This paper presents the design of an active vehicle suspension system without filtered feedback of the control system. A nonlinear spatial model of a passenger car was considered with controlled hydraulic cylinders (actuators), feedback loops without usual low and high pass filters, and with optimal selection of control system parameters so as to reach the most favourable vibration and handling parameters. The vehicle model consists of three segments: mechanical, hydraulic model, and force control. The mechanical model describes the vehicle mass displacement considering the vertical, roll, and pitch movement of the sprung mass and the vertical vibration of the unsprung mass (i.e., the four wheels). The appropriate differential equations are written using of the software package NEWEUL. Vibrations are excited by shocks generated by the road roughness acting on the front and rear wheels. These shocks are described by a polyharmonic time functions. A concept of active suspension control is developed, realised with two groups of feedback reactions. The external feedback is assigned to minimise the influence of the road roughness (for better ride comfort), and the internal feedback to control cylinder forces, thus enabling favourable load distribution and levelling in the case of vehicle maneuver. The active suspension system has four servo valves (one for each actuator), a pump, tanks and hydraulic ducts. By the use of the pump, the oil is forced to the accumulator, from where it is transferred, under pressure, to the servo valves and finally to the actuator chambers. Vertical motion, pitch and roll motion are related to cylinder forces by a transfer matrix calculated using the software Mathematica. Stochastic parameter optimisation, based on nonlinear programming methods, has been used for control parameter optimisation of active suspension. The objective was simultaneous minimization of vertical, roll and pitch acceleration of the sprung mass (required for ride comfort) and the standard deviations of dynamic tire-to-ground contact forces (required for vehicle handling). The vehicle model represents a dynamic system with four excitations (from four wheels), which, in general, are correlated. Using a method of 'constant parameter linear systems', partial coherence functions have been calculated showing the influence of a single excitation source on the vertical, roll and pitch motion of the sprung mass. As for the vertical sprung mass vibration of the vehicle considered here, the average value of the coherence function is approximately 0.7, indicating a significant influence of the road roughness. The average of the partial coherence function of the roll and pitch is approx. 0.45, showing a significantly lower influence of the road roughness excitation on the car body movement. The analysis of the transfer functions, calculated using the software package ANALSIGDEM, shows that dynamic amplification in the interesting frequency range (0-32.5 Hz) strongly depends on frequency, but is always significantly less than 1. The resonance frequency of the sprung mass vertical vibration is approx. 0.8 Hz, for the roll vibration at 1.25 Hz and for the pitch vibration at 0.45 Hz.
A method of vehicle active suspension design
Über eine Methode zur Projektierung von Systemen aktiver Fahrzeugstützen
Forschung im Ingenieurwesen - Engineering Research ; 70 , 3 ; 145-158
2006
14 Seiten, 18 Bilder, 4 Tabellen, 52 Quellen
Article (Journal)
English
aktive Dämpfung , Bewegungsgleichung , Einflussgröße , Frequenzgang , hydraulische Regelung , Kontaktkraft , Korrelationsfunktion , mathematisches Modell , mechanische Schwingung , Parameteroptimierung , Radaufhängung , Regelkreis , Regelungsmodell , Schwingungsanregung , Schwingungsbegrenzung , Stoßdämpfer , Straßenfahrdynamik , Übertragungsfunktion , Personenkraftwagen , Fahrzeugdämpfung , aktives Fahrwerk