Abstract:
A counterbalance system for a tilt-in window and its method of operation. Posts are provided on the sides of a tilt-in window sash that rotate when the sash is tilted. A brake structure is attached to each post. Each brake structure has a first contoured surface that rotates with the post when said sash is tilted. A second contoured surface is provided within the window track. The second contoured surface moves up and down in the track with the post but does not rotate with the post when the sash is tilted. When the window sash is tilted for cleaning, the first contoured surface moves against the second contoured surface within the window track. A cam action occurs that moves the first contoured surface away from the second contoured surface. This causes the brake structure to be biased against the track and lock in a fixed position within the track.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 11/072,122, entitled ROUNDED SHOE AND POSITION BRAKE ASSEMBLY FOR THE COUNTERBALANCE SYSTEM OF A TILT-IN WINDOW, filed Mar. 7, 2005 now U.S. Pat. No. 7,966,770. 
    
    
     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 moving under the force of their own weight. More particularly, the present invention system relates to the brake shoe component of the counterbalance systems for tilt-in windows. 
     2. Description of the Prior Art 
     There are many types and styles of windows. One of the most common types of window is the double-hung window. Double-hung windows are the window of choice for most 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. Additionally, the sashes can be selectively tilted into the home so that the exterior of the sashes can be cleaned from within the home. 
     The sash of a double-hung window has a weight that depends upon the materials used to make the window sash and the size of the window sash. Since the sashes of a double-hung window are free to move up and down within 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, however, 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 for wooden frame windows. The present invention is mainly concerned with the structure of vinyl frame windows. As such, the prior art concerning vinyl frame windows is herein addressed. 
     Vinyl frame, tilt-in, double-hung windows are typically manufactured with guide tracks along the inside of the window frame. Brake shoe assemblies, commonly known as “shoes” in the window industry, are placed in the guide tracks and ride up and down within the guide 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 guide tracks as the window sashes are opened or closed. 
     In prior art counterbalance systems, the shoes serve more than one purpose. The shoes contain a brake mechanism that is activated by the tilt post of the window sash when the window sash is tilted inwardly away from the window frame. The shoe therefore locks the tilt post in place and prevents the base of the sash from moving up or down in the window frame once the sash is tilted open. Second, the shoes engage curl springs. Curl springs are constant force coil springs that supply the counterbalance force to the weight of the window sash. 
     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 and the tilt posts that extend from the window sash into the shoes. 
     Prior art shoes that contain braking mechanisms and engage 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 typically complex assemblies. The shoes must contain a brake mechanism strong enough to lock a sash in place. Furthermore, the shoes must engage at least one strong curl spring. In modern tilt-in window construction, curl springs are made from flat bands of spring steel that are rolled into tight coils. The ends of the curl springs typically attach to the brake shoes at an off-center point. As a result, although the curl springs bias the brake shoes upwardly in the window frame track, the curl springs also apply a torque force to the brake shoes. The torque force tends to cock or rotate the brake shoe within the window track. The shoe binds in the guide track and the window becomes so difficult to open and close that it cannot be considered functional. This cocked orientation also causes the brake shoe to wear against the window track in an uneven manner. Over time, it often becomes more difficult for the oddly worn shoes to move up and down. 
     A need therefore exists in the field of vinyl, tilt-in, double-hung windows, for a counterbalance system that eliminates the uneven wear of brake shoes caused by the spring torque. A need also exists in the field of vinyl, tilt-in double-hung windows for a counterbalance system that provides inexpensive, easily installed brake shoes that are highly reliable. These needs are met by the present invention as described and claimed below. 
     SUMMARY OF THE INVENTION 
     The present invention is a brake shoe assembly used within a counterbalance system for a tilt-in window. The brake shoe assemblies ride in guide tracks within the frame of the window along the sides of the window sashes. Tilt posts extend from the sashes into the brake shoe assemblies, wherein the brake shoe assemblies guide the movement of the tilt posts up and down in the guide tracks. 
     The brake shoe assemblies have housings with opposing face sections and rear sections that are disposed within a periphery of a first curved side edge, a second curved side edge and a bottom edge. The brake shoe attaches to a coil spring that cocks the brake shoe in the guide track. The first curved side edge and the second curved side edge contact the guide track at a tangent when the brake housing is cocked. The tangential contact minimizes wear and prevents the brake shoe housing from binding. 
