JP2007327382A - Multicylinder engine and its egr cooler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce NO<SB>x</SB>, increase output, and improve fuel economy, by implementing high supercharge and a large amount of EGR, and to reduce the number of parts of an EGR device and reduce piping, in a multicylinder engine having an EGR device recirculating part of exhaust from upstream of a turbine of a turbocharger to downstream of a compressor. <P>SOLUTION: In the multicylinder engine, the EGR device 35 comprises: tributary passages 36a, 36b each having one end connected with an exhaust manifold; a confluence passage 36c connecting the other end side of them with a venturi; and an EGR cooler 37 disposed at a connecting part between the tributary passages 36a, 36b and the confluence passage 36c. The EGR cooler 37 has: respective inlet parts 50A, 50B each connected with the tributary passage; a common outlet part 51A connected with the confluence passage; cooling passages 52A, 52B connecting each inlet part with the common outlet part; and a reed valve 53A as a check valve opening/closing each cooling passage with respect to the common outlet part so as to suppress transmission of exhaust pulses between the cooling passages. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technology for realizing exhaust measures (such as NOx reduction) and improving output and fuel consumption in a multi-cylinder engine equipped with an EGR device that circulates exhaust gas from the turbine upstream of the turbocharger to the compressor downstream. The present invention relates to a suitable EGR cooler.

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. In such an EGR system, when 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 is likely to occur, and sufficient EGR cannot be obtained. In Patent Document 1, in order to use exhaust pulsation to improve the EGR rate, the exhaust manifold is divided into cylinder groups that do not overlap in the exhaust stroke, and the manifold (turbine upstream of the turbocharger) and the intake passage (turbocharger A check valve (reed valve) that restricts the backflow of EGR gas (exhaust gas) is provided in the middle of each EGR passage that is individually connected to the downstream of the compressor.
JP 2004-308487 A

  In such a conventional example, the turbine housing of the turbocharger is connected downstream of the exhaust manifold for each cylinder group. For this reason, the turbocharger is restricted to one having a plurality of turbine inlets corresponding to the exhaust manifold for each cylinder group. When the number of turbine inlets is one (single entry system), the blowdown flow from the exhaust manifold on the side of the cylinder group that is injecting exhaust gas through the inside of the turbine housing (the exhaust gas at the initial stage of the exhaust stroke) is in the exhaust (push-out) stroke cylinder Escape to the exhaust manifold on the group side. In other words, exhaust pulses (positive pressure wave peaks) cannot be fully utilized to improve the EGR rate and turbine efficiency. Further, since the EGR passages are individually arranged and the EGR cooler, the EGR valve, and the check valve are arranged in each EGR passage, the number of parts is large and the piping is bulky, resulting in an increase in cost.

  In the multi-cylinder engine having an EGR device that circulates the exhaust gas from the turbine upstream of the turbocharger to the compressor downstream, based on such conventional technology, the present invention provides an exhaust countermeasure (NOx reduction, etc.), output and fuel consumption reduction. In order to promote improvement, the purpose is to provide a means that can achieve high supercharging and large EGR in a wide operating range.

  The first invention is an EGR device that circulates exhaust from the turbine upstream of the turbocharger to the compressor downstream, an exhaust manifold that is divided into two for each cylinder group that does not overlap the exhaust stroke, and an exhaust pulse that flows directly downstream of these exhaust manifolds. An exhaust pulsation amplifying means that suppresses the intake pulsation, and an intake pulsation amplifying means that is disposed upstream of the intake manifold, and the EGR device includes a branch flow path having one end connected to each exhaust manifold, and the other end side of each branch flow path. An EGR cooler disposed at a connection portion between the branch flow path and the combined flow path, each of which is connected to each of the branch flow paths, and the combined flow path. A common outlet connected to each other, a cooling passage connecting each inlet and the common outlet, and an exhaust pulse between these cooling passages is suppressed. Characterized in that it comprises as a reed valve, as check valve for opening and closing the respective cooling passages to a common outlet.

