Abstract:
A balancing spring system for facilitating the opening and the closing of a window sash assembly slidably mounted in channels of opposed window jambs comprises a connector strip. The connector strip has a front surface and a rear surface. The connector strip also has slots extending from the front surface to the rear surface. The connector strip has a connecting head section at a bottom thereof, adapted for connection to the window sash assembly. Curled ribbon springs are adapted to be mounted idle and free to rotate in each of the channels of the window jambs. The curled ribbon springs each have a free end comprising an enlarged head portion at a tip thereof, for connecting the curled ribbon springs to the slots of the connector strip, whereby the curled ribbon springs apply an upward force to the window sash assembly.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to sliding window sash systems and, more particularly, to a balancing spring system for facilitating the manual opening and closing of window sashes.  
         BACKGROUND OF THE INVENTION  
         [0002]    Double hung and single hung windows known in the art comprise vertically translating window sashes. The window sashes slide in channels located alongside the window jambs of a window frame. Either sash can overlap the other sash to provide varying openings of the window. A window sash generally comprises, at its top end, a locking mechanism to engage the window sash in a stationary position along the window jambs.  
           [0003]    Balancing spring systems have been provided to facilitate the opening and closing of window sashes. For instance, window sashes having large dimensions, thick glass or many layers of glass would be a handful to manually lift. Furthermore, such heavy window sashes would also be subject to the risk of forcefully sliding down the window jambs, possibly causing the shattering of the glass and endangering the people of the surrounding environment. Therefore, balancing spring systems known in the art provide spring mechanisms along window jambs to upwardly bias the window sash, such that only a small amount of force needs to be applied to the window sash for the lifting and opening thereof. Also, the window sash is kept in vertical balance within the channels of the window jambs by the spring mechanism. Similarly, only a small amount of force needs to be applied to the window sash for the closing thereof.  
           [0004]    Curled ribbon springs have been used in balancing spring systems as they have the distinct advantage of providing a constant force, whereby the counterbalancing of the window sash is possible by opposing the constant force of such springs to the constant weight of the window sash. A curled ribbon spring consists in a spring ribbon curled around a reel, whereby the ribbon has been formed such that, when a free end portion thereof is extended and uncurled from the reel, that extended free end portion recurls itself around the reel. The recurling force of the curled ribbon spring is a function of the width thereof, amongst other factors.  
           [0005]    U.S. Pat. No. 5,232,208, issued on Aug. 3, 1993 to Braid et al., discloses a frame tensioning arrangement, wherein a ribbon spring is curled to a reel. The curled ribbon spring is idle and free to rotate within a channel of a window jamb. A tongue at a free end of the curled ribbon spring is connected to a window sash shoe. The window sash shoe supports a window sash and comprises a pivoting mechanism enabling the latter to pivot outwardly of the window jambs. The window sash shoe is also slidably mounted in the channel of the window jamb, such that the window sash may move vertically. The curled ribbon spring applies an upward force on the window sash via the shoe, for facilitating the opening and the closing of the window sash.  
           [0006]    If the amount of upward force required to counterbalance the window sash is greater than what can be provided by the curled ribbon spring in place, a few possibilities are at hand to increase the force thereof. As mentioned above, the width of the curled ribbon spring can be increased, but only to a certain extent as the available space within the channel is a limitation.  
           [0007]    Because of the restricted space in the channels of the window jambs, curled ribbon springs have been added in series in window jamb channels rather than having an increase in width to enhance the biasing force thereof. The prior art system of the above referred-to patent discloses slots and indentations on the tongue of the free end of the first curled ribbon spring, whereby a second curled ribbon spring can be attached thereto, for the afore-mentioned purpose. Furthermore, the first and second curled ribbon springs are identical, whereby other curled ribbon springs can be added in series.  
           [0008]    However, it is found that adding either slots or indentations weakens the ribbon spring. Furthermore, the area comprising the slots or indentations is subject to a greater stress as it serves as connections means and thus sustains the biasing forces of the added curled ribbon springs. This may result in the premature failure of the curled ribbon spring. In this case, the repair is a lengthy and inconvenient operation as it requires the removal of the window sash. Furthermore, as the ribbon springs are in series, the replacement of a broken ribbon spring may require the removal of the ribbon springs connected thereto, thereby extending the repair time.  
           [0009]    It is also found that when using stacks of curled ribbon springs that are interconnected as shown in the above described prior art, the lowest curled ribbon spring does not require to be as long as the highest one. This involves keeping an inventory of different lengths of curled ribbon springs for one size of window sash.  
         SUMMARY OF THE INVENTION  
         [0010]    It is a feature of the present invention to provide a balancing spring system for facilitating the manual opening and closing of window sashes and substantially overcoming the above mentioned disadvantages of the prior art.  
