US3745937A

US3745937A - Foldable chair

Info

Publication number: US3745937A
Application number: US00150130A
Authority: US
Inventors: J Gail
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-06-09
Filing date: 1971-06-04
Publication date: 1973-07-17
Anticipated expiration: 1990-07-17
Also published as: FR2096134A5; DE2028381A1; CH528884A; DE2110187A1; ES197684Y; ES197684U; DE2028381B2; GB1331137A; AT306956B

Abstract

A foldable chair having three lower rods and three upper rods pivoted to a center part. A canvas seat is attached to the upper rods, and the lower rods engage the ground in the operative position of the chair. A rod vertically sliding in the center part is connected to the upper and lower rods for unfolding the chair and carries a cup-like locking head at its lower end. The rim of the locking head engages hooks on the lower rods to hold the same in the operative position, and locking rods connect the upper rods to a pivot head on the upper part of the sliding rod. Movement of the pivot head away from the center part is limited by an abutment on the slinding rod, thereby determining the operative position of the upper rods.

Description

1 July 17,1973

[ FOLDABLE CHAIR [76] lnventor: Josef Gail, 8891 Unterwittelsbach,

Germany [22} Filed: June 4, 1971 [21] Appl. No.: 150,130

[30] Foreign Application Priority Data June 9, 1970 Germany P 20 28 381.2 Mar. 3, 1971 Germany P 21 10 187.1

[52] US. Cl 108/128, 297/17, 248/435 [51] Int. Cl. A47c 4/30 [58] Field of Search 297/17, 16, 45;

1,135,864 4/1915 Tomassi 108/157 X 1,344,431 6/1920 Albertie 248/435 X FORElGN PATENTS OR APPLICATIONS 55,186 l/189l Germany 248/435 Primary Examiner-Francis K. Zugel Attorney-Kelman and Bcrman [57] ABSTRACT A foldable chair having three lower rods and three upper rods pivoted to a center part. A canvas seat is at tached to the upper rods, and the lower rods engage the ground in the operative position of the chair. A rod vertically sliding in the center part is connected to the upper and lower rods for unfolding the chair and carries a cuplike locking head at its lower end. The rim of the locking head engages hooks on the lower rods to hold the same in the operative position, and locking rods connect the upper rods to a pivot head on the upper part of the sliding rod. Movement of thepivot head away from the center part is limited by an abutment on the slinding rod, thereby determining the oper ative position of the upper rods.

4 Claims, 13 Drawing, Figures PA mum? I IENIED 5 3,745,837

sum 1 UP 7 INVENTOR Joxe/ 66N/ PAIENIEL JUL 1 1 ms SHEU 3 0F 7 INVENTOR Jase/64 7 PAIENIEU JUL 1 71m

sum

5 or 7 mmvrok 7058 6a// .PAIEMM 3.745.937 SHEU 7 U? 7 INVEN TOR FOLDABLE CHAIR This invention relates to a foldable chair including at least three lower rods and three upper rods which are pivoted to a center part and are foldable in the same direction, a sitting cover of flexible material fixed to the upper ends of said upper rods, and locking means at said center part, said upper and said lower rods being lockable when unfolded into their operational position by said locking means, and said locking means being provided with a slide rod longitudinally slidable in said center part.

From German Pat. 829 490 has become known a foldable chair including three legs, which comprises locking means for locking the upper and lower rods pivotally mounted to a center part which consists of two slidable sleeves when the chair is in its operational position, said upper and lower rods being foldable in one direction along said center part. The rods are provided with locking segments which can be inserted through slots into the center part consisting of two slidable sleeves. The inner one of said sleeves comprises a securing plate which is mounted to the one end of an axially slidable rod which is provided atits other end with a handhold. Together with the rod said securing plate can be moved to a position wherein the locking segments are adjusted to the rods. The inner sleeve is biased against the outer sleeve by means of a spring; furthermore there is provided another spring pressing said securing plate into the adjusting position. This known foldable chair is as can be seen from this short description relatively complicated and expensive in production.

