Study Of Driving Torque Distribution Control Strategy For Articulated Direct Driving Electric Buses

A multi-axle direct wheel driving articulated bus is a new type of distributed driving electric vehicles, which has the advantages of large body capacity, strong road adaptability and zero emission. It is one of the best choices for reducing traffic congestion and air pollution in both large and middle cities. However, the structure of the bus is extremely complicated because of the articulated device, and the dynamic coordination control is tightly coupled to the optimal allocation of energy. What is more, considering the driving conditions, road environment and other random factors, it is a challenge to achieve a safe and efficient control of the bus. In this paper, focusing on the problem of dynamic model and distribution of driving torque, the main contents are stated as follows.To achieve a reasonable model of the multi-axle direct wheel driving articulated bus, the bus is simplified as the front and the rear two parts. Using the Schiehlen multi-body dynamics modeling method and the Jourdain principle of virtual power, a vehicle dynamics model of the bus that has eleven degrees of freedom which include general coordinates such as the angle of the articulated device etc is established, which lays the foundation for the development and simulation of the longitudinal and lateral dynamic control strategy.For estimating the location of the center of mass, the H∞-EKF and H∞-UKF filter combined estimation algorithms are proposed. The input torque and rotational speed of distributed driving electric bus can be obtained in real-time, and then the location of the center of mass can be estimated by only analyzing the longitudinal dynamics of the bus. The algorithm of H∞ is introduced to improve the accuracy of the estimation of the location of the center of mass under the condition of the inaccuracy of the system model and the statistics feature of the noise, which provides basis for the distribution of the driving torque.Focus on the problem of the torque distribution between the middle axle and the rear axle under longitudinal driving cycles, an acceleration slip regulation strategy with an efficiency model is proposed. For general longitudinal driving condition, the driving torque distribution efficiency model between two driving axles is built up by the off-line optimization and the response surface method. For low adhesion road driving condition, a strategy of acceleration slip regulation based on the sliding mode control algorithms is proposed. Compared to the average torque distribution control strategy between middle axle and rear axle, the control strategy based on efficiency model could reduce the overall energy consumption of the vehicle by 5.82%. As for the low adhesion, the split road and other complex roads, the acceleration slip regulation strategy could control the slip ratio in a reasonable range of 15-20%, which can guarantee the safety and stability of the bus.For the torque distribution between coaxial wheels under the condition of steering, a strategy for yaw moment control is presented, which considers the driving efficiency and the control objective of yaw rate. The strategy takes the front body of a two axis four-wheel vehicle as reference, and from which the goal of yaw rate tracking is obtained. The Off-line optimization for additional yaw moment distribution is accomplished, according to the principle of lowest energy consumption. What’s more, a prediction model of BP neural network is built up based on the optimized data, and the torque distribution control between coaxial wheels is achieved. Simulation results show that, in the acceleration steering driving condition with 20km/h low initial velocity and the steering driving condition with 50km/h high initial velocity, the strategy can reduce the yaw rate tracking error by 21.7% and 10.2% and decrease the energy consumption by 1.75% and 4.16%, under the condition of meeting the requirement of longitudinal dynamic demand.After building an experiment platform with two identical driving motors, the characteristics of output torque in double-motor is tested, including consistency and efficiency. Referring to the development process of V model in controller, a driving controller is developed. And the effectiveness of control strategies are proved, based on the road tests of the 18-meter multi-axle direct wheel driving articulated bus, which is developed by project group.