Abstract:
A mass damper for use with a drive shaft center support bearing is located on a non-rotating portion of the bearing and is suspended on a spring element for free vibration and has a resonance that is selected to be the same as that which would otherwise be communicated to the vehicle through the bearing by the drive shaft and drivetrain components. The two embodiments are each tunable so that the damper can be set to have different resonant vibration characteristics, as required for use with different drive shaft and drivetrain configurations.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates generally to the field of vibration isolation in automotive vehicles and more particularly to the area of minimizing the effects of drive shaft vibration resonance. 
       DESCRIPTION OF THE PRIOR ART 
       [0002]    In general, a multi-piece driveshaft requires a support bearing near where the shafts are joined together. The support bearing is also called a drive shaft center support bearing because it is near the center or the junction between a pair of drive shafts. The support bearing usually includes a roller bearing isolated in rubber, and a bracket configuration used as a point of attachment to the vehicle structure. For automotive applications, whether it is attached directly to the vehicle body or to the vehicle frame, the support bearing is the key element for conveying vibration caused by an imbalances in the drive shafts and is the element that has been altered many ways in order to reduce the effect of such vibrations. 
         [0003]    U.S. Pat. No. 6,422,947 describes a driveshaft bearing in which the conventional bearing assembly is mounted in a bracket but separated therefrom by a flexible rubber support member. It is known that such support functions to isolate and reduce the transfer of vibrations from the rotating shaft to the vehicle. 
         [0004]    It is further known that merely isolating the bearing does not completely attenuate the shaft vibrations when they enter into a resonant mode of vibration, typically in the range of 22 Hz˜26 Hz. Vibrations from the resonant mode are significantly higher in intensity and are often felt by the vehicle occupants. When the vehicle shaft rotates through this frequency range it sometimes causes a shudder type disturbance. This disturbance is not only speed sensitive, but also torque sensitive and sensitive to rear suspension jounce. 
         [0005]    U.S. Pat. No. 5,145,025 describes a non-rotating vibration damper for a drive shaft in which an absorber mass is connected via a spring directly to a coaxially arranged ring that is fixed directly to the outer ball bearing race. The vibration damper is described as freely vibrating and as being adjusted to the respective natural frequency of the drive shaft for the purpose of reducing the “bending” vibrations that occur. 
         [0006]    Although this patent describes a damper that may be adjusted, there is no described mechanism for such adjustment. Therefore, once that vibration damper is designed and built for a particular powertrain configuration, it is dedicated to that configuration or another which exhibits the same resonance frequency in drive shaft vibrations. 
       SUMMARY OF INVENTION 
       [0007]    The present invention utilizes the principle of employing a sprung mass inertia on a drive shaft bearing to create and apply an opposing force to a vibrating component that counteracts and thereby inhibits or significantly reduces the vibration from a drive shaft whenever it occurs. In addition, the present invention provides a vibration damper which is tunable so that the same components can be utilized with a variety of powertrain configurations which exhibit different resonant frequency vibrations. 
         [0008]    Many different drive train combinations of drive shafts, engines, transmissions and differentials result in many different resonant vibration frequencies that require damping by the present invention. While it is feasible to design a different damper assembly made up of differing spring and/or mass elements for each desired application, it is more desireable to have a tunable damper which can be used in a wide variety of applications. Therefore, the presention invention includes means for selectively presetting the compression forces on the spring element and/or altering the mass element to thereby tune the damper assembly. 
         [0009]    Two embodiments of the present invention are described which illustrate tunable vibration damping for reducing the effects of drive shaft vibration in its resonant mode. In general, this is achieved by providing a non-rotatable vibration isolator on the support bearing that counteracts the vibrational effects otherwise introduced by the drive shaft. Each embodiment utilizes a mass element symmetrically supported for free vibration on a spring element. The spring element is supported on a non-rotating portion of the drive shaft bearing. 
         [0010]    In the first embodiment, the spring element is in the form of an elastomer of a predetermined size and thickness attached to a collar which extends from the non-rotating portion of the bearing. The mass element is in the form of a cylindrical ring with a central aperture sized to fit over the spring element so as to be held thereon and allowed to freely vibrate. Tuning of the damper assembly is provided by employing an associated tuning ring that is press fitted into the central aperture of the mass element and adjacent the spring element. In order to set the resonant frequency of vibration of the mass damper to match that of a particular driveshaft and powertrain configuration, the tuning ring is axially adjusted towards the spring element to cause it to be further compressed and have altered spring characteristics. 
