JP5447095B2 - 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 end of each of the low speed side passages, communicated with the low speed side passages and collects gas passing through the low speed side passages, and the low speed side Connected to the downstream end of the side collecting portion, communicates with the low speed side collecting portion and the high speed side passages, and passes through the low speed side passages gathered at the low speed side collecting portion. A final collecting portion where the gas that has passed through each of the high-speed side passages gathers, a catalyst device that is provided downstream of the final collecting portion and that can purify the exhaust discharged from each cylinder, Provided in each high-speed side passage, the flow area variable valve that can change the flow area of each high-speed side passage, the flow area variable valve driving means that can drive the flow area variable valve, Valve drive means capable of driving an intake valve and an exhaust valve of the cylinder, and the downstream ends of the low speed side passages connected to the cylinders in which the exhaust order is continuous among the low speed side passages are arranged at positions adjacent to each other. The low-speed collecting portion has a shape in which the flow area is smaller on the downstream side, and the final collecting portion has a flow area at the upstream end of the downstream end of the low-speed collecting portion. Road area and flow at the downstream end of each high-speed passage The valve drive means has a shape that is equal to or greater than the total area of the areas, and the valve drive means is in the low load range where the engine speed is lower than a preset reference speed, at least in the high load range where the required torque for the engine is high. The opening period of the intake valve and the opening period of the exhaust valve of each cylinder are overlapped with each other by a predetermined overlap period, and between the cylinders in which the exhaust sequence is continued, The intake valve and the exhaust valve of each cylinder are driven so that the exhaust valve of the cylinder is opened, and the flow path area variable valve driving means is configured so that each of the high speed side passages is at least in the high load area of the low speed area. The variable flow area control valve is driven so that the flow area is smaller than the maximum area, while each high speed is used in a high speed region where the engine speed is high. There is provided an exhaust system for a multi-cylinder engine, wherein the flow path area variable valve is driven so that a flow path area of a side passage becomes a maximum area.

  According to the present apparatus, the scavenging in the cylinder can be promoted by effectively using the ejector effect in at least the high load region in the low speed region, and the exhaust resistance can be suppressed to be small in the high speed region to promote the scavenging in the cylinder. The engine efficiency can be increased by increasing the intake efficiency in the entire speed range.

  That is, in this device, in at least the high load region of the low speed region, the flow area of the high speed side passage is reduced by the variable flow passage area valve so that the flow area of the independent exhaust passage is reduced, thereby exhausting the independent exhaust. It is configured to pass through the passage at high speed, and gas in the other independent exhaust passage is sucked out by the ejector effect when high-speed exhaust gas is ejected from a predetermined independent exhaust passage. Here, in at least the high load region of the low speed region, the exhaust valves of the other cylinders are opened during the overlap period of the predetermined cylinders, and a predetermined independent exhaust passage is associated with the opening of the exhaust valves. Since high-speed exhaust gas is ejected from the cylinder, gas in the cylinder in the overlap period is sucked out by the ejector effect, so that scavenging in the cylinder in the overlap period, that is, in the cylinder in the intake stroke is promoted to Efficiency is increased.

  In particular, the low speed side passages through which exhaust mainly passes when the flow passage area of the high speed side passages is reduced are such that the low speed side passages connected to the cylinders in which the exhaust order is continuous are mutually connected in the low speed side collecting portion. The low-speed side that is arranged adjacent to each other and that is more effectively connected to the cylinders in the overlap period with the negative pressure caused by the high-speed exhaust gas ejected from the predetermined low-speed side passage as the exhaust valve opens It is possible to act on the passage, and scavenging in the cylinder can be further promoted. Further, the flow area of the low-speed side collecting portion is reduced toward the downstream side, and the exhaust gas ejected from the low-speed side passage flows into the low-speed side collecting portion at a high speed, so that a high ejector effect can be obtained. it can.

