Spring system for stabilizing bifold door hinged positions
FIELD OF THE INVENTION 
     This invention relates generally to door hardware and specifically to a spring for stabilizing bi-fold doors in the open position or in the closed position. 
     BACKGROUND OF THE INVENTION 
     Complex or compound type springs have been proposed for holding bi-fold doors in the closed position or in the open position, and with two stable positions are known for use with box lids and the like. 
     U.S. Pat. No. 3,849,835 issued on Nov. 26, 1974 to Torsti T. T. Jerila shows one of the complex type; examples of other such hinges are shown in the following U.S. Pat. Nos.: 
     2,290,219 to S. E. H. Ulfving, 7-21-42, shows the principle of multi-position (in this case 3-way) stability; 
     515,334 issued to A. S. Held on 2-27-1894, shows a hinge form having an arcuate portion and cross arms; 
     2,541,377 issued to G. W. Neely on 2-13-51, shows a hinge-related spring assembly that snaps doors open and closed at positions 180° apart; 
     2,998,618 issued to L. T. Roy on 9-3-61, shows another arcuate spring arrangement for hinged closures; 
     4,452,373 issued to D. J. and R. J. Pearce on 6-5-84, showed another form of &#34;C&#34;-shaped spring and engagement with pivoted closure. 
     SUMMARY OF THE INVENTION 
     However, it is believed that no spring like that of the present invention has been known or provided the combination of ease of installation with simplicity of mechanism and quiet and efficient operation, all in accordance with these and other objects of this invention, which include provision of a bifold door spring that: 
     is suited for wood or for metal doors; 
     is compact so that the exposed portion of it can lie between the top of the door and almost any header; 
     extends little or not at all beyond the thickness of the door in any position of use; 
     requires a minimum of installation work, normally only laying out of two holes to generous tolerances, drilling same parallel with each other, and inserting the spring assembly ends in the holes; 
     tends to self-align in use even though not perfectly installed; 
     is longwearing and protects wooden doors from mounting-hole enlargement due to wear over periods of time; 
     is independent of, but acts in conjunction with bifold door hinges; 
     is light weight and economical, and that is versatile and size-adaptable to suit most bifold doors. 
     Said another way, a spring system for stabilizing bifolding door hinged positions includes an integral &#34;C&#34;-shaped spring with at each end of the &#34;C&#34;-shape a respective straight shank formed at right angles to the plane of the &#34;C&#34;-shape with the shanks parallel-spaced from each other. On each shank is a rotatable tubular sleeve-bearing with a collar-shaped enlargement at the end adjacent the &#34;C&#34;-shape, and a retainer on the free end of each shank that keeps the tubular sleeve bearings in place. Installation is by insertion of the tubular sleeve bearings in parallel-spaced drilled holes in the top edges of two doors that are hinged together so that the spring assembly has three stable positions; (1) it substantially bridges the hinges and biases the faces of the doors together to keep the doors aligned in the fully open position; (2) it biases the edges of the doors together to keep the doors aligned in the fully closed position; and (3) it keeps the doors stable at a partially open intermediate position at which the axis of hinging between the doors is aligned with and between the spring assembly shanks. 
     The above and other objects and advantages of this invention will become more readily apparent on examination of the following description, including the drawings in which like reference numerals refer to like parts. 
    
    
     FIG. 1 is a perspective view of the preferred embodiment 10 of the spring assembly of this invention; 
     FIG. 2 is a top edge view of the invention installed in a bifold (and holding the doors closed) door system; 
     FIG. 3 is a view like that of FIG. 2 but with the spring assembly holding the bifold doors in half-open position; 
     FIG. 4 is a view like that of FIG. 3 with the doors held open fully; 
     FIG. 5 is a face view of a door partially broken away to show side elevational installation detail of a spring assembly; and 
     FIG. 6 is a side elevational view on a larger scale of a spring assembly showing retention details. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows preferred embodiment 10 of the invention. A piece of spring tempered, preferably circular cross-section wire 20 forms in plan view a &#34;C&#34;-shape 22 or spring loop. The &#34;C&#34;-shape terminates on each end in a respective straight shank 24, 26 at right angles about a radiused portion or bend to the plane of the &#34;C&#34;-shape, the shanks being parallel-spaced and co-extensive. 
     On each of the straight shanks 24, 26, a respective rotatable tubular bearing 28, 30 extends from the radiused bend 32 at the &#34;C&#34;-shape where the bearing has an integral, enlarged collar 34, to a retainer 36 at the free end 38 of the shank. 
     Each bearing has a series of circular grooves 40 on the outer surface that act as glue retainers, as will be seen. 
     FIG. 2 shows coaction of assembly with spring 20 in the embodiment 10 holding closed vertically hinged-together bifold doors 42, 44. Over-center relation of the shank-ends 24, 26 in the spring assembly 10 relative to the axis of hinge 45 joining the doors, keeps the doors tightly closed. The doors are conventionally hinged to a closet wall W; a fixed pivot or hinge pin is represented at H. Conventional track T along the doors and shown in broken lines for exposition is engaged by conventional sliding hinge S on the door 42. 
     FIG. 3 shows the spring assembly holding the doors 42, 44 in half-open position; in-plane alignment of the shanks 24, 26 with axis of the hinge 45 stabilizes the doors in this position. 
     FIG. 4 shows the doors 42, 44 similarly stabilized in the open position by over-center relation of the shank ends 24, 26 to the axis of hinge 45. The door assemblies may be of any conventional type, conventionally hinged together as indicated at the door edges, and slidable on the track T, from which they depend. 
     Installation of the spring assemblies requires only that the holes for each pair of the bearings 28, 30 at the shanks 24, 26 be similarly drilled, one in each door at the hinge end, and sufficiently far from the projected hinge axis to flex the spring enough to press the faces or the edges of doors together as indicated. 
     Preferably each hole for a bearing should lie on the lower centerline of a door in a respective plane diagonally in the door from the hinge axis at about a 30° to 45° angle, so that it is directly in-plane with the hinge axis when the doors are half open. This provides for the over-center action to produce the two (open, closed) stable positions, and the third or half open stable position in which the spring is flexed more than in the others. Pre-load of the spring is easily set by increasing or decreasing the closed-door distance between the holes (as in FIG. 2) for the shanks at time of drilling. 
     FIG. 5 shows a spring assembly 10 installed in a bifolding door panel 44, shown partially broken away for exposition and having, as an example, support by a conventional hinged hanger 48 and track 52, as previously described. 
     Each bearing (28 shown) is held by interference fit in a respective hole 50 drilled in the door and retained further if desired by cement in the grooves 40 on the bearing. 
     FIG. 6 shows further important advantages of the hinge assembly. The radius at 54 of the bend 56 and an upset end 58 with washer 36 capture and retain between them the rotatable anti-friction means or bearing (28 shown), which has in the collar end of the bore an internal radius at 62 matching the bend radius 54, for smooth operation. 
     It will be seen therefore that this invention provides great convenience in installation, prevents damage to doors on which installed, adds practically no mass to the doors, is easily inspected and insofar as can be seen, is decorative. 
     Further, it is clear that the springs will have no tendency to pinch fingers or damage anything they may come in contact with and that they will always keep in normal alignment under conditions of wear and tear that except for the bearing provisions might loosen them. 
     This invention is not to be construed as limited to the particular forms disclosed herein, since these are to be regarded as illustrative rather than restrictive. It is, therefore, to be understood that the invention may be practiced within the scope of the claims otherwise than as specifically described. For example, it will be appreciated that one having ordinary skill in the art can install the invention without inventive modification in a tri-fold door assembly.