Static mixer for exhaust pipe of internal combustion engine, method for production thereof, and exhaust unit comprising such mixer

Abstract

Static mixer (11) for an exhaust pipe of an internal combustion engine, comprising an elongated hollow metal body (13) having a shape substantially corresponding to a rotating body with respect to an axis of symmetry (S), inside which a cavity (15) is defined, where the elongated hollow metal body (13) also defines opposing seats (17, 19), one of which is provided with an axial opening; the invention relates to a mixer comprising a mixer body (1) and defining a closed side wall (23) connected to said opposing bases (17, 19), the side wall (23) having at least one radial opening (25) on which is arranged a concave vane (27) extending radially from a portion of a peripheral edge (29) of the radial opening (25) to the outside of the side wall (23) of the mixer body and comprising a portion of the radial opening (25), the concave vane (27) being arranged so as to extend radially from a portion of the peripheral edge (29) of the radial opening (25) to the outside of the side wall (23) of the mixer body. The invention is characterized in that it is designed to define a respective concave screen or spoon (31) in a first angular direction with respect to the axis of symmetry and an access opening (33) in front of the concave screen or spoon (31) for the passage of gas in an opposite second direction.

Description

[0001] This application is a divisional application of the invention patent application with application number 201980049037.4 and application date of July 23, 2019. Technical Field

[0002] The present invention relates to a static mixer for an exhaust pipe of an internal combustion engine, and also relates to an exhaust unit comprising the mixer and a method for manufacturing the mixer.

[0003] The mixer of the present invention can be applied to the exhaust duct of an internal combustion engine where it is necessary to promote mixing of exhaust gas with a substance or substance mixture that can chemically interact with the exhaust gas. A specific application example of the mixer of the present invention relates to an exhaust unit where selective catalytic reduction (SCR) of nitrogen oxides occurs. Background Art

[0004] Static mixers are commonly used to promote mixing of exhaust gases with a reducing agent introduced in gaseous or liquid form into the exhaust system of an internal combustion engine.

[0005] In this case, the static mixer is primarily intended to promote the formation of a highly homogeneous mixture and to achieve the highest possible evaporation of the reducing agent introduced into the exhaust system.

[0006] To meet this requirement, static mixers are currently being produced which comprise a set of blades with different orientations within a duct in which the exhaust gas and reducing agent mixture flows.

[0007] These blades are generally associated with an annular frame intended to be attached to the inner wall of a duct housing a mixer, wherein said mixer is generally arranged transversely in the duct so that the exhaust gas flow is intercepted by said blades.

[0008] Static mixers generally facilitate mixing of the gas and the reductant due to increased turbulence within the exhaust gas flow.

[0009] However, the placement of static mixers in the gas flow area leads to an increase in pressure within the exhaust system. This pressure increase is a disadvantage because it hinders the discharge of exhaust gases and can be more or less significant, depending on the design of the mixer and the exhaust system.

[0010] Furthermore, the surface of the mixer causes condensation of the reducing mixture, which results in the formation of a liquid film that adheres to the blades and reduces the efficiency of the mixer itself.

[0011] Therefore, when designing a mixer of the above type, two phenomena must be overcome.

[0012] The first phenomenon is caused by excessive pressure in the exhaust system containing the mixer. The second phenomenon is caused by a reduction in the mixing capacity due to the formation of condensate of the reducing agent on the surfaces of the mixer.

[0013] In an attempt to achieve an optimal compromise between the opposing requirements of obtaining good mixing and preventing the above-mentioned disadvantages, different solutions have been proposed to date.

[0014] Some solutions use a matrix of blades whose density, pitch and size are chosen according to the above requirements. An example of such a mixer is disclosed in US 2007 / 0204751.

[0015] Other solutions provide a set of blades that are generally radially arranged in a duct in which the gas flows and is directed so as to mix the gas with the reducing agent mixture. This second type of static mixer is disclosed, for example, in US 7,533,520, US 2009 / 0320453, US 2009 / 0266064 and US 2012 / 320708.

[0016] In all the above solutions, the attempt to find the best compromise between the mixing requirements and the free flow requirements of the exhaust gases is evident.

[0017] Despite these efforts, prior art mixers do not fully address the problem of how to achieve optimal mixing while minimizing the aforementioned drawbacks.

[0018] Furthermore, efforts to date have resulted in increasingly cumbersome, complex, and expensive solutions.

[0019] Therefore, there remains a strong need in the art for a static mixer that is efficient, does not cause a significant pressure increase, is less likely to promote the formation of condensate and does not suffer from the above-mentioned disadvantages with respect to manufacturing complexity and cost.

[0020] Therefore, a first object of the present invention is to achieve such a result by providing a static mixer device for treating exhaust gases which allows for better mixing with smaller pressure increases and reduced condensate formation compared to prior art devices.

