Non-stationary random vibration modelling and analysis via functional series time-dependent ARMA (FS-TARMA) models – A critical survey

SUMMARY This paper illustrates the use of nonlinear control theory for designing electro-hydraulic active suspensions. A nonlinear, “sliding” control law is developed and compared with the linear control of a quarter-car active suspension system acting under the effects of coulomb friction. A comparison will also be made with a passive quarter-car suspension system. Simulation and experimental results show that nonlinear control performs better than PID control and improves the ride quality compared to a passive suspension.

Application of Nonlinear Control Theory to Electronically Controlled Suspensions

In this paper, an indirect adaptive controller is applied to the vehicle active suspension with a hydraulic actuator. The inner loop controller, which is a nonlinear adaptive controller, is designed to control the force generated by the nonlinear hydraulic actuator. The spool valve dynamics of the hydraulic actuator is reduced using a singular perturbation technique. The parameter estimation error used in an indirect adaptation is decreased asymptotically. The absolute velocity of a sprung mass is damped down by its negatively proportional term (sky-hook damper) adopted as an outer loop controller.

Nonlinear indirect adaptive control of a quarter car active suspension

The advantages of an automotive active suspension system have been promised for many years. A fully active suspension based on hydraulic actuators seemed to be a good candidate for fulfilling such expectations. However the high frequency characteristics of such systems have been proved to be problematic for practical implementations. A high fidelity mathematical model capturing realistic dynamic behaviors of the hydraulic active suspension is required for the development of such systems. In this paper, a quarter vehicle model of an hydraulic active suspension system suitable for developing wheel control is developed. The model accounts for the necessary component dynamics contributing to the higher frequency characteristics of the system. They include suspension bushing, actuator friction, hydraulic servo valve and actuator, as well as tire model. Identification of the model parameters with respect to a test vehicle driven through a standard impact bump is presented. The model results and the test data are virtually identical. The model has been shown to be a very effective tool for active suspension wheel mode control design and analysis.

Model identification of an automotive hydraulic active suspension system

A general methodology is presented for investigating ride dynamics of large order vehicle models in a systematic and computationally efficient way. First, the equations of motion of representative vehicle models are set up by applying classical finite element techniques. In the simplest version of these models, the important system parameters are assumed to be constant, leading to linear formulations. Then, more accurate and involved models are examined by including typical nonlinearities in the tires and the shock absorbers of the vehicle suspension. Also, emphasis is placed on taking into account the possibility of temporary separation of a wheel from the ground. These models are strongly nonlinear and as their order increases the existing numerical methodologies for a systematic determination of their dynamics become inefficient to apply. Therefore, the first step of the present methodology is to reduce the dimensions of the original system by applying a component mode synthesis approach. Subsequently, this allows the application of appropriate numerical methodologies for predicting response spectra of the nonlinear models to periodic road excitations. Finally, results obtained by direct integration of the equations of motion are also presented for transient road excitation. In all cases, the accuracy and validity of the applied methodology is verified by comparison with results obtained for the original models.

Ride Dynamics of Nonlinear Vehicle Models Using Component Mode Synthesis

Non-linear dynamic modeling of an automobile hydraulic active suspension system

A parametric approach for the estimation of nonstationary signals is presented. The approach is based on time-varying autoregressive moving average (TARMA) signal representations. The TARMA model coefficients vary in a deterministically organized way and are estimated using a novel fully linear parameter estimation method. The estimation algorithm is based on the properties of the TARMA models that allow their manipulations using operations restricted to the time domain. It is shown that the estimation method is computationally simple, overcomes local extrema problems associated with nonlinear search procedures, and eliminates the need for initial guesses of the parameter values. >

J.A. Levitt

Papers

Non-linear dynamic modeling of an automobile hydraulic active suspension system

Nonstationary signal estimation using time-varying ARMA models