Control device for turbocharged engine

Abstract

To provide a control device for an engine with a supercharger which can inhibit an excessive load from being applied to a connection portion between a waste gate valve and a drive device for driving the waste gate valve.SOLUTION: When a request to close a waste gate valve is issued, a control device for an engine with a supercharger moves the waste gate valve from a valve opening position to a valve closing position by means of drive means, and executes valve closing control for setting torque in a valve closing direction which is to be applied to the waste gate valve from the drive means after the movement to predetermined first torque and pressing the waste gate valve against an opening portion. After the execution of the valve closing control, when a waste gate valve closing duration time reaches a predetermined determination time, the control device executes torque reduction control for reducing the torque in the valve closing direction applied from the drive means to the waste gate valve from the first torque to a smaller second torque.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a control device for a supercharged engine that includes an engine body, an exhaust passage through which exhaust gas discharged from the engine body flows, a turbocharger including a turbine provided in the exhaust passage, and a bypass passage that communicates with an opening formed in the exhaust passage upstream of the turbine and bypasses the turbine. [Background technology]

[0002] As disclosed in Patent Document 1, there is known an engine having a turbocharger, which has a bypass passage that bypasses the turbine, a wastegate valve that opens and closes the bypass passage, and a drive means that drives the wastegate valve to open and close.

[0003] In the engine of Patent Document 1, the drive means includes a motor, a rod that is slidably driven by the motor, and a link member that connects the rod and the wastegate valve. As the rod slides, the link member rotates about a predetermined axis, rotating the wastegate valve together with the rod, thereby opening and closing an opening formed in the exhaust passage at the downstream end of the bypass passage by the wastegate valve. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-96266 Summary of the Invention [Problem to be solved by the invention]

[0005] In an engine such as that disclosed in Patent Document 1, in which a wastegate valve is connected to a drive means so as to rotate about a predetermined axis, the wastegate valve may be disposed so as to block the opening from the bypass passage side when closed. In such a configuration, when the wastegate valve is closed, torque is applied from the exhaust gas to the wastegate valve in a direction that opens it, which may cause the wastegate valve to not remain closed.

[0006] In response to this, the valve can be kept closed by applying a high torque to the wastegate valve from the drive means in the valve closing direction. However, simply applying a high torque to the wastegate valve in the valve closing direction from the drive means could result in excessive load being placed on the connection between the wastegate valve and the drive means (the link material in Patent Document 1) when the opening is displaced toward the bypass passage and the torque applied to the wastegate valve in the valve opening direction increases.

[0007] Specifically, when a high torque in the valve closing direction is being applied to the wastegate valve from the drive means, if a high torque in the opposite direction is applied to the wastegate valve, high torques in opposite directions will be applied to the drive means side and the wastegate valve side of the connecting part, which will increase the load on the connecting part.

[0008] The present invention has been made in consideration of the above-described circumstances, and has an object to provide a control device for a turbocharged engine that can prevent excessive load from being applied to a connection portion between a wastegate valve and a drive device that drives the wastegate valve. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a control device for a turbocharged engine including an engine body, an exhaust passage through which exhaust gas discharged from the engine body flows, a turbocharger including a turbine provided in the exhaust passage, and a bypass passage that communicates with an opening formed in the exhaust passage upstream of the turbine and bypasses the turbine, the control device comprising: a wastegate valve that opens and closes the opening; drive means that drives the wastegate valve; and control means that controls the drive means, an opening edge of the opening portion has a tapered shape in which the diameter on the outlet side closer to the bypass passage is larger than the diameter on the inlet side opposite thereto; The wastegate valve is a valve body that opens and closes the opening, and a valve shaft that is formed rotatably integrally with the valve body; Rotating about an axis extending in a direction intersecting the opening direction of the opening, The valve body is seated on the edge of the opening. the valve is disposed in the bypass passage so as to be displaceable between a closed position where it is fully closed to block the opening from inside the bypass passage, and an open position where it is separated from the opening to open the opening, the valve body is disposed so as to be seated on a middle portion of the opening edge, and when seated on the opening edge, has a tapered shape in which the outlet side has a larger diameter than the inlet side, The driving means The valve shaft has a connecting member welded to it so as to be rotatable integrally with it, and a rotating member that rotates the connecting member around the axis, and the rotating member rotates the connecting member, thereby The wastegate valve is rotated around the axis. height, When a request to fully close the wastegate valve is issued during operation of the engine, the control means moves the wastegate valve from the open position to the closed position by the drive means, and outputs a signal from the drive means to the wastegate valve after it has moved to the closed position. via the connecting member a valve closing control for pressing the wastegate valve against the opening by setting the torque applied in the valve closing direction to a predetermined first torque, and when a valve closing duration, which is a time period during which the wastegate valve continues to be fully closed after the valve closing control is performed, reaches a predetermined judgment time, a signal is output from the drive means. via the connecting member The torque applied to the wastegate valve in the valve closing direction is reduced from the first torque to a second torque smaller than the first torque. This reduces the load on the connecting portion between the connecting member and the wastegate valve. The present invention is characterized in that torque reduction control is carried out (claim 1).

[0010] In the present invention, the wastegate valve is closed. (fully closed) After that, the drive means applies a first torque in the valve closing direction to the wastegate valve, and the wastegate valve is pressed against the opening. (fully closed) can be maintained.

[0011] However, with this configuration, if the wastegate valve remains closed for a predetermined period of time or longer, excessive load may be placed on the connection between the wastegate valve and the drive unit. Specifically, if the wastegate valve remains closed for a predetermined period of time or longer, the boost pressure increases, causing the exhaust gas to become hot. When exposed to hot exhaust gas, the exhaust passage (the portion through which the exhaust gas flows toward the turbine body) may thermally expand, causing its opening to shift toward the bypass passage. Therefore, an increase in the torque applied to the wastegate valve in the valve opening direction may place an excessive load on the connection between the wastegate valve and the drive unit.

