JP2014114788A - Turbocharged engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a turbocharged engine in which a high pressure EGR device and a low pressure EGR device are appropriately used selectively from a view point of improving torque in a high load region requiring torque.SOLUTION: A turbocharged engine includes a high pressure EGR device 50 having an EGR passage 51 communicating an exhaust passage 30 on the upstream side of a turbine 22 and an intake passage 10 on the downstream side of a compressor 23, a low pressure EGR device 60 having an EGR passage 61 communicating the exhaust passage 30 on the downstream side of the turbine 22 and the intake passage 10 on the upstream side of the compressor 23, and control means for controlling EGR valves 53 and 63 so that a flow rate of EGR gas of the low pressure EGR device 60 is larger than a flow rate of the EGR gas of the high pressure EGR device 50 in a first region on a low speed high load side and the flow rate of the EGR gas of the high pressure EGR device 50 is larger than the flow rate of the EGR gas of the low pressure EGR device 60 in a second region on a high speed high load side.

Description

  The present invention relates to a turbocharged engine including a turbocharger including a turbine driven by energy of exhaust gas passing through an exhaust passage and a compressor driven by the turbine to pressurize air in an intake passage.

  The turbocharger achieves high engine output by using the energy of exhaust gas discharged from the engine, and has been widely used in various engines.

  In a turbocharged engine including the turbocharger, Patent Document 1 discloses that a part of exhaust gas that passes through the exhaust passage is recirculated to the intake passage via an EGR passage that connects the exhaust passage and the intake passage. It is disclosed that an EGR (Exhaust Gas Recirculation) apparatus is also provided. By performing EGR (exhaust gas recirculation), the combustion temperature decreases, abnormal combustion such as knocking is suppressed, and emissions such as NOx are reduced. Further, by suppressing knocking, the ignition timing can be advanced, and sufficient torque can be obtained even with relatively little fuel, thereby improving fuel efficiency.

  Patent Document 2 discloses, as the EGR device, a high-pressure EGR device having a high-pressure EGR passage that connects an exhaust passage upstream from the turbine and an intake passage downstream from the compressor, an exhaust passage downstream from the turbine, and upstream from the compressor. And a low pressure EGR device having a low pressure EGR passage communicating with the other intake passage.

JP 2010-24974 A (paragraph 0027) JP 2008-138598 A (paragraphs 0033 and 0035)

  By the way, in the engine operating region, the high load region is a region where torque is required. However, in a turbocharged engine including a high pressure EGR device and a low pressure EGR device, the two EGR devices are abnormal in such a high load region. The problem is how to use them properly from the viewpoint of further improving torque while ensuring suppression of combustion and reduction of emissions.

  Accordingly, an object of the present invention is to provide a turbocharged engine in which a high-pressure EGR device and a low-pressure EGR device are properly used from the viewpoint of improving torque in a high load range where torque is required.

  In order to solve the above problems, the present invention provides a turbocharger including a turbine driven by energy of exhaust gas passing through an exhaust passage and a compressor driven by the turbine to pressurize air in the intake passage. A turbocharged engine equipped with an engine, wherein an EGR passage communicating an exhaust passage upstream from the turbine and an intake passage downstream from the compressor, and a flow rate of a first EGR gas passing through the EGR passage are adjusted A flow rate of the first EGR device including the first EGR valve, the EGR passage communicating with the exhaust passage downstream of the turbine and the intake passage upstream of the compressor, and the flow rate of the second EGR gas passing through the EGR passage A second EGR device including a second EGR valve to be adjusted, and an EGR control for controlling the first EGR valve and the second EGR valve The EGR control means is configured such that, in the engine operating region, the flow rate of the second EGR gas is higher than the flow rate of the first EGR gas in the first region on the low speed and high load side, Controlling the first EGR valve and the second EGR valve so that the flow rate of the first EGR gas is larger than the flow rate of the second EGR gas in the second region on the high load side. A turbocharged engine characterized by the above (claim 1).

  According to the present invention, in the high load region where torque is required, in the first region on the low speed side, the flow rate of the second EGR gas by the second EGR device is the same as that of the first EGR gas by the first EGR device. More than the flow rate. Thereby, the supercharging efficiency is improved in the low speed and high load range, and the torque is improved. That is, since the second EGR gas from the second EGR device is recirculated to the intake passage upstream of the compressor, the amount of work of the compressor increases and the discharge flow rate of the compressor increases. Therefore, even if the boost pressure and thus the pressure ratio of the compressor rises and the engine operating state is the same, the operating point of the compressor moves to a point where the discharge flow rate and pressure ratio of the compressor have increased. Moreover, since the second EGR gas from the second EGR device is extracted from the exhaust passage downstream from the turbine, the driving force of the turbine does not decrease. Therefore, the operation point of the compressor is located where the compressor efficiency is improved, the supercharging efficiency is improved, and the supercharging amount is efficiently increased. As described above, by relatively increasing the flow rate of the second EGR gas in the first region on the low speed and high load side, the supercharging efficiency is improved and the torque is improved.

  According to the present invention, in the high load region where torque is required, in the second region on the high speed side, the flow rate of the first EGR gas by the first EGR device is the second EGR by the second EGR device. More than the gas flow rate. As a result, torque is improved in a high speed and high load range. That is, the first EGR gas from the first EGR device is extracted from the exhaust passage upstream of the turbine and returned to the intake passage downstream of the compressor, so that the exhaust pressure upstream of the turbine is reduced and The intake pressure downstream increases. As a result, since the pumping loss is reduced, the torque is improved by relatively increasing the flow rate of the first EGR gas in the second region on the high speed and high load side. Furthermore, the low temperature EGR gas is introduced into the combustion chamber, the combustion temperature is lowered, knocking is suppressed and the ignition timing can be advanced, and the amount of air is increased due to a decrease in the exhaust gas temperature. Torque is improved in the second region on the high load side. In addition, by suppressing knocking, the ignition timing can be advanced, and sufficient torque can be obtained even with relatively little fuel, thereby improving fuel efficiency.

  As described above, according to the present invention, there is provided a turbocharged engine in which the first EGR device and the second EGR device are properly used from the viewpoint of improving torque in a high load range where torque is required.

  In the present invention, preferably, the EGR control means opens the second EGR valve and closes the first EGR valve in the first region, and closes the first EGR valve in the second region. The EGR valve is opened and the second EGR valve is closed (Claim 2).

  According to this configuration, in the first region on the low speed and high load side, only the second EGR gas from the second EGR device is recirculated to the intake passage, and in the second region on the high speed and high load side, the first EGR device is used. Only the first EGR gas returns to the intake passage. Therefore, the above-described torque improving action is further increased in both regions.

  In the present invention, it is preferable that the EGR control means in the engine operation region in the third region excluding the first region and the second region, the first EGR device and the second EGR. EGR is performed using both of the apparatuses, and in the third region, the flow rate of the second EGR gas is larger than the flow rate of the first EGR gas in a region closer to the first region, The first EGR valve and the second EGR valve are controlled so that the flow rate of the first EGR gas is larger than the flow rate of the second EGR gas in a region closer to the second region. Item 3).

  According to this configuration, in the engine operating region, both the first EGR device and the second EGR device are used in the third region on the low to medium load side where the torque is small, that is, the partial load region. Thus, EGR (exhaust gas recirculation) is performed. For example, when EGR is performed using the first EGR device, the first EGR gas is extracted from the exhaust passage and returned to the intake passage at a portion close to the engine body, so that the state is relatively high. Is introduced into the combustion chamber. Therefore, ignitability can be ensured by performing EGR using the first EGR device. On the other hand, when EGR is performed using the second EGR device, the second EGR gas is extracted from the exhaust passage at a position far from the engine body and is returned to the intake passage, so that the state is relatively low. Is introduced into the combustion chamber. Therefore, an excessive increase in the exhaust gas temperature and the exhaust pressure can be suppressed by performing EGR using the second EGR device. By combining these, it is possible to improve combustibility and improve fuel efficiency by reducing pumping loss.

