Abstract
KEYWORDS – brake force distribution, brake blending, optimization, regenerative braking, electric vehicle
ABSTRACT The optimal brake control in the case of a full electric vehicle must not only guarantee high brake performance but also aim at maximum possible level of energy regenerated during the manoeuvre. Targeting integrated electric vehicle control, the driving comfort should be also considered as a component requiring optimization. These factors have motivated the presented study and allowed to formulate the main objective: Development of optimal brake control strategy based on three criteria – brake performance, energy efficiency, and ride comfort. The research is subjected to a full electric passenger vehicle equipped with four in-wheel motors and an electro-hydraulic brake system. On the first stage of the research, the optimization procedure is proposed for the brake torque distribution. Three domains are chosen for the shaping of the corresponding optimization cost function: the brake performance is being estimated by deceleration tracking during the manoeuvre; the energy consumption is quantified through regenerative energy and tyre dissipation energy; the indicator for the ride comfort (in the case of straight-line braking) is the pitch angle. The verification of the developed brake control functions is carried out using the vehicle simulator in IPG CarMaker and hardware-in-the-loop platform with installed electro-hydraulic brake system. The straight-line braking manoeuvre has been investigated as the case study. The proposed technique allowed to reach an optimal brake force distribution with high level of brake energy recuperation and simultaneous keeping of required safety level. The pitch oscillations caused by the vehicle behaviour at emergency braking have been also reduced as compared with the brake manoeuvre without brake distribution / blending control. The experiments were done on the basis of model- and hardware-in-the-loop simulations. The characteristics of electric motors are deduced from experimental data. The real hardware components of the brake system are used including the hydraulic control unit. The controller is emulated in real-time mode using dSPACE tools. The results of the presented study have showed that an optimal brake control in the case of the electric vehicle allows to achieve a multilateral effect in reduction of the brake distance, increase of brake energy regeneration and improvement of the ride comfort at braking.