Hollow engine valve

Abstract

To provide a hollow engine valve capable of suppressing a decrease in strength by suppressing the temperature rise.SOLUTION: A shaft hollow engine valve which has a shaft part 101 and an umbrella part 102 enlarged in diameter in an umbrella shape in one end of the shaft part 101, and in which a coolant N melting at a predetermined temperature and becoming liquid so as to move in a hollow part 106 is sealed in the hollow part 106 formed inside the shaft part 101 is such that: a sealing amount of the coolant N is 0.3 or more and less than 0.5 to the volumetric capacity of the hollow part 106; and a sealing amount of a powdery or granular getter material G to be sealed in the hollow part 106 together with the coolant N is 0.1 g / cm3 or more and 0.5 g / cm3 or less to a remaining volumetric capacity acquired by excluding the volume of the coolant N from the volumetric capacity of the hollow part 106.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a hollow engine valve.

Background Art

[0002] Conventionally, for an engine valve that allows intake gas to flow into the combustion chamber of an engine such as an automobile or a ship and discharges exhaust gas, there is a hollow engine valve (hereinafter, also simply referred to as an engine valve) in which a coolant such as metallic sodium is enclosed in a hollow portion with a hollow interior (see Patent Document 1).

[0003] Such an engine valve becomes hot when exposed to combustion gas or exhaust gas, but the strength of the valve itself decreases as the temperature rises, so a design for suppressing the temperature rise has been implemented.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the case of such an engine valve having a hollow only in the shaft portion, the conventional design has a limited effect of suppressing temperature rise. For example, in order to improve the performance of the engine valve, it is conceivable to reduce the wall thickness of the shaft portion or make the inside of the umbrella hollow to reduce the weight of the engine valve. However, with simple thinning, the heat capacity decreases, and due to a rapid temperature rise, valve push-up or a decrease in the strength of the valve itself occurs, making it difficult to put into practical use.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a hollow engine valve capable of suppressing temperature rise and maintaining strength.

Means for Solving the Problems

[0007] (1) According to the first aspect of the present invention, in a hollow engine valve having a shaft portion and an umbrella portion that expands in diameter in an umbrella shape at one end of the shaft portion, and a cooling material that melts at a predetermined temperature and can move in a liquid state is enclosed in a hollow portion formed at least inside the shaft portion, the enclosed amount of the cooling material is set to be 0.3 or more and less than 0.5 with respect to the volume of the hollow portion, and the enclosed amount of a powdery or granular getter material enclosed in the hollow portion together with the cooling material is 0.1 g / cm 3 or more and 0.5 g / cm 3 or less with respect to the remaining volume obtained by subtracting the volume of the cooling material from the volume of the hollow portion.

[0008] According to the configuration of (1) above, by appropriately setting the enclosed amount of the getter material enclosed in the hollow portion based on the volume of the hollow portion in which the cooling material can move, the movement of the cooling material is not hindered by the presence of the getter material, and the residual gas in the hollow portion can be adsorbed (removed) to make the inside of the hollow portion vacuum. Therefore, the movement of the cooling material in the hollow portion becomes smooth, and the shaking effect of the cooling material due to the vertical movement of the hollow engine valve can be enhanced.

[0009] Thereby, the cooling effect of the cooling material can be enhanced to suppress the high temperature of the hollow engine valve, and the strength of the shaft hollow engine valve can be maintained.

[0010] (2) According to the second aspect of the present invention, in the first aspect, the shaft diameter D2 of the shaft portion and the hollow diameter D3 of the hollow portion have the relationship of the following mathematical formula (1). (D2 - D3) / 2 = 0.8 mm to 1.0 mm ··· (1)

[0011] According to the configuration of (2) above, by thinning the wall thickness of the shaft portion to 0.8 mm to 1.0 mm, the heat dissipation performance of the shaft portion can be improved, the high temperature of the hollow engine valve can be suppressed, and the strength can be maintained.

