JP2007218171A - Multiple cylinder engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compatibly attain high supercharging and a great amount of EGR in a wide operation range to take exhaust emission measure and improve output/fuel economy in a multiple cylinder engine provided with a turbocharger. <P>SOLUTION: This engine is provided with exhaust manifolds 9a, 9b divided into cylinder groups of which exhaust strokes do not overlap, intake manifolds 3a, 3b divided into cylinder groups of which intake strokes do not overlap, means 23a, 23b preventing reverse flow of exhaust pulse in a merging part of the exhaust manifolds, resonance pipes 40a, 40b connecting a branch part 41 of a intake air passage 2 and a collecting part inlet of each intake manifold as a means amplifying intake pulsation and controlling phase of the intake pulsation, EGR passages 36a, 36b connecting the resonance pipes and the exhaust manifolds in a relation of same cylinder group, and means 50, 51 varying resonance rotation speed of an intake system. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for realizing both high supercharging and a large amount of EGR in a wide operation region in order to improve exhaust measures and improve output and fuel consumption in a multi-cylinder engine equipped with a turbocharger.

  As an engine EGR (Exhaust Gas Recirculation) system, one that circulates part of the exhaust gas from the exhaust system to the intake system is often used. In such an EGR device, 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 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 system that performs EGR by exhaust pulsation using a reed valve (check valve) (Patent Document 1, Patent Document 2), and a system that increases exhaust pulsation (dynamic pressure of EGR gas) using a mixing section in the EGR passage (Patent Document 3) and a method of performing internal EGR using a variable valve (Patent Document 4) are known.
JP 2000-249004 JP 2005-147010 A Special table 2003-534488 JP 2001-107810 A

  In the case of Patent Documents 1 to 3, when the turbocharger connected to the split type exhaust manifold is a single entry system (one turbine inlet), exhaust pulses (positive pressure waves) between cylinder groups having different phases are mutually connected. Because they cancel each other, a sufficient EGR rate cannot be obtained. In the case of Patent Document 4, the exhaust (EGR gas) cannot be cooled. Further, in Patent Document 2, although an EGR passage for connecting the split type exhaust manifold and the split type intake manifold to each other in the same cylinder group is provided, the peak of the exhaust pulse is at the initial stage of the intake stroke. Therefore, the timing of the valley of the intake pulsation (which occurs in the middle of the intake stroke) is not matched, 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 having a turbocharger, a first invention is 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, As a means for preventing the exhaust pulse from flowing back through the merging portion of the exhaust manifold and a means for controlling the amplification of the intake pulsation and the phase of the intake pulsation, the branch portion of the intake passage and the collection portion of each intake manifold are connected. A resonance pipe, an EGR passage for connecting the resonance pipe and the exhaust manifold in the same relationship between the cylinder groups, and means for changing the resonance rotational speed of the intake system are provided.

  The second invention is characterized in that, in the multi-cylinder engine according to the first invention, the length L of each resonance tube is set so as to satisfy the following conditions.

The third invention is characterized in that, in the multi-cylinder engine according to the second invention, the resonance rotational speed N _R1 is set in an operation region in which the compressor outlet pressure is higher than the turbine inlet pressure.

According to a fourth aspect of the invention, in the multi-cylinder engine according to the second aspect of the invention, the means for changing the resonance rotational speed of the intake system sets the resonance rotational speed N _R1 depending on the length L of the resonance tube to the resonance rotational speed on the high speed side. A valve that opens and closes a path that connects the resonance pipes of portions where the resonance pipes have a length L ′ corresponding to the resonance rotational speed N _R2 upstream of the connection with the EGR passage to switch to N _R2 or vice versa. It is characterized by having.

  According to a fifth aspect of the invention, in the multi-cylinder engine according to the fourth aspect of the invention, the means for changing the resonance rotational speed of the intake system includes means for controlling the open / close valve based on the operating state. To do.

  According to a sixth aspect of the present invention, in the multi-cylinder engine according to the first aspect of the invention, as a means for preventing the exhaust pulses from flowing back through the merged portion of the exhaust manifold, the downstream of the collective portion of each exhaust manifold is directed toward these merged portions. It is characterized by having a nozzle portion that narrows to a tapered shape.

