Thrust 3: Effectiveness
Title
3B.1: Passive Noise Control in Fluid Power
Project Leader
Prof. Kenneth Cunefare (Georgia Tech)
Statement of Project Goals
The aim of this project is to improve noise control in fluid power systems by passive means. Excess noise is a problem not only for the attractiveness of existing products, but also as a barrier for entry of fluid power into new markets and technologies. This project seeks passive solutions to the reduction of noise and vibration by means of integrating engineered compliant materials into existing components and technologies. The use of compliant materials is expected to help reduce the size of noise control devices for fluid power.
Project’s Role in Support of the Strategic Plan
The reduction of noise and vibration is a core enabling technology for Goal #2 and Goal #3 in the Strategic Action Plan for the Center. For the Hybrid Passenger Car, noise and vibration reductions are crucial to mass acceptance of the hybrid technology by the public. Noise can not only be a harmful to hearing and impair communication, but can increase mechanical fatigue and reduce component life. Increasing demands on quality make the need for noise reduction a priority for designers. Developing compact and effective noise control solutions is even more important for Goal #3: Portable, Untethered Human-Scale Applications. The limitations on noise output are drastically more stringent for devices to be worn on the body or used in the home compared to industrial applications. Reducing fluid power-related noise and vibration is crucial to supporting the Center's goal of enabling new markets for fluid power.
Acceptable sound power levels for new compact devices will require a much lower coupling coefficient (estimates shown in red) between system and radiated sound power.
Description and Explanation of Research Approach
Excess noise is an ongoing issue in fluid power systems. Noise needs to be controlled not only to meet regulatory standards, but also to meet the expectations of customers and consumers. Fluid-borne noise is generated by pumps and can couple to structures, causing vibration and air-borne noise. The high speed of sound in hydraulic fluid, coupled with the low fundamental frequencies of pumps results in wavelengths of fluid-borne noise that are much longer than the practical size of common noise control components.
The current technology of reducing fluid-borne noise involves both the use of pressurized, gas-filled bladders for adding compliance to fluid power systems as well as integrated design features addressing such noise sources as cavitation and structural vibration. Pressurized bladders are used in commercially-available in-line silencers (one such silencer is used as a benchmark in this research) and in accumulators which act as low-pass filters.
The research approach in this project is unique in its application of a voided, engineered, compliant lining to noise control devices for fluid power systems. There are a number of patents for noise control devices that reference voided polymer materials,1, 2 however, there does not appear to be any product on the market exploiting these patents, nor is there material in the literature. Theoretical models may be found in the literature for annular air silencers3 and for hydraulic silencers using flexible plates4 but none currently addresses annular, compliant-lined hydraulic silencers. Other devices such as Helmholtz resonators and Quincke tubes have been studied but are not found in practice as their size is typically too large for practical application. Helmholtz resonators have been studied extensively for air; one notable study for a fibrous-lined resonator was performed by Selamet.5 A number of studies have evaluated Helmholtz resonators for hydraulic systems, but none have been found that incorporate a lining.6-9 Devices known as tuning coils act as ¼-wavelength resonators and are common in power steering systems. A patent for a tuning coil was first issued in 1967,10 and they were studied in the literature in the mid 1990s.11, 12 Quincke tubes act as ½-wavelength resonators and were evaluated in some of the same literature. Aside from separate noise control components, fluid-borne noise may be abated by integrated design features. For example, changes to the geometry of axial-piston pumps and the use of relief ports in valve plates.13-15
A major barrier in reducing the size of noise control devices for fluid power lies in the properties of the material used in their construction. The material must be significantly more compliant than the working fluid, yet remain compliant while under hydrostatic pressure. Coupled factors include the sound speed and loss factor; a low sound speed is related to reflection losses from the impedance change at the inlet and internal reflections, while the loss factor is the variable governing energy dissipation. In addition, capturing all these factors in a predictive model for a given device is also key to tailoring the material properties and device geometry to a given application. The microvoided urethane used in this research shows significant promise with respect to these aspects.
