Method for manufacturing refrigerant-filled hollow poppet valve for engine

Abstract

Provided is a method for manufacturing a refrigerant-filled hollow poppet valve for an engine to be used mainly at low-to-medium rotation, whereby sufficient sealing and the like of a hollow portion can be ensured even when the refrigerant is loaded at the time of manufacture. In a method for manufacturing a refrigerant-filled hollow poppet valve (1) for an engine, the method involving a refrigerant loading step for loading a refrigerant (8) into a hollow portion (6) on the inner side of a metal stem-umbrella intermediate (2) from an opening (3b) in a base end part (3a) and a joining step for joining a metal stem end member (15) to the base end part (3a), a plug press-fitting step for press-fitting a metal plug (9) having a circumferential outer groove (10) in an outer circumferential wall thereof into the hollow portion (6) through the opening (3b) in the base end part (3a) is performed after the refrigerant loading step and before the joining step.

Description

Manufacturing method for engine refrigerant-filled hollow poppet valve

[0001] This technology relates to a manufacturing method for a hollow poppet valve for an engine that can ensure sufficient sealing performance in the hollow portion during manufacturing.

[0002] Generally, metallic sodium or the like is used in engine refrigerant-filled hollow poppet valves, as disclosed in Patent Document 1 below. Metallic sodium is sealed as a soft solid metal in the hollow portion of the poppet valve during the manufacturing process of the refrigerant-filled hollow poppet valve, which is carried out below its melting point, and liquefies when exposed to high temperatures in the combustion chamber as the hollow poppet valve opens and closes when the engine is running. The liquefied metallic sodium does not vaporize even at a certain high temperature, and flows between the inside of the stem and the inside of the head as the hollow poppet valve opens and closes, absorbing the heat received by the head in the combustion chamber and radiating it from the base end of the stem to the cylinder head.

[0003] However, in refrigerant-filled hollow poppet valves for large marine engines and other applications that operate at low speeds of around 500 to 2000 rpm, or for passenger car engines that operate at low speeds of around 2000 rpm during cruising and at a medium speed of around 5000 rpm during acceleration, if a refrigerant with low fluidity, such as metallic sodium, is used, the refrigerant may not flow sufficiently between the inside of the head portion and the stem portion during valve opening and closing, resulting in insufficient heat dissipation from the head portion of the valve to the cylinder head. For hollow poppet valves used in such environments, a refrigerant that evaporates at room temperature during the refrigerant charging process can be loaded, and heat dissipation from the head portion to the cylinder head can be achieved by utilizing heat exchange, which involves repeated evaporation of the refrigerant due to heating of the head portion as combustion occurs in the engine combustion chamber and liquefaction due to cooling at the stem end.

[0004] On the other hand, in a hollow poppet valve into which a refrigerant is charged, a refrigerant that evaporates at room temperature is charged into the hollow portion of a shaft umbrella intermediate product through an opening at the base end in a refrigerant charging process, and then in a joining process, the shaft end of the shaft umbrella intermediate product is joined to the base end to seal the opening, and before joining the shaft end to the shaft umbrella intermediate product, a metal lid is press-fitted into the opening to seal it in advance in order to prevent refrigerant from leaking from the hollow portion, and then the shaft end is joined.

[0005] WO2020 / 100185 publication

[0006] When a metal plug is press-fitted into the hollow portion of the umbrella intermediate part filled with a refrigerant, the outer wall of the plug may be scraped off with chips due to contact with the inner wall of the hollow portion of the umbrella intermediate part, resulting in damage marks being formed in the longitudinal direction of the umbrella intermediate part. If such damage marks are formed continuously to the base end of the plug, a gap will be formed between the base ends of the plug and the umbrella intermediate part, impairing the sealing of the hollow portion and causing the refrigerant to leak from the base end of the inner wall of the hollow portion of the umbrella intermediate part.

[0007] In the joining process, the shaft end is joined by friction resistance pressure welding to the base end of the umbrella intermediate piece and a metal plug that is press-fitted until it is flush with the base end. However, if the fit strength of the pressed-fit metal plug is insufficient, it will be pushed toward the umbrella portion by the shaft end during friction resistance pressure welding and positioned in a position that is shifted inward from the flush position, which could result in a deterioration in the sealing performance between the plug and the inner peripheral wall of the hollow portion of the umbrella intermediate piece, insufficient friction pressure welding between the plug and the shaft end, further reducing the sealing performance of the hollow portion, or narrowing the internal volume of the hollow portion filled with the refrigerant, causing variations in internal pressure.

[0008] In view of the above problems, the present application provides a method for manufacturing a refrigerant inlet poppet valve for engines used primarily at low to medium revolutions, which can ensure sufficient sealing properties, etc. in the hollow portion during manufacturing.

[0009] In a manufacturing method of a refrigerant-filled hollow poppet valve for an engine, which includes a refrigerant charging step of charging a refrigerant into a hollow portion inside a metal stem intermediate product through an opening at the base end, and a joining step of joining a metal stem end member to the base end, a plug press-fitting step of press-fitting a metal stem having a circumferential outer groove on its outer peripheral wall into the hollow portion through the opening at the base end is performed after the refrigerant charging step and before the joining step.

[0010] (Function) In the plug press-fitting process, when the metal plug is press-fitted into the hollow portion through the opening at the base end of the umbrella intermediate piece, shavings formed on the outer wall of the plug enter and remain in the circumferential outer groove of the outer wall of the plug, which is located closer to the umbrella portion than the base end of the plug, and do not further damage the outer wall of the plug, so that damage marks do not form all the way to the base end of the plug. Also, in the plug press-fitting process, a portion of the inner wall of the hollow portion of the umbrella intermediate piece into which the metal plug is press-fit elastically deforms toward the circumferential outer groove of the plug and bites into the circumferential outer groove, thereby preventing and holding the plug in the extension direction of the hollow portion.

[0011] In addition, in the method for manufacturing a refrigerant-filled hollow poppet valve for an engine, it is more preferable that the metal plug has a plurality of the circumferential outer grooves.

[0012] (Function) In the plug press-fitting process, when the metal plug is pressed into the hollow portion through the opening at the base end of the umbrella intermediate piece, even if the shavings formed on the outer wall of the plug do not enter and remain in the nearest circumferential outer groove of the multiple formed outer wall of the plug, they enter and remain in the next or subsequent circumferential outer groove, preventing further damage to the outer wall of the plug, and preventing damage marks from forming all the way to the base end of the plug. Also, in the plug press-fitting process, parts of the inner peripheral wall of the hollow portion of the umbrella intermediate piece into which the metal plug is pressed elastically deform toward the multiple circumferential outer grooves of the plug and bite into each circumferential outer groove, thereby preventing and holding the plug in the extension direction of the hollow portion.

[0013] In the method for manufacturing a refrigerant-filled hollow poppet valve for an engine, it is more preferable that the inner peripheral wall of the hollow portion has at least one circumferential inner groove.

[0014] (Function) In the plug press-fitting process, when the metal plug is press-fitted into the hollow portion through the opening at the base end of the umbrella intermediate piece, shavings formed on the outer peripheral wall of the plug enter and remain in either one or more circumferential inner grooves formed on the inner peripheral wall of the hollow portion of the umbrella intermediate piece or one or more circumferential outer grooves formed on the outer peripheral wall of the plug, preventing further damage to the outer peripheral wall of the plug and preventing damage marks from forming down to the base end of the plug. Also, in the plug press-fitting process, a portion of the inner peripheral wall of the hollow portion of the umbrella intermediate piece into which the metal plug is press-fit elastically deforms toward the one or more circumferential outer grooves of the plug, and a portion of the outer peripheral wall of the metal plug press-fitted into the inner peripheral wall of the hollow portion of the metal umbrella intermediate piece elastically deforms toward the one or more circumferential inner grooves of the inner peripheral wall, respectively, thereby preventing and holding the plug from moving in the extension direction of the hollow portion.

