JP2002097961A - Method of forming combustion chamber of diesel engine and combustion chamber of diesel engine formed by using the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily determine the data as the components of a combustion chamber capable of easily specifying an ideal shape of the combustion chamber. SOLUTION: In this diesel engine, fuel is directly injected from an injection nozzle into the combustion chamber 1 formed of the lower surface 6 of a cylinder head 5 and a recess 10 formed in a piston head 8 at the end of a compression stroke for moving a piston 3 to a top dead center, and the wall surface of the recess 10 is formed on a convex surface 18a projected to the outside of the piston continuously around the centerline L of the piston. Based on an angle θ2 formed by a virtual centerline 22 of the injected fuel injected from the injection nozzle and moving to the convex surface 18a and the lower surface 6 of the cylinder head, the intersection 24 of the virtual centerline 22 with the wall surface of the combustion chamber and the ratio of a combustion chamber depth H1 to a distance L1 between piston head top faces 9 are obtained to specify the shape of the recess.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a combustion chamber of a diesel engine.

[0002]

2. Description of the Related Art In a diesel engine, a combustion chamber is formed by a cylinder head and a piston head when a piston is at a top dead center, and fuel is directly injected from an injection nozzle toward the combustion chamber. Further, a depression is formed in the piston head in order to mix the fuel with air well in the combustion chamber, and turbulence of air is generated in the depression during the compression stroke during the operation stroke of the internal combustion engine, and the air is directed toward the depression. To inject fuel from the injection nozzle. Therefore, the first condition of the shape of the combustion chamber of the diesel engine is that the structure is such that the injected fuel and the air are sufficiently mixed.

In order to enhance the combustibility, the size and injection state of fine particles (hereinafter referred to as “injected particles”) of the injected fuel (hereinafter referred to as “injected fuel”) are improved by injecting the injection nozzles. We are dealing.

[0004] However, it is not easy to specify the shape of the recess and to determine the parameters such as the fuel injection angle and the amount of protrusion of the injection nozzle so as to maximize the performance of the diesel engine. In this technique, it was determined gradually by repeating various experiments.

[0005]

Various techniques have been proposed to maximize the performance of the engine (for example, Japanese Patent Application Laid-Open Nos. 7-150944 and 8-28).
4667, 10-159566).

However, there is no end to the demand for improving the performance of diesel engines, and there is a need for a proposal of a technology that can be expected to achieve further effects.

In order to satisfy the demand, it is important that the shape of the dent in the combustion chamber can be easily specified. In particular, the blast is injected from the injection hole of the injection nozzle toward the dent. It is important factors to determine the distance L1 between the intersection of the virtual center line of the injected fuel and the combustion chamber wall surface and the top surface of the piston head, and the dimensions of the combustion chamber depth H1.

The present invention has been made in view of the above points, and the problem to be solved is to solve the above-mentioned distance L1 and combustion chamber depth H1 so that the ideal shape of the combustion chamber can be easily determined. It is an object of the present invention to provide a method for forming a combustion chamber of a diesel engine, which can easily determine the dimensions of the combustion chamber, and a combustion chamber for a diesel engine formed by using the method.

[0009]

To achieve the above object, the combustion chamber of the diesel engine of the present invention employs the following means.

(1) At the end of the compression stroke of the piston toward the top dead center, fuel is directly injected from the injection nozzle into the combustion chamber formed by the lower surface of the cylinder head and the depression formed in the piston head, and the wall surface of the depression is formed. Is formed around a piston center line and has a convex curved surface protruding outward from the piston. In the diesel engine, the virtual center line of the fuel injected from the injection hole of the injection nozzle toward the convex curved surface is the cylinder head. The ratio of the depth of the combustion chamber (H1) to the distance L1 between the intersection of the imaginary center line and the wall surface of the combustion chamber and the top surface of the piston head is determined based on the angle (θ2) formed with the lower surface. Specify the shape.

Here, the angle θ2 between the virtual center line of the injected fuel and the lower surface of the cylinder head is constant in the same diesel engine. This is because, in a diesel engine which is a compression ignition type internal combustion engine, fuel is injected when the pressure reaches a specified pressure in a compression stroke. Therefore, the angle θ2 for each type of diesel engine
Is determined.

