JP2014043777A - Combustion chamber structure of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable sufficient scavenging in a cavity in a central portion on a piston crown surface in an engine in which a compression self-ignition is performed when a geometric compression ratio is 15 or more.SOLUTION: A part of a bevel part 1a of an intake valve 1 is overlapped with a cavity 11 formed in a piston 10. A crown surface of the piston 10 has a valve recess 15A (15B, 16A, 16B) for preventing interference of the bevel part 1a with the piston 10 such that the valve recess 15A (15B, 16A, 16B) is continued to the cavity 11. A recess side opening end position 40 that is a position on an opening end for a combustion chamber of a valve recess 15A for an intake valve 1A and is nearer to an exhaust valve 2A, is in the same position as a port side opening end position 41 that is a position on an opening end for the combustion chamber of an intake port 5 and is nearer to an exhaust valve 2A, or in a position nearer to the exhaust valve 2A than the port side opening end position 41.

Description

  The present invention relates to a combustion chamber structure of an engine that performs compression self-ignition.

  In an engine using gasoline or a fuel mainly composed of gasoline, a spark ignition type in which ignition is performed by a spark plug is generally used. On the other hand, recently, from the viewpoint of a significant improvement in fuel efficiency, etc., the compression ratio of the engine is set to a high compression ratio of 15 or more, and the self-combustion (premixing) is performed while using gasoline or fuel mainly composed of gasoline. It is considered to perform compression self-ignition).

  Patent Document 1 discloses a spark ignition type engine that is not a compression self-ignition engine but has a high compression ratio of 13 or more in geometric compression ratio. In Patent Document 1, a pent roof type combustion chamber is formed, which is parallel to the reciprocating linear motion direction of the intake valve, and in a plurality of virtual cutting planes parallel to each other passing through the head portion (brass portion) of the intake valve. When the effective opening area (curtain area area) between the head portion and the valve seat is Si2, the intake valve and the exhaust valve are opened at the central point of the valve overlap period. In any of the virtual cut surfaces, Si1 ≧ Si2 is set so that the intake air from around the head portion can smoothly pass through the lower surface of the head portion to improve scavenging performance and filling efficiency.

  In Patent Document 2, a valve recess is formed on the piston crown surface, and an internal flow on the exhaust valve side of the valve recess is prevented so that the step of the valve recess does not hinder the flow of intake gas from the intake valve side to the exhaust valve side. It is disclosed that the wall surface is formed at an obtuse angle of 100 degrees or more.

JP 2009-162154 A JP 2000-18041 A

  By the way, in order to perform compression self-ignition, in order to diffuse the air-fuel mixture uniformly in the cylinder, it is preferable to dispose the fuel injection valve at the center in the cylinder and uniformly inject the fuel into the entire cylinder. In order to uniformly diffuse the fuel spray injected into the cylinder, the piston crown surface is basically a flat surface extending in a direction perpendicular to the cylinder axis, and the corresponding cylinder head lower surface is also a flat surface. It is also considered to be a flat type combustion chamber (which constitutes a flat type combustion chamber).

  As described above, when the geometric compression ratio is extremely increased, the gap between the cylinder head bottom surface and the piston top surface becomes extremely small at and near the piston top dead center position, and the intake valve and the exhaust valve The scavenging performance during the overlap period when both of them open is extremely deteriorated. In particular, intake air tends to flow from the intake valve side to the exhaust valve side, but sufficient intake air cannot be supplied to the cavity, and scavenging in the cavity tends to be insufficient. If the scavenging in the cavity is not sufficiently performed, the filling efficiency is lowered, which causes a large decrease in output.

  The present invention has been made in consideration of the above-described circumstances, and its purpose is to sufficiently fill the cavity formed in the central portion of the piston top surface in a high compression engine having a geometric compression ratio of 15 or more. An object of the present invention is to provide a combustion chamber structure for an engine that can scavenge.

