Patent Publication Number: US-2015075897-A1

Title: Slip Yoke Assembly For Automotive Drive Train

Description:
RELATED APPLICATION DATA 
     This application is a non-provisional of U.S. Provisional Patent Application Ser. No. 61/876,815, filed on Sep. 12, 2013, titled “Slip Yoke Assembly,” which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to the field of automobile driveshafts. In particular, the present invention is directed to slip yoke assemblies for use in automobile driveshafts. 
     BACKGROUND 
     Automotive drive train assemblies typically include a driveshaft (sometimes referred to as a propshaft), which is used to transmit rotational power (torque) from a driving member, such as the transmission, to a driven member, such as the front or rear axle. Driveshafts generally need to not only transmit torque, but also accommodate angular misalignment between the transmission and axle assemblies, as well as axial length changes caused by movement of the axle assembly due to the action of the vehicle&#39;s suspension. The angular misalignment requirements are frequently met through the use of universal joints (u-joints) at the driveshaft connection points at both the driving and driven member ends of the shaft. The driveshaft axial length change requirements are typically met through the use of a slip yoke assembly. 
     Slip yoke assemblies typically consist of an externally-splined component engaged within an internally-splined component to transmit torque from one rotating shaft to another rotating shaft via the mating splines. The mating splines are configured for relative axial movement, or slip, which accommodates any necessary driveshaft length changes that occur in operation. The mating splines also must prevent angular misalignment and resist bending forces between the driving and driven components. The spline fit, however, can be inconsistent or inadequate due to variations in the spline design, manufacturing process and methods, and due to subsequent wear that may occur in operation. Such inconsistencies or inadequacies can lead to lateral instability of the yoke shaft/sleeve interface. In turn, this can lead to increased overall instability in the driveshaft when rotating at speed, which can contribute to undesirable driveline disturbances, commonly described as driveline Noise, Vibration and Harshness (“NVH”). NVH can occur at any driveshaft torsional load and rotational speed. Though harmful to vehicle performance and occupant comfort whenever it occurs, it is especially detrimental in high performance vehicle drive trains, where relatively high driveshaft torsional loads and rotational speeds are a common occurrence. For example, some high performance applications might develop driveshaft torsional loads of 1,000 lb-ft or more and driveshaft rotational speeds of 9,000 rpm. 
     Also contributing to NVH in many existing slip yoke designs is the use of a bellows-type rubber boot to seal out environmental contaminants and retain lubricants within the slip yoke assembly. The boots typically lack precision guidance features to ensure they remain centralized about the driveshaft axis while the driveshaft is rotating. Any amount of imbalance caused by this eccentricity will translate into shaft imbalance, resulting in vibration. Since the boot is not prevented from shifting laterally during rotation, the magnitude and location of the imbalance can vary and be unpredictable. Along with these negative characteristics is a tendency for the rubber boot to develop surface cuts or breaks over time that allow contaminants to enter the slip yoke assembly. 
     SUMMARY OF THE DISCLOSURE 
     In one implementation, the present disclosure is directed to a slip yoke assembly for use in an automobile driveshaft. The slip yoke assembly includes an outer sleeve having an inner lumen and an internal spline located in a portion of said inner lumen; a yoke shaft slidably disposed within said inner lumen and configured for movement over a working stroke between a fully-inserted position and a design-maximum-extended position, said yoke shaft having an external spline configured to engage said internal spline to form a splined joint; and at least one bearing surface disposed between the outer sleeve and yoke shaft and spaced from the splined joint, said bearing surface configured and dimensioned to resist angular misalignment between said splined sleeve and said yoke shaft. 
     In another implementation, the present disclosure is directed to an aftermarket slip yoke assembly for use in a replacement driveshaft for replacing an automobile original equipment driveshaft of an automobile drive train. The slip yoke assembly includes a splined sleeve having a proximal end; a yoke shaft slidably disposed within said splined sleeve and forming a splined joint therebetween, said yoke shaft having an outer surface; wherein said proximal end of said splined sleeve includes a rod wiper groove configured to house a rod wiper in direct contact with said yoke shaft outer surface to thereby prevent contaminants from entering said slip yoke assembly. 
