Patent Publication Number: US-6662423-B2

Title: Method of producing a drive shaft

Description:
This is a divisional application of U.S. patent application Ser. No. 09/027,082 filed Feb. 20, 1998 now U.S. Pat. No. 6,319,134 which is a continuation of U.S. patent application Ser. No. 08/743,400 filed Nov. 1, 1996, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to drive shafts for automotive vehicles and more particularly to drive shafts that comprise an aluminum torque tube and a connection member at each end of the aluminum torque tube, for connecting the drive shaft in an automotive drive line. 
     The use of aluminum and aluminum alloy components in place of steel components in automobiles is becoming increasingly popular because a substantial weight reduction can be realized without any sacrifice in strength or durability. Moreover aluminum components are more corrosion resistant than their steel counterparts. 
     U.S. Pat. No. 4,527,978 granted to Barry L. Zackrisson Jul. 9, 1985 discloses a drive shaft having a heat-treated aluminum alloy torque tube and a heat-treated aluminum alloy yoke or connection member partially telescoped within each end of the tube and joined to it by welding. The torque tube has a constant outside diameter and a wall thickness which is constant throughout most of the length. However, the wall thickness is increased adjacent each end to compensate for reduced hardness resulting from the welding operation. 
     U.S. patent application Ser. No. 08/692,414 filed Aug. 5, 1996 and assigned to the assignee of this invention, now U.S. Pat. No. 5,672,286 issued Sep. 30, 1997, also discloses a drive shaft having an aluminum torque tube and yokes at each end and a method for welding the aluminum drive shaft components to each other. 
     The size of the aluminum torque tube used in aluminum drive shafts for automotive drive lines is determined in part by the required length and torque capacity of the drive shaft. An aluminum torque tube having a length in the range of 5 to 6 feet, an outer diameter of 5 inches, and a wall thickness of 0.083 inches is typical. The 5.0 inch outer diameter is larger than a comparable steel drive shaft. However, the end sections of the 5.0 inch outer diameter tube can be reduced in diameter and smaller yokes or other connection members can be used at each end. This reduces space requirements at the drive shaft ends which are usually located in crowded environments. The smaller end sections and yokes also reduce weight significantly particularly when the entire drive shaft assembly is taken into account. The end sections are usually reduced by swaging a larger diameter tube blank. 
     While such aluminum drive shafts have been found to be generally satisfactory, experience has shown that noise problems are encountered occasionally when thin walled tubes are used. One such noise problem is a periodic tinkling sound initiated by torque reversal when the torque tube has conical transition sections. We have determined that such a sound is due to an instability phenomenon in the conical transition sections which we characterize as oil canning and which we have found is related to the wall thickness of the aluminum tube. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to provide an aluminum drive shaft comprising a thin walled aluminum torque tube that has reduced diameter end sections that are connected to a larger diameter central section by transition sections that are stable under all normal operating conditions. 
     A feature of the invention is that the aluminum drive shaft includes a thin walled aluminum torque tube that has reduced diameter end sections that are connected to a larger diameter central section by transition sections that have an annular rib to stiffen the transition sections so as to reduce oil canning and noise. 
     Another feature of the invention is that the aluminum drive shaft includes a thin walled aluminum torque tube that has reduced diameter end sections that are connected to a larger diameter central section by transition sections that are formed with a concentric cylindrical band located between inner and outer conical portions to stiffen the transition sections so as to reduce oil canning and noise. 
     Yet another feature of the invention is that the aluminum drive shaft includes a thin walled aluminum torque tube that has reduced diameter end sections that are of sufficient length for use in balancing the aluminum drive shaft. 
     Still yet another feature of the invention is that the aluminum drive shaft includes an aluminum torque tube that has reduced end sections and transition sections that are formed by swaging the ends of an aluminum tube blank radially inwardly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the invention will become more apparent from the following description taken in conjunction with the accompanying drawings wherein like references refer to like parts and wherein: 
     FIG. 1 is a partially sectioned longitudinal view of a known drive shaft assembly having aluminum components including an aluminum torque tube; 
     FIG. 2 is an enlarged fragmentary sectional view of the drive shaft of FIG. 1 showing a reduced end portion and transition portion in detail; 
     FIG. 3 is a partially sectioned longitudinal view of a drive shaft assembly having aluminum components including an aluminum torque tube in accordance with the invention; and 
     FIG. 4 is an enlarged fragmentary sectional view of the drive shaft assembly of FIG. 3 showing a reduced end portion and transition portion in detail. 
    
