JP2001182540A - Combustion chamber for four-stroke engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve a problem that large space is left on a rear side of an poppet part in a poppet valve for integrally making a stem and the poppet part by performing pressing working for a steel plate and thereby a high compression ratio becomes unobtainable by increasing space volume on an upper surface of a piston when using the poppet valve for an engine. SOLUTION: This problem is resolved by constituting at least one of an intake valve and an exhaust valve by a hollow stem and a poppet part connected with an end of the stem, forming a relief hole corresponding to the intake valve and the exhaust valve on an upper surface of a top wall of the piston and forming a semi-spherical projecting part entering the inside of the poppet of a valve element at the time of an overlapping on a bottom part of the relief hole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber of a four-stroke engine, and more particularly to an improvement in a combustion chamber using a steel plate hollow valve as an intake and exhaust valve.

[0002]

2. Description of the Related Art Conventionally, a poppet valve used in a four-stroke engine has a substantially conical umbrella formed at one end of a stem made of steel by forging. In order to reduce the inertial weight of the umbrella, there has been known an umbrella section in which the wall surface of the umbrella section on the combustion chamber side is depressed in a hemispherical shape along the combustion chamber wall. On the other hand, in order to reduce the inertial weight of the poppet valve first, as shown in FIG. 4, the applicant deep-draws a steel plate to form a hollow stem, and integrally forms an umbrella portion on the opening side of the hollow stem. A sheet metal poppet valve in which the opening of the stem is closed by a cover plate has been proposed (Japanese Patent Application No. 10-217179).

[0003]

However, a poppet valve obtained by plastically processing a plate-like material in such a manner has an inner surface of an umbrella portion because the umbrella portion is formed by expanding an end of a stem. ,
That is, a large depression is formed on the back side of the seat surface. Therefore, when this valve was assembled to the cylinder head in the same manner as before, the volume of the combustion chamber on the upper surface of the piston when the piston was at the top dead center, the so-called space volume, increased by the amount of the depression, and prevented the compression ratio from increasing. . It was also considered to provide a cover material not at the opening of the stem but at the opening of the umbrella portion so that the hollow could not be formed.However, if the cover plate receiving high pressure in the combustion chamber is made large, the cover plate becomes thick. I have to take it,
Also, since the area is large, the effect of reducing the weight of the valve is reduced.

For this reason, the space limit is reduced by setting the upper limit position of the piston closer to the cylinder head, but this also causes interference between the intake and exhaust valves and the piston at the time of overlap. There is a defect, and this defect is also provided with an escape hole on the top surface of the piston to avoid collision with the valve, but this is also limited. For this reason, a sufficiently high compression ratio cannot be obtained, and high thermal efficiency or high output as an engine may not be obtained.

[0005]

An object of the present invention is to provide a combustion chamber formed between a piston inserted into a cylinder hole and a cylinder head provided so as to cover an upper portion of the piston. In a four-stroke engine provided with an intake valve and an exhaust valve in an exhaust passage, at least one of the intake valve and the exhaust valve includes a hollow stem and an umbrella portion connected to one end of the stem. This is solved by forming a relief hole on the top wall of the top wall corresponding to the intake valve and the exhaust valve, and forming a hemispherical projection at the bottom of the relief hole that enters the inside of the umbrella of the valve body when overlapping. You. Where,
It is preferable that a concave portion formed corresponding to the hemispherical projection is provided on the lower surface of the top wall of the piston.

[0006]

[Function] The weight of the valve body is reduced by the amount that the back side of the seat surface is greatly depressed. Further, the space volume of the combustion chamber is increased by the amount that the inside of the umbrella of the valve body is greatly depressed, but the increase of the space volume is offset by the volume of the protrusion provided on the upper surface of the top wall of the piston. The increase in the weight of the piston due to the provision of the protrusion on the upper surface of the top wall of the piston is somewhat reduced by providing the concave portion on the lower surface of the top wall.

[0007]

Hereinafter, an embodiment of the present invention will be described. In FIG. 1, reference numeral 10 denotes a four-stroke engine according to the present invention. The engine 10 includes a cylinder 11 having a cylinder hole 11a, a cylinder head 12 mounted so as to cover the cylinder hole 11a, and the cylinder hole 11a.
a and a piston 13 which is reciprocally fitted by a skirt portion 13a. Reference numeral 14 denotes a combustion chamber. Become.

The cylinder head 12 is of a four-valve type having two intake passages 15 and two exhaust passages 17 communicating with the combustion recesses 12a.
The opening leading to the opening is closed by an intake valve 16 and an exhaust valve 18 so as to be openable and closable. Reference numeral 19 denotes a valve operating mechanism for the intake valve 16 and the exhaust valve 18, which is constituted by a camshaft 19a, a valve lifter 19b, a valve spring 19c, and the like.

