Ball Screw Assembly With Bypass Shoe for Peak Load Transfer
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Solution Overview
Problem
Ball screws in applications like Thrust Reverser Actuation Systems require high static load capacity materials for rare high-force events, leading to increased costs and design complexity, despite most operations involving lower forces, as current standards mandate hard materials for all aerospace applications regardless of specific requirements.
Innovation Solution
A ball screw assembly with a bypass shoe mechanism that engages when loads exceed a predetermined threshold, allowing the bypass of the ball track and enabling the use of less hard, less expensive materials by transferring motion through the shoe instead of the balls, thereby reducing the need for high hardness in the ball screw components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ball screw components are designed with high hardness material to handle high failure forces, then static load capacity is improved, but manufacturing cost increases
Solution Approach 1:
The ball screw assembly incorporates a bypass mechanism that dynamically switches between two load paths: the ball track for normal operating loads and the bypass shoe for excessive loads. This dynamic adaptation allows the ball track to be designed for normal loads rather than peak failure loads, enabling the use of less hard, more cost-effective materials while maintaining safety
Solution Approach 2:
The bypass shoe acts as an intermediary element that engages with the screw shaft and nut when loads exceed the predetermined threshold. This intermediary component protects the ball track from excessive loads by providing an alternative load path, allowing the ball track materials to be optimized for normal operating conditions rather than worst-case scenarios
2Reliability
If ball screw components are designed for high static load capacity to handle failure events, then reliability is improved, but device complexity increases
Solution Approach 1:
The ball screw assembly is segmented into distinct functional zones: the ball track for normal operation and the bypass mechanism for excessive loads. This segmentation allows each component to be optimized for its specific function, with the ball track designed for precision and efficiency under normal conditions, and the bypass mechanism activated only when needed, thereby maintaining reliability without requiring the entire system to be over-engineered
Solution Approach 2:
The design incorporates a predetermined load threshold parameter that triggers the bypass mechanism. By defining this specific parameter (preload force), the system automatically transitions between operational modes based on load conditions, providing a simple yet effective way to ensure reliability during failure events without complex control systems or design modifications
3Duration of action of stationary object
If hard materials are used for ball track to achieve high static load capacity, then wear resistance is improved, but material cost increases
Solution Approach 1:
The bypass mechanism effectively protects the expensive ball track from excessive loads that would cause wear and damage. By diverting these extreme loads through the bypass shoe, the ball track experiences only normal operating loads throughout its service life, allowing the use of less expensive materials that would otherwise wear too quickly, thus reducing material costs while maintaining component lifetime
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
This design reduces production costs and complexity by allowing the use of less hard materials while maintaining safety and effectiveness, as the ball screw components only need to handle loads up to the predetermined threshold, and the bypass feature reduces wear and eliminates the need for conventional mechanical load limiters.
Implementation Method 1
when a load applied to the nut exceeds the predetermined preload, the bypass shoe engages with the track such that motion of the screw is transferred to motion of the nut via the shoe and bypasses the balls
Data Source
AI summary
A ball screw assembly includes a screw shaft along which is formed a first helical groove; a nut along which is form a second helical groove; the first helical groove and the second helical groove cooperating to define a track, a plurality of balls arranged in the track and configured to move along the track in response to relative motion between the screw shaft and the nut such that rotational motion of the screw is translated to linear motion of the nut via the balls and vice versa. The assembly also includes a bypass shoe arranged between the nut and the track and spaced from the track by a predetermined preload X, wherein when a load applied to the nut exceeds the predetermined preload, the bypass shoe engages with the track such that motion of the screw is transferred to motion of the nut via the shoe and bypasses the balls.