Abstract:
A windshield wiper park position heater employs an area-type heater construction having a flexible substrate supporting a high resistance heater material between electrodes of a lower resistance electrode material. The high length-to-width of the heater element is accommodated through a bus structure that orients current flow along the shortest dimension of the heater and by supplying power at a midpoint of the bus structure to decrease voltage drop over the longest dimension of the heater. A clip structure allows internal conductive layers of laminated connection point between heater components to be simply joined in the crimping operation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application 62/116,036 filed Feb. 13, 2015, and hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to heaters positionable on automotive windshields to heat the area of the windshield where the windshield wipers park when not used and in particular to a narrow form factor heater providing more uniform heat output. 
       BACKGROUND OF THE INVENTION 
       [0003]    During periods when windshield wipers are not in motion, for example, on a parked car, the wiper blades may freeze to the windshield. This freezing can later damage the windshield wiper blades when the windshield wipers are activated or, by placing excess strain on the wiper motor, can blow electrical fuses rendering the windshield wipers inoperative at a time when they are most needed. 
         [0004]    For this reason, it is known to place electric heaters in the “park position” of the windshield wipers to heat the windshield sufficiently that the motionless wiper blades do not freeze to its surface. Such electrical heaters may be provided by printing a series of thin high resistance conductors directly on the windshield glass surface. Ohmic heating of this conductor, when current passes through it, can warm the adjacent glass sufficiently to prevent freezing of the wiper blades. 
         [0005]    The application of the printed conductor to the windshield is difficult and costly and, if made incorrectly or damaged, can require costly rework or scrapping of the windshield. The conductor must be placed away from the edge of the windshield where mastic is used to adhere the windshield to the vehicle and is normally covered by a black painted border around the windshield. Current designs can require blocking substantial width of usable windshield area. The thin conductors are susceptible to small nicks and breaks which can disable an entire portion of the heater. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a narrow, form factor “area” heater for the windshield wiper park position in the form of a “peel and stick” film that can be applied to the windshield at various stages during manufacture and which is more readily repaired or reworked in the event of failure. A narrow form factor is achieved in an area-type heater without loss of heating uniformity by a conductor bus configuration which promotes current flow first along the length of the heater through low resistance material and then across the width of the heater through the high resistance material. Improved manufacturability of the heater is made possible by a clip system that allows the electrical assembly of multiple film components together into a continuous heater element. 
         [0007]    Specifically, in one embodiment, the invention provides a windshield wiper park position heater having a flexible polymeric insulator sheet adapted to conform to a lower surface of a curved automotive windshield, with a length aligned with a length of a windshield wiper in park position. A conductive heater material is coated on the insulator sheet and a relatively low resistance electrode material is applied to the heater material on opposite sides of gap regions to establish a current flow through the heater material of the gap regions. The gap regions are sized to be distributed along substantially the entire length of the insulator sheet proximate to a contact area of the windshield wiper blade against the windshield in park position when the insulator sheet is applied to the automotive windshield. 
         [0008]    It is thus a feature of at least one embodiment of the invention to provide an area-type heater that is both resistant to damage and that can be constructed before attachment to the windshield to permit the heater to be attached flexibly at different stages in the windshield manufacturing process. It is another feature of at least one embodiment of the invention to provide a more space efficient heating system than can be obtained by single resistance conductors. It is another feature of at least one embodiment of the invention to provide a more robust heater that can be more easily repaired or replaced. 
         [0009]    The length of the insulator sheet may be at least six times longer than a height of the insulator sheet measured along a plane of attachment of the windshield wiper park position heater to a windshield and the electrode material may extend in unbroken bus structures along the length of the windshield wiper park position heater to promote average current flow along the width of the heater. 
         [0010]    It is thus a feature of at least one embodiment of the invention to provide improved heat uniformity in an extremely long aspect ratio needed for heaters of this type by promoting width-wise current flow. 
         [0011]    The flexible polymeric sheet may have a length greater than 40 inches. 
         [0012]    It is thus a feature of at least one embodiment of the invention to provide a single heating unit that can provide defrosting for two windshield wipers on a standard vehicle. 
         [0013]    The windshield wiper park position heater may include an adhesive applied in contact with the high resistance heater material in the gap regions. 
         [0014]    It is thus a feature of at least one embodiment of the invention to permit close thermal proximity between the heater and the windshield and to allow the supporting substrate to trap generated heat against the windshield. 
