Abstract:
A chair height adjustment mechanism includes an energy storage unit which has a compressible fluid. This compressible fluid allows the compressible fluid displaced by the piston rod entering the cylinder, to store energy for subsequent use as the chair seat is raised. This fluid may be of the type that has a dual phase at room temperature such that increase in pressure on the compressible fluid causes a portion of that compressible fluid to transition from gaseous phase to liquid phase. This makes the energy storage unit a constant force spring. The features of this constant force spring may be used in a conventional piston cylinder, shock absorbing device, as well.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention is directed to chair height adjustment mechanisms. More particularly, the present invention is directed to improvements to the adjustment mechanism described and claimed in U.S. Pat. No. 5,511,759 which is hereby incorporated by reference.  
           [0003]    2. Brief Description of the Related Art  
           [0004]    Generally, height adjustment mechanisms comprise a piston and a cylinder connected to a reservoir. To telescopically extend the system, fluid is transferred from the reservoir to the cylinder forcing the piston outward. Conversely, to telescopically contract the system, fluid is transferred from the cylinder to the reservoir, drawing the piston inward. A valve between the cylinder and the reservoir controls the flow of the fluid. Typically an incompressible liquid, such as hydraulic fluid, is used. Thus, once the desired height is selected the valve is closed, trapping the fluid in the cylinder and maintaining the desired height position. When the pressure within the reservoir is greater than the outside ambient pressure, a condition known as preload is achieved. Preload forces the piston outward when the valve is open and no load is applied to the piston. This allows a user to extend the height adjustment to its maximum height and then apply a load until the desired height is reached and then close the valve setting the height. An invention of the U.S. Pat. No. 5,511,759 patent uses an expandable elastomeric chamber to provide preloaded pressure to the piston and cylinder such that the device will telescopically expand when the valve is open and the device is not subject to a load.  
         SUMMARY OF THE INVENTION  
         [0005]    According to a first exemplary embodiment of the present invention, a height adjustment mechanism comprises (a) an outer support tube having a first closed end and a second open end, (b) an inner support tube assembly telescopically received within said outer support tube, said inner support tube assembly including an external tube, an internal tube disposed within said external tube, first means sealing and interconnecting said external and internal tubes at a first pair of ends and second means sealing and interconnecting said external and internal tubes at a second pair of ends thereof, said external tube and said internal tube defining a first chamber there between, (c) a piston assembly interconnected to said outer support tube and telescopically received within said internal tube, said internal tube and said piston assembly defining a second chamber there between, (d) port means allowing fluid flow between said first and second fluid chambers, (e) a hydraulic fluid contained within said port means and said first and second chambers, (f) valve means interactive within said port means for regulating fluid flow between said first and second chambers, and (g) energy storage means including a pressurized fluid cooperating with said first chamber to provide a lift force upon opening said valve means to allow flow of said hydraulic fluid between said outer support tube and said inner support tube assembly.  
           [0006]    According to a second exemplary embodiment of the present invention, a height adjustment mechanism comprises (a) an outer support tube having a first closed end and a second open end, (b) an inner support tube assembly telescopically received within said outer support tube, said inner support tube assembly including an external tube, an internal tube disposed within said external tube, (c) first means sealing and interconnecting said external and internal tubes at a first end including an elastomeric sleeve encircling said internal tube and having a thin, more flexible portion which permits said valve means to be moved between a first closed position and a second open position said first means supporting said valve means and biasing said closeable valve means to said first closed position, (d) second means sealing and interconnecting said external and internal tubes at a second end thereof, said external tube and said internal tube defining a first chamber there between, (e) a piston assembly interconnected to said outer support tube and telescopically received within said internal tube forming a second chamber, (f) port means allowing fluid flow between said first and second fluid chambers, (g) a hydraulic fluid contained within said port means and said first and second chambers, (h) valve means interactive within said port means for regulating fluid flow between said first and second chambers, and (i) a pressurized gas cooperating with said first chamber to provide a preload lift force upon opening said closeable valve to telescopically extend said inner support tube assembly relative to said outer support tube.  
