Block and tackle sash balance brake assembly

1. A locking block and tackle sash balance assembly for a sash window, the sash window pivotable between a pivotably closed orientation and a pivotably open orientation, the assembly comprising:

a channel;

a spring disposed within the channel;

a block and tackle assembly disposed within the channel, the assembly including a moveable pulley and a fixed pulley; and

a locking member coupling the spring to the movable pulley; wherein the locking member is movable between a first position in locking engagement with the channel when the sash is in the open orientation and a second position disengaged from the channel when the sash is in the closed orientation.

2. The assembly of claim 1 including means for biasing the locking member towards the first position.

3. The assembly of claim 2 including means for retaining the locking member in the second position when the sash is in the second orientation.

4. The assembly of claim 3 wherein the retaining means comprises a surface of the locking member engaging the sash.

5. The assembly of claim 2 wherein the biasing means comprises off-center attachment of the locking member to the spring and the movable pulley.

6. The assembly of claim 1 wherein the channel has a plurality of spaced notches, and the locking member includes a tooth to engage one of the notches when the sash is in the open position.

7. The assembly of claim 1 wherein the channel has a plurality of serrations, and the locking member includes a tooth to engage one of the serrations when the sash is in the open position.

8. The assembly of claim 6 , wherein the locking member includes a plurality of teeth to engage a respective plurality of the notches.

9. A sash balance assembly for providing a counterbalancing force to a sash window slidably and pivotally mounted within a frame, the sash window having a stile, the frame having a shoe channel having a rear wall and a front wall having a pair of shoulders separated by a slot, wherein the assembly is adapted to disable the counterbalancing force responsive to pivotal movement of the sash window, the sash balance assembly comprising:

a block and tackle balance assembly having a balance channel;

an active pulley block slidably positioned generally within the balance channel;

wherein the balance channel is adapted to prevent sliding movement of the active pulley block within the balance channel responsive to pivotal movement of the window sash; and,

a locking member rotatably mounted to the active pulley block having a locked position and an unlocked position;

wherein the locking member is adapted to selectively engage the balance channel responsive to pivotal movement of the window sash.

10. The sash balance assembly of claim 9 comprising:

a plurality of protrusions extending from the locking member; and

a plurality of notches in the balance channel;

wherein the protrusions are adapted to engage respective ones of the notches.

11. The sash balance assembly of claim 10 comprising:

an extension spring mounted generally within the balance channel, a first end of the extension spring connected to the balance channel and a second end of the extension spring connected to the locking member;

wherein the active pulley block, locking member and extension spring are adapted to bias the locking member in the locked position.

12. The sash balance assembly of claim 11 comprising:

an engagement pad integrally formed on the locking member adapted to engage the stile when the locking member is in its unlocked position and to extend through the slot when the locking member is in is locked position.