Rotor Shaft Locking Assembly With Interference-Fit Retainer
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Solution Overview
Problem
Existing locking assemblies for securing components in air turbine starters, such as rotatable shafts and gear systems, often require expensive customized nuts and lengthy assembly times, necessitating additional components like shims to achieve proper compression and balancing.
Innovation Solution
A locking assembly comprising a rotor shaft with an inner bore, a gear mounted on its outer diameter, a lock nut threadedly engaged with the rotor shaft, and a retainer with a projection portion that biases the lock nut against the gear, establishing an interference fit to secure the gear and bearing assembly to the rotor shaft, reducing the likelihood of the lock nut loosening during operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If customized nuts and additional components like shims are used to secure the gear system, then the reliability of the locking assembly is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent combines the locking nut and retainer into a single integrated component that performs multiple functions: the retainer is press-fit into the rotor shaft to prevent axial movement, while the lock nut secures the gear to the rotor shaft. This integration eliminates the need for separate shims and multiple fasteners, reducing assembly complexity while maintaining reliability
Solution Approach 2:
The locking assembly is divided into distinct functional segments: the retainer portion that interfaces with the rotor shaft inner bore to prevent axial movement, and the lock nut portion that secures the gear to the rotor shaft. This segmentation allows each component to be optimized for its specific function while simplifying the overall assembly
2Manufacturing precision
If customized nuts and additional components are used to achieve proper compression and balancing, then the manufacturing precision is improved, but the ease of manufacture deteriorates
Solution Approach 1:
The retainer is designed to be press-fit into the rotor shaft's inner bore, creating a self-aligning and self-positioning mechanism that automatically achieves proper compression and balancing without requiring additional shims or adjustment components. The interference fit ensures precise positioning
Solution Approach 2:
The lock nut serves multiple functions: it secures the gear to the rotor shaft, provides axial positioning, and works in conjunction with the retainer to achieve proper compression. This multi-functionality eliminates the need for specialized customized nuts and additional balancing components
3Device complexity
If a simple lock nut is used without additional retainers, then the device complexity is reduced, but the reliability under cyclic loading deteriorates due to increased likelihood of loosening
Solution Approach 1:
The retainer is installed in the rotor shaft's inner bore before the lock nut is secured, creating a preliminary constraint that prevents axial movement of the gear assembly. This preliminary anti-action ensures that the lock nut remains securely positioned against the gear during cyclic loading operations
Solution Approach 2:
The interference fit between the retainer and rotor shaft is established in advance, creating a pre-loaded condition that prevents loosening before the lock nut is fully secured. This preliminary action ensures reliability from the outset of operation
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 solution provides secure retention of the gear and bearing assembly, reduces the risk of lock nut loosening under cyclic loading, simplifies assembly, and minimizes the likelihood of misbalance, while allowing for the use of off-the-shelf components, thus reducing costs and assembly complexity.
Implementation Method 1
a projection portion extending from the step portion. The projection portion is insertable into the inner bore to bias the lock nut against the axial end face of the gear
Implementation Method 2
the step portion is dimensioned to establish an interference fit with the rotor shaft along the inner bore
Data Source
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Figure 5
AI summary
An assembly for a coupling together rotatable components according to an example of the present disclosure includes, among other things, a rotor shaft (142) extending along a centerline axis, the rotor shaft defining an inner bore (170) extending from an axial end of the rotor shaft, a gear (140) mounted on an outer diameter of the rotor shaft, a lock nut (164) threadedly engaged with the outer diameter of the rotor shaft such that the lock nut abuts against an axial end face of the gear, and a retainer (168) including a step portion extending from a head portion and including a projection portion (168C) extending from the step portion. The projection portion is insertable into the inner bore to bias the lock nut against the axial end face of the gear, and the step portion is dimensioned to establish an interference fit with the rotor shaft along the inner bore. A starter assembly and a method of assembly are also disclosed.