Abstract:
A shear mount assembly and a compression mount assembly are combined to control ride harshness of a shock absorber. The shock absorber includes a body and a shock rod having a hydraulically sealed portion within the body and a distally extending free portion. A mount assembly is connected at the free portion having both a compression mount and a shear mount therein. The shear mount absorbs low-input vertical loads transferred from the shock rod, and the compression mount limits vertical displacement of the shear mount and absorbs a medium-input vertical load. The shear mount and the compression mount are tuned by selecting the durometer, dimensions, and physical configuration of each mount.

Description:
FIELD OF THE INVENTION 
     The present invention relates in general to shock absorbers and more specifically to motor vehicle shock absorbers. 
     BACKGROUND OF THE INVENTION 
     Shock absorber shear mounts are intended to isolate the shock rod loads from the vehicle. The challenge for a shear mount design is to provide flexibility to tune a soft rate for ride feel without compromising durability of the shear mount. Common shear mount designs rarely achieve the balance of smooth ride feel and durability of the shear mount. 
     Shear mounts are normally used to absorb low amplitude loads transferred between the shock rod and the vehicle. Common shear mounts are bonded to surfaces adjacent to the shock rod and are capable of absorbing low amplitude shock motion. In order to provide for a soft ride feel, it is desirable to reduce the durometer or hardness of the resilient elements used to form the shear mount. The disadvantage of reducing the durometer of this material is that the durability is reduced. Common shear mounts having durometer values providing for increased durability do not provide a soft ride feel. Increasing the size of the shear mount to provide a greater extended operating range has the disadvantage of increased weight, cost, and space envelope for the shock absorber. 
     It is therefore desirable to provide a shock absorber design which is capable of providing both a soft ride feel and durability for the shock absorber. 
     SUMMARY OF THE INVENTION 
     A shear mount assembly and a compression mount assembly are combined to control ride harshness of a shock absorber. The shock absorber includes a body and a shock rod having a hydraulically sealed portion within the body and a distally extending free portion. A mount assembly is connected at the free portion having both a compression mount and a shear mount therein. The shear mount absorbs low-input vertical loads transferred from the shock rod, and the compression mount both limits vertical displacement of the shear mount to prevent damaging the shear mount and absorbs a medium-input vertical load. 
     The shear mount and the compression mount are tuned by changing mount durometer, mount thickness, and/or mount diameter. The shear mount can be made softer than the compression mount to provide a softer ride feel. The shear mount initially deflects from a shock rod displacement prior to initial displacement of the compression mount, therefore low amplitude loads are absorbed by the shear mount before they can be transferred through the compression mount. The compression mount will not engage until after the shear mount has partially progressed through its rate curve. The compression mount thereafter gradually builds up in compression force to isolate medium-amplitude shock rod inputs. A travel limiter plate joined to the compression mount prevents both over-compression of the compression mount and tearing of the shear mount material. 
     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 exemplary 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 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is perspective view of a shock absorber mount having the combined shear and compression mounts according to the invention. 
         FIG. 2  is an enlarged perspective view of the shock absorber mount shown in FIG.  1 . 
         FIG. 3  is a plan view of an upper stamping containing a shear mount of the invention of  FIGS. 1-2 . 
         FIG. 4  is a side view of the upper stamping of FIG.  3 . 
         FIG. 5  is a cross-sectional view taken through line  5 — 5  of FIG.  3 . 
         FIG. 6  is plan view of a travel limiter plate of the shock absorber mount of  FIGS. 1-5 . 
         FIG. 7  is a cross-sectional view of the travel limiter plate shown in  FIG. 6  taken through line  7 — 7  of FIG.  6 . 
         FIG. 8  is a plan view of an alternate embodiment of a resilient element of the present invention bonded to a travel limiter plate. 
         FIG. 9  is a side view of the resilient element of FIG.  8 . 
         FIG. 10  is a cross-sectional view taken through line  10  of FIG.  8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring to  FIG. 1 , a shock absorber  10  according to a preferred embodiment of the present invention includes a shock absorber body  12  having a shock rod  14  extending from a first end of the shock absorber body  12 . The shock rod  14  has a partial length disposed and hydraulically dampened within the shock absorber body  12 , and a free length distally extending from the shock absorber body  12 . At a second end of the shock absorber body  12 , an attachment  16  is provided. The attachment  16  is known in the art and commonly includes a single piece casting providing a clevis bracket and fastener apertures to clamp the shock absorber body  12  to a vehicle control arm bushing (not shown). A mount assembly  20  is disposed at a distal end of the shock rod  14  free length. A plurality of fasteners  18  extend from the mount assembly  20 . The fasteners  18  are used to mount the shock absorber  10  to a vehicle  35  (shown cut-away). 
