JP2017180364A - Engine with turbo supercharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve energy efficiency while properly increasing a boost pressure.SOLUTION: An engine includes a small turbo supercharger 50, a large turbo supercharger 60, an exhaust-side bypass passage 132 bypassing a small turbine 54, an exhaust-side bypass valve 44a for opening and closing the exhaust-side bypass passage, exhaust flow speed changing means 64d capable of changing an exhaust flow speed by changing an area of the flow channel area of the exhaust flowing into a turbine wheel 641 of a large turbine, an intake-side bypass passage 122 bypassing a small compressor 52, and an intake-side bypass valve 122 capable of opening and closing the intake-side bypass passage. The large turbine 64 is disposed on the exhaust passage 30 to constantly introduce the whole amount of the exhaust thereto. When the exhaust flow rate is small, the exhaust-side bypass valve 44a is closed, and the area of the exhaust flow channel is reduced to be smaller than a maximum area by the exhaust flow speed changing means 64d.SELECTED DRAWING: Figure 1

Description

  The present invention provides an engine body, an intake passage through which intake air introduced into the engine body circulates, an exhaust passage through which exhaust gas discharged from the engine body circulates, and a turbine wheel provided in the exhaust passage and receiving the turbine wheel. A small turbocharger including a small turbine having a turbine case and a small compressor provided in the intake passage and having a compressor wheel and a compressor case for receiving the compressor wheel; and the exhaust passage downstream of the small turbine A large turbine having a turbine wheel and a turbine case that accommodates the turbine wheel, and a large compressor having a compressor wheel and a compressor case that accommodates the compressor wheel that is provided upstream of the small compressor in the intake passage. Equipped with a large turbocharger including It relates to an engine with a volume supercharger.

  Conventionally, a turbocharger has been provided in an engine to increase its output. Further, in order to further increase the engine output, it is also considered to provide two turbochargers in the engine.

  For example, Patent Document 1 discloses an engine provided with a small turbocharger and a large turbocharger. In the engine disclosed in Patent Document 1, a turbine of a large turbocharger and a small turbine of a small turbocharger are provided in an exhaust passage, and a bypass passage that bypasses the small turbine and a wastegate that bypasses the large turbine. A passage, and a bypass valve and a wastegate valve that open and close these passages are provided, and the exhaust bypass valve and the wastegate valve are opened and closed according to operating conditions. Specifically, when the engine speed reaches or exceeds a predetermined value, the exhaust bypass valve is opened, and when the engine speed further increases, the wastegate valve is opened in addition to the exhaust bypass valve. .

  According to this engine, the amount of exhaust gas flowing into each turbine, and thus the supercharging power of each turbine, can be finely adjusted according to the engine speed.

JP-A-62-113829

  However, in the engine of Patent Document 1, as described above, a wastegate passage that bypasses the large turbine provided on the downstream side is provided, and the exhaust bypass is provided in a part of the operation region (region where the engine speed is high). In addition to the valve, the wastegate valve is opened. Therefore, the energy of the exhaust gas is discharged outside without passing through any turbine, and there is a problem that the energy recovery efficiency of the exhaust gas is poor.

  The present invention has been made in view of the circumstances as described above, and provides a turbocharged engine capable of increasing the energy recovery efficiency of exhaust gas while appropriately increasing the supercharging pressure. Objective.

  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 the exhaust passage. A small turbocharger including a small turbine having a turbine wheel provided therein and a turbine case accommodating the turbine wheel; a small turbocharger including a compressor wheel provided in the intake passage and a compressor case accommodating the turbine wheel; and the exhaust A large turbine having a turbine wheel and a turbine case accommodating the turbine wheel provided downstream of the small turbine in the passage, and a compressor wheel provided upstream of the small compressor in the intake passage and the compressor wheel. Large compressor having a compressor case for housing A turbocharger-equipped engine comprising a large turbocharger including the engine and a control unit capable of controlling each part of the engine, wherein the exhaust passage removes exhaust before flowing into the small turbine. The exhaust-side bypass passage that flows downstream by bypassing the exhaust-side bypass passage, the exhaust-side bypass valve that can open and close the exhaust-side bypass passage, and the flow passage area of the exhaust gas flowing into the turbine wheel of the large turbine are changed. An exhaust flow rate changing means capable of changing a flow rate, wherein the intake passage bypasses the small compressor and flows the intake air before flowing into the small compressor downstream, and the intake side bypass An intake-side bypass valve capable of opening and closing a passage, and the capacities of the large turbine and the large compressor are the capacities of the small turbine and the small compressor, respectively. The large turbine is disposed in the exhaust passage so that the entire amount of exhaust gas is always introduced, and the control means, when the exhaust flow rate is smaller than a predetermined value, The exhaust-side bypass valve is closed, and the flow passage area is made smaller than the maximum area by the exhaust flow velocity changing means (claim 1).