  According to a seventh aspect of the present invention, in the multi-cylinder engine according to the first aspect, a variable nozzle type is used as a turbocharger and a compressor is interposed upstream of the branch portion of the intake passage, while the turbine of the turbocharger is joined to the exhaust manifold. It is connected to the part.

  According to an eighth aspect of the present invention, in the multi-cylinder engine according to the first aspect, each EGR passage includes an EGR valve upstream of the check valve and an EGR cooler upstream thereof.

  In the first invention, even when the turbocharger is of a single entry system (one turbine inlet), the check valve for the EGR passage is provided by means for preventing the exhaust pulse from flowing back between the split type exhaust manifolds. The exhaust pulse (positive pressure wave) is transmitted without being weakened, and the check valve is effectively operated, so that a high EGR rate is obtained. Moreover, the instantaneous differential pressure before and after the check valve is expanded by the resonance tube (means for controlling the amplitude of intake pulsation and the phase of intake pulsation), and the EGR rate can be further improved.

  When the engine speed becomes equal to the resonance speed of the intake system, the intake pulsation is amplified by the resonance action. The valley of the intake pulsation occurs in the middle of the intake stroke, but since the amplitude of the intake pulsation is large, a sufficient drop from the exhaust pressure is obtained and the EGR rate is maximized. On the lower speed side than the resonance rotational speed, the phase of the intake pulsation advances, and the valley of the intake pulsation approaches the peak of the exhaust pulse (which occurs during exhaust ejection at the beginning of the exhaust stroke), so that a sufficiently high EGR rate is obtained.

  On the higher speed side than the resonance speed, the phase of the intake pulsation is delayed, and the valley of the intake pulsation moves away from the peak of the exhaust pulse, but the amplitude of the intake pulsation is large, so the EGR rate tends to decrease although it remains slightly. Conceivable. If the resonance rotational speed is changed to the high speed side by means for changing the resonance rotational speed of the intake system on the higher speed side than the resonance rotational speed, the intake pulsation is amplified by the resonance action, and the phase is not delayed. The peak of the intake pulsation occurs in the middle of the intake stroke, and the amplification of the intake pulsation maximizes the EGR rate.

In the second invention, the length L of the resonance tube is set on condition that the resonance rotational speed N _R1 is in the normal rotational speed range of the engine. The resonance rotational speed N _R1 is proportional to f / m, the resonance frequency f is proportional to {A / (LV)} ^1/2 , and when L is set large, the resonance rotational speed N _R1 On the other hand, when L is set small, the resonance rotational speed N _R1 becomes the high speed side. Therefore, the length L of the resonance tube is desirably set so that the resonance rotational speed N _R1 is in the middle speed range in order to sufficiently increase the EGR rate in a wide operation range.

In the third aspect of the invention, the EGR rate is maximized in the operating region where the compressor outlet pressure is higher than the turbine inlet pressure of the turbocharger due to the resonance action. When the turbocharger efficiency becomes maximum at the engine maximum torque point, the EGR rate can be sufficiently increased in a wide operation range by setting the resonance rotational speed N _R1 in the medium speed range including the engine maximum torque point.

In the fourth invention, when the on-off valve is in the closed state, the resonance tube has a length L, and when the engine speed becomes equal to the resonance speed N _R1 corresponding to L, the intake pulsation is amplified by the resonance action. The When the on-off valve is opened, the resonance tube has a length L ′, and when the engine speed becomes equal to the resonance speed N _R2 corresponding to L ′, the intake pulsation is amplified by the resonance action. Since the resonance speed N _R2 corresponding to the length L ′ of the resonance tube is set at a higher speed side than the resonance speed N _R1 corresponding to the length L of the resonance pipe, it is higher than the resonance speed N _R1. Also, the EGR rate can be maximized by the resonance effect.

  In the fifth invention, the on-off valve can be accurately controlled based on the operating state. For example, EGR is controlled in a wide operating range (low speed range to high speed range) by controlling the open / close valve to open and close at the boundary between the medium speed range and the high speed range based on the engine speed representing the operating state. The rate can be increased efficiently and sufficiently. By adding the engine load in addition to the engine speed to the control parameter, it becomes possible to control the on-off valve more finely.

