In this paper the results of initial investigation aiming at integrated control of various chassis subsystems are presented. By using a simplified stability analysis of a nonlinear bicycle model, it is shown that in manoeuvres performed at or close to the limit of adhesion, vehicle stability can be affected by relatively minor changes in the tyre force characeristics, driver inputs, disturbances. etc. This can make vehicle response to driver inputs unpredictible, thus necessitating a closed loop control of vehicle dynamics. This conclusion based on the mathematical model explains difficulties in controlling vehicles in the nonlinear range of tyre operation of which tests drivers are acutely aware. The control authority of each chassis subsystem in terms of an ability to generate a corrective yaw moment has been evaluated using mathematical models of vehicle and tyres. Regions of effectiveness and limitations of each subsystem have been identified. It was shown that active steering of front or rear wheels are both very effective when the tyres are not close to the linear range of operation. However, effectiveness of active front steer in correcting understeer is dramatically reduced during heavy understeer. Similarly, active rear wheel steer is not effective in correcting heavy oversteer. In both instances, the reason is inability of the system to markedly increase the lateral force of a given axle through steering corrections when the slip angle of that axle is large. Active brake control is effective in correcting both understeer and oversteer in all conditions, but the maximum yaw moment generated by braking a single wheel is more than two times larger during oversteer correction than during understeer correction. The maximum corrective yaw moments generated by active roll bars and magneto rheological (MR) dampers are about the same during oversteer and understeer, but they are about four times smaller than the maximum values achievable by active steerig or braking. The test results have confirmed that MR dampers can be quite effective in correcting vehcile yaw response on a dry surface. For example, in a J-turn manoeuvre vehicle yaw rate changed by as much as 60 % between two extreme damper settings. The closed loop yaw control of vehicle using MR dampers was shown to be effective in improving vehicle yaw response and reducing driver effort in transient manoeuvres. Finally, preliminary test results of the integrated control of brakes and MR suspension performed in winter conditions demonstrated that the integrated control of brakes and suspension reduced the time of brake activations by between 23 % and 73 %, depending on the particular test. Overall, vehicle testing has confirmed the main trends predicted by analysis based on mathematical models.


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    Title :

    Improvements in vehicle handling through integrated control of chassis systems


    Additional title:

    Verbesserung des Fahrzeugverhaltens durch eine integrierte Fahrwerkssystem-Regelung


    Contributors:
    Hac, A. (author) / Bodie, M.O. (author)

    Published in:

    Publication date :

    2002


    Size :

    28 Seiten, 15 Bilder, 15 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




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