Abstract:
An elastomeric isolator has an elastomeric body which incorporates an inner structural member and an outer structural member. The elastomeric body includes a shear hub extending between radial flanges or end plates of the inner and outer structural members that undergoes shearing stresses during deflection of the elastomeric isolator. The elastomeric body is bonded to the radial flanges or end plates. The inner structural member includes a radial flange which is axially offset from an axial flange of the outer structural member. The outer structural member includes a radial flange which is axially offset from an axial flange of the inner structural member. With this configuration, excessive stresses on the elastomeric body are avoided during high load movements of the elastomeric isolator.

Description:
FIELD 
     The present disclosure relates to an isolator such as an automotive exhaust system isolator. More particularly, the present disclosure relates to an isolator which is configured to provide a very soft on-center rate, to have the ability to endure spike durability loads and to minimize or eliminate vulnerable stress concentrations. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Typically, automotive vehicles including cars and trucks have an internal combustion engine which is coupled to at least a transmission and a differential for providing power to the drive wheels of the vehicle. An engine exhaust system which typically includes an exhaust pipe, a catalytic converter and a muffler is attached to the engine to quiet the combustion process, to clean the exhaust gases and to route the products of combustion away from the engine to a desired position typically at the rear of the vehicle. The exhaust system is supported by exhaust mounts which are positioned between the exhaust system and the frame or some other supporting structure of the vehicle body. In order to prevent engine vibrations from being transmitted to the car body, the exhaust mounts incorporate flexible members or elastic suspension members to isolate the vehicle&#39;s exhaust system from the vehicle&#39;s body. In order to effectively isolate the vehicle&#39;s exhaust system from the vehicle&#39;s body, it is preferred that the isolator include a soft on-center rate of deflection. 
     The prior art exhaust mounts or isolators have included rubber isolators which are a solid rubber component or a puck that is at least three-quarters of an inch thick and which is provided with at least one pair of apertures extending therethrough. The apertures each receive an elongated metal stud. The metal stuff is provided with an enlarged tapered head that can be forced through the aperture in the isolator, but it cannot be readily removed from the isolator. The opposite end of the stud is welded to or otherwise secured to either a support point in the vehicle or to one of the components of the exhaust system. 
     Other designs for isolators include elastomeric moldings of a spoke design where spokes are loaded in tension and compression and a shear leg design that include a leg that is subjected to shearing in the primary loading direction. Most elastomers which are utilized for exhaust isolators exhibit poor tensile fatigue properties stemming from low tear strength properties. The preferred method to load the elastomeric material is in compression or shear. 
     The prior art puck design is the simplest design, and as discussed above, two pins are inserted at opposite ends of the elastomer and the loads inflict pure tension on the elastomer cords connecting both ends. While this is typically the lowest cost design, it is also the most abusive to the material. In order to offset the failure risk, flexible and/or rigid bands are typically designed inside or around the outside of the elastomeric puck. The advantage of this design is its ability to swivel about one hanger hole to accommodate large positional tolerances for the hanger. 
     The prior art spoke design isolators load the elastomeric material in compression and tension. The tensile loading makes the design vulnerable to fractures in overloaded conditions. The stress magnitude is directly proportional to the load divided by the minimum spoke cross-sectional area. An additional requirement of the spoke design is that the mating component or hanger pin be centered within the deflection zone while statically preloaded by the weight of the exhaust. If it is not, the voids designed into the isolator will be bottomed out or positioned in a groundout condition. This results in the soft on-center rate not being employed, thus defeating the purpose of the isolator. 
     The prior art shear leg design has a primary loading direction which is typically vertical and a secondary loading direction which is typically lateral. When the shear leg design is loaded in its primary loading direction, the loading method is the preferred shear style loading. In addition, this shear style loading is able to be designed desirably soft. However, the secondary loading direction inflicts tensile compressive stresses which are unfavorable for durability. In addition, the secondary loading direction has a rate that is two to three times stiffer than the primary rate which is also an unfavorable condition. 