  In addition, in the third region, the flow rate of the second EGR gas is made larger than the flow rate of the first EGR gas as it is closer to the first region on the low speed and high load side, and the second region on the high speed and high load side is increased. Since the flow rate of the first EGR gas is made larger than the flow rate of the second EGR gas as it is closer to the region, the engine operating state approaches the first region or the second region in the third region. The response of EGR control during a transition such as when the engine operating state shifts from the third region to the first region or the second region is improved.

  In the present invention, preferably, intake and exhaust valve control means for controlling an intake valve for opening and closing an intake port of a cylinder and an exhaust valve for opening and closing an exhaust port are provided, and the intake and exhaust valve control means is provided in the first region. The intake valve and the exhaust valve are controlled so that a valve overlap period in which both the intake valve and the exhaust valve open is formed or expanded when the pressure in the intake port becomes higher than the pressure in the exhaust port. (Claim 4).

  According to this configuration, in the first region on the low speed and high load side, an intake air blow-through flow that blows through the combustion chamber from the intake side to the exhaust side is generated during the valve overlap period. Therefore, an effect of removing residual gas in the cylinder (scavenging effect) is obtained, knocking is suppressed, and the ignition timing can be advanced. As a result, the aforementioned torque improving action in the first region is further increased. Further, by suppressing knocking, the ignition timing can be advanced, and sufficient torque can be obtained even with relatively little fuel, thereby improving fuel efficiency.

  In the present invention, preferably, a wastegate valve control means for opening a wastegate valve of the turbocharger in a fourth region set on the high speed and high load side in the second region is provided. 5).

  According to this configuration, the fourth region is set on the high-speed and high-load side in the second region on the high-speed and high-load side, and the driving force of the turbine is reduced by opening the waste gate valve in the fourth region. To do. Therefore, for example, the supercharging pressure control for preventing the supercharging pressure by the compressor of the turbocharger from exceeding the upper limit provided from the viewpoint of protecting the engine and the supercharger is executed in the fourth region. can do.

  According to the present invention, there is provided a turbocharged engine in which the first EGR device and the second EGR device are properly used from the viewpoint of improving torque in a high load range where torque is required.

It is a figure showing the whole turbocharged engine composition concerning an embodiment of the present invention. It is a side view which shows typically the flow of the gas in the exhaust passage of the said engine. It is a perspective view which shows the exit part of the independent exhaust passage extended from each cylinder of the said engine. It is a block diagram which shows the control system of the said engine. It is the control map which divided the operation area | region of the said engine into the some area | region for every kind of control content. It is a map which overlaps and shows the full load line of the said engine when high pressure EGR is performed in the whole area | region of an engine, and the full load line of the said engine when EGR is not performed. It is a map which shows the full load line of the engine when low pressure EGR is performed in the entire region of the engine operation and the full load line of the engine when high pressure EGR is performed in the entire region of the engine operation. . It is a graph of the performance curve which shows the characteristic of the compressor of the turbocharger for demonstrating the effect | action of low pressure EGR. It is a graph which shows the change according to the crank angle of the exhaust pressure of the engine. It is a time chart which shows the opening / closing timing of the intake / exhaust valve of the said engine for every cylinder.

(1) Overall Configuration of Engine FIGS. 1 and 2 show a turbocharged engine according to an embodiment of the present invention. The engine according to the present embodiment is a four-cycle spark ignition type multi-cylinder engine mounted on a vehicle as a power source for traveling. Specifically, the engine is generated by an in-line four-cylinder engine main body 1 having four cylinders 2A to 2D arranged in a row, an intake passage 10 for introducing air into the engine main body 1, and the engine main body 1. And an exhaust passage 30 for exhausting the exhaust gas.

  A piston (not shown) is inserted into each of the cylinders 2A to 2D of the engine body 1 so as to be reciprocally slidable. A combustion chamber 3 is defined above each piston. In the combustion chamber 3, a mixture of fuel and air injected from an injector 9, which will be described later, burns, and exhaust gas generated by the combustion is discharged from the combustion chamber 3 to the exhaust passage in the exhaust stroke of each cylinder 2 </ b> A to 2 </ b> D. It is discharged to 30.

  An upper portion (cylinder head) of the engine body 1 includes an intake port 4 for introducing air supplied from the intake passage 10 into the combustion chamber of each cylinder 2A to 2D, an intake valve 6 for opening and closing the intake port 4, An exhaust port 5 for leading exhaust gas generated in the combustion chamber of each cylinder 2A to 2D to the exhaust passage 30 and an exhaust valve 7 for opening and closing the exhaust port 5 are provided.

  The intake valve 6 and the exhaust valve 7 are driven to open and close in conjunction with the rotation of the crankshaft of the engine body 1 by a valve operating mechanism (not shown) including a camshaft, a cam and the like. VVT 16 is incorporated in each valve operating mechanism for intake valve 6 and exhaust valve 7. The VVT 16 is an abbreviation for a variable valve timing mechanism, and is a variable valve mechanism for variably setting the opening / closing timings of the intake valve 6 and the exhaust valve 7.

  At the upper part (cylinder head) of the engine body 1, an injector 9 that injects fuel (fuel containing gasoline) toward the combustion chamber 3, and a mixture of fuel and air injected from the injector 9 is caused by spark discharge. One set of spark plugs 8 for supplying ignition energy is provided for each of the cylinders 2A to 2D.

  The spark plug 8 sequentially supplies ignition energy to the air-fuel mixture of each of the cylinders 2A to 2D according to power supply from an ignition circuit (not shown). In the in-line four-cylinder engine as in this embodiment, ignition is performed at a timing shifted by 180 ° CA in the order of the first cylinder 2A → the third cylinder 2C → the fourth cylinder 2D → the second cylinder 2B. An exhaust stroke or the like is performed (see also FIG. 10 described later). Note that “° CA” represents a rotation angle (crank angle) of a crank shaft that is an output shaft of the engine.

  The intake passage 10 is a surge provided in common to the four independent intake passages 11 communicating with the intake ports 4 of the cylinders 2A to 2D and the upstream side of each independent intake passage 11 (upstream side in the flow direction of intake air). The tank 12 and a single tubular intake pipe 13 provided on the upstream side of the surge tank 12 are provided. The intake pipe 13 is provided with an openable / closable throttle valve 14 for adjusting the amount of intake air, and an intercooler 15 for cooling air compressed by a turbocharger 20 described later.

  As shown in FIGS. 1 to 3, the exhaust passage 30 includes a plurality of independent exhaust passages 31, 32, 33 communicating with the exhaust ports 5 of the cylinders 2 </ b> A to 2 </ b> D, and downstream of the independent exhaust passages 31, 32, 33. It has an exhaust collecting portion 34 in which end portions (end portions on the downstream side in the exhaust gas flow direction) are gathered, and a single tubular exhaust pipe 35 provided on the downstream side of the exhaust collecting portion 34. The exhaust pipe 35 is provided with a catalytic converter 36 containing a catalyst such as a three-way catalyst, a silencer (not shown), and the like.

  As described above, in the present embodiment, three independent exhaust passages 31, 32, 33 are prepared for the four cylinders 2A, 2B, 2C, 2D. This is because the central independent exhaust passage 32 has a Y-shaped branch shape so that it can be commonly used for the second cylinder 2B and the third cylinder 2C. That is, the independent exhaust passage 32 is formed by joining the two branch passage portions 32a and 32b extending from the exhaust ports 5 of the second cylinder 2B and the third cylinder 2C and the branch passage portions 32a and 32b. And a common passage portion 32c. On the other hand, the independent exhaust passages 31 and 33 connected to the exhaust ports 5 of the first cylinder 2A and the fourth cylinder 2D are formed in a single tube without branching. Hereinafter, the single tubular independent exhaust passages 31 and 33 are referred to as “first independent exhaust passage 31” and “third independent exhaust passage 33”, respectively, and the independent exhaust passage 32 branched in a bifurcated manner is referred to as “second independent exhaust passage”. It may be referred to as “passage 32”.

