Recirculating Ball Screw Assembly High Speed Centripetal Force
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Solution Overview
Problem
Typical ball screw devices face issues with centripetal forces impeding bearing motion at high speeds and require additional packaging space due to the recirculation tube, limiting their suitability for high-speed applications.
Innovation Solution
The design eliminates the recirculation tube by positioning rolling elements with equal radii around a continuous loop between the shaft and nut, allowing both components to operate at high rotational speeds without impeding the bearings, and incorporates a pulley assembly with a clutch mechanism for decoupling and overrunning capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a recirculation tube is used to circulate bearings, then bearing recirculation is achieved, but centripetal force impedes bearing motion at high speeds
Solution Approach 1:
The patent removes the recirculation tube from the ball screw system. Instead of using a separate tube to recirculate bearings, the design allows bearings to travel directly along the screw threads from the nut back to the shaft, eliminating the component that causes centripetal force issues at high speeds while maintaining bearing recirculation functionality
Solution Approach 2:
The patent inverts the traditional bearing recirculation path. Rather than collecting bearings at the bottom and transporting them back through a recirculation tube, the bearings are allowed to follow the screw threads directly back to the shaft in reverse direction, utilizing the existing thread structure for recirculation
2Reliability
If a recirculation tube is positioned outward from the nut body, then bearing recirculation is enabled, but additional packaging space is required
Solution Approach 1:
The patent merges the bearing recirculation function with the existing screw thread structure. The same threads that transmit mechanical motion also serve as the recirculation path for bearings, eliminating the need for a separate recirculation tube and reducing overall packaging space requirements
Solution Approach 2:
The screw threads perform multiple functions: they transmit mechanical motion from the nut to the shaft, and simultaneously serve as the recirculation path for bearings. This multi-functionality eliminates the need for dedicated recirculation components, reducing packaging space
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 enables smooth operation at high speeds, reduces packaging space, and provides enhanced decoupling and overrunning performance, making it suitable for high-speed applications and meeting automotive industry demands.
Implementation Method 1
It is known that centripetal force on the bearings is determined by the speed of rotation and the bearing's distance from the rotational axis
Data Source
AI summary
Ball screws are described that may be incorporated into other devices such as a pulley assembly or a differential device. The ball screws include a threaded shaft defining a central longitudinal axis with a threaded nut threadedly coupled thereto to define at least one track in between them. Each track forms a continuous loop around an infield protrusion and is filled with a plurality of rolling elements filling. Each rolling element has the same radius from the central longitudinal axis such that the nut can rotate at higher speeds without the rolling elements locking up as a result of centripetal force.