Boost pressure control method and boost pressure control device for internal combustion engine

Abstract

When acceleration is requested, the target pressure ratio (tPR) to be achieved is set based on the target torque. During the period when the actual pressure ratio (rPR) deviates from the target pressure ratio (tPR), the target exhaust valve / stroke (tWGS) is near fully closed through feedback control, thereby improving the response of the boost pressure. If the intake air amount (Qa) and the internal combustion engine rotation speed (NE) exceed the reference amount that becomes the limiting condition before the target pressure ratio is reached, the target exhaust valve / stroke (tWGS) is limited in such a way that the opening increases. As a result, the turbine rotation speed (NT) does not exceed the allowable rotation speed. If the actual pressure ratio (rPR) is close to the target pressure ratio (tPR), the opening is controlled according to the static target exhaust valve / stroke (tWGS) corresponding to the target pressure ratio (tPR).

Description

Technical Field

[0001] The present invention relates to boost pressure control of an internal combustion engine having a turbocharger, and more particularly to boost pressure control for preventing an excessive increase in the rotation speed of the turbocharger and improving the response of the boost pressure when acceleration is requested. Background Art

[0002] A turbocharger that uses exhaust energy to supercharge an internal combustion engine generally has a waste gate valve for bypassing a portion of the exhaust gas without passing through the turbine. Such an internal combustion engine can control the supercharging pressure by controlling the opening of the waste gate valve.

[0003] For example, during rapid acceleration when the accelerator pedal opening increases in a stepwise manner, it is preferred to rapidly increase the boost pressure. Patent document 1 discloses that during rapid acceleration when the operating conditions change in a stepwise manner from a non-boosting region to a boosting region, the wastegate valve is temporarily completely closed, and then the wastegate valve opening is controlled to correspond to the target torque.

[0004] However, if the opening of the waste gate valve is temporarily excessively reduced in order to improve the acceleration responsiveness, the rotation speed of the turbocharger may exceed the allowable rotation speed and excessively increase before the supercharging pressure corresponding to the target torque is reached.

[0005] Therefore, an object of the present invention is to avoid an excessive increase in the rotation speed of a turbocharger and to quickly increase the boost pressure when acceleration is requested for an internal combustion engine having a turbocharger.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-76833 Summary of the invention

[0007] Regarding the boost pressure control of the internal combustion engine involved in the present invention,

[0008] Set the target boost pressure,

[0009] A first target opening is set as the opening of the waste gate valve corresponding to the target supercharging pressure.

[0010] During a period in which the difference between the actual supercharging pressure and the target supercharging pressure is greater than a predetermined value, the opening of the waste gate valve is controlled to a second target opening that is smaller than the first target opening.

[0011] When the control is performed to the second target opening, it is determined whether a restriction condition that the intake air amount is greater than or equal to the intake air amount reference amount is satisfied.

[0012] If the restriction condition is satisfied, the opening of the waste gate valve is controlled in a direction such that the opening of the waste gate valve becomes larger than the second target opening.

[0013] Therefore, when rapid acceleration is requested, the wastegate valve opening is controlled to a second target opening that is smaller than the first target opening in order to improve the response of the boost pressure. Therefore, the boost pressure increases rapidly. Furthermore, during the process of boost pressure increase, if the restriction condition prescribed by the intake air amount is satisfied, the wastegate valve opening is limited to a relatively large opening. As a result, the rotation speed of the turbocharger does not exceed the allowable rotation speed.

[0014] Therefore, it is possible to achieve both prevention of an excessive increase in the rotation speed of the turbocharger and improvement in the response of the supercharging pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural explanatory diagram showing the system structure of the supercharged internal combustion engine according to the present invention.

[0016] Figure 2 This is a block diagram showing the overall configuration of a wastegate valve control system.

[0017] Figure 3 It is a block diagram showing details of the boost pressure control unit.

[0018] Figure 4 : is a flowchart showing the processing flow of the wastegate valve opening control.

