Prop shaft assemblies of the above type are often used in automotive applications to couple the transmission and/or transfer case of a vehicle to the axles in order to transfer power to the wheels.
In a typical prop shaft assembly, a pair of forged end yokes are provided, each having an attachment collar at one end which is press fit together with the opposite ends of a tubular drive shaft and then welded to the shaft to secure them in place. In applications where there is sufficient clearance to accommodate a large diameter drive shaft, it is preferred that the drive shaft employed be one having an inner diameter sufficiently large to accommodate the press fit insertion of the yoke collars into the ends of the shaft, as opposed to using a smaller diameter drive shaft whose outer diameter enables the ends of the shaft to be extended into the collars. One reason the large diameter shaft construction is preferred is that it is comparatively simpler and more cost effective from a manufacturing standpoint to machine the outside diameter of the yoke collars to prepare them for press fit extension and welding within the drive shaft tube, rather than having to machine the inside diameter surface of the collar to accept the shaft.
In some applications, however, the available space for the prop shaft assembly, and particularly the clearance for the shaft which must extend linearly between the yokes, is limited to such a degree that the preferred large diameter drive shaft construction cannot be used. A typical example of such limited clearance applications is front drive axle arrangements, where the prop shaft competes for space with the routing of the exhaust system and various other components in the vicinity of the engine compartment.
The solution, thus far, to such limited space requirements has been to utilize the less desirable small diameter drive shaft construction. In addition to the machining difficulties mentioned above, a small diameter drive shaft is more difficult and costly to balance. Balancing the shaft assembly involved applying weights to the end regions of the shaft to compensate for any imbalance of the assembly. The smaller diameter drive shaft offers less area on which to mount the balancing weights, as well as less net balance correction for attached weight due to the direct relationship between balance weight effectiveness and tube diameter and certain accommodations must be made for the smaller shafts since much of the standard equipment used to support the assembly and apply the weights is set up for the large diameter assemblies.