JP2007263017A - Multiple cylinder engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize high charging/great quantity EGR in a wide operation range to accelerate reduction of NOx and improvement of output/fuel economy in a multiple cylinder engine provided with a turbocharger. <P>SOLUTION: This engine is provided with exhaust manifolds 9a, 9b divided to each group of cylinders in which exhaust strokes do not overlap, exhaust ejectors 23a, 23b narrowing a downstream part of a collection part of each exhaust manifold in a tapered shape toward a turbine inlet of a turbo charger 6, intake manifolds 3a, 3b divided to each group of cylinders in which intake strokes do not overlap, intake resonance pipes 40a, 40b established between the collection part of each manifold and a branch part of an intake pipe, EGR passages 36a, 36b connecting a downstream end part of the intake resonance pipe and the collection part of the exhaust manifold, and a check valve 39 installed in the EGR passage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for reducing NOx and improving output and fuel consumption in a multi-cylinder engine equipped with a turbocharger.

As an engine EGR (Exhaust Gas Recirculation) system, a system that circulates part of the exhaust from the exhaust system to the intake system 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. Therefore, a method of performing EGR using exhaust pulsation (exhaust pulse) with a reed valve (check valve) (Patent Document 1, Patent Document 4), and using a mixing section to increase the static pressure in the subsequent EGR passage (Patent Document 2), and a system (Patent Document 3) using an internal EGR (opening an exhaust valve to allow a part of exhaust gas to flow into a cylinder in an intake stroke) is known.
JP 2000-249004 JP 2003-534488 A JP 2001-107810 A Japanese Utility Model Sho 63-060066

  In the case of Patent Document 1 and Patent Document 2, when the turbocharger connected to the split-type exhaust manifold is of a single entry system (one turbine inlet), the exhaust (push-out) stroke is performed from the exhaust manifold on the cylinder side during exhaust ejection. The exhaust pulse (exhaust pulsation) easily escapes to the exhaust manifold inside, and the exhaust pulse cannot be fully used to improve the EGR rate. In the case of Patent Document 3, the exhaust (EGR gas) cannot be cooled. In Patent Document 4, an intake resonance pipe is provided, and intake throttling is performed to increase the EGR amount. Therefore, deterioration of pumping loss becomes a problem.

  In order to solve such problems, the present invention achieves high supercharging and mass EGR in a wide operating range in a multi-cylinder engine equipped with a turbocharger in order to promote NOx reduction and output / fuel efficiency improvement. The purpose of this is to provide a means.

  In a first aspect of the present invention, in a multi-cylinder engine having a turbocharger, an exhaust manifold divided for each cylinder group in which the exhaust strokes do not overlap, and a downstream portion of each exhaust manifold is tapered toward a turbine inlet of the turbocharger. The exhaust ejector to be throttled, the intake manifold divided for each cylinder group in which the intake strokes do not overlap, the intake resonance pipe set between the collection part of each intake manifold and the branch part of the intake pipe, the downstream end of the intake resonance pipe And an EGR passage that connects between the exhaust manifold and a collecting portion of the exhaust manifold, and a check valve interposed in the EGR passage.

  According to a second aspect of the present invention, in the multi-cylinder engine according to the first aspect, the length L of each intake resonance pipe is set so as to satisfy the following condition. engine.

  According to a third aspect of the invention, in the multi-cylinder engine according to the second aspect of the invention, the resonance rotational speed N is set in an operating region where 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 first aspect of the invention, the EGR passage is connected between the collecting portion of the exhaust manifold and the downstream end portion of the resonance pipe in the same relationship between the cylinder groups. And

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

  In the first aspect of the invention, even when the turbocharger is of a single entry system (one turbine inlet), the exhaust flow is accelerated by the exhaust ejector and the dynamic pressure is increased. The exhaust pulse is prevented from escaping from the manifold to the exhaust manifold on the cylinder side during the exhaust (push-out) stroke, and not only the turbine efficiency is improved, but also the exhaust pulse is transmitted to the check valve in the EGR passage without being weakened. In order to operate the check valve effectively, a high EGR rate can be obtained. Further, when the dynamic pressure increases, the static pressure decreases, so that the exhaust is sucked from the cylinder side exhaust manifold during the exhaust (pushing) stroke, and the pumping loss is reduced.