     The continued development of elastomeric mounts has been directed to elastomeric mounts which include a soft on-center rate while avoiding the undesirable tension loading of the elastomeric bushing and which avoid the vulnerable stress concentrations. While this has been achieved in the prior art shear-hub designs, stress concentrations at the ends of the voids continues to be a problem. 
     SUMMARY 
     The present disclosure provides the art with an elastomeric bushing which uses radial loading which avoids the tension stress loading of the bushing. The radial loading causes shear stresses of the elastomeric bushing regardless of the direction of the loading. Tuning for rate and deflection in specific directions can be independent from other directions by altering voids in the elastomeric bushings. The elastomeric bushing incorporates structural members which avoid the vulnerable stress concentrations. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a perspective view of an elastomeric isolator assembled to a bracket in accordance with the present disclosure; 
         FIG. 2  is a cross-sectional view of the elastomeric isolator illustrated in  FIG. 1 ; 
         FIG. 3  is a perspective view partially in cross-section illustrating the end plates of the elastomeric isolator illustrated in  FIGS. 1 and 2 ; 
         FIG. 4  is a perspective view of an elastomeric isolator in accordance with another embodiment of the present disclosure; 
         FIG. 5  is an end view of the elastomeric isolator illustrated in  FIG. 4 ; 
         FIG. 6  is a cross-sectional view of the elastomeric isolator illustrated in  FIG. 4 ; and 
         FIG. 7  is a perspective view of an exhaust system which incorporates the unique exhaust isolators in accordance with the present disclosure. 
     
    
    
     DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     Referring now to the drawings, there is shown in  FIG. 7  an exhaust system which includes the exhaust system isolators in accordance with the present disclosure and which are designated generally by the reference numeral  10 . A typical vehicle comprises an internal combustion engine (not shown), a body (not shown), a suspension system (not shown) and exhaust system  10  which is attached to the internal combustion engine and which is supported typically beneath the vehicle. The internal combustion engine is designed to power one or more drive wheels of the vehicle and the exhaust system routes the products of combustion to a desired exhaust location around the outside of the vehicle. 
     Exhaust system  10  comprises an intermediate pipe  12 , a muffler  14 , a tailpipe  16  and a plurality of isolator assemblies of various designs. Intermediate pipe  12  is typically connected to the engine or to a catalytic converted (not shown) which is then attached to an exhaust pipe which extends between the engine and the catalytic converter. The catalytic converted may be attached to a single exhaust pipe which leads to a single exhaust manifold or the catalytic converter can be attached to a branched exhaust pipe which leads to a plurality of exhaust pipes which lead to a plurality of exhaust manifolds. Also, intermediate pipe  12  can be attached to a plurality of catalytic converters which connect together prior to reaching muffler  14  using intermediate pipe  12  or the vehicle can have a plurality of exhaust pipes, a plurality of catalytic converters, a plurality of intermediate pipes  12  and a plurality of mufflers  14  which connect together using a single or multiple tailpipes  16 . In addition, the exhaust system isolator of the present disclosure is applicable to any type of exhaust system including but not limited to dual exhaust systems which have two separate parallel exhaust systems extending from the internal combustion system. 
     Exhaust system  10  is utilized to route the exhaust gases from the engine to a desired location around the outside of the vehicle. While traveling through the exhaust system, the catalytic converter cleans the exhaust gases and muffler  14  quiets the noise created during the combustion process in the engine. The present disclosure is directed toward the exhaust system isolators which mount exhaust system  10  to the vehicle while at the same time, isolate the movement of exhaust system  10  with respect to the vehicle. 
     Referring now to  FIGS. 1-3 , an exhaust system isolator assembly  30  comprises a bracket  32  and an exhaust system isolator  34 . Bracket  32  is a metal or plastic component which defines a pair of mounting flanges  36  and an isolator aperture  38 . Each of the pair of mounting flanges  36  defines a mounting bore  40  which accepts a fastener for securing exhaust system isolator assembly  30  to a vehicle frame or another structural component of the vehicle. While  FIG. 1  illustrates flanges  36  being generally perpendicular to each other, it is within the scope of the present disclosure to arrange flanges  36  in any orientation which is required to have bracket  32  properly interface with the mounting structure of the vehicle. 
