JP2012012939A - Cylinder head structure of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve mixing property of fresh air and burned gas as much as possible upon reopening an exhaust valve during an intake stroke.SOLUTION: The circumference edges of openings 41, 43 of a first intake port 12 and a first exhaust port 14, respectively, close to a combustion chamber 6, are chamfered to form tapered faces 51, 53 with the diameters increasing toward the combustion chamber 6. The tapering angle θ3 on the tapered face 53 in the first exhaust port 14 is set to be smaller than the tapering angle θ1 on the tapered face 51 of the first intake port 12.

Description

  The present invention belongs to a technical field related to a cylinder head structure of an engine configured to allow a first exhaust valve to be restarted during an intake stroke following opening and closing during the exhaust stroke.

  2. Description of the Related Art Conventionally, an engine in which an intake swirl flow is generated in a cylinder is known from the viewpoint of improving the combustion efficiency of the engine. In order to generate such an intake swirl flow, the intake port of each cylinder is curved, and the combustion chamber side portion of the intake port progresses toward the combustion chamber side as seen from the cylinder center axis direction. For example, as shown in Patent Document 1, a chamfer is applied to an intake swirl flow traveling side edge portion of an intake port.

  Further, for example, as shown in Patent Document 2, for the purpose of improving combustion, the burned gas (in the exhaust passage) is reopened after the exhaust valve is opened and closed during the intake stroke following the opening and closing during the exhaust stroke. An engine in which exhaust gas) is introduced into a cylinder as internal EGR gas is also known.

Japanese Utility Model Publication No. 2-139331 JP 2000-186517 A

  By the way, when the exhaust valve is restarted during the intake stroke, if the internal EGR amount increases too much, a decrease in the fresh air amount or an increase in smoke will be caused. To prevent this, the lift amount of the exhaust valve Is set smaller than the lift amount of the intake valve. As a result, the amount of burned gas introduced into the cylinder during the intake stroke is reduced, and the flow rate of burned gas when the cylinder is introduced is reduced. For this reason, even if the exhaust port corresponding to the exhaust valve to be restarted is oriented in the direction in which the intake swirl flow proceeds toward the combustion chamber, chamfering is performed on the intake swirl flow advance side edge of the exhaust port. Even if it is applied, combined with the tapered surface at the periphery of the combustion chamber side opening of the exhaust port, the burned gas is introduced into the cylinder from the combustion chamber side opening of the exhaust port. It becomes easy to flow not only in the traveling direction but also in all radial directions.

  Thus, if the burnt gas does not flow in the direction in which the intake swirl flow proceeds, the burnt gas increases the possibility of weakening the intake swirl flow due to fresh air introduced from the intake port into the cylinder. When the intake swirl flow is weakened in this way, mixing of fresh air and burned gas is not sufficiently performed, and there is a high possibility that deterioration of combustibility (increase in smoke) will be caused.

  The present invention has been made in view of such a point, and the object of the present invention is to improve as much as possible the mixing of fresh air and burned gas when the exhaust valve is restarted during the intake stroke. There is in trying to let you.

  In order to achieve the above object, in the present invention, for each cylinder, first and second intake valves that open and close the combustion chamber side openings of the first and second intake ports, respectively, and first and second A first exhaust valve and a second exhaust valve for opening and closing the combustion chamber side opening of the exhaust port, respectively, and the first exhaust valve can be restarted during the intake stroke following the opening and closing during the exhaust stroke. For the engine cylinder head structure, the combustion chamber side portion of the first intake port and the first exhaust port has an intake swirl flow traveling direction toward the combustion chamber as seen from the cylinder central axis direction. And chamfered so that a tapered surface having a diameter increasing toward the combustion chamber side is formed at the peripheral edge portion of the combustion chamber side opening of the first intake port and the first exhaust port. Are applied to the first exhaust port. Taper angle of the tapered surface of the bets has a configuration that is smaller than the taper angle of the tapered surface in the first intake port.

