JP2013079609A - Exhaust system of multi-cylinder engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust system of a multi-cylinder engine, capable of improving volumetric efficiency with a simple configuration, and of increasing engine output.SOLUTION: An exhaust manifold 5 has a plurality of independent exhaust passages 52 and a mixing pipe 50 which is connected to downstream ends of respective independent exhaust passages 52 and into which exhaust having passed through the respective independent exhaust passages 52 flows. The mixing pipe 50 has at least an aggregate part 56 having a channel area reduced from the upstream side to the downstream side. Cross-sectional areas of the downstream ends of the respective independent exhaust passages 52 are formed in a substantially sector form, the downstream ends of the respective independent exhaust passages 52 are connected to the upstream end of the aggregate part 56 of the mixing pipe 50 while the respective independent exhaust passages 52 are bundled so that the sector forms are aggregated to substantially form a circle, and axes of the downstream ends of the independent exhaust passages 52 passing through gravity centers of sector forms are inclined with respect to the axis of the mixing pipe 50 so that the axes approach the axis of the mixing pipe 50 more on the downstream side.

Description

  The present invention relates to an exhaust device for a multi-cylinder engine provided in an automobile or the like.

  2. Description of the Related Art Conventionally, exhaust systems have been developed for the purpose of increasing engine output in engines such as automobiles.

  For example, Patent Document 1 discloses a technique for preventing exhaust interference between cylinders by bundling the exhaust passages of cylinders whose exhaust order is not continuous and collecting them as a tapered exhaust pipe, and by providing an ejector effect to this throttle portion. It is disclosed.

Japanese Unexamined Patent Publication No. 04-036023 (Page 4, Page 5, Figure 3)

  In an engine such as an automobile, the demand for improving the engine output is still high, and it is required to further increase the engine output with a simple configuration.

  In view of such circumstances, an object of the present invention is to provide an exhaust device for a multi-cylinder engine that can improve the volume efficiency with a simple configuration and can further increase the engine output.

  In order to solve the above problems, the present invention is an exhaust system for a multi-cylinder engine having a plurality of cylinders provided with an intake valve capable of opening and closing an intake port and an exhaust valve capable of opening and closing an exhaust port. A plurality of independent exhaust passages connected to the exhaust ports of the cylinders or a plurality of cylinders whose exhaust order is not continuous, and a mixing pipe into which exhaust gas that is connected to the downstream end of each independent exhaust passage and passes through each independent exhaust passage flows The mixing pipe has at least a collecting portion whose flow area decreases from the upstream side toward the downstream side, in other words, a collecting portion whose flow area decreases toward the downstream side. The sectional shapes of the downstream ends of the independent exhaust passages in the direction perpendicular to the axis of the mixing tube are formed in the same substantially fan shape, and the sectors are gathered to form a substantially circle. In the state where the independent exhaust passages are bundled, the downstream ends of the independent exhaust passages are connected to the upstream ends of the collecting portions of the mixing pipes, and the axial center of the downstream portion of the independent exhaust passage passing through the center of gravity of the sector shape The downstream side is inclined with respect to the axis of the mixing pipe so as to be closer to the axis of the mixing pipe, and in a predetermined operation region, the opening period of the exhaust valve of each cylinder and the intake valve The valve opening period overlaps with a predetermined period, and the exhaust valve of each cylinder is opened so that the exhaust valve of the succeeding cylinder opens during the overlap period of the preceding cylinder between the cylinders in which the exhaust order continues. An exhaust device for a multi-cylinder engine is provided with valve drive means for driving an exhaust valve.

  According to the present invention, the exhaust gas that has passed through each independent exhaust passage flows into the mixing pipe, thereby generating a negative pressure in the mixing pipe. Due to this negative pressure, other independent exhaust passages or other cylinders that communicate with the other exhaust passages are generated. An ejector effect is obtained in which the exhaust gas in the exhaust port is sucked out downstream. At that time, since the flow channel area of the collecting pipe collecting portion from which the exhaust is ejected from the downstream end of each independent exhaust passage becomes smaller toward the downstream side, the exhaust passes through the mixing pipe while maintaining a relatively high speed. The negative pressure generated in the mixing tube increases. In addition, in the predetermined operation region, the exhaust valve of the succeeding cylinder is opened during the overlap period of the preceding cylinder between the cylinders in which the exhaust order is continuous, so that the ejector effect of the preceding cylinder during the overlap period is This extends to the intake port, whereby scavenging of the preceding cylinder is promoted, volume efficiency (ηV) is improved, and engine output is further increased.

  Then, according to the present invention, as explained in more detail in the embodiments of the invention, in the direction perpendicular to the axial center of the mixing tube, from the axial center of the mixing tube, in other words, the center of gravity of the sector, The distance from the downstream end of each independent exhaust passage to the center of the flow of exhaust ejected becomes relatively small. Thereby, the axial center of the downstream part of each independent exhaust passage passing through the center of gravity of the sector, in other words, the inclination formed by the flow direction of the exhaust gas ejected from the downstream end of each independent exhaust passage with respect to the axial center of the mixing pipe And the exhaust gas flowing into the mixing tube is prevented from colliding with the inner surface of the mixing tube. As a result, the problem that the exhaust collides with the inner surface of the mixing pipe, the exhaust speed decreases, the negative pressure generated in the mixing pipe is reduced, and the ejector effect is sufficiently exerted with a simple configuration. Nevertheless, the acceleration of scavenging of cylinders, improvement of volumetric efficiency, and improvement of engine output are ensured.

  Similarly, in the direction orthogonal to the axial center of the mixing pipe, the distance from the axial center of the mixing pipe to the center of gravity of the sector is relatively reduced, so that the downstream portion of the independent exhaust passage extends from the center of gravity of the sector. The distance to the intersection of the shaft core and the shaft center of the mixing tube is shortened. Here, the intersection is set in the mixing tube, for example, in order to avoid non-uniform pressure distribution in the mixing tube in a direction orthogonal to the axial center of the mixing tube. As a result, the exhaust gas passes through the mixing tube while maintaining a relatively high speed, and the negative pressure generated in the mixing tube becomes large. However, acceleration of scavenging of cylinders, improvement of volumetric efficiency, and improvement of engine output are ensured.

  Further, since the substantially sector shape, which is the cross-sectional shape of the downstream end of each independent exhaust passage, is gathered point-symmetrically with respect to the center of the substantially circle formed by the gathering of the sector shapes, variations in the cylinder pipe due to the ejector effect are suppressed. As a result, cylinder tube variations are also suppressed in terms of promoting scavenging of cylinders, improving volumetric efficiency, and improving engine output.

  In the present invention, it is preferable that the downstream portion of each independent exhaust passage has a smaller passage area toward the downstream side.

