JP4270189B2 - Combustion chamber structure of internal combustion engine - Google Patents

Description

  The present invention relates to a combustion chamber structure of an internal combustion engine, and more particularly to a combustion chamber structure of an internal combustion engine that can promote the flow of airflows in an intake stroke and a compression stroke.

  In an internal combustion engine, as a means for achieving the demands of improving output, reducing fuel consumption, and detoxifying exhaust gas, appropriately setting the shape of a combustion chamber in a cylinder is performed. For example, a four-cycle gasoline engine (hereinafter simply referred to as an engine) has an intake port that is relatively large, so that the air-fuel mixture is sucked into the combustion chamber in a state of relatively low flow resistance during the intake stroke. Improving efficiency. Further, in order to facilitate the ignition of the air-fuel mixture by the spark plug near the top dead center in the compression stroke, the engine top surface and the piston surface can be collected so that the air-fuel mixture can be collected relatively near the spark plug. The cylinder head bottom surface shape is set.

  Furthermore, when the piston of the cylinder approaches top dead center in the compression stroke, the gap between the periphery of the piston top surface and the lower surface of the cylinder head facing the cylinder sandwiches the air-fuel mixture, creating a squish flow toward the center of the combustion chamber. The squish area is formed so as to secure an extruding squish area, and the squish flow pushed out by being sandwiched between the squish areas further agitates the air-fuel mixture being compressed, thereby promoting combustion.

  For example, in Japanese Patent Application Laid-Open No. 2005-127255 (Patent Document 1), an annular gap is formed as a squish area between the tapered portion of the piston top surface and the peripheral portion of the lower surface of the cylinder head. It is formed by changing in the piston inner circumferential direction. That is, the taper portion between the pair of intake valves and the pair of exhaust valves is formed with a relatively small width in the piston radial direction, and the taper portion between the two intake and exhaust valves is formed with a relatively large width in the piston radial direction. Has been. In this case, in the compression stroke, the air-fuel mixture in the vicinity of each of the intake and exhaust valves is diverted in two directions along the peripheral direction of the combustion chamber, and from a portion having a relatively large gap width between the intake valve and the exhaust valve. The squish flow is pushed out into the recess at the center of the combustion chamber so that the air-fuel mixture in the recess is agitated.

  By the way, it is assumed that the piston of the engine takes a piston top shape as shown in FIGS. 9 (a), 9 (b), 10 (a), and 10 (b). In this case, a tapered portion 100 for generating the squish flow fs during the compression stroke is formed in an annular shape at the periphery of the piston top. Further, in the piston 101 shown in FIGS. 9A and 10A, the width bS in the piston radial direction at the portion of the tapered portion 100 facing the engine longitudinal direction X is relatively small, and the height h1 is also compared. In accordance with this, the central recess 102 on the top surface of the piston 101 is formed in an elliptical shape as shown in FIG. 10 (a) ((a) to (g) in FIG. (Similar configuration), the central recess 102 is formed with a relatively large capacity. Here, as shown in FIG. 9A, a squish region a1 between the taper portion 100 on the piston top surface and the lower surface of the head causes flow resistance when the engine is in the intake stroke. Since the width bS in the piston radial direction is relatively narrow, the flow of intake air into the elliptical central recess 102 having a relatively large capacity is facilitated, and the volumetric efficiency is improved.

  On the other hand, in the piston 103 shown in FIG. 9B, the width bL of the taper portion 104 in the piston radial direction is relatively large over the entire circumference, and the height h2 is also large, and the center of the top surface of the piston 103 is accordingly formed. The concave portion 105 is formed in a circular shape as shown in FIG. 10B, and the central concave portion 105 is formed with a relatively small capacity. In this case, the width bL in the piston radial direction in the squish region a2 formed between the tapered portion 104 of the piston top surface and the lower surface of the head is ensured relatively wide, and the end gas portion is disturbed by the forward squish flow fs and the reverse squish flow -fs. Further, combustion is promoted in the compact combustion chamber by the central concave portion 105 having a relatively small capacity, and ignition advance is possible.

