JP2017214967A - Valve device and welding method of valve shaft and valve body of valve device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the residual stress of a valve shaft and a valve body after welding, and to suppress the occurrence of a welding crack at a welding part.SOLUTION: An EGR valve body 10 comprises: a valve body 12 having a flow passage 20; a valve shaft 14 which is supported to the valve body 12 so as to be reciprocally and linearly movable; an actuator 16 for reciprocally and linearly moving the valve shaft 14; and a valve body 18 which is fixed to a tip of the valve shaft 14 in a state of being fit thereto, and opens and closes the flow passage 20. A material of the valve shaft 14 is a SUS304-equivalent steel material. A material of the valve body 18 is a SUS316L-equivalent steel material. The valve shaft 14 and the valve body 18 are welded to each other at a tip side of the valve shaft 14. A melting rate of the material of the valve shaft 14 is increased so that a point which is defined on the basis of a CR-equivalent and an Ni-equivalent of a welding part 30 belongs to a safety zone which is defined on the basis of a Scheffler state diagram.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a valve device and a method for welding a valve shaft and a valve body in the valve device.

  Conventionally, for example, as a valve device, for example, there is an EGR valve described in Patent Document 1. In Patent Document 1, an EGR valve is fitted to a valve body having a flow path, a valve shaft supported by the valve body so as to be capable of reciprocating linear motion, an actuator for reciprocating linear motion of the valve shaft, and a tip portion of the valve shaft. And a valve body that is fixed in a closed state and that opens and closes the flow path. On the distal end side of the valve shaft, a welded portion is formed between the valve shaft and the inner peripheral portion of the valve body. In Patent Document 1, the material of the valve body is a steel material equivalent to SUS316L. Further, although the material of the valve shaft is not described, it is usually a steel material equivalent to SUS304. Further, Patent Document 1 does not describe the melting rate of the material for the valve stem.

JP2015-224754A

  An example in which a valve shaft made of a steel material equivalent to SUS304 and a valve body made of a steel material equivalent to SUS316L are welded (this is referred to as a “conventional example”) will be described. FIG. 11 is a cross-sectional view showing a welded portion between a valve shaft and a valve body according to a conventional example. As shown in FIG. 11, the weld height a of the welded portion is about 12% of the shaft diameter b of the valve shaft, the bead diameter c of the welded portion is about 1.95 times the shaft diameter b, and the weld penetration (depth) D) 10% (control value) or more of the shaft diameter b, and the protruding amount e of the valve shaft when the valve body is fitted is 5% of the shaft diameter b of the valve shaft.

  For example, the shaft diameter b of the valve shaft is 4 mm, the welding height a is about 0.5 mm, the bead diameter is about 7.8 mm, the penetration amount d is about 0.5 mm, and the protrusion amount e is 0.2 mm. Further, the welding is TIG welding, the welding current is 205 A, and the welding time is 600 ms (see the characteristic line Lb in FIG. 7). In this case, the melting amount of the valve body material (SUS316 equivalent steel) is large, and the melting rate of the valve stem material (SUS304 equivalent steel) is, for example, about 30% (see point x1 in FIG. 10). . Further, the Ni equivalent of the welded portion is 12.4 (mass%) (see point y1 in FIG. 10). Thus, when the melting rate of the material of the valve stem is low, there has been a problem that high temperature cracks, so-called weld cracks, occur due to shrinkage tensile stress generated after welding, that is, residual stress. Incidentally, the incidence of weld cracking in the conventional example was about 8%.

  A problem to be solved by the present invention is a valve device capable of reducing residual stress after welding between a valve shaft and a valve body and suppressing the occurrence of weld cracks in a welded portion, and the valve shaft and valve in the valve device. It is to provide a method for welding with a body.

