JP2022083621A - Combustion chamber structure for engine - Google Patents

Abstract

To provide a combustion chamber structure for an engine capable of improving engine output while suppressing knocking, and of compatibly improving fuel consumption performance and improving the engine output.SOLUTION: A crown surface 50 of a piston 5 includes an exhaust side bottom part 51 at the exhaust side edge, an intake side bottom part 52 at the intake side edge, an exhaust side inclined surface 53 tending from the exhaust side bottom part 51 to the center part of the crown surface 50, an intake side inclined surface 54 tending from the intake side bottom part 52 to the center part of the crown surface 50, and a plane 55, the plane 55 being provided continuously between the upper end of the exhaust side inclined surface 53 and the upper end of the intake side inclined surface 54. Lfr/h as a ratio between a longitudinal width Lfr as the width of the plane 55 in the direction perpendicular to the direction that the intake side and the exhaust side face each other, and a mountain height h as the height of an upheaval part formed by the exhaust side inclined surface 53, the intake side inclined surface 54 and the plane 55 satisfies a relationship of 6.0<Lfr/h<17.5 in a range where the geometric compression ratio of a combustion chamber 6 is 13.5-15.5.SELECTED DRAWING: Figure 8

Description

The present invention relates to a combustion chamber structure of an engine having a combustion chamber having a pent-roof type ceiling surface.

Daily research is being conducted on the structure of the combustion chamber of an engine, especially the structure of a piston, for the purpose of improving thermal efficiency and fuel efficiency. For example, Patent Document 1 discloses a structure in which a combustion chamber provided with a pent-roof type ceiling surface is provided with a cavity on the crown surface of the piston and an inclined surface along the shape of the ceiling surface. According to this combustion chamber structure, deceleration of the tumble flow is suppressed, combustion is promoted, and fuel efficiency is improved.

A simple and effective means for improving fuel efficiency is to set a high compression ratio. However, when the compression ratio is set to high, for example, in the operating region of low rotation and high load, the combustion chamber pressure and temperature at the compression end rise excessively, inducing abnormal combustion. This abnormal combustion is based on the steep self-ignition of unburned fuel gas before the completion of flame propagation combustion, which causes knocking.

Japanese Unexamined Patent Publication No. 2018-162733

Conventionally, in order to prevent the above-mentioned knocking from occurring, measures have been taken to intentionally suppress the engine output. Specifically, the fuel injection timing to the combustion chamber and the ignition timing to the air-fuel mixture are devised to retard the combustion center of gravity and suppress the engine output. Since such means prevent the engine from increasing in output, we would like to avoid it as much as possible. The structural ingenuity of the combustion chamber disclosed in Patent Document 1 can also contribute to the improvement of fuel efficiency, but according to further research by the present inventors, it is not sufficient from the viewpoint of maintaining the tumble flow until the latter half of the compression stroke. It has been found.

An object of the present invention is to provide an engine combustion chamber structure capable of improving engine output while suppressing knocking, and further improving fuel efficiency and engine output at the same time.

The combustion chamber structure of the engine according to one aspect of the present invention is partitioned 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 type ceiling surface formed on a cylinder head. It is a combustion chamber structure of an engine provided with a combustion chamber, and an opening of an intake port for supplying intake air to the combustion chamber and an opening of an exhaust port for discharging exhaust from the combustion chamber are provided on the ceiling surface. When the side formed and the intake port is arranged is the intake side and the side on which the exhaust port is arranged is the exhaust side, the crown surface is arranged near the edge of the crown surface on the exhaust side. From the exhaust side bottom, the intake side bottom arranged near the intake side edge, the exhaust side inclined surface rising from the exhaust side bottom toward the center of the crown surface, and the intake side bottom. The intake side inclined surface rising toward the central portion of the crown surface is continuously provided between the upper end of the exhaust side inclined surface and the upper end of the intake side inclined surface, and the central portion of the crown surface is the said. A front-rear width Lfr, which is the width of the plane in a direction orthogonal to the direction in which the intake side and the exhaust side face each other, including a plane extending in a direction orthogonal to the axial direction of the cylinder, and the exhaust side inclined surface, said. Lfr / h, which is the ratio of the sloped surface on the intake side and the mountain height h, which is the height of the raised portion formed by the plane, has a geometric compression ratio of 13.5 or more and 15.5 or less in the combustion chamber. It is characterized in that the relationship of 6.0 <Lfr / h <17.5 is satisfied in the range of.

According to this combustion chamber structure, since the intake port is formed on the ceiling surface of the pent-roof type, it becomes a combustion chamber in which a tumble flow is formed. The crown surface of the piston is raised in a convex shape by the inclined surface on the exhaust side and the inclined surface on the intake side, and a continuous flat surface is formed in the central portion thereof. The "continuous plane" means a plane in which there are no dents such as cavities.

By forming the continuous plane, the tumble flow can flow along the plane without being obstructed by a depression such as a cavity. Further, by setting the front-rear width Lfr, which is the width of the plane in the direction orthogonal to the direction in which the intake side and the exhaust side face each other, to be large in consideration of the balance with the mountain height h of the crown surface described later, the tumble flow is reduced. It can be made to flow by resistance. By these structural measures, the resistance of the piston crown surface to the tumble flow can be reduced, and the tumble flow can be maintained until the latter half of the compression stroke. When the tumble flow collapses, it produces turbulent energy. Maintaining the tumble flow leads to maintaining the turbulent energy possessed by the tumble flow in a high state. Therefore, it is possible to increase the combustion speed by collapsing the tumble flow in the latter half of the compression stroke and generating high turbulent energy. As a result, combustion can be completed before the occurrence of self-ignition, which causes knocking. Further, since knocking can be suppressed, it is possible to avoid control that intentionally suppresses engine output such as retarding the center of gravity of combustion. As a result, a high compression ratio can be achieved.

In a combustion chamber provided with a pent-roof type combustion chamber ceiling surface as described above, the inclination angles of the exhaust side inclined surface and the intake side inclined surface of the crown surface are substantially along the inclination angle of the combustion chamber ceiling surface. Therefore, the area of the plane tends to become smaller as the mountain height h, which is the height of the raised portion formed by the exhaust side inclined surface, the intake side inclined surface, and the plane, becomes higher, and the mountain height h is before and after the plane. It greatly affects the width Lfr. Increasing the mountain height h leads to increasing the compression ratio. For example, if the mountain height h is set high in an attempt to improve fuel efficiency, the front-rear width Lfr becomes narrow. That is, 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. After all, in order to prevent knocking, suppression control of engine output is required. Therefore, Lfr / h, which is the ratio of the front-rear width Lfr and the mountain height h of the above plane, is set in a high compression ratio range in which the geometric compression ratio of the combustion chamber is 13.5 or more and 15.5 or less. By setting so as to satisfy the relationship of 6.0 <Lfr / h <17.5, it is possible to achieve both improvement of fuel efficiency performance and improvement of engine output.

In the above combustion chamber structure, the ratio Lfr / h of the front-rear width Lfr and the mountain height h is 11.0 <Lfr / h in the range where the geometric compression ratio of the combustion chamber is 13.5 or more and 15 or less. It is desirable to satisfy the relationship of h <17.5.

According to the above combustion chamber structure, the ratio Lfr / h of the front-rear width Lfr and the mountain height h is 11.0 <in the range where the geometric compression ratio of the combustion chamber is 13.5 or more and 15 or less. By setting so as to satisfy the relationship of Lfr / h <17.5, it is possible to better achieve both the improvement of the combustion performance and the improvement of the engine output.

In the above combustion chamber structure, it is desirable that the front-rear width Lfr is larger than 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.

According to this combustion chamber structure, the tumble flow can be flowed with less resistance, so that the tumble flow can be reliably maintained until the latter half of the compression stroke.

In the above combustion chamber structure, it is desirable that the ceiling surface is provided with an ignition unit that realizes flame propagation combustion in the combustion chamber.

According to this combustion chamber structure, it is possible to achieve both improvement in fuel efficiency and improvement in engine output by generating flame propagation combustion in the combustion chamber.

In the above combustion chamber structure, it is desirable that a fuel injection unit that injects fuel into the combustion chamber is arranged on the intake side of the combustion chamber.

According to this combustion chamber structure, the fuel sprayed from the fuel injection portion can be easily put on the tumble flow, and a homogeneous air-fuel mixture can be formed in the combustion chamber.

According to the present invention, it is possible to provide an engine combustion chamber structure capable of improving engine output while suppressing knocking, and further improving fuel efficiency and engine output at the same time.

FIG. 1 is a schematic cross-sectional view of an engine to which the combustion chamber structure of the engine according to the present invention is applied. FIG. 2 is a schematic perspective view showing the structure of one cylinder included in the engine body. FIG. 3 is a schematic plan view showing the structure of the intake / exhaust system of the cylinder and its vicinity. FIG. 4 is a perspective view of the piston. FIG. 5 is a plan view of the crown surface of the piston. FIG. 6 is a side view of the crown surface of the piston. FIG. 7 is a sectional view taken along line VII-VII of FIG. FIG. 8 is a perspective view of the piston with various parameters related to the crown surface of the piston. FIG. 9A schematically shows the flow of the tumble flow in the combustion chamber according to the embodiment of the present invention, and FIG. 9B schematically shows the flow of the tumble flow in the combustion chamber according to the comparative example. It is a figure. 10 (A) and 10 (B) are diagrams schematically showing the flow of the tumble flow in the combustion chamber according to the comparative example. FIG. 11 is a tabular diagram showing the structure and parameters of the piston crown surface according to Examples 1 and 2 of the present invention. FIG. 12 is a tabular diagram showing the structure and parameters of the piston crown surface according to Examples 3 and 4 of the present invention. FIG. 13 is a tabular diagram showing the structure and parameters of the piston crown surface according to Examples 5 and 6 of the present invention. FIG. 14 is a tabular diagram showing the structure and parameters of the piston crown surface according to the seventh embodiment of the present invention and the comparative example. FIG. 15 shows a relative turbulent energy ratio compared with the turbulent energy of the comparative example, with the ratio of the front-rear width of the plane and the mountain height of the crown surface according to Examples 1 to 7 of the present invention as the horizontal axis. Is a graph represented by the vertical axis.

[Overall engine configuration]
Hereinafter, the combustion chamber structure of the engine according to the 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 the combustion chamber structure according to the embodiment of the present invention is applied. The engine shown here is a multi-cylinder gasoline engine mounted on the vehicle as a power source for driving a vehicle such as an automobile. The engine includes an engine main body 1 and an auxiliary machine such as an intake / exhaust manifold and various pumps (not shown) attached to the engine main body 1.

The engine body 1 includes 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. And have. The engine body 1 is typically a multi-cylinder type having a plurality of (for example, four) cylinders, but only one cylinder 2 is shown in FIG. 1 for simplification.

FIG. 2 shows a schematic perspective view of one cylinder 2. The piston 5 is a substantially 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 reciprocally slidable with a predetermined stroke Ls. As will be described in detail later, the crown surface 50, which is the upper surface of the piston 5, is raised in a convex shape and is provided with a plane 55 having a mountain height h. Below the piston 5, a crank shaft 7, which is an output shaft of the engine body 1, is provided. The crank shaft 7 is connected to the piston 5 via a connecting rod 8 and is rotationally driven around the central axis according 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 an injector 15, which will be described later. The supplied fuel burns while being mixed with air in the combustion chamber 6, and the piston 5 pushed down by the expansion force due to the combustion reciprocates in the vertical direction. The combustion chamber 6 includes an inner wall surface of the cylinder 2, a crown surface 50 of the piston 5, and a combustion chamber ceiling surface 6U (including each valve surface of the intake valve 11 and the exhaust valve 12) formed on the bottom surface of the cylinder head 4. It is partitioned by. The combustion chamber ceiling surface 6U is a ceiling surface having a pent-roof shape that is convex upward.

The geometric compression ratio of the combustion chamber 6, that is, the ratio of 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 13.5. It is desirable to set the above high compression ratio. The range of the preferable compression ratio is 13.5 or more and 15.5 or less. By setting such a high compression ratio, fuel efficiency can be improved.

The pent-roof type combustion chamber ceiling surface 6U is formed with an intake port 9 and an exhaust port 10 that open toward the combustion chamber 6. The intake port 9 is a port for supplying intake air to the combustion chamber 6. The intake port 9 of the present embodiment is a tumble port capable of forming a tumble flow (vertical vortex). In FIG. 2, the flow direction of the tumble flow Ft is added. The exhaust port 10 is a port for exhausting the exhaust gas after combustion from the combustion chamber 6. The combustion chamber ceiling surface 6U is provided with an intake valve 11 for opening and closing the intake port 9 and an exhaust valve 12 for opening and closing the exhaust port 10.

As shown in FIGS. 2 and 3, the valve type of the engine of the present embodiment is a 4-valve type of 2 intake valves x 2 exhaust valves. FIG. 3 is a schematic plan view showing the structure of the intake / exhaust system of the cylinder 2 and 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 one for 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. There is.

As shown in FIG. 3, of the first and second intake ports 9A and 9B, the second intake port 9B is provided with a swirl valve 17 capable of opening and closing the second intake port 9B. When the swirl valve 17 is driven in the closed direction, the proportion of intake air flowing into the combustion chamber 6 from the first intake port 9A in which the swirl valve 17 is not provided increases. Therefore, it is possible to strengthen the swirling flow, that is, the swirl flow, which swirls around the cylinder shaft AX (the central shaft of the combustion chamber 6). In FIG. 3, the flow direction of the swirl flow Fs is added. On the contrary, if the swirl valve 17 is driven in the open 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 a diagonal swirl flow mixed with the tumble flow Ft.

The cylinder head 4 is provided with an intake side valve mechanism 13 for driving the intake valve 11 and an exhaust side valve mechanism 14 for driving the exhaust valve 12. These valve valves 13 and 14 drive the intake valve 11 and the exhaust valve 12 so as to be interlocked with the rotation of the crank shaft 7. By this drive, the valve head of the intake valve 11 opens and closes the opening of the intake port 9, and the valve head of the exhaust valve 12 opens and closes the opening of the exhaust port 10. The valve operating mechanisms 13 and 14 incorporate a variable valve timing mechanism (not shown) that changes the opening / closing timing.

An injector 15 (fuel injection section) and a spark plug 16 (ignition section) are assembled to the cylinder head 4. The injector 15 injects fuel supplied from the fuel system (not shown) into the combustion chamber 6. The injector 15 is a peripheral edge of the combustion chamber ceiling surface 6U, and is arranged on the intake side where the intake port 9 is arranged. With such an arrangement, the fuel sprayed from the injector 15 joins the tumble flow Ft, and the fuel is easily distributed throughout the combustion chamber 6 on the tumble flow Ft. That is, a homogeneous air-fuel mixture can be formed in the combustion chamber 6.

The spark plug 16 ignites a 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 so as to be along the cylinder shaft AX. The ignition electrode portion of the spark plug 16 is exposed in 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 air-fuel mixture in the combustion chamber 6, flame propagation combustion occurs in the combustion chamber 6 starting from the ignition point.

[Detailed structure of piston]
Subsequently, with reference to FIGS. 4 to 7, the structure of the piston 5, particularly the structure of the crown surface 50, will be described in detail. In the present embodiment, the crown surface 50 is provided with a shape device that enables the above-mentioned tumble flow Ft to be maintained near the compression top dead center. 4 is a perspective view of the piston 5 shown in FIGS. 1 and 2, FIG. 5 is a plan view of the crown surface 50 of the piston 5, FIG. 6 is a side view of the crown surface 50, and FIG. 7 is FIG. It is a sectional view taken along the line VII-VII of.

In FIGS. 4 to 7, in order to ensure the clarity of the explanation, the direction of XYZ is indicated. 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 crank shaft 7, and the Y direction corresponds to a direction orthogonal to both the Z direction and the X direction. In each figure, the front side, the rear side in the installation direction of the engine body 1, the F side (+ X), the R side (-X), and the intake side (IN side) in the sense that the intake port 9 is arranged. ; + Y), the exhaust side (EX side; -Y) in the sense that the exhaust port 10 is arranged, and the upper (+ Z) and lower (-Z) in the sense of the upper side and the lower side on the cylinder shaft AX. Is attached.

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 made of a cylindrical body, and includes a crown surface 50 forming a part (bottom surface) of the wall surface of the combustion chamber 6 on the upper surface, and a side peripheral surface 5C that is in sliding contact with the inner wall surface of the cylinder 2. The side peripheral surface 5C is provided with a plurality of ring grooves into which the piston ring is fitted. The skirt portion 5B is arranged on the + Y side and the −Y side of the piston head 5A, and suppresses swinging swing during the reciprocating motion of the piston 5. At the center of the skirt portion 5B in the Y direction, a piston boss 5D for partitioning a pin hole extending in the X direction is provided. A piston pin for connecting to the connecting rod 8 is inserted through the piston boss 5D.

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 portion 51, an intake side bottom portion 52, an exhaust side inclined surface 53, an intake side inclined surface 54, a plane 55, a recess-to-recess plane 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 the base surfaces having the lowest height in the + Z direction on the crown surface 50, and the other parts are raised by the mountain height h in the + Z direction from the base surface. It constitutes a raised part.

The exhaust side bottom 51 and the intake side bottom 52 are planes extending in the XY direction orthogonal to the cylinder axis AX, and are at the same height position in the Z direction. The exhaust side bottom portion 51 and the intake side bottom portion 52 may be a surface having a slight inclination with respect to the XY direction, or a surface having a slightly convex or concave curved surface. The exhaust side bottom portion 51 is arranged near the end edge of the crown surface 50 on the EX side (−Y). The intake side bottom portion 52 is arranged near the edge of the crown surface 50 on the IN side (+ Y).

The exhaust side bottom portion 51 is a bow-shaped plane having an arc on the outer peripheral edge on the −Y side (side peripheral surface 5C) of the crown surface 50 and a straight line extending in the X direction as a chord. The bottom portion 52 on the intake side is an arcuate plane having an arc on the outer peripheral edge on the + Y side of the crown surface 50 and a straight line extending in the X direction as a chord. The exhaust side bottom 51 and the intake side bottom 52 are squish areas where a squish flow is formed when the piston 5 heads toward the compression top dead center. In the present embodiment, the surface area of the intake side bottom 52 is set to be wider 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 portion 51 toward the center portion in the Y direction of the crown surface 50 (the radial center portion of the crown surface 50). The lower end of the exhaust side inclined surface 53 is connected to the + Y end edge of the exhaust side bottom portion 51, and the upper end is connected to the −Y end edge of the plane 55 and the recess plane 56. The exhaust side inclined surface 53 includes a pair of recess portions 531 on the + X side and the −X side, and a recess intersection portion 532 located in these recess portions 531. The recess portion 531 is a substantially semicircular recess for avoiding interference with the exhaust valves 12 arranged in the first and second exhaust ports 10A and 10B. The recess intersection portion 532 has a lower bottom edge connected to the exhaust side bottom portion 51 and an upper end edge connected to the recess intersection plane 56 located in the pair of recesses 531 as an upper bottom in a plan view in the + Z direction (FIG. 5). It has a substantially trapezoidal shape. The inclination angles of the recess portion 531 and the recess intersection portion 532 with respect to the Y direction are set to be the same. 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 portion 52 toward the central portion of the crown surface 50 in the Y direction. The lower end of the intake side inclined surface 54 is connected to the −Y end edge of the intake side bottom portion 52, and the upper end is connected to the + Y end edge of the plane 55. In the present embodiment, in a plan view in the + Z direction, both the lower end and the upper end of the intake side inclined surface 54 are edges extending linearly in the X direction. The intake side inclined surface 54 is exemplified as a simple inclined plane, but when interference with the intake valve 11 occurs, a recess portion similar to the recess portion 531 on the exhaust side is provided.

The plane 55 is a plane extending in the XY direction orthogonal to the cylinder axis AX at the central portion of the crown surface 50 in the Y direction. The plane 55 is a plane continuously provided between the upper end of the exhaust side inclined surface 53 and the upper end of the intake side inclined surface 54. The "continuous plane" means a plane in which there are no dents such as cavities. Further, the plane 55 may be a surface having a slight inclination with respect to the XY direction or a surface having a slightly convex or concave curved surface as long as the flow of the tumble flow Ft is not substantially hindered.

More specifically, the plane 55 has a substantially rectangular shape that is long in the X direction in a plan view in the + Z direction. The plane 55 has a first EX edge 551 and a second EX edge 552 as side sides on the −Y side, and an IN end edge 553 as a side side on the + Y side. The first EX end edge 551 is connected to the upper end of the recess portion 531 on the + X side. The second EX end edge 552 is connected to the upper end of the recess portion 531 on the −X side. The IN end edge 553 is connected to the upper end of the intake side inclined surface 54. The + X side and the −X side side sides of the plane 55 have an arcuate shape along the circumference of the side peripheral surface 5C.

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

The recess-to-recess plane 56 extends from the center of the side of the plane 55 on the −Y side in the X direction toward the −Y side, in other words, from between the first EX edge 551 and the second EX edge 552. It is formed so as to extend to the side. The EX end edge 561 of the recess space plane 56 is connected to the upper end of the recess space portion 532 of the intake side inclined surface 54. The recess-to-recess plane 56 is located so as to be sandwiched between the upper ends of the pair of recess portions 531 and has a substantially square shape in a plan view in the + Z direction. It should be noted that the recess-to-recess plane 56 may be omitted, and only the plane 55 may be arranged on the crown surface 50.

[Characteristics of piston crown surface]
FIG. 8 is a diagram showing various parameters related to the crown surface 50 of the piston 5. In the figure, the mountain height h, the 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. It is 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 flat surface 55, and specifically, the exhaust side bottom portion 51 which is the base surface of the crown surface 50. Alternatively, it is the height in the Z direction from the intake side bottom portion 52 to the plane 55 which is the top surface and the plane 56 between recesses. The lateral width Lie is the width in the Y direction 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 width of the plane 55 in the X direction (the width of the plane 55 in the direction orthogonal to the direction in which the intake side and the exhaust side face each other). The side sides of the plane 55 on the + X side and the −X side are arc sides. The front-back width Lfr is the width in the X direction between the portions where these arc sides extend most to the + X side or the −X side. The exhaust side inclined surface angle Exd is an inclined angle of the exhaust side inclined surface 53 with respect to the Y direction. In the present embodiment, since the plane 55 is a horizontal plane along the Y direction, the inclined surface angle Exd is an angle formed by the plane 55 and the exhaust side inclined surface 53.

The surface area S1 of the plane 55 is the area of the portion surrounded by the side sides of the + X side and the −X side and the side sides of the + Y side and the −Y side that partition the plane 55. It is the area calculated by multiplying by. When the recess-to-recess plane 56 is continuously provided on the plane 55 as in the present embodiment, the surface area S1 is treated as the total surface area of the plane 55 and the recess-to-recess plane 56.

The surface area S2 of the exhaust side inclined surface 53 is the total area of the surface area of the pair of recess portions 531 and the surface area of the recess inter-recess portion 532. The stepped portion 53A existing between the recess portion 531 and the recessed 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. Further, the recess inter-recess section 532 may include a recess lower portion 533 (specified in Example 3 and others described later) extending not only between the recess sections 531 but also below the recess section 531. The surface area S2 in this case also includes the surface area of the recess lower 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 constituting the intake side inclined surface 54. When a recess portion for avoiding interference with the intake valve 11 is also formed on the intake side inclined surface 54, the area is the sum of the surface area of the recess portion and the surface area of the recess inter-recess portion.

In the present embodiment, in order to reduce the resistance of the crown surface 50 of the piston 5 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 have the following features (1) to. (3) is set to be provided.
(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 plane 55 is larger than the surface area S3 of the intake side inclined surface 54.
(3) More preferably, the surface area S1 of the plane 55 is 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.

[Significance of the characteristic part of the crown surface]
The significance of the above features (1) to (3) will be described with reference to FIGS. 9 and 10. FIG. 9A is a schematic view showing the flow of the tumble flow Ft when the crown surface 50 of the piston 5 satisfying the features (1) to (3) and the bottom surface of the combustion chamber 6 is formed. The intake air introduced into the combustion chamber 6 from the intake port 9 (tumble port) arranged on the ceiling surface 6U of the pent-roof type combustion chamber forms a tumble flow Ft. Since the flat surface 55, which is a "continuous flat surface", is formed on the crown surface 50, the tumble flow Ft can be flowed along the flat surface 55 without being obstructed by a depression such as a cavity. Further, since the relationship between the surface areas S1 to S3 is set as described in the above features (1) to (3), the flow of the tumble flow Ft is weakened by the presence of the exhaust side inclined surface 53 and the intake side inclined surface 54. It will not change.

Due to the structural ingenuity of the crown surface 50, the resistance of the crown surface 50 to the tumble flow Ft is reduced, and the tumble flow Ft can easily continue its flow in the combustion chamber 6. That is, it is possible to reduce the rate at which the tumble flow Ft collides with the exhaust side inclined surface 53, the inner wall of the cylinder 2, and the like and disappears, so that the tumble flow Ft can be easily maintained 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 inherent in the tumble flow Ft in a high state without loss due to the collision. Therefore, the tumble flow Ft is disintegrated in the latter half of the compression stroke to generate high turbulent energy, so that the combustion speed of the air-fuel mixture in the combustion chamber 6 can be increased.

In the combustion chamber 6, flame propagation combustion of the air-fuel mixture occurs starting from the ignition operation of the spark plug 16. Here, when the cylinder 2 is set to a high compression ratio, the pressure and temperature in the combustion chamber 6 excessively rise at the compression end of the piston 5 to induce abnormal combustion. The abnormal combustion is a steep self-ignition of unburned fuel gas before the completion of flame propagation combustion, and causes knocking. However, by maintaining the tumble flow Ft until the latter half of the compression stroke and increasing the combustion speed, it is possible to complete the combustion before the self-ignition that causes knocking occurs. Since knocking can be suppressed, it is possible to avoid control that intentionally suppresses the engine output, for example, control such as controlling the fuel injection timing of the injector 15 to retard the combustion center of gravity. Further, as a result, a high compression ratio of the cylinder 2 can be achieved, and fuel efficiency can be improved.

Subsequently, a comparative example that does not satisfy the above features (1) to (3) will be described. FIG. 9B is a diagram schematically showing the flow of the tumble flow Ft in the combustion chamber 6 when the crown surface 50 that does not satisfy the above feature (1) is adopted. The tumble flow Ft is a flow that enters the combustion chamber 6 from the IN side, turns at the inner wall of the cylinder 2 on the EX side, and goes toward the IN side along the crown surface 50. When the above feature (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 easily collides with the exhaust side inclined surface 53 until the latter half of the compression stroke. The percentage of tumble flow Ft maintained is reduced. That is, as shown in FIG. 9B, a part of the tumble flow Ft1 goes from the EX side to the IN side so as to be guided by the plane 55, while the other part of the tumble flow Ft2 is in the turn. This is because it later collides with the exhaust side inclined surface 53 and collapses. As described in the 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, it is possible to reduce the tumble flow Ft that collides with the exhaust side inclined surface 53 and disappears.

FIG. 10A is a diagram schematically showing the flow of the tumble flow Ft in the combustion chamber 6 when the above feature (2) is not satisfied. When the above feature (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 likely to be formed. .. The derived flow Ft3 is a flow that deviates from the path of the tumble flow Ft, which is the main flow, and is guided by the intake side inclined surface 54 and becomes a flow 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 shown in the feature (2), by setting the surface area S1 of the plane 55 to be larger than the surface area S3 of the intake side inclined surface 54, the derivative flow Ft3 toward the inner wall of the cylinder 2 along the intake side inclined surface 54 is suppressed. Can be done.

By satisfying at least the above-mentioned feature (1), the maintainability of the tumble flow Ft can be enhanced. In addition to this, by satisfying the feature (2), the maintainability of the tumble flow Ft can be further improved. Further, after satisfying the features (1) and (2), as shown in the feature (3), the surface area S1 of the flat surface 55 is 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. It is desirable to set it larger than. As a result, the collision of the tumble flow Ft with the exhaust side inclined surface 53 shown in FIG. 9 (B) and the cylinder 2 due to the tumble flow Ft being guided by the intake side inclined surface 54 shown in FIG. 10 (A). The collision with the inner wall on the IN side can be further suppressed, and the maintainability of the tumble flow Ft can be further improved.

FIG. 10B is a diagram schematically 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 in which the plane 55 is not a “continuous plane” is a case where the cavity 59 is formed in the plane 55, and FIG. 10 (B) shows the embodiment. The cavity 59 is a portion in which the center region of the plane 55 is recessed in a bowl shape. In this case, the surface area S1 of the plane 55 becomes small, and it becomes difficult to satisfy the above features (1) to (3). Further, the flow of the tumble flow Ft is obstructed by the cavity 59. That is, a part of the tumble flow Ft becomes a derivative flow Ft4 that enters the recess 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 and reduces the tumble flow Ft maintained until the latter half of the compression stroke. Therefore, it is significant that the plane 55 is a "continuous plane".

[About other features of the combustion chamber structure]
Subsequently, the features of the combustion chamber structure other than the above surface areas S1 to S3 will be described. In the present embodiment, in order to improve fuel efficiency and engine output, the Lfr / h, which is the ratio of the front-rear width Lfr, which is the width in the X direction of the plane 55, to the mountain height h of the crown surface 50 is compressed. In the range of ratio = 13.5 or more and 15.5 or less
6.0 <Lfr / h <17.5 ... (A)
Meet the relationship.

In the combustion chamber 6 provided with the pent-roof type combustion chamber ceiling surface 6U, the inclination angles of the exhaust side inclined surface 53 and the intake side inclined surface 54 of the crown surface 50 are substantially along the inclination angle of the combustion chamber ceiling surface 6U. .. Therefore, the area S1 of the plane 55 tends to become narrower as the mountain height h becomes higher, and the mountain height h greatly affects the width Lee and the front-back width Lfr of the plane 55. Increasing the mountain height h leads to increasing the compression ratio. For example, if the mountain height h is set high in order to improve fuel efficiency, the width Lie and the front-rear width Lfr become narrow. That is, the surface area S1 of the plane 55 becomes smaller. 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. After all, in order to prevent knocking, suppression control of engine output is required. However, by setting Lfr / h within the range of the above equation (A), it is possible to achieve both improvement in fuel efficiency and improvement in engine output. From the viewpoint of more desirable compatibility, Lfr / h is set in the range of compression ratio = 13.5 or more and 15.5 or less.
6.0 <Lfr / h <17.5 ... (A1)
By setting so as to satisfy the above relationship, it is possible to achieve both improvement in fuel efficiency and improvement in engine output.

The ratio Lfr / h between the front-rear width Lfr and the mountain height h has a relationship of 11.0 <Lfr / h <17.5 in the range where the geometric compression ratio of the combustion chamber 6 is 13.5 or more and 15 or less. It is desirable to set to satisfy. As a result, it is possible to better achieve both improvement in fuel efficiency and improvement in engine output.

Further, it is desirable that the front-rear width Lfr is larger than the width Lie, which is the width of the plane 55 in the direction in which the intake side and the exhaust side face each other. As a result, the tumble flow can be flowed with less resistance, so that the tumble flow can be reliably maintained until the latter half of the compression stroke.

As schematically shown in FIG. 2, the tumble flow Ft is introduced into the combustion chamber 6 from the intake port 9, folds back at the inner wall surface on the EX side of the cylinder 2, passes over the flat surface 55, and heads toward the IN side. If the front-rear width Lfr is smaller than the width Lie and the plane 55, there is no plane at the ends of the crown surface 50 on the + X side and the −X side. In this case, it becomes difficult for the tumble flow Ft to be guided at the ends on the + X side and the −X side, and a flow loss occurs. On the other hand, by setting the plane 55 having a front-rear width Lfr larger than the width Lie, the tumble flow Ft can be guided even at the ends on the + X side and the −X side, and the maintainability of the tumble flow Ft can be improved. ..

In the present embodiment, a spark plug 16 (ignition unit) that realizes flame propagation combustion is arranged in the combustion chamber 6. As a result, it is possible to achieve both improvement in fuel efficiency and improvement in engine output by generating flame propagation combustion in the combustion chamber 6.

Next, regarding Lie / h, which is the ratio of the width Lie, which is the width in the Y direction of the plane 55, to the mountain height h, in the range of compression ratio = 13.5 or more and 15.5 or less.
2.5 <Lie / h <9.0 ... (B)
It is desirable to satisfy the relationship of.

Similar to the front-rear width Lfr, the higher the mountain height h is set, the narrower the width Lie becomes and the smaller the surface area S1 of the plane 55. Therefore, it becomes difficult to maintain the tumble flow Ft until the latter half of the compression stroke, and it is necessary to suppress the engine output. However, by setting Lie / h within the range of the above equation (B), it is possible to achieve both improvement in fuel efficiency and improvement in engine output. From the viewpoint of more desirable compatibility, Lie / h is set in the range of compression ratio = 13.5 or more and 15.5 or less.
5.0 <Lie / h <9.0 ... (B1)
It is desirable to satisfy the relationship of.

The compression ratio = 13. In the range of 5 or more and 15.5 or less
5000 <(Exd × S1) / h <18000 ... (C)
It is desirable to satisfy the relationship of.

Since the tumble flow Ft flows as described above, the smaller the exhaust side inclined surface angle Exd, the more the flow of the tumble flow Ft is changed at the boundary between the exhaust side inclined surface 53 and the plane 55, or the exhaust side. It is possible to suppress the degree of collision with the inclined surface 53. However, the compression ratio cannot be increased unless the mountain height h is set to a certain height. In order to increase the mountain height h and obtain the surface area S1 of the plane 55, it is necessary to increase the exhaust side inclined surface angle Exd. In consideration of these contradictory requirements, in order to achieve both high compression ratio and maintenance of tumble flow Ft, (Exd × S1) / h may be set in the range of the above equation (C). From the viewpoint of more desirable compatibility, (Exd × S1) / h is set in the range of compression ratio = 13.5 or more and 15.5 or less.
7000 <(Exd × S1) / h <12000 ... (C1)
It is desirable to satisfy the relationship of.

Next, in the combustion chamber 6 partitioned by the crown surface 50 having the flat surface 55, a shape device capable of forming the same in-cylinder flow in the combustion chamber 6 even if the displacement of the engine body 1 is different is shown. As shown in FIG. 3, by regulating the flow of intake air in the second intake port 9B with the swirl valve 17, a swirl flow Fs which is a lateral vortex is formed as an in-cylinder flow in the combustion chamber 6. In the present embodiment, the swirl flow Fs is a diagonal swirl flow mixed with the tumble flow Ft.

When the displacement of the engine body 1 is different, the bore diameter Lb and the stroke Ls (FIG. 2) are also different. The bore diameter B is the inner diameter of the cylinder 2 and is a length substantially corresponding to the diameter of the piston 5. The stroke Ls is the length at which the piston 5 moves in the Z direction between TDC (top dead center) and BDC (bottom dead center). The flow of swirl flow Fs changes when the engine displacement is different, even if the engine speed and load are the same. Therefore, for example, in a combustion simulation or the like, calibration according to the flow of 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 mountain height h and the stroke Ls of the piston 5. Even if the engine displacement is different, the ratio of the mountain height h and the stroke Ls is from the viewpoint of making the flow of the swirl flow Fs the same and realizing the same combustion in the combustion chamber 6 at the same engine speed and the same load. For h / Ls, in the range of compression ratio = 13.5 or more and 15.5 or less
0.045 <h / Ls <0.065 ... (D)
It is desirable to satisfy the relationship of.

When the mountain height h is high and the stroke Ls is small, the swirl flow Fs easily collides 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 generated. Decay. On the other hand, when the mountain height h is low and the stroke Ls is large, the distance that the swirl flow Fs contacts the inner wall surface of the cylinder 2 becomes long, which also causes the swirl flow Fs to be attenuated. However, by setting h / Ls to the range of the above equation (D), the attenuation of the swirl flow Fs due to the high mountain height h and the attenuation of the swirl flow Fs due to the large stroke Ls can be obtained. Can be equal. Therefore, even when the engine displacement is different, the same swirl flow Fs can be formed in the combustion chamber 6, and the same combustion can be realized in the combustion chamber 6.

Further, the flow of the swirl flow Fs is greatly affected by the relationship between the mountain height h and the bore diameter Lb. Even if the engine displacement is different, the ratio of the mountain height h and the bore diameter Lb is from the viewpoint of achieving the same combustion in the combustion chamber 6 with the same engine rotation speed and the same load by making the flow of swirl flow Fs the same. For a certain h / Lb, in the range of compression ratio = 13.5 or more and 15.5 or less
0.055 <h / Lb <0.075 ... (E)
It is desirable to satisfy the relationship of.

When the mountain height h is high and the bore diameter Lb is small, the swirl flow Fs easily collides 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 mountain height h is low and the bore diameter Lb is large, the distance that the swirl flow Fs comes into contact with the inner wall surface of the cylinder 2 becomes long, which also causes the swirl flow Fs to be attenuated. However, by setting h / Lb to the range of the above equation (E), the attenuation of the swirl flow Fs due to the high mountain height h and the attenuation of the swirl flow Fs due to the large bore diameter Lb can be obtained. Can be made equivalent. Therefore, even when the engine displacement is different, the same swirl flow Fs can be formed in the combustion chamber 6, and the same combustion can be realized in the combustion chamber 6.

[Examples and comparative examples of crown surface design]
11 to 14 are tabular views showing the structure and parameters of the crown surface 50 of the piston 5 according to Examples 1 to 7 and Comparative Examples of the present invention. Here, the piston 5 applied to engines having different displacements is illustrated. The pistons 5 of Examples 1 to 5 and Comparative Examples have a displacement of 1.5 liters, a displacement of Example 6 is 2.0 liters, and a displacement of Example 7 is 2.5 liters.

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

For each example, the turbulent energy ratio (turbulent E ratio) based on the analysis value of the turbulent energy is shown. The analysis value of the turbulent energy is the turbulent energy possessed by the in-cylinder flow (tumble flow Ft) when the piston 5 is at the compression top dead center, and the dedicated software (IDAJ Co., Ltd., software name: CONVERGE) is used. It was derived by the analysis calculation used. The turbulence E ratio is the ratio of the analysis values of the turbulence energy of Examples 1 to 7 when the analysis value of the turbulence energy obtained for the “comparative example” of FIG. 14 is set to “1”. The compression ratio for each example is also shown.

Examples 1 and 2 exemplify a plane 55 in which the recess plane 56 is not attached, and Examples 3 to 7 exemplify the plane 55 to which the recess plane 56 is attached. .. Each of the planes 55 of Examples 1 to 7 is a "continuous plane", and no cavity is formed. On the other hand, the comparative example has a cavity 59 in the radial center region of the crown surface 50.

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

In Examples 1 to 7, the ratio Lfr / h of the front-rear width Lfr and the mountain height h is in the range of 6.0 <Lfr / h <17.5, and all the turbulent flow E ratios are the comparative examples (Lfr /). It can be seen that it is larger than the turbulent flow E ratio of h = 2.72). In particular, the turbulent flow E ratio of Examples 2 to 7 (11.0 <Lfr / h <17.5) is 37% or more larger than the turbulent flow E ratio of the comparative example. From these results, it can be said that in Examples 1 to 7, the maintainability of the tumble flow Ft was enhanced, and most of the tumble flow Ft was successfully destroyed 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.

Here, with reference to the graph of FIG. 15, for Examples 1 to 7 (“real 1” to “real 7” in FIG. 15) and comparative example (“comparison” in FIG. 15), the front-back width Lfr of the plane 55. And the relative turbulent energy ratio (turbulent E ratio) compared with the turbulent energy of the comparative example when the ratio Lfr / h of the mountain height h of the crown surface 50 is changed. As shown in the graph of FIG. 15 (table of FIGS. 11 to 14), Examples 1 to 7 (actual) with respect to Comparative Example (comparison) (Lfr / h = 2.72, turbulent flow E ratio = 1). In 1 to 7), turbulence flows in the range where the compression ratio is 13.5 or more and 15.5 (preferably 15) or less and the relationship of 6.0 <Lfr / h <17.5 is satisfied. The E ratio is above 1. Therefore, in Examples 1 to 7 (actual 1 to actual 7), the turbulent energy is improved as compared with the comparative example (comparative), so that it is clear that the engine output can be improved while suppressing knocking. .. Moreover, while improving the turbulence energy, the compression ratio is in the high compression ratio range of 13.5 or more and 15.5 or less, so it is possible to improve fuel efficiency, and as a result, fuel efficiency is improved and engine output is improved. It is clear that it is also possible to achieve both.

Further, looking at the graph of FIG. 15 (table of FIGS. 11 to 14), in Examples 2 to 7 (actual 2 to actual 7), 11.0 <Lfr in the range where the compression ratio is 13.5 or more and 15 or less. The turbulent energy ratio is as high as 1.37 or more within the range satisfying the relationship of / h <17.5. Therefore, in Examples 2 to 7 (actual 2 to actual 7), the engine output can be further improved, and the high compression ratio of 13.5 or more and 15 or less can be maintained, so that the fuel efficiency performance is improved and the engine output is improved. It is clear that the improvement of the above can be better compatible.

[Action effect]
According to the combustion chamber structure of the engine according to the present embodiment described above, the following functions and effects are obtained. First, since the continuous flat surface 55 is formed on the crown surface 50, the tumble flow Ft can be flowed along the flat surface 55 without being obstructed by a depression such as a cavity. Further, by setting the front-rear width Lfr, which is the width of the plane 55 in the direction orthogonal to the direction in which the intake side and the exhaust side face each other, to be large in consideration of the balance with the mountain height h of the crown surface 50, the tumble flow is reduced. It can be made to flow by resistance. Therefore, it is possible to increase the combustion speed by maintaining the tumble flow Ft until the latter half of the compression stroke and then disintegrating it to generate high turbulent energy. As a result, the combustion of the air-fuel mixture in the combustion chamber 6 can be completed before the self-ignition that causes knocking occurs. Since knocking can be suppressed, control that suppresses engine output such as retarding the center of gravity of combustion can be avoided. As a result, a high compression ratio can be achieved.

Further, Lfr / h, which is the ratio of the front-rear width Lfr of the plane 55 to the mountain height h, is set to 6 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. By setting so as to satisfy the relationship of .0 <Lfr / h <17.5, it is possible to achieve both improvement of fuel efficiency performance and improvement of engine output.

The ratio Lfr / h between the front-rear width Lfr and the mountain height h is 11.0 <Lfr / h <17.5 in the range where the geometric compression ratio of the combustion chamber 6 is 13.5 or more and 15 or less. If it is set to satisfy the above conditions, it is possible to better achieve both the improvement of fuel efficiency and the improvement of engine output.

Further, if the front-rear width Lfr is made larger than the width Lie, which is the width of the plane 55 in the direction in which the intake side and the exhaust side face each other, the tumble flow can be made to flow with less resistance, so that the tumble flow can be compressed. It can be reliably maintained until the second half.

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

Further, the injector 15 is arranged on the intake side of the combustion chamber 6. This makes it easier to put the fuel sprayed from the injector 15 on the tumble flow Ft, and a homogeneous air-fuel mixture can 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 56 Recess plane 6 Combustion chamber 6U Combustion chamber ceiling surface (pent roof type ceiling surface)
AX Cylinder shaft Fs swirl flow Ft tumble flow S1 Surface area of plane S2 Surface area of exhaust side inclined surface S3 Surface area of intake side inclined surface

Claims (5)

A combustion chamber structure of an engine including a combustion chamber partitioned by a crown surface of a piston, an inner wall surface of a cylinder in which the piston is slidably housed, and a pent-roof type ceiling surface formed on a cylinder head. hand,
On the ceiling surface, 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, and the side on which the intake port is arranged is the intake side. When the side on which the exhaust port is arranged is the exhaust side,
The crown surface is
An exhaust side bottom portion arranged near the exhaust side edge of the crown surface, and an intake side bottom portion arranged near the intake side edge.
An exhaust-side inclined surface that rises from the exhaust-side bottom to the center of the crown surface,
An intake-side inclined surface that rises from the intake-side bottom to the center of the crown surface,
A plane that is continuously provided between the upper end of the exhaust side inclined surface and the upper end of the intake side inclined surface and extends in a direction orthogonal to the axial direction of the cylinder at the central portion of the crown surface includes.
The front-rear width Lfr, which is the width of the plane in the direction orthogonal to the direction in which the intake side and the exhaust side face each other, and the height of the exhaust side inclined surface, the intake side inclined surface, and the raised portion formed by the plane. Lfr / h, which is the ratio to the mountain height h, is in the range where the geometric compression ratio of the combustion chamber is 13.5 or more and 15.5 or less.
6.0 <Lfr / h <17.5
Combustion chamber structure of the engine characterized by satisfying the relationship of. In the combustion chamber structure of the engine according to claim 1,
The ratio Lfr / h between the front-rear width Lfr and the mountain height h is such that the geometric compression ratio of the combustion chamber is 13.5 or more and 15 or less.
11.0 <Lfr / h <17.5
Combustion chamber structure of the engine that meets the relationship. In the combustion chamber structure of the engine according to claim 1 or 2.
The front-rear width Lfr is a combustion chamber structure of an engine, which is larger than 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. In the combustion chamber structure of the engine according to any one of claims 1 to 3.
An engine combustion chamber structure in which an ignition unit that realizes flame propagation combustion is arranged on the ceiling surface. In the combustion chamber structure of the engine according to any one of claims 1 to 4.
A combustion chamber structure of an engine in which a fuel injection unit that injects fuel into the combustion chamber is arranged on the intake side of the combustion chamber.

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