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RESEARCH PAPERS

Study on the High-Sealing of Roots Rotor With Variable Trochoid Ratio

[+] Author and Article Information
Chiu-Fan Hsieh

Department of Mechanical Engineering, National Chung-Cheng University, 168 San-Hsing, Ming-Hsiung, Chia-Yi 621, Taiwan, R.O.C.naturaltom@gmail.com

Yii-Wen Hwang

Department of Mechanical Engineering, National Chung-Cheng University, 168 San-Hsing, Ming-Hsiung, Chia-Yi 621, Taiwan, R.O.C.imeywh@ccu.edu.tw

J. Mech. Des 129(12), 1278-1284 (Dec 10, 2006) (7 pages) doi:10.1115/1.2779897 History: Received September 01, 2006; Revised December 10, 2006

Vacuum pump plays an important role in the vacuum system. In this paper, a new method is proposed to design the Roots rotor that was the trochoidal curve with variable trochoid ratio. The fifth-order polynomial and cubic spline functions are used to generate smoothly trochoid ratio functions and thus a regular addendum curve for Roots rotor will be generated. Based on the addendum curve, the tooth profile for the complete Roots rotor is derived by the gearing theory. In order to improve the sealing between the rotor tip and the chamber, a design procedure is also developed for roots rotor with high sealing and high area efficiency. In addition, the undercutting equation is used to study the constraints of design parameters and the center of curvature is used to check the occurrence of the carryover on the tooth profile. Finally, some design examples are presented to show the feasibility of the proposed method.

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Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Illustration of shortened epicycloid

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Figure 2

Applied coordinate systems

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Figure 3

Rotor profile with conformity

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Figure 4

Design of the trochoid ratio function

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Figure 5

Result of the rotor profile

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Figure 6

Locus of the rotor profile

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Figure 7

Design procedure for high-sealing rotor

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Figure 8

Design region of two-lobe rotor (θ1=6deg)

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Figure 9

Design region of three-lobe rotor (θ1=4deg)

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Figure 10

Results of the design

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