FORM 2
THE PATENT ACT 1970 (39 of 1970)
&
The Patents Rules, 2003 COMPLETE SPECIFICATION (See Section 10, and rule 13)
1. TITLE OF INVENTION
METHOD FOR MANUFACTURING HOLLOW ENGINE VALVE
2. APPLICANT(S)
a) Name : MITSUBISHI HEAVY INDUSTRIES, LTD.
b) Nationality : JAPANESE Company
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, Oaza 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 a hollow engine valve which can simplify production steps and reduce production cost
BACKGROUND ART
Among engine valves, various engine valves designed as follows are recently provided along with the increase in output and performance of an engine. An inside of the engine valve is formed to be hollow and this hollow portion is filled with metallic sodium serving as a coolant. This design reduces the weight, and improves the thermal conductivity by the action of metallic sodium filled in the hollow portion, compared to a solid engine valve. A conventional method for producing such a hollow engine valve is disclosed in, for example, Patent Documents 1,2.
PRIOR ART DOCUMENT PATENT DOCUMENT
Patent Document 1: Japanese Patent No. 4282900 Patent Document 2: Japanese Patent No. 4390291
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
However, in the conventional method for producing a hollow engine valve, the hollow engine valve as a finished product is obtained by producing multiple members separately and then eventually joining the members to each other. Accordingly, many steps must be performed to produce the hollow engine valve. Hence, this may make the production steps complicated and increase the production cost.

The present invention has been made to solve the problems described above, and an object thereof is to provide a method for producing a hollow engine valve which can simplify production steps and reduce production cost.
MEANS FOR SOLVING THE PROBLEMS
In a method for producing a hollow engine valve according to a first aspect of the invention for solving the aforementioned problems, in which a hollow stem portion of a semi-finished product is shaped into a predetermined shape by sequentially inserting the hollow stem portion into a plurality of shaping holes different in hole shape to, sequentially draw the hollow stem portion in such a way that an outer diameter dimension and an inner diameter dimension of the hollow stem portion are reduced stepwise and a length of the hollow stem portion is increased stepwise, the method for producing a hollow engine valve is characterized by comprising: subjecting the semi-finished product to heat treatment in such a way that a hardness of the semi-finished product becomes equal to or less than a predetermined hardness; shaping a stem end sealing portion by causing a wall thickness of an opening edge portion of the hollow stem portion to be increased toward an inner side of the opening edge portion, by using a last one of the shaping holes which has a hole diameter adjusted; and joining gap portions of the stem end sealing portion together;
The method for producing a hollow engine valve according to a second aspect of the invention for solving the aforementioned problems is characterized by further comprising adjusting a hole diameter of a stem shaping portion in the last one of the shaping holes, the stem shaping portion configured to shape the hollow stem portion.
The method for producing a hollow engine valve according to a third aspect of the invention for solving the aforementioned problems is characterized by further comprising injecting a coolant into the hollow stem portion before the drawing performed by using the last one of the shaping holes.

EFFECT OF THE INVENTION
In the method for producing a hollow engine valve of the present invention, the semi-finished product subjected to heat treatment in such a way that the hardness thereof becomes equal to or less than the predetermined hardness is shaped to have the wall thickness of the opening edge portion of the hollow stem portion increased inward, by using the last shaping hole having the hole diameter thereof adjusted, and the gap portions of the stem end sealing portion shaped by this increase of wall thickness are joined together. By using this method, the number of parts forming the hollow engine valve 1 can be reduced. Thus, the method can simplify production steps and reduce production cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[Fig. 1] Fig. 1 is an overall configuration diagram of a cold forging apparatus to
which a method for producing a hollow engine valve of the present invention is applied.
[Fig. 2] Part (a) includes a vertical cross-sectional view of a die of the cold
forging apparatus which is provided for an n-th drawing step and a vertical cross-sectional view of a semi-finished product shaped with the die, and Part (b) includes a vertical cross-sectional view of a die of the cold forging apparatus which has been conventionally provided for the n-th drawing step and a vertical cross-sectional view of a semifinished product shaped with the die.
[Fig. 3] Fig. 3 is a vertical cross - sectional view of a hollow engine valve
produced by the producing method of the present invention.
MODE FOR CARRYING OUT THE INVENTION
A method for producing a hollow engine valve of the present invention is described below in detail by using the drawings.