     Exhaust system isolator  34  comprises an inner structural member  50 , an outer structural member  52  and an elastomeric body  54  disposed between structural members  50  and  52 . 
     Elastomeric body  54  defines a bore  56  which is designed to accept an inner tube, a bolt, or a hanger pin  58 . Hanger pin  58  is attached to a component of exhaust system  10 . While bracket  32  is disclosed as being attached to a structural component of the vehicle and exhaust system isolator  34  is disclosed as being attached to a component of exhaust system  10 , using hanger pin  58 , it is within the scope of the present disclosure to have bracket  32  attached to exhaust system  10  and exhaust system isolator  34  attached to a structural component of the vehicle using hanger pin  58 . Thus, exhaust system  10  is secured to the vehicle through one or more exhaust system isolator assemblies  30 . 
     Elastomeric body  54  defines an outer circumferential void  60  and an inner circumferential void  62 . While voids  60  and  62  are illustrated as being asymmetrical with respect to bore  56 , it is within the scope of the present disclosure to have voids  60  and  62  symmetrical with bore  56 . The asymmetrical design for voids  60  and  62  permit bore  56  to become disposed at or near the centerline of outer structural member  52  during the assembled or statically loaded condition of exhaust system isolator assembly  30 . 
     As can be seen in the figures, void  60  overlaps with void  62  in the axial direction to define a shear hub  66  which undergoes the shear loading due to the deflection of elastomeric body  54 . During larger loading of exhaust system isolator assembly  30 , voids  60  and  62  close and compressive stresses are imparted to elastomeric body  54  by the sandwiching of elastomeric body  54  between hanger pin  58  and inner structural member  50  and between inner structural member  50  and outer structural member  52 . 
     The design of voids  60  and  62 , specifically their thickness, will determine the amount of travel of bore  56  with respect to outer structural member  52  until the load to radially deflect exhaust system isolator assembly  30  spikes up due to the closing of voids  60  and  62 . Until the closing of voids  60  and  62 , the radial movements of bore  56  cause pure shear in elastomeric body  54  regardless of the loading direction. This shear loading occurs in the portion of elastomeric body  54  disposed between outer structural member  52  and inner structural member  50  as discussed below. Tuning for rate and deflection in selected directions can be accomplished independently from other directions by altering voids  60  and  62  in the selected direction or by adding voids at specific circumferential positions of elastomeric body  54 . 
     Exhaust system isolator  34  avoids tension stress loading in elastomeric body  54  during radial loading. The shear style loading in all directions enables exhaust system isolator  34  to achieve a lower and more stable rate of deflection. This is because the shear modulus (shear loading) is lower than the elasticity modulus (tensile loading). Also, the spring rate of elastomeric materials in shear is more consistent than in tensile. The rates and deflections are capable of being symmetrical about the center axis or they can be tuned using voids  60  and  62  or by otherwise altering the size or shape of elastomeric body  54  or the rigid structures. An additional advantage is that the rate of deflection for shear hub  66  is linear throughout the deflection (until voids  60  and/or  62  close) which adds robustness to the design in regards to the position. This means that any pre-load from positional tolerances will not spike the rates of deflection and make the Noise, Vibration and Harshness (NVH) of the vehicle change with the exhaust geometry tolerances. 
     Inner structural member  50  is an outward flanged tube made of metal or plastic component which includes an axial cylinder  70  and a radial flange  72 . Axial cylinder  70  extends over bore  56  and radial flange  72  extends radially outward from axial cylinder  70  to provide a base for shear hub  66  at one end of shear hub  66 . Elastomeric body  54  is bonded to inner structural member  50  including shear hub  66  being bonded to radial flange  72 . 