     In yet another implementation, the present disclosure is directed to an automobile drive train. The automobile drive train includes an engine and transmission configured to deliver torque to a driveshaft; a rear differential mounted on a suspension configured to receive torque from the driveshaft, the suspension permitting movement of the rear differential relative to the engine and transmission; wherein said driveshaft comprises a slip yoke assembly having; an outer sleeve having an internal spline; a yoke shaft slidably disposed within said outer sleeve, said yoke shaft having an external spline configured to engage said internal spline to form a splined joint; and at least one bearing surface disposed between the outer sleeve and yoke shaft and spaced from the splined joint, said bearing surface configured and dimensioned to resist angular misalignment between said splined sleeve and said yoke shaft 
     These and other aspects and features of non-limiting embodiments of the present invention will become apparent to those skilled in the art upon review of the following description of specific non-limiting embodiments of the invention in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
         FIG. 1A  is a schematic of an example vehicle drive train having a slip yoke assembly; 
         FIG. 1  is an exploded isometric view of an example slip yoke assembly; 
         FIG. 2  is a cross sectional view of the slip yoke assembly of  FIG. 1 ; 
         FIG. 3  is an end view of the slip yoke assembly of  FIGS. 1 and 2 ; 
         FIG. 4  is another cross sectional view of the slip yoke assembly of  FIGS. 1-3 ; 
         FIG. 5  is an enlarged section view of a portion of the slip yoke assembly of  FIGS. 1-4 ; 
         FIG. 6  is another cross sectional view of the slip yoke assembly of  FIGS. 1-5 ; and 
         FIG. 7  is another cross sectional view of the slip yoke assembly of  FIGS. 1-6 . 
     
    
    
     DETAILED DESCRIPTION 
     Automotive drive shafts having slip yoke assemblies are provided that are designed and configured to transmit torque and allow for axial movement while also minimizing driveline vibrations. In some embodiments, the slip yoke assemblies may include one or more bearings that minimize angular misalignment and resist drive shaft bending forces. In other embodiments, the bearings may include a pair of precision mating diameters on a yoke shaft and splined sleeve. In yet other embodiments, the slip yoke assembly may include internal rod wipers to seal out environmental contaminants and retain lubricants. 
       FIG. 1A  illustrates an example automobile drive train  10  that includes components such as an engine  12 , and a transmission  14  and driveshaft  16  for transfer of engine torque to a differential  18 , which in turn transmits the torque to wheels  22  via axle shafts  20 . Differential  18  is configured to move relative to transmission  14 , such that driveshaft  16  must be able to accommodate varying angular alignments and axial distances between the transmission and differential. To accommodate varying angles and axial distances, driveshaft  16  includes universal joints  24  or other appropriate flanges and/or pinion yokes, ect., and a slip yoke assembly  100  for coupling transmission  14  to differential  18 . Universal joints  24 A and  24 B allow for angular misalignment, and slip yoke assembly  100  allows for changes in axial length due to, for example, movement of differential  18  relative to transmission  14 . Various slip yoke assemblies  100  are described and disclosed herein that provide for torque transmission and axial movement. Embodiments described herein also provide opportunities for minimizing driveline NVH and weight and increasing driveline strength and operating speeds. 
       FIGS. 1-7  illustrate an example embodiment of a slip yoke assembly  100  made in accordance with the present invention that is configured and dimensioned to transmit torque while allowing for axial movement with minimal NVH.  FIG. 1  is an isometric exploded view of example slip yoke assembly  100 , which includes a yoke shaft  102  having a first central longitudinal axis A1 configured to be slidably disposed within a splined sleeve  104  having a second central longitudinal axis A2, which forms a splined joint  202  ( FIG. 2 ) that enables torque transmission while also allowing relative axial movement over a working stroke distance L1 ( FIG. 2 ). The working stroke distance L1 is the distance between a fully-inserted position and a design-maximum-extended position. Illustrated slip yoke assembly  100  may have a variety of working strokes, depending, for example, on the intended application. For example, the working stroke may be in the range of approximately 1 inch to approximately 2 inches.  FIG. 2  shows slip yoke assembly  100  in an assembled state, in a mid-stroke position, approximately halfway between a fully-inserted position and a design-maximum-extended position. 
     Illustrated slip yoke assembly  100  is designed to couple to a detachable flange yoke  106 , which forms part of universal joint  24  ( FIG. 1 ) and is designed to couple to a mating flange yoke of universal joint  24 A. Splined joint  202  ( FIG. 2 ) of slip yoke assembly  100  facilitates transmission of torque from a driving member, e.g., vehicle transmission  14  ( FIG. 1A ), to a driven member, e.g., differential  18  ( FIG. 1A ), by way of a mating driveshaft tube  108  and any necessary mating components and hardware, e.g., u-joints, flange and/or pinion yokes, etc.  24 . 
