Hollow engine valve and manufacturing method thereof

Abstract

To provide a hollow engine valve which achieves improvement of strength of a shaft part.SOLUTION: A hollow engine valve 100 is integrally formed from a shaft part 211 to an umbrella part 213 whose diameter expands in an umbrella form at a base end of the shaft part. The umbrella part 213 includes an umbrella surface 213a, and a coolant is enclosed in at least a hollow part 215 which is provided within the shaft part 211 and forms a hollow. A valve umbrella part 210 has: the shaft part 211 located at the tip side; and a neck part 214 which is provided continuously with the umbrella part 213 and has an outer diameter larger than that of the shaft part 211. A thickness of the neck part 214 is larger than a thickness of the shaft part 211. The hollow part 215 is provided having an inner diameter which is constant in at least an area ranging from the shaft part 211 to the neck part 214.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a hollow engine valve and a method for manufacturing the same. [Background technology]

[0002] Conventionally, engine valves for allowing intake gas to flow into the combustion chamber of engines of automobiles, ships, etc. and discharging exhaust gas include hollow engine valves (hereinafter simply referred to as engine valves) that have a hollow interior to enclose a coolant such as metallic sodium that suppresses temperature rise (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-190759 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if CO2 emission regulations become stricter, and Combustion temperatures are rising in both engines and engines, and there are concerns that the neck temperature of hollow engine valves will rise and that they will lack strength.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a hollow engine valve having an improved strength of the stem portion, and a method for manufacturing the same. [Means for solving the problem]

[0006] (1) A first aspect of the present invention is a hollow engine valve having a shaft portion and an umbrella portion that expands in diameter like an umbrella at the base end of the shaft portion, and a coolant is sealed in a hollow portion provided at least inside the shaft portion. The shaft portion has a first shaft portion at the tip side, a second shaft portion at the base end side that has an outer diameter larger than that of the first shaft portion, and a step portion formed by the difference in outer diameter between the first shaft portion and the second shaft portion, and the thickness of the step portion is thicker than the thickness of the second shaft portion.

[0007] According to the above configuration (1), it is possible to improve the strength against bending stress on the step portion.

[0008] (2) A second aspect of the present invention is a hollow engine valve having a stem and an umbrella portion that expands in diameter like an umbrella at the base end of the stem, and a hollow portion provided at least inside the stem, in which a coolant is sealed in a hollow portion. The stem has a main stem portion at the tip end and a neck portion that is provided continuous with the umbrella portion and has an outer diameter larger than that of the main stem, the neck portion having a thickness greater than that of the main stem, and the hollow portion is provided with a constant inner diameter at least across the main stem and the neck.

[0009] According to the above configuration (2), it is possible to improve the strength of the neck portion and also to facilitate the movement of the coolant inside the hollow portion.

[0010] (3) A third aspect of the present invention is a method for manufacturing a hollow engine valve having a shaft portion including a first shaft portion and a second shaft portion that is continuous with the first shaft portion and has an outer diameter larger than that of the first shaft portion, an umbrella portion that expands in diameter like an umbrella at one end of the second shaft portion, and a hollow portion that is hollow inside at least the shaft portion, the method comprising the steps of: a first step of forming a material made of special steel by forging and drilling a semi-finished product having a cylindrical tubular portion that has the same diameter as the outer diameter of the second shaft portion and an umbrella portion at one end of the tubular portion that has the same shape as the umbrella portion; and a second step of forming the shaft portion by reducing the diameter of the cylindrical portion by drawing, wherein in the second step, the cylindrical portion is reduced in diameter to a predetermined specific position in the axial direction of the cylindrical portion, whereby the reduced-diameter portion is the first shaft portion, the non-reduced portion is the second shaft portion, and a portion that is reduced in diameter together with the first shaft portion and formed by the difference in outer diameter between the first shaft portion and the second shaft portion is a step portion, and the thickness of the reduced-diameter first shaft portion and the step portion is thicker than the thickness of the second shaft portion.

[0011] According to the above configuration (3), it is possible to manufacture a hollow engine valve having a stem portion with increased strength.

