JP2009221932A - Engine with supercharger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance supercharge performance effectively and promote temperature rise of catalyst in cold time by using a plurality of exhaust gas turbochargers. <P>SOLUTION: The engine is provided with the first and second exhaust gas turbochargers which are serially connected, catalysts connected to their downstream, a means for controlling a variable exhaust valve so as to reduce an effective opening area of an outlet of an independent exhaust passage in a predetermined supercharge operation area, a means for extending an overlap period of supply and exhaust valves in the predetermined supercharge operation area, a temperature state judging means, a turbine bypass passage for bypassing a turbine of the second turbo supercharger, an exhaust gas flow passage switch valve and a flow passage selecting means. The flow passage selecting means controls the exhaust gas flow passage switch valve so that exhaust gas flows to the catalyst through the turbine of the first exhaust turbo supercharger and the turbine bypass passage during cold time in the predetermined supercharge operation area and the exhaust gas flows through turbines of both the exhaust gas turbo superchargers during a warm time in the predetermined supercharge operation area. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a supercharged engine having a plurality of exhaust turbochargers.

Conventionally, as a means for increasing the engine output torque, a supercharging device for increasing the intake pressure is known. A typical example is an exhaust turbocharger. Further, as shown in Patent Document 1, an engine having a plurality of exhaust turbochargers is also known. The engine disclosed in Patent Document 1 includes two turbochargers of a high-pressure stage and a low-pressure stage, the turbines of these turbochargers are connected in series to an exhaust passage, and the exhaust is both turbochargers. Both turbochargers are driven by passing through.
JP 2004-28104 A

  In the engine described in Patent Literature 1, improvement of supercharging performance can be expected by using a plurality of superchargers. However, even if a plurality of superchargers are used in this way, it is difficult to sufficiently improve the supercharging performance in a low speed operation region where the exhaust flow rate is small.

  In general, an exhaust purification catalyst is provided in the exhaust passage of the engine. However, when the engine is cold, the catalyst often does not reach the activation temperature, and sufficient exhaust purification performance is obtained until the activation temperature is reached. Therefore, in order to improve emission, it is desired to shorten the time until the catalyst reaches the activation temperature.

  In view of the above circumstances, the present invention uses a plurality of exhaust turbochargers and can effectively increase the supercharging performance by increasing the exhaust energy given to the supercharger. It aims at providing the engine with a supercharger which can promote a temperature rise.

  In order to solve the above problems, the present invention provides an engine having a plurality of cylinders, an exhaust manifold having independent exhaust passages that are independently connected to the exhaust ports of the cylinders of the engine, and the exhaust manifold. A plurality of exhaust turbochargers connected in series to an exhaust passage downstream of the collective portion, and a downstream of the turbocharger. A variable exhaust gas purification catalyst and a variable variable opening configured to change an effective opening area of the outlet of the independent exhaust passage between the exhaust manifold and the collecting portion in order to achieve an ejector effect in a predetermined supercharging operation region. An exhaust valve and a variable exhaust valve that controls the variable exhaust valve so that an effective opening area at the outlet of the independent exhaust passage is smaller than an opening area at the maximum opening in the predetermined supercharging operation region. Control means, an overlap control means for controlling valve timing so as to expand an overlap period in which the exhaust valve opening period and the intake valve opening period overlap in the predetermined supercharging operation region, and the engine temperature state Turbine bypass for bypassing one of the turbines of the plurality of exhaust turbochargers and connecting the upstream exhaust passage and the downstream exhaust passage of the bypassed turbine by bypassing the temperature state discrimination means for discrimination An exhaust passage switching valve for selectively circulating exhaust gas to any one of a passage, a turbine other than one of the turbines of the plurality of exhaust turbochargers, and the turbine bypass passage; and an operating state of the engine And a flow path selection means for controlling the exhaust flow path switching valve according to the temperature state and selecting a flow path of the exhaust, the flow path selection means, When the temperature state determination means determines that the temperature is cold in a constant supercharging region, the exhaust passes through one of the turbines of the plurality of exhaust turbochargers and the turbine bypass passage, and the catalyst. When the temperature state determination means determines that the warm state is in the predetermined supercharging region, the exhaust flow path switching valve is set so that the exhaust passes through each turbine of the plurality of exhaust turbochargers. It is intended to be controlled.

  According to this configuration, in the predetermined supercharging region, the overlap period is extended, whereby unburned fuel is discharged to the exhaust passage, and afterburning (combustion in the exhaust passage) occurs. In particular, after the exhaust gas containing unburned fuel is agitated by the turbine of the one exhaust turbocharger, afterburning occurs downstream of the turbine. And when it is cold, the turbines other than the one are bypassed, so that the heat energy due to afterburning is supplied to the catalyst without being taken away by the turbine other than the one, and the temperature rise of the catalyst is promoted. At this time, by controlling the variable exhaust valve so as to reduce the effective opening area of the outlet of the independent exhaust passage, blowdown gas having a high exhaust flow rate is effectively guided to the turbine and the exhaust flow rate is increased by the ejector effect. Since the dynamic pressure supercharging effect by the blowdown gas is increased and the driving force of the turbine is increased, the supercharging performance can be sufficiently enhanced even with the one turbocharger.

