JP4007139B2 - Exhaust system for turbocharged engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust device for a turbocharged engine.
[0002]
[Prior art]
In an automobile engine, the exhaust gas has a considerably high pressure (exhaust pressure). Therefore, a turbocharger is installed to increase the intake pressure or the charging efficiency by effectively using the pressure of the exhaust gas, thereby reducing the engine output. Conventionally, turbocharged engines designed for improvement have been used.
[0003]
In general, exhaust gas discharged from an automobile engine contains air pollutants such as NOx (nitrogen oxide), CO (carbon monoxide), and HC (hydrocarbon). Among these air pollutants, the amount of NOx generated increases as the temperature of the combustion gas in the combustion chamber increases. Therefore, the engine is usually provided with an EGR device that reduces the amount of NOx generated by reducing a part of the exhaust gas as EGR to the intake system and lowering the combustion gas temperature in accordance with the operating state of the engine. Further, when the load is low, by supplying EGR gas to the intake system, the pumping loss can be reduced and the fuel efficiency can be improved.
[0004]
Thus, an EGR device is also provided in an engine with a turbocharger. However, in an engine with a turbocharger, normally, EGR gas flows from the exhaust passage upstream of the turbine via the EGR passage to the intake system downstream of the throttle valve. To be introduced. However, depending on the operating state of the engine, the intake pressure at the EGR introduction position becomes higher than the exhaust pressure, and EGR gas cannot be introduced into the intake system. For this reason, in a turbocharged engine, a method has been proposed that widens the operating range in which EGR gas can be introduced into the intake system.
[0005]
Specifically, for example, there are provided two exhaust groups each formed of exhaust passages of cylinders whose exhaust strokes are not adjacent to each other, and the first exhaust group is connected to the first scroll portion of the twin scroll turbine. The turbocharger which expands the operating range in which EGR can be introduced into the intake system by connecting the second exhaust group to the second scroll portion and taking out EGR gas from one exhaust group An attached engine has been proposed (see, for example, Patent Document 1).
[0006]
[Patent Document 1]
Japanese Unexamined Patent Publication No. 09-053456 (paragraph 12, paragraph 15, FIG. 1)
[0007]
[Problems to be solved by the invention]
However, when the EGR gas is taken out from one exhaust group in this way, the exhaust pulsation causes unevenness in the flow of the EGR gas, and the distribution of the EGR gas to each cylinder is deteriorated. As described above, when the distribution of EGR gas deteriorates, a large amount of EGR gas happens to be supplied to a certain cylinder, and the combustibility of the fuel in the cylinder at that time may decrease, and this is repeated. And the fuel efficiency will be reduced. Therefore, in order to avoid such a problem, the supply amount of EGR gas to the intake system must be set low. For this reason, there is a problem in that the EGR gas cannot be sufficiently supplied to the entire cylinder, the emission performance is lowered, or the fuel consumption performance is lowered.
[0008]
The present invention has been made to solve the above-described conventional problems, and is a turbocharger capable of stably introducing EGR gas into an intake system and improving emission performance and fuel consumption performance. Providing an exhaust system for an attached engine is a problem to be solved.
[0009]
[Means for Solving the Problems]
An exhaust system for an engine with a turbocharger according to the present invention, which has been made to solve the above problems, is provided with (i) a turbocharger including a turbine having a plurality of scroll portions, each having an exhaust stroke adjacent thereto. In an exhaust system of an engine with a turbocharger in which a plurality of exhaust groups composed of mismatched cylinder exhaust passages are separately connected to different scroll parts, (ii) the exhaust groups communicate with each other upstream of the turbine (Iii) an open / close valve that opens and closes the communication path, and (iv) a communication path or a vicinity of the communication path (section from the connection position of the communication path to the exhaust passage to the turbine, or slightly upstream from the connection position) And an EGR passage provided with an EGR valve, and (v) the on-off valve is opened in the low load region in the low speed region, and closed in the high load region. The EGR valve is opened in a low load range in a low speed range.
