EP3180114B1

EP3180114B1 - Dynamic mixer with movable vanes for exhaust gases of i.c. engines

Info

Publication number: EP3180114B1
Application number: EP15767298.1A
Authority: EP
Inventors: Pier Mario Cornaglia; Federica GRASSI; Marco Micheletti; Alessio Tarabocchia; Zakaria TIJI; Giorgio Villata
Original assignee: Officine Metallurgiche G Cornaglia SpA
Current assignee: Officine Metallurgiche G Cornaglia SpA
Priority date: 2014-08-13
Filing date: 2015-08-10
Publication date: 2018-03-21
Anticipated expiration: 2035-08-10
Also published as: ES2674557T3; TR201808542T4; EP3180114A1; WO2016024207A1

Description

Technical Field

The invention relates to a dynamic mixer with movable vanes for exhaust gases of internal combustion (I.C.) engines.
The mixer according to the invention is adapted to be used for treating exhaust gases of I.C. engines and can be incorporated in a system for the selective catalytic reduction (SCR) of nitrogen oxides.

Prior Art

In exhaust systems of I.C. engines, mixers are commonly used for promoting mixing of exhaust gases with a reducing agent introduced in gaseous or liquid state. The mixer intercepts the gas flow, promoting evaporation of the reducing agent introduced in the exhaust system and facilitating formation of a highly homogeneous mixture. The presence of a mixer in the gas exhaust duct, however, inevitably causes partial obstruction and, consequently, a pressure increase inside the exhaust system. This pressure increase is an undesired phenomenon because it is of hindrance to the discharge of exhaust gases. Such drawback can be more or less significant depending on the structure of the mixer, of the exhaust system and of the engine operating regime. Therefore it would be desirable to reduce the pressure increase caused by the mixer, especially with certain operating regimes of the engine.
In addition, as is known, the surface of the mixer can cause condensation of the reducing mixture, with consequent formation of a liquid film which adheres to the mixer walls, thus causing loss of efficiency of the mixer itself.
Thus, two phenomena are to be contrasted when designing a mixer for exhaust gases. The first phenomenon is the one determined by excessive increases in the pressure of the exhaust system housing the mixer. The second phenomenon is the one determined by the reduction in 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 in the course of time. Some solutions provide for a matrix of vanes the density, inclination and size of which are chosen by taking into account the above requirements. US 20070204751 discloses an example of such kind of mixer. Other solutions provide for a set of vanes, which generally are radially arranged within the duct where gases flow and are oriented so as to cause mixing of said gases with the reducing agent mixture. A static mixer of this second type is disclosed for instance in WO2012176127 (A1 ) in the name of the present Applicant.
Mixers used so far are mainly of the static type, i.e. they comprise parts that do not vary their geometry during operation of the engine. The static mixer cannot be adapted to the varying characteristics of exhaust gases, typically pressure, speed, temperature, density and composition. With the spreading of static mixers, it has been possible to see that upon varying of the engine operating regimes and of the aforesaid characteristics of exhaust gases, the mixing capability and the effect of resistance to the passage of the gases, caused by the presence of the mixer, do not remain constant. Nowadays, a static mixer is preferably designed for attaining maximum efficiency at a specific operating regime of the engine and at a specific flow regime of the exhaust gases and the higher the deviation from these values is, the more reduced is usually the efficiency of the mixer.
More recently, so-called "dynamic" mixers with variable geometry have been developed, which are capable of modifying their spatial configuration upon variation of the conditions inside the exhaust duct. The mixers with variable geometry that are presently known are usually developed starting from materials with shape memory properties. These materials can modify their shape and spatial configuration upon temperature variation and to return to their initial shape when the temperature resumes its original value. Examples of this kind of mixers are described in US 2011/0258983 A1 and in US2010071352 (A1 ). The variable geometry mixers known so far therefore require use of materials with special properties. Such materials are generally expensive and are often poorly suited to the conditions in which the mixer operates. Indeed, the mixer operates inside the exhaust duct, where the operating conditions are extremely heavy, mainly because if the high temperatures and pressures.
WO-A-2006138174 on which the preamble of claim 1 is based discloses a dynamic mixer with movable vanes for exhaust gases of I.C. engines.
A first object of the invention is therefore to solve the problem of how to modify the mixer geometry without incurring the drawbacks of the prior art. Another object of the invention is to provide a mixer that meets the aforementioned requirements and is suitable for being manufactured both in a passive configuration, in which geometry variation is determined by the operating conditions, and in an active configuration, in which geometry variation is imposed from the outside. Another object of the invention is to provide a mixer that can be manufactured industrially in a simpler manner and at lower costs with respect to known mixers. A not least object of the invention is to provide a mixer of the kind discussed above which can be employed substantially in any exhaust system in which the selective catalytic reduction (SCR) technology is exploited.
These and other objects are achieved by means of the mixer for the treatment of exhaust gases as claimed in the appended claims.

