JP2013185541A - Egr valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EGR valve which can make compatible the securement of a sealing force of a seal member and the improvement of the durability thereof.SOLUTION: An EGR valve 10 includes a valve housing 12 in which a gas passage 14 for passing EGR gas is formed, a valve seat 18 provided in the gas passage 14, a valve shaft 26 having a valve element 30 for opening and closing the gas passage 14 when seated and separated on/from the valve seat 18, an actuator 13 for moving the valve shaft 26 in the axial direction, and a seal member 60 which is provided on the valve housing 12 and elastically seals a space between the valve housing 12 and the valve shaft 26. A shaft part of the different shaft diameter is formed in the valve shaft 26 so that the clamping margin of the seal member 60 is changed according to the opening/closing of the valve element 30.

Description

  The present invention relates to an EGR valve used in an exhaust gas recirculation device that returns a part of exhaust gas of an internal combustion engine, that is, an engine, as EGR gas to an intake passage.

  The EGR valve has a gas housing formed by a valve housing in which a gas passage through which EGR gas flowing from the exhaust passage of the engine to the intake passage passes, a valve seat provided in the gas passage, and a seat on and off from the valve seat. A valve shaft having a valve body that opens and closes a passage; an actuator that moves the valve shaft in an axial direction; and a seal member that is provided in the valve housing and elastically seals between the valve housing and the valve shaft. (For example, refer to Patent Document 1). The sealing member suppresses leakage of EGR gas, foreign matter, moisture, and the like from the gas passage to the actuator.

Republished patent WO2010 / 018650

  According to the conventional EGR valve, the tightening margin of the seal member with respect to the valve shaft is constant so that the maximum sealing force is always obtained regardless of the change in the opening degree of the valve body. Therefore, when the sealing force is not required, for example, even when the valve is closed, the maximum sealing force (tightening allowance) is obtained. There was a problem of lowering. Conversely, if the sealing force (tightening allowance) of the sealing member is reduced, the durability of the sealing member can be improved, but sufficient sealing force cannot be obtained when the maximum sealing force is required. . The tightening allowance of the seal member is the difference between the shaft diameter of the valve shaft and the hole diameter of the seal member when the shaft diameter (outer diameter) of the valve shaft is larger than the hole diameter (inner diameter) of the seal member. There is a proportional relationship with force.

  The problem to be solved by the present invention is to provide an EGR valve capable of ensuring both the sealing force of the sealing member and improving the durability.

The above-mentioned problem can be solved by an EGR valve having the gist of the structure described in the claims.
According to the EGR valve described in claim 1, a valve housing in which a gas passage through which EGR gas flowing from an exhaust passage of an engine to an intake passage passes is formed, a valve seat provided in the gas passage, and a valve seat A valve shaft having a valve body that opens and closes a gas passage by being seated and separated, an actuator that moves the valve shaft in an axial direction, and provided between the valve housing and the valve shaft elastically The EGR valve includes a sealing member to be sealed, and a shaft portion having a different shaft diameter is formed on the valve shaft so that a tightening margin of the sealing member changes according to opening and closing of the valve body. According to this configuration, for example, when the valve is opened, the shaft diameter of the shaft portion of the valve shaft corresponding to the seal member is set so as to obtain a tightening margin of the seal member that can ensure a sufficient sealing force. Thereby, leakage of EGR gas, foreign matter, moisture, and the like from the gas passage to the actuator can be suppressed. Further, when the valve is closed, intake negative pressure acts on the gas passage, so that leakage of EGR gas, foreign matter, moisture, and the like from the gas passage to the actuator does not occur. Therefore, since no sealing force is required when the valve is closed, the shaft diameter of the shaft portion of the valve shaft corresponding to the seal member is set to be smaller than the tightening allowance of the seal member when the valve body is opened. Set. As a result, the seal member can be prevented from being sagted or worn, and the durability can be improved. Therefore, it is possible to ensure both the sealing force of the sealing member and the improvement of durability.

  According to the EGR valve described in claim 2, the valve shaft is formed with a shaft portion having a shaft diameter at which the tightening margin of the seal member becomes negative when the valve is closed. Therefore, when the valve is closed, the tightening allowance of the seal member becomes negative, so that the seal member can be elastically restored to a free state, which is effective in preventing the seal member from sag and wear. Further, when the valve is closed, the intake negative pressure acting on the gas passage discharges the air in the internal space of the actuator to the gas passage through the gap between the seal member and the valve shaft, and from the outside to the internal space of the actuator. By introducing fresh air, the internal space of the actuator can be scavenged. As a result, it is possible to prevent the accumulation of foreign matters such as deposits in the internal space of the actuator and the passage space that connects the internal space of the actuator and the gas passage.

  According to the EGR valve described in claim 3, the seal member has a lip that has elasticity and a tightening margin for the valve shaft that changes in accordance with a change in pressure of the gas passage as the valve body opens and closes. The shaft diameter of the shaft portion of the shaft is set in consideration of the tightening margin of the lip of the seal member that changes according to the change in the pressure of the gas passage. Therefore, it is possible to optimize the tightening margin of the lip of the seal member according to the change in the pressure of the gas passage accompanying the opening and closing of the valve body.

According to the EGR valve described in claim 4, the valve shaft has an increase in the tightening margin of the lip of the seal member in the low opening range and the medium opening range, and the lip of the seal member in the high opening range. The shaft portions having different shaft diameters are formed in the low opening range, the medium opening range, and the high opening range so as to reduce the tightening allowance. Therefore, in the low opening range and intermediate opening range of the valve body, EGR gas, foreign matter, moisture, etc. from the gas passage to the actuator are increased by increasing the tightening margin of the lip of the seal member and obtaining sufficient sealing force. Leakage can be prevented.
In the high opening range, the pressure in the gas passage is high, and the pressure acts on the lip of the seal member, so that the lip tightening margin (seal force) increases. However, since the sealing force does not need to be higher than the sealing force in the low and medium opening ranges of the valve body, the lip tightening allowance is reduced to prevent lip sag and wear, and durability. Can be improved.

It is sectional drawing which shows the valve closing state of the EGR valve concerning one Embodiment. It is sectional drawing which shows the half-open state of an EGR valve. It is sectional drawing which shows the fully open state of an EGR valve. It is sectional drawing which shows the principal part in the valve closing state of an EGR valve. It is sectional drawing which shows the principal part in the half open state of an EGR valve. It is sectional drawing which shows the principal part in the fully open state of an EGR valve. It is sectional drawing which shows the principal part of a valve shaft. It is sectional drawing which shows a sealing member.

Hereinafter, an embodiment for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the closed state of the EGR valve, FIG. 2 is a cross-sectional view showing the half-open state, and FIG. 3 is a cross-sectional view showing the full-open state. For convenience of explanation, the basic configuration of the EGR valve will be described and then the configuration of the main part will be described. Further, the upper, lower, left and right sides of the EGR valve are determined with reference to FIG.
As shown in FIG. 1, the EGR valve 10 includes a valve housing 12 and an actuator 13 provided on the valve housing 12. The valve housing 12 is formed with an inverted L-shaped gas passage 14 through which EGR gas flowing from an exhaust passage of an engine (not shown) to an intake passage passes. The lower surface opening of the gas passage 14 serves as an inlet 15 through which EGR gas is introduced, and the side opening serves as an outlet 16 through which EGR gas is led out. An annular valve seat 18 positioned above the inlet 15 is concentrically and fixedly attached in the gas passage 14.

  The valve housing 12 is formed with a hollow cylindrical hollow hole 20 concentric with the valve shaft 18. The hollow hole 20 passes through the upper wall portion of the gas passage 14. The hollow hole 20 is formed in a four-step stepped hole shape, and the first hole portion 21, the second hole portion 22, the third hole portion 23, and the fourth hole portion from the top to the bottom. It has a hole 24. The hole diameter of the second hole portion 22 is smaller than the hole diameter (inner diameter) of the first hole portion 21. The diameter of the third hole 23 is larger than the diameter of the second hole 22. The diameter of the fourth hole 24 is larger than the diameter of the third hole 23. In the present embodiment, the hole diameter of the third hole portion 23 is smaller than the hole diameter of the first hole portion 21, and the hole diameter of the fourth hole portion 24 is larger than the hole diameter of the first hole portion 21. .

