The paper presents the method of kinematic road excitation reconstruction based on measured suspension dynamic responses and its reconstruction with use of estimated displacements of unsprung mass as a preliminary approximation of kinematic excitation and tracking control system with a PID controller that allows for faithful reconstruction of unsprung mass accelerations and, in turn, kinematic excitations. The authors performed an experimental verification of the method with use of one axle car trailer and measurements of road profile and acquiring signals of suspension dynamics responses. The signal processing methodology and obtained results are presented for random and determined excitations. The necessary requirements to use the method effectively were defined and its limitations were listed.
Throughout the years, many control strategies for adjustable dampers have been proposed, designed to boost the performance characteristics of a vehicle. Comfort control strategies such as Skyhook (SH), acceleration-driven damping or power-driven damping have been tested many times using simulation models of vehicles. Those tests, however, were carried out using simplified damper models – linear or simple bilinear with symmetric characteristics. This article presents the results of examination of the influence of using more complex damper models, with friction, hysteresis and time delay of state switching implemented, on the chosen dynamic responses of a suspension system for excitations in the typical exploitation frequency range. The results of the test are compared with those found in the literature and with the results of simulations performed with a simplified version of the advanced model used. The main conclusion is that friction and hysteresis add extra force to the already existing damping force, acting like a damping increase for all analysed control strategies. The actuation delays limit the effectiveness in a sense of comfort increasing to only some frequencies. The research shows the importance of including the proposed modules in testing for both adjustable and passive dampers.
The article presents a study of the influence of vehicle’s conditions of use, such as road class, vehicle speed or its load, on its vertical dynamic responses. In the article only the kinematic excitations were analysed, as these are more common than the dynamic ones. The road profiles were artificially generated according to the ISO 8608 standard, which classifies roads based on power spectral density of excitations which they generate. Ride safety, ride comfort and fatigue strength indicators were computed. Ride safety was defined by the DLC – Dynamic Load Coefficient. Ride comfort was judged taking into consideration the recommendations from the ISO 2631 standard (which contains the information on vibration frequencies and their effect on human body, as well as the allowed exposure times to given vibrations) by calculating root mean square values of sprung mass accelerations for bandwidths defined in the standard. Load spectrums for the fatigue analysis were created using forces generated in a simulation as a basis and further research venues were proposed. Lastly conclusions were drawn from the results, that imply that linear models are sufficient for many standard applications on roads of acceptable quality, however the use of non-linear models is recommended in fatigue strength analysis regardless of conditions of use.
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.
Load spectrums for the fatigue analysis were created using suspension responses generated in a simulation of vehicle and suspension vertical dynamics nonlinear model for different conditions of vehicle use. The next stage presented was the use of finite element method and analysis of obtained stresses with its transformation to a set of cycles that are used in the determination of fatigue characteristics. The qualitative and quantitative analysis of the stresses field in the vehicle structure and suspension elements was done and later the influence of suspension responses on the fatigue assessment for most loaded parts of suspension and vehicle structure. Lastly conclusions were drawn from the results describing qualitative and quantitative influence of different road class and load conditions on fatigue assessment of vehicle structure and suspension components. Conclusion on the proposed and used methodology also was drawn.
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