Eccentric Pin Geometry for High-Speed Scroll Machine Rigidity
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Solution Overview
Problem
In scroll fluid machines, the eccentric pin bends due to increased centrifugal force at high speeds, causing partial contact in the bearing that supports the rotating shaft, leading to operational issues.
Innovation Solution
The outer shape of the eccentric pin is designed with a first circular arc exceeding the rotating shaft's edge and a second circular arc with a radius equal to or less than the shaft's edge, enhancing its rigidity and preventing bending. Additionally, a bush assembly with a balance weight and stepped portion is used to increase the rigidity of the joining between components, and the bush is formed from sintered material with a cast iron balance weight for improved stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rotating shaft is rotated at high speed to improve performance, then productivity is improved, but the centrifugal force on the eccentric pin increases causing bending and bearing partial contact
Solution Approach 1:
The outer shape of the eccentric pin is designed with a first circular arc having a first radius Ra that exceeds the portion of the outer edge of the rotating shaft. This curved geometry increases the moment of inertia and rigidity of the eccentric pin, preventing bending under high-speed rotation while maintaining smooth operation.
Solution Approach 2:
The eccentric pin's geometry is modified by changing the radius parameter of its outer shape. The first radius Ra is specifically designed to be larger than the rotating shaft's outer edge radius, which fundamentally changes the pin's stiffness characteristics and enables it to withstand high-speed rotation without bending.
2Strength
If the first radius Ra is increased to improve eccentric pin rigidity, then bending is prevented, but the outer shape may exceed the rotating shaft edge causing processing and assembly inconvenience
Solution Approach 1:
The outer shape of the eccentric pin is divided into two distinct circular arc portions: a first circular arc with radius Ra exceeding the shaft edge for rigidity, and a second circular arc with radius Rb equal to or less than the shaft edge radius for maintaining manufacturability. This segmentation allows each portion to serve its specific function without compromise.
Solution Approach 2:
Different portions of the eccentric pin are given different geometric qualities. The first circular arc portion has a larger radius for rigidity where needed, while the second circular arc portion has a smaller radius matching the shaft edge for ease of manufacture and assembly, creating local optimization throughout the component.
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 configuration prevents bending of the eccentric pin and increases the rigidity of the bush assembly, allowing the scroll fluid machine to operate at high speeds without bearing issues, with the maximum number of rotations per second exceeding 145 rps.
Implementation Method 1
When the rotating shaft is rotated at high speed for improving performance, centrifugal force is increased, and thus action of the centrifugal force on the eccentric pin becomes too large and bending of the eccentric pin in the radial direction is caused
Implementation Method 2
the bush is formed of sintered material, and the balance weight is formed of a cast iron material
Data Source
Figure 1
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AI summary
An outer shape of an eccentric pin (25) of a rotating shaft (19) has: a first circular arc (25a) formed in a range of an outer shape of the rotating shaft (19), with a first radius (Ra) having a length exceeding a part of an outer edge (19b) of the rotating shaft (19), the first radius (Ra) having a center at a position of an eccentric center (LE); and a second circular arc (25b) formed in a portion where the first radius (Ra) exceeds the outer edge (19b), with a second radius (Rb) having a length equal to or less than a radius (R) forming the outer edge (19b), the second radius (Rb) having a center at a position of a shaft center (CE).