Structure-borne sound transmission within electric power steering systems

Zabel, DF

Abstract

Transfer path analysis (TPA) is an established and valuable tool in the automotive industry, to
determine the contributions of structure-borne sound sources to receiver responses at target positions.
The classical TPA approach is based on contact forces at the interface between source
and receiver to characterise the dynamic loads induced by the source and frequency response
functions (FRFs) to quantify the transfer paths of the sound from the interface locations to the
target positions. With knowledge of the determined contributions it is then possible to decide
whether source loads or FRFs must be improved to optimise the target quantities.
Recently a timesaving improvement to classical TPA has been proposed, where the loads are
characterised using the in-situ blocked force method, so that dismantling of source and receiver
is not necessary. This method is therefore called in-situ TPA. However, if the contributions of
internal structure-borne sound sources to the overall vibro-acoustic behaviour of a product are
desired it is of benefit if the target quantities are blocked forces. Thus it would be possible to
virtually couple the product with the properties of an overall receiver. Therefore this thesis presents
a TPA approach called “blocked force transmissibility transfer path analysis” (bfTPA). In
this context, the proposed internal-source-path-receiver-model (ISPRM) poses the theoretical
basis of bfTPA. The aim of the presented novel TPA is to determine the contribution of internal
structure-borne sound sources to an overall target quantity of a product. The presented approach
uses the vector of in-situ blocked forces measured externally at the contact interface of the
overall product and a corresponding set of “blocked force transmissibility” (BFT) functions
relating the external coupling degrees of freedom (DOFs) to the internal source DOFs in order to propagate the external in-situ blocked forces back to multiple internal in-situ blocked forces.
To prove the methodology of the presented approach three case studies, which increase in complexity,
were carried out experimentally. The case studies concern a beam and an electric power
steering system with paraxial servo unit (EPSapa), respectively.
EPSapa systems consist of multiple embedded vibrational components which are defined as
“internal sources”. The electric motor, the ball nut assembly and the toothed belt are identified
as the main internal sources of an EPSapa system. Hence they are characterised by means of
experimentally determined blocked forces. For the determination, micro electro mechanical
systems (MEMS) accelerometers are embedded at the so called “internal interfaces”. This poses
a novel application of the in-situ method in combination with the dealing of continuous and
revolving internal interfaces.
Concluding a further application of the bfTPA methodology is presented. It allows the external
in-situ blocked forces of EPS systems or other products to be predicted based on internal insitu
blocked forces and the BFT functions within internal receivers such as housings, for instance.
Hence, the proposed approach is called “virtual component assembly”. It offers the advantage
to synthesize a virtual EPS system based on the in-situ blocked forces of its components
which are determined on test benches.

Citation

Zabel, D. (2018). Structure-borne sound transmission within electric power steering systems. (Thesis). University of Salford

• Thesis Type: Thesis
• Acceptance Date: Sep 28, 2018
• Deposit Date: Oct 2, 2018
• Publicly Available Date: Sep 3, 2023