Summary of the Invention

The mixer according to the invention comprises a stationary part having a substantially annular shape and a movable part provided with a plurality of vanes. The stationary part is adapted to be connected to an exhaust gases duct of an I.C. engine. The stationary part may also be integrated in an exhaust gases duct of an I.C. engine. The vanes of the movable part are preferably radial and arranged in a sunburst manner and they converge toward the center of the mixer. According to the invention, the vanes are disengaged from the stationary part and have their roots associated to the movable part. By means of this arrangement the relative movement between the two parts of the mixer determines a variation in the geometry of the vane relative to the flow of exhaust gases that hits the mixer. The solution proposed by the present invention therefore advantageously allows to vary the mixer geometry while maintaining a substantially constant form of the vanes, i.e. without intervening on the form of the vanes. The vanes are therefore not deformed by the reciprocal movement of the two mixer parts and can be made with materials and thicknesses suitable for the purpose, possibly also with shape memory properties.
In an embodiment of the invention, the relative movement between the stationary part and the movable part of the mixer is caused by the pressure exerted by the exhaust gases passing through the mixer. Therefore, advantageously, the mixer is made with a passive configuration, i.e. capable of adapting its geometry solely by effect of the conditions in which it operates, depending on the pressure of the gases inside the exhaust duct.
In another embodiment, the relative movement between the stationary part and the movable part of the mixer is caused by a control of the manual type or assisted type independent of the pressure of the gases, such as a hydraulic or pneumatic actuator or a servo-control or a motor-driven control. Advantageously, according to this embodiment, the mixer can be made with an active configuration and vary its geometry upon command given from outside, imparted for instance by means of an electronic unit, for instance depending on the operating conditions of the engine.
In still another embodiment of the invention, the relative movement between the stationary part and the movable part of the mixer is caused both by the pressure exerted by the exhaust gases passing through the mixer and by an actuator. Advantageously, according to this embodiment, the mixer can exploit the advantages of either the passive configuration or the active one, depending on the operating conditions.
According to the invention, elastic elements such as coil springs, which oppose the relative movement between the stationary part and the movable part of the mixer, are preferably provided between the stationary part and the movable part. The elastic elements are preferably provided for bringing the mixer back to its rest condition, corresponding to the absence of exhaust gases flow and absence of actuation by the actuator, if provided. The elastic elements are also preferably chosen so that the quantity of displacement of the movable part follows the desired curve with respect to the exhaust gases pressure values in the duct in which the mixer is installed.
According to a preferred embodiment of the invention, the mixer cooperates with an auxiliary mixer, preferably arranged concentrically relative to the movable part of the main mixer. According to this embodiment of the invention, the auxiliary mixer is preferably of the static type with radial vanes converging toward the center of the auxiliary mixer or arranged in a matrix configuration.

Brief Description of the Drawings

Some preferred embodiments of the invention will be described by way of non-limiting example with reference to the accompanying drawings, in which:

Fig.1 is a perspective view of a first embodiment of the mixer according to the invention;
Fig.2 is an exploded view of the mixer of Fig. 1;
Figs.3A and 3B are front views of the mixer of Fig.1 without closing flange and with its vanes in corresponding configurations;
Fig.4 is a longitudinal section of a second embodiment of the mixer according to the invention;
Fig.5 is an exploded view of the mixer of Fig.4;
Fig. 6 is a side view of the mixer of Fig.4;
Fig.7 is a perspective view of a third embodiment of the mixer according to the invention;
Fig.8 is an exploded view of the mixer of Fig.7;
Figs. 9A and 9B are front views of the mixer of Fig.7, in corresponding configurations;
Figs. 10A and 10B are side views of the mixer of Fig.7, in the configuration of Fig.9A and 9B, respectively;
Fig. 11 is a perspective view of an alternative of the third embodiment of the mixer according to the invention;
Fig. 12 is an exploded view of the mixer of Fig.1 1;
Fig.13 is a perspective view of the mixer of Fig.11 when incorporated in an exhaust gases duct of an I.C. engine;
Fig. 14 is a longitudinal section of the mixer of Fig. 11 when incorporated in an exhaust gases duct of an I.C. engine.

Description of Some Preferred Embodiments of the Invention

In the drawings, same or functionally equivalent parts are designated with the same reference numerals.
Referring to Figs.1 and 2, the mixer 11 according to this first embodiment of the invention has a stationary part 13 comprising an annular ferrule 15, and a movable part 17 provided with a plurality of radial vanes 19 and housed in the ferrule 15. The ferrule 15 comprises, on one face, an axial seat 21 for the movable part 17, said seat being surrounded by a circumferential rim 23. The base of the seat 21 for the movable part 17 comprises four axial pins 25 mutually circumferentially distributed at 90°. The movable part 17 comprises a disk-shaped body in which a peripheral annular supporting frame 27 is defined, from which the radial vanes 19 extend, with their roots associated to the frame 27. In the illustrated embodiment, frame 27 and vanes 19 are made as a single piece, for instance by molding or casting. The frame 27 comprises four slots 29 mutually arranged at 90° for receiving the axial pins 25 and corresponding holes 31 for fastening springs 33 arranged between the pins 25 and the holes 31. The ferrule 15 is closed by a ring-like closing flange 35 abutting against the circumferential rim 23 of the ferrule 15 when said ferrule is coupled to the stationary part 13. To this aim, centering holes are provided in the flange 35 for receiving the ends of the pins 25. The flange 35 is provided with a central bore 37 for the passage of the exhaust gases and comprises an axial extension 39 for fixing the mixer 11 to an exhaust duct section of the exhaust system of an I.C. engine. The movable part 17 is retained within the seat 21 by the flange 35, but it is free to rotate relative to the ferrule 15. The rotation of the movable part 17 in the seat 21 is limited angularly by the slots 29 and is guided by the pins 25. The rotation of the movable part 17 relative to the stationary part 13 takes place along an arc of circle that can reach at most the length of the slots 29. The relative rotation between the movable part 17 and the stationary part 13 takes place in a direction (counter-clockwise in Fig. 2) in opposition to the resistance of the springs 33. On the opposite side of the mixer 11 with respect to the flange 35, the ferrule 15 further comprises an extension 41 made as a cylindrical sleeve. The sleeve 41 is axially divided in two parts 41a,41b for allowing insertion of a possible auxiliary mixer 43 provided with vanes. The auxiliary mixer 43 comprises an annular frame 45 from which the roots of the vanes 47 of the auxiliary mixer 43 originate. In the illustrated embodiment, the vanes 47 extend radially toward the center of the auxiliary mixer 43. The two parts 41a,41b of the sleeve 41 are held together by means of tangential screws 49 that are engaged in a pair of radial projections 51a,51b divided in half between the two sleeve parts and provided on the outside of each part of the sleeve 41. On the inside, the sleeve 41 comprises an annular groove 53 for receiving the annular frame 45 of the auxiliary mixer 43. The sleeve 41 is fixed to an exhaust duct section of a gases exhaust system of an I.C. engine. This exhaust duct section is therefore in communication with the mixer 11 and with the duct section fixed to the flange 35. In this way, flow continuity in the gases exhaust system of the I.C. engine incorporating the mixer 11 is guaranteed.
