Abstract:
A hybrid yoke for a vehicle driveshaft assembly includes a cast iron portion having a pair of opposed yoke arms at a first end. The hybrid yoke also includes a steel portion having a yoke end and a shaft end, the shaft end for coupling to the driveshaft assembly and the yoke end for insertion into a second end of the cast iron portion.

Description:
TECHNICAL FIELD 
   The present invention relates to a yoke and, more particularly, to a hybrid yoke having a cast iron portion and a steel portion for coupling to a vehicle driveshaft. 
   BACKGROUND OF THE INVENTION 
   A vehicle drive shaft, which is usually made from steel tubing, transfers rotational power from the transmission end to the differential of an axle assembly for rotatably driving the vehicle wheels. A yoke is typically welded to the shaft so as to provide a means for connecting two or more driveshafts together. The yoke is also typically made from forging steel to allow for strong bonding between the driveshaft and the yoke. However, forging steel is a relatively expensive material. 
   Thus, it is desirable to reduce the cost of the yoke while maintaining the strength of the bond between the yoke and the driveshaft. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, a hybrid yoke for coupling to a driveshaft of an automotive vehicle includes a cast iron portion having a pair of opposed yoke arms at a first end. The hybrid yoke further includes a steel portion having a yoke end and a shaft end, the shaft end for coupling to the driveshaft assembly and the yoke end for insertion in a second end of the cast iron portion. 
   Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional view of the hybrid yoke of the present invention; 
       FIG. 2  is a cross sectional view illustrating the hybrid yoke of the present invention welded to a vehicle driveshaft; 
       FIG. 3  is a cross sectional view of a preferred interlock feature associated with the hybrid yoke of the present invention; 
       FIG. 3A  is a view of the interlock feature taken in a direction shown by A-A in  FIG. 3 ; 
       FIG. 4  is a cross sectional view of an alternative interlock feature associated with the hybrid yoke of the present invention; 
       FIG. 4A  is a view of the interlock feature taken in a direction shown by A-A in  FIG. 4 ; 
       FIG. 5  is a schematic view illustrating a first method of making the hybrid yoke of the present invention; and 
       FIG. 6  is a schematic view illustrating a second method of making the hybrid yoke of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   As representative of the present invention,  FIG. 1  illustrates a hybrid yoke  10  for coupling to a vehicle driveshaft  12 , both of which are rotatable about a longitudinal axis  14 . The hybrid yoke  10  of the present invention has two portions of materials to replace the traditionally high cost of a forged steel yoke. The major portion is a cast iron portion  16  which provides a low cost material and manufacturing. The other portion is a steel portion  18  for coupling with the driveshaft  12  utilizing a well known friction welding process, as illustrated in  FIG. 2 . 
   The cast iron portion  16  includes a pair of opposing arms  20  at a first end  22  thereof. The pair of opposing arms  20  extends generally axially from the first end  22  of the hybrid yoke  10 . The arms  20  are generally symmetrical and are radially spaced relative to one another. 
   The steel portion  18  has a yoke end  24  and a shaft end  26 . The yoke end of the steel portion  18  is inserted into a second end  27  of the cast iron portion  16  of the hybrid yoke  10 . The shaft end  26  of the steel portion is coupled to the driveshaft  12 . The hybrid yoke  10  including the cast iron portion  16  and the steel portion  18  is generally Y-shaped in form. 
   The cast iron portion  16  and the steel portion  18  is coupled together via an interlock feature that enhances the bond strength between the cast iron material and the steel material, while insuring torque transfer between the hybrid yoke  10  and the driveshaft  12 . In a first embodiment, as shown in  FIGS. 3 and 3A , the cast iron portion  16  has a radially outward extending tab  28  formed at the second end  27  of the hybrid yoke  10 . The steel portion  18  has a radially inward extending groove  30  formed at the yoke end  24  for receiving the tab  28  of the cast iron portion  16 . The tab  28  and groove  30  are preferably segmented for additional strength, but may be formed continuously. 
   In an alternative embodiment, the cast iron portion  16  has a radially inward extending notch  32  formed at the second end  27  and the steel portion  18  has a radially outward extending shoulder  34  formed at the yoke end  24  for cooperating with the notch  32  of the cast iron portion  16 , as shown in  FIGS. 4 and 4A . As in the first embodiment, the notch  32  and shoulder  34  are preferably segmented for additional strength, but may be formed continuously. 
   The hybrid yoke  10  of the present invention is formed by way of an insert casting process. In a first insert casting process, as shown in  FIG. 5 , a precast iron  100  corresponding to the cast iron portion  16  is placed in a mold  110  to act as a mold insert. Then, molten steel  112  is poured into the mold  110  and a solid and diffusion bond between the cast iron  100  and the steel  112  is allowed to form. A coating material, e.g., copper, could be applied to enhance the bonding between the cast iron  100  and the steel  112  at  114  since the cast iron  100  has a different molten temperature than steel  112 . Alternatively, a heating process could be applied in the cast iron  100  close to the conjunction area between the two materials,  114 , if a coating material is not used. 
   In  FIG. 6 , an alternative method for making the hybrid yoke  10  of the present invention is illustrated. Here, a pre-made steel portion  112  is placed into the mold  110  and acts as an insert. Then, molten iron  100  is poured into the mold  110 . Again, a solid and diffusion bond between the cast iron  100  and the steel  112  is allowed to form. As in the first method, a coating material could be applied to enhance the bonding between the cast iron  100  and the steel  112  at  114  since the cast iron  100  has a different molten temperature than steel  112 . 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.