JPS6267221A - Combustion chamber for engine - Google Patents

Abstract

PURPOSE:To reduce noise from an engine so as to improve the characteristics of combustion to providing a hollow section for thermal insulation inside a piston so that it may encircle the circumference of a combustion chamber while its thickness remains approximately constant along the form of the piston upper surface. CONSTITUTION:A hollow section 20 for thermal insulation is formed inside a piston 3 so that it may encircles the circumference of a combustion chamber 4. Its bottom surface 20a is made flat, and the ceiling surface 20b is curved while it is formed into two chains of mountains along the form of the piston upper surface 3, and the thickness of the upper side of the hollow section 20 remains approximately constant throughout a whole area. By this configuration, the piston is reduced in weight at the top of the piston by the weight equivalent to the volume of the hollow section 20, noise is reduced because the rocking motion around a piston pin 18 is restrained, and the upper surface of the piston is prevented from being locally heated up excessively because the thickness of the upper surface side 3a remains roughly even so as to prevent an early ignition.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a combustion chamber of an engine.

(Prior art) It is known that one way to increase engine output is to reduce the volume of the combustion chamber to increase the compression ratio of the air-fuel mixture. As a conventional technique, for example, Japanese Patent Application Laid-Open No. 54-1458
As disclosed in Japanese Patent No. 08, a so-called bowl-in-piston type engine is known in which a recessed combustion chamber is formed on the upper surface of a piston, thereby reducing the volume of the combustion chamber.

On the other hand, in recent years, multi-valve engines have been developed in which a plurality of intake valves or exhaust valves are provided per cylinder to improve intake and exhaust efficiency and thereby increase engine output.

In addition, when applying a bowl-in piston as described above to such a multi-valve engine, it is necessary to make sure that the winter jacket/exhaust valve faces the combustion chamber well, and for this reason, it is necessary to An ennon having a so-called pent-roof type piston has also been developed, which is formed into a pent-roof shape having two inclined surfaces, and a predetermined number of intake and exhaust ports are formed on each of the two inclined surfaces.

By the way, in a piston having a pent roof-like upper surface shape, the weight of the piston top is greater due to the upward swelling than in the case of a general piston whose upper surface shape is a flat surface. The problem is that the eccentric weight of the piston around the pin increases, and as a result, during engine operation, the piston swings around the piston, generating impact noise between it and the inner surface of the cylinder, increasing engine noise. Something was discovered.

On the other hand, when the top surface of the piston is formed into a pent-roof shape, the mountain portions of the top surface of the piston, that is, the upwardly bulging portions located at both ends of the pair of inclined surfaces, are thicker than other portions. This area tends to become a heat point,
A problem arises in that knocking is more likely to occur due to premature ignition of the air-fuel mixture.

Furthermore, when the top surface of the piston is formed into a pent-roof shape, the heat capacity of the piston top is larger than when the piston top is a flat surface.
During low-load operation of an engine with little combustion heat,
The wall temperature of the combustion chamber is lowered, and unburned hydrocarbons (hereinafter referred to simply as HC) are
There is a problem in that it is more likely to occur.

(Object of the Invention) The present invention attempts to solve or improve the problems pointed out in the above-mentioned section of the prior art.
The object of the present invention is to provide a combustion chamber for an engine that can reduce engine noise and improve combustion characteristics.

(Means for Achieving the Object) As a means for achieving the above object, the present invention provides a concave portion on the upper surface of the piston having a pent-roof shape composed of two inclined surfaces, and a recessed portion is provided at the top dead center of the piston. In an engine in which a main combustion chamber is formed by a concave portion and a squish zone having a slight clearance between the piston and the lower surface of the cylinder head on both the intake side and the exhaust side, the combustion chamber is formed inside the piston. A hollow part for heat insulation is formed so as to surround the periphery.

(Function) In the present invention, by the above means, (1) the weight of the piston top part is reduced by the weight corresponding to the volume of the hollow part since the hollow part is formed in the piston top part, and the weight around the piston pin is reduced; (2) Since the hollow part is formed to surround the combustion chamber, (2-a) The wall thickness of the piston top is reduced and the formation of a heat point is suppressed. (2-b) The hollow part functions as a heat insulating layer, suppressing a drop in the wall temperature of the combustion chamber during low-load operation, and reducing HC in the combustion chamber. It is possible to obtain effects such as preventing the occurrence of such problems as much as possible.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS. 1 to 3.

(Structure) FIG. 1 shows a combustion chamber portion of an automobile engine according to an embodiment of the present invention. As shown in FIGS. 1 and 2, this engine is a multi-valve engine equipped with two intake ports A and 6B and one exhaust port 7. The block, 2, is a cylinder head that is abutted and fixed on the upper surface 1b of the cylinder block 1, and 3 is a piston.

