JP3644230B2 - Piston for in-cylinder internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piston of a direct injection internal combustion engine typified by a gasoline engine, in particular, a direct injection capable of both homogeneous combustion and stratified combustion using a tumble component and a swirl component generated in the cylinder. The present invention relates to an improvement of a piston of an internal combustion engine.
[0002]
[Prior art]
A so-called homogeneous combustion is formed by forming a substantially homogeneous air-fuel ratio mixture in the cylinder at the time of fully open output, etc., and a relatively rich mixture is formed only in a part of the cylinder, that is, in the vicinity of the spark plug in the low load range. Various in-cylinder injection internal combustion engines that perform stratified combustion so as to obtain an extremely large average air-fuel ratio have been proposed.
[0003]
As a piston of a direct injection internal combustion engine capable of stratified lean combustion, for example, a piston described in Japanese Patent Publication No. 8-35429 is known. In the internal combustion engine described in this publication, an intake valve side inclined surface and an exhaust valve side inclined surface substantially parallel to the intake and exhaust valve side inclined surfaces of the pent roof type combustion chamber are formed at the top of the piston, and both inclined A non-circular bowl that is eccentric with respect to the piston outer circle is formed on the convex portion having a surface, and a fuel injection valve is arranged so that fuel can be injected and supplied toward the bowl near the top dead center of the piston. . The bowl has a reentrant type configuration so as to contain fuel and swirl inside. In addition, in order to generate a strong swirl in the bowl, one of the pair of intake ports is configured as a helical port, and an air control valve for opening and closing the other intake port is provided.
[0004]
That is, in the internal combustion engine disclosed in this publication, at the time of lean combustion, the air control valve is closed and fresh air is introduced only from one helical port to generate a strong swirl in the cylinder. Since this swirl is introduced into the bowl as the piston rises, fuel is injected into the bowl near the compression top dead center, so that a combustible air-fuel mixture is formed in the bowl and carried to the vicinity of the spark plug. It is. Therefore, ignition is performed by igniting at an appropriate timing.
[0005]
[Problems to be solved by the invention]
However, in the conventional piston for a cylinder injection internal combustion engine described in the above Japanese Patent Publication No. 8-35429, the suction and exhaust valve side inclined surfaces formed at the top of the piston extend to the outer periphery of the piston. In other words, there is almost no horizontal surface at the top of the piston. For this reason, especially in the vicinity of the top dead center of the piston, the swirl component swirling along the cylinder wall surface is greatly hindered, and as a result, the swirl component introduced into the bowl is attenuated, stratified lean combustion becomes unstable, and the fuel efficiency There is a problem of causing deterioration and an increase in HC.
[0006]
In addition, since there is almost no reference horizontal plane on the top surface of the piston, for example, when trying to automatically push the piston into the cylinder using a pushing jig or the like, it is extremely possible to increase the positioning accuracy of the piston. It is difficult and the assembly work becomes complicated.
[0007]
An object of the present invention is to provide a piston of a direct injection internal combustion engine that can achieve both stratified lean combustion and homogeneous combustion at a high level and can be easily assembled to a cylinder.
[0008]
[Means for Solving the Problems]
Accordingly, the invention of claim 1 has two intake valves and two exhaust valves in a pent roof type combustion chamber recessed in the cylinder head, has an ignition plug in the approximate center of the cylinder, and directly in the cylinder. A fuel injection valve that injects fuel is arranged on the intake valve side, and injecting fuel in the vicinity of the intake stroke with a tumble flow component applied to the cylinder realizes homogeneous combustion and also applies a swirl component to the cylinder In a piston of a direct injection internal combustion engine that realizes stratified combustion by performing fuel injection in the vicinity of the compression stroke in such a state, it is substantially parallel to the inclined surface on the exhaust valve side of the pent roof type combustion chamber. An inclined plane or virtual plane that is substantially parallel to the inclined surface on the exhaust valve side, which is an inclined plane, and the inclined surface on the intake valve side of the pent roof type combustion chamber. An intake valve side inclined surface, a pair of side surfaces constituting the side portion of the convex portion formed by both the inclined surfaces, and a substantially circular shape recessed at a position eccentric to the intake valve side with respect to the piston outer circle Characterized in that it has a bowl and a piston reference horizontal plane that is formed continuously along the outer periphery of the piston along the outer periphery of the piston over the entire circumference of the piston and is a plane perpendicular to the piston center line. Yes.