     The brake shoe assemblies also contain an internal brake mechanism that acts to spread the face section of the brake shoe housing from the rear section along at least one edge when the sash of the window is tilted. As the brake shoe housing is spread apart, it interferes with the guide track and becomes locked in place until the window sash is tilted upright to its operational position. 
    
    
     
       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 tilt-in window assembly containing a counterbalance system in accordance with the present invention; 
         FIG. 2  is an enlarged view of the encircled area of the brake shoe assembly contained within  FIG. 1 ; 
         FIG. 3  is a side view of an exemplary embodiment of a brake shoe assembly; 
         FIG. 4  is a side view of the exemplary embodiment of a brake shoe assembly shown in a guide track; 
         FIG. 5  is the same view as  FIG. 4 , with the brake shoe assembly being shown cocked by a curl spring; 
         FIG. 6  is a cross-sectional view of the brake shoe assembly shown in a free position, viewed along section line  6  of  FIG. 5 ; and 
         FIG. 7  is a cross-sectional view of the brake shoe assembly shown in a locked position, viewed along section line  6  of  FIG. 5 . 
     
    
    
     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 two sashes  11 , which include an upper sash and a lower sash. Each of the sashes  11  has two side elements  17 . The sashes  11  are contained within a window frame  14 . The window frame  14  has two vertical sides  16  that extend along the side elements  17  of both sashes  11 . Within each of the vertical sides  16  of the window frame  14  is formed a guide track  18 . 
     Referring to  FIG. 2 , it can be seen that the sash  11  has a tilt post  21  that extends out away from the side of the sash  11  and into the guide tracks  18  in the vertical sides  16  of the window frame  14 . As is later explained in greater detail, a brake shoe assembly  22  is provided that attaches to the tilt post  21 . The brake shoe assembly  22  serves two purposes. First, the brake shoe assembly  22  serves as a brake mechanism that locks the bottom of a sash  11  in place within the guide track  18  when a sash  11  is tilted inwardly. Second, the brake shoe assembly  22  serves as a point of attachment for a curl spring  24 . 
     The curl spring  24  rotates and unwinds from a hub that is anchored high in the guide track  18 . The free end of the curl spring  24  is affixed to the brake shoe assembly  22 . Accordingly, the curl spring  24  applies an upward counterbalance force to each sash  11  that counteracts the weight of each sash  11 . 
     Referring to  FIG. 3 , it can be seen that the brake shoe assembly  22  has a uniquely shaped housing  26 . The brake shoe housing  26  has a face surface  27  and a opposite rear surface (not shown). The housing  26  has a straight bottom edge  29 . The bottom edge  29  has a length L 1 . Two curved side edges  30 ,  31  extend upwardly from opposite sides of the bottom edge  29 . The first curved side edge  30  and the second curved side edge curve toward one another, thereby providing the housing  26  of the brake shoe  22  with curved sides and a curved top. 
     The first and second curved side edges  30 ,  31  of the brake shoe housing  26  have complex curvatures. Both the first curved side edge  30  and the second curved side edge  31  have upper sections and lower sections of dissimilar curvature. The lower section  33  of the first curved side edge  30  and the lower section  35  of the second curved side edge  31  both share the same mild radius of curvature, wherein the radius of curvature is greater than two inches. However, the upper section  37  of the first curved side surface  30  and the upper section  39  of the second curved side surface  31  both have a tighter radius of curvature, wherein the radius of curvature is less than one inch. The radius of curvature for the upper section  37  of the first curved side edge  30  is about double that of the radius of curvature for the upper section  39  of the second curved side edge  31 . As a consequence, the upper section  37  of the first curved side edge  30  curves less than the upper section  39  of the second curved side edge  31  and terminates at a height that is higher than the height of the second side edge  31 . 
     On the first curved side edge  30 , the lower section  33  and the upper section  37  meet at a curve transition point P 1 . Likewise, on the second curved side edge  31 , the lower section  35  and the upper section  39  meet at a curve transition point P 2 . The distance D 1  between the first curve transition point P 1  and the second curve transition point P 2  is the widest part of the brake shoe housing  26 , being at least five percent longer than the length L 1  of the bottom edge  29 . 
