JP2010156230A - Engine piston - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an engine piston capable of preventing a crack in an inlet of a combustion chamber caused by distortion by stress at low cost. <P>SOLUTION: In the piston 1 formed with a cavity 4 constituting a part of a combustion chamber of an engine 3 in a piston top surface 2, the piston top surface 2 between an opening edge of the cavity 4 and an outer peripheral edge 21 of the piston top surface 2 is formed with a plurality of recesses 5(6) that make squish gas G flowing along the piston top surface 2 slow. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an engine piston in which a cavity forming a combustion chamber is formed on a piston top surface.

  With the recent compliance with exhaust gas regulations and higher output, troubles due to increased engine heat load are conspicuous. One of them is a crack at the mouth of the combustion chamber of the piston.

  An example of this will be described with reference to FIGS.

  As shown in FIGS. 5 and 6, a cavity 82 forming a part of the combustion chamber is formed in the top surface 81 of the piston 80 so as to open, and an opening edge of the cavity 82 forms a combustion chamber base 83. A ring-shaped cooling channel 84 is formed inside the piston 80 so as to surround the cavity 82.

  A pin hole 85 (see FIG. 6) for supporting a piston pin (not shown) is formed in the piston 80 below the cavity 82.

  In the piston 80, normally, a thermal stress (compression) due to combustion is generated by the squish gas flow at the combustion chamber base 83 during the combustion stroke (expansion stroke).

  Here, at the mouth of the combustion chamber in the pin direction (that is, above the pin hole 85), the compressive stress, which is a thermal stress, is canceled by the mechanical tensile stress generated by the piston pin in the expansion stroke.

  On the other hand, stress is superimposed by mechanical compression and thermal compressive stress at the combustion chamber mouth in the direction perpendicular to the pin that is spaced approximately 90 ° circumferentially from the combustion chamber mouth in the pin direction. For this reason, the combustion chamber mouth becomes the starting point of the crack, and the crack progresses from the starting point, causing a problem of piston seizure.

  Conventionally, for example, Patent Document 1 proposes a piston that has been subjected to an alumite treatment so as to apply a tensile stress to the top surface of the piston as a piston for preventing cracks at the mouth of the combustion chamber.

  In Patent Document 1, after applying a masking process to the combustion chamber opening above the piston pin, an alumite treatment is applied to the top surface of the piston, thereby applying tensile stress to the portion excluding the combustion chamber opening above the piston pin. Like to do.

Japanese Patent Laid-Open No. 08-177622

  However, the piston of Patent Document 1 requires a masking process and an alumite process at the time of manufacturing, and thus has a problem that the manufacturing cost increases.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an engine piston capable of solving the above-described problems and preventing cracks at the combustion chamber opening due to stress distortion at low cost.

  In order to achieve the above object, the present invention provides a piston in which a cavity forming a part of a combustion chamber of an engine is formed on a piston top surface, between an opening edge of the cavity and an outer peripheral edge of the piston top surface. A plurality of recesses for slowing the flow of squish gas along the piston top surface is formed on the piston top surface.

  Preferably, the concave portion is formed in two portions on the top surface of the piston that are spaced apart from each other in a direction perpendicular to the piston pin axial direction with the cavity interposed therebetween.

  Preferably, the two portions have a fan shape concentric with the piston top surface, extend in a direction orthogonal to the piston pin axial direction and pass through the center of the piston top surface at 30 ° or more 40 °. Each fan has a fan shape extending in the circumferential direction at an angle of less than or equal to °.

  The recess may be made of dimples formed by denting the top surface of the piston in a curved cross section.

  A plurality of the dimples may be arranged side by side along the circumferential direction on the piston top surface to form a dimple group, and a plurality of the dimple groups may be arranged at intervals in the radial direction.

  The recess may be a groove having a curved cross section extending in the circumferential direction of the piston top surface, and a plurality of the grooves may be arranged on the piston top surface with a radial interval.

  The depth of the groove may be such that the groove disposed on the radially outer side becomes shallower.

  According to the present invention, an excellent effect that cracks at the mouth of the combustion chamber due to stress strain can be prevented at low cost is achieved.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The piston (hereinafter referred to as piston) of the engine of this embodiment is applied to, for example, a diesel engine mounted on a vehicle.

  Based on FIG. 1 and FIG. 2, the schematic structure of the engine and piston of this embodiment will be described.

  As shown in FIG. 1, the engine 3 includes a piston 1, a cylinder block 32 in which a cylinder bore 31 that accommodates the piston 1 is formed, and a cylinder head 33 attached to the cylinder block 32.

  The cylinder bore 31 extends in the vertical direction, and its upper end is closed by the cylinder head 33. The cylinder head 33 is joined to the upper surface of the cylinder block 32 by a bolt or the like. Between the upper surface of the cylinder block 32 and the lower surface of the cylinder head 33, a gasket 34 for sealing between both surfaces is provided.

  Further, the piston 1 is accommodated in the cylinder bore 31 so as to be slidable in the vertical direction.

  The piston 1 is formed in a cylindrical shape that extends vertically and has an upper end closed by a head portion 11. A cavity 4 forming a part of the combustion chamber is formed in the upper surface (hereinafter referred to as piston top surface) 2 of the head portion 11 so as to be recessed downward. The cavity 4 forms an opening in the piston top surface 2, and the opening edge forms a combustion chamber mouth 41.

  As shown in FIG. 2, the piston top surface 2 in the illustrated example is formed in a substantially circular shape in plan view, and the cavity 4 opens in a substantially circular shape concentric with the piston top surface 2.

  Returning to FIG. 1, the combustion chamber of the present embodiment is a so-called reentrant combustion chamber, and a projection 42 having a mountain shape protruding upward is formed at the substantially central portion of the bottom surface of the cavity 4. 41 (opening edge) is narrowed. That is, the combustion chamber mouth 41 protrudes radially inward over the entire circumference of the opening so as to narrow the opening of the cavity 4. An annular space S surrounding the protrusion 42 is formed below the combustion chamber mouth 41.

  A plurality of ring grooves 12-14 are formed on the outer peripheral surface of the piston 1 at predetermined intervals in the vertical direction. In the illustrated example, a top ring groove 12, a second ring groove 13, and an oil ring groove 14 are formed on the outer peripheral surface in order from the top. The top ring groove 12 and the second ring groove 13 are fitted with compression rings 15 and 16 for sealing combustion gas, and the oil ring groove 14 is fitted with an oil ring 17 for scraping off lubricating oil.

  A cooling channel 18 for cooling the piston 1 is formed inside the piston 1. The cooling channel 18 has a ring shape surrounding the cavity 4 and is disposed at substantially the same height as the bottom surface of the cavity 4. The cooling channel 18 is supplied with, for example, lubricating oil of the engine 3 and circulates.

  A piston pin 7 is coupled to the piston 1. That is, a boss (not shown) is provided in the skirt portion 19 forming the inner wall of the piston 1 below the cavity 4, and a pin hole (not shown) is formed in the boss, and the piston pin 7 is provided in the pin hole. Inserted and supported. The piston pin 7 is arranged such that its axial direction (piston pin axial direction) A is orthogonal to the axial direction of the piston 1 (vertical direction in FIG. 1).

  In the following description, the axial direction of the piston pin 7 is defined as the pin direction (front and back direction in FIG. 1, vertical direction in FIG. 2) A, and the direction perpendicular to the axial direction of the piston pin 7 is defined as the direction perpendicular to the pin (vertical direction in FIG. Direction, right and left direction in FIG.

  The piston 1 creates a turbulent flow of the squish gas flow during the combustion stroke to minimize the heat reception from the gas to the piston 1 and the combustion chamber mouth 41 (opening edge of the cavity 4) and the piston top surface 2 A plurality of recesses for slowing the flow of the squish gas G along the piston top surface 2 is formed in the piston top surface 2 between the outer peripheral edge portion 21 and the piston. The concave portion of the present embodiment is composed of a large number of mortar-shaped dimples 5 formed by recessing the piston top surface 2 in a curved cross section.