[0012] (3) According to the third aspect of the present invention, in the above first aspect or second aspect, heat insulation or heat shielding treatment is performed on either one or both of the outer surface and the inner surface of the umbrella portion.

[0013] According to the configuration of the above (3), by performing heat insulation or heat shielding treatment on the umbrella portion that is easily affected by the heat of combustion gas or exhaust gas, heat transfer from the combustion gas or exhaust gas is prevented, the temperature rise of the hollow engine valve is suppressed, and the strength of the hollow engine valve can be maintained.

Effects of the Invention

[0014] According to the present invention, the temperature rise of the hollow engine valve can be suppressed and the strength can be maintained.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0016] (This Embodiment) Hereinafter, with reference to FIGS. 1 to 7, the present invention will be described in detail through an embodiment of the invention. However, the following embodiments are illustrative and do not limit the invention according to the claims. Note that the direction of the shaft-hollow engine valve 100 will be described based on the direction (up, down, left, right) in FIG. 1(a).

[0017] (Shaft-hollow engine valve 100) The shaft-hollow engine valve (hereinafter simply referred to as the engine valve) 100 is provided inside the intake port and the exhaust port that communicate with the combustion chamber of an engine (not shown) such as an automobile, and moves in the vertical direction during actual engine operation to open and close the intake port and the exhaust port. The engine valve 100 can supply intake gas from the intake port into the combustion chamber by opening the intake port, and can discharge the exhaust gas in the combustion chamber from the exhaust port to the outside of the combustion chamber by opening the exhaust port.

[0018] As shown in FIG. 1(a), the engine valve 100 includes a round bar-shaped shaft portion 101 and an umbrella portion 102 that is concentrically and umbrella-shapedly expanded in diameter at the lower end portion of the shaft portion 101. A hollow portion 106 is provided inside the shaft portion 101. The umbrella portion 102 has a disk-shaped umbrella surface portion 103 on the lower surface side, a tapered umbrella back portion 104 on the upper surface side, and an outer peripheral portion 105 formed by the thickness of the umbrella portion 102 between the umbrella surface portion 103 and the umbrella back portion 104. The umbrella back portion 104 has a face surface 104a that extends straight upward and centripetally from the upper portion of the outer peripheral portion 105, and a neck portion 104b that is continuously provided from the upper end portion of the face surface 104a and extends curvedly upward and centripetally toward the shaft portion 101.

[0019] (Coating portion C) As shown in the hatched areas of the dots in FIGS. 1(a) and (b), etc., a coating portion C with a heat insulation coating is provided on the surface of the umbrella portion 102 excluding the face surface 104a of the engine valve 100. The coating portion C employs a material (for example, ceramic) with a lower thermal conductivity than the base material (for example, SUS) of the engine valve 100.

[0020] In this way, by applying a heat insulation coating to the surface of the umbrella portion 102, it is possible to prevent heat input from the relatively large-area umbrella portion 102 exposed to combustion gas or exhaust gas, and suppress a rapid temperature rise of the engine valve 100.

[0021] Note that the coating portion C may be provided only on the surface of either one of the umbrella front portion 103 or the umbrella back portion 104. Further, when the coating portion C is provided on the umbrella back portion 104, the coating portion C may also be provided on the face surface 104a. In addition, instead of the heat insulation coating, a heat shielding coating or mirror finishing (for example, with an arithmetic mean roughness Ra of 0.3 or less) may be applied to the umbrella portion 102 of the engine valve 100. In this case, the engine valve 100 can obtain the same effect as when the heat insulation coating is applied to the umbrella portion 102. Also, depending on the part of the engine valve 100, the type of coating may be changed or mirror finishing may be performed.

[0022] (Internal structure of engine valve 100) As shown in FIG. 2, the engine valve 100 includes a valve body 100a formed by a forging process and a shaft hollowing process described later, and a shaft end member 100b that is round bar-shaped with the same diameter and the same material as the shaft portion 101a of the valve body 100a and is fixed to the upper end portion of the shaft portion 101a.

