JP4801826B2 - Direct fuel injection engine - Google Patents

Description

  The present invention provides a piston whose top surface varies in the circumferential direction, such as a pent roof type piston, a cavity recessed in the center of the piston, and a plurality of directions spaced in the circumferential direction within the cavity. The present invention relates to a fuel direct injection engine including a fuel injector that injects fuel along a plurality of fuel injection shafts that are directed toward the fuel cell.

  In an engine equipped with a pent roof type piston, the magnitude of the reverse squish flow that flows from the cavity toward the outer periphery of the piston when the piston starts to descend from top dead center tends to be uneven in the circumferential direction. There is a possibility that the fuel stays at the bottom of the cavity at a portion where the reverse squish flow is small, or the fuel flows out of the cavity at a portion where the reverse squish flow is large.

In order to solve this problem, in the region where the reverse squish flow is small, the fuel injection angle measured downward from the direction of the opening end of the cavity is decreased to inject fuel into a shallow position of the cavity, and in the region where the reverse squish flow is large. A fuel and air mixing state is made uniform over the entire cavity regardless of the size of the reverse squish flow by increasing the fuel injection angle and injecting the fuel into a deep position of the cavity. Proposed by reference 1.
JP 2008-255935 A

  By the way, in the above conventional one, two of the six fuel injection shafts of the fuel injector are oriented along the top (ridge line) of the top surface of the pent roof type piston, but the direction along the top of the piston. Is a direction in which the squish flow becomes remarkably small, so it cannot be compensated only by the change in the fuel injection angle, and the fuel injected along the fuel injection axis directed in the direction along the top of the piston moves upward in the cavity. It becomes difficult to wind up, and there is a possibility that unused air is generated above the fuel injection shaft.

  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 reverse squish flow is uneven in the circumferential direction, the mixed state of fuel and air in the cavity is further improved. The purpose is to make it uniform.

In order to achieve the above object, according to the invention described in claim 1, a piston in which the height of the top surface changes in the circumferential direction, and a cavity recessed in the center of the top surface of the piston, A fuel injector for injecting fuel along a plurality of fuel injection shafts oriented in a plurality of directions spaced apart in the circumferential direction in the cavity, and an angle between the injection shafts formed by two fuel injection shafts adjacent to each other. In the direct fuel injection engine in which the directions of the plurality of fuel injection shafts are set to be substantially uniform between the angles between the injection shafts, the magnitude of the reverse squish flow generated when the piston descends from the top dead center There were changes in the circumferential direction, wherein a direction of the plurality of fuel injection axes, and set off the direction in which the direction and the maximum reverse squish flow is minimized, the plurality with respect to a direction reverse squish flow is minimized Fuel injection shaft When the angle formed is the first separation angle and the angle formed by the plurality of fuel injection shafts with respect to the direction in which the reverse squish flow is maximum is the second separation angle, the minimum of the first and second separation angles The direction of the plurality of fuel injection shafts is set so as to maximize the separation angle, and the squish area changes in the circumferential direction so that the squish area is minimized and the reverse squish flow is minimized. The fuel injection shafts that are oriented in the direction in which the squish area is larger than the fuel injection angle that the fuel injection shafts that coincide and direct in the direction in which the squish area is small with respect to the direction of the opening end of the cavity And the number n of the plurality of fuel injection shafts is an even number not a multiple of 4 or an odd number of 3 or more, and the number n is 4 When the number is an even number that is not a multiple, the direction of the plurality of fuel injection shafts is set so that the minimum separation angle is 360 ° / 4n, and when the number n is an odd number of 3 or more, the minimum separation angle A fuel direct injection engine is proposed in which the directions of the plurality of fuel injection shafts are set so that the angle becomes 360 ° ÷ 8n .