  Here, in the four-cycle four-cylinder engine as in the present embodiment, the ignition is performed in the order of the first cylinder 2A → the third cylinder 2C → the fourth cylinder 2D → the second cylinder 2B. The second cylinder 2B and the third cylinder 2C to which the upstream end of the two independent exhaust passages 32 are connected have a relationship in which the exhaust order (the order in which the exhaust stroke is performed) is not continuous. Therefore, even when the common independent exhaust passage 32 is connected to the second cylinder 2B and the third cylinder 2C as described above, the exhaust gas from both the cylinders 2B and 2C flows to the second independent exhaust passage 32 at the same time. There is no.

  The first and third independent exhaust passages 31 and 33 formed in a single tubular shape are directed toward the center side in the cylinder row direction so as to gradually approach the common passage portion 32c of the second independent exhaust passage 32 positioned therebetween. And extended. The respective downstream end portions of the first and third independent exhaust passages 31 and 33 and the downstream end portion of the second independent exhaust passage 32 (downstream end portion of the common passage portion 32c) are at a predetermined angle (relatively shallow angle). The exhaust collecting part 34 is formed on the downstream side of the independent exhaust passages 31 to 33.

  The single tubular first and third independent exhaust passages 31 and 33 have symmetrical shapes with a center line passing between the second cylinder 2B and the third cylinder 2C interposed therebetween. For this reason, the first independent exhaust passage 31 and the third independent exhaust passage 33 have the same passage length and volume. On the other hand, in the bifurcated second independent exhaust passage 32, the total length of the branch passage portions 32a and 32b and the common passage portion 32c is equal to the length of each of the first and second independent exhaust passages 31 and 32. It is formed to be the same and has the same volume as the first and second independent exhaust passages 31 and 32.

  As shown in FIGS. 2 and 3, the downstream portions of the first and third independent exhaust passages 31 and 33 and the downstream portion (common passage portion 32 c) of the second independent exhaust passage 32 are in the flow direction of the exhaust gas. Are divided into two parts by partition walls 37 extending along the lines. That is, the downstream portions of the first and third independent exhaust passages 31 and 33 and the common passage portion 32c of the second independent exhaust passage 32 have two flow paths 38 and 39 that are partitioned by the partition wall 37, respectively. Yes.

  Each partition wall 37 in the first to third independent exhaust passages 31, 32, 33 extends over a range from a middle portion of the independent exhaust passages 31, 32, 33 to a downstream end portion (connecting portion with the exhaust collecting portion 34). Is provided. In other words, each of the independent exhaust passages 31, 32, 33 is connected to the exhaust collecting portion 34 while being divided into the flow paths 38, 39 (the division state is not canceled in the middle). .

  The exhaust passage 30 is provided with an exhaust throttle valve 40 for changing the flow area of the exhaust gas passing through the first to third independent exhaust passages 31, 32 and 33. This exhaust throttle valve 40 is one of the flow paths 38, 39 provided in the downstream portions of the first to third independent exhaust passages 31, 32, 33 (in this embodiment, a flow path positioned on the upper side in FIG. 3). 39) is opened and closed so that the flow area in each independent exhaust passage 31, 32, 33 is changed. In the following, the flow path 39 opened and closed by the exhaust throttle valve 40 is referred to as “variable flow path 39”, and the other flow path 38 is referred to as “normal flow path 38”.

  Although the exhaust throttle valve 40 is not shown in detail, the three valve bodies provided to block the variable flow paths 39 in the first to third independent exhaust passages 31, 32, 33, A shaft that connects the valve bodies to each other and a drive source (such as an electric motor) that rotationally drives the shaft are provided. The exhaust throttle valve 40 having such a structure can simultaneously open and close the variable flow passages 39 in the independent exhaust passages 31, 32, and 33 as the shaft and the valve body are driven to rotate by the drive source. .

  The engine of the present embodiment is equipped with a turbocharger 20 that is driven by the energy of exhaust gas discharged from the engine body 1.

  The turbocharger 20 includes a turbine housing 21 provided immediately downstream of the exhaust collecting portion 34 of the exhaust passage 30 (between the exhaust collecting portion 34 and the exhaust pipe 35), and a turbine disposed in the turbine housing 21. 22, a compressor 23 disposed in the intake pipe 13, and a connecting shaft 24 that connects the turbine 22 and the compressor 23 to each other. When the exhaust gas is discharged from the cylinders 2A to 2D of the engine body 1 during the operation of the engine, the exhaust gas flows into the turbine housing 21 of the turbocharger 20 through the independent exhaust passages 31, 32, 33 and the like. Thus, the turbine 22 receives the energy of the exhaust gas and rotates at high speed. Further, when the compressor 23 connected to the turbine 22 via the connecting shaft 24 is driven at the same rotational speed as the turbine 22, the intake air passing through the intake pipe 13 is pressurized and each cylinder of the engine body 1 is compressed. Pumped to 2A-2D.

  The exhaust passage 30 is provided with a bypass passage 42 for bypassing the turbine 22 of the turbocharger 20 so as to connect the turbine housing 21 and the exhaust pipe 35 on the downstream side thereof. A wastegate valve 43 is provided in the middle of 42 so as to be openable and closable. When the wastegate valve 43 is opened, at least a part of the exhaust gas discharged from the engine body 1 passes through the bypass passage 42, so that the amount of exhaust gas flowing into the turbine 22 is reduced and the driving force of the turbine 22 is reduced. Is suppressed.

  The exhaust collecting portion 34 of the exhaust passage 30 and the surge tank 12 of the intake passage 10 are connected to each other via a high pressure EGR passage 51. That is, the high pressure EGR passage 51 communicates the exhaust passage 30 upstream from the turbine 22 and the intake passage 10 downstream from the compressor 23. The high pressure EGR passage 51 is a passage for performing so-called exhaust gas recirculation, in which a part of the exhaust gas discharged from the engine body 1 is returned to the intake system. The high pressure EGR passage 51 adjusts the flow rate of the high pressure EGR cooler 52 for cooling the EGR gas (exhaust gas returned to the intake system) and the EGR gas (first EGR gas) passing through the high pressure EGR passage 51. And a high-pressure EGR valve (first EGR valve) 53 that can be opened and closed. A high pressure EGR device 50 is configured including the high pressure EGR passage 51, the high pressure EGR cooler 52, and the high pressure EGR valve 53. The high pressure EGR device 50 corresponds to the first EGR device of the present invention. Hereinafter, EGR performed using the high-pressure EGR device 50 is referred to as “high-pressure EGR”.

  The engine according to the present embodiment includes a low pressure EGR device 60 in addition to the high pressure EGR device 50. That is, the exhaust pipe 35 downstream of the catalytic converter 36 and the intake pipe 13 upstream of the compressor 23 are connected to each other via the low pressure EGR passage 61. That is, the low pressure EGR passage 61 communicates the exhaust passage 30 downstream from the turbine 22 and the intake passage 10 upstream from the compressor 23. The low pressure EGR passage 61 is a passage for performing exhaust gas recirculation, as with the high pressure EGR passage 51. The low-pressure EGR passage 61 includes a low-pressure EGR cooler 62 for cooling the EGR gas, and a low-pressure EGR valve that can be opened and closed for adjusting the flow rate of the EGR gas (second EGR gas) passing through the low-pressure EGR passage 61 ( A second EGR valve) 63. The low-pressure EGR device 60 includes the low-pressure EGR passage 61, the low-pressure EGR cooler 62, and the low-pressure EGR valve 63. The low pressure EGR device 60 corresponds to a second EGR device of the present invention. Hereinafter, EGR performed using the low pressure EGR device 60 is referred to as “low pressure EGR”.

(2) Control System Next, the engine control system will be described with reference to FIG. Each part of the engine of this embodiment is comprehensively controlled by an ECU (engine control unit) 70. As is well known, the ECU 70 is a microprocessor including a CPU, a ROM, a RAM, and the like, and corresponds to the EGR control means, the intake / exhaust valve control means, and the waste gate valve control means of the present invention.

