Patent Publication Number: US-11377988-B2

Title: Tail pipe

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Japanese Patent Application No. 2019-018056 filed on Feb. 4, 2019 with the Japan Patent Office, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a tail pipe. 
     In an exhaust system of an internal combustion engine, a tail pipe is known that is enlarged in diameter toward an exhaust port and that has grooves spirally formed of concavities and convexities on a peripheral wall for the purpose of increasing exhaust efficiency (see Japanese Utility Model Registration No. 3021165). 
     In this tail pipe, exhaust flow is twisted by the grooves, and a flow velocity of the exhaust flow is thereby increased. This results in improving the exhaust efficiency. 
     SUMMARY 
     In tail pipes of exhaust systems, noise is generated by air flow produced when an exhaust gas is discharged into the atmosphere. In the above-described tail pipe, the exhaust efficiency is improved by the above-described action, but noise reduction effect cannot be expected. 
     In one aspect of the present disclosure, it is desirable to provide a tail pipe in which a silencing effect at a discharge port is obtained. 
     One aspect of the present disclosure is a tail pipe comprising: an inner tube comprising a discharge port configured such that an exhaust gas is discharged therefrom; an outer tube arranged so as to form a space between the outer tube and the inner tube by surrounding an outer peripheral surface of the inner tube, an upstream end of the outer tube in a flow direction of the exhaust gas being closed; and at least one communication hole allowing communication between an interior of the inner tube and the space. 
     Such a configuration allows the space inside the outer tube communicating with the interior of the inner tube to function as a resonance chamber. This results in obtaining a silencing effect at the discharge port due to a resonance effect in the space. 
     In one aspect of the present disclosure, the inner tube may comprise an enlarged diameter portion enlarged in diameter toward the discharge port. In such a configuration, a flow velocity of the exhaust gas is reduced by the enlarged diameter portion. This facilitates rapid and uniform mixture of the exhaust gas into the atmosphere, resulting in reducing air flow noise. 
     In one aspect of the present disclosure, the enlarged diameter portion may comprise a gently enlarged portion having a first taper angle, and a sharply enlarged portion having a second taper angle larger than the first taper angle. In such a configuration, the flow velocity of the exhaust gas is changed in a circumferential direction of the tail pipe by the sharply enlarged portion and the gently enlarged portion. Specifically, the exhaust gas discharged along the gently enlarged portion is likely to spread more outward in a radial direction than the exhaust gas discharged along the sharply enlarged portion. Thus, flow velocity distribution of the exhaust gas discharged from the discharge port exhibits an elliptical shape with a portion along the gently enlarged portion as a major axis. Consequently, an area where the exhaust gas contacts the atmosphere is increased, thus facilitating rapid and uniform mixture of the exhaust gas into the atmosphere. This results in facilitating reduction of air flow noise. 
     In one aspect of the present disclosure, the at least one communication hole may be arranged in the sharply enlarged portion. Such a configuration makes it unlikely for the exhaust gas to hit an edge portion of the at least one communication hole, thus reducing separation of the exhaust gas from an inner circumferential surface of the inner tube. Consequently, turbulent flow of the exhaust gas is unlikely to be generated on the inner circumferential surface of the inner tube, resulting in reducing air flow noise (i.e., whistling noise) to be generated when the exhaust gas passes through the at least one communication hole. 
     In one aspect of the present disclosure, the at least one communication hole may be shaped such that a width thereof in a circumferential direction of the inner tube changes along the flow direction of the exhaust gas. Such a configuration reduces an area where the exhaust gas hits the edge portion of the at least one communication hole, as compared with a communication hole with unchanged width in the circumferential direction. As a result, separation of the exhaust gas from the inner circumferential surface of the inner tube is reduced, thus inhibiting generation of air flow noise at the at least one communication hole. 
     In one aspect of the present disclosure, a downstream end of the outer tube in the flow direction of the exhaust gas may be closed. Such a configuration allows the space inside the outer tube to be an enclosed space, thus forming a Helmholtz resonator. This results in improving the silencing effect at the discharge port. 