The object of the present invention is to provide a foldable chair of the afore-mentioned type which is simpler and cheaper.

According to this invention a first solution of this problem comprises a cup-like locking head provided at the lower end of said slide rod; gripping hooks mounted to the upper end of said lower rods for engagement with the cup rim of said locking head; a pivot head slidably mounted on the upper part of said slide rod, said pivot head being slidably movable between said center part and abutment means provided at the upper end of said slide rod; and locking rods pivotally connected to said upper rods and to said pivot head, the length of said slide rod and of said locking rods being such that.

said locking rods and said slide rod define an angle of less than 90 when said gripping hooks are in engagement with the cup rim of said locking head and said pivot head rests against said abutment at the upper end of said slide rod.

The cup rim of said locking head is advantageously directed towards said center part.

A suitable embodiment of the locking head comoffset with respect to each other in peripheral direction.

In a suitable embodiment the sleeve-like intermediate part has a hollow-cylindrical extension at its lower end, the outer face of said gripping hooks abutting against said extension when being in engagement with the cup rim of said locking head.

The lower and upper rods can simply at least partly be made from longitudinal sheet-metal strips which are shaped to a U-configuration. For stability reasons the pivot sections at said lower and upper rods and the gripping hook sections at the lower rods consist of full material.

In preventing the chair from sinking into soft ground the U-shaped sheet-metal strips of said lower rods may be outwardly folded at their lower ends so as to form a foot enlargement.

In an analogous manner it is suitable to outwardly fold the U-shaped upper rods at their upper ends. This makes possible a simple connection of said sitting cover to said upper rods by sheet-metal clamping means seizing the folded sections.

The locking rods can be formed by simple longitudinal sheet-metal strips which engage with their upper ends between the U-shaped legs of said upper rods and are pivoted there by means of rivets.

In an advantageous embodiment the pivot head is made from full material with a central bore for said slide rod. Further, the full material piece is to be provided with slots for receiving the corresponding ends of said locking rods, the connection of said locking rods prises a cylindrical outer face and a frustro-conical inner face diverging towards said center part. For achieving correct adjustment by the gripping hooks these are best adapted to said cylindrical and frustroconical faces.

A practicalembodiment of said center part comprises its being formed as a sleeve-like intermediate part and being provided with pivot joints uniformly distributed along the circumference of said sleeve-like intennediate part, the pivot joints for said lower rods and the pivot joints for said upper rods being arranged in axial distance from each other and being symetrically in said slots being effected by pins inserted into said pivot head.

' The abutment for said pivot head can be formed at the upper end of said slide rod for instance by a nut screwed onto said end.

The chair according to this invention has the advantage of being foldable to the most possible samll dimension. So it can be stowed without any difficulties amongst the other luggage. For instance, such chair is preferably used by anglers.

A second solution according to this invention comprises abutment means at the upper end of said slide rod; a pivot head mounted onto said slide rod and slidable between said center part and said abutment, said pivot head being connected to said upper rods by locking rods pivotally mounted to said upper. rods, the length of said slide rod and of said locking rods being such to define an angle of less'than when said pivot head abuts against the abutment means of said slide rod; a locking sleeve for locking said lower rods and said upper rods when these are in their operational po sition, said locking sleeve being slidable over said center part so as to enclose said center part on its outer face and having a convergent divergent inner bore defined by two conical faces for adjoinment of said lower rods on the one hand and said upper rods on the other hand.