In order to achieve the above object, in the present invention, basically, the opening end position to the combustion chamber of the valve recess for the intake valve formed on the piston crown surface is the opening end position to the combustion chamber of the intake port. Therefore, the intake air is less likely to flow toward the exhaust valve side. Specifically, the following solution is adopted in the present invention. That is, as described in claim 1,
A combustion chamber structure of an engine in which a geometric compression ratio is 15 or more and compression self-ignition is performed at least in a low load range,
A cavity is formed in the center of the piston crown,
When viewed from the cylinder axial direction, a part of the intake valve's bulk is overlapped with the cavity,
A valve recess for preventing interference between the piston portion and the piston is formed on the piston crown so as to be continuous with the cavity.
Of the opening end to the combustion chamber of the valve recess, the recess side opening end position that is closer to the exhaust valve is the same as the port side opening end position that is closer to the exhaust valve of the opening end to the combustion chamber of the intake port. The position is set to be a position closer to the exhaust valve than the port side opening end position,
It is like that. According to the above solution, the intake air introduced from the side close to the exhaust valve among the intake air supplied to the combustion chamber through the peripheral edge of the intake valve collides with the step surface on the side close to the exhaust valve of the valve recess. Thus, a flow toward the lower space of the intake valve (the combustion chamber formed therein) is actively generated and then introduced into the cavity, so that the scavenging performance of the cavity can be improved.

A preferred mode based on the above solution is as described in claim 2 and the following. That is,
The recess-side opening end position is the same position as the extension position when the throat portion of the intake port is extended to the piston crown surface at the compression top dead center through the port-side opening end position, or exhausted from the extension position. The position is set so as to be closer to the valve (corresponding to claim 2). In this case, the intake air introduced from the peripheral portion of the intake valve is preferable for increasing the ratio of colliding with the stepped surface of the valve recess and sufficiently exhibiting the effect corresponding to the first aspect.

  The recess-side opening end is set so that only the portion adjacent to the exhaust valve is located at the same position as the extended position or a position closer to the exhaust valve than the extended position (claims). Item 3). In this case, unnecessarily increasing the valve recess is suppressed, which is preferable in ensuring a high compression ratio.

The piston crown surface is a flat surface that extends in a direction perpendicular to the cylinder axis, except for the cavity and valve recess.
The portion of the cylinder head lower surface facing the flat surface of the piston crown surface is a flat surface extending in a direction perpendicular to the cylinder axis.
(Corresponding to claim 4). In this case, it is preferable to secure a flat surface in a large area range, ensure a uniform squish flow, and ensure uniform combustion.

For one cylinder, two intake valves are provided at an interval in the direction of the crankshaft in one region across the crankshaft,
Two exhaust valves are provided in the region on the other side across the crankshaft, spaced in the direction of the crankshaft,
Spark plugs are disposed between the two intake valves and between the two exhaust valves, respectively.
(Corresponding to claim 5). In this case, it is preferable for improving the intake / exhaust efficiency and ensuring rapid combustion when performing ignition using the spark plug.

  The spark plug is disposed between the two intake valves and between the two exhaust valves, and a recess connected to the cavity is formed (corresponding to claim 6). In this case, it is preferable to further improve the scavenging performance of the cavity by ensuring the space for disposing the spark plug by forming the recess and making the intake air easily introduced into the cavity through the recess.

  According to the present invention, in a high compression ratio engine that performs compression self-ignition, scavenging in the cavity is sufficiently performed, which is preferable in terms of improving the charging efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS The 1st Embodiment of this invention is shown, The simplified top view which looked at one cylinder from the cylinder axial direction upper direction. The top view which shows an example of the piston used in 1st Embodiment. The perspective view of the piston of FIG. X4-X4 line equivalent sectional drawing of FIG. X5-X5 line equivalent sectional drawing of FIG. The characteristic view which shows the example of a setting of the overlap period of an intake / exhaust valve. X7-X7 line equivalent sectional drawing of FIG. The principal part expanded sectional view of FIG. Sectional drawing which shows 2nd Embodiment and respond | corresponds to FIG. Sectional drawing which shows 3rd Embodiment and respond | corresponds to FIG. Sectional drawing which shows 4th Embodiment and respond | corresponds to FIG. The 5th Embodiment is shown and the X12-X12 line equivalent sectional drawing of FIG.

