US2852176A - Folding stairway - Google Patents

Description

Sept. P -V .HARMON FOLDING STAIRWAY I Filed Sept. 15, 1954 2 Sheets-Sheet 1 INVENTOR. PA 04. M f/A EMU/V A TT'OENEY' Unite rornnso srAmwAY Paul V. Harmon, Nashville, Tenn., assignor to Precision Parts Corporation, Nashville, Tenn, a carpet-anon of Tennessee Application September 13, 1954, Serial No. 455,510

Claims. ((11. 22848) This invention relates to folding Stairways.

It is common practice to provide folding and so-called disappearing stairways for providing convenient access to the attics of houses without the loss of floor space accompanying the use of permanent stairs. Such folding stairways usually have sectional stair units which are extended in alinement with each other when the stair is unfolded for use, and which sections are folded one upon another when the stair is moved upwardly into the ceiling frame when not in use.

Folding stairways of this type employ various types of counterbalancing means for holding the stairs in inoperative positions when not in use. Most constructions of this kind employ springs as the counterbalancing means, these springs being efiective for holding the parts inoperative when the stair sections are folded, thus shortening the lever arm tending to swing the stairway downwardly. When the stairway is in unfolded or operative position, the effective lever length of the stair unit overcomes the tension of the counterbalancing spring, such spring fre quently having its connections with the stairway so arranged as to be inefiective for transmitting any lifting force to the stairway when unfolded.

When a stair of this type is unfolded and the parts are in operative positions, it is necessary to provide some form of support for the upper stair section. This usually is accomplished by linkage connecting the upper stair section to the ceiling frame. Such linkage connections usually provide at each side of the stairway two links connected to each other and having their remote ends connected respectively to the upper stair section of the ceiling frame. In the absence of some means specifically provided for such purpose, the weight of the parts will cause the links at opposite sides of the stair to assume dead-center positions, thus making it necessary to break the hinged connections between the pairs of links before the stair can be folded. This disadvantage has been overcome by causing the counterbalancing springs to be bent and thus substantially distorted to exert a turning force on the upper links to break the links from deadcenter positions. Such an arrangement shortens the life of the springs and renders the stair noisy in operation. Other means employed for this purpose have been relatively expensive to manufacture.

An important-object of the present invention is to provide a folding stair having stair sections, the upper of which is provided with supporting link means to carry the load on the stair when the latter is unfolded, and to provide a highly novel and simplified means for preventing the supporting links from assuming dead-center positions when the stair is to be folded.

A further object is to provide such a construction wherein the spring counterbalancing means exerts a direct straight-line pull under all conditions except when the stair is unfolded, in which case there is a very slight deflection imposed on the spring transversely of the line of pull thereof, the spring tension thus being operative character just refeired to wherein the stationary element to exert sufiicient turning force on the upper links to throw slightly out of line the center pivotal connections out effecting any distortion of the balancing springs from their normal shapes.

A further object is to provide such a construction wherein the upper link member on each side of the stair is in the form of a bell crank lever one arm of which has mechanical connection with one end of the associated spring While the other end of each spring is connected to the ceiling frame and to provide a stationary element supported by a ceiling frame and arranged slightly above the line between the end of each spring connected to the bell crank lever and the end connected to the ceiling frame when the stair is unfolded, under which conditions there will be slight deflection-of each spring connection from its normal line to exert a slight turning movement on each bell crank lever to prevent the link connections from occupying dead-center positions when the stair is ready to be folded.

A further object is to provide a construction of the for deflecting each spring under the conditions referred to is a stud forming part of the pivotal support for each bell crank lever.

A further object is to provide such'a construction wherein a link connection is provided between the upper arm of each bell crank lever and the adjacent end of the spring for taking the transverse thrust on each spring connection, thus eliminating the necessity for distorting either spring out of line.

Other objects and advantages of the invention will become apparent during the course of the following description.

