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(11) | EP 2 375 046 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Single valve mixing device for a low pressure EGR system of an internal combustion engine |
| (57) A mixing device (23) for a low pressure EGR system (21) of an internal combustion
engine; the mixing device (23) has: a first intake conduit (25) which can be connected
to an EGR conduit (22); a second intake conduit (26) which can be connected to a suction
of fresh air from the outside; an exit conduit (27) which can be connected to an intake
conduit (6); and a control valve (28), which is placed at a confluence of the intake
conduits (25, 26) and comprises only one shutter (29) which varies the section of
both the intake conduits (25, 26).
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TECHNICAL FIELD
[0001] The present invention relates to a single valve mixing device for a low pressure EGR system of an internal combustion engine.
PRIOR ART
[0002] An EGR (Exhaust Gas Recirculation) system is often present in modern internal combustion engines, which system feeds part of the exhaust gases produced by the combustion into the suction conduit so as to mix the exhaust gases with the fresh air in order to uniform the temperature in each combustion chamber, and consequently reduce the polluting substances present in the exhaust gases which are released into the atmosphere.
[0003] An EGR system comprises an EGR conduit, which connects the exhaust conduit to the suction conduit, and a mixing device which is arranged at the intersection between the EGR conduit and the intake conduit, and which has the function of adjusting the mixing of exhaust gas from the exhaust conduit with the fresh air present in the suction conduit. Typically, the mixing device comprises a butterfly valve, which is arranged at the EGR conduit, is actuated by an electric motor and has the function of varying the section of the EGR conduit to vary the flow of exhaust gases which are introduced into the suction conduit.
[0004] The above-described structure of the mixing device has the advantage of being cost-effective and at the same time of allowing to rather accurately adjust the exhaust gas flow rate introduced into the suction conduit; however, the above-described structure of the mixing device does not allow to accurately adjust the exhaust gas flow rate introduced into the intake conduit in all operative conditions, and in particular when the introduction of a particularly high exhaust gas flow rate into the suction conduit is required.
DESCRIPTION OF THE INVENTION
[0005] It is the object of the present invention to provide a single valve mixing device for a low pressure EGR system of an internal combustion engine, which device is free from the drawbacks described above, and in particular, is easy and cost-effective to implement.
[0006] According to the present invention, a single valve mixing device for a low pressure EGR system of an internal combustion engine is provided as disclosed in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The present invention will now be described with reference to the accompanying drawings, which illustrate a non-limitative embodiment thereof, in which:
- figure 1 is a diagrammatic view of a supercharged internal combustion engine provided with an EGR system using a mixing device made according to the present invention;
- figure 2 is a diagrammatic perspective view, with parts removed for clarity, of the mixing device in figure 1;
- figures 3, 4 and 5 are three section views of the mixing device in figure 1 which show three different positions assumed by a shutter of a control valve;
- figure 6 is a chart which illustrates the evolution of the passage section of the intake conduits of the mixing device in figure 1 as the position of the shutter of the control valve varies;
- figures 7 is a perspective, diagrammatic view with parts removed for clarity of the shutter of the control valve in figures 3, 4 and 5; and
- figure 8 is a perspective view of an insert made of refractory material arranged along a shaft of the control valve in figures 3, 4 and 5.
PREFERRED EMBODIMENTS OF THE INVENTION
[0008] In figure 1, numeral 1 indicates as a whole an internal combustion engine supercharged by a turbocharger supercharging system 2.
[0009] The internal combustion engine 1 comprises four cylinders 3, each of which is connected to a suction manifold 4 by means of at least one respective suction valve (not shown) and to an exhaust manifold 5 by means of at least one respective exhaust valve (not shown). The suction manifold 4 receives fresh air (i.e. air coming from the external environment) through a suction conduit 6, which is provided with an air cleaner 7 and is adjusted by a butterfly valve 8. An intercooler 9 for cooling the sucked air is arranged along the suction conduit 6. An exhaust conduit 10, which feeds the exhaust gases produced by the combustion to an exhaust system, is connected to the exhaust manifold 5, which exhaust conduit emits the gases produced by the combustion into the atmosphere and normally comprises at least one catalyzer 11 and at least one silencer (not shown) arranged downstream of the catalyzer 11.