Prototype hydraulic silencer with microvoided polymer lining.
References
1. J.H. Wheeler and J.P. Frentzos, Fluid noise muffler and method of manufacture, in USPTO. 1995, The Texacone Company, Mesquite, TX: USA. p. 7.
2. J. DiRe, Hydraulic pump with foamed elastomeric member in outlet chamber to reduce liquid-borne noise. 1993, IMO Industries, Inc.: USA.
3. M.B. Xu, et al., Sound attenuation in dissipative expansion chambers. Journal of Sound and Vibration, 2003. 272: p. 1125-1133.
4. S. Ramamoorthy, K. Grosh, and J.M. Dodson, A theoretical study of structural acoustic silencers for hydraulic systems. J. Acoust. Soc. Am., 2002. 5(111): p. 2097-2108.
5. A. Selamet, et al., Helmholtz resonator lined with absorbing material. J. Acoust. Soc. Am., 2005. 117(2): p. 725-733.
6. L. Kela, Resonant frequency of an adjustable Helmholtz resonator in a hydraulic system. Archives of Applied Mechanics, 2008. 79: p. 11.
7. L. Kela and P. Vahaoja, Control of an Adjustable Helmholtz Resonator in a Low-Pressure Hydraulic System. International Journal of Fluid Power, 2009. 10(3): p. 10.
8. E. Kojima and T. Ichiyanagi, Development research of new types of multiple volume resonators, in Bath Workshop on Power Transmission and Motion Control, C.R. Burrows and K.A. Edge, Editors. 1998, Professional Engineering Publishing Ltd.: Bath, U.K. p. 193-206.
9. E. Kojima and T. Ichiyanagi, Research on pulsation attenuation characteristics of silencers in practical fluid power systems. International Journal of Fluid Power, 2000. 1(2): p. 29-38.
10. G.T. Klees, Attenuating Device, in USPTO. 1967: USA.
11. M.C. Hastings and C.-C. Chen. Analysis of Tuning Cables for Reduction of Fluidborne Noise in Automotive Power Steering Hydraulic Lines. in Proceedings of the 1993 Noise and Vibration Conference. 1993: SAE International.
12. J.E. Drew, D.K. Longmore, and D.N. Johnston, Theoretical analysis of pressure and flow ripple in flexible hoses containing tuners. Proceedings of the Institution of Mechanical Engineers, 1998. 212(1): p. 405-422.
13. A. Johannsson, J.-O. Palmberg, and K.E. Rydberg. Cross Angle - A Design Feature for Reducing Noise and Vibrations in Hydrostatic Piston Pumps. in Fifth International Conference on Fluid Power Transmission and Control (ICFP2001). 2001.
14. A. Johansson, J. Andersson, and J.-O. Palmberg, Optimal design of the cross-angle for pulsation reduction in variable displacement pumps, in Bath Workshop on Power Transmission and Motion Control, C.R. Burrows and K.A. Edge, Editors. 2002, Professional Engineering Publishing, Ltd.: Bath, U.K. p. 319-334.
15. A. Johansson and J.-O. Palmberg. Design Aspects for Noise Reduction in Fluid Power Systems. in 10th International Congress on Sound and Vibration. 2003. Stockholm, Sweden.
16. N.E. Earnhart, K.A. Marek, and K.A. Cunefare. Evaluation of hydraulic silencers. in NoiseCon10. 2010. Baltimore, MD.
17. N.E. Earnhart, K.A. Marek, and K.A. Cunefare. Modeling and Validation of an In-Line Hydraulic Silencer. in 6th FPNI PhD Symposium. 2010. West Lafayette, IN.
18. K. Marek, N. Earnhart, and K. Cunefare. Model for the design of a hydraulic silencer with a dispersive liner. in NoiseCon10. 2010. Baltimore, MD.
19. N. Bügener, S. Helduser, and J. Weber. Numerical analysis of a measure to improve the suction performance of hydrostatic pumps. in 6th FPNI-PhD Symposium. 2010. West Lafayette, IN.