Abstract:
A vibration damper for mounting on a structure for damping out resonance frequencies on the structure has a bushing assembly consisting of inner and outer coaxial spaced metal sleeves joined together by an intervening elastomeric member. A metal mass is secured to the outer metal sleeve of the bushing assembly and oscillates about the fixed inner sleeve upon flexing of the elastomeric member. A fastener extends through the bore of the inner sleeve for rotatably suspending the damper on the structure. An extension arm is secured to the inner sleeve and extends radially outwardly and passes between a pair of nubs formed on an outer annulus of the elastomeric member to prevent excessive rotation and erratic motion of the mass due to non-translational forces on the structure.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates to vibration dampers and in particular to a damper for use in a vehicle and specifically to a damper for mounting in the vehicle seat to isolate resident frequencies imparted on the passenger&#39;s seats. Even more particularly the invention relates to such a vibration damper having an anti-rotational device to prevent excessive rotation of the damping mass due to non-translational vehicle inputs. 
     2. Background Information 
     Damping devices and in particular dynamic dampers, are currently used in many applications and in particular in the automobile industry for damping out various vibrations imparted on portions of the vehicle caused by the engine, tires and road conditions. One problem that exists is that vibrations which result from resonance frequencies are imparted on the passenger seats of minivans which eventually could cause discomfort to the passenger. 
     Various types of dampers have been used to dampen out unwanted vibrations on various structures. These are generally of the shear type dampers in which a mass is attached in some fashion to an elastomeric member wherein the elastomeric material is bonded directly to the mass with the elastomer acting in shear. These dampers are then attached in some fashion to the structure or vehicle for damping out the unwanted frequencies. 
     Other types of dampers use a bushing arrangement wherein an elastomer is bonded between inner and outer cylindrical members such as shown in U.S. Pat. No. 5,769,380 and 4,889,328. Various other dampers using an elastomer and a damping mass are shown in U.S. Pat. Nos. 4,580,666; 4,800,306; 3,419,111; 5,876,023; 5,876,024 and 5,799,930. 
     However, a problem that occurs in such dampers is that the dampers are prone to exhibit very erratic motion both translational and rotational caused by excessive rotation due to non-translational vehicle inputs. 
     None of these prior art dampers, especially those that have a suspended mass, have any type of anti-rotational device to limit the angular swing of the mass which reduces the effectiveness desired to be achieved thereby. Likewise, many of the prior art damping devices, especially those intended for use in a vehicle seat, are difficult to manufacture in an economical manner and in a size and weight acceptable for use in the automotive industry. 
     Therefore, the need exists for an improved vibration damper intended primarily for use in a vehicle seat, which is relatively easy and inexpensive to manufacture and which may include an anti-rotational device to avoid erratic motion of the damper. 
     SUMMARY OF THE INVENTION 
     Objectives of the invention include providing an improved vibration damper for suspending on a structure such as a vehicle seat, which has a bushing assembly formed by inner and outer coaxial metal sleeves with an intervening elastomeric member, with a mass being attached to the outer sleeve by a press fit engagement thereby eliminating the need to place the mass in a vulcanizing mold when the elastomeric member is vulcanized and secured to the inner and outer sleeves. 
     Still another objective of the invention is to provide such a vibration damper which includes an anti-rotational device to restrict rotational motion of the damper, preferably by use of a metal extension arm secured to the inner metal sleeve and extending between a pair of elastomeric nubs formed integrally with the elastomeric member of the bushing assembly. 
     A further objective of the invention is to provide such a vibration damper in which the size of the mass can be easily adjusted and changed for particular applications and then press fitted onto the inner sleeve of the bushing assembly thereby providing for a larger range of damping applications with less components. 
     Another objective of the invention is to provide such a vibration damper in which the elastomeric member can have various shapes to achieve different spring characteristics without affecting the primary size and shape of the inner and outer metal sleeves thereby providing increased versatility to the damper. 
     A further objective of the invention is to provide such a vibration damper in which the outer metal sleeve has an annular flange over which the elastomeric material extends so as to act as a bumper to prevent any excess motion of the damper in a direction which is perpendicular to the primary direction of motion. 
     A still further objective of the invention is to provide such a vibration damper whereby after molding the elastomeric member to the inner and outer metal sleeves the bushing assembly is press fitted into the selected mass size, which mass can be manufactured either as a casting or from machined bar stock with a center opening of the mass being machined to tight tolerances so that the bushing can be pressed in and held by a press fit engagement without requiring additional attachment fasteners. 
