Research Papers

Design and Testing of an Adjustable Linkage for a Variable Displacement Pump

[+] Author and Article Information
Shawn R. Wilhelm

e-mail: Wilh0141@UMN.EDU

James D. Van de Ven

Assistant Professor
e-mail: vandeven@UMN.EDU
Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55455

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received August 2, 2012; final manuscript received July 15, 2013; published online September 11, 2013. Assoc. Editor: Jian S Dai.

J. Mechanisms Robotics 5(4), 041008 (Sep 11, 2013) (8 pages) Paper No: JMR-12-1110; doi: 10.1115/1.4025122 History: Received August 02, 2012; Revised July 15, 2013

A variable displacement hydraulic pump/motor with high efficiency at all operating conditions, including low displacement, is beneficial to multiple applications. Two major energy loss terms in conventional pumps are the friction and lubrication leakage in the kinematic joints. This paper presents the synthesis, analysis, and experimental validation of a variable displacement sixbar crank-rocker-slider mechanism that uses low friction pin joints instead of planar joints as seen in conventional variable pump/motor architectures. The novel linkage reaches true zero displacement with a constant top dead center position, further minimizing compressibility energy losses. The synthesis technique develops the range of motion for the base fourbar crank-rocker and creates a method of synthesizing the output slider dyad. It is shown that the mechanism can be optimized for minimum footprint and maximum stroke with a minimum base fourbar transmission angle of 30 deg and a resultant slider transmission angle of 52 deg. The synthesized linkage has a dimensionless stroke of 2.1 crank lengths with a variable timing ratio and velocity and acceleration profiles in the same order of magnitude as a comparable crank-slider mechanism. The kinematic and kinetic results from an experimental prototype linkage agree well with the model predictions.

Copyright © 2013 by ASME
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Fig. 1

Variable displacement linkage

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Fig. 2

Base triangles for determining r1min and r1max

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Fig. 3

Extended and overlapped extremes of fourbar linkage

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Fig. 4

Variable ground pivot locations for extended case

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Fig. 5

Configurations of variable linkage

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Fig. 6

Associated triangle for determining θc and θr1min

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Fig. 7

Variable linkage showing five-ground pivot positions between 0% and 100% displacement and the associated coupler curves

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Fig. 8

Defining angle of axis of slide

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Fig. 9

3D plot of stroke/footprint of case “a” linkage as a function of link lengths R3 and r4

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Fig. 10

Sixbar vector loop diagram

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Fig. 12

Piston acceleration

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Fig. 13

Linkage timing ratio

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Fig. 14

Prototype linkage cad model and rendering with labeled links

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Fig. 15

Prototype variable displacement mechanism

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Fig. 16

Experimental setup

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Fig. 17

Input shaft velocity

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Fig. 20

Piston acceleration




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