Abstract:
A propshaft assembly includes a shaft structure having a hollow cavity and an insert member being positioned within the hollow cavity and engaging the shaft structure. The shaft structure vibrates in response to receipt of an input of a predetermined frequency such that a shell mode anti-node is generated. The insert member is located at a position that approximately corresponds to the anti-node and has a compressive strength that is tailored to an anticipated displacement of the anti-node to thereby attenuate vibration of the shaft structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of co-pending U.S. patent application Ser. No. 11/184,708 filed Jul. 19, 2005. The disclosure of the above application is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention generally relates to vibration attenuation in vehicle drivelines and, more particularly, to an improved noise attenuating propshaft and a method for its construction. 
   BACKGROUND OF THE INVENTION 
   Propshafts are commonly employed for transmitting power from a rotational power source, such as the output shaft of a vehicle transmission, to a rotatably driven mechanism, such as a differential assembly. As is well known in the art, propshafts tend to transmit vibration while transferring rotary power. When the propshaft is excited at a harmonic frequency, vibration and noise may be amplified, creating disturbances that are undesirable to passengers riding in the vehicle. Thus, it is desirable and advantageous to attenuate vibrations within the propshaft in order to reduce noise within the vehicle passenger compartment. 
   Various devices have been employed to attenuate the propagation of noise from propshafts including inserts that are made from cardboard, foam, or resilient materials, such as rubber. The inserts that are typically used for a given propshaft are generally of a construction, size, mass and density to attenuate bending mode vibrations within the propshaft. While such inserts offer various advantages, several drawbacks remain. 
   One such drawback is the susceptibility of current propshaft assemblies to experience shell mode vibrations in the environment in which they are installed. Long aluminum propshafts have been found to produce significant noise resulting from the propshaft being excited at a shell mode natural frequency. Previously known inserts operable to attenuate propshaft tube vibrations are typically heavy and inefficient in attenuating both bending and shell mode vibrations. For long aluminum propshafts that are generally obliged to have damping treatments, these known inserts many times create concerns regarding to their mass loading effect on critical speed as well as their effectiveness on tube shell mode vibrations. It is therefore desirable to provide an improved propshaft with a lightweight however highly efficient damping treatment that is operable to attenuate propshaft tube vibrations to reduce noise transmitted to the vehicle occupants. 
   Furthermore, because different propshaft structures may exhibit different shell mode natural frequencies, it may be desirable to provide a propshaft assembly having an insert operable to be tuned to attenuate specific shell mode natural frequencies. 
   SUMMARY OF THE INVENTION 
   A propshaft assembly includes a shaft structure having a hollow cavity and an insert member being positioned within the hollow cavity and engaging the shaft structure. The shaft structure vibrates in response to receipt of an input of a predetermined frequency such that a shell mode anti-node is generated. The insert member is located at a position that approximately corresponds to the anti-node and has a compressive strength that is tailored to an anticipated displacement of the anti-node to thereby attenuate vibration of the shaft structure. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a schematic illustration of an exemplary vehicle constructed in accordance with the teachings of the present invention; 
       FIG. 2  is a top partially cut-away perspective view of a portion of the vehicle of  FIG. 1  illustrating the rear axle and the propshaft in greater detail; 
       FIG. 3  is a sectional view of a portion of the rear axle and the propshaft; 
       FIG. 4  is a top, partially cut away view of the propshaft; 
       FIG. 5  is a partially cut-away perspective view of the propshaft and an insert member of the present invention; 
       FIG. 6  is a perspective view of the propshaft of  FIG. 5  showing a first shell mode deformed condition; 
       FIG. 7  is a sectional view of the propshaft of  FIG. 6  taken along line  7 - 7  shown in  FIG. 6 ; 
       FIG. 8  is a sectional view of the propshaft of  FIG. 6  taken along line  8 - 8  of  FIG. 6 ; 
       FIG. 9  is a perspective view of the propshaft of  FIG. 5  showing a second shell mode deformed condition; 
       FIG. 10  is a sectional view of the propshaft of  FIG. 9  taken along line  10 - 10  shown in  FIG. 9 ; and 
       FIG. 11  is a sectional view of the propshaft of  FIG. 9  taken along line  11 - 11  shown in  FIG. 9 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIG. 1  of the drawings, a vehicle having a propshaft assembly that is constructed in accordance with the teachings of the present invention is generally indicated by reference numeral  10 . The vehicle  10  includes a driveline  12 , which is drivable via a connection to a power train  14 . The power train  14  includes an engine  16  and a transmission  18 . The driveline  12  includes a propshaft assembly  20 , a rear axle  22  and a plurality of wheels  24 . The engine  16  is mounted in an in-line or longitudinal orientation along the axis of the vehicle  10  and its output is selectively coupled via a conventional clutch to the input of the transmission  18  to transmit rotary power (i.e., drive torque) therebetween. The input of the transmission  18  is commonly aligned with the output of the engine  16  for rotation about a rotary axis. The transmission  18  also includes an output  18   a  and a gear reduction unit. The gear reduction unit is operable for coupling the transmission input to the transmission output at a predetermined gear speed ratio. The propshaft assembly  20  is coupled for rotation with the output  18   a  of the transmission  18 . Drive torque is transmitted through the propshaft assembly  20  to the rear axle  22  where it is selectively apportioned in a predetermined manner to the left and right rear wheels  24   a  and  24   b , respectively. 
