Elevator Tie-Down Compensation via Pit Sheave Tensioning
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Solution Overview
Problem
Conventional elevator systems face challenges in maintaining traction and preventing counterweight jump, especially in high-rise buildings with shallow pit depths, as existing tie-down compensation arrangements require deep pits and are not compatible with all building designs.
Innovation Solution
A tensioning assembly with a load-bearing member, such as a steel-core, rubber-coated belt, and a damper system that absorbs energy to maintain tension and prevent counterweight jump, allowing for a shallower pit depth and effective traction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional tie-down compensation arrangements (chains, free rope, moveable mass) are used, then adequate rope tension and counterweight jump prevention are achieved, but large pit depth is required
Solution Approach 1:
The invention transitions from vertical pit-depth-based tension maintenance to a horizontal wrap-around configuration at the pit bottom. The tension member wraps around a sheave positioned at the pit floor, creating tension through lateral geometry rather than vertical depth, thus eliminating the need for deep pits while maintaining counterweight jump prevention.
Solution Approach 2:
A sheave is introduced as an intermediary element at the pit bottom to redirect and maintain tension in the load-bearing member. This sheave acts as a mediator that converts the geometric wrap-around configuration into effective tension force, preventing counterweight jump without requiring deep pit structures.
2Force
If chain compensation arrangement is used, then tension is provided for certain elevator system designs, but it is not compatible with buildings having rise above 400 feet
Solution Approach 1:
The invention changes the fundamental parameter of tension generation from chain weight (mass-based) to geometric wrap-around configuration (angle-based). This allows the system to scale to higher building rises because the tension effectiveness depends on the wrap angle and sheave position rather than the length and weight of a chain, making it compatible with buildings exceeding 400 feet.
3Weight of moving object
If lightweight cars and counterweights are used, then other advantages are achieved, but traction is reduced due to shifting rope weight effects
Solution Approach 1:
The wrap-around tensioning arrangement pre-establishes constant tension in the load-bearing member through its geometric configuration at the pit bottom. This preliminary tensioning action counteracts the shifting rope weight effects that occur during car movement, maintaining adequate traction throughout the travel range even with lightweight cars and counterweights.
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 ensures consistent traction and minimizes counterweight jump, enabling the use of tie-down compensation in high-rise buildings with shallow pit depths, providing a more compact and functional elevator system.
Implementation Method 1
A damper absorbs energy that otherwise would cause counterweight jump
Implementation Method 2
A base module has at least one sheave that rotates about an axis that remains fixed beneath the lowest position of the cab
Data Source
AI summary
An elevator system (20) includes a tie-down compensation arrangement (40). A tension member (42) extends between a cab (22) and counterweight (26) to provide a desired amount of tension on a load bearing rope or belt (30) that supports the cab and the counterweight. The tension member (42) in one example comprises a coated steel belt. At least one sheave (46) is supported on a base module (48) and remains stationary relative to a floor of a pit (52). A damper (50) is supported for movement with the counterweight (26) or the cab (22) to absorb energy that would otherwise tend to cause counterweight jump following a rapid descent and stop of the cab (22).