     In one aspect of the present disclosure, a downstream end of the outer tube in the flow direction of the exhaust gas may be open so as to allow communication between the space and an outside of the outer tube. In such a configuration, the exhaust gas with a higher velocity discharged from the inner tube is covered by the exhaust gas with a lower velocity discharged from the outer tube, and the atmosphere exists further therearound. This causes gradual decrease in the flow velocity of the exhaust gas flowing on the outer side, thus lowering likelihood of generation of turbulent flow. As a result, generation of air flow noise due to the turbulent flow can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments of the present disclosure will be described below with reference to the accompanying drawings, in which: 
         FIG. 1A  is a schematic plan view of a tail pipe according to an embodiment, and  FIG. 1B  is a schematic side view of the tail pipe of  FIG. 1A ; 
         FIG. 2  is a schematic partial sectional view taken along line II-II of  FIG. 1A ; 
         FIG. 3  is a schematic diagram showing one example of a shape of a communication hole; 
         FIG. 4  is a schematic partial sectional view of a tail pipe according to an embodiment different from that of  FIG. 1A ; 
         FIG. 5  is a schematic plan view of a tail pipe according to an embodiment different from those of  FIGS. 1A and 4 ; and 
         FIG. 6  is a schematic plan view of a tail pipe according to an embodiment different from those of  FIGS. 1A, 4, and 5 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     1. First Embodiment 
     1-1. Configuration 
     A tail pipe  1  shown in  FIGS. 1A and 1B  is provided to an end of an exhaust gas flow path of an internal combustion engine. The tail pipe  1  discharges, into the atmosphere, an exhaust gas discharged from the internal combustion engine. The tail pipe  1  comprises an inner tube  2 , an outer tube  3 , and communication holes  4 A and  4 B. 
     The internal combustion engine to which the tail pipe  1  is applied is not limited in particular. Examples of such an internal combustion engine may include those used for drive or power generation in transport equipment, such as an automobile, a railroad car, a ship, and construction equipment, power generation facilities, and so on. 
     &lt;Inner Tube&gt; 
     The inner tube  2  is a metal pipe through which an exhaust gas G passes. The inner tube  2  comprises a supply port  21  through which the exhaust gas G is supplied, a discharge port  22  through which the exhaust gas G passed through the inner tube  2  is discharged, and an enlarged diameter portion  23  enlarged in diameter toward the discharge port  22 . 
     The enlarged diameter portion  23  comprises a gently enlarged portion  24  having a first taper angle, and two sharply enlarged portions  25 A and  25 B each having a second taper angle larger than the first taper angle. The enlarged diameter portion  23  may comprise one sharply enlarged portion, or three or more sharply enlarged portions. The first taper angle is an angle between a surface of the gently enlarged portion  24  and a central axis of the inner tube  2 . The second taper angle is an angle between a surface of each of the sharply enlarged portions  25 A and  25 B and the central axis of the inner tube  2 . The first taper angle is an acute angle. The second taper angle is an acute angle or a right angle, and is preferably an acute angle. 
     The gently enlarged portion  24  is a portion enlarged in diameter at the constant first taper angle in a region covered by the outer tube  3  to be described later. The gently enlarged portion  24  may have a shape gradually increased in a degree of curve toward the discharge port  22 , namely a flare shape. The gently enlarged portion  24  is provided, in a circumferential direction of the inner tube  2 , throughout a region except where the sharply enlarged portions  25 A and  25 B and straight portions  26 A and  26 B to be described later are formed. 
     The sharply enlarged portions  25 A and  25 B are each arranged in a part of the inner tube  2  in the circumferential direction thereof. The sharply enlarged portions  25 A and  25 B do not overlap with the gently enlarged portion  24  when viewed along an axial direction of the inner tube  2 . In other words, the gently enlarged portion  24  is not formed upstream and downstream of the sharply enlarged portions  25 A and  25 B. 
     In the present embodiment, the sharply enlarged portions  25 A and  25 B are each arranged in a position overlapping with the gently enlarged portion  24  when viewed along the circumferential direction of the inner tube  2 . Further, the sharply enlarged portions  25 A and  25 B are each arranged such that an upstream end thereof (i.e., an end where enlargement in diameter starts) coincides in position with an upstream end of the gently enlarged portion  24  in the axial direction of the inner tube  2 . 