  FIG. 1 is a simplified plan view showing an arrangement relationship of intake / exhaust valves and the like when viewed from the cylinder axial direction with respect to a combustion chamber structure of an engine to which the present invention is applied. In FIG. 1, a symbol X indicates a cylinder axis extending in a direction perpendicular to the paper surface, and a symbol K indicates a crank axis extending in the vertical direction on the paper surface.

  In one cylinder (cylinder), two intake valves 1A and 1B are arranged in a region on one side (left side in the drawing) across the crank axis K. The two intake valves 1A and 1B are arranged side by side in the crank axis K direction. In the following description, when it is not necessary to distinguish between the two intake valves 1A and 1B, the intake valve 1 may be indicated.

  In one cylinder (cylinder), two exhaust valves 2A and 2B are disposed in a region on the other side across the crank axis K. The two exhaust valves 2A and 2B are arranged side by side in the crank axis K direction. In the following description, when it is not necessary to distinguish between the two exhaust valves 2A and 2B, the exhaust valve 2 may be indicated. In FIG. 1, an intake port that is opened and closed by the intake valve 1 is indicated by reference numeral 5 (see also FIG. 9), and an exhaust port that is opened and closed by the exhaust valve 2 is indicated by reference numeral 6.

  On the cylinder axis X, one fuel injection valve 3 is disposed. A first spark plug 4A is disposed between the two intake valves 1A and 1B, and a second spark plug 4B is disposed between the two exhaust valves 2A and 2B. In the following description, when it is not necessary to distinguish between the two spark plugs 4A and 4B, the spark plug 4 may be indicated.

  2 and 3 show the piston 10. A cavity 11 is formed at the center of the crown surface of the piston 10. The cavity 11 is circular when viewed from the cylinder axis X direction, and a mountain-shaped protrusion 11a is formed at the center thereof.

  On the crown surface of the piston 1, recesses 12 </ b> A and 12 </ b> B connected to the cavity 11 are formed at positions corresponding to the spark plugs 4 </ b> A and 4 </ b> B. As shown in FIG. 5, the fuel injection valve 3 is positioned directly above the protrusion 11a of the cavity 11, the first spark plug 4A (ignition portion) is positioned in the recess 12A, and the second ignition is positioned in the recess 12B. The plug 4B (its ignition part) is located. As is clear from FIG. 4, the bottom surfaces of the recesses 12 </ b> A and 12 </ b> B are formed so as to be smoothly connected to the bottom surface of the cavity 11.

  The crown surface (that is, the top surface) of the piston 10 is a flat surface extending in a direction perpendicular to the cylinder axis X except for the cavity 11, the recesses 12A and 12B and a valve recess portion described later, and has the same height. The flat surface portion is indicated by reference numeral 10a.

  The intake valve 1 and the exhaust valve 2 are positioned so that a part thereof overlaps the cavity 11 when viewed from the cylinder axial direction X. In the embodiment, the engine is an automobile engine, but is not limited thereto. Further, in the embodiment, a multi-cylinder engine in which a plurality of cylinders as shown in FIG. 1 are provided in the direction of the crank axis K is used. However, the number of cylinders can be selected as appropriate, and is not limited to an in-line multi-cylinder engine. The present invention can be applied to an appropriate type of engine such as a V-type multi-cylinder engine.

  The geometric compression ratio is set to a very high compression ratio such as 15 or more, more specifically 18 in the embodiment. As the fuel, gasoline or a fuel containing gasoline as a main component is used in the same manner as an ordinary spark ignition engine. As shown in FIGS. 4 and 5, the surface of the lower surface of the cylinder head 30 that faces the flat surface 10 a of the piston 10 is a flat surface that extends in a direction perpendicular to the cylinder axis X. The setting is such that a high scientific compression ratio is ensured and a squish flow is sufficiently obtained. The combustion chamber volume when the piston 10 is at the top dead center position is secured by the cavity 11.

  The intake valve 1 and the exhaust valve 2 have an overlap period in which both are opened for scavenging. FIG. 6 shows an example of setting the overlap period. In the figure, T is the overlap period, Tc is an intermediate position of the overlap period, and the piston top dead center position is advanced from the intermediate position Tc. It is set on the corner side.

