JP6394624B2 - Turbocharged engine - Google Patents

Description

  The present invention relates to a turbocharger comprising an intake passage through which intake air introduced into an engine body flows, an exhaust passage through which exhaust discharged from the engine body flows, a small turbocharger, and a large turbocharger. It relates to an engine with a feeder.

  As an example of the turbocharged engine, one disclosed in Patent Document 1 below is known. The turbocharged engine of Patent Document 1 has a small turbocharger and a large turbocharger, and the type of supercharger that performs supercharging is changed according to operating conditions. It has become. Specifically, in this turbocharged engine, a small turbine with a small capacity and a large turbine with a large capacity are arranged in the exhaust passage in order from the upstream side, and each turbine has a small capacity. A compressor to be driven is provided. Further, a passage that bypasses the small turbine and the small compressor and a valve that opens and closes the passage are provided. When the engine load is low and the engine speed is low, each bypass passage is closed so that supercharging is performed by the small turbo and the large turbo, and each bypass passage is opened in other regions. And supercharging is performed only by a large turbocharger.

  According to the turbocharged engine of Patent Document 1 configured as described above, both turbochargers are used in a region where the engine load is low and the engine speed is low and the flow rate of exhaust gas discharged from the engine is small. By using the machine for supercharging, the intake air can be appropriately supercharged with a small amount of exhaust energy. Can often supercharge intake air.

Japanese Patent No. 5130933

  However, in the turbocharged engine of Patent Document 1, when the transition from the low flow rate region to the high flow rate region is made, the increase in rotation of the large compressor is delayed, and the acceleration performance may not be sufficiently ensured. Specifically, in this turbocharged engine, when the operating region shifts from a low flow region to a high flow region during acceleration, the turbocharger is switched to supercharging only by a large turbocharger. Since the inertia is large, the rotational speed does not increase immediately even if the flow rate of exhaust increases with acceleration. For this reason, the rotation speed and supercharging pressure of the large compressor may not increase at an early stage, and sufficient acceleration performance may not be obtained.

  The present invention has been made in view of the above circumstances, and an engine with a turbocharger that can obtain high acceleration performance while supercharging intake air efficiently using a small turbine and a large turbine. The purpose is to provide.

In order to solve the above problems, the present invention provides an engine main body, an intake passage through which intake air introduced into the engine main body flows, an exhaust passage through which exhaust discharged from the engine main body flows, and a small turbocharger And a large turbocharger, and a turbocharger engine comprising a control means capable of controlling the supercharging operation of each supercharger, wherein the small turbocharger is provided in the exhaust passage A small turbine and a small compressor provided in the intake passage, wherein the large turbocharger is provided downstream of the small turbine in the exhaust passage and is larger than the small turbine. And a large-sized compressor that is provided upstream of the small compressor in the intake passage and is larger than the small compressor. An exhaust bypass passage that communicates a portion upstream and downstream of the turbine to bypass the small turbine, and an exhaust bypass valve that opens and closes the exhaust bypass passage, and the intake passage is the small passage A first bypass passage that connects the upstream portion and the downstream portion of the compressor to bypass the small compressor, a first bypass valve that opens and closes the first bypass passage, and an upstream side of the large compressor A second bypass passage that communicates the portion with the downstream portion to bypass the large compressor, a second bypass valve that opens and closes the second bypass passage, and an upstream end of the second bypass passage are connected to each other. and a throttle valve for changing a flow passage area of the passage between the portion and the large compressor, the control means, it increases the lower the engine speed When the engine at low Kunar low flow region is operated than the predetermined mass flow of exhaust gas discharged from the engine body by a lower engine load than the preset reference load so, the exhaust bypass valve, the first bypass valve and closing the second bypass valve, and while opening the throttle valve, the engine at a high flow rate region where the flow rate of the exhaust by the engine load is higher than the reference load is the predetermined amount or more Is open, the exhaust bypass valve and the first bypass valve are opened, the second bypass valve is closed, the throttle valve is opened, and the transition from the low flow region to the high flow region is performed. At least initially, the exhaust bypass valve and the first bypass valve are closed, the second bypass valve is opened, and the opening of the throttle valve is The opening is smaller than that in the low flow rate and high flow rate regions (Claim 1).

  According to the present invention, it is possible to effectively supercharge intake air with a small amount of exhaust gas by both turbochargers in a low flow rate region, and efficiently supercharge intake air by a large turbocharger in a high flow rate region. Can be paid.

  Moreover, at the time of transition from the low flow rate region to the high flow rate region (at least in the initial stage), the exhaust bypass valve and the first bypass valve are closed, the second bypass valve is opened, and the throttle valve is throttled. (The opening of the throttle valve is set to be smaller than the opening in the low flow and high flow regions), so that the turbo turbocharger speed is increased while increasing the supercharging power of the small turbocharger. Thus, the boost pressure can be increased earlier and the acceleration performance can be improved.

