Patent Description:
The mixer according to the invention can find application in exhaust gas ducts of internal combustion engines in which it is necessary to promote mixing of exhaust gases with a substance, or a mixture of substances, capable of chemically interacting with the exhaust gases. A particular example of application of the mixer according to the invention relates to exhaust units in which a selective catalytic reduction (SCR) of nitrogen oxides takes place.

Static mixers are commonly used in order to promote mixing of the exhaust gases with the reducing agent, introduced in gaseous or liquid state into the exhaust systems of internal combustion engines.

In this context, the static mixer is mainly aimed at promoting the formation of a highly homogeneous mixture and causing the reducing agent introduced into the exhaust system to be evaporated as much as possible.

In order to meet this requirement, static mixers are at present produced, which comprise a set of blades with various orientations inside the duct in which the exhaust gases and the reducing agent mixture flow.

The blades are generally associated with an annular frame intended to adhere to the internal walls of the duct housing the mixer, which is generally transversely arranged in the duct so that the exhaust gas flow is intercepted by said blades.

The static mixer promotes mixing of the gases with the reducing agent, generally thanks to the increase of the turbulence phenomenon within the exhaust gas flow.

Yet, the provision of a static mixer in the region where gases flow causes a pressure increase inside the exhaust system. Such a pressure increase is a drawback, since it is of hindrance to the discharge of the exhaust gases and, generally, it may be more or less significant, depending on the configuration of the mixer and of the exhaust system.

Moreover, the surface of a mixer can cause condensation of the reducing mixture, with consequent formation of a liquid film, which adheres to the blades, thereby causing a reduction in the effectiveness of the mixer itself.

Thus, two phenomena are to be countered when designing a mixer of the abovementioned kind.

The first phenomenon is the one determined by excessive pressure increases in the exhaust system housing the mixer. The second phenomenon is the one determined by the reduction of the mixing capability, resulting from the formation of condensate of the reducing agent on the mixer surfaces.

In an attempt to achieve the best compromise between the opposite requirements of attaining a good mixing and preventing the occurrence of the above drawbacks, different solutions have been proposed hitherto.

Some solutions use a matrix of vanes the density, inclination and size of which are chosen by taking into account the above requirements. <CIT> discloses an example of such kind of mixer.

Other solutions provide a set of blades, which generally are radially arranged within the duct in which the gases flow and are oriented so as to cause mixing of said gases with the reducing agent mixture. Static mixers of this second type are disclosed, for example, in <CIT>, <CIT>, <CIT> and <CIT>.

In all the aforesaid solutions, the effort to find the best compromise between the requirements of mixing and free flowing for the exhaust gases is clearly apparent.

Notwithstanding these efforts, the prior art mixers, however, do not wholly solve the problem of how to obtain the best mixing, while at the same time minimizing the above drawbacks.

Moreover, the efforts made till now result in solutions that are more and more elaborate, complex and expensive to be manufactured.

<CIT> discloses a static mixer according to the preamble of claim <NUM>.

In the field, therefore, there still exists a strong need to have a static mixer which is highly efficient, does not cause significant pressure increases, is scarcely prone to promote the formation of condensate and does not have the above drawbacks related to the manufacturing complexity and costs.

Thus, it is a first object of the invention to achieve such a result, by providing a static mixer device for the treatment of exhaust gases, which enables a better mixing with respect to the prior art devices and causes a reduced pressure increase and a reduced capability to form condensate.

A further object of the invention is to provide a static mixer of the kind discussed above, which can be industrially manufactured in simpler manner and at lower costs than prior art mixers.

A not least object of the invention is to provide a mixer of the aforementioned type, which can be used substantially in any exhaust systems exploiting the selective catalytic reduction SCR technology.

These and other objects are achieved by the static mixer for the treatment of exhaust gases as claimed in the appended claims, which form an integral part of the technical teaching provided herein in connection with the invention.

The mixer according to the invention is defined by claim <NUM> and essentially comprises an elongated hollow metal body, in which a pair of opposite, preferably parallel bases are defined. The body of the mixer has a frustoconical shape.