[0009]
In the above configuration, the convex portion of the piston top portion is configured by the intake valve side inclined surface, the exhaust valve side inclined surface, and the surrounding conical side surface. The convex portion is configured such that the space between the piston top dead center and the combustion chamber on the cylinder head side is as small as possible, and a piston reference horizontal plane exists outside the convex portion. doing.
[0010]
During stratified combustion, swirl is generated in the cylinder by means such as closing one intake port. Here, since the piston reference horizontal plane is formed on the entire outer periphery of the piston, the swirl component swirling in the cylinder can flow well above the piston reference horizontal plane even near the top dead center of the piston. Can be stored with sufficient strength. The swirl is appropriately introduced into the bowl and contained as the piston moves up. Here, since the bowl is substantially circular, a sufficiently strong swirl can be secured in the bowl. The fuel injected toward the bowl in the vicinity of the top dead center is well mixed with air by the swirl secured in the bowl, and the central negative pressure of the in-cylinder swirl held on the piston reference horizontal plane. Thus, it is sucked up to the spark plug position and ignited, and good stratified combustion can be realized.
[0011]
In homogeneous combustion, a tumble flow is generated by the fresh air flowing into the cylinder via the pair of intake valves, and fuel is injected near the intake stroke. Here, the fuel that has entered the bowl is washed away by the tumble flow and is prevented from staying, so that homogeneous combustion with a homogeneous air-fuel mixture can be realized.
[0012]
The outer peripheral edge of the bowl intersects the ridge line between the convex portion and the piston reference horizontal plane , and a swirl passage is secured over the entire circumference of the piston above the piston reference horizontal plane. The swirl component at the time of realizing stratified combustion is preserve | saved, This swirl component is induced | guided | derived into the said bowl from the said crossing part, The gas flow in the said bowl is strengthened, It is characterized by the above-mentioned .
[0013]
According to this configuration , a part of the bowl reaches the piston reference horizontal plane, and the swirl component swirling above the piston reference horizontal plane is smoothly guided into the bowl through this part. As a result, the gas flow in the bowl is further strengthened, and stratified combustion is particularly good.
[0014]
The invention according to claim 2 is characterized in that the piston reference horizontal plane is set to have a constant width over the entire circumference of the piston except for a portion notched by the bowl.
[0015]
According to a third aspect of the present invention, the bowl has a dish shape in which the inner peripheral side wall surface is tapered upward. Thereby, at the time of homogeneous combustion, the fuel in the bowl is washed away by the tumble flow, and the air-fuel mixture is homogenized.
[0016]
【The invention's effect】
According to the piston of the in-cylinder internal combustion engine according to the present invention, a swirl having a sufficient strength can be stored above the piston reference horizontal plane formed on the outer periphery of the piston even near the top dead center of the piston. For this reason, the swirl of sufficient strength can be introduced into the bowl, and the mixing of air and fuel in the bowl is good. In addition, since the air-fuel mixture formed in the bowl can be effectively sucked up to the spark plug position by the central negative pressure of the cylinder swirl, good stratified combustion becomes possible.
[0017]
Also, since the piston reference horizontal plane is formed over the entire circumference of the piston outer periphery, the piston is automatically pushed into the cylinder with high positional accuracy by bringing the tip surface of the pushing jig into contact with the piston reference horizontal plane, for example. And the assembling work is extremely easy. As a result, the manufacturing cost can be greatly reduced.
