JP5472050B2 - Exhaust system for multi-cylinder engine - Google Patents

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 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. In particular, in an engine system in which a structure without a turbocharger is simplified, it is required to increase the engine output with a simple configuration. .

  In view of such circumstances, it is an object of the present invention to provide an exhaust device for a multi-cylinder engine that can increase the engine output by increasing the intake air amount with a simple configuration.

  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. An exhaust system for a multi-cylinder engine having a plurality of cylinders connected to exhaust ports of one cylinder or a plurality of cylinders whose exhaust sequences are not continuous with each other and separated into a low speed side passage and a high speed side passage at least downstream A plurality of independent exhaust passages, connected to the downstream ends of the respective low speed side passages, communicated with the respective low speed side passages, and gathered exhaust passing through the respective low speed side passages, A high-speed side collecting portion connected to the downstream end of the high-speed side passage, communicating with the high-speed side passages, and collecting exhaust passing through the high-speed side passages; A variable flow area variable valve provided in a path and capable of changing a flow area of each high-speed side path, a variable flow area valve driving means that can open and close the variable flow area valve, and each cylinder Valve driving means capable of driving an intake valve and an exhaust valve, and among the low speed side passages, low speed side passages connected to cylinders in which the exhaust order is continuous are connected to the low speed side collecting portion at positions adjacent to each other. Each of the low-speed side passages and the low-speed side collective portion is negatively affected by the ejector effect as exhaust gas is discharged from each cylinder through the low-speed side passages to the low-speed side collective portion. The valve driving means has a valve opening period of an intake valve and an exhaust valve of each cylinder in a low speed region where the engine speed is lower than a preset reference speed. Toga Each cylinder is overlapped so that the overlap period of one cylinder and the time when the exhaust valve of the other cylinder is opened overlap between cylinders in which the exhaust sequence continues. The intake valve and the exhaust valve are driven, and the flow passage area variable valve driving means fully opens the flow passage area variable valve in a high load region where a required torque for the multi-cylinder engine is higher than a predetermined value in the low speed region. The flow rate of the exhaust gas passing through the high speed side passage is reduced to a smaller value, while in the high speed region where the engine speed is higher than the reference rotational speed, the flow path area variable valve is fully opened to open the high speed side passage. And the adjacent high-speed side passages extending along the flow direction of the exhaust gas discharged from the downstream ends of the respective high-speed passages to the high-speed side collecting portion. The intersection angle between the roads is the intersection between the adjacent low speed side passages of the downstream end axis extending along the flow direction of the exhaust discharged from the downstream end of each low speed side passage to the low speed side collecting portion. Provided is an exhaust device for a multi-cylinder engine, which is set to be larger than an angle.

  According to the present invention, the scavenging in the cylinder can be promoted by effectively using the ejector effect in the low speed region, the exhaust resistance can be suppressed to a small value in the high speed region, and the intake efficiency is increased in the entire speed region. Engine output can be increased.

  Specifically, in this configuration, in the low-speed region, the high-speed side passage is shut off to allow exhaust to pass through the low-speed side passage configured to obtain the ejector effect, and during the overlap period of a predetermined cylinder Since the exhaust valves of the other cylinders are opened, the exhaust ports of the cylinders in the overlap period due to the ejector effect as high-speed exhaust is ejected from a predetermined independent exhaust passage when the exhaust valve is opened. Thus, a negative pressure can be generated, and residual gas in the cylinder can be sucked out to the exhaust port side, and scavenging in the cylinder in the overlap period, that is, in the cylinder in the intake stroke can be promoted.

  And in this configuration, in the high speed region where the exhaust resistance may increase due to the large flow rate of the exhaust, the high speed side passage is opened and the exhaust is discharged to the high speed side passage in addition to the low speed side passage. The exhaust resistance can be kept small.

