Patent Publication Number: US-10329993-B2

Title: Vehicle exhaust assembly

Description:
RELATED APPLICATIONS 
     This application is a 35 U.S.C. § 371 national stage application of PCT Application No. PCT/EP2016/062995, filed on Jun. 8, 2016, which claims priority from Great Britain Patent Application No 1510233.8, filed on Jun. 12, 2015, the contents of which are incorporated herein by reference in their entireties. The above-referenced PCT International Application was published in the English language as International Publication No. WO 2016/198436 A1 on Dec. 15, 2016. 
     TECHNICAL FIELD 
     The present disclosure relates to a vehicle exhaust assembly; and to a vehicle comprising a vehicle exhaust assembly. 
     BACKGROUND 
     Automotive vehicles having internal combustion engines are often provided with an exhaust system to expel exhaust gases at the rear of the vehicle. The exhaust system typically includes one or more conduits for porting exhaust gases from the internal combustion engine to one or more tail pipe. The exhaust system can also include after-treatment devices, such as a catalytic converter for trapping particles suspended in the exhaust gases; and one or more silencer for reducing exhaust noise. A typical exhaust system for a road vehicle is made from stainless steel, having a gauge thickness of 1.2 mm or 1.5 mm resulting in a significant mass. 
     In order to reduce the mass of the exhaust system, it is known to use materials other than stainless steel. For example, the exhaust system can be fabricated from titanium, but this typically requires specialised fabrication techniques and is more expensive to produce. There are additional obstacles to reducing the mass of the exhaust system. Notably, larger and more complex after-treatment devices are required to meet increasingly stringent emissions legislation. Moreover, there is an on-going desire to reduce acoustic outputs and/or to tune the acoustic outputs to refine the soundscape within the vehicle. These requirements typically result in larger and more complex exhaust systems. 
     It is against this backdrop that the present invention has been conceived. At least in certain embodiments, the present invention relates to an exhaust system configured to have a lower mass that prior art systems. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention relate to a vehicle exhaust assembly; and to a vehicle comprising a vehicle exhaust assembly. 
     According to a further aspect of the present invention there is provided a vehicle exhaust assembly for an internal combustion engine, the vehicle exhaust assembly comprising an exhaust system and an exhaust mounting assembly for mounting the exhaust system, wherein:
         the exhaust system comprises:
           an inlet section for connection to the internal combustion engine;   an intermediate section connected to the inlet section;   an outlet section for exhausting gases from the internal combustion engine; and   one or more exhaust decoupler for decoupling the intermediate section from the inlet section;   
           the exhaust mounting assembly comprises:
           one or more first isolator device for resiliently constraining movement of the intermediate section of the exhaust system in a longitudinal direction; and   
           one or more second isolator device for resiliently constraining movement of the outlet section of the vehicle exhaust in a transverse direction. In use, vibrations are transmitted to the exhaust system from two primary excitations sources, namely the internal combustion engine and the road surface. These excitations cause the exhaust system to respond in a modal fashion or to impart global ‘cantilevering’ loads, since the exhaust system is more mobile than the internal combustion engine or body structure to which it is attached. The vehicle exhaust assembly according to certain embodiments of the present invention can reduce mechanical loads on the exhaust system. In particular, the exhaust mounting assembly is configured to support the exhaust system to reduce mechanical loading. At least in certain embodiments, this allows the mass of the exhaust system to be reduced. For example, if the mechanical loading on the exhaust system can be reduced or removed, the gauge of the materials used to form the exhaust system can be reduced.       

     The one or more first isolator device can comprise a first resilient isolator element. The first resilient isolator element can, for example, be moulded from an elastomeric material. The elastomeric material can be moulded into a rigid housing or frame, for example using an over-moulding technique. In an alternate arrangement, the first isolator device can be in the form of a first pendulum isolator device. The first pendulum isolator device can be suspended by two or more pins. Other types of isolator device can usefully be employed in the exhaust system. 
     The one or more first isolator device can have an axial dynamic stiffness in said longitudinal direction of less than or equal to 60 N/mm up to an excitation frequency of 180 Hz. The one or more first isolator device can provide greater resilient constraint for the intermediate section in said longitudinal direction than in a vertical direction. The one or more first isolator device can at least substantially inhibit movement of the intermediate section in said transverse direction. The one or more first resilient isolator device can be configured to provide greater resilient constraint in said longitudinal direction than in said vertical direction. The one or more first isolator device can be configured to support the intermediate section in said vertical direction at least substantially without resiliently constraining movement in the vertical direction. 
