JP6476841B2 - In-cylinder injection engine piston - Google Patents

Description

  The present invention relates to a piston used in a cylinder injection engine that directly injects fuel into a cylinder.

  In a cylinder injection gasoline engine equipped with a cylinder injection valve that directly injects fuel into a cylinder, for example, in a high load region, a homogeneous air-fuel ratio mixture is introduced into the cylinder to perform homogeneous combustion, and low In the load region, there is a control that performs stratified lean combustion (stratified combustion) by dividing the inside of the cylinder into a combustible air-fuel mixture layer rich in fuel and a lean air-fuel mixture layer where the fuel is thin or almost only air.

  During stratified combustion, the airflow in the cylinder that accompanies the lowering of the piston is used to prevent the gasoline and air from intermingling uniformly, the combustible mixture layer is around the spark plug at the end of the compression stroke, and the lean mixture layer is the piston. The airflow is controlled so as to gather on the side close to the top surface.

  By the way, Patent Document 1 discloses a technique for forming a concave portion (bowl) having a true circular shape in plan view at a position eccentric to the intake valve side of the piston top surface. When the piston is in the vicinity of the top dead center, the spray axis of the in-cylinder injection valve facing the inside of the cylinder is directed in the recess.

  In this piston, during homogeneous combustion, fresh air is introduced into the cylinder from a pair of intake ports provided in one cylinder, and a tumble flow that is a strong longitudinal vortex is generated. The fuel is injected into the cylinder during the intake stroke, and the fuel is diffused in the cylinder by the tumble flow, so that the air-fuel mixture in the cylinder is homogenized.

  Also, during stratified lean combustion, fresh air is introduced into the cylinder from only one of the paired intake ports by the control of the air control valve provided in the port, and the tumble flow component is relatively weakened. At the same time, the swirl flow that is a vortex along the horizontal direction is strengthened.

  Then, in the latter half of the compression stroke, the fuel injected from the in-cylinder injection valve toward the recess at the top of the piston rides on the swirl flow in the recess and moves toward the ignition plug at the top of the combustion chamber, and ignites around the ignition plug. An easy combustible mixture layer is formed.

Japanese Patent Laid-Open No. 11-210551

  As in the above example, in a direct injection gasoline engine, it is necessary to smoothly guide the fuel injected from the direct injection valve to the vicinity of the spark plug and to form an air-fuel mixture that easily ignites around the spark plug.

  However, in a deep dish-shaped (bowl-shaped) recess as in Patent Document 1, the fuel injected from the in-cylinder injection valve may stay at the bottom of the recess. For this reason, a problem remains in smoothly guiding the fuel around the spark plug.

  Accordingly, an object of the present invention is to efficiently collect the fuel injected from the in-cylinder injection valve around the spark plug.

  In order to solve the above-described problems, the present invention provides a cylinder injection engine piston in which a concave portion is formed on a piston top surface. The end wall of the recess on the recess end portion side is provided between the vertical portion parallel to the axis in an arbitrary cross section parallel to the axis of the piston, the vertical portion, and the recess In-cylinder injection engine piston composed of a curved surface connecting the bottom of

  Moreover, it can be set as the structure which provided the chamfering part in the ridgeline part between the said perpendicular | vertical part and the piston top surface around the said recessed part.

  Here, the maximum width portion having the widest width in a direction orthogonal to the start / end center line connecting the recess start end portion and the recess end portion in the recess and passing through the axis is along the start / end center line. The distance from the maximum width portion to the concave end portion along the start / end center line is shorter than the distance from the axial center to the concave start portion along the start / end center line. Is set.

  Further, the curved radius of the curved surface of the end wall on the concave end portion side is set to be larger than the curved radius of the curved surface provided on the end wall on the concave starting end portion side and rising from the bottom surface of the concave portion. it can.

  In addition, the upper surface of the piston adjacent to the recess on the recess terminal end side may be configured to be higher than the upper surface of the piston adjacent to the recess on the recess start end side.

  The connection point between the vertical portion and the curved surface may be positioned above the height of the upper surface of the piston adjacent to the recess on the recess start end side.

  In the present invention, the recess on the top surface of the piston is provided between the recess start end portion on one side and the recess end portion on the other side across the axis of the piston, and the end wall on the recess end portion side of the recess is In-cylinder injection is adopted because the piston for an in-cylinder injection engine is used, which is composed of a vertical part parallel to the shaft center in an arbitrary cross section parallel to the axis of the piston and a curved surface connecting the vertical part and the bottom surface of the recess. The fuel injected from the valve can be efficiently collected around the spark plug.

