JP2007198342A - Multicylinder engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a supercharged multicylinder engine having an efficient and sufficient flow amount of EGR and intake air while compatibly attaining the reduction of NOx and the improvement of an output and fuel economy. <P>SOLUTION: The multicylinder engine comprises exhaust manifolds 9a, 9b split in cylinder groups whose exhaust strokes are not overlapped with each other, intake manifolds 3a, 3b split in cylinder groups whose intake strokes are not overlapped with each other, EGR passages 36a, 36b provided between the exhaust manifolds 9a, 9b and the intake manifolds 3a, 3b for connecting the cylinder groups to each other, means 23a, 23b for preventing the back flow of exhaust gas between the exhaust manifolds 9a, 9b, and extension parts 50 set on upstream sides of check valves 39 in the EGR passages 36a, 36b to make timing for an exhaust pulse reaching the check valve 39 correspond to timing for an intake pulsation valley to reach the check valve 39. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for realizing both reduction of NOx and improvement of output and fuel consumption in a multi-cylinder engine that performs supercharging.

  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 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 (Patent Document 3), and a variable valve A method of performing internal EGR (Patent Document 4) is known.
JP 2000-249004 JP 2005-147010 A JP 2003-534488 A JP 2001-107810 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, EGR passage connecting the same cylinder group between the exhaust manifold and the intake manifold, means for preventing exhaust from flowing back between the exhaust manifold, and the timing at which the exhaust pulse reaches the check valve And an extension set upstream of the check valve in the EGR passage so as to coincide with the timing at which the valley reaches the check valve.

  According to a second aspect of the invention, in the multi-cylinder engine according to the first aspect of the invention, the check valve is disposed at the most downstream portion of the EGR passage.

  According to a third aspect of the present invention, in the multi-cylinder engine according to the first aspect, the extension portion is constituted by meandering piping.

  According to a fourth aspect of the invention, in the multi-cylinder engine according to the first aspect of the invention, the extension portion is configured by a spiral pipe.

  According to a fifth aspect of the invention, in the multi-cylinder engine according to the first aspect of the invention, the extension portion includes a cooling fin on the outer periphery of the pipe.

  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 has the 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.

  An eighth invention is characterized in that the multi-cylinder engine according to the first invention is provided with means for amplifying the intake negative pressure.

  According to a ninth invention, in the multi-cylinder engine according to the eighth invention, a venturi is arranged for each intake manifold as means for amplifying the intake negative pressure.

  According to a tenth aspect of the invention, in the multi-cylinder engine according to the eighth aspect of the invention, a throttle valve is disposed for each intake manifold as means for amplifying the intake negative pressure.

  According to an eleventh aspect of the invention, in the multi-cylinder engine according to the eighth aspect of the invention, as means for amplifying the intake negative pressure, a resonance pipe for connecting the branch portion of the intake pipe and each intake manifold is provided. And

  In the first aspect of the invention, even when the turbocharger is of a single entry system (one turbine inlet), the EGR passage is non-returned by means for preventing the exhaust from flowing back between the split type exhaust manifolds. The exhaust pulse (crest of positive pressure wave) is transmitted to the valve without being weakened, and the check valve is operated effectively, so a high EGR rate is obtained. In addition, 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 trough, but the EGR passage upstream of the check valve becomes longer due to the extension. The timing to reach the check valve can be delayed. 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. For this reason, since the instantaneous differential pressure before and after the check valve increases, the EGR rate can be further improved.

  In the second aspect of the invention, the check valve is arranged at the most downstream portion of the EGR passage, so that the extension portion can be shortened, and the valley of the intake pulsation becomes the check valve when the exhaust pulse reaches the check valve. It becomes easier to match the arrival timing.

  In the third aspect of the present invention, the extension portion is reduced in size and can be easily accommodated in a severely restricted layout around the engine.

  In the fourth invention, the extension portion can be downsized. Due to the spiral shape, the space utilization rate is low, and the overall size tends to be large compared to the case of meandering, but there is an advantage that the pressure loss is small.

  In the fifth aspect of the invention, the cooling fins provide good heat dissipation of the extension, and can be actively used as an air-cooled or water-cooled heat exchanger (for example, an EGR cooler).

  In the sixth aspect of the invention, the tapered nozzle accelerates the flow of exhaust, increases the dynamic pressure, and lowers the static pressure (exhaust pressure), so that the exhaust can be prevented 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. 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 well, and exhaust backflow can be suppressed. 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.

  In the eighth invention, since the instantaneous differential pressure before and after the check valve further increases due to the amplification of the intake negative pressure, the EGR rate can be further improved.

  In the ninth invention, the intake negative pressure (intake pulsation) is amplified by the intake throttle of the throttle valve, and the instantaneous differential pressure before and after the check valve can be increased.