         [0015]    The heater may be black when viewed from a side opposite a side attached to a windshield. 
         [0016]    It is thus a feature of at least one embodiment of the invention to provide a heater system that blends with the black masking material normally applied around the vehicle windshields. 
         [0017]    The insulator sheet maybe transparent and the heater material may be black. 
         [0018]    It is thus a feature of at least one embodiment of the invention to make dual use of the high carbon content of the high resistance material to also provide for a black pigment effect. 
         [0019]    The electrode material may include upper and lower electrodes extending along a length of the insulator sheet at of opposite edges of the insulator sheet across its width, and the windshield wiper park position heater may further include a feeder electrode extending from one end of the insulator sheet to a connection point with one of the upper and lower electrodes substantially at a midpoint along a length of the flexible polymeric insulator sheet. 
         [0020]    It is thus a feature of at least one embodiment of the invention to reduce the effect of voltage drop along an extended length of upper and lower bus electrodes such as may affect uniformity of heat in a long aspect ratio heater by providing a means for introducing current at a midpoint of the heater assembly. 
         [0021]    The electrode material may include an outer and inner electrode extending along the length of the polymeric insulator sheet, with the outer electrode surrounding the inner electrode wherein the outer electrode has a width less than the inner electrode. 
         [0022]    It is thus a feature of at least one embodiment of the invention to provide a heating zone that encircles the area of the wiper blade for reduced ice adhesion of the wiper blade to the windshield. 
         [0023]    The electrodes of the windshield wiper park position heater may include finger elements extending outwardly into interdigitated arrangement with finger electrodes of another electrode. 
         [0024]    It is thus a feature of at least one embodiment of the invention to provide a large heating area while preventing hot spots in the high resistance material. 
         [0025]    The flexible polymeric insulator sheet, heater material, and electrode material maybe divided into first and second portions joined by ductile metal crimp connectors. 
         [0026]    It is thus a feature of at least one embodiment of the invention to provide a method of fabricating extremely long and thin area-type resistances by allowing piecewise construction that can then be spliced together. 
         [0027]    The ductile metal crimp connectors may include conductive elements piercing the overlapping first and second portions to electrically join the conductive electrode materials on the first and second portions. 
         [0028]    It is thus a feature of at least one embodiment of the invention to provide a method of joining laminated structures having electrodes separated by insulating materials when they are assembled. 
         [0029]    The ductile metal crimp connector may further include a connector for receiving an electrical cable for electrical communication with the inwardly extending teeth. 
         [0030]    It is thus a feature of at least one embodiment of the invention to provide a method of introducing power from the vehicle into the windshield wiper park position heater using conventional cabling. 
         [0031]    The connector may be a crimp sleeve for receiving an electrical cable conductor to be crimped thereabout for electrical connection between the electrical cable conductor and the ductile metal crimp connector. 
         [0032]    It is thus a feature of at least one embodiment of the invention to provide a method of introducing electricity from a cable at a midpoint of the assembly at the same time as connecting the assembly at the midpoint seam. 
         [0033]    The high resistance conductive heater material may be a positive temperature coefficient material. 
         [0034]    It is thus a feature of at least one embodiment of the invention to provide a self-regulating heater surface to provide more uniform heating when parallel current flows are allowed through a resistive material as in an area-type heater. 
         [0035]    Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]      FIG. 1  is a fragmentary view of an automotive windshield showing the location of a windshield wiper park position heater and showing an expanded fragmentary view of a rear side of a heater constructed according to a first embodiment of the invention providing a split return bus; 
           [0037]      FIG. 2  is an expanded fragmentary view similar to that of  FIG. 1  showing a second embodiment using a looping return bus; 
           [0038]      FIG. 3  is an expanded fragmentary perspective view of the assembly of two strip elements to produce the embodiments of  FIG. 1 or 2  using deformable metallic clips; 
           [0039]      FIG. 4  is a cross-sectional view through the assembled strips of  FIG. 3  taken along line  4 - 4  showing an electrical interconnection provided by teeth extending inward from the clips of  FIG. 3 ; 
           [0040]      FIG. 5  is a side view of the deformable metal clips of  FIG. 3  showing a crimped attachment to a power supply cable; 
           [0041]      FIG. 6  is a diagram of a heating area provided by the present invention and a windshield wiper contact area on a windshield showing alternative strategies of heating centered on the contact area and heating concentrated in a periphery around the contact area; 
           [0042]      FIG. 7  is a cross-section along line  7 - 7  of  FIG. 1  through the windshield of a vehicle having an attached windshield wiper park position heater showing the application of the heater to the windshield and connection to the automotive electrical systems; and 
           [0043]      FIG. 8  is a detailed fragmentary view of a portion of the heater of the present invention showing an average current flow across the width of the heater as opposed to along its length for improved heat uniformity in a narrow form factor area-heater. 
