JP2014080898A - Multi-cylinder engine with turbo supercharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve fuel consumption performance while enhancing torque in a wide operation region covering from a low speed region to a high speed region of an engine.SOLUTION: An engine includes a plurality of independent exhaust passages 31, 32, 33 corresponding to respective cylinders, an exhaust gathering part 34 where the downstream ends of the respective independent exhaust passages 31, 32, 33 are gathered into one unit, an exhaust throttle valve 40 for variably setting the distribution area of exhaust gas passing through the inside of the independent exhaust passages 31, 32, 33, a turbo supercharger 20 including a turbine 22 disposed on the downstream side of the exhaust gathering part 34, and control means for controlling the opening/closing operation of the exhaust throttle valve 40. The specifications of the turbo supercharger 20 are set so that an intercept revolving speed is 1/3 or higher of the rated revolving speed of the engine. The control means executes independent exhaust throttle control to close the exhaust throttle valve 40, in a predetermined operation region set to the lower speed side than the intercept revolving speed.

Description

  The present invention relates to a multi-cylinder engine with a turbocharger that includes a plurality of cylinders and a turbocharger that is driven by the energy of exhaust gas discharged from each cylinder.

  Conventionally, in order to achieve higher engine output using exhaust energy in a wider range of operation, it has been proposed to adopt a so-called two-stage supercharging structure in which two turbochargers are connected in series (For example, see Patent Document 1 below).

  Specifically, the turbocharger system described in Patent Literature 1 includes a high-pressure stage turbocharger and a low-pressure stage turbocharger. The high-pressure stage turbocharger has a high-pressure stage turbine provided in the exhaust passage of the engine and a high-pressure stage compressor provided in the intake passage of the engine and driven by the high-pressure stage turbine. Has a low-pressure stage turbine provided in the exhaust passage downstream of the high-pressure stage turbine, and a low-pressure stage compressor provided in the intake passage upstream of the high-pressure compressor and driven by the low-pressure stage turbine. doing.

  In Patent Document 1, the high-pressure turbocharger is mainly operated in an operation region where the engine rotational speed is low and the exhaust energy is small, while the high-pressure turbine is operated in an operation region where the engine rotational speed is high and the exhaust energy is large. Only a low-pressure stage turbocharger is operated by opening a valve (a high-pressure stage turbine bypass valve) or the like provided in a bypass passage to be bypassed.

JP 2012-97606 A

  When the two types of turbochargers are used properly according to the operation region as in Patent Document 1, a sufficient supercharging pressure can be obtained in a wide operation region from the low speed range to the high speed range. High engine torque can be generated.

  However, since the technique disclosed in Patent Document 1 requires two types of turbochargers, there is a problem that, as a matter of course, the manufacturing cost increases and the volume and weight of the entire engine increase. For this reason, it is difficult to adopt the above-described structure using two turbochargers, particularly for compact cars and the like whose sales unit price is not high.

  Therefore, it is conceivable to use only one relatively small turbocharger from the viewpoint of placing more emphasis on the ease of handling the engine (good response when the accelerator is depressed). However, in this case, not only the torque in the engine high speed region is insufficient, but also the flow resistance of the exhaust gas passing through the turbine becomes large especially at a large flow rate, so that the fuel efficiency in the high speed region deteriorates. Problem arises.

  The present invention has been made in view of the circumstances as described above, and can increase the torque in a wide operating range covering from the low speed range to the high speed range of the engine, and is excellent in fuel efficiency. An object of the present invention is to provide an attached multi-cylinder engine.

  In order to solve the above problems, the present invention is a multi-cylinder engine with a turbocharger comprising a plurality of cylinders and a turbocharger driven by the energy of exhaust gas discharged from each cylinder. A plurality of independent exhaust passages whose upstream ends are connected to exhaust ports of one cylinder or a plurality of cylinders whose exhaust order is not continuous, and exhaust in which the downstream ends of each independent exhaust passage are gathered together. A turbocharger comprising: a collecting portion; an exhaust throttle valve that variably sets a flow area of exhaust gas passing through the independent exhaust passage; and a control unit that controls an opening / closing operation of the exhaust throttle valve. A turbine provided on the downstream side of the exhaust collecting portion; and a compressor provided in an intake passage of the engine and driven by the turbine. The supercharging pressure of the compressor is predetermined at a full engine load. When the engine speed at which the upper limit value is reached is defined as the intercept speed, the turbocharger is set so that the intercept speed is 1/3 or more of the rated speed of the engine. The control means executes independent exhaust throttle control for closing the exhaust throttle valve in a predetermined operation region set at a lower speed side than the intercept rotation speed (Claim 1). .

  According to the present invention, in the operation region where the rotational speed is lower than the intercept rotational speed, the independent exhaust throttle control is performed to reduce the flow area in each independent exhaust passage by closing the exhaust throttle valve. The pressure peak value of exhaust gas (blow-down gas) discharged at high speed immediately after opening the valve can be increased. As a result, the driving force acting on the turbine of the turbocharger can be increased (dynamic pressure supercharging effect), and the negative pressure generated in the exhaust collecting part along with the blow-down of the exhaust can be increased to reduce the residual gas in the cylinder. Scavenging can be promoted (ejector effect). As a result of these effects, it is possible to improve the supercharging capability in the engine low speed range and sufficiently increase the engine torque.