When the chair is folded the locking sleeve is slided over the substantially parallel lower and upper rod so that the latter cannot be changed in their position. When the chair is needed the locking sleeve is first drawn from the lower and upper rods, the lower rods are then extended, and the locking sleeve is then slided over the upper rods into the region of the center part. Thereupon the upper rods can be extended, being locked then by the locking rods and by the pivot head to remain in such position. In this operational position of the chair the upper rods abut against the upper conical face and the lower rods abut against the lower conical face of the inner face of said locking sleeve. As mentioned already, the locking sleeve cannot escape in upward direction, because the upper rods are pressed apart by the locking rods and are locked in such position. Consequently, the upper rods can extend only to such degree until abutment against the lower conical face at the inner face of said locking sleeve is achieved.

If the chair is to be folded again the pivot head is pressed against the center part, overcoming the dead center region by an angle of 90 defined by said slide rod and by the locking rods. Such angle provides widest extension of the upper rods. If a person is sitting on the chair the upper rods tend to press tighter against each other on account of the weight acting onto the sitting cover. The consequence is that the pivot head when abutting against the abutment of the slide rod does not slide itself towards the center part if the chair is used, but is subjected to a biasing towards said abutment.

In a suitable further embodiment the sitting cover has such dimensions that it is tensioned by the upper rods if the locking rods and the slide rod define an angle of 90. This means that even then when the sitting cover is not stressed by a sitting person an automatic sliding, e.g. a downsliding movement of the pivot head on account of its own weight towards the center part is impossible, because the sitting over is exerting already a tensional effect onto the upper rods which as mentioned before is highest at the dead center angle of 90 between the locking rods and the slide rod. This dead center angle must be overcome when the pivot head should slide from its normal use position at the abutment towards the center part.

Preferably the center part is made from full material being provided with pivot joints uniformly distributed over its periphery, the pivot joints for said lower rods and the pivot joints for said upper rods alternating in peripheral direction.

Another suitable embodiment may be seen in the features that said pivot joints for said lower rods on the one hand and said pivot joints for said upper rods on the other hand are offset at said center part in longitudinal direction of said slide rod, said pivot joints for said lower rods being closer to said pivot head than said pivot joints for said upper rods, and that said lower rods are bent at their pivot joint end so that the bent section is essentially parallel to said slide rod and does not exceed the circumferential face of said center part when said lower rods are in their operational position.

The pivot joints in said center part are formed by slots on the outer face of said center part which are essentially parallel with respect to said slide rod for taking up the corresponding ends of said lower rods and of said upper rods, and further by pins inserted into said center part transversely of said slots.

In increasing the gripping capacity of the pivot sleeve and in facilitating the releasing of the pivot sleeve from the lower and from the upper rods when the chair is unfolded, the locking sleeve may be provided at its outer face with axial grooves.

A further embodiment may be seen in the feature that said lower and said upper rods are at least partly formed by longitudinal U-shaped sheet-metal strips. The sheet-metal strips of the lower rods may be outwardly folded at their lower ends to form feet. Also the sheet-metal strips of the upper rods may be outwardly folded at their upper ends whereby said sitting cover is fixed to said upper rods by bags sewn to the lower face of said sitting cover and accomodating said folded portions.

The locking rods are preferably formed by simple longitudinal sheet-metal strips which engage with their upper ends between the U-shaped legs of said upper rods and are pivoted there by means of rivets.

A practical embodiment of the pivot head may be seen in the feature that said pivot head consists of a full material piece having a central bore for said slide rod, said full material piece being provided with slots for receiving the corresponding ends of said locking rods; the connection of said locking rods in said slots is effected by pins inserted into said pivot head.

The abutment for said pivot head may be formed at the upper end of said slide rod e.g. by a nut screwed onto said end. The other end of said slide rod may e.g. stationarily be screwed into said center part.

Another suitable further embodiment provides a protective covering for receiving the folded chair, and means at the lower face of the sitting cover for holding said protective covering when the chair is in use. These fixing means can be an elastic band closing a loop by means of a press button.