[0015] In addition, in a manufacturing method of a refrigerant-filled hollow poppet valve for an engine, which includes a refrigerant charging step of charging a refrigerant into a hollow portion inside a metal stem intermediate product through an opening at the base end, and a joining step of joining a metal stem end member to the base end, it is desirable to perform a plug press-fitting step of press-fitting a metal stem into the hollow portion having a circumferential inner groove on its inner wall through the opening at the base end after the refrigerant charging step and before the joining step.

[0016] (Function) In the plug press-fitting process, when the metal plug is press-fitted into the hollow portion through the opening at the base end of the umbrella intermediate piece, shavings formed on the outer wall of the plug enter and remain in the circumferential inner grooves of the inner peripheral wall, which are provided closer to the umbrella portion than the base end of the umbrella intermediate piece, and do not further damage the outer wall of the plug, so that damage marks do not form all the way to the base end of the plug. Also, in the plug press-fitting process, portions of the outer wall of the metal plug press-fitted into the inner peripheral wall of the hollow portion of the metal umbrella intermediate piece elastically deform toward the multiple circumferential inner grooves of the inner peripheral wall and bite into each circumferential inner groove, thereby preventing and holding the plug in the extension direction of the hollow portion.

[0017] In addition, in the method for manufacturing a refrigerant-filled hollow poppet valve for an engine, it is more preferable that the inner peripheral wall of the hollow portion has a plurality of the circumferential inner grooves.

[0018] (Function) In the plug press-fitting process, when the metal plug is press-fitted into the hollow portion through the opening at the base end of the umbrella intermediate piece, even if shavings formed on the outer wall of the plug do not enter and remain in the nearest one of the multiple circumferential inner grooves formed on the inner peripheral wall of the hollow portion of the umbrella intermediate piece, they enter and remain in the next or subsequent circumferential inner grooves, preventing further damage to the outer wall of the plug and preventing damage marks from forming all the way to the base end of the plug. Also, in the plug press-fitting process, a portion of the outer wall of the metal wire press-fitted into the hollow portion of the metal umbrella intermediate piece elastically deforms toward the multiple circumferential outer grooves on the inner peripheral wall and bites into the circumferential inner grooves, thereby preventing and holding the plug in the extension direction of the hollow portion.

[0019] In the method for manufacturing a refrigerant-filled hollow poppet valve for an engine, it is more preferable that the metal plug has at least one circumferential outer groove.

[0020] (Function) In the plug press-fitting process, when the metal plug is press-fitted into the hollow portion through the opening at the base end of the umbrella intermediate piece, shavings formed on the outer wall of the plug enter and remain in either one or more circumferential outer grooves formed on the outer wall of the plug or one or more circumferential inner grooves formed on the inner wall of the hollow portion of the umbrella intermediate piece, preventing further damage to the outer wall of the plug and preventing damage marks from forming down to the base end of the plug. Also, in the plug press-fitting process, a portion of the inner wall of the hollow portion of the umbrella intermediate piece into which the metal plug is press-fit elastically deforms toward the one or more circumferential outer grooves of the plug, and a portion of the outer wall of the metal plug press-fitted into the inner wall of the hollow portion of the metal umbrella intermediate piece elastically deforms toward the one or more circumferential inner grooves of the inner wall, respectively, thereby preventing and holding the plug from moving in the extension direction of the hollow portion.

[0021] According to the manufacturing method for an engine refrigerant-filled hollow poppet valve, when a metal plug is press-fitted into the hollow portion through the opening at the base end of the umbrella intermediate piece, shavings are formed on the outer peripheral wall of the plug. Even if the shavings cause damage to the outer peripheral wall of the plug, they remain in the circumferential outer groove formed on the outer peripheral wall of the plug, preventing continuous damage from the circumferential outer groove to the base end, thereby maintaining a tight seal of the hollow portion and preventing leakage of evaporated refrigerant or fluid refrigerant. Furthermore, when the plug is press-fitted into the opening at the base end of the umbrella intermediate piece, a portion of the inner peripheral wall of the hollow portion at the base end of the plug is wedged into the circumferential outer groove of the plug, so that the base end of the plug is positioned flush with the base end of the umbrella intermediate piece and is held immovable in the extension direction of the hollow portion. Therefore, when the shaft end member is joined to the base end of the umbrella intermediate piece in the joining process, the plug is sufficiently joined to the shaft end member, maintaining a tight seal of the hollow portion. Furthermore, the internal volume of the hollow portion does not change, so the internal pressure of the hollow portion is kept constant.

[0022] According to the manufacturing method for an engine refrigerant-filled hollow poppet valve, even if shavings formed on the outer peripheral wall of the poppet when the poppet is press-fitted into the hollow portion through the opening at the base end of the umbrella intermediate piece do not enter and remain in the nearest circumferential outer groove formed on the outer peripheral wall of the poppet and cause further damage, the shavings enter and remain in the next or subsequent circumferential outer groove, preventing the formation of continuous damage from the circumferential outer groove toward the base end, further improving the sealing of the hollow portion and preventing leakage of evaporated refrigerant or fluid refrigerant. Furthermore, the poppet press-fitted into the opening at the base end of the umbrella intermediate piece is further held immovable in the extension direction of the hollow portion by portions of the inner peripheral wall of the hollow portion of the umbrella intermediate piece biting into the multiple circumferential outer grooves of the poppet, thereby more sufficiently joining the poppet to the shaft end member in the joining process and maintaining the sealing of the hollow portion.

[0023] According to the manufacturing method of the engine refrigerant-filled hollow poppet valve, when the poppet is press-fitted into the hollow portion through the opening at the base end of the umbrella intermediate piece, shavings formed on the outer wall of the poppet enter and remain in either the circumferential outer groove on the outer wall of the poppet or the circumferential inner groove on the inner wall of the hollow portion of the umbrella intermediate piece. This prevents the formation of further continuous damage from the circumferential outer groove or circumferential inner groove where the shavings remain toward the base end, further improving the sealing of the hollow portion and preventing leakage of evaporated refrigerant or fluid refrigerant. Furthermore, the plug pressed into the opening at the base end of the umbrella intermediate piece is held immovable in the extension direction of the hollow piece because a portion of the inner wall of the hollow piece of the umbrella intermediate piece is wedged into one or more circumferential outer grooves of the plug, and a portion of the outer wall of the plug is wedged into one or more circumferential inner grooves of the inner wall of the hollow piece of the umbrella intermediate piece. This ensures a more sufficient joining between the plug and the shaft end member in the joining process, maintaining the airtightness of the hollow piece.

[0024] According to the manufacturing method for an engine refrigerant-filled hollow poppet valve, even if chips are formed on the outer peripheral wall of the plug when the plug is press-fitted into the hollow portion through the opening at the base end of the umbrella intermediate piece, the chips enter the circumferential inner groove formed on the inner peripheral wall of the hollow portion of the umbrella intermediate piece, preventing the formation of continuous damage from the circumferential inner groove to the base end side, thereby maintaining the sealability of the hollow portion and preventing leakage of evaporated refrigerant or fluid refrigerant. Furthermore, when the plug is press-fitted into the opening at the base end of the umbrella intermediate piece, a portion of the outer peripheral wall of the plug enters the circumferential inner groove on the inner peripheral wall of the hollow portion of the umbrella intermediate piece, so that the base end of the plug is positioned flush with the base end of the umbrella intermediate piece and is held immovable in the extension direction of the hollow portion. Therefore, when the shaft end member is joined to the base end of the umbrella intermediate piece in the joining process, the shaft end member is sufficiently joined to the shaft end member, maintaining the sealability of the hollow portion.

