JP2010261511A - Solenoid valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solenoid valve reducing a fluid force applied to a coil spring in a simple configuration. <P>SOLUTION: In this solenoid valve 100 allowing a first hydraulic fluid chamber 136 and a second hydraulic fluid chamber 138 to disconnect from each other or communicate with each other, a rod 114 is moved in an axial direction. A seat 118 having a valve seat 118b allows the first hydraulic fluid chamber 136 and second hydraulic fluid chamber 138 to disconnect from each other or communicate with each other by seating or separating the rod end 114a on or from the valve seat 118b from the side of the first hydraulic fluid chamber 136. The coil spring 122 is externally inserted into the rod 114, and has a predetermined diameter. A hydraulic fluid bypass flow passage is formed between the valve seat 118b and the first hydraulic fluid chamber 136. The opening 188g of the bypass flow passage with respect to the first hydraulic fluid chamber 136 is arranged radially outward of the outside diameter of the coil spring 122. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electromagnetic valve that opens and closes a coil by supplying current to a coil.

  2. Description of the Related Art In recent years, development of an electronically controlled brake system that improves running stability and vehicle safety by electronically controlling braking force applied to each of a plurality of wheels mounted on a vehicle has been actively promoted. In an electronically controlled brake system, an electromagnetic valve that opens and closes a valve by supplying a current to a coil is widely used for increasing and decreasing a wheel cylinder pressure.

  Here, a coil spring for biasing the rod is provided inside the electromagnetic valve. If the coil spring is on the flow path of the brake fluid, the fluid force of the brake fluid acts on the coil spring, the spring characteristics of the coil spring may fluctuate, and the valve opening characteristics of the electromagnetic valve may change.

  In Patent Document 1, the upper end portion of a spring is seated on the flange portion of a large-diameter valve body, and the lower end portion of the spring is a step portion formed on the inner periphery of the valve body at a position above a port through which fluid flows. It is disclosed to be seated.

JP 2001-263528 A

  In the solenoid valve described in Patent Document 1, since the spring is arranged at the step portion formed on the inner periphery of the valve body, the area of the inner peripheral surface of the valve body that slides with the large-diameter valve body is reduced. Depending on the processing accuracy of the inner peripheral surface, unevenness occurs in the sliding characteristics between the valve body and the large-diameter valve body.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electromagnetic valve that can reduce the fluid force applied to the coil spring with a simple configuration.

  In order to solve the above-described problems, an electromagnetic valve according to an aspect of the present invention is an electromagnetic valve that blocks or communicates between a first hydraulic fluid chamber and a second hydraulic fluid chamber, and includes a rod that moves in an axial direction, a valve seat A seat that blocks or communicates between the first hydraulic fluid chamber and the second hydraulic fluid chamber by allowing the end portion of the rod to be seated on or separated from the valve seat from the first hydraulic fluid chamber side; A coil spring that is extrapolated and has a predetermined diameter. A flow path for the hydraulic fluid is formed between the valve seat and the first hydraulic fluid chamber, and the opening of the flow channel with respect to the first hydraulic fluid chamber is disposed radially outside the outer diameter of the coil spring.

  According to this aspect, the hydraulic fluid when the first hydraulic fluid chamber and the second hydraulic fluid chamber communicate with each other in order from the second hydraulic fluid chamber is the valve seat, the flow channel, the opening of the flow channel, and the first hydraulic fluid chamber. Flowing into. At this time, since the hydraulic fluid flowing out from the opening of the flow path passes outside the outer diameter of the coil spring, the fluid force of the hydraulic fluid applied to the coil spring can be reduced.

  You may further provide the spring receiving part contact | abutted with the one end part of a coil spring. One end portion of the coil spring may urge the seat through the spring receiving portion, and the flow path may lead from the valve seat to the outer diameter side of the spring receiving portion. The opening portion of the flow path may be formed on the outer peripheral surface of the spring receiving portion. The spring receiving portion may be formed integrally with the seat. The spring receiving part may be formed of a member different from the sheet. The spring receiving portion may have a spring receiving surface of the spring receiving portion with which one end portion of the coil spring abuts. The opening of the flow path may be formed between the spring receiving surface and the valve seat in the axial direction. Accordingly, the hydraulic fluid flows into the first hydraulic fluid chamber through the opening located below the spring receiving surface with which the coil spring abuts, so that the fluid force applied to the coil spring can be reduced.

