JP3454028B2 - Seat locking mechanism for chair with tiltable seat - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seat locking mechanism for a chair having a tiltable seat, and more specifically, a rear part of the seat can be moved up and down to take a standing posture and a reclining posture. Lock mechanism for fixing a seat portion in a standing posture and a reclining posture in a simple chair.

[0002]

2. Description of the Related Art Conventionally, a mounting body mounted on a leg portion and a front portion of a tilting body for mounting a seat portion on an upper surface thereof are rotatably connected by a horizontal rotary shaft, and tilted with a mount body behind the rotary shaft. The rear part of the tilting body is elastically biased upward between itself and the body, and the rear part of the seat part can move up and down to take a standing posture and a reclining posture. The present applicant has also provided a chair having a tiltable seat with a locking mechanism capable of fixing the.

In a conventional lock mechanism, a crank portion of a lock lever, which penetrates from the side of the mounting body and rotatably holds a shaft portion, is integrally formed with a main body portion fixed inside the mounting body. In addition to being movable within the arcuate locking hole,
The crank portion can be elastically locked in two steps of both ends of the arcuate locking hole, and the end of the arcuate locking hole is located at the end of the locking plate protruding from the tilting body. A first locking recess for stopping against the crank part to maintain the standing posture, and a reclining position by locking the crank part positioned at one end of the arc-shaped locking hole on one side of the locking plate. The second locking recess for maintaining the above is formed. When the crank part is located at the other end of the arcuate locking hole, the locking plate can move freely on the side of the crank part, so that the seat part can move freely as the weight of the seated person moves. It is possible to change the inclination angle.

Here, the locking plate has a protrusion formed between the first locking recess and the second locking recess. The minimum vertical width of the protrusion is determined by the inclination angle θ (radian) between the standing posture and the reclining posture of the seat portion, and the distance r from the rotation axis, and
From the axial center distance rθ of the crank part located in the locking recess,
The value (rθ-D) is obtained by subtracting the diameter D of the crank portion. For example, θ is 0.1 radian (about 6 °) and r is 130 m
When m and D are 8 mm, the minimum vertical width of the protrusion is about 5 mm. When the standing posture is fixed to this protrusion, the center of gravity of the seated person is located further rearward than the lock mechanism, so that the weight of the seated person is 1.2 to 1.
It is expected that a load of about 3 times will be concentrated, and that when the seated person suddenly sits, a load of about 2 times the weight of the seated person will be applied. For example, when used by a seated person weighing 100 kg, the protrusion must be able to withstand a load of at least 200 kg.

Therefore, conventionally, the plate thickness of the locking plate is
Although a very thick one (6 mm) has been used, the projection may not be damaged by metal fatigue due to repeated loading.

[0006]

Therefore, in view of the above-mentioned situation, the present invention is to solve the problem that the rear portion of the seat portion can move up and down to take a standing posture and a reclining posture. In a chair having a tiltable seat part having a lock mechanism capable of fixing the seat part in an upright position and a reclining position, in the upright position, the support strength of the seat part with a fixed tilt angle is increased. The point is to provide a locking mechanism capable of reliably and safely supporting a downward load.

[0007]

According to the present invention, in order to solve the above-mentioned problems, a front portion of a mounting body mounted on a leg portion and a front portion of a tilting body mounting a seat portion on an upper surface thereof can be rotated by horizontal rotating shafts. The rear part of the tilting body is elastically biased upward between the mounting body and the tilting body rearward of the rotation axis, and the rear part of the seat moves up and down to take a standing posture and a reclining posture. A lock lever of a chair for fixing a seat in a standing posture and a reclining posture, the lock lever penetrating from a side of the mounting body and rotatably holding a shaft portion. The crank portion of the arc-shaped locking hole is made movable in an arcuate locking hole formed integrally with the main body fixed to the inside of the mounting body, and the crank part is divided into three end portions and an intermediate portion of the arcuate locking hole. Locking plate that can be elastically locked at the stage, and that is projected on the tilting body A first locking recess that stops at the crank end of the arc-shaped locking hole at the end of the arc-shaped locking hole and maintains a standing posture, and an intermediate position of the arc-shaped locking hole on one side of the locking plate. Forming a second locking recess that locks the crank portion located in the lower part and maintains a reclining posture, on the vertical extension line of the deepest portion of the second locking recess or in the width direction of the locking plate with respect to the extension line. A seat locking mechanism for a chair having an inclinable seat formed by setting a center of a load applied to the first locking recess inward is configured.

