JP2007218167A - Multicylinder engine and egr cooler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To implement reduction in NOx and PM, and improvement in output and fuel economy, by high supercharging and a large amount of EGR. <P>SOLUTION: A multicylinder engine performing supercharging, comprises: exhaust manifolds 9a, 9b divided into cylinder groups in which their exhaust strokes are not overlapped with each other; intake manifolds 3a, 3b divided into cylinder groups in which their intake strokes are not overlapped with each other; EGR passages 36a, 36b connecting the exhaust manifolds with the intake manifolds so that the same cylinder groups are connected; means 23a, 23b preventing back-flow of exhaust pulses between the exhaust manifolds. The multicylinder engine further comprises: check valves 39 disposed to the downstream of EGR coolers 37 of the EGR passages; and EGR gas passages 50 of the EGR coolers 37 which are set as extension parts of the EGR passages 36a, 36b so that the time point when the exhaust pulses reach the check valves matches the time point when troughs of pulsation reach the check valves. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technology for realizing both reduction of NOx and improvement of output and fuel consumption in a supercharged multi-cylinder engine and an EGR cooler suitable for use in the technology.

  As an engine EGR (Exhaust Gas Recirculation) system, a system that circulates part of the exhaust gas from the exhaust system to the intake system via the EGR cooler is often used. Regarding the EGR cooler, those disclosed in Patent Documents 5 to 9 are known. In such an EGR device, when the exhaust gas is circulated from the turbine upstream of the turbocharger to the compressor downstream, an operation region in which the supercharging pressure becomes higher than the exhaust pressure tends to occur, and the EGR cannot be sufficiently obtained.

In order to increase the EGR rate, exhaust throttling by a butterfly valve or intake throttling by a throttle valve can be considered, but deterioration of pumping loss becomes a problem. The VNT (variable nozzle turbocharger) throttle increases not only the exhaust manifold pressure but also the intake manifold pressure. Therefore, to improve the EGR rate, the VNT throttle is increased until the exhaust manifold pressure is higher than the intake manifold pressure. It is necessary to make it effective, and the pumping loss is worsened. Therefore, a method of performing EGR by exhaust pulsation using a reed valve (check valve) (Patent Document 1, Patent Document 2), a method of increasing exhaust pulsation using a mixing section in the EGR passage (Patent Document 3), variable A method of performing internal EGR using a valve (Patent Document 4) is known.
JP 2000-249004 JP 2005-147010 A Special table 2003-534488 JP 2001-107810 A JP 2002-130059 JP 2003-247460 A JP 2001-304047 A JP 2002-188526 A JP 2000-097113 A

  In the case of Patent Literature 1 to Patent Literature 3, when the turbocharger connected to the split type exhaust manifold is a single entry system (one turbine inlet), the exhaust pulse between the cylinder groups (the peak of the positive pressure wave) is generated. Since they cancel each other out, a sufficient EGR rate cannot be obtained. In the case of Patent Document 4, the exhaust (EGR gas) cannot be cooled. In Patent Document 2, although an EGR passage that connects the split type exhaust manifold and the split type intake manifold to each other in the relationship between the same cylinder groups is provided, the exhaust pulse reaches the initial stage of the intake stroke. The timing of the intake pulsation valley does not match and the EGR rate cannot be improved sufficiently.

  An object of this invention is to provide an effective means for solving such a problem.

  In a multi-cylinder engine that performs supercharging, a first invention includes an exhaust manifold that is divided for each cylinder group in which the exhaust strokes do not overlap, an intake manifold that is divided for each cylinder group in which the intake strokes do not overlap, The EGR passage connecting the same cylinder group between the exhaust manifold and the intake manifold, means for preventing the backflow of exhaust pulses between the exhaust manifold, and the reverse installed downstream of the EGR cooler in the EGR passage An EGR gas flow path of an EGR cooler that is set as an extension of the EGR passage to match the timing at which the exhaust pulse reaches the check valve with the timing at which the intake pulsation valley reaches the check valve It is characterized by providing.

