WO2007060831A1

WO2007060831A1 - Exhaust passage changeover valve

Info

Publication number: WO2007060831A1
Application number: PCT/JP2006/322203
Authority: WO
Inventors: Akihide Okuyama
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2005-11-24
Filing date: 2006-10-31
Publication date: 2007-05-31
Also published as: JP2007146687A

Abstract

Provided is a valving element capable of simplifying a structure of an exhaust system of an internal combustion engine while maintaining a function of a communication valve, a waste gate valve, or the like. An exhaust passage changeover valve 20 is mounted on an exhaust pipe 13 and is provided with at lease one movable member 22, 27, 28 a position of which is adjustable relative to a valve body 21 of the exhaust passage changeover valve 20, and a drive mechanism 23 for adjusting the position of the movable member. The drive mechanism 23 adjusts the movable member 22, 27, 28 among a first position where a plurality of pipe portions E1, E2 of an exhaust manifold 13 are shut off from each other, a second position where the plurality of pipe portions E1, E2 of the exhaust manifold 13 communicate with each other, and a third position where the pipe portions E1, E2 of the exhaust manifold 13 communicate with a bypass passage 15.

Description

DESCRIPTION

EXHAUST PASSAGE CHANGEOVER VALVE Technical Field

[0001] The present invention relates to an exhaust passage changeover valve for controlling a flow of burned gas, in an exhaust pipe for discharging exhaust gas flowing out of cylinders of an internal combustion engine, to the outside. Background Art [0002] An internal combustion engine with a turbocharger described in Patent Document 1 (Japanese Patent Application Laid-Open No. 10-

30446) is constructed as follows: two turbines are coupled on the same axis as an axis of a compressor, and two lines of exhaust passages are separately formed in order to prevent mutual interference between exhaust pressures to the respective turbines. There are provided a communication path for establishing mutual communication between these exhaust passages, a communication valve for opening and closing this communication passage, and a device for controlling the opening and closing states according to engine operation states. [0003] Another internal combustion engine with a turbocharger described in Patent Document 2 (Japanese Patent Publication No. 7-

26551) is constructed as follows: exhaust passages extending from respective cylinders are coupled to make two exhaust passages, and these two exhaust passages are further coupled immediately before a turbine to make one exhaust passage. A communication valve for establishing mutual communication between the two exhaust passages is provided in the part where there are the two exhaust passages. There is also a bypass passage extending from one of the two exhaust passages to the exhaust passage downstream of the turbine, and this bypass passage is provided with a waste gate valve for opening and closing the bypass passage. [0004] When the exhaust passages are provided with the communication valve and the waste gate valve as described above, the exhaust system needs to be equipped with a plurality of valving elements and becomes expensive. Since the space for mounting of the engine is limited, the aforementioned complicated structure with the plurality of valving elements is not preferred.

[0005] An object of the present invention is therefore to provide a valving element capable of simplifying the structure of the exhaust system of the internal combustion engine while maintaining the function of the aforementioned communication valve, waste gate valve, or the like.

Disclosure of the Invention

[0006] In order to achieve the above object, the present invention provides an exhaust passage changeover valve mounted on an exhaust pipe extending from a plurality of cylinders of an internal combustion engine, the exhaust pipe being comprised of an upstream exhaust pipe extending before at least one turbine of a turbocharger and consisting of a plurality of pipe portions, and a downstream exhaust pipe extending after the turbine and consisting of a single pipe portion, the exhaust passage changeover valve comprising: at least one movable member a position of which is adjustable relative to a valve body of the exhaust passage changeover valve; and a drive mechanism for adjusting the position of the movable member, wherein the drive mechanism adjusts the movable member among a first position where the plurality of pipe portions of the upstream exhaust pipe are shut off from each other, a second position where the plurality of pipe portions of the upstream exhaust pipe communicate with each other, and a third position where the pipe portions of the upstream exhaust pipe communicate with the pipe portion of the downstream exhaust pipe.

