JP2012172629A - Supercharging system of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a supercharging system of an internal combustion engine, reducing a pumping loss caused by excessive throttling of an exhaust passage and preventing decrease of output torque of the engine.SOLUTION: A turbine wheel 42 is rotated by exhaust energy of the engine 10. A compressor wheel 43 rotates together with the turbine wheel 42 supercharge intake air to the engine 10. A variable throttle part 44 is provided in the exhaust passage 33 on the inlet side of the turbine wheel 42 and varies the opening area of the exhaust passage 33. An actuator 46 drives the variable throttle part 44. An ECU 50 controls the actuator 46 so that exhaust flow speed becomes lower than the exhaust flow speed corresponding to Vmax1. Further, the ECU 50 controls the actuator 46 so that the exhaust flow speed becomes lower than the exhaust flow speed corresponding to Vmax2 when a supercharging condition determination means determines that the intake air to the engine 10 is supercharged and is being increased.

Description

  The present invention relates to a supercharging system for an internal combustion engine (hereinafter referred to as “engine”), and more particularly to a supercharging pressure control technique for a supercharger.

Conventionally, a turbine wheel is rotationally driven by engine exhaust energy, and a compressor wheel that is coaxially connected to the turbine wheel is rotated to supercharge air in an intake passage to a combustion chamber, and output torque of the engine. There are known turbochargers that improve the efficiency. The supercharger described in Patent Document 1 adjusts the flow rate of exhaust gas blown to the turbine wheel by adjusting the opening area of the exhaust passage by a variable throttle provided on the upstream side of the turbine wheel. Here, the degree of opening and closing of the variable throttle is expressed by the VN opening. When the variable throttle is fully open, the value of the VN opening is 0%, and when the variable throttle is fully closed, the value of the VN opening is 100%. It is.
In this supercharger, the maximum value of the VN opening obtained from the engine speed, the fuel injection amount, and the opening of the EGR (exhaust gas recirculation) valve in order to prevent the turbocharger from over-rotating. To card the target VN opening.

JP 2002-047942 A

However, at the time of supercharging (acceleration), if the exhaust passage is excessively throttled by the variable throttle portion, the exhaust pressure in the exhaust passage increases and the pumping loss increases and the engine output torque may decrease. .
The present invention has been made in view of the above problems, and an object of the present invention is to provide an engine supercharging system that reduces a pumping loss due to excessive restriction of an exhaust passage and suppresses a decrease in engine output torque. is there.

According to the invention which concerns on Claim 1, the supercharging system of an engine is provided with a turbine wheel, a compressor wheel, a variable throttle part, a drive part, and a control part. The turbine wheel is provided in an exhaust passage of the internal combustion engine, and is rotated by exhaust energy of the engine. The compressor wheel is provided in the intake passage of the internal combustion engine coaxially with the turbine wheel, and supercharges intake air to the engine by rotating together with the turbine wheel. The variable throttle is provided in the exhaust passage on the inlet side of the turbine wheel, and the opening area of the exhaust passage can be changed. Here, the flow velocity of the exhaust gas flowing through the turbine wheel becomes slower as the opening area becomes larger, and the flow velocity of the exhaust gas flowing through the turbine wheel becomes faster as the opening area becomes smaller. The drive unit drives the variable aperture unit. The control unit controls the drive unit to adjust the opening area and adjust the flow velocity of the exhaust gas flowing through the turbine wheel. Further, the control unit includes a flow velocity calculation unit, a first guard value setting unit, a second guard value setting unit, and a supercharging state determination unit. The flow velocity calculation means calculates the flow velocity of the exhaust gas between the variable throttle and the turbine wheel. The first guard value setting means sets a value corresponding to the exhaust flow velocity that causes the turbine wheel to over-rotate as the first guard value. The second guard value setting means sets a value smaller than the first guard value as the second guard value. The supercharging state determination means determines whether the intake air to the engine is supercharged and the supercharging pressure is increasing. The control unit controls the variable throttle unit so that the flow velocity of the exhaust gas calculated by the flow velocity calculating unit is smaller than the flow velocity of the exhaust gas corresponding to the first guard value.
Here, the flow velocity of the exhaust gas corresponding to the first guard value is the flow velocity of the exhaust gas that causes the turbine wheel to over-rotate. For this reason, excessive rotation of the turbine wheel can be suppressed.

