JP5962835B1 - Engine pistons - Google Patents

Abstract

An object of the present invention is to effectively prevent the attenuation of energy of fuel spray in a cavity by smoothing the shape of the bottom of a combustion chamber. A cavity 21 is recessed at the top of a piston 20, an annular lip portion 22 projecting radially inward is provided at the periphery of the opening of the cavity 21, and a raised portion projecting upward at the bottom of the cavity 21. 25 is provided, and the lower end of the lip portion 22 and the lower end of the raised portion 25 are connected between the lip portion 22 and the raised portion 25 of the cavity 21, and protrudes in a longitudinal section curve shape radially outward and downward. The bending portion 24 is provided, and the longitudinal cross-sectional shape of the bending portion 24 is formed by a curve whose curvature increases toward the piston center side. [Selection] Figure 1

Description

  The present invention relates to an engine piston, and more particularly to a direct injection engine piston.

  Generally, in a direct injection engine such as a diesel engine, fuel is injected from a injector into a cavity recessed at the center of the top of a piston and burned.

  As this type of piston, for example, in Patent Document 1, a lip portion is formed at the periphery of the opening of the cavity, and fuel sprayed in the vicinity of the compression top dead center is caused to collide with the lip portion. A structure is disclosed that is dispersed in the squish area.

  As this type of piston, for example, Patent Document 2 discloses a structure for optimizing the ratio of fuel spray dispersed in the cavity and the squish area by providing a step portion in the lip portion. Yes.

JP 2008-151089 A JP 2014-222041 A

  Incidentally, as shown in FIG. 5, in the structure in which the piston 200 does not have a step portion in the lip portion 220, the fuel spray (see the arrow in the figure) tends to be distributed more in the cavity 210 than in the squish area S. For this reason, considering the distribution of the fuel spray in the vicinity of the center of the combustion chamber A, the amount of fuel spray increases toward the bottom of the cavity 210, making it easier to use the energy of the spray, but the air in the squish area S (oxygen) There is a problem that the use efficiency of) decreases.

On the other hand, as shown in FIG. 6, the structure having a stepped portion 330 on the piston 300 is lip 320, that the amount of fuel spray F _U to squish area S is secured, the air utilization rate of the squish area S Can be improved. However, the energy of the fuel spray F _L in the cavity 310 is made weaker than the structure having no stepped portion (see FIG. 5), the energy and the angle is steeper portion and straight portion and a curved portion in the cavity 320 It tends to be easily attenuated at the connecting portion. For this reason, there is a problem that combustion control by combustion pressure or multistage injection becomes difficult.

  An object of the disclosed technique is to effectively prevent attenuation of energy of fuel spray in the cavity by smoothing the shape of the bottom of the combustion chamber.

  In the disclosed technique, a cavity is provided in the top of a piston, an annular lip projecting radially inward is provided at the periphery of the opening of the cavity, and a protruding part projecting upward is provided at the bottom of the cavity. A curved portion that connects the lower end of the lip portion and the lower end of the raised portion between the lip portion and the raised portion of the cavity and protrudes in a curved shape in a longitudinal section toward the radially outer side and the lower side. Is provided, and the curved section is formed by a curve whose curvature increases as it goes toward the center of the piston.

  A portion directly below the lip where a vertical line extending in the piston axial direction from the most protruding end that protrudes most radially inward of the lip portion intersects with the bending portion; and a lowermost end portion that is most recessed below the bending portion. The vertical cross-sectional shape between them may be formed as a curve whose curvature increases as it goes to the piston center side.

  The curve may be a clothoid curve.

  The raised portion may be provided so as to protrude in a longitudinal section curve shape upward from the bottom of the cavity, and at least a part of a curve defining the longitudinal section shape of the raised portion may be formed by a clothoid curve.

  The lip portion may be provided with an annular step portion that is recessed at a predetermined depth from the inner peripheral upper surface of the lip portion.

  The stepped portion may include an annular flat portion extending radially outward from an inner peripheral edge of the lip portion, and an annular inclined portion inclined obliquely upward from the outer peripheral edge of the flat portion.

  According to the disclosed technology, it is possible to effectively prevent the energy of fuel spray from being attenuated in the cavity by smoothing the shape of the bottom of the combustion chamber.

It is a typical longitudinal section showing a part of engine concerning one embodiment of the present invention. In this embodiment, it is a schematic diagram explaining distribution of the fuel spray when fuel is injected near the compression top dead center of the piston. It is a typical figure explaining the first half of combustion of this embodiment. It is a schematic diagram explaining the second half of combustion of this embodiment. It is a figure explaining the flow of the fuel spray of the conventional structure which does not have a level | step-difference part in a lip | rip part. It is a figure explaining the flow of the fuel spray of the conventional structure which has a level | step-difference part in a lip | rip part.