The piston which shows one Embodiment of this invention is shown, (a) is a top view, (b) is BB sectional drawing of (a), (c) is CC sectional drawing of (a). It is a perspective view of the piston of the embodiment. It is sectional drawing which shows the inside of the cylinder of the engine which accommodated the piston of the embodiment. It is a front view schematic diagram which shows the positional relationship with the top view and in-cylinder injection valve of the piston of the embodiment. (A)-(e) is a top view which shows the procedure which determines the shape of the recessed part of a piston top surface. (A)-(c) is a top view which shows the detail of the recessed part of a piston top surface. It is a top view which shows the piston of other embodiment, and a front view schematic diagram which shows the positional relationship with a cylinder injection valve. It is the top view which shows the piston of other embodiment, and a front view schematic diagram which shows the positional relationship with a cylinder injection valve. It is a principal part expanded sectional view of a piston.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. This embodiment is an in-cylinder injection type four-cycle gasoline engine for automobiles and a piston used in the engine. 1 and 2 show details of the piston, and FIG. 3 shows a main part of the combustion chamber 3 in one cylinder provided in the engine and a configuration of the engine. In FIG. 3, only members and the like directly related to the present invention are shown, and other members and the like are not shown. 3 shows only one cylinder 1, the engine may be a single cylinder or a multi-cylinder having a plurality of cylinders 1.

  As shown in FIG. 3, a piston 2 is accommodated in a cylinder 1 of the engine. A combustion chamber 3 is formed by the inner wall surface of the cylinder 1 and the top surface of the piston 2. Also, the cylinder 1 has an intake port 5 that guides air to the combustion chamber 3, an exhaust port 6 that sends exhaust from the combustion chamber 3, and a cylinder axis from the cylinder head side, that is, along the cylinder axis direction of the cylinder. A spark plug 4 and the like arranged downward are provided. The direction of the spark plug is not limited to this.

  The cylinder 1 is provided with an in-cylinder injection valve 9 that injects fuel directly into the combustion chamber 3. The in-cylinder injection valve 9 is arranged in the vicinity of the upper peripheral edge of the combustion chamber 3 and in the vicinity of the opening of the intake port 5. As shown in FIG. 3, the fuel injection direction of the in-cylinder injection valve 9 gradually approaches the piston head (the top surface of the piston 2) as the spray center line j <b> 0 moves from the peripheral edge of the combustion chamber 3 toward the center. It is an inclined direction. The fuel spray center line j0 is hereinafter referred to as an inclination direction spray center line j0. The fuel is injected so as to spread evenly in a fan shape from the injection port of the in-cylinder injection valve 9 around the inclined spray center line j0.

  In this embodiment, two intake ports 5 are provided for one cylinder. Each intake port 5 is provided with an intake valve 7 that opens and closes an opening to the combustion chamber 3. Two exhaust ports 6 are provided for one cylinder. The two exhaust ports 6 are each provided with an exhaust valve 8 that opens and closes an opening to the combustion chamber 3. The intake valve 7 and the exhaust valve 8 open and close the intake port 5 and the exhaust port 6 at a predetermined timing by the rotation of a camshaft provided on the cylinder head side.

  The intake valve 7, exhaust valve 8, spark plug 4, in-cylinder injection valve 9, and other devices necessary for the operation of the engine are control means provided in an electronic control unit (Electronic Control Unit) provided in a vehicle equipped with the engine. Controlled by.

  Further, in this embodiment, the intake valve 5 can be selectively controlled so that, for example, the opening / closing timings of one intake valve 5 and the other intake valve 5 are the same and different from each other. Further, the exhaust valve 6 can be selectively controlled so that, for example, the opening / closing timings of one exhaust valve 6 and the other exhaust valve 6 are the same and different from each other.

  By controlling these valves and controlling the fuel injection timing, for example, in a high load region, a homogeneous air / fuel mixture is introduced into the combustion chamber 3 to perform homogeneous combustion, and in the low load region, the combustion chamber 3 Stratified lean combustion (stratified combustion) can be performed by dividing into a combustible air-fuel mixture layer rich in fuel and a lean air-fuel mixture layer with thin fuel or almost only air.

  The in-cylinder injection valve 9 is disposed between the two intake valves 7. The in-cylinder injection valve 9 has an inclined spray center line j0 directed toward a portion slightly closer to the in-cylinder injection valve 9 than the axial center O of the piston 2 in a state where at least the piston 2 is near the top dead center. Placed in. The symbol P shown in FIG. 3 indicates the intersection between the tilt direction spray center line j0 and the piston head at the time when the fuel injection by the in-cylinder injection valve 9 in one cycle starts. Here, the axis O of the piston 2 coincides with the cylinder axis of the cylinder 1 where the spark plug 4 is located.

