JP4702409B2 - Spark ignition internal combustion engine - Google Patents

Description

  The present invention relates to a spark ignition internal combustion engine, and more particularly to a high compression ratio specification in which a cylinder has a geometric compression ratio of 13.0 or more.

  Conventionally, in a spark ignition type internal combustion engine, various ideas have been made in the shape of the combustion chamber so as not to inhibit the propagation of the flame spreading from the ignition point of the spark plug to the surroundings. It is disclosed that a spherical cavity (concave portion) is formed at a position corresponding to the spark plug at the top of a piston serving as a floor.

In addition, it has been known that if the cylinder's geometric compression ratio / expansion ratio is set high, the thermal efficiency increases and the fuel consumption can be reduced, but the geometric compression ratio is simply set high. In some cases, it may not be possible to reduce fuel consumption, and knocking may easily occur.
JP 2007-154827 A

  One of the causes of such trouble is considered to be flame propagation. In other words, if the displacement is the same, the higher the geometric compression ratio is set, the smaller the combustion chamber volume near top dead center, so the flame surface interferes quickly with the combustion chamber surface such as the top surface of the piston. This is because the thermal efficiency decreases due to the cooling loss, and abnormal combustion such as self-ignition is likely to occur due to the increase in the combustion period.

  In this regard, if a cavity is formed at the top of the piston as disclosed in Patent Document 1, the interference of the flame with the piston can be delayed, but the volume of the cavity increases the combustion chamber. This is disadvantageous for realizing a high compression ratio.

  In view of such a point, an object of the present invention is to sufficiently improve the flame propagation property of the combustion chamber, to improve the engine efficiency and to reduce the fuel consumption, while setting the geometric compression ratio of the cylinder to 13 or more.

  In order to achieve the above-mentioned object, the present invention optimizes the position, shape and volume of the recess formed at the top of the piston, thereby delaying the interference with the flame as much as possible and reducing the combustion chamber volume associated with the formation of the recess. The increase is suppressed.

Specifically, the invention of claim 1 is directed to a spark ignition internal combustion engine having a single chamber volume of 0.3 liters or more and a geometric compression ratio of 13.0 or more. When a spark plug is disposed facing the ceiling of the chamber, and a recess is formed on the top of the piston, which is the floor of the combustion chamber, corresponding to the spark plug, at least one of the inner surfaces of the recess is formed. the parts, when the piston is at top dead center, after the said ignition plug spherical surface shape you around the ignition point of the combustion chamber volume when the piston within the cylinder is at the top dead center V1 The radius of the virtual sphere centered on the ignition point of the spark plug is set so that the virtual sphere contacts the spherical inner surface of the recess when the piston is at the top dead center in the cylinder. in case of setting the piston top dead The recess so as not even interfere with any of the floor and the ceiling of the combustion chamber, the volume of the non-interference portion of the virtual sphere as V 21, a 0.31 ≦ V21 / V1 ≦ 0.37 where when in And the radius of the virtual sphere centered on the ignition point of the spark plug does not interfere with the combustion chamber wall defining the combustion chamber when the piston is at top dead center. When the volume V22 of the interference part is set to be V22 = 0.15 × V1, the area of the interference surface where the virtual sphere interferes with the combustion chamber wall is S (unit: mm ² ), and V22 The combustion chamber is formed so that S / V22 ≦ 0.12 mm ⁻¹ , where the unit is mm ³ .

  That is, first, a sphere centered on the ignition point is assumed, simulating a flame spreading around from the ignition point of the ignition plug. Then, the top of the piston is simulated by the virtual sphere by forming a spherical recess at least partially so that the virtual sphere is in general contact with the top dead center. Interference with the flame can be delayed. The larger the volume of the recess, the slower the interference with the flame, while the volume of the combustion chamber increases, which is disadvantageous for realizing a high compression ratio.