  A round shaft-like valve shaft 26 is supported in the hollow hole 20 of the valve housing 12 via a bearing cylinder 28 so as to be movable in the vertical direction. The bearing cylinder 28 is fixedly mounted in the second hole portion 22 of the hollow hole 20. A conical valve body 30 is concentrically and fixedly fitted to the lower end portion of the valve shaft 26. The valve body 30 is disposed below the valve seat 18. Further, the valve body 30 moves in the axial direction (vertical direction in FIG. 1) together with the valve shaft 26 and closes the gas passage 14 by seating (contacting) with the valve seat 18, and further downward from the valve seat 18. The gas passage 14 is opened by separating (separating) (see FIGS. 2 and 3).

  The actuator 13 comprises a step motor that drives the valve shaft 26 in the axial direction (vertical direction in FIG. 1). The actuator 13 includes a stator 33 including a coil 32, a resin casing 35 that covers the outer periphery of the stator 33, a magnet rotor 37 that is rotatably disposed in a hollow portion of the stator 33, and a central portion of the magnet rotor 37. And a screw mechanism 38 for connecting the valve shaft 26 to the valve shaft 26. In the magnet rotor 37, a resin cylindrical magnet cylinder 41 is integrated with an outer peripheral portion of a resin rotor main body 40. An upper end portion of the rotor body 40 is rotatably supported by the casing 35 via a first ball bearing 43. A bearing tube 45 is rotatably supported at the lower end of the magnet tube 41 via a second ball bearing 47. A valve shaft 26 is supported by the bearing cylinder 45 so as to be movable in the axial direction while being prevented from rotating in the direction around the axis. In the present embodiment, the output shaft of the actuator 13 and the valve shaft 26 are combined, but a separate valve shaft 26 may be connected to the output shaft of the actuator 13.

  A connector 49 is formed integrally with the casing 35. A connection terminal 50 is disposed in the connector 49. The connection terminal 50 is connected to the stator 33. The valve shaft 26 is formed with a flange-shaped spring receiving portion 52 positioned below the screw mechanism 38. A first coil spring 54 that biases the valve shaft 26 upward is interposed between the opposed surfaces of the spring receiving portion 52 and the second ball bearing 47 (specifically, the inner ring). A second coil spring 56 that biases the magnet rotor 37 upward is interposed between the opposing surfaces of the magnet rotor 37 and the second ball bearing 47 (specifically, the outer ring).

  The actuator 13 is integrated on the valve housing 12 by fastening a casing 35 or the like. Accordingly, the bearing cylinder 45 of the actuator 13 is fixedly attached to the inside of the first hole portion 21 of the hollow hole 20 of the valve housing 12. In the actuator 13, when the coil 32 is energized, the magnet rotor 37 is rotated forward and backward with a predetermined number of steps, and the rotational movement of the magnet rotor 37 is caused by the axial stroke movement (linear movement) of the valve shaft 26 via the screw mechanism 38. As a result, the valve shaft 26 is driven in the axial direction (vertical direction). The EGR valve 10 is installed by fixing the valve housing 12 to the engine head (not shown) of the engine by fastening or the like.

  An annular seal member 60 is mounted in the third hole 23 of the hollow hole 20 of the valve housing 12. The valve shaft 26 is slidably inserted into the hollow portion of the seal member 60. The seal member 60 elastically seals between the valve housing 12 and the valve shaft 26, thereby suppressing leakage of EGR gas, foreign matter, moisture, and the like from the gas passage 14 to the actuator 13.

  A guard plug 62 is mounted in the fourth hole 24 of the hollow hole 20 of the valve housing 12. The guard plug 62 is a metal annular ring and is fixedly mounted in the fourth hole 24. The valve shaft 26 penetrates the hollow portion of the guard plug 62 in a loose fit. An annular gap is set between the guard plug 62 and the valve shaft 26. The guard plug 62 blocks the heat of the EGR gas in the gas passage 14 and protects the seal member 60, the bearing cylinder 28, and the actuator 13.

  The operation of the EGR valve 10 will be described. Now, the EGR valve 10 is in a closed state (fully closed state) in which the valve body 30 is seated on the valve shaft 26 (see FIG. 1). When part of the exhaust gas discharged from the engine is returned to the engine intake passage as EGR gas, the magnet rotor 37 is rotated (for example, normally rotated) by the operation of the actuator 13 to move the valve shaft 26 downward. By moving, the valve body 30 is separated from the valve seat 18 (see FIGS. 2 and 3). Thereby, since the gas passage 14 is opened, the EGR gas passes through the gas passage 14 from the inlet 15 and is recirculated from the outlet 16 to the intake passage of the engine.

