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Experiments and Modeling for Quantifying Noise Sources in Hydraulic Pumps

October 2015

2015 Fluid Power Innovation & Research Conference (FPIRC15)

Timothy Opperwall, Dr. Andrea Vacca

Maha Fluid Power Research CenterPurdue University1500 Kepner Dr.

Lafayette, IN 47905, USA

2Motivation

Fluid-borne noise (FBN)

Pressure fluctuations in the fluid

Structure-borne noise (SBN)

Forces and moments in the structures

Air-borne noise (ABN)

Vibrations transmitted through the air from the structure to the field

• Noise is a key issue for current hydraulic systems and the spread of hydraulics into new fields.

• Displacement machines are the primary sources of noise in fluid power systems.

• Supplement modeling efforts with measurements to determine how noise sources propagate through the system.

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State of the ArtMany researchers working on noise • Edge K. 1999• Kojima E. 2000• Manring N. 2003• Borghi M. 2005• Ericson L. 2009• Klop and Ivantysynova 2011• University research efforts:

Bath, Aachen, Linköping, etc.

CasappaWhisper

Bosch-Rexroth Silence Plus

Concentric Calma

Other investigations on noise specifically in gear pumps• Fiebig W. 2007• Bonanno A. 2008• etc.

Turolla Shhark

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State of the Art

Optimization for noise source reduction

Detailed multi-domain pump models

• Seeniraj and Ivantysynova 2008-2011• Kalbfleisch and Ivantysynova 2012-present• Devendran and Vacca 2010-present

• Vacca et al. (2007-present) - External gear pump model• Ivantysynova et al. (2001 –present) – Axial piston pump model

• Noise reduction research efforts focused on reducing the source terms of the FBN and SBN without considering the propagation through the system.

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Reference Machine: External Gear Pump

• Features

– Simple principle of operation.

– Few components.

– Cheap to manufacture.

– Fixed displacement.

Goal:Develop new analysis methods for use with fluid power components and systems to identify important sources and transmission paths through the system.

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Experimental

Model

Modeling and Experimental Approaches

Pressure ripple Surface acceleration Sound pressure

HYGESim

Forces Pressures

Modal vibration response

Acoustic radiation

7Pressure ripple and Fourier Transform

𝑥𝑖 = 𝑥𝑟𝑎𝑤 − 𝑚𝑒𝑎𝑛(𝑥𝑟𝑎𝑤

𝐴𝑖𝐵𝑁 = 𝑓𝑓𝑡(𝑥𝑖

𝑁𝐹𝐹𝑇𝑖

Frequency vector formed from 0 to FS with resolution FS/NFFTRemove mean value

OR

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Modeling Goal

• Quantify all noise sources that transmit out to the environment from the pump.

• First model iteration only considered outlet pressure ripple.

• All case loads + floating lateral bearing assumption– Basic assumption: No solid contact between the internal components

and the pump case. Modeling the loads on all interior surfaces of the pump body is sufficient since all noise must transmit through the fluid interfaces.

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Modeled port pressuresInlet port pressure

Outlet port pressure

Dual flank frequency

Dual flank frequency

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HP

Gear and bearing forces• Forces on the gear are reacted by the journal bearings.• Forces on the lateral bushings are reacted by the balance

pressure on the back side between the bushing and the case.

Pressures in the tooth-space volumes are reacted by the lateral

bushing balance and not transmitted to the case directly from inside the

meshing zone.

Assuming free floating lateral bushings

LP

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Transition regionFrom 116ᵒ and back one TSV angle (27.7ᵒ) fluctuates from HP to LP

HPLP

Connection to HP

Outlet pressure ripple

More high frequency content

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0 2000 4000 6000 8000 10000

Frequency [Hz]

Drive gear

Slave gear

Lateral plates

Pump body

Simple pipe structure

Closed pipe fluid harmonics

Open pipe fluid harmonics

Main region of excitation and interest Pump

components

Fluid harmonics

Structural Frequency Response

Frequency

Example Frequency Response Function

Resonant frequencies of the pump body.