At least one of the opposite bases, preferably the largest one when said bases have surfaces with different areas, is provided with at least one axial opening. The body of the mixer further comprises a lateral wall defining a corresponding lateral surface extending between said opposite bases. The lateral wall is closed and is provided with at least one lateral opening or window.

The static mixer for exhaust gas ducts of internal combustion engines according to the invention comprises an elongated hollow metal body having a shape, which, relative to a symmetry axis, substantially corresponds to a solid of revolution. Inside the body of the mixer, there is defined a cavity surrounded by a lateral wall connected to opposite bases, at least one of which is provided with a preferably axial opening. According to the invention, the lateral wall is closed and provided with at least one radial opening over which a concave blade is arranged. The concave blade extends radially outward of the lateral wall of the mixer body from a portion of the peripheral edge of the radial opening. The concave blade further surrounds a portion of the radial opening so as to define, in a first angular direction relative to the symmetry axis of the mixer body, a corresponding concave screen or spoon or lobe and, in a second, opposite direction, a mouth intended for the passage of gases and located substantially in front of the concave screen or spoon.

According to the invention, the mixer body can be made of a single part, i.e. as a single piece, or can consist of several sub-parts mutually assembled to form a single element.

In addition, according to the invention, the mixer is preferably configured and housed in an exhaust unit so that the whole gas flow in transit passes through said at least one lateral opening and said flow enters or exits through a single axial opening. For this reason, according to the invention, at least one of the opposite bases of the mixer body, preferably the minor base, is closed so as to prevent transit of gases, i.e. it is exhaust gas-tight.

As will become more evident from the ensuing description of some preferred embodiments of the invention, the mixer according to the invention does not require any additional structures for generating the vortex-like flow in the exhaust gases passing through a treatment unit.

The mouths and openings and corresponding blades make it possible to define substantially a baffle integrated in the mixer body, with a single front for the passage of gases, thanks to which inlet leakages are limited and flows are best directed in order to obtain an optimal vortex-like flow.

With this feature, the mixer finds advantageous application in a plurality of arrangements with the possibility for the exhaust gas flow to flow into the device through the mouths defined by the blades and to exit in the form of a vortex-like flow from the open end, or to flow into the device in the opposite direction, entering from the open end and exiting as a vortex-like flow through the mouths.

The performances of the mixer according to the invention are advantageously independent of, or substantially indifferent to, the angle of incidence of the exhaust gas flow onto the device. As a result, the reducing agent or mixture, for example AdBlue®, can be injected into the gas flow according to a plurality of configurations, i.e. inside or outside the mixer, upstream or downstream of the mixer, in a direction coaxial or incident to the gas flow, along the direction of the exhaust gas flow, in parallel flow, or in counter-flow.

Advantageously, therefore, the mixer according to the invention is a substantially universal device, which does not require any substantial modifications, in exhaust gas treatment units configured even in very different manners.

The static mixer according to the invention can advantageously be applied in exhaust gas ducts of internal combustion engines, for example Diesel cycle engines.

Some preferred embodiments of the invention will be described below with reference to the annexed drawings, in which:.

The same reference numerals have been used in all the figures to identify the same or functionally equivalent components.

Referring to <FIG>, a static mixer <NUM> is illustrated, intended for exhaust gas ducts of internal combustion engines and made in accordance with a preferred embodiment of the invention. The mixer <NUM> comprises a hollow body <NUM> having an elongated shape. In the illustrated embodiment, the body <NUM> has a substantially frustoconical shape relative to a symmetry axis "S", i.e. the body <NUM> is made substantially as a solid of revolution relative to said axis "S". Inside the body <NUM>, there is defined a cavity <NUM> delimited, at its opposite ends, by a pair of bases <NUM>, <NUM> and laterally by a closed lateral wall <NUM> connected to the opposite bases <NUM>,<NUM>.

