JP7825501B2 - Pipe fittings - Google Patents

Description

The present invention relates to pipe fittings, particularly those with multiple start threads.

A "multiple-start thread" refers to a thread with two or more spirally connected threads. Compared to a single-start thread, a multiple-start thread has a longer axial distance (lead) traveled per rotation, assuming the same axial spacing (pitch) between the threads. Therefore, a multiple-start thread can more easily reduce the number of rotations required to move from the make-up start position to the make-up completion position than a single-start thread. Here, the "make-up start position" refers to the relative position of the two threads when the male thread begins to enter the female thread groove, i.e., when the two threads begin to mesh. Meanwhile, the "make-up completion position" refers to the axial length of the range within the female thread groove when the two threads are meshed, i.e., the relative position of the two threads when the required engagement length is reached. When both threads are coaxially arranged, their relative positions are generally determined by a combination of the circumferential angle of one thread relative to the other and the axial distance (if the two threads are interlocked, this distance may be expressed as a negative value).

Due to these advantages, multiple-start threads are often used to shorten the work time required for fastening (see, for example, Patent Document 1). In particular, when multiple-start threads are used in pipe fittings, the work of connecting pipes using the fittings is expedited. Therefore, pipe fittings with multiple-start threads are useful, for example, in piping equipment used in the manufacture of semiconductors, medical products, pharmaceuticals, or food, particularly in areas where pipes are frequently connected and disconnected. This is because reducing the time required to connect and disconnect pipes effectively reduces the burden on workers performing maintenance such as cleaning. Pipe fittings with multiple-start threads are also useful in piping equipment installed in automobiles that carries gasoline, coolant, exhaust gas, etc. Such piping equipment requires particularly high reliability to ensure the safety of automobiles. To meet this demand while maintaining high workability in assembling piping equipment, using multiple-start threads in pipe fittings is effective in quickly and reliably connecting pipes.

JP 2016-169581 A

In a multiple-start thread, the male thread's threads can generally enter any of the female thread's grooves. Therefore, there are as many fastening start positions as there are threads. Different fastening start positions result in different fastening completion positions, so the number of fastening completion positions is equal to the number of threads. However, having multiple fastening completion positions is not desirable depending on the application of the multiple-start thread. For example, the multiple-start thread disclosed in Patent Document 1 is provided at each open end of two steel pipes to be fastened. These open ends are also provided with a pair of marks that align the threads when they reach the fastening completion position. During the steel pipe fastening operation, aligning these marks confirms that the threads have reached the fastening completion position. In this case, to enable similar confirmation of the arrival of each fastening completion position, a different pair of marks must be provided on both steel pipes for each fastening completion position. However, such marking is cumbersome. Furthermore, when a multiple-start thread is used to fasten two parts that are both rotationally asymmetric, the shapes of the two parts may only align at a specific fastening completion position.

For these applications, it is desirable to pre-select a specific one from multiple make-up completion positions (hereinafter referred to as the "correct make-up completion position") and reduce the possibility of the screw reaching a position other than that (hereinafter referred to as the "incorrect make-up completion position"). For example, in the technique disclosed in Patent Document 1, in addition to a pair of marks that align the positions of the screws when they reach the correct make-up completion position, the two steel pipes to be made-up are also marked with a pair of marks that align the positions of the screws when they are engaged at the correct make-up start position. The "correct make-up start position" refers to the one of multiple make-up start positions from which the screw can reach the correct make-up completion position. Therefore, in the make-up operation of steel pipes, it is already possible to determine whether the make-up completion position that the screw will subsequently reach is correct when the screw is engaged at the make-up start position.

However, it is physically possible to engage the multiple-start thread disclosed in Patent Document 1 at a make-up start position other than the correct make-up start position (hereinafter referred to as the "incorrect make-up start position"), or to move it from the incorrect make-up start position to an incorrect make-up completion position. Therefore, there is a possibility that an operator may accidentally overlook the misalignment of the mark pairs, engage the screw at the incorrect make-up start position, and then move it to the incorrect make-up completion position. This could result in impaired make-up workability, and the device disclosed in Patent Document 1 may not be sufficient in some cases.

The object of the present invention is to solve the above problems, and in particular to provide a pipe fitting that improves the workability of connecting pipes by more reliably preventing multiple-start threads from reaching an incorrect tightening completion position.

A pipe fitting according to one aspect of the present invention comprises a male part and a female part. The male part is cylindrical and includes a connection portion for connecting to a first pipe at one axial end and a multiple-start male thread at the other end. The female part is cylindrical and includes a multiple-start female thread at one axial end that can mesh with the male thread of the male part and a connection portion for connecting to a second pipe at the other end. One of the male and female threads includes a protrusion on a circumferential portion of the bearing surface, and the other includes a bearing surface removal portion on a circumferential portion of the bearing surface. The protrusion extends in the axial direction. The bearing surface removal portion is a mark left by removing a continuous area in the circumferential direction. The protrusion and bearing surface removal portion are configured as follows: When the male and female threads are brought coaxially toward each other, if the circumferential angle between the two threads is the value at the incorrect make-up start position, the protrusion will collide with the bearing surface of the other thread before the two threads reach the incorrect make-up completion position. On the other hand, if the circumferential angle between the two threads is the value at the correct tightening start position, the protrusion will enter the bearing surface removal section before the two threads reach the correct tightening completion position, avoiding collision with the bearing surface of the other thread.

This pipe fitting may satisfy all of the following conditions (A), (B), (C), and (D): (A) The rotation angle (hereinafter referred to as the "interference angle") required for the male and female threads to move from the correct fastening start position to the correct fastening completion position is 180° or less. (B) The length of the protrusion is equal to or greater than the distance between the bearing surfaces of the male and female threads when they are engaged at the correct fastening start position. (C) The circumferential width of the bearing surface removal portion is equal to or greater than the interference angle between the male and female threads, and is equal to or less than 360° divided by the number of threads on both threads. (D) The range over which the protrusion moves circumferentially of both threads as the male and female threads move from the correct fastening start position to the correct fastening completion position is included in the range of the bearing surface removal portion circumferentially of both threads.

In the above-described pipe fitting according to the present invention, when the male and female threads are brought coaxially toward each other during the tightening operation between the male and female parts, if the circumferential angle between the two threads is the value at the incorrect tightening start position, the protrusion will collide with the bearing surface of the other thread before the two threads reach the incorrect tightening completion position. This prevents the two threads from approaching each other further, making it physically impossible for the two threads to reach the incorrect tightening completion position. On the other hand, if the circumferential angle between the two threads is the value at the correct tightening start position, the protrusion will enter the bearing surface removal portion before the two threads reach the correct tightening completion position, avoiding collision with the bearing surface of the other thread. The protrusion then moves through the bearing surface removal portion, allowing the two threads to reach the correct tightening completion position. This more reliably prevents the two threads from reaching the incorrect tightening completion position, thereby improving the ease of connecting piping with this pipe fitting.

