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• Mild hybrid is when the purely electric operation mode is not able to follow a full standard driving cycle (0.25 < HF < 0.5). • Minimal hybrid is equipped with a stop and start function, characterized by a decreasing distance in the purely electric mode (0 < HF < 0.1). HF = 0 is applicable to a conventional engine vehicle, whereas HF = 1 is applicable to a “pure” electric vehicle, such as the BEV [43]. Table 1 presents the hybridization factors calculated by using Eq. (1), taking into account the electrical driveline for automotive applications. Compared with cars, the introduction of electric drives in tractors would allow expanded func- tionalities, considering that agricultural machines have a large variety of functional loading and working drives [20, 84]. The working cycle of a vehicle is strongly correlated with the application. In the case of a car, the comparison can be carried out by evaluating the extra-urban cycle and the urban cycle. For example, in the case of the urban cycle, the vehicle recovers energy due to fre- quent accelerations and stops. Working machines even with repetitive movements, such as exca- vators, are able to recover the kinetic energy of the arm. For agricultural tractors and machinery, two tasks [85] have been identified, such as working conditions with steps at which energy recov- ery is possible: transport and front loading. Telescopic handlers also have a similar duty cycle. Unlike in hybrid cars, the hybrid propulsion system in heavy-duty machinery can supply power to the driveline and loading hydraulic circuit [86]. The mechanical power supplied by the ICE flows to recharge the battery pack, actuate the hydraulic pump, and move the driveline (Table 2). Although there is no classification for hybrid heavy-duty machines in the literature, a first orien- tation phase can be determined by defining a hybridization factor for a work vehicle HFWV [87]. 4.1. Driveline power Hybrid architecture in series or in parallel has, in both cases, at least one electric motor (EM1) for moving the vehicle. In order to generalize the different configurations define (EM1), the electric motor used for the traction of the vehicle. Therefore, according to the hybridization factor described in the automotive field, the first term (µ1) of the hybridization factor for heavy-duty vehicles (HFHDV) is as follows: µ 1   =  P e m 1 _______ P e m 1 + P ICE (2) Vehicle Electric motor (kW) ICE (kW) HF Eq. (1) Toyota Prius 31 43 0.42 Toyota Prius 3rd gen. 50 53 0.49 Honda Insight 10 50 0.17 Honda Civic 10 63 0.07 Table 1. HF comparison among automotive vehicles [80]. Hybrid Electric Vehicles12