[0023] The bottomed hollow portion 106 formed inside the shaft portion 101a of the valve body 100a is open at the top by an opening portion 106b provided at the upper portion of the shaft portion 101. Thereby, in the valve body 100a, powdery or granular getter material G (for example, titanium powder) can be introduced into the hollow portion 106 from the opening portion 106b, and a rod-shaped coolant (for example, metallic sodium N) can be inserted (hereinafter, the getter material G and the metallic sodium N are collectively referred to as "coolant, etc.").

[0024] Here, the getter material G such as titanium is introduced into the hollow portion 106 together with the metallic sodium N, thereby removing the corrosion factors of the metallic sodium N and adsorbing (removing) the residual gas in the hollow portion 106 to make the inside of the hollow portion 106 a vacuum. Thereby, the movement of the molten metallic sodium N in the hollow portion 106 can be made smooth.

[0025] Also, the metallic sodium N becomes liquid when heated during actual operation of the engine, and by moving up and down (shaking) inside the hollow portion 106 in accordance with the movement of the engine valve 100, the heat received from the combustion chamber side can be efficiently transferred to the valve guide that guides the up and down movement of the engine valve 100 via the shaft portion 101. That is, due to the shaking effect of the metallic sodium N, the temperature rise (high temperature) of the engine valve 100 can be suppressed.

[0026] After introducing a coolant or the like into the hollow portion 106, the shaft end member 100b is fixed to the upper end portion of the shaft portion 101a of the valve body 100a by friction pressure welding or the like to close the opening portion 106b. Thereby, the hollow portion 106 is sealed, and the coolant or the like is enclosed in the hollow portion 106. Further, the shaft portion 101a becomes integral (non-separable) with the shaft end member 100b to form the shaft portion 101 of the engine valve 100.

[0027] Note that an opening (not shown) for communicating the hollow portion 106 with the outside may be provided in the umbrella surface portion 103, and after introducing a coolant or the like from the opening with the umbrella surface portion 103 (opening) facing upward, the opening may be closed by a lid member (not shown).

[0028] As shown in FIG. 2, the hollow portion 106 is provided with a hollow bottom portion 106a at the lower part, and the position of the hollow bottom portion 106a is set at a position separated from the surface of the umbrella surface portion 103 by a distance D1 (for example, 1.0 mm to 3.0 mm). Thereby, the shaking effect of the metallic sodium N can reach the umbrella surface portion 103.

[0029] (Relationship between the shaft diameter D2 and the hollow diameter D3) In the engine valve 100 shown in Fig. 2, the relationship between the outer diameter D2 of the shaft portion 101 (hereinafter referred to as the shaft diameter D2) and the inner diameter D3 of the hollow portion 106 (hereinafter referred to as the hollow diameter D3) is set such that the wall thickness t of the hollow portion of the shaft portion 101 is 0.8 mm to 1.0 mm. That is, it has the relationship of the following formula 1. [Equation 1] (D2 - D3) / 2 = 0.8 mm to 1.0 mm

[0030] As an example of this embodiment, engine valves 100 of types 1 to 5 (for example, about 90 mm to 130 mm in overall length) used in passenger gasoline vehicles will be described. As shown in Fig. 3, in the type 1 engine valve 100 with a shaft diameter D2 of φ5.0 mm, the hollow diameter D3 is set to φ3.0 mm to φ3.4 mm. In the type 2 engine valve 100 with a shaft diameter D2 of φ5.5 mm, the hollow diameter D3 is set to φ3.5 mm to φ3.9 mm. In the type 3 engine valve 100 with a shaft diameter D2 of φ6.0 mm, the hollow diameter D3 is set to φ4.0 mm to φ4.4 mm. In the type 4 engine valve 100 with a shaft diameter D2 of φ6.5 mm, the hollow diameter D3 is set to φ4.5 mm to φ4.9 mm. In the type 5 engine valve 100 with a shaft diameter D2 of φ7.0 mm, the hollow diameter D3 is set to φ5.0 mm to φ5.4 mm. By setting the hollow diameter D3 according to the shaft diameter D2 in this way, the wall thickness t of the hollow portion of the shaft portion 101 can be set to 0.8 mm to 1.0 mm.

