JP2008215157A - Engine valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve fatigue strength while reducing costs. <P>SOLUTION: This engine valve is manufactured by an engine valve manufacturing method comprising a step of hardening an engine valve molded unit of a solid structure with a valve shaft part and a valve umbrella part are integrally formed by forging ferroalloy material, a step of applying low-temperature tempering to the engine valve molded unit after hardening, a step of machining the engine valve after applying low-temperature tempering, and a process of surface-treating the engine valve after machining at a temperature lower than the temperature of the low-temperature tempering. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an engine valve.

As a conventional engine valve, for example, there is a poppet valve described in Patent Document 1. FIG. 7 is a cross-sectional view showing the poppet valve described in Patent Document 1.
As shown in FIG. 7, the poppet valve 110 described in Patent Document 1 includes a stem member 11 and a cap member 114. The stem member 11 has a hollow structure, and includes a stem portion 112 which forms the main body, a tip portion 118 formed at one end portion (upper end portion in FIG. 7), and the other end portion (lower end portion in FIG. 7). And a formed flare-shaped fillet portion 116. The cap member 114 is attached to the fillet portion 116 of the stem member 111 so as to be closed.

JP-A-9-299816

  In the poppet valve 110 (see FIG. 7) described in Patent Document 1, a step of forming the stem member 111, a step of forming the cap member 114, a step of attaching the cap member 114 to the stem member 111, and the like are necessary. However, since there are many parts and man-hours, there is a problem that the cost is inevitably increased. Further, since the poppet valve 110 has a hollow structure, the outer diameter (also referred to as a shaft diameter) of the stem portion 112 is reduced and / or the thickness of the valve umbrella portion is reduced by the fillet portion 116 and the cap member 114. However, there is a problem that the required fatigue strength cannot be secured.

  Further, in addition to the aforementioned Patent Document 1, even in a solid engine valve in which the valve shaft portion and the valve umbrella portion are integrally formed by forging, the shaft diameter of the valve shaft portion can be reduced and / or the valve umbrella portion can be reduced. When attempting to reduce the wall thickness, there is a problem that the required fatigue strength cannot be secured.

  An object of the present invention is to provide an engine valve capable of improving fatigue strength while reducing cost.

The above-described problem can be solved by an engine valve having the gist of the configuration described in the claims.
That is, according to the engine valve of claim 1, the solidified engine valve molded body in which the valve shaft portion and the valve umbrella portion are integrally formed by forging a material made of an iron alloy is quenched. And a step of subjecting the engine valve molded body after the quenching treatment to a low-temperature tempering treatment. Therefore, since the engine valve has a solid structure, the number of parts and the number of manufacturing steps can be reduced and the cost can be reduced as compared with a hollow structure (see Patent Document 1). Moreover, the fatigue strength of an engine valve can be improved by subjecting a solid engine valve molded body formed by forging an iron alloy material to a quenching process and a low temperature tempering process. Therefore, it is possible to provide an engine valve that can improve fatigue strength while reducing costs. Further, by improving the fatigue strength of the engine valve, it is possible to reduce the outer diameter (also referred to as the shaft diameter) of the valve shaft and / or to reduce the thickness of the valve umbrella, which in turn increases the valve operating speed of the engine. The weight of system parts can be reduced. The quenching process and the low-temperature tempering process for the engine valve molded body can be performed on the entire engine valve molded body, or can be partially performed on a necessary portion of the engine valve molded body.

  Moreover, according to the engine valve concerning Claim 2 of a claim, the hardness after a low temperature tempering process is HV530 or more by Vickers hardness. This is advantageous in reducing the diameter of the valve shaft and / or reducing the thickness of the valve umbrella.

  According to the engine valve of claim 3 of the claims, the step of machining the engine valve after the low-temperature tempering treatment, and the engine valve after the machining at a temperature equal to or lower than the low-temperature tempering treatment temperature. It is manufactured by the manufacturing method of an engine valve provided with the process of performing a surface treatment. Therefore, the engine valve after low-temperature tempering treatment is finished to a final shape by machining, and the engine valve fatigue strength of the engine valve is obtained by subjecting the engine valve after machining to a surface treatment at a temperature lower than the low-temperature tempering treatment temperature. It is possible to improve the wear resistance of the surface of the engine valve without incurring a decrease. The surface treatment can be performed on the entire surface of the engine valve or can be partially applied to a necessary part of the engine valve.

