MOTOR

Abstract

An engine configured to directly inject fuel into a combustion chamber in a cylinder in a predetermined operating range in a period from a second half of a compression stroke to a first half of an expansion stroke and to perform ignition after a top dead center of compression, where the engine has: a piston having a cavity which is downwardly concave in a central region of an upper surface of the piston; a cylinder head configured to form a sloping roof-shaped combustion chamber; a fuel injection valve arranged on the cylinder head so as to be brought into a position corresponding to a central portion of the piston, the fuel injection valve being adapted to inject the fuel into the cavity of the piston in the period from the second half of the compression stroke to the first half of the expansion stroke; and a spark plug arranged on the cylinder head so as to be provided at a position on a radially outer side of the central region of the piston and corresponding to an upper side of the cavity of the piston, the central region corresponding to a position where the fuel injection valve is provided, wherein: the fuel injection valve has a plurality of injection openings arranged in a circumferential direction around a longitudinal axis of the fuel injection valve, through each of which the fuel is injected in a direction inclined relative to the longitudinal axis at a predetermined injection angle; and each of the injection holes is formed such that the injection angle of the injection holes becomes larger as a height of a ceiling of the combustion chamber at a position corresponding to an edge end portion of the cavity in an injection direction of the injection hole is higher, wherein the injection angles of the injection holes are set such that each of the flow path lengths of the injected fuel, each of which is a length of a path along which the fuel injected from the injection hole flows through the cavity to reach the ceiling of the combustion chamber, becomes equal to the flow path length of the injected fuel of the injection hole closest to the spark plug.

Description

Technical area

[0001] The present invention relates to an engine, and more particularly to an engine configured to inject fuel directly into a combustion chamber in a cylinder in a predetermined operating range in a period from a second half of a compression stroke to a first half of an expansion stroke and to perform ignition after a compression top dead center. Background of the invention

[0002] Typically, engines using gasoline or a gasoline-containing fuel as the main component often employ a spark ignition method for performing ignition by a spark plug. In order to improve fuel efficiency and the like, a technology has been developed in recent years in which: a high compression ratio (for example, 14 or more) is used as the geometric compression ratio of the engine; a gasoline or gasoline-containing fuel is used as the main component; and compression self-ignition (specifically, homogeneous charge compression ignition (HCCI)) is performed within a predetermined operating range.

[0003] A combustion chamber structure of an engine configured to perform compression self-ignition is disclosed, for example, in PTL 1. Regarding a combustion chamber structure applied to a high compression ratio engine, PTL 1 discloses a technology for improving filling efficiency by designing the combustion chamber structure to appropriately scavenge an interior of a cavity formed in a central region of a piston upper surface. DE 103 54 827 A1 discloses a fuel injection system including a fuel injection valve configured to generate a partial cone-shaped injection spray. The piston has a piston bowl.

[0004] The document JP 2010-144 540 A describes a direct fuel injection engine which is optimized with regard to the mixing state of fuel and air in a cavity. List of referencesPatent literature

[0005] PTL 1: Japanese Patent Application Laid-Open No. JP 2014 - 43 782 A Description of the inventionTechnical task

[0006] According to the high compression ratio engine described above, in a predetermined operating range (for example, a low-speed high-load range), in order to suppress so-called pre-ignition, it is necessary to: inject fuel from a plurality of injection ports of a fuel injection valve in a period from a second half of a compression stroke to a first half of an expansion stroke; perform forced ignition by a spark plug after a compression top dead center; and complete combustion in a short period of time.

[0007] However, for example, when a combustion chamber ceiling of an engine is formed in a gable roof (slope roof), the shapes of the paths along which the fuel injected from the injection ports flows into the combustion chamber are not equal to each other, so that the arrival positions of the fuel at the time of spark ignition are different from each other. Furthermore, a time from fuel injection to fuel ignition is short. Therefore, a thick part and a thin part of the fuel-air mixture may be generated in the combustion chamber at the time of spark ignition, that is, the homogeneity of the fuel-air mixture in the combustion chamber cannot be ensured. If the homogeneity of the fuel-air mixture is not ensured as mentioned above, the fuel-air mixture containing the fuel is discharged without combustion, or combustion (afterburning) occurs after a combustion time.This impairs fuel efficiency. Furthermore, smoke is produced and emissions are also affected.

