PSI - Issue 12

Francesco Mocera et al. / Procedia Structural Integrity 12 (2018) 213–223 Author name / Structural Integrity Procedia 00 (2018) 000–000

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Fig. 7: Working cycle of the self propelled vertical feed mixer

wagon. On the other hand, there are some ”auxiliary” functions as the milling head and the hydraulic transmission, which require a similar amount of power for short periods of time. The Working Cycle in Fig. 7 would suggest an hybrid architecture with a thermal engine sized to cover the continuous power required by the augers and an electric system to e ffi ciently manage all the hydraulic users and their peak power requests. This translates to

P em 1 P ICE + P em 1

HF mech =

= 0

(4)

taken P em 1 = 0. Looking at the most critical activities when mechanical and hydraulic power are simultaneously supplied by the thermal engine, it is possible to highlight a split of the total available power in a 70% for the mechanical path, and 30% for the hydraulic one. Thus an hybridization of the hydraulic path as

P em 2 P ICE + P em 2

HF hydro =

= 1

(5)

with P ICE = 0 and P em 2 = 0 . 3 P ICEtraditional . This architecture would have HF = 0 . 5. Looking at the duration data of the hydraulic activities, it is possible to see that they engage the thermal engine for almost 30% of the total cycle time. Thus the proposed architecture would benefit both of the downsized engine and the greater working e ffi ciency of a more reactive power source to supply hydraulic auxiliaries. These benefits would be much higher if the entire hydraulic system would be replaced by a full electric systems. All the hydraulic losses related to pipelines and hydraulic transmission would be eliminated thanks to the greater e ffi ciency of the electric power transmission. However, in such a case it would be important to evaluate if a full electric driveline, with several electric motors would be convenient from the control point of view. Finally, a special mention deserves the full electric architecture characterized by HF = 1. The machine has a continuous power request that, in principle, would not match today’s state of the art energy storage systems requiring a high volume battery pack (Vergori, 2018). However, the high repetitiveness of the working cycle and the limited area to be covered in drive mode within the farm allow to design an optimized battery pack that fit well the application. Moreover, a proper design of the electric system would allow the use of the grid for the most demanding operations, i.e. mixing. A Full Electric architecture would be highly simplified compared to the actual ones with the thermal engine and all the related auxiliaries for the exhaust gas after-treatment. From these considerations, the collaboration