  According to a second aspect of the invention, in the multi-cylinder engine according to the first aspect of the invention, the extension portion of the EGR passage is constituted by a heat transfer tube extending in a meandering manner.

  According to a third invention, in the multi-cylinder engine according to the first invention, the extension portion of the EGR passage is constituted by a heat transfer tube extending in a spiral shape.

  According to a fourth aspect of the invention, in the multi-cylinder engine according to the first aspect of the invention, the extension portion of the EGR passage includes a convex portion or a concave portion extending along the flow of EGR gas on the inner surface of the passage.

  According to a fifth aspect of the present invention, in the multi-cylinder engine according to the first aspect, the extension portion of the EGR passage includes a convex portion or a concave portion that spirally extends in the EGR gas flow direction on the inner surface of the passage. To do.

  According to a sixth aspect of the present invention, in the multi-cylinder engine according to the first aspect, as a means for preventing the exhaust gas from flowing back between the exhaust manifolds, a nozzle that narrows the downstream side of the collecting portion of each exhaust manifold toward the merging portion. It comprises a part.

  According to a seventh aspect of the invention, in the multi-cylinder engine according to the first aspect of the invention, a twin-entry turbocharger is provided as means for preventing the exhaust gas from flowing back between the exhaust manifolds.

  In an EGR cooler disposed in an EGR passage of an engine, an eighth invention is an EGR gas flow path constituted by a heat transfer tube extending in a serpentine shape or a spiral shape, and an inner surface of the heat transfer tube extends along the flow of the EGR gas. A convex portion or a concave portion.

  A ninth invention is an EGR cooler disposed in an EGR passage of an engine, wherein an EGR gas flow path constituted by a heat transfer tube extending in a meandering shape or a spiral shape, and an inner surface of the heat transfer tube spirally in the EGR gas flow direction. A convex portion or a concave portion extending in the direction.

  A tenth aspect of the invention is the EGR cooler according to the eighth aspect of the invention or the ninth aspect of the invention, wherein the heat transfer tube is a water cooling type or an air cooling type.

  In the first to seventh aspects of the present invention, even when the turbocharger is of a single entry system (one turbine inlet), the means for preventing the exhaust pulse from flowing back between the split exhaust manifolds is provided. Since the exhaust pulse is transmitted to the check valve in the EGR passage without being weakened, and the check valve is operated effectively, a high EGR rate is obtained.

  The timing at which the exhaust pulsation in the exhaust manifold reaches a peak is earlier than the timing at which the intake pulsation in the intake manifold becomes a valley, but the EGR passage upstream of the check valve becomes longer due to the extension of the EGR passage. Can arrive at the check valve. That is, the timing at which the exhaust pulse reaches the check valve can be made closer to the timing at which the valley of the intake pulsation reaches the check valve. Since the EGR gas is cooled by the EGR cooler and the pressure propagation speed (sound speed) becomes slow, the EGR cooler's cooling performance can be improved by configuring the EGR passage extension as the EGR gas flow path of the EGR cooler. The cooling section upstream of the stop (the passage length where the temperature of the EGR gas is low) also becomes longer, and the time until the exhaust pulse reaches the check valve can be earned efficiently. As a result, since the instantaneous differential pressure before and after the check valve increases, the EGR rate can be further increased.

  In the second invention or the third invention, the EGR gas cooling section can be sufficiently secured while keeping the outer size of the EGR cooler small by the heat transfer tube extending in a meandering manner or the heat transfer tube extending in a spiral shape. From the viewpoint of pressure loss, a spiral having a continuous gentle curve is more advantageous than a meandering shape that bends locally.

  In the fourth invention or the fifth invention, since the surface area in contact with the EGR gas on the inner surface of the passage is increased by the convex portion or the concave portion, the EGR gas can be efficiently cooled. From the viewpoint of pressure loss, the concave portion is more advantageous than the convex portion, and the direction along the EGR gas is more advantageous than the spiral shape.