  Moreover, according to the engine valve concerning Claim 4 of a claim, the martensitic heat-resistant steel with a track record as an iron alloy can be used conveniently.

  According to the engine valve of claim 5 of the claims, it is possible to manufacture an engine valve in which the ratio of the outer diameter of the valve shaft portion to the outer diameter of the valve umbrella portion is 7 or more.

  Further, according to the engine valve of claim 6, the separate member for forming the shaft end surface having an area larger than the area of the shaft end surface of the shaft end portion at the shaft end portion of the valve shaft portion of the engine valve. Are integrated. Therefore, the shaft end surface having an area larger than the area of the shaft end surface of the shaft end portion can be formed by the separate member, and wear of the shaft end surface of the engine valve can be prevented.

  Next, the best mode for carrying out the present invention will be described with reference to examples.

An engine valve according to an embodiment of the present invention will be described. FIG. 2 is a side view showing the engine valve.
As shown in FIG. 2, the engine valve 10 is made of an iron alloy and has a solid structure. The engine valve 10 is integrally formed with a round shaft-shaped valve shaft portion 12 and a substantially circular umbrella-shaped valve umbrella portion 13 continuing to one end portion (the lower end portion in FIG. 2) of the valve shaft portion 12. . The other end portion (upper end portion in FIG. 2) of the valve shaft portion 12 is a shaft end portion 12a. A cotter groove 15 continuous in the circumferential direction is formed on the outer peripheral surface of the base end side (lower side in FIG. 2) of the shaft end portion 12a. The engine valve 10 is manufactured by the following manufacturing method.

Next, a method for manufacturing the engine valve 10 will be described. In addition, FIG. 1 is process drawing which shows the manufacturing method of an engine valve.
As shown in FIG. 1, in the first step P1, an engine valve molded body is formed by forging an iron alloy material. FIG. 3 is a side view showing the engine valve molded body.

  As shown in FIG. 3, the engine valve molded body 20 has a solid structure and is substantially continuous with a round shaft-shaped valve shaft portion 22 and one end portion (the lower end portion in FIG. 3) of the valve shaft portion 22. A circular umbrella-shaped valve umbrella portion 23 is integrally formed. Moreover, as an iron alloy which is a raw material of the engine valve molded body 20, martensitic heat-resistant steels such as SUH1, SUH3, and SUH11 defined in Japanese Industrial Standard (JIS) G4311 can be used. Moreover, as a manufacturing method of the engine valve molded body 20, a general forging method can be applied. However, “Manufacturing of an engine valve” described in Japanese Patent Laid-Open No. 2006-88197 previously proposed by the same applicant. The “method” should be applied.

  Next, in the second step P2 (see FIG. 1), the engine valve molded body 20 (see FIG. 3) is subjected to a quenching process, and the engine valve molded body 20 after the quenching process is tempered at a low temperature. Processing is performed. Here, the quenching treatment temperature and the treatment time for the warm quenching treatment are arbitrarily selected according to the hardness required of the material of the engine valve molded body 20. The low-temperature tempering process is a process for removing strain and brittleness generated by the quenching process. Further, in the example where the martensitic heat-resistant steel as the iron alloy that is the material of the engine valve molded body 20 is SUH3, the tempering temperature (° C.) and the hardness (HV) are as shown by the characteristic line A in FIG. There is an inversely proportional relationship, and there is an inflection region R between 500 ° C and 550 ° C. In the martensitic heat-resisting steel, the inflection region R varies somewhat depending on the material. Here, the tempering treatment at a temperature lower than the maximum temperature Th of the inflection region R is defined as “low temperature tempering treatment”. Further, since the material hardness and the fatigue strength are proportional, the fatigue strength increases as the low temperature tempering treatment is performed. However, if the low-temperature tempering temperature is too low, the brittleness of the material is lowered. For this reason, 450 to 550 degreeC is suitable as low temperature tempering processing temperature. Furthermore, in order to increase the fatigue strength, the low-temperature tempering treatment temperature is more preferably 530 ° C. or less, and most preferably 500 ° C. Further, the processing time required for the low temperature tempering process is arbitrarily selected from the balance between the low temperature tempering temperature and the fatigue strength. In addition, the conventional general tempering process temperature was about 650 degreeC.