  The second invention is an EGR device that circulates exhaust gas from the turbine upstream of the turbocharger to the compressor downstream, an exhaust manifold that is divided into two for each cylinder group that does not overlap the exhaust stroke, and an exhaust pulse that flows directly downstream of these exhaust manifolds. And an exhaust pulsation amplifying means disposed upstream of the intake manifold, and the EGR device includes a branch flow path having one end connected to each exhaust manifold, and the other end side of these branch flow paths. It is characterized by comprising a combined flow path connecting the intake pulsation amplifying means, an EGR cooler disposed in each branch flow path, and a reed valve as a check valve disposed in an outlet portion of each cooler.

  In a third aspect of the invention, the reed valve according to the first aspect of the present invention is interposed between the downstream ends of the two cooling passages facing each other, and includes a pair of valve seats corresponding to the downstream ends of the respective cooling passages. It is configured as a cantilever valve that is pressed against the valve seat on the opposite side by the dynamic pressure of the exhaust gas ejected from the cooling passage to the outlet portion and closes the other cooling passage with respect to the outlet portion. .

  The fourth invention is characterized in that the exhaust pulsation amplifying means according to the first to third inventions is provided with a mixing section for narrowing each exhaust manifold to a converging section immediately downstream in a tapered nozzle shape.

  The fifth invention is characterized in that, as exhaust pulsation amplifying means according to the first to third inventions, a turbine inlet of a turbocharger connects a plurality of turbine housings to downstream ends of the respective exhaust manifolds.

  The sixth invention is characterized in that, as the intake pulsation amplifying means according to the first to third inventions, a venturi is arranged at a connection portion between the intake passage and the EGR passage.

  The seventh invention is characterized in that, as the intake pulsation amplifying means according to the first to third inventions, a throttle valve is disposed at a connection portion between the intake passage and the EGR passage.

  In the first aspect of the invention, the exhaust pulsation amplifying means prevents the exhaust pulse from flowing back immediately downstream of each exhaust manifold, and the exhaust pulse is transmitted to the EGR cooler without being weakened. In addition, the EGR cooler is provided with a reed valve that opens and closes each cooling passage with respect to a common outlet so as to prevent the exhaust pulse from going back and forth between the two cooling passages. It is possible to prevent the exhaust pulse from flowing backward. That is, even in the EGR cooler arranged at the connection portion between the branch flow path and the combined flow path, the interference of the exhaust is prevented, and the exhaust pulse can be effectively used to improve the EGR rate. Further, since the intake air pressure is reduced by the intake pulsation amplifying means, it becomes easier to suck EGR gas into the intake manifold, and the improvement of the EGR rate is promoted. Therefore, when the turbine housing of the turbocharger is connected directly downstream of each exhaust manifold, not only the turbine efficiency can be improved but also the EGR rate can be sufficiently increased even in a single entry system with one turbine inlet. is there. The EGR cooler is equipped with two cooling passages, but it is a single component, and the EGR valve that adjusts the EGR flow rate can be one component if it is installed in the combined flow path. The cost can be reduced.

  In the second aspect of the invention, the exhaust pulsation amplifying means can suppress the exhaust pulse from flowing back immediately downstream of each exhaust manifold. For this reason, the exhaust pulse is transmitted to the EGR cooler without being weakened, and the reed valve can be operated effectively. Since the reed valve is disposed at the outlet of each EGR cooler, it is possible to suppress the backflow of exhaust pulses. That is, the reed valve of each branch channel prevents the interference of the exhaust, and the exhaust pulse can be effectively used to improve the EGR rate. Further, since the intake air pressure is reduced by the intake pulsation amplifying means, it becomes easier to suck EGR gas into the intake manifold, and the improvement of the EGR rate is promoted. Therefore, when the turbine housing of the turbocharger is connected directly downstream of each exhaust manifold, not only the turbine efficiency can be improved but also the EGR rate can be sufficiently increased even in a single entry system with one turbine inlet. is there. Since the EGR device uses a combined flow path, piping can be saved, and an EGR valve that adjusts the EGR flow rate can be reduced by reducing the number of parts because only one component is required if it is installed in the combined flow path. Reduction can be realized.