  Here, if the flow area of the independent exhaust passage is reduced, if the flow rate of the exhaust gas is large, the exhaust resistance may increase, and the exhaust performance may be hindered and the scavenging performance may deteriorate. On the other hand, in this device, in the high speed region where the exhaust flow rate is large, the flow area of the high speed side passage is the maximum area, the flow area of the independent exhaust passage is secured, and the exhaust resistance is kept small. In addition, the intake efficiency can be increased even in a high speed region. In particular, the flow passage area of the final gathering portion is set to be equal to or greater than the total area of the flow passage area at the downstream end of the low speed side gathering portion and the flow passage area at the downstream end of each high speed side passage. The gas that has passed through the gas can flow into the final collecting portion with less resistance without being throttled in the final collecting portion, and the intake efficiency can be improved more reliably.

  In the present invention, it is preferable that the downstream ends of the high speed side passages connected to the cylinders in which the exhaust order is continuous among the high speed side passages are arranged at positions adjacent to each other.

  In this way, the negative pressure caused by the high-speed exhaust gas ejected from the predetermined high-speed side passage as the exhaust valve opens is more effectively applied to the high-speed side passage connected to the cylinder in the overlap period. The scavenging in the cylinder can be further promoted.

  In the present invention, a high speed side collecting portion that communicates with each of the high speed side passages and collects gas passing through the high speed side passages may be provided between the high speed side passages and the final collecting portion. Good. In this case, if the high-speed side assembly portion has a shape in which the flow area is equal to or larger than the total flow area of the downstream ends of the high-speed passages from the upstream end to the downstream end, The gas that has passed through the passage can be passed to the downstream side with less resistance, and the exhaust resistance can be suppressed to a smaller value and the intake resistance in the high speed region can be increased.

  In the present invention, it is preferable that the flow area of each high speed side passage is set larger than the flow area of each low speed side passage (Claim 4).

  In this way, the ejector effect is effectively exerted by reducing the flow area of the independent exhaust passage in the low speed region, and a large flow area of the independent exhaust passage is ensured in the high speed region. As a result, the exhaust resistance can be reduced more reliably and the intake efficiency can be further increased.

  Further, in the present invention, the flow path area variable valve driving means is configured to allow the flow path area of each of the high speed side passages to increase as the engine speed increases in at least the high load area of the low speed area. It is preferable to drive the variable path area valve.

  In this way, the intake efficiency of the entire low speed region can be increased more effectively. That is, on the low speed side where the back pressure is small in the low speed region, the flow area of the independent exhaust passage is sufficiently narrowed so that the intake efficiency can be increased by the ejector effect, and on the high speed side where the back pressure is high, the high speed side The intake efficiency can be increased by reducing the flow amount resistance by reducing the amount of restriction of the passage area of the passage.

  As described above, according to the present invention, the intake efficiency can be sufficiently increased without using a turbocharger. Therefore, the present invention is particularly useful for an apparatus in which a catalyst is directly connected to the downstream end of the final assembly portion and does not have a turbocharger (Claim 6).

  As described above, according to the present invention, the intake efficiency can be increased in the entire speed region by effectively utilizing the ejector effect.

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 looked at the downstream part of the engine main body 1 shown in FIG. 1 from the bottom. FIG. 3 is a side view of a downstream portion of the engine body 1 shown in FIG. 2. It is the IV-IV sectional view taken on the line of FIG. It is a figure for demonstrating the structure of the gathering part of a low speed side channel | path and a high speed side channel | path. It is a figure for demonstrating the valve timing of an intake valve and an exhaust valve. It is the figure which showed the opening degree map of the flow-path area variable valve. It is a schematic block diagram of the exhaust manifold vicinity which concerns on other embodiment of this invention. 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.

  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, four cylinders 12, 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 port 18 of each cylinder 12 is connected to an independent exhaust passage 52 on the downstream side thereof. Of 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 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, whose exhaust strokes are not adjacent to each other and the exhaust order is not continuous, are connected to one independent exhaust passage 52b. 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. In the present embodiment, upstream portions of these independent exhaust passages 52 are formed in the cylinder head 9, and downstream portions of these independent exhaust passages 52 are provided in the exhaust manifold 5.

  In addition to the three independent exhaust passages 52 connected to the exhaust port 18 as described above, the exhaust manifold 5 includes three flow area variable valves 58 and a low speed side collecting portion 56.

