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Technical Paper

Influence of Vehicle Exhaust Y-Pipe on Tailpipe Noise

This paper analyzes the relation between sound pressure at tailpipe and exhaust Y-pipe structure. The length of Y-pipe influences sound order distribution that influences customers' responsiveness of sound. The equal Y-pipe remains the firing order and its harmonic contents while suppressing the half order and other whole order sounds. Various lengths of equal Y-pipe also influence the magnitude and frequency distribution of tailpipe noise. An air-to-air (induction-engine-exhaust) CAE model is built to predict tailpipe noise using up-to-date software. The real air-to-air model simulation shows that the 3rd and 6th orders are the dominating contents for equal Y-pipe exhaust system in 6-cylinder engine applications. The sound pressure of the half order contents increases with the length difference between two branches of a Y-pipe. The results are useful for exhaust Y-pipe design.
Technical Paper

Exhaust System Robustness Analysis Due to Flex Decoupler Stiffness Variation

The function of flex decoupler is to reduce the vibration transferred from the engine to the vehicle body. The stiffness of the flex decoupler is a key parameter in the vibration control. This paper deals with decoupling exhaust hot end and cold end to minimize vibration transfer. A computer aided engineering (CAE) based design of experiment (DOE) is used to investigate the coupling stiffness. A finite element model is built to analyze the exhaust vibration responses. Robustness of the exhaust system is analyzed. The analysis reveals that vertical stiffness of the flex decoupler is the key parameter for the hanger force response. The main control factors for exhaust vertical and lateral bending frequencies are vertical and lateral stiffnesses of the decoupler, respectively.
Technical Paper

Nonlinear Model Validation for Automotive Seat Cushion-Human Body Combined Structure

In this paper, a nonlinear dynamic model for automotive cushion-human body combined structure is developed based on a nonlinear seat cushion model and a linear ISO human body model. Automotive seat cushions have shown to exhibit nonlinear characteristics. The nonlinear seat cushion model includes nonlinear stiffness and nonlinear damping terms. This model is verified by a series of tests conducted on sports car and luxury car seats. The transfer functions from the tests for human body sitting on an automotive seat changes with the vibration platform input magnitudes. This indicates that the combined structure possesses nonlinear characteristics. The nonlinear model is validated by the transfer functions from the test. The paper discusses the influence of the parameters of the nonlinear structure on the design of seat and assessment of human body comfort.
Technical Paper

Nonlinear Model Identification and Procedure for Automotive Seat Cushion Structure

The paper presents a procedure for nonlinear model identification of automotive seat cushion structure. In this paper, two nonlinear models are presented. Tests show that the automotive seat cushion structure is a nonlinear system. The transfer functions obtained from the test data between the seat butt and the seat track show that the magnitude and frequency shift will be smaller as the input is increased. The models predict the transfer functions having the same trend as the results from the tests. The models are quite useful for the analysis other car structures and also provide guidance in the design of seat cushions.
Technical Paper

Flow Excited Noise Analysis of Exhaust

This paper introduces a cumulative effort on the phenomenon of exhaust flow exited noise. The mechanisms of engine combustion noise via the exhaust system and flow excited noise are analyzed. Engine combustion noise contributes most to tailpipe noise at lower engine speed while flow excited noise dominates the tailpipe noise at high engine speed. WAVE model, a one dimension CFD and Acoustics model, is used to distinguish the engine combustion noise and flow excited noise. Both CAE and tests based results are used to draw conclusions. The influence of single system and quasi-dual system on the tailpipe noise is compared with each other. The paper analyzes the balance of different diameter pipes to achieve the desired sound at different rpm range. The evaluation balance between interior sound and tailpipe noise is described.
Technical Paper

Attribute Analysis and Criteria for Automotive Exhaust Systems

This paper summarizes the attributes of automotive exhaust system and provides a guideline for exhaust system design, analysis and development. The exhaust system has various attributes including vibration, acoustics or noise, durability and thermal distribution, flow and power loss, emission, in addition to its interface with vehicle. This paper describes all these attributes and the corresponding performances, and develops criteria for each of the attributes. The paper also describes the interfaces between the exhaust system and powerplant with body structure.