  Specifically, at the time of transition, the exhaust bypass valve is closed, so that the entire amount of exhaust discharged from the engine body is introduced into the small turbine. Therefore, a large amount of exhaust gas can be effectively introduced into this small turbine with small inertia, and the rotational speed of the small turbine can be increased earlier. Further, at this time, the first bypass valve is closed and the second bypass valve is opened, so that the flow path resistance of the intake air toward the small compressor is reduced. As a result, the amount of intake air flowing into the small compressor can be increased, and this large amount of intake air can be effectively supercharged by a small turbine whose rotation speed is promoted, and the boost pressure can be increased earlier. be able to. In addition, at this time, the throttle valve is controlled to reduce the amount of intake air flowing into the large compressor, that is, the amount of working fluid of the large compressor. Therefore, the rotation speed of a large-sized compressor can be increased and the supercharging capability by this can be increased. Therefore, the supercharging pressure can be increased earlier during the transition. In addition, when switching to the control of the high flow rate region in the latter half of the transition or after the transition and supercharging mainly by the large turbocharger, intake is appropriately performed by the large turbocharger rotating at a high rotational speed. Can be supercharged.

  In the present invention, “closing the valve” means restricting the flow of gas, as long as the flow of gas is substantially restricted, and is not limited to fully closing the valve. Similarly, “opening the valve” means that the gas flow is not restricted, and is not limited to the fully opened valve, as long as the gas flow is not substantially restricted. .

  In the present invention, when the rotational speed of the large compressor becomes equal to or higher than a preset reference rotational speed at the time of transition from the low flow rate region to the high flow rate region, the control means may Preferably, each bypass valve is opened, the second bypass valve is closed, and the opening of the throttle valve is opened (Claim 2).

  According to this configuration, since the turbocharger can be switched to supercharging mainly with the large turbocharger while the rotation speed of the large compressor is higher than the reference rotation speed, the supercharging pressure is more reliably increased at the time of this switching. Value can be maintained.

  Further, in the present invention, an exhaust flow rate change capable of changing a flow area of the exhaust gas flowing into at least one of the small turbine and the large turbine in the exhaust passage to change a flow velocity of the exhaust gas flowing into the turbine. Means are preferably provided (claim 3).

  In this way, the supercharging pressure can be set to an appropriate value with higher accuracy by changing the flow rate of the exhaust gas flowing into the turbine.

  In the present invention, it is preferable that the control means reduces the flow area of the exhaust gas by the exhaust gas flow rate changing means when the transition from the low flow rate region to the high flow rate region is started.

  In this way, the flow velocity of the exhaust gas flowing into the small turbine is increased at the start of the transition from the low flow rate region to the high flow rate region and in a state where more intake air is flowing into the small compressor as described above. Therefore, the amount of supercharging by the small turbocharger can be further increased and the acceleration performance can be more reliably increased. However, in the case of such a configuration, the back pressure of the small turbine, that is, the pressure on the upstream side of the large turbine increases, and the increase in the rotational speed of the large turbine may be suppressed. On the other hand, in the present invention, as described above, the rotational speed of the large turbine can be increased during the transition. Accordingly, it is possible to appropriately increase the rotation speeds of the large turbine and the large compressor while increasing the supercharging pressure at an early stage of the transition.

  As described above, according to the turbo overbenefit engine of the present invention, high acceleration performance can be obtained while supercharging intake air efficiently using a small turbine and a large turbine.

1 is a diagram schematically showing an overall configuration of a turbo overbenefit engine according to an embodiment of the present invention. It is a schematic sectional drawing of VGT. It is a block diagram which shows the control system of an engine. It is the flowchart which showed the control procedure at the time of transfer from a low flow area to a high flow area. It is the figure which showed the driving | operation area | region. It is the figure which showed the time change of each parameter at the time of transfer from a low flow area to a high flow area. It is a figure for demonstrating the characteristic of a compressor.

(1) Overall Configuration of Engine FIG. 1 is a plan view schematically showing the overall configuration of a turbo overbenefit engine according to an embodiment of the present invention. The engine shown in this figure is a four-cycle gasoline engine mounted on a vehicle as a power source for traveling, and is an in-line multi-cylinder type having a plurality of (for example, four) cylinders 2 arranged in a direction orthogonal to the paper surface. The engine body 1, the intake passage 20 for introducing combustion air into the engine body 1, the exhaust passage 30 for discharging combustion gas (exhaust gas) generated in the engine body 1, and the exhaust passage 30 circulate. The small turbocharger 50 and the large turbocharger 60 are respectively driven by the exhaust gas.