In the present invention, based on the angle θ2 formed by the virtual center line of the injected fuel with the lower surface of the cylinder head, the combustion chamber with respect to the intersection of the virtual center line with the wall surface of the combustion chamber and the distance L1 between the piston head top surface. It is characterized in that the ratio of the depth H1 is obtained.

As described above, since the angle θ2 formed by the virtual center line of the injected fuel and the lower surface of the cylinder head is constant, if this angle is determined, the intersection of the virtual center line with the wall surface of the combustion chamber and the top of the piston head are determined. As means for unifying the ratio L1 / H1 of the combustion chamber depth H1 to the distance L1 between the surfaces, for example, the ratio is taken on the vertical axis,
A two-dimensional map having an angle θ2 on the horizontal axis is prepared, and when the angle θ2 is determined, the ratio L is calculated from the two-dimensional map.
Find 1 / H1.

When the ratio L1 / H1 is obtained, the distance L1 between the intersection with the combustion chamber wall surface and the top surface of the piston head is determined.
And it becomes easy to determine the combustion chamber depth H1. Because the ratio L1
This is because the dimensions of L1 and H1 may be determined so as to satisfy the relationship of / H1.

To determine the angle θ2, a distance (flying distance of the injected fuel) L3 from the injection hole of the injection nozzle to the intersection of the virtual center line with the combustion chamber wall surface is determined. The distance L3 determines the volume of the combustion chamber depending on the stroke volume (displacement amount) and the compression ratio, and determines the maximum injection pressure of the fuel, the duration of the injection, and the injection nozzle. This is a value obtained by determining the injection hole diameter.

When the flight distance L3 is determined, a point at which the distance dimension from the injection hole of the injection nozzle to the intersection of the virtual center line with the combustion chamber wall surface is determined to be L3 is defined as the intersection. Once the intersection is obtained, the distance L1 between the intersection and the top surface of the piston head and the angle θ2 are determined naturally.

When the angle θ2 is determined, the ratio L1 / H1 is determined from the map. Since L1 has already been obtained, H1 is obtained from the ratios L1 / H1 and L1.

Accordingly, the distance L1 between the intersection point where the virtual center line of the injected fuel injected from the injection hole of the injection nozzle toward the depression intersects the combustion chamber wall surface and the top surface of the piston head, and the combustion chamber Since it becomes easy to determine the dimension of the depth H1, it is possible to easily determine the ideal shape of the combustion chamber. (2) In the above (1), the ratio is preferably obtained by using a specific formula.

In the present invention, the ratio L1 is calculated by using an equation.
/ H1 can be determined precisely. (3) In the above (2), for example, the following quadratic equation can be mentioned as the above formula.

Y = −0.0073x ² + 0.184x−0.76 Here, y: ratio L1 / H1 x: angle θ2 In the conventional techniques, the distance L1 and the combustion chamber depth H1 are determined with respect to the angle θ2. It was not considered what kind of relationship would be, and I had found from experience how to make a certain combustion chamber and how much the angle θ2 should be in it. This formula was established this time as a means. This formula was obtained by experiment. If the distance L1 and the depth of the combustion chamber H1 can be determined while observing the relationship in this mathematical expression, a combustion chamber comparable to any cylinder size (bore size) can be obtained. (4) The combustion chamber of a diesel engine may be formed by using the method for forming a combustion chamber of a diesel engine according to any one of (1) to (3). (5) In the above (4), the convex curved surface of the depression is formed at a specific angle θ at which the virtual center line forms a tangent at the intersection.
The specific angle θi may be varied according to the movement of the piston, and may decrease and increase once when the piston is at the top dead center of the engine.

With this setting, even if the injected fuel hits the inner wall surface of the dent and is reflected, it does not accumulate at a certain location in the dent.

