JP4004179B2 - In-cylinder injection engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an in-cylinder injection engine in which fuel is directly injected into a combustion chamber from a fuel injection device and burned.
[0002]
[Prior art]
Examples of this type include those shown in FIGS. 9 and 10. 9 (a) and 10 (a) are plan views of the piston 1 of the direct injection engine, FIGS. 9 (b) and 10 (b) are cross-sectional views of the piston 1, and FIG. As shown, a cavity 3 that is a recess is formed in the top 2 of the piston 1.
[0003]
In the compression stroke of the in-cylinder injection engine, fuel is directly injected from the fuel injection device 4 obliquely from the right end (base end 3a) of the cavity 3 toward the bottom surface 3b. As a result, the spray G is lifted upward by the vertical wall portion 3d of the tip 3c of the cavity 3, and this fuel is ignited by the spark plug 5 and burned.
[0004]
Thus, by providing the cavity 3 and injecting the fuel therein, the mixing property with the air is improved, and it is lifted upward to ensure the ignitability.
[0005]
[Problems to be solved by the invention]
However, in such a conventional one, the air-fuel mixture is lifted upward by the cavity 3, but the spark plug 5 is configured such that the side electrode 5b wraps around the lower side of the center electrode 5a. Therefore, the air-fuel mixture was blocked by the side electrode 5b.
[0006]
Then, this invention makes it the subject to provide the cylinder injection engine which can improve ignitability more, without being interrupted by a side electrode.
[0007]
[Means for Solving the Problems]
In order to achieve such an object, according to the first aspect of the present invention , a cylinder head is attached to a cylinder block, a piston is disposed on the cylinder block, and ignition is performed at a substantially center of the cylinder head above the piston. In the in- cylinder injection engine in which the plug is disposed and the fuel injection device that directly injects the fuel into the combustion chamber is disposed , the piston has a flat portion formed around the top portion, and the piston is disposed inside the flat portion. A convex part projecting upward from the flat part and a concave cavity are formed across the convex part and the flat part, and the convex part is located in the center of the piston top and extends in the radial direction. An intake side inclined surface and an exhaust side inclined surface whose lower ends reach the planar portion on both sides of the top surface, and at the top dead center position of the piston, Inclined surface The slant angle is larger than the slant surface on the exhaust side and different from the slant angle on the bottom surface of the intake valve, and the gap between the slant surface on the suction side and the bottom surface of the intake valve widens as the slope goes down, The inclined surface on the exhaust side is substantially parallel to the lower surface of the exhaust valve, and the cavity has an egg shape in plan view, and the narrower tip end side of the egg shape is placed in the top surface below the spark plug. is disposed in the base end side of the thicker of the egg shape, across the inclined surface of the intake side is disposed within said planar portion, and is disposed in the injection port near the fuel injector, the fuel the The in-cylinder injection engine is configured to inject from the proximal end side toward the distal end side.
[0008]
According to a second aspect of the present invention, in addition to the configuration according to the first aspect, a flat portion that inclines so that the tip end side is higher is formed on the bottom surface of the cavity, and a base end is a lower end of the inclined surface on the intake side. It is characterized by being formed so as to be positioned below the plane part beyond
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0010]
1 to 8 show an embodiment of the present invention.
[0011]
First, the configuration will be described. Reference numeral 21 in FIG. 1 denotes a cylinder block. A cylinder head 22 is disposed above the cylinder block 21, and a piston 23 is disposed on the cylinder block 21 so as to be movable up and down. Has been.
[0012]
The cylinder head 22 is provided with an intake valve 26 and an exhaust valve 27 for opening and closing two intake ports 24 and two exhaust ports 25, respectively, as shown in FIGS. The intake valve 26 and the exhaust valve 27 are opened and closed at a predetermined timing by an intake side camshaft and an exhaust side camshaft (not shown). Further, as shown in FIG. 3, an on-off valve 45 is disposed inside one of the intake passages 43 that are continuous with each of the pair of intake ports 24.
[0013]
Further, the cylinder head 22 is provided with a fuel injection device 31 and a spark plug 42, and an injection port 31 a of the fuel injection device 31 and a tip end portion 32 a of the spark plug 42 face the combustion chamber 33. The fuel injection device 31 is disposed obliquely in the vicinity of the lower side of the intake port 24, while the spark plug 42 is centered in the plan view of the combustion chamber 33, and vertically along the highest position of the combustion chamber 33. Has been placed.
