JP4495765B2 - Direct fuel injection engine - Google Patents

Description

  The present invention relates to a piston in which the height of the top surface in the piston central axis direction changes in the circumferential direction, a cavity recessed at the center of the top surface of the piston, and a fuel injector that injects fuel into the cavity. And a fuel direct injection engine.

The following patent document shows an enlarged fuel spray angle as viewed in the direction of the piston center axis by forming a fuel injection hole provided at the tip of a fuel injector for a direct fuel injection engine into a long hole in the circumferential direction. 1 is known.
Japanese Utility Model Publication No. 60-159984

  By the way, according to Japanese Patent Application No. 2006-175597, the present applicant, in a fuel direct injection diesel engine equipped with a pent roof type piston, substantially matches the cross-sectional shape of the piston cavity in an arbitrary half plane passing through the piston central axis, Proposals have been made to improve the combustion state of the air-fuel mixture by making the fuel and air mixture in the cavity uniform in the circumferential direction.

  However, even if the cross-sectional shape of the cavity in an arbitrary half plane passing through the piston central axis is substantially the same, if there is a region where fuel is not injected from the fuel injector and a region where fuel is not injected in the cavity, the mixed state of the fuel and air is changed. Since it is difficult to completely uniformize in the circumferential direction, it has been desired to further uniform the mixed state.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to make the mixed state of fuel and air in a cavity uniform in a circumferential direction in a fuel direct injection engine having a pent roof type piston.

In order to achieve the above object, according to the invention described in claim 1, a piston whose top surface in the direction of the central axis of the piston changes in the circumferential direction, and a concave portion in the center of the top surface of the piston. And a fuel injector for injecting fuel into the cavity, wherein N is a natural number of 2 or more, and the inner wall surface of the cavity extends radially from the central axis of the piston and has an equal sandwich angle between them. When the cavity is divided into N virtual cavity sections with N half planes, the shape of the inner wall surface of the cavity is set so that the volumes of the respective virtual cavity sections are substantially equal. set, the number N of the virtual cavity sections and sets equal to the number of fuel injection axes of the fuel injector, when viewed in the piston central axis direction, all of the virtual A direct fuel injection engine fitted to the said fuel injection axis bisectors of the included angle in a cavity section, characterized in that the fuel spray angle of the fuel injection axes were matched to the included angle A direct fuel injection engine is proposed.

  According to the invention described in claim 2, in addition to the structure of claim 1, the cavity passing through the nth fuel injection shaft among the plurality of fuel injection shafts spaced apart in the circumferential direction of the fuel injector. Is the fuel injection cross section Sn, the intersection of the fuel injection cross section Sn and the opening periphery of the cavity is the first specific point An, and passes through the first specific point An and the bottom surface of the cylinder head in the fuel injection cross section Sn The second specific point Bn exists on a line parallel to the first specific point Bn, the third specific point Cn exists on the bottom wall portion of the cavity in the fuel injection cross section Sn, and the second specific point Bn is the first specific point Bn. The third specific point Cn is closer to the piston central axis than the maximum outer diameter position of the bottom wall portion of the cavity, and the first and second specific points An are closer to the piston central axis than the point An. , B A path AnBn that connects the first and third specific points An and Cn along the wall surface of the cavity in the fuel injection cross section Sn and a path AnBn that connects the first and third specific points An and Cn with a line along the bottom surface of the cylinder head in the fuel injection cross section Sn The cross-sectional shape surrounded by the path BnCn connecting the second and third specific points Bn and Cn with the shortest straight line is substantially equal to each fuel injection cross-section Sn, and the piston on the top surface of the piston By changing the shape of the inner wall surface of the cavity so that the reference cross-sectional shape expands as the fuel injection cross-section Sn passes through the fuel injection shaft that exists in the direction in which the height in the central axis direction is low. A direct fuel injection engine is proposed, characterized in that the volume of the typical cavity section is substantially equal.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect, a direct fuel injection engine is proposed in which the top surface of the piston is formed in a pent roof shape. The

According to the configuration of claim 1, the inner wall surface of the cavity recessed in the central portion of the top surface of the piston, and the N half planes extending radially from the piston central axis and having an equal sandwich angle with each other, When the cavity is partitioned into N virtual cavity sections, the shape of the inner wall surface of the cavity is set so that the volumes of the respective virtual cavity sections are substantially equal, and the number N of cavity sections is set as the fuel injection axis. And the bisector of the sandwich angle of all the cavity sections as viewed in the direction of the piston center line coincides with the fuel injection axis, so that the fuel and air mixing state in the cavity is uniform in the circumferential direction. To improve engine output and reduce exhaust harmful substances. Moreover, since the fuel spray angle of the fuel injection shaft is made to coincide with the sandwich angle, there is no area where fuel is not sprayed or areas where fuel is overlapped and sprayed in the cavity. Further, the unused air in the cavity can be minimized and the mixed state of fuel and air can be made more uniform.

  According to the second aspect of the present invention, the cross-sectional shape of the cavity of the prior invention is a reference cross-sectional shape, and the fuel injection cross section that passes through the fuel injection shaft that exists in the direction in which the height of the piston central axis direction of the top surface of the piston is low. Since the volume of each virtual cavity section is made substantially equal by changing the shape of the inner wall surface of the cavity so that the reference cross-sectional shape becomes larger as Sn, each fuel injection cross-section Sn compared to the prior application invention. It is possible to make the mixed state of the fuel and air more uniform.

  According to the third aspect of the present invention, since the top surface of the piston is formed in a pent roof shape, the opening area of the valve hole can be enlarged to improve the intake / exhaust efficiency.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  1 to 13 show a first embodiment of the present invention. FIG. 1 is a longitudinal sectional view of an essential part of a diesel engine, FIG. 2 is a view taken along line 2-2 in FIG. 1, and FIG. 4 is an enlarged view of part 4 of FIG. 1, FIG. 5 is an enlarged sectional view of line 5-5 of FIG. 4, FIG. 6 is a top perspective view of the piston, and FIG. 7 is a sectional view taken along line 8-8 in FIG. 3, FIG. 9 is a sectional view taken along line 9-9 in FIG. 3, and FIG. 10 is a sectional view of the cavity after correction. FIG. 11 is a diagram corresponding to FIG. 8 showing the sectional shape of the cavity after correction, FIG. 12 is an explanatory diagram of a virtual cavity section, and FIG. 13 is changing the direction of the cavity section in the circumferential direction. It is a graph which shows the change rate of the volume of this cavity division when it is made to do.

  As shown in FIGS. 1 to 6, the direct fuel injection type diesel engine includes a piston 13 slidably fitted to a cylinder 12 formed in a cylinder block 11. The piston 13 includes a piston pin 14 and a piston 13. It is connected to a crankshaft (not shown) via a connecting rod 15. Two intake valve holes 17, 17 facing the top surface of the piston 13 and two exhaust valve holes 18, 18 are opened on the lower surface of the cylinder head 16 coupled to the upper surface of the cylinder block 11. The intake port 19 communicates with the intake valve holes 17, 17, and the exhaust port 20 communicates with the exhaust valve holes 18, 18. The intake valve holes 17 and 17 are opened and closed by intake valves 21 and 21, and the exhaust valve holes 18 and 18 are opened and closed by exhaust valves 22 and 22. A fuel injector 23 is provided so as to be positioned on the piston central axis Lp, and a glow plug 24 is provided adjacent to the fuel injector 23.

  The top surface of the piston 13 and the lower surface of the cylinder head 16 facing the piston 13 are not flat but inclined in a pent roof shape having a triangular cross section, and this shape reduces the curvature of the intake port 19 and the exhaust port 20. In addition, the diameters of the intake valve holes 17 and 17 and the exhaust valve holes 18 and 18 can be secured, and the intake efficiency and the exhaust efficiency can be increased.

  A cavity 25 centered on the piston center axis Lp is recessed in the top surface of the piston 13. On the radially outer side of the cavity 25, a pair of inclined surfaces 13 b, 13 b that incline downward from the top portions 13 a, 13 a extending linearly in parallel with the piston pin 14 toward the intake side and the exhaust side, and inclined surfaces 13 b, 13 b A pair of flat surfaces 13c, 13c that are formed in the vicinity of the lower end of the cylinder and orthogonal to the piston center axis Lp, and a pair of cutout portions 13d, 13d in which both ends of the top portions 13a, 13a are cut out flat are formed.

The fuel injectors 23 arranged along the piston center axis Lp send fuel in six directions spaced at 60 ° intervals in the circumferential direction around a fuel injection point Oinj, which is a virtual point on the piston center axis Lp. Spray. Of the six fuel injection shafts, two first fuel injection shafts Li1 overlap with the piston pin 14 when viewed in the direction of the piston center axis Lp, and the other four second fuel injection shafts Li2 It intersects with the direction of the pin 14 at an angle of 60 °. Further, the six first and second fuel injection shafts Li1 and Li2 are inclined obliquely downward as viewed in a direction perpendicular to the piston center axis Lp, and the downward degree is small for the first fuel injection shaft Li1. The second fuel injection axis Li 2 is larger (see FIGS. 8 and 9).

  The fuel injection point at which the fuel injector 23 actually injects fuel is slightly shifted radially outward from the piston center axis Lp, but the fuel injection point Oinj is determined by the first and second fuel injection shafts Li1 and Li2. It is defined as a point that intersects the piston central axis Lp.

  As shown in enlarged views in FIGS. 4 and 5, six fuel injection holes 23 b... Are formed at intervals of 60 ° at the tip 23 a of the fuel injector 23 that protrudes from the lower surface of the cylinder head 16 toward the piston 13. The cross-sectional shape of each fuel injection hole 23b is a long hole (oval shape or track shape for athletics) that is long in the circumferential direction, and the fuel spray angle as viewed in the direction of the piston center axis Lp is wider than usual. It is set to ° (see FIG. 12).

  Next, the sectional shape of the cavity 25 of the prior invention (Japanese Patent Application No. 2006-175597) will be described in detail with reference to FIGS. The reason for explaining the cross-sectional shape of the cavity 25 of the prior invention is that the cross-sectional shape of the cavity 25 of the present invention is obtained by correcting the cross-sectional shape of the cavity 25 of the prior invention. 7 is a cross section in a direction orthogonal to the piston pin 14, and FIG. 8 is a cross section (cross section including the second fuel injection axis Li2) in a direction intersecting the piston pin 14 at 60 °. Is a cross section in the direction along the piston pin 14 (cross section including the first fuel injection axis Li1).

  The invention of the prior application aims at matching the shape of the cavity 25 as much as possible in an arbitrary cross section passing through the piston central axis Lp. The cross-sectional shape of the cavity 25 is divided into two left and right parts with the piston central axis Lp in between, and the two parts are connected in a straight line in the cross section in the direction of the piston pin 14 in FIG. The cross section in the direction orthogonal to the pin 14 and the cross section in the direction intersecting with the piston pin 14 of FIG. 8 at 60 ° are connected in a mountain shape according to the pent roof shape of the piston 13. However, the shape of the main portion of the cross-sectional shape of the cavity 25, that is, the shape shown by shading in FIGS.

  As is apparent from FIGS. 7 to 9, the cavity 25 formed around the piston center axis Lp includes a peripheral wall portion 25 a extending linearly downward from the top surface of the piston 13, and a piston center from the lower end of the peripheral wall portion 25 a. A curved wall portion 25b that curves in a concave shape toward the axis Lp, a bottom wall portion 25c that linearly extends obliquely upward from the radial inner end of the curved wall portion 25b toward the piston central axis Lp, and a piston central axis Lp The top portion 25d is continuous with the radially inner end of the bottom wall portion 25c.

  Lines extending downward and parallel to each other by a distance Ha from lines L-R1 and L-R2 indicating the lower surface of the cylinder head 16 facing the cavity 25 are defined as piston top surface basic lines L-a1 and L-a2. Similarly, lines extending downward in parallel by a distance Hbc from the lines L-R1 and L-R2 indicating the lower surface of the cylinder head 16 are defined as cavity bottom basic lines L-bc1 and L-bc2, and the lower surface of the cylinder head 16 is illustrated. The lines extending downward in parallel from the lines L-R1 and L-R2 by a distance Hd are defined as cavity top basic lines L-d1 and L-d2.

  Intersections between an arc having a radius Ra centered on the fuel injection point Oinj and the piston top surface basic lines L-a1, L-a2 are defined as a1, a2. Similarly, the intersections of the arc of radius Rb centered on the fuel injection point Oinj and the cavity bottom surface basic lines L-bc1, L-bc2 are b1, b2, and the arc of radius Rc centered on the fuel injection point Oinj The intersections of the cavity bottom basic lines L-bc1 and L-bc2 are c1 and c2, and the intersection of the arc having a radius Rd centered on the fuel injection point Oinj and the cavity top basic lines Ld1 and Ld2 is d1. , D2. The intersections e1 and e2 are points where perpendiculars drawn from the intersections d1 and d2 to the piston top surface basic lines L-a1 and L-a2 intersect the piston top surface basic lines L-a1 and L-a2.

  The peripheral wall portion 25a of the cavity 25 is above the straight lines a1b1 and a2b2, the bottom wall portion 25c of the cavity 25 is coincident with the straight lines c1d1 and c2d2, and the curved wall portion 25b of the cavity 25 is the straight lines a1b1 and a2b2 and the straight lines c1d1 and c2d2. Connect smoothly.

  Thus, the shape of the cavity 25 is set so that the shaded cross-sectional shape determined by the intersection points a1, c1, d1, e1 or the intersection points a2, c2, d2, e2 is equal in any cross-section passing through the piston central axis Lp. Is done.

  The intersection points a1 and a2 correspond to the first specific point An of the present invention, the intersection points e1 and e2 correspond to the second specific point Bn of the present invention, and the intersection points d1 and d2 correspond to the third specific point Cn of the present invention. It corresponds to.

  8 and 9, the cross section passing through the first and second fuel injection shafts Li1 and Li2 is shown in FIG. 8 and the shaded portion in the cross section in the direction of the piston pin 14 (fuel injection cross section S1) shown in FIG. The shaded portion in the cross section (fuel injection cross section S2) in the direction intersecting with the piston pin 14 at 60 ° has the same shape.

  In the cross section in the direction of the piston pin 14 shown in FIG. 9, the cross point in the direction crossing the piston pin 14 shown in FIG. 8 at 60 ° is defined as a fuel collision point P1 where the first fuel injection axis Li1 intersects the cavity 25. , A point where the second fuel injection axis Li2 intersects the cavity 25 is defined as a fuel collision point P2. The two fuel collision points P1 and P2 exist at the same position on the cross-section of the same shape shaded. Accordingly, the position of the fuel collision point P2 is lower than the position of the fuel collision point P1, and the second fuel injection shaft Li2 extending from the fuel injection point Oinj injects fuel further downward than the first fuel injection shaft Li1. Become.

  A distance D1 from the fuel injection point Oinj to the fuel collision point P1 is substantially equal to a distance D2 from the fuel injection point Oinj to the fuel collision point P2. The fuel collision angle α1 formed by the tangent line of the cavity 25 at the fuel collision point P1 and the first fuel injection axis Li1 is the fuel collision angle α2 formed by the tangent line of the cavity 25 at the fuel collision point P2 and the second fuel injection axis Li2. It almost agrees.

  As described above, according to the invention of the prior application, in an arbitrary cross section passing through the piston center axis Lp, except for a very small part in the vicinity of the fuel injection point Oinj (a region surrounded by the intersections e1, d1, d2, and e2). The cross-sectional shapes of the cavities 25 are the same. In particular, the two cross sections including the first and second fuel injection shafts Li1 and Li2 (see FIGS. 8 and 9) have the same sectional shape of the cavity 25, and the fuel injection point in the two cross sections. Since the distances D1, D2 from Oinj to the fuel collision points P1, P2 are set to be approximately equal, and the fuel collision angles α1, α2 at the fuel collision points P1, P2 are set to be approximately equal, air and fuel in each part of the cavity 25 It is possible to make the mixed state uniform in the circumferential direction and improve the combustion state of the air-fuel mixture to increase the engine output and reduce harmful exhaust substances.

  Further, in the cross section where the top surface of the piston 13 shown in FIGS. 7 and 8 is inclined, the angle formed by the edge of the opening of the cavity 25 (the portion of the intersection point a2) is flat when the top surface of the piston 13 shown in FIG. Therefore, the heat load of the portion can be reduced and the heat resistance can be improved.

  In the prior invention, the cross-sectional shape of the cavity 25 in FIGS. 7 to 9 is completely the same in the shaded portion, but the intersections e1, d1, d2, e2 near the fuel injection point Oinj. There is a mismatch in the white area surrounded by. The reason is that the two sections sandwiching the piston central axis Lp of the cross-sectional shape of the cavity 25 are connected in a straight line in the cross section in the direction of the piston pin 14 in FIG. 8 and the cross section in the direction intersecting at 60 ° with respect to the piston pin 14 in FIG. 8 is connected in a mountain shape according to the pent roof shape of the piston 13, and is surrounded by intersections e1, d1, d2, and e2. The area of the white area is the largest in the cross section in the direction of the piston pin 14 in FIG. 9, decreases in the cross section in the direction crossing the piston pin 14 in FIG. 8 at 60 °, and the direction perpendicular to the piston pin 14 in FIG. This is because it further decreases in the cross section.

  This embodiment is based on the cross-sectional shape of the cavity 25 in the direction of the piston pin 14 (see FIG. 9) where the area of the white area surrounded by the intersections e1, d1, d2, and e2 is maximized, and the other directions. Is corrected in the direction of expanding the cross-sectional shape (that is, the direction in which the depth of the cavity 25 is increased) to compensate for the difference in the area of the white area surrounded by the intersections e1, d1, d2, and e2. In this way, the air and fuel are mixed more uniformly in the cross section of the cavity 25 in all directions.

  FIG. 10 illustrates a method of correcting the cross-sectional shape of the cavity 25 in the direction orthogonal to the piston pin 14 of FIG. 7, the shape of the chain line indicates that of the prior invention, and the shape of the solid line indicates that of the present embodiment. Is shown.

  The correction of the cross-sectional shape of the cavity 25 according to the present embodiment increases the area of the shaded portion by moving the positions of the intersection b1 and the intersection c1 downward so as to become the intersection b1 ′ and the intersection c1 ′, respectively. Is done.

  First, the intersection point between the cavity bottom surface basic line L-bc1 and the line extending downward from the straight line e1d1 is determined as f1. Subsequently, the cavity bottom surface basic line L-bc1 passing through the intersection point f1 is rotated downward by a predetermined angle β around the intersection point f1 to set a new cavity bottom surface basic line L-bc1 ′. Subsequently, an intersection point between the arc having the radius Rb centered on the fuel injection point Oinj and the new cavity bottom basic line L-bc1 ′ is determined as the b1 ′, and the arc having the radius Rc centered on the fuel injection point Oinj is newly determined. The intersection point with the cavity bottom surface basic line L-bc1 'is determined as c1'.

  Thus, in the cross-sectional shape of the cavity 25 after the correction, the peripheral wall portion 25a of the cavity 25 is on the straight line a1b1 ′, the bottom wall portion 25c of the cavity 25 coincides with the straight line c1′d1, and the curved wall portion of the cavity 25 is obtained. 25b smoothly connects the straight line a1b1 'and the straight line c1'd1.

  An intersection between the cavity bottom surface basic line L-bc1 and the piston center axis Lp is defined as f, and the cavity bottom surface basic line L-bc1 is rotated downward by a predetermined angle β about the intersection point f to obtain a new cavity bottom surface. The basic line L-bc1 ′ may be set.

  Thus, of the path AnCn on the inner wall surface of the cavity 25, the section from the lowest part of the path AnCn to the third specific point Cn is close to the second fuel injection axis Li2, but by changing the shape of the section Combustion deterioration can be prevented by suppressing the adhesion of fuel to the inner wall surface of the cavity 25.

  In the present embodiment, the net average effective pressure NMEP is improved by about 2% with respect to the prior application invention in a state where no soot is generated.

Figure 1 1 is for explaining a method for correcting the cross-sectional shape of the cavity 25 in a direction that intersects the piston pin 14 at 60 ° in FIG. 8, the shape of the chain line indicates that of the prior invention, the solid The shape shows that of the present embodiment.

  Compared to the difference in the area of the white area surrounded by the intersections e1, d1, d2, e2 in FIG. 9 (piston pin 14 direction) and FIG. 7 (piston pin 14 orthogonal direction), FIG. 9 (piston pin 14 direction). 8 and FIG. 8 (direction intersecting with the piston pin 14 at 60 °) is small, so that the sectional shape of the cavity 25 in FIG. 11 (direction intersecting with the piston pin 14 at 60 °) is enlarged. The amount is smaller than the amount of expansion of the cross-sectional shape of the cavity 25 in FIG. 10 (in the direction orthogonal to the piston pin 14).

  Although the correction of the cross-sectional shape of the cavity 25 on one side of the piston central axis Lp has been described above, the correction of the cross-sectional shape of the cavity 25 on the other side of the piston central axis Lp is performed in exactly the same manner.

  As described above, according to the present embodiment, the problems of the prior invention, that is, the cross-sectional shapes of the cavities 25 in the region surrounded by the intersections e1, d1, d2, e2 in the vicinity of the fuel injection point Oinj. Since the mismatch is compensated, the air and fuel mixing state in each part of the cavity 25 is made more uniform in the circumferential direction, and the combustion state of the air-fuel mixture is improved to further increase the engine output and further reduce exhaust harmful substances. Can be achieved.

  FIG. 12 is an explanatory diagram that captures the correction of the cross-sectional shape of the cavity 25 according to the present embodiment from another viewpoint.

  In the figure, six half planes X1 to X6 extend radially from a piston central axis Lp passing through the center of the cavity 25. The angles (sandwich angles) formed by two adjacent half-planes X1 to X6 are all 60 °, and the six bisectors that bisect each half-plane X1 to X6 are the piston center axis Lp. , The first and second fuel injection shafts Li1 and Li2 overlap. The cavity 25 is divided into six virtual cavity sections 25A to 25F by six half planes X1 to X6. According to this embodiment, six cavities 25 are corrected by correcting the cross-sectional shape of the cavity 25 described above. It is possible to theoretically set the volumes of the cavity sections 25A to 25F to be the same.

  However, it is not necessary to set the volumes of the six cavity sections 25A to 25F to be completely the same, and even if they are set to be approximately the same, the fuel mixing state is made more uniform in the circumferential direction than in the prior invention. can do. Specifically, if the volume variation of the six cavity sections 25A to 25F, that is, the difference between the maximum volume cavity section and the minimum volume cavity section is made smaller than that of the prior invention, the fuel mixing state Can be made more uniform in the circumferential direction.

  FIG. 13 shows a range of 60 ° left and right around the piston center axis Lp, with the direction of the cavity section (that is, the direction of the bisector of the sandwich angle of the cavity section) as the direction of the piston pin 14 (0 °). It shows the rate of change of the volume of the cavity section when moved by. A broken line corresponds to the conventional example, and a solid line corresponds to the present embodiment.

  In either case, the direction of the bisector of the sandwich angle of the cavity section intersects the direction of the piston pin 14 at 60 ° (see the cavity sections 25B, 25C, 25E, and 25F in FIG. 12). The rate of change at that time is 0%. In the conventional example shown by a broken line, when the direction of the bisector of the sandwich angle of the cavity section coincides with the direction of the piston pin 14 (see the cavity sections 25A and 25D in FIG. 12), the rate of change becomes 7% at the maximum. However, in the embodiment indicated by the solid line, the rate of change is maximized at the same position, but the value is greatly reduced to a value of only 0.5%.

  Accordingly, one definition of the present invention is that "the variation in volume of each cavity section 25A-25F is more than the variation in volume of each cavity section 25A-25F of the conventional example in which the cavity depth is uniform in the circumferential direction. Can be "small".

  As apparent from FIG. 12, when the number 6 of the virtual cavity sections 25A to 25F is set equal to the number 6 of the fuel injection axes Li1 and Li2 of the fuel injector 23 and viewed in the direction of the piston center axis Lp, Since the bisector of the sandwiching angle coincides with the fuel injection axes Li1 and Li2 and the fuel spray angle γ of the fuel injection shafts Li1 and Li2 coincides with the sandwiching angle, the cavity sections 25A to 25F having the same volume are provided. The spray angle of the fuel injected along the center line is equal to the sandwich angle between the cavity sections 25A to 25F. As a result, there is no region where fuel is not sprayed inside the cavity 25 or regions where fuel is overlapped and sprayed, and the mixed state of the fuel and air in the cavity 25 is achieved by a synergistic effect with the equal volume of the cavity sections 25A to 25F. Further, it can be made uniform to improve engine output and reduce exhaust harmful substances.

  Next, a second embodiment of the present invention will be described with reference to FIG.

  In the first embodiment, the number of virtual cavity sections 25A to 25F is set to six (N = 6), but in the second embodiment, the number of virtual cavity sections is set to eight. It is set (N = 8). Accordingly, the number of fuel injection shafts is eight, the angle formed by adjacent fuel injection shafts is 45 °, and the fuel spray angle γ of each fuel injection shaft is 45 °.

  Also according to the second embodiment, it is possible to achieve the same operational effects as those of the first embodiment described above.

  The embodiments of the present invention have been described above, but various design changes can be made without departing from the scope of the present invention.

  For example, in the embodiment, the number of virtual cavity sections is set to 6 or 8 (N = 6 or N = 8), but the number of the cavity sections may be 2 or more ( N is a natural number of 2 or more).

  In the embodiment, the volume of the virtual cavity sections 25 </ b> A to 25 </ b> F does not include the volume of the portion sandwiched between the top surface of the piston 13 at the top dead center and the bottom surface of the cylinder head 16. The volume up to the opening edge (that is, the volume below the piston top surface basic line L-a1, L-a2) is defined as the volume of the virtual cavity sections 25A to 25F. The same operational effects can be achieved.

  Although the diesel engine has been described in the embodiment, the present invention is not limited to the diesel engine, and can be applied to any type of engine that directly injects fuel into the combustion chamber.

The principal part longitudinal cross-sectional view of the diesel engine which concerns on 1st Embodiment 2-2 line view of FIG. 3-3 line view of FIG. 4 enlarged view of FIG. FIG. 4 is an enlarged sectional view taken along line 5-5. Top perspective view of piston Sectional view along line 7-7 in FIG. Sectional view taken along line 8-8 in FIG. Sectional view along line 9-9 in FIG. The figure corresponding to FIG. 7 showing the cross-sectional shape of the cavity after correction The figure corresponding to the above-mentioned Drawing 8 showing the section shape of the cavity after amendment Illustration of virtual cavity division A graph showing the rate of change in volume of the cavity section when the direction of the cavity section is changed in the circumferential direction The figure corresponding to the said FIG. 2 based on 2nd Embodiment

13 Piston 23 Fuel injector 25 Cavity 25c Bottom wall portion 25A-25F Cavity section Li1 Fuel injection axis Li2 Fuel injection axis Lp Piston center axis X1-X6 Half plane γ Fuel spray angle

Claims (3)

A piston (13) whose height in the piston central axis (Lp) direction of the top surface changes in the circumferential direction; a cavity (25) recessed in the center of the top surface of the piston (13); and the cavity (25) a fuel injector (23) for injecting fuel into the interior,
N is a natural number of 2 or more, and the inner wall surface of the cavity (25) and N half planes (X1 to X6) extending radially from the piston central axis (Lp) and having an equal sandwich angle with each other, When the cavity (25) is divided into N virtual cavity sections (25A to 25F), the volumes of the respective virtual cavity sections (25A to 25F) are substantially equal to each other. )
When the number N of the virtual cavity sections (25A to 25F) is set equal to the number of fuel injection shafts (Li1, Li2) of the fuel injector (23), and viewed in the piston central axis (Lp) direction, A fuel direct injection engine in which the bisector of the included angle coincides with the fuel injection axis (Li1, Li2) in all the virtual cavity sections (25A to 25F) ,
A fuel direct injection engine characterized in that a fuel spray angle (γ) of the fuel injection shaft (Li1, Li2) is made to coincide with the included angle. Of the plurality of fuel injection shafts (Li1, Li2) spaced in the circumferential direction of the fuel injector (23), the cross section of the cavity (25) passing through the nth fuel injection shaft (Li1, Li2) is taken as the fuel injection cross section. Let Sn be
The intersection of the fuel injection cross section Sn and the opening periphery of the cavity (25) is defined as a first specific point An,
A second specific point Bn exists on a line passing through the first specific point An and parallel to the lower surface of the cylinder head (16) in the fuel injection cross section Sn,
A third specific point Cn exists on the bottom wall portion (25c) of the cavity (25) in the fuel injection cross section Sn,
The second specific point Bn is closer to the piston central axis (Lp) than the first specific point An,
The third specific point Cn is located closer to the piston center axis (Lp) than the maximum outer diameter position of the bottom wall portion (25c) of the cavity (25),
A path AnBn connecting the first and second specific points An and Bn along a line along the lower surface of the cylinder head (16) in the fuel injection cross section Sn, and the first and third specific points An and Cn are connected to the fuel injection cross section. A cross-sectional shape surrounded by a path AnCn connecting along the wall surface of the cavity (25) in Sn and a path BnCn connecting the second and third specific points Bn and Cn by the shortest straight line is substantially in each fuel injection cross section Sn. The equal cross section is used as the reference cross-sectional shape,
The reference cross-sectional shape expands as the fuel injection cross section Sn passes through the fuel injection shafts (Li1, Li2) existing in the direction in which the height of the piston central axis (Lp) direction of the top surface of the piston (13) is low. 2. The direct fuel cell according to claim 1, wherein the volume of each of the virtual cavity sections (25 </ b> A to 25 </ b> F) is made substantially equal by changing the shape of the inner wall surface of the cavity (25). Jet engine.   The direct fuel injection engine according to claim 1 or 2, wherein a top surface of the piston (13) is formed in a pent roof shape.

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