[0012] In contrast, in the present invention, when the duration of the wastegate valve being closed reaches a predetermined judgment time, torque reduction control is implemented to reduce the torque in the valve closing direction applied from the drive means to the wastegate valve from the first torque to a second torque that is smaller than the first torque. This reduces the torque in the valve closing direction applied to the drive means side of the connecting portion. This prevents excessive load from being applied to the connecting portion, thereby preventing damage to the connecting portion.

[0013] In the above-described configuration, the second torque is preferably set to a value equal to or greater than a minimum value of torque in the valve closing direction that can maintain the wastegate valve in the valve closed position (claim 2).

[0014] According to this configuration, as described above, it is possible to prevent an excessive load from being applied to the connecting portion between the drive device and the wastegate valve while preventing the wastegate valve from being closed. (fully closed) can be reliably maintained.

[0015] In the above-described configuration, the first torque is preferably set to a value smaller than a maximum value of torque in the valve closing direction that can be applied from the drive means to the wastegate valve (claim 3).

[0016] According to this configuration, even when the valve closure duration is less than the determination time, the load on the connecting portion can be kept small, and damage to the connecting portion can be reliably prevented.

[0017] The turbine housing is where all exhaust gases are introduced when the wastegate valve is fully closed. This makes it prone to thermal expansion.

[0018] Therefore, if the present invention is applied to a configuration in which the turbocharger includes a turbine housing that houses the turbine and the opening is formed in the turbine housing, the load on the connecting portion can be effectively reduced (claim 4).

[0019] Furthermore, as described above, the present invention can reduce the load on the connecting portion. The valve shaft extending from the valve body along the axis Tei , The connecting member a valve shaft welded to the end opposite the body portion; are If the present invention is applied to this configuration, it becomes possible to reduce the welding area between the valve shaft and the connecting member (claim 5). [Effects of the Invention]

[0020] As described above, the control device for a supercharged engine of the present invention can prevent excessive load from being applied to the connecting portion between the wastegate valve and the drive device that drives it. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a diagram showing a configuration of an engine according to an embodiment of the present invention. [Figure 2] FIG. 1 is a schematic side view of a turbocharger. [Figure 3] FIG. 2 is a schematic front view of the turbine. [Figure 4] FIG. 4 is a schematic cross-sectional view taken along line IV-IV in FIG. [Figure 5]3A and 3B are diagrams showing when the wastegate valve is open, in which (a) is a schematic bottom view, and (b) is a schematic cross-sectional view taken along line VV in FIG. 2. [Figure 6] 3A and 3B are diagrams showing the state when the wastegate valve is fully closed, in which (a) is a schematic bottom view and (b) is a schematic cross-sectional view taken along line VV in FIG. 2. [Figure 7] FIG. 2 is a block diagram showing a control system of the engine. [Figure 8] 4 is a flowchart showing a control procedure of a wastegate valve. [Figure 9] 10 is a time chart showing the change over time of each parameter when the wastegate valve is fully closed. [Figure 10] FIG. 4 is a schematic cross-sectional view for explaining torque acting on a wastegate valve and a link plate when a turbine housing thermally expands. DETAILED DESCRIPTION OF THE INVENTION

[0022] (Overall engine configuration) FIG. 1 is a schematic system diagram showing a preferred embodiment of an engine to which a control device according to an embodiment of the present invention is applied. The engine includes an engine body 1 that is driven by a supply of fuel, an intake passage 50 through which intake air introduced into the engine body 1 flows, and an exhaust passage 60 through which exhaust gas discharged from the engine body 1 flows. The engine is also a supercharged engine, and includes a turbocharger 70 that is driven by exhaust gas passing through the exhaust passage 60. That is, the engine has a turbine 81 that is provided in the exhaust passage 60 and driven by the exhaust, and a compressor 91 that is provided in the intake passage 50 and rotationally driven by the turbine 81 to supercharge the intake air. This engine is installed in a vehicle such as an automobile as a power source for driving the vehicle.

[0023] The engine body 1 is an in-line multi-cylinder type having a plurality of cylinders 2a (only one of which is shown in FIG. 1) arranged in a direction perpendicular to the plane of the paper on which FIG. 1 is drawn. The engine body 1 comprises a cylinder block 2 in which the plurality of cylinders 2a are formed, a cylinder head 3 that closes the upper end opening of each cylinder 2a, and a plurality of pistons 4 housed in each cylinder 2a. In this embodiment, the side from the cylinder block 2 toward the cylinder head 3 is considered to be the top, and the opposite is considered to be the bottom. However, this is for the convenience of explanation and is not intended to limit the installation position of the engine.

[0024] A combustion chamber 5 is defined above the piston 4 of each cylinder 2a. Fuel is supplied to the combustion chamber 5 by injection from an injector 10, which will be described later. The mixture of the supplied fuel and air is combusted in the combustion chamber 5, and the expansion force caused by the combustion causes the piston 4 to reciprocate up and down.

[0025] A crankshaft 13, which is the output shaft of the engine body 1, is provided at the bottom of the cylinder block 2 (below the pistons 4). The crankshaft 13 is connected to the pistons 4 and rotates around its central axis in response to the reciprocating motion (up and down movement) of the pistons 4. A crank angle sensor SN1 is attached to the cylinder block 2 to detect the rotation speed of the crankshaft 13, which is the engine speed.

[0026] The cylinder head 3 is formed with an intake port 6 and an exhaust port 7 for each cylinder 2a, which communicate with the combustion chamber 5. The cylinder head 3 is also equipped with a combination of an intake valve 8 that opens and closes the intake port 6, an exhaust valve 9 that opens and closes the exhaust port 7, an injector 10 that injects fuel into the combustion chamber 5, and an ignition plug 11 that ignites the air-fuel mixture, for each cylinder 2a.