  According to the present invention, since the entire amount of exhaust always flows into the large turbine, the energy of the exhaust can be reliably used for supercharging intake air by the large turbine. Therefore, the energy recovery efficiency of the exhaust gas can be increased as compared with the case where the exhaust gas is discharged outside without passing through the turbine. Further, when the exhaust gas flow rate is large and the exhaust gas energy is high, the supercharging pressure can be further increased by effectively using this high energy for supercharging.

  However, when the entire amount of exhaust gas is always introduced into the large turbine, it is necessary to increase the capacity of the turbine in order to ensure turbine efficiency under a high exhaust gas flow rate. However, simply increasing the capacity of the turbine deteriorates the supercharging performance because the inflow speed of the exhaust gas to the turbine wheel of the large turbine decreases when the engine is operated under a condition of a small exhaust flow rate. There is a fear.

  On the other hand, in the present invention, an exhaust flow rate changing means capable of changing the flow rate of the exhaust gas flowing into the turbine wheel of the large turbine while providing the large turbine with a large capacity is provided, and the capacity is increased upstream of the large turbine. A small turbine (small turbine wheel) with small inertia is provided. When the exhaust flow rate is small, the exhaust-side bypass valve is closed and the flow area is made smaller than the maximum area by the exhaust flow rate changing means.

  For this reason, when the exhaust gas flow rate is small, the turbine wheel of the small turbine can be efficiently rotated by this small flow rate exhaust gas to increase the supercharging pressure, and the flow rate of the exhaust gas flowing into the turbine wheel of the large turbine can be increased. The supercharging power by the large turbine can also be increased. Therefore, it is possible to appropriately increase the supercharging pressure in both cases where the exhaust gas flow rate is large and small, while improving the energy recovery efficiency of the exhaust gas.

  In the present invention, the control means includes the exhaust-side bypass valve and the intake-side bypass in at least a high-speed high-load region where the engine load is equal to or higher than the first reference load among high-speed regions where the engine speed is equal to or higher than the first reference speed. While the valve is opened, at least in the low speed and low load region where the engine load is less than the second reference load among the low speed regions where the engine speed is set to be equal to or lower than the first reference rotation speed, the exhaust side The exhaust flow rate changing means is controlled such that the bypass valve and the intake-side bypass valve are closed and the flow passage area of the exhaust gas flowing into the large turbine is smaller when the engine speed is lower. Preferred (claim 2).

  In this way, in a high-speed and high-load region where the exhaust flow rate is high, a high flow rate exhaust gas can be introduced into a large-capacity large turbine, and the supercharging pressure can be further increased by a large turbine, that is, a large turbocharger. . Furthermore, in a low-speed and low-load region where the exhaust flow rate is low, this low flow rate exhaust gas can be introduced into a small turbine, and supercharging can be performed efficiently with a small turbocharger. Moreover, when the engine speed is low and the exhaust flow rate is low, the flow area of the exhaust gas flowing into the turbine wheel of the large turbine is reduced and the flow velocity of the exhaust gas flowing into the turbine wheel of the large turbine is increased, thereby The supercharging power by a large turbine can also be increased. Therefore, it is possible to appropriately increase the supercharging pressure in a wider operating range.

  In the present invention, the control means preferably sets the maximum value of the target value of the supercharging pressure in the high speed and high load region to be equal to or greater than the maximum value of the target value of the supercharging pressure in the low speed region. ).

  As described above, in the present invention, the supercharging pressure can be further increased in the high speed and high load region. Therefore, as in this configuration, even if the maximum value of the boost pressure target value in the high speed and high load region is set to a value higher than the maximum value of the boost pressure target value in the low speed region, this can be realized. it can. By realizing this, the maximum output of the engine can be further increased.

  In the above configuration, a portion of the exhaust passage that is upstream of the upstream end of the exhaust-side bypass passage is communicated with a portion of the intake passage that is downstream of the downstream end of the intake-side bypass passage, It is preferable to have an EGR passage capable of returning a part of the exhaust gas to the intake passage.

  According to this configuration, it is possible to appropriately increase the supercharging pressure while ensuring the EGR amount appropriately and improving the exhaust performance and the like. That is, if the EGR passage is configured such that a portion of the exhaust passage upstream of the small turbine and having a high exhaust pressure communicates with the intake passage, the pressure difference between the inlet and the outlet of the EGR passage is increased. The amount of EGR gas, that is, the amount of exhaust gas recirculated to the intake air can be increased. As a result, the amount of inert gas in the cylinder can be increased to promote the reduction of NOx and the like. However, when configured in this way, the amount of exhaust gas flowing into the large turbine and the small turbine may be reduced during acceleration or the like. In contrast, in the present invention, as described above, a large amount of exhaust gas flowing into the large turbine can be ensured and the exhaust energy can be efficiently used for supercharging. be able to.

