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Research Papers

Kinematic Analysis of a Swash-Plate Controlled Variable Displacement Axial-Piston Pump With a Conical Barrel Assembly

[+] Author and Article Information
Zhiru Shi, Jonathan Granstrom

Department of Mechanical Engineering—Engineering Mechanics, Michigan Technological University, Houghton, MI 49931-1295

Gordon Parker1

Department of Mechanical Engineering—Engineering Mechanics, Michigan Technological University, Houghton, MI 49931-1295ggparker@mtu.edu

1

Corresponding author. Present address: 815 R.L. Smith ME-EM Building, 1400 Townsend Drive, Houghton, MI 49931-1295.

J. Dyn. Sys., Meas., Control 132(1), 011002 (Dec 01, 2009) (8 pages) doi:10.1115/1.4000067 History: Received May 24, 2008; Revised April 02, 2009; Published December 01, 2009; Online December 01, 2009

Variable displacement, swash-plate controlled, axial-piston pumps are widely used in applications that require high pressure and variable flow rates. The pump consists of a rotating barrel assembly that houses several pistons in a circular array. A swash-plate is used to control the displacement of the pistons to adjust the output flow of hydraulic fluid. As the barrel rotates, the pistons slide along the angled swash-plate and draw oil from the supply and then discharge oil into the high pressure circuit. This results in an almost constant output flow rate. This paper analyzes the kinematics of a pump based on its geometry dependent characteristics. The analysis assumes an idealized case in which there is no oil leakage and the fluid is considered to be incompressible. It is revealed through the analysis that the piston displacement and the pump output flow are slightly increased by using a conical barrel. Instantaneous and mean flow rate equations are used to describe the output flow characteristics and flow ripple effect. The output flow rate ripple profile is found to be a function of both swash-plate angle and the conical barrel angle. A term defined as the flow rate uniformity coefficient is used to better quantify the flow ripple phenomenon. A frequency analysis is performed on the output flow rate and an additional order is found to be present when using a conical barrel pump versus one with a cylindrical barrel when the pumps have an odd number of pistons. Conical barrel piston pumps are found to have a slight increase in piston displacement, velocity, and acceleration relative to the rotating barrel frame of reference over a pump with a cylindrical barrel. This translates into an increase in the output flow rate for a conical piston pump under the same operating conditions. The conical barrel is also found to have a reduction in the rotational inertia allowing for faster angular acceleration. The presence of an extra order from a frequency analysis for a conical pump with an odd number of pistons has the potential to cause unwanted noise or vibration to the structure or components attached to the pump.

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Figures

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Figure 1

Internal views of cylindrical barrel (a) and conical barrel (b) piston pumps

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Figure 2

Conical barrel piston pump with an outline to relate physical features of the pump with geometry used in the derivations of the kinematic equations

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Figure 3

Front and side views for a conical barrel pump illustrating the coordinate frame and how the TDP and BDP change with swash-plate angle

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Figure 4

Front and side views for a conical barrel pump used for defining arbitrary piston locations and developing the kinematic relationships

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Figure 5

Relative piston displacement at an arbitrary position

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Figure 6

Piston position and associated valve plate relation showing the number of pistons within the discharge and intake regions of the valve plate of a nine piston Rexroth A4V-125-EL hydraulic piston pump

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Figure 7

Instantaneous flow in one revolution with nine pistons; α=5 deg, β=7 deg, Ap=4.82 cm2(0.7466 in.2), r=5.33 cm (2.1 in.), and ϕ̇=154.46 rad/s (1475 rpm)

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Figure 8

Output flow rate comparison between a conical barrel (β=7 deg) and a cylindrical barrel (β=0 deg) with nine pistons; α=5 deg, Ap=4.82 cm2(0.7466 in.2), r=5.33 cm (2.1 in.), and ϕ̇=154.46 rad/s (1475 rpm)

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Figure 9

Piston motion comparison relative to the rotating reference frame of the barrel between a conical (β=7 deg) and a cylindrical (β=0 deg) barrel with nine pistons; α=5 deg, Ap=4.82 cm2(0.7466 in.2), r=5.33 cm (2.1 in.), and ϕ̇=154.46 rad/s (1475 rpm)

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Figure 10

Change in pump uniformity coefficient with respect to swash-plate angle (α) and barrel angle (β) for a pump with nine pistons; Ap=4.82 cm2(0.7466 in.2), r=5.33 cm (2.1 in.), and ϕ̇=154.46 rad/s (1475 rpm)

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Figure 11

Order spectrum for a pump with nine pistons using a cylindrical barrel versus a conical barrel; α=5 deg, β=7 deg, Ap=4.82 cm2(0.7466 in.2), r=5.33 cm (2.1 in.), and ϕ̇=154.46 rad/s (1475 rpm)

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Figure 12

Inertia comparison diagram between a cylindrical and a conical barrel

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