US3736021A

US3736021A - Folding wheel chair

Info

Publication number: US3736021A
Application number: US00134589A
Authority: US
Inventors: O F Maclaren
Original assignee: O F Maclaren
Current assignee: Andrews Maclaren Ltd
Priority date: 1970-04-17
Filing date: 1971-04-16
Publication date: 1973-05-29
Anticipated expiration: 1990-05-29
Also published as: CA940037A; JPS4719962U; DE2118136A1; CH519334A; JPS5027731Y2; GB1321085A

Abstract

A folding wheeled chair or the like having bottom and back frame portions connected together at one end by a double-axis pivot joint and foldable brace members pivotably attached at the other ends of the frame portions. Each of the bottom and back frame portions are formed by interpivoted cross members and means are provided to lock the frames in an extended condition. Wheels are provided at the four corners of the bottom frame portion. The chair may be collapsed by pivoting the frame portions with respect to themselves and to each other while folding the brace members until a cane-like configuration is obtained.

Description

United States Patent n91 MacLaren 1 1 May 29, 1973 [54] FOLDING WHEEL CHAIR FOREIGN PATENTS OR APPLICATIONS [76] Inventor: Owen Finlay MacLaren, 14 1,154,362 4/1969 Great Britain Daventry Road, Barby, Near Rugby, 681,490 10/1952 Great Britain ..297/45 E l d 1,070,000 2/1954 France ..297/45 [22] Filed: 1971 Primary Examiner-James T. McCall [21 APPL No; 134,589 Assistant ExaminerGarry Moone Attorney- Stevens, Davis, Miller et a1.

[30] Foreign Application Priority Data [57] ABSTRACT Apr. 17, 1970 Great Britain ..18,489/70 A folding wheeled chair or the like having bottom and back frame portions connected together at one end by 52 US. Cl ....297/42, 280/39 a double-axis pivot joint and foldable brace members 511 1m. 01. ..A47c 4/00 pivotably attached at the other ends of the frame p [58] Field of Search ..297/45, 43; 280/39, tions- Each of the bottom and back frame Portions are 280/475. 5/111 fonned by interpivoted cross members and means are provided to lock the frames in an extended condition. Wheels are provided at the four corners of the bottom [56] References cued frame portion. The chair may be collapsed by pivoting UNITED STATES PATENTS the frame portions with respect to themselves and to each other while folding the brace members until a 3,390,893 7/1968 MacLaren ..280/39 cane 1ike fi ti is m 2,911,245 11/1959 Kurz ..5/1l1 3,485,510 12/1969 Merlan.... ..297/45 9 Claims, 6 Drawing Figures .arm v Patented May 29, 1973 3,133,021

6 Sheets-Sheet 1 OWEN F. MACLAREN INVEWTOR BY WM W m /47:.ORNYS Patented May 29, 1973 6 Sheets-Sheet 2 Famed May 29,1913 3,136,021

6 Sheets-Sheet I5 Patented May 29, 1973* I 3,736,021

6 Sheets-Sheet 4 Patented May 29, 1973 6 Sheets-Sheet 5 Patented May 29, 1973 6 Sheets-Sheet 6 1 FOLDHNG WHEEL CHAIR This invention relates to a folding wheel chair or kindred structure. As is stated in UK. Pat. No. 1,154,362 there are many folding structures for instance such as baby carriages and invalid chairs for invalid adults which fold into a form which is comparatively flat. It is, however, highly desirable that wheel chairs particularly for certain uses should be capable of being folded in a manner which, in the above Patent, is described as stick folding, that is to say when folded the elements forming the structure come together in a bundle. There are two particular requirements which are perhaps not as obvious as those of lightness, mechanical strength and reasonable cost; they are that the chair should be very quickly and easily extended or folded and that when folded it should fall within dimensional limits and incidentally should be of such weight, and size, that it can be mailed as a parcel. Chairs made according to the above numbered Patent are highly successful (and meet these requirements) when made in a size suitable for small children. The present invention seeks to provide a chair which while still complying with the very exacting requirements is large enough and strong enough to accommodate an occupant of much bigger size and weight. Indeed the permissible occupant weight at which the present design is aimed is about 154 lbs. (70 kilos) and larger models are envisaged and this is more particularly related to the requirements of spastic or similarly handicapped children of an age at which mobility and amusement are important. When used for people of that weight (and the use is often a question of institutional care and nursing) it is highly desirable that the chair should be easily maneuvered directionally and this is yet another requirement of at least secondary importance which the invention meets. A still further requirement for which provision is made in the invention is that means may be provided if necessary for example by adding accessory fittings to the chair so that the occupant may be self-propelling and self-steering, or to provide a table for food or occupational games.