Here, with the crank portion of the lock lever positioned in the intermediate portion of the arcuate locking hole, the axial position of the lock lever shaft portion and the crank portion is a circumference about the rotary shaft. It is preferable to set on the line.

Further, a lower load receiving portion for receiving a lower load applied to a crank portion of the lock lever positioned at one end of the arcuate locking hole is formed in the main body portion, and an intermediate portion of the arcuate locking hole is formed. An upper load receiving portion for receiving an upper load applied to the crank portion located on the main body portion,
It is also preferable to form an elastic receiving portion that elastically holds the crank portion around the other arcuate locking holes.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a more detailed description will be given based on an embodiment of the present invention shown in the accompanying drawings. FIG. 1 is a side view of a chair according to the present invention, FIG. 2 is a front view of the same, and FIGS. 3 to 7 show respective parts of a locking device of a seat part, in which 1 is a leg part, 2 is a seat part, and 3 is a back part. The leaning portions 4 indicate locking devices, respectively.

The chair according to the present invention comprises a seat portion 2 supported by a leg portion 1, and a backrest portion 3 which is elastically connected to a rear rising portion of the seat portion 2 so as to be tiltable forward and backward. , The rear portion of the seat portion 2 is elastically lowered as the weight of the seated person moves backward by the locking device 4 provided between the seat portion 2 and the leg portion 1,
The structure is such that it moves up to its original position as the weight moves forward. Of course, the rear portion of the seat portion 2 may be in an intermediate position between the uppermost position (standing posture) and the lowermost position (reclining posture) depending on the sitting posture of the seated person.

The locking device 4 is supported by a metal mounting body 6 having a rear end portion mounted on the upper end of a gas cylinder 5 standing on the leg portion 1, and a bearing 7 on the front portion of the mounting body 6. A tilting body 9 made of metal, the front part of which is rotatably connected by a horizontal rotating shaft 8, a biasing means 10 for elastically biasing the rear part of the tilting body 9 upward, and the mounting body 6. A lock mechanism 11 for fixing the tilted state of the tilting body 9 with respect to the tilting body 9 and a damper mechanism 12 for buffering the movement of the tilting body 9 when the tilting body 9 is tilted about the rotating shaft 8. Here, the center of gravity of the seated person sitting on the seat portion 2 is set near the gas cylinder 5.

The mounting body 6 has a box-like shape that is open upward and has a tapered tip portion 5 of the gas cylinder 5 at the rear end portion.
A tapered mounting tube 13 into which A is fitted is vertically penetrated, and the bearing 7 is fixed to the front end portion thereof.
The urging means 10 is provided at an intermediate portion of the lock mechanism 11, and the main body 11A of the lock mechanism 11 is provided between the urging means 10 and the mounting pipe 13. The operation pin 5B of the gas cylinder 5 is exposed inside the attachment body 6.

The tilting body 9 has a substantially box-like shape that is opened downward, and has a structure in which the front portion corresponding to the bearing 7 and the damper mechanism 12 is bifurcated, and the bifurcated portions penetrate both sides. A bearing 7 in which the installed rotating shaft 8 is fixed to the mounting body 6.
Is rotatably supported by and is connected to the mounting body 6,
The urging means 10 is provided between the mounting plate 14 for fixing the seat portion 2 to the upper surface and the lower surface plate 15 of the mounting body 6, and the locking plate 11B of the lock mechanism 11 is provided on the lower surface of the mounting plate 14. It is installed below. Then, the tilting body 9 corresponds to the mounting body 6
Is shaped to cover the upper part of.

