WO1996010687A1

WO1996010687A1 - Resonator

Info

Publication number: WO1996010687A1
Application number: PCT/US1995/013062
Authority: WO
Inventors: Robert O. Willis; Rondal W. Turnbow
Original assignee: Arvin Industries, Inc.
Priority date: 1994-09-30
Filing date: 1995-10-02
Publication date: 1996-04-11

Abstract

A resonator (10) is provided for use in an automotive exhaust system. The resonator (10) includes a rigid outer tube (12) and a rigid inner tube (14) extending along a longitudinal axis (15) through the outer tube (12). The outer tube (12) includes an inlet end (28) and an outlet end (30). The inner tube (14) includes an inlet end (32) fixed to the inlet end (28) of the outer tube (12), an outlet end (34) fixed to the outlet end (30) of the outer tube (12), and at least one corrugation (36) situated between the inlet end (32) and the outlet end (34) to allow expansion and contraction axially along the longitudinal axis (15) relative to the outer tube (12).

Description

RESONATOR

Background and Summary of the Invention

The present invention relates to a noise attenuation device, and particularly to a resonator provided in an automotive exhaust system for damping the noise and vibration of engine exhaust. More particularly, the present invention relates to a resonator that includes an inner tube situated within an outer tube.

Automotive engine exhaust is noisy and must be quieted in some manner to satisfy automobile users. Typically, a muffler or resonator is included in an engine exhaust system for this purpose. A conventional muffler generally includes a series of pipes and chambers inside a housing and is designed to quiet engine exhaust passing therethrough in route to the tail pipe. A resonator is generally a smaller unit used for narrow band tuning. A resonator of the type used in an automotive exhaust system typically includes an outer tube and an inner tube extending through the outer tube. Exhaust gas from an automobile engine passes through the inner tube of the resonator as it travels through the automotive exhaust system from the engine to the tail pipe. The inner tube typically includes some means for the exhaust gas to pass from an interior region in the inner tube into a space around the inner tube and between the inner tube and outer tube to attenuate the noise produced by the exhaust gas. Typically, the inner tube is formed to include holes, perforations, or louvers for this reason.

The exhaust gas travelling through a resonator typically reaches high temperatures (e.g., above 1500°F (815^βC) ) . One problem associated with conventional resonators is that unwanted noise is created when thermal forces generated by the hot exhaust gas cause thermal expansion and contraction of the inner tube relative to the outer tube. This excess noise is often called "ping" and is extremely undesirable.

Thermal expansion and contraction occurs when (1) inner and outer tubes in a resonator are cyclically heated and cooled between an ambient outside temperature and the high temperature of the exhaust gas, and (2) when the inner and outer tubes have different heating and cooling rates. Typically, the inner tube expands relative to the outer tube when the automobile engine begins to operate and the exhaust system is heating up and then contracts relative to the outer tube when the automobile engine is turned off and the exhaust system is cooling down.

In a conventional resonator one end of a metal inner tube is attached to a first end of a metal outer tube and an opposite end of the inner tube engages and is free to move on a second end of the outer tube while the inner tube is positioned to lie in an interior region defined by the outer tube. Upon expansion or contraction of such an inner tube relative to its companion outer tube there is metal-on-metal contact between the opposite end of the inner tube and the second end of the outer tube. This metal-on-metal contact creates an undesirable, loud "pinging" noise. When the outside ambient temperature is very cool, such as during the winter months, a pinging noise generated by a conventional resonator sounds to many people like a firing machine gun. Ping is a sound created by metal rubbing against metal when an inner tube is in movable contact with an outer tube and no satisfactory means is provided for differential expansion or no buffer material is provided to separate such rubbing metal surfaces.

Another type of conventional resonator fixes a metal inner tube to a metal outer tube at an inlet and places a "spacing ring" between the inner tube and the outer tube at an opposite outlet end. This spacing ring serves as a buffer between the metal inner tube and the metal outer tube. See, for example, U.S. Patent No. 5,056,832 to Nagagawa et al. The addition of such a spacing ring leads to additional expense to produce and install the ring as well as to size the inner and outer tubes to accommodate the ring.

It has also been observed that some known resonators are made to include slots or convex dimples or made of aluminum material in an effort to reduce the ping problem. Nevertheless, consumers would welcome a resonator that operated without creating any noticeable pinging noise.

