JP2017125471A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine capable of increasing a compression ratio while suppressing an S/V ratio, and improving combustion efficiency by forming sufficient tumble flow with sucked air-fuel mixture.SOLUTION: In a four-valve type internal combustion engine, a boundary face (50B) between a pair of adjacent intake valve ports (51, 51) on a combustion chamber ceiling face (50) is formed so as to have intake wide width boundary faces (50Bp, 50Br) at both sides across an intake narrow width boundary face (50Bq). A center-side intake wide width boundary face (50Bp) at a central side of the combustion chamber ceiling face, of the intake wide width boundary face, is raised while forming a smooth inclined face to form a center-side raised portion (50P).SELECTED DRAWING: Figure 5

Description

  The present invention relates to an internal combustion engine, and more particularly to a 4-valve 4-stroke internal combustion engine having two intake valves and two exhaust valves per cylinder.

In the four-valve type four-stroke internal combustion engine, two intake valve ports that open and close the intake valve and two exhaust valve ports that open and close the exhaust valve open side by side on the combustion chamber ceiling surface facing the piston top surface of the cylinder head. ing.
From the intake valve port and the exhaust valve port facing the combustion chamber in the cylinder head, the intake port and the exhaust port are curved and extended in directions away from each other.

  Of the intake air that is guided by the intake port and flows into the combustion chamber, if the intake valve port edge is divided into an exhaust valve port side inner port edge and an opposite outer port edge, the exhaust of the intake valve port The intake air drawn from the inner rim side on the valve port side flows into the exhaust side, descends the exhaust side of the cylinder bore, and then bends the flow along the piston top surface to raise the intake side, so-called tumble Form.

The boundary surface between the two adjacent intake valve ports on the combustion chamber ceiling surface of the cylinder head becomes wider as it goes from the narrowest portion where the width is minimized to both the center side and the peripheral side of the combustion chamber ceiling surface. Thus, a central wide surface and a peripheral wide surface are formed.
The combustion chamber ceiling surface is generally a curved surface or flat surface that is recessed in a dome shape or penthouse shape, has a flat surface with no irregularities, and the boundary surface between two adjacent intake valve ports on the combustion chamber ceiling surface is also generally irregular It is a flat surface without any gap (see, for example, Patent Document 1).

  Of the intake air that forms a tumble that is inhaled from the inner rim side of the intake valve port, the intake air near the central wide portion surface that is the interface between the two intake valve ports is the intake side of the intake port. Since the air flow has a wide flat surface that is perpendicular to the flow of the air flow, separation occurs in the flow of the intake air at the central wide surface of the opening of this intake port, causing a reverse flow that partially entrains the wide side of the central side. However, it is not efficiently inhaled and the formation of a sufficient tumble flow is prevented.

Therefore, a series of raised portions are formed between two intake valve ports adjacent to the cylinder chamber combustion chamber ceiling and between the two exhaust valve ports, and the cylinder head combustion chamber is completely divided into two by the raised portions. There is an example (see Patent Document 2).
Of the intake air sucked from the inner edge side of the intake valve port, the intake air approaching the boundary between the two intake valve ports can enter the combustion chamber without being separated by being guided by the raised portion.
Moreover, since the raised portion is large and the capacity of the combustion chamber of the cylinder head is small, the compression ratio can be increased.

JP 2014-025429 A JP 05-179959 A

In the internal combustion engine disclosed in Patent Document 2, the combustion chamber of the cylinder head is divided into two by a raised portion, and the intake air sucked into one combustion chamber forms a tumble, and the other combustion chamber sucks from the intake port The inhaled air is designed to form a swirl.
Therefore, since the intake air sucked into the other combustion chamber does not form a tumble flow, it is difficult to form a sufficient tumble flow.

  Further, as in Patent Document 2, when the raised portion becomes large enough to divide the combustion chamber of the cylinder head into two, the S / V ratio becomes large and the thermal efficiency is lowered, and the combustion chamber is partitioned by the raised portion. Generation of the turbulent flow of the air-fuel mixture around the center spark plug in the combustion chamber is inhibited, and ignition of the air-fuel mixture and promotion of combustion are hindered.

  The present invention has been made in view of the above points, and the object of the present invention is to increase the compression ratio while keeping the S / V ratio low, and to improve the combustion efficiency by forming a sufficient tumble flow with the intake air-fuel mixture. It is in the point which provides the internal combustion engine which can aim at.

In order to achieve the above object, an internal combustion engine according to the present invention comprises:
In a four-valve internal combustion engine in which two intake valve ports for opening and closing an intake valve and two exhaust valve ports for opening and closing an exhaust valve are formed side by side on the combustion chamber ceiling surface facing the piston top surface of the cylinder head,
An intake boundary surface between a pair of adjacent intake valve ports on the combustion chamber ceiling surface is formed with an intake wide boundary surface on both sides of the intake width narrow boundary surface,
Of the wide intake boundary surface, the central intake wide boundary surface on the center side of the combustion chamber ceiling surface is raised to form a smooth inclined surface to form a central intake boundary raised portion.

  According to this configuration, the boundary surface between two adjacent intake valve ports on the ceiling surface of the combustion chamber is formed as a wide intake boundary surface on both sides of the narrow intake boundary surface, and the wide intake boundary on both sides is formed. Because the center side intake wide boundary surface of the center of the combustion chamber ceiling surface rises to form a center side intake boundary raised portion, the inner edge of the intake valve port (the edge on the exhaust valve port side) side Of the intake air that forms a tumble that is sucked into the combustion chamber from the intake air, the intake air near the boundary surface (central intake wide boundary surface) between the two intake valve ports is separated along the raised central intake boundary ridge It is possible to smoothly flow into the combustion chamber without generating a sufficient tumble flow and improve the combustion efficiency.

Of the boundary surface between the two intake valve ports, the narrow intake boundary surface where the two adjacent intake valve ports are particularly close to each other does not bulge and forms a flat surface, but since the width is narrow, the intake valve port intake air The intake air sucked into the combustion chamber near the narrow boundary surface joins and mixes with the intake air sucked from the adjacent intake valve port without causing separation and is efficiently filled.
In addition, the intake side narrow boundary surface is not raised, and the central side intake wide boundary surface is raised to form the central side intake boundary raised portion, but the intake width narrow boundary surface is not raised and is not too large in the combustion chamber. By providing a large intake boundary ridge, the compression ratio can be increased while keeping the S / V ratio low and improving the thermal efficiency.

In the above configuration,
Of the wide intake boundary surfaces (51a, 51b), the peripheral wide intake boundary surface on the peripheral side of the ceiling surface of the combustion chamber is raised to form a smooth inclined surface to form the peripheral intake boundary raised portion. May be.

  According to this configuration, the peripheral side intake wide boundary surface on the peripheral side of the combustion chamber ceiling surface is raised to form the peripheral side intake boundary raised portion, so that the outer peripheral side on the opposite side to the inner peripheral edge of the intake valve port Of the intake air taken from the intake air, the intake air near the boundary surface between the two intake valve ports (periphery side wide intake boundary surface) smoothly enters the combustion chamber without causing separation along the peripheral side intake boundary ridge. It flows in and is efficiently filled.

In the above configuration,
The inclined surface of the peripheral-side intake boundary ridge may have a larger inclination angle than the inclined surface of the central-side intake boundary ridge.

The air-fuel mixture sucked along the center-side intake boundary ridge has a small inclination angle of the inclined surface of the center-side intake boundary ridge, so that it easily flows toward the exhaust side and more easily forms a tumble.
Since the air-fuel mixture sucked along the peripheral-side intake boundary ridge has a large inclination angle of the inclined surface of the peripheral-side intake boundary ridge, filling into the combustion chamber is further promoted.

In the above configuration,
The center side intake boundary ridge and the peripheral side intake boundary ridge may be gradually raised higher from the side closer to each other.

  According to this configuration, the central side intake boundary ridge and the peripheral side intake boundary ridge are gradually raised higher from the side closer to the far side, so the inclination of the central side intake boundary ridge and the peripheral side intake boundary ridge is inclined. Therefore, the intake air can be smoothly and efficiently filled into the combustion chamber without disturbing the intake air flow.

In the above configuration,
The central intake boundary ridge may be continued from the highest bulged portion to a raised annular opening edge of a spark plug hole formed in the vicinity of the central cylinder axis of the combustion chamber ceiling surface.

  According to this configuration, since the center side intake boundary bulge portion continues from the highest bulge portion to the raised annular opening edge of the spark plug hole at the center of the combustion chamber ceiling surface, along the central side intake boundary ridge portion, The intake air that flows into the combustion chamber is almost unaffected by the electrode of the spark plug located at the apex of the central intake boundary ridge, and thus flows smoothly into the combustion chamber without causing turbulence.

In the above configuration,
An inner diameter of the exhaust valve port is formed smaller than an inner diameter of the intake valve port,
The spark plug hole at the center of the combustion chamber ceiling surface may be formed at a position biased toward the intake valve port side.

  According to this configuration, since the spark plug hole is formed at a position biased toward the intake valve port side, the spark plug has an exhaust flow resistance in the vicinity of the exhaust valve port where turbulent flow with an inner diameter smaller than that of the intake valve port is likely to occur. Thus, the generation of turbulent flow can be avoided and the exhaust efficiency can be improved.

In the above configuration,
An exhaust boundary surface between a pair of adjacent exhaust valve ports on the ceiling surface of the combustion chamber is formed with a wide exhaust boundary surface on both sides across the exhaust narrow boundary surface,
Of the wide exhaust boundary surface, the central exhaust wide boundary surface on the center side of the combustion chamber ceiling surface and the peripheral exhaust wide boundary surface on the peripheral side of the combustion chamber ceiling surface each protrude with a smooth inclined surface. Thus, a central exhaust boundary raised portion and a peripheral exhaust boundary raised portion may be formed.

According to this configuration, the wide center side exhaust wide boundary surface and the peripheral exhaust side wide boundary surface of the exhaust boundary surface are bulged with a smooth inclined surface, respectively, and the central side exhaust boundary ridge and the peripheral side exhaust boundary ridge The exhaust discharged from the combustion chamber to the pair of exhaust valve ports is smoothly divided into the exhaust valve ports on both sides by the central exhaust boundary raised portion and the peripheral exhaust boundary raised portion, and the respective inclinations are formed. Rectified along the surface and discharged without resistance, and the exhaust width narrow boundary surface between the central side exhaust boundary ridge and the peripheral side exhaust boundary ridge is narrow even if it is not raised. Is small.
Therefore, the exhaust resistance can be reduced and the exhaust efficiency can be improved, and the S / V is set to an appropriate size that is not too large in the combustion chamber with the central exhaust boundary ridge and the peripheral exhaust boundary ridge. The compression ratio can be increased while keeping the ratio low and improving the thermal efficiency.

In the above configuration,
An inner diameter of the exhaust valve port is formed smaller than an inner diameter of the intake valve port,
The inclined surface of the central exhaust boundary raised portion and the peripheral exhaust boundary raised portion may have a larger inclination angle than the inclined surfaces of the central intake boundary raised portion and the peripheral intake boundary raised portion. .

  According to this configuration, since the turbulent flow is likely to occur in the vicinity of the exhaust valve port whose inner diameter is smaller than that of the intake valve port, the inclined surface of the exhaust side raised portion of the center side exhaust boundary raised portion and the peripheral side exhaust boundary raised portion By increasing the inclination angle, the rectification can be promoted and the exhaust efficiency can be increased.

In the above configuration,
The inclined surface of the peripheral exhaust boundary raised portion may have a larger inclination angle than the inclined surface of the central exhaust boundary raised portion.

  According to the above configuration, the inclined surface having a larger inclination angle of the peripheral exhaust boundary raised portion can promote exhaust of exhaust that tends to stay around the periphery of the combustion chamber, suppress the stay, and improve exhaust efficiency.

  In the above-described configuration, the center side exhaust boundary ridge and the peripheral side exhaust boundary ridge are longer than the length of the narrow intake width boundary surface between the center side intake boundary ridge and the peripheral side intake boundary ridge. The length of the narrow exhaust boundary surface may be made smaller.

  According to the above-described configuration, by making the length of the narrow exhaust boundary boundary relatively small, the exhaust gas rectification by the central exhaust boundary raised portion and the peripheral exhaust boundary raised portion is further promoted, and the length of the narrow intake boundary surface is increased. By making the depth relatively large, it is further promoted that the intake air sucked into the combustion chamber near the boundary between the narrow intake air width of the intake valve port joins and is mixed with the intake air sucked from the adjacent intake valve port. .

In the above configuration,
A squish surface is formed near the periphery of the combustion chamber ceiling surface,
The peripheral side intake boundary ridge and the peripheral side exhaust boundary ridge may be continuous with the squish surface (50s).

  According to the above configuration, since the peripheral intake boundary ridge and the peripheral exhaust boundary ridge are continuous with the squish surface, the piston is sandwiched between squish areas when the piston approaches top dead center in the final stage of the compression stroke. The peripheral air intake boundary ridge and the peripheral exhaust boundary ridge do not prevent the air-fuel mixture at the peripheral edge of the combustion chamber from blowing out toward the electrode of the ignition plug at the center of the combustion chamber.

  In the present invention, since the intake side wide boundary surface on the center side of the combustion chamber ceiling surface rises out of the intake wide boundary surfaces on both sides of the intake width narrow boundary surface, the central intake boundary raised portion is formed. Of the intake air that forms the tumble that is sucked into the combustion chamber from the inner edge side of the mouth, the intake air near the boundary surface (central intake wide boundary surface) between the two intake valve ports rises to the central intake boundary bulge It is possible to smoothly flow into the combustion chamber without causing separation along the portion, thereby forming a sufficient tumble flow and improving the combustion efficiency.

The narrow intake interface has a flat surface that does not rise, but is narrow, so that the intake air that is sucked into the combustion chamber near the narrow intake interface of the intake valve port does not cause separation, It efficiently fills by merging with the intake air drawn from the intake valve port.
By providing a central intake boundary bulge portion that is not too large in the combustion chamber without causing the intake air narrow boundary surface to rise, the compression ratio can be increased while keeping the S / V ratio low and improving the thermal efficiency.

1 is a left side sectional view of an internal combustion engine including a cylinder head according to an embodiment of the present invention. It is the bottom view seen from the mating face (bottom face) side with the cylinder block of the cylinder head. FIG. 5 is a cross-sectional view of the cylinder head (a cross-sectional view taken along line III-III in FIGS. 2 and 4). It is the bottom view expanded from FIG. 2 of the cylinder head. It is the perspective view which looked at the cylinder head diagonally from the bottom face side. It is a top view which shows an intake port and a combustion chamber. FIG. 7 is a cross-sectional view taken along the line VII-VII in FIG. 6 showing the inside of the intake port and the combustion chamber. It is a side view which shows an intake port, a combustion chamber, and a cylinder bore. FIG. 9 is a cross-sectional view taken along the line IX-IX in FIG. 8 showing the inside of the intake port, the combustion chamber, and the cylinder bore. It is the XX sectional view taken on the line of FIG. 8 which shows the inside of a combustion chamber.

Hereinafter, an embodiment according to the present invention will be described with reference to FIGS.
FIG. 1 is a left side sectional view of an internal combustion engine mounted on a small vehicle such as a motorcycle according to an embodiment to which the present invention is applied, and is shown in a posture in a state mounted on the vehicle.
In the description of the present specification, the directions of front, rear, left and right are based on a normal standard in which the straight traveling direction of the vehicle according to the present embodiment is the front, and in the drawings, FR indicates the front.

  The internal combustion engine 1 according to the present embodiment is a water-cooled in-line four-cylinder mounted on a motorcycle with its crankshaft 2 oriented in the vehicle width direction of a motorcycle (not shown) that is a vehicle to be mounted, that is, in the left-right direction. This is a 4-valve 4-stroke internal combustion engine.

As shown in FIG. 1, a crankcase 10 that supports a crankshaft 2 arranged in the vehicle width direction is divided into upper and lower parts that are divided vertically by a dividing surface 10 a around the crankshaft 2.
A cylinder block 11 is integrally formed at the upper front portion of the upper crankcase 10A with the cylinder axis Lc of four cylinder bores 11a (only the left cylinder bore 11a shown in FIG. The cylinder head 12 is overlapped and fastened, and the cylinder head 12 is covered with a cylinder head cover 13.
On the other hand, an oil pan 14 is attached under the lower crankcase 10B. An oil filter 15 is provided at the front of the lower crankcase 10B.

The internal combustion engine 1 of the present embodiment has a transmission 3 incorporated in its crankcase 10 and constitutes a so-called power unit.
The crankcase 10 extends rearward from the crankshaft 2 and includes, in addition to the crankshaft 2, a main shaft 21, a countershaft 22 and the like of the transmission 3 disposed in the crankcase 10 behind the crankshaft 2. The shaft is oriented in the vehicle width direction parallel to the crankshaft 2 and is rotatably supported.
Similarly to the crankshaft 2, the countershaft 22 is held on the split surface 10a between the upper crankcase 10A and the lower crankcase 10B, and the main shaft 21 is held on the upper crankcase 10A.

  The transmission 3 is a constantly meshing gear transmission, and a transmission gear group mounted on each of the main shaft 21 and the counter shaft 22 meshes with a pair of gears. Switching is performed and a shift is performed.

The rotation of the crankshaft 2 is transmitted to the main shaft 21 via a clutch (not shown), and the countershaft 22 is shifted and driven to rotate by the gear switching of the transmission gear group of the transmission 3.
The countershaft 22 penetrates to the left of the crankcase 10 and protrudes to the outside to become the final output shaft of the internal combustion engine 1, and an output sprocket (not shown) is spline fitted to the protruding portion.
Hereinafter, although not shown, a drive chain wound around the output sprocket is laid over a driven sprocket on the rear wheel side, and rotational power is transmitted to the rear wheel.

As shown in FIG. 1, a piston 25 sliding in a cylinder bore 11a is connected to a crank pin 2p of a crankshaft 2 via a connecting rod 26 to constitute a crank mechanism.
In the cylinder head 12, a surface facing the top surface of the piston 25 sliding in the cylinder bore 11 a is recessed in a dome shape to form a combustion chamber ceiling surface 50, and the combustion chamber 4 is formed inside the combustion chamber ceiling surface 50. Is formed.

  The internal combustion engine 1 is a four-valve internal combustion engine having two intake valves 31 and two exhaust valves 32 per cylinder, and is a bottom view of the cylinder head 12 viewed from the mating surface 12a side with the cylinder block 11. With reference to FIG. 2, two intake valve ports 61 for opening and closing the intake valve 31 and two exhaust valve ports 62 for opening and closing the exhaust valve 32 are provided on the combustion chamber ceiling surface 50 opposed to the piston top surface of the cylinder head 12. Opened side by side (see FIG. 2, FIG. 4 and FIG. 5).

The combustion chamber ceiling surface 50 has a dome-shaped curved surface, and intake valve ports 61 are opened side by side on substantially the second half of the combustion chamber ceiling surface 50, and the exhaust valve is located on the first half of the combustion chamber ceiling surface 12b. The mouth 62 is opened side by side.
The inner diameter of the exhaust valve port 62 is smaller than the inner diameter of the intake valve port 61.

The cylinder head 12 is curved backward from the intake valve port 61 to extend the intake port 33, and is curved forward from the exhaust valve port 62 to extend the exhaust port 34 (see FIG. 1).
Referring to FIG. 2, the intake ports 33, 33 extending rearward from the left and right intake valve ports 61, 61 are gathered in the collective intake port 33a on the upstream side, and the collective intake port 33a includes A throttle body (not shown) is connected.
Further, the exhaust ports 34a, 34a extending forward from the left and right exhaust valve ports 62, 62 are gathered in the collective exhaust port 34a on the downstream side, and the exhaust pipe 16 is connected to the collective exhaust port 34a. Is done.

In the combustion chamber ceiling surface 50 of each combustion chamber 4 in the cylinder head 12, an ignition plug hole 68 into which the ignition plug 28 is screwed is provided in the vicinity of the center cylinder axis Lc. The intake valve ports 61 and 61 and the exhaust valve ports 62 and 62 are greatly opened (see FIG. 2).
The spark plug hole 68 is formed at a position that is biased toward the intake valve ports 61 and 61 rather than the exhaust valve ports 62 and 62 (see FIGS. 2 and 4).
The spark plug 28 screwed into the spark plug hole 68 at the center of the combustion chamber ceiling surface 50 has the tip electrode portion 28a facing the combustion chamber 4 (see FIG. 3).

The intake valve 31 is slidably supported by a valve guide 35 having a valve shaft portion 31s fitted on the upper wall of the intake port 33, and an umbrella portion 31u at the tip of the valve shaft portion 31s opens and closes the intake valve port 61. .
Similarly, the exhaust valve 32 is slidably supported by a valve guide 35 fitted to the upper wall of the exhaust port 34 with a valve shaft portion 32s, and an umbrella portion 32u at the end of the valve shaft portion 32s is connected to the exhaust valve port 62. Open and close.

The intake port edge 61E of the intake valve port 61 is a valve seat with which the valve face of the umbrella portion 31u of the intake valve 31 abuts.
Similarly, the exhaust port edge 62E of the exhaust valve port 62 is a valve seat with which the valve face of the umbrella portion 32u of the exhaust valve 32 abuts.

  The valve operating mechanism for driving the intake valve 31 and the exhaust valve 32 is a well-known DOHC type, and will not be described in detail. The intake cam 43 provided on the intake cam 43 and the exhaust cam shaft 42 pushes the valve lifters 45 and 45 respectively placed on the upper ends of the intake valve 31 and the exhaust valve 32 to crank the intake valve 31 and the exhaust valve 32. The intake valve port 61 and the exhaust valve port 62 are opened and closed by reciprocating at a predetermined timing according to the rotational position of the shaft 2.

  The dome-shaped combustion chamber ceiling surface 50 of each combustion chamber 4 in the cylinder head 12 is a squish surface 50 s that forms a tapered surface that is partially close to a plane on the front, rear, left, and right of the peripheral edge (thin spots in FIGS. 4 and 5). The combustion chamber ceiling surface 50 excluding the intake valve ports 61 and 61 and the exhaust valve ports 62 and 62 inside the squish surface 50s is generally a concave concave surface 50d (in FIG. 4 and FIG. 5). A dark dotted pattern).

4 and 5, the boundary surface 51 between the two adjacent intake valve ports 61, 61 on the combustion chamber ceiling surface 50 has a width in which the two adjacent intake valve ports 61, 61 are particularly close to each other. It consists of a narrow intake width narrow boundary surface 51c and intake wide boundary surfaces 51a, 51b having wider widths on both sides of the intake width narrow boundary surface 51c.
Of the wide intake boundary surfaces 51a and 51b, the center spark plug hole 68 side of the combustion chamber ceiling surface 50 is the central intake wide boundary surface 51a (the dark dotted pattern portion in FIGS. 4 and 5). The peripheral edge side is the peripheral-side intake wide boundary surface 51b (the dark dotted pattern portion in FIGS. 4 and 5).

The center-side intake wide boundary surface 51a forms a smooth inclined surface on the left and right toward the left and right intake valve ports 61, 61, and is tapered to form a center-side intake boundary raised portion 52.
The peripheral-side intake wide boundary surface 51b also has a smooth inclined surface to the left and right toward the left and right intake valve ports 61, 61, and is tapered to form a peripheral-side intake boundary raised portion 53.

Further, as shown in FIG. 3, the center side intake boundary bulge portion 52 and the peripheral side intake boundary bulge portion 53 are inclined and protruded so as to gradually become higher from the side closer to each other.
The inclined surface of the peripheral-side intake boundary raised portion 53 has a larger inclination angle than the inclined surface of the central-side intake boundary raised portion 52.

The center side intake boundary bulge 52 is located on the raised annular opening edge 58 of the spark plug hole 68 at a position slightly offset near the center of the combustion chamber ceiling surface 50 from the highest bulge portion to the intake valve ports 61, 61. It is continuous.
The peripheral-side intake boundary ridge 53 is continuous with the peripheral squish surface 50 s of the combustion chamber ceiling surface 50.

On the other hand, the boundary surface 55 between the two adjacent exhaust valve ports 62, 62 on the combustion chamber ceiling surface 50 is substantially the same, and referring to FIGS. 4 and 5, the two adjacent exhaust valve ports 62, 62 62 is composed of a narrow exhaust narrow boundary surface 55c that is particularly close to the exhaust narrow boundary surface 55c, and wide exhaust boundary surfaces 55a and 55b that are wide on both sides of the narrow exhaust boundary surface 55c.
Of the wide exhaust boundary surfaces 55a and 55b, the spark plug hole 68 side near the center of the combustion chamber ceiling surface 50 is the central exhaust wide boundary surface 55a (the dark scattered pattern portion in FIGS. 4 and 5), and the combustion chamber ceiling surface. The peripheral side of 50 is the peripheral exhaust wide boundary surface 55b (the dark dotted pattern portion in FIGS. 4 and 5).

The center-side exhaust wide boundary surface 55a has a smooth inclined surface on the left and right toward the left and right exhaust valve ports 62, 62, and is tapered to form a center-side exhaust boundary raised portion 56.
Further, the peripheral exhaust side wide boundary surface 55b also forms a smooth inclined surface on the left and right toward the left and right intake valve ports 61, 61, and is tapered to form a peripheral exhaust side boundary raised portion 57.

As shown in FIG. 3, the center side exhaust boundary raised portion 56 and the peripheral side exhaust boundary raised portion 57 are inclined and raised so as to gradually become higher from the side closer to each other.
The inclined surface of the peripheral exhaust boundary raised portion 57 has a larger inclination angle than the inclined surface of the central exhaust boundary raised portion 56.

The central exhaust boundary raised portion 56 is continuous from the highest raised portion to the raised annular opening edge 58 of the ignition plug hole 68 at the substantially center of the combustion chamber ceiling surface 50.
The peripheral side exhaust boundary raised portion 57 is continuous with the peripheral squish surface 50 s of the combustion chamber ceiling surface 50.

The inclined surfaces of the center-side exhaust boundary raised portion 56 and the peripheral-side exhaust boundary raised portion 57 have a larger inclination angle than the inclined surfaces of the central-side intake boundary raised portion 52 and the peripheral-side intake boundary raised portion 53 described above.
Further, the length of the narrow exhaust width narrow boundary surface 55c between the central side exhaust boundary raised portion 56 and the peripheral side exhaust boundary raised portion 57 is such that the center side intake boundary raised portion 52 and the peripheral side intake boundary raised portion 53 It is smaller than the length of the narrow intake air narrow boundary surface 51c.

The intake air flow in the internal combustion engine 1 having the cylinder head 12 as described above will be considered based on FIGS.
The intake air sucked into the combustion chamber 4 from the intake valve port 61 of the intake port 33 spreads in the radial direction along the upper surface of the umbrella portion 31u of the intake valve 31 moved away from the intake port edge 61E of the intake valve port 61. Into the combustion chamber 4 (see FIG. 7).

In FIG. 7, the flow direction of the intake air is indicated by a thick arrow, and the distribution of the intake air velocity is indicated by a dotted pattern density.
A high-speed part of the intake speed is shown by a dark dotted pattern, a medium-speed part is shown by a medium-spotted dot pattern, a low-speed part is shown by a thin dotted pattern, and a very low-speed part is outlined.

When the intake port edge 61E of the intake valve port 61 is divided into an inner intake port edge 61Ei on the exhaust valve port 62 side and an outer intake port edge 61Eo on the opposite side (see FIG. 4), The intake air sucked from the inner intake port edge 61Ei side of the intake valve port 61 from the port 33 flows into the combustion chamber 4 without greatly changing the direction between the inner intake port edge 61Ei and the umbrella portion 31u of the intake valve 31. On the other hand, the intake air sucked from the outer intake port edge 61Eo of the intake valve port 61 flows into the combustion chamber 4 with the direction greatly changed between the outer intake port edge 61Eo and the umbrella portion 31u of the intake valve 31. .
Therefore, the intake air sucked from the inner intake port edge 61Ei has less resistance than the intake air sucked from the outer intake port edge 61Eo, and flows in a large amount.

  As shown in FIG. 7, the intake air sucked from the inner intake port edge 61Ei is the fastest at the place where it flows into the combustion chamber 4 along the inner intake port edge 61Ei, and flows into the combustion chamber 4 at this high speed. The intake air flows through the combustion chamber 4 toward the exhaust valve port 62 side where the exhaust valve 32 is closed, descends the exhaust side of the cylinder bore 11a from the exhaust side periphery of the combustion chamber 4, and then flows along the top surface of the piston. Bending toward the intake side and ascending the intake side forms a vertical vortex, so-called tumble.

  Of the intake air that forms a tumble that is sucked into the combustion chamber 4 from the inner intake port edge 61Ei side of the intake valve port 61, the central wide portion that is the boundary surface 50B between the two adjacent intake valve ports 61, 61 The intake air near the surface 50Bp flows into the combustion chamber 4 without causing separation smoothly along the center-side intake boundary raised portion 50P of the center-side wide portion surface 50Bp as shown by the white arrow in FIG. be able to.

  FIG. 9 (sectional view taken along the line IX-IX in FIG. 8) showing the inside of the intake port 33, the combustion chamber 4, and the cylinder bore, and FIG. 10 (sectional view taken along the line XX in FIG. 8) showing the inside of the combustion chamber are shown in FIG. Similar to FIG. 7, the distribution of the intake air velocity is indicated by a dotted pattern density.

In FIG. 9 and FIG. 10, of the intake air that is sucked into the combustion chamber 4 from the inner intake port edge 61Ei side of the intake valve port 61, the intake air near the central wide portion surface 50Bp extends along the central intake boundary raised portion 50P. The place through which the gas flows into the combustion chamber 4 is indicated by an elliptical black frame Z.
The place indicated by the black frame Z is indicated by a dark dotted pattern, the intake speed is high, and the intake air smoothly flows into the combustion chamber 4 without causing separation along the central intake boundary raised portion 50P. Is shown.

  In this way, among the intake air that forms the tumble that is sucked into the combustion chamber 4 from the inner intake port edge 61Ei side of the intake valve port 61, the intake air near the central wide portion surface 50Bp rises to the central intake boundary raised portion. Since it flows smoothly into the combustion chamber 4 without causing separation, a sufficient tumble flow can be formed to improve the combustion efficiency.

  Of the boundary surface 50B between the two adjacent intake valve ports 61, 61, the two intake valve ports 61, 61 are particularly close to each other, and the intake width narrow boundary surface 50Bq is not raised but forms a flat surface. Because it is narrow, the intake air that is sucked into the combustion chamber 4 near the intake width narrow boundary surface 50Bq of the intake valve port 61 is merged with the intake air that is sucked from the adjacent intake valve port 61 and efficiently filled before separation occurs. Is done.

  Further, the narrow intake boundary 50Bq is not raised, but the central intake wide boundary 50Bp is raised to form the central intake boundary raised portion 50P. However, the narrow intake boundary 50Bq is not raised, and the inside of the combustion chamber 4 is not raised. By providing a moderately large raised portion that is not too large, the compression ratio can be increased while keeping the S / V ratio low and improving the thermal efficiency.

In the cylinder head 12, the peripheral side intake wide boundary surface 50Br of the boundary surface 50B between the two adjacent intake valve ports 61, 61 on the combustion chamber ceiling surface 50 also protrudes, and the peripheral side intake boundary raised portion 50R is formed.
Of the intake air drawn from the outer edge side 50Eo opposite to the inner intake edge 61Ei of the intake valve port 61, the intake air near the peripheral intake wide interface 50Br between the two intake valve ports is white in FIG. As indicated by the extraction arrow, the air smoothly flows into the combustion chamber 4 without causing separation along the peripheral-side intake boundary raised portion 50R, and is efficiently filled.

The inclined surface of the peripheral-side intake boundary raised portion 53 changes its direction toward the peripheral-side intake wide boundary surface 50Br and flows into the combustion chamber 4 by making the inclination angle larger than the inclined surface of the central-side intake boundary raised portion 52. Thus, the intake air can smoothly flow into the combustion chamber 4 along the inclined surface having a relatively large inclination angle, and the combustion chamber 4 is further charged.

  Between the central intake boundary raised portion 50P and the peripheral intake boundary raised portion 50R formed on the boundary surface 50B between the two adjacent intake valve ports 61, 61, there is no flat intake width narrow boundary surface 50Bq between the peripheral intake boundary raised portions 50R. Therefore, it is possible to provide a moderately sized raised portion in the combustion chamber 4, and it is possible to increase the compression ratio while suppressing the S / V ratio and improving the thermal efficiency.

  As shown in FIG. 3, the center side intake boundary bulge 50P and the peripheral side intake boundary bulge 50R formed on the boundary surface 50B between the two adjacent intake valve ports 61, 61 are far from the sides close to each other, as shown in FIG. Since the bulge gradually rises to the side, the intake air is smoothly and efficiently introduced into the combustion chamber 4 without causing disturbance in the intake air flow at the inclined hem portion of the central intake boundary ridge 50P and the peripheral intake boundary ridge. Can be filled.

  As shown in FIG. 3, since the center side intake boundary raised portion 50P continues from the highest raised portion to the ignition plug hole 68 at the substantially center of the combustion chamber ceiling surface 50, along the center side intake boundary raised portion 50P. The intake air flowing into the combustion chamber 4 smoothly flows into the combustion chamber 4 without being substantially affected by the electrode portion 28a of the spark plug 28 located at the apex of the central intake boundary raised portion 50P.

Since the spark plug hole 68 is formed at a position biased toward the intake valve ports 61 and 61, the electrode portion 28a of the spark plug 28 is located near the exhaust valve port 62 where turbulent flow with an inner diameter smaller than that of the intake valve port 61 is likely to occur. It is possible to improve the exhaust efficiency by avoiding the occurrence of turbulent flow due to the resistance of the exhaust flow.

A wide central side exhaust wide boundary surface 55a and a peripheral side wide exhaust boundary surface 55b of the exhaust boundary surface 55 between the two exhaust valve ports 62 and 62 are each raised with a smooth inclined surface to form a central exhaust boundary. Since the raised portion 56 and the peripheral exhaust boundary raised portion 57 are formed, the exhaust discharged from the combustion chamber 4 to the pair of exhaust valve ports 62 and 62 is exhausted from the central exhaust boundary raised portion 56 and the peripheral exhaust boundary raised portion. 57 smoothly flows to the exhaust valve ports on both sides, is rectified along the respective inclined surfaces and discharged without resistance, and the exhaust between the central exhaust boundary raised portion 56 and the peripheral exhaust boundary raised portion 57 is exhausted. Since the narrow boundary surface 55c is narrow even if it does not rise, the exhaust resistance is small.
Therefore, the exhaust resistance can be reduced and the exhaust efficiency can be improved, and the center side exhaust boundary raised portion 56 and the peripheral side exhaust boundary raised portion 57 can be appropriately sized not too large in the combustion chamber 4. The compression ratio can be increased while keeping the S / V ratio low and improving the thermal efficiency.

In the vicinity of the exhaust valve port 62 whose inner diameter is smaller than that of the intake valve port 61, turbulent flow is likely to occur, so that the center side intake boundary bulge 52 and the peripheral side intake boundary bulge 53 are centered from the inclined surface of the intake side bulge. By increasing the inclination angle of the inclined surfaces of the exhaust-side raised portions of the side exhaust boundary raised portion 56 and the peripheral side exhaust boundary raised portion 57, rectification can be further promoted and the exhaust efficiency can be improved.

The inclined surface of the peripheral exhaust boundary raised portion 57 has a larger inclination angle than the inclined surface of the central exhaust boundary raised portion 56, and the inclined surface of the peripheral exhaust boundary raised portion 57 has a larger inclined angle. It is possible to increase the exhaust efficiency by encouraging the exhaust of the exhaust gas that tends to stay around the periphery of the gas to suppress the stay.

The length of the narrow exhaust narrow boundary surface 55c between the central exhaust boundary raised portion 56 and the peripheral exhaust boundary raised portion 57 is set between the central intake boundary raised portion 52 and the peripheral intake boundary raised portion 53. Since the width of the narrow intake width narrow boundary surface 51c is smaller than that of the narrow intake width narrow boundary surface 51c, the exhaust air rectification by the central exhaust boundary raised portion 56 and the peripheral exhaust boundary raised portion 57 is further promoted, and the length of the intake narrow boundary surface 51c is increased. By making the depth relatively large, the intake air sucked into the combustion chamber 4 near the narrow intake boundary surface 51c of the intake valve port 61 joins and is mixed with the intake air sucked from the adjacent intake valve port 61. Is further encouraged.
Therefore, both exhaust efficiency and intake efficiency can be improved.

  Further, as shown in FIG. 3, the peripheral side intake boundary bulge 53 and the peripheral side exhaust boundary bulge 57 are continuous with the squish surface 50s, so that the piston 25 approaches top dead center at the final stage of the compression stroke. When the air-fuel mixture at the peripheral portion of the combustion chamber 4 sandwiched between the squish areas blows out toward the electrode portion 28a of the spark plug 28 at the center of the combustion chamber, the peripheral-side intake boundary raised portion 53 and the peripheral-side exhaust boundary raised portion 57 does not hinder and ignition can be performed accurately.

  Although the internal combustion engine according to the embodiment of the present invention has been described above, the aspect of the present invention is not limited to the above-described embodiment, and is implemented in various aspects within the scope of the gist of the present invention. Is included.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Crankshaft, 3 ... Transmission, 4 ... Combustion chamber, 10 ... Crankcase, 11 ... Cylinder block, 11a ... Cylinder bore, 12 ... Cylinder head, 12a ... Connection surface, 13 ... Cylinder head cover, 14 ... oil pan, 15 ... oil filter, 16 ... exhaust pipe,
20 ..., 21 ... Main shaft, 22 ... Counter shaft, 23 ..., 24 ... Connecting rod, 25 ... Piston, 28 ... Spark plug,
31 ... Intake valve, 32 ... Exhaust valve, 33 ... Intake port, 34 ... Exhaust port, 35 ... Valve guide,
41 ... intake camshaft, 42 ... exhaust camshaft, 43 ... intake cam, 44 ... exhaust cam, 45 ... valve lifter,
50 ... combustion chamber ceiling surface, 50d ... concave curved surface, 50s squish surface,
51 ... Intake side boundary surface, 51a ... Center side wide intake boundary surface, 51b ... Large side intake wide boundary surface, 51c ... Narrow intake width boundary surface, 52 ... Center side intake boundary raised portion, 53 ... Marginal side intake boundary raised portion ,
55 ... exhaust side boundary surface, 55a ... center side wide exhaust boundary surface, 55b ... perimeter side wide exhaust boundary surface, 55c ... exhaust width narrow boundary surface, 56 ... center side exhaust boundary raised portion, 57 ... perimeter side exhaust boundary raised portion ,
58… Ring opening edge,
61 ... Inlet valve port, 61E ... Inlet port edge, 62 ... Exhaust valve port, 68 ... Spark plug hole.

Claims (11)

An intake valve port (61) for opening and closing the intake valve (31) and an exhaust valve port (62) for opening and closing the exhaust valve (32) on the combustion chamber ceiling surface (50) facing the piston top surface of the cylinder head (12) In a four-valve internal combustion engine in which two are formed side by side,
An intake boundary surface (51) between a pair of adjacent intake valve ports (61, 61) on the combustion chamber ceiling surface (50) has an intake wide boundary surface on both sides of the narrow intake boundary surface (51c). (51a, 51b)
Of the wide intake boundary surfaces (51a, 51b), the central intake wide boundary surface (51a) on the center side of the combustion chamber ceiling surface (50) is raised to form a smooth inclined surface, and the central intake boundary raised portion An internal combustion engine characterized in that (52) is formed.   Of the intake wide boundary surfaces (51a, 51b), a peripheral side intake wide boundary surface (51b) on the peripheral side of the combustion chamber ceiling surface (50) bulges to form a smooth inclined surface to form a peripheral side intake boundary raised portion The internal combustion engine according to claim 1, wherein (53) is formed.   The internal combustion engine according to claim 2, wherein the inclined surface of the peripheral-side intake boundary bulge portion (53) has a larger inclination angle than the inclined surface of the central-side intake boundary ridge portion (52).   The internal combustion engine according to claim 2 or 3, wherein the central intake boundary ridge (52) and the peripheral intake ridge (53) are gradually raised from a side closer to the far side to a side farther from each other. organ.   The central intake boundary ridge (52) is a raised annular opening edge of a spark plug hole (68) formed in the vicinity of the center cylinder axis of the combustion chamber ceiling surface (50) from the highest bulged portion ( 58. The internal combustion engine according to claim 2, wherein the internal combustion engine is continuous with (58). The inner diameter of the exhaust valve port (62) is smaller than the inner diameter of the intake valve port (61),
The internal combustion engine according to claim 5, wherein the spark plug hole (68) in the center of the combustion chamber ceiling surface (50) is formed at a position biased toward the intake valve port (61). The exhaust boundary surface (55) between the pair of adjacent exhaust valve ports (62, 62) on the combustion chamber ceiling surface (50) has a wide exhaust boundary surface on both sides of the narrow exhaust boundary surface (55c). (55a, 55b)
Of the wide exhaust boundary surfaces (55a, 55b), a central exhaust wide boundary surface (55a) on the center side of the combustion chamber ceiling surface (50) and a peripheral exhaust gas wide side on the peripheral side of the combustion chamber ceiling surface (50). The boundary surface (55b) is bulged with a smooth inclined surface to form a central side exhaust boundary bulge portion (56) and a peripheral side exhaust boundary bulge portion (57), respectively. The internal combustion engine according to claim 6. An inner diameter of the exhaust valve port (52) is formed smaller than an inner diameter of the intake valve port (61),
From the inclined surfaces of the central intake boundary ridge (52) and the peripheral intake boundary ridge (53), the central exhaust boundary ridge (56) and the inclined surface of the peripheral exhaust boundary ridge (57) The internal combustion engine according to claim 7, wherein the angle of inclination is larger.   9. The internal combustion engine according to claim 7, wherein the inclined surface of the peripheral exhaust boundary raised portion (57) has a larger inclination angle than the inclined surface of the central exhaust boundary raised portion (56). organ.   The central exhaust boundary ridge (56) and the periphery of the peripheral side intake boundary ridge (52) and the peripheral intake side ridge (53) are narrower than the intake width narrow boundary surface (51c). The internal combustion engine according to any one of claims 7 to 9, wherein a length of the narrow exhaust boundary surface (55c) between the edge side exhaust boundary raised portions (57) is smaller. A squish surface (50 s) is formed near the periphery of the combustion chamber ceiling surface (50),
11. The peripheral edge intake boundary ridge (53) and the peripheral edge exhaust boundary ridge (57) are continuous with the squish surface (50s). Internal combustion engine.

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