AbstractNarrow commuter vehicles have attracted considerable interest in recent years as a means of reducing congestion and emissions in the urban environment. In order for these vehicles to provide similar levels of safety as bigger passenger vehicles, they must be relatively tall and fully enclosed. Due to the tall and narrow nature of the vehicle, they are prone to rolling over during cornering. To prevent this from happening, it is necessary to tilt the vehicle into the turn in order to compensate for the moment due to the lateral force generated by the tyres. The success of this type of vehicle depends primarily on the control strategy used to tilt the vehicle. Although a number of theoretical models have been developed outlining possible tilt control strategies, experimental data is scarce.
CLEVER is a direct tilt controlled three-wheel prototype vehicle that was developed at the University of Bath as part of an EU funded project. The current control strategy utilises measurements of speed and steer to predict the lateral acceleration and hence the tilting angle required to balance the vehicle during cornering. The cabin of the vehicle is then tilted to the desired angle using two hydraulic actuators. Although the vehicle performs well in steady state, transient dynamics have been shown to lead to instability and ultimately roll-over of the vehicle.
The aim of the work presented here is to create an understanding of the dynamics that lead to the transient state instability and design a control method which will improve the handling characteristics of the vehicle and prevent dangerous transients. In order to study the vehicle’s dynamics and test the new control system, a full multi-body model is developed using the SimMechanics software package. The model is validated using data from numerous experimental tests performed with the prototype vehicle. Using the full vehicle model, it is possible to analyse the scenarios that could lead to the transientstate roll-over of the vehicle, creating a good understanding of the dynamics that lead to these potentially dangerous situations. Taking these dynamics into account, a lateral dynamics optimisation study is performed which proves the necessity for independent control of the tilting mechanism and the lateral acceleration, confirming the need for combined steer and direct tilt control. The new control system is then developed using a linearised model in order to optimise the controller in the frequency domain and is tested using the non-linear multi-body model. A simple combined control approach is presented and shown to significantly reduce transient roll moments, resulting in a much safer and more predictable handling characteristic.
Although a number of control strategies have been proven successful in simulation by other researchers, these relied on complex switching strategies and weighting functions to switch between steer tilt control and direct tilt control and often required numerous sensor inputs. The system proposed by the author combines both steer and tilt control concurrently, using the driver steering input and vehicle speed as the only input parameters. The simplified principle of the control strategy is anticipated to facilitate implementation in a prototype vehicle.
|Date of Award
|1 Jan 2010
|Jos Darling (Supervisor) & Andrew Plummer (Supervisor)
- three-wheeled vehicle