  In addition, in this configuration, the crossing angle between the adjacent high speed side passages extending along the flow direction of the exhaust gas discharged from the downstream end of each high speed side passage to the high speed side collecting portion is set large. Therefore, the exhaust discharged from the downstream end of the predetermined high-speed side passage to the high-speed side collecting portion is sent to the high-speed side collecting portion as compared with the case where the crossing angle is small and each high-speed side passage is in a posture closer to parallel. In addition, it can proceed more easily toward the other high speed side passages, that is, the exhaust gas can be discharged into the high speed side collecting portion with less resistance. Therefore, in the high speed region where the exhaust passes through the high speed side passage, it is possible to further reduce the exhaust resistance and promote scavenging in the cylinder.

  On the other hand, since the crossing angle between the adjacent low speed side passages of the axis of the downstream end extending along the flow direction of the exhaust gas discharged from the downstream end of each low speed side passage to the low speed side collecting portion is set. Further, it is possible to suppress the exhaust discharged from the downstream end of the low speed side passage to the low speed side collecting portion from proceeding to another low speed side passage. That is, it is possible to suppress the expansion of the exhaust gas at the low-speed side collecting portion and to cause the exhaust gas to flow down through the low-speed side collecting portion at a higher speed. Therefore, in the low speed region where the exhaust passes through the low speed side passage, the higher ejector effect, that is, the negative pressure generated around the exhaust and thus the exhaust port as the exhaust passes through the low speed side collecting portion at high speed. The amount can be increased, and scavenging in the cylinder can be more reliably promoted.

  As a specific value of the crossing angle between the adjacent low speed side passages of the axis of the downstream end extending along the flow direction of the exhaust gas discharged from the downstream end of each low speed side passage to the low speed side collecting portion. , Less than 30 degrees, and the intersection between adjacent high speed side passages of the axial center of the downstream end extending along the flow direction of the exhaust gas discharged from the downstream end of each high speed side passage to the high speed side collecting portion. Specific values of the angle include 30 degrees or more and 60 degrees or less (claim 2).

  The crossing angle of less than 30 degrees means that the crossing angle is 0 degrees, and the downstream end that extends along the flow direction of the exhaust gas discharged from the downstream end of each low speed side passage to the low speed side collecting portion. Including the case where the axial centers of these extend parallel to each other.

  Further, in the present invention, the high-speed side assembly portion has a shape having an outer surface surrounding an axis extending in the exhaust flow direction, and at least some of the downstream ends of the plurality of high-speed side passages are formed on the high-speed side assembly. It is preferable that it is connected to the outer surface of the part (Claim 3).

  In this way, the exhaust gas that flows into the high-speed side collecting portion from the predetermined high-speed side passage and travels downstream through the high-speed side collecting portion can more easily travel toward the other high-speed side passages. The exhaust resistance of the exhaust can be reduced, and scavenging in the cylinder can be further promoted.

  Here, as a specific configuration of the low-speed side passage for effectively obtaining the ejector effect, the low-speed side assembly portion has at least one flow path area of an upstream end and a downstream end of the low-speed side assembly. The low-speed side passage has a diameter a of a perfect circle having the same area as the flow-path area of the downstream end portion thereof, and the downstream of the low-speed-side assembly portion. Examples include a shape in which the relationship with the diameter D of a perfect circle having the same area as the end is a / D ≧ 0.5 (Claim 4).

  As described above, according to the present invention, the engine output can be increased by increasing the intake efficiency in the entire speed region.

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 figure which abbreviate | omitted the high speed side channel | path, the high speed side gathering part, etc. in FIG. It is the figure which abbreviate | omitted the low speed side channel | path, the low speed side gathering part, etc. in FIG. It is a schematic longitudinal cross-sectional view of the engine system corresponding to FIG. It is the VV sectional view taken on the line of FIG. It is a figure for demonstrating the valve opening timing and valve closing timing of an intake valve and an exhaust valve in the exhaust apparatus of the multicylinder engine which concerns on embodiment of this invention. It is a figure for demonstrating the valve timing of an intake valve and an exhaust valve.

