# On the Effect of DLC and WCC Coatings on the Efficiency of Manual Transmission Gear Pairs
## 3 Results
### Simulation Results
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Scenario 1**} & \multicolumn{3}{c}{**Scenario 2**} \\ \hline \multirow{2}{*}{**Engaged Gear**} & **Input Velocity** & **Input Torque** & \multirow{2}{*}{**Engaged Gear**} & **Input Velocity** & **Input Torque** \\  & **[rpm]** & **[Nm]** & & **[rpm]** & **[Nm]** \\ \hline
1 & 2000 & 15 & 1 & 1100 & 30 \\
2 & 1800 & 50 & 2 & 1500 & 10 \\
3 & 1400 & 45 & 3 & 1500 & 100 \\
4 & 1500 & 44 & 4 & 1300 & 110 \\
5 & 2000 & 150 & 5 & 1600 & 150 \\
6 & 1400 & 180 & 6 & 1690 & 150 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Scenarios of operating conditions examined. Figure 9: Real Driving Emissions (RDE) driving cycle. The results are presented as power losses due to the direct relation with efficiency:  
\[\textit{Power Loss}=\left[\left(T_{f,k}+\ T_{g,p,k}+T_{g,b,k}\right)+\ \sum_{i=1}^{6}\left(T_{ff,i}-T_{Fp,i}\right)\right]n \tag{29}\]  
Figure 10 presents the results of the simulations for the operating conditions of scenario 1, when all gears are considered uncoated. It has to be noted that the uncoated gear model has been validated experimentally at system level, as presented in [29]. For each gear, as described in Table 7, different operating conditions apply. Hence, even though the results are presented on the same figure, for each gear they refer to different snapshot of the RDE cycle and the time shown on the x axis refers to the duration of the simulation at the corresponding RDE time snapshot. As mentioned before, the power gain by using coated gears is traced for the engaged gear pair of the transmission only due to the fact that engaged gears have the highest values of power losses. Consequently, for each gear that is shown in the following figures the gear is considered engaged and performing under the operating conditions of Table 7. In the following figures, the oscillation of power losses at each instant of time due to the varying meshing stiffness can also be observed. Similarly to Figure 10, the same rules apply for Figure 11, which shows the power losses of each gear for the same operating conditions of the first scenario considering DLC coating. The results of Figure 11 reveal that the use of DLC coatings leads to power loss reduction for all gears under certain working conditions. Even though the coating type used for all gears is the same, the effect is different since the performance is affected by the operating conditions and the gear geometry, as discussed in the methodology section. For the operating conditions of scenario 1, the lesser effect on power loss is found on the first gear of the transmission where the power gain is around 6%. The power gain in the middle gear pairs is around 10-15%. The use of WCC coating has a similar effect, as presented in Figure 12 for the same operating conditions of scenario 1. Since the surface properties of the two coatings differ as measured experimentally, a different effect on the power loss change was expected. However, it should be noted that the power loss was reduced in all coated gears. In order to further verify the effects of each coating type, both coatings were tested under different operating conditions, described as scenario 2 (see Table 7). Figure 10: Power losses for uncoated gears, scenario 1. For the case of uncoated gears operating under the conditions of scenario 2, the power losses are shown in Figure 13. The power losses when using DLC and WCC coatings are presented in Figures 14 and 15, respectively, for the operating conditions of scenario 2. Based on the results obtained for scenario 2, it is obvious that for this case as well, the use of either type of coating can lead to improvement of the gearbox efficiency. Even though for this scenario the effect of each coating is similar as well, it is clear that the WCC shows a slightly better performance especially on the higher gear pair power losses. However, the range of power loss gain for all gears is between 12% and 60%.