As shown in FIGS. 3 and 5, the bearing 7 has a metal holding frame 16 welded to the front portion of the lower plate 15 of the mounting body 6 and extends laterally to the holding frame 16. In addition to having the accommodation groove 17 which is open upward, it has fixing plates 18 and 18 extending to the front and rear of the upper edge, and the bushes 19 and 19 made of synthetic resin which are vertically divided into two in the accommodation groove 17 are interposed between the rotary shaft 8 The holding plate 20 is screwed into the front and rear fixing plates 18 and 18 so as to come into contact with the upper surface of the bush 19 above.
The structure is fixed by.

The urging means 10, as shown in FIG.
The strength knob 23 is fixed to the lower end of the screw shaft 22 penetrating the lower surface plate 15 of the mounting body 6 and in sliding contact with the lower surface of the lower surface plate 15, and the screw shaft 2 on the upper surface side of the lower surface plate 15 is fixed.
A bearing 24 is interposed between the annular flange portion 22A protruding from the lower surface 2 and the lower surface plate 15 to allow the screw shaft 21 to rotate at a fixed position and to be fixed to a receiving plate 25 on the upper portion of the screw shaft 22. The nut 26 is screwed, the lower end of the compression coil spring 27 is abutted against the receiving plate 25, and the upper end of the compression coil spring 27 is projected downward on the mounting plate 14 of the tilting body 9 to form an annular convex portion 28. It is a structure that is externally attached to and is stopped by the mounting plate 14. Then, by rotating the strength knob 23, the receiving plate 25 is displaced up and down with respect to the screw shaft 22 to change the compression state of the compression coil spring 27, and the tilting body 9 around the rotation shaft 8 is rotated. The elastic resistance to the rearward descent is adjusted.

As shown in FIGS. 3 and 4, the lock mechanism 11 includes a crank portion 29B of a lock lever 29 which penetrates the mounting body 6 from the side and rotatably holds a shaft portion 29A. Main body 11A fixed inside the mounting body 6
The arc-shaped locking hole 30 formed integrally with the arc-shaped locking hole 30, and the crank portion 29B can be elastically locked in three steps of both end portions and the intermediate portion of the arc-shaped locking hole 30. Locking plate 11 protruding from the lower surface of the mounting plate 14 of the tilting body 9
This is a structure in which a first locking recess 31 is formed at the tip of B, and a second locking recess 32 is formed on one side surface above it. When the crank portion 29B is located at one end of the arcuate locking hole 30, the locking plate 11B can pass vertically on the side of the crank portion 29B, that is, the tilting body 9 can freely tilt. None, the crank portion 29 at the other end of the arcuate locking hole 30
When B is located, the first locking recess 31 of the locking plate 11B
Engages with the crank portion 29B to regulate the downward movement of the rear portion of the tilting body 9 to maintain the standing posture, and with the rear portion of the tilting body 9 sunk to the lowermost position, the arcuate locking hole 30 By arranging the crank portion 29B at the intermediate portion, the crank portion 29B engages with the second locking concave portion 32 to regulate the upward movement of the rear portion of the tilting body 9 and maintain the reclining posture. Here, when the lock lever 29 is rotated about the shaft portion 29A, the crank portion 29B eccentric to the shaft portion 29A moves along the arcuate locking hole 30.

As shown in FIGS. 3, 6 and 7, the damper mechanism 12 is located at a position slightly separated from the rotary shaft 8 and where the side surfaces of the mounting body 6 and the tilting body 9 overlap. In this structure, the slider 33 is attached to one side surface via the compression rubber 34, and the slider 33 is slidably contacted to the other side surface. The damper mechanism 12 stabilizes the rotating operation of the tilting body 9 around the rotation shaft 8.
That is, while preventing the rattling of the seat portion 2 to the side,
A sudden movement is restricted in the rotation around the rotation shaft 8 and a gentle tilting movement of the seat portion 2 is realized.