  Information from various sensors is input to the ECU 70. For example, an engine or a vehicle includes an engine speed sensor SN1 for detecting the rotation speed of the engine, that is, the rotation speed of the crankshaft of the engine body 1, and an engine water temperature sensor SN2 for detecting the temperature of engine coolant. An air flow sensor SN3 for detecting the flow rate of the intake air passing through the intake pipe 13, and an accelerator opening sensor SN4 for detecting the opening (accelerator opening) of an accelerator pedal (not shown) operated by the driver The information detected by each of these sensors is sequentially input to the ECU 70 as an electrical signal.

  ECU70 controls each part of an engine, performing various calculations etc. based on the input signal from each said sensor (SN1-SN4 etc.). That is, the ECU 70 is electrically connected to the spark plug 8, the injector 9, the intake and exhaust valve VVTs 16 and 16, the throttle valve 14, the exhaust throttle valve 40, the wastegate valve 43, the high pressure EGR valve 53, and the low pressure EGR valve 63. The control signal for driving is output to each of these devices based on the result of the calculation.

(3) Control according to operation region Next, a specific example of engine control performed by the ECU 70 will be described with reference to the control map of FIG.

  In FIG. 5, WOT represents the full load line of the engine (engine torque when the accelerator is fully opened). In this embodiment, since the turbocharger 20 is provided in the engine, the full load line WOT of the engine is a natural intake line (not shown) that is the upper limit of the engine torque at the time of natural intake (no supercharge). )) Is set higher.

  The point IC existing on the full load line WOT is a so-called intercept point. In this intercept point IC, since the supercharging pressure by the compressor 23 of the turbocharger 20 reaches a predetermined upper limit value from the viewpoint of protecting the engine and the supercharger 20, on the higher rotation side than the intercept point IC, Supercharging pressure control is performed to prevent the supercharging pressure from rising above the upper limit value. Hereinafter, the engine rotational speed Ni corresponding to the intercept point IC is referred to as “intercept rotational speed Ni”.

  According to the map of FIG. 5, a rotational speed No lower than the intercept rotational speed Ni (hereinafter referred to as “intermediate rotational speed No”) is set, and in the engine operating range, the rotational speed No is lower than the intermediate rotational speed No. The first region R1 is set on the high load side (torque side) in the speed range. On the other hand, the second region R2 is set on the high load side in the speed region on the higher rotation side than the intermediate rotation speed No. A third region R3 is set in the remaining region excluding these first and second regions R1 and R2.

  A fourth region R4 is set in the second region R2. The fourth region R4 is a region on the highest rotation and high load side in the second region R2. Hereinafter, unless otherwise specified, the second region R2 includes the fourth region R4.

  During engine operation, the ECU 70 sequentially determines in which region the engine is operated in the control map of FIG. 5 based on information obtained from the engine speed sensor SN1, the airflow sensor SN3, the accelerator opening sensor SN4, and the like. Then, the intake valve 6, the exhaust valve 7, the exhaust throttle valve 40, the waste gate valve 43, the high pressure EGR valve 47, and the low pressure EGR valve 53 are controlled for each region according to the determination result.

  As will be described in detail later, in this embodiment, the ECU 70 controls the high pressure EGR valve 47 and the low pressure EGR valve 53 in all the regions R1, R2, R3, and R4 of the control map shown in FIG. I do.

  Next, how the control map shown in FIG. 5 is set in this embodiment will be described.

  First, in FIG. 6, a solid line (high pressure EGR) represents a full load line of the engine when high pressure EGR is performed in the entire operation region of the engine, and a chain line (no EGR) indicates the engine when EGR is not performed. Represents the full load line. FIG. 6 also shows the intercept point IC and the intercept rotation speed Ni when high pressure EGR is performed. As shown in the figure, when high pressure EGR is performed, torque is improved in the high speed region and torque is decreased in the low speed region, compared to when high pressure EGR is not performed.

  The reason why the torque is improved in the high speed range is that, in high pressure EGR, EGR gas (first EGR gas) is extracted from the exhaust passage 30 upstream from the turbine 22 and recirculated to the intake passage 10 downstream from the compressor 23. The exhaust pressure upstream of the turbine 22 is reduced, the intake pressure downstream of the compressor 23 is increased, the pumping loss is reduced, and the low temperature EGR gas is introduced into the combustion chamber, thereby lowering the combustion temperature. That is, knocking is suppressed and the ignition timing can be advanced, and the amount of air is increased due to a decrease in exhaust gas temperature. In addition, by suppressing knocking, the ignition timing can be advanced, and sufficient torque can be obtained even with relatively little fuel, thereby improving fuel efficiency.

  The reason why the torque decreases in the low speed range is that the amount of fresh air decreases due to EGR, the amount of fresh air decreases, and the supercharging pressure decreases due to the decrease in the exhaust pressure upstream of the turbine 22.

  In FIG. 7, a broken line (low pressure EGR) represents a full load line of the engine when low pressure EGR is performed in the entire engine operating region, and a solid line (high pressure EGR) represents a high pressure in the entire engine operating region. Represents the full load line of the engine when EGR is performed. FIG. 7 also shows the intercept point α and the intercept rotational speed No (equal to the intermediate rotational speed No) when low pressure EGR is performed. As shown in the figure, when low pressure EGR is performed, torque is improved in a low speed region as compared to when high pressure EGR is performed. That is, the full load line of the engine when the low pressure EGR is performed can compensate for a decrease in torque in the low speed region in the full load line of the engine when the high pressure EGR is performed. The reason is as follows.

  FIG. 8 is a graph of a performance curve showing the characteristics of the compressor of the turbocharger, for explaining the action of the low pressure EGR.

  In FIG. 8, the vertical axis represents the pressure ratio of the compressor, and the horizontal axis represents the discharge flow rate of the compressor. In the graph of FIG. 8, each of the lines SL, RL, and CL represents a surge line, a rotation limit line, and a choke line, and a region surrounded by these lines is an operable region of the compressor. In addition, a curve group such as a contour line illustrated in this operable region is an isoefficiency line connecting operating points where the efficiency of the compressor is equal, and the curve located at the center side of the region has a higher efficiency. Represents.

  In FIG. 8, the change of the operating point of the compressor when the engine is operated under a specific condition is shown as an operation line. Note that the pressure ratio of the working line has reached its peak from the middle (shifted to a horizontal straight line), but this is supercharged to the upper limit value set from the viewpoint of protecting the engine and the turbocharger. This indicates that supercharging pressure control (for example, control for opening the wastegate valve) is executed because the pressure has reached. This will be described later.

  Now, it is assumed that the discharge flow rate of the compressor and the pressure ratio of the compressor are at point P1 without EGR. The compressor operating point P1 is a point where the flow rate and the pressure ratio are relatively small. At this time, the operating state of the engine is in the low speed and high load region, that is, the first region R1 in FIG.

  When low-pressure EGR is performed in this state, EGR gas (second EGR gas) is returned to the intake passage 10 upstream of the compressor 23 in the low-pressure EGR, so that the work amount of the compressor 23 increases and the discharge flow rate of the compressor 23 increases. (In the figure, the increment of the discharge flow rate is indicated by a sign ΔQ). Therefore, even if the supercharging pressure and the pressure ratio of the compressor 23 are increased and the engine operating state is the same, the operating point of the compressor 23 moves from the initial point P1 to another point P2 on the operating line. This point P2 is a point where the discharge flow rate and the pressure ratio have increased from the initial point P1. In addition, since the EGR gas (second EGR gas) is extracted from the exhaust passage 30 downstream of the turbine 22 in the low pressure EGR, the driving force of the turbine 22 does not decrease. Therefore, as is apparent from FIG. 8, the point P2 is located at a place where the compressor efficiency is improved from the initial point P1. Therefore, the supercharging efficiency is improved, and the supercharging amount is efficiently increased. As described above, the torque in the low speed and high load region (the first region R1 in FIG. 5) is improved by performing the low pressure EGR.