  On the other hand, during the warm period in the predetermined supercharging region, the unburned fuel is discharged into the exhaust passage by extending the overlap period, and afterburning is performed downstream of the turbine of the one turbocharger. The occurrence is the same as in the cold state, but the thermal energy from afterburning is supplied to the other turbines, and the driving force of the turbines is increased. Thereby, the output of a supercharger and a transient response (responsiveness of the torque rise at the time of acceleration) can be improved.

  In the engine with a supercharger of the present invention, the plurality of exhaust turbochargers have different turbine diameters, and when the engine state determination means determines that it is cold in the predetermined supercharging region, The exhaust gas preferably passes through a turbine having the smallest diameter among the turbines of the plurality of exhaust turbochargers and a turbine bypass passage that bypasses the other turbines.

  In this manner, when the unburned fuel is discharged into the exhaust passage by expanding the overlap period in the predetermined supercharging region, the turbocharger turbine is small and has a high rotational speed. By stirring the exhaust gas, the stirring action can be enhanced and the afterburn can be surely generated.

  Further, the variable exhaust valve control means has a smaller effective opening area at the outlet of the independent exhaust passage than when it is warm when the temperature state determination means determines that it is cold in the predetermined supercharging region. It is preferable to control the variable exhaust valve.

  In this way, in the predetermined supercharging region, when the engine is warm, the degree of throttling of the outlet of the independent exhaust passage by the variable exhaust valve is adjusted so that knocking does not occur even when the engine temperature is high, but knocking occurs. When it is difficult to cool, the ejector effect is enhanced by narrowing the outlet of the independent exhaust passage. Thereby, at the time of the cold in the predetermined supercharging region, the supercharging performance is sufficiently improved even when only one turbocharger is substantially driven.

  As described above, according to the engine with a supercharger of the present invention, when it is cold in a predetermined supercharging region, the unburnt fuel is discharged to the exhaust passage by extending the overlap period, and one turbo By causing afterburning by the stirring action of the turbine of the supercharger and supplying the thermal energy to the catalyst, the temperature rise of the catalyst can be promoted and the time until the catalyst is activated can be shortened. In addition, when the engine is warm in a predetermined supercharging region, it is possible to increase the driving force of the turbine by supplying thermal energy from afterburning to a turbine other than one turbine, and to effectively use a plurality of turbochargers. It can be used to increase the supercharging performance.

  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 according to an embodiment of the present invention. 2 is a partial side sectional view of FIG.

  The supercharged engine shown in FIG. 1 is an in-line four-cylinder four-cycle engine. The cylinder block 2 of the engine 1 includes first to fourth cylinders 3a, 3b, 3c, and 3d (referred to collectively as cylinder 3). Are 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, a rotation speed sensor SN4, an intake air temperature sensor SN5, and the like. Moreover, in order to detect the driving | running state of the vehicle carrying this engine 1, accelerator opening sensor SN6, vehicle speed sensor SN7, etc. are provided in the vehicle.

  Further, as shown in the timing chart of FIG. 3, in the engine 1 of this embodiment, each cylinder 3 is sequentially ignited at every crank angle of 180 degrees (hereinafter referred to as 180 ° CA), as in a general four-cylinder engine. It is driven by shifting each stroke so that the time comes. The ignition order is so-called # 1 → # 3 → # 4 → # 2 (#x indicates the x-th cylinder). Therefore, 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 FIG. 3, when the first cylinder 3a starts blowdown, the second cylinder 3b is in a 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.

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

  As shown in FIGS. 1 and 4, the first exhaust passage 16 a and the fourth exhaust passage 16 d maintain an independent state over the entire length thereof, but the second exhaust passage 16 b and the third exhaust passage 16 c are arranged 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 downstream independent exhaust passages 16a, 16bc, and 16d.

  A mounting frame 17 is provided on the downstream side of the exhaust manifold 16, and as shown in FIG. 4, the mounting frame 17 defines outlets 17a, 17bc, 17d of the independent exhaust passages 16a, 16bc, 16d. Yes.

  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 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 refers to an opening area for each of the outlets 17a, 17bc, and 17d through which the exhaust gas We can flow through the outlets 17a, 17bc, and 17d.

  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. Due to this ejector effect, in this embodiment, as will be described in detail later, even in a relatively low speed and low load operation region, an input flow rate (supplied to the turbine 41) of the turbine 41 of the exhaust turbocharger 40 described later is provided. 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.

