Abstract:
A cushion that is heated convectively using a positive coefficient of resistance type resistive heating element that is provided with heat exchanging surfaces, includes a mattress pad, seat or the like with a bottom surface secured around its perimeter to an air permeable top surface, forming a plenum and containing tubular spacer material therein. The plenum is connected to a power unit housing a blower, a heating module and a controller unit. The heating module preferably includes a PTC type heating element in conduction with a base plate and a number of heat exchanger fins. Preferably the heating element is sandwiched between a pair of the base plates and the heat exchanger fins, and there is a seal between the base plates to minimize air flow from the blower from passing there between. A remote control for the user&#39;s convenience may be provided, and a foldable antenna attachable to the convective unit facilitates wireless communication between the remote control and controller unit. The user resting atop the cushion is able to control the blower and heating module to deliver air of a desired temperature and quantity to the cushion and through the top surface. The invention advantageously replaces the current carrying, conductive wires and insulation found inside prior art heated mattresses, enhancing safety and performance while at the same time offering a cooled or ventilated capability.

Description:
CROSS REFERENCE TO RELATED DOCUMENTS  
       [0001]     This application is continuation-in-part of utility patent application Ser. No. 11/024,073 (filed Dec. 27, 2004) entitled “Variable Temperature Cushion And Heat Pump.” 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to temperature controlled mattress pads, seats or other cushions, and more particularly to such a cushion that is heated by a positive temperature coefficient (PTC) element and ventilated as well.  
         [0004]     2. Description of the Related Art  
         [0005]     Resistance wires oftentimes with PTC resistive elements are the conventional way of heating a cushion by conduction. This suffers from certain disadvantages, however, including that the electrical conductors are located within the cushion itself. Over time, the wires, carbon fiber strips or the like being subject to repeated weight loads and mechanical stresses may become physically damaged causing sparks from short circuits, and an occasional fire. Voltages as low as 6V can produce noticeable sparking, even at current levels in the 1-200 milliamp range.  
         [0006]     Insulation is commonly used in the prior art, not only to limit peak heating at the conductor but also to spread the heating effect out (or average it) over the surface to be heated. The disadvantage here is that it takes longer to reach an adequate heating level, because of the drop in heating efficiency caused by the insulation. The overall efficiency of the heating apparatus is compromised as the insulation slows the heating of the outer surface of the cushion.  
         [0007]     Additionally, resistance heated type, prior art mattress pads don&#39;t offer cooling or ventilation. This is a major disadvantage in many parts of the world where the population lacks means such that air-conditioning is unavailable and a substantial portion of the year relaxing or sleeping is uncomfortable due to very warm ambient air conditions.  
       OBJECTS OF THE INVENTION  
       [0008]     Accordingly, it is an object of the present invention to construct a temperature-controlled cushion that is heated without the conventional resistance wires or PTC resistive elements in conductive mode within the cushion itself,  
         [0009]     It is a further object of the present invention to construct such a cushion while minimizing the use of insulation.  
         [0010]     It is a still further object of the present invention to provide such a cushion that also includes a cooled or ventilated mode.  
         [0011]     It is a still further object of the present invention to provide such a cushion that includes convenient controls for the user.  
         [0012]     It is a still further object of the present invention to provide such a cushion that is simple and relatively inexpensive to manufacture.  
         [0013]     It is a still further object of the present invention to provide an accompanying power unit that is quiet and compact, and located remote from the cushion;  
         [0014]     These and other objects of the present invention will become apparent upon reference to the following detailed description and accompanying drawings.  
       SUMMARY OF THE INVENTION  
       [0015]     Disclosed is a new approach for a cushion that is heated convectively using a positive coefficient of resistance type resistive heating element that is provided with heat exchanging surfaces, or alternatively a thermoelectric device with heat exchanging surfaces, or a Stirling Cycle heat pump with PTC heater mounted on the cold head and heat exchanging surfaces attached to the PTC heater and/or cold head.  