     A spring attachment slot  42  is formed in the brake shoe housing  26 . The spring attachment slot  42  separates the upper section  37  of the first curved side edge  30  from the upper section  39  of the second curved side edge  31 . The slot  42  has an enlarged opening  43  at its distal end. The shape of the slot  42  and its enlarged opening  43  creates a large hook projection  45 . 
     Referring to  FIG. 4  in conjunction with  FIG. 3 , the brake shoe  22  is shown inside the guide track  18  of the window frame. The guide track  18  has two opposing vertical walls  48 . The distance D 2  between two opposing vertical walls  48  is only slightly greater than the distance D 1  between the curve transition points P 1 , P 2 . 
     The curl spring  24  is attached to the brake shoe  22  within the guide track  18 . The curl spring  24  is essentially a two-dimensional ribbon having a wide face surface and a very narrow side edge. The curl spring  24  is oriented so that the face surface of the curl spring  24  lay at a perpendicular to the rear wall of the guide track  18  between the two opposing vertical walls  48 . 
     A hole  47  is formed through the curl spring  24  near its free end. When the free end of the curl spring  24  is inserted into the slot  42  on the brake shoe  22 , the hook projection  45  engages the hole  47  in the curl spring  24  and prevents the curl spring  24  from being inadvertently pulled out of the slot  42 . It will therefore be understood that the engagement of the hook projection  45  with the hole  47  in the curl spring  24  mechanically interconnects the brake shoe housing  26  and the curl spring  24 . 
     The brake shoe housing  26  is shown with an imaginary centerline  32  extending down the center of the brake shoe housing  26  between the first and second curved side edges  30 ,  31 . The imaginary centerline  32  lays perpendicular to the bottom edge  29  of the brake shoe housing  26 . For the purposes of this specification, the brake shoe housing  26  is considered to be in a “straight” orientation when the imaginary centerline  32  is vertical and the bottom edge  29  is horizontal. 
     A brake mechanism  34  is contained within the brake shoe housing  26 . The brake mechanism  34  includes a cam actuator  36 . The cam actuator  36  rotates within the brake shoe housing  26 , as will later be explained. A portion of the cam actuator  36  extends through an access hole in the face surface  27  of the brake shoe housing  26 . A recess  38  is formed within the exposed portion of the cam actuator  36 . The recess  38  receives the horizontal tilt post  21  ( FIG. 2 ) that extends from the window sash. Consequently, when the window sash is tilted, the cam actuator  36  is caused to turn within the brake shoe housing  26 . 
     Referring to  FIG. 5  in conjunction with  FIG. 3 , it can be seen that when the brake shoe assembly  22  is placed within a guide track  18  of a window frame, the curl spring  24  applies a turning torque to the brake shoe assembly  22 . The torque causes the brake shoe assembly  22  to cock slightly within the confines of the guide track  18 . The brake show assembly  22  cocks in a plane that is perpendicular to the two opposing vertical walls  48  of the guide track  18 . As a consequence, the imaginary centerline  32  of the brake shoe housing  26  is turned away from its initial vertical orientation by a slight displacement angle A 1 . The displacement angle A 1  is typically only a few degrees, but may be as large as ten degrees. The displacement angle A 1  at which the brake shoe assembly  22  is tilted changes slightly as the sash of a window is raised and lowered. As the sash of a window is raised and lowered, the orientation of the curl spring  24  relative to the brake shoe assembly  22  changes slightly. This results in different torque forces being applied to the brake shoe assembly  22 . Thus, variations in the displacement angle A 1  of the brake shoe assembly  22  occur as a window sash is raised and lowered. 
     As the brake shoe assembly  22  tilts within the guide track  18 , the upper portion  37  of the first curved side edge  30  and the lower portion  35  of the second curved side edge  31  contact the opposing vertical walls  48  of the guide track  18 . Since the side vertical walls  48  are flat, the walls  48  contact the first and second curved side edges  30 ,  31  at a tangent to those curved surfaces. 
     The tangential contact between the first and second curved side edges  30 ,  31  of the brake shoe housing  26  and the opposing vertical walls  48  of the guide track  18  provide very little frictional resistance to the movement of the brake shoe assembly  22  within the guide track  18 . Furthermore, since the first and second curved side edges  30 ,  31  bend toward one another, there are no salient points on the brake shoe housing  26  that can wear into the vertical walls  48  of the guide track  18  and bind the brake shoe assembly  22 . The result is a brake shoe assembly  22  that is more reliable and is less likely to bind than traditional prior art devices. 
