Concept Layout and System Simulation of a 48-V Diesel Hybrid

Abstract

In order to take the next step in CO2 reduction for diesel drivetrains, further electrification is a viable option. This raises the question: How much electrification — defined here in terms of system voltage — is necessary? To answer this question, a simulation was performed on theoretical recuperation potential with different e-motor power ratings. Here the NEDC was used as it represents the currently defined requirement. Boundaries of the simulation were a belt-starter-generator (BSG) architecture and no limitation due to energy storage capacity. The result of this simulation is shown in ➊. 100 % would mean that all the potential resulting from the deceleration phases could be used. Based on a current 12-V system, a certain limitation of about 20 to 30 % recuperation potential is experienced. Installing an electric motor in the range of 10 kW opens further recuperation potential of up to 80 % as well as further CO2 reduction. However, this exceeds the limits of the standard 12-V electrical system and requires a higher voltage level of 48 V. Open image in new window ➊ NEDC recuperation potential With a 48-V electrical system available a further step can be taken with the integration of an electric supercharger in order to increase low-end torque performance and dynamic response. Increased costs needs to result in further customer benefits besides the reduction in fuel consumption in order to create an attractive product for the market. Therefore, it was decided to additionally increase the power rating of the internal combustion engine while keeping single stage boosting. In ➋ the general strategy to reach the goal in terms of CO2 reduction by 20 % and increased fun to drive is described. Starting with the base engine definition as available on the market, the fuel consumption can be reduced by downsizing, and/or downspeeding; which compromises fun to drive. By replacing the standard turbocharger with a larger one the rated power was increased by 25 %. The further adaptation of a BSG with approximately 10 kW improves the performance from standstill significantly and the additional implementation of an electric supercharger assists in transient conditions, providing a level of fun to drive comparable or even better than the base engine. Open image in new window ➋ Generic roadmap towards improved fuel effi ciency and fun to drive The figures above serve as a general starting point for the considerations to follow. Finally, the realistic CO2 potential will be discussed after going through the system definition step-by-step.