JP4799435B2 - Multi-cylinder engine - Google Patents

Description

  The present invention relates to a technology for realizing exhaust countermeasures (NOx reduction, etc.) 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 gas from the exhaust system to the intake system is often used.

  In Patent Document 1, an exhaust manifold divided for each cylinder group whose exhaust strokes do not overlap, an intake manifold divided for each cylinder group whose intake strokes do not overlap, and an exhaust manifold and a corresponding intake manifold EGR passage that connects the EGR passage, EGR valve that opens and closes the EGR passage, a check valve disposed on the exhaust manifold side of the EGR passage, and an intake resonance pipe that is set between the branch portion of the intake pipe and the intake manifold Is disclosed.

In the case of Patent Document 1, interference between the exhaust pulsation and the intake pulsation is avoided by the check valve (reed valve) in the EGR passage, and the intake pulsation is increased by the intake resonance pipe, thereby improving the EGR rate. In order to widen the inertial supercharging region by the intake resonance pipe, in Patent Document 2, the air column frequency of the intake resonance pipe can be changed by arranging a plurality of on-off valves between the intake resonance pipes.
Japanese Utility Model Sho 63-060066 No. 02-041309

  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. Although the check valve of the EGR passage avoids interference between exhaust pulsation and intake pulsation, when the turbocharger is a single entry system (one turbine inlet), exhaust (extrusion) is performed from the exhaust manifold on the cylinder side during exhaust injection. ) Exhaust pulses (positive pressure waves) easily escape to the exhaust manifold during the stroke, and exhaust pulsation cannot be fully used to improve the EGR rate. Also, when the load suddenly increases or accelerates, due to the inertia of the turbocharger or the volume of the intake / exhaust system, the turbocharger's rotation rise may be delayed, and the supercharging pressure may be insufficient. May increase PM.

  An object of the present invention is to realize a high supercharging and a large amount of EGR in a wide operating region so as to promote exhaust countermeasures and improvement of output and fuel consumption in consideration of such problems to be solved.

In a first aspect of the present invention, in a multi-cylinder engine including a turbocharger, an exhaust manifold divided for each cylinder group in which exhaust strokes do not overlap, and a downstream portion of each exhaust manifold is narrowed to a tapered shape toward a turbine inlet of the turbocharger. exhaust ejector, an intake manifold at which the intake stroke is divided for each cylinder group do not overlap, the intake resonance tube set between the intercooler downstream of the branch portion of the intake pipe and the intake manifold, the exhaust manifold and the intake manifold between the EGR passage connecting the relationship between the same cylinder group, an EGR valve disposed in the EGR passage, a check valve disposed in the EGR valve downstream of the EGR passage, during or load surge during acceleration of the engine and comprising means for temporarily closing controlled to the EGR valve, the.

Then, the intake resonance tube is, in the present invention is set to satisfy the conditions described in Equation 1, the resonance rotational speed N is the operating region where the compressor outlet pressure of the turbine inlet pressure of the turbocharger is higher It is characterized by being set to.

The second invention is the multi-cylinder engine according to the first invention, the EGR valve is characterized in that disposed as close as possible to the inlet side of the EGR passage.

According to a third aspect of the present invention, in the multi-cylinder engine according to the first or second aspect, the EGR passage includes an EGR cooler disposed between the EGR valve and the check valve. To do.

  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 (positive pressure wave) is prevented from escaping from the manifold to the exhaust manifold on the cylinder side during the exhaust (push-out) stroke, improving turbine efficiency and reducing the exhaust pulse to the check valve in the EGR passage. High EGR rate is obtained because the check valve is effectively operated without being transmitted. 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 intake pulsation are controlled by the intake resonance pipe, the instantaneous differential pressure before and after the check valve is expanded, and the EGR rate 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.

  As a result, during normal operation, high supercharging and large amount of EGR are possible while suppressing pumping loss. When shifting to a sudden increase in load or acceleration, the EGR valve closes, so the intake pulsation is not attenuated, and a sufficient amount of intake air is secured to each cylinder by resonant supercharging. The amount of (particulate matter) generated can be suppressed.

In this case , the resonance rotational speed N is proportional to (f / m), the resonance frequency f is proportional to [A / {L (Vi + Ve)}] ^1/2 , and the resonance frequency f is the same. In this case, the length L of the intake resonance pipe or the volume Vi of the intake manifold can be set smaller by the volume Ve downstream of the EGR valve in the EGR passage. That is, it is possible to design the dimensions of the intake system compactly.

Further, the resonance supercharging increases the EGR rate to the maximum in the operation region where the compressor outlet pressure is higher than the turbine inlet pressure. 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 second invention , the volume Ve downstream of the EGR valve in the EGR passage can be increased by bringing the EGR valve as close as possible to the inlet (exhaust manifold) side of the EGR passage. In addition, by bringing the EGR valve as close as possible to the inlet side of the EGR passage, the volume of the exhaust system (dead space) at the time of sudden load increase (including acceleration) can be minimized, and the turbocharger The effect of improving responsiveness can also be expected .

