JPH07122407B2 - Engine combustion chamber structure - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a combustion chamber structure of an engine provided with a ball-in piston having a recess at the top of the piston. More specifically, the above recess is provided at the top of the piston. The present invention relates to a combustion chamber structure of an engine in which a pair of pentroof-shaped ridges facing each other are formed. This is used in the field of, for example, a gasoline engine equipped with an electronically controlled fuel injection device mounted on an automobile or the like.

(Prior Art) Conventionally, as a combustion chamber structure of an engine, a ball-in-piston type in which a combustion chamber is formed compactly by providing a pent roof-shaped (roof type) raised portion on the top of the piston in order to improve the combustibility of the engine Is known (see, for example, Japanese Utility Model Laid-Open No. 59-96323).

In this combustion chamber structure, the cross section of the combustion chamber ceiling wall in the direction orthogonal to the cylinder row direction is formed into a substantially triangular pent roof shape, while the lower part of the combustion chamber is formed below the combustion chamber. At the top of the piston, squish zones are formed on both sides of the piston top along the shape of the above-mentioned pentroof-like ridge and extending in the cylinder row direction, and recesses are formed between the squish zones. This is a compression stroke in which the piston rises, and in the squish zone, a squish flow is generated in the mixture to effectively disturb it and promote atomization, while in the ignition / combustion stroke, a compact combustion is formed. With the chamber, the propagation of combustion flame can be improved and the combustion stability can be improved.

(Problems to be Solved by the Invention) However, in the above-described conventional structure, unburned gas is accumulated between the both ends of the protrusion of the piston top in the cylinder row direction and the lower surface of the cylinder head, and the discharge amount of hydrocarbons is large. Tended to be.

Therefore, in order to solve such a problem, the concave portion is formed in an elliptical shape that is elongated in the cylinder row direction and extends to the piston end portion, and the bottom portion of the concave portion is formed into a spherical shape. The applicant has already proposed a combustion chamber structure of an engine in which an ignition plug is arranged substantially at the center of the above.

In this combustion chamber structure, since the portions corresponding to the raised portions at both ends of the conventional recess in the cylinder row direction are eliminated, the unburned gas accumulation phenomenon as described above is eliminated, and the amount of hydrocarbon emission is reduced. To be done.

By the way, in the compression stroke of the piston, if a swirl flow swirling along the top plane of the piston is applied in addition to the squish flow, the mixture is more effectively disturbed,
It has been confirmed that atomization is further promoted, fuel efficiency can be improved by using a lean fuel, generation of harmful NO _x can be suppressed, and combustion stability can be further improved.

However, in the piston having the above-described shape, the pent roof-shaped ridge rises suddenly downstream from the above-mentioned concave portion on the upstream side in the flow direction of the swirl flow due to the intake inertia. The drawback is that the flow is damped.

The present invention has been made in order to solve such a problem, and in addition to forming a combustion chamber of an engine compact, in addition to a squish flow, a piston top part capable of imparting a swirl flow along the top plane of the piston. An object of the present invention is to provide an engine combustion chamber structure having the shape of

(Means for Solving the Problem) In order to achieve the above object, a solution means of the present invention is a combustion chamber structure of an engine in which a ceiling wall of the combustion chamber is formed in a pent roof shape, and A swirl intake port for generating a swirl of intake air circulating around the circumference is provided, and the swirl intake port is opened to one slope of the pent roof-shaped combustion chamber ceiling wall. Then, the upper surface of the piston is formed into a pent roof shape along the ceiling wall of the combustion chamber, and a long recess is formed at the top of the piston in a direction substantially orthogonal to the intake inflow direction of the swirl intake port. Thus, on the upper surface of the piston, a pair of pent roof-shaped raised portions having a pair of ridge lines extending along the longitudinal direction of the recess as the top and facing each other across the recess. Further, on the longitudinal end side of each pentroof-like ridge, and on the one end side upstream of the concave side in the flow direction of the swirl flow by the swirl intake port, lower than the ridge line and the concave section. Slopes that are smoothly connected are formed.