[0010]
According to the exhaust system for an engine with a turbocharger, the supercharging performance is improved and the output torque of the engine is sufficiently increased in a low speed / high load range. Further, in a low speed / low load range where there is little demand for supercharging work, the communication passage is opened, and EGR gas is extracted from the exhaust passages of all the cylinders with less exhaust pulsation. Therefore, the distribution of EGR gas to each cylinder is improved, the mixture or fuel in the combustion chamber is improved, and the fuel efficiency is improved. Further, since the distribution of EGR gas to each cylinder is improved, a large amount of EGR gas (exhaust gas) can be recirculated to the intake system or the combustion chamber, so that the amount of NOx generated can be reduced, and The fuel efficiency can be further improved by reducing the pumping loss.
[0011]
In the exhaust system of the turbocharged engine, it is preferable that the on-off valve is opened in a high speed range. In this way, the exhaust resistance can be reduced and the supercharging efficiency can be increased in a high speed region where the exhaust flow rate is large.
[0012]
In the exhaust system of the turbocharged engine, the opening / closing control of the opening / closing valve in the low speed range causes the load to increase and become higher than the switching load in the operating state where the supercharging pressure is equal to or lower than the exhaust pressure upstream of the turbine. It is sometimes preferable to close the on-off valve. In this case, the on-off valve is closed when the average value of the supercharging pressure (static pressure state) and the average value of the exhaust pressure upstream of the turbine (static pressure state) are substantially equal (or substantially equal). Also good. In this way, pulsation of EGR gas in the EGR passage can be reduced in the low speed / partial load region. For this reason, the EGR gas can be supplied to the intake system or the combustion chamber with good cylinder distribution up to a region where the exhaust pressure is slightly higher than the supercharging pressure. As a result, the fuel efficiency can be improved by reducing the pumping loss due to EGR, and the emission performance can be improved by reducing the NOx generation amount by the reduction of the combustion gas temperature.
[0013]
In the exhaust system for the turbocharged engine, the switching load and the upper limit load of the lean burn region may be the same.
Alternatively, the upper limit load of the lean burn region may be set on the lower load side than the switching load, the air-fuel ratio may be set to the stoichiometric air-fuel ratio, and EGR gas may be supplied to the intake system in the region between the two loads. .
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described.
As shown in FIGS. 1 to 4, a turbocharged engine CE (hereinafter referred to as “engine CE”) provided with an exhaust device according to the present invention includes first to fourth cylinders A to D. It is an inline 4-cylinder engine. In the engine CE, ignition is performed in the order of the first cylinder A, the third cylinder C, the fourth cylinder D, and the second cylinder B. Therefore, the exhaust strokes of the first cylinder A and the fourth cylinder D are not adjacent to each other, and the exhaust strokes of the second cylinder B and the third cylinder C are not adjacent to each other.
[0015]
Although not shown in detail, in each of the cylinders A to D of the engine CE, when two intake valves (not shown) are opened, they pass through two intake ports (not shown). Thus, air for fuel combustion is taken into the combustion chambers 1a to 1d from the intake system. Then, fuel (gasoline) is directly injected into the air in each of the combustion chambers 1a to 1d from a fuel injection valve (not shown) at a predetermined timing to form an air-fuel mixture. This air-fuel mixture is compressed by a piston (not shown), and is ignited and burned by a spark plug (not shown) at a predetermined timing. Combustion gas, that is, exhaust gas, is discharged to an exhaust system via an exhaust port (not shown) when an exhaust valve (not shown) is opened.
[0016]
One common intake passage 2 is provided in the intake system for supplying fuel combustion air to the combustion chambers 1a to 1d of the first to fourth cylinders A to D. The common intake passage 2 has an air intake 3, an air cleaner 4 for removing dust and the like in the air, and an air flow sensor (see FIG. (Not shown), a blower 5p of the twin-scroll turbocharger 5, an intercooler 6 that cools the air that has been pressurized by the blower 5p and becomes hot, and a throttle valve 7 that throttles the air. . The downstream end of the common intake passage 2 is connected to a surge tank 8 that stabilizes the air flow. The surge tank 8 includes first and second branch intake passages 9a for the first to fourth cylinders A to D, each having a downstream end connected to two intake ports of the first to fourth cylinders A to D. 10a-9d, 10d are connected.