In the drawings I have shown one embodiment of the invention. In this showing:

Figure l is a perspective view of the stairway showing the parts unfolded into operative positions,

Figure 2 is a substantially enlarged detail sectional view on line 2 -2. of Figure 1,

Figure 3 is a central vertical longitudinal sectional view through the ceiling frame and upper portion of the stairway showing the latter in unfolded position, certain of the operating connections being shown in dotted lines in the positions they will assume when the stair is folded,

Figure 4 is a similar sectional view showing the parts completely folded,

Figure 5 is an enlarged fragmentary sectional view on line 5-5 of Figure 3, and

Figure 6 is an enlarged detail sectional view of one of the pivotal supports for one of the bell crank levers, and associated parts.

Referring to the drawings, the numeral 10 designates a ceiling frame as a whole adapted to be fixed in the ceiling of a building in the usual manner. tangular and includes transverse ends 11 and 12 and side members 13.

The stair indicated as a whole by the numeral 16 is adapted to be supported by the frame 10 and to be folded thereinto when the structure is not in use. The stair 16 includes a plurality of sections 17, 18 and 19, the first two of which are hinged to each other at 20 whereby the section 18 folds upwardly in the position shown in Figure l to assume a position over the section 17. The sections 18 and 19 are hinged together as at 21, and it will be apparent that in folding the sections, the section 18 will swing relatively upwardly about the hinges 20 while the section 19 swings relatively downwardly about.

This frame is recsuch plate (Figure the hinges 21, the sections thus assuming the folded positions shown in Figure 4.

A cover for the bottom of the frame is provided and is indicated by the numeral 24. This cover fits into the bottom of the frame 10 when the parts are folded, as shown in Figure 4, and is hinged as at- 25 to the frame 10. The cover 24 is provided with batten strips 26 secured thereto at spaced points, and the ladder section 17 is secured in any suitable manner to the batten strips.

Each of the ladder sections is provided with the usual steps 27 connected between the side runners 2 5- cf the ladder sections. To each side runner of the upper ladder section 17 is pivotally connected as at 30, a link 31. Each side frame 13 carries a bell crank lever 32 comprising a pair of arms 33 and 34. Each arm 33 forms in effect a link pivotally connected at its lower end as at 35 to the upper end of one of the links 31. Each side frame 13 carries a plate 36 to which is attached a pin 37 pivotally supporting the associated bell crank lever 32. Each pin carries at its free end a head or stud 38 the annular surface of which may be convexed as at 39 for a purpose to be described.

A counterbalancing spring assembly 42 is provided adjacent each side frame member 13. Each such spring assembly comprises a tension spring 43 having one end fixed to a plate 44 by means of an eye 45 carried by Bach plate 44 is arranged adjacent the frame member 12. The opposite end of each spring is connected as at 46 to a link or reach rod 47 and the other end of such rod or link is connected by a pin 48 to the arm 34 of the associated bell crank lever. The stud 38 is so arranged that when the parts are in the unfolded positions shown in Figures 1 and 3, the top of the stud 38 is above a line between the associated eye 45 and pin 48. Under such conditions, the rod or link 47 will be deflected upwardly as clearly shown in Figure 3. It is preferred that the member 43 be formed of a steel rod or heavy steel wire, although it has been found in practice that this member may be formed very readily of a piece of steel cable.

As stated, the parts when unfolded occupy the positions shown in Figure 1. To facilitate ascending the stair one of the side frame members 28 of the ladder section 17 is preferably provided with a hand rail 5i). This rail readily may be supported with respect to the adjacent side frame of the ladder section 17 by brackets 51.

Operation The parts normally occupy the positions shown in Figure 4. The end of the cover 24 remote from the hinge is provided with some type of hand grip (not shown) to facilitate pulling the stairway downwardly. Such hand grips are conventional. When the parts are in such positions, the springs 43 are positioned as shown in dotted lines in Figure 4, exerting a pull upon the arms 34 of the bell crank lever 32 whereby the pivot pins exert an upward force through links 31 to hold the ladder parts in folded positions.

When the ladder is to be used, the hand grip is pulled downwardly until the ladder section 17 and cover 24 assume the positions shown in Figures 1 and 3. At this time, the sections 18 and 19 will be superimposed above the ladder section 37, remaining in the relative positions shown in Figure 4. The operator will grasp the lower step 27 of the ladder section 19 and pull to the right as viewed in Figures 1 and 3, thus unfolding the ladder sections to permit them to swing downwardly to operative positions. Under such conditions, the lower ends of the side frame members 23 of the ladder section i9 will engage the floor when the ladder is ready for use.