It would therefore be advantageous to provide a resonator that eliminated the pinging noise problem created by metal-on-metal contact between its inner and outer tubes and had a minimum number of parts. A resonator that solves the pinging problem with a minimal number of parts reduces the cost of manufacturing and assembly time required to make the resonator. According to the present invention, a resonator is provided to attenuate vehicle exhaust noise. The resonator includes an outer tube and an inner tube extending along a longitudinal axis through the outer tube. The inner tube includes an inlet end appended to an inlet end of the outer tube and an outlet end appended to an outlet end of the outer tube. In addition, the inner tube is formed to include at least one extensible section such as a set of corrugations situated between its inlet and outlet ends. During heating or cooling of the resonator, the at least one set of corrugations expands or contracts axially along the longitudinal axis of the inner tube to allow expansion or contraction of the inner tube relative to the outer tube.

Illustratively, because the metal inner tube is fixed at each end to the metal outer tube, there is no metal-on-metal rubbing or moving contact between one end of the metal inner tube and an adjacent end of the metal outer tube when the inner tube expands or contracts relative to the outer tube during periodic exposure to hot engine exhaust gas. The expansion and contraction of the corrugations formed in the inner tube does not create metal-on-metal rubbing or moving contact. Therefore, the pinging noise commonly associated with conventional resonators is minimized, retarded, or eliminated. In a preferred embodiment of the present invention, the inner tube is formed to include a first set of corrugations adjacent to the inlet end and a second set of corrugations adjacent to the outlet end. The first and second sets of corrugations each include four individual corrugations. The inner tube is also formed to include an aperture through which a tuning throat extends. Exhaust gas passes through the tuning throat from an interior region of the inner tube into an annular space around the inner tube and between the inner tube and outer tube to attenuate noise produced by the exhaust gas.

In another preferred embodiment of the present invention, the inner tube is formed to include louvers adjacent to the inlet end and a set of corrugations adjacent to the outlet end. The set of corrugations includes four individual corrugations. A cylindrical

"overlap" tuner is appended to an exterior surface of the inner tube adjacent to the inlet end of the inner tube so that the overlap tuner covers or overlaps the louvers. Exhaust gas passes from an interior region of the inner tube into a longitudinally-extending passageway formed around the inner tube and between the cylindrical overlap tuner and inner tube. The exhaust gas then exits from the longitudinally-extending passageway into an annular space around the inner tube and between the inner tube and outer tube to attenuate noise produced by the exhaust gas. In yet another preferred embodiment of the present invention, the inner tube is formed to include a first set of corrugations adjacent to the inlet end, a second set of corrugations adjacent to the outlet end, and perforations between the inlet end and outlet end. The first and second sets of corrugations each include two individual corrugations. Exhaust gas passes through the perforations from an interior region of the inner tube and into an annular passageway formed around the inner tube between the outer tube and inner tube. Illustratively, baffling or packing material such as stainless steel wool is placed next to the perforations in the annular passageway in the annular space between the first and second sets of corrugations. Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.

Brief Description of the Drawings

The detailed description particularly refers to the accompanying figures in which:

Fig. 1 is a sectional view of a preferred embodiment of a resonator used in a vehicle exhaust system showing an outer tube and an inner tube positioned to lie inside of the outer tube and fixed to opposite ends of the outer tube, the inner tube being formed to include two spaced-apart sets of corrugations to permit the inner tube to expand relative to the outer tube even though each end of the inner tube is welded to one end of the surrounding outer tube;

Fig. 2 is a sectional view of another embodiment of the present invention showing a resonator having an outer tube, an inner tube positioned to lie inside of the outer tube and fixed to opposite ends of the outer tube, the inner tube being formed to include a set of corrugations adjacent to its outlet end and louvers adjacent to its inlet end, and an overlap tuner fixed to the inner tube and arranged to surround and cover the louvers formed in the inner tube; and

Fig. 3 is a sectional view of yet another embodiment of the present invention showing a resonator having an outer tube, a perforated inner tube positioned to lie inside of the outer tube and fixed to opposite ends of the outer tube, the inner tube being formed to include two spaced-apart sets of corrugations, and packing material situated in an annular gap or passageway provided around the inner tube and between the inner tube and outer tube.

