JPH02149724A - Combustion chamber of engine - Google Patents

Abstract

PURPOSE:To make it possible to reduce HC by forming the inclination of a piston head side dome part toward squish area greater the less the inclination of a cylinder head side dorm part toward squish area. CONSTITUTION:Dome parts 21a, 21b are formed on the top surface part of the piston head 23 of a piston 20 inserted in a cylinder bore 3, in correspondence with dome parts 5a, 5b on a cylinder head side. The constitution is so made that the inclination of the dome parts 5a, 5b toward squish area is formed greater for portions where the inclination of the dome parts 21a, 21b is lesser. Therefore, the shape of a combustion chamber 5 is brought as much as closer to a spherical form so that the capacity of the combustion chamber can be expanded without expanding the cylinder diameter. Furthermore, since the inclination of each dome part 5a, 5b, 21a, 21b is set in a way to mutually converse their dimensions, the intrusion and propagation of flame into squish area in the expansion stroke are made easier to reduce HC.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the structure of a combustion chamber of an engine.

(Prior art) For example, forming a swirl (induction turbulence) or squish (compression turbulence) in the air-fuel mixture within an engine combustion chamber, or combining both the swirl and squish, in order to improve the combustion performance of the engine. etc. have been well known for a long time.

Conventionally, as a means for forming the swirl, for example, as shown in Japanese Unexamined Patent Publication No. 198315/1983, a swirl opening in the cylinder circumferential direction is provided in addition to a normal main boat in the intake boat section into the engine combustion chamber. Forming a dedicated swirl boat, for example, for low engine load and
In the low rotation range, where the intake flow velocity is originally low and combustion performance is poor, the swirl boat forms a swirl and actively increases the mixture flow velocity, thereby improving the mixing performance of fuel and air and at the same time reducing the flame propagation velocity. While quickly and effectively stratifying the air-fuel mixture to sufficiently improve ignitability and combustion performance, the swirl forming means can be combined with, for example, two domes (hemispherical combustion chambers) to improve engine combustion. While improving the degree of uniform volume by making the combustion chamber more compact and making the combustion chamber shape closer to a sphere, it also effectively suppresses squish during the compression or expansion stroke by forming a predetermined squish area between the periphery of the cylinder bore and the periphery of the cylinder bore. There are things that have been made possible.

In this way, the swirl boat is used to form a swirl flow in the engine combustion chamber, increasing the flow velocity of the air-fuel mixture especially during the intake stroke and improving the mixing condition. If a predetermined squish region is formed between the two and the squish during the compression or expansion stroke accelerates the flame propagation speed,
The engine's ignitability and combustibility are improved, and the combustion state is stabilized, especially in low engine load and low rotational engine regions where the intake air charge is small and the intake flow velocity is low, making lean burn operation possible. It also has the advantage of improving fuel efficiency.

(Problem to be Solved by the Invention) However, even when a dome portion is formed on the lower surface of the cylinder head as in the above-mentioned configuration, and a squish region is formed around the dome portion along the inner peripheral edge of the cylinder bore, For example, assuming that the upper surface on the piston head side is flat, when attempting to expand the volume of the combustion chamber, the cylinder diameter must be expanded or the size or depth of the dome portion of the combustion chamber on the cylinder head side must be increased. It will have no choice but to expand. However, enlarging the above cylinder diameter goes against the request to make the engine more compact.
On the other hand, changing the size of the dome portion on the cylinder head side leads to a reduction and restriction of the skin area. Furthermore, increasing the depth of the dome portion is inevitably limited due to the structure of the cylinder head, and there is a problem in that the compression ratio decreases.

Originally, the combustion chamber volume of an engine is largest when it is spherical in terms of its surface area and external shape.

It also becomes more equal and higher. Therefore, when setting the actual engine combustion chamber shape, it is preferable to make the shape of the combustion chamber as close to a spherical shape as possible. The dome part on the cylinder head side was originally formed from such a point of view, but as mentioned above, the upper surface part on the piston head side is flat, which makes the combustion chamber spherical, which is the original shape of the dome-shaped combustion chamber.
This results in a problem that limits the improvement of the degree of isovolume.

That is, if the upper surface of the piston is flat, no matter how dome-shaped the combustion chamber on the cylinder head side is, the overall shape will end up being only a flattened hemisphere. Furthermore, in order to generally increase the intake air filling rate, the intake boat side opening is formed to have a larger diameter than the exhaust boat side opening. Therefore, when trying to form two sets of large-diameter openings and small-diameter openings in the dome-shaped combustion chamber, the spherical radius of one of the two sets of dome parts is increased to increase the area. It is convenient to form a dome surface of 1, while the spherical radius of the other dome is made relatively small to form a dome of small area.

However, if this is done, the wall surface inclination angles of the dome surfaces on the intake side and the exhaust side will be different.