According to the invention, the lateral wall <NUM> is provided with a plurality of radial openings <NUM>, over each of which a corresponding concave blade <NUM> is arranged. The concave blade <NUM> extends radially outward of the lateral wall <NUM> of the body of the mixer <NUM> from a portion of the peripheral edge <NUM> of the radial opening <NUM>. In addition, each concave blade <NUM> surrounds a portion of the radial opening <NUM> and defines, in a first angular direction, clockwise relative to the symmetry axis in <FIG>, a corresponding concave screen or spoon <NUM> and, in a second angular direction, counter-clockwise in <FIG>, a mouth <NUM> intended for the passage of gases and located substantially in front of the concave screen or spoon <NUM>. In the illustrated embodiment, there is a total of six radial openings <NUM>, which are identical and equally spaced relative to one another, i.e. arranged angularly spaced at <NUM>° from one another. In addition, still referring to the illustrated embodiment, the opening <NUM> and the mouth <NUM> have an approximately quadrilateral shape, with the major sides arranged in an approximately axial direction, i.e. approximately parallel to the axis of revolution of the body <NUM>.

According to the illustrated embodiment of the invention, the body <NUM> of the mixer <NUM> comprises a minor base <NUM>, which can be closed or open depending on the applications, and a major base <NUM>, preferably always open. In the shown embodiment, the minor base <NUM> is provided with an opening 17a for allowing entrance of the jet coming from a sprayer or nozzle spraying a mixture of a substance, usually containing urea, capable of promoting the desired chemical reaction in the exhaust gases. Preferably, said sprayer entirely occupies the opening 17a and the corresponding nozzle is oriented inward of the cavity <NUM>, whereby said minor base is impermeable to the gases passing through the mixer <NUM>.

As can be better appreciated from <FIG>, the mouth <NUM> is delimited by a peripheral edge <NUM> subtending a minimum surface area, substantially incident on the lateral wall <NUM> of the body <NUM> of the mixer <NUM>. The edge <NUM> of the mouth <NUM> further has, preferably, on the lateral wall <NUM>, a portion in common with the edge <NUM> of the radial opening <NUM>.

Referring in particular to <FIG> and <FIG>, in the illustrated embodiment, said peripheral edge <NUM> lies substantially on a plane P1, incident relative to the lateral wall <NUM> of the body <NUM> of the mixer <NUM>. In addition, still referring to the illustrated embodiment, said plane P1 is inclined by an angle δ of about <NUM>° relative to the planes P2 and P3 on which the opposite parallel bases, <NUM> and <NUM> lie, respectively. The minimum surface subtended by the peripheral edge <NUM> can further have a helicoidal development, irrespective of whether it is a flat or curved surface, and can therefore be inclined relative to the axis of revolution S and to the planes P2 and P3. In the helicoidal configuration, said angle δ will therefore be other than <NUM>° and, depending on the embodiments, may preferably be between <NUM>° and <NUM>°.

The plane P1 of each mouth <NUM> is further preferably tangent to the same cylinder coaxial to the longitudinal axis "S" of the body of the mixer <NUM>. In the illustrated embodiment, the radius of the cylinder to which the planes P1 are tangent is approximately equal to the radius of said opening 17a; in other embodiments, said cylinder may have radiuses different from those of the opening 17a and, furthermore, said opening 17a may be absent. According to this embodiment of the invention, the mouth <NUM> is oriented so as to allow passage of the gases from and towards the inner cavity <NUM> of the mixer <NUM>, mainly in a direction tangential to the lateral wall <NUM> of the mixer body, i.e. according to a direction perpendicular to the plane of <FIG> and parallel to the plane of <FIG>. Therefore, according to this arrangement of the mouths <NUM>, when the mixer <NUM> is housed in an exhaust system of an internal combustion engine, the gases discharged from the engine, can, depending on the arrangement of the mixer <NUM> in the exhaust system, either enter the cavity <NUM> of the mixer <NUM> tangentially, passing at first through the mouth <NUM> and then through the opening <NUM>, or exit said cavity <NUM> by passing at first through the opening <NUM> and then through the mouth <NUM>, eventually reaching the environment outside the mixer <NUM>. In both cases, the path followed by the exhaust gases between the mouth <NUM> and the opening <NUM>, or vice versa, will be a substantially vortex-like path, as the mouth <NUM> and the opening <NUM> are oriented on planes or surfaces inclined relative to each other.

According to the embodiment shown in <FIG>, the mouth <NUM> is oriented so as to minimize the passage of the gases from and towards the inner cavity <NUM> of the mixer <NUM> in an axial direction, i.e. in a direction parallel to the symmetry axis "S".