[0017]
In the exhaust system for discharging the combustion gas or exhaust gas in the combustion chambers 1a to 1d of the first to fourth cylinders A to D into the atmosphere, the upstream ends are respectively connected to the exhaust ports of the first to fourth cylinders A to D. Connected branch exhaust passages 11a to 11d for the first to fourth cylinders A to D are provided. Here, the branch exhaust passages 11a to 11d are grouped (grouped) into the first and second exhaust groups so that the branch exhaust passages of the cylinders whose exhaust strokes are not adjacent to each other belong to the same exhaust group. Has been. Specifically, the branch exhaust passages 11a and 11d of the first and fourth cylinders A and D whose exhaust strokes are not adjacent to each other belong to the first exhaust group, and the second and third cylinders B and C whose exhaust strokes are not adjacent to each other. The branched exhaust passages 11b and 11c belong to the second exhaust group.
[0018]
The downstream ends of the branch exhaust passages 11a and 11d belonging to the first exhaust group are connected to the first collective exhaust passage 12, and the downstream ends of the branch exhaust passages 11b and 11c belonging to the second exhaust group are connected to the second collective exhaust passage 13. Has been. The downstream end of the first collective exhaust passage 12 is connected to the first scroll portion 21 of the turbine 5t of the turbocharger 5, and the downstream end of the second collective exhaust passage 13 is connected to the second scroll portion 22 of the turbine 5t. Has been. Both scroll portions 21 and 22 are connected to one common exhaust passage 14.
[0019]
Although not shown in detail, in the turbine 5t of the twin-scroll turbocharger 5, a partition wall extending in a direction substantially perpendicular to the turbine axis is provided in the housing, and the exhaust spiral chamber is provided by this partition wall. Or the scroll is divided into two in the turbine axis direction. One of the exhaust swirl chambers or scrolls (one closer to the blower 5p) divided into two in this way is the first scroll part 21 and the other is the second scroll part 22. Thus, in the turbocharger 5 or the turbine 5t, the occurrence of exhaust interference is prevented and the supercharging efficiency is increased.
[0020]
The exhaust system includes an exhaust bypass passage 15 that bypasses the turbine 5t and connects the second collective exhaust passage 13 upstream of the turbine and the common exhaust passage 14 downstream of the turbine, and a waist that opens and closes the exhaust bypass passage 15. A gate valve 16 is provided. In order to prevent the supercharging pressure from exceeding the upper limit supercharging pressure, when the exhaust gas flow rate is large, for example, at high speed and high load, the wastegate valve 16 is opened and the exhaust gas in the second collective exhaust passage 13 is opened. A part or the whole of the engine bypasses the turbine 5 t and is discharged to the common exhaust passage 14 via the exhaust bypass passage 15.
[0021]
Further, in this exhaust system, a communication passage 17 that connects the first collective exhaust passage 12 and the second collective exhaust passage 13 upstream of the turbine, and an on-off valve 18 that opens and closes the communication passage 17 are provided. The communication passage 17 is connected to the second collective exhaust passage 13 upstream of the connection position of the exhaust bypass passage 15 to the second collective exhaust passage 13.
[0022]
An EGR passage 19 that connects the communication passage 17 on the second collective exhaust passage side (or the first collective exhaust passage side) from the open / close valve 18 and the common intake passage 2 or the surge tank 8 downstream from the throttle valve 7 is provided. Is provided. The EGR passage 19 is provided with an EGR valve 20 that opens and closes the EGR passage 19 or controls the flow rate of EGR gas. The EGR passage 19 may be connected not to the communication passage 17 but to the first collective exhaust passage 12 or the second collective exhaust passage 13 upstream of the turbine. The EGR passage 19 may be connected to the branch exhaust passages 11a to 11d as long as the EGR passage 19 is not affected by the dynamic pressure.
