Abstract:
An exhaust insulator adapted for use in a motor vehicle exhaust system includes a vibration dampening mechanism and a heat shield. The heat shield snaps into position around the vibration dampening mechanism. The insulator is used in conjunction with a hanger which connects the exhaust pipes to the vehicle chassis.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   This invention relates generally to insulators for vehicle exhaust systems and more specifically to an insulator for a vehicle exhaust system that includes a shield that snaps onto the insulator to protect it from excessive heat build-up and consequent possible failure due to heat damage. 
   2. Background Information 
   As motorists drive their vehicles over roads, they encounter potholes, bumps and other uneven surfaces that shake and jolt the vehicle body. These vibrations and jarring shocks to the vehicle body may cause damage to various components and connections. One of the systems of the vehicle that may be damaged by such vibrations is the exhaust system. The vibrations may cause cracks in the welds between components of the system. 
   In order to dampen these vibrations and to reduce the potential side effects, manufacturers have customarily used rubber vibration insulators or dampers in the connections between the exhaust system and the vehicle chassis. These vibration dampers have worked fairly well until recently. 
   In the past, exhaust systems on automobiles included fairly long, straight sections of pipe that allowed air to flow freely and rapidly from the engine to the exterior. Hangers connected the exhaust pipes to the vehicle bodies and dampers were located periodically along the length of these pipes to support the system and insulate occupants from vibration in the pipes. The exhaust system allowed exhaust gases to escape from the vehicle and also allowed heat from the engine to be rapidly dissipated. 
   Specifically, elastomeric hangers provided a number of benefits, including retention of the exhaust system to the car, as well as providing a flexible attachment that could accommodate expansion and contraction of the exhaust system as a result of heating and cooling during vehicle operation. Still further, these elastomeric bushings would isolate vibrations in the system and system noise from reaching the vehicle occupants. 
   Problems with this system began to appear with the introduction of catalytic converters. Catalytic converters are used to reduce the release of noxious gases into the atmosphere. They tend to work best if they are heated and consequently they are located as near to the engine block as possible, but sufficiently far away to prevent the device from overheating and being damaged. Exhaust gases are hottest when they exit the engine and manufacturers have utilized this heat to heat up the catalytic converters to improve their performance. Sometimes manufacturers preheat the catalytic converter using a small electric resistance heater. Catalytic converters restrict the free airflow through the exhaust system. The noxious gases are filtered out, but the converters drastically reduce the rate of heat loss through the exhaust system. Heat tends to build up in the area surrounding the catalytic converter and through the rest of the exhaust system. As the catalytic converter slows the air flow through the exhaust system, the rate of heat loss from the system decreases and consequently there is a greater increase in the temperature of the exhaust pipes. This heat build-up in the rest of the system may result in the vibration insulators becoming overheated and damaged. The insulator may fail, resulting in an increase in disturbances from the exhaust system and ultimately in damage to or loss of the exhaust system itself. 
   Manufacturers have attempted to shield components from the heat build up caused by the reduction in the exhaust gas flow rate. Their attempts have included the use of metallic heat shields positioned above the catalytic convertor and along the exhaust system in order to prevent heat from entering the cab of the vehicle and to prevent fires and the like when heat is positioned adjacent to wire harnesses or other flammable material. Metallic shields are expensive to manufacture and fairly difficult to install if a problem is diagnosed. As such, these shields have not been utilized to protect exhaust insulators or vibration dampeners. As the exhaust system is relatively cheap to replace, this type of shield has not traditionally been used to protect the exhaust system. Other possible solutions to this problem have been the use of air spaces or gaps to separate components from each other, as well as the use of double layer exhaust pipes which include an air space between the two layers. However, these solutions have been fairly costly and it has been difficult to retrofit cars with these systems. The industry desires a device that addresses these problems. 
   BRIEF SUMMARY OF THE INVENTION 
   The invention provides a heat shield for a vibration insulator that is used with a vehicle exhaust system. The vibration insulator is adapted for use in a motor vehicle having a chassis, an engine and an exhaust system that includes exhaust pipes. The heat shield is disposed over a portion of the vibration insulator to reduce the heat that reaches the vibration insulator, thereby reducing the likelihood of the failure of the vibration insulator. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a side view of an exhaust system for a motor vehicle showing portions of the vehicle body in phantom. 