  According to this configuration, since the downstream area of each independent exhaust passage has a smaller flow area toward the downstream side, the exhaust gas that has passed through each independent exhaust passage flows into the mixing pipe at a relatively high speed and enters the mixing pipe. The generated negative pressure is further increased. As a result, the ejector effect is more fully exhibited, and further enhancement of cylinder scavenging, improvement in volumetric efficiency, and improvement in engine output are further ensured.

  In the present invention, it is preferable that the mixing tube has a straight portion on the axial center thereof, on the downstream side of the collecting portion, and extending to the downstream side while maintaining the flow path area of the downstream end of the collecting portion. Item 3).

  According to this configuration, when the exhaust gas passes through the straight portion having the minimum flow path area of the mixing tube, the region in which the negative pressure increases in the mixing tube is increased by this straight portion, and the ejector effect is increased. .

  In the present invention, it is preferable that the center of the circle formed by collecting the sectors coincides with the axial center of the mixing tube.

  According to this configuration, since the substantially sector shape, which is the cross-sectional shape of the downstream end of each independent exhaust passage, gathers point-symmetrically with respect to the axial center of the mixing pipe, the cylinder pipe variation of the ejector effect is further suppressed, As a result, the cylinder tube variation is further suppressed in terms of acceleration of scavenging of the cylinder, improvement in volumetric efficiency, and improvement in engine output.

  In the present invention, the engine is an engine having four or more cylinders, and at least one of the independent exhaust passages is preferably an independent exhaust passage connected to exhaust ports of a plurality of cylinders whose exhaust order is not continuous ( Claim 5).

  According to this configuration, for example, in the case of a four-cylinder engine, two or three independent exhaust passages are bundled and connected to the mixing pipe, and the sectional shape of the downstream end of each independent exhaust passage is approximately 180 ° or 120 °. It is formed in a fan shape. Further, for example, in the case of a five-cylinder engine, three independent exhaust passages are bundled and connected to the mixing pipe, and the cross-sectional shape of the downstream end of each independent exhaust passage is formed in a substantially fan shape of 120 °.

  According to the present invention, in the direction orthogonal to the axial center of the mixing pipe, the distance from the axial center of the mixing pipe to the center of the flow of exhaust gas ejected from the downstream end of the independent exhaust passage is relatively small. The exhaust that has flowed into the mixing pipe is prevented from colliding with the inner surface of the mixing pipe, and the exhaust passes through the mixing pipe while maintaining a relatively high speed, so that the negative pressure generated in the mixing pipe is large. Thus, the ejector effect is sufficiently exerted, and the cylinder scavenging is promoted, the volume efficiency is improved, and the engine output is improved while the structure is simple.

1 is a schematic configuration diagram of an engine system including an exhaust device for a multi-cylinder engine according to an embodiment of the present invention. It is the elements on larger scale of FIG. It is a schematic side view of the exhaust manifold and catalyst device of the engine. FIG. 4 is a sectional view taken along the line IV-IV in FIG. 2. FIG. 5 is a cross-sectional view taken along line VV in FIG. 3. It is a perspective view of the exhaust manifold. It is a perspective view of the state where a mixing pipe was removed from the exhaust manifold. FIG. 7 is a perspective view of the exhaust manifold as viewed upside down in the drawing compared to FIG. 6. FIG. 8 is a perspective view of a state in which a mixing tube is removed from the exhaust manifold as viewed upside down in the drawing compared to FIG. 7. It is explanatory drawing of the valve timing of the intake valve and exhaust valve of the said engine. It is explanatory drawing of the valve opening time (valve opening start time) and valve closing time of the said intake valve and an exhaust valve. It is explanatory drawing of the aspect which bundles several independent exhaust passages and connects to the upstream end of the gathering part of a mixing pipe, (a) and (b) are outside the scope of the present invention, and (c) is the present invention. It is within the range. It is explanatory drawing of an effect | action of embodiment of this invention. It is explanatory drawing of another effect | action of embodiment of this invention. It is explanatory drawing of the pressure distribution in the downstream part of the independent exhaust passage of the said engine, and a mixing pipe. It is explanatory drawing of the speed distribution of the exhaust_gas | exhaustion in the downstream part of the independent exhaust passage of the said engine, and a mixing pipe. (A), (b) and (c) is explanatory drawing of the modification of embodiment of this invention, respectively. (A) And (b) is explanatory drawing of a specific example of the structure which implement | achieves Fig.17 (a). It is explanatory drawing of the exhaust manifold which concerns on embodiment of this invention in the case of a 5-cylinder engine. It is explanatory drawing of another exhaust manifold which concerns on embodiment of this invention in the case of a 5-cylinder engine.

  Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, the present invention is applied to the engine system shown in FIGS. 1 is a schematic configuration diagram of an engine system 100 including an exhaust device for a multi-cylinder engine according to an embodiment of the present invention, FIG. 2 is a partially enlarged view of FIG. 1, and FIG. FIG. 6 is a schematic side view of the catalyst device 6 (note that only one independent exhaust passage 52 is shown in FIG. 3).

  The engine system 100 includes an engine body 1 having a cylinder head 9 and a cylinder block, an ECU 2 for engine control, a plurality of intake pipes 3 connected to the engine body 1, and an exhaust manifold 5 connected to the engine body 1. And a catalyst device 6 connected to the exhaust manifold 5.

  A plurality of cylinders 12 (see FIG. 2) into which pistons are respectively inserted are formed in the cylinder head 9 and the cylinder block. In this embodiment, the engine body 1 is an in-line four-cylinder engine, and four cylinders 12 are formed in series in the cylinder head 9 and the cylinder block. Specifically, a first cylinder 12a, a second cylinder 12b, a third cylinder 12c, and a fourth cylinder 12d are formed in order from the right in FIG. Each cylinder head 9 is provided with a spark plug 15 so as to face a combustion chamber partitioned above the piston.

  The engine body 1 is a four-cycle engine. As shown in FIG. 10, the cylinders 12a to 12d are ignited by the spark plug 15 at a timing shifted by 180 ° CA, and the intake stroke and the compression stroke are performed. The expansion stroke and the exhaust stroke are each shifted by 180 ° CA. In the present embodiment, ignition is performed in the order of the first cylinder 12a → the third cylinder 12c → the fourth cylinder 12d → the second cylinder 12b, and the exhaust stroke and the like are performed in this order.

  Two intake ports 17 and two exhaust ports 18 opening toward the combustion chamber are provided at the top of each cylinder 12. The intake port 17 is for introducing intake air into each cylinder 12. The exhaust port 18 is for exhausting the exhaust from each cylinder 12. Each intake port 17 is provided with an intake valve 19 for opening and closing the intake port 17 to communicate or block the intake port 17 and the inside of the cylinder 12. Each exhaust port 18 is provided with an exhaust valve 20 for opening and closing the exhaust port 18 to communicate or block the exhaust port 18 and the inside of the cylinder 12. The intake valve 19 is driven by an intake valve drive mechanism (valve drive means) 30 to open and close the intake port 17 at a predetermined timing. The exhaust valve 20 is driven by an exhaust valve drive mechanism (valve drive means) 40 to open and close the exhaust port 18 at a predetermined timing.