  The flow rate of EGR gas returning to the intake passage of the engine is controlled by varying the distance of the valve body 30 with respect to the valve seat 18 so-called valve opening. That is, the stroke amount (movement amount) of the valve body 30, that is, the valve opening degree is varied by operating the actuator 13, that is, rotating (forward or reverse) the magnet rotor 37 and moving the valve shaft 26 in the vertical direction. Can do. The EGR valve 10 is fully opened when the valve opening is the maximum (see FIG. 3), and is half open when the valve opening is between the closed valve and the fully opened (see FIG. 2). In the present specification, when the valve body 30 is in the open state, a region where the valve opening is small is referred to as a low opening region, and a region where the valve opening is large is referred to as a high opening region. The middle range is called the middle opening range.

  When stopping the recirculation of the EGR gas, the valve body 30 is seated on the valve seat 18 by operating the actuator 13, that is, rotating (reversely rotating) the magnet rotor 37 and moving the valve shaft 26 upward ( (See FIG. 1). As a result, the gas passage 14 is closed (fully closed), so that the recirculation of the EGR gas is stopped.

Next, the structure of the principal part of the EGR valve 10 will be described. 4 is a cross-sectional view showing the main part in the closed state of the EGR valve (see FIG. 1), FIG. 5 is a cross-sectional view showing the main part in the half-open state (see FIG. 2), and FIG. 7 is a cross-sectional view showing the main part of the valve shaft, and FIG. 8 is a cross-sectional view showing the seal member.
As shown in FIG. 8, for example, an oil seal is used for the seal member 60. The seal member 60 has an annular main portion 64 made of a rubber-like elastic material, and an inverted conical cylindrical lip 65 protruding on the inner peripheral surface of the main portion 64. The lip 65 is formed to be elastically deformable in the radial direction. In FIG. 8, the lip 65 is in a free state, and its hole diameter (inner diameter) is 65d.

  As shown in FIG. 4, the seal member 60 is disposed by mounting the main portion 64 in the third hole portion 23 of the hollow hole 20 of the valve housing 12 using elasticity. . The valve shaft 26 is inserted into the hole of the lip 65 so as to be slidable in the vertical direction. Further, since the lip 65 has elasticity and is arranged so that the small-diameter side faces downward, the lip 65 receives the pressure of the gas passage 14 and elastically deforms according to the change in the pressure to thereby tighten the allowance for the valve shaft 26. Changes.

  The valve shaft 26 has three stages of shaft portions having different shaft diameters in the shaft portion corresponding to the lip 65 of the seal member 60 in the drive (operation) range associated with opening and closing of the valve body 30 (see FIG. 1). (See FIGS. 4, 5, and 6) That is, the valve shaft 26 has a first shaft portion 71, a second shaft portion 72, and a third shaft portion 73 from the bottom to the top. That is, the valve shaft 26 has a first shaft portion 71, a second shaft portion 72, and a third shaft portion 73 from the bottom to the top (see FIG. 7).

  As shown in FIG. 4, the first shaft portion 71 is a shaft portion to which the lip 65 of the seal member 60 corresponds when the EGR valve 10 is closed (fully closed) (see FIG. 1). The shaft portion 71 is formed with a shaft diameter 71d (see FIG. 7) smaller than the hole diameter (inner diameter) 65d (see FIG. 8) of the lip 65 in the free state of the seal member 60. For this reason, when the EGR valve 10 is closed, the allowance of the lip 65 of the seal member 60 with respect to the first shaft portion 71 is negative. At this time, since the lip 65 and the first shaft portion 71 are separated from each other, a predetermined annular gap 68 is formed between the lip 65 and the first shaft portion 71 (see FIG. 4).

  As shown in FIG. 5, the second shaft portion 72 has a lip 65 of the seal member 60 in a low opening range and an intermediate opening range (see FIG. 2) in the opened state of the EGR valve 10. Is the corresponding shaft part. The shaft portion 72 is formed with a shaft diameter 72d (see FIG. 7) larger than the hole diameter 65d (see FIG. 8) of the lip 65 in the free state of the seal member 60. For this reason, in the low opening range and the middle opening range of the EGR valve 10, the tightening margin of the lip 65 of the seal member 60 with respect to the second shaft portion 72 is a value necessary for sealing. The lip 65 of the seal member 60 is in elastic contact with the outer peripheral surface of the second shaft portion 72, and with respect to the outer peripheral surface of the second shaft portion 72 as the valve shaft 26 moves in the axial direction. Slide relatively.

