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Estimation of Brake Friction Coefficient for Blending Function of Base Braking Control
Abstract:
The brake architecture of hybrid and full electric vehicle includes the distinctive function of brake blending. Known approaches draw upon the maximum energy recuperation strategy and neglect the operation mode of friction brakes. Within this framework, an efficient control of the blending functions is demanded to compensate external disturbances induced by unpredictable variations of the pad disc friction coefficient. In addition, the control demand distribution between the conventional frictional brake system and the electric motors can incur failures that compromise the frictional braking performance and safety. However, deviation of friction coefficient value given in controller from actual one can induce undesirable deterioration of brake control functions. The main objective of the presented study is to propose a method to compensate disturbances induced by variations of brake linings friction coefficient through modifications of the brake torque demand for the enhancement of both brake performance and active safety.
The achievement of a compensation mechanism requires the estimation of relevant vehicle states. Hereunto, a novel technique based on a linear Kalman observer is proposed for the online estimation of the brake friction coefficient by relying upon the wheel speed sensors and inertia measurement unit (IMU). Such a tool enables a more efficient use of the frictional brakes aimed at minimizing losses of friction coefficient by keeping them in the optimal operational conditions. A simulation analysis will be carried out using the commercial vehicle dynamics simulation software IPG CarMaker to test the functionality of the developed estimator in the real-time mode. Experimental results from brake dynamometric test rig will be considered in the vehicle dynamics simulation software to reproduce the real behaviour of brake linings friction coefficient. The resulting improvements in brake control functions will be analysed against longitudinal base braking cases involving blending functions also in presence of failure of the electric motors.