  According to the electromagnetic valve according to the present invention, the fluid force applied to the coil spring can be reduced with a simple configuration.

It is sectional drawing of the solenoid valve which concerns on embodiment. (A) is a cross-sectional view of a part of the solenoid valve in which no bypass channel is formed, and (b) is a cross-sectional view of a part of the solenoid valve according to the embodiment. It is a figure which shows the fluid force concerning a rod and a coil spring when it opens. It is sectional drawing of the modification of the solenoid valve which concerns on embodiment.

  FIG. 1 is a cross-sectional view of a solenoid valve 100 according to an embodiment. The electromagnetic valve 100 according to the embodiment may be a linear valve used in a vehicle brake circuit. In the solenoid valve 100, the amount of current supplied is adjusted by an electronic control unit (hereinafter referred to as "ECU") provided in the vehicle, and the opening of the valve is adjusted. The solenoid valve 100 closes in a state where a valve closing current is supplied, shuts off the flow of hydraulic fluid, and opens normally when the supply of electric current is reduced or stopped to flow the hydraulic fluid. It is a solenoid valve.

  The solenoid valve 100 includes a guide 110, a shaft 112, a rod 114, a plunger 116, a seat 118, a sleeve 120, a coil spring 122, a coil yoke 126, a ring yoke 128, and a coil 130. For convenience, the upper side in the drawing will be described as the upper side and the lower side will be described as the lower side.

  The guide 110 is a magnetic body formed in a columnar shape. A sheet fitting hole 110a is formed on the upper side from a substantially axial center, and a shaft sliding hole 110c on the lower side is coaxial with the central axis of the guide 110. It is provided so that it may penetrate. An insertion hole 110d having a slightly larger inner diameter than the shaft sliding hole 110c is provided at the upper end of the shaft sliding hole 110c. Further, the guide 110 is provided with a lead-out port 110b penetrating in a radial direction from the inner wall of the sheet insertion hole 110a to the outer surface. The lead-out port 110b communicates with the hydraulic pressure supply / discharge pipe of the brake circuit, and guides the hydraulic fluid flowing into the first hydraulic fluid chamber 136 from the second hydraulic fluid chamber 138 to the hydraulic pressure supply / discharge pipe. The opening of the outlet port 110b on the first hydraulic fluid chamber 136 side is disposed at a position larger than the predetermined diameter of the coil spring 122 and larger than the outer diameter of the spring receiving portion 118e.

  The shaft 112 is formed of a non-magnetic material, and is provided with a shaft fitting insertion portion 112a having a diameter smaller than that of other portions over a predetermined length from an upper end portion. A rod fitting insertion hole 112b, which is a bottomed hole, is provided at the lower end of the shaft 112 coaxially with the central axis.

  The rod 114 is made of a nonmagnetic material, and the rod end portion 114a is formed in a hemispherical shape. The rod 114 moves in the central axis direction, and the rod end portion 114a is seated on or separated from the valve seat 118b of the seat 118 from the first hydraulic fluid chamber 136 side, whereby the first hydraulic fluid chamber 136 and the second hydraulic fluid chamber. 138 is cut off or communicated.

  A rod fitting insertion portion 114b is provided over a predetermined length from the upper end opposite to the rod end portion 114a. The rod fitting insertion portion 114b is fitted into the rod fitting insertion hole 112b of the shaft 112, and the rod 114 is fixed coaxially to the shaft 112. A flange portion 114c is provided between the rod end portion 114a and the rod fitting insertion portion 114b. The flange portion 114 c locks the upper end portion of the coil spring 122. Further, the flange portion 114 c comes into contact with the lower end of the shaft 112.

  The plunger 116 is a magnetic body formed in a cylindrical shape, and a shaft fitting insertion hole 116a is provided so as to penetrate coaxially with the central axis. The plunger 116 is provided with an insertion portion 116b having a smaller diameter than the other outer peripheral surface over a predetermined length from the lower end. The plunger 116 is fixed to the shaft 112 by inserting the shaft fitting insertion portion 112a of the shaft 112 into the shaft fitting insertion hole 116a from the lower end side where the insertion portion 116b is provided.