  That is, normally, the amount of fresh air introduced into the cylinder from the first intake port is larger than the amount of burned gas from the first exhaust port 14, and when the fresh air is introduced into the cylinder. Since the flow velocity is faster than the flow velocity when the burned gas is introduced into the cylinder, the first swirl flow direction is directed toward the combustion chamber side even if the taper angle of the tapered surface of the first intake port is relatively large. The fresh air from the first intake port basically flows in the intake swirl flow traveling direction. On the other hand, when the taper angle of the taper surface of the first exhaust port is the same as the taper angle of the taper surface of the first intake port, the first exhaust port advances the intake swirl flow toward the combustion chamber side. Even if the direction is directed, the burned gas, which has a smaller introduction amount than the above-mentioned fresh air and has a slow flow rate when the cylinder is introduced, is only in the direction in which the intake swirl flow proceeds from the combustion chamber side opening of the first exhaust port. It is easy to flow in other directions. However, in the present invention, since the taper angle of the taper surface of the first exhaust port is smaller than the taper angle of the taper surface of the first intake port, the burned gas is opened to the combustion chamber side of the first exhaust port. Therefore, it is difficult to flow in any radial direction, but the first exhaust port is directed in the intake swirl flow traveling direction toward the combustion chamber side, so that it is relatively easy to flow in that direction. Therefore, the possibility that the burned gas weakens the intake swirl flow due to the fresh air introduced into the cylinder from the intake port is reduced, and the mixing property between the fresh air and the burned gas can be improved. Therefore, the mixing property of the air-fuel mixture of the fresh air and the burned gas and the fuel is improved, and the combustibility can be improved.

  In the cylinder head structure of the engine, the combustion chamber side portion of the second intake port is oriented in a direction different from the intake swirl flow traveling direction toward the combustion chamber side when viewed from the cylinder axial direction. The peripheral edge of the combustion chamber side opening of the second intake port is chamfered so as to form a taper surface whose diameter increases toward the combustion chamber side, and the taper surface in the second intake port Further chamfering is applied to the corner between the intake swirl flow traveling side portion of the cylinder head and the combustion chamber side surface of the cylinder head, and the taper angle of the tapered surface of the second intake port is determined by the first intake port. It is preferable that the taper angle is set smaller than the taper angle of the taper surface.

  As a result, the taper angle of the taper surface of the second intake port is smaller than the taper angle of the taper surface of the first intake port, so that fresh air from the second intake port is absorbed by the second intake port. Although it is difficult to flow in any radial direction from the opening on the combustion chamber side, further chamfering is applied to the intake swirl flow advance side, so that the above-mentioned fresh air flows relatively easily in the intake swirl flow advance direction. Become. For this reason, the possibility that the burned gas from the first exhaust port will be inhibited from flowing in the direction of travel of the intake swirl flow due to the fresh air from the second intake port is reduced. Therefore, the mixing property between fresh air and burned gas can be further improved.

  In the cylinder head structure of the engine, further chamfering is provided at corners of the tapered swirl flow advance side portion of the first intake port and the first exhaust port and the combustion chamber side surface of the cylinder head. Are preferably applied respectively.

  This makes it easier for the fresh air from the first intake port and the burned gas from the first exhaust port to flow in the direction of the intake swirl flow, and the mixing of fresh air and burned gas is improved. This can be further improved.

  As described above, according to the cylinder head structure of the engine of the present invention, the taper angle of the taper surface in the first exhaust port is set smaller than the taper angle of the taper surface in the first intake port. Even if the amount of burned gas from one exhaust port is less than the amount of fresh air from the first intake port and the flow rate of the burned gas is slower than the flow rate of the fresh air, the burned gas is sucked It is easy to flow in the direction of travel of the swirl flow, and the mixing property between the fresh air and the burned gas can be improved, so that the combustibility can be improved.

1 is a schematic view showing a configuration of an engine that employs a cylinder head structure according to an embodiment of the present invention. FIG. 4 is a plan view schematically showing first and second intake ports and first and second exhaust ports. It is the perspective view seen from the top which shows the combustion chamber side opening of each port. It is the IV-IV sectional view taken on the line of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic configuration of an engine 1 employing a cylinder head structure according to an embodiment of the present invention. This engine 1 is a diesel engine mounted on a vehicle, and a cylinder block provided with a plurality (four in this embodiment (see FIG. 2)) of cylinders 2 (only one is shown in FIG. 1). 3, a cylinder head 4 disposed on the cylinder block 3, and an oil pan 9 disposed below the cylinder block 3 and storing lubricating oil. In each cylinder 2 of the engine 1, pistons 5 are fitted so as to be able to reciprocate. A deep dish-shaped combustion chamber 6 is formed on the top surface of the piston 5. The piston 5 is connected to the crankshaft 8 via a connecting rod 7.