     As known in the art, a jounce bumper  22  is provided adjacent to the mount assembly  20 . High amplitude loads from the shock body  12  are transferred to the jounce bumper  22  via a striker  24 . A spring  26  is retained adjacent to the mount assembly  20  by a spring isolator  28 . The spring  26  provides force to return the shock absorber  10  to a null position following a load input. A preload fastener  30  connectably joins the mount assembly  20  to the shock absorber  10  via a threaded surface  31  of the shock rod  14 . 
     According to a preferred embodiment of the present invention, a shear mount assembly  32  and a compression mount assembly  34  are provided with the mount assembly  20 . The compression mount assembly  34  absorbs medium amplitude (input) loads from the shock rod  14 , and the shear mount assembly  32  absorbs low amplitude (input) loads from the shock rod  14 . The jounce bumper  22  is provided independent from the mount assembly  20  to absorb high amplitude (input) loads from the shock body  12 . 
     Referring to  FIG. 2 , the mount assembly  20  is shown in greater detail. The mount assembly  20  further includes an upper stamping  36  and a lower stamping  38 . The upper stamping  36  and the lower stamping  38  house both the shear mount assembly  32  and the compression mount assembly  34 . The shear mount assembly  32  is formed by bonding a shear mount  40  on an inner diameter to an cuter diameter of an inner sleeve  42 . The inner sleeve  42  has an aperture  44  longitudinally disposed there-through to provide radial clearance about the shock rod  14 . An outer diameter of the shear mount  40  is bonded to a first cylinder  46  formed in the upper stamping  36 . 
     The compression mount assembly  34  includes a travel limiter plate  50  slidably disposed within a slot formed in and/or bonded to a resilient element  52 . The travel limiter plate  50  and the resilient element  52  together form the compression mount assembly  34 . A ferrule  56  formed at one end of the travel limiter plate  50  is disposed within the aperture  44  and immediately adjacent to the shock rod  14 . The ferrule  56  slidably adjoins the shock rod  14 . 
     A shoulder  58  is machined, welded, or otherwise provided on the shock rod  14 . The shoulder  58  contacts an undersurface of the travel limiter plate  50  adjacent to the ferrule  56 . The shock rod  14  is driven in the shock rod deflection directions “A” such that a vertical upward motion (if oriented as shown in  FIG. 2 ) forces the shoulder  58  into contact with the travel limiter plate  50  and the inner sleeve  42 . Low amplitude vertical inputs from the shock rod  14  are first absorbed by deflection of the shear mount  40 . In an exemplary embodiment, the shear mount  40  will upwardly deflect approximately 2 mm before the resilient element  52  begins to compress. An upper surface  59  of the resilient element  52  contacts an underside of an inner horizontal surface  60  of the upper stamping  36  after the approximate 2 mm deflection of the shear mount  40 . The resilient element  52  can deflect a maximum amount of approximately 8-10 mm. The total deflection of the shear mount  40  is therefore approximately 10 mm to 12 !mm from a non-deflected state to a fully deflected state. During this upward motion along the shock rod deflection axis “A”, the ferrule  56  of the travel limiter plate  50  translates upon the shock rod diameter “B”. The clearance between the travel limiter plate  50  and the inner horizontal surface  60  provides an allowable displacement “C” of approximately 10-12 mm. This displacement protects the shear mount  40  from excessive deflection which could damage the shear mount  40 . This displacement also includes a maximum compression of the resilient element  52 . 
     A similar clearance of approximately 10-12 mm is provided between a lower surface  61  of the resilient element  52  and a lower stamping plate  62 . This clearance prevents the ferrule  56  from sliding free from: the aperture  44  when the shoulder  58  travels in a downward direction along the shock rod deflection axis “A”. 
     Referring to  FIGS. 3-5 , an alternate embodiment of a shear mount  63  connected to the upper stamping  36  is shown. The shear mount  63  can be bonded to the first cylinder  46  similar to the shear mount  40  or can be press fit into the first cylinder  46 . In the embodiment shown, the shear mount  63  is also provided with an upper extension ring  70  and a lower extension ring  72  to hold the shear mount  63  at the junction with the first cylinder  46 . The aperture  44  is similarly provided within the shear mount  63  to provide clearance about the shock rod diameter “B” of the shock rod  14  (shown in FIG.  2 ). 
     As best seen in  FIG. 5 , the upper stamping  36  includes the first cylinder  46 , the inner horizontal surface  60 , a second cylinder  64 , and an outer horizontal plate  66 . As best seen in  FIG. 3 , a plurality of apertures  68  is formed in the outer horizontal plate  66 . The apertures  68  locate the fasteners  18  (shown in FIG.  1 ). A peripheral skirt  67  forms an outer perimeter for the upper stamping  36 . The spring isolator  28  (shown in  FIG. 1 ) is disposed between the second cylinder  64  and the skirt  67 . The upper stamping  36  has an upper stamping diameter “D” as shown in FIG.  3 . 