  5A and 5B are perspective views showing a schematic configuration of the variable exhaust valve 30 according to the embodiment of FIG. 1, wherein FIG. 5A shows a state when the valve is closed and FIG. 5B shows a state when the valve is opened.

  As shown in FIGS. 1, 2, and 5, the variable exhaust valve 30 is housed in the housing 31 interposed between the exhaust manifold 16 and the exhaust turbocharger 40, which will be described later, and the exhaust manifold 16. Flaps 35 that change the effective opening area of the outlets 17a, 17bc, and 17d, and a flap that is pivotally supported by the housing 31 so that the flaps 35 swing around an axis that intersects the direction in which the exhaust gas We flows as indicated by an arrow Z1. A shaft 37, an actuator 38 such as a motor that rotates the flap shaft 37, and a return spring 39 that biases the flap 35 in the valve opening direction via the flap shaft 37.

  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.

  As shown in FIG. 1 and FIG. 2, the housing 31 is partitioned with a collecting portion 31 c where the exhausts We from the independent exhaust passages 16 a, 16 bc, 16 d merge. 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.

  As shown in FIGS. 2 and 5, the outer periphery of the flap 35 has a fan-shaped fan-shaped surface 36 having a flap shaft 37 as a main part of the fan. 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 to reduce the flow rate of the exhaust We (see FIG. 5A). 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, 17d are opened (see FIG. 5B).

  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 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, even in an operating situation where the exhaust flow velocity is large due to blowdown, vibration is less likely to occur.

  As shown in FIG. 1, the engine with a supercharger according to the present embodiment includes a plurality of turbochargers. In the present embodiment, the engine includes first and second turbochargers 40 and 50. Yes. The turbines 41 and 51 of these turbochargers 40 and 50 are connected in series to the exhaust passage 60 downstream of the variable exhaust valve 30.

  The exhaust turbochargers 40 and 50 include turbines 41 and 51 provided in the exhaust passage 60, compressors 42 and 52 provided in the intake passage 80, and a shaft connecting the compressors 42 and 52 to the turbines 41 and 51. 43, 53, and is a device that drives the compressors 42, 52 by rotating the turbines 41, 51 with the exhaust gas We, and compresses the intake air Wi to increase the intake pressure. In the present embodiment, as the first turbocharger 40, the turbine 41 and the compressor 42 are small turbochargers having a relatively small diameter (is approximately the same as a turbocharger employed in an engine that increases torque in a normal low speed range)? On the other hand, as the second turbocharger 50, the turbine 51 and the compressor 52 are larger turbochargers (usually larger in diameter than the first turbocharger 40). Superchargers that are the same as or larger than those used in engines that increase torque at high speeds are used.

  In the exhaust passage 60, the turbine 41 of the first turbocharger 40 is disposed upstream of the turbine 51 of the second turbocharger 50. Further, an exhaust purification catalyst 65 is provided downstream of the turbine 51 of the second turbocharger 50. In the present embodiment, the catalyst 65 is a three-way catalyst that is activated in a predetermined temperature range and can remove hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust.

  The exhaust passage 60 bypasses the turbine 41 of the first turbocharger 40 and bypasses the turbine 51 of the second turbocharger 50 and the first turbine bypass passage 61 that connects the upstream side and the downstream side thereof. A second turbine bypass passage 62 that connects the upstream side and the downstream side is provided. The second turbine bypass passage 62 bypasses one of the plurality of exhaust turbocharger turbines, and connects the upstream exhaust passage and the downstream exhaust passage of the bypassed turbine. Corresponds to the passage.

  At locations where the first turbine bypass passage 61 diverges from the exhaust passage 60, there is a state in which exhaust flows through the turbine 41 (a state where the passage on the turbine 41 side is opened and the first turbine bypass passage 61 is closed), and a first turbine bypass A first exhaust flow path switching valve 63 that can be switched to a state in which exhaust gas is circulated through the passage 61 (a state in which the passage on the turbine 41 side is closed and the first turbine bypass passage 61 is opened) is provided. Further, at a location where the second turbine bypass passage 62 branches from the exhaust passage 60, a state in which exhaust gas is circulated to the turbine 51 (a state in which the passage on the turbine 51 side is opened and the second turbine bypass passage 62 is closed), A second exhaust flow path switching valve 64 that can be switched to a state in which the exhaust gas flows through the turbine bypass passage 62 (a state in which the passage on the turbine 51 side is closed and the second turbine bypass passage 62 is opened) is provided. The second exhaust flow path switching valve 64 is an exhaust flow path switching valve that alternatively connects one of the turbine other than one of the turbines of the plurality of exhaust turbochargers and the turbine bypass passage. Equivalent to.

