JPH0949350A - Backlash preventing mechanism for angular core shaft of lock - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlash preventing mechanism capable of surely preventing a backlash in the angular hole of an angular core shaft, having a simple structure, and reducing the manufacturing cost. SOLUTION: A latch hub 30 is constituted of the first plate-like latch hub 31 coupled with a latch bolt and two second resin latch hubs 32, 32 pinching the first latch hub 31 from both sides. Projections 32e, 32e protruded inward are formed at least on opposite inner wall faces 32d, 32d on one side of the angular hole 32c of the second latch hub 32 respectively. The inner wall sections having the projections 32e, 32e are formed hollow. The upper second latch hub 32 faces the lower second latch hub 32 in the rotated state by 90 deg..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lock shaft in which a latch bolt is retracted and retracted through a latch hub into which the shaft is inserted by rotating a rotary operation member such as a lever handle or a knob. The present invention relates to a lock prevention mechanism of a square-core shaft rattling for preventing rattling that occurs when it is fitted into a latch hub.

[0002]

2. Description of the Related Art For example, a lock of a lever handle lock or a knob lock is provided with a square core shaft at its shaft core acting portion.

As shown in FIG. 12, a latch hub 51 provided in a conventional lock of this type is provided with a square hole 52, and one square core shaft 5 having a square cross section is formed in the square hole 52.
3 has a structure in which it is inserted. Then, when the door is opened, the latch hub 51 is rotated by rotating the rectangular core shaft 53 with a lever handle (not shown), and the latch bolt 54 is retracted so that the door can be opened. The latch hub 51 is made of brass, for example, and engages with the latch bolt 54 by a U-shaped engaging portion 55 formed in the upper portion, as shown in FIG. The latch hub 51 has a square hole 5 at the center.
It is molded as solid, that is, solid, except that 2 is penetrated.

In order to fit the square core shaft 53 into the square hole 52, the square hole 52 and the square core shaft 53 each have a high-precision surface finish, but there is still rattling between the two. There is a problem that it cannot be avoided completely.

In order to deal with this problem, as shown in FIG. 14, for example, one half-split shaft is screwed to a vertical split half-core shaft 63 fitted in a square hole 62 of a knob 61. There is a structure in which the tip end portion of the set screw 64 that has been penetrated through is pressed against the opposing surface of the other half shaft. Further, in another conventional example, as shown in FIG. 15, a square core shaft 71 composed of two half-divided bodies each having a triangular cross-section is obliquely pressed against a square hole 73 by a set screw 72. There is one.

However, in each of the above-mentioned two conventional examples, both of them are effective in preventing rattling, but since the square core shafts 63 and 71 are divided, the square core shafts 63 and 71 are strong. However, the handling of the knob 61 or the lever handle tends to damage the square shafts 63 and 71. That is, the square core shaft 63.7
Since it is known that the strength of No. 1 decreases substantially in proportion to the number of divisions of the square core shafts 63 and 71, it is desirable that the square core shafts 63 and 71 be formed of a single member.

On the other hand, there is one disclosed in Japanese Utility Model Laid-Open No. 61-1564 in order to prevent rattling by using the square core shaft as a single member. The technology disclosed in the above publication is shown in FIG.
As shown in (b), a leaf spring 82 having a wavy bent protrusion 81 is provided on one surface of a square core shaft 83.
Is pressed against the fitting hole 85 of the lever handle 84 and the wall surface of the square hole of the latch hub (not shown) to prevent rattling.

[0008]

However, in the above-described conventional lock / unlocking angular core shaft rattling prevention mechanism, the rattling can be prevented by fixing the wavy plate spring 82 to one surface of the angular core shaft 83, but the plate spring 82 is prevented. However, there is a problem in that the number of parts increases due to the addition of, and consequently the manufacturing cost cannot be reduced.

The present invention has been made in view of the above-mentioned conventional problems, and its object is to ensure that rattling in a square hole of a square core shaft is ensured on the assumption that a square core shaft made of a single member is used. It is an object of the present invention to provide a lock mechanism for preventing rattling of the center axis of the lock, which can be prevented and the structure can be simplified to reduce the manufacturing cost.