  These dimples 5 are provided only in a portion where cracks of the combustion chamber mouth 41 are likely to concentrate. Specifically, as shown in FIG. 2, the dimple 5 is composed of two portions (hereinafter referred to as “pin perpendicular portions”) 23, 23 defined on the piston top surface 2, and the piston pin shaft sandwiching the cavity 4. It is formed in two pin right angle portions 23, 23 that are separated from each other in a direction T perpendicular to the direction A.

  The pin right angle portion 23 has a fan shape concentric with the piston top surface 2 when the piston top surface 2 is viewed in plan. The fan-shaped pin right angle portion 23 spreads in the circumferential direction at a predetermined angle α around a straight line L extending in the pin right angle direction T through the center C of the piston top surface 2.

  The predetermined angle α is preferably not less than 30 ° and not more than 40 °. The predetermined angle α is obtained in advance through experiments and simulations, or empirically from past actual machine data.

  Further, the dimples 5 are arranged in the radial direction of the piston top surface 2 so as to be along the flow direction of the squish gas G on the piston top surface 2 in the combustion stroke.

  More specifically, a plurality of dimples 5 are arranged densely along the circumferential direction on the piston top surface 2 to form a dimple group, and a plurality (five) of the dimple groups are arranged at intervals in the radial direction. Is done. In the illustrated example, the number of dimples 5 is different for each dimple group.

  Returning to FIG. 1, in each dimple 5, the side wall surface on the radially outer side (right side in FIG. 1) of the piston top surface 2 deflects and returns the squish gas G flowing into the dimple 5 from the piston top surface 2. A return surface 51 is formed. The return surface 51 extends while curving upward from the bottom surface of the dimple 5, and the upper end portion is substantially perpendicular to the piston top surface 2. The dimple 5 in the illustrated example is formed in a substantially hemispherical shape.

  The shape (diameter, depth, etc.) of the dimples 5 and the radial and circumferential intervals between the dimples 5 are appropriately set based on, for example, the squish flow velocity. The diameter of the dimple 5 is sufficiently smaller than at least the diameter of the cavity 4.

  The dimple 5 is formed by machining with a cutting tool, laser machining, or the like. For example, the dimple 5 is machined when the cavity 4 or the ring groove 12-14 is NC machined.

  Next, the operation of the piston 1 of the present embodiment will be described based on FIGS.

  In the combustion stroke (expansion stroke) of the engine 3, the piston 1 is lowered from the compression top dead center by the pressure of the combustion gas.

  When the piston 1 descends, in the vicinity of the cavity 4, a flow occurs so that the high-temperature combustion gas in the cavity 4 flows out, and as shown in FIG. 1, an S-shaped squish is generated. Yes. The squish gas G generated by the squish flows out of the cavity 4 and then flows outward along the radial direction of the piston top surface 2.

  At that time, heat is transferred from the high-temperature squish gas G flowing through the piston top surface 2 to the piston top surface 2, and the heat contributes to the generation of thermal stress in the piston 1.

  Here, the piston 1 of the present embodiment has a structure having a plurality of recesses (dimples) 5 on the piston top surface 2 and slows the flow of the quiche gas by the dimples 5 to generate turbulent flow so that the heat received by the piston 1 is received. Is reduced.

  That is, in this embodiment, a part of the squish gas G flowing from the cavity 4 along the piston top surface 2 flows into the dimple 5 on the piston top surface 2. The gas flowing into the dimple 5 flows along the wall surface in the dimple 5, and the flow direction is deflected from the radially outer side to the radially inner side by the return surface 51.

  As a result, the gas R flowing out of the dimple 5 flows opposite (reversely) to the squish gas G. The gas R from the dimple 5 collides with the squish gas G, and the flow of the squish gas G Become slow. As shown in FIG. 2, the squish flow velocity V1 of the pin right-angle portions (regions) 23, 23 provided with the dimple 5 is smaller than the squish flow velocity V2 of the other portions.

  When the flow velocity of the squish gas G decreases, the heat transfer from the squish gas G to the piston top surface 2 is reduced, and the thermal stress generated at the combustion chamber base 41 is reduced.

  As described above, in the present embodiment, the flow of the high-temperature squish gas G flowing in the combustion stroke is delayed by the dimple 5 on the piston top surface 2 to reduce the thermal stress, thereby preventing cracks in the combustion chamber mouth 41 due to stress distortion. can do. In addition, cracks can be prevented at a lower cost than when the piston 1 is subjected to the alumite treatment.

