Patent ID: 6948215

Claim:
A window balance comprising: a window frame, a window sash movably mounted in said window frame, a torsion spring having a first end and a second end, a spiral rod within said torsion spring having a third end near the first end, a fourth end near the second end, and a first axis through the third end and the fourth end, a threaded follower mounted on said spiral rod for being rotated by said spiral rod when said follower is moved along said spiral rod between the third end and the fourth end of said spiral rod, said threaded follower being attached to the first end of said torsion spring for rotating the first end of said torsion spring by rotation of said follower, first means for attaching the second end of said torsion spring to a window sash for axial movement of said torsion spring by the sash for moving said follower along said spiral rod by moving the sash, attached to said window sash, a gear assembly comprising a first gear and a second gear, fixedly mounted on said window frame, attached to the third end of said spiral rod preventing axial movement of said spiral rod with respect to the window frame and for rotating said spiral rod by said first gear when said first gear is driven by said second gear for changing base force in said torsion spring, an axially extending first element mounted on one of said first means and said gear assembly, a second element mounted on the other of said first means and said gear assembly axially receiving said first element spaced radially from the axis of the spiral rod when the follower is adjacent to the third end of said spiral rod so that said first element extending a first length into said second element prevents axial rotation of said first means with respect to said gear assembly, the first length being such that said first element is withdrawn from said second element permitting axial rotation of said first means with respect to said gear assembly when said first means is moved axially away from said gear assembly.