# Hybrid Power System Design for Multifunctional Mini-Loader Vehicles
## 4 Discussion  
The results of the planned experiments demonstrate that the vehicle meets the design requirements which are longer operating time, better energy efficiency and less air pollution; however, there are some areas that require continuous improvement, including the hydraulic pump performance, climbing ability, obstacle crossing ability, and trench crossing ability and tools. which are discussed as follows. 1. Longer operating time and better energy efficiency: The engine can operate at optimum conditions for a longer time, and can rest in the non-optimal operating range. Therefore, through the design of this study, the operation time and energy efficiency can be improved by using EM to provide power or starting battery charging mode to convert wasted power into electricity. 2. Less air pollution: Air pollution can be reduced because the power system can adjust output torque in different operation conditions in a hybrid power mode. Avoiding inefficient engine operation can reduce carbon emissions caused by fuel combustion. With the help of hybrid powertrain design and the auxiliary output of generators and electric motors, the engine can run in the optimum efficiency range for a longer time, thus reducing air pollution and improving energy efficiency. 3. Hydraulic pump performance: The electric hydraulic pump module successfully dumped the cargo into the cargo bed. During the dumping process, it is observed that when too close to the  
Figure 10: Field test. (**a**) Vehicle testing of passing through a door; (**b**) vehicle testing of climbing 10% slope; (**c**) vehicle testing of climbing 30% slope; (**d**) vehicle testing of crossing a short step; (**e**) vehicle testing of crossing a trench. cargo, the operator is likely to inhale dust or be injured by small dumping. Therefore, the MB-3 hydraulic valve and the solenoid valve are modified to an electronic control mode, and a remote controller of the hydraulic valve is added for operators to use from 1 m away from the loading platform, improving the comfort and safety of personnel. 4. Climbing ability: In the three power mode tests, the vehicle climbed 10% and 30% slopes. However, because the centers of gravity of the hybrid power system and the hydraulic system are closer to the user, when the slope angle is too large, the system may tilt upwards or slip downwards, and personnel may be injured. This problem can be overcome by two ideas. The first idea is changing the position of the center of gravity by moving forward the motor/generator and the battery module to the space above the electric hydraulic pump. The second idea is adding a parking brake to supply a moderate reverse force. 5. Obstacle crossing ability: The test results demonstrate that the vehicle can cross a short step of 140 mm in height. However, because of the center of gravity of the hybrid power system being closer to the user, when the empty vehicle tracks halfway on the step, the track on the step is slightly dangling. Nevertheless, this does not cause a safety issue. The dangling phenomenon in the unloaded vehicle can be overcome that similar to discussion point 2. This idea not only reduces the overall height of the hybrid power module on the vehicle, but also improves the torque gap between clockwise and counterclockwise. 6. Trench crossing ability: The loader crossed a 300 mm trench, but because the center of gravity is closer to the user, it should be noted that an unloaded vehicle may tilt upwards. The solution is the same as the second and third discussion points, which can be overcome by adjusting the center of gravity of the vehicle. This is conducive to overcoming the doubts of tilt upwards and slight dangling caused by climbing, and obstacle and trench crossing when the vehicle has no load. 7. The current designed tools are suitable for excavation, soil transport, and soil loosening functions.