Research on Response Characteristics and Energy Efficiency of Power Unit Used for Electric Driving Mobile Machine

Nowadays, the hydraulic pump driven by the diesel engine is widely used as the power unit for mobile machines, which consumes a large amount of fuel and cause high emissions. One solution is to use the electric driving mode. In this paper, the energy consumption characteristics of 4 electro-hydraulic power units, which are a fixed speed motor or a variable speed motor to drive a fixed displacement hydraulic pump or a variable displacement hydraulic pump, are compared and analyzed respectively. The results show that the power unit which a variable displacement hydraulic pump is driven by a variable speed asynchronous motor has the highest cost-performance ratio. However, due to the limitation of the battery peak current, the dynamic response of the power unit is slow. To solve this problem, a new power unit is proposed which add an accumulator to the hydraulic pump outlet to recover the power unit braking kinetic energy. The high-pressure oil stored in the accumulator can be absorbed into the hydraulic pump inlet to improve the power unit starting and braking performance and energy efficiency. The starting and braking characteristics of the power unit with and without the accumulator are compared experimentally. The results show that, if the power unit is driven by the motor alone, the power unit response is slow, and the load pressure has a significant influence on the response time. After adding the accumulator to the hydraulic pump, the power unit starting and braking time could be shortened significantly, and the starting power demand is also reduced. The proposed power unit is further used to drive a hydraulic excavator. Under the same working conditions and operating characteristics, energy consumption can be reduced by 28.5% compared with using the variable displacement hydraulic pump alone.