JP4712844B2 - Combustion chamber structure of internal combustion engine - Google Patents

Description

  The present invention relates to a combustion chamber structure of an internal combustion engine that realizes an improvement in intake efficiency at medium and high loads in an internal combustion engine having a variable valve lift mechanism.

  Many 4-cycle gasoline engines and diesel engines (hereinafter simply referred to as “engines”) are equipped with various valve opening characteristics variable mechanisms to improve output and fuel consumption and reduce harmful exhaust gas components. ing. As a valve opening characteristic variable mechanism, there is a mechanism that switches between a low speed type cam and a high speed type cam according to the operating condition, but in recent years, in order to realize further improvement of transient characteristics and reduction of throttle, etc. A variable valve lift mechanism that continuously and variably controls the lift amount of the valve has appeared (see Patent Document 1). In an engine equipped with this type of variable valve lift mechanism, a shroud having a predetermined circumference may be provided along the outer edge of the intake port in order to improve combustion efficiency during low lift (see Patent Documents 2 and 3). ).

The shroud of Patent Document 2 is projected from the combustion chamber wall of the cylinder head, the shroud surface is formed in a cylindrical shape along the axis of the intake port, and the end surface on the combustion chamber side is the axis of the intake valve. It is an orthogonal flat surface. When the intake valve is in a low lift, intake air that flows into the combustion chamber from the intake port generates a swirl flow by being blocked by the shroud surface. Moreover, although the shroud of patent document 3 is substantially the same as that of patent document 2, the end surface inclines toward the combustion chamber side.
JP 2008-25412 A JP 59-7730 A JP-A-56-57906

  In an engine equipped with a variable valve lift mechanism and a shroud, when the load is low and the lift is low, the intake air is blocked by the shroud to generate a strong swirl flow, improving the ignition efficiency while improving the combustion efficiency. At the time of medium and high lifts with a relatively heavy load such as time, a contradictory performance is required to achieve higher intake efficiency by suppressing intake loss due to the shroud.

  As shown in FIG. 8, in Patent Document 2, the intake air that has flowed from the intake port 6 flows into the combustion chamber 5 after passing through the shroud surface 51 of the shroud 41 during the middle lift of the intake valve 11. At this time, since the end surface 61 of the shroud 41 on the combustion chamber 5 side is a flat surface, the area of the intake passage 53 defined by the intake valve 11 and the shroud 41 (that is, the umbrella portion 11a of the intake valve 11). The distance L) increases rapidly and pressure loss due to vortex flow or the like occurs. In addition, since the shroud surface 51 and the end surface 61 form an angle of 90 °, a right-angled edge 54 is formed at this portion. Such a relatively sharp edge 54 makes it difficult for the heat received from the combustion gas to be released (because the heat is poor), which causes a local thermal deformation of the cylinder head, which becomes a heat spot that causes knocking. If it is operated for a long period of time, there is a concern of causing cracks due to thermal fatigue. As shown in FIG. 9, in Patent Document 3, the end surface 61 of the shroud 41 on the combustion chamber 5 side is an inclined surface. Become. However, since the increase rate of the flow path area is still large, there is still concern about a decrease in intake efficiency.

  The present invention has been made in view of the above situation, and an object of the present invention is to provide a combustion chamber structure of an internal combustion engine that realizes an improvement in intake efficiency at medium and high loads in an internal combustion engine equipped with a variable valve lift mechanism. To do.

The combustion chamber structure of the internal combustion engine according to the first invention comprises a combustion chamber wall (2a) formed in the cylinder head (2) , a cylinder bore (1a) drilled in the cylinder block (1) , and a piston (4 top and the combustion chamber of) the (internal combustion engine 5) is defined (E), wherein the combustion chamber wall (2a), the intake port is opened and closed by the valve head of the intake valve (11) (11a) ( 6a) is opened, is projected at a predetermined peripheral length along the outer periphery of the opening edge portion of the intake port shroud (41) is to be subjected to the formation of the swirl flow (6a), the intake valve (11) is A concave curved surface (52) facing the outer edge of the umbrella portion (11a) when the lift amount is a predetermined amount is formed continuously on the shroud surface (51) of the shroud (41) , and the combustion chamber wall (2a) Cylinder bore (1 ) And the connecting portion are at least partially continuous with the concave surface (52), said shroud surface (51) and said concave surface (52) and is characterized in that an obtuse angle.