[0025] According to the manufacturing method for an engine refrigerant-filled hollow poppet valve, even if shavings formed on the outer peripheral wall of the poppet when the poppet is press-fitted into the hollow portion through the opening at the base end of the umbrella intermediate piece do not enter and remain in the nearest circumferential inner groove formed on the inner peripheral wall of the hollow portion of the umbrella intermediate piece and cause further damage, the shavings enter and remain in the next or subsequent circumferential inner groove, preventing continuous damage from the remaining circumferential inner groove toward the base end, thereby further improving the sealing of the hollow portion and preventing leakage of evaporated refrigerant or fluid refrigerant. Furthermore, the poppet press-fitted into the opening at the base end of the umbrella intermediate piece has portions of its outer peripheral wall engaging with the multiple circumferential inner grooves on the inner peripheral wall of the hollow portion of the umbrella intermediate piece, further preventing it from moving in the extension direction of the hollow portion. This more sufficiently bonds the poppet to the shaft end member in the joining process, maintaining the sealing of the hollow portion.

[0026] According to the manufacturing method of the engine refrigerant-filled hollow poppet valve, when the poppet is press-fitted into the hollow portion through the opening at the base end of the intermediate piece, shavings formed on the outer wall of the poppet enter and remain in one or more circumferential outer grooves on the outer wall of the poppet or one or more circumferential inner grooves on the inner wall of the hollow portion of the intermediate piece. This prevents the formation of continuous damage from the circumferential outer groove or circumferential inner groove where the shavings remain to the base end side, further improving the sealing performance of the hollow portion and preventing leakage of evaporated refrigerant or fluid refrigerant. Furthermore, the plug pressed into the opening at the base end of the umbrella intermediate piece is held immovable in the extension direction of the hollow piece because a portion of the inner peripheral wall of the hollow piece of the umbrella intermediate piece is embedded in one or more circumferential outer grooves of the plug, and a portion of the outer peripheral wall of the plug is embedded in one or more circumferential inner grooves of the inner peripheral wall of the hollow piece of the umbrella intermediate piece. This ensures a more sufficient joining between the plug and the shaft end member in the joining process, maintaining the airtightness of the hollow piece.

[0027] 1A is a cross-sectional view illustrating a manufacturing process of a first embodiment of a method for manufacturing a refrigerant-filled hollow poppet valve for an engine, in which (a) shows a refrigerant charging process for charging a refrigerant into a hollow portion of a cap intermediate product, (b) shows a plug press-fitting process for press-fitting a metal plug into the hollow portion through an opening at the base end of the cap intermediate product, (c) shows a joining process for joining a shaft end member to the cap-equipped cap intermediate product with the press-fit plug, and (d) shows the refrigerant-filled hollow poppet valve after the joining process. (a) is an explanatory cross-sectional view illustrating the plug press-fitting process in the first embodiment, in which (a) is an explanatory cross-sectional view illustrating the plug press-fitting process in chronological order from left to right, (b) is an enlarged cross-sectional view illustrating scratches formed on the outer wall of the plug after the plug press-fitting process, and (c) is an enlarged cross-sectional view illustrating a wedged portion of the cap intermediate product that has wedged into the circumferential outer groove of the plug due to elastic deformation after press-fitting. (a) An explanatory diagram of the plug press-fitting process in the second embodiment, (a) is an explanatory cross-sectional view illustrating the plug press-fitting process in chronological order from the left to the center and right, (b) is an enlarged cross-sectional view illustrating scratches formed on the outer wall of the plug after the plug press-fitting process, and (c) is an enlarged cross-sectional view illustrating multiple bite portions of the umbrella intermediate product that have been bitten into multiple circumferential outer grooves of the plug due to elastic deformation after press-fitting. (a) An explanatory diagram of the plug press-fitting process in the third embodiment, (a) is an explanatory cross-sectional view illustrating the plug press-fitting process in chronological order from the left to the center and right, (b) is an enlarged cross-sectional view illustrating scratches formed on the outer wall of the plug after the plug press-fitting process, and (c) is an enlarged cross-sectional view illustrating multiple bite portions of the umbrella intermediate product that have been bitten into multiple circumferential inner grooves of the hollow part of the umbrella intermediate product due to elastic deformation after press-fitting. (a) An explanatory diagram of the plug press-in process in the fourth embodiment. (a) is an explanatory cross-sectional view illustrating the plug press-in process in chronological order from the left figure to the center figure and the right figure. (b) is an enlarged cross-sectional view illustrating scratches formed on the outer wall of the plug after the plug press-in process. (c) is an enlarged cross-sectional view illustrating multiple engagement portions of the plug that have each been engaged in the circumferential inner grooves on the inner wall of the hollow portion of the shaft cap intermediate product due to elastic deformation after press-in.(a) An explanatory diagram of the plug press-in process in the fifth embodiment. (a) is an explanatory cross-sectional view illustrating the plug press-in process in chronological order from the left figure to the center figure and the right figure. (b) is an enlarged cross-sectional view illustrating scratches formed on the outer wall of the plug after the plug press-in process. (c) is an enlarged cross-sectional view illustrating the biting portion of the umbrella intermediate part that has bitten into the circumferential outer groove of the plug due to elastic deformation after press-in, and the biting portion that has bitten into the circumferential inner groove of the inner wall of the hollow part of the umbrella intermediate part.

[0028] A preferred first embodiment of the method for manufacturing a hollow poppet valve for an engine that is filled with refrigerant will be described with reference to Figures 1 and 2. In each of Figures 1 to 6, the head side of the intermediate shaft piece of the hollow poppet valve for an engine that is filled with refrigerant will be described as the leading end side, and the first shaft side will be described as the base end side.

[0029] The shaft cap intermediate piece 2 in Fig. 1(a) is formed by forging a metal round bar made of heat-resistant steel or the like having high heat resistance (SUH3 is one example, but is not limited to this) multiple times. The shaft cap intermediate piece 2 has a shank 3, a neck 4 that smoothly connects to the shank 3 at a continuation point 3c and has a concave arc-shaped waist when viewed from the front and side, and a cap 5 that includes the neck 4 and gradually increases in diameter from the shaft to the tip. A bottomed cylindrical hollow portion 6 with a constant inner diameter is provided at the center of the shaft cap intermediate piece 2 from the base end 3a of the shank 3 to the inside of the cap 5.

[0030] As shown in Figure 1(a), in a refrigerant charging process, a refrigerant 8 that evaporates at room temperature is charged into the hollow portion 6 of the cap intermediate product 2 through the opening 3b of the base end 3a using a refrigerant charging machine (not shown) under room temperature or other conditions. The refrigerant 8 is charged from the bottom 6a of the hollow portion 6 to the vicinity of the connecting point 3c. After the refrigerant 8 is charged, the hollow portion 6 is charged with an inert gas, for example, by placing the cap intermediate product 2 in an inert gas atmosphere, as necessary. In a plug press-fitting process shown in Figure 1(b), a metal plug is press-fitted into the hollow portion 6 through the opening 3b, sealing the hollow portion 6 of the cap intermediate product charged with the refrigerant and inert gas. Note that the metal plug is shown schematically in Figure 1, and the metal plug and the plug press-fitting process will be described in detail elsewhere. In the joining process shown in FIG. 1(c), the tip end of the shaft end member 15 is friction-welded to the base end portion 3a of the shaft cap intermediate part 2 after the press-fitting, thereby forming the refrigerant-filled hollow poppet valve shown in FIG. 1(d).

