JP4827757B2 - Multi-cylinder engine - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a technique for realizing high supercharging and large amount of EGR in a wide operating range in order to promote exhaust countermeasures (NOx reduction, etc.) and improvement of 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 such an EGR system, when exhaust gas is circulated from the turbocharger 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 EGR cannot be performed sufficiently.

In the case of Patent Document 1, a check valve (reed valve) is interposed in the EGR passage. In the case of Patent Document 2, a cross-section airfoil hollow structure (EGR nozzle) is arranged downstream of the turbocharger compressor so as to cross the center of the intake passage, and intake air (air supply) is provided by the cross-section airfoil hollow structure. When the flow is divided and a negative pressure is generated downstream thereof, the EGR gas is sucked downstream from the outlet of the hollow structure. In the case of Patent Document 3, a venturi is formed downstream of the compressor of the turbocharger (in the middle of the intake passage), and an outlet portion (injection tube) of the EGR passage is coaxially disposed at the inlet portion thereof, so An annular path that increases the flow rate of the intake air (supply air) is formed between the section and the outlet of the EGR passage. Due to this annular path, the dynamic pressure of the intake air increases and the static pressure decreases, so that the EGR gas is sucked downstream from the outlet of the EGR passage.
JP 09-137754 A JP 2000-097111 A Special table 2003-507633

  In the conventional example such as Patent Document 1, interference between the exhaust pulsation and the intake pulsation can be avoided by the check valve of the EGR passage. However, when the turbocharger is of a single entry system (one turbine inlet), the exhaust jet The exhaust pulse (positive pressure wave) easily escapes from the exhaust manifold on the cylinder side to the exhaust manifold during the exhaust (push-out) stroke, and exhaust pulsation cannot be fully used to improve the EGR rate.

  In the conventional examples such as Patent Document 2 and Patent Document 3, since the intake throttle is effective and the EGR gas is sucked out by the hollow structure having a cross-sectional wing shape or the annular passage of the venturi inlet portion, the low pressure is low. If EGR is performed with an intake throttle in the middle load range, the EGR amount becomes excessive, which may lead to a shortage of intake air amount. The hollow structure (Patent Document 2) and the injection tube (Patent Document 3) can be converted between an operating state in which intake air is throttled and a retracted state in which the flow of intake air is not hindered. Is also complicated and expensive.

  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.

A first invention is a multi-cylinder engine equipped with a turbocharger , wherein an exhaust manifold divided for each cylinder group in which exhaust strokes do not overlap, and a tapered shape with a downstream portion of each exhaust manifold directed toward a turbine inlet of the turbocharger An exhaust system ejector that restricts the intake stroke and an intake manifold that is divided for each cylinder group in which the intake strokes do not overlap, and an EGR passage that connects between the turbine upstream of the turbocharger and the compressor downstream, and an intermediate portion of the intake passage And an intake system ejector for narrowing the outlet portion of the EGR passage toward the merging portion .

Then, the intake system ejector reduces the passage area in the middle of the intake passage toward the junction with the EGR passage, and the passage area of the exit portion of the EGR passage toward the junction with the intake passage. The EGR nozzle, and a throat-shaped diffuser that expands after reducing the passage area of the merged portion to the downstream side, and the EGR passage is disposed on the upstream side of the check valve disposed on the downstream side The EGR valve and the EGR cooler are provided.

The second invention is the multi-cylinder engine according to the first invention, the opening area facing the merging portion of the intake nozzle, the opening area facing the confluent portion of the EGR nozzle, the intake passage area immediately upstream each It is characterized by being set to about 1/4.

The third invention is the multi-cylinder engine according to the first or second aspect, the minimum passage area of the diffuser, the opening area facing the merging portion of the intake nozzle, facing the confluent portion of the EGR nozzle It is characterized by being set to be approximately the same as the sum of the opening area.

According to a fourth aspect of the present invention, in the multi-cylinder engine according to any one of the first to third aspects, the EGR passage is connected to the same cylinder group between the exhaust manifolds and the intake manifolds. It is characterized by connecting to the relationship .

