JP5971321B2 - Combustion chamber structure of direct injection engine - Google Patents

Description

  The technology disclosed herein relates to a combustion chamber structure of a direct injection engine.

  Patent Document 1 discloses a technique for increasing the thermal efficiency of an engine by reducing cooling loss. Specifically, the combustion is accelerated by adding ozone to the intake air, thereby suppressing the flame that reaches the wall surface defining the combustion chamber. Since the heat transmitted to the wall surface is reduced by suppressing the flame reaching the wall surface, the cooling loss is reduced.

  Patent Document 2 discloses a pent roof type combustion chamber structure. In this pent roof type combustion chamber structure, the ceiling of the cylinder head is formed so as to have two slopes connected by a ridge line, an opening of an intake port is provided on one slope, and an exhaust is provided on the other slope. A port opening is provided. As a result, the combustion chamber volume is reduced while ensuring a relatively large intake and exhaust valve diameter.

JP 2013-194712 A JP 2007-1000054 A

  In the pent roof type combustion chamber structure as disclosed in Patent Document 2, the intake air that flows into the combustion chamber from the intake port descends on the exhaust side, changes direction toward the intake side along the piston top surface, and the intake side Then, it becomes a swirling flow of a vertical vortex that rises and changes its direction toward the exhaust side in the vicinity of the ceiling of the cylinder head, that is, a tumble flow. Here, since the tumble flow in the vicinity of the ceiling portion is a flow from the intake side to the exhaust side, the fuel spray injected from the fuel injection valve arranged on the ceiling portion rides on the tumble flow, and the exhaust side It is easy to fly to. As a result, the fuel spray and the air-fuel mixture easily reach the exhaust-side wall surface among the wall surfaces that define the combustion chamber, which may increase cooling loss.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to prevent an increase in cooling loss due to the tumble flow.

  A combustion chamber structure of a direct injection engine disclosed herein has a ceiling portion including two head side slopes connected at a valley portion, and a ridge portion that defines a part of a pent roof type combustion chamber. And includes a piston inserted into the cylinder, and a fuel injection valve provided in the trough, and has a top surface including two piston-side inclined surfaces facing the two head-side inclined surfaces. An intake port is opened on the head-side slope, an exhaust port is opened on the other head-side slope, and the end of each head-side slope opposite to the trough is A head side hem surface that is bent and expanded in a mountain fold shape from the head side inclined surface is provided, and a concave cavity is formed across the ridge portion on the top surface, and the ridge portion of each piston side inclined surface and The opposite end has a trough from the piston side slope. A piston-side hem surface that bends and expands like a ring is provided, spanning between each head-side flank and each piston-side hem surface between each head-side flank and each piston-side flank, A bent squish area is formed, and on the exhaust port side, a squish area between the head-side inclined surface and the piston-side inclined surface and a squish area between the head-side skirt surface and the piston-side skirt surface are formed. The angle is larger than the angle formed by the squish area between the head-side slope and the piston-side slope and the squish area between the head-side bottom face and the piston-side bottom face on the intake port side.

  According to this configuration, on each of the intake port side and the exhaust port side, a squish area extends from between each head side inclined surface and each piston side inclined surface to between each head side bottom surface and each piston side bottom surface. Is formed. Since the head-side inclined surface and the head-side skirt surface are bent, and the piston-side inclined surface and the piston-side skirt surface are bent, the squish area is also bent. The squish flow generated in the squish area flows into a cavity formed on the top surface of the piston.

  Here, a squish area between the head-side slope and the piston-side slope on the exhaust port side (hereinafter referred to as “slope area”) and a squish area between the head-side bottom face and the piston-side bottom face (hereinafter referred to as “hem”). The angle formed by “area”) is larger than the angle formed by the slope area and the skirt area on the intake port side. Thereby, on the exhaust port side, the attenuation when the squish flow flows from the skirt area to the slope area becomes small, and on the intake port side, the attenuation when the squish flow flows from the skirt area to the slope area becomes large. As a result, the squish flow that flows into the cavity through the skirt area and the slope area on the exhaust side is stronger than the squish flow that flows into the cavity through the skirt area and the slope area on the intake side.

  On the other hand, in the cavity, the tumble flow due to the intake flow from the intake port remains, and the tumble flow near the ceiling of the cylinder head flows from the intake side to the exhaust side. That is, the squish flow from the exhaust side flows in a direction that cancels out the tumble flow in the vicinity of the ceiling of the cylinder head, and the squish flow from the intake side flows in a direction that promotes the tumble flow. As described above, by increasing the squish flow from the exhaust side and weakening the squish flow from the intake side, the tumble flow can be weakened by the squish flow. As a result, the fuel spray and the air-fuel mixture that reach the exhaust side portion of the inner surface of the cavity can be reduced.

  The “angle between the squish area (slope area) between the head-side slope and the piston-side slope and the squish area (hem area) between the head-side skirt and the piston-side skirt” refers to the head side. An angle formed by an intermediate surface between the inclined surface and the piston-side inclined surface, and an intermediate surface between the head-side skirt surface and the piston-side skirt surface, which is an angle formed by a smaller angle than 180 degrees.

  Further, the head side skirt surface and the piston side skirt surface may be orthogonal to the axis of the cylinder.

  According to this configuration, the skirt area is perpendicular to the cylinder axis and the angle between the exhaust port side slope area and the skirt area is relatively large. The corner is relatively large. Therefore, the squish flow from the exhaust side has a larger component in the direction orthogonal to the cylinder axis, that is, a component corresponding to the side of the fuel spray injected from the combustion injection valve. As a result, fuel spray and air-fuel mixture injected from the fuel injection valve and flowing on the tumble flow and flowing obliquely downward on the exhaust side can be pushed back obliquely downward on the exhaust side, that is, toward the bottom wall of the cavity. . As a result, the fuel spray that tends to spread to the exhaust side can be compactly collected.

  On the other hand, the inclination angle of the inclined area on the intake side with respect to the axial center of the cylinder is relatively large. Thereby, when the squish flow from the intake side flows into the cavity, a component toward the injection port of the fuel injection valve increases. As a result, the scattering distance of the fuel spray can be suppressed, and the fuel spray reaching the inner peripheral surface of the cavity can be reduced.

  Further, the head-side hem surface on the exhaust port side is disposed closer to the valley side in the axial direction of the cylinder than the head-side hem surface on the intake port side, and the piston on the exhaust port side The side hem surface may be arranged closer to the ridge portion in the axial direction of the cylinder than the piston side hem surface on the intake port side.

  According to the above configuration, the inclination angle of the head-side slope on the intake port side with respect to the axis of the cylinder is smaller than the head-side slope on the exhaust port side, so that the valley portion tends to shift to the intake port side with respect to the cylinder axis. It is in. On the other hand, by arranging the position of the head side hem surface on the exhaust port side in the axial direction of the cylinder closer to the valley side than the head side hem surface on the intake port side, the valley portion is brought closer to the axis of the cylinder. be able to. Since the fuel injection valve is provided in the valley, the fuel injection valve can be brought close to the axis of the cylinder by bringing the valley close to the axis of the cylinder.

  Similarly, since the inclination angle of the piston side inclined surface on the intake port side with respect to the cylinder axis is smaller than that on the exhaust port side, the ridge portion tends to be shifted to the intake port side from the cylinder axis. On the other hand, the position of the piston side hem surface on the exhaust port side in the axial direction of the cylinder is arranged closer to the ridge side than the piston side hem surface on the intake port side, thereby bringing the ridge portion closer to the axis of the cylinder. be able to. Since the cavity is formed so as to cross the ridge, the cavity can be brought closer to the cylinder center by bringing the ridge closer to the cylinder axis.

  In addition, a recess for arranging the fuel injection valve may be formed in the trough, and a nozzle hole of the fuel injection valve may be provided in the recess.

  According to this configuration, the nozzle hole of the fuel injection valve is provided in the recess. Since the nozzle hole is surrounded by the inner peripheral wall of the recess, the fuel spray injected from the nozzle port spreads into the combustion chamber while being guided by the inner peripheral wall of the recess. At this time, the spread and scattering distance of the combustion spray vary depending on the presence and size of the inner peripheral wall of the recess. Specifically, fuel spray has the property of entraining surrounding air and being encouraged by the entrained air, thereby increasing the scattering distance. On the other hand, if the inner peripheral wall of the recess exists around the fuel spray, the amount of air entrained in the fuel spray is small, so that the scattering distance of the fuel spray is reduced. Here, in a configuration in which the valley portion is largely deviated from the axis of the cylinder, if the fuel injection valve is arranged near the axis of the cylinder, the recess is not formed on the valley portion but on one of the head side slopes. The fuel injection valve is formed in the recess. In that case, since the slope on the head side is inclined, the inner peripheral wall of the recess is not uniform over the entire periphery of the injection port of the fuel injection valve, and the inner peripheral wall is short on the side close to the valley part and separated from the valley part. On the side, the inner wall becomes longer. As a result, the scattering distance of the fuel spray becomes longer on the side closer to the valley, and the scattering distance of the fuel spray becomes shorter on the side away from the valley, resulting in a non-uniform fuel spray shape. On the other hand, as described above, the position of the head-side hem surface on the exhaust port side in the axial direction of the cylinder is arranged closer to the valley side than the head-side hem surface on the intake port side. It can be close to the axis. If the valley is close to the axis of the cylinder, a recess can be formed in the valley and a fuel injection valve can be provided in the recess. As a result, the inner peripheral wall of the recess can have the same shape on the intake side and the exhaust side, and the spraying condition of the fuel spray can be the same on the intake side and the exhaust side.

  Further, the head side hem surface may be provided at a position where the head is immersed more than a mating surface with the cylinder block in the cylinder head.

  In addition, the head-side hem surface and the mating surface are inclined between the head-side hem surface and the mating surface of the cylinder head while being inclined away from the axis of the cylinder toward the mating surface. A connecting head side taper surface is provided, and the piston side hem is inclined between the piston side hem surface and the side circumferential surface of the piston while being inclined away from the axial center of the cylinder toward the side circumferential surface. A piston-side taper surface connecting the surface and the side peripheral surface may be provided, and a squish area may be formed between the head-side taper surface and the piston-side taper surface.

  According to this configuration, a squish flow is also generated between the head-side tapered surface and the piston-side tapered surface on the outer peripheral side of the head-side skirt surface and the piston-side skirt surface. The squish flow generated between the head-side tapered surface and the piston-side tapered surface also flows into the cavity through the skirt area and the slope area.

  Furthermore, the geometric compression ratio may be set to 15 or more.

  In an engine having such a large geometric compression ratio, the squish area is relatively large and the cavity is relatively small, so that the squish flow is relatively strong. By effectively using this squish flow, an increase in cooling loss due to the tumble flow can be suppressed.

  According to the combustion chamber structure of the direct injection engine, an increase in cooling loss due to the tumble flow can be prevented.

It is the schematic which shows the structure of an engine. It is a longitudinal cross-sectional view of the engine output shaft direction showing the configuration of the combustion chamber. It is a perspective view which shows the top surface shape of a piston. It is a longitudinal cross-sectional view of the combustion chamber corresponding to the IV-IV line of FIG. FIG. 5 is an enlarged view of an intake side squish area in FIG. 4. It is an enlarged view of the exhaust side squish area in FIG. It is a perspective view which shows the top surface shape of the piston which concerns on a modification.

  Hereinafter, embodiments will be described with reference to the drawings. The following description is exemplary.

  FIG. 1 shows a configuration of an engine 1 according to the embodiment. Although not shown, the crankshaft 15 of the engine 1 is connected to drive wheels via a transmission. The vehicle is propelled by the output of the engine 1 being transmitted to the drive wheels. Here, the fuel of the engine 1 is gasoline in the present embodiment, but it may be gasoline containing bioethanol or the like, and may be any fuel as long as it is a liquid fuel containing at least gasoline.

  The engine 1 includes a cylinder block 12 and a cylinder head 13 placed thereon, and a plurality of cylinders 11 are formed inside the cylinder block 12 (only one is shown in FIG. 1). . The engine 1 is a multi-cylinder engine. Although not shown, a water jacket through which cooling water flows is formed inside the cylinder block 12 and the cylinder head 13. In each cylinder 11, a piston 16 connected to a crankshaft 15 via a connecting rod 14 is slidably fitted. The piston 16 divides the combustion chamber 17 together with the cylinder 11 and the cylinder head 13.

  In the present embodiment, the ceiling portion 130 (the lower surface of the cylinder head 13) of the combustion chamber 17 is provided with the intake-side inclined surface 131 provided with the opening 180 of the intake port 18 and ascending toward the center of the cylinder 11. The exhaust port 19 is provided with an opening 190, and has an exhaust-side slope 132 that has an upward slope toward the center of the cylinder 11, and a valley 133 that connects the intake-side slope 131 and the exhaust-side slope 132. ing. The combustion chamber 17 is a pent roof type combustion chamber. In addition, the trough part 133 is a ridge part of a pent roof, and the case where it passes through the bore center (axial center) of the cylinder 11 and the case where it does not pass through may be possible. The intake side slope 131 and the exhaust side slope 132 are examples of the head side slope.

  Further, the top surface 160 of the piston 16 protrudes in a triangular roof shape so as to correspond to the intake side inclined surface 131 and the exhaust side inclined surface 132 of the ceiling portion 130. Specifically, the top surface 160 has an intake side slope 161 that has an upward slope toward the center of the piston 16 on the intake side, and an exhaust side slope 162 that has an upward slope toward the center of the piston 16 on the exhaust side. And a ridge 163 (see FIG. 3) that connects the intake-side inclined surface 161 and the exhaust-side inclined surface 162. The intake side inclined surface 161 faces the intake side inclined surface 131, and the exhaust side inclined surface 162 faces the exhaust side inclined surface 132. The ridge portion 163 faces the valley portion 133. Thereby, the geometric compression ratio of the engine 1 is set to a high compression ratio of 15 or more. A concave cavity 164 is formed on the top surface 160 of the piston 16. The shape of the top surface 160 of the piston 16 will be described in detail later. The intake side slope 161 and the exhaust side slope 162 are examples of the piston side slope.

  Although only one is shown in FIG. 1, two intake ports 18 are formed in the cylinder head 13 for each cylinder 11. The opening portion 180 of the intake port 18 is provided on the intake side inclined surface 131 of the cylinder head 13 along the direction of the engine output shaft (that is, the crankshaft 15). The intake port 18 passes through this opening portion 180 and the combustion chamber 17. Communicating with The openings 180 of the two intake ports 18 are disposed symmetrically with respect to the bore center of the cylinder 11, and the axis of the throat portion of the intake port 18 is symmetrical with respect to the bore center of the cylinder 11. Is provided. Similarly, two exhaust ports 19 are formed in the cylinder head 13 for each cylinder 11. The opening 190 of the exhaust port 19 is provided on the exhaust-side inclined surface 132 of the cylinder head 13 along the direction of the engine output shaft, and the exhaust port 19 communicates with the combustion chamber 17 through the opening 190. The openings 190 of the two exhaust ports 19 are arranged symmetrically with respect to the bore center of the cylinder 11.

  The intake port 18 is connected to the intake passage 181. Although not shown, the intake passage 181 is provided with a throttle valve for adjusting the intake flow rate. The exhaust port 19 is connected to the exhaust passage 191. Although not shown, an exhaust gas purification system having one or more catalytic converters is disposed in the exhaust passage 191. The catalytic converter includes a three-way catalyst.

  The cylinder head 13 is provided with an intake valve 21 and an exhaust valve 22 so that the intake port 18 and the exhaust port 19 can be shut off (closed) from the combustion chamber 17, respectively. The intake valve 21 is driven by an intake valve drive mechanism, and the exhaust valve 22 is driven by an exhaust valve drive mechanism. The intake valve 21 and the exhaust valve 22 reciprocate at a predetermined timing to open and close the intake port 18 and the exhaust port 19, respectively, and perform gas exchange in the cylinder 11. Although not shown, the intake valve drive mechanism and the exhaust valve drive mechanism each have an intake cam shaft and an exhaust cam shaft that are drivingly connected to the crankshaft 15, and these camshafts are synchronized with the rotation of the crankshaft 15. Then rotate. In this example, the intake valve driving mechanism and the exhaust valve driving mechanism are a hydraulic or electric variable phase mechanism (Variable Valve Timing: VVT) capable of continuously changing the phase of the intake camshaft within a predetermined angle range. 23 and 24 are included at least. The intake valve driving mechanism and / or the exhaust valve driving mechanism may be provided with a variable lift mechanism capable of changing the valve lift amount together with the VVTs 23 and 24. The lift variable mechanism may be a CVVL (Continuous Variable Valve Lift) capable of continuously changing the lift amount. The valve mechanism that drives the intake valve 21 and the exhaust valve 22 may be any type, for example, a hydraulic or electromagnetic drive mechanism may be employed.

  A fuel injection valve 6 that directly injects fuel into the combustion chamber 17 is attached to the cylinder head 13. That is, the engine 1 is a direct injection engine. The fuel injection valve 6 is provided in a valley 133 of the ceiling portion 130, and, as shown in FIG. 2, is one side in the engine output axis direction (the paper surface in FIG. 2) with respect to the axial center (bore center) X of the cylinder 11. This is on the left side, and in this embodiment, the engine 1 is disposed on the non-transmission side, which corresponds to the so-called front side of the engine. The trough 133 is formed with a recess 133a for disposing the fuel injection valve 6 (see also FIG. 4). The injection port of the fuel injection valve 6 is disposed in the recess 133 a and faces the combustion chamber 17. The fuel injection valve 6 is also disposed such that its injection axis is along the axis of the cylinder 11. The fuel injection valve 6 is provided so as to face the cavity 164. The fuel injection valve 6 injects fuel into the cavity 164.

  As will be described in detail later, the fuel injection valve 6 has a (combustible) air-fuel mixture layer and a surrounding heat insulating gas layer in the combustion chamber 17 (that is, in the cavity 164), as conceptually shown in FIG. Is configured to be formed. The fuel injection valve 6 may be, for example, an externally opened fuel injection valve. The outer-open fuel injection valve can change the particle size of the fuel spray to be injected by adjusting the lift amount. As disclosed in Japanese Patent Application No. 2013-242597 filed earlier by the applicant of the present application, a fuel injection mode based on multi-stage injection is appropriately selected by utilizing the characteristics of this outer valve-open fuel injection valve. By controlling, the scattering distance in the traveling direction of the fuel spray and the spread of the fuel spray with respect to the injection axis can be adjusted. Therefore, by injecting fuel at the timing near the compression top dead center, It is possible to form a gas mixture layer in the part and a heat insulating gas layer in the outer periphery. In addition to the fuel-open valve of the open valve type, the VOC (Valve Covered Orifice) nozzle type injector also changes the effective cross-sectional area of the injection port by adjusting the degree of cavitation generated at the nozzle port. It is possible to change the particle size of the fuel spray. Accordingly, the cavity 164 is adjusted by adjusting the scattering distance in the traveling direction of the fuel spray injected at the timing near the compression top dead center and the spread of the fuel spray with respect to the injection axis as in the case of the outer valve fuel injection valve. It is possible to form an air-fuel mixture layer in the inner central part and an insulating gas layer in the outer periphery.

  In addition, by injecting the fuel heated to a predetermined temperature by the heater into the combustion chamber 17 in a high-pressure atmosphere, the air-fuel mixture layer is formed in the central portion of the cavity 164 by bringing the fuel into a supercritical state. It is possible to form a heat insulating gas layer on the outer periphery. In this technique, the fuel spray penetration is shortened by instantaneously vaporizing the fuel injected into the combustion chamber 17, and an air-fuel mixture layer is formed in the cavity 164 in the vicinity of the fuel injection valve 6 as shown in FIG. To form. The fuel injection valve is, for example, a multi-hole type fuel injection valve having a plurality of injection holes, and includes a heater for heating the fuel. Further, a fuel injection valve other than this configuration may be used. Since the structure of such a fuel injection valve is well-known, detailed description here is abbreviate | omitted.

  A spark plug 7 is attached to the cylinder head 13. As shown in FIG. 2, the spark plug 7 is provided in the valley portion 133 of the ceiling portion 130, and is disposed so as to be shifted from the bore center X of the cylinder 11 to the other side in the engine output shaft direction (that is, the engine rear side). It is installed. The spark plug 7 is disposed so as to be inclined with respect to the axis of the cylinder 11 in the direction in which the tip approaches the fuel injection valve 6. As a result, the fuel injection valve 6 and the spark plug 7 are disposed close to each other in the vicinity of the bore center X of the cylinder 11.

  As described above, the engine 1 has the geometric compression ratio ε set to 15 or more. The geometric compression ratio may be 40 or less, and particularly preferably 20 or more and 35 or less. Since the engine 1 is configured such that the higher the compression ratio is, the higher the expansion ratio is. Therefore, the engine 1 is also an engine 1 having a relatively high expansion ratio at the same time as the high compression ratio. The engine 1 is basically configured to burn the fuel injected into the cylinder 11 in the entire operation region by compression ignition, and the high geometric compression ratio stabilizes the compression ignition combustion.

  The combustion chamber 17 is defined by the inner peripheral surface of the cylinder 11, the top surface 160 of the piston 16, the lower surface (ceiling portion 130) of the cylinder head 13, and the valve head surfaces of the intake valve 21 and the exhaust valve 22. Is formed. In order to reduce the cooling loss, the combustion chamber 17 is insulated by providing a heat shielding layer on these sections. The heat shielding layer may be provided on all of these section screens, or may be provided on a part of these section screens. Further, although it is not a wall surface that directly partitions the combustion chamber 17, a heat shield layer may be provided on the port wall surface near the opening on the ceiling 130 side of the combustion chamber 17 in the intake port 18 or the exhaust port 19.

  These thermal barrier layers are set to have a lower thermal conductivity than the metal base material constituting the combustion chamber 17 in order to prevent the heat of the combustion gas in the combustion chamber 17 from being released through the section screen. The

  Further, the heat shielding layer preferably has a volumetric specific heat smaller than that of the base material in order to reduce cooling loss. That is, it is preferable to reduce the heat capacity of the heat shield layer so that the temperature of the section screen of the combustion chamber 17 changes following the fluctuation of the gas temperature in the combustion chamber 17.

The thermal barrier layer may be formed, for example, by coating a ceramic material such as ZrO ₂ on the base material by plasma spraying. The ceramic material may contain a number of pores. If it does in this way, the thermal conductivity and volume specific heat of a thermal insulation layer can be made lower.

  In the present embodiment, in addition to the heat shield structure of the combustion chamber, a heat insulation layer is formed by a gas layer in the cylinder 11 (that is, in the combustion chamber 17), so that the cooling loss is greatly reduced. Yes.

  Specifically, the cavity 164 is formed from the injection tip of the fuel injection valve 6 after the compression stroke so that a gas layer containing fresh air is formed at the outer peripheral portion in the combustion chamber 17 and an air-fuel mixture layer is formed at the center. By injecting the fuel into the interior, as shown in FIG. 2, an air-fuel mixture layer is formed at the center of the cavity 164 in the vicinity of the fuel injection valve 6, and a gas layer containing fresh air is formed around it. The stratification is realized. Here, the air-fuel mixture layer is a layer constituted and formed by a combustible air-fuel mixture, and the combustible air-fuel mixture may be an air-fuel mixture having an equivalent ratio φ = 0.1 or more, for example. The gas layer may be only fresh air, and may contain burned gas (EGR gas) in addition to fresh air. It should be noted that there is no problem even if a small amount of fuel is mixed in the gas layer, and the fuel layer may be leaner than the gas mixture layer so that the gas layer can serve as a heat insulating layer.

  If the fuel is compressed and ignited and burned in the state where the gas layer and the mixture layer are formed as described above, the gas layer between the mixture layer and the wall surface of the cylinder 11 causes the flame of the mixture layer flame cylinder 11. The contact with the wall surface is suppressed, and the gas layer becomes a heat insulating layer, so that release of heat from the wall surface of the cylinder 11 can be suppressed. As a result, the cooling loss can be greatly reduced.

  It should be noted that if the cooling loss is simply reduced, the reduced cooling loss is converted into exhaust loss and does not contribute much to the improvement in the illustrated thermal efficiency. The energy of the combustion gas corresponding to the reduced cooling loss is efficiently converted into mechanical work. That is, it can be said that the illustrated thermal efficiency is greatly improved in the engine 1 by adopting a configuration that reduces both the cooling loss and the exhaust loss.

  In order to form such an air-fuel mixture layer and a gas layer in the combustion chamber 17, it is desirable that the gas flow in the combustion chamber 17 is weak at the timing of fuel injection. For this reason, the intake port is configured to have a straight shape in which swirl does not occur or hardly occurs in the combustion chamber 17, and the tumble flow is also weakened as much as possible.

  Next, the shape of the top surface 160 of the piston 16 constituting the combustion chamber will be described in more detail with reference to the drawings. FIG. 3 is a perspective view showing the shape of the top surface 160 of the piston 16. In FIG. 3, the right front side of the page is the intake side, the left back side of the paper is the exhaust side, the left front side of the page is one side in the engine output axis direction (that is, the front side of the engine), and the right back side of the page is the other side in the engine output axis direction (that is, , The rear side of the engine).

  As described above, the top surface 160 of the piston 16 is configured such that the intake side inclined surface 161 and the exhaust side inclined surface 162 are each ascending toward the center of the piston 16, as shown in FIG. As a result, the top surface 160 of the piston 16 has a triangular roof shape that gradually protrudes from both sides toward the center when viewed from the one side of the engine output shaft in the direction along the engine output shaft. It is made.

  The intake-side inclined surface 161 has a relatively recessed valve recess 161a and a relatively projecting island-shaped portion 161b. The surface of the valve recess 161a and the surface of the island-shaped portion 161b are substantially flat surfaces. The valve recess 161a is a part for avoiding interference with the intake valve 21 when the opening operation is performed. The valve recess 161a has a shape slightly larger than the outer shape of the intake valve 21 in plan view. Since the two intake valves 21 are provided close to the intake-side inclined surface 131 of the ceiling portion 130 and the outer shape of the valve head of the intake valve 21 is circular, the valve recess 161a has two circles partially overlapping each other. It has a shape like this. As a result of the valve recess 161a being formed in such a shape, a portion of the intake-side inclined surface 161 opposite to the ridge 163 and corresponding to the space between the valve heads of the two intake valves 21 has a substantially triangular shape. An island-shaped portion 161b is formed.

  The exhaust side slope 162 has a relatively recessed valve recess 162a and a relatively projecting island-like portion 162b. The surface of the valve recess 162a and the surface of the island-shaped portion 162b are substantially flat surfaces. The valve recess 162a is a part for avoiding interference with the exhaust valve 22 when performing the opening operation. The valve recess 162a has a shape slightly larger than the outer shape of the exhaust valve 22 in plan view. Since the two exhaust valves 22 are provided close to the exhaust-side inclined surface 132 of the ceiling 130 and the outer shape of the valve head of the exhaust valve 22 is circular, the valve recess 162a has two circles partially overlapping each other. It has a shape like this. As a result of the valve recess 162a being formed in such a shape, a portion of the exhaust-side slope 162 opposite to the ridge 163 and corresponding to the space between the valve heads of the two exhaust valves 22 has a substantially triangular shape. An island-shaped portion 162b is formed.

  The ridge 163 is not a sharp shape but a curved R surface, and smoothly connects the intake-side inclined surface 161 and the exhaust-side inclined surface 162. The ridge 163 extends in the engine output shaft direction.

  Further, the top surface 160 of the piston 16 is provided between the side peripheral surface 16a of the piston 16 and the ridge 163, and the side peripheral surface 16a and the ridge are inclined while approaching the cavity 164 toward the ridge 163. Further, a tapered surface 165 that connects 163 is provided. A portion 165 a on the side peripheral surface 16 a side of the tapered surface 165 is formed as a conical side surface and is provided over the entire outer peripheral portion of the top surface 160. Of the tapered surface 165, the portion 165 b on the ridge 163 side has a larger inclination angle with respect to the axis of the cylinder 11 than the portion 165 a on the side circumferential surface 16 a side. It is provided only outside in the radial direction from the portion 163. The tapered surface 165 is provided corresponding to the curved shape of the ceiling portion 130 of the cylinder head 13. This is an advantageous configuration for increasing the geometric compression ratio of the engine 1.

  As described above, the cavity 164 is recessed in the top surface 160 of the piston 16. As shown in FIG. 2, the cavity 164 is provided such that the size thereof gradually decreases as the cavity 164 is recessed from the opening edge. The cavity 164 includes a side wall 1641 that is continuous with the top surface 160 of the piston 16, and a side wall. The bottom wall 1642 is continuous with 1641. As shown in FIG. 2, the cavity 164 has a bathtub-like shape in a longitudinal section passing through the center of the piston 16. The side wall 1641 has a different angle from the top surface 160 and the bottom wall 1642 of the piston 16, and is between the top surface 160 and the side wall 1641 of the piston 16 and between the side wall 1641 and the bottom wall 1642. Each has an R-plane.

  As shown in FIG. 3, the cavity 164 has a substantially elliptical opening edge 164a. This ellipse is an ellipse in a broad sense and includes an oval shape and an oval shape. As shown in FIG. 2, the cavity 164 also has a central position (more precisely, a midpoint between the intake-side edge and the exhaust-side edge at a position corresponding to the maximum width of the cavity 164, and The center position, which is the midpoint between one end edge in the engine output shaft direction and the other end point, is provided so as to coincide with the injection axis of the fuel injection valve 6. As described above, this is an advantageous configuration for forming an air-fuel mixture layer at the center of the cavity 164. As described above, since the injection axis of the fuel injection valve 6 is shifted to one side in the engine output shaft direction, the cavity 164 is also at the engine output with respect to the center of the piston 16 at the top surface 160 of the piston 16. It will be shifted to one side in the axial direction.

  The cavity 164 is formed across the ridge 163 across the intake-side inclined surface 161 and the exhaust-side inclined surface 162. Thereby, the ridge 163 is divided into two with the cavity 164 interposed therebetween. Further, since the opening edge 164a of the cavity 164 is substantially elliptical, and the intake side inclined surface 161 and the exhaust side inclined surface 162 are downwardly inclined, a part of the intake side inclined surface 161 and the exhaust side inclined surface 162 are swollen by the cavity 164, respectively. . The opening edge 164a of the cavity 164 in the intake side inclined surface 161 and the exhaust side inclined surface 162 has a curved shape so as to be gradually depressed downward from the ridges 163 on both sides. Further, as the cavity 164 is provided so as to be shifted from the bore center of the cylinder 11 as described above, the opening edge 164a of the cavity 164 on the intake side inclined surface 161 and the exhaust side inclined surface 162 also has a bore as shown in FIG. Rather than being symmetrical about the center, it is shifted to one side in the engine output shaft direction. In addition, the ridge 163 on one side in the engine output axis direction is relatively short and the ridge 163 on the other side in the engine output axis direction is relatively long.

  Thus, in the configuration in which the top surface 160 of the piston 16 is raised so as to correspond to the ceiling portion 130 of the cylinder head 13, the squish area becomes large. Specifically, as shown in FIG. 2, the combustion chamber 17 includes a main combustion chamber 171 surrounded by a ceiling portion 130 of the cylinder head 13 and a cavity 164 of the piston 16, and a ceiling portion 130 of the cylinder head 13 and the piston 16. And a squish area sandwiched between top surfaces 160. In the squish area, a squish flow toward the cavity 164 is generated at the end of the compression stroke (near top dead center). The squish flow flows into the cavity 164 from the opening edge 164 a of the cavity 164.

  The squish area includes a ridge squish area 172 (see FIG. 2) between the valley 133 of the cylinder head 13 and the ridge 163 of the piston 16, and mainly the intake-side slope 131 of the cylinder head 13 and the intake air of the piston 16. The exhaust side squish area 173 (see FIG. 4) formed between the side slope 161 and the exhaust side squish mainly formed between the exhaust side slope 132 of the cylinder head 13 and the exhaust side slope 162 of the piston 16. And an area 174 (see FIG. 4). As shown in FIG. 2, the ridge squish area 172 is formed at two locations with the cavity 164 interposed therebetween. Further, as shown in FIG. 4, the intake-side squish area 173 and the exhaust-side squish area 174 are arranged at positions facing each other with the cavity 164 interposed therebetween.

  Here, the intake side squish area 173 and the exhaust side squish area 174 will be described in detail. 5 is an enlarged view of the intake side squish area 173 in FIG. 4, and FIG. 6 is an enlarged view of the exhaust side squish area 174 in FIG.

  As shown in FIG. 5, an intake-side skirt surface 134 that bends and expands in a mountain-folded manner from the intake-side inclined surface 131 is provided at the end of the intake-side inclined surface 131 of the cylinder head 13 opposite to the trough 133. It has been. The intake side skirt surface 134 is provided at a position where the cylinder head 13 is immersed more than the mating surface 13 a with the cylinder block, and is orthogonal to the axis X of the cylinder 11. Between the intake side hem surface 134 and the mating surface 13a of the cylinder head 13, the intake air connected to the intake side hem surface 134 and the mating surface 13a while being inclined away from the axis X of the cylinder 11 toward the mating surface 13a. A side taper surface 135 is provided. The intake side hem surface 134 is an example of a head side hem surface, and the intake side taper surface 135 is an example of a head side taper surface.

  On the other hand, at the end of the intake side slope 161 of the piston 16 opposite to the ridge 163 (not shown in FIG. 5), there is an intake side skirt surface 166 that is bent and expanded from the intake side slope 16 in a valley fold shape. Is provided. The intake side skirt surface 166 is orthogonal to the axis X of the cylinder 11. Between the intake side hem surface 166 and the side peripheral surface 16a of the piston 16, the intake side hem surface 166 and the side peripheral surface 16a are inclined while being separated from the axis X of the cylinder 11 toward the side peripheral surface 16a. A connecting tapered surface 165a is provided. The tapered surface 165a is a portion 165a on the side circumferential surface 16a side of the tapered surface 165 that connects the side circumferential surface 16a and the ridge 163, and is formed by a conical side surface. The intake side skirt surface 166 is an example of a piston side skirt surface, and the taper surface 165a is an example of a piston side taper surface.

  In this way, it is bent between the intake side inclined surface 131 and the intake side inclined surface 161, between the intake side hem surface 134 and the intake side hem surface 166, and further between the intake side tapered surface 135 and the tapered surface 165a. The intake side squish area 173 is formed. The intake-side squish area 173 includes an intake-side slope area 173a between the intake-side slope 131 and the intake-side slope 161, an intake-side skirt area 173b between the intake-side skirt face 134 and the intake-side skirt face 166, and intake air An intake side taper area 173c between the side taper surface 135 and the taper surface 165a is included.

  As shown in FIG. 6, an exhaust side skirt surface 136 that is bent and expanded in a mountain fold shape from the exhaust side inclined surface 132 is provided at the end of the exhaust side inclined surface 132 of the cylinder head 13 opposite to the valley 133. It has been. The exhaust-side skirt surface 136 is provided at a position that is deeper than the mating surface 13 a of the cylinder head 13, and is orthogonal to the axis X of the cylinder 11. The exhaust side skirt surface 136 is disposed closer to the valley 133 side in the direction of the axis X of the cylinder 11 than the intake side skirt surface 134. That is, the exhaust side skirt surface 136 is immersed in the mating surface 13 a more than the intake side skirt surface 134. Between the exhaust side skirt surface 136 and the mating surface 13a of the cylinder head 13, the exhaust gas connected to the exhaust side hem surface 136 and the mating surface 13a while being inclined away from the axis X of the cylinder 11 toward the mating surface 13a. A side tapered surface 137 is provided. The exhaust side skirt surface 136 is an example of a head side skirt surface, and the exhaust side taper surface 137 is an example of a head side taper surface.

  On the other hand, at the end of the exhaust side slope 162 of the piston 16 opposite to the ridge 163 (not shown in FIG. 6), there is an exhaust side bottom face 168 that is bent and expanded in a valley fold from the intake side slope 161. Is provided. The exhaust side skirt surface 168 is orthogonal to the axis X of the cylinder 11. The exhaust side skirt surface 168 is disposed closer to the ridge 163 side in the direction of the axis X of the cylinder 11 than the intake side skirt surface 166. In other words, the exhaust side skirt surface 168 is higher than the intake side skirt surface 166. Between the exhaust side skirt surface 168 and the side peripheral surface 16a of the piston 16, the exhaust side skirt surface 168 and the side peripheral surface 16a are inclined while being inclined away from the axis X of the cylinder 11 toward the side peripheral surface 16a. A connecting tapered surface 165a is provided. The tapered surface 165a is a portion 165a on the side circumferential surface 16a side of the tapered surface 165 that connects the side circumferential surface 16a and the ridge 163, and is formed by a conical side surface. The exhaust side skirt surface 168 is an example of a piston side skirt surface, and the taper surface 165a is an example of a piston side taper surface.

  In this way, it is bent from between the exhaust side inclined surface 132 and the exhaust side inclined surface 162 to between the exhaust side bottom surface 136 and the exhaust side bottom surface 168 and between the exhaust side tapered surface 137 and the tapered surface 165a. The exhaust side squish area 174 is formed. The exhaust side squish area 174 includes an exhaust side slope area 174a between the exhaust side slope 132 and the exhaust side slope 162, an exhaust side skirt area 174b between the exhaust side skirt face 136 and the exhaust side skirt face 168, and exhaust gas. An exhaust side taper area 174c between the side taper surface 137 and the taper surface 165a is included.

  The squish flow generated in the intake-side squish area 173 and the exhaust-side squish area 174 flows into the radially inner cavity 164 because there is no destination on the radially outer side due to the inner peripheral surface of the cylinder 11 or the like.

  Here, the angle α2 formed by the exhaust side slope area 174a and the exhaust side skirt area 174b is larger than the angle α1 formed by the intake side slope area 173a and the intake side skirt area 173b. The “angle α1 formed between the intake-side slope area 173a and the intake-side skirt area 173b” is an intermediate surface between the intake-side slope 131 and the intake-side slope 161, the intake-side skirt face 134, and the intake-side skirt face 166. Means an angle formed with the intermediate plane between the two and smaller than 180 degrees. “An angle α2 formed by the exhaust side slope area 174a and the exhaust side bottom area 174b” is an intermediate surface between the exhaust side slope 132 and the exhaust side slope 162, the exhaust side bottom face 136, and the exhaust side bottom face 168. It means the angle formed by the intermediate plane between them and the angle formed by smaller one than 180 degrees. That is, the degree of bending of the exhaust side slope area 174a and the exhaust side skirt area 174b is smaller than the degree of bending of the intake side slope area 173a and the intake side skirt area 173b.

  By doing so, the attenuation when the squish flow flows into the intake side slope area 173a from the intake side skirt area 173b on the intake side increases. On the other hand, on the exhaust side, attenuation when the squish flow flows from the exhaust side skirt area 174b into the exhaust side slope area 174a is reduced. As a result, the squish flow that flows into the cavity 164 through the exhaust side squish area 174 is stronger than the squish flow that flows into the cavity 164 through the intake side squish area 173.

  In the cavity 164, as shown in FIG. 4, the tumble flow T remains. The tumble flow T can be suppressed by relatively strengthening the squish flow from the exhaust side. More specifically, the intake air that flows into the cylinder 11 through the opening 180 of the intake port descends along the inner peripheral surface of the cylinder 11 on the exhaust side, and then flows toward the intake side on the top surface 160 of the piston 16. Then, it rises along the inner peripheral surface of the cylinder 11 on the intake side, flows toward the exhaust side at the ceiling 130, and forms a tumble flow T. Thus, in the vicinity of the ceiling portion 130, the tumble flow T flows from the intake side to the exhaust side. The fuel injection valve 6 is provided in the trough portion 133 of the ceiling portion 130, and when the fuel spray and the air-fuel mixture injected from the fuel injection valve 6 get on the tumble flow T, the fuel spray and the air-fuel mixture become the cavity 164. It is easy to reach the side wall 1641 on the exhaust side. In contrast to such a tumble flow T, the squish flow S2 from the exhaust side flows in a direction that cancels the tumble flow T, and the squish flow S1 from the intake side flows in a direction that promotes the tumble flow T. Since the squish flow S2 from the exhaust side is strong and the squish flow S1 from the intake side is weak, the tumble flow T1 can be weakened by the squish flow as a whole. As a result, fuel spray and air-fuel mixture that reach the exhaust-side side wall 1641 of the cavity 164 can be reduced.

  In addition, the inclination angle β2 of the exhaust side slope area 174a with respect to the axis X of the cylinder 11 is larger than the inclination angle β1 of the intake side slope area 173a with respect to the axis X of the cylinder 11. As a result, the squish flow from the exhaust side has less component toward the injection port of the fuel injection valve 6 than the squish flow from the intake side, and the component toward the direction orthogonal to the axis X or the bottom wall 1642 of the cavity 164. The component which goes to increases. That is, it is possible to push back the fuel spray injected from the fuel injection valve 6 and about to flow obliquely downward on the exhaust side on the tumble flow T diagonally downward on the intake side. As a result, the fuel spray can be made compact, and the fuel spray and the air-fuel mixture reaching the exhaust-side side wall 1641 of the cavity 164 can be further reduced. On the other hand, the squish flow from the intake side has more components toward the injection port of the fuel injection valve 6 than the squish flow from the exhaust side. Thereby, the scattering distance of the fuel spray can be suppressed, and the fuel spray reaching the side wall 1641 and the bottom wall 1642 of the cavity 164 on the intake side can be reduced.

  Further, the exhaust side skirt surface 136 is disposed closer to the valley 133 in the direction of the axis X than the intake side skirt surface 134.

  As a result, a trough 133 that is a portion where the intake-side inclined surface 131 and the exhaust-side inclined surface 132 intersect with each other approaches the axis X of the cylinder 11. As described above, since the inclination angle of the intake-side inclined surface 131 and the inclination angle of the exhaust-side inclined surface 132 are different, if the position of the intake-side skirt surface 134 and the exhaust-side skirt surface 136 in the direction of the axis X is the same. , The valley 133 is displaced from the axis X of the cylinder 11. On the other hand, by disposing the exhaust side skirt surface 136 on the valley 133 side in the direction of the axis X, the exhaust side inclined surface 132 having a relatively large inclination angle with respect to the axis X is formed in the valley 133 in the direction of the axis X. Can be translated sideways. As a result, the valley 133 comes closer to the axis X of the cylinder 11.

  And since the fuel injection valve 6 is provided in the trough part 133, the fuel injection valve 6 can be brought close to the axis X by bringing the trough part 133 close to the axis X. That is, an air-fuel mixture can be formed in the vicinity of the axis X in the combustion chamber 17.

  More specifically, as shown in FIGS. 2 and 4, the trough 133 is formed with a recess 133 a for disposing the fuel injection valve 6. The nozzle hole of the fuel injection valve 6 is surrounded by the inner peripheral wall of the recess 133a. The spread and scattering distance of the combustion spray vary depending on the presence and size of the inner peripheral wall of the recess 133a. Specifically, fuel spray has the property of entraining surrounding air and being encouraged by the entrained air, thereby increasing the scattering distance. On the other hand, if the inner peripheral wall of the recess 133a exists around the fuel spray, the amount of air trapped in the fuel spray is small, so the scattering distance of the fuel spray is reduced. Here, in a configuration in which the valley portion 133 is largely deviated from the axis X of the cylinder 11, if the fuel injection valve 6 is arranged near the axis X, the fuel injection valve 6 is not the valley portion 133 but the intake side slope. The concave portion is also formed on the intake side inclined surface 131 or the exhaust side inclined surface 132. In that case, since the intake-side inclined surface 131 and the exhaust-side inclined surface 132 are inclined, the inner peripheral wall of the recess is not uniform over the entire periphery of the injection port of the fuel injection valve 6, and the inner peripheral wall is closer to the valley portion 133. The inner wall is longer on the side away from the trough 133. As a result, the spray distance of the fuel spray becomes longer on the side closer to the valley portion 133, and the distance of the fuel spray becomes shorter on the side away from the valley portion 133, so that the shape of the fuel spray becomes uneven. On the other hand, as described above, by arranging the exhaust side skirt surface 136 closer to the valley portion 133 in the direction of the axis X than the intake side skirt surface 134, the valley portion 133 can be brought closer to the axis X. If the trough part 133 is close to the axis X, the recessed part 133a can be formed in the trough part 133, and the fuel injection valve 6 can be arrange | positioned to this recessed part 133a. As a result, the inner peripheral wall of the recess 133a can have the same shape on the intake side and the exhaust side, and the fuel spray scattering conditions can be made the same on the intake side and the exhaust side. Thereby, the shape of fuel spray can be made uniform between the exhaust side and the intake side.

  Similarly, the exhaust side skirt surface 168 of the piston 16 is disposed closer to the ridge 163 side in the direction of the axis X than the intake side skirt surface 166.

  Since the inclination angle of the intake side inclined surface 161 with respect to the axis X is smaller than that of the exhaust side inclined surface 162, the ridge 163 tends to shift to the intake side from the axis X. On the other hand, by arranging the position of the exhaust side skirt surface 168 in the axial center X direction closer to the ridge 163 side than the intake side skirt surface 166, the ridge 163 can be brought closer to the axis X. Since the cavity 164 is formed so as to cross the ridge 163, the cavity 164 can be brought closer to the axis X by bringing the ridge 163 closer to the axis X. That is, combustion can be performed in the vicinity of the axis X.

  Further, in the present embodiment, the intake side hem surface 134 and the exhaust side hem surface 136 are immersed more than the mating surface 13 a of the cylinder head 13 in order to form the intake side hem area 173 b and the exhaust side hem area 174 b. Thereby, the possibility of peeling of the heat shield layer formed on the intake side skirt surface 134 and the exhaust side skirt surface 136, and further on the intake side taper surface 135 and the exhaust side taper surface 137 can be reduced. For example, there may be a configuration in which the intake side skirt surface 134 or the exhaust side skirt surface 136 is formed on the mating surface 13 a of the cylinder head 13. In this case, if a heat shield layer is formed on the intake side skirt surface 134 or the exhaust side skirt surface 136, a heat shield layer is formed on the mating surface 13a. Since the mating surface 13a forms the outer surface of the cylinder head 13 and is exposed to the outside, there is a possibility that the mating surface 13a may come into contact with another object during the conveyance of the cylinder head 13 or the like. Therefore, when a heat shield layer is formed on the mating surface 13a, the heat shield layer may come into contact with another object and peel off. On the other hand, since the intake side hem surface 134 and the exhaust side hem surface 136 are provided at positions recessed from the mating surface 13a, a heat shield layer may be formed on the intake side hem surface 134 and the exhaust side hem surface 136. The heat shield layer is not exposed to the outside. Therefore, the possibility of peeling of the heat shield layer can be reduced. Further, as a result of the intake side skirt surface 134 and the exhaust side skirt surface 136 being immersed from the mating surface 13a, the intake side tapered surface 135 and the exhaust side tapered surface 137 can also be immersed from the mating surface 13a. Thereby, the possibility of peeling of the heat shield layer formed on the intake side taper surface 135 and the exhaust side taper surface 137 is also reduced.

  Further, by forming the intake side hem surface 166 or the exhaust side hem surface 168 on a surface orthogonal to the axis X of the cylinder 11, the intake side hem surface 166 or the exhaust side hem surface 168 is assembled to the piston 16. It can be used to check accuracy. For example, after assembling the piston 16, the top dead center position of the piston 16 and the like can be confirmed using the intake side bottom surface 166 or the exhaust side bottom surface 168.

  As described above, the combustion chamber structure of the engine 1 has the ceiling portion 130 including the intake side inclined surface 131 and the exhaust side inclined surface 132 connected by the valley portion 133, and defines a part of the pent roof type combustion chamber 17. The cylinder head 13 has a top surface 160 that is connected by a ridge 163 and includes an intake-side inclined surface 161 and an exhaust-side inclined surface 162 that face the intake-side inclined surface 131 and the exhaust-side inclined surface 132 of the ceiling portion 130. The piston 16 to be inserted and the fuel injection valve 6 provided in the valley 133 are provided. The intake port 18 has an intake port 18 opened on the intake side inclined surface 131, and the exhaust port 19 opened on the exhaust side inclined surface 132. The intake side slope 131 and the exhaust side slope 132 of each of the intake side slope 131 and the end opposite to the valley 133 are bent and spread from the intake side slope 131 and the exhaust side slope 132 in a mountain fold shape. 34 and an exhaust side skirt surface 136 are provided, and a concave cavity 164 is formed across the ridge 163 on the top surface 160, and each of the intake side inclined surface 161 and the exhaust side inclined surface 162 is opposite to the ridge 163. Are provided with an intake-side flank 166 and an exhaust-side flank 168 that are bent and expanded in a valley fold from the intake-side inclined surface 161 and the exhaust-side inclined surface 162. A bent intake-side squish area 173 is formed between the intake-side skirt surface 166 and the intake-side skirt surface 166, and the exhaust-side skirt surface is formed between the exhaust-side inclined surface 132 and the exhaust-side inclined surface 162. A bent exhaust-side squish area 174 is formed between 136 and the exhaust-side skirt surface 168, and an angle α2 formed between the exhaust-side slope area 174a and the exhaust-side skirt area 174b is an intake-side oblique surface. It is smaller than an angle α1 formed by the surface area 173a and the intake side skirt area 173b.

  According to this configuration, the squish flow S2 flowing into the cavity 164 from the exhaust side squish area 174 can be made stronger than the squish flow S1 flowing into the cavity 164 from the intake side squish area 173. By strengthening the squish flow from the exhaust side, the tumble flow T in the vicinity of the ceiling portion 130 can be weakened. As a result, fuel spray and air-fuel mixture that reach the side wall 1641 of the cavity 164 can be reduced, and cooling loss can be reduced.

  The geometric compression ratio of the engine 1 is set to 15 or more.

  In the engine 1 having such a large geometric compression ratio, the squish area is relatively large and the cavity 164 is relatively small, so that the squish flow is relatively strong. By effectively using this squish flow, an increase in cooling loss due to the tumble flow can be suppressed.

<< Other Embodiments >>
As described above, the embodiment has been described as an example of the technique disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to an embodiment in which changes, replacements, additions, omissions, and the like are appropriately performed. Moreover, it is also possible to combine each component demonstrated by the said embodiment and it can also be set as new embodiment. In addition, among the components described in the accompanying drawings and detailed description, not only the components essential for solving the problem, but also the components not essential for solving the problem in order to exemplify the above technique May also be included. Therefore, it should not be immediately recognized that these non-essential components are essential as those non-essential components are described in the accompanying drawings and detailed description.

  About the said embodiment, it is good also as following structures.

  The configuration of the piston 16 is merely an example, and the present invention is not limited to this. For example, although the cavity 164 is arranged offset, the cavity 164 may be arranged at the center of the bore. Further, the shape of the valve recess and the island-shaped portion can be arbitrarily set.

  For example, as shown in FIG. 7, the ridge 163 may be an island-shaped portion. The island-shaped portion of the ridge 163 protrudes from the valve recess 162a of the exhaust-side inclined surface 162 in a step shape, and also protrudes from the valve recess 161a of the intake-side inclined surface 161 in a step shape. However, the surface of the ridge 163 is an evenly curved R surface.

  Further, the configuration is not limited to the configuration shown in FIG. Similarly, the island-like portion 162b of the exhaust side slope 162 may be deleted, and the exhaust side slope 162 may be a substantially flat surface. That is, the presence or absence of island portions on the intake side slope 161, the exhaust side slope 162, and the ridge 163 can be arbitrarily set.

  Further, the intake-side skirt surface 134, the exhaust-side skirt surface 136, the intake-side skirt surface 166, and the exhaust-side skirt surface 168 may not be orthogonal to the axis X of the cylinder 11. That is, the intake side skirt surface 134, the exhaust side skirt surface 136, the intake side skirt surface 166, and the exhaust side skirt surface 168 may be inclined with respect to the axis X of the cylinder 11.

  Further, the interval between the squish areas may not be constant. For example, the interval between the intake-side squish areas 173 may gradually increase toward the cavity 164.

  Further, the intake side taper surface 135, the exhaust side taper surface 137, and the taper surface 165a may be omitted, and the intake side taper area 173c and the exhaust side taper area 174c may be omitted.

  As described above, the technology disclosed herein is useful for the combustion chamber structure of a direct injection engine.

1 Engine 11 Cylinder 12 Cylinder Block 13 Cylinder Head 130 Ceiling Part 131 Inlet Side Slope (Head Side Slope)
132 Exhaust side slope (head side slope)
133 Valley 133a Recess 134 Inlet side hem surface (head side hem surface)
135 Intake side taper surface (head side taper surface)
136 Exhaust side bottom surface (head side bottom surface)
137 Exhaust side taper surface (head side taper surface)
16 Piston 160 Top surface 161 Suction side slope (piston side slope)
162 Exhaust side slope (piston side slope)
163 Edge 164 Cavity 165a Tapered surface (piston side tapered surface)
166 Inlet side hem surface (piston side hem surface)
168 Exhaust side bottom surface (piston side bottom surface)
17 Combustion chamber 173 Intake side squish area 173a Intake side slope area 173b Intake side skirt area 173c Intake side taper area 174 Exhaust side squish area 174a Exhaust side slope area 174b Exhaust side skirt area 174c Exhaust side taper area 18 Intake port 19 Exhaust port 6 Fuel injection valve X axis

Claims (7)

A cylinder head having a ceiling part including two head side slopes connected by a valley part and defining a part of a pent roof type combustion chamber;
A piston having a top surface including two piston-side inclined surfaces that are connected at a ridge and are opposed to the two head-side inclined surfaces;
A fuel injection valve provided in the valley,
An intake port is opened on one of the head side slopes, and an exhaust port is opened on the other head side slope,
Each of the head side slopes is provided with a head side hem surface that is bent and expanded in a mountain fold shape from the head side slope on the end opposite to the valley.
On the top surface, a recessed cavity is formed across the ridge,
Each piston-side inclined surface is provided with a piston-side hem surface that is bent and expanded in a valley fold shape from the piston-side inclined surface at the end opposite to the ridge portion,
A bent squish area is formed between each head-side slope and each piston-side slope between each head-side bottom face and each piston-side bottom face,
On the exhaust port side, the angle formed by the squish area between the head side slope and the piston side slope and the squish area between the head side bottom face and the piston side bottom face is on the intake port side. A combustion chamber structure of a direct injection engine smaller than an angle formed by a squish area between the head side slope and the piston side slope and a squish area between the head side bottom face and the piston side bottom face. The combustion chamber structure of a direct injection engine according to claim 1,
The combustion chamber structure of a direct-injection engine in which the head side skirt surface and the piston side skirt surface are orthogonal to the axis of the cylinder. The combustion chamber structure of a direct injection engine according to claim 2,
The head-side hem surface on the exhaust port side is disposed closer to the valley side in the axial direction of the cylinder than the head-side hem surface on the intake port side,
The piston chamber bottom surface on the exhaust port side is a combustion chamber structure of a direct injection engine arranged on the ridge side in the axial direction of the cylinder with respect to the piston side bottom surface on the intake port side. In the combustion chamber structure of the direct injection engine according to claim 3,
The trough is formed with a recess for disposing the fuel injection valve,
The injection port of the fuel injection valve is a combustion chamber structure of a direct injection engine provided in the recess. In the combustion chamber structure of a direct injection engine according to any one of claims 1 to 4,
The combustion chamber structure of a direct-injection engine in which the said head side skirt surface is provided in the position where it was immersed rather than the mating surface with a cylinder block among the said cylinder heads. The combustion chamber structure of a direct injection engine according to claim 5,
A head-side taper between the head-side hem surface and the mating surface of the cylinder head is connected to the head-side hem surface and the mating surface while being inclined away from the axis of the cylinder toward the mating surface. A surface is provided,
Between the piston side hem surface and the side peripheral surface of the piston, a piston connected to the piston side hem surface and the side peripheral surface while being inclined away from the axial center of the cylinder toward the side peripheral surface Side tapered surface is provided,
A combustion chamber structure of a direct injection engine in which a squish area is formed between the head-side tapered surface and the piston-side tapered surface. The combustion chamber structure of a direct injection engine according to any one of claims 1 to 6,
A combustion chamber structure of a direct injection engine in which the geometric compression ratio is set to 15 or more.

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