  The cylinder head 4 is formed with first and second intake ports 12 and 13 and first and second exhaust ports 14 and 15 for each cylinder 2. These first and second intake ports 12 and 13 open to the surface (lower surface) of the cylinder head 4 on the combustion chamber 6 side and one side surface (side surface on the intake side) of the cylinder head 4, and The second exhaust ports 14 and 15 open to the combustion chamber 6 side surface of the cylinder head 4 and the other side surface (exhaust side surface) of the cylinder head 4.

  The cylinder head 4 includes first and second intake valves 16 and 17 that open and close the combustion chamber 6 side openings 41 and 42 of the first and second intake ports 12 and 13, respectively, for each cylinder 2. First and second exhaust valves 18 and 19 for opening and closing the combustion chamber 6 side openings 43 and 44 of the first and second exhaust ports 14 and 15 are disposed.

  Further, the cylinder head 4 is provided with an injector 20 for injecting fuel and a glow plug 25 for warming the intake air to improve the ignitability of the fuel when the engine 1 is cold. The injector 20 is disposed such that its fuel injection port faces the combustion chamber 6 from the ceiling surface of the combustion chamber 6, and fuel is directly injected and supplied to the combustion chamber 6 in the compression stroke. The injector 20 is connected to a common rail (not shown) via a fuel supply pipe 21 and is configured so that fuel is supplied from a fuel tank (not shown) via the fuel supply pipe 21 and the common rail. . Excess fuel is returned to the fuel tank through the return pipe 22.

  An intake passage 30 is connected to the one side surface (side surface on the intake side) of the cylinder head 4 so as to communicate with the first and second intake ports 12 and 13 of each cylinder 2. An air cleaner (not shown) that filters intake air is disposed at the upstream end of the intake passage 30, and the intake air filtered by the air cleaner passes through the intake passage 30 and the intake ports 12, 13 to each cylinder 2. Supplied in. A surge tank 33 is disposed near the downstream end of the intake passage 30. The intake passages 30 on the downstream side of the surge tank 33 are independent passages 30a and 30b that branch corresponding to the first and second intake ports 12 and 13 for each cylinder 2, respectively. , 30b are connected to the intake ports 12, 13 of each cylinder 2, respectively.

  On the other hand, an exhaust passage 40 for discharging burned gas (exhaust gas) from within each cylinder 2 is connected to the other side surface (exhaust side surface) of the cylinder head 4. The upstream portion of the exhaust passage 40 is formed as independent passages 40a and 40b that branch in correspondence with the first and second exhaust ports 14 and 15 for each cylinder 2, and each of the independent passages 40a and 40b. The upstream ends are connected to the exhaust ports 14 and 15 of each cylinder 2, respectively. The downstream ends of the independent passages 40a, 40b of all the cylinders 2 are combined into one.

  In the present embodiment, the engine 1 is configured so that the first exhaust valve 18 can be restarted during the intake stroke following the opening and closing during the exhaust stroke, and the operating state of the engine 1 is within a predetermined operating range. During the intake stroke, the first exhaust valve 18 is opened and closed together with the first and second intake valves 16 and 17, and the burned gas (exhaust gas) in the exhaust passage 40 (independent passages 40a and 40b) is opened. Gas) is introduced into the cylinder 2 (combustion chamber 6) as internal EGR gas. The predetermined operation region is a low rotation / low load operation region preset in the control map (particularly, a low rotation / low load operation region when the engine is cold and the engine water temperature is equal to or lower than a predetermined value). On the other hand, when the operating state of the engine 1 is in an operating region other than the predetermined operating region, the restart valve of the first exhaust valve 18 is not performed during the intake stroke (the first and second normal valves are performed as usual). The intake valves 16 and 17 are opened). That is, the engine 1 has a first valve characteristic that causes the first exhaust valve 18 to resume during the intake stroke following opening and closing during the exhaust stroke, and the restart valve of the first exhaust valve 18 during the intake stroke. A variable valve mechanism capable of switching the valve characteristic is provided in addition to the second valve characteristic that is not performed, and the variable valve mechanism is configured to switch the valve characteristic according to the operating state of the engine 1. Yes. Although the specific configuration of the variable valve mechanism is omitted here, the configuration described in Patent Document 2 or an electromagnetic drive type in which the first exhaust valve 18 is driven by suction with an electromagnetic coil are employed. Can do. Note that, during the intake stroke, the second exhaust valve 19 does not restart and maintains the closed state. This is because the second exhaust port 15 is directed in a direction opposite to the later-described intake swirl flow traveling direction toward the combustion chamber when viewed from the central axis direction of the cylinder 2. This is because the burned gas from 15 is likely to weaken the intake swirl flow.

  The lift amount when the first exhaust valve 18 is restarted in the intake stroke is set to be smaller than the lift amounts of the first and second intake valves 16 and 17. This is because if the amount of internal EGR is excessively large, the amount of fresh air is reduced and the smoke is increased.

  As shown in FIG. 2, the combustion chamber 6 side openings 41, 42 of the first and second intake ports 12, 13 and the combustion chamber 6 side openings of the first and second exhaust ports 14, 15 for each cylinder 2. 43 and 44 are respectively located at the four apexes of the quadrangular shape when viewed from the central axis direction of the cylinder 2. That is, when viewed from the side opposite to the combustion chamber 6 side (upper side) in the central axis direction of the cylinder 2, the combustion in the combustion chamber 6 side opening 42 of the second intake port 13 and the combustion of the first intake port 12 is clockwise. The chamber 6 side opening 41, the combustion chamber 6 side opening 44 of the second exhaust port 15, and the combustion chamber 6 side opening 43 of the first exhaust port 14 are arranged in this order.

  In each cylinder 2, a clockwise intake swirl flow S as seen from above is generated. In the present embodiment, the portion of the first intake port 12 on the combustion chamber 6 side is viewed from the direction of the central axis of the cylinder 2 and the intake swirl flow traveling direction toward the combustion chamber 6 (to be precise, the first The intake port 12 is formed so as to be directed in the direction of travel of the intake swirl flow that flows in the vicinity of the combustion chamber 6 side opening 41 of the intake port 12 (see FIG. 2). As a result, fresh air from the first intake port 12 can easily flow in the direction in which the intake swirl flow proceeds. On the other hand, the portion of the second intake port 13 on the combustion chamber 6 side is a direction different from the intake swirl flow traveling direction toward the combustion chamber 6 side as viewed from the central axis direction of the cylinder 2 (intake swirl flow traveling direction ( To be precise, the second intake port 13 is directed in the direction opposite to the direction of travel of the intake swirl flow that flows in the vicinity of the combustion chamber 6 side opening 42 of the second intake port 13. The fresh air from 13 is made easy to flow toward the intake swirl flow traveling direction. Thus, the intake swirl flow S is generated.

  In addition, the portion of the first exhaust port 14 on the combustion chamber 6 side is also viewed from the direction of the central axis of the cylinder 2 in the intake swirl flow traveling direction toward the combustion chamber 6 (more precisely, the first exhaust port 14 The direction of travel of the intake swirl flow flowing in the vicinity of the combustion chamber 6 side opening 43 is directed (see FIG. 2). However, the amount of burned gas introduced into the cylinder 2 from the first exhaust port 14 is smaller than the amount of fresh air introduced into the cylinder 2 from the first intake port 12, and the burned gas Since the flow velocity when the cylinder 2 is introduced is slower than the flow velocity when the fresh air cylinder 2 is introduced, even if the first exhaust port 14 is directed in the direction in which the intake swirl flow proceeds toward the combustion chamber 6 side. The burnt gas easily flows from the combustion chamber 6 side opening 43 of the first exhaust port 14 not only in the intake swirl flow traveling direction but also in other directions (in all radial directions). In the present embodiment, as will be described later, the burned gas from the first exhaust port 14 also flows easily in the intake swirl flow traveling direction.

  As shown in FIGS. 3 and 4, in the cylinder head 4, a tapered surface 51 whose diameter increases toward the combustion chamber 6 side is formed at the peripheral portion of the combustion chamber 6 side opening 41 of the first intake port 12. Chamfering is applied. This chamfering facilitates insertion of the valve seat 80 from the opening 41. Similarly, a tapered surface 52 (shown only in FIG. 3) whose diameter increases toward the combustion chamber 6 side is also formed at the peripheral portion of the combustion chamber 6 side opening 42 of the second intake port 12. The chamfer is given to. Furthermore, tapered surfaces 53 and 54 (shown only in FIG. 3) whose diameters increase toward the combustion chamber 6 side also at the peripheral portions of the combustion chamber 6 side openings 43 and 44 of the first and second exhaust ports 14 and 15. ) Is formed so that each is chamfered.

  The taper angle of the taper surface 51 in the first intake port 12 is θ1 (see FIG. 4), the taper angle of the taper surface 52 in the second intake port 13 is θ2, and the taper surface 53 of the first exhaust port 14 is The taper angle is θ3, and the taper angle of the taper surface 54 in the second exhaust port 15 is θ4.

In this embodiment,
θ3 <θ1
To meet the relationship.

  That is, the amount of fresh air introduced into the cylinder 2 from the first intake port 12 is larger than the amount of burned gas introduced into the cylinder 2 from the first exhaust port 14, and the fresh air Since the flow velocity when the cylinder 2 is introduced is faster than the flow velocity when the burned gas cylinder 2 is introduced, even if the taper angle θ1 of the taper surface 51 of the first intake port 12 is relatively large, the flow rate is directed toward the combustion chamber 6. Thus, the first intake port 12 oriented in the direction of travel of the intake swirl flow makes it easier for the fresh air from the first intake port 12 to flow in the direction of travel of the intake swirl flow. On the other hand, assuming that θ3 is the same as θ1, as described above, the burned gas flows from the combustion chamber 6 side opening 43 of the first exhaust port 14 not only in the intake swirl flow traveling direction but also in other directions. It becomes easy to flow. Therefore, the taper angle θ3 of the taper surface 53 in the first exhaust port 14 is set smaller than the taper angle θ1 of the taper surface 51 in the first intake port 12. As a result, the burnt gas hardly flows in any radial direction from the combustion chamber 6 side opening 43 of the first exhaust port 14, but the first exhaust port 14 takes in the air toward the combustion chamber 6 side. By directing the swirl flow traveling direction, it is relatively easy to flow in that direction.

  The taper angle θ1 of the taper surface 51 in the first intake port 12 is preferably set to 70 ° to 90 °, and the taper angle θ3 of the taper surface 53 in the first exhaust port 14 is 40 ° to 60 °. It is preferable to set to.

  Further, in the present embodiment, in order for the fresh air from the first intake port 12 to flow more easily in the intake swirl flow traveling direction, the taper at the first intake port 12 is changed in the cylinder head 4. Further chamfering is applied to the corner between the intake swirl flow traveling side portion of the surface 51 and the surface of the cylinder head 4 on the combustion chamber 6 side (the surface where the first intake port 12 opens). Thus, the first intake port 12 has a peripheral portion of the opening 41 on the combustion chamber 6 side in addition to the tapered surface 51 on the entire periphery, and only the intake swirl flow traveling side portion on the combustion chamber 6 side. An inclined surface 61 that is inclined with respect to the center line of the combustion chamber 6 side opening 41 of the port 12 is formed (see FIGS. 3 and 4). It can be said that the inclined surface 61 is a part of a tapered surface that is decentered toward the intake swirl flow traveling side with respect to the tapered surface 51.

  Similarly, in order to make it easier for the burned gas from the first exhaust port 14 to flow in the direction in which the intake swirl flows, the cylinder head 4 has a tapered surface 53 on the first exhaust port 14. Further chamfering is applied to the corner portion between the intake swirl flow traveling side portion and the surface of the cylinder head 4 on the combustion chamber 6 side (surface where the first exhaust port 14 opens). At the periphery of the combustion chamber 6 side opening 43 of the first exhaust port 14, in addition to the tapered surface 53 of the entire circumference, only the intake swirl flow traveling side portion on the combustion chamber 6 side has the first exhaust port 14. An inclined surface 63 inclined with respect to the center line of the combustion chamber 6 side opening 43 is formed (see FIG. 3). It can be said that the inclined surface 63 is a part of a tapered surface that is decentered toward the intake swirl flow traveling side with respect to the tapered surface 53.

  The inclination angle (α shown in FIG. 4) of the inclined surface 61 with respect to the center line of the combustion chamber 6 side opening 41 of the first intake port 12 is larger than θ1 / 2. The inclination angle of the inclined surface 63 with respect to the center line of the combustion chamber 6 side opening 43 of the first exhaust port 14 is larger than θ3 / 2. In the present embodiment, the inclined angles of both the inclined surfaces 61 and 63 are the same.

In order to facilitate the flow of fresh air from the second intake port 13 directed in the direction opposite to the direction of travel of the intake swirl toward the combustion chamber 6 toward the direction of travel of the intake swirl, In the form, in the cylinder head 4, the intake swirl flow advancing side portion of the tapered surface 52 in the second intake port 13 and the surface on the combustion chamber 6 side of the cylinder head 4 (surface on which the second intake port 13 opens). The corners are further chamfered,
θ2 <θ1
To meet the relationship.

  By the further chamfering, at the peripheral edge of the combustion chamber 6 side opening 42 of the second intake port 13, in addition to the tapered surface 52 of the entire circumference, only the intake swirl flow traveling side portion on the combustion chamber 6 side, An inclined surface 62 inclined with respect to the center line of the combustion chamber 6 side opening 42 of the second intake port 13 is formed (see FIG. 3). It can be said that the inclined surface 62 is a part of a tapered surface that is decentered toward the intake swirl flow traveling side with respect to the tapered surface 52. The inclination angle of the inclined surface 62 with respect to the center line of the combustion chamber 6 side opening 42 of the second intake port 13 is larger than θ2 / 2. In the present embodiment, the inclination angle is the same as the inclination angles of the inclined surfaces 61 and 63.

  Thus, since the taper angle θ2 of the taper surface 52 in the second intake port 13 is set smaller than the taper angle θ1 of the taper surface 51 in the first intake port 12, the second intake port 13 The fresh air is less likely to flow in any radial direction from the combustion chamber 6 side opening 42 of the second intake port 13, but is relatively in the intake swirl flow traveling direction due to the inclined surface 62 on the intake swirl flow traveling side. It becomes easy to flow.

  The taper angle θ2 of the tapered surface 52 in the second intake port 13 is preferably set to 40 ° to 60 °, and in the present embodiment, is the same as the taper angle θ3.

  In the intake stroke, since the second exhaust valve 19 is closed, the taper angle θ4 of the tapered surface 54 in the second exhaust port 15 may be set regardless of the intake swirl flow. The taper angle θ1 may be the same. Further, it is not necessary to further chamfer the corner portion between the intake swirl flow traveling side portion of the tapered surface 54 and the surface of the cylinder head 4 on the combustion chamber 6 side (surface where the second exhaust port 15 opens), Only the tapered surface 54 exists at the peripheral edge of the opening 44 on the combustion chamber 6 side of the second exhaust port 15.

  Therefore, in the present embodiment, the taper angle θ3 of the taper surface 53 in the first exhaust port 14 is set to be smaller than the taper angle θ1 of the taper surface 51 in the first intake port 12, so that the first exhaust Even if the amount of burned gas from the port 12 is less than the amount of fresh air from the first intake port and the flow rate of the burned gas is slower than the flow rate of the fresh air, the burned gas is drawn into the intake swirl flow. It can be made easier to flow in the traveling direction. As a result, the mixing property between fresh air and burned gas can be improved, and therefore the mixing property between the mixture of fresh air and burned gas and fuel can be improved, thereby improving the combustibility. it can.

  Further, since the taper angle θ2 of the tapered surface 52 in the second intake port 13 is set to be smaller than the taper angle θ1 of the tapered surface 51 in the first intake port 12, fresh air from the second intake port is set. Becomes easier to flow in the direction of the intake swirl flow. Here, since the combustion chamber 6 side opening 42 of the second intake port 13 is adjacent to the combustion chamber 6 side opening 43 of the first exhaust port 14, fresh air from the second intake port advances the intake swirl flow. When the direction is opposite to the direction, there is a high possibility that the burned gas from the first exhaust port 14 is inhibited from flowing in the direction of travel of the intake swirl flow. However, since the fresh air from the second intake port is easy to flow in the direction in which the intake swirl flows, the fresh air from the second intake port 13 causes the burned gas from the first exhaust port 14 to flow. It is unlikely that the flow in the direction of travel of the intake swirl flow is hindered, and a stronger intake swirl flow S can be generated. Therefore, the mixing property of fresh air and burned gas can be further improved.

  The present invention is not limited to the embodiment described above, and can be substituted without departing from the spirit of the claims.

  For example, in the above-described embodiment, the inclined surfaces 61 and 63 are formed on the peripheral portions of the combustion chamber 6 side openings 41 and 43 of the first intake port 12 and the first exhaust port 14, respectively. Is not necessarily required and may be omitted.

  Further, the taper angle θ2 of the taper surface 52 in the second intake port 13 is set smaller than the taper angle θ1 of the taper surface 51 in the first intake port 12, but not limited to this, θ2 ≧ θ1. Also, the present invention can be applied. However, as described above, from the viewpoint of improving the mixing property between fresh air and burned gas, θ2 <θ1 is preferable.

  The above-described embodiments are merely examples, and the scope of the present invention should not be interpreted in a limited manner. The scope of the present invention is defined by the scope of the claims, and all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  INDUSTRIAL APPLICABILITY The present invention is useful for an engine cylinder head structure that is configured to allow a first exhaust valve to be restarted during an intake stroke following opening and closing during the exhaust stroke.

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Cylinder 4 Cylinder head 12 1st intake port 13 2nd intake port 14 1st exhaust port 15 2nd exhaust port 16 1st intake valve 17 2nd intake valve 18 1st exhaust valve 19 Second exhaust valve 51 Tapered surface in first intake port 52 Tapered surface in second intake port 53 Tapered surface in first exhaust port 61 Inclined surface in first intake port 52 Inclined in second intake port Surface 53 Inclined surface at first exhaust port

Claims (3)

For each cylinder, first and second intake valves that open and close the combustion chamber side openings of the first and second intake ports, respectively, and first and second that open and close the combustion chamber side openings of the first and second exhaust ports, respectively. And a second exhaust valve, and an engine cylinder head structure configured to allow the first exhaust valve to be restarted during an intake stroke following opening and closing during the exhaust stroke,
The combustion chamber side portions of the first intake port and the first exhaust port are each directed in the direction in which the intake swirl flow proceeds toward the combustion chamber when viewed from the cylinder center axis direction.
Chamfering is performed on the peripheral portion of the combustion chamber side opening of the first intake port and the first exhaust port so as to form a tapered surface whose diameter increases toward the combustion chamber side,
A cylinder head structure for an engine, wherein a taper angle of the taper surface in the first exhaust port is set smaller than a taper angle of the taper surface in the first intake port. The cylinder head structure of the engine according to claim 1,
The portion on the combustion chamber side of the second intake port is oriented in a direction different from the intake swirl flow traveling direction toward the combustion chamber when viewed from the cylinder axial direction.
The peripheral edge of the combustion chamber side opening of the second intake port is chamfered so as to form a tapered surface whose diameter increases toward the combustion chamber side,
Further chamfering is applied to the corners of the tapered swirl flow advance side portion of the second intake port and the surface of the cylinder head on the combustion chamber side,
A cylinder head structure for an engine, wherein a taper angle of the taper surface in the second intake port is set smaller than a taper angle of the taper surface in the first intake port. The engine cylinder head structure according to claim 1 or 2,
Further chamfering is performed on the corners of the tapered swirl flow advance side portion of the tapered surface and the combustion chamber side surface of the cylinder head in the first intake port and the first exhaust port, respectively. The cylinder head structure of the engine.

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