Abstract:
A spring seat isolator/damper is employed with a coil spring having flexible modes corresponding to frequencies of loading causing significantly higher dynamic stiffness amplitudes for the spring. The spring seat isolator/damper has an elastomeric member with a spring seat isolator portion and a mass damper portion, and with the spring seat isolator portion adapted to mount to and receive loads from a vehicle suspension. A damper mass operatively engages the mass damper portion of the elastomeric member such that the damper mass and the damper portion of the elastomeric member have a natural frequency that is substantially equal to at least one of the plurality of flexible modes of the coil spring. This damper, then, will substantially reduce the dynamic stiffness of the spring for that flexible mode.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This clams the benefit of United States provisional patent application identified as Application No. 60/333,655, filed Nov. 27, 2001. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    This invention relates in general to spring seats, and more particularly to spring seats in vehicle suspensions combined with tuned mass dampers.  
           [0003]    Spring seats are generally provided at the top and bottom ends of a coil spring, such as one provided in the suspension of a vehicle. This coil spring will have a dynamic stiffness that varies with the frequency of the input load. At certain frequencies, the dynamic stiffness will have peak values substantially above the nominal level of stiffness for the spring, called flexible modes of the coil spring. The spring stiffness for these flexible modes may have a spring rate (Newton/millimeter) that is several orders of magnitude greater that the nominal static spring stiffness. In other words, when the spring has a flexible mode in a certain direction, it will be very stiff in that direction at that certain frequency. Since the spring is very stiff at a flexible mode in that direction, it will provide significantly reduced isolation characteristics. For a coil spring in a vehicle suspension, for example, this reduced isolation means that road vibration excitation will be transferred through to the strut, and hence body/frame, almost as if passing through a solid body with high stiffness. Since one of the purposes of the coil spring in a suspension is to isolate the vehicle body from road vibration excitation, the dynamic stiffness at these flexible modes is undesirable. For example, at these flexible mode frequencies, unwanted noise and vibration can pass through the vehicle body to the passenger compartment.  
           [0004]    The spring seats to which the coil spring mounts are made of an elastomeric material, such as rubber or microcellular urethane (MCU), creating a spring seat isolator, which will improve the isolation characteristics of the spring/seat assembly somewhat. However, these spring seat isolators essentially improve the isolation somewhat over the entire frequency range, without targeting one or more specific flexible modes of the spring that are of concern. Moreover, they are limited in the ability to even attempt to tune the spring seat because the material cannot be made too soft as that could adversely affect the vehicle ride and handling. Additionally, to have an optimum of effectiveness at reducing the dynamic spring stiffness amplitudes at the flexible modes, any type of damper must be tuned within a relatively tight tolerance with the correct amount of damping power.  
           [0005]    Thus, it is desirable to provide spring seat isolators in a coil spring assembly that will significantly reduce at least one amplitude of the flexible mode for the spring mounted in the seats, while still allowing for adequate material properties needed to assure appropriate ride and handling characteristics for a vehicle.  
         SUMMARY OF INVENTION  
         [0006]    In its embodiments, the present invention contemplates a spring seat isolator/damper adapted for use with a coil spring having a plurality of flexible modes The spring seat isolator/damper includes an elastomeric member having a spring seat isolator portion and a mass damper portion, with the spring seat isolator portion adapted to mount to and receive loads from a vehicle suspension. The spring seat isolator/damper also has a damper mass operatively engaging the mass damper portion of the elastomeric member such that the damper mass and the damper portion of the elastomeric member have a natural frequency that is substantially equal to at least one of the plurality of flexible modes of the coil spring.  