  In the sixth aspect of the invention, the flow of exhaust is accelerated by the tapered nozzle, the dynamic pressure is increased, and the static pressure (exhaust pressure) is lowered, so that the backflow of exhaust pulses between the exhaust manifolds can be suppressed. For this reason, the exhaust pulse is transmitted to the check valve in the EGR passage without being weakened, and the check valve is effectively operated, so that a high EGR rate is obtained. In addition, if the ejector action occurs due to the flow velocity of the blow-down flow (jet exhaust at the beginning of the exhaust stroke) that blows out from the tapered nozzle, the exhaust is sucked from the exhaust manifold on the cylinder side during the exhaust stroke (push-out). Loss can also be improved.

  In the seventh invention, since the turbocharger is a twin entry system (two types of turbine inlets), exhaust interference can be avoided, energy transmission to the turbine can be maintained satisfactorily, and the backflow of exhaust pulses can also be achieved. It is suppressed, the exhaust pulse is transmitted to the check valve in the EGR passage without being weakened, and the check valve is effectively operated, so that a high EGR rate is obtained.

  In the eighth invention to the tenth invention, the EGR gas flow path of the EGR cooler can sufficiently secure the flow path length while keeping the outer size of the EGR cooler small by the heat transfer tube extending in a meandering shape or a spiral shape. . Further, since the surface area of the inner surface of the heat transfer tube is increased by the convex portion or the concave portion, the EGR gas can be cooled more efficiently. For this reason, in the multi-cylinder engine according to the first aspect of the invention, it is suitable as an EGR cooler disposed upstream of the check valve in the EGR passage.

  In FIG. 1, reference numeral 2 denotes an intake passage of a multi-cylinder engine 1 (6-cylinder diesel engine), which includes intake manifolds 3 a and 3 b and an intake pipe 4. The intake manifolds 3a and 3b are divided into cylinder groups (# 1, 2, 3 and # 4, 5, 6) in which the intake strokes do not substantially overlap. The intake pipe 4 is branched on the downstream side of the intercooler 5 and connected to the collective part of the manifolds 3a and 3b. 6a is a compressor of the turbocharger 6, and 7 is an air cleaner.

  Reference numeral 8 denotes an exhaust passage of the engine 1 and includes exhaust manifolds 9 a and 9 b and an exhaust pipe 10. The exhaust manifolds 9a and 9b are divided into cylinder groups (# 1, 2, 3 and # 4, 5, 6) in which the exhaust strokes do not substantially overlap, and a turbocharger is formed at the junction 11 of these manifolds 9a and 9b. The exhaust pipe 10 is connected via a turbine 6b. The compressor 6a of the turbocharger 6 is driven by the rotation of the turbine 6b and supercharges intake air to each cylinder. As the turbocharger 6, a variable nozzle type having one turbine inlet (single entry type) is used. 12 is a muffler.

  The junction 11 is configured as shown in FIG. The exhaust manifolds 9a and 9b are gathered together at one flange 20 on the downstream side of the gathering part, and the joining part 11 is opened at the joint surface. The downstream of the gathering portion gathered in one flange 20 is formed in nozzle portions 23 a and 23 b that narrow the passage toward the joining portion 11 in a tapered shape. Reference numeral 25 denotes a turbine housing, in which a flange 26 corresponding to the flange 20 of the exhaust manifolds 9 a and 9 b is formed, and an inlet of the turbine 6 b opens at a joint surface of the flange 26. The flange 26 of the turbine housing 25 is connected to the flange 20 of the exhaust manifolds 9a and 9b. A throat-shaped diffuser portion 29 is formed inside the turbine housing 25 that once squeezes the merging portion 11 downstream of the nozzle portions 23 a and 23 b and then gradually expands.

