JP2008255934A - Fuel direct injection engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformize a mixing state of fuel and air within a cavity, even if the magnitude of squish stream is nonuniform in circumferential direction in a fuel direct injection engine. <P>SOLUTION: In a cross-section where a squish stream flowing toward a cavity 25 from the outer periphery of a piston 13 is large because the width W2 of a squish area SA is large, and a squish clearance C2 is small, a collision angle α2 with which fuel injection axis Li2 collides with the cavity 25 is made large, and in a cross-section where squish stream is small because the width of squish area SA is small, and the squish clearance is large, a collision angle with which the fuel injection axis Li2 collides with the cavity 25 is made small. Thereby, because the tendency of the fuel outflow to the outside of the cavity 25 becomes weak in a cross-section where the squish stream is small, and the tendency of the fuel outflow to the outside of the cavity 25 becomes strong in a cross-section where the squish stream is large, a mixing state of fuel and air can be uniformized over the whole area of the cavity 25. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piston whose top surface varies in the circumferential direction, a cavity recessed in the central portion of the piston, and a plurality of fuels oriented in a plurality of directions spaced in the circumferential direction in the cavity. The present invention relates to a direct fuel injection engine including a fuel injector that injects fuel along an injection axis.

  In general, the top surface of a piston of a direct fuel injection diesel engine is formed flat, but a direct fuel injection diesel engine in which the top surface of the piston protrudes in a pent roof shape is known from Patent Document 1 below.

  When the cavity is formed in the top surface of the pent roof type piston, the height of the opening of the cavity changes in the circumferential direction. Therefore, if the height of the bottom wall portion of the cavity is made constant in the circumferential direction, the depth of the circumferential wall portion of the cavity changes in the circumferential direction, and the mixed state of fuel and air injected from the fuel injector is changed. There is a problem that the engine becomes uneven in the circumferential direction, resulting in a decrease in engine output and an increase in exhaust harmful substances.

In order to solve this problem, the technique described in Patent Document 1 changes the height of the bottom wall portion of the cavity so as to follow the change in the height of the opening of the cavity. The depth is made constant in the circumferential direction, so that the mixed state of fuel and air in the cavity is made uniform in the circumferential direction.
JP-A-62-255520

  In the Japanese Patent Application No. 2006-175597, the applicant of the present application is an arbitrary cross section orthogonal to the top surface of the piston through the fuel injection point of the fuel injector in order to make the mixed state of fuel and air uniform in the circumferential direction of the cavity. Proposes a cavity whose cross-sectional shape is matched.

  However, even if the cross-sectional shape of the cavity is matched as described above, the diesel engine with a pent roof type piston tends to have uneven squish flow in the circumferential direction. May flow out of the cavity, or fuel may be pushed into the bottom of the cavity at a large portion of the squish flow, which may deteriorate the combustion state of the air-fuel mixture.

  The present invention has been made in view of the above circumstances, and in a direct fuel injection engine, even if the size of the squish flow is not uniform in the circumferential direction, the fuel and air mixing state in the cavity is made uniform. For the purpose.

  In order to achieve the above object, according to the invention described in claim 1, a piston whose top surface changes in the circumferential direction, a cavity recessed in the center of the piston, and the cavity In a direct fuel injection engine having a fuel injector that injects fuel along a plurality of fuel injection shafts oriented in a plurality of directions that are spaced apart in the circumferential direction, the size of the squish flow changes in the circumferential direction, A second collision angle at which a second fuel injection shaft directed in a direction with a large squish flow collides with the cavity is larger than a first collision angle at which a first fuel injection shaft directed in a small flow direction collides with the cavity. There is proposed a direct fuel injection engine characterized in that it is set as follows.

  According to the invention described in claim 2, the piston whose height of the top surface changes in the circumferential direction, the cavity recessed in the central portion of the piston, and the circumferential direction in the cavity are separated from each other. In a fuel direct injection engine comprising a fuel injector that injects fuel along a plurality of fuel injection axes directed in a plurality of directions, a squish area changes in a circumferential direction, and the squish area is oriented in a small direction. The second collision angle at which the second fuel injection shaft directed in the direction in which the squish area is larger is set to be larger than the first collision angle at which the fuel injection shaft collides with the cavity. A direct fuel injection engine is proposed.

  According to the invention described in claim 3, the piston whose top surface changes in the circumferential direction, the cavity recessed in the central portion of the piston, and the circumferential direction in the cavity are separated from each other. In a fuel direct injection engine comprising a fuel injector for injecting fuel along a plurality of fuel injection axes directed in a plurality of directions, the width of the squish area changes in the circumferential direction, and the first direction directs in the direction in which the width is small. The second collision angle at which the second fuel injection shaft, which is directed in the direction in which the width is larger, than the first collision angle at which one fuel injection shaft collides with the cavity, is set to be larger. A direct fuel injection engine is proposed.

  According to the invention described in claim 4, the piston whose top surface changes in the circumferential direction, the cavity recessed in the central portion of the piston, and the circumferential direction in the cavity are separated from each other. In a fuel direct injection engine comprising a fuel injector that injects fuel along a plurality of fuel injection axes directed in a plurality of directions, the ridge line length of the squish area changes in the circumferential direction, and the ridge line length is small The second collision angle at which the second fuel injection shaft, which is directed in the direction in which the ridge line length is larger, is larger than the first collision angle at which the first fuel injection shaft that is directed toward the cavity collides with the cavity. A direct fuel injection engine characterized by being set to be proposed.

  According to the invention described in claim 5, the piston whose top surface changes in the circumferential direction, the cavity recessed in the central portion of the piston, and the circumferential direction in the cavity are separated from each other. In a fuel direct injection engine comprising a fuel injector that injects fuel along a plurality of fuel injection axes directed in a plurality of directions, a squish clearance changes in a circumferential direction, and a first direction in which the squish clearance is large is directed. The second collision angle at which the second fuel injection shaft directed in the direction in which the squish clearance is smaller than the first collision angle at which the fuel injection shaft collides with the cavity is set to be larger. A direct fuel injection engine is proposed.

  According to the invention described in claim 6, in addition to the structure of any one of claims 1 to 5, the second collision angle is 90 ° or more. 1 is proposed.

  According to the invention described in claim 7, in addition to the configuration of any one of claims 1 to 6, the cross section of the cavity passing through the nth fuel injection shaft is defined as a fuel injection cross section Sn, The intersection of the fuel injection cross section Sn and the peripheral edge of the opening of the cavity is defined as a first specific point An, and a second specific point is formed on a line passing through the first specific point An and parallel to the lower surface of the cylinder head in the fuel injection cross section Sn. A point Bn exists, a 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 closer to the piston center axis than the first specific point An. The third specific point Cn is located closer to the piston center axis than the maximum outer diameter position of the bottom wall portion of the cavity, and the first and second specific points An and Bn are in the fuel injection cross section Sn. To the cylinder A path AnBn connected by a line along the lower surface of the door, a path AnCn connecting the first and third fixed points An and Cn along the wall surface of the cavity in the fuel injection cross section Sn, and the second and third specific points Bn. , Cn and a path BnCn connecting the shortest straight lines have a cross-sectional shape substantially equal in each fuel injection cross-section Sn.

  According to the invention described in claim 8, in addition to the structure of any one of claims 1 to 7, the fuel injected by the fuel injector is allowed to enter the cavity before the top dead center of the piston. A fuel direct injection engine characterized by collision is proposed.

  According to the configuration of the first aspect, even if the size of the squish flow that flows from the outer peripheral portion of the piston toward the cavity changes in the circumferential direction, the first collision angle decreases in the direction in which the squish flow is small and the fuel is generated. The tendency to flow out of the cavity is weakened, and the second collision angle increases in the direction in which the squish flow is large, and the tendency for fuel to flow out of the cavity is strong. Thus, the mixed state of fuel and air can be made uniform.

  According to the second aspect of the present invention, since the squish area changes in the circumferential direction, the squish flow is small even if the size of the squish flow that flows from the outer periphery of the piston toward the cavity changes in the circumferential direction. The first collision angle becomes smaller in the direction (ie, the direction where the squish area is smaller) and the tendency of the fuel to flow out of the cavity becomes weaker. The second collision angle becomes smaller in the direction where the squish flow is larger (ie, where the squish area is larger). Since the fuel tends to flow out to the outside of the cavity with increasing size, the mixed state of fuel and air can be made uniform over the entire cavity regardless of the size of the squish flow.

  According to the third aspect of the present invention, even if the size of the squish flow that flows from the outer periphery of the piston toward the cavity changes in the circumferential direction because the width of the squish area changes in the circumferential direction, In the direction in which the squish area is small (ie, the width of the squish area is small), the first collision angle is small and the tendency of the fuel to flow out of the cavity is weakened. Since the second collision angle becomes larger and the tendency of the fuel to flow out of the cavity becomes stronger, the mixed state of fuel and air can be made uniform over the entire cavity regardless of the size of the squish flow. .

  Further, according to the configuration of claim 4, even if the size of the squish flow that flows from the outer periphery of the piston toward the cavity changes in the circumferential direction because the ridge line length of the squish area changes in the circumferential direction, In the direction where the squish flow is small (that is, the direction where the ridge line length of the squish area is small), the first collision angle becomes small and the tendency for the fuel to flow out of the cavity is weakened. The second collision angle increases in the direction where the length is large), and the tendency of the fuel to flow out of the cavity becomes stronger. Therefore, the mixed state of the fuel and air can be maintained over the entire cavity regardless of the size of the squish flow. It can be made uniform.

  According to the fifth aspect of the present invention, since the squish clearance changes in the circumferential direction, the squish flow is small even if the size of the squish flow flowing from the outer periphery of the piston toward the cavity changes in the circumferential direction. The first collision angle becomes smaller in the direction (that is, the direction where the squish clearance is larger) and the tendency of the fuel to flow out of the cavity becomes weaker. Since the fuel tends to flow out to the outside of the cavity with increasing size, the mixed state of fuel and air can be made uniform over the entire cavity regardless of the size of the squish flow.

  According to the sixth aspect of the present invention, the fuel that has collided with the cavity at the second collision angle of 90 ° or more is guided by the wall surface of the cavity and flows to the opening side. Can be diffused uniformly.

  According to the configuration of claim 7, a plurality of fuel injection shafts from a fuel injector disposed on the piston central axis in a cavity recessed in the central portion of the piston whose top surface changes in the circumferential direction. , The cross section of the cavity passing through the nth fuel injection axis is defined as the fuel injection cross section Sn, and is defined by the first to third specific points An, Bn, Cn on the fuel injection cross section Sn. Since the cross-sectional shape of each cavity is set to be substantially equal in each fuel injection cross section Sn, the mixed state of fuel and air in each fuel injection cross section Sn is made uniform to improve engine output and reduce exhaust harmful substances. Can do. Further, since the opening edge of the cavity in the portion where the top surface of the piston is inclined is not sharpened, the heat stress surface is also superior.

  According to the eighth aspect of the invention, since the fuel injected by the fuel injector collides with the cavity before the top dead center of the piston, the fuel collides with the cavity at the timing when the squish flow is generated, The fuel to be spilled can be effectively contained in the squish flow.

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

  1 to 9 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 is a graph showing the rate of change of the cavity volume in the range of 30 ° to the left and right of the fuel injection shaft when the direction of the fuel injection shaft is changed in the circumferential direction. It is a figure which shows the change of the wrinkle generation amount by a 2nd collision angle.

  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 Li2 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 will be described in detail with reference to FIGS. 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).

  What is important here is that all of the cross sections in FIGS. 5 to 7 are cross sections in a direction perpendicular to the top surface of the piston 13 through the fuel injection point Oinj. The cross section in the direction perpendicular to the piston pin 14 in FIG. 5 and the cross section in the direction of the piston pin 14 in FIG. 7 have their cut surfaces orthogonal to the top surface of the piston 13 and include the piston central axis Lp. On the other hand, the cross section in the direction intersecting with the piston pin 14 of FIG. 6 at 60 ° passes through the second fuel injection axis Li2 and is orthogonal to the top surface of the piston 13 (that is, the inclined surfaces 13b and 13b). The cross section does not include the piston center axis Lp. That is, in FIG. 3, the cut surface along line 5-5 and the cut surface along line 7-7 are orthogonal to the paper surface, but the cut surface along line 6-6 is not orthogonal to the paper surface, The piston 13 is orthogonal to the inclined surfaces 13b and 13b.

  One feature of the present embodiment is that the shape of the cavity 25 substantially matches in any cross section that passes through the fuel injection point Oinj and is orthogonal to the top surface of the piston 13. The cross-sectional shape of the cavity 25 is divided into two parts on the left and right with the fuel injection point Oinj in between. The two parts are connected in a straight line in the cross section in the direction of the piston pin 14 in FIG. A cross section in a direction perpendicular to the pin 14 and a cross section in a 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 main portion of the cross-sectional shape of the cavity 25, that is, the shape of the portion shown by shading 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.

  Intersection points 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, the arc of radius Rc centered on the fuel injection point Oinj and the aforementioned The intersections of the cavity bottom basic lines L-bc1 and L-bc2 are c1 and c2, and the intersection of the arc of 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 line a1b1, a2b2 and the straight lines c1d1 and c2d2. Connect smoothly.

  Thus, 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 orthogonal to the top surface of the piston 13 through the fuel injection point Oinj. Thus, the shape of the cavity 25 is set.

  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 wall surface of the cavity 25 is defined as the fuel collision point P1, and the direction intersecting the piston pin 14 shown in FIG. In the cross section, a point where the second fuel injection axis Li2 intersects the wall surface of the cavity 25 is defined as a fuel collision point P2. The two fuel collision points P1 and P2 exist at different positions on the shaded fuel injection cross sections S1 and S2 having the same shape. That is, the position corresponding to the fuel collision point P1 on the fuel injection cross sections S1 and S2 having the same shape is P2 ', but the actual fuel collision point P2 exists at a position lower than P2' (a position deep in the cavity 25). To do. Therefore, the tangent of the cavity 25 at the fuel collision point P2 and the second fuel injection axis Li2 are compared with the first collision angle α1 formed by the tangent of the cavity 25 at the fuel collision point P1 and the first fuel injection axis Li1. 2 Collision angle α2 increases. In the embodiment, the first and second collision angles α1 and α2 are both 90 ° or more, but the first collision angle α1 may be less than 90 °, and the second collision angle α2 is 90 ° or more. Is desirable.

  Next, the operation of the embodiment of the present invention having the above configuration will be described.

  According to the present embodiment, in an arbitrary cross section passing through the fuel injection point Oinj and orthogonal to the top surface of the piston 13, only a part of the vicinity of the fuel injection point Oinj (intersection points e1, d1, d2, e2 are surrounded). The cross-sectional shape of the cavity 25 is formed to be the same except for the other regions. In particular, since the cross-sectional shape of the cavity 25 is the same in two cross sections including the first and second fuel injection shafts Li12 and Li2 (see FIGS. 6 and 7), the air and fuel in each part of the cavity 25 are formed. The mixed state can be made uniform in the circumferential direction, and the combustion state of the air-fuel mixture can be improved to increase the engine output and reduce exhaust harmful 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.

  Of the cross section of the cavity 25 passing through the fuel injection point Oinj, the cross section that greatly affects the mixing of fuel and air is not a cross section including the piston central axis Lp but a cross section orthogonal to the top surface of the piston 13. This is because the circumferential diffusion of the fuel fine particles in the cavity 25 occurs in the direction along the top surface of the piston 13, and the cross section orthogonal to the diffusion direction is a cross section orthogonal to the top surface of the piston 13. In the present embodiment, the shape of the cavity 25 is substantially matched in an arbitrary cross section passing through the fuel injection point Oinj and orthogonal to the top surface of the piston 13, so that the mixed state of the fuel and air in each part of the cavity 25 is changed. It can be made more uniform.

  Since the intersection points d1 and d2 are located at the boundary between the bottom wall portion 25c and the top portion 25d of the cavity 25, the intersection points d1 and d2 and the intersection points e1 and e2 are made as close as possible to the piston center axis Lp. The ratio occupied in the fuel injection cross section Sn can be increased, and the variation in the mixed state of the fuel and air in each cross section in the circumferential direction of the cavity 25 can be minimized.

  FIG. 8 shows that when the direction of the fuel injection shaft is moved in the range of 60 ° to the left and right around the piston center axis Lp with the direction of the piston pin 14 as a reference (0 °), each 30 ° to the left and right of the fuel injection shaft. The rate of change of the volume of the cavity 25 in the range is shown. The solid line corresponds to the present embodiment in which the cross-sectional shape of the cavity 25 in an arbitrary cross-section orthogonal to the top surface of the piston 13 passes through the fuel injection point Oinj, and the broken line indicates the conventional example (described in Patent Document 1). Corresponding to the invention. As can be seen from the figure, the volume change rate exceeds 20% in the conventional example, whereas the volume change rate is suppressed to less than 10% in the present embodiment.

  In the present invention, the shape of the cavity 25 is substantially the same in an arbitrary cross section that passes through the fuel injection point Oinj and is orthogonal to the top surface of the piston 13. A slight change in shape such that the rate of change is less than 10%, for example, when the fuel injection cross section Sn passes through the piston center axis Lp, or when the fuel injection cross section Sn is slightly inclined from the state perpendicular to the top surface of the piston 13 Is defined as allowing.

  By the way, when the piston 13 approaches the top dead center in the compression stroke, an annular squish area SA formed between the top surface surrounding the cavity 25 of the piston 13 and the lower surface of the cylinder head 16 (see FIGS. 5 to 7). As a result, the squish flow that flows radially inward from the squish area SA toward the cavity 25 is generated. In the present embodiment, since the piston 13 has a pent roof-like top surface, the size of the squish flow becomes uneven in the circumferential direction.

  The size of the squish flow depends on the shape of the squish area SA. In the present embodiment, the squish flow is the smallest in the cross section along the piston pin 14 (see FIG. 7), and the cross section in the direction perpendicular to the piston pin 14. (See FIG. 5), the squish flow becomes the largest. Therefore, a cross section in a direction intersecting at 60 ° with respect to the piston pin 14 including the second fuel injection axis Li2 rather than the squish flow in the cross section (see FIG. 7) along the piston pin 14 including the first fuel injection axis Li1. The squish flow in FIG. 6) becomes larger.

  As apparent from FIG. 3, the reason is that the shape of the cavity 25 seen in the direction of the piston center line Lp is an elliptical shape with the major axis aligned with the direction of the piston pin 14. This is because the width W1 of the squish area SA is reduced in the cross section, and the width W2 of the squish area SA is increased in the cross section in the direction intersecting the piston pin 14 at 60 °.

  As described above, the size of the squish flow basically depends on the radial widths W1 and W2 of the squish area SA, but it can be said that it also depends on the ridge line length of the squish area SA in the radial direction. The ridge line length in the radial direction of the squish area SA is the length of a bent broken line along the squish area SA shown as a cross section, and the smaller the ridge line length, the smaller the squish flow becomes. The larger the squish flow becomes, the larger.

  Further, the size of the squish flow also depends on the squish clearance, which is the thickness of the squish area SA at the top dead center of the piston 13, and the squish flow increases when the squish clearance is small, and the squish flow increases when the squish clearance is large. Get smaller. In the present embodiment, in the cross section in the direction along the piston pin 14 (see FIG. 7), the squish clearance C1 increases and the squish flow decreases, and the cross section in the direction intersecting the piston pin 14 at 60 ° (see FIG. 6). ), The squish clearance C2 decreases and the squish flow increases.

  As described above, when the size of the squish flow becomes uneven in the circumferential direction according to the shape of the squish area SA, the squish flow is generated even if the fuel injector 23 uniformly injects fuel into the cavity 25. In the large part, the fuel is confined in the bottom of the cavity 25 and does not diffuse uniformly. Conversely, in the part where the squish flow is small, the fuel flows out of the cavity 25 and passes through the fuel injection point Oinj. Even if the cross-sectional shape of the cavity 25 is the same in any cross section orthogonal to the top surface, the advantages cannot be fully utilized, the combustion state of the air-fuel mixture deteriorates, the exhaust harmful substances increase, May occur.

  However, according to the present embodiment, the first collision angle α1 is small (close to a right angle) in a cross section with a small squish flow, that is, a cross section along the piston pin 14 including the first fuel injection axis Li1 (see FIG. 7). Therefore, the fuel that has collided with the cavity 25 is bounced back to the wall surface of the cavity 25, and the tendency to run up to the opening side along the wall surface of the cavity 25 becomes weak. Therefore, even if the squish flow is small, the fuel can be uniformly diffused inside the cavity 25 while preventing the fuel from flowing out from the opening of the cavity 25.

  Further, since the second collision angle α2 is large (obtuse angle) in a cross section where the squish flow is large, that is, a cross section in a direction intersecting with the piston pin 14 including the second fuel injection axis Li2 at 60 ° (see FIG. 6). The fuel that has collided with 25 is not rebounded to the wall surface of the cavity 25, and the tendency to run up to the opening side along the wall surface of the cavity 25 becomes strong. Therefore, even if the squish flow is large, the fuel can be uniformly diffused inside the cavity 25 while preventing the fuel from flowing out from the opening of the cavity 25.

  As described above, by making the first and second collision angles α1 and α2 different at the fuel collision points P1 and P2 at which the first and second fuel injection axes Li1 and Li2 intersect the wall surface of the cavity 25, the cavity 25 is changed. The collision fuel tends to rush toward the opening along the wall surface of the cavity 25 and the tendency that the squish flow traps the fuel in the cavity 25, and the fuel is uniformly diffused throughout the cavity 25 to the outside. Outflow can be prevented, combustion state of the air-fuel mixture can be improved, and generation of exhaust harmful substances and soot can be suppressed.

  FIG. 9 is a diagram showing changes in the amount of soot generated by the first and second collision angles α1 and α2, in which the horizontal axis represents the first collision angle α1, the vertical axis represents the second collision angle α2, and the color The dark portion indicates that the amount of soot is large. An upward straight line A passing through the origin corresponds to the first collision angle α1 = second collision angle α2, and wrinkles are generated in an area above the straight line A, that is, in a region where the second collision angle α2> the first collision angle α1. It can be seen that is decreasing. The straight line B corresponds to the second collision angle α2 = 90 °, and is an area above the straight line A and above the straight line B, that is, the second collision angle α2> the first collision angle α1 and the second collision. It can be seen that the generation of wrinkles is particularly remarkably reduced in the region where the angle α2 ≧ 90 °.

  Since the squish flow is generated before the piston 13 reaches the top dead center of the compression stroke, the timing at which the fuel injected by the fuel injector 23 collides with the cavity 25 is preferably before the top dead center. In the case of performing fuel injection a plurality of times in one cycle, the timing at which the main injection fuel that injects the largest amount of fuel collides with the cavity may be set before the top dead center.

  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, the cavity 25 of the embodiment has the same cross-sectional shape in an arbitrary cross section orthogonal to the top surface of the piston 13 through the fuel injection point Oinj, but the present invention has the same cross-sectional shape. It can also be applied to those that do not.

  In the embodiment, the fuel injectors 23 inject fuel in six directions spaced apart by 60 °, but the fuel injection directions are not limited to six directions.

  Moreover, although embodiment demonstrated the fuel direct injection diesel engine, this invention is applicable with respect to fuel direct injection engines other than a diesel engine.

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. A graph showing the rate of change of cavity volume in the range of 30 ° to the left and right of the fuel injection shaft when the direction of the fuel injection shaft is changed in the circumferential direction. The figure which shows the change of the amount of wrinkles generated by the 1st, 2nd collision angle

Explanation of symbols

13 Piston 23 Fuel Injector 25 Cavity 25c Bottom Wall C1 Squish Clearance C2 Squish Clearance Li1 First Fuel Injection Shaft Li2 Second Fuel Injection Shaft SA Squish Area W1 Squish Area Width W2 Squish Area Width α1 First Collision Angle α2 Second Collision angle

Claims (8)