  The engine as described above performs compression self-ignition at least in a low load region (more specifically, premixed compression self-ignition called HCCI, HCCI = Homogenous-Charge Compression-Ignition). In the low load range where compression self-ignition is performed (the load range where compression self-ignition is relatively performed as the engine speed increases is set to the lower load side), it is sufficiently higher than the compression top dead center The fuel is injected from the fuel injection valve 3 before and the piston is self-ignited (rapid combustion) when the piston is near the compression top dead center. The air-fuel ratio at the time of executing the compression self-ignition is lean with G / F (weight ratio) being 20 or more when G is the total gas amount of new air and EGR gas and F is the fuel amount.

  From the middle load range to the high load range, fuel is injected from the fuel injection valve 3 immediately before the compression top dead center, and ignition by spark ignition by the two spark plugs 2 is performed. The air-fuel ratio when performing this spark ignition is made sufficiently richer than the air-fuel ratio when performing compression self-ignition (however, the stoichiometric air-fuel ratio or a lean air-fuel ratio less than that).

  As shown in FIGS. 2 and 3, a total of four valve recesses 15 </ b> A, 15 </ b> B, 16 </ b> A, and 16 </ b> B are formed on the crown surface of the piston 10. The valve recess 15A corresponds to the intake valve 1A, and the valve recess 15B corresponds to the intake valve 1B. Further, the valve recess 16A corresponds to the exhaust valve 2A, and the valve recess 16B corresponds to the exhaust valve 2B. The valve recesses 15A, 15B, 16A, and 16B have a uniform depth, for example, as shallow as about 1 mm.

  Next, the configuration between the intake valve 1A and the exhaust valve 2A will be described with reference to FIG. First, the bulk (head) of the intake valve 1A is indicated by reference numeral 1a, and the valve shaft is indicated by reference numeral 1b. Further, the exhaust portion of the exhaust valve 2A is indicated by reference numeral 2a, and the valve shaft is indicated by reference numeral 2b. Each valve shaft 1b, 2b extends in parallel with the cylinder axis X. The intake port 5 is opened and closed by the bulk 1a of the intake valve 1A, and the exhaust port 6 is opened and closed by the bulk 2b of the exhaust valve 2A.

  When the piston 10 is at the compression top dead center, the lower surface of the cylinder head 30 is close to the flat surface 10a of the piston crown surface located between the above-mentioned lumps 1a and 2a (in the embodiment, the gap is For example, it is extremely small, about 0.7 mm).

  FIG. 8 is an enlarged view of the portion of the intake valve 1 </ b> A of the intake portion 1 a and the flat surface 10 a in FIG. 7. In FIG. 8, the opening end position (upper end position) to the combustion chamber closest to the exhaust valve 2A in the valve recess 15A for the intake valve 1A is shown as a recess side opening end position 40. In addition, among the opening ends of the intake port 5 to the combustion chamber, the opening end position closest to the exhaust valve 2 </ b> A is indicated as a port side opening end position 41. Further, for the throat portion of the intake port 5, an extension line passing through the port side opening end position 41 is indicated by a symbol W.

  As is clear from FIG. 8, the recess-side opening end position 40 is set closer to the exhaust valve 2 </ b> A than the port-side opening end position 41. In the embodiment, the recess-side opening end position 40 is set on the side closer to the exhaust valve 2 </ b> A than the extension line W. As a result, most of the intake air introduced into the combustion chamber from the side near the exhaust valve 2A in the peripheral edge of the intake valve 1A collides with the step surface 42 between the valve recess 15A and the flat surface 10a. . Then, most of the intake air collided with the stepped surface 42 is changed in direction to the lower side of the intake valve 1A and is introduced into the cavity 11 through the lower side of the intake valve 1A as indicated by the white arrow. This will improve the scavenging performance of the cavity 11.

  Of the intake air introduced toward the stepped surface 42, only a small amount flows to the exhaust valve 2A side through the space above the flat surface 10a. If the recess-side opening end position 40 is positioned closer to the intake valve 1A side than the port-side opening end position 41, most of the intake air introduced from the portion closer to the exhaust valve 2A side into the combustion chamber is a flat surface. 10a, and it becomes easy to flow to the exhaust valve 2A side along the flat surface 10a.