  The independent exhaust passage 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, in the vicinity of the upstream end of the exhaust manifold 5. In the present embodiment, as shown in FIGS. 2 and 3, the high-speed side passages 53 extend rearward linearly from the upstream portion of the independent exhaust passage 52 formed in the cylinder head 9 and then curve downward. The low speed side passage 54 is curved downward from the vicinity of the upstream end of the exhaust manifold 5 and passes below the high speed side passage 53 and extends linearly in the same manner as the high speed side passage 53. It has a shape that curves backward and downward.

  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 flow area of each high speed side passage 53 is set larger than the flow area of the low speed side passage 54.

  The flow passage area variable valve 58 is for changing the flow passage area of each high-speed passage 53 and thereby changing the flow passage area of each independent exhaust passage 52. Each of these flow path area variable valves 58 is provided in each high speed side passage 53. In this embodiment, these variable flow area valves 58 are provided in the vicinity of the upstream end in the high speed side passage 53 and in the vicinity where the inside of the high speed side passage 53 and the low speed side passage 54 are separated.

  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 has a fully open position (broken line in FIG. 3) extending in a direction substantially parallel to the exhaust flow direction and a fully closed position (solid line in FIG. 3) extending in a direction substantially perpendicular to the exhaust flow direction. And the high speed side passage 53 is opened and closed to change the flow area of the high speed side passage 53. In FIG. 3, in order to more clearly show the fully open position and the fully closed position of the flow path area variable valve 58, the flow path area variable valve 58 that is disposed in the high speed side passage 53 and should be indicated by a broken line is shown. A solid line indicates the closed position.

  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 low speed side collecting portion 56 is a portion provided on the downstream side of the low speed side passage 54. The low speed side collecting portions 56 are connected to the downstream ends of the low speed side passages 54 in communication with the low speed side passages 54, and the gas that has passed through the low speed side passages 54 flows into the low speed side collecting portions 56. Then, the low speed side gathering unit 56 gathers. In the low speed side assembly portion 56, the downstream ends of the three low speed side passages 54 are arranged at positions adjacent to each other.

  The low-speed side collecting portion 56 has a substantially cylindrical shape, and a cross section of the upstream end thereof has a substantially circular shape. Each low-speed passage 54 has a substantially circular cross section on the upstream side and a substantially cylindrical shape, while the cross section in the vicinity of the downstream end 55 gradually becomes a fan shape as it goes from the circular toward the downstream. These low speed side passages 54 are gathered so that each downstream end forming a fan shape forms a substantially circular cross section as a whole, and are connected to the upstream end of the circular cross section of the low speed side gathering portion 56. The cross-sectional shape and cross-sectional area of the upstream end of the portion 56 and the cross-sectional shape and cross-sectional area of the entire downstream end of the three low-speed passages 54 are set to be substantially the same. That is, in FIG. 5 schematically showing the configuration of each passage, 3 × A1 (the total sectional area of the downstream end of the low speed side passage 54) = S10 (the sectional area of the upstream end of the low speed side collecting portion 56) is set. Has been.

  The low-speed side gathering portion 56 has a shape that decreases in diameter from the upstream end toward the downstream and decreases in cross-sectional area, that is, the flow passage area toward the downstream, and downstream of the low-speed side gathering portion 56. The cross-sectional area S11 at the end is set smaller than the cross-sectional area S10 at the upstream end (S11 <S10 = 3 × A1). Exhaust gas flows in at a high speed from each low speed side passage 54 into the low speed side collecting portion 56 configured to reduce the flow path area in this way.

  A casing 62 (described later) of the catalyst device 6 is connected to the downstream end of the low speed side collecting portion 56, and the exhaust gas flowing into the low speed side passage 54 passes through the low speed side collecting portion 56 at a high speed, and then It flows into the casing 62.

  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 the downstream portion of the casing 62, and a predetermined space in which the gas flowing into the casing 62 can be mixed is formed in the upstream portion of the casing 62.

