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CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present invention relates to, and is entitled to the benefit of the earlier filing date and priority of: U.S. Provisional patent application Ser. No. 10/812,244 or 60/651,459, filed Mar. 29, 2004, entitled “Sacrificial Shield For A Window Assembly”, U.S. patent application Ser. No. 10/646,468, filed Aug. 20, 2003, and U.S. Provisional Patent Application Ser. No. 60/404,666 filed Aug. 20, 2002, the disclosures of which are hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to window assemblies and apparatus for protecting the primary glazing panel of a vehicle.  
       BACKGROUND  
       [0003]     Primary glazing panel installations are usually formed of heavy tempered plate glass. The panels are usually sealed around the edges to prevent the entrance of water, dirt, wind, etc. The primary glazing panel installations, especially the ones used in public transportation buses, tend to be expensive and difficult to replace. To protect the primary glazing from vandalism or other damage, replaceable protective glazing panels have been used on the inside of motor vehicles. Examples of sacrificial glazing installations include those described in U.S. Pat. Nos. 5,735,089; 5,809,707; 6,205,723; 6,408,574; 6,688,044, the disclosures of which are incorporated herein by reference.  
         [0004]     However, there is a need in the market for low cost sacrificial glazing installations and methods which are simple and fast to perform, that protect the primary glazing, or that tend to be tamper resistant.  
       SUMMARY OF INVENTION  
       [0005]     Disclosed herein are window assemblies, sacrificial glazing installations, and methods of installing and removing sacrificial glazing panels that can provide low cost sacrificial glazing installations and methods which are simple and fast to perform, that protect the primary glazing, reduce rattling or that tend to be more tamper resistant, which embodiments will be evident from the ensuing disclosure.  
         [0006]     In one embodiment the window assembly comprises a frame for mounting to a vehicle; a primary glazing bonded to the frame; a support for holding a sacrificial glazing adjacent the primary glazing, the support having a channel with a lip; a flexible sacrificial glazing panel formed of a material, sized and having a thickness to permit flexing of the panel to removably seat the sacrificial glazing panel within the channel.  
         [0007]     In another embodiment, the window assembly comprises a sacrificial glazing that includes a frame having a perimeter channel which is configured to receive a correspondingly configured plastic sacrificial glazing panel. The sacrificial glazing panel is flexible and sized relative to the frame perimeter channel such that upon being bowed to bring a pair of opposite edges together, another edge of the panel is able to be inserted into a receiving channel section. The perimeter channel is preferably deeper in the receiving section to allow substantial vertical (or sideways) movement of the panel once the sacrificial glazing panel is inserted into the frame perimeter channel in order that an opposite glazing panel will clear the edge lip portion of the associated channel section.  
         [0008]     In another embodiment, the window assembly comprises a sacrificial glazing assembly having a support and a sacrificial window panel positioned in the support and a resiliently compressible element(s) for biasing the sacrificial panel in the support. The resiliently compressible element may be disposed in a bottom of a panel receiving channel section in the support.  
         [0009]     The resiliently compressible element may act as a positioner element that allows an installed sacrificial glazing panel to be repositioned after initial installation so as to locate the inserted panel edge well within a retainer lip of a receiving channel section of a support. In a preferred embodiment, forcible movement of an inserted edge of a sacrificial glazing panel against a compressible positioner element allows the panel to be moved past an equilibrium position. Further application of a force on the panel allows an opposite edge of the panel to be moved into the retainer lip. Upon release of the force, the positioner element will move the sacrificial glazing panel to an equilibrium position which in turn may seat the opposite edge of the panel in the opposite channel section. Removal of the sacrificial panel is enabled upon a subsequent outward bowing thereof which draws the pair of opposite panel edges together sufficiently to clear lip portions of an associated pair of channel sections, so that the panel can be titled and lifted out of the frame.  
         [0010]     The resiliently compressible positioner element may be any suitable device, including a wave spring, compressible foam strip(s), compressible elastomeric seal(s) or spring(s) and slider assemblies, etc.  