     The one or more second isolator device can comprise a second resilient isolator element. The second resilient isolator element can, for example, be moulded from an elastomeric material. The elastomeric material can be moulded into a rigid housing or frame, for example using an over-moulding technique. In an alternate arrangement, the second isolator device can be in the form of a second pendulum isolator device. The second pendulum isolator device can be suspended by two or more pins. Other types of isolator device can usefully be employed in the exhaust system. 
     The first isolator device and the one or more second isolator device can have like configurations. For example, the same isolator element can be used in the first and second resilient isolator devices. 
     The one or more second isolator device can have an axial dynamic stiffness in said transverse direction of less than or equal to 60 N/mm up to an excitation frequency of 180 Hz. The second isolator device can provide greater resilient constraint for the rear section in said transverse direction than in a vertical direction. The second isolator device can at least substantially inhibit movement of the rear section in said longitudinal direction. The second resilient isolator device can be configured to provide greater resilient constraint in said transverse direction than in said vertical direction. The second isolator device can be configured to support the intermediate section in said vertical direction at least substantially without resiliently constraining movement in the vertical direction. 
     The exhaust mounting assembly may comprise one of the first isolator devices only. In such an embodiment, the positioning and dynamic stiffness of the one first isolator device may be such that a single such device is sufficient to support the intermediate section and to resiliently restrain movement in the longitudinal direction. The one first isolator device may be positioned near to the intermediate section centre of mass, for example near to a silencer. As only one first isolator device is needed, the weight of the exhaust assembly is kept to a minimum. 
     The exhaust mounting assembly may comprise one of the second isolator devices only. In such an embodiment, the positioning and dynamic stiffness of the one second isolator device may be such that a single such device is sufficient to support the outlet section and to resiliently restrain movement in the transverse direction. The one second isolator device may be positioned near to the outlet section centre of mass, for example near to a silencer. Such an embodiment may be particularly useful in an exhaust assembly comprising a single tailpipe only. As only one second isolator device is needed, the weight of the exhaust assembly is kept to a minimum. 
     The exhaust mounting assembly may comprise two of the second isolator devices only. In such an embodiment, the positioning and dynamic stiffness of the two second isolator devices may be such that two such devices are sufficient to support the outlet section and to resiliently restrain movement in the transverse direction. The two second isolator devices may be positioned near to respective silencers of the outlet section, for example. Such an embodiment may be particularly useful in a twin-sided exhaust assembly comprising first and second tailpipes. As only two second isolator devices are needed, the weight of the exhaust assembly is kept to a minimum. 
     The exhaust system can comprise a plurality of exhaust decouplers. The exhaust decouplers can be disposed in a series configuration. Alternatively, the exhaust decouplers can be disposed in a parallel configuration. The inlet section can comprise a plurality of conduits for connection to the internal combustion engine, the conduits each comprising one of said exhaust decoupler. 
     The one or more exhaust decoupler can each comprise a flexible conduit. The one or more exhaust decoupler can comprise a convoluted tube to form a sealed fluid duct. Alternatively, or in addition, the one or more exhaust decoupler can each comprise a flexible metal braided (or knitted) conduit. The braided (or knitted) conduit can form an outer sleeve. The outer sleeve can be operative to provide dynamic damping and/or to limit constraining functions. The one or more exhaust decoupler can have a length greater than or equal to 180 mm. The exhaust decoupler can have a length of 200 mm. The one or more exhaust decoupler can be configured to reduce excitation of the intermediate section to less than 0.18 mm at frequencies less than or equal to 500 Hz. The one or more exhaust decoupler can each have an axial dynamic stiffness of less than or equal to 50 N/mm up to an excitation frequency of 160 Hz. The one or more exhaust decoupler can each have a lateral dynamic stiffness of less than or equal to 60 N/mm up to an excitation frequency of 180 Hz. 
     At least in certain embodiments, the exhaust system can comprise one or more second exhaust decoupler. For example, one or more second exhaust decoupler can be provided in said intermediate section and/or in said outlet section. One or more second exhaust decoupler can be provided to decouple the intermediate section from the outlet section. A second exhaust decoupler could be provided in the exhaust system within the after-treatment system; and/or between an after-treatment device and an acoustic silencer. The after-treatment device and the acoustic silencer could be decoupled from each other. 