In the drawings:

FIG. 1 shows a prespective view of the chair according to the first-mentioned solution in the operative position;

FIG. 2 shows a partly sectional and enlarged view of the central portion of the chair as shown in FIG. 1;

FIG. 3 shows a partial section along lines III-III of FIG. 2;

FIG. 4 shows a partial section along lines IV-IV of FIG. 2;

FIG. 5 shows an exploded view of detail V as shown in FIG. 1;

FIG. 6 shows the central portion of the chair as shown in FIG. 1, however in folded chair position;

FIG. 7 shows a perspective view of thechair in opertive position according to the second-mentioned solutron;

FIG. 8 shows an enlarged sectional view through the central portion of the chair as shown in FIG. 7 along a section al plane through the slide rod;

FIG. 9 shows a section transverse to the longitudinal direction of the slide rod through the lower rods of the chair as shown in FIG. 7, the central portion being visible from below;

FIG. 10 shows an exploded perspective view of another arrangement for the connection of the sitting cover;

FIG. 1 I shows a section through the assembled fixing arrangement as shown in FIG. 10;

FIG. 12 shows the connection of the sitting cover as shown in FIGS. 10 and 11, seen from above;

FIG. 13 shows a perspective view of the folded chair wrapped by the protective covering.

The chair as shown in FIGS. 1 to 6 in its working position has three

lower leg rods

1, 2, 3 and three upper supporting

rods

4, 5, 6. The

lower rods

1, 2, 3 and the

upper rods

4, 5, 6 are pivoted to a center part 8. The

upper rods

4, 5, 6 carry at their upper ends an attached sitting cover 7 made from flexible or pliable material.

The center part consists of a sleeve-like intermediate part 55 with pivot joints 14 to 19 uniformly distributed along its circumference. The pivot joints 15, 17, 19 for the

lower rods

1, 2, 3 and the pivot joints 14, l6, 18 for the

upper rods

4, 5, 6 are arranged one after the other axially to said center part 8 and are offset with respect to each other in peripheral direction by 60. The sleeve-like intermediate part 55 of said center part 8 has a hollow-cylindrical extension 54 at its lower end. A bore 31 which receives a slide rod 9 extends through the center part 8.

A locking head 12 is attached to the lower end of slide rod 9 by means of a nut 13 and an intermediate disc 58. The locking head 12 has a cylindrical cup shape. The cup rim 52 of the locking head 12 flares towards the center part 8.

The

lower rods

1, 2, 3 are provided at their center part end with gripping hooks 50 which have such shape that they are adapted with their inner face to the cup rim 52 and to the outer face of said locking head 12, when said locking head 12 has achieved such position that the gripping hooks 50 engage with thecup rim 52 of said locking head 12. The back face of the gripping hooks 50 is adapted in this case to the hollowcylindrical extension 54 of the sleeve-like intermediate part 55.

A pivot head 10 is slidably mounted on the upper end of said slide rod. For limitting the sliding movement of the pivot head, a stop nut 11 with an intermediate disc 57 is screwed onto the upper end of said slide. rod 9. The pivot head 10 is a unitary piece of material provided with a bore 30 which said slide rod 9 can pass through. The piece is further provided with

slots

24, 25, 26 for taking up the corresponding ends of links or locking

rods

21, 22, 23. The locking rods or

links

21, 22, 23 are pivotally mounted in the pivot head 10 by

pins

27, 28, 29.

The other end of each of said locking

rods

21, 22, 23 is pivoted to said

upper rods

4, 5, 6 respectively.

For the most part the lower and the upper rods are made from longitudinal sheet-metal strips shaped to a U-configuration. The pivotal sections at the lower and upper'rods 1 to 6 and the gripping hook sections 50 at the lower rods consist however of full material. The locking

rods

21, 22, 23 consist of simple longitudinal sheet-metal strips which engage with their upper ends between the U-shaped sheet-metal strips of the

upper rods

4, 5, 6 and are pviotaly mounted there by means of rivets.

For folding the chair to the smallest possible dimensions, the

lower rods

1, 2, 3 as well as the

upper rods

4, 5, 6 are provided with recesses 35 to 40, for receiving said pivot head 10 when the chair is folded (see FIG. 6).