[0031] Note that for engine valves used in commercial diesel vehicles (for example, about 200 mm in overall length and about φ12 mm in shaft diameter), the wall thickness t can also be set to 0.8 mm to 1.0 mm with the relationship between the shaft diameter D2 and the hollow diameter D3 as described above. That is, the relationship between the shaft diameter D2 and the hollow diameter D3 is not limited by the size of the engine valve.

[0032] As described above, by making the wall thickness t of the hollow portion of the shaft portion 101 thin within the above range, the heat dissipation performance of the shaft portion 101 can be improved, and the cooling effect (heat removal effect) due to the shaking of the getter material G and metallic sodium N with the optimized filling amount described later can be enhanced. Thereby, the high temperature rise of the engine valve 100 can be suppressed, and the strength of the engine valve 100 can be maintained.

[0033] (Optimal filling amount of getter material G) The optimal filling amount A1 of the getter material G of the engine valve 100 of the present embodiment is based on the volume of the remaining hollow portion 106 obtained by subtracting the volume ∨2 of the metallic sodium N from the volume ∨1 of the hollow portion 106 (hereinafter referred to as the hollow remaining volume), and a specific value K (0.1 g / cm 3 0.5 g / cm or more 3 0.5 g / cm or less) (see Equation 2 below). [Equation 2] A1 = K(∨1 - ∨2) K = 0.1 g / cm 3 ~0.5 g / cm 3

[0034] The specific value K was calculated based on the results of a verification experiment regarding the cooling effect due to the difference in the filling amount of the getter material G. In the verification experiment, as shown in FIG. 4, the filling amount of the getter material G was increased step by step from a specific value K = 0 (no getter material G is filled) to 0.1 g / cm 3 until K = 0.5 g / cm 3 was verified. Note that the verification experiment regarding the getter material G was carried out in an environment equivalent to the environment of the engine valve 100 during actual engine operation.

[0035] As a result, as shown in FIG. 4, the temperatures of the umbrella outer surface portion 103 and the umbrella inner surface portion 104 of the engine valve 100 were as follows. When the filling amount of the getter material G is 0 g, the temperature of the umbrella outer surface portion 103 is 668°C, the temperature of the umbrella inner surface portion 104 is 669°C, and when the filling amount of the getter material G is 0.1 g / cm with respect to the hollow remaining volume 3 the temperature of the umbrella outer surface portion 103 is 647°C, the temperature of the umbrella inner surface portion 104 is 643°C, and when the filling amount of the getter material G is 0.2 g / cm with respect to the hollow remaining volume3 In the case of [specific conditions], the temperature of the outer surface 103 of the umbrella is 638 °C, the temperature of the inner surface 104 of the umbrella is 636 °C, and the filling amount of the getter material G is 0.3 g / cm with respect to the hollow residual volume. 3 In the case of [specific conditions], the temperature of the outer surface 103 of the umbrella is 637 °C, the temperature of the inner surface 104 of the umbrella is 635 °C, and the filling amount of the getter material G is 0.4 g / cm with respect to the hollow residual volume. 3 In the case of [specific conditions], the temperature of the outer surface 103 of the umbrella is 633 °C, the temperature of the inner surface 104 of the umbrella is 632 °C, and the filling amount of the getter material G is 0.5 g / cm with respect to the hollow residual volume. 3 In the case of [specific conditions], the temperature of the outer surface 103 of the umbrella became 637 °C, and the temperature of the inner surface 104 of the umbrella became 635 °C.

[0036] Also, as shown in FIG. 4, when looking at the cooling effect at each filling amount of the getter material G in comparison with the case where the filling amount is 0 g, when the filling amount of the getter material G is 0.1 g / cm with respect to the hollow residual volume. 3 In the case of [specific conditions], the temperature difference from the case where the filling amount is 0 g is -21 °C for the outer surface 103 of the umbrella and -26 °C for the inner surface 104 of the umbrella. When the filling amount of the getter material G is 0.2 g / cm with respect to the hollow residual volume. 3 In the case of [specific conditions], the temperature difference from the case where the filling amount is 0 g is -30 °C for the outer surface 103 of the umbrella and -33 °C for the inner surface 104 of the umbrella. When the filling amount of the getter material G is 0.3 g / cm with respect to the hollow residual volume. 3 In the case of [specific conditions], the temperature difference from the case where the filling amount is 0 g is -31 °C for the outer surface 103 of the umbrella and -34 °C for the inner surface 104 of the umbrella. When the filling amount of the getter material G is 0.4 g / cm with respect to the hollow residual volume. 3 In the case of [specific conditions], the temperature difference from the case where the filling amount is 0 g is -35 °C for the outer surface 103 of the umbrella and -37 °C for the inner surface 104 of the umbrella. When the filling amount of the getter material G is 0.5 g / cm with respect to the hollow residual volume. 3 In the case of [specific conditions], the temperature difference from the case where the filling amount is 0 g is -31 °C for the outer surface 103 of the umbrella and -34 °C for the inner surface 104 of the umbrella.

[0037] That is, if the filling amount of the getter material G is at least 0.1 g / cm with respect to the hollow residual volume. 3 or more, the temperature difference from the case where the filling amount is 0 g becomes lower than -20 °C and exhibits an obvious cooling effect. Furthermore, from 0.2 g / cm 3 to 0.5 g / cm 3Up to this point, the temperature difference from the case where the encapsulation amount is 0 g became lower than -30°C, and a higher cooling effect was exhibited.

[0038] From the results of the above verification experiments, the optimal encapsulation amount A1 of the getter material G is set to a specific value K of 0.1 g / cm 3 ~0.5 g / cm 3 (more preferably 0.2 g / cm 3 ~0.5 g / cm 3 ) with respect to the hollow remaining volume.

[0039] As described above, by appropriately setting the encapsulation amount of the getter material G encapsulated into the hollow portion 106 based on the volume of the space in the hollow portion 106 where the metallic sodium N can move, the getter material G does not inhibit the movement of the metallic sodium N. Therefore, the movement of the metallic sodium N in the hollow portion 106 becomes smoother. As a result, it becomes possible to enhance the shaking effect of the coolant due to the vertical movement of the engine valve 100. Therefore, it is possible to suppress the temperature rise of the engine valve 100 and maintain the strength of the engine valve 100.

[0040] Note that the optimal encapsulation amount A1 of the getter material G can also be applied to an umbrella hollow engine valve having a hollow not only in the shaft portion but also in the umbrella portion.

[0041] (Optimal encapsulation amount of metallic sodium N) The optimal encapsulation amount A2 of the metallic sodium N of the engine valve 100 of the present embodiment is set to less than 0.5 (preferably 0.3) with respect to the volume ∨1 of the hollow portion 106 (see the following Mathematical Formula 3). [Equation 3] A2 = ∨1 × 0.3

[0042] Conventionally, for example, the amount of sodium metal N enclosed was set to be 0.5 or more and 0.6 or less with respect to the volume ∨1 of the hollow portion 106. However, in this case, since the sodium metal N itself occupies half of the movable space of the sodium metal N in the hollow portion 106, the sodium metal N could not be efficiently moved. Therefore, the shaking effect of the engine valve 100 was not exerted, and a sufficient cooling effect could not be obtained. However, in the engine valve 100 of the present embodiment, by making the amount of sodium metal N enclosed less than 0.5 with respect to the volume ∨1 of the hollow portion 106 (for example, 0.3 is preferable), a sufficient movable space for the sodium metal N in the hollow portion 106 can be secured. As a result, it becomes possible to enhance the shaking effect of the sodium metal N, so that the temperature rise of the engine valve 100 can be suppressed and the strength of the engine valve 100 can be maintained.

