JP3389263B2 - Spark ignition internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for disposing an ignition plug at an optimum flow velocity position in an internal combustion engine having a combustion chamber at the top of a piston.

[0002]

2. Description of the Related Art In an internal combustion engine of a type in which a combustion chamber is recessed at the top of a piston, it is necessary to dispose a spark plug at a position where the flow velocity at the ignition timing is optimum. If it becomes large, the voltage required for ignition rises, the frequency of ignition mistakes increases, the operating performance deteriorates, and the life of the spark plug shortens. Especially in the case of a lean burn engine, the combustion limit becomes narrow and the low N
In addition to the difficulty in Ox operation, the minimum ignition energy increases as the air-fuel mixture becomes leaner, and the flow velocity increases due to the squish flow, making it even more difficult to obtain the optimum flow velocity near the spark plug. .

Generally, a combustion chamber is provided at the center of the piston top and an ignition plug is arranged at the center of the combustion chamber to obtain an optimum flow velocity, but when the engine becomes small, a relatively large space is required. The intake plug and the exhaust valve that occupy the exhaust gas are restricted, and particularly in the two-valve type, since the spark plug is provided at a position eccentric from the center of the cylinder, it is difficult to obtain the optimum flow velocity. Even if the combustion chamber is eccentrically arranged correspondingly, for example, in the case of a cylinder with a cooling cavity, a predetermined thickness is required between the cooling cavity and the combustion chamber, and the spark ignition internal combustion engine is used. Since an engine generally has a relatively large combustion chamber in order to reduce the compression ratio, it is difficult to make the combustion chamber eccentric in a small engine. Even if the combustion chamber can be eccentrically arranged, the optimum flow velocity cannot be obtained simply by aligning the centers of the spark plug and the combustion chamber.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of these problems, and an object thereof is to arrange an ignition plug at an optimum flow velocity position under various restrictions.

[0005]

In order to achieve the above object, in the first invention of this application, a combustion chamber is recessed in the top of the piston, and the spark plug is provided at a position eccentric from the center of the cylinder. In the internal combustion engine, the combustion chamber is provided at an eccentric position with respect to the cylinder, and the position of the vortex center in the combustion chamber caused by the swirl flow and the squish flow and the position of the spark plug are made to coincide with or almost coincide with each other. A spark plug is arranged. According to the second aspect of the present invention, the cutout portion is formed in a portion of the piston top portion close to the ignition plug to reduce the area of the squish generation portion formed on the piston top portion on the ignition plug side, and the cutout portion is formed in the combustion chamber. It is formed on the upstream side of the swirl flow with respect to the line connecting the center and the spark plug position. In the third aspect of the invention, the combustion chamber volume is increased on the spark plug side by making the combustion chamber deeper on the side closer to the spark plug so that the central axis of the swirl flow coincides with or substantially coincides with the position of the spark plug. is doing.

[0006]

According to the first aspect of the invention, the spark plug is placed at the center of the vortex generated by the swirl flow and the squish flow, rather than simply making the spark plug and the center of the combustion chamber coincide with each other, so that the optimum position near the spark plug is achieved. The flow rate can be obtained.
In the second aspect of the invention, since the area of the squish generating portion is reduced on the spark plug side, even if the combustion chamber cannot be eccentrically arranged, the squish flow from the side where the cutout portion is provided becomes weak and the flow velocity is at the minimum position. Moves to the spark plug side, and the flow velocity near the spark plug decreases. Moreover, since the cut portion is formed on the upstream side of the swirl flow, the combined flow velocity of the squish flow and the swirl flow can be reduced near the ignition plug to achieve the optimum flow velocity.

In the third invention, the law that the center of the vortex moves to the position where the moment of inertia of the vortex fluid is minimized is applied, and the volume of the combustion chamber is increased on the spark plug side. Since the center position of the swirl flow moves to the spark plug side, the flow speed near the spark plug can be reduced to obtain the optimum flow speed.

[0008]

[Embodiments] Next, respective embodiments shown in the drawings will be described. Figure 1
2 and FIG. 2 are explanatory views of an embodiment of the first invention. In the figure, 1 is a piston, 2 is a combustion chamber recessed at the top of the piston 1, P is a spark plug position, and 3 and 4 are intake valves and exhaust valves provided on the cylinder side. When the cylinder diameter is small, the intake valve 3 and the exhaust valve 4 occupy a relatively large space, so that the spark plug cannot be provided at the center of the cylinder, and is provided at the position P as shown in FIG. 2 (a). To be

FIG. 2 shows the relationship between the position of the combustion chamber and the flow velocity distribution of the swirl flow. The case where the combustion chamber 2 is provided in the center of the piston 1 (a) and the case where it is provided eccentrically (b) are shown. ). O is the center of the piston 1 and O'is the center of the combustion chamber 2. It should be noted that these figures are diagrams when the swirl flow is generated in the clockwise direction. When the combustion chamber 2 is provided in the center of the piston 1, the flow velocity becomes the lowest at the center O as shown in (a), but when it is eccentrically arranged, the distribution changes as shown in (b). , The position C of the vortex center where the influence of the squish flow and the swirl flow is combined and the flow velocity becomes the minimum, is eccentric from the piston center O, and the swirl flow affects the combustion chamber 2
It swirls to the downstream side of the swirl flow by an angle θ with respect to the eccentric direction. The movement of the vortex center increases as the eccentricity of the combustion chamber 2 increases.