  In the third invention, the reed valve is pressed against the valve seat on the opposite side by the dynamic pressure of the exhaust gas ejected from the one cooling passage to the outlet portion, and the other cooling passage is closed with respect to the outlet portion. Not only can the exhaust pulse travel between the two cooling passages, but when the low-pressure side cooling passage is closed, the high-pressure side cooling passage is open, so the intake pressure (supercharging pressure) is reduced. As long as the exhaust pressure on the high pressure side is not exceeded, the backflow of EGR gas accompanying the rise in intake pressure can be suppressed.

  In the fourth aspect of the invention, the flow of exhaust is accelerated and the dynamic pressure is increased by the tapered nozzle-shaped mixing portion, so that the exhaust manifold on the cylinder side during the exhaust (push-out) stroke from the exhaust manifold on the cylinder side being exhausted is discharged. The exhaust pulse can be prevented from escaping. In addition, when the dynamic pressure increases due to the tapered nozzle-shaped mixing section, the static pressure decreases and the exhaust is sucked from the exhaust manifold during the exhaust (push-out) stroke, so that the pumping loss during the exhaust (push-out) stroke is also reduced. .

  In the fifth aspect of the invention, the turbine inlet has two turbine housings to prevent the interference of exhaust and improve the rotation of the turbine. In addition, the EGR rate can be transmitted to the EGR passage without weakening the exhaust pulse. It can be raised enough.

  In the sixth aspect of the invention, the venturi accelerates the flow of intake air, increases the dynamic pressure, and lowers the static pressure. Therefore, EGR gas can be easily sucked into the intake manifold, and the improvement of the EGR rate is promoted.

  In the seventh invention, the flow of the intake air is suppressed by the throttle valve, and it becomes easy to suck the EGR gas into the intake manifold, thereby promoting the improvement of the EGR rate.

  In FIG. 1, reference numeral 2 denotes an intake passage of a multi-cylinder engine 1 (6-cylinder diesel engine), which includes an intake manifold 3 and an intake pipe 4. 6a is a compressor of the turbocharger 6, 5 is an intercooler, 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.

  As shown in FIG. 2, the exhaust manifolds 9 a and 9 b 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 23a and 23b, the dynamic pressure is increased, and the static pressure is lowered, so that the backflow of the exhaust pulse between the exhaust manifolds 9a and 9b can be suppressed. . Further, when the dynamic pressure is increased and the static pressure is lowered by the flow velocity of the blowdown flow (the exhaust gas discharged at the initial stage of the exhaust stroke) ejected from the nozzle portion 23a or 23b, and the ejector action is generated, 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 a 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. An EGR passage 36 is provided for connection to the amplifying means. The EGR passage 36 includes branch passages 36a and 36b whose one ends are connected to the aggregate portions of the exhaust manifolds 9a and 9b, and a joint passage 36c that connects the other end of the branch passages 36a and 36b and the venturi 40, respectively. The EGR coolers 37a and 37b are disposed in the branch flow paths 36a and 36b, respectively, and the EGR valve 38 (means for adjusting the EGR flow rate) is disposed in the combined flow path 36c. A venturi 40 is disposed immediately upstream of the intake manifold 3 (downstream of the intercooler 5), and a joint channel 36c of the EGR device 35 is opened in the venturi 40. The venturi 40 accelerates the flow of intake air, increases the dynamic pressure, and lowers the static pressure, so that EGR gas can be easily sucked into the intake manifold 3.

  3 and 4 illustrate the configuration of the EGR coolers 37a and 37b. The exhaust (EGR gas) inlet 50 and outlet 51, the cooling passage 52 formed between them, and the cooling passage are illustrated. And a reed valve 53 (check valve) that opens and closes the outlet 52 with respect to the outlet 51. The cooling passage 52 is composed of a predetermined number of heat transfer tubes 52a, and a flow path 56 surrounded by a cylindrical body 52b is formed around the cooling passage 52, and the EGR gas passing through the heat transfer tubes 52a and the inside of the body 52b (flow path 56). ) To exchange heat with the cooling water flowing through. 55 is an inlet part of the cooling water, 56 is also an outlet part, and these are connected to the cooling water circulation circuit of the engine 1.

  The reed valve 53 is in contact with the valve seat 54 and shuts off (closes) between the cooling passage 52 and the outlet 51 in a natural state where the amount of bending is zero, while the pressure on the cooling passage side is higher than the pressure on the outlet side. If the pressure increases, the valve seat 54 is separated from the valve seat 54 due to the pressure difference, and the cantilever valve communicates (opens) between the cooling passage 52 and the outlet 51. A valve stopper 57 regulates the maximum opening of the reed valve.

  With such a configuration, the exhaust of the engine 1 is divided by the exhaust manifolds 9a and 9b for each cylinder group in which the exhaust strokes do not overlap, and the turbine 6b of the turbocharger 6 is fed from the tapered nozzle-shaped mixing portions 23a and 23b. To the downstream side. At that time, the dynamic pressure is increased and the static pressure is decreased by the mixing portions 23a and 23b having the tapered nozzle shape, and therefore, the exhaust manifold 9a or 9b on the cylinder side that is exhausting the exhaust gas from the cylinder side that is in the exhaust (extrusion) stroke process. The exhaust pulse is prevented from escaping to 9b or 9a. Therefore, the exhaust pulse is transmitted not only to the turbine 6b but also to the EGR passage 36 without being weakened.

  When the pressure on the cooling passage side becomes lower than the pressure on the outlet side due to its own elastic force, the reed valve 53 is pressed by the valve seat 54 and blocks the communication between the cooling passage 52 and the outlet portion 51. In other words, when the pressure on the intake side exceeds the pressure on the exhaust side, the reed valve 53 closes, so that the backflow of EGR gas can be suppressed. Further, between the two EGR coolers 37a, 37b, the other reed valve 53 is closed by the exhaust pulse from one, so that interference of the exhaust is prevented, and the exhaust pulse can be efficiently used to improve the EGR rate. It is.

  Since the intake pressure is reduced (intake negative pressure is amplified) by the venturi 40, the EGR gas is easily sucked into the intake manifold 3, and the improvement of the EGR rate is promoted. Accordingly, the turbine housing 25 of the turbocharger 6 is connected directly downstream of the exhaust manifolds 9a and 9b. Even in the single entry system with one turbine inlet, not only the turbine efficiency is improved, but also the EGR rate is reduced. It can be raised enough. Further, when the dynamic pressure is increased by the mixing portion 23a or 23b having a tapered nozzle shape, the static pressure is reduced, and the exhaust is sucked from the exhaust manifold 9b or 9a during the exhaust (pushing) stroke to the diffuser portion 29. Reduced. Since the EGR device 35 uses the combined flow path 36c, piping is saved, and only one EGR valve 38 for adjusting the EGR flow rate is required for the combined flow path 36c, so the number of parts can be reduced and the cost can be reduced. realizable.

  5 to 9 show other embodiments, and the EGR passage 36 includes branch passages 36a and 36b whose one ends are connected to the collection portions of the exhaust manifolds 9a and 9b, and branch passages 36a and 36b, respectively. A combined flow path 36c that connects the other end side and the venturi 40, an EGR cooler 37 that is disposed at a connection portion between the branch flow paths 36a and 36b and the combined flow path 36c, and an EGR valve 38 ( Means for adjusting the EGR flow rate).

  The EGR cooler 37 includes individual inlet portions 50a and 50b connected to the branch passages 36a and 36b, a common outlet portion 51A connected to the combined passage 36c, and an outlet portion common to the individual inlet portions 50a and 50b. The cooling passages 52A and 52B are respectively formed between the cooling passage 52a and the reed valve 53A for opening and closing the cooling passages 52A and 52B with respect to the common outlet 51A (see FIGS. 5 and 6). Each of the cooling passages 52A and 52B includes a predetermined number of heat transfer tubes 52a, and a flow path 56A surrounded by a cylindrical body 52b is formed around the cooling passages 52A and 52B. The EGR gas passing through the heat transfer tubes 52a and the inside of the body 52b (flow) Heat exchange is performed with the cooling water flowing through the path 56A). 55A is an inlet part of the cooling water, 56a and 56b are also outlet parts, and these are connected to the cooling water circulation circuit of the engine 1.

  The reed valve 53A is interposed between the downstream ends of the two cooling passages 52A and 52B facing each other. Specifically, as shown in FIGS. 8 and 9, a pair of valve seats 54a and 54b corresponding to the downstream ends of the cooling passages 52A and 52B are formed inside the cylindrical casing 60, and the reed valve 53A is The other side of the cooling passage 52B is pressed against the opposite valve seat 54b or 54a by the dynamic pressure of the exhaust pulse that is sandwiched on one side of the valve seats 54a and 54b and passes from one cooling passage 52A or 52B to the outlet 51A. Or it is comprised by the cantilever valve which closes 52A with respect to 51 A of exit parts. In this case, the reed valve 53A is a cantilever valve that opens away from the valve seats 54a and 54b in a natural state where the amount of flexure is 0. Therefore, the reed valve 53A has an exhaust pulse as compared with a normal reed valve that is pushed open by exhaust. Can easily pass through, and can be expected to improve the EGR rate.

  In this embodiment, the reed valve 53A can prevent the exhaust pulse from going back and forth between the cooling passages 52A and 52B. In other words, in the EGR cooler 37, exhaust interference is prevented, and the exhaust pulse can be effectively used to improve the EGR rate. Further, the reed valve 53A closes the low pressure side of the cooling passages 52A and 52B and opens the high pressure side, so that the backflow of EGR gas can be suppressed even when the pressure on the intake side exceeds the pressure on the exhaust side. It is. Accordingly, the turbine housing 6b of the turbocharger 6 is connected immediately downstream of the exhaust manifolds 9a and 9b. Even in the single entry system with one turbine inlet, not only the turbine efficiency is improved, but also the EGR rate is reduced. It can be raised enough. The EGR cooler 37 includes two cooling passages 52A and 52B. However, the EGR cooler 37 is a single component, and only one recirculation valve 53A and one EGR valve 38 for adjusting the EGR flow rate are required for the combined flow path 36c. The number of parts and the number of pipes can be reduced to 35, and the cost can be reduced. It is also conceivable to arrange a check valve for restricting the backflow of the EGR gas at the connection portion between the EGR passage 36 and the venturi 40. 5, parts that are the same as those in FIG. 1 are given the same reference numerals, and redundant descriptions are omitted.

  1 and 5, a throttle valve (throttle valve) may be used as an alternative to the venturi 40. The throttle valve suppresses the flow of intake air, facilitates the intake of EGR gas into the intake manifold 3, and promotes the improvement of the EGR rate. The tapered nozzle-shaped mixing portions 23a and 23b are not formed integrally with the exhaust manifolds 9a and 9b, but as a separate spacer as shown in FIG. 10, the flange 20 of the exhaust manifolds 9a and 9b and the flange 26 of the turbine housing 25 You may interpose between. The diffuser portion 29 is not formed integrally with the turbine housing 25, but is 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. Also good.