[0007] This configuration enables the following operation: when the movable member of the exhaust passage changeover valve is adjusted to the first position by the drive mechanism, the plurality of pipe portions of the upstream exhaust pipe are shut off from each other and thus strong exhaust flows are supplied to the turbine of the turbocharger to enhance rotation of the turbine. When the movable member of the exhaust passage changeover valve is adjusted to the second position by the drive mechanism, the plurality of pipe portions of the upstream exhaust pipe communicate with each other, and thus exhaust emissions in the plurality of pipe portions are made actively to interfere with each other to cause internal EGR (Exhaust Gas Recirculation), whereby nitrogen oxides NOx in the exhaust emissions can be reduced. When the movable member of the exhaust passage changeover valve is adjusted to the third position by the drive mechanism, the pipe portions of the upstream exhaust pipe communicate with the pipe portion of the downstream exhaust pipe, and thus the exhaust emissions flowing in the pipe portions of the upstream exhaust pipe are made to escape to the downstream exhaust pipe, so as to weaken the exhaust flows supplied to the turbine of the turbocharger and thus restrain rotation of the turbine. Since the exhaust passage changeover valve with the above function is constructed as a single valving element, the exhaust passage changeover valve is able to reduce the mount space of the valving element and reduce the cost of the valving element. [0008] In the above-described exhaust passage changeover valve, preferably, the movable member includes a first seal member for shutting off communication between the plurality of pipe portions of the upstream exhaust pipe, and a second seal member for shutting off communication between the pipe portions of the upstream exhaust pipe and the pipe portion of the downstream exhaust pipe. Since in this configuration the movable member includes the first seal member and the second seal member, it increases degrees of freedom for design of the exhaust passage changeover valve and makes the mount space of the exhaust passage changeover valve smaller. [0009] In the aforementioned exhaust passage changeover valve, preferably, the first seal member is arranged so that a position thereof is adjusted by the drive mechanism, and the second seal member is arranged so that a position thereof is adjusted by contact with the first seal member. In this configuration, the second seal member comes into contact with the first seal member whereby the position thereof is adjusted with reception of a force. Therefore, even in the case where the movable member is comprised of a plurality of members (first seal member and second seal member), the single drive mechanism is able to adjust the positions of those members, whereby the cost of the exhaust passage changeover valve can be kept low.

[0010] In the aforementioned exhaust passage changeover valve, preferably, the position of the movable member is adjusted by the drive mechanism whereby the movable member moves from the first position, via the second position to the third position. This configuration is able to structurally prevent occurrence of a situation in which the plurality of pipe portions of the upstream exhaust pipe do not communicate with each other, at the time when the movable member is adjusted to the third position to establish communication between the pipe portions of the upstream exhaust pipe and the pipe portion of the downstream exhaust pipe. In this configuration, when the movable member is adjusted to the third position to establish communication between the pipe portions of the upstream exhaust pipe and the pipe portion of the downstream exhaust pipe, the plurality of pipe portions of the upstream exhaust pipe are always in a mutually communicating state, and pressures in the plurality of pipe portions of the upstream exhaust pipe are equally reduced, so as to prevent occurrence of trouble such as deterioration of fuel consumption or increase of friction of pistons.

[0011] In the aforementioned exhaust passage changeover valve, preferably, the movable member is arranged to come into contact with a valve seat so as to be able to change over the communication or shutoff between the pipe portions, and the drive mechanism reduces a moving speed of the movable member in a transition from a noncontact state in which the movable member is away from the valve seat, into a contact state in which the movable member is in contact with the valve seat. In this configuration, when the movable member transitions from the noncontact state in which the movable member is away from the valve seat, into the contact state in which the movable member is in contact with the valve seat, the moving speed of the movable member is reduced by adjustment of the drive mechanism, so as to alleviate impact upon a collision between the movable member and the valve seat. Brief Description of the Drawings

[0012] Fig. 1 is a configuration diagram showing a schematic configuration of an internal combustion engine.

Fig. 2 is a first sectional view showing an internal structure of an exhaust passage changeover valve. Fig. 3 is a front view showing apertures formed in an exhaust manifold.

Fig. 4 is a second sectional view showing the internal structure of the exhaust passage changeover valve.

Fig. 5 is a third sectional view showing the internal structure of the exhaust passage changeover valve.

Fig. 6 is a graph showing set values of boost pressure against engine rotation speed.

Fig. 7 is a graph showing set values of lift amount against engine load. Fig. 8 is a flowchart showing a process for controlling a lift amount of a first seal member.

Fig. 9 is a timing chart showing various characteristics during an accelerating run.

Fig. 10 is a flowchart showing a process of relieving collision between first and second seal members. Best Modes for Carrying out the Invention

[0013] A preferred embodiment of the exhaust passage changeover valve according to the present invention will be described below with reference to the drawings. Fig. 1 shows an engine (internal combustion engine) 1 on which the exhaust passage changeover valve of the present embodiment is mounted. The external air is taken as intake air through an air filter 3 into an intake passage 2 of the engine 1. The engine 1 is provided with a turbocharger 4. The turbocharger 4 is an ordinary turbocharger 4 in which a compressor wheel 4a is arranged on the intake passage 2 and in which a turbine wheel 4b is arranged on an exhaust passage 5, so as to implement supercharging through the use of exhaust flows.

