CAPÍTULO 2. DISEÑO DE LA RED DE COMUNICACIONES
2.3 Diseño de variantes
The results from this research programme provide further impact to academia and industry through collaborative studies with other researchers. Data from cell durability experiments have been used within studies investigating factors that cause aging within battery cells, as well as defining how external mechanisms influence the control parameters of battery management software. The findings of these collaborative studies have been published within [40] and [39] respectively. Overall, this research has identified best in class engineering procedure with respect to conducting vibration measurement, characterisation and durability testing on EV RESS components. It provides impact by applying state-of-the-art vibration characterisation and testing techniques to the novel field of EV battery cells and modules, within a single research program
Opportunities for Further Work
7.2
Table 66 defines the work undertaken within this thesis.
Table 66: Summary of Research Undertaken and Areas for Further Investigation Description
Defining the In- Service Environment Natural Vibration Behaviour of EV Components Vibration Durability Single Axis Durability Multi Axis Durability (6DOF) Cells Cylindrical Cells (18560)
**
Pouch Cells
Prismatic Cells Modules Assembled from Cylindrical Cells (18560)
Assembled from Pouch Cells Assembled from Prismatic Cells Pack Assembled from Cylindrical Cells (18560)
*
Assembled from PouchCells
*
Assembled from
Prismatic Cells
*
Note:
*= Additional analysis presented in Table 67 **= Not defined via modal analysis
It highlights the gaps that exist in the existing knowledge with respect to the three key areas that are required to define the vibration durability of an EV RESS. Opportunities for further work in each of these areas are discussed in greater detail. 7.2.1 Opportunities for Further Work with Respect to Defining the In-Service
Environment and Development of Test Standards
As highlighted in Section 3.6 the in-vehicle measurement data used within this study was derived from A and C segment vehicles. Whilst the experiments performed have illustrated trends with regard to the robustness of 18650 cells and modules, the conclusions with respect to the durability life can only be attributable to city and medium size cars. Table 67 illustrates the measurement data for the different pack constructions vs market segments.
Table 67: Summary of Vehicle Pack Type Measured by Vehicle Segment Vehicle Segment
Classification Cylindrical Cell Pack Pouch Cell Pack Prismatic Cell Pack A Segment Vehicles (City Cars)
B Segment Vehicles (Small Cars) C Segment Vehicles (Medium Cars)
D Segment Vehicles (Large Cars) E Segment Vehicles (Executive Cars) F Segment Vehicles (Luxury Vehicles) J Segment Vehicles (Sports Utility Vehicles and 4 x 4) M Segment Vehicles (Multi-Purpose Vehicles) S Segment Vehicles (Sports Cars)This table clearly illustrates that just for measurement data from the pack itself, there are 24 permutations of pack construction and vehicle segment that require measurement to be able to determine the variations in operational loading that a battery assembly could witness within a BEV application. The data collated within this study have been recorded from a small sample size of vehicles from the A and C classes. As a result the synthesised profiles may display some behaviour that is unique to the vehicles or vehicle class that may not be suitable for RESS destined for larger vehicles such as SUV’s or luxury products. Therefore, it is recommended to perform a future measurement study with a larger fleet size of different evaluation vehicles from different vehicle classes. This fleet should also include HEV so that the differences in vibration loading associated with the typical battery locations
associated with these products can be defined and understood. In addition, an opportunity exists for a study to focus if there are differences, if any, between the batteries installed in HEV application compared to that in a BEV function.
The road load data utilised in this investigation evaluated the vibration experienced by the battery casing of three current production BEV’s when subjected to a range of proving ground surfaces. Whilst these measurement locations will undoubtedly support the development of future standards and test methods, an understanding of the internal vibration conditions of the battery assembly could be used to improve EV cell standards. Therefore it is recommended that a future study is performed where accelerometers are placed upon the internal components (such as cells and bus bars) of RESS and the response of these items to proving ground durability surfaces are recorded.
The main limitation of the derived profiles is that they use surface weightings based on an adapted ICEV structural durability schedule. Whilst it could be argued that future BEV usage will be comparable to that of ICEV customers due to improvements in product range, a study does need to be performed that determines the exact 90th percentile customer usage for EV’s and that fully defines the acceleration loading with regard to discreet events to eliminate uncertainty from the processing method.
Further, this study has focused on European usage, and has not considered the implications of different markets on the durability requirements for RESS. Therefore it would be beneficial if future surface weightings also considered regional variances with regard to measured accelerations and customer usage.
This study focused on deriving a set of vibration profiles that could be performed on a wide range of shaker systems. Subsequently the derived profiles applied vibration within the frequency range of 5 to 200 Hz. It may be beneficial to perform an additional set of synthesised profiles that define spectra outside of this bandwidth so that the DUT could be excited at frequencies below 5 Hz and above 200 Hz on suitable facilities.
The critical review of standards highlighted that an opportunity exists for a standard to be developed that in a single rig based test combines vibration, dynamic charge discharge (such as that from a legislative drive cycle) and climatic cycling. However further vehicle data and research is required to determine how these different ageing mechanisms interact to allow for suitable time compression of these attributes within a single test.
7.2.2 Opportunities for Further Work with Regard to Defining Natural Vibration