  In FIG. 8, point P3 is a point at which supercharging pressure control for preventing the supercharging pressure from rising beyond the upper limit value is started. When the flow rate becomes larger than this point P3, for example, the waste gate valve 43 is opened, the exhaust pressure upstream from the turbine 22 is reduced, and the supercharging pressure is kept constant so as not to exceed the upper limit value. In this case, since the amount of reduction of the exhaust pressure for maintaining the supercharging pressure constant is small, the increase of the exhaust pressure with respect to the supercharging pressure gradually increases on the side where the flow rate is larger than the point P3. This causes an increase in pumping loss and leads to a deterioration in fuel consumption performance. Therefore, it is preferable that the low pressure EGR is performed on the side where the flow rate is smaller than the point P3 (the side indicated by the symbol ArLo in the drawing), although it has the effect of improving the torque in the low speed region.

  Here, FIG. 6 shows a line X5 extending from the intercept point IC to the high speed side and the low torque side. This line X5 is a line indicating that the supercharging pressure control is executed on the higher speed side when high pressure EGR is performed in the entire operation region of the engine. Therefore, hereinafter, this line is referred to as “supercharging pressure control start line X5 at the time of high pressure EGR”. Similarly, FIG. 7 shows a line X4 extending from the intercept point α to the high speed side and the low torque side. This line X4 is a line indicating that the supercharging pressure control is executed on the higher speed side when the low pressure EGR is performed in the entire operation region of the engine. Therefore, hereinafter, this line is referred to as “supercharging pressure control start line X4 at the time of low pressure EGR”. And as demonstrated with reference to FIG. 8, it is preferable to perform low pressure EGR by the side ArLo whose flow volume is smaller than the point P3 from which supercharging pressure control is started. If this is applied to the supercharging pressure control start line X4 at the time of low pressure EGR in FIG. 7, it is preferable not to perform the low pressure EGR in the region on the high speed side from the supercharging pressure control start line X4 at the time of low pressure EGR. Can do.

  In summary, in the present embodiment, the full load line of the engine when the high pressure EGR shown by the solid line in FIG. 6 is performed and the full load of the engine when the low pressure EGR shown by the broken line in FIG. 7 is performed. The control map shown in FIG. 5 is set by superimposing lines.

  Here, in the present embodiment, the intersection of the full load line when the high pressure EGR is performed and the full load line when the low pressure EGR is performed coincides with the intercept point α when the low pressure EGR is performed.

  As a result, in the WOT shown in FIG. 5, the line Y1 on the low speed side from the intercept point α is the line X1 on the low speed side from the intercept point α in the entire load line at the low pressure EGR shown in FIG. In the WOT shown in FIG. 5, the line Y2 on the high speed side from the intercept point α is the line X2 on the high speed side from the intersection of all the load lines at the time of the high voltage EGR shown in FIG. Equivalent to.

  Further, the boundary line Y3 between the first region R1 and the third region R3 shown in FIG. 5 corresponds to the line X3 on the lower speed side than the intersection of all the load lines at the time of the high pressure EGR shown in FIG. The boundary line Y4 between the second region R2 and the third region R3 shown in FIG. 5 corresponds to the supercharging pressure control start line X4 at the time of low pressure EGR shown in FIG. 7, and the line Y5 shown in FIG. This corresponds to the supercharging pressure control start line X5 at the time of high pressure EGR shown in FIG.

  Hereinafter, the contents of control performed by the ECU 70 for each region will be described.

[I] First region R1
As can be seen from the setting of the control map shown in FIG. 5, the first region R <b> 1 is a region where torque cannot be secured with the high pressure EGR and torque can be secured with the low pressure EGR. Therefore, during operation in the first region R1, the ECU 70 executes the following control.
Close the high pressure EGR valve 53 and open the low pressure EGR valve 63.
Close the exhaust throttle valve 40 (execution of independent exhaust throttle control).
-Form or expand the valve overlap period of intake and exhaust valves 6 and 7.
-Close the wastegate valve 43.

  In the first region R1, the high pressure EGR is stopped and the low pressure EGR is performed. That is, the flow rate of the second EGR gas by the low pressure EGR device 60 is larger than the flow rate of the first EGR gas by the high pressure EGR device 50. More specifically, all the EGR gas becomes the second EGR gas by the low pressure EGR device 60, and the flow rate of the first EGR gas by the high pressure EGR device 50 becomes zero. Therefore, as described with reference to FIG. 8, in the high load region where torque is required, the supercharging efficiency is improved and the torque is improved in the first region R1 on the low speed side.

  Further, in the first region R1, an independent exhaust throttle control for closing the exhaust throttle valve 40 (control for reducing the flow area in the independent exhaust passages 31, 32, 33 by closing the exhaust throttle valve 40) is performed. The variable flow paths 39 in the first to third independent exhaust passages 31, 32, 33 are blocked. This means that the flow area in each independent exhaust passage 31, 32, 33 has been substantially reduced. Then, the exhaust gas discharged from each of the cylinders 2A to 2D of the engine main body 1 passes only through the regular flow path 38 in each independent exhaust passage 31, 32, 33, and maintains the high flow rate, and the exhaust collecting portion 34 and It flows into the turbine 22.

  Further, in the first region R1, the exhaust gas discharged from each of the cylinders 2A to 2D flows into the turbine 22 of the turbocharger 20 by closing the wastegate valve 43, and is supercharged by the compressor 23. Well done.

  Further, in the first region R1, by driving each VVT 16 for the intake valve 6 and the exhaust valve 7, a valve overlap period in which both the intake valve 6 and the exhaust valve 7 open is formed or expanded. That is, as shown in FIGS. 9 and 10, both the intake valve 6 and the exhaust valve 7 are opened over a relatively long period OL from the second half of the exhaust stroke of each cylinder 2A to 2D to the first half of the intake stroke. Thus, the opening / closing timing of the intake / exhaust valves 6 and 7 is set. The period, that is, the valve overlap period OL overlaps with the time when the pressure (intake pressure) in the intake port 4 becomes higher than the pressure (exhaust pressure) in the exhaust port 5 in the first region R1. In FIG. 10, the lift curve of the exhaust valve 7 is expressed as EX, and the lift curve of the intake valve 6 is expressed as IN.

  Thus, the valve overlap period OL is formed or expanded in the first region R1 where the supercharging pressure is higher than the exhaust pressure. During this valve overlap period OL, the intake port passes through the combustion chamber 3. An intake air flow (blow-through flow) that blows from 4 to the exhaust port 5 is formed. This blow-through flow pushes the burned gas (residual gas) remaining in the combustion chamber 3 to the exhaust port 5, that is, promotes scavenging.

[Ii] Second region R2
The second region R2 (including the fourth region) is a region where it is preferable not to perform the low pressure EGR because the pumping loss is increased as can be seen from the setting process of the control map shown in FIG. Therefore, during operation in the second region R2, the ECU 70 executes the following control.
Close the low pressure EGR valve 63 and open the high pressure EGR valve 53.
-Open the exhaust throttle valve 40 (non-execution of independent exhaust throttle control).
Close the wastegate valve 43 (open in the fourth region R4).

  In the second region R2, the low pressure EGR is stopped and the high pressure EGR is performed. That is, the flow rate of the first EGR gas by the high pressure EGR device 50 is larger than the flow rate of the second EGR gas by the low pressure EGR device 60. More specifically, all of the EGR gas becomes the first EGR gas by the high pressure EGR device 50, and the flow rate of the second EGR gas by the low pressure EGR device 60 becomes zero. Therefore, as described with reference to FIG. 8, an increase in pumping loss that occurs when low-pressure EGR is performed is avoided, and instead, the first EGR gas extracted from the exhaust passage 30 upstream from the turbine 22 Since the refrigerant is returned to the intake passage 10 downstream from the compressor 23, the pumping loss is reduced.

  Further, in the second region R2, the flow rate of the first EGR gas by the high pressure EGR device 50 is larger than the flow rate of the second EGR gas by the low pressure EGR device 60, and as described with reference to FIG. In the high load region where torque is required, the torque is improved in the second region R2 on the high speed side by reducing pumping loss, suppressing knocking, decreasing exhaust gas temperature, and the like. Further, by suppressing knocking, the ignition timing can be advanced, and sufficient torque can be obtained even with relatively little fuel, thereby improving fuel efficiency.