  The intake valve drive mechanism 30 has an intake camshaft 31 that is in contact with the intake valve 19 and an intake VVT (Variable Valve Timing Mechanism (variable valve timing mechanism)) 32. The intake camshaft 31 is connected to the crankshaft via a known power transmission mechanism such as a chain / sprocket mechanism, and rotates with the rotation of the crankshaft to drive the intake valve 19 to open and close.

  The intake VVT 32 is for changing the valve timing of the intake valve 19. The intake VVT 32 is arranged coaxially with the intake camshaft 31 and changes the phase difference between a predetermined driven shaft that is directly driven by the crankshaft and the intake camshaft 31, thereby the crankshaft and the intake air By changing the phase difference from the camshaft 31, the valve timing of the intake valve 19 is changed. As a specific configuration of the intake VVT 32, for example, a plurality of liquid chambers arranged in the circumferential direction are provided between the driven shaft and the intake camshaft 31, and a pressure difference is provided between the liquid chambers to thereby change the position. Examples thereof include a hydraulic mechanism that changes a phase difference, an electromagnetic mechanism that has an electromagnet between the driven shaft and the intake camshaft 31, and changes the phase difference by applying electric power to the electromagnet. . The intake VVT 32 changes the phase difference based on the target valve timing of the intake valve 19 calculated by the ECU 2.

  The exhaust valve drive mechanism 40 has the same structure as the intake valve drive mechanism 30. That is, the exhaust valve drive mechanism 40 is in contact with the exhaust valve 20 and changes the phase difference between the exhaust camshaft 41 connected to the crankshaft and the exhaust camshaft 41 and the crankshaft, thereby And an exhaust VVT 42 for changing the valve timing of the valve 20. The exhaust VVT 42 changes the phase difference based on the target valve timing of the exhaust valve 20 calculated by the ECU 2. The exhaust camshaft 41 rotates with the rotation of the crankshaft under this phase difference, and opens and closes the exhaust valve 20 at the target valve timing.

  In the present embodiment, the intake VVT 32 and the exhaust VVT 42 open the intake valve 19 and the exhaust valve 20 while keeping the valve opening period and the lift amount, that is, the valve profile, of the intake valve 19 and the exhaust valve 20 constant. The valve timing (the valve opening start timing shown in FIG. 11) and the valve closing timing are each changed.

  The intake port 17 of each cylinder 12 is connected to the intake pipe 3 on the upstream side. Specifically, four intake pipes 3 are provided corresponding to the number of cylinders, and two intake ports 17 provided in each cylinder 12 are connected to one intake pipe 3.

  The exhaust manifold 5 includes, in order from the upstream side, three independent exhaust passages 52 and a mixing pipe 50 that is connected to the downstream end of each independent exhaust passage 52 and into which exhaust gas that has passed through each independent exhaust passage 52 flows. . The mixing tube 50 has, on its axis L1 (see FIG. 3), a collecting portion 56 whose flow area decreases from the upstream side in order from the upstream side, and a flow area (mixing) at the downstream end of the collecting portion 56. The straight portion 57 that extends to the downstream side while maintaining the minimum flow area of the pipe 50, and the diffuser portion 58 that has a larger flow area toward the downstream side.

  Each independent exhaust passage 52 is connected to the exhaust port 18 of each cylinder 12. Specifically, among the cylinders 12, the exhaust port 18 of the first cylinder 12a and the exhaust port 18 of the fourth cylinder 12d are individually connected to one independent exhaust passage 52a, 52d. On the other hand, the exhaust port 18 of the second cylinder 12b and the exhaust port 18 of the third cylinder 12c, in which the exhaust strokes are not adjacent to each other and the exhaust order is not continuous, are not exhausted simultaneously from these cylinders. From the viewpoint of simplification, it is connected to one common independent exhaust passage 52b. More specifically, the independent exhaust passage 52b connected to the exhaust port 18 of the second cylinder 12b and the exhaust port 18 of the third cylinder 12c is separated into two passages on the upstream side thereof, The exhaust port 18 of the second cylinder 12b is connected to the other, and the exhaust port 18 of the third cylinder 12c is connected to the other.

  In this embodiment, as shown in FIGS. 6 to 9, the independent exhaust passage 52 b corresponding to the second cylinder 12 b and the third cylinder 12 c is located between these cylinders 12 b and 12 c, that is, substantially at the center of the engine body 1. The independent exhaust passages 52a and 52d, which extend linearly toward the collecting portion 56 of the mixing pipe 50 at positions facing the portions, respectively, correspond to the first cylinder 12a and the fourth cylinder 12d, respectively. , 12d extending from the position opposite to 12d toward the collecting portion 56 of the mixing tube 50.

  These independent exhaust passages 52a, 52b, 52d are independent of each other, and exhaust exhausted from the second cylinder 12b or the third cylinder 12c, exhaust exhausted from the first cylinder 12a, and exhaust from the fourth cylinder 12d. The exhausted air is discharged to the downstream side through the independent exhaust passages 52a, 52b, 52d independently of each other. Exhaust gas that has passed through the independent exhaust passages 52 a, 52 b, 52 d flows into the collecting portion 56 of the mixing pipe 50.

  Each of the independent exhaust passages 52 and the collecting portions 56 is disposed around the high-speed exhaust as the exhaust gas is ejected from the independent exhaust passages 52 at a high speed and the exhaust gas flows into the collecting portion 56 at a high speed. A negative pressure is generated in the adjacent independent exhaust passage 52 and the exhaust port 18 communicating with the independent exhaust passage 52 by the negative pressure action, ie, ejector effect, generated in the mixing pipe 50, and the exhaust in the exhaust port 18 is It has a shape that is sucked out downstream.

  Specifically, the collecting portion 56 has a shape in which the flow passage area becomes smaller toward the downstream side so that the exhaust discharged from each independent exhaust passage 52 flows downstream while maintaining a high speed. doing. In the present embodiment, the flow passage area at the downstream end of the collecting portion 56 is set to be smaller than the total flow passage area at the downstream end of each independent exhaust passage 52 in order to further increase the exhaust speed. In the present embodiment, the collecting portion 56 has an inverted truncated cone shape (funnel shape) whose diameter is reduced toward the downstream side.

  And the downstream part of each said independent exhaust passage 52 has the shape where the flow-path area becomes small so that it goes downstream so that exhaust_gas | exhaustion is injected in the said gathering part 56 from each independent exhaust passage 52 at high speed. Yes. In this embodiment, as shown in FIG. 4, each independent exhaust passage 52 is reduced in cross-sectional area from the upstream portion (imaginary line) having a substantially elliptical cross section toward the downstream, and at the downstream end thereof. It has a sector shape with a cross-sectional area (flow channel area) that is approximately 1/3 of the elliptical cross-sectional area of the upstream portion. As shown in FIG. 5, these independent exhaust passages 52 are connected to the upstream end of the collective portion 56 by gathering so that the downstream ends in the form of a fan are adjacent to each other to form a substantially circular cross section as a whole. (See FIGS. 7 and 9).

  That is, the cross-sectional shape of the downstream end of each independent exhaust passage 52 in the direction orthogonal to the axis L1 of the mixing pipe 50 is formed in substantially the same sector shape (see FIGS. 4 and 5), and the sector shape is gathered and substantially The downstream ends of the independent exhaust passages 52 are connected to the upstream end of the collecting portion 56 of the mixing pipe 50 in a state where the independent exhaust passages 52 are bundled so as to form a circle. At that time, as shown in FIG. 12C, the center of the circle coincides with the axis L <b> 1 of the mixing tube 50. Further, the axial center of the downstream portion of the independent exhaust passage 52 that passes through the fan-shaped center of gravity X (see FIG. 4 and FIG. 12C: described as “nozzle center” in FIG. 12C). As shown in FIG. 3, L2 is inclined with respect to the axis L1 of the mixing tube 50 so as to be closer to the axis L1 of the mixing tube 50 toward the downstream side.

  The reason why the exhaust manifold 5 has such a configuration in the present embodiment is as follows. That is, consider increasing the negative pressure in the mixing tube 50 in order to improve the ejector effect. Basically, the flow area of the independent exhaust passage 52 and the nozzle (the opening at the downstream end of the independent exhaust passage 52. In this embodiment, it is formed in a fan shape as shown in FIGS. 4 and 5). , And the flow channel area of the mixing tube 50 are roughly determined by the engine displacement. As a measure for increasing the negative pressure generated in the mixing pipe 50, it is possible to prevent the high-speed exhaust flow flowing into the mixing pipe 50 from colliding with the inner surface of the mixing pipe 50 (measure 1), and the exhaust is relatively It is proposed to pass through the mixing tube 50 while maintaining a high speed (preferably, to pass through the straight portion 57 having the minimum flow path area of the mixing tube 50) (Measure 2). This is because, by the measure 1, the problem that the exhaust gas collides with the inner surface of the mixing pipe 50, the speed of the exhaust gas decreases, and the negative pressure generated in the mixing pipe 50 is reduced. This is because, by the measure 2, the exhaust gas passes through the mixing pipe 50 (preferably, the straight portion 57) at a relatively high speed, and the negative pressure generated in the mixing pipe 50 increases. In any case, the negative pressure generated in the mixing tube 50 is increased, so that the ejector effect is sufficiently exerted and the structure is simple, but the scavenging of the cylinder is improved, the volume efficiency is improved, and the engine output is increased. Improvement is ensured.

  As a configuration capable of achieving measures 1 and 2, the distance R from the center (axial center L1) of the mixing tube 50 to the center of the nozzle (fan-shaped center of gravity X) is reduced in the direction orthogonal to the axial center L1 of the mixing tube 50. (See FIG. 12 (c)).

  As a result, for the measure 1, the flow of the exhaust gas ejected from the downstream end of each independent exhaust passage 52 (in other words, the axial center L2 of each independent exhaust passage 52 passing through the nozzle center (fan-shaped center of gravity X)). ) Is reduced with respect to the axis L1 of the mixing tube 50, and the exhaust gas flowing into the mixing tube 50 is prevented from colliding with the inner surface of the mixing tube 50. For example, as shown in FIG. 13, in a direction (lateral direction in the drawing) orthogonal to the axis L1 of the mixing tube 50, the distance R from the axis L1 is relatively large with the relatively small nozzle center Xa. Comparing with the nozzle center Xb, the inclination of the axis L2a downstream of the independent exhaust passage 52 passing through the nozzle center Xa with respect to the axis L1 of the mixing pipe 50 becomes relatively small, and the independent center passing through the nozzle center Xb. The inclination that the shaft core L2b in the downstream portion of the exhaust passage 52 forms with respect to the shaft core L1 of the mixing pipe 50 is relatively large. In order to avoid uneven pressure distribution in the straight portion 57 in the direction orthogonal to the axis L1 of the mixing pipe 50, the axis L2 downstream of the independent exhaust passage 52 and the axis L1 of the mixing pipe 50 are Crossed within the straight portion 57 (for example, when the exhaust gas does not flow uniformly into the straight portion 57 and does not flow in the vicinity of the axial center L1 of the mixing tube 50, the straight portion 57 in the direction orthogonal to the axial center L1) The pressure distribution of the exhaust pipe becomes non-uniform, and an exhaust backflow from the downstream side to the upstream side occurs in a region where the pressure is relatively low. As a result, the negative pressure in the mixing pipe 50 is reduced, and the ejector effect is reduced. Problems arise). As a result, when the distance R from the axis L1 to the nozzle center Xb is relatively large, the exhaust gas that has flowed into the mixing pipe 50 collides with the inner surface of the mixing pipe 50, the exhaust speed decreases, and the mixing pipe 50 When the distance R from the shaft center L1 to the nozzle center Xa is relatively small while the negative pressure generated in the inside becomes small, the exhaust gas flowing into the mixing tube 50 collides with the inner surface of the mixing tube 50. As a result, the exhaust gas collides with the inner surface of the mixing tube 50 to reduce the speed of the exhaust gas and the negative pressure generated in the mixing tube 50 is reduced. .

  Regarding Measure 2, by reducing the distance R from the axis L1 to the nozzle center X, the axis L2 downstream of the independent exhaust passage 52 and the axis L1 of the mixing pipe 50 from the nozzle center X The distance to the intersection of For example, as shown in FIG. 14, in a direction orthogonal to the axial center L1 of the mixing tube 50 (lateral direction in the drawing), the distance R from the axial center L1 is relatively large with the relatively small nozzle center Xa. Comparing with the nozzle center Xc, the intersection Y where the axial center L2a in the downstream portion of the independent exhaust passage 52 passing through the nozzle center Xa intersects the axial center L1 of the mixing pipe 50 is relatively close to the nozzle center Xa. The intersection Z where the axial center L2c downstream of the independent exhaust passage 52 passing through the nozzle center Xc intersects the axial center L1 of the mixing pipe 50 is relatively far from the nozzle center Xc (the axial center relative to the axial center L1). Consider the case where the inclination of L2a and the inclination of the axis L2c are the same). Since the intersection point Y is in the straight portion 57, nonuniform pressure distribution in the straight portion 57 in the direction orthogonal to the axial center L1 of the mixing pipe 50 is avoided, and the exhaust from the downstream side to the upstream side as described above is avoided. Backflow is suppressed. On the other hand, since the intersection Z is on the downstream side of the straight portion 57, the uneven pressure distribution in the straight portion 57 in the direction orthogonal to the axis L1 of the mixing tube 50 is not avoided, and from the downstream side as described above. Backflow of the exhaust to the upstream side will occur. As a result, when the distance R from the axis L1 to the nozzle center Xc is relatively large, the distance from the nozzle center Xc to the intersection Z between the axes L2c and L1 becomes relatively long, and the exhaust gas is exhausted. When the distance R from the axial center L1 to the nozzle center Xa is relatively small, the negative pressure in the mixing tube 50 is reduced and the ejector effect is reduced. Since the distance from Xa to the intersection Y between the shaft cores L2a and L1 is relatively short, the backflow of the exhaust does not occur, and the negative pressure in the mixing tube 50 and the ejector effect are suppressed from being reduced. is there.

  FIG. 12 shows some of the modes in which a plurality (three in the illustrated example) of independent exhaust passages 52 are bundled and connected to the upstream end of the collecting portion 56 of the mixing pipe 50.

  FIG. 12A shows a case where the nozzle shape at the downstream end of the independent exhaust passage 52 is circular. The arrangement of the three nozzles at the downstream end of the independent exhaust passage 52 is excellent in point symmetry with respect to the axis L1 of the mixing pipe 50, but the distance R from the axis L1 to the nozzle center X is relatively large. Therefore, the measures 1 and 2 are difficult to achieve, and it is difficult to increase the negative pressure in the mixing tube 50 in order to improve the ejector effect.

  FIG. 12B shows a case where the three nozzles at the downstream end of the independent exhaust passage 52 are arranged in parallel so as to form a substantially circle. Although the distance R from the axis L1 of the mixing tube 50 to the nozzle center X is relatively small, the arrangement of the three nozzles at the downstream end of the independent exhaust passage 52 is inferior in point symmetry with respect to the axis L1. For this reason, the cylinder tube variation of the ejector effect increases, and as a result, the cylinder tube variation also increases in terms of promoting scavenging of the cylinder, improving the volume efficiency, and improving the engine output.

  On the other hand, as shown in FIG. 12C, the three nozzle shapes at the downstream end of the independent exhaust passage 52 are formed into the same 120 ° fan shape, and these fan shapes are assembled to form a substantially circle. When the three independent exhaust passages 52 are bundled together, the distance R from the axial center L1 of the mixing pipe 50 to the nozzle center X is relatively small, and the arrangement of the three nozzles is the axial center of the mixing pipe 50. Since the point symmetry with respect to L1 is excellent, the measures 1 and 2 are achieved, the negative pressure in the mixing pipe 50 can be increased to improve the ejector effect, and the cylinder pipe variation of the ejector effect is suppressed. As a result, cylinder tube variations are also suppressed in terms of promoting scavenging of the cylinder, improving volumetric efficiency, and improving engine output.

  FIG. 15 shows the results of examining the pressure distribution in the downstream portion of the independent exhaust passage 52 and the mixing pipe 50 when the connection mode between the independent exhaust passage 52 and the mixing pipe 50 is FIG. The results of examining the distribution are shown in FIG.

  FIG. 15 shows the high-pressure, high-speed gas (so-called blowdown gas) discharged from the predetermined cylinder 12 through the independent exhaust passage 52 to the mixing pipe 50 after the opening of the exhaust valve 20 of the predetermined cylinder 12 is started. The pressure distribution in the above state is shown. As shown in FIG. 15, the pressure gradually decreases from the upstream side of the independent exhaust passage 52 toward the vicinity of the upstream end (collecting portion 56) of the mixing pipe 50, and a sufficiently large negative pressure is generated in the mixing pipe 50. Has occurred. As a result, the pressure at the downstream end of the other independent exhaust passage 52 is sufficiently reduced, and the ejector effect can be sufficiently exerted. Further, the pressure in the mixing pipe 50 gradually increases from the collecting portion 56 toward the downstream side, and the exhaust pressure is recovered as it passes through the straight portion 57 and the diffuser portion 58.

  In FIG. 16, the length of the arrow indicates the exhaust speed of each part, and the region where the arrow is long is the region where the exhaust speed is high. Exhaust gas (exhaust jet) ejected from the downstream end of the independent exhaust passage 52 is represented by a solid portion in FIG. As shown in FIG. 16, the direction of the exhaust jet flow represented by the axis L <b> 2 flows relatively uniformly around the axis L <b> 1 of the mixing pipe 50 in the straight portion 57, and the exhaust gas flowing into the mixing pipe 50 Is suppressed from colliding with the inner surface of the mixing pipe 50 and flowing down at a high speed, and the backflow of exhaust gas from the downstream side to the upstream side is also suppressed.

  The exhaust gas flowing into the straight portion 57 flows into the diffuser 58 portion.

  The diffuser portion 58 has a shape in which the flow path area increases toward the downstream side, and the high-speed exhaust discharged from the collective portion 56 passes through the straight portion 57 and the diffuser portion 58. Pressure is restored. In the present embodiment, the diffuser portion 58 has a truncated cone shape whose diameter increases toward the downstream side.

  The catalyst device 6 is connected to the downstream side of the diffuser portion 58, and the exhaust gas that has passed through the diffuser portion 58 flows into the casing 62 of the catalyst device 6.

  The catalyst device 6 is a device for purifying the exhaust discharged from the engine body 1. The catalyst device 6 includes a catalyst main body 64 such as a three-way catalyst and a casing 62 that accommodates the catalyst main body 64. The casing 62 has a substantially cylindrical shape extending in parallel with the exhaust flow direction. The catalyst body 64 is accommodated in a central portion in the upstream and downstream direction of the casing 62, and a predetermined space is formed at the upstream end of the casing 62. The downstream end of the diffuser portion 58 is connected to the upstream end of the casing 62, and the exhaust discharged from the diffuser portion 58 flows into the upstream end of the casing 62 and then proceeds to the catalyst body 64 side.

  As described above, in the present embodiment, the jet of exhaust flows around the axis L1 of the mixing pipe 50, and the exhaust flows uniformly into the straight portion 57, the diffuser portion 58, and the catalyst body 64. The exhaust is effectively purified by the catalyst body 64.

  The ECU 2 stores the target opening timings of the target valve timings of the intake valve 19 and the exhaust valve 20 set in advance according to the operating conditions, and the ECU 2 calculates the current operating conditions based on signals from various sensors. At the same time, target values corresponding to these operating conditions are extracted, and the intake VVT 32 and the exhaust VVT 42 are driven so that the valve timings of the intake valve 19 and the exhaust valve 20 become the target values.

  Next, target valve timings of the intake valve 19 and the exhaust valve 20 will be described.

  The target valve timings of the intake valve 19 and the exhaust valve 20 are set in the predetermined operating range (for example, the entire operating range, a partial range such as a predetermined reference rotational speed or less, a low speed / high load range, etc.). The open valve period of the exhaust valve 20 and the open valve period of the intake valve 19 overlap with each other across the intake top dead center (TDC), and one cylinder ( During the overlap period T_O / L of the preceding cylinder) 12, the exhaust valve 20 of the other cylinder (following cylinder) 12 is set to start opening. Specifically, as shown in FIG. 10, the exhaust valve 20 of the third cylinder 12c opens during the period in which the exhaust valve 20 and the intake valve 19 of the first cylinder 12a overlap, and the third cylinder The exhaust valve 20 of the fourth cylinder 12d opens during the period in which the exhaust valve 20 and the intake valve 19 of 12c overlap, and the exhaust valve 20 and the intake valve 19 of the fourth cylinder 12d overlap. The exhaust valve 20 of the second cylinder 12b opens during the period when the exhaust valve 20 of the second cylinder 12b opens, and the exhaust valve 20 of the first cylinder 12a opens while the exhaust valve 20 and the intake valve 19 of the second cylinder 12b overlap. It is set to be.

  In the engine system 100, the valve opening timing (valve opening start timing) and the valve closing timing of the intake valve 19 and the exhaust valve 20, respectively, are as shown in FIG. The time when the lift rises or falls steeply, for example, the time when the lift is 0.4 mm.

  Next, the intake performance in the engine system 100 configured as described above will be described.

  When the exhaust valve 20 of a predetermined cylinder 12 is opened, the exhaust is discharged from the cylinder 12 to the corresponding exhaust port 18 and the independent exhaust passage 52 at a high speed. In particular, immediately after the opening of the exhaust valve 20 is started, exhaust (so-called blowdown gas) is discharged from the cylinder 12 at a very high speed.

  Here, in the engine system 100, as described above, the independent exhaust passage 52 and the collecting portion 56 of the mixing pipe 50 are ejected from the predetermined independent exhaust passage 52 to the collecting portion 56 at a high speed. A negative pressure is generated in the other independent exhaust passage 52 by the ejector effect so that the gas in the exhaust port 18 communicating with the other independent exhaust passage 52 and the other independent exhaust passage 52 is sucked out downstream. It is configured. Then, during an overlap period of a predetermined cylinder (preceding cylinder) 12, the exhaust valve 20 of another cylinder 12 (subsequent cylinder) whose exhaust order is set immediately after the preceding cylinder 12 is set to open. Has been.

  Therefore, as the exhaust valve 20 of the exhaust stroke cylinder 12 is opened and the blowdown gas is ejected from the exhaust stroke cylinder 12 through the independent exhaust passage 52 to the collecting portion 56 at a high speed, the ejector effect causes A negative pressure is generated in the exhaust port 18 of the intake stroke cylinder 12 during the overlap period, so that the ejector effect extends to the intake port 17 of the intake stroke cylinder 12 during the overlap period. Scavenging in the intake stroke cylinder 12 is promoted.

  The features of this embodiment are summarized below.

  In the present embodiment, an exhaust device for a multi-cylinder engine having a plurality of cylinders 12 provided with an intake valve 19 capable of opening and closing the intake port 17 and an exhaust valve 20 capable of opening and closing the exhaust port 18 is provided. The exhaust manifold 5 is connected to a plurality of independent exhaust passages 52 respectively connected to the exhaust ports 18 of one cylinder 12 or a plurality of cylinders 12 whose exhaust order is not continuous, and to the downstream ends of the independent exhaust passages 52. And a mixing pipe 50 into which the exhaust gas that has passed through the independent exhaust passage 52 flows. The mixing pipe 50 has at least a collecting portion 56 whose flow path area decreases from the upstream side toward the downstream side, in other words, a collecting portion 56 whose flow path area decreases toward the downstream side. The mixing tube 50 further has a straight portion 57 on the axial center L1 on the downstream side of the collecting portion 56 and extending downstream while maintaining the flow path area of the downstream end of the collecting portion 56. The cross-sectional shapes of the downstream ends of the independent exhaust passages 52 in the direction perpendicular to the axis L1 of the mixing tube 50 are formed in substantially the same sector shape, and the sectors are gathered to form a substantially circle. In a state where the independent exhaust passages 52 are bundled, the downstream end of each independent exhaust passage 52 is connected to the upstream end of the collecting portion 56 of the mixing pipe 50. At that time, the center of the circle coincides with the axis L1 of the mixing tube 50. In addition, the axial center L2 of the downstream portion of the independent exhaust passage 52 passing through the sector-shaped center of gravity X is inclined with respect to the axial center L1 of the mixing tube 50 so that the downstream side is closer to the axial center L1 of the mixing tube 50. doing. Further, in a predetermined operation region, the opening period of the exhaust valve 20 and the opening period of the intake valve 19 of each cylinder 12 overlap each other for a predetermined period, and the preceding cylinders 12 and 12 have a continuous exhaust sequence. Valve drive means 30 and 40 for driving the intake valve 19 and the exhaust valve 20 of each cylinder 12 are provided so that the exhaust valve 20 of the subsequent cylinder 12 opens during the overlap period of the cylinder 12 to be operated. .

  In the present embodiment, the exhaust gas that has passed through each independent exhaust passage 52 flows into the mixing pipe 50, thereby generating a negative pressure in the mixing pipe 50, and this negative pressure causes communication with the other independent exhaust passage 52 or this. An ejector effect is obtained in which the exhaust gas in the exhaust port 18 of the other cylinder 12 is sucked out downstream. At that time, the gathering portion 56 of the mixing pipe 50 from which the exhaust gas is ejected from the downstream end of each independent exhaust passage 52 has a smaller flow path area toward the downstream side, so that the mixing pipe is maintained while maintaining a relatively high speed. 50, particularly in the present embodiment, the negative pressure generated in the mixing pipe 50 through the straight portion 57 having the minimum flow path area of the mixing pipe 50 increases. In addition, in the predetermined operation region, the exhaust valve 20 of the succeeding cylinder 12 is opened during the overlap period of the preceding cylinder 12 between the cylinders 12 and 12 in which the exhaust order is continuous, so that the ejector effect is overlapped. This extends to the intake port 17 of the preceding cylinder 12 during the period, thereby promoting scavenging of the preceding cylinder 12, improving the volumetric efficiency (ηV), and further increasing the engine output.

  In addition, in this embodiment, in the direction orthogonal to the axis L1 of the mixing pipe 50, the axial center L1 of the mixing pipe 50 (particularly, in this embodiment, the cross-sectional shape of the downstream end of each independent exhaust passage 52 is substantially the same. The distance R from the center of the sector X) to the center of gravity X of the sector, in other words, from the downstream end of each independent exhaust passage 52 to the center of the flow of exhaust gas is relatively small. Become. Thereby, the axial center L2 of the downstream part of each independent exhaust passage 52 passing through the sector-shaped center of gravity X, in other words, the flow direction of the exhaust gas ejected from the downstream end of each independent exhaust passage 52 is the axis of the mixing tube 50. The inclination made with respect to L1 is reduced, and the exhaust gas flowing into the mixing pipe 50 is prevented from colliding with the inner surface of the mixing pipe 50. As a result, the problem that the exhaust gas collides with the inner surface of the mixing pipe 50 and the speed of the exhaust gas is reduced and the negative pressure generated in the mixing pipe 50 is reduced is suppressed, and the ejector effect is sufficiently exerted. In spite of the simple configuration, the scavenging of the cylinder 12 is promoted, the volumetric efficiency is improved, and the engine output is improved.

  Similarly, in the direction perpendicular to the axial center L1 of the mixing tube 50, the distance R from the axial center L1 of the mixing tube 50 to the center of gravity X of the sector is relatively small, so that from the sectoral center of gravity X, The distance to the intersection Y between the shaft core L2 in the downstream portion of the independent exhaust passage 52 and the shaft core L1 of the mixing pipe 50 is shortened. Here, the intersection Y avoids, for example, non-uniformity of the pressure distribution in the straight portion 57 (more generally, the pressure distribution in the mixing tube 50) in the direction orthogonal to the axis L1 of the mixing tube 50. Therefore, it is set in the straight portion 57 (more generally, in the mixing tube 50). As a result, while the exhaust gas is maintained at a relatively high speed, the exhaust gas passes through the mixing tube 50, particularly in the present embodiment, the straight portion 57 having the minimum flow area of the mixing tube 50, and is generated in the mixing tube 50. As a result, the ejector effect is sufficiently exerted, and the scavenging of the cylinder 12 is promoted, the volumetric efficiency is improved, and the engine output is ensured with a simple configuration.

  Furthermore, the substantially sector shape, which is the cross-sectional shape of the downstream end of each independent exhaust passage 52, is substantially the center of a circle formed by the aggregation of the sector shapes (particularly, in this embodiment, the axis L1 of the mixing tube 50). Because of the point symmetry, the cylinder pipe variation due to the ejector effect is suppressed. As a result, the cylinder tube variation is also suppressed for the scavenging acceleration of the cylinder 12, the improvement of the volume efficiency, and the improvement of the engine output.

  In the present embodiment, the downstream area of each independent exhaust passage 52 has a smaller flow area on the downstream side. As a result, the exhaust gas that has passed through each independent exhaust passage 52 flows into the mixing pipe 50 at a relatively high speed, and the negative pressure generated in the mixing pipe 50 further increases. As a result, the ejector effect is more fully exhibited, and further enhancement of scavenging of the cylinder 12, improvement of volume efficiency, and improvement of engine output are further ensured.

  In the present embodiment, the mixing tube 50 has a straight portion 57 extending on the downstream side of the collecting portion 56 while maintaining the flow passage area at the downstream end of the collecting portion 56 on the axial center L1. Have. As a result, when the exhaust gas passes through the straight portion 57 having the minimum flow path area of the mixing pipe 50, the region in which the negative pressure increases in the mixing pipe 50 is increased by the straight portion 57, and the ejector effect is increased. Increase.

  In the present embodiment, the center of the circle formed by collecting the sectors coincides with the axis L1 of the mixing tube 50. Thereby, since the substantially sector shape which is a cross-sectional shape of the downstream end of each independent exhaust passage 52 gathers point-symmetrically with respect to the axis L1 of the mixing pipe 50, the cylinder pipe variation of the ejector effect is further suppressed, As a result, the cylinder tube variation is further suppressed in terms of acceleration of scavenging of the cylinder, improvement in volumetric efficiency, and improvement in engine output.

  The modifications of this embodiment are summarized below.

  The shape of the nozzle that is the opening at the downstream end of the independent exhaust passage 52 may be a sector of 180 ° as shown in FIG. Moreover, as shown in FIG.17 (b), a 90 degree fan shape may be sufficient. In the case of a 180 ° fan shape, two independent exhaust passages 52 are bundled and connected to the mixing pipe 50 in a four-cylinder engine. Therefore, each independent exhaust passage 52 is connected to the exhaust ports 18 and 18 of the two cylinders 12 and 12 whose exhaust order is not continuous. In the case of a 90 ° sector, four independent exhaust passages 52 are bundled and connected to the mixing pipe 50 in a four-cylinder engine. Therefore, each independent exhaust passage 52 is connected to the exhaust port 18 of one cylinder 12.

  The nozzle-shaped sector does not need to form a perfect circle when gathered, as shown in FIG. 17C, without departing from the spirit of the present invention. As shown in the figure, the arc portion may expand outward or contract inward. Therefore, the nozzle shape may be substantially fan-shaped, for example, within a tolerance range or within an individual difference range, and the circle formed when assembled is not limited to a perfect circle but may be a substantially circle. Also, the nozzle-shaped fan-shaped corners are not limited to acute angles, and may be rounded (see FIGS. 7 and 9).

  FIGS. 18A and 18B show a specific example of a configuration for realizing FIG. 17A in which the nozzle shape is a fan shape with a 180 ° (note that FIG. 18B is shown in FIG. 18A). It is a sectional view taken along line bb). In the four-cylinder engine, independent exhaust passages 52 connected to the exhaust ports 18 and 18 of the first cylinder 12a and the fourth cylinder 12d and independent ports connected to the exhaust ports 18 and 18 of the second cylinder 12b and the third cylinder 12c. The exhaust passage 52 is bundled and connected to the mixing pipe 50. By disposing the mixing pipe 50 at a substantially central portion of the engine body 1, the independent exhaust passages 52 are left and right symmetrical, and the left and right exhaust passages have the same volume, which is advantageous in terms of the ejector effect. It is done.

  19 and 20 show the configuration of the exhaust manifold 5 according to this embodiment when the engine is a five-cylinder engine.

  Also in the case of a five-cylinder engine, at least one of the independent exhaust passages 52... 52 is preferably the independent exhaust passage 52 connected to the exhaust ports 18 of the plurality of cylinders 12 whose exhaust order is not continuous. The illustrated example shows a case where there are three independent exhaust passages 52. Of the three independent exhaust passages 52, two independent exhaust passages 52 are connected to the exhaust ports 18 of the plurality of cylinders 12 whose exhaust order is not continuous. In FIG. 19, from the right side of the drawing, the independent exhaust passage 52 connected to the exhaust ports 18 of the first cylinder and the fourth cylinder, and the independent exhaust passage 52 connected to the exhaust ports 18 of the second cylinder and the fifth cylinder. The independent exhaust passage 52 connected to the exhaust port 18 of the third cylinder is bundled and connected to the mixing pipe 50. In FIG. 20, from the right side in the drawing, the independent exhaust passage 52 connected to the exhaust ports 18 of the first cylinder and the fifth cylinder and the independent exhaust passage 52 connected to the exhaust ports 18 of the third cylinder and the fourth cylinder. The independent exhaust passage 52 connected to the exhaust port 18 of the second cylinder is bundled and connected to the mixing pipe 50. In the case of a five-cylinder engine, as an aspect of bundling three independent exhaust passages 52, in addition to FIG. 19 and FIG. 20, it is connected to the exhaust ports 18 of the second and fifth cylinders from the right side in the drawing. There is a mode in which the independent exhaust passage 52, the independent exhaust passage 52 connected to the exhaust ports 18 of the third and fourth cylinders, and the independent exhaust passage 52 connected to the exhaust port 18 of the first cylinder are bundled. . Among these, the embodiment of FIG. 19 is more preferable from the viewpoint that the independent exhaust passages 52 are symmetric and the exhaust passages have the same volume on the left and right sides, and an advantageous result is obtained in terms of the ejector effect. .

  In the present embodiment, for example, in the case of a four-cylinder engine, two or three independent exhaust passages 52 are bundled and connected to the mixing pipe 50, and the sectional shape of the downstream end of each independent exhaust passage 52 is 180 ° or 120 °. It is formed in a substantially fan shape. Further, for example, in the case of a 5-cylinder engine, three independent exhaust passages 52 are bundled and connected to the mixing pipe 50, and the cross-sectional shape of the downstream end of each independent exhaust passage 52 is formed in a substantially fan shape of 120 °.

  The shape (fan shape) of the nozzle that is the opening at the downstream end of the independent exhaust passage 52 may be formed only at the downstream end of the independent exhaust passage 52, or formed from the downstream end to the upstream side by a predetermined length. May be. Further, the circular shape formed by collecting the fan shapes may be formed only at the downstream end of the independent exhaust passage 52 (when each independent exhaust passage 12 gathers only at the connection portion with the mixing pipe 50), or , And may be formed from the downstream end to the upstream side by a predetermined length (each independent exhaust passage 12 gathers from the downstream end by a predetermined length upstream, and in that state extends downstream to connect to the mixing pipe 50. If you want to).

  The fan-shaped center of gravity (nozzle center) X of the nozzle is the sector-shaped center of gravity in FIG. 12C, but the sector-shaped center of gravity X represents the center of the flow of exhaust gas ejected from the downstream end of the independent exhaust passage 52. As long as it is considered that the axial center L2 of the downstream portion of the independent exhaust passage 52 passing through the fan-shaped center of gravity X represents the flow direction of the exhaust gas ejected from the downstream end of the independent exhaust passage 52, The sector-shaped center of gravity X is not limited to the sector-shaped center of gravity. For example, the position can be set to a half of the sector radius on a line segment that divides the sector opening angle into two.

  The mixing tube 50 may include only the collecting portion 56 in which the flow area is reduced (the straight portion 57 and the diffuser portion 58 are not provided), and includes only the collecting portion 56 and the diffuser portion 58 in which the flow area is increased. A thing (thing without the straight part 57) may be sufficient. The ejector effect can be obtained even when the mixing tube having such a configuration is used. For example, when the mixing tube 50 is shortened due to layout restrictions during mass production design, the mixing tube including only the collecting portion 56 or the straight portion is omitted and the collecting portion 56 and the diffuser portion 58 are directly and smoothly curved. It can be set as the mixing tube of the shape which connects.

  The center of the circle formed by the assembly of the sectors may not necessarily coincide with the axis L1 of the mixing tube 50. For example, the center of the circle may be slightly deviated from the axis L1 of the mixing tube 50. As a result, the ejector effect can be obtained even when the flow velocity distribution of the exhaust gas at the nozzle at the downstream end of the independent exhaust passage 52 is biased due to the influence of the bending of the independent exhaust passage 52 upstream from the mixing pipe 50. Can be increased.

DESCRIPTION OF SYMBOLS 1 Engine main body 5 Exhaust manifold 12 Cylinder 17 Intake port 18 Exhaust port 19 Intake valve 20 Exhaust valve 30 Intake valve drive mechanism (valve drive means)
40 Exhaust valve drive mechanism (valve drive means)
50 Mixing pipe 52 Independent exhaust passage 56 Collecting part 57 Straight part L1 Shaft core of the mixing pipe L2 Shaft core downstream of the independent exhaust passage X Fan-shaped center of gravity Y, Z Intersection

Claims (5)

An exhaust device for a multi-cylinder engine having a plurality of cylinders provided with an intake valve capable of opening and closing an intake port and an exhaust valve capable of opening and closing an exhaust port,
A plurality of independent exhaust passages connected to the exhaust ports of one cylinder or a plurality of cylinders whose exhaust order is not continuous, and exhaust gas that is connected to the downstream ends of the independent exhaust passages and passes through the independent exhaust passages flows in. An exhaust manifold having a mixing tube;
The mixing tube has at least a collecting portion in which a flow path area decreases from the upstream side toward the downstream side,
The cross-sectional shape of the downstream end of each independent exhaust passage in the direction orthogonal to the axis of the mixing tube is formed in the same substantially fan shape,
The downstream ends of the independent exhaust passages are connected to the upstream end of the collecting portion of the mixing pipe in a state where the independent exhaust passages are bundled so that the sectors are gathered to form a substantially circle
The axis of the downstream portion of the independent exhaust passage passing through the sector-shaped center of gravity is inclined with respect to the axis of the mixing tube so that the downstream side is closer to the axis of the mixing tube,
In addition, in a predetermined operating region, the opening period of the exhaust valve and the opening period of the intake valve of each cylinder overlap each other for a predetermined period, and the overlap of the preceding cylinders between the cylinders in which the exhaust sequence is continuous An exhaust system for a multi-cylinder engine, comprising valve drive means for driving an intake valve and an exhaust valve of each cylinder so that an exhaust valve of a subsequent cylinder opens during the period. The exhaust system for a multi-cylinder engine according to claim 1,
An exhaust system for a multi-cylinder engine, wherein a downstream area of each independent exhaust passage has a smaller flow path area toward the downstream side. The exhaust system for a multi-cylinder engine according to claim 1 or 2,
The multi-cylinder engine is characterized in that the mixing tube has a straight portion on the axial center thereof on the downstream side of the collecting portion and maintaining a flow passage area at the downstream end of the collecting portion and extending downstream. Exhaust system. The exhaust system for a multi-cylinder engine according to any one of claims 1 to 3,
An exhaust system for a multi-cylinder engine, characterized in that the center of the circle formed by gathering the sector shapes coincides with the axial center of the mixing pipe. The multi-cylinder engine exhaust system according to any one of claims 1 to 4,
The engine is an engine with 4 or more cylinders,
At least one of the independent exhaust passages is an independent exhaust passage connected to exhaust ports of a plurality of cylinders whose exhaust order is not continuous.