| 摘要 |
A multiple spring counterbalance includes a torsion spring and a tension spring for exerting a combined lifting force on a window sash. A spiral rod is threadably engaged with a follower nut for converting a torque applied by the torsion spring into a lifting force on the window sash. The spiral rod has a pitch that is varied along one part of its length to produce a substantially constant combined lifting force throughout most of a range of sash travel between a lowered position and an intermediate position. However, the pitch is further varied along another part of the length of the spiral member to produce a larger combined lifting force within a remaining portion of the range of sash travel from the intermediate position to the raised position. |