  The inventor diligently studied the cause of the occurrence of weld cracks in the welded portion between the valve stem and the valve body in the conventional example, and came to the following conclusion. That is, the presumed mechanism that weld cracks occur is that phosphorus and sulfur are segregated at the grain boundary due to the start of solidification of the weld, the bond strength of the crystal boundary becomes weak, and the bond strength becomes weaker than the residual stress, A weld crack occurs where phosphorus segregates. The reason why phosphorus and sulfur are segregated at the grain boundaries is because there are few ferrite structures that dissolve phosphorus and sulfur in solid solution. That is, because the material of the valve body is a steel material equivalent to SUS316L, which is disadvantageous to weld cracking, and the melting rate of the material of the valve shaft (steel material equivalent to SUS304) is as low as about 30% (see point x1 in FIG. 10), The point determined based on the Cr equivalent and the Ni equivalent in the weld zone deviates from the safety range determined based on the Schaeffler state diagram. That is, the Ni equivalent (see point y1 in FIG. 10) exceeds 12 (mass%) which is the upper limit of the Ni equivalent in the safe range. For this reason, a weld crack occurs. Therefore, increasing the melting rate of the valve stem material (SUS304 equivalent steel) so that the points determined based on the Cr equivalent and Ni equivalent in the weld belong to the safety range determined based on the Schaeffler phase diagram. Thus, it has been found that the occurrence of weld cracks can be suppressed.

  The said subject can be solved by the valve apparatus of this invention, and the welding method of the valve shaft and valve body in the valve apparatus. The first invention is fitted to a valve body having a flow path, a valve shaft supported by the valve body so as to be capable of reciprocating linear motion, an actuator for reciprocating linear motion of the valve shaft, and a tip of the valve shaft. And a valve body that opens and closes the flow path, wherein the valve stem material is stainless steel, and the valve body material is equivalent to a stainless steel material having high corrosion resistance. A high Ni-containing steel material, and on the tip side of the valve shaft, between the valve shaft and the inner peripheral portion of the valve body, a welded portion fixed to each other by melting is formed. In the valve device, the melting rate of the material of the valve shaft is increased so that a point determined based on the Cr equivalent and Ni equivalent in the weld belongs to a safety range determined based on the Schaeffler state diagram. According to this configuration, the melting rate of the material of the valve stem is increased so that the points determined based on the Cr equivalent and Ni equivalent in the weld belong to the safety range determined based on the Schaeffler state diagram. Thereby, the residual stress after welding with a valve stem and a valve body can be reduced, and generation | occurrence | production of the weld crack in a welding part can be suppressed.

  In a second aspect based on the first aspect, the weld height of the welded portion is 20% or more of the shaft diameter of the valve shaft, and the bead diameter of the welded portion is 2 of the shaft diameter of the valve shaft. It is a valve device that is less than double. According to this configuration, it is possible to suppress an increase in the melt amount of the valve body material with respect to the melt amount of the valve shaft material in the welded portion, and to increase the melting rate of the valve shaft material.

  According to a third invention, in the first or second invention, the material of the valve shaft is a steel material equivalent to SUS304, the material of the valve body is a steel material equivalent to SUS316L, and the Ni equivalent of the welded portion is 12 It is a valve device which is (mass%) or less. According to this configuration, the Ni equivalent of the welded portion can belong to a safety range determined based on the Schaeffler state diagram.

  According to a fourth aspect of the present invention, there is provided a valve body having a flow path, a valve shaft supported by the valve body so as to be capable of reciprocating linear motion, an actuator for reciprocating linear motion of the valve shaft, and a tip of the valve shaft. A valve body that is fixed in a closed state and that opens and closes the flow path, wherein the valve shaft is made of stainless steel, and the valve body The material is a high Ni-containing steel material equivalent to a stainless steel material having high corrosion resistance, and the valve shaft and the inner peripheral portion of the valve body are fixed to each other by melting both at the tip side of the valve shaft. The valve stem and the melted valve body so that the point determined based on the Cr equivalent and Ni equivalent in the weld belongs to a safety range determined based on the Schaeffler state diagram. Valve device for welding A welding method with definitive valve shaft and the valve body. According to this configuration, the valve shaft and the valve body are welded so that the points determined based on the Cr equivalent and the Ni equivalent in the weld belong to the safety range determined based on the Schaeffler state diagram. Thereby, the residual stress after welding with a valve stem and a valve body can be reduced, and generation | occurrence | production of the weld crack in a welding part can be suppressed.