       
    
    
       [0044]    Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0045]    Referring now to  FIG. 1 , a windshield  10  of an automobile  12  or other vehicle may have a lower front portion defining a windshield wiper park position  14  being a position on the outside of windshield  10  at which windshield wiper blades (not shown for clarity) will rest when the windshield wipers are inactive. The windshield wiper park position  14  will generally extend along a horizontal axis  15  defined by a line of contact between the windshield wiper blade and the windshield  10  in the park position. 
         [0046]    The present invention provides a heater strip  16  that, in one embodiment, extends along the full length of the windshield wiper park position  14  and that is attached at a lower edge of the glass of the windshield  10  inside the vehicle. The heater strip  16  receives a source of electrical current from the automobile power system (e.g., 12 volts) to heat to the windshield wiper park position  14  preventing ice from adhering the windshield wipers to the windshield  10 . 
         [0047]    In one embodiment, as shown, the heater strip  16  generally includes an electrically insulating, flexible polymer support film  18  holding on its top surface (positioned toward the glass of the windshield  10 ) a resistive layer  20  generating heat with the passage of electricity therethrough. Positioned on top of the resistive layer  20  is a set of conductive interdigitated electrodes  22  communicating with the resistive layer  20  to pass current therethrough. The interdigitated electrodes  22  extend alternately from an electrode bus  24  and a return bus  26  while the electrode bus  24  and return bus  26  run horizontally along the length of the windshield wiper park position  14 . 
         [0048]    Alternatively, for any of the embodiments described herein and represented, for example, in  FIG. 3 , the interdigitated electrodes  22 , the electrode bus, and the return bus  26  may be applied directly to the flexible polymer support film  18  and then covered with the resistive layer  20 . In either case, there is a direct connection between the interdigitated electrodes  22  and the resistive layer  20  allowing current flow through the latter from the former. 
         [0049]    The resistive layer  20  may be constructed of an electrically conductive material having a high resistance to provide low current draw and to generate heat over its surface. Preferably, the resistive layer  20  is a conductive polymer, for example, having a fine particulate filler and may be a conductive polyester material exhibiting a positive temperature coefficient (PTC). Positive temperature coefficient materials have rising resistance with increased temperature and thus provide a form of temperature feedback preventing hotspots. Positive temperature coefficient (PTC) heaters, suitable for the present invention, are also disclosed in U.S. Pat. Nos. 4,857,711 and 4,931,627 to Leslie M. Watts hereby incorporated in their entireties by reference. Resistive layer  20  may, for example, be screen printed on the flexible polymer support film  18 . 
         [0050]    The interdigitated electrodes  22 , the electrode bus  24 , and the return bus  26  may, for example, be a low resistance printed material, for example, a silver ink comprising metallic silver particles in a binder or a metal foil or the like. Generally, the interdigitated electrodes  22 , electrode bus  24 , and return bus  26  will have much lower resistance than the resistive layer  20  and ideally as low as practical. The interdigitated electrodes  22  and the electrode bus  24  and the return bus  26  may likewise be screenprinted onto the other components. For example, the resistive layer  20  may be printed or otherwise applied to the flexible polymer support film  18  and then the interdigitated electrodes  22 , electrode bus  24 , and return bus  26  printed on top of that or the interdigitated electrodes  22 , electrode bus  24 , and return bus  26  may be printed or otherwise applied to the flexible polymer support film  18  and then the resistive layer  20 , printed on top of that. This latter configuration may help retain and protect the conductive layer. 