  Here, in the present invention, the intercept rotation speed is set to 1/3 or more of the rated rotation speed of the engine. This means that a relatively large turbine is used as the turbine of the turbocharger. Means. When the turbine is large, it is inherently difficult to sufficiently ensure the supercharging capability in the engine low speed range, and the torque in the low speed range tends to be low. In order to solve such a problem, in the present invention, by exhibiting the dynamic pressure supercharging effect and the ejector effect based on the independent exhaust throttle control, it is possible to sufficiently compensate for the lack of supercharging capability in the engine low speed range. The above problems can be effectively solved and the torque in the low speed range can be increased.

  On the other hand, since the exhaust gas flow rate is higher on the higher speed side than the intercept rotation speed, a large driving force can be applied to the turbine without performing the above-described independent exhaust throttle control, etc. The supercharging capability of the supercharger can be sufficiently increased. Moreover, in the present invention, since the turbine is large, the supercharging capability in the high speed region of the engine is inherently high, and the peak value of the supercharging pressure can be set to a sufficiently high value.

  Furthermore, if the turbine is large, the exhaust gas flow resistance is unlikely to increase in the high speed region of an engine with a large exhaust gas flow rate. In addition, in the present invention, the flow area in the independent exhaust passage is expanded by stopping the independent exhaust throttle control in a region higher than the intercept rotation speed, so that the pumping loss can be greatly reduced. The fuel consumption performance in the engine high speed range can be effectively improved.

  As described above, according to the engine of the present invention, a relatively large turbine is used to improve the torque and fuel consumption in the engine high speed region, while executing the independent exhaust throttle control or the like in the engine low speed region. The torque can be improved by the dynamic pressure supercharging effect and the ejector effect. As a result, high torque can be generated in a wide driving range covering the low speed range to the high speed range of the engine, and the fuel efficiency can be improved.

  In the present invention, preferably, at least the downstream portion of each independent exhaust passage is divided into two flow paths by a partition extending along the flow direction of the exhaust gas, and the exhaust throttle valve is configured by the two flow paths. One of them is provided so as to be opened and closed (Claim 2).

  According to this configuration, the flow area in the independent exhaust passage can be changed with a simple configuration in which one of the two flow paths partitioned by the partition wall is blocked or opened by the exhaust throttle valve. The execution and stop of the exhaust throttle control can be switched quickly and reliably.

  In the present invention, preferably, it further includes a variable valve mechanism capable of changing an opening / closing timing of at least one of the intake valve and the exhaust valve of each cylinder, and the control means is at least in an operation region in which the independent exhaust throttle control is executed. The valve variable mechanism is controlled such that a valve overlap period during which both the intake valve and the exhaust valve are opened is ensured by a predetermined amount or more (Claim 3).

  According to this configuration, when the above-described independent exhaust throttle control is executed in a region lower than the intercept rotation speed, the ejector effect is exerted on the cylinder during the valve overlap period, so that the exhaust port blows through from the intake port to the exhaust port. Intake air flow (blow-through) occurs. As a result, scavenging is further promoted and the flow rate of the exhaust gas is increased to increase the driving force of the turbine, so that the torque in the engine low speed region can be increased more effectively.

  In the present invention, it is preferable to further include an electric supercharger that pressurizes intake air by a driving force of an electric motor, and the control means is the specific operation region set in the region of the slowest and high load side. The electric supercharger is activated (claim 4).

  According to this configuration, since the supercharging capability is supplemented by the operation of the electric supercharger in the extremely low speed region where the turbocharging capability of the turbocharger is difficult to be exhibited, the torque in the extremely low speed region can be reliably increased. it can. Note that the use of the electric supercharger in this case is only auxiliary, so the performance of the electric supercharger does not have to be high, and the cost increases and the weight increases due to the addition of the electric supercharger. Can be minimized.

  As described above, according to the multi-cylinder engine with a turbocharger of the present invention, it is possible to increase the torque in a wide operating range covering the low speed range to the high speed range of the engine, and to improve the fuel efficiency performance. Can do.

1 is a diagram illustrating an overall configuration of a multi-cylinder engine with a turbocharger according to an embodiment of the present invention. It is a side view which shows typically the gas flow in the exhaust manifold of the said engine. It is a perspective view of the said exhaust manifold. It is a perspective view which shows the exit part of the independent exhaust passage of the said exhaust manifold. It is a graph of the performance curve which shows the characteristic of the compressor of the said turbocharger. 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 several area | region for every kind of control content. It is a graph which shows the change according to the crank angle of the exhaust pressure of the said engine. It is a time chart which shows the opening / closing timing of the intake / exhaust valve of the said engine for every cylinder. It is the figure which piled up and showed the change of the operation point of the compressor at the time of an accelerator full opening on the graph which modeled the performance curve of the compressor.

(1) Overall Configuration of Engine FIGS. 1 and 2 show a multi-cylinder engine with a turbocharger according to an embodiment of the present invention. The engine shown in this figure is a 4-cycle spark ignition type multi-cylinder engine mounted on a vehicle as a power source for traveling. Specifically, the engine of the present embodiment includes an in-line four-cylinder engine body 1 having four cylinders 2A to 2D arranged in a row, an intake manifold 10 for introducing air into the engine body 1, and an engine body. 1 and an exhaust manifold 30 for exhausting the exhaust gas generated in 1.

  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 manifold 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 manifold 10 into the combustion chambers of the cylinders 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 chambers of the cylinders 2A to 2D to the exhaust manifold 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. VVT 16 is an abbreviation for Variable Valve Timing Mechanism, and is a variable valve mechanism for variably setting the opening / closing timing 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 the present 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. 9 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 manifold 10 has four independent intake passages 11 communicating with the intake ports 4 of the cylinders 2A to 2D, and a surge provided in common on the upstream side of each independent intake passage 11 (upstream side in the flow direction of intake air). And a tank 12. A single intake passage 13 is provided further upstream of the surge tank 12. The intake passage 13 has an openable / closable throttle valve 14 for adjusting the intake air amount, and a turbocharger described later. An intercooler 15 for cooling the air compressed by the machine 20 is provided.