FIG. 5 shows how the sitting cover is' connected to the ends of said

upper rods

4, 5, 6. The U-shaped ends of said

upper rods

4, 5, 6 are upwardly folded at their upper ends. The corresponding ear of said sitting cover 7 is imposed on the folded

portions

32, 33 and fixed by means of a sheet-metal clamp 34.

In a similar manner the U-shaped sheet-metal strips of the

lower rods

1, 2, 3 are outwardly folded at their lower ends to form feet.

The chair shown in FIGS. 7 to 13 has three lower rods or

legs

101, 102, 103 and three upper rods or supports 104, 105, 106. The

lower rods

101, 102, 103 and the

upper rods

104, 105, 106 are pivoted to a center part 108. A sitting cover 107 made from flexible mate- 6 rial is carried by the upper ends of said

upper rods

104, 105, 106.

The center part 108 is made from full material, pivot joints 114 to 119 being uniformly distributed along the circumference of said center part 108. The pivot joints 115, 117, 119 for the

lower rods

101, 102, 103 and the pivot joints 114, 116, 118 for the

upper rods

104, 105, 106 are alternating on the circumferential face of the center part 108. Furthermore, the pivot joints 115, 117, 119 for the lower rods 10], 102, 103 on the one hand and the pivot joints 114, 116, 118 for the

upper rods

104, 105, 106 on the other hand are offset on said center part 108. Two pivot joints parallel to each other in circumferential direction are offset by an angle of 60. The pivot joints are formed by slots at the outer face of said center part 108 for receiving the corresponding ends of said

lower rods

1101, 102, 103 and of said

upper rods

104, 105, 106, the mentioned ends of said lower rods and said upper rods being held in the slots by

pins

154, 159 inserted into said center part 108 transverseley of said slots (see FIG. 9).

The central portion of the center part 108 is provided with a tapped hole 132 into which one end of a slide rod 109 is stationarily screwed. To the other end of said slide rod 109 is screwed a nut 1 11 which serves as abutment. A pivot head 110 provided with a corresponding bore 131 is slidably mounted on said slide rod 109. The pivot head 110 shows 3 slots, only the

slots

124 and 125 being visible. A locking rod enters each of said slots. Again only the locking

rods

121, 122 are visible. From FIG. 8 can be recognized that e.g. the locking rod 121 is held in the slot 124 of said pivot. head 110 by means of a pin 128. The other ends of the locking rods are pivoted to the corresponding

upper rods

104, 105, 106. The upper rods consist of U-shape-d sheet-metal strips. The corresponding ends of said locking rods are secured to the upper rods by means of rivets.

Also the

lower rods

101, 102, 103 consist of longitudinal U-shaped sheet-metal strips. The center part end of each of the lower rods is bent, as can be seen from FIG. 8. The bent section 148 is essentially parallel to said slide rod and does not project beyond the circumferential face of said center part 108, when said lower rods are in their operational position.

The sheet-metal strips of the

lower rods

101, 102, 103 are outwardly folded at their lower ends to form

feet

135, 136, 137. y

In the same way the sheet-metal strips of the

upper rods

104, 105, 106 are outwardly folded at their upper ends. These folded portions are inserted into pockets 138, 139, sewn to the lower face of said sitting cover 107. Thus is effected the connection of the sitting cover 107 to the

upper rods

104, 105, 106.

The sitting cover 107 is tensioned by said

upper rods

104, 105, 106, when the slide rod 109 and the locking

rods

121, 122 define an angle of 90. The length of the slide rod 109 and of the locking

rods

121, 122 is such that the locking

rods

121, 122 and the slide rod 109 define an angle of 90, when said pivot head 110 abuts against said nut 111 of said slide rod 109.