[0010]

In order to solve the above-mentioned problems, the lock core angular axis rattling prevention mechanism of the invention according to claim 1 inserts the angular core axis by rotating the rotating operation member. In the lock center square core rattling prevention mechanism for retracting the latch bolt through the latch hub, the latch hub is
A plate-shaped first latch hub that engages with the latch bolt, and is made of resin so as to sandwich the first latch hub from both sides.
Two second latch hubs, each of the first latch hub and the two second latch hubs has a square hole for inserting the square core shaft in the central position, while each of the second latch hubs At least one of the inner wall surfaces of the square hole facing each other is formed with an inwardly projecting convex portion, and each inner wall portion having the convex portion is formed hollow, and one of the second latch hubs is The second latch hub is opposed to the second latch hub in a state of being rotated by 90 degrees.

According to the above construction, when the square core shaft is inserted into the square hole of the latch hub, the convex portions projecting inward are formed on the inner wall surfaces of at least one of the square holes of the respective second latch hubs facing each other. Since the square core is formed respectively, the square core shaft is pressed by the two convex portions facing each other, and the rattle of the square core shaft in the facing direction can be prevented.

In each of the second latch hubs of the present invention, one of the second latch hubs is opposed to the other of the second latch hubs in a state of being rotated by 90 degrees. Therefore,
The square core shaft is pressed by each convex portion in both of two directions perpendicular to the insertion direction. That is, the four side surfaces of the square core shaft are pressed. As a result, it is possible to reliably prevent rattling of the square core shaft.

By the way, when the square core shaft is inserted into the square hole of the latch hub, when the square core shaft is inserted, the protrusion formed on the inner wall surface of the second latch hub collides with the square core shaft. . However, in the present invention, the second latch hub is made of resin, and each inner wall portion having a convex portion is formed hollow. That is, the back surface of the convex portion is hollow. Therefore, the convex portion can be bent toward the hollow portion. As a result, when the square core shaft is inserted, by bending the convex portion toward the hollow portion, the square core shaft can be easily inserted into the square hole of the second latch hub.
On the contrary, when the convex portion is bent toward the hollow portion, the elasticity of the convex portion for pressing the square core shaft can be increased. Therefore, it is possible to more reliably prevent the rattling of the square core shaft.

Further, since another member such as a leaf spring is not required, the structure can be simplified and the manufacturing cost can be reduced.

In order to solve the above-mentioned problems, the lock core angular core rattling prevention mechanism of the invention according to claim 2 is the lock core angular core rattling prevention mechanism according to claim 1, wherein
A notch portion reaching the hollow portion is formed around the convex portion on the inner wall surface of the latch hub on which the convex portion of the square hole is formed and in the fitting insertion direction of the square core shaft.

That is, according to the structure of the invention of claim 1, since the back surface of the convex portion of the square hole in the second latch hub is hollow, when the square core shaft is inserted into the square hole of the second latch hub, It is possible to bend the convex part to the hollow part side,
If the entire surface of the inner wall surface where the convex portion of the square hole was formed had a so-called fixed-end beam structure, the strength of the beam would increase,
The amount of bending of the convex portion toward the hollow portion may be insufficient.

However, in the present invention, since the notch portion reaching the hollow portion is formed around the convex portion on the inner wall surface on which the convex portion is formed and in the fitting direction of the square core shaft, the convex portion is formed. The width of the fixed beam at both ends is small in the fitting direction of the square core axis, so that the strength of the beam can be weakened and the elasticity of the convex portion can be increased. Therefore, the convex portion can be more easily bent toward the hollow portion.

As a result, when the square core shaft is inserted, the square core shaft can be inserted into the square hole of the second latch hub more easily by bending the convex portion toward the hollow portion more easily. In addition, the increase in elasticity makes it possible to prevent the rattling of the square core shaft more reliably.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. In the lock of the present embodiment, the latch bolt is retracted and retracted through the latch hub into which the square core shaft is inserted by the rotation operation of the rotation operation member. As the rotation operation member, the lever handle or Although a knob can be used, an application example to a lever handle will be described here.

The lever handle lock 1 as a lock of the present embodiment is attached to a door in a private room such as a Western room in a house or a condominium or a bathroom. As shown in FIGS. 2 and 3, the lever handle lock 1 has an indoor door lock 2 attached to the indoor surface of the door and an outdoor door lock 3 attached to the outdoor surface of the door. ing. The indoor side door lock 2 and the outdoor side door lock 3 are arranged to face each other across both sides of the door, and the door is fixed between the indoor side door lock 2 and the outdoor side door lock 3. The latch member 4 is provided. The latch member 4 is provided with a lever handle 5 as a rotation operation member for the indoor door lock 2 and a latch bolt 7 that is retracted and retracted by a lever handle 6 as a rotation operation member for the outdoor door lock 3. There is.

