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Research Papers

Design of Rotor for Internal Gear Pump Using Cycloid and Circular-Arc Curves

[+] Author and Article Information
T. H. Choi, M. S. Kim, J. H. Bae

 School of Mechanical Engineering at Pusan National University, 30 Jangjeon-Dong, Geumjeong-Gu, Pusan 609-735, Republic of Korea

G. S. Lee

 Research Institute at SAMHAN Co., Ltd., 40-2 Ungnam-Dong, Seongsan-Gu, Changwon 642-290, Republic of Korea

S. Y. Jung

 Research Institute of Mechanical Technology at Pusan National University, 30 Jangjeon-Dong, Geumjeong-Gu, Pusan 609-735, Republic of Korea

C. Kim1

 Research Institute of Mechanical Technology at Pusan National University, 30 Jangjeon-Dong, Geumjeong-Gu, Pusan 609-735, Republic of Koreachulki@pusan.ac.kr

1

Corresponding author.

J. Mech. Des 134(1), 011005 (Jan 04, 2012) (12 pages) doi:10.1115/1.4004423 History: Received January 12, 2011; Revised June 09, 2011; Accepted June 14, 2011; Published January 04, 2012; Online January 04, 2012

In the case of internal gear pumps, the eccentricity of the outer rotor, which resembles a circular lobe, must be limited to a certain value in order to avoid the formation of cusps and loops; furthermore, the tip width of the inner rotor, which has a hypocycloid curve and an epicycloid curve, should not be allowed to exceed the limit value. In this study, we suggest that the tip width of the inner rotor be controlled by inserting a circular-arc curve between the hypocycloid and epicycloid curves. We also suggest that the outer rotor be designed using the closed-form equation for the inner rotor and the width correction coefficient. Thus, it is possible to design a gerotor for which there is no upper limit on the eccentricity, as in this case, undercut is prevented and there is no restriction on the tip width. We also develop an automated program for rotor design and calculation of the flow rate and flow rate irregularity. We demonstrate the superior performance of the gerotor developed in this study by analyzing the internal fluid flow using a commercial computational fluid dynamics (CFD)-code.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Outer rotor resembling a circular lobe and inner rotor of Type I gerotor

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Figure 2

Inner rotor of Type II gerotor and rolling circles of cycloid curves

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Figure 3

Inner rotor in new design and rolling circles of cycloid curves

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Figure 4

Moving and rotating angles of rolling circles on hypocycloid curve

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Figure 5

Range angle of circular-arc curve

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Figure 6

Moving and rotating angles of rolling circles on epicycloid curve

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Figure 7

Inner rotor tracing according to rotating simulation. (a) Trajectory curve. (b) Rotating simulation.

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Figure 8

Interference between inner rotor and outer rotor

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Figure 9

Observed trend in interference during rotor rotation

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Figure 10

Avoiding interference using width correction coefficient, n

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Figure 11

Condition for avoiding interference

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Figure 12

New design of gerotor

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Figure 13

Exhaust chamber and imaginary contact points on rotors

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Figure 14

Area of outer and inner rotors required to calculate chamber area

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Figure 15

Imaginary contact points on side boundaries of chamber. (a) Case I (SklI=ΔPliO2Plo+ΔPliO1O2). (b) Case II (SklII=ΔPlmO1O2-ΔPloPlmPli). (c) Case III (SkrIII=ΔO1PriO2+ΔPriProO2). (d) Case IV (SkrIV=ΔO1PrmO2-ΔPrmProPri).

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Figure 16

Automated design program. (a) Automated algorithm for rotor design and calculation of cost function. (b) Design variables for automated design program. (c) Graph of instantaneous flow rate and rotor information.

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Figure 17

Prototype rotors. (a) e = 1.29. (b) e = 1.30. (c) e = 1.31. (d) e = 1.41.

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Figure 18

Numerical model for CFD

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Figure 19

Moving grids applied at the gerotor

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Figure 20

CFD results of velocity distribution and flow rate

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