[0019] Figure 5 It is a characteristic diagram showing the static target wastegate / stroke characteristics of the feedforward control unit.

[0020] Figure 6 It is a characteristic diagram showing the range of restriction conditions for the intake air amount and the engine rotation speed.

[0021] Figure 7 This is a time chart showing an example of changes in boost pressure and the like during acceleration. DETAILED DESCRIPTION

[0022] Hereinafter, an embodiment of the present invention will be described in detail based on the drawings.

[0023] Figure 1 1 is an explanatory diagram showing a schematic structure of a supercharged internal combustion engine 1 for a vehicle to which control of an embodiment of the present invention is applied. The internal combustion engine 1 is, for example, a spark ignition type internal combustion engine of a four-stroke cycle using gasoline as fuel, and a pair of intake valves 4 and a pair of exhaust valves 5 are arranged on the top wall surface of a combustion chamber 3 formed by a piston 2, and a spark plug 6 and a fuel injection valve 7 are arranged in the central portion surrounded by the intake valves 4 and the exhaust valves 5.

[0024] The fuel injection valve 7 is an electromagnetic or piezoelectric injection valve that is opened by applying a driving pulse signal, and injects a quantity of fuel substantially proportional to the pulse width of the driving pulse signal into the cylinder. In addition, in the present invention, a port injection type internal combustion engine that injects fuel into an intake port 8 on the upstream side of the intake valve 4 can be constructed.

[0025] An electronically controlled throttle valve 11 whose opening is controlled according to a control signal from an engine controller 10 is installed on the upstream side of the manifold 9a of the intake passage 9 connected to the intake port 8, and a compressor 12A of a turbocharger 12 is arranged on the upstream side thereof. An air flow meter 13 for detecting the amount of intake air and an air filter 14 are arranged on the upstream side of the compressor 12A. In addition, an intercooler 16 is arranged between the compressor 12A and the throttle valve 11. An intake pressure sensor 17 for detecting the intake pressure is arranged in the manifold 9a. In addition, a boost pressure sensor 18 for detecting the outlet pressure (i.e., boost pressure) of the compressor 12A is arranged between the intercooler 16 and the throttle valve 11. In addition, a temperature / pressure sensor 19 for detecting the atmospheric temperature and atmospheric pressure is arranged on the upstream side of the compressor 12A.

[0026] On the other hand, the turbine 12B of the turbocharger 12 is arranged in the exhaust passage 22 connected to the exhaust port 21 that opens and closes the exhaust valve 5, and a catalyst 23 composed of a three-way catalyst is installed on the downstream side of the turbine 12B. A waste gate valve 24 is provided at the inlet of the turbine 12B to guide a part of the exhaust gas to bypass the turbine 12B for supercharging pressure control. The waste gate valve 24 is an electronically controlled structure whose opening is controlled by an electric actuator 25.

[0027] An air-fuel ratio sensor 26 for detecting the exhaust air-fuel ratio is provided at the inlet side of the catalyst 23. The catalyst 23 is shown as one catalyst in the drawing, and is generally composed of a pre-catalyst located in the engine room of the vehicle and a main catalyst located under the vehicle floor.

[0028] In addition to the opening control of the throttle valve 11, the engine controller 10 controls the fuel injection amount and injection timing of the fuel injection valve 7, the ignition timing of the spark plug 6, etc. The engine controller 10 also controls the air-fuel ratio by the air-fuel ratio sensor 26.

[0029] In addition, as described later, the engine controller 10 controls the opening of the wastegate valve 24, thereby controlling the boost pressure and further the torque of the internal combustion engine 1. Basically, the torque of the internal combustion engine 1 is controlled by controlling the opening of the throttle valve 11 in the non-boost region where the requested torque is small, and the torque of the internal combustion engine 1 is controlled by controlling the opening of the wastegate valve 24 in the boost region where the requested torque is large and the throttle valve 11 is fully opened.