  5th invention is the welding method of the valve stem and valve body in the valve apparatus of Claim 4 in 4th invention, Comprising: The protrusion amount of the said valve shaft at the time of fitting the said valve body is set. It is the welding method of the valve shaft and valve body in a valve apparatus which performs the said welding in the state made into 30% or more of the shaft diameter of the said valve shaft. According to this configuration, the melting rate of the valve shaft material can be increased.

  6th invention is the welding method of the valve axis | shaft and valve body in a valve apparatus in which the said welding is TIG welding in 4th or 5th invention. According to this structure, the workability | operativity of welding with a valve stem and a valve body can be improved by performing TIG welding.

It is sectional drawing which shows the EGR valve | bulb concerning Embodiment 1. FIG. It is sectional drawing which shows the welding part of a valve stem and a valve body. It is a top view which shows the welding part of a valve stem and a valve body. It is sectional drawing which shows the state which fitted the valve body to the valve stem. It is sectional drawing which shows the welding state of a valve stem and a valve body. It is a state figure of Schaeffler concerning explanation of a fusion ingredient of a welding part. It is a graph which shows the relationship between welding time and welding current. It is a graph which shows the relationship between the welding time when the protrusion amount of a valve shaft is 0.2 mm, and a bead diameter. It is a graph which shows the relationship between the welding time when the protrusion amount of a valve shaft is 1.6 mm, and a bead diameter. It is a graph which shows the relationship between the protrusion amount of a valve stem, the melting rate of the material of a valve stem, and Ni equivalent. It is sectional drawing which shows the welding part of the valve stem concerning a prior art example, and a valve body.

  Hereinafter, an embodiment for carrying out the present invention will be described with reference to the drawings. In the present embodiment, a poppet valve type EGR valve is exemplified as the valve device. The EGR valve is used in an exhaust gas recirculation device (EGR device) that returns a part of the exhaust gas of an engine, which is an internal combustion engine, to the intake passage as EGR gas, and adjusts the EGR gas flow rate. FIG. 1 is a sectional view showing an EGR valve. Although the vertical and horizontal orientations of the EGR valve are determined based on FIG. 1, it does not specify the arrangement form of the EGR valve.

  As shown in FIG. 1, the EGR valve 10 includes a valve body 12, a valve shaft 14, an actuator 16, and a valve body 18. The valve body 12 is made of metal and has an EGR gas flow path 20. The flow path 20 is formed in an L shape. The upper opening of the flow path 20 is an inlet 20a through which EGR gas is introduced, and the side opening is an outlet 20b through which EGR gas is led out. In the valve body 12, a hollow cylindrical shaft support hole 12a penetrating in the vertical direction is formed concentrically with the inlet 20a. An annular valve seat 22 having a valve hole 22a is attached in the middle of the flow path 20, that is, in the lower part of the inlet 20a. The valve seat 22 is made of metal and is arranged so as to be concentric with the inlet 20a.

  The valve shaft 14 is made of stainless steel and has a round shaft shape. The valve shaft 14 is supported so as to be capable of reciprocating linearly in the vertical direction through two upper and lower thrust bearings 24 and 25 with respect to the shaft support hole 12a of the valve body 12. The valve shaft 14 is disposed so as to be concentric with the valve seat 22. Between the shaft support hole 12a of the valve body 12 and the valve shaft 14, a seal member 26 that elastically seals between the two and a deposit guard plug 27 that guards the two from deposits are provided. The deposit guard plug 27 is disposed in the upper end opening of the shaft support hole 12a. The seal member 26 is disposed between the upper thrust bearing 24 and the deposit guard plug 27.