           [0007]    The present invention further contemplates a spring/seat assembly. The spring/seat assembly includes a coil spring having a first end and a second end, and having a plurality of flexible modes. A first spring seat isolator is mounted to the first end of the spring, and includes a first elastomeric member having a first spring seat isolator portion and a first mass damper portion, with the first spring seat isolator portion adapted to mount to and receive loads from a vehicle suspension; and a first damper mass operatively engaging the first mass damper portion of the first elastomeric member such that the first damper mass and the first damper portion of the first elastomeric member have a natural frequency that is substantially equal to at least one of the plurality of flexible modes of the coil spring. The spring/seat assembly also includes a second spring seat isolator mounted to the second end of the spring, and including a second elastomeric member having a second spring seat isolator portion adapted to mount to and receive loads from the vehicle suspension.  
           [0008]    An embodiment of the present invention also contemplates a method for reducing an amplitude of a dynamic stiffness for at least one flexible mode of a coil spring having a first end and a second end, the method comprising the steps of: providing a first spring seat isolator mounted to the first end of the spring and having a first elastomeric portion and a first damping mass portion; and tuning the first elastomeric portion and the first damping mass portion to have a natural frequency substantially equal to at least one of the flexible modes of the coil spring.  
           [0009]    An advantage of the present invention is that the amplitude of transmitted vibration through a spring/seat assembly can be significantly reduced at one or more flexible modes of the spring.  
           [0010]    Another advantage of the present invention is that the reduced amplitude of transmitted vibration will reduce the road noise and vibration transmitted into a passenger compartment of a vehicle.  
           [0011]    A further advantage of the present invention is that the amplitude of vibration transmitted through the spring/seat assembly can be accomplished while still allowing for an appropriate stiffness of the elastomeric material for the spring seat in order to assure that that the vehicle ride and handling are as desired. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0012]    [0012]FIG. 1 is a perspective view of a combined isolator/damper assembly in accordance with an embodiment of the present invention;  
         [0013]    [0013]FIG. 2 is a perspective, partial cutaway view, similar to FIG. 1, on an enlarged scale, of the combined isolator/damper assembly;  
         [0014]    [0014]FIG. 3 is a plan view, on an enlarged scale, of the combined isolator/damper assembly of FIG. 1;  
         [0015]    [0015]FIG. 4 is a section cut, on an enlarged scale, taken along line  4 - 4  in FIG. 3;  
         [0016]    [0016]FIG. 5 is a perspective view of a damper mass of the isolator/damper assembly of FIG. 1;  
         [0017]    [0017]FIG. 6 is a perspective view of an insert of the isolator/damper assembly of FIG. 1;  
         [0018]    [0018]FIG. 7 is a schematic, elevation view of a spring/seat assembly in accordance with a second embodiment of the present invention;  
         [0019]    [0019]FIG. 8 is a schematic, elevation view similar to FIG. 7, but illustrating a third embodiment of the present invention;  
         [0020]    [0020]FIG. 9 is a schematic, elevation view similar to FIG. 7, but illustrating a fourth embodiment of the present invention;  
         [0021]    [0021]FIG. 10 is a sectional view of a isolator/damper assembly in accordance with a fifth embodiment of the present invention;  
         [0022]    [0022]FIG. 11 is a sectional view of an isolator/damper assembly similar to FIG. 10, but illustrating a sixth embodiment of the present invention; and  
         [0023]    [0023]FIG. 12 is a sectional view of an isolator/damper assembly similar to FIG. 10, but illustrating a seventh embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0024]    FIGS.  1 - 6  illustrate a combined isolator/damper assembly  10 , which includes a spring seat isolator portion  12  and a linear mass damper portion  14 . The assembly  10  includes an insert  16 , preferably stamped metal, which is overmolded with an elastomeric member  18 . The elastomeric member  18  is preferably formed of either a rubber or a MCU. After overmolding, a damper mass  20  is mounted on the elastomeric member  18  and three ears  22  are formed over the elastomeric member  18  to hold the damper mass  20  in place.  