According to the present invention, since the intake flow path is defined between the umbrella portion of the intake valve and the concave curved surface, an abrupt change in the flow path area is suppressed and the intake flow velocity is less likely to decrease. Further, since the intake air flowing from the intake port flows smoothly in the combustion chamber, the intake efficiency can be further improved .

Hereinafter, an embodiment of a combustion chamber structure according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing a main part of an engine according to the embodiment, FIG. 2 is a view showing an operating state during a high lift of the intake side valve operating device, and FIG. It is a figure which shows the operation state at the time of a lift. 4 is a bottom view showing a main part of the cylinder head according to the embodiment, FIG. 5 is a VV enlarged sectional view in FIG. 4, and FIG. 6 is a VI-VI enlarged sectional view in FIG. FIG. 7 is an enlarged sectional view taken along line VII-V in FIG.

<< Configuration of Embodiment >>
<Overall configuration>
An engine (internal combustion engine) E shown in FIG. 1 is a DOHC 4-valve type 4-cycle in-line four-cylinder gasoline engine mounted on an automobile. A cylinder block 1 in which a piston 4 is slidably fitted in a cylinder bore 1a, and a cylinder bore 1a and a cylinder head 2 having a combustion chamber wall 2a defining a pent roof type combustion chamber 5 together with the top of the piston 4. Both pistons 4 are connected to the crankshaft via a connecting rod (not shown), and apply a rotational force to the crankshaft by reciprocating in the cylinder bore 1a.

  The cylinder head 2 includes two intake ports 6 and two exhaust ports 7 that open to the combustion chamber 5, and the intake valve 11 and the exhaust valve 12 that open and close the intake and exhaust ports 6 and 7 are slidable. keeping. 1 is a valve spring that urges the intake and exhaust valves 11 and 12 in the valve closing direction. The members indicated by reference numerals 13 and 14 are press-fitted into the open ends of the intake and exhaust ports 6 and 7, respectively. Valve seat.

  A cam holder 17 is fastened to the upper surface of the cylinder head 2, and an intake cam shaft 15 and an exhaust cam shaft 16 are rotatably held by the cam holder 17. Both camshafts 15 and 16 are rotationally driven at a rotational speed half that of the crankshaft via a crank sprocket, cam chain, and cam sprocket (not shown). An intake rocker arm 21 and a sub cam 22 are interposed between the intake camshaft 15 and the intake valve 11. An exhaust rocker arm 23 is interposed between the exhaust camshaft 16 and the exhaust valve 12.

Next, the operation of the intake side valve operating apparatus will be described with reference to FIGS.
For example, when the engine E is operated in a high speed rotation region or a high load region, the holder 25 occupies the maximum lift position shown in FIG. At this time, the control cam 26a comes into contact with the roller 27 at a position where the cam crest has the maximum height in the rotation range. The sub cam 22 that is driven by the rotating intake cam 15a and rotates in the clockwise direction rotates the intake rocker arm 21 in the clockwise direction by the drive surface 28a of the drive cam portion 28, and the intake valve 11 includes the intake cam 15a. When contacting the roller 24 at the apex of the cam crest, the valve is opened with the maximum lift amount that is the maximum value in the change range of the maximum lift amount that can be changed by the transmission mechanism T.

  When the engine E shifts to a lower speed rotation region or a smaller load region, as shown in FIG. 3, as the control shaft 26 is driven by an electric motor (not shown) and rotates counterclockwise, The holder 25 urged by the control urging member 29 rotates clockwise around the holder center line Lh when the roller 27 comes into contact with the lower cam crest of the control cam 26a. . By this rotation of the holder 25, the swing center line Lr rotates clockwise, and at the same time, the roller 27 rotates counterclockwise around the swing center line Ls by the urging member 31 contacting the shaft end 30a. Thus, the roller 32 contacts the drive cam portion 33 at a position moved from the drive surface 33a side to the non-drive surface 33b side. For this reason, when the intake rocker arm 21 is driven by the drive surface 33a, the maximum lift amount of the intake valve 11 is continuously reduced.

