## 4 Optimizing Power Flow in EV Powertrains
### Continuously Variable Transmission (CVT)
In the work, three powertrain models were evaluated; first, the base powertrain model taken from the actual EV that used single speed  
Figure 9: CVT with electro-hydraulic actuation system presented in [61]. transmission, second, the modified powertrain model, which essentially the based model with CVT instead of the single speed transmission, and lastly, the optimized powertrain model, in which the CVT ratio as well as the size of the main powertrain components were optimized based on the actual driving data obtained from road and dynamometer tests. Similar to [61], the CVT evaluated in [62] also used electro-hydraulic actuation system for belt's clamping and ratio changing. However, the design integrated the cooling system of both the CVT and the motor, where the heat from the CVT fluid was dissipated to the motor's coolant through a heat exchanger, and then the coolant would be cooled down by the radiator (Figure 10). As a result, an extra radiator for the CVT was unnecessary, and this led to a more compact and cost-effective thermal management system. By simulating all the powertrain models under WLTC, the results showed that the optimized powertrain model performed the best in terms of efficiency (11.19 kWh/100 km, means 2.1% improvement against the base model with 11.43 kWh/100 km) and cost (2% cost reduction against the base model). In terms of cooling power consumption, the optimized model also gained an improvement of 30% as compared to the base model, and this means that the integrated thermal management system was not only cost effective, but it was also very efficient in controlling the operating temperature of the motor and the CVT. Besides, the integrated system also presents an opportunity for further integration with the battery's thermal management system which will potentially lead to further improvements in terms of cost and efficiency. Nevertheless, power losses in the hydraulic actuation system can still be expected, and it is interesting to evaluate how the optimized CVT performs against a two-speed transmission with optimized gear ratios. Another paper that discussed the potential cost benefit of using CVT in an EV can be found in [63]. Here, the application of CVT was complemented by the hybrid battery technology that incorporated a supercapacitor, and the cost benefits considered not only the component and electricity cost, but also the battery replacement cost. The CVT used an electro-mechanical actuation system for clamping and ratio changing, which means it featured a self-lock mechanism to maintain the belt's clamping force without using hydraulic pressure. The actuation system comprised of two DC motors with presumably  
Figure 10: Integrated thermal management system for motor and CVT proposed in [62]. power screw mechanism, each for actuating the primary pulley and the secondary pulley. So, theoretically, it was more efficient than the CVT described in [61; 62] thanks to the self-lock capability. However, detail description on the CVT's actual electro-mechanical actuation system was not described in the paper. The CVT losses model was developed to estimate its efficiency, and based on the model, the efficiency was estimated between the range of 78% to 89%. When simulated under a combined driving cycle of HWFET and FTP-75, the usage of the electro-mechanical CVT reduced the motor's losses by 37.9%, which was translated into 8.3% improvement in the power consumption of the vehicle when compared against single speed transmission. In terms of battery degradation, using CVT reduced the degradation by 7.2% as opposed to the single speed transmission, and, with the proposed hybrid battery technology, the improvement rate can be increased further to 17.5%. The battery degradation was defined in terms of capacity loss percentage, estimated using the LiFePO4 cell's dynamic model that took into account the charging rate and the battery temperature during driving [64; 65].