     The sharply enlarged portions  25 A and  25 B each comprise, on a downstream side thereof, the straight portions  26 A and  26 B, respectively, having a constant inside diameter. A width of each of the straight portions  26 A and  26 B in the circumferential direction of the inner tube  2  becomes gradually smaller toward the discharge port  22 . However, the width of each of the straight portions  26 A and  26 B in the circumferential direction of the inner tube  2  may be constant. 
     In the present embodiment, the sharply enlarged portions  25 A and  25 B are arranged in positions opposite each other in a radial direction of the inner tube  2  (i.e., positions spaced 180° apart in the circumferential direction of the inner tube  2 ). However, the sharply enlarged portions  25 A and  25 B do not necessarily have to be arranged in such relative positions. 
     &lt;Outer Tube&gt; 
     The outer tube  3  is a metal pipe arranged outside the inner tube  2  so as to surround an outer peripheral surface of the inner tube  2 . 
     The inside diameter of the outer tube  3  excluding an upstream end  31  may be more than or equal to 1.15 times and less than or equal to 1.5 times larger than the outside diameter of the inner tube  2  excluding the enlarged diameter portion  23  (i.e., than the outside diameter of a portion having a constant outside diameter). 
     As shown in  FIG. 2 , the outer tube  3  is arranged so as to form a space S between the outer tube  3  and the inner tube  2  by surrounding the outer peripheral surface of the inner tube  2 . In the outer tube  3 , the upstream end  31  and a downstream end  32  in a flow direction of the exhaust gas G are both closed. 
     Specifically, the upstream end  31  of the outer tube  3  is reduced in diameter toward an outside thereof in an axial direction. The upstream end  31  is fixed to a portion of the inner tube  2  located upstream of the enlarged diameter portion  23 , circumferentially throughout by welding, for example. 
     The downstream end  32  of the outer tube  3  is fixed to downstream ends of the gently enlarged portion  24  and the straight portions  26 A and  26 B of the inner tube  2  (i.e., to ends forming the discharge port  22 ), circumferentially throughout by welding, for example. The outer tube  3  contacts outer peripheral surfaces of the straight portions  26 A and  26 B of the inner tube  2 . The outer tube  3  excluding the upstream end  31  has a constant diameter. 
     A shape of a section of the outer tube  3  perpendicular to an axial direction thereof does not have to be a perfect circle. In the present embodiment, an opening of the outer tube  3  at the downstream end  32  coincides in position with the discharge port  22  of the inner tube  2  in the axial direction of the inner tube  2 . However, the opening of the outer tube  3  at the downstream end  32  may be located more outside in the axial direction of the inner tube  2  than the discharge port  22  of the inner tube  2 . In other words, the outer tube  3  may protrude outside of the inner tube  2  in the axial direction thereof. 
     From the viewpoint of design, the inner tube  2  at the discharge port  22  and the outer tube  3  at the downstream end  32  may be inclined with respect to the radial direction of the inner tube  2 . In other words, the downstream ends of the inner tube  2  and the outer tube  3  may each have a cut surface inclined with respect to a plane perpendicular to the central axis of the inner tube  2 . 
     &lt;Communication Hole&gt; 
     The communication holes  4 A and  4 B each allow communication between an interior of the inner tube  2  and the space S. In the present embodiment, the sharply enlarged portions  25 A and  25 B each contain a single hole, namely the communication holes  4 A and  4 B, respectively. However, the sharply enlarged portions  25 A and  25 B may each contain two or more communication holes as long as a silencing effect for a target frequency is obtained. 
     In the present embodiment, the communication holes  4 A and  4 B are not arranged in any portion of the inner tube  2  other than the sharply enlarged portions  25 A and  25 B. 
