A Practical Method to Predict NVH in an Automotive Hydraulic System 2005-01-1816
An automotive hydraulic system including pump, power steering gear, fan, and Active Hydraulic Suspension (AHS) is modeled and validated through bench testing. A Computer Aided Engineering (CAE) simulation capability is developed for design control of flow and pressure dynamics. The generated fluid-borne pump noise resulting from interaction with circuitry components is obtained from transfer matrix methods utilizing MATLAB and SIMULINK. Hose and tube components are modeled as continuous sections. Non-tubular components including fan, AHS, gear, and cooler are treated as lumped sections with point transfer functions. The reservoir is represented by low pressure termination points from entrance lines. Impedance at these points is defined as the pressure-flow ratio obtained from measurements at line entrance to the reservoir. Hydraulic fan and AHS are each considered to have branched flow with discharge to both high and low pressure lines. Gear and cooler are represented by direct flow-through functions.
Point transfer matrices are developed and verified at each component level. Impedance measurements are taken at entrance and exit locations throughout an application range of static gear pressures. Consequently, both flow and pressure data are continuously linked from pump to reservoir. In general excellent agreement is obtained between prediction and test. A SIMULINK CAE program is developed which enables engineered noise attenuation components to be inserted and rapidly evaluated in alternative circuit designs.
Structural-borne noise design data for tubing, including support brackets, is calculated from free vibration analysis of fluid filled conduits. A two-dimensional plane-frame finite element with axial, transverse, and rotational capability is utilized. Displacement in three degrees of freedom at all tube nodes is obtained for each resonant frequency calculated with MATLAB functions.