JP2713448B2 - Engine combustion chamber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a structure of a combustion chamber of an engine.

(Prior Art) For example, to form a swirl (induction turbulence) or a squish (a compression turbulence) in an air-fuel mixture in an engine combustion chamber in order to improve the combustion performance of the engine, or to combine both the swirl and the squish Is well known in the art.

Conventionally, as a means for forming the swirl, for example, a swirl forming opening in the cylinder circumferential direction in addition to a normal main port is provided at an intake port portion into an engine combustion chamber disclosed in Japanese Patent Application Laid-Open No. 57-198315. The swirl port is formed, for example, in a region where the intake air velocity is low and the combustion performance is poor in an engine low load / low rotation region, the swirl port is used to form a swirl and the air-fuel mixture flow rate is positively increased so that combustion and air are increased. At the same time as increasing the flame propagation speed and effectively stratifying the air-fuel mixture to sufficiently improve the ignitability and combustion performance, and furthermore, the swirl forming means is connected to, for example, two dome portions ( Combination of a hemispherical combustion chamber) makes the combustion chamber of the engine more compact and equals volume by making the shape of the combustion chamber closer to a sphere While improving, there is that to be able to effectively realize in squish the compression or expansion stroke by forming a predetermined squish area between the cylinder bores periphery.

As described above, the swirl port is used to form a swirl flow in the engine combustion chamber to increase the flow rate of the air-fuel mixture in the intake stroke, thereby improving the mixing state. In addition, the outer periphery of the dome-shaped combustion chamber and the periphery of the cylinder bore are formed. When a predetermined squish region is formed between the squish and the squish in the compression or expansion stroke to promote the flame propagation speed, the ignitability and combustibility of the engine are improved, and especially the intake charge itself is small and the intake flow velocity is also reduced. There is an advantage that the combustion state can be stabilized in a low engine low load and low rotation range, and lean burn operation can be performed, and fuel efficiency can be improved.

(Problems to be Solved by the Invention) However, even when the dome portion is formed on the lower surface of the cylinder head and a squish area along the inner peripheral edge of the cylinder bore is formed around the dome portion as in the above configuration. For example, assuming that the upper surface of the piston head side is flat, first, for example, when trying to increase the volume of the combustion chamber, the cylinder diameter is increased or the size or depth of the dome portion of the cylinder head side combustion chamber is reduced. It will have to expand. However, enlarging the cylinder diameter is contrary to the demand for downsizing the engine, and changing the size of the dome portion on the cylinder head side leads to reduction and restriction of the squish area. Further, increasing the depth of the dome portion necessarily has a limit in terms of the configuration of the cylinder head, and there is a problem that the compression ratio is reduced.

Originally, the combustion chamber volume of an engine is the largest in the case of a spherical shape in terms of its surface area and external shape. In addition, the isocapacity increases. Therefore, it is preferable to make the shape of the combustion chamber as close as possible to a spherical shape even when setting the actual shape of the engine combustion chamber. The dome part on the cylinder head side is
Although it is originally formed from such a viewpoint, the point that the dome-shaped combustion chamber becomes spherical and the improvement of isocapacity is limited due to the fact that the upper surface of the piston head side is flat as described above. This causes problems. That is, if the top surface of the piston is flat, no matter how much the cylinder head side combustion chamber is formed in a dome shape, the overall shape will ultimately be a flat hemisphere.
Moreover, in general, the intake port side opening is formed to have a larger diameter than the exhaust port side opening in order to increase the intake filling rate. Therefore, when two sets of such a large-diameter opening and a small-diameter opening are to be formed in the dome-shaped combustion chamber, the spherical radius of one dome of the two sets of dome parts is increased to increase the large area. It is convenient to form a dome with a small area by making the spherical radius of the other dome relatively small while forming the dome surface of the dome. But if you do so,
The dome surfaces on the intake side and the exhaust side have different wall inclination angles. In such a case, assuming that the piston head upper surface is flat as described above, the squish angle is firstly too small, and in particular, the combustion flame in the expansion stroke is extinguished by the wall surface, and the quench zone is substantially reduced. In addition to the problem that the amount of HC is increased due to the enlargement, there is a problem that the phenomenon occurs remarkably particularly on the dome side having a large sphere radius.

(Means for Solving the Problems) The present invention has been made for the purpose of solving the above-described problems. First, a concave portion is formed on the lower surface of a cylinder head, and the concave portion is formed along the inner peripheral edge of the cylinder bore around the concave portion. Engine with a squish area
A concave portion corresponding to the cylinder head side concave portion is also formed on the piston head upper surface portion of the piston fitted in the cylinder bore, and the inclination of the piston head side concave portion to the squish region is determined by the cylinder head side concave portion. On the other hand, the smaller the degree of inclination to the squish area is, the larger it is formed.