  As shown in FIGS. 1 to 4, the exhaust manifold 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. And an exhaust collecting portion 34 in which end portions (end portions on the downstream side in the exhaust gas flow direction) are gathered. A single exhaust passage 35 is provided further downstream of the exhaust collecting portion 34. In the exhaust passage 35, a catalytic converter 36 incorporating a catalyst such as a three-way catalyst, a silencer (not shown), and the like. Is provided.

  As described above, in this 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 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 will be 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 will be 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 this 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 into 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). Therefore, the exhaust collecting portion 34 is formed on the downstream side of each independent exhaust passage 31 to 33.

  The single tubular first independent exhaust passage 31 and the third independent exhaust passage 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 4, the downstream portions of the first and third independent exhaust passages 31 and 33 and the downstream portion of the second independent exhaust passage 32 (common passage portion 32 c) 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 manifold 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, 33. The 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, the flow located on the lower side of FIG. 4). The passage area in each independent exhaust passage 31, 32, 33 is changed by blocking the passage 39) so that it can be opened and closed. 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, 33 as the shaft and the valve body are driven to rotate by the drive source. .

  The engine of this embodiment is equipped with a turbocharger 20 and an electric supercharger 26.

  The turbocharger 20 is a supercharger that is driven by the energy of the exhaust gas discharged from the engine body 1, and is located immediately downstream of the exhaust collecting portion 34 of the exhaust manifold 30 (between the exhaust collecting portion 34 and the exhaust passage 35. A turbine housing 21 provided between the turbine housing 21, a turbine 22 provided in the turbine housing 21, a compressor 23 provided in the intake passage 13, and a connecting shaft 24 that connects the turbine 22 and the compressor 23 to each other. And have. When the exhaust gas is exhausted 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 exhaust manifold 30, thereby causing the turbine 22 to flow. Receiving exhaust gas energy, it 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 passage 13 is pressurized, and each cylinder of the engine body 1 is compressed. Pumped to 2A-2D.

  Unlike the turbocharger 20, the electric supercharger 26 has a compressor (not shown) that is directly driven by an electric motor 27, and is driven by the driving force of the electric motor 27 (regardless of exhaust energy). The intake air in the intake passage 13 is pressurized.

  The exhaust passage 35 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 passage 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 exhaust manifold 30 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 manifold 30 and the surge tank 12 of the intake manifold 10 are connected to each other via an EGR passage 45. The EGR passage 45 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 EGR passage 45 is provided with an EGR cooler 46 for cooling the EGR gas (exhaust gas returned to the intake system), and an openable EGR valve 47 for controlling the flow rate of the EGR gas passing through the EGR passage 45. It has been.

(2) Characteristics of Turbocharger In this embodiment, a combination of a relatively large turbine 22 and a compressor 23 is used as the turbocharger 20. The reason is as follows.

  Conventionally, from the viewpoint of improving torque response particularly when accelerating from a low speed range, the size of the turbine is often reduced relative to the compressor so that a high pressure ratio can be obtained even in a low speed range where the flow rate of exhaust gas is small. It was. The turbine cannot rotate at high speed without a certain amount of exhaust gas, but if it is a small turbine, it can rotate at high speed even if the flow rate of exhaust gas is small, so the pressure ratio of the compressor in the low speed range is increased ( In other words, the supercharging ability in the low speed range can be increased).

  FIG. 5 is a performance curve graph showing the characteristics of the compressor, in which 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. 5, each line SL, RL, CL represents a surge line, a rotation limit line, and a choke line, respectively, and a region surrounded by these lines is a compressor operable region. 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.

  As has been widely used in the past, when a relatively small turbine is used, the rotational speed of the turbine immediately increases during acceleration from the low speed range of the engine, and the pressure ratio of the compressor also increases accordingly. Rise relatively sharply. Thus, since a high pressure ratio can be obtained even with a small flow rate, as a characteristic of the compressor at the time of acceleration, a curve with a large slope such as the curve L2 in FIG. 5 is obtained. As a result, a relatively high boost pressure can be obtained even in the low speed region of the engine, so that the torque of the engine in the low speed region increases and the acceleration response from the low speed region is improved. In the curve L2, the pressure ratio reaches a peak from the middle (shifts to a horizontal straight line), which is supercharged to the upper limit value provided from the viewpoint of protecting the engine and the turbocharger. This indicates that the Westgate valve has been opened because pressure has been reached.

  As described above, downsizing the turbine is advantageous for reinforcing the torque in the low speed region of the engine, but on the other hand, in the high speed region of the engine, the flow resistance of the exhaust gas when passing through the turbine. However, there is a disadvantage that the pumping loss increases. Further, since the vicinity of the surge line SL of the compressor is frequently used, it cannot be said that it is an efficient usage when viewed from the compressor alone.

  In contrast, in this embodiment, a relatively large turbine 22 is used. For this reason, when the engine is accelerated from a low speed region, as shown by a curve L1 in FIG. 5, a portion where the efficiency of the compressor 23 is high (near the contour ridge) is frequently used. Is preferable.

  However, in a situation where the flow rate of the exhaust gas is small as in the early stage of acceleration, the rotational speed of the turbine 22 does not increase easily, and the pressure ratio of the compressor 23 increases only slowly. This means that the torque in the engine low speed region does not increase sufficiently, and the acceleration response from the low speed region becomes worse.