  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 exhaust device for the multi-cylinder engine. The engine system 100 includes an engine body 1 having a cylinder head 9 and a cylinder block, an ECU 2 for engine control, an exhaust manifold 5 connected to the engine body 1, and a catalyst device 6 connected to the exhaust manifold 5. I have.

  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, and as shown in FIG. 6, 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 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 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 open and close the intake valve 19.

  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. 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 exhaust manifold 5 includes three independent exhaust passages 52, three flow area variable valves 58 and a high speed side collecting portion 57, a mixing pipe (low speed side collecting portion) 56a, a straight pipe 56b, and a diffuser 56c (see FIG. 2). ) And.

  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 separated into two passages on the upstream side thereof, and the second cylinder is provided in one of the two passages. The exhaust port 18 of 12b is connected, and the exhaust port 18 of the third cylinder 12c is connected to the other.

  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.

  Each of the independent exhaust passages 52 is separated into a high speed side passage 53 and a low speed side passage 54 on the downstream side thereof. In the present embodiment, as shown in FIG. 4, the low speed side passage 54 extends downstream along the independent exhaust passage 52 upstream from the separation point from the high speed side passage 53, and the high speed side passage is provided. 53, after curving upward from the low speed side passage 54, extends to the downstream side substantially parallel to the low speed side passage 54. Further, the high speed side passage 53 and the low speed side passage 54 corresponding to the exhaust ports 18 of the second cylinder 12b and the third cylinder 12c are linearly opposed to the central portion of these cylinders, that is, the substantially central portion of the engine body 1. The high speed side passage 53 and the low speed side passage 54 corresponding to the exhaust ports 18 of the other cylinders extend from the positions facing the corresponding exhaust ports 18 to the second cylinder 12b and the third cylinder 12c. It curves and extends toward the passages 52 and 54. The cross-sectional areas, that is, the flow areas of the respective high-speed passages 53 are set to be the same, and the cross-sectional areas, that is, the flow areas of the respective low-speed passages 54 are set to be the same.

  The mixing pipe 56a is connected to the downstream side of each low speed side passage 54, and the exhaust gas that has passed through each low speed side passage 54 gathers in the mixing pipe 56a. In the mixing pipe 56a, the three low speed side passages 54 are connected at positions where their downstream ends are adjacent to each other.

  Each of the low speed side passages 54 and the mixing pipes 56a has a negative pressure generated around the high speed exhaust gas as the exhaust gas is ejected from the low speed side passages 54 at a high speed and the exhaust gas passes through the mixing pipe 56a at a high speed. Due to the pressure action, that is, the ejector effect, the adjacent low speed side passage 54 and the exhaust port 18 corresponding to the low speed side passage 54 have a negative pressure, and the gas in the exhaust port 18 is sucked downstream. doing.

  In the present embodiment, each of the low-speed passages 54 has a shape in which the flow passage area decreases toward the downstream, and exhaust gas is ejected from each low-speed passage 54 at a high speed to the downstream side. ing. More specifically, as shown in FIG. 5, each low-speed passage 54 is reduced in cross-sectional area from the upstream portion having a substantially circular cross section toward the downstream, and at the downstream end, the circular shape of the upstream portion is reduced. It has a sector shape that is approximately 1/3 of the cross-sectional area. These low speed side passages 54 are aggregated and connected to the mixing pipe 56a so that each downstream end forming a fan shape forms a substantially circular cross section as a whole.