In addition, when it is determined that the intake air to the engine is supercharged and increasing by the supercharging state determination unit, the control unit determines that the exhaust flow velocity calculated by the flow velocity calculation unit corresponds to the second guard value. The variable restrictor is controlled so as to be smaller than the flow velocity of.
Thereby, excessive throttling of the exhaust passage on the inlet side of the turbine wheel can be suppressed. Therefore, an increase in the exhaust pressure in the exhaust passage between the engine and the turbine wheel can be suppressed, and the pumping loss can be reduced.

According to the second aspect of the present invention, the second guard value setting means sets the second guard value to a value corresponding to the exhaust flow velocity that causes a decrease in engine output torque due to pumping loss.
Thereby, at the time of supercharging, the fall of the engine output torque by pumping loss can be suppressed.

The schematic diagram which shows the whole engine system provided with the supercharging system of one Embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view showing a turbocharger according to an embodiment of the present invention, (A) is a cross-sectional view of the supercharger when the variable throttle unit is fully opened, and (B) is a cross-section of the supercharger when the variable throttle unit is fully closed. Figure. The characteristic view which shows the characteristic of the supercharging system of one Embodiment of this invention. The flowchart which shows control of the supercharging system of one Embodiment of this invention. The flowchart which shows control of the supercharging system of one Embodiment of this invention. The characteristic view which shows the characteristic of the supercharging system of one Embodiment of this invention. The characteristic view which shows the characteristic of the supercharging system of one Embodiment of this invention. The characteristic view which shows the characteristic of the supercharging system of one Embodiment of this invention. The characteristic view which shows the characteristic of the supercharging system of one Embodiment of this invention.

Hereinafter, a supercharging system according to an embodiment of the present invention will be described with reference to the drawings.
(One embodiment)
FIG. 1 shows a diesel engine system (hereinafter simply referred to as “engine system”) to which a supercharging system according to an embodiment of the present invention is applied. As shown in FIG. 1, the engine system 1 includes an engine 10, an intake system 20, an exhaust system 30, a supercharger 40, and an ECU 50.

  The engine 10 includes a fuel injection valve 11, a cylinder 12, and a piston 13. The piston 13 is supported on the inner wall of the cylinder 12 so as to be able to reciprocate. A combustion chamber 14 is formed between the piston 13 and the cylinder 12. Although the engine 10 has a plurality of cylinders 12, only one is shown in FIG. 1 for convenience. The engine 10 includes an intake valve 15 and an exhaust valve 16.

  The intake system 20 has an intake pipe 21. The intake pipe 21 is formed with an intake port 22 at one end and is open to the outside air. The other end of the intake pipe 21 is connected to the engine 10. The intake pipe 21 forms an intake passage 23 that connects the intake port 22 and the combustion chamber 14 of the engine 10. In the intake passage 23, an air cleaner 24, a compressor wheel 43 of the supercharger 40, an intercooler 25, a throttle 26, a surge tank 27, and the like are provided in this order from the intake port 22 side. The intake valve 15 is opened and closed between the intake passage 23 and the combustion chamber 14. Hereinafter, in the intake passage 23, the intake port 22 side is referred to as "upstream side", and the intake valve 15 side is referred to as "downstream side".

  Here, the throttle 26 has a throttle valve 28. The throttle valve 28 is a butterfly valve that opens and closes the intake passage 23. The surge tank 27 is provided on the downstream side of the throttle 26. The intake air is distributed to the plurality of combustion chambers 14 of the engine 10 via the surge tank 27.

  The exhaust system 30 has an exhaust pipe 31. One end of the exhaust pipe 31 is connected to the engine 10. The other end of the exhaust pipe 31 serves as an exhaust port 32 and is open to the outside air. The exhaust pipe 31 forms an exhaust passage 33 that connects the combustion chamber 14 of the engine 10 and the exhaust port 32. The exhaust passage 33 and the combustion chamber 14 are opened and closed by the exhaust valve 16 described above. Hereinafter, in the exhaust passage 33, the exhaust valve 16 side is referred to as “upstream side”, and the exhaust port 32 side is referred to as “downstream side”.