  On the other hand, after the engine rotational speed has increased to some extent, a large pressure ratio can be obtained in accordance with the rotational increase of the turbine 22, and sufficient torque can be secured. In addition, the flow resistance when the exhaust gas flow rate is high (the resistance when the exhaust gas passes through the turbine 22) is smaller than when the turbine is small, thus reducing the pumping loss in the engine high speed range and improving fuel efficiency. Can be made.

  As described above, the configuration of the present embodiment in which the turbine 22 is enlarged is advantageous in terms of securing torque in the high speed range and fuel consumption, but has a problem that the torque in the low speed range cannot be sufficiently produced. Therefore, in order to cope with such a problem, in the present embodiment, the torque in the low speed range is executed by executing the independent exhaust throttle control in which the exhaust throttle valve 40 is closed and the variable flow path 39 is shut off in the low speed range. The shortage is made up (details will be described later).

(3) 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) 50. As is well known, the ECU 50 is a microprocessor including a CPU, a ROM, a RAM, and the like, and corresponds to a control unit according to the present invention.

  Information from various sensors is input to the ECU 50. 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 cooling water. An air flow sensor SN3 for detecting the flow rate of the intake air passing through the intake passage 13, and an accelerator opening sensor SN4 for detecting the opening (accelerator opening) of an unillustrated accelerator pedal operated by the driver; The information detected by each of these sensors is sequentially input to the ECU 50 as an electrical signal.

  ECU50 controls each part of an engine, performing various calculations etc. based on the input signal from said each sensor (SN1-SN4 etc.). That is, the ECU 50 includes the spark plug 8, the injector 9, the VVTs 16 and 16 for intake and exhaust valves, the throttle valve 14, the exhaust throttle valve 40, the wastegate valve 43, the EGR valve 47, and the electric motor 27 for the electric supercharger 26. The control signal for driving is output to each of these devices based on the result of the above calculation and the like.

(4) Control according to operation region Next, a specific example of engine control performed by the ECU 50 will be described with reference to the control map of FIG.

  In FIG. 7, WOT represents the full load line of the engine (engine torque when the accelerator is fully opened). In this embodiment, since the turbocharger 20 and the electric supercharger 26 are provided in the engine, the full load line WOT of the engine is the upper limit of the engine torque at the time of natural intake (no supercharging). It is set higher than the natural intake line NA.

  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, the waste gate valve 43 is set to prevent the supercharging pressure from rising further. Control that opens and flows a part of the exhaust gas to the bypass passage 42 (bypassing the turbine 22) is executed. Hereinafter, the engine rotation speed Ni corresponding to the intercept point IC is referred to as “intercept rotation speed Ni”.

  The point X existing on the full load line WOT on the higher speed side than the intercept point IC is the maximum output point at which the engine output is maximized. Hereinafter, the engine rotation speed Nx corresponding to the maximum output point X is referred to as “rated rotation speed Nx”. The rated rotational speed Nx takes a relatively high speed value, but does not necessarily coincide with the maximum allowable rotational speed of the engine (speed that enters the so-called red zone).

  As described above, in this embodiment, since the relatively large turbine 22 is used, the supercharging pressure by the compressor 23 does not reach the upper limit value unless the engine speed is increased to some extent. For this reason, the engine rotational speed corresponding to the intercept point IC, that is, the intercept rotational speed Ni is a value equal to or more than 1/3 of the rated rotational speed Nx of the engine. In other words, the specification of the turbocharger 20 of the present embodiment is set such that the intercept rotational speed Ni is equal to or higher than 1/3 of the rated rotational speed Nx of the engine.

  According to the map of FIG. 7, the third region R3 is set on the high load side (the higher torque side) in the speed region on the lower rotation side than the intercept rotation speed Ni, and further than the third region R3. A fourth region R4 is set on the high load side. On the other hand, the second region R2 is set on the high load side in the speed range higher than the intercept rotation speed Ni. In addition, the remaining areas excluding the second, third, and fourth areas R2, R3, and R4, that is, the area extending downward with the intercept point IC as the apex, and the area on the lower load side than the natural intake line NA The first region R1 is set.

  During engine operation, the ECU 50 sequentially determines in which region the engine is operated in the control map of FIG. 7 based on information obtained from the engine speed sensor SN1, airflow sensor SN3, accelerator opening sensor SN4, and the like. Then, the following control is executed according to the determination result.

(I) First region R1
First, control when the engine is operated in the first region R1 will be described. During operation in the first region R1, the ECU 50 executes the following control.
-Open the exhaust throttle valve 40 (non-execution of independent exhaust throttle control).
-Close the wastegate valve 43.
-The electric supercharger 26 is stopped.

  That is, in the first region R1, 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. Thereby, in each independent exhaust passage 31,32,33, exhaust gas can distribute | circulate through both the regular flow path 38 and the variable flow path 39, and the distribution | circulation resistance of exhaust gas is reduced. For this reason, exhaust gas is discharged smoothly even under operating conditions in which the amount of exhaust gas discharged from each cylinder 2A to 2D per unit time increases, such as in the high speed region in the first region R1. Pumping loss is reduced.

  In the first region R1, the wastegate valve 43 is closed so that all the exhaust gas discharged through the independent exhaust passages 31, 32, 33 flows into the turbine 22 of the turbocharger 20. As a result, the turbine 22 rotates in response to the energy of the exhaust gas, and the compressor 23 is driven by the turbine 22 and supercharging by the compressor 23 is performed.

  In the first region R1, the electric motor 27 of the electric supercharger 26 is stopped, and supercharging by the electric supercharger 26 is not performed.

  The EGR valve 47 is opened at least on the low load side in the first region R1. Thereby, the exhaust gas recirculation operation through the EGR passage 45 is performed, and the pumping loss in the low load region is reduced.

