Mild hybrids with CVT: comparison of electrical and mechanical torque assist

This paper evaluates two mild hybrid drive trains for a mid-class passenger car with a gasoline engine by means of comptuer simulation. The term mild hybrid is used for vehicles with sustained electric propulsion. The mild hybrid drive trains both have a Continuously Variable Transmission (CVT) with a Van Doorne metal V-belt and a torque assist device used to enhance fuel economy, driveability, comfort and emissions at minimal additional costs. The aim is to carry out an objective analysis of the electrical and mechanical torque assist systems on acceleration performance with equally efficient engine operation. In the electrical torque assist system, a 4.5 kW (10 kW peak) starter-alternator with NiMH battery is added to the CVT drive train and the mechanical torque assist system connects a 0.4 kg.m2 flywheel inertia in parallel to the CVT using a power splitting planetary gear set.