  The actuator 16 is installed on the lower surface side of the valve body 12 by fastening or the like. The actuator 16 is, for example, a step motor, and is a drive source that drives the valve shaft 14, that is, reciprocates linearly. The rotational motion of the rotor 28 rotated forward and backward by energization of the actuator 16 is converted into a linear reciprocating motion (stroke motion) of the valve shaft 14 via the screw mechanism 29. In the present embodiment, the output shaft of the actuator 16 also serves as the valve shaft 14, but a separate valve shaft may be connected to the output shaft. Since the step motor is a well-known one, detailed description is omitted. The actuator 16 is controlled to open and close by a control device (ECU) (not shown).

  The valve body 18 is formed in a poppet shape, that is, an inverted conical shape. The valve body 18 is formed with a round hole-shaped shaft hole 18a penetrating in the axial direction. The valve body 18 has an upper end surface 18b formed of a plane orthogonal to the axis (see FIG. 4 described later). The valve body 18 is fixed by welding (reference numeral 30 is attached to the welded portion) in a state of being fitted to the distal end portion (upper end portion) of the valve shaft 14. The valve body 18 can open and close the flow path 20 by moving up and down integrally with the valve shaft 14, that is, can be separated from and seated on the valve seat 22. The valve seat 22 and the valve body 18 constitute an EGR gas metering unit. The welded structure between the valve shaft 14 and the valve body 18 will be described later.

  Here, the material of the valve shaft 14 is a steel material equivalent to SUS304 (hereinafter referred to as “SUS304”). The valve shaft 14 is formed by forging. The material of the valve body 18 is a steel material equivalent to SUS316L (hereinafter referred to as “SUS316L”) corresponding to a high Ni-containing steel material equivalent to a stainless steel material having high corrosion resistance in order to cope with poor fuel. The valve body 18 is formed by cutting. The valve shaft 14 may be formed by cutting. The outer shape of the valve body 18 may be formed by forging, and the shaft hole 18a may be formed by cutting.

  Table 1 is an example of a chemical composition table showing chemical composition (mass%) of SUS304 which is a material of the valve shaft 14 and SUS316L which is a material of the valve body 18. In addition, the value of Table 1 is an average value for 10 lots of each steel material. From Table 1, it can be seen that SUS316L has a higher Ni content and higher corrosion resistance than SUS304.

  The EGR valve 10 is installed, for example, by fastening with respect to an engine head of an engine (not shown). The flow path 20 of the EGR valve 10 is interposed in the middle of the EGR passage for returning engine exhaust gas (EGR gas) to the intake passage. The EGR valve 10 controls the flow rate of EGR gas by adjusting the opening degree of the valve body 18 by opening / closing control of the ECU.

  Next, a method for welding the valve shaft 14 and the valve body 18 in the EGR valve 10 will be described. 4 is a cross-sectional view showing a state in which the valve body is fitted to the valve shaft, and FIG. 5 is a cross-sectional view showing a welded state between the valve shaft and the valve body. Prior to welding the valve shaft 14 and the valve body 18, parts other than the valve body 18 are assembled to the valve body 12. Under the control of the actuator 16, the valve shaft 14 is positioned at an initial position which is a control reference position.

  As shown in FIG. 4, the valve body 18 is fitted to the valve shaft 14 and seated on the valve seat 22. At this time, the tip end portion of the valve shaft 14 protrudes from the upper end surface 18 b of the valve body 18 with a protrusion amount E. In this state, the valve shaft 14 and the valve body 18 are TIG welded using a TIG (Tungsten Inert Gas) welder (see FIG. 5).

  That is, as shown in FIG. 5, a cylindrical ground electrode 34 is concentrically disposed on the valve body 18. A cylindrical welding torch 36 is disposed in the ground electrode 34 so as to form a double ring shape. From the welding torch 36, a shielding gas (see arrow G in FIG. 5) for performing TIG welding is ejected. The shield gas is, for example, an inert gas such as helium gas or argon gas. A welding electrode rod 38, which is a tungsten electrode, is disposed in the center of the welding torch 36. The welding electrode rod 38 protrudes toward the vicinity of the tip of the valve shaft 14 located directly below. The welding electrode rod 38 and the ground electrode 34 are connected to a welding power source (not shown).