  As shown in FIGS. 1 and 2, the piston 2 has a columnar or cylindrical shape on the piston head side, and a piston boss portion 2b between a pair of piston skirts 2a and a piston skirt 2a. Moreover, the peripheral part is provided with a cooling channel 2c which is an annular space over the entire circumference along the circumferential direction.

  The outer peripheral surface of the piston 2 is provided with a groove 2e in which the piston ring 2d is accommodated. In this embodiment, three grooves 2e are formed corresponding to the three piston rings 2d. A portion on the top surface side of the most groove 2e on the piston head side is a top land.

  A recess 10 is formed in the piston head so that the fuel injected from the in-cylinder injection valve 9 is directed. The recess 10 is provided on the top surface of the piston.

  The recess 10 includes a recess start end A2 on one side, ie, the in-cylinder injection valve 9 side, and a recess end end A1 on the opposite side of the in-cylinder injection valve 9 across the axis O of the piston 2. Between.

  As shown in FIG. 4, the recess start end A2 and the recess end A1 are connected, pass through the axis O of the piston 2, and extend from the axis O along the start / end center line j2 orthogonal to the axis O. The distance L1 to the end portion A1 is set to be shorter than the distance L2 from the axis O to the recess start end portion A2. The start / end center line j2 is a direction orthogonal to the axial direction of the piston boss 2b in plan view.

  The position of the recess start end portion A2 is centered by a distance L3 from the directly below position J with reference to a directly below position J positioned at a distance L11 along the axis O from the nozzle position J ′ of the in-cylinder injection valve 9. Located on the O side. The recess start end A2 is set so that the fuel injection region from the in-cylinder injection valve 9 is within the bottom surface 11 of the recess 10. The direct position J is located on the inner side from the outer edge of the piston 2 by a distance L4.

  The position of the concave end portion A1 is such that the fuel that hits the bottom surface 11 of the concave portion 10 is guided to the concave end portion A1 and changes its direction toward the spark plug 4 by hitting the end wall of the concave end portion A1. It is set at a position where a thick fuel layer can be formed. In this embodiment, the position of the concave end portion A1 is such that the axis O of the piston 2 and the intersection A3 of the start / end center line j2 and the end edge of the piston 2 are divided into approximately 1: 2. However, the internal ratio can be appropriately determined according to the diameter of the piston 2, the fuel injection pressure, and other engine specifications.

  In addition, the concave portion 10 of the piston 2 has a curve radius that is relatively larger than the start end side curved section 12 along the end edge on the concave end end section A2 side, and relative to the start end side curved section 12 along the end edge on the concave end section A1 side. Has a large end-side curve section 13.

  The terminal-side curved section 13 has a portion with a radius r−1 that is longer than one half of the distance L1 + L2 between the recess start end A2 and the recess end A1. In addition, the start-side curve section 12 has a portion with a radius r-3 that is shorter than one half of the distance L1 + L2 between the recess start end A2 and the recess end A1.

  In this embodiment, the start-side curve section 12 and the end-side curve section 13 are curve sections (R3, R1) each having a single curve radius r-3, r-1, but the radius is halfway through this. It may be changed. However, it is desirable that there is no break point in the middle, and there is no discontinuous portion in the curvature, and the curvature changes continuously. At this time, it is desirable that the start side curve section 12 has a radius shorter than one half of the distance L1 + L2 over the entire section. Similarly, it is desirable that the terminal side curve section 13 has a radius longer than one half of the distance L1 + L2 over the entire section.

  A side curve section 19 having a curve radius r-2 that is relatively smaller than the curve radius r-1 of the end side curve section 13 is connected to both ends of the end side curve section 13 respectively. The side curve section 19 has a portion having a radius r-2 shorter than half of the distance L1 + L2.

  In this embodiment, the curve radius r-2 of the side curve section 19 is set to be the same as the curve radius r-3 of the start side curve section 12. If the curve radius r-2 of the side curve section 19 and the curve radius r-3 of the start end side curve section 12 are the same, processing during manufacturing can be facilitated. However, the curve radius r-2 and the curve radius r-3 can be set differently.

  In this embodiment, the side curve section 19 is a curve section (R2) made up of a single curve radius r-2, but the radius may be changed midway. However, it is desirable that there is no break point in the middle, and there is no discontinuous portion in the curvature, and the curvature changes continuously. At this time, it is desirable that the side curve section 19 has a radius shorter than one half of the distance L1 + L2 over the entire section.

  Attaching sections 18 that gradually move away from the start / end center line j2 as they move away from the recess start end A2 are connected to both ends of the start end side curve section 12, respectively. In this embodiment, the attachment section 18 is composed of a straight straight portion (U1). Note that the attachment section 18 is not limited to the straight portion, and may have a round shape (arc shape) having a sufficiently large radius.

  The attachment section 18 is configured by connecting an end portion of the start end side curve section 12 and an end portion of the side curve section 19. The attachment section 18 is parallel to the injection outer edge line j1 indicating the outer edge of the fuel injection region by the in-cylinder injection valve 9 with respect to the injection width direction orthogonal to the start / end center line j2. The fuel injection region by the in-cylinder injection valve 9 is a fan-shaped region in the injection outer edge line j1 indicated by an angle α in FIG.

  However, you may arrange | position the attachment area 18 which consists of this straight part so that it may make a slight angle mutually, without making it parallel to the injection outer edge line j1. However, it is desirable that the attachment section 18 is outside the injection outer edge line j1. Further, as long as the attachment section 18 is along the injection outer edge line j1, a part or all of the attachment section 18 may be configured by a smooth curve without a break point. At this time, the curve included in the attachment section 18 has a radius that is larger than that of the start end curve section 12, the end end curve section 13, and the side curve section 19 so that the fuel can be smoothly guided to the side curve section 19 side. It is desirable that the arc shape is large.

  As in this embodiment, when the terminal side curve section 13 is a curve having a single curve radius r-1, the center O1 of the arc of the terminal side curve section 13 is the in-cylinder injection valve 9 in one cycle. The recess start end A2 by a distance L8 from the intersection P between the fuel spray direction spray center line j0 and the bottom surface 11 of the recess 10 at the start of fuel injection (late stage of compression stroke, eg, 40CA before compression top dead center). Placed on the side. A symbol L5 in the figure is a distance in a direction along the start / end center line j2 between the axis O and the center O1.

Further, the arc of the center O1 of the terminating side curved section 13, than the midpoint C ₀ of intersection C between the edge of the injection casing lines j1 and recess 10, a distance L8-L9 are arranged in a recess starting end A2 side The Here the distance L9 is the distance along the starting and end center line j2 between the intersection P and the center point C _0.

When the start end side curve section 12 is a curve having a single curve radius r-3, the arc center O3 of the start end side curve section 12 is the intersection of the inclined direction spray center line j0 and the bottom surface 11 of the recess 10. The distance L8 + L6 is disposed closer to the recess start end A2 than P. The center of the arc O3 start end side curved section 12, than the midpoint C ₀ of intersection C between the edge of the injection casing lines j1 and the recess 10 (see distance W3 from the starting and end center line j2 in the figure). The distance L8−L9 + L6 is arranged on the concave start end A2 side. Here, the distance L6 is a distance along the start / end center line j2 between the center O1 and the center O3.

  The intersection C is an intersection of the side curve section 19 and the injection outer edge line j1. Further, the maximum width portion Wmax is located on the opposite side to the side where the intersection C is located, with a line passing through the intersection P and perpendicular to the start / end center line j2. The maximum width portion Wmax is located in the side curve section 19, and is the position where the width of the recess 10 is the widest in the injection width direction orthogonal to the start / end center line j2.

  The maximum width portion Wmax is located closer to the recess start end portion A2 than the axis O along the start / end center line j2, and the distance from the maximum width portion Wmax to the recess end portion A1 along the start / end center line j2 is The distance from the axis O to the recess start end A2 is set shorter.

  In the figure, reference sign B1 is a connection point between the terminal side curve section 13 and the side curve section 19, reference sign B2 is a point where the maximum width portion Wmax is reached, and reference sign B3 is a connection point between the side curve section 19 and the mounting section 18. , B4 is a connection point between the attachment section 18 and the start end side curve section 12. The alignments of the sections on both sides across each connection point have the same tangent direction at the connection point, and are smoothly connected without a break point.

Note that the positions of the intersection point P, the middle point C ₀ , and the maximum width portion Wmax may coincide with each other along the direction of the start / end center line j2. For example, of the three points, the intersection point P and the middle point C ₀ are aligned along the direction of the start / end center line j2, and the maximum width portion Wmax and the position of the intersection point P are the start / end center line j2. A mode in which the positions coincide with each other, a mode in which the position of the maximum width portion Wmax and the middle point C ₀ coincide with each other in the direction of the start / end center line j2, or the positions of the three points A mode in which they all match along the direction of j2 is conceivable. However, from the viewpoint of efficiently capturing the injected fuel in the recess 10 having a limited area, the position of the intersection point P and the position of the maximum width portion Wmax are identical along the direction of the start / end center line j2. It is desirable to do it.

