JP5531922B2 - Intake and exhaust system for multi-cylinder engine - Google Patents

Description

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

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

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

JP 2009-97335 A

  In an engine such as an automobile, the demand for improving the engine output is still high. 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, an object of the present invention is to provide an intake / exhaust device for a multi-cylinder engine that can increase the intake air amount with a simple configuration and increase the engine output.

In order to solve the above problems, the present invention provides a plurality of cylinders each having an intake port and an exhaust port and provided with an intake valve capable of opening and closing the intake port and an exhaust valve capable of opening and closing the exhaust port. An intake / exhaust device for a multi-cylinder engine having an intake passage connected to an intake port of each cylinder and one cylinder or an exhaust port of a plurality of cylinders whose exhaust sequences are not continuous with each other A plurality of independent exhaust passages that are separated into a low speed side passage and a high speed side passage at least on the downstream side, and connected to the downstream ends of the low speed side passages, and communicated with the low speed side passages. Connected to the low speed side collecting portion where the exhaust gas that has passed through the passage gathers, and the downstream end of each of the high speed side passages, and communicates with each of the high speed side passages to each of the high speed sides A high-speed side collecting portion that collects exhaust gas that has passed through the passage, a flow area variable valve that is provided in each of the high-speed side passages and can change the flow area of each high-speed side passage, and the flow area variable valve And a valve driving means capable of driving the intake valve and the exhaust valve of each cylinder, and is connected to a cylinder in which the exhaust order is continuous in each of the low speed side passages. The low speed side passages are connected to the low speed side collecting portions at positions adjacent to each other, and the low speed side passages and the low speed side collecting portions are exhausted from the cylinders through the low speed side passages to the low speed side collecting portions. As the exhaust gas is discharged, the other low-speed side passages adjacent to each other have a negative pressure due to the ejector effect, and the valve driving means has a shape in which the engine speed is lower than a preset reference speed. ,Previous Between the cylinders in which the intake valve opening period and the exhaust valve opening period of each cylinder overlap with each other with a predetermined overlap period and the exhaust sequence continues, the overlap period of one cylinder and the exhaust of the other cylinder The intake valve and the exhaust valve of each cylinder are driven so that the timing when the valve is opened, and the intake valve of each cylinder is driven in a high speed region where the engine speed is higher than the reference speed. The intake valve and the exhaust valve of each cylinder are driven so that the valve opening period and the valve opening period of the exhaust valve overlap with each other by a predetermined overlap period. At least in the high load region where the required torque for the multi-cylinder engine is higher than a predetermined value, the flow passage area variable valve is made smaller than the fully open position so that the high speed side passage is While reducing the flow rate of exhaust gas passing through, in the high speed region, the flow path area variable valve is fully opened to open the high speed side passages, and the length and the cross sectional area of each high speed side passage are determined by the engine speed A positive pressure wave of the exhaust gas discharged from the cylinder through the high-speed side passage to the high-speed side collecting portion in the vicinity of the opening timing of the exhaust valve under the operating condition set to the exhaust synchronized rotation speed set in the high-speed region Is reflected at the high-speed side collecting portion to become a negative pressure wave, the negative pressure wave passes through the high-speed side passage and reaches the exhaust port of the cylinder where the exhaust is discharged, and the cylinder of the cylinder where the exhaust is discharged The low speed side gathering portion is set to have a dimension that overlaps the overlap period, and the flow area of at least one of the upstream end and the downstream end of the low speed side gathering portion is the largest among the flow passage areas of the low speed side gathering portion. small The low-speed side passage has a perfect circle diameter a having the same area as the flow path area of the downstream end portion thereof, and a perfect circle having the same area as the downstream end of the low-speed side assembly portion. Provided is an intake / exhaust device for a multi-cylinder engine having a shape in which a relationship with a diameter D is a / D ≧ 0.5 .

  According to the present invention, the ejector effect is effectively used in the low speed region to promote scavenging in the cylinder, the exhaust resistance is suppressed to be small in the high speed region, and the reflection of the pulsating pressure wave of the exhaust is used to improve the inside of the cylinder. Scavenging can be promoted, and the engine output can be increased by increasing the intake efficiency in the entire speed region.