In order to obtain such an effect, the specific angle θi is made variable in accordance with the movement of the piston, and when the piston is at the top dead center of the engine, the specific angle θi is temporarily reduced and then increased. The present inventor has found through experiments that the present invention is effective in improving the engine shaft torque. In other words, decreasing and increasing the specific angle θi implies that the injected fuel collides with the inner surface of the depression and diffuses at a specific reflection angle. Therefore, if the reflection angle changes, the diffusivity of the injected fuel on the inner surface of the depression will increase. Is improved. As a result, the diffusion of the air-fuel mixture is improved. (6) In the above (5), the minimum angle of the specific angle θi is 2
By setting the angle to 8 ° to 36 °, a good air-fuel mixture can be formed, and the expansion of the range in which the injected fuel adheres to the wall surface of the combustion chamber can be suppressed. In addition, the amount of change up to the minimum angle is about 5 °, that is, 4 to 6
By setting the angle in degrees, a rapid change in the flight distance L3 of the injected fuel can be suppressed. If it is possible to suppress a rapid change in the flight distance L3 of the injected fuel, it is preferable since the diffusion of the air-fuel mixture is improved. (7) In any one of the above (4) to (6), when the depression is viewed in a cross section, the convex curved surface has two continuous curved portions having different radii of curvature, and a portion having a large radius of curvature. The small portions may be located at locations near and away from the piston center line, respectively.

By doing so, the flow path of the air-fuel mixture in the depression becomes gently inclined. That is, in the convex curved surface of the depression, a portion having a small radius of curvature is located near the piston center line, and if a large portion is located far away, the air density in the small portion increases and the air-fuel mixture does not turn. However, in the present invention, since a portion having a large radius of curvature is placed near the piston center line and a portion having a small radius of curvature is located far from the piston center line, the air-fuel mixture spreads to every corner of the combustion chamber. For this reason, engine performance is improved. (8) It is preferable that the ratio between the portion having a large radius of curvature and the portion having a small radius of curvature is 1.15: 1.

According to an experiment conducted by the inventor of the present invention, it has been found that the flow of the air-fuel mixture becomes smooth when the ratio of the two is in the above relationship.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a combustion chamber forming method for a diesel engine according to the present invention and a combustion chamber formed by using the method will be described with reference to the accompanying drawings.

FIG. 1 shows a state in which the piston 3 of the diesel engine according to the present embodiment is at the end of the compression stroke toward the top dead center in a vertical section parallel to the longitudinal direction of the cylinder. 5 shows a state in which the combustion chamber 1 of the diesel engine of the present invention is defined in a cylinder (not shown) by the lower surface 6 of the piston 5 and the depression 10 formed in the piston head 8. However, in this embodiment, since the cylinder is omitted, the combustion chamber is formed by the depression 1 formed in the lower surface 6 of the cylinder head 5 and the piston head 8.
0, but to be precise, at the end of the compression stroke in which the piston 3 goes to the top dead center, it includes a depression 10 and the top surface 9 of the piston head 8 and the cylinder bore (not shown) And a space surrounded by the lower surface 6 of the cylinder head 5 is called a combustion chamber.

Since the piston 3 reciprocates in the cylinder in conjunction with the movement of a crankshaft and a connecting rod (not shown), the volume of the combustion chamber 1 changes repeatedly with the movement.

Reference numeral 12 in the figure denotes an injection hole of a high-pressure injection type injection nozzle (not shown). The injection nozzle is attached to the cylinder head 5 so as to face the combustion chamber 1. When the diesel engine enters the compression stroke, the compression action starts, and the pressure in the combustion chamber (in the cylinder) gradually increases. When the pressure reaches a specified pressure, the fuel is sprayed from the injection hole 12 toward the inner peripheral surface of the depression 10. It is designed to be injected directly.

An intake port and an exhaust port (not shown) are formed in the cylinder head 5, and an intake valve and an exhaust valve are attached to these ports, respectively. In order to form a swirl as a swirling flow in the air flowing into the combustion chamber 1 from the intake port, for example, a helical type port is adopted as the intake port.

During the compression stroke, turbulence of air occurs in the depression 10 of the combustion chamber 1 and the depression 1
By injecting the fuel toward zero, the air and the fuel, for example, light oil, are appropriately mixed in the depression 10 to form an air-fuel mixture. Since the diesel engine is a compression ignition type internal combustion engine, the air-fuel mixture self-ignites, the fuel explodes and burns, and the diesel engine shifts to an explosion combustion process.

Next, the depression 10 will be described with reference to FIGS. FIG. 2 is an enlarged view of a part of FIG.