Embodiment
First,.as shown in Fig. 3, a hollow engine valve 1 produced by the producing method of the present invention is used as an intake valve or an exhaust valve of an engine in a vehicle or the like. An inside of the hollow engine valve 1 is filled with metallic sodium N as a coolant.
The hollow engine valve 1 is one in which a valve umbrella portion 11, a hollow stem portion 12, and a stem end sealing portion 15 are shaped integrally. A hollow hole 13 is formed in the inside of the hollow engine valve 1, extending through the valve umbrella portion 11 and the hollow stem portion 12. Moreover, although described in detail later, in the stem end sealing portion 15, an opening edge portion on a base end (upper end) side of the hollow stem portion 12 is shaped to close by causing the wall thickness thereof to be increased toward an inner side of the opening edge portion, with the hollow hole 13 filled with the metallic sodium N. Lastly, gap portions in a center portion of the stem end sealing portion 15 are joined together.
Specifically, the hollow engine valve 1 is produced by using a cold forging apparatus 20 to be described later and the like. Metallic sodium N is injected into the hollow hole 13 during the cold forging, and the joining of the stem end sealing portion 15 is thereafter performed. Thus, the hollow engine valve 1 as a finished product can be obtained. Note that, the hollow engine valve 1 is sometimes not filled with metallic sodium N depending on usage conditions.
Next, the configuration of the cold forging apparatus 20 is described by using Fig. 1 and parts (a) and (b) of Fig. 2.
The cold forging apparatus 20 shown in Fig. 1 shapes the hollow engine valve 1 by sequentially drawing (cold-forging) a semi-finished product la. A press bed 21 is provided in a lower portion of the cold forging apparatus 20 while a ram 22 is

provided in an upper portion of the cold forging apparatus 20 to face the press bed 21. The ram 22 is supported to be moveable in a vertical direction.
Tubular dies Dil, Di2, Di(m-l), Dim, Di(n-l), and Din' are provided on a bottom face of the ram 22 in line along a conveyance direction of the semi-finished products. Here, index m refers to m-th in the order and index n refers to n-th (last) in the order. Moreover, mdn').
The hollow engine valve lx is shaped to have a length (height) of In, which is larger than In' (ln>ln'), by performing drawing with the die Din described above.

Moreover, by this drawing, the hollow engine valve lx is shaped such that the hollow stem portion has an outer diameter of dn, which is larger than the outer diameter dn', and an inner diameter of dn2.
In other words, compared to the die Din, the die Din1 is set in such a way that the inner diameter dn' is smaller than the inner diameter dn. By using this die Din', the hollow engine valve 1 having the stem end sealing portion 15 for closing the opening portion of the hollow stem portion 12 can be shaped.
The hollow engine valve 1 is produced as follows. First, a solid round-bar-shaped material which is not illustrated is subjected to hot.forging and the semi-finished product la is thereby shaped. Thereafter, the semi-finished product la is subjected to heat treatment in such a way that the hardness thereof becomes equal to or less than a predetermined hardness. Next, the semi-finished product la having the hardness equal to or lower than the predetermined hardness is positioned at a point on the press bed 21 of the cold forging apparatus 20 which corresponds to the die Dil.
Then, elevation and decent operations of the ram 22 and conveyance operations and positioning operations of the conveyance means are performed sequentially and n times of drawing are sequentially performed with the dies Dil, Di2, Di(m-l), Dim, Di(n-l), and Din1. As a result, the semi-finished product la is sequentially shaped into the semi-finished products lb, lc, lm, and In. This shaping causes the outer diameter dimension and the inner diameter dimension of each hollow stem portion to be reduced stepwise and the length of each hollow stem portion to be increased stepwise, and the hollow engine valve 1 is eventually formed.
Subjecting the semi-finished product la to heat treatment in such a way that the hardness thereof becomes equal to or less than the predetermined hardness has the following effect. In each of the semi-finished product la and the semi-finished products lb, lc, lm, and In thereafter, it becomes easier to increase the wall

