Abstract:
An adapter for providing a lever attachment to a round door knob has a hollow threaded cylinder fitted with a lever which cylinder slides over the knob and is frictionally secured to the knob by compressing the knob between one end of the cylinder and a tightened split ring threaded into the other end of the cylinder. Elastomeric material placed on either or both sides of the knob increase the friction and prevent slipping of the adapter on the knob after tightening.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to lever type door knobs, and more particularly to an adapter for retrofitting conventional door knobs with a lever. 
     Because of the desire to assist the handicapped in their access to public facilities, efforts are being exerted through laws and regulations to make such access a reality by requiring the construction of ramps, elevators, toilet facilities, etc. suitable for use by the handicapped. Included among these requirements is that door knobs be of the lever type so that a door may be opened by a person having less manual dexterity than is required to turn a conventional round knob. Unfortunately, the cost of replacing each round door knob with a lever is much greater than might be expected because not only must the round knob be replaced, but also the inner mechanism of the door lock. The inner mechanism must be modified because the turning force produced by the off-axis weight distribution of the handle portion causes the lock mechanism designed for a round knob to either completely or partially open the door lock because the spring which holds the tongue of the lock in the extended position (the locking position) is too weak to withstand the turning force produced by the lever. Therefore, for retrofitting a round knob type of door latch, not only must the knob be replaced by a lever, but also the spring must be replaced by a stiffer spring or if that is not possible, the latch mechanism must also be replaced. The cost of replacing round knob combination passage and lock assemblies with a lever handle configuration currently requires the replacement of a passage latch which has stiffer springs to counteract the off axis lever weight and the installation of a separate mortise lock. 
     SUMMARY OF THE INVENTION 
     It is therefore a principle object of this invention to provide an adapter which will allow a conventional round knob type of latch to be converted into a lever type without even the necessity of removing the round knob. 
     It is a feature of the invention that the attachment of the lever to the round knob does not require that the spring of the latch be replaced by one of greater stiffness. 
     It is a further object of this invention is that only a limited number of sizes of adapters will be required for conversion of the vast majority of round knobs of different diameters, thicknesses and profiles such as spherical, elliptical, tulip, inverted tulip, double tulip, etc. 
     These objects and features of the invention are achieved by providing a hollow cylinder which slips over the round knob and is secured to the knob. The cylinder has an attached handle which projects at a right angle to the axis of the cylinder. The cylinder has an end which is closed, or alternatively, partially closed. The other end is internally threaded to receive an externally threaded annular ring adapted to slip over the supporting shaft of the knob. Threading the ring into the cylinder causes the cylinder to be secured to the knob to provide a handle-type latch mechanism. 
    
    
     IN THE FIGURES 
     Other advantages, features and objects of the invention will appear from the following description taken together with the drawings in which: 
     FIG. 1 is a cross-sectional view of the lever adapter of this invention. 
     FIG. 2 is an exploded perspective view of the lever adapter. 
     FIG. 3 is a plan view of the split compressor ring. 
     FIGS. 4-6 show cross-sectional views of other embodiments of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the cross-sectional view of FIG. 1 showing a section of a door 9 with the adapter 10 of the invention attached to the door knob 13 and referring also to the exploded view of the adapter 10 in FIG. 2, there it is seen that adapter 10 comprises an internally threaded cap or cylinder 11 having a collar 12 at one end. The internal diameter of the cylinder 11 is sufficiently large to allow the cylinder to slip over the knob 13. A circular gasket 14 is inserted into the cylinder 11 before the cylinder is placed over the knob 13. The collar 12 may have an axially centered hole 12&#39; to provide access to a keyhole in knob 13 if desired. A second circular gasket 15 which has been severed may be put around the neck 16 of knob 13. Alternatively, if the gasket is sufficiently stretchable, it may be used in its unsevered form by slipping it over the knob 13. 
     An externally threaded pressure ring 17 is split to allow its placement over the knob neck 16 without disassembly of any part of the latch of which the knob is a part. The ring 17 is split and forms two half-rings 17&#39; and 17&#34;. The pins 18 of half-ring 17&#34; mate with holes 19 of half-ring 17&#39; to cause the ring 17 to have a continuous thread 20 which allows ring 17 to be threaded into cylinder 11 by its thread 21. The ring 17 has a hole 17&#39;&#39;&#39; large enough to allow ring 17 to encircle neck 16. Each half-ring 17&#39;, 17&#34; has an axially directed hole 22 which allows ring 17 to be tightened against knob 13 by a spanner wrench. Substantial force may be exerted in tightening ring 17 in order to prevent the assembled adapter 10 from slipping on knob 13 in normal operation. 