         [0011]    In the second embodiment, the spring element is in the form of an elastomer that is located between the non-rotating collar and the mass element. The mass element is made up of several arcuate sections configured to be clamped together and onto the spring element and collar by fasteners. The sections of the mass element are adapted to allow the attachment of additional added mass elements to change the resonant vibration frequency of the mass damper assembly. Additional tuning is provided by controlling the torque applied to the fasteners when attaching the segments together, since the amount of tighteninig directly effects the compression forces present on the spring elements. Further tuning is provided by employing segmented spring elements that have different spring characteristics with opposing mass element sections. In this manner, the mass damper assembly can provide damping when it is necessary to oppose the effects of vibrations occurring at separate resonant frequencies and in orthogonal directions transverse to the axis of the bearing. 
         [0012]    It is an object of the present invention to provide a vibration damper assembly for use with a drive shaft bearing in an automotive vehicle which employs a plurality of drive shafts connected together for rotation about their respective axis adjacent to the bearing. The drive shaft bearing supports the drive shafts on the vehicle and includes a bearing housing that is connectable to the vehicle, an immovable outer race element connected to the housing, an inner race element and a plurality of rotatable bearings captured between the inner and outer races. A non-rotating cylindrical collar is connected to the outer race and extends co-axially therefrom and spaced from contact with the shaft. The damper mass assembly includes a circular spring element mounted on the collar extension and a mass element suspended on the collar by the spring element to provide counteracting forces to vibrations induced by a mounted drive shaft while it is rotating within the inner race. The assembly also includes means for selectively presetting or adjusting the compression forces present on the spring element in order to tune the damper assembly to a predetermined resonant frequency of vibration characteristic. 
         [0013]    It is another object of the present invention to provide a tuning mechanism that comprises an annular ring that is adjacent to the spring element and is press fitted in the mass element to a degree that alters the compression forces present on the spring element and thereby tune the damper assembly to a predetermined resonant frequency of vibration characteristic. 
         [0014]    It is a further object of the present invention to provide a mass element that is adjustable to alter the compression forces on the spring element and thereby tune the damper assembly to a predetermined resonant frequency of vibration characteristic. 
         [0015]    It is a still further object of the present invention to provide a mass element that accepts additional mass elements for attachment and thereby tune the damper assembly to a predetermined resonant frequency of vibration characteristic. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a representation of a prior art drive train with a conventional drive shaft support bearing. 
           [0017]      FIG. 2  is a plan view representation of a drive shaft support bearing containing a first embodiment of the present invention. 
           [0018]      FIG. 3  is a cross-sectional view representation of the drive shaft support bearing taken along section lines  3 - 3  in  FIG. 2 . 
           [0019]      FIG. 4  is an enlarged view representation of the mass element, spring element and tuning element of the first embodiment represented in  FIG. 3 . 
           [0020]      FIG. 5  is another enlarged view of the mass element, spring element and tuning ring of the first embodiment represented in  FIGS. 3 and 4  adjusted to alter the resonant frequency of vibration of the damper assembly. 
           [0021]      FIG. 6  is a perspective representation of a second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    A multi-piece driveshaft is represented in  FIG. 1  and is typical of the types of driveshafts commonly used in the automotive industry. As shown, a driveshaft support bearing and connecting assembly  12  is associated with a vehicle having a multi-piece driveshaft that includes a first shaft segment or member  12  which is axially coupled by a universal joint  6  to the vehicle&#39;s transmission (not shown) and a second shaft segment or member  4  which is operatively and axially coupled to shaft  2  by a universal joint  8  and by universal joint  10  to the vehicle&#39;s differential (not shown). Bearing assembly  12  includes a bearing assembly a bracket assembly and a protective cover or shield member shown in  FIGS. 2 and 3 . 
         [0023]    The support drive shaft bearing  101  represented in  FIGS. 2 and 3  bears a first embodiment of the present invention. A housing is shown as comprising an upper cover  102  and a lower cover  104 . The covers are typically made of preformed (stamped) sheet metal and welded together to form the housing. Brackets  107  and  103  extend from the housing and are used to attach the bearing to the vehicle or the frame of the vehicle to provide support for the bearing. A bearing isolator  108  is captured within the housing and is an annular elastomer formed with spring breaks  111  to allow for flexibility of movement in the bearing through several axes. A bearing retainer sleeve  105  is held within the bearing isolator  108 . A bearing assembly  110  is captured within bearing retainer sleeve  105 . Bearing assembly  110  comprises an outer race  114 , an inner race  112 , roller elements  116  and seals  109 . Outer race  114  is press fitted within bearing retainer sleeve  105  so as to be retained in the housing. 