  In the first to fifth aspects of the invention, even when the turbocharger is of a single entry system (one turbine inlet), the exhaust system ejector accelerates the exhaust flow and increases the dynamic pressure. The exhaust pulse (positive pressure wave) is prevented from escaping from the exhaust manifold on the cylinder side to the exhaust manifold on the cylinder side during the exhaust (push-out) stroke, which not only improves turbine efficiency but also reverses the EGR passage The exhaust pulse is transmitted to the valve without being weakened, and the check valve is operated effectively, so a high EGR rate is 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 operation region where the supercharging pressure is higher than the exhaust pressure, the intake system ejector increases the dynamic pressure of the intake air and decreases the static pressure at the merging portion, so that EGR gas is sucked. For this reason, the instantaneous differential pressure before and after the check valve is expanded, and the EGR rate is improved. In the operation region where the exhaust pressure is higher than the supercharging pressure, the intake system ejector raises the dynamic pressure of the EGR gas and lowers the static pressure, so that the intake air is sucked. That is, the intake system ejector assists the turbocharger supercharging work, and the effect of suppressing the decrease in the intake air amount accompanying the increase in the EGR rate can be obtained.

  As a result, high supercharging and large amount of EGR are possible in a wide range of operation, and it is possible to promote exhaust countermeasures and improvements in output and fuel consumption.

In the intake ejector , the dynamic pressure is efficiently converted into static pressure by the diffuser, and the intake manifold pressure can be increased.

In the second invention or the third invention , optimization of the ejector effect by the jet of intake air and the ejector effect by the jet of EGR gas can be obtained, and high supercharging and large volume can be achieved while suppressing the pumping loss in a wide operating range. EGR is possible.

In the fourth aspect of the invention, when the EGR passage connects each exhaust manifold and each intake manifold in the same cylinder group relationship, the exhaust pulsation peaks overlap the intake pulsation valleys . Further, when the EGR passage connects each exhaust manifold and each intake manifold in a relationship between different cylinder groups, exhaust pulsation peaks overlap at the end of the intake stroke .

  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.

  The junction 11 is configured as shown in FIG. The exhaust manifolds 9a and 9b are gathered together at one flange 21 on the downstream side of the gathering portion, and the joining portion 11 is opened at the joint surface. The downstream of the gathering portion gathered in one flange 21 is formed in tapered exhaust nozzles 23a and 23b (which constitute an exhaust system ejector 23 together with a diffuser 29 described later) for narrowing 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 29 is formed inside the turbine housing 25 that expands after the passage area of the merging portion 11 downstream of the exhaust nozzles 23a and 23b is reduced to the downstream side.

  In the merging portion 11, the exhaust nozzles 23a and 23b accelerate the exhaust flow and increase the dynamic pressure. Therefore, the exhaust on the cylinder side during the exhaust (push-out) stroke from the exhaust manifold 9a or 9b on the cylinder side during exhaust ejection is performed. Exhaust gas is prevented from escaping to the manifold 9b or 9a. In the exhaust system ejector 23, when the dynamic pressure increases by the tapered exhaust nozzles 23 a and 23 b, the static pressure decreases. Therefore, the exhaust gas is exhausted from the cylinder side exhaust manifold 9 b or 9 a during the exhaust (pushing) stroke to the diffuser 29. It is sucked. Thereafter, the dynamic pressure is efficiently converted into a static pressure by the diffuser 29, and the exhaust pressure to the scroll is increased.

  In FIG. 2, A is an opening area facing the merging portion 11 of the exhaust nozzles 23a and 23b, and is set to about 1/4 of the maximum opening area B of the exhaust valve 33 per cylinder (see FIG. 3). The maximum opening area B is B = n × π × D × L (n: number of exhaust valves 33 per cylinder D: substantial diameter of the exhaust valve 33 L: maximum lift of the exhaust stroke of the exhaust valve 33) Defined. In the case of FIG. 3, each cylinder is provided with two exhaust valves 33 (33a, 33b), so n is 2.

  When the opening area A facing the merging portion 11 of the exhaust nozzle portions 23a and 23b is larger than about ¼ of the maximum opening area B of the exhaust valve 33 per cylinder, in an operation region where the exhaust manifold pressure is relatively low, When the flow velocity of the exhaust gas ejected from the exhaust nozzles 23a and 23b tends to be insufficient and the NOx reduction effect is reduced, if the opening area A is smaller than about 1/4 of the maximum opening area B, the exhaust manifold pressure becomes relative. In a driving region that becomes higher in general, the pumping loss increases, and the fuel consumption deteriorates. By setting the opening area A of the exhaust nozzles 23a and 23b to about 1/4 of the maximum opening area B of the exhaust valve 33, an optimal EGR flow rate can be obtained while suppressing pumping loss.