     The handle 23 is attached to the cylinder 11 by a screw 25. Alternatively, the handle 23 may be attached to the cylinder 11 by an adhesive, such as an epoxy, or by any other suitable means including being formed as a unit with the cylinder 11. The handle 23 which normally assumes a horizontal position when secured to the knob 13 may because of its off-axis weight produce a turning torque on the knob 13. To reduce the turning torque of handle 23 it has a hollowed out portion 26 and is preferably made of a material having small mass. If the turning torque is sufficiently large to partially disengage the latch by turning the knob 13 against the restraining force of a spring contained within the latch, a counterweight may be provided to counter the turning torque of the handle or lever 23. A counterweight may be provided by selection of the material of the half-ring 17&#39; to have a mass substantially greater than that of the half-ring 17&#34;. As an example half-ring 17&#39; may be made of lead whereas half-ring 17&#34; may be a light-weight plastic. When ring 17 is tightened into cylinder 11, the heavier half-ring would be tightened to a position where it was radially opposite the handle or lever 23. Alternatively, a counterweight could be attached to the cylinder 11 at a position radially opposite the handle 23. It will be apparent that other counterweighting techniques could be used. 
     The split ring 17 is preferably formed with an internally beveled portion 24 which provides a radially inwardly directed force on the elastomeric ring 15 to prevent it from being jammed between the threads 20, 21 and thereby making it difficult to exert the necessary amount of frictional force on the knob 13 in order to prevent slipping of the adapter 10. 
     Although cylinder 11 is shown with an integral collar 12 at one end in FIGS. 1 and 2, an alternative embodiment shown in FIG. 4 has a collar 27 which is threaded into the cylinder 11. Collar 27 has a beveled portion 28 to serve a function equivalent to that of bevel 24 of ring 17. Collar 27 may be made of two half or semi-collars 27&#39;, 27&#34;, with one being of a denser material and positioned opposite the lever 23 to act as an additional counterweight. Collar 27 does not require spanner wrench holes 22 since it may be hand threaded into cylinder 11 before cylinder 11 is placed over the knob 13. By having the collar 27 removable different configurations of the collar suitable for different shapes of knobs may be inserted into cylinder 11. Collars of different center hole 27&#39;&#39;&#39; sizes, different widths and with different bevels may be used as illustrated in FIGS. 5 and 6. 
     The axial length of the cylinder 11 is designed to accomodate a majority of the usually encountered knob sizes and the radially directed ring 17 and collar 27 of FIGS. 1 and 4 are generally satisfactory. However, where the knob 13&#34; is unusually long and projects axially beyond the limits which can be accomodated by the radial rings of FIG. 4, the collar 29 (and ring 30) may project outwardly as shown in FIG. 6 where collar 29 has a configuration which allows a larger than ordinary knob 13&#34; to be contained within the same size cylinder 11 as in FIGS. 1 and 4. Conversely, the collar 29 may be inserted in the opposite direction to project inwardly as shown in FIG. 5 to accomodate a knob 13&#39; with a very shallow axial length. Ring 30 is a modified form of the ring 17 where the inner portion 31 has a more extended taper which shape may be more desirable for knobs where a smaller elastomer ring 15 diameter is used with knobs as shown in FIGS. 5 and 6. 
     Although the adapter 10 has been described as being made of a plastic, it will be apparent that other materials such as a metal may be used. The lever 23 is generally made of a light-weight material to minimize the weight of the counterbalance where such is needed. It will also be apparent that the split ring 17, 30 may also be formed as an incomplete ring with a gap large enough to slip over the neck 16 of the knob. It is also apparent that the split ring 17 need not have alignment pins 18 if the inconvenience of their absence is acceptable to the installer. It will be further recognized that the ring 17 may have an internal thread and the cylinder an external thread if desired. Of course in that case, ring 17 would require a collar which would squeeze ring 15 against knob 13. 
     It is understood that the above-described embodiments of the invention are illustrative only and that modifications thereof may occur to those skilled in the art. Accordingly, it is desired that this invention is not to be limited to the embodiments disclosed herein but is to be limited only as defined by the appended claims.