JP4741379B2 - Multi-cylinder engine - Google Patents

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, a system 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. 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), exhaust pulses (positive pressure waves) between cylinder groups having different phases are used. Mountains) cancel each other, so 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 passages that connect the same cylinder group between the exhaust manifold and the intake manifold, means for preventing exhaust from flowing back between the exhaust manifolds, and a check arranged at the most downstream part of each EGR passage Each EGR passage is provided with an EGR cooler upstream of the check valve, and the timing at which the peak of exhaust pulsation in the exhaust manifold reaches the check valve In order to approach the timing at which the valley reaches the check valve, a passage portion including the passage length of the section between the check valve upstream of the check valve and the EGR cooler is connected to the downstream side of the check valve. Characterized in that set to be longer than the portion.

In the multi-cylinder engine according to the first aspect of the present invention, the multi-cylinder engine according to the first aspect of the present invention has a tapered shape with the downstream portion of the exhaust manifold as a means for preventing the exhaust gas from flowing backward between the exhaust manifolds toward the junction. It is characterized by having a nozzle part for narrowing down .

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

According to a fourth invention, in the multi-cylinder engine according to the first invention, there is provided means for amplifying the intake negative pressure .

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

A sixth invention is characterized in that, in the multi-cylinder engine according to the fourth invention , a throttle valve is arranged for each intake manifold as means for amplifying the intake negative pressure.

According to a seventh aspect of the invention, in the multi-cylinder engine according to the fourth aspect of the invention , as a 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 check valve is arranged at the most downstream part of the EGR passage and is downstream of the check valve. Since the EGR passage on the side is short and the EGR passage on the upstream side is long, the timing at which the exhaust pulse reaches 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 this case , the EGR gas (exhaust gas) is cooled by the EGR cooler upstream of the check valve, and the propagation speed of the pressure wave becomes slow, so that it is possible to gain time until the exhaust pulse reaches the check valve. The EGR cooler is preferably arranged as upstream as possible in the EGR passage in order to take a long section with the check valve (passage length in which the temperature of the EGR gas is low).

In the second 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 be improved.

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

In the fifth 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 sixth invention , the venturi accelerates the flow of intake air, increases the dynamic pressure, and decreases 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 seventh 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 is increased and the static pressure is lowered by the flow velocity of the blow-down flow (ejection exhaust 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 (extrusion) 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 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. The exhaust manifolds 9a and 9b 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 increases, and the static pressure decreases. 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 part (near the outlet part) 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. 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. The EGR cooler 37 is preferably arranged on the upstream side of the EGR passages 36a and 36b as much as possible in order to increase the section with the check valve 39 (passage length with low EGR gas temperature).

  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, disposed in an intermediate portion between the EGR cooler 37 and the EGR valve 38 in FIG. 1) 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 arranged at the most downstream portion of the EGR passages 36a and 36b. 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. The arrival timing A can be made closer 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 rates in the case of E and G, where 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, even in the single entry type turbocharger 6, the backflow of the exhaust is suppressed, and the exhaust pulse to the turbine 6 b is strengthened by the ejector action of the merging portion 11, so that 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, the EGR passage portion on the downstream side of the check valve 39 is short without changing the overall length of the EGR passages 36a and 36b. Since the passage portion becomes longer, the timing at which the exhaust pulse reaches the check valve 39 can be delayed. That is, the timing at which the exhaust pulse reaches the check valve 39 is brought closer to the timing 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).

  Since the turbocharger 6 is a variable nozzle type, by adding variable nozzle control, high supercharging and large amount of EGR are possible in a wide operating range, reducing NOx and PM (Particulate Matter) and improving output and fuel consumption. It is possible to achieve a high level of compatibility. In the EGR passages 36a and 36b, the EGR cooler 37 has a large section (passage length where the temperature of the EGR gas is low) with the check valve 39. Can earn time until it reaches the check valve 39. 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 6b can be maintained well. Further, since an action similar to that of the nozzle portions 23a and 23b and the diffuser portion 29 occurs inside the turbine, the exhaust pulse is transmitted to the check valves 39 in the EGR passages 36a and 36b without being weakened, and the check valves 39 are effectively used. High EGR rate is obtained because it is operated.

  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 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.

  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 section 25 Turbine housing 29 Throat diffuser section 35 EGR device 37 EGR cooler 38 EGR valve 39 Check valve (reed valve)
40a, 40b Venturi 41a, 41b Throttle valve 42a, 42b Resonance tube

Claims (7)

In a multi-cylinder engine that performs supercharging, an exhaust manifold that is divided for each cylinder group in which the exhaust strokes do not overlap, an intake manifold that is divided for each cylinder group in which the intake strokes do not overlap, and these exhaust manifolds and intake manifolds An EGR passage that connects the same cylinder group to each other, a means for preventing exhaust from flowing back between the exhaust manifolds, and a check valve disposed at the most downstream portion of each EGR passage,
In each EGR passage, an EGR cooler is arranged upstream of the check valve, and when the exhaust pulsation peak in the exhaust manifold reaches the check valve, the intake pulsation valley in the intake manifold becomes the check valve. In order to approach the arrival timing, the passage portion including the passage length of the section between the check valve upstream of the check valve and the EGR cooler is set longer than the passage portion downstream of the check valve. This is a multi-cylinder engine.   The means for preventing exhaust gas from flowing back between the exhaust manifolds is provided with a nozzle portion that narrows the downstream of the collection portion of each exhaust manifold toward the merge portion. Multi-cylinder engine. The multi-cylinder engine according to claim 1 , further comprising a twin-entry turbocharger as means for preventing the exhaust gas from flowing backward between the exhaust manifolds.   The multi-cylinder engine according to claim 1, further comprising means for amplifying the intake negative pressure.   The multi-cylinder engine according to claim 4, wherein a venturi is arranged for each intake manifold as means for amplifying the intake negative pressure.   The multi-cylinder engine according to claim 4, wherein a throttle valve is arranged for each intake manifold as means for amplifying the intake negative pressure.   The multi-cylinder engine according to claim 4, further comprising: a resonance pipe that connects a branch portion of the intake pipe and each intake manifold as means for amplifying the intake negative pressure.