JP2011094496A - Combustion chamber structure of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion chamber structure of an internal combustion engine, which reduces a heat loss to a piston to enhance heat efficiency without a reduction of mixing performance of a fuel spray with air. <P>SOLUTION: This combustion chamber structure of the engine E constitutes a reentrant type combustion chamber 10 where a cavity 5e faces a cylinder head 3, by forming the cavity 5e reducing its diameter orthogonal to the cylinder axis X direction toward the opening end 5f side, on the top surface 5a of the piston 5 slidably fitted in a cylinder 4. A plurality of dimples 11 running along a flow of a combustion air-fuel mixture are formed on the conical wall surface 5d side more than the maximum diameter part 5m of the cavity 5e in a circular arc cross-sectional wall surface 5c among an inner wall surface for defining the combustion chamber 10 in the piston 5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a combustion chamber structure of an internal combustion engine in which a reentrant type cavity is formed on the top surface of a piston, and relates to a technique for improving heat efficiency by reducing heat loss to the piston.

  Generally, in a diesel engine, in order to increase the compression ratio, the top surface of a piston at the compression top dead center is brought close to the end surface of the cylinder head, and a cavity (recess) serving as a combustion chamber is formed on the top surface of the piston. This type of combustion chamber is classified into a reentrant type, a toroidal type, a bathtub type and the like according to the shape of the cavity. Of these, the reentrant type has a cavity with a diameter that decreases toward the opening end, and the inner wall surface that defines the cavity has a curved shape that overhangs, increasing the air overflow motion and near the cavity lip at the opening end. The fuel spray is injected into the fuel, and the fuel is burned while being mixed with air efficiently by flowing along the curved inner wall surface with the momentum.

  Here, in order to improve the mixing performance of the fuel spray, in the toroidal combustion chamber in which the same number of pocket-shaped recesses as the number of fuel injections are formed on the inner wall surface of the cavity, adjacent recesses are separated from each other by a predetermined distance. In a combustion chamber structure that is arranged and injects fuel between recesses (see Patent Document 1), or in a reentrant combustion chamber, a position that is shifted in the circumferential direction from a portion where fuel spray collides on the inner wall surface of the combustion chamber In addition, a combustion chamber structure (see Patent Document 2) in which a plurality of depressions that do not reach the piston top surface is formed has been proposed.

  On the other hand, as a means to improve the fuel spray mixing performance, the swirl is developed in the reentrant combustion chamber, and the turbulent air turbulence generated by the fuel spray generates a strong turbulence, so that the injected fuel does not hit directly. A combustion chamber structure in which a protrusion having a flat upper surface is formed at the bottom of the combustion chamber, and a corner on the outer periphery of the upper surface of the protrusion is recessed (see Patent Document 3). There is also a combustion chamber structure in which an air confinement recess having an opening (throat portion) for injecting air immediately after compression top dead center is formed at a position facing the fuel spray on the inner wall surface (see Patent Document 4). Proposed.

Japanese Utility Model Publication No. 56-2020 JP-A-10-82323 Japanese Patent No. 3220192 Japanese Patent Laid-Open No. 5-141245

  However, in the above-described conventional combustion chamber structure, each of the cavity is formed with a recess, a depression, a hollow and a recess, and the mixing performance of fuel spray and air is improved by disturbing the air flow. However, heat loss in the combustion chamber is not considered. That is, in the above combustion chamber structure, the surface area of the inner wall surface of the piston that defines the combustion chamber is increased, and the fuel spray is burned while moving along the inner wall surface of the piston, so that the inner wall surface of the piston is directly exposed to the flame. Therefore, the surface temperature becomes high, the heat loss to the piston is large, and the thermal efficiency is poor.

  The present invention has been devised to solve the problems imposed on the prior art, and its main object is to reduce the mixing performance of the fuel spray and air without reducing the mixing performance of the piston. An object of the present invention is to provide a combustion chamber structure of an internal combustion engine that can improve heat efficiency by reducing heat loss.

  In order to solve such a problem, the first invention has a diameter perpendicular to the cylinder axis (X) direction on the top surface (5a) of the piston (5) slidably fitted in the cylinder (4). Of the internal combustion engine (E) that forms a cavity (5e) that becomes smaller toward the open end (5f), and the cavity (5e) forms a reentrant combustion chamber (10) facing the cylinder head (3). In the combustion chamber structure, the cylinder head (3) is provided with a fuel injection valve (9) for injecting fuel toward the combustion chamber (10) to define the combustion chamber (10) in the piston (5). A dimple (11) is formed on the inner wall surface (5b, 5c, 5d) at a position where the fuel spray from the fuel injection valve (9) does not directly hit.

