JP6281585B2 - Intake and exhaust structure of internal combustion engine - Google Patents

Description

  The technique disclosed herein relates to an intake / exhaust structure of an internal combustion engine in which exhaust gas recirculation (EGR), in which a part of exhaust gas is drawn back to a cylinder through an exhaust port during an intake stroke, so-called internal EGR is performed.

  Patent Document 1 discloses an engine that performs internal EGR by opening an exhaust valve twice in an exhaust stroke and an intake stroke. In a general engine including an engine in which such internal EGR is performed, the cylinder liner wall surface on the ceiling surface that defines the cylinder in which the intake port facing the cylinder of the intake port and the exhaust port facing the cylinder of the exhaust port It is opened at a position close to the center line of the cylinder as viewed in the axial direction of the crankshaft.

  Further, in Patent Document 2, in order to enable smooth discharge of burned gas from a cylinder, the upstream portion of the exhaust port has a substantially square cross-sectional shape having two parallel surfaces, while the throat portion continues from the cylinder. Has a circular cross-sectional shape, and an exhaust port structure is disclosed in which an upstream portion and a throat portion of the exhaust port are continuous by a smooth surface.

JP 2013-133765 A JP 2011-247270 A

  When internal EGR as disclosed in Patent Document 1 is performed and the burned gas is pulled back to the cylinder, most of the burned gas that has been pulled back is introduced into the cylinder and immediately along the cylinder liner wall near the exhaust port. Flowing. For this reason, much of the heat of the burned gas is taken away by the engine cooling water through the cylinder liner wall surface, and the temperature of the burned gas is lowered by the influence of the cooling loss thereby, and the desired combustion chamber temperature is exceeded. However, the temperature of the engine becomes low and the thermal efficiency of the engine decreases. Such a decrease in thermal efficiency is caused by the fact that the burned gas that flows along the cylinder liner wall surface from the exhaust port by the internal EGR when the structure of the exhaust port having a smooth inner wall surface as disclosed in Patent Document 2 is adopted. Since the amount tends to increase, it becomes more prominent.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to improve the thermal efficiency of the internal combustion engine by suppressing the cooling loss when the internal EGR is performed. It is in.

  In order to achieve the above object, the technique disclosed herein reduces the amount of burned gas that flows along the cylinder liner wall surface from the exhaust port when the burned gas is drawn back to the cylinder by the internal EGR. In addition, the intake and exhaust structure has been devised.

  Specifically, the technology disclosed herein includes a cylinder in which a reciprocable piston is inserted, an intake port that sucks air into the cylinder, and an exhaust port that discharges burned gas from the cylinder. And an intake / exhaust structure of an internal combustion engine. The exhaust port facing the inside of the cylinder of the exhaust port is opened at a position biased toward the cylinder liner wall surface side of the cylinder on the ceiling surface defining the cylinder. In the intake / exhaust structure of the internal combustion engine, an internal EGR is performed in which part of the burned gas is drawn back to the cylinder through the exhaust port during the intake stroke.

  If the amount of burned gas flowing along the cylinder liner wall surface from the exhaust port during internal EGR is large, the heat of the burned gas taken away by the engine coolant through the cylinder liner wall surface as described above. In addition to the increase, tumble flow tends to occur in the cylinder. When a tumble flow is generated in the cylinder, the flow rate of the burned gas flowing along the cylinder liner wall surface increases, and accordingly, the heat of the burned gas taken away by the engine coolant through the cylinder liner wall surface increases. Therefore, the cooling loss when performing the internal EGR is increased.

  Therefore, in the first aspect of the intake / exhaust structure, the burned gas that is drawn back into the cylinder by the internal EGR is formed in the inner wall surface of the exhaust port on the cylinder liner wall surface side close to the exhaust port. A separation flow generation unit is provided that separates the circulation flow from the inner wall surface of the exhaust port and generates a separation flow that flows in a direction away from the cylinder liner wall surface at a position where the exhaust port passes.

  According to the first aspect, the burned gas circulation flow by the internal EGR is separated from the inner wall surface of the exhaust port by the separation flow generation unit, and a separation flow that flows away from the cylinder liner wall surface is generated at the exhaust passage passage position. As a result, a large amount of burned gas that is drawn back to the cylinder flows in the flow direction of the separation flow, and the amount of burned gas that flows along the cylinder liner wall surface from the exhaust port can be reduced. Further, the amount of burned gas flowing along the cylinder liner wall surface from the exhaust port can be reduced, so that generation of a tumble flow can be suppressed. As a result, the heat of the burned gas taken by the engine coolant via the cylinder liner wall surface can be reduced, and the cooling loss when the internal EGR is performed can be suppressed.

  1st aspect WHEREIN: It is preferable that the said separated flow production | generation part is an edge part formed toward the inside of the said exhaust port formed by the inner wall face of the said exhaust port.

  In the case where the separated flow generation unit is configured by a member different from the engine block, the separate member may be damaged by being exposed to a high-temperature exhaust flow. In addition, it is difficult to install such another member in the exhaust port so as to function satisfactorily as a separation generation unit. On the other hand, according to the above configuration, since the separation flow generation portion is configured by the shape of the inner wall surface of the exhaust port, there is no fear that the separation flow generation portion will be damaged even if exposed to a high temperature exhaust flow, The mold for forming the exhaust port (core) can be combined with the exhaust port to form the separated flow generating portion, and the separated flow generating portion can be easily built into the exhaust port.

  1st aspect WHEREIN: The part on the opposite side to the said cylinder liner wall surface side close | similar to the said exhaust port among the inner wall surfaces of the said exhaust port is from the part upstream from the throat part of the said exhaust port to the said exhaust port. It is preferably formed on a smoothly continuous surface.

  According to this configuration, the inner wall surface of the exhaust port is formed on a smoothly continuous surface including the portion corresponding to the separation flow generating portion, so that the airflow resistance at the exhaust port is reduced and the existing exhaust gas from the cylinder through the exhaust port is reduced. Fuel gas can be discharged smoothly. Thereby, pump loss can be reduced and it becomes advantageous to the improvement of a fuel consumption.

  Further, in the second aspect of the intake / exhaust structure, the exhaust gas recirculation is pulled back into the cylinder by the exhaust gas recirculation to a portion of the peripheral edge of the exhaust port on the ceiling surface that is close to the exhaust port. A separation flow generating section is provided for separating a circulating flow of burned gas from the ceiling surface and generating a separation flow flowing inwardly from the cylinder liner wall surface.

  According to the second aspect, the burned gas circulation flow by the internal EGR is separated from the ceiling surface of the cylinder by the separation generation unit, and the separation flow that flows from the cylinder liner wall surface to the position inward of the cylinder is generated. As a result, a large amount of the burned gas drawn back to the cylinder flows in the direction of the separation flow, and the amount of burned gas flowing along the cylinder liner wall surface from the exhaust port can be reduced. Thereby, the heat of the burned gas taken by the engine coolant through the cylinder liner wall surface can be reduced, and the cooling loss when the internal EGR is performed can be suppressed.

  2nd aspect WHEREIN: It is preferable that the said separated flow production | generation part is a level | step-difference part formed toward the said cylinder formed by the said ceiling surface.

  According to this configuration, since the separation flow generation unit is configured by the shape of the ceiling surface, there is no fear that the separation flow generation unit will be damaged even if it is exposed to a high-temperature exhaust flow. The shape of the separated flow generating portion can be made together with the surface, and the separated flow generating portion can be easily built on the ceiling surface.

  In the first and second aspects, the intake port facing the cylinder of the intake port has a cylinder surface of the cylinder on the opposite side of the exhaust port across the center line of the cylinder on the ceiling surface defining the cylinder. You may open in the position biased to the liner wall surface side. In this case, it is preferable that the inner wall surface of the intake port is formed on a surface that smoothly continues from the portion upstream of the throat portion of the intake port to the intake port.

  According to this configuration, since the inner wall surface of the intake port is formed on a smoothly continuous surface including a bent portion from the upstream side to the throat portion from the throat portion, air is smoothly drawn into the cylinder through the intake port. be able to. Thereby, the intake amount of air (fresh air) into the cylinder through the intake port can be increased, and the fresh air charging efficiency at the time of normal operation without internal EGR can be increased.

  In the first and second aspects, the inclination angle of the center line passing through the center of the exhaust port in the throat portion of the exhaust port with respect to the center line of the cylinder is greater than 0 degree and not more than 25 degrees. It is preferable.

  According to this configuration, since the portion from the throat portion to the exhaust port in the exhaust port is provided in a substantially upright shape with respect to the circumferential direction of the cylinder, the circulation flow of the burned gas drawn back into the cylinder by the internal EGR The flow in the circumferential direction along the cylinder liner wall can be weakened, and the generation of swirl flow can be suppressed. Therefore, the heat of the burned gas taken by the engine coolant through the cylinder liner wall surface can be further reduced, and the cooling loss when the internal EGR is performed can be further suppressed.