[0027] The intake passage 50 is connected to one side of the cylinder head 3 so as to communicate with the intake ports 6 of each cylinder 2a. Arranged in the intake passage 50, in this order from upstream to downstream, are an air cleaner 51, a compressor 91 of the turbocharger 70, a throttle valve 52, an intercooler 53, and a surge tank 54. The air cleaner 51 is a filter that removes foreign matter from the intake air. The throttle valve 52 is a valve that can adjust the flow rate of intake air flowing through the intake passage 50. The intercooler 53 is a heat exchanger that cools the intake air compressed by the turbocharger 70 (compressor 91). The surge tank 54 is a tank that provides space for evenly distributing the intake air to each cylinder 2a. An air flow sensor SN2 is attached to the intake passage 50 between the air cleaner 51 and the compressor 91 to detect the flow rate of intake air passing through this section. A supercharging pressure sensor SN3 is attached to the surge tank 54 to detect the pressure inside the surge tank 54, that is, the supercharging pressure which is the pressure of the intake air after being supercharged by the compressor 91.

[0028] The exhaust passage 60 is connected to one side of the cylinder head 3 (the side opposite to the intake passage 50) so as to communicate with the exhaust ports 7 of each cylinder 2a. In the exhaust passage 60, a turbine 81 of a turbocharger 70 and a catalytic device 61 incorporating a catalyst such as a three-way catalyst are provided in this order from the upstream side.

[0029] (Turbocharger) The turbocharger 70 includes a turbine unit 80 including a turbine 81 and a compressor unit 90 including a compressor 91 .

[0030] The turbine unit 80 has a turbine 81 and a turbine housing 82 that houses the turbine 81. The turbine 81 is a radial turbine that has multiple blades on its outer periphery and rotates when exhaust gas collides with these blades. Hereinafter, the turbine 81, or the so-called turbine impeller, will be referred to as the turbine body 81. The compressor unit 90 has a compressor 91 and a compressor housing 92 that houses the compressor 91. The compressor 91 also has multiple blades on its outer periphery. The turbocharger 70 further has a connecting shaft 71 that connects the turbine body 81 and the compressor 91, and a center housing 72 that houses the connecting shaft 71.

[0031] Fig. 2 is a schematic side view of the turbocharger 70. As shown in Fig. 2, the turbocharger 70 is arranged such that the turbine housing 82 and the compressor housing 92 are aligned in a row with the center housing 72 sandwiched between them. In the following description, the alignment direction, which is the axial direction of the connecting shaft 71, will be referred to as the left-right direction, and the turbine housing 82 side will be referred to as the right. In the following description, the up-down direction in Fig. 2 will be simply referred to as the up-down direction, and the direction perpendicular to the plane of Fig. 2 (the direction perpendicular to the up-down direction and the left-right direction) will be referred to as the front-rear direction, and the front side of the plane of Fig. 2 will be referred to as the front.

[0032] FIG. 3 is a schematic front view (viewed from the right side) of the turbine unit 80. Note that the turbine body 81 is not shown in FIG. 3. The turbine housing 82 has an inlet section 83 connected to the exhaust passage 60 upstream of the turbine unit 80 to introduce exhaust gas into the turbine housing 82, a turbine scroll section 84 extending along the outer periphery of the turbine body 81 and surrounding the entire circumference of the turbine body 81, and an outlet section 85 connected to the exhaust passage 60 downstream of the turbine unit 80 to discharge exhaust gas from the turbine housing 82. The inlet section 83, the turbine scroll section 84, and the outlet section 85 are integrally formed with one another. The turbine housing 82 is made, for example, by casting. Note that, as shown in FIG. 1, the turbine unit 80 of this embodiment is a twin-scroll turbine, and the turbine scroll section 84 is divided into two passages in the left-right direction.

[0033] The turbine scroll portion 84 is provided on the left side of the turbine housing 82. On the inner peripheral side of the turbine scroll portion 84, a turbine body accommodating portion 84a in which the turbine body 81 is accommodated is defined.

[0034] The introduction section 83 is located to the right of the turbine scroll section 84 in the left-right direction, and opens rearward at the bottom of the right part of the turbine housing 82. The introduction section 83 extends from its open end toward the center of the front part of the turbine housing 82 in the up-down direction, and is connected to the turbine scroll section 84 in this vicinity. The introduction section 83 is provided along the outer periphery of the turbine main body accommodating section 84a, and has a curved shape that expands diagonally downward and forward.

[0035] The outlet section 85 is composed of a first outlet section 86 that forms a lower part thereof and extends rightward from the right side wall 83a of the introduction section 83, and a second outlet section 87 that forms an upper part of the outlet section 85 and extends rightward from the turbine scroll section 84 (a portion of the turbine scroll section 84 that does not overlap with the introduction section 83 in a front view). The first outlet section 86 and the second outlet section 87 define a substantially elliptical space that extends in the vertical direction in a front view.

[0036] The inner space of the upper part of the discharge section 85, which mainly constitutes the second discharge section 87, is connected to the turbine body accommodating section 84a, and exhaust gas that has passed through the turbine body 81 is introduced into the discharge section 85 and then flows into the exhaust passage 60 downstream of the turbine unit 80.

[0037] An opening 88 penetrating the right side wall 83a of the introduction portion 83 from front to back is provided in a portion that forms the inner wall of the first outlet portion 86. The introduction portion 83 and the outlet portion 85 communicate with each other via this opening 88. In this embodiment, the opening 88 has a circular shape.

