Patent Publication Number: US-6041476-A

Title: Inverted block and tackle window balance

Description:
TECHNICAL FIELD 
     The invention relates to the field of block and tackle window balances for offsetting the weight of a window sash throughout a range of travel within a window frame. 
     BACKGROUND OF THE INVENTION 
     Block and tackle window balances have become popular because of their compact size and ease of installation. They combine a system of pulleys with an extension spring to convert high spring tension applied over a short working distance to a lower spring tension applied over a longer working distance. The extension spring and pulley system are arranged within a rigid balance channel, with the extension spring anchored at one end of the balance channel and the pulley system anchored at the other end. In most block and tackle balances, the balance channel is mounted in the jamb of the window frame; and a cord, which is reeved through the pulley system, is attached to a sash shoe that slides in the jamb with the sash. The extension spring and pulley system are sized so that a desired lifting force is applied to the window sash throughout the entire range of sash travel within the window frame. A disadvantage of this type of balance is that the movement of the sash is limited by the presence of the balance in the jamb. In some cases, the travel is limited so much that the lower sash of the open window blocks egress through the window in escaping a fire. 
     To solve the problem of limited sash movement, the balance can be mounted upside down in the window sash with the balance channel attached to the sash shoe and the cord attached to the window jamb or frame. However, prior art window balances of this kind tend to be susceptible to contamination from dirt and dust, especially when mounted upside down. Particles work their way between the pulley bores and the pulley axles, increasing friction and wear. Thus, prior art block and tackle window balances are not as durable or reliable as is desired. 
     Some prior art block and tackle window balances that are less susceptible to contamination require the use of bushings and other parts. This is disadvantageous in that the use of additional parts increases the complexity of the machines and the likelihood of their failure. Also, the additional parts increase the cost of manufacture and assembly of the window balances. 
     SUMMARY OF THE INVENTION 
     My inventive block and tackle window balance greatly reduces the invasion of the hub/axle interface by particulate contaminants. I form the pulleys with steps in their hubs so that they can engage mating steps on the rivets that serve as their axles. In addition, I mount the two pulleys at the open end of the balance so that they run against each other, effectively sealing the space between the pulley hubs. The steps in the pulley hubs can be recesses or protrusions, depending on their location and particular duty. My window balance provides better protection from dirt and dust contamination without the extra parts required by prior art window balances, keeping the balance relatively simple and less costly to manufacture and assemble. Additionally, because my window balance is less susceptible to contamination, it can be mounted to move with the sash of a window or to remain fixed relative to the frame of a window, depending on the requirements of a particular installation, and can be mounted invertedly without significantly reducing its useful life. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top schematic view of the invention. 
     FIG. 2 is a cross section taken along line II--II in FIG. 1 showing the first pair of pulleys. 
     FIG. 3 is a cross section taken along line III--III in FIG. 1 showing the second pair of pulleys. 
     FIG. 4 is a view taken along line IV--IV in FIG. 2 to illustrate the flats of a preferred pulley axle and the groove in which the axle is mounted. 
     FIG. 5 is a side view of a portion of the invention as shown in FIG. 1. 
     FIG. 6 is a schematic representation of the placement of my invention in a window. 
    