  The sheet 118 is a nonmagnetic material formed in a columnar shape. The seat 118 includes a large diameter portion 118d that is inserted into the sheet insertion hole 110a, and a spring receiving portion 118e that has a smaller diameter than the large diameter portion 118d. The sheet 118 is inserted into the sheet insertion hole 110a of the guide 110 from the spring receiving portion 118e side, and is fitted so as not to come out of the guide 110. That is, the outer diameter of the large diameter portion 118d is equal to the inner diameter of the sheet insertion hole 110a.

  The large-diameter portion 118d of the seat 118 is provided with an introduction port 118a and a second hydraulic fluid chamber 138 coaxially with the central axis. The second hydraulic fluid chamber 138 is narrowed in the deep portion above the drawing, and a communication hole is formed. A tapered valve seat 118b is formed on the opposite side of the second hydraulic fluid chamber 138 in which the communication hole is formed. The communication hole of the valve seat 118b is smaller in diameter than the rod 114 and the second hydraulic fluid chamber 138.

  The spring receiving portion 118e locks the lower end portion of the coil spring 122. The spring receiving portion 118e may be formed in a cylindrical shape protruding upward from the large diameter portion 118d. The spring receiving portion 118e of the seat 118 is provided with a rod insertion hole 118f that communicates with the valve seat 118b coaxially with the central axis, and a through hole 118c is provided in the middle of the rod insertion hole 118f. The rod end 114a is inserted into the rod insertion hole 118f so as to be seated on or separated from the valve seat 118b. The through hole 118c serves as a flow path for the hydraulic fluid that leads from the gap between the rod end portion 114a and the valve seat 118b to the outer diameter side of the spring receiving portion 118e. The opening 118g on the outer diameter side of the through hole 118c is provided on the outer peripheral surface of the spring receiving portion 118e. The spring receiving portion 118e is formed integrally with the seat 118.

  The sleeve 120 is formed in a cup shape integrally coupled to a main body portion 120a which is a magnetic body formed in a columnar shape so that the cylindrical portion is coaxial. The cylindrical portion has a guide portion 120b formed of a nonmagnetic material. The guide part 120b is provided over a predetermined length from the opening end on the lower side.

  After the plunger 116 is inserted into the cylindrical portion of the sleeve 120, the guide 110 is fitted into the cylindrical portion of the sleeve 120 from the side where the insertion hole 110 d is provided, and the guide 110 is fixed to the sleeve 120. The shaft 112, the rod 114, and the seat 118 are sequentially inserted into the predetermined holes, and the rod end portion 114a is provided so as to be movable in a direction toward the valve seat 118b and a direction away from the valve seat 118b. The rod end 114a is prevented from communicating with the first hydraulic fluid chamber 136 and the second hydraulic fluid chamber 138 by being seated on the valve seat 118b, and is separated from the first hydraulic fluid chamber 136 by being separated from the valve seat 118b. The two hydraulic fluid chambers 138 are communicated.

  The coil 130 is wound around a bobbin 132 outside the sleeve 120 so as to surround the outside of the plunger 116. The coil yoke 126 is a magnetic body formed in a cup shape, and an insertion hole for the sleeve 120 is provided at the center. The coil yoke 126 is disposed outside the coil 130 in the radial direction so that the coil yoke 126 surrounds the coil 130. The ring yoke 128 is a disk-shaped magnetic body, and is fixed to the guide 110 by fitting a central insertion hole into the outer periphery of the guide 110. The coil yoke 126 is attached to the sleeve 120 and the ring yoke 128. Thus, the outer periphery of the coil 130 is covered with the coil yoke 126 and the ring yoke 128 which are magnetic materials.

  The bottom portion 120 c of the sleeve 120 is located above the plunger 116. When a current is supplied to the coil 130, a first repulsive force is generated between the upper end portion 116 c of the plunger 116 and the bottom portion 120 c of the sleeve 120 in the lower side of the drawing. When the plunger 116 moves up and down by electromagnetic force, the shaft 112 and the rod 114 also move up and down together with the plunger 116.