[0014]
As shown in FIGS. 1 and 2, the spark plug 42 is provided with a center electrode 42a at the center, and three side electrodes 42b around the center electrode 42a at intervals of 120 ° along the radial direction. Arranged. These side electrodes 42b are bent at a substantially right angle, the tip portion 42c faces the side of the center electrode 42a, and a spark gap is formed between the side surface of the center electrode 42a and the side electrode tip portion 42c. . The center electrode 42a and the like are located above the cavity tip 39a.
[0015]
The intake port 24 is formed obliquely on the fuel injection device 31 side, and a masking 46 is provided at the lower edge 24b of the intake port 24a of the intake port 24 as shown in FIG. As shown in the figure, when the intake valve 26 is opened, the amount of inflow air is larger on the upper edge portion 24c side of the intake port 24a than on the lower edge portion 24b side. As a result, as shown in FIG. 6A, when the inside of the combustion chamber 33 is viewed with the distal end 39a of the piston cavity 39 on the left side and the base end 39b on the right side, the intake port 24 has an intake port 24a. As shown by an arrow X in the figure, the air flowing into the combustion chamber 33 is configured to generate a counterclockwise tumble.
[0016]
On the other hand, the shape of the top portion 36 of the piston 23 is formed as follows.
[0017]
That is, a flat portion 37 is formed in the periphery, and a convex portion 38 that protrudes upward and a cavity 39 that is a concave shape across the convex portion 38 and the flat portion 37 are formed inside the flat portion 37. ing.
[0018]
As shown in FIGS. 1 and 2, the convex portion 38 has a top surface 38a formed in a planar shape and an inclined surface 38b reaching the top surface 38a. The top surface 38a is located at the center of the piston top and extends in the radial direction. The inclined surface 38b has a flat intake-side inclined surface 38b1 and an exhaust-side inclined surface 38b2 whose lower ends reach the flat portion 37 on both sides of the top surface 38a. As shown in FIG. 1, at the top dead center position of the piston 23, the inclination angle of the inclined surface 38b1 on the intake side is larger than the inclined surface 38b2 on the exhaust side and is different from the inclination angle on the lower surface of the intake valve 26. The gap between the inclined surface 38b1 and the lower surface of the intake valve 26 widens as it goes downward, and the exhaust-side inclined surface 38b2 and the lower surface of the exhaust valve 27 are substantially parallel.
[0019]
Further, the cavity 39 has an egg shape in plan view, and the narrow tip end 39a of the egg shape is disposed in the top surface 38a at the center of the top surface of the piston 23 (below the ignition plug 42). In addition, the thick base end 39b of the egg shape is disposed in the flat portion 37 across the inclined surface 38b1 on the intake side, and is disposed in the vicinity of the injection port 31a of the fuel injection device 31. . Further, as shown in FIG. 4B and the like, the bottom surface 39c of the cavity 39 is formed so as to be inclined so that the tip end 39a side becomes higher, and is set to an angle α ° (5 ° to 7 °) here. Has been. As shown in FIG. 1, the cavity bottom surface 39 c has a flat portion that is inclined so that the tip end side is higher so that the base end is positioned below the flat surface portion 37 beyond the lower end of the inclined surface 38 b 1 on the intake side. Is formed. Furthermore, the radius of curvature R of the R-shaped portion 39e extending from the bottom surface 39c on the tip end portion 39a side to the vertical wall 39d is set to 13 mm here.
[0020]
The relationship between the inclination angle α ° of the cavity bottom surface 39c and the curvature radius R of the R-shaped portion 39e is such that when the inclination angle is 0 °, that is, when the inclination is not inclined, the curvature radius R is 15 mm or more. When the bottom surface 39c is inclined, the radius of curvature R is preferably set to 8 mm to 15 mm.
[0021]
Further, as shown in FIG. 4C, the R-shaped portion 39g between the cavity bottom surface 39c and the side wall 39f is set to 8 mm to 10 mm here, and is formed smaller than the R-shaped portion 39e. Yes. Of course, both can be formed the same. In this case, both R-shaped portions 39g and 39e can be formed continuously with one tool.
[0022]
And the squish area is provided between the inclined surface 38b of this piston convex part 38, and the combustion chamber ceiling inclined surface 33a (refer FIG.6 (c)).
[0023]
Next, the operation will be described.
[0024]
First, in the BDC (bottom dead center) shown in FIG. 6A, outside air is introduced into the combustion chamber 33 from the opened intake valve 26, and a counterclockwise tumble as shown by an arrow X in the figure occurs. . This is because a large amount of air is sucked in from the upper edge 24c side of the intake port 24a, and thus counterclockwise tumble occurs.
