Schaeffler Group's (Germany) FAG Bearing has introduced a different drive arrangement for wheel bearing hub assembly units, and it will be finding its way onto a production vehicle.

Traditionally, the mechanical connection for driven wheels is via an axle with CV joints at each end. The outboard CV joint is splined and slides through a matching broached hole through the wheel bearing spindle. The CV joint and hub assembly are held in place by an axle nut through the end of the CV joint.




FAG points out that the traditional drive arrangement has its faults; there must be clearance to allow the CV joint to slide into the wheel bearing unit. Under day-to-day loads and use, but especially in high horsepower situations with high torque loading and tire friction, those splined areas can be stressed and loosen or fail. Even if they don't fail, over time the wear can cause driveline lash, felt inside the vehicle as harshness and/or vibration. In extreme cases, the splines or bearings can fail.

Reducing the radial clearance to zero in that arrangement is complex and expensive.



FAG's arrangement puts axial splines (essentially gear teeth) on the back side of the hub assembly unit. Matching axial gear teeth are formed on the end of the CV joint, and the whole unit is held in place with a long bolt.

Rather than machine the area as with traditional gear teeth, FAG uses high-precision orbital cold forming.

FAG claims that extensive testing shows the axial spline arrangement allows higher torque transmission than the traditional splined CV method, primarily because the gear teeth operate on a much larger pitch circle.

Orbital forming originally got a foothold at FAG because it allows undriven wheel hub units to be assembled without the traditional interior hub and nut holding the unit together. Instead, the inner is orbitally fixed. FAG has been expanding the use of orbital forming since the late 1980's.

In total, FAG claims approximately 10% weight reduction by adopting this drive system, up to 1kg or 2.2 pounds. The weight loss program brings another, perhaps more obscure, advantage -- reducing unsprung weight, which can help automakers improve vehicle chassis dynamics and handling.

At least one automaker has been convinced -- the hub assembly and CV arrangement will appear by mid-2009 on a lineup of unidentified AWD sedans.

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