JP2003056321A - Combustion chamber for four-stroke engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion chamber exhibiting improved thermal efficiency by reducing a temperature gradient between an intake valve and an exhaust valve and reducing a thermal strain of a cylinder head as well as by reducing inertial weight of the intake valve and increasing output of an engine. SOLUTION: This combustion chamber for four-stroke engine is equipped with a combustion space partitioned and formed by an inner surface of a cylinder, a piston top part inserted in it, and a cylinder head closing a top opening of a cylinder hole. An intake passage and an exhaust passage opened to the cylinder head are closed by the intake valve and the exhaust valve in such a way as capable of being opened and closed. A flare part and a stem part forming the intake valve and the exhaust valve are integrally formed by a thin tubular member. An inner surface of the intake valve is opened to the combustion space.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a cylinder head with a poppet valve for opening and closing an intake passage and an exhaust passage in a combustion chamber suitable for a high-performance four-stroke engine for vehicles such as motorcycles and passenger cars. It relates to the so-called overhead valve type.

[0002]

2. Description of the Related Art Generally, an overhead valve type combustion chamber of a four-stroke engine is a combustion chamber formed on a top surface of a cylinder hole and a piston fitted therein and a bottom surface of a cylinder head that closes an upper opening of the cylinder hole. It is constituted by a combustion space formed by the recess. An intake passage and an exhaust passage are opened in the combustion space, and they are closed by an intake valve and an exhaust valve, respectively. Since this type of combustion chamber has high combustion efficiency and high-speed rotation, it is commonly used for motorcycles or passenger cars.

Conventionally, in the above-mentioned overhead valve type combustion chamber, it is known that the intake valve and the exhaust valve provided in the combustion chamber are set to have the largest possible diameter in order to improve the performance of the engine. The upper limit of the engine speed is regulated by the inertial weight of the intake valve, which has a larger diameter than the exhaust valve. Therefore,
In order to eliminate such a problem, a three-valve or five-valve engine in which the number of intake valves is larger than that of exhaust valves has been proposed. In addition, a technique for making the intake / exhaust valve hollow to reduce the weight has been proposed (for example, JP-A-11-315356).
Issue).

Further, while the intake valve is cooled by the airflow flowing in during the intake stroke, the exhaust valve is further heated by the burnt gas during the exhaust stroke. The temperature gradient between the intake valve and the exhaust valve is large, so that the thermal strain generated in the cylinder head is also large.

[0005]

However, in order to increase the number of intake valves, a so-called four-valve type combustion chamber equipped with two intake and exhaust valves, which has been widely used in recent years, has a further one. Even if an attempt was made to increase the number of intake valves, the shape of the combustion chamber became flat, and conversely, the flame propagation speed was decreased, which sometimes hindered the improvement of output. Further, the manufacturing cost of the technique for filling the sodium of the poppet valve with the hollow stem is high, and thus it is difficult to apply it to a large number of intake / exhaust valves constituting a multi-valve combustion chamber.

[0006]

SUMMARY OF THE INVENTION The above-mentioned problems are solved by a combustion space defined by an inner surface of a cylinder, a top surface of a piston fitted therein, and a cylinder head closing an upper opening of a cylinder hole. An intake passage and an exhaust passage that open to the lower surface of the cylinder head that forms the space are openably and closably closed by an intake valve and an exhaust valve, and a flare portion and a stem portion that form the intake valve and the exhaust valve are provided. The problem can be solved by integrally forming the thin pipe material and opening the inner surface of the intake valve into the combustion space.
In this case, it is preferable that the end portion of the intake valve on the side of the stem portion be closed by an end member, and the end portion of the flare portion continuous with the stem portion be opened toward the combustion chamber. Further, it is preferable that the exhaust valve is formed into a hollow by closing an end portion of the flare portion and the stem portion by an end member, and sodium is enclosed in the hollow portion.

[0007]

The intake valve and the exhaust valve both have a tubular stem and a hollow interior, so they are lightweight. Of the two valves, the exhaust valve that easily overheats due to exhaust is filled with sodium to improve heat transfer, and the intake valve that is cooled by intake opens the inside of the stem to the combustion space through the flare and actively introduces combustion gas. Is heated.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below. In FIG. 1, 10 is a four-stroke engine according to the present invention. The four-stroke engine 10 has a combustion chamber 11.
The combustion chamber 11 has a cylinder hole 13 formed in a cylinder block 12 and a piston 1 slidably fitted therein.
4 and a cylinder head 15 that closes the end of the cylinder hole 13 forms an expandable and contractible combustion space.

On the lower surface of the cylinder head 15, there is formed a combustion recess 15a forming a wall surface of the combustion chamber 11. An intake passage 16 and an exhaust passage 17 are opened in the combustion concave portion 15a, and the openings of the passages 16 and 17 are openably and closably closed by an intake valve 18 and an exhaust valve 19, respectively.

The intake valve 18 and the exhaust valve 19 are shown in FIGS.
As shown in FIG. 3, each has a stem portion 21 made of a thin pipe material formed by plastically working a stainless material, and an umbrella-shaped flare portion 22 integrally formed at one end thereof. A valve portion 23 formed of a conical surface is formed on the outer surface of the peripheral edge of the. Reference numeral 24 denotes a valve seat 24, which is shrink-fitted and fixed to the cylinder head 15 to seat the valve portion 23.

