JP2016121573A - Internal combustion engine piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent atomization fuel from being adhered at a piston having a concavity part formed at its top surface without reducing a compression ratio.SOLUTION: A concavity part 9 is constituted of the first group of concave grooves 7 facing toward an opening of a fuel injection hole of an injector 5 and the second group of concave grooves 8 positioned between the adjoining first concave grooves 7. The concavity part 9 is formed in such a shape that outer ends 7a of the first concave grooves 7 are protruded outward in a radial direction and outer ends 8a of the second concave grooves 8 are also protruded toward a center of axis 10 to make a petal having their irregularities continuous in smooth. A central part 11 of the concavity part 9 has substantially the same depth over its entire circumference and the first concave grooves 7 are deeper than the second concave grooves 8 as they are far away from the central part 11. Since a dispersion distance of the atomized fuel can be increased without increasing a volume of the concavity part 9, it is possible to prevent adhesion of fuel without changing the compression ratio.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a piston mainly used in a diesel engine.

  In a diesel engine, fuel is injected into a combustion chamber (cylinder) by an injector. In the injector, a large number of fuel injection holes are formed so as to jump in the circumferential direction, and the fuel ejected from each fuel injection hole is atomized and diffuses away from the fuel injection holes.

  In a diesel engine, atomized fuel reacts with air (oxygen) during combustion and burns, but there is a phenomenon in which combustion diffuses. In order to improve fuel dispersibility and equalize combustion, pistons A recess is formed on the top surface of the.

  As an example, in Patent Document 1, while forming the injector in a rotary manner, the outer shape of the recess is formed into a petal shape in which the concave portion far from the axial center and the protruding portion close to the axial center are smoothly continuous, It is disclosed that the fuel is ejected toward the protrusion in the high load region, and the fuel is ejected toward the recess in the middle and low load region.

  That is, in Patent Document 1, by causing fuel to collide with the outer end of the concave portion and igniting it in the middle and low load region, while suppressing the entrainment of air, the entrainment of combustion gas is promoted and the generation of nitrogen oxides is suppressed. On the other hand, in the high load region, the fuel is collided with the outer end of the protrusion and ignited, thereby promoting the introduction of air and suppressing the entrainment of combustion gas to prevent the generation of smoke.

JP 04-228846 A

  Now, since the speed of the fuel jetted from the injector decreases in proportion to the distance, if the piston has a certain size, the fuel burns without adhering to the inner peripheral wall of the recess. In the case of an internal combustion engine such as 3-4 cylinders with a displacement of 1000 cc or less, the diameter of the piston is small, so the fuel collides with the inner peripheral surface of the recess before the atomization completely, and the atomization is insufficient Or the fuel adhering to the inner surface of the outer periphery of the recess may cause incomplete combustion and cause smoke.

  In this regard, it is considered that the size of the recess should be as large as possible. However, if the size of the recess is increased, the volume of the recess may increase and the compression ratio may decrease.

  The present invention has been made in view of such a situation, and it is possible to accurately prevent or suppress the adhesion of fuel to the inner peripheral surface of the recess without increasing the volume of the recess. It is the purpose.

  The present invention relates to a piston used in an internal combustion engine having an injector in which fuel injection holes are formed in a circumferential direction.

The piston has, on its top surface, a group of first concave grooves facing the opening direction of the fuel injection holes of the injector and a second concave groove facing the outside between the adjacent fuel injection holes of the injector. Are formed so as to be continuous with each other, and an outer periphery of a recess formed by the group of the first concave grooves and the group of the second concave grooves is the first concave when viewed from the axial direction. The outer end of the groove is concave toward the axial center, and the outer end of the second concave groove has a curved continuous petal shape so that it protrudes toward the axial center.
Furthermore, each said 1st ditch | groove and each 2nd ditch | groove are the same depth in the center part near an axial center, and the depth of a 1st ditch | groove is the depth of a 2nd ditch | groove, so that it distances from a center part. The adjacent first groove and second groove are smoothly continuous in the circumferential direction.

  The inner surface of the outer end of each concave groove may be substantially parallel to the axis of the piston, or may be inclined so as to move away from the axis as approaching the top surface. Or it is also possible to form it in the state where it was beaten in the radial direction so that the location of the top surface overhangs toward the axis.