  Further, the crossing angles of the axial centers C1, C2, and C3 at the downstream ends of the low speed side passages 54 extending along the flow direction of the exhaust gas discharged from the low speed side passages 54 to the mixing pipe 56a, and adjacent low speeds. The crossing angle α (see FIG. 2) between the axial centers of the downstream ends of the side passages 54 is set to 7 degrees, and each low speed side passage 54 is connected to the mixing pipe 56a in a state of being nearly parallel. That is, in each low speed side passage 54, the exhaust discharged from the predetermined low speed side passage 54 to the mixing pipe 56 a does not travel toward the other low speed side passage 54, and the expansion of the exhaust gas in the mixing pipe 56 a and the exhaust gas are not detected. The speed reduction is configured to be kept small.

  The mixing tube 56a is a true circle having the same area as the cross-sectional area of the downstream end of the low speed side passage 54, with the diameter of a perfect circle having the same area as the flow path area at the downstream end being D1 (see FIG. 4). When the diameter of the circle is a (see FIG. 4), the shape is a / D = 0.65.

  Here, the specific structure of the mixing pipe 56a is not limited to the above, but the mixing pipe 56a has a shape in which the flow area of at least one of the upstream end and the downstream end is the smallest flow area, If a / D is set in the range of a / D ≧ 0.5, it is known that the exhaust passes through the mixing pipe 56a at a sufficiently high speed and the ejector effect is sufficiently obtained. What has the above shapes is preferable. In order to further increase the flow rate of the exhaust gas into the mixing pipe 56a, when a portion having a reduced flow area, that is, a throttle portion is provided at the downstream end of the low-speed side passage 54, the throttle portion The diameter of the channel area is preferably a, and the mixing tube 56a is preferably shaped so that a / D ≧ 0.5.

  The exhaust gas flowing into the mixing pipe 56a passes through the straight pipe 56b and the diffuser 56c and flows out downstream. The straight pipe 56c has the same cross-sectional shape as the downstream end of the mixing pipe 56a, that is, the shape extending to the downstream side with the same flow area, continuously from the mixing pipe 56a. The diffuser 56c continuously extends from the straight pipe 56b to the downstream side, and has a shape in which the diameter of the diffuser 56c increases toward the downstream and the flow passage area increases.

  On the other hand, the high-speed side collecting portion 57 is connected to the downstream side of each high-speed side passage 53, and the exhaust gas that has passed through each high-speed side passage 53 is collected in the high-speed side collecting portion 57. The high-speed side passage 53 and the high-speed side collecting portion 57 are different from the low-speed side passage 54 and the mixing pipe 56a in that the exhaust gas flowing from the high-speed side passage 53 into the high-speed side collecting portion 57 is easily expanded and the exhaust resistance is small. The shape is such that

  Specifically, the high speed side passage 53 has a shape extending downstream with a substantially constant flow area, and the flow area is larger than the flow area at the downstream end of the low speed passage 54. Is set. In the present embodiment, the flow area of one high speed side passage 53 is set to substantially match the total flow area of the downstream ends of the three low speed side passages 54. The high-speed side collecting portion 57 has a substantially cylindrical shape extending along the flow direction of the exhaust gas, and has a shape in which the flow path area is substantially constant throughout.

  Further, the crossing angles of the axial centers C11, C12, C13 at the downstream ends of the high speed side passages 53 extending along the flow direction of the exhaust gas discharged from the high speed side passages 53 to the high speed side collecting portion 57 are adjacent to each other. The crossing angle β (see FIG. 3) between the axial centers of the downstream ends of the high speed side passage 53 is set to 45 degrees, which is larger than the crossing angle α between the axial centers of the downstream ends of the low speed side passage 54. .

  In this manner, in the high speed side collecting portion 57, unlike the low speed side passage 54 side, the exhaust discharged from the predetermined high speed side passage 53 to the high speed side collecting portion 57 is directed toward the other high speed side passage 53 side. It is relatively easy to proceed so that expansion of the exhaust gas at the high-speed side gathering portion 57 is promoted, and as a result, exhaust resistance is further reduced. In particular, in the present embodiment, a high speed side passage 53 corresponding to the first cylinder 12a and a high speed side passage 53 corresponding to the fourth cylinder 12d are provided on the outer peripheral surface (outer surface) of the high speed side collecting portion 57 at each downstream end. Are connected so as to be substantially opposed to each other, and the exhaust discharged from the predetermined high-speed side passage 53 more easily proceeds toward the other high-speed side passage 53 side, and the exhaust resistance is effectively reduced. Has been.