     Another objective of the invention is to provide such a vibration damper in which the damper is attached easily to the vehicle by use of a single bolt or other fastener which extends through the bore of the inner metal sleeve to suspend the damper from the structural member, such as the interior of a vehicle seat. 
     These objectives and advantages are obtained by the vibration damper of the present invention, the general nature of which includes inner and outer coaxial sleeves defining an annular space therebetween; an elastomeric member disposed in at least a portion of the annular space and secured to the inner and outer sleeves and interconnecting said sleeves; a mass secured to the outer sleeve for movement with said sleeve; attachment means for mounting the inner sleeve to the structure whereby said outer sleeve and mass is free to oscillate about said inner sleeve to dampen out vibration on the structure; and an anti-rotation device for limiting angular movement of the mass about the inner sleeve. 
     These objectives and advantages are further obtained by the method of the present invention, the general nature of which may be stated as including the steps of providing a mass having an opening formed therein; providing inner and outer coaxial sleeves; securing an elastomeric member to said inner and outer sleeves in an annular space formed between said sleeves to form a bushing assembly; and securing the bushing assembly to the mass within the opening in said mass. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the invention, illustrative of the best mode in which applicants have contemplated applying the principles, is set forth in the following description and is shown in the drawings and is particularly and distinctly pointed out and set forth in the appended claims. 
     FIG. 1 is a fragmentary diagrammatic view with portions broken away showing the vibration damper of the present invention mounted on a structure, such as the interior of a vehicle seat 
     FIG. 2 is an arranged front plan view of the vibration damper looking in the direction of a  2 — 2 , FIG. 1; 
     FIG. 3 is an enlarged fragmentary side elevational view of FIG. 1 showing the vibration damper mounted on the structure; 
     FIG. 4 is a back plan view of the vibration damper of FIG. 2; 
     FIG. 5 is a sectional view taken on line  5 — 5 , FIG. 2; 
     FIG. 6 is an enlarged plan view of the bushing assembly removed from the damper; and 
     FIG. 7 is a sectional view taken on line  7 — 7 , FIG.  6 . 
    
    
     Similar numerals refer to similar parts throughout the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The vibration damper of the present invention is indicated generally at  1 , and is shown in FIG. 1 mounted on a bracket  2  located within the interior of a vehicle seat  3 , which in the preferred embodiment will be a passenger seat of a minivan. Although the damper is intended primarily for use within a vehicle seat, it need not be limited to such an application but could be used for other types of dynamic damping applications. 
     Referring to FIGS. 2-7, damper  1  includes a mass  5  which preferably is formed of metal such as a metal casting or cut from bar stock, or formed of various other types of metals or heavy materials. Mass  5  preferably has a rectangular shape as shown in FIG. 2 although other configurations could be used without departing from the concept of the invention. A central opening  6  (FIG. 5) is formed through mass  5  and preferably is accurately machined, the purpose of which is discussed further below. A bushing assembly indicated generally at  10 , is shown particularly in FIGS. 6 and 7 and includes an inner sleeve  11  and an outer sleeve  12  which are coaxially aligned and form an intervening annular space  14 . Sleeves  11  and  12  are connected by an elastomeric member indicated generally at  13 , located in annular space  14 . In the preferred embodiment, inner sleeve  11  preferably is formed of metal tubing or a wrapped sleeve configuration, with outer sleeve  12  being formed of metal such as a steel stamping. The diameter of outer sleeve  12  is determined based upon the spring rate necessary to obtain the correct natural frequency. Elastomeric member  13  preferably is non-symmetrical and includes an inner annulus  15  which extends about inner sleeve  11 , and an outer annulus  16  connected to inner annulus  15  by a pair of radial extending diametrically aligned legs  17  which form voids  18  therebetween. 
     In accordance with one of the features of the method of the invention for forming vibration damper  1 , the uncured elastomeric material which forms elastomeric member  13  will be injected between inner and outer sleeves  11  and  12  in an appropriate mold to form bushing assembly  10  with elastomeric member  13  being bonded to the spaced sleeves during the vulcanizing process. Before placing the metal sleeves in the vulcanizing mold, the metal preferably is first phosphated and cemented to provide for a satisfactory bond between the elastomeric member and the metal sleeves. As shown in FIG. 2, the elastomeric member  13  is non-symmetrical with the radial legs  17  extending in the vertical direction with respect to the mounting of damper  1  as shown in FIG. 1, whereas in the lateral direction the elastomeric material is highly voided as shown by voids  18 . This sectional configuration results in a higher spring rate in the vertical direction and a lower spring rate in the lateral direction which has been found to provide the desired damping characteristics when used in vehicle seat  3 . 