[0023]
Here, when the pressure of the exhaust gas in the communication passage 17 or the second collective exhaust passage 13 is higher than the intake pressure downstream of the throttle valve 7, the exhaust gas depends on the pressure difference and the opening of the EGR valve 20. A part of the gas is supplied as EGR gas to the common intake passage 2 or the surge tank 8 via the EGR passage 19. When the EGR gas is thus supplied to the intake system, and thus the combustion chambers 1a to 1d, the temperature of the combustion gas in the combustion chambers 1a to 1d is lowered, the amount of NOx generated is reduced, and the emission performance is improved. In addition, the pumping loss is reduced (particularly when the intake negative pressure is strong (intake pressure is low), such as at low loads), and fuel efficiency is improved.
[0024]
Hereinafter, a control method of the communication passage 17 to the on-off valve 18 and the EGR passage 19 to the EGR valve 20 in the engine CE will be specifically described.
FIG. 5 shows an operation region of the engine CE using the engine speed and the engine load as parameters. In FIG. 5, a curve L ₁ shows a relationship between the engine speed and the engine load in the full load state (WOT) when the on-off valve 18 is closed and the communication path 17 is closed. . Curve L ₂ is when the on-off valve 18 is opened is communicating passage 17 is opened, shows the relationship between the engine speed and the engine load in the full load (WOT). N ₀ indicates an engine speed (hereinafter referred to as “switching speed”) that becomes a boundary between a low speed range (low speed range) and a high speed range (high speed range), and T ₀ indicates a low load range and a high speed range. A load that is a boundary with the load range (hereinafter referred to as “switching load”) is shown.
[0025]
(At low speed and high load)
At the time of low speed and high load, that is, during operation in the low speed and high load range indicated by region I in FIG. 5, the on-off valve 18 is closed and the communication path 17 is closed. Further, the EGR valve 20 is closed and the EGR passage 19 is closed. At this time, EGR gas is not supplied to the intake system. In this case, since the communication passage 17 is closed, the first collective exhaust passage 12 of the first exhaust group and the second collective exhaust passage 13 of the second exhaust group are isolated from each other. Accordingly, the exhaust gases of the first and fourth cylinders A and D belonging to the first exhaust group are supplied to the first scroll portion 21 of the turbine 5t, and the exhaust gases of the second and third cylinders B and C belonging to the second exhaust group are included. The gas is supplied to the second scroll part 22 of the turbine 5t.
[0026]
Thus, at low speeds and high loads, the turbocharger 5 functions in the same way as an ordinary twin scroll turbocharger, preventing exhaust interference, increasing turbocharging efficiency, and sufficient engine output torque. Enhanced. The reason why the supply of EGR gas to the intake system is stopped at low speed and high load is because it is necessary to increase the charging efficiency and ensure high output.
[0027]
(At low speed and low load)
At low speed / low load, that is, during operation in the low speed / low load range indicated by region II in FIG. 5, the on-off valve 18 is opened and the communication path 17 is opened. Further, the EGR valve 20 is opened, the EGR passage 19 is opened, and EGR gas is supplied to the intake system. In this case, since the communication passage 17 is opened, the EGR gas is taken out from the branch exhaust passages 11a to 11d of all the cylinders A to D with little exhaust pulsation. Therefore, the distribution of EGR gas to the cylinders A to D is improved, the air-fuel mixture or the fuel in the combustion chambers 1a to 1d is improved, and the fuel efficiency is improved. Further, since the distribution of EGR gas to each cylinder A to D is improved, a large amount of EGR gas (exhaust gas) can be recirculated to the intake system or the combustion chambers 1a to 1d, thereby reducing the amount of NOx generated. In addition, the fuel efficiency can be further improved by reducing the pumping loss. In this case, since exhaust interference occurs, the supercharging capability is reduced, but there is no particular problem because there is little demand for supercharging work at low speed and low load.
[0028]
In the opening / closing control of the opening / closing valve 18 in the low speed region, an operating state in which the supercharging pressure (intake pressure downstream of the throttle valve) is equal to or lower than the exhaust pressure (exhaust gas pressure in the communication passage 17 or the second collecting exhaust passage 13). in on-off valve 18 is closed when the load is higher than the threshold engine load T ₀ rises. The on-off valve 18 is closed when the average value of the supercharging pressure and the average value of the exhaust pressure upstream of the turbine are substantially equal.