           [0011]    According to the above feature of the present invention, from a broad aspect, the present invention provides a balancing spring system for facilitating the opening and the closing of a window sash assembly slidably mounted in channels of opposed window jambs. The balancing spring system comprises a connector strip having an elongated rectangular shape defining a front surface and a rear surface. The connector strip also has at least two slots formed therein. Each of the slots extends from the front surface to the rear surface. The connector strip has a connecting head section at a bottom end thereof, adapted for connection to a window sash. At least a first and a second curled ribbon spring are adapted to be mounted idle and free to rotate in one of the channels of the window jambs. The first and second curled ribbon spring each have a connecting free end section, for connecting the first and second curled ribbon spring to the slots of the connector strip, whereby the first and second curled ribbon springs apply an upward force to the window sash assembly.  
           [0012]    According to a further broad aspect of the present invention there is provided a connector strip adapted for connecting a window sash assembly slidably mounted in channels of opposed window jambs to a biasing mechanism applying an upward force to the window sash assembly. The connector strip has an elongated rectangular shape defining a front surface and a rear surface and at least two slots therein. Each of the slots extends from the front surface to the rear surface and is adapted for connecting the connector strip to the biasing mechanism. The connector strip has a connecting head section at a bottom thereof adapted for connecting the connector strip to the window sash assembly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    A preferred embodiment of the present invention will now be described in detail having reference to the accompanying drawings in which:  
         [0014]    [0014]FIG. 1 is a schematic front elevational view, partly fragmented, of a balancing spring system mounted to a window sash assembly in accordance with the present invention;  
         [0015]    [0015]FIG. 2 is a perspective view of the balancing spring system;  
         [0016]    [0016]FIG. 3 is a front elevational view of a connector strip in accordance with the present invention;  
         [0017]    [0017]FIG. 4 is a side elevational view of the connector strip; and  
         [0018]    [0018]FIG. 5 is a perspective view of a spring cassette in accordance with the present invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]    According to the drawings and more particularly to FIGS. 1 and 2, a balancing spring system in accordance with the present invention is generally shown at  10 , FIG. 1 showing the location thereof in a window frame. The balancing spring system is shown secured in a channel  1  to a window jamb  2 , and connected to a window sash shoe  3 . The shoe  3  is slidably mounted in the channel  1 . A window sash  4  comprises a frame member  5  and a glass  6 . The frame  5  is connected to the shoe  3  by a pivot  7 , whereby the window sash  4  translates vertically in response to the sliding motion of the shoe  3  in the channel  1 , as demonstrated by arrow A. Still referring to FIG. 1, only one balancing spring system  10  is shown, but the opposed window jamb  2 ′ also has a channel  1 ′ holding an identical balancing spring system (not shown). However, in some applications, a single balancing system may be provided in one of the channels.  
         [0020]    As best shown in FIG. 2, the balancing spring system  10  comprises a connector strip  11  and a plurality of spring cassettes  12  (e.g. four cassettes) removably secured to the connector spring  11 . Referring now to FIGS.  3 - 4 , it can be seen that the connector strip  11  is an elongated rectangular strip having a front surface  13  and a rear surface  14 . An inverted T-shaped connector portion  15  is located at a bottom end thereof, and comprises a throat section  16  and a horizontal end section  17 . The throat section  16  is of narrowed width with respect to the width of the connector strip  11 .  
         [0021]    The connector strip  11  further comprises pairs of indentations  18   a ,  18   b ,  18   c  and  18   d  in the front surface  13  thereof, disposed on each side of a slot  20   a ,  20   b ,  20   c  and  20   d , respectively. The indentations  18   a ,  18   b ,  18   c  and  18   d  are generally equally spaced apart therein, with the indentation  18   a  being adjacent the bottom end of the connector strip  11  and the indentation  18   d  adjacent a top end thereof. Corresponding protrusions  19   a ,  19   b ,  19   c  and  19 d are formed on the rear surface  14  as a result from the indentations  18   a ,  18   b ,  18   c , and  18   d , respectively. The slots  20  are generally rectangular-shaped and vertically oriented on a central longitudinal axis of the connector strip  11 .  
         [0022]    The connector strip  11  is adapted to be secured to a window sash shoe, such as the shoe  3  of FIG. 1, by its inverted T-shaped connector portion  15  being held captive therein, as known in the art. The connector strip  11  will thereafter be connected to spring cassettes  12 , as will be explained hereinafter.  
         [0023]    Referring to FIG. 5, there is shown one of the cassettes  12 . The cassette  12  comprises a casing  25 , defined by a front wall  26 , a rear wall  27 , side walls  28  and  29 , a top wall  30  and a bottom wall  31 . A reel  32  of curled ribbon spring  33  is enclosed in the casing  25 . The reel  32  of curled ribbon spring  33  is idle and free to rotate within the casing  25 . An opening  34  is defined in the side wall  28 . The opening  34  is sized such that a free end  35  of the ribbon spring  33  can be displaced therethrough. An inverted T-shape connector portion  36  is located at the tip of the free end  35 . The T-shape connector portion  36  has a vertical throat section  40  and a horizontal end section  41 . The vertical throat section  40  is of narrowed width with respect to the width of the curled ribbon spring  33 .  