  The engine body 1 includes a cylinder block 3 in which a cylindrical cylinder 2 is formed, a cylinder head 4 attached to the cylinder block 3 so as to close the upper surface of the cylinder 2, and a reciprocating motion to each cylinder 2. And an inserted piston 5.

  A combustion chamber 6 is defined above the piston 5, and fuel mainly composed of gasoline injected from the injector 11 is supplied to the combustion chamber 6. The supplied fuel burns in the combustion chamber 6 and is pushed down by the expansion force generated by the combustion, whereby the piston 5 reciprocates in the vertical direction.

  Below the piston 5, a crankshaft 15 that is an output shaft of the engine body 1 is disposed. The crankshaft 15 is connected to the piston 5 via the connecting rod 14 and rotates around the central axis according to the reciprocating motion of the piston 5.

  The cylinder head 4 includes an injector 11 that injects fuel (gasoline) toward the combustion chamber 6 as described above, and an ignition plug 12 that ignites a mixture of fuel and air injected from the injector 11. One set is provided for each cylinder 2.

  In addition, the cylinder head 4 receives an intake port 7 for introducing air (intake air) supplied from the intake passage 20 into each cylinder 2 corresponding to each cylinder 2, and exhaust generated in each cylinder 2. An exhaust port 8 for leading to the exhaust passage 30, an intake valve 9 for closing the intake port 7 so as to be opened and closed, and an exhaust valve 10 for closing the exhaust port 8 so as to be opened and closed are provided.

  The intake passage 20 is provided so as to be connected to each intake port 7. In the intake passage 20, an air cleaner 21, a large compressor 62, a small compressor 52, an intercooler 22, and a throttle valve 23 are provided in this order from the upstream side.

  The large compressor 62 is a component of the large turbocharger 60. That is, the large turbocharger 60 has a large turbine 64 provided in the exhaust passage 30 and driven to rotate by exhaust, and a large compressor 62 provided in the intake passage 20 and driven to rotate by the large turbine 64. When the exhaust is introduced into the large turbine 64 and rotates, the large compressor 62 rotates and supercharges the intake air.

  Similarly, the small compressor 52 is a component of the small turbocharger 50. That is, the small turbocharger 50 includes a small turbine 54 provided in the exhaust passage 30 and driven to rotate by exhaust, and a small compressor 52 provided in the air passage 20 and driven to rotate by the small turbine 54. When the exhaust is introduced into the small turbine 54 and rotates, the small compressor 52 rotates and supercharges the intake air.

  Here, the small turbocharger 50, that is, the small turbine 54 and the small compressor 52 have a smaller capacity than the large compressor 62, that is, the large turbine 54 and the large compressor 52, and accordingly, the inertia of the small turbocharger 50 is It is smaller than the large turbocharger 60.

  The intake passage 20 is provided with a first bypass passage 121 that bypasses the small compressor 52 and a second bypass passage 122 that bypasses the large compressor 62.

  Specifically, the first bypass passage 121 communicates a branch portion 121 a located between the small compressor 52 and the large compressor 62 in the intake passage 20 and a portion 121 b downstream of the small compressor 52. Yes. The second bypass passage 122 communicates a portion 122 b between the branch portion 121 a and the large compressor 62 and a portion 122 a upstream of the large compressor 62.

  The first bypass passage 121 is provided with a first bypass valve 41 that opens and closes the first bypass passage 121. In a state where the first bypass valve 41 is fully closed (a state where the first bypass passage 121 is blocked), the entire amount of intake air flows into the small compressor 52. On the other hand, in a state where the first bypass valve 41 is open, most of the intake air bypasses the small compressor 52 and flows down. That is, since the small compressor 52 becomes a resistance against the circulation of the intake air, most of the intake air flows into the first bypass passage 121 having a smaller resistance when the first bypass valve 41 is open.

  Similarly, the second bypass passage 122 is provided with a second bypass valve 42 for opening and closing the second bypass passage 122. When the second bypass valve 42 is fully closed (the second bypass passage 122 is blocked), the entire amount of intake air flows into the large compressor 62. On the other hand, when the second bypass valve 42 is open, most of the intake air bypasses the large compressor 62 and flows down. That is, since the large compressor 62 becomes resistant to the flow of intake air, most of the intake air flows into the second bypass passage 122 having a smaller resistance when the second bypass valve 42 is open.

  Further, the intake passage 20 is a throttle that changes the flow area of the passage 20a to a passage 20a between the portion 122a of the intake passage 20 to which the upstream end of the second bypass passage 122 is connected and the large compressor 62. A valve 43 is provided. Accordingly, in the state where the second bypass valve 42 is opened, if the opening of the throttle valve 43 is set to the closed side rather than the fully opened state, the amount of intake air flowing into the large compressor 62 is reduced, and more Intake air flows into the second bypass passage 122 and travels toward the small compressor 52.