         [0016]     The present invention includes a mattress pad, seat or other cushion with a bottom surface secured around its perimeter to an air permeable top surface (forming a plenum or air-flow structure) and containing tubular spacer material or equivalent therein. The plenum has an opening for a (preferably insulated) air duct which leads to a power unit housing a blower, a heating module and a controller unit. Besides obvious uses in the home or an automobile, the invention as disclosed herein may also be used for patient warming in medical and surgical settings.  
         [0017]     The heating module preferably includes a PTC type heating element in conduction with a base plate and a number of heat exchanger fins. Preferably the heating element is sandwiched between a pair of the base plates and the heat exchanger fins, and there is a seal between the base plates to minimize air flow from the blower from passing there between. A remote control for the user&#39;s convenience may be provided and a foldable antenna attachable to the convective unit facilitates wireless communication between the remote control and controller unit, although corded remote control may also be utilized or the controls located on the power unit itself. The power unit may include multiple PTC elements including of varying capability to allow the user to more precisely control the output temperature of the air, and may include a speed control for the blower.  
         [0018]     The user resting atop the cushion is able to control the blower and heating module to deliver air of a desired temperature and quantity to the cushion and through the top surface. The advantages of the subject invention over the prior art in heating mode for mattress pads, seats and other cushions are substantial. Since there are no current conducting wires or carbon fiber strips within the cushion structure, the convective cushion is much safer than the prior art when used as a mattress pad. This is because the PTC heating element is located remotely from the cushion and is connected to the cushion only with an air duct hose, eliminating all mechanical stress to any electrical wires from weight applied to the sleeping or seating surface. Because the heating medium is air, and not hot current conductor wires, it isn&#39;t necessary to use insulation to spread the heating effect over the entire surface of the cushion. By using air, the heating effect is gentle and effective without the need for insulation, so the overall heating mode efficiency is higher and more evenly distributed over the heated surface.  
         [0019]     The present invention, besides replacing basic electric resistance wire heated mattress pads as well as other resistance element heated cushions, also offers a feature that the prior art cannot using the same equipment and that is a ventilation mode for warm weather. By causing ambient air to move within the air flow structure (which is much more efficiently done with tubular spacer fabric as described elsewhere herein, and in U.S. Pat. Nos. 6,263,530 and 6,085,369, but can be done less efficiently with other air flow structure materials), a meaningful percentage of excess body heat can be removed during warm weather while the user is seated on or sleeping on the cushion of the subject invention.  
         [0020]     As long as ambient temperature is below the user&#39;s body skin temperature (which averages out to approximately 96 degrees Fahrenheit over much of the body), there must (according to Newton&#39;s Law of thermal transfer), be a thermal exchange between the source of heat at a higher temperature (body skin surface), and a heat sink at a lower temperature, by ambient air under forced convection (macrocosmically) and free convection, (microcosmically). The terms macrocosm and microcosm simply refer to the relatively large bulk air flow (or forced convection), produced through the cushion air flow structure by the blower and the relatively very small air convection movement (free convection), produced at the microcosmic level by the delta T or difference in the relatively warm air nearest the user&#39;s skin and the relatively cool air brought into close proximity via forced convection. The microcosmic level is that level within the padding and textiles which is the interface between the user and the air flowing through the cushion. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0021]      FIG. 1  is a side elevation view of the convective cushion of the preferred embodiment of the present invention placed atop a conventional mattress;  
         [0022]      FIG. 2  is a plan view of the convective unit with a portion of the housing removed to show its contents;  
         [0023]      FIG. 3  is an enlarged plan view of the PTC resistive heating element  30 ;  
         [0024]      FIG. 4  is an end view of the assembly of  FIG. 3 ;  
         [0025]      FIG. 5  is another side elevation view of the same assembly, in the air flow direction, looking through the heat exchanger fins;  
         [0026]      FIG. 6  is a cross-sectional view of the air duct;  
         [0027]      FIG. 7  is a side view of the convective unit with an optional attachable folding antenna with an attached air duct hose  40  to convey conditioned air to the cushion.  