  In the sixth aspect of the invention, the tapered nozzle portion accelerates the flow of exhaust, increases the dynamic pressure, and lowers the static pressure (exhaust pressure), thereby preventing the exhaust pulse from flowing back between the exhaust manifolds. . Therefore, 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. Also, if the ejector action occurs due to the flow rate of the blowdown flow (jet exhaust at the beginning of the exhaust stroke) that blows out from the tapered nozzle, exhaust is sucked from the exhaust manifold on the cylinder side during the exhaust stroke (extrusion). Not only is efficiency improved, but pumping loss is also improved.

  In the seventh aspect of the invention, by controlling the nozzle opening with a variable nozzle type turbocharger, it is possible to achieve both high supercharging and a large amount of EGR even in a low speed and high load region, and to take measures against exhaust (NOx and PM Reduction) and advanced improvement in output and fuel consumption.

  In the eighth invention, since the EGR gas (exhaust gas) is cooled by the EGR cooler and flows through the EGR valve and the check valve, the durability of these valves can be ensured satisfactorily.

  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 8 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, which once squeezes the merging portion 11 downstream of the nozzle portions 23a and 23b 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. Therefore, the exhaust pulse flows back between the exhaust manifolds 9a and 9b (exhaust stroke). In addition to restraining the initial blowout exhaust from escaping from one exhaust manifold 9a or 9b to the other exhaust manifold 9b or 9a), the flow rate of the blowdown flow (pumped exhaust at the beginning of the exhaust stroke) blown out from the nozzle portion 23a or 23b When the dynamic pressure increases, the static pressure decreases, and the ejector action occurs, the exhaust is sucked into the diffuser section 29 from the cylinder side exhaust manifold 9b or 9a during the exhaust (pushing) stroke. 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 (reed valve) 39 for regulating the backflow of the EGR gas are interposed. The check valve 39 is disposed downstream of the EGR passages 36a and 36b. An EGR valve 38 is disposed upstream of the check valve 39 and an EGR cooler 37 is disposed upstream thereof. Since the EGR passages 36a and 36b are connected to each other in the same cylinder group, the exhaust stroke and the intake stroke overlap between the cylinders belonging to the same cylinder group, so that the EGR rate can be improved.

  In the branch path of the intake pipe 4, the resonance pipes 40a and 40b (amplification of the intake pulsation and the phase of the intake pulsation are controlled between the inlet portion of the intake manifolds 3a and 3b and the upstream branch 41 (branch point). Means). The length L of the resonance tubes 40a and 40b is set so as to satisfy the following conditions.

The resonance speed N _R1 is proportional to f / m, the resonance frequency f is proportional to {A / (LV)} ^1/2 , and when L is set large, the resonance speed N _R1 On the other hand, when L is set small, the resonance rotational speed N _R1 becomes the high speed side. In this case, the resonance rotational speed N _R1 is determined by the length L of the resonance tubes 40a and 40b, so that the EGR is difficult (the turbocharger efficiency becomes maximum and the vicinity thereof, and the compressor outlet pressure is higher than the turbine inlet pressure). Higher). When the turbocharger efficiency is maximized at the engine maximum torque point, the resonance rotational speed N _R1 is set to a medium speed range including the engine maximum torque point.

The EGR passages 36a and 36b are connected to the downstream side of the resonance tubes 40a and 40b (positions as close as possible to the inlets of the collecting portions of the intake manifolds 3a and 3b). In the resonance tubes 40a and 40b, in order to switch the resonance rotation speed N _R1 to the resonance rotation speed N _R2 on the higher speed side or vice versa, upstream of the connection portion 42 with the EGR passages 36a and 36b (the resonance tubes 40a and 40b are resonant). A passage 50 that connects a portion having a length L ′ corresponding to the rotational speed N _R2 ) and a valve 51 that opens and closes the passage 50 are provided.

When the on-off valve 51 is in the closed state, the resonance tubes 40a and 40b have a length L, and when the engine speed becomes equal to the resonance speed N _R1 corresponding to L, the intake pulsation is amplified by the resonance action. When the on-off valve 51 is opened, the resonance tubes 40a and 40b have a length L ′, and when the engine speed becomes equal to the resonance speed N _R2 corresponding to L ′, the intake pulsation is amplified by the resonance action. The resonance speed N _R2 corresponding to the length L ′ of the resonance tubes 40a, 40b is set at a higher speed than the resonance speed N _R1 corresponding to the length L of the resonance tubes 40a, 40b. _{Even at a} higher speed side than _R1 , the EGR rate can be maximized by the resonance action as will be described later.

