WO2006126963A1

WO2006126963A1 - Apparatus for recirculation of exhaust gases in a combustion engine

Info

Publication number: WO2006126963A1
Application number: PCT/SE2006/050140
Authority: WO
Inventors: Magnus Nilsson; Mikael Lindgren; Björn Lindgren
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2005-05-24
Filing date: 2006-05-18
Publication date: 2006-11-30
Anticipated expiration: 2007-11-24
Also published as: DE112006001330T5; SE0501180L; SE528644C2

Abstract

The present invention relates to a device for recirculation of exhaust gases of a combustion engine (1). The recirculating exhaust gases are intended to be led from an exhaust line (3) of the combustion engine (1) via a return line (9) to an inlet line (7) which is intended to lead air to the combustion engine (1). The device (11) can be fitted close to a connection between the return line (9) and the inlet line (7). The device (11) comprises means (13, 15, 19) for controlling the flow of exhaust gases from the return line (9) to the inlet line (7) and for mixing the exhaust gases with the air in the return line (7).

Description

Apparatus for recirculation of exhaust gases of a combustion engine

BACKGROUND TO THE INVENTION AND STATE OF THE ART

The present invention relates to a device for recirculation of exhaust gases of a combustion engine according to the preamble of claim 1.

The technique known as EGR (Exhaust Gas Recirculation) is a known means of leading part of the exhaust gases from a combustion process in a combustion engine back, via a return line, to an inlet line for supply of air to the combustion engine. A mixture of air and exhaust gases is thus supplied via the inlet line to the engine's cylinders in which the combustion takes place. Adding exhaust gases to the air causes a lower combustion temperature, resulting inter alia in a reduced content of nitrogen oxides NO_x in the exhaust gases. This technique is used for both Otto engines and diesel engines.

The return line for the exhaust gases comprises a plurality of components, e.g. an EGR valve. The EGR valve is usually situated at the beginning of the return line upstream of an EGR cooler. The EGR valve is used for shutting off the exhaust gas flow in the return line during certain operating states of the combustion engine. The EGR valve may also be used for controlling the amount of exhaust gases returned to the combustion engine. The EGR valve is controlled by an electrical control unit on the basis of information about the combustion engine's prevailing operating state. The electrical control unit may be a computer unit provided with suitable software.

Systems for recirculation of exhaust gases comprise in some cases a mixing device arranged in a region close to a connection between the return line and the inlet line. The purpose of the mixing device is to mix the exhaust gases from the return line with the air in the inlet line. WO 99/43493 refers to such a mixing device which comprises a stationary tubular cylindrical body with air flowing through the inside of it.

Returning exhaust gases are led substantially uniformly in at the periphery of the cylindrical body via a spiral exhaust gas duct which extends round the cylindrical body.

US 6,425,382 refers to a mixing device which comprises a stationary tubular element. The returning exhaust gases are supplied radially externally about the tubular element and the air is led radially internally through the tubular element. The tubular element has a star-shaped end portion which causes the exhaust gases and the air to undergo mixing substantially immediately downstream of said end portion.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a device in a system for recirculation of exhaust gases, which device provides control of the recirculating exhaust gas flow while at the same time causing effective mixing of exhaust gases and air.

This object is achieved with the device of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 1. Conventional EGR valves are usually fitted at the beginning of the return line at a position upstream of an EGR cooler which is intended to cool the exhaust gases. It is possible, however, to fit such an EGR valve at substantially any desired position in the return line in order to control the flow of exhaust gases to the return line. A mixing device which effects a mixing of exhaust gases and the air has nevertheless to be applied close to a connection between the return line and the inlet line. A device according to the invention which both controls the flow of exhaust gases from the return line to the inlet line and mixes the exhaust gases with the air has therefore also to be fitted close to the connection between the return line and the inlet line. A system for recirculation of exhaust gases comprising such a device which acts as both EGR valve and mixing device thus involves a smaller number of components than a conventional system. A system for recirculation of exhaust gases with such a device will therefore occupy less space and be less expensive to make than a conventional system which comprises a separate EGR valve and a separate mixing device. In addition, the pressure drop in the return line will be considerably smaller witii the device according to the invention than when using a conventional EGR valve and mixing device.