When the pressure caused by the passage of exhaust gases through the mixer 11 overcomes the resistance of the springs 33, this causes rotation of the movable part 17 relative to the stationary part 13. The configurations taken by the mixer 11 during passage of the gases are better visible in Figs. 3A and 3B. In Fig.3A there can be seen the mixer 11 substantially at rest, i.e. when the springs 33 are relaxed. In this configuration the vanes 19 of the movable part 17 occupy the gaps defined between the vanes 47 of the auxiliary mixer 43, for maximizing the turbulence effect. In Fig.3B there can be seen the mixer 11 when it is subjected to the pressure of exhaust gases. In this configuration the vanes 19 of the movable part 17 and the vanes 47 of the auxiliary mixer 43 are aligned, for maximizing the gap for the passage of the gases. Between the configurations of Figs.3A and 3B there is provided a rotation of the movable part 17 relative to the stationary part 13, which rotation in the shown example is approximately 20° - 30°. In the illustrated embodiment, the rotation of the movable part 17 relative to the stationary part 13 takes place by virtue of the pressure of the exhaust gases which intercept the vanes 19 of the movable part. These vanes 19 are therefore configured for causing rotation of the movable part when the pressure of the gas hitting them increases. The mixer 11 is made so that the gases encounter at first the vanes 19 of the movable part 17 and then the vanes 47 of the auxiliary mixer 43 or vice versa, as needed.
Referring to Figs. 4, 5 and 6, the mixer 11 according to this second embodiment of the invention has a stationary part 13 comprising an annular ferrule 61 and a movable part 17 provided with a plurality of vanes 19 and housed in the ferrule 61. A rotary sleeve 63 is provided between the ferrule 61 and the movable part 17. The movable part 17 comprises a disk-shaped body in which a peripheral annular supporting frame 27 is provided, from which the radial vanes 19 with their roots connected to the frame 27 extend. The supporting frame 27 is housed in the rotary sleeve 63 and is attached thereto. The sleeve 63 is adapted to rotate, together with the frame 27 and the vanes 19 carried by the frame 27, relative to the ferrule 61. The sleeve 63 is surrounded by a toothed crown 65 having helical teeth and attached to the sleeve 63, for engagement of a tangential worm screw 67. The screw 67 is mounted on the driven shaft 69 of a gear motor 71 equipped with an electric motor 73. The screw 67 is housed in a transverse seat 77 provided tangentially on the ferrule 61, provided with bearings 77a,77b and radially open for allowing engagement of the screw 67 with the teeth of the crown 65. The mixer 11 according to this embodiment of the invention comprises a closing flange 79 opposite to the ferrule 61 with respect to the crown 65 and provided with a central bore 37 for passage of the exhaust gases. The flange 79 comprises an axial extension 39 for fixing the mixer 11 to an exhaust duct section 201 of the exhaust system of an I.C. engine. A sliding element 75 is provided between the rotary sleeve 63 and the ferrule 61. In the illustrated embodiment, the element 75 is a roller bearing 75. The bearing 75 has the purpose of allowing rotation of the movable part 17 relative to the stationary part 13 of the mixer. The mixer 11 may be provided with an auxiliary mixer 43 for instance with vanes 47, of the static type and arranged coaxially to the movable part 17. The mixer 11 is illustrated as being incorporated in an exhaust gases duct. A first duct section 201 is inserted in the flange 79 and firmly fixed, for instance by welding, to the extension 39 of the flange 79. The auxiliary mixer 43 is fixed by means of known means to the first duct section 201. A second duct section 203 is firmly fixed, for instance by welding, to the ferrule 61. The mixer 11 may be made so that the gases encounter at first the vanes 19 of the movable part 17 and then the vanes 47 of the auxiliary mixer 43 or vice versa, as needed.
Referring to Figs.7 and 8, the mixer 11 has a stationary part 13 comprising an annular ferrule 81 and a movable part 17 provided with a plurality of radial vanes 19 housed in the ferrule 81. The stationary part 13 further comprises a pair of flanges 83,85 surrounding the annular ferrule 81. The movable part 17 comprises a plurality of hinge pins 87 attached to the roots of the vanes 19 and provided with control cams 89. The ferrule 81 comprises a set of radial holes 91 angularly distributed in a regular manner. The holes 91 house the hinge pins 87 allowing rotation of the vanes 19 relative to the ferrule 81. The cam 89 of the pins 87 extends outside the ferrule 81 and is received in a seat 93 defined by the cooperation between corresponding half- seats 93a,93b provided in the two flanges 83,85, respectively. A first flange 83, or inner flange, further comprises a circumferential radial outer edge 97 provided with radial portions 97a interrupted by the half-seats 93a. The portions 97a extend radially outside the flange 83 and comprise a halfmoon-shaped seat 99 in which the head of a screw 101 axially arranged outside the flange 83 is retained. The inner flange 83 is further provided with a sleeve 103 extending axially from the opposite side of the ferrule 81. A second flange 85 or outer flange comprises a circumferential edge 105 abutting against the edge 97 of the inner flange 83 when the two flanges 83,85 are coupled to each other. When the two flanges 83,85 are coupled to each other, the edge 105 cooperates