  The exhaust pipe 31 is provided with an exhaust purification unit 35 and a turbine wheel 42 of the supercharger 40 in order from the exhaust port 32 side. The exhaust purification unit 35 is provided on the upstream side of the exhaust port 32 in the exhaust passage 33. Thereby, the exhaust gas flowing through the exhaust passage 33 is purified and discharged from the exhaust port 32 to the outside.

The supercharger 40 includes a housing 41, a turbine wheel 42, a compressor wheel 43, a variable throttle unit 44, and an actuator 46.
The housing 41 has a substantially cylindrical shape, and houses the turbine wheel 42, the compressor wheel 43, and the variable throttle unit 44 therein. The housing 41 constitutes a part of the intake passage 21 and a part of the exhaust passage 31, and has an exhaust suction port 411, an exhaust discharge port 412, an intake suction port 413, and an intake discharge port 414. The exhaust suction port 411 is opened on the engine 10 side, and the exhaust discharge port 412 is opened on the exhaust port 32 side. Further, the intake / intake port 413 is opened to the intake port 22 side, and the intake / exhaust port 414 is opened to the engine 10 side. Here, the exhaust suction port 411 corresponds to the “turbine wheel inlet” in the claims.

  The turbine wheel 42 is rotatably provided in the exhaust passage 33 and is rotated by the exhaust discharged from the combustion chamber 14. The compressor wheel 43 is provided coaxially with the turbine wheel 42 by a shaft 45 and is disposed in the intake passage 23. Therefore, the compressor wheel 43 rotates together with the turbine wheel 42 and supercharges the intake air supplied to the combustion chamber 14.

  In the case of this embodiment, a variable throttle 44 is provided in the vicinity of the upstream side of the turbine wheel 42. The variable throttle 44 adjusts the opening area of the exhaust passage 33 between the exhaust suction port 411 and the turbine wheel 42. As shown in FIG. 2, a plurality of variable throttle portions 44 are provided on the radially outer side of the turbine wheel 42. The variable throttle 44 is driven by an actuator 46 and opens and closes to thereby cause a flow rate of exhaust flowing through the turbine wheel 42 (hereinafter simply referred to as “exhaust flow rate” means “flow rate of exhaust flowing through the turbine wheel 42”). ). In the present embodiment, as the actuator 46, for example, an actuator driven by air pressure or hydraulic pressure is used. Here, the actuator 46 corresponds to a “drive unit” in the claims.

  Here, the relationship between the operation | movement of the variable throttle | throttle part 44 and the exhaust flow velocity which flows into the turbine wheel 42 is demonstrated based on FIG. FIG. 2A is a schematic cross-sectional view showing the variable aperture 44 when fully opened, and FIG. 2B is a schematic cross-sectional view showing the variable aperture 44 when fully closed. As shown in FIG. 2A, when the variable aperture portion 44 is fully opened, the opening area between the plurality of variable aperture portions 44 is maximized. That is, the opening area of the exhaust passage 33 in the vicinity of the upstream side of the turbine wheel 42 is maximized. On the other hand, as shown in FIG. 2B, when the variable throttle portion 44 is fully closed, the opening area between the plurality of variable throttle portions 44 is minimized. That is, the opening area of the exhaust passage 33 in the vicinity of the upstream side of the turbine wheel 42 is minimized. Hereinafter, the degree of opening and closing of the variable throttle unit 44 is represented by a VN opening, the VN opening when the variable throttle unit 44 is fully opened is 0%, and the VN opening when the variable throttle unit 44 is fully closed is 100%. Here, for example, when the pressure of the exhaust gas upstream of the turbine wheel 42 is constant, the exhaust flow velocity when the variable throttle portion 44 is fully closed is higher than the exhaust flow velocity when the variable throttle portion 44 is fully opened.