The present invention may therefore be regarded as being a more developed or sophisticated form of the invention of the above Patent and in particular it combines light weight, the dimensional limitation above mentioned, very easy folding and extending, steerability, adequate resilient suspension, adequate eflective tire area, effectively locking brake means, the possibility of self-propulsion by the occupant, all combined with sufficient rigidity when extended to give confidence and appropriate anatomical support to the occupant.

The general structure of a chair according to the invention is of the kind described and Claimed in UK. Pat. No. 1,154,362, US. Pat. No. 3,390,893, Canadian Pat. No. 798,194, German Petty Pat. No. 1,947,820, Japanese Pat. No. 45/13549 and French Pat. No. 1,507,446. The present invention, however, involves features which contribute in some degree to the particular qualities which have been mentioned above.

According to one feature of the invention the following statements in regard to the present invention, and

terconnected at corners, pivotally interconnected by laterally spaced folding brace or strut elements which are (when extended) held spaced by collapsing strut means such as to keep the frames extended when in use, all of which is in accordance with the above numbered Patent.

The invention further includes the provision'of a leg element on each side of the volume frame, a first end of each leg element being pivotally attached to an interconnected X-frame corner, the second end being pivotally attached to a folding brace element. The first end of each leg element may conveniently be extended downwards and adapted to bear a wheel or a pair of wheels. The leg elements described serve to afford the simultaneous folding of the volume frame in both planes throughout its range of movement.

According to the invention and in order to afford the requisite structural strength and rigidity when extended at least two collapsing strut interconnections are provided one associated with the brace elements and the other with the rear X-frame. In order to ensure that the loads due to the occupant are applied where they can best be met by the structure the elements forming the seat and the back (which are basically of fabric) are supported in such a manner that at two corners of each, they are slidable on the structural framework, while the other two corners are pivotted. Further in order to afford resilient suspension and, as is perhaps more important, to afiord some equalization of the loads transmitted from the wheels to the structure (whereby stresses are reduced) the chair is provided with resilient suspension mechanism between its frame elements and each of the four pairs of wheels which mechanism includes a lever fitted to the frame element and at its end rotatably supporting the pair of wheels and this lever supports a further intermediate link element so arranged that when the wheel pair is loaded, an elastomeric pad is resiliently compressed; such suspension may also be provided with an elastomeric recoil cushion. Further according to the invention two of the wheel pairs together with the resilient suspension above mentioned aremounted on spindles which are rotatably mounted on substantially vertical axes at the ends of two of the frame members of the chair and the geometry particularly in regard to the suspension levers is arranged to be such that these wheels can castor, to enable the chair to be readily maneuverable: (this provision also protects the structure from lateral rocking stress if the person pushing the chair tries to turn it off a straight course). Thus castoring is in itself a step towards lightening the structure as well as being a considerable convenience. Again and particularly in relation to this castoring feature the invention includes an interattachment for an element such as the above referred to spindle to a tubular frame member in which an elastomeric plug is compressed endwise within the tube and therefore seeks to expand radially and this is made use of to tighten one tubular element within another by expanding the former. Thus it can be arranged that a complete fitting such as a castoring fitting or the attachment of non-castoring wheel pairs may be fastened in position simply by the use of a spanner or key on a nut or the head of a stub without any additional boring or drilling operations. As a consequence of allowing castoring so that there is no directional stability, the invention provides for braking on both the non-castoring wheels; braking on only one would leave the chair free to spin round as on a pivot, which could be alarming or even dangerous.

The invention also includes, in cases where it is required, means whereby the occupant of the chair can be self-propelling and self-steering and such means includes drive mechanism to the two non-castoring wheel pairs (or to one wheel of each such pair) which drive mechanism is arranged not to interfere with the folding of the chair (and not to interfere with directional) and is accessible to the occupant for manual operation. The invention includes one particular way of doing this, namely by the provision of a belt C passing around one of the non-castoring wheels and preferably in a groove in the tire thereto, the belt also passing around an idle pulley arranged somewhere in the region of the hip of the occupant or between the hip and the knee and external to the framework, together with resiliently loaded means such as a jockey pulley or a fairlead the resilient loading being such that when the frame of the chair is folded the jockey pulley or fairlead take up the slack of the belt which is the result of folding.