[0038] The introduction section 83 is located upstream of the turbine body 81, and the discharge section 85 is located downstream of the turbine body 81, and the opening 88 connects the upstream and downstream parts of the exhaust passage 60 with respect to the turbine body 81. When the wastegate valve 20 (described later) is open and the opening 88 is open, part of the exhaust gas introduced into the introduction section 83 is introduced through the opening 88 without passing through the turbine scroll section 84 and the turbine body 81. The exhaust gas is introduced into the outlet portion 85, and then is discharged to the exhaust passage 60 downstream of the turbine unit 80. Thus, in this embodiment, the outlet portion 85 communicates with the opening portion 88 and functions as a bypass passage that bypasses the turbine body 81. That is, in this embodiment, the outlet portion 85 corresponds to the "bypass passage" in the claims.

[0039] (Wastegate valve and drive unit) The engine is provided with a wastegate valve 20 that can open and close the opening 88, and a wastegate valve drive device 30 that drives the wastegate valve 20 to open and close. Hereinafter, the wastegate valve drive device 30 will be referred to as a WG drive device 30.

[0040] Fig. 4 is a partial cross-sectional view taken along line IV-IV in Fig. 3. As shown in Fig. 4, the wastegate valve 20 has a valve main body 21 and a valve shaft 24 that are integrally formed with each other.

[0041] The valve body 21 has a valve head 22 that has a disk shape corresponding to the opening edge 88a of the opening 88 and opens and closes the opening 88, and a head support part 23 that protrudes from the surface of the valve head 22. As shown in FIG. 3, the head support part 23 is provided at a position offset from the center of the valve head 22. The valve shaft 24 has a cylindrical shape and extends from the tip of the head support part 23 in parallel with the surface of the valve head 22. In this embodiment, the valve shaft 24 is covered by a cylindrical cover member 25.

[0042] The wastegate valve 20 opens and closes an opening 88 by being rotated about a central axis X1 of the valve shaft 24 by the WG drive device 30. The wastegate valve 20 is supported by the turbine housing 82 so as to open and close the opening 88 within the outlet portion 85, that is, so as to be displaceable within the outlet portion 85 between a valve-closed position in which the opening 88 is closed from the inside thereof and a valve-open position in which the wastegate valve 20 is separated from the opening 88 to open the opening 88. Specifically, a mounting hole 85a is formed in the turbine housing 82 (outlet portion 85), and the valve shaft 24 is inserted into this mounting hole 85a, thereby supporting the wastegate valve 20 on the turbine housing 82. The wastegate valve 20 is supported by the turbine housing 82 in a state in which the central axis X1 of the valve shaft 24 is substantially perpendicular to the opening direction of the opening 88 (the direction along the chain line X2 in FIG. 4 ) and rotates about the central axis X1 of the valve shaft 24.

[0043] When the wastegate valve 20 is fully closed, all of the exhaust gas discharged from the engine body 1 and introduced into the introduction portion 83 passes through the turbine body 81, driving it to rotate. On the other hand, as described above, when the wastegate valve 20 is open, a portion of the exhaust gas introduced into the introduction portion 83 bypasses the turbine body 81 and is introduced into the outlet portion 85. The flow rate of this exhaust gas bypassing the turbine body 81 is changed by the opening degree of the wastegate valve 20. As a result, the force with which the exhaust gas rotates the turbine body 81 and the boost pressure are changed by the opening degree of the wastegate valve 20. Note that hereinafter, the opening degree when the wastegate valve 20 is fully closed is defined as 0. Furthermore, opening the opening degree of the wastegate valve 20 is referred to as increasing the opening degree, and closing the opening degree of the wastegate valve 20 is referred to as decreasing the opening degree.

[0044] As shown in Fig. 4, in this embodiment, the opening edge 88a of the opening 88, which is the seating portion 88a on which the valve head 22 sits, is tapered, with the diameter on the outlet portion 85 side being larger than that on the introduction portion 83 side. The peripheral surface of the opening 88 side of the valve head 22 is also tapered such that the side closer to the head support portion 23 (the portion located on the outlet portion 85 side when in the fully closed position) has a larger diameter than the far side (the introduction portion 83 side), and the valve head 22 sits on the middle part of the tapered seating portion 88a. The amount of change in the valve opening area in response to a change in the opening of the valve 20 is kept small, making it possible to finely change the flow rate of exhaust gas bypassing the turbine body 81, and therefore the supercharging pressure.

[0045] The WG drive device 30 has an electric actuator 31, a link arm portion 34, a link plate 37, and a WG position sensor SN4. The WG drive device 30 corresponds to the "drive means" in the claims, the electric actuator 31 and the link arm portion 34 correspond to the "rotating member" in the claims, and the link plate 37 corresponds to the "connecting member" in the claims.

[0046] The electric actuator 31 includes a motor 32 and a rod 33 that is slidably driven by the motor 32. The WG position sensor SN4 detects the position of the rod 33. The electric actuator 31 is configured to change the direction of movement of the rod 33 depending on the direction of current supplied to the motor 32. The electric actuator 31 is also configured to change the force applied from the motor 32 to the rod 33 according to the duty ratio, which is the ratio of ON to OFF of the voltage applied to the motor 32. Changing this duty ratio allows the movement speed and position of the rod 33 to be changed. Specifically, the force applied from the motor 32 to the rod 33 increases as the duty ratio increases. In the following description and drawings, the motor 32 of the electric actuator 31 is referred to as the WG motor 32, and the duty ratio of the voltage applied to the WG motor 32 is referred to as the drive duty. In the following description and drawings, the motor 32 of the electric actuator 31 is also referred to as the WG motor 32. The WG motor 32 may be, for example, a servo-type DC motor.

[0047] The electric actuator 31 is supported by the compressor housing 92 so that the rod 33 protrudes rightward from the WG motor 32 and reciprocates left and right.

[0048] The link arm portion 34 has a first link arm portion 35 connected to the tip (right end portion) of the rod 33 and extending rightward therefrom, and a second link arm portion 36 connected to the right end portion of the first link arm portion 35 and extending rightward therefrom. The link arm portion 34 is connected to the rod 33 so as to move left and right in accordance with the movement of the rod 33.