  As described above, according to the turbocharged engine of the present invention, it is possible to appropriately increase the supercharging pressure while increasing the energy recovery efficiency of the exhaust gas.

1 is a plan view schematically showing an overall configuration of a turbocharged engine according to an embodiment of the present invention. It is a schematic sectional drawing of VGT. It is the figure which showed the control block of the engine. It is the flowchart which showed the control procedure of an exhaust-gas bypass valve, an intake-air bypass valve, and VGT. It is the figure which showed the operation area | region of an exhaust gas bypass valve, an intake bypass valve, and VGT. It is the figure which showed the operation area | region of the intake bypass valve. It is the figure which showed the operation area | region of the exhaust bypass valve. It is the figure which showed the driving | operation area | region of VGT. It is the figure which showed the target value of the supercharging pressure in full load.

(1) Overall Configuration of Engine FIG. 1 is a diagram schematically showing an overall configuration of a turbo overbenefit engine according to an embodiment of the present invention. The engine shown in the figure is a four-cycle engine mounted on a vehicle as a power source for traveling, and is an in-line multi-cylinder engine body having a plurality of (for example, four) cylinders 2 arranged in a direction orthogonal to the paper surface. 1, an intake passage 20 for introducing combustion air into the engine body 1, an exhaust passage 30 for discharging combustion gas (exhaust gas) generated in the engine body 1, and exhaust gas flowing through the exhaust passage 30 Are provided with a small turbocharger 50 and a large turbocharger 60, and an EGR device 80, respectively.

  A piston 5 is inserted into each cylinder 2 so as to be able to reciprocate.

  A combustion chamber 6 is defined above the piston 5, and fuel is injected into the combustion chamber 6 from an injector (not shown). The engine body 1 according to the present embodiment is a diesel engine, and the fuel injected from the injector is mixed with air and self-ignited in the combustion chamber 6. The piston 5 is pushed down by the expansion force due to the combustion and 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 a connecting rod, and rotates around its central axis in accordance with the reciprocating motion of the piston 5.

  In the engine body 1, specifically, in the cylinder head, an intake port 7 for introducing air (intake air) supplied from the intake passage 20 to each cylinder 2 corresponding to each cylinder 2, An exhaust port 8 for leading the generated exhaust to the exhaust passage 30, an intake valve 9 that closes the intake port 7 so that it can be opened and closed, and an exhaust valve 10 that closes the exhaust port 8 so that it can be opened and closed are provided. Yes.

  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 includes a large turbine 64 provided with a large turbine wheel (blade wheel) 641 provided in the exhaust passage 30 and driven to rotate by exhaust and a large turbine case 642 that accommodates the large turbine wheel, and the intake passage 20. A large compressor wheel (blade wheel) 621 that is driven by a large turbine wheel 641 and a large compressor case 622 that accommodates the large compressor wheel (blade wheel) 621, and exhaust gas is introduced into the large turbine 64. When the large turbine wheel 641 rotates, the large compressor wheel 621 rotates to supercharge 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 that includes a small turbine wheel (blade wheel) 541 that is provided in the exhaust passage 30 and is driven to rotate by exhaust, and a small turbine case 542 that accommodates the small turbine wheel 541 and the intake passage 20. And a small compressor wheel (blade wheel) 521 that is rotationally driven by a small turbine wheel 541 and a small compressor 52 including a small compressor case 522 that accommodates the small compressor wheel (blade wheel) 521, and exhaust gas is introduced into the small turbine 54. When the small turbine wheel 541 rotates, the small compressor wheel 521 rotates to supercharge intake air.

  Here, the large turbocharger 60 is larger than the small turbocharger 50, the capacity of the large turbine 64 is larger than the capacity of the small turbine 54, and the capacity of the large compressor 62 is larger than the capacity of the small compressor 52. It is set large. Accordingly, the large turbocharger 60 introduces a larger flow rate of exhaust into the large turbine 64 so that the larger amount of intake air can be supercharged by the large compressor 62 with high efficiency. The inertia of the small turbocharger 50 is smaller than that of the large turbocharger 60.

  The intake passage 20 is provided with an intake-side bypass passage 122 that bypasses the small compressor 52, that is, an intake-side bypass passage 122 that bypasses the small compressor 52 and flows intake air downstream. Specifically, the intake-side bypass passage 122 communicates a portion of the intake passage 20 between the small compressor 52 and the large compressor 62 and a portion downstream of the small compressor 52.