         [0011]     In an alternative embodiment, the sacrificial glazing panel may be suspended in the panel support. In one embodiment, the sacrificial glazing panel is suspended by removable plugs inserted into the lip of a lower channel section. The lower channel may be a deeper receiving channel section than an opposing channel. A bottom edge of the sacrificial glazing panel may be rested on the plugs to hold the panel in an elevated position in the lower channel so that the top edge is retained by the lip of the top channel section. Removal of the plugs allows the sacrificial glazing panel to be lowered sufficiently so that the upper edge clears the top channel section lip portion, in preparation for removal of the panel.  
         [0012]     In another embodiment, the deeper channel section is in the top channel section to eliminate the need for positioner elements.  
         [0013]     In still another embodiment, a foamed elastomer is inserted into one or more channels of the support to hold and isolate the sacrificial glazing panel in the retainer. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a vertical sectional view of a window having upper and lower glazing assemblies each including a sacrificial glazing panel installation according to the invention.  
         [0015]      FIG. 2  is a front view of the window shown in  FIG. 1 .  
         [0016]      FIG. 3  is a fragmentary sectional view of a horizontal section taken through the window shown in  FIG. 2   
         [0017]      FIG. 4  is a fragmentary sectional view of an alternate embodiment of a sacrificial glazing panel installation.  
         [0018]      FIG. 5  is a fragmentary section view of a second alternate embodiment of a sacrificial glazing panel installation.  
         [0019]      FIG. 6  is a fragmentary section view of a third alternate embodiment of a sacrificial glazing panel installation.  
         [0020]      FIG. 7  is a fragmentary section view of a fourth alternate embodiment of a sacrificial glazing panel installation.  
         [0021]      FIG. 8  is a view of the sacrificial glazing panel installation show in  FIG. 7 , but with the positioner plugs removed.  
         [0022]      FIG. 9  is a front view of a window having sideways movable glazing panels incorporating a sacrificial glazing panel installation.  
         [0023]      FIG. 10  is a view of the section  10 - 10  taken in  FIG. 9 .  
         [0024]      FIG. 11  is a view of the section  11 - 11  taken in  FIG. 9 .  
         [0025]      FIG. 12A  is a fragmentary section view of a fifth alternate embodiment of a sacrificial glazing panel during installation in a receiving channel section.  
         [0026]      FIG. 12B  is a fragmentary section view of a fifth alternate embodiment of a sacrificial glazing panel installed in a receiving channel section.  
         [0027]      FIG. 13  is a fragmentary section view of a sixth alternate embodiment of a sacrificial glazing panel installation.  
         [0028]      FIG. 14  is a load-displacement relationship for a foamed elastomer. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0029]     In the following description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so constructed in as much as the invention is capable of taking many forms and variations within the scope of the appended claims.  
         [0030]     Referring to the drawings, and particularly to  FIGS. 1-3 , depicted therein is a vehicle window assembly  10  which includes an upper glazing assembly  12  and a lower glazing assembly  14  for mounting in a vehicle body. The primary glazing may be bonded to the frame or compressed fit therein with a frame and seal assembly  18 . If bonded, the primary glazing may be bonded by any suitable method, such as adhesives, molded together, etc. A bonded primary glazing offers advantages in certain applications. The primary glazing may be flush mounted. The frame may be made of any suitable material, such as metal or a polymer. The frame may be aluminum. Primary glazing panels may be constructed of any suitable material, such as tempered glass, laminated glass, acrylic, polycarbonate, etc.  
         [0031]     As shown, the window assembly includes two window sections each having a primary glazing panel  20 A,  20 B, and associated seals carried in respective retainer frames. Although the description is to a multi-window assembly, the window assembly may also be modified to be a single window assembly.  
         [0032]     The window assembly as shown includes a retainer perimeter frame section  24 A and straight mullion frame sections  24 B, each defining perimeter channels  26  for receiving the primary glazing panels  20 A,  20 B.  
         [0033]     The retainer frame sections  24 A,  24 B may also be used to mount sacrificial glazing panels  22 A,  22 B. Each sacrificial glazing panel  22 A,  22 B has a top, bottom and side edges A, B, C, D, each edge may be received in an associated perimeter channel section defined by a respective retainer section  24 A and  24 B. The retainer frame sections act as one type of support for the sacrificial glazing panels.  
         [0034]     Upper channels  28 A,  28 B and lower channels  30 A,  30 B are formed in part by outer lip portions L which define a glazing opening smaller in size than the size of the sacrificial glazing panels  22 A,  22 B.  