According to the first aspect of the present invention, in the engine in which the magnitude of the reverse squish flow that flows from the cavity toward the outer periphery of the piston changes in the circumferential direction, the fuel is injected from the fuel injector into the cavity at a uniform angle between the injection axes. The direction of the plurality of fuel injection shafts to be injected is set so as to deviate from the direction in which the reverse squish flow is minimized and the direction in which the reverse squish flow is maximized. It is difficult for the fuel injected from the outside of the cavity to roll up outside the cavity, and the generation of unused air above the fuel injection shaft is prevented, and the mixed state of fuel and air in the cavity becomes partially uneven. It can be prevented, and since the reverse squish flow is set by removing the direction that maximizes directed to a direction in which the reverse squish flow is maximized Charge fuel injected from the injection shaft is rolled up strongly to the outside of the cavity can be mixed state of the fuel and air in the cavity is prevented from being partially uneven.

The angle formed by the plurality of fuel injection shafts with respect to the direction in which the reverse squish flow is minimized is defined as the first separation angle, and the angle formed by the plurality of fuel injection shafts with respect to the direction in which the reverse squish flow is maximized is defined as the second separation angle. Since the direction of the plurality of fuel injection shafts is set so as to maximize the minimum separation angle between the first and second separation angles, the reverse squish flow is minimized in the direction of the fuel injection shaft. It is possible to make the mixed state of the fuel and air in the cavity uniform by moving as far as possible from both the direction and the maximum direction.

In addition, the fuel injection angle decreases in the direction where the reverse squish flow is small (ie, the direction where the squish area is small) and the fuel is injected into a shallow position of the cavity, and the fuel is injected in the direction where the reverse squish flow is large (ie where the squish area is large) Since the angle is increased and the fuel is injected deep into the cavity, the mixed state of fuel and air can be made uniform over the entire cavity regardless of the magnitude of the reverse squish flow.

In particular, when the number n of the plurality of fuel injection shafts is an even number that is not a multiple of 4 or an odd number that is 3 or more, and the number n is an even number that is not a multiple of 4, the minimum separation angle is 360 ° / 4n. When the direction of a plurality of fuel injection shafts is set and the number n is an odd number of 3 or more, the direction of the plurality of fuel injection shafts is set so that the minimum separation angle is 360 ° ÷ 8n. The separation angle can be easily calculated.

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

  1 to 9 show a first embodiment of the present invention. FIG. 1 is a longitudinal sectional view of an essential part of a diesel engine, FIG. 2 is a view taken along line 2-2 in FIG. 1, and FIG. 4 is 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. 7 is a cross-sectional view taken along line 7-7, FIG. 8 is a view showing first to third fuel injection cross sections of the cavity, and FIG. 9 is a left-right view of the fuel injection shaft when the direction of the fuel injection shaft is changed in the circumferential direction. It is a graph which shows the change rate of the cavity volume of the range of 30 degrees.

  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.

  As apparent from FIGS. 3 and 4, the fuel injector 23 arranged along the piston central axis Lp has a circumferential direction around the fuel injection point Oinj that is a virtual point on the piston central axis Lp. Fuel is injected in six directions arranged at a fuel injection shaft interval β (see FIG. 3). The directions of the first to sixth fuel injection axes Li <b> 1 to Li <b> 6 do not coincide with the direction of the piston pin 14 (the direction of the top portions 13 a and 13 a of the piston 14) nor the direction orthogonal to the direction of the piston pin 14. Further, the first to sixth fuel injection axes Li1 to Li6 are inclined obliquely downward as viewed in the direction perpendicular to the piston center axis Lp, and the downward degree is smaller as the fuel injection axis is closer to the direction of the piston pin 14. The fuel injection axis that is closer to the direction orthogonal to the direction of the piston pin 14 is larger.

  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, FIG. 6 is a cross section in a direction intersecting the piston pin 14 at 60 °, and FIG. 7 is a cross section in a direction along the piston pin 14. .

