JP2009222000A - Fuel direct injection engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel direct injection engine provided with a pentroof piston in which strengths of squish flow and reverse squish flow are made uniform as much as possible in the circumferential direction of the squish area. <P>SOLUTION: In the fuel direct injection engine provided with the pentroof piston 13, because a width W of the squish area 26 varies in the circumferential direction, the strengths of squish flow and reverse squish flow vary in the circumferential direction. Recessed parts 13e and 13f for expanding the squish capacity are formed on a top face of the piston 13 facing the squish area 26 in a direction perpendicular to a piston pin axial center L2. The squish flow and reverse squish flow are weakened, therefore, and the squish capacity in the piston pin axial center L2 direction and the squish capacity in the direction perpendicular to the direction are made substantially equal. Strengths of the squish flow and reverse squish flow are thereby made uniform in the circumferential direction to improve combusting state of air-fuel mixture, and, it contributes to improvement of the engine output and reduction in hazardous substances in the emission. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention includes a piston having a pent roof-type top surface that includes two inclined surfaces that are inclined with a top portion extending in a direction parallel to the piston pin axis, the height of the piston central axis direction changing in the circumferential direction; A cylinder head having a pent roof-type lower surface facing the top surface of the piston, a cavity recessed in the center of the top surface of the piston, a radially outer portion of the piston, and the cylinder head The present invention relates to a direct fuel injection engine including an annular squish area formed between the lower surface and the lower surface.

  In general, the top surface of a piston of a fuel direct injection engine is formed flat, but a fuel direct injection engine in which the top surface of the piston protrudes like a pent roof is known.

  It is known that the strength of the squish flow generated by a piston having a pent roof-like top surface depends on the ratio between the cavity inlet diameter and the cylinder bore diameter, that is, the radial width of the squish area. For pistons with a pent roof-like top surface, if the reach of fuel injected into the cavity from each injection hole of the fuel injector is set equal, the cavity inlet becomes elliptical and the radial width of the squish area becomes the circumference. Will change direction. Specifically, the squish flow becomes stronger in the portion where the width of the squish area is wide (the portion where the top surface of the piston is low), and the squish flow becomes weak in the portion where the width of the squish area is narrow (the portion where the top surface of the piston is high). There's a problem.

  Therefore, according to Patent Document 1 below, the applicant of the present invention is directed to a direct fuel injection diesel engine in which a ratio D / B between a cavity inlet diameter D and a cylinder bore diameter B in a plane orthogonal to the piston central axis changes in the circumferential direction. The squish clearance formed between the top surface of the radially outer piston and the lower surface of the cylinder head increases as the ratio D / B decreases, and decreases as the ratio D / B increases. A direct fuel injection engine set up in this way is proposed.

According to this direct fuel injection engine, the squish clearance formed between the top surface of the piston and the bottom surface of the cylinder head is increased where the ratio D / B is small, that is, where the radial width of the squish chestnut area is large. By setting and decreasing the ratio D / B where the radial width of the squish chest area is small, the strength of the squish flow and the reverse squish flow is made uniform in the circumferential direction of the piston. In addition, the uniform mixing of the fuel can be promoted to reduce exhaust harmful substances.
JP 2008-002399 A

  By the way, the above conventional ones aim to equalize the strength of the squish flow and the reverse squish flow in the circumferential direction of the piston by paying attention to the squish clearance, but the strength of the squish flow and the reverse squish flow Since the squish clearance is not the only major parameter for determining the squish clearance, it is not always sufficient to equalize the strength of the squish flow and the reverse squish flow in the circumferential direction of the piston.

  The present invention has been made in view of the above circumstances, and in a fuel direct injection engine having a pent roof type piston, the strength of the squish flow and the reverse squish flow is made as uniform as possible in the circumferential direction of the squish area. The purpose is to do.

  In order to achieve the above object, according to the first aspect of the present invention, the apparatus includes two inclined surfaces that are inclined with a top portion extending in a direction parallel to the piston pin axis, and the height in the piston central axis direction is high. A piston having a pent roof type top surface changing in the circumferential direction, a cylinder head having a pent roof type bottom surface facing the top surface of the piston, and a cavity recessed in the center of the top surface of the piston; In the fuel direct injection engine having an annular squish area formed between a radially outer portion of the piston and a lower surface of the cylinder head, the squish in a direction perpendicular to the piston pin axis Forming a recess for enlarging the squish volume on at least one of the top surface of the piston facing the area and the cylinder head; , Direct fuel injection engine, characterized in that it has substantially equal to the direction of the squish volume perpendicular to the piston pin axis direction of the squish volume and piston pin axis is proposed.

  According to the invention described in claim 2, in addition to the configuration of claim 1, the intake valve hole facing one of the two inclined surfaces of the piston and the opposite one of the two inclined surfaces. An exhaust valve hole having a smaller diameter than the intake valve hole; an intake valve that opens and closes the intake valve hole; and a lower surface of the umbrella portion sinks upward with respect to a lower surface of the cylinder head in the closed state; and the exhaust valve hole And an exhaust valve in which the lower surface of the umbrella portion sinks upward with respect to the lower surface of the cylinder head when the valve is closed, and the sink volume of the intake valve is larger than the sink volume of the exhaust valve A direct fuel injection engine is proposed in which the volume of the recess on the intake side is smaller than the volume of the recess on the exhaust side.

  According to the invention described in claim 3, in addition to the structure of claim 2, two each of the intake valve hole and the exhaust valve hole are formed, and the intake side is seen in the piston central axis direction. The recess is formed so as not to overlap the intake valve hole between the two intake valve holes, and the recess on the exhaust side is not overlapped with the exhaust valve hole between the two exhaust valve holes. A fuel direct injection engine characterized by being formed is proposed.

  According to a fourth aspect of the present invention, in addition to the configuration of the third aspect, the depth of the recess on the intake side is substantially equal to the sinking amount of the intake valve, and the depth of the recess on the exhaust side. Is proposed, which is substantially equal to the amount of subsidence of the exhaust valve.

  According to the fifth aspect of the present invention, the pent roof includes two inclined surfaces that are inclined with a top portion extending in a direction parallel to the piston pin axis, and the height in the piston central axis direction changes in the circumferential direction. A piston having a top surface of the mold, a cylinder head having a bottom surface of a pent roof mold facing the top surface of the piston, a cavity recessed in the center of the top surface of the piston, and more than the cavity of the piston In a direct fuel injection engine including an annular squish area formed between a radially outer portion and a lower surface of the cylinder head, N is a natural number of 2 or more, and the inner wall surface of the cavity and a piston central axis The squish volume is divided into N virtual squish volume sections with N half-planes extending in the radial direction and having equal sandwich angles with each other. A recess is formed in at least one of the top surface of the piston and the lower surface of the cylinder head facing the squish area including a direction orthogonal to the piston pin axis so that the respective virtual squish volume sections are substantially equal. A fuel direct injection engine characterized by forming is proposed.

  According to the structure of claim 1, when the cavity is formed at the center of the top surface of the pent roof type of the piston, the radial width of the squish area in the piston pin axial direction is reduced, and the squish flow and the reverse squish flow are reduced. The radial width of the squish area in the direction orthogonal to the pin axis increases and the squish flow and the reverse squish flow increase, but the top surface of the piston and the cylinder head facing the squish area in the direction orthogonal to the piston pin axis A squish flow and a reverse squish flow are weakened by forming a recess that enlarges the squish volume on at least one of the lower surfaces, and the squish flow and the reverse squish flow in the direction perpendicular to the piston pin axis direction and the piston pin axis direction are substantially equal. can do. As a result, the squish flow and the reverse squish flow can be made uniform in the circumferential direction to improve the combustion state of the air-fuel mixture, contributing to an increase in output and a reduction in exhaust harmful substances.

  According to the second aspect of the present invention, since the sinking volume of the intake valve is larger than the sinking volume of the exhaust valve and the volume of the recess on the intake side is smaller than the volume of the recess on the exhaust side, the sinking of the intake valve The intake side squish flow and reverse squish flow, which are greatly reduced by a large volume, are compensated by reducing the volume of the recess on the intake side to reduce the squish flow and reverse squish flow, and the exhaust valve sinks. The exhaust side squish flow and reverse squish flow, which are reduced by a small volume, are compensated by increasing the volume of the recess on the exhaust side to greatly reduce the squish flow and reverse squish flow. Regardless of the subduction volume, the size of the squish flow and the reverse squish flow can be made uniform in the circumferential direction.

  According to the third aspect of the present invention, two intake valve holes and two exhaust valve holes are formed, and the intake-side recess is located between the two intake valve holes when viewed in the piston central axis direction. The exhaust side recess is formed so as not to overlap the exhaust valve hole between the two exhaust valve holes, so that the recess formed on the top surface of the piston is the intake valve hole or It is possible to prevent the thickness of the squish area from locally increasing at the portion overlapping the exhaust valve hole.

  According to the fourth aspect of the present invention, the depth of the recess on the intake side is substantially equal to the sinking amount of the intake valve, and the depth of the recess on the exhaust side is approximately equal to the sinking amount of the exhaust valve. A more uniform squish by preventing the thickness of the squish area on the lower surface of the umbrella portion of the intake and exhaust valves and the thickness of the squish area on the upper surface of the recesses on the intake and exhaust sides from changing discontinuously. It can contribute to the generation of flow and reverse squish flow.

  According to the configuration of claim 5, when the cavity is formed in the center of the top surface of the pent roof type of the piston, the radial width of the squish area in the piston pin axial direction is reduced, and the squish flow and the reverse squish flow are reduced. The radial width of the squish area in the direction perpendicular to the piston pin axis increases, and the squish flow and the reverse squish flow increase. However, when the squish volume is divided into N virtual squish volume sections, Since the concave portion is formed on at least one of the top surface of the piston and the bottom surface of the cylinder head facing the squish area in the direction orthogonal to the piston pin axis so that the squish volume sections are substantially equal, the squish flow and the reverse squish flow To improve the combustion state of the air-fuel mixture, It can contribute to the reduction of the gas hazardous substances.

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

  1 to 12 show an embodiment of the present invention. FIG. 1 is a longitudinal sectional view of a main part of a diesel engine, FIG. 2 is a view taken along line 2-2 in FIG. 1, and FIG. FIG. 4 is a top perspective view of the piston, FIG. 5 is a sectional view taken along line 5-5 in FIG. 3, FIG. 6 is a sectional view taken along line 6-6 in FIG. 3, and FIG. FIG. 8 shows a sectional shape of the cavity after correction, corresponding to FIG. 5, FIG. 9 shows a sectional shape of the cavity after correction, FIG. 10 corresponds to FIG. 6, and FIG. FIG. 11 is a graph showing the change rate of the volume of the cavity section when the direction of the cavity section is changed in the circumferential direction, and FIG. 12 is a change in the circumferential direction of the squish volume. It is a graph which shows.

  As shown in FIGS. 1 to 3, the direct fuel injection type diesel engine includes a piston 13 slidably fitted into a cylinder 12 formed in a cylinder block 11, and 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.

  As apparent from FIGS. 1 and 4, 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. As a result, the intake valve holes 17 and 17 and the exhaust valve holes 18 and 18 can be ensured in diameter and the intake efficiency and 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 shaft Li1 is large (see FIGS. 6 and 7).

  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 center axis Lp.

  Next, the cross-sectional shape of the cavity 25 of the prior application invention (see Japanese Patent Application Laid-Open No. 2008-002399) 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. 5 is a cross section in a direction orthogonal to the piston pin 14, and FIG. 6 is a cross section in a direction crossing the piston pin 14 at 60 ° (cross section including the second fuel injection axis Li2). 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. 6 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 hatching in FIGS.

  As is apparent from FIGS. 5 to 7, the cavity 25 formed around the piston center axis Lp has a circumferential 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 circumferential 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 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 surface 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 coincides with the straight lines c1d1 and c2d2, and the curved wall portion 25b of the cavity 25 has 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.

  6 and FIG. 7, the cross section passing through the first and second fuel injection shafts Li1 and Li2 is shown in FIG. 6 as a shaded portion in the cross section in the direction of the piston pin 14 (fuel injection cross section S1). 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. 7, the point where the first fuel injection axis Li1 intersects the cavity 25 is defined as the fuel collision point P1, and the cross section in the direction intersecting the piston pin 14 shown in FIG. , 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 axes Li1 and Li2 (see FIGS. 6 and 7) have the same cross-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.

  Also, in the cross section where the top surface of the piston 13 shown in FIGS. 5 and 6 is inclined, the angle formed by the edge of the opening of the cavity 25 (intersection point a2) is flat when the top surface of the piston 13 shown in FIG. 7 is flat. 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. 5 to 7 is completely the same in the shaded portion, but the intersection points 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 portions 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. 7, but the cross section in the direction orthogonal to the piston pin 14 in FIG. 6 and the cross section in the direction intersecting with the piston pin 14 at 60 ° in FIG. 6 are connected in a mountain shape according to the pent roof shape of the piston 13, and thus are surrounded by intersection points e 1, d 1, d 2, e 2. The area of the white area is the largest in the cross section in the direction of the piston pin 14 in FIG. 7, decreases in the cross section in a direction intersecting with the piston pin 14 in FIG. 6 at 60 °, and is orthogonal 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. 7) where the area of the white area surrounded by the intersections e1, d1, d2, and e2 is maximized, and 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. 8 illustrates a method for correcting the cross-sectional shape of the cavity 25 in the direction orthogonal to the piston pin 14 of FIG. 5, 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.

  FIG. 9 illustrates a method for correcting the cross-sectional shape of the cavity 25 in the direction intersecting with the piston pin 14 of FIG. 6 at 60 °. The shape of the chain line indicates that of the prior invention, and the shape of the solid line. Indicates the present embodiment.

  FIG. 7 (in the direction of the piston pin 14) compared to the difference in the area of the white area surrounded by the intersections e1, d1, d2, e2 in FIG. 7 (in the direction of the piston pin 14) and FIG. 5 (in the direction orthogonal to the piston pin 14). 6 and FIG. 6 (direction intersecting with the piston pin 14 at 60 °) are small, the sectional shape of the cavity 25 is enlarged in FIG. 9 (direction intersecting with the piston pin 14 at 60 °). The amount is smaller than the amount of expansion of the cross-sectional shape of the cavity 25 in FIG. 8 (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. 10 is an explanatory diagram that captures 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 substantially the same, the mixed state of the fuel can be improved as compared with the invention of Patent Document 1 or the prior invention. It can be made more uniform in the circumferential direction. Specifically, 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 should be made smaller than that of the invention of Patent Document 1 or the prior application invention. In this case, the mixed state of the fuel can be made uniform in the circumferential direction.

  FIG. 11 shows a range of 60 ° to the 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 with the direction of the piston pin 14 at 60 ° (see the cavity sections 25B, 25C, 25E, and 25F in FIG. 10). The rate of change at that time is 0%. In the conventional example indicated by the 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. 10), the rate of change is 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%.

  Next, the homogenization of the squish flow and the reverse squish flow will be described.

  When the piston 13 is at the top dead center, the top portions 13 a and 13 a of the top surface of the piston 13, the inclined surfaces 13 b and 13 b, the flat surfaces 13 c and 13 c, and the notches 13 d and 13 d are annularly formed between the bottom surface of the cylinder head 16. The squish area 26 (see FIGS. 8 and 9) is formed. The shape of the cavity 25 as viewed in the direction of the piston center axis Lp is an elliptical shape whose major axis coincides with the direction of the piston pin axis L2. The reason is that the top surface of the piston 13 is not flat but formed in a pent roof shape (see FIG. 3).

  The width in the radial direction of the squish area 26, that is, the widths of the inclined surfaces 13b and 13b, the flat surfaces 13c and 13c, and the notches 13d and 13d are not constant, but differ in the circumferential direction of the piston 13. The reason is that, as described above, the shape of the cavity 25 as viewed in the direction of the piston center axis Lp is an elliptical shape whose major axis coincides with the direction of the piston pin axis L2, and as a result, the squish area in the direction of the piston pin axis L2 The width W of the squish 26 and the squish flow and the reverse squish flow are reduced, and the width W of the squish area 26 in the direction perpendicular to the piston pin axis L2 is increased and the squish flow and the reverse squish flow are increased (see FIG. 3). ).

  FIG. 7 is a longitudinal section of the piston 13 along the direction of the piston pin 14. In this cross-sectional position, the piston 13 is cut along the linear top portions 13a and 13a, and notches 13d and 13d that are inclined downward are formed at both ends of the top portions 13a and 13a. The width W of the squish area 26 at the positions of the notches 13d and 13d is the smallest in the circumferential direction of the piston 13.

  FIG. 5 is a longitudinal section of the piston 13 along a direction orthogonal to the piston pin 14, and the piston 13 is cut at a portion including the flat surfaces 13 c and 13 c at this sectional position. The width W of the squish area 26 in the portion including the flat surfaces 13c and 13c is the largest in the circumferential direction of the piston 13, but two concave portions 13e and 13f are formed on the top surface of the piston 13 in that portion.

  As apparent from FIGS. 3 and 4, the intake-side recess 13e is formed on the top surface of the piston 13 sandwiched between the two intake valve holes 18, 18, and the exhaust-side recess 13f is 2 It is formed on the top surface of the piston 13 sandwiched between the individual exhaust valve holes 18, 18. The area of the recess 13e on the intake side (or the width Ai in the direction of the piston pin axis L2) is larger than the area of the recess 13f on the exhaust side (or the width Ae in the direction of the piston pin axis L2), but the depth of the recess 13e on the intake side Bi is set smaller than the depth Be of the recess 13f on the exhaust side, and the volume Ce of the recess 13f on the exhaust side is larger than the volume Ci of the recess 13e on the intake side.

  In this embodiment, when the width Ai of the recess 13e on the intake side is used as a reference, the width Ae of the recess 13f on the exhaust side is Ae = 0.67Ai, and the depth Bi of the recess 13e on the intake side is used as a reference. The depth Be of the exhaust-side recess 13f is Be = 1.86Bi, and the volume Ce of the exhaust-side recess 13f is Ce = 1.21Ci based on the volume Ci of the intake-side recess 13e.

  As is clear from FIG. 9, the lower surface of the umbrella portion 21 a of the intake valve 21 seated on the valve seat of the intake valve hole 17 is above the lower surface of the cylinder head 16 to avoid interference with the top surface of the piston 13. The lower surface of the umbrella portion 22a of the exhaust valve 22 seated on the valve seat of the exhaust valve hole 18 sinks above the lower surface of the cylinder head 16 so as to avoid interference with the top surface of the piston 13. Yes. The two intake valve holes 17 and 17 and the intake-side recess 13e do not overlap when viewed in the piston central axis Lp direction, and the two exhaust valve holes 18 and 18 and the exhaust-side recess 13f Does not overlap when viewed in the direction of the piston center axis Lp. Therefore, a sudden increase in the squish clearance h between the lower surfaces of the umbrella portions 21a and 21a of the intake valves 21 and 21 and the upper surface of the recess 13e on the intake side, which occurs when they are overlapped, is prevented, and the exhaust valve 22 , 22 can be prevented from increasing rapidly between the lower surfaces of the umbrella portions 22a, 22a and the upper surface of the exhaust-side recess 13f.

  The sinking amount Di of the umbrella portion 21a of the intake valve 21 is substantially equal to the depth Bi (see FIG. 4) of the recess 13e on the intake side, whereby the umbrella portion 21a of the intake valve 21 in the region a of FIG. The squish clearance h on the lower surface and the squish clearance h on the upper surface of the recess 13e on the intake side are prevented from changing suddenly. Further, the sinking amount De of the exhaust valve 22 substantially coincides with the depth Be (see FIG. 4) of the recess 13f on the exhaust side, whereby the squish on the lower surface of the umbrella portion 22a of the exhaust valve 22 in the region b of FIG. It is prevented that the clearance h and the squish clearance h on the upper surface of the exhaust-side recess 13f are suddenly changed.

  As described above, since the recesses 13e and 13f are formed in the direction orthogonal to the piston pin axis L2 in which the width W of the squish area 26 becomes large, the squish flow or the reverse that becomes strong when the width W of the squish area 26 is large. The squish flow can be weakened by the volumes Ci and Ce of the recesses 13e and 13f, and the squish flow or the reverse squish flow can be made uniform throughout the circumferential direction of the piston 13. In particular, since the recesses 13e and 13f are formed at positions away from the first and second fuel injection shafts Li1 and Li2, the fuel injected from the fuel injector 23 into the cavity 25 is discharged from the recesses 13e and 13f. Blowing outside the cavity 25 is prevented.