(Ii) Second region R2
During operation in the second region R2, the ECU 50 executes the following control.
-Open the exhaust throttle valve 40 (non-execution of independent exhaust throttle control).
-Open the wastegate valve 43.
-The electric supercharger 26 is stopped.

  The second region R2 is a region including the full load line WOT on the higher speed side than the intercept rotational speed Ni, and a region in which the supercharging pressure by the compressor 23 of the turbocharger 20 becomes excessive unless the wastegate valve 43 is opened. It is. Therefore, in the second region R2, in order to protect the engine body 1 and the turbocharger 20, the wastegate valve 43 is opened to such an opening that the supercharging pressure does not exceed the upper limit value.

  The control in the second region R2 is basically the same as the control in the first region R1 described above except that the wastegate valve 43 is opened.

  By the way, the increase in the supercharging pressure can also be suppressed by opening the EGR valve 47. For this reason, in part of the second region R2, control for opening the EGR valve 47 may be executed instead of opening the waste gate valve 43 or simultaneously with opening the waste gate valve 43.

(Iii) Third region R3
During operation in the third region R3, the ECU 50 executes the following control.
Close the exhaust throttle valve 40 (execution of independent exhaust throttle control).
・ Expand the valve overlap period of intake and exhaust valves 6 and 7.
-Close the wastegate valve 43.
-The electric supercharger 26 is stopped.

  That is, in the third region R3, the independent exhaust throttle control for closing the exhaust throttle valve 40 is executed, whereby 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 through only 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.

  In the third region R3, the waste gate valve 43 is closed. As a result, all the exhaust gas discharged from each of the cylinders 2A to 2D flows into the turbine 22 of the turbocharger 20, and the supercharging by the compressor 23 is performed to the maximum extent.

  Further, in the third region R3, each VVT 16 for the intake valve 6 and the exhaust valve 7 is driven, so that the valve overlap period in which both the intake valve 6 and the exhaust valve 7 are opened is the first region R1 and the second region R3. It is set to be longer than that in the region R2. That is, as shown in FIGS. 8 and 9, both the intake valve 6 and the exhaust valve 7 are opened over a relatively long period OL from the latter 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 above-described control is executed not only during steady operation in the third region R3, but also during a transition period in which the engine operating point tends to shift from the low load region to the third region R3. That is, the load (required torque based on the accelerator opening) increases during operation in the low speed region of the engine, and accordingly, the engine operation point moves upward in FIG. 7 toward the third region R3. Sometimes, prior to the actual transition to the third region R3, control is performed to close the exhaust throttle valve 40 and expand the valve overlap period.

(Iii) Fourth region R4
During operation in the fourth region R4, the ECU 50 executes the following control.
Close the exhaust throttle valve 40 (execution of independent exhaust throttle control).
・ Expand the valve overlap period of intake and exhaust valves 6 and 7.
-Close the wastegate valve 43.
-The electric supercharger 26 is operated.

  Since the fourth region R4 is the condition of the lowest rotation and the highest load, supercharging is performed by the electric supercharger 26 in addition to the turbocharger 20, and sufficient torque is obtained despite the low rotation. To be able to. That is, in the fourth region R4, the waste gate valve 43 is closed and the electric motor 27 for the electric supercharger 26 is driven.

  Note that the supercharging by the electric supercharger 26 (drive of the electric motor 27) is not only during steady operation in the fourth region R4, but the engine operating point tends to shift from the low load region to the fourth region R4. It is also executed during the transition period. That is, the load (required torque based on the accelerator opening) increases during operation in the low speed region of the engine, and accordingly, the engine operating point moves upward in FIG. 7 toward the fourth region R4. Sometimes, prior to the actual transition to the fourth region R4, the electric motor 27 for the electric supercharger 26 is driven.

  Except for the point that supercharging by the electric supercharger 26 is added as described above, the control in the fourth region R4 is basically the same as the control in the third region R3 described above.

(5) Operation, etc. As described above, in the multi-cylinder engine with a turbocharger of this embodiment, the first and third upstream ends connected to the exhaust port 5 of one cylinder (2A or 2D). Independent exhaust passages 31, 33, a second independent exhaust passage 32 having an upstream end connected to each exhaust port 5 of a plurality of cylinders (2B and 2C) in which the exhaust order is not continuous, and these independent exhaust passages 31, 32 , 33 are provided with an exhaust collecting portion 34 in which the downstream end portions gather together, and an exhaust throttle valve 40 for variably setting the exhaust gas flow area passing through the independent exhaust passages 31, 32, 33. Is used as the exhaust manifold 30. The turbocharger 20 includes a turbine 22 provided on the downstream side of the exhaust collecting portion 34 and a compressor 23 provided in the intake passage 13 and driven by the turbine 22. The intercept rotational speed Ni is set to 1/3 or more of the rated rotational speed Nx of the engine. The engine is provided with an ECU 50 that controls each part including the exhaust throttle valve 40. This ECU 50 is in a predetermined operation region (regions R3 and R4 in FIG. 7) set at a lower speed side than the intercept rotation speed Ni. Independent exhaust throttle control for closing the exhaust throttle valve 40 is executed, and control for expanding the valve overlap period in which both the intake valve 6 and the exhaust valve 7 are opened is executed. According to such a configuration, it is possible to increase the torque in a wide driving range covering from the low speed range to the high speed range of the engine, and improve the fuel efficiency.