  What is important here is that the cross sections in FIGS. 5 to 7 are cross sections in the direction perpendicular to the top surface (that is, the inclined surfaces 13b and 13b) 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 in FIG. 6 at 60 ° is orthogonal to the top surface of the piston 13 and does not include the piston central 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.

  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 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 that is 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.

  FIG. 8A shows a cross section (first fuel injection cross section S1) of the cavity 25 including the first and fourth fuel injection shafts Li1 and Li4 closest to the direction of the piston pin 14, and FIG. FIG. 8C shows the cross section of the cavity 25 (second fuel injection cross section S2) including the third and sixth fuel injection shafts Li3 and Li6 that are second closest to the direction of the piston pin 14, and FIG. 6 schematically shows a cross section (third fuel injection cross section S3) of the cavity 25 including the second and fifth fuel injection shafts Li2 and Li5 farthest from (closest to the direction orthogonal to the direction of the piston pin 14).

  In the first fuel injection cross section S1 of FIG. 8A, the point where the first and fourth fuel injection axes Li1 and Li4 intersect the wall surface of the cavity 25 is defined as a fuel collision point P1, and the second fuel of FIG. In the injection section S2, the point where the third and sixth fuel injection axes Li3 and Li6 intersect the wall surface of the cavity 25 is defined as a fuel collision point P2, and in the third fuel injection section S3 in FIG. A point where the five fuel injection axes Li2 and Li5 intersect with the wall surface of the cavity 25 is defined as a fuel collision point P3. The three fuel collision points P1, P2, and P3 are present at different positions on the shaded first to third fuel injection sections S1 to S3 having the same shape.

  That is, in the second fuel injection cross section S2, the position corresponding to the fuel collision point P1 in the first fuel injection cross section S1 is P2 ', but the actual fuel collision point P2 is lower than P2' (deep in the cavity 25). Position). Therefore, compared with the first fuel injection angle α1 formed by the first and fourth fuel injection axes Li1 and Li4 with respect to the straight line connecting the fuel injection point Oinj and the first specific point An that defines the opening end of the cavity 25. The second fuel injection angle α2 formed by the third and sixth fuel injection axes Li3 and Li6 increases.

  In the third fuel injection section S3, the position corresponding to the fuel collision point P2 in the second fuel injection section S2 is P3 ′, but the actual fuel collision point P3 is lower than P3 ′ (a position where the cavity 25 is deep). ). Therefore, compared to the second fuel injection angle α2 formed by the third and sixth fuel injection axes Li3 and Li6 with respect to the straight line connecting the fuel injection point Oinj and the first specific point An that defines the opening end of the cavity 25. The third fuel injection angle α3 formed by the second and fifth fuel injection axes Li2 and Li5 increases.

  In other words, on the first fuel injection surface S1 in FIG. 8A, the first and fourth fuel injection shafts Li1 and Li4 are directed to the shallow position of the cavity 25 (position close to the opening end), and in FIG. In the third fuel injection surface S3, the second and fifth fuel injection shafts Li2 and Li5 are directed to a deep position of the cavity 25 (position close to the bottom wall), and in the second fuel injection surface S2 of FIG. The sixth fuel injection shafts Li3 and Li6 are directed to a middle deep position of the cavity 25.

  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 cavity 25 is formed to have the same cross-sectional shape except for the region), so that the air and fuel mixing state in each part of the cavity 25 is made uniform in the circumferential direction, and the combustion state of the mixture is improved. It is possible to increase 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. 9 shows that when the direction of the fuel injection shaft is moved to the left and right within the range of 60 ° around the piston central axis Lp with the direction of the piston pin 14 as a reference (0 °), each 30 ° 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 corresponds to a comparative example that does not have the configuration. To do. 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. Further, when the piston 13 starts to descend from the top dead center, the volume of the squish area SA increases, and a reverse squish flow that flows radially outward from the cavity 25 toward the squish area SA is generated. At each position in the circumferential direction of the piston 13, the squish flow and the reverse squish flow are in opposite directions and have substantially the same size, but in this embodiment, the piston 13 has a pent roof-like top surface. Thus, the size of the squish flow and the reverse squish flow becomes uneven in the circumferential direction.

