JP6006276B2 - Internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine.

  In a spark ignition type internal combustion engine in which a piston is reciprocated in a cylinder formed in a cylinder block and a combustion chamber is defined between a cylinder head and a piston disposed on the upper surface of the cylinder block, compression is performed in the combustion chamber. When the mixed gas mixture is ignited by the spark discharge of the spark plug, a flame nucleus is generated, and the flame is transmitted through the combustion chamber from the flame nucleus.

  On the other hand, since the temperature of the air-fuel mixture rises due to compression in the compression process or compression of the combustion gas, the unburned air-fuel mixture (end gas) located far from the spark plug self-ignites before the flame reaches, Knocking may occur. In order to suppress knocking, it is preferable to prevent the end gas from self-igniting before the flame arrives, and various techniques for suppressing knocking have been proposed.

  For example, there is a piston provided with a cooling structure in order to suppress the temperature rise of the air-fuel mixture during the compression stroke (see Patent Document 1). Also, in order to increase the flame propagation speed (speed at which the flame travels through the unburned mixture) by disturbing the expansion flow of the unburned mixture generated in front of the flame zone, the peripheral edge of the top surface of the piston There is one in which a ring-shaped protrusion is provided on the part (see Patent Document 2). In addition, in order to perform sufficient combustion at the outer peripheral edge of the combustion chamber at an early stage of combustion, a subchamber having a nozzle hole that opens in the circumferential direction is provided at a symmetrical position of the peripheral edge of the combustion chamber. There is one in which a strong flow toward the room is caused to cause self-ignition of the high-temperature air-fuel mixture flowing into the sub-chamber, thereby causing a flame to be ejected from the nozzle hole into the combustion chamber (see Patent Document 3). .

  On the other hand, carbon adhering to the peripheral part of the combustion chamber may become a fire type as a cause of causing knocking. Since carbon adheres to the peripheral edge of the combustion chamber when the lubricating oil adhering to the inner peripheral surface of the cylinder is scraped up by the piston, the adhering of the lubricating oil adhering to the inner peripheral surface of the cylinder is suppressed. Therefore, there is a structure in which a groove and a land are provided in the top land portion of the piston so that the inclination of the piston is suppressed by the land and the lifting of the lubricating oil is suppressed by the groove (see Patent Document 4).

JP 2006-152879 A Japanese Patent Laid-Open No. 10-306726 JP-A-7-269349 Japanese Utility Model Publication No. 62-122154

  However, the technique described in Patent Document 1 has a complicated structure in which a refrigerant is sealed in a cooling passage provided in a piston, and there is a problem that the manufacturing cost increases. Moreover, in the thing of patent document 2, since a protrusion is provided in the top surface of a piston, when the protrusion amount of a protrusion is large, it will be necessary to form relief in the upper surface side (cylinder head side) of the opposing combustion chamber etc. There is a problem that the complexity of making a significant design change according to the individual internal combustion engine increases. Also, the one of Patent Document 3 has a complicated structure in which a sub chamber is provided in the combustion chamber and a nozzle hole that communicates the sub chamber and the combustion chamber is provided, and there is a problem that the manufacturing cost increases. Moreover, in the thing of patent document 4, since a groove | channel and a land are alternately arrange | positioned over the perimeter of a piston, depending on the magnitude | size of a groove | channel, the fall of a compression ratio will be caused, In that case, a countermeasure is taken. There is a problem that the design is complicated.

  In view of the above background, it is an object of the present invention to suppress knocking of an internal combustion engine with a simple structure.

  In order to solve the above problems, the present invention provides a combustion chamber (5) between a piston (3) reciprocating in a cylinder (4) formed in a cylinder block (1) and a cylinder head (2). A defined internal combustion engine, characterized in that an elongated recess (11) extending in the circumferential direction is provided at one or two positions on the peripheral edge of the top surface (3a) of the piston. .

  According to this structure, since the surface area of the part which provided the recessed part in the piston peripheral part increases, the coolability of the part improves and knocking can be suppressed. By limiting the number of the concave portions to one or two, it is possible to suppress a decrease in compression ratio and an increase in heat loss due to the provision of the concave portions.