The cylinder head 2 has a substantially dish-shaped recess 14 formed in its lower surface 2a at a position overlapping the piston insertion hole 15.
ing. This recessed portion 14 has two sloped surfaces 14a and +4b that slope upwardly by -F from two opposing positions in the radial direction toward the center thereof. Among these two inclined surfaces 14a and 14b, one inclined surface 14a (
A first inlet boat 6 (hereinafter referred to as the first inclined boat) 14a is provided with a first inlet boat 6 that is opened only during high-load operation of the engine.
A and a second intake boat 6B, which is opened throughout the entire load range of the engine, are opened in parallel. Note that this first intake boat 6A has a first
An on-off valve 13 for opening and closing the intake boat 6A is provided. On the other hand, the exhaust port 7 is opened in the second inclined surface 14b.

In FIG. 1, reference numeral 8 is an intake valve, 9 is an exhaust valve, and 10 is an intake valve.
is a spark plug.

As shown in FIG. 3, the piston 3 has a concave portion 5 in the center of its upper surface 3a, which has an appropriate volume and functions as a combustion chamber 4.
is formed. Further, the upper surface 3a of this piston 3 has two slopes parallel to the pair of slopes 14a and 14b of the recess I4 of the bipedal cylinder head 2, as shown in FIGS. 1 and 2. It is formed into a pent roof shape having surfaces 3b and 3c. When this piston 3 is installed on the engine side, one inclined surface 3b
(hereinafter referred to as the first inclined surface) is the cylinder head 2
The first inclined surface 14a of the cylinder head 2 and the other inclined surface 3C (hereinafter referred to as the second inclined surface) are connected to the second inclined surface 14a of the cylinder head 2.
The slanted surfaces 14b of the slanted surfaces 14b are opposed to each other. Also, at the top dead center position of the piston 3, the first
As shown in the figure, two inclined surfaces 3 b, 3 on the piston 3 side
c and two inclined surfaces 14a, 14 on the cylinder head 2 side.
b are closely opposed to each other, and the first inclined surface 3 of the piston 3
The intake side squish zone 11 has a slight clearance between the first inclined surface 14a of the cylinder head 2 and the second inclined surface 3C of the piston 3, and the second inclined surface 14b of the cylinder head 2. Exhaust side squish zones 12 are formed with a small clearance therebetween.

On the other hand, the pair of inclined surfaces 3b of the piston upper surface 3a
, 3c (that is, the portions corresponding to the tops of the pent roof shape) are curved surfaces 3d.

It is said to be 3e. A pair of radially opposing curved surfaces 3d and 3e of the piston 3 are connected to the cylinder head 2 at the top dead center position of the piston 3, as shown in FIG.
A pair of left and right curved surfaces 14c of the recess I4.

+4d, respectively, forming end squish zones 16 and 17 closely opposing each other and each having a slight clearance.

Further, by applying the present invention, this piston 3 has a hollow part for heat insulation inside so as to surround the periphery of the recessed part 5 (i.e., the combustion chamber 4) as shown in FIGS. 1 and 2. 20
is formed. This hollow part 20 is integrally formed with a salt core during casting of the piston 3, and is
As shown in FIG. 2, FIG. 2, and FIG. 5 (expanded views of the hollow portion 20), the bottom surface 20a thereof is a flat surface.

On the other hand, the ceiling surface 20b of the hollow portion 20 is curved into a double mountain shape along the shape of the upper surface 3a of the piston 3, and the wall thickness on the upper side of the hollow portion 20 is approximately uniform throughout the entire area. It's sato.

Therefore, as shown in FIG. 5, the hollow portion 5 corresponds to a low ceiling portion 21 with a low ceiling height corresponding to a pair of inclined surfaces 3b, 3c of the piston upper surface 3a, and a pair of curved surfaces 3d, 3e. The high ceiling portions 22 having a high ceiling height are alternately continuous in the circumferential direction of the piston.

(Operation and effect thereof) The air-fuel mixture sucked into the combustion chamber 4 of the engine via the intake boats 6A, 6B is compressed by the piston 3, and ignited and combusted by the ignition plug IO. In this case, the air-fuel mixture in the combustion chamber 4 is in each squish zone 11, 12, 1
The squish generated by 6.17 causes proper mixing and agitation, making the ignitability good.

By the way, in such a piston 3 whose two surfaces are formed into a pent roof shape, the weight of the piston top portion is greater than that of a normally formed piston whose upper surface is a flat surface. The swinging moment around the pin 18 increases, and as the engine operates, the piston 3 swings around the piston pin 18 and repeatedly contacts the inner surface of the piston insertion hole i5 of the cylinder block l, causing a gap between the two. As mentioned above, the engine noise tends to increase due to the impact sound of the engine.

However, in this piston 3, by applying the present invention, a hollow part 2 for heat insulation is formed so as to surround the recessed part 5 (namely 1') located at the top of the piston and the combustion chamber 4).
0, the weight of the piston top portion is reduced by a weight corresponding to the volume of the hollow portion 20, and the swinging moment of the piston 3 around the piston pin 18 is reduced by that amount. That is, although this piston 3 is a pent-roof type piston in which the weight of the piston top portion tends to increase, the weight of the piston top portion is reduced as much as possible, and the piston pin 1 of the piston 3 is
It is possible to suppress the oscillation of the piston 3, thereby reducing the engine noise caused by the oscillation of the piston 3 as much as possible, which is effective in reducing engine noise.

Further, the hollow part 20 functions as a heat insulating layer, and in this embodiment in particular, the hollow part 20 is made to follow the shape of the piston top surface 3a so that a thick part with a substantially uniform thickness is formed. Since the piston is provided with
A substantially uniform heat insulating effect can be obtained over the entire area a. Therefore, the wall temperature of the combustion chamber 4 can be maintained at a high temperature even during low-load operation of the engine with a small amount of combustion heat, and the H
The generation of C is suppressed as much as possible, and the exhaust emission characteristics of the engine are improved.

Further, since the wall thickness on the piston upper surface 3a side is substantially uniform over the entire area, there is no possibility that a portion of the piston 14 surface 3a becomes a heat point and abnormally rises in temperature. Therefore, premature ignition of the air-fuel mixture due to high heat at the heat point is prevented, and the occurrence of engine knock is effectively suppressed.

On the other hand, when the engine is operated under a high load, the upper surface 38 of the piston becomes slightly overheated due to the heat of combustion, which may impair its durability, so it is necessary to cool the upper surface of the piston. In this case, if an oil jet is provided in the low ceiling part 21 of the hollow part 20 as shown in FIG. The ceiling surface 20b of the piston flows from the low ceiling section 21 side to the high ceiling section 22 side, and during the flow, the portions of the piston upper surface 3a corresponding to the inclined surfaces 3b and 3c are cooled, and the high ceiling section 22 is cooled. It acts to intensively cool down the highest portion S where the temperature is most likely to rise. Therefore, the piston top surface 3a
A higher level of cooling effect can be obtained over the entire area.

(Effects of the Invention) According to the present invention, a concave portion is provided in a piston having a pent roof shape composed of two inclined surfaces, and a main combustion chamber is formed by the concave portion at the top dead center of the piston. In an engine in which a squish zone having a slight clearance is formed between the piston and the lower surface of the cylinder head on both sides of the exhaust side, a hollow part for heat insulation is provided inside the piston so as to surround the combustion chamber. It is characterized by the formation of

Therefore, according to the combustion chamber of the engine of the present invention, (1)
By forming the hollow part, the weight of the piston top part is reduced by the weight corresponding to the volume of the hollow part, so the rocking of the piston around the piston pin is suppressed, and engine noise is reduced as much as possible (2 ) Since the hollow part is formed to surround the combustion chamber, (2-a) the wall thickness of the piston top is reduced, suppressing its formation as a heat point, and reducing the knock caused by premature ignition of the air-fuel mixture. (2-b) The hollow part functions as a heat insulating layer, suppressing the decrease in the wall temperature of the combustion chamber during low-load operation, and minimizing the generation of HC in the combustion chamber. This results in significant effects in terms of reducing engine noise and improving combustion characteristics.

Further, as in the above embodiment, a hollow portion is formed to surround the combustion chamber, and a thick portion having a substantially uniform thickness is formed along the shape of the upper surface of the piston. (+) A substantially uniform heat insulating effect is obtained over the entire area of the piston top, and the HC reduction effect in the combustion chamber is further promoted. (2) The ceiling surface of the hollow part is mountain-shaped in the circumferential direction of the piston. For example, an inlet hole for an oil jet may be provided at a low position on the ceiling surface of the hollow part, and an oil jet may be inserted into the hollow part when cooling the piston top part is required, such as during high load operation of the engine. When the piston top part is cooled by injection, the oil flows sequentially from the lowest to the highest part of the ceiling surface of the hollow part, and reaches the highest ceiling height part where it is most likely to become a heat point. Because it accumulates and acts to effectively cool the area,
Effects such as the cooling effect being further improved can be obtained.

[Brief explanation of drawings]

FIG. 1 shows an automobile engine 20 according to an embodiment of the present invention.
...Longitudinal cross-sectional view of the combustion chamber part of the hollow gin, Figure 2 is from ■-■ in Figure 1
3 is a longitudinal sectional view, FIG. 3 is a layout of the Ennon boat shown in FIG. 1, FIG. 4 is a perspective view of the piston shown in FIG. 1, and FIG.
The figure is a developed view of the hollow part of the piston shown in FIG. 1. 1... Cylinder block 2... Cylinder head 3... Piston 4... Combustion chamber 5... Concave portion 6... Intake boat 7... ... Exhaust boat 8 ... Intake valve 9 ... Exhaust valve IO ... Spark plug 11 ... Intake side squish zone 12 ... Exhaust side squish zone 13 ...・Opening/closing valve 14... Concave portions 16, 17... End squish zone = 16-

Claims (1)

[Scope of Claims] 1. A concave portion is provided on the upper surface of the piston having a pent roof shape composed of two inclined surfaces, and the concave portion forms a main combustion chamber at the top dead center of the piston. In an engine in which a squish zone is formed with a slight clearance between the piston and the lower surface of the cylinder head on both sides of the piston, a hollow part for heat insulation is formed inside the piston so as to surround the combustion chamber. An engine combustion chamber characterized by: 2. The combustion chamber for an engine according to claim 1, wherein the hollow portion is provided so that a thick portion having a substantially uniform thickness is formed along the shape of the upper surface of the piston.