[0025]
Next, at BTDC 60 ° shown in FIG. 6B, the piston 23 rises and the air is pushed up, so that the flow indicated by the arrow S is generated. At the same time, as shown in FIG. 7, at BTDC 63 ° to 58 °, fuel is injected from the fuel injection device 31 into the cavity 39, and the fuel adhering to the cavity bottom surface 39c is vaporized and rises.
[0026]
Further, due to the flow indicated by the arrow S, the tumble flow X shown in FIG. 6A gradually changes as indicated by the arrow X1.
[0027]
In this way, the tumble is lost as the piston 23 ascends, so that the entire tumble flow is lost (the tumble collapses) and becomes a fine turbulent flow component.
[0028]
As a result, the fuel is mixed well with the air.
[0029]
And in BTDC30 degree shown in FIG.6 (c), since the squish area is formed between the inclined surface 38b of the piston convex part 38, and the ceiling inclined surface 33a of the combustion chamber 33, (b) of FIG. ) Flow S changes to a flow as indicated by an arrow S1 in FIG. Due to the so-called squish effect at this time, the air-fuel mixture is stirred more favorably, and an upward flow Y is generated at the tip 39 a in the piston cavity 39. Further, the flow of the gas-liquid mixture at BTDC 20 ° is as shown in FIG.
[0030]
Due to the effects of the tumble and squish as described above, the fuel and air are mixed well, and the shape of the cavity 39 causes the gas-liquid mixture rich in fuel to be collected at the tip 39a and lifted from the other parts. .
[0031]
On the other hand, when the fuel is injected from the injection port 31a of the fuel injection device 31 in the range of 60 ° to 80 ° in FIG. Since the width H on the base end portion 39b side of the cavity 39 is widened, as shown by an arrow A in FIG. 4A, air due to the in-cylinder swirl flow enters the spray end G on the base end portion 39b side. Air is likely to be mixed in, and since the injection angle θ is somewhat large as described above, air is also likely to be mixed in this respect.
[0032]
The spray G hits the bottom surface 39c of the cavity 39, is guided toward the tip 39a side by the bottom surface 39c, and is pressed against the side wall 39f by the in-cylinder swirl flow flowing from one side as described above. The side wall 39f guides the tip 39a. The side wall 39f is higher than the conventional one shown in FIG. 9B and the like, and at the same time, the curvature radius R of the R-shaped portion 39g is small, so that side leakage of the spray G can be prevented.
[0033]
Next, the spray G is guided by the R-shaped portion 39e and the vertical wall 39d of the cavity tip portion 39a and lifts upward. In this case, it is easy to lift the spray G by making the bottom surface 39c into a slope shape, and the accumulation of the spray G in this portion can be suppressed by increasing the R-shaped portion 39e.
[0034]
And as shown to (a), (b) of FIG. 5, at the front-end | tip part 39a of the egg-shaped thin one, the front part which spray G once spread is narrowed and concentrated, and stratification is carried out. As shown in FIG. 7, it is ignited by the spark plug 42 at around BTDC 20 °.
[0035]
In this case, the fuel and air are sufficiently mixed to suppress the generation of smoke, and at the same time, the stratification is achieved and the transfer to the spark plug 42 is favorably performed, thereby stabilizing the combustion. To do.
[0036]
In addition, since the stratification is achieved, the ignition plug 42 can be prevented from being heated since the ignitability can be ensured even if the amount of projection of the spark plug 42 into the combustion chamber 33 is shortened.
[0037]
In addition, as shown in FIGS. 1 and 2, the spark plug 42 has a tip portion 42c of the side electrode 42b that faces the center electrode 42a laterally, so that a spark can fly to the side. Become. Therefore, the air-fuel mixture that has risen is not blocked by the side electrodes 42b, but rises directly to the part where the spark is flying, so that the ignition performance is good.
[0038]
On the other hand, an opening / closing valve 45 is disposed inside one of the pair of intake passages 43. Since the opening / closing valve 45 is closed in the low rotation speed region, the other intake passage is introduced into the combustion chamber 33. 43, that is, air flows in from a position biased with respect to the combustion chamber 33, so that a swirl is generated in the combustion chamber 33. Accordingly, here, the flow of tumble and swirl is combined, and the gas-liquid mixing performance is further improved. The on-off valve 45 is electronically controlled in order to control the swirl flow in the cylinder according to the demand at the time of stratified combustion or uniform lean combustion.
[0039]
Incidentally, FIG. 8 shows a graph of the relationship between the intake air amount and the rotational speed when the air-fuel ratio is changed. The combustion as described above is performed in the shaded portion in the figure, that is, the air-fuel ratio. (A / F) is in the range of 30-70.