Accordingly, the center O'of the combustion chamber 2 is eccentric to the spark plug direction as shown in FIG. 1 in accordance with this amount of movement, and further, the swirl flow upstream of the spark plug position P by an angle θ. If it is installed at a position that is relatively rotated to
The position C where the flow velocity is lowest and the spark plug position P can be matched.

It is known that the minimum ignition energy in a lean burn engine is minimized at a certain flow velocity, but the above-mentioned arrangement optimizes the flow velocity near the spark plug to minimize the ignition energy. It becomes possible to obtain the flow velocity. Therefore, the ignition is likely to be unstable because the fuel is lean, and the ignition is stable even in a lean-burn engine that uses the squish flow to disturb the flow of the air-fuel mixture in the combustion chamber for rapid combustion. As a result, fluctuations in the rotational speed can be reduced, and low NOx operation can be easily performed with high efficiency. In addition, the required voltage for the spark plug is reduced and the life of the spark plug is improved.

FIGS. 3 to 6 are explanatory views of the second invention. First, a case where only the squish flow is considered will be described. In the figure, 5 is a spark plug, 6 is a cylinder head to which the spark plug 5 is attached, and the position P of the spark plug 5 is eccentric because of the intake valve and the exhaust valve. In this example, the combustion chamber 2 is provided in the center of the piston 1, and a cutout portion 7 is formed continuously with the outer periphery of the combustion chamber 2 at a portion near the ignition plug 5 at the top of the piston 1. The cutout portion 7 is formed to be shallow, for example, in a circular shape around the position P. The other portion of the upper surface of the piston 1, that is, the portion where the cutout portion 7 and the combustion chamber 2 are not formed, is the squish generation portion 8
However, the area of the squish generation portion 8 is reduced on the spark plug 5 side compared to other portions due to the cutout portion 7.

The arrow in FIG. 4 indicates the squish flow generated at the compression top dead center of the piston 1, and its length represents the flow velocity. As shown in FIG. Since the area of is smaller than that of others, the flow velocity is small. Therefore, when the excision part 7 is not formed,
As shown in (b), the squish flow gathers in the center of the piston 1 and the flow velocity becomes the lowest here, whereas in this embodiment, the position of the lowest flow velocity moves to the spark plug 5 side, and By properly selecting the sheath size, it becomes possible to move the position of the lowest flow velocity to the position P of the spark plug 5.

Therefore, even when the combustion chamber 2 cannot be eccentrically arranged corresponding to the spark plug 5, an optimum flow velocity can be obtained near the spark plug, and the problems of the lean burn engine as described above are solved. It becomes possible to do. Figure 5
Is another embodiment, and is an example in which the cutout portion 7 is formed with a constant width from the combustion chamber 2 to the outer circumference of the piston 1. Even in this case, the area of the squish generating portion 8 can be reduced on the spark plug 5 side with respect to other portions, and the flow velocity near the spark plug can be reduced to be optimum as in the embodiment of FIG. The flow rate can be obtained.

Although only the squish flow is taken into consideration in the above, a swirl flow is likely to occur in the case of a two-valve engine in which the spark plug is eccentrically arranged with a relatively small size. The present invention relates to the case where the swirl flow is added to the squish flow as described above, and FIG. 6 shows an embodiment thereof. That is, FIG. 3C illustrates the case where the counterclockwise swirl flow exists in FIG. 3, and the flow toward the combustion chamber 2 is a vortex flow that is a combination of the squish flow and the swirl flow, and the flow velocity is the lowest. The position C of the center of the vortex moves to the downstream side of the swirl flow with respect to the eccentric direction of the spark plug 5.

Therefore, if the cutting portion 7 is formed at the upstream side of the swirl flow, that is, at the position swung clockwise in the example of the figure, corresponding to the movement of the position C of the vortex center, the minimum flow velocity position can be obtained. It is possible to match C with the position P of the spark plug 5 to obtain an optimum flow velocity near the spark plug 5,
This is particularly effective in the case of a relatively small two-valve engine. 6A shows a case where the cutout portion 7 has a shallow circular shape as in FIG. 3, and FIG. 6B shows a cutout portion 7 having a constant width from the combustion chamber 2 to the outer circumference of the piston 1 as in FIG. Each case is illustrated.

By the way, in the lean-burn engine, the turbulence of the air flow due to the squish flow is used for rapid combustion, and as described above, reducing the area of the squish generation part 8 by providing the cutting portion 7 weakens the squish flow. It may be better to avoid it because it does. The third invention is suitable for such a case. FIG. 7 shows an embodiment thereof, in which the bottom surface of the combustion chamber 2 provided in the piston 1 is inclined to deepen the side close to the spark plug 5. The fluid that is vortexing moves at a position where the moment of inertia is minimized, that is, as shown in FIG.
There is a law that the center of the vortex moves to a position where the amount S represented by the equation (1) is minimized, where L is the distance from the center of the vortex. Automatically moves to the vicinity of the spark plug 5.