  C is the minimum passage area of the diffuser, and is set to approximately the same (0.75 to 1.1 times) as the sum of the opening area A of the exhaust nozzle 23a and the opening area A of the exhaust nozzle 23b. In the case of 0.75 <C / (A + A) <1.1, the dynamic pressure of the exhaust gas ejected from the exhaust nozzles 23a and 23b is efficiently converted to a static pressure, and the ejector effect due to the exhaust jet can be maximized. Sufficient EGR flow can be secured while suppressing pumping loss. In the case of C / A <1.5, the exhaust pressure rises excessively due to the flow path resistance of the diffuser, so that the exhaust pulse easily flows backward. In the case of C / A> 2.2, the dynamic pressure of the exhaust gas ejected from the exhaust nozzles 23a and 23b is rapidly attenuated, the static pressure is not sufficiently lowered, and the exhaust pulse easily flows backward.

  In FIG. 1, reference numeral 35 denotes an EGR passage 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 branch passages 36a and 36b are connected to the exhaust manifolds 9a and 9b, respectively, and the combined passage 36c is connected to the EGR nozzle 40b (see FIG. 4) of the intake system ejector 40.

  In the branch paths 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 on the downstream side of the EGR passages 36a and 36b, and the EGR valve 38 is disposed on the upstream side thereof. The EGR cooler 37 is interposed upstream of the EGR valve 38. Since the EGR gas is cooled by the EGR cooler 37 and flows through the EGR valve 38 and the check valve 39, the durability of the valves 38 and 39 can be ensured satisfactorily.

  An intake system ejector 40 is provided upstream of the branch point 45 of the intake pipe 4. FIG. 4 shows the configuration of the intake system ejector 40, and an intake nozzle 40 a that reduces the passage area in the middle of the intake pipe 4 toward the junction with the EGR passage 36, and a passage at the outlet of the EGR passage 36. An EGR nozzle 40b that reduces the area toward the junction with the intake pipe 4 and a throat-shaped diffuser 40c that expands after the passage area of the junction is reduced downstream. The branch pipe 4 downstream of the intercooler 5 is connected to the intake nozzle 40a, the combined flow path 36c of the EGR passage 36 is connected to the EGR nozzle 40b, and the intake pipe 4 upstream of the branch point 45 is connected to the diffuser 40c.

  In the operation region where the boost pressure is higher than the exhaust pressure, when the intake air flow velocity is accelerated by the intake nozzle 40a, the dynamic pressure increases, and the static pressure decreases, the EGR gas is transferred from the EGR nozzle 40b to the diffuser 40c. Sucked out. For this reason, the instantaneous differential pressure before and after the check valve 39 is expanded, and the EGR rate is improved. In the operation region where the exhaust pressure is higher than the supercharging pressure, the EGR nozzle 40b accelerates the flow rate of the EGR gas, the dynamic pressure increases, and the static pressure decreases, so that the intake air is supplied from the intake nozzle 40a to the diffuser 40c. Sucked out. That is, the supercharge work of the turbocharger 6 is assisted by the ejector action by the jet of EGR gas, and the effect of suppressing the reduction of the intake air amount accompanying the increase of the EGR rate can be obtained.

  In FIG. 4, X is an opening area facing the diffuser 40c of the intake nozzle 40a, Y is an opening area facing the diffuser 40c of the EGR nozzle 40b, and Z is a minimum passage area of the diffuser 40c. Based on the experimental results, the opening area X of the intake nozzle 40a and the opening area Y of the EGR nozzle 40b are determined based on the experimental results in order to optimize the ejector effect by the jet of intake air and the ejector effect by the jet of EGR gas. It is set to about 1/4 of the passage area of the tube 4. The minimum passage area Z of the diffuser 40c is set to be approximately equal to the sum of the opening area X of the intake nozzle 40a and the opening area Y of the EGR nozzle 40b.

  With this configuration, even in the single entry type turbocharger 6, the exhaust system ejector 23 suppresses the back flow of the exhaust pulse (positive pressure wave), so that the turbine efficiency can be improved. Further, since the exhaust pulse is transmitted to the check valve 39 in the EGR passage 36 without being weakened, and the check valve 39 is effectively operated, a high EGR rate is obtained. Further, the pumping loss can be improved because the exhaust manifold pressure on the cylinder side during the exhaust (pushing) stroke is lowered by the ejector action by the exhaust jet.

  In the intake system ejector 40, for example, in a high load range, the supercharging pressure is higher than the exhaust pressure, but the moment before and after the check valve 39 in the EGR passage 36 is caused by the ejector action of the intake air jet. The differential pressure is expanded and the EGR rate is improved. In the low and medium load range, the exhaust pressure is higher than the supercharging pressure, but the turbocharger's supercharging work is assisted by the ejector action of the EGR gas jet, and the EGR rate The effect of suppressing the decrease in the intake air amount accompanying the increase can be obtained. That is, the intake air amount of each cylinder (# 1 to # 6) is sufficiently ensured even in the low and medium load range, and in the case of a diesel engine, the generation amount of PM (particulate matter) can be suppressed. .