           [0007]    According to a third exemplary embodiment of the present invention, a constant force spring comprises (a) a piston cylinder having a first closed end, (b) a piston received and slidable within said piston cylinder, (c) a first chamber defined between said first closed end of said piston cylinder and said piston, (d) seal means provided on said piston sealing said piston against said piston cylinder making said first chamber substantially leakproof, and (e) a fluid confined within said first chamber, said fluid being in said first chamber will be partially liquid and partially gaseous with vapor pressures at room temperature in the range of between 50 psi and 150 psi such that a compressive force on said first chamber by said piston will cause a portion of said gaseous fluid to move into a liquid state exhibiting a constant force opposing said compressive force.  
           [0008]    According to a fourth exemplary embodiment of the present invention, a means for controlling flow of hydraulic fluid in a piston cylinder comprises a valve member comprising (a) an elastomeric sleeve portion which fits over an inner support tube and seals against said inner support tube to prevent undesired fluid flow between said elastomeric sleeve portion and said inner support tube, said elastomeric sleeve portion including passageway means to permit desired flow of hydraulic fluid between said elastomeric sleeve portion and said inner support tube, said elastomeric sleeve portion fitting within an outer support tube and being sealed with respect thereto to prevent undesired flow of hydraulic fluid between said elastomeric sleeve portion and said outer support tube, (b) a flexible intermediate section interconnected to said elastomeric sleeve portion, (c) a generally tabular portion extending outwardly from said flexible intermediate section, (d) a rigid valve seat element which has i) a stem portion extending through an end portion of said inner support tube, a portion of said stem portion being received within said generally tubular portion, and ii) a flat valve seat projecting from said stem portion that abuts and seals against an inner surface portion of said inner support tube, and (e) a manually engageable valve actuator having a portion which surrounds an upper periphery of said generally tubular portion, whereby when said manually engageable valve actuator is depressed, said generally tubular portion is moved axially unseating said valve seat from said inner surface portion of said inner support tube permitting hydraulic fluid within said inner support tube to flow in a direction to and from said outer support tube through said passageway means.  
           [0009]    Still other objects, features, and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of embodiments constructed in accordance therewith, taken in conjunction with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The invention of the present application will now be described in more detail with reference to preferred embodiments of the apparatus and method, given only by way of example, and with reference to the accompanying drawings, in which:  
         [0011]    [0011]FIG. 1A is a longitudinal cross-sectional view of a first preferred embodiment of the height adjustment mechanism of the present invention that can use any one of FIG. 2A, 2B,  2 D, or  2 F, depicting preferred embodiments of energy storage devices;  
         [0012]    [0012]FIG. 1B is a longitudinal cross-sectional view of a second preferred embodiment of the height adjustment mechanism of the present invention;  
         [0013]    [0013]FIG. 2A is a longitudinal cross-sectional view of a first embodiment of an energy storage device useful in the height adjustment mechanism of the present invention;  
         [0014]    [0014]FIG. 2B is a longitudinal cross-sectional view of a second preferred embodiment of an energy storage device useful in the height adjustment mechanism of the present invention;  
         [0015]    [0015]FIG. 2C is a partial view of the sealing means of the energy storage device in the circled area of FIG. 2B;  
         [0016]    [0016]FIG. 2D is an exploded side view in partial section of a third embodiment of the energy storage device;  
         [0017]    [0017]FIG. 2E is a side view of a fourth embodiment of the energy storage device prior to final assembly;  
         [0018]    [0018]FIG. 2F is a longitudinal cross-sectional view depicting the fourth embodiment of the energy storage device of FIG. 2E in final assembly.  
