Modern downsized internal combustion engines benefit from high-efficiency turbocharging systems for increasing their volumetric efficiency. However, despite the efficiency increase, turbochargers often lack fast transient response due to the nature of the energy exchange with the engine, which deteriorates the vehicle’s drivability. An electrically-assisted turbocharger can be used for improving the transient response without any parasitic losses to the engine while providing energy recovery for increasing overall system efficiency. The present study provides a detailed numerical investigation on the potential of e-turbocharging to control load and if possible replace the wastegate valve. A parametric study of the optimum compressor/turbine sizing and wastegate area was performed for maximum torque, fast response time and energy regeneration across the real driving conditions speed/load area of the engine. The results showed that the implementation of a motor-generator could contribute to reducing the response time of the engine by up to 90% while improving its thermal efficiency and generating up to 6.6 kWh of energy. Suppressing the wastegate can only be achieved when a larger turbine is implemented, which as a result deteriorates the engine’s response and leads to energy provision demands at low engine speeds.

The engine downsizing approach can be considered as state-of-the-art automotive propulsion system. However, future trends are also indicating a trend to a further reduction of the number of engine architectures, normally accompanied with a reduction of the number of cylinders in internal combustion engines, including prospective use of alternative fuels such as compressed natural gas or the downsized engine embedded in a powertrain with electrically driven propulsion systems. Hitherto, different simulation approaches are employed to evaluate the trade-off between noise, vibration and harshness, driveability, and fuel consumption. This paper presents the coupling of two simulation tools, each one an established tool in its discipline, namely a 1D-gas-dynamics tool for a downsized internal combustion engine including a dedicated boost-pressure control approach, and a multibody dynamics tool to simulate the powertrain and vehicle dynamics, using the functional mock-up interface. Using this approach as an industry first application, a significant reduction of development time while avoiding duplication of powertrain subsystem modeling, is achieved. This enables a transient simulation and supports a fast analysis of different powertrain architectures. It, furthermore, allows a detailed look at the impact of powertrain subsystems like the architecture of the internal combustion engine, flywheel, and driveline design on relevant vehicle attributes. Moreover, the transient simulation approach allows the investigation of lag effects caused by the air-path characteristics of the internal combustion engine, or transient effects brought up with the advent of hybrid powertrain architectures. The application case of this tool chain presented in this paper revealed that engine architecture reduction should be carried out carefully in order to not compromise driveability of the engine later on. This could bear the risk of sacrificing fuel economy due to a higher lugging limit, often linked to a reduced firing order of the engine, caused by a reduction of the number of cylinders. The paper finally discusses prospective solutions in terms of conventional mechanical solutions and added electrified propulsion including potential limitations to overcome this issue.