     Referring to  FIGS. 6 and 7 , the travel limiter plate  50  is further detailed. The travel limiter plate  50  has a travel limiter plate diameter “E”. The ferrule  56  has a ferrule outer diameter “F” which slidably mates within the aperture  44  of the inner sleeve  42  (shown in FIG.  2 ). A raised face  74  is provided to align the resilient element  52  between the travel limiter plate  50  and the inner horizontal surface  60  to establish the allowable deflection “C” (shown in FIG.  2 ). The resilient element  52  (shown in  FIG. 2 ) is bonded to a bonding surface  76  radially disposed on the travel limiter plate  50 . The travel limiter plate diameter “E” is selected such that an outer diameter of the resilient element  52  is controlled to extend beyond the travel limiter plate diameter “E” when the resilient element  52  is installed on the travel limiter plate  50 .  FIG. 6  further shows that a ferrule inner diameter “G” is provided. The ferrule inner diameter “G” is sized to provide a sliding fit between the travel limiter plate  50  and the shock rod  14  about the shock rod diameter “B”. 
     Referring to  FIGS. 8-10 , an alternate embodiment for a resilient element  78  is shown. The resilient element  78  differs from the resilient element  52  (shown in  FIG. 2 ) by the alternating use of ridges  80  and grooves  82 . The ridges  80  and the grooves  82  allow radial expansion of the resilient element  78  when it is compressed. The resilient element  78  is bonded to the travel limiter plate  50  and provides the ferrule inner diameter “G” as previously discussed. A resilient element outer diameter “H”, a resilient element thickness J, and a resilient element inner diameter “K” are also shown. These diameters and thicknesses are similar between the resilient element  78  and the resilient element  52 . 
     Material for the shear mount  40 , the shear mount  63 , the resilient element  52 , and the resilient element  78  can be rubber or similar elastomeric compounds having a shore-D durometer ranging from approximately 45 to approximately 75. In a preferred embodiment, the materials of the shear mount have a lower durometer than the material of the compression mount. By providing a softer material for the shear mount, the shock absorber  10  can be tuned to provide a softer ride for the low amplitude vertical loads imparted by the shock rod  14 . A softer material used for the shear mount isolates small inputs to make them transparent to a vehicle operator. The compression mount assembly  34  does not engage until after the shear mount has partially progressed through its rate curve. The compression mount assembly then works in compression and gradually builds up its rate to isolate larger vertical inputs (i.e., medium amplitude inputs). The jounce bumper  22  (shown in  FIG. 1 ) absorbs high amplitude vertical inputs after both the shear mount and the resilient element reach their maximum deflection. 
     The material selected for the shear mounts and the compression mounts of the present invention can also be selected to have the same durometer. It is known that increasing the durometer for the mounts increases durability, at the expense of ride feel. A softer material used for the mounts decreases durability but provides an overall softer ride feel. The choice of shear mount and compression mount material durometer is therefore a design issue depending upon several factors including the vehicle weight, the envelope available for the shock absorber  10 , and the magnitude of the loads the shock absorber  10  must absorb. The shear mount can be tuned by changing at least one of a diameter, a length, and a durometer. The compression mount can be tuned by changing at least one of a thickness, a surface geometry, and a durometer. In a preferred mode of assembly, the compression mount assembly is press fit into the lower stamping  38 . This provides additional damping and resistance to deflection for the travel limiter plate  50 . In another embodiment of the present invention, the diameter of the resilient element (i.e., the resilient element outer diameter “H” shown in  FIG. 10 ) can be reduced to provide clearance to the lower stamping  38 . 
     A shock absorber of the present invention provides the following advantages. By providing separate shear mount and compression mount assemblies, low amplitude loads such as small bumps and stones in a vehicle&#39;s path can be absorbed by the shear mount assembly prior to deflection of the compression mount. By using a softer material for the shear mount, the low amplitude loads can be absorbed with little or no transfer of energy to a driver of the vehicle. By providing a separate compression mount from the shear mount assembly, the compression mount can absorb a medium amplitude input and also provide a positive stop to prevent tear out or shear of the shear mount assembly. By providing a separate shear mount and compression mount, either or both mounts can be tuned by adjusting size and/or durometer to change the ride feel of the shock absorber. 
     The material for the travel limiter plate is preferably of a high strength steel for resistance to permanent deflection and to absorb impact loads. Alternate materials such as corrosion resistant steels, aluminum, etc. can also be substituted if strength is similar to the high strength steels. Materials for the stampings, the spring, the shock rod, the fasteners, and the jounce bumper of the shock absorber of the present invention are known in the art. Only a portion of the spring  26  is shown for clarity, as its attachment to the shock absorber body  12  is known. Additional skirts or covers provided to protect the shock absorber  10  of the present invention from water, dirt or road debris are also known and are therefore not shown for clarity. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.