Friction Vacuum Pump with Variable Gap Width
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Solution Overview
Problem
Turbomolecular pumps with Holweck pump stages face limitations in vacuum quality due to wide gaps caused by manufacturing tolerances, centrifugal forces, and thermal expansion, which affect compression efficiency, especially with light gases like helium.
Innovation Solution
A vacuum pump design featuring a rotor supported by both roller and permanent magnet bearings, with a non-constant gap width that decreases towards the roller bearing, allowing for a tighter gap and improved vacuum data by optimizing the gap dimensions based on the maximum radial deflection at different axial heights.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a constant gap width is used between the sleeve and stator, then the pump structure is simple to manufacture, but the vacuum quality and compression efficiency deteriorate due to wide gaps caused by manufacturing tolerances, centrifugal forces, and thermal expansion
Solution Approach 1:
The gap width between the sleeve and stator is designed to vary locally along the axial direction rather than being uniform. The gap is narrower in regions where higher compression efficiency is needed and wider in regions where manufacturing tolerances and thermal expansion have greater impact. This local variation in gap quality allows the system to optimize compression performance for light gases while accommodating manufacturing constraints.
2Manufacturing precision
If the gap width is reduced to improve compression efficiency, then vacuum quality improves, but the pump becomes more sensitive to manufacturing tolerances and thermal expansion
Solution Approach 1:
The gap width parameter is changed from a constant value to a variable value that changes along the axial direction of the pump. By carefully designing the gradient of gap width variation, the system achieves narrow enough gaps to provide high vacuum quality and compression efficiency while having sufficient margin in other regions to tolerate manufacturing tolerances and thermal expansion without failure.
3Reliability
If permanent magnet bearings are used to support the rotor, then friction and wear are reduced, but the bearing play causes larger gap widths that deteriorate compression performance
Solution Approach 1:
The gap width is designed to be larger in the region where permanent magnet bearings are located to accommodate their inherent play, while being narrower in the pumping regions where compression efficiency is critical. This local differentiation allows the system to maintain the reliability advantages of permanent magnet bearings while minimizing their negative impact on compression performance.
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 design significantly enhances pumping efficiency and compression performance, particularly for light gases, by creating a tight gap that compensates for the play in permanent magnet bearings and radial deflections, resulting in improved vacuum data and performance.
Implementation Method 1
the rotor of the vacuum pump is rotatably supported by a roller bearing and the gap width decreases in the direction of the roller bearing
Implementation Method 2
In addition to the roller bearing, a permanent magnet bearing is used to support the rotor
Implementation Method 3
The non-constant gap width can be matched in a simple manner to the maximum radial deflection of the rotor to be expected in the area of the respective axial height
Implementation Method 4
A mostly smooth sleeve rotates in a stator arranged inside or outside the sleeve, which stator usually has several helical grooves on the side facing the sleeve
Data Source
Figure 1
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AI summary
The pump has a rotor (2) rotatably supported by a rolling bearing (4), and comprising a case (10) that is fastened at a hub (8). A stator (20) is concentrically arranged to the case under formation of a gap (30) with a gap width (100), where the gap width is decreased to the rolling bearing. A permanent magnet bearing is attached to an end (12) of the case for supporting the rotor, where another end (14) of the case is arranged at height of the rolling bearing. A turbo-molecular pumping structure is provided between the hub and the permanent magnet bearing.