At the other end of the stem portion 21, a shaft-shaped end member 2 is provided.
5 are fitted and fixed by friction welding. End member 25
A cotter groove is formed in the intake valve 18 and the exhaust valve 1
9 is a retainer 27 via a valve cotter 26 as in the conventional case.
, And is urged in the closing direction by a valve spring 28 via the retainer 27. Reference numeral 29 is a valve operating cam.
Regarding the exhaust valve 19, an end surface of the flare portion 22 on the combustion space side is closed by an end plate 31, and sodium is enclosed inside.

In the combustion chamber 11 implemented in the above-described mode, the lower portion of the cylinder head 15 has a tubular stem portion 21.
From the flare portion 22 provided with the valve portion 23 to the flare portion 22 is constituted by an intake valve 18 formed in a thin plate and an exhaust valve 19 formed of a hollow valve enclosing sodium. Therefore, the intake valve 18 is lighter than the conventional poppet valve and the sodium-filled hollow valve, and can have a large diameter without increasing the inertial weight. Further, since the flare portion 22 is also formed in a plate shape following the stem portion 21, the temperature is likely to rise due to combustion heat, and the exhaust valve 19 that is naturally high in temperature is generated.
There is less temperature gradient between and.

Further, since the exhaust valve 19 is a hollow sodium valve, the exhaust valve 19 is made light by utilizing the characteristic of sodium having good heat conductivity.

Next, when the four-stroke engine 10 is operated, as the piston 14 descends, first, the intake valve 18 opens and intake air flows from the intake passage 16. When the piston 14 reverses and rises, the intake air in the combustion chamber 11 is compressed, and a part thereof enters the stem portion 21 through the flare portion 22 of the intake valve 18.

When the compressed intake air is ignited by the spark plug, the fuel in the intake air explosively burns and the pressure in the combustion chamber 11 rises sharply. Therefore, the piston 14 receives the action of high-pressure combustion gas. It is pushed down. During this combustion process,
The combustion gas of high heat comes into contact with the intake valve 18 and the exhaust valve 19 to heat them, and at the same time, the fuel contained in a part of the intake air that has entered the flare portion 22 and the stem portion 21 also burns and heats. Are heated by the high heat in the combustion chamber 11.

When the piston 14 goes up and the exhaust valve 19 opens to start the exhaust stroke, the burned gas flows into the exhaust passage 17. During this time, the exhaust valve 19 is heated to high heat because it is in the flowing burnt gas, but it is well cooled by the action of sodium having excellent heat conductivity and is protected from overheating. Further, since the intake valve 18 is cooled by the inflowing airflow during the subsequent intake stroke, the high temperature state is not maintained for a long time and is similarly protected from overheating. Thus, the engine output can be increased and the temperature gradient between the intake valve and the exhaust valve can be reduced, so that the heat transfer is reduced and the thermal efficiency is improved.

[0017]

According to the first aspect of the present invention, the maximum rotation speed of the four-stroke engine can be set high, and the intake / exhaust valve is not overheated even at high output operation. According to the invention of claim 2, since the flare portion following the stem portion has a plate shape, the intake valve is made lightweight, and the heat capacity becomes small and the temperature gradient between the intake valve and the exhaust valve becomes small, so that the cylinder head is made. The thermal strain of can be reduced. According to the invention of claim 3, since the exhaust valve is a hollow type with sodium sealed,
It is lightweight and has good heat dissipation and excellent durability. And so on.

[Brief description of drawings]

1 is a cross-sectional view showing a main part of a four-stroke engine showing an embodiment of the present invention, and is a cross-sectional view corresponding to a cross-section taken along line I-I in FIG. 2;

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a side view in which a part of an intake valve is sectioned.

FIG. 4 is a side view in which a part of an exhaust valve is sectioned.

[Explanation of symbols]

10 ... 4 stroke engine 11 ... Combustion chamber 12 ... Cylinder block 13 ... Cylinder hole 14 ... Piston 15 ... Cylinder head 15a ... Burning recess 16 ... Intake passage 17 ... Exhaust passage 18 ... Intake valve 19 ... Exhaust valve 21 ... ・ Stem part 22 ... Flare section 23 ... Valve 24 ... 25 ... End members 26 ... Valve cotter 27 ... Retainer 28 ... Valve spring 29 ... Valve cam 30 ... End plates

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Claims (3)

[Claims] 1. A cylinder head having a combustion space defined by an inner surface of a cylinder, a top surface of a piston fitted therein, and a cylinder head closing an upper opening of a cylinder hole, and forming the space. The intake passage and the exhaust passage open to the lower surface of the are closed so as to be openable and closable by the intake valve and the exhaust valve, and the flare portion and the stem portion forming the intake valve and the exhaust valve are integrally formed by a thin pipe material. , A combustion chamber of a four-stroke engine in which the inner surface of the intake valve is opened into the combustion space. 2. The four-stroke engine according to claim 1, wherein the intake valve has a stem-side end closed by an end member, and an end of a flare continuous with the stem is opened toward the combustion chamber. Engine combustion chamber. 3. The combustion system for a four-stroke engine according to claim 1, wherein the exhaust valve is formed by closing the ends of the flare portion and the stem portion with end members to form a hollow and enclosing sodium therein. Room.