The accompanying drawings illustrate an application of the invention; this example is illustrative of a wheeled chair which is designed to meet the requirements of handicapped children, in general terms of age group 4-9 years. The application of the invention is of course not limited as to age or weight of the user but the foregoing provides a general indication of a known demand.

In the following description reference is made to the accompanying drawings in which:

FIG. 1 is a side elevation of the extended structure of a wheel chair according to the invention, there being illustrated in chain-line a simple construction for selfpropulsion;

FIG. 2 is an elevational view from the front of the chair;

FIG. 3 is a side elevation of the same, illustrating a partially-folded situation;

FIG. 4 is a further front elevation the structure being partially folded as in FIG. 2;

FIG. 5 illustrates the chair in its completely folded condition; and

FIG. 6 is a partial view illustrating on a larger scale, part of the structure seen in the preceding Figures, to make clear the wheel suspension system.

Reference is to all Figures. Two X-frames are provided; l is the rear frame and 2 the bottom frame; each consists of two

tubular members

1A and 1B and 2A and 28 on elements 1B or 2B of each X-frame, being slightly bent so that although they are pivotted at their

intersections

1C, 2C, their extremities lie substantially in respective common planes. The complete structure includes side elements 3 and 4 which can conveniently be regarded as hypotenuse" or brace elements. Such elements are each formed by two lengths of tube section, seen as 3A and 3B in FIG. 1. These are connected pivotally in a knuckle-joint part 3E, 4E, such that when 3A and 3B (in the extended configuration of the chair) are almost aligned the joints at 3E, 4E, keep them in alignment; and in that situation the elements 3, 4, each act as one single brace or strut. For greater security each of these knuckle-joints has a releasable catch, formed by a lever 3F (4F) pivotted at 3G (4G) to the strut length 3A (4A) and loaded by a tension spring 3H (4H) to tend to engate a notch with a stud at 3J (4J). When the brace 3 (4) is fully extended it is positively locked by such catch, which is easily released to collapse the frame. The self-locking of the brace by its own alignment, is thereby ensured. As a strut, the two ends of each strut 3 and 4 are pivotally connected as at 3C and 3D to the distal comers of the X-frames l and 2, by joints which have freedom of universal movement to the extent required by the extension and folding of the structure. The side elements 3 and 4 in the extended state of the chair, constitute framemembers which are basically straight, and which geometrically may each be regarded as the hypotenuse of a near-rightangle triangle as viewed in side elevation (FIG. 1). They brace the whole structure when aligned, as in FIG. 1. The volume-frame so constituted therefore consists of two hypotenuse braces or struts 3 and 4, and two X-frames 1 and 2. The rigidity of this volume-frame is ensured by two pairs of collapsible struts which are toggle links 5, 6, an

upper pair

5A, 5B, and a

lower pair

6A, 6B. These are knuckle jointed at 5C and 6C respectively, in joints which just pass the dead-center condition when the chair is extended, i.e., as seen in FIG. 1. During folding, they go through the angles to be seen in FIG. 4. The links 5, 6, are pivotally attached at 5D, 6D, respectively to the

X-frame members

1A, 1B and to the

hypotenuse strut parts

3B, 4B. It will be seen that the toggle links 5, 6, in effect spread and lock the X-frame 1 directly, acting between 1A and 1B. The

other links

6A, 6B, act directly between the

lower brace elements

3B, 4B, and therefore almost directly on the X-frame 2. The lower toggle (6A, 6B) contributes importantly to the rigidity of the volumeframe as a whole. There are, of course, forms of collapsible strut other than toggle links and these are regarded herein as equivalents. For example, there may be one single strut element pivotted to member 3B and slidable against member 4B, so that when forced into a right-angle position between these members it has the same function as the toggle arrangement. Or, there may be two members one pivotted to 3B and the other to 4B, their other ends sliding against 4A and 3A respectively: this again is mechanically equivalent to a toggle. Circumstances can be imagined in which such equivalents might be regarded by the designer as preferable.