Further, the lower surface plate 1 is provided on the rear portion of the mounting body 6.
5, the rear portion of the upper surface plate 35 is welded substantially parallel to the upper portion of the upper plate 5, and the lower end of the leg plate 36 extending downward from the front edge of the upper surface plate 35 is welded to the lower surface plate 15 so that the lower surface plate 15 and the upper surface plate 35. The mounting pipe 13 is welded to penetrate through. The main body portion 11 of the lock mechanism 11 is provided at the front portion of the upper surface plate 35 and the upper end portions of the leg plates 36 at the substantially central portion in the width direction.
A notch opening 37 for mounting A is formed. Further, a cushioning material 38 is attached to the edge 35A of the upper surface plate 35 slightly protruding rearward from the rear end of the mounting body 6, and the tilting body 9 is attached.
A bent piece 39 extending downward from the rear end and further bent slightly forward is disposed below the cushioning member 38, and the bent piece 39 cushions the rear portion of the tilting body 9 at the highest position. It is set so that the mounting plate 14 abuts on the cushioning material 38 at a position where it abuts on the material 38 and the rear part of the tilting body 9 is at the lowest position.

The shaft portion 29A of the lock lever 29
On the side opposite to the side through which the shaft is provided, an intermediate portion 40B that is bent at a right angle from the shaft portion 40A of the up-and-down lifting lever 40 is rotatably held, and is bent at a right angle from the intermediate portion 40B. The tip of the crank portion 40C extending in parallel with is abutted against the tip of the operation pin 5B of the gas cylinder 5. Then, by raising the shaft portion 40A of the up / down lift lever 40 upward, the operation pin 5B is pushed in by the tip of the crank portion 40C, and the height of the seat portion 2 can be adjusted by the gas cylinder 5. A handle 29C is fitted to the tip of the shaft portion 29A of the lock lever 29, and a handle 40D is also fitted to the tip of the shaft portion 40A of the vertical lifting lever 40. Here, the handle 29C has a shape suitable for the rotation of the lock lever 29, and the handle 40D is the up / down lift lever 40.
The shape is suitable for vertical movement.

The shaft portion 29 of the lock lever 29 is
The portion where A penetrates the mounting body 6 and the vertical lifting lever 4
A spacer 41 made of synthetic resin is fitted to a portion where the shaft portion 40A of 0 penetrates the mounting body 6. The spacers 41 have the same shape on both sides of the mounting body 6, but respectively support the shaft portion 29A of the lock lever 29 rotatably without rattling, and the shaft portion 4 of the up / down lift lever 40.
It is a structure that can support 0A so that it can slide up and down without rattling.

Further details of the present invention will be described with reference to FIGS. The lock mechanism 11 of the present invention includes the mounting body 6
The crank portion 29B of the lock lever 29 which rotatably holds the shaft portion 29A penetrating from the side of the
It is movable in the arcuate locking hole 30 formed integrally with the main body 11A fixed inside the
B can be elastically locked in three stages of both end portions 30A and 30B of the arcuate locking hole 10 and the intermediate portion 30C, and a circle is formed at the tip of the locking plate 11B protruding from the tilting body 9. A first locking recess 31 that stops at a crank portion 29B located at one end 30A of the arc-shaped locking hole 30 and maintains a standing posture, and an arc-shaped locking hole 30 on one side of the locking plate 11B. Middle part 3
The second locking recess 32 that locks the crank 29B located at 0C to maintain the reclining posture is formed.
On or at the deepest vertical extension line L of the locking recess 32
To the inside of the locking plate 11B in the width direction of the first locking recess 3
The gist is that the center of the load applied to No. 1 is set.