  As shown in FIGS. 1 and 2, the piston 2 includes concave recesses 21 and 23 for preventing interference with the intake and exhaust valves 7 and 8 around the concave portion 10. Further, the piston 2 includes a starting end side peripheral portion 22 along a peripheral portion on the intake valve 7 side, and a terminal end peripheral portion 24 along a peripheral portion on the exhaust valve 8 side.

  Moreover, the peripheral edge to the said injection width direction of the piston 2 is provided with the inclined side top face 25 and the side peripheral edge part 26 which is a surface direction perpendicular | vertical to an axial center. The side peripheral edge portion 26 faces the upper wall surface of the cylinder 1 and forms a squish area for sending fuel from the peripheral edge portion in the combustion chamber 3 to the center.

  Between the recess 10 and the recess 23 and between the recess 10 and the side top surface 25, a piston top surface 27 that is a surface direction perpendicular to the axis O is provided. Depending on the specifications, the piston top surface 27 may not be provided.

  As shown in the sectional view of FIG. 9, the edge of the recessed portion 10 is chamfered portion 14, vertical portion 15, and end-side rounded portion 16 in order from the piston top surface 27 to the bottom surface 11 on the recessed terminal portion A1 side. Is provided. This configuration is adopted in all the sections of the terminal side curve section 13 and the side curve section 19. The terminal-side rounded portion 16 is provided in a range of a central angle α1 (α1 = 90 °) and a height B so as to connect the bottom surface 11 and the vertical portion 15. As shown in the cross-sectional view of FIG. 9, the vertical portion 15 is formed in parallel to the axis O in any cross section parallel to the axis O.

  In FIG. 9, symbol Q <b> 1 is a connection point between the bottom surface 11 of the recess 10 and the terminal-side rounded portion 16. At the connection point Q1, the flat surface of the bottom surface 11 and the curved surface of the terminal-side rounded portion 16 are smoothly connected so that there are no break points. Reference sign Q <b> 2 is a connection point between the terminal-side rounded portion 16 and the vertical portion 15. This connection point Q2 is also smoothly connected so that the cylindrical surface of the vertical portion 15 and the curved surface of the terminal-side rounded portion 16 do not have a break point. Reference numerals Q3 and Q4 are start and end points of the chamfered portion 14 having a horizontal dimension C1 and a vertical dimension C2. The horizontal dimension C1 and the vertical dimension C2 can be freely set as long as the height A of the vertical portion 15 can be sufficiently secured.

  The fuel injected from the in-cylinder injection valve 9 hits the bottom surface 11 of the recess 10 and then reaches the terminal side curve section 13. Alternatively, it reaches the attachment section 18 or the side curve section 19, moves along the attachment section 18 or the side curve section 19, and reaches the terminal side curve section 13. Here, the fuel runs up the terminal side rounded portion 16 smoothly contacted with the flat bottom surface 11, is guided in a direction parallel to the axis O along the vertical portion 15, and smoothly toward the spark plug 4 side. Be guided.

  Here, as shown in FIG. 9, the bottom surface 11 of the recess 10 faces downward (crank side) with a neutral line f <b> 1 of the piston 2 connecting the upper surface of the start-side peripheral edge 22 and the upper surface of the terminal-side peripheral edge 24 as a boundary. The piston top surface 27 is located on the upper side (cylinder head side). The terminal-side rounded portion 16 is connected to the vertical portion 15 at a position above the neutral line f1. The neutral line f1 is a reference plane for calculating the compression height (the center of the piston boss 2b, that is, the distance from the center of the piston pin to the shoulder of the piston 2). Since the end-side rounded portion 16 and the vertical portion 15 are connected at a position above the neutral line f1, the curve radius R1 of the end-side rounded portion 16 can be increased, and smooth fuel induction to the spark plug 4 side is achieved. Is possible.

  A height h2 from the neutral line f1 to the piston top surface 27 is set to be lower than a height h3 from the neutral line f1 to the bottom surface 11 of the recess 10. The height h1 from the bottom surface 11 of the recess 10 to the piston top surface 27 is the sum of the height h2 and the height h3.

  Since the ridge line portion between the vertical portion 15 and the piston top surface 27 is not rounded, and the ridge line portion is constituted by the chamfered portion 14 formed of the C surface, the vertical portion 15 is wider along the axis of the piston 2. Can be an area. This is because if the ridge portion is rounded, the length of the vertical portion 15 (length in the axial direction) cannot be secured sufficiently. In addition, by making the ridge part round, the airflow flows along the arc of the rounded part, but by using the chamfered portion 14 made of the C surface, the airflow is peeled off and easily supplied to the vicinity of the plug.

  Further, since the ridge line portion is constituted by the chamfered portion 14, the depth of the concave portion 10 (corresponding to the height h1) can be reduced, and various measures for ensuring rigidity, such as thickening the top land. Can be made unnecessary. Moreover, if the recessed part 10 is shallow, the separation from the cooling channel 2c can be sufficiently secured.

  In addition, in the recessed part starting end part A2 side and the attachment area 18 side, the edge of the recessed part 10 is the starting end side round part comprised by the starting end side round part 17 which connects the bottom face 11 and the starting end side peripheral part 22 and the recess 21. 17 is provided in the range of the central angle α2 (α2 <90 °).

  In this embodiment, the curve radius R1 of the end-side radius portion 16 and the curve radius R2 of the start-side radius portion 17 are the same, but from the viewpoint of securing the rigidity of the piston member, the curve radius of the start-side radius portion 17 is the same. R2 is desirably set smaller than the curve radius R1 of the terminal-side rounded portion 16. In addition, the numerical value and magnitude relationship of the curve radius R1 and the curve radius R2 are not limited to these embodiments.

  In FIG. 9, reference sign Q <b> 5 is a connection point between the bottom surface 11 of the recess 10 and the starting end side round portion 17. At this connection point Q5, the flat surface of the bottom surface 11 and the curved surface of the starting end side round portion 17 are smoothly connected so that there is no break point. Reference sign Q <b> 6 is a connection point between the starting end side round portion 17 and the starting end side peripheral edge portion 22. Reference sign Q7 is a virtual point obtained by extending the start end side rounded portion 17 until the central angle α2 = 90 °. You may provide the chamfering part which consists of C surfaces in the ridgeline part of the connection point of the starting end side round part 17 and the starting end side peripheral part 22 shown with the code | symbol Q6.

  The position of the recess end portion A1 is such that the fuel hitting the bottom surface 11 of the recess 10 hits the end wall of the recess end portion A1 and changes its direction toward the spark plug 4 to form a thick fuel layer around the spark plug 4 If it is a position, it can be set freely.

  The effect obtained by providing the vertical portion 15, the terminal-side rounded portion 16, and the chamfered portion 14 on the end wall on the concave end portion A <b> 1 side is not limited to the planar shape of the concave portion 10 of the above-described embodiment. The end wall can exert the fuel injected from the in-cylinder injection valve 9 in various pistons 2 that need to smoothly guide to the space near the spark plug 4. For example, the present invention can also be adopted in the piston 2 having the concave portion 10 having a perfect circular shape in plan view.

  As described above, the concave portion 10 formed in the piston head is provided between the concave portion start end A2 on one side and the concave end portion A1 on the other side across the axis O of the piston 2, and the concave portion 10 extends from the axial center O. The distance L1 to the end portion A1 is made shorter than the distance L2 from the axis O to the recess start end portion A2, and the start end curve section 12 is formed along the edge on the recess start end portion A2 side with the recess end portion A1. Since the terminal-side curve section 13 having a relatively larger curve radius than the start-end-side curve section 12 is provided along the side edge, the recess 10 is formed in a cylinder without excessively increasing the range of the recess 10 of the piston head. A range necessary and sufficient to receive the fuel injected from the inner injection valve 9 can be set. This is because the radius of the end side curve section 13 is relatively large and the radius of the start end side curve section 12 is relatively small.

  Moreover, since the side curve section 19 having a relatively smaller curve radius than the end side curve section 13 is provided on both sides of the end side curve section 13, the range of the recess 10 is further increased in the vicinity immediately below the spark plug 4. The fuel can be secured widely, and the fuel from the in-cylinder injection valve 9 can be efficiently captured.

  Furthermore, since the attachment section 18 along the injection outer edge line j1 is provided on both sides of the start end side curve section 12, and the attachment section 18 is set outside the injection outer edge line j1, the fuel from the in-cylinder injection valve 9 is removed from the recess 10 outside. Therefore, the fuel can be efficiently captured without being lost, and the fuel can be guided to the terminal side curve section 13 through the attachment section 18 and the side curve section 19.

  For this reason, the range of the concave portion 10 is kept to the minimum necessary, and the fuel injected from the in-cylinder injection valve 9 is efficiently taken into the concave portion 10 of the piston 2 while suppressing the rigidity reduction and weight increase of the piston 2. Necessary fuel can be collected around the spark plug 4.