  As shown in FIG. 6, the third shaft portion 73 corresponds to the shaft portion to which the lip 65 of the seal member 60 corresponds in the high opening range (see FIG. 3) in the open state of the EGR valve 10. It is. The shaft portion 73 is formed with a shaft diameter 73d (see FIG. 7) that is larger than the hole diameter 65d (see FIG. 8) of the lip 65 in the free state of the seal member 60 and smaller than the shaft diameter 72d of the second shaft portion 72. Has been. For this reason, in the high opening range of the EGR valve 10, the tightening margin of the lip 65 of the seal member 60 with respect to the third shaft portion 73 is greater than the tightening margin of the lip 65 of the seal member 60 with respect to the second shaft portion 72. The quantitative value is a small value. The lip 65 of the seal member 60 is in elastic contact with the outer peripheral surface of the third shaft portion 73, and with respect to the outer peripheral surface of the third shaft portion 73 as the valve shaft 26 moves in the axial direction. Slide relatively.

  According to the EGR valve 10 described above, when the valve is opened (see FIGS. 5 and 6), it corresponds to the seal member 60 so that a margin for tightening the seal member 60 that can ensure a sufficient sealing force is obtained. The shaft diameter 72d (see FIG. 7) of the second shaft portion 72 of the valve shaft 26 and the shaft diameter 73d (see FIG. 7) of the third shaft portion 73 are set. Thereby, leakage of EGR gas, foreign matter, moisture, and the like from the gas passage 14 to the actuator 13 can be suppressed. Further, when the valve is closed (see FIG. 4), the intake negative pressure acts on the gas passage 14, so that leakage of EGR gas, foreign matter, moisture and the like from the gas passage 14 to the actuator 13 does not occur. Therefore, since no sealing force is required when the valve is closed, the sealing member 60 is provided with a tightening allowance (including a negative tightening allowance) smaller than that of the seal member 60 when the valve body 30 is opened. A shaft diameter 71d (see FIG. 7) of the first shaft portion 71 of the corresponding valve shaft 26 is set. As a result, the seal member 60 can be prevented from being sagted or worn, and the durability can be improved. Therefore, ensuring of the sealing force of the sealing member 60 and improvement of durability can be achieved at the same time.

  Further, the valve shaft 26 is formed with a first shaft portion 71 having a shaft diameter 71d (see FIG. 7) in which the tightening allowance of the seal member 60 is negative when the valve is closed (see FIG. 4). Therefore, when the valve is closed, the tightening margin of the seal member 60 becomes negative, so that the seal member 60 can be elastically restored to a free state, which is effective in preventing the seal member 60 from being sagged or worn. Further, when the valve is closed, air in the internal space of the actuator 13 is discharged to the gas passage 14 through the gap 68 between the seal member 60 and the valve shaft 26 by the intake negative pressure acting on the gas passage 14, and the actuator 13 By introducing fresh air from the outside into the internal space, the internal space of the actuator 13 can be scavenged. As a result, it is possible to prevent the accumulation of foreign matters such as deposits in the internal space of the actuator 13 and the passage space connecting the internal space of the actuator 13 and the gas passage 14.

  In the above-described embodiment, the first shaft portion 71 of the valve shaft 26 has a shaft diameter at which the tightening allowance of the lip 65 of the seal member 60 is negative, but the shaft portion 72 has a tightening allowance of the seal member 60 of 0 ( The shaft diameter may be zero), or may be a positive shaft diameter if the tightening margin is smaller than the tightening margin for the second shaft portion 72. In this case, when the tightening margin becomes negative due to elastic deformation of the lip 65 of the seal member 60 due to the intake negative pressure acting on the gas passage 14 when the valve is closed, the internal space of the actuator 13 is scavenged. Is possible.

  Further, the seal member 60 is elastic and has a lip 65 (see FIGS. 4, 5, and 6) in which the tightening margin with respect to the valve shaft 26 changes according to the change in the pressure of the gas passage 14 as the valve body 30 is opened and closed. The shaft diameters 71d, 72d, and 73d (see FIG. 7) of the shaft portions 71 to 73 of the valve shaft 26 are tightened with the lip 65 of the seal member 60 that changes in accordance with the change in the pressure of the gas passage 14. It is set considering the cost. Therefore, the tightening allowance of the lip 65 of the seal member 60 can be optimized according to the change in the pressure of the gas passage 14 accompanying the opening and closing of the valve body 30.