     Turning to each of the slip yoke assembly&#39;s  100  components in more detail, example slip yoke assembly includes detachable flange yoke  106 , which is removeably coupled to a proximal end  108  of yoke shaft  102  with a plurality of bolts or screws  110 . Having a detachable flange yoke  106  may provide several benefits, including ease of manufacturing and increased flexibility in material selection. For example, in the illustrated embodiment, flange yoke  106  may be formed from cast aluminum, while illustrated yoke shaft  102  may be formed from steel with additional anti-friction coatings. Thus, having a detachable flange yoke  106  potentially addresses different design considerations relevant to optimizing weight, strength, and dynamic balance for flange yoke  106  and yoke shaft  102 . Alternative slip yoke assembly embodiments may have a flange yoke that is integrally formed with yoke shaft  102 , or otherwise not removeably coupled to the yoke shaft. In yet other embodiments, flange yoke  106  may be made from materials other than aluminum, and the flange yoke and yoke shaft  102  may be made from the same type of material. 
     As shown in  FIGS. 1 and 2  and in greater detail in  FIGS. 4 and 6 , illustrated flange yoke  106  and yoke shaft  102  may have various precision locating features  112  that facilitate ease of assembly of the flange yoke to the yoke shaft and ensure the flange yoke is precisely located relative to the yoke shaft to ensure optimal vibration performance, including at high rotational speeds. In the illustrated embodiment, complementary precision locating features  112  are located on proximal end  112  of yoke shaft  102  and distal end  114  of flange yoke  106 . Locating features  112  include precision locating faces  116  and  602  ( FIG. 6 ) which ensure proper angular alignment. Locating features  112  in the illustrated embodiment also include a pair of alignment pins  118  located approximately 180 degrees apart from one another on shaft proximal end  112 , and a complementary pair of alignment pin recesses  603  ( FIG. 6 ) on flange distal face  114 . Illustrated alignment pins  118  are hollow to minimize weight and integrally formed with shaft proximal face  112 . Alternative embodiments may have less or more than two alignment pins  118 , pins separated by less or more than 180 degrees, and may also have one or more pins located in flange distal face  114  with complementary recesses in shaft proximal face  116 . Precision locating features  112  also include a precision locating inner diameter  120  on shaft proximal face  116  that is configured to slidably couple to precision locating outer diameter  604  ( FIG. 6 ) on flange distal face  114 . Shaft proximal face  116  also includes a pattern of threaded holes  122  (only one labeled to avoid clutter) for engagement with bolts  110 . 
     Illustrated yoke shaft  102  and splined sleeve  104  are designed and configured with complementary features that facilitate torque transmission and relative axial movement and may also improve vibrational performance. Illustrated shaft  102  and sleeve  104  include splined joint  202  ( FIG. 2 ) comprising an external spline  124  formed in an outer surface of shaft  102  that is configured and dimensioned to mate with an internal spline  126  formed in an inner wall of sleeve  104 .  FIG. 7  further illustrates shaft  102  viewed from a proximal end of the shaft and showing external spline  124 . Shaft  102  and sleeve  104  also include a proximal bearing  204  ( FIG. 2 ) and a distal bearing  206  located on opposite ends of splined joint  202 . Proximal and distal bearings  204  and  206  are configured and dimensioned to prevent angular misalignment of the driveshaft and resist bending forces transmitted to the slip yoke assembly  100  by other driveline components, and function as the primary source of slip yoke location and alignment. Thus, proximal and distal bearings  204  and  206  can minimize primary sources of driveline NVH, which may enable higher rotational speeds and optimal vibrational performance. Also, splined joint  202  does not need to be designed to resist bending forces or angular misalignment such that a length S1 of the splined joint  202  may be less than in conventional slip yoke assemblies and the manufacturing tolerances of one or both of internal and external splines  124  and  126  may be relaxed without substantially impacting NVH performance. With such features, vibrational performance of slip yoke assembly  100  should not be appreciably impacted by wear of the internal or external splines, which can increase durability and lifetime of assembly  100 . 