  The ECU 50 is constituted by a microcomputer including a CPU, a ROM, a RAM, and the like (not shown). The ECU 50 controls each part of the vehicle according to the computer program recorded in the ROM. Further, the ECU 50 controls the actuator 46 and adjusts the opening / closing state of the variable throttle unit 44. The ECU 50 corresponds to a “control unit” in the claims. Various sensors are connected to the ECU 50. Here, the turbine wheel 42, the compressor wheel 43, the variable throttle 44, and the ECU 50 constitute an engine supercharging system 2.

  In the present embodiment, the engine supercharging system 2 is provided with various sensors such as an engine speed sensor 51, a supercharging pressure sensor 52, a pressure sensor 53, a temperature sensor 54, and an intake flow rate sensor 55. The engine speed sensor 51 is provided in the vicinity of the engine 10 and detects the speed of the engine 10. The supercharging pressure sensor 52 is provided in the surge tank 27 and detects the pressure of supercharged intake air. The pressure sensor 53 and the temperature sensor 54 are provided in the exhaust passage 33 between the exhaust valve 16 and the supercharger 40 and detect the pressure and temperature of the exhaust discharged from the combustion chamber 14. The intake flow rate sensor 55 is provided on the downstream side of the air cleaner 24 and detects the flow rate of intake air taken into the intake passage 23.

Next, output characteristics of the engine system 1 having the above configuration will be described with reference to FIG.
FIG. 3 shows the relationship between the supercharging pressure ratio of the compressor wheel 43, the exhaust flow velocity, the output torque of the engine 10, and the VN opening of the variable throttle 44 when the engine 10 is operated at a medium load and a low load. FIG. Here, the supercharging pressure ratio refers to the ratio between the pressure on the downstream side of the compressor wheel 43 and the pressure on the upstream side. Further, the solid line indicates the output characteristic at the time of medium load operation of the engine 10, and the broken line indicates the output characteristic at the time of low load operation of the engine 10.

  Here, a state in which the engine 10 is operated at a medium load will be described. In the region where the VN opening of the variable throttle section 44 is X% or less, the exhaust gas flow velocity increases, so that the supercharging pressure ratio of the compressor wheel 43 and the output torque of the engine 10 increase.

In the region where the VN opening of the variable throttle 44 is X% or more, when the exhaust flow rate increases, the supercharging pressure ratio of the compressor wheel 43 increases, but the output torque of the engine 10 decreases.
Accordingly, it can be seen that if the VN opening of the variable throttle 44 is excessively throttled (for example, the VN opening of the variable throttle 44 is set to X% or more), the output torque of the engine 10 tends to decrease.

Here, control of the supercharger 40 of this embodiment is demonstrated based on FIG. 4 and FIG. FIG. 4 shows a process flowchart relating to the control of the supercharger 40 by the ECU 50.
In S101, the target boost pressure Pimtrg is set. The target supercharging pressure Pimtrg is a supercharging pressure that is set based on the engine speed Ne and the injection amount Qfin during normal operation, and is acquired in advance by experiments or the like and stored as a map in the ROM of the ECU 50. The engine speed Ne is detected by the engine speed sensor 51.

  In S102, the actual boost pressure Pim is calculated. The actual boost pressure Pim is detected by the boost pressure sensor 52. The detected actual boost pressure Pim is stored in the RAM of the ECU 50. Here, in order to represent the change with time of the actual supercharging pressure Pim, in the detection cycle, the actual supercharging pressure detected last time is Pim (N-1), and the actual supercharging pressure detected this time is Pim (N). .

  In S103, a supercharging pressure deviation Pimdel is calculated. Here, the supercharging pressure deviation Pimdel is calculated by subtracting the actual supercharging pressure Pim from the target supercharging pressure Pimtrg.

  In S104, the required VN opening Vnreq is calculated. Here, the required VN opening degree Vnreq is calculated based on the supercharging pressure deviation Pimdel. The required VN opening Vnreq is calculated by performing feedback control on the reference VN opening based on the operating conditions of the engine 10. Here, the operating condition of the engine 10 is determined by the supercharging pressure deviation Pimdel. The basic VN opening is determined in advance based on the engine speed Ne and the injection amount Qfin and is stored as MAP in the ROM of the ECU 50.

