JP4973541B2 - Supercharged engine system - Google Patents

Description

  The present invention relates to a supercharged engine system, and more particularly to a supercharged engine system equipped with an exhaust turbocharger.

  As a means for increasing the output torque of the engine, a supercharging device for increasing the intake pressure is known. A typical example is an exhaust turbocharger. For example, an exhaust turbocharger disclosed in Patent Document 1 is a turbine scroll provided in an exhaust passage and a compressor scroll provided in an intake passage connected by a shaft. The compressor scroll is driven by rotating it, and the intake pressure is increased.

The exhaust turbocharger disclosed in Patent Document 1 discloses a configuration in which a variable vane is provided in a nozzle portion of a turbine in order to achieve both a torque increase in a wide operation region and an improvement in fuel consumption. This variable vane is controlled to open and close with a low supercharging pressure in the partial load operation region, thereby suppressing the flow rate of exhaust gas flowing into the turbine scroll and reducing the back pressure, thereby suppressing the reduction in fuel consumption. On the load side, opening / closing control is performed with a high supercharging pressure, thereby increasing the flow rate of the exhaust gas flowing into the turbine scroll and increasing the output.
JP-A-9-112285

  Generally, a small exhaust turbocharger increases the torque in the engine low speed operation region, and a large exhaust turbocharger increases the torque in the engine high speed operation region. Therefore, in order to improve the supercharging performance in the high rotation range, the exhaust turbocharger is becoming larger.

  However, in recent years, in addition to the supercharging performance in the high rotation range, the demand for reduction in fuel consumption and improvement in output in the low speed operation range has been further increased.

  As a method of using a large exhaust turbocharger and improving the supercharging performance in the engine low-speed operation region, it is common to use an electric supercharger that electrically drives the exhaust turbocharger. However, since the supercharge request in the engine low speed operation region (for example, 2000 rpm or less) is relatively frequent, it is not preferable to drive the electric supercharger or the like every time because the battery is consumed greatly.

  The present invention has been made in view of the above problems, and is provided with a supercharger capable of exhibiting high supercharging performance over a wide engine operating range while reducing the operating rate of an electric supercharger or the like as much as possible. The challenge is to provide an engine system.

In order to solve the above-described problems, the present invention is configured to open and close the intake valve and the exhaust valve so that the valve opening periods of the intake valve and the exhaust valve overlap each other in the vicinity of the exhaust top dead center in a predetermined operation range. An engine configured to be able to change timing, an exhaust manifold independently connected to each exhaust port of a plurality of cylinders provided in the engine, and having an independent exhaust passage, and each independent exhaust of the exhaust manifold At least in a predetermined engine low-speed operation region, a collective part in which the downstream side of the passage is gathered into one, an exhaust turbocharger connected to the downstream side of the collective part, and the collective part and the Variable exhaust valve operated in an independent exhaust throttle mode that reduces the effective opening area of the outlet of the independent exhaust passage to the exhaust manifold from the maximum value The engine low speed operation region where the variable exhaust valve is operated in the independent exhaust throttle mode, when the exhaust turbocharger the engine in an overlapping region between the supercharge operating range of operation of the operation, unburned fuel Is discharged from the engine and burned upstream of the exhaust turbocharger, at least the air-fuel ratio is made richer than the stoichiometric air-fuel ratio within the combustible range and the intake valve and the exhaust valve are opened. A supercharger-equipped engine comprising combustion control means for controlling combustion of the air-fuel mixture in the engine in a post-combustion mode that expands an overlap amount that overlaps a period beyond a preset range System. In this aspect, in a predetermined engine low-speed operation region, the variable exhaust valve is switched to the independent exhaust throttle mode in which the effective opening area of the outlet of the independent exhaust passage is reduced below the maximum value, whereby the ejector effect is achieved at the outlet of the exhaust manifold. Obtainable. The ejector effect means that part of the velocity energy of the driving fluid ejected from the nozzle is converted into pressure energy, and the fluid to be sucked is sucked and discharged by the pressure energy. Due to this ejector effect, the input flow rate of the exhaust turbocharger (the amount of exhaust per unit time supplied to the exhaust turbocharger) can be increased even in a relatively low speed and low load operation region. Moreover, the increase of the blowdown peak due to the ejector effect can promote the improvement of the dynamic pressure supercharging effect and the scavenging performance.

In addition, when the engine is operated in the overlapping region of the engine low speed operation region where the variable exhaust valve operates in the independent exhaust throttle mode and the supercharging operation region where the exhaust turbocharger operates , unburned fuel is Since the combustion condition of the air-fuel mixture is set so that it is combusted on the upstream side of the exhaust turbocharger, this setting causes a so-called “afterburn” phenomenon. This post-burning phenomenon is caused by making the air-fuel ratio richer than the stoichiometric air-fuel ratio within the combustible range and increasing the overlap amount at which the opening timing of the intake valve and the exhaust valve overlaps. It is a phenomenon that is discharged during the overlap period, and further mixed with ambient air in a high pressure state due to an increase in blowdown peak due to the ejector effect, and combusts upstream of the exhaust turbocharger. When the overlap amount is increased during operation in the independent exhaust throttle mode, initially, the burned gas that is scavenged increases as the overlap amount increases, so the charging efficiency by scavenging is improved and the output is improved. However, when the overlap amount exceeds a certain value, the amount of fresh air remaining in the cylinder is not proportional to the blow-through amount due to the overlap, and the output becomes flat. However, if the overlap amount continues to increase even after the output has leveled off, this time, unburned fuel is discharged into the exhaust passage, and the discharged unburned fuel burns upstream of the exhaust turbocharger. As a result, it was found that the afterburning phenomenon occurs. When the afterburning phenomenon occurs, the pressure of the exhaust gas increases, so that the boost pressure rises and the boost performance can be greatly improved. Therefore, even when a relatively large exhaust turbocharger is employed, a large supercharging performance can be obtained in the low speed operation region of the engine.

  In a preferred embodiment, when the combustion of the air-fuel mixture of the engine is controlled in the afterburning mode and the electric supercharger provided in the intake passage of the engine, the valve opening periods of the intake valve and the exhaust valve are over. When the overlap amount to be wrapped is within a predetermined torque stop range, an electric supercharging control means for controlling the operation of the electric supercharger is provided. In this mode, when the intake valve and the exhaust valve are operating with an overlap amount that does not cause the afterburning phenomenon, the electric supercharger operates and the boost pressure is increased to compensate for the shortage of output. Can do. As described above, when the overlap amount is increased during the operation in the independent exhaust throttle mode, the scavenging performance is between the overlap amount in which the scavenging performance is improved and the overlap amount in which the supercharging performance is improved by the afterburning phenomenon. May saturate, and a torque stop range may occur where no afterburning phenomenon occurs. Therefore, in this aspect, while the intake valve and the exhaust valve are operating in such a torque stop range, it is possible to supplement the supercharging capability with the electric supercharger and maintain a high output in a wide operation region. I am trying to do it. In addition, since the operating region in which the electric supercharger operates is only the torque stop range described above, the operating rate of the electric supercharger can be reduced to the minimum necessary.

  In a preferred aspect, the combustion control means controls the amount of overlap in which the valve opening periods of the intake valve and the exhaust valve overlap each other at a crank angle of at least 90 ° or more in the afterburning mode. In this aspect, in the operation state to be operated in the afterburning mode, the afterburning phenomenon occurs with a high probability, and the supercharging performance can be improved to improve the output.

  As described above, in the present invention, the combustion of the air-fuel mixture of the engine is controlled in the afterburning mode in the predetermined operating region, so that the scavenging can be improved and the supercharging input can be performed by the independent exhaust throttle mode executed in the operating region. Combined with the effect of improving the supercharging performance by increasing the flow rate or the like, the improvement of the supercharging performance by the afterburning phenomenon can further reduce the fuel consumption and the output. Therefore, according to the present invention, there is a remarkable effect that high supercharging performance can be exhibited over a wide engine operation region while reducing the operating rate of the electric supercharger or the like as much as possible.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of a supercharged engine system (hereinafter abbreviated as an engine) according to the embodiment of FIG. 2 is a partial side sectional view of FIG.

