Hollow engine valve and its manufacturing method

Abstract

Provided is a hollow engine valve that increases the strength of a shaft part.　A hollow engine valve 100 that includes a shaft part 111, an umbrella part 113 that spreads like an umbrella at a base end of the shaft part 111, and a cooling material that is sealed inside a hollow part 115 that is provided inside at least the shaft part 111. The shaft part 111 has a first shaft part 111a that is on a tip end side, a second shaft part 111b that is on the base end side and has a larger outer diameter than the first shaft part 111a, and a step part 111c that is formed as a result of the difference in the outer diameters of the first shaft part 111a and the second shaft part 111b. The thickness t2 of the step part 111c is greater than the thickness t1 of the second shaft part 111b.

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 used to introduce intake gas into the combustion chamber of engines of automobiles, ships, etc. and expel 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] JP 2017-190759 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, as CO2 emission regulations become stricter and combustion temperatures rise, there are concerns that the neck temperature of these hollow engine valves will rise and they will lack strength.

[0005] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a hollow engine valve having an improved strength of a stem portion, and a manufacturing method thereof. [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 into an umbrella shape at a 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 on a tip side, a second shaft portion on a base end side having 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 step portion has a thickness greater than that of the second shaft portion.

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

[0008] (2) A second aspect of the present invention is a hollow engine valve having a shaft portion and an umbrella portion that expands in an umbrella shape at a 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 main shaft portion at a tip side and a neck portion that is continuous with the umbrella portion and has an outer diameter larger than that of the main shaft portion, the neck portion has a thickness greater than that of the main shaft portion, and the hollow portion is provided with a constant inner diameter at least over the main shaft portion and the neck portion.

[0009] According to the above configuration (2), the strength of the neck portion can be improved, and the movement of the coolant inside the hollow portion can be made smoother.

[0010] (3) A third aspect of the present invention is a manufacturing method for a hollow engine valve including a shaft portion having a first shaft portion and a second shaft portion provided continuously with the first shaft portion and having an outer diameter larger than that of the first shaft portion, an umbrella portion having an umbrella shape at one end of the second shaft portion, and a hollow portion at least inside the shaft portion, the manufacturing method including a first step of forming a semi-finished product having a cylindrical tubular portion having the same diameter as the outer diameter of the second shaft portion and an umbrella portion having the same shape as the umbrella portion at one end of the cylindrical portion by forging and drilling a special steel material; 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 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 is 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 first shaft portion and the step portion are thicker than the thickness of the second shaft portion.

[0011] According to the above configuration (3), a hollow engine valve having a stem portion with increased strength can be manufactured.

[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 an umbrella shape at a base end of the stem portion, a neck portion connected 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 forming a semi-finished product including a cylindrical tubular portion having an opening at a tip end and an umbrella portion expanding in an umbrella shape at a base end of the tubular portion by forging and drilling a special steel material; and a second step of forming a neck portion, wherein in the first step, a neck tapered portion that is thicker than the wall thickness of the tubular portion and exponentially reduces in diameter toward the tip side is formed on the base end side of the tubular portion, and the second step includes a first molding step of reducing the outer diameter of the tubular portion including the neck tapered portion until the inner diameter of the neck tapered portion becomes the specific diameter to form a semi-finished neck portion, and a second molding step of reducing the outer diameter of the tubular portion on the tip side of the semi-finished neck until the inner diameter of the tubular portion becomes 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 can move smoothly within the hollow portion. Effect of the Invention

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

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

[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) A first embodiment will be described with reference to Figures 1 to 3. Note that the direction of the hollow engine valve 100 in this embodiment will be described based on the direction of the engine valve 100 (valve umbrella portion 110) in Figure 1 (for example, the tip side (shaft end member 120 side) of the shaft portion 111 is up, and the base side (umbrella portion 113 side) of the shaft portion 111 is down).

[0018] (Hollow Engine Valve 100) A hollow engine valve (hereinafter simply referred to as engine valve) 100 is a valve body provided in a cylinder head of an engine (not shown) for an automobile or the like, and disposed inside an intake port and an exhaust port communicating with a combustion chamber, and is capable of opening and closing the intake port and exhaust port by moving vertically when the engine is in operation. The engine valve 100 is capable of supplying intake gas from the intake port into the combustion chamber by opening the intake port, and is capable of discharging exhaust gas from the combustion chamber to the outside of the combustion chamber by opening the exhaust port.

