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Reducing Noise Levels in Automotive Steering Systems
Posted Tue February 14, 2006 @12:00PM
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Application By Emilio Paladino, Technical Service Manager, ESSS and
Celso Takemori, Researcher, ESSS and
Leonardo Lessa, Product Engineering Coordinator, DHB Componentes Automotivos

The positive displacement pump used to power hydraulic-assisted steering is one of the main noise sources in an automotive steering system. DHB Componentes Automotivos, a manufacturer of steering systems for automotive and marine applications located in Brazil, is using ANSYS CFX software to analyze and understand the flow behavior within their pumps.

Customers are now looking for cars with very low noise levels. As engines are improved for quiet operation, noise from other areas such as the steering system is becoming more and more apparent. Noise level is now the first requirement analyzed when an automotive manufacturer selects a hydraulic steering system.


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The Advanced Engineering Department of DHB wanted to predict the flow behavior by analyzing recirculation zones and pressure profiles in order to understand how noise is generated by the flow field in this complex piece of equipment. To achieve this goal, DHB engineers and ESSS (the ANSYS distributor in South America) worked to develop a CFD model to predict the complex flow inside the pump.

ANSYS CFX was chosen by DHB due to ease of use, leading technology for moving meshes and generalized grid interfaces and robustness in the solution of complex problems, as well as excellent customer support.

The capability to deal with complex geometries was also essential. The intricate stationary region of the component was meshed using Tetra/Prism mesh, and a hexa mesh was used for the rotor. ANSYS ICEM CFD software was used to create both high-quality hexahedral and tetrahedral meshes. ANSYS CFX was used to compute the 3-D flow field of the hydraulic pump. Evaluating a pump design required DHB to accurately model the geometry, including moving mesh. Due to high pressure values present during the compression/expansion process, the simulation also included liquid compressibility effects.

The mesh movement was a particularly big challenge to model: DHB and ESSS engineers needed to define the radius of each point on the mesh as a function of space and time, given by the cam annulus. This was done through user FORTRAN routines, which could be easily linked to the CFX solver.

Although physical testing may never be replaced entirely, DHB engineers are convinced that no better way has been found to analyze the complex fluid dynamics of this hydraulic pump design than using CFX. Using numerical simulation, DHB engineers are now able to understand the possible sources of the noise generated by the flow field, especially the effect of the “v-notch” expansion chamber in the pressure fluctuations. The v-notch works as a relief valve, reducing pressure transients and, consequently, noise levels.

Using ANSYS CFX, DHB can now pre-evaluate designs more accurately at lower costs and in less time, which will considerably reduce turnaround time for a physical model test. By combining numerical and experimental results, time-to-market will be drastically reduced.

DHB is one of the largest manufacturers of automotive components in Brazil, providing quality service to the Brazilian market and several countries to which it exports its products. DHB is focused on investing in continuous improvement, combining technological evolution with respect to the environment and the well-being of all the people who are part of the process. The company employs more than 1,000 people and supplies products to clients worldwide, including General Motors, Ford, Fiat, Peugeot, Renault and Volkswagen.

hydraulic pump
Geometry of the hydraulic pump.

 

v-notch
V-notch (expansion chamber) detail close-up

 

pressure fluctuation
Effect of the expansion chamber on pressure fluctuations. Click image for animation.

 

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Related Links
  • ANSYS CFX
  • DHB
  • ESSS
  • Hexa
  • ICEM CFD
  • Tetra
  • More on Application
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