  In the present invention, the recess has a petal shape so that the first groove located in the fuel ejection area extends far from the axis, so that the distance at which the fuel scatters without increasing the volume of the recess. Can be increased. For this reason, even in a piston of a small displacement multi-cylinder internal combustion engine, it is possible to prevent or significantly suppress the occurrence of smoke by preventing the fuel from adhering to the inner surface without causing a reduction in the compression ratio. .

  In Patent Document 1, the location of the protrusion is deeper than the location of the recess at the center location, and the location of the recess is greater than the location of the projection at the midway portion away from the axis. The depth is changing. Therefore, the relationship between the valley and the ridge line is different between the central portion and the outer peripheral portion, and for this reason, the bottom surface of the concave portion has a complicated shape. There is concern that the propagation of the flame is suppressed, leading to incomplete combustion and a reduction in the combustion rate.

  On the other hand, in the present invention, the first concave groove and the second concave groove have the same depth at the central portion of the piston, and the first concave groove and the second concave portion adjacent to each other outside the central portion. Since the depth of the groove is different from that of the groove, the bottom surface of the recess has a relatively simple and smooth shape. For this reason, it is smoothly performed that a part of the fuel sprayed in the first concave groove flows into the second concave groove, and that the flame propagates from the first concave groove to the second concave groove. Thereby, it can contribute to complete combustion and combustion speed increase, and can contribute to the improvement of output and the improvement of fuel consumption.

It is a figure which shows embodiment, (A) is a top view, (B) is the figure which expanded the (A) partially and displayed the atomized fuel. (A) is the figure which displayed the atomized fuel by overlapping the II'-II 'sectional view of FIG. 1 (A) and the II "-II" sectional view, and (B) is a partial view of (A). The figure and (C) are sectional drawings seen from the circumferential direction in CC point of (B).

(1). Structure Next, an embodiment of the present invention will be described with reference to the drawings. The internal combustion engine of the embodiment is a diesel engine, and the piston 1 is slidably fitted in a cylinder (a cylinder bore) 3 formed in the cylinder block 2, and a cylinder head 4 is fixed to the upper surface of the cylinder block 2. Yes. An injector 5 is mounted in a non-rotatable manner at a position located at the axial center of the cylinder 3 on the lower surface of the cylinder head 4. The injector 5 has a nozzle 6 protruding into the combustion chamber, and eight fuel injection holes (not shown) are formed at equal intervals on the outer peripheral surface of the nozzle 6. The fuel injection hole is inclined slightly downward.

  On the top surface 1 a of the piston 1, eight first concave grooves 7 facing the fuel injection direction of the injector 5 and eight second concave grooves positioned on the radially outer side of the portion between the adjacent fuel injection holes. 8 are formed in a continuous state in the circumferential direction, and one recess 9 is formed by the group of the first groove 7 and the group of the second groove 8. The recess 9 is formed in a range of the top surface 1a of the piston 1 that is slightly wider than half of the radius.

  As shown in FIG. 1, the curved outer surface of the recess 9 is smoothly continuous so that the outer periphery of the recess 9 is far from the axis 10 at the location of the first recess 7 and close to the axis 10 at the location of the second recess 8. It has a petal shape. Therefore, the outer end 7 a of the first groove 7 is a recess toward the axis 10, and the outer end 8 a of the second groove 8 is a protrusion toward the axis 10.

  As shown in FIG. 2, a certain range of the central portion 11 of the recess 9 is such that the first concave groove 7 and the second concave groove 8 have the same depth, and on the radially outer side of the central portion 11, The depth of the first groove 7 is gradually larger than the depth of the second groove 8. Therefore, the side surface of the recess 9 becomes a valley at the location of the first groove 7 and becomes a ridgeline at the location of the second recess 8, and the valley and the ridgeline are circumferential in the direction away from the central portion 11. The width of has increased. In addition, it can also be seen that the recess 9 is composed of a central portion 11 having substantially the same depth and a group of first and second concave grooves 7 and 8 having different depths.