with the portions 97a of the inner flange 83 for retaining the head of the screws 101 in the halfmoon-shaped seats 99. The outer flange 85 is provided with a sleeve 107 extending axially from the opposite side with respect to the sleeve 103 of the inner flange 83. Both sleeves 103,107 are fixed to corresponding exhaust duct sections for connecting the mixer 11 to a gas exhaust system of an I.C. engine. The duct sections are therefore in mutual communication as well as in communication with the mixer 11, without interruptions. In the shown example, there are four screws 101 that are mutually arranged at 90° and hold an axially movable annular frame 109 surrounding the sleeve 103 of the inner flange 83. The screws 101 further engage with their ends in corresponding threaded holes 111 of a stationary frame 113 surrounding the sleeve 103. The movable frame 109 is provided with holes 115 for the passage of the shafts of the screws 101. Coil springs 117 surrounding the shafts of the screws 101 are provided between the stationary frame 113 and the movable frame 109. The cams 89 rest on the movable frame 109. The screws 101 act as guides for the movable frame 109. The screws 101 may be replaced for instance by pins or other guiding systems.
When the pressure exerted by the exhaust gases passing through the mixer 11 overcomes the resistance of the springs 117, rotation of the movable part 17 of the mixer 11 relative to the stationary part 13 is caused. The configurations taken by the mixer during its operation are better visible in Figs.9A,9B and 10A,10B. In Fig.9A and 10A there can be seen the mixer 11 at rest, i.e. when the springs 117 are relaxed. In this configuration the vanes 19 of the movable part 17 are substantially mutually coplanar in order to exert maximum resistance to the gases and maximize the turbulence effect. In Fig.9B,10B there can be seen the mixer 11 when it is subjected to a pressure of exhaust gases that is sufficient for overcoming the resistance of the springs. In this configuration the vanes 19 of the movable part 17 are rotated in order to increase the gap allowing passage of the gases through the mixer. Between the configurations of Figs. 9A,10A and 9B,10B there is provided a rotation of the movable part 17 relative to the stationary part 13, which in the shown example is approximately 15-85°, preferably approximately 70°, of the movable part 17 relative to the stationary part 13 and of the pins 87 carrying the vanes 19 relative to the ferrule 81. The mixer 11 must be mounted so that the pressure of the gases causes rotation of the vanes 19 by overcoming the resistance of the springs 117. According to the described arrangement, the gases must pass through the mixer in such a way that they encounter at first the sleeve 107 and then the sleeve 103.
Referring to Figs. 11 to 14, a motorized alternative of the above-illustrated third embodiment will now be described. In this alternative, the movable part 17 comprises a rotary sleeve 63 surrounded by a toothed crown 65 attached to the sleeve 63. In the shown example, the crown 65 has helical teeth for engagement of a tangential worm screw 67. The worm screw 67 is mounted on the drive shaft 69 of a gear motor 71 equipped with an electric motor 73. The rotary sleeve 83 is provided with abutment protrusions 119. The protrusions 119 cooperate with lever arms 121 mounted on the cams 89 and extending toward the rotary sleeve 63. The rotary sleeve 63 surrounds the sleeve 107 of the outer flange 85. A roller bearing 75 allowing rotation of the rotary sleeve 63 relative to the stationary sleeve 107 is interposed between the rotary sleeve 63 and the stationary sleeve 107. When the gear motor 71 is operated, rotation of the worm screw 67 causes rotation of the rotary sleeve 63 and consequently of the protrusions 119. Rotation of the protrusions 119 causes rotation of the lever arms 121 in opposition to the resistance of the springs 117. This motorized alternative allows to control rotation of the vanes 19 independently of the pressure exerted by the flow of exhaust gases. The mixer 11 according to this alternative can be mounted, as needed, so that the gas encounter at first the sleeve 107 and then the sleeve 103 or vice versa.
As can be better seen in Fig.14, the sleeve 103 of the inner flange 83 and the sleeve 107 of the outer flange 85 are fixed to corresponding sections 203,201 of a gas exhaust duct of an I.C. motor. When the mixer 11 is incorporated in the exhaust duct, the two sections 201,203 are in mutual communication through the mixer 11 without interruptions.
The components of the mixer according to the present invention in the described embodiments are preferably made of metal. In addition, components such as sleeves, ferrules, flanges and frames preferably have a circular configuration. Configurations other than the circular one, for instance oval or rectangular configurations, may be provided for adapting to corresponding sections of exhaust ducts. Movably fixed parts of the are preferably connected to one another by welding or other means for permanent connections such as gluing.

