JP2012246904A - Piston, and spark-ignition internal combustion engine with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston that can suppress damage (surface roughening) from being generated on a top land surface.SOLUTION: A spark-ignition internal combustion engine provided with this piston 20, has a combustion chamber equipped with two intake valves 42, two exhaust valves 52, and an ignition plug 60, wherein the combustion chamber is defined by a cylinder head under surface as an in-cylinder ceiling 16, a cylinder block, and a crown face of the piston, and the ignition plug 60 is arranged at the almost center of the combustion chamber. The piston 20 has: valve recesses formed on the crown face of the piston; and protrusions 75 each formed between the two intake valve recesses 70F, 70R and generating squish flow in cooperation with the in-cylinder ceiling. The two intake valve recesses 70F, 70R are formed so that each amount overlapped with an outer circumferential side surface 22 of the piston, is different in a plan view.

Description

  The present invention relates to a piston for a spark ignition type internal combustion engine and a spark ignition type internal combustion engine provided with the same.

  In general, in a spark ignition type internal combustion engine, the flame surface of an air-fuel mixture ignited at the center of the combustion chamber propagates to the outer edge of the combustion chamber. For example, sufficient mixing of air and fuel is performed at the outer edge of the combustion chamber. Otherwise, it is known that the burning rate is insufficient and knocking is likely to occur. Therefore, in order to suppress the occurrence of such knocking, the shape of the combustion chamber including the piston shape is improved in order to control the flow of the air-fuel mixture or combustion fluid in the combustion chamber.

  As such an internal combustion engine, for example, an engine having a combustion chamber shape as shown in FIGS. 5 and 6 is known. That is, this includes two intake valves IN, IN and two exhaust valves EX, EX, and is provided by a cylinder ceiling SC on the bottom surface of the cylinder head, a cylinder block (not shown here), and a crown surface of the piston P. A combustion chamber of an internal combustion engine in which an ignition plug IGN is disposed at substantially the center of the defined combustion chamber, and intake valve recesses INR, INR for avoiding interference with the intake and exhaust valves described above on the crown surface of the piston And a piston P in which exhaust valve recesses EXR and EXR are formed. Here, the intake valve recesses INR and INR and the exhaust valve recesses EXR and EXR are arranged symmetrically with respect to a plane including the center line O of the piston P and extending in the radial direction (hereinafter referred to as a center boundary plane CF). Has been. An intake valve-side protrusion INP that forms a squish flow in cooperation with the in-cylinder ceiling SC is formed between these two intake valve recesses INR and INR, that is, in a region including the center boundary plane CF. In addition, between the two exhaust valve recesses EXR and EXR (similarly, the region including the center boundary plane CF), a projection EXP on the exhaust valve side that forms a squish flow in cooperation with the in-cylinder ceiling SC. An internal combustion engine in which is formed is known. For example, see Patent Document 1.

JP 2007-303339 A

  By the way, an internal combustion engine including the piston P having the above-described configuration, in particular, a valve recess is formed on the crown surface of the piston P, and between these two intake valve recesses INR and INR and two exhaust valve recesses EXR and EXR, respectively. In an internal combustion engine having a piston P formed with protrusions INP and EXP that form a squish flow in cooperation with the cylinder ceiling SC on the lower surface of the cylinder head, a squish flow is formed to promote agitation of the air-fuel mixture. In this way, the occurrence of knocking is suppressed, but the suppression action is not sufficient, and the vicinity of the piston surface, in particular, the portion where the protrusion INP on the intake valve side is formed in the region including the center boundary plane CF There was a problem that damage (surface roughness) occurred on the surface of the top land in Japan. Such surface roughness is undesirable because it leads to damage of the piston as the use of the internal combustion engine continues.

  Therefore, the present invention eliminates such conventional problems and suppresses surface damage, particularly damage (surface roughness) from occurring on the surface of the top land near the portion where the protrusion on the intake valve side is formed. It is an object of the present invention to provide a piston capable of achieving the above and a spark ignition type internal combustion engine using the same.

  As a result of diligent research using actual machine tests and CFD analysis, the present inventor has obtained the knowledge that the cause and mechanism of the surface roughness of the piston used in the conventional internal combustion engine are as follows. This will be described with reference to FIG. 7 showing the combustion chamber of the internal combustion engine as seen through the bottom surface of the cylinder head. First, FIG. 7A shows a state in which, in the internal combustion engine, the air-fuel mixture is ignited by the spark plug IGN and the flame is propagated. In this state, the ignition plug IGN is centered around the burned area AC of the air-fuel mixture after the flame surface is burned and propagated, whereas the unburned area NC indicated by the stippling is the two intake valves IN, It remains on the outer edge of the combustion chamber outside IN. FIG. 7B shows a state in which knocking due to the spontaneous combustion of the air-fuel mixture has occurred. The occurrence of this knocking depends on the pressure / temperature history received by the unburned air-fuel mixture, but most of the position is near the spark plug IGN in the unburned region NC on the intake valve IN side in the vicinity of the above-described center boundary plane CF. For convenience). FIG. 7C shows how the pressure waves collide thereafter. That is, when knocking occurs at the position X, a pressure wave due to the propagation propagates to people in the combustion chamber. A pressure wave passing through three typical paths among them, the first pressure wave PW1 that goes over the protrusion INP on the intake valve IN side and reaches the outer edge of the combustion chamber, and rotates from one side of the intake valve recess INR, respectively. A second pressure wave PW2 that reaches the outer edge of the combustion chamber and a third pressure wave PW3 that goes around from the other side of the intake valve recess INR and reaches the outer edge of the combustion chamber. Of these first to third pressure waves PW1 to PW3, the second and third pressure waves PW2 and PW3 are such that one and the other of the two intake valve recesses INR have the same size and are relative to the central boundary plane CF. Since they are arranged symmetrically, they simultaneously reach the vicinity of the center of the outer edge of the combustion chamber on the intake valve IN side. However, since the first pressure wave PW1 and the second and third pressure waves PW2 and PW3 have different paths (distances) through which the first pressure wave PW1 and the third pressure wave PW2 and PW3 pass, they reach one point at the same time and have a collision. However, the propagation speed of pressure waves will be different due to temperature differences in these paths (depending on whether they are burned area AC or unburned area NC), path resistance or the presence of obstacles, etc. As a result, these first to third pressure waves PW1 to PW3 simultaneously reach and collide with a point Y at the center of the outer edge of the combustion chamber on the intake valve IN side, as shown in FIG. 6B. There was found. Thus, it has been found that the damage (roughness) of the piston surface is erosion caused by excessive pressure generated by such pressure waves being concentrated at one point on the outer edge of the combustion chamber on the intake valve IN side. is there.

  Therefore, one form of a piston for a spark ignition internal combustion engine of the present invention that achieves the above object comprises two intake valves and an exhaust valve, a cylinder ceiling under the cylinder head, a cylinder block, and a crown of the piston. Piston for a spark ignition internal combustion engine in which a spark plug is disposed in the approximate center of a combustion chamber defined by the surface, and is formed on the crown of the piston to avoid interference between the two intake valves and the exhaust valve And a protrusion formed between the two intake valve recesses to form a squish flow in cooperation with the in-cylinder ceiling, each of the two intake valve recesses having an outer peripheral side surface of the piston. And the amount of overlap in a plan view is different.

  According to one aspect of the above-described piston for a spark ignition type internal combustion engine, the two intake valve recesses formed on the crown surface of the piston are formed such that the overlapping amounts in plan view with the outer peripheral side surface of the piston are different from each other. Has been. Here, assuming that knocking occurs at the above-described position X in the combustion chamber, a typical pressure wave caused by the knocking is generated through a squish flow forming protrusion formed between two intake valve recesses. Propagating to the outer peripheral side surface of the piston via the second path passing through one of the two intake valve recesses and the third path passing the other side formed so that the overlapping amount in plan view with the outer peripheral side surface of the piston is different Will do. However, since the second path and the third path have different path resistances on the way, the propagation speeds of the second and third pressure waves passing through the second path and the third path are also different. Rather, simultaneous overlap at one point with these and the first pressure wave passing through the first path is also avoided. Thus, excessive pressure is not generated on the surface of the top land near the portion where the protrusion on the intake valve side is formed, and damage (surface roughness) can be suppressed.