     Shapes of the communication holes  4 A and  4 B each may be an ellipse, a polygon, or the like, instead of the shown perfect circle. Further, the communication holes  4 A and  4 B may be shaped such that a width thereof in the circumferential direction of the inner tube  2  changes along the flow direction of the exhaust gas G. This reduces an area where the exhaust gas G hits an edge portion of each of the communication holes  4 A and  4 B, as compared with the communication holes  4 A and  4 B with unchanged width in the circumferential direction. As a result, separation of the exhaust gas G from an inner circumferential surface of the inner tube  2  is reduced, thus inhibiting generation of air flow noise at the communication holes  4 A and  4 B. Examples of such a shape may include a teardrop shape shown in  FIG. 3 , as well as a rhombus and an ellipse. 
     A flange or a louver protruding inward or outward of the inner tube  2  may be provided around the communication holes  4 A and  4 B. In other words, the communication holes  4 A and  4 B may be drilled by processing such as burring, and cutting to raise. Sizes of the communication holes  4 A and  4 B may be designed as appropriate. 
     1-2. Actions 
     In the tail pipe  1 , the space S communicating with the interior of the inner tube  2  through the communication holes  4 A and  4 B forms a resonance chamber in the vicinity of the discharge port  22  of the inner tube  2 . This results in obtaining a silencing effect at the discharge port  22 . 
     Further, a flow velocity of the exhaust gas G is reduced by the enlarged diameter portion  23 , and flow layers of the exhaust gas G having different flow velocities in the circumferential direction of the inner tube  2  are formed by the gently enlarged portion  24  and the sharply enlarged portions  25 A and  25 B. 
     These flow layers allow the exhaust gas G discharged from the discharge port  22  into the atmosphere to be assimilated and mixed into the atmosphere relatively rapidly. Thus, generation of turbulent flow and/or vortex is inhibited at the discharge port  22 . 
     1-3. Effects 
     The embodiment detailed above produces the following effects. 
     (1a) The space S inside the outer tube  3 , communicating with the interior of the inner tube  2 , functions as the resonance chamber. This results in obtaining the silencing effect at the discharge port  22  due to a resonance effect in the space S. 
     (1b) The flow velocity of the exhaust gas G is reduced by the enlarged diameter portion  23  provided to the inner tube  2 . This facilitates rapid and uniform mixture of the exhaust gas G into the atmosphere, resulting in reducing air flow noise. 
     (1c) The flow velocity of the exhaust gas G is changed in a circumferential direction of the tail pipe  1  by the sharply enlarged portions  25 A and  25 B and the gently enlarged portion  24 . Specifically, the exhaust gas G discharged along the gently enlarged portion  24  is likely to spread more outward in the radial direction than the exhaust gas G discharged along the sharply enlarged portions  25 A and  25 B. Thus, flow velocity distribution of the exhaust gas G discharged from the discharge port  22  exhibits an elliptical shape with a portion along the gently enlarged portion  24  as a major axis. Consequently, an area where the exhaust gas G contacts the atmosphere is increased, thus facilitating rapid and uniform mixture of the exhaust gas G into the atmosphere. This results in facilitating reduction of air flow noise. 
     (1d) The communication holes  4 A and  4 B are arranged in the sharply enlarged portions  25 A and  25 B, respectively. This makes it unlikely for the exhaust gas G to hit the edge portion of each of the communication holes  4 A and  4 B, thus reducing separation of the exhaust gas G from the inner circumferential surface of the inner tube  2 . Consequently, turbulent flow of the exhaust gas G is unlikely to be generated on the inner circumferential surface of the inner tube  2 , resulting in reducing air flow noise (i.e., whistling noise) to be generated when the exhaust gas G passes through the communication holes  4 A and  4 B. 
     (1e) The downstream end  32  of the outer tube  3  is closed to thereby allow the space S inside the outer tube  3  to be an enclosed space, thus forming a Helmholtz resonator. This results in improving the silencing effect at the discharge port  22 . 
     2. Second Embodiment 
     2-1. Configuration 
     A tail pipe  1 A shown in  FIG. 4  comprises the inner tube  2 , an outer tube  3 A, and the communication holes  4 A and  4 B. The inner tube  2  and the communication holes  4 A and  4 B are the same as those of the tail pipe  1  of  FIG. 1 . 
     The outer tube  3 A is the same as the outer tube  3  of the tail pipe  1  of  FIG. 1  except for a configuration of a downstream end  32 A. In the outer tube  3 A, an upstream end  31 A in the flow direction of the exhaust gas G is closed, whereas the downstream end  32 A is not closed but open. 