[0012] (4) A fourth aspect of the present invention is a method for manufacturing a hollow engine valve including a stem portion, an umbrella portion expanding in diameter like an umbrella at a base end of the stem portion, a neck portion provided contiguous to the umbrella portion on the base end side of the stem portion and having an outer diameter larger than that of the stem portion, and a hollow portion having a predetermined specific diameter provided inside at least the stem portion, the method comprising the steps of: a first step of forging a material made of special steel and drilling a hole to form a semi-finished product including a cylindrical tubular portion having an opening at a tip end and an umbrella portion expanding in diameter like an umbrella at a base end of the tubular portion; and a second step of reducing the diameter of the tubular portion by drawing to form a hollow engine valve including the stem portion and the umbrella portion. and a second step of forming a neck portion, wherein in the first step, a tapered neck portion that is thicker than the wall thickness of the tubular portion and that exponentially tapers in diameter toward the tip is formed on the base end side of the tubular portion, and the second step includes a first molding step in which the outer diameter of the tubular portion including the tapered neck portion is reduced until the inner diameter of the tapered neck portion reaches the specific diameter to form a semi-finished neck portion, and a second molding step in which the outer diameter of the tubular portion distal to the semi-finished neck is reduced until the inner diameter of the tubular portion reaches the specific diameter, thereby forming the reduced diameter portion as the shaft portion and the non-reduced diameter portion as the neck portion.

[0013] According to the above configuration (4), it is possible to manufacture a hollow engine valve in which the strength of the neck portion is increased and the coolant moves smoothly within the hollow portion. [Effects of the Invention]

[0014] According to the present invention, a hollow engine valve having an improved stem strength can be manufactured. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a longitudinal sectional view of a hollow engine valve according to a first embodiment. [Figure 2] 4A to 4C are schematic diagrams showing the manufacturing process of the hollow engine valve. [Figure 3] 4A to 4C are schematic diagrams showing the manufacturing process of the hollow engine valve. [Figure 4] FIG. 6 is a longitudinal sectional view of a hollow engine valve according to a second embodiment. [Figure 5] 4A to 4C are schematic diagrams showing the manufacturing process of the hollow engine valve. [Figure 6] 4A to 4C are schematic diagrams showing the manufacturing process of the hollow engine valve. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, the present invention will be described in detail with reference to one embodiment of the invention with reference to FIGS. 1 to 6. However, the following embodiment is merely an example and does not limit the invention according to the claims.

[0017] (First embodiment) The first embodiment will be described with reference to Figures 1 to 3. The orientation of the hollow engine valve 100 of this embodiment will be described based on the orientation of the engine valve 100 (valve head portion 110) in Figure 1 (for example, the tip side (shaft end member 120 side) of the stem portion 111 is the top, and the base side (head portion 113 side) of the stem portion 111 is the bottom).

[0018] (Hollow Engine Valve 100) A hollow engine valve (hereinafter simply referred to as engine valve) 100 is a valve element provided in the cylinder head of an engine (not shown) of an automobile or the like, and is disposed inside an intake port and an exhaust port that communicate with a combustion chamber, and moves up and down when the engine is running to open and close the intake port and exhaust port. By opening the intake port, the engine valve 100 allows intake gas to be supplied from the intake port into the combustion chamber, and by opening the exhaust port, exhaust gas from the combustion chamber can be discharged out of the combustion chamber through the exhaust port.

[0019] As shown in FIG. 1, the engine valve 100 includes a valve head portion 110 which is a main body portion, and a shaft end member 120 which is a cover portion.

[0020] The valve head portion 110 includes a rod-shaped stem portion 111 and a head portion 113 that is provided continuously with the lower end of the stem portion 111 and expands concentrically downward into an umbrella shape.

[0021] The shaft portion 111 comprises an upper first shaft portion 111a and a lower second shaft portion 111b having an outer diameter larger than that of the first shaft portion 111a, and a tapered step portion 111c that gradually reduces in diameter toward the top is provided between the first shaft portion 111a and the second shaft portion 111b to connect the two shaft portions 111a and 111b, which have different outer diameters.

[0022] The shaft portion 111 of the valve head portion 110 has a hollow portion 115 with a bottom that is open at the top. The hollow portion 115, i.e., the inner shape of the valve head portion 110, is substantially similar to the outer shapes of the first shaft portion 111a and the second shaft portion 111b. Specifically, the inner diameter Φd' of the first shaft portion 111a is set smaller than the inner diameter Φd of the second shaft portion 111b, and the hollow portion 115 in the stepped portion 111c (the inner shape of the stepped portion 111c) is tapered, gradually decreasing in diameter toward the top.