<Cylinder head combustion chamber wall shape>
As shown in FIG. 4, shrouds (shown in black in FIG. 4) 41 and 42 are formed on the combustion chamber wall 2a of the cylinder head 2 along the outer edges of both intake ports 6a and 6b. ing. The shrouds 41, 42 are formed counterclockwise along the outer periphery of the opening of the intake ports 6a, 6b with respect to the center P of the combustion chamber wall 2a. Therefore, at the time of low lift, the intake air flowing into the combustion chamber 5 from the intake ports 6a and 6b is blocked by the shrouds 41 and 42, thereby generating a clockwise swirl flow as shown by arrows in FIG. . In the case of the present embodiment, the circumferential length of the shrouds 41 and 42 is set to approximately ¼ (that is, in an angular range of approximately 90 °) with respect to the outer circumferential length of the intake ports 6a and 6b. It can be set within an arbitrary angle range of 0 ° to 180 °.

  As shown in FIGS. 4 and 5, the shroud 41 has an annular shroud surface 51 located immediately below the valve seat 13, and a concave curved surface that is continuous with the shroud surface 51 at the lower end of the shroud surface 51. 52 (shown by smudging in FIG. 4) is formed. When the intake valve 11 is in the minimum lift state (indicated by a two-dot chain line in FIG. 5), the umbrella portion 11a of the intake valve 11 faces the shroud surface 51. At this time, the umbrella portion 11a and the shroud surface 51 The distance (that is, the cross-sectional area of the intake passage) is small, and very little air is sucked from the side where the shroud 41 is formed.

  On the other hand, in the intermediate lift state (the state indicated by the solid line in FIG. 5), the distance L (that is, the cross-sectional area of the intake flow channel 53) increases as the lift amount increases while the concave curved surface 52 and the umbrella portion 11a face each other. ) Gradually increases, and when the lift state is further increased, the umbrella portion 11a is positioned closer to the cylinder bore 1a (see FIG. 6) than the position facing the concave curved surface 52. Further, since the shroud surface 51 and the concave curved surface 52 form an obtuse angle, an obtuse angle edge 54 is formed at this portion. And in the site | part shown in FIG. 5, the lower end of the concave curved surface 52 and the combustion chamber wall 2a are continuing via the gentle curved surface 55. FIG. The concave curved surface 52 is formed by a disk-shaped cutting tool (such as a milling cutter) 56 having a convex spherical outer periphery on the tip side, as indicated by a two-dot chain line in FIG.

  As shown in FIGS. 4 and 6, a part of the concave curved surface 52 extends toward the cylinder bore 1 a of the cylinder block 1, and the connecting portion between the combustion chamber wall 2 a and the cylinder bore 1 a is the concave curved surface 52. Is continuous by. As shown in FIGS. 4 and 7, a concave curved surface 52 is also processed in a portion where the shroud 41 is not formed, and intake efficiency is ensured by increasing the flow path of the intake air. Any of these concave curved surfaces 52 can be simultaneously processed by the cutting tool 56 described above.

  In forming the concave curved surface 52 on the cylinder head 2 side, after setting the height of the shrouds 41 and 42, the combustion chamber wall 2a is cut by the cutting tool 56 so as to secure a space for the intake air to flow into. . The concave curved surface 52 is formed so as to be connected to the ceiling of the combustion chamber 5 when formed between the openings of the two intake ports 6 (or in the vicinity of the center of the combustion chamber 5), but extends toward the cylinder bore 1a. In this case, the portion cut into the curved surface reaches the lower surface of the cylinder head 2 and is directly connected to the cylinder bore 1a.

  On the other hand, in forming the concave curved surface 52 on the cylinder bore 1a side, as shown in FIG. 5, a straight line Lt extending from the lower end portion of the valve seat 13 connected to the shrouds 41, 42 to the cylinder bore 1a side is drawn. The concave curved surface 52 may be formed so as to form a tangent line. As a result, a sufficient flow path area can be secured while avoiding a sudden increase, and the intake air can be smoothly flowed into the cylinder bore 1a during the middle / high valve lift.

<< Operation of Embodiment >>
In the engine E of the present embodiment, as shown in FIG. 3, in the low load and low rotation region, the control shaft 26 is rotated counterclockwise to be in a low lift state, thereby reducing the intake air amount. Then, the intake air from the intake ports 6a and 6b is blocked by the shroud surfaces 51 of the shrouds 41 and 42, thereby generating a swirl flow as indicated by arrows in FIG.

  As shown in FIGS. 5 and 6, the intake air passes through an intake passage 53 formed between the umbrella portion 11 a of the intake valve 11 and a concave curved surface 52 continuous with the lower end of the shroud surface 51. . At this time, in the present embodiment, since the distance L between the umbrella portion 11a and the concave curved surface 52 (that is, the cross-sectional area of the intake flow path 53) does not increase rapidly, intake air caused by eddy currents or the like, which has been a problem in the conventional apparatus. A decrease in efficiency is effectively suppressed. Further, since the edge 54 of the continuous portion of the shroud surface 51 and the concave curved surface 52 is obtuse, the heat received from the combustion gas is easily dissipated, and cracks due to thermal fatigue or the like even when the engine E is operated for a long period of time. It becomes difficult to happen. In addition, in the portion shown in FIG. 6, the connecting portion between the combustion chamber wall 2a and the cylinder bore 1a is continuous by the concave curved surface 52, so that the intake air flows smoothly into the combustion chamber 5. Furthermore, since the concave curved surface 52 of the combustion chamber wall 2a can be simultaneously processed by the single cutting tool 56, the cutting tool is not required to be replaced, and the number of processing steps and processing time can be reduced.

  Although the description of the specific embodiment is finished as described above, the present invention can be widely modified without being limited to the above-described embodiment and some modified examples. For example, although the above embodiment is an application of the present invention to an in-line four-cylinder DOHC gasoline engine, it is naturally applicable to a V-type engine, a diesel engine, or the like. Further, the overall shape of the shroud, the shape of the concave curved surface, and the like are not limited to those illustrated in the present embodiment, and can be appropriately changed depending on design, manufacturing convenience, and the like.

It is a longitudinal section showing an important section of an engine concerning an embodiment. It is a figure which shows the operation state at the time of the high lift of the intake side valve operating apparatus which concerns on embodiment. It is a figure which shows the operation state at the time of the low lift of the intake side valve operating apparatus which concerns on embodiment. It is a bottom view which shows the principal part of the cylinder head which concerns on embodiment. It is VV expanded sectional drawing in FIG. It is VI-VI expanded sectional drawing in FIG. It is a VII-V expanded sectional view in FIG. It is a principal part longitudinal cross-sectional view which shows the 1st example of the conventional type shroud. It is a principal part longitudinal cross-sectional view which shows the 2nd example of the conventional type shroud.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder block 1a Cylinder bore 2 Cylinder head 2a Combustion chamber wall 4 Piston 5 Combustion chamber 6 Intake port 11 Intake valve 11a Umbrella part 41 Shroud 51 Shroud surface 52 Concave surface 53 Intake flow path 54 Edge 56 Cutting tool E Engine T Transmission mechanism

Claims (1)

A combustion chamber (5) is defined by the combustion chamber wall (2a) formed in the cylinder head (2), the cylinder bore (1a) drilled in the cylinder block (1), and the top of the piston (4). In the internal combustion engine (E)
The combustion chamber wall (2a) has an intake port (6a) opened and closed by an umbrella portion (11a) of the intake valve (11).
A shroud (41) provided for forming a swirl flow is provided with a predetermined circumference along the outer periphery of the opening edge of the intake port (6a),
A concave curved surface (52) facing the outer edge of the umbrella portion (11a) when the intake valve (11) has a predetermined lift amount is formed continuously on the shroud surface (51) of the shroud (41),
The connecting portion of the combustion chamber wall (2a) with the cylinder bore (1a) is at least partially continuous with the concave curved surface (52),
A combustion chamber structure of an internal combustion engine, wherein the shroud surface (51) and the concave curved surface (52) form an obtuse angle.

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