  In FIG. 1, reference numeral 55 denotes a control unit that controls a variable nozzle mechanism (not shown) of the turbine 6b, an EGR valve 38 of the EGR passages 36a and 36b, and an open / close valve 51 of the passage 50, and detects an operating state necessary for the control. As means, an engine rotation sensor 56 for detecting the engine speed from the flywheel rotation and an engine load sensor 57 for detecting the engine load from the accelerator opening (the pedal operation amount) are provided.

FIG. 6 is a flowchart illustrating the control contents of the control unit 55. In S1 and S2, a detected value of the engine speed and a detected value of the engine load (accelerator opening) are read. In S3 to S5, the variable nozzle mechanism, the EGR valve 38, and the open / close valve 51 are sequentially controlled based on these detected values. 3 to 5 illustrate control characteristics of the control unit 55. In S3, the turbine nozzle opening of the turbocharger 6 is determined based on FIG. 3 from the detected value of the engine speed and the detected value of the engine load. Control the degree. In S4, the opening degree of the EGR valve 38 is controlled based on the detected value of the engine speed and the detected value of the engine load based on FIG. In S5, ON / OFF (switching) of the on-off valve 51 is controlled based on the detected value of the engine speed based on FIG. In FIG. 5, the opening / closing valve 51 opens when the detected value of the engine speed becomes equal to or higher than the set value N ₀ , while closing when the detected value of the engine speed becomes lower than the set value lower than the set value N _0. To be controlled.

  With such a configuration, even in the single entry type turbocharger 6, the backflow of the exhaust pulse is suppressed by the tapered nozzles 23 a and 23 b, and the exhaust pulse to the turbine 6 b is strengthened by the ejector action of the merging portion 11. Therefore, the turbine efficiency can be improved. In addition, since the back flow of the exhaust pulse is suppressed, the exhaust pulse is transmitted to the check valve 39 in the EGR passages 36a and 36b without being weakened, and the check valve 39 is effectively operated, so that a high EGR rate is obtained. is there. Further, 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 improved.

  In the closed state of the on-off valve 51, when the engine speed becomes equal to the resonance speed of the intake system, the intake pulsation is amplified by the resonance action. The valley of the intake pulsation occurs in the middle of the intake stroke, but since the amplitude of the intake pulsation is large, a sufficient drop from the exhaust pressure is obtained and the EGR rate is maximized. On the lower speed side than the resonance rotational speed, the phase of the intake pulsation advances, and the valley of the intake pulsation approaches the peak of the exhaust pulse (which occurs during exhaust ejection at the beginning of the exhaust stroke), so a sufficiently high EGR rate is obtained ( (See FIGS. 10 and 11). On the higher speed side than the resonance rotational speed, the phase of the intake pulsation is delayed, and the valley of the intake pulsation moves away from the peak of the exhaust pulse, but the amplitude of the intake pulsation is large, so the EGR rate tends to decrease although it stays slightly. Yes (see FIGS. 14 and 15).

When the engine speed reaches the set value N ₀ or more, the opening of the opening and closing valve 51, resonance tube 40a, because 40b length L ', and the resonance rotation speed N _R2 is set, than the resonance rotational speed N _R1 Even on the high speed side, the intake pulsation is amplified by the resonance action, and no phase delay occurs. The peak of the intake pulsation occurs in the middle of the intake stroke, but the EGR rate is maximized by the amplification of the intake pulsation (see FIGS. 12 and 13).

  In addition to means for preventing the backflow of the exhaust pulse and the exhaust ejector effect associated therewith, the means for controlling the amplification of the intake pulsation and the phase of the intake pulsation, and the means for changing the resonance rotational speed of the intake system, In the low speed range to the high speed range, the instantaneous differential pressure before and after the check valve 39 can be effectively increased. In addition, since the control characteristics of the EGR valve 38 (see FIG. 4) work together with the control characteristics of the variable nozzle turbocharger 6 (see FIG. 3), high supercharging and large amount of EGR are possible even in the low speed and high load range. It can greatly promote exhaust measures (reduction of NOx and PM) and improvement of output and fuel consumption.