         [0019]    [0019]FIG. 3 is a cross-sectional side view of a third embodiment of the height adjustment mechanism of the present invention;  
         [0020]    [0020]FIG. 4 is a longitudinal cross-sectional view of a fourth embodiment of the height adjustment mechanism of the present invention;  
         [0021]    [0021]FIG. 5 is a longitudinal cross-sectional view of a fifth embodiment of the height adjustment mechanism of the present invention; and  
         [0022]    [0022]FIG. 6 is a longitudinal cross-sectional view of an embodiment of a constant force spring of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    The improvements of the subject invention include improved reliability and consistency of performance, reduced manufacturing expense, elimination of critical leak paths, and improved preload capability. Revision of the fluid channel, valve and seal mechanisms to perform these tasks with a single element at a point internal to the outermost periphery of the unit serves to eliminate the leakage while improving the consistency of performance of the valve and reducing manufacturing costs.  
         [0024]    The preload provided to the system by the system adjustment mechanism is important because when the adjustment mechanism is used in combination with a repositionable device such as a chair, for example, and the valve is open and the seat unloaded, the mechanism will rise to its upper position to be in a position for ready adjustment. In addition, the preload serves to increase the amount of energy stored by the descent of the loaded chair during adjustment. Several embodiments of improved means to achieve preload are taught by this disclosure. These embodiments chiefly entail some form of elastomeric bladder which can be inflated to a desired pressure to provide the desired preload. These bladders are inserted into a reservoir having rigid walls where the preload is achieved by the bladder(s) being compressed by the surrounding hydraulic fluid. These bladders can also be filled with a fluid that is in two phases (gas and liquid) at a desired pressure and temperature. This allows for the pressure to remain constant as the internal volume of the bladder changes, provided two phases are present. The constant pressure provides uniform fluid flow from the reservoir to the cylinder when the valve is open and no load is applied to the piston for extending the height adjustment mechanism to the maximum extended position. The constant pressure eliminates the potential problem of having too much pressure when the piston is at the bottom of the cylinder and too little pressure when the piston is extended to the top of the cylinder.  
         [0025]    Another aspect of the invention is the provision of a constant force spring. The constant force spring works on the same principle as described above. A working fluid having gas and liquid phases at normal, or desired, operating temperatures and pressures exerts a constant pressure against a piston for the full range of motion of the piston within a cylinder. Provided the working fluid remains in a two phase state, the force against the piston will be constant for the full range of motion forming a constant force spring. Suitable working gases include, but are not limited to, HF 6 , 1,1,1,2-tetrafluoroethane, pentafluoroethane, difluoroethane, and 1,1,1-trifluoroethane, and preferably, but not necessarily, are non-toxic, nonflammable, and non-ozone depleting. When the piston compresses the gas phase of this fluid, the gas phase will be converted to liquid rather than increasing the internal pressure within the piston cylinder. The two phase fluid can be either a primary fluid or a secondary fluid used in conjunction with an incompressible liquid-phase fluid, such as hydraulic fluid. Such hydraulic fluids might include castor oil, glycerol and various glycols. In other applications, this constant force spring can provide a low stiffness mounting that will provide excellent vibration isolation, particularly at low frequency.  
         [0026]    Referring to the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures.  
         [0027]    A first preferred embodiment of the height adjustment mechanism of the present invention is shown in FIG. 1A, generally at  20 . Height adjustment mechanism  20  includes an outer support tube  22  which is closed on a first end  24  and open on a second end  26  and an inner support tube assembly  30  is telescopically received within and protruding from the second open end  26  of the outer support tube  22 . A sleeve  27  of self-lubricating bearing material is affixed within the open end  26  of outer support tube  22 . Inner tube assembly  30  includes an external tube  32  and an internal tube  34  disposed therein. External tube  32  and internal tube  34  are sealed and connected together at first ends  31  and  33  by first sealing and connecting means  36 . First sealing and connecting means  36  includes a spacer  38 , O-ring  39 , and elastomeric element  40 .  