In the closed state, the above-mentioned latch bolt 7 advances and is fitted into a latch hole (not shown) formed in the door frame, whereby the lever handle 5 or the lever handle 6 is rotated unless it is rotated. Is not open.

As shown in FIG. 4, the outdoor door lock 3 for retracting the latch bolt 7 has an outdoor seat 8 which abuts against the door. As shown in FIG. 5, an outdoor-side reinforcement long seat 9 fitted to the outdoor-side long seat 8 is provided.

A through hole 10 is formed in the above-mentioned outdoor reinforcement long seat 9.
・ 10 is drilled. As shown in FIG. 2, screws 11 and 11 having a plus-shaped groove on the head are fitted and inserted into these through holes 10 and 10. The indoor side door lock 2 and the outdoor side door lock 3 are fastened by being screwed into the screw-threaded portions 22c and 22c of the back plate 22 in FIG.

Further, the outer surface of the outdoor door lock 3 has a structure shown in FIG.
As shown in, the lever handle 6 gripped when the door is opened and closed and the thumb turn 21 are connected to rotate integrally,
In addition, an emergency turn 12 that unlocks the locked state of the door by the thumb turn 21 from the outside is provided.

As shown in FIG. 2, the lever handle 6 is provided with a not-shown quadrangular prismatic square core shaft fitting hole at the center of rotation, and the square core shaft fitting hole is formed in the square core shaft fitting hole. Latch member 4
The square core shaft 13 made of a single member that is penetrated through is fitted. Then, as shown in FIG. 4, by rotating the lever handle 6 in the direction A, the tip of the latch bolt 7 is moved into and out of the latch member 4 so that the door can be opened. On the other hand, when the lever handle 6 is returned in the B direction, the latch bolt 7 is moved into the latch hole of the door frame and the door is closed.

On the other hand, as shown in FIGS. 2 and 3, the indoor side door lock 2 attached to the indoor side is the outdoor side door lock 3 described above.
Similarly to the above, it has an indoor long seat 20 that comes into contact with the door. As shown in FIG. 6, a lever handle 5 that is gripped when the door is opened and closed, and a thumb turn 21 that locks the latch bolt 7 so as to lock the latch bolt 7 are provided on the surface of the indoor long seat 20. .

As shown in FIG. 2, the lever handle 5 is provided with a quadrangular prism-shaped rectangular core shaft fitting hole 5a at the center of rotation, and the rectangular core shaft fitting hole 5a has a rectangular core. When the shaft 13 is fitted, the lever handle 5 becomes the outdoor door lock 3
6 in conjunction with the lever handle 6 of FIG.
It is designed to rotate in the direction.

Here, the latch member 4 will be described in detail. As shown in FIGS. 7A and 7B, the latch member 4 has a case 42 covered with a cover 41.
The case 42 is provided with a retractable latch bolt 7 partly protruding from the opening 43a of the front plate 43, and a rotatable square shaft 13 is attached to the latch bolt 7 for retracting. A latch hub 30 is provided for this purpose.

The latch bolt 7 has an L portion 7 at the rear end.
a is formed, and the L portion 7a is provided on the standing portion of FIG.
The hanging part 45a of the retractor 45 also shown in (a) and (b).
Is locked. And FIG. 7 (a)
As shown in (b), between the latch bolt 7 and the hanging portion 45a of the retractor 45, a latch spring 46 composed of a coil spring having a relatively weak elasticity is contracted, and by this latch spring 46, The latch bolt 7 is biased so that the latch head portion 7b is held in a locked position where it protrudes from the front plate 43.

A retractor spring 47, which is a coil spring, is provided between the hanging portion 45a of the retractor 45 and the upright portion 42a of the case 42. This retractor spring 47 allows the retractor 45 to be retracted. In the figure, when the latch bolt 7 is moved in the right direction to move the latch bolt 7 in and out, the latch bolt 7 is biased in the advancing direction.

On the other hand, the above-mentioned latch hub 30 comprises a first latch hub 31 and two second latch hubs 32, 32 provided with the first latch hub 31 sandwiched therebetween.