thickness of the hollow stem portion and harder to increase the length of the hollow stem portion as the hardness of the semi-finished product becomes smaller.
By drawing the tempered semi-finished product In with the shaping hole Mn' of the die Din' adjusted to have the inner diameter of dn' as described above, the hollow engine valve 1 can be shaped to have the wall thickness of the opening edge portion of the hollow stem portion 12 increased toward the inner side thereof. Moreover, in the drawing with dies Dil, Di2, Di(m-l), Dim, and Di(n-l), since hole shapes of the respective shaping holes Ml, M2, M(m-l), Mm, and M(n-l) of these dies are not adjusted from the conventional ones, the shaping is performed with the opening edge portion of each hollow stem portion opened.
Incidentally, in the drawing with the die Din1, when the opening edge portion of the hollow stem portion 12 is not closed toward an inner side thereof by performing the drawing once, the drawing is performed multiple times until the wall thickness of the opening edge portion increases and the opening edge portion is thereby closed. Moreover, since the shaping holes Ml, M2, M(m-1), Mm, M(n-1), and Mn' do not press lower portions of the valve umbrella portions in the semi-finished products la, lb, 1m, and 1n, the outer diameters of the umbrella portions of the semi-finished products at the largest portions are maintained at Do.
Here, the hollow hole 13 is already filled with metallic sodium N after any one of the steps of drawing with the dies Dil, Di2, Di(m-l), Dim, and Di(n-l) in the cold forging apparatus 20. Hence, after the drawing to close the opening edge portion is performed, the hollow engine valve 1 as a finished product can be produced by joining the gap portions of the stem end sealing portion 15 together by, for example, filler welding or non-filler welding. Incidentally, the stem end sealing portion 15 is not exposed to an exhaust gas of a high temperature. Hence, the joining of the gap portions may be performed by blazing or the like, instead of welding.

In the method of producing a hollow engine valve of the present invention, the semifinished product In subjected to heat treatment in -such a way that the hardness thereof becomes equal to or less than a predetermined hardness is shaped to have the wall thickness of the opening edge portion of the hollow stem portion 12 increased toward an inner side thereof, by using the shaping hole Mn' of the die Din' adjusted to have the inner diameter of dn\ Thereafter, the gap portions of the stem end sealing portion 15 shaped by the increase in wall thickness are joined together. By using this method, the number of parts forming the hollow engine valve 1 can be reduced. Thus, the method can simplify production steps and reduce production cost.
Industrial Applicability
The present invention can be applied to a hollow engine valve producing apparatus which is designed to produce hollow engine valves different in shape in a single producing apparatus by making dies replaceable.

WE CLAIM:-
1. A method for producing a hollow engine valve in which a hollow stem
portion of a semi-finished product is shaped into a predetermined shape by
sequentially inserting the hollow stem portion into a plurality of shaping
holes different in hole shape to sequentially draw the hollow stem portion in
such a way that an outer diameter dimension and an inner diameter
dimension of the hollow stem portion are reduced stepwise and a length of
the hollow stem portion is increased stepwise, the method for producing a
hollow engine valve characterized by comprising:
subjecting the semi-finished product to heat treatment in such a way that a
hardness of the semi-finished product becomes equal to or less than a
predetermined hardness;
shaping a stem end sealing portion by causing a wall thickness of an opening
edge portion of the hollow stem portion to be increased toward an inner side
of the opening edge portion, by using a last one of the shaping holes which
has a hole diameter adjusted; and
joining gap portions of the stem end sealing portion together.
2. The method for producing a hollow engine valve according to claim 1,
characterized by further comprising
adjusting a hole diameter of a stem shaping portion in the last one of the . shaping holes, the stem shaping portion configured to shape the hollow stem portion.

3. The method for producing a hollow engine valve according to claim 1, characterized by further comprising
injecting a coolant into the hollow sten1 portion before the drawing performed by using the last one of the shaping holes-