Referring to <FIG>, the geometry of the mixer according to a preferred embodiment of the invention will be described in detail.

<FIG> shows a general sectional plane Sn, perpendicular to the axis of revolution "S", transversely cutting through the body <NUM> of the mixer <NUM> along the dashed line Rn. In <FIG>, the plane Sn intersects the edge <NUM> of the radial opening <NUM> at the points xn and xn+hn and the edge <NUM> of the mouth <NUM> at the points xn and yn. The segment hn represents the transverse width on the plane Sn of the radial opening <NUM>, defined by the angle αn between the straight line hn and the straight line tangent to the circumference at xn. In this embodiment of the invention, the radial opening <NUM> and the mouth <NUM> share the portion of their respective edges <NUM> and <NUM> on the lateral wall <NUM>, whereby the point xn in which said edges <NUM> and <NUM> intesect the plane Sn coincides. The radial opening <NUM> is extended over by the blade <NUM>, the profile of which is defined by the angles βn and γn formed between the straight line hn and the tangent to the blade <NUM>, respectively, at the points yn and xn + hn. On the plane Sn, the blade <NUM> is contained between the circumferences with radius Dxn and Dyn > Dxn, both centered on the symmetry axis S of the solid of revolution which defines the body <NUM> of the mixer <NUM>. By joining the points xn and yn to a straight line Zn, having an angle θn between <NUM>°÷<NUM>° relative to the tangent to the circumference with radius Dxn at the point xn, it is possible to obtain the plane on which the surface subtended by the edge <NUM> of the mouth <NUM> extends, in the case where said mouth extends over a plane, as in the example of the <FIG>, or the straight lines approximating said surface at each section Sn in the case of the non-plan minimum surface area, subtended by the edge <NUM>.

Referring to <FIG>, with "A" indicating the minimum surface area subtended by the edge <NUM> of the mouth <NUM>, be it plan or curved, and with "a" indicating the area of the projection of said surface on a plane P4 perpendicular to the straight line Q passing through the geometric center CG of said surface and the axis of revolution "S", according to the invention the following will preferably be obtained: <MAT>.

By geometric center CG of the minimum surface area subtended by the edge <NUM>, it is meant the "median position" of the points of the profile generated by said surface, relative to any tridimensional reference system, i.e. the arithmetic mean of the positions of each of said points along the directions x, y, z of any spatial reference system.

<FIG> represent an embodiment of the invention in which the edge <NUM> of the mouth <NUM> lies on a curved surface and, with "b" indicating the projection of the minimum surface area that is subtended by the edge <NUM> on a plane perpendicular to the axis of revolution "S" and does not intercept the said surface, according to the invention the following will preferably be obtained: <MAT>.

In other words, assuming that the major base <NUM> of the body <NUM> of the mixer <NUM> lies on a plane perpendicular to the axis of revolution "S", the projection of the minimum area surfaces subtended by the edge <NUM> of the mouths <NUM> on said plane will have an area b smaller by <NUM>% than the area A of said minimum surface area.

Advantageously, according to the invention, the mixer <NUM> can be used, without substantial modifications or adaptations, in a plurality of applicative conditions. The mixer <NUM> can be oriented within an exhaust gas treatment unit with its axis of revolution "S" along any direction relative to the predominant direction of the gases. For example, the mixer <NUM> can be oriented with the axis of revolution "S" perpendicular or parallel to the advancing direction of the exhaust gases. In addition, whatever the configuration adopted for the body of the mixer <NUM> within the exhaust gas treatment unit may be, the mixer <NUM> can be associated to a sprayer of a substance suitable for causing the desired chemical reaction, for example a reducing agent such as urea, oriented substantially according to any direction relative to the axis of revolution "S". In particular, the spraying nozzle can be oriented with its longitudinal axis parallel to the axis of revolution "S" of the mixer <NUM>, either in the same direction as the flow of exhaust gases, or in counter-flow, or the spraying nozzle can be oriented with its axis along a direction inclined relative to the axis of revolution "S". In addition, still according to the invention, the mixer <NUM>, when having different opposite bases, for example when the body <NUM> is made with a frustoconical shape, can be indifferently oriented with the minor base upstream of the major base <NUM>, or vice versa, in the predominant direction of advancing of the exhaust gases.