  The coil spring 122 is extrapolated to the rod 114 and has a predetermined diameter. A coil spring 122 is disposed between the flange portion 114 c of the rod 114 and the seat 118. One end of the coil spring 122 abuts on the flange portion 114c of the rod 114, and the other end of the coil spring 122 abuts on the spring receiving surface of the upper end surface of the spring receiving portion 118e to urge the rod 114 upward in the drawing. . One end portion of the coil spring 122 biases the flange portion 114c of the rod 114 upward, and the other end portion of the coil spring 122 biases the seat 118 downward via the spring receiving portion 118e. Here, since the seat 118 is fixed to the guide 110, when no electromagnetic force is applied to the solenoid valve 100, the rod end portion 114a is separated from the valve seat 118b by the biasing force of the coil spring 122. .

  By the way, when the solenoid valve 100 is opened, if the coil spring 122 is on the flow path of the hydraulic fluid, the coil spring 122 receives fluid force from the hydraulic fluid. The spring characteristics of the coil spring 122 can be changed by the fluid force of the hydraulic fluid in accordance with the flow rate or turbulent flow of the hydraulic fluid, and the valve opening characteristics of the electromagnetic valve 100 can be changed.

  Therefore, in the electromagnetic valve 100 of the embodiment, a bypass flow path is formed in which the hydraulic fluid that flows from the second hydraulic fluid chamber 138 through the communication hole of the valve seat 118b flows around the coil spring 122. Specifically, a flow path for the hydraulic fluid is formed between the valve seat 118b and the first hydraulic fluid chamber 136 across the opening 118g for communicating from the valve seat 118b to the first hydraulic fluid chamber 136. This bypass flow path is formed from the communication hole of the valve seat 118b to the opening 118g of the through hole 118c through the gap between the rod end 114a and the valve seat 118b and the through hole 118c. That is, the bypass flow path is a flow path that leads from the valve seat 118b to the outer diameter side of the spring receiving portion 118e. Further, the bypass channel is formed in a space in the sheet 118. As a result, when the solenoid valve 100 is opened, the hydraulic fluid flows from the second hydraulic fluid chamber 138 sequentially to the outlet port 110b through the valve seat 118b and the through hole 118c, and is applied to the coil spring 122. The fluid force can be reduced. Here, the bypass flow path will be described with reference to FIG.

  Fig.2 (a) shows sectional drawing of a part of solenoid valve in which the bypass flow path is not formed, FIG.2 (b) shows sectional drawing of a part of solenoid valve 100 which concerns on embodiment. The arrows shown in FIGS. 2A and 2B indicate the flow of hydraulic fluid when the valve is opened.

  The arrows in FIG. 2A indicate that the hydraulic fluid that has come out from the gap between the valve seat of the seat 142 and the lower end portion of the rod 144 passes around the coil spring 146 and flows to the outlet port 110b. Therefore, the fluid force of the hydraulic fluid that intersects the coil spring 146 is loaded on the coil spring 146.

  On the other hand, the arrow in FIG. 2 (b) indicates that the hydraulic fluid exiting from the valve seat 118b is in order, the gap between the rod end 114a and the valve seat 118b, the through hole 118c, the opening 118g, the first hydraulic fluid chamber 136, and the lead-out. It shows that it is flowing to the port 110b. Since the hydraulic fluid that has exited from the opening 118 g of the bypass channel passes outside the outer diameter of the coil spring 122, it does not intersect with the coil spring 122. Thereby, the fluid force of the hydraulic fluid loaded on the coil spring 122 at the time of valve opening can be reduced.

  Returning to FIG. An opening 118 g of the bypass flow path with respect to the first hydraulic fluid chamber 136 is disposed on a radially outer side than the outer diameter of the coil spring 122. As a result, the hydraulic fluid flowing from the opening 118g of the through hole 118c to the outlet port 110b passes outside the outer diameter of the coil spring 122, so that the coil spring 122 is almost affected by the fluid force of the hydraulic fluid passing through the bypass channel. Can not be.

  Since the outer diameter of the spring receiving portion 118 e is larger than the outer diameter of the coil spring 122, the opening 118 g of the detour channel is located on the outer diameter side of the predetermined diameter of the coil spring 122. The bypass passage opening 118g is disposed between the spring receiving surface of the spring receiving portion 118e and the valve seat 118b in the axial direction. As a result, the hydraulic fluid flows into the first hydraulic fluid chamber 136 through the opening 118g located below the spring receiving surface with which the coil spring 122 abuts, so that the hydraulic fluid exiting from the communication hole of the valve seat 118b is coil spring 122. Therefore, the fluid force applied to the coil spring 122 can be reduced.