[0010] The supercharging system 2 of the internal combustion engine 1 comprises a turbocharger 12 provided with a turbine 13, which is arranged along the exhaust conduit 10 in order to rotate at high speed under the bias of the exhaust gases expelled from the cylinders 3, and a turbocharger 14, which is arranged along the suction conduit 6 and is mechanically connected to the turbine 13 in order to be rotatably fed by the turbine 13 itself so as to increase the pressure of the air fed into the suction conduit 6.
[0011] A bypass conduit 15 is provided along the exhaust conduit 10, which bypass conduit is connected in parallel to the turbine 13 so that the ends thereof are connected upstream and downstream of the turbine 13 itself; a wastegate 16 is arranged along the bypass conduit 15, which wastegate is adapted to adjust the exhaust gas flow rate through the bypass conduit 15 and is controlled by a pneumatic actuator 17. A bypass conduit 18 is provided along the intake conduit 6, which bypass conduit is connected in parallel to the turbocharger 14 so that the ends thereof are connected upstream and downstream of the turbocharger 14 itself; a Poff valve 19 is arranged along the bypass conduit 18, which Poff valve is adapted to adjust the exhaust gases which flow through the bypass conduit 18 and is controlled by an electric actuator 20.
[0012] The internal combustion engine 1 comprises a low pressure EGR system 21, which recalculates part of the exhaust gas present in the exhaust conduit 10 by introducing such exhaust gases into the suction conduit 6. The EGR system 21 comprises an EGR conduit 22, which connects the exhaust conduit 10 to the suction conduit 6, and a three-way mixing device 23, which is arranged at the intersection between the EGR conduit 10 and the suction conduit 6, and which has the function of adjusting the mixing of the exhaust gases from the exhaust conduit 10 with the fresh air present in the suction conduit 6. According to a preferred embodiment, a heat exchanger 24 is arranged along the EGR 22 for cooling the exhaust gases from the exhaust conduit 10.
[0013] The low pressure EGR system 21, i.e. the EGR conduit 22, originates from the exhaust conduit 10 downstream of the catalyzer 11 so as to take the exhaust gases which have been already treated by the catalyzer 11 itself and which have a pressure only slightly higher than the atmospheric pressure; in this manner, the exhaust gases recirculated by the EGR conduit 22 are "cleaner", i.e. have a lower content of polluting substances. Such a configuration is also named "Long-Route" EGR, because the EGR conduit 22 must be longer than normal to reach downstream of the catalyzer 11.
[0014] The three-way mixing device 23 connects the suction manifold 6 to the EGR conduit 22. As shown in greater detail in figure 2, the mixing device 23 comprises an intake conduit 25, which is connected in series to the EGR conduit 22, an intake conduit 26, which is connected in series to a conduit coming from the air cleaner 7, and an exit conduit 27, which is connected in series to the intake conduit 6. As shown in figure 2, the exit conduit 27 is parallel and offset with respect to the intake conduit 26, while the intake conduit 25 forms an angle of approximately 70° with the exit conduit 27 and with the intake conduit 26. In particular, the intake conduit 26 is offset with respect to the exit conduit 27 and thus at the intake conduct 25 there is a curve which joins the intake conduit 26 to the exit conduit 27.
[0015] A single control valve 28, which varies the section of both intake conduits 25 and 26, is placed at a confluence of the intake conduits 25, 26. The control valve 28 comprises a single shutter 29 which is rotably mounted to turn about an axis of rotation 30 between two limit positions shown in figures 3 and 5. In particular, the shutter 29 turns about the axis of rotation 30 between a limit position of minimum EGR (shown in figure 3), in which the shutter 29 completely closes the intake conduit 25 and leaves the intake conduit 26 completely open, and a limit position of maximum EGR (shown in figure 5), in which the shutter 29 closes nearly completely the intake conduit 26 and leaves the intake conduit 25 completely open. There is a series of intermediate positions (of the type shown in figure 4) arranged between the two limit positions illustrated in figures 3 and 5, in which the intake conduit 25 is partially open and the intake conduit 26 is either completely or only partially open.