  Hereinafter, based on an accompanying drawing, the piston of the engine concerning one embodiment of the present invention is explained. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  FIG. 1 is a schematic longitudinal sectional view showing a part of an engine according to the present embodiment. The engine 10 of the present embodiment is preferably a direct injection diesel engine, and includes a cylinder block 11 and a cylinder head 12 disposed on the cylinder block 11.

  The cylinder head 12 is formed with an intake port 14 that introduces fresh air into the combustion chamber A by opening and closing the intake valve 13 and an exhaust port 16 that leads exhaust gas from the combustion chamber A by opening and closing the exhaust valve 15. . An injector 17 that directly injects fuel into the combustion chamber A is provided between the ports 14 and 16 of the cylinder head 12.

  A plurality of fine nozzle holes (not shown) are formed in the nozzle portion 17A of the injector 17, and fuel is injected radially into the combustion chamber A from these nozzle holes.

  The cylinder block 11 is formed with a cylindrical cylinder bore 11A. A piston 20 is accommodated in the cylinder bore 11A so as to be reciprocally movable in the vertical direction.

A cavity 21 that is recessed at a predetermined depth from the top surface 20 </ b> A of the piston 20 is recessed at the top of the piston 20. An annular lip portion 22 that protrudes radially inward is provided on the periphery of the opening of the cavity 21. When the fuel is injected from the injector 17 when the piston 20 reaches the vicinity of the compression top dead center, the fuel spray F collides with the lip portion 22 and flows into the squish area S above the lip portion 22. and the spray F _U, is adapted to be dispersed in the fuel spray F _L flowing into the lower portion of the cavity 21 than the lip portion 22.
2 is provided with a stepped portion 23 formed by cutting the upper corner of the lip portion 22 into a substantially L-shaped cross section at a predetermined depth. More specifically, the step portion 23 includes an annular flat surface portion 23A that extends flatly from the inner peripheral edge portion (protruding end) of the lip portion 22 radially outward, and the top surface of the piston 20 from the outer peripheral edge of the flat surface portion 23A. And an annular inclined surface portion 23B extending obliquely toward 20A. Thus, by providing the step portion 23 on the upper surface of the lip portion 22, the optimization of the spray distribution of the fuel spray F _U dispersed in the squish area S, the fuel spray F _L which is dispersed in the cavity 21 Comes to be planned.

  The cavity 21 is connected to a raised portion 25 that is formed so as to protrude upward from the center of the bottom of the cavity 21 so as to protrude upward, a lower end 22A of the lip portion 22, and a lower end 25A of the raised portion 25. And a curved portion 24 that is curved in a longitudinally curved shape so as to protrude radially outward and downward.

  In the present embodiment, the first curved portion CL1 that defines the vertical cross-sectional shape of the curved portion 24 and the second curved portion CL2 that defines the vertical cross-sectional shape from the lower end of the raised portion 25 to the vicinity of the top portion are each formed by a clothoid curve. Has been. More specifically, the first curved portion CL1 of the curved portion 24 is defined by a first clothoid curve that is convex radially outward and downward and has a curvature that increases toward the piston center side. The two curve portions CL2 are defined by a second clothoid curve that is convex upward. The first curved line portion CL1 includes at least a first line portion 24A directly below the lip where a vertical line VL descending in the piston axial direction from the most protruding end that protrudes most radially inward of the lip portion 22 intersects the first curved portion CL1. A range up to the lowermost end 24B where the first curved portion CL1 is most depressed downward is formed by a first clothoid curve.

That is, the longitudinal cross-sectional shape of the cavity 21 is formed in a substantially S shape by the first and second clothoid curves that do not include a straight portion, and the curvature of the first curved portion CL1 is set to increase toward the piston center side. becomes as smooth flow towards the ridge 25 where the fuel spray F _L flowing into the cavity 21 is located at the center of the combustion chamber a.

  Next, based on FIGS. 2-4, the effect | action by the piston 20 of this embodiment is demonstrated.

As shown in FIG. 2, when the fuel is injected from the injector 17 in the vicinity of the compression top dead center of the piston 20, the fuel spray F collides with the lip portion 22 of the cavity 21, so that it is higher than the lip portion 22. a fuel spray F _U flowing into the squish area S of and dispersed in the fuel spray F _L flowing into the lower portion of the cavity 21 than the lip portion 22. In the present embodiment, since the step portion 23 to the lip portion 22 is provided, optimization of the spray distribution of the fuel spray F _U dispersed in the squish area S, the fuel spray F _L which is dispersed in the cavity 21 Is designed.

That is, as shown in FIG. 3, the first half of the combustion, by fuel spray F _U is effectively diffused into the squish area S, effectively utilizing combustion air (oxygen) in the squish area S is realized Is done.

