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Four wheel steering Vs Front wheel Steering
Engineering and Construction
Pages 12 (3012 words)
1. Introduction Typical vehicle models for 4WS (four wheel steering) are composed of steering as well as roll motion, drive train and tyre dynamics. Some models for vehicles are modelled along the 2 DOF (degrees of freedom) bicycle model but such models fail to compensate for roll angle modelling and only relate lateral acceleration and yaw rates.
The vehicle is symmetrical about the x-z axis; 2. The vehicle’s total mass is lumped; 3. The vehicle’s roll axis is fixed and ; 4. The road’s surface conditions are consistent throughout the modelling; 5. Small angle approximations apply to the vehicle’s motion. The dynamics of the 4WS vehicle system can be divided broadly into three categories which are: 1. Tyre side forces; 2. Yaw moments; 3. Roll moments. These aspects of the steering system will be investigated separately based on three kinds of steering systems which are the 2WS (two wheel steering) with front wheel steering, 4WS under 40 km/h where the wheels are steered in opposite phases and 4WS over 40 km/h where the wheels are steered in the same phase. The three modes of steering and the relevant dynamics and motion investigation are discussed below. 2. Vehicle Dynamics Where: The variables , and all represent various kinds of disturbances that may affect the lateral, yaw and roll directions such as drag effects, side wind gusts, braking on ice, modelling uncertainties, loads, a flat tyre, an uneven road etc. These external disturbances may exert a sizeable influence in certain circumstances but for the sake of this investigation these disturbances will be neglected. ...
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