  If the dimple is formed at a position where the fuel spray directly hits, the flame enters the dimple with the momentum of the spray, so that the surface area of the inner wall surface of the piston increases, so that the heat loss increases. Therefore, according to the present invention, since the dimple is formed at a position where the fuel spray is not directly applied, the flame does not enter the dimple and the air stays in the dimple as a heat insulating layer in the portion where the spray is not directly applied. The rise in the surface temperature is suppressed, the heat loss to the piston is reduced, and the thermal efficiency is improved.

  Further, according to a second aspect of the invention, in the combustion chamber structure of the internal combustion engine (E) according to the first aspect of the invention, the fuel injection valve (9) has a cavity (5e) when the piston (5) is at the compression top dead center. The fuel is injected toward the vicinity of the opening end (5f) of the combustion chamber, and the dimple (11) has a bottom surface of the combustion chamber (10) that is more than the maximum diameter portion (5m) of the cavity (5e) perpendicular to the cylinder axis (X) direction. It is arranged on the (conical wall surface 5d) side.

  According to the present invention, a part of the fuel spray injected by the fuel injection valve collides with the vicinity of the opening end of the cavity, and the other part becomes an air-fuel mixture on the curved inner wall surface of the reentrant combustion chamber. Burns while moving along. And since the dimple is arranged on the combustion chamber bottom side than the maximum diameter part of the inner wall surface of the piston, it is difficult for the flowing air-fuel mixture to enter the dimple, and the heat is securely retained in the dimple to form a heat insulating layer. And heat loss to the piston can be reduced.

  According to a third invention, in the combustion chamber structure of the internal combustion engine (E) according to the first or second invention, the dimple (11) has a ratio (a / r) of the depth (a) to the radius (r). ) Is set to 0.8 or less.

  Depending on the dimple radius and the dimple depth, the effect of reducing the heat loss is changed. According to the present invention, by setting the ratio of the depth to the radius of the dimple to 0.8 or less, heat loss can be reduced as compared with the case where no dimple is formed.

  According to a fourth invention, in the combustion chamber structure of the internal combustion engine (E) according to the third invention, the dimple (11) has a ratio (a / r) of the depth (a) to the radius (r) of 0. It is characterized by being set in the range of 3 to 0.7.

  According to the present invention, the heat loss can be more efficiently reduced by setting the ratio of the depth to the dimple radius in the range of 0.3 to 0.7.

  The fifth invention is characterized in that in the combustion chamber structure of the internal combustion engine (E) according to the first to fourth inventions, a plurality of dimples (11) are formed along the flow of the combustion mixture. .

  According to the present invention, the energy of the combustion mixture can be utilized more efficiently by forming more dimples at positions that are effective for reducing the heat loss in the combustion chamber.

  Thus, according to the present invention, it is possible to provide a combustion chamber structure of an internal combustion engine that can reduce heat loss to the piston and improve thermal efficiency without deteriorating the mixing performance of fuel spray and air.

It is principal part sectional drawing of the internal combustion engine which concerns on embodiment. It is an expanded sectional view of a combustion chamber concerning an embodiment. It is a graph which shows the change of the various characteristics according to a dimple shape. It is the IV-IV arrow line view in FIG.

  Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the accompanying drawings. In this embodiment, the present invention is applied to an in-line four-cylinder diesel engine (hereinafter simply referred to as engine E), and FIG. 1 shows a state where the piston 5 is at the top dead center. In the description, it is assumed that the vertical direction is determined based on the state where the engine E is disposed with the cylinder axis X being vertical.

  As shown in FIG. 1, the engine E is slidable on a cylinder block 1, a cylinder head 3 fastened to the top of the cylinder block 1 via a gasket 2, and a cylinder 4 formed inside the cylinder block 1. The crankshaft (not shown) is rotationally driven through the connecting rod 6 connected to the piston 5 by the reciprocating motion of the piston 5. The cylinder head 3 is provided with two intake valves 7 and two exhaust valves 8. These intake and exhaust valves 7 and 8 are provided above the cylinder head 3 and connected to the crankshaft, not shown. It is opened and closed via a camshaft and a rocker arm. A reentrant cavity 5e centered on the cylinder axis X is recessed in the central portion of the top surface 5a of the piston 5 to form a combustion chamber 10, and the cylinder head 3 that defines the upper surface of the combustion chamber 10 is provided. A fuel injection valve 9 is arranged on the cylinder axis X so that the injection port faces the center of the combustion chamber 10.

  Although not shown, a low-pressure pump is provided in the fuel tank of the engine E, the fuel pumped from the low-pressure pump is supplied to the high-pressure pump, and the fuel pumped from the high-pressure pump is supplied to the common rail. . The high-pressure fuel accumulated in the common rail is supplied to the fuel injection valve 9, and the fuel injection valve 9 is driven to open by the engine ECU, whereby a predetermined amount of high-pressure fuel spray is injected into the combustion chamber 10 at a predetermined timing. Is done.

  The top surface 5a of the piston 5 at the compression top dead center is substantially the same position as the top surface 1a of the cylinder block 1, and the top surface 5a of the piston 5 formed in an annular shape so as to surround the combustion chamber 10 is formed by a valve recess. It is not a flat surface. A squish corresponding to the thickness of the gasket 2 is formed between the top surface 5 a of the piston 5 and the lower surface 3 a of the cylinder head 3 at the compression top dead center.

  Referring also to FIG. 2, the piston 5 is continuous from the top surface 5a via the chamfered portion 5h to the cylindrical wall surface 5b and continuously from the lower end of the cylindrical wall surface 5b via the chamfered portion 5i. An arc cross-sectional wall surface 5c having an outer diameter larger than the diameter of the cylindrical wall surface 5b and a conical wall surface 5d that continues from the lower end of the arc cross-sectional wall surface 5c and protrudes toward the lower surface 3a of the cylinder head 3 And have. A cavity 5e is defined by the cylindrical wall surface 5b, the arc-shaped wall surface 5c and the conical wall surface 5d of the piston 5, and the cavity 5e constitutes a combustion chamber 10 facing the lower surface 3a of the cylinder head 3. As a result, the combustion chamber 10 includes a reentrant cavity 5e whose diameter perpendicular to the cylinder axis X direction decreases toward the opening end 5f in the arc-shaped cross-section wall surface 5c, and the cylindrical wall surface 5b is the opening end 5f of the cavity 5e. A cavity lip is formed on the substrate. In the present embodiment, the apex of the conical wall surface 5d is chamfered to be a spherical surface.

  The piston 5 includes a lower half of the arc-shaped cross-section wall surface 5c, more specifically, the lower half of the conical wall surface 5d side (bottom surface side of the combustion chamber 10) from the maximum diameter portion 5m of the cavity 5e orthogonal to the cylinder axis X direction. A plurality of hemispherical dimples 11 are recessed in the part. In the present embodiment, the dimples 11 are formed in three rows at equal intervals in the cylinder axis X direction. As shown in the enlarged view of FIG. 2, each dimple 11 is defined by a hemispherical concave surface 5 g that forms a part of the outer surface of the sphere 12 indicated by an imaginary line, and its depth a and the radius ( Hereinafter, the ratio a / r with respect to the radius r of the dimple 11 is set to about 0.6.

  As shown in FIG. 2, the fuel injection valve 9 injects fuel spray toward the lower half of the cylindrical wall surface 5b when the piston 5 is at the top dead center. Further, the fuel injection valve 9 injects fuel in a pilot injection that injects fuel in the latter stage of the compression process, and in an expansion process and an exhaust process, in addition to the main injection that injects fuel when the piston 5 is at the top dead center. Perform post-injection. In the combustion chamber structure having such a configuration, the fuel spray injected toward the cylindrical wall surface 5b by the main injection is mixed with the compressed air and burned while a part of the fuel spray is injected into the cylindrical wall surface 5b and the circular cross section. It collides with the upper part of the shape wall surface 5c, and most of it moves in the vicinity of the arc-shaped wall surface 5c by flow. Here, since the dimple 11 is formed in the lower half portion of the arc-shaped cross-section wall surface 5c, the flame does not enter the dimple 11 and air remains in the dimple 11 and functions as a heat insulating layer. Heat transfer from the flame in the lower half of the wall surface 5c to the piston 5 is prevented. Therefore, the temperature rise of the part is suppressed, the heat loss to the piston 5 is reduced, and the thermal efficiency is increased.

  On the contrary, when the dimple 11 is provided on the cylindrical wall surface 5b and the arc-shaped cross-section wall surface 5c directly hit by the fuel spray, the flame enters the dimple 11 with the force of the spray, so that the surface area of the inner wall surface of the combustion chamber 10 On the contrary, the heat loss increases as the size increases. Therefore, it is important to provide the dimple 11 at a position where the fuel spray from the fuel injection valve 9 does not directly hit.

  Next, the shape and arrangement of the dimple 11 will be described. FIG. 3 shows a ratio a / r between the depth a and the radius r of the dimple 11 in a combustion chamber structure in which 24 dimples 11 are arranged in a row at a pitch of 15 degrees in the circumferential direction on the lower half of the arc-shaped cross-section wall 5c. 4A shows changes in various characteristics when the angle is changed, where FIG. 5A shows the surface area of the concave surface 5g defining the dimple 11, and FIG. 5B shows the heat transfer coefficient of the concave surface 5g defining the dimple 11. (C) shows heat loss due to the concave surface 5 g defining the dimple 11. As shown in (A), when the ratio a / r is large, the surface area of the concave surface 5g defining the dimple 11 becomes large. As shown in (B), when the ratio a / r is large, the dimple 11 is defined. The heat transfer coefficient of the concave surface 5g is reduced. The heat loss due to the concave surface 5g defining the dimple 11 is greatly reduced when the ratio a / r is set in the range of 0.3 to 0.7, as shown in (C). On the other hand, if the ratio a / r is larger than 0.8, the heat loss due to the concave surface 5g defining the dimple 11 increases conversely. Therefore, the heat loss reduction effect by the dimple 11 is exhibited when the ratio a / r is set to 0.8 or less, and is effectively exhibited when the ratio a / r is set within the range of 0.3 to 0.7. .

  Further, referring to FIG. 4 showing an IV-IV arrow in FIG. 2, the fuel injection valve 9 is directed in six directions divided at equal intervals in the circumferential direction of the piston 5 and toward the cylindrical wall surface 5b. Fuel is injected from the injection port. In addition to the flow of fuel spray indicated by arrows in FIG. 2, a swirl 13 indicated by white arrows swirling clockwise in the drawing when air is drawn from the intake valve is provided inside the combustion chamber 10. It has occurred. Therefore, the combustion mixture of the fuel injected from the fuel injection valve 9 and the compressed air not only moves in the radial direction in the combustion chamber 10 but also moves in the circumferential direction at the same time, and the lower half of the arc-shaped cross-section wall 5c. When moving along the part, as shown by a black arrow in FIG. 4, it moves obliquely leftward toward the center of the combustion chamber 10. Therefore, in the present embodiment, the dimples 11 in each row are arranged along the flow of the combustion mixture. With such an arrangement, heat transfer from the flame is efficiently performed by the dimples 11 in the portion of the inner wall surface of the combustion chamber 10 where heat loss should be reduced, that is, the portion exposed to the flame of the combustion mixture. In an area where the necessity of reducing heat loss is low, the energy of the combustion mixture can be efficiently utilized by the smooth inner wall surface of the combustion chamber 10 so that the formation of the swirl 13 is not affected. Become. Moreover, heat transfer is more efficiently prevented by shifting the position of the dimples 11 for each row and arranging them in a zigzag pattern.

  Although the description of the specific embodiment is finished as described above, the present invention is not limited to the above embodiment and can be widely modified. For example, in the above embodiment, the dimples 11 are arranged in three rows along the flow of the combustion mixture on the arc-shaped cross-sectional wall surface 5c, but the dimples 11 are also provided on the conical wall surface 5d, or the dimples 11 are arranged in the cavity 5e. A configuration in which the dimples 11 are arranged along the circumferential direction, a configuration in which the dimples 11 are arranged in one or two rows, or four or more rows, a configuration in which the dimples 11 are arranged in a lattice shape, or the like may be used. Further, in the above embodiment, the size of the dimple 11 is not mentioned, but the dimple 11 may have any size as long as heat transfer from the flame can be reduced, such as fuel pressure, intake pressure, swirl 13. What is necessary is just to set suitably according to the flow velocity etc. of this. Also, the shape is not limited to a hemisphere. In addition, the specific shape and arrangement of each member and part can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 3 Cylinder head 4 Cylinder 5 Piston 5a Top surface 5b Cylindrical wall surface 5c Circular cross-section-shaped wall surface 5d Conical wall surface 5e Cavity 5f Open end 5g Concave surface 5m Maximum diameter part 9 Fuel injection valve 10 Combustion chamber 11 Dimple E Engine X Cylinder axis

Claims (5)

On the top surface of the piston slidably fitted in the cylinder, a cavity whose diameter perpendicular to the cylinder axial direction becomes smaller toward the opening end side is formed, and a reentrant combustion chamber facing the cylinder head is formed in the cavity. A combustion chamber structure of an internal combustion engine,
The cylinder head is provided with a fuel injection valve that injects fuel toward the combustion chamber,
A combustion chamber structure of an internal combustion engine, wherein dimples are formed on an inner wall surface defining the combustion chamber of the piston at a position where fuel spray from the fuel injection valve does not directly hit. The fuel injection valve injects fuel toward the vicinity of the opening end of the cavity when the piston is at the compression top dead center,
2. The fuel injection device for an internal combustion engine according to claim 1, wherein the dimple is disposed on a bottom surface side of the combustion chamber with respect to a maximum diameter portion of the cavity orthogonal to a cylinder axial direction.   The fuel injection device for an internal combustion engine according to claim 1 or 2, wherein a ratio of a depth to a radius of the dimple is set to 0.8 or less.   The fuel injection device for an internal combustion engine according to claim 3, wherein the dimple has a ratio of a depth to a radius in a range of 0.3 to 0.7.   The fuel injection device for an internal combustion engine according to any one of claims 1 to 4, wherein a plurality of the dimples are formed along a flow of the combustion air-fuel mixture.

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