  In the merging portion 11, the flow of exhaust is accelerated by the tapered nozzle portions 23 a and 23 b, the dynamic pressure is increased, and the static pressure is lowered, so that the backflow of exhaust pulses between the exhaust manifolds 9 a and 9 b is suppressed. In addition, the dynamic pressure is increased and the static pressure is lowered by the flow velocity of the blow-down flow (the exhaust gas discharged in the early stage of the exhaust stroke) that blows out from the nozzle portion 23a or 23b. When the ejector action occurs, the cylinder in the exhaust (extrusion) stroke The exhaust is sucked into the diffuser portion 29 from the side exhaust manifold 9b or 9a. Thereafter, the flow of the exhaust is decelerated by the diffuser unit 29, and the static pressure (exhaust pressure) of the scroll is increased.

  In FIG. 1, reference numeral 35 denotes an EGR device that circulates part of the exhaust gas from the upstream side of the turbine 6b of the turbocharger 6 to the downstream side of the compressor 6a of the turbocharger 6, and includes exhaust manifolds 9a and 9b and intake manifolds 3a and 3b (intake pipe 4 EGR passages 36a and 36b are provided for connecting the same cylinder group to each other. In the EGR passages 36a and 36b, an EGR cooler 37 for cooling the EGR gas, an EGR valve 38 for adjusting the EGR flow rate, and a check valve 39 (reed valve) for regulating the backflow of the EGR gas are interposed.

  The check valve 39 is disposed on the downstream side (near the outlet) of the EGR passages 36a and 36b, and the EGR valve 38 is disposed on the upstream side of the check valve 39. The EGR cooler 37 is disposed on the upstream side (near the inlet) of the EGR passages 36a and 36b, and the timing at which the exhaust pulse reaches the check valve 39, as described later, is the timing at which the valley of the intake pulsation reaches the check valve. In order to match, an EGR gas flow path is set as an extension 50 of the EGR passages 36a and 36b.

  The EGR gas flow path 50 of the EGR cooler 37 makes the EGR passage upstream of the check valve 39 longer, and the timing at which the exhaust pulse reaches the check valve 39 can be delayed. Since the EGR gas is cooled by the EGR cooler 37 and the pressure propagation speed (sound speed) becomes slow, the check valve 39 is set by setting the EGR gas flow path of the EGR cooler 37 as the extension 50 of the EGR passages 36a and 36b. The upstream cooling section (passage length in which the temperature of the EGR gas is low) also becomes long, and the time until the exhaust pulse reaches the check valve 39 can be efficiently obtained.

  In the case of FIG. 3, the EGR gas flow path 50 is constituted by a heat transfer tube 50a extending in a meandering manner. The heat transfer tube 50a is manufactured by extrusion molding, and a large number of convex portions 51 (thin plate-like projections) along the flow of EGR gas are arranged on the inner surface of the tube 50a in the circumferential direction of the tube 50a. A large number of plate fins 52 are arranged in parallel, and the meandering heat transfer tube 50a is assembled so that the linear portion of the EGR gas flow path 50 penetrates the plate fins 52 in the orthogonal direction. That is, the heat transfer tube 50a is unitized together with a large number of plate fins 52, and constitutes an air-cooled heat exchanger (EGR cooler 37) in the EGR passages 36a and 36b.

  Since the heat transfer tube 50a meanders, the outer size of the EGR cooler 37 can be kept small. The inner surface of the heat transfer tube 50a has an increased surface area in contact with the EGR gas due to the convex portions 51 along the flow of the EGR gas, so that the EGR gas passing through the heat transfer tube 50a can be efficiently cooled. Since the convex portion 51 follows the flow of the EGR gas, it can be integrally formed easily and easily by extrusion molding of the heat transfer tube 50a. As an alternative to the convex portion 51, a large number of concave portions extending in parallel with the flow of the EGR gas on the inner surface of the tube 50a may be arranged in the circumferential direction of the tube 50a. 56a and 56b are connecting flanges of the heat transfer tube 50a.