[0040]
【The invention's effect】
As described above, according to the first aspect of the present invention , outside air is introduced into the combustion chamber from the intake valve, tumble is generated, the piston is then lifted, the air is pushed up, and the fuel injection device As the fuel is injected into the cavity and the fuel adhering to the bottom of the cavity is vaporized and rises, the overall tumble flow is lost, it becomes a fine turbulent flow component, and the fuel is well mixed into the air To be done. A squish area is formed between the inclined surface of the piston convex part and the ceiling inclined surface of the combustion chamber, so that a squish effect is produced, and the mixture is agitated better, and at the tip in the cavity. , An upward flow occurs. Due to the effect of squish, fuel and air are mixed well, and the shape of the cavity raises the gas-liquid mixture that is collected at the tip and richer in fuel than the other parts. When fuel is injected from the injection port of the fuel injection device, the width of the base end side of the cavity becomes wider with respect to the shape of the spray, so that air from the in-cylinder swirl flow enters the base end side and sprays. Since air is easily mixed in and the injection angle is somewhat large as described above, air is also easily mixed in this respect. The spray hits the bottom surface of the cavity and is guided toward the front end side at this bottom surface, and is pressed against the side wall by the in-cylinder swirl flow flowing from one side as described above, while the front end side is formed on this side wall. Is directed toward the stratified, stratified, transferred to the spark plug, ignited by the spark plug, and the combustion is stabilized.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a direct injection engine according to an embodiment of the present invention.
FIG. 2 is a plan view of the piston according to the same embodiment.
FIG. 3 is a rear view of the cylinder head according to the same embodiment.
4A and 4B are views showing the piston according to the embodiment, wherein FIG. 4A is a plan view of the piston, FIG. 4B is a cross-sectional view taken along line AA in FIG. 4A, and FIG. It is sectional drawing which follows the BB line.
5A is a plan view corresponding to FIG. 4A, and FIG. 5B is a cross-sectional view corresponding to FIG. 4B.
6 is an explanatory diagram showing the relationship between the position of a piston and the flow of an air-fuel mixture or the like according to the second embodiment, where FIG. 6A is a BDC for the piston, FIG. 6B is a BTDC 60 °, and FIG. ° and (d) are explanatory diagrams in the state of BTDC 20 °.
FIG. 7 is a diagram showing injection timing and the like according to the same embodiment.
FIG. 8 is a graph showing the relationship between the intake air amount and the rotation speed when the air-fuel ratio is changed according to the same embodiment.
9A and 9B are diagrams showing a conventional piston and the like, in which FIG. 9A is a plan view of the piston, and FIG. 9B is a cross-sectional view of the piston.
10A is a plan view corresponding to FIG. 12A, and FIG. 10B is a cross-sectional view corresponding to FIG. 12B.
[Explanation of symbols]
21 Cylinder block
22 Cylinder head
23 Piston
31 Fuel injector
31a Injection port
33 Combustion chamber
36 Top
39 cavity
39a Tip
39b Base end
42 Spark plug
42a Center electrode
42b Side electrode
42c Tip G spray

Claims (2)

A cylinder head is mounted on the cylinder block, a piston is disposed on the cylinder block, and a spark plug is disposed substantially at the center of the cylinder head above the piston, and further fuel is injected directly into the combustion chamber. In the cylinder injection engine provided with the device,
The piston has a flat portion around the top,
A convex portion protruding upward from the flat portion and a concave cavity are formed across the convex portion and the flat portion inside the flat portion,
The convex portion includes a flat top surface extending in the radial direction at the center of the top of the piston, a flat intake-side inclined surface on the both sides of the top surface and a lower end reaching the flat portion, and an exhaust side An inclination angle of the intake-side inclined surface is larger than that of the exhaust-side inclined surface and is different from an inclination angle of the lower surface of the intake valve at the top dead center position of the piston. The clearance between the inclined surface and the lower surface of the intake valve widens as it goes downwardly, and the inclined surface on the exhaust side and the lower surface of the exhaust valve are substantially parallel,
The cavity is
The egg shape is shown in plan view.
The tip side of the egg-shaped thin one is placed in the top surface below the spark plug,
The base end side of the thicker egg-shaped portion is disposed in the flat portion across the inclined surface on the intake side, and is disposed in the vicinity of the injection port of the fuel injection device,
An in-cylinder injection engine characterized in that fuel is injected from the base end side toward the tip end side. The bottom surface of the cavity is formed with a flat portion that is inclined so that the tip end side is higher so that a base end is positioned below the flat surface portion beyond a lower end of the inclined surface on the intake side. The in-cylinder injection engine according to claim 1.

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