  In the second region R2, the engine speed is relatively high and the flow rate of the exhaust gas is large. Therefore, the exhaust throttle valve 40 is opened to cope with this, and the first to third independent exhaust passages 31, 32, 33 are provided. Each variable flow path 39 is opened. As a result, the exhaust gas from each of the cylinders 2 </ b> A to 2 </ b> D is smoothly discharged to the downstream side through both the regular flow path 38 and the variable flow path 39 in each independent exhaust passage 31, 32, 33.

  Further, in the second region R2 other than the fourth region R4, the exhaust gas discharged from each of the cylinders 2A to 2D flows into the turbine 22 of the turbocharger 20 by closing the wastegate valve 43, Sufficient supercharging by the compressor 23 is performed.

  On the other hand, in the fourth region R4, the supercharging pressure control is executed by opening the wastegate valve 43, and the supercharging pressure by the compressor 23 sets the upper limit value provided from the viewpoint of protecting the engine and the turbocharger 20. It is prevented from rising beyond.

[Iii] Third region R3
The third region R3 is a region where both the high pressure EGR and the low pressure EGR can be performed, as can be seen from the setting process of the control map shown in FIG. Therefore, during operation in the third region R3, the ECU 70 executes the following control.
Open both the high pressure EGR valve 53 and the low pressure EGR valve 63.
-Open the exhaust throttle valve 40 (non-execution of independent exhaust throttle control).
-Close the wastegate valve 43.

  That is, both the low pressure EGR and the high pressure EGR are performed in the third region R3. As a result, in the partial load region where the torque is small, the characteristics of the high pressure EGR and the low pressure EGR (response, temperature of the EGR gas, etc.) are taken into consideration, ensuring ignitability, exhaust gas temperature and exhaust pressure depending on the situation. It is possible to suppress excessive rise, achieve simultaneous improvement of combustibility and fuel consumption, and the like.

  In the third region R3, the ECU 70 increases the flow rate of the second EGR gas from the low-pressure EGR device 60 in the region closer to the first region R1 than the flow rate of the first EGR gas from the high-pressure EGR device 50. The high pressure EGR valve 53 and the low pressure EGR valve 63 are controlled so that the flow rate of the first EGR gas from the high pressure EGR device 50 is larger than the flow rate of the second EGR gas from the low pressure EGR device 60 in the region closer to the second region R2. To do. In FIG. 5, the broken lines and arrows shown in the third region R3 schematically show the contents of this control.

  In the third region R3, the exhaust throttle valve 40 is opened, and the variable flow paths 39 in the first to third independent exhaust passages 31, 32, 33 are opened. As a result, the exhaust gas from each of the cylinders 2 </ b> A to 2 </ b> D is smoothly discharged to the downstream side through both the regular flow path 38 and the variable flow path 39 in each independent exhaust passage 31, 32, 33.

  Further, in the third region R3, the exhaust gate exhausted from each of the cylinders 2A to 2D flows into the turbine 22 of the turbocharger 20 by closing the wastegate valve 43, and is supercharged by the compressor 23. Well done.

(4) Operation, etc. The engine according to the present embodiment includes a turbine 22 driven by the energy of exhaust gas passing through the exhaust passage 30 and a compressor 23 driven by the turbine 22 to pressurize the air in the intake passage 10. A turbocharged engine including a turbocharger 20 including the following characteristic configuration.

  First, a high pressure EGR passage 51 that connects the exhaust passage 30 upstream of the turbine 22 and the intake passage 10 downstream of the compressor 23, and a high pressure EGR valve 53 that adjusts the flow rate of the first EGR gas that passes through the high pressure EGR passage 51. The 1st EGR apparatus 50 containing these is provided.

  Further, a low pressure EGR passage 61 that communicates the exhaust passage 30 downstream from the turbine 22 and the intake passage 10 upstream from the compressor 23, and a low pressure EGR valve 63 that adjusts the flow rate of the second EGR gas passing through the low pressure EGR passage 61. The 2nd EGR apparatus 60 containing these is provided.

  Further, in the engine operating region, the flow rate of the second EGR gas is higher than the flow rate of the first EGR gas in the first region R1 on the low speed and high load side, and the first region in the second region R2 on the high speed and high load side. The ECU 70 that controls the high pressure EGR valve 53 and the low pressure EGR valve 63 is provided so that the flow rate of the EGR gas is greater than the flow rate of the second EGR gas.

  According to this configuration, in the high load region where torque is required, in the first region R1 on the low speed side, the flow rate of the second EGR gas by the low pressure EGR device 60 is higher than the flow rate of the first EGR gas by the high pressure EGR device 50. Is also a lot. More specifically, in the present embodiment, the flow rate of the first EGR gas by the high pressure EGR device 50 is zero, and the second EGR gas by the low pressure EGR device 60 is recirculated to the intake passage 10. Thereby, the supercharging efficiency is improved in the low speed and high load range, and the torque is improved. That is, as described with reference to FIG. 8, the second EGR gas from the low pressure EGR device 60 is recirculated to the intake passage 10 upstream from the compressor 23, so that the amount of work of the compressor 23 increases and the compressor 23 The discharge flow rate increases. Therefore, even if the supercharging pressure and thus the pressure ratio of the compressor 23 are increased and the engine operating state is the same, the operating point of the compressor 23 moves from the initial point P1 to the point P2 where the discharge flow rate and pressure ratio of the compressor 23 have increased. Moreover, since the second EGR gas from the low pressure EGR device 60 is extracted from the exhaust passage 30 downstream of the turbine 22, the driving force of the turbine 22 does not decrease. Therefore, the operation point P2 of the compressor 23 is located where the compressor efficiency is improved, the supercharging efficiency is improved, and the supercharging amount is efficiently increased. As described above, by relatively increasing the flow rate of the second EGR gas in the first region R1 on the low speed and high load side, the supercharging efficiency is improved and the torque is improved.

  Further, according to the above configuration, in the high load region where torque is required, in the second region R2 on the high speed side, the flow rate of the first EGR gas by the high pressure EGR device 50 is the same as that of the second EGR gas by the low pressure EGR device 60. More than the flow rate. More specifically, in the present embodiment, the flow rate of the second EGR gas by the low pressure EGR device 60 is zero, and the first EGR gas by the high pressure EGR device 50 is recirculated to the intake passage 10. As a result, torque is improved in a high speed and high load range. That is, as described with reference to FIG. 6, the first EGR gas by the high-pressure EGR device 50 is extracted from the exhaust passage 30 upstream from the turbine 22 and recirculated to the intake passage 10 downstream from the compressor 23. Therefore, the exhaust pressure upstream of the turbine 22 is reduced, and the intake pressure downstream of the compressor 23 increases. As a result, since the pumping loss is reduced, the torque is improved by relatively increasing the flow rate of the first EGR gas in the second region R2 on the high speed and high load side. Furthermore, the low temperature EGR gas is introduced into the combustion chamber, the combustion temperature is lowered, knocking is suppressed and the ignition timing can be advanced, and the amount of air is increased due to a decrease in the exhaust gas temperature. Torque is improved in the second region R2 on the high load side. In addition, by suppressing knocking, the ignition timing can be advanced, and sufficient torque can be obtained even with relatively little fuel, thereby improving fuel efficiency.

  As described above, according to the present embodiment, a turbocharged engine in which the high-pressure EGR device 50 and the low-pressure EGR device 60 are properly used from the viewpoint of improving torque in a high load range where torque is required is provided.

  In particular, in the present embodiment, the ECU 70 opens the low pressure EGR valve 63 and closes the high pressure EGR valve 53 in the first region R1, and opens the high pressure EGR valve 53 and opens the low pressure EGR valve in the second region R2. 63 is closed.

  According to this configuration, in the first region R1 on the low speed and high load side, only the second EGR gas by the low pressure EGR device 60 is recirculated to the intake passage 10, and in the second region R2 on the high speed and high load side, the second region is set by the high pressure EGR device 50. Since only one EGR gas is recirculated to the intake passage 10, the above-described torque improving effect is further increased in both regions R1 and R2.