  Although the maximum depth of the first concave groove 7 is about twice the maximum depth of the second concave groove 8, the ratio of the depths of the two can be arbitrarily set. As clearly shown in FIG. 2C, the adjacent first concave groove 7 and second concave groove 8 have a curved surface and are smoothly continuous in the circumferential direction.

  The outer end surface 7a of the first groove 7 and the outer end surface 8a of the second groove 8 (in other words, the outer peripheral surface of the recess 9) are separated from the shaft center 10 as they approach the top surface 1a of the piston 1. It is inclined with respect to the core 10 by a slight angle θ1, θ2. 2B, the outer end surfaces 7a, 8a are formed substantially parallel to the axis 10, and the upper ends of the outer end surfaces 7a, 8a are formed as shown by the dotted lines in FIG. It is also possible to overhang on the side of the axis 10 (ie, to form the outer end surfaces 7a and 8a so as to flared outward).

(2). Action / Effect / Others As shown in FIGS. 1B and 2A, when the fuel is ejected from each fuel injection hole of the first groove 7, 1 is ejected into the groove 7. In this case, since the outer end 7a of the first concave groove 7 is located farther than the outer end 8a of the second concave groove 8, the scattering distance of the atomized fuel can be increased without increasing the volume of the concave portion 9. Can be big. As a result, the atomized fuel can be prevented or remarkably suppressed from adhering to the outer end 7a of the first concave groove 7. Therefore, it is possible to prevent the occurrence of smoke without reducing the compression ratio.

  The atomized fuel 12 diffuses while being ignited by pressurization, but the adjacent first and second concave grooves 7 and 8 are smoothly continuous with the outer end portions 7a and 8a and the bottom surface. Therefore, the atomized fuel and flame flow smoothly from the first concave groove 7 to the second concave groove 8, which can contribute to complete combustion and improvement in flame propagation speed.

  In particular, since the first concave groove 7 and the second concave groove 8 have the same depth in the central portion 11 of the concave portion 9, the first concave groove 7 to the second concave groove also in the vicinity of the central portion 11. The smooth flow of fuel and flame in FIG. 8 can further contribute to the dispersibility of the fuel and the increase in the combustion speed.

  If the outer ends 7a, 8a of the both concave grooves 7, 8 are inclined outward as in the embodiment, the flow of fuel from the outer end of the first concave groove 7 back to the second concave groove 8 is guided. This is more effective in preventing fuel from adhering to the ends 7a and 8a.

  The present invention can be embodied in various ways other than the above-described embodiment. For example, in the illustrated embodiment, eight fuel injection holes are formed in the first concave groove 7, but other numbers of fuel injection holes may be used. The range in which the recesses are provided and the depths of the first and second grooves can also be arbitrarily designed. Moreover, although this invention is suitable for the piston of a diesel engine, it is applicable also to the piston of a direct-injection gasoline engine.

  The present invention is actually applicable to a piston of an internal combustion engine. Therefore, it can be used industrially.

DESCRIPTION OF SYMBOLS 1 Piston 1a Top surface of piston 2 Cylinder block 3 Cylinder 4 Cylinder head 5 Injector 6 Nozzle 7 1st groove 7a Outer end of 1st groove 8 Second groove 8a Outer end of 2nd groove 9 Recess 10 Piston Axis of center 11 Center of recess 12 Atomized fuel

Claims (1)

A piston used in an internal combustion engine having an injector in which fuel injection holes are formed by jumping in the circumferential direction,
On the top surface, a group of first concave grooves facing the opening direction of the fuel injection hole of the injector and a group of second concave grooves facing the outside between adjacent fuel injection holes of the injector are mutually connected. The outer periphery of the recess formed by the first groove group and the second groove group is formed in a continuous manner when viewed from the axial direction, and the outer end of the first groove is Concave toward the axis and the outer end of the second groove has a curved and continuous petal shape that is convex toward the axis.
Furthermore, each said 1st ditch | groove and each 2nd ditch | groove are the same depth in the center part near an axial center, and the depth of a 1st ditch | groove is the depth of a 2nd ditch | groove, so that it distances from a center part. The adjacent first and second grooves are smoothly continuous in the circumferential direction.
Piston for internal combustion engine.

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