[0008] The present invention has been made to solve the above problems, and an object of the present invention is to provide an engine adapted to inject fuel in a period from a second half of a compression stroke to a first half of an expansion stroke and to perform ignition after a compression top dead center, the engine being capable of properly ensuring homogeneity of a fuel-air mixture in a combustion chamber at an ignition timing. Solution to the task

[0009] To achieve the above object, an engine according to the present invention is an engine configured to directly inject fuel into a combustion chamber in a cylinder in a predetermined operating range in a period from a second half of a compression stroke to a first half of an expansion stroke and to perform ignition after a compression top dead center, the engine comprising: a piston having a cavity that is downwardly concave in a central region of an upper surface of the piston; a cylinder head configured to form a sloping roof-shaped combustion chamber;a fuel injection valve arranged on the cylinder head so as to be brought into a position corresponding to a central region of the piston, the fuel injection valve being configured to inject the fuel into the cavity of the piston in the period from the second half of the compression stroke to the first half of the expansion stroke;and a spark plug arranged on the cylinder head so as to be provided at a position on a radially outer side of the central region of the piston and corresponding to an upper side of the cavity of the piston, the central region corresponding to a position where the fuel injection valve is provided, wherein: the fuel injection valve has a plurality of injection ports arranged in a circumferential direction around a longitudinal axis of the fuel injection valve, and through each of which the fuel is injected in a direction inclined relative to the longitudinal axis at a predetermined injection angle; and each of the injection ports is formed such that the injection angle of the injection port becomes larger as a height of a ceiling of the combustion chamber is higher at a position corresponding to an edge end portion of the cavity in an injection direction of the injection port.

[0010] According to the present invention configured as above, each of the plurality of injection holes arranged in the circumferential direction around the longitudinal axis of the fuel injection valve, through each of which the fuel is injected in a direction inclined relative to the longitudinal axis at a predetermined injection angle, is formed such that the injection angle of the injection hole becomes larger as a height of a ceiling of the combustion chamber at a position corresponding to an edge end portion of the cavity in an injection direction of the injection hole is higher. Therefore, the increase in the flow path length of the injected fuel due to the high height of the ceiling of the combustion chamber at a position corresponding to the edge end portion of the cavity in the injection direction of the injection hole can be suppressed by the increase in the injection angle of the injection hole.This allows the points in time at which the fuel injected from the injection ports reaches the combustion chamber ceiling to be set equal to one another. This reliably ensures the homogeneity of the fuel-air mixture in the combustion chamber at the ignition point.

[0011] Furthermore, in the present invention, the injection angles of the injection holes are set such that each of the flow path lengths of the injected fuel, each of which is a length of a path along which the fuel injected from the injection hole flows through the cavity to reach the ceiling of the combustion chamber, becomes equal to the flow path length of the injected fuel of the injection hole closest to the spark plug.

[0012] According to the present invention configured as above, the timing at which the fuel injected from each injection port reaches the combustion chamber ceiling can be set equal to the timing at which the fuel-air mixture containing the fuel injected from the injection port closest to the spark plug reaches the vicinity of the spark plug. Thus, while ensuring the homogeneity of the fuel-air mixture in the combustion chamber at the ignition timing, the ignitability of the spark plug can be properly ensured. Advantageous effects of the invention

[0013] The engine according to the present invention is an engine configured to inject fuel in a period from a second half of a compression stroke to a first half of an expansion stroke and to perform ignition after a compression top dead center, and wherein the homogeneity of a fuel-air mixture in a combustion chamber of the engine can be suitably ensured. Brief description of the drawings Fig. 1 is a schematic plan view showing a cylinder of an engine according to an embodiment of the present invention, viewed from a lower side in an axial direction of the cylinder. Fig. 2 is a plan view showing a piston according to the embodiment of the present invention, viewed from an upper side in the axial direction of the cylinder. Fig. 3 is a partially sectioned view along line III-III of Fig. 1, which shows the piston, a cylinder head and the like according to the embodiment of the present invention. Fig. 4 is a plan view showing a tip end portion of a fuel injection valve according to the embodiment of the present invention, viewed from a lower side in a direction along a longitudinal axis of the fuel injection valve. Fig. 5 is a partially sectioned view along line VV of Fig. 4, which shows the tip end portion of the fuel injection valve according to the embodiment of the present invention. Fig. 6 is a schematic plan view showing a cylinder of the engine according to the embodiment of the present invention, viewed from the lower side in the axial direction of the cylinder, and is a diagram showing a plurality of fuel injection areas in respective injection directions of injection ports of the fuel injection valve according to the embodiment of the present invention. Fig. 7 is a partially sectioned view along line VII-VII of Fig. 6, which shows the piston, the cylinder head and the like according to the embodiment of the present invention, and which is a diagram showing flow paths of the fuel injected from the injection ports of the fuel injection valve according to the embodiment of the present invention. Fig. 8 is a partially sectioned view along line VIII-VIII of Fig. 6, which shows the piston, the cylinder head and the like according to the embodiment of the present invention, and which is a diagram showing the flow paths of the fuel injected from the injection ports of the fuel injection valve according to the embodiment of the present invention. Fig. 9 is a table showing diameters and injection angles of the injection holes of the fuel injection valve according to the embodiment of the present invention. Description of the embodiments

[0014] Hereinafter, an engine according to an embodiment of the present invention will be explained with reference to the drawings.