         [0028]    Elastomeric element  40  is a unitary member including sleeve portion  42  that fits over internal tube  34 ; a smaller diameter cylindrical portion  44  that receives a stem portion  52  of valve element  50 ; a thin, flexible portion  46  interconnecting sleeve  42  and cylindrical portion  44  which permits the valve element  50  to be moved between a first closed position (shown in FIG. 1A) in which valve  53  engages valve seat  51  and a second open position by means of a manually engageable valve actuator  54 , the first sealing and connecting means supporting the valve element  50  and biasing the closeable valve element  50  to its closed position. Valve actuator  54  has a cylindrical portion  56  which surrounds an upper end of cylindrical portion  44 .  
         [0029]    External tube  32  and internal tube  34  are interconnected and sealed at second ends  35  and  37 , respectively, by a second connecting and sealing means  48 . This sealed area between external tube  32  and internal tube  34  includes a first annular shaped chamber  28 . In the FIG. 1A embodiment, sealing element  48  also captures the ends of a thin-walled elastomeric bladder  60  between itself and the external tube  32  and internal tube  34 . The interior  67  of bladder  60  can be inflated with a secondary fluid to a desired pressure level (e.g., between about 50 psi (345 kPa) and about 200 psi (1380 kPa)) through an opening (not shown) in sealing element  48  forming an energy storage device to provide a desired preload. The thin walled elastomeric bladder  60  can be any one of the preferred embodiments of energy storage devices of FIG. 2A, 2B,  2 D, or  2 F, inserted in place of bladder  60  in chamber  28 . Gases suitable as a secondary fluid include air, dry nitrogen, and carbon dioxide, depending on the choice of elastomeric material of bladder  60 . Examples of materials suitable for bladder  60  are natural rubber, nitrile, and butyl. If constant pressure is desired, the interior  67  of bladder  60  can be filled with a secondary fluid comprising a two phase fluid that is in the form of liquid and gas at the desired pressure and temperature. By way of example and not of limitation, a secondary fluid can be a two-phase fluid at a temperature of about 75° F. (24° C.) at a pressure of between about 50 psi (345 kPa) and about 150 psi (1035 kPa). The preload offsets the weight of the chair seat itself and provides a lifting force when the valve is opened to restore the chair seat to an upper most position for subsequent adjustment. By controlling the size of the opening between valve  53  and valve seat  51 , the chair operator can control the rate at which the operating fluid  69  passes through the valve and, hence, the rate of descent of the chair.  
         [0030]    A piston rod assembly  62  is received within inner tube  34 , extends through second seal element  48  and is attached to outer support tube  22  at  61 . Piston rod assembly includes a housing  64 , a piston rod  66 , a piston head  68  and a cush  70 . A second chamber  58  is defined by inner tube  34  and piston assembly  62 . First chamber  28  and second chamber  58  are filled with an operating fluid  69 ; operating fluid  69  is preferably hydraulic fluid, and when valve  53  is opened, fluid can flow between first chamber  28  and second chamber  58 , depending on which chamber has the higher fluid pressure level. If the chair operator is not seated on the chair, the pressure in first chamber  28  will exceed the pressure in second chamber  58  because of the preload delivered by the energy storage device of bladder  60 . If the operator is seated, whether or not the seat has been extended to its upper position, but not at the minimum height, unseating valve  53  will cause fluid to flow from chamber  58  to chamber  28  as the chair is lowered under the operator&#39;s weight until the operator releases the valve actuator  54  or the minimum height is reached.  