[0030] In the engine controller 10, in addition to the respective detection signals of the above-mentioned air flow meter 13, intake pressure sensor 17, boost pressure sensor 18, temperature / pressure sensor 19, and air-fuel ratio sensor 26, detection signals of a crank angle sensor 31 for detecting the rotation speed of the internal combustion engine, a water temperature sensor 32 for detecting the cooling water temperature, and an accelerator opening sensor 33 for detecting the accelerator opening corresponding to the driver's stepping on the accelerator pedal are also input.

[0031] Next, based on Figure 2 and Figure 3 The functional block diagram of FIG. 1 will explain the opening control of the waste gate valve 24 in the supercharging region (in other words, supercharging pressure control) of the engine controller 10.

[0032] Figure 2 2 shows the overall structure of the control system of the wastegate valve 24. The control system mainly includes an ETD (engine torque request) unit 41, a boost pressure control unit 42, and a wastegate valve operation control unit 43.

[0033] The ETD unit 41 sets the target torque that the internal combustion engine 1 should generate by the so-called torque request method. The accelerator opening APO detected by the accelerator opening sensor 33 and the internal combustion engine rotation speed NE detected by the crank angle sensor 31 are input to the ETD unit 41, and the requested torque is calculated based on the above parameters. Moreover, the torque consumed as the drive of various auxiliary machines, friction loss, etc. is added to the requested torque to obtain the target torque that the internal combustion engine 1 should generate. The ETD unit 41 further sets the target boost pressure based on the target torque. For example, when accelerating with the accelerator opening APO changing in a stepwise manner, the boost pressure that should be finally achieved is the target boost pressure. In addition, as the "boost pressure", the pressure (absolute pressure) on the outlet side of the compressor 12A can be simply treated as the "boost pressure", or the ratio of the pressure on the inlet side of the compressor 12A to the pressure on the outlet side (i.e., the pressure ratio) can be treated as the "boost pressure". In the present embodiment, as the "boost pressure", the pressure ratio of the pressure on the inlet side of the compressor 12A detected by the temperature / pressure sensor 19 (atmospheric pressure) and the pressure on the outlet side of the compressor 12A detected by the boost pressure sensor 18 is used. Therefore, the ETD unit 41 outputs the target boost pressure, more specifically, the target pressure ratio.

[0034] The boost pressure control unit 42 receives the target pressure ratio outputted from the ETD unit 41 and the actual pressure ratio (i.e., the actual boost pressure) based on the detection values ​​of the temperature / pressure sensor 19 and the boost pressure sensor 18, and successively calculates and outputs the target wastegate / stroke in such a manner that the actual pressure ratio gradually approaches the target pressure ratio by using feedforward control and feedback control in the manner described below. The "wastegate / stroke" refers to the stroke value of the electric actuator 25 in a linear form that specifies the opening of the wastegate valve 24, and is substantially equivalent to the opening of the wastegate valve 24. Therefore, the target wastegate / stroke is equivalent to the target opening of the wastegate valve 24. The larger the wastegate / stroke, the larger the opening of the wastegate valve 24, and the larger the amount of exhaust bypass that does not pass through the turbine 12B. On the contrary, the smaller the wastegate / stroke, the closer the opening of the wastegate valve 24 is to being completely closed.

[0035] The wastegate valve operation control unit 43 controls the stroke of the electric actuator 25 according to the target wastegate / stroke, and inputs the actual stroke detected by the position sensor (not shown) of the electric actuator 25 itself as a feedback signal. The wastegate valve operation control unit 43 controls the stroke of the electric actuator 25 by feedback control (or a combination of feedback control and feedforward control) based on the deviation between the actual stroke and the target wastegate / stroke, for example, by duty control of the electric motor, so as to achieve the target wastegate / stroke. The wastegate valve operation control unit 43 corresponds to the "actuator control unit" in the technical claims.

[0036] Figure 3 : is a functional block diagram showing the details of the boost pressure control unit 42. The boost pressure control unit 42 includes a feedforward control unit 51 that performs calculations of the operation amount based on the feedforward method, and a feedback control unit 52 that performs calculations of the operation amount based on the feedback method. Basically, the feedforward control unit 51 is equivalent to the "first target opening setting unit" in the technical solution, and the feedback control unit 52 is equivalent to the "second target opening setting unit" in the technical solution.

[0037] The feedforward control unit 51 takes the target pressure ratio and the engine speed NE outputted from the ETD unit 41 as inputs, and successively calculates the target wastegate / stroke corresponding to the "first target opening" corresponding to the target pressure ratio. Specifically, the feedforward control unit 51 mainly includes a static wastegate / stroke calculation unit 53 that takes the target pressure ratio and the engine speed NE as parameters and outputs the corresponding static wastegate / stroke, and includes an intake air temperature correction unit 54 that takes the atmospheric temperature as input and calculates the correction amount corresponding to the atmospheric temperature, and an atmospheric pressure correction unit 55 that takes the atmospheric pressure as input and calculates the correction amount corresponding to the atmospheric pressure.

[0038] The static waste gate / stroke calculation unit 53 is composed of, for example, a map in which corresponding static waste gate / strokes are allocated in advance using the target pressure ratio and the engine rotation speed NE as parameters. Figure 5 : is a characteristic diagram schematically showing an example of the characteristics of the static wastegate / stroke of the static wastegate / stroke calculation unit 53. The larger the target pressure ratio, the smaller the static wastegate / stroke. Moreover, if the internal combustion engine rotation speed NE increases, the static wastegate / stroke increases. The characteristic of the static wastegate / stroke represents the static relationship between the target pressure ratio and the opening of the wastegate valve 24 required for the target pressure ratio. In other words, it is equivalent to the relationship between the pressure ratio and the opening of the wastegate valve 24 when the internal combustion engine 1 is in a stable state. Under this static wastegate / stroke, even when the target pressure is relatively high, the rotation speed of the turbocharger 12 will not exceed the allowable rotation speed.

[0039] The correction amounts outputted by the intake air temperature correction unit 54 and the atmospheric pressure correction unit 55 are added to the static wastegate / stroke outputted by the static wastegate / stroke calculation unit 53. Thus, the corrected static wastegate / stroke can be obtained. The intake air temperature correction unit 54 gives the correction amount in the direction that the wastegate / stroke increases as the atmospheric temperature increases. The atmospheric pressure correction unit 55 gives the correction amount in the direction that the wastegate / stroke increases as the atmospheric pressure decreases.

[0040] The feedback control unit 52 receives the target pressure ratio output by the ETD unit 41 and the actual pressure ratio that becomes the feedback signal as input, and successively calculates the feedback / waste gate / stroke through feedback control based on the deviation between the two. As a feedback control method, PID control is used, for example. Feedback control other than the PID method may also be used. In order to improve the response of the boost pressure during rapid acceleration, the gain of the feedback control is set higher. When the deviation between the target pressure ratio and the actual pressure ratio is large, in order to make the pressure ratio close to the target pressure ratio with good responsiveness, the feedback / waste gate / stroke is output in the direction of reducing the opening of the waste gate valve 24 through feedback control such as PID control.

[0041] In the adding unit 56, the feedback / wastegate / stroke (i.e., the feedback control amount) outputted from the feedback control unit 52 is added to the corrected static wastegate / stroke (i.e., the feedforward control amount) outputted from the feedforward control unit 51, thereby obtaining the target wastegate / stroke. As a result, for example, when the deviation between the target pressure ratio and the actual pressure ratio is large during rapid acceleration, the target wastegate / stroke is smaller than the corrected static wastegate / stroke, that is, the opening of the wastegate valve 24 becomes a small opening. Although it depends on the degree of rapid acceleration and the gain of the feedback control, the opening of the wastegate valve 24 can be completely closed at the initial stage of acceleration when the target pressure ratio and the actual pressure ratio deviate. The relatively small target wastegate / stroke reflected in the feedback / wastegate / stroke in this way corresponds to the "second target opening" in the technical claims.

