## 4 Optimizing Power Flow in EV Powertrains
### Multispeed Discrete Transmission
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Literature, Year** & \multicolumn{2}{c}{**Summary of the Works**} & \multicolumn{2}{c}{**Significant Findings**} \\ \hline [PERSON] et al., 2019 [39] & - & Optimizing the number of gears (between 2, 3 and 4 gear ratios and continuous) and gear ratios using dynamic programming based on a specific vehicle powertrain system with battery and motor’s efficiency models & - & Increasing the number of gears led to improvement in power consumption. \\ [PERSON] et al., 2019 [39] & - & Simulated under four different driving cycles & - & Continuous ratio provided the best results in power consumption, hence indicating the potentials of CVT. \\  & & namely Urban Dynamometer Driving & - & However, increasing the number of discrete gears usually led to more complex shifting mechanism, which may negate the gain in power consumption. \\  & & Schedule, (UDDS), NEDC, Highway Fuel & - & However, increasing the number of discrete gears usually led to more complex shifting mechanism, which may negate the gain in power consumption. \\  & & Economy Test (HWFET) and LA92. & - & However, increasing the number of discrete gears usually led to more complex shifting mechanism, which may negate the gain in power consumption. \\  & & & - & Highlighting the driving tendency of the driver with different gear ratios. \\  & & & For instance, it was argued that the gear ratio 0.100 allowed for faster acceleration, hence the driver tend to accelerate more aggressively, resulting in 4.2\% more power consumed. \\  & & & Highlight the contributions of multispeed gear ratios in providing flexibility for driving performance and efficiency. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._Another novel synchronizer design that featured springs inside it was also presented in [45]. Meanwhile, the work in [46] reported the optimization of the gearshifting with the objectives to minimize shifting time, friction work, due to the engagement and disengagement of the clutch during shifting, and jerking. The optimization was conducted using the Legendre pseudospectral method and the gearshifting model was simplified as two degree of freedom (2-DOF) and 4-DOF dynamic models based on a friction clutch and a sleeve shifting mechanism in a two-speed transmission. The results were divided into four different patterns: the least shifting time, the least friction work, the least jerking, and finally, the compromised solution. In the compromise solution, obtained in the 2-DOF model simulation, the shifting time was recorded at 0.92 s, with the square of continuous jerking measured at 0.48 (m/s)2, and the friction work at 1856 J. In the work, however, no detailed descriptions of the actual actuators used for the clutch and the gearshift sleeve was provided, which can be the focus for future works. Subsequent research work performed to analyze the performance of shifting mechanism was described in [47; 48], where a two-speed dry clutch inverse AMT (I-AMT) was used to vary the gear ratios with very minimal torque interruptions with help from two one-way clutches. The one-way clutches, on the other hand, were integrated into the first gear and the second gear separately, hence the shifting can be achieved by actuating only a single dry clutch. Prior to that works, another study has been carried out, as described in [50], to evaluate the clutch control of a wet dual clutch two-speed transmission for EV application. The objective of the study was to experimentally quantify the clutch control's performance in terms of jerking and engagement time. However, because of the usage of the wet clutch, some power was lost due to the clutch actuation. Not only that, but the gearshift quality was also less desirable due to the high jerking at around 10 m/s3, signifying noticeable torque interruption during the shifting. Besides, the sticking characteristics of the wet clutch, due to its hydraulic system, caused difficulty to optimize the clutch control for minimum jerking and engagement time.