[0021] Another object of the present invention is to provide a static mixer of the above-mentioned type which can be manufactured industrially more simply and at a lower cost than the mixers of the prior art.

[0022] An important object of the present invention is to provide a mixer of the above type which can be used in essentially any exhaust system using selective catalytic reduction (SCR) technology.

[0023] These and other objects are achieved by a static mixer for exhaust gas treatment and a method for producing the same as claimed in the appended claims, which form an integral part of the technical teaching provided by the present invention. Summary of the Invention

[0024] The mixer of the present invention mainly comprises an elongated hollow metal body, in which a pair of opposite, preferably parallel bases are defined. The body of the mixer can be essentially any elongated shape, and preferably, it is a cylindrical truncated cone. When the bases have surfaces of different areas, at least one of the opposite bases, preferably the largest one, is provided with at least one axial opening. The body of the mixer also includes side walls, which define corresponding side surfaces extending between the opposite bases. Advantageously, according to the present invention, the side walls are closed and provided with at least one lateral opening or window.

[0025] Preferably, the static mixer for the exhaust duct of an internal combustion engine of the present invention comprises an elongated hollow metal body having a shape which substantially corresponds to that of a rotating body relative to the axis of rotation. Inside the body of the mixer, a cavity is defined which is surrounded by side walls connected to relative bases, at least one of the bases being provided with a preferably axial opening. According to the invention, the side walls are closed and provided with at least one radial opening on which concave blades are arranged. The concave blades extend radially from a portion of the peripheral edge of the radial opening to the outside of the side wall of the mixer body. The concave blades also surround a portion of the radial opening so as to define a corresponding concave screen or spoon or petal in a first angular direction relative to the axis of symmetry with the mixer body; and in an opposite second direction, define an inlet and outlet for the passage of gas, which inlet and outlet are substantially located in front of the concave screen or spoon or petal.

[0026] According to the invention, the mixer body may be made from a single component, ie as a single part, or may comprise a plurality of sub-components which are assembled to each other to form a single part.

[0027] Furthermore, according to the present invention, the mixer is preferably arranged and housed in the exhaust unit so that the entire airflow passes transversely through the at least one transverse opening and flows in or out through a single axial opening. To this end, according to the present invention, when the mixer body has a frustoconical shape, at least one of the opposing bases of the mixer cone, preferably the smallest base, is sealed to prevent gas flow, i.e., it is exhaust-tight. This gas-tight base can be sealed by the material of the mixer body or by a separate component, such as a reducing agent nozzle.

[0028] As will become more apparent from the following description of some preferred embodiments of the present invention, the mixer of the present invention does not require any additional structure to create a swirling flow in the exhaust gas passing through the treatment unit.

[0029] The inlets and the openings and the corresponding blades make it possible to define substantially on the mixer body a baffle having a single front through which the gas passes, thanks to which the leakage at the inlet is limited and the flow is best directed to obtain an optimal volute flow.

[0030] By this feature, the mixer can be advantageously used in a variety of arrangements that allow the exhaust gas flow to flow into the device through the inlet and outlet defined by the blades and exit from the open end in the form of a spiral flow, or flow into the device from the opposite direction, entering from the open end and flowing out of the inlet and outlet in the form of a vortex.

[0031] Advantageously, the performance of the mixer of the present invention is independent, or substantially independent, of the inflow angle of the exhaust gas into the device. Thus, the reducing agent or mixture, such as AdBlue, can be mixed in a variety of configurations. ® Injection into the air flow, i.e. inside or outside the mixer, upstream or downstream of the mixer, coaxial with the air flow or in the direction of inflow, along the direction of exhaust gas flow, parallel flow or counter flow.

[0032] Advantageously, the mixer according to the invention is therefore a substantially universal device which does not require any substantial modifications even in exhaust gas treatment units which are constructed in very different ways.

[0033] The static mixer of the present invention can be advantageously used in the exhaust duct of an internal combustion engine, for example a diesel cycle engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Some preferred embodiments of the present invention will be described below with reference to the accompanying drawings, in which: Figure 1 According to a preferred embodiment of the present invention, a perspective front view of a mixer is shown; Figure 2 Shown Figure 1 Rear perspective view of the mixer in FIG; Figure 3 Shown Figure 1 A side plan view of the mixer in FIG. Figure 4 Shown Figure 1 Rear plan view of the mixer in FIG; Figure 5 Shown in cross-section with Figure 1 The corresponding view; Figure 6 Shown in Figure 5 Schematic diagram of the geometric shape of the mixer in cross section; 7A and 7B show perspective views of variations of the mixer, showing geometrical surfaces; Figure 7C Shown Figure 7A and 7B A plan view of the mixer in FIG. Figure 8 A schematic cross-sectional view of a longitudinal plane of a preferred embodiment of a mixer associated with a nozzle is shown; Figures 9-11 Schematic diagrams showing respective embodiments of the exhaust gas treatment unit of the present invention; Figures 12A-12C side views showing corresponding intermediate steps in the manufacture of the mixer of the present invention; Figure 12D Shows the Figure 12B A cross-sectional view showing the intermediate results compared to the final result.