         [0025]    The insert  16  includes a series of holes  24  in a circular portion  26 . Extending from the circular portion  26  are three arms  28 , each aligning with one of the ears  22  of the damper mass  20 . The holes  24  help to better secure the elastomeric member  18  to the insert  16 , while the circular portion helps the elastomeric member  18  retain its shape under loading and to redistribute loads. The insert  16  can be relatively small—just sufficient to transmit forces introduced into it. The insert  16  and a seat portion  30  of the elastomeric member  18  surrounding the insert essentially form the spring seat isolator portion  12  of the isolator/damper assembly  10 , and function similarly to a conventional spring seat isolator—that is, to transfer loads to and from a spring.  
         [0026]    The arms  28 , the damper mass  20 , and a spring/damper portion  32  of the elastomeric member  18  located between the arms  28  and damper mass  20 , essentially form the linear mass damper portion  14  of the isolator/damper assembly  10 . The arms  28  transfer the vibrational load from the spring seat isolator portion  12  to the spring/damper portion  32 , with the spring/damper portion  32  being a tuned shearing area. The spring/damper portion  32  act as a spring and as a damper in a spring-mass-damper arrangement, while the damper mass  20  acts as the mass portion of a spring-mass-damper arrangement. Consequently, the durometer, shear modulus, shape, thickness, and particular elastomeric material must be chosen to act in concert with the chosen amount of mass for the damper mass  20  and the mass of the insert  16  to reach a resonant frequency at a desired flexible mode of the spring to which the isolator/damper assembly  10  is mounted. That is, the resonant frequency of the linear mass damper portion  14  is tuned to have a resonant frequency that coincides with the flexible mode of the spring for which a reduction in the dynamic stiffness is desired—this will cause the damper to absorb a significant amount of energy out of the system (by converting it to heat) at that frequency, significantly reducing the dynamic stiffness of the overall assembly at that particular flexible mode.  
         [0027]    In order to tune the linear mass damper portion  14  to the desired frequency, then, the flexible modes (i.e. the peaks of the dynamic stiffness curve) of the particular spring are needed. While the nominal static stiffness of a coil spring is relatively straight forward, the dynamic stiffness of the particular coil spring can depend upon the particular loads applied to the spring. In the case of a coil spring employed in the suspension of a vehicle, then, it is preferred to determine the flexible modes by compressing the spring to simulate the loading it will receive for the typical weight of the vehicle (and passengers) on which it will be mounted. Then, the spring is excited over various frequencies with, for example, a sinusoidal excitation, while the dynamic stiffness of the spring is measured. The stiffness peaks are the flexible modes. Once the flexible modes are determined, the particular flexible mode for which damping is desired is chosen, and then the linear mass damper portion  14  can be tuned to this particular frequency.  
         [0028]    [0028]FIG. 7 illustrates a second embodiment of the present invention. For this embodiment, similar elements are similarly designated relative to the first embodiment, but with 100-series numbers. An isolator/damper assembly  110  acts as a lower seat isolator for mounting with an axle side of a vehicle suspension. A generally conventional spring seat isolator  140  acts as an upper seat isolator for mounting with a body side of a vehicle suspension. This spring seat isolator is preferably formed of rubber or MCU, and transfers the spring loading in a conventional fashion known to those skilled in the art. A coil spring  142  is mounted between and supported by the isolator/damper assembly  110  and the spring seat isolator  140  to form a spring/seat assembly  144 . The coil spring  142  is generally conventional and preferably formed of metal, as is known to those skilled in the art. The isolator/damper assembly  110  is similar to that disclosed in the first embodiment. It includes a seat spring isolator portion  112  and a linear mass damper portion  114 . The linear mass damper portion  114  includes a damper mass  120 , coupled to a spring/damper portion  132 , with the spring/damper portion  132  secured to a bracket  116 .  
         [0029]    As in the first embodiment, the mass damper portion  114  is tuned to a resonant frequency that matches a flexible mode in the spring  142  for the particular vehicle with which it is being used. The main difference being that the damper mass  120  and spring/damper portion  132  are generally around an inner radius within the coils of the spring  142 , rather than generally around an outer radius outside of the coils of the spring  142 .  
