Dynamics simulation

of an innovative rolling three wheels vehicle

 

Prof. Vittore Cossalter

Graduating student: Davide Danesin

Department of Mechanical Engineering, Padua University, Italy

 

For decades two and four wheel vehicles have been the most important means of people transport by road. Honda and Mercedes are now exploring new technical solutions especially in the field of three wheel vehicles.The principal aim of these researches is to increase safety, handling and to merge the stability typical of four wheel vehicles and the manoeuvrability/compactness of two wheel vehicles in only one kind of vehicle. The most followed way to realize this merging is to build a three wheel vehicle characterized by the capability of rolling.

The aim is to exam the dynamics of this kind of vehicle and investigating the most important design parameters with the final target of providing strong indications necessary to the building of a first prototype ( a innovative vehicle is ongoing of patenting).

Fig.1 View of the prototype

The model is characterized by two principal frames. The front frame consists of the front wheel, forks and main structure. The rear frame consists of the two rear wheels,the engine and the structure which support both of them. The front frame roll around an axes fixed respect to the rear frame which doesn't roll.

The most interesting field of the research is to experiment different mechanism linking the front to the rear frame. In particular, by changing the kinematics, we translate and rotate the front frame's roll axle obtaining very different vehicle behaviors.

In this kind of vehicles the front frame is linked to the rear frame by a spatial mechanism. The different geometry of mechanism changes the position of the instant rotation center of the front frame.

SolidEdge parametric features is used to generate many models, then in little time they have been carefully assembled. The model, which has sprang out, has been read by to Working Model integrated in Solid Edge.

In Working Model the vehicle was provided with a mathematical tire model that uses one force and two torques for the front wheel, and only one force for the two rear wheels. Lateral tire force is proportional to the sideslip and to the wheel roll, whereas the two torques compute the moving of the contact point between tire and ground.

To test the vehicle's performance and behaviour the model was provided with a proportional-derivative-integrative control. This has been realized by using the OLE Automation capability of Working Model: an external Visual Basic program gives the input to the steering torque. The control calculates torque value following a cubic spline interpolated trajectory. Various maneuvers have been implemented. The control system drives all vehicles trough the same trajectory, and their performances are measured evaluating vertical and lateral tire loads, steering torque, roll and yaw velocity and others."

Fig.2 Roll, steer, yaw angles and yaw velocity versus time

Fig. 3 Example of movie of the new vehicle

Fig.4 Steering torque versus time

Fig.4 Imposed roll angle versus time

The input steering torque requered to obtain the imposed roll angle depends on the angle of the roll axes respect to the road.

The variation of the steering torque are shown in the next figure.

Fig.4 Steering torque versus time for different angles between the roll angle and the road

Fig.6 Vehicle velocity during acceleration and braking versus time