Shaft Housing Assembly Rotational Tolerance Ring Engagement
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Solution Overview
Problem
Conventional methods of assembling a housing and shaft using tolerance rings often require significant axial force, which can lead to surface damage and particle generation, especially in delicate applications like hard disk drives and bearing assemblies.
Innovation Solution
A method involving a pre-assembly with a shaft and housing, where a band of resilient material with projections is used, allowing the shaft to be secured by rotating it to align projections with varying surface parts, minimizing axial dragging and requiring less assembly effort, while maintaining strong frictional engagement to prevent relative movement under normal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional axial pressing method is used to assemble shaft and housing with tolerance ring, then secure engagement and torque transmission are achieved, but surface damage and particle generation occur due to high axial force
Solution Approach 1:
The patent transitions from axial force application to rotational force application. The shaft is rotated relative to the tolerance ring during assembly, causing the projections to engage with the varying radius surface and compress radially rather than being compressed axially. This dimensional change from axial to rotational assembly eliminates surface damage while maintaining secure engagement.
Solution Approach 2:
Instead of pressing the shaft axially into the tolerance ring, the patent inverts the approach by rotating the shaft so that the tolerance ring projections ride up the varying radius surface and compress the shaft radially. This inversion of the assembly mechanism achieves secure engagement without the harmful axial dragging that causes surface damage.
2Strength
If high axial force is applied during assembly to ensure secure engagement, then torque transmission capability is improved, but assembly difficulty increases due to required assembly force
Solution Approach 1:
The patent changes the assembly dimension from axial pressing to rotational engagement. By rotating the shaft during assembly, the tolerance ring projections compress the shaft radially through the varying radius surface, achieving secure engagement and torque transmission capability without requiring high axial assembly forces.
Solution Approach 2:
The patent utilizes a varying radius surface parameter on the shaft that changes with rotation. As the shaft rotates, the radius varies to guide the tolerance ring projections and achieve progressive radial compression, transforming the assembly process into one that requires minimal force while ensuring secure engagement.
3Strength
If tolerance ring projections are compressed axially to create interference fit, then retention force is provided, but axial dragging causes particle generation
Solution Approach 1:
The patent eliminates axial dragging by changing the compression mechanism from axial to rotational. The shaft rotates relative to the tolerance ring, causing projections to compress radially rather than drag axially, providing retention force without generating particles through friction and contact.
Solution Approach 2:
Instead of axially pressing the shaft through the tolerance ring projections, the patent inverts the mechanism by rotating the shaft so that the varying radius surface guides the projections to compress radially. This inversion provides the necessary retention force while eliminating the axial dragging that causes particle generation.
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
This method reduces surface damage and particle generation by minimizing axial force during assembly, allowing for secure engagement of the shaft and housing with reduced effort and minimal surface contact, enabling effective torque and axial force transmission while allowing relative movement under extreme conditions.
Implementation Method 1
The projections are compressed. Each projection acts as a spring and exerts a radial force against the shaft and the surface of the bore, providing an interference fit between the shaft and the housing. Rotation of the housing or the shaft will produce similar rotation in the other of the shaft or the housing, as torque is transmitted by the ring.
Implementation Method 2
A tolerance ring generally comprises a band of resilient material, for example a metal such as spring steel, the ends of which are brought together to form a ring.
Data Source
AI summary
A shaft is held in place within the bore of a housing by a band of resilient material that is located between the shaft and the housing and has a series of projections extending radically inwards. The shaft surface has a first part that lies closer to the longitudinal axis of the bore than a second part, when the shaft and housing are assembled. The shaft is initially inserted into the resilient band, which is held within the bore, such that the first part of the shaft surface is oriented towards one of the projections of the resilient band. In this orientation of the shaft, the projection is not compressed. By orienting the second part of the shaft surface the projection, the projection is brought under compression and the shaft is held firmly within the bore.