Further, in the same configuration, the swirl is generated by the swirl port when the load is low.

(Operation) In the combustion chamber structure of the engine of the present invention, in the engine in which a recess is first formed on the lower surface of the cylinder head and a squish area is provided along the inner peripheral edge of the cylinder bore around the recess, the engine is fitted into the cylinder bore. A concave portion corresponding to the cylinder head side concave portion is also formed on the piston head upper surface portion of the inserted piston, and the inclination of the piston head side concave portion to the squish region is adjusted to the same squish region of the cylinder head side concave portion. On the other hand, the smaller the inclination, the larger the conversely. Therefore, in the case of this structure, the shape of the combustion chamber is made as close to a spherical shape as possible, and the volume of the combustion chamber can be increased without increasing the cylinder diameter.

Further, since the inclination degrees of the corresponding concave portions on the cylinder head side and the piston head side are set to have a magnitude opposite to each other, the flame can easily enter and propagate into the squish region in the expansion stroke. And HC can be effectively reduced.

In the above case, when the swirl port is configured to generate swirl at low load,
The high-speed swirl flow flowing in from the swirl port is smoothly introduced in a swirling state from the circumferential direction to the inside of the cylinder-side recess, so that atomization and mixing of the injected fuel can be improved and the effect can be improved. It becomes possible to stratify the air-fuel mixture, thereby improving the combustibility.

(Effect of the Invention) Therefore, according to the combustion chamber structure of the engine of the present invention, it is possible to provide an engine that is compact, has high combustion efficiency, and has a low HC generation degree.

(Embodiment) Figs. 1 to 5 show a combustion chamber structure of an engine according to an embodiment of the present invention.

First, FIG. 1 shows a longitudinal sectional structure of the combustion chamber of the engine. In the figure, reference numeral 1a denotes a cylinder block, and 1b denotes a cylinder block which is located above the cylinder block 1a and integrally provided via a gasket 2. This is a cylinder head that forms a predetermined engine cylinder together with 1a. A cylinder bore 3 having a predetermined diameter and a predetermined length is formed inside the cylinder block 1a (a water jacket and the like are omitted in the figure for simplification of description).

In addition, a surface of the lower surface of the cylinder head 1b corresponding to the cylinder bore 3 is provided with a first surface which separates two regions of an intake side 4a and an exhaust side 4b from each other as shown in FIGS. 1 and 2, for example.
(A circular concave portion) 5a and a second dome portion (circular concave portion) 5b, a multi-sphere engine combustion chamber 5 is formed. The first dome portion 5a forming the combustion chamber 5
As shown in FIG. 2, the second dome portion 5b has a larger diameter than the first dome portion 5a, and the second dome portion 5b has a larger diameter than the first dome portion 5a. From the exhaust side 4b to the darma shape, and squish areas 7a, 7b are formed on the outer peripheral side of both dome areas, wide on the intake side 4a and relatively narrow on the exhaust side 4b. . The squish regions 7a and 7b have a function of improving the flame propagation speed by forming a so-called squish (compression vortex) particularly in the engine compression or expansion stroke, thereby improving the combustion performance. .

Reference numeral 8 denotes an intake port, and 9 denotes an exhaust port. The intake port 8 includes two sets of ports, a main port 8A and a swirl port (secondary port) 8B, and the main port 8A has the main port 8A.
A shutter valve 10 for opening and closing 8A is provided. The shutter valve 10 is closed, for example, in a low-speed, low-load region, and has a high flow rate into the engine combustion chamber 5 only from the swirl port 8B, and has a large diameter projecting portion of the exhaust-side second dome portion 5b.
By making the fuel flow toward the inner circumferential surface portion 14 slightly inside (end side) than the circumferential surface 13 to improve the atomization of the injected fuel and the mixing of the fuel and the air, the combustion chamber is effectively improved. The mixture is stratified. As a result, the flammability is improved as much as possible, so that the drop in the engine torque in the low-speed load region can be covered, and the fuel efficiency can be improved.

On the other hand, when the operating state of the engine becomes a high-speed and high-load state, the shutter valve 10 is largely opened to increase the diameter of the entire intake passage of the intake port 8, and a sufficient amount of intake air and air is reduced in a state where the intake resistance is small. The output will be improved in response to the high load state of the supplied engine.

Reference numeral 11 denotes a fuel injector having a timed injection function for injecting fuel in synchronization with, for example, an intake stroke of the engine. As shown in FIG. 2, the fuel injector 11 is substantially in the same direction as the inflow direction of the swirl flow from the connection portion between the main intake port 8A and the intake manifold 12 continuous with the intake port 8A, and Electrode part 15a of plug 15
The injection direction is set so that fuel is injected synchronously outward from the position (radial direction of the dome portion). As a result, the fuel injected by the timed injection in synchronism with the engine intake stroke rides on the swirl flow formed by the swirl port 8B without directly hitting the electrode portion 15a of the spark plug 15.
5 are gathered near the electrode portion 15a. As a result,
In particular, the concentration of the air-fuel mixture near the electrode portion 15a of the ignition plug 15 becomes rich, and the ignitability is improved. This effect
Further, in combination with the relationship between the installation position and the installation angle of the ignition plug 15 described below, a more effective operation is realized.