[0019] As shown in FIG. 1, an 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 shaft portion 111 and an umbrella portion 113 that is provided continuously with the lower end portion of the shaft portion 111 and that 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. Between the first shaft portion 111a and the second shaft portion 111b, a tapered step portion 111c is provided which gradually reduces in diameter toward the top in order to connect the two shaft portions 111a, 111b which have different outer diameters.

[0022] The shaft portion 111 of the valve head portion 110 has a bottomed hollow portion 115 that is open at the top. The hollow portion 115, i.e., the inner shape of the valve head portion 110, is approximately 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 at the stepped portion 111c (the inner shape of the stepped portion 111c) is tapered so that the diameter gradually decreases 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 seats 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 charged 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 to close the opening of the shaft portion 111. This seals the hollow portion 115 and seals the coolant, etc. within the hollow portion 115. As a result, the shaft end member 120 becomes integrated (inseparable) with the shaft portion 111 to form the shaft portion 111, completing the engine valve 100 in which the coolant, etc. is sealed.

[0026] If necessary, all or part of the engine valve 100 (all or part of the umbrella portion 113, and all or part of the shaft 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 process of forming the valve head portion 110 is roughly divided into a first process (see FIG. 2) of forming a semi-finished product 300 from the solid round bar 10, and a second process (see FIG. 3) of forming 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 of the shaft portion 111 in the valve head portion 110, a cylindrical hole 305 before processing of the hollow portion 115 in the valve head portion 110, and an umbrella-shaped portion 303 before processing of the umbrella portion 113 in the valve head portion 110.

[0029] The tubular 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 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 solid round bar 10 made of, for example, a cylindrical special steel as shown in Fig. 2(1) is squeezed to form an squeezed solid bar 20 by providing a semi-finished shaft portion 21, which is a portion corresponding to a shaft portion 111 of an engine valve 100 that is reduced in diameter, and a head portion 23 having an outer diameter larger than that of the semi-finished shaft portion 21, as shown in Fig. 2(2). In addition, by forging the squeezed solid bar 20, an umbrella-shaped portion 33 is formed by expanding the diameter of the head portion 23 of the squeezed solid bar 20 as shown in Fig. 2(3), and an umbrella-equipped solid bar 30 is formed by shortening the semi-finished shaft portion 21 in the axial direction and providing a solid shaft 31 with an expanded diameter. In the squeezing and forging steps in the first step, the work is loaded into a die K having a downwardly concave forming portion S, and pressed from above by a press device (not shown) having a punch P. 2(3) is turned upside down to form a solid shaft 31, and a bottomed cylindrical hole 305 is drilled in the axial direction with, for example, a drill M to provide a tubular portion 301, as shown in Fig. 2(4), to form a semifinished product 300. The shape of the umbrella portion 303 of the semifinished product 300 is the same as the umbrella portion 33 of the umbrella 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, and the cylindrical hole 305 may be provided 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 stand up by drawing, instead of by drilling a hole or the like.

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

[0033] The dies 51-53 each have a forming hole 50 that penetrates from top to bottom. The forming hole 50 has a reduced diameter section 50a having a constant inner diameter, and a tapered section 50b that expands in diameter downward from the lower end of the reduced diameter section 50a. The reduced diameter section 50a reduces the diameter of the tubular section 301 of the semifinished product 300 to form the first shaft section 111a of the valve head section 110, and the tapered section 50b is capable of forming the step section 111c of the valve head section 110. The dies 51 to 53 are arranged in the second step according to the progress of the 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 to form the semifinished product 320 shown in Fig. 3(2), and then the reciprocating motion of the die 52 forms the semifinished product 330 shown in Fig. 3(3), and 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 portion corresponding to the first shaft portion 111a of the valve head portion 110 and the portion corresponding to the step portion 111c of the valve head portion 110 in the semi-finished product 300 shown in Figure 3 (1) and 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. Moreover, the semi-finished product 330 shown in FIG. 3(3) is obtained by further reducing and thickening the inner and outer diameters of the semi-finished first shaft portion 321a and the semi-finished step portion 321c of the semi-finished product 320 in the previous process, and by extending them in the axial direction to form the semi-finished first shaft portion 331a, the semi-finished step portion 331c, and the stepped semi-finished hollow portion 335. In addition, the valve head portion 110 shown in Figure 3 (4) is formed by further reducing and thickening the inner and outer diameters of the semi-finished first shaft portion 331a and the semi-finished step portion 331c of the semi-finished product 330 in the previous process, and by extending them in the axial direction to form the first shaft portion 111a, the step portion 111c, and the 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 makes it possible to improve the strength of the step portion 111c where the maximum bending stress occurs, and to suppress deterioration and damage of the engine valve 100.