  Here, referring to FIG. 1, the point of introducing the intake air into the cavity 11 using the stepped surface 42 will be described in more detail. First, let the direction perpendicular to the crank axis K pass through the center of the bulkhead portion 1a in the intake valve 1A is the X axis, and the direction extending parallel to the crank axis X is the Y axis. Of the four regions divided by the X axis and the Y axis, the region A that is farthest from the cylinder axis X is defined as the third quadrant. Then, a region C that becomes the second quadrant, a region D that becomes the first quadrant, and a region B that becomes the fourth quadrant are assumed in order clockwise from the region A that becomes the third quadrant.

  The intake air introduced into the combustion chamber from the peripheral portion of the region B, which is the region close to the exhaust valve 2A in the Casa 1a, conventionally flows easily toward the exhaust valve 2A side as indicated by the arrow β. It was. In the present invention, most of the intake air that has been directed to the exhaust valve 2A side is introduced into the space below the intake valve 1A using the step surface 42 and flows toward the cavity 11 as indicated by the arrow α. Thus, the scavenging performance of the cavity 11 is improved. The above is the same for the other intake valve 1B.

  FIG. 9 shows a second embodiment of the present invention. The same components as those in the above-mentioned embodiment are given the same reference numerals, and a duplicate description thereof is omitted (this is the following third embodiment). The same applies to the following embodiments). In the present embodiment, the step surface 42B (corresponding to 42 in FIG. 8) is linearly inclined so as to approach the intake valve 1A side toward the bottom surface of the valve recess 15A (in the embodiment, an inclination setting of approximately 45 degrees). ). Thereby, the intake air introduced into the combustion chamber from the vicinity of the exhaust valve 2A is more easily introduced toward the lower side of the intake valve 1A at the step surface 42B.

  FIG. 10 shows a third embodiment of the present invention. In this embodiment, instead of the linear step surface 42B in the embodiment of FIG. 9, a concave step surface 42C that is curved in an arc shape so as to be concave toward the intake valve 1A side is provided. As a result, the intake air introduced into the combustion chamber from the vicinity of the exhaust valve 2A is more easily introduced toward the lower side of the intake valve 1A at the step surface 42C.

  FIG. 11 shows a fourth embodiment of the present invention. In the present embodiment, the axis of the intake valve 1A (the same applies to 1B), that is, the valve shaft 1b is slightly inclined with respect to the cylinder axis X. The inclination direction is a direction away from the cylinder axis X almost (away toward the upper side in FIG. 11) away from the bulkhead 1a. With such a setting, the gap portion 1a of the intake valve 1A is made larger toward the cavity 11 with respect to the bottom surface of the valve recess 15A. Thereby, in particular, in the area A and the area B in FIG. 1, the intake air introduced to the lower side of the bulkhead portion 1 a can easily flow toward the cavity 11, which is further preferable for improving the scavenging performance of the cavity 11.

  FIG. 12 shows a fifth embodiment of the present invention. In the present embodiment, the cross section is a cross sectional view corresponding to the line X12-X12 in FIG. 1, and the flat surface 10a shown in FIG. 12 is present at the boundary with the other intake valve 1B. . In the portion located at the boundary between the valve recess 15A and the flat surface 10a, the recess side opening end position is indicated by reference numeral 50, the port side opening end position is indicated by reference numeral 51, and the step surface of the valve recess 15A is indicated by reference numeral 52. An extension line of the throat portion passing through the port side opening end position 51 is indicated by a symbol W2.

  In the present embodiment, the recess side opening end position 50 is set to be closer to the intake valve 1A than the port side opening end position 51 and the extension line W2. As a result, the intake air introduced into the combustion chamber from the port-side opening end position 51 side is likely to collide with the flat surface 10a instead of the stepped surface 52, and is directly transmitted on the flat surface 10a to the other intake valve. The flow to the 1B side is encouraged. That is, in FIG. 1, the intake air introduced from the peripheral portion of the region C or region D into the combustion chamber easily flows toward the recess 12 </ b> A between the other intake valve 1 </ b> B. 11 is easily introduced into the air intake 11 (the scavenging ability of the cavity 11 is further improved).

