Abstract:
A counterbalance system for a tilt-in window and its associated method of operation. The system uses wound spring elements to provide a counterbalancing force to the sashes of the window. The wound springs are configured to define open central regions. Hubs are attached to tilt posts that extend from the sashes of the window. The hubs extend into the open central regions of the wound springs, thereby supporting the wound springs within the frame of the window. A brake structure is disposed between the wound springs and the tilt posts. The brake structure creates multiple braking actions. First, the brake structure itself creates an interference fit within the frame of the window as the sashes tilt. Second, the brake structure displaces the wound spring and causes the wound spring to press against the frame of the window as the sashes tilt.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   In general, the present invention relates to counterbalance systems for windows that prevent open window sashes from closing under the force of their own weight. More particularly, the present invention system relates to counterbalance systems for tilt-in windows that use curl springs to create a counterbalancing force. 
   2. Description of the Prior Art 
   There are many types and styles of windows. One of the most common types of windows is the double-hung window. A double-hung window is the most common window found in traditional home construction. A double-hung window consists of an upper window sash and a lower window sash. Either the upper window sash or the lower window sash can be selectively opened and closed by a person sliding the sash up and down within the window frame. 
   A popular variation of the double-hung window is the tilt-in double-hung window. Tilt-in double-hung windows have sashes that can be selectively moved up and down. However, the sashes can also be selectively tilted into the home so that the exterior of the sashes can be cleaned from within the home. 
   The sash of double-hung windows has a weight that depends upon the materials used to make that window sash and the size of the window sash. Since the sashes of a double-hung window are free to move up and down in the frame of a window, some counterbalancing system must be used to prevent the window sashes from always moving to the bottom of the window frame under the force of their own weight. 
   For many years counterbalance weights were hung next to the window frame in weight wells. The weights were attached to the window sash using a string or chain that passed over a pulley at the top of the window frame. The weights counterbalanced the weight of the window sashes. As such, when the sashes were moved in the window frame they had a neutral weight and friction would hold them in place. 
   The use of weight wells prevents insulation from being packed tightly around a window frame. Furthermore, the use of counterbalance weights on chains or strings cannot be adapted well to tilt-in double-hung windows. Accordingly, as tilt-in windows were being developed, alternative counterbalance systems were developed that were contained within the confines of the window frame and did not interfere with the tilt action of the tilt-in windows. 
   Modern tilt-in double-hung windows are primarily manufactured in one of two ways. There are vinyl frame windows and wooden frame windows. In the window manufacturing industry, different types of counterbalance systems are traditionally used for vinyl frame windows and wooden frame windows. The present invention is mainly concerned with the structure of vinyl framed windows. As such, the prior art concerning vinyl framed windows is herein addressed. 
   Vinyl framed, tilt-in, double-hung windows are typically manufactured with tracks along the inside of the window frame. Brake shoe mechanisms, commonly known as “shoes” in the window industry, are placed in the tracks and ride up and down within the tracks. Each sash of the window has two tilt pins or tilt posts that extend into the shoes and cause the shoes to ride up and down in the tracks as the window sashes are opened or closed. 
   The shoes serve two purposes. First, the shoes contain a brake mechanism that is activated when a window sash is tilted inwardly away from the window frame. The shoe therefore locks the base of the sash in place and prevents the base of the sash from moving up or down in the window frame once the sash is titled open. Second, the shoes support curl springs. Curl springs are constant force coil springs that supply a constant retraction force when unwound. Traditionally, curl springs are placed within the shoe in the same way a metal tape is placed within the housing of a tape measure. One end of the curl spring is anchored to the frame of the window while the main body of the curl spring is wound inside of the shoe. As the shoes move within the tracks, the curl spring rotates inside the shoe. Often as the curl spring rotates in the shoe, the curl spring moves around within the confines of the shoe and makes an undesirable noise. 
   Single curl springs are used on windows with light sashes. Multiple curl springs are used on windows with heavy sashes. The curl springs provide the counterbalance force to the window sashes needed to maintain the sashes in place. The counterbalance force of the curl springs is transferred to the window sashes through the structure of the shoes. 
   Prior art shoes that contain braking mechanisms and support counterbalance curl springs are exemplified by U.S. Pat. No. 6,378,169 to Batten, entitled Mounting Arrangement For Constant Force Spring Balance; U.S. Pat. No. 5,463,793 to Westfall, entitled Sash Shoe System For Curl Spring Window Balance; and U.S. Pat. No. 5,353,548 to Westfall, entitled Curl Spring Shoe Based Window Balance System. 