  In the case of FIG. 4, the heat transfer tube 50 b extending in a meandering manner is provided with two protrusions 53 extending spirally in the flow direction of the EGR gas on the inner surface of the tube 50 b. The convex portion 53 is formed by denting the outer surface of the tube 50b. Thereby, the inner and outer surface areas of the pipe 50b are enlarged, and the EGR gas passing through the heat transfer pipe 50b can be efficiently cooled. A casing 54 accommodates a heat transfer tube 50b extending in a meandering manner, and forms a cooling water passage 55 around the heat transfer tube 50b. In the cooling water channel of the engine, a water-cooled heat exchanger (EGR cooler 37) is configured by connecting the inlet 54a of the casing 54 to the upstream side and the outlet 54b to the downstream side.

  Since the cooling water does not flow through the meandering heat transfer tube 50b but flows inside the casing (around the heat transfer tube), sufficient cooling performance can be obtained without increasing the capacity of the cooling pump. As a means to replace the convex portion 53, a concave portion (formed by raising the outer surface of the tube 50b) that spirally extends in the EGR gas flow direction on the inner surface of the tube 50b may be provided. 57a and 57b are connecting flanges of the heat transfer tube 50b.

  FIG. 5 is a characteristic diagram illustrating the simulation results of intake and exhaust pulsations, where E is the exhaust pulsation immediately upstream of the check valve 39, F is the intake pulsation immediately downstream of the check valve 39, and G is a conventional reverse pulsation as a comparative example. A stop valve (disposed in an intermediate portion between an EGR cooler in which an EGR passage extension is not set as an EGR gas passage in the EGR passage) and a downstream EGR valve is displayed.

  The timing at which the exhaust pulsation in the exhaust manifolds 9a and 9b reaches a peak is earlier than the timing at which the intake pulsation in the intake manifolds 3a and 3b becomes a trough. In the case of G, the exhaust pulse reaches the initial stage of the intake stroke. The timing of the intake pulsation valley does not match and the EGR rate cannot be improved sufficiently. In the case of E, the check valve 39 is disposed on the downstream side (near the outlet) of the EGR passages 36a and 36b. The EGR cooler 37 is arranged on the upstream side (near the inlet) of the EGR passages 36a and 36b, and an extension 50 of the EGR passages 36a and 36b is set as an EGR gas passage of the cooler 37. As a result, the EGR passage portion downstream of the check valve 39 is short and the upstream EGR passage portion is long, and the timing B when the exhaust pulse reaches the check valve 39 is reached when the exhaust pulse reaches the check valve 39. To be close to. Since the EGR gas is cooled by the EGR cooler 37 and the pressure propagation speed (sound speed) is slowed down, the extension part 50 of the EGR passages 36a and 35b is configured as an EGR gas flow path of the EGR cooler 37. In addition to improving the cooling performance, the cooling section upstream of the check valve 39 (the passage length where the temperature of the EGR gas is low) also becomes long, and the time until the exhaust pulse reaches the check valve 39 can be efficiently obtained.

  FIG. 6 is a characteristic diagram for comparing the EGR flow rates in the case of E and G. K represents the EGR rate in the case of E, and M represents the EGR rate in the case of G. In the case of E, the timing A at which the exhaust pulse reaches the check valve 39 can be made closer to the timing B at which the valley of the intake pulsation reaches the check valve 39, so that the moment before and after the check valve is more instantaneous than in the case of G. The differential pressure is large, and K has a higher EGR rate than M.

  With such a configuration, even in the turbocharger 6 of the single entry system (one turbine inlet), the backflow (exhaust interference) of the exhaust pulse is suppressed by the tapered nozzles 23a and 23b, and the ejector action of the merging portion 11 is achieved. Thus, the exhaust pulse to the turbine 6a is strengthened, and the turbine efficiency is improved. Further, since the back flow of the exhaust pulse is suppressed, the exhaust pulse is transmitted without being weakened to the check valve 39 of the EGR passages 36a and 36b, and the check valve 39 is effectively operated, so that a high EGR rate is obtained. is there. The exhaust manifold pressure on the cylinder side during the exhaust (push-out) stroke is reduced by the ejector action of the merging portion 11, so that the pumping loss can be reduced.

