Patent Abstract:
A shaft structure and at least two insert members. The shaft structure has a longitudinally extending cavity and is configured to vibrate in response to the receipt of an input of a predetermined frequency such that at least two second bending mode anti-nodes are generated in spaced relation to one another along the longitudinal axis of the shaft structure. The insert members are disposed within the longitudinally extending cavity and engage an inner wall of the shaft structure. Each of the insert members is located at a position that approximately corresponds to an associated one of the anti-nodes and has a density that is tailored to an anticipated displacement of the associated anti-node. A method for attenuating noise transmission from a vehicle driveline is also disclosed.

Full Description:
FIELD OF THE INVENTION 
     The present invention generally relates to noise 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 sound while transferring rotary power. When the propshaft is excited a harmonic frequency, vibration and noise may be amplified, creating noise that is 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 identical in their configuration (i.e., construction, size, mass and density) and are installed in the propshaft such that they are equidistantly spaced along the length of the propshaft. Construction in this manner is advantageous in that it greatly simplifies the manufacturer of the propshaft. Despite this advantage, several drawbacks remain. 
     For example, symmetric positioning of the identically-configured inserts within the propshaft typically does not maximize the attenuation of the vibration within the propshaft. Accordingly, it is desirable to provide an improved propshaft that attenuates vibrations within the propshaft to a larger degree than that which is taught by the prior art. 
     SUMMARY OF THE INVENTION 
     In one preferred form, the present invention provides a shaft structure and at least two insert members. The shaft structure has a longitudinally-extending cavity and is configured to vibrate in response to the receipt of an input of a predetermined frequency such that at least two second bending mode anti-nodes are generated in spaced relation to one another along the longitudinal axis of the shaft structure. The insert members are disposed within the longitudinally extending cavity and engage an inner wall of the shaft structure. Each of the insert members is located at a position that approximately corresponds to an associated one of the anti-nodes and has a density that is tailored to an anticipated displacement of the associated anti-node. A method for attenuating noise transmission from a vehicle driveline is also disclosed. 
     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 embodiment 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 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 schematic illustration of the maximum displacement associated with the bending mode of the propshaft; and 
     FIG. 6 is a plot illustrating noise as a function of the propshaft speed for three differently configured propshafts. 
    
    
     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  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 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 . More specifically, drive torque received the input shaft  120  is transmitted by the pinion teeth  124  to the teeth  126  of the ring gear  72  such that drive torque is distributed through the differential pinions  88  to the first and second side gears  82  and  86 . 
     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. 
     With additional reference to FIG. 4, the propshaft assembly  20  is shown to include a shaft structure  200 , first and second trunnion caps  202   a  and  202   b , first and second insert members  204   a  and  204   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, 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 . 
     A splined portion of the yoke assembly  208  is rotatably coupled with the transmission output shaft  18   a  and the yoke flange  210  is rotatably coupled with the input shaft  120 . The first and second universal joints  212  and  214  facilitate a predetermined degree of vertical and horizontal offset between the transmission output shaft  18   a  and the input shaft  120 . 
     The shaft structure  200  is illustrated to be generally cylindrical, having a hollow central cavity  220  and a longitudinal axis  222 . In the particular embodiment illustrated, the ends  224  of the shaft structure  200  are shown to have been similarly formed in a rotary swaging operation such that they are necked down somewhat relative to the central portion  226  of the shaft structure  200 . 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. 
     The first and second insert members  204   a  and  204   b  are fabricated from an appropriate material and positioned within the hollow cavity at locations approximately corresponding to the locations of the second bending mode anti-nodes  230 . The configuration of each of the first and second insert members  204   a  and  204   b  is tailored to the anticipated maximum displacement of the shaft structure  200  at the anti-nodes  230  when the propshaft assembly  20  is excited at a predetermined frequency and the insert members  204   a  and  204   b  are not present. In this regard, the density, mass and/or resilience of the first and second insert members  204   a  and  204   b  is selected to provide a predetermined reduction in the anticipated maximum displacement of the shaft structure  200  at the anti-nodes  230 . 
     In the example provided, the first and second insert members  204   a  and  204   b  are identically sized, being cylindrical in shape with a diameter of about 5 inches and a length of about 18 inches. The first and second insert members  204   a  and  204   b  are disposed within the hollow central cavity  220  and engage the inner wall  228  of the shaft structure  200 . Preferably, the first and second insert members  204   a  and  204   b  engage the shaft structure  200  in a press-fit manner, but other retaining mechanisms, such as bonds or adhesives, may additionally or alternatively be employed. 
     The predetermined frequency at which vibration dampening is based is determined by monitoring the noise and vibration of the propshaft assembly  20  while performing a speed sweep (i.e., while operating the driveline  12  from a predetermined low speed, such as 750 r.p.m., to a predetermined high speed, such as 3250 r.p.m.). In the example provided, the first harmonic of the meshing of the pinion teeth  124  with the teeth  126  of the ring gear  72  was found to produce hypoid pear mesh vibration that excited the second bending and breathing modes of the propshaft assembly  20  when the propshaft assembly  20  was rotated at about 2280 r.p.m., as shown in FIG.  5 . As a result of the configuration of the propshaft assembly  20 , the anticipated maximum displacement of the anti-node  230   b  is shown to be significantly larger than the anticipated displacement of the anti-node  230   a , which is generated in a spaced relation from anti-node  230   b . Accordingly, if the first and second insert members  204   a  and  204   b  are not tailored to their respective anti-node  230 , noise attenuation may not be as significant as possible and in extreme cases, could be counter-productive. As such, the first insert member  204   a  is constructed from a material that is relatively denser than the material from which the second insert member  204   b  is constructed. In the embodiment shown, the first insert member  204   a  is formed from a CF-47 CONFOR™ foam manufactured by E-A-R Specialty Composites having a density of 5.8 lb/ft 3 , while the second insert member  204   b  is formed from a CF-45 CONFOR™ foam manufactured by E-A-R Specialty Composites having a density of 6.0 lb/ft 3 . The foam material is porous, being of an open-celled construction, and has a combination of slow recovery and high energy absorption to provide effective damping and vibration isolation. 
     FIG. 6 is a plot that illustrates the noise attenuation that is attained by the propshaft assembly  20  as compared with an undamped propshaft assembly and a conventionally damped propshaft assembly. The plot of the undamped propshaft assembly is designated by reference numeral  300 , the plot of the conventionally damped propshaft assembly is designated by reference numeral  302  and the plot of the propshaft assembly  20  is designated by reference numeral  304 . The undamped propshaft assembly lacks the first and second insert members  204   a  and  204   b  but is otherwise configured identically to the propshaft assembly  20 . The conventionally damped propshaft assembly includes a single foam damping insert that is approximately 52 inches long and approximately centered within the propshaft. The foam insert has a density of about 1.8 lbs/ft 3  and provides a degree of dampening that is generally similar to other commercially-available damped propshaft assemblies. Notably, the propshaft construction methodology of the present invention provides significant noise reduction at the predetermined frequency as compared with the undamped and conventionally damped propshaft assemblies. 
     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. Therefore, it is intended that the invention not be limited to the particular embodiment 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.

Technology Classification (CPC): 5