Ballscrew Actuator Sealing with Vented Chamber Lubrication
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Solution Overview
Problem
Ballscrew actuators experience lubricant leakage, leading to frequent reapplication needs and ineffective lubrication distribution within the helical raceway, particularly during reapplication, which affects the operational efficiency and reliability of applications like aircraft engines.
Innovation Solution
A dual-seal system is implemented, comprising an outboard seal and an inboard seal, where the outboard seal minimizes leakage at the axial end and the inboard seal, made of a polymer compound, reduces friction and leakage during reapplication by forming a chamber with the ballnut, and a vent passage in the outboard seal allows pressure equalization to direct lubricant flow effectively, while the ballnut seal supplies lubricant to the annular groove.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single seal is used in the ballscrew assembly, then the device complexity is reduced, but lubricant leakage increases leading to frequent reapplication needs
Solution Approach 1:
The seal system is divided into two separate seals: a first seal (outboard seal) positioned at the outboard end of the ballnut and a second seal (inboard seal) positioned at the inboard end of the ballnut. Each seal independently prevents lubricant leakage from its respective end, thereby improving overall lubricant retention without requiring a single complex sealing mechanism. This segmentation allows each seal to be simpler in design while collectively providing superior sealing performance.
2Reliability
If lubricant is injected into the chamber during reapplication, then the lubrication of contact surfaces is improved, but lubricant leakage during reapplication increases
Solution Approach 1:
A vent passage is introduced as an intermediary element within the first seal structure. This vent passage allows trapped air and excess lubricant to escape from the chamber during the lubricant injection process, preventing pressure buildup that would otherwise force lubricant past the seals. The vent passage thus mediates between the lubricant injection process and the sealing system, enabling effective lubrication while minimizing lubricant loss.
3Duration of action of moving object
If the ballscrew assembly is sealed to prevent lubricant leakage, then maintenance intervals are extended, but lubricant distribution within the helical raceway becomes ineffective
Solution Approach 1:
The seal system is designed to be dynamically adaptive to the operational state of the ballscrew assembly. During normal operation, the seals maintain a sealed configuration to prevent lubricant leakage and extend maintenance intervals. During lubricant reapplication, the vent passage in the first seal becomes active, allowing temporary pressure equalization and lubricant distribution throughout the helical raceway. This dynamic behavior allows the system to switch between sealed and vented states based on operational 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
The dual-seal system significantly reduces lubricant leakage, ensures effective lubrication distribution throughout the helical raceway, and minimizes friction, thereby extending the maintenance interval and ensuring reliable operation of ballscrew actuators in applications like aircraft engines.
Implementation Method 1
a vent passage in the outboard seal allows pressure equalization to direct lubricant flow effectively
Implementation Method 2
Ballscrew actuators are generally lubricated in order to facilitate relative motion between a screw, nut and balls
Data Source
Figure 1
Figure 2
AI summary
A ballscrew assembly (2) comprises a ballnut (6) having a first helical groove (10) and a ballscrew (4) comprising a second helical groove (8) opposed to the first helical groove (10) so as to form a helical raceway (12). A plurality of balls is disposed in the helical raceway (12). A first seal (20) is disposed at a first axial end (16) of the ballnut (6) to seal between the ballscrew (4) and the ballnut (6). A second seal (22) is provided for selectively sealing between the ballscrew (4) and a second axial end (18) of the ballnut (6), the second seal (22) comprising a ballscrew seal (26) mounted for axial movement with the ballscrew (4), and configured to make sealing engagement with the ballnut (6) when the ballscrew (4) is in a first axial position relative to the ballnut (6) to form a chamber between the first and second seals (20, 22), but not to make sealing engagement with the ballnut (6) when the ballscrew assembly (2) is in a second axial position relative thereto.