[0023] As shown in FIG. 1, the thickness t3 (e.g., 1.6 mm) of the first shaft portion 111a and the thickness t2 (e.g., 1.6 mm) of the step portion 111c are thicker than the thickness t1 (e.g., 1.0 mm) of the second shaft portion 111b (t3=t2>t1).

[0024] This improves the strength of the step portion 111c of the shaft portion 111 where the maximum bending stress occurs when the engine valve is seated during engine operation, thereby suppressing deterioration and damage to the engine valve 100.

[0025] After a getter material such as titanium (not shown) or a coolant such as metallic sodium is introduced into the hollow portion 115 of the valve head portion 110, the shaft end member 120 is joined (for example, by friction welding) to the upper end of the shaft portion 111, thereby closing the opening of the shaft portion 111. This seals the hollow portion 115, and the coolant, etc. is sealed within the hollow portion 115. As a result, the shaft end member 120 becomes integral with (and inseparable from) the shaft portion 111, forming the shaft portion 111, and the engine valve 100, in which the coolant, etc. is sealed, is completed.

[0026] If necessary, all or part of the engine valve 100 (all or part of the head portion 113, all or part of the stem portion 111) may be coated with a heat insulating coating made of a metal with low thermal conductivity, such as ceramic, or may be subjected to surface treatment such as nitriding or polishing.

[0027] (Method of manufacturing the valve head portion 110 of the engine valve 100) The molding process of the valve head portion 110 can be broadly divided into a first step (see Figure 2) of molding a semi-finished product 300 from a solid round bar 10, and a second step (see Figure 3) of molding the valve head portion 110 from the semi-finished product 300.

[0028] As shown in Figure 2 (4), the semi-finished product 300 has a tubular portion 301 before processing the shaft portion 111 of the valve head portion 110, a cylindrical hole 305 before processing the hollow portion 115 of the valve head portion 110, and an umbrella-shaped portion 303 before processing the umbrella portion 113 of the valve head portion 110.

[0029] The cylindrical portion 301 has an outer diameter ΦD (e.g., Φ7 mm), an inner diameter (hole diameter) Φd (e.g., Φ5 mm), and a thickness t1 (e.g., 1.0 mm), and is formed into a straight cylindrical shape. The umbrella-shaped portion 303 has the same shape as the umbrella portion 113.

[0030] (1st step) In this embodiment, in the first step, a cylindrical solid round bar 10 made of, for example, special steel, as shown in Figure 2(1) is extruded to form an extruded solid rod 20, as shown in Figure 2(2) , by providing a semi-finished shank portion 21, which is a portion corresponding to the shank portion 111 of the engine valve 100 with a reduced diameter, and a head portion 23 having an outer diameter larger than that of the semi-finished shank portion 21. Furthermore, by forging the extruded solid rod 20, an umbrella-shaped portion 33 is formed by expanding the diameter of the head portion 23 of the extruded solid rod 20, as shown in Figure 2(3) , and the semi-finished shank portion 21 is shortened in the axial direction and provided with an expanded diameter solid rod 31, as shown in Figure 2(4) . In the extrusion and forging steps, the workpiece is loaded into a die K having a downwardly concave forming portion S, and is pressed from above by a press device (not shown) having a punch P to form the workpiece. 2(3) is turned upside down to form a solid shaft 31, and a bottomed cylindrical hole 305 is drilled in the axial direction using, for example, a drill M to form a tubular portion 301, as shown in FIG. 2(4), to form a semifinished product 300. The shape of the umbrella-shaped portion 303 of the semifinished product 300 is the same as the umbrella-shaped portion 33 of the umbrella-shaped solid rod 30, and the outer diameter of the tubular portion 301 is the same as that of the solid shaft 31.

[0031] In the first step of this embodiment, the squeezing process may be omitted, or the cylindrical hole 305 may be formed before forming the umbrella-shaped portion 33. The cylindrical hole 305 may be formed in stages, for example, by forming one end of the solid round bar 10 into a cup shape by forging and then squeezing the outer wall to make it stand up by drawing, instead of by drilling or the like.