That is, the ignition flag 15 is located, for example, at the swirl inflow portion in the exhaust-side second dome portion 5b, and furthermore, as shown in FIG. larger at the same downstream theta ₂ than the swirl upstream theta ₁ the setting angle theta with respect to the surface) (theta ₂
> Θ ₁ ) and a wedge-shaped concave portion 35 is formed and installed.

Therefore, by the timed injection, the relatively rich air-fuel mixture effectively riding on the swirl flow as described above rises upward in the vicinity of the electrode portion 15a of the spark plug 15 as shown by an arrow (a) in the figure. Shed (bent),
The ignition plug 15 stays in the stratified state near the electrode portion 15a for a predetermined time. Therefore, the effect of improving the ignitability is more effectively improved.

Reference numeral 20 denotes a piston fitted in the cylinder bore 3 via a piston ring 20a so as to be vertically slidable. The piston 20 is vertically movably supported by a connecting rod 22 via a piston pin 21.
On the piston head upper surface portion 23, a first dome portion 21a and a second dome portion 21b having a concave shape in the opposite direction corresponding to the shape of the combustion chamber 5 on the cylinder head side are formed to intersect with each other. . And in this case, the piston head
The swirl downstream projection 24 between the first and second dome portions 21a and 21b on the 23 side is provided at a position downstream of the swirl far from the ignition plug 15, and the ignition is performed via the ignition plug 15 as described above. The stratified mixed gas flow is further disturbed by the downstream projection 24 to form a turbulent flow due to the tumble air motion, and the swirl end combustion performance is also greatly improved. The relationship between the shapes of the piston head side first and second domes 21a, 21b and the shapes of the cylinder head side first and second domes 5a, 5b is, for example, as shown in FIG. On the other hand, in the portion (θ ₃ , θ ₃ ′) where the inclination of the first and second dome portions 5a, 5b on the cylinder head side to the squish regions 7a, 7b is small (θ ₃ , θ ₃ ′), it is set large (θ).
₄ , θ ₄ ′) so that they are mutually complementary. As a result, the sphericity of the entire combustion chamber is maintained at a constant level, and the equal volume is improved at a constant compression ratio while achieving a large intake port diameter. .

Therefore, the squish formed during the compression or expansion stroke occurs evenly on both the intake side and the exhaust side, so that an effective flame propagation speed can be secured and a stable combustion state can be always realized. it can. As a result, HC
Is also reduced. In FIGS. 1 and 2, reference numeral 31a denotes an intake valve, and 31b denotes an exhaust valve. The intake valve 31a is, for example, a second valve for improving swirl efficiency.
As shown in the figure, it is preferable to offset the predetermined position 1 in the direction opposite to the outlet of the swirl port 8B.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a structure of a combustion chamber of an engine according to an embodiment of the present invention. FIG. 2 is a sectional view taken along the line AA of FIG. FIG. 3 is an enlarged cross-sectional view (sectional view taken along the line BB of FIG. 2) of the vicinity of a spark plug mounting portion of the structure of the embodiment, FIG. 4 is a plan view showing a shape of an upper surface of a piston head in the structure of the embodiment, FIG. 5 is a longitudinal sectional view schematically showing a relative shape between a cylinder head side combustion chamber and a piston head side combustion chamber in the structure of the embodiment. 1a cylinder block 1b cylinder head 2 gasket 3 cylinder bore 4a intake side 4b exhaust side 5 combustion chamber 5a first dome part 5b second dome part 7a … Intake side squish area 7b… exhaust side squish area 8… intake port 8A… main port 8B… swirl port 9… exhaust port 10… shutter valve 20… piston 21a… first dome 21b …… the second dome

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-52-25911 (JP, A) JP-A-60-53613 (JP, A) JP-A-60-73833 (JP, U)

Claims (2)

(57) [Claims] In an engine having a recess formed on a lower surface of a cylinder head and a squish area provided along an inner peripheral edge of the cylinder bore around the recess, an upper surface of a piston inserted into the cylinder bore is provided on an upper surface of the piston head. Also, a concave portion corresponding to the cylinder head side concave portion is formed, and the degree of inclination of the piston head side concave portion to the squish region is formed to be larger as the inclination of the cylinder head side concave portion to the squish region is smaller. A combustion chamber for an engine. 2. A combustion chamber for an engine according to claim 1, wherein a swirl is generated by a swirl port when the load is low.