  The supercharged engine system includes an in-line four-cylinder four-cycle engine 1.

  The cylinder block 2 of the engine 1 has first to fourth cylinders 3a, 3b, 3c, and 3d (referred to collectively as cylinders 3) arranged on one horizontal line. The configuration of each cylinder 3 is common, and as shown in FIG. 2, an intake port 6 for sucking intake Wi and an exhaust port 8 for discharging exhaust We are provided above the combustion chamber 4. The intake port 6 is provided with an intake valve 7 for opening and closing the intake port 6, and the exhaust port 8 is provided with an exhaust valve 9 for opening and closing the intake port 7. Further, the cylinder head (not shown) is provided with a spark plug 5 that generates a spark at the top of the combustion chamber 4. In addition, fuel supply means (not shown) including the fuel injection valve 10 (see FIG. 2) is provided at appropriate positions.

  In order to detect the operating state of the engine 1, the engine 1 is provided with a crank angle sensor SN1, an engine water temperature sensor SN2, an air flow sensor SN3, and an intake air temperature sensor SN4. Moreover, in order to detect the driving | running state of the vehicle carrying this engine 1, accelerator opening sensor SN5, vehicle speed sensor SN6, etc. are provided in the vehicle.

  Further, the engine 1 of this embodiment, like a general four-cylinder engine, shifts each stroke so that each cylinder 3 sequentially reaches the ignition timing at every crank angle of 180 degrees (hereinafter referred to as 180 ° CA). Driving. The ignition order is so-called # 1 → # 3 → # 4 → # 2 (#x indicates the x-th cylinder). Table 1 shows the transition of the stroke of each cylinder 3, and FIG. 3 shows a timing chart.

  Referring to Table 1 and FIG. 3, each row represents the first cylinder 3a to the fourth cylinder 3d, and each column represents the transition of the stroke every 180 ° CA. As shown in Table 1, for example, when the first cylinder 3a is in the expansion stroke, the second cylinder 3b is in the exhaust stroke, the third cylinder 3c is in the compression stroke, and the fourth cylinder 3d is in the intake stroke.

  FIG. 2 shows a state in which the first cylinder 3a is in a transition period (near the bottom dead center) from the expansion stroke to the exhaust stroke. At this time, the exhaust valve 9 is opened and the exhaust We begins to be discharged from the combustion chamber 4 to the exhaust port 8 (blowdown).

  As shown in Table 1 and FIG. 3, when the first cylinder 3a starts blowdown, the second cylinder 3b is in the transition period (near top dead center) from the exhaust stroke to the intake stroke. In this transition period, as shown in the figure, a period during which both the intake valve 7 and the exhaust valve 9 are open, that is, a so-called overlap period is provided.

  Four independent exhaust passages 16 a, 16 b, 16 c, and 16 d that form the upstream side of the exhaust manifold 16 are connected to the exhaust port 8 of each cylinder 3.

  As shown in FIG. 2, a flange 16e fixed to a cylinder head (not shown) is provided at the upstream end of the independent exhaust passages 16a to 16d of the exhaust manifold 16, and the independent exhaust passage of the exhaust manifold 16 is provided via the flange 16e. 16a to 16d are connected to the exhaust ports 8 of the first to fourth cylinders 3a to 3d, respectively. Each of the independent exhaust passages 16a to 16d is set to an opening area S1 having the same area as a circle of φ36 mm over the entire length.

  FIG. 4 is an external perspective view showing the main part according to the embodiment of FIG. FIG. 5 is an external perspective view showing an enlarged main part according to the embodiment of FIG.

  As shown in FIGS. 1, 4, and 5, the first exhaust passage 16 a and the fourth exhaust passage 16 d maintain an independent state over their entire length, but the second exhaust passage 16 b and the third exhaust passage 16 c are It is gathered on the downstream side to form an auxiliary collective exhaust passage 16bc. Accordingly, three independent exhaust passages (a first exhaust passage 16a, an auxiliary collective exhaust passage 16bc, and a fourth exhaust passage 16d) are formed near the downstream end of the exhaust manifold 16. The first and fourth exhaust passages 16a and 16d and the auxiliary collective exhaust passage 16bc have a shallow angle (preferably substantially parallel) so that the first exhaust passage 16a and the fourth exhaust passage 16d sandwich the auxiliary collective exhaust passage 16bc from both sides. ) They are arranged in parallel and constitute the exhaust manifold 16 as a whole. Hereinafter, unless otherwise specified, the independent exhaust passage refers to three independent exhaust passages on the downstream side.

  The first exhaust passage 16a and the fourth exhaust passage 16d, and the second exhaust passage 16b and the third exhaust passage 16c are symmetrical to each other. Therefore, the first exhaust passage length La and the fourth exhaust passage length Ld are substantially equal. Further, the length of the second exhaust passage 16b including the length of the auxiliary collective exhaust passage 16bc is set to the second exhaust passage length Lb, and the length of the third exhaust passage 16c including the length of the auxiliary collective exhaust passage 16bc is set. When the third exhaust passage length Lc is set, the second and third exhaust passage lengths Lb and Lc are configured to be substantially equal to the first exhaust passage length La, respectively.

  Further, in the present embodiment, the first exhaust passage length La is configured to be 200 mm or less. The first passage volume Va and the fourth passage volume Vd are substantially equal. Further, the volume of the second exhaust passage 16b including the volume of the auxiliary collective exhaust passage 16bc is the second exhaust passage volume Vb, and the volume of the third exhaust passage 16c including the volume of the auxiliary collective exhaust passage 16bc is the third exhaust passage volume. In the case of Vc, the second and third exhaust passage volumes Vb and Vc are configured to be substantially equal to the first exhaust passage volume Va, respectively.

  A mounting frame 17 is provided on the downstream side of the exhaust manifold 16, and as shown in FIG. 5, the mounting frame 17 defines outlets 17a, 17bc, 17d of the independent exhaust passages 16a, 16bc, 16d. Yes. Each of the outlets 17a, 17bc, and 17d is set to an opening area S1 having the same area as a circular cross-sectional area of 36 mm, similarly to the upstream independent exhaust passages 16a, 16bc, and 16d.

  The exhaust manifold 16 is connected to the housing 31 of the variable exhaust valve 30 via the mounting frame 17.

  The variable exhaust valve 30 is a valve that changes the effective opening area S2 of each of the outlets 17a, 17bc, and 17d while maintaining the independent state of the three independent exhaust passages 16a, 16bc, and 16d. Here, the effective opening area S2 refers to an opening area for each of the outlets 17a, 17bc, 17d through which the exhaust gas We can flow through the outlets 17a, 17bc, 17d. In the following description, the effective opening area S2 is equal to the effective opening area S2. The diameter of the circle is referred to as an effective opening diameter D2. As will be described in detail later, the variable exhaust valve 30 is provided in order to improve the supercharging performance due to the ejector effect. Here, the ejector effect means that part of the velocity energy of the driving fluid ejected from the nozzle is converted into pressure energy, and the fluid to be sucked is sucked and discharged by the pressure energy. With this ejector effect, in this embodiment, as will be described in detail later, even in a relatively low speed and low load operation region, the input flow rate of the exhaust turbocharger 50 (supplied to the exhaust turbocharger 50). The amount of exhaust per unit time) is increased, and the increase of the blowdown peak can promote the dynamic pressure supercharging effect and the scavenging performance.

  FIG. 6 is a perspective view showing a schematic configuration of the variable exhaust valve 30 according to the embodiment of FIG. 1, wherein (A) shows a state when the valve is closed, and (B) shows a state when the valve is opened.

  Referring to FIGS. 4 and 6, the variable exhaust valve 30 includes a housing 31 interposed between the exhaust manifold 16 and the exhaust turbocharger 50, and is accommodated in the housing 31, and has an outlet 17 a of the exhaust manifold 16. A flap 35 that changes the effective opening area S2 of 17bc and 17d, a flap shaft 37 that is pivotally supported by the housing 31 so that the flap 35 swings around an axis that intersects the direction in which the exhaust gas Wet flows, and a flap shaft 37 An actuator 38 such as a motor to be rotated and a return spring 39 that urges the flap 35 in the valve opening direction via the flap shaft 37 are provided.