Specifically, in this configuration, in the low speed region, the high speed side passage is shut off, and the exhaust gas is allowed to pass through the low speed side passage and the low speed side collecting portion configured to obtain the ejector effect. Since the exhaust valves of the other cylinders are opened during the overlap period, when the exhaust valve is opened, high-speed exhaust gas is ejected from a predetermined low-speed side passage, so that the ejector effect causes the overlap period. The gas in the exhaust port of a certain cylinder can be sucked downstream, and scavenging in the cylinder during the overlap period can be promoted.
In particular, 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 collection unit, and the low-speed side passage is The relationship between the diameter a of the perfect circle having the same area as the flow path area of the downstream end portion and the diameter D of the perfect circle having the same area as the downstream end of the low-speed side assembly is a / D ≧ 0.5 Therefore, the ejector effect can be effectively obtained.

  In this configuration, since the exhaust flow rate is high, the exhaust resistance may increase, so the high speed side passage is opened and the exhaust gas is discharged to the high speed side passage side in addition to the low speed side passage. In addition, the exhaust resistance can be suppressed to be small, and the scavenging in the cylinder can be promoted.

  In addition, in this configuration, the length and the cross-sectional area of the high-speed side passage through which the exhaust passes in the high-speed region are the operating conditions in which the engine speed is the exhaust tuning speed higher than the reference speed, that is, the predetermined speed included in the high-speed area The positive pressure wave of the exhaust discharged from the cylinder through the high speed side passage to the high speed side collecting portion in the vicinity of the opening start timing of the exhaust valve is reflected at the high speed side collecting portion and becomes a negative pressure wave. The time when the negative pressure wave reaches the exhaust port of the cylinder where the exhaust gas is exhausted through the high-speed side passage and the overlap period of the cylinder where the exhaust gas is exhausted are set so as to overlap each other. Therefore, in the high speed region, the gas in the cylinder during the overlap period can be sucked out to the exhaust port side by the negative pressure wave, and scavenging in the cylinder is further promoted. Door can be.

  In the present invention, the length and the cross-sectional area of each of the high speed side passages are determined so that the positive pressure wave of the exhaust gas is reflected twice by the high speed side collecting portion under the condition that the engine speed is the exhaust tuning speed. It is preferable that the dimension is set such that the time when the exhaust port is reached overlaps with the overlap period.

  By doing so, it is possible to obtain the scavenging promotion effect by the negative pressure generated along with the reflection of the positive pressure wave while suppressing the length of the high speed side passage.

  In the present invention, the length and the cross-sectional area of each intake passage until the pressure wave of the intake pulsation generated when the intake valve is opened are reflected from the intake valve by the intake pulsation. The primary intake tuning rotation speed at which the primary peak of the intake valve is generated in the vicinity of the intake valve and the intake valve closing timing are substantially the same and the inertial supercharging effect of the intake is obtained is higher than the reference rotation speed, In addition, the intake non-synchronized rotational speed at which the primary valley of the intake pulsation occurs in the vicinity of the intake valve and the intake valve close timing is set to a dimension that is lower than the reference rotational speed. (Claim 3).

  According to this configuration, the inertia of the intake air in addition to the effect of reducing the exhaust resistance and the effect of the pressure wave of the exhaust gas in the high speed region while facilitating scavenging in the cylinder by effectively using the ejector effect in the low speed region. The introduction of intake air into the cylinder can be promoted using the supercharging effect.

  The inertial supercharging effect of intake air means that a negative pressure pulsation wave generated in the vicinity of the intake valve when the intake valve is opened propagates to the upstream side of the intake passage through the intake passage, and this intake passage has a predetermined volume. The positive pressure wave is generated by reversing and reflecting at the part, and the positive pressure pulsation wave propagates through the intake passage and reaches the intake valve during the intake stroke, so that intake into the cylinder is promoted. In the intake stroke, the pressure pulsation wave is inverted once and reflected by the volume portion and reflected to reach the intake valve just before the intake valve is closed to promote intake near the primary intake tuning speed. Can do.

  Therefore, according to the configuration in which the primary intake synchronized rotational speed is set higher than the reference rotational speed, the inertial supercharging effect of the intake air in a high speed region where the engine rotational speed is higher than the reference rotational speed. Thus, intake into the cylinder can be promoted. In particular, the non-synchronized rotational speed at which the primary trough of the intake pulsation in which the inertia supercharging effect cannot be obtained and the valve closing timing of the intake valve are substantially the same is lower than the reference rotational speed. Since it is comprised, scavenging performance can be more reliably improved over the high-speed area | region.

