JP5817302B2 - Intake and exhaust system for multi-cylinder engine - Google Patents

Description

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

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

  For example, Patent Document 1 is a device having a turbocharger, which is connected to an exhaust port of each cylinder and independent from each other, and an independent passage provided upstream of the turbocharger. Are provided, and a valve provided in the collecting portion and capable of changing the flow area of each independent passage is disclosed. In this apparatus, the flow area of the independent exhaust passage is reduced by the valve, so that the exhaust of the cylinder in the exhaust stroke flows from the predetermined independent passage into the collecting portion at a relatively high speed. The amount of gas supplied to the turbocharger by causing the negative pressure generated in the surrounding area to act on another independent passage in the collecting portion and sucking the exhaust gas in the other independent passage downstream by the so-called ejector effect. To increase the engine output.

JP 2009-97335 A

  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 intake / exhaust device for a multi-cylinder engine that can increase the intake air amount with a simple configuration and increase the engine output.

In order to solve the above problems, the present invention provides a plurality of cylinders each having an intake port and an exhaust port and provided with an intake valve capable of opening and closing the intake port and an exhaust valve capable of opening and closing the exhaust port. And an independent exhaust passage connected to exhaust ports of one cylinder or a plurality of cylinders whose exhaust order is not continuous with each other, and a gas passing through each of the independent exhaust passages is gathered And a valve drive means capable of driving the intake valve and the exhaust valve of each cylinder, the valve drive means at least rotating the engine In the low-speed and high-load region where the engine load is lower than a preset predetermined rotational speed and the engine load is higher than a preset predetermined load, the intake air of each cylinder Between the cylinders in which the valve opening period and the exhaust valve opening period overlap with each other by a predetermined overlap period and the exhaust sequence continues, the exhaust valve of the other cylinder opens during the overlap period of one cylinder. The intake valve and the exhaust valve of each cylinder are driven so as to overlap each other, and the downstream end and the collecting portion of each independent exhaust passage pass from the exhaust port of each cylinder through the downstream end of the independent exhaust passage. As the exhaust gas is discharged to the collecting portion, the shape of the flow path area becomes smaller toward the downstream side so that a negative pressure is generated in the exhaust port connected to another adjacent independent exhaust passage by the ejector effect. The downstream ends of the independent exhaust passages are arranged in a circumferential direction of a circle centering on the axis of the collecting portion in a state where the downstream ends of the independent exhaust passages connected to the cylinders in which the exhaust order is continuous are adjacent to each other. Arrange them evenly Together are, the and the axis of each downstream end connected to the collecting part to be inclined in a direction toward the axis of the collecting part according to the respective toward the downstream, from said downstream end of said respective independent exhaust passages A part of the inner peripheral surface of the collective portion is a part of each independent exhaust passage so that the exhaust jet discharged to the collective portion can flow down in a state of sticking to the inner peripheral surface of the collective portion. It extends downstream from a position substantially coincident with a part of the downstream end of the inner peripheral surface, and the part is inclined at substantially the same angle as the inclination angle of the axis of the downstream end of each independent exhaust passage. An intake / exhaust device for a multi-cylinder engine is provided.

  According to the present invention, each independent exhaust passage and the collecting portion are configured so as to obtain the ejector effect, and the exhaust valves of other cylinders are opened during the overlap period of a predetermined cylinder in the low speed and high load region. Therefore, at least in this low speed and high load region, negative pressure can be generated in the exhaust port of the cylinder during the overlap period by the ejector effect, and scavenging during the overlap period can be promoted by this negative pressure.

  In the present invention, the inner peripheral surface of the collecting portion extends downstream from a position where a part of the inner peripheral surface substantially coincides with a part of the inner peripheral surface of the downstream end of each independent exhaust passage. The portion is inclined at substantially the same angle as the inclination angle of the axis of the downstream end of each independent exhaust passage. For this reason, exhaust gas can flow down in the collecting portion while being stuck to a part of the inner peripheral surface of the collecting portion, and the exhaust gas spreads in a direction perpendicular to the axis of the collecting portion. It is possible to more reliably avoid the situation in which the exhaust gas speed decreases and the exhaust speed decreases due to the collision with the inner peripheral surface of the collecting portion. Further, by suppressing the decrease in the exhaust speed, the higher ejector effect, that is, the amount of negative pressure in the exhaust port can be increased, and thereby high scavenging performance can be realized.