  The exhaust passage 30 is provided so as to be connected to each exhaust port 11 of the engine body 1. A small turbine 54, a large turbine 64, and a catalyst device 90 are provided in the exhaust passage 30 in order from the upstream side.

  As described above, the small turbine 54 receives the energy of the exhaust and rotates the small compressor 52. The large turbine 64 rotates the large compressor 52 in response to the exhaust energy.

  The small turbine 54 is an impeller that has a plurality of blades and rotates when exhaust collides with the blades. In the present embodiment, the small turbine 54 is a VGT (Variable Geometry Turbine) as shown in FIG. 2, and a plurality of nozzle vanes 54 b whose angles can be changed are provided around the small turbine 54. In addition, a rod 54c associated with each nozzle vane 54b and a vane actuator 54d that changes the angle of each nozzle vane 54b by driving the rod 54c forward and backward are provided. When the nozzle vane 54b is driven by the vane actuator 54d and the rod 54c in the closing direction (the direction in which the distance between the adjacent nozzle vanes 54b is reduced), the area of the flow path of the exhaust gas flowing into the small turbine 54 is reduced. The flow rate of the inflowing exhaust increases.

  Thus, in this embodiment, each nozzle vane 54b, rod 54c, and vane actuator 54d can change the flow area of the exhaust flowing into the small turbine 54 to change the flow speed of the exhaust. Functions as a means.

  The exhaust passage 30 is provided with an exhaust bypass passage 132 that bypasses the small turbine 54.

  Specifically, the exhaust bypass passage 132 communicates a portion 132 b between the small turbine 54 and the large turbine 64 in the exhaust passage 30 and a portion 132 a upstream of the small turbine 54.

  An exhaust bypass valve 44 that opens and closes the exhaust bypass passage 132 is provided. When the exhaust bypass valve 44 is fully closed (the exhaust bypass passage 132 is blocked), the entire amount of exhaust gas flows into the small turbine 54. On the other hand, in a state where the exhaust bypass valve 44 is open, most of the exhaust flows by bypassing the small turbine 54. That is, since the small turbine 54 is resistant to the flow of exhaust gas, when the exhaust bypass valve 44 is open, most of the exhaust gas passes through the small turbine 54 through the exhaust bypass passage 132 having a lower resistance. It flows down without.

  In the present embodiment, the exhaust passage 30 is provided with a waste gate passage 133 that bypasses the large turbine 64, and a waste gate valve 45 that opens and closes the waste gate passage 45.

  Specifically, the wastegate passage 133 communicates a portion of the exhaust passage 30 downstream of the downstream end 132 b of the exhaust bypass passage 132 with the portion 133 a downstream of the large turbine 64. . When the wastegate valve 45 is fully closed, the entire amount of exhaust gas flows into the large turbine 64, while when the wastegate valve 45 is open, most of the exhaust gas flows down by bypassing the large turbine 64.

  Further, the engine of the present embodiment includes an EGR device 80 that recirculates a part of exhaust gas to intake air. The engine includes a portion of the exhaust passage 30 upstream of the small turbine 54 and the intake passage 20. Among them, an EGR passage 81 that communicates with a portion downstream of the throttle valve 23, an EGR valve 82 that opens and closes the EGR passage 82, and an EGR cooler 83 that cools the gas in the EGR passage 81 are provided.

(2) Control System Next, the engine control system will be described with reference to FIG. The engine system of the present embodiment is controlled by an ECU (engine control unit, control means) 500 mounted on the vehicle. As is well known, ECU 500 is a microprocessor including a CPU, ROM, RAM, I / F, and the like.

  ECU 500 receives information from various sensors. For example, the ECU 500 is provided in the vehicle, an engine speed sensor SN1 for detecting the rotational speed of the eccentric shaft 23, that is, the engine speed, an airflow sensor SN2 for detecting the intake air amount introduced into each cylinder 2. An accelerator opening sensor SN3 for detecting the opening of an accelerator pedal (not shown) operated by the driver, and a supercharging pressure sensor SN4 for detecting a supercharging pressure (pressure downstream of the small compressor 52 in the intake passage 20). The large compressor rotational speed sensor SN5 that detects the rotational speed of the large compressor 62 is electrically connected, and receives input signals from these sensors.

  The ECU 500 executes various calculations based on the input signals from the sensors SN1 to SN5, etc., and each bypass valve 41, 42, 44, throttle valve 43, wastegate valve 45, small turbine 54, and other engines. A control signal is output to each of these parts (the spark plug 12, the injector 11, the throttle valve 23, etc.).

  Specifically, ECU 500 issues commands to the valves and actuators that drive the valves to open and close these valves and valves.