     In the illustrated exemplary embodiment, proximal and distal bearings  204  and  206  are formed from proximal and distal outer locating diameters  128  and  130  ( FIG. 1 ) on shaft  102  and proximal and distal inner locating diameters  132  and  134  on sleeve  104 . Thus, in the illustrated example, shaft proximal locating diameter  128  and sleeve proximal locating diameter  132  are configured to come into direct sliding contact, thereby forming a bearing surface therebetween and forming proximal bearing  204 . In alternative embodiments, additional or alternative structures such as bushings or other separate bearings may be added to form all or part of the proximal bearing. Illustrated distal bearing  206  also includes a reducer bushing  136  that is sized to be positioned between distal inner and outer locating diameters  130  and  134  and form a bearing surface between an inner surface of bushing  136  and distal outer locating diameter  130 . Bushing  136  may be inserted into a distal end  138  of sleeve  104  and, in the illustrated embodiment, the bushing is held in place via an interference fit between an outer diameter of the bushing and distal inner locating diameter  134 . Assembly  100  may also include a retaining ring  208  ( FIG. 2 ), which is used to ensure the bushing does not move axially in operation. Because illustrated inner and outer locating diameters  128 - 134  are simple, round features, a precision slip fit may be achieved using relatively straightforward and common manufacturing processes and methods. In operation, locating diameters  128 - 134  and external and internal splines  124  and  126  are free to slide axially relative to each other, thereby providing the axial length change characteristics required of the driveshaft. 
     As shown in  FIG. 2 , in the illustrated embodiment, shaft  102  has a stepped-outer-diameter design, where shaft distal outer locating diameter  130  ( FIG. 1 ) has a diameter D3 ( FIG. 2 ) that is less than a diameter D2 ( FIG. 2 ) of shaft proximal outer locating diameter  128 . D3 is also slightly less than a minor diameter D1 ( FIGS. 2 and 7 ) of the splined joint  202  and D2 is slightly greater than a major diameter D4 ( FIGS. 2 and 7 ) of the splined joint  202 . Both of sleeve locating diameters  132  and  134  have a diameter that is slightly greater than shaft proximal diameter D2. Having sleeve  104  with inner locating diameters  132  and  134  that are larger than splined joint major diameter D4 facilitates ease of manufacturing internal spline  126 , for example, with a broaching machine process. Shaft  102  stepped outer diameter can facilitate assembly by allowing shaft distal locating diameter  130  to be inserted past internal spline  126 . 
     As also shown in  FIG. 2 , proximal bearing  204  extends along an axial contact length L2 and has a corresponding bearing surface area, and distal bearing  206  extends along an axial contact length L3 and has a corresponding bearing surface area. In the illustrated embodiment, when shaft  102  is fully inserted in sleeve  104 , length L2 is approximately equal to the length of sleeve internal locating diameter  132 . As shaft  102  extends out of sleeve  104 , the length of L2 decreases. As described above,  FIG. 2  shows assembly  100  in a mid-stroke position such that length L2 illustrated in  FIG. 2  is approximately half way between a maximum axial contact length when shaft  102  is fully inserted and a minimum contact length when the shaft is fully extended to the design maximum extended position. In the illustrated example, length L3 is equal to the width of bushing  136 . As shown, length L2 and the corresponding bearing surface area of proximal bearing  204  is greater than length L3 and the corresponding bearing surface area of distal bearing  206 . Such a length differential can allow proximal bearing  204  to function as a primary radial load bearing, while distal bearing  206  can have a primary function of axial alignment and a secondary function of radial load. In the illustrated embodiment, a minimum ratio of axial contact length L2 or L3 to its corresponding shaft diameter D2 or D3 (L2/D2 or L3/D3) when shaft  102  is in a design maximum extended position is in the range of about 0.6 to about 2.0. In the illustrated exemplary embodiment, L3/D3 may be closer to approximately 0.6 and L2/D2 may be closer to approximately 2. In other examples L3/D3 may be substantially the same as L2/D2 or less than L2/D2. In yet other embodiments, one or both of L2/D2 and L3/D3 may in the range of about 0.5 to about 2.1; or about 0.7 to about 1.9; or about 0.8 to about 1.8; or about 0.9 to about 1.7; or about 1.0 to about 1.6; or about 1.1 to about 1.5, or about 1.2. In yet another example, over the entire operating stroke, both proximal bearing  204  and distal bearing  206  have a minimum L/D ratio (L2/D2 or L3/D3) of about 0.6 or about 0.65 or about 0.67, or about 0.7 
     In the illustrated embodiment, proximal and distal bearings  204  and  206  are separated by a relatively large distance as compared to a corresponding spline length of engagement in a conventional slip yoke, resulting in improved support of yoke shaft  102  in both static and dynamic conditions, especially when at design maximum extended position, or full extension. The fixed locations of sleeve internal locating diameters  132  and  134  results in an overall yoke shaft supported length L5 ( FIG. 2 ) that does not vary in operation, which may further improve stability. Likewise, the effects of any clearance between mating locating diameters  128 - 134  of yoke shaft  102  and splined sleeve  104  may be minimized due to the relatively large distance between the proximal and distal diameters. Therefore, manufacturing variables and operational wear may be less critical to the performance of the assembled unit. 
