Optimisation of the characteristics of the elasto-damping elements of a passenger car by means of a modified Nelder-Mead method
by Miroslav Demic
International Journal of Vehicle Design (IJVD), Vol. 10, No. 2, 1989

Abstract: A motor vehicle is a complex oscillatory system with a number of elasto-damping elements, the characteristics of which are in most cases of non-linear character. Due to the car's motion on the road, and also to the effects of the powertrain and the rotating elements, the vehicle performs stochastic, secondary, spatial oscillatory motion that affects the stability and comfort parameters, and may lead to fatigue of vital parts of the car, which in turn may threaten traffic safety. The negative effects of the secondary oscillatory motion of the vehicle may be reduced by way of optimisation of the characteristics of the elasto-damping elements (oscillatory parameters) of the vehicle. In the work reported in the paper, the author has modified the method of Nelder-Mead by introducing design-dependent bounds on the oscillatory parameter values. For illustration, the method was applied to the plane model of a passenger car in order to minimise simultaneously vertical oscillations of the front and rear wheels, pitch, and vertical oscillations of a partially loaded vehicle. The following values of the optimal parameters were calculated for a car with front wheel mass m₁ = 55 kg, rear wheel mass m₂ = 50 kg, sprung mass m = 1095 kg, moment of inertia about the lateral axis J = 1685 kgm² and axle distance L = 2.5 m: x(l) = 15049.77 daN/m; x(2) = 11946.16 daN=m; x(3) = 1954.894 daN/m; x(4) = 907.2481 daN/m³; x(5) = 495.0496 daNs/m; x(6) = 299.9992 daNs/m; x(7) = 2000.834 daN/m; x(8) = 97 1.8788 daN/m³; x(9) = 55.5049 daNs²/m²; x(10)= 60.61329 daNs²/m². These values were computed on the condition that the object function has a minimum, that the resonant frequencies of the aforementioned masses are located within the recommended bounds, and that the oscillatory parameters are within the prescribed bounds. The parameters computed provide for optimal comfort of the vehicle considered when driving on asphalt roads at high speeds of about 30 m/s.

Online publication date: Mon, 26-May-2014

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