  The diameter of the through hole 118c is formed larger than the minute gap between the rod insertion hole 118f and the rod 114. Thereby, hydraulic fluid flows through a detour channel. You may form the direction of the through-hole 118c toward the derivation | leading-out port 110b so that the hydraulic fluid which exits from the opening part 118g may go to the derivation | leading-out port 110b. For example, the through hole 118c may be formed so that the central axis of the through hole 118c is directed to the outlet port 110b.

  FIG. 3 shows the fluid force applied to the rod 114 and the coil spring 122 when the valve is opened. The vertical axis of the figure shows the fluid force (N), and the horizontal axis shows the distance (mm) at which the rod end 114a and the valve seat 118b are separated. A curve 12 in this figure indicates the fluid force in the solenoid valve provided with no bypass flow path shown in FIG. 2A, and a curve 14 indicates the fluid force in the solenoid valve 100 according to the embodiment. The fluid force shown in this figure indicates the sum of the fluid forces loaded on the rod 114 and the coil spring 122, respectively.

  When the valve seat 118b is closed, that is, when the separation distance is zero, the fluid force applied to the rod 114 is the same. When the separation distance increases from zero, the electromagnetic valve 100 is opened, and a fluid force is applied to the coil spring shown in FIG. On the other hand, the fluid force is hardly applied to the coil spring 122 shown in FIG. The fluid force applied to the rod is the same, and the difference between the curve 12 and the curve 14 is the difference in the fluid force applied to the coil spring. Comparing the curve 12 and the curve 14, by providing the bypass flow path, the fluid force applied to the coil spring 122 of the electromagnetic valve 100 according to the embodiment is greatly reduced than the fluid force applied to the coil spring of the solenoid valve having no bypass flow path. It has been shown that. Moreover, it becomes easy to control the solenoid valve 100 in brake control by using the solenoid valve 100 according to the embodiment.

  FIG. 4 is a cross-sectional view of a modified example of the electromagnetic valve 100 according to the embodiment. This figure shows a part of the solenoid valve 100. In the electromagnetic valve 100, the spring receiving portion 134 is formed in a cup shape and is formed of a member different from the seat 118.

  The spring receiving portion 134 includes a central hole 134b into which the rod end portion 114a is inserted, and an opening 134a provided in the cylindrical portion of the spring receiving portion 134. The protruding portion 118h is provided on the upper side of the sheet 118 in the drawing, and protrudes a predetermined distance upward in the axial direction from the upper end of the large diameter portion 118d. A tapered valve seat 118b is provided on the upper surface of the protrusion 118h. The open end of the spring receiving portion 134 is fitted into the outer periphery of the protruding portion 118h. The central hole 134b of the spring receiving portion 134 and the communication hole of the valve seat 118b are provided coaxially. A third hydraulic fluid chamber 140 is formed by the inner periphery of the spring receiving portion 134 and the upper end surface of the seat 118, and the rod end portion 114 a is inserted into the third hydraulic fluid chamber 140.

  The upper end portion of the coil spring 122 is in contact with the flange portion 114 c of the rod 114, and the lower end portion of the coil spring 122 is in contact with the spring receiving surface on the upper end surface of the spring receiving portion 134. The coil spring 122 biases the rod 114 upward, and the coil spring 122 biases the spring receiving portion 134 in the direction opposite to the rod 114. Further, the end portion of the coil spring 122 biases the sheet 118 via the spring receiving portion 134.

  A bypass flow path for the hydraulic fluid is formed between the valve seat 118b and the first hydraulic fluid chamber 136 across the opening 134a of the spring receiving portion 134 for communicating with the first hydraulic fluid chamber 136 from the valve seat 118b. . A bypass flow path is formed in which the hydraulic fluid that exits from the second hydraulic fluid chamber 138 through the communication hole of the valve seat 118 b flows around the coil spring 122. This bypass flow path is formed from the communication hole of the valve seat 118b to the opening 134a through the third hydraulic fluid chamber 140. That is, the bypass flow path is a flow path that leads from the valve seat 118b to the outer diameter side of the spring receiving portion 134. As a result, the hydraulic force of the hydraulic fluid applied to the coil spring 122 by the hydraulic fluid that has flowed into the first hydraulic fluid chamber 136 passes through the outer diameter side of the coil spring 122 can be reduced.