  The mounting frame 17 is fixed to the upstream end of the housing 31, whereby the housing 31 has a first independent exhaust passage 16 a, a fourth independent exhaust passage 16 d, and an auxiliary collective exhaust passage 16 bc of the exhaust manifold 16. The outlets 17a, 17bc and 17d are connected in parallel.

  A flange 31a is provided on the downstream end side of the housing 31, and is joined to the housing 51 of the exhaust turbocharger 50 via the flange 31a. The housing 31 is bent downward in the middle for the convenience of the layout of the exhaust turbocharger 50. Depending on the installation position of the exhaust turbocharger 50, such bending is not necessary. Different bending angles may also be used.

  On the upstream side of the flange 31 a in the housing 31, a collecting portion 31 c where exhaust gases We from the independent exhaust passages 16 a, 16 bc, 16 d merge is defined. On the upstream side of the collecting portion 31 c, a bulging portion 31 b that bulges upward in a direction orthogonal to the main flow of the exhaust gas We flowing in the housing 31 is formed, and the flap 35 is around the axis of the flap shaft 37. It is accommodated in the bulging portion 31b so as to be able to advance and retract by rotating.

  Referring to FIG. 6, the flap 35 is a hollow body whose inside is hollow for weight reduction, and has a fan-shaped fan-shaped surface 36 having a flap shaft 37 as a main fan on the outer periphery thereof. When the flap 35 is rotated so as to protrude downward from the bulging portion 31 b, the fan-shaped surface 36 faces the outlets 17 a, 17 bc and 17 d of the exhaust manifold 16 connected to the housing 31 and is discharged from the exhaust manifold 16. The exhaust gas We is displaced to a position for reducing the flow rate of the exhaust We (see FIG. 6A). On the other hand, when the flap 35 is rotated to a position where it enters the bulging portion 31b, the fan-shaped surface 36 is displaced to a position where the outlets 17a, 17bc, and 17d are opened (see FIG. 6B).

  In this embodiment, even when the variable exhaust valve 30 is in the fully closed position, a small amount of exhaust We (for example, 20% of the total exhaust flow) is configured to flow to the collecting portion 31c.

  In the present embodiment, the fan-shaped surface 36 is configured to adjust the effective opening area S2 of each of the outlets 17a, 17bc, and 17d on the upstream side of the flap shaft 37 in the main stream of the exhaust We. Moreover, it arrange | positions so that the diameter which passes along the horizontal line of the flap axis | shaft 37 may face the inner side of the gathering part 31c as much as possible. Therefore, the torque around the flap shaft 37 that acts on the flap 35 when the exhaust Wet abuts on the fan-shaped surface 36 is smaller than the configuration in which the plate-like vane that blocks the exhaust flow is upstream of the rotation shaft. Thus, vibration is less likely to occur even in an operating situation where the exhaust flow velocity Qe is large due to blowdown.

  A waist gate opening 31e is formed on the side of the bulging portion 31b of the housing 31. The wastegate opening 31e communicates with each of the outlets 17a, 17bc, and 17d within a range in which the flap 35 extends from the predetermined opening / closing position shown in FIG. The wastegate opening 31e is controlled to be opened and closed by a not-illustrated wastegate valve mechanism formed in the side portion of the housing 31. In addition, since the wastegate valve mechanism itself can divert a well-known structure as it is, description about the detail is abbreviate | omitted.

  As shown in FIGS. 1, 2, and 4, the wastegate opening 31 e bypasses the exhaust turbocharger 50 via the discharge passage 61 and is connected to the upstream side of the catalyst 63 in the main exhaust passage 60. Has been. More specifically, in the present embodiment, the catalyst 63 is disposed immediately below the exhaust turbocharger 50, and the main exhaust passage 60 connected to the exhaust turbocharger 50 is connected to the exhaust turbocharger 50. A curved portion 60 a is formed between the catalyst 63 and the catalyst 63. The downstream end of the discharge passage 61 is connected to the main exhaust passage 60 as a waste gate passage by connecting the downstream end of the discharge passage 61 to the outer circumferential side of the curved portion 60a in the arc direction. In the present embodiment, a cooler 64 is provided in the discharge passage 61. Further, in this embodiment, in order to detect the temperature state of the catalyst 63, the exhaust gas temperature sensor SN7 is provided at an appropriate place so that the temperature state of the catalyst 63 can be detected by the temperature of the exhaust gas We. In the present embodiment, the catalyst 63 is a three-component catalytic converter (TWC). The three-component catalytic converter efficiently removes hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas from the engine, and the activation temperature thereof is, for example, 200 ° C to 250 ° C.

  Next, an exhaust turbocharger 50 is connected to the downstream side of the housing 31 (collecting portion 31 c) of the variable exhaust valve 30. As shown also in FIG. 1, the exhaust turbocharger 50 is connected between the variable exhaust valve 30 and the main exhaust passage 60, and a housing 51 that guides the exhaust We from the exhaust manifold 16 to the main exhaust passage 60. A turbine scroll 54 disposed at the upstream end of the main exhaust passage 60 in the housing 51, a compressor scroll 52 provided in the intake passage 80, and a shaft 53 connected to the compressor scroll 52. The compressor scroll 52 is driven by rotating the turbine scroll 54 with the exhaust We, and the intake air Wi is compressed to increase the intake pressure. The exhaust turbocharger 50 of the present embodiment is a large turbo with a strong torque increasing action mainly in the high speed operation region.

  In the present embodiment, a rotational speed sensor SN8 for detecting the rotational speed of the exhaust turbocharger 50 is provided (see FIG. 1).

  Next, a throttle valve 81 is provided in the intake passage 80 of the engine 1, and the intake flow rate is adjusted by the throttle valve 81.

  An intercooler 82 is disposed between the throttle valve 81 and the compressor scroll 52 of the exhaust turbocharger 50, and an electric supercharger 83 is disposed between the intercooler 82 and the throttle valve 81. Is provided. The electric supercharger 83 is configured by an impeller or the like that is directly driven by an electric motor. Further, the intake passage 80 is provided with a bypass passage 84 that bypasses the electric supercharger 83 from the downstream side of the intercooler 82 and communicates with the upstream side of the throttle valve 81. The bypass passage 84 is provided with an intake control valve 85 that is driven by an actuator (not shown) to adjust the air flow rate of the bypass passage 84.

  As shown in FIG. 1, the engine 1 is provided with a variable valve timing mechanism 12. The variable valve timing mechanism 12 of the present embodiment is a so-called VVT (Variable Valve Timing) in which the valve opening / closing valve timing is moved back and forth to the parallel movement pressure while the valve opening periods of the intake valve 7 and the exhaust valve 9 are maintained. As a VVT system, the valve timing may be continuously changed or may be changed in two or more steps.

  The variable valve timing mechanism 12 of the present embodiment includes an intake side intake VVT 12i (intake valve timing changing means) and an exhaust side exhaust VVT 12e (exhaust valve timing changing means), and both the intake valve 7 and the exhaust valve 9 are provided. The valve timing can be changed.

  The operation of the engine 1 is electrically controlled by an engine control unit (ECU) 20. The engine control unit 20 is a control unit composed of a microprocessor having a CPU, a memory, a counter timer group, an interface, and a bus connecting these units.

  As described in FIG. 1, the engine control unit 20 includes, as input elements, a crank angle sensor SN1, an engine water temperature sensor SN2, an airflow sensor SN3, an intake air temperature sensor SN4, an accelerator opening sensor SN5, a vehicle speed sensor SN6, and an exhaust temperature. Various detection means such as a sensor SN7 and a rotation speed sensor SN8 are connected. On the other hand, as control elements, fuel supply means (not shown) including the fuel injection valve 10, an actuator (not shown) of the throttle valve 81, an electromagnetic valve (not shown) provided in the variable valve timing mechanism 12, a variable exhaust valve 30 actuators 38, an electric supercharger 83, an actuator (not shown) of the intake control valve 85, and the like are connected.