[0035] Throughout the drawings, the same reference numbers are used to indicate identical or functionally equivalent components. DETAILED DESCRIPTION

[0036] refer to Figure 1-Figure 4 , shows a static mixer 11 for use in an exhaust duct of an internal combustion engine, manufactured in accordance with a preferred embodiment of the present invention. The mixer 11 comprises a hollow body 13 having an elongated shape. In the illustrated embodiment, the body 13 has a generally frustoconical shape relative to an axis of symmetry "S," i.e., the body 13 is substantially shaped as a solid of revolution relative to the axis "S." Within the body 13, a cavity 15 is defined, which is bounded at opposite ends by a pair of bases 17, 19 and laterally by a closed sidewall 23 connected to the opposing bases 17, 19.

[0037] According to the present invention, the side wall 23 is provided with a plurality of radial openings 25, and a corresponding concave blade 27 is provided on each radial opening 25. The concave blade 27 extends radially from a portion of the peripheral edge 29 of the radial opening 25 to the outside of the side wall 23 of the main body of the mixer 11. In addition, each concave blade 27 surrounds a portion of the radial opening 25 and is disposed relative to the radial opening 25. Figure 4 In the clockwise direction of the axis of symmetry in the first angular direction, a corresponding concave screen or spoon 31 is defined, and in the second angular direction, Figure 41. In the counterclockwise direction of the concave screen or spoon 31, a gas passageway 33 is defined, which is located substantially in front of the concave screen or spoon 31. In the example shown, there are a total of six radial openings 25, which are identical and equally spaced relative to each other, i.e., spaced apart at an angle of 60° from each other. Furthermore, still referring to the embodiment shown, the openings 25 and the openings 33 have a substantially quadrilateral shape, with their long sides arranged in a substantially axial direction, i.e., approximately parallel to the axis of rotation of the body 13.

[0038] According to the embodiment of the invention shown, the body 13 of the mixer 11 comprises a small base 17 that can be closed or opened depending on the application, and a larger base 19 that is preferably always open. In the embodiment shown, the small base 17 is provided with an opening 17a to allow the entry of a mixture of substances, typically containing urea, sprayed from a spray head or nozzle, which promotes the desired chemical reaction in the exhaust gas. Preferably, the spray head completely occupies the opening 17a, and the corresponding nozzle is oriented toward the interior of the chamber 15, so that the small base is gas-tight to the gas passing through the mixer 11.

[0039] from Figure 1 As can be better understood in the figure, the port 33 is defined by a peripheral edge 35 having a minimum surface area, which port 33 is substantially incident on the side wall 23 of the body 13 of the mixer 11. The edge 35 of the port 33 preferably has a common portion on the side wall 23 with the edge 29 of the radial opening 25.

[0040] Specific reference Figure 3 and Figure 4 In the embodiment shown, the peripheral edge 35 lies substantially in a plane P1, incident on the sidewall 23 of the body 13 of the mixer 11. Furthermore, still with reference to the embodiment shown, the plane P1 is tilted at an angle δ of approximately 90° relative to the planes P2 and P3, respectively, on which the opposing parallel bases 17 and 19 lie. Whether planar or curved, the smallest surface enclosed by the peripheral edge 35 can also have a helical development and thus be tilted relative to the axis of rotation S and relative to the planes P2 and P3. Thus, in a helical configuration, the angle δ is no longer 90° and, depending on the embodiment, is preferably between 45° and 135°.

[0041] The plane P1 of each port 33 is also preferably tangential to the same cylinder coaxial with the longitudinal axis "S" of the body of the mixer 11. In the embodiment shown, the radius of the cylinder tangential to the plane P1 is approximately equal to the radius of the opening 17a; in other embodiments, the cylinder may have a radius different from that of the opening 17a, or the opening 17a may not be present. According to this embodiment of the invention, the ports 33 are oriented primarily tangentially to the side wall 23 of the mixer body, i.e., in a direction parallel to the longitudinal axis "S" of the mixer body. Figure 3 The direction perpendicular to the plane and Figure 4 The inlet and outlet 33 are arranged in a direction parallel to the plane of the mixer 11 so that the gas can flow out of the inner cavity 15 of the mixer 11 and pass through the inner cavity 15 of the mixer 11. Therefore, according to this arrangement of the inlet and outlet 33, when the mixer 11 is accommodated in the exhaust system of an internal combustion engine, the gas exhausted from the engine can enter the cavity 15 of the mixer 11 tangentially, first through the inlet and outlet 33 and then through the opening 25; or first through the opening 25 and then through the inlet and outlet 33 to leave the cavity 15 and finally reach the external environment of the mixer 11. In both cases, because the inlet and outlet 33 and the opening 25 are oriented obliquely relative to each other on a plane or surface, the path of the exhaust gas between the inlet and outlet 33 and the opening 25 will be a path that is substantially similar to a vortex, and vice versa.

