JP2001200753A - Cylinder head structure of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylinder head, capable of maintaining sufficient strength also relating to both a cylinder internal pressure and a thermal load, by devising the thickness in a lower end wall of the cylinder head. SOLUTION: A cylinder head lower end wall 15, constituting a ceiling surface of a combustion chamber 20, is formed so as to have a small thickness as the lower end wall goes to the side of a cylinder center line C, and a diametric direction output end part in a large thickness side is formed in a large thickness dimension t2, capable of corresponding to a cylinder internal pressure, for instance, formed into cone shape. A sloped upper surface 17 of the cylinder head lower end wall 15 is utilized for the bottom surface of cooling water jackets 27, 28, to attain facilitation of casting work with lightening of weight in a cylinder head 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cylinder head structure for an engine.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional cylinder head 1 in which a lower surface 16 of a cylinder head lower end wall 15 is provided in a combustion chamber 2.
0, and is formed on a plane perpendicular to the cylinder center line C and has a uniform thickness t1.

The thickness t1 of the cylinder head lower end wall 15
Is set in consideration of the deformation due to the in-cylinder pressure and the thermal strain due to the heat load. In order to sufficiently withstand the in-cylinder pressure, it is necessary to increase the wall thickness and increase the rigidity of the cylinder head lower end wall 15. On the other hand, in order to suppress thermal distortion due to a thermal load, it is necessary to regulate the wall thickness. Generally, the thickness is increased to give priority to the reliability with respect to the in-cylinder pressure, so that heat distortion due to a thermal load is sacrificed.
By the way, as the wall thickness increases, the cylinder head lower end wall 1
5, the temperature difference between the upper surface 57 and the lower surface 16 increases, so that the heat inside the wall is confined, and the influence of thermal strain increases.

[0004]

In recent engines, the average effective pressure (Pme) and the maximum combustion pressure (Pmax) have been increased in accordance with the increase in output power. When the thickness t1 of the cylinder head lower end wall 15 is increased, deformation due to thermal strain becomes remarkable, and the weight of the cylinder head 1 also increases. Also, cylinder head 1
The volume of the lower cooling water jackets 47 and 48 is also greatly limited, and it becomes difficult to form the cooling water jackets 47 and 48 during cylinder head casting. That is, when the sand for forming the cooling water jacket is reduced, the sand at the time of casting is seized and the rate of defective products increases.

On the other hand, in order to suppress thermal distortion due to heat load,
If the thickness is restricted to a small value, the strength against the in-cylinder pressure tends to be insufficient.

[0006]

SUMMARY OF THE INVENTION In the present invention, the cylinder head lower end wall is largely affected by the in-cylinder pressure on the mating surface side with the cylinder block, that is, on the radially outer end side. Paying attention to the fact that the influence is large on the center side of the cylinder, by devising the thickness of the lower end wall of the cylinder head, it is possible to maintain sufficient strength against both the above-mentioned in-cylinder pressure and heat load. It is intended to provide a cylinder head.

Another object of the present invention is to reduce the incidence of defective products during casting of a cylinder head.

[0008]

In order to solve the above-mentioned problems, the invention according to claim 1 of the present application is to reduce the thickness of the lower wall of the cylinder head constituting the ceiling surface of the combustion chamber toward the cylinder center line side. And a radially outer end on the thicker side has a wall thickness dimension that can correspond to the in-cylinder pressure.

According to a second aspect of the present invention, in the cylinder head structure of the engine according to the first aspect,
The inclined upper surface of the lower wall of the cylinder head is the bottom surface of the cooling water jacket.

[0010]

FIG. 1 is a partial plan view of a single cylinder head 1 for a multi-cylinder diesel engine to which the present invention is applied, and a fuel injection valve is mounted at a position corresponding to a cylinder center line C of the cylinder head 1. A hole 3 is formed, and a pair of exhaust valve holes 5 and a pair of intake valve holes 6 are formed around the fuel injection valve mounting hole 3. An exhaust passage 10 communicating with each exhaust valve hole 5 merges with each cylinder and reaches a corresponding exhaust port 7. An intake passage 11 communicating with each intake valve hole 6 merges with each cylinder and a corresponding intake port 8. Has been reached.

A plurality of fastening bolt insertion holes 12, a valve arm operating push rod insertion hole 13, a valve arm cover mounting hole 14, a valve arm holder mounting hole, and the like are formed in the upper end mating surface of the cylinder head 1. .

FIG. 2 is an enlarged cross-sectional view taken along the line II-II of FIG. 1, and the same parts as those of FIG. 3 are denoted by the same reference numerals. FIG.
, The lower surface 16 of the cylinder head lower end wall 15 constitutes a ceiling surface (explosion surface) of the combustion chamber 20, is formed in a plane perpendicular to the cylinder center line C, and the head gasket 4 is fastened with fastening bolts or the like. It is fastened to the upper end surface of the cylinder block 2 through the middle. A cylinder liner 18 for forming a combustion chamber 20 is fitted on the inner wall of the cylinder block 2.
9 are fitted.

A cylindrical valve holder 21 is fitted into the fuel injection valve mounting hole 3, and the fuel injection valve 22 is inserted into the valve holder 21.
Is fitted. Lower end nozzle portion 22 of fuel injection valve 22
a faces the combustion chamber 20.

In the cylinder head 1, upper and lower cooling water jackets 25, 2 surrounding the exhaust passage 10 and the intake passage 11 are provided.
The cooling water jackets 25, 26, 27, 28 communicate with each other and are connected to a cooling water jacket 32 from a communication hole 31 in the cylinder block 2 via a lower end communication hole 30. At the same time, it is connected to a cooling water outlet collecting pipe (not shown) via the upper end communication hole 33.

An annular fuel injection valve cooling water chamber 3 is provided around an outer periphery of a vertically intermediate portion and a lower end portion of the valve holder 21.
The lower cooling water chamber 36 communicates with the lower cooling water jackets 27 and 28 through a communication hole 37 formed in a cross shape when viewed from above, and the annular cooling water in the middle portion is formed. The chamber 35 is provided with upper and lower cooling water jackets 2 through communication holes 38 and the like.
6 and 28.

The thickness of the lower end wall 15 of the cylinder head is formed so as to become thinner from the outer end in the radial direction toward the cylinder center line C side.
6 is formed on a mortar-shaped inclined surface having a constant inclination angle θ. The thickness t2 of the outer end on the thick side is set to a thickness that can sufficiently cope with the in-cylinder pressure, while the thickness t3 of the portion on the cylinder center line C side can suppress the occurrence of thermal strain due to a thermal load. It is about the thickness. The thickness t3 of the cylinder center line C side portion is smaller than the thickness t1 of the conventional example of FIG.
Is formed to be the same as or thicker than the thickness t1 in FIG. 3, although it depends on conditions such as the effective pressure radius of the engine to be applied.

The inclined upper surface 17 of the lower end wall 15 of the cylinder head formed in a mortar shape is used as it is as the bottom surface of the lower cooling water jackets 27 and 28. Therefore, the volume of the lower cooling water jackets 27 and 28 is not shown. 3 is larger than the conventional one.

[0018]

During operation of the engine, cooling water discharged from a cooling water pump (not shown) is supplied to a cooling water jacket 32 of the cylinder block 2 to cool the periphery of the cylinder liner and the like, and then pass through the communication holes 31 and 30 to form a cylinder. Enter the head 1.

In the cylinder head 1, the lower cooling water jackets 27 and 28, the annular passages 36 and 35, and the upper cooling water jackets 25 and 26 and the like are circulated, whereby the cylinder head lower end wall 15, the exhaust passage 10 and the intake passage 11 are formed. After cooling around the fuel injection valve 22 and the like, it is returned to the heat exchanger from the upper end communication hole 33 via a thermostat or the like.

Since the lower end wall 15 of the cylinder head is formed thicker at the outer peripheral end portion in the radial direction fastened to the cylinder block 2, it is possible to maintain sufficient rigidity against the in-cylinder pressure. On the other hand, since the thickness on the side of the cylinder center line C is made thin, it is possible to suppress the occurrence of heat distortion in the cylinder head lower end wall 15 and the occurrence of thermal distortion. That is, sufficient strength can be maintained for both the in-cylinder pressure and the stress caused by the heat load, and the average effective pressure (Pme)
And an increase in the maximum combustion pressure (Pmax).

When casting the cylinder head 1, sand is set to form the cooling water jackets 25, 26, 27, 28 and the like.
In the case of 28, the bottom surface is an inclined surface 17 and the volume is larger than that of the conventional one (FIG. 3), and the size of the sand particle is also large. The rate of non-defective products is reduced.

[0022]

As described above, according to the present invention,
(1) The cylinder head lower end wall 15 constituting the ceiling surface of the combustion chamber is formed so that the thickness becomes thinner toward the cylinder center line side, and the radially outer end of the thick side is a cylinder. Since the wall thickness is set to be compatible with the internal pressure, it is possible to maintain sufficient rigidity against the cylinder internal pressure.On the other hand, the wall thickness on the cylinder center line side is reduced, so that It is possible to suppress generation of heat distortion due to heat build-up. That is, sufficient strength can be maintained for both the in-cylinder pressure and the stress caused by the heat load, and it is possible to cope with an increase in the average effective pressure (Pme) and the maximum combustion pressure (Pmax). Further, the weight of the cylinder head can be reduced.

(2) When the inclined upper surface 17 of the lower end wall 15 of the cylinder head is the bottom surface of the cooling water jackets 27 and 28, the volume of the lower cooling water jackets 27 and 28 can be increased as compared with the conventional case (FIG. 3). As a result, the size of sand particles for forming a cooling water jacket used at the time of casting can be increased, and the volume of the sand particles is too small as in the prior art, so that sand is seized at the time of casting and the rate of defective products is reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of a single cylinder head of an engine to which the invention according to claims 1 and 2 of the present application is applied.

FIG. 2 is an enlarged cross-sectional view taken along the line II-II of FIG.

FIG. 3 is an enlarged longitudinal sectional view of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder head 2 Cylinder block 15 Cylinder head bottom wall 16 Lower surface (combustion chamber ceiling surface, explosion surface) 17 Inclined upper surface 20 Combustion chamber 22 Fuel injection valve

Claims (2)

[Claims] 1. A lower end wall of a cylinder head constituting a ceiling surface of a combustion chamber is formed so as to become thinner toward a cylinder center line side, and a radially outer end portion on a thicker side is formed as follows.
A cylinder head structure for an engine having a wall thickness capable of coping with an in-cylinder pressure. 2. The cylinder head structure for an engine according to claim 1, wherein an inclined upper surface of a lower end wall of the cylinder head is formed by:
A cylinder head structure for an engine, wherein the cylinder head structure serves as a bottom surface of a cooling water jacket.