The influence of shock absorber characteristics’ nonlinearities on suspension Frequency Response Function estimation and possibilities of simplified characteristics modelling

Abstract

The paper shortly presents shock absorber design evolution and resulting achieved characteristics. The way in which suspension performance is evaluated is described giving information about models used for suspension parameter tuning during simulation testing of suspension transmissibility (FRF - Frequency Response Function) for most important suspension assessment criteria. More detailed information about models of shock absorber (damper) nonlinearities of characteristics allows for description of methods of linear and nonlinear suspension models FRF estimation. Testing linear suspension model is possible with the use of analytical transfer function formulas which were used to verify methods for estimation FRF using estimated power spectral density functions of excitation and response signals. Designing appropriate input signal allowing to get useful response signals was necessary to for the success of this research. Proposed FRF estimation method was used for linear estimation of nonlinear suspension for a given range of working condition. It was demonstrated that there is no single value of a damping coefficient which would make the linear model responses similar to the responses of the nonlinear one. Then the bilinear model was proposed, giving good damper static nonlinear characteristic.

The Influence of Friction Force and Hysteresis on the Dynamic Responses of Passive Quarter-Car Suspension with Linear and Non-Linear Damper Static Characteristics

“…Important frequencies when analysing suspension dynamics cover a range from 0.5 Hz to 25 Hz. The frequency values changed in a non-linear fashion in order to allow more cycles to occur in a lower range, which gives better results when calculating transfer functions (8). Additionally, frequencies <0.5 and >25 Hz were added to the simulation in order to further stabilise the results of the tfestimate MatLab function, which was used to estimate the transfer function of the suspension.…”