  The casing 62 of the catalyst device 6 is connected to the downstream end of the low speed side assembly portion 56 and the downstream end of each high speed side passage 53 in a state of communicating with the low speed side assembly portion 56 and the high speed side passages 53. Therefore, the exhaust gas that has passed through the low-speed side collecting portion 56 and the exhaust gas that has passed through the high-speed side passages 53 flow into the casing 62 and gather at the upstream portion of the casing 62.

  Thus, in the present embodiment, the upstream portion 62a of the casing 62 of the catalyst device 6 functions as a collecting portion where the gases that have passed through the independent exhaust passages gather. The exhaust gas flowing into the low-speed side passage 54 flows into the casing 62 after flowing into the low-speed side collecting portion 56, while the gas flowing into the high-speed side passage 53 flows into the casing 62 without collecting on the way. As a result, the casing 62 gathers.

  In the present embodiment, the three high speed side passages 53 are arranged at positions adjacent to each other at the upstream end of the casing 62.

  The upstream portion 62a of the casing 62 has a cross-sectional area S20 at its upper end larger than the total area of the cross-sectional area S11 at the downstream end of the low-speed side assembly portion 56 and the cross-sectional area A2 at the downstream end of each high-speed side passage 53. , And has a shape that increases in diameter toward the downstream for a predetermined distance from the upstream end. That is, in FIG. 5, 3 × A2 + S11 (the sum of the total cross-sectional area A2 of the downstream end of the high speed side passage 53 and the cross sectional area S11 of the downstream end of the low speed side assembly portion 56)> S20 (upstream of the casing 62) The cross-sectional area is set to S20 <S21 (the cross-sectional area on the downstream side of the casing 62). The exhaust gas that has passed through each high-speed passage 53 flows into the casing having a large cross-sectional area and a large volume. Therefore, the exhaust gas that passes through each high-speed passage 53 flows smoothly into the casing 62 in a state where the back pressure is kept small and the exhaust resistance is low.

  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 calculates target valve timings of the intake valve 19 and the exhaust valve 20 according to operating conditions, calculates a target opening degree of the flow path area variable valve 58, and controls the valves of the intake valve 19 and the exhaust valve 20. The intake VVT 32, the exhaust VVT 42, and the valve actuator 58b are driven so that the timing and the opening degree of the flow path area variable valve 58 become these target values.

  The target valve timing of the intake valve 19 and the exhaust valve 20 is a low speed region where the engine speed is lower than the reference speed N1, and a required torque for the engine, that is, a high load region where the engine load is higher than the reference load Q1, that is, a low speed high load. In the region R1 (see FIG. 7), as shown in FIG. 6, the exhaust valve 20 and the intake valve 19 both open for a predetermined overlap period T_O / L, that is, the exhaust valve 20 opens. And the opening period of the intake valve 19 are overlapped, and the exhaust valve 20 is set to start opening during the overlapping period T_O / L of the other cylinders 12. Specifically, the exhaust valve 20 of the third cylinder 12c is opened while the intake valve 19 and the exhaust valve 20 of the first cylinder 12a overlap, and the intake valve 19 and the exhaust of the third cylinder 12c are exhausted. The exhaust valve 20 of the fourth cylinder 12d opens during the period in which the valve 20 overlaps, and the second cylinder during the period in which the intake valve 19 and the exhaust valve 20 of the fourth cylinder 12d overlap. The exhaust valve 20 of 12b is opened, and the exhaust valve 20 of the first cylinder 12a is set to open while the intake valve 19 and exhaust valve 20 of the second cylinder 12b overlap.

  On the other hand, in the high speed region R3 (see FIG. 7) where the engine speed is higher than the reference speed N1, the target valve timing of the intake valve 19 and the exhaust valve 20 is such that the overlap period T_L / O is in the low speed and high load region. It is set to be shorter (including 0 ° C. A) than the overlap period set by R1.

  Further, in the low speed region R2 (see FIG. 7) where the engine speed is lower than the reference speed N1 and the engine load is lower than the reference load Q1, the target valves of the intake valve 19 and the exhaust valve 20 are set. The timing is set so that the overlap period T_L / O between the exhaust valve 20 and the intake valve 19 is shorter than the overlap period set in the low speed and high load region R1.