     The exhaust system may comprise one of the exhaust decouplers only. In such an embodiment, the positioning and dynamic stiffness of the one exhaust decoupler may be such that a single such device is sufficient to decouple the intermediate section from the inlet section. 
     The exhaust system can be made of metal sheet having a gauge thickness of between 0.4 mm and 0.7 mm. The exhaust system can be made of stainless steel. 
     The intermediate section of the exhaust system can comprise an after-treatment device, such as a catalytic converter. The intermediate section can comprise one or more intermediate conduit. The after-treatment device has an external wall which can have a plurality of out-of-plane features. In particular, the external wall can comprise a plurality of like indentations. The indentations can project inwardly and can be arranged in a regular, or irregular (for example, a Computer Aided Engineering (CAE) derived) pattern. For example, the indentations can be in the form of hexagonal indentations arranged in an interlocking pattern. 
     The outlet section and/or the intermediate of the exhaust system can comprise one or more acoustic silencer. Each acoustic silencer can have a sidewall having a structured composition, for example comprising a plurality of out-of-plane features. For example, the sidewall can comprise a plurality of outwardly directed projections. The outwardly directed projections can be arranged in a repeating pattern. For example, the structured sheet material can comprise an array of polygonal projections arranged in an interlocking pattern. 
     The gauge thickness of the sidewall of the one or more acoustic silencer may be less than the gauge thickness of a conduit of at least one of the intermediate section and the outlet section. 
     The outlet section of the exhaust system can comprise at least one active acoustic control device. 
     Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which: 
         FIG. 1  shows a vehicle incorporating a vehicle exhaust assembly in accordance with an embodiment of the present invention; 
         FIGS. 2A-D  show perspective views of the vehicle exhaust assembly shown in  FIG. 1 ; 
         FIG. 3  shows a schematic representation of the vehicle exhaust assembly shown in  FIG. 1 ; 
         FIG. 4A  shows first and second graphs showing the axial dynamic stiffness of an exhaust decoupler in the vehicle exhaust assembly shown in  FIG. 1 ; 
         FIG. 4B  shows third and fourth graphs showing the lateral and radial dynamic stiffness of an exhaust decoupler in a variant of the vehicle exhaust assembly shown in  FIG. 1 ; 
         FIG. 5A  shows a resilient isolator element for an isolator device of the vehicle exhaust assembly; and 
         FIG. 5B  shows a fifth graph showing the stiffness of the resilient isolator element shown in  FIG. 5A . 
     
    
    
     DETAILED DESCRIPTION 
     A vehicle exhaust assembly  1  in accordance with an embodiment of the present invention will now be described with reference to the accompanying figures. The vehicle exhaust assembly  1  in the present embodiment is for use in a vehicle  2  to expel exhaust gases from an internal combustion engine (not shown). The internal combustion engine is front-mounted in the vehicle  2  and the vehicle exhaust assembly  1  extends under the body of the vehicle  2 , as shown schematically in  FIG. 1 . The vehicle  2  is an automobile in the present embodiment, but the techniques and apparatus described herein can be applied to other types of vehicles. 
     A vehicle reference frame comprises a longitudinal axis X, a transverse axis Y and a vertical axis Z. The vehicle exhaust assembly  1  is described herein using the vehicle reference frame. The terms longitudinal, transverse and vertical (and derivatives thereof) used herein correspond to the vehicle reference frame. 
     As shown in  FIG. 2A , the vehicle exhaust assembly  1  comprises an exhaust system  3  and an exhaust mounting assembly  4 . The exhaust system  3  routes exhaust gases from the internal combustion engine to the rear of the vehicle  2 . The exhaust system  3  comprises an inlet section  5 , an intermediate section  6 , and an outlet section  7 . The inlet section  5  comprises an exhaust decoupler  8  and an inlet conduit  9 . As shown in  FIG. 2B , the exhaust decoupler  8  is a flexible coupling (providing a super-soft coupling element) and comprises a decoupler inlet  10 , a decoupler outlet  11  and a decoupler sidewall  12 . The exhaust decoupler  8  forms a flexible conduit for reducing the transmittal of vibrations into the intermediate section  6  of the exhaust system  3 . The decoupler sidewall  12  in the present embodiment is formed by a flexible metal braid. The inlet conduit  9  is a stainless steel pipe having a diameter of 65 mm and is connected to an exhaust port of the internal combustion engine. The inlet conduit  9  is substantially rigid (i.e. inflexible) and connects to the decoupler inlet  10 . In use, the vibrations are the result of two primary excitations in the form of the internal combustion engine and/or the road surface. The exhaust decoupler  8  is generally cylindrical and has a length (measured along a central longitudinal axis) of 180 mm. The decoupler outlet  11  has a diameter of 60 mm and connects to the intermediate section  6  of the exhaust system  3 . In certain arrangements, more than one exhaust decoupler  8  could be provided in said inlet section  5 . 