In S105, the first guard value Vmax1 and the second guard value Vmax2 are set.
The first guard value Vmax1 is a guard value for preventing excessive rotation of the turbine wheel 42 of the supercharger 40. In the present embodiment, the exhaust flow velocity that causes excessive rotation of the turbine wheel 42 of the supercharger 40 is set to the first guard value Vmax1 (see FIG. 6).

  The second guard value Vmax2 is a guard value for preventing the output torque of the engine 10 from decreasing below the allowable torque. In the present embodiment, the exhaust flow velocity that causes the output torque of the engine 10 to be lower than the allowable torque is set to the second guard value Vmax2 (see FIG. 6). Further, the allowable torque of the engine 10 varies depending on the operating conditions of the engine 10. Therefore, the second guard value Vmax2 is set based on MAP that has been converted to MAP in advance by the engine speed Ne and the injection amount Qfin (see FIG. 7).

In S106, the intake exhaust flow velocity Vin of the exhaust intake port 411 of the variable throttle 44 is calculated.
The intake exhaust flow velocity Vin is a flow velocity of exhaust flowing in the exhaust passage 33 between the exhaust valve 16 and the variable throttle portion 44.

The exhaust gas density Rou is calculated based on the following equation 1. Here, Pex is the pressure of the exhaust gas flowing through the exhaust passage 33 between the variable throttle unit 44 and the exhaust valve 16, and is detected by the pressure sensor 53. Tex is the temperature of the exhaust gas flowing through the exhaust passage 33 between the variable throttle 44 and the exhaust valve 16 and is detected by the temperature sensor 54. R is a gas constant.
Rou = Pex / (R × Tex) Formula 1

The exhaust gas flow rate Gex is calculated based on the following equation 2. Here, Gair is the flow rate of the intake air supplied to the engine 10 and is detected by the intake flow rate sensor 55. Gfuel is a flow rate of fuel injected into the combustion chamber 14 of the engine 10 and is calculated by the ECU 50 based on the injection amount Qfin.
Gex = Gair + Gfuel Equation 2
A volume flow rate Gvol_ex of the exhaust gas is calculated based on the following formula 3.
Gvol_ex = Gex / Rou Formula 3
The intake / exhaust flow velocity Vin is calculated based on the following equation 4. Here, Ain is the opening area of the exhaust inlet 411 of the supercharger 40.
Vin = Gvol_ex / Ain Formula 4

In S107, the variable throttle part downstream side exhaust flow velocity Vout on the downstream side of the variable throttle part 44 is calculated based on the following equation (5). Here, the variable throttle downstream side exhaust flow velocity Vout corresponds to the above-described exhaust flow velocity. (Hereinafter, the exhaust flow velocity Vout on the downstream side of the variable throttle section is simply referred to as “exhaust flow velocity Vout”). Here, Aout is an opening area of the exhaust passage 33 in the vicinity of the upstream side of the turbine wheel 42 due to the opening / closing state of the variable throttle 44. Aout is determined in advance based on the actual VN opening degree Vnact of the variable throttle unit 44, and is stored as MAP in the ROM of the ECU 50.
Vout = Vin × (Ain / Aout) Equation 5

  In S108, the ECU 50 compares the exhaust flow velocity Vout detected in S107 with a preset first guard value Vmax1. When the exhaust flow velocity Vout is smaller than the first guard value Vmax1 (S108: YES), the process proceeds to S109. On the other hand, when the exhaust gas flow velocity Vout is equal to or higher than the first guard value Vmax1 (S108: NO), the process proceeds to S110.