[0014] An air-cooling type intercooler 6, which decreases temperature of intake air raised with increase in pressure due to supercharging by the turbocharger 4, is located downstream of the turbocharger 4 on the intake passage 2. The intercooler 6 lowers the temperature of intake air to increase charging efficiency. An intake pressure sensor 7 for detecting the pressure of intake air is provided downstream of the intercooler 6. A throttle valve 8 for adjusting an intake air mass is located further downstream of the intercooler 6. A travel (opening level) of the throttle valve 8 is determined according to a driver's operation amount on an accelerator pedal. In association with the throttle valve 8, a throttle position sensor 9 for detecting the travel thereof is also provided. The intake air passing through the throttle valve 8 is mixed with fuel injected from an injector (not shown) to make an air-fuel mixture. [0015] The intake passage 2 is branched at a position immediately anterior to an engine body 10, into four pipe portions Bl, B2, B3, B4 to form an intake manifold 11. Each of the pipe portions B1-B4 of the intake manifold 11 is made to communicate with one of first to fourth cylinders #1, #2, #3, and #4 inside the engine body 10. An intake valve (not shown) is arranged to open and close between each pipe portion B1-B4 of intake manifold 11 and an interior of each cylinder #1- #4. The air-fuel mixture guided through the intake manifold 11 into the interior of each cylinder #l-#4 is compressed by a piston and thereafter ignited to burn. Although not shown, reciprocating motions of the pistons with increase of pressure in the cylinders #l-#4 during combustion are taken out via a crank shaft and connecting rods to an output shaft. A crank position sensor 12 for detecting a rotational position of the crank shaft is mounted near the crank shaft of the engine 1. The crank position sensor 12 can also detect the engine rotation speed Ne from a positional change of the crank position. [0016] An exhaust manifold (upstream exhaust pipe) 13 is mounted on the exhaust side of the engine body 10. The exhaust manifold 13 has four pipe portions Dl, D2, D3, D4, and each of the pipe portions D1-D4 is made to communicate with one of the first to fourth cylinders #l-#4.

An exhaust valve (not shown) is arranged to open and close between the interior of each cylinder #l-#4 and the exhaust manifold 13. When the exhaust valve is open, the piston pushes out burned gas in the cylinder #l-#4 into the exhaust manifold 13. In the exhaust manifold 13, the pipe portion Dl in communication with the first cylinder #1 and the pipe portion D4 in communication with the fourth cylinder #4 are combined together and the pipe portion D2 in communication with the second cylinder #2 and the pipe portion D3 in communication with the third cylinder #3 are combined together. As the four pipe portions Dl- D4 are combined together in this manner, two lines of pipe portions El, E2 are constructed. Then the combined lines of pipe portions El, E2 are connected to the turbocharger 4 so as to introduce their respective exhaust flows separately to the turbine wheel 4b. When the pistons of the first cylinder #1 and the fourth cylinder #4 are located at the top dead center, the pistons of the second cylinder #2 and third cylinder #3 are located at the bottom dead center.

[0017] An exhaust passage changeover valve 20 is provided midway of the two lines of pipe portions El, E2 of the exhaust manifold 13. The exhaust passage changeover valve 20 has a function of changing over communication or a shutoff between the two lines of pipe portions El, E2. The exhaust passage changeover valve 20 is connected to a bypass passage 15 communicating with an exhaust pipe (downstream exhaust pipe) 14 located downstream of the turbine wheel 4b, and has a function of changing over communication or a shutoff between the two lines of pipe portions and the downstream exhaust pipe 14. The structure and operation of the exhaust passage changeover valve 20 will be described later in detail.

[0018] An Electrical Control Unit (ECU) 16 is a control unit for controlling the operation of engine 1, and is used, particularly, for control of the exhaust passage changeover valve 20 in the present embodiment. The ECU 16 is composed of a CPU, a RAM, a ROM, etc. and executes control programs stored in the ROM. For control of the exhaust passage changeover valve 20, the ECU 16 takes in detected values by the intake pressure sensor 7, throttle position sensor 9, the crank position sensor 12, etc., calculates an electric current command value (or voltage command value) for controlling the exhaust passage changeover valve 20 to a desired state, and supplies an electric current

(or voltage) according to this electric current command value (or voltage command value) to the exhaust passage changeover valve 20. The ECU 16 uses the detected value by the throttle position sensor 9 as "engine load," and the detected value by the crank position sensor 12 as "engine rotation speed." However, the engine load and engine rotation speed may be detected by other methods.

[0019] Fig. 2 shows an internal structure of the exhaust passage changeover valve 20. The exhaust passage changeover valve 20, as described previously, is mounted on the two lines of pipe portions El, E2 after the combined part of the exhaust manifold 13, and is mounted, particularly, at a position where the two lines of pipe portions El, E2 are in contact with each other. At the position where the exhaust passage changeover valve 20 is mounted, the two lines of pipe portions El, E2 are of flat plate shape, and a planar mounting surface 21a of the exhaust passage changeover valve 20 is fixed in close contact to this part 17 of flat plate shape.

[0020] A base 21 being a main body of the exhaust passage changeover valve 20 is a member of approximately cylindrical shape and stands upright from the flat-plate-shape part 17 of the exhaust manifold 13, and a space for placement of components constituting the exhaust passage changeover valve 20 is formed inside the base 21. A rod 22 movable perpendicularly to the flat-plate-shape part 17 of the exhaust manifold 13 is arranged in the center of the interior space of the base 21, and this rod 22 moves when a drive force is applied thereto by an actuator (drive mechanism) 23 located at the distal end of the base 21. The position of the rod 22 is detected by a rod stroke sensor 32.