(Operation) Accordingly, in the present invention, a pair of pentroof-like ridges whose tops are ridge lines that face each other across a concave portion formed long in a direction substantially orthogonal to the intake air inflow direction and extend along the longitudinal direction of the concave portion. In the swirl flow direction, an inclined portion lower than the ridge line and smoothly connected to the recess is formed on one end side upstream from the recess side in the swirl flow direction. It smoothly flows from the concave part to the raised part along the inclined part, and the flow of the air-fuel mixture flowing due to the intake inertia becomes smooth without being attenuated,
Generation of swirl flow is promoted.

(Effect of the Invention) According to the combustion chamber structure of the engine of the present invention, the recess provided in the piston top is formed to be long in the direction substantially orthogonal to the intake air inflow direction, while the pair of opposed recesses sandwiches the recess. A sloping squish flow is formed at the top of the piston during the compression stroke because an inclined portion that smoothly connects to the recess is formed on one end side of the pentroof-shaped ridge that is upstream of the recess in the swirl flow direction. In addition to,
Generation of swirl flow is promoted. Therefore, since the air-fuel mixture is effectively disturbed and the mist vaporization is promoted, combustion stability is improved, fuel economy is improved, and generation of hydrocarbons is suppressed.

(Example) Below, this invention is demonstrated in detail based on the Example.

As shown in FIGS. 1 (a) and 1 (b), the combustion chamber structure of the engine according to the present embodiment has a recess 2 provided at the top of the piston 1 in a direction substantially orthogonal to the intake air inflow direction 3. While it is formed to be long, the concave portion 2 is sandwiched so as to face the concave portion 2.
Of the pair of pentroof-shaped ridges 4, 4 having the ridges extending along the longitudinal direction of the apex on the one end side upstream from the recess 2 side in the flow direction of the swirl flow 5 and lower than the ridges. Inclined portion 6 smoothly connected to the concave portion 2
Are formed.

Such a piston 1 is adopted in a combustion chamber structure of an engine equipped with an electronically controlled fuel injection device. In FIG. 2 showing a YY cross section orthogonal to the cylinder row direction, a cylinder head 8 is mounted on the cylinder block 7, and the cylinder head 8 is connected to the combustion chamber 9 by the two cylinders shown in FIG. Intake ports 10A, 10B and two exhaust ports 11
A and 11B are formed. Then, a swirl intake port 12 for constantly opening and generating a swirl flow 5 of intake air in the combustion chamber 9 is provided close to the intake port 10A,
The intake air is introduced almost in contact with the top of the piston 1 along the outer circumference thereof. In addition, the cylinder head 8 includes the intake ports 10A and 10B and the exhaust port 11
An intake valve 13 and an exhaust valve 14 that control the opening and closing of A and 11B as appropriate are provided via a valve guide 15. The high load passages 17A and 17B are connected to the intake ports 10A and 10B, and the low load passage 18 is connected to the swirl intake port 12.

The above-mentioned ceiling wall of the combustion chamber 9 is formed in a pent roof shape having a substantially triangular roof shape in a cross section orthogonal to the cylinder row direction, and the swirl intake port 12 is opened on one of the slopes. There is. Then, as described above, a pair of pentroofs formed along the ceiling wall of the combustion chamber 9 is formed on the top of the piston 1 which is located below the combustion chamber 9 and forms a part of the combustion chamber 9. On the raised portions 4, 4, squish zones 16, 16 each having a substantially crescent shape in plan view are formed (see FIG. 1). This squish zone
As described above, between 16 and 16, the concave portion 2 has an oblong shape that is long in a direction substantially orthogonal to the intake air inflow direction 3 and slightly widens in the central portion, and extends to both top end edges of the piston 1, Moreover, as shown in FIG. 1 (b), the ellipse is formed to have a spherical shape in which the central portion is deepened. Then, from the bottom of the concave portion 2, the pent roof-shaped raised portion 4,
The swirl flow 5 can pass over the ridges 4 and 4 without being attenuated along the inclined portion 6 formed over one end of the swirl 4. Although not shown, the tip of the spark plug attached to the cylinder head 8 faces the center of the upper portion of the recess 2.