As described above, the engine valve molded body 20 is subjected to quenching treatment and low temperature tempering treatment at about 500 ° C. with respect to the conventional general tempering treatment temperature of about 650 ° C. The hardness (see Fig. 4) can be improved by 1.5 times (Vickers hardness of about HV360 to about HV530), and the material hardness and the fatigue strength are proportional to each other. The strength can be improved by a factor of 1.5.
Further, in the present embodiment, the hardness of the engine valve 10 after the second step P2 is HV530 (Rockwell hardness: HRC51) or more in terms of Vickers hardness. Further, in the present embodiment, the quenching process and the low temperature tempering process for the engine valve molded body 20 are performed on the entire engine valve molded body 20, but may be partially performed on necessary portions.

  Next, in a third step P3 (see FIG. 1), the engine valve that has been subjected to the quenching process and the low-temperature tempering process is subjected to machining so that the final-shaped engine valve 10 (see FIG. 2). .) Finished. Here, as machining, grinding of the outer peripheral surface of the valve umbrella portion 13 of the engine valve 10 (see FIG. 2), grinding of the outer peripheral surface of the valve shaft portion 12 and the shaft end surface 12b, and grinding of the cotter groove 15 are performed. Etc.

  Next, in the fourth step P4 (see FIG. 1), the engine valve 10 subjected to the machining is subjected to a surface treatment at a temperature equal to or lower than the low temperature tempering treatment temperature. Does not occur. As this surface treatment, a nitriding treatment is suitable. Further, the temperature of the nitriding treatment is suitably a temperature not higher than the low temperature tempering treatment temperature, that is, 300 ° C. to 450 ° C. Furthermore, the nitriding temperature is more preferably 450 ° C. or less, and most preferably 400 ° C. For this reason, “nitriding” in this specification can be called “low temperature surface hardening”. Further, the processing time required for the nitriding process is arbitrarily selected according to the hardness required of the engine valve 10. As the nitriding treatment, for example, a “steel nitriding method” described in JP-A-3-44457 can be applied.

  As described above, since the surface treatment of the engine valve 10 is performed according to the required hardness of the engine valve 10, so-called a hardened layer is formed on the surface of the engine valve 10. Can be improved. The surface treatment for the engine valve 10 is performed on the entire surface of the engine valve 10 in this embodiment, but may be partially performed on a necessary surface portion. Further, as the surface treatment, in addition to nitriding treatment, treatments such as salt bath nitriding treatment, gas soft nitriding, ion nitriding, Cr plating, CrN coating, DLC, carburizing, induction hardening, and electric discharge hardening can be applied.

  An example of an engine valve mechanism that uses the engine valve 10 (see FIG. 2) manufactured by the above-described manufacturing method (see FIG. 1) will be described. Here, an OHC (overhead camshaft) mechanism is exemplified as the valve mechanism of the engine. FIG. 5 is a cross-sectional view showing the valve mechanism of the engine.

  As shown in FIG. 5, in the valve operating mechanism of the engine, the valve shaft portion 12 of the engine valve 10 as an intake valve or an exhaust valve is axially inserted into a valve guide 32 fixed to the cylinder head 31 of the engine 30 (see FIG. 5). 5 is slidably inserted in the vertical direction). A spring retainer 35 is attached to the shaft end 12 a of the engine valve 10 via a cotter 34 engaged with the cotter groove 15. A spring seat portion 31 a surrounding the valve guide 32 is provided on the upper surface side of the cylinder head 31. A valve spring 36 made of a coil spring is interposed between the spring seat portion 31a and the spring retainer 35 in a compressed state. Further, a valve seat 39 is fixed to the opening on the combustion chamber side of the port 38 as the intake port or the exhaust port of the cylinder head 31 of the cylinder head 31. The port 38 is closed when the valve umbrella portion 13 of the engine valve 10 urged upward by the elasticity of the valve spring 36 contacts the valve seat 39.

  The cylinder head 31 is provided with a camshaft 40 and a rocker shaft 42 that are rotationally driven by a crankshaft (not shown). The cam follower portion 43a of the rocker arm 43 supported by the rocker shaft 42 is slidably contacted with a cam surface 40a of the cam shaft 40. Further, the valve contact portion 43 b of the rocker arm 43 is slidably contacted with the shaft end surface 12 b of the shaft end portion 12 a of the engine valve 10.