  The flow passage area variable valve 58 is for changing the flow passage area of each high speed side passage 53 and thereby changing the flow passage area of each high speed side passage 53. Each of these flow path area variable valves 58 is provided in each high speed side passage 53.

  The flow path area variable valve 58 rotates about the rotation shaft 58a as the rotation shaft 58a provided at the center thereof is driven to rotate. In the present embodiment, a common rotation shaft 58a is fixed to each flow path area variable valve 58, and the three flow path area variable valves 58 rotate integrally. Each flow path area variable valve 58 extends in a direction substantially parallel to the exhaust flow direction and opens to the high speed side passage 53 (broken line in FIG. 4), and extends in a direction substantially perpendicular to the exhaust flow direction. It rotates between the fully closed position (solid line in FIG. 4) that blocks the passage 53, and opens and closes the high speed side passage 53 to change the flow area of the high speed side passage 53.

  The pivot shaft 58a is rotationally driven by a valve actuator (flow path area variable valve driving means) 58b provided at the end thereof. The valve actuator 58b rotates the pivot shaft 58a in accordance with the target opening degree of the flow path area variable valve 58 calculated by the ECU 2, and drives the flow path area variable valve 58 to the fully closed or fully opened position. . The valve actuator 58b may be any one as long as it can rotate the flow path area variable valve 58 by rotationally driving the rotation shaft 58a.

  The downstream end of the diffuser 56c and the downstream end of the high speed side collecting portion 57 are connected to a casing 62, which will be described later, of the catalyst device 6, and the exhaust gas that has passed through the diffuser 56c and the high speed side collecting portion 57 is placed in the casing 62. Inflow.

  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 62 a of the casing 62. The downstream ends of the diffuser 5c and the high speed side collecting portion 57 are connected to the upstream end 62a of the casing 62, and the exhaust discharged from these downstream ends is collected at the upstream end 62a of the casing 62, and then the catalyst body. Proceed to the 64 side.

  The ECU 2 is a controller based on a known microcomputer, and includes a CPU for executing a program, a memory including a RAM and a ROM for storing a program and data, and an I / O for inputting and outputting various signals. It has a bus. The ECU 2 receives signals from various sensors via the I / O bus and performs various calculations based on the signals.

  The ECU 2 stores the target valve timings of the intake valve 19 and the exhaust valve 20 and the target opening of the flow path area variable valve 58 set in advance according to the operating conditions. The ECU 2 receives signals from various sensors. Based on this, the current operating condition is calculated and a target value corresponding to this operating condition is extracted, and the valve timing of the intake valve 19 and the exhaust valve 20 and the opening of the flow path area variable valve become this target value. The intake VVT 32, the exhaust VVT 42, and the valve actuator 58b are driven.

  Next, the target valve timing of the intake valve 19 and the exhaust valve 20 and the target opening of the flow path area variable valve 58 will be described.

  The target valve timing of the intake valve 19 and the exhaust valve 20 is that the intake top dead center (the open valve period of the exhaust valve 20 and the open valve period of the intake valve 19 are in the low speed region where the engine speed is lower than the reference engine speed ( 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. 6, 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 The exhaust valve 20 of the fourth cylinder 12d opens while the intake valve 19 and exhaust valve 20 of 12c overlap, and the intake valve 19 and exhaust valve 20 of the fourth cylinder 12d overlap. The exhaust valve 20 of the second cylinder 12b is opened during the period in which the exhaust valve 20 is open, and the exhaust valve 20 of the first cylinder 12a is opened during the period in which the intake valve 19 and the exhaust valve 20 of the second cylinder 12b are overlapping. It is set to do.

  Further, the target valve timings of the intake valve 19 and the exhaust valve 20 are set such that the exhaust valve 20 is opened and the intake valve 19 is opened in the high speed region where the engine speed is higher than the reference speed N1, as in the low speed region. While the valve period is set to overlap, the overlap period T_L / O is set to be smaller than the overlap set in the low speed region. For example, the overlap period T_O / L in the low speed region is set to 60 ° C. A or more and set to 80 ° C. A, while the overlap period T_O / L in the high speed region is set to 40 ° C. or less, for example. Has been.

  The target opening degree of the flow path area variable valve 58 is set to be fully closed in the low speed load region, and is set to be fully open in the high speed region.

  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 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 low speed region, the flow path area variable valve 58 is closed, and the exhaust discharged from the cylinder 12 flows only into the low speed side passage 54. As described above, the low-speed side passage 54 and the mixing pipe 56a are configured so that the exhaust in the other low-speed side passages 54 is discharged from the predetermined low-speed side passage 54 to the mixing pipe 56a by the ejector effect. It is configured to be sucked out downstream. In the low speed region, when the exhaust valve 20 of the exhaust stroke cylinder 12 starts to be opened, another cylinder 12 whose exhaust sequence is set immediately before the exhaust stroke cylinder 12 (hereinafter referred to as an intake stroke cylinder as appropriate). 12) is set to be during the overlap period.

  Accordingly, in the low speed region, the exhaust gas in the exhaust stroke cylinder 12 flows into the low speed side passage 54 and is ejected from the low speed side passage 54 to the mixing pipe 56a at a high speed. Residual gas in the stroke cylinder 12 is sucked out to the exhaust port 18 side, scavenging of the intake stroke cylinder 12 is promoted, and intake efficiency and thus engine output is increased.

  In particular, the crossing angle α between the axial centers of the downstream ends of the adjacent low-speed passages 54 is set to 7 degrees, and each low-speed passage 54 is connected to the mixing pipe 56a in a state of being nearly parallel, and the exhaust stroke The speed of the exhaust discharged to the mixing pipe 56a from the low speed side passage 54 connected to the cylinder 12 is maintained high. Therefore, the periphery of the exhaust discharged from the exhaust stroke cylinder 12 can be set to a higher negative pressure, and a larger amount of residual gas in the intake stroke cylinder 12 can be sucked out.

  Further, the downstream end of each low speed side passage 54 is disposed adjacent to the mixing pipe 56a. Therefore, the suction force by the low speed side passage 54 connected to the exhaust stroke cylinder 12 effectively acts on the low speed side passage 54 connected to the intake stroke cylinder 12.

  Here, as described above, the flow path area of the low-speed side passage 54 is narrowed down on the downstream side so that the ejector effect can be effectively obtained. Therefore, when the exhaust gas passes only through the low speed side passage 54, if the engine speed increases and the exhaust gas flow rate increases, the exhaust resistance increases and the pump loss increases. As a result, the engine output deteriorates. .

  On the other hand, in the engine system 100, the flow path area variable valve 58 is opened in the high speed region, and the exhaust discharged from the cylinder 12 has a small exhaust resistance in addition to the low speed side passage 54. It flows into the high-speed side passage 53 configured as described above. Therefore, in this high speed region, the pump loss is kept small and the engine output is increased.

  In particular, in the present engine system 100, the crossing angle β between the axial centers of the downstream ends of the adjacent high speed side passages 53 is set to 45 degrees, and the expansion of exhaust in the high speed side assembly 57 is promoted to further increase the exhaust resistance. It is comprised so that it may reduce, The said pump loss can be restrained small effectively, and an engine output can be raised.