  With this configuration, the engine control unit 20 functions as a combustion control unit that performs combustion control such as fuel supply amount, throttle opening, or ignition timing. The engine control unit 20 as the combustion control means performs drive control of the variable valve timing mechanism 12. In addition, the engine control unit 20 also functions as variable exhaust valve control means for driving and controlling the variable exhaust valve 30.

  FIG. 7 is a characteristic diagram showing a setting example of an operation region for performing control according to the operation state according to the embodiment of FIG. In FIG. 7, the horizontal axis indicates the engine speed Ne (rpm), and the vertical axis indicates the required torque τ (N · m). The characteristic WOT indicates the maximum load torque (engine fully open operation region). The supercharging operation regions R10, R11, R20, and R21 on the high load side and the natural intake operation regions R12 and R22 on the low load side are set with the characteristic NA as a boundary.

  With reference to FIG. 7, in the present embodiment, among the operation regions R10 to R22, in the supercharging operation region R10 and the natural intake operation region R12 on the low speed side, the independent exhaust throttle mode is set to be executed. Yes. In the independent exhaust throttle mode, the engine control unit 20 as the variable exhaust valve control means drives the variable exhaust valve 30 to maximize the effective opening area S2 of each outlet 17a, 17bc, 17d of the independent exhaust passages 16a, 16bc, 16d. In this control, the engine control unit 20 sends an opening signal to the actuator 38 of the variable exhaust valve 30, and the actuator 38 flaps. In this control, the shaft 37 is rotationally driven to adjust the rotation angle of the flap 35. In the independent exhaust throttling mode, the variable exhaust valve 30 can be fully closed or changed so that the effective opening area S2 is narrowed as the required load increases, depending on the operating region. In the present embodiment, in the supercharging operation region R11 of a predetermined low rotation speed (for example, 2000 rpm) or less, adjustment control that reduces the effective opening area S2 is executed as the load increases. In the operation regions R20, R21, and R22, the effective opening area S2 is set to fully open.

  Next, when the operation range is the low speed side supercharging operation region R10 or the supercharging operation region R11 (in the illustrated example, the supercharging operation region of 2000 rpm or less), the engine control unit 20 is overrun in a so-called afterburning mode. Control lap amount and fuel injection amount. This post-burning mode is a state in which at least the air-fuel ratio is made richer than the stoichiometric air-fuel ratio within the combustible range so that unburned fuel is discharged from the engine 1 and burned upstream of the exhaust turbocharger 50. An operation mode in which the lap amount is expanded beyond a preset range.

  FIG. 8 is a graph for explaining the afterburning phenomenon according to the present embodiment. In FIG. 8, the horizontal axis indicates the overlap amount (overlap period) OL indicated by the crank angle, and the vertical axis indicates the output (KPa).

  Referring to FIG. 8, when the overlap amount OL is increased during the operation in the independent exhaust throttle mode, initially, the burned gas scavenged increases with the increase of the overlap amount OL. Although the charging efficiency is improved and the output is improved, when the overlap amount OL exceeds a certain amount, the amount of fresh air remaining in the cylinder is not proportional to the blow-through amount due to the overlap, and the output becomes flat (torque retention) range). However, if the overlap amount OL continues to increase beyond the torque stoppage range where the output leveled off, this time, unburned fuel is discharged into the exhaust passage, and the discharged unburned fuel is discharged from the exhaust turbocharger. It has been found that afterburning causes an afterburning phenomenon.

  When such a post-burn phenomenon occurs, the supercharging pressure increases due to combustion in the exhaust passage, so that the supercharging performance is greatly improved, and the output of the engine 1 is improved and the fuel consumption is reduced. In addition, since the exhaust temperature increases, it is possible to contribute to the activation of the catalyst 63. Therefore, in the present embodiment, the afterburning phenomenon is positively used according to the operating state of the engine 1 to improve the output and the exhaust purification performance.

  FIG. 9 is a graph showing the relationship between the overlap amount OL and the engine rotational speed Ne. In FIG. 9, the horizontal axis represents the engine rotation speed Ne (rpm), and the vertical axis represents the overlap amount OL indicated by the crank angle.

  As a result of earnest research by the present inventors, the overlap amount OL required for the afterburn phenomenon to occur becomes smaller as the engine rotational speed Ne increases. For example, in the case of 1500 rpm, 90 ° CA or more, It became clear that afterburn phenomenon occurred. Therefore, in the operation region shown in FIG. 7, when the engine control unit 20 is switched to the afterburning mode in the supercharging operation regions R10 and R11, the engine control unit 20 sets the overlap amount OL of the valve opening periods IN and EX to 90 ° CA or more. And the engine 1 is controlled.

  Next, the overlap between the intake valve 7 and the exhaust valve 9 in the afterburning mode is preferably set before and after the exhaust top dead center with the exhaust valve 9 closed late.

  FIG. 10 is an exhaust characteristic diagram, where (A) is an independent exhaust throttle mode (when the variable exhaust valve is fully closed), and (B) is a normal operation mode (when the variable exhaust valve is fully open). In FIG. 10, the horizontal axis represents the crank angle θ (deg: top dead center is 0 ° CA) of the first cylinder 3a, and the vertical axis represents the exhaust pressure (KPa) and the valve opening period (mm). The opening periods of the intake valve 7 and the exhaust valve 9 are indicated by IN and EX, respectively.

  Referring to FIG. 10A, the blowdown characteristic in the independent exhaust throttle mode is hardly affected by the blowdown peak of the other cylinders due to the exhaust effect of the exhaust by the ejector effect. Therefore, it is preferable to delay the valve closing timing of the exhaust valve 9 from the viewpoint of improving the output and overlap the valve opening periods EX and IN before and after the exhaust top dead center.

  On the other hand, as shown in FIG. 10B, the exhaust pressure when the variable exhaust valve is fully closed is affected by the blowdown peak of the other cylinders. If it overlaps after the point, the exhaust pressure will exceed the supercharging pressure and scavenging may not be possible.

  Therefore, in the present embodiment, a relatively large overlap amount OL (for example, 65 ° CA) is adopted only in the supercharging operation region R20 shown in FIG. 7, and the operation regions R12, R21, and R22 overlap as much as possible. The amount OL is set small (for example, 0 ° CA to 40 ° CA). When the intake valve opening period IN and the exhaust valve opening period EX are overlapped in the operation regions R12, R20 to R22, the overlap amount OL delays the closing timing of the exhaust valve 9 as the engine rotational speed Ne increases. It is expanded by advancing the valve opening timing of the valve 7 (may be performed by either the exhaust VVT 12e or the intake VVT 12i). The specific overlap amount OL is determined for each engine 1 based on an experiment or the like, mapped, and stored in the memory of the engine control unit 20, and from the map stored according to the driving situation. Control is performed by reading the overlap amount OL.

  Next, in the afterburning mode, the fuel injection amount is adjusted, and the air-fuel ratio is set to rich (A / F is, for example, 14.0 to 12.7) in the combustible range. By setting the air-fuel ratio, unburned fuel is combusted by blowdown when discharged from the exhaust valve 9 to the exhaust passage into the independent exhaust passages 16a to 16d of the exhaust manifold 16, and is supercharged by the exhaust turbocharger 50. It becomes possible to raise a pressure suitably.

  In addition, the engine control unit 20 normally controls the operation of the engine 1 in an electric supercharge bypass mode in which the intake air Wi-by bypasses the electric supercharger 83, and operates the electric supercharger 83 in a predetermined operation state. The engine 1 can be operated and controlled in the electric supercharging mode. In the electric supercharge bypass mode, the electric supercharger 83 shown in FIG. 1 is stopped, the intake control valve 85 of the bypass passage 84 is fully opened, and the intake air Wi that has passed through the intercooler 82 causes the electric supercharger 83 to be opened. The engine 1 is bypassed and supplied to the engine 1. In the electric supercharging mode, the electric supercharger 83 shown in FIG. 1 is operated, the intake control valve 85 in the bypass passage 84 is fully closed, and the intake air Wi that has passed through the intercooler 82 is supplied to the electric supercharger. 83 is supercharged and supplied to the engine 1.