     The intermediate section  6  comprises a silencer  13 , and first and second intermediate conduits  14 - 1 ,  14 - 2 . The silencer  13  has one inlet  15 , first and second outlets  16 - 1 ,  16 - 2 , and a sidewall  17 . The inlet  15  of the silencer  13  is connected to the decoupler outlet  11 ; and the first and second intermediate conduits  14 - 1 ,  14 - 2  are connected to the first and second outlets  16 - 1 ,  16 - 2  respectively. Optionally, an exhaust decoupler could be provided in each of said first and second intermediate conduits  14 - 1 ,  14 - 2 . The first and second intermediate conduits  14 - 1 ,  14 - 2  each have a diameter of 70 mm and are made of stainless steel having a gauge thickness of 0.5 mm (or less). The first and second intermediate conduits  14 - 1 ,  14 - 2  are substantially rigid (i.e. inflexible). 
     The outlet section  7  comprises first and second exhaust silencers  18 - 1 ,  18 - 2 , and first and second tailpipes  19 - 1 ,  19 - 2 . The first and second intermediate conduits  14 - 1 ,  14 - 2  are connected to the first and second exhaust silencers  18 - 1 ,  18 - 2  respectively. The first and second tailpipes  19 - 1 ,  19 - 2  are disposed at the rear of the vehicle  2  to expel exhaust gases from the exhaust system  3 . 
     The exhaust mounting assembly  4  provides a semi-rigid structure to support the exhaust system  3  under the body of the vehicle  2 . The exhaust mounting assembly  4  comprises a first mounting assembly  20  for mounting the intermediate section  6  of the exhaust system  3 . The first mounting assembly  20  comprises first and second opposing isolator devices  20 - 1 ,  20 - 2  fixedly attached to a mounting plate  21  which is fastened to the vehicle body. As shown in  FIG. 2C , the first isolator device  20 - 1  comprises a first housing  22 - 1  and a first resilient isolator element  23 - 1 . The first housing  22 - 1  is in the form of a rigid metal frame into which the first resilient isolator element  23 - 1  is over-moulded. The first resilient isolator element  23 - 1  has a first central aperture  24 - 1  for receiving a first mounting pin  25 - 1 . The second isolator device  20 - 2  comprises a second housing  22 - 2  and a second resilient isolator element  23 - 2 . The second housing  22 - 2  is in the form of a rigid metal frame into which the second resilient isolator element  23 - 2  is over-moulded. The second resilient isolator element  23 - 2  has a second central aperture (not visible) for receiving a second mounting pin (not visible). The first and second mounting pins  25 - 1 ,  25 - 2  are connected respectively to a first bracket  26 - 1  and a second bracket (not visible). The first and second brackets  26 - 1  are rigidly mounted to the first and second intermediate conduits  14 - 1 ,  14 - 2 , for example by welding, brazing or mechanical fasteners. The first and second resilient isolator elements  23 - 1 ,  23 - 2  provide a semi-rigid mounting arrangement for the intermediate section  6  of the exhaust system  3 . The first and second resilient isolator elements  23 - 1 ,  23 - 2  thereby form a localised body interface between the first and second brackets  26 - 1  and the first and second intermediate conduits  14 - 1 ,  14 - 2 . Alternatively, or in addition, a metal retaining band or collar can be disposed around the outside of the silencer to mount the intermediate section  6 . One or more additional mounting bracket can optionally be provided along the length of the first and second intermediate conduits  14 - 1 ,  14 - 2 , for example at a mid-point, to provide additional support. The first and second mounting pins  25 - 1 ,  25 - 2  have a first head  27 - 1  and a second head (not visible) for engaging an outer surface of the first and second resilient isolator elements  23 - 1 . The first and second isolator devices  20 - 1 ,  20 - 2  are disposed on opposing sides of the first and second intermediate conduits  14 - 1 ,  14 - 2 . The first and second isolator devices  20 - 1 ,  20 - 2  are arranged coaxially such that the first and second central apertures  24 - 1  are disposed on a transverse axis parallel to the transverse axis Y of the vehicle  2 . 