[0031] Next, the plug press-fitting process of a first embodiment of the manufacturing method for a refrigerant-filled hollow poppet valve will be described in detail with reference to Figures 2(a) to 2(c). The plug 9 used in the plug press-fitting process of the first embodiment is formed by cutting a metal round bar made of heat-resistant steel (such as, but not limited to, SUH3) with high heat resistance. The plug 9 is composed of a main body 9b and a tapered portion 9c that smoothly connects to the tip of the main body 9b. The main body 9b has a first main body portion 9b1 and a second main body portion 9b2 that connect to the base end of the tapered portion 9c, and a ring-shaped circumferential outer groove 10 that is recessed into the inside of the main body portion 9b and is formed continuously between the first and second main body portions.

[0032] As shown in the center diagram of Figure 2(a), the inner diameter d2 of the hollow portion 6 is slightly smaller than the outer diameter d1 of the first and second body portions 9b1 and 9b2 of the body portion 9b so that the main body portion 9b of the plug 9 can be press-fitted. The outer diameter of the tip of the tapered portion 9c is also smaller than the inner diameter d2. In the plug press-fitting process, the plug 9 is inserted with the tapered portion 9c pointing downward through the opening 3b with the base end 3a of the shaft cap intermediate product 2 facing upward, as shown in the left diagram of Figure 2(a). As shown in the center diagram of Figure 2(a), the tapered portion 9c inserted into the hollow portion 6 begins to scrape away part of the outer wall when it comes into contact with the opening periphery 3d of the base end 3a of the shaft portion 3, because the outer diameter d1 of the main body portion 9b is slightly larger than the inner diameter d2 of the hollow portion 6. This causes scraping 11 of the plug 9 to form at the contact point. As shown in the right diagram of Figure 2(a), the plug 9 is pressed into the main body 9b until the base end 9a of the plug is flush with the base end 3a of the shaft 3, while the shavings 11 are caught between the outer wall of the plug 9 and the inner wall of the hollow portion 6 of the shaft cap intermediate part 2.

[0033] 2(b) is an explanatory diagram assuming that the front of the plug 9 inside the hollow portion 6 is seen from the direction of arrow A (only the shaft portion 3 of the intermediate product 2 is shown in cross section), and during the plug press-fitting process, shavings 11 caught between the outer peripheral wall of the plug 9 and the inner peripheral wall of the hollow portion 6 form damage marks 14 on the outer peripheral wall of the plug 9 that continue from the contact position between the tapered portion 9c of the plug 9 and the opening peripheral edge portion 3d to the base end of the first main body portion 9b1 (the position of the tip end 10a of the outer peripheral groove 10), and enter the gap 13 between the outer peripheral groove 10 and a biting portion 12 described below. If the shavings 11 are cut off from the outer peripheral wall of the plug 9 when caught between the outer peripheral wall of the plug 9 and the inner peripheral wall of the hollow portion 6, they will remain in the gap 13 of the outer peripheral groove 10. The shavings 11 remaining in the gap 13 of the circumferential outer groove 10 will no longer form continuous damage marks on the outer wall of the second main body portion 9b2 from the base end 10b of the circumferential outer groove 10 to the base end 9a of the plug 9, so no gap is formed from the hollow portion 6 to the outside of the plug 9, and the plug 9 maintains the sealing properties of the hollow portion 6 of the shaft umbrella intermediate product 2 which contains the refrigerant 8 and inert gas.

[0034] 2(c), a biting portion 12 is formed on a part of the inner peripheral wall of the hollow portion 6 of the umbrella intermediate part 2, which protrudes and bites into the circumferential outer groove 10 of the outer peripheral wall of the plug 9 due to elastic deformation after the plug 9 is pressed in. During friction welding in the joining process shown in FIG. 1(c), the plug 9, which is pressed in so that the base end 3a of the shank 3 and the base end 9a are flush with each other, is pressed downward by the tip end 15a of the shaft end member 15, but the biting portion 12 on the inner peripheral wall of the hollow portion 6 firmly bites into the circumferential outer groove 10 of the plug 9, so that the plug 9 is positioned and fixed without shifting downward within the hollow portion 6. As a result, the airtightness of the hollow portion 6 of the umbrella intermediate part 2 is maintained, the internal volume of the hollow portion does not change, and the internal pressure is kept constant.

[0035] Next, a second preferred embodiment of the method for manufacturing a refrigerant-filled hollow poppet valve for an engine will be described with reference to Figure 3. The method for manufacturing a refrigerant-filled hollow poppet valve for an engine of the second embodiment uses the same intermediate shaft member 2, refrigerant 8, and shaft end member 15 as those used in the first embodiment, except that the shape of the plug 17 used in the plug press-fitting step is different from that of the plug 9 used in the first embodiment. Therefore, in the description of the second embodiment, a description of the common steps (refrigerant charging step, joining step) and means will be omitted and only the plug press-fitting step will be described.

[0036] The plug press-fitting process of the first embodiment of the method for manufacturing a medium-filled hollow poppet valve for an engine will be described in detail with reference to Figures 3(a) to 3(c). The plug press-fitting process is performed as shown in Figure 1(b) after the same refrigerant charging process as that performed in Figure 1(a) of the first embodiment. As shown in the left diagram of Figure 3(a), the plug 17 used in the plug press-fitting process of the second embodiment has two ring-shaped circumferential grooves on the outer circumferential wall of the body, which differs from the plug 9 of the first embodiment, which has only one circumferential groove, but has a common configuration with the plug 9.

[0037] 3(a) to 3(c) , the plug 17 is formed by machining a metal round bar made of heat-resistant steel (SUH3, for example, but not limited to) similar to the plug 9 shown in FIGS. 2(a) to 2(c) , and specifically has the following configuration: As shown in FIGS. 3(a) to 3(c), the plug 17 is composed of a main body portion 17b and a tapered portion 17c having a tapered shape. The main body portion 17b is composed of a first main body portion 17b1 smoothly continuing from the base end of the tapered portion 17c, a second main body portion 17b2, a third main body portion 17b3 provided at the base end 17a of the plug 17, a first outer circumferential groove 18 formed continuously between the first main body portion 17b1 and the second main body portion 17b2, and a second outer circumferential groove 19 formed continuously between the second main body portion 17b2 and the third main body portion 17b3. The first and second outer circumferential grooves 18, 19 are formed as two ring-shaped grooves recessed toward the center of the main body 17b. The number of outer circumferential grooves on the main body of the plug 17 is not limited to two, as long as there are multiple grooves.

[0038] As shown in the center diagram of Figure 3(a), the inner diameter d2 of the hollow portion 6 of the shaft portion 3 of the umbrella intermediate product 2 is slightly smaller than the outer diameter d1 common to the first to third main body portions 17b3-17b3 of the plug 17, and the outer diameter of the tip of the tapered portion 17c is smaller than the inner diameter d2. In the plug press-fitting process, the plug 17 is inserted from above the opening 3b of the umbrella intermediate product 2 with the tapered portion 17c facing downward, as shown in the left diagram of Figure 3(a). As shown in the center diagram of Figure 3(a), the tapered portion 17c inserted into the hollow portion 6 comes into contact with the opening peripheral edge portion 3d of the shaft portion 3, which begins to scrape away part of the outer peripheral wall, and shavings 20 of the plug 17 are formed at the contact site. As shown in the right diagram of Figure 3(a), the main body 17b of the plug 17 is pressed into place until the base end 17a of the plug 17 is flush with the base end 3a of the shaft 3, while the shavings 20 are trapped between the outer wall of the plug 17 and the inner wall of the hollow portion 6 of the shaft cap intermediate product 2.