  In the present embodiment, the reference rotational speed is set when the flow path area variable valve 58 is closed to shut off the high speed side passage 53 and allow exhaust to pass only through the low speed side passage 54 side. The pump loss is set to a rotational speed at which the pump loss is suppressed to less than a predetermined value, and the pump loss is configured to be more reliably suppressed to a small value. Specifically, the reference rotational speed N1 is set to 4500 rpm.

  As described above, in the engine system 100, scavenging in the cylinder 12 can be promoted by effectively using the ejector effect in the low speed region, and the exhaust resistance is suppressed to be small in the high speed region. Scavenging and intake can be promoted, and the engine output can be increased by increasing the intake efficiency in the entire speed range.

  Here, the specific values of the crossing angle α between the axial centers of the downstream ends of the adjacent low-speed side passages 54 and the crossing angle β of the axial centers of the downstream ends of the adjacent high-speed side passages 53 are not limited to the above. It is only necessary that the crossing angle β of the side passage 53 is set larger than the crossing angle α of the low speed side passage 54. However, since it is known that a high ejector effect can be obtained if the intersection angle α is less than 30 degrees, the intersection angle α of the low speed side passage 54 is preferably set to less than 30 degrees. Further, since it is known that a high pump loss reduction effect can be obtained if the intersection angle β is 30 degrees or more and 60 degrees or less, the intersection angle β of the high speed side passage 53 is set to 30 degrees or more and 60 degrees or less. It is preferable.

  Further, the connection structure between the high speed side passage 53 and the high speed side collecting portion 57 is not limited to the structure in which the two high speed side passages 53 are connected to the outer peripheral surface of the high speed side collecting portion 57 as described above. For example, the downstream end of the high speed side passage 53 may be connected to the upstream end face of the high speed side collecting portion 57 so as to be aligned in the same plane. However, if at least two high speed side passages 53 are connected to the outer peripheral surface of the high speed side collecting portion 57 as described above, the downstream end of one high speed side passage 53 faces the other high speed side passage 53 side. Since the exhaust discharged from the passage 53 can be advanced to the other high speed side passage 53, the exhaust resistance can be reduced more efficiently.

  Further, the flow path area variable valve 58 is fully opened only in a high load area where the required torque for the engine is higher than a predetermined value in the low speed area, and the flow path area variable valve 58 is opened in the other low load areas in the low speed area. May be opened at a full opening or an opening smaller than the full opening.

  Further, the position of the catalyst device 6 is not limited to the above. However, according to the engine system 100, the intake efficiency can be increased by reducing the ejector effect and the exhaust resistance, which is useful in an engine system that does not have a turbocharger. And when it does not have a turbocharger in this way, the catalyst device 6 can be directly connected to each independent exhaust passage 53 as in the above embodiment, and can be arranged at a more upstream position. The temperature of the exhaust gas flowing into the catalyst body 64 can be maintained high, and the catalyst body 64 can be activated early.

  In the embodiment, the case where the independent exhaust passage 52 is connected downstream of the exhaust port 18 and the high speed side passage 53 and the low speed side passage 54 are separated downstream of the independent exhaust passage 52 will be described. However, for example, a high speed side passage may be connected to one exhaust port 18 of the two exhaust ports, and a low speed side passage may be connected to the other exhaust port 18 independently of the high speed side passage. The exhaust valve 20 of the exhaust port 18 connected to the high speed side passage may function as the flow path area variable valve. That is, the flow passage area of the high speed side passage may be changed by opening and closing one of the exhaust valves 20.

DESCRIPTION OF SYMBOLS 1 Engine main body 5 Exhaust manifold 6 Catalytic device 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 53 High speed side passage 54 Low speed side passage 56a Mixing pipe (low speed side collecting portion)
57 High-speed side collecting portion 58 Flow path area variable valve 58b Valve actuator (flow path area variable valve driving means)

Claims (4)

An exhaust system for a multi-cylinder engine having a plurality of cylinders each having an intake port and an exhaust port, and having an intake valve capable of opening and closing the intake port and an exhaust valve capable of opening and closing the exhaust port,
A plurality of independent exhaust passages that are respectively connected to exhaust ports of one cylinder or a plurality of cylinders whose exhaust order is not continuous with each other, and that are separated into a low speed side passage and a high speed side passage at least downstream,
Connected to the downstream end of each of the low-speed side passages, communicated with the low-speed side passages, and the low-speed side collecting portion that collects exhaust gas that has passed through the low-speed side passages;
Connected to the downstream end of each of the high speed side passages, communicated with the high speed side passages, and the high speed side collecting portion where the exhaust passing through the high speed side passages gathers;
A flow path area variable valve provided in each high speed side passage and capable of changing a flow area of each high speed side passage;
A flow path area variable valve driving means capable of opening and closing the flow path area variable valve;
Valve drive means capable of driving the intake valve and the exhaust valve of each cylinder,
Of the low-speed passages, the low-speed passages connected to the cylinders in which the exhaust order is continuous are connected to the low-speed collecting portion at positions adjacent to each other,
Each of the low-speed side passages and the low-speed side collecting portion has negative pressure in the other low-speed side passages adjacent to each other due to the ejector effect as exhaust is discharged from each cylinder through the low-speed side passages to the low-speed side collecting portion. Have a shape
The valve drive means has a predetermined overlap period between the valve opening period of the intake valve and the valve opening period of the exhaust valve in each cylinder in a low speed region where the engine speed is lower than a preset reference speed. At the same time, the intake valve and exhaust valve of each cylinder are driven so that the overlap period of one cylinder overlaps with the timing when the exhaust valve of the other cylinder is opened between the cylinders in which the exhaust order is continuous. And
The flow path area variable valve driving means is configured to make the flow path area variable valve smaller than fully open in the high load area where the required torque for the multi-cylinder engine is higher than a predetermined value in the low speed area. While reducing the flow rate of the exhaust gas passing through the engine, in the high speed region where the engine speed is higher than the reference speed, the flow path area variable valve is fully opened to open the high speed side passage,
The angle of intersection between adjacent high speed side passages extending along the flow direction of the exhaust gas discharged from the downstream end of each high speed side passage to the high speed side collecting portion is determined by each low speed side passage. The crossing angle between adjacent low-speed passages of the axial center of the downstream end extending along the flow direction of the exhaust gas discharged from the downstream end to the low-speed collecting portion is set. Exhaust system for multi-cylinder engines. The exhaust system for a multi-cylinder engine according to claim 1,
The intersecting angle between adjacent low speed side passages of the axis of the downstream end extending along the flow direction of the exhaust gas discharged from the downstream end of each low speed side passage to the low speed side collecting portion is set to be less than 30 degrees. And
The crossing angle between adjacent high speed side passages extending along the flow direction of the exhaust gas discharged from the downstream end of each high speed side passage to the high speed side collecting portion is not less than 30 degrees and not more than 60 degrees. An exhaust system for a multi-cylinder engine, characterized in that The exhaust system for a multi-cylinder engine according to claim 1 or 2,
The high speed side assembly has a shape having an outer surface surrounding an axis extending in the exhaust flow direction,
An exhaust system for a multi-cylinder engine, wherein a downstream end of at least a part of the plurality of high speed side passages is connected to an outer surface of the high speed side collecting portion. The exhaust system for a multi-cylinder engine according to any one of claims 1 to 3,
The low-speed side assembly has a shape in which at least one flow path area of the upstream end and the downstream end is the smallest area among the flow areas of the low-speed side assembly,
In the low speed side passage, the relationship between the diameter a of the perfect circle having the same area as the flow path area of the downstream end portion thereof and the diameter D of the perfect circle having the same area as the downstream end of the low speed side collecting portion is a / An exhaust device for a multi-cylinder engine having a shape satisfying D ≧ 0.5.

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