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Research Papers

Physical Limitations for the Bandwidth Frequency of a Pressure Controlled, Axial-Piston Pump

[+] Author and Article Information
Noah D. Manring1

Mechanical and Aerospace Engineering Department,  University of Missouri, Columbia, MO 65211ManringN@missouri.edu

Viral S. Mehta

Hydraulic Research and Development, Caterpillar Inc. Peoria, IL 61656mehta_viral@cat.com

Pressure-controlled pumps tend to behave as second-order systems while displacement controlled pumps often behave as first-order systems [14].

1

Corresponding author.

J. Dyn. Sys., Meas., Control 133(6), 061005 (Sep 29, 2011) (12 pages) doi:10.1115/1.4004056 History: Received February 15, 2010; Revised February 15, 2011; Published September 29, 2011; Online September 29, 2011

The objectives of this paper are to identify the design parameters that have the greatest impact on the bandwidth frequency of a pressure controlled, axial-piston pump. This study is motivated by the fact that a physical limitation for these machines has been observed in practice, as it has been difficult to increase the bandwidth frequency much beyond 25 Hz. Though much research has been done over the past thirty years to understand the dynamical behavior of these machines, the essential design-characteristics that determine the bandwidth frequency of the pump remain elusive. In part, this is due to the fact that the machine is complex and when coupled with a hydraulic control valve that is disturbed by steady and transient fluid-momentum effects this dynamical property becomes difficult to assess. In order to achieve the objectives of this research, this paper presents the most comprehensive pump-and-valve model of a pressure controlled, axial-piston machine available in the literature to date. The pump model includes the effects of the discrete pumping-elements acting on the swash plate, while the valve model includes both steady and transient fluid-momentum forces. To identify the dominate features of the model, nondimensional analysis is employed and the complexity of the model is subsequently reduced by eliminating negligible terms. Furthermore, a closed-form expression for the bandwidth frequency is employed and perturbation analysis is used to identify the dominant set of parameters that impact the bandwidth frequency of the pump. In conclusion, it is shown that, by far, the greatest impact on the bandwidth frequency may be achieved by reducing the swept volume of the control actuator and by increasing the flow capacity of the control valve.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

A schematic of the pressure controlled, axial-piston, swash-plate type, variable-displacement pump (Section A-A is shown in Fig. 3)

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Figure 2

A schematic of the pump discharge line used for modeling the discharge pressure of the variable-displacement pump

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Figure 3

A partial free-body-diagram of the swash-plate (Section A-A is referred to in Fig. 1)

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Figure 4

Partial free-body-diagrams for the actuators and pistons

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Figure 5

Pressure profile for illustrating the essential characteristics of Pn

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Figure 6

Schematic of the control actuator for modeling the fluid pressure, Pc

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Figure 7

Shematic of the three-way control valve with fluid control-volumes and a free-body-diagram of the spool

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Figure 8

Block diagram for the reduced order system

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