  Moreover, the said combustion chamber (5) is formed in the shape which has a squish part (9) which produces a squish between the peripheral parts of the top surface of the said piston, and the said recessed part (11) respond | corresponds to the said squish part It is good to be provided in the part to do.

  According to this, a squish flow from the piston peripheral portion, which is likely to cause knocking, to the combustion chamber center side is generated, and the piston peripheral portion that may become high temperature before the flame reaches can be cooled by the squish flow. In addition, since the concave portion is provided in the squish portion, it is possible to further suppress the occurrence of knocking.

  Moreover, the said recessed part (11) is good to be provided in the cylinder (4) side which adjoins. According to this, in an internal combustion engine in which a plurality of cylinders are arranged in series, when the space between the cylinders is narrowed for compactness and the water jacket between the cylinders is omitted, the axial direction of the crankshaft of the combustion chamber Therefore, knocking can be suppressed by providing a recess in that portion to improve the cooling performance.

  Moreover, it is good for the part (3c * 3d) which reaches the top surface of the said piston of the said recessed part to expand toward the axial direction of the said piston. According to this, the gas compressed in the concave portion can easily flow out of the concave portion, the generation of high-pressure gas in the concave portion can be suppressed, and knocking can be suppressed.

  Thus, according to the present invention, with a simple structure, it is possible to suppress a reduction in compression ratio and an increase in heat loss due to the provision of the recess, and to suppress knocking of the internal combustion engine.

Side sectional view showing a main part of an internal combustion engine to which the present invention is applied Top view of the piston as seen in the direction of the arrow along the line II-II in FIG. Main part enlarged side sectional view showing the sectional shape of the recess Diagram showing knock frequency Top view of cylinder block showing another arrangement example of recess The figure corresponding to FIG. 3 which shows the other cross-sectional shape of a recessed part

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a side sectional view showing an essential part of an internal combustion engine to which the present invention is applied, and FIG. 2 is a top view of a piston viewed in the direction of an arrow along a line II-II in FIG. In FIG. 1, a cylinder head 2 is fixed on the upper surface of a cylinder block 1. The cylinder block 1 is formed with a cylindrical cylinder 4 that reciprocally receives the piston 3 in the vertical direction in the figure. The cylinder head 2 has an inner peripheral surface of the cylinder 4 and a top surface 3 a of the piston 3. Are formed two inclined surfaces 4a and 4b that define a pent roof type combustion chamber 5. An intake port 6 is opened on one inclined surface 4a, and an exhaust port 7 is opened on the other inclined surface 4b. Both ports 6 and 7 are opened and closed by intake and exhaust valves (not shown), respectively. The cylinder head 2 is provided with a spark plug 8 at a position between the inclined surfaces 4a and 4b and in the center of the combustion chamber 5. The top surface 3a of the piston 3 may be partially provided with, for example, relief for the intake and exhaust valves, but is formed as a flat surface as a whole.

  The air-fuel mixture in the combustion chamber 5 is ignited by the ignition of the spark plug 8, thereby generating flame propagation that spreads around the spark plug 8, but the unburned air-fuel mixture (end gas) located far from the spark plug 8 is Knocking occurs by self-ignition before the flame reaches. One factor that causes the end gas to self-ignite is that when the end gas far from the spark plug 8 is pressed against the inner peripheral surface of the piston 3 or the cylinder 4 and compressed by the combustion gas expanded by the flame propagation, There are cases where high pressure and high temperature / pressure exceed the limits. Also, the lubricating oil adhering to the inner peripheral surface of the cylinder 4 is pumped up by the piston 3, and the pumped-up lubricating oil is carbonized by combustion and becomes a fire type by depositing carbon, and the end gas becomes high temperature by the fire type. May self-ignite.

  In order to suppress the knocking as described above, it is preferable to prevent the end gas in the combustion chamber 5 from self-igniting before the flame arrives. As one of countermeasures, the shape of the combustion chamber 5 is made a pent roof type in order to shorten the flame propagation distance so that the flame reaches the end gas before the end gas self-ignites. In the case of the pent roof type, the spark plug 8 is disposed at substantially the center of the combustion chamber 5.

  In order to prevent the end gas from self-igniting, it is preferable to suppress the temperature rise of the end gas in order to prolong the time required to reach the self-ignition temperature. As one of the measures for that, the squish part 9 which produces a squish in the peripheral part of the combustion chamber 5 which is a part far from the spark plug 8 is provided. The squish portion 9 may have a known structure. In the present embodiment, a surface parallel to the peripheral edge portion of the top surface 3a of the piston 3 is formed on the cylinder head 2 side on each of the peripheral portion of the combustion chamber 5 and on the intake port 6 side and the exhaust port 7 side. Has been. As a result, when the piston 3 reaches top dead center, a narrow gap is formed between the top surface 3a and the parallel surface of the cylinder head 2, and squish flows from the peripheral edge of the combustion chamber 5 toward the center. Such a flow of squish acts to stir the air-fuel mixture and increase the flame propagation speed, and it is possible to suppress the temperature rise of the end gas at the peripheral edge of the combustion chamber 5.

  Further, the piston 3 is provided with an elongated recess 11 that opens in the peripheral portion of the top surface 3a and extends in the circumferential direction when viewed from above. The recess 11 in the illustrated example is also open to the top land 3b of the piston 3, and as shown in FIG. 3, the radial direction of the piston 3 is a width W, and the axial direction of the piston 3 is a depth D. In this case, the width W and the depth D may be formed in a rectangular cross-sectional shape having substantially the same length. The width W is preferably within the range of the maximum length of the squish portion 9 in the radial direction of the piston 3. The depth D is within the range of the axial length of the piston 3 of the top land 3b.

  By providing the concave portion 11 in this manner, the surface area is increased by the concave portion 11, so that the cooling performance of the portion where the concave portion 11 is provided in the peripheral portion of the piston 3 can be improved, and the temperature rise of the end gas near the concave portion 11 It is suppressed. The recess 11 may be provided only in a portion where the end gas may self-ignite when the top surface 3a of the piston 3 is a flat surface, and does not need to be provided over the entire circumference of the piston 3. Thereby, the influence which a compression ratio reduces by providing the recessed part 11 can be suppressed, and this invention can be applied also to the conventional internal combustion engine, without making a design change other than piston 3.

  Next, the suitable example of the location which provides the recessed part 11 is demonstrated.

  As a portion where the temperature of the end gas is high at the peripheral edge of the combustion chamber 5, there is a vicinity of the exhaust port 7. Therefore, the recess 11 is preferably provided on the exhaust port 7 side. Further, due to the tumble generated in the combustion chamber 5 in the exhaust stroke, the high temperature gas also flows to the intake port 6 side opposite to the exhaust port 7. In that case, a recess 11 may be provided on the intake port 6 side.

  1 and 2 show an example in which concave portions 11 are provided at two locations, that is, an intake side IN where the intake port 6 is provided and an exhaust side EX where the exhaust port 7 is provided. In FIG. 2, a region indicated by a two-dot chain line on the intake side IN and the exhaust side EX is the squish portion 9. The recess 11 is provided in an arc shape around a predetermined angular range around the axis of the piston 3. The upper limit of the angle range extending in the circumferential direction of the recess 11 is preferably 90 degrees, but the minimum angle range that can suppress knocking is preferable in order to reduce the influence on the compression ratio as much as possible.

  As described above, the recesses 11 are preferably provided at one place that is one of the intake side IN and the exhaust side EX, or at two places that are both. By limiting the number and size of the places where the recesses 11 are provided, the reduction in the compression ratio due to the provision of the recesses 11 can be minimized.

  In the case where the recess 11 is provided on the intake side IN, in consideration of the bias of the initial flame and the occurrence of a combustion delay portion where the temperature increase of the end gas is suppressed by the squish flow, Consider the initial flame bias, the occurrence of end gas combustion delay due to the squish flow, and the temperature rise of the end gas due to high exhaust valve temperature. According to each, the width W and depth D of the recessed part 11 and the extension range (angle) of the circumferential direction are set.