  On the other hand, in the intake passage 80 of the engine 1, the compressors 42 and 52 of the turbochargers 40 and 50 are arranged in series, and an intercooler 85 for cooling the intake air is provided downstream thereof. A throttle valve 86 for adjusting the intake air flow rate is provided downstream of the intercooler 85, and the intake air that has passed through the throttle valve 86 is supplied to each cylinder through the intake manifold 87.

  Furthermore, a first compressor bypass passage 81 that bypasses the compressor 42 of the first turbocharger 40 and connects the upstream side and the downstream side of the intake passage 80 and the compressor 52 of the second turbocharger 50. And a second compressor bypass passage 82 connecting the upstream side and the downstream side of the compressor.

  At locations where the first compressor bypass passage 81 branches from the intake passage 80, a state in which intake air flows to the compressor 42 (a state in which the passage on the compressor 42 side is opened and the first compressor bypass passage 81 is closed), and a first compressor bypass A first intake flow path switching valve 83 that can be switched to a state in which intake air flows through the passage 81 (a state in which the compressor 42 side passage is closed and the first compressor bypass passage 81 is opened) is provided. Further, at a location where the second compressor bypass passage 82 branches from the intake passage 80, a state in which intake air is circulated to the compressor 52 (a state in which the passage on the compressor 52 side is opened and the second compressor bypass passage 82 is closed), A second intake flow path switching valve 84 that can be switched to a state in which intake air flows through the compressor bypass passage 82 (a state in which the compressor 52 side passage is closed and the second compressor bypass passage 82 is opened) is provided.

  The exhaust flow path switching valves 63 and 64 and the intake flow path switching valves 83 and 84 are actuated by actuators 63a, 64a, 83a, and 84a in response to signals from the engine control unit 20, which will be described later. .

  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 changed continuously or may be changed stepwise by two or more stages.

  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 air flow sensor SN3, a rotation speed sensor SN4, an intake air temperature sensor SN5, an accelerator opening sensor SN6, a vehicle speed. Various detection means such as the sensor SN7 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 86, an electromagnetic valve (not shown) provided in the variable valve timing mechanism 12, and a variable exhaust valve 30 actuators 38, exhaust passage switching valves 63, 64, and actuators 63a, 64a, 83a, 84a of intake passage switching valves 83, 84 are connected.

  FIG. 6 shows a functional configuration of the engine control unit 20. The engine control unit 20 performs combustion control by controlling fuel supply amount, throttle opening, ignition timing, and the like. Further, the engine control unit 20 is controlled by controlling the variable exhaust valve control means 21 that controls the variable exhaust valve 30 according to the operating state and the engine temperature state, and the intake VVT 12i and the exhaust VVT 12e according to the operating state. Overlap control means 22 for controlling a lap period (a period in which the exhaust valve open period and the intake valve open period overlap), a temperature state determination means 23 for determining the temperature state of the engine based on the engine water temperature, etc., the operating state and the engine The switching valve 63, 64, 83, 84 is controlled according to the temperature state of the exhaust gas to control the switching valve 63, 64, 83, 84 to functionally include an exhaust passage and an intake passage.

  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 this figure, the horizontal axis indicates the engine speed Ne (rpm), and the vertical axis indicates the required load (required torque) τ (N · m).

  In the operation characteristics shown in the figure, a low-speed dynamic pressure supercharging operation region (predetermined supercharging operation region) R1 and a high-speed operation region R2 are set with a line from a predetermined low speed and high load to a high speed and low load as a boundary. Has been.

  In the dynamic pressure supercharging operation region R1, the variable exhaust valve control means 21 is set to execute the independent exhaust throttle mode. In the independent exhaust throttle mode, the engine control unit 20 as the variable exhaust valve control means 21 drives the variable exhaust valve 30 to maximize the effective opening area of each outlet 17a, 17bc, 17d of the independent exhaust passages 16a, 16bc, 16d. In this control, the engine control unit 20 sends a control signal to the actuator 38 of the variable exhaust valve 30, and the actuator 38 is a flap shaft. In this control, the rotation angle of the flap 35 is adjusted by driving the rotation 37. In the independent exhaust throttle mode, the variable exhaust valve 30 can be fully closed or changed so that the effective opening area is reduced as the required load increases, depending on the operating region. In the high speed operation region R2, the variable exhaust valve 30 is set to fully open.

  In the dynamic pressure supercharging operation region R1, the overlap period and the fuel injection amount are controlled in a so-called afterburning mode. The afterburning mode is that at least the air-fuel ratio is made richer than the stoichiometric air-fuel ratio within the combustible range and the overlap period is set in advance so that unburned fuel is discharged from the engine 1 and burned in the exhaust passage. This is an operation mode that expands beyond the set range (the range set when the normal combustion state is set).