JP 2005-127255 A

By the way, in the piston 101 of FIGS. 9A and 10A, the central recess 102 is wide and elliptical and has a relatively large capacity, which is easy to knock and causes a problem in aiming at the ignition advance angle. It is likely to occur.
On the other hand, in the piston 103 of FIG. 9B and FIG. 10B, the central recess 105 forms a compact combustion chamber having a relatively small volume and thus improves ignitability, but the width in the piston radial direction is improved. Since the squish region a2 is formed by the tapered portion 104 having a relatively large bL, in this case, the flow resistance for the intake flow e (see FIG. 9B) from the intake port into the central recess 105 is compared. The volume efficiency is likely to be suppressed.

  The present invention has been made to solve the above-described problems, and the object of the present invention is combustion of an internal combustion engine capable of improving the output by ensuring the intake air amount and enabling the ignition advance angle. It is to provide a chamber structure.

  To achieve the above object, the combustion chamber structure of an internal combustion engine according to claim 1 is a combustion chamber structure of an internal combustion engine in which a combustion chamber is formed by being surrounded by a cylinder head lower surface, a piston upper surface and a cylinder. The lower surface of the head has a circular shape in plan view, and at least one intake valve is provided on one side with a predetermined string extending in the longitudinal direction of the engine in the plan view circular shape, and at least one exhaust valve is provided on the other side. On the upper surface of the piston, a conical taper portion protruding from the periphery toward the center of the piston is formed along the periphery, and a recess is formed in the center, and the taper portion is located near the string at the exhaust valve. The width of the piston radial direction of the intake valve arrangement side part is formed smaller than the arrangement side part of the intake valve, and both parts are continuously formed with a step. It is a feature that was.

  The combustion chamber structure of the internal combustion engine according to claim 2 is the combustion chamber structure of the internal combustion engine according to claim 1, wherein the cylinder head lower surface is provided with a pair of intake valves on one side with the predetermined string interposed therebetween and the other side. It is characterized in that a pair of exhaust valves is provided.

  The combustion chamber structure of the internal combustion engine according to claim 3 is the combustion chamber structure of the internal combustion engine according to claim 1, wherein the one surface and the other surface of the cylinder head lower surface face each other with the string as a vertex. It is characterized by being formed in an inverted V-shaped cross section.

  According to the combustion chamber structure of the internal combustion engine of claim 1 of the present invention, when the intake valve is opened, the intake air that is directed from the opening of the intake port into the combustion chamber is in the gap between the conical taper portion on the upper surface of the piston facing the opening. In addition to flowing in, the taper can easily flow over the inner end edge where the intake valve is located relatively short on the front side of the step, and flow into the central recess, facilitating volume efficiency by promoting inflow. In addition, since it is possible to secure a relatively large portion of the taper portion in the radial direction of the piston, it is easy to make the central concave portion compact and to facilitate the ignition advance of the air-fuel mixture in the central concave portion. Since the intake side and exhaust side tapered portions on the upper surface have different shapes, it is easy to increase the output.

  According to the combustion chamber structure of the internal combustion engine of claim 2, even when a pair of intake valves are provided on one side across the string, the intake air that is directed into the combustion chamber from the openings of both intake ports is a piston opposed to both openings. It flows into the gap with the conical taper portion on the upper surface, and it easily crosses the inner end edge where the installation side portion of the intake valve is formed relatively short on the front side of the step in the taper portion and easily enters the central recess. It is possible to flow in, volume efficiency can be achieved by facilitating inflow, and it is easy to make the central recess compact and facilitate ignition advance. From these points, the taper on the piston upper surface side and the pair of exhaust valve side on the piston upper surface It becomes easy to increase output because the part has an irregular shape.

  According to the combustion chamber structure of the internal combustion engine of claim 3, the upper surface of the piston opposed to each other is formed in a reverse V-shaped cross section in which one surface and the other surface of the cylinder head lower surface face each other. Securing a gap with the conical tapered portion at the periphery of the squeeze is facilitated, the generation of the squish flow is promoted, and the combustion efficiency can be improved.