     Outer structural member  52  is an inward flanged tube made of metal or plastic component which includes an axial cylinder  76  and a radial flange  78 . Axial cylinder  76  extends over elastomeric body  54  and is designed to be press-fit or otherwise assembled into isolator aperture  38 . A radially outwardly extending flange  80  assists in the assembly of exhaust system isolator  34  to bracket  32  as well as providing hoop strength for axial cylinder  76 . Radial flange  78  extends radially inward from axial cylinder  76  to provide a base for shear hub  66  at the opposite end of shear hub  66 . Elastomeric body  54  is bonded to outer structural member  52  including shear hub  66  being bonded to radial flange  78 . 
     Referring now to  FIG. 2 , it can be seen that the axial left end of inner structural member  50  extends further out or to the left from the axial end of outer structural member  52  such that the entire axial cylinder  76  of outer structural member  52  is axially spaced from radial flange  72  of inner structural member  50 . Thus, at the left side in  FIG. 2 , outer structural member  52  is axially short of inner structural member  50  and this permits shear hub  66  to act as a cushion during high loads without affecting or causing shear stress in the bond between radial flange  72  of inner structural member  50  and elastomeric body  54 . In a similar manner, it can be seen that the axial right end of outer structural member  52  extends further out or to the right from the axial end of inner structural member  50  such that the entire axial cylinder  70  of inner structural member  50  is axially spaced from radial flange  78  of outer structural member  52 . Thus, at the right side in  FIG. 2 , inner structural member  50  is axially short of outer structural member  52  and this permits shear hub  66  to act as a cushion during high loads without affecting or causing shear stress in the bond between radial flange  78  of outer structural member  52  and elastomeric body  54 . Also, as illustrated in  FIG. 2 , elastomeric body  54  defines a relieved portion  82  disposed adjacent the inner end of radial flange  78  of outer structural member  52  to lower the stress on the bonding section between radial flange  78  and elastomeric body  54  during high loading where voids  60  and  62  are closed. 
     In addition, the location of shear hub  66  between radial flange  72  and radial flange  78  and the bonding of shear hub  66  and elastomeric body  54  to radial flange  72  and radial flange  78  eliminates the transmission of stress through void toe radiuses  84  and  86  of voids  60  and  62 , respectively, thus avoiding stress concentration seen in conventional shear-hub designs. 
     Referring now to  FIGS. 4-6 , an exhaust system isolator  134  in accordance with another embodiment of the present disclosure is disclosed. Exhaust system isolator  134  comprises inner structural member  50 , outer structural member  52  and an elastomeric body  154 . Exhaust system isolator  134  is the same as exhaust system isolator  34  except that elastomeric body  154  replaces elastomeric body  54 . 
     Elastomeric body  154  is the same as elastomeric body  54  except that elastomeric body  154  extends radially outward from outer structural member  52  to define a pair of mounting bores  170 . Mounting bores  170  are each designed to accept a hanger pin  58  such that the pair of hanger pins  58  mating with mounting bores  170  are attached to the structural member of the vehicle and hanger pin  58  mating with bore  56  is attached to a component of exhaust system  10 . Also, it is within the scope of the present disclosure to have the pair of hanger pins  58  mated with mounting bores  170  attached to the component of exhaust system  10  and the hanger pin  58  mating with bore  56  attached to the structural portion of the vehicle if desired. 
     The mounting system for exhaust system isolator  34  and  134  is not limited to using bracket  32  or mounting bores  170 . Any of the mounting systems disclosed in Applicant&#39;s co-pending application Ser. No. 11/233,283, the disclosure of which is incorporated herein by reference, could be utilized to mount exhaust system isolator  34  to the vehicle. 
     The overall size of exhaust system isolator can be tuned to accommodate a required packaging size dictated by a vehicle&#39;s design. Factors which need to be considered when tuning an exhaust gas isolator include the requirement that the voids overlap enough in the axial direction to avoid any tension of the elastomeric body at max travel; the widths of the voids must be large enough to allow Noise, Vibration and Harshness (NVH) travel before bottoming out and spiking rates; the thickness of the shear hub should be large enough to provide the desired or center rate; and the inner and outer structural members and bracket length are large enough to provide compressive stresses manageable under peak durability loads.