There are two leg elements 7, 8 in the form of tubes which are pivotally attached respectively at 7A, 8A, to the

brace members

3A, 4A. The elements 7, 8, have pivotted to them universally at 9 the lower corners of the X-frame 1 and similarly the rear corners of the X-frame 2, at 10. Each such universal connection is, conveniently, constructed by the use of two pivot pins at right angles; the two connections at respective corners are so near to each other that for all practical purposes it can be considered that the two X-frames are interpivotted with each other as well as with the respective leg element, on intersecting axes. Each leg element 7, 8, which serves to co-ordinate the folding of the complete structure in its two planes of freedom, so that a single folding action only is necessary, is extended downwards below the

pivotal complex

9, 10, and slightly bent, to mount a rear wheel-pair 11 comprising co-axial wheels which have solid elastomeric tires. As seen more clearly in FIG. 6 each wheel pair runs on a spindle 12 carried by a pair of lever-like plates 13 which are pivotal on a pin 14 supported by the bottom end of the leg 7 or 8 and which are held spaced by a rivet 14A. The plates 13 are also pivotally attached by a pair of coaxial pins 15 to a U-sectioned stirrup 16. In the channel constituted by the stirrup and the bottom end of the leg 7 (8) is provided a block 17 of rubber or other elastomer (see FIG. 6) which acts as a compression spring controlling the up-and-down movements of the wheel-pair 11 relatively to the leg 7. The plates 13 are also interconnected by a pin 18 which is surrounded by a length of rubber or elastomeric tubing 19; when this abuts the bottom of the leg 7 it acts as a recoil cushion, to damp out shock if the wheel-pair drops suddenly relatively to its leg. This simple and effective resilient suspension is well adapted to the use of paired wheels (in itself an important factor in weight distribution combined with small dimensions) and, as will now be seen, it lends itself to repetition for castoring wheels, a requirement related to the weight of the occupant, to maneuverability, and to the balancing out of loads in the structure.

Turning nowto the front wheels of the chair, and as best seen in the side elevations (FIGS. 1 and 3), the bottom ends of the

members

3B, 4B, have inserted into them short bent lengths of tube 20 to mount the two front wheel-pairs. These are illustrated with the same references because they, and their resilient suspensions, are identical with the rear (non-castoring) pairs. The difference resides only in the mounting, as follows. In this case, the extension part 20 rotatably carries a sleeve 21 and it is to this sleeve that the whole wheel pair and suspension unit is attached. The sleeve 21 is rotatable through 360 and thus each front wheel pair is fully free to castor about the axis of the sleeve 21, which is vertical; the wheel spindle 12 is so located by reason of the lever-like plates 13 that the wheel pair trails for castoring purposes. A thrust bearing is provided at the end of tube 20. This may consist of a sandwich of steel plastics steel washers, or of a ballbearing or taper roller bearing.

Reverting to the rear wheel pairs, each pair is provided with a brake, convenient for foot operation. Each brake comprises a pedal lever 30 (FIG. 3) and a pair of

toggle arms

31, 32, with a spring 33, all so arranged that when depressed at its end 30A by foot, the spring 33, by exerting a pull at the pivot point joining 31 and 32 pulls the bent-over end 32A of the remote toggle arm 32 into direct and forcible contact with the tire of a wheel of the pair. The brake is released by opposite action, upward movement at 3A pulling it off by collapsing the toggle formed by 31, 32 the third pivot, between 30 and 31, is located offset from the line of the other two thus affording a dead-center effect to hold the brake off. If only one wheel is braked the chair can be spun on that one because the front wheels castor and the other rear wheels are free. It is therefore a feature of the invention that two brakes are fitted and it can be seen that this provision derives, fundamentally, from the requirement for a lightweight structure capable of carrying considerableweight.

The fittings at the ends of tubular members, for example the front wheel pair assemblies, may be attached by providing, in manner known per se, a tube within a rubber sleeve in compression between two annular faces (e.g., washers) which is squeezed axially by tightening a nut or stud, thus compressing the sleeve axially. This can be so arranged that an inner tubular member is firmly tightened within an outer tube, and it affords a very simple form of interattachment which may, incidentally, be a bad transmitter of vibration.