  In general, the variable valve timing mechanism 12 is configured to switch the opening timing of the intake valve 7 and the exhaust valve 9 by switching the hydraulic pressure. Therefore, when the overlap amount OL of the opening timing is switched, FIG. You may be forced to pass the indicated torque stop range. Therefore, in the present embodiment, when the valve timing is switched to obtain the target torque, when the overlap amount OL of the valve opening periods IN and EX is in an operating state that passes through the torque stop range, the electric supercharger 83 is used. Is used to assist the supercharging performance. Thus, in this embodiment, the engine control unit 20 is configured to function as an electric supercharging control means.

  When the engine 1 is cold, the catalyst 63 often does not reach the activation temperature, and depending on the operating conditions, it may take a considerable time for the catalyst 63 to rise to the activation temperature. Therefore, in the present embodiment, when the temperature state related to the catalyst 63 is equal to or lower than a predetermined set temperature Tst set near the activation temperature, as is apparent from the flowchart described below, regardless of the operation region. The variable exhaust valve 30 is operated in the independent exhaust throttle mode, and the combustion condition of the engine 1 is set in the afterburning mode. The temperature state associated with the catalyst 63 may be the temperature of the catalyst 63 itself or a substitute characteristic (for example, exhaust temperature).

  Next, a control example of the engine system according to the present embodiment will be described.

  11 and 12 are flowcharts showing an example of control of the engine system in one embodiment of the present invention.

  First, referring to FIG. 11, the engine control unit 20 first executes initialization of flags and memory as an initial operation (step ST1). Here, in the present embodiment, the electric supercharging bypass mode is selected by the initial operation of step ST1, and the intake control valve 85 provided in the bypass passage 84 of the electric supercharger 83 is set to be fully opened, and the intercooler The intake air Wi that has passed through 82 is supplied to the engine 1 by bypassing the electric supercharger 83 by the bypass passage 84.

  After the initial operation shown in step ST1, the engine control unit 20 reads each detection signal input from the input element (step ST2), and calculates the required torque of the engine 1 based on the value of the read detection signal. (Step ST3). After calculating the required torque, the engine control unit 20 determines that the temperature of the catalyst 63 is the activation temperature of the catalyst 63 based on the detection signal (specifically, the detection value of the exhaust temperature sensor SN7) read in step ST2. It is determined whether or not a predetermined set temperature Tst determined based on the above has been reached (step ST4). If the catalyst 63 has not reached the set temperature Tst, the process proceeds to the flow after step ST6 in order to promote the temperature rise of the catalyst temperature. As a result, in an operating state where the catalyst temperature is low, such as when cold, it is possible to promote the temperature increase of the catalyst 63 due to the afterburning phenomenon.

  On the other hand, when the catalyst temperature has reached the activation temperature, it is determined whether or not the target operation region is the low-speed supercharging operation region R10 (step ST5).

  If the target operation region is the supercharging operation region R10, the engine control unit 20 sets the variable exhaust valve 30 to fully closed (independent exhaust throttle mode) (step ST6). At the same time, the control mode of the engine 1 is set to the afterburning mode, and the overlap amount OL and the air-fuel ratio of the valve opening period IN and EX are set to the above-described setting conditions (step ST7). As a result, an ejector effect is generated by the exhaust flow, the input flow rate of the exhaust turbocharger 50 (the amount of exhaust We supplied to the exhaust turbocharger 50) is increased, and the turbine scroll 54 is driven. The boost pressure can be improved by increasing the force. Further, since the exhaust gas We as the fluid to be sucked out is sucked out and scavenging is promoted, the exhaust resistance of the cylinder 3 is reduced. Furthermore, the pressure of the blowdown gas can be increased to improve the dynamic pressure supercharging performance.

  In more detail with reference to FIG. 2, as described above, in the state of FIG. 2, the first cylinder 3a is immediately after the exhaust We valve is opened, and the second cylinder 3b is in the overlap period. Exhaust gas We (blow-down gas) guided to the first exhaust passage 16 a is throttled by the variable exhaust valve 30. The throttled blowdown gas increases in flow rate and decreases in pressure. The throttled blowdown gas functions as a driving fluid that provides an ejector effect, and sucks exhaust We as the suctioned fluid flowing through the auxiliary collective exhaust passage 16bc (and the second exhaust passage 16b) and introduces it into the collecting portion 31c. Even if the exhaust valve 9 of the second cylinder 3b is closed (after the overlap period), if the ejector effect of the driving fluid continues, the second exhaust passage 16b and the auxiliary collective exhaust passage 16bc. The exhaust gas We remaining in the gas can be sucked out, and scavenging can be promoted. Although FIG. 2 shows the case where the first cylinder 3a is in the blow-down state, as apparent from Table 1 and FIG. 3, the same applies to other cases. In the present embodiment, the outlets 17a, 17bc, 17d of the three independent exhaust passages 16a, 16bc, 16d are arranged in parallel in the vicinity of the mounting frame 17, and each of the outlets 17a, 17bc, 17d extends to the collecting portion 31c after flowing into the housing 31. Since the parallel arrangement of the outlets 17a, 17bc and 17d is maintained, a high ejector effect can be obtained.

  Next, the control of step ST7 causes the valve opening period IN of the intake valve 7 and the valve opening period EX of the exhaust valve 9 to overlap, and the overlap amount OL is set to at least 90 ° CA or more. Combined with the rich air / fuel ratio being set to 14 or more, the unburned fuel in the cylinder rides on the high-speed exhaust flow and is discharged toward the exhaust turbocharger 50, before the turbine scroll 54. Burns in (afterburn phenomenon). As a result of the afterburning phenomenon, the exhaust temperature increases and the supercharging pressure for driving the turbine scroll 54 increases significantly. Therefore, high supercharging performance can be exhibited even in the cold state, and the output of the engine 1 is improved. Contribute to. Furthermore, since the catalyst 63 is also heated by the rise in exhaust temperature due to the afterburning phenomenon, it becomes possible to reach the activation temperature in a relatively short operating time and exhibit high exhaust purification performance when cold. .

  Next, in step ST5, when the target operation region is not the supercharging operation region, the engine control unit 20 further determines that the target operation region is operated in the independent exhaust throttle mode. It is determined whether or not it is R11 (step ST8).

  If the operation region is the supercharging operation region R11, the engine control unit 20 sets the opening of the variable exhaust valve 30 according to the target load (step ST9), and proceeds to step ST7 to burn after combustion. Run the mode. As a result, it is possible to improve the supercharging performance due to the afterburning phenomenon also in the supercharging operation region R11 of FIG.

  Furthermore, in the determination of step ST8, when the target operation region is not the supercharging operation region R11, the engine control unit 20 further performs a natural intake operation region R12 in which the target operation region is operated in the independent exhaust throttle mode. It is determined whether or not (step ST10).

  If the operation region is the natural intake operation region R12, the engine control unit 20 sets the variable exhaust valve 30 to be fully closed (step ST11). As a result, it is possible to improve the dynamic pressure supercharging effect by the ejector effect and increase the supercharging input flow rate, and the supercharging performance is enhanced, so that the scavenging performance is improved and the output of the engine 1 is improved. And fuel consumption can be reduced. In this operating state, the overlap amount OL and the air-fuel ratio are controlled according to the engine speed and target load in the operating region (step ST12).

  Further, in the determination of step ST10, when the target operation region is not the natural intake operation region R12, the engine control unit 20 sets the variable exhaust valve 30 to fully open (step ST14), and then proceeds to step ST12 and subsequent steps. Thus, the overlap amount OL and the air-fuel ratio are controlled in accordance with the engine speed and the target load in the operation region.

  Next, the control after executing the process of step ST7 or step ST12 will be described with reference to FIG.

