PSI - Issue 12

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

220

8

• Preliminary activities: it was a group of activities necessary at the beginning of the working cycle. The machine had to move from one stock to another in order to take the necessary ingredients. After that, a first mixing session helped to achieve a uniform compound before the silage load. • Silage load: the machine reached the silage stock and had to dig into it to load the silage in the wagon. This operation consisted in a slight forward movement to help the milling head always having new material available. Thus, the hydraulic arm which held the head was used to bring it from the highest to the lowest point of the stock. • Mixing and cutting: this was the main mixing session. All the ingredients had been loaded into the tank, thus the augers had to sustain the movement of the entire mass (4000 kg). This operation was crucial both to auto matically cut all the ingredient to the desired size and to have them uniformly distributed in the final meal. • Meal unload: the machine was then driven to the livestock shed to download the prepared meal. The augers are active in this phase in order to use the generated centrifugal force to push the compound out of the tank. The results in Fig. 6a - 6b show two major working activities: the silage load with power peaks near to the maximum available installed power and the mixing phase characterized by the higher average power value. The former showed such a high power demand when the milling head had to cut the silage stock being pushed against it. At that moment the power coming from the engine was used both for mixing, slightly move the vehicle and for the milling head. The latter showed high mean power values due to the energy necessary to mix all the mass within the wagon tank. From the measurements, it was possible to highlight how each activity had a well defined duration. Thus each of them has a di ff erent impact on the total fuel consumption depending on its actual duration Fig. 6c - 6d. The greater the influence of the single activity on the working cycle, the greater should be the e ff ort to improve its e ffi ciency. An improvement on the e ffi ciency of a certain activity is weighted by its percentage on the entire working cycle. From Fig. 6c, the Working Cycle diagram for the self propelled vertical feed mixer can be defined as shown in Fig. 7. It can be obtained considering the mean duration of each phase in each daily test compared to the average duration of the overall cycle. The results from Fig. 6c confirms also the overall fuel consumption of each phase, although they may seem in contradiction to results from Fig. 6a - 6b. The preliminary activities may not require high amount of power due to the fact that the mass in the tank is not the final one, but the duration of the first mixing phase increase the amount of total energy to be involved.

5. Design of an electrified architecture

As stated by (Soma`, 2016), the first design stage of an electrified working machine with several power users to be satisfied ( mechanical and hydraulic in this case ) should use the new definition of hybridization factor HF to classify the di ff erent proposed solutions. It is defined as

1 2 ( HF mech + HF hydro )

(1)

HF =

with

P em 1 P ICE + P em 1 P em 2 P ICE + P em 2

HF mech =

(2)

(3)

HF hydro =

HF hydro and HF mech represent the hybridization of the mechanical and hydraulic power paths; P em 1 and P em 2 are the electric power involved on the mechanical and hydraulic path; P ICE is the power coming from the thermal engine that goes into the specific path. From experimental data it is clear that the main activity of this machine is a quite constant load profile whose intensity depends on the amount of mass to be mixed. Thus, the load intensity can be related to the tank size of the mixer