End plated shear-hub isolator

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.

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

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's exhaust system from the vehicle's body. In order to effectively isolate the vehicle's exhaust system from the vehicle'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.

DESCRIPTION

Referring now to the drawings, there is shown inFIG. 7an exhaust system which includes the exhaust system isolators in accordance with the present disclosure and which are designated generally by the reference numeral10. A typical vehicle comprises an internal combustion engine (not shown), a body (not shown), a suspension system (not shown) and exhaust system10which 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 system10comprises an intermediate pipe12, a muffler14, a tailpipe16and a plurality of isolator assemblies of various designs. Intermediate pipe12is 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 pipe12can be attached to a plurality of catalytic converters which connect together prior to reaching muffler14using intermediate pipe12or the vehicle can have a plurality of exhaust pipes, a plurality of catalytic converters, a plurality of intermediate pipes12and a plurality of mufflers14which connect together using a single or multiple tailpipes16. 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 system10is 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 muffler14quiets the noise created during the combustion process in the engine. The present disclosure is directed toward the exhaust system isolators which mount exhaust system10to the vehicle while at the same time, isolate the movement of exhaust system10with respect to the vehicle.

Referring now toFIGS. 1-3, an exhaust system isolator assembly30comprises a bracket32and an exhaust system isolator34. Bracket32is a metal or plastic component which defines a pair of mounting flanges36and an isolator aperture38. Each of the pair of mounting flanges36defines a mounting bore40which accepts a fastener for securing exhaust system isolator assembly30to a vehicle frame or another structural component of the vehicle. WhileFIG. 1illustrates flanges36being generally perpendicular to each other, it is within the scope of the present disclosure to arrange flanges36in any orientation which is required to have bracket32properly interface with the mounting structure of the vehicle.

Exhaust system isolator34comprises an inner structural member50, an outer structural member52and an elastomeric body54disposed between structural members50and52.

Elastomeric body54defines a bore56which is designed to accept an inner tube, a bolt, or a hanger pin58. Hanger pin58is attached to a component of exhaust system10. While bracket32is disclosed as being attached to a structural component of the vehicle and exhaust system isolator34is disclosed as being attached to a component of exhaust system10, using hanger pin58, it is within the scope of the present disclosure to have bracket32attached to exhaust system10and exhaust system isolator34attached to a structural component of the vehicle using hanger pin58. Thus, exhaust system10is secured to the vehicle through one or more exhaust system isolator assemblies30.

As can be seen in the figures, void60overlaps with void62in the axial direction to define a shear hub66which undergoes the shear loading due to the deflection of elastomeric body54. During larger loading of exhaust system isolator assembly30, voids60and62close and compressive stresses are imparted to elastomeric body54by the sandwiching of elastomeric body54between hanger pin58and inner structural member50and between inner structural member50and outer structural member52.

The design of voids60and62, specifically their thickness, will determine the amount of travel of bore56with respect to outer structural member52until the load to radially deflect exhaust system isolator assembly30spikes up due to the closing of voids60and62. Until the closing of voids60and62, the radial movements of bore56cause pure shear in elastomeric body54regardless of the loading direction. This shear loading occurs in the portion of elastomeric body54disposed between outer structural member52and inner structural member50as discussed below. Tuning for rate and deflection in selected directions can be accomplished independently from other directions by altering voids60and62in the selected direction or by adding voids at specific circumferential positions of elastomeric body54.

Exhaust system isolator34avoids tension stress loading in elastomeric body54during radial loading. The shear style loading in all directions enables exhaust system isolator34to 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 voids60and62or by otherwise altering the size or shape of elastomeric body54or the rigid structures. An additional advantage is that the rate of deflection for shear hub66is linear throughout the deflection (until voids60and/or62close) 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 member50is an outward flanged tube made of metal or plastic component which includes an axial cylinder70and a radial flange72. Axial cylinder70extends over bore56and radial flange72extends radially outward from axial cylinder70to provide a base for shear hub66at one end of shear hub66. Elastomeric body54is bonded to inner structural member50including shear hub66being bonded to radial flange72.

Outer structural member52is an inward flanged tube made of metal or plastic component which includes an axial cylinder76and a radial flange78. Axial cylinder76extends over elastomeric body54and is designed to be press-fit or otherwise assembled into isolator aperture38. A radially outwardly extending flange80assists in the assembly of exhaust system isolator34to bracket32as well as providing hoop strength for axial cylinder76. Radial flange78extends radially inward from axial cylinder76to provide a base for shear hub66at the opposite end of shear hub66. Elastomeric body54is bonded to outer structural member52including shear hub66being bonded to radial flange78.

Referring now toFIG. 2, it can be seen that the axial left end of inner structural member50extends further out or to the left from the axial end of outer structural member52such that the entire axial cylinder76of outer structural member52is axially spaced from radial flange72of inner structural member50. Thus, at the left side inFIG. 2, outer structural member52is axially short of inner structural member50and this permits shear hub66to act as a cushion during high loads without affecting or causing shear stress in the bond between radial flange72of inner structural member50and elastomeric body54. In a similar manner, it can be seen that the axial right end of outer structural member52extends further out or to the right from the axial end of inner structural member50such that the entire axial cylinder70of inner structural member50is axially spaced from radial flange78of outer structural member52. Thus, at the right side inFIG. 2, inner structural member50is axially short of outer structural member52and this permits shear hub66to act as a cushion during high loads without affecting or causing shear stress in the bond between radial flange78of outer structural member52and elastomeric body54. Also, as illustrated inFIG. 2, elastomeric body54defines a relieved portion82disposed adjacent the inner end of radial flange78of outer structural member52to lower the stress on the bonding section between radial flange78and elastomeric body54during high loading where voids60and62are closed.

In addition, the location of shear hub66between radial flange72and radial flange78and the bonding of shear hub66and elastomeric body54to radial flange72and radial flange78eliminates the transmission of stress through void toe radiuses84and86of voids60and62, respectively, thus avoiding stress concentration seen in conventional shear-hub designs.

Referring now toFIGS. 4-6, an exhaust system isolator134in accordance with another embodiment of the present disclosure is disclosed. Exhaust system isolator134comprises inner structural member50, outer structural member52and an elastomeric body154. Exhaust system isolator134is the same as exhaust system isolator34except that elastomeric body154replaces elastomeric body54.

Elastomeric body154is the same as elastomeric body54except that elastomeric body154extends radially outward from outer structural member52to define a pair of mounting bores170. Mounting bores170are each designed to accept a hanger pin58such that the pair of hanger pins58mating with mounting bores170are attached to the structural member of the vehicle and hanger pin58mating with bore56is attached to a component of exhaust system10. Also, it is within the scope of the present disclosure to have the pair of hanger pins58mated with mounting bores170attached to the component of exhaust system10and the hanger pin58mating with bore56attached to the structural portion of the vehicle if desired.

The mounting system for exhaust system isolator34and134is not limited to using bracket32or mounting bores170. Any of the mounting systems disclosed in Applicant'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 isolator34to the vehicle.

The overall size of exhaust system isolator can be tuned to accommodate a required packaging size dictated by a vehicle'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.