Turning back now to the general structure of the wheel chair, attention is called particularly to FIGS. 1

and 3. The back-rest of the chair is basically a panel 35 of fabric, attached by its side margins to two rigid elements 36. Each element 36 is pivotted at its upper end at 37 to a slide member 37A which slides on member 3A (4A) and at its lower end at 33 it is pivotted to a seat tube 41 (see below) to a slide part 34 which is slidable on 7 or 8. By comparing FIGS. 1 and 3 it can be seen that in folding the chair the slides 34 move relatively downwards. The panel 35 collapses (see FIG. 3) during folding, by the approach laterally of the braces 3, 4.

The seat is a second fabric panel 40 and is attached at its lateral margins to two rigid seat tube or rod parts 41 which are preferably of somewhat oval section (see FIG. 2). The parts 41 are pivotted at 3F, 4F, to the

brace elements

38, 4B, and project somewhat forward of the brace members (see FIG. 1), as well as extending rearwards to pivot joints at 42 to slide parts 43 which are on the leg members 7, 8. When the chair is being folded the slides 43 move downwards, (see FIG. 3).

A foot rest in the form of a strip of fabric 50, extends to across the chair between the bottom ends of

elements

3B, 4B and adjustment of its position may be provided, for example by attaching it to movable clips or collars, such as 50A to which the strip is preferably pivotally attached as at 50B.

The upper ends of the

elements

3A, 4A, are bent over to form handles (see e.g., FIG. 1) and a strip of fabric is preferably provided, as at 51, to prevent accidentally letting go of the handles. Near the bottom ends of the members 3B, there is provided a spring catch to retain the folded condition of the chair. This conveniently takes the form of an elastic moulding of plastic material, formed as a bell crank and having a springy arm 55, an arm 56 notched at 56A, and a pivot at 56B to the member 38; on the member 3A is a stud 56C to engage the notch 56A.

If it be required to provide for self-propulsion of the chair this is perhaps best to be done by having a detachable accessory kit which may be attached to the chair when extended, but not itself be foldable. However, it is possible to embody means for self-propulsion in a foldable form, and an indication of this is shown diagrammatically in FIG. 1 in chain line. One of the wheels of each of the rear wheel pairs 11 is provided with a grooved pulley 11A either on its outer or inner flank. In the groove runs a belt, or chain, or cable 60 nearly parallel and coextensive with a leg 7; the belt runs over a pair of pulleys 62 borne for free rotation on or near the axis of interconnection between the leg 7 and strut part 3A; the path of the belt 60 thence runs over a pulley 63 borne by a fitting 63A on strut member 3A. The pulley 63 has, fast with it, a hand crank 64 or a hand wheel, located accessibly to the occupant of the chair: the handle 64 or wheel may be easily detachable or foldable. The belt 60 may be led into and run mainly within the leg 7 and if required strut part 3A. The pulleys may be protected by shrouding. Braking operable by the occupant may be provided, either by way of releasable cable-grip or by stopping the handle 64 or wheel. There are various alternatives, for self propulsion, such as a chain and free-wheel sprocket the chain being spring returned after being pulled by a hand lever. Further jockey pulley or fairlead provision may be made to keep the belt or cable in tension or to take up slack when the chair is folded. A pair of the wheels 1 1 may be inter-attached so that both of the pair are driven by the pulley 11A. Such a device may well be adequate for the relatively minor and easy selfpropelled mobility required when the chair is used on ordinary floors and passageways, and for such use has no pretensions to being completely effective in all circumstances, e.g. if obstacles or rough ground are encountered.

The structure lends itself to the provision of a table for food or playthings. Such a device is indicated in FIG. 1 in broken-line. In this example a table-top is in two

halves

70, 71, the forward half 71 having pins 71A to engage sockets 70A for coplanar interattachment; the pins 71A may be hinged to 71 so as to be foldable to reduce overall dimensions. The half 70 has, attached by vertical pivots 73, two rearwardly extending arms 74 which have bifurcated ends at 74A to slide into engagement on studs 74B which are fixed to the elements 3 and project laterally. On the arms 74 are provided spring catches 75 (which may be identical with the catch 56) to engage and lock on the studs 74B. Pivotted to the arms 74 on a transverse axis by pins 76 are struts 77 of which the ends are formed to spigot into the tubular ends of the seat members 41.