  The size of the reverse squish flow depends on the shape of the squish area SA, and in the present embodiment, the reverse squish flow is the smallest in the cross section in the direction along the piston pin 14 (see FIG. 7), and the direction orthogonal to the piston pin 14 The reverse squish flow becomes the largest in the cross section (see FIG. 5). Therefore, the reverse squish flow in the first fuel injection cross section S1 (see FIG. 8A) including the first and fourth fuel injection shafts Li1 and Li4 close to the direction of the piston pin 14 is small and orthogonal to the direction of the piston pin 14. The reverse squish flow in the third fuel injection cross section S3 (see FIG. 8C) including the second and fifth fuel injection shafts Li2 and Li5 close to the direction of travel is large, and the third and sixth fuel injection shafts Li3 and Li6 The reverse squish flow in the second fuel injection cross section S2 including (see FIG. 8B) has an intermediate size.

  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 W of the squish area SA is reduced to W1 in the cross section, and the width W of the squish area SA is increased to W2 in the cross section perpendicular to the piston pin 14.

  Thus, the magnitude of the reverse squish flow basically depends on the radial width W of the squish area SA, but it can also be said that it depends on the radial ridgeline length of the squish area SA. 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 reverse squish flow, and the ridge line length. The larger the is, the larger the reverse squish flow becomes.

  Further, the magnitude of the reverse squish flow also depends on the squish clearance C, which is the thickness of the squish area SA at the top dead center of the piston 13. When the squish clearance C is small, the reverse squish flow becomes large and the squish clearance C is If it is large, the reverse squish flow becomes small. In the present embodiment, in the cross section in the direction along the piston pin 14 (see FIG. 7), the squish clearance C becomes larger as C1 and the reverse squish flow becomes small, and the cross section in the direction perpendicular to the piston pin 14 (see FIG. 5). ), The squish clearance C is reduced to C2, and the reverse squish flow is increased.

  As described above, if the size of the reverse squish flow becomes non-uniform in the circumferential direction according to the shape of the squish area SA, the reverse squish will be applied even if the fuel injector 23 uniformly injects fuel into the cavity 25. In the portion where the flow is large, the fuel is sucked out from the opening end of the cavity 25, and conversely, in the portion where the reverse squish flow is small, the fuel stays at the bottom 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 of the gas, the advantage cannot be fully utilized, the combustion state of the air-fuel mixture deteriorates, the exhaust harmful substances increase, There is a possibility of wrinkles.

  However, according to the present embodiment, the direction of the piston pin 14 in which the reverse squish flow becomes the smallest in the first fuel injection cross section S1 including the first and fourth fuel injection shafts Li1 and Li4 on the side where the reverse squish flow is small. The first fuel injection angle α1 in the first fuel injection cross section S1 is decreased and the fuel is injected into a shallow position of the cavity 25, so that the fuel stays at the bottom of the cavity 25 even if the reverse squish flow is small. And the fuel can be more evenly diffused inside the cavity 25.

  Further, the third fuel injection cross section S3 including the second and fifth fuel injection shafts Li2 and Li5 on the side where the reverse squish flow is large is shifted from the direction orthogonal to the direction of the piston pin 14 where the reverse squish flow is the largest, By increasing the third fuel injection angle α3 in the third fuel injection cross section S3 and injecting the fuel into a deep position of the cavity 25, the fuel is prevented from flowing out of the cavity 25 even if the reverse squish flow is large. Can be uniformly diffused inside the cavity 25.