  In each region, the target valve timing of the exhaust valve 20 and the intake valve 19 is detailed according to the engine speed NE or according to the engine speed NE and the engine load while maintaining the setting of the overlap period as described above. The ECU 2 stores a map of the preset target valve timings of the exhaust valve 20 and the intake valve 19. Then, the ECU 2 extracts each target valve timing from this map according to the operating conditions.

  The reference rotation speed N1 is, for example, 2000 rpm, and the reference load Q1 is, for example, the indicated mean effective pressure BMEP = 5 bar. Further, the overlap period T_O / L of the low speed and high load region R1 is set to 60 ° C. A or more, for example, and the overlap period T_O / L of the high speed region R3 is set to 40 ° C. or less, for example.

  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.

  The target opening degree of the flow path area variable valve 58 is set to be fully closed in the low speed and high load region R1, while being set to fully open in the other regions R2 and R3. That is, in the low-speed and high-load region R1, the high-speed passages 53 are blocked, and the exhaust discharged from the engine body 1 flows downstream only through the low-speed passage 54. On the other hand, in the other regions R2 and R3, the high speed side passages 53 are opened, and the exhaust discharged from the engine body 1 flows downstream through the high speed side passages 53 and the low speed side passages 54.

  The ECU 2 stores a map of the preset target opening degree of the variable flow area 58, and the ECU 2 extracts the target opening degree of the variable flow area valve 58 from the map according to the operating conditions. To do.

  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 flows into the corresponding independent exhaust passage 52 from the exhaust port 18 of the cylinder 12 at a high speed. In particular, immediately after the exhaust valve 20 is opened, a very high-speed gas (so-called blowdown gas) flows from the cylinder 12.

  Here, in the low speed and high load region R <b> 1, the high speed side passage 53 is blocked and only the low speed side passage 54 of the independent exhaust passage 52 is opened, and the exhaust flows only into the low speed side passage 54. As described above, the flow area of the low speed side passage 54 is set to be smaller than that of the independent exhaust passage 52 and the high speed side passage 53. Further, the flow rate area of the low speed side gathering portion 56 provided downstream of the low speed side passage 54 becomes smaller toward the downstream side. Therefore, the exhaust gas passes through the low-speed side collecting portion 56 at a high speed.

  Thus, when high-speed exhaust gas is ejected from the predetermined low-speed side passage 54 to the low-speed side collecting portion 56, it communicates with the low-speed side collecting portion 56 by the negative pressure action generated around the exhaust gas, that is, the ejector effect. The other low speed side passage 54 is subjected to a force for sucking the gas inside thereof to the downstream side. When the exhaust valve 20 of the exhaust stroke cylinder 12 is opened, the other cylinders 12 whose exhaust order is set immediately before the exhaust stroke cylinder 12 (hereinafter referred to as the intake stroke cylinder 12 as appropriate) The exhaust valve 20 and the intake valve 19 are both open. Therefore, the suction force acts on the gas in the intake stroke cylinder 12 via the low speed side passage 54 connected to the intake stroke cylinder 12. By this suction force, the residual gas in the intake stroke cylinder 12 is sucked out from the cylinder 12 vigorously.

  In particular, the downstream ends of the respective low speed side passages 54 are arranged adjacent to each other in the low speed side collecting portion 56. 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, and a large amount of residual gas is sucked out from the intake stroke cylinder 12. It is.

  Here, the second cylinder 12b and the third cylinder 12c are connected to the same independent exhaust passage 52, and the exhaust discharged from the second cylinder 12b and the third cylinder 12c flows into the same low speed side passage 54. However, the exhaust order of the second cylinder 12b and the third cylinder 12c is not continuous, and the exhaust discharged from the cylinders 12b and 12c passes through the low speed side passage 54 without interference.

  Thus, in the engine system 100, the ejector effect is effectively exhibited in the low speed and high load region R1, the scavenging of each cylinder 12 is promoted, the intake efficiency is increased, and the engine output is increased.