When this pipe fitting satisfies all of the above conditions (A)-(D), it is physically impossible for the male and female threads to mesh at an incorrect fastening start position. In fact, when the two threads are meshed, if the circumferential angle between the two threads is the value for the correct fastening start position, the protrusion enters the seating surface removal section and avoids collision with the seating surface of the other thread, so that the two threads reach the correct fastening start position. The protrusion then moves through the seating surface removal section, so that the two threads reach the correct fastening completion position. On the other hand, if the circumferential angle between the two threads is the value for the incorrect fastening start position, the protrusion will collide with the seating surface of the other thread before or simultaneously with the two threads reaching the incorrect fastening start position. This makes it physically impossible for the two threads to mesh at an incorrect fastening start position. Naturally, it is also physically impossible for the two threads to reach the incorrect fastening completion position, making this pipe fitting even easier to connect piping.

Each of the male and female parts may include a protrusion extending from a portion of its circumferential direction toward the outer periphery. The protrusions on both parts are configured to align the circumferential positions of the male and female threads when they reach the correct fastening position. Due to the protrusions, the shapes of both parts are rotationally asymmetric. Therefore, by seeing that the protrusions on both parts have aligned circumferential positions, the worker can visually confirm that the two threads have reached the correct fastening position. Therefore, the pipe fitting of the present invention further improves the workability of connecting piping.

The protruding portions of the male and female parts may have the same outline when viewed from the axial direction of each part. Because the outlines of the protruding portions of both parts appear to overlap perfectly, the worker can confirm at a glance that both threads have reached the correct tightening position. Therefore, the pipe fitting of the present invention further improves the workability of connecting piping.

The protrusions of the male and female parts may be configured to engage with each other in a snap-fit manner when the male and female threads reach the correct fastening position. This generates at least one of sound and vibration when the protrusions engage with each other. By hearing the sound or feeling the vibration, the worker can confirm by ear or hand that the two threads have reached the correct fastening position. Therefore, the pipe fitting of the present invention further improves the workability of connecting piping.

The protrusions on the male and female parts may be configured to engage with each other when the male and female threads reach the correct tightening position, preventing the two threads from rotating in the reverse direction, i.e., in the loosening direction. This prevents the two threads from loosening due to external vibrations or shocks or changes in shape over time.

1 is a perspective view showing the appearance of a pipe joint according to an embodiment of the present invention. FIG. 2 is an exploded view of the pipe joint shown in FIG. 3 is a cross-sectional view taken along the line III-III shown in FIG. 1. 3A and 3B are a plan view and a side view, respectively, showing the appearances of the male part and the female part shown in FIG. 2 when the male part and the female part are arranged coaxially and the circumferential angle between the male thread and the female thread is at the correct fastening start position. 3A and 3B are a plan view and a side view showing the appearance of the pipe joint when the male thread and the female thread shown in FIG. 2 have reached a correct fastening completion position. 3A and 3B are a plan view and a side view, respectively, showing the appearances of the male part and the female part shown in FIG. 2 when the male part and the female part are arranged coaxially and the circumferential angle between the male thread and the female thread is a value at an incorrect fastening start position.

Figure 1 is a perspective view showing the appearance of a pipe fitting 100 according to an embodiment of the present invention, Figure 2 is an exploded view of the pipe fitting 100, and Figure 3 is a cross-sectional view taken along line III-III in Figure 1. The pipe fitting 100 is preferably used to connect a first hose 510 to a second hose 520 inside an automobile (see Figure 3). The first hose 510 and the second hose 520 are made of a resin such as high-density polyethylene (HDPE), and are preferably included in the cooling line of a battery pack in an electric vehicle (EV), and are used as piping for carrying coolant (LLC).

The pipe fitting 100 is a combination of a male part 200 and a female part 300. Both parts 200, 300 are cylindrical parts made of resin such as polyamide (PA) or glass fiber reinforced polyamide (PA-GF). In a cross section perpendicular to their respective central axes 201, 301, their inner circumferential surfaces are circular (see FIG. 2) and their inner diameters are equal (see FIG. 3). As shown in FIG. 3, the male part 200 is connected to a first hose 510, and the female part 300 is connected to a second hose 520. Furthermore, when the two parts 200, 300 are coaxially fastened to each other, the internal space of the first hose 510 communicates with the internal space of the second hose 520 through their internal spaces. In other words, the internal spaces of the two parts 200, 300 function as a flow path for the LLC connecting the two hoses 510, 520.
[Structure of male part]

One axial end 210 of the male component 200 (the left end in Figures 2 and 3; hereafter referred to as the "first end") is the connection point with the first hose 510 and is arranged coaxially within the first hose 510 (see Figure 3). Because the outer diameter of the first end 210 is larger than the inner diameter of the first hose 510, when the first end 210 is press-fitted into the first hose 510, the open end of the first hose 510 is pushed open. The resulting restoring force of the open end tightens the first end 210 inward, securing the first hose 510 to the first end 210 and creating a seal between the inner surface of the first hose 510 and the outer surface of the first end 210.

The other axial end 220 of the male part 200 (the right end in FIGS. 2 and 3 ; hereinafter referred to as the "second end") is the connection portion with the female part 300 and includes an opening 221, an annular groove 230, a flange 240, and a male thread 250. The opening 221 is a cylindrical wall that separates the entrance and exit of the internal space of the male part 200. The annular groove 230 is a ring-shaped groove that coaxially surrounds the opening 221 and preferably extends to near the boundary between the first end 210 and the second end 220 in the axial direction of the male part 200 (see FIG. 3). The depth of the annular groove 230 in the axial direction is sufficiently greater than the wall thickness of the opening 221. The flange 240 is an arc-shaped portion that surrounds only a portion of the outer periphery of the second end 220 in the circumferential direction (the upper portion in FIGS. 2 and 3 ) and is adjacent to the first end 210 in the axial direction of the male part 200. The male thread 250 is provided on the outer periphery of the second end 220 in a region adjacent to the flange 240 in the axial direction of the male part 200 (the region to the right of the flange 240 in Figures 2 and 3), and coaxially surrounds the annular groove 230.
[Structure of female part]

One axial end 310 of the female part 300 (the left end in Figures 2 and 3; hereafter referred to as the "first end") is the connection point with the male part 200 and includes an opening 311, an annular protrusion 330, a flange 340, and an internal thread 350. The opening 311 is a cylindrical wall that separates the entrance and exit to the internal space of the female part 300, and has the same inner diameter as the opening 221 of the male part 200. The annular protrusion 330 protrudes coaxially from the periphery of the opening 311 (to the left in Figures 2 and 3), and its cross section perpendicular to its axial direction is annular. Furthermore, the inner and outer diameters of the annular protrusion 330 are designed so that it can be press-fit into the annular groove 230 of the male part 200 (see below for details). The flange 340 is a circular member that coaxially surrounds the annular protrusion 330, with one end in the axial direction of the female part 300 (the right end in Figures 2 and 3) coaxially connected to the opening 311, and the opposite end face 341 in the axial direction (the left end face in Figures 2 and 3) extending beyond the tip 331 (the left end in Figures 2 and 3) of the annular protrusion 330. The female thread 350 is provided on the inner surface of the flange 340 and coaxially surrounds the annular protrusion 330.