  As described above, the injected fuel is obtained by rotating the first and sixth fuel injection shafts Li1 to Li6 clockwise by a rotation angle of 15 ° and making the first to third fuel injection angles α1 to α3 different. In the bottom of the cavity 25 and the tendency of the reverse squish flow to suck out the fuel from the cavity 25, the fuel is uniformly diffused throughout the cavity 25 to prevent outflow to the outside, and the air-fuel mixture This can improve the combustion state of the exhaust gas and suppress the generation of exhaust harmful substances and soot.

  By the way, in this Embodiment, the direction of the 1st-6th fuel-injection axis | shaft Li1-Li6 is the direction (direction where a reverse squish flow becomes the minimum) of the piston pin 14, and the direction orthogonal to the direction of the piston pin 14 ( In the direction in which the reverse squish flow is maximized) and in a direction away from the maximum. That is, in FIG. 10B, when the number n of fuel injection shafts is n = 6, the direction of the first fuel injection shaft Li1 is shifted by 15 ° clockwise relative to one of the directions of the piston pin 14 serving as a reference. As described above, the six first fuel injection shafts Li1 to Li6 are rotated by 15 °.

  As a result, the first separation angle γ1 formed by the directions of the first and fourth fuel injection axes Li1 and Li4 with respect to the direction of the piston pin 14 is γ1 = 15 °, and with respect to the direction orthogonal to the direction of the piston pin 14 The second separation angle γ2 formed by the directions of the second and fifth fuel injection axes Li2 and Li5 is γ2 = 15 °, and the reverse squish flow is minimized in the directions of the first to sixth fuel injection axes Li1 to Li6. The direction of the piston pin 14 and the direction orthogonal to the direction of the piston pin 14 where the reverse squish flow is maximized can be separated to the maximum.

  Thus, in the case of n = 6, the first fuel injection shaft Li1 is rotated in the clockwise direction by the rotation angle = 15 ° with respect to one of the reference piston pin 14 directions. Since the direction of the six fuel injection shafts Li1 to Li6 can be maximally separated from the direction in which the reverse squish flow becomes the minimum and the direction in which the reverse squish flow becomes the maximum, the reverse squish flow is excessively small. Is retained in the cavity 25 to prevent the amount of unused air above the cavity 25 from increasing, and the reverse squish flow is excessive, so that the fuel is rolled up toward the inside of the cavity 25 to the outside. The fuel can be prevented from flowing out, and the fuel can be diffused more uniformly throughout the cavity 25.

  Increasing the first separation angle γ1 of one fuel injection shaft decreases the first separation angle γ1 of the other fuel injection shaft, and increasing the second separation angle γ2 of one fuel injection shaft increases the other fuel injection shaft. When the second separation angle γ2 of the fuel injection shaft decreases and the first separation angle γ1 of one fuel injection shaft increases, the second separation angle γ2 of the other fuel injection shaft decreases, and the second separation angle of one fuel injection shaft Increasing γ2 may decrease the first separation angle γ1 of the other fuel injection shaft. Therefore, in order to maximize the minimum separation angle among the first and second separation angles γ1 and γ2 of all the fuel injection shafts, that is, the first to sixth fuel injection shafts Li1 to Li6 generate a reverse squish flow. In order to be as far as possible from the minimum and maximum directions, when the number of fuel injection shafts n = 6, the direction of the first fuel injection shaft Li1 is 15 ° clockwise from the direction of the piston pin 14. Rotate.

  Next, the relationship between the number n of fuel injection shafts and the rotation angle of the fuel injection shaft will be considered.

  As shown in FIG. 10, when the number n of fuel injection axes is an even number that is not a multiple of 4, that is, n = 2, n = 6, n = 10,..., The rotation angle is calculated at 360 ° / 4n.