  In this state, TiG welding is performed by supplying a welding current from the welding power source to the welding electrode rod 38 while the shielding gas is ejected from the welding torch 36 around the welding electrode rod 38. Then, due to an arc generated immediately below the welding electrode rod 38, the valve shaft 14 and the inner peripheral portion of the valve body 18 are melted (welded) between the valve shaft 14 and the inner peripheral portion of the valve body 18 on the distal end side (upper end side) of the valve shaft 14. The welded portions 30 fixed to each other are formed (see FIGS. 2 and 3).

  FIG. 2 is a sectional view showing a welded portion between the valve shaft and the valve body, and FIG. 3 is a plan view of the same. As shown in FIG. 3, the welded portion 30 is formed in a circular shape that is concentric with the valve shaft 14 in plan view. Further, in the welded portion 30 (see FIG. 2), reference numeral A denotes a welding height, C denotes a bead diameter, and D denotes a penetration amount (depth). B indicates the shaft diameter of the valve shaft.

The results of various experiments and studies are described below. CAE was examined for the protrusion amount E (see FIG. 4) of the valve shaft 14. According to the result, as the protruding amount E increases, the residual stress after welding decreases as the welding height A (see FIG. 2) increases. Therefore, it can be determined that it is advantageous for suppressing weld cracking (hot cracking). It was also recognized that increasing the protrusion amount E increases the melting rate of the valve stem material (SUS304) and provides a ferrite structure, which is advantageous for suppressing weld cracking. In addition, the melting rate of the material of the valve stem in the weld is
Melting rate of valve shaft material (%) = melting amount of valve shaft material × 100 / (melting amount of valve shaft material + melting amount of valve body material)
Is calculated by

  From Table 1 above, SUS304 has a Cr equivalent of 18.04 (mass%) and a Ni equivalent of 10.02 (mass%). SUS316L has a Cr equivalent of 16.5 (mass%) and a Ni equivalent of 12.05 (mass%). For this reason, in FIG. 6 which showed the Schaeffler state diagram concerning description of the fusion | melting component of a welding part, SUS304 is located in the point Z1 and SUS316L is located in the point Z2. That is, although SUS304 belongs to the safety range, SUS316L is out of the safety range, so that it can be said that the weldability is poor. Therefore, by increasing the melting amount of SUS304, the point determined based on the Cr equivalent and Ni equivalent can be shifted to the safe range (downward in FIG. 6). In this case, welding cracks can be suppressed by setting the upper limit of the Ni equivalent, which is a target value for preventing weld cracks, to 12 (mass%) or less.

  Next, welding conditions for improving the melting ratio of SUS316L and SUS304 were examined. FIG. 7 is a graph showing the relationship between welding time and welding current. In the case of the conventional example, as indicated by the characteristic line Lb in FIG. 7, the welding current was 205 A and the welding time was 600 ms. In this case, since the welding current is large, the energy applied to the joint between the valve shaft and the valve body is large, so that heat is applied over a wide range. Therefore, the bead diameter c (see FIG. 11) is increased by increasing the melting amount of the valve body material (SUS316L).

  Therefore, by lowering the welding current and increasing the welding time, the energy applied to the joint between the valve shaft and the valve body is reduced, so that the valve body melts from the tip of the valve shaft and heat transfer. Therefore, the melting amount of the valve body material (SUS316L) is reduced while the melting amount of the valve shaft material (SUS304) is increased. Thereby, it is estimated that the bead diameter C (refer to FIG. 2) is reduced, so that the melting rate of the valve shaft material (SUS304) is increased. In FIG. 7, the characteristic line La in this embodiment is a case where the welding current is 150 A and the welding time is 1000 ms, and is considered suitable for mass production based on the non-defective area confirmation result (described later). Is.