  In this regard, the present inventor has set the ratio of the volume of the concave portion, which is roughly spherical as described above, to the total volume of the combustion chamber including this (hereinafter also referred to as the concave portion / combustion chamber volume ratio). There is an appropriate range, and if the volume of the recess is set to be so, the interference with the flame surface can be sufficiently delayed while realizing the required high compression ratio, thereby achieving the expected fuel consumption reduction effect It was found that it can be obtained.

  More specifically, the present inventor diligently researched changes in the combustion speed and fuel consumption rate under the same operating conditions while changing the volume of the recesses variously. As shown in the graph of FIG. 6 (a), it was found that there was a certain correlation. According to this graph, the crank angle has a so-called inflection point in the range of 52 to 55 °, and it can be said that the fuel consumption rate can be effectively reduced if the combustion period is shorter than that.

Then, when the relationship between the combustion period and the recess / combustion chamber volume ratio is examined next, the relationship between them is as shown in the graph of FIG. 5B (in the graph , V21 is described as “V2”). In order to make the combustion period 52 to 55 ° or less in terms of crank angle, it has been found that the concave combustion chamber volume ratio V 21 / V1 should be set to 0.31 to 0.35 or more. Here, since it is important to delay the interference with the flame for the concave portion, among the virtual spheres that simulate the flame as described above, the floor portion and the ceiling portion of the combustion chamber including the piston at the top dead center are included. in any convenience the volume V 21 of the non-interference portion which does not interfere is also used as the volume of the recess.

As described above, the concave portion is formed so that the concave portion / combustion chamber volume ratio V 21 /V1≧0.31 while setting the total volume of the combustion chamber so that the geometric compression ratio of the cylinder becomes 13 or more. By doing so, the propagation property of the flame surface in the combustion chamber can be sufficiently increased to shorten the combustion period, and the fuel consumption of the spark ignition internal combustion engine can be reduced.

However, as can be seen from the graph of FIG. 6 (a), even when the crank angle is 52 to 53 ° as a boundary, even if the combustion period becomes shorter than that, the rate of decrease in the fuel consumption rate accompanying this is rapidly increasing. It gets smaller. Therefore, it is better not to make the recess / combustion chamber volume ratio V 21 / V 1 too large considering that the larger the volume of the recess, the more disadvantageous it is for realizing a high compression ratio. The V 21 /V1≦0.37 from the graph.

The volume V22 of the non-interfering portion of the virtual sphere that does not interfere with the radius of the virtual sphere with the combustion chamber wall that defines the combustion chamber when the piston is at the top dead center is V22 = 0.15 × V1. In such a case, the value of S / V22 is 0.12 mm, as can be seen from the graph of FIG. 5B (in the graph, V22 is described as “V2”). ^-1 From this point, it was found that the fuel efficiency improvement rate increased rapidly as this value decreased. Thus, when the radius of the virtual sphere is set to be V22 = 0.15 × V1, S / V22 ≦ 0.12 mm ^-1 The fuel consumption can be reduced by designing the shape of the combustion chamber so that

  In order to reduce the total volume of the combustion chamber and increase the geometric compression ratio while forming the recess at the top of the piston as described above, the top of the piston is connected to the top of the piston. It is preferable to form a raised portion so as to correspond to the shape of the above (claim 2).

  In addition, as is well known in the art, for good flame propagation, it is preferable that the spark plug face the center of the combustion chamber ceiling, and correspondingly, the recess should open near the center of the piston top. (Claim 3).

  Further, if a fuel injection valve is provided so that fuel is directly injected into the combustion chamber, the intake air is cooled by the heat of vaporization of the fuel thus injected, so that abnormal combustion due to self-ignition of the air-fuel mixture is suppressed. Accordingly, the compression ratio of the cylinder can be set higher accordingly.