  As a specific configuration of the downstream end of each independent exhaust passage and the collecting portion, the downstream end of each independent exhaust passage is substantially the whole of the downstream end on the circumference of a circle centering on the axis of the collecting portion. The upstream end of the inner peripheral surface of the collective portion has a circular shape that substantially matches the circle formed by the entire downstream end of each independent exhaust passage, and the inner peripheral surface of the collective portion Examples of the surface include those having a substantially frustoconical surface centered on the axis of the aggregate portion (claim 2).

  Here, each of the independent exhaust passages and the collective portion has a diameter of a perfect circle having the same area as the flow passage area at the downstream end of each of the independent exhaust passages, and the flow passage area at the downstream end of the collective portion. Assuming that the diameter of a perfect circle having the same area as D is D, the higher the a / D, the higher the ejector effect can be obtained. However, a / D increases to 0.7 or more and is discharged from the downstream end of the independent exhaust passage. When the flow path area at the downstream end of the collecting portion through which the exhaust passes is very small, the exhaust collides with the inner peripheral surface of the collecting portion as it spreads in the direction perpendicular to the axial direction in the collecting portion. Therefore, if the present invention is applied at a / D ≧ 0.7, the collision can be avoided and a high ejector effect and consequently high scavenging performance can be realized (claim 3).

1 is a schematic configuration diagram of an engine system including an intake / 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 the III-III sectional view taken on the line of FIG. It is the IV-IV sectional view taken on the line of FIG. It is a figure for demonstrating the valve timing of an intake valve and an exhaust valve. It is a figure for demonstrating the valve-opening timing and valve-closing timing of an intake valve and an exhaust valve which concern on embodiment of this invention. It is a figure for demonstrating the subject of this invention. It is the figure which showed the speed distribution of the exhaust_gas | exhaustion vicinity of the collection part which concerns on embodiment of this invention.

  An embodiment of an exhaust device for a multi-cylinder engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an engine system 100 including an intake / exhaust device for the multi-cylinder engine. FIG. 2 is a partially enlarged view of FIG. 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.

  The engine body 1 and the intake pipe 3 will be described.

  A plurality of cylinders 12 into which pistons are respectively inserted are formed in the cylinder head 9 and the cylinder block. In the present 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. 5, the cylinders 12a to 12d are ignited by the spark plug 15 at a timing shifted by 180 ° C. A, and the intake stroke and the compression stroke are performed. The expansion stroke and the exhaust stroke are each shifted by 180 ° C. A. 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 that open 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 these exhaust ports 18 to communicate or block these exhaust ports 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 includes an intake camshaft 31 and an intake VVT 32 connected to the intake valve 19. 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 The valve timing of the intake valve 19 is changed by changing the phase difference from the camshaft 31. 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. A hydraulic mechanism that changes the phase difference, an electromagnetic mechanism that has an electromagnet provided between the driven shaft and the intake camshaft 31, and changes the phase difference by applying electric power to the electromagnet, etc. Is mentioned. 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 changes the valve timing of the exhaust valve 20 by changing the phase difference between the exhaust camshaft 41 and the crankshaft, and the exhaust camshaft 41 connected to the exhaust valve 20 and the crankshaft. And an exhaust VVT 42 to be used. 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 to drive the exhaust valve 20 to open and close 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 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.

  Next, the exhaust manifold 5 will be described.

  The exhaust manifold 5 includes, in order from the upstream side, three independent exhaust passages 52, a collecting portion 56, and a mixing portion 57 and a diffuser portion 58 arranged coaxially with the collecting portion 56.