[0018]
In addition, according to the invention of claim 2 , since the outer peripheral portion of the piston top has a uniform height and radial width over the entire circumference, the thickness of the piston outer peripheral portion slidably contacting the cylinder wall surface is made uniform over the entire circumference. The heat radiation characteristics and the amount of thermal deformation of the outer periphery of the piston can be made uniform over the entire circumference. As a result, for example, a part of the piston in the circumferential direction is locally thermally deformed, and there is no possibility of premature seizing of the cylinder wall.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
First, the configuration of a direct injection internal combustion engine in which the piston 4 of the present invention is used will be described with reference to FIGS. As illustrated, a plurality of cylinders 3 are arranged in series on the cylinder block 1, and a cylinder head 2 is fixed so as to cover the upper surface thereof. A piston 4 is slidably fitted in the cylinder 3. The combustion chamber 11 recessed in the cylinder head 2 has a so-called pent roof type, and a pair of intake valves 5 is provided on one inclined surface 11a and a pair of exhaust valves 6 is provided on the other inclined surface 11b. Are arranged respectively. A spark plug 7 is disposed at a substantially central position of the cylinder 3 surrounded by the pair of intake valves 5 and the pair of exhaust valves 6.
[0021]
The cylinder head 2 is formed with a pair of intake ports 8 corresponding to the pair of intake valves 5 independently of each other. That is, the pair of intake ports 8 do not merge in the cylinder head 2 and open independently on the side surfaces of the cylinder head 2. An exhaust port 9 is formed corresponding to the exhaust valve 6.
[0022]
The electromagnetic fuel injection valve 10 having a substantially cylindrical shape is disposed on the lower surface portion of the cylinder head 2 near the side wall of the cylinder 3 on the intake valve 5 side, and is attached in such a posture that its central axis is directed obliquely downward. In particular, as shown in FIG. 2, the fuel injection valve 10 is disposed between two intake valves 5.
[0023]
As will be described later, a circular bowl 12 is formed on the top of the piston 4 disposed in the cylinder 3 at a position eccentric to the intake valve 5 side, and the piston 4 is in the vicinity of the top dead center. In addition, the spray axis of the fuel injection valve 10 is directed to the bowl 12.
[0024]
The pair of intake ports 8 are connected to a pair of intake passages 14a and 14b that are independently formed on the intake manifold 13 side. A butterfly valve type air control valve 15 for opening and closing the intake passage 14b is interposed in the one intake passage 14b. The air control valve 15 is controlled to open and close according to engine operating conditions by a drive mechanism (not shown) via a shaft 16. In the state where the air control valve 15 is closed, fresh air flows only through the intake port 8 connected to the other intake passage 14a. However, the intake port 8 is not a helical port, but is a loosely curved substantially straight line. Port shape.
[0025]
The basic operation of the internal combustion engine will be briefly described. First, a homogeneous air-fuel mixture is formed in the cylinder 3 at the time of full load of the engine or in a region where the air-fuel ratio is relatively small in the lean combustion region. Homogeneous combustion is performed. During the homogeneous combustion, the air control valve 15 is controlled to be in an open state, and fresh air is introduced into the cylinder 3 from both the pair of intake ports 8. Thereby, a strong tumble flow (longitudinal vortex) is generated in the cylinder 3. The fuel is injected and supplied into the cylinder 3 during the intake stroke. This fuel is actively diffused in the cylinder 3 by the tumble flow, and homogenization is promoted without staying in the bowl 12.
[0026]
On the other hand, in a lean combustion region where the air-fuel ratio is very large in a low load region, stratified lean combustion is performed that enables reliable ignition by stratification of the air-fuel mixture. During this stratified lean combustion, the air control valve 15 is closed, and fresh air flows into the cylinder 3 from only one intake port 8. Thereby, in the cylinder 3, the tumble component is relatively weakened and a swirl flow along the horizontal direction is generated strongly. During this stratified lean combustion, fuel is injected from the fuel injection valve 10 toward the bowl 12 in the latter half of the compression stroke. This injected fuel rides on the swirl flow confined in the bowl 12 at the top of the piston 4 and moves toward the spark plug 7 to form an ignitable air-fuel mixture around the spark plug 7. Ignition combustion is possible by igniting.