Hereinafter, the combustion chamber structure of the internal combustion engine of the present invention will be described.
The combustion chamber structure of an internal combustion engine according to the present invention is applied to a DOHC-4 valve type four-cylinder engine (hereinafter simply referred to as engine 1) as an internal combustion engine.
Here, the engine 1 has a cylinder block 2 in which four cylinders S whose main body forms a combustion chamber C are sequentially arranged in the engine longitudinal direction (perpendicular to the plane of the paper) X at equal intervals, and an oil pan 3 coupled to the lower part thereof. And a cylinder head 4 and a head cover 5 coupled to the upper portion thereof.

  The cylinder block 2 includes a water jacket 6 covering each cylinder S, an outer wall 201, a lower skirt portion 202, a crankshaft 7 which is long in the longitudinal direction (perpendicular to the plane of the drawing) X, and each cylinder S of the crankshaft 7 Connecting rods 8 respectively connected to the opposed parts, and pistons 9 pin-connected to the upper ends of the connecting rods 8. Note that FIG. 1 shows only one cylinder, and the other cylinders have the same configuration, and therefore, a duplicate description is omitted.

  In the cylinder head 4, an intake port ip on the intake passage I side and an exhaust port ep on the exhaust passage E side communicating with the combustion chamber C are formed in a bifurcated shape at a portion facing each cylinder S (see FIG. 4). I and the combustion chamber C are controlled to open and close by a pair of intake valves 11, and the exhaust passage E and the combustion chamber C are controlled to open and close by a pair of exhaust valves 12.

  The valve mechanism of the engine 1 is a DOHC type, and as a result, the intake valve 11 and the exhaust valve 12 are driven to open and close as the crankshaft 7 rotates. Further, the engine 1 is configured as an intake pipe injection type (MPI) engine 1, and an injector 13 is provided at an intake port ip of each cylinder (only one is shown here), and each injector 13 is a fuel (not shown). It is connected to a supply system and is controlled to be opened and closed by an unillustrated injection coil and an engine controller connected thereto.

  The air-fuel mixture in the combustion chamber C of the engine 1 is ignited by a spark plug 14 provided at the center of the lower surface of the cylinder head 4. Each spark plug 14 performs the ignition operation of the air-fuel mixture sequentially by the action of an ignition circuit (not shown). The exhaust gas after burning here flows down from the exhaust port ep to the exhaust passage E as the piston rises when the exhaust valve 12 is opened, and is discharged outside through a catalytic converter and a silencer (not shown).

As shown in FIG. 5, the combustion chamber C in each cylinder S of the engine 1 is formed by being surrounded by a cylinder facing surface Fs, a piston upper surface Fp, and a cylinder inner surface Fc that are lower surfaces of the cylinder head. The volume is varied according to the above.
Here, as shown in FIG. 4, the cylinder facing surface Fs, which is the lower surface of the cylinder head, has a circular shape in plan view, and extends in the engine longitudinal direction X of the circular shape in plan view and intersects the piston center line Lp. A pair of intake valves 11 is disposed on one side with a pair of exhaust valves 12 disposed on the other side with a two-point difference line (see two-point difference line) therebetween.

As shown in FIG. 5, the cylinder facing surface Fs, which is the lower surface of the cylinder head, has the chord A as a vertex, and the intake side surface (one side) Fsi and the exhaust side surface (other side) Fse each form an inclined plane, The cross section is shaped like an inverted V so as to face each other.
A pair of openings O (intake port ip side) for communicating and blocking between the intake port ip and the combustion chamber C by the intake valve 11 is formed on the intake side surface Fsi, and the exhaust port ep and the combustion chamber C are connected to the exhaust side surface Fse. A pair of openings O (exhaust port ep side) for communicating and blocking with the exhaust valve 12 are provided.

As shown in FIGS. 1 and 2, the piston 9 fitted in the cylinder S so as to be slidable up and down has a top portion 901 facing the combustion chamber C, and a cylindrical skirt portion 902 and its lower part from the lower peripheral edge of the top portion 901. The connecting rod pivotal support portion 903 that extends continuously is integrally formed. The connecting rod pivot 903 is pin-coupled to the connecting rod 8 via a piston pin 904 that intersects the piston center line Lp, whereby the piston 9, connecting rod 8, and crankshaft 7 form a crank mechanism. The combustion pressure received in the combustion stroke is converted into the rotational force of the crankshaft 7.
As shown in FIGS. 1 to 4, the top portion 901 of the piston 9 is formed with a conical taper portion 16 protruding from the periphery toward the center of the piston along the periphery of the piston top surface Fp. A central recess 17 is formed at the center.

  As shown in FIGS. 2 and 4, the conical taper portion 16 of the piston protrudes in an annular shape, and a pair of valve recesses 18 for the intake valve 11 is formed on the intake port ip side, and a pair of exhaust ports is formed on the exhaust port ep side. Valve recesses 19 for the valves 12 are provided intermittently, and each is formed by cutting into a concave shape. The valve recesses 18 and 19 function to avoid mutual interference by fitting part of the bottom surfaces of the opposing valves in the latter half of the compression stroke of the piston 9 and contribute to securing a high compression ratio of the engine. is doing.

Since each of the valve recesses 18 and 19 has the pair of intake valves 11 and exhaust valves 12 inclined in the opposite direction with respect to the piston center line Lp (see FIGS. 1 and 3), the bottom surface of each valve is accordingly The bottom surfaces of the valve recesses 18 and 19 that have an inclination and are opposed thereto are also inclined with respect to the piston top surface Fp.
As shown in FIGS. 4 and 5, the taper portion 16 protruding in a conical surface from the piston top portion 901 has a string A (see FIG. 5) that overlaps the center line Lx in the engine longitudinal direction X intersecting the piston center line Lp. The two side portions are formed so as to have different shapes, that is, formed in different shapes.

  In FIG. 4, the taper portion 16 in the vicinity of the upper and lower two positions of the string A (also in the vicinity of the center line Lx in the engine longitudinal direction X) is the piston of the arrangement side portion e1 of the exhaust valve 12 on the left side of the page. The piston radial direction width b2 of the arrangement side portion e2 of the intake valve 11 on the right side is formed smaller than the radial width b1. Further, the abutting portions of both the portions e1 and e2 form a stepped portion c that maintains a step δ (= b1−b1) in the piston radial direction, and is continuously formed by excluding the edge-shaped portion by the radius r portion. The

Here, the exhaust side surface Fse and the intake side surface Fsi, which are the lower surface of the cylinder head 4 serving as the upper wall of the combustion chamber C, are arranged so that their shapes follow the lower wall of the combustion chamber C, that is, with a predetermined gap from the tapered portion 16. It is formed so as to be opposed to each other.
4 and 5, in the left half portion of the string A in the peripheral portion of the combustion chamber C, a pair of exhaust valve recess interspaces m1 in the taper portion 16 of the piston top surface Fp serving as the bottom surface of the combustion chamber C and A butt portion m2 is formed, and the width b1 in the piston radial direction of the squish region se formed between the exhaust side Fse (see FIG. 3) that is the lower surface of the cylinder head that is the upper wall is formed relatively large. The

On the other hand, in FIGS. 3 and 4, in the right half of the string A in the peripheral portion of the combustion chamber C, the region between the pair of intake valve recesses in the taper portion 16 of the piston top surface Fp serving as the bottom surface of the combustion chamber C. n1 and butt portion n2 are formed. These piston radial widths are different from b1 and b2 (<b1). Accordingly, the width in the piston radial direction of the squish area si (see FIG. 3) formed between the intake side Fsi that is opposed to these and the intake side Fsi is also different. The right half of the string A of the taper portion 16 is formed with a small piston radial width b2 (<b1) at the butting portion n2, and thereby the flow resistance of the intake air from the opening O of the intake port ip to the combustion chamber C is reduced. The volume efficiency can be improved by reducing the suction resistance. In FIG. 4, the stepped portion c between the pair of upper and lower butted portions m2 in the left half of the string A and the pair of upper and lower butted portions n2 in the right half is the right half. It can function as a guide for deflecting the flow direction of the airflow detoured to the pair of upper and lower butting portions n2 from the paired intake valve recess inter-region n1 side to the central concave portion 17 side that is the histone center line Lp side. A strong airflow can be flowed into the central recessed part 17 side, and it can contribute to the combustion promotion by stirring of air-fuel | gaseous mixture.
The operation of the engine 1 having such a combustion chamber structure of the internal combustion engine will be described.
It is assumed that when the engine is driven, the end of the exhaust stroke and the start of the intake stroke are reached.
At this time, the piston 9 is in the vicinity of the top dead center, the bottom of the exhaust valve 12 changes in the closing direction from the state in which the exhaust valve 12 approaches the exhaust valve recess 19, and the opening operation is performed in the direction in which the intake valve bottom approaches the intake valve recess 18. Exhaust is exhausted from the opening O of the port ep, and intake starts to flow in from the opening O of the intake port ip.