     When located in said first and second central apertures  24 - 1 , the first and second mounting pins  25 - 1 ,  25 - 2  extend transversely. 
     As illustrated in  FIGS. 2C and 3 , the first and second resilient isolator elements  23 - 1 ,  23 - 2  are configured to resiliently constrain movement of the first and second mounting pins  25 - 1 ,  25 - 2  in a longitudinal direction (i.e. parallel to a longitudinal axis X of the vehicle  2 ), for example due to shunt loads resulting from dynamic acceleration/deceleration of the vehicle  2 . By constraining movement in said longitudinal direction, the first and second isolator devices  20 - 1 ,  20 - 2  protect the exhaust decoupler  8  from over-extension and compression. The first and second resilient isolator elements  23 - 1 ,  23 - 2  are arranged to provide an axial dynamic stiffness in said longitudinal direction which is less than or equal to 60 N/mm up to an excitation frequency of 180 Hz. The first and second resilient isolator elements  23 - 1 ,  23 - 2  can also constrain or inhibit movement of the first and second mounting pins  25 - 1 ,  25 - 2  in a vertical direction (i.e. parallel to a vertical axis Z of the vehicle  2 ). The first and second resilient isolator elements  23 - 1 ,  23 - 2  can provide greater resilient constraint for the intermediate section  6  in the longitudinal direction than in the vertical direction. The first and second resilient isolator elements  23 - 1 ,  23 - 2  can at least substantially inhibit movement of the first and second mounting pins  25 - 1 ,  25 - 2  in a transverse direction (i.e. parallel to a transverse axis Y of the vehicle  2 ). 
     The exhaust mounting assembly  4  comprises a first silencer mounting assembly  28 - 1  for mounting the first exhaust silencer  18 - 1 ; and a second silencer mounting assembly  28 - 2  for mounting the second exhaust silencer  18 - 2 . As shown in  FIG. 2D , the first silencer mounting assembly  28 - 1  comprises a third isolator device  20 - 3  fixedly attached to a first hanger  29 - 1  which is fastened to the vehicle body. The third isolator device  20 - 3  comprises a third housing  22 - 3  and a third resilient isolator element  23 - 3 . The third housing  22 - 3  is in the form of a rigid metal frame into which the third resilient isolator element  23 - 3  is over-moulded. The third resilient isolator element  23 - 3  has a fourth central aperture  24 - 3  for locating a third mounting pin  25 - 3 . The third mounting pin  25 - 3  is fixedly mounted to the first exhaust silencer  18 - 1 . The third mounting pin  25 - 3  has a third head (not visible) for engaging an outer surface of the third resilient isolator element  23 - 3 . As illustrated in  FIGS. 2D and 3 , the third resilient isolator element  23 - 3  is configured to constrain movement of the third mounting pin  25 - 3  in a transverse direction (i.e. parallel to a transverse axis Y of the vehicle  2 ). The third resilient isolator element  23 - 3  can also constrain or inhibit movement of the third mounting pin  25 - 3  in a vertical direction (i.e. parallel to a vertical axis Z of the vehicle  2 ) and/or a longitudinal direction (i.e. parallel to a longitudinal axis X of the vehicle  2 ). The third resilient isolator element  23 - 3  can improve positional control of the first tailpipe  19 - 1 . The appearance of the first tailpipe  19 - 1  in relation to the surrounding bumper/trim can be improved. 