  In that case, the fuel injection valve is arranged so as to inject fuel from the peripheral edge of the combustion chamber toward the center, so that the fuel injected from the first half to the middle of the intake stroke of the cylinder is supplemented by a recess at the top of the piston. And the effect which suppresses adhesion to a cylinder internal peripheral surface is also expectable (Claim 5).

  In addition, the stroke of the cylinder is preferably longer than the bore. This is because the larger the bore of the cylinder, the flatter the combustion chamber shape, and this tends to be disadvantageous for flame propagation. Therefore, even if the combustion chamber volume is reduced for higher compression ratio, it becomes too flat. This is to prevent it from occurring.

As described above, according to the present invention, the concave portion is formed in the top portion of the piston in association with the spark plug facing the ceiling portion of the combustion chamber, and at least a part of the inner surface of the piston is at the top dead center. the ignition point of the spark plug and the to that spherical surface shape centered on, further, the virtual sphere centered at the ignition point of the spark plug, the radius, when the piston is at the top dead center in the cylinder, the When the virtual sphere is set so as to contact the spherical inner surface of the concave portion, the ratio V 21 / V1 of the volume V 21 of the non-interfering portion of the virtual sphere to the combustion chamber volume V 1 is 0.31 or more and 0.37 or less . As described above, the concave portion is formed and the radius of the virtual sphere centered on the ignition point of the ignition plug is set so that the volume V22 of the non-interference portion of the virtual sphere is V22 = 0.15 × V1. Set to In case, the virtual sphere the area of the interfering interference surface and the combustion chamber wall S (Unit: mm ²⁾ and to the combustion unit of V22 as mm ^3, so that the S / V22 ≦ 0.12 mm ^-1 By forming the chamber, it is possible to sufficiently increase the flame propagation property by delaying the interference between the piston and the flame as much as possible while geometrically realizing a high compression ratio of 13 or more. Therefore, engine efficiency is improved and fuel consumption is reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the following description of preferable embodiment is only an illustration essentially, and is not intending restrict | limiting this invention, its application thing, or its use.

  FIG. 1 is a schematic view of an engine E (spark ignition internal combustion engine) according to the present invention. The engine E includes a cylinder block 1 and a cylinder head 2 assembled on the cylinder block 1, and as shown in FIG. 2, the cylinder C reciprocates up and down along the axis c1 in the drawing. Thus, the piston 3 is accommodated. The piston 3 is connected to a crankshaft 4 rotatably supported at the lower portion of the cylinder block 1 by a connecting rod, so that the reciprocating motion of the piston 3 is converted into the rotational motion of the crankshaft 4.

  As shown in the figure, a combustion chamber 5 is formed above the piston 3 in the cylinder C, and the ceiling portion 5 a is formed by a recess formed for each cylinder C on the lower surface of the cylinder head 2. In this embodiment, the combustion chamber 5 is a so-called pent roof type, and its ceiling portion 5a has a triangular roof shape composed of two inclined surfaces on the intake side and the exhaust side, and the intake ports 6 and 6 are provided on the inclined surfaces. And two exhaust ports 7 and 7 are opened.

  Although only shown in FIG. 1, an intake valve 8 is disposed at the opening of each intake port 6, and an exhaust valve 9 is disposed at the opening of each exhaust port 7. It is opened and closed at a predetermined timing.

  In addition, an injector 10 (fuel injection valve) is arranged below the intake ports 6 and 6 so that an injection hole faces between the openings and fuel is injected from the peripheral portion of the combustion chamber 5 toward the center. It is installed. The injector 10 is connected to a fuel supply system having a high-pressure fuel pump or the like via a fuel distribution pipe (not shown). Although the direct injection method is assumed in the present embodiment, the present invention can also be applied to the port injection method.