Referring in particular to <FIG>, there is illustrated a configuration, in which both opposite bases <NUM>, <NUM> of the body <NUM> of the mixer <NUM> are open. The numeral <NUM> indicates a general spraying nozzle located in front of the opening 17a or, more preferably, within said opening 17a of the base <NUM>, which, in the illustrate embodiment, corresponds to the minor base, the body <NUM> having a frustoconical shape, so as to completely engage said opening 17a, thus preventing the exhaust gases from entering through said opening 17a and making said base <NUM> impermeable to the exhaust gases. Preferably, according to the invention, the nozzle <NUM> is arranged relative to the body <NUM> in such a way that the jet of substance exiting the nozzle, typically having a frustoconical shape, indicated with the reference numeral 71a in the figure, does not impinge upon the wall of the cavity <NUM> within the mixer <NUM> and is distributed in the flow of gases, immediately downstream of the second base <NUM>, opposite to the base from which the jet 71a enters the body <NUM> of the mixer.

Referring to <FIG>, these show corresponding embodiments of an exhaust gas treatment unit <NUM> of an internal combustion engine <NUM>, in which a static mixer <NUM> is incorporated, made according to the invention. The treatment unit <NUM> connects an internal combustion engine <NUM>, which, in the illustrated example, is a Diesel cycle engine, to an outlet duct <NUM> communicating with the outer environment, arrow F1. The unit <NUM> comprises at least one intermediate duct <NUM> for the passage of the exhaust gases coming from the engine <NUM> and directed to the outlet duct <NUM>. The intermediate duct <NUM> generally houses at least a first exhaust gas treatment unit <NUM>, upstream of the mixer <NUM>, and at least a second exhaust gas treatment unit <NUM>, downstream of the mixer <NUM>.

For example, the first unit <NUM> arranged upstream of the mixer <NUM> may comprise an "Oxidation Catalyst" (DOC), possibly associated with a "Diesel Particulate Filter" (DPF), and the second unit <NUM> arranged downstream of the mixer <NUM> may comprise a "Selective Catalytic Reduction" (SCR) unit, or an SCR unit incorporated in a "soot filter" (SCRoF), possibly associated with an "Ammonia Slip Catalyst" (ASC) or a "Clean-Up Catalyst" (CUC), or a "Diesel Particulate Filter" (DPF), possibly associated with an "Ammonia Slip Catalyst" (ASC) or a "Clean-Up Catalyst" (CUC) device.

In the illustrated embodiments, a static mixer <NUM> made according to the present invention and having a substantially bell-like or frustoconical shape is provided between the first unit <NUM> and the second unit <NUM>. More precisely, and relative to the preferential direction of flowing of the exhaust gases through the intermediate duct <NUM> (arrows F2, F3), the first unit <NUM> is arranged downstream of the internal combustion engine <NUM> and upstream of the mixer <NUM>, and the mixer <NUM> is arranged upstream of the second unit <NUM>. According to the described arrangement, therefore, the exhaust gases exiting the internal combustion engine <NUM> flow, in order, through the first unit <NUM>, the mixer <NUM> and second unit <NUM>, before passing through the outlet duct <NUM> and being introduced into the atmosphere, arrow F1.

Referring now in particular to <FIG>, there is illustrated a first embodiment of the exhaust gas treatment unit <NUM>. According to this embodiment, the mixer <NUM> comprises a minor base <NUM> having the aperture 17a for entrance of a flow of substance, for example urea, exiting a spraying nozzle <NUM>, preferably associated with a sprayer entirely occupying the opening 17a so as to prevent passage of the exhaust gases through said opening 17a. According to the invention, the opening 17a, if any, is configured for preventing passage of the exhaust gases therethrough. The opposite base <NUM> of the mixer <NUM> is open and allows exit of the exhaust gases coming from the I. engine <NUM> and radially directed against the lateral wall <NUM> of the mixer <NUM>. In the shown embodiment, the intermediate duct <NUM> defines a substantially "L"-shaped path and includes a first portion 81a defining a chamber <NUM> housing the first unit <NUM> and the mixer <NUM>, and a second portion 81b partially penetrating in the chamber <NUM> and surrounding the second base <NUM> of the mixer so that the entire flow of exhaust gases exiting the opening of the base <NUM> is directed inside said second duct portion 81b, where the exhaust gases assume a whirlpool vortex-like path, arrows F4. Preferably, both portions 81a, 81b have a cylindrical cross-section and are straight, and the portion 81b is oriented with its axis substantially perpendicular to the axis of the section 81a. In addition, the mixer <NUM> housed within the chamber <NUM> is arranged substantially coaxial to the second duct portion 81b and receives the exhaust gas, axially flowing through the first duct portion <NUM>, through the mouths <NUM> and the corresponding radial openings <NUM>, arrows F2.