[0038] On the other hand, in the second step, the semi-finished second shaft portions 321b, 331b and the umbrella portions 323, 333 in the semi-finished products 320, 330 shown in Figures 3(2) and 3(3) 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 shaft portions 321b, 331b and the second shaft 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 to both, so a description of the common components will be omitted. The direction of the hollow engine valve 200 of this embodiment will be described based on the direction of the engine valve 200 (valve head portion 210) in Fig. 4 (for example, the tip side (shaft end member 120 side) of the shaft portion 211 is up, and the base end side (umbrella portion 213 side) of the shaft portion 211 is down).

[0040] As shown in FIG. 4, the valve head portion 210 includes a rod-shaped shaft portion (main shaft portion) 211 and an umbrella portion 213 that is provided continuously with the lower end portion of the shaft portion 211 and expands concentrically downward into an umbrella 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 provided in a port of a cylinder head of the engine, the engine valve 200 is arranged so that the umbrella front surface 213a faces the combustion chamber side of the engine and the umbrella back surface 213b faces the port side.

[0042] As shown in Fig. 4, a neck 214 is formed at the lower part of shaft 211, continuing from the upper part of umbrella back surface 213b, and has an outer diameter larger than shaft 211. A tapered step 214a that narrows toward the top is provided between neck 214 and shaft 211 where neck 214 is not provided, 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 manner, 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 inside of the valve head portion 210 is provided with a hollow portion 215 that is open at the top and extends from the shaft portion 211 to the head portion 213. The hollow portion 215 has a bottom, and the hollow portion 215 of the shaft 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 (to the bottom), and the inner diameter Φd (for example, φ10 mm) of the bottom portion 215a is the largest diameter in the hollow portion 215.

[0046] This ensures a sufficient volume for the hollow portion 215 of the umbrella portion 213, and allows a certain amount of getter material (e.g., titanium powder) or coolant (e.g., metallic sodium) to be enclosed 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 movement of the coolant in the hollow portion 215 can be made smoother, 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 process for forming the valve head portion 210 in this embodiment includes a first process (see FIG. 5) of forming a semifinished product 400 from the solid round bar 10, and a second process (see FIG. 6) of forming the valve head portion 210 from the semifinished 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. In addition, 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 solid rod 40 with an umbrella shown in Fig. 5 (3) is formed by forging the pressed solid rod 20 shown in Fig. 5 (2) to expand the diameter of the head portion 23 to provide an umbrella-shaped portion 43, and by shortening the semi-finished shaft portion 21 in the axial direction and expanding the diameter to provide a solid shaft 41. The solid shaft 41 is provided with a neck tapered portion 44 on the umbrella portion 43 (base end) side, which gradually reduces in diameter from the umbrella portion 43 toward the solid shaft 41 (tip). In this case, the neck tapered portion 44 extends from the umbrella surface 43a of the umbrella portion 43 by a distance L (e.g., 17 mm, about 1 / 3 of the total length R) with respect to the total length R (e.g., 48 mm) of the solid rod 40 with an umbrella, forming an exponentially inclined surface with a taper angle α° (e.g., 3°). As a result, the neck tapered portion 44 has a gradually increasing wall thickness toward the base end.

[0050] Furthermore, the semi-finished product 400 shown in Fig. 5(4) is produced by drilling a cylindrical hole 405 having an inner diameter Φd in a solid shaft 41 obtained by turning the umbrella solid rod 40 shown in Fig. 5(3) upside down, thereby forming a tubular portion 401. Since the semi-finished product 400 has the same outer shape as the umbrella 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, a cold forging process is performed using a plurality of dies 61, 62, and 63 (hereinafter collectively referred to as dies 61 to 63) to reduce the diameter of the tubular portion 401 stepwise to form the valve head portion 210. The number (types) of dies may be appropriately increased or decreased depending on the number of steps, etc.