Claims

Dynamic mixer (11) with movable vanes (19) for exhaust gases of I.C. engines, comprising a stationary annular part (13) adapted to be connected to an exhaust gases duct of I.C. engines and a movable part (17) provided with a plurality of vanes (19), wherein the vanes (19) are disengaged from the stationary part (13) and have their roots associated to the movable part (17) so that the relative movement between the two parts (13,17) of the mixer causes a variation in the geometry of the vanes (19) with respect to the flow of exhaust gases that hits the mixer, while maintaining substantially constant form of the vanes,
wherein the relative movement between the stationary part (13) and the movable part (17) is caused by the pressure exerted by the exhaust gases passing through the mixer and/or by a control of the manual type or assisted type independent of the pressure of the gases, characterizd in that:
elastic elements (33;117) which oppose the relative movement between the stationary part (13) and the movable part (17) caused by the pressure exerted by the exhaust gases passing through the mixer and/or by the manual or assisted control are arranged between the stationary part (13) and the movable part (17).
Mixer according to claims 1, wherein an auxiliary static mixer (43) is provided which is equipped with vanes (47) and is arranged concentrically relative to the movable part (17).
Mixer according to claims 1 or 2, wherein the movable part (17) is movable angularly relative to the stationary part (13).
Mixer according to claim 3, wherein the movable part (17) is retained within a seat (21) obtained in the stationary part (13) and is free to rotate relative to the stationary portion (13), rotation of the movable part (17) relative to the fixed part (13) being limited angularly by slots (29) provided in the movable part which is guided by guide pins (25) that are attached to the stationary part (13) and received within the slots (29).
Mixer according to claim 3, wherein the movable part (17) comprises radial vanes (19), arranged in a sunburst manner and converging toward the center of the mixer (11), and a plurality of hinge pins (87) attached to the roots of the vanes (19) and provided with control cams (89) for causing rotation of the vanes (19) around the axis of the pins (87).
Mixer according to claim 3, wherein the stationary part (13) comprises an annular ferrule (61) housing the movable part (17), and wherein a rotary sleeve (63) adapted to rotate relative to the annular ferrule (61) together with the movable part (17) and the vanes (19) is provided between the annular ferrule (61) and the movable part (17), the sleeve (63) being surrounded by a toothed crown (65) attached to the sleeve (63) for engagement of a tangential worm screw (67) mounted on the driven shaft (69) of a gear motor (71) equipped with an electric motor (73).
Mixer according to claim 5, wherein the control cams (89) interfere with an annular frame (109) axially movable along axial guides (101) relative to a stationary frame (113), elastic elements (33;117) being provided between the stationary frame (113) and the movable frame (109) so that when the pressure exerted by the exhaust gases passing through the mixer (11) overcomes the resistance of the elastic elements (33;117), rotation of the vanes (19) of the mixer relative to the stationary part (13) is caused.
Mixer according to claim 7, wherein the movable part (17) further comprises a rotary sleeve (63) provided with abutment protrusions (119) cooperating with lever arms (121) mounted on the cams (89) and extending toward the rotary sleeve (63) so that when the sleeve (63) is rotated rotation of the protrusions (119) causes rotation of the lever arms (121) and of the vanes (19) against the resistance of the elastic elements (33;117),