     Referring to  FIG. 6 , it can be seen that the brake shoe housing  26  has a face surface  27  and a rear surface  49 . A first lateral groove  50  is formed across the face surface  27  of the brake shoe housing  26 . A parallel second lateral groove  52  is formed in the rear surface  49  of the brake shoe housing  26  at a corresponding position. Above the level of the first and second lateral grooves  50 ,  52 , the brake shoe housing  26  is mostly solid. However, below the level of the first and second lateral grooves  50 ,  52 , the brake shoe housing  26  is divided into a separate face section  54  and rear section  56 . 
     The first and second lateral grooves  50 ,  52  thin the material of the brake shoe housing  26  in the face section  54  and the rear section  56 . The first and second lateral grooves  50 ,  52  therefore create living hinges that allow the face section  54  and the rear section  56  of the brake shoe housing  26  to be selectively spread apart by the application of a spreading force. 
     In  FIG. 6 , it can be seen that the cam actuator  36  that extends through the brake shoe housing  26  contains a cylindrical body  58 . On the exterior of the cylindrical body  58  is a cam arm  60 . The cam arm  60  extends across no more than half the circumference of the cylindrical body  58 . 
     Inside the brake shoe housing  26 , the face section  54  of the housing  26  and the rear section  56  of the housing  26  are separated by a severance space  62 . The severance space  62  is narrow below the level of the first and second lateral grooves  50 ,  52 . However, just above the first and second lateral grooves  50 ,  52  there is an enlarged area  64 . 
     When the sash of a window is in its functional, non-tilted position, the tilt-post  21  of the window orients the cam actuator  36  so that the cam arm  60  is positioned within the enlarged area  64  of the severance space  62 . Such an orientation is shown in  FIG. 6 . When in such an orientation, the cam arm  60  does not act to spread the face section  54  of the housing  26  from the rear section  56  of the housing  26 . Rather, the enlarged area  64  is slightly wider than the cam arm  60 , thus the cam arm  60  has no effect on the brake shoe housing  26 . 
     The distance between the face surface  27  of the brake shoe assembly  22  and the rear surface  49  of the brake shoe assembly  22  is smaller than the distance in between a forward wall  65  and a rearward wall  66  of the window frame guide track  18 . The brake shoe assembly  22  is therefore free to move within the window frame guide track  18  uninhibited. 
     Referring now to  FIG. 7 , it can be seen that the tilt-post  21  from the window has rotated. This rotation occurs when the sash of the window is tilted inwardly. As the tilt-post  21  rotates, the cam actuator  36  rotates. This causes the cam arm  60  to rotate out of the enlarged area  64  of the severance space  62 . As the cam arm  60  rotates out of the enlarged area  64 , the cam arm  60  passes in between the face section  54  and the rear section  56  of the brake shoe housing  26 . This forces the face section  54  and the rear section  56  of the brake shoe housing  26  to spread apart. 
     The face section  54  and the rear section  56  hinge about the first and second lateral grooves  50 ,  52  as they spread. As such, the distance between the face surface  54  and the rear surface  56  increases and is at its maximum proximate the bottom edge  29 . As the face section  54  and the rear section  56  spread, both sections  54 ,  56  contact, and are biased against, the forward wall  65  and rearward wall  66  of the window frame guide track  18 . This causes the brake shoe assembly  22  to bind within the window frame guide track  18  and lock into place. It will therefore be understood that once a window sash is tilted and the cam actuator  36  is caused to turn, the brake shoe housing  26  spreads and the brake shoe assembly  22  locks in place within the window frame guide track  18 . 
     Once the window sash is rotated back to its functional position, the cam arm  60  on the cam actuator  36  rotates back to the enlarged area  64  of the severance space  62 . The bias force separating the face section  54  and the rear section  56  of the brake shoe housing  26  is removed. The face section  54  and the rear section  56  then converge back toward each other until the brake shoe assembly  22  is again free to move up and down within the confines of the window frame guide track  18 . 
     It will be understood that the embodiment of the present invention counterbalance system that is described and illustrated herein is 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.