1 is an overall schematic configuration diagram showing an embodiment of the present invention. It is sectional drawing explaining the mixing part of a tapered nozzle shape similarly. It is a sectional view explaining an EGR cooler similarly. FIG. 4 is a sectional view taken along the line XX in FIG. 3. It is a general schematic block diagram explaining another embodiment. It is a sectional view explaining an EGR cooler similarly. FIG. 7 is a sectional view taken along the line XX in FIG. 6. It is sectional drawing of a reed valve similarly. FIG. 9 is a left side view of FIG. 8. It is sectional drawing explaining the mixing part of a tapered nozzle shape as another modification. It is sectional drawing explaining a diffuser part as another modification.

Explanation of symbols

1 Multi-cylinder engine 2 Intake passage 3, 3a, 3b Intake manifold 5 Intercooler 6 Turbocharger (variable nozzle type turbocharger)
6a Compressor 6b Turbine 8 Exhaust passage 9a, 9b Exhaust manifold 23a, 23b Tapered nozzle part 35 EGR device 37a, 37b, 37 EGR cooler 38 EGR valve 40 Venturi 50, 50A, 50B EGR cooler inlet 51, 51A EGR cooler 52, 52A, 52B EGR cooler cooling passage 53, 53A Reed valve 54, 54a, 54b Valve seat 57 Valve stopper

Claims (7)

  EGR system that circulates exhaust gas from upstream of turbocharger turbine to downstream of compressor, exhaust manifold divided into two for each cylinder group where exhaust strokes do not overlap, and exhaust pulsation that suppresses backflow of exhaust pulses directly downstream of these exhaust manifolds The EGR device includes an amplifying means and an intake pulsation amplifying means disposed upstream of the intake manifold, and the EGR device includes a branch flow path having one end connected to each exhaust manifold, the other end side of these branch flow paths, and the intake pulsation amplification means. The EGR cooler is disposed at the connection portion between the branch flow path and the combined flow path, and the EGR cooler has an individual inlet portion connected to the branch flow path and a common outlet connected to the combined flow path. And cooling passages connecting the respective inlet portions and the common outlet portion, and so as to prevent the exhaust pulses from going back and forth between these cooling passages. Lead valve as a check valve for opening and closing the 却通 path to a common outlet section, a multi-cylinder engine, characterized in that it comprises a.   EGR system that circulates exhaust gas from upstream of turbocharger turbine to downstream of compressor, exhaust manifold divided into two for each cylinder group where exhaust strokes do not overlap, and exhaust pulsation that suppresses backflow of exhaust pulses directly downstream of these exhaust manifolds The EGR device includes an amplifying means and an intake pulsation amplifying means disposed upstream of the intake manifold, and the EGR device includes a branch flow path having one end connected to each exhaust manifold, the other end side of these branch flow paths, and the intake pulsation amplification means. A multi-cylinder engine comprising: a combined flow path connecting the two, an EGR cooler disposed in each branch flow path, and a reed valve as a check valve disposed in an outlet portion of each cooler.   The reed valve is interposed between the downstream ends of the two cooling passages facing each other, and includes a pair of valve seats corresponding to the downstream ends of the respective cooling passages, and the dynamic pressure of the exhaust gas ejected from one cooling passage to the outlet portion The multi-cylinder engine according to claim 1, wherein the multi-cylinder engine is configured as a cantilever valve that is pressed by the valve seat on the opposite side and closes the other cooling passage with respect to the outlet portion.   The multi-cylinder engine according to any one of claims 1 to 3, wherein the exhaust pulsation amplifying means is provided with a mixing section that narrows each exhaust manifold into a converging section immediately downstream in a tapered nozzle shape.   The multi-cylinder engine according to any one of claims 1 to 3, wherein, as exhaust pulsation amplifying means, a turbine inlet of a turbocharger has two turbine housings connected to the downstream end of each exhaust manifold.   The multi-cylinder engine according to any one of claims 1 to 3, wherein a venturi or an ejector is disposed at a connection portion between the intake passage and the EGR passage as the intake pulsation amplification means.   The multi-cylinder engine according to any one of claims 1 to 3, wherein a throttle valve is disposed at a connection portion between the intake passage and the EGR passage as the intake pulsation amplifying means.

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