  In the tenth invention, the venturi accelerates the flow of intake air, increases the dynamic pressure, and reduces the static pressure. That is, the intake negative pressure is amplified, and the instantaneous differential pressure before and after the check valve can be increased by the ejector action.

  In the eleventh aspect of the invention, the intake negative pressure is amplified by the resonance action of the resonance tube, and the instantaneous differential pressure before and after the check valve can be increased. In addition, since the inertia supercharging works, the intake flow rate can be obtained efficiently and sufficiently.

  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 23 a and 23 b, the dynamic pressure is increased, and the static pressure is lowered, so that the exhaust is prevented from flowing back between the exhaust manifolds 9 a and 9 b. In addition, if the dynamic pressure increases and the static pressure decreases due to the flow velocity of the blow-down flow (the exhaust gas discharged at the initial stage of the exhaust stroke) that blows out from the nozzle portion 23a or 23b, and the ejector action occurs, the cylinder side during the exhaust (push-out) stroke The exhaust is sucked into the diffuser portion 29 from the exhaust manifold 9b or 9a. Thereafter, the flow of 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. Venturis 40a and 40b are provided in the branch passages of the intake pipe 4, and EGR passages 36a and 36b are opened in the venturis 40a and 40b. By the venturis 40a and 40b, the flow of the intake air is accelerated, the dynamic pressure is increased, and the static pressure is decreased. That is, the intake negative pressure is amplified, and the check valve 39 is opened by the ejector action, so that the EGR gas is easily sucked into the intake manifolds 3a and 3b.

  The check valve 39 is disposed in the most downstream portion (near the outlet portion) of the EGR passages 36a and 36b, and the extension portion 50 is provided in the upstream EGR passage. As will be described later, the extension portion 50 is configured so that the check valve 39 of the EGR passages 36a and 36b matches the timing A when the exhaust pulse reaches the check valve 39 with the timing B when the valley of the intake pulsation reaches the check valve 39. It is set upstream, is constituted by a meandering pipe 50 a, and is arranged between the check valve 39 and the EGR valve 38 downstream of the EGR cooler 37. The EGR cooler 37 cools the EGR gas, slows the pressure propagation speed, and allows time for the exhaust pulse to reach the check valve 39. Therefore, the EGR cooler 37 is preferably arranged as upstream as possible in the EGR passages 36a and 36b in order to increase the section (the passage length where the temperature of the EGR gas is low) with the check valve 39.

  FIG. 3 is a characteristic diagram illustrating the simulation result of intake and exhaust pulsation, 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 the previous check. The exhaust pulsation immediately downstream of the valve (for example, in an EGR passage without an extension portion, disposed in the middle portion between the EGR cooler and the 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 at the most downstream portion of the EGR passages 36a and 36b, and an extension 50 is provided upstream thereof. As a result, the EGR passage portion on the downstream side of the check valve 39 is short and the upstream EGR passage portion is long, and the timing at which the exhaust pulse reaches the check valve 39 is delayed by that amount. The timing A at which the valve 39 is reached can be brought close to the timing B at which the valley of the intake pulsation reaches the check valve 39.

  FIG. 4 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 instantaneous differential pressure before and after the check valve is larger than that in the case of G, and K has a higher EGR rate than M.

  With such a configuration, in the turbocharger 6 of the single entry system (one turbine inlet), the backflow of exhaust (exhaust interference) is suppressed by the tapered nozzles 23a and 23b, and the ejector action of the merging portion 11 Since the exhaust pulse to the turbine 6a is strengthened, the turbine efficiency can be improved. Further, since the backflow of the exhaust gas is suppressed, the exhaust pulse is transmitted to the check valves 39 of 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. . 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 check valve 39 is disposed at the most downstream portion of the EGR passages 36a and 36b and the extension portion 50 is provided upstream thereof, the timing at which the exhaust pulse reaches the check valve 39 can be delayed. That is, the timing A at which the exhaust pulse reaches the check valve 39 is brought closer to the timing B at which the valley of the intake pulsation reaches the check valve 39 (see FIG. 3). 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. 4). In this case, by arranging the check valve 39 at the most downstream part of the EGR passages 36a and 36b, the extension 50 (pipe 50a) can be shortened, and the intake pulse pulsates the timing A when the exhaust pulse reaches the check valve 39. This makes it easier to match the timing B at which the valley reaches the check valve 39. The extension 50 can be downsized efficiently because the pipe 50a meanders.