[0042] according to Figure 1-Figure 4 In the embodiment shown, the ports 33 are oriented to minimize the passage of gas from and towards the interior 15 of the mixer 11 in the axial direction, ie, in a direction parallel to the axis of rotation "S".

[0043] refer to Figure 5 and Figure 6 , the geometry of the mixer in the preferred embodiment of the present invention will be described in detail.

[0044] Figure 5 A general section S is shown perpendicular to the axis of rotation "S" and transversely cutting through the body 13 of the mixer 11 along the dashed line Rn. n .exist Figure 6 In the plane S n At point x n and x n + h n The intersection of the radial opening 25 with the edge 29 and the point x n and y n The line segment h intersects with the edge 35 of the entrance 33. n The plane S representing the radial opening 25 n The horizontal width on the n and in xn The angle α between the lines tangent to the circumference n In this embodiment of the invention, the radial opening 25 and the port 33 share a portion of their respective edges 29 and 35 on the side wall 23, so that the edges 29 and 35 are aligned with the plane S n Intersection point x n The blade 27 extends on the radial opening 25, and the outline of the blade 27 is formed by the straight line h n and the tangent line of the blade 27 are located at point y n and x n +h n Angle β at n and γ n In plane S n The blade 27 is contained within a radius Dx n And Dy n > Dx n The circumference of the two circles is centered on the axis of symmetry S of the body of rotation of the mixer 11. n and y n Connect to line Z n , wherein the straight line Zn has an angle θ of 0°-90° with the tangent line to the circle with radius Dxn at point xn n , we can get the plane on which the surface surrounded by the edge 35 of the outlet 33 extends, in which case the outlet extends on the plane, as shown in FIG. Figure 1-Figure 4 As shown in the example in , or, in the case of a non-planar minimum surface area surrounded by an edge 35, the straight line approaches the surface in each portion Sn.

[0045] refer to Figures 7A-7C "A" represents the minimum surface area enclosed by the edge 35 of the inlet and outlet 33, whether it is a plane or a curved surface, and "a" represents the projected area of ​​the surface on a plane P4 perpendicular to a line Q passing through the geometric center CG of the surface and the rotation axis S. According to the present invention, the following results are preferably obtained:

[0046] The geometric center CG of the minimum surface area enclosed by the edge 35 refers to the "middle position" of the contour points generated by the surface relative to any three-dimensional reference system, that is, the arithmetic mean of the position of each of the points along the x, y, z directions of any spatial reference system.

[0047] Figures 7A-7Crepresents an embodiment of the invention, in which the edge 35 of the opening 33 is located on a curved surface, and "b" represents the projection of the minimum surface area enclosed by the edge 35 on a plane perpendicular to the axis of rotation "S" and not intersecting the surface, according to the invention, preferably the following results will be obtained:

[0048] In other words, assuming that the main base 19 of the body 13 of the mixer 11 is located on a plane perpendicular to the rotation axis "S", the area b of the projection of the minimum surface area enclosed by the edge 35 of the outlet 33 on the plane will be 30% smaller than the area A of the minimum surface area.

[0049] Advantageously, according to the present invention, mixer 11 can be used in a variety of applications without requiring substantial modification or adjustment. Mixer 11 can be oriented within the exhaust treatment unit with its axis of rotation "S" in any direction relative to the predominant direction of the gases. For example, mixer 11 can be oriented with the axis of rotation "S" perpendicular or parallel to the direction of travel of the exhaust gases. Furthermore, regardless of the configuration of the mixer's 11 body within the exhaust treatment unit, mixer 11 can be associated with a nozzle for injecting a substance suitable for producing a desired chemical reaction, such as the reducing agent urea, oriented in substantially any direction relative to the axis of rotation "S." In particular, the nozzle can be oriented with its longitudinal axis parallel to the mixer's 11 axis of rotation "S," either co-currently with or counter-currently with the direction of exhaust gas flow, or with its axis oriented obliquely relative to the axis of rotation "S." Furthermore, also according to the present invention, when mixer 11 has different opposing bases, such as when body 13 is shaped as a frustum of a cone, it can be oriented independently of the minor base upstream of main base 19 in the direction of travel of the exhaust gases, and vice versa.

[0050] Specific reference Figure 8 , which shows a configuration of the present invention in which the two opposing bases 17, 19 of the body 13 of the mixer 11 are open. Reference numeral 71 denotes a nozzle located in front of or, more preferably, within the opening 17a of the base 17. In the embodiment shown, the base 17 corresponds to a small base, and the body 13 has a frustoconical shape, so as to completely engage the opening 17a, thereby preventing the ingress of exhaust gases through the opening 17a and rendering the base 17 impenetrable to the exhaust gases. Preferably, according to the present invention, the nozzle 71 is arranged relative to the body 13 so that the jet of material leaving the nozzle does not strike the walls of the cavity 15 within the mixer 11 and is distributed in the air flow downstream of the second base 19, which is opposite to the base of the body 13 from which the jet 71a enters the mixer. The nozzle 71 generally has a frustoconical shape, as indicated by reference numeral 71a in the figure. Reference Figures 9-11 , which shows a corresponding embodiment of an exhaust gas treatment unit 51 for an internal combustion engine 53, in which the static mixer 11 according to the present invention is installed. Treatment unit 51 connects internal combustion engine 53, in the example shown, a diesel-cycle engine, to an outlet duct 55 that communicates with the external environment (arrow F1). Unit 51 includes at least one intermediate duct 57 for the passage of exhaust gas from engine 53 to outlet duct 55. Intermediate duct 57 typically houses at least a first exhaust gas treatment unit 59 upstream of mixer 11 and at least a second exhaust gas treatment unit 61 downstream of mixer 11.

[0051] For example, the first unit 59 arranged upstream of the mixer 11 may include an oxidation catalyst (DOC) which may be associated with a diesel particulate filter (DPF), and the second unit 61 arranged downstream of the mixer 11 may include a selective catalytic reduction (SCR) unit which may be associated with an ammonia slip catalyst (ASC) or a cleanup catalyst (CUC), or an SCR unit including a soot filter (SCRoF), or a diesel particulate filter (DPF) which may be associated with an ammonia slip catalyst (ASC) or a cleanup catalyst (CUC) device.

[0052] In the illustrated embodiment, a static mixer 11 manufactured in accordance with the present invention and having a generally bell-shaped or frusto-conical shape is disposed between a first unit 59 and a second unit 61. More precisely, and with respect to the preferential flow direction of the exhaust gases through the intermediate duct 57 (arrows F2, F3), the first unit 59 is arranged downstream of the internal combustion engine 53 and upstream of the mixer 11; and the mixer 11 is arranged upstream of the second unit 61. Thus, according to the illustrated arrangement, the exhaust gases exiting the internal combustion engine 53 pass sequentially through the first unit 59, the mixer 11, and the second unit 61 before passing through the outlet duct 55 and into the atmosphere (arrow F1).

[0053] Now specific reference Figure 9, which shows a first embodiment of the exhaust gas treatment unit 51. According to this embodiment, the mixer 11 includes a small base 17 having an opening 17a for the flow of a substance, such as urea, exiting a nozzle 71. The nozzle 71 is preferably associated with a nozzle head that completely occupies the opening 17a, thereby preventing exhaust gas from passing through the opening 17a. According to the present invention, the opening 17a (if present) is configured to prevent the passage of exhaust gas. The opposite base 10 of the mixer 11 is open to allow exhaust gas from the internal combustion engine 53 to exit and be directed radially toward the side wall 23 of the mixer 11. In the illustrated embodiment, the intermediate duct 57 defines a generally L-shaped path and includes a first portion 81a defining a cavity 83 for accommodating the first unit 59 and the mixer 111, and a second portion 81b extending partially through the cavity 81 and surrounding the second base 19 of the mixer. This allows the entire exhaust flow exiting the opening of the base 19 to be directed into the interior of the second duct portion 81b, where the exhaust gas follows a swirling path, as indicated by arrow F4. Preferably, both portions 81a and 81b have a cylindrical cross-section and are straight, with portion 81b oriented with its axis substantially perpendicular to the axis of portion 81a. Furthermore, the mixer 11, housed within cavity 83, is arranged substantially coaxially with the second duct portion 81b and receives the exhaust gas flowing axially through the first duct portion 81, the port 33, and the corresponding radial openings 25, as indicated by arrow F2.

[0054] According to this embodiment, the nozzle 71 is preferably configured so that the mixture ejected from the nozzle 71 does not strike the inner surface of the side wall 23 of the mixer 11, and is primarily mixed with the exhaust gas outside the mixer body and within the second duct portion 81b. Also according to this first embodiment, the jet of material ejected from the nozzle 71 flows parallel to the direction of exhaust gas flow downstream of the mixer 11, as indicated by arrows F3 and F4.

[0055] Reference Figure 10A and 10B , which shows a second embodiment of the exhaust gas treatment unit 51 in two embodiment variants. According to this embodiment, the mixer 11 is comprised in Figure 10A The open small base 17 in the first variant and Figure 10B The second variant of the mixer 11 is shown with the small base 17 closed. The opposite base of the mixer 11 is open, allowing the exhaust gas from the internal combustion engine 53 to be discharged and directed radially onto the side wall 23 of the mixer 11. In the embodiment shown, the intermediate duct 57 has a generally straight shape and defines a cavity 85 therein, which primarily accommodates the first unit 59, the mixer 11, and the second unit 61. The intermediate duct 57 also includes a screen 87 that defines a passage for the gas leaving the mixer 11.

[0056] according to Figure 10A In a variant of the first embodiment, the nozzle 71 is arranged in front of the opening 17a of the base 17, or more preferably, inside said opening 17a, so as to completely occupy the gap of said opening 17a, thereby preventing the passage of the exhaust gases and making said base 17 impermeable to them, and the jet ejected by the nozzle 71 is directed into the cavity 15. In this variant of the first embodiment, the nozzle 71 is oriented so as to spray the mixture of substances in a parallel stream relative to the main direction of advancement of the exhaust gases in the intermediate duct 57, as indicated by the arrow F4.

[0057] according to Figure 10B In a variant of the second embodiment, the nozzles 71 are arranged in front of the large, open base 19 of the mixer 11. In this second embodiment variant, the nozzles 71 are oriented so as to spray the mixture of substances in a countercurrent manner relative to the main direction of advancement of the exhaust gases in the intermediate duct 57, as indicated by the arrow F4.

[0058] The screen 87 provided downstream of the mixer 11 partially surrounds the mixer 11 and is arranged to convey the exhaust gas having passed through the mixer 11 towards the second exhaust gas treatment unit 61 accommodated in the intermediate duct 57 .

[0059] Additionally, similar to the first embodiment, exhaust gas from the engine 53 radially strikes the sidewall 23 of the mixer 11 and penetrates into the cavity 15 provided in the mixer 11 via the port 33 and the corresponding radial opening 25 as indicated by arrow F2.

[0060] Preferably, the intermediate duct 57 has a cylindrical section and the mixer 11 is housed inside the duct 57 with its axis of rotation substantially perpendicular to the longitudinal axis of the duct 57 and coaxial with said screen 87 .

[0061] According to this embodiment, the nozzle 71 is preferably configured such that the mixture of substances sprayed from the nozzle 71 does not hit the surface of the side wall 23 of the mixer 11 and is mainly mixed with the exhaust gas outside the main body of the mixer 11 .

[0062] Now refer to Figure 11 , which shows a third embodiment of an exhaust gas treatment unit 51. According to this embodiment, the mixer 11 includes a small, preferably closed, base 17. Conversely, the opposite base 19 of the mixer 11 is always open to allow the exhaust gas from the internal combustion engine to enter, be guided axially to the mixer 11, and ultimately to the cavity 15 defined within the mixer 11. In the embodiment shown, the intermediate duct 57 has a generally straight shape and primarily accommodates the first unit 59, the mixer 11, and the second unit 61. Furthermore, a nozzle 71 protrudes into the duct 57 downstream of the mixer 11.

[0063] In this embodiment, the nozzles 71 are oriented to spray the mixture of substances in a parallel stream relative to the main direction of travel of the exhaust gases within the intermediate duct 57, as indicated by arrows F3, F4, F5. Furthermore, the nozzles 71 are located downstream of the mixer 11 and are arranged to direct the mixture of substances into the duct 57, where the exhaust gases follow a swirling path, as indicated by arrows F4.

[0064] Preferably, the pipe 57 is straight and has a cylindrical cross section. In addition, the mixer 11 is arranged substantially coaxially with the pipe 57 and receives the exhaust gas flowing axially through the pipe 57 portion located upstream of the mixer 11 through the open large base 19.

[0065] According to this embodiment of the invention, the inlet and outlet ports 33 and the corresponding radial openings 25 provided on the side wall 23 of the mixer 11 help to generate a swirling motion of the exhaust gas, thereby ensuring optimal mixing of the urea mixture introduced by the injection head 71 .

[0066] Reference Figures 12A-12D , which shows a method for manufacturing a static mixer according to a preferred embodiment of the present invention, wherein the body 13 of the mixer 11 is obtained by a metal sheet cold forming process.

[0067] Shaping is preferably carried out as a sequence of consecutive stretching and shearing operations.

[0068] refer to Figure 12A and Figure 12B , which shows a sequence of intermediate steps in the method according to a preferred embodiment of the present invention, wherein a bell-shaped body 113 having a side wall 23 and comprising a closed small base 17 and an open large base 19 is obtained by molding a metal sheet. This first machining cycle is suitable for providing the side wall of the body 13 with the desired shape, which, depending on the embodiment, has a cross-section that is, for example, substantially circular, hexagonal, octagonal or pentagonal. At the end of the first machining cycle, the body has a closed side wall 23 that is substantially smooth and regular.

[0069] Figure 12C A further intermediate step of the method of the invention is shown after the above cycle, in which the body 113 is subjected to a cutting operation, preferably a laser cutting operation, in order to obtain the access opening 33 .

[0070] At the end of the above cycle, the body 113 is subjected to a further stretching step in order to particularly perfect the shape of the body 113 of the mixer and the edges of the orifice 33 .

[0071] Reference Figure 12D , which shows that Figure 12B A cross section showing the intermediate results compared to the final result is shown. Figure 12DIn FIG. 1 , it can be seen that the blades 27 and the port 33 extend over the radial opening 25 and that the radial opening 25 is formed by deformation of the side surface of the body 113 .

[0072] Numerous variations and modifications may be made to what has been described and illustrated in the present invention within the same principles of the invention.

Claims

1. An internal combustion engine exhaust gas treatment unit (51), characterized in that: The unit comprises: an intermediate duct (57) connecting the exhaust pipe of the internal combustion engine (53) to an outlet duct (55) communicating with the external environment; and a static mixer (11) housed in the intermediate duct (57) and having a frustoconical shape; wherein the intermediate pipe (57) accommodates at least one first exhaust gas treatment unit (59) upstream of the mixer (11), and accommodates at least one second exhaust gas treatment unit (61) downstream of the mixer (11); wherein the first exhaust treatment unit (59) is arranged downstream of the internal combustion engine (53) and upstream of the mixer (11); and the mixer (11) is arranged upstream of the second exhaust treatment unit (61), so that the exhaust gas leaving the internal combustion engine (53) flows through the first exhaust treatment unit (59), the mixer (11) and the second exhaust treatment unit (61) in sequence before passing through the outlet pipe (55) and being introduced into the atmosphere; wherein the first gas treatment unit (59) arranged upstream of the mixer (11) comprises an oxidation catalyst (DOC) which can be associated with a diesel particulate filter (DPF), and the second gas treatment unit (61) arranged downstream of the mixer (11) comprises a selective catalytic reduction (SCR) unit which can be associated with an ammonia slip catalyst (ASC) or a cleanup catalyst (CUC), or an SCR unit including a soot filter (SCRoF), or a diesel particulate filter (DPF) which can be associated with an ammonia slip catalyst (ASC) or a cleanup catalyst (CUC) device; The static mixer comprises an elongated hollow metal body (13), which has a shape roughly corresponding to that of a rotating body relative to an axis of symmetry (S), defines a cavity (15) therein, and defines opposite bases (17, 19) on the elongated hollow metal body (13), one of which is provided with an axial opening; and defines a closed side wall (23) connected to the opposite bases (17, 19), the side wall (23) having at least one radial opening (25), wherein concave blades (27) are arranged on the radial opening, the concave blades radially extending from a portion of the peripheral edge (29) of the radial opening (25) to the outside of the side wall (23) of the mixer body and surrounding a portion of the radial opening (25), so as to define a corresponding concave screen (31) in a first angular direction relative to the axis of symmetry, and an inlet and outlet (33) for gas to pass through and substantially located in front of the concave screen (31) in an opposite second direction; wherein one of the bases of the frustoconical body (13) of the mixer (11) is closed and thus exhaust-tight; wherein a substantially vortex-shaped path of the gas is established between the radial opening (25) and the inlet and outlet (33) by the concave blades (27) in a plane perpendicular to the axis of symmetry (S) of the mixer body, and vice versa; The inlet and outlet (33) has an approximately quadrilateral shape, and the ratio between the projected area "b" of the minimum surface area enclosed by the edge (35) of the inlet and outlet (33) on a plane perpendicular to the symmetry axis (S) and not intersecting the surface and the area "A" of the minimum surface area satisfies the following equation: ； wherein said inlet and outlet (33) for the passage of gas is delimited by a peripheral edge (35) lying substantially on a plane (P1) incident with respect to the closed side wall (23) of the elongated hollow metal body; The plane (P1) is inclined relative to the planes (P2, P3), and the relative bases (17, 19) are respectively located on the planes (P2, P3); wherein the plane (P1) of each inlet and outlet (33) is tangential to the same cylinder coaxial with the longitudinal axis ("S") of the body (13) of the mixer (11); wherein the inlet and outlet (33) for the passage of gas is oriented so that gas from and towards the inner cavity (15) of the mixer (11) passes mainly in a tangential direction relative to the side wall (23) of the mixer body; wherein the inlet and outlet ports (33) are oriented to minimize the passage of gas from and toward the interior cavity (15) of the mixer (11) in an axial direction relative to the side wall (23) of the mixer body, i.e., in a direction parallel to the axis of symmetry ("S"); The mixer (11) comprises a small base (17) having an opening (17a) for the inflow of a substance such as urea leaving a nozzle (71), said nozzle (71) being associated with a nozzle that completely occupies the opening 17a, so as to prevent the exhaust gases from passing through said opening (17a): The intermediate duct (57) defines a generally L-shaped path and includes: a first portion (81a) defining a cavity (83) for accommodating the first unit (59) and the mixer (11); and a second portion (81b) partially extending through the cavity (83) and surrounding the second base (19) of the mixer, such that the entire exhaust gas flow discharged from the opening of the base (19) is guided into the interior of the second duct portion (81b), where the exhaust gas takes a vortex-shaped path; wherein both duct sections (81a, 81b) have a cylindrical cross-section and are straight, and the second duct section (81b) is oriented with its axis substantially perpendicular to the axis of the first duct section (81a); wherein the mixer (11) housed in the cavity (83) is arranged substantially coaxially with the second pipe portion (81b) and receives exhaust gas flowing axially through the first pipe portion (81), through the inlet and outlet (33) and the corresponding radial opening (25) provided on the truncated conical side surface of the mixer body; wherein all exhaust gases leaving the internal combustion engine (53) and flowing through the first conduit portion (81a) flow through the inlet and outlet (33) of the static mixer (11) before passing through the outlet conduit (55) and being introduced into the atmosphere; wherein the exhaust gas from the internal combustion engine (53) enters the cavity (15) of the mixer (11) tangentially, first passes through the inlet and outlet (33) and then passes through the radial openings (25) to radially impact the side wall (23) of the mixer (11), and penetrates into the cavity (15) provided in the mixer (11) via the inlet and outlet (33) and the corresponding radial openings (25), wherein the inlet and outlet (33) and the corresponding radial openings (25) provided on the side wall (23) of the mixer (11) contribute to generating a swirling motion of the exhaust gas; wherein the opposite base (19) of the mixer (11) is open and allows exhaust gas from the internal combustion engine (53) to be discharged and directed radially to the side wall (23) of the mixer (11); The nozzle (71) is configured so that the mixture ejected from the nozzle (71) does not hit the inner surface of the side wall (23) of the mixer (11), and is mainly mixed with the exhaust gas outside the main body of the mixer (11) and in the second pipe part (81b), and the jet of the substance ejected from the nozzle (71) flows in parallel with the exhaust gas flow direction downstream of the mixer (11).

2. The internal combustion engine exhaust gas treatment unit according to claim 1, characterized in that: The inlet and outlet (33) for the passage of gas is defined by a peripheral edge (35) corresponding to the minimum surface area substantially incident on the side wall (23) of the mixer body.

3. The internal combustion engine exhaust gas treatment unit according to claim 1 or 2, characterized in that: Through the proximal end point (x n ) and the distal end point (y n ) of the straight line (Z n ) in a section plane perpendicular to the axis of symmetry (S n ) and the proximal edge of the radial opening (25) and the distal edge (35) of the inlet and outlet (33) and the proximal intersection (x n ) forms an angle (θ n ).

4. The internal combustion engine exhaust gas treatment unit according to claim 3, characterized in that: For each section perpendicular to the axis of symmetry (S n ), the inlet and outlet (33) is on the first circumference (Dx n ) and the second circumference (Dy n ) radially extending between, wherein the first circumference (Dx n ) through the proximal intersection point (x n ) and its center is on the axis of symmetry; the second circumference (Dy n ) through the distal end point (y n ) and its center is on the said symmetry axis.

5. The internal combustion engine exhaust gas treatment unit according to claim 4, characterized in that: The ratio between the projected area "a" of the minimum surface area enclosed by the edge (35) of the inlet and outlet (33) on a plane perpendicular to a line (Q) passing through the geometric center of the minimum surface and the axis of symmetry (S) and the area "A" of the minimum surface area satisfies the following equation: 。 6. The internal combustion engine exhaust gas treatment unit according to any one of claims 1 to 5, characterized in that: The rotating body comprises a cone, wherein the opposite bases (17, 19) are circular and extend in respective parallel planes perpendicular to the axis of symmetry (S), the side wall (23) of the cone or cylinder being provided with a plurality of radial openings (25), corresponding concave blades (27) and an inlet and outlet (33) for the passage of gas.

7. The internal combustion engine exhaust gas treatment unit according to claim 1, characterized in that: The radius of the cylinder tangent to the plane (P1) of the port (33) is approximately equal to the radius of the opening (17a) of the closed base (17).

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