|M.Sc Student||Nachum Medlinger|
|Subject||Algorithms for Rollover Avoidance Control of Off-Road|
|Department||Department of Agricultural Engineering||Supervisor||Professor Emeritus Gutman Per-Olof|
One of the must hazardous dynamic instability, a vehicle may encounter, is the rollover instability. Several factors are known to have a significant impact on the
rollover, among them are the vehicle design parameters: track width, C.G height and suspensions compliance; and the dynamic modes: lateral acceleration and roll, which the outcome of the tyre-ground interaction under the manoeuvre induced by the driver. Thus, in order to control or avoid vehicle rollover, one can adjust its design parameters (which is a very complicated problem from a mechanical point-of-view), or control the vehicle's dynamic modes. The dynamic modes control can be applied in two fundamental methods: controlling the mode itself, without changing the driver induced manoeuvre, e.g. adjusting the pitch or roll modes by active suspensions; controlling the manoeuvre itself be regulating either velocity or steering. The first method is much more common, mainly because the driver's intention is maintained, yet it is limited for rather small control action. Whilst, in the second method, the driver's intention is hardly maintained, yet it is much more suitable for large, emergency, control action.
In this work, the method of steering regulation for emergency, rollover avoidance, is adopted, by initiating an auxiliary steering signal, once rollover danger is detected. The control system disengages once the rollover danger is gone.
A 3 degrees-of-freedom, nonlinear mathematical model of an or-road
vehicle in a rollover situation is developed, on which the control algorithm is designed. The nonlinear model is decomposed to a linear part and a nonlinear disturbance. Taking into account only the worst case of the nonlinear disturbance, the nonlinear model is further reduced into a linear mode and a constant step
disturbance. By utilizing the QFT method for robust control design, a robust controller for rollover avoidance is designed. The designed control scheme is evaluated via simulation of a much wider simulation model.
The design model is then adjusted for off-road vehicle, and the QFT method is implemented again, combined with an additional nonlinear Lyapunov control loop, to formulate a comprehensive control system for off-road rollover avoidance. The
developed control system is tested via simulation of a multi-body off-road vehicle model. Simulations of various velocities from 5 to 20 m/s, various soil cone-index from 450 to 1800 KPa and various ground disturbances from 10 to 30 cm bumps were conducted. The suggested control algorithm successfully imposed moderate
steering correction signals, that prevented the vehicle from rolling over, yet it is important to add that the on-line simulation model, design model and controller development are but a pre-amble of the off-road development.