   Prior art “shoes” for curl spring counterbalance systems are complex assemblies. The shoes must contain a brake mechanism strong enough to lock a sash in place. Furthermore, the shoes must engage and retain the end of at least one strong curl spring. Prior art shoes are always in contact with the tracks on the sides of the window frame. Accordingly, as wear, dirt and grime accumulate over time, it often becomes more difficult for the shoes to move up and down. The “shoe” of a window assembly is therefore the first part of a window assembly to fail and require replacement. A shoe can fail either by failing to smoothly move within the window frame track or by failing to lock in place when a window sash is tilted open. 
   Another disadvantage of prior art shoes is that the shoes take space in the tracks on the side of the window sashes. Accordingly, the window sash cannot be fully opened to the top of the window track because of the physical presence of the shoes. Building codes exist that define the minimal size of a window opening in many applications. The minimal size opening is required so that people can pass through the open window in case of an emergency. Accordingly, due to the presence of prior art shoes, windows that have sashes that are larger than building code requirements may not be able to open to a size that meets the building code requirement. 
   A need therefore exists in the field of vinyl, tilt-in, double-hung windows, for a counterbalance system that eliminates the need for shoes. As such, window assemblies can be made more reliable, less noisy, less expensive and with larger effective openings. This need is met by the present invention as described and claimed below. 
   SUMMARY OF THE INVENTION 
   The present invention is a counterbalance system for a tilt-in window and its associated method of operation. The system uses wound spring elements to provide a counterbalancing force to the sashes of the window. The wound springs are configured to define open central regions. Hubs are attached to tilt posts that extend from the sashes of the window. The hubs extend into the open central regions of the wound springs, thereby supporting the wound springs within the frame of the window. A brake structure is disposed between the wound springs and the tilt posts. The brake structure automatically locks the tilt posts into fixed positions as the sashes of the tilt-in window are tilted inwardly. The brake structure creates two braking actions. First, the brake structure itself creates an interference fit within the frame of the window as the sashes tilt. Second, the brake structure displaces the wound spring and causes the wound spring to press against the frame of the window as the sashes tilt. The two separate braking actions create a strong and effective brake for the tilt posts of the sashes without the use of traditional window brake shoe assemblies. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is made to the following description of an exemplary embodiment thereof, considered in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a partially fragmented view of a window assembly in accordance with the present invention; 
       FIG. 1A  is an enlarged view of the section of  FIG. 1  contained within circle  1 A; 
       FIG. 2  is a perspective, exploded view of the counterbalance system shown in  FIG. 1 ; 
       FIG. 3  is a perspective view of an exemplary embodiment of the brake head component of the counterbalance system; 
       FIG. 4A  is a side view of the counterbalance system in a window frame track; 
       FIG. 4B  is a front view of the counterbalance system shown in  FIG. 4A ; 
       FIG. 5A  is a side view of the counterbalance system in a window frame track; and 
       FIG. 5B  is a front view of the counterbalance system shown in FIG.  5 A. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , there is shown an exemplary embodiment of a vinyl, tilt-in, double-hung window assembly  10 . The window assembly  10  has an upper sash  11  and a lower sash  12 . The upper sash  11  and the lower sash  12  are contained within a window frame  14 . The window frame  14  has two vertical sides  16  that extend along the sides of both sashes  11 ,  12 . Within each of the vertical sides  16  of the window frame  14  is formed a track  18 . 
   A tilt post  20  extends outwardly from either side of the base of each sash  11 ,  12 . The tilt posts  20  extend into the tracks  18  in the vertical sides  16  of the window frame  14 . As is later explained in greater detail, a brake head  22  is disposed at the tip of the tilt post  20  within the track  18 . The brake head  22  serves two purposes. First, the brake head  22  serves as a brake mechanism that locks the tilt post  20  in place within the track  18  when a sash  11 ,  12  is tilted inwardly. Second, the brake head  22  serves as a hub for a curl spring  24 , wherein a curl spring  24  passes around the brake head  22 . 
   The curl spring  24  rotates about the brake head  22 . The free end of the curl spring  24  is affixed to the window frame  14  higher along the track  18 . Accordingly, the curl spring  24  applies an upward counterbalance force to the tilt post  20  that counteracts the weight of the sash  12 . 