[0021] A support portion 21b extending from the distal end side toward the exhaust manifold 13 inside the base 21 is formed in the base 21. The support portion 21b is of cylindrical shape arranged concentrically with the rod 22, and two bushes 25, 26 are fixed at the tip thereof. Each of the two bushes 25, 26 is of ring shape and is made of a sliding material such as a sintered alloy. One bush 25 is fixed to the interior surface of the support portion 21b, and the other bush 26 is fixed to the exterior surface of the support portion 21b. The intermediate part of the rod 22 is supported with a small clearance by the bush 25 fixed to the interior surface of the support portion 21b, and the distal end of the rod 22 is supported by the actuator 23. The bush 26 fixed to the exterior surface of the support portion 21b is used for supporting a second seal member 27 described later. [0022] The actuator 23 for giving a drive force to the rod 22 is arranged to incorporate a solenoid and an electric current is supplied to this solenoid to give the drive force to the rod 22. This principle is much the same as that of an ordinary solenoid valve. However, for giving the drive force to the rod 22, the actuator 23 may adopt another method. For example, the actuator 23 may be arranged to incorporate a motor and to give the drive force to the rod 22 by use of a mechanical system such as a screw feed system. The actuator 23 may also be constructed in combination with a mechanical element such as a diaphragm and thereby give the drive force to the rod 22.

[0023] Two apertures 18A, 18B penetrating to the interiors of the two lines of corresponding pipe portions El, E2 are formed in the flat-plate- shape part 17 of the exhaust manifold 13. When the two apertures

18A, 18B are viewed in a state in which the exhaust passage changeover valve 20 is removed from the exhaust manifold 13, they are seen as shown in Fig. 3. The two lines of pipe portions El, E2 extend in parallel and the two apertures 18 A, 18B are formed near the part where the two lines of pipe portions El, E2 are in contact with each other.

One aperture 18A is formed in the pipe portion El in which the exhaust emission discharged from the two cylinders #1, #4 flows, while the other aperture 18B is formed in the pipe portion E2 in which the exhaust emission discharged from the two cylinders #2, #3 flows. [0024] Returning to Fig. 2, a first seal member 28 of disk shape is fixed to the tip of the rod 22. The disk surface of the first seal member 28 is so sized that it is greater than the two apertures 18A, 18B formed in the exhaust manifold 13 and that the first seal member 28 covers the two apertures 18 A, 18B when the first seal member 28 is pushed against the flat-plate-shape part 17 of the exhaust manifold 13 (cf. Fig. 3). In a state in which the first seal member 28 covers the two apertures 18A, 18B in this manner, the two lines of pipe portions El, E2 are shut off from each other. On the other hand, when the rod 22 moves away from the exhaust manifold 13 to keep the first seal member 28 apart from the two apertures 18A, 18B, the two lines of pipe portions El, E2 become communicating with each other through the interior space of the exhaust passage changeover valve 20.

[0025] In the rod 22, a portion 22a apart from the exhaust manifold 13 has a diameter smaller than that of a portion 22b closer to the exhaust manifold 13, and a press member 29 of disk shape with a through hole in the center is put on the smaller-diameter portion 22a and down to the position of a step between the two portions 22a, 22b. A coil spring 30 is installed in a compressed state between the press member 29 and the actuator 23, and thus the coil spring 30 exerts a pressing force toward the exhaust manifold 13 on the rod 22. The rod 22 is subject to the pressing force by the coil spring 30, the drive force by the aforementioned actuator 23, etc., whereby it is adjusted at a position where those forces are balanced. In a state in which the rod 22 is subject to no drive force from the actuator 23, the rod 22 is pushed toward the exhaust manifold 13 by the pressing force of the coil spring 30, whereby the first seal member 28 shuts off the two lines of pipe portions El, E2 (cf. Fig. 2). As described previously, the flat-plate- shape part 17 of the exhaust manifold 13 against which the first seal member 28 is pushed, is used as a valve seat of the exhaust passage changeover valve 20. [0026] When the rod 22 is subject to a drive force from the actuator 23, the first seal member 28 moves away from the exhaust manifold 13 whereupon the two lines of pipe portions El, E2 come to communicate with each other. When the rod 22 is then subject to a stronger drive force from the actuator 23, the first seal member 28 comes into contact with the second seal member 27 located in the interior space of the exhaust passage changeover valve 20, as shown in Fig. 4. Before the first seal member 28 is brought into contact* with the second seal member 27, each of the two lines of pipe portions El, E2 of the exhaust manifold 13 is kept from communicating with the bypass passage 15. The second seal member 27 has a cylindrical portion 27a arranged concentrically with the rod 22, and a flange portion 27b of ring shape formed at one end of the cylindrical portion 27a, and a cross section of the cylindrical portion 27a and flange portion 27b is L-shape. A groove is formed between an external portion 21c and the support portion 21b of the base 21, and a coil spring 31 is placed between a bottom surface of the groove and the second seal member 27. The coil spring 31 is placed in a compressed state and pushes the second seal member against a valve seat 2 Id formed inside the base 21. [0027] When the rod 22 is subject to a much stronger drive force from the actuator 23, the first seal member 28 pushes the second seal member 27 to move the second seal member 27 to the distal end side, as shown in Fig. 5. As the second seal member 27 is pushed, the second seal member 27 moves away from the valve seat 21 d whereupon the two apertures 18A, 18B of the exhaust manifold 13 come to communicate with the bypass passage 15 connected to the exhaust passage changeover valve 20. The second seal member 27 is supported by the bush 26 fixed to the exterior surface of the support portion 21b and, while the second seal member 27 is pushed by the first seal member 28, the second seal member 27 slides on the bush 26 to move perpendicularly to the flat-plate-shape part 17 of the exhaust manifold 13.