         [0030]    [0030]FIG. 8 illustrates a third embodiment of the present invention. For this embodiment, similar elements are similarly designated relative to the second embodiment, but with 200-series numbers. An isolator/damper assembly  210  acts as an upper seat isolator for mounting with a body side of a vehicle suspension. A generally conventional spring seat isolator  240  acts as a lower seat isolator for mounting with a body side of a vehicle suspension. The coil spring  142  is mounted between and supported by the isolator/damper assembly  210  and the spring seat isolator  240  to form a spring/seat assembly  244 . Other than locating the isolator/damper assembly  210  on top of the coil spring  142 , this spring/seat assembly  244  is the same as and operates in the same way as the spring/seat assembly of the second embodiment.  
         [0031]    [0031]FIG. 9 illustrates a fourth embodiment of the present invention. For this embodiment, similar elements are similarly designated relative to the second embodiment, but with 300-series numbers. The spring  142  is again mounted on top of the isolator/damper assembly  110  (forming the lower seat isolator), but the assembly forming the upper seat isolator assembly is also an isolator/damper assembly  348 . The second isolator/damper assembly  348  is configured essentially the same as the isolator/damper assembly  210  of FIG. 8, with a spring seat isolator portion  312  and a linear mass damper portion  314 . This spring/seat assembly  344  now includes two isolator/dampers  110 ,  348 . For this embodiment, then, the resonant frequencies of the damper portions  114 ,  314  can be tuned to the same frequency in order to act in concert to reduce the spring stiffness at a particular flexible mode. Or, if so desired, each damper portion  114 ,  314  can be tuned to a different resonant frequency associated with a different flexible mode in order to decrease the dynamic stiffness of the spring for two different flexible modes. The same type of arrangement can also be applied to the other embodiments disclosed herein in that there can be isolator/damper assemblies mounted at each end of the coil spring—or only at one end, with a conventional spring seat isolator at the other end.  
         [0032]    [0032]FIG. 10 illustrates a fifth embodiment of the present invention. For this embodiment, similar elements are similarly designated relative to the first embodiment, but with 400-series numbers. An isolator/damper assembly  410  is illustrated where the damper mass  420  is molded into the elastomeric member  418 . Again, there is a spring seat isolator portion, indicated generally at  412 , which serves the conventional purpose of a spring seat, and a linear mass damper portion, indicated generally at  414 , which is tuned to a desired resonant frequency that corresponds to a spring flexible mode. Since this is all molded as one piece, the ability to vary the durometer and shear modulus of the elastomeric material is limited. Consequently, the tuning of the mass damper portion  414  can be accomplished by varying the geometry of the elastomeric material around the damper mass  420 , as well as the size of the damper mass  420  (i.e., changing the amount of mass and its contact area with the elastomeric material). This embodiment has the advantage over the previous embodiments in that there are fewer parts and a simpler construction, but the amount of amplitude reduction for the dynamic stiffness at the flexible mode being addressed is probably less with this type of configuration.  
         [0033]    [0033]FIG. 11 illustrates a sixth embodiment of the present invention. For this embodiment, similar elements are similarly designated-relative to the fifth embodiment, but with 500-series numbers The isolator/damper assembly  510  is essentially the same as in the fifth embodiment except that the damper mass  520  has a smaller radius, thus reducing the contact area  550  with the elastomeric member  518 . The reduced contact area lowers the resonant frequency for the mass damper portion  514 .  
         [0034]    [0034]FIG. 12 illustrates a seventh embodiment of the present invention. For this embodiment, similar elements are similarly designated relative to the fifth embodiment, but with 600-series numbers. The isolator/damper assembly  610  again has a damper mass  620  integrally molded into the elastomeric member  618 , but it is located adjacent an exterior surface rather than an interior surface. This configuration may be required due to packaging reasons. Otherwise, the assembly  610  operates the same as in the fifth embodiment.  
         [0035]    While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.