  As shown in FIG. 12, after executing the processing of step ST7 or step ST12, the engine control unit 20 displays the overlap amount OL of the valve opening periods IN and EX in accordance with the setting change of the variable valve timing mechanism 12. It is determined whether or not the engine is in an operating state that passes through the torque stop range shown in FIG. 8 (step ST15), and if it passes through the torque stop range, it is further determined whether or not torque is insufficient (step ST15). ST16). The torque shortage is determined, for example, by determining whether or not the engine rotational speed Ne is below an assumed speed within a preset time.

  When it is determined in step ST16 that torque shortage has occurred, the engine control unit 20 controls the operation of the engine 1 in the electric supercharging mode (step ST17). As a result, the electric supercharger 83 operates and the intake control valve 85 of the bypass passage 84 is fully closed, and the intake air Wi that has passed through the intercooler 82 is supercharged to the electric supercharger 83 and supplied to the engine 1. Is done.

  After driving the electric supercharger 83 in the electric supercharging mode, the process returns to step ST2 and the above-described control is repeated.

  On the other hand, if it is determined in step ST15 that it has not passed the torque retention range, or if it is determined in step ST16 that there is no torque shortage, the engine control unit 20 changes the operation mode of the electric supercharger 83. The electric supercharging bypass mode is set (step ST18). As a result, the electric supercharger 83 is stopped, the intake control valve 85 in the bypass passage 84 is fully opened, and the intake air Wi that has passed through the intercooler 82 bypasses the electric supercharger 83 and is supplied to the engine 1.

  Next, the engine control unit 20 determines whether or not torque over has occurred (step ST19). If the value is 1, that is, if the catalyst 63 is lower than the predetermined set temperature Tst, the engine control unit 20 executes the torque suppression control subroutine ST20. If the value is not 1, the process returns to step ST2. The above control is repeated.

  FIG. 13 is a flowchart of the torque suppression control subroutine shown in step ST20 of FIG.

  Referring to FIG. 13, when torque suppression control subroutine ST20 is executed, engine control unit 20 executes ignition retard ST201 (step ST201), and thereafter determines whether torque over is still occurring. (Step ST202). By the ignition retard, the combustion in the cylinder becomes slow, the kinetic energy in the expansion stroke is reduced, and the exhaust gas temperature is also lowered, so that the supercharging pressure is lowered. If torque over is also caused by the ignition retard, the engine control unit 20 further reduces the opening of the throttle valve 81 (throttle opening) (step ST203), and then whether or not torque over still occurs. Is determined (step ST204). By reducing the throttle opening, the filling amount in the cylinder is reduced and the torque is reduced. Also, the blowdown is lowered and the supercharging pressure is reduced. If the torque over occurs even if the throttle opening is reduced, the engine control unit 20 further controls the variable valve timing mechanism 12 to reduce the overlap amount OL (step ST205). It is determined whether torque over has occurred (step ST206). By reducing the overlap amount OL, scavenging is suppressed and torque is reduced. Also, the blowdown is lowered and the supercharging pressure is reduced.

  As a result of executing the processing of steps ST201, ST203, ST205, when the torque over is resolved, the process returns to the original routine. On the other hand, if the torque over is still not resolved even after the process of step ST205 is executed, the process of step ST203 and subsequent steps is executed again.

  As described above, in the present embodiment, in the predetermined engine low speed operation region R10 to R12, the effective opening area S2 of the outlets 17a to 17d of the independent exhaust passages 16a to 16d can be changed to the independent exhaust throttle mode that reduces the maximum value. By switching the exhaust valve 30, an ejector effect can be obtained at the outlets 17a to 17d of the exhaust manifold 16. The ejector effect can increase the input flow rate of the exhaust turbocharger 50 (the amount of exhaust gas supplied to the exhaust turbocharger 50 per unit time) even in a relatively low speed and low load operation region. it can. Moreover, the increase of the blowdown peak due to the ejector effect can promote the improvement of the dynamic pressure supercharging effect and the scavenging performance.

In addition, an overlapping region of the engine low speed operation region R10 to R12 in which the variable exhaust valve 30 operates in the independent exhaust throttle mode and the supercharging operation region R10, R11, R20, R21 in which the exhaust turbocharger 50 operates , that is, When the engine 1 is operated in the supercharging operation regions R10 and R11 on the low speed side, the combustion condition of the air-fuel mixture is set so that unburned fuel is combusted on the upstream side of the exhaust turbocharger 50. This setting causes a so-called afterburning phenomenon. When the afterburning phenomenon occurs, the pressure of the exhaust gas increases, so that the boost pressure rises and the boost performance can be greatly improved. Therefore, even when a relatively large exhaust turbocharger 50 is employed, a large supercharging performance can be obtained in the low speed operation region of the engine 1.

  Further, in the present embodiment, the overlap amount OL when the combustion of the air-fuel mixture of the engine 1 is controlled in the afterburning mode and the electric supercharger 83 provided in the intake passage 80 of the engine 1 is a predetermined torque retention range. In this case, an electric supercharging control means (engine control unit 20) for controlling the operation of the electric supercharger 83 is provided. For this reason, in the present embodiment, when the intake valve 7 and the exhaust valve 9 are operated with an overlap amount OL that does not cause the afterburning phenomenon, the electric supercharger 83 is operated to increase the supercharging pressure. The shortage of output can be compensated. As shown in FIG. 8, when the overlap amount OL is increased during operation in the independent exhaust throttle mode, the overlap amount OL that improves scavenging performance and the overlap amount OL that improves supercharging performance due to the afterburning phenomenon During this time, there may be a torque retention range where scavenging is saturated and afterburning phenomenon does not occur. Therefore, in the present embodiment, while the intake valve 7 and the exhaust valve 9 are operating in such a torque stop range, the supercharging capability is supplemented by the electric supercharger 83, and a high output is obtained in a wide operation region. It is so that it can be maintained. In addition, since the operating range in which the electric supercharger 83 operates is only the above-described torque stop range shown in FIG. 8, the operating rate of the electric supercharger 83 can be reduced to a necessary minimum.

  In the present embodiment, the combustion control means controls the overlap amount OL to at least 90 ° or more in crank angle in the afterburning mode. For this reason, in this embodiment, in the operation state to be operated in the afterburning mode, the afterburning phenomenon occurs with a high probability, and the supercharging performance can be improved to improve the output.

  As described above, in the present embodiment, in the predetermined operation region R10, R11, the combustion of the air-fuel mixture of the engine 1 is controlled in the afterburning mode. Therefore, scavenging in the independent exhaust throttle mode executed in the operation region R10, R11. Combined with the improvement effect of the supercharging performance due to the improvement of the turbocharging and the increase of the supercharging input flow rate, etc., the improvement of the supercharging performance due to the afterburning phenomenon can further reduce the fuel consumption and the output. Therefore, according to the present invention, there is a remarkable effect that high supercharging performance can be exhibited over a wide engine 1 operation region while reducing the operating rate of the electric supercharger 83 and the like as much as possible.

  Next, further technical features in the present embodiment will be described.

(1) Improvement of supercharging capability by dynamic pressure supercharging In this embodiment, since the above independent exhaust passages 16a to 16d are employed, a dynamic pressure supercharging effect can be achieved. The dynamic pressure supercharging is to increase the supercharging capability of the exhaust turbocharger 50 by using exhaust blowdown. As is well known, the effective exhaust time per exhaust stroke (hereinafter referred to as “blow-down period”) is the peak value (hereinafter referred to as “blow-down peak”) of the exhaust flow velocity Qe immediately after the exhaust We valve is opened. The larger the value, the shorter. However, the dynamic pressure supercharging characteristic (pressure ratio determined by the flow velocity) has a quadratic curve characteristic. Therefore, when the blowdown peak is high, even if the reduction due to the shortening of the blowdown period is subtracted, the time-averaged turbine driving force increases compared to when the blowdown peak is low.

  FIG. 14 is an exhaust blowdown characteristic diagram (actual measurement value). The abscissa indicates the crank angle θ (deg: top dead center is 0 ° CA) of the first cylinder 3a, and the ordinate indicates the exhaust flow velocity Qe (kg / s). Blowdown occurs at a cycle of 180 ° CA for each exhaust stroke of each cylinder 3. The illustrated example shows blowdown occurring in the first cylinder 3a between 180 ° CA and 360 ° CA.