[0049] The link plate 37 is connected to the right end of the second link arm portion 36. Specifically, the link plate 37 has a generally rectangular plate shape extending in the vertical direction, and the right end of the second link arm portion 36 is connected to the lower end of the link plate 37.

[0050] The valve shaft 24 is connected to the upper end of the link plate 37 so as to move integrally therewith. Specifically, a through hole 37a is formed in the upper end of the link plate 37, penetrating from the front to the back of the plate. An attachment portion 24a having a smaller diameter than the remaining portions is provided at one axial end 24a of the valve shaft 24, which is the end opposite the head support portion 23. The valve shaft 24 is connected to the link plate 37 by inserting the attachment portion 24a into the through hole 37a of the link plate 37 and welding the attachment portion 24a to the area surrounding the through hole 37a of the link plate 37. In other words, a weld W is formed around the attachment portion 24a of the valve shaft 24, and this weld W connects the valve shaft 24 and the link plate 37.

[0051] In this embodiment, as described above, the valve head 22 is tapered and is configured to seat midway on the tapered seating portion 88a. Therefore, if there is a discrepancy between the radial dimension of the valve head 22 and the dimension of the seating portion 88a, the valve head 22 will not seat properly on the seating portion 88a even when the wastegate valve 20 is moved to the fully closed position, and exhaust gas may leak from the gap. For this reason, in this embodiment, high precision is required for the dimensions of the valve head 22, and in order to achieve this high precision, the valve shaft 24 and the ring The valve shaft 24 is welded to the valve plate 37 by laser welding. However, since laser welding makes it difficult to achieve high welding accuracy if the weld length is long, it is necessary to shorten the weld length. For this reason, the diameter of the valve shaft 24 is made relatively small.

[0052] The WG drive device 30 moves the rod 33 in the left-right direction to rotate the wastegate valve 20 about the central axis X1 of the valve shaft 24 to open and close the opening 88. Hereinafter, the central axis X1 of the valve shaft 24 will be referred to as the rotation axis X1.

[0053] This will be explained in detail using Figures 5 and 6. Each (a) in Figures 5 and 6 is a bottom view of the turbine unit 80, and each (b) in Figure 6 is a schematic cross-sectional view of each (a) taken along line VV in Figure 3. When the rod 33 moves leftward from the state shown in Figure 5(a) (pulled toward the WG motor 32), the second link arm portion 36 also moves leftward as indicated by arrow Y1, resulting in the state shown in Figure 6(a). When the second link arm portion 36 moves leftward, the link plate 37 rotates around the rotation axis X1 so that its lower end moves leftward as indicated by arrow Y2 in Figure 5(a). In other words, the link plate 37 rotates clockwise as viewed from below. As described above, the link plate 37 and the valve shaft 24 move together. As a result, the valve shaft 24, i.e., the wastegate valve 20, also rotates clockwise around the rotation axis X1 as viewed from below, as indicated by arrow Y3 in Figure 5(b). As a result, the opening of the wastegate valve 20 is reduced. In FIG. 6, the wastegate valve 20 has been rotated to the closed position where it blocks the opening 88, and its opening is set to 0. When opening the wastegate valve 20 or increasing its opening, the various parts are moved in the opposite direction to the above. That is, the rod 33 and the link arm part 34 move to the right, and as a result, the link plate 37 and the valve shaft 24 rotate from below around the rotation axis X1. Look When rotated counterclockwise, the opening of the wastegate valve 20 increases.

[0054] Hereinafter, the direction in which the rod 33, link arm portion 34, link plate 37, and wastegate valve 20 move and the opening degree of the wastegate valve 20 increases is referred to as the valve opening direction. That is, in this embodiment, the rightward direction is referred to as the valve opening direction for the rod 33 and link arm portion 34, and the rightward direction is referred to as the valve opening direction for the link plate 37 and wastegate valve 20 when viewed from below. anti The clockwise direction is referred to as the valve opening direction. The direction of movement of each part that is opposite to the valve opening direction and that closes the wastegate valve 20 (the direction in which the opening of the wastegate valve 20 decreases) is referred to as the valve closing direction.

[0055] (Wastegate valve control) Next, the control of the wastegate valve 20 will be described. FIG. 7 is a block diagram showing the control system of the engine. Each part of the engine, such as the injector 10, the spark plug 11, the throttle valve 52, and the wastegate valve 20, is controlled by an ECU (engine control unit) 100 mounted on the vehicle. As is well known, the ECU 100 is a microprocessor composed of a CPU, ROM, RAM, I / F, etc. The ECU 100 is functionally provided with a boost pressure control unit 101 that adjusts the opening of the wastegate valve 20 to control the boost pressure. This boost pressure control unit 101 corresponds to an example of the "control means" in the claims.

[0056] Information from various sensors is input to the ECU 100. For example, the ECU 100 is electrically connected to a crank angle sensor SN1, an air flow sensor SN2, a boost pressure sensor SN3, and a working wheel position sensor SN4, and receives input signals from these sensors. The vehicle is also provided with an accelerator pedal position sensor SN5 that detects the position of an accelerator pedal (not shown) operated by the driver, and the detection result thereof is also input to the ECU 100.

[0057] FIG. 8 shows a wastegate valve control circuit implemented by the ECU 100 (boost pressure control unit 101). 2 is a flowchart showing the control procedure of 20.

[0058] First, in step S1, the ECU 100 reads various information such as engine speed detected by sensors SN1 to SN5. As described above, the opening of the wastegate valve 20 changes depending on the position of the rod 33. Thus, in step S1, the ECU 100 sequentially calculates the current opening of the wastegate valve 20 from the position of the rod 33 detected by the WG position sensor SN4. Hereinafter, the current opening of the wastegate valve 20 calculated based on the detection value of the WG position sensor SN4 will be referred to as the actual valve opening, where appropriate.