That is, the first locking recess 3 of the locking plate 11B.
The minimum vertical width of the protrusion 42 formed between the first locking concave portion 32 and the first locking concave portion 32 is substantially the same as the conventional one, but the crank portion 29B is engaged with the first locking concave portion 31 in the standing posture. In this state, even if the weight of the seated person is applied to the lower surface of the protrusion 42 as a concentrated load via the seat portion 2, the center of the load is on the vertical extension line L of the deepest portion of the second locking recess 32 or Since the protrusion 42 is located inward of the extension line L in the width direction of the locking plate 11B, the protrusion 42 is not deformed or broken, and as a result, the supporting strength is improved.

Further, the intermediate portion 30 of the arcuate locking hole 30.
With the crank portion 29B of the lock lever 29 positioned at C, the shaft portion 29A of the lock lever 29 and the crank portion 2 are
The axial position of 9B is set on a circumferential line centered on the rotary shaft 8. As a result, as shown in FIG. 11, the crank portion 29B is located on the intermediate portion 30C, and the second locking recess 32 of the locking plate 11B is engaged with the crank portion 29B (reclining posture), the tilting is performed. Even if the ascending force acts on the body 9, this ascending force acts inward in the direction of the radius of rotation (R ₁ ) of the crank portion 29B with the shaft portion 29A as the center of rotation, so that the crank portion 29B may rotate. On the contrary, even if the descending force acts on the tilting body 9, it acts outward in the turning radius (R ₁ ) direction of the crank portion 29B.
9B never rotates. On the other hand, as shown in FIG. 10, a crank portion 29B is located at one end 30A of the arcuate locking hole 30, and the first locking recess 3 is located in the crank portion 29B.
In the state where 1 is stopped (standing posture), the load applied to the seat portion 2 is transmitted to the crank portion 29B via the locking plate 11B,
A radius R centering on the rotary shaft 8 is provided on the crank portion 29B.
_The descending force acts in the tangential direction (T) of the circumference of ₂ , and the descending force is the crank part 29B with the shaft 29A as the center of rotation.
Although it is slightly deviated from the turning radius (R ₁ ) direction, the component force in the direction of rotating the crank portion 29B is small and the descending force acts in the direction of pressing the crank portion 29B against the one end 30A of the arcuate locking hole 30. Therefore, the crank portion 29B does not rotate.

Further, one end 30 of the arcuate locking hole 30.
The lower load receiving portion 43 for receiving a lower load applied to the crank portion 29B of the lock lever 29 positioned at A is formed in the main body portion 11A, and the crank portion positioned at the intermediate portion 40B of the arcuate locking hole 30. The upper load receiving portion 44 for receiving the upper load applied to 29B is provided in the main body 1
The elastic receiving portion 45 that elastically holds the crank portion 29B is formed around the other arcuate locking hole 30. As a result, in the standing posture, the weight of the seated person is received by the lower load receiving portion 43 via the seat portion 2, the tilting body 9, the locking plate 11B, and the crank portion 29B, and similarly in the reclining posture, the upper load receiving portion. The tilting body 9 due to the restoring force of the compression coil spring 27 of the biasing means 10 by 44
It receives the ascending power of the rear part. The second locking recess 3
Since 2 is formed from the side of the locking plate 11B to the inner part in the width direction, the seated person leans against the backrest portion 3 in the reclining posture, and the weight further moves to the rear to tilt the tilting body 9.
Even when a descending force that exceeds the restoring force of the compression coil spring 27 acts on the second locking recess 32, the second locking recess 32 abuts the crank portion 29B, and further descending is restricted. Then, as shown in FIG. 9, when the crank portion 29B is engaged with the other end 30B of the arcuate locking hole 30, the locking plate 11B can freely pass behind the crank portion 29B, and the lock is achieved. It will be in the released state. In this state, depending on the balance between the elastic force of the compression coil spring 27 and the load of the seated person, it is possible to take a free posture between the standing posture and the reclining posture.

