### Gear Ratio Optimization of a Multi-Speed Transmission for Electric Dump Truck Operating on the Structure Route

Senqi Tan, Jue Yang, Xinxin Zhao, Tingting Hai, Wenming Zhang
2018 Energies
Research demonstrated that the application of a multi-speed transmission could improve the dynamic and economic performance of electric vehicles. This paper deals with a novel multi-speed transmission for the electric dump truck (EDT) operating on the structure route (SR), which has a definite starting point and end point without complex traffic conditions. To optimize the gear ratio and shift schedule to reduce energy consumption in such conditions, the mathematical model of the transmission
more » ... the transmission and the dynamic model of the EDT are initially required. Following this, the shift schedule is presented according to the motor efficiency map. After that, the gear ratio optimization is carried out by a particle swarm optimization (PSO) algorithm. Moreover, the proposed EDT is compared with an EDT with a single-speed transmission. The simulation results show that the energy consumption is reduced by 6.1%. Energies 2018, 11, 1324 2 of 17 as well as dual motor multi-speed EV transmissions [14] . Each form has its own advantages and disadvantages. Additionally, some algorithms for the improvement of the economic performance, which concentrated on the passenger cars on road condition, have been presented. Datong et al. [15] presented a method of gear ratio optimization via Genetic Algorithm (GA), which only aimed at minimizing the energy consumption. Wu et al. [16] built a Battery Electric Vehicle model with Matlab SIMULINK and AUTONOMIE and used Dynamic Programming (DP) to find the optimal gear ratio, taking added weight and lower transmission efficiency into consideration. Sorniotti et al. [17] and Morozov et al. [18] established the multi-objective optimization model of the two-speed transmission for electric delivery step van in different ways, taking the economic performance and dynamic performance into consideration at the same time. However, the optimization processes were carried out based on the hypothesis that different ratio combinations obey the same shift schedule. Gao et al. [19] presented a way to define the shift schedule of several different drive cycles via the maximum overlapping area of gear operational points, which exhibits a strong robustness, as the schedule is the compromise of the optimal operating point under different cycle conditions. This paper designed a two-speed transmission for the electric dump truck (EDT) in particular, which consists of two planetary sets instead of parallel axis gear trains. Generally speaking, planetary gears are more suitable for heavy-duty trucks as the epicyclic gear train has the advantages of reduction volume, light weight, compact structure and high power density [20, 21] . Following this, the mathematical model and the EDT dynamic model are developed for simulation. Based on the efficiency map of the motor, the dynamic shift schedule has been proposed and applied to the EDT simulation model. Following this, a gear ratio optimization strategy for the novel transmission has been proposed, based on the classical dump truck working cycle of an iron mine in China. The simulation results show that the transmission with an optimized gear ratio can improve the energy conversion efficiency while maintaining the satisfactory acceleration ability. The paper is organized as follows: Section 2 is devoted to the model development of the transmission and the EDT. The shift schedule is presented in Section 3. Section 4 shows the optimization solutions and simulation results. Finally, the summary and conclusions are given in Section 5. Modeling and Analysis of Electric Dump Truck In this paper, the developed simulation model of the EDT, established in the Matlab/Simulink (R2016b) with state flow, consists of the environment information, road spectrum, energy and powertrain system, vehicle control system and driver system, which is a proportional-integral-derivative (PID) control model that allows for the reference velocity to be followed, as shown in Figure 1 . The overall status information is collected by the vehicle control system, and the corresponding information is fed back to the driver model. Some of the basic parameters related to the EDT are shown in Table 1 [22]. Energies 2018, 11, x FOR PEER REVIEW 2 of 17