies.com or call 860-571-3602.