[0028] A water jacket 21e internally having a passage for circulation of cooling water is formed on the distal end side of the base 21. By circulating cooling water in the water jacket 2 Ie, the actuator 23 is prevented from increasing its temperature excessively, whereby the operation of actuator 23 can be assured. [0029] In the above-described embodiment, the members arranged movable relative to the valve body 21, e.g., the rod 22, first seal member 28, and second seal member 27, correspond to the movable member in the scope of claims. When the first seal member 28 and second seal member 27 are positioned so as to shut off the two lines of pipe portions El, E2 of the exhaust manifold 13 from each other as shown in Fig. 2, the position of the first seal member 28 and second seal member 27 is referred to as a first position. When the first seal member 28 and second seal member 27 are positioned so as to allow the two lines of pipe portions El, E2 of the exhaust manifold 13 to communicate with each other as shown in Fig. 4, the position of the first seal member 28 and second seal member 27 is referred to as a second position. When the first seal member 28 and second seal member 27 are positioned so as to allow the two lines of pipe portions El, E2 of the exhaust manifold 13 to communicate with the downstream pipe portion as shown in Fig. 5, the position of the first seal member 28 and second seal member 27 is referred to as a third position.

[0030] When the movable member 22, 27, 28 of the exhaust passage changeover valve 20 is controlled to the first position by the actuator 23, the two lines of pipe portions El, E2 of the exhaust manifold 13 are shut off from each other and thus strong exhaust flows are supplied to the turbine wheel 4b of the turbocharger 4, so as to enhance rotation of the turbine wheel 4b. When the movable member 22, 27, 28 of the exhaust passage changeover valve 20 is controlled to the second position by the actuator 23, the two lines of pipe portions El, E2 of the exhaust manifold 13 come to communicate with each other, and thus the exhaust emissions through the two lines of pipe portions El, E2 are made actively to interfere with each other to cause internal EGR (Exhaust Gas Recirculation), whereby nitrogen oxides NOx in the exhaust emissions can be reduced. When the movable member 22, 27, 28 of the exhaust passage changeover valve 20 is controlled to the third position by the actuator 23, the two lines of pipe portions El, E2 of the exhaust manifold 13 come to communicate with the downstream exhaust pipe 14, and thus the exhaust emissions flowing in the exhaust manifold 13 are made to escape to the downstream exhaust pipe 14, so as to weaken the exhaust flows supplied to the turbine wheel 4b of the turbocharger 4 and restrain rotation of the turbine wheel 4b. The above-described exhaust passage changeover valve 20 is able to make the mount space of the valving element smaller and to reduce the cost of the valving element because the exhaust passage changeover valve 20 having the above function is constructed as a single valving element. [0031] In the above-described embodiment, the movable member 22,

27, 28 is subjected to the position adjustment by the actuator 23, whereby it moves from the first position, via the second position to the third position. This configuration is able to structurally prevent occurrence of a situation in which when the movable member 22, 27, 28 is adjusted to the third position to allow the two lines of pipe portions