       FIG. 2  is an exploded perspective view of a vibration insulator and the heat shield. 
       FIG. 3  is a perspective view of the heat shield. 
       FIG. 4  is an enlarged side view of the highlighted area of the exhaust system shown in FIG.  1 . 
       FIG. 5  is a partially cut away front view of the vibration insulator and heat shield taken through line  5 — 5  of FIG.  4 . 
       FIG. 6  is an exploded partial cross-section of the vibration insulator, heat shield and hanger bars. 
       FIG. 7  is a partial cross-section of the vibration insulator, heat shield and hanger bars taken through line  7 — 7  of FIG.  5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , there is generally shown an automobile  10  having a body  12  and an exhaust system  14  connected to the body  12  by at least hangers  16 . Other parts of the automobile  10  are not shown in detail for clarity and these other parts are of conventional structure and function and are know to those skilled in the art. 
   Exhaust system  14  is connected at one end to a manifold (not shown) that funnels exhaust gases from the cylinders (not shown) into exhaust system  14 . A number of exhaust pipe sections  18 ,  20 ,  22  connect the components of exhaust system  14  together. A catalytic converter  24  is connected to the manifold (not shown) by pipe section  18  and to a muffler  26  by pipe section  20 . Muffler  26  is connected to a tail pipe  28  by pipe section  22 . Tail pipe  28  is open to the atmosphere to allow the exhaust gases to escape from the exhaust system  14 . The various components of exhaust system  14  are connected together in the conventional manner by the use of welds and clamps. 
   Referring to  FIGS. 1 and 4 , exhaust system  14  is connected to body  12  by hangers  16 . Each hanger  16  includes an upper arm  30  that is welded, bolted or otherwise attached to the chassis  32  of body  12 . Lower arm  34  is connected to pipe section  22 . A vibration insulator  36  is disposed between upper and lower arms  30 ,  34 . 
   Vibration insulator  36  defines two bores  38 ,  38 ′ ( FIG. 2 ) through which upper arm  30  and lower arm  34  may be received. Vibration insulator  36  may be manufactured in any shape or configuration and is typically manufactured from an elastomer, such as EPDM. EPDM is able to withstand temperatures ranging from 210 to 250 degrees Fahrenheit and is flexible enough to dampen vibrations. In the preferred embodiment, insulator  36  may be manufactured of any elastomer covered by ASTM D2000 classifications M and DA, although other compounds may be used without departing from the spirit of the present invention. Upper arm  30  is received through bore  38  and lower arm  34  is received through bore  38 ′. A suitable lock  40  such as a flange on arms  30  and  34 , a pin, a cap, or other types of known elements prevents insulator  36  from sliding off of arms  30  and  34  when insulator  36  is in use. In another embodiment, insulator  36  is frictionally held on arms  30  and  34 . A cup-shaped heat shield  42  ( FIG. 6 ) defines a central cavity  44  into which insulator  36  may be received. Shield  42  is configured to generally cover insulator  36  while allowing the rear face  46  of insulator  36  to remain uncovered. This configuration allows heat shield  42  to be easily placed over or removed from insulator  36 . Heat shield  42  defines two apertures  48 ,  48 ′. Upper arm  30  may be received through aperture  48  and lower arm  34  may be received through aperture  48 ′. Heat shield  42  is essentially diamond shaped having rounded corners  67  and straight sidewalls  65  extending between the rounded corners. However, heat shield  42  may take a variety of configurations without departing from the spirit of the present invention. The inner perimeter surface  52  of heat shield  42  includes at least two beads  68  for retention of the insulator  36 . Heat shield  42  may be manufactured from a silicone elastomer, fluorolastomer, ethylene acrylic or any other suitable material. Suitable metals and fabric could also be used. A suitable silicone elastomer would be SAE J200 M8GE 406 A19 B37 G11 selected from a group of compounds having the following properties:
         A19—Heat resistance testing up to 225° for 70 hours   B37—Compression set testing at 175° for 22 hours.   G11—Tear resistance: 5 kN/m under 7 MPa load.       