  Next, in the present embodiment, the ECU 70 performs EGR using both the high pressure EGR device 50 and the low pressure EGR device 60 in the third region R3 excluding the first region R1 and the second region R2 in the engine operation region. Do.

  According to this configuration, in the third region R3 on the low to medium load side where the torque is small in the engine operation region, that is, in the partial load region, EGR is performed using both the high pressure EGR device 50 and the low pressure EGR device 60. Done. For example, when the EGR is performed using the high-pressure EGR device 50, the first EGR gas is extracted from the exhaust passage 30 and returned to the intake passage 10 at a portion close to the engine body, so that the temperature of the first EGR gas is relatively high. It is introduced into the combustion chamber 3 in a state. Therefore, ignitability can be ensured by performing EGR using the high-pressure EGR device 50. On the other hand, when the EGR is performed using the low-pressure EGR device 60, the second EGR gas is extracted from the exhaust passage 30 at a portion far from the engine body and is returned to the intake passage 10, so that the temperature is relatively low. It is introduced into the combustion chamber 3 in a state. Therefore, by performing EGR using the low pressure EGR device 60, it is possible to suppress an excessive increase in the exhaust gas temperature and the exhaust pressure. By combining these, it is possible to improve combustibility and improve fuel efficiency by reducing pumping loss. The ratio between the flow rate of EGR gas from the high pressure EGR device 50 and the flow rate of EGR gas from the low pressure EGR device 60 is determined according to the situation, taking into consideration the characteristics of the high pressure EGR and low pressure EGR (response, temperature of EGR gas, etc.). do it.

  Next, in the present embodiment, in the third region R3, the ECU 70 causes the flow rate of the second EGR gas by the low pressure EGR device 60 to be the first by the high pressure EGR device 50 in the region closer to the first region R1 on the low speed and high load side. The flow rate of the first EGR gas by the high pressure EGR device 50 is higher than the flow rate of the second EGR gas by the low pressure EGR device 60 in a region closer to the second region R2 on the high speed and high load side. The high pressure EGR valve 53 and the low pressure EGR valve 63 are controlled so as to increase.

  According to this configuration, when the operating state of the engine approaches the first region R1 or the second region R2 in the third region R3 and the operating state of the engine changes from the third region R3 to the first region R1 or the second region R2. Responsiveness of EGR control at the time of transition such as transition is improved.

  Next, in the present embodiment, the ECU 70 causes the valve overlap in which both the intake valve 6 and the exhaust valve 7 are opened when the pressure in the intake port 4 becomes higher than the pressure in the exhaust port 5 in the first region R1. The intake valve 6 that opens and closes the intake port 4 and the exhaust valve 7 that opens and closes the exhaust port 5 of the cylinders 2A to 2D are controlled so that the period OL is formed or expanded.

  According to this configuration, in the first region R1 on the low speed and high load side, an intake blow-through flow that blows through the combustion chamber 3 from the intake side to the exhaust side is generated during the valve overlap period OL. Therefore, the scavenging effect of removing the residual gas in the cylinders 2A to 2D is obtained, knocking is suppressed, and the ignition timing can be advanced. As a result, the aforementioned torque improving action in the first region R1 is further increased. Further, by suppressing knocking, the ignition timing can be advanced, and sufficient torque can be obtained even with relatively little fuel, thereby improving fuel efficiency. Next, this point will be described in more detail.

  That is, in the present embodiment, the low-pressure EGR valve 63 is opened and the exhaust gas after passing through the turbine 22 in the operation region (first region R1, second region R2) where the flow rate of the exhaust gas is a predetermined value or less. A part is returned to the intake passage 10 upstream of the compressor 23 as EGR gas. Then, since the intake air mixed with the EGR gas and the fresh air flows into the compressor 23, the flow rate of the intake air pumped by the compressor 23 increases. This leads to an increase in the pressure ratio of the compressor 23, that is, an increase in the supercharging pressure, so that the supercharging pressure can be increased to a value equal to or higher than the exhaust pressure even under a condition where the load is not so high.

  Since the valve overlap period OL of the intake and exhaust valves 6 and 7 is formed or expanded in the first region R1 with a high load, each cylinder has a synergistic effect with the increase in the supercharging pressure higher than the exhaust pressure. A blow-through flow through which intake air blows from the intake port 4 of 2A to 2D to the exhaust port 5 is generated with sufficient strength (see arrows Wi and We in FIG. 2). Such a blow-through flow exhibits a scavenging effect of removing residual gas in each cylinder 2A to 2D. Therefore, in each of the cylinders 2A to 2D, an environment in which knocking hardly occurs despite the operation in a high load region. Is created. This makes it possible to advance the ignition timing, so that a sufficient output can be obtained even with a relatively small amount of fuel, leading to an improvement in fuel consumption.

  In particular, in the present embodiment, the exhaust passage 30 of the engine has the first and third independent exhaust passages 31 and 33 whose upstream ends are connected to the exhaust port 5 of one cylinder (2A or 2D), and the exhaust order is the same. A second independent exhaust passage 32 having an upstream end connected to each exhaust port 5 of a plurality of non-continuous cylinders (2B and 2C) and one downstream end of each of the independent exhaust passages 31, 32, 33 And an exhaust throttle valve 40 that variably sets the flow area of the exhaust gas passing through the independent exhaust passages 31, 32, 33. The ECU 70 closes the exhaust throttle valve 40 and closes the independent exhaust passages 31, 32, 32 in addition to forming or expanding the valve overlap period OL of the intake / exhaust valves 6, 7 during operation in the first region R 1. Independent exhaust throttling control is performed to reduce the flow area in the engine 33. According to such a configuration, the residual gas can be scavenged more reliably by the so-called ejector effect that occurs in association with the blow-down of the exhaust gas (the high-pressure, high-speed exhaust flow generated immediately after the exhaust valve 7 is opened). Can do. The ejector effect is an action of sucking a driven fluid by using a negative pressure generated around a high-speed jet.

  FIG. 9 is a graph in which the abscissa indicates the crank angle of a specific cylinder and the ordinate indicates the pressure of exhaust gas discharged from each of the cylinders 2A to 2D (measured value at the exhaust collecting portion 34). In this graph, BDC, TDC, BDC... On the horizontal axis respectively indicate the bottom dead center and top dead center of the specific cylinder, and the interval from BDC to TDC or TDC to BDC is 180 ° CA in terms of crank angle. It is. The engine according to this embodiment is a four-cylinder engine, and the ignition interval between the cylinders 2A to 2D is 180 ° CA. Accordingly, the engine is generated immediately after the exhaust valves 7 of the cylinders 2A to 2D are opened. The exhaust gas blowdown occurs every 180 ° CA. For this reason, the BDC, TDC, BDC... Of the specific cylinder and the blowdown occurrence position substantially coincide with each other.

  In the graph of FIG. 9, when the specific cylinder is in the vicinity of the exhaust top dead center (TDC), high-speed exhaust gas is ejected by blowdown from the succeeding cylinder that reaches the exhaust stroke next to the specific cylinder ( (See arrow We0 in FIG. 2). This blowdown gas generates a strong negative pressure around it when it flows into the exhaust collecting part 34. In particular, in the first region R1, since the independent exhaust throttle control for reducing the flow area in the independent exhaust passages 31, 32, 33 is executed, the flow speed of the blowdown gas discharged from each cylinder 2A to 2D is made faster. And a stronger negative pressure is generated. This strong negative pressure acts on the exhaust port 5 of the specific cylinder by going back the independent exhaust passage (any one of 31, 32, 33) and lowers the pressure of the exhaust port 5 (the waveform shown by the broken line in FIG. 9). And exhaust gas is sucked out through the exhaust port 5 (ejector effect).

  In addition, at this time, in the first region R1, such a strong ejector effect is obtained, and the valve overlap period OL of the intake and exhaust valves 6 and 7 is formed or expanded as described above. A large drop ΔH as shown in FIG. 9 is generated between the pressure of the intake port 4 (that is, the supercharging pressure) and the pressure of the exhaust port 5 during the valve overlap period OL of 2A to 2D. This pressure difference ΔH enhances the blow-through flow (see arrows Wi and We in FIG. 2) through which intake air blows from the intake port 4 to the exhaust port 5 and further promotes scavenging of residual gas.

