JP7575666B2 - Engine combustion chamber structure - Google Patents

Description

The present invention relates to a combustion chamber structure for an engine equipped with a combustion chamber having a pent roof type ceiling surface.

In order to improve thermal efficiency and fuel economy, research is being conducted daily on the structure of engine combustion chambers, and in particular the structure of pistons. For example, Patent Document 1 discloses a structure in which a piston crown surface has a cavity and an inclined surface that follows the shape of a pent roof-shaped ceiling surface in a combustion chamber. This combustion chamber structure suppresses the deceleration of the tumble flow, promotes combustion, and improves fuel economy.

A straightforward and effective way to improve fuel economy is to set a high compression ratio. However, a high compression ratio can cause the pressure and temperature in the combustion chamber at the end of compression to rise excessively, for example in the low-speed, high-load operating range, inducing abnormal combustion. This abnormal combustion is due to the sudden self-ignition of unburned fuel gas before the flame propagation combustion is completed, which causes knocking.

JP 2018-162733 A

Conventionally, measures have been taken to suppress engine output in order to prevent the occurrence of the above-mentioned knocking. Specifically, the timing of fuel injection into the combustion chamber and the ignition timing of the air-fuel mixture are devised to retard the center of gravity of combustion and suppress engine output. Such measures are preferably avoided as much as possible because they hinder the increase in engine output. The structural innovation of the combustion chamber disclosed in Patent Document 1 can also contribute to improving fuel efficiency, but further research by the inventors has revealed that it is not sufficient in terms of maintaining the tumble flow until the latter half of the compression stroke.

The object of the present invention is to provide an engine combustion chamber structure that can improve engine output while suppressing knocking, and can achieve both improved fuel economy and improved engine output.

According to one aspect of the present invention, there is provided a combustion chamber structure for an engine, the combustion chamber being defined by a crown surface of a piston, an inner wall surface of a cylinder in which the piston is slidably accommodated, and a pent roof-shaped ceiling surface formed in a cylinder head, the ceiling surface being provided with an opening of an intake port for supplying intake air to the combustion chamber, and an opening of an exhaust port for discharging exhaust gas from the combustion chamber, the side on which the intake port is provided being defined as the intake side, and the side on which the exhaust port is provided being defined as the exhaust side, the crown surface being defined as an exhaust side bottom portion disposed near an edge of the crown surface on the exhaust side, an intake side bottom portion disposed near an edge of the intake side, an exhaust side inclined surface rising from the exhaust side bottom portion toward a center of the crown surface, an intake side inclined surface rising from the intake side bottom portion toward the center of the crown surface, and the the upper end of the exhaust-side inclined surface and the upper end of the intake-side inclined surface are provided continuously so that no depression is present between them, and the crown surface includes a rectangular plane extending in a direction perpendicular to the axial direction of the cylinder at the center of the crown surface and being long in the perpendicular direction , and the ratio Lie/h of a width Lie of the plane in a direction in which the intake side and the exhaust side face each other, to a mountain height h of a protrusion formed by the exhaust-side inclined surface, the intake-side inclined surface, and the plane satisfies the relationship of 2.5<Lie/h<9.0 when the geometric compression ratio of the combustion chamber is in the range of 13.5 to 15.5, a fuel injection unit that injects fuel into the combustion chamber is disposed on the intake side of the combustion chamber, and the exhaust-side bottom and the intake-side bottom extend in a direction perpendicular to the axial direction of the cylinder .

With this combustion chamber structure, an intake port is formed in the pent roof-shaped ceiling surface, resulting in a combustion chamber in which tumble flow is formed. The piston crown surface is raised in a convex shape by the exhaust side inclined surface and the intake side inclined surface, and a continuous flat surface is formed in the center. Note that "continuous flat surface" means a flat surface that does not have any recesses such as cavities.

By forming the continuous plane, the tumble flow can flow along the plane without being hindered by a cavity or other depression. Furthermore, by setting the width Lie, which is the width of the plane in the direction in which the intake side and the exhaust side face each other, large while taking into consideration the height h of the crown surface described below, the tumble flow can flow with little resistance. These structural improvements reduce the resistance of the piston crown surface to the tumble flow, and the tumble flow can be maintained until the latter half of the compression stroke. When the tumble flow collapses, turbulent energy is generated. Maintaining the tumble flow leads to maintaining the turbulent energy held by the tumble flow in a high state. Therefore, by collapsing the tumble flow in the latter half of the compression stroke and generating high turbulent energy, it is possible to increase the combustion speed. This allows the combustion to be completed before the occurrence of self-ignition, which is a cause of knocking. And since knocking can be suppressed, it is possible to avoid control that deliberately suppresses engine output, such as retarding the combustion center of gravity. As a result, a high compression ratio can be achieved.

In a combustion chamber having a pent roof type combustion chamber ceiling surface as described above, the inclination angle of the exhaust side inclined surface and the intake side inclined surface of the crown surface is generally in line with the inclination angle of the combustion chamber ceiling surface. Therefore, the crest height h, which is the height of the protuberance formed by the exhaust side inclined surface, the intake side inclined surface, and the plane, greatly affects the width Lie of the plane. Increasing the crest height h leads to increasing the compression ratio. For example, if the crest height h is set high in order to improve fuel efficiency, the width Lie becomes narrow. In other words, the surface area of the plane becomes smaller. In this case, even if the fuel efficiency is improved, it becomes difficult to maintain the tumble flow until the latter half of the compression stroke. Ultimately, in order to prevent knocking, suppression control of the engine output is required. Therefore, by setting Lie/h, which is the ratio of the width Lie of the above plane to the peak height h, to satisfy the relationship 2.5 < Lie/h < 9.0 in the high compression ratio range in which the geometric compression ratio of the combustion chamber is 13.5 or more and 15.5 or less, it is possible to achieve both improved fuel efficiency and improved engine output.
In addition, in the above combustion chamber structure, a fuel injection unit that injects fuel into the combustion chamber is disposed on the intake side of the combustion chamber. With this combustion chamber structure, the fuel sprayed from the fuel injection unit can be easily entrained in the tumble flow, and a homogeneous mixture can be formed in the combustion chamber.

In the above combustion chamber structure, it is desirable that the ratio Lie/h of the width Lie to the peak height h satisfies the relationship 5.0<Lie/h<9.0 when the geometric compression ratio of the combustion chamber is in the range of 13.5 to 15.

According to the above combustion chamber structure, the ratio Lie/h of the width Lie to the peak height h is set to satisfy the relationship 5.0 < Lie/h < 9.0 when the geometric compression ratio of the combustion chamber is in the range of 13.5 to 15, thereby making it possible to better achieve both improved fuel economy and improved engine output.

In the above combustion chamber structure, it is desirable that the front-to-rear width Lfr, which is the width of the plane in a direction perpendicular to the direction in which the intake side and the exhaust side face each other, is greater than the lateral width Lie.

This combustion chamber structure allows the tumble flow to flow with less resistance, ensuring that the tumble flow can be maintained until the latter half of the compression stroke.

In the above combustion chamber structure, it is desirable that an ignition unit that realizes flame propagation combustion within the combustion chamber is disposed on the ceiling surface.

This combustion chamber structure allows for both improved fuel economy and improved engine output by generating flame propagation combustion within the combustion chamber.

The present invention provides an engine combustion chamber structure that can improve engine output while suppressing knocking, and can achieve both improved fuel economy and improved engine output.

FIG. 1 is a schematic cross-sectional view of an engine to which a combustion chamber structure according to the present invention is applied. FIG. 2 is a schematic perspective view showing the structure of one cylinder provided in the engine body. FIG. 3 is a schematic plan view showing the structure of the cylinder and the intake and exhaust system in its vicinity. FIG. 4 is a perspective view of the piston. FIG. 5 is a plan view of the piston crown. FIG. 6 is a side view of the piston crown. FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. FIG. 8 is a perspective view of a piston, with various parameters related to the piston crown surface noted. FIG. 9(A) is a schematic diagram showing the flow of the tumble flow in a combustion chamber according to an embodiment of the present invention, and FIG. 9(B) is a schematic diagram showing the flow of the tumble flow in a combustion chamber according to a comparative example. 10A and 10B are diagrams illustrating the flow of the tumble flow in a combustion chamber according to a comparative example. FIG. 11 is a table showing the structure and parameters of the piston crown surface according to the first and second embodiments of the present invention. FIG. 12 is a table showing the structure and parameters of the piston crown surface according to the third and fourth embodiments of the present invention. FIG. 13 is a table showing the structure and parameters of the piston crown surface according to the fifth and sixth embodiments of the present invention. FIG. 14 is a table showing the structures and parameters of the piston crown surfaces according to the seventh embodiment of the present invention and the comparative example. FIG. 15 is a graph showing the ratio of the width of the flat surface to the peak height of the crown surface for Examples 1 to 7 of the present invention and the comparative example on the horizontal axis, and the relative turbulence energy ratio compared to the turbulence energy of the comparative example on the vertical axis.

[Overall engine configuration]
Hereinafter, a combustion chamber structure of an engine according to an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a schematic cross-sectional view of an engine to which a combustion chamber structure according to an embodiment of the present invention is applied. The engine shown here is a multi-cylinder gasoline engine mounted on a vehicle such as an automobile as a power source for driving the vehicle. The engine includes an engine body 1 and auxiliary devices such as intake and exhaust manifolds and various pumps, not shown, attached thereto.

The engine body 1 has a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close the cylinder 2 from above, and a piston 5 housed in the cylinder 2. The engine body 1 is typically a multi-cylinder type having multiple cylinders (e.g., four), but for simplicity, only one cylinder 2 is shown in FIG. 1.

Figure 2 shows a schematic perspective view of one cylinder 2. The piston 5 is a generally cylindrical body having an outer diameter corresponding to the bore diameter Lb of the cylinder 2, and is housed in the cylinder 2 so as to be able to slide back and forth at a predetermined stroke Ls. As will be described in detail later, the top surface of the piston 5, which is the crown surface 50, is raised in a convex shape and is provided with a flat surface 55 with a crest height h. Below the piston 5, the crankshaft 7, which is the output shaft of the engine body 1, is provided. The crankshaft 7 is connected to the piston 5 via a connecting rod 8, and is driven to rotate around a central axis in response to the reciprocating motion of the piston 5.

A combustion chamber 6 is defined above the piston 5. The fuel is supplied to the combustion chamber 6 by injection from the injector 15, which will be described later. The supplied fuel is mixed with air in the combustion chamber 6 and combusted, and the piston 5 is pushed down by the expansion force caused by the combustion, causing it to reciprocate in the vertical direction. The combustion chamber 6 is defined by the inner wall surface of the cylinder 2, the crown surface 50 of the piston 5, and the combustion chamber ceiling surface 6U (including the valve surfaces of the intake valve 11 and exhaust valve 12) formed on the bottom surface of the cylinder head 4. The combustion chamber ceiling surface 6U is a ceiling surface that has an upwardly convex pent roof shape.

The geometric compression ratio of the combustion chamber 6, that is, the ratio between the volume of the combustion chamber 6 when the piston 5 is at top dead center and the volume of the combustion chamber 6 when the piston 5 is at bottom dead center, is desirably set to a high compression ratio of 13.5 or more. The preferred compression ratio range is 13.5 to 15.5. Setting such a high compression ratio can improve fuel efficiency.

The pent roof type combustion chamber ceiling surface 6U is provided with an intake port 9 and an exhaust port 10 that open toward the combustion chamber 6. The intake port 9 is a port that supplies intake air to the combustion chamber 6. In this embodiment, the intake port 9 is a tumble port that can form a tumble flow (vertical vortex). The flow direction of the tumble flow Ft is indicated in FIG. 2. The exhaust port 10 is a port that discharges exhaust gas after combustion from the combustion chamber 6. The combustion chamber ceiling surface 6U is provided with an intake valve 11 that opens and closes the intake port 9, and an exhaust valve 12 that opens and closes the exhaust port 10.

The valve type of the engine of this embodiment is a four-valve type with two intake valves and two exhaust valves, as shown in Figures 2 and 3. Figure 3 is a schematic plan view showing the structure of the cylinder 2 and the intake and exhaust system in its vicinity. The intake port 9 has a first intake port 9A and a second intake port 9B. The exhaust port 10 has a first exhaust port 10A and a second exhaust port 10B. One intake valve 11 is provided for each of the first intake port 9A and the second intake port 9B, and one exhaust valve 12 is provided for each of the first exhaust port 10A and the second exhaust port 10B.

As shown in FIG. 3, the second intake port 9B of the first and second intake ports 9A and 9B is provided with a swirl valve 17 that can open and close the second intake port 9B. When the swirl valve 17 is driven in the closing direction, the proportion of intake air flowing into the combustion chamber 6 from the first intake port 9A, which is not provided with the swirl valve 17, increases. This makes it possible to strengthen the swirling flow that rotates around the cylinder axis AX (the central axis of the combustion chamber 6), that is, the swirl flow. The flow direction of the swirl flow Fs is also indicated in FIG. 3. Conversely, if the swirl valve 17 is driven in the opening direction, the swirl flow Fs can be weakened. As described above, since the intake port 9 is a tumble port, the swirl flow Fs formed when the swirl valve 17 is closed becomes an oblique swirl flow mixed with the tumble flow Ft.

The cylinder head 4 is provided with an intake-side valve mechanism 13 that drives the intake valve 11, and an exhaust-side valve mechanism 14 that drives the exhaust valve 12. These valve mechanisms 13, 14 drive the intake valve 11 and exhaust valve 12 in conjunction with the rotation of the crankshaft 7. This drive causes the valve head of the intake valve 11 to open and close the opening of the intake port 9, and the valve head of the exhaust valve 12 to open and close the opening of the exhaust port 10. The valve mechanisms 13, 14 incorporate a variable valve timing mechanism (not shown) that changes the opening and closing timing.

An injector 15 (fuel injection unit) and a spark plug 16 (ignition unit) are attached to the cylinder head 4. The injector 15 injects fuel supplied from a fuel system (not shown) into the combustion chamber 6. The injector 15 is disposed on the periphery of the combustion chamber ceiling surface 6U, on the intake side where the intake port 9 is disposed. With this arrangement, the fuel sprayed from the injector 15 merges with the tumble flow Ft, and is easily distributed throughout the combustion chamber 6 by riding on the tumble flow Ft. In other words, a homogeneous mixture can be formed in the combustion chamber 6.

The spark plug 16 ignites the mixture of fuel injected from the injector 15 into the combustion chamber 6 and air introduced into the combustion chamber 6 through the intake ports 9 (9A, 9B). The spark plug 16 is attached to the cylinder head 4 along the cylinder axis AX. The ignition electrode portion of the spark plug 16 is exposed inside the combustion chamber 6 at the radial center of the combustion chamber ceiling surface 6U and faces the flat surface 55 of the crown surface 50 of the piston 5. When ignition energy is supplied from the spark plug 16 to the mixture in the combustion chamber 6, flame propagation combustion occurs in the combustion chamber 6 starting from the ignition point.

[Detailed structure of piston]
Next, the structure of the piston 5, particularly the structure of the crown surface 50, will be described in detail with reference to Figures 4 to 7. In this embodiment, the crown surface 50 is shaped in such a way that the above-mentioned tumble flow Ft can be maintained until the compression top dead center. Figure 4 is a perspective view of the piston 5 shown in Figures 1 and 2, Figure 5 is a plan view of the crown surface 50 of the piston 5, Figure 6 is a side view of the crown surface 50, and Figure 7 is a cross-sectional view taken along line VII-VII in Figure 5.

In Fig. 4 to Fig. 7, to ensure clarity of explanation, XYZ direction indications are used. The Z direction corresponds to the cylinder axis AX direction, the X direction corresponds to the front-rear direction of the engine body 1, which is the extension direction of the crankshaft 7, and the Y direction corresponds to the direction perpendicular to both the Z direction and the X direction. In each figure, the F side (+X) and R side (-X) are indicated as the front and rear sides in the installation direction of the engine body 1, the intake side (IN side; +Y) as the side where the intake port 9 is arranged, the exhaust side (EX side; -Y) as the side where the exhaust port 10 is arranged, and the top (+Z) and bottom (-Z) as the top and bottom sides on the cylinder axis AX are indicated.

The piston 5 includes a piston head 5A and a skirt portion 5B connected to the lower side (-Z side) of the piston head 5A. The piston head 5A is a cylinder with a crown surface 50 on the upper surface that constitutes a part (bottom surface) of the wall surface of the combustion chamber 6, and a side peripheral surface 5C that slides against the inner wall surface of the cylinder 2. The side peripheral surface 5C is provided with a plurality of ring grooves into which piston rings are fitted. The skirt portion 5B is disposed on the +Y side and -Y side of the piston head 5A, and suppresses the oscillation of the piston 5 during reciprocating motion. A piston boss 5D that defines a pin hole extending in the X direction is provided at the center of the skirt portion 5B in the Y direction. A piston pin is inserted into the piston boss 5D for connection to the connecting rod 8.

The crown surface 50 is a substantially circular surface facing the combustion chamber ceiling surface 6U in the Z direction. The crown surface 50 includes an exhaust side bottom 51, an intake side bottom 52, an exhaust side inclined surface 53, an intake side inclined surface 54, a flat surface 55, an inter-recess flat surface 56, an F side side wall 57, and an R side side wall 58. Of these parts, the exhaust side bottom 51 and the intake side bottom 52 are base surfaces that are the lowest in height in the +Z direction on the crown surface 50, and the other parts form raised parts that are raised from the base surface in the +Z direction by a mountain height h.

The exhaust side bottom 51 and the intake side bottom 52 are planes extending in the XY directions perpendicular to the cylinder axis AX, and are at the same height in the Z direction. The exhaust side bottom 51 and the intake side bottom 52 may be surfaces that are slightly inclined with respect to the XY directions, or surfaces that have a slight convex or concave curve. The exhaust side bottom 51 is located near the edge of the EX side (-Y) of the crown surface 50. The intake side bottom 52 is located near the edge of the IN side (+Y) of the crown surface 50.

The exhaust side bottom 51 is a bow-shaped plane whose arc is the -Y side outer periphery (side periphery 5C) of the crown surface 50 and whose chord is a straight line extending in the X direction. The intake side bottom 52 is a bow-shaped plane whose arc is the +Y side outer periphery of the crown surface 50 and whose chord is a straight line extending in the X direction. The exhaust side bottom 51 and the intake side bottom 52 are squish areas where a squish flow is formed when the piston 5 moves toward the top dead center of compression. In this embodiment, the surface area of the intake side bottom 52 is set to be larger than the surface area of the exhaust side bottom 51.

The exhaust side inclined surface 53 is an inclined surface that gradually rises from the exhaust side bottom 51 toward the Y-direction center of the crown surface 50 (the radial center of the crown surface 50). The lower end of the exhaust side inclined surface 53 is connected to the +Y edge of the exhaust side bottom 51, and the upper end is connected to the -Y edge of the plane 55 and the inter-recess plane 56. The exhaust side inclined surface 53 includes a pair of recesses 531 on the +X side and the -X side, and an inter-recess portion 532 located in these recesses 531. The recesses 531 are approximately semicircular depressions to avoid interference with the exhaust valves 12 arranged in the first and second exhaust ports 10A and 10B. The inter-recess portion 532 has an approximately trapezoidal shape in a plan view in the +Z direction (FIG. 5), with the lower edge connected to the exhaust side bottom 51 as the lower base and the upper edge connected to the inter-recess plane 56 located in the pair of recesses 531 as the upper base. The inclination angles of the recessed portion 531 and the inter-recess portion 532 with respect to the Y direction are set to be the same. However, the inclination angles may be slightly different.

The intake side inclined surface 54 is an inclined surface that gradually rises from the intake side bottom 52 toward the center of the crown surface 50 in the Y direction. The lower end of the intake side inclined surface 54 is connected to the -Y edge of the intake side bottom 52, and the upper end is connected to the +Y edge of the plane 55. In this embodiment, in a plan view in the +Z direction, the lower and upper ends of the intake side inclined surface 54 are both edges that extend linearly in the X direction. A simple inclined plane is exemplified as the intake side inclined surface 54, but if interference with the intake valve 11 occurs, a recess similar to the exhaust side recess 531 is provided.

Plane 55 is a plane that extends in the XY direction perpendicular to cylinder axis AX at the center of crown surface 50 in the Y direction. Plane 55 is a plane that is continuously provided between the upper end of exhaust side inclined surface 53 and the upper end of intake side inclined surface 54. Note that "continuous plane" means a plane that does not have a cavity or other depression. Furthermore, plane 55 may be a surface that has a slight inclination with respect to the XY direction, or a surface that has a slight convex or concave curve, within a range that does not substantially impede the flow of tumble flow Ft.

More specifically, the plane 55 has a generally rectangular shape that is long in the X direction when viewed in a plan view in the +Z direction. The plane 55 has a first EX edge 551 and a second EX edge 552 as its -Y side edges, and an IN edge 553 as its +Y side edge. The first EX edge 551 is connected to the upper end of the recessed portion 531 on the +X side. The second EX edge 552 is connected to the upper end of the recessed portion 531 on the -X side. The IN edge 553 is connected to the upper end of the intake side inclined surface 54. The +X side and -X side edges of the plane 55 have an arc shape that follows the circumference of the side peripheral surface 5C.

The inter-recess plane 56 is a plane disposed between a pair of recessed portions 531 of the exhaust-side inclined surface 53. The inter-recess plane 56 is also a plane extending in the XY direction and is a plane that exists in the same plane as the plane 55, that is, a plane that is located at the same height in the Z direction as the plane 55. The inter-recess plane 56 is a plane that is continuous with the plane 55. The plane 55 and the inter-recess plane 56 form the top surface of the raised portion on the crown surface 50, and are the surfaces that are highest in the +Z direction.

The inter-recess plane 56 is formed so as to extend to the -Y side from the center in the X direction of the -Y side edge of the plane 55, in other words, so as to extend to the -Y side from between the first EX edge 551 and the second EX edge 552. The EX edge 561 of the inter-recess plane 56 is connected to the upper end of the inter-recess portion 532 of the intake side inclined surface 54. The inter-recess plane 56 is located so as to be sandwiched between the upper ends of the pair of recess portions 531, and has a roughly square shape when viewed from above in the +Z direction. Note that the inter-recess plane 56 may be omitted, and only the plane 55 may be disposed on the crown surface 50.

[Features of the piston crown surface]
8 is a diagram showing various parameters related to the crown surface 50 of the piston 5. In the diagram, the crown height h, the lateral width Lie and the front-rear width Lfr of the plane 55, the exhaust-side inclined surface angle Exd, the surface area S1 of the plane 55, the surface area S2 of the exhaust-side inclined surface 53, and the surface area S3 of the intake-side inclined surface 54 are shown.

The mountain height h is the height of the raised portion formed by the exhaust side inclined surface 53, the intake side inclined surface 54, and the plane 55, and specifically, the Z-direction height from the exhaust side bottom 51 or intake side bottom 52, which is the base surface of the crown surface 50, to the plane 55 and the inter-recess plane 56, which is the top surface. The horizontal width Lie is the Y-direction width of the plane 55 (the width of the plane 55 in the direction in which the intake side and the exhaust side face each other). The front-rear width Lfr is the X-direction width of the plane 55 (the width of the plane 55 in the direction perpendicular to the direction in which the intake side and the exhaust side face each other). The +X side and -X side sides of the plane 55 are arc sides. The front-rear width Lfr is the X-direction width between the parts where these arc sides extend most to the +X side or -X side. The exhaust side inclined surface angle Exd is the inclination angle of the exhaust side inclined surface 53 with respect to the Y direction. In this embodiment, the plane 55 is a horizontal plane along the Y direction, so the inclined surface angle Exd is the angle between the plane 55 and the exhaust side inclined surface 53.

The surface area S1 of the plane 55 is the area of the portion enclosed by the +X and -X side edges and the +Y and -Y side edges that define the plane 55, and is roughly the area calculated by multiplying the horizontal width Lie by the front-to-rear width Lfr. In the present embodiment, when the inter-recess plane 56 is connected to the plane 55, the surface area S1 is treated as the combined surface area of the plane 55 and the inter-recess plane 56.

The surface area S2 of the exhaust side inclined surface 53 is the sum of the surface area of the pair of recessed portions 531 and the surface area of the inter-recess portion 532. The step portion 53A between the recessed portion 531 and the inter-recess portion 532 is not included in the surface area S2. This is because the step portion 53A does not substantially affect the flow of the tumble flow Ft. In addition, the inter-recess portion 532 may include not only between the recessed portions 531 but also a lower recess portion 533 (explained in Example 3 and other examples described below) that extends below the recessed portion 531. In this case, the surface area S2 also includes the surface area of the lower recess portion 533.

In the example of FIG. 8, the surface area S3 of the intake side inclined surface 54 is simply the area of the inclined plane that constitutes the intake side inclined surface 54. If a recess that avoids interference with the intake valve 11 is also formed in the intake side inclined surface 54, the surface area S3 is the sum of the surface area of the recess and the surface area of the portion between the recesses.

In this embodiment, in order to reduce the resistance of the piston crown surface 50 to the tumble flow Ft and maintain the tumble flow Ft until the latter half of the compression stroke, the above surface areas S1, S2, and S3 are set to have the following characteristics (1) to (3).
(1) The surface area S1 of the flat surface 55 is larger than the surface area S2 of the exhaust side inclined surface 53.
(2) Preferably, the surface area S1 of the flat surface 55 is greater than the surface area S3 of the intake side inclined surface 54.
(3) More preferably, the surface area S1 of the flat surface 55 is greater than the sum of the surface area S2 of the exhaust-side inclined surface 53 and the surface area S3 of the intake-side inclined surface 54.

[Significance of crown features]
The significance of the above features (1) to (3) will be explained with reference to Figures 9 and 10. Figure 9 (A) is a schematic diagram showing the flow of the tumble flow Ft when the bottom surface of the combustion chamber 6 is formed by the crown surface 50 of the piston 5 that satisfies the features (1) to (3). The intake air introduced into the combustion chamber 6 from the intake port 9 (tumble port) arranged on the pent roof type combustion chamber ceiling surface 6U forms the tumble flow Ft. Since the crown surface 50 has a plane 55 that is a "continuous plane", the tumble flow Ft can flow along the plane 55 without being hindered by a cavity or other depression. In addition, since the relationship between the surface areas S1 to S3 is set according to the above features (1) to (3), the flow of the tumble flow Ft is not weakened by the presence of the exhaust side inclined surface 53 and the intake side inclined surface 54.

The above-mentioned structural design of the crown surface 50 reduces the resistance of the crown surface 50 to the tumble flow Ft, making it easier for the tumble flow Ft to continue its flow within the combustion chamber 6. In other words, the proportion of the tumble flow Ft that collides with the exhaust side inclined surface 53 or the inner wall of the cylinder 2 and is lost is reduced, making it easier to maintain the tumble flow Ft until the latter half of the compression stroke. When the tumble flow Ft collapses, turbulent energy is generated. Maintaining the tumble flow Ft leads to maintaining the turbulent energy that the tumble flow Ft inherently possesses at a high level without loss due to the collision. Therefore, by collapsing the tumble flow Ft in the latter half of the compression stroke and generating high turbulent energy, it is possible to increase the combustion speed of the mixture in the combustion chamber 6.

In the combustion chamber 6, the ignition operation of the spark plug 16 is the starting point, and flame propagation combustion of the mixture occurs. Here, if the cylinder 2 is set to a high compression ratio, the pressure and temperature in the combustion chamber 6 rise excessively at the compression end of the piston 5, inducing abnormal combustion. The abnormal combustion is abrupt self-ignition of unburned fuel gas before the completion of flame propagation combustion, which causes knocking. However, by maintaining the tumble flow Ft until the latter half of the compression stroke and accelerating the combustion speed, it is possible to complete the combustion before the occurrence of self-ignition, which is a cause of knocking. And since knocking can be suppressed, it is possible to avoid control that deliberately suppresses engine output, such as control of the fuel injection timing of the injector 15 to retard the center of gravity of the combustion. As a result, a high compression ratio can be achieved in the cylinder 2, which makes it possible to improve fuel efficiency.

Next, a comparative example that does not satisfy the above characteristics (1) to (3) will be described. FIG. 9(B) is a diagram that shows the flow of the tumble flow Ft in the combustion chamber 6 when a crown surface 50 that does not satisfy the above characteristic (1) is adopted. The tumble flow Ft enters the combustion chamber 6 from the IN side, turns at the inner wall of the cylinder 2 on the EX side, and flows toward the IN side along the crown surface 50. When the above characteristic (1) is not satisfied, that is, when the surface area S2 of the exhaust side inclined surface 53 is larger than the surface area S1 of the plane 55, the tumble flow Ft is more likely to collide with the exhaust side inclined surface 53, and the proportion of the tumble flow Ft that is maintained until the latter half of the compression stroke decreases. That is, as shown in FIG. 9(B), a part of the tumble flow Ft1 flows from the EX side to the IN side as guided by the plane 55, but the other part of the tumble flow Ft2 collides with the exhaust side inclined surface 53 after the turn and collapses. As per feature (1), by setting the surface area S1 of the flat surface 55 to be larger than the surface area S2 of the exhaust side inclined surface 53, the tumble flow Ft that collides with the exhaust side inclined surface 53 and disappears can be reduced.

10(A) is a diagram showing the flow of the tumble flow Ft in the combustion chamber 6 when the above characteristic (2) is not satisfied. When the above characteristic (2) is not satisfied, that is, when the surface area S3 of the intake side inclined surface 54 is larger than the surface area S1 of the plane 55, the flow of the derived flow Ft3 along the intake side inclined surface 54 is easily formed. The derived flow Ft3 is a flow that deviates from the path of the main flow, the tumble flow Ft, and is guided by the intake side inclined surface 54 toward the IN side inner wall surface of the cylinder 2. Eventually, the derived flow Ft3 collides with the inner wall surface of the cylinder 2 and disappears. Therefore, the derived flow Ft3 becomes a loss of the tumble flow Ft, and reduces the tumble flow Ft maintained until the latter half of the compression stroke. As per feature (2), by setting the surface area S1 of the flat surface 55 to be larger than the surface area S3 of the intake side inclined surface 54, the derived flow Ft3 toward the inner wall of the cylinder 2 along the intake side inclined surface 54 can be suppressed.

By satisfying at least the above characteristic (1), the maintainability of the tumble flow Ft can be improved. In addition, by satisfying characteristic (2), the maintainability of the tumble flow Ft can be further improved. Furthermore, after satisfying characteristics (1) and (2), it is desirable to set the surface area S1 of the flat surface 55 to be larger than the sum of the surface area S2 of the exhaust side inclined surface 53 and the surface area S3 of the intake side inclined surface 54, as in characteristic (3). This can further suppress the collision of the tumble flow Ft with the exhaust side inclined surface 53 shown in FIG. 9(B) and the collision of the tumble flow Ft with the IN side inner wall of the cylinder 2 due to the guide of the tumble flow Ft by the intake side inclined surface 54 shown in FIG. 10(A), and further improve the maintainability of the tumble flow Ft.

Figure 10(B) is a diagram showing the flow of the tumble flow Ft in the combustion chamber 6 when the plane 55 is not a "continuous plane". A typical example of the plane 55 not being a "continuous plane" is when a cavity 59 is formed in the plane 55, and Figure 10(B) shows this state. The cavity 59 is a portion in which the center region of the plane 55 is recessed into a bowl shape. In this case, the surface area S1 of the plane 55 becomes small, making it difficult to satisfy the above characteristics (1) to (3). In addition, the flow of the tumble flow Ft is obstructed by the cavity 59. That is, a part of the tumble flow Ft becomes a derived flow Ft4 that enters the depression of the cavity 59. The derived flow Ft4 collides with the wall surface of the cavity 59 and disappears. Therefore, the derived flow Ft4 becomes a loss, which reduces the tumble flow Ft that is maintained until the latter half of the compression stroke. Therefore, it is significant that the plane 55 is a "continuous plane".

[Other features of the combustion chamber structure]
Next, features of the combustion chamber structure other than the surface areas S1 to S3 will be described. In this embodiment, in order to improve fuel efficiency and engine output, the ratio Lie/h of the width Lie, which is the width of the plane 55 in the Y direction, to the height h of the crown surface 50 is set to the following value within the range of the compression ratio = 13.5 to 15.5:
2.5<Lie/h<9.0...(A)
It fulfills the relationship.

In the combustion chamber 6 having a pent roof type combustion chamber ceiling surface 6U, the inclination angle of the exhaust side inclined surface 53 and the intake side inclined surface 54 of the crown surface 50 is generally in line with the inclination angle of the combustion chamber ceiling surface 6U. For this reason, the crest height h has a large effect on the width Lie of the plane 55. Increasing the crest height h leads to increasing the compression ratio. For example, if the crest height h is set high in order to improve fuel efficiency, the width Lie becomes narrow. In other words, the surface area S1 of the plane 55 becomes small. In this case, even if the fuel efficiency is improved, it becomes difficult to maintain the tumble flow Ft until the latter half of the compression stroke. In the end, in order to prevent knocking, suppression control of the engine output is required. However, by setting Lie/h within the range of the above formula (A), it is possible to achieve both improvement in fuel efficiency and improvement in engine output. From the viewpoint of making this balance more desirable, Lie/h is set to be in the range of compression ratio = 13.5 to 15.5,
5.0<Lie/h<9.0...(A1)
By setting the above relationship to be satisfied, it is possible to achieve both improved fuel economy and improved engine output.

The ratio Lie/h of the width Lie to the crest height h is preferably set to satisfy the relationship 5.0 < Lie/h < 9.0 when the geometric compression ratio of the combustion chamber 6 is in the range of 13.5 to 15. This makes it possible to better balance improved fuel economy and improved engine output.

Furthermore, it is desirable that the front-to-rear width Lfr, which is the width of the plane 55 in the direction perpendicular to the direction in which the intake side and the exhaust side face each other, is larger than the lateral width Lie. This allows the tumble flow to flow with less resistance, so that the tumble flow can be reliably maintained until the latter half of the compression stroke.

As shown in FIG. 2, the tumble flow Ft is introduced into the combustion chamber 6 from the intake port 9, turns around at the inner wall surface on the EX side of the cylinder 2, and passes over the plane 55 toward the IN side. If the plane 55 has a front-to-rear width Lfr smaller than the lateral width Lie, no plane exists at the +X and -X ends of the crown surface 50. In this case, the tumble flow Ft is difficult to guide at the +X and -X ends, resulting in flow loss. On the other hand, by making the plane 55 have a front-to-rear width Lfr larger than the lateral width Lie, the tumble flow Ft can be guided even at the +X and -X ends, improving the maintainability of the tumble flow Ft.

In this embodiment, an ignition plug 16 (ignition unit) that realizes flame propagation combustion is arranged in the combustion chamber 6. This makes it possible to achieve both improved fuel economy and improved engine output by generating flame propagation combustion in the combustion chamber 6.

Next, regarding the ratio Lfr/h of the front-rear width Lfr, which is the width in the X direction of the plane 55, to the mountain height h, in the range of the compression ratio = 13.5 or more and 15.5 or less,
12.0<Lfr/h<16.0...(B)
It is desirable to satisfy the following relationship.

As with the lateral width Lie, the higher the crest height h is set, the narrower the front-rear width Lfr becomes, and the smaller the surface area S1 of the flat surface 55 becomes. Therefore, it becomes difficult to maintain the tumble flow Ft until the latter half of the compression stroke, and it becomes necessary to suppress the engine output. However, by setting Lfr/h within the range of the above formula (B), it is possible to achieve both improved fuel economy and improved engine output. From the viewpoint of making it more desirable to achieve both, Lfr/h is set to:
13.5<Lfr/h<14.5...(B1)
It is desirable to satisfy the following relationship.

Regarding (Exd×S1)/h, which shows the relationship between the exhaust-side inclined surface angle Exd, which is the angle between the plane 55 and the exhaust-side inclined surface 53, the surface area S1 of the plane 55, and the crest height h, in the range of the compression ratio = 13.5 or more and 15.5 or less,
5000<(Exd×S1)/h<18000...(C)
It is desirable to satisfy the following relationship.

Since the tumble flow Ft flows as described above, the smaller the exhaust side inclined surface angle Exd, the more the degree to which the flow of the tumble flow Ft is changed at the boundary between the exhaust side inclined surface 53 and the flat surface 55, or the degree to which the tumble flow Ft collides with the exhaust side inclined surface 53 can be suppressed. However, unless the crest height h is set to a certain height, the compression ratio cannot be increased. In order to increase the crest height h and to increase the surface area S1 of the flat surface 55, it is necessary to increase the exhaust side inclined surface angle Exd. In consideration of these conflicting demands, in order to achieve both a high compression ratio and the maintenance of the tumble flow Ft, it is sufficient to set (Exd x S1)/h in the range of the above formula (C). From the viewpoint of making it more desirable to achieve both, (Exd x S1)/h is set to the range of the above formula (C) in which the compression ratio is in the range of 13.5 to 15.5,
7000<(Exd×S1)/h<12000...(C1)
It is desirable to satisfy the following relationship.

Next, we will show a geometrical design that allows the same in-cylinder flow to be formed in the combustion chamber 6, which is defined by the crown surface 50 having a flat surface 55, even if the displacement of the engine body 1 is different. As shown in Figure 3, a swirl flow Fs, which is a transverse vortex, is formed as the in-cylinder flow in the combustion chamber 6 by restricting the flow of intake air in the second intake port 9B with the swirl valve 17. In this embodiment, the swirl flow Fs is an oblique swirl flow mixed with the tumble flow Ft.

When the displacement of the engine body 1 differs, the bore diameter Lb and stroke Ls (Figure 2) also differ. The bore diameter B is the inner diameter of the cylinder 2, and is a length that is approximately equivalent to the diameter of the piston 5. The stroke Ls is the length that the piston 5 moves in the Z direction between TDC (top dead center) and BDC (bottom dead center). When the engine displacement differs, the flow of the swirl flow Fs changes even if the engine speed and load are the same. For this reason, for example, in combustion simulations, calibration according to the flow of the swirl flow Fs is required for each displacement, which is a bottleneck in engine development.

The flow of the swirl flow Fs is greatly affected by the relationship between the peak height h and the stroke Ls of the piston 5. Even if the engine displacement is different, in order to make the flow of the swirl flow Fs the same and to realize the same combustion in the combustion chamber 6 at the same engine speed and load, the ratio of the peak height h to the stroke Ls, that is, h/Ls, is set as follows within the range of the compression ratio = 13.5 to 15.5:
0.045<h/Ls<0.065...(D)
It is desirable to satisfy the following relationship.

When the peak height h is high and the stroke Ls is small, the swirl flow Fs is more likely to collide with the raised portion (exhaust side inclined surface 53, intake side inclined surface 54, and flat surface 55) of the crown surface 50 of the piston 5, and the swirl flow Fs is attenuated. On the other hand, when the peak height h is low and the stroke Ls is large, the distance over which the swirl flow Fs contacts the inner wall surface of the cylinder 2 becomes long, which also causes the swirl flow Fs to attenuate. However, by setting h/Ls within the range of the above formula (D), the attenuation of the swirl flow Fs caused by the high peak height h and the attenuation of the swirl flow Fs caused by the large stroke Ls can be made equal. Therefore, even if the engine displacement is different, an equivalent swirl flow Fs can be formed in the combustion chamber 6, and equivalent combustion can be achieved in the combustion chamber 6.

In addition, the flow of the swirl flow Fs is also greatly affected by the relationship between the crest height h and the bore diameter Lb. Even if the engine displacement is different, in order to make the flow of the swirl flow Fs the same and to realize the same combustion in the combustion chamber 6 at the same engine speed and load, the ratio of the crest height h to the bore diameter Lb, that is, h/Lb, is set as follows within the range of the compression ratio = 13.5 to 15.5:
0.055<h/Lb<0.075...(E)
It is desirable to satisfy the following relationship.

When the crest height h is high and the bore diameter Lb is small, the swirl flow Fs is more likely to collide with the raised portion of the crown surface 50 of the piston 5, and the swirl flow Fs is attenuated. On the other hand, when the crest height h is low and the bore diameter Lb is large, the distance over which the swirl flow Fs contacts the inner wall surface of the cylinder 2 becomes longer, which also causes the swirl flow Fs to attenuate. However, by setting h/Lb within the range of the above formula (E), the attenuation of the swirl flow Fs caused by the high crest height h and the attenuation of the swirl flow Fs caused by the large bore diameter Lb can be made equal. Therefore, even if the engine displacement is different, it is possible to form an equivalent swirl flow Fs in the combustion chamber 6 and achieve equivalent combustion in the combustion chamber 6.

[Examples and Comparative Examples of Crown Design]
11 to 14 are diagrams in the form of a table showing the structure and parameters of the crown surface 50 of the piston 5 according to Examples 1 to 7 of the present invention and a comparative example. Here, pistons 5 applied to engines with different displacements are illustrated. The pistons 5 of Examples 1 to 5 and the comparative example have a displacement of 1.5 liters, the piston 5 of Example 6 has a displacement of 2.0 liters, and the piston 5 of Example 7 has a displacement of 2.5 liters.

For each example in Figures 11 to 14, an external perspective view of the crown surface 50 is shown. Also shown are the width Lie of the plane 55, the peak height h of the crown surface 50, the ratio Lie/h of the width Lie to the peak height h, and the front-to-rear width Lfr of the plane 55.

For each example, a turbulent energy ratio (turbulent E ratio) based on the analytical value of the turbulent energy is shown. The analytical value of the turbulent energy is derived by analytical calculation using dedicated software (IDAJ Corporation, software name: CONVERGE) to calculate the turbulent energy possessed by the in-cylinder flow (tumble flow Ft) when the piston 5 is at the compression top dead center. The turbulent E ratio is the ratio of the analytical value of the turbulent energy of Examples 1 to 7 when the analytical value of the turbulent energy obtained for the "Comparative Example" in Figure 14 is set to "1". The compression ratio for each example is also shown.

Examples 1 and 2 illustrate planes 55 that are not accompanied by inter-recess planes 56, while examples 3 to 7 illustrate planes 55 that are accompanied by inter-recess planes 56. All planes 55 in examples 1 to 7 are "continuous planes" and do not form cavities. On the other hand, the comparative example has a cavity 59 in the radial center region of the crown surface 50.

In Examples 1 to 7, different shapes of the crown surface 50 are shown, in which the lateral width Lie of the plane 55, the peak height h of the crown surface 50, and the front-to-rear width Lfr of the plane 55 are changed.

In Examples 1 to 7, the ratio Lie/h of the width Lie to the peak height h is in the range of 2.5<Lie/h<9.0, and it can be seen that all turbulent E ratios are greater than the turbulent E ratio of the comparative example (Lie/h=1.95). In particular, the turbulent E ratios of Examples 3 to 7 (5.0<Lie/h<9.0) are more than 50% greater than the turbulent E ratio of the comparative example. From these results, it can be said that in Examples 1 to 7, the maintenance of the tumble flow Ft is improved, and most of the tumble flow Ft is successfully collapsed in the latter half of the compression stroke. Therefore, according to Examples 1 to 7, high turbulent energy can be generated in the latter half of the compression stroke, and the combustion speed can be increased.

Now, referring to the graph of FIG. 15, the relative turbulence energy ratio (turbulence E ratio) compared to the turbulence energy of the comparative example when the ratio Lie/h of the width Lie of the flat surface 55 to the height h of the crown surface 50 is changed will be compared for Examples 1 to 7 ("Ex. 1" to "Ex. 7" in FIG. 15) and the comparative example ("Comparative" in FIG. 15). As shown in the graph of FIG. 15 (tables of FIGS. 11 to 14), in the comparative example (Comparative) (Lie/h = 1.95, turbulence E ratio = 1), in all of Examples 1 to 7 (Ex. 1 to Ex. 7), the turbulence E ratio exceeds 1 in the range where the compression ratio is 13.5 to 15.5 (preferably 15) and the relationship of 2.5 < Lie/h < 9.0 is satisfied. Therefore, in Examples 1 to 7 (Ex. 1 to Ex. 7), the turbulence energy is improved compared to the comparative example (Comparative), so it is clear that the engine output can be improved while suppressing knocking. Moreover, while improving turbulent energy, the compression ratio is in the high compression ratio range of 13.5 to 15.5, which also improves fuel efficiency, making it clear that it is possible to achieve both improved fuel efficiency and improved engine output.

Furthermore, looking at the graph in Figure 15 (tables in Figures 12 to 14), in Examples 3 to 7 (Experiment 3 to Experiment 7), when the compression ratio is in the range of 13.5 to 15 and inclusive, the turbulent energy ratio is a high ratio of 1.5 or more, within the range that satisfies the relationship 5.0 < Lie/h < 9.0. Therefore, in Examples 3 to 7 (Experiment 3 to Experiment 7), it is possible to further improve engine output, and at the same time, it is possible to maintain a high compression ratio of 13.5 to 15 and inclusive, and it is clear that it is possible to better achieve both improved fuel economy and improved engine output.

[Action and Effect]
The combustion chamber structure of the engine according to the present embodiment described above provides the following advantageous effects. First, the crown surface 50 has a continuous plane 55, so that the tumble flow Ft can flow along the plane 55 without being hindered by a cavity or other recess. In addition, the width Lie of the plane 55 in the direction in which the intake side and the exhaust side face each other is set large while taking into consideration the crest height h of the crown surface 50, so that the tumble flow can flow with little resistance. Therefore, the tumble flow Ft is maintained until the latter half of the compression stroke and then collapsed to generate high turbulent energy, thereby making it possible to increase the combustion speed. This allows the combustion of the mixture in the combustion chamber 6 to be completed before the occurrence of self-ignition, which is a cause of knocking. Since knocking can be suppressed, it is possible to avoid control that suppresses engine output, such as retarding the combustion center of gravity. As a result, a high compression ratio can be achieved.

In addition, by setting Lie/h, which is the ratio of the horizontal width Lie of the plane to the height h of the peak, to satisfy the relationship 2.5<Lie/h<9.0 in the high compression ratio range where the geometric compression ratio of the combustion chamber is 13.5 or more and 15.5 or less, it is possible to achieve both improved fuel economy and improved engine output.

The ratio Lie/h of the width Lie to the peak height h can be set to satisfy the relationship 5.0 < Lie/h < 9.0 when the geometric compression ratio of the combustion chamber 6 is in the range of 13.5 to 15, thereby making it possible to better achieve both improved fuel economy and improved engine output.

In addition, if the front-to-rear width Lfr in the direction perpendicular to the direction in which the intake side and exhaust side of the plane 55 face each other is made larger than the lateral width Lie, the tumble flow can flow with less resistance, so that the tumble flow can be reliably maintained until the latter half of the compression stroke.

In addition, the spark plug 16 that realizes flame propagation combustion is disposed on the combustion chamber ceiling surface 6U facing the plane 55 of the crown surface 50. In this embodiment, it is disposed at the center of the combustion chamber 6 (on the cylinder axis AX). The intake air that is compressed without weakening the tumble flow Ft is in a state of high turbulence energy at the position facing the plane 55. By disposing the spark plug 16 in such a position, the combustion speed of the flame propagation combustion can be increased. As a result, by generating flame propagation combustion in this way in the combustion chamber 6, it is possible to achieve both improved fuel efficiency and improved engine output.

Furthermore, the injector 15 is disposed on the intake side of the combustion chamber 6. This makes it easier for the fuel sprayed from the injector 15 to be carried by the tumble flow Ft, allowing a homogeneous mixture to be formed in the combustion chamber 6.

1 Engine body 15 Injector (fuel injection part)
16 Spark plug (ignition part)
2 Cylinder 5 Piston 50 Crown surface 51 Exhaust side bottom 52 Intake side bottom 53 Exhaust side inclined surface 54 Intake side inclined surface 55 Flat surface 56 Inter-recess flat surface 6 Combustion chamber 6U Combustion chamber ceiling surface (pent roof type ceiling surface)
AX Cylinder axis Fs Swirl flow Ft Tumble flow S1 Flat surface area S2 Exhaust side inclined surface area S3 Intake side inclined surface area

Claims (4)

A combustion chamber structure for an engine having a combustion chamber defined by a crown surface of a piston, an inner wall surface of a cylinder in which the piston is slidably accommodated, and a pent roof-shaped ceiling surface formed in a cylinder head,
An opening of an intake port for supplying intake air to the combustion chamber and an opening of an exhaust port for discharging exhaust gas from the combustion chamber are formed on the ceiling surface. When the side on which the intake port is disposed is defined as the intake side and the side on which the exhaust port is disposed is defined as the exhaust side,
The crown surface is
an exhaust side bottom portion disposed near an end edge of the crown surface on the exhaust side, and an intake side bottom portion disposed near an end edge of the crown surface on the intake side;
an exhaust side inclined surface that rises from the exhaust side bottom toward a center portion of the crown surface;
an intake side inclined surface that rises from the intake side bottom toward a center portion of the crown surface;
a rectangular flat surface that is continuously provided so that there is no recess between an upper end of the exhaust side inclined surface and an upper end of the intake side inclined surface, and that extends in a direction perpendicular to an axial direction of the cylinder at a central portion of the crown surface and is long in the perpendicular direction ;
The ratio Lie/h of a width Lie, which is the width of the plane in the direction in which the intake side and the exhaust side face each other, to a mountain height h, which is the height of a protrusion formed by the exhaust-side inclined surface, the intake-side inclined surface, and the plane, is, when the geometric compression ratio of the combustion chamber is in the range of 13.5 to 15.5,
2.5<Lie/h<9.0
Fulfilling the relationship,
a fuel injection unit that injects fuel into the combustion chamber is disposed on the intake side of the combustion chamber,
The exhaust side bottom portion and the intake side bottom portion extend in a direction perpendicular to an axial direction of the cylinder.
A combustion chamber structure of an engine. The combustion chamber structure of the engine according to claim 1,
The ratio Lie/h of the width Lie to the peak height h is, when the geometric compression ratio of the combustion chamber is in the range of 13.5 or more and 15 or less,
5.0<Lie/h<9.0
The combustion chamber structure of the engine satisfies the above relationship. The combustion chamber structure of the engine according to claim 1 or 2,
A combustion chamber structure for an engine, wherein a front-to-rear width Lfr, which is a width of the plane in a direction perpendicular to a direction in which the intake side and the exhaust side face each other, is greater than the lateral width. The combustion chamber structure of the engine according to any one of claims 1 to 3,
An engine combustion chamber structure, wherein an ignition unit that realizes flame propagation combustion within the combustion chamber is disposed on the ceiling surface .