  When the afterburning mode is set, the unburned fuel is discharged into the exhaust passage, and the discharged unburned fuel is burned in the exhaust passage, thereby causing the afterburning phenomenon. In addition, as a result of the inventor's earnest research, the overlap period OL required for the afterburn phenomenon to occur becomes smaller as the engine rotational speed Ne increases. For example, at 1500 rpm, the overlap period OL is 90 ° CA or more. It became clear that afterburning phenomenon occurred. Therefore, in the operation region shown in FIG. 7, when the dynamic pressure supercharging operation region R1 is switched to the afterburning mode, the engine control unit 20 sets the overlap period OL of the valve opening periods IN and EX to 90 ° CA or more. And the engine 1 is controlled.

  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. 8 is an exhaust characteristic diagram, where (A) is an independent exhaust throttle mode, and (B) is a normal operation mode (when the variable exhaust valve is fully open). In FIG. 8, 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 lift amount (mm). The opening periods of the intake valve 7 and the exhaust valve 9 are indicated by IN and EX, respectively.

  Referring to FIG. 8A, 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. 8B, the exhaust pressure when the variable exhaust valve is fully open is affected by the blowdown peak of other cylinders, so that the valve opening periods EX and IN are exhaust top dead centers. If they overlap thereafter, the exhaust pressure will exceed the boost pressure, and scavenging may not be possible.

  Therefore, in the present embodiment, a relatively large overlap period OL (for example, 65 ° CA) is adopted in the dynamic pressure supercharging operation region R1 shown in FIG. 7, and the overlap period OL is maximized in the high speed operation region R2. Is set small (for example, 0 ° CA to 40 ° CA).

  In addition, when the engine 1 is cold, the catalyst 65 often does not reach the activation temperature, and depending on the operating conditions, it may take a considerable time for the catalyst 65 to rise to the activation temperature. Therefore, in the present embodiment, as will be described in detail later, when it is cold in the dynamic pressure supercharging operation region R1, in order to promote the temperature rise of the catalyst 65, the flow path selection means 24 causes the exhaust to be exhausted. Exhaust flow path switching valves 63 and 64 are controlled so as to flow to the catalyst 65 through the turbine 41 and the second turbine bypass passage 62 of the first turbocharger 40, while the temperature in the dynamic pressure supercharging operation region R1 is controlled. When it is time, the exhaust flow path switching valves 63 and 64 are controlled so that the exhaust passes through the turbines 41 and 51 of the turbochargers 40 and 50.

  Next, an example of engine control according to the present embodiment will be described with reference to the flowchart of FIG.

  In this figure, the engine control unit 20 first reads data such as the engine water temperature, the required load, and the engine speed (step S1). Then, the current operating state of the engine is examined based on data such as the required load and the engine speed (step S2), and it is determined whether the operating state is in the dynamic pressure supercharging operation region R1 or the high speed operation region R2. To do.

  If it is determined in this determination that it is in the dynamic pressure supercharging operation region R1, the variable exhaust valve is adjusted to an opening that is smaller than fully open and set according to the operating state (step S3). Further, a combustion condition for the afterburning mode is set (step S4). That is, as described above, the valve opening / closing timing by the intake VVT 12i and the exhaust VVT 12e is set so as to increase the overlap period, and the fuel injection amount is set so as to make the air-fuel ratio rich.

  Next, it is determined whether or not the engine water temperature is higher than a predetermined temperature T (step S5). Then, when it is determined that the engine water temperature is cold when the engine water temperature is equal to or lower than the predetermined temperature T (when the determination in step S5 is NO), as shown in FIG. While controlling the first exhaust flow path switching valve 63 in a state in which the exhaust gas is circulated (a state in which the passage on the turbine 41 side is opened and the first turbine bypass passage 61 is closed), the turbine 51 of the second turbocharger 50 is bypassed. The second exhaust flow path switching valve 64 is controlled to be in a state of being closed (a state in which the passage on the turbine 51 side is closed and the second turbine bypass passage 62 is closed) (step S6). Corresponding to the control of the exhaust flow path switching valves 63 and 64, the first intake flow path switching valve 83 is in a state in which intake air is circulated to the compressor 42 of the first turbocharger 40 (passage on the compressor 42 side). Is opened and the first compressor bypass passage 81 is closed), and the second intake flow switching valve 84 is in a state of bypassing the compressor 52 of the second turbocharger 50 (the compressor 52 side passage is closed and the first compressor bypass passage 81 is closed). 2 state in which the compressor bypass passage 82 is opened).

  Further, in this case, the variable exhaust valve 30 has an opening (for example, fully closed) smaller than the set opening (step S7).

