Screw Expander Noise Reduction via Rotor Profile Torque Alignment
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Solution Overview
Problem
Screw machines, such as compressors and expanders, face challenges in reducing noise levels due to non-uniform contact forces and imperfections in rotor manufacture and assembly, leading to issues like chatter and rattle, which affect efficiency and compliance with environmental noise regulations.
Innovation Solution
The design of screw machines involves modifying the 'N' rotor profile to ensure that the gate rotor torque from pressure forces acts in the same direction as the drag torque, with contact occurring at the rotor flat flank instead of the round flank, and adjusting the ratio of the main rotor addendum to the rack radius to optimize torque direction and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional rotor profiles are used, then manufacturing is simpler, but noise levels increase due to non-uniform contact forces
Solution Approach 1:
The patent modifies the rotor profile parameters, specifically the addendum radius ratio (a/r), to change the contact force distribution. By adjusting this geometric parameter, the pressure distribution along the contact line becomes more uniform, reducing noise-generating vibrations while maintaining the basic rotor structure
Solution Approach 2:
The invention introduces asymmetric features in the rotor profile design, particularly in the land and groove configurations. This asymmetry is deliberately designed to balance the contact forces during operation, preventing the non-uniform force distribution that causes chatter and rattle noises
2Power
If rotor contact forces are increased to improve power transmission, then torque transmission improves, but noise from chatter and rattle increases
Solution Approach 1:
The patent optimizes the contact force distribution by modifying rotor profile parameters rather than simply increasing overall contact force. The adjusted addendum radius ratio and land/groove dimensions create a more uniform pressure distribution that transmits torque effectively while minimizing the peaks and valleys in force that cause chatter and rattle
Solution Approach 2:
The rotor profiles are pre-designed with optimized geometry before assembly to ensure uniform contact force distribution from the start of operation. This preliminary optimization of the contact pattern prevents the development of chatter and rattle conditions rather than attempting to correct them during operation
3Object-affected harmful factors
If manufacturing precision is increased to reduce noise, then noise levels decrease, but manufacturing cost and complexity increase
Solution Approach 1:
The patent achieves noise reduction through optimized geometric parameters in the rotor profile design itself. By carefully selecting the addendum radius ratio and land/groove dimensions, the design compensates for normal manufacturing tolerances, reducing noise without requiring ultra-precise manufacturing processes
Solution Approach 2:
The noise-reducing features are built into the rotor profile design before manufacturing. The optimized geometry pre-compensates for potential manufacturing variations, allowing standard manufacturing precision to achieve the noise reduction goals without requiring exceptional precision or additional corrective manufacturing steps
Data Source
Figure 1(a)~1(d)
Figure 2(a)~2(b)
Figure 2(c)~2(d)
AI summary
A reduced noise screw expander is described, which comprises a main rotor and a gate rotor each having an 'N' profile. The rotors are designed so that the torque on the gate rotor caused by pressure forces is in the same direction as the torque on the gate rotor caused by frictional drag forces. A method of designing a screw machine exhibiting reduced noise is also described. The screw machine has two or more rotors having an 'N' profile, and the method involves determining a ratio r/r1,where r is the main rotor addendum and r1 is the radius of the rack round side, and ensuring that this ratio is greater than 1.1 where the screw machine is to be a screw compressor or less than or equal to 1.1 where the screw machine is to be a screw expander.