  That is, in the above embodiment, the exhaust throttle valve 40 is closed in the operation region (the third region R3 and the fourth region R4) where the rotational speed is lower than the intercept rotational speed Ni, so that the inside of each independent exhaust passage 31, 32, 33 Since the independent exhaust throttle control for reducing the distribution area of the turbocharger 20 is executed, the supercharging capability of the turbocharger 20 can be further enhanced by the so-called dynamic pressure supercharging effect utilizing the exhaust gas blowdown.

  FIG. 8 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 and TDC on the horizontal axis indicate the bottom dead center and top dead center of the specific cylinder, respectively, and the interval from BDC to TDC is 180 ° CA in terms of crank angle. The characteristic line A shown in the figure shows the pressure of the exhaust gas when the independent exhaust throttle control is executed, and the characteristic line B shows the pressure of the exhaust gas when the independent exhaust throttle control is not executed. Show.

  The engine of this embodiment is a four-cylinder engine, and the ignition interval between the cylinders 2A to 2D is 180 ° CA. Accordingly, in accordance with this, blow-down (high pressure) of exhaust gas generated immediately after the exhaust valve 7 is opened.・ High-speed exhaust flow) also occurs every 180 ° CA. According to the graph of FIG. 8, the peak value of the exhaust pressure due to blowdown is higher on the characteristic line A with independent exhaust throttle control than on the characteristic line B without independent exhaust throttle control. This is because the independent exhaust throttling control is performed, whereby the variable flow passage 39 in each of the independent exhaust passages 31, 32, 33 is blocked, the exhaust gas flow area is reduced, and the exhaust gas is concentrated in a short time. This is because it began to flow through.

  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 shown by the characteristic line A, when the blowdown peak is increased by the independent exhaust throttle control, compared to the characteristic line B having a low blowdown peak (when the independent exhaust throttle control is not executed). Thus, even if the reduction due to the shortening of the blowdown period is subtracted, the average driving force (time average value of the driving force) received by the turbine 22 from the exhaust gas increases.

  Further, as shown in the characteristic line A with independent exhaust throttle control, when the blow-down period is shortened, the bottom value of the exhaust pressure generated after the blow-down peak is lower (the boost pressure that is the pressure on the intake side). The value is greatly reduced). Therefore, when the independent exhaust throttle control is executed, the drop (shown as ΔHp in FIG. 8) from the peak value to the bottom value of the exhaust pressure becomes larger. This leads to the exhaust gas being discharged more smoothly and the residual gas in the cylinders 2A to 2D being reduced (accelerating scavenging), which in turn leads to an improvement in engine torque.

  In addition, in the above embodiment, during the operation in the third region R3 and the fourth region R4 that execute the independent exhaust throttle control, the valve overlap period indicated by OL in FIG. 8 is expanded, and the exhaust top dead center (exhaust stroke) is increased. Since both the intake valve 6 and the exhaust valve 7 are opened over a relatively long period before and after the top dead center between the intake stroke and the intake stroke (TDC in FIG. 8), the so-called ejector effect is effectively exhibited. Scavenging can be further promoted. The ejector effect is an action of sucking a driven fluid using a negative pressure generated around a high-speed jet.

  That is, when a certain cylinder is in the vicinity of the exhaust top dead center (TDC) (hereinafter, this cylinder is referred to as a preceding cylinder), a subsequent cylinder that reaches the exhaust stroke next to the preceding cylinder has a high speed by blowdown. Exhaust gas is ejected (see arrow We0 in FIG. 2). When this blowdown gas flows into the exhaust collecting portion 34, a strong negative pressure is generated around the blowdown gas, and this strong negative pressure travels back to the exhaust manifold 30 and acts on the exhaust port 5 of the preceding cylinder. It tries to suck exhaust gas from the preceding cylinder (ejector effect). In addition, at this time, in the preceding cylinder, as shown in FIG. 9, a valve overlap period (OL) is formed, and both the intake valve 6 and the exhaust valve 7 are open, so that the intake port 4 enters the cylinder. A flow is generated in which the sucked air is blown directly into the exhaust port 5 (see arrows Wi and We in FIG. 2), and scavenging is further promoted by the blow-in of the sucked air.

  Further, when the above-described blow-through flow (the flow of intake air blown from the intake port 4 to the exhaust port 5) is generated by the ejector effect, the blow-through flow is converted into burned gas (gas generated by combustion of the air-fuel mixture). By adding, the flow rate of the exhaust gas from each of the cylinders 2A to 2D increases. Since the driving force of the turbine 22 is proportional to the flow rate of the exhaust gas, when the flow rate of the exhaust gas increases due to the ejector effect, the driving force of the turbine 22 increases in proportion to this and the supercharging capability of the turbocharger 20 Will improve.

  Further, when the ejector effect is present, blowdown gas that has flowed into the exhaust collecting portion 34 through any one of the independent exhaust passages 31, 32, 33 from each of the cylinders 2A to 2D flows into the other independent exhaust passage (reverses flow). Since the phenomenon is prevented, there is an advantage that the dynamic pressure supercharging effect is further promoted. That is, when the blowdown gas wraps around, the apparent volume of the exhaust manifold 30 increases, so the peak value of the exhaust pressure due to the blowdown (blowdown peak) decreases, and the turbine 22 The driving force will decrease. On the other hand, as shown in the above embodiment, when the valve overlap period is extended while executing the independent exhaust throttle control, the ejector effect from the preceding cylinder is sufficiently increased. As a result of the suction, the above-described reduction in the blowdown peak is prevented, so that the driving force of the turbine 22 can be sufficiently obtained, and the dynamic pressure supercharging effect can be further promoted.