[0042] Here, when the actual pressure ratio is sufficiently close to the target pressure ratio (in other words, when the actual pressure ratio reaches the target pressure ratio), the feedback of the feedback control unit 52 is stopped, and the corrected static wastegate / stroke of the feedforward control unit 51 is output as the target wastegate / stroke. This can suppress hunting, for example. In addition, the feedforward control and the feedback control can be performed alternately, and the feedforward control is stopped and the feedback control is performed when the actual pressure ratio deviates from the target pressure ratio.

[0043] In order to avoid excessive increase in the rotation speed of the turbocharger 12 during the boost pressure increase process during rapid acceleration, the boost pressure control unit 42 further includes: a restriction region determination unit 57 that determines whether the intake air amount Qa and the internal combustion engine rotation speed NE are in (satisfy) a prescribed restriction condition; and a limiter unit 58 that limits the target wastegate / stroke to a prescribed restriction value when the prescribed restriction condition is satisfied. That is, as described above, the static wastegate / stroke (or the corrected static wastegate / stroke) output by the feedforward control unit 51 is set so that the rotation speed of the turbocharger 12 (turbine rotation speed) does not exceed the allowable rotation speed, but the feedback control amount is added thereto to make the opening of the wastegate valve 24 smaller, so there is a possibility that the rotation speed of the turbocharger 12 exceeds the allowable rotation speed depending on the conditions.

[0044] The restricted region determination unit 57 determines whether the rotation speed of the turbocharger 12 is about to exceed the permissible rotation speed based on the intake air amount Qa and the internal combustion engine rotation speed NE. Specifically, if the intake air amount Qa is greater than or equal to the intake air amount reference amount and the internal combustion engine rotation speed NE is greater than or equal to the internal combustion engine rotation speed reference amount, it is determined that the restricted condition is met. Here, in one embodiment, the intake air amount reference amount and the internal combustion engine rotation speed reference amount are as follows: Figure 6 That is, the intake air amount reference amount and the engine rotation speed reference amount have the following characteristics, that is, the larger the intake air amount, the lower the engine rotation speed reference amount, and the higher the engine rotation speed, the lower the intake air amount reference amount. Figure 6 In FIG. 1 , the area to the upper right of line L1 becomes the restriction condition.

[0045] As described above, when the intake air amount Qa and the engine rotation speed NE satisfy the restriction condition, the target waste gate valve / stroke is restricted in the restrictor unit 58 in the direction in which the opening of the waste gate valve 24 increases. The target waste gate valve / stroke after restriction by the restrictor unit 58 corresponds to the "third target opening" in the technical claims. The restriction method can be appropriately performed by addition of a predetermined amount, multiplication of a predetermined coefficient, etc. In this embodiment, the target waste gate valve / stroke after restriction is set in advance as a table with the engine rotation speed NE as a parameter, and the target waste gate valve / stroke after restriction corresponding to the engine rotation speed NE at this time is read out, thereby replacing the target waste gate valve / stroke before restriction and outputting the target waste gate valve / stroke after restriction. In addition, the target waste gate valve / stroke after restriction is set to a value that is larger as the engine rotation speed NE is higher (that is, the opening of the waste gate valve 24 is larger).

[0046] In addition, the rotation speed of the turbocharger 12 is affected by the intake air temperature (atmospheric temperature) and atmospheric pressure. Therefore, the intake air amount reference amount and the internal combustion engine rotation speed reference amount, which are limiting conditions, can be corrected according to the intake air temperature and atmospheric pressure. Regarding the intake air temperature, the correction is performed in the following manner, that is, the higher the intake air temperature, the lower the intake air amount reference amount is, and the lower the internal combustion engine rotation speed reference amount is. For example, the correction is performed in the following manner, that is, the higher the intake air temperature, the lower the intake air amount reference amount is. Figure 6 The more the line L1 in FIG. 1 shifts to the lower left, the larger the area serving as the restriction condition becomes.

[0047] In addition, the atmospheric pressure is corrected in such a way that the lower the atmospheric pressure, the lower the intake air amount reference amount and the lower the engine speed reference amount. Figure 6 The more the line L1 in FIG. 1 shifts to the lower left, the larger the area serving as the restriction condition becomes.

[0048] Next, the operation of the opening degree control of the waste gate valve 24 will be described. Figure 7 This is a timing diagram showing an example of changes in boost pressure, etc. during acceleration in a slightly simplified manner, where (a) represents the engine rotation speed NE, (b) represents the intake air volume Qa, (c) represents the accelerator opening APO, (d) represents the wastegate / stroke WGS, (e) represents the pressure ratio PR, and (f) represents the turbine rotation speed NT (supercharger rotation speed). In this acceleration example, at a relatively high engine rotation speed NE, the accelerator opening APO changes in a stepwise manner to be greater than or equal to a specified value. Based on this change in the accelerator opening APO, the target pressure ratio tPR corresponding to the target torque increases sharply and deviates greatly from the actual pressure ratio rPR. As a result, the feedback control amount of the aforementioned feedback control unit 52 is given a larger amount in the direction of decreasing the wastegate / stroke WGS, for example, the target wastegate / stroke tWGS is equivalent to being completely closed. The target wastegate stroke tWGS changes with a slight lag, and the actual wastegate stroke rWGS is equivalent to being completely closed. As the turbine rotation speed NT increases, the actual pressure ratio rPR increases relatively rapidly.

[0049] In this Figure 7In the example shown in FIG. 1 , before the actual pressure ratio rPR reaches the target pressure ratio tPR, the intake air amount Qa exceeds the intake air amount reference amount that becomes the restriction condition, which is not shown in the figure, but the engine rotation speed NE also exceeds the engine rotation speed reference amount at the same time. Therefore, the target wastegate / stroke tWGS becomes the restricted target wastegate / stroke by the action of the aforementioned limiter unit 58. That is, the target value is restricted in the direction of increasing the opening as the opening of the wastegate valve 24. The restriction of the opening of the wastegate valve 24 suppresses the increase of the turbine rotation speed NT, and does not exceed the allowable rotation speed as shown in the figure.

[0050] Then, the actual pressure ratio rPR reaches the target pressure ratio tPR (i.e., a state that is sufficiently close), and the addition of the feedback control amount of the feedback control ends. Therefore, thereafter, the target wastegate / stroke tWGS (which is equivalent to the "first target opening state" in the technical proposal) based on the static wastegate / stroke of the feedforward control unit 51 is given, and the actual wastegate / stroke rWGS is obtained based on this. In addition, as described above, the actual wastegate / stroke rWGS is equivalent to the actual value of the opening of the wastegate valve 24.

[0051] Figure 4 The processing flow of the wastegate valve opening control is shown in the form of a flowchart. The illustrated flow is repeatedly executed. In step 1, the target torque that the internal combustion engine 1 should generate is set mainly based on the accelerator opening APO and the internal combustion engine rotation speed NE. And, in step 2, the target pressure ratio (in other words, the target boost pressure) that should be achieved is set based on the target torque. In step 3, the actual pressure ratio (in other words, the actual boost pressure) is read.

[0052] Next, in step 4, it is determined whether the difference between the target pressure ratio and the actual pressure ratio increases to a level that requires feedback control. If the difference between the target pressure ratio and the actual pressure ratio is less than a predetermined value, the process proceeds to step 5 and feedforward control is selected. Furthermore, in step 6, the target wastegate / stroke is calculated based on the aforementioned static characteristics. Furthermore, the process proceeds from step 6 to step 10, and the electric actuator 25 is driven / controlled based on the target wastegate / stroke.

[0053] Therefore, in the case of slow acceleration, the opening of the waste gate valve 24 is mainly controlled by the feedforward control, and even when the supercharging pressure is high, there is almost no possibility that the rotation speed of the turbocharger 12 exceeds the allowable rotation speed.

[0054] If the difference between the target pressure ratio and the actual pressure ratio is greater than a predetermined value in step 4, the process proceeds to step 7, where feedback control is selected in addition to (or instead of) feedforward control. Furthermore, in step 8, the target wastegate / stroke is calculated by feedback control in such a way that the actual pressure ratio quickly approaches the target pressure ratio.

[0055] After the target wastegate / stroke is calculated, it is determined in step 9 whether the intake air amount and the engine speed are included in the aforementioned restriction conditions.

[0056] If it is not a restriction condition, the process proceeds to step 10, and the electric actuator 25 is driven / controlled based on the target wastegate / stroke obtained by feedback control. If it is a restriction condition, the process proceeds to step 11, and the target wastegate / stroke is restricted as described above. For example, the restricted target wastegate / stroke is given in the direction in which the opening of the wastegate valve 24 is further increased by using a restriction value corresponding to the rotation speed of the internal combustion engine. Then, in step 10, the electric actuator 25 is driven / controlled in the same manner.

[0057] When the actual pressure ratio is sufficiently close to the target pressure ratio by the feedback control, the process proceeds from step 4 to steps 5 and 6 to switch to the above-mentioned feedforward control.

[0058] Thus, in the above embodiment, during the period when the actual supercharging pressure (actual pressure ratio) is lower than the target supercharging pressure (target pressure ratio), the wastegate valve 24 is controlled according to the second target opening (feedback / wastegate / stroke) which is smaller than the first target opening (static wastegate / stroke) which is a static target value corresponding to the target supercharging pressure to be achieved, thereby improving the responsiveness of the supercharging pressure change during acceleration and the acceleration responsiveness. Furthermore, during the period of operation at such a second target opening, if the intake air amount and the engine rotation speed exceed the reference amount which becomes the restriction condition, the engine is restricted to the third target opening (wastegate / stroke after restriction) which is larger than the second target opening (feedback / wastegate / stroke), so that the rotation speed of the turbocharger 12 does not exceed the allowable rotation speed.

[0059] In particular, the rotation speed of the turbocharger 12 is prevented from excessively increasing based on the intake air amount and the engine rotation speed, so there is no need to provide a rotation speed sensor in the turbocharger 12. Even if the turbocharger 12 has a rotation speed sensor, it can function as a so-called fail-safe.

[0060] In addition, by using both the intake air volume and the internal combustion engine rotation speed as limiting conditions, the rotation speed of the turbocharger 12 can be more reliably grasped, and an excessive increase in the rotation speed can be effectively avoided. That is, the opening of the wastegate valve 24 is not unnecessarily restricted, and the rotation speed of the turbocharger 12 can be made not to exceed the allowable rotation speed and the response of the boost pressure can be improved.

[0061] One embodiment of the present invention has been described in detail above, but the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, the intake air quantity reference value and the internal combustion engine rotation speed reference value that become the limiting conditions are as follows: Figure 6 The reference amount is set as shown in the line L1 in FIG. 1 , but the setting of the reference amount is not limited thereto, and the reference amount may be set in an appropriate manner so that the rotation speed of the turbocharger 12 does not increase excessively. In the above embodiment, if the restriction condition is satisfied, the opening of the waste gate valve is restricted to the third target opening that is larger than the second target opening, but the opening of the waste gate valve may be set to the first target opening.

Claims

1. A method for controlling boost pressure of an internal combustion engine, the internal combustion engine having a turbocharger, the turbocharger having a wastegate valve, wherein: Set the target boost pressure, A first target opening is set as the opening of the waste gate valve corresponding to the target supercharging pressure. During a period in which the difference between the actual supercharging pressure and the target supercharging pressure is greater than a predetermined value, the opening of the waste gate valve is controlled to a second target opening that is smaller than the first target opening. When the control is performed to the second target opening, it is determined whether the restriction conditions that the intake air amount is greater than or equal to the intake air amount reference amount and the engine rotation speed is greater than or equal to the engine rotation speed reference amount are satisfied. If the restriction condition is satisfied, the opening of the wastegate valve is controlled in a direction such that the opening of the wastegate valve is larger than the second target opening. Here, the intake air amount reference amount and the engine rotation speed reference amount serving as the above-mentioned restriction conditions have the following characteristics: the larger the intake air amount, the lower the engine rotation speed reference amount, and the higher the engine rotation speed, the lower the intake air amount reference amount.

2. The boost pressure control method for an internal combustion engine according to claim 1, wherein: If the restriction condition is satisfied, the opening of the wastegate valve is restricted to a third target opening greater than the second target opening. If the difference between the actual supercharging pressure and the target supercharging pressure is smaller than a predetermined value, the opening of the waste gate valve is controlled to the first target opening.

3. The boost pressure control method for an internal combustion engine according to claim 1 or 2, wherein: The target supercharging pressure is set when the accelerator opening changes to a value greater than or equal to a predetermined value and acceleration is requested.

4. The boost pressure control method for an internal combustion engine according to claim 1 or 2, wherein: The second target opening degree is successively set by feedback control based on the deviation between the target supercharging pressure and the actual supercharging pressure.

5. The boost pressure control method for an internal combustion engine according to claim 1 or 2, wherein: The first target opening degree is set sequentially by feedforward control based on static characteristics using the target supercharging pressure and the engine rotation speed as parameters.

6. The boost pressure control method for an internal combustion engine according to claim 2, wherein: The third target opening degree is set to an opening degree smaller than the first target opening degree.

7. The boost pressure control method for an internal combustion engine according to claim 2, wherein: The intake air amount reference amount and the engine speed reference amount serving as the above-mentioned limiting conditions are corrected according to the intake air temperature so as to become values ​​on the lower intake air amount side and the lower engine speed side as the intake air temperature increases.

8. The boost pressure control method for an internal combustion engine according to claim 2, wherein: The intake air amount reference amount and the engine rotation speed reference amount, which are the above-mentioned limiting conditions, are corrected according to the atmospheric pressure so that the lower the atmospheric pressure, the lower the intake air amount and the lower the engine rotation speed.

9. A boost pressure control device for an internal combustion engine, wherein: The boost pressure control device of the internal combustion engine comprises: A turbocharger having a wastegate valve whose opening can be controlled via an actuator; A boost pressure sensor, which detects actual boost pressure; a target boost pressure setting unit that sets a target boost pressure; a first target opening setting unit for setting a first target opening corresponding to the target supercharging pressure as a target opening of the waste gate valve; a second target opening setting unit for setting a second target opening smaller than the first target opening as the target opening while the difference between the actual supercharging pressure and the target supercharging pressure is greater than a predetermined value; a restricted region determination unit for determining whether or not restriction conditions are satisfied that the intake air amount is greater than or equal to an intake air amount reference amount and the engine rotation speed is greater than or equal to an engine rotation speed reference amount when the engine is operated at the second target opening; a limiter section that controls the opening of the waste gate valve in a direction such that the target opening is larger than the second target opening when it is determined that the limit condition is satisfied; as well as an actuator control unit, which controls the actuator according to the target opening, The intake air amount reference amount and the engine rotation speed reference amount serving as the above-mentioned restriction conditions have the following characteristics: the larger the intake air amount, the lower the engine rotation speed reference amount, and the higher the engine rotation speed, the lower the intake air amount reference amount.

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