     Outer metal sleeve  12  is formed with an outwardly extending annular flange  20  over which the elastomeric material of outer annulus  16  extends as shown in FIGS. 6 and 7. This covering of elastomeric material acts as a bumper to prevent any excess motion of the damper in a direction which is perpendicular to the rotational direction of motion indicated by arrow A in FIG.  2 . Flange  20  also functions as a stop when bushing assembly  10  is mounted within central opening  6  of mass  5 , preferably by a press fit engagement therebetween. 
     In accordance with another feature of the invention, an anti-rotational device indicated generally at  25 , is mounted on bushing assembly  10 . Device  25  includes a metal extension arm  26  which extends radially outwardly from inner sleeve  11 . Arm  26  terminates in a hub  28  which preferably is press fitted into inner bore  30  of sleeve  11  so as to be securely fixed therewith. 
     Damper  1  is easily mounted on bracket  2  or other type of support structure, by use of a bolt  32  which extends through bore  30  of inner sleeve  11  and presses tightly against hub  28  securing damper  1  to bracket  2 . Other types of mounting mechanisms than bolt  32  can be used without effecting the invention. When mounted on bracket  2 , damper  1  is suspended entirely by bolt  32  enabling mass  5  to oscillate freely about inner sleeve  11  since inner sleeve  11  is firmly secured to the bracket by bolt  32 , as shown by arrow A, FIG. 2, upon the flexing of elastomeric legs  17 . 
     Fixed arm  26  extends between a pair of spaced nubs  35  to limit the rotational or angular movement of mass  5 . Nubs  35  preferably are formed of an elastomeric material as an integral part of outer annulus  16 . Nubs  35  extend upwardly outwardly from annulus  16  and engage the outer extended fixed end of arm  26  and function as stops to limit the rotational angular movement of annulus  16  and correspondingly mass  5 . Heretofore, known bushing type dampers have no anti-rotational devices and are proned to exhibit very erratic motion both translational and rotational, and permit excessive rotation due to non-translational vehicle inputs. Nubs  35  provide limit stops in all directions and will provide the restrictions necessary to minimize noise during off road durability testing and actual on road riding experience. Nubs  35  can be designed depending upon their circumferential spacing about outer annulus  16 , to allow a specific amount of travel of the mass at the spring rate necessary to obtain the proper natural frequency while avoiding the erratic behavior as occurs with prior art dampers. Arm  26  is fixed at the desired location between a pair of adjacent nubs  35  and is secured in its desired position by the clamping engagement of bolt  32  against the outer surface of hub  28  as shown in FIG.  5 . 
     The simplified method of the present invention of manufacturing and assembling damper  1  includes mass  5  being formed by various inexpensive procedures since tolerances are not critical except for the formation of opening  6  which may require precision machining in order to provide for the desired press fit engagement with the outer surface of outer sleeve  12 . Likewise, bushing assembly  10  is formed at the time elastomeric member  13  is formed and vulcanized enabling bushing assembly  10  to be formed at a remote location and then assembled easily into mass  5  at a separate location, after which only the insertion of bolt  32  into bore  30  is required to mount damper  1  on a supporting structure. 
     Accordingly, the improved vibration damper and method of producing the same provides a structure and method which requires very simply tooling yet provides a robust low scrap product which is easily manufactured and assembled and easily installed on various types of supporting brackets, and which offers a limit stop in all directions that will provide the restrictions necessary to minimize noise and vibration. It also provides a damper in which the elastomeric member can have various shapes to achieve various damping characteristics without affecting the primary size and shape of the inner and outer metal sleeves and attached damping mass. 
     Accordingly, the improved vibration damper is simplified, provides an effective, safe, inexpensive, and efficient device and associated method which achieves all the enumerated objectives, provides for eliminating difficulties encountered with prior devices and methods, and solves problems and obtains new results in the art. 
     In the foregoing description, certain terms have been used for brevity, clearness and understanding; but no unnecessary limitations are to be implied therefrom beyond the requirement of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed. 
     Moreover, the description and illustration of the invention is by way of example, and the scope of the invention is not limited to the exact details shown or described. 
     Having now described the features, discoveries and principles of the invention, the manner in which the improved vibration damper is construed and used, the characteristics of the construction, and the advantageous, new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts, combinations and method steps, are set forth in the appended claims.