  Here, in the above embodiment, by using a relatively large turbine as the turbine 22 of the turbocharger 20, the intercept rotational speed Ni is set to be 1/3 or more of the rated rotational speed Nx of the engine. Yes. For this reason, if the above-described independent exhaust throttle control (control to close the exhaust throttle valve 40 and shut off the flow path 39) is not executed in the low speed region R3 where the exhaust gas flow rate is small, A driving force for rotating the turbine 22 at a high speed cannot be obtained sufficiently, and only a torque such as a line P in FIG. 7 which is a boundary between the first region R1 and the third region R3 can be obtained. On the other hand, when the dynamic pressure supercharging effect and the ejector effect are exhibited by expanding the valve overlap period while executing the independent exhaust throttle control as in the above embodiment, the turbine 22 Since the average driving force that acts is increased, even the large turbine 22 can be rotated at a sufficiently high speed. Thereby, since the supercharging capability in the low speed region by the turbocharger 20 can be sufficiently increased, the region R3 having a torque higher than that of the line P can be realized.

  The improvement of the supercharging capability as described above can be explained by the following theory using the performance curve of the compressor 23. FIG. 10 shows the change (characteristic line C) of the operating point of the compressor when the accelerator is fully opened on the graph schematically showing the performance curve of the compressor 23. As shown in the rising portion of the characteristic curve C in the figure, which is located on the relatively low flow rate side, the pressure ratio of the compressor 23 does not naturally increase unless the flow rate increases to some extent (that is, the engine speed does not increase). And not) In particular, when a relatively large turbine 22 is used as in the above embodiment, this tendency becomes significant.

  However, in the above embodiment, scavenging is promoted by the dynamic pressure supercharging effect and the ejector effect, and a flow of intake air that blows from the intake port 4 to the exhaust port 5 is created. When the amount to be discarded outside the cylinder) is subtracted, the operating point of the compressor 23 moves to the left side of FIG. 10 where the flow rate is lower. For example, when the point C1 set at the rising portion of the characteristic line C is set as the starting point, the point C1 moves to the point C2 on the left side relatively by subtracting the amount of the blown-in air. Since the movement to the point C2 means that a large pressure ratio can be achieved even if the flow rate is small, the same effect as if the turbine 22 and the compressor 23 are downsized is produced. In addition, the flow rate of the movement from point C1 to C2, that is, the flow rate of the intake air blown through from the intake port 4 to the exhaust port 5, increases the driving force of the turbine 22, so that the compressor 23 performs useless work. I don't mean. Thus, according to the configuration of the above-described embodiment using the dynamic pressure supercharging effect and the ejector effect, the operating point of the compressor 23 in the low speed region is shown in FIG. The pressure ratio (supercharging pressure) in the low speed region can be effectively improved.

  As described above, in the above embodiment, independent exhaust throttle control and valve over which close the exhaust throttle valve 40 in a predetermined operation region (third region R3 and fourth region R4) whose rotational speed is lower than the intercept rotational speed Ni. Since the lap period expansion control is executed together, the turbocharger 20 can sufficiently increase the supercharging capability by exerting the dynamic pressure supercharging effect and the ejector effect, and the engine torque in the low speed range can be increased. It can be improved effectively.

  On the other hand, since the exhaust gas flow rate is higher on the higher speed side than the intercept rotation speed Ni, a large driving force can be applied to the turbine 22 without performing the above-described independent exhaust throttle control or the like. In addition, the supercharging capability of the turbocharger 20 can be sufficiently increased. Moreover, in the above embodiment, since the intercept rotational speed Ni is set to 1/3 or more of the rated rotational speed Nx of the engine (that is, the turbine 22 is large), the supercharging capability in the high speed region of the engine is inherently high. The peak value of the supercharging pressure can be set to a sufficiently high value. This means that an engine with excellent merchantability that does not have a peaking feeling in the high speed range (slow acceleration growth) is realized.

  Furthermore, if the turbine 22 is large, the exhaust gas flow resistance is unlikely to increase in the high speed range of an engine having a large exhaust gas flow rate. In addition, in the above embodiment, the flow area in the independent exhaust passages 31, 32, 33 is expanded by stopping the independent exhaust throttle control in a region higher than the intercept rotation speed Ni, so that the pumping loss is reduced. This can greatly reduce the fuel efficiency in the engine high speed range.

  As described above, according to the engine of the above-described embodiment, the independent exhaust throttle control or the like is executed in the low speed region of the engine while using the relatively large turbine 22 to improve the torque and fuel consumption in the high speed region of the engine. As a result, the torque can be improved by the dynamic pressure supercharging effect and the ejector effect. As a result, high torque can be generated in a wide driving range covering the low speed range to the high speed range of the engine, and the fuel efficiency can be improved.

  Further, in the above-described embodiment, the second independent exhaust passage 32 having a bifurcated upstream side is connected to the exhaust port 5 of two cylinders (second cylinder 2B and third cylinder 2C) whose exhaust order is not continuous. By connecting single tubular first and third independent exhaust passages 31 and 33 to the exhaust port 5 of the first cylinder 2A or the fourth cylinder 2D, three independent exhausts are provided for the four cylinders 2A to 2D. The passages 31, 32, and 33 were prepared, and the volumes of the independent exhaust passages 31, 32, and 33 were set to be the same. According to the layout of the exhaust manifold 30 including such independent exhaust passages 31, 32, 33, the above-described dynamic pressure supercharging effect and ejector effect can be effectively prevented from varying among the cylinders, and each cylinder 2A to 2D can be prevented. The torque improvement allowance can be evenly aligned.