According to this embodiment, the sprayer <NUM> is preferably configured so that the mixture sprayed by the nozzle <NUM> does not impinge against the inner surface of the lateral wall <NUM> of the mixer <NUM> and becomes mixed with the exhaust gas mainly outside the body of the mixer <NUM>, inside the second duct portion 81b. Still according to this first embodiment described, the jet of substance sprayed by the spraying nozzle <NUM> is directed in parallel flow relative to the flowing direction of the exhaust gases downstream of the mixer <NUM>, arrows F3,F4.

Referring to <FIG> and <FIG>, there is illustrated a second embodiment of the exhaust gas treatment unit <NUM>, in two embodiment variants. According to this embodiment, the mixer <NUM> comprises, in a first variant in <FIG>, an open minor base <NUM>, and, in a second variant in <FIG>, a closed minor base <NUM>. The opposite base <NUM> of the mixer <NUM> is always open and allows exit of the exhaust gases coming from the I. engine <NUM> and radially directed against the lateral wall <NUM> of the mixer <NUM>. In the illustrated embodiment, the intermediate duct <NUM> has a substantially straight shape and defines therein a chamber <NUM> housing, mainly, the first unit <NUM>, the mixer <NUM> and the second unit <NUM>. Said intermediate duct <NUM> further comprises a screen <NUM> defining a passage for the gases exiting the mixer <NUM>.

According to the first embodiment variant in <FIG>, the spraying nozzle <NUM> is arranged in front of the opening 17a of the base <NUM>, or, more preferably, within said opening 17a, so as to entirely occupy the gap of said opening 17a, thus preventing passage of the exhaust gases and making said base <NUM> impermeable to the exhaust gases, and the jet emitted by the sprayer <NUM> is directed into the cavity <NUM>. In this first embodiment variant, the spraying nozzle <NUM> is oriented so as to spray a mixture of substance in parallel flow relative to the predominant direction of advancing of the exhaust gases through the intermediate duct <NUM>, arrows F4.

According to the second embodiment variant in <FIG>, the spraying nozzle <NUM> is arranged in front of the open major base <NUM> of the mixer <NUM>. In this second embodiment variant, the spraying nozzle <NUM> is oriented so as to spray a mixture of substance in counter-flow relative to the predominant direction of advancing of the exhaust gases through the intermediate duct <NUM>, arrows F4.

The screen <NUM> provided downstream of the mixer <NUM> partially surrounds the mixer <NUM> and is arranged to convey the exhaust gases that have passed through the mixer <NUM> towards the second exhaust gas treatment unit <NUM> housed within the intermediate duct <NUM>.

In addition, similarly to the first embodiment, the exhaust gases coming from the engine <NUM> radially impinge against the lateral wall <NUM> of the mixer <NUM> and penetrate into the cavity <NUM> provided within the mixer <NUM> through the mouths <NUM> and the corresponding radial <NUM>, arrows F2.

Preferably, the intermediate duct <NUM> has a cylindrical cross-section and the mixer <NUM> is housed within the duct <NUM> with its axis of revolution substantially perpendicular to the longitudinal axis of the duct <NUM> and coaxial to the screen <NUM>.

According to this embodiment, the sprayer <NUM> is preferably configured so that the mixture of substance sprayed by the nozzle <NUM> does not impinge against the surface of the lateral wall <NUM> of the mixer <NUM> and becomes mixed with the exhaust gas mainly outside the body of the mixer <NUM>.