[0029]
Thus, EGR gas pulsation in the EGR passage 19 can be reduced in the low speed / partial load region. For this reason, the EGR gas can be supplied to the intake system or the combustion chambers 1a to 1d with good cylinder distribution up to a region where the exhaust pressure is slightly higher than the supercharging pressure. As a result, the pumping loss due to EGR can be reduced to improve the fuel efficiency, and the NOx generation amount can be reduced due to the decrease in the combustion gas temperature to improve the emission performance.
[0030]
Further, in this engine CE, in the low speed / low load range, the lean burn is performed with the air / fuel ratio leaner than the stoichiometric air / fuel ratio (A / F = 14.7) in order to improve fuel efficiency and reduce NOx generation. Is preferably performed. In this case, a large amount of EGR (exhaust gas recirculation) can be performed in the lean burn region, and fuel efficiency and emission performance can be improved. In this case, it is preferable that the upper limit load in the lean burn region is matched with the switching load T ₀ in the low speed region.
However, an upper limit load of the lean burn zone may be set to the low load side than the switching load T ₀ in the low speed range. In this case, it is preferable to set the air-fuel ratio to the stoichiometric air-fuel ratio and supply EGR gas to the intake system in the region between both loads.
[0031]
(At high speed)
At high speed, that is, at the time of operation in the high speed region indicated by region III in FIG. 5, the on-off valve 18 is opened and the communication path 17 is opened. Further, the EGR valve 20 is opened, the EGR passage 19 is opened, and EGR gas is supplied to the intake system. Normally, the exhaust flow rate is large at high speeds, so the exhaust resistance increases. However, by opening the communication path 17 in this way, the exhaust resistance can be reduced and the supercharging efficiency can be increased. Further, the pumping loss can be reduced by supplying the EGR gas, and the fuel efficiency can be improved.
[0032]
As described above, in the low speed / low load range and the high speed range, the on-off valve 18 is opened to open the communication passage 17, thereby improving fuel efficiency and improving the distribution of EGR gas to the cylinders A to D. However, the results of verifying this effect through experiments or simulations are shown below.
[0033]
In FIG. 6, the cylinder pressure (combustion chamber) when the communication path 17 is opened (hereinafter referred to as “when communicating”) and when the communication path 17 is closed (hereinafter referred to as “when not communicating”). The relationship between pressure and cylinder volume (combustion chamber volume) is shown. According to FIG. 6, the negative work is clearly smaller at the time of communication (solid line) than at the time of non-communication (broken line). Therefore, it is presumed that the fuel efficiency is effectively improved during communication.
[0034]
FIG. 7 shows a change characteristic of the EGR gas flow rate (EGR valve flow rate) with respect to the crank angle during communication and during non-communication. According to FIG. 7, the fluctuation of the EGR gas flow rate is clearly smaller at the time of communication (solid line) than at the time of non-communication. Therefore, when communicating, it is presumed that the distribution of EGR gas to each of the cylinders A to D can be improved, and as a result, the supply amount of EGR gas to the intake system or the combustion chambers 1a to 1d can be increased. .
[0035]
FIG. 8 and FIG. 9 compare the results of measuring the distribution of EGR gas to each cylinder A to D during non-communication and communication with the case of a normal engine that does not group exhaust systems. And show. According to FIG.8 and FIG.9, at the time of communication (FIG. 9), the distribution property of EGR gas to each cylinder AD is clearly improved compared with the time of non-communication (FIG. 8).
[0036]
FIG. 10 shows a change characteristic of the average effective pressure Pe with respect to the EGR rate during communication and during non-communication. In FIG. 10, a region where the average effective pressure Pe is lower than each curve is a region where EGR gas can be supplied, and a region where the average effective pressure Pe is higher than each curve is a region where EGR gas cannot be supplied. According to FIG. 10, the region where the EGR gas can be supplied is wider at the time of communication (solid line) than at the time of non-communication (broken line). Therefore, it can be seen that the EGR gas can be more effectively supplied to the intake system during communication.
