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The present paper describes a longitudinal control strategy in time-varying road surface adhesion conditions, for a vehicle equipped with 4 in-wheel electric motors. The controller task is to ensure two main functions : braking (achieving an ABS-like function, i.e., no wheel skid), and traction control (TCS-like function, i.e., low wheel slip) using the electric motor torques as the unique actuators signal sources. The torque of electric motors is available almost instantaneously. In addition, information about its values can be measured, starting from the current that passes through the motor, which means that advanced control techniques can be applied directly on the transmitted torque. In order to generate the appropriate anti-skid or anti-slip torque for each wheel, firstly, an estimation of the instantaneous friction between the wheel and the road has to be made. Next, the maximum friction between the wheel and the road is computed with the help of an algorithm based on Dugoff tire model, without prior knowledge of the road conditions. Ultimately, the control strategy will compute a maximum torque that is allowed to be transmitted at each wheel in order to achieve TCS and ABS functions, along with a given reference speed to track. The only variables required in this strategy are the wheel acceleration, the instantaneous torque generated by the electric motors and the chassis acceleration. [ABSTRACT FROM PUBLISHER]

The main purpose of this study is the description of the qualitative dynamical response of a rotary drilling system with a drag bit, using a model that takes into consideration the axial and the torsional vibration modes of the bit. The studied model, based on the interface bit-rock, contains a couple of wave equations with boundary conditions consisting of the angular speed and the axial speed at the top additionally to the angular and axial acceleration at the bit whose contain a realistic frictional torque. Our analysis is based on the center manifold Theorem and Normal forms theory whose allow us to simplify the model. [ABSTRACT FROM PUBLISHER]

The present paper describes a torque controller for a vehicle equipped with 4 electric motors, one at each wheel. The controller is set up to ensure two main functions: braking with anti-skidding and traction control using the electric motor torque as the unique actuator signal source. Unlike the torque generated by classic internal combustion engines, the torque of electric motors is available almost instantaneously. In addition, it can be measured on-line, which means that advanced control techniques can be applied. In order to generate the appropriate anti-skid or anti-slip torque for each wheel, one has to estimate the friction between the wheel and the road. In the first step, the instantaneous friction coefficient and the maximum friction coefficient between the wheel and the road are estimated, without prior knowledge of the road conditions. Next, the approach relies on a feedback sliding mode control scheme to ensure the vehicle is operated in the maximum friction zone in both hard acceleration and braking phases, along with a given reference speed to track. The only variables used in this strategy are the wheel acceleration, the instantaneous torque generated by the electric motors and the chassis acceleration. [ABSTRACT FROM PUBLISHER]

Obtaining the Puiseux Series expansion of multiple imaginary (characteristic) roots (MIRs) is a fundamental issue in the stability analysis of time-delay systems. However, this issue has not been fully investigated up to date. This work focuses on the Puiseux Series expansion of MIRs for a class of linear time-delay systems including commensurate delays. For an MIR of any multiplicity, we propose an algorithm for defining the structure of the Puiseux Series, as well as the explicit computation of the corresponding coefficients. By using the proposed method, we can find all the Puiseux Series corresponding to all the root trajectories. Some illustrative examples complete the work. [ABSTRACT FROM PUBLISHER]