  Further, since the range of the concave portion 10 is kept to the minimum necessary, it is not necessary to increase the thickness of the top land. In this respect as well, a decrease in rigidity and an increase in weight of the piston 2 can be suppressed. Moreover, since the separation between the end edge of the recess 10 and the outer edge of the piston 2 can be sufficiently ensured, it is possible to suppress a decrease in rigidity of the portion provided with the cooling channel 2c.

  FIGS. 5 and 6 are schematic views showing the design procedure and operational effects of the recess 10 according to the present invention.

  First, in the plan view of the piston head shown in FIG. 5 (a), an intersection P between the position J directly below the in-cylinder injection valve 9 and the inclined spray center line j0 and the piston head at the start of fuel injection is an engine specification. Determined by.

  As shown in FIG. 5 (b), the recess 10 includes a recess start end A 2 on the cylinder injection valve 9 side across the axis O of the piston 2, and a recess end A 1 on the opposite side of the cylinder injection valve 9. Between. Here, as shown in FIG. 5B, if the shape of the recess 10 is a perfect circle (curved radius r-0) as in the prior art, the radius of the true circle is the recess start end A2 and the recess end A1. Is half the distance between. However, if the concave portion 10 is a perfect circle, the region S1 shown in FIG. Further, the presence of the region S2 that protrudes outward from the jet outer edge line j1 unnecessarily widens the area of the recess 10 and is inefficient.

  Therefore, in the present invention, as shown in FIG. 5C, the curve radius on the recess terminal end A1 side (curve radius r-1 of the terminal end curve section 13) is set between the recess start end A2 and the recess end A1. It was larger than half of the distance between them. Thereby, the area S1 can be reduced to the area S1 '.

  However, according to this curve radius r-1, the separation T1 from the outer edge of the piston 2 is reduced on the side of the recess 10. For this reason, the side curve section 19 having a relatively smaller curve radius r-2 than the end side curve section 13 is provided on both sides of the end side curve section 13. As a result, as shown in FIG. 5D, the separation T1 can be secured as wide as the separation T1 '.

  Here, the connection point B1 between the end side curve section 13 and the side curve section 19 secures a distance W1 from the start / end center line j2, and from the start / end center line j2 near the axis O of the piston. The distance W2 (W2> W0) is secured.

  Next, as shown in FIG. 5E, the curve radius on the recess start end A2 side (the curve radius r-3 of the start end side curve section 12) is set as the distance between the recess start end A2 and the recess end A1. It was smaller than one half of. As a result, the end side curve section 13 having a relatively large curve radius is arranged on the end side, and the start end side curve section 12 having a relatively small curve radius is arranged on the start end side.

  And since the end of the side curve section 19 and the end of the start end side curve section 12 are connected by the mounting section 18 along the injection outer edge line j1 indicating the outer edge of the fuel injection region by the in-cylinder injection valve 9. is there.

  As a result, as shown in FIG. 6A, compared to the case where a true circular recess is employed as in the prior art, the recess 10 is made wider by the region V1 on the recess terminal end A1 side than the intersection P. The recess 10 can be narrowed by the region V2 on the recess start end A2 side of the intersection P.

  Further, as shown in FIG. 6 (b), the intersection P between the tilt direction spray center line j0 and the piston head at the start of fuel blowing is positioned at the maximum width portion Wmax that connects between the points B2 to thereby reduce the fuel. Can be efficiently captured in the recess 10.

  Further, as shown in FIG. 6 (c), a line segment connecting the intersection C between the injection outer edge line j1 and the edge of the recess 10 and a line segment connecting the recess start end A2 and the recess end A1 are diagonal lines. When the rectangular shape is considered, the fact that the inner angle α1 on the end side is larger than the inner angle α2 on the start end side is also an effective element for efficiently capturing the fuel in the recess 10.

The same applies to the case of considering a quadrangle whose diagonal is the line segment of the maximum width portion Wmax connecting the points B2 and the line segment connecting the recess start end portion A2 and the recess end portion A1.
The maximum width portion Wmax is located closer to the recess start end portion A2 than the axis O along the start / end center line j2, and the distance from the maximum width portion Wmax to the recess end portion A1 along the start / end center line j2 is Since it is set to be shorter than the distance from the axis O to the recess start end A2, the line segment of the maximum width Wmax connecting the points B2 and the line connecting the recess start end A2 and the recess end A1 When considering a quadrangle with a diagonal line, as in the example of FIG. 6C, the inner angle α1 on the end side becomes larger than the inner angle α2 on the start side.

  Another embodiment is shown in FIG. 7, and yet another embodiment is shown in FIG.