[0016] The above is illustrated in figure 6, in which according to the angular position · of the shutter 29 about the rotation axis 30 (shown in abscissa) a solid line shows the degree of opening/closing of the intake conduit 25 and a dotted line shows the degree of opening/closing of the intake conduit 26. In figure 5 it is apparent that in the limit position of minimum EGR (shown on the extreme left of the chart) the intake conduit 25 is completely closed and the intake conduit 26 is completely open, and in the limit position of maximum EGR (shown on the extreme right of the chart) the intake conduit 25 is completely open and the intake conduit 26 is nearly completely closed. Furthermore, moving from the limit position of minimum EGR towards the limit position of maximum EGR the intake conduit 25 opens while the intake conduit 26 remains all open for a given interval until the intake conduit 25 reaches a predetermined, partial opening position; only starting from such a predetermined partial opening position of the intake conduit 25 the intake conduit 26 closes while the intake conduit 25 continues to open. It is worth observing that for the sake of simplicity in figure 5 the laws of variation of the degree of opening of the intake conduits 25 and 26 are considered linear while in actual fact such laws have an at least partially curvilinear pattern.
[0017] As shown in figure 2, the control valve 28 comprises an actuating device 31 which adjusts the angular position of the shutter 29 about the axis of rotation 30. In particular, the actuating device 31 comprises an electric motor (not shown) and a geared transmission (not shown) which transmits motion from a shaft of an electric motor to the shutter 29 of the control valve 28; overall, the geared transmission has a transmission ratio which demultiplies the rotation speed of the electric motor shaft (i.e. the shaft of the electric motor turns faster than the shutter).
[0018] According to a possible embodiment (not shown) the actuating device 31 further comprises a return spring which tends to push the shutter 29 of the control valve 28 to the limit position of minimum EGR (in which the intake conduit 26 is completely open and the intake conduit 25 is completely closed) thus in complete absence of exhaust gas recirculated in the suction conduit 6. In case of malfunction of the electric motor 31 of the actuating device 31, the return spring guarantees that the shutter 29 is moved and maintained in neutral position free from recirculated exhaust gases in the suction conduit 6.
[0019] The actuating device 31 comprises a box 32 which has a cylindrical housing 33 in which an electric motor is arranged, and a housing in which the geared transmission is arranged. Preferably, the box 32 is provided with a removable cover, which is equipped with an annular seal for ensuring adequate tightness. According to preferred embodiment, the housing 32 is supported solely by the intake conduit 26 (i.e. does not touch in any manner the intake conduit 25 itself and is instead arranged at a given distance from the intake conduit 25 itself); in this manner, the heat released by the exhaust gases present in the intake conduit 25 is not significantly transmitted to the box 32, and thus to the actuating device 31 arranged inside the box 32. The box 32 may be independent and separable from the intake conduit 26 and may be consequently fixed to the intake conduit 26 by means of screws to allow a same box 32 (i.e. the same actuating device 31) to be fitted in intake conduits 26 of different size thus obtaining a scalability of the mixing device 23; in other words, the mixing device 23 has a modular structure because the same box 32 (i.e. the same actuating device 31) may be fitted on conduits 25, 26 and 27 of variable dimension so as to make a wide range of mixing devices 23 which differ from one another for their active flow rate. Alternatively, the box 32 forms a single indivisible (monolithic) body with the intake conduit 26.
[0020] Preferably, cooling fins 35 are provided which connect the cylindrical housing 33 to the outer wall of the intake conduit 26; the function of the cooling fins 35 is to transfer by conduction part of the heat produced by the electric motor from the inside of the cylindrical housing 33 towards the intake conduits 26 is continuously cooled by the fresh air which flows into the intake conduit 26 itself.
[0021] As shown in figures 3-5, the shutter 29 comprises a shaft 36 rotably mounted about the rotation axis 30, a plate which as a flat shape and is rigidly connected to the shaft 36 to turn with the shaft 36 about the axis of rotation 30, and a protuberance 38 having a shape of a truncated cone that rises cantilever from the plate 37. The control valve 28 comprises a valve seat 39 which is obtained at the exit opening of the intake conduit 25 and reproduces in negative at least part of the shape of the protuberance 38 of the shutter 29 (thus the valve seat 39 has a shape of a truncated cone). When the control valve 28 is in the limit position of minimum EGR (shown in figure 3) in which the shutter 29 completely closes the intake conduit 25, the protuberance 38 of the shutter 29 is thus inserted in the valve seat 39; thus the seat of the shutter 29 is made on the truncated cone shape side surface of the protuberance 38.
[0022] According to a preferred embodiment, the protuberance 38 of the shutter 29 has a radial elastic deformability allowing the protuberance 38 to adapt to the shape of the valve seat 39 when inserted inside the valve seat 39 itself. In other words, because of the inevitable constructive tolerances, differences of shape and/or dimensions between the protuberance 38 of the shutter 29 and the valve seat 39 always exist; in order to compensate for such differences, the protuberance 38 by being inserted in the valve seat 39 is deformed elastically guaranteeing in this manner a perfect sealing (i.e. significantly preventing the leakage of exhaust gas present in the intake conduit 25). As shown in figure 7, the protuberance 38 consists of a thin steel plate which is fixed to the plate 37 in a few welding points 40 and has axial weakening cuts 41. By virtue of the presence of a limited number of welding points 40 and the presence of axial weakening cuts 41, the protuberance 38 offers a relatively high radial elastic deformability, which allows to elastically adapt to the shape of the valve seat 39. In this manner, the shutter 29 may be made entirely of steel and not require the presence of rubber seals; such a feature is very important because the exhaust gases which flow through the intake conduit 25 and strike the shutter 29 have a temperature of approximately 350°C which makes the presence of a rubber seal problematic.
[0023] According to a preferred embodiment shown in figure 8, the shaft 36 of the control valve 28 has an outer portion 42 which protrudes through a through hole provided with a seal for coupling to an actuating device 31. By virtue of the fact that the box 32 is separate from the intake conduit 25, the heat of the intake conduit 25 may be transmitted to the box 32 only by radiation or convection and not by conduction; the overheating of the box 32 can be limited in this manner. In order to further reduce the transmission of heat from the intake conduit 25 to the box 32 and to the geared transmission 37 of the actuating device 31, at least one part of the outer portion 42 of the shaft 31 of the control valve 28 is made of a heat-insulating material; in particular, the outer portion 42 of the shaft 36 of the control valve 28 comprises an insert 53 made of heat-insulating material, and in particular of refractory material (typically ceramic). It is worth noting that the insert 43 has the function of both heat insulation (i.e. of obstructing the transmission of heat by conduction along the shaft 36 and towards the box 32 and the geared transmission 37) and motion transmission (i.e. of transmitting rotation motion along the shaft 36 between shaft 29 and geared transmission 37).
[0024] As shown in figure 8, the insert 43 made of heat-insulating material constitutes part of the outer portion 42 of the shaft 36 of the control valve 28 and is arranged between two sections of the outer portion 42 so as to thermally separate the two sections of the outer portion 42 (i.e. preventing heat transmission by conduction) and maintaining a mechanical continuity of the shaft 36 to transmit the rotation movement along the shaft 36 between the shutter 29 and the geared transmission 37. The heat-insulating material insert 43 is mechanically fitted on both sides of the corresponding sections of the outer portion 42; the fixed joints between the insert 43 and the two sections of the outer portion 42 also have an angular bond so as to prevent the relative rotation between the insert 53 and the two sections of the outer portion 42 to transmit rotary movement along the shaft 36 between the shutter 29 and the geared transmission 37. According to the embodiment shown in figure 8, each fixed joint between the insert 43 and the section of the outer portion 42 comprises a cross-shaped protuberance 44, which axially rises from the insert 43 and is inserted in a seat 45, which is obtained in the section of the outer portion 42 which reproduces in negative the shape of the protuberance 44.
[0026] Firstly, the above-described mixing device 23 is simple and cost-effective to make because it has a single control valve 28 which allows to choke both intake conduits 25 and 26 in differentiated manner.
[0027] Furthermore, by virtue of the fact that the control valve 28 chokes both intake conduits 25 and 26 in differentiated manner, it is possible to control again in optimal manner the mixing of cool air in the intake conduit 26 with the exhaust gases present in the intake conduit 25. In particular, in the limit position of maximum EGR (or in proximity to such a position) the intake conduit 26 is nearly completely closed and thus it is possible to introduce into the suction pipe 6 a particular highly exhaust gas flow rate, which is always adjustable with extreme accuracy.
[0028] In the above-described mixing device 23 modifying the mixing features of the exhaust gases present in the EGR conduit 22 with the fresh air present in the suction conduit 6 is simple by modifying the shape of the shutter 29 (shutter 29 which has a very low replacement cost).
[0029] Finally, the above-described mixing device 23 has a high reliability over time, because the actuating device 31 accommodated in the box 32 (and in particular the electric motor of the actuating device 31) is adequately protected from excessive overheating essentially caused by the heat transmitted by the intake conduit 25, which is heated by the exhaust gases, which indicatively have a temperature of 350-400°C. The thermal protection of the electric motor is obtained by creating a separation between the box 32 and the intake conduit 25, inserting the insert 43 made of thermally insulating material into the outer portion 42 of the shaft 36 of the control valve 28, and making the cooling fins 35 between the box 32 and in the intake conduit 26.
1. Mixing device (23) for a low pressure EGR system (21) of an internal combustion engine
(1); the mixing device (23) comprises:
a first intake conduit (25) which can be connected to an EGR conduit (22);
a second intake conduit (26) which can be connected to a suction of fresh air from the outside; and
an exit conduit (27) which can be connected to an intake conduit (6);
the mixing device (23) is characterized by the fact that it comprises a control valve (28), which is placed in correspondence of a confluence of the intake conduits (25, 26) and comprises only one shutter (29) which varies the section of both the intake conduits (25, 26).
2. Mixing device (23) according to claim 1, wherein the shutter (29) of the control valve
(28) comprises:
a shaft (36) mounted rotatable around an axis (30) of rotation;
a plate (37) which has a flat shape and is rigidly connected to the shaft (36) to rotate with the shaft (36) around the axis (30) of rotation; and
a protuberance (38) having a shape of a truncated cone that rises cantilever from the plate (37).
3. Mixing device (23) according to claim 2, wherein the control valve (28) comprises
a valve seat (39) that is obtained in correspondence of the exit opening of the first
intake conduit (25) and reproduces in negative at least part of the shape of the protuberance
(38) of the shutter (29); when the control valve (28) is in a limit position of minimum
EGR the protuberance (38) of the shutter (29) fits inside the valve seat (39).
4. Mixing device (23) according to claim 3, wherein the protuberance (38) of the shutter
(29) has a radial elastic deformability allowing the protuberance (38) to adapt to
the shape of the valve seat (39) when inserted inside the valve seat (39).
5. Mixing device (23) according to claim 4, wherein the protuberance (38) consists of
a thin steel plate that is fixed to the plate (37) in a few welding points (40) and
has axial weakening cuts (41).
6. Mixing device (23) according to one of the claims from 1 to 5, wherein the shutter
(29) rotates around an axis (30) of rotation between a limit position of minimum EGR,
in which the shutter (29) completely closes the first intake conduit (25) and leaves
fully open the second intake conduit (26), and a limit position of maximum EGR, in
which the shutter (29) almost completely closes the second intake conduit (26) and
leaves completely open the first intake conduit (25).
7. Mixing device (23) according to one of the claims from 1 to 6, wherein the valve (28)
comprises an actuating device (31) that control the angular position of the shutter
(29) around an axis (30) of rotation and comprises: an electric motor and a geared
transmission that transmits motion from a shaft of the electric motor to a shaft (36)
of the shutter (29) of the control valve (28).
8. Mixing device (23) according to claim 7, wherein the actuating device (31) comprises
a housing (32) which is supported solely by the second intake conduit (26) and has
a first cylindrical housing (33) within which the electric motor is placed and a second
housing (34) within which the geared transmission is placed.
9. Mixing device (23) according to claim 8, wherein the housing (32) comprises cooling
fins (35) connecting the cylindrical housing (33) to an outer wall of the intake conduit
(26).
10. Mixing device (23) according to claim 7, 8 or 9, wherein the shaft (36) of the shutter
(29) presents an external portion (42) protruding from the first intake conduit (25);
at least one part of the external portion (42) of the shaft (36) of the shutter (29)
is made of thermally insulating material.
11. Mixing device (23) according to claim 10, wherein the external portion (42) of the
shaft (36) of the shutter (29) comprises an insert (43) made of heat-insulating material
that fits mechanically on both sides on the corresponding sections of the external
portion (42) of the shaft (36) of the shutter (29).
12. EGR System (21) of an internal combustion engine (1) comprising a mixing device (23)
according to one of claims from 1 to 11.
13. EGR System (21) according to claim 12 and comprising an EGR conduit (22) that originates
from an exhaust conduit (10) downstream of a device for reducing pollutants.