         [0035]     The upper mullion channel section  30 A has an elastomeric member installed in the bottom. As shown in  FIG. 2 , the elastomeric member is a pair of double bowed leaf springs  32 . The leaf springs act as a biasing member that allows the repositioning of the lower edge B of sacrificial glazing panel  22 A at an intermediate position in the channel section  28 A after downward pressure of the glazing panel  22 A has been released. Repositioning allows the top edge A of the panel to be raised to a location within the channel lip L to securely retain the glazing in the channel section  28 A.  
         [0036]     The sacrificial glazing panels  22 A,  22 B are preferably flexible. A flexible glazing panel may be constructed of relatively thin material, (such as less than one half inch, and more preferably ⅛ th  inch plus or minus 7/64 th ). Suitable materials include plastic, polycarbonate, acrylic, etc. The panel is preferably of a size greater than the opening defined by the retaining lips L, but of a size smaller than a diameter defined by the support or channels. The sacrificial glazing panel is preferably of a size such that when the center of the panel  22 A,  22 B is bowed, as with the use of a pair of handled suction cups, the side edges C, D can be drawn in to allow one edge to be removed or inserted from or into a receiving channel section, such as channel section  30 A or  30 B.  
         [0037]     The top and bottom channel sections  28 A,  28 B may be shallower then the opposing mullion channels  30 A,  30 B so that when one edge of the sacrificial glazing panel  22 A or  22 B is first inserted and moved sufficiently towards the bottom of the respective channel  30 A,  30 B the opposite edge clears the lip L of the respective channel section  28 A,  28 B to allow the glazing panel  22 A or  22 B to be completely moved into the frame. Upon release, the side edges C, D of the sacrificial glazing panel  22 A,  22 B move apart to be received and retained in the associated side channels  34  ( FIG. 3 ) of the perimeter frame sections  24 A and  24 B.  
         [0038]     To remove a sacrificial glazing panel  22 A, the glazing panel may be forcibly pressed downward to compress the double bowed leaf springs  32 , moving the top edge A down sufficiently to clear the lip L of the associated channel section  28 A. The sacrificial glazing panel  22 A may also be bowed to draw together side edges C, D to clear lip L of the side channel  34  and allow the sacrificial glazing panel  22 A to be titled and lifted out.  
         [0039]     The bottom edge B of the lower sacrificial glazing panel  22 B, as shown, is gravity biased down into the channel section  28 B, and then panel  22 B thus need only be lifted up until the bottom edge clears the associated channel section lip L and the panel  22 A is then bowed to allow titling out and removal. Thus, a positioner element may not be necessary to retain the top edge.  
         [0040]      FIG. 4  shows an arrangement of one or more compressible foam pieces  36  positioned to engage the lower edge B of an upper sacrificial glazing panel  22 A to hold the same in a channel of a sacrificial glazing panel support formed by a lip L.  
         [0041]      FIG. 5  shows a compressible elastomeric element  38  which has a space  40  allowing downward movement when removing the sacrificial glazing panel  22 A from lip L.  
         [0042]      FIG. 6  shows a slide  42  and compression spring  44  engaging the underside of the slide  42  to urge the same up to position the upper edge of the sacrificial glazing panel  22 A within an upper channel section.  
         [0043]      FIGS. 7 and 8  show an arrangement comprised of a series of removable headed plugs  46  insertable in the lip L of the lower channel  30 A. The plugs  46  may each have a stem  50  for protruding through an opening  52  and into the channel  30 A of a frame or lip to hold the sacrificial glazing panel  22 A in an up or seated position.  
         [0044]     Upon removal of the plugs  46 , the sacrificial glazing panel  22 A is lowered sufficiently to clear the lip L of the upper channel  28 A, so that upon bowing of the panel  22 A, it may be titled out of removed as described above.  
         [0045]     The glazing panels may also be shifted sideways in the frame for removal.  FIG. 9-11  show a window assembly  54  comprised of a pair of side glazing assemblies  56  and  58 , each mounted in a frame and seal assembly  64 . Each glazing assembly  56 ,  58  includes a primary glazing panel  60 A,  60 B and sacrificial glazing panel  62 A,  62 B mounted in a retainer frame as in the above described embodiments.  