  On the other hand, in the high speed region R3, the high speed side passage 53 is open, and the exhaust gas flowing into the independent exhaust passage 52 from the exhaust port 18 of the cylinder 12 flows into the high speed side passage 53 in addition to the low speed side passage 54. . As described above, the flow area of the high speed side passage 53 is set larger than the flow area of the low speed side passage 54, and most of the exhaust gas passes through the high speed side passage 53. The gas that has passed through the high speed side passage 53 flows into the casing 62 of the catalyst device 60. The upstream portion 62a of the casing 62 where the gas that has passed through the high speed side passages 53 gathers is set to have a flow path area larger than the total area of the downstream ends of the high speed side passages 53 and further toward the downstream side. It has a shape that expands in diameter. Therefore, the exhaust gas that has passed through each high speed side passage 53 smoothly passes through the high speed side passage 53 with less resistance. Accordingly, the pressure at the downstream end of the high speed side passage 53, that is, the back pressure of each high speed side passage 53 is kept low.

  In this way, in the engine system 100, in the high speed region R3 where the exhaust flow rate is large and the back pressure tends to be high, the high speed side passage 53 is opened and the exhaust gas is discharged in a state with less resistance, thereby scavenging the cylinder 12. Is promoted to ensure engine output.

  Further, in the low speed and low load region R2, the pressure of the intake air is small. Therefore, if the intake valve 19 and the exhaust valve 20 are overlapped, the exhaust may flow backward to the intake side.

  On the other hand, in the present engine system 100, the intake valve 19 and the exhaust valve 20 do not overlap in the low speed and low load region R2, and the high speed side passage 53 is opened. Therefore, the backflow is more reliably avoided and the back pressure is suppressed to be small, whereby scavenging is performed smoothly and the intake amount is secured.

  As described above, according to the engine system 100, the intake efficiency can be increased and the engine output can be increased in the entire speed region.

  Here, in the said embodiment, although the said low speed side collection part 56 was made into the shape which shrinks | reduces gradually as the flow path area goes downstream, the low speed side collection part 56 has the flow path area in the downstream side. The flow path area may be reduced stepwise in the upstream / downstream direction.

  In the embodiment, the case where the low speed side collecting portion 56 and the high speed side passages 53 are gathered in the upstream portion 62a of the casing 62 of the catalyst device 6 has been described. However, as shown in FIG. Between the high-speed passages 53 and the high-speed passages 53, high-speed collecting portions 156 that communicate with the high-speed passages 53 and through which the gases that have passed through the high-speed passages 53 merge may be provided. In this case, the high-speed side collecting portion is configured such that the gas that has passed through each high-speed side passage 53 flows to the downstream side with a lower resistance without being throttled in the high-speed side collecting portion 156 so that the back pressure is reduced. It is preferable that 156 has a shape in which the flow area is equal to or larger than the total area of the flow areas at the downstream ends of the high-speed passages from the upstream end to the downstream end.

  In the above embodiment, the flow area variable valve 58 is driven to the fully closed position in the low speed and high load area R1, but the position of the flow area variable valve 58 in the low speed and high load area R1 is as follows. The position is not limited to the fully closed position, and may be a position closer to the closed side than the fully opened position, that is, a position where the flow passage area of the high speed side passage 53 is reduced more than the maximum area.

  In the case where the position of the variable flow area 58 in the low speed and high load region R1 is set to the open side with respect to the fully closed position, the exhaust in the low speed and high load region R1 changes the flow area in the high speed side passage 53. The ejector effect can be obtained also in the high-speed side passage 53 by passing through the throttle at the position where the valve 58 is provided. Therefore, when set in this way, the negative pressure generated by the exhaust injected from the high speed side passage connected to the cylinder in the exhaust stroke is caused by the exhaust in the high speed side passage connected to the cylinder in the intake stroke. It is preferable to arrange the downstream ends of the high-speed passages connected to the cylinders in which the exhaust sequence is continuous at positions adjacent to each other so as to effectively act and promote scavenging of the cylinders.