   With additional reference to  FIGS. 2 and 3 , the rear axle  22  is shown to include a differential assembly  30 , a left axle shaft assembly  32 , and a right axle shaft assembly  34 . The differential assembly  30  includes a housing  40 , a differential unit  42  and an input shaft assembly  44 . The housing  40  supports the differential unit  42  for rotation about a first axis  46  and further supports the input shaft assembly  44  for rotation about a second axis  48  that is perpendicular to the first axis  46 . 
   The housing  40  is initially formed in a suitable casting or stamping process and thereafter machined as required. The housing includes a wall member  50  that defines a central cavity  52  having a left axle aperture  54 , a right axle aperture  56 , and an input shaft aperture  58 . The differential unit  42  is disposed within the central cavity  52  of the housing  40  and includes a case  70 , a ring gear  72  that is fixed for rotation with the case  70 , and a gearset  74  that is disposed within the case  70 . The gearset  74  includes first and second side gears  82  and  86  and a plurality of differential pinions  88 , which are rotatably supported on pinion shafts  90  that are mounted to the case  70 . The case  70  includes a pair of trunnions  92  and  96  and a gear cavity  98 . A pair of bearing assemblies  102  and  106  are shown to support the trunnions  92  and  96 , respectively, for rotation about the first axis  46 . The left and right axle assemblies  32  and  34  extend through the left and right axle apertures  54  and  56 , respectively, where they are coupled for rotation about the first axis  46  with the first and second side gears  82  and  86 , respectively. The case  70  is operable for supporting the plurality of differential pinions  88  for rotation within the gear cavity  98  about one or more axes that are perpendicular to the first axis  46 . The first and second side gears  82  and  86  each include a plurality of teeth  108  which meshingly engage teeth  110  that are formed on the differential pinions  88 . 
   The input shaft assembly  44  extends through the input shaft aperture  58  where it is supported in the housing  40  for rotation about the second axis  48 . The input shaft assembly  44  includes an input shaft  120 , a pinion gear  122  having a plurality of pinion teeth  124  that meshingly engage the teeth  126  that are formed on the ring gear  72 , and a pair of bearing assemblies  128  and  130  which cooperate with the housing  40  to rotatably support the input shaft  120 . The input shaft assembly  44  is coupled for rotation with the propshaft assembly  20  and is operable for transmitting drive torque to the differential unit  42 . 
   The left and right axle shaft assemblies  32  and  34  include an axle tube  150  that is fixed to the associated axle aperture  54  and  56 , respectively, and an axle half-shaft  152  that is supported for rotation in the axle tube  150  about the first axis  46 . Each of the axle half-shafts  152  includes an externally splined portion  154  that meshingly engages a mating internally splined portion (not specifically shown) that is formed into the first and second side gears  82  and  86 , respectively. 
     FIG. 4  depicts the propshaft assembly  20  to include a shaft structure  200 , first and second trunnion caps  202   a  and  202   b , first and second spiders  206   a  and  206   b , a yoke assembly  208  and a yoke flange  210 . The first and second trunnion caps  202   a  and  202   b , the first and second spider  206   a  and  206   b , the yoke assembly  208  and the yoke flange  210  are conventional in their construction and operation and as such, need not be discussed in detail. Briefly, the first and second trunnion caps  202   a  and  202   b  are fixedly coupled to the opposite ends of the shaft structure  200 , typically via a weld. Each of the first and second spiders  206   a  and  206   b  is coupled to an associated one of the first and second trunnion caps  202   a  and  202   b  and to an associated one of the yoke assembly  208  and the yoke flange  210 . The yoke assembly  208 , first spider  206   a , and first trunnion cap  202   a  collectively form a first universal joint  212 , while the yoke flange  210 , second spider  206   b  and second trunnion cap  202   b  collectively form a second universal joint  214 . 