    
     DESCRIPTION OF THE INVENTION 
     Referring now to the drawing, FIG. 1 shows a known drive shaft  10  that comprises a tubular drive shaft or torque tube  12  having yokes  14  at each end for installing the drive shaft  10  in a motor vehicle. The torque tube  12  is made from a tube of 6061 aluminum alloy thermally treated to a T-6 condition that has a 5.0 in outer diameter and a 0.083 inch wall thickness to provide the required torque capacity and other desired operating characteristics for a drive shaft between 5 and 6 feet in length. The torque tube  12  has a cylindrical section  16  at each end that is reduced to a diameter of approximately 4.0 inches by a swaging process. This process increases the wall thickness in the end sections to about 0.093 inches. The yokes  14  which are also made of an aluminum alloy and preferably the same aluminum alloy are press fit in the reduced diameter end sections  16  and then welded to the end of the tube by a circumferential weld bead  17  as shown at the right hand end in FIG.  1 . Yokes  14  are used to connect drive shaft assembly  10  into an automotive drive line by well known Cardan joints. The smaller diameter end sections  16  accommodate smaller yokes  14  and reduce space requirements at the drive shaft ends which are generally located in a crowded environment. Significant weight savings are also realized particularly when the smaller Cardan or alternative universal joints are taken into account. 
     The cylindrical section  16  of reduced diameter at each end of the torque tube  12  is joined to the larger central section  18  by transition sections  19  that are substantially conical. These known drive shafts  10  having the torque tubes  12  perform quite satisfactorily in most instances. However, some known drive shafts produce noise occasionally, in the nature of a periodic tinkling sound which appears to be initiated by torque reversal. We have found that this periodic clinking sound is due to an instability phenomenon in the conical transition sections  19  which we characterize as oil canning. 
     In essence, the conical transition sections  19  bend back and forth between an inward concave shape and an outward convex shape as illustrated graphically by dashed line  20  and  21  in FIG.  2 . This oil canning phenomenon is related to the wall thickness and shear web of the transition sections  19  which in the example under consideration is nominally 0.088 inches. The likelihood of the instability occurring increases as the wall thickness of the transition section  19  decreases. We have found that the amplitude of the oil canning phenomenon that produces audible noise is in the range of about 0.030 to 0.045 inches of transition deflection. 
     Referring now to FIG. 3 a drive shaft  110  in accordance with the invention is disclosed. Drive shaft  110  comprises a tubular drive shaft or torque tube  112  having yokes  114  at each end for installing the drive shaft  110  in a motor vehicle. The torque tube  112  is made from a tube of 6061 aluminum alloy thermally treated to a T-6 condition having an outer diameter of approximately 5.0 inches and a wall thickness of 0.083 inches in order to provide the required torque capacity and other desired operating characteristics. The torque tube  112  has a cylindrical section  116  at each end that is reduced to an outer diameter of approximately 4.0 inches to accommodate smaller aluminum alloy yokes  114  that are pressed in each end and welded. 
     These cylindrical end sections  116  are preferably kept at a substantial length so that weights can be attached to the cylindrical end sections  116  to dynamically balance the drive shaft  110 . The cylindrical end section  116  would typically have a length of about 4.0 inches for this purpose. 
     Transition sections  119  join the cylindrical sections  116  of reduced diameter at each end to the larger central section  118 . These transition sections  119  are shaped to reduce oil canning significantly if and when such an instability is encountered. More specifically, the transition sections  119  include an annular stiffening rib that is located between inner and outer conical portions  122  and  124  as best shown in FIG.  4 . The annular stiffening rib  120  is in the form of a concentric circular band that has a nominal outer diameter of about 4.5 inches and that is located approximately half way between the end section  116  and the central section  118  in the radial direction and in the longitudinal direction. The circular band which provides the annular stiffening rib  120  has a length of about 0.5 inches in the axial or longitudinal direction. 
     The end sections  116  and transition sections  119  can be formed by a swaging operation in two stages. The outer conical section  124  and a cylindrical section of about 4.5 inch outer diameter that extends to the end of the tube is formed in the first stage. The inner conical section  122  and the fully reduced end section  116  is then formed in the second stage leaving a concentric circular band midway between the inner and outer conical sections  122  and  124 . 
     By shaping the transition section  119  in this manner we have reduced the amplitude of the oil canning significantly from a range of about 0.030-0.045 inches to a range of about 0.005-0.015 inches. This reduces any noise to a level that is not audible without any need for increasing the wall thickness of the tube blank. 
     While this particular transition shape performs satisfactorily for the particular drive shaft described above, other transition shapes and/or methods of forming transitions are also possible and in some other instances may be more desirable. Also while we have illustrated a torque tube which is reduced at both ends, some drive shaft applications may require a reduction at only one end section. Furthermore the invention contemplates use of other aluminum alloys and aluminum matrix materials comprising an aluminum oxide and an aluminum alloy material. In other words, the invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words  20  of description rather than of limitation. 
     Obviously, many modifications and variations of the present invention in light of the above teachings may be made. It is, therefore, to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.