Detailed Description of the Drawings

A resonator 10 according to a first embodiment of the present invention is shown in Fig. 1. The resonator 10 is part of an automotive exhaust system that takes automotive exhaust gas from an engine (not shown) and transfers it to a tail pipe (not shown) at the back end of an automobile so that the exhaust gas can be quietly exhausted into the atmosphere. The automotive exhaust system is a high temperature environment in which there are many tubular metal elements or pipes joined together. Differences in heating and cooling rates of the metal elements or pipes can result in these elements expanding and contracting relative to one another. The expansion and contraction of these elements often creates a loud pinging noise due to metal-on-metal rubbing or moving contact between the elements.

The resonator 10 includes an outer tube 12, an inner tube or passage tube 14, a longitudinal axis 15, and a tuning throat 17 as shown in Fig. 1. The outer tube 12 includes a shell 16, first and second necks 18, 20, first and second throats 22, 24, central section 26, inlet end 28, and outlet end 30. The shell 16 is a tubular element that extends along the central section 26 of the outer tube 12 between inlet and outlet ends 28, 30. At the inlet end 28, the outer tube 12 narrows in cross-section through the first neck 18 to the first throat 22 and at the outlet end 30, the outer tube 12 narrows in cross-section through the second neck 20 to the second throat 24. The first throat 22 is typically connected to the automotive exhaust system to admit exhaust gas into the resonator 10 and the second throat 24 is typically connected to the automotive exhaust system to discharge exhaust gas out of the resonator 10.

The inner tube 14 includes an inlet end 32 appended to the inlet end 28 of the outer tube 12, an outlet end 34 appended to the outlet end 30 of the outer tube 12, a central section 35, and an interior region 37 as shown in Fig. 1. The inner tube 14 is formed to include first and second sets of corrugations 36, 38 spaced apart from each other and situated between the inlet end 32 and outlet end 34. The first and second sets of corrugations 36, 38 are formed from a series of ridges 39 and grooves 41 that are arranged to lie in concentric relation about longitudinal axis 15 as shown in, for example, Fig. 1. The ridges 39 are equal in diameter and the grooves 41 are equal in diameter.

The first and second sets of corrugations 36, 38 form separate, axially spaced-apart extensible sections that permit the inner tube 14 to expand and contract axially along the longitudinal axis 15 when (1) the resonator 10 is heating up or cooling down and (2) the inner tube 14 and outer tube 12 are expanding or contracting relative to one another at different rates. Because the inner tube 14 is appended (e.g., welded) to the outer tube 12 at both the inlet and outlet ends 28, 30, the inlet and outlet ends 32, 34 of the inner tube 14 are unable to move relative to the outer tube 12 and thus there is no metal-on-metal rubbing or moving contact between the ends of inner tube 14 and outer tube 12. Eliminating the metal-on-metal rubbing or moving contact between the inner tube 14 and outer tube 12 minimizes, retards, or eliminates the pinging noise commonly associated with conventional resonators during warm-up or cool-down phases of the engine exhaust system.

The inner tube 14 is formed to include an aperture 42 in the central section 35 through which the tuning throat 17 extends as shown, for example, in Fig. 1. The tuning throat 42 is a cylindrical hollow tube that permits the exhaust gas to travel from the interior region 37 of the inner tube 14 into a longitudinal extending annular space 44 around the inner tube 14 and between the inner tube 14 and outer tube 12. The noise produced by the exhaust gas is attenuated when the exhaust gas travels into the space 44.

A second embodiment of the present invention is shown as resonator 50 in Fig. 2. Resonator 50 includes a similar outer tube 12, inner tube 52, and a cylindrical overlap tuner 54 appended to an exterior surface of inner tube 52. The inner tube 52 includes an inlet end 56 fixed to the inlet end 28 of outer tube 12, an outlet end 58 fixed to the outlet end 30 of the outer tube 12, a central section 55, and an interior region 57. The inner tube 52 is formed to include a set of corrugations 60 formed from a series of ridges 59 and grooves 61 that are positioned to lie in concentric relation about longitudinal axis 15 and situated between the inlet end 56 and the outlet end 58.

The ridges 39 are equal in diameter and the grooves 41 are also equal in diameter. The set of corrugations 60 acts similarly to the first and second corrugations 36, 38 in resonator 10 to form extensible sections that allow the inner tube 52 to contract or expand axially relative to the outer tube 12 when the resonator 50 is heating up or cooling down.