[0052] The dies 61 to 63 each have a forming hole 60 that penetrates from top to bottom. The forming hole 60 has a reduced diameter section 60a having a constant inner diameter and a tapered section 60b that expands in diameter downward from the lower end of the reduced diameter section 60a. The reduced diameter section 60a can form the shaft section 211 and neck section 214 of the valve head section 210 by reducing the diameter of the tubular section 401 and the neck tapered section 404 of the semifinished product 400 depending on the type of die, and the tapered section 60b can form a part of the semifinished neck section 414 of the semifinished product 410 shown in Fig. 6(2) described later and the step section 214a of the valve head section 210 shown in Fig. 6(3). The dies 61 to 63 are arranged in the second step according to the progress of the 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 the die 61 is forged) 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 a semifinished product 410 shown in Fig. 6(2) (hereinafter referred to as 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 a valve head portion 210 shown in Fig. 6(3) (hereinafter referred to as second forming). The second position C2 can be appropriately changed depending on the specifications of the engine valve.

[0054] Specifically, in the first forming, the portion corresponding to the shaft 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) are gradually reduced in diameter and thickened using dies 61 and 62, and are stretched in the axial direction to form the semi-finished shaft portion 411 having an inner diameter Φd1 and the semi-finished neck portion 414 having an inner diameter Φd2, thereby forming the semi-finished product 410.

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

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

[0057] Next, in the second forming, 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 by 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 semi-finished 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 semi-finished product 400 and the inner diameter Φd of the cylindrical hole 405 are maintained in the outer shape of the umbrella portion 213 of the valve umbrella portion 210 and the inner diameter of the bottom portion 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 shaft 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 hollow portion 215 formed from neck portion 214 to umbrella portion 213 toward bottom portion 215a where the inner diameter Φd is maintained, the capacity of hollow portion 215 can be secured, making it possible to seal in a certain amount of getter material (e.g., titanium powder, etc.) or coolant (e.g., metallic sodium).

[0061] In addition, by making the hollow portion 215 molded 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, and the cooling efficiency due to the shaking effect of the engine valve 200 can be improved. [Explanation of symbols]

[0062] K Dice P Punch S molding section 10 Solid round bar 20 Pressed solid bar 21 Semi-finished shaft section 23 Head section 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 Neck tapered 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 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 Neck tapered portion 405 Cylindrical bore 410 Semi-finished product 411 Semi-finished shaft part

Claims

1. A hollow engine valve has a shaft portion and an umbrella portion that expands in diameter like an umbrella at a base end of the shaft portion, the hollow portion being filled with a coolant, the hollow portion being provided inside the shaft portion and including a first shaft portion having a hollow portion and a second shaft portion having a hollow portion, The shaft portion has a first shaft portion having a reduced diameter on a tip end side, a second shaft portion having a non-reduced diameter on a base end side having an outer diameter larger than that of the first shaft portion, and a step portion having a hollow portion formed by the difference in outer diameter between the first shaft portion and the second shaft portion, A hollow engine valve, wherein the thickness of each of the first shaft portion and the step portion is greater than the thickness of the second shaft portion.

2. A method for manufacturing a hollow engine valve including a shaft portion having a first shaft portion and a second shaft portion provided continuously with the first shaft portion and having an outer diameter larger than that of the first shaft portion, an umbrella portion having an umbrella-like expanded diameter at one end of the second shaft portion, and a hollow portion at least inside the shaft portion, The method includes a first step of forming a semi-finished product from a special steel material by forging and drilling, the semi-finished product having a cylindrical tubular portion having the same diameter as the outer diameter of the second shaft portion, and an umbrella portion having the same shape as the umbrella portion at one end of the tubular portion; and a second step of forming the shaft portion by reducing the diameter of the tubular portion in the semi-finished product by drawing. 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 a reduced portion is defined as the first shaft portion, a non-reduced portion is defined as the second shaft portion, and a portion that is reduced in diameter together with the first shaft portion and that is formed by a difference in outer diameter between the first shaft portion and the second shaft portion is defined as a step portion, A method for manufacturing a hollow engine valve, wherein the thickness of the reduced diameter first shaft portion and the thickness of the step portion are greater than the thickness of the second shaft portion.

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