A fundamental case study on the Prius and IMA drivetrain concepts

In this paper the drivetrain concepts of the IMA and the Prius are analyzed and evaluated in order (i) to disclose potential limitations in fuel economy and performance and (ii) to quantify the design and cost trade-offs involved in achieving this (limited) fuel economy and performance. This has been done by performing a cross-technology exchange study. The V-belt CVT of the IMA with respect to the E-CVT of the Prius results in an approximately 4% higher fuel consumption. Regarding the engine displacement and combustion cycle, the following can be concluded, downsizing the engine from 1.5l-Otto to 1.4l-Otto results in an 8% improvement in fuel economy. Changing the combustion cycle from Otto to Diesel and from Otto to Atkinson saves about 13% and 16% respectively. The Honda IMA and the Toyota Prius have set their acceleration performance target 0 – 100 [km/h] to that of a conventional vehicle equipped with 1.6l-Otto and a 2.0l-Otto engine respectively. Thereto, the IMA requires in combination with a 1.4l-Otto engine 10 [kW] and the Prius requires in combination with a 1.5l-Atkinson engine 20 [kW] of additional battery power assist. Applying hybrid functions for the IMA, such as brake energy recovery, with an off-line optimal engine control strategy and Idle-Stop results in an additional fuel saving of respectively 18% and 6%. In future work, the drivetrains of the IMA and Prius will be further analysed, by determining the optimal control strategy independent of the pre-scribed optimal operation line condition for the engine with help of dynamic programming. The engine operation point is then determined by ratios of the E-CVT, CVT, the wheel speed, the battery power flow and required vehicle drive power. The goal is to determine the influence of the system component (Primary power source (P), Secondary power source (S) and Transmission technology (T)) efficiencies on the overall vehicle performance (fuel economy, emissions and dynamic performance). The final objective of the underlying research is to determine the minimum specifications of P, S and T achieving a pre-defined fuel economy and performance, with constraints on cost and lifetime. Once these are determined new technologies for P, S and T can be selected and designed.