The piston (13) whose height of the top surface changes in the circumferential direction, the cavity (25) recessed in the central portion of the piston (13), and the circumferential direction in the cavity (25) are separated from each other. In a fuel direct injection engine comprising a fuel injector (23) for injecting fuel along a plurality of fuel injection shafts (Li1, Li2) directed in a plurality of directions,
The size of the squish flow changes in the circumferential direction, and the squish flow is greater than the first collision angle (α1) at which the first fuel injection shaft (Li1) directed in the direction in which the squish flow is small collides with the cavity (25). The fuel direct injection engine, wherein the second fuel injection shaft (Li2) oriented in the direction in which the angle is large is set such that the second collision angle (α2) at which the second fuel injection shaft (Li2) collides with the cavity (25) is increased. The piston (13) whose height of the top surface changes in the circumferential direction, the cavity (25) recessed in the central portion of the piston (13), and the circumferential direction in the cavity (25) are separated from each other. In a fuel direct injection engine comprising a fuel injector (23) for injecting fuel along a plurality of fuel injection shafts (Li1, Li2) directed in a plurality of directions,
From the first collision angle (α1) at which the squish area (SA) changes in the circumferential direction and the first fuel injection shaft (Li1) directed in the direction in which the squish area (SA) is small collides with the cavity (25). The second fuel injection shaft (Li2) oriented in the direction in which the squish area (SA) is large is set such that the second collision angle (α2) at which the squish area (SA) collides with the cavity (25) is increased. Fuel direct injection engine. The piston (13) whose height of the top surface changes in the circumferential direction, the cavity (25) recessed in the central portion of the piston (13), and the circumferential direction in the cavity (25) are separated from each other. In a fuel direct injection engine comprising a fuel injector (23) for injecting fuel along a plurality of fuel injection shafts (Li1, Li2) directed in a plurality of directions,
The width (W1, W2) of the squish area (SA) changes in the circumferential direction, and the first fuel injection shaft (Li1) directed in the direction in which the width (W1) is small collides with the cavity (25). The second collision angle (α2) at which the second fuel injection shaft (Li2) directed in the direction in which the width (W2) is larger than the collision angle (α1) collides with the cavity (25) is set to be larger. A fuel direct injection engine characterized by that. The piston (13) whose height of the top surface changes in the circumferential direction, the cavity (25) recessed in the central portion of the piston (13), and the circumferential direction in the cavity (25) are separated from each other. In a fuel direct injection engine comprising a fuel injector (23) for injecting fuel along a plurality of fuel injection shafts (Li1, Li2) directed in a plurality of directions,
A ridge line length of the squish area (SA) changes in the circumferential direction, and a first collision angle (α1) at which the first fuel injection shaft (Li1) directed in a direction in which the ridge line length is small collides with the cavity (25). ), The second collision angle (α2) at which the second fuel injection shaft (Li2) directed in the direction in which the ridge line length is larger collides with the cavity (25) is set larger. Fuel direct injection engine. The piston (13) whose height of the top surface changes in the circumferential direction, the cavity (25) recessed in the central portion of the piston (13), and the circumferential direction in the cavity (25) are separated from each other. In a fuel direct injection engine comprising a fuel injector (23) for injecting fuel along a plurality of fuel injection shafts (Li1, Li2) directed in a plurality of directions,
The first collision angle (α1) at which the squish clearance (C1, C2) changes in the circumferential direction and the first fuel injection shaft (Li1) directed in the direction in which the squish clearance (C1) is large collides with the cavity (25). ) Is set such that the second collision angle (α2) at which the second fuel injection shaft (Li2) oriented in the direction in which the squish clearance (C2) is smaller collides with the cavity (25) is larger. Fuel direct injection engine.   The fuel direct injection engine according to any one of claims 1 to 5, wherein the second collision angle (α2) is 90 ° or more. A section of the cavity (25) passing through the nth fuel injection axis (Li1, Li2) is defined as a fuel injection section Sn,
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 section Sn, and the first and third fixed points An and Cn are connected to the fuel injection section Sn. The cross-sectional shape surrounded by the path AnCn connecting along the wall surface of the cavity (25) and the path BnCn connecting the second and third specific points Bn and Cn with the shortest straight line is substantially equal in each fuel injection cross section Sn. The direct fuel injection engine according to any one of claims 1 to 6, wherein   8. The fuel according to claim 1, wherein the fuel injected by the fuel injector (23) collides with the cavity (25) before top dead center of the piston (13). Direct fuel injection engine.

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