The diameter D2 of the opening 14 of the depression 10 is
Is smaller than the maximum diameter D1. Further, the bottom 16 of the depression 10 has a bottom peripheral groove 18 formed of a convex curved surface (a wall surface of the combustion chamber) 18 a that is continuous around the piston center line L and protrudes outward from the piston 3.
The bottom 16 has a mountain-shaped convex portion 20 at the center. In FIG. 2, what is indicated by reference numeral 22 is the jetted surface 12 of the injection nozzle 12 and the convex surface 18 of the bottom peripheral groove 18.
a virtual center line of the injected fuel toward
2 based on the angle θ2 formed by the cylinder head lower surface 6,
The ratio L1 / H1 of the depth H1 of the combustion chamber to the distance L1 between the intersection 24 of the virtual center line 22 and the convex curved surface 18a and the top surface 9 of the piston head determines the ratio L1 / H1.
Specify the shape of

More specifically, the ratio is determined by using a specific formula, and specifically, is determined by the following quadratic equation.

Y = −0.0073x ² + 0.184x−0.76 (1) Here, y: ratio L1 / H1 x: angle θ2 The virtual center line 22 of the injected fuel forms the lower surface 6 of the cylinder head. The angle θ2 is constant for the same diesel engine. This is because, in a diesel engine which is a compression ignition type internal combustion engine, fuel is injected when the pressure reaches a specified pressure in a compression stroke. Therefore, the angle θ2 is determined for each type of diesel engine.

As described above, since the angle θ2 formed by the virtual center line 22 of the injected fuel and the cylinder head lower surface 6 is constant, if this angle θ2 is determined, the intersection 24 of the virtual center line 22 with the combustion chamber wall surface and the piston Distance L between head top surface 9
As means for unifying the ratio L1 / H1 of the combustion chamber depth H1 to 1 as one unit, for example, the ratio L1 / H1 is plotted on the vertical axis and the angle θ2 is plotted on the horizontal axis in FIG.
A two-dimensional map M as shown in FIG.
Is determined, the ratio L1 / H1 is determined from the two-dimensional map M. For example, the ratio L1 / H1 when θ2 is 15 deg
Is about 0.36.

When the ratio L1 / H1 is determined, the distance L between the intersection point 24 with the combustion chamber wall surface and the piston head top surface 9 is determined.
1 and the combustion chamber depth H1 can be easily determined. Because the ratio L
This is because the dimensions of L1 and H1 may be determined so as to satisfy the relationship of 1 / H1.

In order to determine the angle θ2, the intersection point 2 between the injection hole 12 of the injection nozzle and the virtual center line 22 and the combustion chamber wall surface is determined.
A flying distance L3 of the injected fuel, which is a distance up to 4, is obtained.

The distance L3 determines the volume of the combustion chamber depending on the stroke volume (displacement amount) and the compression ratio, and determines the maximum injection pressure of the fuel and the duration of the fuel injection. Is determined, and the injection hole diameter (not shown) of the injection nozzle is determined.

When the flight distance L3 is determined, a point where the distance dimension from the injection hole 12 of the injection nozzle to the intersection 24 of the virtual center line 22 with the wall surface of the combustion chamber becomes L3 is determined. If this intersection 24 is found, this intersection 2
The distance L1 between the piston head 4 and the piston head top surface 9 and the angle θ2 are naturally determined.

When the angle θ2 is determined, the ratio L1 / H1 is determined from the two-dimensional map. Since the flight distance L1 has already been determined, the combustion chamber depth H1 is determined from the ratio L1 / H1 and the distance L1.

Accordingly, the distance between the intersection point 24 where the virtual center line 22 of the injected fuel which is injected from the injection hole 12 of the injection nozzle toward the depression 10 crosses the combustion chamber wall surface and the piston head top surface 9. Since it is easy to determine the dimensions of L1 and the depth H1 of the combustion chamber, it is possible to easily determine the ideal shape of the combustion chamber. Further, the ratio L1 / H1 can be accurately obtained by using the above formula (1).

In the prior art, the relationship between the distance L1 and the depth H1 of the combustion chamber with respect to the angle θ2 is not considered, and a certain combustion chamber is formed and the angle θ2 is set in the combustion chamber. I had found from my experience how much to use, but I have now established this formula as a means to quantify this experience. The formula has been obtained by experiments, and is set so as to maximize the performance of the diesel engine. By observing the relationship in this formula, the distance L1 and the combustion chamber depth H
If 1 or the like is determined, a combustion chamber comparable to any cylinder size (bore size) can be formed.