The combustion chamber structure of the engine configured as described above operates as follows at a low load with reference to FIG.

When the load is low, the shutter valve (not shown) closes, the air-fuel mixture does not flow from the high-load passages 17A and 17B, and in the intake stroke, the air-fuel mixture is supplied only from the low-load passage 18 to the swirl intake port 12. After that, it is introduced into the combustion chamber 9 through the intake port 10A. The air-fuel mixture before being mixed for atomization as described later is introduced in an intake air inflow direction 3 which is a tangential direction to the top of the piston 1 and a direction along the outer circumference of the top of the piston 1. Then, due to the intake inertia, the pent roof-shaped ridges 4, 4 flow along the inclined portions 6, 6 formed at each one end portion without being attenuated,
A swirl flow 5 flows around the outer circumference of the top of the piston 1 along the inner circumference of the combustion chamber 9. Therefore, the air-fuel mixture has a concave portion 2 on the upstream side and the ridges 4, 4 on the downstream side in the swirl circulation direction.
By the inclined portion 6 and the intermediate portion 6, the air flows while floating in the vertical direction, so that mixing is effectively performed and atomization is promoted. This swirl flow 5 is maintained until just before the transition from the intake stroke to the compression stroke through the compression stroke.

When shifting to the compression stroke, in addition to the swirl flow 5, as the piston 1 rises, the air-fuel mixture is pressed between the squish zones 16 and 16 and the ceiling wall of the combustion chamber 9 facing the squish zones 16, 16 to generate a squish flow. The generated air-fuel mixture is mixed more effectively, further promoting atomization.

In the subsequent ignition / combustion process, a sufficiently atomized air-fuel mixture is ignited by the ignition plug and explodes and burns in the combustion chamber 9 formed compactly, so that flame propagation is good and high output is obtained. be able to.

As described above, the combustion chamber structure of the engine according to the present embodiment has extremely good combustion stability, burns the fuel under high compression with a high air-fuel ratio, obtains good fuel efficiency, and generates NO _x . It can be kept low.

In addition, the situation of mixing the air-fuel mixture at the time of high load is different from the above, and a large amount of air-fuel mixture is introduced into the combustion chamber 9 as a counterflow from the high-load passages 17A, 17B through the two intake ports 10A, 10B. It

Above are two intake ports 10A and 10B and two exhaust ports 11
Although the engine having the A and 11B and equipped with the electronically controlled fuel injection device has been described as an example, the present invention can be implemented regardless of the number of ports or the fuel supply mode.

[Brief description of drawings]

FIG. 1 (a) is a plan view of a piston top portion shown in an embodiment of a combustion chamber structure of an engine of the present invention, FIG. 1 (b) is a front view thereof, and FIG. 2 is combustion in a direction orthogonal to a cylinder row direction. FIG. 3 is a cross-sectional view of the chamber structure, and FIG. 3 is a plan view near the top of the piston for explaining the operation. 1 ... Piston, 2 ... Recessed portion, 4 ... Pent roof-like raised portion,
5 ... swirl flow, 6 ... slope.

Claims (1)

[Claims] 1. A combustion chamber structure of an engine, wherein a ceiling wall of the combustion chamber is formed in a pent roof shape, and a swirl intake port for generating swirl of intake air circulating along an inner circumference of the combustion chamber is provided. , The swirl intake port is opened to one slope of the pentroof-shaped combustion chamber ceiling wall, and the upper surface of the piston has a pentroof shape along the combustion chamber ceiling wall, and the intake air from the swirl intake port is provided at the top of the piston. A long recess is formed in a direction substantially orthogonal to the inflow direction, and a pair of ridge lines extending along the longitudinal direction of the recess are formed on the upper surface of the piston by the formation of the recess and are opposed to each other across the recess. Of the pentroof-like ridges are formed, and the swirl suction port is provided on the side of the longitudinal end of each of the pentroof-like ridges. In the flow direction of the Le stream at one end of which the upstream of the concave side, a combustion chamber structure for an engine, characterized in that the formation of the inclined portion smoothly connected to the lower and the recess than the edge line.