CONSTRUCTION AND METHOD FOR PRODUCING PROPULSARY ARROW OUE HAS ENLARGED END SECTIONS This invention relates in general to propulsion shaft structures for automotive vehicles and particularly to the construction of a tubular impulse shaft portion and its connection with end yokes of the structure. . BACKGROUND OF THE INVENTION Propulsion shaft structures of the above type are often used in automotive applications to couple the transmission and / or transfer room of a vehicle to the axles in order to transfer energy to the wheels. In a typical propulsion shaft structure, a pair of forged end yokes is provided, each having a connecting collar at one end which snaps together with the opposite ends of a tubular impulse shaft and is then attached by welding to the arrow to hold them in place. In applications where there is sufficient spacing to allow a large diameter pulse arrow, it is preferred that the pulse shaft employed be one having a sufficiently large inside diameter to allow snap-fit insertion of the yoke collars at the ends of the arrow, as opposed to using an impulse arrow of smaller diameter, whose outer diameter allows the ends of the arrow to extend into the collars. One reason that the large diameter arrow construction is preferred is that it is comparatively simpler and more cost effective from a manufacturing point of view to machine the outer diameter of the yoke collars to prepare them for pressure adjustment extension and Weld inside the impulse arrow tube instead of having to machine the inside diameter surface of the collar to accept the arrow. In some applications, however, the space available for the structure of the propelling arrow and particularly the spacing for the arrow that must extend linearly between the yokes is limited to such a degree that the preferred large diameter impulse shaft construction does not can be used A typical example of these limited spacing applications are front displacement axle structures, where the propelling arrow competes for space with the steering of the exhaust system and various other components in the vicinity of the engine compartment. The solution to date, to these limited space requirements has been to use the less desirable small diameter impulse shaft construction. In addition to the machining difficulties mentioned above, a small diameter pulse arrow is more difficult and expensive to compensate. The balance of the arrow assembly involves applying weights or ballasts to the elastic end regions to compensate for any imbalance in the structure. The smaller diameter impulse arrow offers less area in which the compensating weights or ballasts are mounted, as well as less net balance correction for connected weight due to the direct relationship between compensation weight effectiveness and tube diameter and must make certain adjustments for the smaller arrows since much of the standard equipment used to support the structure and apply the weights is configured for large diameter structures. SUMMARY OF THE INVENTION According to the invention, a propulsive arrow structure has an initial small diameter pulse arrow whose outer diameter is small enough to allow a limited address space environment. The opposite ends of the small diameter pulse arrow are then enlarged so that the inner diameter of the end positions are dimensioned to press-fit the collars of a pair of end yokes at the ends of a tube. impulse arrow, which are then joined by welding in the usual way. The invention in this manner provides an impulse arrow which is a hybrid of classes between the small and large diameter arrows mentioned above. The arrow has a small diameter middle section that meets the limited addressing space requirements of many front-drive shaft applications, however, it has large diameter end sections to advantageously receive the collars of the yokes at the ends of the arrow. This hybrid construction in this way combines the benefits offered by both the diameter and small impulse arrows while overcoming these limitations. The enlarged ends make it possible to use the preferred outer diameter machining of the yoke collars and also allows the arrow structure to be balanced using standard compensation weights and compensating equipment designed for large diameter tube structures. The Drawings A currently preferred embodiment of the invention is described in the following description and the accompanying drawings, wherein:
Figure 1 is a longitudinal fragmentary front elevational view of a propelling arrow structure constructed in accordance with a currently preferred embodiment of the invention; Figure 2 is an enlarged fragmentary exploded view of the propeller arrow components of Figure 1 with the pre-assembled and pre-enlarged condition; and Figure 3 is an enlarged fragmentary longitudinal view shown partially in section of one end of the propeller shaft structure. Detailed Description Now with reference to Figure 1, an automotive propelling arrow structure constructed in accordance with a currently preferred embodiment of the invention, is generally indicated by the reference number 10 and comprises an elongated pulse arrow 12 having yokes 14, 16 connected to their opposite ends. The yokes 14, 16 are forged components, each having a rod or connector collar 18 at one end having an outer engagement surface 20 machined to a pre-determined diameter Dy. An example of the spaced fins 22 are formed at the opposite end of the yokes 14, 16. The fins 22 are formed with aligned transverse holes 24 to gouge, in the usual manner, a spider or piece with radial arms carried by another yoke 28 to provide a cardan universal joint at each end of the arrow 12. The arrow 12 comprises a longitudinally extending length of cylindrical metal pipe material with opposite open ends 30, 32. Initially, the tubular arrow 12 is of small diameter uniform on its length to be sub-dimensioned with respect to the yokes 14, 16 that are connected to it. The arrow 12 has an initial outside diameter D0 that is relatively smaller than that of the diameter D of the yoke rods 18. The small outside diameter size of the tube 12 is chosen to facilitate linear addressing of the arrow 12 in applications where the Space is limited, such as for example in automotive front axle applications, to couple a vehicle transfer enclosure to the front axle drive components. In the illustrated example, the arrow has an initial outside diameter D0 of about 44.5 mm, with a uniform minimum wall thickness of about 2.4 mm and a total length dimension of about 679 to 740 mm. While specific dimensions and ranges were previously given for purposes of illustration, those skilled in the art will appreciate that other dimensions are possible and contemplated by the invention based on the limitations of particular space and length requirements for the particular application. The tubular shaft 12 has an initial inner diameter Dt that is partly regulated by the initial outer diameter D0 and a wall thickness of the tube, but is in any case smaller in diameter than that of outer diameter D and of the yoke collars 18. According to the invention, opposite end sections 34, 36 of the arrow 12 are enlarged to an enlarged inner diameter of sufficient size to provide a press fit connection with the collar 18 of the yokes 14, 16. In In the illustrated example, the arrow 12 has an enlarged inner diameter of in the range of about 49.2 to 49.33 mm, which corresponds in size to the diameter D and of the yoke collars 18. The small diameter middle section 38 of the arrow is not affected by the enlargement of the end sections 34, 36 and as such retains the dimensions of original diameter and wall thickness. The enlargement of the end sections 34, 36 of the arrow 12 can be carried out by a flare or mechanical formation operation in which the arrow 12 is clamped in an attachment (not shown) and an enlarged forming mandrel (not shown). shown) extends at each of the opposite ends 30, 32 to stretch the pipe 12 in the vicinity of the end section 34, 36 to the enlarged inner diameter De. The enlargement of the end sections 34, 36 produces a corresponding reduction in their wall thickness by approximately 0.3 mm. As best illustrated in Figure 3, the length of the enlarged end sections 34, 36 is relatively greater than that of the length of the yoke rods 18. The extended length provides a region 42 inwards of the yokes 14, 16 for engaging and supporting the arrow 12 during insertion of the collars 18 at the ends of the arrow 12. The region 42 further provides a site for coupling and holding the arrow 12 by a standard large diameter compensation fitting (not shown) and for connecting one or more standard large diameter compensation weights 44 on each of the end sections 34, 36. After the enlarged end sections 34, 36 have been formed, the yokes 14, 16 are connected by press fit. of the rods 18 on the yokes at the open ends 30, 32 of the end sections 34, 36 until the end of the arrow 12 confronts the shoulder confinement shoulders 14a, 16a of the yokes 14, 16 respectively. vamente. The yokes 14, 16 are then fixed permanently to the arrow 12 by welds 46 in the usual manner. Compensation weights 44 are preferably selected and fastened by welding at the appropriate locations in the end sections 34, 36 to correct any imbalance of the structure 10. The extended length of the end sections 34, 36 allows the weights 44 are connected in a longitudinally spaced location of the insert rods 18 of the yokes 14, 16 so as not to impair the integrity of the yoke-to-arrow welds 46. The described embodiment is representative of a presently preferred embodiment of the invention and is It is intended to be illustrative rather than definitive. The invention is defined in the claims.