  The rocker arm 43 is swung based on the rotation of the camshaft 40. When the valve contact portion 43 b of the rocker arm 43 is lowered, the engine valve 10 is pushed down against the elasticity of the valve spring 36. As a result, the valve umbrella 13 is separated from the valve seat 39 and the port 38 is opened. Further, when the valve contact portion 43 b of the rocker arm 43 rises, the engine valve 10 is raised by the elastic restoring force of the valve spring 36. Thereby, the port 38 is closed again. In addition to the engine valve 10, the cotter 34, the spring retainer 35, the valve spring 36, and the rocker arm 43 correspond to a “valve valve system component” in this specification.

  According to the engine valve 10 described above, a solid engine valve molded body 20 (see FIG. 3) in which the valve shaft portion 22 and the valve umbrella portion 13 are integrally formed by forging a material made of an iron alloy is quenched. And a process for subjecting the engine valve molded body 20 after the quenching treatment to a low temperature tempering treatment (see FIG. 1). Therefore, since the engine valve 10 has a solid structure (see FIG. 2), the number of parts and the number of manufacturing steps can be reduced and the cost can be reduced as compared with the hollow structure (see Patent Document 1). . Moreover, the fatigue strength of the engine valve 10 is improved by subjecting the engine valve molded body 20 (see FIG. 3) having a solid structure formed by forging an iron alloy material to a quenching process and a low temperature tempering process. can do. Therefore, it is possible to provide the engine valve 10 that can improve the fatigue strength while reducing the cost.

  Further, by improving the fatigue strength of the engine valve 10, the shaft diameter 12d of the valve shaft portion 12 (see FIG. 2) is reduced and / or the thickness of the valve umbrella portion 13 (the thickness in the vertical direction in FIG. 2) is reduced. The thickness can be reduced, and the engine valve 10 can be reduced in weight. Further, as the shaft diameter 12d of the valve shaft portion 12 is reduced, the diameter of the cotter 34, the spring retainer 35, and the valve spring 36, which are valve system components of the engine 30 (see FIG. 5), can be reduced. They can be reduced in weight. Accordingly, the rocker arm 43 can be reduced in size, and the rocker arm 43 can be reduced in weight. In this way, it is possible to reduce the weight of the valve operating system components (engine valve 10, cotter 34, spring retainer 35, valve spring 36, rocker arm 43) of the engine 30.

Further, when the stress analysis of the engine valve 10 (see FIG. 2) according to the present embodiment was performed, the stress caused by the reduction in the diameter of the valve shaft portion 12 as compared with the conventional engine valve made of iron alloy and solid structure. In contrast to the increase, by improving the fatigue strength by low-temperature tempering treatment, it is possible to achieve a safety factor equivalent to that of a conventional engine valve, and to ensure equivalent reliability. That is, according to the engine valve 10 (see FIG. 2) according to the present embodiment, the stress increase due to the reduction of the shaft diameter 12d of the valve shaft portion 12 by about 20% is about 40%, whereas the low temperature tempering process. Fatigue strength is improved by about 40%. Therefore, a safety factor equivalent to that of a solid engine valve made of a conventional iron alloy can be achieved, and equivalent reliability can be ensured.
As a result, the shaft diameter 12d of the valve shaft portion 12 can be reduced by about 20%, the engine valve 10 alone can be reduced by about 20%, and the valve system parts (engine valve 10, cotter 34, spring retainer 35) can be reduced. It has been confirmed that the inertial mass of the valve spring 36 and the rocker arm 43) is reduced by about 16%. Incidentally, when the safety factor S is the stress intensity σ _a generated when the fatigue strength of the material is σ _s ,
S = σ _S / σ _a
It is calculated | required by the numerical formula of.

Further, by reducing the shaft diameter 12d of the valve shaft portion 12 of the engine valve 10 (see FIG. 2), the valve shaft portion with respect to the outer diameter (referred to as “umbrella diameter”) 13d of the valve umbrella portion 13 is achieved. The engine valve 10 having a large ratio of 12 shaft diameters 12d (referred to as “umbrella / shaft ratio”) can be manufactured.
Table 1 specifically shows a relationship among the umbrella diameter 13d, the shaft diameter 12d, the umbrella / shaft ratio, the tempering temperature, and the material hardness according to the engine valves of Examples 1 to 4 and Conventional Examples 1 and 2.