More specifically, the main body 11A is shown in FIG.
As shown in FIG. 5, the support part 46 is integrally molded of hard synthetic resin, and has a support part 46 having the arcuate locking hole 30 and a support part for fixing the support part 46 in the cutout opening 37. The receiving portion 46 has a block shape, and the supporting portion 47 has a plate shape.
It is in the shape of a letter. Then, the receiving portion 46 and the supporting portion 47
A slit 48 that is opened downward is formed between and, the slit 48 is fitted onto the leg plate 36, the support portion 47 is brought into contact with the outer surface of the leg plate 36, and the main body portion 11A is attached to the mounting body 6. When it is attached to the
A lower end of a holding piece 35B having a substantially L-shaped cross section, which extends downwardly from one side edge of the cutout opening 37 of the upper surface plate 35, is laterally fitted into the lower part of the upper plate 35 to restrict lifting of the main body 11A. . It should be noted that the lateral movement of the main body 11A is restricted by an appropriate retaining means such as an engaging claw or a screw. Further, the arcuate locking hole 30 forms an upper elastic piece 49 extending upward in a semi-circular shape from the end so that the crank part 29B can be elastically engaged with the other end 30B, and the intermediate part 40B. Lower elastic piece 5 extending from below the lower end to below the other end 30B
0 is formed, and a convex portion 51 is further formed on the lower surface portion of the one end 30A and the intermediate portion 40B, and the crank portion 29 is stably provided at both positions.
B can be engaged.

The locking plate 11B is formed by bending a thick metal plate into an L-shape when viewed from the front, welding the horizontal portion 52 to the lower surface of the mounting plate 14 of the tilting body 9, and attaching the front edge of the vertical portion 53. The first locking recess 31 and the second locking recess 32 are formed in the portion.

[0028]

According to the seat locking mechanism of the chair having the tiltable seat of the present invention as described above, the following remarkable effects are obtained.

According to the first aspect, the rear portion of the seat portion can move up and down to take the standing posture and the reclining posture,
In a chair having a tiltable seat part having a lock mechanism capable of fixing the seat part in a standing posture and a reclining posture, in a chair having a fixed tilt angle, the support strength of the seat part is increased, and particularly in an upright posture. It is possible to reliably and safely support the downward load on the.

According to the second aspect of the present invention, the crank portion is positioned in the middle portion of the arcuate locking hole, and the second locking concave portion of the locking plate is engaged with the crank portion (reclining position), the tilting is performed. The crank part does not rotate even when a rising force or a descending force is applied to the body, and the crank part is located at one end of the arcuate locking hole, and the first locking recess is stopped at the crank part. In this state (upright posture), the load applied to the seat acts as a downward force on the crank portion in the tangential direction of the circumference centered on the rotation axis, and the downward force causes the crank portion to rotate about the shaft portion. Although it is slightly deviated from the radial direction of rotation, the component force in the direction to rotate the crank part is small and the descending force acts in the direction to press the crank part to one end of the arcuate locking hole, so the crank part must rotate. There is no.

According to the third aspect, in the standing posture, the weight of the seated person can be received by the lower load receiving portion from the locking plate via the crank portion, and in the reclining posture, the upper load receiving portion biases the weight. In the state where the rear part of the tilting body can receive a rising force due to the restoring force of the tilting part, its supporting strength is high, and the crank part is elastically engaged with the other end of the arcuate locking hole, the locking plate is It is possible to freely pass behind the crank portion, the lock is released, and there is no risk of the crank portion coming off from the other end and colliding with the locking plate while locking the seat portion.

[Brief description of drawings]

FIG. 1 is a side view of a chair according to the present invention.

FIG. 2 is a front view of the same.

FIG. 3 is a vertical sectional view showing a rocking device for a chair according to the present invention.

FIG. 4 is a partially omitted plan view showing a state where each component is attached to the attachment body.

FIG. 5 is an exploded perspective view showing a structure of a bearing.

