Seite - 16 - in Hybrid Electric Vehicles

The hydraulic system has a conventional architecture. Table 4 shows the main parameters of this work vehicle. A parallel hybrid power train configuration has two separate power sources that can directly power the loader. The disadvantage of a parallel configuration is that the engine cannot always be controlled in its high-efficiency operating region because it is still mechanically coupled to the wheels with an increased efficiency compared with the con- ventional model and a fuel consumption reduction of 10%[116]. Figure 7 shows a schematic of the Volvo L220F parallel hybrid electric wheel loader (HEWL). The vehicle has a parallel hybrid electric architecture for both the driving and the loading system. The basic idea of this parallel hybrid layout is to supply additional electric power when necessary, regenerating the machine during normal operations and minimizing the consumption in idle conditions. The power required by the device can be flexibly provided by using a work pump, which is driven by the pump motor shows the main parameters of the Volvo L220F. Mecalac proposed a similar architecture for the 12 MTX hybrid model and claimed to save up to 20% in fuel consumption [117]. However, the parallel configuration is still on the researching stage, and Liugong has applied a solution with super-capacitors instead of batteries [118] as schematically shown in Figure 8. At the CONEXPO International Trade Fair for Construction Machinery (2011), John Deere presented the first prototype of its hybrid wheel loader, the 944K hybrid. In February 2013, the entry of the first hybrid wheel loader, the 644K hybrid, in the market was announced with a reduction in fuel consumption up to 25% [119]. In this smaller model, a single electric machine provides all the power needed to drive the vehicle. The vehicle driveline has a series electric hybrid architecture, with the electric motor directly powered by the inverter without an energy storage system. Figure 9 shows a schematic view of John Deere 644K hybrid wheel loader [120]. The installed electrical machines are liquid-cooled brushless permanent magnet motors. The innovative architecture proposed by Merlo, as shown in Figures 10 and 11, is considered as a fully series architecture for vehicle traction and as a parallel architecture for the opera- tion of hydraulic systems. This kind of innovative, patented series-parallel architecture, with a split input for hydraulic lifting, allows both the electrical and the mechanical components to be arranged in a way that is compatible with the current layout and performance of Merlo machines. The main objectives of this hybrid telehandler are an overall improvement in per- formance, a decrease in daily fuel consumption in ordinary work activities, and a reduction in noise emissions. Moreover, the proposed configuration is capable of working in full electric, zero-emission mode for indoor use, such as in cattle sheds, stables, industrial and food pro- cessing warehouses, and buildings. In Ref. [87], it has been demonstrated a fuel consumption reduction of 30% with the same level of dynamic performance compared with the conven- tional telehandler. Claas proposed a parallel mild hybrid solution for the Scorpion telehandler. The simulation results reported in Refs. [121, 122] show a reduction in fuel consumption of about 20% and emissions for this parallel hybrid solution compared with the traditional model. The solution proposes the use of the electric motor as a power boost to maintain the performance while using a smaller diesel motor. Hybrid Electric Vehicles16