  When it is determined that the operating state is in the dynamic pressure supercharging operation region R1 and the engine water temperature is warmer than the predetermined temperature T in step S5, as shown in FIG. While controlling the first exhaust flow path switching valve 63 in a state in which the exhaust gas is circulated to the turbine 41 of the supercharger 40 (a state in which the passage on the turbine 41 side is opened and the first turbine bypass passage 61 is closed), the second turbocharger is controlled. The second exhaust passage switching valve 64 is controlled so that the exhaust gas is also circulated through the turbine 51 of the feeder 50 (a state where the turbine 51 side passage is opened and the second turbine bypass passage 62 is closed) (step S8). Corresponding to the control of the exhaust flow path switching valves 63 and 64, the first intake flow path switching valve 83 is in a state in which intake air is circulated to the compressor 42 of the first turbocharger 40 (passage on the compressor 42 side). Is opened and the first compressor bypass passage 81 is closed), and the second intake flow switching valve 84 is in a state in which intake air is circulated to the compressor 52 of the second turbocharger 50 (opens the passage on the compressor 52 side). The second compressor bypass passage 82 is closed).

  When it is determined in step S2 that the operation state is in the high-speed operation region R2, as shown in FIG. 13, the turbine 41 of the first turbocharger 40 is bypassed (the passage on the turbine 41 side is closed). The first exhaust passage switching valve 63 is controlled in a state where the first turbine bypass passage 61 is opened), and the exhaust gas is circulated to the turbine 51 of the second turbocharger 50 (the passage on the turbine 51 side is opened and the first turbine bypass passage 61 is opened). 2) The second exhaust passage switching valve 64 is controlled to a state in which the turbine bypass passage 62 is closed (step S9). Corresponding to the control of the exhaust flow path switching valves 63, 64, the first intake flow path switching valve 83 bypasses the compressor 42 of the first turbocharger 40 (closes the passage on the compressor 42 side). The first compressor bypass passage 81 is opened), and the second intake passage switching valve 84 is in a state in which intake air is circulated to the compressor 52 of the second turbocharger 50 (the passage on the compressor 52 side is opened and the second intake passage switching valve 84 is opened). 2) The compressor bypass passage 82 is closed.

  Furthermore, in this case, the variable exhaust valve 30 is opened (step S10), and the combustion conditions in the normal operation are set (step S11). That is, the valve opening / closing timing by the intake VVT 12i and the exhaust VVT 12e is set so as to reduce the overlap period, and the fuel injection amount is set so that the air-fuel ratio is substantially the stoichiometric air-fuel ratio.

  According to the engine with the supercharger of the present embodiment as described above, when the engine operating state is in the dynamic pressure supercharging operation region R1 and the engine water temperature is cold when the engine water temperature is equal to or lower than the predetermined temperature T, the afterburning mode is set. As the combustion conditions are set and the exhaust flow path switching valves 63 and 64 are controlled to the state shown in FIG. 10, the exhaust gas causes the turbine 41 of the first turbocharger 40 to flow as shown by the arrows in FIG. As described above, the exhaust passage is set so as to bypass the turbine 51 of the second turbocharger 50 and flow to the catalyst 65. Thereby, the temperature rise of the catalyst 65 is promoted.

  That is, when the exhaust gas is sent to the catalyst through the turbine of the turbocharger, during the small overlap operation, the exhaust heat is taken away by the turbine, so that the exhaust temperatures P3 and P4 before the catalyst are relatively low. On the other hand, at the time of large overlap operation, although the exhaust temperature P1 of the independent exhaust passages 16a to 16d is lowered due to the scavenging effect, the unburned fuel is discharged into the exhaust passage and is agitated by the turbine. As a result, afterburning occurs, and the exhaust temperatures P3 and P4 before the turbine and before the catalyst rise above the exhaust temperature P2 before the turbine.

  In particular, since afterburning is affected by the exhaust temperature and the rotational speed of the turbine to be agitated, it is ensured that the agitation action is enhanced by stirring with the turbine 41 of the first turbocharger 40 that is small and has a high rotational speed. Afterburning can occur. Then, since the turbine 51 of the second turbocharger 50 is bypassed, thermal energy due to afterburning is supplied to the catalyst 65 without being taken away by the turbine 51. Thereby, the temperature rise of the catalyst 65 is promoted, and the time until the catalyst 65 is heated to the activation temperature is shortened.

  In addition, during this cold time, the second turbocharger 50 does not substantially operate and supercharging is performed only by the first turbocharger 40, but the supercharging is performed by closing the variable exhaust valve 30. The effect is enhanced.

  That is, immediately after the exhaust valve 9 is opened, the exhaust flow velocity becomes high due to the blow-down phenomenon in which high-pressure gas from the combustion chamber is ejected, and the blow-down gas is guided to the turbine, so that a dynamic pressure supercharging effect is obtained. In particular, by reducing the opening of the variable exhaust valve 30 provided in the vicinity of the outlets of the independent exhaust passages 16a, 16bc, 16d, the exhaust discharged from the cylinders in the blow-down period to one independent exhaust passage is variable. When passing through the exhaust valve 30, the exhaust gas is sucked out from the other independent exhaust passage by the ejector effect, and the exhaust flow rate is increased, so that the dynamic pressure supercharging effect is enhanced and the turbine 41 of the first turbocharger 40 is driven. The force can be increased and the boost pressure can be increased. In addition, the scavenging performance is enhanced by the ejector effect of sucking out the exhaust gas.

