Torque vectoring using e-axle configuration for 4WD battery electric truck: Utilizing control allocation for motion control and steer by propulsion

Examensarbete för masterexamen
Master's Thesis
Systems, control and mechatronics (MPSYS), MSc
Fahlgren, Emil
Söderberg, Daniel
With the rise of electric drives in vehicle applications, configurations of new powertrain design are emerging. In recent years, this trend has shifted to include heavy vehicles as well. In this thesis, a concept 4x4 battery electric truck with a distributed powertrain is investigated. By using four individual motors on two separate e-axles, different coordination possibilities are available for motion control of the truck. This thesis focuses on using torque vectoring as a principle to allocate the requested global torque. Furthermore, a novel method mentioned to as steer by propulsion (SBP) is proposed, where the steering of the vehicle can be controlled solely by using the electric machines on the front axle. Investigations are conducted to explore the effectiveness of this method on vehicle performance and energy consumption. To distribute the control requests across the available actuators, control allocation (CA) is used. Here, the problem is formulated as a quadratic programming (QP) problem. High level controllers provide the requested global forces as an input to the control allocation, which in turn allocates torques to the separate wheel controllers. Furthermore, different formulations of the control allocator and motion controller are presented and compared. The control system is simulated with a vehicle model provided by Volvo, and the results indicate that steer by propulsion is able to follow a reference path with a lateral offset of a magnitude of an acceptable level. Furthermore, the simulations show that SBP can repeat this behavior at high speeds as well with an oscillatory behavior. Therefore, the method is recommended to use mainly at vehicle speeds below 50 km/h. Finally, simulations show that SBP increases the energy consumption by 2-4 %. Considering that the consumption is on par with using power steering, SBP will be viable for redundancy with some limitations.
Control system design , optimal control , control allocation , steer by propulsion , optimization , electric powertrains , e-axles , battery electric trucks
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