Co-Design of CVT-Based Electric Vehicles

Abstract

For an electric vehicle (EV) with a continuously variable transmission (CVT), a novel convex programming (CP)-based co-design method is proposed to minimize the total-cost-of-ownership (TCO). The integration of the electric machine (EM) and the CVT is the primary focus. The optimized system with co-design reduces the TCO by around 5.9% compared to a non-optimized CVT-based EV (based on off-the-shelf components) and by around 2% compared to the EV equipped with a single-speed transmission (SST). By taking advantage of the control and design freedom provided by the CVT, the optimal CVT, EM and battery sizes are found to reduce the system cost. It simultaneously finds the optimal CVT speed ratio and air-flow rate of the cooling system reducing the energy consumption. The strength of co-design is highlighted by comparing to a sequential design, and insights into the design of a low-power EV that is energy-efficient and cost-effective for urban driving are provided. A highly integrated EM-CVT system, which is efficient, low-cost and lightweight, can be expected for future EV applications.

Energy-optimal Design and Control of Electric Powertrains under Motor Thermal Constraints

“…However, we can easily extend our framework to account for the temperatures, capturing the full thermal behavior of an EV. Interested readers are directed to [19] for more information. Third, convex approximations to the nonlinear EM power losses may result in frequent under-or overestimation of the power losses.…”

“…In this section, we derive an LPTN model, based on [10], [19], [20]. In addition to the EM components presented in Section II-C, we include the overhanging copper windings, further referred to as end-windings (edwg), in our thermal model because the end-windings reach higher temperatures and are the limiting factors in high-performance operations [21].…”

Review of the Methods to Optimize Power Flow in Electric Vehicle Powertrains for Efficiency and Driving Performance

“…This presented an opportunity to apply the same CVT with different sets of discretized ratios to suit the requirements of diverse EV segments, which can contribute in terms of cost reduction in the transmission production. One of the latest works describing the application of CVT in an EV powertrain can be accessed in [62]. This work presented an optimization of the EV ownership cost by taking into account the components' cost and the electricity cost for all the components involved in the powertrain; battery, motor (with inverter), and, CVT.…”

“…This work presented an optimization of the EV ownership cost by taking into account the components' cost and the electricity cost for all the components involved in the powertrain; battery, motor (with inverter), and, CVT. The optimization was carried out using convex programming design optimization, with the targets to min- One of the latest works describing the application of CVT in an EV powertrain can be accessed in [62]. This work presented an optimization of the EV ownership cost by taking into account the components' cost and the electricity cost for all the components involved in the powertrain; battery, motor (with inverter), and, CVT.…”

“…In the work, three powertrain models were evaluated; first, the base powertrain model taken from the actual EV that used single speed 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 com ponents were optimized based on the actual driving data obtained from road and dyna mometer tests. Similar to [61], the CVT evaluated in [62] also used electro-hydraulic actu ation 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).…”