    
     DESCRIPTION OF THE INVENTION 
     As seen in the accompanying Figures, my block and tackle window balance 1 includes a balance channel 2 preferably mounted in the shoe channel 55 of a window 51 and attached at one end to a sash shoe 50 that moves with the sash 53 in the shoe channel 55. I mount the shoe channel 55 on the jamb 54 of the window between the jamb 54 and the sash 53. The balance channel 2 supports a series of pulleys 11, 12, 31, 32 over which I reeve a cord 6. I attach an attachment end 8 of the cord 6 to the window jamb 54 or to the window frame 52. I attach a support plate end 7 of the cord 6 to a sliding support plate 35. The support plate 35 is biased against movement from a rest position by a spring 4 attached to the balance channel 2. Alternatively, a more conventional mounting arrangement can be used with the balance channel 2 fixed relative to the window jamb 54 and the attachment end 8 of the cord attached to the sash shoe 50. 
     As seen particularly in FIG. 2, an axle 15 mounted in grooves 24 in one end of the balance channel 2 supports a first pair 10 of pulleys 11, 12. The pulleys 11, 12 in the first pair 10 sit adjacent one another and include hub steps 13 in the form of recesses about the axial bores 14 of the pulleys 11, 12. The sides or rims 23 of the pulleys 11, 12 adjacent one another can slide or rub against each other and effectively seal the cavity 22 formed by their hub steps 13 against contamination from dirt and dust. 
     The axle 15 is preferably a rivet including flats 16 formed over portions of the circumferential surface of the axle 15 such that the flats 16 engage the grooves 24 in the balance channel 2, holding the axle 15 against rotation. The preferred rivet 15 also includes heads 17 that prevent axial movement of the axle 15. As shown in FIG. 4, I prefer to use a hexagonal arrangement of the flats 16 similar to that used in common nuts and bolt heads. The axle 15 can also include a flange 18 with a protruding flange step 19 that mates with a hub step 13 of one the pulleys of the first pair, such as the first pulley 11. I prefer to mount a washer 20 on the axle 15 between the other of the pulleys of the first pair 10 (the second pulley 12) and the wall 3 of the balance channel. The washer 20 can include a protruding washer step 21 that mates with a hub step 13 of the second pulley 12. The mating steps 13, 19, 21 effectively seal the washer/pulley, flange/pulley, and pulley/axle bearing surfaces from contamination by dirt and dust particles, reducing wear of these parts and increasing the effective life of the window balance. 
     A second pair 30 of pulleys 31, 32 is mounted on the support plate 35. The pulleys 31, 32 of the second pair 30 also include hub steps 33, but I prefer to form these hub steps 33 as protrusions about the axial bores 34 of the pulleys 31, 32. Axles 37, 38, preferably in the form of rivets, rotatably mount the pulleys 31, 32 on the support plate 35, the heads 39 of the rivets engaging or abutting respective hub steps 33 of the pulleys 31, 32. I prefer to form the hub steps 33 so that they have substantially the same diameter as the heads 39 of the rivets 37, 38. The hub steps 33 of the pulleys 31, 32 farthest from the rivet heads 39 abut the support plate 35. As with the first pair of pulleys 10, the mating steps 33 and rivet heads 39 effectively seal the pulley/axle bearing surfaces from contamination by dirt and dust particles, reducing wear of these parts and increasing the effective life of the window balance. 
     When installed, one end 8 of the cord 6 is preferably attached to the window frame 52 or the window jamb 54, the other being attached to the support plate 35. In this arrangement, I slidingly mount the balance channel 2 in the shoe channel 55 with one end connected to the sash shoe 50 so that the balance channel 2 can move with the sash 53 in the shoe channel 55. Alternatively, the end 8 of the cord 6 can be attached to the sash shoe 50 mounted in the conventional manner, the other end 7 of the cord being attached to the support plate 35. In the conventional arrangement, the balance channel 2 is fixed with respect to the frame 52. In either arrangement, the support plate 35 slides in the balance channel 2. I prefer to run the cord 6 from the support plate 35 to the first pulley 11, then to the fourth pulley 32, then to the second pulley 12, then to the third pulley 31, and then out the end of the balance channel 2 in which the first pair of pulleys 10 is mounted. The end 8 of the cord 6 not attached to the support plate 35 includes a limit stop 9 to prevent the cord 6 from being pulled into the balance channel 2 when it is free. 
     The support plate 35 carries a guide 36 that keeps the support plate 35 properly aligned and oriented in the balance channel 2 while sliding and while resting. The support plate 35 also includes a spring attachment point 40, such as a hole, to which an end of a biasing spring 4 is attached. The other end of the biasing spring 4 is attached to the balance channel 2 via, for example, a support rivet 5. The spring 4 provides the force that balances the weight of the window sash 53. As the window sash 53 is moved, the cord 6 moves and rolls over the pulleys 11, 12, 31, 32, which rotate accordingly, and the support plate 35 slides. Travel of the support plate 35 is limited between its resting position and its extended position by the limit stop 9 on the cord 6 and the first pair of pulleys 10, respectively. 
     Parts List 
     1 Window balance 
     2 Balance channel 
     3 Walls of balance channel 
     4 Spring 
     5 Spring support/rivet 
     6 Cord 
     7 Support plate end of cord 
     8 Free end/attachment end of cord 
     9 Limit stop of cord 
     10 First pulley pair 
     11 First pulley 
     12 Second pulley 
     13 Hub steps/recesses of pulleys of first pair of pulleys 
     14 Axial bores of pulleys of first pair 
     15 Axle/rivet supporting first pair 
     16 Flats of axle 
     17 Heads of axle 
     18 Flange of axle 
     19 Flange step/protrusion 
     20 Washer 
     21 Washer step/protrusion 
     22 Cavity/space formed by hub steps of first pair 
     23 Rims of pulleys of first pair 
     24 Mounting groove of axle of first pair 
     30 Second pulley pair 
     31 Third pulley 
     32 Fourth pulley 
     33 Hub steps/protrusions of pulleys of second pair of pulleys 
     34 Axial bores of pulleys of second pair 
     35 Support plate 
     36 Guide for support plate 
     37 Support/rivet for third pulley 
     38 Support/rivet for fourth pulley 
     39 Heads of rivets for third and fourth pulleys 
     40 Attachment point for spring; hole in support plate 
     50 Pivot block or sash shoe 
     51 Window 
     52 Window frame 
     53 Window sash 
     54 Window jamb