The inner tube 52 is formed to include longitudinally-extending rows of louvers 62 adjacent to the inlet end 56 such that the central section 55 is between the louvers 62 and the set of corrugations 60. The overlap tuner 54 is appended to the inner tube 52 to overlie and surround the portion of the inner tube 52 having the louvers 62 and form a longitudinally-extending annular passageway 67 around the inner tube 52 and between the inner tube 52 and the overlap tuner 54.

The overlap tuner 54 includes first end 63, second end 65, throat 66 appended to the inner tube 52 adjacent to the inlet end 56, neck 68, and longitudinally-extending shell 70 having circumferentially spaced-apart indentations 72 at the second end 65. The indentations 72 are either press fit or spot welded to the inner tube 52 to prevent the overlap tuner 54 from rattling when the automobile engine is operating. Exhaust gas passes from the interior region 57 of the inner tube 52 through the louvers 62 and into the annular passageway 67. The passageway 67 includes an annular opening 69 that faces toward the set of corrugations 60. The exhaust gas is directed through the annular opening 69 and into the larger downstream annular space 64 around the inner tube 52 and between the inner tube 52 and outer tube 12 to attenuate the noise created by the exhaust gas.

A third embodiment of the present invention is shown as resonator 80 in Fig. 3. Resonator 80 includes a similar outer tube 12 and an inner tube 82. Inner tube 82 includes an inlet end 84 appended to the inlet end 28 of the outer tube 12, outlet end 86 appended to the outlet end 30 of the outer tube 12, central section 85 situated between the inlet end 84 and outlet end 86, interior region 87, and first and second sets of corrugations 88, 90 formed from a series of ridges 89 and grooves 91 that are position to lie in concentric relation about longitudinal axis 15 and situated between the inlet end 84 and outlet end 86. More specifically, the first set of corrugations 88 is situated adjacent to the inlet end 84 and the second set of corrugations 90 is situated adjacent to the outlet end 86. The ridges 89 have an equal diameter and the grooves 91 have an equal diameter. The central section 87 extends along the longitudinal axis 15 between the first and second sets of corrugations 88, 90. The first and second sets of corrugations 88, 90 form separate, axially spaced-apart extensible sections that act similarly to the set of corrugations 60 in resonator 50 and the first and second sets of corrugations 36, 38 in resonator 10 to permit the inner tube 82 to expand and contract axially relative to the outer tube 12.

Inner tube 82 is formed to include a cylindrical array of perforations 92 situated in the central section 87 and between the first and second sets of corrugations 88, 90. The perforations 92 permit the exhaust gas to pass out of the interior region 87 of the inner tube 82 and into a longitudinally extending annular space 94 around the inner tube 82 and between the inner tube 82 and outer tuber 12. Stainless steel wool or another suitable packing material 96 is placed in the gap 94 surrounding the perforations 92 to attenuate any noise produced as the exhaust gas travels through the perforations 92. The packing material 96 is situated longitudinally through the gap 94 between the first and second sets of corrugations 88, 90. The sets of corrugations 36, 38, 60, 88, 90 shown in Figs. 1-3 include different numbers of individual corrugations 98. For example, first and second set of corrugations 36, 38 shown in Fig. 1 and the set of corrugations 60 in Fig. 2 each include four individual corrugations 98 whereas first and second set of corrugations 88, 90 illustrated in Fig. 3 each include two individual corrugations 98. In alternative embodiments of the present invention, any number of sets of corrugations may be used and one or more individual corrugations within each set may be used.

As shown in the preferred embodiments of the present invention in Figs. 1-3, the inlet end 32, 56, 84 of the inner tube 14, 52, 82 is fixed within the first throat 22 of the outer tube 12 and the outlet end 34, 58, 86 of the inner tube 14, 52, 82 is fixed within the second throat 24 of the outer tube 12. In preferred embodiments, the upstream and outlet ends 32, 34, 56, 58, 84, 86 are welded within the first and second throats 22, 24 at locations 99 as shown in Figs. 1-3. In alternative embodiments of the present invention, any suitable means of fixing each of the inner tubes 14, 52, or 82 to a companion outer tube 12 may be used.

The sets of corrugations 36, 38, 60, 88, 90 permit the inner tube 14, 52, or 82 to expand and contract axially along the longitudinal axis 15 of the resonator 10, 50, 80 relative to the outer tube 12. The ability of the sets of corrugations 36, 38, 60, 88, 90 to expand and contract permit the inner tube 14, 52, or 82 to be appended to the outer tube 12 at both the inlet end 32, 56, or 84 and the outlet end 34, 58, or 86. By fixing the inner tube 14, 52, or 82 to the outer tube 12 at both ends 32, 34, 56, 58, 84, 86, there is no metal-on-metal contact when the inner tube 14, 52, or 82 and outer tube 12 expand and contract relative to each other. Therefore, the "pinging" noise commonly associated with conventional acoustical resonators during warm-up or cool down is minimized, retarded, or eliminated.