The above-mentioned first latch hub 31 is shown in FIG. 9 (a).
As shown in (b), it is formed of a metal plate in a substantially circular shape, and the substantially one half is a large diameter portion 31a having a larger radius than the other one half. At the center of the first latch hub 31, a cross hole 31b having a cross-shaped cross section and a square hole 31 having a square cross section smaller than the cross hole 31b.
The holes c and c are provided in an overlapping manner.

The second latch hub 32 is made of a resin product and is formed in a cylindrical shape as shown in FIGS. Then, as shown in FIG.
The lower side is a large diameter portion 32a and the upper side is a small diameter portion 32b. Further, as shown in FIG. 10A, a square hole 32c having a square cross section is penetrated in the center, and the square core shaft 13 described above is formed.
Is to be inserted.

Square hole 3 in the second latch hub 32 described above
As shown in FIG. 1, convex portions 32e and 32e projecting inward are formed on the inner wall surfaces 32d and 32d facing each other of 2c, and the convex portions 32e and 32e are formed.
The inner wall portions having are formed hollow. That is, the back sides of the convex portions 32e and 32e are hollow portions 32f and 32e.
It is formed as f.

Further, the inner wall surface 32 of the second latch hub 32 on which the convex portions 32e of the square hole 32c are formed.
Around the convex portions 32e and 32e in d and 32d and in the fitting direction of the square core shaft 13, that is, the second upper side in FIG.
Below the protrusions 32e, 32e of the latch hub 32, notches 32g, 32 reaching the hollows 32f, 32f are formed.
g is formed.

On the other hand, the second of the other shown on the lower side in FIG.
The latch hub 32 is formed of exactly the same as the second latch hub 32 shown on the upper side in FIG.
The second latch hub 32 on the upper side is arranged to face the second latch hub 32 on the lower side while being rotated by 90 degrees.

Then, the second latch hubs 32, 32 have
A pair of engagement protrusions 3 for engaging the first latch hub 31.
2h and 32h are formed so that they can be inserted into the cross holes 31b and 31b of the first latch hub 31 (see FIG. 9A).

The latch member 4 of the lock 1 having the above structure
The operation of is outlined. First, in the locked state of the lock 1, as shown in FIGS. 7 (a) and 7 (b), the latch bolt 7 holds the advanced state, and at this time, the retractor 45 is moved to the left side in FIG. And
Engaging end 3 of first latch hub 31 in latch hub 30
The entire 1d is in contact with the rising portion 45b of the retractor 45.

When the lever handle 5 or the lever handle 6 is rotated from this state, as shown in FIG.
The rectangular core shaft 13 is in a state of being rotated by about 45 degrees. Then, the first latch hub 31 rotates integrally with the rotation of the square core shaft 13, and at this time, the engaging end 31 of the first latch hub 31 rotates.
The corner portion of d presses the rising portion 45b of the retractor 45,
The retractor 45 is moved to the right as shown in the figure. Along with this, the hanging portion 45a of the retractor 45 moves the latch bolt 7 to the right, and the latch bolt 7 is moved in and out.

As can be seen from the operation of the above-mentioned latch member 4, in the lock 1 according to the present embodiment, the portion on which the force acts is the square core shaft 13, the first latch hub 31, the retractor 45 and the latch bolt 7. However, these are all made of a metal material so that the load is not applied to the resin material.

Thus, the lock 1 according to the present embodiment
In the rattling prevention mechanism of the rectangular core shaft 13 of the latch hub 30
When the square core shaft 31 is inserted through the square holes 31c and 32c of
Since the inner wall surfaces 32d and 32d of at least one of the square holes 32c of the second latch hub 32 which face each other have inwardly projecting projections 32e and 32e, respectively, the two opposite projections 32e and 32e. The rectangular core shaft 13 is pressed by 32e, and the rectangular core shaft 1 in the opposing direction is pressed.
The rattling of 3 can be prevented.

Here, each of the second latch hubs 32, 32 is
One of the second latch hubs 32 is connected to the other second latch hub 3
They are opposed to each other in a state of being rotated by 90 degrees. Therefore, the rectangular core shaft 13 is pressed by the respective convex portions 32e ... In both of the two right-angled directions with respect to the insertion direction. That is, the four side surfaces of the square core shaft 13 are pressed. As a result, the rattling of the square core shaft 13 can be reliably prevented.

By the way, the square hole 31c of the latch hub 30
When the square-core shaft 13 is inserted into the shaft 32c, when the square-core shaft 13 is inserted, the protrusion 32e projecting from the inner wall surface 32d of the second latch hub 30 collides, which is an obstacle to the insertion. However, in the present embodiment, the second
The latch hub 32 is made of resin and has a convex portion 32.
Each inner wall portion having e is formed hollow. That is, the back surface of the convex portion 32e is a hollow portion 32f. Therefore, the convex portion 32e can be bent toward the hollow portion 32f.

As a result, when the square core shaft 13 is inserted, the square core shaft 13 can be easily inserted into the square hole 32c of the second latch hub 32 by bending the convex portion 32e toward the hollow portion 32f. On the contrary, the convex portion 32e has the hollow portion 3
By bending to the 2f side, the elasticity for pressing the convex portion 32e against the square core shaft 13 can be increased. Therefore, the rattling of the square shaft 13 can be prevented more reliably.

Further, since another member such as a leaf spring is not required, the structure can be simplified and the manufacturing cost can be reduced.

Further, in the above-mentioned latch hub 30, the second
In the latch hub 32, the notch 3 that reaches the hollow portion 32f around the convex portion 32e on the inner wall surface 32d in which the convex portion 32e of the square hole 32c is formed and in the fitting direction of the square core shaft 13 is formed.
2 g are formed.

That is, since the back surface of the convex portion 32e of the square hole 32c in the second latch hub 32 is hollow,
When the square core shaft 13 is inserted into the square hole 32c of the second latch hub 32, the convex portion 32e can be bent toward the hollow portion 32f, but the inner wall surface 32d having the convex portion 32e of the square hole 32c is formed. Since the entire surface has a so-called fixed beam structure at both ends, the strength of the beam is increased and the hollow portion 32 of the convex portion 32e is increased.
The amount of bending toward the f side may be insufficient.

However, in the present embodiment, a notch 32g reaching the hollow portion 32f is formed around the convex portion 32e in the inner wall surface 32d having the convex portion 32e and in the fitting insertion direction of the square core shaft 13. Therefore, the width of the both-end fixed beam in which the convex portion 32e is formed has a small width in the fitting insertion direction in the square core shaft 13, thereby weakening the strength of the beam and increasing the elasticity of the convex portion 32e. Can be increased. Therefore, the convex portion 32e can be more easily bent toward the hollow portion 32f.

As a result, when the square core shaft 13 is inserted, the convex portion 32e is more easily bent toward the hollow portion 32f, so that the square core shaft 13 is fixed to the square hole 32c of the second latch hub 32.
Can be inserted more easily. In addition, the increase in elasticity makes it possible to more reliably prevent the angular core shaft 13 from rattling.

[0050]

As described above, in the lock core square shaft rattling prevention mechanism according to the first aspect of the present invention, the latch hub has the plate-shaped first latch hub that engages with the latch bolt and the first latch hub on both sides. And two second latch hubs made of resin so as to be sandwiched between the first latch hub and the two second latch hubs. On the other hand, on the inner wall surfaces of at least one of the square holes in each of the second latch hubs, which face each other, inwardly projecting portions are formed, and each inner wall portion having these protruding portions is formed hollow. Is
One of the second latch hubs is configured to face the other second latch hub in a state of being rotated by 90 degrees.

As a result, when the square core shaft is inserted through the square hole of the latch hub, the inwardly projecting convex portions are formed on the inner wall surfaces of at least one of the square holes of the respective second latch hubs facing each other. Therefore, the square core shaft is pressed by the two convex portions facing each other, and the rattling of the square core shaft in the facing direction can be prevented.

Further, the second latch hubs of the respective second latch hubs are opposed to each other in a state in which one second latch hub is rotated by 90 degrees with respect to the other second latch hub. Therefore, the square axis is
The protrusions are pressed in both of the two directions perpendicular to the insertion direction.

That is, the four side surfaces of the square core shaft are pressed. As a result, it is possible to reliably prevent rattling of the square core shaft.

Further, since the second latch hub is made of resin and each inner wall portion having the convex portion is formed hollow, the convex portion can be bent toward the hollow portion side. As a result, when the square core shaft is inserted, by bending the convex portion toward the hollow portion, the square core shaft can be easily inserted into the square hole of the second latch hub. On the contrary, when the convex portion is bent toward the hollow portion, the elasticity of the convex portion for pressing the square core shaft can be increased. Therefore, it is possible to more reliably prevent the rattling of the square core shaft.