What has been described above is the method for forming a combustion chamber of a diesel engine according to the present invention.

The combustion chamber formed by the method for forming a combustion chamber of a diesel engine is the combustion chamber 1 of the diesel engine according to the present invention.

According to the internal combustion engine using such a combustion chamber 1, an engine shaft torque as shown in FIG. 4 can be obtained.

FIG. 4 is an engine shaft torque-engine speed diagram in which the vertical axis indicates engine shaft torque and the horizontal axis indicates engine speed. In the figure, the symbols L1 / H1 large, L1 / H1 suitable and L1 / H1 small mean the ratio L1 respectively.
3 is a graph when / H1 is large, a graph based on the ratio L1 / H1 when the combustion chamber 1 of the present embodiment is applied, and a graph when the ratio L1 / H1 is small.

The following can be understood from the engine shaft torque-engine speed diagram of FIG.

In the graph having a large ratio L1 / H1, when the engine speed is low, the engine shaft torque is higher than the other graphs, but the engine speed is higher than the other graphs when the engine speed is higher. It can be seen that the shaft torque decreases. Conversely, in the graph with the ratio L1 / H1 small, when the engine speed is high, the engine shaft torque is higher than that in the graph with the ratio L1 / H1 large, but when the engine speed is low, the other engine speeds are taken as boundaries. It can be seen that the engine shaft torque is lower than the two graphs.

On the other hand, the ratio L1 /
The graph suitable for H1 shows that when the engine speed is high, the ratio L1 / H1 is large and the ratio L1 / H starts at a certain engine speed.
It can be seen that the engine shaft torque is improved as compared with the case of one small. Even when the engine speed is low, the ratio L1 / H
It can be seen that the engine shaft torque is higher than one. Therefore, according to the diesel engine to which the combustion chamber 1 according to the present embodiment is applied, it can be said that the engine performance can be maximized.

The combustion chamber 1 according to this embodiment has the following features. This will be described with reference to FIGS.

FIG. 5 is an enlarged view of a main part of the combustion chamber 1.

FIG. 6 is a combination of upper and lower divided graphs. The vertical axis of the upper half graph shows the point of intersection 24 between the injection hole 12 of the injection nozzle and the virtual center line 22 with the wall surface of the combustion chamber.
, The vertical axis of the lower half of the graph represents a specific angle θi that forms the imaginary center line 22 with the tangent 26 at the intersection 24, and the horizontal axis of both graphs represents the crank angle. It is.

In the upper half of FIG. 6, the graph shown by the broken line is the case of the diesel engine to which the combustion chamber 1 of this embodiment is applied, and the graph shown by the solid line is the case of the conventional diesel engine. In addition, characters on the vertical axis that are long and short mean that the flight distance L3 is long and short.

In the lower half of the graph of FIG. 6, a line extending up and down as indicated by reference numeral B is a boundary line indicating a boundary between increase and decrease of the crank angle.

FIG. 7 is an engine shaft torque-engine speed diagram in which the vertical axis indicates engine shaft torque and the horizontal axis indicates engine speed. Also, in FIG. 7, the graphs indicated by the arrows accompanied by the signs θi small and θi large and the characters of the invention are graphs showing changes in the engine shaft torque, and the graphs with small θi indicate the case where θi is small and large θi. The graph shows the case where θi is large, and the graph of the invention shows the case where the combustion chamber 1 of the present embodiment is applied to a diesel engine.

FIG. 8 is a graph showing a hydrocarbon emission amount (HC emission amount) obtained by plotting HC emission amount on the vertical axis and θi on the horizontal axis.
It is a θi diagram.

The convex curved surface 18 a of the bottom peripheral groove 18 in the depression 10 has a specific angle θi between the imaginary center line 22 and the tangent 26 at the intersection 24, and the specific angle θi is variable according to the movement of the piston 3. When the piston 3 is at the top dead center of the engine, it starts decreasing and then increases (see FIG. 6).

The minimum angle of the specific angle θi is approximately 28 to 3
By setting the angle to 6 °, a favorable mixture can be obtained, and the expansion of the range in which the injected fuel adheres to the wall surface of the combustion chamber can be suppressed. Therefore, the amount of hydrocarbon HC emission decreases (see FIG. 8). However, if the minimum angle of the specific angle θi is smaller than 28 °, HC rapidly increases, so it is desirable to secure at least 28 °.

The change amount up to the minimum angle is 5 °.
By setting the front and rear directions, that is, 4 to 6 degrees, it is possible to suppress a rapid change in the flight distance L3 of the injected fuel (see FIG. 6). If it is possible to suppress a rapid change in the flight distance L3 of the injected fuel, it is preferable since the diffusion of the air-fuel mixture is improved.

With such a setting, even if the injected fuel strikes the convex curved surface 18a, which is the inner wall surface of the depression 10, and is reflected, it does not accumulate at a certain location in the depression 10.

In order to obtain such an effect, the specific angle θi is made variable in accordance with the movement of the piston 3, and when the piston 3 is at the top dead center of the engine, the specific angle θi once decreases and then increases. The present inventor has found through experiments that the present invention is effective in improving the engine shaft torque. That is, decreasing and increasing the specific angle θi implies that the injected fuel collides with the inner wall surface of the depression and diffuses with a specific reflection angle (not shown). The diffusivity on the inner surface of the depression is improved.

As a result, the diffusion of the air-fuel mixture is improved, so that the engine shaft torque can be increased (see FIG. 7). In other words, in the graph according to the invention of FIG. 7, it can be said that a stable engine shaft torque can be obtained irrespective of the magnitude of the engine speed, as compared to other large θ and small θ graphs. Therefore,
According to the diesel engine to which the combustion chamber 1 according to the present embodiment is applied, it can be said that the engine performance can be maximized.

In FIG. 7, in the left half with respect to the top of the graph, the large θi and small θi graphs overlap each other.

The combustion chamber 1 according to the present embodiment further has the following features. This will be described with reference to FIGS.

As shown in FIG. 9, when the depression 10 is viewed in a cross section, the convex curved surface 18a of the bottom peripheral groove 18 has two continuous curved portions having different radii of curvature, and a portion having a large radius of curvature ( That is, the portion having a curvature radius of Rb2 and the small portion (that is, a portion having a curvature radius of Rb1) are located at positions near and away from the piston center line L, respectively. The ratio between the portion having a large radius of curvature and the portion having a small radius of curvature is 1.15: 1.

By doing so, the flow path of the air-fuel mixture in the depression 10 is gently inclined. That is, the convex curved surface 18a of the bottom peripheral groove 18 of the depression 10
Of these, if a portion having a small radius of curvature is located near the center line of the piston, and if a large portion is located far away, the air density at the small portion increases and the air-fuel mixture does not turn. However, in the combustion chamber 1 of the present embodiment, a portion having a large radius of curvature (that is, a portion having a radius of curvature Rb2) is provided at a location near the piston center line L, and a portion having a small radius of curvature (ie, a portion having a radius of curvature Rb1) is provided. Since the air-fuel mixture is located far from the piston center line L, the air-fuel mixture spreads to every corner of the combustion chamber. Therefore, engine performance is improved (see FIG. 10).

FIG. 10 is an engine shaft torque-engine speed diagram showing the engine shaft torque on the vertical axis and the engine speed on the horizontal axis. A broken line graph is a diesel engine to which the combustion chamber 1 according to the present embodiment is applied, and a solid line graph is a conventional diesel engine shown as a comparative example. As is apparent from this figure, the engine shaft torque is better in the diesel engine to which the present invention is applied.

When the ratio of the portion having a large radius of curvature to the portion having a small radius of curvature is 1.15: 1, it has been confirmed by the present inventor that the flow of the air-fuel mixture in the combustion chamber 1 is smooth. It is known.

[0069]

According to the present invention, the specification of the ideal combustion chamber shape can be easily determined, and the improvement of the engine shaft torque can be expected. Further, the amount of HC emission can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an internal combustion engine to which a combustion chamber of a diesel engine according to the present invention is applied.

FIG. 2 is a partially enlarged sectional view of FIG. 1, illustrating one of the features of the present invention.

FIG. 3 shows the ratio L1 / H1 on the vertical axis and the angle θ2 on the horizontal axis.
2D map as shown in Fig. 3

FIG. 4 shows an engine shaft torque for explaining the effect of the present invention.
Engine speed diagram

FIG. 5 corresponds to FIG. 2 and illustrates one of the other features of the present invention.

FIG. 6 is a combination of upper and lower divided graphs, and the vertical axis of the upper half graph is the distance L3 from the injection hole of the injection nozzle to the intersection of the virtual center line with the combustion chamber wall surface;
The vertical axis of the lower half graph is a specific angle θi at which the virtual center line is a tangent at the intersection, and the horizontal axis of both graphs is the crank angle.

FIG. 7 shows an engine shaft torque for explaining the effect of the present invention.
Engine speed diagram

FIG. 8 is a diagram showing HC emissions-θi diagram.

FIG. 9 is a diagram corresponding to FIG. 2 and illustrating one of further features of the present invention.

FIG. 10 is an engine shaft torque-engine speed diagram for explaining the effect of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Combustion chamber 3 Piston 5 Cylinder head 6 Cylinder head lower surface 8 Piston head 9 Piston head top surface 10 Depression formed in piston head 12 Injection hole of injection nozzle 14 Depression opening 16 Depression bottom 18 Bottom peripheral groove 18a Convex surface ( 20 Wall shape of combustion chamber 20 Convex portion of chevron 22 Virtual center line of injected fuel θ2 Angle between virtual center line and lower surface of cylinder head 24 Intersection point where virtual center line intersects with combustion chamber wall surface 26 Tangent line at intersection B Boundary of increase / decrease in crank angle D1 Maximum diameter of the depression D2 Opening diameter L Piston center line L1 Distance between the intersection and the top surface of the piston head L3 Distance from the injection hole of the injection nozzle to the intersection of the virtual center line with the combustion chamber wall surface H1 Combustion Room depth Rb2 Larger radius of curvature Rb1 Smaller radius of curvature θi The virtual center line is tangent to the tangent at the intersection. Be specific angle

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masanao Daigo 2-1-1 Toyota-cho, Kariya-shi, Aichi F-term in Toyota Industries Corporation (reference) 3G023 AA02 AA07 AA19 AB05 AC04 AD02 AD08 AD09 AD14 AD29

Claims (8)

[Claims] At the end of a compression stroke in which a piston goes to a top dead center, fuel is directly injected from an injection nozzle into a combustion chamber formed by a lower surface of a cylinder head and a depression formed in the piston head, and the wall surface of the depression is In a diesel engine formed on a convex curved surface that is continuous around a piston center line and protrudes outward from the piston, an imaginary center line of injected fuel that is injected from an injection hole of the injection nozzle toward the convex curved surface is a lower surface of the cylinder head. By calculating the ratio of the depth of the combustion chamber (H1) to the distance L1 between the intersection of the virtual center line with the wall surface of the combustion chamber and the top surface of the piston head based on the angle (θ2) And a method for forming a combustion chamber of a diesel engine. 2. The method according to claim 1, wherein the ratio is determined using a specific formula. 3. The method according to claim 2, wherein the equation is a quadratic equation: y = −0.0073x ² + 0.184x−0.76 where y: ratio L1 / H1 x: angle θ2 4. A diesel engine combustion chamber formed by using the diesel engine combustion chamber forming method according to claim 1. 5. The convex curved surface of the depression has a specific angle (θi) formed by the virtual center line and a tangent at the intersection, and the specific angle (θi) varies according to the movement of the piston. 5. The combustion chamber for a diesel engine according to claim 4, wherein the piston once increases and then increases when the piston is at a top dead center of the engine. 6. A minimum angle of the specific angle (θi) is 28 °.
~ 36 °, and the amount of change up to the minimum angle is 5 °
The combustion chamber of a diesel engine according to claim 5, wherein the combustion chamber is located before and after. 7. When the depression is viewed in a transverse cross section, the convex curved surface has two continuous curved portions having different radii of curvature, and a portion having a large radius of curvature and a portion having a small radius of curvature are respectively located near the center line of the piston. The combustion chamber of a diesel engine according to any one of claims 4 to 6, wherein the combustion chamber is located at a distant location. 8. The combustion chamber of a diesel engine according to claim 7, wherein the ratio between the portion having a large radius of curvature and the portion having a small radius of curvature is 1.15: 1.