  This will be described with reference to Table 1. For example, when the umbrella diameter 13d of the valve umbrella portion 13 of the engine valve according to the conventional example 1 is Φ32 mm and the shaft diameter 12d of the valve shaft portion 12 is Φ5.5 mm, the “umbrella / axial ratio” is 5.8. When the diameter of the umbrella 13d is Φ32 mm and the diameter Φ5.5 mm of the shaft diameter 12d is reduced to Φ4.5 mm, the “umbrella / axis ratio” increases to about 7.1 (see Example 1). In that case, when the shaft diameter 12d is Φ4.5 mm, the shaft cross-sectional area is about 66% with respect to Φ5.5 mm, and the stress is about 1.5 times, whereas the low temperature tempering process at about 550 ° C. The material hardness is about 1.5 times (in the example of SUH3, the Vickers hardness is improved from about HV360 to about HV530), and the fatigue strength is improved to about 1.5 times, so that the equivalent safety factor can be achieved. Equivalent reliability can be ensured.

  Further, when the umbrella diameter 13d of the valve umbrella portion 13 of the engine valve which is the conventional example 2 is reduced to Φ38 mm and the shaft diameter 12d of the valve shaft portion 12 is reduced from Φ5.5 mm to Φ4.2 mm, the “umbrella / axis ratio” is about 9 (see Example 4). In that case, when the shaft diameter 12d is Φ4.2 mm, the shaft cross-sectional area is about 58% with respect to Φ5.5 mm, and the stress is about 1.7 times, whereas the low-temperature tempering process at about 400 ° C. The material hardness is about 1.7 times (in the example of SUH3, the Vickers hardness is improved from about HV360 to about HV620), and the fatigue strength is improved to about 1.7 times, so that the safety factor can be equivalent and equivalent. Ensuring reliability.

  As a result, the umbrella / shaft ratio of the engine valve 10 can be increased to a value exceeding the conventional limit of 6.9, that is, 8.5, and further set to a value of approximately 9.0. Is possible. The expansion of the umbrella diameter 13d of the valve umbrella portion 13 is effective in improving the intake and exhaust efficiency of the engine. Further, the weight reduction by reducing the shaft diameter 12d of the valve shaft portion 12 is effective for improving the high-speed response of the engine.

  Further, the hardness of the engine valve 10 after the low temperature tempering treatment is HV530 or more in terms of Vickers hardness. This is advantageous in reducing the diameter of the valve shaft and / or reducing the thickness of the valve umbrella.

  The engine valve after the low-temperature tempering process is machined, and the engine valve 10 after the machining is surface-treated at a temperature equal to or lower than the low-temperature tempering temperature. Therefore, the engine valve after the low temperature tempering process is finished to a final shape by machining, and the engine valve 10 after the machining is subjected to a surface treatment at a temperature equal to or lower than the low temperature tempering process temperature. The wear resistance of the surface of the engine valve 10 can be improved without causing a decrease in fatigue strength.

  Further, it is convenient to use martensitic heat-resistant steel that has a proven record as an iron alloy of the engine valve molded body 20.

  Further, it is possible to manufacture an engine valve 10 in which the ratio of the shaft diameter 12d of the valve shaft portion 12 to the umbrella diameter 13d of the valve umbrella portion 13 is 7 or more.

  In addition, since the existing equipment can be used for each of the quenching process, the low-temperature tempering process, and the surface treatment process, it is possible to further reduce the cost.

  Further, as described above, when the shaft diameter 12d of the valve shaft portion 12 of the engine valve 10 is reduced, the valve contact portion 43b (see FIG. 5) of the rocker arm 43 contacts and slides on the shaft end portion 12a. When the contact area of the shaft end surface 12b decreases and the surface pressure increases, there is a possibility that the wear of the shaft end surface 12b increases. The countermeasure in such a case is shown in FIG. FIG. 6 is a cross-sectional view showing another member at the shaft end of the engine valve.

As shown in FIG. 6, a cap-like separate member 17 is attached to and integrated with the shaft end portion 12 a of the valve shaft portion 12 of the engine valve 10. On the outer peripheral surface of the shaft end portion 12a of the valve shaft portion 12, a male screw portion 12c is formed. Further, the separate member 17 is formed in a bottomed cylindrical shape, and includes a disk-shaped end plate portion 18 and a cylindrical tubular portion 19. The outer diameter 18 d of the end plate portion 18 is larger than the shaft diameter 12 d of the valve shaft portion 12. For this reason, the end surface by the end plate part 18, that is, the shaft end surface 18 a has an area larger than the area of the shaft end surface 12 b of the valve shaft part 12.
An internal thread portion 19 a is formed on the inner peripheral surface of the cylindrical portion 19. The female thread portion 19a is formed so as to be capable of being screwed to the male thread portion 12c of the shaft end portion 12a of the valve shaft portion 12. The separate member 17 is made of, for example, an iron alloy and is subjected to a quenching process.