  According to the intake / exhaust structure of the internal combustion engine, it is possible to suppress the cooling loss when the internal EGR is performed and to improve the thermal efficiency of the internal combustion engine.

1 is a cross-sectional view illustrating a schematic configuration of an engine according to a first embodiment. It is sectional drawing of the engine in the II-II line of FIG. FIG. 2 is a schematic view of an upper part of a cylinder of the engine according to the first embodiment when viewed from below. FIG. 4 is an enlarged view of a portion surrounded by IV in FIG. 1. It is an enlarged view of the part enclosed by V of FIG. It is a map showing the relationship between the engine operating region and the optimum gas ratio. It is a figure which shows the opening / closing pattern of an intake valve and an exhaust valve. It is a conceptual diagram which shows the flow of the fresh air and burned gas when internal EGR is performed with the engine which concerns on Embodiment 1. FIG. It is a conceptual diagram which shows the flow of fresh air and burned gas when internal EGR is performed with the engine which concerns on a reference example. FIG. 5 is a cross-sectional view showing a main configuration of an engine according to a second embodiment. It is the schematic which looked at the upper part of the cylinder of the engine which concerns on Embodiment 2 from the downward direction. It is sectional drawing of the cylinder head in the XII-XII line | wire of FIG.

  Hereinafter, exemplary embodiments will be described in detail with reference to the drawings.

Embodiment 1
FIG. 1 shows a schematic configuration of an engine 1 (an example of an internal combustion engine) to which the intake / exhaust structure of the first embodiment is applied. FIG. 2 is a sectional view of the engine 1 taken along the line II-II in FIG. FIG. 3 shows a schematic view of the upper part of the cylinder 7 of the engine 1 as viewed from below. FIG. 4 shows an enlarged view of a portion surrounded by IV in FIG. FIG. 5 shows an enlarged view of a portion surrounded by V in FIG.

  The engine 1 is an in-line four-cylinder engine mounted on an automobile, and is designed to perform compression auto-ignition combustion (CI combustion) and spark ignition combustion (SI combustion) using internal EGR.

  As shown in FIG. 1, the engine 1 includes a cylinder block 3 and a cylinder head 5 assembled on the cylinder block 3. The cylinder block 3 is provided with four cylinders 7 (only one is shown in FIG. 1). These four cylinders 7 are arranged in a row adjacent to each other in a direction in which a crankshaft (not shown) extending in a direction perpendicular to the paper surface of FIG. 1 extends.

  A water jacket 8 through which cooling water flows is formed inside the cylinder block 3 and the cylinder head 5. The water jacket 8 of the cylinder block 3 surrounds the outer periphery of each cylinder 7. On the other hand, the water jacket 8 of the cylinder head 5 is disposed at the top of each cylinder 7 as shown in FIG. These water jackets 8 suppress overheating of the engine 1 due to combustion by cooling water flowing inside.

  In each cylinder 7, as shown in FIG. 1, a piston 11 connected to a crankshaft via a connecting rod 9 is fitted. The piston 11 can reciprocate within the cylinder 7 (can be moved up and down). The top surface 13 of the piston 11, the ceiling surface 15 provided on the lower surface of the cylinder head 5, and the cylinder liner wall surface 17 define a combustion chamber 19 for burning the air-fuel mixture.

  The top surface 13 of the piston 11 is provided with a cavity 21 that is recessed downward. The piston has a flat top surface 23 around this cavity 21. The cavity 21 is formed over the entire circumference around the center line X of the cylinder 7. The cavity 21 has a shape in which the inner diameter gradually increases from the bottom toward the opening.

  The cavity 21 forms a substantially conical convex portion 24 at the center of the top surface 13 of the piston 11. The convex portion 24 extends upward from the bottom of the cavity 21 along the center line X of the cylinder 7, that is, toward the ceiling surface 15 of the cylinder head 5. The upper end of the convex portion 24 is approximately the same height as the flat top surface 23 of the piston 11.

  As shown in FIGS. 1 and 2, two intake ports 25 are formed in the cylinder head 5 for each cylinder 7. Each intake port 25 is a circular port that sucks air into the cylinder 7 and communicates with the combustion chamber 19. The intake ports 27 facing the combustion chambers 19 of the two intake ports 25 are aligned with the axial direction of the crankshaft of the engine 1 and are opened at a position biased toward the cylinder liner wall surface 17 side on the ceiling surface 15 of the cylinder head 5. .

  These two intake ports 25 are independent ports having separate intake ports 27 facing the outside of the cylinder head 5. Each of these intake ports 25 is provided with an intake valve 29 for opening and closing the intake port 27, as shown in FIGS. The intake valve 29 is driven by an intake valve mechanism (not shown), and opens and closes the intake port 27 at a predetermined timing.

  The cylinder head 5 is also formed with two exhaust ports 31 for each cylinder 7. Each of these exhaust ports 31 is a circular port for discharging burned gas from the cylinder 7 and communicates with the combustion chamber 19. Exhaust ports 33 facing the combustion chambers 19 of the two exhaust ports 31 are positions on the ceiling surface 15 of the cylinder head 5 that are biased toward the cylinder liner wall surface 17 on the opposite side of the intake port 27 across the center line X of the cylinder 7. Is open.

  These two exhaust ports 31 are V-shaped or Y-shaped collective ports having a common exhaust port 35 facing the outside of the cylinder head 5 when the engine 1 is viewed in the vertical direction. Each exhaust port 31 is provided with an exhaust valve 37 for opening and closing the exhaust port 33. The exhaust valve 37 is driven by an exhaust valve mechanism (not shown), and opens and closes the exhaust port 33 at a predetermined timing.

  The exhaust valve mechanism is provided with a device for adjusting the lift timing of the exhaust valve 37 (VVT: Variable Valve Timing) and a device for adjusting the lift amount (VVL: Variable Valve Lift). Thereby, the engine 1 can open and close the exhaust valve 37 not only in the exhaust stroke but also in the intake stroke.

  The ceiling surface 15 of the cylinder head 5 has an inclined surface 39 inclined upward from the intake side toward the center line X of the cylinder 7, and an inclined surface inclined upward from the exhaust side toward the center line X of the cylinder 7. It is a so-called pent roof shape including the surface 41. The ceiling surface 15 of the cylinder head 5 also includes a flat surface 43 facing the flat top surface 23 of the piston 11 on each of the outside of the intake side inclined surface 39 and the outside of the exhaust side inclined surface 41.

  Furthermore, an injector 45 shown in FIG. 2 is attached to the cylinder head 5 for each cylinder 7. The injector 45 is disposed on the ceiling surface 15 of the cylinder head 5 where the intake-side inclined surface 39 and the exhaust-side inclined surface 41 intersect, specifically, on the center line X of the cylinder 7. The injector 45 directly injects fuel (for example, gasoline) toward the combustion chamber 19 at a predetermined timing in accordance with an operation signal from the engine control unit.

  The cylinder head 5 is also provided with first and second spark plugs 47 and 49 for each cylinder 7. The first spark plug 47 is disposed between the two intake ports 27 on the intake side across the center line X of the cylinder 7. The second spark plug 49 is disposed between the two exhaust ports 33 on the exhaust side across the center line X of the cylinder 7. These two spark plugs 47 and 49 ignite the air-fuel mixture at a predetermined timing, for example, simultaneously, according to an operation signal from the engine control unit when performing SI combustion.

  FIG. 6 shows an example of a map representing the relationship between the operating region of the engine 1 and the optimum gas ratio. In the engine 1, as shown in FIG. 6, the operating state is switched between CI combustion and SI combustion according to the engine load. Specifically, it is set so that CI combustion is performed in a relatively low load region and SI combustion is performed in a relatively high load region. Internal EGR is performed during CI combustion.

  Then, when internal ERG is being performed, a cylinder in which air (fresh air) introduced into the cylinder 7 through the intake ports 25 and 27 and burned gas drawn back to the cylinder 7 through the exhaust ports 29 and 31 are combined. The ratio of the amount of burned gas out of the total amount of gas filled in 7 is generally higher as the engine load is smaller.

  Therefore, in the low load region where the CI combustion is performed, in the region where the engine load is relatively low, the amount of burned gas is larger than the amount of fresh air, and the flow of burned gas becomes dominant in the combustion chamber 19. . On the other hand, the amount of fresh air is larger than the amount of burned gas and the flow of fresh air is dominant in the combustion chamber 19 in the region where the engine load is relatively high in the low load region where CI combustion is performed. Become.

  FIG. 7 shows an example of opening / closing patterns of the intake valve 29 and the exhaust valve 37. In FIG. 7, the solid line indicates the opening / closing pattern of the exhaust valve 37, and the broken line indicates the opening / closing pattern of the intake valve 29. In the exhaust stroke, as shown in FIG. 7, the two exhaust valves 37 are both opened and closed in synchronization with the opening and closing timing and the opening and closing amount. In the intake stroke, the two exhaust valves 37 are both opened / closed in synchronization with the opening / closing timing and the opening / closing amount. That is, the two exhaust valves 37 are opened and closed twice in one combustion cycle, once in each of the exhaust stroke and the intake stroke.

  In the intake stroke, since it is required to stably introduce the necessary amount of burned gas into the cylinder 7 by the internal EGR, the exhaust valve 37 is opened and closed in the initial stage of the intake stroke. In particular, it is preferable to perform the opening / closing operation in the intake stroke continuously with the opening / closing operation in the exhaust stroke, that is, without providing an interval. By doing so, the burned gas can be introduced by the internal EGR with sufficient time, so that the necessary burned gas can be stably introduced.

  The opening operation of the intake valve 29 is started after the opening operation of the exhaust valve 37. As a result, the burned gas is introduced into the cylinder 7 prior to the fresh air, so that variation in the gas ratio can be effectively suppressed while the burned gas ratio is high. In particular, it is preferable to set the opening operation of the intake valve 29 during the opening operation of the exhaust valve 37. In this way, fresh air can be smoothly introduced into the cylinder 7 and the variation in the gas ratio can be more effectively suppressed.

  Further, the amount of burned gas introduced by the internal EGR increases as the descending speed of the piston 11 increases. Usually, such a period during which the descending speed of the piston 11 is fast is usually an initial stage of the intake stroke, that is, the intake air. Since it is between the top dead center at the start of the stroke and the point where the crank angle becomes 90 degrees (90 CA after TDC), the burned gas can be efficiently introduced into the cylinder 7 by the internal EGR.

  If a swirl flow is generated in the combustion chamber 19 during the internal EGR, the flow rate of the burned gas flowing along the cylinder liner wall surface 17 increases, so that the burnt gas drawn back to the cylinder 7 through the exhaust port 35 Heat is easily taken away by the cooling water in the water jacket 8 through the cylinder liner wall surface 17. For this reason, it is preferable to suppress the generation of a swirl flow during the internal EGR.

  In the swirl flow, when the amount of burned gas is larger than the amount of fresh air, the portion from the throat portion 31 a of the exhaust port 31 to the exhaust port 33 is inclined with respect to the center line X of the cylinder 7. If the amount of fresh air is larger than the amount of burned gas, the portion from the throat portion 25a of the intake port 25 to the intake port 27 is inclined with respect to the center line X of the cylinder 7. It tends to occur more easily.

  Therefore, in this engine 1, as shown in FIG. 1, a portion from the throat portion 31 a of the exhaust port 31 to the exhaust port 33 and a portion from the throat portion 25 a of the intake port 25 to the intake port 27 are formed in the cylinder 7. A shape slightly inclined with respect to the center line X, that is, a shape substantially upright with respect to the circumferential direction of the cylinder 7 is formed.

  Specifically, the inclination angle αi of the center line Ci passing through the center of the intake port 27 in the throat portion 25a of the intake port 25 with respect to the center line X of the cylinder 7 and the center of the exhaust port 33 in the throat portion 31a of the exhaust port 31. The inclination angle αe of the center line Ce passing through is set to be greater than 0 degree and 25 degrees or less. In the present embodiment, the inclination angle αi of the intake port 2525 and the inclination angle αe of the exhaust port 31 are the same angle.

  According to such shapes of the intake port 25 and the exhaust port 31, the circumferential flow along the cylinder liner wall surface 17 of the circulating flow of burned gas drawn back to the cylinder 7 by the internal EGR is weakened. Thereby, it is possible to effectively suppress the occurrence of the swirl flow when the internal EGR is performed.

  Further, if the amount of burned gas flowing along the cylinder liner wall surface 17 from the exhaust port 31 when the burned gas is drawn back to the cylinder 7 by the internal EGR is large, the heat of the burned gas is immediately introduced into the cylinder 7. A large amount of water is taken away by the cooling water in the water jacket 8 through the cylinder liner wall surface 17. In addition, since the directivity in the direction around the axis extending in the direction perpendicular to the center line X of the cylinder 7 is increased in the flow of burned gas, a tumble flow tends to occur inside the combustion chamber 19.

  When a tumble flow is generated in the combustion chamber 19 during the internal EGR, the flow rate of the burned gas flowing along the cylinder liner wall surface 17 is increased, and accordingly, the cooling in the water jacket 8 is performed via the cylinder liner wall surface 17. Since the heat of the burnt gas taken away by water increases, the cooling loss increases, and the thermal efficiency of the engine 1 is reduced due to the influence. For this reason, it is preferable to suppress the occurrence of tumble flow when performing internal EGR.

  Therefore, in the engine 1, as shown in FIG. 4, a portion of the inner wall surface of the exhaust port 31 on the side of the cylinder liner wall surface 17 close to the exhaust port 35 serves as a separation flow generating portion. An edge portion 51 that is angular toward the end is provided. The edge portion 51 is an end portion on the exhaust downstream side of the throat portion 31 a of the exhaust port 31, and a range where the distance between the exhaust port 33 and the cylinder liner wall surface 17 is relatively short in the circumferential direction of the exhaust port 31, for example, the exhaust port 31. It is formed by the inner wall surface of the exhaust port 31 in a range of a central angle of about 120 degrees.

  The angle β of the inner wall surface of the exhaust port 31 at the edge portion 51 is set to 140 degrees or less, and is set to, for example, about 80 degrees to 140 degrees. According to the intake / exhaust structure of the engine 1 having such an edge portion 51, the burned gas flowing along the cylinder liner wall surface 17 from the exhaust port 31 is reduced while the internal EGR is being performed, and the combustion chamber 19 Generation of tumble flow at the can be suppressed.

  That is, when internal EGR is performed, the circulating flow of burned gas is separated from the inner wall surface of the exhaust port 31 by the edge portion 51 in the process of being drawn back into the cylinder 7 through the exhaust port 31. As a result, a separated flow that flows in a direction away from the cylinder liner wall surface 17 is generated at the passage position of the exhaust port 33 in the circulating flow of burned gas. As a result, a large amount of the burned gas drawn back to the cylinder 7 flows in the direction of the separation flow, and the amount of burned gas flowing from the exhaust port 31 along the cylinder liner wall surface 17 is reduced, and the generation of the tumble flow is suppressed accordingly. The

  A portion of the inner wall surface of the exhaust port 31 opposite to the cylinder liner wall surface 17 near the exhaust port 33 is a bent portion from a portion upstream of the throat portion 31a of the exhaust port 31 to the throat portion 31a. That is, it is formed on a surface that smoothly continues to the exhaust port 33 including the portion corresponding to the edge portion 51.

  As a result, the burned gas is smoothly discharged from the cylinder 7 through the exhaust port 31. According to such a configuration, the pump loss in the engine 1 is reduced, which is advantageous in improving fuel consumption.

  Further, the inner wall surface of the intake port 25 is a surface that is smoothly continuous over the entire area from the upstream side of the throat portion 25a of the intake port 25 to the intake port 27 including a bent portion extending from the throat portion 25a. Is formed. That is, a portion corresponding to the edge portion 51 of the exhaust port 31 in the inner wall surface of the intake port 25 is configured by a curved surface having no corners as shown in FIG.

  As a result, fresh air is smoothly drawn into the cylinder 7 through the intake port 25. According to such a configuration, since the intake amount of air (fresh air) into the cylinder 7 through the intake port 25 is increased, it is possible to increase the fresh air charging efficiency during normal operation without internal EGR.

  FIG. 8 shows a conceptual diagram of the flow of fresh air and burned gas when internal EGR is performed in the engine 1. FIG. 9 shows a conceptual diagram of the flow of fresh air and burned gas when internal EGR is performed in the engine 1 according to the reference example.

  When the exhaust port 31 is not provided with the edge portion 51, that is, when the inner wall surface of the exhaust port 31 is formed on a smooth continuous surface as in the intake port 25, as shown in FIG. In addition, most of the burned gas drawn back into the cylinder 7 by the internal EGR flows along the cylinder liner wall surface 17 which is introduced into the cylinder 7 and immediately close to the exhaust port 33. For this reason, much heat of burned gas is taken away by the cooling water in the water jacket 8 through the cylinder liner wall surface 17, and the thermal efficiency of the engine 1 is lowered due to the influence of the cooling loss.

  On the other hand, according to the intake and exhaust structure of the engine 1 according to the first embodiment, as shown in FIG. 8, the burned gas circulation flow by the internal EGR is separated from the inner wall surface of the exhaust port 31 by the edge portion 51. Since the separation flow that flows in the direction away from the cylinder liner wall surface 17 at the passage position of the exhaust port 33 is generated, as described above, when the internal EGR is performed, the exhaust port 31 extends along the cylinder liner wall surface 17. It is possible to reduce the flow of burned gas and suppress the generation of a tumble flow. Thereby, the heat of the burned gas taken by the cooling water in the water jacket 8 through the cylinder liner wall surface 17 can be reduced. As a result, it is possible to improve the thermal efficiency of the engine 1 by suppressing the cooling loss when the internal EGR is performed.

<< Embodiment 2 >>
The engine 1 according to the second embodiment is different from the first embodiment in the configuration of the separated flow generation unit. In the second embodiment, the configuration of the separated flow generation unit is the same as that of the first embodiment except that the configuration of the separated flow generation unit is different from that of the first embodiment. Therefore, only the separated flow generation unit having a different configuration is described. The same components are left to the description of the first embodiment based on FIGS. 1 to 9, and the detailed description thereof is omitted.

  FIG. 10 shows a main configuration of the engine 1 according to the second embodiment. FIG. 11 shows a schematic view of the upper part of the cylinder 7 of the engine 1 as viewed from below. FIG. 12 is a sectional view of the cylinder head 5 taken along the line XII-XII in FIG. In FIG. 11, the intake valve 29 and the exhaust valve 37 are not shown.

  In the engine 1 of the present embodiment, as shown in FIGS. 10 to 12, the cylinder liner wall surface 17 adjacent to the exhaust port 33 among the peripheral portions of the exhaust ports 33 of the exhaust ports 31 on the ceiling surface 15 of the cylinder head 5. A stepped portion 53 that is angular toward the inside of the cylinder 7 is provided as a separated flow generating portion in the side portion. The step 53 is formed by the ceiling surface 15 at a position where the exhaust valve 37 does not interfere with the exhaust valve 37 in a state where the exhaust port 33 is closed.

  Each inner wall surface of the two exhaust ports 37 extends to the exhaust port 33 including the portion from the upstream side of the throat portion 25a of the exhaust port 37 to the throat portion 31a, like the intake port 25. It is formed on a smoothly continuous surface. That is, a portion corresponding to a portion where the edge portion 51 of the first embodiment is provided in the inner wall surface of the exhaust port 31 is configured by a curved surface having no corners as shown in FIG.

  In the intake / exhaust structure of the engine 1 having such a stepped portion 53, when the internal EGR is being performed, the circulation flow of the burned gas drawn back into the cylinder 7 is a stepped portion as shown by an arrow in FIG. 53 is peeled off from the ceiling surface 15 of the cylinder head 5. As a result, a separated flow that flows from the cylinder liner wall surface 17 to an inward position of the cylinder 7 is generated in the burned gas circulation flow. As a result, a large amount of the burned gas drawn back to the cylinder 7 flows in the direction in which the separation flow flows, and the amount of burned gas flowing from the exhaust port 31 along the cylinder liner wall surface 17 decreases.

  Therefore, also by the intake / exhaust structure of the engine 1 according to the second embodiment, the heat of the burned gas taken away by the cooling water in the water jacket 8 through the cylinder liner wall surface 17 when the internal EGR is performed. As a result, the cooling loss when the internal EGR is performed can be suppressed, and the thermal efficiency of the engine 1 can be improved.

  As described above, a preferred embodiment has been described as an example of the technique disclosed herein. However, the technology disclosed herein is not limited to this, and can also be applied to embodiments in which changes, replacements, additions, omissions, etc. have been made as appropriate. Moreover, it is also possible to combine each component demonstrated by the said embodiment into a new embodiment. In addition, the constituent elements described in the accompanying drawings and the detailed description may include constituent elements that are not essential for solving the problem. For this reason, it should not be immediately recognized that these non-essential components are essential because they are described in the accompanying drawings and detailed description.

  For example, the first and second embodiments may be configured as follows.

  In the first embodiment, the separation flow generating portion is the edge portion 51 formed by the inner wall surface of the exhaust port 31, and in the second embodiment, the step portion 53 in which the separation flow generating portion is formed by the ceiling surface 15. However, the present invention is not limited to this. The separated flow generation unit of the first and second embodiments may be configured by a member different from the cylinder head 5.

  In the first embodiment, the description has been given of the double opening operation in which the two exhaust valves 37 are opened and closed once in each of the exhaust stroke and the intake stroke, but the present invention is not limited to this. When performing the internal EGR, it is only necessary that the exhaust valve 37 is open during the intake stroke. Therefore, the exhaust valve 37 may be kept open from the exhaust stroke to the intake stroke.

  As described above, the technique disclosed herein is useful for an intake / exhaust structure of an internal combustion engine in which internal EGR is performed.

DESCRIPTION OF SYMBOLS 1 ... Engine (internal combustion engine), 3 ... Cylinder block, 5 ... Cylinder head, 7 ... Cylinder,
9 ... Connecting rod, 11 ... Piston, 13 ... Top surface, 15 ... Ceiling surface,
17 ... Cylinder liner wall surface, 19 ... Combustion chamber, 21 ... Cavity, 23 ... Flat top surface,
24 ... convex part, 25 ... intake port, 25a ... throat part, 27 ... intake port,
29 ... Intake valve, 31 ... Exhaust port, 31a ... Throat part, 33, 35 ... Exhaust port,
37 ... exhaust valve, 39, 41 ... inclined surface, 43 ... flat surface, 45 ... injector,
47 ... 1st spark plug, 49 ... 2nd spark plug, 51 ... edge part (separation flow production | generation part),
53 ... Step part (separation flow generation part)

Claims (7)

A cylinder fitted with a reciprocating piston;
An intake port for sucking air into the cylinder;
An exhaust port for discharging burned gas from the cylinder,
An exhaust port facing the inside of the cylinder of the exhaust port is opened at a position biased toward the cylinder liner wall surface side of the cylinder on the ceiling surface defining the cylinder,
An intake / exhaust structure of an internal combustion engine in which exhaust gas recirculation is performed to draw a part of burned gas back to the cylinder through the exhaust port during an intake stroke
A portion of the inner wall surface of the exhaust port close to the exhaust port on the cylinder liner wall surface side is separated from the inner wall surface of the exhaust port by a circulating flow of burned gas drawn back into the cylinder by the exhaust gas recirculation. And a separation flow generation section for generating a separation flow that flows in a direction away from the wall surface of the cylinder liner at the passage position of the exhaust port. The intake / exhaust structure according to claim 1,
2. The intake / exhaust structure according to claim 1, wherein the separated flow generating portion is an edge portion that is formed by an inner wall surface of the exhaust port and is square toward the exhaust port. The intake / exhaust structure according to claim 1,
Of the inner wall surface of the exhaust port, a portion on the side opposite to the cylinder liner wall surface side that is close to the exhaust port smoothly continues from the portion upstream of the throat portion of the exhaust port to the exhaust port. An intake / exhaust structure characterized by being formed on a surface. A cylinder fitted with a reciprocating piston;
An intake port for sucking air into the cylinder;
An exhaust port for discharging burned gas from the cylinder,
An exhaust port facing the inside of the cylinder of the exhaust port is opened at a position biased toward the cylinder liner wall surface side of the cylinder on the ceiling surface defining the cylinder,
An intake / exhaust structure of an internal combustion engine in which exhaust gas recirculation is performed to draw a part of burned gas back to the cylinder through the exhaust port during an intake stroke
Of the peripheral portion of the exhaust port on the ceiling surface, a portion of the cylinder liner wall surface adjacent to the exhaust port is provided with a circulating flow of burned gas drawn back into the cylinder by the exhaust gas recirculation from the ceiling surface. An intake / exhaust structure characterized in that a separation flow generating section is provided that generates separation flow that is separated and flows from the cylinder liner wall surface to a position away from the cylinder inward. The intake / exhaust structure according to claim 4,
The intake / exhaust structure according to claim 1, wherein the separated flow generating portion is a stepped portion formed by the ceiling surface and squared toward the inside of the cylinder. In the intake / exhaust structure according to any one of claims 1 to 5,
An intake port facing the inside of the cylinder of the intake port is opened at a position opposite to the exhaust port across the center line of the cylinder and at a position biased toward the cylinder liner wall surface side of the cylinder on the ceiling surface defining the cylinder And
An intake / exhaust structure in which an inner wall surface of the intake port is formed on a surface that extends smoothly from a portion upstream of a throat portion of the intake port to the intake port. In the intake / exhaust structure according to any one of claims 1 to 6,
An intake / exhaust structure, wherein an inclination angle of a center line passing through a center of the exhaust port in a throat portion of the exhaust port with respect to a center line of the cylinder is greater than 0 degree and not more than 25 degrees.

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