A convertible window system having two window sashes, a weatherstripping, and a tilt pivot assembly. The window system can be readily switched between single-hung and double-hung configuration. The weatherstripping assembly, which is operatively connected to each of the two sashes, has a number of regions. Each of these regions has different attributes which determine the types of translations and rotations that can be performed on a sash with a predetermined force. In a preferred embodiment, an upper sash can be removed from a window frame by the application of a predetermined force on the top of the sash while the sash is within a predetermined range of the weatherstripping assembly without the need for withdrawing guide pins from the channel of the weatherstripping assembly.

FIELD OF THE INVENTION 
     The present invention relates to the field of windows generally and particularly to a window that in shipment is configured as a single-hung window but may optionally be converted to a double-hung window in use. 
     BACKGROUND OF THE INVENTION 
     Various types of double-hung windows are well known. Such windows are commonly used in houses and buildings for providing increased ventilation capacity. Such windows typically include a window frame, a weatherstripping assembly, an upper sash and a lower sash. The window frame is the stationary part of the window. It typically consists of a head jamb, a window sill, side jambs, extension jambs and a blind stop. The upper and lower sashes are slidably connected within the window frame. 
     Typically, the weatherstripping assembly is attached to the window frame, and serves to form a weather-tight seal between the window frame and each of the sashes. The weatherstripping assembly additionally houses the components of the balance assembly, if a balance assembly is utilized in the window system. Springs are often used in balance assemblies to apply an upward force on a sash and reduce the amount of effort required to lift the sash. Double-hung windows generally have two window sashes, each of which can be removed or translated independently. Furthermore, there is no window system which allows a user to readily convert between a single-hung and a double-hung window configuration. 
     Tilting double-hung windows are designed to be tilted for the purpose of accessing both sides of a window sash from one side of a window frame. Typically, such window systems will have guide pins at the top of each sash. These guide pins interconnect with the weatherstripping assembly to keep the sash aligned with the window frame. In order to remove a window sash, the guide pins are retracted from the weatherstripping assembly and the upper part of the sash can then be rotated about the pivot axis. 
     Current techniques of repairing, maintaining and cleaning sashes for double-hung windows are inadequate because they do not allow for ready removal of either or both the window sashes. 
     Current techniques for shipping or transporting window systems have been developed to ship double-hung window systems. For example, some window systems utilize straps and pads to prevent translation and rotation of the individual sashes during movement. Utilizing straps costs additional time and money. 
     Current techniques for securing window sashes in a double-hung window are similarly inadequate. For example, when a window is open a limited amount, the locking mechanism can no longer provide a secure environment within the house. These and other drawbacks exist. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to overcome these and other drawbacks of known systems and techniques. 
     Another object of the present invention is to provide readily removable window sashes. 
     Another object of the present invention is to provide a window system that is readily convertible between a double-hung and a single-hung window system. 
     Another object of the present invention is to provide the security of a locked window while one or more window sashes are open. 
     Another object of the present invention is to provide the security of a locked window while one or more window sashes are open and, at the same time, comply with building code egress requirements. 
     According to one preferred embodiment, a window system is provided with two removable window sashes. These window sashes enable ready removal for replacement, maintenance or cleaning. 
     According to another preferred embodiment, a window system is provided that enables conversion between single-hung and double-hung operation. The conversion can be for purposes of shipping, for reasons desired by a building owner, or for other reasons. 
     According to another preferred embodiment, a window system is provided having an upper sash that cannot be removed until a lower sash is removed. The window system may have a weatherstripping assembly having two horizontally displaced channels. At least one of these channels may be vertically divided into four regions. In the first region, the upper sash may be held into place by a guide rail extending into a grove of the upper sash. In the second region, a normal force is preferably applied to the side of the sash to prevent unintentional rotation of the sash. In the third region, there preferably are no obstacles, thereby enabling free movement of engaging elements within the third region. In a final region, an extrusion prevents translation of engaging elements to limit the range of translation of the sash. 
     One of the highly advantageous features of the invention is due to the fact that in shipment, the convertible window assembly of the preferred embodiments has an upper sash which is securely retained in position via screws, which are inserted through holes formed in a tilt pivot assembly. This configuration eliminates the need to ship the window with additional strapping or other devices which are traditionally required to hold the window square in shipment. The provision of holding the window square in shipment not only protects the integrity of the entire window system, including the panes, it also simplifies installation. That is, the convertible window assembly of the preferred embodiment when it arrives at its ultimate destination is in a condition where it is substantially square. Consequently, the builder need only insert the window into the frame and attach the frame to the building structure with little, if any, shimming required. The convertible window assembly according to the preferred embodiments thus greatly reduces the installation time required of the builder by substantially reducing or eliminating altogether any requirement for shimming the window during installation. 
     Other objects, features and advantages of the preferred embodiments will be apparent when the detailed description of the preferred embodiments is read in conjunction with the drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of the window system in accordance with the present invention; 
     FIG. 2 shows an enlarged, perspective view of section A of FIG. 1, focusing on the tilt pivot assembly; 
     FIG. 3 shows an exploded view of the tilt pivot assembly and the components with which the tilt pivot assembly operatively interacts; 
     FIG. 4 shows a side view of the weatherstripping assembly; 
     FIG. 5 shows a cross-section of the weatherstripping assembly taken along the line  5 — 5  of FIG. 4; 
     FIG. 6 shows a cross-section of the weatherstripping assembly taken along the line  6 — 6  of FIG. 4; 
     FIG. 7 shows a cross-section of the weatherstripping assembly taken along the line  7 — 7  of FIG. 4; 
     FIG. 8 shows a cross-section of the weatherstripping assembly taken along the line  8 — 8  of FIG. 4; 
     FIG. 9 shows a perspective view of the tilt pivot pin assembly; 
     FIG. 10 shows a perspective view of the tilt pivot shoe assembly; 
     FIG. 11 shows a side view of the tilt pivot shoe assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates one embodiment of the window system  100 . Preferably, the window system  100  comprises at least a window frame  200 , an upper sash  300 , a lower sash  400 , and a tilt pivot assembly  500  (shown in FIG.  2 ). The upper sash  300  and the lower sash  400  are generally contained within the window frame  200 . Window frame  200  may be attached to a wall of a building or other structure by means that are well known in the art. 
     With reference to FIG. 2, which is an enlarged view of section A from FIG. 1, the tilt pivot assembly  500  is preferably operatively associated with the upper sash  300 . The weatherstripping assembly  220  operatively engages with the tilt pivot assembly  500 . In a preferred embodiment, the weatherstripping assembly forms an upper sash track  222  which restrains the tilt pivot assembly  500  to moving in a vertical direction upon removal of retaining screw  523 , as described in more detail below. The tilt pivot assembly  500  may comprise a tilt pivot pin assembly  520 , and a tilt pivot shoe assembly  510 , as described in more detail below. 
     FIG. 3 is an exploded view of section A from FIG.  1 . Window jamb  210  preferably includes an inside tilt stop  212  and a blind stop  214 . Stops  212  and  214  preferably have retaining fins  213  and  215 , respectively, for securing the weatherstripping assembly  220  to the window frame  200 . In use, weatherstripping assembly  220  may form a weather-tight seal between the upper sash  300  and the window frame  200 . Weatherstripping assembly  220  may optionally house the tilt pivot shoe bracket  511  and the upper spring  236 . The upper spring  236  is preferably attached to the pivot shoe bracket  511 , which in turn operatively engages the tilt pivot pin assembly  520 . Because the tilt pivot pin assembly  520  is operatively attached to the upper sash  300  in a preferred embodiment, the upper spring  236  and pivot shoe bracket  511  may serve as a balance assembly for the upper sash  300 , as is well known in the art. 
     As best seen in FIG. 9 in conjunction with FIG. 3, the tilt pivot pin assembly  520  may include a pivot pin base plate  527  which attaches to a side of a lower rail  303  of the top sash  300 . Assembly  520  also includes a pivot pin support fin  525  formed integrally with the pivot pin base plate  527 . Support fin  525  is adapted to extend along the bottom of the lower rail  303  of the top sash  300 . Additionally, the tilt pivot pin assembly  520  may include a cylindrical engaging element  524  extending from an opposite side of the pivot pin base plate  527  with respect to the pivot pin support fin  525 . Engaging element  524  preferably has an engaging element hole  526 , and a retaining screw  523  (FIG. 3) which is removably inserted through the engaging element hole  526 . In use, the retaining screw  523  is preferably secured through the weatherstripping assembly  220 , and into the window jamb  210 . 
     FIGS. 10 and 11 illustrate a preferred form of the tilt pivot shoe assembly  510 . The tilt pivot shoe assembly  510  may include a pivot shoe bracket  511 , a first and second bracket strut  514  and  515 , and a first and second engaging element retaining fin  512  and  513 , respectively. The tilt pivot shoe assembly  510  preferably has a generally U-shaped configuration. The first retaining fin  512  may additionally have a spring notch  517 , a spring notch support flange  518 , and a spring notch base plate  519  for connecting the tilt pivot shoe bracket  511  to the upper sash spring  236  (FIG.  3 ). 
     Referring again to FIG. 3, in use the cylindrical engaging element  524  operatively engages the pivot shoe bracket  511 . Retaining screw  523  may be secured through the engaging element hole  526  (FIG. 9) and secured to the window jamb  210  through the weatherstripping assembly  220 . A series of retaining screw retaining holes (not shown) can also be used to allow the position of a sash to be indexed to any desired location. The retaining screw retaining hole can be reinforced to withstand repeated insertions and extractions of the retaining screw  523 . Instead of using a retaining screw  523 , any suitable method of operatively engaging the cylindrical engaging element  524  to the window frame  200  can be used. For example, the engaging element could be provided with extendible guide pins or any other retractable pins. 
     Although the preferred embodiment is shown as having cylindrical engaging elements  523  with retaining screws  524  only on the upper sash, the invention is not limited to this configuration, as the tilt pivot assembly  500  could be applied to both the upper and lower sashes. Additionally, this invention could utilize removable guide pins instead of retaining screws  523 . Such a configuration would enable, for example, use of readily removable guide pins in conjunction with modified retaining screws. The modified retaining screws could have non-standard exposed faces, requiring a key tool such as an Allen wrench to insert or extract them. For example, if the objective is to provide an open sash for ventilation while maintaining a secure environment, a designer could select modified retaining screws for the externally exposed engaging elements and utilize readily adjustable extendible guide pins on an engaging element that is not accessible from outside the premises. Such a configuration would allow for ventilation and security, and could be configured to satisfy various egress building code requirements. 
     When the retaining screw  523  is not utilized, the tilt pivot shoe assembly  510  may be used as a balance in conjunction with upper sash spring  236 , as is well known in the art. The weatherstripping  220  preferably serves as a balance housing for the upper sash  300  and the lower sash  400 . The weatherstripping  220  may have two main structural elements, an upper sash weatherstripping assembly  221  and a lower sash weatherstripping assembly  225 . The upper and lower sash weatherstripping assemblies  221  and  225  generally have three sides, forming a substantially box U-shape. At the terminal points of the upper sash weatherstripping assembly  221  are the exterior and interior upper pivot shoe bracket retaining fins  223  and  224 , respectively (FIG.  3 ). The pivot shoe bracket retaining fins  223 ,  224  retain the pivot shoe bracket  511  within the confines of the weatherstripping assembly  220 . 
     With reference to FIG. 4, the weatherstripping assembly  220  preferably has at least four different cross sections/regions on the upper sash track  222 . Each of these different cross sections is depicted in FIGS. 5-8. The upper sash  300  preferably can be translated vertically between a first and second position. The first position is the uppermost position of the upper sash  300  in the window frame  200 , defined by contact between the top rail of the upper sash  302  (FIG. 1) and the window frame  200 . The second position is the lowermost position of the upper sash  300 , defined by contact between the cylindrical engaging element  524  fixedly attached to the upper sash  300  and a stopping extrusion  233  (FIG. 8) integrally formed on the weatherstripping assembly  220 , as discussed in more detail below. 
     A preferred embodiment of the first region, or the “retaining” region, is depicted in FIG.  5 . This region preferably includes a retaining extrusion  231 . Retaining extrusion  231  can operatively engage with the upper sash  300  to prevent pivoting of the upper sash  300  while any portion of the upper sash  300  is contiguous with, or, in other words, above the lowest portion of the retaining extrusion  231 . For example, the retaining extrusion  231  could fit within a channel along the side of the upper sash  300 . Although the upper retaining mechanism is depicted as an extrusion in one embodiment, the use of any mechanism that will operatively retain the upper sash  300  in the weatherstripping assembly  220  in the upper portion of a window frame  200  is contemplated. For example, it is possible to use an extrusion attached to the upper sash  300  that can fit within a channel of the weatherstripping assembly  220 . 
     A preferred embodiment of the second region, or the “resistance” region, is depicted in FIG.  6 . At least in the resistance region, it is preferable to have a extrusion that prevents the upper sash  300  from rotating to the exterior of the building when a predetermined force is applied to the upper sash top rail  302 . In a preferred embodiment, the exterior sash retaining rail  234  extends along the entire vertical length of each side of the weatherstripping assembly  220 . The resistance region can have a resistance extrusion  232  which creates a frictional force opposing motion when force is applied to the upper sash top rail  302  in an inward direction. Although a predetermined force will be sufficient to overcome the friction force of the resistance extrusion  232 , the upper sash  300  preferably will not rotate out of the window frame  200  without the application of a predetermined force. 
     A preferred embodiment of the third region, or “free” region, is depicted in FIG.  7 . The free region preferably has an upper sash track  222  free of extrusions. The cylindrical engaging element  524  of tilt pivot pin assembly  520  may be inserted into the gap between the interior and exterior pivot shoe bracket retaining fins  223  and  224 . A pivot shoe bracket  511  is preferably inserted into the upper sash track  222  and retained by the interior and exterior pivot shoe bracket retaining fins  223  and  224 . An upper sash spring  236  may be operatively connected between the pivot shoe bracket  511  and the top of weatherstripping assembly  220 . Additionally, the cylindrical engaging element  524  may be operatively interconnected with the pivot shoe bracket  511  in order to provide a balance to the upper sash  300 , as is well known in the art. 
     A preferred embodiment of the fourth region, or “stopping” region, is depicted in FIG.  8 . The stopping region preferably has a stopping extrusion  233  that prevents the cylindrical engaging element  524  from translating below the top of the stopping extrusion  233 . 
     The preferred embodiment enables removal of the upper sash  300  without the use of retaining pins on the upper rail  302  of the upper sash  300 . In the preferred embodiment, the lower sash  400  must be removed in order for the upper sash  300  to be removed. As stated previously, the exterior sash retaining rail  234  preferably prevents the upper sash  300  from rotating to the outside of the premises. While the upper sash  300  is in the first position, or upper position, the upper sash  300  is operatively engaged by the retaining extrusion  231  to prevent rotation of the upper sash  300  into a first rotation position. While the upper sash  300  is in the second position, or lower position, the lower sash top rail  402  preferably contacts the side rails of the upper sash to prevent rotation of the upper sash  300  into the first position. Because the upper sash  300  preferably cannot rotate, the upper sash  300  cannot be removed while lower sash  400  is operatively engaged by the weatherstripping assembly  220 . 
     Referring now to FIGS. 1 and 4, a preferred process of removing the upper sash  300  and the lower sash  400  from the window frame will be disclosed. First, the lower window sash  400  is removed. This process may involve the withdrawal of retaining pins also known as tilt latches (not shown) from the lower sash track  226 . The lower sash  400  can then be rotated inward while the lower engaging elements (not shown) are still operatively engaged by the weatherstripping assembly  220 . The lower sash  400  is preferably rotated approximately 90 degrees to a first rotation position. Once in a first rotation position, the lower sash  400  can be rotated about a second axis of rotation. This second axis of rotation is perpendicular to the first axis of rotation, and it lies on the same plane as the lower sash  400  while the lower sash  400  is in the first rotation position. Rotation about this second axis of rotation releases the lower sash  400  engaging elements (not shown) from the lower pivot shoe bracket  530  (FIG.  4 ). 
     Upon removal of the lower sash  400 , the upper sash  300  is preferably translated into the second or lowermost position, described previously. Once in the second position, the upper portion of the upper sash  300  operatively engages the resistance extrusion  232  of the weatherstripping assembly  220 . Then, upon application of a predetermined force at the upper portion of the upper sash  300  in an inward direction, the upper sash  300  may rotate about a first axis to a first rotation position. The first axis is defined by a line connecting the cylindrical engaging elements  524  on the left and right side of the bottom rail  303  of the upper sash  300 . 
     The upper sash  300  is preferably rotated approximately 90 degrees to a first rotation position. Once in a first rotation position, the upper sash  300  can be rotated about a second axis of rotation. This second axis of rotation is perpendicular to the first axis of rotation, and lies on the same plane as the upper sash  300  while the upper sash is in a first rotation position. Rotation about the second axis of rotation preferably releases the cylindrical engaging elements  524  of the upper sash  300  from the pivot shoe brackets  511 . 
     Although the present invention has been described in relation to a preferred embodiment, it is understood that the disclosure is illustrative. The descriptions provided in the disclosure should not be construed to limit any aspect of the present invention. Those skilled in the art will recognize additional embodiments and applications of the present invention. Accordingly, the present invention is limited only to the extent of the following claims.