  The separate member 17 is integrated into a cap shape by screwing the female thread portion 19a to the male thread portion 12c of the shaft end portion 12a with respect to the shaft end portion 12a of the valve shaft portion 12. Then, the valve contact portion 43b (see FIG. 5) of the rocker arm 43 is brought into contact with the shaft end surface 18a of the end plate portion 18 of the separate member 17. In the state where the valve shaft 12 is inserted from below into the valve guide 32 (see FIG. 5), another member 17 is attached to the shaft end 12a of the valve shaft 12 and integrated.

  Therefore, the separate member 17 can form the shaft end surface 18a having an area larger than the area of the shaft end surface 12b of the shaft end portion 12a of the valve shaft portion 12, thereby preventing wear of the shaft end surface 12b of the engine valve 10. Can do. The separate member 17 only needs to have at least the shaft end surface 18a having excellent wear resistance, and the material, surface treatment, shape, and the like are not limited. Further, the separate member 17 can be integrated with the shaft end portion 12a of the valve shaft portion 12 not only by screwing but also by attachment means such as press-fitting, adhesion, and brazing.

Although the embodiments of the present invention have been described above, it is added that the embodiments of the present invention described herein have the following technical matters in addition to the technical matters described in the claims. Keep it.
(1) The engine valve according to any one of claims 1 to 4,
When the umbrella diameter of the valve umbrella is Φ32 mm to Φ38 mm and the shaft diameter of the valve shaft is Φ4.2 mm to Φ4.5 mm, the ratio of the shaft diameter of the valve shaft to the umbrella diameter of the valve umbrella is An engine valve characterized by being 7.1 or more and 9 or less.
If comprised in this way, the ratio of the shaft diameter of the valve shaft part with respect to the umbrella diameter of a valve umbrella part, making the umbrella diameter of a valve umbrella part equivalent to the conventional (refer to the conventional examples 1 and 2 in Table 1). An engine valve with a value of 7.1 or more and 9 or less can be obtained.

  The present invention is not limited to the above-described embodiments, and modifications can be made without departing from the gist of the present invention. For example, the engine valve 10 of the present invention is not limited to an indirect drive type such as an OHC mechanism, but can also be applied to a direct drive type valve operating mechanism that is directly driven by the camshaft 40. Moreover, what is necessary is just to perform the 3rd process P3 and / or the 4th process P4 as needed during the manufacturing process of the engine valve 10.

It is process drawing which shows the manufacturing method of the engine valve concerning one Example of this invention. It is a side view which shows an engine valve. It is a side view which shows an engine valve molded object. It is a graph which shows the relationship between the tempering process temperature of SUH3, and hardness. It is sectional drawing which shows the valve operating mechanism of an engine. It is sectional drawing which shows another member of the axial edge part of an engine valve. It is sectional drawing which shows the poppet valve concerning a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine valve 12 Valve shaft part 12a Shaft end part 12b Shaft end surface 13 Valve umbrella part 17 Separate member 20 Engine valve molded object

Claims (6)

Quenching the solid engine valve molded body in which the valve shaft portion and the valve umbrella portion are integrally formed by forging an iron alloy material; and
An engine valve manufactured by a method for manufacturing an engine valve, comprising: subjecting the engine valve molded body after the quenching treatment to a low-temperature tempering treatment. The engine valve according to claim 1,
An engine valve characterized in that the hardness after the low temperature tempering treatment is HV530 or more in terms of Vickers hardness. The engine valve according to claim 1 or 2,
Machining the engine valve after the low-temperature tempering treatment;
An engine valve manufactured by a method for manufacturing an engine valve comprising: subjecting the engine valve after machining to a surface treatment at a temperature equal to or lower than the low-temperature tempering temperature. The engine valve according to any one of claims 1 to 3,
An engine valve characterized in that the iron alloy is martensitic heat resistant steel. The engine valve according to any one of claims 1 to 4,
A ratio of the outer diameter of the valve shaft portion to the outer diameter of the valve umbrella portion is 7 or more. The engine valve according to any one of claims 1 to 5,
An engine valve characterized in that another member forming a shaft end surface having an area larger than the area of the shaft end surface of the shaft end portion is integrated with the shaft end portion of the valve shaft portion.

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