         [0046]     A curved corner generally rectangular perimeter frame section  66  and a straight divider frame section  68  respectively define sacrificial glazing panel receiving channel sections  70 A,  70 B. The vertical divider channel section  70 B is deeper than the opposing perimeter channel sections  70 A to allow horizontal shifting movement of the sacrificial glazing panel  62 A,  62 B during installation and removal as described above, instead of the vertical movement described above.  
         [0047]     The divider channel section  70 B receives at least one double bowed leaf spring  72 , which may be disposed against the bottom thereof. There may be a pair of springs  72  normally position to bias one side edge of the sacrificial glazing panels  62 A,  62 B so as to be retained by the lip L of the opposite section of the perimeter channel sections  70 A in a similar fashion to the above described embodiment.  
         [0048]     Thus, in practice, sacrificial glazing panels  62 A,  62 B can be shifted sideways by compressing the double bowed leaf springs  72  to allow the side edge E to clear the lip L. Upon bowing the sacrificial glazing panels  62 A,  62 B the top and bottom edges are drawn together to clear the lip L of the top and bottom perimeter channel sections  70 A to enable tilting out and removal of the sacrificial glazing panels  62 A or  62 B. Installation may be carried out in a complementary fashion.  
         [0049]      FIGS. 12A-12B  show an arrangement of a window assembly  10  having a primary glazing  22 A supported in a frame  18  against seals  26 . The window assembly  10  has a sacrificial glazing assembly disposed adjacent to the primary glazing assembly, which as shown is connected to the frame of the primary glazing assembly. The sacrificial glazing assembly has a sacrificial glazing panel support  19 . The sacrificial glazing panel support  19  has a first channel  28 C and an opposing second channel  30 C which allows the edge B of the sacrificial glazing panel  22 C to first be inserted into the second channel  30 C and then moved sufficiently in the second channel  30 C to allow the second edge A of panel  22 C to clear the lip L of the channel section  28 C and allow the sacrificial glazing panel  22 C to be completely moved into and retained between the first and second channels  28 C and  30 C as shown in  FIG. 12B . Once the edge B of panel  22 C clears the lip L, and the edge A of panel  22 C clears the lip L, the bottom edge rests on elastomeric element  33  in the bottom of one channel but does not rest on the actual bottom surface of the channel.  
         [0050]     The insertion of the sacrificial glazing may be aided by a flexible panel and bowing of this panel. Upon release of the bowing of the glazing panel  22 C, the side edges C, D of the sacrificial glazing panel  22 C move apart to be received and retained in the associated side channels of the perimeter frame sections  24 C. In this position, the panel  22 C is supported by the elastomeric element  33  in the bottom channel  30 C, which may move up and down in response to inertia, gravitational forces and other forces experienced by the mass transit vehicle during its normal operation, but edges of panel  22 C do not touch the bottom or top surface of the channels.  
         [0051]      FIG. 13  shows an embodiment of a window assembly  10  with a primary glazing  20 A and a sacrificial glazing assembly disposed adjacent to the primary glazing. In this case the resiliently compressible positioner element includes a compressible foam elastomeric element  38 A. The compressible foam elastomeric element may be inserted into a top channel, side channel, bottom channel or any combination of the above. As shown, a compressible foam elastomeric element  38 B is inserted in a top channel  28 D and an opposing bottom channel  30 D. The foam elements  38 A and  38 B are highly compliant but resilient, and preferably fill their respective channels.  
         [0052]     The foamed elastomeric elements  38 A,  38 B are preferably made of highly compliant material, such as micro cellular polyurethane (MCU), etc. A highly compliant material is desired since the sacrificial glazing must be easily installed, yet held in place in the top channel  28 C and bottom channel  30 C. A highly compliant material is also desired since it can dampen vibrations transmitted to the glazing panel by operation of the vehicle. Alternatively, the foamed elastomeric material may be selected from fluoracarbon, highly saturated nitrile (HBNR), methyl acrylate acid polymer, silicone, EPDM, Neoprene.RTM, natural rubber, plyisoprene or any suitable thermoset elastomer or thermoplastic or optionally any other elastomeric foamed material suitable for the application, including plastomers and thermoplastics.  
         [0053]     Foamed micro cellular polyurethane is a polymer product obtained from the interaction of the die-isocyanate glycol and a blowing agent. The glycol may be a polyol that can be either the polyester or polyether type. Both types generally have hydroxyl groups that are free to react with the di-isocyanate. The isocyanate reacts with water to produce carbon dioxide gas for foaming. Foam density may be determined by the quantity of water present in the formulation and may be characterized by the weight of the polyurethane material divided by the overall volume of the part. Once intimately mixed, the ingredients are discharged from a mixer and deposited into a mold or an extruder where the complex chemical reactions take place to form the micro cellular polyurethane.  
         [0054]     The chemical reactions are primarily exo-thermic which convert the liquid into a foam. This technology is generally known in the prior art. See Rubber Technology, Third Edition, edit by the Maurice Morton-Van Norstand Reinhold, ISBN 0-422-2642204, pages 555-560, which is incorporated by reference herein. The damping characteristics of a micro cellular polyurethane foam are adjusted by the amount of gases trapped in the body of the polyurethane. Thus, the stiffness, and the vibration characteristics of the micro cellular polyurethane can be adjusted by varying MCU density to meet specific application requirements. Micro cellular polyurethane foam density varies from 0.3 to 0.8 grams per cubic centimeter. The characteristics of MCU or foamed elastomers, as compared to solid rubber, are primarily influenced by the micro cellular structure of the material and not by the chemical backbone or primary polymeric material. Due to the micro cellular nature of the MCU material, polyurethane cells will collapse on to each other under a compressing load.  
         [0055]     As stated previously, the micro cellular polyurethane has a cell like structure that includes cell unites filled with gases such as air. When the micro cellular polyurethane is compressed, the cell structures tend to collapse and push the air out of the cells. This material behavior results in a more gradual absorption of sudden load changes, hence a more gradual load absorption, as shown in  FIG. 14 .  
         [0056]     As a load on the elastomeric member increases from a no-load condition, the stiffness as shown in Segment A in  FIG. 14 , increases. With further increases in load, the stiffness flattens somewhat as shown in Segment B. This is the “soft” segment where the micro cellular cells of the MCU begin to collapse upon themselves. As the load increases even further and the cells are substantially collapsed upon themselves, the stiffness increases as shown in Segment C in  FIG. 14 . Those skilled in the art will recognize that the curve shown in  FIG. 14  is representative of the general stiffness response to load and displacement for MCU material with an MCU density of 0.3 to 0.8 per cubic centimeter.  
         [0057]     In practice, the glazing panel  22 D is inserted into the bottom channel  30 D and moved into contact with the foamed elastomeric element  38 A. The element  38 A is designed so that when the glazing panel is pressed into the foamed element  38 A, the force and weight of the panel causes the cells to collapse so as to operate in Segment C of  FIG. 14 . Panel  22 D is then moved adjacent to the lip L of the top channel  28 D. Next panel  22 D is moved into the top channel  28 C, then moved into contact with the foamed elastomeric element  38 B. After panel  22 D is pressed into the foamed element  38 A and panel  22 D is released, a biasing force from the foamed elastomeric element  38 A presses the opposite edge of panel  22 D into the foamed element  38 B so that the panel compresses the cells in the element  38 B and the foamed element  38 B operates in Segment C in  FIG. 14 . The elastomeric elements may have different elastomeric properties, such as stiffness or resiliency. For example, the bottom elastomeric element may have a greater rebound force than the upper elastomeric element. Those skilled in the art recognize that foamed elastomeric element  38 A can also be made to operate in Segment B in  FIG. 14  depending on the depth of the channel and the weight of the panel so long as the foamed elastomeric element  38 B operates in Segment C in  FIG. 14 . Thus, a simple and quick installation or removal of sacrificial glazing panels can be performed with a minimum use of tools.  
         [0058]     Claim terms should be interpreted as generally understood by one skilled in the art at the time of filing unless expressly defined otherwise. Order of steps in method claims can be done in any reasonable order and therefore should not be given significance unless specifically stated.

Summary:
Installation structure and method for installing and removing a sacrificial glazing panel. There is also disclosed a flexible sacrificial glazing panel formed of a material, sized and having a thickness to permit flexing of the panel to allow easy removal and seating of the sacrificial glazing panel within a support structure.