Ball Screw Return Path Geometry for Load Path Clearance
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Solution Overview
Problem
Conventional ball screw devices face interference issues in automotive applications due to the circulation path design, which affects their ability to achieve a small size, high thrust generation with low drive torque, and large load capacity, particularly when the lead of the thread groove is set to 0.6 or more relative to the ball diameter.
Innovation Solution
The ball screw device incorporates a circulation path with a return path, scooping paths, and connecting paths, where the scooping paths have an arc-shaped center line curving outward in the radial direction, and the connecting paths have a straight and arc-shaped configuration, ensuring the radius of curvature and length of the paths are optimized to prevent interference with the load path, with specific conditions such as D/L ≥ 0.6 and R1cos(90°-θ)+S > D, and the tangent lines aligned at connecting points for smooth ball movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the lead of the thread groove is set to 0.6 or more relative to the ball diameter to achieve high thrust generation with low drive torque, then the thrust generation efficiency is improved, but the circulation path interferes with the load path
Solution Approach 1:
The circulation path is designed to extend in the axial direction rather than only in the radial direction. By adding the axial dimension to the circulation path configuration, the path can bypass the load path interference zone while still connecting the ball supply and return regions, enabling both high lead (0.6 or more) and interference-free operation
Solution Approach 2:
The circulation path employs curved configurations with specific radius of curvature requirements. The curved design allows the circulation path to smoothly navigate around the load path in three-dimensional space, preventing interference while maintaining continuous ball flow. The curvature radius is specifically controlled to ensure the path clears the load path when the lead is 0.6 or more
2Volume of moving object
If the ball screw device is designed for small size to improve fuel efficiency and running performance, then the device compactness is improved, but the circulation path design becomes more difficult to avoid interference
Solution Approach 1:
By utilizing the axial direction for circulation path extension, the design efficiently uses the available three-dimensional space within the compact nut. This dimensional approach allows the circulation path to achieve the necessary length for smooth ball return without increasing the radial or axial dimensions of the overall device, maintaining compactness while avoiding interference
Solution Approach 2:
The circulation path is designed with flexible routing that adapts to the specific geometric constraints of each application. The path configuration can be optimized for different lead values and ball diameters while maintaining a consistent design framework, reducing the complexity of redesigning for different size requirements
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 provides a circulation path route suitable for automotive applications, preventing interference with the load path and ensuring efficient ball movement, thus enhancing the device's performance in generating thrust with small drive torque and maintaining load capacity.
Implementation Method 1
a ball screw device rolls and moves balls between a screw shaft and a nut
Data Source
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AI summary
A ball screw device having a circulation path suitable for automotive applications is achieved. The circulation path 9 that returns balls 4 from the end point to the start point of the load path 8 includes a return path 20, scooping paths 21, and connecting paths 22. The scooping path 21 has an arc-shaped center line that is curved outward in the radial direction as going toward the reference imaginary flat plane α including the center axis O2 of the screw shaft 2 and the center line of the return path 20 in the circumferential direction. The connecting path 22 is arranged on the reference imaginary flat plane α and includes a straight path 22a having a linear center line extending in a direction orthogonal to the center axis O2 of the screw shaft 2. When the radius of curvature of the center line of the scooping path 21 is R1, the scooping angle is θ, and the entire length of the straight path 22a is S, R1cos(90°-θ)+S is made larger than the diameter D of the balls 4.