   Referring to  FIG. 1A  in conjunction with  FIG. 1 , it can be seen that a tilt post  20  extends outwardly from either side of the base of each sash  11 ,  12 . The tilt posts  20  extend into the tracks  18  in the vertical sides  16  of the window frame  14 . As is later explained in greater detail, a brake head  22  is disposed at the tip of the tilt post  20  within the track  18 . The brake head  22  serves two purposes. First, the brake head  22  serves as a brake mechanism that locks the tilt post  20  in place within the track  18  when a sash  11 ,  12  is tilted inwardly. Second, the brake head  22  serves as a hub for a curl spring  24 , wherein a curl spring  24  passes around the brake head  22 . 
   Referring to  FIG. 2 , it can be seen that the tilt post  20  is a metal post that is mounted directly to the window sash  12 . The tilt post has a non-circular cross-section. In the shown embodiment, the tilt post  20  has a rectangular cross-sectional shape. However, this is only exemplary and it should be understood that other non-circular shapes can be used. 
   The brake head  22  is a structure that passes over the end of the tilt post  20 . A recess (shown in  FIG. 3 ) is provided in the tip of the brake head  22 . The recess is shaped to receive the tip of the tilt post  20 . The tip of the tilt post  20  passes into the recess in the brake head  22 . As a result, once the brake head  22  passes into the tilt post  20 , a keyed connection occurs and the brake head  22  cannot be rotated without the rotation of the entire tilt post  20 . 
   The brake head  22  is a structure that includes flanges  30  and a cylindrical hub  32  that extends behind the flanges  30 . The purpose and function of the flanges  30  is later explained. The cylindrical hub  32  is sized to pass into an annular spring bearing  34 . As such, the annular spring bearing  34  is free to rotate around the cylindrical hub  32  of the brake head  22 . The spring bearing  34  passes into the center of a standard window curl spring  24 . The spring bearing  34  may be slotted so that the spring bearing  34  can be momentarily compressed when inserted into the center of the curl spring  24 . Once inserted into the center of the curl spring  24 , the spring bearing  34  expands so that no space exists between the exterior of the spring bearing  34  and the interior of the curl spring  24 . 
   In the embodiment of  FIG. 2 , it can be seen that the tilt post  20  and the brake head  22  are manufactured as separate elements that are assembled together. It will be understood that such a manufacturing method is merely exemplary and that the tilt post  20  and brake head  22  can be manufactured as a single piece. For example, the brake head  22  and tilt post  20  can be cast or machined as a single metal piece. Alternatively, a plastic brake head can be molded around a metal tilt post, thereby creating one inseparable assembly. The two piece assembly illustrated in  FIG. 2  is used because it is considered the lowest cost method of producing the brake head/tilt post assembly. 
   Referring to  FIG. 3 , it can be seen that the brake head  22  has a complex shape. The cylindrical hub  32  of the brake head  22  comprises the majority of the brake head  22 . However, flanges  30  radially extend from the cylindrical hub  32  at one end of the cylindrical hub  32 . The flanges  30  extend above and below the cylindrical hub  32 . No flanges  30  extend from the sides of the cylindrical hub  32 . As a result, the flanges  30  combine to provide the brake head  22  with an elongated configuration at one end of the cylindrical hub  32 . 
   The flanges  30  above and below the cylindrical hub  32  have a stepped structure. Each of the flanges  30  have a distal edge  36  at their tip and a second edge  38  interposed between the distal edge  36  and the center of the hub  32 . The flanges  30  have a first thickness near the distal edge  36 . Further down from each distal edge  36  is a step that forms the second edge  38 . Accordingly, below the second edge  38 , the flanges  30  are thicker and lay flush with the front end of the cylindrical hub  32 . However, above the second edges  38 , the flanges  30  are recessed. The flanges  30  are further thinned near the distal edges  36  by the presence of a bevel  37  that leads to the distal edge  36 . 
   Referring now to  FIGS. 4A and 4B , it can be seen that the track  18  in each side of the window frame is accessible through a long slot  40  that runs along the length of the window frame. When the window sash  12  ( FIG. 1 ) is not tilted, the tilt post  20  orients the brake head  22  in the track  18  so that the flanges  30  on the brake head  22  do not engage the window track  18  or the slot  40  at any point. The brake head  22  is therefore free to move up and down along the length of the track  18  without touching the track  18 . The brake head  22  supports the spring bearing  34  ( FIG. 2 ) in the center of the curl spring  24 . Accordingly, as the brake head  22  moves up and down in the track  18 , the curl spring  24  is moved up and down in the track  18 , wherein the curl spring  24  either winds or unwinds depending upon the direction of movement. However, the curl spring  24  is not confined within a shoe, and the only movement of the curl spring  24  is its rotation around the brake head  22 . As such, each curl springs  24  is prevented from making contact noise as it winds and unwinds. 