  FIG. 10A shows the case of n = 2, and in this case, the rotation angle = 360 ° / 8 = 45 °. Therefore, the first separation angle γ1 formed by the directions of the first and second fuel injection axes Li1 and Li2 with respect to the direction of the piston pin 14 is 45 °, and is the first with respect to the direction orthogonal to the direction of the piston pin 14. The second separation angle γ2 formed by the directions of the second fuel injection axes Li1 and Li2 is 45 °, and the direction of the first and second fuel injection axes Li1 and Li2 is the direction of the piston pin 14 that minimizes the reverse squish flow. And the direction perpendicular to the direction of the piston pin 14 where the reverse squish flow is maximized.

  FIG. 10B shows a case where n = 6. In this case, the rotation angle = 360 ° / 24 = 15 °, and the first and fourth fuel injection shafts Li 1, Li 4 with respect to the direction of the piston pin 14. The first separation angle γ1 formed by the direction of is 15 °, and the second separation angle γ2 formed by the directions of the second and fifth fuel injection axes Li2 and Li5 with respect to the direction orthogonal to the direction of the piston pin 14 is 15 °. And the directions of the first to sixth fuel injection axes Li1 to Li6 with respect to the direction of the piston pin 14 that minimizes the reverse squish flow and the direction orthogonal to the direction of the piston pin 14 that maximizes the reverse squish flow Can be separated as much as possible.

  FIG. 10C shows a case where n = 10. In this case, the rotation angle = 360 ° / 40 = 9 °, and the first and sixth fuel injection shafts Li1, Li6 with respect to the direction of the piston pin 14 are shown. The first separation angle γ1 formed by the direction of is 9 °, and the second separation angle γ2 formed by the directions of the third and eighth fuel injection axes Li3 and Li8 with respect to the direction orthogonal to the direction of the piston pin 14 is 9 °. And the directions of the first to tenth fuel injection axes Li1 to Li10 with respect to the direction of the piston pin 14 that minimizes the reverse squish flow and the direction orthogonal to the direction of the piston pin 14 that maximizes the reverse squish flow Can be separated as much as possible.

  As shown in FIG. 11, when the number n of fuel injection shafts is a multiple of 4, that is, when n = 4, n = 8, n = 12,..., The rotation angle is calculated at 360 ° / 2n.

  FIG. 11A shows a case where n = 4. In this case, the rotation angle = 360 ° / 8 = 45 °. Therefore, the first separation angle γ1 formed by the directions of the first to fourth fuel injection axes Li1 to Li4 with respect to the direction of the piston pin 14 is 45 °, and is the first with respect to the direction orthogonal to the direction of the piston pin 14. The second separation angle γ2 formed by the directions of the fourth fuel injection axes Li1 to Li4 is 45 °, and the direction of the first to fourth fuel injection axes Li1 to Li6 is the direction of the piston pin 14 that minimizes the reverse squish flow. And the direction perpendicular to the direction of the piston pin 14 where the reverse squish flow is maximized.

  FIG. 11B shows a case where n = 8, and in this case, the rotation angle = 360 ° / 16 = 22.5 °, and the first, fourth, fifth, The first separation angle γ1 formed by the directions of the eighth fuel injection axes Li1, Li4, Li5, and Li8 is 22.5 °, and the second, third, sixth, and second directions are perpendicular to the direction of the piston pin 14. The second separation angle γ2 formed by the directions of the seventh fuel injection axes Li2, Li3, Li6, and Li7 is 22.5 °, and the reverse squish flow is minimized in the directions of the first to eighth fuel injection axes Li1 to Li8. The direction of the piston pin 14 and the direction orthogonal to the direction of the piston pin 14 where the reverse squish flow is maximized can be separated as much as possible.

  FIG. 11C shows a case where n = 12, and in this case, the rotation angle = 360 ° / 24 = 15 °, and the first, sixth, seventh and twelfth directions with respect to the direction of the piston pin 14. The first separation angle γ1 formed by the directions of the fuel injection axes Li1, Li6, Li7, Li12 is 15 °, and the third, fourth, ninth, and tenth fuel injections with respect to the direction orthogonal to the direction of the piston pin 14 The second separation angle γ2 formed by the directions of the axes Li3, Li4, Li9, and Li10 is 15 °, and the directions of the first to twelfth fuel injection axes Li1 to Li12 are the direction of the piston pin 14 that minimizes the reverse squish flow. , It can be separated to the maximum with respect to the direction orthogonal to the direction of the piston pin 14 where the reverse squish flow is maximized.