         [0051]    Referring still to  FIG. 1 , in a first embodiment, the return bus  26  may extend generally horizontally by a full width of the windshield  10  leading from a first terminal  30  attached to a negative polarity of the automotive electrical system (typically 12 volts), and the interdigitated electrodes  22  may extend downward therefrom. The electrode bus  24  may connect to a second terminal  32  attach to the positive polarity of the automotive electrical system and may extend horizontally spaced below the return bus  26  to a midpoint  34  approximately halfway along the width of the windshield  10  providing a feeder electrode. At this midpoint  34 , the electrode bus  24  splits to provide a first horizontally extending power supply bus arm  36  continuing across the windshield  10  away from the second terminal  32  and a second power supply bus arm  38  turning and proceeding backward toward the second terminal  32 . Interdigitated electrodes  22  extend upward from both power supply bus arm  36  and power supply bus arm  38  to fit between the downwardly extending interdigitated electrodes  22  attached to the return bus  26 . 
         [0052]    The result of this bifurcation in the power bus is to reduce the difference in path length of electrical current between terminals  30  and  32  for paths through interdigitated electrodes  22  at the far right end of the heater strip  16  as opposed to at the far left end of the heater strip  16  thereby providing more uniform heating. 
         [0053]    Referring now to  FIG. 2  in an alternative embodiment, the return bus  26  may completely encircle the electrode bus  24  with the upper and lower horizontal runs of the return bus  26  having a width  27  approximately one-half the width  27 ′ of the electrode bus  24 . The interdigitated electrodes  22  may extend outward from the electrode bus  24  on its upper and lower sides and end surfaces while the interdigitated electrodes  22  from the return bus  26  may extend inwardly in between those interdigitated electrodes  22  of the electrode bus  24 . Otherwise the construction may be similar to that described with respect to  FIG. 1  providing, for example, a polymer support film  18  over-printed with either the resistive layer  20  on which conductive interdigitated electrodes  22 , electrode bus  24 , and return bus  26  are placed or over-printed with the conductive interdigitated electrodes  22 , electrode bus  24 , and return bus  26  on which the resistive layer  20  is printed. 
         [0054]    Referring now to  FIGS. 3 and 5 , for reasons of manufacturing convenience, the heater strip  16  may be constructed in two separate components  42   a  and  42   b , for example, separated along line  40  of  FIG. 1 . The electrode bus  24  of each of the separate components  42   a  and  42   b  and the return bus  26  of each of the separate components  42   a  and  42   b  may be each joined together, respectively, by overlapping the adjacent ends of the separate components  42   a  and  42   b  and connecting the overlapped portions with clips  44 . The clips  44  may be ductile metal strips folded in a U-shape to provide opposed arms  43   a  and  43   b  that fit positioned in opposition on the overlapping edges of the separate components  42   a  and  42   b  to have the arms  43  of the U compressed inwardly until the they fold together sandwiching the edges of the separate components  42   a  and  42   b  to hold them together. 
         [0055]    Referring also to  FIG. 4 , the inner surfaces of the arms  43  of the clips  44  may have inwardly extending prongs  46 , for example, formed by rough punching of holes  48  in those arms or by cutting and forming tab-form teeth. The prongs  46  puncture the material of the components  42  to pass through the metal conductive layer of either the electrode bus  24  or return bus  26 , the resistive layer  20 , the polymer support film  18 , and an adhesive layer  52  of the first component  42   a  and then through at least the corresponding metal layer of the electrode bus  24  or return bus  26 , resistive layer  20 , and the second component  42   b  to join all of these layers together electrically. The prongs  46  are held firmly in place by an opposed compressive force applied by the bottom arm of the clip  44  which may also have upwardly facing prongs (not shown). 
         [0056]    In this example, the adhesive layer  52  is shown on top of the electrode bus  24  and return bus  26  with respect to the polymer support film  18 , but in an alternative configuration the adhesive layer  52  can be placed directly on the polymer support film  18  on a side opposite the electrode bus  24  and return bus  26 . In either case the adhesive layer  52  helps stabilize the connection of the first and second components  42   a  and  42   b.    
         [0057]    Referring again to  FIGS. 3 and 5 , the clips  44  may include upwardly extending deformable crimp elements  50  which may be crimped about a conductor  54  of a power lead or the like and connected to the automotive electrical system to provide a convenient method of attaching power to the heater strip  16 . When the clips  44  are centered approximately on the heater strip  16 , this attachment method introduces power in a manner that provides improved power distribution by reducing the total run length differences of the power as distributed to the various interdigitated electrodes  22 . 
         [0058]    Clearly this technique may be used to assemble more than two components  42  together for the construction of the heater strip  16 . 