In the third invention , the EGR cooler increases the density of the EGR gas and can increase the substantial EGR amount.

  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 9a and 9b and an exhaust pipe 20. 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 20 is connected via the 6 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 (# 1, 2, 3, # 4, 5, 6). As the turbocharger 6, a variable nozzle type having one turbine inlet is employed. 12 is a muffler.

  As shown in FIG. 2, the exhaust manifolds 9 a and 9 b are gathered together at one flange 21 at the downstream of the gathering portion, and the joining portion 11 is opened at the joint surface. The downstream portion of the gathering portion gathered at one flange 21 is formed in tapered exhaust ejectors 23 a and 23 b that narrow the passage toward the joining portion 11. A turbine housing 25 is formed with a flange 26 corresponding to the flange 21 of the exhaust manifolds 9 a and 9 b, 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 21 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 the downstream side of the intercooler 5 of the intake manifold 4 and the intake pipe 4 EGR passages 36a and 36b are provided to connect the branch portions 40a and 40b to the same cylinder group.

  In the EGR passages 36a and 36b, an EGR cooler 37 that cools the EGR gas, an EGR valve 38 that adjusts the EGR flow rate, and a check valve 39 (reed valve) that regulates the backflow of the EGR gas are interposed. The check valve 39 is disposed downstream of the EGR passages 36a and 36b, and an EGR cooler 37 is interposed upstream thereof. The EGR valve 37 is disposed upstream of the EGR cooler 27 (as close as possible to the inlets of the EGR passages 36a and 36b). In this case, 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, thereby effectively promoting the improvement of the EGR rate. It can be.

  In the branch passages 40a and 40b of the intake pipe 4, the intake resonance pipe (the intake pulsation of the intake manifolds 3a and 3b) is connected between the connection part 42 (exit) of the EGR passages 36a and 36b and the branch part 41 (branch point) upstream thereof. The means for controlling the amplitude and the phase) are set.

  The intake resonance tubes 40a and 40b are set so as to satisfy the following conditions.

The resonance rotational speed N is proportional to (f / m), the resonance frequency f is proportional to [A / {L (Vi + Ve)}] ^1/2 , and the resonance frequency f is the same as the EGR. The length L of the intake resonance pipes 40a and 40b or the volume Vi of the intake manifolds 3a and 3b can be set small by the volume Ve downstream of the EGR valve 38 in the passages 36a and 36b. That is, it is possible to design the dimensions of the intake system compactly by the volume Ve downstream of the EGR valve 38 in the EGR passages 36a and 36b.

  The resonance rotational speed N is set in an operation region where EGR is difficult (the turbocharger efficiency is at and near the maximum, and the compressor outlet pressure is higher than the turbine inlet pressure). 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.

  In FIG. 1, 50 is a control unit for controlling an actuator (not shown) of a variable nozzle mechanism (not shown) of the turbine 6b and an EGR valve 38 of the EGR passages 36a and 36b. As the detection means, an engine rotation sensor 51 that detects the engine speed from the flywheel rotation and an engine load sensor 52 that detects the engine load from the accelerator opening (the pedal operation amount) are provided.

  FIG. 3 is a flowchart for explaining the control contents of the control unit 50, and is repeated every predetermined control cycle. In S1 and S2, the detected value of engine speed N and the detected value of engine load L are read.

  In S3 to S6, the variable nozzle mechanism and the EGR valve 38 are sequentially controlled based on these detected values. In S3, the variable nozzle mechanism is controlled to the turbine nozzle opening obtained from the map data as shown in FIG. In S4, it is determined whether or not the engine has a sudden load increase (including acceleration). When the determination of S4 is no (during steady operation), the EGR valve 38 is controlled to the valve opening obtained from the map data as shown in FIG. 5, while when the determination of S4 is yes (when the load suddenly increases), Regardless of the engine speed N and the engine load L, the EGR valve 38 is controlled to be fully closed.

  With this configuration, even in the single-entry turbocharger 6, the backflow of exhaust pulses (positive pressure waves) can be suppressed by the tapered exhaust ejectors 23a and 23b, 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. Further, because of the ejector effect, the exhaust manifold pressure on the cylinder side during the exhaust (push-out) stroke is reduced, so that the pumping loss can be improved.

  In the intake system, the amplitude and phase of intake pulsation are controlled by the intake resonance tubes 40a and 40b. 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 shifts from the middle of the intake stroke to the first half, but the intake pulsation is amplified, so the instantaneous differential pressure before and after the check valve is expanded. 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.