  Each independent exhaust passage 52 is connected to the exhaust port 18 of each cylinder 12. Specifically, in the cylinder 12, the exhaust port 18 of the first cylinder 12a and the exhaust port 18 of the fourth cylinder 12d are individually connected to the independent exhaust passages 52a and 52d, respectively. On the other hand, the exhaust ports 18 of the second cylinder 12b and 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, so that the structure is simplified. It is connected to one independent exhaust passage 52b. More specifically, the independent exhaust passage 52b connected to the exhaust port 18 of the second cylinder 12b and the third cylinder 12c is formed on the upstream side of the second cylinder 12b, and one of the second cylinders 12b is connected to the second cylinder 12b. The exhaust port 18 is connected to the other end, and the exhaust port 18 of the third cylinder 12c is connected to the other end. In the present embodiment, the independent exhaust passage 52 corresponding to the exhaust port 18 of the second cylinder 12b and the third cylinder 12c is linearly opposed to the central portion of the cylinders 12b and 12c, that is, the substantially central portion of the engine body 1. The independent exhaust passages 52 corresponding to the exhaust ports 18 of the other cylinders 12a and 12d are independent exhausts corresponding to the second cylinder 12b and the third cylinder 12c from positions corresponding to the corresponding exhaust ports 18. It extends curvedly toward the passage 52.

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

  Each of the independent exhaust passages 52 and the collective portions 56 are arranged around the high-speed exhaust as the exhaust is ejected from the independent exhaust passages 52 at a high speed and the exhaust flows into the collective portion 56 at a high speed. Due to the generated negative pressure action, that is, the ejector effect, negative pressure is generated in another adjacent independent exhaust passage 52 and the exhaust port 18 communicating with the independent exhaust passage 52, and the gas in the exhaust port 18 is sucked downstream. It has such a shape.

  Specifically, each of the independent exhaust passages 52 has a shape in which the flow passage area decreases toward the downstream side so that the exhaust gas is ejected from each independent exhaust passage 52 into the collecting portion 56 at a high speed. Yes. In this embodiment, as shown in FIG. 3, each independent exhaust passage 52 is reduced in cross-sectional area from the upstream portion having a substantially elliptical cross section toward the downstream, and at the downstream end of the upstream portion. It has a sector shape that is approximately 1/3 of the elliptical cross-sectional area. The independent exhaust passages 52 are aggregated and connected to the collective portion 56 so that their downstream ends forming a sector shape are adjacent to each other to form a substantially circular cross section as a whole.

  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. The inner peripheral surface of the collecting portion 56 is inclined in a direction approaching the axis L1 of the collecting portion 56 as it goes downstream. In the present embodiment, the inner peripheral surface of the collecting portion 56 has a truncated cone shape that decreases in diameter toward the downstream.

  Here, when the jet of exhaust discharged from each independent exhaust passage 52 to the collecting portion 56 flows into the collecting portion 56 and spreads in a direction perpendicular to the axis L1 of the collecting portion 56, the present inventors As shown in FIG. 7, the exhaust speed decreases due to the expansion, that is, the expansion, and the exhaust speed collides with the inner peripheral surface of the collecting portion 56, and the upstream speed decreases. It was discovered that the flow direction was changed as a result of re-squeezing on the downstream side after expanding, and the resistance increased. The diameter of a perfect circle having the same area as the cross-sectional area of the downstream end of the independent exhaust passage 52 is a (see FIG. 2), and the same area as the flow path area of the downstream end of the collecting portion 56 and the mixing portion 57 is used. Assuming that the diameter of a perfect circle is D (see FIG. 2), the higher the a / D, the higher the ejector effect can be obtained. On the other hand, when a / D is set in the range of 0.7 or more, It was determined that a collision occurred and the exhaust speed decreased. This reduction in the exhaust speed in the collecting portion 56 reduces the scavenging performance by reducing the ejector effect, that is, the force for sucking the exhaust in the other exhaust port 18 downstream.

  Therefore, the inventors flow down the exhaust jet flow discharged from the downstream end of each independent exhaust passage 52 to the collecting portion 56 in a state of being stuck to the inner peripheral surface of the collecting portion 56 while a / D ≧ 0.7. In this way, the spread of the exhaust is suppressed to suppress the decrease in the exhaust speed, thereby ensuring a high ejector effect and thus a high scavenging performance. That is, the present inventors have used the Coanda effect that a flow is attracted to the object when the object is arranged around the flow.