  At this time, the tapered portion 16 of the piston top surface Fp at the peripheral portion of the combustion chamber C and the peripheral portion of the lower surface of the cylinder head 1 are close to each other, and the flow of intake air from the openings O of the pair of intake ports ip in the right half portion. However, in this case, in the pair of intake valve recess inter-region n1, the pair of upper and lower butting portions n2 are relatively small in width in the piston radial direction b1 (> b2) and relatively small in width b2. The intake air flow is diverted and detoured, and the intake air flow also receives a function of deflecting the combustion chamber C toward the center by the step portion c, and can smoothly flow into the central recess 17 to reduce the intake resistance of the intake air. Contributes to improved efficiency.

  It is assumed that the engine 1 enters a compression stroke and the piston 9 rises toward the compression top dead center. In this case, the air-fuel mixture in the combustion chamber C formed by being surrounded by the cylinder facing surface Fs that is the lower surface of the cylinder head, the piston upper surface Fp, and the cylinder inner surface Fc is reduced in volume as the piston 9 rises and is pressurized. Is done. Next, a squish flow fs is ejected from the squish region se and si formed by the cylinder facing surface Fs, which is the lower surface of the cylinder head, and the tapered portion 16 of the piston top portion 901 to the central concave portion 17, and the air-fuel mixture in the central concave portion 17 is further stirred. This facilitates ignition and promotes combustion.

  In particular, in the taper portion 16 of the piston top portion 901, the exhaust side surface (left surface in FIG. 4) Fse and the squish region se between the pair of exhaust valve recesses m1 and the butting portion m2 with the string A as the apex are the entire region. The width b1 in the piston radial direction is formed to be relatively large (see the solid line display in FIG. 3), and a sufficient squish flow fs can be formed. Moreover, the squish area si formed between the intake side surface (the right side surface in FIG. 4) Fsi and the pair of intake valve recess areas n1 with the string A as the apex is similarly formed with a relatively large width b1 in the piston radial direction. And a sufficient squish flow can be formed.

  As described above, according to the combustion chamber structure of the internal combustion engine shown in FIGS. 1 to 5, the squish flow fs in the exhaust side and intake side squish regions se and si with the string A as the apex is sufficiently generated. As shown in FIG. 7 (b), the compact central concave portion 17 with a relatively small volume compared to the conventional central concave portion 102 having an elliptical shape and a large volume can surely promote the stirring of the air-fuel mixture, ensuring ignitability and combustion. It can be promoted and can contribute to the improvement of engine output.

  FIGS. 8A and 8B show the results of the ignition timing characteristic test and the volumetric efficiency characteristic that the present inventor conducted using the same engine and only the pistons having different shapes. Each diagram here shows the case where the tapered portion to which the present invention is applied is an irregularly shaped piston (application of the present invention: ○), the case of the conventional piston 101 (small tapered portion: □) in FIG. The comparison with the conventional piston 103 (taper portion large: Δ) in FIG. 9B is shown in comparison. As is clear from FIG. 8A, in the case of the piston to which the present invention is applied (application of the present invention: ◯), the ignition advance angle δT is compared with the measured value under other same conditions in each rotation speed range. It was confirmed that (measured values under the same conditions in which each black mark in the figure was compared) could be achieved. Further, as is clear from FIG. 8B, in the case of the piston to which the present invention is applied (application of the present invention: ◯), it is confirmed that the volume efficiency increase amount δQ is achieved in each rotation speed range. It was.