  Further, a spark plug 11 is disposed in the cylinder head 2 so as to extend along the cylinder axis c1, and an electrode at the tip (lower end) faces the combustion chamber 5 from the vicinity of the center of the ceiling portion 5a. The ignition coil unit 12 is connected to the base end (upper end) side of the spark plug 11 as shown only in FIG. 1, and sparks are generated between the electrodes at a predetermined timing, so that the air-fuel mixture in the combustion chamber 5 is obtained. Is supposed to ignite. In this way, ignition near the center of the combustion chamber 5 is preferable because of good flame propagation as is well known in the art.

  As shown in FIG. 2, a protruding portion 31 that protrudes toward the center from the intake side and the exhaust side so as to correspond to the triangular roof shape of the ceiling portion 5 a at the top of the piston 3 that is the floor portion of the combustion chamber 5. Is formed. This is useful for adjusting the volume of the combustion chamber 5 and setting the geometric compression ratio of the cylinder C to be high, and the height of the combustion chamber 5 as a whole is approximately the same. It can be said that it is preferable also for sex.

  Further, a bowl-shaped recess 32 is formed in the vicinity of the center at the top of the piston 3 so as to open at the raised portion 31. As will be described later in detail as the main characteristic portion of the present invention, the recess 32 is provided in correspondence with the ignition point between the electrodes of the spark plug 11 (assuming the center between the electrodes; see point CP in FIG. 3A). And the flame propagation property improves and the thermal efficiency of the engine E improves because the shape and volume are set appropriately.

(Combustion chamber configuration)
By the way, in the present embodiment, the volume of the combustion chamber 5 is adjusted by forming a raised portion 31 on the top of the piston 3 and the geometric compression ratio of the cylinder C is set to 13.0 or more. Yes. This is for improving thermal efficiency and reducing fuel consumption. As is well known, the geometric compression ratio is V1, the volume of the combustion chamber 5 (total volume including the volume of the recess 32) when the piston 3 is at top dead center (TDC), and the displacement (stroke volume). V0 is represented as (V0 + V1) / V1.

  The volume V <b> 1 is a so-called gap volume, and the intake valve 8 and the exhaust valve 9 are closed when the piston 3 is at the top dead center, and they face the injector 10, the spark plug 11, that is, the combustion chamber 5. What is defined by the surface of the component attached to the recess of the cylinder head 2, the inner peripheral surface of the cylinder C, the top surface of the piston 3 including the inner surface of the recess 32, and the clearance between the cylinder head 10 and the cylinder block 20 It is.

  Generally, in an engine, setting a high compression ratio / expansion ratio of a cylinder should improve thermal efficiency and reduce fuel consumption, but simply setting a high geometric compression ratio does not improve fuel efficiency. This is because if the geometric compression ratio is set high, the volume V1 becomes relatively small if the displacement is the same, and the flame easily interferes with the ceiling or floor (piston top surface) of the combustion chamber at an early stage. This is because the propagation property deteriorates. Therefore, if the causal relationship between fuel consumption reduction and flame propagation is known, it is considered that efficient engine design is possible.

  In the present invention, as shown in FIG. 3, firstly, a sphere IS centered on the ignition point CP is assumed by imitating a flame spreading from the ignition point CP of the ignition plug 10 to the surroundings. Since the flame spreads radially, the virtual sphere IS models the range of propagation of the flame surface, and its radius r indicates the degree of progression of the flame surface. That is, the virtual sphere IS when the radius r is relatively small represents a relatively early time after ignition, and represents a relatively late time when the radius r is relatively large.

As the radius r increases as shown in FIGS. 3A to 3B, the interference with the combustion chamber ceiling 5a of the virtual sphere IS increases. In order to quantitatively consider this, the volume of the non-interfering portion that does not interfere with the combustion chamber ceiling 5a and the piston 3 in the virtual sphere IS when the piston 3 is at the top dead center is expressed as V2 (unit: mm ^3). In this case, the area of the interference surface where the virtual sphere IS interferes with the combustion chamber ceiling 5a and the piston 3 will be described as an interference area S (unit: mm ² ).

