This paper presents an optimal algorithm to enhance the performance of an On-Demand All-Wheel Drive (ODAWD) vehicle by traction improvement through regulation of wheel slip. A 'Minimum Fuel Problem' is developed with a cost function minimising the slip error and the control action defined as the ratio of the total torque transmitted to the non-driven wheels (rear wheels). A simplified vehicle model (bicycle model) is used to develop the proposed controller to optimally reduce the wheel slip error by engaging and dynamically controlling a hydraulic clutch. The controller performance was validated on a realtime Hardware-in-Loop (HIL) bench. The research results obtained from both offline and real-time HIL simulations indicate that the proposed control algorithm is successful in optimally regulating the slip ratios based on the arbitrary performance index used. The offline simulation was performed on a personal computer with average processing power and the results indicates a slip reduction of 50% as was validated from the HIL bench system. The real-time HIL simulation on different road surfaces indicated that the maximum amount of slip reduction was observed at low-medium friction coefficient surfaces. As observed from the packed snow surface, the reduction of slip being 50% it produced a velocity improvement at the maximum of around 30 %. Further, it was observed from the icy road surface that although the reduction in front wheel slip ratio is much lesser than in the packed snow instance, the velocity improvement was a significant 50 %. However, this is attributed to the increased traction achieved from the very high proportion of torque transmitted to the rear wheels. Although it was observed from low friction surfaces that the control algorithm was showing significant results, the higher friction coefficient surfaces (wet Jennite and wet Asphalt) fail to provide significant results. The reason is the less amount of slippage observed in the front wheels while its simulated without the controller. As observed from the performance indices since the traces are close to zero, the optimal algorithm fails to achieve at a lesser performance index. It can also be seen that the PID controller plays quite a role deciding the delay and the overshoot/dampening, which will be propagated to the optimal control algorithm's calculations. The slip spikes observed at the front wheels and rear wheels are based on the nonlinear gear shifting events. An optimal control algorithm was presented for traction improvement of an ODAWD vehicle by regulating wheel slip in an acceleration event. A TPBVP (two point boundary value problem) was investigated through numerical methods and a simplified model of the above problem was integrated to a validated 14 degree-of-freedom detailed vehicle model in MATLAB/SIMULINK software interface. Simulation results prove the implementation of the above nonlinear control algorithm enhances traction at an acceleration event by regulating the slip while on a low friction coefficient surface.


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    Title :

    Optimal control of an On-Demand All-Wheel Drive system (ODAWD) for vehicle traction enhancement


    Contributors:

    Published in:

    Publication date :

    2011


    Size :

    29 Seiten, 28 Bilder, 22 Quellen



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




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