In the illustrated embodiments of the present invention, the noise created by the exhaust gas is attenuated by permitting the exhaust gas to travel into an annular space 44, 64, or 94 formed around the inner tube 14, 52, or 82 and between the inner tube 14, 52, or 82 and outer tube 12. In alternative embodiments, a Helmholtz resonator or similar device (not shown) may be positioned within the resonator to assist in exhaust gas noise attenuation.

Although this invention has been described in detail with reference to certain embodiments, variations and modifications exist within the scope and spirit of the invention as described and as defined in the following claims.

Claims

CLAIMS :

1. A resonator for use in an automotive exhaust system, the resonator comprising a rigid outer tube having an inlet end and an outlet end, and a rigid inner tube extending along a longitudinal axis through the outer tube from the inlet end to the outlet end of the outer tube, the inner tube including an inlet end fixed to the inlet end of the outer tube, an outlet end fixed to the outlet end of the outer tube, an interior region, and at least one corrugation situated between the inlet end and the outlet end.

2. The resonator of claim 1, wherein the at least one corrugation is configured to expand and contract axially along the longitudinal axis relative to the outer tube.

3. The resonator of claim l, wherein the inlet end of the outer tube includes a first throat and the outlet end of the outer tube includes a second throat, the first and second throats include means for communicating with the automotive exhaust system, the inner tube is appended to the outer tube within the first and second throats, and the at least one corrugation is situated between the first and second throats.

4. The resonator of claim 3, wherein the inner tube further includes another corrugation spaced apart from the at least one corrugation.

5. The resonator of claim 1, wherein the inner tube is formed to include a first set of corrugations adjacent to the inlet end, a second set of corrugations adjacent to the outlet end, and a central section extending along the longitudinal axis between the first and second sets of corrugations.

6. The resonator of claim 5, wherein the first and second sets of corrugations are formed from a series of ridges and grooves concentric about the longitudinal axis, the ridges have an equal diameter and the grooves have an equal diameter.

7. The resonator of claim 5, wherein the inner tube is formed to include an aperture in the central section through which a tuning throat extends to permit exhaust gas to pass from the interior region of the inner tube through the tuning throat and into a longitudinally extending annular space around the inner tube and between the inner tube and outer tube, the tuning throat is positioned along the longitudinal axis between the first and second sets of corrugations.

8. The resonator of claim 5, wherein the first and second sets of corrugations each include four individual corrugations.

9. The resonator of claim 5, wherein the inner tube is formed to include a plurality of apertures in the central section to permit exhaust gas to pass from the interior region of the inner tube through the apertures and into a longitudinally extending annular space around the inner tube and between the inner tube and outer tube, the apertures are situated along the longitudinal axis between the first and second sets of corrugations.

10. The resonator of claim 9, further comprising packing material situated in the annular space around the central section of the inner tube, between the outer tube and inner tube, and between the first and second sets of corrugations.

11. The resonator of claim 5, wherein the first and second sets of corrugations each include two individual corrugations.

12. The resonator of claim 1, wherein the inner tube is formed to include louvers adjacent to the inlet end, a set of corrugations adjacent to the outlet end, and a central section extending along the longitudinal axis between the set of corrugations and the louvers.

13. The resonator of claim 12, further including an overlap tuner appended to the inner tube and arranged to cover the louvers and the set of corrugations is situated along the longitudinal axis between the overlap tuner and the outlet end.

14. The inner tube of claim 13, wherein an annular passageway is formed between the inner tube and overlap tuner to permit airflow to pass from the interior region, into the annular passageway, and into a larger downstream annular space between the inner tube and outer tube, the airflow is directed through the passageway toward the set of corrugations.

15. The resonator of claim 12, wherein the set of corrugations includes four individual corrugations.

16. A resonator for use in an automotive exhaust system, the resonator comprising an outer tube having an inlet and outlet end, and an inner tube extending through the outer tube along a longitudinal axis from the inlet end to the outlet end of the outer tube, the inner tube including an inlet end fixed to the inlet end of the outer tube, an outlet end fixed to the outlet end of the outer tube, an interior region, and extensible means for expanding and contracting relative to the outer tube so that the inner tube is able to vary in length along the longitudinal axis to compensate for differences in heating and cooling rates of the inner and outer tube, the extensible means being situated between the inlet end and the outlet end.

17. The resonator of claim 16, wherein the inner tube and outer tube are rigid.

18. The resonator of claim 16, wherein the inner tube is formed to include an array of louvers and the extensible means is situated along the longitudinal axis between the louvers and the outlet end.

19. The resonator of claim 18, wherein a longitudinally-extending shell is appended to the inner tube adjacent to the inlet end and is arranged to overlie and cover the louvers, an annular passageway is formed in the space around the inner tube and between the inner tube and the longitudinally-extending shell, the annular passageway way includes an annular opening facing toward the extensible means.

20. The resonator of claim 18, wherein the inner tube further includes a central section situated along the longitudinal axis between the louvers and the extensible means, the extensible means is situated along the longitudinal axis between the outlet end and the louvers.

21. The resonator of claim 16, wherein the extensible means includes a first extensible section situated adjacent to the inlet end and a second extensible section situated adjacent to the outlet end.

22. The resonator of claim 21, wherein the inner tube includes a central section situated along the longitudinal axis between the first and second extensible sections, the central section is formed to include an array of apertures to permit airflow out of the interior region of the inner tube and into a longitudinally-extending annular space around the inner tube and between the inner tube and outer tube.

23. The resonator of claim 21, wherein the inner tube is formed to include at least one aperture situated along the longitudinal axis between the first and second extensible sections.

24. The resonator of claim 23, further including a packing material situated in an annular space around the inner tube and between the inner tube and outer tube to cover the at least one aperture, the first extensible section is situated between the inlet end and the packing material and the second extensible section is situated between the outlet end and the packing material.

25. The resonator of claim 23, further including a cylindrical hollow tube extending through the at least one aperture to permit airflow to pass from the interior region of the inner tube into an annular space around the inner tube and between the inner tube and outer tube, the first extensible section is situated along the longitudinal axis between the cylindrical hollow tube and the inlet end and the second extensible section is along the longitudinal axis between the cylindrical hollow tube and the outlet end.

26. An inner tube for use in a large differential temperature environment where the inner tube extends along a longitudinal axis through an outer tube, the inner and outer tubes expand and contract relative to one another as the temperature changes, the inner tube comprising an outlet end, an inlet end, an interior region, an extensible section situated along the longitudinal axis between the inlet end and the outlet end to expand and contract axially along the longitudinal axis relative to the outer tube, and means for appending the inlet end and outlet end to the outer tube so that the outer tube covers the outlet end, inlet end, and extensible section.

27. The inner tube of claim 26, further including a central section situated along the longitudinal axis between the inlet end and outlet end and a second extensible section spaced apart from the first extensible section.

28. The inner tube of claim 27, wherein the first extensible section is situated between the inlet end and the central section and the second extensible section is situated between the outlet end and the central section.

29. The inner tube of claim 27, wherein the extensible section is formed from a series of parallel ridges and grooves concentric about the longitudinal axis.

30. The inner tube of claim 29, wherein the ridges have an equal diameter and the grooves have an equal diameter.

31. The inner tube of claim 26, further including means for permitting airflow to pass through the inner tube and into a longitudinally extending annular space around the inner tube and between the inner tube and outer tube, the airflow permitting means situated along the longitudinal axis between the first and second extensible sections.

32. The inner tube of claim 31, wherein the airflow permitting means includes a cylindrical array of perforations and a packing material is situated in the annular space between the inner tube and outer tube and longitudinally between the first and second extensible sections.

33. The inner tube of claim 31, wherein the airflow permitting means includes an aperture formed in the inner tube and a cylindrical hollow tube extending through the aperture, the cylindrical hollow tube is situated between the first and second extensible sections.

34. The inner tube of claim 26, formed to include longitudinally-extending rows of louvers adjacent to the inlet end and further including a longitudinally-extending shell overlying and surrounding the louvers, the extensible section is situated between the longitudinally-extending shell and the outlet end.

35. The inner tube of claim 34, further including a central section extending along the longitudinal axis between the louvers and the extensible section.

36. The inner tube of claim 35, wherein the extensible section is situated along the longitudinal axis between the central section and the outlet end.