  Next, the welding state was confirmed by a short shot. FIG. 8 shows the result when the protrusion E (see FIG. 4) of the valve shaft 14 is 0.2 mm. In FIG. 8, the characteristic line Lc shows the characteristic with a welding current of 150 A, and the characteristic line Ld shows the characteristic with a welding current of 200 A. Both are the results when welding was performed with a welding time of 100 ms and 300 ms.

  Further, FIG. 8 shows the result when the protruding amount E (see FIG. 4) of the valve shaft 14 is 1.6 mm. In FIG. 9, the characteristic line Le shows the characteristic with a welding current of 150 A, and the characteristic line Lf shows the characteristic with a welding current of 200 A. Both are the results when welding was performed with a welding time of 100 ms and 300 ms.

  8 and 9, when the welding current is lower and the welding time is shorter, the valve body is melted by heat transfer from the valve shaft, and welding with a small bead diameter is possible. The melting rate of SUS304 is It can be seen that it is increased.

  Next, the good quality area of the welding condition change was confirmed. Here, welding was performed at welding currents of 100 A, 125 A, 150 A, 175 A, and 200 A and welding times of 500 ms, 1000 ms, 1500 ms, and 2000 ms, respectively.

(1) When the welding current was 100 A, the welding time was 500 ms or 1000 ms, the bead diameter C was too small and the penetration amount D was insufficient, but a good product was obtained when the welding time was 1500 ms.
(2) When the welding current was 125 A, a good product was obtained at any welding time.
(3) At a welding current of 150 A, a temper color appeared in part with a welding time of 2000 ms and seizure occurred, but a good product was obtained at other welding times.
(4) At a welding current of 175 A, a temper color appeared in part at a welding time of 2000 ms and seizure occurred, but a good product was obtained at other welding times.
(5) At a welding current of 200 A, a good product was obtained with a welding time of 500 ms. However, the welding time was 1000 ms and the bead diameter C was excessive, and the welding time was 1500 ms and the bead diameter C was excessive and partly tempered. Color appeared and burn-in occurred. In addition, when the welding time was 2000 ms, the bead diameter C was excessive and the temper color appeared, and seizure occurred.

  Therefore, from the above (1) to (5), it is considered that the welding condition is that the welding current is set to 150 A and the welding time is set to 1000 ms, so that the defective product generation rate is small and suitable for mass production (in FIG. 7). , See characteristic line La). In this case, the bead diameter C (see FIG. 2) is reduced from about 7.8 mm of the conventional bead diameter c (see FIG. 11) to 6.7 mm. Further, the penetration amount D (see FIG. 2) can ensure 0.4 mm or more as a management value for obtaining a predetermined welding strength.

  Next, the effect at the time of changing welding conditions was examined. Welding was performed by setting the protrusion E of the valve shaft 14 (see FIG. 4) to 0.2 mm, which is the same as that of the conventional example, the welding current under welding conditions was 150 A, and the welding time was 1000 ms. In this case, the melting rate of the valve shaft material (SUS304) was 47% (see point x2 in FIG. 10). Therefore, the bead diameter C is reduced because the valve shaft material (SUS304) is melted more preferentially than the valve body material (SUS316L) by reducing the welding current under welding conditions and extending the welding time. Thus, the melting amount of the valve body material (SUS316L) is reduced. Therefore, the melting rate of the valve body material (SUS316L) can be increased from 30% (see point x1 in FIG. 10) to 47% (see point x2 in FIG. 10), which is advantageous in suppressing weld cracking. I understand. Further, the Ni equivalent of the welded portion is 12.02 (mass%) (see point y2 in FIG. 10).