According to a preferred embodiment of the invention, said means comprise a movable control element which can be placed in a first position resulting in the formation of a passage which allows a flow of exhaust gases from the return line to the inlet line, and in a second position whereby no such passage is formed, thus preventing any flow of the exhaust gases from the return line to the inlet line. Such a movable control element provides a simple and effective means of controlling the recirculating flow of exhaust gases from the return line to the inlet line. With advantage, the control element can be placed in at least one third position which results in a reduced flow of exhaust gases from the return line to the inlet line via a passage with a smaller cross-sectional area than that of the passage in the first position. Flows of exhaust gases of at least two different magnitudes can thus be led from the return line to the inlet line. The control element can preferably be placed in a large number of intermediate positions between said first position and said second position. This makes it possible for a corresponding number of different sizes of passage to be provided and a corresponding number of varying flows of exhaust gases to be led from the return line to the inlet line. The exhaust gas flow to the inlet line can therefore be controlled so that the desired flow can with good precision always be led to the inlet line in keeping with the combustion engine's operating state. The control element may be arranged for movement to and fro between the first position and the second position. This will provide the control element with an uncomplicated motion and make it possible to place the control element in substantially any desired position between said first and second extreme positions. The exhaust gas flow to the inlet line can therefore be controlled in a simple manner and with very good precision.

According to another preferred embodiment of the invention, said means comprise a housing which has an exhaust gas duct with an inlet aperture for receiving exhaust gases from the return line, and an outlet aperture which is connected to said passage. The housing is fitted at the connection between the return line and the inlet line. The inlet line has with advantage a circumferential radial aperture, and the outlet aperture of the exhaust gas duct has an extent externally about the circumferential radial aperture. Such an outlet aperture makes it possible for the exhaust gases to be distributed and supplied substantially uniformly to the inlet aperture via the circumferential radial aperture. Such a distributed supply of the exhaust gases to the inlet line facilitates the mixing of the exhaust gases with the air in the inlet line.

According to another preferred embodiment of the invention, the housing comprises a surface close to the outlet aperture and adapted to cooperating with a surface of the control element, whereby said surfaces are adapted to defining said passage for supply of returning exhaust gases to the inlet line. The housing is stationary and close to the connection between the return line and the inlet line, whereas the control element is arranged for movement. It is therefore advantageous to form the passage for supply of exhaust gases to the inlet line by means of a stationary surface in the housing and a movable surface of the control element. Moving the control element relative to the housing causes said surfaces to move relative to one another, thereby making it possible to vary the dimensions of the passage and hence also the exhaust flow led through the passage to the inlet line.

According to another preferred embodiment of the invention, the control element is tubular and said passage for supply of returning exhaust gases is situated radially externally about the tubular control element and the air in the inlet line is adapted to flowing internally through the tubular control element. In this case, the exhaust gases are with advantage supplied in an annular passage formed radially externally about the tubular control element before they mix with the air which has flowed internally through the tubular control element. The control element comprises, at a downstream end with respect to the directions of flow of the exhaust gases and the air, portions situated at various radial distances from a central axis which extends through the tubular control element. Such portions result in the exhaust gases externally about the control element and the air inside the control element being at different radial distances from the central axis when they leave the control element. This results in the exhaust gases and the air being subjected to immediate good mixing substantially just after they have left the control element. Only a very short distance is therefore required for mixing the exhaust gases with the air in the inlet line. The portion of the inlet line which extends between the return line for the exhaust gases and the combustion engine can therefore be made very short.