  The opening 134a is disposed between the spring receiving surface of the spring receiving portion 134 and the valve seat 118b in the axial direction. Thereby, since the opening part 134a is located below the coil spring 122, it is possible to prevent the hydraulic fluid flowing through the bypass flow path from directly contacting the coil spring 122. The outer diameter of the cylindrical portion of the spring receiving portion 134 is larger than the outer diameter of the coil spring 122, and the opening 134 a of the bypass flow path with respect to the first hydraulic fluid chamber 136 is disposed radially outside the outer diameter of the coil spring 122. As a result, the hydraulic fluid that has passed through the bypass flow path passes through the outer diameter side of the coil spring 122 and flows to the outlet port 110b, and the fluid force that the hydraulic fluid applies to the coil spring 122 can be reduced.

  The present invention is not limited to the above-described embodiments, and an appropriate combination of the elements of each embodiment is also effective as an embodiment of the present invention. Various modifications such as design changes can be added to each embodiment based on the knowledge of those skilled in the art, and embodiments to which such modifications are added can also be included in the scope of the present invention.

  For example, the outlet port 110b, the opening 118g and the opening 134a of the bypass channel may be provided at the same position in the axial direction. For example, the center of each hole is provided at the same position in the axial direction. Further, the opening 118g and the opening 134a and the outlet port 110b may be provided so as to overlap in the axial direction. As a result, the hydraulic fluid can easily pass from the opening of the bypass channel to the outlet port 110b.

  DESCRIPTION OF SYMBOLS 100 Solenoid valve, 110 Guide, 110a Sheet insertion hole, 110b Derivation port, 110c Shaft sliding hole, 110d Insertion hole, 112 Shaft, 112a Shaft insertion part, 112b Rod insertion hole, 114 Rod, 114a Rod end part, 114b Rod insertion part, 114c Flange part, 116 plunger, 116a Shaft insertion hole, 116b insertion part, 116c upper end part, 118 seat, 118a introduction port, 118b valve seat, 118c through hole, 118d large diameter part, 118e Part, 118f rod insertion hole, 118g opening part, 118h projecting part, 120 sleeve, 120a body part, 120b guide part, 120c bottom part, 122 coil spring, 126 coil yoke, 1 8 ring yoke, 130 coil, 132 bobbins, 134 spring receiving portion, 134a opening, 134b central hole, 136 a first hydraulic fluid chamber, 138 the second hydraulic fluid chamber, 140 the third hydraulic fluid chamber.

Claims (6)

A solenoid valve that shuts off or communicates between the first hydraulic fluid chamber and the second hydraulic fluid chamber,
An axially moving rod;
A seat having a valve seat, wherein the end of the rod is seated on or separated from the valve seat from the first hydraulic fluid chamber side, so that the first hydraulic fluid chamber and the second hydraulic fluid chamber are shut off or A communicating sheet;
A coil spring extrapolated to the rod and having a predetermined diameter,
Forming a flow path of hydraulic fluid between the valve seat and the first hydraulic fluid chamber;
The electromagnetic valve according to claim 1, wherein an opening of the flow path with respect to the first hydraulic fluid chamber is disposed radially outside the outer diameter of the coil spring. A spring receiver that contacts one end of the coil spring;
One end portion of the coil spring urges the sheet through the spring receiving portion,
The electromagnetic valve according to claim 1, wherein the flow path leads from the valve seat to an outer diameter side of the spring receiving portion.   The electromagnetic valve according to claim 2, wherein the opening of the flow path is formed on an outer peripheral surface of the spring receiving portion.   The electromagnetic valve according to claim 2, wherein the spring receiving portion is formed integrally with the seat.   The solenoid valve according to claim 2, wherein the spring receiving portion is formed of a member different from the seat. The spring receiving portion has a spring receiving surface of the spring receiving portion with which one end of the coil spring abuts.
The electromagnetic valve according to claim 2, wherein the opening of the flow path is formed between the spring receiving surface and the valve seat in the axial direction.

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