University of Twente Student Theses


A physical multi-body car model using 3-D (screw) bond graphs

Boer, G.R. de (2002) A physical multi-body car model using 3-D (screw) bond graphs.

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Abstract:The goal of the project was to realize an infrastructure of a car in 20-SIM using (screw) bond graphs. Bond graph description is an energy based means of modeling physical systems. This model can be used for investigation of the X-bywire concept and independent wheel steering. Enquiry into the basic features of a car provided for the necessary insight in the course of development of the car. Rigid bodies have been used to describe the most signicant masses of the car. These are interconnected as so-called kinematic pairs. Within these kinematic pair connections, constraints are used to restrict the separate elements of the car to specic motions only. Setting the steering angle has been realized with the use of the Ackermann algorithm, which distinguishes between the track (and thus also the radius of curving) of the two front wheels. For more realistic steering behavior, the steering axes of both front wheels have been canted slightly, according to the Kingpin and Caster angles in genuine cars. The resulting model is a realistic reaction of a car is obtained. With the use of Gauss-maps on the surfaces of the tire and the ground, a contact determining algorithm has been developed. The velocity of the contact point of the wheel relative to the contact point of the surface is fed to a buffer returning an oppositely oriented force. Thus a forward propulsion is accomplished. Monitoring the force in the contact point and switching to coulomb friction behavior in case the force exceeds a set threshold value, enables the modeling of slip behavior. The slip in the horizontal plain has been coupled. Slip in one direction results in a loss of grip in the perpendicular direction as well. It can be concluded that with the use of 20-SIM a physically correct, energy based model of a car has been realized. All basic functionality of a car is comprised. The model has been parameterized for easy customizing to specific desires. It is recommended that the (rear or front wheel) torque-based, PID controlled drive is replaced by a velocity driven system. A rear wheel version of the Ackermann algorithm has then to be implemented as well. Thus removing the correctional in uence of the PID controller might seriously diminish simulation time. Moreover an investigation to minimizing the number of rigid bodies or kinematic connections in the model can prove to be worthwhile. This could also significantly reduce the simulation time of the model. Furthermore the center of mass of the car needs some looking into. It is currently situated in the middle of the car body. In real cars the engine and car framework are most weighty and they are predominantly in the lower part of the car body. Hence the center of mass should be shifted downwards and to the front of the car.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology
Programme:Electrical Engineering MSc (60353)
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