  Further, in the low speed and high load region R1, the flow path area variable valve 58 may be changed stepwise or continuously between a fully open position and a fully closed position. In this case, the flow passage area variable valve 58 is preferably driven so that the flow passage area of the high-speed passage 53 increases as the engine speed increases. In this way, in the region where the engine speed NE is low and the exhaust flow rate is low, scavenging can be promoted by the ejector effect by restricting the flow passage area of the high-speed side passage 53, while the exhaust gas having a high engine speed NE is high. In a region where there is a large flow rate, the scavenging can be promoted and the intake efficiency can be increased by suppressing the exhaust resistance by increasing the flow passage area of the high-speed side passage.

  Further, the position of the catalyst device 6 is not limited to the above. However, according to the present engine system 100, the intake efficiency can be increased by reducing the ejector effect and the back pressure, 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.

  Further, the high speed side passage 53 may be blocked also in the low speed and low load region R2.

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 56 Low speed side collecting portion 58 Flow path area variable valve 58b Valve actuator (flow path area variable valve driving means)
62a Casing upstream part (final assembly part)
64 Catalyst body 156 High-speed side assembly

Claims (6)

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 gathers the gas passing through the low speed side passages; and
The gas that is connected to the downstream end of the low-speed side collecting portion, communicates with the low-speed side collecting portion and the high-speed side passages, and passes through the low-speed side passages gathered at the low-speed side collecting portion and the high-speed A final gathering portion where the gas that has passed through the side passages gathers;
A catalyst device provided on the downstream side of the final collecting portion and capable of purifying the exhaust discharged from each cylinder;
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 driving the flow path area variable valve;
Valve drive means capable of driving the intake valve and the exhaust valve of each cylinder,
The downstream ends of the low speed side passages connected to the cylinders in which the exhaust order is continuous among the low speed side passages are arranged adjacent to each other,
The low-speed side assembly has a shape in which the flow path area is smaller on the downstream side,
The final gathering portion has a shape in which the flow passage area at the upstream end thereof is equal to or greater than the total flow passage area at the downstream end of the low speed side passage and the flow passage area at the downstream end of each high speed passage.
The valve driving means includes a valve opening period of each of the cylinders and an exhaust valve in a low speed region where the engine speed is lower than a preset reference speed, and at least in a high load region where a required torque for the engine is high. Each of the exhaust valves of the other cylinder is opened during the overlap period of one cylinder between the cylinders in which the exhaust order is continued, and the opening period of the other cylinder overlaps with a predetermined overlap period. Drive the intake and exhaust valves of the cylinder,
The variable flow area variable valve driving means drives the variable flow area variable valve so that the flow area of each high speed side passage is smaller than the maximum area in at least the high load area of the low speed area. An exhaust system for a multi-cylinder engine, wherein the flow passage area variable valve is driven so that the flow passage area of each of the high speed side passages becomes a maximum area in a high speed region where the engine speed is high. An exhaust system for a multi-cylinder engine according to claim 1,
An exhaust system for a multi-cylinder engine, wherein downstream ends of the high-speed side passages connected to the cylinders in which the exhaust order is continuous among the high-speed side passages are arranged adjacent to each other. An exhaust system for a multi-cylinder engine according to claim 1 or 2,
A high-speed side collecting portion that is interposed between the high-speed side passages and the final collecting portion and communicates with the high-speed side passages and collects gas passing through the high-speed side passages;
The exhaust of a multi-cylinder engine, wherein the high speed side collecting portion has a shape in which a flow path area is equal to or greater than a total flow area of the downstream ends of the high speed side passages from an upstream end to a downstream end. apparatus. An exhaust device for a multi-cylinder engine according to any one of claims 1 to 3,
An exhaust system for a multi-cylinder engine, wherein the flow passage area of each high speed side passage is set larger than the flow passage area of each low speed side passage. An exhaust device for a multi-cylinder engine according to any one of claims 1 to 4,
The variable flow area variable valve driving means drives the variable flow area valve so that the flow area of each high-speed side passage increases as the engine speed increases in at least the high load area of the low speed area. An exhaust system for a multi-cylinder engine. An exhaust system for a multi-cylinder engine according to any one of claims 1 to 5,
The exhaust device for a multi-cylinder engine, wherein the catalyst device is directly connected to a downstream end of the final assembly portion.

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