  The intake side bypass passage 122 is provided with an intake side bypass valve 41a for opening and closing the intake side bypass passage 122. When the intake side bypass valve 41a is fully closed (the intake side bypass passage 122 is closed), the entire amount of intake air flows into the small compressor 52. On the other hand, in a state where the intake side bypass valve 41a is open, most of the intake air bypasses the small compressor 52 and flows downstream. That is, since the small compressor 52 becomes a resistance against the flow of the intake air, most of the intake air flows into the intake-side bypass passage 122 having a smaller resistance when the intake-side bypass valve 41a is open. The intake side bypass valve 41a is opened and closed by a negative pressure type valve actuator 41b.

  The exhaust passage 30 is provided so as to be connected to each exhaust port 8 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 wheel 541 receives the energy of the exhaust and rotates the small compressor wheel 521. The large turbine wheel 641 receives the energy of the exhaust and rotates the large compressor wheel 621.

  The large turbine wheel 641 is an impeller that has a plurality of blades and rotates when exhaust collides with the blades. 2, the large turbine 64 is a VGT (Variable Geometry Turbine), and a plurality of nozzle vanes 64b whose angles can be changed are provided around the large turbine wheel 641, and each nozzle vane 64b is provided. And a vane actuator 64d that changes the angle of each nozzle vane 64b by driving the rod 64c forward and backward. When the nozzle vane 64b is driven in the closing direction (the direction in which the distance between adjacent nozzle vanes 64b is reduced) by the vane actuator 64d and the rod 64c, the area of the flow path of the exhaust gas flowing into the large turbine wheel 641 becomes small. The flow rate of the exhaust gas flowing into the gas increases.

  Thus, in this embodiment, each nozzle vane 64b, rod 64c, and vane actuator 64d can change the flow area of the exhaust flowing into the large turbine wheel 641 to change the flow speed of the exhaust. Functions as a changing means.

  On the other hand, the small turbine 54 is not provided with the vane as described above, and is a so-called FGT (Fixed Geometry Turbine) in which the flow rate of the inflowing exhaust gas cannot be changed.

  The exhaust passage 30 is provided with an exhaust side bypass passage 132 that bypasses the small turbine 54, that is, an exhaust side bypass passage 132 that bypasses the small turbine 54 and flows the exhaust gas downstream. Specifically, the exhaust-side bypass passage 132 communicates a portion upstream of the small turbine 54 and a portion of the exhaust passage 30 between the small turbine 54 and the large turbine 64.

  The exhaust-side bypass passage 132 is provided with an exhaust bypass valve 44a that opens and closes the exhaust-side bypass passage 132. In a state where the exhaust bypass valve 44a is fully closed (a state where the exhaust side bypass passage 132 is closed), the exhaust gas is exhausted from the engine body 1 when the EGR gas is recirculated as will be described later. The total amount of gas excluding this EGR gas from the exhaust gas) flows into the small turbine 54. On the other hand, in a state where the exhaust bypass valve 44a is open, most of the exhaust flows downstream 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 44a is open, most of the exhaust gas passes through the exhaust-side bypass passage 132 having a smaller resistance and passes through the small turbine 54. It flows downstream without passing.

  The exhaust bypass valve 44a is opened and closed by an electric valve actuator 44b. As will be described later, the opening degree of the exhaust bypass valve 44a is changed between the fully closed state and the fully opened state according to the operating conditions, and is driven by the electric valve actuator 44b. The opening degree is appropriately controlled.

  Here, in the conventional apparatus such as Patent Document 1, a wastegate passage for exhausting the exhaust gas outside without passing through the turbine and a wastegate valve for opening and closing the exhaust passage are provided. In the form, these passages and valves are not provided, and the entire amount of exhaust always flows into the large turbine 64. That is, in the engine system according to the present embodiment, the exhaust discharged from the engine body 1 is always discharged to the outside through the large turbine 64.

  The EGR device 80 is a device for recirculating a part of the exhaust (EGR gas) discharged from the engine body 1 to the intake air.

  The EGR device 80 includes a first EGR passage 81 and a second EGR passage 84 that respectively connect the exhaust passage 30 and the intake passage 20, and a first EGR valve 82 and a second EGR valve 85 that open and close these, respectively. An EGR cooler 83 is provided in the first EGR passage 81, and the EGR gas is cooled by the EGR cooler 83 while passing through the first EGR passage 81 and then flows into the intake passage 20. On the other hand, the EGR cooler is not provided in the second EGR passage 84, and when passing through the second EGR passage 84, the EGR gas flows into the intake passage 20 at a high temperature.

  The first EGR passage 81 and the second EGR passage 84 communicate a portion of the exhaust passage 30 upstream of the upstream end of the exhaust side bypass passage 132 and a portion of the intake passage 20 downstream of the throttle valve 23. The exhaust before flowing into the turbines 54 and 64 is introduced into the EGR passages 81 and 84, respectively.