  Next, the effect was verified. FIG. 10 is a graph showing the relationship between the protruding amount of the valve shaft, the melting rate of the material of the valve shaft, and the Ni equivalent. As shown in FIG. 10, the amount of protrusion E (see FIG. 4) of the valve shaft 14 is increased to 1.2 mm and the effect of changing the welding current and welding time of the welding conditions causes the valve shaft material (SUS304) to melt. It was confirmed that the rate increased greatly. That is, the melting rate of the conventional valve stem material (SUS304), which was 30% (see point x1 in the figure), is increased to 66% (see point X1 in the figure). Along with this, the Ni equivalent of the weld decreases to 11.6 (mass%) (see point Y1 in the figure). Further, when the protrusion amount E is increased to 1.6 mm, the melting rate increases to 73% (see the point X2 in the figure). Along with this, the Ni equivalent of the weld decreases to 11.5 (mass%) (see point Y2 in the figure). Therefore, it is confirmed that the Ni equivalent is 12 (mass%) or less, which is the upper limit value of the Ni equivalent in the safety range determined based on the Schaeffler phase diagram, regardless of whether the protrusion E is 1.2 mm or 1.6 mm. It was done. Therefore, it can be determined that welding cracks can be suppressed.

  Next, the effect was confirmed. When the protruding amount E of the valve shaft 14 (see FIG. 4) is 1.2 mm and 1.6 mm, the welding current is 150 A, the welding time is 1000 ms, and the valve shaft and the valve body are welded, in either case, It was confirmed that there was an effect of suppressing weld cracking. Moreover, in embodiment, it was confirmed that the penetration amount D (refer FIG. 2) of the welding part 30 is 0.4 mm or more, and weld strength 256N or more is ensured. Incidentally, the penetration amount D is preferably set to 0.4 to 1.04 mm. Further, it was confirmed that the protruding amount E (see FIG. 4) of the valve shaft 14 is 1.2 to 1.6 mm, and the residual stress of the welded portion can be reduced to −243 to −324 MPa. In addition, the residual stress of the welding part of the prior art example was -196 MPa.

  Based on the examination result, the welding height A of the welded portion 30 (see FIG. 2) is set to 20% or more of the shaft diameter B of the valve shaft 14. In addition, the bead diameter C of the welded portion 30 is not more than twice the shaft diameter B of the valve shaft 14. Further, the penetration amount D of the welded portion 30 is set to 10% (control value) or more of the shaft diameter B of the valve shaft 14. Further, the protruding amount E (see FIG. 4) of the valve shaft 14 is 30% or more of the shaft diameter B of the valve shaft 14. For example, when the shaft diameter B of the valve shaft 14 is 4 mm, the welding height A is 0.8 mm or more, the bead diameter C is 8 mm or less, the penetration amount D is 4 mm or more, and the protrusion amount E is 1.2 mm or more.

  According to the EGR valve 10 described above, the melting rate of the material of the valve shaft 14 is increased so that the points determined based on the Cr equivalent and Ni equivalent in the welded portion 30 belong to the safety range determined based on the Schaeffler state diagram. Has been. Thereby, the residual stress after welding with the valve stem 14 and the valve body 18 can be reduced, and generation | occurrence | production of the weld crack in the welding part 30 can be suppressed.

  Further, the welding height A of the welded portion 30 is 20% or more of the shaft diameter B of the valve shaft 14, and the bead diameter C of the welded portion 30 is not more than twice the shaft diameter B of the valve shaft 14. Therefore, an increase in the melting amount of the material of the valve body 18 with respect to the melting amount of the material of the valve shaft 14 in the welded portion 30 can be suppressed, and the melting rate of the material of the valve shaft 14 can be increased.

  The valve shaft 14 is made of SUS304, the valve body 18 is made of SUS316L, and the Ni equivalent of the welded portion 30 is 12 (mass%) or less. Therefore, the Ni equivalent of the welded portion 30 can belong to a safety range determined based on the Schaeffler state diagram.