  In FIG. 12, the position of the port side opening end position 50 is closer to the intake valve 1A than at least the extension line W2, more preferably closer to the intake valve 1A than the port side opening end position 51 as shown in FIG. The closer side is preferable.

  Although the embodiment has been described above, the present invention is not limited to the embodiment, and can be appropriately changed within the scope described in the scope of claims. For example, the invention includes the following cases. . Only one intake valve 1 may be provided for each cylinder, and similarly only one exhaust valve 2 may be provided (the number of intake / exhaust valves can be appropriately selected). Of course, the object of the present invention is not limited to what is explicitly stated, but also implicitly includes providing what is substantially preferred or expressed as an advantage.

  The present invention is suitable, for example, as an automobile engine.

X: Cylinder axis X1: Virtual line (a line parallel to the cylinder axis)
K: Crank axis α: Flow of intake air (flow from region B to the cavity through the lower side of the intake valve)
β: Intake flow (flow from region B to exhaust valve)
W: Extension line (extension line of the throat that passes through the open end position on the port side)
A: Area (3rd quadrant)
B: Area (fourth quadrant)
C: Area (second quadrant)
D: Area (first quadrant)
1 (1A, 1B): Intake valve 1a: Casa 1b: Valve shaft 2 (2A, 2B): Exhaust valve 2a: Casa 2b: Valve shaft 3: Fuel injection valve 4A, 4B: Spark plug 5: Intake port 6 : Exhaust port 10: Piston 10a: Flat surface 11: Cavity 11a: Protrusion 12A, 12B: Recess (for spark plug installation)
15A, 15B: Valve recess (for intake valve)
16A, 16B: Valve recess (for exhaust valve)
40: Recess side opening end position 41: Port side opening end position 42, 42B, 42C: Step surface

Claims (6)

A combustion chamber structure of an engine in which a geometric compression ratio is 15 or more and compression self-ignition is performed at least in a low load range,
A cavity is formed in the center of the piston crown,
When viewed from the cylinder axial direction, a part of the intake valve's bulk is overlapped with the cavity,
A valve recess for preventing interference between the piston portion and the piston is formed on the piston crown so as to be continuous with the cavity.
Of the opening end to the combustion chamber of the valve recess, the recess side opening end position that is closer to the exhaust valve is the same as the port side opening end position that is closer to the exhaust valve of the opening end to the combustion chamber of the intake port. The position is set to be a position closer to the exhaust valve than the port side opening end position,
An engine combustion chamber structure characterized by that. In claim 1,
The recess-side opening end position is the same position as the extension position when the throat portion of the intake port is extended to the piston crown surface at the compression top dead center through the port-side opening end position, or exhausted from the extension position. A combustion chamber structure for an engine, characterized in that the combustion chamber structure is set to a position closer to the valve. In claim 2,
The engine having the recess-side opening end set so that only a portion adjacent to the exhaust valve is located at the same position as the extension position or a position closer to the exhaust valve than the extension position. Combustion chamber structure. In any one of Claims 1 thru | or 3,
The piston crown surface is a flat surface that extends in a direction perpendicular to the cylinder axis, except for the cavity and valve recess.
The portion of the cylinder head lower surface facing the flat surface of the piston crown surface is a flat surface extending in a direction perpendicular to the cylinder axis.
An engine combustion chamber structure characterized by that. In any one of Claims 1 thru | or 4,
For one cylinder, two intake valves are provided at an interval in the direction of the crankshaft in one region across the crankshaft,
Two exhaust valves are provided in the region on the other side across the crankshaft, spaced in the direction of the crankshaft,
Spark plugs are disposed between the two intake valves and between the two exhaust valves, respectively.
An engine combustion chamber structure characterized by that. In claim 5,
A combustion chamber structure for an engine, wherein the ignition plug is disposed between the two intake valves and between the two exhaust valves, and a recess connected to the cavity is formed.

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