  Further, the sink volume Ei of the intake valves 21 and 21 (the area of the intake valve hole 17 × the sink amount of the intake valve 21) is the sink volume Ee of the exhaust valves 22 and 22 (the area of the exhaust valve hole 18 × the exhaust valve 22). Since the volume Ci of the intake-side recess 13e is smaller than the volume Ce of the exhaust-side recess 13f, the intake-side recess 21e is greatly reduced by the larger sink volume Ei. The squish flow and the reverse squish flow are compensated by reducing the volume Ci of the recess 13e on the intake side to reduce the squish flow and the reverse squish flow, and the subsidence volume Ee of the exhaust valves 22 and 22 is small. The exhaust side squish flow and the reverse squish flow are reduced and the volume Ce of the recess 13f on the exhaust side is increased to reverse the squish flow and reverse Compensating by greatly reducing the squish flow, the sizes of the squish flow and the reverse squish flow are made uniform in the circumferential direction regardless of the subduction volumes Ei, Ee of the intake valves 21, 21 and the exhaust valves 22, 22. be able to.

  FIG. 12 shows changes in the squish volume for each region having a sandwich angle of 10 ° centered on the piston center axis Lp. The embodiment in which the recesses 13e and 13f are formed on the top surface of the piston 13 is shown in FIG. It can be seen that the change in the circumferential direction of the squish volume is smaller than in the conventional example.

  Moreover, when this invention is caught from another viewpoint, it can be expressed as follows.

  When the squish volume (volume of the squish area 26) is divided into six virtual squish volume sections by six half planes X1 to X6 that divide the cavity 25 into six virtual cavity sections 25A to 25F. By forming the recesses 13e and 13f so that the virtual squish volume sections are substantially equal, the squish flow and the reverse squish flow are made uniform in the circumferential direction to improve the combustion state of the air-fuel mixture and output. Can contribute to the improvement of emissions and the reduction of hazardous substances.

  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 recesses 13e and 13f are formed on the top surface side of the piston 13, but the recesses may be formed on the lower surface side of the cylinder head 16, and the top surface side of the piston 13 and the cylinder head 16 may be formed. You may form in both of the lower surface side of.

  In the embodiment, the top portions 13a, 13a of the piston 13 are arranged in parallel with the piston pin axis L2, but the top portions 13a, 13a are not necessarily parallel to the piston pin axis L2, and the piston pin axis L2 and What is necessary is just to arrange | position in the plane which passes piston central axis Lp.

  In the embodiment, the number of virtual cavity sections 25A to 25F and the number of squish volume sections are set to 6 (N = 6), but the number of cavity sections 25A to 25F and the number of squish volume sections are set. The number may be two or more (N is a natural number of 2 or more).

  At this time, the number of the cavity sections 25A to 25F, the number of the squish volume sections, and the number of the fuel injection shafts are not necessarily matched, but by matching them, one cavity section 25A to 25F and the squish volume One fuel injection shaft corresponds to the section, and the fuel mixing state can be made uniform in the circumferential direction. In addition, if the bisector of the angle between the cavity sections 25A to 25F and the squish volume section coincides with the fuel injection axis, the fuel injection shaft is positioned at the center of one cavity section 25A to 25F and squish volume section. Thus, the fuel mixing state can be made more uniform.

  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.

Diesel engine longitudinal section 2-2 line view of FIG. 3-3 line view of FIG. Top perspective view of piston Sectional view along line 5-5 in FIG. 6-6 sectional view of FIG. Sectional view along line 7-7 in FIG. The figure corresponding to FIG. 5 showing the cross-sectional shape of the cavity after correction The figure corresponding to the above-mentioned Drawing 6 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 Graph showing change in squish volume in circumferential direction

Explanation of symbols

13 Piston 13a Top 13b Inclined surface 13e Recess 13f Recess 16 Cylinder head 17 Intake valve hole 18 Exhaust valve hole 21 Intake valve 21a Umbrella part 22 Exhaust valve 22a Umbrella part 25 Cavity 25A-25F Cavity section 26 Squish area Bi Intake side recess Depth Be Exhaust-side recess depth Ci Inlet-side recess volume Ce Exhaust-side recess volume Di Intake valve sink amount De Exhaust valve sink amount Ei Intake valve sink volume Ee Exhaust valve sink Insertion volume L2 Piston pin axis Lp Piston center axis X1 to X6 Half plane

Claims (5)

A pent roof type that includes two inclined surfaces (13b) that are inclined with a top portion (13a) extending in a direction parallel to the piston pin axis (L2) interposed therebetween, and whose height in the direction of the piston central axis (Lp) changes in the circumferential direction. A piston head (13) having a top surface, a cylinder head (16) having a pent roof type lower surface facing the top surface of the piston (13), and a concave portion at the center of the top surface of the piston (13). An annular squish defining a squish volume between the cavity (25) and a radially outer portion of the piston (13) at top dead center than the cavity (25) and the lower surface of the cylinder head (16) In a direct fuel injection engine comprising an area (26),
A recess for expanding the squish volume on at least one of the top surface of the piston (13) and the bottom surface of the cylinder head (16) facing the squish area (26) in a direction perpendicular to the piston pin axis (L2). 13e, 13f), and the squish volume in the direction perpendicular to the piston pin axis (L2) and the squish volume in the direction perpendicular to the piston pin axis (L2) are made substantially equal. . The intake valve hole (17) facing one of the two inclined surfaces (13b) of the piston (13) and the intake valve hole (17) facing the other of the two inclined surfaces (13b) are smaller in diameter. The intake valve hole (18) and the intake valve hole (17) are opened and closed, and the lower surface of the umbrella portion (21a) sinks upward with respect to the lower surface of the cylinder head (16) in the closed state. 21) and an exhaust valve (22) that opens and closes the exhaust valve hole (18) and in which the lower surface of the umbrella (22a) sinks upward with respect to the lower surface of the cylinder head (16) in the closed state. Prepared,
The sink volume (Ei) of the intake valve (21) is larger than the sink volume (Ee) of the exhaust valve (18), and the volume (Ci) of the recess (13e) on the intake side is the recess on the exhaust side. The direct fuel injection engine according to claim 1, wherein the direct fuel injection engine is smaller than a volume (Ce) of (13f).   Two intake valve holes (17) and two exhaust valve holes (18) are formed, and when viewed in the piston central axis (Lp) direction, the recess (13e) on the intake side is the two intake valve holes. The exhaust-side recess (13f) is formed so as not to overlap the intake valve hole (17) during (17), and the exhaust-side recess (13f) is located between the two exhaust valve holes (18). The direct fuel injection engine according to claim 2, wherein the direct fuel injection engine is formed so as not to overlap with the fuel direct injection engine.   The depth (Bi) of the intake side recess (13e) is substantially equal to the sinking amount (Di) of the intake valve (21), and the depth (Be) of the exhaust side recess (13f) is the exhaust valve. The direct fuel injection engine according to claim 3, wherein the direct fuel injection engine is substantially equal to a sinking amount (De) of (22).   A pent roof type that includes two inclined surfaces (13b) that are inclined with a top portion (13a) extending in a direction parallel to the piston pin axis (L2) interposed therebetween, and whose height in the direction of the piston central axis (Lp) changes in the circumferential direction. A piston head (13) having a top surface, a cylinder head (16) having a pent roof type lower surface facing the top surface of the piston (13), and a concave portion at the center of the top surface of the piston (13). An annular squish defining a squish volume between the cavity (25) and a radially outer portion of the piston (13) at the top dead center than the cavity (25) and the lower surface of the cylinder head (16) In a direct fuel injection engine having an area (26), N is a natural number of 2 or more, and the inside of the cavity (25) The squish volume is divided into N virtual squish volume sections by a wall surface and N half planes (X1 to X6) extending radially from the piston central axis (Lp) and having an equal sandwich angle with each other. The top surface of the piston (13) facing the squish area (26) including a direction orthogonal to the piston pin axis (L2), and so that each of the virtual squish volume sections is substantially equal, A direct fuel injection engine, wherein a recess (13e, 13f) is formed in at least one of the lower surfaces of the cylinder head (16).

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