         [0024]    A hole  37  is generally centered in the front wall  26  of the cassette and extends through to the rear wall  27  thereof. The hole  37  is bounded by a cylindrical wall  38 . A countersink  39  is located between the cylindrical wall  38  and the front wall  26 . The portion of the cylindrical wall  38  within the casing  25  serves as a pivot for the reel  32  of curled ribbon spring  33 . Furthermore, the hole  37  and the countersink  39  are sized to receive a fastening element therein, such as a screw. Consequently, the spring cassette  12  can be fixedly mounted to a window jamb, within a channel, as shown in FIG. 1.  
         [0025]    Still referring to FIG. 5, the spring cassette  12  also comprises legs  42  downwardly projecting from the bottom wall  31 , and complementary grooves  43  in the top wall  30  thereof. As shown in FIG. 2, similar cassettes  12  can be connected together one on another to form a stack. For instance, the legs  42  of a cassette B are mounted in complementary engagement with the grooves  43  of cassette A. Although the curled ribbon spring  33  has been described as being enclosed in a casing, it is readily understood that the curled ribbon spring  33  may be mounted with a different type of support to the channel of a window jamb.  
         [0026]    According to the window sash weight, the available space in the window jamb channels and the upward force supplied by a cassette, the number of cassettes required for the counterbalancing of the window sash is determined. For instance, a stack of four cassettes  12  is shown in FIG. 2. Once the stack of cassettes  12  is assembled, it is secured in the channel alongside the window jamb, as schematically shown in FIG. 1. As described above, fasteners such as screws are used for this purpose. It is noted that the stack of cassettes  12  is disposed above the top of the window sash  4 , such that the upward force thereof may be supplied throughout the vertical displacement of the window sash  4 . Also, a connector strip  11  is fixedly mounted to the shoe  3 , as described previously.  
         [0027]    When the connector strip  11  is mounted to the shoe  3 , and the stack of cassette  12  is secured within the channel  1 , the curled ribbon springs  33  of each cassette  12  of the stack is connected to the connector strip  11 . As best shown in FIG. 2, this is achieved by the inverted T-shape connector portion  36  of the free end  35  of the curled ribbon spring  33  being captively engaged in the slot  20 /indentation  18  configuration of the connector strip  11 . It is noted that the narrowed width of the vertical member  40  of the T-shape connector portion  36  is generally similar to the width of the slot  20  of the connector strip  11 , whereby the horizontal member  41  is abutted at both its ends on either side of the slot  20 . As shown in FIG. 2, cassettes A, B, C and D are connected to the slots  20   a ,  20   b ,  20   c  and  20   d , respectively. It is also noted that the indentations  18   a - 18   d  allow for the horizontal members  41  of the curled ribbon spring  33  connected thereto to be generally co-planar with the front surface  13  of the connector strip  11 , whereby optimizing the space utilization. It is noted that other connection means may be used to secure the free ends  35  of the curled ribbon springs  33  to the connector strip  11 , such as corresponding hooks and slots, fasteners or the like.  
         [0028]    When the balancing spring system  10  is connected to the window sash  4  on each side thereof, a portion of the curled ribbon spring  33  is extended out of its cassette  12 , whereby it exerts an upward force on the window sash  4  as it is biased to recurl. Thus, the window sash  4  is subject to the constant upward force of the balancing spring system  10  connected thereto, whereby it remains idle in any vertical position along the window jamb  2  as it is also subject to the downward force of its weight. In consequence thereof, only a slight amount of force needs to be applied to displace the window sash  4  vertically upon the window jamb  2 .  
         [0029]    As the connector strip  11  need not be resilient materials, it may be comprised of a strong or reinforced rigid materials, whereby it can sustain stress for longer periods and thus be more durable. Accordingly, the attachment between the cassettes and the sash is much stronger with the use of the connector strip than the prior art systems and the curled ribbon springs  33  are not weakened at their connecting point as is the case with some of the prior art, as discussed herein. Furthermore, the curled ribbon springs  33  of the stack of cassettes  12  are independently connected to the connector strip  11 , whereby they can individually be replaced in the event of a ribbon spring failure. The distance between the slots  20  of the connector strip  11  is generally equivalent to the distance between the curled ribbon springs  33 . This ensures that the curled ribbon springs  33  can all be of the same length, whereby the need to keep an inventory of various lengths of curled ribbon spring for one size of window sash is eliminated.  
         [0030]    It is within the ambit of the present invention to cover any obvious modifications of the embodiments described herein, provided such modifications fall within the scope of the appended claims.