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050

1000

50

1000

50

100

Sound Pressure MapSPL = 74.813 dBA ref 20E-6 Pa

74

75

76

77

78

79

80

Air-borne Noise Radiation

• Klop R. and Ivantysynova M. 2010 • Bendant J.S. 2000

A microphone pair intensity probe.Segmented and windowed, FFT.Cross-spectral density method.

Summed over the grid points, intensity and respective areas.

050

1000

50

1000

50

100

Sound Intensity Map [dB ref 1E-12 W/m2]SWL = 81.4963 dB ref 1E-12 W

60

65

70

75

80

SPL ref 20 µPa RMS, SWL ref 10−12 W

Example predicted sound pressure radiated from external gear pump at one frequency.

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Multi-Domain Noise Measurements

55cm

Pressure ripple

Accelerometers

Microphone

0 to 105 [Pa]

0 to 20 [m/s2]

0 to 2 [Pa]

Item Type Description

Pressure sensors Kistler type 603B1, 0-1000bar, accuracy 1.1%FS

Sampled at 15kS/s

Accelerometers Three locations, 3-axis, PCB model 356A16, sensitivity 10mV/(m/s2)

Sampled at 15kS/s

Sound intensity probe GRAS, three microphones Type 40A0 – Sensitivity 0.2 dB ref 2∙10-5 Pa, ½“ diameter

Sampled at 52kS/s

GRAS, Type 26CB, ¼“ diameter pre-amplifier

500rpm to 2100rpm at 10rpm increments100bar pressure at pump outlet.

15𝐴𝑖𝐵𝑁 =

𝑓𝑓𝑡(𝑥𝑖

𝑁𝐹𝐹𝑇𝑖3 domain Fourier transformsFBN

SBN

ABN

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Power Spectral Density

FBN SBN ABN

𝑓𝑛 =𝑛 ∙ 𝑛𝑐 ∙ 𝑟𝑝𝑚𝑠ℎ𝑎𝑓𝑡

60𝑠

𝑚𝑖𝑛Pump source frequencies

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Anti-correlation

𝑇𝑝 𝑖 𝑗 =𝐴𝑏𝑖𝐵𝑁

𝐴𝑏𝑗𝐵𝑁

Assumption: source frequency content increase in frequency as speed increases

large

Signal i

small

largeSignal j

small

Signal icomponent is

amplified

Signal icomponent is

reduced to small

Signal icomponent

slightly amplified

Signal i component is reduced even

more

Amplifies components that are only present in one measured signal.Eliminates components that match well between two signals.

At each frequency:

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• Strong vertical bands in anti-correlation = Frequencies present in one domain but not the other.

• Goal is to identify resonances in the system that are speed independent• Sum the function across all speeds to minimize errors.

Anti-correlation 𝑇𝑝 𝑖 𝑗 =𝐴𝑏𝑖𝐵𝑁

𝐴𝑏𝑗𝐵𝑁

SBN/FBN ABN/FBN ABN/SBN

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Sum of anti-correlation functions

• Pump is not vibrating in a resonant way below 2kHz.

• Pipe is vibrating at resonant frequencies.

SBN/FBN ABN/FBN ABN/SBN

• Broadband noise frequencies underlying when FBN removed.

• O~1m standing waves in the air.

• Less high frequency content remains than in ABN/FBN using outlet

• High frequencies are present in SBN, but not FBN

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Conclusions• Can better understand noise in each domain through comparing

experiments and modeling.

– FBN, HYGESim validated in pressure ripple measurements

– SBN, Measured surface vibrations, structure participation

– ABN, Measured sound radiation, predicted sound radiation

• Results

– Experimental techniques point out the direction for the model so that the sources and propagation can be simulated more efficiently.

– Indicates which performance regimes an optimization will be effective, or what to optimize at different operating conditions.

• Potentials

– Applying new knowledge to improving pump and system designs through structural modifications, targeted speed ranges, etc.

– Predicting noise improvements for prototypes before production.

– Identifying sources and transmission paths.