When a person is sitting on the chair the

upper rods

104, 105, 106 are pulled toward each other by the stress exerted onto said sitting cover 107. Thus the upper rods tend to press the locking

rods

121, 122 with their pivot head end in upward direction. The pivot head 110 abuts then against the nut 111 of said slide rod 109. Thus is achieved that the

upper rods

104, 105, 106 cannot move closer to each other.

The pressure exerted onto the chair by a sitting person forces further the

lower rods

101, 102, 103 to extend apart. A locking sleeve 112 is provided to prevent such movement. For effecting this locking function, the locking sleeve is situated near the center part 108 and engages the latter. The inner diameter of said locking sleeve 112 decreases from its ends towards its central range, thus forming two conical edge faces 145, 146 against which the

lower rods

101, 102, 103 and the

upper rods

104, 105, 106 can abut. Since the

upper rods

104, 105, 106 are secured in their extended position by the locking rods or

links

121, 122, when said pivot head 110 abuts against said screw 111, the locking sleeve 112 cannot effect an upward movement. Thus it prevents said

lower rods

101, 102, 103 from outward movement exceeding the maximum extended position. The outer face of said locking sleeve 112 is provided with grooves 160 parallel to said slide rod.

In folded position, when the

lower rods

101, 102, 103 are upwardly folded and are parallel with said

upper rods

104, 105, 106, said locking sleeve 112 is slided over the upper rods and over the lower rods. The thus folded chair can now be enclosed in a protective covering 141 (FIG. 13) provided with a zipper 147. When the chair is needed this protective covering 141 can be folded and fixed to the lower face of said sitting cover 107. For holding said protective covering 141 at the lower face of said sitting cover 107 there is provided an elastic band 142 closing a loop by means of a

press button

143, 144 or to be buttoned as flap to said sitting cover 107.

FIGS. to 12 show another arrangement for fixing said sitting cover 107. This arrangement is only shown in connection with the upper rod 106. It consists substantially of a plastic clamping means 170 which comprises a portion 172 insertable between the legs of said sheet-metal strips, and which further comprises a bearing plate 171. The lower face of saidbearing plate 171 is provided with a clamping collar 173 having a small distance from the legs of said sheet-metal strips. As can be seen from FIGS. 11 and 12, the sitting cover 107 is spread over said bearing plate 171, folded over the border and clamped between the ends of said sheet-metal strips and said clamping collar 173. The insertable portion 172 has a bore 174 being in alignment with a bore 175 in said upper rod. A securing splint 176 is passed through the two

bores

174, 175.

What is claimed is:

1. A folding chair comprising in combination:

a. a seat assembly;

b. a leg assembly; and

c. a center part connecting said seat assembly and said leg assembly, said seat assembly including 1. a plurality of elongated supporting members,

2. a plurality of first pivots, each pivot securing one longitudinally terminal portion of a respective supporting member to said center part for movement of the supporting member between an operative position in which said supporting members diverge upwardly away from said center part in the working position of said chair, and a folded position in which said supporting members are elongated in a common direction,

3. a seat member of pliable material attached to the other longitudinally terminal portions of said supporting members,

4. a slide rod fixedly fastened to said center part and extending therefrom in said common direction,

5. a pivot head movable on said slide rod toward and away from said center part,

6. stop means limiting movement of said pivot head on said slide rod to a lowermost position adjacent said center part and to a topmost position remote from said center part, and

7. a plurality of links hingedly connecting said pivot head to said supporting members respectively, said links extending upward from said pivot head toward said supporting members in said lowermost position of said pivot head and downward from said pivot head and away from said slide rod in said topmost position of said pivot head; said leg assembly including 8. a plurality of elongated leg members,

9. a plurality of second pivots, each second pivot securing one longitudinally terminal portion of a respective leg member to said center part for movement of the leg member between an operative position in which said leg members diverge downwardly from said center part in the working position of said chair, and a folded position in which said leg members are elongated in said common direction, said first pivots being downwardly offset from said second pivots in said working position of said chair, and

10. securing means responsive to movement of said supporting members toward said operative position for securing said leg members in said operative position thereof; and said securing means including 11. an annular locking member having an axis extending in said common direction, said locking member having two axially spaced rim portions and being axially movable toward and away from a position of abutting engagement of said rim portions with said leg members and said supporting members respectively in which said locking member holds said leg members in said operative positions thereof, and

12. abutment means on said seat assembly responsive to the weight of a load supported by said seat member for securing said locking member in said position thereof, said abutment means releasing said leg members in response to movement of said supporting members out of the operative position of the latter.