  Further, as a control of the small turbine 54, the ECU 500 outputs a drive signal to the vane actuator 64d to control the angle of the nozzle vane 54b of the small turbine 54 (hereinafter referred to as VGT opening as appropriate). Here, the larger the value of the VGT opening, the larger the flow passage area of the exhaust passage toward the blades of the small turbine 54, and the smaller the value, the smaller the flow passage area. It is.

  The control contents of each bypass valve 41, 42, 44, throttle valve 43, and small turbine 54 (VGT opening) by ECU 500 will be described with reference to the flowchart of FIG.

  First, ECU 500 determines in step S2 whether or not it is a transition from the low flow rate region to the high flow rate region. That is, in this embodiment, the engine operating region is partitioned as shown in FIG. 5, and the engine speed and the engine load are smaller than the line L1 in FIG. The low flow rate region A1 is set in a region where the flow rate is lower than the predetermined value, and the high flow rate region A2 is set in a region other than that where the engine speed or engine load is high and the exhaust flow rate is higher than the predetermined value. Is set. ECU 500 always determines whether the current operation region is one of these regions A1 or A2 according to the engine speed and the engine load (required engine torque). In step S2, the arrow in FIG. When the current operation region is the high flow region A2 and the previous operation region is the low flow region A1, it is determined that the transition is from the low flow region A1 to the high flow region A2. To do.

If the determination in step S2 is no, the process proceeds to step S10. In step S10,
It is determined whether or not the current operation region is the high flow rate region A2. If this determination is YES, the flow rate is in the high flow area A2, and the transition is not in progress, the process proceeds to step S11.

  In step S11, each of the exhaust bypass valve 44 and the first bypass valve 41 is fully opened (if it is already fully opened, it is kept fully open).

  After step S11, the process proceeds to step S12, and the second bypass valve 42 is fully closed (if the valve is already fully opened, the fully closed state is maintained). Further, in step S13, which proceeds after step S12, the throttle valve 43 is fully opened (if the valve is already fully opened, the full opening is maintained), and the process is terminated (return to step S1).

  Thus, in the present embodiment, when the operation is performed in the high flow rate region A2 (except during the transition), the exhaust bypass valve 44 and the first bypass valve 41 are each fully opened. Therefore, most of the exhaust gas flows directly into the large turbine 64 without passing through the small turbine 54, and most of the intake air flows down without passing through the small compressor 52. Further, since the second bypass valve 42 is fully closed, the entire amount of intake air flows into the large compressor 62. Accordingly, supercharging is mainly performed by the large turbocharger 60 in the high flow rate region A2. In addition, since the throttle valve 43 is fully opened, the intake air efficiently flows into the large compressor 62 with less resistance.

  On the other hand, if the determination in step S10 is NO and the vehicle is operating in the low flow area A1, the process proceeds to step S21. In step S21, the exhaust bypass valve 44 and the first bypass valve 41 are fully closed (when the valve is already fully opened, the valve is kept fully closed). After step S21, the process proceeds to step S12 and step S13, and as described above, the second bypass valve 42 is fully closed and the throttle valve 43 is fully opened to end the process (return to step S2).

  Thus, in this embodiment, when the operation is performed in the low flow rate region A1, the exhaust bypass valve 44, the first bypass valve 41, and the second bypass valve 42 are fully closed. Accordingly, the entire amount of intake air passes through the large compressor 62 and then flows into the small compressor 52. Further, the entire amount of exhaust gas flows into the small turbine 54 and then flows into the large turbine 64. The second bypass valve 42 is fully closed and the throttle valve 43 is fully opened, so that the intake air efficiently flows into the large compressor 62 as described above.

  On the other hand, if the determination in step S2 is YES and it is determined that the transition from the low flow rate region A1 to the high flow rate region A2 has been performed, the process proceeds to step S31. In step S31, the VGT opening is closed.

  After step S31, the process proceeds to step S32, and the exhaust bypass valve 44 and the first bypass valve 41 are fully closed.

  After step S32, the process proceeds to step S33, and the second bypass valve 42 is fully opened.

  After step S33, the process proceeds to step S34, and the throttle valve 43 is set to the closed side rather than fully opened. Specifically, the opening degree of the throttle valve 43 is set to a predetermined opening degree that is closer to the opening side than the fully closed position and closer to the closing side than the fully opened position. This opening is set in advance, for example.

  After step S34, the process proceeds to step S35. In step S35, it is determined whether or not the large compressor rotational speed, which is the rotational speed of the large compressor 62 detected by the large compressor rotational speed sensor SN5, is equal to or higher than the reference rotational speed. The reference rotational speed is set in advance.