[0032] (2nd process) 3, in the second step, the diameter of the tubular portion 301 is reduced stepwise by cold forging using a plurality of dies 51, 52, and 53 (hereinafter collectively referred to as dies 51 to 53) to form the valve head portion 110. The number (types) of dies may be increased or decreased as appropriate depending on the number of steps, etc.

[0033] The dies 51 to 53 each have a forming hole 50 that penetrates vertically. The forming hole 50 has a reduced diameter portion 50a with a constant inner diameter and a tapered portion 50b that expands in diameter downward from the lower end of the reduced diameter portion 50a. The reduced diameter portion 50a reduces the diameter of the tubular portion 301 of the semifinished product 300, enabling the formation of the first shaft portion 111a of the valve head portion 110, and the tapered portion 50b enables the formation of the step portion 111c of the valve head portion 110. The dies 51 to 53 are arranged in accordance with the progress of the second step, and the diameter relationship of each forming hole 50 (reduced diameter portion 50a and tapered portion 50b) is die 51 > die 52 > die 53.

[0034] In the second step, the die 51 shown in Fig. 3(1) reciprocates from above the semifinished product 300, with the intermediate position (specific position) C of the semifinished product 300 as the turning point, thereby forming the semifinished product 320 shown in Fig. 3(2). Further, the reciprocating motion of the die 52 forms the semifinished product 330 shown in Fig. 3(3). Finally, the reciprocating motion of the die 53 forms the valve head portion 110 shown in Fig. 3(4). Note that the intermediate position C can be changed as appropriate depending on the specifications of the engine valve.

[0035] Specifically, the semi-finished product 320 shown in Figure 3(2) is obtained by reducing the inner diameter and outer diameter of the part corresponding to the first shaft portion 111a of the valve head portion 110 and the part corresponding to the step portion 111c of the valve head portion 110 in the semi-finished product 300 shown in Figure 3(1), increasing the thickness (hereinafter referred to as thickening), and stretching them in the axial direction to form a semi-finished first shaft portion 321a, a semi-finished step portion 321c, and a stepped semi-finished hollow portion 325. Furthermore, the semi-finished product 330 shown in Figure 3 (3) is formed by further reducing and thickening the inner and outer diameters of the semi-finished first shaft portion 321a and semi-finished step portion 321c of the semi-finished product 320 in the previous process, and extending them in the axial direction to form the semi-finished first shaft portion 331a, semi-finished step portion 331c, and stepped semi-finished hollow portion 335. In addition, the valve head portion 110 shown in Figure 3 (4) is formed by further reducing the inner diameter and outer diameter of the semi-finished first shank portion 331a and semi-finished step portion 331c of the semi-finished product 330 in the previous process, thickening them, and extending them in the axial direction to form the first shank portion 111a, step portion 111c, and stepped hollow portion 115.

[0036] As a result, the thickness t3 of the first shaft portion 111a and the thickness t2 of the stepped portion 111c can be made thicker than the thickness t1 of the second shaft portion 111b of the valve head portion 110.

[0037] This improves the strength of the step portion 111c where the maximum bending stress occurs, and suppresses deterioration and damage of the engine valve 100.

[0038] 3(2) and 3(3), the semi-finished second shank portions 321b and 331b and the umbrella portions 323 and 333 are not subject to molding, and therefore the shapes of each portion are maintained. Therefore, the outer diameter ΦD and inner diameter Φd of the cylindrical portion 301, the semi-finished second shank portions 321b and 331b, and the second shank portion 111b, and the shapes of the umbrella portions 303, 323, 333, and the umbrella portion 113 are the same.

[0039] (Second embodiment) An engine valve 200 according to a second embodiment will be described with reference to FIGS. The engine valve 200 of this embodiment differs from the engine valve 100 of the first embodiment in the shape and processing method of the valve head portion 210, but the other components (shaft end member 120, coolant, etc., and heat insulating coating) are common, so a description of the common components will be omitted. The orientation of the hollow engine valve 200 of this embodiment will be described based on the orientation of the engine valve 200 (valve head portion 210) in Figure 4 (for example, the tip side (shaft end member 120 side) of the stem portion 211 is up, and the base side (head portion 213 side) of the stem portion 211 is down).