The other axial end 320 of the female component 300 (the right end in FIGS. 2 and 3; hereinafter referred to as the "second end") is the connection part with the second hose 520 and is disposed coaxially within the second hose 520 (see FIG. 3). Because the outer diameter of the second end 320 is larger than the inner diameter of the second hose 520, when the second end 320 is press-fitted into the second hose 520, the open end of the second hose 520 is forced open. The resulting restoring force of the open end tightens the second end 320 in the inward circumferential direction, so that the second hose 520 is fixed to the second end 320 and a seal is formed between the inner circumferential surface of the second hose 520 and the outer circumferential surface of the second end 320.
[Male and female threads]

The male thread 250 is a multiple-start thread, for example a double-start right-hand thread, and includes a first thread 251 and a second thread 252 (see Figures 2 and 3). These threads 251, 252 have, for example, a trapezoidal cross section, and form right-handed spirals of the same shape and size around the central axis 201 of the male part 200, with the same shape and size except for the ends of each spiral. The tips of these spirals, i.e., tip 253 of first thread 251 and tip 254 of second thread 252, differ from each other in their circumferential positions around the male thread 250 by 360° divided by the number of threads "2" on the male thread 250, or 180°.

The female thread 350 is a multiple-start thread, such as a double-start right-hand thread, that can mesh with the male thread 250, and includes a first thread groove 351 and a second thread groove 352 (see Figures 2 and 3). These thread grooves 351, 352 have, for example, a trapezoidal cross section, and describe right-handed spirals of the same shape and size around the central axis 301 of the female part 300, with the shape and size being equal except for the ends of each spiral. The ends of these spirals, i.e., the end 353 of the first thread groove 351 and the end of the second thread groove 352 (not shown), differ from each other in their circumferential positions around the female thread 350 by 360° divided by the number of threads on the female thread 350, i.e., 180°.

Since both the male thread 250 and the female thread 350 are right-handed threads, when they are coaxially meshed with each other, clockwise rotation relative to the direction toward the other thread along their respective central axes 201, 301 is the forward direction, i.e., the direction in which the thread tightens, and counterclockwise rotation is the reverse direction, i.e., the direction in which the thread loosens. In Figure 2, for the male thread 250, clockwise MCL is the forward direction relative to the right along its central axis 201, and counterclockwise MCC is the reverse direction. For the female thread 350, clockwise FCL is the forward direction relative to the left along its central axis 301, and counterclockwise FCC is the reverse direction.

Since both the male thread 250 and the female thread 350 have two threads, there are two possible fastening start positions. One (hereinafter referred to as the "correct fastening start position") is the relative position of the two threads 250, 350 when the tip 253 of the first thread 251 begins to enter the tip 353 of the first thread groove 351, and the tip 254 of the second thread 252 begins to enter the tip 354 of the second thread groove 352. The other (hereinafter referred to as the "incorrect fastening start position") is the relative position of the two threads 250, 350 when the tip 253 of the first thread 251 begins to enter the tip 354 of the second thread groove 352, and the tip 254 of the second thread 252 begins to enter the tip 353 of the first thread groove 351.

Like the make-up start position, there are also two make-up completion positions. Hereinafter, the make-up completion position that can be reached from the correct make-up start position will be referred to as the "correct make-up completion position," and the make-up completion position that can be reached from the incorrect make-up start position will be referred to as the "incorrect make-up completion position." At the make-up completion position, the engagement length between the male thread 250 and the female thread 350 reaches a target value. This target value is designed so that the connection between the male part 200 and the female part 300 can sufficiently withstand external forces and the annular protrusion 330 of the female part 300 is press-fitted to the required depth into the annular groove 230 of the male part 200 (see below for details). Furthermore, the leads of the two threads 250, 350 are designed so that the rotation angle required for the two threads 250, 350 to move from the make-up start position to the make-up completion position, i.e., the engagement angle, is preferably 180° or less, more preferably 90°.
[Flange]

4 to 6 are a plan view (a) and a side view (b) showing the appearance of the coaxially arranged male part 200 and female part 300 when viewed from the first end 210 side of the male part 200. In particular, FIG. 4 shows the appearance when the circumferential angle between the male thread 250 and the female thread 350 is the value at the correct fastening start position. FIG. 5 shows the appearance when both threads 250, 350 have reached the correct fastening completion position. FIG. 6 shows the appearance when the circumferential angle between both threads 250, 350 is the value at the incorrect fastening start position.
-Screw bearing surface, bearing surface removal part, protrusion-

2 and 4-6, the flange 240 of the male part 200 is arc-shaped and has a larger outer diameter than the male thread 250. Meanwhile, the outer diameter RR of the portion 242 of the second end 220 of the male part 200 not surrounded by the flange 240 is smaller than the outer diameter RF of the flange 240 and preferably equal to the outer diameter of the male thread 250. As a result, the end face 241 of the flange 240 in the axial direction of the male part 200, closer to the male thread 250, is a circular surface including a notch 242 on a portion of its outer edge (see FIG. 2). The width WR of the notch 242 along the circumferential direction of the male part 200, when converted to a rotation angle around the central axis 201, preferably satisfies the following: the fit angle between the male thread 250 and the female thread 350 is 90° or greater, and the value obtained by dividing 360° by the number of threads "2" on both threads 250, 350 is 180° or less: 90°≦WR≦180°. More preferably, the width WR is 120°: WR=120°.

As shown in Figures 2 and 4-6, the flange 340 of the female part 300 is annular, and its end face 341 is a continuous annular surface around the entire circumference. Preferably, as shown in Figures 4-6(a), the outer diameter RF of the flange 340 is equal to the outer diameter RF of the flange 240 of the male part 200. A protrusion 342 protrudes from a circumferential portion of the end face 341 (the lower part in Figures 1-6) in the axial direction of the female part 300 (to the left in Figures 1-3 and 4-6(b), and forward in Figures 4-6(a)). The protrusion 342 is highlighted by hatching in Figures 4-6. As shown in FIG. 4(a), the cross section of the protrusion 342 is, for example, an arc shape concentric with the end face 341, and its inner diameter RP is equal to or greater than the outer diameter RR of the portion of the flange 240 of the male part 200 narrowed by the notch 242 and equal to or less than the outer diameter RF of the remaining portion: RR≦RP≦RF. The outer diameter of the protrusion 342 is preferably equal to the outer diameter RF of the flange 340 of the female part 300. The width WP of the protrusion 342 in the circumferential direction of the female part 300, when converted to a rotation angle about the central axis 301, is preferably slightly less than 30°: WP ≈ 30°. Furthermore, the difference WR - WP between the width WP of the protrusion 342 and the width WR of the notch 242 is preferably such that the fit angle between the male thread 250 and the female thread 350 is equal to or greater than 90°: WR - WP ≧ 90°.

As shown in Figures 2 and 4-6(b), the end face 241 of the flange 240 of the male part 200 and the end face 341 of the flange 340 of the female part 300 are both perpendicular to the axial direction. As shown in Figure 5(b), when the male thread 250 and the female thread 350 reach the correct fastening completion position, the end faces 241, 341 come into contact with each other and are pressed against each other by the axial force of the two threads 250, 350. In this sense, each end face 241, 341 will be referred to as the "bearing surface" of each thread 250, 350 hereinafter. Furthermore, the notch 242 in the flange 240 of the male part 200 is a mark left by removing a portion of the circumferential bearing surface 241 of the male thread 250, and therefore the notch 242 will be referred to as the "bearing surface removal portion" hereinafter.