  In the intake system, the amplitude and phase of the intake pulsation are controlled by the intake resonance pipe, and the instantaneous differential pressure before and after the check valve (the difference between the intake pressure and the exhaust pressure exceeding this) is expanded, and the EGR rate is increased. This can be further improved. When the engine rotation speed becomes equal to the resonance rotation speed (the natural frequency of the intake system), the intake pulsation is resonated and amplified, increasing the instantaneous differential pressure before and after the check valve. 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, so the instantaneous differential pressure before and after the check valve increases. On the higher speed side than the resonance rotational speed, the phase of the intake pulsation is delayed, and an intake pulsation valley occurs in the latter half of the intake stroke, so the instantaneous differential pressure before and after the check valve is slightly reduced, but the first half of the intake stroke As a result, a peak of the intake pulsation is generated, so that the pumping loss is reduced. The amplitude of the intake pulsation is larger on the downstream side than on the upstream side of the intake resonance pipe, and the EGR passage is connected to the downstream end of the intake resonance pipe (immediately upstream of the intake manifold assembly). The instantaneous differential pressure can be sufficiently expanded.

In the second invention, the length L of the resonance tube is set on condition that the resonance rotational speed N is within the operating rotational speed range of the engine. The resonance rotation speed N is proportional to (f / m), the resonance frequency f is proportional to (A / LV) ^1/2 , and when L is set large, the resonance rotation speed N is low. On the other hand, when L is set small, the resonance rotational speed N becomes the high speed side. Therefore, the length L of the resonance tube is desirably set so that the resonance rotational speed N 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 is maximized 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 in the medium speed range including the engine maximum torque point.

  In the fourth invention, since the EGR passages 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 effectively improved. Can promote.

  In the fifth 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 addition, by obtaining the time until the exhaust pulse reaches the check valve, the timing of the valley of the intake pulsation and the peak of the exhaust pulsation upstream of the check valve can be matched.

  In FIG. 1, reference numeral 10 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 engine exhaust passage, which 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 is employed. 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 portion of the gathering portion gathered at one flange 20 is formed in tapered exhaust ejectors 23 a and 23 b that narrow the passage toward the joining portion 11. 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 exhaust ejectors 23 a and 23 b and then gradually expands.

  In the merging portion 11, the exhaust flow is accelerated by the tapered exhaust ejectors 23 a and 23 b, and the dynamic pressure rises. Therefore, the cylinder in the exhaust (push-out) stroke from the exhaust manifold 9 a or 9 b on the cylinder side that is exhausting the exhaust. The exhaust is prevented from escaping to the side exhaust manifold 9b or 9a. When the dynamic pressure increases by the tapered exhaust ejectors 23a and 23b, the static pressure decreases. Therefore, the exhaust is sucked into the diffuser portion 29 from the cylinder side exhaust manifold 9b or 9a during the exhaust (pushing) stroke. Thereafter, the dynamic pressure is efficiently converted into a static pressure by the diffuser unit 29, and the exhaust pressure to 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, and a collecting portion 40a of the intake manifolds 9a and 9b , 40b are provided with EGR passages 36a, 36b that connect 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 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 improvement of the EGR rate can be effectively promoted.

  In the branch passages 40a and 40b of the intake pipe 4, the space between the connection portion 42 (exit) of the EGR passages 36a and 36b and the upstream branch portion 41 (branch point) is the intake resonance pipe (intake pulsation of the intake manifolds 3a and 3b). (Means for controlling the amplitude and phase). The length L of the intake resonance tubes 40a and 40b is set so as to satisfy the following conditions.

The resonance rotation speed N is proportional to (f / m), the resonance frequency f is proportional to (A / LV) ^1/2 , and when L is set large, the resonance rotation speed N is low. On the other hand, when L is set small, the resonance rotational speed N becomes the high speed side. In this case, the resonance rotational speed N is in an operating region where the EGR is difficult due to the length L of the intake resonance pipe (the turbocharger efficiency is at and near the maximum, and the compressor outlet pressure is higher than the turbine inlet pressure). Is set. When the turbocharger efficiency becomes maximum at the engine maximum torque point, the resonance rotational speed N is set to a medium speed range including the engine maximum torque point.

  The EGR passages 36a and 36b are connected to the downstream ends of the intake resonance tubes 40a and 40b (immediately upstream of the gathered portions of the intake manifolds 3a and 3b). FIG. 3 illustrates the intake vibration mode. The amplitude of the intake pulsation is greater on the downstream side than on the upstream side of the intake resonance tubes 40a and 40b. When the EGR passages 36a and 36b are connected to the upstream side where the amplitude of the intake pulsation is small in the intake resonance pipes 40a and 40b, the difference between the intake pressure and the exhaust pressure exceeding this (the instantaneous differential pressure before and after the check valve 39) The EGR flow rate cannot be obtained sufficiently (see FIGS. 10 and 11). In this embodiment, since the EGR passages 36a and 36b are connected to the downstream end portion where the amplitude of the intake pulsation is large, the difference between the intake pressure and the exhaust pressure exceeding this is large, and the EGR flow rate can be sufficiently obtained ( (See FIGS. 4 to 11). In FIG. 3, the EGR passages 36a and 36b are connected to positions separated by L ′ from the inlets of the collecting portions of the intake manifolds 3a and 3b. L 'should be as small as possible.