  Of course, it is possible to make the volumes of the independent exhaust passages uniform without using the layout as described above. For example, it is naturally possible to connect single tubular (total of four) independent exhaust passages to the exhaust ports 5 of the cylinders 2A to 2D, and to make the volumes all the same. However, in this case, the independent exhaust passage connected to the second cylinder 2B and the third cylinder 2C on the center side in the cylinder row direction (with a smaller volume than the independent exhaust passage for the cylinders 2A and 2D outside thereof) A layout that makes it unnaturally circumvents) is necessary. This is not preferable because it causes an increase in exhaust resistance and hinders downsizing of the exhaust manifold.

  On the other hand, when the layout of the exhaust manifold 30 as shown in the above embodiment is adopted (that is, when the common independent exhaust passage 32 is provided for the second cylinder 2B and the third cylinder 2C), the above-mentioned is described. Since such a problem does not occur, the volumes of the independent exhaust passages 31, 32, and 33 can be easily made uniform while the exhaust manifold 30 is effectively made compact.

  Moreover, in the said embodiment, the downstream part of each independent exhaust passage 31,32,33 is divided into the regular flow path 38 and the variable flow path 39 by the partition 37 extended along the flow direction of exhaust gas, and exhaust gas The throttle valve 40 is provided so as to block one of the two flow paths 38 and 39 (the variable flow path 39) so that it can be opened and closed. According to such a configuration, one of the two flow paths 38 and 39 partitioned by the partition wall 37 is blocked or opened by the exhaust throttle valve 40, and the inside of the independent exhaust passages 31, 32, and 33 The distribution area can be changed, and the execution and stop of the independent exhaust throttle control can be switched quickly and reliably.

  Further, in the above embodiment, the electric motor 27 is operated in the specific operation region set in the region of the slowest speed and the high load side, that is, the fourth region R4 shown in FIG. Since the charging is performed, it is possible to reliably increase the torque in the extremely low speed region in which the supercharging capability of the turbocharger 20 is difficult to be exhibited.

  By the way, in the said embodiment, since the torque in a low speed region is reinforced by execution of independent exhaust throttle control etc., the improvement margin of the torque by the electric supercharger 26 does not need to be so large. For this reason, it is not necessary to use a high-performance supercharger as the electric supercharger 26, and an increase in cost and weight due to the addition of the electric supercharger 26 can be minimized.

  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.

  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 third single tubes are connected to the first cylinder 2A or the fourth cylinder 2D. Although the independent exhaust passages 31 and 33 are connected, as described above, a single tubular passage similar to the first and third independent exhaust passages 31 and 33 may be connected to all the cylinders 2A to 2D.

  In the above embodiment, each valve mechanism for the intake valve 6 and the exhaust valve 7 is provided with a VVT 16 (valve variable mechanism) for changing the valve opening / closing timing. However, the valve overlap period is used as an operating condition. The VVT 16 may be provided only in either one of the intake valve 6 and the exhaust valve 7.

2A to 2D Cylinder 4 Exhaust port 5 Intake valve 6 Exhaust valve 9 VVT (Valve variable mechanism)
13 Intake Passage 20 Turbocharger 22 Turbine 23 Compressor 26 Electric Supercharger 27 Electric Motor 31 First Independent Exhaust Passage 32 Second Independent Exhaust Passage 33 Third Independent Exhaust Passage 34 Exhaust Collecting Section 37 Bulkhead 38 Regular Use Flow (Flow Road)
39 Variable flow path (flow path)
40 Exhaust throttle valve 50 ECU (control means)
Ni intercept speed Nx (engine) rated speed

Claims (4)

A multi-cylinder engine with a turbocharger comprising a plurality of cylinders and a turbocharger driven by the energy of exhaust gas discharged from each cylinder,
A plurality of independent exhaust passages whose upstream ends are connected to exhaust ports of one cylinder or a plurality of cylinders whose exhaust order is not continuous; and an exhaust collecting portion in which the downstream ends of each independent exhaust passage are gathered together. An exhaust throttle valve that variably sets the flow area of the exhaust gas passing through the independent exhaust passage, and control means for controlling the opening / closing operation of the exhaust throttle valve,
The turbocharger has a turbine provided on the downstream side of the exhaust collecting portion, and a compressor provided in an intake passage of an engine and driven by the turbine,
When the engine rotation speed when the supercharging pressure of the compressor reaches a predetermined upper limit value at the full load of the engine is defined as the intercept rotation speed, the intercept rotation speed is 1/3 or more of the rated rotation speed of the engine. The specifications of the turbocharger are set in
The turbocharger-equipped multi-cylinder engine characterized in that the control means executes independent exhaust throttle control for closing the exhaust throttle valve in a predetermined operation region set at a lower speed side than the intercept rotation speed. . The multi-cylinder engine with a turbocharger according to claim 1,
At least the downstream part in each of the independent exhaust passages is divided into two flow paths by a partition extending along the flow direction of the exhaust gas,
The multi-cylinder engine with a turbocharger, wherein the exhaust throttle valve is provided so as to shut off one of the two flow paths so as to be openable and closable. The multi-cylinder engine with a turbocharger according to claim 1 or 2,
A valve variable mechanism capable of changing the opening / closing timing of at least one of the intake valve and the exhaust valve of each cylinder;
The control means controls the variable valve mechanism so that a valve overlap period during which both the intake valve and the exhaust valve are open is secured a predetermined amount or more at least in an operation region where the independent exhaust throttle control is executed. Features a multi-cylinder engine with turbocharger. The multi-cylinder engine with a turbocharger according to any one of claims 1 to 3,
An electric supercharger that pressurizes intake air by the driving force of the electric motor;
The turbocharger-equipped multi-cylinder engine characterized in that the control means operates the electric supercharger in a specific operation region set in the region of the slowest and high load side.

Images