         [0031]    A second embodiment of the height adjustment mechanism of the present invention is shown in FIG. 1B, generally at  20   b . The second embodiment height adjustment mechanism  20   b  includes many of the elements of the first embodiment height adjustment mechanism shown in FIG. 1A, and also includes bands  65 U,  65 L, bladder  60   a  and chamber  28   a . In this embodiment, thin walled elastomeric bladder  60   a  is attached around internal tube  34  by bands  65 U and  65 L. First chamber  28   a  does not contain an operating fluid  69  but, rather, is pressurized by a secondary fluid, as described in FIG. 1A, forming an energy storage device to provide the desired preload, and when valve  53  is opened while the operator is seated, the fluid bulges bladder  60   a  outwardly against the preload pressure in chamber  28   a , in effect, storing energy for later use. This embodiment functions equivalently to that of FIG. 1A above in that the preload provides a pressure imbalance between first chamber  28  (the space between bladder  60   a  and internal tube  34 ) and second chamber  58  such that when the chair is not loaded and the valve is opened fluid flows in to second chamber  58  raising the level of the chair. The height of the chair is adjusted by the user sitting on the chair and releasing the valve until the desired height is achieved.  
         [0032]    [0032]FIG. 2A depicts a first preferred embodiment of an energy storage device generally at  60   b . Storage device  60   b  is a thin walled bladder that has been molded into a cylinder with a fill port  59 . Once bladder  60   b  has been filled with a secondary fluid to the desired pressure, fill port  59  can be mechanically plugged or heat sealed. As with the previous embodiments, the cylindrical bladder  60   b  is positioned in first chamber  28  directly in the operating fluid  69  to provide a preload to the operating fluid  69 .  
         [0033]    [0033]FIGS. 2B and 2C depict a second preferred embodiment of a energy storage device generally at  60   c . Energy storage device  60   c  includes a first inner elastomeric tube  72  and a second outer elastomeric tube  74 . The preferred materials for the inner elastomeric tube  72  and outer elastomeric tube  74  are natural rubber, nitrile, or butyl. A closure ring  76  closes off a first pair of ends  71  and  73 , respectively, of tubes  72  and  74 . A second closure ring  78  closes off a second pair of ends  75  and  77 , respectively, of tubes  72  and  74  (see FIG. 2C detail). The preferred materials for the closure rings are nylon, steel, or aluminum. The ends  71  and  73  are wrapped around closure ring  76  and ends  75  and  77  around closure ring  78 . An expandable plug or series of plugs  80  can be inserted into the slots in closure rings  76  and  78  and expanded like a rivet to lock them in place. Expandible plugs can take the form of metal double-walled, semi-annular ring segments, the lower extremity of the walls being deflectable outwardly to lock in the slots in closure rings  76  and  78 . Energy storage device  60   c  can be inflated with a secondary fluid to the desired pressure through an opening  79  and then plugged by expandable plugs  80 . As with the previous embodiments, the energy storage device  60   c  is positioned in first chamber  28  directly in the operating fluid  69  to provide a preload to the operating fluid  69 .  
         [0034]    A third preferred embodiment of the energy storage device is shown in FIG. 2D generally at  60   d . Bladder  60   d  comprises a cylindrical tube whose ends are sealed by closure members  84  and  86 . The preferred materials for the closure members  84  and  86  are nylon, steel, or aluminum. The bladder  60   d  is preferably made from natural rubber, nitrile, or butyl. The extremities  81  and  82  are wrapped around members  84  and  86  and secured by expandable plugs  88 . Plug  88  is used to close off fill port  87 , as well as anchor end  84  of tube  60   d . Tube(s)  60   d  can be pre-pressurized with a secondary fluid and as many tubes may be added to chamber  28  as are needed to provide the desired level of preload.  
         [0035]    A fourth preferred embodiment of the energy storage device of the present invention is depicted in FIGS. 2E and 2F, generally at  60   e . In this embodiment bladder  60   e  is formed as a molded tube having a first section  92 , a second section  94 , and a tapered transitional section  96  connecting the first and second sections. First section  92  is pulled through section  94  and, once the bladder  60   e  is pressurized with a secondary fluid to a desired level to provide the desired preload, the two ends  91 ,  93  can be bonded together and sealed, as shown in FIG. 2F. As with the previous embodiments, the cylindrical bladder  60   e  is positioned in first chamber  28  directly in the operating fluid  69  to provide a preload to the operating fluid  69 . The preferred materials for the bladder are rubber, nitrile, and butyl.  
