Linear Roller Bearing Assembly for Stirling Engine Stroke
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Solution Overview
Problem
Current linear bearing technologies for Stirling engines and cryocoolers face limitations in stroke capability, frequency of operation, radial load capacity, and susceptibility to wear and contamination, particularly due to the loosening of straps around rollers, which degrades performance and efficiency.
Innovation Solution
A linear roller bearing assembly featuring a hub and collar with roller bearing sub-assemblies, where straps are wrapped partially around rollers and connected to both the hub and collar, allowing for movement along a selected direction for approximately half the circumference, preventing sliding and rotational contact, thus minimizing wear and maintaining precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If straps are wrapped around rollers in linear bearings, then the bearing can guide linear movement, but the straps loosen around the rollers over time causing lateral slide and rotational slip
Solution Approach 1:
The bearing assembly is divided into multiple independent roller bearing sub-assemblies (first, second, third, and fourth sub-assemblies) arranged radially around the hub. Each sub-assembly independently supports lateral loads in specific directions, preventing any single loose strap from causing overall bearing failure. This segmentation maintains reliability even when individual straps loosen.
Solution Approach 2:
The roller bearing sub-assemblies are positioned at radially opposite locations (e.g., first and third sub-assemblies opposite each other, second and fourth sub-assemblies opposite each other). This opposing arrangement creates counterbalancing support forces that prevent lateral slide and rotational slip of the hub, compensating for strap loosening in any single location.
2Reliability
If linear bearings are used to prevent contact between piston and cylinder, then wear and energy loss are reduced, but the bearings must support lateral and rotational loads which complicates the design
Solution Approach 1:
The roller bearing sub-assemblies are strategically positioned at specific radial locations around the hub rather than uniformly distributed. This asymmetric arrangement optimizes the support for anticipated lateral and rotational loads while minimizing the number of sub-assemblies needed, reducing overall complexity.
Solution Approach 2:
Each roller bearing sub-assembly performs multiple functions: it guides linear movement of the hub, supports lateral loads in its specific direction, and contributes to preventing rotational slip through the radial pattern arrangement. This multi-functionality reduces the need for separate components for each function.
3Reliability
If gas bearings are used in Stirling engines and cryocoolers, then wear is minimized during operation, but they are expensive to manufacture due to extremely close dimensional tolerances and can lock up if foreign particles are lodged between surfaces
Solution Approach 1:
The roller bearing sub-assemblies use simpler, more manufacturable components with relaxed tolerances compared to gas bearings. The straps and rollers can be manufactured using conventional machining processes without requiring extremely close dimensional tolerances, significantly reducing manufacturing cost while maintaining adequate service life.
Solution Approach 2:
The roller bearing sub-assemblies act as intermediary components between the hub and the external environment. They provide a robust mechanical interface that is less sensitive to foreign particle contamination compared to the precision surfaces of gas bearings, preventing lock-up while still minimizing wear through rolling contact.
4Length of moving object
If the hub and collar move relative to each other for longer stroke length, then power or work output is achieved, but the movement is limited to approximately one quarter of the circumference due to bearing configuration
Solution Approach 1:
The bearing design transitions from limiting movement to one dimension (quarter circumference in single-direction bearings) by adding radial symmetry with multiple sub-assemblies arranged in a circular pattern. This allows the hub to move approximately half the circumference in opposite directions from mid-stroke, effectively doubling the stroke length capability.
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 enhances guidance precision, stroke length, and frequency of operation while reducing wear and contamination, leading to improved performance and efficiency in Stirling engines and cryocoolers by maintaining concentricity and preventing energy loss through precise alignment and reduced friction.
Implementation Method 1
roller bearing sub-assemblies disposed in a radial pattern around the hub. The roller bearing sub-assemblies are configured to guide linear movement of the hub relative to the collar
Implementation Method 2
The rollers can therefore slide laterally or slip rotationally within the straps to degrade the performance of the linear bearing
Implementation Method 3
straps wrapped partially around different portions of the roller. Each of the straps is connected to the hub and/or the collar
Data Source
AI summary
Linear roller bearing assemblies can include a hub, a collar around the hub and roller bearing sub-assemblies disposed in a radial pattern around the hub. The roller bearing sub-assemblies can guide linear movement of the hub relative to the collar along a selected direction. Each roller bearing sub-assembly can include a roller and straps wrapped partially around the roller. Each strap is connected to at least one of the hub and the collar. And at least one of the straps can be connected to the roller while at least one of the straps can be circumferentially free of the roller. The hub and collar are moveable relative to each other along the selected direction for a distance that is approximately half of a circumference of the roller. Methods of forming linear roller bearing assemblies are also disclosed, as are multi-cylinder Stirling engines and a thermal energy recovery system.