  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 pulsation, so the difference between the intake pressure and the exhaust pressure exceeding this is expanded, and the EGR rate is sufficient (See FIGS. 6 and 7). On the higher speed side than the resonance rotational speed N, the phase of the intake pulsation is delayed, and an intake pulsation valley occurs in the latter half of the intake stroke, so the EGR rate slightly decreases. 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, during normal operation (see FIGS. 6 and 7), high supercharging and large amount of EGR are possible while suppressing pumping loss. In addition, by controlling the turbine nozzle opening and the EGR valve opening, it is possible to achieve high supercharging and large amount of EGR while suppressing the pumping loss even in the high load high rotation range.

  When transitioning to transient operation, when the load suddenly increases (including acceleration), the EGR valve 38 closes, so the intake and exhaust pulsations do not cancel each other, and the intake pulsation may increase due to resonance supercharging. A sufficient amount of intake air is supplied to each cylinder (# 1 to # 6) (see FIGS. 8 to 10). Therefore, in the case of a diesel engine, the generation amount of PM (particulate matter) can be suppressed.

  As for the intake resonance tubes 40a and 40b, when the resonance frequency f is the same, the volume Ve of the EGR passages 36a and 36b downstream of the EGR valve 38, the length L of the intake resonance tubes 40a and 40b, or the volumes of the intake manifolds 3a and 3b. Vi can be set small. In other words, by bringing the EGR valve 38 as close as possible to the inlet (exhaust manifold) side of the EGR passages 36a, 36b, the volume Ve downstream of the EGR valve 38 in the EGR passages 36a, 36b can be increased, and the dimensions of the intake system can be efficiently reduced. It becomes possible to design compactly. Further, by bringing the EGR valve 38 as close as possible to the inlet side of the EGR passages 36a, 36b, the exhaust system volume (dead space) is minimized when the EGR valve 38 is fully closed at the time of engine acceleration or sudden load increase. An effect of increasing the transient response of the turbocharger 6 can be expected.

  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 21 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, but as shown in FIG. 11, the flanges 21 of the exhaust manifolds 9a and 9b and the flanges 26 of the turbine housing 25 are provided as separate spacers. You may interpose between.

  As for the turbocharger 6, it is conceivable to use a twin entry system (two turbine inlets) instead of the single entry system. In the case of the twin entry method, since the passage from the two turbine inlets to the scroll is partitioned inside the turbine housing, the exhaust ejectors 23a and 23b in FIG. 1 can be omitted.

It is a whole schematic block diagram. It is a block diagram which concerns on the confluence | merging part of an exhaust manifold. It is a flowchart explaining the control content of a control unit. It is map data which illustrates the control characteristic of a variable nozzle mechanism. It is map data which illustrates the control characteristic of an EGR valve. FIG. 5 is a characteristic diagram of intake and exhaust pulsation during steady operation. It is a characteristic view of the EGR flow rate at the time of steady operation. FIG. 6 is a characteristic diagram of intake pulsation and in-cylinder pressure at the time of sudden increase in load. It is a characteristic view of the intake flow rate at the time of sudden increase in load. FIG. 6 is a characteristic diagram of in-cylinder pressure vs. in-cylinder volume when the load suddenly increases. 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)
3a, 3b Intake manifold 5 Intercooler 6 Turbocharger (variable nozzle type turbocharger)
6a Compressor 6b Turbine 8 Exhaust passage 9a, 9b Exhaust manifold 10 Intake passage 23a, 23b Tapered exhaust ejector 25 Turbine housing 29 Throat-shaped diffuser 35 EGR device 36a, 36b EGR passage 37 EGR cooler 38 EGR valve 39 Check valve (Reed valve)
40a, 40b Intake resonance pipe 41 Intake pipe branch point 50 Control unit

Claims (3)

In a multi-cylinder engine equipped with a turbocharger,
An exhaust manifold that is divided into cylinder groups whose exhaust strokes do not overlap,
Exhaust ejector throttling the downstream portion in a shape tapered toward the turbine inlet of the turbocharger of the exhaust manifold, an intake manifold at which the intake stroke is divided for each cylinder group do not overlap, the intercooler downstream of the intake manifold and the intake pipe branch intake resonance tube set between the parts, an EGR passage that connects to the relationship between the same cylinder group between the exhaust manifold and the intake manifold, EGR valve disposed in the EGR passage, the EGR passage A check valve disposed downstream of the EGR valve, and means for temporarily closing the EGR valve when the engine accelerates or when the load suddenly increases.
The intake resonance pipe is set so as to satisfy the following conditions, and the resonance rotational speed N is set in an operation region where the compressor outlet pressure is higher than the turbine inlet pressure of the turbocharger. A featured multi-cylinder engine.
Record

The multi-cylinder engine according to claim 1, wherein the EGR valve is disposed as close as possible to an inlet side of the EGR passage . The multi-cylinder engine according to claim 1 or 2, wherein the EGR passage includes an EGR cooler disposed between an EGR valve and a check valve .

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