JP4514637B2 - Water-cooled internal combustion engine - Google Patents

Description

  The present invention relates to a water-cooled internal combustion engine having a cylinder head in which an intake port and an exhaust port and a water jacket through which cooling water flows is formed and which is equipped with a spark plug, and more particularly to the structure of the water jacket.

As this type of water-cooled internal combustion engine, for example, one disclosed in Patent Document 1 includes a cylinder head in which two intake ports, two exhaust ports, and a first liquid passage through which a coolant flows are formed. The coolant flowing through the first fluid passage passes through the vicinity of the intake port, the exhaust port, and the spark plug, and then gathers in a water gallery communicating with the coolant discharge opening. The water gallery is formed so as to cross over the two intake ports.
Japanese Patent No. 3461773

By the way, in the prior art, the spark plug is positioned coaxially with the cylinder axis by projection onto the bottom surface of the cylinder head. However, when a single camshaft is provided in the cylinder head, for example, an SOHC type internal combustion engine, the spark plug may be inclined with respect to the cylinder axis to avoid interference with the camshaft. is there. When the spark plugs are arranged so as to be inclined in this manner, the intervals between the intake port and the exhaust port and the spark plugs are narrowed, and a coolant flow path can be formed around the spark plugs over the entire circumference. This makes it difficult to reduce the cooling performance of the spark plug and the surrounding cylinder head.
Further, when the coolant after cooling the spark plug and the surrounding cylinder head portion is gathered above the intake port (on the side opposite to the cylinder), the cylinder head becomes larger in the cylinder axial direction.

  The present invention has been made in view of such circumstances, and the invention according to claims 1 to 4 is a water-cooled internal combustion engine including a cylinder head on which a spark plug is mounted inclined with respect to a cylinder axis. An object of the present invention is to improve the cooling performance of the spark plug by cooling water and the surrounding cylinder head and to reduce the size of the cylinder head in the cylinder axial direction. A second object of the present invention is to prevent an increase in the size of the cylinder head in the direction in which the two ventilation ports sandwiching the inter-port passage are separated.

According to a first aspect of the present invention, there is provided a cylinder head in which an intake port and an exhaust port that are open to a combustion chamber formed between the cylinders and a water jacket through which cooling water flows are formed and a spark plug is mounted. In the water-cooled internal combustion engine in which at least one of the intake port and the exhaust port includes a plurality of ventilation ports, the water jacket is disposed between the spark plug and the cylinder axis inclined with respect to the cylinder axis. a central portion located in the counter-cylinder side for each vent port, a peripheral portion positioned on the cylinder side with respect to the respective vent port radially outward of the said central portion, said plurality of vent ports (13, water-cooled internal combustion engine der characterized by having a port-to-port passage is formed communicating with the peripheral portion and the central portion between of two through air ports (13, 14) of 14) .

  According to this, even if the cylinder hole has a small diameter, etc., the spark plug is inclined with respect to the cylinder axis, so that a water passage surrounding the spark plug over the entire circumference cannot be formed. Because the passage between the ports establishes the flow of the cooling water between the central portion and the peripheral portion, the cooling water in the central portion does not stagnate in the central portion. Cooling of the surrounding cylinder head part is promoted. Further, the passage between the ports communicates with the peripheral portion located on the cylinder side of each ventilation port radially outward, so that the cylinder in the cylinder axial direction is compared with the case where the peripheral portion is on the opposite cylinder side of each ventilation port. The size of the head can be reduced.

  According to a second aspect of the present invention, in the water-cooled internal combustion engine according to the first aspect, the cross section of the passage between the ports has a width in the cylinder axial direction with respect to a width in the separation direction of the two ventilation ports. It is a large shape.

  According to this, the flow rate of the cooling water in the central portion can be promoted by increasing the flow rate of the cooling water in the inter-port passage without increasing the interval between the ventilation ports sandwiching the inter-port passage. .

  According to a third aspect of the present invention, in the water-cooled internal combustion engine according to the first aspect, the plurality of ventilation ports constitute only the intake port, and the water jacket includes the central portion and A first annular portion and a second annular portion sharing the inter-port passage, wherein the first annular portion surrounds all the exhaust ports and the spark plugs, and the second annular portion includes at least one Surrounding the intake port.

  According to this, the amount of cooling water that has become hot due to heat exchange with the exhaust port and the spark plug and the temperature of cooling water that has flowed between the exhaust ports and flows into the central portion is reduced. Since the flow rate of the relatively low-temperature cooling water flowing into the cylinder increases, cooling of the spark plug and the surrounding cylinder head portion is promoted.

  According to a fourth aspect of the present invention, in the water-cooled internal combustion engine according to the first aspect of the present invention, the water jacket is composed of a peripheral portion, a radial direction portion, and an inter-port passage communicating with each other within the range of the one cylinder. The peripheral portion includes a communication passage that communicates with a water jacket formed in the cylinder and includes the peripheral portion, and the radial direction portion extends from the peripheral portion only between the intake port and the exhaust port. Extending inward in the radial direction, the end portion thereof constitutes the central portion, and the cooling water flows through the inter-port passage from the central portion to the peripheral portion.

  According to this, since the relatively low-temperature cooling water from the surroundings flows into the center part after flowing into the central part, for example, the high-temperature cooling that has passed between the plurality of exhaust ports or between the exhaust ports and the spark plugs. Compared with the case where water flows into the center, relatively low-temperature cooling water flows into the center.

  According to invention of Claim 1, the following effect is show | played. That is, since the cooling water does not stagnate in the central portion, the cooling performance of the spark plug and the surrounding cylinder head portion by the cooling water in the central portion is improved, and the peripheral portion is on the cylinder side of each ventilation port. Therefore, the cylinder head is downsized in the cylinder axial direction.

  According to invention of Claim 2, in addition to the effect of the invention of the cited claim, there exists the following effect. That is, it is possible to improve the cooling performance of the spark plug and the surrounding cylinder head portion by the cooling water at the central portion without increasing the size of the cylinder head in the direction in which both the ventilation ports sandwiching the inter-port passage.

  According to invention of Claim 3, in addition to the effect of the invention of the cited claim, there exist the following effects. That is, since the high-temperature cooling water is restricted from flowing into the central portion, the cooling performance of the spark plug and the surrounding cylinder head is improved by the relatively low-temperature cooling water at the central portion.

  According to invention of Claim 4, in addition to the effect of the invention of the cited claim, there exists the following effect. That is, the cooling performance of the spark plug and the surrounding cylinder head portion is improved by the relatively low-temperature cooling water that flows from the peripheral portion only between the intake port and the exhaust port and flows into the central portion.

Embodiments of the present invention will be described below with reference to FIGS.
Referring to FIG. 1, a water-cooled internal combustion engine E to which the present invention is applied is mounted on a scooter type motorcycle as a vehicle in a horizontal arrangement in which a rotation center line L0 of a crankshaft 7 is directed in the left-right direction. The internal combustion engine E constitutes a power unit together with a power transmission device including a belt-type continuously variable transmission M in which the crankshaft 7 also serves as the drive shaft of the drive pulley Ma, and the power generated by the internal combustion engine E is to the right of the internal combustion engine E. Is transmitted to a rear wheel, which is a drive wheel as a drive target, via a continuously variable transmission M arranged in the vehicle.

  The internal combustion engine E is a SOHC type V-type two-cylinder four-stroke internal combustion engine, a pair of cylinders 1a and 1b arranged in a V-shape, and directions A1 and C1 of cylinder axes L1a and L1b in the cylinders 1a and 1b. A pair of cylinder heads joined to the cylinders 1a and 1b and joined to the cylinders 1a and 1b at the tip ends in the cylinder axial directions A1 and A2 respectively. The engine main body is composed of 3a and 3b and a pair of head covers 4a and 4b coupled to the cylinder heads 3a and 3b.

  In the specification, up, down, front, back, left, and right mean up, down, front, back, left, and right, respectively, based on a normal use state of a motorcycle or the internal combustion engine E that is a device equipped with the internal combustion engine E. .

  Each of the pair of banks B1 and B2 constituting the V bank is composed mainly of the cylinder 1a and the cylinder 1b. More specifically, the first bank B1 as the front bank includes a cylinder 1a that has a cylinder axis L1a that is slightly tilted forward and obliquely upward and is largely tilted forward, a cylinder head 3a, and a head cover 4a. The second bank B2 as a rear bank includes a cylinder 1b having a cylinder axis L1b slightly inclined rearward and obliquely upward, a cylinder head 3b, and a head cover 4b.

  Each member including the cylinder heads 3a and 3b provided in both banks B1 and B2 and the structure thereof are basically the same. Therefore, the following description will be made focusing on the first bank B1.

  Referring to FIGS. 2 to 4, the piston 5 that fits in the cylinder hole 1 c of the cylinder 1 a so as to be able to reciprocate is supported by a crankshaft 7 that is rotatably supported by the crankcase 2 via a connecting rod 6 (see FIG. 1). ). The cylinder head 3a has an intake port 11 having a combustion chamber 10 formed between the cylinder 1a facing the piston 5 in the cylinder axial direction A1 and a pair of intake ports 13a, 14a opened to the combustion chamber 10. An exhaust port 15 having a pair of exhaust ports 17a and 18a that open to the combustion chamber 10 and an insertion hole 21 into which a spark plug 20 that is mounted to be inclined with respect to the cylinder axis L1a are inserted.

  Referring to FIGS. 2, 4 and 6 together, the intake port 11 includes a collection port 12 having an intake inlet 12a and a plurality of intake ports 13a and 14a branched from the collection port 12 at a branch portion 11a. In this embodiment, it is composed of a pair of branch ports 13 and 14 as a pair of ventilation ports. The exhaust port 15 includes a collective port 16 having an exhaust outlet 16a, and a plurality of exhaust ports 17a and 18a branched from the collective port 16 at a branch portion 15a, respectively, and in this embodiment, a pair of branch ports 17 and 18 Consists of

  The spark plug 20 that is screwed into the cylinder head 3a so that the electrode portion 20a faces the central portion 61 of the combustion chamber 10 is installed in a direction perpendicular to the reference plane P1 (see FIG. 6A). 13 and 14 and the branch ports 17 and 18 are inclined to an inclined side which is one side (right side in this embodiment) with respect to a plane P2 including the cylinder axis L1a and orthogonal to the reference plane P1.

  Here, the reference plane P1 is a plane including the cylinder axis L1a, and the cylinder 1a, the cylinder head 3a, and the like are arranged on the intake side where the whole or most of the intake port 11 is disposed with respect to the reference plane P1, and the reference plane P1. The plane P1 is a plane that bisects the side on which the whole or most of the exhaust port 15 is disposed with respect to the exhaust side.

  2 to 4, the cylinder head 3a has a pair of intake valves 23 and a pair of exhaust valves 24 that open and close a pair of intake ports 13a and 14a and a pair of exhaust ports 17a and 18a, respectively. Provided. Each intake valve 23 and each exhaust valve 24 are driven by a valve cam provided on one camshaft 27 that is rotationally driven by the power of the crankshaft 7 transmitted through a valve train transmission mechanism 25 having a chain 25a. The valve operating device 26 including the rocker arm 28 that is driven to swing is opened and closed at a predetermined timing. A cam shaft 27 having a rotation center line L2 parallel to the rotation center line L0 (see FIG. 1) of the crankshaft 7 is disposed at a position intersecting the cylinder axis L1a.

  1 and 2, an intake device 30 including a throttle body 31 provided with a throttle valve 31a and an intake connection pipe 32 connecting the throttle body 31 and the cylinder head 3a is disposed in the bank space. Intake air introduced from an air cleaner (not shown) of the intake device 30 flows through an intake passage 33 formed by the throttle body 31 and the intake connection pipe 32, and is supplied from a fuel injection valve 34 attached to the throttle body 31. The fuel is mixed with the fuel to form an air-fuel mixture, and the air-fuel mixture is sucked into the combustion chamber 10 through the intake port 11. The combustion gas generated in the combustion chamber 10 drives the piston 5 with the pressure, and then is discharged to the outside as an exhaust gas through an exhaust device having an exhaust pipe (not shown) connected to the exhaust port 15.

  The cooling system of the internal combustion engine E is formed in each of a water pump 40 that is rotationally driven by the power of the crankshaft 7 to pump cooling water, a radiator 41, a thermostat 42, and a cylinder 1a and a cylinder head 3a of the first bank B1. The water jackets W1 and W2 and the water jackets (not shown) formed in the cylinder 1b and the cylinder head 3b of the second bank B2, respectively. It consists of a passage.

  Then, the cooling water pumped by the water pump 40 flows into the water jacket W1 of the cylinder 1a through the introduction water passage 43 located on the exhaust side of the cylinder 1a, and then the communication passage 51 formed in the lower deck of the cylinder head 3a. And flows into the water jacket W2 and heated by the heat from the exhaust port 15 and the combustion chamber 10, the cylinder head 3a, the ignition plug 20, and the portion around the ignition plug 20 in the cylinder head 3a (hereinafter simply referred to as "ignition"). The cylinder head portion around the stopper 20 is called “cooling”. Thereafter, the cooling water flows from the cooling water jacket W2 through the water passage formed by the conduit 44 positioned above the cooling water jacket W2, flows into the water jacket of the cylinder 1b of the second bank B2, cools the cylinder 1b, and then the cylinder head 3b. Then, the cylinder head 3b, the spark plug 20, and the cylinder head portion around the spark plug 20 are cooled, and then flow into a thermostat 42 attached to the cylinder head 3b. After the warming-up of the internal combustion engine E is completed, the cooling water from the thermostat 42 is guided to the radiator 41 through a conduit, and the cooling water that has dissipated heat and is cooled by the radiator 41 is sucked into the water pump 40.

The water jacket W2 will be mainly described with reference to FIGS. 2 to 6, but the water jacket of the cylinder head 3b of the second bank B2 has the same structure.
4 to 6, the water jacket W2 includes a peripheral portion 50, a radial portion 60, and an inter-port passage 70 that communicate with each other in the range of one cylinder 1a when viewed from the cylinder axial direction A1. Is done.

  An annular peripheral portion 50 that is located radially outward from a center portion 61 that will be described later and surrounds the combustion chamber 10 around the cylinder axis L1a includes a plurality of communication passages 51 that communicate with the water jacket W1 and an intake side. An outlet 52 is provided at the top of the water jacket W2 to guide the cooling water to the second bank B2, and an annular bottom 53 is located on the cylinder side with respect to the intake port 11 or the exhaust port 15.

  The radial direction part 60 is radial from the peripheral part 50 only between the intake port 11 and the exhaust port 15 that are separated by a distance larger than the distance between both branch ports 13 and 14 and the distance between both branch ports 17 and 18. A central portion 61 that extends inward and intersects the cylinder axis L1a is provided at the end portion thereof. The central portion 61 includes a portion 61a between the spark plug 20 and the cylinder axis L1a that is inclined with respect to the cylinder axis L1a, and is located on the side opposite to the cylinder with respect to the branch ports 13 and 14 of the intake port 11. . Further, the central portion 61 is surrounded by the branch ports 13, 14, 17, 18 and the spark plug 20, and is positioned so as to overlap with the electrode portion 20a of the spark plug 20 when viewed from the cylinder axial direction A1 (FIG. 3). FIG. 6 (A)).

  The inter-port passage 70 is formed between the two branch ports 13 and 14, and communicates the central portion 61 and the peripheral portion 53a that is a part of the bottom portion 53 (see also FIG. 2). The peripheral portion 53a located above the central portion 61 is located on the cylinder side with respect to the branch ports 13 and 14 on the outer side in the radial direction than the central portion 61. The peripheral portion 53a is located between the branch ports 13 and 14 in this embodiment as viewed from the cylinder axial direction A1, but may be located at a position overlapping the branch portion 11a or the collecting port 12 of the intake port 11. Good. Therefore, the inter-port passage 70 extends from the non-cylinder side to the cylinder side between the branch ports 13 and 14 as the distance from the cylinder axis L1a increases. Further, the flow path cross section of the inter-port passage 70 (indicated by the two-dot chain line hatching in FIG. 5) is the separation direction of the two branch ports 13 and 14 (that is, the arrangement direction of the two intake ports 13a and 14a). The width in the cylinder axial direction A1 is longer than the width of.

  In this specification or claims, the cylinder side and the non-cylinder side are the positions in the cylinder axis direction A1 at positions where the distance from the cylinder axis L1a is equal to the reference member or part. The side where the cylinder 1a is located and the side opposite to the side where the cylinder 1a is located in the position in the cylinder axial direction A1 are meant. The radial direction means a radial direction centered on the cylinder axis.

  In addition, the radial direction portion 60 has only the opposite side to the spark plug 20 across the cylinder axis L1a or the opposite side (that is, the inclined side with respect to the plane P2) so that the central portion 61 becomes the end portion. It communicates with the surrounding part 50 only on the opposite side. For this reason, the water jacket W2 has a first annular portion and a second annular portion that share the central portion 61, the inter-port passage 70, and the outlet 52. The first annular portion is composed of a central portion 61, an inter-port passage 70, and a portion 50a on the inclined side of the peripheral portion 50 and a portion 50b1 on the opposite side to the exhaust side. , 18, spark plug 20 and one branch port 14 on one side. The second annular portion is constituted by a central portion 61, an inter-port passage 70, and a portion 50b2 on the intake side mainly on the anti-inclined side of the peripheral portion 50. Enclose.

  Corresponding to the cooling water pumped by the water pump 40 flowing into the water jacket W2 of the cylinder 1a from the exhaust side, most of the cooling water in the water jacket W2 is from the exhaust side from the exhaust side. Also flows toward the intake side located above. Therefore, in the water jacket W2, the cooling water flowing into the peripheral portion 50 from the communication passage 51 on the exhaust side flows to the outlet 52 through the side of the spark plug 20 at the portion 50a of the peripheral portion 50 on the inclined side. On the anti-inclined side, since there is the inter-port passage 70, a part of the cooling water flowing through the peripheral portion 50 becomes a branching flow toward the central portion 61, and the side of the spark plug 20 in the central portion 61 After flowing through the inter-port passage 70, the peripheral portion 53 a merges with cooling water from the inclined portion 50 a of the peripheral portion 50 and the anti-inclined portion 50 b of the peripheral portion 50, and then toward the outlet 52.

  As described above, since the inter-port passage 70 is provided, a flow from the portion 50b of the peripheral portion 50 to the inter-port passage 70 through the central portion 61 is generated. Therefore, the inter-port passage illustrated in FIG. Generation of cooling water stagnation at the central portion 91 of the water jacket 90 without 70 is prevented, and cooling of the spark plug 20 and the cylinder head portion around the spark plug 20 is promoted.

Next, operations and effects of the embodiment configured as described above will be described.
The water jacket W2 formed in the cylinder head 3a is located on the side opposite to the cylinder with respect to the branch ports 13 and 14 of the intake port 11 between the spark plug 20 inclined with respect to the cylinder axis L1a and the cylinder axis L1a. A central portion 61, a peripheral portion 53 a positioned on the cylinder side with respect to each branch port 13, 14 on the radially outer side than the central portion 61, and the central portion 61 formed between both branch ports 13, 14. By having the inter-port passage 70 communicating with the peripheral portion 53a, the spark plug 20 is inclined with respect to the cylinder axis L1a due to the small diameter of the cylinder hole 1c, etc. Even when the water passage surrounding the periphery cannot be formed, the inter-port passage 70 establishes the flow of the cooling water between the central portion 61 and the peripheral portion 53a. However, the central part 61 is not Cooling of the cylinder head portion around the spark plug 20 and the ignition plug 20 by water is accelerated, the cooling of the cylinder head portion around the spark plug 20 and the ignition plug 20 by the cooling water at the central portion 61 is improved. Further, since the inter-port passage 70 communicates with the peripheral portion 53a located on the cylinder side of each branch port 13 and 14 in the radially outward direction, the peripheral portion 53a is on the opposite cylinder side of each branch port 13 and 14. Since the dimension of the cylinder head 3a in the cylinder axial direction A1 can be reduced as compared with the case, the cylinder head 3a is downsized in the cylinder axial direction A1.

  The cross section of the flow path of the inter-port passage 70 has a shape in which the width in the cylinder axial direction A1 is larger than the width in the separation direction of both the branch ports 13 and 14, so that both the branch ports 13 sandwiching the inter-port passage 70 are sandwiched. , 14 without increasing the spacing between the ports, the flow rate of the cooling water in the inter-port passage 70 can be increased and the flow of the cooling water in the central portion 61 can be promoted. Without increasing the size, it is possible to improve the cooling performance of the spark plug 20 by the cooling water in the central portion 61 and the cylinder head portion around the spark plug 20.

  The water jacket W2 includes the first annular portion that surrounds both the branch ports 17 and 18 of the exhaust port 15 and the spark plug 20, and the second annular portion that surrounds one branch port 13 of the intake port 11. The amount of cooling water that has become hot due to heat exchange with the exhaust port 15 and the spark plug 20 and the cooling water that has flowed through the branch ports 17 and 18 of the exhaust port 15 and flows into the central portion 61 is reduced. Accordingly, the flow rate of the relatively low-temperature cooling water flowing from the portion 50b of the peripheral portion 50 into the central portion 61 is increased, so that the cooling of the spark plug 20 and the cylinder head portion around the spark plug 20 is promoted. As a result, since the high-temperature cooling water is restricted from flowing into the central portion 61, the cooling performance of the spark plug 20 and the cylinder head portion around the spark plug 20 is reduced by the relatively low-temperature cooling water in the central portion 61. Will improve.

  Further, since the first annular portion also surrounds the branch port 14 of the intake port 11, the high-temperature cooling water after cooling the spark plug 20 at the portion 50 a of the peripheral portion 50 is formed between the spark plug 20 and the branch port 14. Since the flow does not flow into the central portion 61, the flow rate of the relatively low-temperature cooling water flowing from the portion 50b of the peripheral portion 50 to the central portion 61 is further increased. The cooling performance of the spark plug 20 and the cylinder head portion around the spark plug 20 is further improved by the relatively low-temperature cooling water.

The water jacket W2 includes a peripheral portion 50, a radial direction portion 60, and an inter-port passage 70 that communicate with each other. The peripheral portion 50 includes a communication passage 51 that communicates with the water jacket W2 of the cylinder 1a and a peripheral portion 53a. The radial direction portion 60 extends radially inward from the peripheral portion 50 only between the branch port 13 of the intake port 11 and the branch port 17 of the exhaust port 15, and its end portion forms the central portion 61. The cooling water flows through the inter-port passage 70 from the central portion 61 to the peripheral portion 53a, so that the relatively low-temperature cooling water from the portion 50b of the peripheral portion 50 flows into the central portion 61 and then flows through the inter-port passage 70. Therefore, as compared with the case where the high-temperature cooling water passing between the two branch ports 17 and 18 of the exhaust port 15 and between the exhaust port 15 and the spark plug 20 flows into the central portion 61, the relatively low-temperature cooling water. Flows into the central portion 61, so that the intake port is introduced from the portion 50b of the peripheral portion 50. The cooling performance of the ignition plug 20 and the cylinder head around the ignition plug 20 is improved by the relatively low temperature cooling water that flows into the central portion 61 only through the gap between the exhaust port 11 and the exhaust port 15.
In addition, by providing the cooling water outlet 52 connected to the conduit 44 at a position higher than the central portion 61 of the water jacket W2, the air in the water jacket W2 can be discharged efficiently.

Hereinafter, an embodiment in which a part of the configuration of the above-described embodiment is changed will be described with respect to the changed configuration.
In the embodiment, the two ventilation ports are composed of the branch ports 13 and 14 and only the intake port 11 is configured. However, the two ventilation ports are the branch ports 13 and 14 of the intake port 11 and the branch port of the exhaust port 15. It may consist of at least one of 17 and 18, and may constitute at least one of the intake port 11 and the exhaust port 15. For example, when cooling water flows from the intake side in the water jacket W2, the inter-port passage 70 may be formed between the pair of branch ports 17 and 18 of the exhaust port 15, and in this case, each of the exhaust ports 15 The branch ports 17 and 18 are ventilation ports.
At least one of the intake port 11 and the exhaust port 15 may be configured by a pair of or a plurality of ventilation ports that do not have a collection port and are independent of each other. The exhaust port may be a port that does not have a branch port.

The first annular portion may surround both the branch ports 17 and 18 of the exhaust port 15 and only the spark plug 20, and in this case, the water jacket W2 includes the first annular portion and the second annular portion. In addition, a third annular portion surrounding the branch port 14 is provided. When the intake port 11 has three or more branch ports, the second annular portion may surround two or more branch ports.
The cooling water may flow in the inter-port passage 70 from the peripheral portion 53a toward the central portion 61.
The internal combustion engine may be a multi-cylinder internal combustion engine other than the V-type two cylinders, or may be a single cylinder internal combustion engine. In a multi-cylinder internal combustion engine in which at least two cylinders are arranged in series, the present invention is applied within the range of one cylinder.

1 is a right side view of a power unit including a water-cooled internal combustion engine to which the present invention is applied. It is principal part sectional drawing of the 1st bank of the internal combustion engine of FIG. It is principal part sectional drawing in the III-III line of FIG. FIG. 2 is a perspective view in which a water jacket, an intake port and an exhaust port in a cylinder head of a first bank of the internal combustion engine of FIG. 1 are visualized. It is a perspective view from another angle of the water jacket of FIG. (A) is the schematic diagram of FIG. 4 seen from the cam shaft side in the cylinder axis direction, and (B) is a diagram corresponding to (A) when there is no passage between ports.

Explanation of symbols

3a ... Cylinder head, 11 ... Intake port, 13, 14 ... Branch port, 15 ... Exhaust port, 20 ... Spark plug, 50 ... Peripheral part, 53a ... Peripheral part, 61 ... Central part, 70 ... Passage between ports, E ... Internal combustion engine, L1a ... cylinder axis, W2 ... water jacket.

Claims (4)

An intake port and an exhaust port which are formed between the cylinder and which are formed in a combustion chamber; a water jacket through which cooling water flows; and a cylinder head to which a spark plug is attached, the intake port and the exhaust port In the water-cooled internal combustion engine in which at least one of the plurality of ventilation ports is configured,
The water jacket has a central portion located on the side opposite to the cylinder with respect to each vent port between the spark plug inclined to the cylinder axis and the cylinder axis, and radially outward from the central portion. a peripheral portion positioned on the cylinder side with respect to the respective vent port, and the port between passage for said plurality of formed between the two through the gas port of the vent port communicating with the peripheral portion and the central portion A water-cooled internal combustion engine characterized by comprising:   2. The water-cooled internal combustion engine according to claim 1, wherein a flow path cross section of the inter-port passage has a shape in which a width in a cylinder axial direction is larger than a width in a separation direction of the two ventilation ports.   The plurality of ventilation ports constitute only the intake port, and the water jacket has a first annular portion and a second annular portion sharing the central portion and the inter-port passage in the range of one cylinder. 2. The water-cooled internal combustion engine according to claim 1, wherein the first annular portion surrounds all the exhaust ports and the spark plugs, and the second annular portion surrounds at least one of the intake ports. .   The water jacket includes a peripheral portion, a radial direction portion, and a passage between the ports that are in communication with each other in a range of the cylinder, and the peripheral portion is a communication passage that is in communication with a water jacket formed in the cylinder. And the peripheral portion includes the peripheral portion, and the radial portion extends radially inward from the peripheral portion only between the intake port and the exhaust port, and the end portion thereof constitutes the central portion. 2. The water-cooled internal combustion engine according to claim 1, wherein the cooling water flows through the inter-port passage from the central portion to the peripheral portion.

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