  In the above configuration, it is preferable that the primary intake tuning rotational speed and the exhaust tuning rotational speed are different from each other.

  In this way, the engine speed at which the intake acceleration effect due to the exhaust pressure wave becomes the highest is different from the engine speed at which the intake acceleration effect due to the inertial supercharging effect of the intake air becomes the highest. Can be promoted.

  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 intake / 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 timing of an intake valve and an exhaust valve. It is the figure which showed the pressure change of the exhaust port together with the valve lift curve. It is a figure for demonstrating the valve opening timing and valve closing timing of an intake valve and an exhaust valve in the intake / exhaust apparatus of the multicylinder engine which concerns on embodiment of this invention. It is a graph for demonstrating the effect of this invention. It is the figure which showed typically the mode of the intake air pulsation near an intake valve.

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

  FIG. 1 is a schematic configuration diagram of an engine system 100 including an intake / exhaust device for the multi-cylinder engine. The engine system 100 includes an engine main body 1 having a cylinder head 9 and a cylinder block, an ECU 2 for engine control, a plurality of intake pipes 3 connected to the engine main body 1 constituting an intake passage, and these intake pipes 3. A surge tank 4, an exhaust manifold 5 connected to the engine body 1, and a catalyst device 6 connected to the exhaust manifold 5.

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

  Each intake pipe 3 is connected to the surge tank 4 on the upstream side, and air stored in the surge tank is distributed to each intake pipe 3. The surge tank 4 extends in the direction in which the intake pipes 3 are arranged, and has a sufficient volume capable of storing air for distribution to the intake pipes 3. Accordingly, when the intake valve 19 is opened, the negative pressure wave generated in the vicinity of the intake valve 19 propagates through the intake pipe 3 and reaches the surge tank 4 and is inverted and reflected by the surge tank 4 to become a positive pressure wave. . This positive pressure wave returns to the intake valve 19 side, reverses and reflects near the inlet of the cylinder 12 to become a negative pressure wave, and propagates again to the sirgin tank 4 side. In this way, pressure pulsation (intake pulsation) as shown in FIG. 10 occurs in the intake pipe 3. FIG. 10 is a diagram schematically showing a pressure change due to the intake pulsation in the vicinity of the intake valve 19 with the horizontal axis as time. As shown in FIG. 10, in the vicinity of the intake valve 19, after the start of opening of the intake valve 19 (time t0), peaks (high pressure state) and valleys (low pressure state) appear alternately while being attenuated. .

  Inertial supercharging effect of intake air means that immediately before the intake valve 19 is closed, the vicinity of the intake valve 19 is in a mountain state and the pressure on the intake port 17 side is increased, and intake to the cylinder 12 is promoted. That's it. In particular, the first peak due to the positive pressure wave generated by reversing and reflecting the negative pressure wave once by the surge tank 4 has a large pressure, and a high inertial supercharging effect can be obtained.

  In the present embodiment, the length L_in of the intake pipe 3 (FIG. 1) is obtained so that a high inertia supercharging effect due to the primary peak is obtained in a high speed region where the engine speed is higher than a reference speed N1 described later. And a cross-sectional area, that is, an area in a direction orthogonal to the flow direction of the exhaust gas or a flow path area is set. Further, in this high-speed region, the intake air valve 19 is prevented from becoming a valley near the intake valve 19 immediately before the intake valve 19 is closed, so that the inertia supercharging effect can be obtained in the entire high-speed region. The length L_in and the cross-sectional area of the tube 3 are set.

  That is, the primary intake synchronized rotation speed Nin_1a at which the time t1a (see FIG. 10) at which the primary peak of the intake pulsation occurs in the vicinity of the intake valve 19 and the closing timing of the intake valve 19 is substantially the same is the reference value. The time t1b (see FIG. 10) at which the primary trough of the intake pulsation occurs in the vicinity of the intake valve 19 and the closing timing of the intake valve 19 so as to be higher than the rotational speed N1 and the closing timing of the intake valve 19 are substantially the same. The length L_in and the cross-sectional area of the intake pipe 3 are set so that the non-intake synchronized rotational speed Nin_1b is lower than the reference rotational speed N1.

  Here, in order to obtain a high inertial supercharging effect due to the primary mountain in a higher speed region, the length L_in of the intake pipe 3 is made shorter or the cross-sectional area of the intake pipe 3 is made larger. However, since a change in the cross-sectional area of the intake pipe 3 is greatly limited in layout, in this embodiment, by shortening the length L_in of the intake pipe 3, a high inertial supercharging effect can be obtained in a high speed region. I try to get it.

  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 FIGS. 2 and 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 53 is curved upward from the low speed side passage 54 and then extends downstream in parallel with 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.

  Specifically, 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 to the downstream side at a high speed. 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 pipe 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, where D is a diameter of a perfect circle having the same area as the flow path area at the downstream end thereof ( 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 easily expands and the exhaust resistance decreases. It has such a shape.

  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, and unlike the low speed side passage 54 and the mixing pipe 56a, this high speed side collecting portion 57 is. Then, the exhaust discharged from the predetermined high-speed side passage 53 to the high-speed side collecting portion 57 can be relatively easily advanced toward the other high-speed side passage 53 side. In this way, the high speed side assembly 57 is configured such that the expansion of the exhaust is promoted and the exhaust resistance is further reduced. In particular, in the present embodiment, on the outer peripheral surface of the high speed side collecting portion 57, the high speed side passage 53 corresponding to the first cylinder 12a and the high speed side passage 53 corresponding to the fourth cylinder 12d are substantially opposed to each other at their downstream ends. In this state, the exhaust discharged from the predetermined high-speed side passage 53 more easily proceeds toward the other high-speed side passage 53, and the exhaust resistance is effectively reduced.

  The high-speed side collecting portion 57 configured as described above has a sufficient volume with respect to the exhaust gas discharged from the high-speed side passage 53, and propagates from the cylinder 12 through the high-speed side passage 53 to the high-speed side. The pressure wave that reaches the gathering portion 57 is inverted and reflected by the high-speed side gathering portion 57.

  For example, immediately after the opening of the exhaust valve 20 is started, a positive pressure wave having a high pressure is generated in the exhaust port 18 as the exhaust valve 20 is opened. When reaching the part 57, the high-speed side assembly part 57 inverts and reflects, thereby generating a negative pressure wave with a large negative pressure amount. The negative pressure wave propagates through the high speed side passage 53 to the exhaust port 18 side. FIG. 7 shows the pressure change in the exhaust port 18 together with the valve lift of the exhaust valve 20. As shown in FIG. 7, the pressure in the exhaust port 18 becomes a maximum value immediately after the start of the exhaust valve 20 opened at the crank angle θ_EVO (crank angle θ_Pmax). The pressure in the exhaust port 18 becomes the maximum negative pressure at the crank angle θ_Pmin with the arrival of the negative pressure wave.

  In the engine system 100, the exhaust valve of a predetermined cylinder 12 is set at an exhaust tuning rotational speed Nex in which the length L_ex (see FIG. 3) and the cross-sectional area of each high-speed passage 53 are set higher than the reference rotational speed N1. The positive pressure wave of high pressure generated by opening the exhaust valve 20 during the valve opening period of 20 is reversed and reflected by the high-speed side collecting portion 57 and is reversed during the valve opening period of the exhaust valve 20. When the negative pressure wave having a large negative pressure amount generated by the reflection returns to the exhaust port 18 of the cylinder 12 where the exhaust valve 20 is opened, the cylinder 12 where the exhaust valve 20 is opened will be described later. The overlap period is set to a size that overlaps. Further, in the present embodiment, the exhaust synchronized rotation speed Nex is set to be different from the primary intake synchronized rotation speed Nin_1a.

  That is, in the engine system 100, at the exhaust synchronized rotation speed Nex, a negative pressure wave having a large negative pressure reaches the exhaust port 18 of the cylinder during the overlap period, and the cylinder during the overlap period is caused by the negative pressure wave. The gas in 12 is sucked out to the exhaust port 18 side.

  Here, in order to increase the exhaust synchronized rotation speed Nex, the length L_ex of each high speed side passage 53 may be shortened or the cross-sectional area of each high speed side passage 53 may be increased. Since the change in the cross-sectional area of 53 has a great layout restriction, in this embodiment, the exhaust tuning rotation speed Nex is adjusted by adjusting the length L_ex of each high-speed side passage 53.

  In the present embodiment, the length L_ex and the cross-sectional area of each high speed side passage 53 are set to twice at the high speed side collecting portion 57 at the exhaust port 18 of the cylinder during the overlap period at the exhaust synchronized rotation speed Nex. Inverted and reflected negative pressure waves having a large negative pressure amount are set back, and the length L_ex of the high-speed side passage 53 is shortened while the gas in the cylinder 12 at the exhaust tuning rotation speed Nex is directed to the exhaust port 18 side. It is configured to obtain a suction effect.

  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 timings of the intake valve 19 and the exhaust valve 20 are the intake top dead center between the valve opening period of the exhaust valve 20 and the valve opening period of the intake valve 19 in a low speed region where the engine speed is lower than the reference speed N1. (TDC) is overlapped, and 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, as shown in FIG. 7, immediately after the opening of the exhaust valve 20 (crank angle θ_Pmax), a very high-pressure, high-speed gas (so-called blowdown gas) is discharged from the cylinder 12.

  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 gas is ejected from the predetermined low speed side passage 54 to the mixing pipe 56a at a high speed due to 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 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 the present embodiment, the reference rotational speed N1 is set when the flow passage area variable valve 58 is closed to shut off the high speed side passage 53 so that the exhaust gas passes only through the low speed side passage 54. 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 more reliably suppressed to a small value. Specifically, the reference rotational speed N1 is set to 4500 rpm.

  Moreover, in the engine system 100, as described above, by adjusting the length L_ex and the cross-sectional area of each high speed side passage 53, the engine speed is set to the exhaust synchronized rotation speed Nex set higher than the reference speed N1. Under the operating conditions in this high speed region, the negative pressure wave having a large negative pressure amount reaches the exhaust port 18 of the cylinder 12 during the overlap period, and the negative pressure wave causes the inside of the cylinder 12 during the overlap period. The gas is sucked out to the exhaust port 18 side. Therefore, in this high speed region, in addition to the reduction of the pump loss, scavenging is promoted by this negative pressure wave, thereby further increasing the engine output. In this embodiment, the exhaust synchronized rotation speed Nex is set to 5000 rpm, and the length L_ex of the high speed side passage 53 is set to 150 mm in accordance with this. The diameter of the high speed side passage 53 is set to 32 mm.

  Further, in the engine system 100, as described above, by adjusting the length L_in and the cross-sectional area of each intake pipe 3, the primary intake synchronized rotation speed Nin_1a that provides the inertial supercharging effect of the intake air is set to the reference rotation. It is set to be higher than the number N1 and to be within the high speed region. Therefore, in this high speed region, the intake efficiency is increased by the inertia supercharging effect of the intake air, and the engine output is increased. In particular, the non-synchronized rotational speed Nin_1b at which the primary valley of the intake pulsation in which the inertial supercharging effect of the intake air cannot be generated and the closing timing of the intake valve 19 is substantially the same is greater than the reference rotational speed. Since it is configured to be low, the intake efficiency can be increased over the entire high speed region. Specifically, the primary intake synchronized rotation speed Nin_1a is set to 5500 rpm, and the length L_in of the intake pipe 3 is set to 400 mm in accordance with this. In addition, the diameter of the intake pipe 3 is set to 45 mm, and the displacement of the engine body 1 in this embodiment having four cylinders is 2 liters. Further, the non-tuned rotation speed Nin_1b is set to around 3500 rpm.

  Further, since the exhaust synchronized rotation speed Nex and the primary intake synchronized rotation speed Nin_1 are set to different values, the engine output is increased over a wide range in the high speed region.

  As described above, in the present engine system 100, the ejector effect is effectively used in the low speed region to promote scavenging in the cylinder 12, while suppressing the exhaust resistance in the high speed region and reflecting the pulsating pressure wave of the exhaust gas. Further, scavenging and intake in the cylinder 12 can be promoted by utilizing the intake inertia effect, and the intake efficiency can be increased and the engine output can be increased in the entire speed range.

  FIG. 9 shows a graph showing the relationship between engine speed and volumetric efficiency and a graph showing the relationship between engine speed and torque in the engine system 100. In this figure, the solid line represents the volumetric efficiency and torque in the engine system 100, and the broken line represents the volumetric efficiency and torque when the flow path area variable valve 58 is closed at all engine speeds. As shown in this figure, in the engine system 100, the flow area variable valve 58 is opened in the high speed region and the exhaust gas flows out to the high speed side passage 53 side, thereby reducing the exhaust resistance and pulsation pressure of the exhaust gas. Volume efficiency, that is, intake efficiency and torque can be increased by utilizing wave reflection.

  Here, the length L_ex and the cross-sectional area of each high-speed side passage 53 are the high pressure generated when the exhaust valve 20 is opened at the exhaust tuning rotation speed Nex set to a value higher than the reference rotation speed N1. The positive pressure wave is inverted and reflected by the high-speed side collecting portion 57, and the negative pressure wave having a large negative pressure generated by the inversion and reflection during the opening period of the exhaust valve 20 is opened by the exhaust valve 20. It is only necessary to set the size such that the timing of returning to the exhaust port 18 of the cylinder 12 and the overlap period of the cylinder 12 in which the exhaust valve 20 is open overlap, and the number of inversions of the positive pressure wave Is not limited to the above two times. However, the negative pressure amount of the negative pressure wave decreases as the number of inversions increases. When the number of inversions is one, the length L_ex of the high speed side passage 53 becomes longer and the distance between the cylinder 12 and the catalyst device 6 becomes longer. As a result, the temperature of the exhaust gas flowing into the catalyst device 6 is desired. The temperature may be lower than that. Therefore, it is preferable that the length L_ex of each high-speed side passage 53 is set such that the positive pressure wave is inverted twice.

  The length L_in and the cross-sectional area of each of the high-speed passages 53 and the intake pipes 3 are such that the exhaust tuning rotation speed Nex and the primary intake tuning rotation speed Nin_1a coincide with each other. May be set. However, if these are configured differently, the engine output can be increased over a wider range in the high-speed region.

  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 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 intake / exhaust device for a multi-cylinder engine having a plurality of cylinders, each having an intake port and an exhaust port, and an intake valve capable of opening and closing the intake port and an exhaust valve capable of opening and closing the exhaust port. ,
An intake passage connected to each intake port of each cylinder;
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
In the valve driving means, the opening period of the intake valve and the opening period of the exhaust valve of each cylinder overlap in a predetermined overlap period in a low speed region where the engine speed is lower than a preset reference speed. In addition, the intake valve and the exhaust valve of each cylinder are set so that the overlap period of one cylinder overlaps with the timing when the exhaust valve of the other cylinder is opened between cylinders in which the exhaust order is continuous. Each cylinder is driven so that the opening period of the intake valve and the opening period of the exhaust valve overlap each other in a predetermined overlap period in a high speed region where the engine speed is higher than the reference speed. Drive the intake and exhaust valves of the
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 high-speed region, open the high-speed side passage by fully opening the variable flow area valve in the high-speed region,
The length and the cross-sectional area of each high-speed side passage are determined from the cylinder in the vicinity of the opening timing of the exhaust valve in the operating condition where the engine speed is the exhaust synchronized rotation speed set in the high-speed region. The positive pressure wave of the exhaust discharged through the high speed side passage to the high speed side collecting portion is reflected by the high speed side collecting portion to become a negative pressure wave, and this negative pressure wave is discharged through the high speed side passage. The time when the exhaust port of the cylinder is reached and the overlap period of the cylinder where the exhaust gas is discharged are set to overlap .
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 intake / exhaust device for a multi-cylinder engine having a shape satisfying D ≧ 0.5 . The intake / exhaust device for a multi-cylinder engine according to claim 1,
The length and the cross-sectional area of each high-speed side passage are such that the positive pressure wave of the exhaust is reflected twice by the high-speed side collecting portion and the exhaust port of the cylinder under the condition that the engine speed is the exhaust tuning speed. An intake / exhaust device for a multi-cylinder engine, characterized in that the dimension is set such that the time of arrival and the overlap period overlap. The multi-cylinder engine intake / exhaust device according to claim 1 or 2,
The length and the cross-sectional area of each intake passage until the pressure wave of the intake pulsation generated when the intake valve is opened are reflected from the intake valve by the first peak of the intake pulsation. The timing that occurs in the vicinity of the intake valve and the closing timing of the intake valve are substantially the same, and the primary intake synchronized rotational speed that provides the inertial supercharging effect of intake is higher than the reference rotational speed, and the intake pulsation The intake non-synchronized rotational speed at which the primary valley occurs in the vicinity of the intake valve and the intake valve close timing are set to dimensions that are lower than the reference rotational speed. Multi-cylinder engine intake and exhaust system. The intake / exhaust device for a multi-cylinder engine according to claim 3,
An intake / exhaust device for a multi-cylinder engine, wherein the primary intake synchronized rotational speed and the exhaust synchronized rotational speed are different.

Images