     The second silencer mounting assembly  28 - 2  comprises a fourth isolator device  20 - 4  fixedly attached to a second hanger  29 - 2  which is fastened to the vehicle body. The fourth isolator device  20 - 4  comprises a fourth housing (not visible) and a fourth resilient isolator element  23 - 4 . The fourth housing is in the form of a rigid metal frame into which the fourth resilient isolator element  23 - 4  is over-moulded. The fourth resilient isolator element  23 - 4  has a fourth central aperture (not visible) for locating a fourth mounting pin  25 - 4 . The fourth mounting pin  25 - 4  is fixedly mounted to the first exhaust silencer  18 - 1 . The fourth mounting pin  25 - 4  has a fourth head (not visible) for engaging an outer surface of the fourth resilient isolator element  23 - 4 . The vehicle exhaust assembly  1  is shown schematically in  FIG. 3 , albeit with the second exhaust silencer  18 - 2  omitted for clarity. 
     As illustrated in  FIG. 3 , the fourth resilient isolator element  23 - 4  resiliently constrains movement of the fourth mounting pin  25 - 4  in a transverse direction (i.e. parallel to the transverse axis Y of the vehicle  2 ). The fourth resilient isolator element  23 - 4  is arranged to provide an axial dynamic stiffness in said transverse direction which is less than or equal to 60 N/mm up to an excitation frequency of 180 Hz. The fourth resilient isolator element  23 - 4  can also support the fourth mounting pin  25 - 4  in a vertical direction (i.e. parallel to the vertical axis Z of the vehicle  2 ). The fourth resilient isolator element  23 - 4  can provide greater resilient constraint in said transverse direction than in said vertical direction. The fourth resilient isolator element  23 - 4  can at least substantially inhibit movement of said fourth mounting pin  25 - 4  in a longitudinal direction (i.e. parallel to a longitudinal axis Y of the vehicle  2 ). The fourth resilient isolator element  23 - 4  can improve positional control of the second tailpipe  19 - 2 . The appearance of the second tailpipe  19 - 2  in relation to the surrounding bumper/trim can be improved. 
     The exhaust mounting assembly  4  facilitates a lightweight construction of the exhaust system  3 . The mechanical properties of the exhaust mounting assembly  4  which provide this functionality will now be described. As outlined above, the exhaust decoupler  8  has a length of 180 mm to reduce transmittal of vibrations from the inlet section  5  to the intermediate section  6 . The exhaust decoupler  8  could be longer, for example 200 mm. The axial mechanical properties of the exhaust decoupler  8  are illustrated in first and second graphs  100 ,  105  shown in  FIG. 4A . The first graph  100  shows the axial dynamic stiffness (N/mm) for an excitation amplitude of 0.2 mm in relation to frequency (Hz); and the second graph  105  shows the axial dynamic stiffness (N/mm) for excitation amplitudes of 0.1 mm and 0.2 mm in relation to frequency (Hz). A first plot  106  in the second graph  105  represents the axial dynamic stiffness for an axial excitation amplitude of 0.1 mm; and a second plot  107  represents the axial dynamic stiffness for an axial excitation amplitude of 0.2 mm. As represented by the dashed lines in the first and second graphs  100 ,  105 , the axial dynamic stiffness of the exhaust decoupler  8  is less than 50 N/mm up to an exciting frequency of 160 Hz. The exhaust decoupler  8  is configured to reduce excitation to less than 0.18 mm at exciting frequencies less than or equal to 500 Hz. The lateral and radial mechanical properties of the exhaust decoupler  8  are illustrated in third and fourth graphs  110 ,  115  shown in  FIG. 4B . The third graph  110  shows the lateral dynamic stiffness (N/mm) for an excitation amplitude of 0.2 mm in relation to frequency (Hz); and the fourth graph  115  shows the radial dynamic stiffness (N/mm) for excitation amplitudes of 0.1 mm and 0.2 mm in relation to frequency (Hz). A first plot  116  in the fourth graph  115  represents the radial dynamic stiffness for a radial excitation amplitude of 0.1 mm; and a second plot  117  represents the radial dynamic stiffness for a radial excitation amplitude of 0.2 mm. As represented by the dashed lines in the third and fourth graphs  110 ,  115 , the dynamic stiffness of the exhaust decoupler  8  is less than 60 N/mm for an exciting frequency less than or equal to 180 Hz. 