[0039] 3(b) is an explanatory diagram assuming that the front of the plug 17 inside the hollow portion 6 is seen from the direction of arrow B (the cap intermediate product 2 is shown in cross section), and during the plug press-fitting process, shavings 20 caught between the outer peripheral wall of the plug 17 and the inner peripheral wall of the hollow portion 6 first form a damage mark 25 on the outer peripheral wall of the plug 17 that continues from the contact position with the tapered portion 17c of the plug 17 to the base end of the first main body portion 17b1 (the position of the tip end 18a of the first outer circumferential groove 18), and then enter a gap 23 between the first outer circumferential groove 18 and a biting portion 21 (described later). If the shavings 20 are cut off from the outer peripheral wall of the plug 17 when caught between the outer peripheral wall of the first main body portion 17b1 of the plug 17 and the inner peripheral wall of the hollow portion 6, they will remain in the gap 23 of the first outer circumferential groove 18. The shavings 20 remaining in the first outer circumferential groove 18 will no longer form continuous damage marks on the outer wall of the second main body portion 17b2 from the base end 18b of the first outer circumferential groove 18 to the tip end 19a of the second outer circumferential groove 19.

[0040] On the other hand, if the shavings 20 that have entered the first outer groove 18 are not severed from the outer peripheral wall of the plug 17, the shavings 20 become entangled between the outer peripheral wall of the second main body portion 17b2 and the inner peripheral wall of the hollow portion 6, forming damage marks 26 shown in Figure 3(b) that continue from the base end 18b of the first outer groove 18 to the base end of the second main body portion 17b2 (the position of the tip end 19a of the second outer groove 19), and enter a gap 24 between the second outer groove 19 and a biting portion 22 described below. If the shavings 20 are severed from the outer peripheral wall of the plug 17 when they are entangled between the outer peripheral wall of the second main body portion 17b2 and the inner peripheral wall of the hollow portion 6, the shavings remain in the gap 24 of the second outer groove 19. The shavings 20 remaining in the second outer circumferential groove 19 do not form continuous damage marks on the outer peripheral wall of the second main body portion 17b2 from the base end portion 19b of the second outer circumferential groove 19 to the base end portion 17a of the plug 17. As a result, no gap is formed from the hollow portion 6 to the outside of the plug 9, and the plug 9 maintains the sealing performance of the hollow portion 6 of the umbrella intermediate part 2 in which the refrigerant 8 and the inert gas are sealed.

[0041] In the plug press-in process of the second embodiment, even if the shavings 20 that are not cut off before entering the first circumferential outer groove 18 do not remain in the gap 23 of the first circumferential outer groove 18 and form damage marks 26 on the second main body portion 17b2 on the base end side of the first circumferential outer groove 18, if they are caught between the outer peripheral wall of the second main body portion 17b2 and the inner peripheral wall of the hollow portion 6 and cut off, they will remain in the gap 24 of the second circumferential outer groove 19, making it less likely that damage marks continuing from the second circumferential outer groove 19 to the base end 17a will be formed on the outer peripheral wall of the third main body portion 17b3. In other words, by providing multiple circumferential outer grooves in the plug, even if the shavings 20 cannot be collected in the first circumferential outer groove, the possibility of collecting them in further circumferential outer grooves on the base end side increases. Therefore, when the plug pressing process of the second embodiment is performed, the plug 17 more easily maintains the sealing of the hollow portion 6 of the shaft umbrella intermediate product 2 in which the refrigerant 8 and inert gas are sealed, compared to the plug pressing process of the first embodiment.

[0042] 3(c), a first biting portion 21 and a second biting portion 22 are formed on a part of the inner peripheral wall of the hollow portion 6 of the umbrella intermediate part 2, which protrude and bite into the first outer peripheral groove 18 and the second outer peripheral groove 19, respectively, of the outer peripheral wall of the plug 17 due to elastic deformation after the plug 17 is pressed in. During friction welding in the same joining process as in FIG. 1(c), the plug 17, which is press-fitted so that the base end 3a and the base end 17a of the shaft part 3 are flush with each other, is positioned without shifting downward even when pressed downward by the tip end of the shaft end member, because the biting portions 21, 22 firmly bite into the first outer peripheral groove 18 and the second outer peripheral groove 19, respectively. As a result, the airtightness of the hollow portion 6 of the umbrella intermediate part 2 is maintained, the internal volume of the hollow portion does not change, and the internal pressure is kept constant.

[0043] Next, a third preferred embodiment of the method for manufacturing a refrigerant-filled hollow poppet valve for an engine will be described with reference to Figure 4. The method for manufacturing a refrigerant-filled hollow poppet valve for an engine of the third embodiment differs from the first embodiment in the shape of the plug 27 used in the plug press-fitting step and the shape of the inner peripheral wall of the hollow portion 6' of the shaft portion 3' of the cap intermediate piece. However, the same refrigerant 8 and shaft end member 15 as those used in the first embodiment are used, and the same steps (refrigerant charging step, joining step) and means are used. Therefore, in the description of the second embodiment, the description of the common steps will be omitted, and only the plug press-fitting step will be described.

[0044] The plug press-fitting process of a third embodiment of the manufacturing method for a medium-filled hollow poppet valve for an engine will be described in detail with reference to Figures 4(a) to 4(c). The plug press-fitting process is performed as shown in Figure 1(b) after the same refrigerant charging process as that performed in Figure 1(a) of the first embodiment. As shown in the left diagram of Figure 3(a), the plug 27 used in the plug press-fitting process of the second embodiment differs from the plug 9 of the first embodiment, which has a circumferential groove, in that it does not have a ring-shaped circumferential groove on the outer peripheral wall of the main body. However, it shares a common structure with the plug 9. Furthermore, the cap intermediate of the third embodiment differs from the cap intermediate 3 of the first embodiment in the shape of the shaft portion 3', but shares a common structure with the cap intermediate 2 shown in Figures 1 and 2. Specifically, the shaft portion 3' of the third embodiment differs from the shaft portion 3 of the first embodiment, which does not have a circumferential inner groove on the inner wall of the hollow portion 6', only in that it has a single ring-shaped circumferential inner groove 28 that is recessed outward on the inner wall of the hollow portion 6'.

[0045] The plug 17 shown in Figures 4(a) to (c) is formed by machining or the like from a metal round bar made of heat-resistant steel or the like (SUH3, for example, but not limited to, the same as the plug 9 shown in Figures 2(a) to (c)), and specifically has the following configuration. As shown in Figures 4(a) to (c), the plug 27 is composed of a main body portion 27b and a tapered portion 27c having a tapered shape. The main body portion 27b smoothly connects to the base end of the tapered portion 27c. Meanwhile, as shown in Figures 4(a) to (v), a single circumferential inner groove 28 is formed by machining or the like on the inner peripheral wall of the hollow portion 6' of the shaft portion 3' of the intermediate shaft cap piece.

[0046] As shown in the center diagram of Figure 4(a), the inner diameter d2 of the hollow portion 6' of the shaft portion 3' of the intermediate product is slightly smaller than the outer diameter d1 of the main body 27b of the plug 27, and the outer diameter of the tip of the tapered portion 27c is smaller than the inner diameter d2 of the hollow portion 6'. In the plug press-fitting process, the plug 27 is inserted from above the opening 3b' of the intermediate product with the tapered portion 27c facing downward, as shown in the left diagram of Figure 1(a). As shown in the center diagram of Figure 4(a), the tapered portion 27c inserted into the hollow portion 6 comes into contact with the opening peripheral edge 3d' of the shaft portion 3', which begins to scrape away part of the outer wall, leaving shavings 29 of the plug 27 at the contact site. As shown in the right diagram of Figure 4(a), the plug 27 is pressed into the main body 27b until the base end 27a of the plug 27 is flush with the base end 3a' of the shaft portion 3', while the shavings 29 are caught between the outer wall of the plug 27 and the inner wall of the hollow portion 6 of the shaft cap intermediate product 2.