     Specifically, the downstream end  32 A of the outer tube  3 A has an opening  33 A allowing communication between the space S and the outside of the outer tube  3 A. Thus, the space S of the present embodiment is not enclosed but open to the atmosphere. The outer tube  3 A except for the upstream end  31 A is spaced apart from the inner tube  2 . 
     In the present embodiment, the opening  33 A of the outer tube  3 A at the downstream end  32 A is located more outside in the axial direction of the inner tube  2  than the discharge port  22  of the inner tube  2 . In other words, the outer tube  3 A protrudes outside of the inner tube  2  in the axial direction thereof. This causes the exhaust gas G discharged from the discharge port  22  to expand at the opening  33 A, thus enabling further reduction of the velocity of the exhaust gas G discharged from the opening  33 A. However, the opening  33 A of the outer tube  3 A may coincide in position with the discharge port  22  of the inner tube  2  in the axial direction of the inner tube  2 . 
     The minimum distance D in the radial direction of the inner tube  2  between the enlarged diameter portion  23  of the inner tube  2  and the outer tube  3 A (i.e., a thickness of the space S at the discharge port  22 ) is designed to have a size allowing the space S to function as the resonance chamber for the exhaust gas G. 
     2-2. Actions 
     In the tail pipe  1 A, the exhaust gas G passes through the space S and is discharged from the opening  33 A of the outer tube  3 A. Thus, flow layers of the exhaust gas G having different flow velocities in the radial direction of the inner tube  2  are formed. 
     Further, in the tail pipe  1 A, an outer-side flow of the exhaust gas G discharged from the opening  33 A of the outer tube  3 A reduces the velocity of a central flow of the exhaust gas G discharged from the discharge port  22  of the inner tube  2 . 
     2-3. Effects 
     The embodiment detailed above produces the following effect. 
     (2a) The exhaust gas G with a higher velocity discharged from the inner tube  2  is covered by the exhaust gas G with a lower velocity discharged from the outer tube  3 , and the atmosphere exists further therearound. This causes gradual decrease in the flow velocity of the exhaust gas G flowing on the outer side, thus lowering likelihood of generation of turbulent flow. As a result, generation of air flow noise due to the turbulent flow can be reduced. 
     3. Other Embodiments 
     Although the embodiments of the present disclosure have been described so far, the present disclosure is not limited to the above-described embodiments, and can be practiced in various forms. 
     (3a) In the tail pipes of the above-described embodiments, the sharply enlarged portions  25 A and  25 B do not necessarily have to overlap with the gently enlarged portion  24  when viewed along the circumferential direction of the inner tube  2 . For example, as shown in  FIG. 5 , the sharply enlarged portion  25 A may be arranged upstream of the gently enlarged portion  24 . This promotes spreading of the exhaust gas G by the enlarged diameter portion  23 , thus facilitating rapid and uniform mixture of the exhaust gas G into the atmosphere. 
     (3b) In the tail pipes of the above-described embodiments, the communication holes  4 A and  4 B do not necessarily have to be arranged in the sharply enlarged portions  25 A and  25 B, respectively. For example, as shown in  FIG. 6 , two or more communication holes  4 C may be arranged in the gently enlarged portion  24 . Alternatively, communication holes may be arranged in both of the gently enlarged portion and the sharply enlarged portion(s). 
     (3c) In the tail pipes of the above-described embodiments, the enlarged diameter portion  23  does not necessarily have to comprise the gently enlarged portion  24  and the sharply enlarged portions  25 A and  25 B. The enlarged diameter portion  23  may comprise only the gently enlarged portion  24 . Furthermore, the inner tube  2  does not necessarily have to comprise the enlarged diameter portion  23 . 
     (3d) The function(s) performed by a single element in the above-described embodiments may be performed by two or more elements. The function(s) performed by two or more elements may be performed by a single element. Part of the configuration of the above-described embodiments may be omitted. At least part of the configuration of the above-described embodiments may be added to or replace the configuration of the above-described other embodiments. Any modes encompassed by technical ideas specified by claim language are embodiments of the present disclosure.