(2) Control contents Next, an 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 rotation speed of the crankshaft 15, that is, the engine speed, an airflow sensor SN2 for detecting the intake air amount introduced into each cylinder 2. It is electrically connected to an accelerator opening sensor SN3 or the like that detects the opening of an accelerator pedal (not shown) operated by the driver, and receives input signals from these sensors.

  The ECU 500 executes various calculations based on the input signals from the sensors SN1 to SN3 and the like, and the intake bypass valve 41a, the exhaust bypass valve 44a, the nozzle vane 64b of the VGT, that is, the nozzle vane 64b provided around the large turbine 64. , And other parts of the engine (first EGR valve 82, second EGR valve 85, throttle valve 23, etc.), respectively.

  Specifically, the ECU 500 issues commands to the valve actuators 41b and 44b that drive the bypass valves 41a and 44a, respectively, and opens and closes the valves 41a and 44a. In the present embodiment, the intake bypass valve 41a is switched between fully closed and fully open. On the other hand, the opening degree of the exhaust bypass valve 44a is changed to each opening degree from fully closed to fully open.

  Further, the ECU 500 issues a command to the vane actuator 64d that drives the nozzle vane 64b to change the VGT opening that is the opening of the nozzle vane 64b.

  Here, the VGT opening degree is a parameter that increases the flow path area of the exhaust toward each blade of the large turbine wheel 641 as the value increases, and decreases the flow path area as the value decreases. . During the operation of the engine body 2, the VGT opening is not fully closed, and is changed between the minimum opening set to the opening side with respect to the full closing and the full opening.

  In addition, the ECU 500 issues commands to actuators (not shown) that drive the EGR valves 82 and 85, respectively, to change the opening degrees of the EGR valves 82 and 85. Similarly, the ECU 500 issues a command to an actuator (not shown) that drives the throttle valve 23 to change the opening of the throttle valve 23.

  The control contents of the bypass valves 41a and 44a and the VGT opening by the ECU 500 will be described with reference to the flowchart of FIG. 4 and FIG. FIG. 5 shows the control region of the bypass valves 41a, 44a, etc., with the horizontal axis representing the engine speed and the vertical axis representing the engine load.

  As shown in FIG. 4, ECU 500 reads the engine speed, the accelerator opening, and the like in step S1. Then, the process proceeds to step S2.

  In step S2, it is determined whether the engine speed is less than a preset second reference speed N2. As shown in FIG. 5, the second reference rotational speed N2 is a relatively low value, and in step S2, it is determined whether or not the engine rotational speed is in the low rotational speed region A1 less than the second reference rotational speed N2. In the present embodiment, the second reference rotational speed N2 is set to be smaller as the engine load increases.

  If the determination in step S2 is YES and the engine speed is less than the second reference speed N2 and the engine is operating in the low speed range A1, the process proceeds to step S3. In step S3, the VGT opening is set to the minimum opening.

  After step S3, the process proceeds to step S4. In step S4, it is determined whether the engine load is less than a preset second reference load T2. That is, in step S4, as shown in FIG. 5, the engine speed is lower than the second reference speed N2 and the engine load is lower than the second reference load T2, and the exhaust flow rate is smaller than a predetermined value. It is determined whether it is an area. In the present embodiment, the second reference load T2 is a relatively low value and is set to a constant value regardless of the engine speed.

  If the determination in step S4 is YES and the engine load is less than the second reference load T2 and the vehicle is operating in the low speed and low load region A1_a, the process proceeds to step S5. In step S5, the intake bypass valve 41a is fully closed. Further, after step S5, the process proceeds to step S6, the exhaust bypass valve 44a is fully closed, and the process ends (returns to step S1).

  Thus, in the low speed and low load region A1_a, the VGT opening is set to the minimum opening. As a result, the flow rate of the exhaust gas flowing into the large turbine wheel 641 is maximized, and the supercharging force of the large compressor 62 is increased. Further, in the low speed and low load region A1_a, the intake bypass valve 41a is fully closed. As a result, the entire amount of intake air passes through the small compressor 52, and the intake air is supercharged by the small compressor 52 in addition to the large compressor 62 and then flows into the engine body 1. Further, in the low speed and low load region A1_a, the exhaust bypass valve 44a is fully closed. Along with this, the entire amount of exhaust exhausted from the engine main body 1 (excluding the amount recirculated to the intake passage 20 as EGR gas) flows into the small turbine 54, whereby the small turbine wheel 541 and thus the small compressor wheel 521 rotate. Driven.

  On the other hand, if the determination in step S4 is NO and the engine load is equal to or higher than the second reference load T2, that is, the engine speed is less than the second reference speed N2 and the engine load is equal to or higher than the second reference load T2. When the operation is performed in the load region A1_b, the process proceeds to step S12.

  In step S12, the intake bypass valve 41a is fully closed. After step S12, the process proceeds to step S13.

  In step S13, the opening degree of the exhaust bypass valve 44a is set to the basic RV opening degree. The basic RV opening is an opening that is set so that the supercharging pressure becomes a target pressure for each operating condition. The target supercharging pressure and the basic RV opening are determined by the engine speed and the engine load. Is preset. Accordingly, in step S13, the basic RV opening is determined in accordance with the current engine speed and engine load, and the processing is ended with the opening of the exhaust bypass valve 44a being set to the determined basic RV opening (step S1). ).

  As described above, in the present embodiment, in the low speed and high load region A1_b, similarly to the low speed and low load region A1_a, the VGT opening is set to the minimum opening and the flow velocity of the exhaust gas flowing into the large turbine wheel 641 is maximized. In addition, the intake bypass valve 41a is fully closed and the entire amount of intake air flows into the small compressor 52 and is supercharged thereby, while the exhaust bypass valve 44b is set to the basic RV opening.

  Returning to step S2, if the determination in step S2 is NO, that is, if the engine speed is greater than or equal to the second reference speed N2, the process proceeds to step S10. In step S10, the VGT opening is set to the basic VGT opening. The basic VGT opening is an opening that is set so that the supercharging pressure becomes a target pressure for each operating condition, and the basic VGT opening is set in advance by the engine speed and the engine load. Accordingly, in step S10, the basic VGT opening is determined according to the current engine speed and the engine load, and the VGT opening is set to the basic VGT opening.

  After step S10, the process proceeds to step S11. In step S11, it is determined whether or not the engine speed is less than the first reference speed N1 set to a value higher than the second reference speed N2. That is, in step S11, it is determined whether or not the engine speed is a medium speed region A2 that is equal to or greater than the second reference speed N2 and less than the first reference speed N1. In the present embodiment, as shown in FIG. 5, the first reference rotational speed N1 is set to be smaller as the engine load becomes higher.

  If the determination in step S11 is YES and the vehicle is operating in the medium speed region A2, the process proceeds to step S12. Then, as described above, in step S12, the intake bypass valve 41a is fully closed, and in the subsequent step S13, the exhaust bypass valve 44a is set to the basic RV opening, and the process is terminated (return to step S1).

  Thus, in the medium speed region A2, the intake bypass valve 41a is fully closed, whereby the entire amount of intake air is introduced into the small compressor 52 and supercharged by the large compressor 62 and the small compressor 52. Further, the VGT opening is set to the basic VGT opening, and the exhaust bypass valve 44b is set to the basic RV opening so that the supercharging pressure becomes the target value.

  On the other hand, when the determination in step S11 is NO and the engine speed is equal to or higher than the first reference speed N1, that is, as shown in FIG. 5, in the high speed region A3 where the engine speed is equal to or higher than the first reference speed N1. When driving | running | working is made, it progresses to step S21.

  In step S21, the intake bypass valve 41a is fully opened. Then, in step S22, which proceeds after step S21, the exhaust bypass valve 44b is fully opened, and the process ends (returns to step S1).

  Thus, in the present embodiment, in the high speed region A3, the intake bypass valve 41a is fully opened, and almost the entire amount of intake air is introduced into the engine body 1 without passing through the small compressor 52. Further, the exhaust bypass valve 44 a is fully opened, and the entire amount of exhaust (amount excluding EGR gas) is directly introduced into the large turbine 64 without passing through the small turbine 54. Accordingly, the intake air is supercharged only by the large compressor 62. In the high speed region A3, the VGT opening is set to the basic VGT opening, whereby the supercharging pressure is controlled to the target pressure.

  As described above, in the present embodiment, as shown in FIG. 6, the intake bypass valve 41 a is fully closed in the region where the engine speed is less than the first reference rotational speed N1 (low speed area A1, medium speed area A2). Is done. On the other hand, in the high speed region A3, the intake bypass valve 41a is fully opened.

  Further, as shown in FIG. 7, the exhaust bypass valve 44a is fully closed in the low speed and low load region A1_a. On the other hand, in the high speed region A3, the exhaust bypass valve 44a is fully opened. In the other region A10, the exhaust bypass valve 44a has a basic RV opening.

  Here, the basic RV opening is set to increase as the engine load and the engine speed increase, for example.

  Note that the basic RV opening may be fully opened in a region near the first reference rotational speed N1 in the region A10 excluding the low speed and low load region A1_a and the high speed region A3.

  Further, as shown in FIG. 8, in the low speed region A1, the VGT opening is the minimum opening. On the other hand, in the medium speed region A2 and the high speed region A3, the VGT opening is the basic VGT opening. Here, the basic VGT opening is set to a larger value (open side value) as the engine load and the engine speed increase, for example.

  The target boost pressure, which is the target value of the boost pressure, is set to a higher value as the engine load increases at each engine speed. In the present embodiment, as shown in FIG. 9, the target supercharging pressure is increased in the vicinity of the full load region C (see FIG. 5) as the engine speed increases. More specifically, in the low speed region A1 and the medium speed region A2, the target supercharging pressure is increased as the engine speed increases, and in the high speed region A3, the target supercharging pressure is constant regardless of the engine speed. The value is the same as the maximum value of the target boost pressure in the speed region A2.

(3) Operation and the like As described above, in the present embodiment, a passage that bypasses the large turbine 64 located on the downstream side is not provided, and the large amount of exhaust (EGR) discharged from the engine body 1 is contained in the large turbine 64. The amount excluding gas) always flows into the large turbine 64 and drives the large turbine wheel 641.

  Accordingly, the large turbocharger 60 can always be supercharged by the energy of the exhaust, and the supercharging pressure can be further increased as compared with the case where the large turbine 64 is bypassed and the exhaust is discharged to the outside. In addition, the energy recovery efficiency of the exhaust can be increased, and the energy efficiency of the entire engine system can be increased.

  Here, in the case where the entire amount of exhaust gas is always introduced into the large turbine 64 as described above, the capacity of the large turbine 64 and the large turbocharger are ensured in order to ensure the efficiency of the large turbine 64 under a high exhaust flow rate. It is necessary to increase the capacity of the machine 60 sufficiently. However, simply increasing the turbine capacity increases the inertia of the large turbine wheel 641 at the same time, and also decreases the flow velocity of the exhaust gas flowing into the large turbine wheel 641 in the low speed and low load region A1_a where the exhaust flow rate is small. There is a possibility that the increase in the rotational speed of the large turbine wheel 641 is delayed and the supercharging performance is deteriorated.

  On the other hand, in this embodiment, the large turbine 64 is VGT. In the low-speed and low-load region A1_a, the VGT opening is reduced and the flow velocity of the exhaust gas flowing into the large turbine wheel 641 is increased. Therefore, the supercharging force by the large turbocharger 60 can be increased even in the low speed and low load region A1_a.

  In addition, in the present embodiment, a small turbocharger 50 is provided in addition to the large turbocharger 60, and a passage (an intake side bypass passage 122, an exhaust side bypass passage) that bypasses the small compressor 52 and the small turbine 62, respectively. 132). In the low-speed and low-load region A1_a, the exhaust bypass valve 44a and the intake bypass valve 41a are closed so that supercharging is performed also by the small turbocharger 50. Therefore, the supercharging pressure can be more reliably increased in the low speed and low load region A1_a. That is, since the small turbine wheel 541 has small inertia, even if the exhaust gas flow rate is small, the rotation increases early and the supercharging pressure can be increased. Therefore, as described above, the supercharging pressure can be further reliably increased by performing supercharging by the small turbocharger 50 in the low speed and low load region A1_a.

  Further, in the present embodiment, by increasing the capacity of the large turbocharger 60 as described above, the large turbocharger is used in a region where the exhaust flow rate is large, specifically, in a region where the engine load is high in the high speed region A3. The supercharger 60 can efficiently use the high flow rate exhaust gas to supercharge the intake air. Therefore, the supercharging pressure in this region can be increased. That is, as shown in FIG. 9, it is possible to realize this by setting the maximum value of the target value of the supercharging pressure in the high speed region A3 to be equal to or greater than the maximum value of the target value of the supercharging pressure in the low speed region A1. Become. Therefore, the maximum output of the engine can be increased.

  In the present embodiment, as described above, the amount of EGR gas can be secured while increasing the energy recovery efficiency of the exhaust gas and increasing the supercharging pressure.

  That is, as described above, if the EGR passages 81 and 84 are configured so that the portion of the exhaust passage 30 upstream of the small turbine 52 and the portion having a high exhaust pressure communicates with the intake passage 20, The pressure difference between the inlet and outlet of the EGR passages 81 and 84 can be increased to increase the amount of EGR gas. However, when configured in this manner, the amount of exhaust gas flowing into the large turbine 64 and the small turbine 54 may be reduced during acceleration or the like.

  On the other hand, in the present embodiment, as described above, even when the flow rate of the exhaust gas flowing into the turbines 54 and 64 is small, the boost pressure is efficiently increased by using the energy of the exhaust gas for supercharging. Can be raised appropriately. Accordingly, it is possible to increase the supercharging pressure while securing the EGR gas amount and improving the exhaust performance (for example, while reducing the NOx emission amount).

(4) Modified Example In the above embodiment, the case where the engine body is a diesel engine has been described, but the engine body may be another engine.

  Moreover, the setting of the target value of the supercharging pressure is not limited to the example shown in FIG.

  In the above-described embodiment, the case where the intake bypass valve 41a and the exhaust bypass valve 44a are fully opened in the entire high speed region A3 has been described. However, the first reference load in which the engine load is preset in the high speed region A3. These bypass valves 41a and 44a may be fully opened only in a high-speed and high-load region that is equal to or higher than T1 (see FIG. 5).

  In the above embodiment, the case where the bypass valves 41a and 44a are fully opened in the high speed region A3 has been described. However, the specific opening is not limited to this, and the intake side bypass passage 122 and the exhaust side bypass passage 142 The opening may be such that almost the entire amount of intake and exhaust flows. Similarly, when the bypass valves 41a and 44a are fully closed in the above embodiment, the openings of the bypass valves 41a and 44a may be opened by a predetermined amount instead. That is, it is sufficient that the opening is such that intake and exhaust do not substantially flow through the intake side bypass passage 122 and the exhaust side bypass passage 142.

  Moreover, the specific setting of the target values of the basic RV opening, the basic VGT opening, and the supercharging pressure is not limited to the above. For example, in the above-described embodiment, the case where the VGT opening is set to the minimum opening in the low speed region A1 has been described. However, the VGT opening in the low speed region A1 may be an opening smaller than the full opening, and the minimum opening A larger opening may be used. Further, the exhaust bypass valve 44b may be fully closed in the low speed and high load region A1_b.

1 Engine Body 20 Intake Passage 30 Exhaust Passage 41a Intake Bypass Valve 44a Exhaust Bypass Valve 50 Small Turbocharger 52 Small Compressor 54 Small Turbine 60 Large Turbocharger 62 Large Compressor 64 Large Turbine 122 Intake Side Bypass Path 132 Exhaust Side Bypass Passage 521 Small compressor wheel 522 Small compressor case 541 Small turbine wheel 542 Small turbine case 621 Large compressor wheel 622 Large compressor case 641 Large turbine wheel 642 Large turbine case

Claims (4)

An engine body, an intake passage through which intake air introduced into the engine body circulates, an exhaust passage through which exhaust gas discharged from the engine body circulates, a turbine wheel provided in the exhaust passage and containing a turbine case A small turbocharger including a small turbine and a small turbocharger provided in the intake passage and having a compressor wheel and a compressor case for receiving the compressor wheel; and provided in a downstream side of the small turbine in the exhaust passage. A large turbine including a large turbine having a turbine wheel and a turbine case for accommodating the turbine wheel, and a large compressor having a compressor wheel and a compressor case for accommodating the compressor wheel provided upstream of the small compressor in the intake passage. Controls the machine and parts of the engine An engine with a turbocharger and a capacity control means,
The exhaust passage includes an exhaust-side bypass passage that flows exhaust before flowing into the small turbine, bypassing the small turbine, downstream, an exhaust-side bypass valve that can open and close the exhaust-side bypass passage, and the large turbine An exhaust flow rate changing means capable of changing the flow area of the exhaust flowing into the turbine wheel to change the flow rate of the exhaust,
The intake passage includes an intake-side bypass passage that flows the intake air before flowing into the small compressor, bypassing the small compressor and flowing downstream, and an intake-side bypass valve that can open and close the intake-side bypass passage;
Each capacity of the large turbine and the large compressor is set larger than each capacity of the small turbine and the small compressor,
The large turbine is arranged in the exhaust passage so that the entire amount of exhaust is always introduced,
The control means closes the exhaust-side bypass valve when the exhaust flow rate is smaller than a predetermined value, and makes the flow passage area smaller than the maximum area by the exhaust flow velocity changing means. Supercharged engine. In the turbocharged engine according to claim 1,
The control means includes
In at least a high speed and high load region where the engine load is equal to or higher than the first reference load in a high speed region where the engine speed is equal to or higher than the first reference speed, the exhaust side bypass valve and the intake side bypass valve are opened while the engine speed is At least in the low speed and low load area where the engine load is lower than the second reference load among the low speed areas less than the second reference speed set below the first reference speed, the exhaust side bypass valve and the intake side bypass valve are With close
An engine with a turbocharger, wherein the exhaust flow rate changing means is controlled so that a flow passage area of exhaust flowing into the large turbine is smaller with respect to a higher engine rotational speed. The turbocharged engine according to claim 2,
The turbocharged engine characterized in that the control means sets the maximum value of the target value of the supercharging pressure in the high speed and high load region to be equal to or greater than the maximum value of the target value of the supercharging pressure in the low speed region. . In the turbocharged engine according to any one of claims 1 to 3,
A part of the exhaust gas is formed by communicating a portion of the exhaust passage upstream from the upstream end of the exhaust bypass passage with a portion of the intake passage downstream of the downstream end of the intake bypass passage. A turbocharged engine having an EGR passage capable of returning the air to the intake passage.

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