[0047] 4(b) is an explanatory diagram assuming that the front of the plug 27 inside the hollow portion 6' is seen from the direction of arrow C (the shaft portion 3' is shown in cross section). During the plug press-fitting process, shavings 29 caught between the outer peripheral wall of the plug 27 and the inner peripheral wall of the hollow portion 6' form a damage mark 31 on the outer peripheral wall of the plug 27 that continues from the contact position with the tapered portion 27c of the plug 27 to the position of the tip end 28a of the circumferential inner groove 28 formed in the inner peripheral wall of the hollow portion 6', and enter a gap 30 between the circumferential inner groove 28 and a biting portion 32 (described later). If the shavings 29 are cut off from the outer peripheral wall of the plug 27 when caught between the outer peripheral wall of the main body portion 27b of the plug 27 and the inner peripheral wall of the hollow portion 6', they will remain in the gap 30 of the circumferential inner groove 28. The shavings 29 remaining in the gap 30 of the circumferential inner groove 28 will no longer form continuous damage marks on the outer wall of the main body 27b from the base end 28b of the circumferential inner groove 28 to the base end 9a of the plug 9, so no gap is formed from the hollow portion 6' to the outside of the plug 9, and the plug 27 maintains the sealing properties of the hollow portion 6' of the shaft umbrella intermediate product which contains the refrigerant 8 and inert gas.

[0048] 4(c), a portion of the outer wall of the main body 27b of the plug 27 is elastically deformed after being press-fitted into the inner wall of the hollow portion 6' of the umbrella intermediate product, forming a biting portion 32 that protrudes and bites into the circumferential inner groove 28 of the inner wall of the hollow portion 6'. During friction welding in the same joining process as in FIG. 1(c), the plug 27 is press-fitted so that the base end 3a' of the shaft portion 3' and the base end 27a are flush with each other. Even when the plug 27 is pressed downward by the tip end of the shaft end member, the biting portion 32 firmly bites into the circumferential inner groove 28, so that it is positioned without shifting downward. As a result, the airtightness of the hollow portion 6' of the umbrella intermediate product is maintained, the internal volume of the hollow portion does not change, and the internal pressure is kept constant.

[0049] Next, a fourth preferred embodiment of the method for manufacturing a refrigerant-filled hollow poppet valve for engines will be described with reference to FIG. 5. The method for manufacturing a refrigerant-filled hollow poppet valve for engines of the fourth embodiment is a method in which the cap intermediate product 2' used in the plug press-fitting process of the third embodiment is replaced with a cap intermediate product 2''. The cap intermediate product 2'' has a common structure with the hollow portion 6' of the cap intermediate product, except that the shape of the inner peripheral wall of the hollow portion 6'' of the shaft portion 3'' differs from that of the hollow portion 6'' of the shaft portion 3' of the third embodiment. Furthermore, the method for manufacturing a refrigerant-filled hollow poppet valve for engines of the fourth embodiment is performed using the same refrigerant 8 and shaft end member 15 as those used in the first embodiment, and is performed using the same steps and means as those of the first embodiment (refrigerant charging process, joining process). Therefore, in the description of the fourth embodiment, a description of the common steps will be omitted, and only the plug press-fitting process will be described.

[0050] The plug press-fitting process of a fourth embodiment of the method for manufacturing a medium-filled hollow poppet valve for an engine will be described in detail with reference to Figures 5(a) to 5(c). The plug press-fitting process is performed as shown in Figure 1(b) after the same refrigerant charging process as that performed in Figure 1(a) of the first embodiment. As shown in the left diagram of Figure 5(a), the shaft portion 3'' of the cap intermediate product 2'' used in the plug press-fitting process of the second embodiment differs from the shaft portion 3' of the third embodiment, which has only one circumferential groove, in that it has two ring-shaped inner grooves on the inner circumferential wall of the hollow portion 6''. However, the shaft portion 3'' has a common configuration with the shaft portion 3'. Note that the number of circumferential grooves in the hollow portion 6'' of the shaft portion 3'' is not limited to two, as long as there are multiple grooves.

[0051] Specifically, as shown in FIG. 5( a), a first circumferential inner groove 34 on the tip end side and a second circumferential inner groove 35 on the base end side are formed on the inner peripheral wall of the hollow portion 6″ of the shaft portion 3″ of the umbrella intermediate product 2″ by machining or the like, and the second circumferential inner groove 35 is formed at a position spaced from the base end 3a″ of the shaft portion 3″ toward the tip end. The first circumferential inner groove 34 and the second circumferential inner groove 35 are each formed as two ring-shaped grooves recessed in a radial direction from the center of the shaft portion 3″. The inner diameter d2 of the hollow portion 6″ of the shaft portion 3″ of the umbrella intermediate product 2″ shown in the central view of FIG. 5( a) is slightly smaller than the outer diameter d1 of the plug 27, and the outer diameter of the tip of the tapered portion 27c is smaller than the inner diameter d2. In the plug press-fitting process, the plug 27 is inserted from above the opening 3b" of the intermediate product 2" with the tapered portion 27c facing downward, as shown in the left diagram of FIG. 5(a). As shown in the center diagram of FIG. 5(a), the tapered portion 27c inserted into the hollow portion 6" begins to scrape a portion of the outer peripheral wall by contacting the opening peripheral edge portion 3d" of the stem portion 3", and shavings 42 of the plug 27 are formed at the contact site. As shown in the right diagram of FIG. 5(a), the body portion 27b of the plug 27 is pressed into the intermediate product 2" until the base end 27a of the plug 27 is flush with the base end 3a" of the stem portion 3", while shavings 29 are caught between the outer peripheral wall of the plug 27 and the inner peripheral wall of the hollow portion 6" of the intermediate product 2".

[0052] 5(b) is an explanatory diagram assuming that the front of the plug 27' in the hollow portion 6" is seen from the direction of arrow D (the shank 3" is shown in cross section). During the plug press-fitting process, shavings 42 caught between the outer peripheral wall of the plug 27 and the inner peripheral wall of the hollow portion 6" first form a damage mark 40 on the outer peripheral wall of the plug 27 that continues from the contact position between the tapered portion 27c of the plug 27 and the opening peripheral edge portion 3d" of the shank 3" to the position of the tip end 34a of the first orbital inner groove 34, and then enter the gap 38 between the first orbital inner groove 34 and a biting portion 36 (described later). If the shavings 42 are caught between the outer peripheral wall of the main body 27b of the plug 27 and the inner peripheral wall of the hollow portion 6 and are cut off from the outer peripheral wall of the plug 27 before entering the gap 38 of the first orbital inner groove 34, they remain in the gap 38 of the first orbital inner groove 34. The shavings 42 remaining in the gap 38 of the first circumferential inner groove 34 will no longer form continuous damage marks (damage marks similar to those indicated by symbol 41) on the outer wall of the region indicated by symbol 27b2 of the main body portion 27b from the base end 34b of the first circumferential inner groove 34 to the tip end 35a of the second circumferential inner groove 35.

[0053] On the other hand, if the shavings 42 that have entered the gap 38 of the first inner groove 34 are not cut off from the outer peripheral wall of the plug 27, the shavings 42 are again caught between the outer peripheral wall of the region of the main body 27b designated by reference symbol 27b2 and the inner peripheral wall of the hollow portion 6″, rearward of the base end 34b of the first inner groove 34, forming a damage mark 41 as shown in FIG. 5( b ) that continues from the base end 34b of the first inner groove 34 to the position of the tip end 35a of the second inner groove 35, and then enter the gap 39 between the second inner groove 35 and a biting portion 37, which will be described later. If the shavings 42 are cut off from the outer peripheral wall of the plug 27 when they are again caught between the outer peripheral wall of the main body 27b and the inner peripheral wall of the hollow portion 6″, they remain in the gap 39 of the second inner groove 35. The shavings 42 remaining in the gap 39 of the second inner groove 35 do not form a continuous damage mark extending from the base end 35b of the second inner groove 35 to the base end 27a of the plug 27, even in the region of the main body 27b indicated by the reference symbol 27b3. As a result, no gap is formed from the hollow portion 6" to the outside of the plug 27, and the plug 27 maintains the sealing performance of the hollow portion 6" of the umbrella intermediate part 2" in which the refrigerant 8 and the inert gas are sealed.

[0054] In the plug press-in process of the fourth embodiment, even if the shavings 42 that are not cut off before entering the first circumferential inner groove 34 do not remain in the gap 38 of the first circumferential inner groove 34 and form damage marks 41 in the area indicated by symbol 27b2 of the main body 27b of the plug 27, if they are caught between the outer peripheral wall of the area indicated by symbol 27b2 of the main body 27b and the inner peripheral wall of the hollow portion 6'' and are cut, they will remain in the gap 39 of the second circumferential inner groove 35, making it less likely that damage marks will be formed on the outer peripheral wall of the area indicated by symbol 27b3 of the main body 27b that continues from the second circumferential inner groove 35 to the base end 3a'' of the shaft portion 3''. In other words, by providing multiple circumferential inner grooves in the hollow portion 6'', even if the shavings 42 cannot be collected in the first circumferential inner groove, the possibility of them being collected in further circumferential inner grooves on the base end side increases. Therefore, when the plug press-fitting process of the fourth embodiment is performed, the sealability of the hollow portion 6'' of the shaft umbrella intermediate product 2'', which contains the refrigerant 8 and inert gas, is more easily maintained by the plug 27 than in the plug press-fitting process of the third embodiment.

[0055] 5(c), a first biting portion 36 and a second biting portion 37 are formed on a part of the inner peripheral wall of the hollow portion 6" of the umbrella intermediate product 2" due to elastic deformation after the plug 27 is press-fitted. The first biting portion 36 and the second biting portion 37 respectively protrude and bite into the first circumferential inner groove 34 and the second circumferential inner groove 35 formed on the inner peripheral wall of the shaft portion 3" of the hollow portion 6" of the umbrella intermediate product 2". During friction welding in the same joining process as in FIG. 1(c), the plug 27 is press-fitted so that the base end 3a" and the base end 27a of the shaft portion 3" are flush with each other. Even when the plug 27 is pressed downward by the tip end of the shaft end member, the biting portion 36 and the biting portion 37 firmly bite into the first circumferential inner groove 34 and the second circumferential inner groove 35, respectively, and are therefore positioned without any downward displacement. As a result, the hermeticity of the hollow portion 6" of the umbrella intermediate product 2" is maintained, the internal volume of the hollow portion 6" does not change, and the internal pressure is kept constant.

[0056] Next, a fifth preferred embodiment of a method for manufacturing a refrigerant-filled hollow poppet valve for an engine will be described with reference to FIG. 6. The fifth embodiment of the method for manufacturing a refrigerant-filled hollow poppet valve for an engine involves forming one circumferential outer groove 46 on the outer peripheral wall of the plug 45 shown in FIG. 5(a) and one circumferential inner groove 47 on the inner peripheral wall of the hollow portion 6''' of the shaft portion 3''' of the intermediate shaft part 2''' and then performing the plug press-fitting process. This method is performed using the same refrigerant 8 and shaft end member 15 as those used in the first embodiment, and is performed using the same steps (refrigerant charging step, joining step) and means as those used in the first embodiment. The plug 45 shown in FIG. 6(a) has the circumferential outer groove 46 offset toward the base end from the circumferential outer groove 10 of the plug 9 of the first embodiment, and is also configured in the same material and shape as the plug 9. Furthermore, the inner peripheral wall of the hollow portion 6''' of the shaft portion 3''' of the umbrella intermediate product 2''' has a circumferential inner groove 47 at a position offset toward the tip from the inner peripheral wall of the hollow portion 6' of the shaft portion 3' of the umbrella intermediate product 2' of the third embodiment, and has a configuration in common with the umbrella intermediate product 2' having the shaft portion 3' of the third embodiment. In the description of the fifth embodiment, the description of the common steps will be omitted, and only the press-fitting step will be described.

[0057] The plug press-fitting process of a fifth embodiment of the manufacturing method for a medium-filled hollow poppet valve for an engine will be described in detail with reference to Figures 6(a) through 6(c). The plug press-fitting process is performed as shown in Figure 1(b) after the same refrigerant charging process as that performed in Figure 1(a) of the first embodiment. The metal plug 45 comprises a main body portion 45b and a tapered portion 45c smoothly connected to the tip of the main body portion 45b. The main body portion 45b has a first main body portion 45b1 and a second main body portion 45b2 connected to the base end of the tapered portion 45c, and a ring-shaped circumferential outer groove 46 recessed into the inside of the main body portion 45b, which is formed by machining or the like between the first main body portion 45b1 and the second main body portion 45b2. The tip end of the first main body portion 45b1 smoothly connects to the base end of the tapered portion 27c. 5(a), a single circumferential inner groove 47 is formed in the inner peripheral wall of the hollow portion 6''' of the stem portion 3''' of the intermediate product 2''' by machining or the like. The circumferential outer groove 46 is formed in the stem 45 so as to be positioned above (or below) the circumferential inner groove 47 when the stem 45 is press-fitted into the hollow portion 6'''.

[0058] At least one of the circumferential outer groove 46 of the plug 45 and the circumferential inner groove 47 on the inner peripheral wall of the hollow portion 6'" may be formed in multiple numbers. The circumferential inner groove 47 may be formed in the inner peripheral wall of the hollow portion 6'" of the shaft portion 3'" at a position spaced away from the base end portion 3 a''' toward the tip end portion of the shaft portion 3''' and at a position offset toward the base end portion of the circumferential outer groove 46 when the plug 45 is completely press-fitted.

[0059] As shown in Figure 6(a), the circumferential outer groove 46 of the plug 45 used in the sixth embodiment is formed at a position spaced from the base end 45a of the plug 45 toward the tip end. The relationship between the inner diameter d2 of the hollow portion 6''' of the shaft portion 3''' of the umbrella intermediate part 2''' and the outer diameter d1 of the plug 45, as shown in the center diagram of Figure 5(a), is the same as that of the plug 9 of the first embodiment, and the outer diameter of the tip end of the tapered portion 45c is smaller than the inner diameter d2. In the plug press-fitting process, the plug 45 is inserted from above the opening 3b''' of the umbrella intermediate part 2''' with the tapered portion 45c facing downward, as shown in the left diagram of Figure 6(a). As shown in the center diagram of Figure 6(a), the tapered portion 45c inserted into the hollow portion 6''' comes into contact with the opening peripheral portion 3d''' of the stem portion 3''', and begins to scrape away part of the outer peripheral wall, and shavings 48 of the plug 45 are formed at the contact site. As shown in the right diagram of Figure 6(a), the plug 45 is pressed into the main body portion 45b until the base end 45a of the plug 45 is flush with the base end 3a''' of the stem portion 3''', while the shavings 48 are caught between the outer peripheral wall of the plug 45 and the inner peripheral wall of the hollow portion 6''' of the shaft cap intermediate product 2'''.

[0060] Figure 6(b) is an explanatory diagram assuming that the front of the plug 45 inside the hollow portion 6''' is seen from the direction of arrow E (the shaft portion 3''' is shown in cross section), and during the plug press-in process, shavings 48 caught between the outer wall of the plug 27 and the inner wall of the hollow portion 6''' first form a damage mark 53 on the outer wall of the plug 45 that continues from the contact position between the tapered portion 45c of the plug 45 and the opening peripheral portion 3d''' of the shaft portion 3''' to the position of the tip portion 47a of the circumferential inner groove 47 of the shaft portion 3''', and then enters the gap 51 between the circumferential inner groove 47 and the biting portion 49 described later. If the shavings 48 are caught between the outer peripheral wall of the first body portion 45b1 of the body portion 45b of the plug 45 and the inner peripheral wall of the hollow portion 6''', and are cut off from the outer peripheral wall of the plug 45 before entering the inner circumferential groove 47, the shavings 48 will remain in the gap 51 of the inner circumferential groove 47. The shavings 48 that remain in the gap 51 of the inner circumferential groove 47 will no longer form a continuous damage mark (damage mark similar to the symbol 53) on the outer peripheral wall of the first body portion 45b1 from the base end 47b of the inner circumferential groove 47 to the tip end 46a of the outer circumferential groove 46 of the plug 45.

[0061] On the other hand, if the shavings 48 that have entered the inner circumferential groove 47 are not cut off from the outer peripheral wall of the plug 45, the shavings 48 are again caught up between the outer peripheral wall of the first main body portion 45b1 and the inner peripheral wall of the hollow portion 6''', rearward of the base end of the inner circumferential groove 47, forming a continuous damage mark 54 from the base end 47b of the inner circumferential groove 47 to the tip end 46a of the outer circumferential groove 46 of the plug 45, and entering the gap 52 between the outer circumferential groove 46 of the plug 45 and a biting portion 50 described below. If the shavings 48 are cut off from the outer peripheral wall of the plug 45 when they are again caught up between the outer peripheral wall of the main body portion 45b and the inner peripheral wall of the hollow portion 6''', they will remain in the gap 52 of the outer circumferential groove 46 of the plug 45. The shavings 48 remaining in the gap 52 of the outer circumferential groove 46 do not form continuous damage marks on the outer peripheral wall of the second main body portion 45b2 from the base end 46b of the outer circumferential groove 46 to the base end 45a of the plug 45. As a result, no gap is formed from the hollow portion 6''' to the outside of the plug 45, and the plug 45 maintains the sealing performance of the hollow portion 6''' of the umbrella intermediate part 2''' in which the refrigerant 8 and the inert gas are sealed.

[0062] In the clasp press-fitting process of the sixth embodiment, even if the shavings 48 that are not cut off from the outer wall of the clasp 45 before entering the circumferential inner groove 47 formed on the inner wall of the hollow portion 6''' of the shaft portion 3''' do not remain in the gap 51 of the circumferential outer groove 46 and form a continuous damage mark 54 in the first main body portion 45b1 of the clasp 45 from the base end 46b of the circumferential outer groove 46 to the base end 45a of the clasp 45, when they are cut off from the outer wall of the clasp 45 when they are again caught between the outer wall of the body portion 45b and the inner wall of the hollow portion 6''', they remain in the gap 52 of the circumferential outer groove 46 formed on the outer wall of the clasp 45, making it less likely that a continuous damage mark will be formed in the second main body portion 45b2 from the circumferential outer groove 46 to the base end 3a''' of the shaft portion 3'''. In other words, by combining the circumferential inner groove 47 in the hollow portion 6'' with the circumferential outer groove 46 on the outer wall of the plug 45 at positions offset from each other in the extension direction of the shaft portion 3''', even if the shavings 48 cannot be collected in the initial circumferential inner groove 47, the possibility of them being collected in the circumferential outer groove 46 on the base end side increases.Therefore, when the plug pressing process of the fifth embodiment is performed, the plug 45 more easily maintains the sealing of the hollow portion 6''' of the shaft umbrella intermediate product 2''' in which the refrigerant 8 and inert gas are sealed, compared to the plug pressing processes of the first and third embodiments.

[0063] As shown in FIG. 6( c), an outer engaging portion 49 of the outer peripheral wall of the plug 45 is formed on a part of the inner peripheral wall of the hollow portion 6''' of the umbrella intermediate product 2''', which protrudes and engages with the circumferential inner groove 47 formed on the inner peripheral wall of the shaft portion 3''' of the hollow portion 6''' of the umbrella intermediate product 2''', due to elastic deformation after the outer peripheral wall of the plug 45 and the hollow portion 6''' are pressed into each other, and an inner engaging portion 50 is formed on the inner peripheral wall of the hollow portion 6''' of the shaft portion 3''', which protrudes and engages with the circumferential outer groove 46 formed on the outer peripheral wall of the plug 45. 1(c), the plug 45 is pressed in so that the base end 3a''' of the shaft portion 3''' is flush with the base end 45a. Even when the plug 45 is pressed downward by the tip of the shaft end member, the outer engaging portion 49 is firmly engaged with the circumferential inner groove 47, and the inner engaging portion 50 is firmly engaged with the circumferential outer groove 46, so that the plug 45 is positioned without shifting downward. As a result, the airtightness of the hollow portion 6'' of the shaft umbrella intermediate product 2''' is maintained, the internal volume of the hollow portion 6'' does not change, and the internal pressure is kept constant.

[0064] DESCRIPTION OF SYMBOLS 1 Refrigerant-filled hollow poppet valve of engine 2, 2', 2'', 2''' Shaft umbrella intermediate part 3a, 3a', 3a'', 3a''' Base end part 3, 3b', 3b'', 3b''' Base end opening 8 Liquid refrigerant 9 Plug 10 Circumferential outer groove 15 Shaft end member 18, 19 Multiple circumferential outer grooves 27 Plug 28 Circumferential inner groove 34, 35 Multiple circumferential inner grooves 45 Plug 46 Circumferential outer groove 47 Circumferential inner groove

Claims

1. A method for manufacturing a refrigerant-filled hollow poppet valve for an engine, which includes a refrigerant charging step of charging a refrigerant into the hollow space inside a metal stem intermediate from an opening at the base end, and a joining step of joining a metal stem end member to the base end, characterized in that a plug press-fitting step of press-fitting a metal plug having a circumferential outer groove on its outer peripheral wall into the hollow space from the opening at the base end is carried out after the refrigerant charging step and before the joining step.

2. A method for manufacturing a refrigerant-filled hollow poppet valve for an engine as set forth in claim 1, wherein said metal plug has a plurality of said circumferential outer grooves.

3. A method for manufacturing a refrigerant-filled hollow poppet valve for an engine according to claim 1 or 2, characterized in that the inner peripheral wall of the hollow portion has at least one circumferential inner groove.

4. A method for manufacturing a refrigerant-filled hollow poppet valve for an engine, which includes a refrigerant charging step of charging a refrigerant into a hollow portion inside a metal stem intermediate product from an opening at the base end, and a joining step of joining a metal stem end member to the base end, characterized in that a plug press-fitting step of press-fitting a metal plug into the hollow portion having a circumferential inner groove on its inner wall from the opening at the base end is carried out after the refrigerant charging step and before the joining step.

5. A method for manufacturing a refrigerant-filled hollow poppet valve for an engine as set forth in claim 4, characterized in that the inner peripheral wall of the hollow portion has a plurality of the circumferential inner grooves.

6. A method for manufacturing a hollow poppet valve for an engine according to claim 4 or 5, wherein the metal plug has at least one circumferential outer groove.

Images