   The shaft structure  200  is illustrated to be generally cylindrical, having a hollow central cavity  220  and a longitudinal axis  222 . The shaft structure  200  is preferably formed from a welded seamless material, such as aluminum (e.g., 6061-T6 conforming to ASTM B-210) or steel. 
     FIG. 5  shows an insert member  250  may be inserted into the shaft structure  200  to attenuate shell mode vibration that is produced during transmission of rotary power by the propshaft assembly  20 . In the particular example provided, a single insert member  250  is employed. The insert member  250  is a substantially cylindrical structure having a shape that is generally complimentary to the inside surface of the shaft structure  200 . In the embodiment illustrated, the insert member  250  is configured as an elongated cylinder with a generally circular cross-section. The insert member  250  is further defined by a plurality of closed cells  252  interconnected to one another. 
   In the exemplary insert member  250 , closed cells  252  are arranged in a honeycomb pattern where each cell  252  includes a substantially hexagonal cross-section. Each cell may be shaped as a right hexagonal prism having a predetermined length. A cell length “L” ranging from about 1 mm to 2 mm is contemplated to provide desirable stiffness and energy absorption characteristics for at least one shaft structure having a known length, diameter, wall thickness and material. Because the frequencies at which the shell modes are excited vary from component to component, the length and width of the cells may be varied to tune the insert to isolate certain frequencies. In similar fashion, the insert material may be changed to target certain frequencies for attenuation. One embodiment of the invention utilizes an insert member constructed from polypropylene. Other materials such as aluminum may also be used. Insert  250  is constructed from a material having a compressive strength in the range of 140-250 psi. This compressive strength is sufficient to resist the radially inward deflection of portions of the shaft structure. As such, the insert  250  increases structural stiffness of the tube to provide energy absorption during the shell vibration modes. 
   The insert  250  includes an outer surface  254  defining a first outer diameter when insert  250  is in a “free” or unloaded condition. The first outer diameter is greater than an inner diameter defined by an inner surface  256  of shaft structure  200 . To assemble propshaft assembly  20 , an adhesive  258  is applied to outer surface  254 . A force is applied to insert  250  to reduce the first outer diameter to a second outer diameter less than the inner diameter of inner surface  256 . Insert  250  is positioned within cavity  220  where the external force is released. Insert  250  is constructed from a substantially elastomeric material such that insert  250  tends to spring back to its original un-deformed stated. Shaft structure  200  resists this tendency and an equilibrium is reached where insert  250  biasedly engages shaft structure  200 . The biased engagement as well as the adhesive bond between the insert  250  and inner surface  256  assures that insert  250  maintains a proper load-transfer-type engagement with shaft structure  300 . 
     FIGS. 6-8  depict a first shell mode of vibration of shaft structure  200 .  FIGS. 9-11  depict shaft structure  200  in a deformed state while in a second shell mode. In the first shell mode depicted in  FIGS. 6-8 , portions  260  of shaft structure  200  move radially inwardly towards longitudinal axis  222  while portions  262  move radially outwardly from longitudinal axis  222 . The maximum amplitude of deflection during a first shell mode occurs at approximately the midpoint along the length of shaft structure  200 . The maximum deflection location is termed an anti-node. 
     FIGS. 9-11  depict the second shell mode of vibration for shaft structure  200 . The second shell mode includes a first anti-node  270  and a second anti-node  272  spaced apart from one another along the length of shaft structure  200 . Portions  274  located at first anti-node  270  deflect radially inwardly while portions  278  deflect radially outwardly. The radially inwardly deflecting portions are substantially diametrically opposed from one another as are the radially outwardly deflecting portions. The radially inwardly extending portions  274  are aligned along an axis Y while the radially outwardly extending portions  278  are aligned along an axis X orthogonal to axis Y. 
   Radially inwardly extending portions  280  are substantially diametrically opposed from one another and axially located along shaft structure  200  at second anti-node  272 . The radially inwardly extending portions  280  are positioned along axis X. Radially outwardly extending portions  282  are substantially diametrically opposed to one another and aligned along axis Y. The magnitude of deflections both radially inwardly and radially outwardly at second anti-node  272  are substantially similar to the magnitude of deflections located at first anti-node  270 . However, the shell mode shape of second anti-node  272  has been rotated substantially 90 degrees about longitudinal axis  222  in relation to the shape of shaft structure  200  at first anti-node  270 . 
   While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. It is, therefore, intended that the invention not be limited to the particular embodiments illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims.