## 5 Comparison and Future Works Related to the Methods for Optimizing Power Flow in EV Powertrains
### Key Areas for Future Research Works
At the moment, very limited works have been carried out to analyze thoroughly the application of electro-mechanical CVT for EV. Based on the latest review paper on an electro-mechanical CVT with metal belt in [91], some of the designs are capable not only of self-locking the ratio and belt's clamping force, but also precisely controlling them. Controlling the belt's clamping force, particularly, is the key to optimize the CVT efficiency as well as to optimize the durability of the electro-mechanical actuation system, as extensively explained in [92]. This means that transmission losses can be minimized as much as possible, though thorough studies still need to be performed since electro-mechanical CVT is still not a mature technology and so far, not being implemented for commercialization. Therefore, key research area here is the optimization of the ratio and clamping control algorithms in the electro-mechanical actuation system for CVT with metal belt. Another area that can be focused on is the possibility of implementing geartrain-based CVT, which eliminates the application of the metal belt entirely. In the context of multi-motor configurations, key research areas that can be pursued are the control algorithm for traction distribution on the wheels and the durability of the powertrain system. Apart from optimum power consumption and driving performance, multi-motor configuration offers the chance to implement steering assist and wheels' traction control. However, since the powertrain is now attached directly to wheels, it now becomes part of the unsprung mass. As a result, the powertrain is now subjected to harsh operating condition involving direct vibrations caused by the road surface, as well as water splash and debris from the road surface. This factor very likely will affect the durability and maintenance routine of the powertrain, which requires further study to evaluate its significance to the overall ownership cost of the EV. In terms of maintenance, refs. [93; 94] discussed the gap between the operation cost for ICE and EV. In general, the purchasing cost for EV is higher due to the high battery cost, while the cumulative maintenance cost for ICE will be greater over time due to the frequent maintenance requirement for its powertrain. Depending on the vehicle segment, EV can achieve cost parity with the equivalent ICE model in around 8 years of ownership. Therefore, detail studies to determine the acceptable cost parity between ICE vehicle, multispeed discrete transmission, CVT with metal belt, multi-motors configuration and the conventional single-speed transmission EV are still required. Another topic that is relevant for future research work here is the lubrication and cooling of the powertrain, which is particularly crucial for the CVT with metal belt. If an integrated cooling and lubrication system can be developed for all components (i.e., battery, motor and transmission) in an EV powertrain, the ownership cost of the EV can be reduced significantly. Study by [62] have started to evaluate the possibility of integrating the cooling system for the CVT fluid and the motor's fluid, and this helps in making the powertrain system more compact and cost effective. Latest review on the lubrication for EV powertrain can be accessed here [95; 96] which explored the possibility of integrating the cooling system for all components of an EV powertrain. The literatures also evaluate various possible lubricants for specific EV powertrain that have different requirements than the conventional ICE powertrain. The subsequent research area that worth studying in the future is the possibility to implement the same EV powertrain configuration for diverse vehicle segments for cost savings in production [97; 98]. As highlighted in [99], CVTs with metal belts or chains present the opportunity for application in various EV segments thanks to their continuous ratio range.