Abstract
Electric vehicles are spreading in automotive industry pushed by the need of reducing greenhouse gas. However, the use of multiple electric motors, i.e., one per wheel, allows to redefine the vehicle powertrain layout with great benefits on vehicle dynamics. Electric motors braking torque is in general not enough to produce high decelerations. Hydraulic friction brakes are still necessary for safety reasons and to avoid oversized motors. This paper presents a control strategy for distributed electric motors (EM), one per wheel, to maximize the regenerative braking. The controller handles cooperative braking among EMs and hydraulic brakes, which are still necessary to guarantee top braking performance of the car. The proposed algorithm considers the driver requested braking torque as well as the required yaw moment by stability control system. Motor efficiency map and wheel normal load are considered to optimally distribute the torques. With respect to conventional distribution strategies, the presented algorithm improves performance, maximizing the regenerative braking power.
Highlights
In recent years, the interest towards electric vehicles (EVs) leads to the possibility of reinventing several vehicle subsystems, for both light and heavy-duty vehicles [1], in particular the powertrain. e use of multiple electric motors (EMs), one per wheel, allows to precisely control the torque at each wheel showing superior performance with respect to a traditional internal combustion engine (ICE) vehicle [2]
To test the performances of the new braking control algorithm, a vehicle model developed in a simulation environment in Matlab/Simulink is used. e vehicle is modelled according to a 14 d.o.f. model (ViCar Realtime), which is based on D segment passengers’ car. e model accounts for the following: (i) ree displacements of the vehicle center of mass (c.o.m); (ii) ree rotations of the car body; (iii) Four vertical displacements of unsprung masses; (iv) Four wheels angular velocities about hub axis
Design Variable Space. e design variables space can be described considering the friction brake system, the EMs architecture, and the maximum torque that can be transmitted to the road. e friction brake torque is proportional to the pressure times a constant gain (Kb) as TF − Kbpcal
Summary
The interest towards electric vehicles (EVs) leads to the possibility of reinventing several vehicle subsystems, for both light and heavy-duty vehicles [1], in particular the powertrain. e use of multiple electric motors (EMs), one per wheel, allows to precisely control the torque at each wheel showing superior performance with respect to a traditional internal combustion engine (ICE) vehicle [2]. The demand of extremely reliable motors and the cost reduction pushes the research to find innovative solution for controlling Permanent Magnets EMs with powerful sensorless solutions ([4,5,6,7]) Another interesting feature offered by DEMs is the possibility of applying Torque Vectoring (TV) to improve the stability and performance of the car ([8,9,10,11]). [22] proposes a regenerative braking distribution strategy based on multiinput fuzzy control logic while considering the battery SOC, the brake strength, and the motor speed. The distribution algorithm accounts for the wheels applicable torque, because friction is limited by the normal load Both longitudinal and lateral load transfer are considered to evaluate the wheel condition. The paper shows the simulation results in typical driving maneuvers, where the proposed controller is compared to two other strategies normally adopted in commercial cars
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