         [0028]      FIG. 8  is a side view of a convective seat cushion for a vehicle with a compact power unit installed at the bite line between the seat and backrest in accordance with an alternate embodiment;  
         [0029]      FIG. 9  is a side view of the power unit optionally installed at the front of the seat;  
         [0030]      FIG. 10  is a cross-sectional view of the power unit optionally installed at the top of the backrest;  
         [0031]      FIG. 11  is a front elevation view of the cushion with a damper valve for regulating the airflow;  
         [0032]      FIG. 12  shows the modified airflow of  FIG. 8  when the damper valve is closed;  
         [0033]      FIG. 13  shows the modified airflow of  FIG. 9  when the damper valve is closed; and,  FIG. 14  shows the modified airflow of  FIG. 10  when the damper valve is closed. 
     
    
     LISTING OF REFERENCE NUMERALS  
       [0000]    
       
          convective cushion  10   
          plenum  12   
          air impervious bottom surface  14   
          air-permeable top surface  16   
          vent  17   
          tubular spacer material  18   
          power unit  20   
          housing  21   
          blower  22   
          circuit board box  24   
          adaptor  26   
          air outlet  27   
          air duct inlet  28   
          PTC resistive heating element  30   
          heat exchanging fins  32   
          power terminals  34   
          PTC heating element  36   
          base plates  38   
          air seal or gasket  39   
          air duct hose  40   
          flexible air duct  42   
          insulated sleeve  44   
          sleeve splines  46   
          remote IR sensor, detector  50   
          length of wire  52   
          articulated folding strut, antenna  60   
          IR sensor  62   
          adapter plug  64   
          hinge points  66   
          vehicle seating cushion  130   
          seat rest  132   
          backrest  134   
          compact power unit  150   
          straight air duct  194   
          special air duct  195   
          special duct  196   
          Zipper™ valve or damper  198   
       
     
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0071]     Initially referring to  FIG. 1 , shown is the convective cushion  10  placed upon a conventional mattress, including a plenum  12  constructed of a bottom surface  14  secured around its perimeter to a top surface  16 . The bottom surface  14  is preferably air impervious, although placement on a conventional mattress may render an air permeable surface largely impervious. The top surface  16  is air-permeable although sufficiently impervious that a greater air pressure can be maintained inside the enclosed space.  
         [0072]     Inside the plenum  12  is tubular spacer material  18  or equivalent. U.S. Pat. Nos. 6,085,369 and 6,263,530 pioneered the use of such tubular spacer fabric  18  as an air flow structure for seats, mattresses, mattress pads, and other articles of furniture that can be sat on or laid down upon. Although the preferred embodiment of this invention utilizes the same tubular spacer fabric  18  as described in the issued Feher &#39;369 and &#39;530 patents, it is possible to utilize other air flow structures such as Muller Textile&#39;s 3 Mesh or Strahle and Hess&#39; assembled woven tube fabric, as well as any other air flow structure; however there may be substantially reduced levels of performance when compared to tubular spacer material  18  as disclosed in the above U.S. Pat. Nos. and herein.  
         [0073]      FIG. 2  shows a power unit  20  for the convective cushion  10 , which includes a blower  22  for blowing air across one a PTC resistive heating module  30  including heat exchanging surfaces  32  (see  FIGS. 3-5 ), and pushing the air into the plenum  12  for heating the cushion  10 . Alternatively, the PTC module  30  need not be energized, resulting in a ventilating function as a result of circulating ambient air through the cushion air flow structure  12 . The PTC heating module  30  with heat exchanging fins  32  is located in an adaptor  26  that matches the module  30  to the blower air outlet  27  and the air duct inlet  28  in the most aerodynamically efficient manner within the space limitations of the power unit  20  housing  21  dimensions. Details such as a power cord and plugs and sockets are not shown.  
