Understeer characteristics for energy-efficient fully electric vehicles with multiple motors

Electric vehicles with multiple motors allow torque-vectoring, which generates a yaw moment by assigning different motor torques at the left and right wheels. This permits designing the steady-state cornering response according to several vehicle handling quality targets. For example, as widely discussed in the literature, to make the vehicle more sports-oriented, it is possible to reduce the understeer gradient and increase the maximum lateral acceleration with respect to the same vehicle without torque-vectoring. This paper focuses on the novel experimentally-based design of a reference vehicle understeer characteristic providing energy efficiency enhancement over the whole range of achievable lateral accelerations. Experiments show that an appropriate tuning of the reference understeer characteristic, i.e., the reference yaw rate of the torque-vectoring controller, can bring energy savings of up to ~11% for a case study four-wheel-drive electric vehicle demonstrator. Moreover, during constant speed cornering, it is more efficient to significantly reduce the level of vehicle understeer, with respect to the same vehicle with even torque distribution on the left and right wheels.

[1]  Y. Hori,et al.  Four-wheel driving-force distribution method based on driving stiffness and slip ratio estimation for electric vehicle with in-wheel motors , 2012, 2012 IEEE Vehicle Power and Propulsion Conference.

[2]  Aldo Sorniotti,et al.  Design and comparison of the handling performance of different electric vehicle layouts , 2014 .

[3]  Jiabin Wang,et al.  Torque Distribution Strategy for a Front- and Rear-Wheel-Driven Electric Vehicle , 2012, IEEE Transactions on Vehicular Technology.

[4]  Patrick Gruber,et al.  A Fast and Parametric Torque Distribution Strategy for Four-Wheel-Drive Energy-Efficient Electric Vehicles , 2016, IEEE Transactions on Industrial Electronics.

[5]  Antonella Ferrara,et al.  Integral Sliding Mode for the Torque-Vectoring Control of Fully Electric Vehicles: Theoretical Design and Experimental Assessment , 2015, IEEE Transactions on Vehicular Technology.

[6]  Jun Wang,et al.  Motor torque based vehicle stability control for four-wheel-drive electric vehicle , 2009, 2009 IEEE Vehicle Power and Propulsion Conference.

[7]  Xibo Yuan,et al.  Torque distribution strategy for a front and rear wheel driven electric vehicle , 2012 .

[8]  Aldo Sorniotti,et al.  Driving modes for designing the cornering response of fully electric vehicles with multiple motors , 2015 .

[9]  Aldo Sorniotti,et al.  Optimal Wheel Torque Distribution for a Four-Wheel-Drive Fully Electric Vehicle , 2013 .

[10]  Patrick Gruber,et al.  Wheel Torque Distribution Criteria for Electric Vehicles With Torque-Vectoring Differentials , 2014, IEEE Transactions on Vehicular Technology.