  FIG. 4 is a graph showing the knock frequency when a standard internal combustion engine mounted on a commercially available small vehicle is targeted and the recess 11 is provided as shown in FIGS. 1 and 2 and the engine is operated at 1500 rpm. . In the figure, the horizontal axis represents the crank angle (ATDC) at which the combustion mass ratio becomes 50%, and the vertical axis represents the knock frequency (%). Further, when the concave portion 11 is not provided, that is, the case where the top surface 3a of the piston 3 is a flat surface is indicated by a two-dot chain line, and the width W and the depth D of the concave portion 11 are changed as two patterns. A case where the thickness D is 5 mm is indicated by a solid line, and a case where the width W is 10 mm and the depth D is 5 mm is indicated by a broken line.

  Further, when the ignition timing is retarded, the knocking frequency becomes 0%, the case where the top surface 3a is a flat surface is indicated by a circle, the width W of the recess 11 is 5 mm, and the depth D is 5 mm. This case is indicated by a triangle mark, and the case where the width W of the recess 11 is 10 mm and the depth D is 5 mm is indicated by a square mark. When the top surface 3a is a flat surface, the crank angle at which the knocking frequency is 0% and the combustion mass ratio is 50% is 20.7 degrees, but the recess 11 is provided and the width W is 10 mm and deep. When the depth D was 5 mm, it was improved to 19.9 degrees, and when the width W was 5 mm and the depth D was 5 mm, it was greatly improved to 18.9 degrees. Thus, since the ignition timing range in which knocking does not occur is expanded with a simple structure in which the recess 11 is provided, occurrence of knocking can be easily suppressed.

  FIG. 5 is a top view of a cylinder block 1 of a multi-cylinder internal combustion engine in which a plurality of cylinders are arranged in series. The figure shows an example of three cylinders. In addition, the upper side of the figure is the timing bet (T / B) side, and the lower side is the flywheel (F / W) side. Further, in the illustrated internal combustion engine, in order to shorten the length of the cylinder block 1 in the cylinder row direction, the water jacket W between the cylinders 4 is omitted and the space between the adjacent cylinders 4 is narrowed. Therefore, the water jacket W is provided so as to enclose the four rows of cylinders as a whole.

  In the internal combustion engine configured as described above, the outer portions of the cylinders 4 (both ends of the crankshaft in the axis C direction) positioned at both ends in the cylinder row direction are surrounded by the water jacket W to ensure necessary cooling performance. Can be done. On the other hand, in the part where the cylinder 4 is adjacent, the cooling performance by the water jacket W decreases. Accordingly, the piston 3 on the timing belt (T / B) side, which is one end in the direction of the axis C of the crankshaft, is provided with a recess 11 only on the side (lower side in the figure) with respect to the adjacent cylinder 4, and similarly the axis of the crankshaft The piston 3 on the flywheel (F / W) side which is the other end in the C direction may be provided with a recess 11 only on the side (upper side in the drawing) with respect to the adjacent cylinder 4. In addition, the cooling performance of the portion where the cylinder 4 is adjacent to the central piston 3 in the drawing in which the cylinder 4 is adjacent to both sides of the crankshaft in the axis C direction is reduced. It is preferable to provide the recesses 11 at the portions on both sides in the axis C direction.

  As described above, the recess 11 may be provided at one place on either side of the crankshaft axis C direction or at two places on both sides. In this case as well, the reduction in the compression ratio due to the provision of the recesses 11 can be minimized by limiting the number and size of the locations where the recesses 11 are provided in the same manner as described above.

  In the case where the recess 11 is provided in a portion on the axis C direction side of the crankshaft, in addition to the bias of the initial flame, the combustion speed in the timing belt (T / B) or flywheel (F / W) direction Considering the delay (influence of tumble) and the difference in cooling performance due to the layout of the water jacket W as described above, the width W and depth D of the recess 11 and the extending range (angle) in the circumferential direction are set. To do.