When the table is to be removed, the latches 75 are disengaged, the fork ends 74A are thereby released from the studs 74B, the struts 77 are freed from the members 41. The table is now detached. The struts 77 are folded up to the arms 74, and these are then folded against the near edge of the half 70 (the struts 77 swinging with them). 70 and 71 are detached, and the whole table is now of such (folded) dimensions that it can be stowed within the dimensional envelope of the folded chair. A box or pocket may be provided for its stowage.

I claim:

1. A folding wheel chair having a frame structure comprising a bottom cross frame of interpivoted rigid members, a back cross frame of interpivoted rigid members, a double-axis pivot joint inter-pivotally attaching one of each of the bottom frame members to one of each of the back frame members at each of two comers of said cross frames, said axes being oriented to permit the members of each cross frame to pivot with respect to each other and to permit said cross frames to pivot with respect to each other, two foldable brace members pivotally attached to the bottom cross frame near the other two comers of the bottom cross frame, respectively, and to the back cross frame near the other two comers of the back cross frame, respectively, a leg element on each side of the frame structure, a first end of each leg element pivotally attached at one of said inter-pivotally attaching corners and the second end of each leg element pivotally attached to the foldable brace member on the same side of the frame structure as the leg whose end is attached thereto, two substantially parallel seat bars pivotally attached to the brace members on each side of the frame structure, one end of each seat bar slidably attached to the leg element on the same side of the frame structure as the seat bar attached thereto, first releasable means to hold the members of the back cross frame in an extended position when the assembly is unfolded, second releasable means to hold said brace members in an extended position when the assembly is unfolded, and wheels provided at each bottom corner of said frame structure.

2. A folding wheel chair according to claim 1, in which said first releasible means comprise toggle links.

3. A folding wheel chair according to claim 1, in which each said brace member comprises two pivotally interattached members and a spring lock to lock said pivotally interattached members in their aligned extended condition.

4. A folding wheel chair according to claim 1, in which one pair of said wheels are laterally disposed and freely castorable through 360, the other pair of said wheels are laterally disposed and have a fixed direction of tracking.

5. A folding wheel chair according to claim 4, further comprising brake means for braking said pair of fixed tracking wheels.

6. A folding wheel chair according to claim 1, further comprising lever arms each having one end pivotally attached to the frame structure and said wheels mounted on a free end thereof, and elastomeric pads mounted on either side of said lever arms to check the vertical movement thereof and provide a shock absorbing action.

7. A folding wheel chair according to claim 10, further comprising two substantially parallel laterallyspaced seat-back bars pivotally attached at one end to said seat bars and slidably attached at the other end to said brace members.

8. A folding wheel chair according to claim 1 additionally comprising a seat of pliable material attached between said two seat bars.

9. A folding wheel chair according to claim 7 additionally comprising a seat-back of pliable material attached between said seat-back bars.

Claims

1. A folding wheel chair having a frame structure comprising a bottom cross frame of interpivoted rigid members, a back cross frame of interpivoted rigid members, a double-axis pivot joint inter-pivotally attaching one of each of the bottom frame members to one of each of the back frame members at each of two corners of said cross frames, said axes being oriented to permit the members of each cross frame to pivot with respect to each other and to permit said cross frames to pivot with respect to each other, two foldable brace members pivotally attached to the bottom cross frame near the other two corners of the bottom cross frame, respectively, and to the back cross frame near the other two corners of the back cross frame, respectively, a leg element on each side of the frame structure, a first end of each leg element pivotally attached at one of said inter-pivotally attaching corners and the second end of each leg element pivotally attached to the foldable brace member on the same side of the frame structure as the leg whose end is attached thereto, two substantially parallel seat bars pivotally attached to the brace members on each side of the frame structure, one end of each seat bar slidably attached to the leg element on the same side of the frame structure as the seat bar attached thereto, first releasable means to hold the members of the back cross frame in an extended position when the assembly is unfolded, second releasable means to hold said brace members in an extended position when the assembly is unfolded, and wheels provided at each bottom corner of said frame structure.

4. A folding wheel chair according to claim 1, in which one pair of said wheels are laterally disposed and freely castorable through 360*, the other pair of said wheels are laterally disposed and have a fixed direction of tracking.

7. A folding wheel chair according to claim 10, further comprising two substantially parallel laterally-spaced seat-back bars pivotally attached at one end to said seat bars and slidably attached at the other end to said brace members.