         [0036]    [0036]FIG. 3 shows a third embodiment of the height adjustment mechanism of the present invention. While the thin walled bladder of earlier embodiments is preferred due to the material savings and the resultant reduced cost, the benefits of the present invention can be realized with conventional thick walled bladders  11  of the type used in U.S. Pat. No. 5,511,759. Simply adding an energy storage device from any of the embodiments of FIGS.  2 A- 2 E to that of FIG. 2D, shown here as  60   d  of FIG. 2D, will provide the improved preload pressurization that this invention makes available.  
         [0037]    Another aspect of the present invention is depicted in FIGS.  4 - 6 . In FIGS. 4 and 5, this aspect is shown as embodied as a pressurized accumulator in a device such as the inner tube assembly  30  of the chair height adjuster of FIG. 1A discussed above. In FIG. 4, operating fluid  69  is pumped between first chamber  28  and second chamber  58  by piston  66 , while a secondary fluid is captured between bladder  60   f  and internal tube  34  forming interior space  67  creating an energy storage device. The secondary fluid is present as an equilibrium combination of both liquid and gaseous phases. The internal pressure of the interior space  67  is maintained at the vapor pressure of the gas as long as some liquid phase is present. Movement of piston  66  inward causes the gas to compress. However, rather than elevating the pressure, some of the gas is converted to liquid such that the internal pressure remains generally constant dependent on the secondary fluid temperature. Preferred secondary fluids include, but are not limited to, substitutes for Freon-12 such as: 1,1,1,2-tetrafluoroethane; pentafluoroethane; difluoroethane; and 1,1,1-trifluoroethane, all of which exhibit vapor pressures in the range of approximately 50 to 150 PSI (345 to 1035 kPa) for fluid temperatures in the range of 60-100° F. (16-38° C.). Thus, the force of the pressure of the secondary fluid against bladder  60   f  is transferred to primary fluid  69 , maintaining a generally constant force against piston  66  and creating a generally constant force spring.  
         [0038]    [0038]FIG. 5 depicts an alternate embodiment of the constant force spring of FIG. 4 in which the secondary fluid  90  is simply mixed with the operating fluid  69 . The differences in density will typically cause the secondary fluid  90  to float atop the operating fluid  69  whereby the space occupied by the secondary fluid  90  of chamber  28  acts as an energy storage device. Siphon tube  88  permits the denser primary working fluid  69  to move between first chamber  28  and second chamber  58  through the secondary fluid  90  floating atop the primary fluid  69  in first chamber  28 .  
         [0039]    [0039]FIG. 6 applies the teachings of a constant force spring to a conventional piston cylinder  92  that can be utilized to isolate sensitive equipment such as electronic devices, from low frequency vibrations. The piston  66  in cylinder  92  has low mechanical stiffness and any vibrational movement of the equipment being protected will be dampened by the transition of the working fluid  90  between its gaseous and fluid phases, in lieu of creating a rise in internal pressure, forming a constant force spring. Air vent  97  is provided in bushing  95  so that air can flow to and from the chamber  98  formed by cylinder  92 , piston head  68 , and bushing  95 . The airflow permitted by air vent  97  prevents pressure fluctuations in chamber  98  that could reduce the effectiveness of the constant force spring. Piston head  68  has an O-ring seal  96  to prevent gas from escaping from the system. Even if a small amount of the gaseous phase escaped from the cylinder  92 , the fluid phase would replace it maintaining equilibrium pressure between the fluid and gas phases. Accordingly, the constant force spring of the subject invention will continue to function properly until the liquid phase of the secondary fluid  90  is depleted.  
         [0040]    While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention.