Exhaust recirculation system of internal combustion engine

Abstract: In a multi-cylinder internal combustion engine (1), intake air aspirated to a collector (4) from an intake passage (6) of circular cross-section is provided to the cylinders via branch pipes (5A - 5D) connected to the collector (4). The exhaust gas recirculation system has an exhaust gas recirculation pipe (7) which branches off from an exhaust passage (3) and is connected to the intake passage (6). An exhaust gas inlet (8) leads recirculated exhaust gas from the exhaust recirculation pipe (7) substantially tangentially into the intake passage (6). In preferred embodiments, there are two exhaust gas inlets (8,9) 180° apart.

Description: This invention relates to multi-cylinder internal combustion engine, such as a diesel engine of an automobile, with an exhaust recirculation system. In regard to an exhaust recirculation system (EGR system) wherein a part of the exhaust is recirculated into the intake air to perform combustion control of an internal combustion engine, various devices have been proposed to promote mixing of intake air and recirculated exhaust gas. Jikkai Hei 3-114563 published by the Japanese Patent Office in 1991 discloses a system wherein an insulator is gripped between a throttle case and surge tank in the intake passage of the engine, a pair of exhaust inlets are provided at an 180-degree interval in the insulator towards the center of the intake passage, and exhaust gas is mixed with intake air through these exhaust gas inlets. Jikkai Hei 3-114564 published in 1991 by the Japanese Patent Office discloses a device wherein an annular passage for leading exhaust gas surrounds the intake passage, and exhaust gas is led into the intake air via plural holes connecting the annular passage and intake passage. Tokkai Hei 5-106519 published by the Japanese Patent Office in 1993 discloses a system wherein a minute throughhole connecting an exhaust port and intake port of an engine. Further, this prior art discloses that the air-fuel mixture of fuel injected into the intake port and intake air is heated by the exhaust gas led to the intake port, and swirl promoted by the throughhole arranged on a tangential line of the cross-section of the inlet port accelerates evaporation of the fuel adhering to the wall of the inlet port. When exhaust gas is introduced from a right-angled direction as in Jikkai Hei 3-114563 and Jikkai Hei 3-114564 towards the center of the intake passage of a multi-cylinder engine, the exhaust gas forms an uneven flow in the passage due to the flow of intake air in the intake passage, and this causes unevenness in the exhaust concentration in each part of the cross-section of the passage. As a result, the exhaust gas concentration in the intake air will vary greatly depending on the cylinder. In general, in diesel engines which do not have a throttle, the flow of intake air is close to laminar flow, so this phenomenon is very pronounced, and as a result, a difference easily arises in the exhaust recirculation rate depending on the cylinder. On the other hand, when the exhaust gas is supplied to the intake air through a minute throughhole formed in the cylinder head as in Tokkai Hei 5-106519, the exhaust recirculation rate is limited, and as the exhaust gas is mixed with the intake air just before the combustion chamber, the exhaust gas and intake air are aspirated into the combustion chamber without being properly mixed, and a variation in the running conditions of the engine has a direct effect on the exhaust recirculation rate (EGR rate). Such characteristics may makes the EGR rate of the engine unstable. DE-A-3 511 094 and JP-A-05-223016 disclose internal combustion engines in accordance with the preamble of claim 1. It would be desirable to be able to make the EGR rate of each cylinder of a multi-cylinder engine uniform, while preventing the variation of the running conditions of the engine from affecting the EGR rate. The present invention provides a multi-cylinder internal combustion engine with an exhaust recirculation system, as set forth in claim 1. The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of an exhaust recirculation system (not in accordance with the invention). Fig. 2 is a cross-sectional view of an intake passage, showing a construction of an exhaust gas inlet. Fig. 3 is a schematic perspective view of a collector and the intake passage, describing the flow of intake air and exhaust gas. Fig. 4 is a cross-sectional view of the intake passage taken at the exhaust gas inlet for the purpose of describing a flow of exhaust gas led into the intake passage. Fig. 5 is a diagram showing theEGR rate in each cylinder of an engine with the exhaust recirculation system illustrated in Fig. 1. Fig. 6 is a schematic cross-sectional view of an intake passage with a pair of exhaust gas inlets. Fig. 7 is a cross-sectional view of an intake passage with a pair of exhaust gas inlets. Fig. 8 is similar to Fig. 7, but showing exhaust gas inlets of elliptical shape. Figs. 9A and 9B are cross-sectional views of exhaust gas inlets taken along lines IXA-IXA and IXB - IXB of Fig. 8. Fig. 10 is similar to Fig. 7, but showing exhaust gas inlets of different sizes. Figs. 11A and 11B are cross-sectional views of exhaust gas inlets taken along lines XIA -XIA and XIB - XIB of Fig. 11. Fig. 12 is similar to Fig. 7, but showing a modification. Fig. 13 is similar to Fig. 7, but showing another modification. Fig. 14 is a cross-sectional view of an exhaust gas inlet and a rib taken along a line XIV - XIV of Fig. 13. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1 of the drawings, an intake manifold 2 is installed on one side of a four-cylinder diesel engine 1, and an exhaust manifold 3 is installed on the other side. The intake manifold 2 comprises a collector 4 extending in the direction of the row of cylinders of the engine, and branch pipes 5A - 5D which connect the collector 4 with cylinders #1 to #4 of the engine. The collector 4 has a longitudinal axis X as shown in the figure and the branch pipes 5A - 5D are connected to the collector 4 from a direction perpendicular to the longitudinal axis X. An intake passage 6 is connected to one end of the collector 4 from a direction corresponding to the longitudinal axis X. Fresh air is introduced into the intake passage 6 through an air cleaner, not shown in the figure. An exhaust recirculation pipe 7 is connected to the intake passage 6 at right-angles to the intake passage 6 via an exhaust gas inlet 8. The exhaust recirculation pipe 7 branches from an exhaust passage 14 connected to the exhaust manifold 3, and recirculates part of the exhaust gas of the engine 1 to the intake passage 6. An exhaust recirculation control valve or the like, not shown in Fig. 1, is installed in the exhaust recirculation pipe 7. Next, referring to Fig. 2, the exhaust gas inlet 8 comprises an exhaust gas conduit 8B and an opening 8A located on a tangent line of a circular cross-section of the intake passage 6. Due to the construction of this exhaust gas inlet 8, recirculated exhaust gas flowing from the exhaust recirculation pipe 7 into the intake passage 6 sets up a flow along the cylindrical wall of the intake passage 6 as shown in Fig. 4. The intake passage 6 comprises a pipe of circular cross-section of molded aluminum alloy. The exhaust gas inlet 8 is precast as a boss together with the pipe, and the exhaust recirculation pipe 7 comprising a metal pipe is connected to this boss. In Fig. 2, the exhaust gas inlet 8 and the branch pipes 5A - 5D are located on the same side of the intake passage 6, but the location of the exhaust gas inlet 8 relative to the intake passage 6 is not limited to this and the angle between the exhaust gas inlet 8 and the branch pipes 5A - 5D may be freely set. Next, referring to Fig. 3, fresh air aspirated through the intake passage 6 sets up a laminar flow as shown by arrows with broken lines. The recirculated exhaust gas flowing into the intake passage 6 from the exhaust gas inlet 8 forms a swirl along the cylindrical wall surface of the intake passage 6, as shown by arrows with solid lines in Figs. 3 and 4. Due to the effect of the flow of fresh air, this swirl sets up a spiral flow towards the collector 4, and due to the dispersion of the recirculated exhaust gas toward the inside, it mixes with the fresh air flowing inside the spiral. On the other hand, as the direction of the spiral flow is effectively perpendicular to the flow of fresh air, turbulence is set up at the boundary between the fresh air and the recirculated exhaust gas. The energy of this turbulence promotes mixing of the fresh air and the recirculated exhaust gas. Thus, the exhaust concentration of the intake air flowing into the collector 4 is made more uniform by the spiral flow due to the exhaust gas inlet 8 which promotes mixing of the fresh air and recirculated exhaust gas, and deviation of the EGR rate in the cylinders #1 - #4 become small as shown in Fig. 5. Moreover, due to the mixing of recirculated exhaust gas and fresh air upstream of the collector 4, the exhaust recirculation rate is not easily influenced by the running conditions of the engine 1. In Fig.6 two exhaust gas inlets 8 and 9 are provided on the outer circumference of the intake passage 6 at a 180-degree interval. The exhaust gas inlets 8 and 9 are arranged so as to set up a swirl in the same direction. The exhaust gas inlet 8 comprises an exhaust gas conduit 8B and opening 8A. the exhaust gas inlet 9 comprises an exhaust gas conduit 9B and opening 9A. The exhaust gas conduits 8B and 9B are respectively connected to the exhaust recirculation pipe 7. The exhaust gas inlets 8 and 9 are formed on the same cross-section of the intake passage 6 as shown in Fig. 6, but they may be slightly offset from each other in the direction of the fresh air flow in the intake passage 6. Exhaust gas flows into the intake passage 6 from two positions respectively in tangential directions, so the swirl of recirculated exhaust gas is enhanced. In Fig. 7 there are two exhaust gas inlets 8 and 9 in the intake passage 6 as in Fig.6. The exhaust gas conduits 8B and 9B are precast as a part of the exhaust gas inlets 8 and 9 together with the intake passage 6. The exhaust gas conduit 8B leading to the opening 8A has a short straight conduit, but the exhaust gas conduit 9B leading to the opening 9A forms a long circular arc along the outer circumference of the intake passage 6. The exhaust gas conduits 8B, 9B are connected to the exhaust recirculation pipe 7 via a common flange 10 which is also precast as a part of the exhaust gas inlets 8 and 9. The cross-sectional area of the exhaust gas conduit 9B gradually decreases as it approaches the opening 9A as shown by S1 - S5 in the figure. The cross-sectional area of the exhaust gas conduit 8B also gradually decreases as it approaches the opening 8A as shown by S6 and S7 in the figure. This arrangement of the exhaust gas conduits 8B, 9B has the following effect. The long, arc-shaped exhaust gas conduit 9B has a supercharging effect due to the inertial force of the exhaust gas flowing inside it. In addition, as the cross-sectional areas of the exhaust gas conduits 8B and 9B respectively decrease toward the openings 8A and 9A, the speed of the exhaust gas flowing into the intake passage 6 increases, and the exhaust gas is therefore mixed sufficiently with fresh air even at a low exhaust recirculation rate. In Figs. 8, 9A, and 9B the exhaust gas conduits 8B and 9B are also disposed around the intake passage 6 as in Fig. 7, but have different cross-sections. The openings 8A, 9A of the exhaust gas inlets 8, 9 are formed in an elliptical shape with identical dimensions as shown in Figs. 8A and 9A. The long axis of the ellipse is set parallel to the direction of fresh air flow of the intake passage. The cross-sections of the exhaust gas conduits 8B and 9B accordingly have an elliptical shape, and respectively decrease as they approach the openings 8A and 9A. Accordingly, the thickness of the swirl set up by the recirculated exhaust gas flowing into the intake passage 6 is thinner. Therefore, the flow of recirculated exhaust gas flowing into the intake passage 6 is not swept away easily by the flow of fresh air of the intake passage 6, and a swirl is more firmly established along the cylindrical walls of the intake passage 6. In Figs. 10, 11A, and 11B the opening 9A of the exhaust gas inlet 9 is set larger than the opening 8A of the exhaust gas inlet 8. In accordance with the invention, the cross-sectional area of the exhaust gas conduit 9B is set to be larger than that of the exhaust gas conduit 8B. The exhaust gas conduit 9B is longer than the exhaust gas conduit 8B, so by setting the opening 9A to be larger than opening 8A in this manner, the flowrate ratio of the exhaust gas conduits 8B, 9B become almost equal, which creates a desirable environment for setting up a swirl. In Fig. 12, throughholes 11 are formed in the cylindrical wall of the intake passage 6 to connect the exhaust gas conduits 8B, 9B and the intake passage 6. A part of the recirculated exhaust gas of the exhaust gas conduits 8B, 9B flows into the intake passage 6 through these throughholes 11, so turbulence in the intake passage 6 is promoted, and mixing of exhaust gas with fresh air is promoted. Moreover, since the exhaust gas flows in from various points on the cylindrical wall of the intake passage 6, the concentration of the exhaust gas in the intake passage 6 is made uniform. In Figs. 13 and 14, ribs 12, 13 are provided immediately upstream of the openings 8A, 9A in the intake passage 6. The ribs 12 and 13 respectively project from the inner wall of the intake passage 6 into the intake passage 6 like a weir which is perpendicular to the flow of fresh air of the intake passage 6. Crests 12A and 13A of the weir are on a straight line of the same height as the openings 8A, 9A. In other words, the ribs 12, 13 have a crescent shape, and the maximum value of the height from the inner circumference of the intake passage 6 to the crests 12A and 13A is equal to the length of the short axis of the elliptically-shaped cross-sections of the openings 8A, 9A. The ribs 12, 13 thus arranged prevent the flow of intake air shown by arrows with broken lines in Fig. 14 from colliding with the recirculated exhaust gas flowing into the intake passage 6 from the exhaust gas inlets 8 and 9. As a result, the recirculated exhaust gas which flows into the intake passage 6 is not easily swept out by fresh air, and the swirl flow along the cylindrical walls of the intake passage 6 is set up more easily.

Claims: A multi-cylinder internal combustion engine with an exhaust recirculation system for a vehicle, wherein intake air aspirated to a collector (4) from an intake passage (6) of circular cross-section is provided to cylinders (#1-#4) via branch pipes (5A-5D) connected to the collector (4), the intake passage (6) preferably functioning to aspirate fresh air in the form of laminar flow, the intake passage (6) not being provided with a throttle that is associated with an accelerator pedal of the vehicle, and part of the exhaust gas of the engine (1) is recirculated to the intake passage (6) from an exhaust passage (3), the exhaust gas recirculation system including: an exhaust recirculation pipe (7) which branches off from the exhaust passage (3) and is connected to the intake passage (6); a first exhaust gas inlet (8) comprising a first exhaust gas conduit (8B) connected to the intake passage (6) via a first opening so as to lead recirculated exhaust gas from the exhaust recirculation pipe (7) substantially tangentially into the intake passage (6); and a second exhaust gas inlet (9) comprising a second exhaust gas conduit (9B) connected to the intake passage (6) via a second opening (9A) which is located at a 180-degree interval from the first opening (8A) so as to lead recirculated exhaust gas from the exhaust recirculation pipe (7) substantially tangentially into the intake passage (6); characterized in that the cross-sectional area of the second exhaust gas conduit (9B) is larger than the cross-sectional area of the first exhaust gas conduit (8B). An internal combustion engine as claimed in claim 1, wherein the collector (4) has a longitudinal axis which is perpendicular to the branch pipes (5A-5D) and the intake passage (6) is connected to the collector (4) from a direction corresponding to the longitudinal axis. An internal combustion engine as claimed in claim 1 or 2, wherein a single flange (10) connects the first exhaust gas conduit (8B) and second exhaust gas conduit (9B) to the exhaust recirculation pipe (7). An internal combustion engine as claimed in any preceding claim, wherein the second exhaust gas conduit (9B) is formed along an outer circumference of the intake passage (6) and has a longer flowpath than the first exhaust gas conduit (8B). An internal combustion engine as claimed in any preceding claim, wherein the first exhaust gas conduit (8B) and second exhaust gas conduit (9B) are formed together with the intake passage (6) by casting. An internal combustion engine as claimed in any preceding claim, wherein the first opening (8A) and second opening (9A) are each formed in an oblong shape of which a long axis is substantially parallel to the direction of flow of fresh air in the intake passage (6). An internal combustion engine as claimed in any preceding claim, wherein the cross-sectional area of the first exhaust gas conduit (8B) gradually decreases toward the first opening (8A), and the cross-sectional area of the second exhaust gas conduit (9B) gradually decreases toward the second opening (9A). An internal combustion engine as claimed in any preceding claim, wherein at least one of the first and second exhaust gas conduits (8B,9B) is further connected to the intake passage (6) via at least one throughhole (11). An internal combustion engine as claimed in any preceding claim, wherein the intake passage (6) has a first rib (12) projecting towards the center of the intake passage (6) upstream of the first opening (8A), and a second rib (13) projecting towards the center of the intake passage (6) upstream of the second opening (9A), each rib preferably extending in a circumferential direction on an inner circumference of the intake passage (6). An internal combustion engine as claimed in claim 9, wherein the first opening (8A) has a first long axis substantially parallel to the direction of flow of fresh air in the intake passage (6) and a first short axis perpendicular thereto, the second opening (9A) has a second long axis substantially parallel to the direction of flow of fresh air in the intake passage (6) and a second short axis perpendicular thereto, the first rib (12) has a height substantially equal to the length of the first short axis, and the second rib (13) has a height substantially equal to the length of the second short axis.

Inventors: MATAYOSHI YUTAKA, MORI KOUJI, NODA YASUSHI, MATAYOSHI, YUTAKA, MORI, KOUJI, NODA, YASUSHI
Applicants: NISSAN MOTOR, NISSAN MOTOR CO., LTD.
Application year: 1999
Main classification: F02M25
IPC codes: F02M25, F02M35