  In the above description, of the tapered portion 16 of the piston top portion 901, the butting portion n2 facing the intake side surface (one side) Fsi with the chord A as the apex is different from the pair of intake valve recess inter-region n1, and in the piston radial direction. The width was formed as large as b1 and contributed to the generation of the squish flow. In some cases, as shown by a two-dotted line d1 in FIG. 4, it was formed to be equal to the width b1 in the piston radial direction at the pair of upper and lower butting portions n2. Then, the inflow resistance of the intake air flow may be reduced to improve the volume efficiency. The width b1 in the piston radial direction is set to an intermediate value between b1 and b2, and the inflow resistance is reduced and the squish flow is reduced. It is also possible to set the generation so as to be obtained appropriately.

  Further, the tapered portion 16 of the piston top portion 901 in the engine of FIG. 1 is formed so as to have different shapes on the intake port ip side and the exhaust port ep side across the string A intersecting the piston center line. Accordingly, as shown by a two-dotted line in FIG. 6, when it is desired to enhance the effect of reducing the suction resistance, the string A may be set so as to be biased toward the exhaust side (the left side in the figure). In order to improve the combustion efficiency, it may be set so as to be biased toward the intake side (left side in the figure) as indicated by a two-dot difference line.

1 is a schematic cross-sectional view of an engine to which a fuel control device for an engine according to an embodiment of the present invention is applied. It is a perspective view of the piston of the engine of FIG. The piston top part of the engine of FIG. 1, the suction | inhalation resistance, and the production | generation explanatory drawing of the squish flow are shown. FIG. 2 is an enlarged plan view of a piston top portion and intake / exhaust ports of the engine of FIG. 1. It is a schematic perspective view explaining the relationship between the piston top part of the engine of FIG. 1, and a cylinder head lower surface. It is a top view of the modification of the piston top part of the engine of FIG. 1 is a plurality of perspective views showing a piston top portion of the engine of FIG. 1 and sequentially changing the viewing direction angle from (a) to (g) from a side view to a plan view. (B) shows a conventional example, in which the tapered portions on the intake side and the exhaust side have different shapes. 2 is a functional characteristic diagram of the engine fuel control device of FIG. 1 and a conventional example, where (a) is an ignition timing characteristic, and (b) is a characteristic diagram showing a volumetric efficiency characteristic. FIG. It is side surface explanatory drawing of the taper part of the piston top part in the conventional engine, (a) shows the case of a small taper part, (b) shows the case of a large taper part. It is plane explanatory drawing of the taper part of the piston top part in the conventional engine, (a) shows the case of a small taper part, (b) shows the case of a large taper part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 11 Intake valve 12 Exhaust valve 16 Taper part 17 Center recessed part b1, b2 Piston radial width e1 Exhaust valve arrangement side part e2 Intake valve arrangement side part A String C Combustion chamber Fp Piston upper surface X Engine longitudinal direction

Claims (3)

In the combustion chamber structure of the internal combustion engine in which the combustion chamber is formed by being surrounded by the cylinder head lower surface, the piston upper surface and the cylinder,
The lower surface of the cylinder head has a circular shape in plan view, and at least one intake valve is provided on one side and at least one exhaust valve is provided on the other side across a predetermined string extending in the engine longitudinal direction of the circular shape in plan view. And
On the upper surface of the piston, a conical taper portion protruding from the peripheral edge toward the piston center along the peripheral edge is formed and a concave portion is formed in the center,
The tapered portion is formed at a position in the vicinity of the chord so that the width in the piston radial direction of the portion on the side where the intake valve is disposed is smaller than the portion on the side where the exhaust valve is disposed, and both portions are continuously formed with a step. A combustion chamber structure of an internal combustion engine characterized by that. The combustion chamber structure of the internal combustion engine according to claim 1,
2. The combustion chamber of an internal combustion engine according to claim 1, wherein the cylinder head lower surface is provided with a pair of intake valves on one side and a pair of exhaust valves on the other side across the predetermined string. Construction. The combustion chamber structure of the internal combustion engine according to claim 1,
2. The internal combustion engine according to claim 1, wherein the lower surface of the cylinder head is formed in an inverted V-shaped cross section so that the surface on one side and the surface on the other side face each other with the string as a vertex. Combustion chamber structure.

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