FORMACIÓN DE LA COMUNA - 3 QUINTA NORMAL : SU ORIGEN MIXTO CON PRODUCCION

3 QUINTA NORMAL : SU ORIGEN MIXTO CON PRODUCCION

3.1 FORMACIÓN DE LA COMUNA

Once the cells presented in Table 19 were characterised as described in Section 5.3.4 they were prepared for their respective vibration test. Within investigation 1 the 27 NMC 18650 cells were then divided into three equal batches, comprising nine cells each. The first batch was subjected to the random vibration profiles defined in the USABC Procedure 10 standard whilst the second batch was subjected to the WMG-MPG vibration profiles presented in Chapter 3. The remaining cells were defined as control samples. Control samples were either co-located within the same environmental conditions (within the manufacturer supplied shipping carton), but not subject to any vibration loading as the test cells or remained in climatically controlled storage at the university.

Within investigation 2 the twelve NCA 18650 cells were divided into two groups. The first group of nine cells were subjected to the USABC Procedure 10 vibration profiles, whilst the second group of three cells were control samples. The control samples were placed in the manufacturer supplied shipping carton in the test facility but were not subjected to vibration.

Depending on the vehicle packaging constraints and application, 18650 cells are packaged in different orientations within different automotive battery packs [2, 90, 146, 147]. Therefore, one of the objectives of this study is to evaluate the effect of the X, Y and Z “vehicle axis” vibration profiles, to the three possible X, Y and Z-axis cell orientations. The vehicle and cell axis conventions are defined in Figure 54.

Figure 54: a) Axis Convention of Vehicle Vibration Durability Profiles (SAE J670e) [41], b) Axis Convention of Cells

Both vibration tests comprise a vertical (Z-axis) profile in addition to vibration profiles defined for the horizontal plane (X-axis and Y-axis). As part of the experimental procedure, each profile is sequentially applied to the cells to achieve the desired 100,000 miles of representative EV life. The three different combinations of vibration load with respect to each cell orientation are defined below:

 Z:Z to X:X to Y:Y  Z:X to X:Y to Y:Z  Z:Y to X:Z to Y:X

Using the above notation, for each pair of letters, the first letter refers to the vehicle axis, whilst the second refers to cell orientation. For simplicity, this report identifies the cell orientation in relationship to the vertical (Z axis) of the vehicle. For example a cell that was subjected to the vibration sequence of Z:X to X:Y to Y:Z, is referred to as being evaluated in the Z:X orientation. Figure 55 presents the orientation of the 9 cells mounted onto the durability fixture for the three orientations associated with the test programme.

Due to limited equipment availability, a single axis shaker was employed for durability testing. Because the orientation of the EMS could not be changed, the cells had to be rotated on the durability fixture between the X, Y and Z axis to achieve the correct loading. This test methodology is termed as not testing “with respect to gravity” and does not take into account changes in cell mass during the re-orientation of cells with respect to the input axis of vibration. Within these experiments, it is assumed that this limitation will not significantly impact the results. However, this is discussed further in Section 5.6.

Durability testing was conducted within an air-conditioned laboratory at a temperature of 21 ± 5 °C. The closed loop application of the vibration profile was achieved by using an averaging control strategy, as defined within [148] that includes a ± 3 dB alarm limits, ± 6 dB abort limits and 3 sigma limit control to ensure the safe execution of the test.

Z (up / down) X (fwd / aft) Y (left / right) Z X Y a) b)

Figure 55: Experimental Orientations and Test Positions on Durability Fixture

Once the cells were installed to the durability fixture and mounted onto the EMS table, the Z-axis vibration profile of either USABC Procedure 10 or WMG-MPG was applied first (Table 20). On completion, the cells were left to stabilize for a minimum of 4 hours. The cells were then moved on the durability fixture to the corresponding vehicle X-axis and subjected to the X-axis vibration profile (Table 21). Finally, the cells were repositioned on the durability fixture to facilitate the application of the vehicle Y-axis vibration profile (Table 22). At the end of the vibration profile, the cells were left to stabilize for 4 hours prior to visual inspection.

Table 20: Z-Axis Vibration Profiles Schedule

USABC Procedure 10 WMG-MPG

Profile Description Duration

(HH:MM) Profile Description

Duration (HH:MM)

Subject cells to 9 minutes of Vertical Profile 1 at 1.9 Grms in the Z-axis orientation of the cells under assessment.

00:09

Subject cells to 150 hours of vertical Frequency in the Z-axis

orientation of the cells under assessment.

150:00 Subject cells to 5 hours and 15

minutes of Vertical Profile 1 at 0.75 Grms in the Z-axis orientation of the cells under assessment.