In S109, the ECU 50 calculates a supercharging state determination flag Xpim. Here, the ECU 50 determines whether or not the current actual supercharging pressure Pim (N) satisfies the following formula 6 for a predetermined time. When the current actual supercharging pressure Pim (N) satisfies Expression 6, assuming that the duration is T, the ECU 50 determines whether T satisfies Expression 7 below. P0 and T0 are preset constants. When the current actual supercharging pressure Pim (N) and the duration T satisfy Expression 6 and Expression 7, Xpim = ON is set. On the other hand, if any one of the current actual supercharging pressures Pim (N) and T does not satisfy Expression 6 or Expression 7, Xpim = OFF is set.
Pim (N) -Pim (N-1)> P0 Formula 6
T> T0 Expression 7

  In S111, the ECU 50 determines the operating state of the engine 10 by determining whether or not the intake air is supercharged to the engine 10 and the supercharging pressure is increasing. The ECU 50 determines that the engine 10 is accelerating by determining that the intake air is supercharged to the engine 10 and the boost pressure is increasing when Xpim = ON is set in S109 (S111: YES). Then, the process proceeds to S112. On the other hand, when Xpim = OFF is set in S109 (S111: NO), the process proceeds to S115.

  In S112, the ECU 50 compares the exhaust flow velocity Vout detected in S107 with a preset second guard value Vmax2. When the exhaust flow velocity Vout is smaller than the second guard value Vmax2 (S112: YES), the process proceeds to S113. On the other hand, when the exhaust gas flow velocity Vout is greater than or equal to the second guard value Vmax2 (S112: NO), the process proceeds to S114.

  In S110, S113, S114, and S115, the ECU 50 calculates the target VN opening Vntrg. Here, in order to represent the change with time of the target VN opening Vntrg, the previous target VN opening is set to Vntrg (N−1), and the current target VN opening is set to Vntrg (N).

In S110 and S114, the ECU 50 calculates the target VN opening degree Vntrg based on the following formula 8.
Vntrg (N) = Vntrg (N−1) Equation 8
When the exhaust flow velocity Vout is greater than or equal to the first guard value Vmax1, or when the exhaust flow velocity Vout during acceleration operation of the engine 10 is greater than or equal to the second guard value Vmax2, the ECU 50 indicates that the variable throttle unit 44 is too closed. The previous target VN opening Vntrg (N-1) is set to the current target VN opening Vntrg (N).

In S113 and S115, the ECU 50 calculates the target VN opening degree Vntrg based on the following formula 9.
Vntrg = Vnreq Equation 9
When the engine 10 is not accelerating, or when the exhaust flow velocity Vout during acceleration of the engine 10 is smaller than the second guard value Vmax2, the ECU 50 sets the required VN opening Vnreq calculated in S104 to the target VN opening. Set to Vntrg.

  In S116, the ECU 50 calculates the actuator control value Dvn based on the target VN opening Vntrg calculated in S110, S113, S114, and S115. In the case of the present embodiment, the ECU 50 calculates the actuator control value Dvn based on MAP (see FIG. 8) representing the relationship between the actuator control value Dvn and the target VN opening degree Vntrg.

Next, the effect of the above control of the present embodiment will be described with reference to FIG.
FIG. 9 shows changes in output torque, exhaust flow velocity, target VN opening, supercharging pressure, engine speed, and fuel injection amount when the VN opening is controlled when the engine 10 is supercharged. It is a time chart which shows. For convenience of explanation, the change when the control by the second guard value is performed is indicated by a solid line, and the change when the control by the second guard value is not performed is indicated by a broken line.

  As shown in FIG. 9, acceleration starts when the accelerator is depressed at time T1. At this time, the VN opening of the variable throttle unit 44 is once fully opened (0%) and is controlled to the closed side by feedback control. By controlling the VN opening to the closed side, the exhaust flow velocity flowing to the turbine wheel 42 increases, and the rotational speed of the turbine wheel 42 increases. For this reason, the rotational speed of the compressor wheel 43 increases, and the supercharging pressure to the engine 10 increases. Therefore, the output torque of the engine 10 increases, and the rotational speed of the engine 10 increases. However, if the VN opening is controlled too close, the exhaust flow rate exceeds the second guard value.

  As indicated by a broken line in FIG. 9, if the VN opening is controlled too close at time T2, the exhaust flow velocity exceeds the second guard value, and the output torque of the engine 10 decreases. For this reason, when the exhaust gas flow rate exceeds the second guard value, the increasing speed of the engine speed decreases.