  When the effective opening area at the outlet of the independent exhaust passage is narrowed to a certain degree or more during warm weather, knocking is likely to occur. However, since knocking is difficult to occur during cold weather, the effective opening area at the outlet of the independent exhaust passage (variable exhaust valve 30). Can be further reduced, thereby increasing the dynamic pressure supercharging effect.

  In this way, at the time of cold, the supercharging pressure can be sufficiently increased even if supercharging is performed only by the small first turbocharger 40.

  On the other hand, when the engine operating state is in the dynamic pressure supercharging operation region R1 and the engine water temperature is warmer than the predetermined temperature T, the combustion condition in the afterburning mode is set and the variable exhaust valve 30 is operated. The opening degree is adjusted according to the state, and the exhaust flow path switching valves 63 and 64 are controlled to the state shown in FIG. 12, so that the exhaust is supercharged as shown by the arrow in FIG. The exhaust passage is set so as to pass through the turbine 41 of the machine 40 and the turbine 51 of the second turbocharger 50. As a result, the turbochargers 40 and 50 cooperate to enhance the supercharging action.

  That is, the unburned fuel is discharged into the exhaust passage 60 by setting the combustion condition in the afterburning mode and the afterburning is generated downstream of the turbine by being stirred by the turbine 41 as in the cold state. However, when it is warm, heat energy from afterburning is supplied to the turbine 51 of the second turbocharger 50.

  The outlets of the independent exhaust passages 16a, 16bc, and 16d are appropriately throttled by the variable exhaust valve 30, and the energy of the exhaust gas supplied to the turbine 41 is increased by the ejector effect, whereby the first turbocharger 40 The supercharging action is enhanced and the supercharging action of the second turbocharger 50 is enhanced by the thermal energy from afterburning, so that the output of the supercharger and the transient response (responsiveness of torque increase during acceleration) can be reduced. Can be improved.

  Further, when the engine operating state is in the high-speed operation region R2, the combustion condition in the normal operation is set, the variable exhaust valve 30 is opened, and the exhaust flow path switching valves 63 and 64 are in the state shown in FIG. As shown by the arrows in the figure, the exhaust flow path is such that the exhaust bypasses the turbine 41 of the first turbocharger 40 and passes through the turbine 51 of the second turbocharger 50. Is set. Thus, effective supercharging is performed in the high speed operation region R2 where the displacement is large.

  That is, since the exhaust amount is large in the high-speed operation region R2, a sufficient supercharging action can be obtained only with the large second turbocharger 50. In this case, by bypassing the turbine 41 of the small first turbocharger 40, an increase in exhaust pressure due to the exhaust resistance in the turbine 41 can be suppressed. Further, by opening the variable exhaust valve 30, an increase in exhaust pressure due to the exhaust resistance can be suppressed. Moreover, discharge | emission of unburned fuel is suppressed by making an overlap period small.

  By these actions, the supercharging action by the second turbocharger is enhanced, the increase in exhaust pressure is suppressed, and the engine output is effectively increased.

  FIG. 14 is a graph showing engine torque characteristics. The horizontal axis represents the engine speed (rpm), and the vertical axis represents the engine torque (N · m). The characteristic indicated by the solid line is the characteristic of the present embodiment, the characteristic indicated by the broken line is the characteristic when the conventional exhaust system and a general large exhaust turbocharger are used, and the characteristic indicated by the alternate long and short dash line is the characteristic of the conventional exhaust system. This is a characteristic when a general small exhaust turbocharger is used.

  As shown in the figure, the characteristic indicated by the broken line shows a strong torque increasing action in the high speed range by the large exhaust turbocharger, and the characteristic indicated by the one-dot chain line shows a strong torque increasing action in the low speed range by the small exhaust turbocharger. On the other hand, according to the turbocharger of the present embodiment, the supercharging performance is enhanced in each operation region R1, R2 as described above, so that the low speed operation region is changed to the high speed operation region as indicated by the solid line characteristics. Increases in engine torque are achieved over a wide range.

  In addition, the specific structure of the engine with a supercharger of the present invention is not limited to the above embodiment, and can be appropriately changed without departing from the gist of the present invention.

  For example, in the above embodiment, the first and second turbochargers 40 and 50 are provided, but three or more turbochargers may be provided. In this case, one turbocharger is a small turbocharger having a smaller turbine diameter than the other turbochargers, and when it is cold in the dynamic pressure supercharging operation region R1, the exhaust is one turbocharger. And the turbine bypass passage that bypasses the other turbines, and the exhaust flow path is switched so that the exhaust passes through the turbine of each turbocharger when warm in the dynamic pressure supercharging operation region R1. Just keep it.