[0059] Next, in step S2, the ECU 100 sets a target boost pressure, which is a target value of the boost pressure. The ECU 100 sets the target boost pressure based on the operating state of the engine. For example, the ECU 100 calculates the engine load from the accelerator pedal opening detected by the accelerator opening sensor SN5 and the engine speed detected by the crank angle sensor SN1, and sets the target boost pressure based on the calculated engine load and engine speed.

[0060] Next, in step S3, the ECU 100 determines whether or not there is a full closure request, which is a request to close (fully close) the wastegate valve 20. For example, the ECU 100 determines that there is a full closure request when the target boost pressure set in step S2 is greater than the current boost pressure detected by the boost pressure sensor SN3 by a predetermined value or more. Note that instead of or in addition to this determination, it may be determined that there is a full closure request when the engine is operating in a preset operating range based on the engine speed and engine load.

[0061] If the determination in step S3 is NO and there is no full closure request, the ECU 100 proceeds to step S6, where it adjusts the drive duty of the WG motor 32 based on the target boost pressure set in step S2. Specifically, the ECU 100 sets a target valve opening, which is a target value for the opening of the wastegate valve 20, based on the target boost pressure. Then, it sets the drive duty of the WG motor 32 so that the actual valve opening becomes the target valve opening. In step S6, the direction of the current supplied to the WG motor 32 is also set in addition to the drive duty. Specifically, if the target boost pressure is higher than the current boost pressure detected by the boost pressure sensor SN3, the direction of the current supplied to the WG motor 32 is set to a direction that moves the rod 33 in the valve closing direction, and if the target boost pressure is higher than the current boost pressure, the direction is set to the opposite direction. In the following, the direction of the current supplied to the WG motor 32 that moves the rod 33 in the valve closing direction is referred to as the valve closing direction, and the opposite direction is referred to as the valve opening direction. After setting the drive duty and the direction of the energizing current in this way, the ECU 100 issues a command to the WG drive device 30 so that these are realized.

[0062] On the other hand, if the determination in step S3 is YES and there is a request for full closure, the ECU 100 determines in step S4 whether the wastegate valve 20 is fully closed.

[0063] If the determination in step S4 is NO and the wastegate valve 20 is open, the ECU 100 first sets the drive duty of the WG motor 32 to a first duty, and then reduces it to a second duty that is smaller than the first duty in step S7. The first duty and the second duty are set in advance and stored in the ECU 100. In step S7, the ECU 100 causes the direction of the current flowing through the WG motor 32 to close the valve.

[0064] The second duty is set to a value greater than the reference duty, which is the minimum drive duty that can fully close the wastegate valve 20 and maintain that state.

[0065] Specifically, as shown in FIG. 6(b), when the wastegate valve 20 is fully closed, a pressure F1 is applied to the valve head 22 of the wastegate valve 20 from the exhaust gas in the introduction portion 83. As a result, a torque T1 in the valve-opening direction (hereinafter referred to as exhaust gas pressing torque T1) is applied to the wastegate valve 20 from the exhaust gas. Therefore, in order to fully close the wastegate valve 20 and maintain it in that state, the WG drive device 30 must apply a torque in the valve-closing direction to the wastegate valve 20 that resists the exhaust gas pressing torque T1. In other words, the WG motor 32 applies a force F2 in the valve-closing direction to the rod 33 and link arm portion 34, which in turn applies a torque T2 in the valve-closing direction to the wastegate valve 20 via the link plate 37, and this torque T2 must be equal to or greater than the exhaust gas pressing torque T1. The reference duty is the minimum drive duty that can make this torque T2 (the torque applied to the wastegate valve 20 in the valve-closing direction) equal to or greater than the exhaust gas pressing torque T1, and is the drive duty value at which torque T2 is equal to the exhaust gas pressing torque T1.

[0066] By setting the second duty in this manner, when the drive duty is set to the first duty, which is larger than the second duty, in step S7 and then set to the second duty, the wastegate valve 20 is fully closed. Furthermore, by switching from the first duty to the second duty, the wastegate valve 20 is fully closed early, preventing the wastegate valve 20 from colliding forcefully with the seating portion 88a. Specifically, by setting the drive duty to the relatively large first duty, the opening degree of the wastegate valve 20 is reduced early to an opening degree close to fully closed. Then, by subsequently setting the drive duty to the relatively small second duty, the movement speed of the wastegate valve 20 until it is fully closed is kept low, preventing the wastegate valve 20 from colliding forcefully with the seating portion 88a.

[0067] The first DUTY and the second DUTY are set in advance and stored in the ECU 100. As described above, the second DUTY is a value smaller than the first DUTY, and the second DUTY is set to a value smaller than 100%. For example, while the reference DUTY is about 10%, the second DUTY is set to 45% and the first DUTY is set to 100%.

[0068] Returning to FIG. 8, if the determination in step S4 is YES and the wastegate valve 20 is already fully closed, the ECU 100 determines in step S5 whether the duration of the wastegate valve 20 being fully closed (the duration during which the wastegate valve 20 is continuously fully closed) is equal to or longer than a determination time. Specifically, the ECU 100 has a timer function, and when it detects that the wastegate valve 20 has changed from an open state to a fully closed state based on a change in the actual valve opening, it turns on the timer, and makes the determination in step S5 based on the value of this timer. The determination time is set in advance and stored in the ECU 100. For example, the determination time is set to 200 ms.

[0069] If the determination in step S5 is NO, meaning that the full-closure duration is less than the determination time, then in step S8, the ECU 100 sets the drive duty to the second duty. As described above, in this embodiment, the drive duty when the wastegate valve 20 is fully closed is also the second duty, and the drive duty is maintained at the second duty from when the wastegate valve 20 is fully closed until the full-closure duration reaches the determination time. Note that in step S5, as in step S7, the energization current of the WG motor 32 is set in the valve closing direction. The second duty is a value greater than the reference duty. As a result, in step S8, the torque T2 applied to the wastegate valve 20 in the valve closing direction is set to a predetermined first torque Tx greater than the exhaust gas pressing torque T1, and the wastegate valve 20 is pressed against the seating portion 88a.

[0070] The above steps S7 and S8 correspond to the "valve closing control" in the claims. That is, in steps S7 and S8, the ECU 100 performs valve closing control by moving the wastegate valve 20 from the valve open position to the valve closed position, and setting the torque T2 in the valve closing direction applied to the moved wastegate valve 20 to a first torque Tx that is greater than the exhaust gas pressing torque T1, thereby pressing the wastegate valve 20 against the opening 88.

[0071] Returning to step S5, if the determination in step S5 is YES and the full-closure duration is equal to or greater than the determination time, the ECU 100 changes the drive duty to a torque reduction duty that is smaller than the second duty in step S9. The torque reduction duty is preset and stored in the ECU 100. As described above, the drive duty is set to the second duty from when the wastegate valve 20 is fully closed until the full-closure duration reaches the determination time. Thus, when the full-closure duration exceeds the determination time, the drive duty is reduced. When the drive duty is reduced, the torque T2 in the valve closing direction applied to the wastegate valve 20 is reduced from the first torque Tx described above to a second torque Ty that is smaller than the first torque Tx. This step S9 corresponds to the "torque reduction control" in the claims. That is, in step S9, the ECU 100 performs torque reduction control to reduce the torque in the valve closing direction applied to the wastegate valve 20 from the first torque Tx when the drive duty is the second duty to the second torque Ty that is smaller than the first torque Tx.

[0072] In this embodiment, the torque reduction duty is set to a value equal to or greater than the reference duty, and the second torque Ty is set to be equal to or greater than the exhaust gas pressing torque T1. As a result, the wastegate valve 20 is maintained fully closed even after step S9 is performed. For example, the reference duty is 10%, the second duty is 45%, and the torque reduction duty is set to 25%.

[0073] FIG. 9 is a time chart showing an example of changes over time in the drive duty, the opening degree of the wastegate valve 20, and the torque applied to the wastegate valve 20 in the valve closing direction when a full closure request is issued while the wastegate valve 20 is open. In the example of FIG. 9, a full closure request is issued at time t1. Accordingly, the drive duty is set to the first duty at time t1. By setting the drive duty to the first duty, a high torque in the valve closing direction is applied to the wastegate valve 20, and the opening degree of the wastegate valve 20 decreases quickly. Thereafter, at time t2, the drive duty is switched to the second duty. As a result, the torque applied to the wastegate valve 20 in the valve closing direction is reduced to the first torque Tx, and the opening degree of the wastegate valve 20 decreases gradually until the wastegate valve 20 is fully closed at time t3. In the example of FIG. 9, the full closure request continues to be issued after time t3, and the drive duty is maintained at the second duty even after time t3, so that the wastegate valve 20 remains fully closed. Furthermore, the torque applied to the wastegate valve 20 in the valve closing direction is also maintained at the first torque Tx. Then, when the determination time has elapsed from time t3, that is, when the full closure duration reaches the determination time, at time t4, the drive duty is reduced to the torque reduction duty, and the torque applied to the wastegate valve 20 in the valve closing direction is reduced to the second torque Ty.

[0074] (effect, etc.) As described above, in this embodiment, even after a full closure request is issued and the wastegate valve 20 is fully closed, the first torque Tx in the valve closing direction that is greater than the exhaust gas pressing torque T1 is applied to the wastegate valve 20, and the wastegate valve 20 is pressed against the opening 88. Therefore, the wastegate valve 20 can be reliably maintained in the fully closed position against the exhaust gas pressing torque T1.

[0075] However, when the wastegate valve 20 is closed (fully closed)This causes an increase in boost pressure and an increase in the temperature of the exhaust gas, which causes thermal expansion of the turbine housing 82. When the turbine housing 82 thermally expands, the wastegate valve 20 is pressed in the valve-opening direction by the periphery of the opening 88, as shown by arrow F10 in FIG. 6(b), and a torque T10 in the valve-opening direction is applied to the wastegate valve 20. Therefore, if a relatively large torque (first torque Tx) in the valve-closing direction is applied to the wastegate valve 20 as described above, a high load is applied to the connection between the wastegate valve 20 and the link plate 37. That is, as shown in FIG. 10, at the welded portion W that connects the link plate 37 and the wastegate valve 20, the first torque Tx in the valve-closing direction is applied to the link plate 37 side, while a torque Tz in the valve-opening direction, which is the sum of the exhaust gas pressing torque T1 and the torque T10 due to thermal expansion, is applied to the wastegate valve 20 side. In other words, a high torque Tz in the opposite direction to the link plate 37 side is applied. This increases the load on the welded portion W, which may be damaged.

[0076] In contrast, in this embodiment, when the duration of the wastegate valve 20 being closed reaches or exceeds the determination time and it is considered that torque T10 in the valve opening direction due to thermal expansion is applied to the wastegate valve 20, the torque in the valve closing direction applied to the wastegate valve 20 is reduced from the above-mentioned first torque Tx to a smaller second torque Ty. This makes it possible to reduce the load on the welded portion W and suppress damage to the welded portion W.

[0077] In particular, in this embodiment, the opening 88 is formed in the turbine housing 82, through which all exhaust gas is introduced when the wastegate valve 20 is fully closed, and the area around the opening 88 is prone to thermal expansion. In other words, the load on the connecting portion W is prone to become excessive. Therefore, by implementing the control to reduce the torque described above, the load on the connecting portion W can be effectively reduced.