In this embodiment, as shown in FIG. 4, the intake valve 16 and the exhaust valve 18 have a hollow stem 21 formed by deep drawing a steel plate, and an umbrella formed continuously at one end thereof. And a part 22. Reference numeral 23 denotes a closing lid, which is welded to the outside (combustion chamber side) of the opening to close the opening of the stem 21. Like the conventional poppet valve, the umbrella portion 22 is formed in a substantially umbrella shape having a conical portion 22a whose diameter is increased by drawing a curve from the stem 21 and a seat surface 22b formed at the outer end thereof. Since the material is made of a plate material, a relatively large substantially conical space 24 is left behind the conical portion 22a and the seating surface 22b. 26 is a cotter groove.

The piston 13 has a substantially triangular chevron 13c extending in the pin direction on the upper surface of the top wall 13b, and one slope of the chevron 13c is connected to the two intake valves 16,16.
And the other slope faces both exhaust valves 18, 18 to form a so-called hemispherical combustion chamber. In a high compression ratio engine having a hemispherical combustion chamber, a relief hole 25 is provided on the upper surface of the top wall of the piston 13 to avoid interference between the intake valve 16 and the exhaust valve 18 when the intake valve 16 and the exhaust valve 18 are simultaneously opened. It is prepared. In the present invention, a hemispherical projection 25a projecting in the valve direction is provided on the bottom surface of the escape hole 25.
Are formed.

Thus, in the four-stroke engine 10, the piston 13 reaches the top dead center in the compression stroke and the intake and exhaust strokes. When the piston 13 is in the state of FIG. 1 in which the piston 13 is at the compression top dead center, the intake valve 16 and the exhaust valve 18 are both closed, and there is a relatively large gap between them, so that no interference occurs. The volume of the combustion chamber 14 is increased by the space 24 formed between the valves 16 and 18, but the volume of the combustion chamber 14 is reduced by the volume of the projection 25a protruding from the top surface of the piston 13 to offset the increase in the volume of space. I do.

In the state shown in FIG. 3 in which the piston 13 is located at the top dead center of the intake and exhaust ports, both the intake valve 16 and the exhaust valve 18 are open. The fuel gas is in a state of being discharged. At this time,
The umbrella portions 22 of both valves 16 and 18 are provided with escape holes 25 of the piston 13.
And the projection 25a provided on the bottom surface of the escape hole 25 enters the space 24 inside the umbrella portion 22, and removes fresh air or burnt gas existing there.

[0013]

According to the first aspect, the intake valve and the exhaust valve are made by plastically processing a plate material, and can be made lightly. In addition, the increase in the space volume of the combustion chamber due to the use of such a valve is offset by the projection provided on the top wall of the piston, and is minimized. According to the second aspect, even if the projection is provided on the top wall of the piston, the increase in the weight of the piston due to the projection can be minimized. And so on.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a four-stroke engine showing an embodiment of the present invention, showing a state of a compression top dead center of a piston.

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

FIG. 3 is a cross-sectional view corresponding to FIG. 1, showing a state of top dead center of intake and exhaust of the piston.

FIG. 4 is a sectional view showing an example of a sheet metal hollow valve according to a conventional example.

[Explanation of symbols]

 10. Four-stroke engine 11 Cylinder 11a Cylinder hole 12 Cylinder head 12a Compression recess 13 Piston 13a Skirt part 13b Top wall 13c ... chevron 14 ... combustion chamber 15 ... intake passage 16 ... intake valve 17 ... exhaust passage 18 ... exhaust valve 19 ... valve Mechanism 19a ・ ・ ・ Cam shaft 19b ・ ・ ・ Valve lifter 19c ・ ・ ・ Valve spring 21 ・ ・ ・ ・ ・ ・ Stem 22 ・ ・ ・ ・ ・ ・ Valve 22a ・ ・ ・ Conical part 22b ・ ・ ・ Seat surface 23 ・ ・ ・ ・ ・ ・ Closed lid 24: a substantially conical space 25: an escape hole 25a: a protrusion

Claims (2)

[Claims] A combustion chamber is formed between a piston inserted into a cylinder hole and a cylinder head provided to cover an upper portion of the piston. An intake valve is provided in an intake passage leading to the combustion chamber, and an exhaust valve is provided in an exhaust passage. In the four-stroke engine provided with at least one of the intake valve and the exhaust valve, at least one of the intake valve and the exhaust valve is constituted by a hollow stem and an umbrella portion connected to one end of the stem. A combustion chamber in which a relief hole is formed corresponding to the valve, and a hemispherical projection is formed at the bottom of the relief hole to enter the inside of the umbrella part when overlapping. 2. The combustion chamber according to claim 1, wherein a concave portion formed corresponding to the hemispherical projection is provided on a lower surface of a top wall of the piston.