Referring now to <FIG>, there is illustrated a third embodiment of the exhaust gas treatment unit <NUM>. According to this embodiment, the mixer <NUM> comprises a preferably closed minor base <NUM>. The opposite base <NUM> of the mixer <NUM>, instead, is always open and allow entrance of the exhaust gases coming from the I. engine and axially directed against the mixer <NUM> and eventually reaching the cavity <NUM> defined within the mixer <NUM>. In the illustrated embodiment, the intermediate duct <NUM> has a substantially straight shape and houses therein mainly the first unit <NUM>, the mixer <NUM> and the second unit <NUM>. In addition, the spraying nozzle <NUM> protrudes into the duct <NUM>, downstream of the mixer <NUM>.

In this embodiment, the spraying nozzle <NUM> is oriented so as to spray a mixture of substance in parallel flow relative to the predominant direction of advancing of the exhaust gases through the intermediate duct <NUM>, arrows F3,F4,F5. In addition, the spraying nozzle <NUM> is provided downstream of the mixer <NUM> and is arranged so as to direct the mixture of substance into the duct <NUM>, where the exhaust gases assume a whirlpool vortex-like path, arrows F4.

Preferably, the duct <NUM> is straight and has a cylindrical cross-section. In addition, the mixer <NUM> is arranged substantially coaxial to the duct <NUM> and receives the exhaust gas axially flowing through the portion of the duct <NUM> located upstream of the mixer <NUM>, through the open major base <NUM>.

According to this embodiment of the invention, the mouths <NUM> and the corresponding radial openings <NUM> provided on the lateral wall <NUM> of the mixer <NUM> help in producing the whirlpool vortex-like motion of the exhaust gases, thus determining optimum mixing of the urea mixture introduced by the sprayer <NUM>.

Referring to <FIG>, the method of making a static mixer according to a preferred embodiment of the invention will be described, in which the body <NUM> of the mixer <NUM> is obtained by means of a metal sheet cold molding process.

Molding preferably takes place in a sequence of successive drawing and shearing operations.

Referring to <FIG>, there is illustrated an intermediate sequence of steps of the method according to this preferred embodiment of the invention, in which a bell-shaped body <NUM> having a lateral wall <NUM> and comprising a closed minor base <NUM> and an open major base <NUM> is obtained, by molding, from a metal sheet. This first working cycle is adapted to provide the lateral surface of the body <NUM> with the desired shape, having a cross-section that, depending on the embodiments, may be, for example, substantially circular, hexagonal, octagonal, pentagonal. At the end of this first working cycle, the body <NUM> has a closed lateral wall <NUM>, which is substantially smooth and regular.

<FIG> shows a further intermediate step of the method according to the invention, following the cycle described above, in which the body <NUM> is subjected to a cutting operation, preferably a laser-cutting operation, to obtain the mouths <NUM>.

At the end of the cycle described above, the body <NUM> is subjected to a further drawing step, in particular to prefect the shape of the body <NUM> of the mixer and the edges of the mouths <NUM>.

Claim 1:
Static mixer (<NUM>) for exhaust gas ducts of internal combustion engines, comprising an elongated hollow metal body (<NUM>) having a shape which, relative to a symmetry axis (S), substantially corresponds to a solid of revolution defining at its inside a cavity (<NUM>), in which opposite bases (<NUM>,<NUM>) are defined, at least one of which is provided with an axial opening, and a closed lateral wall (<NUM>) is defined connected to the opposite bases (<NUM>,<NUM>) and having at least one radial opening (<NUM>) over which a concave blade (<NUM>) is arranged extending radially outward of the lateral wall (<NUM>) of the mixer body from a portion of the peripheral edge (<NUM>) of the radial opening (<NUM>) and surrounding a portion of the radial opening (<NUM>) so as to define, in a first angular direction relative to the symmetry axis, a corresponding concave screen (<NUM>) and, in a second, opposite direction, a mouth (<NUM>) intended for the passage of gases and located substantially in front of the concave screen (<NUM>), wherein the body (<NUM>) of the mixer (<NUM>) has a frustoconical shape, characterized in that one of the basis of the body (<NUM>) of the mixer (<NUM>) is closed and thus exhaust-gas tight.