  Here, the two intake valve recesses may be formed with different sizes.

  The two intake valve recesses have the same size, but may be formed at different positions.

  Note that the intake valves themselves corresponding to the two intake valve recesses may have different sizes or positions in accordance with the intake valve recesses as long as interference with the intake valve recesses is avoided.

1 is a partial cross-sectional view of an internal combustion engine according to an embodiment of the present invention. It is a perspective view which shows (A) cylinder head lower surface part which defines the combustion chamber in the internal combustion engine which concerns on embodiment of this invention, and (B) piston crown surface part, respectively. It is a top view which shows (A) cylinder head lower surface part of FIG. 2, and (B) piston crown surface, respectively. It is a top view which shows a mode that the pressure wave of 3 persons propagates in the piston which concerns on embodiment of this invention. It is a perspective view which respectively shows (A) cylinder head lower surface part and (B) piston crown surface part which define the combustion chamber in the conventional internal combustion engine. It is a top view which shows (A) cylinder head lower surface part of FIG. 4, and (B) piston crown surface, respectively. It is a figure for demonstrating the cause and mechanism which damage (surface roughness) produces in the conventional internal combustion engine, (A) is at the time of ignition, (B) is at the time of knocking occurrence, and (C) is a subsequent pressure wave. It shows how it propagates and collides.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

  First, an outline of an internal combustion engine 10 according to an embodiment of the present invention will be described with reference to FIG. The internal combustion engine 10 includes a cylinder block 12, a cylinder head 14 fastened to the cylinder block 12, and a piston 20 that reciprocates in a bore formed in the cylinder block 12, and a pent roof type in-cylinder ceiling portion on the lower surface of the cylinder head 14. 16, the cylinder block 12, and the crown surface of the piston 20 define a combustion chamber 30. The cylinder head 14 is formed with two intake ports 40, 40 and two exhaust ports 50, 50 communicating with the combustion chamber 30, and two intake valves 42, 42 at the open end of each combustion chamber 30 side. And two exhaust valves 52, 52 (note that only one intake port 40 and one exhaust port 50 are shown in FIG. 1). An ignition plug 60 is disposed at substantially the center of the combustion chamber 30, in other words, approximately at the center of the pent roof type in-cylinder ceiling portion 16.

  Further, an intake valve recess 70 and an exhaust valve recess 80 described later for avoiding interference with the intake valve 42 and the exhaust valve 52 described above are formed on the crown surface of the piston 20 (note that the intake valve recess 70 and the exhaust valve 80 are exhausted). Only one valve recess 80 is shown in FIG. 1). Between the two intake valve recesses 70, a protrusion 75 on the intake valve side that forms a squish flow in cooperation with the in-cylinder ceiling 16 is formed, and between the two exhaust valve recesses 80. An exhaust valve-side protrusion 85 is formed in cooperation with the in-cylinder ceiling portion 16 to form a squish flow. Reference numeral 90 denotes an injector that injects fuel into the intake port 40.

  Here, FIG. 2A and FIG. 2B, which are perspective views showing a cylinder head lower surface portion defining the combustion chamber 30 in the above-described internal combustion engine 10 and a crown surface portion of the piston 20, are plan views. This will be described in more detail with reference to (A) and (B) of FIG.

  As shown in FIGS. 2 (A) and 3 (A), two intake valves 42 and 42 and two exhaust valves 52 and 52 are provided on the lower surface of the cylinder head that defines the combustion chamber 30 in the internal combustion engine 10. And a spark plug 60 is disposed substantially in the center of the combustion chamber 30 defined by the cylinder ceiling 16 on the lower surface of the cylinder head, a cylinder block (not shown here), and the crown surface of the piston 20.

  As shown in FIG. 2B, the generally cylindrical piston 20 has an outer peripheral side surface 22 and a crown surface 24 (hereinafter referred to as a piston outer peripheral side surface 22 and a piston crown surface 24, respectively). . Plural (usually three) ring grooves are formed on the piston outer peripheral side surface 22 to accommodate a piston ring (not shown). FIG. 2B shows only the uppermost ring groove in which a top ring (not shown) is accommodated, that is, only the top ring groove 26, and the second ring oil groove and the oil ring groove for other second rings and oil rings. Is not shown.