[0015] First, before explaining details of the embodiment of the present invention, a basic configuration of the engine according to the embodiment of the present invention will be briefly explained. The engine according to the embodiment of the present invention drives at a high compression ratio, such as a geometric compression ratio of 14 or more (preferably 18 to 20), and also performs homogeneous charge compression ignition, called HCCI, in a predetermined low-load range. Furthermore, in a predetermined operating range (for example, a low-speed high-load range), the engine according to the embodiment of the present invention injects fuel (performs retarded injection) in a period from a second half of a compression stroke to a first half of an expansion stroke to suppress preignition and the like, and performs ignition after a compression top dead center.Such a basic configuration of the engine is realized by the control of an “ECU” (“Electronic Control Unit”) in a vehicle.

[0016] Next, a combustion chamber structure of the engine according to the embodiment of the present invention will be described particularly with respect to Fig. 1 to 3 explained.

[0017] Fig. 1 is a schematic plan view showing a cylinder of the engine according to the embodiment of the present invention, viewed from a lower side in an axial direction of the cylinder. Fig. 2 is a plan view showing a piston according to the embodiment of the present invention, viewed from an upper side in the axial direction of the cylinder. Fig. 3 is a partially sectioned view along line III-III of Fig. 1, which shows the piston, a cylinder head, and the like according to the embodiment of the present invention. It is noted that Fig. Figure 3 is a diagram illustrating the situation when the piston is at the top dead center of compression.

[0018] In Fig. 1, reference symbol Z denotes a cylinder axis extending in a direction perpendicular to the blade surface, and reference symbol Y denotes a line segment extending upward / downward in the blade surface and corresponding to a crank axis. The engine according to the present embodiment uses a combustion chamber with a combustion chamber ceiling on the cylinder head that is formed in a gable roof (roof-slope-shaped) manner (see also Fig. 3). The line segment indicated by reference symbol Y corresponds to a sloping roof-shaped ridgeline (hereinafter appropriately referred to as a "sloping roof ridgeline") defining the combustion chamber. Furthermore, reference symbol X denotes a line segment extending through a center of the combustion chamber, that is, a central axis of the cylinder, and perpendicular to the sloping roof ridgeline Y. It is noted that Fig. 3 is a sectional view taken along a plane extending along the line segment X perpendicular to the roof slope ridge line Y, showing a part of the piston, the cylinder head, and the like.

[0019] As in Fig. 1, a cylinder has two intake valves 1 in one of the areas (ie a left area in Fig. 1) surrounding the roof slope ridge line Y. These two intake valves 1 are provided such that they are aligned in a direction along the roof slope ridge line Y. The reference numerals 5 in Fig. 1 denote intake ports which are opened and closed by the respective intake valves 1. Furthermore, the cylinder has two exhaust valves 2 which are provided in the other of the regions (ie, a right-hand region in Fig. 1) surrounding the roof slope ridge line Y. The two exhaust valves 2 are provided such that they are aligned in the direction along the roof slope ridge line Y. The reference numerals 6 in Fig. 1 denote exhaust ports that are opened and closed by the respective exhaust valves 2. Furthermore, a fuel injection valve 3 is provided on the cylinder axis Z. Furthermore, one of the two spark plugs 4 is provided between the two intake valves 1, and the other of the two spark plugs 4 is provided between the two exhaust valves 2.

[0020] Next is Fig. 2 shows a cavity 11 which is concave downwards in a central region of an upper surface of a piston 10 (see also Fig. 3). Specifically, the cavity 11 is formed to have a substantially circular shape as viewed from a direction along the cylinder axis Z, and a mountain-shaped protruding portion 11a is formed in a central portion of the cavity 11. A concave portion 11b having a lower height than the protruding portion 11a is formed on a radially outer side of the protruding portion 11a so as to surround the protruding portion 11a. The fuel injection valve 3 is disposed directly above the protruding portion 11a of the cavity 11, and the two spark plugs 4 are disposed in the concave portion 11b of the cavity 11 (see also Fig. 1 and Fig. 3).

[0021] Furthermore, an annular region 13 extending from an outer edge of the cavity 11 to an outer edge of the surface of the piston 10 and surrounding a radially outer side of the cavity 11 is provided in an upper region of the piston 10. The annular region 13 has four valve recesses 15, each of which is concave downward by, for example, about 1 mm. These four valve recesses 15 are provided at positions corresponding to the two intake valves 1 and at positions corresponding to the two exhaust valves 2. Furthermore, the regions 17 respectively located between the adjacent valve recesses 15 are not concave (i.e., they are higher than the valve recesses 15) and are substantially flat. Hereinafter, the region 17 between the valve recesses 15 is appropriately referred to as the "piston upper surface region 17."

[0022] Next, as in Fig. 3, the fuel injection valve 3 is provided in a region of a cylinder head 40, the region corresponding to the central region of the piston 10. Specifically, the fuel injection valve 3 is provided such that a longitudinal axis of the fuel injection valve 3 coincides with the cylinder axis Z. The fuel injection valve 3 injects fuel directly into the combustion chamber 30. The fuel injection valve 3 has a plurality of injection ports 27, and the fuel is sprayed from the injection ports 27 to form a conical shape symmetrical about the cylinder axis Z.In this case, an injection angle θ of the fuel injected by the fuel injection valve 3 through the injection holes 27 is set such that the injected fuel enters the cavity 11 of the piston 10 (see the arrows in ) in the period from the second half of the compression stroke to the first half of the expansion stroke (for example, 60□ before the top dead center) based on the control of the ECU. Fig. 3), in other words, the fuel does not impact the annular portion 13 of the piston 10 or a cylinder side wall (for example, a cylinder liner). Furthermore, the injection angle θ of the fuel injection valve 3 is set such that a spray collision distance from a fuel injection position to a position of the cavity 11 where the fuel impacts is greater than a length (partial length) from the fuel injection position to a position where an initial split of the fuel occurs.

[0023] Note that the injection angle θ corresponds to an inclination angle of the injection direction of the fuel injected from each injection port 27, which inclination angle is defined based on the longitudinal axis (ie, the cylinder axis Z) of the fuel injection valve 3. Furthermore, the fuel is supplied to the fuel injection valve 3 at a relatively high fuel pressure (for example, 40 to 120 MPa).

[0024] Furthermore, the two spark plugs 4 are provided in regions of the cylinder head 40, the regions being located on a radially outer side of the central region of the piston 10 and corresponding to an upper side of the cavity 11 of the piston 10. To be specific, each of the spark plugs 4 is provided at a position such that an electrode 4a of a tip end portion of the spark plug 4 is located within the cavity 11 in a radial direction. Furthermore, each of the spark plugs 4 is arranged such that the electrode 4a is located along a combustion chamber ceiling 30a (in other words, along a lower surface of the cylinder head 40; the same applies in the following explanations). Specifically, each of the spark plugs 4 is provided on the cylinder head 40 such that an inclination direction of the electrode 4a is set along an inclination of the combustion chamber ceiling 30a, while suppressing protrusion of the electrode 4a toward the combustion chamber 30 as much as possible.

[0025] It is noted that in Fig. 3, a region designated by a reference symbol SA denotes a squish area, which is a space formed in a gap between the upper piston surface portion 17 and the combustion chamber ceiling 30a. The squish area SA is formed not only in the gap between the upper piston surface portion 17 and the combustion chamber ceiling 30a, but also in a gap between the combustion chamber ceiling 30a and each of the upper surfaces of the valve recesses 15 (see Fig. 2) provided at positions corresponding to the intake valves 1 and the exhaust valves 2.

[0026] Next, the fuel injection valve 3 according to the embodiment of the present invention will be described in more detail with reference to Fig. 4 and Fig. 5 explained. Fig. 4 is a plan view showing a tip end portion of the fuel injection valve 3 according to the embodiment of the present invention, viewed from a lower side in a direction along the longitudinal axis of the fuel injection valve 3. Fig. 5 is a partially sectioned view along line VV of Fig. 4, which shows the tip end portion of the fuel injection valve 3 according to the embodiment of the present invention.

[0027] As in Fig. 4 and Fig. 5, the fuel injection valve 3 has a bottomed, cylindrical valve body extending in the direction along the longitudinal axis of the fuel injection valve 3.

[0028] A columnar needle 21 extending in the direction along the longitudinal axis of the fuel injection valve 3 is provided in the valve body 19. The needle 21 is moved in an up / down direction along the longitudinal axis of the fuel injection valve 3 by a high-response solenoid (not shown). A bottom surface of the valve body 19 is formed into a concave spherical shape that is concave downward. A seat portion 23 is formed in an outer peripheral portion of the bottom surface of the valve body 19. A tip end portion of the needle 21 moved downward by the high-response solenoid is pressed against the seat portion 23. Further, a space between an inner peripheral surface of the valve body 19 and an outer peripheral surface of the needle 21 is a fuel passage 25.Furthermore, a plurality of injection ports 27 are formed on the bottom surface of the valve body so as to be located on a tip end side of the seat portion 23.

[0029] The injection holes 27 are arranged in a circumferential direction around the longitudinal axis of the fuel injection valve 3. Each of the injection holes 27 is formed such that the fuel is injected in a direction inclined relative to the longitudinal axis of the fuel injection valve 3 at a predetermined injection angle θ. In the present embodiment, as shown in Fig. 4, ten injection holes 27 are arranged on the fuel injection valve 3 at equal angular intervals (ie, at intervals of 36°) in the circumferential direction around the longitudinal axis of the fuel injection valve 3. Furthermore, as shown in Fig. 5, each of the injection holes 27 is formed such that an angle formed by a central axis of the injection hole 27 and the longitudinal axis of the fuel injection valve 3 becomes θ.

[0030] Next, the sizes and injection angles of the injection holes 27 of the fuel injection valve 3 according to the embodiment of the present invention will be described with reference to Fig. 6 to 9 explained.

[0031] Fig. 6 is a schematic plan view showing a cylinder of the engine according to the embodiment of the present invention, viewed from the lower side in the axial direction of the cylinder, and is a diagram showing a plurality of fuel injection areas in respective injection directions of the injection ports 27 of the fuel injection valve 3 according to the embodiment of the present invention. Fig. 7 is a partially sectioned view along line VII-VII of Fig. 6, which shows the piston 10, the cylinder head 40 and the like according to the embodiment of the present invention, and is a diagram showing the flow paths of the fuel injected from the injection ports 27 of the fuel injection valve 3 according to the embodiment of the present invention. Fig. 8 is a partially sectioned view along line VIII-VIII of Fig. 6, which shows the piston 10, the cylinder head 40 and the like according to the embodiment of the present invention, and is a diagram showing the flow paths of the fuel injected from the injection ports 27 of the fuel injection valve 3 according to the embodiment of the present invention. Fig. 9 is a table showing diameters and injection angles of the injection holes 27 of the fuel injection valve 3 according to the embodiment of the present invention.

[0032] First, as in Fig. 6, in order to determine the sizes of the injection ports 27, the combustion chamber 30 is divided into a plurality of fuel injection areas at the compression top dead center by virtual vertical surfaces each extending in a cylinder radial direction from the longitudinal axis of the fuel injection valve 3 through a center between the adjacent injection ports 27.

[0033] In the example of Fig. 6, ten injection holes 27 of the fuel injection valve 3 are indicated by the respective letters AJ, and the directions in which the injection holes 27 point are indicated by chain lines. To be precise, when the cylinder is viewed from the lower side in the axial direction of the cylinder, the fuel injection hole 27 formed on the blade surface of Fig. 6, the injection port 27 directed upward in the direction along the roof slope ridge line Y is designated by the letter A, and the other injection ports 27 are designated by the respective letters BJ in a clockwise direction.

[0034] Then, a fuel injection area VA in the injection direction of the injection port A is defined by: a virtual perpendicular surface PAB extending in the radial direction of the cylinder from the longitudinal axis (i.e., the cylinder axis Z) of the fuel injection valve 3 through the center between the adjacent injection ports A and B; and a virtual perpendicular surface PJA extending in the radial direction of the cylinder from the longitudinal axis (i.e., the cylinder axis Z) of the fuel injection valve 3 through the center between the adjacent injection ports J and A. Similarly, the fuel injection areas VB to VJ are defined in the respective injection directions of the injection ports B to J. As in Fig. 6, each of the fuel injection portions is formed in a fan shape in plan view, and the fuel injection portions are arranged in the circumferential direction around the longitudinal axis of the fuel injection valve 3.

[0035] Each of the injection holes 27 is formed such that, in the case where the combustion chamber 30 is divided into the plurality of fuel injection areas corresponding to the respective injection holes 27 as explained above, and when the volume of the fuel injection area in the injection direction of the injection hole 27 is large, an opening area of ​​the injection hole 27 is large. More preferably, the injection holes 27 are formed such that a ratio of the opening areas of the injection holes 27 and a ratio of the volumes of the fuel injection areas in the respective injection directions of the injection holes 27 agree with each other.

[0036] In the example of Fig. 6 are the volumes of the fuel injection areas V A and V F, each defined to extend in the direction along the roof slope ridge line Y and each having a greatest height (ie distance between the upper surface of the piston 10 and the combustion chamber ceiling 30a), the greatest, and the volumes of the fuel injection areas V C , V D , V H and V I , each defined to extend in a direction closest to the line segment X perpendicular to the roof slope crest line Y, are the smallest. As in Fig. 9, in the present embodiment, when each of the smallest volumes of the fuel injection areas V C , V D , V B , V I is assumed to be 1, the ratio of the volumes of the fuel injection areas is given by “(V C , V D , V B , V I ) : (V B , V E , V G , V J ) : (V A , V F) = 1 : 1.1 : 1.3".

[0037] In the present embodiment, the diameters of the injection holes 27 are set such that: the ratio of the opening areas of the injection holes 27 matches the ratio of the volumes of the fuel injection areas in the respective injection directions of the injection holes 27, that is, “(C, D, H, I) : (B, E, G, J) : (A, F) = 1 : 1.1 : 1.3” is realized; and an average value of the diameters of the circular injection holes 27 is 0.100 mm. As shown particularly in Fig. As shown in Figure 9, each of the diameters of the injection ports C, D, H, and I is set to 0.095 mm. Each of the diameters of the injection ports B, E, G, and J is set to 0.100 mm. Each of the diameters of the injection ports A and F is set to 1.3 mm.

[0038] Furthermore, to determine the injection angles of the injection ports 27, the flow path lengths of the injected fuel are set. Each of the flow path lengths of the injected fuel is a length of a path along which the fuel injected from the injection port 27 flows through the cavity 11 to reach the combustion chamber ceiling 30a.

[0039] The flow path length of the injected fuel is calculated as the sum of: a distance from the injection port 27 of the fuel injection valve 3 to a position where the fuel injected at the injection angle θ impacts a surface of the cavity 11; and a path length from the position where the fuel impacts the surface of the cavity 11 to the combustion chamber ceiling 30a through the concave portion 11b of the cavity 11.

[0040] In the example of Fig. 7 is a flow path length of the injected fuel L Cthe injection opening C a sum of: a distance L C1 from the injection port C to a position where the injection angle θ C injected fuel hits the surface of the cavity 11; and a path length L C2 from the position where the fuel hits the surface of the cavity 11 to the combustion chamber ceiling 30a through the concave portion 11b of the cavity 11. A flow path length of the injected fuel L H from the injection opening H is a sum of: a distance L H1 from the injection port H to a position where the injection angle θ H injected fuel hits the surface of the cavity 11; and a path length L H2 from the position where the fuel hits the surface of the cavity 11 to the combustion chamber ceiling 30a through the concave portion 11b of the cavity 11.

[0041] In the example of Fig. 8 is a flow path length of the fuel injected from the injection port A L A a sum of: a distance L A1 from the injection port A to a position where the injection angle θ A injected fuel hits the surface of the cavity 11; and a path length L A2 from the position where the fuel hits the surface of the cavity 11 to the combustion chamber ceiling 30a through the concave portion 11b of the cavity 11. A flow path length of the fuel injected from the injection port F L F is a sum of: a distance L F1 from the injection port H to a position where the injection angle θ F injected fuel hits the surface of the cavity 11; and a path length L F2from the position where the fuel hits the surface of the cavity 11 to the combustion chamber ceiling 30a through the concave portion 11b of the cavity 11.

[0042] When the injection angles of the injection holes 27 are equal to each other, and when a height of the combustion chamber ceiling 30a at a position corresponding to an edge end portion 11d of the cavity 11 in the injection direction of each injection hole 27 is large (that is, when a distance from the edge end portion 11d of the cavity 11 to the combustion chamber ceiling 30a is large), the corresponding flow path length of the injected fuel is large. Furthermore, when the heights of the combustion chamber ceiling 30a at positions corresponding to the edge end portion 11d of the cavity 11 in the injection directions of the injection holes 27 are equal to each other, and when the injection angle θ of each injection hole 27 is large, the corresponding flow path length of the injected fuel is small.

[0043] Therefore, in the present embodiment, each of the injection holes 27 is formed such that when the height of the combustion chamber ceiling 30a at a position corresponding to the edge end portion 11d of the cavity 11 in the injection direction of the injection hole 27 is large, the injection angle of the injection hole 27 is large. Thus, the flow path lengths of the injected fuel of the injection holes 27 become equal to each other.

[0044] In the example of Fig. 6, the heights of the combustion chamber ceiling 30a are smallest at positions corresponding to the edge end portion 11d of the cavity 11 in the injection directions of the injection ports C, D, H, and I directed in the direction closest to the line segment X perpendicular to the roof slope ridge line Y. The heights of the combustion chamber ceiling 30a are largest at positions corresponding to the edge end portion 11d of the cavity 11 in the injection directions of the injection ports A and F directed in the direction along the roof slope ridge line Y.

[0045] For example, as in Fig. 7 and Fig. 8 shown, a height h C the combustion chamber ceiling 30a at a position corresponding to the edge end portion 11d of the cavity 11 in the injection direction of the injection port C and a height h Hof the combustion chamber ceiling 30a at a position corresponding to the edge end portion 11d of the cavity 11 in the injection direction of the injection port H are equal to each other. However, both a height h A the combustion chamber ceiling 30a at a position corresponding to the edge end portion 11d of the cavity 11 in the injection direction of the injection port A as well as a height h F the combustion chamber ceiling 30a at a position corresponding to the edge end portion 11d of the cavity 11 in the injection direction of the injection port F is greater than the height h C . Therefore, the injection angle θ C the injection opening C and the injection angle θ H the injection opening H are set equal to each other, and both the injection angle θ A the injection opening A as well as the injection angle θ F the injection opening H is considered to be larger than the injection angle θ Cof the injection port C. Thus, the flow path lengths of the injected fuel of the injection ports A, C, F and H become equal to each other.

[0046] In the present embodiment, as shown in Fig. 9, when each of the heights h C , h D , h H and h I the combustion chamber ceiling 30a at positions corresponding to the edge end portion 11d of the cavity 11 in the injection directions of the injection ports C, D, H and I is set as 0 mm, each of the heights h B , h E , h G and h J the combustion chamber ceiling 30a at positions corresponding to the edge end portion 11d of the cavity 11 in the injection directions of the injection ports B, E, G and J 0.90 mm, and each of the heights h A and h Fof the combustion chamber ceiling 30a at positions corresponding to the edge end portion 11d of the cavity 11 in the injection directions of the injection ports A and F becomes 2.80 mm. When each of the injection angles θ C , θ D , θ H and θ 1 of the injection ports C, D, H and I is set to 50□ each corresponding to the smallest height of the combustion chamber ceiling 30a, each of the flow path lengths L C , L D , L H and L I of the injected fuel 40 mm.

[0047] In this case, if each of the injection angles θ B , θ E , θ G and θ J of the injection ports B, E, G and J is set to 52□, and each of the injection angles θ A and θ Fof the injection ports A and F is set to 55□, each of the injected fuel flow path lengths of the injection ports 27 is 40 mm. Thus, all of the injected fuel flow path lengths of the injection ports 27 become equal to each other.

[0048] Next, modified examples of the embodiment of the present invention will be explained.

[0049] In the above embodiment, it was explained that the engine has a combustion chamber 30 with a sloped roof shape (see, for example, Fig. 3). However, the present invention is also applicable to an engine having a combustion chamber 30 of a shape other than the sloped roof shape (such as a hemispherical shape or a tub shape).

[0050] In the above embodiment, it was explained that the fuel injection valve 3 has ten injection holes 27. However, the present invention is also applicable to an engine having a combustion chamber 30 with a fuel injection valve 3 having a plurality of injection holes 27 other than the ten injection holes 27.

[0051] Next, operational advantages of the motors according to the embodiment of the present invention and the modified examples of the embodiment of the present invention will be explained.

[0052] First, each of the plurality of injection ports 27 arranged in the circumferential direction around the longitudinal axis of the fuel injection valve 3 is formed such that in the case where the combustion chamber 30 at the compression top dead center is divided into the plurality of fuel injection regions in the respective injection directions of the injection ports 27 by the perpendicular surfaces each extending in the radial direction of the cylinder from the longitudinal axis of the fuel injection valve 3 through the center between the adjacent injection ports 27, and when the volume of the fuel injection region in the injection direction of the injection port 27 is large, the opening area of ​​the injection port 27 is large.Therefore, even if the volumes of the fuel injection areas in the respective injection directions of the injection ports 27 are different from each other, for example, because the combustion chamber 30 of the engine is formed in a sloped roof shape, the fuel can be injected from the injection ports 27 in amounts corresponding to the volumes of the fuel injection areas. This can ensure the homogeneity of the fuel-air mixture in the combustion chamber 30 at the ignition timing.

[0053] Specifically, the injection ports 27 are configured such that the ratio of the opening areas of the injection ports 27 and the ratio of the volumes of the fuel injection areas in the respective injection directions of the injection ports 27 are consistent with each other. Therefore, the amount of fuel injected from the injection port 27 can be set to be proportional to the volume of the fuel injection area in the injection direction of the injection port 27. Thus, even when the volumes of the fuel injection areas are different from each other, the concentrations of the fuel-air mixtures in the fuel injection areas can be set to be equal to each other. Thus, the homogeneity of the fuel-air mixture in the combustion chamber 30 at the ignition timing can be reliably ensured.

[0054] Each of the plurality of injection holes 27 arranged in the circumferential direction around the longitudinal axis of the fuel injection valve 3, through each of which the fuel is injected in a direction inclined relative to the longitudinal axis at a predetermined injection angle, is formed such that when the height of the ceiling of the combustion chamber 30 at a position corresponding to the edge end portion 11d of the cavity 11 in the injection direction of the injection hole 27 is large, the injection angle of the injection hole 27 is large. Therefore, the increase in the flow path length of the injected fuel caused by the large height of the ceiling of the combustion chamber 30 at a position corresponding to the edge end portion 11d of the cavity 11 in the injection direction of the injection hole 27 can be suppressed by the increase in the injection angle of the injection hole 27.This allows the times at which the fuel 27 injected from the injection ports reaches the combustion chamber ceiling 30a to be set to be equal to one another. Thus, the homogeneity of the fuel-air mixture in the combustion chamber 30 at the ignition point can be reliably ensured.

[0055] Specifically, the injection angles of the injection holes 27 are set such that each injected fuel flow path length, that is, the length of the path along which the fuel injected from the injection hole 27 flows through the cavity 11 to reach the ceiling of the combustion chamber 30, becomes equal to the injected fuel flow path length of the injection hole 27 closest to the spark plug 4. Therefore, the timing at which the fuel injected from each injection hole 27 reaches the combustion chamber ceiling 30a can be set equal to the timing at which the fuel-air mixture containing the fuel injected from the injection hole 27 closest to the spark plug 4 reaches the vicinity of the spark plug 4.Thus, while ensuring the homogeneity of the fuel-air mixture in the combustion chamber 30 at the ignition timing, the ignitability of the spark plug 4 can be suitably ensured. List of reference symbols 1 intake valve 2 exhaust valve 3 Fuel injection valve 4 Spark plug 4a Electrode 5 Inlet channel 6 exhaust channel 10 pistons 11 Cavity 11a protruding area 11b concave area 11c curved surface of the cavity 11d Edge end area of ​​the cavity 13 annular area 15 Valve recess 17 upper piston surface area 19 Valve body 21 needle 23 Seating area 25 Fuel passage 27 Injection opening 30 combustion chamber 30a combustion chamber ceiling 40 cylinder head

Claims

[1] An engine configured to directly inject fuel into a combustion chamber in a cylinder in a predetermined operating range in a period from a second half of a compression stroke to a first half of an expansion stroke and to perform ignition after a compression top dead center, where the engine has: a piston having a cavity which is downwardly concave in a central region of an upper surface of the piston; a cylinder head configured to form a sloping roof-shaped combustion chamber; a fuel injection valve arranged on the cylinder head so as to be brought into a position corresponding to a central portion of the piston, the fuel injection valve being configured to inject the fuel into the cavity of the piston in the period from the second half of the compression stroke to the first half of the expansion stroke; and a spark plug arranged on the cylinder head so as to be provided at a position on a radially outer side of the central region of the piston and corresponding to an upper side of the cavity of the piston, the central region corresponding to a position where the fuel injection valve is provided, wherein: the fuel injection valve has a plurality of injection openings arranged in a circumferential direction around a longitudinal axis of the fuel injection valve, through each of which the fuel is injected in a direction inclined relative to the longitudinal axis at a predetermined injection angle; and each of the injection holes is formed such that the injection angle of the injection holes becomes larger as a height of a ceiling of the combustion chamber at a position corresponding to an edge end portion of the cavity in an injection direction of the injection hole is higher, wherein the injection angles of the injection holes are set such that each of the flow path lengths of the injected fuel, each of which is a length of a path along which the fuel injected from the injection hole flows through the cavity to reach the ceiling of the combustion chamber, becomes equal to the flow path length of the injected fuel of the injection hole closest to the spark plug.

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