As shown in Figures 2 and 4(b), the tip 353 of the first thread groove 351 of the female thread 350 and the tip 354 of the second thread groove 352 are both located axially further back (to the right in Figures 2 and 4(b)) than the bearing surface 341 of the female thread 350. Therefore, as shown by the two-dot chain line in Figure 4(b), the distance LS between the bearing surfaces 241, 341 when the two threads 250, 350 are engaged in the correct fastening start position is shorter than the length LM of the male thread 250: LS < LM. Preferably, the length LP of the protrusion 342 in the axial direction of the female thread 350 is designed to be equal to or greater than this distance LS: LP ≥ LS.
-Protruding part-

As shown in Figures 1 to 6, a protrusion 243 extends from a portion of the circumference of the flange 240 of the male part 200 in the outer circumferential direction of the male part 200 (upward in Figures 1 to 3 and 5, leftward in Figure 4(a), and rightward in Figure 6(a)). As a result, preferably as shown in Figures 1, 2, and 4-6(a), the male part 200 has a rotationally asymmetric shape, and in particular, its outline as viewed from the axial direction is teardrop-shaped. Preferably, as shown in Figures 2, 4-6(a), the tip 244 of the protrusion 243 in the outer circumferential direction of the male part 200 (upper end in Figures 2 and 5(a), left end in Figure 4(a), and right end in Figure 6(a)) is located in the center of the flange 240 in the circumferential direction of the male part 200. That is, the position of the tip 244 of the protrusion 243 in the circumferential direction differs by 120° from each end of the seat surface removal portion 242 in the circumferential direction. Furthermore, this position is preferably the same as the position of the tip 253 of the first thread 251, as shown in Figures 2 and 6(b).

As shown in Figures 2 and 6(b), a step 248 extends from the tip 244 (top end in Figure 2) of the protrusion 243 of the male part 200 in the forward rotation direction MCL of the male thread 250 (clockwise to the right in Figure 2, downward in Figure 6(b)). The step 248 is a raised portion from the end face of the protrusion 243 located on the same side as the bearing surface 241 of the male thread 250 (right side in Figures 2 and 6(b)). The tip face 249 (right end face in Figures 2 and 6(b)) of the step 248 in the axial direction of the male part 200 (right side in Figures 2 and 6(b)) is perpendicular to that axial direction and is located at the same location as the bearing surface 241 of the male thread 250 or further outward (right side in Figures 2 and 6(b)).

As shown in Figures 1-6, a protrusion 343 extends from a portion of the circumference of the flange 340 of the female part 300 (the upper part in Figures 1-6) toward the outer periphery of the female part 300 (upward in Figures 1-6). As a result, preferably, as shown in Figures 1, 2, and 4-6(a), the female part 300 has a rotationally asymmetric shape, and in particular, its outline as viewed in the axial direction is teardrop-shaped. More preferably, as shown in Figure 5(a), the protrusion 243 of the male part 200 and the protrusion 343 of the female part 300 have the same outline as viewed in the axial direction of each part 200, 300. Preferably, as shown in Figure 2, the tip 344 (upper end in Figure 2) of the protrusion 343 on the outer periphery of the female part 300 is located at a position rotated 90° from the tip 353 of the first thread groove 351 in the reverse direction FCC of the female thread 350 (counterclockwise relative to the left in Figure 2) by the engagement angle between the male thread 250 and the female thread 350, and at a position rotated 120° from the protrusion 342 in the forward direction FCL of the female thread 350 (clockwise relative to the left in Figure 2).

As shown in Figures 1-3 and 4-6(b), the protrusion 343 of the female part 300 includes a thin plate portion 345 and a thick plate portion 346. The plate surfaces of both the thin plate portion 345 and the thick plate portion 346 are perpendicular to the axial direction of the female part 300 (the left-right direction in Figures 1-3 and 4-6(b)), and they face each other with a gap GP between them. In the axial direction of the female part 300, the thin plate portion 345 is thinner than the thick plate portion 346. Of the plate surfaces of the thin plate portion 345, the side 347 farthest from the thick plate portion 346 (the left plate surface in Figures 2, 3, 4-6(b)) is located in the same location as the bearing surface 341 of the female thread 350 in the axial direction of the female part 300.

As shown in Figures 2 to 4 and 6, a step 348 extends from a tip 344 (the upper end in Figures 2 to 4 and 6) of the protrusion 343 of the female part 300 in the forward rotation direction FCL of the female thread 350 (clockwise relative to the left in Figure 2, and leftward in Figures 4(a) and 6(a)). The step 348 is a portion that protrudes from a plate surface 347 of the thin plate portion 345 (the plate surface on the left side in Figures 2, 3, 4(b) and 6(b)). The range of the step 348 in the radial direction of the female part 300 (see Figures 2 to 4) at least partially overlaps with the range of the step 248 in the radial direction of the male part 200 (see Figures 2 and 5(b)). Preferably, a tip end surface 349 (the left end surface in Figures 2, 3, 4(b) and 6(b)) of the step portion 348 in the axial direction of the female part 300 is inclined with respect to both the axial direction and the circumferential direction of the female part 300, and the further away from the tip end 344 (the upper end in Figures 2 to 4 and 6) of the protrusion 343 in the forward rotation direction FCL of the female thread 350 (clockwise with respect to the left in Figure 2, and leftward in Figures 4(a) and 6(a)), the closer to the plate surface 347 of the thin plate portion 345 it is.
[Connecting hoses using pipe joints]

The operation of connecting the second hose 520 to the first hose 510 using the pipe coupling 100 is preferably performed in the following procedure: First, the first end 210 of the male part 200 is press-fitted into the open end of the first hose 510, and the second end 320 of the female part 300 is press-fitted into the open end of the second hose 520. In other words, the parts 200, 300 are connected to the hoses 510, 520. Next, the second end 220 of the male part 200 and the first end 310 of the female part 300 are coaxially butted together, and the position at which the male thread 250 and the female thread 350 begin to fasten is found.
- When the screw is close to the correct tightening start position -

In the arrangement of the male part 200 and female part 300 shown in Figure 4, the circumferential angle between the male thread 250 and the female thread 350 is the value at the correct fastening start position. That is, in the circumferential direction of both threads 250, 350, the tip 253 of the first thread 251 is located in the same location as the tip 353 of the first thread groove 351, and the tip 254 of the second thread 252 is located in the same location as the tip 354 of the second thread groove 352. At this time, in the circumferential direction, the protrusion 342 of the female part 300 is located within the range of the seat surface removal portion 242 of the male part 200, particularly within the range of one circumferential end 245 (the lower end in Figure 4) of that portion. Because the inner diameter RP of the protrusion 342 is equal to or greater than the outer diameter RR of the seating surface removal portion 242 (RP≧RR), when the two screws 250, 350 are brought closer together, the protrusion 342 enters one end 245 of the seating surface removal portion 242, avoiding collision with the flange 240 of the male component 200. Therefore, the two screws 250, 350 reach the correct fastening start position. That is, the tip 253 of the first thread 251 reaches the tip 353 of the first thread groove 351, and the tip 254 of the second thread 252 reaches the tip 354 of the second thread groove 352.