  FIG. 4 is an explanatory diagram of the non-interference volume V2 and the interference area S. As an example, the virtual sphere IS interferes with the ceiling portion 5 a of the combustion chamber 5, that is, the cylinder head 2, the intake valve 8, the exhaust valve 9, and the spark plug 11, but has a radius r that does not interfere with the piston 3. For a small state, (a) a virtual sphere IS, (b) a volume V2, and (c) an interference area S are schematically shown. The volume V2 is a three-dimensional volume in which the interference part with the combustion chamber ceiling 5a and the piston 3 is removed from the virtual sphere IS, and the interference area S is the area of the part that interferes with them.

-First evaluation index: relationship between r, V2 and S-
In this embodiment, the relationship between the radius r, the volume V2 (in the first evaluation index, which corresponds to V22 of claim 1), and the area S is used as the first evaluation index for reducing fuel consumption. Yes, when the radius r is set to satisfy V2 = 0.15 × V1, the shape of the combustion chamber 5 is set so that S / V2 ≦ 0.12 (mm ⁻¹ ). We are trying to reduce it. This conclusion is based on the experimental results described below.

  That is, in the first experiment described below, for a spark ignition engine with a bore of 87.5 mm and a stroke of 83.1 mm, a plurality of types of pistons having different shapes are created and replaced to have the same fuel economy under the same conditions (engine Measurement was performed at a speed of 1500 rpm, an average effective pressure Pe = 262 kPa, an air-fuel ratio A / F = 14.7, and an EGR rate = 20%). FIG. 5 (a) is a diagram showing the calculation results of the volume V2 / volume V1 and the interference area S / volume V2 for some pistons used in the experiment, and a plurality of radii r of the virtual sphere IS. , Obtained by setting.

The value of the volume V2 / volume V1 is related to the radius r, and a relatively small value of V2 / V1 corresponds to a case where the radius r is relatively small and indicates a relatively early stage of flame propagation. On the other hand, a relatively large value of V2 / V1 corresponds to a relatively large radius r and indicates a relatively late period of flame propagation. The volume V2 of the non-interference portion of the virtual sphere IS is an index representing the size of the flame, and the interference area S / volume V2 is the ratio of the interference area to the flame size that changes moment by moment in the course of propagation of the flame. Become.

  Lines L0 and L1 are not shown in the figure, but are the calculation results for a piston with a substantially flat top surface, L0 is a geometric compression ratio of 11.2, and L1 is a geometric compression. Each corresponds to a ratio of 15.0. Comparing the line L1 with the line L0, it can be seen that, in the case of a flat piston, the higher the height, the more early the flame propagation, the more the flame starts to interfere.

  Lines L31 to L34 are the calculation results related to the piston having a bowl-shaped recess at the top as shown in FIG. 2, and these are obtained by changing the size of the recess and the shape of the piston top surface other than the recess. The geometric compression ratio is in the range of 14.0 to 15.0. When these pistons are used, the start of interference with the flame is delayed due to the provision of the recess, and the value of S / V2 is too small when the ratio of volume V2 / volume V1 is in the range of 10% to 20%. It is no longer rising.

  Note that the line L4 is a calculation result when the recess has a rectangular cross section, and in this case, the geometric compression ratio is in the range of 14.0 to 15.0. Compared with the piston indicated by the line L1, the degree of interference between the flame accompanying the flame propagation and the inner wall of the combustion chamber is moderate, but compared with the pistons of the lines L31 to L34, the S / V2 of The effect of the value is small. This means that the interference between the flame and the inner surface of the recess occurs earlier than the pistons of the lines L31 to L34.