In the embodiment of FIG. 7, the curve radius r−3 of the start end side curve section 12 on the recess start end A2 side is set to be smaller than the curve radius r−2 of the side curve section 19. Here, the intersection point C midpoint C ₀ between the edge of the injection casing lines j1 and the recess 10 is coincident with the intersection point P, it coincides with the middle point C ₀ and the intersection point P, mismatch freely set it can.

  Further, in the embodiment of FIG. 8, the curve radius r-3 of the start end side curve section 12 on the recess start end A2 side is slightly larger than that of the embodiment of FIG. It is arranged in a direction inclined with respect to j1. Although the attachment section 18 and the injection outer edge line j1 do not intersect, the extension line intersects at a thin angle in the region outside the recess 10. The fuel can be guided to the side curve section 19 by such an aspect of the mounting section 18 as well. However, it is desirable that the attachment section 18 and the jet outer edge line j1 are gradually narrowed from the recess start end A2 side toward the recess end end A1 side.

  In these embodiments, the fuel injection mode by the in-cylinder injection valve 9 is uniform around the tilt direction spray center line j0, and the tilt direction spray center line j0 and the start / end center line j2 are in a plan view. However, depending on the form of fuel injection and the position of the in-cylinder injection valve 9, the shape of the piston 2 including the recess 10 is the target. An embodiment in which the shape of the piston 2 is not targeted with the start / end center line j2 interposed therebetween is also conceivable.

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston 2a Piston skirt 2b Piston boss | hub part 2c Cooling channel 3 Combustion chamber 4 Spark plug 5 Intake port 6 Exhaust port 7 Intake valve 8 Exhaust valve 9 In-cylinder injection valve 10 Recess 11 Bottom face 12 Start side curve section 13 End side curve Section 14 Chamfered section 15 Vertical section 16 Terminal side rounded section 17 Starting end rounded section 18 Straight section (mounting section)
19 Side curve section 21, 23 Recess 22 Start side peripheral edge 24 End side peripheral edge 25 Side top face 26 Side peripheral edge 27 Piston top face

Claims (6)

In the in-cylinder injection engine piston in which a concave portion is formed on the piston top surface,
The recessed portion is provided between a recessed portion start end portion on one side which is the in- cylinder injection valve side across the axis of the piston and a recessed portion end portion on the other side which is the opposite side of the in-cylinder injection valve ,
The concave portion has a curve radius that is relatively larger than a curve radius of the start end side curved section along an edge on the recess end portion side along a start end side curve section along the edge on the recess start end side. It has a terminal curve section,
A side curve section having a curve radius relatively smaller than a curve radius of the terminal side curve section is connected to both ends of the terminal side curve section, respectively.
Linear attachment sections that gradually move away from a start / end center line connecting the recess start end portion and the recess end portion as they move away from the recess start end portion are connected to both ends of the start end side curve section, respectively, Connected to the end of the side curve section,
The end walls of the end-side curved section and the entire side-curved section of the concave portion have a vertical portion parallel to the axial center in an arbitrary cross section parallel to the axial center of the piston, the vertical portion, and the concave portion. A curved surface connecting the bottom surface, and a chamfered portion is provided at a ridge line portion between the vertical portion and the piston top surface around the recess in all the sections of the terminal side curve section and the side curve section. In-cylinder injection piston.   The fuel injected from the in-cylinder injection valve hits the bottom surface of the recess, reaches the mounting section or the side curve section, moves along the mounting section or the side curve section, and moves to the end side. The in-cylinder injection engine piston according to claim 1, which reaches a curved section. The maximum width portion having the widest width in a direction orthogonal to the start / end center line connecting the start end portion of the recess and the end portion of the recess in the recess and passing through the axis is the axis centered along the start / end center line. Is located closer to the concave start side,
The in-cylinder injection according to claim 1 or 2, wherein a distance from the maximum width portion to the concave end portion along the start / end center line is set shorter than a distance from the axial center to the concave end portion. Type piston for the engine. 4. The cylinder according to claim 3, wherein a curved radius of the curved surface of the end wall on the concave end portion side is set larger than a curved radius of a curved surface provided on the end wall on the concave starting end portion side and rising from the bottom surface of the concave portion. Piston for internal injection engine. The upper surface of the piston adjacent to the concave portion on the concave end portion side is set higher than the upper surface of the piston adjacent to the concave portion on the concave start end side. In-cylinder injection piston. The in-cylinder injection engine piston according to claim 5, wherein a connection point between the vertical portion and the curved surface is located above a height of an upper surface of the piston adjacent to the concave portion on the concave start end side.

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