  On the other hand, in this embodiment, the VN opening degree is controlled so that the exhaust flow velocity does not exceed the second guard value. For this reason, as shown by the solid line in FIG. 9, the exhaust flow velocity is kept smaller than the second guard value. Then, the engine speed continuously increases and the output torque of the engine 10 continues to increase without decreasing. Thus, in this embodiment, the torque fall by pumping loss can be suppressed by controlling VN opening degree.

(Other embodiments)
In the above embodiment, the supercharging system is applied to a diesel engine system. On the other hand, in another embodiment, the supercharging system may be applied to a gasoline engine system.

  In the above embodiment, an actuator driven by air pressure or hydraulic pressure is provided. On the other hand, in another embodiment, an electric actuator such as a stepping motor or a DC motor may be provided.

  In the above embodiment, the first guard value and the second guard value are set to the exhaust flow velocity. On the other hand, in other embodiments, the VN opening degree or the like may be set using the value associated with the exhaust flow velocity such as the VN opening degree as the first guard value and the second guard value.

  In the above embodiment, the first guard value is set to the exhaust flow velocity that causes the turbine wheel to over-rotate. On the other hand, in another embodiment, an exhaust flow velocity that is smaller than the exhaust flow velocity that causes excessive rotation of the turbine wheel may be set as the first guard value.

In the above embodiment, the second guard value is set to an exhaust flow velocity that causes the output torque of the engine to fall below the allowable torque. On the other hand, in another embodiment, an exhaust flow velocity smaller than the exhaust flow velocity that causes the engine output torque to fall below the allowable torque may be set as the second guard value.
The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

DESCRIPTION OF SYMBOLS 1 ... Engine system 2 ... Engine supercharging system (Internal combustion engine supercharging system)
10 ... Engine (internal combustion engine)
23 ... Intake passage 33 ... Exhaust passage 42 ... Turbine wheel 43 ... Compressor wheel 44 ... Variable throttle 46 ... Actuator (drive unit)
50... ECU (control unit, flow velocity calculation means, first guard value setting means, second guard value setting means, and supercharging state determination means)
411 ... Exhaust air inlet (inlet of turbine wheel)
Vmax1 ... first guard value Vmax2 ... second guard value

Claims (2)

A turbine wheel provided in an exhaust passage of the internal combustion engine and driven to rotate by exhaust energy of the internal combustion engine;
A compressor wheel which is provided in the intake passage of the internal combustion engine coaxially with the turbine wheel and supercharges intake air to the internal combustion engine by rotating together with the turbine wheel;
A variable throttle portion provided in the exhaust passage on the inlet side of the turbine wheel, and capable of changing an opening area of the exhaust passage;
A drive unit for driving the variable aperture unit;
A control unit that adjusts the opening area by controlling the drive unit and adjusts the flow velocity of the exhaust gas flowing through the turbine wheel, and
The controller is
A flow rate calculating means for calculating a flow rate of exhaust gas between the variable throttle and the turbine wheel;
First guard value setting means for setting a value corresponding to a flow rate of exhaust gas that causes over-rotation of the turbine wheel to a first guard value;
Second guard value setting means for setting a value smaller than the first guard value as a second guard value; and
Supercharging state determination means for determining whether or not the intake air to the internal combustion engine is supercharged and the supercharging pressure is increasing,
Controlling the variable throttle so that the flow velocity of the exhaust gas calculated by the flow velocity calculating means is smaller than the flow velocity of the exhaust gas corresponding to the first guard value;
When it is determined by the supercharging state determining means that the intake air to the internal combustion engine is supercharged and the supercharging pressure is increasing, the exhaust flow velocity calculated by the flow velocity calculating means corresponds to the second guard value. A supercharging system for an internal combustion engine, wherein the variable throttle unit is controlled to be smaller than a flow rate of exhaust gas.   2. The internal combustion engine according to claim 1, wherein the second guard value setting unit sets a value corresponding to a flow rate of exhaust gas that causes a decrease in output torque of the internal combustion engine due to a pumping loss as the second guard value. Engine supercharging system.

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