CVT, Promising Solutions for Electrification 2019-01-0359
A single speed transmission for electric vehicles (EV) puts specific requirements on the electric motor and battery to enable the full characteristics as offered by the internal combustion engine such as driving large distances at higher speed or towing a trailer. EV developers are facing several challenges in extending driving range, reducing recharge times and finding a performance and efficiency compromise between low and high-speed conditions. This study proposes a combination of a dedicated electric machine and a Continuously Variable Transmission (CVT) that offers a chance to overcome these challenges. The result is an efficient and cost effective solution where the surplus cost of the CVT is recovered within the powertrain by lowering cost of the electric components, cooling system and battery.
A CVT reduces the maximum torque and speed requirement of the electric machine which enables a reduced size and cost of the active parts. The combination of a downsized electric machine and a pushbelt CVT can deliver the good performance that consumers expect from their EV.
This paper combines the results of research into various topics to support these statements. A simulation based comparative study of various EV powertrain configurations shows that with respect to the single speed EV, efficiency benefits around 13% on WLTC are possible. A cost study based on the bill of materials furthermore concludes that a 6% cost benefit is achievable.