FIG. 6 is a partially cutaway exploded perspective view showing a relationship between a mounting body and a tilting body and a damper mechanism.

FIG. 7 is a transverse sectional view of the same.

FIG. 8 is an exploded perspective view showing a main part of the lock mechanism of the present invention.

FIG. 9 is a partial cross-sectional view showing a state where the lock is released and the seat can be freely locked.

FIG. 10 is a partial cross-sectional view showing a state maintained in a standing posture.

FIG. 11 is a partial cross-sectional view showing a state maintained in a reclining posture.

[Explanation of symbols]

1 leg 2 seat 3 Backrest 4 Locking device 5 Gas cylinder 5A Tapered tip 5B Operation pin 6 Attachment 7 Bearing 8 Rotating shaft 9 tilting body 10 biasing means 11 Lock mechanism 11A Main body 11B Locking plate 12 Damper mechanism 13 Mounting tube 14 Mounting plate 15 Bottom plate 16 Holding frame 17 accommodation groove 18 fixing plate 19 Bush 20 Presser plate 21 screw 22 screw shaft 22A Annular flange 23 Strength knob 24 bearing 25 support plate 26 nuts 27 compression coil springs 28 annular projection 29 lock lever 29A Shaft part 29B Crank part 29C Handle 30 Arc-shaped locking hole 30A One end 30B Other end 30C Intermediate part 31 First locking recess 32 second locking recess 33 slider 34 Compressed rubber 35 Top plate 35A Edge 35B Holding piece 36 Leg plate 37 Notch opening 38 cushioning material 39 bent pieces 40 Vertical lift lever 40A Shaft 40B middle part 40C crank part 40D handle 41 spacer 42 protrusion 43 lower load receiving part 44 Upper load receiving part 45 Elastic receiving part 46 receiving part 47 supporting part 48 slit 49 upper elastic piece 50 Lower elastic piece 51 Convex part 52 horizontal part 53 vertical part

Claims (3)

(57) [Claims] 1. A mounting body mounted on a leg portion and a front portion of a tilting body for mounting a seat portion on an upper surface thereof are rotatably connected by a horizontal rotation shaft, and a mounting body and a tilting body rearward of the rotation shaft. The rear part of the tilting body is elastically urged upward during the period, and the rear part of the seat part can move up and down to take a standing posture and a reclining posture, and the seat portion is fixed in the standing posture and the reclining posture. A seat lock mechanism for a chair, wherein a crank portion of a lock lever penetrating from a side of the attachment body and rotatably holding a shaft portion is fixed to a main body portion fixed inside the attachment body. It is movable in the integrally formed arc-shaped locking hole, and the crank portion can be elastically locked in three steps of both end portions and the intermediate portion of the arc-shaped locking hole, and is projected to the tilting body. Crank part located at one end of the arcuate locking hole at the tip of the locking plate First to stop and keep standing posture
The engaging recess and the second engaging recess that engages with the crank portion located in the middle of the arcuate engaging hole on one side surface of the engaging plate to maintain the reclining posture are formed. The tiltable seat portion is characterized in that the center of the load applied to the first locking recess is set on the vertical extension line of the deepest portion of the stop recess or inward of the extension line in the width direction of the locking plate. Chair seat locking mechanism. 2. With the crank portion of the lock lever positioned in the middle portion of the arcuate locking hole, the shaft position of the lock lever and the crank portion are aligned on a circumferential line centered on the rotation axis. The seat lock mechanism for a chair having a tiltable seat according to claim 1. 3. A lower load receiving portion for receiving a lower load applied to a crank portion of a lock lever positioned at one end of the arcuate locking hole is formed in the main body portion, and an intermediate portion of the arcuate locking hole is formed. An upper load receiving portion for receiving an upper load applied to the crank portion positioned in the main body portion, and an elastic receiving portion elastically holding the crank portion around other arcuate locking holes. A seat lock mechanism for a chair having a tiltable seat according to item 1 or 2.