  Since the EGR passages 36a and 36b are connected to each other in the same cylinder group, the exhaust stroke and the intake stroke substantially overlap between the cylinders belonging to the same cylinder group, so that the improvement of the EGR rate can be promoted. The intake pulsation trough occurs in the middle of the intake stroke, whereas the exhaust pulse peak occurs early in the exhaust stroke (during exhaust ejection). In this embodiment, by setting the EGR gas flow path 50 of the EGR cooler 37 in a meandering manner as an extension of the EGR passages 36a and 36b, the cooling section upstream of the check valve 39 can be made longer, so the exhaust pulse is reversed. The timing A that reaches the stop valve 39 can be matched with the timing B that the valley of the intake pulsation reaches the check valve 39 (see FIG. 5). As a result, since the instantaneous differential pressure before and after the check valve 39 increases, the EGR rate can be further improved (see FIG. 6).

  Since the turbocharger 6 is a variable nozzle type, by adding variable nozzle control, high supercharging and large amount of EGR are possible in a wide operating range, reducing NOx and PM (Particulate Matter) and improving output and fuel consumption. It is possible to achieve a high level of compatibility. Since the EGR valve 38 and the check valve 39 (reed valve) are disposed on the downstream side of the EGR cooler 37, the durability of the valves 38 and 39 is also ensured.

  The diffuser portion 29 is not formed integrally with the turbine housing 25 but may be interposed between the flange 26 of the turbine housing 25 and the flange 20 of the exhaust manifolds 9a and 9b as a separate spacer as shown in FIG. Good. The tapered nozzle portions 23a and 23b are not formed integrally with the exhaust manifolds 9a and 9b. As shown in FIG. 8, the flanges 20 of the exhaust manifolds 9a and 9b and the flange 30 of the turbine housing 25 are provided as separate spacers. You may interpose between.

  It is conceivable to use a twin entry type turbocharger as means for preventing the exhaust pulse from flowing back between the exhaust manifolds 9a and 9b. In that case, since there are two turbine inlets, exhaust interference can be avoided, and energy transmission to the turbine 6b can be maintained well. Further, an ejector action similar to that of the nozzle portions 23a, 23b and the diffuser portion 29 is generated inside the turbine 6b, and the exhaust pulse is transmitted to the check valve 39 without being weakened in the EGR passages 36a, 36b. A high EGR rate is obtained in order to operate 39 effectively.

  In FIG. 1, the downstream of the branch part 60 (branch point) of the intake pipe 4 is constituted by resonance pipes 42a and 42b, and the outlets of the EGR passages 36a and 36b are connected to the resonance pipes 42a and 42b. When the resonance rotational speed is set from the length and cross-sectional area of the resonance pipes 42a and 42b and the volume of the intake manifolds 3a and 3b, and the engine rotational speed (excitation frequency by the piston) becomes equal to the resonant rotational speed, The intake pulsation is amplified, and the instantaneous differential pressure before and after the check valve 39 can be increased. Further, since the inertia supercharging works, the intake air flow rate can be obtained efficiently and sufficiently.

  3 and 4, the EGR gas passage 50 of the EGR cooler 37 is constituted by the heat transfer tubes 40a and 40b extending in a meandering manner, but can also be constituted by a heat transfer tube extending in a spiral shape. From the viewpoint of pressure loss, a spiral shape in which a substantially constant and gentle curve continues is preferable to a meandering shape that bends locally. Further, the protrusion 53 of FIG. 4 (the inner surface of the heat transfer tube 50b extends in parallel with the flow of the EGR gas) than the protrusion 51 of FIG. 3 (the inner surface of the heat transfer tube 50a extends spirally in the EGR gas flow direction). ) Is advantageous because the pressure loss is small.