  In the piston 20, a top land 28 is formed above the top ring groove 26. Here, the top land 28 refers to the entire meat portion of the piston 20 located above the top ring groove 26. The portion of the piston outer peripheral side surface 22 belonging to the top land 28 forms the top land outer peripheral side surface 29.

  The piston crown surface 24 is formed with an intake valve recess 70 and an exhaust valve recess 80, which will be described later, in order to avoid interference with the intake valve 42 and the exhaust valve 52 described above (the intake valve recess 70 and the exhaust valve recess 80). As for 80, only one is shown in FIG. 1). Between the two intake valve recesses 70, a protrusion 75 on the intake valve side that forms a squish flow in cooperation with the in-cylinder ceiling 16 is formed, and between the two exhaust valve recesses 80. An exhaust valve-side protrusion 85 is formed in cooperation with the in-cylinder ceiling portion 16 to form a squish flow.

  As described above, the piston crown surface 24 is formed with the intake valve recess 70 and the exhaust valve recess 80 in order to avoid interference with the intake valve 42 and the exhaust valve 52 described above. Here, with respect to the intake valve recess 70 and the exhaust valve recess 80, a plane that includes the center line of the piston 20 and passes between the two intake valve recesses 70 and the two exhaust valve recesses 80 (the above-described central boundary plane CF). 2), the subscript “F” is attached to the front side of FIG. 2B and the subscript “R” is attached to the back side. 3 (B)) are substantially partial circles having the same diameter and are arranged symmetrically with respect to the central boundary plane CF.

  In contrast, the intake valve recesses 70F and 70R have different diameters in the plan view (FIG. 3B) and the intake valve recesses 70F on the front side are larger than the intake valve recesses 70R on the back side. The intake valve recesses 70F and 70R are disposed asymmetrically with respect to the central boundary plane CF.

  As is well known, the bottom surfaces of the intake valve recesses 70F and 70R and the exhaust valve recesses 80F and 80R are inclined so that the height position decreases as the distance from the center line of the piston 20 increases. The front-side intake valve recess 70F and the back-side intake valve recess 70R are formed so as to have different amounts of overlap in plan view with the outer peripheral side surface 22 of the piston, more specifically, with the top land outer peripheral side surface 29. As a result, the top land 28 or the top land outer peripheral side surface 29 has a shape that is notched downward at the upper end edge of the top land 28 or the front side intake valve recess 70R, that is, the front side. In addition, notch-shaped portions 72F and 72R on the back side are formed. These front-side and back-side cutout portions 72F and 72R are arranged asymmetrically with respect to the central boundary plane CF, and the sizes thereof are also different. In other words, the circumferential length LF of the notch shape portion 72F on the near side is formed to be longer than the circumferential length LR of the notch shape portion 72R on the back side. Thus, as will be described later, the path resistances passing through these notch-shaped portions 72F and 72R are made different. On the other hand, the front side exhaust valve recess 80 </ b> F and the back side exhaust valve recess 80 </ b> R are formed to have the same overlap amount in plan view with the top land outer peripheral side surface 29. Accordingly, the front and rear cutout portions 82F and 82R are formed at the upper end edge of the top land 28 or the outer peripheral side surface 29 of the top land at the continuous position with the front exhaust valve recess 80F and the rear exhaust valve recess 80R. Although formed, the front-side and back-side cutout portions 82F and 82R are arranged symmetrically with respect to the central boundary plane CF and have the same size.

  Here, the intake valve side protrusion 75 formed between the two intake valve recesses 70 and the exhaust valve side protrusion 85 formed between the two exhaust valve recesses 80 will be described. Both the squish forming protrusion 75 on the intake valve side and the squish forming protrusion 85 on the exhaust valve side are located on the outer peripheral side of the piston crown surface 24, and are substantially fan-shaped in plan view (FIG. 3B). In addition, the cross-sectional shape in the direction of the center boundary plane CF is common in that it is substantially triangular. Accordingly, the squish-forming projections 75 and 85 are respectively inclined to the outer peripheral surfaces 75a and 85a, which are gently lowered and connected to the piston outer peripheral surface 22 substantially smoothly, and the inner inclined surfaces 75b and 85b facing the center side of the combustion chamber. And edge portions (top edge portions) 75c and 85c extending between the outer inclined surfaces 75a and 85a and the inner inclined surfaces 75b and 85b. Here, the squish forming protrusion 85 on the exhaust valve side is arranged symmetrically with respect to the central boundary plane CF, whereas the squish forming protrusion 75 on the intake valve side has different intake valve recess sizes. Since it is formed so as to be sandwiched between 70F and 70R, as is clear from FIG. 3B, it is asymmetrical with respect to the center boundary plane CF, and its fan shape is also biased toward the back intake valve recess 70R side. Has been.