After the male thread 250 and the female thread 350 reach the correct fastening start position, the male part 200 is rotated in the forward rotation direction MCL of the male thread 250 (clockwise in FIG. 4A), or the female part 300 is rotated in the forward rotation direction FCL of the female thread 350 (counterclockwise in FIG. 4A). Because the bearing surface removed portion 242 extends from one end 245 in the forward rotation direction DCL of the female thread 350 (counterclockwise in FIG. 4A), the protrusion 342 moves in the bearing surface removed portion 242 as both threads 250, 350 rotate forward. Therefore, the first thread 251 enters the first thread groove 351, and the second thread 252 enters the second thread groove 352. That is, both threads 250, 350 begin to mesh with each other. Because the difference in width WR-WP between the seat surface removed portion 242 and the protrusion 342 is equal to or greater than the fit angle of both screws 250, 350 = 90°, the protrusion 342 moves without being obstructed by the flange 240 of the male component 200 until it reaches the end 246 (the right end in FIG. 5 ) on the opposite side of the seat surface removed portion 242. Therefore, both screws 250, 350 reach the correct fastening completion position, and fastening of the male component 200 and the female component 300 is completed.
- When the screw is close to the incorrect tightening start position -

6 shows the arrangement of the male part 200 and the female part 300, in which the circumferential angle between the male thread 250 and the female thread 350 is a value at an incorrect fastening start position. That is, in the circumferential direction of both threads 250, 350, the tip 253 of the first thread ridge 251 is located at the same location as the tip 354 of the second thread groove 352, and the tip 254 of the second thread 252 is located at the same location as the tip 353 of the first thread groove 351. At this time, in the circumferential direction, the protrusion 342 of the female part 300 is located within the range of the bearing surface 241 of the male thread 250. Meanwhile, the inner diameter RP of the protrusion 342 is equal to or smaller than the outer diameter RF of the flange 240 (RP≦RF), and the length LP of the protrusion 342 is equal to or larger than the distance LS between the bearing surfaces 241, 341 of both threads 250, 350 that are engaged at the correct fastening start position (LP≧LS). Therefore, when the two screws 250, 350 are brought closer to each other, the protrusion 342 collides with the bearing surface 241 of the male screw 250 before or at the same time that the tips 253, 254 of the threads 251, 252 reach the tips 353, 354 of the thread grooves 351, 352. In this way, the two screws 250, 350 are prevented from coming closer to each other, and it is therefore physically impossible to engage the two screws 250, 350 at an incorrect fastening start position, i.e., to have the tip 253 of the first thread 251 enter the tip 354 of the second thread groove 352 and the tip 254 of the second thread 252 enter the tip 353 of the first thread groove 351.
[The significance of the fit angle being 180° or less]

In the male part 200, the first end 210 and the second end 220 are integrated, and in the female part 300, the first end 310 and the second end 320 are integrated. Therefore, to engage the male thread 250 and the female thread 350, the entire male part 200 and the entire female part 300 must be rotated relative to each other. In the operation of connecting the hoses 510 and 520, the parts 200 and 300 are connected to the hoses 510 and 520 before engaging the threads 250 and 350. Therefore, when engaging the threads 250 and 350, the relative rotation of the parts 200 and 300 inevitably twists at least one of the hoses 510 and 520. Therefore, it is preferable to previously apply a twist in the opposite direction to the twist that will occur at that time to one of the hoses 510 and 520. This ensures that when both screws 250, 350 reach the complete fastening position, no twist remains in either hose 510, 520. When the fit angle of both screws 250, 350 is 180° or less, the twist in the opposite direction that must be applied in advance to either hose 510, 520 is also 180° or less. Therefore, the rotation of male part 200 or female part 300 required to apply this twist in the opposite direction can be performed by an operator with one hand.
[Press-fitting of annular protrusion into annular groove]

The annular protrusion 330 of the female part 300 has a wall thickness slightly larger than the radial width of the annular groove 230 of the male part 200, an inner diameter equal to or slightly smaller than the diameter of the inner peripheral surface of the annular groove 230, and an outer diameter equal to or slightly larger than the diameter of the outer peripheral surface of the annular groove 230. Therefore, when the male thread 250 and the female thread 350 move from the correct fastening start position to the correct fastening completion position, the axial force of the two threads 250, 350 presses the annular protrusion 330 into the annular groove 230, causing the inner peripheral surface of the annular protrusion 330 to tightly contact the inner peripheral surface of the annular groove 230 and the outer peripheral surface of the annular protrusion 330 to tightly contact the outer peripheral surface of the annular groove 230 (see Figure 3). These tight contact areas, i.e., the seal area SR, seal the gap between the opening 221 of the male part 200 and the opening 311 of the female part 300. To ensure a sufficiently high seal for this gap, the width of the sealing region SR in the axial direction of both parts 200, 300, i.e., the length of the portion of the annular protrusion 330 that is to be press-fitted into the annular groove 230, is designed. Furthermore, the target value for the fit length of both screws 250, 350 is designed based on this length, and the complete fastening position is determined.

Because the axial force of the male thread 250 and the female thread 350 is used to press-fit the annular protrusion 330 into the annular groove 230, the force required for press-fitting must be reduced to keep the tightening torque of the two threads 250, 350 to a level that can be applied by bare hands. Therefore, the wall thickness of the opening 221, the width and depth of the annular groove 230, and the thickness and length of the annular protrusion 330 are designed so that distortion of the wall of the opening 221 due to press-fitting is sufficiently small. Specifically, the depth of the annular groove 230 is designed to be sufficiently large relative to the wall thickness of the opening 221, preferably three times or more, and the axial distance from the seal region SR to the bottom 231 of the annular groove 230 is designed to be sufficiently large, preferably more than ten times, the increase in the width of the annular groove 230 due to press-fitting.
[Role of the protrusion]

As shown in Figures 3 and 5, the length LM of the male thread 250 is preferably designed so that the bearing surfaces 241, 341 of the male thread 250 and female thread 350 come into contact with each other when they reach the correct fastening position. However, in reality, it is difficult to confirm that the two threads 250, 350 have reached the correct fastening position just by the contact between the bearing surfaces 241, 341. Furthermore, each time the male part 200 and female part 300 are fastened together, there is likely to be a large deviation between the final relative positions of the two threads 250, 350 and the correct fastening position.

As explained below, the protrusion 243 of the male part 200 and the protrusion 343 of the female part 300 allow the operator to easily confirm that the male thread 250 and the female thread 350 have reached the correct fastening position. This allows the pipe fitting 100 to easily connect the hoses 510, 520. Furthermore, the deviation between the final relative positions of the two threads 250, 350 and the correct fastening position is reliably kept within an acceptable range. Therefore, it is unlikely that the area of the seal region SR will be insufficient due to insufficient engagement length of the two threads 250, 350, or that excessive creep deformation of the two parts 200, 300 will occur due to excessive tightening torque of the two threads 250, 350. As a result, the pipe fitting 100 has high reliability due to its high sealing performance.

In the male part 200, the protrusion 243 is located in the same circumferential position as the tip 253 of the first thread 251. In the female part 300, the protrusion 343 is located at a position rotated 90° from the tip 353 of the first thread groove 351 in the reverse direction FCC of the female thread 350, where the engagement angle between the male thread 250 and the female thread 350 is equal to 90° (see Figure 2). When both threads 250, 350 are in the correct fastening start position, the tip 253 of the first thread 251 is located at the tip 353 of the first thread groove 351, so the protrusion 243 of the male part 200 is located at a position rotated 90° from the protrusion 343 of the female part 300 in the forward direction FCL of the female thread 350 (see Figure 4(a)). Therefore, only when both screws 250, 350 reach the correct fastening completion position does the circumferential position of the protrusions 243, 343 of both parts 200, 300 align with the tip ends 244, 344, and their outlines appear to completely overlap from the axial direction (see Figure 5(a)). This allows the operator to confirm at a glance that both screws 250, 350 have reached the correct fastening completion position. Furthermore, because even slight misalignment between the tip ends 244, 344 of the protrusions 243, 343 and the outlines of the protrusions 243, 343 are noticeable, it is easy to minimize these misalignments to an unnoticeable level. As a result, the misalignment between the final relative positions of both screws 250, 350 and the correct fastening completion position is reliably kept within the tolerance range.

In the protrusion 243 of the male part 200, the tip surface 249 of the step 248 is located in the same axial position as the seat surface 241 of the male thread 250 or further outward (to the right in Figure 2), while in the protrusion 343 of the female part 300, the tip surface 349 of the step 348 is located further outward (to the left in Figure 2) than the seat surface 341 of the female thread 350. Therefore, when the two threads 250, 350 reach the correct tightening completion position, the step portions 248, 348 engage with each other in a snap-fit manner, as described below.

Just before the two screws 250, 350 reach the correct fastening position, the tip surface 249 of the step 248 of the male part 200 collides with the tip surface 349 of the step 348 of the female part 300. Due to its inclination, the tip surface 349 of the female part 300 receives axial pressure from the tip surface 249 of the male part 200. This causes the thin plate portion 345 of the female part 300 to bend toward the thick plate portion 346. As a result, as the two screws 250, 350 continue to rotate forward, the step portions 248, 348 overcome each other, and the two screws 250, 350 reach the correct fastening position. At the same time, the thin plate portion 345 returns to its original bending state, causing the tip surface 349 of the female part 300 to strike the surface of the protrusion 243 of the male part 200. The sound produced at this time reverberates in the gap GP between the thin plate portion 345 and the thick plate portion 346. By hearing this reverberation, the worker can confirm by ear that both screws 250, 350 have reached the correct fastening completion position. Furthermore, by feeling the vibration caused by the inclined surface 349 of the female part 300 striking, the worker can also confirm by hand that both screws 250, 350 have reached the correct fastening completion position.

In addition to the above functions, the protrusions 243, 343 make it easier to rotate the male part 200 and the female part 300 with bare hands. This makes it easier to connect the hoses 510, 520 using the pipe fitting 100. In fact, when rotating the two parts 200, 300 relative to each other, the worker can hook their fingers on the protrusions 243, 343, making it easier to apply circumferential force to the two parts 200, 300. Furthermore, because the protrusions 243, 343 are farther from the central axes 201, 301 of the same parts 200, 300 than other parts of the same parts 200, 300, even when the same amount of circumferential force is applied, a larger torque is applied to each part 200, 300. Therefore, by applying a circumferential force to each protrusion 243, 343, the worker can easily apply a sufficiently large torque to each part 200, 300.

Furthermore, the protrusions 243, 343 prevent the male thread 250 and the female thread 350 from loosening after they reach the correct fastening position. This makes the pipe fitting 100 highly reliable against external vibration shocks or changes in shape over time. In fact, as described above, when the two threads 250, 350 reach the correct fastening position, the steps 248, 348 of the two parts 200, 300 engage with each other. Even if the two threads 250, 350 are subsequently subjected to torque that encourages reverse rotation due to external vibration shocks or the like, the steps 248, 348 will contact each other's circumferential side surfaces, preventing the two threads 250, 350 from reversing. In this way, the protrusions 243, 343 can prevent the two threads 250, 350 from loosening. In particular, because the step portions 248, 348 are adjacent to the tips 244, 344 (upper ends in Figures 2 and 3) of the protrusions 243, 343, they are farther from the central axes 201, 301 of the same parts 200, 300 than other parts of the same parts 200, 300. Therefore, even if the torque that encourages the screws 250, 350 to rotate in the reverse direction is large, the force that presses the step portions 248, 348 against each other is sufficiently weak, and the effect of preventing the screws 250, 350 from loosening due to the mutual engagement of the step portions 248, 348 is sufficiently high.
Advantages of the embodiment

The pipe fitting 100 satisfies all of the following conditions (A), (B), (C), and (D). (A) The fit angle between the male thread 250 and the female thread 350 = 90° is less than or equal to 180°. (B) The length LP of the protrusion 342 of the female part 300 is greater than or equal to the distance LS between the bearing surfaces 241, 341 of the two threads when they are engaged in the correct fastening start position: LP≧LS. (C) The circumferential width WR of the bearing surface removal portion 242 is greater than or equal to the fit angle between the two threads = 90°, and is less than or equal to 180° when 360° is divided by the number of threads on both threads (2): 90°≦WR≦180°. (D) The range over which the protrusion 342 moves in the circumferential direction of the screws 250, 350 as the screws 250, 350 move from the correct fastening start position to the correct fastening completion position is included in the range of the bearing surface removal portion 242 in the circumferential direction of the screws 250, 350.

Because the pipe fitting 100 satisfies all of the above conditions (A)-(D), it is physically impossible for the male thread 250 and the female thread 350 to mesh together at an incorrect make-up start position. In fact, when the two threads 250, 350 mesh together, if the circumferential angle between the two threads 250, 350 is the value at the correct make-up start position, the protrusion 342 enters the bearing surface removed portion 242 to avoid collision with the bearing surface 241 of the male thread 250, and the two threads 250, 350 reach the correct make-up start position (see FIG. 4). Thereafter, the protrusion 342 moves through the bearing surface removed portion 242 without being obstructed by the flange 240 of the male part 200 (see FIG. 4), and the two threads 250, 350 reach the correct make-up completion position (see FIG. 5). On the other hand, if the circumferential angle between the two threads 250, 350 is a value at the incorrect fastening start position, the protrusion 342 will collide with the bearing surface 241 of the male thread 250 before the two threads 250, 350 reach the incorrect fastening start position, or simultaneously with their arrival (see FIG. 6 ). Therefore, it is physically impossible for the two threads 250, 350 to mesh at the incorrect fastening start position. Naturally, therefore, it is also physically impossible for the two threads 250, 350 to reach the incorrect fastening completion position. In this way, this arrival is reliably prevented, and therefore the pipe fitting 100 provides high workability when connecting the hoses 510, 520.
[Modification]

(1) The resin material of the pipe fitting 100 is not limited to PA or PA-GF. Various other resins can be used, including low-density polyethylene, polypropylene, polycarbonate, polyamide, polyacetal, polyether ether ketone, polyphenylene sulfide, and polyimide. These may be selected appropriately depending on the field or application of the pipe fitting 100, the material of the hoses 510 and 520, etc.