[0040] As shown in FIG. 4, the valve head portion 210 comprises a rod-shaped shaft portion (main shaft portion) 211 and an umbrella portion 213 that is provided continuously with the lower end of the shaft portion 211 and expands concentrically downward in an umbrella-like shape.

[0041] A flat umbrella front surface 213a is provided on the lower end surface of the umbrella portion 213, and an umbrella-shaped umbrella back surface 213b is provided on the upper surface. When the engine valve 200 is installed in a port of the engine cylinder head, the engine valve 200 is positioned so that the umbrella front surface 213a faces the combustion chamber of the engine and the umbrella back surface 213b faces the port side.

[0042] As shown in Figure 4, a neck 214 is formed at the bottom of the shaft 211, continuing from the top of the umbrella back surface 213b and having a larger outer diameter than the shaft 211. A tapered step 214a that narrows in diameter upward is provided between the neck 214 and the shaft 211 without the neck 214, in order to connect the two components 211, 214, which have different outer diameters.

[0043] The thickness t5 (for example, 1.8 mm) of the neck portion 214 is thicker than the thickness t4 (for example, 1.6 mm) of the shaft portion 211 (t4 <t5)。

[0044] By providing the thick neck portion 214 in the engine valve 200 in this way, the strength of the neck portion, where the temperature rises most, can be improved, and deterioration and damage of the engine valve 200 can be suppressed.

[0045] The interior of the valve head portion 210 is provided with a hollow portion 215 that is open at the top and extends from the stem portion 211 to the head portion 213. The hollow portion 215 has a bottom, and the hollow portion 215 of the stem portion 211 (including the neck portion 214) has a constant inner diameter Φd2 (a specific diameter, for example, Φ3 mm). The hollow portion 215 of the head portion 213 expands in diameter downward (toward the bottom), with the inner diameter Φd (for example, Φ10 mm) of the bottom portion 215a being the largest diameter within the hollow portion 215.

[0046] This ensures a sufficient volume for the hollow portion 215 of the umbrella portion 213, allowing a certain amount of getter material (e.g., titanium powder) or coolant (e.g., metallic sodium) to be sealed in the hollow portion 215. Furthermore, since there are no steps or the like in the hollow portion 215 of the shaft portion 211, the coolant can move smoothly in the hollow portion 215, and the cooling efficiency due to the shaking effect of the engine valve 200 can be improved.

[0047] (Method of manufacturing the valve head portion 210 of the engine valve 200) The molding process for the valve head portion 210 in this embodiment consists of a first step (see Figure 5) of molding a semi-finished product 400 from a solid round bar 10, and a second step (see Figure 6) of molding the valve head portion 210 from the semi-finished product 400.

[0048] The first step shown in Fig. 5 is performed in the same procedure as the first step in the first embodiment, and therefore a detailed description thereof will be omitted. Also, the solid round bar 10 shown in Fig. 5(1) and the squeezed solid bar 20 shown in Fig. 5(2) have the same shapes as those in the first embodiment, and therefore a description thereof will be omitted.

[0049] The umbrella-shaped solid rod 40 shown in Figure 5(3) is obtained by forging the squeezed solid rod 20 shown in Figure 5(2) to form an umbrella-shaped portion 43 by expanding the diameter of the head portion 23, and by shortening and expanding the diameter of the semi-finished shaft portion 21 in the axial direction to form a solid shaft 41. The umbrella-shaped portion 43 (base end) of the solid shaft 41 is provided with a neck tapered portion 44 whose diameter gradually decreases from the umbrella portion 43 toward the solid shaft 41 (tip end). The neck tapered portion 44 extends a distance L (e.g., 17 mm, approximately 1 / 3 of the total length R) from the umbrella surface 43a of the umbrella portion 43 with respect to the total length R (e.g., 48 mm) of the umbrella-shaped solid rod 40, forming an exponentially inclined surface with a taper angle α° (e.g., 3°). As a result, the thickness of the neck tapered portion 44 gradually increases toward the base end.

[0050] Furthermore, the semi-finished product 400 shown in Fig. 5(4) is obtained by drilling a cylindrical hole 405 having an inner diameter Φd in a solid shaft 41 obtained by turning the umbrella-type solid rod 40 shown in Fig. 5(3) upside down, thereby forming a tubular portion 401. Furthermore, since the semi-finished product 400 has the same outer shape as the umbrella-type solid rod 40, it is provided with a neck tapered portion 404 having the same shape as the neck tapered portion 44.