In such a case, if the top surface of the piston head were flat as described above, the squish angle would be too small, and the combustion flame, especially in the expansion stroke, would be extinguished by the wall surface, effectively blocking the quench zone. There is a problem that the amount of Hc that is generated is increased, and that this phenomenon is particularly noticeable on the dome side where the radius of the sphere is large.

(Means for Solving the Problems) The present invention has been made with the aim of solving the above problems, and includes forming a dome portion on the lower surface of the cylinder head, and forming a dome portion around the dome portion on the inner peripheral edge of the cylinder bore. In an engine in which a squish region is provided along the cylinder bore, a dome portion corresponding to the cylinder head side dome portion is also formed on the upper surface of the piston head of the piston inserted into the cylinder bore, and the piston head side dome portion In contrast, the degree of inclination of the cylinder head side dome portion toward the squish region is made larger as the degree of inclination of the cylinder head-side dome portion toward the squish region is smaller.

(Function) In the combustion chamber structure of the engine of the present invention, first, a dome portion is formed on the lower surface of the cylinder head, and a squish region is provided around the dome portion along the inner peripheral edge of the cylinder bore. A dome portion corresponding to the cylinder head side dome portion is also formed on the upper surface of the piston head of the piston that is fitted into the piston,
Further, the degree of inclination of the piston head-side dome portion toward the squish region is conversely formed such that the smaller the degree of inclination of the cylinder head-side dome portion toward the squish region, the greater the degree of inclination of the piston head side dome portion toward the squish region. Therefore, in the case of this structure, the shape of the combustion chamber can be made as close to a spherical shape as possible, and the volume of the combustion chamber can be expanded without increasing the cylinder diameter.

In addition, since the inclinations of the corresponding dome portions on the cylinder head side and the piston head side are set in opposite sizes, it is possible to facilitate the entry and propagation of flame into the squish region during the expansion stroke. This makes it possible to effectively reduce HC.

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

(Example) FIGS. 1 to 5 show the combustion chamber structure of an engine according to an example of the present invention.

First, Figure 1 shows the longitudinal cross-sectional structure of the combustion chamber of the engine.
In the figure, reference numeral 1a denotes a cylinder block, and 1b denotes a cylinder head that is located on the upper part of the cylinder block 1a and is integrally provided through a gasket 2, constituting a predetermined engine cylinder together with the cylinder block la. A cylinder bore 3 having a predetermined diameter and a predetermined length is formed inside the cylinder block la (in order to simplify the explanation, water jackets and the like are omitted from the drawings).

Further, the surface of the lower surface of the cylinder head that corresponds to the cylinder bore 3 is a first dome portion that mutually separates two areas, an intake side 4a and an exhaust side 4b, as shown in FIGS. 1 and 2, for example. A sub-spherical engine combustion chamber 5 is formed of a (circular recessed portion) 5a and a second dome portion (circular recessed portion) 5b. The first part forming the combustion chamber 5
As shown in FIG.
is formed with a predetermined larger diameter, and when viewed from above, the intake side 4
It is deformed into a daruma shape from a to the exhaust side 4b, and on the outer periphery of both dome areas, there is a skin area 7 that is wider on the intake side 4a and relatively narrower on the exhaust side 4b.
a, 7 b. The squish area 7a
, 7b functions to improve combustion performance by increasing the flame propagation speed by forming a so-called squish (compression vortex) particularly in the relevant region during the engine compression or expansion stroke.

Further, numeral 8 is an intake boat, and 9 is an exhaust boat. The intake boat 8 is configured with two sets of boats, a main boat 8A and a swirl boat (secondary boat) 8B, and a switch valve 10 for opening and closing the main boat 8A is provided on the main boat 8A side. ing. The shutter valve lO closes, for example, in a low speed and low load region, and allows a high flow rate into the engine combustion chamber 5 only from the swirl boat 8B, and from the protrusion 13 of the large-diameter second dome portion 5b on the exhaust side. By causing the injected fuel to flow in the circumferential direction toward the inner circumferential surface portion 14 on the inside (end side) of the haze, the injected fuel can be atomized well, and the mixture of fuel and air can be effectively mixed while improving the mixing of the fuel and air. The aim is to create a layered structure. As a result, combustibility is improved as much as possible, making it possible to compensate for the drop in engine torque in the low-speed, low-load region, and improving fuel efficiency.

On the other hand, when the engine is operating at high speed and high load,
The shutter valve lO is wide open and the intake boat 8
The overall diameter of the intake passage is enlarged to supply a sufficient amount of intake air with low intake resistance and to improve output in response to high engine load conditions.

Further, reference numeral 11 denotes a fuel injector that is configured to have a timed injection function that injects fuel in synchronization with the intake stroke of the engine, for example. The fuel injector 11 is connected to the main intake bow 1-
8A and the intake manifold 1 connected to the intake boat 8A
As shown in FIG.
The injection direction is set so that the fuel is synchronously injected outward from the position of the electrode portion 15a (in the radial direction of the dome portion). As a result, the fuel injected in synchronization with the engine intake stroke due to the timed innoction rides on the swirl flow formed by the swirl boat 8B and does not directly hit the electrode portion 15a of the spark plug 15. The particles are collected near the electrode portion 15a.

As a result, the air-fuel mixture concentration especially near the electrode portion 15a of the spark plug 15 becomes rich, and ignition performance improves. This effect is combined with the relationship between the installation position and installation angle of the spark plug 15, which will be described below, to achieve a more effective effect.

That is, the ignition plug 15 is located, for example, at the swirl inlet in the second dome portion 5b on the exhaust side, and furthermore, as shown in FIG. The installation angle θ with respect to the swirl upstream side is 0. The downstream side θ is larger than (θ
, >θ1), and a wedge-shaped concave portion 35 is formed.

Therefore, due to the above-mentioned timed injection, the relatively rich air-fuel mixture that effectively rides the swirl flow as described above rises upward near the electrode portion 15a of the spark plug 15 as shown by the arrow (a) in the figure. Flowing (bent)
, remains in a stratified state near the electrode portion 15a of the spark plug 15 for a predetermined period of time. Therefore, the above-mentioned effect of improving ignitability can be more effectively improved.

Next, reference numeral 20 denotes a piston fitted into 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, and the piston head upper surface 23 has a concave groove in the opposite direction corresponding to the shape of the combustion chamber 5 on the cylinder head side. The first dome portion 21a and the second dome portion 21b are formed to intersect with each other. In this case, the first and second dome portions 21a on the piston head 23 side,
The protrusion 24 on the downstream side of the swirl between the spark plugs 21b is located far downstream from the spark plug 15, and
As mentioned above, the stratified mixture flow ignited via the spark plug 15 is further disturbed by the downstream protrusion 24, forming a turbulent flow due to tumble air motion, and further increasing the combustion performance on the swirl end side. It's supposed to improve.

The piston head side first and second dome portions 2
The relationship between the shapes of 1a and 21b and the shapes of the first and second dome portions 5a and 5b on the cylinder head side is, for example, as shown in FIG. a, 5 b skin area 7 a,
On the contrary, in the portion (05, 03') where the degree of inclination toward 7b is small, the angle is set to be large (θ4.04'), so that a mutually complementary relationship is established. As a result, the sphericity of the combustion chamber as a whole is maintained at a constant level, the diameter of the intake boat is increased, and the uniformity of volume is improved under a certain compression ratio. .

Therefore, the squish formed during the compression or expansion stroke occurs equally on both the intake side and the exhaust side, ensuring an effective flame propagation speed and always achieving a stable combustion state. can. As a result, H.C.
The amount of generation is also reduced.

In addition, in the above FIG. 1 and FIG. 2, the reference numeral 31a is
The intake valve 31b is an exhaust valve, and in order to improve the swirl efficiency, the intake valve 31a is preferably offset by a predetermined position U in the direction opposite to the outlet of the swirl boat 8B, as shown in FIG. 2, for example.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing the structure of a combustion chamber of an engine according to an embodiment of the present invention, FIG. 2 is a sectional view taken along line A-A in FIG. FIG. 3 is an enlarged cross-sectional view of the vicinity of the spark plug mounting part of the same embodiment structure (FIG. 2 BB sectional view), FIG. 4 is a plan view showing the shape of the top surface of the piston head in the same embodiment structure, FIG. 5 is a longitudinal cross-sectional view schematically showing the relative shapes of the cylinder head-side combustion chamber and the piston head-side combustion chamber in the same embodiment structure. Ia... Ib--・ 2... 3... 4a... 4b... 5... 5a-ψ・ 5b... 7a... ・Cylinder block・Cylinder head・Gasket, cylinder bore, intake side, exhaust side, combustion chamber, first dome section, second dome section, intake side squish area 7b, 8, 8A, 8B, 10, 20, 1a 1b, exhaust side squish area, Intake boat, main boat, swirl boat, exhaust boat, shutter valve piston, first dome section, second dome section

Claims (1)

[Claims] 1. In an engine in which a dome portion is formed on the lower surface of the cylinder head and a squish area is provided around the dome portion along the inner peripheral edge of the cylinder bore, the piston head upper surface portion of the piston inserted into the cylinder bore is also A dome portion corresponding to the cylinder head side dome portion is formed, and the degree of inclination of the piston head side dome portion toward the squish region is reversed as the degree of inclination of the cylinder head side dome portion toward the squish region is smaller. The combustion chamber of an engine is characterized by its large shape.