(2) In the pipe fitting 100, the male part 200 includes an annular groove 230 into which the annular protrusion 330 of the female part 300 is press-fit. Conversely, the female part 300 may include an annular groove into which the annular protrusion of the male part 200 is press-fit.

(3) In the male part 200, the seat surface removal portion 242 is 120° away from the tip 253 of the first thread 251 in the circumferential direction. In the female part 300, the protrusion 342 is 210° away from the tip 353 of the first thread groove 351 in the reverse direction FCC of the female thread 350, which is the angle of engagement between the male thread 250 and the female thread 350 = 90° + 120°. However, the present invention is not limited to these arrangements. Whether or not the protrusion 342 enters the bearing surface removal portion 242 before the two screws 250, 350 reach the fastening completion position is determined by the relative positions of the bearing surface removal portion 242 and the protrusion 342 when the two screws 250, 350 are engaged, and is not directly dependent on the relative positions of the bearing surface removal portion 242 and the tip 253 of the first thread 251, or the relative positions of the protrusion 342 and the tip 353 of the first thread groove 351.

(4) The threads 251, 252 of the male thread 250 and the grooves 351, 352 of the female thread 350 both have trapezoidal cross sections, but may have other polygonal shapes such as triangles, rectangles, or sawtooth shapes, or may have rounded peaks or valleys. Furthermore, while the number of threads on both threads 250, 350 is two, they may have three or more. Since there are three or more fastening start positions, the same number as the number of threads, two or more correct fastening start positions may be selected. Accordingly, the number of seating surface removal portions 242 on the male part 200 may be increased to the same number as the correct fastening start positions, and the upper limit of each width WR may be narrowed to the distance between the tips of the threads and grooves in the circumferential direction of each thread 250, 350, i.e., 360°/number of threads (≧3). This allows the protrusion 342 to enter the bearing surface removal portion 242 when the circumferential angle between the two screws 250, 350 is the value at the correct fastening start position when the two screws 250, 350 are engaged, and to collide with the bearing surface 241 when the value is the incorrect value at the fastening start position. Note that two or more adjacent bearing surface removal portions 242 may be combined into one.

(5) In the pipe fitting 100, the male part 200 includes the seating surface removal portion 242, and the female part 300 includes the protrusion 342. Conversely, the female part 300 may include the seating surface removal portion and the male part 200 may include the protrusion. The cross section of the protrusion 342 is arc-shaped, but it may also be other shapes, such as polygonal or circular. The seating surface removal portion 242 is a notch in the outer edge of the seating surface 241 of the male thread 250. However, the seating surface removal portion may be a mark left by removing a continuous area in the circumferential direction from the seating surface. For example, the seating surface of the male thread may be a continuous annular surface around the entire circumference, with a groove or recess formed therein extending circumferentially and used as the seating surface removal portion. In this case, the radial extent and axial depth of the seating surface removal portion need only be designed to be sufficient to accommodate the protrusion inside.

(6) Because the pipe fitting 100 satisfies all of the above conditions (A)-(D), it is physically impossible for the male thread 250 and the female thread 350 to mesh at an incorrect fastening start position. However, satisfying all of conditions (A)-(D) is not essential for the present invention. If any of the conditions is relaxed, it may be physically possible for the two threads 250, 350 to mesh at either the correct or incorrect fastening start position. However, for the present invention, it is sufficient that it is physically impossible for the two threads 250, 350 to reach an incorrect fastening completion position. Specifically, when the two threads 250, 350 are brought coaxially closer to each other during the fastening operation of the male part 200 and the female part 300, if the circumferential angle between the two threads 250, 350 is the value at the incorrect fastening start position, the protrusion 342 should collide with the bearing surface 241 of the male thread 250 before the two threads 250, 350 reach the incorrect fastening completion position. On the other hand, if the circumferential angle between the two screws 250, 350 is the value at the correct fastening start position, the protrusion 342 will enter the bearing surface removal portion 242 before the two screws 250, 350 reach the correct fastening completion position, thereby avoiding collision with the bearing surface 241 of the male screw 250.

For example, the length LP of the protrusion 342 of the female part 300 may be below the lower limit LS specified in condition (B) (LP < LS). In this case, it is physically possible for the male thread 250 and the female thread 350 to mesh at an incorrect make-up start position. However, because the circumferential width of the bearing surface 241 is sufficiently wider than the fit angle of the two threads 250, 350, even if the two threads 250, 350 rotate forward from the incorrect make-up start position, the protrusion 342 will collide with the bearing surface 241 of the male thread 250 before they reach the incorrect make-up completion position. Therefore, it is physically impossible for the two threads 250, 350 to reach the incorrect make-up completion position.

Condition (C) may be relaxed, and the circumferential width WR of the bearing surface removed portion 242 of the male part 200 may be less than the fit angle between the male thread 250 and the female thread 350. In this case, the bearing surface removed portion 242 and the protrusion 342 of the female part 300 may satisfy the following conditions (E) and (F) instead of conditions (B) and (D). (E) The length LP of the protrusion 342 is less than the distance between the bearing surfaces 241, 341 of the two screws 250, 350 when the two screws 250, 350 are rotated forward by a predetermined angle DF from the correct fastening start position. (F) When the two screws 250, 350 are arranged coaxially, if the circumferential angle between them is the value at the correct fastening start position, the protrusion 342 is separated from the bearing surface removed portion 242 by the angle DF in the reverse direction MCC of the male thread 250.

The upper limit LS defined by condition (E) is shorter than the lower limit LS defined by condition (B). Therefore, when condition (E) is met, the protrusion 342 does not reach the seating surface 241 of the male thread 250 in the state defined by condition (F). Therefore, the two threads 250, 350 can be engaged at the correct fastening start position. Furthermore, when condition (F) is met, when the two threads 250, 350 are rotated forward by at least angle DF from the correct fastening start position, the protrusion 342 enters the seating surface removal portion 242. Thereafter, the protrusion 342 moves within the seating surface removal portion 242, and the two threads 250, 350 reach the correct fastening completion position before the protrusion 342 collides with the flange 240 of the male part 200.

If condition (E) is met, it is physically possible for the two screws 250, 350 to mesh at an incorrect make-up start position. However, if condition (F) is also met, when the two screws 250, 350 are meshed at an incorrect make-up start position, the protrusion 342 is spaced from the bearing surface removal portion 242 in the reverse direction MCC of the male thread 250 by an angle equal to the sum of angle DF and 360°/number of threads. If the engagement angle of the two screws 250, 350 is narrower than this angle, even if the two screws 250, 350 rotate forward from the incorrect make-up start position, the protrusion 342 will collide with the bearing surface 241 of the male thread 250 before they reach the incorrect make-up completion position. Therefore, it is physically impossible for the two screws 250, 350 to reach the incorrect make-up completion position.

Condition (A) may be relaxed, and the engagement angle between the male thread 250 and the female thread 350 may exceed 180°, or even 360° (1 rotation). In this case, if the protrusion 342 is sufficiently shorter than the lower limit LS specified by condition (B), the two threads 250, 350 can be engaged at the correct fastening start position. Furthermore, since condition (C) cannot be satisfied, the width WR of the bearing surface removal portion 242 may be designed to be equal to or less than 360°/number of threads, for example, 360°/2 = 180°. Furthermore, the protrusion 342 and the bearing surface removal portion 242 may be designed as follows: When the two threads 250, 350 rotate forward from the correct fastening start position and the remaining rotation angle to the correct fastening completion position is reduced to the width WR of the bearing surface removal portion 242, the protrusion 342 will enter the bearing surface removal portion 242. The protrusion 342 then moves within the seat removal portion 242, allowing both screws 250, 350 to reach the correct tightening completion position.

On the other hand, because the length LP of the protrusion 342 is below the lower limit LS, it is physically possible for the two screws 250, 350 to mesh at an incorrect make-up start position. However, if the two screws 250, 350 rotate forward from the incorrect make-up start position and the remaining rotation angle to the incorrect make-up completion position is reduced to the width WR of the bearing surface removal portion 242, the protrusion 342 will collide with the bearing surface 241 of the male screw 250. Therefore, it is physically impossible for the two screws 250, 350 to reach an incorrect make-up completion position.

(7) In the pipe fitting 100, the protruding portion 243 of the male part 200 pushes aside the thin plate portion 345 of the protruding portion 343 of the female part 300, causing the steps 248, 348 to climb over each other and engage. In addition to the steps 248, 348, various other snap-fit structures are possible. For example, a claw portion may be provided on one of the protruding portions 243, 343, and a claw receiving portion may be provided on the other. The claw portion protrudes axially from one of the protruding portions 243, 343 and can bend outward. When the male thread 250 and female thread 350 reach the correct tightening completion position, the claw portion bends and its tip engages with the claw receiving portion. The operator can easily confirm that the screws 250, 350 have reached the correct tightening completion position by visually confirming that the claws are caught in the claw receivers and by listening or manually listening for the sound or vibration of the tips of the claws striking the claw receivers. Furthermore, the mutual engagement between the claws and the claw receivers prevents the screws 250, 350 from rotating backward. This prevents the screws 250, 350 from loosening due to external vibrations or shocks or changes in shape over time.

(8) In the pipe fitting 100, the male part 200 and the female part 300 have rotationally asymmetric shapes due to the presence of the protrusions 243, 343. This makes it easy to confirm that the male thread 250 and the female thread 350 have reached the completed fastening position during the fastening operation of the two parts 200, 300, and ensures that the deviation between the final relative positions of the two threads 250, 350 and the completed fastening position is within an acceptable range. However, because the two threads 250, 350 are multiple-start threads, it is necessary to select at least one of the multiple completed fastening positions as the correct one, as it matches the circumferential positions of the protrusions 243, 343. This is why the completed fastening positions of the two threads 250, 350 can be correct or incorrect. However, this reason is not a necessary premise for the present invention. For whatever reason, the present invention is effective when only certain of the multiple completed fastening positions of a multiple-start thread are necessary.

100 Pipe fitting 200 Male part 201 Central axis of male part 210 First end of male part 220 Second end of male part 221 Opening of male part 230 Annular groove 231 Bottom of annular groove 240 Flange of male part 241 Bearing surface of male thread 242 Removal portion of male part 243 Protrusion of male part 244 Tip of protrusion of male part 245 One end of removal portion of male part 246 Opposite end of removal portion of male part 248 Step of male part 249 Tip surface of step of male part 250 Male thread 251, 252 Thread of male thread 253, 254 Tip of thread of male thread 300 Female part 301 Central axis of female part 310 First end of female part 311 Opening of female part 320 Second end of female part 330 Annular protrusion 331 Tip of annular protrusion 340 Flange of female part 341 Bearing surface of female thread 342 Protrusion of female part 343 Protruding portion of female part 344 Tip of protruding portion of female part 345 Thin plate portion 346 Thick plate portion 347 Outer plate surface of thin plate portion 348 Step portion of female part 349 Tip surface of step portion of female part 350 Female thread 351, 352 Thread groove of female thread 353 Tip of thread groove of female thread 510 First hose 520 Second hose

Claims (6)

a male part having a cylindrical shape, one axial end of which includes a connection portion for connecting to the first pipe, and the other axial end of which includes a multi-start male thread;
a female part having a cylindrical shape, one axial end of which includes a multiple-start female thread that can mesh with the male thread, and the other axial end of which includes a connection portion with a second pipe,
Of the male thread and the female thread,
One of the bearings includes a protrusion extending in the axial direction on a part of the circumferential direction of the bearing surface,
The other includes a bearing surface removal portion, which is a trace of a circumferentially continuous area removed in a circumferential part of the bearing surface,
When the male thread and the female thread are brought closer to each other coaxially during the fastening operation of the male part and the female part,
If the circumferential angle between the two threads is a value at an incorrect make-up start position, the protrusion collides with the bearing surface of the other thread before the two threads reach an incorrect make-up completion position,
a pipe fitting characterized in that the protrusion and the seating surface removal portion are configured so that, when the circumferential angle between both threads is the value at the correct make-up start position, the protrusion enters the seating surface removal portion before the both threads reach the correct make-up completion position, thereby avoiding collision with the seating surface of the other thread. a fit angle, which is a rotation angle required for the male screw and the female screw to move from a correct fastening start position to a correct fastening completion position, is 180° or less;
the length of the protrusion is equal to or greater than the distance between the bearing surfaces of the male thread and the female thread when they are engaged at a correct fastening start position,
The width of the seat surface removal portion in the circumferential direction is equal to or greater than the fit angle and is equal to or less than the value obtained by dividing 360° by the number of threads of both threads,
a range in which the protrusion moves in the circumferential direction of both threads as the male thread and the female thread move from a correct make-up start position to a correct make-up completion position is included in the range of the bearing surface removed portion in the circumferential direction of both threads;
2. The pipe fitting according to claim 1. Each of the male part and the female part includes a protrusion extending from a part in the circumferential direction toward the outer periphery,
The protrusions of the male part and the female part are configured to align the male part and the female part in the circumferential direction when the male thread and the female thread reach a correct fastening completion position.
2. The pipe fitting according to claim 1. A pipe fitting as described in claim 3, wherein the protrusions of the male and female parts have the same outline when viewed from the axial direction of the male and female parts. A pipe fitting as described in claim 3, wherein the protrusions of the male and female parts are configured to snap-fit together when the male and female threads reach the correct fastening position. A pipe fitting as described in claim 3, wherein the protrusions on the male and female parts engage with each other when the male and female threads reach the correct tightening position, preventing reverse rotation of the two threads.