  In addition, the cross-sectional shape of the recessed part 11 is not restricted to the rectangle shown in FIG. FIG. 6 shows another example of the cross-sectional shape. In addition, about the part similar to the above, the same code | symbol is attached | subjected and the detailed description is abbreviate | omitted. The recessed part 11 of this 2nd Embodiment is formed so that the part which reaches the top surface 3a of piston 3 may spread in the axial direction of piston 3 toward the center of top surface 3a. In the figure, the height direction of the wall surface extending in an arc shape so as to confront the inner peripheral surface of the cylinder 4 in the concave portion 11 (the depth direction of the concave portion 11 which is the axial direction of the piston 3) from the intermediate portion to the top surface 3a. A slope 3c is formed in a slanting direction toward the center. In addition, you may provide the inclined surface 3d which goes to the axial direction of piston 3 and the center side of the top surface 3a from the bottom face of the recessed part 11 (two-dot chain line of a figure).

  In this way, the recess 11 is formed in a shape having a cross section that expands in the axial direction of the piston 3 and toward the center of the top surface 3a, whereby the end gas compressed in the recess 11 in the compression stroke is Therefore, high pressure and high temperature in the recess 11 are suppressed. Moreover, since the increase in the surface area can be improved while suppressing the reduction in the compression ratio when the recess 11 is provided, the cooling performance due to the increase in the surface area can also be improved. In addition, as a shape of the part expanded to the top surface 3a side of the recessed part 11, it is not limited to a slope, A curved surface may be sufficient.

  Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to such embodiments and can be easily understood by those skilled in the art. As long as it does not deviate from the above, it can be appropriately changed. In addition, all the components shown in the above embodiment are not necessarily essential, and can be appropriately selected without departing from the gist of the present invention.

  The occurrence of knocking is greatly influenced by the flow of the air-fuel mixture in the combustion chamber 5, and the main factors affecting the change in the flow are the valve timing, the shape of the intake / exhaust port, and the position of the squish portion 9. . On the other hand, the specifications of the internal combustion engine targeted by the present invention do not change those specifications. For example, the valve timing is not specially closed late, the port shape is not specialized for swirl or tumble, and the squish part 9 is also not used. Corresponding to the pent roof type, it is provided at two locations of the intake side IN and the exhaust side EX, and the arrangement is not specially changed. In the present invention, the recess 11 is provided only at a position where knocking is likely to occur when the top surface 3a of the piston 3 is a flat surface, as described above, without specially taking measures against knocking. The structure suppresses knocking.

1 Cylinder block 2 Cylinder head 3 Piston 3a Top surface 3c, 3d Slope (portion of the concave portion reaching the top surface of the piston)
4 Cylinder head 5 Combustion chamber 9 Squish part 11 Recess

Claims (4)

An internal combustion engine in which a combustion chamber is defined between a piston and a cylinder head that reciprocate in a cylinder formed in a cylinder block,
The top surface of the piston is formed as a flat surface as a whole,
The combustion chamber is formed in the cylinder head in parallel to the top surface of the piston in the radial direction of the piston from the two inclined surfaces formed in the cylinder head and the lower edge of each of the inclined surfaces. Having two squish portions composed of parallel planes that form a gap between the piston and the squish when the top dead center is reached,
In one or two places on the peripheral edge of the top surface of the piston, the piston has a width less than the maximum length of the squish portion in the radial direction of the piston and has an arc shape over a predetermined angular range in the circumferential direction of the piston. extending to the circumferential direction of the internal combustion engine, wherein a concave portion of the elongated and shaped having an end portion is provided on both sides.   2. The internal combustion engine according to claim 1, wherein the concave portion is provided in a portion overlapping the squish portion in a circumferential direction of the piston in a top view of the piston. The internal combustion engine is a multi-cylinder internal combustion engine having a plurality of the cylinders arranged in series;
The internal combustion engine according to claim 1, wherein the concave portion is provided on an adjacent cylinder side.   The internal combustion engine according to any one of claims 1 to 3, wherein a portion of the concave portion reaching the top surface of the piston is expanded toward an axial direction of the piston.

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