  A central recess 95 that is slightly recessed is formed at the center of the piston crown surface 24. An ignition plug 60 is attached to the cylinder head 14 directly above the central recess 95.

  According to the internal combustion engine 10 according to the above-described embodiment, if knocking occurs in the combustion chamber 30 at the position X on the above-described center boundary plane CF, the first to first typical pressure waves are generated. As shown in FIG. 4, the third pressure waves PW1 to PW3 pass through the squish flow forming protrusions 75 formed so as to be sandwiched between two intake valve recesses 70F and 70R having different sizes. The path of the piston passes through the second path passing through the rear intake valve recess 70R and the rear notch shape portion 72R, and the third path passing through the front intake valve recess 70F and the front notch shape portion 72F. It propagates to the outer peripheral side surface 22, more specifically, the top land outer peripheral side surface 29. However, in the middle of the second route and the third route, the notch shape portion 72R on the back side and the notch shape portion 72F on the near side are disposed asymmetrically with respect to the center boundary plane CF, and the size thereof is also Since they are formed differently and have different path resistances, the propagation speeds of the second pressure wave PW2 and the third pressure wave PW3 passing therethrough are also different, and the outer peripheral side surface of the piston corresponding to the central boundary plane CF Near the center of 22 (indicated by M in FIG. 4), no merging occurs. Therefore, it is also possible to avoid collision of these and the first pressure wave PW1 passing through the first path along the central boundary plane CF at the same time at one point (three points). Thus, since the timing of collision of the pressure waves is shifted and the pressure amplification points are dispersed, the surface of the topland outer peripheral side surface 29 near the portion where the protrusion 75 on the intake valve 42 side is formed is damaged (surface roughness). It is suppressed from occurring.

  In the above description, the two intake valve recesses have been described as an embodiment in which each of the two intake valve recesses is formed to have a different size as a form in which the amount of overlap with the outer peripheral side surface of the piston is different. Embodiments can also be adopted. For example, although not shown, the two intake valve recesses have the same size, but may be formed at different positions in order to make the overlap amount different. If it does in this way, the penetration | invasion position to the outer peripheral side surface of each piston of a pressure wave will differ, and a pressure amplification location will be disperse | distributed similarly. Furthermore, it goes without saying that the intake valves themselves corresponding to the two intake valve recesses may have different sizes or positions in accordance with the intake valve recesses as long as interference with the intake valve recesses is avoided.

20 Piston 22 Piston outer peripheral surface 24 Piston crown surface 29 Topland outer peripheral surface 70F Front intake valve recess 70R Front intake valve recess 72F Front notch shape portion 72R Back notch shape portion 75 Projection for squish formation 80F Exhaust valve recess on the near side 80R Exhaust valve recess on the back side 85 Projection for squish formation CF Center boundary plane

Claims (4)

A spark ignition internal combustion engine having two intake valves and an exhaust valve, and having an ignition plug disposed substantially in the center of a combustion chamber defined by a cylinder ceiling under the cylinder head, a cylinder block, and a crown surface of a piston Piston for
A valve recess formed on the crown of the piston to avoid interference between the two intake valves and the exhaust valve;
A protrusion formed between the two intake valve recesses to form a squish flow in cooperation with the in-cylinder ceiling,
The piston is characterized in that the two intake valve recesses are formed so as to have different amounts of overlap in plan view with the outer peripheral side surface of the piston.   The piston according to claim 1, wherein the two intake valve recesses are formed with different sizes.   The piston according to claim 1, wherein the two intake valve recesses are formed at different positions.   A spark ignition type internal combustion engine comprising the piston according to any one of claims 1 to 3.

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