  Further, in the first region R1, the exhaust pressure peak value (blowdown peak) due to the blowdown is further increased with the independent exhaust throttle control. This is because by executing the independent exhaust throttle control, the variable flow passage 39 in each of the independent exhaust passages 31, 32, 33 is shut off, the exhaust gas flow area is reduced, and the exhaust gas is concentrated in a short time. Because it started to flow. This exhibits the effect of increasing the supercharging pressure (dynamic pressure supercharging effect).

  Here, the effective exhaust time (blow-down period) per exhaust stroke becomes shorter as the exhaust pressure peak value (blow-down peak) appearing immediately after the exhaust valve 7 is opened is higher. On the other hand, it is known that the effect of dynamic pressure supercharging has a quadratic characteristic with respect to the blowdown peak. Therefore, as in this embodiment, when the blowdown peak is increased by the independent exhaust throttle control, the reduction due to the shortening of the blowdown period is subtracted compared to the case where the independent exhaust throttle control is not executed. The average driving force that the turbine 22 receives from the exhaust gas will increase. In the present embodiment, since the turbocharging device 20 can further increase the supercharging capability due to such a dynamic pressure supercharging effect, a high supercharging is performed while the low pressure EGR is performed in the first region R1 where the load is high. The engine torque can be increased by securing a sufficient amount of fresh air by the pressure.

  Next, in the present embodiment, the ECU 70 opens the wastegate valve 43 of the turbocharger 20 in the fourth region R4 that is set on the high speed and high load side in the second region R2.

  According to this configuration, the fourth region R4 is set on the further high-speed and high-load side in the second region R2 on the high-speed and high-load side, and the wastegate valve 43 is opened in the fourth region R4, thereby driving the turbine 22 Power is reduced. Therefore, for example, the supercharging pressure control for preventing the supercharging pressure by the compressor 23 of the turbocharger 20 from rising beyond the upper limit value provided from the viewpoint of protecting the engine and the supercharger 20 is the fourth region. It is executed in R4.

  In the embodiment, the ratio of the flow rate of the second EGR gas by the low pressure EGR device 60 and the flow rate of the first EGR gas by the high pressure EGR device 50 in the first region R1 is set to 100: 0. As long as the flow rate of the second EGR gas is higher than the flow rate of the first EGR gas, the present invention is not limited to this. Similarly, in the embodiment, the ratio of the flow rate of the first EGR gas by the high pressure EGR device 50 and the flow rate of the second EGR gas by the low pressure EGR device 60 in the second region R2 is set to 100: 0. As long as the flow rate of the first EGR gas is higher than the flow rate of the second EGR gas, the present invention is not limited to this.

  In the above embodiment, the separate exhaust collecting portion 34 is provided between the first to third independent exhaust passages 31, 32, 33 and the turbine housing 21, but the separate exhaust collecting portion 34 is omitted. Thus, the downstream end of each independent exhaust passage 31, 32, 33 may be directly connected to the turbine housing 21. In this case, the upstream portion of the turbine housing 21 (the portion located upstream of the turbine 22) functions as an exhaust collecting portion.

  Further, in the above-described embodiment, the second independent exhaust passage 32 branched in a bifurcated manner is connected to the second cylinder 2B and the third cylinder 2C, and the first and second single tubes are connected to the first cylinder 2A or the fourth cylinder 2D. By connecting the three independent exhaust passages 31 and 33, the three independent exhaust passages 31, 32 and 33 are provided for the four cylinders 2A to 2D. By connecting the same single tubular exhaust passage to all the cylinders 2A to 2D, four independent exhaust passages having the same number as the cylinders 2A to 2D may be provided.

  In the above-described embodiment, each valve mechanism for the intake valve 6 and the exhaust valve 7 is provided with the VVT 16 for changing the valve opening / closing timing. However, if the valve overlap period OL can be changed according to the operating conditions. Alternatively, the VVT 16 may be provided only in one of the intake valve 6 and the exhaust valve 7.

  In the above embodiment, the low pressure EGR passage 61 is connected to the exhaust passage 30 downstream of the catalytic converter 36, but may be connected upstream of the catalytic converter 36 as long as it is downstream of the turbine 22.

  In the above embodiment, in order to enhance the scavenging effect in the first region R1, the ejector effect and the valve overlap are used, and further, the independent exhaust throttle control is executed. However, the present invention is not limited to this. For example, from the exhaust manifold Uses twin scroll turbo and valve overlap in which the flow path to the turbine housing is divided into two to reduce interference of exhaust energy from multiple cylinders, or continuously variable valve lift device (CVVL: Continuously Variable Valve Lifting) The scavenging effect can also be enhanced by using (Mechanism) and valve overlap.

2A to 2D cylinders 4 Intake port 5 Exhaust port 6 Intake valve 7 Exhaust valve 10 Intake passage 16 VVT
20 Turbocharger 22 Turbine 23 Compressor 30 Exhaust passage 31 First independent exhaust passage 32 Second independent exhaust passage 33 Third independent exhaust passage 34 Exhaust collecting portion 40 Exhaust throttle valve 42 Bypass passage 43 Westgate valve 50 High pressure EGR device ( First EGR device)
51 High-pressure EGR passage 53 High-pressure EGR valve (first EGR valve)
60 Low pressure EGR device (second EGR device)
61 Low pressure EGR passage 63 Low pressure EGR valve (second EGR valve)
70 ECU (EGR control means, intake / exhaust valve control means, wastegate valve control means)
Ni intercept rotation speed No intermediate rotation speed OL valve overlap period R1 first region R2 second region R3 third region R4 fourth region

Claims (5)

A turbocharged engine comprising a turbocharger including a turbine driven by energy of exhaust gas passing through an exhaust passage and a compressor driven by the turbine to pressurize air in the intake passage,
A first EGR device including an EGR passage communicating with an exhaust passage upstream of the turbine and an intake passage downstream of the compressor, and a first EGR valve for adjusting a flow rate of the first EGR gas passing through the EGR passage. When,
A second EGR device including an EGR passage communicating with an exhaust passage downstream of the turbine and an intake passage upstream of the compressor, and a second EGR valve for adjusting a flow rate of a second EGR gas passing through the EGR passage. When,
EGR control means for controlling the first EGR valve and the second EGR valve,
In the engine operating region, the EGR control means is configured such that the flow rate of the second EGR gas is higher than the flow rate of the first EGR gas in the first region on the low speed and high load side, and the first region on the high speed and high load side. In the second region, the first EGR valve and the second EGR valve are controlled so that the flow rate of the first EGR gas is larger than the flow rate of the second EGR gas. Supercharged engine. The turbocharged engine according to claim 1,
The EGR control means opens the second EGR valve in the first region and closes the first EGR valve, and opens the first EGR valve in the second region. A turbocharged engine characterized by closing the second EGR valve. The turbocharged engine according to claim 1 or 2,
In the engine operating region, the EGR control means uses both the first EGR device and the second EGR device in the third region excluding the first region and the second region. In the third region, the region closer to the first region has a higher flow rate of the second EGR gas than the flow rate of the first EGR gas, and is closer to the second region. The turbocharged engine, wherein the first EGR valve and the second EGR valve are controlled so that the flow rate of the first EGR gas is larger than the flow rate of the second EGR gas. . The turbocharged engine according to any one of claims 1 to 3,
Intake and exhaust valve control means for controlling an intake valve for opening and closing the intake port of the cylinder and an exhaust valve for opening and closing the exhaust port are provided,
In the first region, the intake / exhaust valve control means is configured to form or expand a valve overlap period in which both the intake valve and the exhaust valve are opened when the pressure in the intake port becomes higher than the pressure in the exhaust port. The turbocharged engine is characterized by controlling the intake valve and the exhaust valve. The turbocharged engine according to any one of claims 1 to 4,
A turbocharged engine comprising wastegate valve control means for opening a wastegate valve of a turbocharger in a fourth region set on the high speed and high load side in the second region.

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