     The first, second, third and fourth resilient isolator elements  23 - 1 ,  23 - 2 ,  23 - 3 ,  23 - 4  are made of an elastomeric material, such as a rubber compound. The first, second, third and fourth resilient isolator elements  23 - 1 ,  23 - 2 ,  23 - 3 ,  23 - 4  can have the same or different mechanical properties. A resilient isolator element  23  is shown in  FIG. 5A  by way of example. The resilient isolator element  23  in the present embodiment is available from the applicant and has part number C2P13213. The resilient isolator element  23  is illustrated in a YZ plane and a fifth graph  120  illustrating the mechanical properties in the Z-axis is shown in  FIG. 5B . In the Y direction, loading is transmitted directly by the resilient isolator element  23  to the housing  22 . In the Z direction, shear loading of the resilient isolator element  23  improves isolation performance, since it is free to move within an air gap. The arrangement of the resilient isolator element  23  thereby provides different mechanical properties in the Y and Z directions. The resilient isolator element  23  is configured to negate stiffness behaviours in the X direction (i.e. out-of-plane stiffness). The resilient isolator element has an axial dynamic stiffness along the Z-axis of less than or equal to 60 N/mm up to an excitation frequency of 180 Hz. A first plot  125  in the fifth graph  120  shows the axial dynamic stiffness of the resilient isolator element with a preload of 40 N; and a second plot  130  shows the axial dynamic stiffness of the resilient isolator element with a preload of 80 N. The second plot  130  represents axial dynamic stiffness along the Z-axis which is less than or equal to 60 N/mm (up to an excitation frequency of 180 Hz), as represented by the dashed lines in the fifth graph  120 . At least in certain embodiments, the local body interface stiffness should be not less than ten (10) times the dynamic stiffness in a vertical direction. 
     The resilient isolator element  23  shown in  FIG. 5A  is representative of the first, second, third and fourth resilient isolator elements  23 - 1 ,  23 - 2 ,  23 - 3 ,  23 - 4 . However, it will be understood that the relative orientation of the resilient isolator element  23  is changed depending on its application. The orientation of the isolator elements  23 - 1 ,  23 - 2 ,  23 - 3  affect centre of mass constraints under vehicle dynamic behaviour. When implemented as the first and second resilient isolator elements  23 - 1 ,  23 - 2 , the resilient isolator element  23  is disposed in a XZ plane such that the axial dynamic stiffness along the X-axis is less than or equal to 60 N/mm (up to an excitation frequency of 180 Hz). When implemented as the third and fourth resilient isolator elements  23 - 3 ,  23 - 4 , the resilient isolator element  23  is disposed in a YZ plane such that the axial dynamic stiffness along the Y-axis is less than or equal to 60 N/mm (up to an excitation frequency of 180 Hz). 
     At least in certain embodiments of the present invention the vehicle exhaust assembly  1  can result in a mass reduction of approximately 50% (10-15 kg). Moreover, vehicle exhaust assembly  1  can remove the need for structural vibration palliatives to address noise, vibration and harshness (NVH). 
     The exhaust system  3  has been described as being made of stainless steel. In certain embodiments, stainless steel, such as Inconel, could be used to fabricate the exhaust system  3 . It will be appreciated that titanium or other metals could be used in place of stainless steel. 
     It will be appreciated that changes and modifications can be made to the vehicle exhaust assembly  1  described herein without departing from the scope of the present application. For example, the diameters of the various conduits could be changed from the values specified herein. Likewise, the gauge thickness of the material used to form the conduits could be varied from the values specified herein. Furthermore, it will be appreciated that the geometry of the vehicle exhaust assembly  1  could be modified, for example to suit different vehicles and different powertrain configurations. 
     The exhaust system  3  has been described as comprising one exhaust decoupler  8  disposed in the inlet section  5 . In alternate arrangements, the exhaust system  3  can comprise more than one exhaust decoupler  8 . The inlet section  5  could comprise more than one exhaust decoupler  8  disposed in a series arrangement in the inlet conduit  9 . Alternatively, the inlet section  5  can comprise a plurality of inlet conduits  9 . One or more exhaust decoupler  8  can be disposed in each of said inlet conduits  9 . Alternatively, or in addition, the intermediate section  6  can comprise one or more exhaust decoupler. For example, the first and second intermediate conduits  14 - 1 ,  14 - 2  can each comprise one or more exhaust decoupler. An exhaust decoupler can be disposed between the silencer  13  and the first and second intermediate conduits  14 - 1 ,  14 - 2 ; and/or between the first and second intermediate conduits  14 - 1 ,  14 - 2  and the first and second exhaust silencers  18 - 1 ,  18 - 2 . Alternatively, or in addition, the outlet section  7  can comprise one or more exhaust decoupler.