  As shown in FIG. 12, when the number n of fuel injection shafts is an odd number of 3 or more, that is, when n = 3, n = 5, n = 7, n = 9, n = 11..., The rotation angle is 360 °. It is calculated by / 8n. Note that when n = 1 (when there is one fuel injection shaft), the diffusion of fuel in the cavity 25 becomes extremely non-uniform and is excluded.

  FIG. 12A shows a case where n = 3. In this case, the rotation angle = 360 ° / 24 = 15 °. Therefore, the first separation angle γ1 formed by the direction of the first fuel injection axis Li1 with respect to the direction of the piston pin 14 is 15 °, and the direction of the third fuel injection axis Li3 with respect to the direction orthogonal to the direction of the piston pin 14 The second separation angle γ2 formed by the direction is 15 °, the direction of the first to third fuel injection axes Li1 to Li3 is the direction of the piston pin 14 that minimizes the reverse squish flow, and the piston that maximizes the reverse squish flow. The distance from the direction perpendicular to the direction of the pin 14 can be maximized.

  FIG. 12B shows a case where n = 5. In this case, the rotation angle = 360 ° / 40 = 9 °, and the direction of the first fuel injection axis Li1 is formed with respect to the direction of the piston pin 14. The first separation angle γ1 is 9 °, and the second separation angle γ2 formed by the direction of the second fuel injection shaft Li2 with respect to the direction orthogonal to the direction of the piston pin 14 is 9 °, and the first to fifth fuel injection shafts. The directions of Li1 to Li5 can be maximally separated from the direction of the piston pin 14 in which the reverse squish flow is minimized and the direction orthogonal to the direction of the piston pin 14 in which the reverse squish flow is maximized.

  FIG. 12C shows a case where n = 7. In this case, the rotation angle = 360 ° / 56 = 6.43 °, and the direction of the first fuel injection axis Li1 is relative to the direction of the piston pin 14. The first separation angle γ1 formed is 6.43 °, and the second separation angle γ2 formed by the direction of the sixth fuel injection axis Li6 with respect to the direction orthogonal to the direction of the piston pin 14 is 6.43 °. The direction of the seventh fuel injection shafts Li1 to Li7 is maximized with respect to the direction of the piston pin 14 at which the reverse squish flow is minimized and the direction orthogonal to the direction of the piston pin 14 at which the reverse squish flow is maximized. Can be separated.

  FIG. 12D shows the case of n = 9. In this case, the rotation angle = 360 ° / 72 = 5 °, and the direction of the first fuel injection axis Li1 is formed with respect to the direction of the piston pin 14. The first separation angle γ1 is 5 °, and the second separation angle γ2 formed by the direction of the third fuel injection shaft Li3 with respect to the direction orthogonal to the direction of the piston pin 14 is 5 °, and the first to ninth fuel injection shafts. The directions of Li1 to Li9 can be maximally separated from the direction of the piston pin 14 in which the reverse squish flow is minimized and the direction orthogonal to the direction of the piston pin 14 in which the reverse squish flow is maximized.

  FIG. 12E shows a case where n = 11. In this case, the rotation angle = 360 ° / 88 = 4.09 °, and the direction of the first fuel injection shaft Li1 is relative to the direction of the piston pin 14. The first separation angle γ1 formed is 4.09 °, and the second separation angle γ2 formed by the direction of the ninth fuel injection axis Li9 with respect to the direction orthogonal to the direction of the piston pin 14 is 4.09 °, The direction of the eleventh fuel injection axes Li1 to Li11 is maximized with respect to the direction of the piston pin 14 at which the reverse squish flow is minimized and the direction orthogonal to the direction of the piston pin 14 at which the reverse squish flow is maximized. Can be separated.

