Identification and quantification of transient structure-borne sound sources in electrical steering systems

Sturm, M

Abstract

During driving on rough roads, rattle noise may emanate from (electric power) rack-and-pinion steering gears as a result of reverse feedback from the road. This project is in collaboration with a German steering system manufacturer and aims to develop a methodology facilitating identification and quantification of transient structure-borne sound sources within electrical steering systems. To achieve this aim, a conceptual source-path-receiver model has been developed that discloses the theoretical locations and associated mechanisms of all possible transient sound sources inside the steering gear. This information forms the basis for a subsequent measurement step which is required to experimentally quantify the strength of each individual source. The measurement approach is based on a time domain equivalent of the in-situ blocked force method; thus facilitating independent source characterisation on the fully assembled structure. The time domain (TD) approach relies on a robust inversion routine that uses an adaptive algorithm to simultaneously reconstruct multi-channel (blocked) force signatures from operational responses and the corresponding impulse response functions both measured (in-situ) on the (assembled) structure. The TD inversion routine is derived from the least mean square (LMS) algorithm which is widely used in adaptive filter design. The accuracy and sensitivity of the TD inversion routine is elaborated and compared to the standard frequency domain inverse method using simple numerical examples. Its general applicability for sophisticated technical structures is evaluated by example of an electric powered steering system being subjected to artificial excitation. The use of the TD approach for characterisation of transient structure-borne sound sources based on the blocked force method is discussed and different procedures to improve the force estimation accuracy are proposed. These procedures can be classified into methods that (i) help to evaluate the quality of pre-measured frequency response functions (FRFs) which are required to set up the (inverse) system model, (ii) measurement routines that may help to improve future FRF measurements conducted in-situ, i.e. whilst the steering gear is connected to a special rattling test bench, (iii) correction strategies to separate contributions from known (external) structure-borne sound sources different from the desired (internal) rattling sources and (iv) criteria that in theory allow for monitoring the performance of the iterative TD inversion routine precisely. Finally, the developed methodology is used to identify and quantify rattle sources within a steering system under realistic testing conditions.

Citation

Sturm, M. Identification and quantification of transient structure-borne sound sources in electrical steering systems. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Mar 7, 2014
• Publicly Available Date: Apr 5, 2016
• Keywords: structual dynamics, inverse methods, time domain inversion routine, adaptive algorithm
• Additional Information: Funders : ZF Lenksysteme GmbH, Schwäbisch Gmünd, Germany