# Power Train System Control of Electric Loader Based on Positive Flow System
## 1 Introduction  
Loaders are widely used in various earthworks. However, the existing loaders with high energy consumption and poor emission gradually are unable to cope with the increasingly stringent global emission and energy-saving regulations. It is urgent to study energy conservation and emission reduction for loaders [1].  
Currently, the research on energy-saving and emission reduction for loaders mainly focuses on hydraulic systems and power train systems. Hydraulic energy-saving technologies are mainly conducted on flow matching such as negative flow systems [2], positive flow systems, load sensing systems [3], and independent meter-in and meter-out control systems [4], so as to reduce the overflow loss and throttling loss of the hydraulic system.  
In terms of the power train system, the energy-saving technologies are mainly carried out based on traditional engine [5], hybrid technology [6, 7, 8, 9], and pure electric technology [10, 11]. The traditional engine energy-saving technologies are mainly based on the electronic fuel injection control and the automatic idle speed control. However, the improvement of power train system energy efficiency is unsatisfactory. Hybrid technologies use an auxiliary power source to stabilize the working points of engine in high efficiency areas so as to improve the energy efficiency of the engine. However, the system structures and control strategies are complex. Besides, the engine is still retained. The comprehensive energy efficiency is also restricted. In the pure electric technology, the engine is replaced bythe motor. Zero emission, low noise, and high efficiency of the power train system can be realized. It is considered to be one of the main trends for loaders in the future.  
The technical research on the electrification of construction machinery is still in its infancy. At present, there are few technical reports on the electrification of Loaders. [PERSON] et al. developed a 5-t pure electric loader and appeared at the 2020 Shanghai Bauma exhibition. The loader adopted dual electric motor to realize the decoupling between the traveling system and the hydraulic system. A separate electric motor was employed to drive the working pump and the steering pump. The energy consumption of the loader was 30-35 kWh/h. [PERSON] et al. carried out simulation research on a pure electric loader, including the energy management [12] and the braking energy regeneration [13].  
In terms of other construction machinery, [PERSON] et al. used an asynchronous motor for an excavator, and a control method of variable speed-variable displacement for flow matching was proposed. Besides, the research on independent meter-in and meter-out was further studied [14]. In addition, an asynchronous motor electro-hydraulic excavator system based on a distributed variable speed volume control was also studied. The system used multiple motor pump units combined with open volume control and asymmetric closed volume control to drive the load, which significantly improved the energy efficiency of the whole machine [15]. [PERSON] et al. studied an electric heavy forklift and proposed a novel power train system based on a dual-electric machine [16]. [PERSON] et al. carried out corresponding research on the control algorithm of the steering system for a pure electric forklift [17]. [PERSON] et al. studied a load-sensitive system, a positive flow system, and a motorized automatic idle speed control of the electric excavator [18; 19; 20].  
In this paper, an electric motor with excellent speed regulation characteristic was employed. A positive flow system based on variable speed control for constant displacement pump was proposed for an electric loader. The control performance and energy saving were studied.