[0043] Note that the optimal enclosed amount A2 of the sodium metal N can also be applied to the above umbrella-shaped hollow engine valve.

[0044] (Overall Optimization of Cooling Design) As described above, the engine valve 100 of the present embodiment is provided with the hollow portion 106 only in the shaft portion 101, and the thickness t of the hollow portion of the shaft portion 101 is thinned in the range of φ0.8 mm to φ1.0 mm, thereby improving the heat transfer amount of the shaft portion 101. As a result, the cooling effect due to the shaking of the getter material G and the sodium metal N with the optimized enclosed amount can be synergistically enhanced. Further, a coating portion C is provided on the umbrella portion 102 where the hollow portion 106 is not provided, and heat transfer from the outside can be suppressed.

[0045] In this way, in the shaft portion 101 of the engine valve 100, the cooling effect due to the shaking of the sodium metal N is enhanced, and in the umbrella portion 102, the rapid temperature rise of the umbrella portion 102 due to heat insulation is suppressed, so that the temperature rise of the entire engine valve 100 can be suppressed, and the strength of the engine valve 100 can be maintained.

[0046] (Apparatus for Coating) In this embodiment, in order to coat the umbrella portion 102 of the engine valve 100, as shown in FIG. 5, the engine valve 100 is provided with a work holding device H that can hold the engine valve 100 so as to be rotatable in a plurality of directions, and a spraying device S that can spray a predetermined coating material (for example, ceramic) onto the target work.

[0047] The work holding device H fixes the upper end portion of the shaft portion 101 of the engine valve 100 by a holding portion H1 that is rotationally driven by a driving means (for example, a motor or the like, not shown), so that the engine valve 100 can be held rotatably in the S1 direction around the axis of the shaft portion 101 shown in FIG. 5 and in the S2 direction perpendicular to the axial direction.

[0048] In this way, while appropriately rotating the engine valve 100 in the S1 direction or the S2 direction by the work holding device H, the spraying device S sprays ceramic or the like onto the engine valve 100, so that the umbrella portion 102 excluding the masking M applied to the shaft portion 101 of the engine valve 100 can be coated evenly.

[0049] (Manufacturing Method of Engine Valve 100) In the forging process of the engine valve 100 of this embodiment, hot forging is performed on a solid round bar (not shown) made of special steel having a predetermined shape (for example, a cylindrical shape), and heat treatment such as annealing is performed to form a semi-finished product 200 shown in FIG. 6(1). Note that the shaft diameter of the shaft portion 201 and the shape and size of the umbrella portion 202 of the semi-finished product 200 are substantially the same as those of the shaft portion 101 and the umbrella portion 102 of the finished engine valve 100.

[0050] Next, in the shaft hollowing process, as shown in FIG. 6(2), the upper portion of the shaft portion 201 of the semi-finished product 200 is cut by a cutter CW, and as shown in FIG. 6(3), a hollow portion 106 is drilled from the cut upper end portion with a drilling drill D to form the valve body 100a. At this time, the wall thickness t of the shaft portion 101 is formed slightly thicker than 0.8 mm to 1.0 mm by the amount of cutting in the polishing process described later.

[0051] Next, in the step of enclosing a coolant or the like, as shown in Fig. 6(4), after introducing the getter material G in the optimum enclosed amount from the opening 106b of the hollow portion 106 of the valve body 100a, the metallic sodium N in the optimum enclosed amount is inserted. Then, as shown in Fig. 6(5), an axial end member 100b is fixedly attached to the upper end portion of the shaft portion 101 of the valve body 100a by friction pressure welding to close the opening 106b and enclose the coolant or the like, thereby forming the engine valve 100 (before finishing).

[0052] Next, the polishing and coating process (finishing process) is composed of a polishing process of polishing the engine valve 100 for each part and a coating process of coating the umbrella portion 102 of the engine valve 100. In the polishing process, as shown in Fig. 7(1), the upper end portion of the shaft portion 101 of the engine valve 100 is polished with a grindstone W.

[0053] Next, in the coating process, as shown in Fig. 7(2), a spraying device S sprays, for example, a ceramic solvent with low thermal conductivity onto the engine valve 100 held while being appropriately rotated in the S1 direction or the S2 direction by a work holding device H. As a result, a ceramic sprayed film is formed on the umbrella portion 102 (the umbrella front surface portion 103 and the umbrella back surface portion 104) of the engine valve 100 where masking M is not applied on the surface of the engine valve 100, and the coating portion C is appropriately provided.

[0054] Again, in the polishing process, as shown in Fig. 7(3), the face surface 104a of the umbrella back surface portion 104 of the engine valve 100 is polished with a grindstone W. Since the face surface 104a is the surface that abuts against the closing port of each port when the engine valve 100 closes the intake port or the exhaust port in the combustion chamber of the engine, airtightness is required and it is polished so as to be free from unevenness.

[0055] Note that the polishing of the face surface 104a may be performed before the coating process shown in Fig. 7(2). That is, since the face surface 104a is coated after the base treatment by polishing, it is finished without unevenness.

[0056] In the final polishing process, after removing the masking M, as shown in FIG. 7(4), the outer peripheral surface of the shaft portion 101 of the engine valve 100 is polished with a grinding stone W. Note that the upper end portion polishing process shown in FIG. 7(1) and the shaft portion polishing process shown in FIG. 7(4) may be interchanged. The engine valve 100 of the present embodiment is completed by the above steps.

Explanation of Reference Numerals

[0057] C Coating portion G Getter material H Work holding device M Masking N Sodium metal S Spraying device W Grinding stone 100 Shaft hollow engine valve 100a Valve body 100b Shaft end member 101 Shaft portion 102 Umbrella portion 103 Umbrella surface portion 104 Umbrella back portion 104a Face surface 104b Head portion 105 Outer peripheral portion 106 Hollow portion 106a Hollow bottom 106b Opening portion 200 Semi-finished product 201 Shaft portion 202 Umbrella portion

Claims

Claim 1 A hollow engine valve having a shaft portion and an umbrella portion that expands in diameter in an umbrella shape at one end of the shaft portion, and a coolant that melts at a predetermined temperature and can move in a liquid state within a hollow portion formed at least inside the shaft portion is enclosed in the hollow portion. In the hollow engine valve, the coolant is metallic sodium, the enclosed amount of the coolant is set such that the lower limit is 0.3 or more and the upper limit is less than 0.5 with respect to the volume of the hollow portion, The encapsulation amount of the powdery or granular getter material encapsulated in the hollow portion together with the coolant is 0.1 g / cm ３ or more and 0.5 g / cm ３ or less with respect to the remaining volume obtained by subtracting the volume of the coolant from the volume of the hollow portion. A hollow engine valve characterized by the above is provided. Claim 2 The hollow engine valve according to claim 1, characterized in that the shaft diameter D2 of the shaft portion and the hollow diameter D3 of the hollow portion have the relationship of the following formula (1). (D2 - D3) / 2 = 0.8 mm to 1.0 mm... (1) Claim 3 The hollow engine valve according to claim 1 or 2, characterized in that heat insulation or heat shielding treatment is performed on one or both of the umbrella surface portion and the umbrella back portion of the umbrella portion.

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