1 is an overall schematic configuration diagram according to an embodiment of the present invention. It is a block diagram which concerns on the confluence | merging part of an exhaust manifold. (A) is a plan view, (b) is a front view, and (c) is a right side view of an EGR cooler. (A) is a plan view, (b) is a front view, and (c) is a right side view of an EGR cooler. It is a characteristic view which illustrates the simulation result of intake / exhaust pulsation. It is a characteristic view which illustrates the simulation result of an EGR flow rate. It is a block diagram which concerns on the confluence | merging part of an exhaust manifold. It is a block diagram which concerns on the confluence | merging part of an exhaust manifold.

Explanation of symbols

1 Multi-cylinder engine (6-cylinder diesel engine)
2 Intake passage 3a, 3b Intake manifold 5 Intercooler 6 Turbocharger (variable nozzle type turbocharger)
6a Compressor 6b Turbine 8 Exhaust passages 9a, 9b Exhaust manifolds 23a, 23b Tapered nozzle part 25 Turbine housing 29 Throat diffuser part 35 EGR device 37 EGR cooler 38 EGR valve 39 Check valve (reed valve)
42a, 42b Resonance tube 50 EGR passage extension (EGR gas passage of EGR cooler)
50a, 50b Heat transfer tube 51, 53 Convex part 52 Plate fin 54 Casing

Claims (10)

  In a multi-cylinder engine that performs supercharging, an exhaust manifold that is divided for each cylinder group in which the exhaust strokes do not overlap, an intake manifold that is divided for each cylinder group in which the intake strokes do not overlap, and these exhaust manifolds and intake manifolds An EGR passage connecting the same cylinder group to each other, a means for preventing an exhaust pulse from flowing back between the exhaust manifolds, a check valve interposed downstream of the EGR cooler in the EGR passage, and an exhaust pulse An EGR gas passage of an EGR cooler that is set as an extension of the EGR passage so that the timing at which the valve reaches the check valve matches the timing at which the valley of the intake pulsation reaches the check valve Multi-cylinder engine.   The multi-cylinder engine according to claim 1, wherein the extension portion of the EGR passage is constituted by a heat transfer tube extending in a meandering manner.   The multi-cylinder engine according to claim 1, wherein the extension portion of the EGR passage is configured by a heat transfer tube extending in a spiral shape.   The multi-cylinder engine according to claim 1, wherein the extension portion of the EGR passage includes a convex portion or a concave portion extending along the flow of EGR gas on the inner surface of the passage.   2. The multi-cylinder engine according to claim 1, wherein the extension portion of the EGR passage includes a convex portion or a concave portion that spirally extends on the inner surface of the passage in the EGR gas flow direction.   2. The multiple nozzle according to claim 1, further comprising a nozzle portion that narrows the downstream side of the collecting portion of each exhaust manifold toward the joining portion as a means for preventing the exhaust gas from flowing back between the exhaust manifolds. Cylinder engine.   2. The multi-cylinder engine according to claim 1, further comprising a twin-entry turbocharger as means for preventing the exhaust gas from flowing backward between the exhaust manifolds.   In the EGR cooler arranged in the EGR passage of the engine, an EGR gas flow path constituted by a heat transfer tube extending in a serpentine shape or a spiral shape, and a convex portion or a concave portion extending along the EGR gas flow on the inner surface of the heat transfer tube An EGR cooler characterized by comprising:   In the EGR cooler arranged in the EGR passage of the engine, an EGR gas flow path constituted by a heat transfer tube extending in a serpentine shape or a spiral shape, and a convex portion extending spirally in the EGR gas flow direction on the inner surface of the heat transfer tube or An EGR cooler comprising a concave portion.   The EGR cooler according to claim 8 or 9, wherein the heat transfer tube is of a water cooling type or an air cooling type.

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