         [0024]    Bearing retainer sleeve  105  is a cylindrical element with an inwardly folded end to capture outer race  114 . Bearing retainer sleeve  105  also has a flared collar  106  that extends axially and outward from the bearing assembly  110 . 
         [0025]    A first embodiment of a resonant vibration damper assembly of the present invention is shown in  FIG. 3  as residing on non-rotating collar  106  of bearing retainer  105 . A spring element  120 , which is exemplified here as an elastomer material having preselected spring properties, is attached to collar  106 . In  FIG. 3 , collar  106  is represented as having apertures  121  evenly disposed over its circumference. Spring element  120  is formed to have radially and inwardly extending legs  123  that correspond to the locations of apertures  121 . Legs  123  are fitted in apertures  121  and provide an attachment of spring element  120  that restricts any tendency for lateral movement or dislocation along the surface of collar  106 . A mass element  122 , shown here as a cylindrically formed steel ring, is mounted on spring element  120 . Mass element  122  and spring element  120  are selected to provide a freely vibrating mass that has a resonant frequency of vibration which corresponds to the frequency of vibration present at the support bearing from the drive train shafts. 
         [0026]    In  FIGS. 3 ,  4  and  5 , the tuning means includes a steel ring member  124  which is sized to be interference fitted (press fitted) into the central aperture of mass element  122  adjacent spring element  120 . In any axial location within mass element  122 , ring member  124  contacts spring element  120  to some extent. At each location, spring element  120  experiences different compression forces and therefore different spring characteristics which effect the resonance performance of the damper assembly. I  FIG. 5 , ring member  124  is shown located inward of mass element  122  more than is indicated in  FIG. 4 . As such, spring member  120  exhibits some distortion due to additional compression forces caused by the contact with ring member  124  and a rigid annular lip  125  extending from mass element  122 . 
         [0027]    A second embodiment of the present invention is shown in  FIG. 6 . In that embodiment, a damper assembly  200  includes a mass element which is made up of a plurality of sub-elements. Together, the sub-elements form a central aperture which encircles one or more spring elements. Each of the arcuate sub-elements  222 A-D is identical and is represented as a ninety degree segment. Like each sub-element, sub-element  222 A has a pair of connecting flanges. Coneting flanges  221 A and  223 A respectively contain an open aperture  225 A and a threaded aperture  227 . When assembled, flange  221 A is opposed against flange  223 D and flange  223 A is opposed against  221 B. Screws or similar fasteners (not shown) are inserted into the open and treaded apertures to complete the assembly of the mass element  200 . 
         [0028]    Spring elements are indicated in the drawing as separate arcuate members associated with each segment of the mass element. In the case of sub-element  222 A, it contains an inner arcuate surface  229 A. Spring element  220 A resides adjacent surface  229 A. Likewise, all other sub-elements  222 B,  222 C and  222 D each contain spring elements adjacent their respective inner surfaces  229 B,  229 C and  229 D. 
         [0029]    As in the case of the first embodiment, the damper assembly of this second embodiment is configured to be mounted on the non-rotating portion of the bearing assembly and preferrably on the flared collar  106  of the bearing retainer sleeve  105  in place of the damper assembly shown in  FIG. 3 . 
         [0030]    This second embodiment has several tuning features that enhance the performance of the damper assembly. A plurality of threaded sockets are disposed evenly and symmetrically on each sub-element and are labeled  231 A-D. Each socket is aligned across the center of the damper assembly to be in alignment with a like aperture on an opposing sub-element. Tuning of the resonant vibration frequency of the damper assembly can be changed by symmetrically adding mass to the opposing sub-elements. 
         [0031]    This may be achieved by either attaching pairs of opposing screws such as  232 B and  232 D alone, or to by using screws  232 B and  232 D to attach additional opposing mass elements such as  230   b  and  230 D. Additional tuning of the damper assembly is achieved by adjusting the torque applied to the screws attaching each flange when the assembly of the sub-elements is made, or thereafter during service. In this manner, the compression forces applied to the spring elements is set and therefore sets the resonant vibration frequency of the mass damper assembly. 
         [0032]    Additionally, it has been found that by using different materials for spring elements on opposing sub-elements, the damping mass can be set to have the characteristics of a first resonant frequency of vibration in a first direction transverse to the axis and a second resonant frequency of vibration in a second direction orthogonal to the first direction. In this manner, when a drive shaft exhibits both vertical and horizontal patterns of resonant vibrational different frequencies, this second embodiment can be set to counteract such characteristics and reduce the vibrational effects that would otherwise be transferred to the vehicle. 
         [0033]    It should be understood that the foregoing description of the embodiments is merely illustrative of many possible implementations of the present invention and is not intended to be exhaustive.