Screw Actuator Auto-Lubrication for Continuous Ballscrew Service
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Solution Overview
Problem
Ballscrew actuators require frequent manual replenishment of lubricant, which is costly and disrupts the operation of aircraft systems, as lubricant escapes through seals and must be manually re-injected into the interface between the ballscrew and ballnut.
Innovation Solution
A screw actuator design incorporating a lubricant reservoir, pressuriser, and lubricant supply piston that automatically replenishes lubricant into the interface between the nut and screw through axial movement, using a spring-loaded piston and valve system to control lubricant flow, reducing the need for manual intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If manual lubricant replenishment is performed, then the lubricant interface is maintained, but operational continuity is disrupted and maintenance costs increase
Solution Approach 1:
The lubricant supply piston automatically replenishes lubricant in the interface between the ballscrew and ballnut during normal operation, eliminating the need for manual intervention. The piston is mounted on the ballscrew and moves axially with it, automatically injecting lubricant as the actuator operates
Solution Approach 2:
The lubricant supply piston is pre-positioned on the ballscrew and the lubricant is pre-stored in the reservoir. The system is designed so that lubricant replenishment occurs automatically before the lubricant is completely depleted, ensuring continuous protection without waiting for manual maintenance
2Loss of substance
If manual lubricant replenishment is performed, then lubricant loss is compensated, but maintenance time and costs increase
Solution Approach 1:
The lubricant supply piston automatically compensates for lubricant loss during normal actuator operation. As the ballscrew rotates and the nut moves axially, the piston moves with it and continuously replenishes lubricant into the interface, eliminating the need for scheduled manual maintenance
Solution Approach 2:
The lubricant replenishment occurs continuously during normal operation rather than in discrete manual intervals. The piston moves axially with the ballscrew throughout its stroke, continuously injecting lubricant to maintain the interface without interruption to the actuator's function
3Extent of automation
If a lubricant supply piston mounted on the screw is used, then automated lubricant replenishment is achieved, but the piston must be designed to both move axially with the screw and rotationally slip
Solution Approach 1:
The piston is designed with different surface properties at different locations. The mounting surface on the ballscrew has high friction characteristics to enable axial movement with the screw, while the outer surface has low friction characteristics to enable rotational slipping. This localized differentiation of friction properties allows the piston to simultaneously achieve axial following and rotational independence
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 system ensures continuous lubrication of the screw/nut interface, reducing the frequency of manual lubricant replenishment and maintaining prolonged corrosion resistance, allowing the actuator to remain in service longer without maintenance.
Implementation Method 1
The lubricant pressuriser may comprise a pressurisation piston slidably mounted within the lubricant reservoir and a spring for urging the pressurisation piston into the lubricant reservoir to pressurise the lubricant.
Implementation Method 2
The lubricant supply piston is mounted on the external helical formation of the screw with sufficient friction that in response to relative rotational movement of the screw and the nut resulting in relative axial movement of the screw and the nut, the lubricant supply piston can move axially with the screw relative to the nut through the lubricant receiving chamber so as to force lubricant from the lubricant receiving chamber into an interface between the nut and the screw
Implementation Method 3
Ballscrew actuators are lubricated in order to facilitate relative motion between a ballscrew, ballnut and balls.
Data Source
AI summary
A screw actuator comprises a nut having an internal helical formation and a screw having an external helical formation and rotatably received within the nut, relative rotational movement of the nut and screw causing axial movement of one of the nut and screw relative to the other of the nut and screw. The actuator further comprises a lubricant reservoir and a lubricant pressuriser for pressurising lubricant within the lubricant reservoir. A lubricant receiving chamber is formed in the nut. The screw extends through the lubricant receiving chamber. A lubricant supply passage fluidly connects the lubricant reservoir and the lubricant receiving chamber. A valve controls the flow of lubricant between the lubricant reservoir and the lubricant receiving chamber. A lubricant supply piston is received in the lubricant receiving chamber and is mounted on the external helical formation of the screw.