     With assembly  100  in the mid-stroke position shown in  FIG. 2 , assembly  100  has an unsupported length L4 extending from an axis of rotation  210  of flange  106  to a proximal end  212  of proximal bearing  204 . As shown in  FIG. 2 , in the illustrated embodiment, unsupported length L4 varies depending on the position of shaft  102 , with assembly  100  having a maximum unsupported length L4 when the shaft is in the design maximum extended position, and a minimum unsupported length L4 when the shaft is fully inserted into sleeve  104 . Assembly  100  has supported length L5 extending from proximal end  212  of proximal bearing  204  to distal end  214  of distal bearing  206 . In the illustrated embodiment, the ratio of supported length L5 to shaft proximal outer diameter D2 (L5/D2) may be greater than or equal to 2.5. For a given load, providing a L5/D2 ratio of ≧2.50 serves to reduce the individual bearing loads imparted to each of proximal and distal bearings  204  and  206  caused by shaft bending as compared to the loads imparted in a splined section of conventional yoke shafts. By including proximal and distal bearings  204  and  206  and providing a L5/D2 of ≧approximately 2.5, the loads applied to splined joint  202  are reduced, thereby reducing spline wear and improving shaft alignment. In other embodiments, L5/D2 may be equal to or greater than 2.0, or 2.2, or 2.4, or 3.0. Also, in the illustrated embodiment, the ratio of supported length L5 to unsupported length L4 (L5/L4) when shaft  102  is at the maximum design extended position is greater than or equal to about 1.5. For example, illustrated assembly  100  has a minimum ratio of supported length to unsupported length of about 1.5. Having a minimum L5/L4 ratio of ≧approximately 1.5 serves to reduce the misalignment effects caused by any clearance present between the mating yoke shaft  102  and sleeve locating diameters  128 - 134 . In other embodiments, the yoke shaft assembly may have a minimum L5/L4 ratio of about 1.75 or 2.0. 
     In the illustrated embodiment, yoke shaft  102  may be made from steel, for example, low carbon steel or alloy steel, and splined sleeve  104  and reducer bushing  136  may be made from aluminum, for example, 6061-T4 or 6061-T6 aluminum. Illustrated alignment pins  118  ( FIG. 1 ) may be made from steel. The illustrated shaft  102  also may have an anti-friction coating, for example, a Nylon 11 coating. In alternative embodiments, the shaft may have a hard-anodic coating with a friction reducing additive such as PTFE. In yet other embodiments, shaft  102  may also be made from aluminum, such as 6061-T4 or 6061-T6 aluminum. 
     Slip yoke assembly  100  may also include various features to prevent contaminants from entering the assembly while also providing lubricant retention. The sealing features in illustrated assembly  100  include a rod wiper  140  disposed within a rod wiper groove  142  in a proximal end  144  of sleeve  104  and a cup plug  146  coupled to distal end  138  of the sleeve. As shown in  FIG. 2  and in greater detail in  FIG. 5 , illustrated rod wiper  140  has two sealing lips,  502  and  504 , which are configured to contact proximal outer diameter  128  of yoke shaft  102 . Sealing lip  502  serves to prevent environmental contaminants from entering the inner workings of assembly  100  and sealing lip  504  limits the escape of lubricants, such as grease, from the assembly. Rod wiper  140  is retained in sleeve  104  by way of groove  142 . A third sealing lip  506  serves to prevent environmental contaminants from entering the assembly via a path between the outer diameter of wiper  140  and groove  142 . As best seen in  FIG. 5 , illustrated rod wiper groove  142  has a width W1 that is less than a width W2 of rod wiper  140  extending between sealing lips  502  and  504 , which may help maintain rod wiper  140  in the appropriate location, and may improve the effectiveness of sealing lip  502 . Rod wiper groove  142  also has a proximal wall  508  ( FIG. 5 ) having a length L6 and a distal wall  510  having a length L7. In the illustrated embodiment, L6 is less than L7, which may also help maintain rod wiper  140  in the appropriate location, and improve the effectiveness of sealing lip  502 . Rod wiper  140  may be made from a variety of materials, including various types of rubbers, or polymers, including, for example, polyurethane. 