  If the determination in step S35 is YES and the large compressor speed is increased to a reference speed or higher, the process proceeds to step S11. And step S11-S13 are implemented and a process is complete | finished (it returns to step S2). That is, when the rotation speed of the large compressor becomes equal to or higher than the reference rotation speed, the same control as in the normal high flow rate region A2 is performed, the exhaust bypass valve 44 and the first bypass valve 41 are each fully opened, and the second bypass valve 42 is While being fully closed, the throttle valve 43 is fully opened.

  On the other hand, if the determination in step S35 is NO and the large compressor speed has not yet reached the reference speed, the process returns to step S32. Then, steps S32 to S35 are repeated.

  As described above, in the present embodiment, when the low flow rate region A1 is shifted to the high flow rate region A2, the exhaust bypass valve 44 and the first bypass valve 41 are all turned on until the large compressor rotational speed reaches the reference rotational speed. The second bypass valve 42 is fully opened, and the throttle valve 43 is on the closed side with respect to the fully opened state. Accordingly, during this period, the entire amount of exhaust gas flows into the small turbine 54 and then flows into the large turbine 64. Further, the amount of intake air flowing into the large compressor 62 is reduced, and the entire amount of intake air flows into the small compressor 52.

  When the large compressor rotational speed reaches the reference rotational speed, the exhaust bypass valve 44, the first bypass valve 41 and the throttle valve are fully opened, and the second bypass valve 42 is fully closed, so that the normal high flow rate region is reached. Control similar to A2 is performed, and the intake air is supercharged mainly by the large turbocharger 60.

  In this embodiment, the wastegate valve 45 is basically fully closed, and opens when the supercharging pressure exceeds a predetermined limit pressure.

(3) Operation, etc. FIG. 6 schematically shows changes in parameters at the time of transition from the low flow rate region A1 to the high flow rate region A2. In FIG. 6, as a comparative example, the broken line in FIG. 6 does not perform control to fully open the second bypass valve 42 and fully close the throttle valve 43 at the time of transition, and fully close the second bypass valve 42 before and after the transition. Each change is shown when the throttle valve 43 is kept fully open.

  As shown in FIG. 6, in the present embodiment, at time t1, as indicated by a chain line, the engine load (required torque that is a required engine torque) increases and the operation region changes from the low flow region A1 to the high flow rate. Even when the region A2 is entered, the exhaust bypass valve 44 is kept fully closed. Therefore, the entire amount of exhaust gas is introduced into the small turbine 54, and the rotational speeds of the small turbine 54 and the small compressor 52 can be increased earlier immediately after time t1.

  Specifically, after time t1, as the engine load increases, the amount of exhaust discharged from the engine body 2 increases. At this time, the exhaust bypass valve 44 is maintained fully closed as described above. Therefore, the entire amount of the increased amount of exhaust gas can be introduced into the small turbine 54 that has a small inertia and easily rises in rotation. Therefore, the rotation speeds of the small turbine 54 and the small compressor 52 can be increased. In the present embodiment, as described above, the opening degree of the VGT is set to the close side immediately after the transition. Therefore, the rotation speeds of the small turbine 54 and the small compressor 52 are further increased.

  In addition, at this time, the first bypass valve 41 is fully closed, the second bypass valve 42 is fully opened, and the throttle valve 43 is closed, so that more intake air does not pass through the large compressor 62. Then, it flows into the small compressor 52. Therefore, the increased intake air can be effectively supercharged by the small turbine 54 and the small compressor 52 whose rotational speed is increased as described above. Therefore, the supercharging pressure can be increased more reliably. That is, in the comparative example, when the second bypass valve 42 is maintained fully closed and the throttle valve 43 is maintained fully open before and after the transition, the small compressor 52 passes through the large compressor 62. After that, only the intake air flows in, and the flow rate of the intake air flowing into the small compressor 52 is kept small by the large compressor 62 becoming a resistance. Therefore, the rotation of the small turbine 54 and the small compressor 52 cannot be effectively applied to the intake air, and the increase of the supercharging pressure can be suppressed low. On the other hand, in the present embodiment, it is possible to effectively supercharge intake air by the small compressor 52 by increasing the flow rate of the intake air flowing into the small compressor 52.

  Further, in the present embodiment, at time t1, the throttle valve 43 is closed, and the amount of intake air flowing into the large compressor 62 is reduced. That is, the amount of working fluid driven by the large compressor 62 is reduced. Therefore, the rotation speed of the large compressor 62 can also be increased.

  This will be described in detail with reference to FIG. FIG. 7 is a diagram showing the characteristics of the compressor, where the horizontal axis represents the flow rate of the working fluid flowing into the compressor, and the vertical axis represents the pressure ratio before and after the compressor (upstream pressure divided by downstream pressure). Fig. 5 is a diagram showing the rotation speed of the compressor and the driving force of the compressor (force required to drive the compressor). Specifically, in FIG. 7, each solid line is a line connecting points where the driving force of the compressor is the same, and each broken line Nc1 to Nc5 is a line connecting points where the rotation speed of the compressor is the same. It is. Here, the rotation speed increases from Nc1 to Nc5. In addition, in FIG. 7, the efficiency of the compressor is also shown by a chain line (each chain line is a line connecting points where the efficiency is the same).

  As shown in FIG. 7, when the driving force is the same, the rotational speed of the compressor increases when the flow rate of the working fluid flowing into the compressor decreases. For example, the driving force is the same at point A and point B, but the rotational speed of the compressor is higher at point B.

  Therefore, when the throttle valve 43 is closed as described above and the amount of intake air flowing into the large compressor 62, that is, the flow rate of the working fluid is reduced, the rotational speeds of the large compressor 62 and the large turbine 64 are increased. That is, since the energy of the exhaust gas flowing into the large turbine 64 and the driving force of the large compressor 62 does not change by opening / closing the throttle valve 43, when the throttle valve 43 is closed and the flow rate is reduced, the large compressor 62 and The rotation speed of the large turbine 64 increases. As is apparent from FIG. 7, when the flow rate of the working fluid is reduced and the rotational speed is increased in this way, the pressure ratio of the compressor also increases. Therefore, supercharging by the large compressor 62 is promoted by closing the throttle valve 43, and the supercharging pressure is further increased.

  Thus, in the present embodiment, the supercharging pressure can be increased early immediately after the transition from the low flow rate region A1 to the high flow rate region A2 at time t1, and the engine torque is increased accordingly. Increase acceleration performance.

  In this embodiment, when the rotation speed of the large compressor reaches the reference rotation speed at time t2, the exhaust bypass valve 44, the first bypass valve 41, and the throttle valve 43 are fully opened, and the second bypass valve 42 is As described above, the intake air is supercharged mainly by the large turbocharger 60. At this time, since the rotation speed of the large compressor 62 is sufficiently increased, the time t2 is reached. In this case, it is possible to appropriately increase the supercharging pressure or maintain it at an appropriate value. As shown in FIG. 7, after the time t2, the rotational speed of the small compressor 52 decreases as the amount of exhaust gas flowing into the small turbine 54 decreases.

(4) Modified Example In the above embodiment, the period from the low flow rate region A1 to the high flow rate region A2 is the period during which the second bypass valve 42 is opened and the throttle valve 43 is closed. The case where the rotation speed of the large compressor reaches the reference rotation speed after the start has been described, but the control may be performed at least at the initial stage of the transition. Here, at the time of the transition, the actual values of the engine speed and the engine torque change from the values in the low flow area A1 to the values in the high flow area A2, and then these actual values are in the high flow area A2. The period until the value is reached. For example, the control may be performed over the entire period at the time of the transition. Further, the control may be performed during a period from when the transition is started until a predetermined time elapses.

  In the above embodiment, when the rotation speed of the large compressor 62 reaches the reference rotation speed, the exhaust bypass valve 44 and the first bypass valve 41 are fully opened from the fully closed state, and the second bypass valve 42 is fully opened from the fully closed state. Although the case where the throttle valve 43 is fully opened has been described, these opening degrees may be gradually changed. For example, when the rotational speed of the large compressor 62 reaches a predetermined rotational speed that is smaller than the reference rotational speed, the opening degree of each of the valves 41 to 43 may be gradually changed toward fully closed or fully opened.

  Moreover, although the said embodiment demonstrated the case where the small turbine 54 was VGT, the small turbine 54 is good also as a normal turbine which does not have the nozzle vane 54b. However, if the small turbine 54 is set to VGT and the VGT opening is closed on the transition as described above, the rotational speed of the small turbine 54 can be increased earlier and the acceleration performance can be more reliably increased.

  However, when the small turbine 54 is set to VGT and the VGT opening is changed to the closed side at the time of the transition as described above, the back pressure of the small turbine 54 increases, the pressure on the upstream side of the large turbine 64 increases, and the large turbine 64 There is a possibility that the increase in the number of rotations is suppressed. However, in the present embodiment, as described above, the rotational speed of the large compressor 62 and the large turbine 64 can be increased by reducing the amount of intake air flowing into the large compressor 62 during the transition. Therefore, acceleration performance can be more reliably improved by using the small turbine 54 as VGT.

  Further, the large turbine 64 may be VGT. Even in this case, the boost pressure can be set to a more appropriate value by adjusting the VGT opening degree of the large turbine 64. That is, at the time of the transition, if the VGT opening degree of the large turbine 64 is set to the closed side, the rotation speed of the large turbine 64 can be further increased and the supercharging pressure can be increased. However, if the VGT opening degree of the large turbine 64 is set to the closing side at the time of transition, the upstream pressure of the large turbine 64, that is, the back pressure of the small turbine 54 increases, so it is preferable to keep the closing amount of the VGT opening small. . In the present embodiment, as described above, the rotational speed of the large compressor 62 and the large turbine 64 can be increased by reducing the amount of intake air flowing into the large compressor 62 during the transition. Therefore, even if the closing amount of the VGT opening is suppressed to a low level, these rotational speeds can be sufficiently increased.