         [0074]     Also shown in  FIG. 2  is a box  24  for any necessary or desired electrical circuits for mode switching, switching between multiple heaters, on and off, etc., plus wireless remote control circuits if desired. A speed control printed circuit board may be incorporated in the space  24  shown in  FIG. 2 , which could be used to control heating as well as ventilation by coordinating PTC elements with AC power control to regulate air flow, perhaps offering more flexibility in comfort settings than the simplest form which relies solely on the PTC switch temperature characteristics of the PTC elements with a fixed air flow rate.  
         [0075]     The box  24  may optionally include a Triac or other semiconductor power control for the PTC heating elements to enable the PTC elements to operate below their switch temperature design point. The PTC element switch temperature is the temperature at which the resistance starts to rise exponentially. The elements  36  are called Positive Temperature Coefficient because, unlike NTC, or Negative Temperature Coefficient type materials, the electrical resistivity rises with increasing temperature, instead of dropping with increasing temperature. Most materials exhibit PTC characteristics because increasing temperature causes more ionic movement, crystal lattice vibration, and/or molecular motion, any of which can interfere with electron mobility. The switch temperature of ceramic PTC devices is determined by the amount of doping with certain elements, such as strontium, for example, before firing.  
         [0076]     In order to operate the PTC heating elements  36  below their design point switch temperature it is necessary to either increase the heat load beyond the capabilities or rating of the elements, by increasing air flow beyond the design point for example, or by reducing voltage to the elements, which reduces the power rating of the elements relative to the load. For a mattress pad application of the convective cushion  10  it may be more desirable to use a power reduction instead of an air flow increase, in order to maintain a very low noise level for a comfortable sleeping environment.  
         [0077]      FIG. 3  shows the PTC heating module  30  with heat exchanging fins  32  running in the Y axis and power terminals  34  on the right side. Two PTC elements  36  can be seen, represented by dashed lines, mounted in the middle of the heat exchangers  32 . The preferred PTC elements  36  are rated 50 Watts each and 120 VAC, with a switching temperature of about 38-45 deg. C. max., and are manufactured by Advanced Thermal Products, Inc. of Saint Mary&#39;s, Pa. Other elements with different power and voltage ratings can be used; however the above is the preferred embodiment because it is unnecessary to produce air at more than about 45 deg. C. max. to affect good heating performance and using elements rated for 120 VAC eliminates the need for a power supply which reduces the cost of the product while increasing product reliability. If a more powerful heating effect is desired, it is a simple matter of using higher rated elements or more of the same power rated elements  36 .  
         [0078]      FIGS. 4, 5  show the PTC heating elements  36  mounted between two base plates  38  of the heat exchangers  32 . These plates  38  are heavier than the fins  32  and serve to spread the heat outward from the PTC heating elements  36  to the far edges of the heat exchangers  32  as efficiently as possible without excessive thickness and weight. An air seal or gasket  39  is also shown in this view the purpose of which is important. The seal  39  prevents air flow between the two heat exchangers  32 , which forces all of the air flow through the fins  32 , increasing thermal transfer efficiency. The reason that this became an issue was that the thickness of the PTC heating elements rated for 120 VAC is twice that of PTC heating elements rated for 12-24 VDC. The extra thickness results in a gap of sufficient size to permit excessive air flow between the two heat exchanger base plates  38 . The seal  39  addresses this issue to produce a more efficient apparatus that operates reliably at or very close to the switch temperature.  
         [0079]     The PTC heating module assembly  30  can be made with a single heat exchanger  32 ; however such an arrangement would not be as efficient from a thermal point of view. The heat exchangers  32  are preferably made of copper, although aluminum or any other thermally and electrically conductive material can also be used. Although solder can be used to bond the PTC heating elements  36  to the heat exchanger base plates  18 , a flexible adhesive with good thermal and electrical conductivity is preferred to prevent excessive stress buildup and possible PTC element  36  cracking due to differences in coefficient of thermal expansion (CTE) between the PTC heating element  36  material and the heat exchanger  32  material, which can be substantial, for example, approximately  10 : 1  for the PTC elements  36  and copper.  