As previously stated, the stud 33 constitutes a stationary element carried by each side frame 13 above a line drawn between the associated eye and pivot pin 43. In the interest of achieving the greatest possible simplicity, this stationary element preferably is the stud 33 fixed to the pivot pin 37. When the parts are in the folded position referred to above, each spring unit 42 has its elements in alinernent from end to end. This alinement is preserved as the parts swing downwardly with the pivot pins 30 and 35 following the arcs shown in construction lines in Figure 3, until the operative positions of the parts are reached. As the ladder sections approach positions in alinement with each other, each rod 47 will bear upon the surface 39 of the associated stud, thus arresting downward movement of the portion of the rod 47 engaging the stud. The pivot pin 48 at each side of the frame wii} continue to move downwardly to a slight extent, thns flexing the rod 47 upwardly as shown in Figure 3, assuming the rod to be made of flexible material. A rigid rod or a rod formed of a flexible cable, will serve substantially equally as well as a flexible steel rod.

ra'hcn the parts reach the positions referred to, each spring unit 42 will have the parts thereof subjected to a force laterally of the normal line of the parts thereof and the tension of each spring, transmitted to its associated pin 43 above the axis of the pivoted pin 37, will exert a slight turning movement on the associated bell crank lever 32. Unless the ladder is occupied by a relatively heavy person, or a person carrying a load on the stairway, the pivot pins 35 will occupy positions slightly to the right in Figures 1 and 3 of a plane passing through the axes of the pivot pins 30 and 37. Thus the pivot pins 35 will be prevented from assuming deadcenter positions relative to the pivot pins 3% and 37.

in connection with the foregoing, it will be noted that a line between the axis of the pin 48 and the point of contact of the link 47 with the stud 38 is at a slight angle to a line between the axes of the pins 37 and 48. The positioning of the parts in the manner shown in Figure 3, therefore, preserves a short moment arm in the lever arm 34 whereby the spring tension exerted endwise through the link 47 exerts a slight turning movement of the bell crank lever 32. The deflection of the spring unit, moreover, causes the application to the pivot pin 48 of an upward component of force to assist in such turning movement. These two forces in practice have been found adequate, even under rather substantial loads on the stairway, to maintain the pivot pin 35 at each side of the stairway slightly out of a dead-center position for the purpose stated.

If the stairway is being subjected to heavy weights, the pivot' pins referred to may swing approximately into alined or dead-center positions, further deflecting each spring unit from its normal straight-line condition. When such heavy weight is released from the stairs, however, the pivot pins 35 will return to the approximate positions shown in Figures 1 and 3. This permits the stairs to be folded and there is no necessity for having to break the joint between the links 31 and the lever arms 33. This is accomplished without the use of extra springs and without the necessity of having to bend or otherwise distort the springs 43. Each of these springs is always straight from end to end under all conditions. This fact prolongs the life of the springs as compared with those constructions in which the springs are bent or distorted, and an occasional drop of oil at the points 45, 46 and 43 (Figure 5) will prevent the occurrence of any annoying spring noises.

As previously stated, a heavy weight upon the stairs may swing the pivots 3!), 35 and 37 substantially into a common plane. However, this does not noticeably affect the position of the stair 17. From Figure 3, it will be noted that if the pivot pins 35 move to the left to the alined positions referred to, the horizontal component of movement of such pins will be accompanied by a downward vertical component of movement of the pivot pins 30 but the latter movement will be negligible and will not be noticed by a person using the stairs.

The stairs are readily folded by swinging the sections 18 and i9 upwardly over the section 17 and then by pushing upwardly on the free end of the cover 24. The

out-of-line positions of the pivot pins 35 relative to the pivot pins 30 and 37 permits the stair to swing upwardly with extremely limited force, and when the parts assume folded positions, they will be counterbalanced by the springs 43 to remain in folded positions.

From the foregoing it will be apparent that the construction is extremely simple and economical to manufacture. The simplicity of the construction makes it extremely rugged and long-lasting, as well as quiet in operation, and the structure has substantially unlimited life.

It is to be understood that the form of the invention illustrated is to be taken as a preferred example of the same and that the scope of the invention is limited only by the appended claims.

I claim:

1. A folding stairway comprising a rectangular open frame having end and side walls, a ladder hinged at one end to one end wall of said frame, a bell crank lever having relatively long and relatively short arms substantially at right angles to each other, a pivot pin connecting said bell crank lever at the junction of said arms with one of said side walls, a first link pivotally connected at one end to the end of the long arm of said bell crank lever and at its other end to said ladder, a spring assembly comprising a tension coil spring, means connecting one end of said spring to said frame adjacent said one end wall, and a second link connected at one end to the other end of said spring, said link being directly connected at its other end to the end of said short arm of said bell crank lever, the points of connection of said second link with said short arm of said bell crank lever and with said other end of said spring and the point of connection of said one end of said spring with said frame lying in a straight line throughout the greater portion of the movement of said bell crank lever between open and closed positions of said ladder, said short arm of said bell crank lever projecting generally away from said one end wall when said ladder is in lower position and projecting generally upwardly when said ladder is in closed position, said straight line being substantially perpendicular to said short arm of said bell crank lever when said ladder is in closed position, the point of connection of said second link with said other end of said spring, when said ladder is in open position, lying between said pivot pin and said one end wall, and a stationary element engageable with said second link solely when said ladder approaches open position to deflect said link slightly upwardly, a line between said stationary element and the point of connection of said second link with said short arm of said bell crank lever being at a slight angle to a line between said pivot pin and the point of connection of said second link with said short arm of said bell crank ever to preserve in the latter a relatively small moment arm acted on by said spring assembly to tend to turn said bell crank lever about said pivot pin.

2. A folding stairway according to claim 1 wherein said stationary means comprises a relatively large head carried by said pivot pin, said head engaging said second link at a point intermediate the ends thereof and supporting such point appreciably above the axis of said pivot pin.

3. A folding stairway comprising a rectangular open frame having end and side walls, a ladder hinged at one end to one end wall of said frame, a bell crank lever having relatively long and relatively short arms substantially at right angles to each other, a pivot pin connecting said bell crank lever at the junction of said arms with one of said side walls, a first link pivotally connected at one end to the end of the long arm of said bell crank lever and at its other end to said ladder, a spring assembly comprising a tension coil spring, means connecting one end of said spring to said frame adjacent said one end wall, and a second link connected at one end to the other end of said spring, said link being directly connected at its other end to the end of said short arm of said bell crank lever, the points of connection of said second link with said short arm of said bell crank lever and with said other end of said spring and the point of connection of said one end of said spring with said frame lying in a straight line throughout the greater portion of the movement of said bell crank lever between open and closed positions of said ladder, said short arm of said bell crank lever projecting generally away from said one end wall when said ladder is in lower position and projecting generally upwardly when said ladder is in closed position, said straight line being substantially perpendicular to said short arm of said bell crank lever when said ladder is in closed position, the point of connection of said second link with said other end of said spring, when said ladder is in open position, lying between said pivot pin and said one end wall, and a stationary element engageable with said second link solely when said ladder approaches open position to deflect said link slightly upwardly, said second link being formed of relatively stiff material whereby the deflection of said second link out of said straight line transmits to the end of said short arm of said bell crank lever a force transversely thereof tending to turn said bell crank lever about said pivot pin.

4. A folding stairway according to claim 3 wherein said stationary means comprises a relatively large head carried by said pivot pin and engaging said second link at a point intermediate the ends thereof and supporting such point appreciably above the axis of said pivot pin.

5. A folding stairway according to claim 3 wherein a line between the point of engagement of said second link with said stationary means and the point of connection of said second link with said short arm of said bell crank lever is at a slight angle to a line between the axis of said pivot pin and the point of connection of said second link with said short arm of said bell crank lever to preserve in said short arm a relatively short moment arm acted on by the tension of said spring assembly to cooperate with said force transmitted transversely to said short arm of said bell crank lever to tend to turn said bell crank lever about said pivot pin.

References Cited in the file of this patent UNITED STATES PATENTS 320,692 Ready June 23, 1885 2,095,392 Marschke Oct. 12, 1937 2,506,380 Myers May 2, 1950 2,649,237 Bjorklund et al. Aug. 20, 1953

Images