  Moreover, according to the welding method of the valve shaft 14 and the valve body 18 in the EGR valve 10 described above, the point determined based on the Cr equivalent and Ni equivalent in the welded portion 30 is within the safety range determined based on the Schaeffler state diagram. The valve shaft 14 and the valve body 18 are welded so as to belong. Thereby, the residual stress after welding with the valve stem 14 and the valve body 18 can be reduced, and generation | occurrence | production of the weld crack in the welding part 30 can be suppressed.

  Further, welding is performed in a state where the protruding amount E of the valve shaft 14 when the valve body 18 is fitted is 30% or more of the shaft diameter B of the valve shaft 14. Therefore, the melting rate of the material of the valve shaft 14 can be increased.

  Moreover, the workability | operativity of welding with the valve stem 14 and the valve body 18 can be improved by performing TIG welding.

[Other Embodiments] The present invention is not limited to the embodiments and can be modified without departing from the gist of the present invention. For example, the valve device of the present invention is not limited to the EGR valve 10 and can be applied to valve devices for other uses. Further, as the actuator 16, a DC motor may be used instead of the step motor. The valve shaft 14 and the valve body 18 may be welded by welding other than TIG welding, for example, laser welding. Further, the material of the valve body 18 may be a high Ni content steel material equivalent to a stainless steel material having high corrosion resistance other than SUS316L.

10 ... EGR valve (valve device)
DESCRIPTION OF SYMBOLS 14 ... Valve shaft 16 ... Actuator 18 ... Valve body 20 ... Flow path 30 ... Welding part A ... Welding height B ... Shaft diameter C ... Bead diameter E ... Projection amount

Claims (6)

A valve body having a flow path;
A valve shaft supported by the valve body so as to be capable of reciprocating linear movement;
An actuator for reciprocating linear movement of the valve shaft;
A valve body that is fixed in a state of being fitted to a distal end portion of the valve shaft and opens and closes the flow path;
A valve device comprising:
The valve stem material is stainless steel,
The material of the valve body is a high Ni content steel material equivalent to a stainless steel material having high corrosion resistance,
On the tip side of the valve shaft, a welded portion is formed between the valve shaft and the inner peripheral portion of the valve body.
The valve device in which the melting rate of the material of the valve shaft is increased so that a point determined based on Cr equivalent and Ni equivalent in the weld belongs to a safety range determined based on a Schaeffler state diagram. The valve device according to claim 1,
The weld height of the weld is 20% or more of the shaft diameter of the valve shaft,
The valve device, wherein a bead diameter of the welded portion is not more than twice a shaft diameter of the valve shaft. The valve device according to claim 1 or 2,
The material of the valve stem is a steel material equivalent to SUS304,
The material of the valve body is a steel material equivalent to SUS316L,
The valve device, wherein the Ni equivalent of the weld is 12 (% by mass) or less. A valve body having a flow path;
A valve shaft supported by the valve body so as to be capable of reciprocating linear movement;
An actuator for reciprocating linear movement of the valve shaft;
A valve body that is fixed in a state of being fitted to a distal end portion of the valve shaft and opens and closes the flow path;
A method of welding the valve stem and the valve body in the valve device,
The valve stem material is stainless steel,
The material of the valve body is a high Ni content steel material equivalent to a stainless steel material having high corrosion resistance,
On the tip side of the valve shaft, a welded portion is formed between the valve shaft and the inner peripheral portion of the valve body.
The valve stem in the valve device that welds the valve stem and the valve body so that a point determined based on the Cr equivalent and Ni equivalent in the weld belongs to a safety range determined based on the Schaeffler state diagram. And welding method of valve body. A method for welding the valve shaft and the valve body in the valve device according to claim 4,
A welding method between a valve shaft and a valve body in a valve device, wherein the welding is performed in a state in which a protruding amount of the valve shaft when the valve body is fitted is 30% or more of a shaft diameter of the valve shaft. A method of welding the valve shaft and the valve body in the valve device according to claim 4 or 5,
The welding is a method of welding the valve shaft and the valve body in the valve device, which is TIG welding.

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