     Illustrated cup plug  146  is designed to couple to distal end  138  of sleeve  104 . In the example embodiment, cup plug  146  has a lip  148  that is sized and configured to be positioned in a cup plug groove  150  in sleeve  104  to thereby secure the cup plug to the sleeve. Cup plug  146  also has a plurality of notches  152  (only one labeled to avoid clutter), which allow deformation of lip  148  for ease of installation. Cup plug  146  also includes a vent hole  154 , which is designed to prevent pressure buildup within slip yoke assembly  100  during operation, while minimizing entry of contaminants and maximizing lubrication retention. Illustrated vent hole  154  is a single orifice located substantially in a center of cup plug  146 . Cup plug  146  may be made from a variety of materials, including a variety of types of composite plastics. 
     Illustrated assembly  100  also includes mating driveshaft tube  108 , which couples assembly  100  to downstream drive train components. In the illustrated embodiment, driveshaft tube  108  has an inner diameter D5 ( FIG. 1 ) that is sized and configured for an interference fit with a sleeve outer locating diameter  156 . Sleeve outer locating diameter  156  is designed to provide a precision location and alignment of assembly  100  and tube  108 . Sleeve  104  also has a shoulder  158  for precise axial location of mating driveshaft tube  108 . As shown in  FIGS. 1 and 2 , outer locating diameter  156  and shoulder  158  are located adjacent splined joint  202  and positioned between proximal and distal bearings  204  and  206 . Such a location ensures that any inadvertent material distortion due to attachment of tube  108  to sleeve  104 , such as distortion due to welding, does not impact bearings  204  and  206 . Illustrated sleeve  104  may be secured to tube  108  in a variety of ways, including via welding, such as a single welded joint  216  where sleeve  104  abuts shoulder  158  ( FIG. 2 ). Illustrated tube  108  may be made from a variety of materials, including aluminum or a carbon fiber composite, in which case joints may be integrally bonded rather than welded. 
     In some embodiments, slip yoke assembly  100  may also include features configured to prevent separation of yoke shaft  102  from splined sleeve  104  during operation. For example, an outer, detachable sleeve or retainer may be fastened to either the yoke shaft or splined sleeve (not shown). The sleeve or retainer may be designed to make contact with a shoulder, retaining ring or other such feature or device on the mating yoke shaft or splined sleeve, but would otherwise be free to move axially along with the component it is fastened to. The additional retaining feature would limit the amount of axial movement, thereby preventing separation of the yoke shaft from the splined sleeve. In other embodiments, the retaining feature may be positioned internally within the slip yoke assembly. In yet other embodiments, a retaining feature may be incorporated into the splined sleeve. For example, the retaining feature may include a plurality of pins mounted radially on the periphery of the splined sleeve. For example, the axes of one or more of the pins may extend radially inward to make contact with, for example, a slot, shoulder or other feature on the yoke shaft, thereby limiting the axial movement of the yoke shaft within the assembled unit. 
     The illustrated yoke shaft assembly is designed and configured to be lightweight while providing opportunities for improved vibrational performance, including in high-performance applications. For example, use of illustrated assembly  100  in an appropriate drive shaft setup may result in a driveshaft dynamic balance equal to or less than approximately 0.10-0.15 oz-in at each end of the driveshaft at approximately 5,000-9,000 rpm. The design drive shaft torque capacity of the assemblies disclosed herein may vary depending on the intended application, for example, maximum design torque capacities may be in a range of approximately 2,500-7,000 lb-ft. 
     The slip yoke assemblies disclosed herein may be used in a variety of applications, including in an Original Equipment (OE) automobile design, or as an aftermarket improvement for example, an improvement for high-performance applications, including rear wheel drive automobiles, including, for example, independent rear-suspension automobiles. Example applications include later-model Chevrolet Camaros® and modified early or late model Ford Mustangs®, as well as a number of other foreign and domestic automobiles. In one example, the drive shaft of a vehicle having a relatively heavy single or multi-piece steel OE driveshaft may be replaced with a drive shaft including a slip yoke assembly made in accordance with the present invention. Such a replacement can result in a reduction of weight and rotating mass, which is particularly beneficial for high-performance and racing applications. 
     Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.