         [0080]     Referring back to  FIG. 1 , the power unit  20  may be mounted on the floor, with a flexible air duct hose  40  attached to one end of the convective cushion  10 , which is preferably at the foot of the bed. Although it is possible in some instances to introduce air into the convective cushion  10  at the head of the bed it is preferred to put the air in at the foot of the bed for several reasons. The power unit  20  is designed to be very quiet, however it is not totally silent so the father away it is from the user&#39;s ears the better. For heating mode, the extremities tend to require more heating than the trunk of the body; therefore putting the warmed air in at the foot puts the warmest air in at the place where it&#39;s needed most, the extremities, or feet and legs. Lastly, there may not be enough space between the bed and the wall at the head of the bed to accommodate the air duct hose  40 .  
         [0081]      FIG. 1  shows how some of the air percolates or vents up through the cushion  10 , which is enclosed in a textile envelope  12  and secured to, in this case, a bed, resulting in ventilating or heating air flowing under the covers (not shown), however most of the ventilating or heating air flows through the cushion  10  air flow structure  18  and vents out at the end  17  opposite from where it entered.  
         [0082]      FIG. 1  also shows how to achieve an infra-red type remote control with the convective cushion  10  as a mattress pad. Ordinarily, the power unit  20  is placed on the floor at the foot of the bed in order to enable a short length of air duct hose and to minimize blower noise perceived by the user. Unfortunately, this places the power unit  20  out of the line of sight of an infra-red (IR), type remote control, which is less expensive than a radio frequency (RF), type remote. The more expensive RF remote has the advantage of not requiring a line of sight to function. Shown is connecting a remote IR sensor, or detector  50 , to the power unit  20  with a length of wire  52  (most beds are at least  6  feet in length, so the length of wire  52  needed is at least that long, plus approximately three feet for slack), to enable the user to use an IR remote (not shown) without a line of sight to the power unit  20 . Alternatively, either an IR or RF type remote may be designed to be used with the PTC power unit  20  in order to enable control of ventilation, or heating, and degrees of ventilation and heating, without the need for a cord connecting the remote to the power unit  20 .  
         [0083]     The solution of  FIG. 7  is to place an IR sensor  62  on the end of an articulated folding strut, or antenna  60 , attached to the power unit  20 . When the antenna  60  is unfolded vertically, the user has a line of sight to the IR detector or sensor  62 , enabling use of the IR type remote control. The IR sensor strut  60  should be capable of extending vertically at least  24  inches or more, and can be attached to the power unit  20  permanently or can use an adapter  64  to plug into the power unit  20  housing before or after unfolding. A telescopic strut (not shown) could also be used, but managing the wire on the inside during collapse of the telescopic type of antenna is more complex and bulky than using a folding strut  60  with rotary electrical contacts at the hinge points  66 . The folding antenna  60  design can be such that the middle leg folds to nest within the top leg and the bottom leg folds to nest within the middle leg, etc. The legs can be made of flat strips of metal or plastic with the top leg overlapping the middle one and so on. Power to the sensor  62  and signals from the sensor  62  can be transmitted to the control circuit  24  in the power unit  20  via either wires in the antenna  60  or via the arms of the antenna  60  and a third wire if the arms are made of conductive material or if they are provided with conductive circuit traces and rotating contacts in the joints.  
         [0084]      FIGS. 1, 6  and  7  show the PTC heater assembly  30  with blower  22  connected to the mattress pad  10  via a length of flexible air duct  40 . A good example of such an air duct  42  is known as Uniloop, made by Flexhaust, Inc. It is important for good performance of the preferred embodiment  10  to ensure that there is low heat loss in the air duct  42  in cold weather and in heating mode. Although there are numerous materials and techniques that can be used to make a flexible insulated air duct for the purposes of the subject invention, one example is to make an insulation sleeve  44  for the Uniloop air duct hose out of Volara, made by Voltek Corp., which is a polymeric foam with very small closed cells enabling a relatively high R rating, or insulation rating for a relatively thin material cross section. In this case a Volara sleeve or layer approximately 0.08″ thick produces very good results. A preferred form of the Volara insulation sleeve  44  would be extruded with internal splines  46  as shown in  FIG. 6  to create small air gaps between the sleeve  44  and the air duct  42  to enhance the insulation performance of the sleeve with minimal bulk.  
         [0085]     This is one way of making an insulated air duct hose  40  for the preferred embodiment  10  that remains flexible and non-bulky while enabling higher performance and efficiency for the subject cushion or mattress pad in heating mode under cold ambient air temperature conditions. However it is configured, an insulated air duct hose  40  is important for best cold weather heating mode performance, especially because the air delta T in heating mode is substantially higher than in ventilation mode, in which there is no delta T because ambient air is being used for ventilation. If a source of air cooled below ambient is used, then the insulated air duct  40  will improve efficiency, however, not to the same extent, as active cooling mode delta T will still usually be less than half that of heating mode delta T. For example, heating mode may easily entail an air delta T of 45+ deg. F., while active cooling mode with thermoelectric or Stirling Cycle devised as disclosed in some of my other patents, will generally not exceed 20-30 deg. F.  
         [0086]     Referring to  FIGS. 8-14 , an alternate embodiment vehicle seating cushion may be described, in particular application of the PTC air heating and ventilating system to a seat cushion consisting of a seat rest and backrest capable of sustaining internal air flow that will communicate thermally and convectively with the user contacting surfaces, in communication with the PTC power unit or air heating and ventilating system, via a variety of optional air pathways. As shown in  FIG. 8 , preferably a compact power unit  150  is installed proximate the “bite line” or separation between the seat rest  132  and backrest  134  portion of the cushion  130 , with a straight air duct  194  running from the mouth  162  of the power unit  150  to the cushion  130 . This set up is preferred as conditioned air entering the middle portion of the cushion  130  is more easily evenly distributed throughout the seat rest  132  and backrest  134 . Alternatively, the power unit  150  can be installed forward of the seat rest  132  with a special air duct  195  ( FIG. 9 ) or above and aft the backrest  134  with special duct  196  ( FIG. 10 ). These configurations are useful for use with seats that do not have an opening or slot at the “biteline” between the seat and backrest cushion of the seat upon which the PTC cushion is to be installed, in order to facilitate installation of the cushion.  
         [0087]     Note the airflow direction through the cushion  130  varies depending upon where the power unit  150  is placed, with the air primarily exiting the cushion  130  remote from the power unit  150 . The set up with the power unit  150  forward the seat rest  132  is advantageous for ease of control in that the power unit  150  controls could be located directly on the unit  150  and easily accessible between the user&#39;s legs when seated on the cushion  130 . When the power unit  150  is located aft of the user, a wired control extends to the user or to a location accessible to the user or a remote wireless control could be used.  
         [0088]      FIG. 11  shows a Zipper™ valve or damper  198  installed in the middle portion of the cushion  130 . The damper valve  198  serves to control the air flow between the seat rest  132  and backrest  134  portions of the cushion  130 . For example, when the power unit  150  is installed at the bite line and the valve  198  is completely closed, air flows only through the backrest  134  and not the seat rest  132  ( FIG. 12 ). Other examples, when the power unit  150  is installed atop the backrest  134  and the valve  198  closed air flows again only through the backrest  134  ( FIG. 13 ), or when the power unit  150  is installed forward the seat rest  132  and the valve  198  closed air flows only through the seat rest  132  ( FIG. 14 ), in both these instances the air exiting the cushion  130  through the duct  194  at the bite line. It is also possible to open or close the valve  198  to intermediate positions in order to vary the thermal effect of the cushions, by controlling the amount of air flowing through the cushions.  
         [0089]     The present invention has been described in connection with preferred and alternate embodiments, but it is understood that modifications will occur to those skilled in the appertaining arts that are within the spirit of the invention disclosed and within the scope of the claims.