According to another preferred embodiment of the invention, said means comprises an actuator which is connected to the control element and by means of which it is possible to move the control element to at least the first position and the second position. Such an actuator maybe of substantially any desired kind and be operated electrically, hydraulically or pneumatically. The control element has with advantage a portion which is situated outside the inlet line and is in contact with the actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is described below by way of example with reference to the attached drawings, in which:

Fig. 1 depicts a system for recirculation of exhaust gases of a supercharged combustion engine with a device according to the invention, Fig. 2 depicts the device in more detail in a fully open position, Fig. 3 depicts a section along the plane A-A in Fig. 2,

Fig. 4 depicts the device in Fig. 2 in a partly open position and Fig. 5 depicts the device in Fig. 2 in a fully closed position.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig. 1 depicts a system for recirculation of the exhaust gases of a supercharged combustion engine. Such recirculation is usually called EGR (Exhaust Gas Recirculation). Adding exhaust gases to the compressed air which is led to the engine's cylinders lowers the combustion temperature and hence also the content of nitrogen oxides (NO_x) formed during the combustion engine's combustion processes. The combustion engine 1 is with advantage an engine for powering a heavy vehicle. The exhaust gases from the cylinders of the combustion engine 1 are led via an exhaust manifold 2 to an exhaust line 3. The exhaust gases in the exhaust line 3, which are at above atmospheric pressure, are led to a turbine 4. The turbine 4 is thus provided with driving power which is transmitted via a connection to a compressor 5. Via an air filter 6, the compressor 5 draws in ambient air in an inlet line 7. The air is compressed by the compressor 5 to above atmospheric pressure. After compression, the air is at a relatively high temperature. A charge air cooler 8 is arranged in the inlet line 7 to cool the compressed air before it is led to the combustion engine 1.

A system for effecting recirculation of part of the exhaust gases in the exhaust line 3 comprises a return line 9 which extends between the exhaust line 3 and the inlet line 7. The return line 9 comprises an EGR cooler 10 in which the exhaust gases are cooled. The return line 9 comprises a device 11 whose purpose is to control the flow of exhaust gases from the return line 9 to the inlet line 7 and to mix exhaust gases from the return line 9 with the air in the inlet line 7. The device 11 is fitted close to a connection between the return line 9 and the inlet line 7. Such a device 11 may replace a conventional EGR valve whose purpose is to control the flow of exhaust gases from the return line 9 to the inlet line 7, and a mixing device whose purpose is to mix exhaust gases from the return line 9 with the air in the inlet line 7. The number of components of the system which makes recirculation of exhaust gases possible can thus be reduced. A control unit 12 is adapted to activating an actuator 13 for controlling the device 11 on the basis of information about the prevailing operating state of the combustion engine 1 so that a desired amount of exhaust gases is recirculated to the combustion engine. The control element 12 may be a computer unit provided with suitable software. The actuator 13 may be powered electrically, hydraulically or pneumatically.

If the combustion engine is a supercharged Otto engine, the exhaust gases in the return line 9 can be led directly into the inlet line 7, since the exhaust gases in the exhaust line 3 of an Otto engine in substantially all operating states will be at a higher pressure than the compressed air in the inlet line 7. If the combustion engine is a supercharged diesel engine, the pressure of the exhaust gases in the exhaust line 3 will in certain operating states be lower than the pressure of the compressed air in the inlet line 7. The device 11 can be used for stopping the exhaust gas flow in the return line 9 in operating situations in which the exhaust gas pressure is lower than the pressure of the air in the inlet line 7. When the exhaust gases from the return line 9 have mixed with the compressed air in the inlet line 7, the mixture is led via a manifold 14 to the respective cylinders of the combustion engine 1.

Fig. 2 depicts in more detail the device 11 described above. The inlet line 7 comprises close to the connection with the return line 9 a first line portion 7a and a second line portion 7b. The adjacent ends of the line portions 7a, b are arranged at a distance from one another so that a circumferential radial aperture 7c is formed between the line portions 7a, b. The device 11 comprises a housing 15 shaped in such a way that when fitted it spans the radial aperture 7c between the line portions 7a, b. The housing 15 is securably fastened to an end portion of the second line portion 7b. The housing 15 comprises an inlet aperture 16 for an exhaust gas duct 17 which extends substantially one turn externally about the radial aperture 7c. The exhaust gas duct 17 is intended to receive exhaust gases from the return line 9. The exhaust gas duct 17 comprises an outlet aperture 18 which is situated radially internally and which extends substantially round the whole of the radial aperture 7c. The dimensions of the exhaust gas duct 17 decrease substantially progressively in the direction of flow of the exhaust gases.

The device 11 comprises a tubular control element 19 arranged inside the housing 15 close to the radial aperture 7c between the line portions 7a, b. The tubular control element 19 has a first portion 19a with a substantially constant cross-sectional area and a second portion 19b with a varying cross-sectional area. The control element's first portion 19a has an inside surface 19c substantially corresponding in shape and size to an outside surface 7d of the first line portion 7a. The control element's first portion 19a thus comprises a portion arranged for movement externally about the first line portion 7a. The control element's first portion 19a has an outside surface 19d substantially corresponding in shape and size to an inside surface 15a of the housing. The control element's first portion 19a thus comprises a portion arranged for movement inside the housing 15. The control element's first portion 19a is arranged for movement in a radial gap between the housing 15 and the first line portion 7a. The actuator 13 is fastened to an outside surface of the first line portion 7a. The actuator has protruding means 13a which can be given a variable protruding length. In this case, the outer end of the protruding means 13a is connected to an outside surface of the control element's first portion 19a. It is therefore possible by means of the protruding means 13a to move the control element 19 to various positions relative to the housing 15 along a substantially rectilinear to-and-fro path. The contact region between the control element's outside surface 19d and the housing's surface 15a may possibly be provided with an appropriate seal means for ensuring that no exhaust gases leak out to an environment. In a corresponding manner, the contact region between the control element's inside surface 19c and the outside surface 7d of the first line portion 7a may also be provided with an appropriate seal means for ensuring that compressed air does not leak out to the environment via that contact region.

The control element's second portion 19b comprises an inclined surface 19e which is intended, together with an inclined surface 15b of the housing 15, to define an annular outlet passage 20 for the exhaust gases. The outlet passage 20 is connected to the outlet aperture 18 of the exhaust gas duct 17. Exhaust gases from the return line 9 can therefore be led via the exhaust gas duct 17, the outlet aperture 18 and said passage 20 into the second part of the line portion 7b^**. at a position radially external to the control element 19. The control element's second portion 19b is thus of varying cross- sectional area. Its cross-sectional area at a downstream end in the direction of flow of the exhaust gases is substantially star-shaped, as may be seen in Fig. 3. The control element 19 has in this case alternating radially outer portions 19f and radially inner portions 19g with respect to a central axis 21 which extends through the control element 19. The exhaust gases are thus led into the second line portion 7b at various radial distances from the central axis 21. The air in the inlet line 7 flows internally through the tubular control element 19. The alternating radially outer portions 19f and radially inner portions 19g of the control element 19 also result in the air being at various radial distances from the central axis 21 when it leaves the control element 19.

25 ETC.? As both the exhaust gases and the compressed air are at alternating radial distances from the central axis 21 when they leave the control element 19, they undergo substantially immediate and good mixing in the second part of the line portion 7b.

Fig. 2 depicts the control element 19 in its first extreme position, in which the control element's inclined surface 19e is at a maximum distance from the housing's inclined surface 15b. When the control element is in this extreme position, the passage 20 is of maximum width, with the result that a maximum flow of exhaust gases can be led from the return line 9 to the inlet line 7. In certain operating states of the combustion engine it is advantageous to reduce the amount of exhaust gases returning to the combustion engine 1. If the control unit 12 receives such information, the actuator 13 is activated so that it moves the outer end of the protruding means 13a outwards to a desired position. The actuator 13 thus moves the control element 19 from the first extreme position to the position depicted in Fig. 4. In this situation the control element's inclined surface 19e is significantly closer to the housing's inclined surface 15b. The width of the outlet passage 20 is thus reduced. When the control element 19 is in this position, a reduced flow of exhaust gases is led from the return line 9 to the inlet line 7.

In certain operating states of the combustion engine it is advantageous to ensure that no returning exhaust gases are led to the combustion engine 1. If the control unit 12 receives such information, the actuator means 13 is activated so that the outer end of the protruding means 13a assumes a maximum protruding position. The actuator means 13 therefore moves the control element 19 to a second extreme position. Fig. 5 shows the control element 19 in this second extreme position. The control element's inclined surface 19e is then in contact with the housing's inclined surface 15b. The width of the outlet passage 20 is thus reduced to nil. When the control element 19 is in this position, no exhaust gases can be led from the return line 9 to the inlet line 7. The control element 19 can as necessary be placed in substantially any desired position between the first extreme position corresponding to a fully open state and the second extreme position corresponding to a fully closed state. Thus the outlet passage 20 can be given a substantially continuously variable width, and a desired flow of returning exhaust gases can with good precision be led into the inlet line 7 in the various operating states of the combustion engine.

The invention is in no way limited to the embodiments to which the drawings refer but may be varied freely within the scopes of the claims.

Claims

1. A device for recirculation of exhaust gases of a combustion engine (1), whereby the recirculating exhaust gases are intended to be led from an exhaust line (3) of the combustion engine (1) via a return line (9) to an inlet line (7) which is intended to lead air to the combustion engine (1), characterised in that the device (11) can be fitted close to a connection between the return line (9) and the inlet line (7) and that the device (11) comprises means (13, 15, 19) for controlling the flow of exhaust gases from the return line (9) to the inlet line (7) and for mixing the exhaust gases with the air in the inlet line (7).

2. A device according to claim 1, characterised in that said means comprise a movable control element (19) which can be placed in a first position resulting in the formation of a passage (20) which allows a flow of exhaust gases from the return line (9) to the inlet line (7), and in a second position whereby no such passage is formed, thus preventing any flow of exhaust gases from the return line (9) to the inlet line (7).

3. A device according to claim 2, characterised in that the control element (19) can be placed in at least one third position resulting in a reduced flow of exhaust gases from the return line (9) to the inlet line (7) via a passage (20) which has a smaller cross- sectional area than that of the passage (20) in the first position.

4. A device according to claim 2 or 3, characterised in that the control element (19) is arranged for movement to and fro between the first position and a second position.

5. A device according to any one of claims 2 to 4, characterised in that said means comprise a housing (15) which has an exhaust gas duct (17) with an inlet aperture (16) for receiving exhaust gases from the return line (9), and an outlet aperture (18) which is connected to said passage (20).

6. A device according to claim 5, characterised in that the inlet line (7) has a circumferential radial aperture (7c) and that the outlet aperture (18) of the exhaust gas duct (17) has an extent externally about the radial aperture (7c).

7. A device according to claim 5 or 6, characterised in that the housing (15) comprises close to the outlet aperture (18) a surface (15b) which is adapted to cooperating with a surface (19e) of the control element (19), whereby said surfaces (15b, 19e) are adapted to defining said passage (20) for supply of returning exhaust gases to the inlet line (7).

8. A device according to any one of claims 2 to 7, characterised in that the control element (19) is tubular and that said passage (20) for supply of returning exhaust gases is situated radially externally about the tubular control element (19) and that the air in the inlet line (7) is adapted to flowing internally through the tubular control element (19).

9. A device according to claim 8, characterised in that the control element (19) comprises, at a downstream end with respect to the directions of flow of the exhaust gases and the air, portions (19f, 19g) situated at various radial distances from a central axis (21) which extends through the tubular control element (19).

10. A device according to any one of claims 2 to 9, characterised in that said means comprises an actuator (13) which is connected to the control element (19) and by means of which it is possible to move the control element (19) to at least the first position and the second position.