  Specifically, a part of the upstream end of the inner peripheral surface of the collecting part 56 and a part of the downstream end of the inner peripheral surface of each independent exhaust passage 52 are substantially matched, and the collecting part with respect to the axis L1 of the collecting part 56 The inclination angle γ (see FIG. 2) of the inner peripheral surface of 56 and the inclination angle α (see FIG. 2) of the axis L2 at the downstream end of each independent exhaust passage 52 with respect to the axis L1 of the collecting portion 56 are substantially matched. A part of the collecting portion 56 is inclined at the same angle from the downstream end of the independent exhaust passage 52, and is configured to extend continuously.

  In the present embodiment, the circle formed at the entire downstream end of each independent exhaust passage 52 is configured to substantially coincide with the circle at the upstream end of the inner peripheral surface of the collecting portion 56.

  Here, the amount of radial deviation between the circle formed by the entire downstream end of the independent exhaust passage 52 and the circle at the upstream end of the inner peripheral surface of the collective portion 56 corresponding thereto is the downstream of each independent exhaust passage 52. The exhaust jet flow discharged from the end to the collecting portion 56 can be appropriately set as long as it can flow down in a state of sticking to the inner peripheral surface of the collecting portion 56. For example, in the example shown in FIG. 2, as shown in FIG. 4, which is a sectional view taken along the line IV-IV in FIG. 2, the downstream of the independent exhaust passage 52 is lower than the circle C <b> 1 at the upstream end of the inner peripheral surface of the collecting portion 56. The circle C2 constituted by the ends has a larger diameter. Specifically, when the inner diameter of the circle C1 at the upstream end of the collecting portion 56 is set to 51 mm, the circle C1 at the upstream end of the inner peripheral surface of the collecting portion 56 is the downstream end of the independent exhaust passage 52. It is set to the outside in the radial direction by about 2 mm from the constructed circle C2. However, if the collecting portion 56 is located radially inward from the downstream end of each independent exhaust passage 52, the upstream end of the collecting portion 56 may hinder the flow of exhaust into the collecting portion 56. The collecting portion 56 is preferably located at the downstream end of each independent exhaust passage 52 or at the radially outer side.

  Further, the amount of deviation between the inclination angle γ of the inner peripheral surface of the collecting portion 56 and the inclination angle α of the downstream end of each independent exhaust passage 52 is also the exhaust discharged to the collecting portion 56 from the downstream end of each independent exhaust passage 52. The jet flow can be set as appropriate as long as it can flow down in a state of sticking to the inner peripheral surface of the collecting portion 56. However, the inclination angle of the collecting portion 56 when the inclination angle with respect to the axis L1 of the collecting portion 56 of the radially outer portion of the inner peripheral surface of each independent exhaust passage 52 and extending on the circumference is β. If γ is larger than the inclination angle β, when the exhaust jet flows into the collecting portion 56, it may collide with the inner peripheral surface of the collecting portion 56 and reduce the exhaust speed. Therefore, the inclination angle γ of the collecting portion 56 is preferably smaller than the inclination angle of the radially outer portion of each independent exhaust passage 52. In the example shown in FIG. 2, when the inclination angle of the radially outer portion of the inner peripheral surface of each independent exhaust passage 52 with respect to the axis L1 of the collective portion 56 is β, the inclination angle γ of the inner peripheral surface of the collective portion 56 Is set so as to substantially satisfy γ = (α + β) / 2.

In the example shown in FIG. 2, the dimensions are set as follows. The diameter of the circle formed at the entire downstream end of each independent exhaust passage 52 is set to 47 mm. The downstream end of each independent exhaust passage 52 is set so that the diameter a of a perfect circle having the same area as the cross-sectional area is 25 mm. As described above, the diameter of the upstream end of the collecting portion 56 is set to 51 mm, which is larger than the circle formed at the downstream end of the independent exhaust passage 52. The downstream end of the collective portion 56 is set so that the diameter D of a perfect circle having the same area as the cross-sectional area is 29 mm. The inclination angle α of the axis L2 at the downstream end of each independent exhaust passage 52 with respect to the axis L1 of the collecting portion 56 is set to 7 degrees. The inclination angle β of the portion extending on the circumference of the inner peripheral surface of each independent exhaust passage 52 with respect to the axis L1 of the collecting portion 56 is set to 14 degrees. Accordingly, the inclination angle γ with respect to the axis L1 of the gathering portion 56 is set to 10 degrees.

  FIG. 8 shows the state of the exhaust flow in each independent exhaust passage 52 and the collecting portion 56 according to the present embodiment configured as described above, specifically, the result of examining the exhaust velocity distribution.

  As shown in FIG. 8, in the present embodiment, the exhaust jet discharged from each independent exhaust passage 52 is stuck to the inner peripheral surface of the collective portion 56 without spreading in a direction orthogonal to the axis L1 of the collective portion 56. It is flowing down. And it is avoided that an exhaust jet collides with the surface on the opposite side to the ejection location of an exhaust jet among the inner peripheral surfaces of the gathering part 56, and the resistance is kept small and the speed is kept high. It is flowing down.

  The mixing portion 57 connected to the downstream end of the collecting portion 56 configured as described above has a substantially cylindrical shape. And the said diffuser part 58 connected to the downstream end of this mixing part 57 has a shape which a flow-path area expands, so that it goes downstream. The high-speed exhaust discharged from the collecting unit 56 recovers pressure by passing through the mixing unit 57 and the diffuser unit 58. In the present embodiment, the diffuser portion 58 has a truncated cone shape whose diameter increases toward the downstream side.

  Next, the catalyst device 6 will be described.

  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 the upstream / downstream 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.

  Next, the ECU 2 will be described.

  The ECU 2 can control the valve timing of the intake valve 19 and the exhaust valve 20. The ECU 2 calculates current operating conditions based on signals from various sensors, and controls the valve timings of the intake valve 19 and the exhaust valve 20 so as to become pre-stored target valve timings according to the operating conditions. .

  The target valve timings of the intake valve 19 and the exhaust valve 20 are such that the valve opening period of the exhaust valve 20 and the valve opening period of the intake valve 19 overlap with the intake top dead center (TDC) in the entire operation range, In addition, the exhaust valve 20 is set to start opening during the overlap period T_O / L of the other cylinders 12. Specifically, as shown in FIG. 5, the exhaust valve 20 of the third cylinder 12c opens during the period in which the intake valve 19 and the exhaust valve 20 of the first cylinder 12a overlap, and the third cylinder During the period in which the intake valve 19 and the exhaust valve 20 of 12c overlap, the exhaust valve 20 of the fourth cylinder 12d opens, and the intake valve 19 and the exhaust valve 20 of the fourth cylinder 12d overlap. The exhaust valve 20 of the second cylinder 12b is opened during the period, and the exhaust valve 20 of the first cylinder 12a is opened while the intake valve 19 and the exhaust valve 20 of the second cylinder 12b overlap. It is set to do.

  In the engine system 100, the valve opening timing and the valve closing timing of the intake valve 19 and the exhaust valve 20, respectively, are as follows. As shown in FIG. It is a time of falling, for example, a time of 0.4 mm lift.

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

  When an exhaust valve 20 of a predetermined cylinder 12 (hereinafter referred to as an exhaust stroke cylinder 12 as appropriate) is opened, 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.

  In the engine system 100, as described above, the independent exhaust passage 52 and the collecting portion 56 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 passage 52 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 to the downstream side. Then, during an overlap period of a predetermined cylinder 12 (intake stroke cylinder), the exhaust valve 20 of another cylinder 12 (exhaust stroke cylinder) whose exhaust order is set to one after this intake stroke cylinder 12 opens. Is set to

  Accordingly, as the exhaust valve 20 of the exhaust stroke cylinder 12 opens 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, thereby promoting scavenging in the intake stroke cylinder 12 during the overlap period.

  In the present embodiment, as described above, the exhaust jet discharged from each independent exhaust passage 52 flows down in a state of being stuck to the inner peripheral surface of the collective portion 56 without spreading in a direction perpendicular to the axis L1 of the collective portion 56. Thus, the exhaust gas flows through the collecting portion 56 at a high speed. Therefore, a higher ejector effect, that is, a higher engine output can be obtained.

Here, in the above-described embodiment, control is performed so that the intake valve 19 and the exhaust valve 20 overlap in the entire operation region, and the valve opening start timing of the exhaust valve 20 of the other cylinder 12 overlaps this overlap period. as has been described to implement this control, the engine rotational speed is lower than a predetermined rotational speed, and performs only a high low-speed and high-load area than a predetermined load load of the engine is set in advance It may be. That is, in the operating region where the engine speed is high, the exhaust gas flow rate increases, so that the scavenging promotion effect obtained by reducing the pump loss may be higher than the scavenging promotion effect obtained by the ejector effect. Therefore, in such a case, it is preferable to control the intake valve 19 and the exhaust valve 20 so that the scavenging promotion effect can be further enhanced.

  Further, as described above, in order to reduce the pump loss in the operation region where the engine speed is high, the region from the region where the flow area is reduced in each of the independent exhaust passages 52 to the downstream portion of the diffuser portion 58 is bypassed. The passage is shaped so that the flow area is constant and the exhaust resistance is not increased, and a valve for opening and closing the passage is attached to the passage so that the valve is operated in the operating region where the engine speed is low. It is possible to configure so that the exhaust passes only through the independent exhaust passage 52 and opens the valve in an operating region where the engine speed is high so that the exhaust also passes through the bypass passage side. .

DESCRIPTION OF SYMBOLS 1 Engine main body 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)
52 Independent exhaust passage 56 Assembly

Claims (3)

An intake / exhaust device for a multi-cylinder engine having a plurality of cylinders each having an intake port and an exhaust port, and provided with an intake valve capable of opening and closing the intake port and an exhaust valve capable of opening and closing the exhaust port. ,
An independent exhaust passage connected to exhaust ports of one cylinder or a plurality of cylinders whose exhaust sequences are not continuous with each other;
A collecting portion connected to the downstream end of each independent exhaust passage so that the gas that has passed through each independent exhaust passage gathers;
Valve drive means capable of driving the intake valve and the exhaust valve of each cylinder,
Said valve driving means, at least at high low speed and high load region than predetermined load the load on the lower engine than a predetermined rotational speed rotational speed is set in advance of the engine is set in advance, the intake valves of the respective cylinders Between the cylinders in which the valve opening period and the exhaust valve opening period overlap with each other by a predetermined overlap period and the exhaust sequence continues, the exhaust valve of the other cylinder opens during the overlap period of one cylinder. Drive the intake and exhaust valves of each cylinder so that they overlap at the same time,
The downstream end of each independent exhaust passage and the collective portion are connected to another independent adjoining by an ejector effect as exhaust is discharged from the exhaust port of each cylinder through the downstream end of the independent exhaust passage to the collective portion. In order to generate a negative pressure in the exhaust port connected to the exhaust passage, the flow path area has a shape that decreases toward the downstream side,
The downstream ends of the independent exhaust passages are evenly arranged in the circumferential direction of a circle centering on the axis of the collecting portion in a state where the downstream ends of the independent exhaust passages connected to the cylinders in which the exhaust order is continuous are adjacent to each other. And is connected to the collective portion so as to incline in a direction closer to the axial line of the collective portion as the axis of each downstream end goes downstream.
The inner peripheral surface of the collective portion is arranged so that the exhaust jet discharged from the downstream end of each independent exhaust passage can flow down in a state of sticking to the inner peripheral surface of the collective portion. A part extends downstream from a position substantially coincident with a part of the downstream end of the inner peripheral surface of each independent exhaust passage, and the part is inclined by the axis of the downstream end of each independent exhaust passage. An intake / exhaust device for a multi-cylinder engine, which is inclined at substantially the same angle as the angle. The intake / exhaust device for a multi-cylinder engine according to claim 1,
The downstream ends of the independent exhaust passages are arranged on the circumference of a circle centered on the axis of the collecting portion so as to form a substantially circular shape throughout the downstream ends,
The upstream end of the inner peripheral surface of the gathering portion presents a circle that substantially matches the circle formed by the entire downstream end of each independent exhaust passage,
An intake / exhaust device for a multi-cylinder engine, wherein an inner peripheral surface of the collective portion has a substantially truncated cone shape centering on an axis of the collective portion. The multi-cylinder engine intake / exhaust device according to claim 1 or 2,
Each of the independent exhaust passages and the collecting portion has a diameter of a perfect circle having the same area as the flow passage area at the downstream end of each of the independent exhaust passages, and has the same area as the flow passage area at the downstream end of the collecting portion. An intake / exhaust device for a multi-cylinder engine having a shape in which a / D is 0.7 or more, where D is the diameter of a perfect circle having

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