  Then, the fuel consumption is measured by the plurality of types of pistons, and the results are summarized in the relationship between the fuel consumption improvement rate and the interference area S / volume V2, and the volume V2 / volume V1 is in the range of 0 to 40%. A certain correlation was observed between the fuel efficiency improvement rate and the interference area S / volume V2 when the value of volume V2 / volume V1 was 15%. The fuel efficiency improvement rate was calculated based on the fuel efficiency of any piston as a base model. When the geometric compression ratio is different from that of the base model, the fuel efficiency improvement rate is corrected according to the geometric compression ratio to obtain the fuel efficiency improvement rate (estimated value) when the geometric compression ratio is the same.

  FIG. 5B shows the case where the value of volume V2 / volume V1 where a positive correlation is found as described above is 15%, that is, the radius r of the virtual sphere IS is V2 = 0.15 × V1. The correlation between the fuel efficiency improvement rate and the interference area S / volume V2 when set to. According to this figure, since the value of S / V2 is around 0.12, as this value becomes smaller, the fuel efficiency improvement rate rises rapidly, particularly when it becomes 0.10 or less. That is, it can be said that there is a so-called inflection point in the range of S / V2 values of 0, 10 to 0.12.

  Therefore, when the radius r is set to be V2 = 0.15 × V1, the fuel consumption can be reduced by designing the shape of the combustion chamber 5 so that S / V2 ≦ 0.12. It is preferable to satisfy /V2≦0.10. Here, in order to reduce the interference area S when the volume V2 is 15% of the volume V1, the bowl-shaped recess as described above is formed at the top of the piston 3 so that the flame does not interfere with the piston 3 by this time. However, simply forming the recesses 32 increases the volume of the combustion chamber 5, which is disadvantageous for realizing a high compression ratio.

-Second evaluation index: V2 / V1-
Therefore, the position, shape and volume of the recess 32 were optimized so as to make the interference with the flame as slow as possible while paying attention to the increase in the volume of the combustion chamber 5 as described above. In order to delay the interference with the flame, it is sufficient to form a spherical concave portion such that the virtual sphere IS is in contact with the top of the piston 3, but from the viewpoint of durability of the piston 3, the bottom surface of the concave portion is also spherical. Since this may be difficult, a part of the inner surface of the recess 32 is formed in a spherical shape with which the virtual sphere IS is in contact.

In addition, when the radius r is set so that the virtual sphere IS is in contact with a part of the surface of the concave portion 32 thus formed into a spherical shape, the volume V2 (first) of the non-interference portion of the virtual sphere IS . 2 (corresponding to V21 of claim 1) is roughly regarded as the volume of the recess 32, and the ratio V2 / V1 of the volume V2 to the combustion chamber volume V1 is used for reducing fuel consumption in the present embodiment. The second evaluation index. As the volume V2 / volume V1, that is, the volume ratio of the recess / combustion chamber is larger, the interference of the flame with the piston is delayed, and the flame propagation property is improved.

And this inventor experimented by changing various shapes of the protruding part 31 and the recessed part 32 of the piston 3 so that the value of the volume V2 / volume V1 may change, and the fuel consumption rate and combustion period of the engine E were changed. As a result of the examination, it was found that the fuel consumption rate can be effectively reduced by keeping the value of volume V2 / volume V1 within a predetermined range ( 0.31 ≦ V2 / V1 ≦ 0.37). This will be described below.

  That is, as in the first experiment, a plurality of types of pistons were prepared for a spark ignition engine having a bore of 87.5 mm and a stroke of 83.1 mm, and the cylinder bore was changed to 83.0 mm, 72.0 mm, etc. Similarly, multiple types of pistons are prepared for each type of engine, and the fuel consumption and fuel efficiency under the same operating conditions (engine speed = 1500 rpm, average effective pressure Pe = 262 kPa, air-fuel ratio A / F = 14.7, EGR rate = 20%) A second experiment was conducted to measure the burning rate. The result of this experiment is summarized in relation to the fuel consumption rate and the combustion period in the graph of FIG. 6 (a). From this figure, the fuel consumption rate and the combustion period are independent of the bore / stroke ratio, piston shape, etc. It can be seen that there is a certain correlation with.