Therefore, by selecting the shape of the bottom surface of the combustion chamber 2 so that the axis X-X after this movement coincides with the position of the spark plug 5, the flow velocity near the spark plug is reduced and optimum. It is possible to obtain the flow velocity. The amount of movement of the center of the vortex can be relatively accurately calculated, and therefore the design is easy. Also, the combustion chamber as in the embodiment has a simple shape and can be formed by casting, which is advantageous in cost. Is. As described above, the third invention does not weaken the squish flow, and moreover, the same effect as when the center of the vortex is moved by the imbalance of the volume of the combustion chamber to decenter the combustion chamber is obtained. In a relatively large spark ignition type internal combustion engine, it is considered to be particularly suitable as a countermeasure when it is difficult to decenter the combustion chamber 2 due to the cooling cavity 9 as shown in FIG. 7. The bottom surface of the combustion chamber 2 may have a shape other than the inclined plane as shown in FIG. 7, such as a curved surface or a stepped shape whose depth changes discontinuously.

[0019]

As is apparent from the above description, the first invention of this application aims to make the position of the vortex center in the combustion chamber caused by the swirl flow and the squish flow and the position of the spark plug match or substantially match. The combustion chamber and the spark plug are arranged eccentrically. Therefore, in an internal combustion engine in which the spark plug is provided eccentrically from the center of the cylinder, an optimum flow velocity can be obtained near the spark plug, energy required for ignition can be reduced, and the life of the spark plug can be improved. In the lean burn engine, the ignitability is improved and the lean burn limit is widened, so that NOx can be reduced and stable operation with little fluctuation in the rotational speed can be performed.

A second aspect of the invention is to reduce the area of the squish generating portion on the spark plug side by forming a cut portion at a portion of the piston top portion close to the spark plug, and at the same time, cut the cut portion at the center of the combustion chamber and the spark plug position. It is formed upstream of the swirl flow from the line connecting to and. Therefore, the position where the flow velocity becomes the minimum can be moved to the spark plug side to obtain the optimum flow velocity near the spark plug, and the same effect as the first invention described above can be obtained even in the case of an engine in which the combustion chamber cannot be eccentrically arranged Can be obtained. A third aspect of the invention is such that the volume of the combustion chamber is increased on the spark plug side so that the center of the vortex automatically moves near the spark plug. Therefore, particularly in a lean burn engine, it is possible to obtain the same effect as the first aspect of the invention without weakening the squish flow.

[Brief description of drawings]

FIG. 1 is a plan view of a piston according to an embodiment of the first invention.

FIG. 2 is an operation explanatory diagram of the embodiment.

FIG. 3 is a sectional view and a plan view for explaining a second invention.

FIG. 4 is an operation explanatory diagram of the case of FIG. 3 and a conventional example.

5A and 5B are a cross-sectional view and a plan view of a modified example of FIG.

FIG. 6 is a plan view and an operation explanatory view of an embodiment of the second invention.

FIG. 7 is a sectional view and a plan view of an embodiment of the third invention.

FIG. 8 is a diagram showing mathematical formulas for explaining the operation of the embodiment.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-55-119913 (JP, A) JP-A-62-157221 (JP, A) Actual development 58-142326 (JP, U) Actual extension 3- 30528 (JP, U) (58) Fields surveyed (Int.Cl. ⁷ , DB name) F02B 23/08 F02B 23/06

Claims (3)

(57) [Claims] 1. In an internal combustion engine in which a combustion chamber is provided in the top of a piston and an ignition plug is provided at a position eccentric from the center of the cylinder, the combustion chamber is provided at a position eccentric to the cylinder and a swirl flow is provided. A spark ignition internal combustion engine characterized in that the combustion chamber and the spark plug are arranged so that the position of the vortex center in the combustion chamber caused by the squish flow and the position of the spark plug coincide with or almost coincide with each other. 2. In an internal combustion engine in which a combustion chamber is recessed in the piston top and the ignition plug is provided at a position eccentric from the center of the cylinder, a cutout is formed in a portion of the piston top near the ignition plug, It is characterized in that the area of the squish generating portion formed at the top of the piston is reduced on the spark plug side, and the cutout portion is formed on the upstream side of the swirl flow with respect to the line connecting the center of the combustion chamber and the spark plug position. Spark ignition internal combustion engine. 3. In an internal combustion engine in which a combustion chamber is provided in the top of a piston and the ignition plug is provided at a position eccentric from the center of the cylinder, the combustion chamber volume is increased by making the combustion chamber deeper on the side closer to the ignition plug. Increase on the spark plug side,
A spark ignition type internal combustion engine, characterized in that the central axis of the swirl flow is arranged so as to coincide with or almost coincide with the position of the spark plug.