  In addition, the processing cost can be reduced by limiting the place where the dimple 5 is formed to the pin right-angled portion 23 where the mechanical compressive stress and the thermal compressive stress act.

  Next, another embodiment according to the present invention will be described based on FIG. 3 and FIG.

  This embodiment has substantially the same structure as the embodiment of FIGS. 1 and 2 except that the shape of the recesses is different. Therefore, the same elements as those shown in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof is omitted.

  The concave portion of the present embodiment includes a groove 6 having a curved cross section extending in the circumferential direction of the piston top surface 2, and a plurality of (four in the illustrated example) grooves 6 are spaced from the piston top surface 2 in the radial direction. Be placed.

  Specifically, the groove 6 has an arc shape concentric with the piston top surface 2 when the piston top surface 2 is viewed in a plan view, and extends over the entire region of the pin perpendicular portion 23 in the circumferential direction. That is, the groove 6 has a circular arc whose central angle is the predetermined angle α.

  The depth h of the groove 6 gradually decreases toward the outer peripheral side (right side in FIG. 4). That is, the groove depth h becomes shallower as the groove 6 is arranged on the radially outer side.

  Each groove 6 is an R groove having a rounded bottom surface and a rounded corner, and the illustrated groove 6 has a U-shaped cross-sectional shape. In the groove 6, like the dimple 5, the radially outer side wall surface of the piston top surface 2 forms a return surface 51 for deflecting the squish gas.

  Also in this embodiment, the same effect as the above-described embodiment can be obtained.

  In addition, this invention is not limited to the above-mentioned embodiment, Various modifications and application examples can be considered.

  For example, the cross-sectional shapes of the dimples and grooves are not limited to those described above, and may be a parabola, an ellipse, or the like.

  The arrangement of the dimples is not limited to that described above, and for example, the dimples may be arranged in a staggered manner or randomly.

  The combustion chamber is not limited to the reentrant type, and various types such as a toroidal type are conceivable.

FIG. 1 is a schematic sectional side view of an engine and its piston according to an embodiment of the present invention. FIG. 2 is a schematic plan view of the piston of the present embodiment. FIG. 3 is a schematic sectional side view of a piston according to another embodiment. FIG. 4 is a schematic plan view of a piston according to another embodiment. FIG. 5 is a schematic sectional side view of a conventional piston. FIG. 5 is a schematic plan view of a conventional piston.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piston 2 Piston top surface 3 Engine 4 Cavity 5 Dimple 6 Groove 21 Outer peripheral edge 41 Combustion chamber mouth (opening edge)
G Squish gas

Claims (7)

In the piston in which a cavity forming a part of the combustion chamber of the engine is formed on the top surface of the piston,
A plurality of recesses for slowing the flow of squish gas along the piston top surface are formed on the piston top surface between the opening edge of the cavity and the outer peripheral edge of the piston top surface. The piston of the engine.   2. The engine piston according to claim 1, wherein the recess is formed in two portions on the top surface of the piston, which are separated from each other in a direction perpendicular to the piston pin axial direction with the cavity interposed therebetween.   The two portions are fan-shaped concentric with the piston top surface, and extend in a direction orthogonal to the piston pin axial direction and have a straight line passing through the center of the piston top surface of 30 ° or more and 40 ° or less. The engine piston according to claim 2, wherein each of the pistons has a fan shape extending in the circumferential direction at an angle.   The engine piston according to any one of claims 1 to 3, wherein the recess is made of a dimple formed by denting the top surface of the piston into a curved cross section.   The engine piston according to claim 4, wherein a plurality of the dimples are arranged side by side along the circumferential direction of the piston top surface to form a dimple group, and a plurality of the dimple groups are arranged at intervals in the radial direction.   The said recessed part consists of a groove | channel of the cross-sectional curve shape extended in the circumferential direction of the said piston top surface, and this groove | channel is multiply arranged by the said piston top surface at intervals in radial direction. Engine pistons.   The engine piston according to claim 6, wherein a depth of the groove becomes shallower as a groove disposed on a radially outer side.

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