  As a result, high supercharging and large amount of EGR are possible in a wide operating range while suppressing pumping loss. By adding variable nozzle control of the turbocharger 6, it is possible to achieve high supercharging and large-volume EGR while suppressing pumping loss even in high-load and high-speed ranges, and measures against exhaust (such as NOx reduction) and improved output and fuel consumption It is possible to achieve a high balance 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 system, since the passage from the two turbine inlets to the scroll is partitioned inside the turbine, this can be omitted for the exhaust system ejector 23 of FIG.

  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 exhaust nozzles 23a and 23b are not formed integrally with the exhaust manifolds 9a and 9b, but are provided as separate spacers between the flange 21 of the exhaust manifolds 9a and 9b and the flange 26 of the turbine housing 25 as shown in FIG. You may interpose.

  As shown in FIG. 7, the EGR passage 36 may connect the exhaust manifolds 9a and 9b and the intake manifolds 3a and 3b to the same relationship (parallel state) between the cylinder groups. In this case, the intake system ejector 40 is disposed in the middle of each intake branch pipe. As a result, the intake pulsation valleys and the exhaust pulsation peaks overlap between the same cylinder group, and a particularly high EGR rate is obtained.

  As for the EGR passage 36, it is conceivable that the exhaust manifolds 9a and 9b and the intake manifolds 3a and 3b are connected in a relationship (cross state) between different cylinder groups as shown in FIG. In this case, the intake system ejector 40 is disposed in the middle of each intake branch pipe. As a result, exhaust pulsation peaks overlap at the end of the intake stroke between different cylinder groups, and a high EGR rate can be obtained while suppressing a decrease in the intake air amount.

  7 and FIG. 8, the same parts as those in FIG.

It is a whole schematic block diagram. It is sectional drawing which concerns on the structure of an exhaust system ejector. It is explanatory drawing which concerns on the structure of an exhaust system ejector. It is sectional drawing which concerns on the structure of an intake system ejector. It is sectional drawing which concerns on the structure of an exhaust system ejector. It is sectional drawing which concerns on the structure of an exhaust system ejector. It is a whole schematic block diagram. It is a whole schematic block diagram.

Explanation of symbols

1 Multi-cylinder engine (6-cylinder diesel engine)
3a, 3b Intake manifold 4 Intake pipe 5 Intercooler 6 Turbocharger (variable nozzle type turbocharger)
6a Compressor 6b Turbine 8 Exhaust passage 9a, 9b Exhaust manifold 10 Intake passage 20 Exhaust pipe 23 Exhaust system ejector 25 Turbine housing 36 EGR passage 37 EGR cooler 38 EGR valve 39 Check valve (reed valve)
40 Intake system ejector 40a Intake nozzle 40b EGR nozzle 40c Diffuser

Claims (4)

In a multi-cylinder engine equipped with a turbocharger,
Exhaust manifolds divided for each cylinder group in which the exhaust strokes do not overlap, an exhaust system ejector that narrows the downstream portion of each exhaust manifold toward the turbine inlet of the turbocharger, and a cylinder group in which the intake strokes do not overlap An intake manifold that is divided every time,
An EGR passage that connects between the turbine upstream of the turbocharger and the compressor downstream, and an intake system ejector that narrows the outlet portion of the EGR passage toward the joining portion in the middle of the intake passage and the EGR passage. ,
The intake system ejector includes an intake nozzle that reduces the passage area in the middle of the intake passage toward the junction with the EGR passage, and an EGR that reduces the passage area of the exit portion of the EGR passage toward the junction with the intake passage. A nozzle, and a throat-shaped diffuser that expands after reducing the passage area of these junctions to the downstream side,
The multi-cylinder engine , wherein the EGR passage includes a check valve disposed on the downstream side, and an EGR valve and an EGR cooler disposed on the upstream side . 2. The opening area facing the merging portion of the intake nozzle and the opening area facing the merging portion of the EGR nozzle are each set to about ¼ of the intake passage area immediately upstream. Multi-cylinder engine. Minimum passage area of the diffuser, said the opening area facing the confluent portion of the intake nozzle, the opening area facing the confluent portion of the EGR nozzle, the sum and claim 1 or claim, wherein the set to the same extent Item 3. The multi-cylinder engine according to Item 2. 4. The EGR passage according to claim 1, wherein the exhaust manifold and the intake manifold are connected in a relationship between the same cylinder groups or in a relationship between different cylinder groups. The multi-cylinder engine as described in one .

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