Construction and method of making prop shaft having enlarged end sections

An automotive prop shaft assembly particularly suited for coupling a transfer case to the front axle drive components comprises a tubular drive shaft having an initial uniform inner diameter relatively smaller than the outer diameter of a pair of forged insert yokes to be attached to the ends of the shaft. A section of each end of the tube is enlarged so that its inner diameter is sized to receive the yokes into the ends of the tube with an interference fit. The shaft and yokes are then welded together and weights fixed to the end sections to correct for imbalance.

This invention relates generally to propeller shaft assemblies for 
automotive vehicles and particularly to the construction of the tubular 
drive shaft portion and its connection with the end yokes of the assembly. 
BACKGROUND OF THE INVENTION 
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. 
SUMMARY OF THE INVENTION 
According to the invention, a prop shaft assembly has an initial small 
diameter drive shaft whose outer diameter is sufficiently small to 
accommodate a limited routing space environment. The opposite ends of the 
small diameter drive shaft are then enlarged in order that the inner 
diameter of the end portions are sized to receive with a press fit the 
collars of a pair of end yokes into the ends of the drive shaft tube which 
are then welded in the usual manner. 
The invention thus provides a drive shaft that is a hybrid of sorts between 
the small and large diameter shafts mentioned above. The shaft has a small 
diameter mid-section that addresses the limited routing space requirements 
of many front drive axle applications, yet has large diamater end sections 
to advantageously receive the collars of the yokes into the ends of the 
shaft. Such hybrid construction thus combines the benefits offered by both 
the large and small diameter drive shaft while overcoming these 
limitations. The enlarged ends make it possible to utilize the preferred 
outer diameter machining of the yoke collars and further enable the shaft 
assembly to be balanced using standard balance weights and balancing 
equipment designed for the large diameter tube assemblies.

DETAILED DESCRIPTION 
Referring now to FIG. 1, an automotive propeller shaft assembly constructed 
in accordance with a presently preferred embodiment of the invention is 
indicated generally by the reference numeral 10 and comprises an elongate 
drive shaft 12 having yokes 14, 16 attached to its opposite ends. 
The yokes 14, 16 are forged components, each having a connecting collar or 
shank 18 at one end presenting an outer mating surface 20 machined to a 
predetermined diameter D.sub.y. Laterally spaced ears 22 are formed at the 
opposite end of the yokes 14, 16. The ears 22 are formed with aligned 
cross holes 24 for journaling, in the usual manner, a spider 26 carried by 
another yoke 28 to provide a Cardan-type universal joint at each end of 
the shaft 12. 
The shaft 12 comprises a longitudinally extending length of cylindrical 
metal tubing material having opposite open ends 30, 32 thereof. Initially, 
the tubular shaft 12 is of uniform small diameter along its length so as 
to be undersized with respect to the yokes 14, 16 that is attached to. The 
shaft 12 has an initial outer diameter D.sub.o that is relatively smaller 
than that of the diameter D.sub.y of the yoke shanks 18. The small outer 
diameter size of the tube 12 is selected to facilitate linear routing of 
the shaft 12 in applications where space is limited, such as, for example, 
in automotive front axle applications for coupling a vehicle's transfer 
case to the front axle drive components. 
In the example illustrated, the shaft has an initial outer diameter D.sub.o 
of about 44.5 mm with a uniform minimum wall thickness of about 2.4 mm and 
an overall length dimension of about 679-740 mm. While specific dimensions 
and ranges are given above for purposes of illustration, those skilled in 
the art will appreciate that other dimensions are possible and 
contemplated by the invention based on the particular space limitations 
and length requirements for the particular application. 
The tubular shaft 12 has an initial inner diameter D.sub.I that is governed 
in part by the initial outer diameter D.sub.o and the wall thickness of 
the tube but, in any event is smaller in diameter than that of the outer 
diameter D.sub.y of the yoke collars 18. 
In accordance with the invention, opposite end sections 34, 36 of the shaft 
12 are enlarged to an expanded inner diameter D.sub.e of sufficient size 
to provide a press fit connection with the collar 18 of the yokes 14, 16. 
In example illustrated, the shaft 12 has an expanded inner diameter 
D.sub.e in the range of about 49.2 to 49.33 mm, which corresponds in size 
with the diameter D.sub.y of the yoke collars 18. The small diameter 
midsection 38 of the shaft is unaffected by the enlargement of the end 
sections 34, 36 and as such retains the original diameter and wall 
thickness dimensions. 
The enlargement of the end sections 34, 36 of the shaft 12 may be carred 
out by a mechanical forming or flaring operation in which the shaft 12 is 
clamped in a fixture (not shown) and an enlarged forming mandrel (not 
shown) extended into each of the open ends 30, 32 to stretch the tubing 12 
in the vicinity of the end sections 34, 36 to the enlarged inner diameter 
D.sub.e. The enlargement of the end sections 34, 36 produces a 
corresponding reduction in their wall thickness by about 0.3 mm. 
As illustrated best in FIG. 3, the length of the enlarged end sections 34, 
36 is relatively greater than that of the length of the yoke shanks 18. 
The extended length provides a region 42 inward of the yokes 14, 16 for 
engaging and supporting the shaft 12 during insertion of the collars 18 
into the ends of the shaft 12. The region 42 further provides a location 
for engaging and supporting the shaft 12 by a standard large diameter 
balancing fixture (not shown) and for attaching one or more standard large 
diameter balance weights 44 along each of the end sections 34, 36. 
After the enlarged end sections 34, 36 have been formed, the yokes 14, 16 
are attached by press fitting the shanks 18 of the yokes into the open 
ends 30, 32 of the end sections 34, 36 until the end of the shaft 12 
confront abutting shoulders 14a, 16a of the yokes 14, 16, respectively. 
The yokes 14, 16 are then fixed permanently to the shaft 12 by weldments 
46 in the usual manner. 
The balance weights 44 are selected and secured preferably by welding in 
the appropriate locations on the end sections 34, 36 to correct any 
imbalance of the assembly 10. The extended length of the end sections 34, 
36 enables the weights 44 to be attached at a location longitudinally 
spaced from the insert shanks 18 of the yokes 14, 16 so as not to impair 
the integrity of the yoke-to-shaft weldments 46. 
The disclosed embodiment is representative of a presently preferred form of 
the invention, and is intended to be illustrative rather than definitive 
thereof. The invention is defined in the claims.