Patent Publication Number: US-2013252749-A1

Title: Propshafts and propshaft assemblies and methods for fabricating propshafts

Description:
TECHNICAL FIELD 
     The present invention relates generally to propshafts, propshaft assemblies, and methods for fabricating propshafts, and more particularly to fiber reinforced composite propshafts for transferring torque in a motor vehicle, propshaft assemblies that include such propshafts, and methods for fabricating such propshafts. 
     BACKGROUND 
     Motorized vehicles traditionally include a propeller shaft, i.e., propshaft, for transmitting an output torque from a transmission or transfer case through a differential to the wheels of the vehicle. For example, a transmission receives a drive torque from an internal combustion engine and employs gear ratios to modify the input torque to obtain various desired output torques. The output torque is then transmitted, e.g., directly from the transmission or indirectly from a transfer case, through a propshaft assembly to a front or rear differential unit, which evenly distributes the torque between a pair of axle shafts. The axle shafts, in turn, cause movement of the vehicle through the vehicle wheels. 
     During operation, propshaft assemblies are subjected to significant torsion and shear stresses and must be strong enough to bear these stresses. These assemblies, however, need to avoid too much weight that would otherwise substantially increase their inertia. Fiber reinforced composite propshafts offer significant weight savings over propshafts made from more traditional materials, such as metals, without decreasing the mechanical properties of the propshafts. The reduction in mass has a direct impact on the force required to accelerate and decelerate the vehicle. Due to the relatively low density and high mechanical properties of fiber reinforced composite propshafts, the moment of inertia (e.g. measure of the rotational inertia of the part) is significantly less than steel propshafts, thereby improving the overall vehicle performance. 
     Propshaft assemblies often include a shaft body having universal joints coupled at both ends for transmitting rotational energy and torque along the shaft body, and an intermediate slip yoke assembly for allowing for some axial movement along the shaft body to facilitate assembly, manage build variation, and the like. Current slip yoke assemblies for fiber reinforced composite propshafts are relatively large and heavy so that they can handle the significant loads carried by propshafts. As such, fiber reinforced composite propshaft assemblies often require significant package space, which is often very limited, to accommodate a slip yoke assembly. Additionally, the significant weight of these slip yoke assemblies can diminish some or many of the benefits of using a fiber reinforced composite propshaft. 
     Accordingly, it is desirable to provide fiber reinforced composite propshafts for transferring torque in a motor vehicle that allow for some axial movement while reducing package space requirements and/or weight, propshaft assemblies that include such propshafts, and methods for fabricating such propshafts. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background. 
     SUMMARY 
     Propshafts and propshaft assemblies for transferring torque in motor vehicles, and methods for fabricating such propshafts are provided herein. In accordance with an exemplary embodiment, a propshaft for transferring torque in a motor vehicle comprises a fiber reinforced composite tube having a channel and a splined female insert. The fiber reinforced composite tube comprises a composite wall that is disposed around the channel. The splined female insert comprises a buried wall portion that is disposed in the channel operatively coupled to the composite wall. The buried wall portion has an inner surface and a plurality of internal splines formed along the inner surface. 
     In accordance with another exemplary embodiment, a propshaft assembly for transferring torque in a motor vehicle comprises a first propshaft member and a second propshaft member. The first propshaft member comprises a fiber reinforced composite tube and a splined female insert. The fiber reinforced composite tube has a channel and comprises a composite wall that is disposed around the channel. The splined female insert comprises a buried wall portion that is disposed in the channel operatively coupled to the composite wall. The buried wall portion has an inner surface and a plurality of internal splines formed along the inner surface. The second propshaft member comprises a male yoke. The male yoke has external splines that are engaged with the internal splines of the buried wall portion to allow telescopic movement between the male yoke and the splined female insert. 
     In accordance with another exemplary embodiment, a method for fabricating a propshaft for transferring torque in a motor vehicle is provided. The method comprises the steps of providing a fiber reinforced composite tube. The fiber reinforced composite tube comprises a composite wall that is disposed around a channel. A splined female insert is positioned into the fiber reinforced composite tube such that a buried wall portion of the splined female insert is positioned in the channel operatively coupled to the composite wall. The buried wall portion has a plurality of internal splines formed along an inner surface of the buried wall portion. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
         FIG. 1  is a perspective cut-away view of a propshaft assembly in accordance with an exemplary embodiment; 
         FIG. 2  is a partial perspective view of a fiber reinforced composite tube in accordance with an exemplary embodiment; 
         FIG. 3  is a perspective view of a splined female insert in accordance with an exemplary embodiment; 
         FIG. 4  is a partial perspective view of the fiber reinforced composite tube of  FIG. 2  assembled with the splined female insert of  FIG. 3  in accordance with an exemplary embodiment; 
         FIG. 5  is a partial perspective cut-away view of a propshaft assembly in accordance with an exemplary embodiment; and 
         FIG. 6  is a flowchart of a method for fabricating a propshaft for transferring torque in a motor vehicle in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following Detailed Description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
     Various embodiments contemplated herein relate to fiber reinforced composite propshafts for transferring torque in a motor vehicle, propshaft assemblies that include such propshafts, and methods for fabricating such propshafts. Unlike the prior art, the exemplary embodiments taught herein provide a propshaft that comprises a fiber reinforced composite tube that includes a composite wall disposed around a channel. A splined female insert is arranged in the channel of the fiber reinforced composite tube. A wall portion of the splined female insert that is buried or positioned in the channel is operatively coupled to the fiber reinforced composite tube along the composite wall so that the splined female insert rotates together with the fiber reinforced composite tube to transfer torque in the motor vehicle. 
     In an exemplary embodiment, a plurality of internal splines is formed along an inner surface of the buried wall portion of the splined female insert. A male yoke that has external splines is operatively coupled with the splined female insert along the buried wall portion that is positioned in the channel to form an axial slip connection. In particular, the external splines of the male yoke are rotationally engaged with the internal splines of the splined female insert for transmitting rotational energy and torque while allowing for some telescopic movement, e.g., axial movement, between the male yoke and the splined female insert. 
     By positioning at least a portion of the axial slip connection formed by the male yoke and the splined female insert in the channel of the fiber reinforced composite tube, the package space requirements and weight for the propshaft can be reduced. In particular, the male yoke and the splined female insert are at least partially packaged in the internal channel space of the fiber reinforced composite tube and therefore, less package space is required outside of the fiber reinforced composite tube for packaging the axial slip connection. Additionally, the size and/or thickness of the splined female insert can be significantly reduced because the buried wall portion of the splined female insert is surrounded and structurally supported by the composite wall of the fiber reinforced composite tube. In particular, the composite wall is made from a relatively high strength fiber reinforced composite material, such as, for example, a resin matrix reinforced with carbon fibers and/or the like. The high strength fiber reinforced composite material, which is operatively coupled to the splined female insert, reinforces the splined female insert so that the splined female insert can be made with less structure, e.g., relatively thin and/or with less material, while still being strong enough to bear the significant loads carried by the propshaft. As such, the splined female insert can be made relatively light so that the axial slip connection including the splined female insert in combination with the male yoke weighs less than conventional slip yoke assemblies for propshafts. 
     Referring to  FIG. 1 , a perspective cut-away view of a propshaft assembly  10  in accordance with an exemplary embodiment is provided. Exemplary embodiments of the propshaft assembly  10  are for transferring torque in a motor vehicle and comprise a first propshaft member  12  and a second propshaft member  14 . The first propshaft member  12  is configured as a fiber reinforced composite propshaft and comprises a fiber reinforced composite tube  16  that is operatively coupled to a splined female insert  18  and an end yoke  20 . The second propshaft number  14  comprises a shaft body  22  that is operatively coupled to a male yoke  24  and an end yoke  26 . As illustrated, the end yokes  20  and  26  are configured as universal joints for allowing some rotational movement as is well known in the art. 
     Referring to  FIG. 2 , a partial perspective view of the fiber reinforced composite tube  16  in accordance with an exemplary embodiment is provided. The fiber reinforced composite tube  16  is configured as a shaft body and comprises a composite wall  28  that is disposed around a channel  30 . The composite wall  28  is formed of a fiber reinforced composite material that comprises a resin, such as an epoxy resin or the like, that is reinforced with fibers, such as carbon fibers, glass fibers, or the like. The reinforcing fibers, for example, may be wound at various angles and impregnation with the resin that is subsequently cured to form the fiber reinforced composite tube  16  as is well known in the art. Fiber reinforced composite tubes for propshafts are commercially available from a number of companies including Toray Industries, Inc., headquartered in Tokyo, Japan. 
     The fiber reinforced composite tube  16  has a first axial end portion  34  that has a plurality of groove  36  formed along an internal surface  32  of the composite wall  28 . In an exemplary embodiment, the grooves  36  extend longitudinally along the internal surface  32  a distance (indicated by double headed arrow “d 1 ”) from an outer-most end  38  of at least about 50 mm, for example of from about 50 to about 100 mm. In one exemplary embodiment, the fiber reinforced composite tube  16  has an internal diameter (indicated by double headed arrow “d 2 ”) of from about 20 to about 25 mm, and a wall stock thickness (indicated by single headed arrows “t”) of from about 3 to about 5 mm. 
     Referring to  FIG. 3 , a perspective view of the splined female insert  18  in accordance with an exemplary embodiment is provided. The splined female insert  18  may be formed of metal, such as by a metal drawing process or the like. As illustrated, the splined female insert  18  has a tubular configuration comprising a wall  40  that is disposed around a channel space  42 . The wall  40  comprises a buried wall portion  44  (e.g. portion of the wall  40  that is inserted into (or buried in) the channel  30  of the fiber reinforced composite tube  16  when assembled) and an exposed wall portion  46  (e.g. portion of the wall  40  that is disposed outside of the channel  30  of the fiber reinforced composite tube  16  when assembled) that extends longitudinally from the buried wall portion  44 . The buried wall portion  44  as an outer surface  48  and a plurality of external splines  50  formed longitudinally along the outer surface  48 . In an exemplary embodiment, the external splines  50  are configured as fine splines having a height of about 1 mm or less, for example of from about 0.5 to about 1 mm, and a number of external splines  50  disposed along the outer surface  48  may be, for example, from about 50 to about 72. In one exemplary embodiment, the splined female insert  18  has an outer diameter (indicated by double headed arrow “D 1 ”) of from about 20 to about 25 mm, and the wall  40  including the buried wall portion  44  has a thickness (indicated by single headed arrows “T”) of about 3 mm or less, for example of from about 2 to about 3 mm. In another exemplary embodiment, the buried wall portion  44  has a length (indicated by double headed arrow “L”) of at least about 50 mm, for example of from about 50 to about 100 mm. 
     Referring also to  FIGS. 2 and 4 , where like reference numbers refer to like components, the buried wall portion  44  of the splined female insert  18  is disposed in the channel  30  along the first axial end portion  34  of the fiber reinforced composite tube  16  and is operatively coupled to the composite wall  28 . In an exemplary embodiment, the grooves  36  of the fiber reinforced composite tube  16  are matched and aligned with the external splines  50  to operatively couple the splined female insert  18  to the composite wall  28  for rotational energy and torque transfer. 
     As illustrated, the wall  40  of the splined female insert  18  has a plurality of internal splines  54  extending longitudinally along the inner surface  52  of the buried wall portion  44  and optionally the exposed wall portion  46 . In an exemplary embodiment, the internal splines  54  formed along the exposed wall portion  46  extend into the buried wall portion  44 , and thus, extend longitudinally into the channel of the fiber reinforced composite tube  16  a distance (indicated by double headed arrow “d 3 ” in  FIG. 1 ) of at least about 50 mm, for example of from about 50 to about 100 mm when assembled. In one exemplary embodiment, a number of internal splines  54  disposed along the inner surface  52  is from about 17 to about 32, for example of from about 25 to about 32. 
     Referring to  FIGS. 1 and 4 , the second propshafts member  14  has a plurality of external splines  56  formed longitudinally along an outer surface  58  of the male yoke  24 . The male yoke  24  is disposed in the channel space  42  of the splined female insert  18  such that the external splines  56  are engaged with the internal splines  54  of the splined female insert  18  providing common rotational motion while allowing for some relative axial movement between the male yoke  24  and the splined female insert  18 . As such, telescopic movement can occur between the male yoke  24  and the splined female insert  18  to define an axial slip connection between the first and second propshafts members  12  and  14 . In an exemplary embodiment, the external splines  56  of the male yoke  24  extend into the channel space  42  of the splined female insert  18  along the buried wall portion  44  a distance (indicated by double headed arrow “d 4 ”) of at least about 30 mm, for example of from about 50 to about 75 mm. 
     Referring to  FIG. 5 , a partial perspective cut-away view of a propshaft assembly in accordance with an exemplary embodiment is provided. The propshaft assembly  10  further comprises a boot  60 . The boot  60  is disposed around the exposed wall portion  46  of the first propshaft member  12  and the shaft body  22  of the second propshafts member  14  to provide a protective covering for the internal splines  54  and the external splines  56  from outside elements, such as water, dirt, and the like. The boot  60  may be flexible to allow for relative axial movement between the first and second propshafts members  12  and  14  and can be formed, for example, from an elastomeric material. 
     Referring to  FIG. 6 , a flowchart of a method  100  for fabricating a propshaft for transferring torque in a motor vehicle in accordance with an exemplary embodiment is provided. The method  100  comprises providing a fiber reinforced composite tube (step  102 ) that comprises a composite wall disposed around a channel. A splined female insert is positioned into the fiber reinforced composite tube (step  104 ) such that a buried wall portion of the splined female insert is positioned in the channel operatively coupled to the composite wall. In an exemplary embodiment, the splined female insert is advanced into the channel using a push-fitting process. The buried wall portion has a plurality of internal splines formed along an inner surface of the buried wall portion. 
     Accordingly, fiber reinforced composite propshafts for transferring torque in a motor vehicle, propshaft assemblies that include such propshafts, and methods for fabricating such propshafts. Unlike the prior art, the exemplary embodiments taught herein provide a propshaft that comprises a fiber reinforced composite tube that includes a composite wall disposed around a channel. A splined female insert is arranged in the channel of the fiber reinforced composite tube. A wall portion of the splined female insert that is buried or positioned in the channel is operatively coupled to the fiber reinforced composite tube along the composite wall. A plurality of internal splines is formed along an inner surface of the buried wall portion of the splined female insert. A male yoke that has external splines is operatively coupled with the splined female insert along the buried wall portion in the channel to form an axial slip connection. By positioning at least a portion of the axial slip connection in the channel of the fiber reinforced composite tube, the package space requirements and weight for the propshaft can be reduced. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the disclosure, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the disclosure. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the disclosure as set forth in the appended claims.