Brake Shoe Housing Supports Coil Spring Head to Reduce Fatigue
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Solution Overview
Problem
The existing counterbalance systems for tilt-in double-hung windows, particularly those using coil springs, experience fatigue due to concentrated tension and compression stresses, leading to premature failure as the window sashes are repeatedly opened and closed.
Innovation Solution
A brake shoe housing with a receptacle slot and open relief supports the coil spring's shaped head, reducing stress concentrations and preventing excessive cocking, thereby extending the service life of the coil spring and preventing wear on the brake shoe housing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the coil spring is repeatedly subjected to tension and compression forces during window operation, then the counterbalance function is maintained, but fatigue stresses concentrate at the shaped head of the spring ribbon leading to premature failure
Solution Approach 1:
The patent introduces a brake shoe assembly as an intermediary component between the coil spring and the window sash. The brake shoe housing contains a receptacle that receives and supports the shaped head of the coil spring, distributing the stresses away from the critical shaped head area. This intermediary structure prevents direct stress concentration at the spring's weakest point while maintaining the counterbalance function.
Solution Approach 2:
The brake shoe housing with its receptacle slot and open relief provides a protective structure that cushions and distributes the tension and compression forces before they reach the shaped head of the coil spring. This pre-cushioning effect prevents fatigue damage by spreading the stress over a larger area and reducing peak stresses at the critical junction.
2Ease of manufacture
If the shaped head of the coil spring is used to connect to the brake shoe, then the spring can be attached to provide counterbalance force, but the reduced width area creates stress concentration points that lead to fatigue failure
Solution Approach 1:
The brake shoe housing acts as an intermediary that receives the shaped head of the coil spring in a dedicated receptacle slot. This intermediary structure protects the inherently weak shaped head area from direct stress concentration while maintaining the simple attachment geometry needed for ease of manufacture.
3Volume of moving object
If multiple smaller coil springs are ganged together to provide counterbalance force for heavier sashes, then the space restrictions are satisfied, but the complexity of the spring assembly increases
Solution Approach 1:
The patent acknowledges that for heavier window sashes, multiple smaller coil springs must be ganged together to provide sufficient counterbalance force within the limited space. Each spring is individually attached to the brake shoe assembly, allowing modular scaling of the counterbalance capacity without requiring a completely different design approach.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly extends the service life of the coil spring and brake shoe housing by distributing stress and preventing wear, ensuring a more reliable counterbalance system for tilt-in windows.
Implementation Method 1
Curl springs are constant force coil springs, made from wound length of metal ribbon, that supply the counterbalance force needed to suspend the weight of the window sash.
Implementation Method 2
The shoes contain a brake mechanism that is activated by the tilt post of the window sash when the window sash is tilted inwardly away from the window frame. The shoe therefore locks the tilt post in place and prevents the base of the sash from moving up or down in the window frame once the sash is tilted open.
Data Source
AI summary
An assembly of components that are use in a counterbalance system for a tilt-in window. A coil spring of wound ribbon is provided that has a shaped head. A brake shoe housing is provided that connects to the coil spring in such a manner that fatigue stresses are reduced in the coil spring as the tilt-in window is operated. The brake shoe housing has a receptacle slot formed into one of its side surfaces. An open relief is formed immediately above the receptacle slot. The open relief abuts against and supports the ribbon of the coil spring just behind the shaped head. By engaging the shaped head of the coil spring and supporting the coil spring adjacent to the shaped head, stresses experienced by the shaped head are greatly reduced. The result is a coil spring that has a much longer service life.