  Further, the valve shaft 26 increases the tightening allowance of the lip 65 of the seal member 60 in the low opening range and the medium opening range (see FIG. 5), and in the high opening range (see FIG. 6). The second shaft portion 72 and the third shaft portions 72d and 73d having different shaft diameters 72d and 73d (see FIG. 7) in the low opening range, the medium opening range and the high opening range so as to reduce the tightening allowance of the 60 lip 65. The shaft portion 73 is formed (see FIGS. 5 and 6). Therefore, in the low opening range and the middle opening range of the valve body 30, the tightening margin of the lip 65 of the seal member 60 with respect to the second shaft portion 72 is increased to obtain a sufficient sealing force. Thus, leakage of EGR gas, foreign matter, moisture, and the like from the actuator to the actuator 13 can be prevented. Further, in the high opening range, the pressure of the gas passage 14 is high, and the pressure acts on the lip 65 of the seal member 60, thereby increasing the tightening margin (seal force) of the lip 65 with respect to the third shaft portion 73. . However, since the sealing force does not need to be increased more than the sealing force in the low opening range and medium opening range of the valve body 30, the lip 65 can be reduced by reducing the tightening margin of the lip 65 with respect to the third shaft portion 73. It can prevent dripping and wear and improve durability.

  The present invention is not limited to the above-described embodiment, and modifications can be made without departing from the gist of the present invention. For example, in the above embodiment, the second shaft portion 72 and the third shaft portion 73 having different shaft diameters are formed in the low opening range, the medium opening range, and the high opening range, but the third shaft portion The shaft diameter 73 d of 73 may be set to be the same as the shaft diameter 72 d of the second shaft portion 72. Further, in the embodiment, the first shaft portion 71 having the shaft diameter 71d in which the tightening margin of the seal member 60 is negative when the valve is closed is formed. The shaft portion 71 is a seal when the valve body 30 is opened. The fastening allowance may be smaller than the fastening allowance of the member 60. Further, as the seal member 60, a seal member having elasticity and a lip 65 that changes the tightening margin with respect to the valve shaft 26 in accordance with a change in pressure of the gas passage 14 as the valve body 30 is opened and closed is used. It is also possible to use a seal member in which the tightening allowance for the valve shaft 26 does not change or hardly changes according to the change in the pressure of the gas passage 14 as the valve body 30 is opened and closed. Further, the presence or absence of the lip 65 of the seal member 60 does not affect the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 ... EGR valve 12 ... Valve housing 13 ... Actuator 14 ... Gas passage 18 ... Valve seat 26 ... Valve shaft 30 ... Valve body 60 ... Seal member 65 ... Lip 71 ... 1st axial part 72 ... 2nd axial part 73 ... Third shaft

Claims (4)

A valve housing in which a gas passage through which EGR gas flowing from the exhaust passage of the engine to the intake passage passes is formed;
A valve seat provided in the gas passage;
A valve shaft having a valve body that opens and closes the gas passage by being seated and separated from the valve seat;
An actuator for moving the valve shaft in an axial direction;
An EGR valve comprising: a seal member provided on the valve housing and elastically sealing between the valve housing and the valve shaft;
The EGR valve is characterized in that a shaft portion having a different shaft diameter is formed on the valve shaft so that a tightening margin of the seal member changes according to opening and closing of the valve body. The EGR valve according to claim 1,
An EGR valve characterized in that a shaft portion having a shaft diameter at which a tightening margin of the seal member is negative when the valve is closed is formed on the valve shaft. The EGR valve according to claim 1 or 2,
The seal member has a lip having elasticity and a tightening margin for the valve shaft that changes in accordance with a change in pressure of the gas passage accompanying opening and closing of the valve body,
An EGR valve characterized in that the shaft diameter of the shaft portion of the valve shaft is set in consideration of a tightening margin of a lip of the seal member that changes in accordance with a change in pressure of the gas passage. The EGR valve according to claim 3,
The valve shaft has a low lip tightening allowance in the low opening range and medium opening range, and a low lip tightening allowance in the high opening range. An EGR valve characterized in that shaft portions having different shaft diameters are formed in an opening region, a middle opening region, and a high opening region.

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