Again back to FIG. 2, the flow of the fuel spray F _L which flows from the lip portion 22 into the cavity 21. In the cavity cross-sectional shape of the prior art structure shown by a broken line in FIG. 2, and steep angle of inclination of the ridge, the poor connection between the straight portion and the curved portion, the fuel spray F _L the attenuation of the energy is increased, early By being wound up, there was a problem that combustion using the air at the center of the combustion chamber A could not be effectively performed. In contrast, in the present embodiment, the fuel spray F _L is moved along the two first and second clothoid curve CL1,2 defining a longitudinal sectional shape of the cavity 21, in particular the first clothoid curve CL1, the piston Since the curvature is set to be larger toward the center side, the fuel spray _FL is smoothly flowed toward the raised portion 25 located in the center of the combustion chamber A without greatly reducing its energy. Become.

That is, as shown in FIG. 4, the second half of the combustion, that the fuel spray F _L which flows along the clothoid curve reaches smoothly to near the center of the combustion chamber A, used to maximize the energy of the fuel spray F _L In addition, combustion using the air (oxygen) near the center of the combustion chamber A is realized.

As described above in detail, according to this embodiment, it has a stepped portion 23 provided on the lip portion 22, and the fuel spray F _U dispersed in the squish area S, the fuel spray F is dispersed into the cavity 21 The spray distribution with _L can be optimized. Thus, the first half of the combustion, the fuel spray F _U is effectively diffused into the squish area S, can be achieved effectively utilizing combustion air (oxygen) in the squish area S.

In addition, the first and second clothoid curves CL1, the first curved portion CL1 that defines the vertical cross-sectional shape of the curved portion 24, and the second curved portion CL2 that defines the vertical cross-sectional shape from the lower end of the raised portion 25 to the vicinity of the top portion. In particular, the first clothoid curve CL1 is set to have a larger curvature as it goes toward the piston center, so that the fuel spray _FL is located at the center of the combustion chamber A without greatly reducing its energy. It flows toward the raised portion 25. Thus, the second half of the combustion, that the fuel spray F _L reaches smoothly to near the center of the combustion chamber A, the energy of the fuel spray F _L used maximally, and the air near the center of the combustion chamber A ( It is possible to realize combustion that effectively uses (oxygen).

  That is, according to the present embodiment, the first half of the combustion is performed using the outer peripheral side (squish area S side) in the combustion chamber A, and the second half of the combustion is performed near the center in the combustion chamber A. By performing the combustion, combustion using the air in the combustion chamber A can be performed effectively, and the combustion efficiency can be reliably improved.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, the first curved line portion CL1 may be formed with a clothoid curve from the outermost end portion 24C that protrudes most outward in the radial direction to the lowermost end portion 24B that is recessed most downward.

  Further, the first curved line portion CL1 may form a clothoid curve from the outermost end portion 24C that protrudes most outward in the radial direction to the lower end 25A of the raised portion.

  In addition, the first curved line portion CL1 may form a clothoid curve from the lower end of the lip portion to the lower end 25A of the raised portion.

  Further, the first curved portion CL1 may be formed with a clothoid curve from the lower end of the lip portion to the lowermost end portion 24B that is most depressed downward.

  Moreover, the curve which prescribes | regulates the longitudinal cross-sectional shape of the cavity 21 is not limited to a clothoid curve, If it does not prevent the flow of fuel spray, a cubic parabola (cubic curve) or a sine curve (sine half-wave decreasing curve) etc. Other curves may be used. The engine 10 is not limited to a direct injection diesel engine, and may be another direct injection engine such as a direct injection gasoline engine.

DESCRIPTION OF SYMBOLS 10 Engine 11 Cylinder block 12 Cylinder head 13 Intake valve 14 Intake port 15 Exhaust valve 16 Exhaust port 17 Injector 20 Piston 21 Cavity 22 Lip part 23 Step part 23A Flat surface part 23B Inclined surface part 24 Curved part 25 Raised part

Claims (5)

A cavity is recessed at the top of the piston, an annular lip projecting radially inward is provided at the periphery of the opening of the cavity, and a ridge projecting upward is provided at the bottom of the cavity. between the lip portion and the raised portion, thereby connecting the ridge bottom end and the lip bottom, the curved portion is provided which protrudes in the longitudinal sectional curved radially outward and downward, wherein A curved portion, a portion directly below the lip where a vertical line extending in the piston axial direction from the most projecting end that projects most radially inward of the lip portion intersects, and a bottom end portion that is most recessed below the curved portion. The piston of the engine formed with a curve whose curvature increases as the longitudinal cross-sectional shape of the gap increases toward the piston center . The piston of the engine according to claim 1, wherein the curve is a clothoid curve. The bulge portion is provided so as to protrude upward in a longitudinal section from the bottom of the cavity, and at least a part of a curve defining the longitudinal section shape of the bulge is formed by a clothoid curve. Or the piston of the engine of 2 . The piston of the engine according to any one of claims 1 to 3 , wherein the lip portion is provided with an annular step portion that is recessed at a predetermined depth from an upper surface on the inner peripheral side of the lip portion. The stepped portion is a flat portion of the annular extending radially outwardly from the inner peripheral edge of the lip, in claim 4 including the inclined portion of the annular inclined from the outer peripheral edge of the flat portion obliquely upward The piston of the described engine.

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