## 4 Optimizing Power Flow in EV Powertrains
### Multispeed Discrete Transmission
(2021) & Optimizing gear ratios of a two-speed DCT by taking into account the motor’s efficiency and transmission efficiency model. The model provided precise transmission efficiency for different gear ratios (usually assumed to be a constant). & - Efficiency improvement between 10.7\% to 12.1\%. In terms of transmission efficiency, work in [PERSON] et al. (2021) [PERSON] et al. (2021) & 36 different gear ratios (usually assumed to be a constant). & - The optimized two-speed DCT was simulated in an EV powertrain model for WLTP cycle. & - Acceleration was about the same for both transmissions. \\  & Then, it was compared against a single-speed transmission powertrain model for the same driving cycle. & - Details of the shifting mechanism was not provided. \\ \hline [PERSON] et al., 2020 [PERSON] et al. (2020) & Optimizing two-speed transmission for fast 0–100 km/h acceleration and high efficiency using GA. & - Different gear ratios required to meet different objectives (fastest acceleration, lowest power consumption, compromised based on weightage) as shown in Figure 7. \\  & (max. torque and RPM) were also optimized within a specified range of 150–200 Nm and 8000–12,000 RPM. & - Highlighting the limitation of two-speed discrete transmission, potential of using CVT which allows continuous ratio range, hence possible to meet the different objectives. \\  & (-) Compromised solutions between the acceleration and efficiency were also determined based on weightage. & - The optimization of \\  & (-) Powertrain model include regenerative &  
The latest works related to gearshifting mechanism and its control are described in [41; 42; 43; 44; 45; 46; 47; 48; 49; 50]. Researchers in [41; 42; 43] argued that criteria for the EV motor to operate efficiently is not just the application of the multispeed discrete transmission but also smooth gearshifting process with minimum jerking and actuation power usage. Reference [44], on the other hand, explained jerking effects in relation to friction clutch, one-way clutch and types of the driveline. The jerking effects were evaluated under three common shifting scenarios: upshifting during driving, downshifting during driving, and downshifting during braking. In general, smooth shifting is not only beneficial for driving comfort, where it avoids excessive jerking and torque interruption, but it also helps in terms of the overall powertrain efficiency. Thus, a novel clutchless AMT was proposed in [41; 42; 43] featuring a unique synchronizer called bilateral Harpoon-shift synchronizer. Such a synchronizer uses a torque spring, constructed based on multiple bended coil springs, inside the dog body's internal groove to keep the dog gear damped to the guide ring (Figure 8). This results in quick synchronization of the guide ring and the dog gear without using frictional cones, and also smooth shifting due to the spring's damping effect. Additionally, the spring also helps in reducing the required axial force for shifting; minimizing the required DC motor's work to actuate the fork for shifting. Hence, faster and more efficient shifting process can be done with a compact DC motor. However, the spring also causes additional normal force between the guide ring and the sleeve, and this causes friction force between them during the shifting process. This eventually leads to an extra load that must be overcome by the motor.