  Moreover, although the said embodiment demonstrated the case where each bypass valve 41,42,44 was switched to full close and full open, it is not necessarily required to switch to full close and full open. That is, even if each valve 41, 42, 44 is opened by a predetermined amount, the flow of gas is regulated by each valve 41, 42, 44 in the same manner as when the valve 41, 42, 44 is substantially fully closed (almost no gas flows). In this case, instead of the control of fully closing each bypass valve 41, 42, 44 in the embodiment, the control is performed so that the opening degree of each bypass valve 41, 42, 44 is equal to or less than the predetermined amount. May be.

  Similarly, even if each valve 41, 42, 44 is closed by a predetermined amount from the fully open state, if the gas flow is hardly restricted by each valve 41, 42, 44, as in the case where the valve 41, 42, 44 is substantially fully opened, Instead of the control of fully opening each bypass valve 41, 42, 44 in the embodiment, the control may be performed such that the opening degree of each bypass valve 41, 42, 44 is greater than or equal to the predetermined amount. Further, in the throttle valve 48, instead of the control for fully opening the throttle valve 48, a control for opening the throttle valve 48 to a predetermined amount or more may be performed.

1 Engine Body 20 Intake Passage 30 Exhaust Passage 41 First Bypass Valve 42 Second Bypass Valve 43 Throttle Valve 44 Exhaust Bypass Valve 50 Small Turbocharger 52 Small Compressor 54 Small Turbine 60 Large Turbocharger 62 Large Compressor 64 Large Turbine 121a Branch portion 121 First bypass passage 122 Second bypass passage 132 Exhaust bypass passage

Claims (4)

An engine main body, an intake passage through which intake air introduced into the engine main body flows, an exhaust passage through which exhaust discharged from the engine main body flows, a small turbocharger and a large turbocharger, and A turbocharger engine having a control means capable of controlling a supercharging operation,
The small turbocharger has a small turbine provided in the exhaust passage and a small compressor provided in the intake passage,
The large turbocharger is provided downstream of the small turbine in the exhaust passage and larger than the small turbine, and provided upstream of the small compressor in the intake passage. And a large compressor that is larger than the small compressor,
The exhaust passage includes an exhaust bypass passage that bypasses the small turbine by communicating an upstream portion and a downstream portion of the small turbine, and an exhaust bypass valve that opens and closes the exhaust bypass passage.
The intake passage communicates a portion on the upstream side and a portion on the downstream side of the small compressor to bypass the small compressor, a first bypass valve for opening and closing the first bypass passage, A second bypass passage that connects the upstream portion and the downstream portion of the large compressor to bypass the large compressor, a second bypass valve that opens and closes the second bypass passage, and the second bypass passage A throttle valve that changes the flow area of the passage between the portion to which the upstream end of the large-scale compressor is connected and the large compressor,
The control means includes
The flow rate of the exhaust gas is operated engine at low Kunar low flow areas than the predetermined amount of engine load than a preset reference load so as to be higher the lower the engine rotational speed is discharged from the engine body by low The exhaust bypass valve, the first bypass valve and the second bypass valve are closed and the throttle valve is opened,
When the engine load is the flow rate of the exhaust at higher than the reference load is operated engine at a high flow rate region to be a predetermined amount or more, open the exhaust bypass valve and the first bypass valve, the second Close the bypass valve and open the throttle valve;
At least at the beginning of the transition from the low flow region to the high flow region, the exhaust bypass valve and the first bypass valve are closed and the second bypass valve is opened, and the opening of the throttle valve is A turbocharged engine characterized by having a smaller opening than in the low flow rate region and the high flow rate region. In the turbocharged engine according to claim 1,
When the rotational speed of the large-sized compressor is equal to or higher than a preset reference rotational speed at the time of transition from the low flow area to the high flow area, the control means sets the exhaust bypass valve and the first bypass valve, respectively. A turbocharged engine characterized by opening, closing the second bypass valve, and opening the throttle valve. The turbocharged engine according to claim 1 or 2,
Exhaust gas flow rate changing means capable of changing a flow rate area of the exhaust gas flowing into at least one of the small turbine and the large turbine in the exhaust passage and changing a flow velocity of the exhaust gas flowing into the turbine. An engine with a turbocharger. In the turbocharged engine according to claim 3 ,
The turbocharged engine according to claim 1, wherein when the transition from the low flow rate region to the high flow rate region starts, the control unit reduces the exhaust passage area by the exhaust flow rate changing unit.

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