1 is a schematic configuration diagram of an engine with a supercharger according to an embodiment of the present invention. It is a fragmentary sectional view of the engine of FIG. It is a timing chart which concerns on embodiment of FIG. It is an external appearance perspective view which shows the principal part. It is a perspective view which shows schematic structure of a variable exhaust valve, (A) shows the state at the time of valve closing, and (B) shows the state at the time of valve opening. It is a block diagram which shows the functional structure of an engine control unit. It is a characteristic view which shows the setting of the driving | operation area | region for performing control according to a driving | running state. It is an exhaust characteristic diagram, (A) is an independent exhaust throttle mode, (B) is a normal operation mode. It is a flowchart which shows an example of control by an engine control unit. It is explanatory drawing which shows the distribution | circulation state of exhaust_gas | exhaustion and intake air when it is a cold time in a dynamic pressure supercharging operation | movement area | region. It is a graph which shows the measured value of the exhaust temperature of several places in order to show the temperature change by the afterburn phenomenon of the engine with a supercharger which concerns on this embodiment. It is explanatory drawing which shows the distribution | circulation state of exhaust_gas | exhaustion and intake air in the case of warm time in a dynamic pressure supercharging operation area | region. It is explanatory drawing which shows the distribution | circulation state of exhaust_gas | exhaustion in the case of being in a high-speed driving | operation area | region. It is a graph which shows the characteristic of an engine torque.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 3a-3d Cylinder 8 Exhaust port 12 Variable valve timing mechanism 16 Exhaust manifold 16a, 16bc, 16d Independent exhaust passage 17a Outlet 20 Engine control unit 21 Variable exhaust valve control means 22 Overlap control means 23 Temperature state discrimination means 24 Flow path Selection means 30 Variable exhaust valve 31c Collecting part 40, 50 Turbocharger 41, 51 Turbine 42, 52 Compressor 60 Exhaust passage 61, 62 Turbine bypass passage 63, 64 Exhaust passage switching valve 65 Catalyst

Claims (3)

An engine with multiple cylinders,
An exhaust manifold having independent exhaust passages independently connected to the exhaust ports of each cylinder of the engine;
A collecting portion in which the downstream sides of the independent exhaust passages of the exhaust manifold are gathered together;
A plurality of exhaust turbochargers connected in series to the exhaust passage downstream of the assembly;
An exhaust purification catalyst connected downstream of the exhaust turbocharger;
A variable exhaust valve configured to change an effective opening area of the outlet of the independent exhaust passage between the exhaust manifold and the collecting portion in order to achieve an ejector effect in a predetermined supercharging operation region;
Variable exhaust valve control means for controlling the variable exhaust valve so as to make the effective opening area of the outlet of the independent exhaust passage smaller than the opening area at the maximum opening in the predetermined supercharging operation region;
Overlap control means for controlling the valve timing so as to expand the overlap period in which the exhaust valve open period and the intake valve open period overlap in the predetermined supercharging operation region;
Temperature state determination means for determining the temperature state of the engine;
A turbine bypass passage that bypasses one of the plurality of exhaust turbocharger turbines and connects an upstream exhaust passage and a downstream exhaust passage of the bypassed turbine;
An exhaust passage switching valve for selectively circulating exhaust gas to any one of a turbine other than one of the turbines of the plurality of exhaust turbochargers and the turbine bypass passage;
Flow path selection means for controlling the exhaust flow path switching valve according to the operating state and temperature state of the engine to select the flow path of the exhaust,
In the predetermined supercharging region, the flow path selection unit is configured to detect exhaust gas as one of the turbines of the plurality of exhaust turbochargers and the turbine when the temperature state determination unit determines that the time is cold. When the temperature state determining means determines that it is warm in the predetermined supercharging region through the bypass passage, the exhaust gas passes through the turbines of the plurality of exhaust turbochargers. An engine with a supercharger characterized by controlling the exhaust flow path switching valve as described above. The supercharged engine according to claim 1,
The plurality of exhaust turbochargers have different turbine diameters, and when the engine state determining means determines that the engine is in a cold state in the predetermined supercharge region, the exhaust is the plurality of exhaust turbochargers. An engine with a supercharger, characterized in that it passes through a turbine having the smallest diameter among the turbines of the turbine and a turbine bypass passage that bypasses the other turbines. The engine with a supercharger according to claim 1 or 2,
The variable exhaust valve control means is configured to reduce the effective opening area of the outlet of the independent exhaust passage in the predetermined supercharging region when the temperature state determination means determines that it is cold compared to when it is warm. An engine with a supercharger characterized by controlling the variable exhaust valve.

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