   In the preferred embodiment, the silicone elastomer is taken from the group ASTM D2000 classification GE, FC, FE and FK, although others could be used without departing from the spirit of the present invention. These silicone elastomers are designed to withstand high heat without failing, melting or drooping. Shield  42  is preferably soft and flexible so that it may be easily snapped into position over insulator  36  and is able to flex with the insulator. Positioning heat shield  42  over insulator  36  allows for the superior strength and structural properties of EPDM to be utilized, while enabling insulator  36  to withstand higher temperatures. 
   Insulator  36  shown in  FIGS. 2 and 7  is known in the prior art and other insulators may be used in combination with the heat shield of the invention without departing from the scope of this invention. Insulator  36  as shown in  FIG. 2 , is basically clover shaped, having four round protuberances, two of the protuberances  60 ,  60 ′ being somewhat larger than the other protuberances  62 ,  62 ′. Bores  38 , 38 ′ are defined in the smaller protuberances  62 ,  62 ′. Valleys or depressions  63  ( FIG. 5 ) are defined between adjacent protuberances  60 , 62  and the straight sidewalls  65  of heat shield  42  to provide air gaps that insulate insulator  36  from heat. Vibration insulator  36  two cavities  64 , two on front surface  54  and two on the rear surface (not shown). Front surface  54  and rear surface (not shown) of insulator  36  are basically identical in appearance. Projections  66  are formed on outer perimeter surface  50  of insulator  36 . Heat shield  42  is held on insulator  36  by friction and the cooperation of beads  68  on heat shield  42  with projections  66  on insulator  36 . The shape of insulator  36  with protuberances  60 , 60 ′,  62 ,  62 ′, cavities  64  and projections  66  allows for the creation of air spaces between insulator  36  and heat shield  42 . Additionally, front surfaces  54  of protuberances  60 , 60 ′ are set back a small distance from the front surface  70  of protuberance  62 , 62 ′ and this creates an additional air space  72  between front surface  54  and inner perimeter surface  52  of heat shield  42 . These air spaces allow for the dispersion of heat from the insulator/shield  36 , 42  combination. 
   The device of the present invention is used in the following manner. In order to install shield  42 , lock  40  is released (when present) and insulator  36  is slipped off upper and lower arms  30 ,  34 . Heat shield  42  is positioned over insulator  36  so that the outer peripheral wall  50  of insulator  36  slides into central cavity  44  and along inner peripheral wall  52  of shield  42 . Shield  42  and insulator  36  are pushed together until front surface  70  of protuberances  62 ,  62 ′ abuts inner surface  52  of shield  42 . Apertures  48 ,  48 ′ and bores  38 ,  38 ′ are aligned with each other. Additionally, beads  68  interlock with projections  66 . The shield/insulator combination is then brought toward upper and lower arms  30 ,  34 . Free ends  56 ,  56 ′ of upper and lower arms  30 ,  34  are inserted through apertures  48 ,  48 ′ and aligned bores  38 ,  38 ′. Lock  40  (if required) is then applied to upper and lower arms  30 ,  34  to lock the shield/insulator component onto arms  30 ,  34 . Alternatively, shield  42  and insulator  36  may be forced over lock  40  while it is in place. Similarly, shield  42  may be applied to insulator  36  during original equipment manufacturing. In this situation, insulator  36  and shield  42  would be shipped to the manufacturer as an assembly and applied when the vehicle is being manufactured. 
   In order to replace either shield  42  or insulator  36 , lock  40  is released, the shield/insulator component  42 / 36  is removed by simply pulling it off free ends  56 ,  56 ′ of arms  30 ,  34  or the shield/insulator component  42 / 46  can be pulled over lock  40 . If it is desired to remove shield  42  from insulator  36 , the mechanic merely needs to insert his/her fingers between the outer peripheral wall  50  of insulator  36  and inner peripheral wall  52 , and then to pull shield  42  off insulator  36 . Because shield  42  is manufactured from a soft, flexible material it may be easily snapped into place over insulator  36  and may be just as easily removed. 
   While this method of positioning shield  42  over insulator  36  has been described, shield  42  may be inserted onto upper and lower arms  30 ,  34  first and then insulator  36  may be inserted onto upper and lower arms  30 ,  34  and then pushed into shield  42 . The heat shield thermally insulating the vibration insulator from heat generated by the vehicle exhaust system. 
   In the foregoing description, certain terms have been used for brevity, clearness, and understanding. 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 are an example and the invention is not limited to the exact details shown or described.