Screw Compressor Rotor Stiffness and Vibration Control
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Solution Overview
Problem
Existing twin-rotor screw compressors face limitations in frequency range and vibration sensitivity due to discharge pulsation, particularly when the male rotor is cantilevered, which restricts motor frequency and increases the risk of resonance-induced damage.
Innovation Solution
The compressor employs a unique lobe configuration with a seven-lobed male rotor and an eight-lobed female rotor, featuring a lower tip-to-root ratio, which increases rotor stiffness and alters resonance characteristics, allowing for higher speed operation and reduced vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a cantilevered male rotor configuration is used, then the compressor structure is simplified, but the frequency range is limited and vibration sensitivity increases
Solution Approach 1:
The patent changes the geometric parameters of the rotor lobes by reducing the tip-to-root ratio to approximately 1.3:1 to 1.4:1. This parameter modification increases rotor stiffness and alters resonance characteristics, enabling the compressor to operate at higher frequencies (up to 150Hz) while reducing vibration sensitivity, thus resolving the contradiction between structural simplicity and frequency range limitations
2Strength
If the tip-to-root ratio of rotor lobes is increased, then the lobes become stiffer, but the compressor capacity decreases
Solution Approach 1:
The patent optimizes the tip-to-root ratio parameter to a specific range of 1.3:1 to 1.4:1, which provides sufficient rotor stiffness to reduce vibration and enable higher operating frequencies while maintaining adequate compressor capacity. This balanced parameter selection resolves the contradiction between rotor stiffness and compressor productivity
Solution Approach 2:
The patent employs composite rotor designs combining different materials or material properties in the rotor structure to achieve optimal stiffness-to-capacity characteristics, allowing the rotor to maintain sufficient rigidity for high-frequency operation while preserving adequate compression capacity
3Object-generated harmful factors
If the lobe count is increased, then the pulsation magnitude decreases, but the device complexity increases
Solution Approach 1:
The patent employs asymmetric lobe configurations with different lobe counts for the male and female rotors (e.g., 7 lobes for male rotor, 8 lobes for female rotor), creating an asymmetric tooth profile that reduces discharge pulsation magnitude. This asymmetric design resolves the contradiction by achieving smoother discharge without requiring symmetric increases in lobe count that would proportionally increase complexity
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 reduces refrigerant mass flow and pulsation magnitude, decreases sound and vibration, and enables higher compressor speeds up to 120Hz while maintaining sufficient capacity and reducing the risk of resonance excursions.
Implementation Method 1
A male rotor has a working portion having a plurality of lobes of a count and at least a first shaft portion protruding beyond a first end of the male rotor working portion and mounted for rotation about a first axis. A female rotor has a working portion having a plurality of lobes of a count (NF) and mounted for rotation about a second axis so as to be enmeshed with the male rotor working portion.
Implementation Method 2
A bearing cavity includes at least one bearing rotatably supporting the rotor shaft.
Implementation Method 3
A contacting seal is sealingly engaged with the rotor shaft and disposed in the bearing cavity proximate the partition.
Implementation Method 4
A partition through which the rotor shaft extends separates the bearing cavity from the compression chamber.
Data Source
Figure 1~2
Figure 3
AI summary
A compressor (22) comprises a housing (50) having a first port (26) and a second port (28). A male rotor (52) has a working portion (64) having a plurality of lobes (110) of a count (NM) and at least a first shaft portion (62) protruding beyond a first end (68) of the male rotor working portion and mounted for rotation about a first axis (500). A female rotor (54) has a working portion (66) having a plurality of lobes (112) of a count (NF) and mounted for rotation about a second axis (502) so as to be enmeshed with the male rotor working portion. An electric motor (56) is within the housing and has a stator (58) and a rotor (60) mounted to the first shaft portion. The compressor has no additional compressor rotors. The lobe count of the male rotor is less than the lobe count of the female rotor. A combined lobe count (NM + NF) is at least fifteen.