  A characteristic C12 is a characteristic of the present embodiment. On the other hand, the characteristic C102 is a characteristic obtained with a standard exhaust manifold having a larger passage volume than in the present embodiment. The characteristic C12 has a larger blowdown peak than the characteristic C102, and the blowdown period is shortened accordingly. For this reason, the characteristic C12 has a higher dynamic pressure supercharging effect than the characteristic C102. In the actual measurement value, the turbine scroll speed per unit time of the characteristic C12 increased by 43% compared to the characteristic C102.

  Further, by shortening the blow-down period, the exhaust pressure after the blow-down peak is lowered, the exhaust resistance is lowered, the residual gas is reduced, and the intake charge amount and the knock resistance are improved.

  The most effective means for obtaining a large exhaust blowdown peak such as characteristic C12 is to reduce the volume of the exhaust manifold 16. For this purpose, the first passage volume Va (≈second passage volume Vb≈third passage volume Vc≈fourth passage volume Vd) shown in FIG. 5 may be reduced. In view of the fact that it is not preferable to reduce the effective opening area, the exhaust resistance increases. To reduce the first passage volume Va, the length of the first exhaust passage 16a should be as short as possible. It will be. Specifically, it is preferable that the length La (see FIG. 4) of the first exhaust passage 16a is not more than 6 times the opening diameter D1 (see FIG. 2) of the same circle as the opening area of the first exhaust passage 16a. In this embodiment, since the opening diameter D1 = φ36 mm and the length La ≦ 200 mm as described above, this condition is satisfied, and effective dynamic pressure supercharging can be expected.

(2) Ejector Effect As described above, in the present embodiment, a large ejector effect can be obtained by the independent exhaust throttle mode using the independent exhaust passages 16a, 16bc, 16d and the variable exhaust valve 30.

  The advantages of the ejector effect according to this embodiment mainly include the following four points.

  First, it is an increase in the input flow rate of the exhaust turbocharger 50 (the amount of exhaust We supplied to the exhaust turbocharger 50 per unit time). The input flow rate immediately after the exhaust We valve is opened adds the exhaust flow rate sucked by the ejector effect to the exhaust flow rate at the time of normal blowdown, resulting in increased driving force of the turbine scroll 54 and improved supercharging pressure. Can be made. Therefore, in the partial load operation region, high turbocharging performance can be exhibited even in the operation region that has conventionally avoided the flow of exhaust gas to the exhaust turbocharger in order to reduce the back pressure. Can do.

  Secondly, the scavenging of the exhaust gas We is promoted. Due to the ejector effect, the exhaust We as the fluid to be sucked out is sucked and scavenging is promoted, so that the exhaust resistance of the cylinder 3 is reduced. Further, since the intake of air in the overlap period is promoted by the promotion of scavenging, the intake air amount can be increased and the engine torque can be increased.

  Third, promotion of dynamic pressure supercharging. As described above, the effect of dynamic pressure supercharging can be obtained by reducing the volume of the exhaust manifold 16, but the effect can be further promoted as described below by the ejector effect.

  If the variable exhaust valve 30 is not present or is fully open and the ejector effect cannot be expected, the blowdown gas flows into the other exhaust passage (reverses flow) through the collecting portion 31c. This acts as if the volume of the exhaust passage is apparently increased. On the other hand, if there is an ejector effect by the variable exhaust valve 30, the blow-down gas sucks the exhaust We as the driven fluid from the other exhaust passage as the driving fluid. That is, it does not wrap around other exhaust passages. This brings about the effect of reducing the exhaust passage volume in the dynamic pressure supercharging.

  As described above, when the entire exhaust passage volume (exhaust manifold volume) is the same, the present embodiment having the ejector effect by the variable exhaust valve 30 promotes the dynamic pressure supercharging more than the one without the ejector effect. It can be done.

  Fourthly, the post-burning phenomenon is actively utilized by increasing the overlap amount OL.

  Even if the overlap amount OL is set to a large value, the possibility of exhaust gas flowing backward due to the intake negative pressure is reduced. Therefore, a relatively large overlap amount OL is secured even in the natural intake operation region R12 to further promote scavenging. Can contribute. In addition, in the supercharging operation regions R10 and R11 at low speed, it is possible to ensure a large overlap amount OL (90 ° CA or more in crank angle) that causes the unburned fuel to be burned after. For this reason, the driving | operation by the above-mentioned afterburning modes is enabled, and it becomes possible to contribute further to reduction of a fuel consumption, and an output improvement.

  As described above, the first passage volume Va to the fourth passage volume Vd of the exhaust manifold 16 are substantially equal to each other. If there is a large difference between the volumes of these independent exhaust passages, the scavenging promotion effect due to the ejector effect also varies greatly between the cylinders. As a result, there is a difference in the anti-knocking performance depending on the scavenging performance. As a result, the setting corresponding to the cylinder 3 having the lowest anti-knocking performance is inevitably set. It becomes useless. In addition, the cylinder-to-cylinder variation also occurs in the intake amount increasing effect due to the ejector effect.

  According to the configuration of the present embodiment, since the first passage volume Va to the fourth passage volume Vd are substantially equal to each other, there is no such problem, and the advantage of the ejector effect can be obtained more effectively.

  By the way, in a general engine with a supercharger, if the length La of the first exhaust passage 16a and the length Ld of the fourth exhaust passage 16d are naturally laid out, the collecting portion 31c is closer to the center. The layout is substantially symmetrical as in the present embodiment arranged in the above. Then, if the second exhaust passage 16b and the third exhaust passage 16c are independent of each other, it is natural that the length thereof becomes shorter than the length La and the length Ld. In order to forcibly align this with the length La, a layout such as unnaturally detouring is required. This is not preferable because it causes an increase in exhaust resistance or prevents the length La and the length Ld from being shortened in order to establish the layout.

  According to the present embodiment, since the auxiliary collective exhaust passage 16bc that collects the second exhaust passage 16b and the third exhaust passage 16c, which tend to be small in volume, is provided, the length of the auxiliary collective exhaust passage 16bc is included. The second exhaust passage length Lb and the third exhaust passage length Lc are easily made substantially equal to the first exhaust passage length La and the fourth exhaust passage length Ld. As a result, the first passage volume Va to the fourth passage The volumes Vd can be set substantially equal to each other.

  Note that the second exhaust passage 16b and the third exhaust passage 16c are independent of each other even if they are assembled. As shown in Table 1 and FIG. 3, since the ignition order of the second cylinder 3b and the third cylinder 3c is not adjacent to each other, the exhaust valve 9 starts to open before the bottom dead center and closes after the top dead center. Considering this, there is no period in which the exhaust valve 9 of the second cylinder 3b and the exhaust valve 9 of the third cylinder 3c are both open. Therefore, there is no mutual exhaust interference, and in the exhaust stroke of the second cylinder 3b, the auxiliary collective exhaust passage 16bc can be regarded as a pseudo extension of the second exhaust passage 16b, and in the exhaust stroke of the third cylinder 3c. The auxiliary collective exhaust passage 16bc can be regarded as an extension of the third exhaust passage 16c in a pseudo manner.

  Thus, in this embodiment, although it is a 4-cylinder engine, the mutually independent relationship is implement | achieved by the three independent exhaust passages. By doing so, the layout can be made compact, and the connecting portion between the housing 31 and the exhaust turbocharger 50 can be downsized.

  As described above, the dynamic pressure supercharging effect and the ejecting effect, which are the main technical features of the present embodiment, have been described, but these are closely related and cooperate to improve the supercharging performance, and further reduce fuel consumption. Contributes to improved output.

  FIG. 15 is a graph showing the charging efficiency ηc in the operation regions R10 to R12 operated in the independent exhaust throttle mode. In FIG. 15, the horizontal axis indicates the engine rotation speed Ne (rpm), and the vertical axis indicates the charging efficiency ηc (%). A characteristic C13 is a characteristic of the present embodiment in which the dynamic pressure supercharging and the independent exhaust throttle mode are used in combination. A characteristic C103 is a characteristic shown for comparison, and is a characteristic when a conventional general exhaust manifold (without the variable exhaust valve 30) is used. The filling efficiency ηc of the characteristic C13 is increased by about 20 to 30 points with respect to the characteristic C103. This is the effect of increasing the supercharging pressure by the dynamic pressure supercharging and the independent exhaust throttle mode using the variable exhaust valve 30.

  FIG. 16 is a graph showing the net average effective pressure (BMEP) of the engine in the supercharging operation regions R10 to R12. In FIG. 16, the horizontal axis indicates the engine rotation speed Ne (rpm), and the vertical axis indicates the net average effective pressure (kPa). A characteristic C14 is a characteristic of the present embodiment in which the dynamic pressure supercharging and the independent exhaust throttle mode are used together (a characteristic corresponding to the characteristic C13 in FIG. 15). A characteristic C104 is a characteristic shown for comparison, and corresponds to the characteristic C103 in FIG. The net average effective pressure of the characteristic C14 is increased by about 200 to 400 kPa with respect to the characteristic C104. This is an effect that the charging efficiency is increased (FIG. 15) by the dynamic pressure supercharging and the independent exhaust throttle mode using the variable exhaust valve 30, that is, the engine torque is increased.

  Next, a description will be given of a further technique employed in the present embodiment in order to achieve the ejector effect more remarkably.

  FIG. 17 is a graph showing the relationship between the effective opening ratio Rd of the exhaust passage and the volume efficiency ηv in the present embodiment. The upper part of the horizontal axis shows the effective opening diameter D2 (mm).

  The lower part of the horizontal axis indicates the effective aperture ratio Rd (%). The effective opening ratio Rd is the area ratio of each opening diameter D1 to the effective opening diameter D2 of each outlet 17a, 17bc, 17d. That is, Rd = (D2 / D1) 2 × 100 (%), or Rd = (S2 / S1) × 100 (%).

  A characteristic C15 shown in FIG. 17 indicates a characteristic at an engine rotational speed Ne = 1500 rpm, and C16 indicates a characteristic at 2000 rpm. As is clear from these characteristics, there is a particularly preferable range in which the volumetric efficiency ηv is particularly high in the range of the effective aperture diameter D2 = 22 to 28 mm (effective aperture ratio Rd: range of 37 to 61%). This indicates that a particularly remarkable ejector effect can be obtained in this preferred range. Therefore, by setting the effective opening diameter D2 within this preferable range, a higher supercharging effect can be obtained and the engine torque can be further increased.

  In addition, in the supercharging operation regions R10 and R11 shown in FIG. 7, by setting the operation mode to the afterburning mode, the supercharging performance can be enhanced in combination with the dynamic pressure supercharging effect and the ejector effect, It is also possible to contribute to the exhaust gas purification performance when cold.

  The above-described embodiments can be appropriately changed without departing from the gist of the present invention.

  For example, the set values such as the length La, the volume Va, the diameters D1 and D2 of the first exhaust passage 16a and the like are not limited to the above values. These values may be suitably set according to the size of the engine and the displacement.

  Further, the valve timing change control by the variable valve timing mechanism 12 has many advantages to be executed except for the operation control in the afterburning mode, but it is not always necessary. Even without this, the basic effect of the present invention is sufficient. Obtainable.

  Further, instead of the flap 35 of the variable exhaust valve 30, a rotor that switches the flow path according to the phase may be adopted.

  Further, as the electric supercharger, as shown in FIG. 1, in addition to the electric turbocharger 83 (so-called e-Boost) having a different configuration from the exhaust turbocharger 50, the turbine scroll 54 of the exhaust turbocharger 50. It is also possible to adopt a type in which the motor is driven by a motor (so-called e-Turbo).

  Thus, the above-described embodiment is merely an example of a preferred specific example of the present invention, and the present invention is not limited to the above-described embodiment. It goes without saying that various modifications are possible within the scope of the claims of the present invention.

1 is a schematic configuration diagram of a supercharged engine according to a first embodiment of the present invention. It is a partial sectional side view of FIG. 2 is a timing chart according to the embodiment of FIG. It is an external appearance perspective view which shows the principal part which concerns on embodiment of FIG. It is an external appearance perspective view which expands and shows the principal part which concerns on embodiment of FIG. It is a perspective view which shows schematic structure of the variable exhaust valve which concerns on embodiment of FIG. 1, (A) shows the state at the time of valve closing, and (B) shows the state at the time of valve opening. It is a characteristic view which shows the example of a setting of the driving | operation area | region for performing control according to the driving | running state which concerns on embodiment of FIG. It is a graph for demonstrating the afterburn phenomenon concerning this embodiment. It is a graph which shows the relationship between the amount of overlaps, and engine speed. It is an exhaust characteristic diagram, (A) is an independent exhaust throttle mode (when the variable exhaust valve is fully closed), (B) is a normal operation mode (when the variable exhaust valve is fully open). It is a flowchart which shows the example of control of the engine system in one Embodiment of this invention. It is a flowchart which shows the example of control of the engine system in one Embodiment of this invention. It is a flowchart which shows the torque suppression control subroutine of FIG. It is an exhaust blowdown characteristic figure. It is a graph which shows the charging efficiency in a low-speed supercharging operation area | region. It is a graph which shows the net average effective pressure of an engine in a low-speed supercharging operation field. It is a graph which shows the relationship between the throttle degree of an exhaust passage, and volumetric efficiency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine with a supercharger 3 Cylinder 10 Fuel injection valve 12 Variable valve timing mechanism 16 Exhaust manifold 16a Independent exhaust passage 16b Exhaust passage 16bc Auxiliary collective exhaust passage 16c Exhaust passage 16d Independent exhaust passage 17a-17d Outlet 20 Engine control unit (combustion control) And an example of electric supercharging control means)
30 Variable exhaust valve 31c Collecting part 50 Exhaust turbocharger 80 Intake passage 83 Electric supercharger R10 (low speed) supercharging operation area R11 (low speed) supercharging operation area R12 Natural intake operation area R20 (medium speed) supercharging operation Region R21 (High speed) Supercharging operation region R22 (Medium high speed) Natural intake operation region

Claims (3)

In a predetermined operation region, an engine configured to be able to change the opening and closing timing of each of the intake valve and the exhaust valve so that the opening periods of the intake valve and the exhaust valve overlap each other in the vicinity of the exhaust top dead center;
An exhaust manifold connected independently to each exhaust port of a plurality of cylinders provided in the engine and having an independent exhaust passage;
A collecting portion in which the downstream sides of the independent exhaust passages of the exhaust manifold are gathered together;
An exhaust turbocharger connected to the downstream side of the collecting portion;
At least in a predetermined engine low-speed operation region, in order to achieve an ejector effect, the engine is operated in an independent exhaust throttle mode in which the effective opening area at the outlet of the independent exhaust passage is reduced below the maximum value between the collecting portion and the exhaust manifold. Variable exhaust valve
And low engine speed operating region where the variable exhaust valve is operated in the independent exhaust throttle mode, wherein when said engine exhaust turbo supercharger in an overlapping region between the supercharge operating range of operation of the operation, unburned fuel At least the air-fuel ratio is made richer than the stoichiometric air-fuel ratio within the flammable range and the intake valves and the exhaust valves are opened so that they are discharged from the engine and burned upstream of the exhaust turbocharger. And a combustion control means for controlling the combustion of the air-fuel mixture of the engine in a post-combustion mode that expands an overlap amount that overlaps a predetermined range or more. . The engine system with a supercharger according to claim 1,
An electric supercharger provided in the intake passage of the engine;
When the combustion amount of the air-fuel mixture of the engine is controlled in the afterburning mode, if the overlap amount in which the valve opening periods of the intake valve and the exhaust valve overlap each other is within a predetermined torque stop range, the electric motor An engine system with a supercharger comprising: an electric supercharge control means for controlling the operation of the supercharger. The supercharged engine system according to claim 1 or 2,
The combustion control means controls, in the afterburning mode, an overlap amount in which the valve opening periods of the intake valve and the exhaust valve overlap each other so that a crank angle is at least 90 ° or more. Supercharged engine system.

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