[0051] (2nd process) 6, in the second step, the diameter of the tubular portion 401 is reduced stepwise by cold forging using a plurality of dies 61, 62, and 63 (hereinafter collectively referred to as dies 61 to 63) to form the valve head portion 210. The number (types) of dies may be increased or decreased as appropriate depending on the number of steps, etc.

[0052] Each of the dies 61 to 63 has a forming hole 60 that penetrates vertically. The forming hole 60 has a reduced diameter portion 60a with a constant inner diameter and a tapered portion 60b that expands in diameter downward from the lower end of the reduced diameter portion 60a. Depending on the type of die, the reduced diameter portion 60a reduces the diameter of the tubular portion 401 and the neck tapered portion 404 of the semifinished product 400, thereby enabling the formation of the stem portion 211 and neck portion 214 of the valve head portion 210. The tapered portion 60b is capable of forming a portion of the semifinished neck portion 414 of the semifinished product 410 shown in Figure 6(2) (described later) and a step portion 214a of the valve head portion 210 shown in Figure 6(3). The dies 61 to 63 are arranged in accordance with the progress of the second step, and the diameter relationship of each forming hole 60 (reduced diameter portion 60a and tapered portion 60b) is die 61 > die 62 > die 63.

[0053] In the second step, a die 61 (which becomes a die 62 after forging) shown in Fig. 6(1) reciprocates from above the semifinished product 400, with a first position C1 of the semifinished product 400 (semifinished product 410) as a turning point, thereby forming the semifinished product 410 shown in Fig. 6(2) (hereinafter referred to as the first forming), and further, a die 63 reciprocates with a second position C2 above the first position C1 of the semifinished product 410 as a turning point, thereby forming the valve head portion 210 shown in Fig. 6(3) (hereinafter referred to as the second forming). Note that the second position C2 can be changed as appropriate depending on the specifications of the engine valve.

[0054] Specifically, in the first molding, the die 61 and the die 62 are used to gradually reduce the diameter and thicken the portion corresponding to the stem portion 211 of the valve head portion 210 in the semi-finished product 400 shown in Figure 6 (1) and the portion corresponding to the neck portion 214 of the valve head portion 210 (inner diameter, outer diameter), and stretch them in the axial direction to form a semi-finished stem portion 411 with an inner diameter Φd1 and a semi-finished neck portion 414 with an inner diameter Φd2, thereby forming the semi-finished product 410.

[0055] At this forming stage, semi-finished neck portion 414 is thicker than semi-finished shank portion 411 due to the thickness of neck tapered portion 404 of semi-finished product 400. Furthermore, the outer diameters of semi-finished shank portion 411 and semi-finished neck portion 414 are formed by die 62 to be the same up to the vicinity of first position C1 (the movement range of reduced diameter portion 60a in die 62), but the inner diameter Φd2 of semi-finished neck portion 414 is formed to be smaller than the inner diameter Φd1 of semi-finished shank portion 411 due to inwardly constricted portion 415a.

[0056] That is, in the first forming, cold forging is performed on the cylindrical portion 401 until the inside diameter of the semi-finished neck portion 414 becomes Φd2.

[0057] Next, in the second molding, the semi-finished shaft portion 411 (inner diameter, outer diameter) above the semi-finished neck portion 414 of the semi-finished product 410 shown in Figure 6 (2) is further reduced in diameter and thickened using a die 63, and is stretched in the axial direction to form the shaft portion 211 and neck portion 214 with an inner diameter of Φd2, and the step portion 214a.

[0058] That is, in the second forming, cold forging is performed on the semifinished shaft portion 411 until the inner diameter of the entire shaft portion 211 becomes Φd2. Note that in the second step, the outer shape of the umbrella-shaped portion 403 of the semifinished product 400 and the inner diameter Φd of the cylindrical hole 405 are maintained by the outer shape of the umbrella portion 213 of the valve head portion 210 and the inner diameter of the bottom 215a of the hollow portion 215, respectively.

[0059] As a result, in the valve head portion 210 of this embodiment, by making the thickness of the neck portion 214 thicker than the thickness of the stem portion 211, the strength of the neck portion, where the temperature rises the most, can be improved, and deterioration and damage to the engine valve 200 can be suppressed.