  Since the turbocharger 6 is a variable nozzle type, by adding variable nozzle control, it is possible to achieve high supercharging and large-volume EGR in a wide operating range, and achieve a high degree of compatibility between NOx reduction and improved output and fuel efficiency. It can be done. In the EGR passages 36a and 36b, the EGR cooler 37 takes a large section (passage length where the temperature of the EGR gas is low) with the check valve 39. Therefore, when the EGR passage 37a is disposed at the most upstream portion of the EGR passages 36a and 36b, the exhaust pulse is generated. Time to reach the check valve 39 can be earned. Further, 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 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. 6, 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 gas from flowing backward 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 6a can be maintained well. In addition, although the ejector action unlike the nozzle portions 23a, 23b and the diffuser portion 29 does not occur, the exhaust pulse is transmitted to the check valves 39 of the EGR passages 36a, 36b without being weakened, and the check valves 39 are effectively operated. Therefore, a high EGR rate can be obtained.

  In the embodiment of FIG. 7, throttle valves 41a and 41b are arranged for each of the intake manifolds 3a and 3b instead of the venturis 40a and 40b. The outlet portions of the EGR passages 36a and 36b are connected to the collective portions of the intake manifolds 3a and 3b. The intake negative pressure (intake pulsation) is amplified by the intake throttles of the throttle valves 41a and 41b. The differential pressure is increased.

  In the EGR passages 36 a and 36 b, the extension 51 is constituted by a spiral pipe 51 a and is disposed between the check valve 39 and the EGR valve 38. Since the pipe 51a of the extension 51 is spiral, the space utilization rate is low, and compared to the meandering (extension 50 in FIG. 1), the overall size tends to be large, but EGR gas flows easily and pressure loss. This is advantageous.

  In the embodiment of FIG. 8, instead of the venturis 40a and 40b, resonance pipes 42a and 42b that connect the branch portion 43 of the intake pipe 4 and the intake manifolds 3a and 3b are arranged, and EGR is provided in the resonance pipes 42a and 42b. The outlet portions of the passages 36a and 36b are connected. In this case, the suction negative pressure is amplified by the resonance action of the resonance tubes 42a and 42b, and the instantaneous differential pressure before and after the check valve 39 can be increased. In addition, since the inertia supercharging works, the intake flow rate can be obtained efficiently and sufficiently. L is the length of the resonance tubes 42a and 42b.

  In the EGR passages 36 a and 36 b, the extension 52 is constituted by a meandering pipe 52 a and is arranged upstream of the EGR valve 38. In order to obtain good heat dissipation of the extension 52, a large number of cooling fins (not shown) are provided on the outer periphery of the pipe 52a (passage). Thereby, the extension part 52 can be actively used as an air-cooled or water-cooled heat exchanger. For this reason, in the case of illustration, the EGR cooler (37 in FIGS. 1 and 7) is omitted.

  7 and 8, the same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

1 is an overall schematic configuration diagram according to an embodiment of the present invention. It is the block diagram which similarly concerns on the confluence | merging part of an exhaust manifold. It is a characteristic view which similarly illustrates the relationship between intake / exhaust pulsation and the arrangement of check valves. It is a characteristic view which similarly illustrates the relationship between the EGR flow rate and the arrangement of check valves. 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. It is a whole schematic block diagram concerning another embodiment. It is a whole schematic block diagram concerning another embodiment.

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 Venturi 41a, 41b Throttle valve 42a, 42b Resonant tube 50, 51, 52 Extension 50a, 51a, 52a Extension piping

Claims (11)

  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 The EGR passage connecting the same cylinder group between each other, means for preventing the exhaust from flowing back between the exhaust manifold, and the intake pulsation trough check the timing when the exhaust pulse reaches the check valve A multi-cylinder engine comprising: an extension set upstream of the check valve in the EGR passage so as to match the timing of reaching the EGR passage.   The multi-cylinder engine according to claim 1, wherein the check valve is arranged at the most downstream portion of the EGR passage.   The multi-cylinder engine according to claim 1, wherein the extension portion is constituted by meandering piping.   The multi-cylinder engine according to claim 1, wherein the extension portion is constituted by a spiral pipe.   The multi-cylinder engine according to claim 1, wherein the extension portion includes a cooling fin on an outer periphery of the pipe.   2. The multi-cylinder according to claim 1, further comprising a nozzle portion that narrows a downstream portion of each exhaust manifold toward a joining portion as a means for preventing a backflow of exhaust gas between the exhaust manifolds. engine.   The multi-cylinder engine according to claim 1, further comprising a twin-entry turbocharger as a means for preventing the exhaust gas from flowing backward between the exhaust manifolds.   The multi-cylinder engine according to claim 1, further comprising means for amplifying the intake negative pressure.   The multi-cylinder engine according to claim 8, wherein a venturi is arranged for each intake manifold as means for amplifying the intake negative pressure.   The multi-cylinder engine according to claim 8, wherein a throttle valve is arranged for each intake manifold as means for amplifying the intake negative pressure.   9. The multi-cylinder engine according to claim 8, further comprising: a resonance pipe that connects between a branch portion of the intake pipe and each intake manifold as means for amplifying the intake negative pressure.

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