El, E2 of the exhaust manifold 13 to communicate with the downstream exhaust pipe 14, the two lines of pipe portions El, E2 of the exhaust manifold 13 fail to communicate with each other. If the two lines of pipe portions El, E2 of the exhaust manifold 13 should be in a mutually non-communicating state during control of boost pressure through communication between the two lines of pipe portions El, E2 of the exhaust manifold 13 and the downstream exhaust pipe 14, the pressure in the exhaust manifold 13 could be increased in either one of the pipe portions El, E2 in a non-communicating state with the downstream exhaust pipe 14 to increase a pumping loss, so as to degrade fuel consumption of engine 1. If the pressure in the exhaust manifold 13 should increase in either of the pipe portions El, E2 in the non- communicating state with the downstream exhaust pipe 14, sliding friction would increase between the cylinders #l-#4 and pistons. In contrast to it, in the case where the position of the movable member 22, 27, 28 is adjusted in the order of the first position, the second position, and the third position, as described above, the two lines of pipe portions El, E2 of the exhaust manifold 13 always communicate with each other at the time of establishment of communication between the pipe portions El, E2 of the exhaust manifold 13 and the downstream exhaust pipe 14, and thus the pressures in the two lines of pipe portions El, E2 of the exhaust manifold 13 are equally lowered. This can prevent occurrence of trouble such as deterioration of fuel consumption or increase of friction. [0032] In the aforementioned embodiment the first seal member 28 and the second seal member 27 are constructed as separate members, and this configuration increases degrees of freedom for design of the exhaust passage changeover valve 20 and makes the mount space of the exhaust passage changeover valve 20 smaller. However, another embodiment may be arranged as follows: the exhaust passage changeover valve 20 is configured so that a single seal member changes over the communication or shutoff between the two lines of pipe portions El, E2 of the exhaust manifold 13 and the bypass passage 15. For example, it can be realized as follows: the second seal member 27 is excluded from the exhaust passage changeover valve 20 shown in Fig. 2, and the diameter of the first seal member 28 is increased so as to minimize the clearance between a peripheral surface 28a of the first seal member 28 and an inner peripheral surface 2 If of the base 21. When the exhaust passage changeover valve 20 is constructed in this configuration, the communication or shutoff between the two lines of pipe portions El, E2 of the exhaust manifold 13 and the bypass passage 15 can be changed over by simply adjusting the position of the first seal member 28.

[0033] The operation and setting of the exhaust passage changeover valve 20 will be described below with reference to Figs. 6 and 7. Fig. 6 shows set values of boost pressure as a control target for boost pressure against engine rotation speed. In a low rpm region of engine

1, the boost pressure set value increases according to increase in the engine rotation speed, to increase the engine output. On the other hand, in a high rpm region where the engine rotation speed exceeds a predetermined rpm threshold THl, the boost pressure set value gently decreases according to increase in the engine rotation speed. When the boost pressure is set in this manner, the boost pressure is prevented from increasing excessively in the high rpm region of the engine 1. [0034] In order to implement the setting of boost pressure as described above, the first seal member 28 is controlled by setting of lift amounts as shown in Fig. 7. Here a lift amount refers to a distance L between the flat-plate-shape part 17 and the first seal member 28 in the direction perpendicular to the flat-plate-shape part 17 of the exhaust manifold 13. Symbol Sl indicates a setting of lift amounts for the range where the engine rotation speed is smaller than the rpm threshold THl, and symbol S2 indicates a setting of lift amounts for the range where the engine rotation speed is greater than the rpm threshold THl .

[0035] When the engine rotation speed is smaller than the rpm threshold THl and when the engine load is smaller than a load threshold TH2, the lift amount set value of the first seal member 28 is set to Ll ; on the other hand, when the engine load is larger than the load threshold TH2, the lift amount set value of the first seal member 28 is set to 0.

When the engine rotation speed is larger than the rpm threshold THl and when the engine load is smaller than the load threshold TH2, the lift amount set value of the first seal member 28 is set to Ll ; on the other hand, when the engine load is larger than the load threshold TH2, the upper limit of the lift amount set value of the first seal member 28 is set to L2.

[0036] Here the distance Ll is a distance L between the flat-plate-shape part 17 and the first seal member 28 in a state in which the opening level of the passage to establish the communication between the two lines of pipe portions El, E2 is maximum, as shown in Fig. 4. On the other hand, the distance L2 is a distance L between the flat-plate-shape part 17 and the first seal member 28 in a state in which the opening level of the passage to establish the communication between the two lines of pipe portions El , E2 and the bypass passage 15 is maximum, as shown in Fig. 5. When the upper limit of the lift amount set value of the first seal member 28 is set to L2, the first seal member 28 is controlled between Ll and L2.

[0037] The ECU 16 controls the lift amount of the first seal member 28 in accordance with the aforementioned lift amount settings. The processing by the ECU 16 will be described with reference to the flowchart of Fig. 8. The processing shown in Fig. 8 is repeatedly carried out during the operation of engine 1 by the ECU 16. First, the ECU 16 takes in the detected value by the crank position sensor 12, the detected value by the throttle position sensor 9, and the detected value by the rod stroke sensor 32 (S801). Here the detected value by the crank position sensor 12 is used as the engine rotation speed and the detected value by the throttle position sensor 9 as the engine load. Next, the ECU 16 determines the lift amount set value corresponding to the combination of the engine rotation speed and the engine load thus detected, with reference to the lift amount settings of Fig. 7 (S802). [0038] Then the ECU 16 controls the actuator 23 so that the lift amount of the first seal member 28 becomes the determined lift amount set value (S803). Specifically, when the lift amount set value is determined to be 0, the ECU 16 supplies no electric current to the actuator 23 so as to give no drive force to the rod 22. When the lift amount set value is determined to be Ll, the ECU 16 supplies an electric current to the actuator 23 to give a drive force to the rod 22 and control it so that the lift amount of the first seal member 28 becomes Ll. When the lift amount set value is determined to be L2, the ECU 16 supplies an electric current to the actuator 23 to control the lift amount of the first seal member 28 between Ll and L2 so that the detected value by the intake pressure sensor 7 becomes a permitted maximum boost pressure.

[0039] Next, let us describe a situation in which the ECU 16 performs the aforementioned control during an accelerating run of a vehicle, with reference to Fig. 9. Fig. 9 shows temporal changes of various characteristics of the engine 1 and exhaust passage changeover valve 20 during the accelerating run of the vehicle.

[0040] While the vehicle is not accelerated yet (before a time tθ), a driver's step-on amount on the accelerator pedal is small; therefore, the throttle opening level is small and the engine load is smaller than the load threshold TH2. Since the engine load is small, the ECU 16 selects Ll as the lift amount set value to control the lift amount of the first seal member 28 to Ll . Since this establishes communication between the two lines of pipe portions of the exhaust manifold 13, the exhaust emissions in the two lines of pipe portions are made actively to interfere with each other to cause internal EGR, whereby nitrogen oxides NOx in the exhaust can be reduced.

[0041] During an accelerating period of the vehicle (times tθ-tl), the driver's step-on amount on the accelerator pedal is large; therefore, the throttle opening level is large and the engine load is larger than the load threshold TH2. On the other hand, the engine rotation speed is not raised to the rpm threshold THl . Since the engine rotation speed is smaller than the rpm threshold THl and the engine load is larger than the load threshold TH2, the ECU 16 selects 0 as the lift amount set value to control the lift amount of the first seal member 28 to 0. This results in shutting off the two lines of pipe portions El, E2 of the exhaust manifold 13, whereby strong exhaust flows are supplied to the turbine wheel 4b to enhance rotation of the turbine wheel 4b. [0042] When the speed of the vehicle increases so that the engine rotation speed reaches the threshold THl, the boost pressure becomes the upper limit Pmax and adjustment of boost pressure is started. During this period (times tl-t2), the driver's step-on amount on the accelerator pedal is large; therefore, the throttle opening level is large and the engine load is larger than the load threshold TH2. The engine rotation speed increases over the rpm threshold THl. Since the engine rotation speed is larger than the rpm threshold THl and the engine load is larger than the load threshold TH2, the ECU 16 selects L2 as the upper limit of the lift amount set value and controls the lift amount of the first seal member 28 between Ll and L2 so that the detected value by the intake pressure sensor 7 is maintained at the upper limit Pmax of boost pressure. [0043] After completion of acceleration of the vehicle (after a time t2), the driver's step-on amount on the accelerator pedal is small; therefore, the throttle opening level is small and the engine load is smaller than the load threshold TH2. Since the engine load is small, the ECU 16 selects Ll as the lift amount set value to control the lift amount of the first seal member 28 to Ll . This results in establishing communication between the two lines of pipe portions El, E2 of the exhaust manifold 13 and thus the exhaust emissions in the two lines of pipe portions El, E2 are made actively to interfere with each other to cause internal EGR, whereby nitrogen oxides NOx in the exhaust can be reduced. [0044] Immediately after the time TO, the lift amount of the first seal member 28 varies rapidly from Ll to 0, and thus the first seal member

28 comes to collide hard with the valve seat 17. Immediately after the time T2, similarly, the lift amount of the first seal member 28 also varies rapidly from L2 to Ll, and thus the second seal member 27 comes to collide hard with the valve seat 2 Id. Such hard collisions of the first and second seal members 27, 28 with the valve seats 17, 21 d will result in early abrasion of the first, second seal members 27, 28 and valve seats 17, 21d and degradation of durability of the exhaust passage changeover valve 20. [0045] It is thus preferable to reduce the speed of the first, second seal member 27, 28 during the periods in which the first, second seal member 27, 28 comes to the vicinity of the valve seat 17, 2 Id, as indicated by dotted lines Ul, U2 in the timing chart of Fig. 9. By reducing the speed of the first, second seal member 27, 28, it is feasible to alleviate the impact which the first, second seal member 27, 28 exerts on the valve seat 17, 2 Id. The alleviation of impact reduces the strength required for the first, second seal members 27, 28 and valve seats 17, 2 Id, so that the exhaust passage changeover valve 20 can be made lighter, for example, based on reduction in the thicknesses of the first, second seal members 27, 28 and valve seats 17, 2 Id. [0046] The processing executed by the ECU 16 in order to reduce the speed of the first, second seal members 27, 28 will be described with reference to the flowchart of Fig. 10. The processing shown in Fig. 10 is repeatedly executed during control of the exhaust passage changeover valve 20 by the ECU 16.

[0047] First, the ECU 16 takes in the detected value by the rod stroke sensor 32 to acquire the lift amount L of the first seal member 28

(SlOl). Next, the ECU 16 calculates a time derivative dL/dt of the lift amount L of the first seal member 28 and determines whether this time derivative is smaller than 0 (S 102). When the time derivative dL/dt is smaller than 0, the ECU 16 moves to step 103 to determine whether the present status is a situation in which the first seal member 28 can collide with the valve seat 17, or a situation in which the second seal member 27 can collide with the valve seat 2 Id. On the other hand, when the time derivative dL/dt is larger than 0, the ECU 16 terminates the processing because the present status is not a situation in which the first or second seal member 27, 28 collides with the valve seat 17, 2 Id.

[0048] Next, the ECU 16 determines whether the lift amount L of the first seal member 28 is smaller than Ll (S103). When the lift amount L is smaller than Ll, the present status is a situation in which the first seal member 28 can collide with the valve seat 17, and thus the ECU moves to step 104 in order to avoid the collision of the first seal member

28. On the other hand, when the lift amount is larger than Ll, the present status is a situation in which the second seal member 27 can collide with the valve seat 2 I d, and thus the ECU moves to step 105 in order to avoid the collision of the second seal member 27. [0049] In the step 104, the ECU 16 determines whether the lift amount

L of the first seal member 28 is smaller than Ln. When the lift amount L is smaller than Ln, the first seal member 28 is located at a position where it is close to the valve seat 17, and a collision is close between the first seal member 28 and the valve seat 17; therefore, the ECU controls the lift amount of the first seal member 28 so that dL/dt = LT (constant) (S 106). Here the constant LT is a set value of speed of the first seal member 28 prepared for alleviating the collision between the first seal member 28 and the valve seat 17. The control to achieve dL/dt = LT makes the speed of the first seal member 28 smaller and the impact on the first seal member 28 and the valve seat 17 smaller than in the case where the lift amount of the first seal member 28 varies rapidly from Ll to 0. On the other hand, when the lift amount L is larger than Ln, the first seal member 28 is located at a position away from the valve seat 17, and the ECU 16 terminates the processing. [0050] In the step 105, the ECU 16 determines whether the lift amount L of the first seal member 28 is smaller than (Ll + Ln). When the lift amount L is smaller than (Ll + Ln), the second seal member 27 is located at a position close to the valve seat 2 Id, and a collision is close between the second seal member 27 and the valve seat 2 Id; therefore, the ECU controls the lift amount of the first seal member 28 so that dL/dt = LT (constant) (S 106). The control to achieve dL/dt = LT makes the speed of the second seal member 27 smaller and the impact on the second seal member 27 and the valve seat 21 d smaller than in the case where the lift amount of the first seal member 28 varies rapidly from L2 to Ll. On the other hand, when the lift amount L is larger than (Ll + Ln), the second seal member 27 is located at a position away from the valve seat 2 Id and the ECU 16 terminates the processing.

Claims

1. An exhaust passage changeover valve mounted on an exhaust pipe extending from a plurality of cylinders of an internal combustion engine, the exhaust pipe being comprised of an upstream exhaust pipe extending before at least one turbine of a turbocharger and consisting of a plurality of pipe portions, and a downstream exhaust pipe extending after the turbine and consisting of a single pipe portion, the exhaust passage changeover valve comprising: at least one movable member a position of which is adjustable relative to a valve body of the exhaust passage changeover valve; and a drive mechanism for adjusting the position of the movable member, wherein the drive mechanism adjusts the movable member among a first position where the plurality of pipe portions of the upstream exhaust pipe are shut off from each other, a second position where the plurality of pipe portions of the upstream exhaust pipe communicate with each other, and a third position where the pipe portions of the upstream exhaust pipe communicate with the pipe portion of the downstream exhaust pipe.

2. The exhaust passage changeover valve according to Claim

1, wherein the movable member includes a first seal member for shutting off communication between the plurality of pipe portions of the upstream exhaust pipe, and a second seal member for shutting off communication between the pipe portions of the upstream exhaust pipe and the pipe portion of the downstream exhaust pipe.

3. The exhaust passage changeover valve according to Claim 2, wherein the first seal member is arranged so that a position thereof is adjusted by the drive mechanism, and wherein the second seal member is arranged so that a position thereof is adjusted by contact with the first seal member.

4. The exhaust passage changeover valve according to any one of Claims 1 to 3, wherein the position of the movable member is adjusted by the drive mechanism whereby the movable member moves from the first position, via the second position to the third position.

5. The exhaust passage changeover valve according to any one of Claims 1 to 4, wherein the movable member is arranged to come into contact with a valve seat so as to be able to change over the communication or shutoff between the pipe portions, and wherein the drive mechanism reduces a moving speed of the movable member in a transition from a noncontact state in which the movable member is away from the valve seat, into a contact state in which the movable member is in contact with the valve seat.