[0027]
Next, with reference to FIGS. 3-5, the structure of the piston 4, especially the structure of the top part is demonstrated in detail.
[0028]
In the piston 4, a convex portion 21 is provided on the top surface according to the shape on the cylinder head 2 side. The convex portion 21 is basically composed of four surfaces. That is, the intake valve side inclined surface 22 and the exhaust valve side inclined surface 23, which are planes substantially parallel to the two inclined surfaces 11a and 11b (FIGS. 1 and 2) constituting the pent roof type combustion chamber 11 on the cylinder head 2 side, The convex portion 21 is constituted by a pair of conical side surfaces 24 and 25 each having a conical surface concentric with the outer circle of the piston 4. The pair of conical side surfaces 24 and 25 constitutes the side portion of the convex portion 21.
[0029]
In addition, the part in which the bowl 12 mentioned later is formed in the said intake valve side inclined surface 22 is a virtual plane. In this embodiment, the conical side surfaces 24 and 25 are continuous with each other through the lower edge of the exhaust valve side inclined surface 23. Further, the apex angles of the conical side surfaces 24 and 25 in the convex portion 21 are very small, and the conical side surfaces 24 and 25 are formed to stand up as shown in FIGS.
[0030]
A piston reference horizontal surface 26 is formed on the outer periphery of the convex portion 21. The piston reference horizontal plane 26 is composed of a single plane orthogonal to the center line of the piston 4, and is continuous in an annular shape over the entire circumference of the piston 4. The thrust and anti-thrust portions of the piston reference horizontal surface 26 correspond to the squish areas 2a and 2b (see FIG. 1) left as flat surfaces on both sides of the combustion chamber 11 on the cylinder head 2 side, respectively. Contributes to the generation of
[0031]
Further, the bowl 12 is recessed over the intake valve side inclined surface 22 and the exhaust valve side inclined surface 23. The bowl 12 has a substantially circular shape when viewed on the plane of the piston 4, has a bottom surface formed in a substantially flat surface, and has a dish shape in which an inner peripheral side wall surface is gently expanded upward and tapered. .
[0032]
Here, the outer peripheral edge of the bowl 12 intersects the ridge line 27 between the convex portion 21 and the piston reference horizontal surface 26 on the intake valve 5 side. That is, a part of the bowl 12 reaches the piston reference horizontal surface 26, and conversely, a part of the piston reference horizontal surface 26 is cut out by the bowl 12.
[0033]
The piston reference horizontal plane 26 has a constant radial width L1 over the entire circumference including the virtual piston reference horizontal plane cut out by the bowl 12. The radial width L1 of the piston reference horizontal surface 26 is set to be longer than at least the width of the squish areas 2a and 2b (see FIG. 1). Therefore, even when the piston 4 is located near the top dead center, a space that is continuous over the entire circumference of the piston, that is, a swirl path, remains above the piston reference horizontal plane 26.
[0034]
As shown in FIG. 2, when the piston 4 is at the top dead center, the spark plug 7 is disposed so as to enter the bowl 12 and to be positioned on the outer periphery thereof.
[0035]
Further, the structure of the top portion of the piston 4 configured as described above is configured symmetrically about a diameter line (that is, a CC line in FIG. 4) in a direction orthogonal to the piston pin. In addition, the fuel injection valve 10 is arrange | positioned so that a fuel may be injected along CC line used as this symmetry axis.
[0036]
In the configuration of the present embodiment as described above, when the piston 4 approaches top dead center, the intake valve side inclined surface 22 and the exhaust valve side inclined surface 23 of the piston 4 correspond to the cylinder head 2 side shown in FIG. The swirl passages above the bowl 12 and the piston reference horizontal plane 26 occupy most of the volume remaining in the cylinder 3 because they are close to the inclined surfaces 11a and 11b. That is, since the piston reference horizontal plane 26 is formed along the outer periphery of the piston 4, a swirl passage is secured over the entire piston circumference above the piston reference horizontal plane 26 even when the piston 4 is located near the top dead center. . For this reason, the swirl S1 having a sufficient strength can be stored even in the vicinity of the top dead center of the piston 4. As a result, the swirl component S2 introduced into the bowl 12 becomes sufficiently strong, and the air-fuel mixture in the bowl 12 is made favorable by the central negative pressure of the swirl component S1 stored with sufficient strength. Since it can be sucked up to the position of the spark plug 7, good stratified combustion can be realized.
