Screw Actuator Self-Lubrication Using a Slip-Mounted Piston
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Solution Overview
Problem
Ballscrew actuators require frequent manual replenishment of lubricant, which is costly and disrupts aircraft operations, as lubricant escapes through seals and is not effectively retained.
Innovation Solution
A screw actuator system with a lubricant reservoir, pressurizer, and lubricant supply piston that automatically replenishes lubricant into the interface between the nut and screw through axial movement, using a spring-loaded pressurizer and valve mechanism to control lubricant flow, allowing the piston to slip rotationally at an axial limit to maintain continuous lubrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If seals are provided at either end of the ballnut to retain lubricant, then lubricant retention is improved, but lubricant still escapes from the interface requiring manual replenishment
Solution Approach 1:
The lubricant reservoir is pre-filled with lubricant and the pressurizer is pre-loaded with spring energy. When the actuator operates, the lubricant is automatically delivered to the interface without requiring manual intervention. The system performs the lubrication action in advance and automatically, eliminating the need for operators to periodically replenish lubricant.
Solution Approach 2:
The actuator system lubricates itself through the automatic delivery mechanism. The pressurizer uses the actuator's own operational movements to drive the lubricant from the reservoir through the passage to the interface, creating a self-sustaining lubrication system that does not require external manual service.
2Reliability
If manual lubricant replenishment is performed at regular intervals, then lubrication is maintained, but costly maintenance activities and operational disruptions occur
Solution Approach 1:
The automatic lubricant delivery system ensures continuous lubrication of the interface throughout the actuator's operational life. The lubricant is delivered continuously or periodically based on actuator operation, eliminating the gaps and disruptions associated with manual replenishment schedules.
Solution Approach 2:
The system pre-stores lubricant in the reservoir and pre-loads the pressurizer mechanism, so that lubrication is automatically available when needed during operation, preventing any disruption to productivity.
3Ease of operation
If a lubricant delivery mechanism is implemented, then manual replenishment is reduced, but device complexity increases
Solution Approach 1:
The lubricant delivery system is integrated into the actuator's existing structure. The reservoir, pressurizer, and delivery passage are combined with the ballnut and actuator components, sharing space and structural elements, which minimizes the increase in overall device complexity.
Solution Approach 2:
The pressurizer mechanism utilizes the actuator's operational movements for dual purposes: driving the actuator function and simultaneously delivering lubricant. This multi-functionality reduces the need for separate dedicated lubrication components, thereby limiting complexity increase.
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
Reduces the need for manual lubricant replenishment, ensuring continuous lubrication and prolonged corrosion resistance, allowing the actuator to operate for 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 to 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
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A screw actuator (2) comprises a nut (6) having an internal helical formation (8) and a screw (4) having an external helical formation (12) and rotatably received within the nut (6), relative rotational movement of the nut (6) and screw (4) causing axial movement of one of the nut (6) and screw (4) relative to the other of the nut (6) and screw (4). The actuator (2) further comprises a lubricant reservoir (30) and a lubricant pressuriser (34) for pressurising lubricant (22) within the lubricant reservoir (30). A lubricant receiving chamber (40) is formed in the nut (6). The screw (4) extends through the lubricant receiving chamber (40). A lubricant supply passage (42) fluidly connects the lubricant reservoir (30) and the lubricant receiving chamber (40). A valve (64) controls the flow of lubricant (22) between the lubricant reservoir (30) and the lubricant receiving chamber (40). A lubricant supply piston (44) is received in the lubricant receiving chamber (40) and is (44) mounted on the external helical formation (12) of the screw (4). The lubricant supply piston (44) is mounted to the screw (4) with sufficient friction that in response to relative rotational movement of the screw (4) and the nut (6) resulting in relative axial movement of the screw (4) and the nut (6), the lubricant supply piston (44) can move axially with the screw (4) relative to the nut (6) through the lubricant receiving chamber (40) so as to force lubricant (22) from the lubricant receiving chamber (40) into an interface (28) between the nut (6) and the screw (4), but such that the lubricant supply piston (44) may rotationally slip on the screw (4) when the lubricant supply piston (44) reaches an axial limit position within the lubricant receiving chamber (40).