FORM 2
THE PATENT ACT 197 0 (39 of 1970)
&
The Patents Rules, 2003 COMPLETE SPECIFICATION (See Section 10, and rule 13)
1. TITLE OF INVENTION
METHOD FOR PRODUCING METALLIC-SODIUM-FILLED ENGINE VALVE
2. APPLICANT(S)
a) Name : MITSUBISHI HEAVY INDUSTRIES, LTD.
b) Nationality : JAPANESE Company
r c) Address : 16-5, KONAN 2-CHOME,
MINATO-KU, TOKYO 1088215, JAPAN
AND
a) Name : YOSHIMURA COMPANY
b) Nationality : JAPANESE Company
c) Address : 2685-173, AZA MINAMIHARA,
OA2A NAKASHIDAMI, MORIYAMA-KU, NAGOYA-SHI, AICHI 4630002, JAPAN
3. PREAMBLE TO THE DESCRIPTION
The following specification" particularly describes the invention and the manner in which it is to be performed : -

Technical Field
The present invention relates to a method for producing an engine valve filled inside with metallic sodium.
Background Art
In an engine valve of an automobile or the like, in order to respond to an increase in performance, a reduction in fuel consumption of an engine, and the like, the weight is reduced and the heat transmission is increased by providing a hollow portion in the engine valve and filling the hollow portion with metallic sodium.
Such an engine valve is produced as follows. First, for example, in a solid round-bar shaped material, an umbrella portion is formed by forging or the like and a hollow portion is formed with a punch and the like in an inner part of a portion that becomes a stem portion. Thereafter, the stem portion is inserted into multiple tubular dies different in size sequentially and is drawn sequentially in such a way that sizes of an outer diameter and an inner diameter of the stem portion are reduced stepwise and the length of the stem portion is increased stepwise. The stem portion having an intended size is thus formed (for example, see Patent Literature 1 listed below).
Next, (1) solid metallic sodium is extruded into a bar shape, cut into a predetermined length, and then inserted into the hollow portion; or (2) solid metallic sodium is heated to melt (about 120°C to 300°C) into a liquid state and then put into the hollow portion by injecting a predetermined amount of metallic sodium into the hollow portion. Thereafter, an opening at an upper end of the stem portion is sealed (for example, see Patent Literature 2 listed below). The engine valve filled inside with metallic sodium is thus produced.

Citation List Patent Literatures
Patent Literature 1: Japanese Patent No. 4390291
Patent Literature 2: Japanese Patent Application Publication No. Hei 3-018605
Summary of Invention Technical Problem
However, a conventional method for producing a metallic-sodium-filled engine valve as described above has the following problems.
(1) Solid metallic sodium is difficult to extrude and the workability of shaping the solid metallic sodium is thereby poor.
(2) When liquid metallic sodium adheres to an inner wall of the elongated hollow portion (a diameter of about 2 to 4 mm) during the injection of metallic sodium into the hollow portion, metallic sodium immediately cools and becomes solid thereby closing the hollow portion. Thus, liquid metallic sodium needs to be injected while the stem portion is heated (98°C or higher) and the workability of injection is thereby poor.
The present invention is made in view of the problems described above, and an object thereof is to provide a method for producing a metallic-sodium-filled engine valve by which metallic sodium can be easily put into the inside of an engine valve.
Solution to Problem
In a method for producing an engine valve filled inside with metallic sodium, according a first aspect of the invention for solving the aforementioned problems, the engine valve is produced by: shaping a stem portion having a hollow portion to

an intended size by sequentially drawing the stem portion in such a way that sizes of an outer diameter and an inner diameter of the stem portion are reduced stepwise; and putting metallic sodium into the hollow portion of the stem portion, the method characterized by comprising shaping the stem portion to the intended size by drawing the stem portion after putting a block-shaped piece of solid metallic sodium into the hollow portion of the stem portion.
The method for producing a metallic-sodium-filled engine valve according to a second aspect of the invention is characterized in that in the method according to the first aspect of the invention, the stem portion is shaped to the intended size by drawing the stem portion until the inner diameter of the hollow portion of the stem portion is reduced to a specified size, then putting the block-shaped piece of solid metallic sodium into the hollow portion of the stem portion, and thereafter further drawing the stem portion.
The method for producing a metallic-sodium-filled engine valve according to a second aspect of the invention is characterized in that, in the method according to the first aspect of the invention, the stem portion is shaped to the intended size by drawing the stem portion after putting the block-shaped piece of solid metallic sodium into the hollow portion of the stem portion before performing the drawing of the stem portion.
Advantageous Effects of Invention
In the method for producing a metallic-sodium-filled engine valve of the present invention, the block-shaped piece of metallic sodium is put into the hollow portion of the stem portion and the stem portion is then shaped to the desired size by drawing the stem portion. Thus, metallic sodium can be put into the hollow portion by simply cutting out the block-shaped piece of metallic sodium block from raw sodium in a size easy to handle and then putting the block-shaped piece of metallic

sodium into the hollow portion. Hence, metallic sodium can be easily put into to the inside of the engine valve.
Brief Description of Drawings
Fig. 1 is a view for explaining procedures in a main embodiment of a method for producing a metallic-sodium-filled engine valve of the present invention.
Fig. 2 is a view for explaining procedures in another embodiment of a method for producing a metallic-sodium-filled engine valve of the present invention.
Description of Embodiments
Embodiments of a method for producing a metallic-sodium-filled engine valve of the present invention are described below based on the drawings. However, the present invention is not limited to the embodiments described below based on the drawings.