   It will be understood that when the sash  12  ( FIG. 2 ) of the window is closed, the brake head  22  and the curl spring  24  are both free to move in the track  18 . This allows the window sash  12  ( FIG. 2 ) to move up and down unencumbered in the window frame. 
   Referring to  FIGS. 5A and 5B , it can be seen that when the sash of the window is tilted forward, the tilt post  20  rotates. This causes the brake head  22  to rotate in the track  18 . As the brake head  22  rotates in the track  18 , two simultaneous braking actions occur that lock the brake head  22  in place within the track  18 . The first braking action is caused by the flanges  30  that extend from the brake head  22 . As the brake head  22  rotates, the flanges  30  rotate towards 90 degrees within the confines of the track  18 . The second edges  38  of the flanges  30  rotate within the slot opening  40 . The distal edges  36  of the flanges  30  rotate into the track  18  just behind the slot opening  40 . The bevel  37  leading to the distal edges  36  of the flanges  30  prevent the distal edges  36  from catching on the open edges of the slot  40  as the flanges  30  rotate past these edges. As the flanges  30  rotate toward 90 degrees, contact occurs between the flanges  30  and the track  18  at two different points. As the distal edges  36  of the flanges  30  rotate, they contact the interior of the track  18 , causing an interference fit. Simultaneously, the second edges  38  rotate and contact the open edges of the slot  40 . This also causes an interference fit. Consequently, as the brake head  22  rotates, an interference occurs between the structure of the track  18  and both the distal edges  36  and the second edges  38  of the flanges  30 . This wedges the brake head  22  in place and prevents the brake head  22  from being moved in the track  18 . 
   As the brake head  22  is being rotated in the track  18  to cause an interference fit, yet another braking action is occurring. As the brake head  22  rotates in the track  18 , the distal edges  36  of the flanges  30  enter the inside of the track  18 . Due to the thickness of the flanges  30 , the cylindrical hub  32  is driven farther into the track  18  as the distal edges  36  of the flange  30  rotate into the inside of the track  18 . 
   The cylindrical hub  32  supports the curl spring  24  within the track  18 . As the cylindrical hub  32  is driven farther into the interior of the track  18  by the entrance of the flanges  30  into the track  18 , the curl spring  24  is driven further into the interior of the track  18 . The brake head  22  is sized so that as the flanges  30  turn into the track  18 , the curl spring  24  becomes compressed between the rear wall  46  of the track  18  and the flanges  30  on the brake head  22 . The combined width of the curl spring  24  and the flanges  30  of the brake head  22  in the track  18  is wider than the track  18 . Thus, an interference fit is created when the brake head  22  is rotated and the flanges  30  enter the track  18 . The interference fit biases the curl spring  24  against the rear wall  46  of the track  18 . This prevents the curl spring  24  from moving in the track  18 . The abutment against the rear wall  46  of the track  18  also hinders the curl spring  24  from winding or unwinding. 
   Accordingly, when the brake head  22  is rotated from the free moving orientation of  FIG. 4A  into the locked position of  FIG. 5A , multiple locking actions occur. The flanges  30  of the brake head  22  contact the interior of the track and the edges of the slot in the track  18 , thereby locking the brake head  22  in place. Furthermore, the brake head  22  biases the curl spring  24  against the rear wall  46  of the track  18 , thereby locking the curl spring  24  in place. The combined locking actions create a very strong overall locking mechanism that prevents the tilt post  20  from moving within the window track  18  once the window sash  12  ( FIG. 1 ) is titled. 
   From the description of the function of the brake head  22 , it will be understood that the brake head  22  itself is a solid object with no moving parts. The brake head  22  is attached to the tilt post  20  and rotates with the tilt post  20 . When in a first orientation, the brake head  22  moves freely in the track  18  of the window. When rotated, the brake head  22  creates multiple interferences with both the structure of the track  18  and the curl spring  24  in the track. However, since the brake head  22  itself is a solid, one-piece structure with no moving parts, it is highly reliable and resists wear much better than prior art brake shoes that contain complex moving brake assemblies. 
   It will be understood that the embodiments of the present invention counterbalance system that are described and illustrated herein are merely exemplary and a person skilled in the art can make many variations to the embodiment shown without departing from the scope of the present invention. All such variations, modifications and alternate embodiments are intended to be included within the scope of the present invention as defined by the appended claims.