  According to the figure, when the combustion period changes due to a change in the shape of the recess of the piston, etc., the fuel consumption rate suddenly increases as the combustion period increases from around 52 ° in crank angle. This tendency is remarkable beyond CA. In other words, there is a so-called inflection point in the range of the combustion period of 52 to 55 ° CA, and it can be said that the fuel efficiency can be effectively reduced if the combustion period is shorter than that.

  On the other hand, as shown in FIG. 5B, there is a simple relationship between the volume V2 / volume V1 and the combustion period, in which the combustion period is shortened as V2 / V1 is increased. This is considered to be because the interference with the flame of the piston 3 is delayed by increasing the volume of the recess 32, and the flame propagation property is improved. And the combustion period becomes 55 ° CA because the value of V2 / V1 exceeds 0.31, so when read with the result of FIG. It can be said that the volume V1 may be set to 0.31 or more.

However, as can be seen from the graph in FIG. 5A, even when the combustion period is further shortened from 50 to 52 ° CA, the rate of decrease in the fuel consumption rate accompanying this is rapidly decreasing. Then, if the volume of the concave portion 32 is increased in order to shorten the combustion period, the volume of the combustion chamber 5 is increased, which is disadvantageous for realizing a high compression ratio. It values it is better not so large from the graph, you and V2 / V1 ≦ 0.37.

  In both the first and second experiments described above, the stroke volume (single chamber volume) of the cylinder C single chamber, that is, the displacement V0 is 0.3 liters or more, and the geometric compression ratio is 14. The above correlation was observed in the engine E having a geometric compression ratio of 14.0 or more, or 14.5 or more, and the fuel consumption in such a high compression ratio engine. It can be said that it is effective in reducing the above.

  In this regard, the lower the geometric compression ratio, the larger the volume of the combustion chamber 5 and the better the flame propagation, so the above correlation also exists in engines with a compression ratio of less than 14.0 However, considering the balance with the improvement in thermal efficiency due to the high compression ratio, it can be considered that this is at least effective in reducing fuel consumption when the geometric compression ratio is 13.0 or higher.

  Therefore, according to the spark ignition engine E according to this embodiment, the single chamber volume of the cylinder C is 0.3 liters or more, the geometric compression ratio is 13.0 or more, and the combustion chamber ceiling 5a When a concave portion 32 is formed on the top of the piston 3 in association with the spark plug 11 that faces, at least a part of the inner surface of the concave portion 32 is exposed to the ignition point of the spark plug 11 when the piston 3 is at the top dead center. In addition to the spherical shape that is in contact with the virtual sphere IS centered on CP, the ratio V2 / V1 of the volume V2 of the non-interfering portion of the virtual sphere IS to the combustion chamber volume V1 is within a predetermined range (0.31 to 0). .37), the interference between the piston 3 and the flame can be delayed to the maximum while realizing a high compression ratio of 13 or more, and the flame propagation property can be sufficiently enhanced. As a result, engine efficiency is improved and fuel consumption is reduced.

  The engine E of this embodiment employs a so-called direct injection system in which fuel is directly injected from the injector 10 facing the combustion chamber 5, and the intake air is cooled by the heat of vaporization of the fuel thus injected. Abnormal combustion due to self-ignition and the like is suppressed, and this is an advantageous configuration for setting a high compression ratio of the cylinder C.

  Moreover, the injector 10 is arranged so as to inject fuel from the peripheral edge of the combustion chamber 5 toward the center, and the fuel injected from the first half of the intake stroke of the cylinder C to the middle is supplemented by the recess 32 of the piston 3. The effect of suppressing the adhesion to the inner peripheral surface of the cylinder C can also be expected.

  In addition, the structure of the spark ignition type internal combustion engine which concerns on this invention is not limited to the said embodiment, Various structures other than that are included. For example, the engine E is not limited to the four-valve type as in the above embodiment, and may be a three-valve engine with one exhaust port for each cylinder C.

