Abstract:
A bonded drive shaft includes an elongated tube having an internal bore and at least one end fitting for connecting to a drive component. The end fitting includes first and second locating portions that engage the internal bore to precisely and firmly locate the end fitting with respect to the tube. The end fitting also includes an adhesive gap portion positioned between the locating portions to form a generally annular adhesive receiving gap between the first locating portion, the second locating portion, the adhesive gap portion and the internal bore of the elongated tube. Adhesive is injected into the adhesive receiving gap to bond the end fitting to the elongated tube.

Description:
This application claims priority to U.S. patent application Ser. No. 60/534,362 of Mark Williams, filed Jan. 6, 2004, the entire contents of which are incorporated by reference herein. 

   BACKGROUND 
   Automotive drive shafts are typically constructed by welding a tubular member to end fittings that include universal joints for connection to drive and driven connection devices for the transmission of power. Aluminum materials are presently used for such components for weight reduction and performance advantages, with the tubular members being welded to the end fittings. The welding methods used to connect such components have several disadvantages: 
   1. Drive shaft strength is limited because only lower strength weldable alloys can be used for the sub-component tubular members and end fittings. 
   2. The heat treated aluminum tube is annealed by the heat used in the weld zone, diminishing the effect of the heat treatment and the strength of the tube. 
   3. Distortion and the stress forces created by the heating and cooling of the weld joint are difficult to control. 
   4. Welding induced mechanical run out can require excessive balancing weight and straightening operations. 
   5. Welding of Duralcan Metal Matrix Composite Aluminum is difficult and the quality of the welds is inconsistent. 
   It is also known to adhesively bond end fittings to carbon fiber tubes, but in the past this has been accomplished by brushing adhesive onto the end fitting and/or tube prior to assembling the end fitting onto the tube, then inserting the end fitting into the tube. This has been found to be wasteful of adhesive, as excess adhesive is used to assure proper bonding when the components are assembled. Further, because there is little ability to control flow of the applied adhesive as the components are assembled, there is no certainty that maximum surface contact between the components and the adhesive is achieved to maximize the bond strength. Finally, because there is such little ability to control the flow and positioning of the adhesive, the balance of the drive shaft can be negatively affected by a non-uniform positioning of the adhesive around the drive shaft. 
   SUMMARY OF THE INVENTION 
   The present invention includes a method for bonding an end fitting to a drive shaft tube, without the use of welding. The present invention also includes the bonded drive shaft. 
   The method of the present invention of manufacturing a bonded drive shaft includes providing an elongated tube having an internal bore and providing at least one end fitting. The end fitting includes a portion for connecting to a drive component and an elongated tubular portion. The elongated tubular portion includes a first locating portion distant from the connecting portion, a second locating portion proximal to the connecting portion and an adhesive gap portion positioned between the first locating portion and the second locating portion. The elongated tubular portion is positioned in the internal bore of a first end of the elongated tube such that the first locating portion and the second locating portion engage the internal bore of the elongated tube and center the end fitting with respect to the elongated tube. Adhesive is then injected into a generally annular adhesive receiving gap formed between the first locating portion, the second locating portion, the adhesive gap portion and the internal bore of the elongated tube to bond the end fitting to the tube. A second end fitting can also be bonded to an opposite end of the tube in a similar manner. In a preferred embodiment, the first and second locating portions provide an interference fit between the elongated tube and the end fitting to position the end fitting concentrically with the elongated tube and to maintain the positioning of the end fitting with respect to the elongated tube until the adhesive is cured. 
   In a preferred embodiment the end fitting is made of a high strength non-weldable aluminum alloy that is stronger than weldable aluminum alloys and the metal tube is made of a metal matrix composite aluminum. 
   Other objectives, features and advantages of the present invention can be discerned from the present description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial side elevational phantom view of a drive shaft of the present invention; 
       FIG. 2  is a partial side sectional view of the drive shaft of  FIG. 1 ; 
       FIG. 3  is an end elevational view of the drive shaft of  FIG. 1 ; 
       FIG. 4  is an enlarged partial side sectional view of Detail B as shown in  FIG. 2 ; 
       FIG. 5  is an enlarged partial side sectional view of Detail C as shown in  FIG. 2 ; 
       FIG. 6  is a partial enlarged side sectional view of the drive shaft of  FIG. 1 ; 
       FIG. 7  is a partial end sectional view as taken along view fine G-G of  FIG. 1 ; 
       FIG. 8  is an enlarged partial side sectional view of a portion of  FIG. 7 ; 
       FIG. 9  is similar to  FIG. 1  but also shows a second fitting on a second side of the drive shaft; and 
       FIG. 10  is a partial sectional view of an alternative embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention includes a method for bonding an end fitting to a drive shaft tube, without the use of welding. The present invention also includes the bonded drive shaft. 
   In the present invention, a bonded drive shaft  10  includes a tube  12  and an end fitting (or yoke fitting)  14 . The drive shaft  10  will normally include two end fittings  14  on opposite ends of the tube  12 . A first end fitting  14  is shown in  FIG. 1  and both the first end fitting  14  and a second end fitting  114  of the same shaft are shown in  FIG. 9 . The two end fittings  14  and  114  can be substantively identical or can be different, as the application warrants. 
   The tube  12  can be made of aluminum, steel, carbon fiber or other high strength material, alloy or composite. In one preferred embodiment, the tube is an extruded tube made from Duralcan Metal Matrix Composite Aluminum. The end fitting  14  includes bosses  16  for supporting a u-joint, as is known. The end fitting  14  can be made of aluminum, steel, carbon fiber or other high strength material, alloy or composite. In a preferred embodiment, the end fitting  14  is machined from a high strength non-weldable aluminum alloy that is significantly stronger than aluminum alloys that are weldable. Through the use of the present invention, such a non-weldable aluminum alloy can be used for the end fittings  14  of the drive shaft  10 , as well as for the tube  12 , and can provide a combination of increased strength and/or lighter weight as compared to components manufactured from weldable aluminum alloys. 
   The end fitting  14  includes a tubular portion  18  that is constructed and arranged to fit into an internal bore  20  of the tube  12 . The tubular portion includes a first locating portion  22 , a second locating portion  26  and an adhesive gap portion  24  spaced between the two locating portions (see  FIGS. 2 and 6 ). The locating portions  22  and  26  are dimensioned to provide a desired fit with the internal bore  20  of the tube  12 . The fit can be adjusted as desired and need not be an interference fit, but in a preferred embodiment, an interference fit of approximately 0.002 inches is used. This interference fit accurately positions the end fitting  14  in the tube  12  and provides a light retention force to maintain this position of the end fitting  14  in the tube  12  until the end fitting  14  has been permanently bonded to the tube  12 , as described below. 
   The adhesive gap portion  24  of the end fitting  14  has a smaller diameter than the flanking locating portions  22  and  26  and provides a space or adhesive receiving gap  25  between the end fitting  14  and the tube  12  to accommodate adhesive  28 . In a preferred embodiment, the adhesive receiving gap  25  between the tube  12  and the adhesive gap portion  24  of the end fitting is 0.014 inches wide. This dimension can be varied as desired according to the type of adhesive used or for other reasons. The dimension need not be uniform along an axial length of die adhesive receiving gap but can varied to provide specific desired characteristics For instance, the dimension can be tapered from one end to the other where such an arrangement can provide improved bond characteristics. Because of the accurate positioning of the end fitting  14  in the tube  12  by the locating portions  22  and  26 , the gap  25  for the adhesive  28  is perfectly concentric around the tube and has an exact, defined volume within which to inject adhesive. Because the tube can be supplied from the tube manufacturer in a finished state with a constant inside diameter and outside diameter, it is preferred in such an instance to have the locating portions and adhesive gap portion provided on the end fitting so that further machining operations on the tube are not required. However, the present invention is not limited to such an embodiment and the locating portions and/or adhesive gap portions can alternatively be provided on the tube  12  (See  FIG. 9 ), or in another embodiment, the locating portions and adhesive gap portion can be divided between the tube and the end fitting. As seen in  FIG. 9  adhesive receiving gap  125  is positioned on the tube  12  for receiving an adhesive. The tube  12  also includes locating portions  122  and  126  to accurately position the second end fitting  114  in the tube  12 .  FIG. 10  shows an alternative embodiment end twine  214  which combines various aspects of the two previously discussed embodiments. The end fitting  214  includes locating portion  26  for locating against tube  12  and locating portion  22  for locating against  1 ocating portion  122  of tube  12  to create adhesive receiving gap  225  therebetween. 
   The end fitting  14  further includes an injection port  30  into which the adhesive  28  can be injected. The injection port  30  passes through the second locating portion  26  into the adhesive receiving gap  25  and is preferably configured to accept an injection mechanism in an air-tight manner to inject adhesive  28  from the injection mechanism into the adhesive receiving gap  25 . In a preferred embodiment, an injection syringe is used as the injection mechanism and the injection port has a diameter of 0.156 inches to snugly receive the injection syringe. Other configurations can be used to provide a sealed connection between an adhesive injection mechanism and the injection port  30 . 
   An air bleed port  32  is positioned on the first locating portion  22  to allow air to bleed from the adhesive receiving gap  25  as adhesive is injected into the adhesive receiving gap  25 . In a preferred embodiment, the air bleed port is positioned 180° away from the injection port  30  around the end fitting  14 . This allows the adhesive to spread completely around the circumference of the end fitting  14  and tube  12  as it is injected into the adhesive receiving gap  25  to provide maximum surface contact and thus, maximum bond strength, between the adhesive  28 , the end fitting  14  and the tube  12 . This also helps maintain the balance of the drive shaft since the adhesive is uniformly spread around the circumference of the drive shaft  10 . It has been found that when the air bleed port  32  is not positioned approximately 180° away from the injection port  30 , the adhesive does not spread evenly around the circumference of the tube  12  and end fitting  14 . However, the invention is not limited to such a 180° spacing. The air bleed port  32  can be sized as desired to provide proper air bleed during adhesive injection and additional air bleed ports with different positioning can also be provided if desired, as can additional injection ports. In one embodiment, an epoxy adhesive is used, although other types of adhesives can also be used. 
   The exact volume defined by the locating portions, the adhesive gap portion and the tube  12  is useful during the bonding process. Because this volume is known and exact, it is also known how much adhesive is required to fill the adhesive receiving gap  25 . This prevents injecting too much adhesive into the adhesive receiving gap  25  that may then escape through the air bleed port  32 , thereby wasting adhesive and potentially negatively affecting the balance of the drive shaft  10  due to a local accumulation of adhesive around the air bleed port  32 . 
   In the method of the present invention, the end fitting  14  is inserted into the tube  12  with the locating portions providing an exact concentric positioning of the end fitting  14  with respect to the tube  12  and an exact volume to the adhesive receiving gap  25 . The interference fit between the end fitting  14  and the tube  12  allows the drive shaft to be handled prior to full cure of the adhesive  28 . The injection mechanism is connected to the injection port  30  and a predetermined amount of adhesive sufficient to fill the adhesive receiving gap  25  is injected into the adhesive receiving gap  25 . Air is allowed to bleed from the adhesive receiving gap  25  during the injection process through an air bleed port  32  positioned approximately 180° away from the injection port  30  to provide uniform, controlled flow of the adhesive  28  around the circumference of the drive shaft  10 . This maximizes surface contact between the adhesive  28 , the tube  12  and the end fitting  14  and minimizes imbalance due to nonuniform flow of the adhesive  28 . By predetermining the amount of injected adhesive  28  based on the volume of the adhesive receiving gap  25 , excess adhesive is not injected into the drive shaft, which otherwise could flow through the air bleed port  32  and accumulate in one position, thereby potentially affecting the balance of the drive shaft. 
   If desired, the drive shaft can be rotated, about any axis, to aid the flow of the adhesive through centrifugal force, though this has not been found to be necessary. It has been found that placing the drive shaft  10  in an orientation such that the injection port  30  is lower than the air bleed port  32  during the adhesive injection process can help air pockets and air bubbles to flow upward and out through the air bleed port  32 , resulting in a more complete adhesive fill in the adhesive receiving gap  25 . During the adhesive injection process, the injection pressure on the adhesive through the injection port  30  can be maintained for a period of time after the last portion of the adhesive  28  has been injected into the adhesive receiving gap  25  to assist the adhesive in uniformly flowing throughout the adhesive receiving gap  25  and to prevent any back flow of adhesive  28  through the injection port  30 . The pressure hold period assists in the air bleeding process by providing additional time for trapped air to escape through the air bleed port. This pressure hold time can vary from a few seconds to over an hour but is preferably at least 5-10 minutes. Because of the interference fit between the end fitting  14  and the tube  12 , the drive shaft can then be balanced prior to full curing of the adhesive  28 , which full curing can take several hours. This aids in the efficiency of producing the bonded drive shafts. 
   It has been found that pretreating the tube  12  and end fittings prior to the bonding process can improve the strength of the adhesive bond. In a preferred method, the end fitting is first media blasted (blasted with sand or another media) to provide a roughened surface texture that increases the bond of the adhesive. The end fitting is then ultrasonically cleaned to remove contaminates and then chromated. The chromate layer increases the bond strength of the adhesive to the end fitting. The end fitting is then rinsed in distilled or deionized water and dried before positioning the end fitting  14  in the tube  12 . The same process is also preferably used on the interior of the tube to increase the strength of the adhesive bond with respect to the tube  12 . Other surface treatments on the end fitting  14  and/or tube  12  can also be used. 
   The various features described herein can be combined in different combinations to create different embodiments within the scope of the invention. 
   The present invention provides for one or more of the following features: 
   1. Higher strength non-weldable materials can be used, since there is no welding of such components. 
   2. By utilizing the metal matrix composite aluminum for the tubular structure the shaft critical speed is increased by 22% compared to steel or 6061-T6 aluminum tubing. 
   3. The bonding allows the shaft to have the full strength of the selected materials, as there is no annealing (and loss of strength) due to the softening that occurs during the welding process. 
   4. Since there is no welding, there is no distortion due to welding which would negatively affect the accuracy and run-out provided by the mechanical alignment by the locating portions and the resulting mechanical mating. 
   5. The locating portions on one of the components provide a controlled constant gap for the adhesive bond line. 
   6. The method uses an injection hole for adhesive with an opposed end air bleed hole to allow a substantially 100% fill with a precisely controlled volume of adhesive. 
   7. The mechanical press fit of the locating portions allow the drive shaft to be handled, and other mechanical components installed and balanced, without waiting for the full adhesive cure period. 
   8. The balance characteristics are much improved and require less weight for balancing, as a result of the concentric improvements inherent to the bonding process.