Further, since another member such as a leaf spring is not required, the structure can be simplified and the manufacturing cost can be reduced.

As described above, the lock core angular center rattling prevention mechanism of the invention according to claim 2 is the lock core angular core shaft rattling prevention mechanism according to claim 1, wherein the protrusion of the square hole in the second latch hub is used. A notch portion reaching the hollow portion is formed around the convex portion on the inner wall surface formed with and in the fitting direction of the square core shaft.

As a result, in addition to the effect of the invention according to the first aspect, the width of the fixed-end beam having the projections formed therein is small in the fitting direction of the square core axis, and the strength of the beam is weakened. However, the elasticity of the convex portion can be increased. Therefore, the convex portion can be more easily bent toward the hollow portion.

As a result, when the square core shaft is inserted, the square core shaft can be inserted into the square hole of the second latch hub more easily by flexing the convex portion toward the hollow portion more easily. In addition, there is an effect that it is possible to more reliably prevent rattling of the square core shaft due to the increase in elasticity.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an exploded configuration example of a latch hub in a lock core square shaft rattling prevention mechanism according to the present invention.

FIG. 2 is an exploded perspective view showing the structure of the lock.

FIG. 3 is a front view showing the structure of the lock.

FIG. 4 is a right side view showing the structure of the outdoor door lock before the lock.

FIG. 5 is a sectional view showing a structure of the outdoor door lock before the lock.

FIG. 6 is a left side view showing the structure of the door lock inside the lock.

FIG. 7 is a right side view showing a closed state of the lock lock member, in which (a) is a partially cutaway view;
(B) is a sectional view.

8A and 8B show a structure of a retractor in the latch member, where FIG. 8A is a right side view and FIG. 8B is a sectional view.

9A and 9B show a structure of a first latch hub in the above-mentioned latch member, wherein FIG. 9A is a right side view and FIG. 9B is a sectional view.

10A and 10B show a structure of a second latch hub in the latch member, where FIG. 10A is a right side view, FIG. 10B is a sectional view taken along line YY of FIG. 10A, and FIG. XX sectional drawing, (d) is a left side view.

FIG. 11 is a right side view showing a partially opened state of the door in the latch member of the lock.

FIG. 12 is a right side view showing a structure of a conventional lock with a part thereof broken away.

FIG. 13 is a rear view showing the structure of the latch hub used for the lock.

FIG. 14 shows another conventional example and is a cross-sectional view showing the structure of a square core shaft.

FIG. 15 is a cross-sectional view showing still another conventional example and showing the structure of a square core shaft.

FIG. 16 shows still another conventional example, (a)
Is a perspective view showing a square core shaft and a lever handle, and (b) is an enlarged perspective view showing the square core shaft to which a leaf spring is attached.

[Explanation of symbols]

 1 Lock 5/6 Lever Handle (Rotating Operation Member) 7 Latch Bolt 13 Square Core Shaft 21 Thumb Turn 30 Latch Hub 31 First Latch Hub 31c Square Hole 32 Second Latch Hub 32c Square Hole 32d Inner Wall Surface 32e Projection 32f Hollow Section 32g Notch

Claims (2)

[Claims] 1. A lock-prevention square-core-shaft rattling prevention mechanism in which a latch bolt is retracted and retracted through a latch hub into which a square-core shaft is inserted by rotating the rotary operation member, wherein the latch hub is engaged with the latch bolt. Plate-shaped first
It is composed of a latch hub and two second latch hubs made of resin so as to sandwich the first latch hub from both sides, and a square core shaft is fitted to the central position of each of the first latch hub and the two second latch hubs. While the square holes for inserting are formed, the inwardly projecting convex portions are formed on the inner wall surfaces of at least one of the square holes of each of the second latch hubs facing each other, and the convex portions are formed. Each of the inner wall portions having a hollow is formed, and one of the second latch hubs is opposed to the other of the second latch hubs in a state of being rotated by 90 degrees. . 2. A cutout portion reaching a hollow portion is formed around the convex portion on the inner wall surface of the second latch hub on which the convex portion of the square hole is formed and in the fitting insertion direction of the square core shaft. The lock prevention mechanism of the square core shaft according to claim 1, which is characterized in that.