| Popis: |
A simplified theory on the vehicle stability in curve is explained in this paper; it allows the calculation of the force on the wheels during the motion in curve, supposing unchanging the position of the rolling centre; moreover it does not take in account the turn of the wheels and the behaviour of the tires, so that the theory can be applied to 2WS and 4WS vehicles for vertical loads calculation. The virtual simulations of 2WS and 4WS vehicles are executed, extracting all the data interesting the vehicle stability; it needs the distinction between manoeuvrability and handling. The simulations of two different tests are executed: the elk test like manoeuvrability test and a similar one at low speed as handling test. The values of vertical forces are compared one another and with the results by the simplified theory of the above. The results of horizontal (longitudinal and transversal) forces and the self alignment moment are compared with those obtained by magic formulae of Pacejka. All the comparisons are very satisfactory for both 2WS and 4WS vehicles, indicating that 4WS vehicle has a greater stability in curve, in every situation and that the theoretical formula of the weight displacement gives good results. Moreover the better performances of 4WS vehicle in terms of the slip angle, of the weight displacement and of the forces give in general a substantial contribute to the safety of the vehicles, well as an increase of driveability. 4WS has lower yaw-rate in high speed, smaller slip angle and lateral acceleration, so it has better robustness. Besides2WS loses stability in advance when steering angles of front wheels are greater. |