[0037]
At the time of homogeneous combustion, a tumble flow is formed in the cylinder 3 by the fresh air flowing in from the pair of intake ports 8 and fuel injection is performed during the intake stroke. Since the substantially circular bowl 12 is located on the center line (the CC line in FIG. 4) of the pair of intake ports 8 that have an expanded dish shape and the tumble flow is concentrated. The fuel that has entered 12 is easily washed away by the tumble flow. Therefore, a homogeneous air-fuel mixture can be formed even at high loads, and good homogeneous combustion is possible. That is, stratified combustion and homogeneous combustion can be achieved at a high level.
[0038]
Further, since a part R (see FIGS. 3 and 4) of the bowl 12 reaches the piston reference horizontal plane 26, the swirl component S1 swirling above the piston reference horizontal plane 26 via this part R is effectively contained in the bowl 12. To be guided to. As a result, the gas flow (swirl component) S2 in the bowl 12 is further strengthened, and the combustion efficiency particularly during stratified combustion is improved.
[0039]
Moreover, since the bowl 12 is substantially circular, the swirl component S2 introduced into the bowl 12 can be stored while maintaining a sufficient strength.
[0040]
6A and 6B are sectional views taken along lines BB and CC in FIG. 4, respectively. In the drawing, the broken line indicates the piston 40 according to the comparative example. In this comparative example, the outer edge of the convex portion 41 is continuous with the outer peripheral edge of the piston, and the piston reference horizontal surface 26 as in this embodiment exists. Not. In such a comparative example, the convex portion 41 is relatively close to the cylinder 3 wall surface at the circumferential position shown in (a), and the convex portion 41 is relatively separated from the cylinder 3 wall surface at the circumferential position shown in (b). It will be far away. That is, since the thickness of the piston 40 varies depending on the circumferential position, the heat dissipation characteristics, thermal deformation amount, and the like of the piston 40 are not uniform in the circumferential direction. As a result, for example, the amount of thermal deformation of the piston 40 locally increases in a part of the circumferential direction, and there is a possibility that an early seizure phenomenon of the cylinder 3 wall portion due to the tilt of the piston 40 may occur.
[0041]
On the other hand, in the piston 4 of the present embodiment, the piston reference horizontal surface 26 having a uniform radial width L1 is formed over the entire circumference of the piston, so that the outer periphery of the top of the piston 4 has a uniform height and diameter over the entire circumference. It becomes the direction width L1. Therefore, the thickness of the outer peripheral portion of the piston 4 slidably contacting the wall surface of the cylinder 3 can be made uniform over the entire circumference, and the heat radiation characteristics, the amount of thermal deformation, etc. of the outer peripheral portion of the piston 4 are made uniform over the entire circumference. As a result, unlike the comparative example, there is no possibility that a part of the circumferential direction of the piston is thermally deformed locally or that the cylinder is prematurely seized.
[0042]
FIG. 7 shows a pushing jig used when the piston 4 is assembled in the cylinder 3.
[0043]
The pushing jig 30 has a cylindrical portion 31 having substantially the same diameter as the piston 4, and three positioning projections 32 are provided on the outer peripheral portion of the cylindrical portion 31 at appropriate intervals. The front end surfaces 32a of these positioning projections 32 are set to the same plane as a reference at the time of assembly, and the piston 4 is moved while the front end surfaces 32a of these positioning projections 32 are brought into contact with the piston reference horizontal surface 26 of the piston 4. It is pushed into the cylinder 3. Thus, in this embodiment, since the piston reference horizontal surface 26 is formed on the entire top surface of the piston 4, the assembly work of the piston 4 to the cylinder 3 can be performed by using an appropriate pushing jig 30. It can be performed automatically with high accuracy and has very good assembly workability.
[0044]
In addition, this invention is not limited to the said Example, For example, like the 2nd Example shown to FIG. 9, 10, the radial direction width | variety of the piston reference horizontal surface 26 may not be constant. That is, in the second embodiment, the radial width of the piston reference horizontal surface 26 is set to be relatively large on the intake valve 5 side.
[0045]
The radial width of the piston reference horizontal surface 26 may be set so as to increase on the exhaust valve 6 side, contrary to the second embodiment.
[0046]
Even in the configuration as shown in the second embodiment, as in the first embodiment, the present invention is characterized by improving the assembly workability of the piston 4 while achieving both stratified combustion and homogeneous combustion at a high level. Effects can be achieved.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a configuration of a direct injection internal combustion engine according to the present invention.
FIG. 2 is a bottom view showing a state in which the cylinder head is viewed from the lower surface side.
FIG. 3 is a perspective view showing a first embodiment of a piston according to the present invention.
4 is a plan view of the piston of FIG. 3;
5 is a cross-sectional view taken along line AA in FIG.
6A and 6B are cross-sectional views showing a piston of an example and a comparative example, wherein FIG. 6A is a cross-sectional view along the line BB in FIG.
FIG. 7 is a plan view of a piston pushing jig.
8 is a cross-sectional view taken along the line DD of FIG.
FIG. 9 is a plan view of a piston according to a second embodiment of the present invention.
10 is a cross-sectional view taken along line EE in FIG.
[Explanation of symbols]
4 ... Piston 12 ... Bowl 21 ... Convex part 22 ... Intake valve side inclined surface 23 ... Exhaust valve side inclined surface 24, 25 ... Conical side surface (side part)
26 ... Piston reference horizontal plane 27 ... Ridge line

Claims (3)

A pent roof type combustion chamber recessed in the cylinder head has two intake valves and two exhaust valves, and has a spark plug in the center of the cylinder, and a fuel injection valve that directly injects fuel into the cylinder It is arranged on the valve side and realizes homogeneous combustion by injecting fuel near the intake stroke with a tumble flow component in the cylinder, and fuel injection near the compression stroke with a swirl component in the cylinder In the piston of a direct injection internal combustion engine that realizes stratified combustion by performing
The exhaust valve side inclined surface which is a plane inclined substantially parallel to the inclined surface on the exhaust valve side of the pent roof type combustion chamber and the inclined surface on the intake valve side of the pent roof type combustion chamber so as to be substantially parallel to the inclined surface. An intake valve side inclined surface composed of an inclined plane or a virtual plane, a pair of side surfaces constituting the side portion of the convex portion formed by both the inclined surfaces, and a concave portion at a position eccentric to the intake valve side with respect to the piston outer circle. A substantially circular bowl provided, and a piston reference horizontal plane that is formed continuously around the entire circumference of the piston along the outer periphery of the piston so as to surround the convex portion, and is a plane perpendicular to the piston center line; Have
The outer peripheral edge of the bowl intersects the ridge line between the convex portion and the piston reference horizontal plane only at one place on the intake valve side ,
In addition, a swirl passage is secured over the entire circumference of the piston above the piston reference horizontal plane, and the swirl component when the stratified combustion is realized is preserved by the swirl passage, and the bowl is removed from the intersecting portion of the swirl component. A piston of a direct injection internal combustion engine, wherein the piston is guided inward to reinforce gas flow in the bowl . 2. The piston of a direct injection internal combustion engine according to claim 1, wherein the piston reference horizontal plane is set to have a constant width over the entire circumference of the piston except for a portion notched by the bowl.   3. The piston of a direct injection internal combustion engine according to claim 1, wherein the bowl has a dish shape whose inner peripheral side wall surface is tapered upward.

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