         [0059]    Referring now to  FIG. 6 , the heater strip  16  may be aligned with and circumscribe a contact area between the windshield wiper blade and the windshield defining a windshield wiper park position  14 . In the embodiment shown in  FIG. 1 , a directly heated area  60  provided by the heater strip  16 , corresponding generally to the gaps between the electrodes  24 ,  26 , and  22  over the resistive layer  20 , may underlie and closely surround the windshield wiper park position  14 . Alternatively the directly heated area may be separated into upper and lower heated areas  60 ′ and  60 ″ that flank the upper and lower sides of the windshield wiper park position  14  without underlying the windshield wiper park position  14 . This configuration moves the heated areas  60  slightly outward to de-ice a broader area of the windshield (for the same heated area) relying on conduction between the heated areas  60 ′ and  60 ″ to indirectly heat the area under the wiper park position  14 . Generally, the area of the electrodes  22 ,  26  and  24  will not generate heat because the electrode materials effectively short out the resistive layer  20  preventing heating current therethrough. These two approaches therefore also allow positioning of the cold spots as may be desired for best performance. 
         [0060]    Referring now to  FIGS. 4 and 7 , the adhesive layer  52  of the heater strip  16  may be pressed against the inner surface of the windshield  10  to attach the heater strip  16  to the windshield along the length of the windshield wiper park position  14 . The adhesive layer  52  may be a pressure sensitive adhesive exposed by removal of a release liner  61  therefrom before application to the windshield  10 . As depicted, the resistive layer  20  is sandwiched between the polymer support film  18  and the glass of the windshield  10  providing greatest thermal communication between the resistive layer  20  and the glass of the windshield  10  and allowing the polymer support film  18  to provide both a protective layer against abrasion or damage to the resistive layer  20  and the electrodes  24 ,  26  and  22  and also to trap heat from the resistive layer  20  against dispersion within the automobile interior. 
         [0061]    The polymer support film  18  may be a black material or may be transparent to allow the black of the resistive layer  20  to be visible therethrough to present a black appearance when the heater strip  16  is viewed along a viewing direction  64  from the interior of the automobile. This black appearance matches the black masking  56  found at the interior edges of the windshield in the region of the windshield wiper park position  14  to which the heater strip  16  is attached. 
         [0062]    The clip  44  may be held against the windshield  10  by an additional adhesive layer or material such as double stick tape  67  and may communicate through cable  53  with control electronics  66 , for example, a timer, limiting the amount of time of operation of the heater strip  16  to an amount of time necessary to melt typical ice accumulation. In this regard, the timer of the control electronics  66  may pass or block power from an automotive battery  68  and allows the heater strip  16  to be used in a maximum heat output mode for rapid defrosting of the windshield wipers without concern that this high heat mode could unduly waste power or damage the components of the heater strip  16  after cooling ice has dissipated and the interior cabin temperature of vehicle increases, for example, through the use of conventional windshield defrosters and the like. The timer  66  may communicate with an activation switch  70  to automatically activate when the switch is pressed by the driver. 
         [0063]    Referring now to  FIG. 8 , the arrangement of the electrodes  26 ,  24 , and  22  is such as to promote a net current flow  72  along a generally vertical or width-oriented direction perpendicular to the horizontal axis  15  defining the length. This net current flow  72  is generally the vector sum of individual current flow  74 , the latter along paths of shortest resistance between the electrodes  26 ,  24 , and  22 . By orienting the net current flow  72  along the width direction, only after distribution of electrical current along the lower resistance bus structure of electrodes  26  and  24 , improved uniformity of temperature can be attained along the horizontal axis  15  in extremely high aspect ratio designs of this kind. In this regard, the length of the heater strip  16  measured along the horizontal axis  15  may be eight or more times the width of the heater strip  16  measured perpendicularly to horizontal axis  15 . In one embodiment, the length of the heater strip  16  measured along horizontal axis  15  may be greater than 20 inches, for example, when an individual heater strip  16  is used for each windshield wiper blade or greater than 40 inches when a single heater strip  16  is used for both windshield wipers. The width of the heater strip  16  is measured generally perpendicularly to horizontal axis  15  in the plane of the windshield and will normally be less than three inches to fit unobtrusively at the lower edge of the windshield. 
         [0064]    Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
         [0065]    When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0066]    Various features of the invention are set forth in the following claims. It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. 
         [0067]    All of the publications described herein, including patents and non-patent publications are hereby incorporated herein by reference in their entireties.