  10 and 11 show a low speed range (open / close valve is closed), and FIGS. 12 and 13 show a medium speed range (open / close valve is closed) to a high speed range (open / close valve is open), FIG. , FIG. 15 exemplifies a simulation result in a high speed range (the on-off valve is in a closed state).

  In the EGR passages 36a and 36b, since the EGR valve 38 and the check valve 39 (reed valve) are arranged on the downstream side of the EGR cooler 37, the durability of these valves 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. 17, 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.

Regarding the control characteristics of the on-off valve 51, it may be possible to set the engine load and the engine speed as parameters as shown in FIG. In that case, in the high load region, the EGR rate is improved as indicated by line A in FIG. 9 by turning on and off the switching valve 51. In a low load to a medium load, the EGR rate is improved as indicated by line B in FIG. 8 and 9, the C line and the D line illustrate the change in the EGR rate when the resonance speed N _R1 is fixed, and the E line and the F line illustrate the change in the EGR rate when the resonance speed N _R2 is fixed.

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. It is a characteristic view explaining the control content of a turbine nozzle. It is a characteristic figure explaining the control contents of an EGR valve. It is a characteristic view explaining the control content of an on-off valve. It is a flowchart explaining the control content of a control unit. It is a characteristic view explaining the control content of an on-off valve. It is an EGR characteristic view of a low load region to a medium load region related to control of the on-off valve. FIG. 6 is an EGR characteristic diagram in a high load range related to control of the on-off valve. It is a characteristic view which illustrates the simulation result of the intake-exhaust pulsation of a low speed area. It is a characteristic diagram which illustrates the simulation result of the EGR flow rate in a low speed region. It is a characteristic view which illustrates the simulation result of the intake-exhaust pulsation of a medium-high speed range. It is a characteristic view which illustrates the simulation result of the EGR flow rate in the middle and high speed range. It is a characteristic diagram which illustrates the simulation result of the intake-exhaust pulsation of a high speed region. It is a characteristic diagram which illustrates the simulation result of the EGR flow rate in a high speed region. It is the block diagram which similarly concerns on the confluence | merging part of an exhaust manifold. It is the block diagram which similarly 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)
40a, 40b Resonance pipe 41 Branch point of intake pipe 42 Connection portion between EGR passage and resonance pipe 50 Passage connecting resonance pipes 51 Open / close valve 55 Control unit 56 Engine rotation sensor 57 Engine load sensor

Claims (8)

  In a multi-cylinder engine equipped with a turbocharger, 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 a joining portion of these exhaust manifolds A means for preventing the exhaust pulse from flowing backward, a resonance pipe connecting the branch portion of the intake passage and the collection portion of each intake manifold as means for controlling the amplification of the intake pulsation and the phase of the intake pulsation, and these resonances A multi-cylinder engine comprising an EGR passage that connects a pipe and an exhaust manifold in the same cylinder group relationship, and means for varying a resonance rotational speed of an intake system. The multi-cylinder engine according to claim 1, wherein the length L of each resonance tube is set so as to satisfy the following conditions.

The multi-cylinder engine according to claim 2, wherein the resonance rotational speed N _R1 is set in an operation region where the compressor outlet pressure is higher than the turbine inlet pressure. Means for the resonance rotational speed of the intake system is variable, each of the connection portions upstream of the EGR passage to switch the resonance rotational speed N _R1 with respect to the length L of the resonance tube resonance rotational speed N _R2 or vice versa fast side The multi-cylinder engine according to claim 2, further comprising: a valve that opens and closes a passage that connects the resonance tubes of a portion having a length L 'corresponding to the resonance rotational speed N _R2 .   5. The multi-cylinder engine according to claim 4, wherein the means for changing the resonance rotational speed of the intake system includes means for controlling the open / close valve based on an operating state.   2. A means for preventing a backflow of exhaust pulses from flowing into the merged portion of the exhaust manifold, further comprising a nozzle portion that narrows the downstream of the collective portion of each exhaust manifold toward the merged portion. The multi-cylinder engine described in 1.   The multi-cylinder according to claim 1, wherein a variable nozzle type is used as a turbocharger and a compressor is interposed upstream of a branch portion of the intake passage, while a turbine of the turbocharger is connected to a merging portion of an exhaust manifold. engine.   2. The multi-cylinder engine according to claim 1, wherein each EGR passage includes an EGR valve upstream of the check valve and an EGR cooler upstream thereof.

Images