[0037]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an exhaust device for an engine with a turbocharger that can stably introduce EGR gas into an intake system and can improve emission performance and fuel consumption performance.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of an engine with a turbocharger according to an embodiment of the present invention.
FIG. 2 is a plan view of the turbocharged engine shown in FIG.
FIG. 3 is a side view of the turbocharged engine shown in FIG. 1;
4 is a front view of the turbocharged engine shown in FIG. 1. FIG.
FIG. 5 is a diagram showing an operation region in which engine speed and engine load are parameters, and shows a control method of the on-off valve.
FIG. 6 is a graph showing the relationship between cylinder pressure and cylinder volume when communicating and when not communicating.
FIG. 7 is a graph showing a change characteristic with respect to a crank angle of an EGR gas flow rate (EGR valve flow rate) during communication and during non-communication.
FIG. 8 is a graph showing the result of measuring the distribution of EGR gas to each cylinder during non-communication in comparison with the case of a normal engine in which the exhaust system is not grouped.
FIG. 9 is a graph showing the result of measuring the distribution of EGR gas to each cylinder during communication in comparison with a normal engine that does not have an exhaust system grouped.
FIG. 10 is a graph showing a change characteristic with respect to an EGR rate of an average effective pressure Pe during communication and during non-communication.
[Explanation of symbols]
CE: Engine with turbocharger, A to D: 1st to 4th cylinder, 1a to 1d ... Combustion chamber, 2 ... Common intake passage, 3 ... Air intake port, 4 ... Air cleaner, 5 ... Turbocharger, 5p ... blower, 5t ... turbine, 6 ... intercooler, 7 ... throttle valve, 8 ... surge tank, 9a-9d ... first branch intake passage, 10a-10d ... second branch intake passage, 11a-11d ... branch exhaust passage, DESCRIPTION OF SYMBOLS 12 ... 1st collective exhaust passage, 13 ... 2nd collective exhaust passage, 14 ... Common exhaust passage, 15 ... Exhaust bypass passage, 16 ... Waste gate valve, 17 ... Communication passage, 18 ... Open / close valve, 19 ... EGR passage, 20 ... EGR valve, 21 ... first scroll part, 22 ... second scroll part.

Claims (6)

A turbocharger including a turbine having a plurality of scroll portions is provided, and a plurality of exhaust groups each composed of an exhaust passage of a cylinder whose exhaust strokes are not adjacent to each other are connected to different scroll portions, respectively. In the exhaust system of the turbocharged engine,
A communication passage for communicating each exhaust group upstream of the turbine;
An on-off valve that opens and closes the communication path;
An EGR passage connected to the communication passage or the exhaust passage near the communication passage and provided with an EGR valve;
An exhaust system for an engine with a turbocharger, wherein the on-off valve is opened in a low load region in a low speed region and closed in a high load region, and the EGR valve is opened in a low load region in a low speed region. The exhaust system for an engine with a turbocharger according to claim 1, wherein the on-off valve is opened in a high speed range. In the open / close control of the open / close valve in the low speed range, the open / close valve is closed when the load rises and becomes higher than the switching load in an operating state where the supercharging pressure is equal to or lower than the exhaust pressure upstream of the turbine. The exhaust system for an engine with a turbocharger according to claim 1 or 2. The exhaust of the turbocharged engine according to claim 3, wherein the on-off valve is closed when the average value of the supercharging pressure and the average value of the exhaust pressure upstream of the turbine become substantially equal. apparatus. The exhaust system for an engine with a turbocharger according to any one of claims 1 to 4, wherein the switching load and the upper limit load in the lean burn region are the same. The upper limit load of the lean burn region is set on the lower load side than the switching load, the air-fuel ratio is set to the stoichiometric air-fuel ratio in the region between the two loads, and EGR gas is supplied to the intake system The exhaust system for an engine with a turbocharger according to any one of claims 1 to 4.

Images