  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.

  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.

  In the embodiment, the fuel injection shaft interval β, which is the interval between two adjacent fuel injection shafts among the plurality of fuel injection shafts arranged in an umbrella shape, is an angle when viewed in the piston center line Lp direction. Although defined, the fuel injection shaft interval β may be defined as an angle actually formed by two adjacent fuel injection shafts.

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 which shows the 1st-3rd fuel injection cross section of a cavity. 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 rotation angle of the fuel injection shaft and the first and second separation angles γ1, γ2 when the number of fuel injection shafts is a multiple of 2 and not a multiple of 4. The figure which shows the rotation angle of a fuel-injection axis when the number of fuel-injection axes is a multiple of 4, and 1st, 2nd separation angles (gamma) 1, (gamma) 2. The figure which shows the rotation angle of the fuel injection shaft when the number of fuel injection shafts is an odd number of 3 or more, and the first and second separation angles γ1, γ2.

13 Piston 13a Top 13b Slope 23 Fuel injector 25 Cavity C Squish clearance Li1, Li2 ... Fuel injection axis SA Squish area W Squish area width α Fuel injection angle β Injection axis angle γ1 First separation angle (separation angle)
γ2 Second separation angle

Claims (1)

Piston (13) in which the height of the top surface changes in the circumferential direction, cavity (25) recessed in the center of the top surface of the piston (13), and circumferential direction in the cavity (25) A fuel injector (23) for injecting fuel along a plurality of fuel injection shafts (Li1, Li2...) Directed in a plurality of directions spaced apart from each other.
The plurality of fuel injection shafts (Li1) so that an injection shaft angle (β) formed by two fuel injection shafts (Li1, Li2...) Adjacent to each other is substantially uniform between the injection shaft angles (β). , Li2 ...) in the direct fuel injection engine in which the direction is set,
The magnitude of the reverse squish flow generated when the piston (13) descends from the top dead center changes in the circumferential direction, and the reverse squish flow flows in the direction of the plurality of fuel injection shafts (Li1, Li2,...). set Remove the direction in which the direction and the maximum becomes the minimum,
An angle formed by the plurality of fuel injection shafts (Li1, Li2,...) With respect to the direction in which the reverse squish flow is minimized is defined as a first separation angle (γ1), and the plurality of the plurality of fuel injection shafts (Li1, Li2. When the angle formed by the fuel injection axes (Li1, Li2,...) Is the second separation angle (γ2), the smallest separation angle (γ1, γ2) of the first and second separation angles (γ1, γ2) is Set the direction of the plurality of fuel injection shafts (Li1, Li2...) To maximize,
The squish area (SA) changes in the circumferential direction, and the direction in which the squish area (SA) is minimized coincides with the direction in which the reverse squish flow is minimized.
The fuel injection shaft (Li1, Li2,...) Oriented in the direction in which the squish area (SA) is smaller than the fuel injection angle (α) formed with respect to the direction of the opening end of the cavity (25). SA) is set so that the fuel injection angle (α) formed by the fuel injection shafts (Li1, Li2,...) Oriented in the direction in which SA) is large with respect to the direction of the opening end of the cavity (25) is large;
The number n of the plurality of fuel injection shafts (Li1, Li2,...) Is an even number that is not a multiple of 4 or an odd number that is not less than 3, and when the number n is an even number that is not a multiple of 4, the minimum separation angle is 360 °. The direction of the plurality of fuel injection shafts (Li1, Li2,...) Is set to be ÷ 4n, and when the number n is an odd number of 3 or more, the minimum separation angle is 360 ° ÷ 8n. A direct fuel injection engine characterized in that the directions of the plurality of fuel injection shafts (Li1, Li2,...) Are set .

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