[0078] Furthermore, in this embodiment, the diameter of the valve shaft 24 is reduced because the connecting portion W is formed by laser welding, resulting in a relatively small weld area. As a result, the connecting portion W is susceptible to damage. Therefore, by implementing the control to reduce the torque described above, damage to the connecting portion W can be effectively suppressed. In other words, according to this embodiment, the connecting portion W can be formed by laser welding while suppressing damage to the connecting portion W. Furthermore, by forming the connecting portion W by laser welding as described above, it is possible to suppress exhaust gas leakage while achieving precise control of the boost pressure by tapering the valve head 22.

[0079] In this embodiment, even if the valve closing duration is equal to or longer than the judgment time, the drive duty (torque reduction duty) is set to be equal to or higher than the reference duty. Therefore, as described above, the torque in the valve closing direction (second torque Ty) applied to the wastegate valve 20 can be made equal to or higher than the exhaust gas pressing torque T1, and the wastegate valve 20 is closed. (fully closed) can be maintained.

[0080] In this embodiment, the wastegate valve 20 is closed. (fully closed) Then, during the period until the valve closing duration reaches the judgment time, the drive duty is set to a second duty which is smaller than 100%, and the torque in the valve closing direction applied to the wastegate valve 20 is set to a value smaller than the maximum value of the torque in the valve closing direction that can be applied from the WG drive device 30 to the wastegate valve 20. Therefore, even during the above period, the load on the connecting portion W can be kept small.

[0081] (Variation) In the above embodiment, the link plate 37 and the wastegate valve 20 are connected by laser welding, but the connection structure is not limited to this.

[0082] Furthermore, in the above embodiment, the opening 88 is described as being formed in the turbine housing 82, but the opening 88 may be formed in the exhaust passage 60 upstream of the turbine body 81, and is not limited to the above.

[0083] Furthermore, in the above embodiment, the wastegate valve 20 is controlled by the ECU 100. However, the wastegate valve 20 may be controlled by a microcomputer or the like provided separately from the ECU 100, or by a combination of the ECU 100 and another microcomputer or the like.

[0084] In the above embodiment, the turbine unit 80 is a twin-scroll turbine having two scroll portions, but the number of scroll portions is not limited to this. The engine body 1 may not have the spark plug 11, or may have a number of cylinders other than four. [Explanation of symbols]

[0085] 1 Engine body 20 Wastegate valve 21 Valve body 24 valve shaft 30 WG drive device (drive means) 32 WG motor (rotating member) 37 Link plate 60 Exhaust passage 70 Turbocharger 81 Turbine (turbine body) 82 Turbine housing 85 Outlet section (bypass passage) 88 Opening 100 ECU 101 Supercharging pressure control unit (control means)

Claims

1. A control device for a supercharged engine including an engine body, an exhaust passage through which exhaust gas discharged from the engine body flows, a turbocharger including a turbine provided in the exhaust passage, and a bypass passage communicating with an opening formed in the exhaust passage upstream of the turbine and bypassing the turbine, a wastegate valve that opens and closes the opening; a driving means for driving the wastegate valve; a control means for controlling the driving means, an opening edge of the opening portion has a tapered shape in which the diameter on the outlet side closer to the bypass passage is larger than the diameter on the inlet side opposite thereto; The wastegate valve has a valve body that opens and closes the opening, and a valve shaft that is rotatable integrally with the valve body, and is disposed in the bypass passage so as to rotate about an axis that extends in a direction intersecting an opening direction of the opening, and to displace between a closed position in which the valve body is seated on an edge of the opening to fully close the opening and block the opening from inside the bypass passage, and an open position in which the valve body is separated from the opening to open the opening, the valve body is disposed so as to be seated on a middle portion of the opening edge, and when seated on the opening edge, has a tapered shape in which the outlet side has a larger diameter than the inlet side, the drive means includes a connecting member welded to the valve shaft so as to be rotatable integrally with the valve shaft, and a rotating member that rotates the connecting member about the axis, and the rotating member rotates the connecting member to rotate the wastegate valve about the axis, The control means When a request to fully close the wastegate valve is made during operation of the engine, the drive means moves the wastegate valve from the valve open position to the valve closed position, and a valve closing control is performed in which a torque in a valve closing direction applied from the drive means via the connecting member to the wastegate valve after it has moved to the valve closed position is set to a predetermined first torque, thereby pressing the wastegate valve against the opening; a control device for a supercharged engine, wherein, when a valve-close duration, which is a time period during which the wastegate valve remains fully closed, reaches a predetermined judgment time after the valve-close control is performed, a torque reduction control is performed to reduce the torque in the valve-closing direction, which is applied to the wastegate valve from the drive means via the connecting member, from the first torque to a second torque which is smaller than the first torque, thereby reducing the load on a connecting portion between the connecting member and the wastegate valve.

2. 2. The control device for a supercharged engine according to claim 1, a second torque set to a value equal to or greater than a minimum value of torque in a valve closing direction that can maintain the wastegate valve in the valve closed position;

3. The control device for a supercharged engine according to claim 1 or 2, a first torque set to a value smaller than a maximum value of torque in a valve closing direction that can be applied from the drive means to the wastegate valve;

4. The control device for a supercharged engine according to any one of claims 1 to 3, The turbocharger includes a turbine housing that houses the turbine, 2. A control device for a turbocharged engine, wherein the opening is formed in the turbine housing.

5. The control device for a supercharged engine according to any one of claims 1 to 4, the valve shaft extends from the valve body along the axis; 10. A control device for a turbocharged engine, wherein the connecting member is welded to an end of the valve shaft opposite to the valve body.

6. 2. The control device for a supercharged engine according to claim 1, The control means a torque applied to the wastegate valve from the drive means in the valve closing direction to be greater than the first torque when the valve closing control is performed, and then the torque is reduced to the first torque.

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