2. Chair according to claim 1, the pivots securing said leg members being nearer said pivot head than the pivots securing said supporting members.

3. Chair according to claim 2, wherein said one longitudinally terminal portion of each of said leg members is angularly offset from the remainder of said leg portion and engaging said annular locking member in said operative position of said leg members and of said sup porting members.

4. Chair according to claim 1, wherein said annular locking member is formed with a central opening of a size sufficient for receiving said central part and said supporting members in the folded position of the supporting members.

Claims

1. A folding chair comprising in combination: a. a seat assembly; b. a leg assembly; and c. a center part connecting said seat assembly and said leg assembly, said seat assembly including 1. a plurality of elongated supporting members, 2. a plurality of first pivots, each pivot securing one longitudinally terminal portion of a respective supporting member to said center part for movement of the supporting member between an operative position in which said supporting members diverge upwardly away from said center part in the working position of said chair, and a folded position in which said supporting members are elongated in a common direction, 3. a seat member of pliable material attached to the other longitudinally terminal portions of said supporting members, 4. a slide rod fixedly fastened to said center part and extending therefrom in said common direction, 5. a pivot head movable on said slide rod toward and away from said center part, 6. stop means limiting movement of said pivot head on said slide rod to a lowermost position adjacent said center part and to a topmost position remote from said center part, and 7. a plurality of links hingedly connecting said pivot head to said supporting members respectively, said links extending upward from said pivot head toward said supporting members in said lowermost position of said pivot head and downward from said pivot head and away from said slide rod in said topmost position of said pivot head; said leg assembly including 8. a plurality of elongated leg members, 9. a plurality of second pivots, each second pivot securing one longitudinally terminal portion of a respective leg member to said center part for movement of the leg member between an operative position in which said leg members diverge downwardly from said center part in the working position of said chair, and a folded position in which said leg members are elongated in said common direction, said first pivots being downwardly offset from said second pivots in said working position of said chair, and 10. securing means responsive to movement of said supporting members toward said operative position for securing said leg members in said operative position thereof; and said securing means including 11. an annular locking member having an axis extending in said common direction, said locking member having two axially spaced rim portions and being axially movable toward and away from a position of abutting engagement of said rim portions with said leg members and said supporting members respectively in which said locking member holds said leg members in said operative positions thereof, and 12. abutment means on said seat assembly responsive to the weight of a load supported by said seat member for securing said locking member in said position thereof, said abutment means releasing said leg members in response to movement of said supporting members out of the operative position of the latter.

3. Chair according to claim 2, wherein said one longitudinally terminal portion of each of said leg members is angularly offset from the remainder of said leg portion and engaging said annular locking member in said operative position of said leg members and of said supporting members.

7. a plurality of links hingedly connecting said pivot head to said supporting members respectively, said links extending upward from said pivot head toward said supporting members in said lowermost position of said pivot head and downward from said pivot head and away from said slide rod in said topmost position of said pivot head; said leg assembly including

8. a plurality of elongated leg members,

10. securing means responsive to movement of said supporting members toward said operative position for securing said leg members in said operative position thereof; and said securing means including

11. an annular locking member having an axis extending in said common direction, said locking member having two axially spaced rim portions and being axially movable toward and away from a position of abutting engagement of said rim portions with said leg members and said supporting members respectively in which said locking member holds said leg members in said operative positions thereof, and