# Power Train System Control of Electric Loader Based on Positive Flow System
## 6 Experiment Research  
Further, experimental research was carried out. The schematic diagram and physical diagram of the experimental platform are shown in Figures 17 and 18. In this system, a Li-ion battery was employed. A traveling electric motor and a hydraulic pump electric motor were used, respectively. A high-voltage management unit was used to realize power distribution. A VCU was used to collect the signals of the pilot handle and to control the electric motors. The system parameters are shown in Table 1.  
Figure 17: System structure diagram of the pure electric loader.  
Figure 18: Test prototype of the 1.6 t pure electric loader.  
Firstly, the relationship between electric motor speed and pilot pressure was verified. When a step signal of the pilot pressure was input, the electric motor speed changed with the pilot pressure given in Figure 19. It can be seen that from 560-600 ms, the pilot pressure increased from 0-1.7 MPa, and the electric motor speed also increased from 300-2200 rpm. The electric motor speed response curve when the pilot pressure ramp signal was input is given Figure 20. As can be seen, the pilot pressure of system rose from 0-1.9 MPa between 23 and 27 s. At the same time, the electric motor speed increased from 300 rpm at 23 s to 2200 rpm at 26.5 s. Therefore, the variable-speed positive flow system can effectively follow the step input and the ramp input.  
Further, the energy saving characteristics of the system were studied. Because there was no flow sensor installed in the test prototype, the flow of the pump could not be detected directly. While, the hydraulic pump was driven by the electric motor to supply oil to the system. Therefore, the energy saving characteristic was studied by calculating the energy consumption of the electric motor indirectly.  
Figure 19: Step response curve of the electric motor speed with pilot pressure.  
Figure 20: Ramp response curve of the electric motor speed with pilot pressure.  
For comparison, the energy efficiency characteristics of the constant speed system were also analyzed. The same actions were applied to these two different systems. The cylinder displacement curves are shown in Figure 21. Due to the manual operation for the pilot handle, there was a slight difference between the rising and falling speed of the two systems. However, this does not affect the analysis of the energy saving of the control strategy. It can be seen that the rising time of each system was about 9000 ms and the falling time was about 10,000 ms.  
The electric motor output power comparison curves of the positive flow system based on the variable speed and the constant speed are given in Figure 22, respectively.  
It can be found that there was little difference in the electric motor output power of the two systems during boom rising or falling. The main difference happened when the boom moved to the maximum displacement and the pilot handle did not act. In order to obtain the specific energy consumed, integration for data in was carried out and is shown in Figure 22. Among them, the energy consumed by the electric motor in the constant speed system was 472.846 kJ. While, the energy consumed by the electric motor in the system based on variable speed control was 351.010 kJ. Compared with the constant flow system,  
Figure 21: Comparison curve of cylinder displacement under different modes. (**a**) Cylinder displacement under constant speed; (**b**) cylinder displacement under variable speed.  
Figure 22: Electric motor power comparison curve under different modes. (**a**) Power of constant speed control; (**b**) power of variable speed control.  
the energy consumption of the proposed system was reduced by 121.836 kJ. The energy saving was improved by 25.77% in one cycle of the boom cylinder rising and falling.