[0060] Furthermore, by gradually expanding the diameter of the hollow portion 215 formed from the neck portion 214 to the umbrella portion 213 toward the bottom portion 215a where the inner diameter Φd is maintained, the capacity of the hollow portion 215 can be secured, thereby making it possible to seal in a certain amount of getter material (e.g., titanium powder) or coolant (e.g., metallic sodium).

[0061] Furthermore, by making the hollow portion 215 formed from the shaft portion 211 to the neck portion 214 have a constant inner diameter Φd2, the coolant moves smoothly within the hollow portion 215 when the engine is operating, thereby improving the cooling efficiency due to the shaking effect of the engine valve 200. [Explanation of symbols]

[0062] K Dice P Punch S molding part 10 Solid round bar 20 Pressed solid bar 21 semi-finished shaft portion 23 head portion 30 Solid rod with umbrella 31 Solid shaft 33 Half-finished umbrella section 40 Solid rod with umbrella 41 Solid shaft 43 Umbrella-shaped portion 44 Tapered neck portion 50 Molding hole 50a Reduced diameter part 50b Tapered portion 51, 52, 53 Dies 60 Molding hole 60a Reduced diameter part 60b Tapered portion 61, 62, 63 Dies 100 hollow engine valve 110 valve head portion 111 Shaft part 111a 1st shaft part 111b second shaft portion 111c step portion 113 Umbrella part 115 Hollow part 120 Shaft end member 210 Valve head part 211 Shaft part 213 Umbrella part 213a Umbrella surface 213b Back of umbrella 214 Neck 215 Hollow part 300 Semi-finished product 301 Cylindrical part 303 Umbrella-shaped part 305 Cylindrical hole 320 Semi-finished product 321a Semi-finished first shaft part 321b Semi-finished second shaft part 321c Semi-finished step part 323 Semi-finished umbrella part 325 Semi-finished hollow part 330 Semi-finished product 331a Semi-finished first shaft part 331b Semi-finished second shaft portion 331c Semi-finished step portion 333 Semi-finished umbrella part 335 Semi-finished hollow part 400 Semi-finished product 401 Cylindrical part 403 Umbrella-shaped portion 404 Tapered neck portion 405 Cylindrical hole 410 Semi-finished product 411 Semi-finished shaft part

Claims

1. A hollow engine valve is formed integrally from a stem portion to an umbrella portion that expands in diameter like an umbrella at a base end of the stem portion, the umbrella portion including an umbrella surface that is free of joints and / or fastenings, and a coolant is sealed in at least a hollow portion provided inside the stem portion, the valve head portion has the stem portion on the tip side and a neck portion that is continuous with the head portion and has an outer diameter larger than that of the stem portion, The thickness of the neck portion is greater than the thickness of the shaft portion, A hollow engine valve characterized in that the hollow portion has a constant inner diameter at least over the stem portion and the neck portion, and the hollow portion of the head portion expands in diameter toward the bottom portion.

2. A method for manufacturing a hollow engine valve comprising: a stem portion; an umbrella portion that expands in diameter like an umbrella at a base end of the stem portion; a neck portion that is continuous with the umbrella portion on the base end side of the stem portion and has an outer diameter larger than that of the stem portion; and a hollow portion that is provided inside at least the stem portion and has a predetermined specific diameter, The method includes a first step of forging a material made of special steel and forming a semi-finished product having a cylindrical tubular portion with an opening at the tip and an umbrella-shaped portion that expands in diameter like an umbrella at the base end of the tubular portion by forging and drilling; and a second step of forming the shaft portion and the neck portion by reducing the diameter of the tubular portion by drawing. In the first step, a neck tapered portion is formed on the base end side of the cylindrical portion, the neck tapered portion being thicker than the cylindrical portion and having a diameter that exponentially decreases toward the tip end, a second molding step of reducing the outer diameter of the cylindrical portion including the tapered neck portion until the inner diameter of the tapered neck portion reaches the specific diameter to form a semi-finished neck portion; and a second molding step of reducing the outer diameter of the cylindrical portion distal to the semi-finished neck portion until the inner diameter of the cylindrical portion reaches the specific diameter, thereby forming the reduced diameter portion as the stem portion and the non-reduced diameter portion as the neck portion.

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