  With such a configuration, even in the single entry type turbocharger 6, the backflow of exhaust pulses can be suppressed by the tapered exhaust ejectors 23 a and 23 b, so that the turbine efficiency can be improved. Further, 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. In addition, since the exhaust manifold pressure on the cylinder side during the exhaust (pushing) stroke is reduced by the ejector action of the merging portion 11, an improvement in pumping loss can be obtained.

  In the intake system, the amplitude and phase of intake pulsation are controlled by the intake resonance tubes 40a and 40b, the instantaneous differential pressure before and after the check valve 39 is expanded, and the EGR rate can be further improved.

  When the engine rotation speed becomes equal to the resonance rotation speed N, the intake pulsation is resonated and amplified. The valley of the intake pulsation occurs in the middle of the intake stroke. However, since the intake pulsation is amplified, the difference between the intake pressure and the exhaust pressure exceeding this is expanded (see FIG. 6). For this reason, the turbocharger efficiency is at and near the maximum, and the compressor outlet pressure (supercharging pressure) is higher than the turbine inlet pressure (exhaust pressure). Conventionally, the turbocharger efficiency is improved in the operation region where EGR is difficult. The resonance effect can maximize the EGR rate without reducing it (see FIG. 7).

  On the lower speed side than the resonance rotational speed N, the phase of the intake pulsation advances, and the valley of the intake pulsation approaches the peak of the exhaust pulse, so the difference between the intake pressure and the exhaust pressure exceeding this is expanded, and the EGR rate is sufficient (See FIGS. 4 and 5). On the higher speed side than the resonance rotational speed N, the phase of the intake pulsation is delayed, and the valley of the intake pulsation occurs in the latter half of the intake stroke, so the EGR rate slightly decreases (see FIGS. 8 and 9). On the high speed side, a peak of intake pulsation occurs in the first half of the intake stroke, so that the pumping loss is reduced.

  As a result, it is possible to achieve high supercharging and large-volume EGR while suppressing pumping loss in a wide operating range, which can greatly promote the reduction of NOx and the improvement of output and fuel consumption. Since the connecting portion 42 of the EGR passages 36a and 36b is set at the downstream end of the intake resonance tubes 40a and 40b, compared to the case where the EGR passages 36a and 36b are connected to the upstream side of the intake resonance tubes 40a and 40b, The difference between the intake pressure and the exhaust pressure exceeding this is large, and a sufficient EGR flow rate can be obtained. Further, if a means for changing the setting of the resonance rotational speed N (for example, means for changing the substantial length L of the intake resonance tubes 40a and 40b) is added, in the high speed range (see FIGS. 8 and 9). However, the resonance action causes a valley of the intake pulsation to occur in the middle of the intake stroke, so that the EGR rate can be sufficiently improved.

  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 exhaust ejectors 23a and 23b are not formed integrally with the exhaust manifolds 9a and 9b. As shown in FIG. 13, the flanges 20 of the exhaust manifolds 9a and 9b and the flange 26 of the turbine housing 25 are provided as separate spacers. You may interpose between.

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 explanatory drawing which concerns on an intake vibration mode. 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 speed range. It is a characteristic diagram which illustrates the simulation result of the EGR flow rate in the medium 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 a characteristic view which illustrates the simulation result of intake and exhaust pulsation as a comparative example. It is a characteristic view which illustrates the simulation result of an EGR flow rate as a comparative example. 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)
40a, 40b Resonant pipe 41 Branch point of intake pipe 42 EGR passage outlet (connecting portion)

Claims (5)

  In a multi-cylinder engine equipped with a turbocharger, an exhaust manifold divided for each cylinder group in which the exhaust strokes do not overlap, an exhaust ejector that narrows the downstream of the collection portion of each exhaust manifold toward the turbine inlet of the turbocharger, and an intake stroke Intake manifolds divided for each cylinder group that do not overlap, intake resonance pipes set between the collection parts of the intake manifolds and branch parts of the intake pipes, the downstream ends of the intake resonance pipes and the collection parts of the exhaust manifolds A multi-cylinder engine comprising: an EGR passage connecting between the two and a check valve interposed in the EGR passage. The multi-cylinder engine according to claim 1, wherein the length L of each intake resonance pipe is set so as to satisfy the following condition.

  The multi-cylinder engine according to claim 2, wherein the resonance rotational speed N is set in an operation region in which the compressor outlet pressure is higher than the turbine inlet pressure.   2. The multi-cylinder engine according to claim 1, wherein the EGR passage is connected between a collecting portion of the exhaust manifold and a downstream end portion of the resonance pipe in a relationship between the same cylinder groups.   The multi-cylinder engine according to claim 1, wherein the EGR passage includes an EGR valve upstream of the check valve and an EGR cooler upstream thereof.

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