  Further, although not particularly mentioned in the embodiment, the cylinder C preferably has a longer stroke than the bore. The larger the bore of the cylinder C, the flatter the shape of the combustion chamber 5 tends to be disadvantageous for flame propagation. Therefore, in order to achieve a high compression ratio of 13 or more, a longer stroke is preferable. is there.

  Furthermore, in the above embodiment, a four-cycle multi-cylinder gasoline engine E is assumed as an example, but the present invention can also be applied to other types of spark ignition type internal combustion engines.

1 is a schematic view of a spark ignition internal combustion engine according to an embodiment. It is a perspective view which shows the structure of the combustion chamber in a cylinder centering on the top part of a piston. It is explanatory drawing which shows the relationship between virtual sphere IS and a recessed part. It is explanatory drawing of the volume and interference area of the non-interference part of a virtual sphere. (a) is a graph showing the correlation between S / V2 and V2 / V1, and (b) is a graph showing the correlation between S / V2 and the fuel efficiency improvement rate. (b) is a graph showing the correlation between the combustion period and the fuel consumption rate, and (b) is a graph showing the correlation between the recess / burning chamber volume ratio and the combustion period.

E Spark ignition engine (spark ignition internal combustion engine)
IS Virtual sphere CP Ignition point C Cylinder 2 Cylinder head 3 Piston 31 Raised portion 32 Recessed portion 5 Combustion chamber 5a Ceiling portion 10 Injector (fuel injection valve)
11 Spark plug

Claims (6)

A spark ignition internal combustion engine having a single chamber volume of 0.3 liters or more and a geometric compression ratio of 13.0 or more,
While a spark plug is disposed facing the ceiling of the combustion chamber in the cylinder, a concave portion is formed on the top of the piston that becomes the floor of the combustion chamber, corresponding to the spark plug,
At least a portion of the inner surface of the recess, forms a spherical surface shape you around the ignition point of the spark plug when the piston within the cylinder is at the top dead center,
The combustion chamber volume when the piston is at top dead center is V1,
When the virtual sphere centered on the ignition point of the spark plug is set so that the radius of the virtual sphere is in contact with the spherical inner surface of the recess when the piston is at top dead center in the cylinder , the piston does not interfere with any of the floor and the ceiling of the combustion chamber when in the top dead center, the volume of the non-interference portion of the virtual sphere as V 21,
0.31 ≦ V21 / V1 ≦ 0.37
Wherein a recess so that,
The volume of a non-interfering portion of the virtual sphere that does not interfere with the combustion chamber wall defining the combustion chamber when the piston is at top dead center with respect to the virtual sphere centered on the ignition point of the spark plug When V22 is set to be V22 = 0.15 × V1, the area of the interference surface where the virtual sphere interferes with the combustion chamber wall is S (unit: mm ² ), and the unit of V22 is mm ³ As
S / V22 ≦ 0.12 mm ⁻¹
A spark ignition type internal combustion engine characterized in that the combustion chamber is formed to be   2. The spark ignition internal combustion engine according to claim 1, wherein a ridge is formed at the top of the piston so as to correspond to the shape of the ceiling of the combustion chamber, and the recess is opened at the ridge.   3. The spark ignition internal combustion engine according to claim 1, wherein the spark plug faces the vicinity of the center of the combustion chamber ceiling, and correspondingly, a recess is opened near the center of the piston top.   The spark ignition internal combustion engine according to any one of claims 1 to 3, wherein a fuel injection valve is provided so as to inject fuel directly into the combustion chamber.   The spark-ignition internal combustion engine according to claim 4, wherein the fuel injection valve is arranged so as to inject fuel from the peripheral edge of the combustion chamber toward the center.   The spark ignition internal combustion engine according to any one of claims 1 to 5, wherein a stroke is longer than a bore of the cylinder.

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