Nose-wheel Steering Actuator with Roller-Screw Coupling
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Solution Overview
Problem
Existing nose-wheel steering actuators are typically large, difficult to align, and require complex mechanical and hydraulic balancing, making them cumbersome and unreliable for compact applications.
Innovation Solution
A compact actuator design featuring a tubular shaft with a low friction roller-screw coupling between the shaft and a sleeve, where the coupling is aligned with the rack formation, providing concentric component placement, mechanical balance, and reduced dimensions, supported by a stiff shaft and housing, with a magnetic damping arrangement to mitigate vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional electric motor driven linear actuator with threaded nut and ball-screw coupling is used, then the actuator can provide reliable linear motion, but the actuator becomes of relatively large dimensions and difficult to accommodate
Solution Approach 1:
The patent merges the low friction coupling elements directly with the rack formation by providing rack teeth on the sleeve that engage with pinion teeth on the shaft, eliminating the need for separate ball-screw or threaded nut components. This integration reduces the overall actuator dimensions while maintaining reliable linear motion transmission.
Solution Approach 2:
The shaft serves multiple functions: it acts as the drive member rotated by the motor, provides structural support for the sleeve, and forms part of the low friction coupling mechanism through its pinion teeth. This multi-functionality reduces the number of separate components needed, compacting the actuator design.
2Ease of operation
If a traditional actuator arrangement with separate shaft and rack is used, then linear motion can be achieved, but alignment of the shaft and rack becomes difficult and requires complex mechanical balancing
Solution Approach 1:
By integrating the pinion teeth directly onto the shaft and rack teeth onto the sleeve, the patent eliminates the need for separate alignment procedures between independent shaft and rack components. The concentric arrangement ensures automatic alignment, removing complex mechanical balancing requirements.
Solution Approach 2:
The patent creates a concentric, co-axial arrangement where the shaft and sleeve are naturally aligned along the same central axis. This equipotential geometric relationship eliminates alignment difficulties and reduces the need for complex mechanical balancing procedures.
3Strength
If the low friction screw coupling is located away from the rack formation, then the shaft can be longer providing more support, but the actuator dimensions increase significantly
Solution Approach 1:
The patent resolves the conflict between support length and compactness by changing the spatial arrangement: instead of extending the shaft axially to provide support, the shaft's rotational strength and the sleeve's positioning provide support in a radial/concentric configuration. This allows adequate support while maintaining compact actuator dimensions.
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 design results in a compact, reliable, and mechanically balanced actuator that simplifies alignment and support, reduces hydraulic imbalances, and minimizes wear, while effectively steering the nose-wheel with reduced parasitic friction and improved load distribution.
Implementation Method 1
a low friction screw coupling between the shaft and the sleeve and arranged such that rotation of the shaft drives the sleeve for axial movement
Implementation Method 2
A damping arrangement is conveniently provided to damp the rotation of the shaft. The damping arrangement may be, for example, of magnetic form.
Data Source
AI summary
An actuator comprises a shaft 12 arranged to be driven for rotation by an electrically powered motor 18, a sleeve 22 encircling at least part of the shaft 12 and carrying a toothed rack formation 26, and a low friction screw coupling 36 between the shaft 12 and the sleeve 22 and arranged such that rotation of the shaft 12 drives the sleeve 22 for axial movement, wherein the low friction screw coupling 36 is adjacent and aligned with the rack formation 26.